1131 10 13654 https://digitalcollections.lakeheadu.ca/files/original/5ffcbed7cc177d297ac2ee2615cd77b6.jpg aac24a396390e0406e4ea9b594f276a4 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 Cairine Budner fonds 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 Group of athletes training for track and field events Subject The topic of the resource Sports Description An account of the resource Black and white photograph of male athletes stretching outdoors in Intola. High jump apparatus is visible in the photograph Date A point or period of time associated with an event in the lifecycle of the resource July 1931 Contributor An entity responsible for making contributions to the resource Donor. T. Lake Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0011c (xviii) scan#BUD-0013 1931 athletes gymnasts High jump Intola July track & field https://digitalcollections.lakeheadu.ca/files/original/13bb2098842c9871c61c193c7700287c.jpg f282983316bfda5ee16267b2c89fcad3 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 Cairine Budner fonds 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 Athletic group training for track and field events Subject The topic of the resource Sports Description An account of the resource Black and white photograph of male athletes stretching outdoors at Intola. High jump apparatus is visible in the photograph Date A point or period of time associated with an event in the lifecycle of the resource July 1931 Contributor An entity responsible for making contributions to the resource Donor T. Lake Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0011c (xvii) scan#BUD-0012 1931 athletes gymnasts High jump Intola July track & field https://digitalcollections.lakeheadu.ca/files/original/b16deb1b63cbbb7d491e737384f9e21b.jpg 308f7d0e8d9885541d57ac191bf67a3b 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 Cairine Budner fonds 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 Athletic group practicing routines on bars in Intola Subject The topic of the resource Sports Description An account of the resource Black and white photograph of male athletes practicing their gymnastic routines on bars Date A point or period of time associated with an event in the lifecycle of the resource July 1931 Contributor An entity responsible for making contributions to the resource Donor T. Lake Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still images Identifier An unambiguous reference to the resource within a given context PHIII-0011c (xv) scan#BUD-0011 1931 athletes bars gymnasts Intola routines https://digitalcollections.lakeheadu.ca/files/original/b0803129b8f1ac00e705739c674f874b.jpg 5e150a5d208cc62505110f6766cd3930 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 Cairine Budner fonds 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 Nahjus Women's gymnastics group at the Northern Lights Grand Sports and Musical Festival Subject The topic of the resource Sports Description An account of the resource Black and white photograph of the Nahjus women's gymnastics group lined up ready to perform their rhythmic drill at the Northern Lights Grand Sports and Musical Festival in Timmins, Ontario Contributor An entity responsible for making contributions to the resource Donor L.empi St. Amand Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0011c (xiii) scan#BUD-0010 athletes Grand Sports & Music Festival gymnastics Nahjus Women's Group Northern Lights Timmins https://digitalcollections.lakeheadu.ca/files/original/c0084a3638f8f21806f3f6469782fd3f.jpg b238cfedad518746c54fb37b73040668 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 Cairine Budner fonds 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 Lakehead Track & Field group Subject The topic of the resource Sports Description An account of the resource Black and white photograph of the Lakehead Track & Field group with the Duluth team (Big D) during the competition. Men and women athletes are wearing their jerseys. Athletes are standing and seated on the grass watching the competition Date A point or period of time associated with an event in the lifecycle of the resource 1920s Rights Information about rights held in and over the resource Public domain Format The file format, physical medium, or dimensions of the resource Photograph Type The nature or genre of the resource Still image Identifier An unambiguous reference to the resource within a given context PHIII-0011c (ix) scan #BUD-0009 Contributor An entity responsible for making contributions to the resource Donor Onni Airola 1920s Athletics Big D competition Duluth Lakehead Track & Field Onni Airald 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/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/11c9d1d86b50e5a7348f083a877476c3.pdf 671b46482ec80859cddc170b04d8d1d3 PDF Text Text C O O P E R A T I V E EXTENSION E X T E N S I O N PROGRAMS PROGRAMS COOPERATIVE I University U n i v e r s i t yofo fWisconsin—Madison Wisconsin-Madison U n i v e r s i t y of o fWisconsin—Extension Wisconsin-Extension University Nineteenth Annual Annual Nineteenth Lake Superior Superior Geology Geology Institute on Lake May 3-6,1973 3-6,1973 Madison, Madison, Wisconsin Wisconsin I P1 ERTS-1 satellite Photo Far infrared band photographed on August 12, 1972 Sponsored Sponsored by the the Geological and and Natural Natural History History Survey Survey Wisconsin Geological Extension Wisconsin - Extension University of Wisconsin and the Departments of the theUniversity University of of Wisconsin WisconsinSystem System Departments of of Geology of - �Technical Program Program and Abstracts ffor or tthe h e 19th Annual GEOLOGY INSTITUTE ON LAKE SUPERIOR GEOLOGY held held at at Sheraton Inn Inn Madison, Wisconsin May May 3—6, 3-6, 1973 1973 �MADISON PRAIRIE Central South South --Central MADISON, MADISON, WISCONSIN WISCONSIN OREGON OREGON 4 0 SHERATON SHERATON INN INN 1 1 MADISON MADISON INN INN 22 MAYFLOWER MAYFLOWER MOTEL MOTEL 33 44 NATIONAL NATIONAL MOTOR MOTOR INN INN 55 QUALITY QUALITY INN INN 66 Short Short Course Course Dorms: Dorms: 77 MURPHY'S MURPHY'S 88 99 POOLE'S POOLES PARK PARK MOTOR MOTOR INN INN HUMPHRY HUMPHRY HALL HALL JORNS JORNS HALL HALL RESTAURANT RESTAURANT CUBA CUBA CLUB CLUB ROHOE'S ROHDES STEAK STEAK HOUSE HOUSE 10 107777SIRLOIN SIRLOIN STRIP STRIP 11 DEPARTMENT DEPARTMENT of of GEOLOGY GEOLOGY 11 and and GEOPHYSICS, GEOPHYSICS, SCIENCE SCIENCE HALL HALL 12 GEOLOGICAL 12WISCONSIN WISCONSIN GEOLOGICAL and and NATURAL NATURAL HISTORY HISTORYSURVEY SURVEY �19th 1 9 t h Annual Annual Institute I n s t i t u t e of Lake Superior S u p e r i o r Geology Geology Sheraton Sheraton Inn, Inn, Madison, Madison, Wis. Wis. May May 3—6, 3-6, 1973 1973 Sponsored Sponsored by by the t h e Wisconsin Geological & Natural History Survey Survey and and Departments of of Geology, Geology, the t h e University U n i v e r s i t y of of Wisconsin Wisconsin System. System. Individuals Individuals from from the t h e U.S. U.S. Geological Survey, Survey, Department of Geology Geology of of the t h e University University of of Kansas, Kansas, and and the t h e Inland Inland Steel S t e e l Corporation Corporation also a l s o contributed c o n t r i b u t e d greatly g r e a t l y to to arranging arranging the t h e program program and and field f i e l d trips. trips. INSTITUTE BOAFZI OF OF DIRECTORS DIWCTORS INSTITUTE BOARD * J.W. J.W. * * * Avery Avery (Treasurer), ( T r e a s u r e r ) , Jones Jones && Laughlin Laughlin Steel S t e e l Corp., Corp., Negaunee, Negaunee, Michigan. Michigan. R.D. R.D. Reed Reed (Secretary), ( S e c r e t a r y ) , Michigan Michigan Geological Geological Survey, Survey, Lansing Lansing Michigan. Michigan. M.E. M.E. Ostrom, Ostrom, Wisconsin Wisconsin Geological Geological && Natural Natural History H i s t o r y Survey, Survey, Madison, Madison, Wisconsin. Wisconsin. J. J. Kalliokoski, K a l l i o k o s k i , Michigan Michigan Technological Technological University, University, Roughton, Houghton, Michigan. Michigan. D.M. D.M. Davidson, Davidson, Jr., Jr., Dept. Dept. of of Geology, Geology, University U n i v e r s i t y of of Minnesota Minnesota at a t Duluth, Duluth, Duluth, Duluth, Minnesota. Minnesota. M.W. M.W. Bartley, B a r t l e y , Thunder Thunder Bay, Bay, Ontario, Ontario, CANADA CANADA * Permanent Permanent members members * LOCAL LCZALCOMMITTEE CWITTEE M.E. M.E. Ostrom, Ostrom, Conference Conference Chairman Chairman Technical Technical Program Program C. C. Craddock, Craddock, Chairman Chairman B. E. Cameron Cameron C. C. Dutton Dutton G. G. Medaris Medaris G. G. Mursky Mursky Field F i e l d Trips Trips M. M. Roshardt, Roshardt, Coordinator Coordinator W. W . Broughton Broughton C. Dutton C. Dutton A. A. Heyl Hey1 H. H. Klemic Klemic G. G. LaBerge LaBerge G. G. Medaris Medaris P. P. Myers Myers G. G. Mursky Mursky J. J. Ohlson Ohlson L. L. Weis Weis W. W. West West ft. Van Schmus R. Van Schmus 11]. iii Physical P h y s i c a lArrangements Arrangements P. P. Olcott, O l c o t t Chairman , Chairman Short Short Course Course Office Office College College of of Agricultural Agricultural and and Life L i f e Sciences Sciences U n i v e r s i t y of of Wisconsin— WisconsinUniversity Extension Extension �CARL APPRECIATION CARL E. E. DUTTON DIJTTON -- AN APPFZCIATION Carl Dutton's career half C a r l Dutton's c a r e e r in i n geology extends through nnearly early h alf a century, and most of this time his headquarters have been in Science century, of t h i s h i s headquarters in Hall H a l l on the t h e Madison campus campus of of the t h e University U n i v e r s i t y of of Wisconsin. Wisconsin. H has Ree has worked extensively Michigan, Wisconsin, Wisconsin, and Minnesota, Minnesota, and he is e x t e n s i v e l y in i n Michigan, is well Precambrian geologists Superior w e l l known to t o Precambrian g e o l o g i s t s throughout throughout the t h e Lake S uperior meeting, h his t h e occasion of of this t h i s meeting, i s ccolleagues o l l e a g u e s and friends f r i e n d s in in area. On the Madison extend this t h i s appreciation a p p r e c i a t i o n for f o r his h i s many many contributions. contributions. iv �Carl C a r l was was born born in i n Dunkirk, Dunkirk, Ohio, Ohio, on on January January 24, 24, 1904. 1904. H Hee was educated DePauw University University (LA., aatt DePauw (B.A., 1926), 1926), the t h e University U n i v e r s i t y of of Illinois I l l i n o i s (M.A., (M.A., 1928), 1928), and tthe University and he U n i v e r s i t y of of Minnesota (Ph.D., (Ph.D., 1931). 1931). Carl C a r l and and Val Val Dutton Dutton have have two sons professor sons — John, a meteorology p r o f e s s o r at a t Pennsylvania Pennsylvania State S t a t e University, University, and Robert, Robert, aa physician in i n San San Francisco Francisco — and ffive i v e grandsons. They have have H i l l s , just j u s t west w e s t of of the t h e Madison Madison campus, campus, since s i n c e 1946. 1946. llived i v e d in i n Shorewood Shorewocd Hills, Carl C a r l has divided his h i s life l i f e between various v a r i o u s academic positions p o s i t i o n s and the the U.S. Geological Geological Survey, Survey, and and he he iis widely respected respected aas s widely s a tteacher e a c h e r and a ffield ield U.S. geologist. Assistant g e o l o g i s t . He was aa Teaching A s s i s t a n t at a t Illinois, I l l i n o i s , an an Instructor I n s t r u c t o r at at Minnesota, Assistant Minnesota, and and an an A s s i s t a n t Professor P r o f e s s o r at a t Wayne State S t a t e University U n i v e r s i t y and and at a t the the University Hee joined U n i v e r s i t y of of Michigan. Michigan. H joined the t h e U.S. U.S. Geological Geological Survey Survey in i n 1943, 1943, becoming Regional Geologist in i n 1946 1946 and and Research Research Geologist Geologist in i n 1962. 1962. Since has p participated Mineral Resources Resources ccooperative coming to t o Madison he has a r t i c i p a t e d in i n tthe h e Mineral ooperative program of History i s t o r y Survey and the the of the t h e Wisconsin Geological & Natural H U.S. Geological Survey, Survey, he has taught some cclasses e c t u r e d in i n tthe he U.S. taught sane l a s s e s & llectured Department of Geology and and Geophysics, Geophysics, and and he has been a valued counselor and friend f r i e n d to t o many professors p r o f e s s o r s and and students. students. During his Carl h i s stay s t a y at a t the t h e University U n i v e r s i t y of of Minnesota C a r l was introduced intrcduced geological problems of of tthe Canadian S Shield Professors tto o tthe he g e o l o g i c a l problems h e southern Canadian h i e l d by P rofessors Grout, John Gruner, His doctoral dissertation Frank Grout, Gruner, and and George George Schwartz. Schwartz. H is d octoral d issertation on the t h e conglomerates and and structure s t r u c t u r e of of the t h e Ensign Ensign Lake Lake area, a r e a , Cook Cook County, County, Minnesota, Minnesota, under Professor P r o f e s s o r Gruner was the t h e beginning of of his h i s life—long life-long Hee also ffascination a s c i n a t i o n with with the t h e Precambrian. Precambrian. H a l s o became interested i n t e r e s t e d in i n iron iron formations and llater Michigan, eeventually formations a t e r began a rresearch e s e a r c h program in i n Michigan, ventually achieving achieving international i n t e r n a t i o n a l rrecognition e c o g n i t i o n as a s an authority a u t h o r i t y on on iron i r o n ores. o r e s . He He paper on U.S. U.S. iiron ore deposits att tthe Geological gave a paper ron o re d eposits a h e International I n t e r n a t i o n a l Geological Algiers U.N. Committee on Iron Ore Congress in in A l g i e r s in i n 1952, 1952, served on tthe h e U.N. Resources in 1953-54, and spent spent ssix weeks sstudying deposits Resources i n Geneva in i n 1953-54, i x weeks t u d y i n g iron iron d eposits AID I D program in i n Yugoslavia Yugoslavia in i n 1961. 1961. Carl C a r l is i s aa Fellow Fellow of of the the with the the A Society of America America and and sserves Membership S Secretary Geological S o c i e t y of e r v e s as a s tthe h e Membership e c r e t a r y ffor or tthe h e Society S o c i e t y of of Economic Economic Geologists. Geologists. Through the papers and t h e years y e a r s Carl C a r l has has produced prcduced many many papers and geologic geologic maps, maps, has worked worked ffor many y years and only aa few few can can be be mentioned mentioned here, here. lie H e has o r many e a r s in in the district of Michigan Michigan and Wisconsin, Wisconsin, and is co—author t h e Menominee iron iron d i s t r i c t of i s GO-author of USGS P.P. i s also a l s o co—author co-author of of USGS Maps MF—99 MF-99 of P.P. 513 513 and and Map Map 1—466. 1-466. He is MF-l81 on the He and MF-181 t h e bedrock geology geology of of the t h e Cuyuna Cuyuna district, d i s t r i c t , Minnesota. Minnesota. He iis s widely known for f o r aa series s e r i e s of of papers on on iron i r o n ore o r e resources r e s o u r c e s of of the t h e U.S., U.S., some foreign f o r e i g n countries. c o u n t r i e s . He is i s co—author co-author of of USGS USGS P.P. P.P. North America, and and some MF—225 on the ore deposits of tthe River— 570 and Map MF-225 t h e geology and o re d e p o s i t s of h e Iron I r o n RiverCrystal C r y s t a l Falls F a l l s district, d i s t r i c t , Michigan. Michigan. A very important contribution c o n t r i b u t i o n is i s aa series series of llithologic, geophysical, and mineral mineral commodity commodity maps of of Precambrian rocks of i t h o l o g i c , geophysical, Wisconsin, published as These maps are iin n Wisconsin, a s USGS USGS Map Map 1—631. 1-631. a r e aa complete of a available Wisconsin Precambrian, Precambrian, including compilation of v a i l a b l e information on tthe h e Wisconsin including previously unpublished d data numerous field many p r e v i o u s l y unpublished a t a ccarefully a r e f u l l y eextracted x t r a c t e d from numerous field Carl notebooks on hand in i n the t h e files f i l e s of of the t h e State S t a t e Survey. Survey. IIn n aaddition, ddition, C a r l has has written has served as w r i t t e n papers ffor o r several s e v e r a l guidebooks and has a s a leader l e a d e r on many ffield i e l d trips, t r i p s , both formal formal and and informal. informal. Carl i s indeed indeed a gentlemen and aa scholar s c h o l a r in i n the t h e highest highest C a r l Dutton is and aa wonderful wonderful man man tto have aas ttradition, r a d i t i o n , and o have s aa cco1league o l l e a g u e We W e thank thank him him for for his h i s long service s e r v i c e and and numerous contributions c o n t r i b u t i o n s to t o our our profession, p r o f e s s i o n , our our state, state, and our u university; his n i v e r s i t y ; for for h i s enduring interest i n t e r e s t and ccareful a r e f u l work in i n the the Precambrian; for his patient his Precambrian; for h i s generous and p a t i e n t assistance a s s i s t a n c e to to h i s ffellow ellow geologists g e o l o g i s t s in i n the t h e classroom, classroom, the t h e office, o f f i c e , the t h e laboratory, l a b o r a t o r y , and and the t h e field; field; and for his We for h i s cheerful c h e e r f u l optimism, optimism, quiet q u i e t modesty, modesty, and and gently g e n t l y dignity. d i g n i t y . We having C Carl us campus, and w wee hope enjoy and appreciate a p p r e c i a t e having a r l among u s on tthis h i s campus, he remains with with us u s for f o r many many years. years. - - v �TABLE TABLE OF OF EVENTS EVEWTS Wednesday, May 2, 1973 May 2, 1973 7:00—9:00 7:OO-9:OO p.m. p.m. Registration R egistration Conference Smoker (Cash Conference (Cash Bar) Bar) Mezzanine Mezzanine Ballroom North Registration Registration Technical Session S e s s i o n 11 Luncheon Technical Session S e s s i o n 22 Happy Hour (Cash Happy (Cash Bar) Bar) Banquet Mezzanine Ballroom North Ballroom South South Ballroom North Ballroom South South Ballroom South South Technical Session S e s s i o n 33 Luncheon Technical Session S e s s i o n 44 Business Meeting Buses for f o r Field F i e l d Trips T r i p s 22 && 33 leave Sheraton Inn leave Inn Parking Parking Lot Lot Ballroom Ballroom Ballroom Ballroom Thursday, May Thursday, May 3, 3, 1973 1973 8:00—10:00 8:OO-1O:OO a.m. a.m. 8:30—12:00 noon 8:30-12:OO 12:00—1:00 p.m. 12:OO-1:OO p.m. 1:30—5:10 1 ~ 3 0 - 5 : l Op.m. p.m. 6:00—7:00 6:OO-7:OO p.m. p.m. 7:00—8:30 p.m. 7:OO-8:30 p.m. Friday, F r i d a y , May 4, 4, 1973 1973 8:30—12:00 noon 8:30-12:OO 12:00—1:00 12:OO-1:OO p.m. p.m. 1:30—4:45 1:30-4:45 p.m. p.m. 4:45—5:00 4~45-5:00 p.m. p.m. 7:00 p.m. 7:OO p.m. Saturday, Saturday, May 5, 5 , 1973 1973 7:30 a.m. a.m. 6:00 p.m. 10:00 p.m. Bus for leaves f o r Field F i e l d Trip T r i p 11 leaves Sheraton Inn Parking Lot Bus ffor Field or F i e l d Trip Trip 1 1 returns returns Sheraton Inn Parking Lot Field Trip Bus ffor or F ield T r i p 2 returns returns Sheraton Inn Inn Parking Parking Lot Lot Sunday, May 6, 6 , 1973 1973 7:00 7:OO p.m. p.m. Bus for f o r Field F i e l d Trip T r i p 33 returns returns Sheraton Inn Inn Parking Lot vi North South South North North �TECHNICAL TECHNICALPROGRAM PROGRAM - SESSION SESSION 11 — Morning, Morning, Thursday, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Alan Alan T. T. Broderick Broderick and and L. L. Gordon Gordon Medaris, Medaris, Jr. Jr. 8:30 M.E. M.E. Ostrom Ostrom Welcoming Welcoming Remarks Remarks 8:40 P.K. P.K. Sims Sims Tectonic Tectonic history h i s t o r y of of Early E a r l y Precambrian Precambrian rocks in the Vermilion district, rocks i n t h e d i s t r i c t , northnortheastern e a s t e r n Minnesota. Minnesota. p. 34—35 34-35 p. 9:05 Edward Edward M. M. Ripley Ripley & & ' Donald Donald M. M. Davidson, Davidson, Jr. Jr. Structural Structural ultramafic ultramafic 9:25 M.S. M.S. Lougheed Lougheed && J.J. J. J. Mancuso Mancuso 9:50 Discussion Discussion of of papers papers evolution e v o l u t i o n of of the t h e Deer Deer complex, Minnesota. complex, Minnesota. p. p. Lake Lake 29 29 The The biogenic biogenic origin o r i g i n of of primary primary minerals minerals in i n Lake Superior Superior Precambrian Precambrian ironironformation. formation. p. 21—22 21-22 p. 10:00 Coffee Coffee break break 10:30 Klaus J. Schultz S c h u l t z && Klaus J. Edward Edward M. M. Ripley Ripley Petrology Petrology of of some some Early E a r l y Precambrian Precambrian differentiated d i f f e r e n t i a t e d ultramafic u l t r a m a f i c bodies bodies in in northeastern n o r t h e a s t e r n Minnesota. Minnesota. p. 32—33 32-33 p. 10:50 M.G. M.G. Mudrey, Mudrey, Jr. Jr. && A.L. A.L. Geldon Geldon AA Lower Lower Precambrian Precambrian lamprophyre lamprophyre pluton pluton near n e a r Ely, Ely, Minnesota. Minnesota. p. 25 25 p. 11:10 John John S. S. Klasner Klasner && Thomas Thomas R. R. Turner Turner Precambrian Precambrian north—south north-south oriented o r i e n t e d faults faults in the western Marquette i n t h e western Marquette district, district, northern n o r t h e r n Michigan. Michigan. p. 17—18 17-18 p. 11:30 Jens F. Touborg Touborg Jens F. 11:50 11:50 Discussion Discussion of of papers papers 12:00 12:OO Adjourn Adjourn 12:00 12:OO Luncheon Luncheon Structural S t r u c t u r a l and and stratigraphical s t r a t i g r a p h i c a l analysis analysis of of the t h e Geco Geco sulphide s u l p h i d e deposit d e p o s i t in in Manitouwadge, Manitouwadge, northwestern northwestern Ontario. Ontario. p. 38-39 38-39 p. Ballroom Ballroom South South vii vii �- SESSIII SESSION 22 — Afternoon, Thursday, May May 3, 3, 1973 1973 Co—chairmen: Co-chairmen: Paul G. G. Schmidt Schmidt and and Greg Greg Mursky Mursky Paul 1:30 M.D. Lewan M.D. Lewan Geochemistry Geochemistry of the the calcium-carbon calcium—carbon dioxide metasomatism dioxide metasomatism at a t Presque Presque Marquette, Michigan. p. 19—20 19-20 IIsle, s l e , Marquette, Michigan. p. 1:50 D.M. Mickelson D.M. Summary l a c i a l geology of of Summary of g glacial north—central Wisconsin. p. 24 24 north-central p. 2:15 E. Wm. Wm. Heinrich E. A n unusual manganese manganese deposit in in An Keweenawan lava, lava, Copper Copper Harbor, Michigan. p. 12 p. 12 2:35 Thomas A. A. Vogel & & Nancy Alyanak "Framboidal" "~ramboidal" chalcocite from White Pine, Michigan. Pine, p. 42 42 p. 2:55 Discussion of papers 3:05 Coffee break 3:35 Roger W. W. Cooper Cooper The Keweenawan volcanics north of of Gogebic range range in i n Wisconsin. Wisconsin. the Gogebic p. P. 99 3:55 John C. C. Green Progress report Progress report of of the t h e Coimuittee Committee on Keweenawan Keweenawan Stratigraphy. Stratigraphy. p. 11 11 p. 4:15 R.J. R. J. Stevenson Stevenson A Keweenawan Keweenawan layered layered mafic intrusion intrusion Finland, Lake near Finland, Lake County, County, Minnesota. Minnesota. p. 36 36 p. 4:35 W.F. W.F. Cannon Cannon High grade magnetite magnetite deposits deposits at High grade at Republic, Michigan: Their bearing Republic, Michigan: Their on the genesis genesisof ofMarquette MarquetteRange Range hard ore. 6-8 hard ore. p. 6—8 5:00 Discussion of papers 5:10 Adjourn 6:00 Happy Ballroom South South (cash (cash bar) Happy hour Ballroom 7:00 Banquet Ballroom South Address by Dr. Cameron Dr. Eugene Cameron ANIM&L, VEGETABLE, VEGETABLE, OR OR M MINERAL? ANIMAL, INERAL ? viii v iii �- Friday, May 4, SESSION SESSION 33 — Morning, Friday, 4, 1973 1973 Co-chairmen: Co—chairmen: Ralph W. Carl E. Dutton Ralph W. Marsden Marsden and and C a r l E. 8:30 Richard Berger Richard and oothers and thers Environmental Environmental geology geology and and land land use planning, Chassel planning, Chassel quadrangle, quadrangle,Houghton Houghton p. 3—4 County, Michigan. p. 3-4 8:50 Ennny Booy & E mmy B00y Ruth J. J. Sobanski Sobanski Engineering geology of of the t h e Military Military Hill H i l l landslides, l a n d s l i d e s , Ontonagon Ontonagon County, County, Michigan. P. 5 p. 5 9:10 C.R. Bentley C.R. Magnetotelluric evidence for f o r lateral lateral variations v a r i a t i o n s of of ccrustal r u s t a l structure s t r u c t u r e in in northern n o r t h e r n Wisconsin. P. 2 2 p. 9:30 F. Touborg Jens F. The Atikokan Iron I r o n Range Range and and its its iron-copper m mineralization. iron-copper ineralization. p. p. 40 9:50 Discussion of Discussion of papers 10:00 Coffee break 10:30 G. G. Mursky Mursky and others others Mineralogical and and chemical studies studies of greenstones in 26-27 of i n Wisconsin. Wisconsin. p. p. 26—27 10:50 W.R. Van W.R. Van Schmus Schmus Geochronology of of Precambrian Rocks iin n eeastern a s t e r n Wisconsin. p. 41 41 p. 11:10 L.G. Medaris, Jr. L.G. Jr. and others others late b a t h o l i t h — a late The Wolf River batholith massif in Precambrian rapakivi r a p a k i v i massif in northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. p. 23 23 p. 11:30 J.L. J.L. Anderson Graphical analysis a n a l y s i s of of portions p o r t i o n s of of the granite the g r a n i t e system with application application biotite—bearing tto o b i o t i t e - b e a r i n g granitic g r a n i t i c melts melts and gneisses. and g neisses. P. p. 11 11:50 Discussion of of papers 12:00 Adjourn 12:00 Luncheon - Ballroom South South ix �- SESSION SESSION 44 — Afternoon, Friday, Friday, May 4, 4, 1973 1973 Co—chairmen: Co-chairmen: Paul C. Paul C. Tychsen Tychsen and and Perry P e r r y Olcott Olcott The ppetrology e t r o l o g y and geochemistry of Round Lake Lake iintrusion, n t r u s i o n , northwestern Wisconsin. p. 30 30 p. 1:30 D.L. D.L. E.N. E.N. Roder & Cameron Cameron 1:50 J.E. Thresher J.E. The formation of of the t h e Pittsville Pittsville (Wisconsin) migmatite. 37 (Wisconsin) p. 37 p. 2:10 Robert A. A. Jenkins Jenkins The geology of of Pembine and and Beecher townships, Marinette townships, M a r i n e t t e County, County, Wisconsin. p. 15—16 15-16 p. 2:30 John M. M. Ohlson Ohison The iron i r o n ore o r e deposits d e p o s i t s at a t Black River Falls, F a l l s , Wisconsin, Wisconsin, geology operations. p. 28 and o perations. p. 28 2:50 Discussion of of papers papers 3:00 Coffee break 3:30 0.H. Dury G.H. Southwest Wisconsin as a s aa duricrusted duricrusted pediplain. p ediplain. p. 10 10 p. 3:50 A.V. A.V. Ileyl Hey1 Mississippi Upper M i s s i s s i p p i valley v a l l e y lead—zinc lead-zinc district. d istrict. p. 13—14 13-14 p. 4:10 S.B. Romberger S.B. Upper Mississippi M i s s i s s i p p i valley v a l l e y base base metal metal deposits: d e p o s i t s : experimental solutions s o l u t i o n s to to p. 31 problems of ore genesis. p. 31 problems of o r e g e n e s i s . 4:30 Discussion of of papers 4:45 Business Meeting Business 5:00 Adjourn 7:00 from parking parking lot. Buses for f o r field f i e l d trips t r i p s 22 and and 3 3 leave l e a v e from lot. x �GRAPHICAL ANALYSIS OF OF PORTIONS GRAPHICAL ANALYSIS PORTIONS OF OF THE THEGRANITE GRANITESYSTEM SYSTEMWITH WITH APPLICATION TO BIOflTE—BEARING GRANITIC MELTS AND GNEISSES APPLICATION TO BIOTITE-BEARING GRANITIC MELTS AND GNEISSES Department of Geology and Anderson, Department of Geology J. LL.. Anderson, Wisconsin, Madison, Wisconsin Wisconsin. Madison, Wisconsin 53706 53706 Geophysics. University University of Geophysics, of ABSTRACT ABSTRACT - phase relations in biotite—bearing modelto to describe describe phase granitic melts ite-bearing granitic melts model analysis SiOy - KA1Si3O8 analysis of ofthe thesystem system SiC2 KAlSi30g NaA1Si1OS — FeO Fe2O3 provides a tentative Hz0 - K2MgSiAL20 1120 provides KgMgfiSifiAlzOzo Graphical Graphical CaAl2Si2O8 CaAl SigOg — — — gneisses. Defining and gneisses. Defining 'FeO' 'FeO' as as an an arbitrary arbitrary combination combination of of FeO FeO and Moreover,it it has specifies the and Fe20 theoxygen oxygen fugacity. Moreover, has been been and Fe20 specifies split the system system into three four comoonent comoonent subsystems necessax necessary to split to of the the components components 110, KMgSi6fl2G20, to evaluate evaluate separately separately the effect of and Quartz, alkali feldspar, and CaAl2Si2Op on the the rest rest of of the the system. system. Quartz, CaAl Si 0 on plagioclase, iotite, magnetite, plagioclgse: !?iotite, magnetite,granitic granitic melt, melt, and and vapor vapor are are the the considered phases. considered phases. Application Apolication of of Schreinemakers' Schreinemakers' rules rules combined combined biotite — magnetite magnetite with with experimental experimental data data on on alkali alkali feldspar feldspar — biotite and of topologies. topologies. The The and crystal—melt crystal-melt equilibria equilibria generates generatesan. an array of system system is is characterized characterized by by degenerate degenerate equilibria, equilibria. - - In In application, application, several several conclusions conclusions can can be be made made which which are are as as 1) degrees of 1 ) Dependent Dependent on on the the number number of of degrees of freedom, freedom, the the KK/Na /N~ Fe/Mg ratios in biotite can and ~ e/~ ratios g in biotite can be be aa function function of of temperature, temperature,total total pressure, potential of water, water, oxygen fugacity, and the pressure, chemical chemical potential oxygen fugacity, the bulk fugacity is buffered and fluid fluid If oxygen oxygen fugacity composition composition of of the the rock. rock. If pressure equals equa total totalpressure, pressure,divariant divariant assemblages assemblages (with (with respect respect to to F) have T and and P) have fixed fixed biotite biotite compositions. compositions. Such Such assemblages assemblages become become T trivariant H20 is not in in excess such as in %O H2O - undersaturated trivariant if if HgO undersaturated additional degree of freedom allows only one of of the two melts, melts. One additional ratios will vary with ratios (i.e., (i.e., Fe/Mg ~e/Mgor or K/Na) K/N~)to to be be fixed. fixed. The other other will the bulk composition the composition of of the the rock, rock. As to which of of the the two two ratios ratios will Another degree degree of of freedom freedom will this is is depends depends on on the the assemblage, assemblage. Another Biotite allow ratiosto tovary varywith withthe thebulk bulkcomposition, composition. 2) 2) Biotite allow both ratios follows: follows: - stability can of partial stability canstrongly stronglyinfluence influencethe thecomposition composition of partialmelts melts derived assemblage quartz—plagioclase—biotite— quartz-plagioclase-biotitederived from from gneisses gneissesofofthe the assemblage of partial partial Ifthe thebiotite biotiteremains remainsstable stablebeyond beyond conditions conditions of magnetite. magnetite. If melting onlytonalitic tonalitic melts can result. result. 3) melting only melts can Alternatively, this this 3) Alternatively, coexist in assemblage assemblage cannot cannot coexist in equilibrium equilibrium with introduced granitic granitic south of Stevens melt. A possible example is an injection gneiss south Point, Wisconsin, where the Point, Wisconsin, the alkali alkali feldspar feldspar in in the granitic granitic veins veins isolated from to is isolated from the the host host rock rock by by plagioclase. plagioclase. LiV) 4) Application Application to ranakivi massifs, such batholith of ranakivi granite granite massifs, such as as the Wolf River River batholith of Topological changes Wisconsin, Wisconsin, is is possible, possible. Topological changes suggesting suggesting feldspar feldspar mantling and replacementofofalkali alkalifeldsoar feldsparby bybiotite biotite exist. exist. mantlinc and the the replacement The feasibility of is being The feasibility ofsuch such explanations explanations is being studied, studied. 1 �MAGNETOTELLURIC EVIDENCE FOR FOR LATERAL LATERAL VARIATIONS OF MAGNETOTELLURIC EVIDENCE OF CRUSTAL STRUCTURE CRUSTAL STRUCTURE IN NORTHERN NORTHERN WISCONSIN WISCONSIN C. R. R. Bentley, Bentley, Department Department of Geology and of Geology and Geophysics, Geophysics,University University of of C. Wisconsin—Madison,Madison, Madison, Wisconsin, Wisconsin, 53706. Wisconsin-Madison, 53706. ABSTRACT ABSTRACT IIff two-dimensional two-dimensional inhomogeneity inhomogeneity iis s the reason reason ffor o r apparent apparent anisotropy anisotropy studies, then of the the pair of iinn magnetotelluric magnetotelluric studies, then one one of of curves curves at a t each each site site should be close to t o that t h a twhich whichwould would be be observed observed over over aa one-dimensional one-dimensional earth. should be close Ontthis On h i s basis, sites s i t e sini nWisconsin Wisconsin can can be be divided divided into i n t o three three geographically geographically The systematic systematic distinct w i t h decidedly decidedly different d i f f e r e naverage t average curves. curves. The d i s t i n c tgroups groups with grouping implies tthat grouping ofof ssites i t e s implies h a t the the differences differences rreflect e f l e c t real real differences differences justvariations variationsin in local near-surface conditions. conditions. the crust, crust, not notjust within the thethe local near—surface That implication boundary That implication isi sstrengthened strengthenedby bythe thefact f a cthat t t h one a t one boundarybetween between groups correspondstto groups corresponds o an an abrupt change change iinn structure structurededuced deduced completely completely independently from from seismic seismic and andgravity gravity data in independently data alone alone (Ocola (Ocola and and Meyer, Meyer, in The two-dimensional two—dimensionalassumption assumption alsoimplies implies tthat press, J.G.R.). press, J.G.R.). The also h a t the the c o r r e c t " curve curve of of each each pair corresponds corresponds t otocurrent t o the the "correct' currentflow flow parallel parallel to current direction directioncorresponding corresponding to t o the the two-dimensional boundary. two-dimensional boundary. Plotting current acceptedcurve curveaat eachs site accepted t each i t e reveals reveals a a parallelism parallelism with withcontours contours ofofBouguer Bouguer gravity anomalies, controlling gravity anomalies, suggesting suggesting tthat h a t the the two—dimensionality two-dimensional i t y control 1ing the the tensor orientation isi snot notnear—surface near-surface aatt all, a l l ,asashas haspreviously previouslybeen been tensor assumed, associatedinstead insteadwith withgross grosscrustal crystal structure. t i sis associated assumed, b ubut 2 �ENVIRONMENTAL GEOLOGY GEOLOGYAND ANDLAND LAND U USE ENVIRONMENTAL SE PLANNING, CHASSELL QUADRANGLE, COUNTY, MICHIGAN QUADRANGLE, HOUGHTON HOUGHTON COUNTY, CHASSELL Richard M. Hamil, Hamil, Department Department of of Geology Geology Richard Berger, Berger, Eniny Emy Booy, Booy, and and Brenton Brenton M. and Geol ogi cal Engineeri ng, Michigan Technol ogi cal University, and Geological Engineering , Mi chi gan Techno1ogi cal University, Houghton, Mi chi gan 49931. Houghton , Michigan ABST RACT ABSTRACT The Chassell ChassellQuadrangle Quadrangle locatedinin the the southeastern southeasternquarter quarter of of the The i s islocated It formerly uutilized I t includes includes land land which which was was formerly t i l i z e d for f o rcopper copper area iiss sparsely o r agriculture. The The area sparselypopulated populatedand andmay may mining as aswell well as as ffor mining evaluation of geological be developmenti ninthe the future. future. An An evaluation geological be expected expected tto o undergo undergo development factors affecting such development factors affecting such developmenthas hasbeen beenmade. made. Keweenaw Peninsula. Keweenaw Peninsula. About 85 85 percent percentof of the the land has About has a a slope less less than than 15 15 percent, percent, with withmore more About one one quarter quarter than than half of of that t h a thaving having aaslope slope less less than than 55percent. percent. About of the the land land ininthe thequadrangle quadranglehas has more more than than 50 50 feet f e e t of ofoverburden, overburden, another another quarter (mostly (mostly overlying overlying the the Jacobsville Jacobsville sandstone sandstone in the the eastern eastern area) area) 30 tto 30 o 50 50 ffeet, e e t , and and the the rest r e s t (mostly (mostly in in the thewesterly westerly areas areas overlying overlying the the Portage Lake Lake Lava Lava flows) flows) between and 30 30 ffeet Portage between 00 and e e t of of overburden. overburden. Most of of these Most these soils loam s o i l s are are classified c l a s s i f i e dasassilty s i l tto y sandy t o sandy loam(USDA (USDA cclassification) l a s s i f i c a t i o n )oro rSM SM or or SC (Unified Soil Soil Classification) SC (Unified Classification)having havinga alow lowshrink—swell shrink-swell potential potential and and There iiss aa prevalent prevalent hardpan hardpan layer good permeability permeability (about (about 2.2 2.2 inches/hour). inches/hour). There good pHofof the the soils s o i l s isi ssomesomeThe pH at a t variable variabledepth depth which which isi sa asandy sandyloam loam or o rSC. SC. The The corrosion corrosion hazard hazardf for metal and andconcrete toncrete iiss low. - 55 ttoo 6.6. The o r metal low. what acid — what 10 percent percentofof the the land There generally aa thin thin topsoil. About There iis s generally About 10 land area area is is Theseare aremostly mostly on on the the floodplains underlain organic ssoils. underlain by by alluvium and and organic o i l s . These of wouldseverely severely thepotential potentialf ofor of rivers rivers which which would r e restrict s t r i c t the r uutilization. tilization. areas are generally classified areas are c l a s s i f i e dasasmarshland. marshland. These Underground water supply providedbybythe theglacial glacial ddrift Underground water supply i sisprovided r i f tand andbedrock. bedrock. Wherethe theglacial glacial ddrift Portage Where r i f tisi sdeep deepand and ini nparts partsofofthe the PortageLake LakeLava Lava series series Jacobsville The Jacobsvi l l esandstone sandstone there there is i s sufficient s u f f i c i e n water t waterfor f o domestic r domestic supplies. supplies. The There are some problemswith with Fe has some problems Fe content has ssufficient u f f i c i e n twater water for f o rdomestic domestic use. use. There in water water from from the the glacial glacialand andJacobsville Jacobsvillesources; sources;septic s e p t itanks c tanksmay maycontaminate contaminate some the shallow shallow aquifers. some ofof the About 80 80 percent percent of of the land theChassell ChassellQuadrangle Quadrangleisi swell—drained. well-drained. About land ini nthe There The Pilgrim, Pike, The Pilgrim, Pike, and and Sturgeon Sturgeon Rivers Rivers drain drain the thearea area tot oPortage PortageLake. Lake. There and during during spring spring thaw flooding permanent marshland marsh1 and and thaw temporary temporary flooding iiss substantial substanti a1permanent occurs iinn many uplandareas areasdue duet otothe theimpermeability impermeability of of the the underlying many upland underlying bedbedoccurs areasdirections directions of of surface drainage ddiffer rock. In some some areas surface drainage i f f e r from from the the drainage drainage patterns at bythe the glacial glacial patterns a t depth depth due due to t o the thepresence presence of of bedrock bedrock ridges ridges masked masked by ddrift. rift. Old mine openings openingsdodonot notappear appeart otobe beaamajor majorhazard hazardinin future planning, Old mine planning, bbut u t shaft locations locations will willhave have to t obe be taken taken into intoaccount. account. 3 �About 20percent percentofof the the land land iiss currently About 20 currentlyowned owned by by large private private organorganExceptffor holdings, most of the land izations. Except o r small small state s t a t e and and municipal municipal holdings, most of land of the the quadrangle quadrangle iis s held held by by small small individual individual landholders. landholders. Current forestryand andfarming fanningwith w i t hpotatoes, potatoes, Current uutilization t i l i z a t i o n isi smostly mostlyini nforestry There iiss less less strawberries, and and dairy dairy products products being being the thedominant dominant crops. crops. There commercial and g h t industrial industrial purposes. purposes. than used ffor o r connnercial than 10 10 percent percent of of the the land used andl ilight Recreational useofof the the land, land, e.g. e.g. hunting snowmobilingi sisf afairly hunting and and snowmobiling irly Recreational use usewill will probably widespread. Future Future use probably include include mining mining and and recreation as as well well as agriculture. Development Development industry willbebep partially as of of industry will a r t i a l l y controlled by by access water which which iiss abundant along the the shores of Portage u t less less access tto o water abundant along shores of Portage Lake Lake bbut accessible in major majorquantities quantities further inland. accessible in inland. 4 �ENGINEERINGGEOLOGY GEOLOGY THEMILITARY MILITARYHILL HILL LANDSLIDES, ENGINEERING OFOFTHE LANDSLIDES, ONTONAGONCOUNTY, COUNTY, MICHIGAN MICHIGAN ONTONAGON EmmyBooy Booyand andRuth RuthJ.3.Sobanski, Sobanski, Department Department ooff Geology Geology and and Geological Geological Emmy Engineering, Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan Michigan 49931. Engineering, Michigan Michigan Technological ABSTRACT The vvalley The a l l e y of o fthe t h eEast EastBranch Branchofo the f t hOntonagon e OntonagonRiver, River,Ontonagon Ontonagon County, County, Michigan i is throughaat hthick Michigan s downcut downcut through i c k sseries e r i e s of o f glacial g l a c i a lake—deposited l lake-deposited clays, clays, Thesecclays have proven provenaa hazard hazardt to tthe h e Ontonagon Ontonagon clays. These l a y s have o construction c o n s t r u c t i o n and and maintenanceoof 45because becauseo foft hthe numerous slopef afailures maintenance f tthe h e U.S. U.S. Highway Highway 45 e numerous slope i l u r e s ooff various sizes are rrepetitive These f afailures i l u r e s are e p e t i t i v e in in various s i z e s abutting a b u t t i n g on on the t h ehighway. highway. These nature, rreflecting nature, e f l e c t i n g variation v a r i a t i o n ini nmoisture moisture content content with w i t h precipitation p r e c i p i t a t i o nand and snowmelt. snowmel t. The nature ooff the clayscauses causes The llayered a y e r e d nature t h e Ontonagon Ontonagon clays s usubstantial b s t a n t i a l v avariability riability in i n the t h e physical p h y s i c a l properties p r o p e r t i e s of o f the t h e mass mass bboth o t h l alaterally t e r a l l y and and vvertically. e r t i c a l l y . IInn general tthe material be cclassified general he m a t e r i a l can can be l a s s i f i e d as as clays c l a y s and and clay—silts c l a y - s i l t s with w i t h fine f i n esand sand percent to contents ranging contents ranging from from less l e s s than than 11 percent t o 14 14 percent. percent. Atterberg those ffor A t t e r b e r g LLimits i m i t s of o f these these materials m a t e r i a l s range range from from those o r inorganic i n o r g a n i c clays clays P l a s t i c limits l i m i t srange range from from of o f low low pplasticity l a s t i c i t y to t o those those of o f high high pplasticity. l a s t i c i t y . Plastic 24 50,.liquid limits l i m i t sfrom from 27 27 to t o 100, 100, and and pplasticity l a s t i c i t yindices i n d i c e s from from 12 12 to t o 58. 58. 24 tto o 5O,Jiquid There appearst otobebenonoc oconsistent of physical There appears n s i s t e n t p apattern t t e r n o of f vvariation a r i a t i o n of p h y s i c a l properties properties of (e.g. at o f the t h e material m a t e r i a l wwith i t h llocation o c a t i o n wwithin i t h i n iindividual n d i v i d u a l sslides l i d e s (e.g. a t toes toes of o f slides slides or o r on on the t h e failure f a i l u r eplace placeata the t t h escarp) scarp)nor n owith r w i t helevation e l e v a t i o above n abovea adatum datum nor nor along along the t h e general general north—south north-south ttrend r e n d of o f the t h ehighway. highway. The nnatural moisture content content ooff these The a t u r a l moisture these failure-prone f a i l u r e - p r o n e materials m a t e r i a l s ranges ranges from from 18 tto percent iin takeni nint hthe 18 o 41 41 percent n samples samples taken e l late a t e Fall F a l l of o f1972. 1972. This T h i s approaches approaches water has observed aatt various times the Free water has been been observed times t h e pplastic l a s t i c llimits i m i t s of o f the t h e soils. s o i l s . Free of water ttable o f year y e a r on on these these slides s l i d e s and and the t h e ground ground water a b l e is i s frequently f r e q u e n t l yextremely extremely close close to Averagep rprecipitation e c i p i t a t i o n i in n tthis h i s area area is i s 34 34 inches, inches, much much oof f iitt t o the t h e surface. surface. Average meltwater iinn the t h e form form of o f snowfall s n o w f a l l whose whose meltwater i s isa as isignificant g n i f i c a n t ffactor a c t o r in i n the the frequent frequent occurrence occurrence ooff Spring Spring sslides. lides. IIttisi sextremely extremely uunlikely n l i k e l y tthat h a t chemical chemical o or r e electrical l e c t r i c a l sstabilization t a b i l i z a t i o n ooff these slopes wwill Surface drainage drainage appears i l l prove prove useful. u s e f u l . Surface appears tto o be be the t h e most most these slopes economic formo fofslope slopec ocontrol economic form n t r o l i in n tthis h i s instance. instance. 5 �HIGH-GRADE MAGNETITE HIGH-GRADE MAGNETITE DEPOSITS DEPOSITS AT AT REPUBLIC, REPUBLIC, MICHIGAN: MICHIGAN: THEIR BEARING ON THE GENESIS O F MARQUETTE RANGE HARD ORE* ORE* OF U.S. Geological Survey, Survey, Washington, D.C. D.C. 20244 20244 W.F. Cannon, U.S. W.F. ABSTRACT ABSTRACT Hard ore (60—65 (60-65 percent Fe) in i n the Marquette Iron Range consists c o n s i s t s of I t characteristicalcharacteristicalconcentrations of specularite, s p e c u l a r i t e , magnetite, and and martite. martite. It thethe Negaunee lly y occurs at a t the thetop topofof NeqauneeIron—formation Iron-formation and and over over a few feet feet grades grades llaterally a t e r a l l y and downward into i n t o jaspilite j a s p i l i t e (30-35 (30-35 percent percent Fe). Fe). Van Hise Hise classic and Leith (1911) (1911) developed the now c l a s s i c concept tthat h a t tthe h e ore was formed by surface weathering and leaching of silica s i l i c a from from the iron-formation iron-formation prior prior to deposition of the unconformably overlying Goodrich Quartzite, and the t o deposition of the unconformably overlying Goodrich Quartzite, and the ore produce tthe o r e was was later l a t e rdeformed deformed and and metamorphosed metamorphosed t to o produce h e present present specularite— speculariterich "This hypothesis hypothesis has has withstood withstood critical c r i t i c aexamination l examinationby bymany many r i c h rock. rock. This geologists; evidence in its support is especially compelling in the eastern geologists; evidence i n i t s support i s especially compelling i n the eastern part p a r t of the t h e Marquette Marquette Range. Range. Boyum (1964) (1964) and Anderson (1968) (1968) have suggested suggested that concept, although although probably probably valid, v a l i d , is i snot not adequate adequate tto o explain explain aall ll t h a t this concept, ffeatures e a t u r e s of of the the ore ore bodies. bodies. M y own leadsme me My ownreexamination reexaminationofofthese these deposits deposits leads to support conclusions. II believe to supportBoyum's Boyum's and and Anderson's conclusions. believe that t h a tmuch much of of the the ore, o r e , especially e s p e c i a l l y specularite—rich s p e c u l a r i t e - r i c h ore, ore, has formed as suggested suggested by Van Van Hise and Leith, magnetite-rich ore (commonly Leith, but that t h a t magnetite-rich (commonly greater g r e a t e r than than 90 90 percent magnetite) has has aa different magnetite) d i f f e r e n t origin. origin. - At the Republic open pit, the jaspilite unit at the top of the Negaunee A t the Republic open p i t , the j a s p i l i t e u n i t a t t h e t o p of the Negaunee Iron-formation Iron-formation iiss presently presentlybeing beingmined. mined. The The jjaspilite a s p i l i t e is i s the the host h o s t rock rock The ffor o r magnetite-rich magnetite-rich hard hardore, o r e which , whichwas waspreviously previouslymined minedunderground. underground. The piti t provides p provides exceptional exceptionalexposures exposures of ofthe t h ehigh—grade high-grade magnetite magnetite ore ore bodies bodies and and ttheir h e i r contacts contacts with with the the surrounding surrounding j jaspilite. aspilite. Three ccritical r i t i c a l features features Three common hard—oredeposits deposits iinn the common t otoaall l l magnetite—rich magnetite-rich hard-ore t h e Marquette Marquette Range Range and and difficult d i f f i c u l ttot oexplain explainby bythe theweathering weathering hypothesis hypothesis are a r e shown shown tthere h e r e bbetter e t t e r than than at other a t any any o t h e r locality. locality. 1) Although Althoughsspecularite alll lhard—ore bodies, magnetite 1) p e c u l a r i t e is i scommon common tto o a hard-ore bodies, magnetite i s the thepredominant predominant mineral n many, a r t i c u l a r l y in i n higher higher grade grade is mineral iin many,pparticularly metamorphic rocks toward toward the the west west end end of of the the Marquette Marquette Range. Range. The magnetite-rich magnetite-rich ore ore contains contains ttextural The e x t u r a l evidence evidence iindicating n d i c a t i n g tthat hat formedaafter it has formed f t e r regional regional deformation. deformation. it a) a) The ore iiss massive, textures are massive, deformational deformational textures a r e absent, absent, and and "The ore magnetite grains aare magnetite grains r e largely l a r g e l y euhedral euhedral and and undistorted. undistorted. b) b) Bodies of massive massiveore ore sharply sharply truncate truncate schistose Bodies of s c h i s t o s e and and crenulated specularite—rich crenulated specularite-rich jjaaspilite. spilite. c c)) The magnetite-rich oreis icommonly s commonlysomewhat somewhat vuggy vuggy and porous, porous, The magnetite-rich ore containing sspecularite, containing p e c u l a r i t e , dolomite, dolomite, and and quartz crystals c r y s t a l s in i n vugs. vugs. 6 �2) 2) Magnetite—rich Magnetite-rich ore ore is i s characteristically c h a r a c t e r i s t i c a l l y associated associated with w i t h quartz quartz veins. (+ dolomite, s u l f i d e ) veins. dolomite, sulfide) ±. ± 3) 3) Although ~ l t h o u g hthe the magnetite—rich magnetite-rich ore ore invariably invariably occurs occurs in i n hematitic hematitic iron—formation iron-formation (jaspilite), ( j a s p i l i t e ) , the the ore o r e bodies are a r e surrounded surrounded by by narrow narrow haloes haloes in i n which which jasper jasper was was converted converted to t o gray gray chert c h e r t or or milky milky quartz quartz and and some some specularite s p e c u l a r i t e was was reduced reduced to t o magnetite, magnetite, i s associated associated i n d i c a t i n g that t h a t the the formation formation of of magnetite-rich magnetite-rich ore ore is indicating with w i t h aa reducing reducing process process rather r a t h e r than than an anoxidizing oxidizingprocess process such such as as weathering. weathering. + The magnetite—richore oreiis s probably probably of of hydrothermal hydrothermal origin o r i g i nand andbecause because The magnetite-rich s the only only recognized recognizedpost postiron—formation iron-formation Penokean regional metamorphism iis Penokean regional metamorphism the fluids f l u i d swere wereprobably probably derived derivedby by dehydration dehydration and and dedethermal event, event, the thermal carbonatization carbonatization of ofthe theiron—formation iron-formation and and underlying underlying rocks rocks during during progressive progressive regional metamorphism metamorphism which which reached reached sillimanite s i l l i m a n i t e grade grade at a t Republic. Republic. regional topt oof thethe Negaunee l o c a l i z a t i o n of of the t h eore o r eatathe t the p of NegauneeIron-formation Iron-formation The localization The might be explained explained through throughthe the buffering buffering aaction might be c t i o n of of the theiron-formation iron-formation on on A s fluids f l u i d s(considered (consideredhere hereasa sF120 H20 for for the oxygen oxygen fugacity h e fluids. f l u i d s . As the fugacity of of tthe CO2 rrich) i c h ) are a r e expelled expelled during during metamorphism metamorphism s i m p l i c i t y but but probably probably also a l s o CO2 simplicity w i l l contact contact first f i r s t the the and pass pass upward upward through through the t h e rock rock section, s e c t i o n , they they will and magnetite-silicate and r e l a t i v e l y reduced reduced magnetite-silicate andmagnetite—carbonate magnetite-carbonate uunits n i t s iin n the the relatively lower lower part p a r t of ofthe theNegaunee Negaunee and and will w i l ltend tendtoward towardan anequilibrium equilibriumoxygen oxygen fugacity determined on figure f i g u r e1,1, determined by by aa buffer b u f f e r curve curve fugacity (f02), ( f o 2 ) ,such such as a s point p o i n t 11on such as curve curve A, A, and and will w i l l contain contain concentrations of ferrous ferrous and and ferric f e r r i c iron iron such A s fluids f l u i d spass passupward upward and and species appropriate appropriate for f o r that t h a tf02 f o 2and andtemperature. temperature. As species contact the jaspilite, whichthe thej jaspilite contact the j a s p i l i t e , a aredox redoxreaction reaction must must occur occur iin n which a s p i l i t e is is partly of sspecularite p a r t l y reduced reduced by by the the conversion conversion of p e c u l a r i t e to t o magnetite magnetite and and the the fluids fluids are bybythethe hematite— a r e oxidized oxidized to toachieve achievean anf07, f o such suchasa point s p o i n2, t 2determined , determined hematiteThe increased increased f02 f of of the t h e fluids f l u i d sand andconsequent consequent B). Tfie magnetite buffer magnetite buffer fcurve urve B). 02 lower species lower ssolitility o l u b i l i t yofofferrous ferrousiron iron speciesand andthe theoxidation oxidationofofsome some ferrous ferrous iron i r o n to t o less l e s s soluble soluble ferric f e r r i c species species results r e s u l t s in i n the the precipitation p r e c i p i t a t i o n of of Textures clearly clearly magnetite. Textures magnetite. indicate i n d i c a t e that t h a t silica s i l i c a was removed removed during during the the wasp precipitated its hydrothermal activity a c t i v i t yand and the themagnetite magnetite presumably presumably was r e c i p i t a t e d iin n its hydrothermal Because t the h e equilibrium equilibriumff02 of the buffered assentlages is of the buffered assemblages i s very very place. Because small atmffor the02 probable small small (10-40 (10-40 to t o10—20 10-20 atm o r the probable conditions conditionsof ofmetamorphism), metamorphism), small volumes of l a r g e volumes volumes of l u i d , and and the t h e system system can can volumes of rock rock can can buffer buffer very very large of ffluid, buffered until u n t i l all a l l hematite hematite in i n the the jaspilite j a s p i l i t e is i s converted converted to t o magnetite. magnetite. remain buffered I propose that t h a t the the magnetite—rich magnetite-rich ore ore has has formed formed by: by: 1) 1) the reduction reduction of hematite to t o magnetite magnetite during duringa ahematite—magnetite hematite-magnetite b u f f e r reaction; reaction; 2) 2) buffer of the precipitation p r e c i p i t a t i o nofofmagnetite magnetitefrom fromhydrothermal hydrothermal (metamorphic) (metamorphic) ffluids l u i d s as a s the the the fluids oxidized during duringt that reaction and and tthe f l u i d s were were oxidized h a t bbuffer u f f e r reaction h e ssolubility o l u b i l i t y of of i r o nwas was decreased. decreased. ferrous iron 7 �2 t HEM. 1 Fe—SILICATE T Figure Figure 1.-— I.-- T—f0 T-f diagram showing e l a t i v e positions p o s i t i o n sofof hematite-magnetite diagram showingrrelative hematite—magnetite 02 buffer buffer curvi curveand and aabuffer buffercurve curvedetermined determined by by the the equilibruim: equilibruim: quartz magnetite == Fe—silicate. F e - s i l i c a t e . Points Points 1 1 and and 22 iillustrated l l u s t r a t e d difdifquartz ++ magnetite ference ference in i n f02 f o2 controlled controlledby by the thebuffered bufferedassemblages assemblages at a t constant constantT. T. The formation ore t oto require e s t r i c t e d set set The formationofof magnetite-rich magnetite—rich oreappears appears requirea ar restricted of of conditions: conditions : 1) must reach 1)Metamorphism Metamorphism must reach a t at l eleast a s t bbiotite i o t i t e grade, grade, although although most most l l large l a r g e ones ones are a r e in i n garnet garnet or o rhigher higher grade. grade. ore bodies bodies and and aall ore 2) 2 ) Iron-formation Iron-formation with mostly ferric f e r r i c iron, i r o n , such as a s jaspilite, j a s p i l i t e , must be physically physically above above iron-formation iron-formation with w i t h abundant abundant ferrous ferrous iron. iron. 3) 3) A stratigraphic s t r a t i g r a p h i c or o r structural s t r u c t u r a l trap t r a p capable of concentrating concentrating the the flow flow of of fluids f l u i d s must must be be present. present. The The Goodrich Goodrich Quartzite Quartzite and and metadiabase metadiabase sills s i l l s and and dikes dikes were were apparently apparently relatively r e l a t i v e l y impermeable, impermeable, and the Negaunee—Goodrich Negaunee-Goodrich contact contact near near anticlinal a n t i c l i n a l crests c r e s t s and and dikedikeand the quartzite q u a r t z i t e intersections i n t e r s e c t i o n s were were favorable favorable loci l o c i for f o rore o r eformation. formation. The absenceofofany anyofof these these tthree The absence h r e e conditions conditions iinhibits n h i b i t s the t h eformation formation of of magnetite-rich magnetite-rich ore. ore. References References Paderson, G . J . , 1968, 1968, The The Marquette Marquette district, d i s t r i c t , Michigan, Michigan, in i n Ridge, Ridge, J.D., J.D., Anderson, G.J., (ed.), (Graton-Sales (ed. ) , Ore deposits of the t h e United United States, S t a t e s , 1933—1967 1933-1967T~raton-Sales Volume), V. 1: 1:New New York, York, Pat. Am. Inst. I n s t . Mining, Metall., Metall., and and Petroleum Petroleum Volume), V. Engineers, Engineers, p. p. 505—517. 505-517. Boyum, B.H., 1964, 1964, The The Marquette Marquette mineral mineral district, d i s t r i c t , Michigan: Michigan: Inst. I n s t . on on Boyum, B.H., Lake Lake Superior Superior Geology, Geology, 10th, l o t h , Ishpeming, Ishpeming, Mich., Mich., May May 1964, 1964, Guidebook, Guidebook, 13 13 p. p Van C.R., and and Leith, Leith, C.K., C.K., 1911, 1911, The The geology geology of of the the Lake Lake Superior Superior Van Hise, Hise, C.R., region: region: U.S. U.S. Geol. Geol. Survey Survey Mon. Mon. 52, 52, 641 641 p. p. * Work Work done doneinicooperation n cooperation with Geological Survey Division, with Geological Survey Division, Michigan Dept. * of of Natural Natural Resources Resources 8 Michigan Dept. �THE VOLCANICS NORTH THE KEWEENAWAN KEWEENAWAN VOLCANICS NORTH OF OF THE THE GOGEBIC GOGEBICRANGE RANGE IN I NWISCONSIN WISCONSIN Roger W. W. Cooper, Cooper, Department Department of o fGeology Geologyand andGeophysics, Geophysics, Roger U n i v e r s i t yofoWisconsin—Madison, f Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin 53706 53706 University ABSTRACT ABSTRACT The sequencennorth The Keweenawan Keweenawan v ovolcanic l c a n i c sequence o r t h of o f the t h eGogebic GogebicRange Range has has aa total t o t a lthickness thicknessofo more f more than than 35,000 35,000 feet f e e t and and an an attitude a t t i t u d e ofo fabout about This sequence of volcanic flows was investigated NW. T h i s sequence o f v o l c a n i c f l o w s was i n v e stigated N65-75 E, 70-80 N65—75 70—80 NW. to t o determine determine iiff aa stratigraphic s t r a t i g r a p h i c division d i v i s i o nofothe f t h eflows f l o w sinto i n tmappable o mappable units units Four units have been defined on the basis of texture, Four u n i t s have been d e f i n e d on t h e basis o f t e x t ure, c o u l d be be achieved. achieved. could petrographic characteristics, c h a r a c t e r i s t i c s ,and andchemical chemi c a l analyses. analyses. petrographic Unit U n i t 1, 1, which which is i s the t h e basal basal unit, u n i t , consists c o n s i s t s of o fabout about 5000 5000 ffeet e e t of of p i l l o w basalts b a s a l t sand and subalkaline subal k a l i n e basalts. basalts. The The basalts b a s a l t sare aremedium— medium- to to pillow The ttextures e x t u r e s most most common common i nint hthis i s unit unit f i n e - g r a i n e d and and grayish—green. grayish-green. The fine—grained are are intergranular i n t e r g r a n u l a r and and subophitic, s u b o p h i t i c , with w i t hophitic o p h i t itexture c t e x t u rless e l e scommon. s common. Unit U n i t 22 is i sabout about 20,000 20,000 ffeet e e t thick t h i c k and and consists c o n s i s t s of o f flows flows more more alkaline alkaline are aaphanitic The fflows l o w s are p h a n i t i c tto o fine-grained, fine-grained, than those those found U n i t 1. 1. The than found iinn Unit most common common The most t e xtextures t u r e s a are r e i nintergranular tergranular b l u i s h - g r a y to t oreddish-brown. reddish-brown. The bluish-gray Flows ooff rather r a t h e r basic basic and iintersertal n t e r s e r t a l with w i t hmicrophenocrysts microphenocrysts of o f plagioclase. plagioclase. Flows and composition neart hthe bottomo of and f felsic composition near e bottom f t hthe e uunit n i t give g i v e way way tto o intermediate i n t e r m e d i a t e and elsic flows upward. upward. flows Unit p o o r l yexposed exposed but b u t estimated estimated to t o be be 2000 2000 tto o 4000 4000 ffeet e e t thick. thick. U n i t 33 isi spoorly ItI tisi scomposed composed o of f pporphyritic o r p h y r i t i c f felsic e l s i c flows flows that t h a t have have aa ppink i n k t to o sslightly lightly purple abundantphenocrysts phenocrystsoof p u r p l e groundmass groundmass wwith i t h abundant f ffeldspar e l d s p a r and and quartz. Unit by gglacial U n i t 44 is i swidely w i d e l y covered covered by l a c i a l drift d r i f but t b uestimated t estimatedtot obe beabout about The flows appear to be mainly mafic, gray, and usually The flows appear t o be m a i n l y m a f i c , gray, and u sually 10,000 ffeet e e t thick. thick. 10,000 The flows are highly vesicular; pipe The flows are h i g h l y v e s i c u l a r ; p i p e n o t more more than than 20—25 20-25 f efeet e t tthick. hick. not amygdules and e s i c u l a rtops topsare are common. Interbedded Interbedded wwith i t h these these flows f l o w s are are amygdules and vvesicular common. The pebbles pebbles found found sedimentary rocks ranging from sedimentary rocks from conglomerate conglomerate ttoo shale. shale. The interbedded flows and These interbedded and i n these these beds beds are are predominantly predominantly f felsites. e l s i t e s . These in sedimentary beds beds pass pass upward upward into i n t othe t h eCopper CopperHarbor HarborConglomerate. Conglomerate. sedimentary The sequenced idisplays general compositional The Keweenawan Keweenawan v ovolcanic l c a n i c sequence s p l a y s aa general compositional trend upward t r e n d from from subalkaline s u b a l k a l i n e ttholeiitic h o l e i i t i basalts c b a s a l tat s athe t t hbase e base upwardthrough through After the extrusion o f these these the t h e porphyritic p o r p h y r i t i c felsic f e l s i c flows flows of o f Unit U n i t 3. 3. A f t e r t h e e x t r u s i o n of f e l s i cflows flowsthere t h e r eappears appears to t ohave have been been iintermittent n t e r m i t t e n t volcanism volcanism of o f aa felsic more alongwwith more mmafic a f i c nnature a t u r e along i t h eerosion r o s i o n o of f t the h e ffelsic e l s i c flows. flows. 9 �SOUTHWEST WISCONSIN PEDIPLAIN SOUTHWEST WISCONSINAS ASA ADIJRICRIJSTED DURICRUSTED PEDIPLAIN Dury, Departments of GG. . HH. . Dury, o f Geography and and Geology, Geology, The The University U n i v e r s i t y of o f Wisconsin-Madison, Wisconsin-Madison, Science S c i e n c e Hall, H a l l , Madison, Madison, Wisconsin Wisconsin 53706. 53706. ABSTRACT ABSTRACT The Driftless D r i f t l e s s Area of of Southwest Wisconsin and and adjacent adjacent parts p a r t s of of Minnesota, Iowa, Iowa, and and Illinois I l l i n o i s consists c o n s i s t s of o f dissectdissected e d plateau p l a t e a u country c o u n t r y traversed t r a v e r s e d by by the t h e Wisconsin Wisconsin and and MississMississhas iippi p p i Rivers. R i v e r s . IIn n tthe h e ppast, a s t , the t h e area area h a s been described d e s c r i b e d in in terms o of orr more more ppeneplains, terms o of terms f one o e n e p l a i n s , aand/or n d / o r iin n terms f a sseries e r i e s of o f cuestas. cuestas. IIn n aactuality, c t u a l i t y , it i t is i s recognizable r e c o g n i z a b l e as a s aa dissected d i s s e c t e d pedipedithe few residuals that have escaped plain: p lain: the residuals t h a t e s c a p e d planation p l a n a t i o n rise rise ssharply h a r p l y from the t h e summit surface s u r f a c e and and exhibit e x h i b i t typical t y p i c a l pedipedii s widespread, widespread, ment profiles. p r o f i l e s . Evidence of o f deep deep weathering w e a t h e r i n g is On carbonates, the rregardless e g a r d l e s s of o f lithology. l i t h o l o g y . On c a r b o n a t e s , t h e deep deep weatherweathering i n g pprofiles r o f i l e s consist c o n s i s t of o f rotted r o t t e d rock r o c k and and red r e d residuum; residuum; but but part p a r t of o f the t h e latter l a t t e r may have been introduced i n t r o d u c e d subsequently subsequently weathering. tto o deep w e a t h e r i n g . On On arenites, a r e n i t e s , the t h e profiles p r o f i l e s are a r e varyingly varyingly horizonated h o r i z o n a t e d into i n t o pallid, p a l l i d , mottled, m o t t l e d , and and duricrusted d u r i c r u s t e d zones, zones, tthe h e ppallid a l l i d zones zones frequently f r e q u e n t l y showing tthe h e rresults e s u l t s of o f attack attack on q quartz grains, and the crusts ranging from highly uartz grains, the c r u s t s ranging highly fferruginous e r r u g i n o u s to t o highly h i g h l y siliceous. s i l i c e o u s . Crust C r u s t texture t e x t u r e can can be be Ferruginous nodules rreplicated e p l i c a t e d in i n Australian A u s t r a l i a n samples. s a m p l e s . F e r r u g i n o u s n o d u l e s in in Wisconsin pprofiles widely have developed tthe h e Wisconsin r o f i l e s aappear ppear w i d e l y tto o have within w i t h i n bedrock. bedrock. On O n eeither i t h e r side s i d e of of the t h e lower lower Wisconsin river, r i v e r , the the deeply-weathered d e e p l y - w e a t h e r e d and and d.uricrusted d u r i c r u s t e d ssurface u r f a c e defines d e f i n e s aa wide wide of which tthe glacial sshallow h a l l o w vvalley, a l l e y , iinto n t o tthe h e ffloor loor o f which he g lacial ssluiceway l u i c e w a y is i s incised. i n c i s e d . IInvestigation n v e s t i g a t i o n of o f ppossible o s s i b l e comparcompari s in i n proproaable b l e rrelationships e l a t i o n s h i p s for f o r the t h e Mississippi M i s s i s s i p p i trench t r e n c h is Ass could c o u l d bbe e expected, e x p e c t e d , there t h e r e is i s evidence e v i d e n c e that t h a t the the ggress. ress. A weathering was, to deep w e a t h e r i n g was, t o some extent e x t e n t at a t least, l e a s t , aa groundgroundwater and some some thin t h i n crusts c r u s t s appear a p p e a r to t o have have been been w a t e r phenomenon; and ddeposited e p o s i t e d under carbonates c a r b o n a t e s in i n the t h e subsurface. subsurface. Outstanding problems include O u t s t a n d i n g problems i n c l u d e the t h e distribution d i s t r i b u t i o n of o f the the deeply-weathered d e e p l y - w e a t h e r e d surface s u r f a c e in i n glaciated, g l a c i a t e d , in i n addition a d d i t i o n to t o ununglaciated, g l a c i a t e d , areas; a r e a s ; the t h e relationship r e l a t i o n s h i p of o f some some ferruginous ferruginous ccrusts r u s t s tto o ssuiphide u l p h i d e deposition d e p o s i t i o n or o r translocation; t r a n s l o c a t i o n ; and the the off the ttime-stratigraphic i m e - s t r a t i g r a p h i c pposition osition o t h e latest l a t e s t local l o c a l episode episode off deep weathering. o weathering. 10 �PROGRESS REPORT PROGRESS REPORT OF OFTHE THECOMMITTEE COMMITTEEON ONKEWEENAWAN KEWEENAWAN STRATIGRAPHY STRATIGRAPHY C. Green, Green, Geology Department, Department, University of of Minnesota, Minnesota, Duluth, John C. Duluth, Duluth, Duluth, Minnesota 55812 and Minnesota Geological Survey ABSTRACT A BSTRACT An A n informal Committee on Keweenawan Stratigraphy was formed in in February 1973 of p participants 1973 in i n response to t o tthe h e wishes of a r t i c i p a n t s at a t the Symposium Symposium on Late Precambrian Geology of of the t h e Lake Superior Area at a t the Annual Meeting members are a r e George V. V. Cohee, Cohee, Campbell Campbell t h e G.S.A. G.S.A. in i n Minneapolis. Minneapolis. Its members of the Craddock, H. Dott, A. Hubbard, Hubbard, Craddock, Robert H. Dott, John C. C. Green (chairman), (chairman), Harold A. Wm. H. Vs. H. Mcllwaine, McIlwaine, Glenn Glenn B. B. Morey, Morey, and and Walter Walter S. S. White. White. Some Some rather r a t h e r wide differences of of opinion and usage aare by tthe differences r e represented by h e members and because of s i n c e its i t s organization, organization, few few areas a r e a s of complete of the short s h o r t time elapsed since consensus have developed by the t h e mid—March mid-March abstract a b s t r a c t deadline. deadline. name "Keweenawan" The name "Keweenawan" appears appears to t o be be widely widely considered considered as a s applying to, to, not formally defined as, as, aa p provincial supergroup, a ass iif f not r o v i n c i a l llithostratigraphic i t h o s t r a t i g r a p h i c supergroup, part well as a s to t o that that p a r t of of geologic time t i m e when the Keweenawan Supergroup was being formed. formed. It would then be composed composed of of various groups and formations, formations, but many of these stratigraphic s t r a t i g r a p h i c units u n i t s have yet y e t to t o be formally formally defined. defined. An An attempt will w i l l be be made made to t o clarify c l a r i f y their t h e i r stratigraphic s t r a t i g r a p h i c relationships. relationships. wrestling with with tthe of tthe most appropriate The Committee is aalso l s o wrestling h e problem of h e most which tto of the sstratigraphic t r a t i g r a p h i c llevels e v e l s aatt which o define the base and tthe h e top of Keweenawan, the assumption that t h a t there there should be some some unifying geotectonic geotectonic Keweenawan, on the many respects respects tthe Disturbance" coherence implied implied by by the t h e name. name. IIn n many h e "Keweenawan Disturbance" could be compared with with tthe of Late T Triassic h e Palisades Disturbance of r i a s s i c time, time, and 8, "Keweenawan" rocks could be defined a as of tthis Keweenawan" rocks s those formed aass a result r e s u l t of his event ofevents eventsiin the area Mid—Continent Gravity High event or o r complex complex of n the a r e a of of tthe h e Mid-Continent High or o r aatt least l e a s t the the Lake Superior Superior District. District. 11 �AN AN UNUSUAL UNUSUAL MANGANESE MANGANESE DEPOSIT IN I NKEWEENAWAN KEWEENAWAN LAVA LAVA COPPER HARBOR, MICHIGAN COPPER HARBOR, MICHIGAN E. Heinrich, Department E. Wm. Wm. Heinrich, Department of o f Geology Geology and and Mineralogy, Mineralogy, U n i v e r s i t y of o fMichigan, Michigan, Ann Ann Arbor, Arbor, Michigan. Michigan. University ABSTRACT ABSTRACT One ooff the t h e rare r a r enon—cupriferous non-cupriferous mineral mineraldeposits depositsin iKeweenawan n Keweenawan lava lava One i s the t h emanganese manganese occurrence occurrence just j u s teast e a sof t oManganese f ManganeseLake Lake and and about about one one is m i l e south south of o fCopper Copper Harbor Harbor in i n sec. 58N,R.R.26W. 26W. Butler sec. 4,4, T.T.58N, mile B u t l e rand andBurbank Burbank (1929, p. p. 59) 59) rrefer e f e r to t o that t h a t deposit d e p o s i t as t h e Manganese Manganese mine" tate as "... the mine" and and sstate that t h a t "... some some ore was was shipped t h e mine." mine. " shipped from from the "... "... The ddeposit e p o s i t is i s aacalcite—rich c a l c i t e - r i c hreplacement replacement lens lensini nananamygdaloid amygdaloid The t h a t is i sstratigraphically s t r a t i g r a p h i c a l lay short a s h odistance r t d i s t a n cbelow e belowthe t h ebase baseofo fthe t h eCopper Copper that Harbor Harbor ("Great") ("Great") Conglomerate. Conglomerate. Old workingsi nindicate Old workings d i c a t e tthat h a t the t h e mineralimineral iz a t i o n extends extends east-west along t h ethe s t strike r i k e oof f tthe h e amygdaloid amygdaloid f ofor r aatt least least zation east—west along a few few hundred hundred ffeet. e e t . The The replacement o n s i s t s ooff material m a t e r i a l grading grading replacementrock rockcconsists from nearly n e a r l y pure pure coarse—grained coarse-grained wwhite h i t e ccalcite a l c i t etot ohigh—grade high-grade black black from manganese oxide ore. The manganese oxide The manganese manganese minerals c l u d e hypogene hypogene brauni te, mineralsi ninclude braunite, o r i e n t i t eand andmanganite manganiteand andsome some supergene supergene ppyrolusite. yrolusite. A orientite A trace t r a c e of o f chalcochalcocite c i t eand and very very minor minor goethite g o e t h i t eare arethe t h eonly o n l other y o t h ehypogene r hypogene species, species, and and l i m o n i t e , chalcedony chalcedony and and opal opal ini nsmall smallamounts m o u n t sare aresupergene. supergene. The The limonite, manganese minerals i n and ace t hthe e ccalcite. alcite. manganese mineralsv evein andrep1 replace T h i s occurrence occurrence of o f orientite, o r i e n t i t ea, hydrous a hydrous calcium-manganese s silicate, ilicate, This calcium—manganese i s believed b e l i e v e d to t obe beonly o n l ythe t h esecond second recorded recorded ffor o r the t h e world. world. (The is (The type type locality l o c a l i t yisi in s i Oriente n O r i e n t Province, e Province,Cuba.) Cuba.) The mineral appears as gglistening The mineral appears as listening copper-red needles forming minute minute rradial exceedingly copper-red need1 es forming a d i a l aggregates aggregates and and exceeding1 y ffineine- grained matted matted lenses. lenses. The amygdaloid,oother than being beingeextensively replaced by by ccalcite, The hhost o s t amygdaloid, t h e r than x t e n s i v e l y replaced alcite, which which aalso l s o f fills i l l s the t h e vesicles v e s i c l e s eentirely n t i r e l y alone, alone, iis s relatively r e l a t i v e l y fresh. f r e s h . Neither Neither native n a t i v e copper copper nor n o r the t h e characteristic c h a r a c t e r i s t i suite c s u i of t e accompanying o f accompanyingsecondary secondary s i l i c a t e sisi present, s present,although althoughnative n a t i v ecopper coppermineralization m i n e r a l i z a t i o nofothe f t hcross— e crosssilicates f i s s u r e type type occurs occurs at a t the t h e Clark Clark mine mine a short s h o r t distance d i s t a n c e to t o the t h e south. south. fissure The ddeposit e p o s i t is i s believed b e l i e v e d to t obe bepenesyngenetic penesyngenetic and rigin. The and volcanogenic volcanogenici nin oorigin. 12 �UPPERMISSISSIPPI MISSISSIPPI VALLEY UPPER VALLEY LEAD—ZINC LEAD-ZINC DISTRICT DISTRICT A. V. V. Heyl, A. Heyl, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, Colorado Colorado 80225. ABSTRACT ABSTRACT The UpperMississippi MississippiValley Valley ddistrict The Upper i s t r i c thas hasbeen been the the source source of of about about aa billion bi 1 liondollars do1 l a r (present—day s (present-day prices) worth worth of of zinc zincand and lead, lead, and and minor minor amountsofof copper copper and and barite. barite. Ore amounts Ore deposits deposits are are chiefly chiefly ininlimestone limestone and and dolomite of of the Galena, Decorah,and andP lPlatteville dolomite Galena, Decorah, a t t e v i l l e Formations, Formations, aall l l of of Middle Middle Locally, small of lead, Ordovician age. age. Locally, small deposits deposits of lead, zinc, zinc, and and iron iron sulfide s u l f i d ehave have been mined mined from from underlying underlying Lower been Lower Ordovician Ordovi cian dolomite do1 omi t eand andUpper Upper Cambrian Cambrian sandstoneand andover1 overlying UpperOrdovician Ordovicianshale shale and andSiSilurian sandstone yi ng Upper 1uri an dolomite. do1 omi t e . No No post—Precambrian igneous rocks known theregion, region, and andggranitic post-Precambrian igneous rocks areareknown in in the r a n i t i c and and metasedimentaryPrecambrian Precambrian basement rocks unconformably underlie metasedimentary basement rocks unconformably underlie thethed idistrict strict at algal reefs a t depths depths of 1,500 1,500 to t o 2,000 2,000 feet. f e e t . No No algal reefs are are known known in the the Middle Middle Ordovician rocks, rocks, and b u t not not an an unconformity, unconformi t y , separates separates these these Ordovician and a diastem, di astern, but rocks rocks from from Upper Upper Ordovician Ordovician shale. The The sstrata t r a t a are are gently gently flexed and and faulted, probably largely largely the probably the result r e s u l tofofgentle gentlecompressive compressive and and rotational rotational adjustments adjustments in the along the underlying underlying crystalline c r y s t a l l i nbasement, e basement,especially especially alonglineaments lineamentsbetween between basement blocks. blocks. Folds basement Folds of three three orders orders ofofmagnitude magnitude are are recognized, recognized, and and many relatedjoints joints and reverse, sstrike—slip, normalf faults of small many related and reverse, t r i k e - s l i p , and and normal a u l t s of small to to moderate displacements displacements are are present. moderate The zinc—leaddeposits depositsrange rangei ninplan plan from fromllinear The zinc-lead i n e a r through through arcuate arcuate to to Theyare areepigenetic epigeneticand andp opostlithification Most ore eelliptical. l l i p t i c a l . They s t l i t h i f i c a t i o n deposits. deposits. Most and vugs, i n fractures, fractures,breccias, brecci as, and vugsbut , b usome t someimpregnated impregnated openspaces spaces in ffilled i 11edopen and replaced replaced wall wallrock. openspace spacei is along shears, small reverse and rock. The The open s a1 ong shears, reverse and and bedding—plane joints re1 related bedding-pl ane f a ufaults, l t s , joints ated tto o intermediate intermediate tto o small small folds, folds, and and within structures. Sphalerite and galena are are the the principal within solution—slump solution-slump structures. and galena ore minerals, and ore and the the general general sequence sequence of deposition depositionofofmain mainore oreand andgangue gangue minerals was: quartz, iillite, was: quartz, l l i t e dolomite, , dolomite, pyrite, pyrite,marcasite, marcasite, cobaltite(?), cobal t i t e ( ? ) , sphalerite, galena, chalcopyrite,mmillerite, sphalerite, galena, chalcopyrite, i l l e r i t e , barite, b a r i t e , and and calcite. c a l c i t e . Wallrock Wall rock rocks,ssilicification, aalterations l t e r a t i o n s include include solution of the the carbonate carbonate rocks, i l i c i f i c a t i o n dolomiti— , dolomititype of of clay, zation, changes changes i in n type clay, addition additionofoftrace traceelements, elements, and and sanding sanding of dolomite. Country rock between orebodies bodiesiis Country rock between ore s unaltered. Oxygen-isotope, carbon-isotope, lead-isotope, Oxygen-isotope, carbon-isotope, lead-isotope, sulfur—isotope, sulfur-isotope, and and Bubbles in sphalerite—stratigraphy studies studies are or in progress. sphalerite-stratigraphy are completed completed or progress. Bubbles sulfide and mineralsare are ffilled sulfide and gangue gangue minerals i l l e dwith withconcentrated concentratednear—neutral near-neutral chloride brines that lead iinn the brines t h a t have have filling f i l l i n temperatures g temperaturesofof1200 120' tot o40°C. 40°C The The lead the galena iiss notably galena notably radiogenic. radiogenic. Themetals metals and andsulfur sulfur are postulated The postulated to t o be be derived derived from fromheated heated basin basin brines that were later diluted by meteoric waters. magmaticf lfluid brines t h a t were l a t e r diluted by meteoric waters. A A magmatic u i d contribution possible, but b u t iti tisi snot notsupported supported by by present present ffluid l u i d inclusion inclusion data. data. bution is possible, magmatichearth hearthinin the the basin basin areas AA magmatic areas ttoo the the south south and and southwest southwest is i s the themost most possible heat possible heat source. source. AA large lateral l a t e r a component l component of of flow flowthrough throughpermeable permeable Cambriansandstone sandstone updip from basinsi sisprobable, probable, bbut u t available available evidence evidence Cambrian updip from thethebasins 13 �the ddistrict Within the istrict suggests flow through fracture zones. suggests some some flow through basement basement fracture zones. Within the ore from tthe aquifers through ore solutions solutions flowed flowed upward upward from h e aquifers through available fracture fracturesystems systems into i n t oMiddle MiddleOrdovician Ordovician strata s t r a t awhere wherethey theyleached leachedcarbonate carbonate physicalrrestraints properties of of the rocks. rocks. Changes Changes i ninphysical e s t r a i n t s and and chemical chemical properties the ore ore solutions n andnear nearopen openspaces spaces solutions allowed allowed ore ore minerals minerals tot obebedeposited depositedini and derived from from leaching. leaching. derived 14 �THE THE GEOLOGY GEOLOGY OF OF BEECHER BEECHER AND AND PEMBINE PEMBINE TOWNSHIPS TOWNSHIPS MARINETTE MARINETTE COUNTY, COUNTY, WISCONSIN WISCONSIN Robert A. Jenkins Jenkins Robert A. Department of of Geology Geology and and Geophysics Geophysics Department University of of Wisconsin—Madison, Wisconsin-Madison, Madison, Madison, Wisconsin Wisconsin University Four Four metavolcanic metavolcanic formations, formations, separated separated by by major major faults, faults, occur occur in in Beecher Beecher and and Pembine Pembine townships townships in in northeastern northeastern Marinette County, County, Wisconsin. Wisconsin. The formations formations are are the the Quinnesec Quinnesec Marinette Formation, the the Mc Allister Allister Formation, Formation, the the Beecher Beecher Formation, Formation, Formation, the Pemene Pemene Formation. Formation. The relative relative ages ages are are uncertain uncertain and the but but the the order order of of naming naming is is suggested suggested as as the the order order of of decreasing decreasing age. All All the the formations formations have been been folded folded and and regionally regionally metametaage. morphosed morphosed to to greenschist greenschist facies. facies. In In general general the the rocks rocks have have not not been been strongly strongly sheared sheared or or altered, altered, and and primary structures structures volcanics have been been intruded intruded by by are well well preserved. preserved. The The volcanios are granite, granodiorites,quartz quartzdiorites, diorites,and andultrainafics. ultramafics. granite, granodiorites, The The Quinnesec Quinnesec Formation, Formation, over over 10,000 10,000 ft. thick, thick, consists consists predominantly predominantly of of tholeiitic tholeiitio metabasalts metabasalts and and cala-alkaline cala-alkaline metametaandesites. The formation formation is is isoclinally isoclinally folded; folded; axial axial planes planes andesites. of the the folds folds are are vertical vertical and and strike strike east. east. The The andesites andesites are are of of of two two types, types, one one nonporphyritic nonporphyritic and and pillowed, pillowed, having having its its source to the west and the other, other, porphyritic porphyritic and mainly agglomeratic, 100 to to 1,000 1,000 agglomeratic, having having its its source source to to the the east. east. AA 100 ft. thick is interlayered interlayered with with the the thick porphyritic porphyritic rhyolite rhyolite flow flow is andesites. andesites. The Mc Allister Formation, Formation, 1,000 1,000 to to nossibly ~ossibly10,000 10,000 ft ft The thick, consists consists of of metamorphosed metamorphosed tholeiitic tholeiitio basalt basalt agglomeragglomerthick, ate. alps vertically, vertically, and and faces faces ate. The The formation formation strikes strikes east, east, aips south. Fragment Fragment size in in the formation formation increases increases from from west west to to south. east, suggesting suggesting aa vent vent to to the the east. east. east, The Beecher Beecher Formation, Formation, at at least least 10,000 10,000 ft. thick, thick, strikes strikes N50°W, N~O'W, dips dips vertically, vertically, and and faces faces north. north. The The lower lower 9,000 9,000ft. ft. consists mainly mainly of of rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The upper upper consists 1,000 ft. of the formation rhyformation is is an an alternation alternation of of bedded bedded rhy— olitic olitic tuffs tuffs and and acidic acidic fragmentals. fragmentals. The lower lower part part of of the the formation formation is is more highly sheared sheared and and altered than than other other formformations ations in in the the area. area. This This may be be due due to to intrusion intrusion of of the the Amberg Amberg granite granite into into the the lower lower part part of of the the formation. formation. Formation consists consists of 7,000 ft. of microspher— The Pemene Formation of microspherulitic ulitic soda soda rich rich rhyolite rhyolite and and rhyodacite rhyodacite flows. flows. The The flows flows are interlayered units and interlayered with a few few thin thin sedimentary sedimentary units and were Individual flows apparently apparently extruded extruded subaqueously. subaqueously. Individual flows are are 500 500 to 1,200 1,200 ft. thick and traceable traceable laterally laterally for for over over four four miles. miles. the The formation formation is is folded folded into into an an east east trending trending asemmetric asemmetric on the north limb limb dip dobly doublyplunging plunging syncline. syncline. The units on 55 SS and and those those on on the the south south limb limb are are vertical. vertical. 55 Thin various rock rock types Thin sections sections of the various types have been been examined examined 15 �ffor o r primary structures s t r u c t u r e s and to t o determine determine metamorphic metamorphic grade. grade. Whole rock major element analyses a n a l y s e s have have been been run r u n using u s i n g the the eelectron l e c t r o n microprobe. microprobe. These analyses a n a l y s e s have been used to to iidentify d e n t i f y rock types o determine h e petrochemical types and and tto determine tthe petrochemical c h a r a c t e r i s t i c s of the t h e voloanios. volcanics. characteristics t r e n d s indicate I n d i c a t e that t h a t the t h e rocks r o c k s of of the the The petrochemical trends aarea r e a may be the t h e products of several s e v e r a l cycles c y c l e s of of volcanism. volcanism. Each formation is i s chemically chemically distinctive. d i s t i n c t i v e . The Qtxinnesec Quinnesec the n north Formation grades from f r o m tholelitic t h o l e l i t i c bbasalts a s a l t s Iin n the o r t h to to ccab-alkaline a l c - a l k a l i n e andesites a n d e s l t e s in i n tne tne south, south, suggesting suggesting that t n a t it It may have formed at a t the t h e edge edge of of an an island i s l a n d arch a r c h enviornment. enviornment. Mc Ablister Preliminary analyses a n a l y s e s indicate i n d i c a t e that t h a t the the M c A l l l s t e r Formation basaLts. It may therefore t h e r e f o r e correlate correlate cconsists o n s i s t s of ttholeittic h o l e l l t i c basalts. Formation oor may rrepresent with part p a r t of of the t h e Quinriesec Quinnesec Formation r Iit t may epresent a sseparate e p a r a t e volcanic v o l c a n i c cycle. c y c l e . The Beecher Formation Formation rhyolites rhyolltes and rrhyodacites are typical cab—alkaline h y o d a c i t e s a r e t y p i c a l c a l c - a l k a l i n e acidic a c i d i c vobcanics. volcanlcs. They may tie be the of the t h e aacidic c i d i c end product of t h e Quinnesec The pemene Pemene Formation rrhyolites volcanism. h y o l i t e s aare r e characterized characterized These These by higher h i g h e r Na20 Na20 and lower lower K20 K20 than t h a n normal normal rhyolites. rhyolites. volcanios are distinctly different from the rocks of the volcanics are d i s t i n c t l y d i f f e r e n t the rocks the Beecher Formation and therefore t h e r e f o r e probably rrepresent e p r e s e n t a separate separate period of volcanism. volcanism. The age of of the not t h e volcanism in i n the t h e area a r e a is is n o t positively positively known b but Rebelbo (1969) U-Pb d date z i r c o n U-Pb ate (1969) rreport e p o r t a zircon u t Banks and Rebello for a rhyolite just to the west of the area of 1905 (+30 for r h y o l i t e just t o the of a r e a of 1905 (+30 to to -10) m.y. This rrhyolite -10) m.y. h y o l i t e probably correlates c o r r e l a t e s with the the Beecher If this correlation is correct then the acidic Formation. cidic Formation. I f t h i s c o r r e l a t i o n i s correct then the a possibly volcanism and p o s s i b l y tthe h e mafic volcanism in In the t h e area a r e a is is upper Middle Precambrian in age. Middle Precanbrian i n age. 16 �PRECAMBRIAN PRECAMBRIAN NORTH-SOUTH NORTH-SOUTH ORIENTED ORIENTED FAULTS FAULTS IN IN THE THE WESTERN WESTERN MARQUETTE MARQUETTE DISTRICT, DISTRICT,NORTHERN NORTHERNMICHIGAN MICHIGAN John S. S. Klasner Klasner John Western Illinois W e s t e r n Illinois University University Macomb, Macomb. Illinois Illinois Thomas Thomas R. R. Turner Turner Michigan Michigan Technological Technological University University Houghton, Michigan Houghton, Michigan ABSTRACT ABSTRACT Recent has R e c e n t mapping mapping in in northern n o r t h e r n Michigan Michigan h a s indicated indicated the the presence p r e s e n c e of of prominent 100W W to t oNN 200 20' E E faults, faults, many many of of which which offset offset east-west east-west prominentNN100 T h e s e faults faults are a r e expressed e x p r e s s e d as a s shear shear trending Keweenawandiabase Keweenawan diabase dikes. dikes. These trending zones zones in in lower lower Precambrian P r e c a m b r i a n granites, g r a n i t e s ,offsets offsetsininthe thecontact contactbetween between middle middle and anddiscontinuities discontinuities and lower lower Precambrian P r e c a m b r i a n rocks, r o c k s , topographic topographic lineaments, l i n e a m e n t s ,and in aeromagnetic a e r o m a g n e t i c trends. trends. in Regionally Regionally tthese h e s e faults f a u l t s are a r e on on trend t r e n d with with major m a j o r lineaments l i n e a m e n t s observed observed ontthe Hinze and and others o t h e r s (1966) (1966) on h e bbasis a s i s of of aaeroeroby by other workers w o r k e r s in in the the area. a r e a . Hinze magnetic studies in eastern Lake Superior show a major north-northeast a m a j o r n o r t h n o r t h e a st magnetic studies i n e a s t e r n Lake S u p e r i o r show trending trending fault fault extending extending nnorth o r t h aacross c r o s s the the lake l a k e just just east e a s tof of the the tip t i pof of the the in nnorth Keweenaw Peninsula. Peninsula. La L a Berge B e r g e (1972) (1972) in o r t h central c e n t r a l Wisconsin Wisconsin has has Keweenaw mapped These mapped major m a j o r northeast n o r t h e a s t trending trending shear s h e a rzones zonesup u pto t oone onemile m i l eininwidth. width. These features f e a t u r e s coupled coupled with with major m a j o r lineations lineations on on psuedo psuedo radar r a d a rphotographs photographs suggest suggest that t h a t aa major m a j o r fault fault zone zone bisects b i s e c t s the the arcuate a r c u a t eshaped shapedarea a r e aoutlined outlinedby by the the midmidcontinent continent gravity gravity high high and and proposed proposedKeweenawan Keweenawan rift. rift. With movement, studies With rregard e g a r d to to the the timing timing of of movement, studies in in the the western w e s t e r n part part of near of the the northern n o r t h e r n complex complex n e a r Herman, Herman, Michigan Michigan suggest s u g g e s t that that at a t least l e a s t some some of the faults may m a y have have been r i o r tto o Penokean e t a m o r p h i s m . For For of been active active pprior Penokeanmmetamorphism. example, north-south fault example, aa body body of of gabbro gabbro occupies occupies aa north-south fault tthat h a t cuts cuts granite granite gneiss, g n e i s s , and and the the gabbro gabbro is i sinterpreted i n t e r p r e t e dtot ohave havebeen beenmetamorphosed m e t a m o r p h o s e d by by Penokean oorr some s o m e earlier e a r l i e r thermal t h e r m a levent. event. Penokean In places dikes aare In many many p l a c e s east-west e a s t - w e s t Keweenawan Keweenawan dikes r e offset offset at a t the the northnorthhas found ffor the dikes No evidence evidence h a s been been found o r sshearing h e a r i n g of of the d i k e s at a t these these south faults. No faults faults and and in in some s o m e instances i n s t a n c e sthe theKeweenawan Keweenawan dikes dikes have have been been found found to t o intrude intrude N e v e r t h e l e s s , the the conclusion conclusion seems s e e m s inescapable inescapable that that along the fault f a u l tzone. zone. Nevertheless, along the numerous occurrence of offset dikes at the north-south faults must denote the n u m e r o u s o c c u r r e n c e of offset dikes a t the north-south faults m u s t denote post-Keweenawan post-Keweenawan fault fault movement. movement. 17 �References Hinze, Wrn. O'Hara, N. W., Trow, Wm. J., O'Hara, N. W., Trow, 3. J. W. W. and and Secor, G. G. B., 1966, 1966, Aeromagnetic Studies Studies ofofEEastern Lake Superior, Superior, in the the EEarth Aeromagnetic a s t e r n Lake arth Beneath the Continents, G. U. U. Geo& Smith, ed. ed. ,, A. G. Beneath the Continents, Steinhart Steinhart & physical physical Monograph Monograph 10, 10, pp. pp. 95-110. 95-110. La Zones in in the the PPreL a Berge, G. G. L., L . , 1972, 1972, Lineaments Lineaments and and Mydonite Mydonite Zones re1: 18th 18th Ann. Ann. Inst. Inst. on on Lake Lake ccambrian a m b r i a n of of northern n o r t h e r nWisconsin Wisconsin [abs. [abs,}: Superior Geology, Michigan, ppaper 27. Superior Geology, Houghton, Houghton, Michigan, a p e r 27. 18 �- GEOCHEMISTRYOF OF THE THE CALCIUM GEOCHEMISTRY CALCIUM - CARBON CARBON DIOXIDE DIOXIDEMETASOMATISM METASOMATISM AT PRESQUE MICHIGAN PKESQUE ISLE, ISLE, MARQUETTE, MICHIGAN M. D. Lewan, Lewan, Department Department of of Geology Geology and and Geological Geological Engineering, Engineering, M. Michigan Michigan Technological Technological University Presently With Shell Presently With Shell Oil Oil Company, Company, New New Orleans, Orleans, Louisiana Louisiana 70160 70160 ABSTRACT ABSTRACT A highly veined rock rock composed of of dolomite dolomite and quartz quartz with with peridotite at minor hematite, hematite, overlies overlies the the Presque Presque Isle Isle serpentinized serpentinized peridotite Marquette, Michigan. Marquette, Michigan. Petrographic Petrographic and field observations observations clearly clearly indicate indicate that that this this rock rock was was originally originally highly highly serpentinized serpentinized peridotite peridotite which has since since been been subjected subjected to to metasomatic metasomatic solutions. solutions. which has The The author author (Lewan, (Lewan, 1972) has interpreted interpreted this this dolomite-quartz dolomite-quartz rock as originally being a peripherial shear zone which which developed during the tectonic tectonic intrusion intrusion of of the the peridotite. peridotite. Either during during or or after after its its emplacement water water from the surrounding country rocks circulated through emplacement this highly fractured fractured peripherial peripherial zone zone causing causing extensive extensive serpentinizaserpentinization tion to the the still still warm warm but but cooling cooling peridotite. peridotite. Following Following the the period of of serpentinization a potash rich granite was was emplaced and and was was apparently serpentinization illitized by late late stage stage magmatic along its its outer outer boundary boundary where where illitized magmatic water water along it contact with with the comes in contact it comes the peridotite. peridotite. Both the the highly highly serpentinized serpentinized peridotite and illitized metasomatic soluperidotite illitized granite were susceptable susceptable to metasomatic soluwhich resulted in the formation of the now now existing existing dolomite-quartz tions which rock. objective of this was to investigate rock. The objective this study was investigate the chemical conditions which may may have induced this period parameters and prevailing conditions of metasomatism. of metasomatism. Comparative analysis of the chemical chemical composition composition of the Comparative the dolomite-quartz rock dolomite-quartz rock with the serpentinized peridotite and illitized granite indicates were introduced into granite indicates that calcium and carbon dioxide were system with with partial removal the system removal of of silica silica and and magnesium. Experimental Experimental work by Gordon with free work Gordon and and Greenwood Greenwood (1970) (1970) and Ellis (1959), (1959), along along with free metasomatism probably never energy calculations calculations suggest suggest that that the metasomatism exceeded 300°C. Luce (1972) has has shown shown that that serpentine serpentine is is most most soluble soluble 300°C Luce exceeded waters which which gradually become become more more basic basic as as the serpentine in acidic waters dissolution continues. dissolution continues. This increase in in pH probably also accompanied metasomatic solutions serpenthe metasomatic solutions during during the the dissolution dissolution of of the the highly highly serpenperipherial zones which which eventually eventually resulted resulted in tinized and illitized peripherial mobilization of silica the mobilization silica released released from from the the serpentine serpentine lattice lattice and and the the precipitation of precipitation of dolomite. dolomite. pre-Jacobsville This period of metasomatism has been dated as pre-Jacobsville peridotite sandstone and post-granite sandstone post-granite illitization. illitization. The occurrence of the peridotite greenstone terrain offers offers an-attractive anattractive hypothesis in greenstone hypothesis that that this this metasomatism may may have been a result somatism result of of the the expulsion expulsion of of fluids fluids from from neighneighboring rocks rocks during during the the regional regional metamorphism metamorphism of of the the area. area. 19 �REFERENCES REFERENCES CITED CITED Ellis, Carbon Dioxide (1959), The The Solubility Solubility of of Calcite Calcite in in Carbon Dioxide Ellis, A. J. (1959), Solutions, Am. 3. Sci., 257, pp 354-365. Solutions, Am. J. 257, pp 354-365. Cordon, M., and and Greenwood, Greenwood, H. H. 3. J. (1970), (1970), The The Reaction: Reaction: Dolomite Dolomite Gordon, T. T. M., + Quartz + Water == Talc +Quartz +Water Talc + Calcite Calcite + Carbon Carbon Dioxide, Dioxide, Am. Am. 3. J. Sc!., Sci., 268, 268, pp 225—242. 225-242. pp + + Lewan, and Weathering Weathering of the Lewan, M. XL D. (1972), (1972), Metasornatism Metasomatism and the Presque Presque Isle Isle Serpentinized Serpentinized Peridotite, Peridotite, Marquette, Marquette, Michigan, Michigan, Michigan Michigan Technological Technological University, University, unpublished unpublished M.S. M.S. Thesis, Thesis, 55 55 pp. pp. Luce, Luce, R. R. Kinetics Kinetics W., Bartlett, W., and Parks, Parks, G. 0. A A. Dissolution W., Bartlett, R. R. W., . (1972), (1972), Dissolution of Magnesium Silicates, Geochim. Cosmochim. Acta, of Magnesium Silicates, Geochim. Cosmochim. Acta, 36, 36,pp pp 35-50. 35-50. 20 �THE BIOGENIC ORIGIN THE ORIGIN OF OFPRIMARY PRIMARY MINERALS MINERALS IN IN LAKE LAKE SUPERIOR SUPERIORPRECAMBRIAN PRECAMBRIAN IRON-FORMATION IRON-FORMATION M. Lougheed and 7. J. Mancuso, Department M. S. S. Lougheed and J. J. Mancuso, Geology, Department of of Geology, Bowling Bowling Green University, University, Bowling Bowling Green, Green, Ohio Ohio 43403 43403 ABSTRACT ABSTRACT Primary Primary minerals minerals in in the the Lake Lake Superior Superior Precambrian Precambrian ironironformations formations are are the the direct direct products products of of the the life life processes processes of of a melange of filamentous filamentous and and unicellular unicellular organisms organisms together together with minerals so with associated associated bacteria. bacteria. Primary Primary minerals so formed formed are are aragonite Pyrite is aragonite and/or calcite, calcite, magnetite, magnetite, and and opal. opal. Pyrite is formed formed during decay decay of of organic organic material material with with attendant attendant sulfate sulfate reducing bacteria and is therefore later in origin than reducing than the the above above three three minerals although although it it too too is is of of biogenic biogenic origin origin and may be Hematite occurs be considered considered primary. primary. Hematite occurs as as an an alteraalteration product of earlier earlier formed minerals and is not considered a primary mineral. a primary mineral. bacteria and is therefore later in Aragonite Aragonite or or calcite calcite crystals crystals are are biogenically deposited deposited structural structural elements elements occurring occurring as as submicron submicron width width prisms prisms oriented normal to an algal mat, mat, and producing in turn a carbonate mat. carbonate mat. A succession succession of of algal algal and carbonate carbonate mats (laminae) occurs occurs in horizontally horizontally banded banded iron-formation; iron-formation; in in domical or columnar domical columnar stromatolites; stromatolites; as as coatings coatings on on granules granules (pellets); or forming forming micro—oncoliths. micro-oncoliths. Micro-oncoliths Micro-oncoliths are are typically 0—50 microns microns in Calcium carbonate typically 220-50 in diameter. diameter. Calcium carbonate can can be dolomitized, dolomitized, sideratized, sideratized, or or silicified. silicified. Magnetite initially occurs subMagnetite occurs as as a a diffuse diffuse cloud cloud of of subwithin the micron sized sized crystals crystals within the protoplasm of unicellular unicellular Too plants. plants. Too high aa concentration concentration of of oxygen oxygen produced produced by by photosynthesis in photosynthesis in these these unicellular unicellular plants can can be lethal lethal to them; they therefore therefore oxidize oxidize iron iron that that is is dissolved dissolved in in the the water to to produce magnetite, thereby attenuating attenuating a a lethal lethal buildup of oxygen. oxygen. During During deposition deposition and and early early diagenesis diagenesis buildup of magnetite may may be be recrystallized to the submicron crystals of magnetite form Diagenesis may subseform coarser coarser octahedra octahedra of of magnetite. magnetite. Diagenesis subsequently produce quently produce megascopic megascopic subhedral subhedral masses masses of of magnetite. magnetite. Some magnetite is produced by oxidation of siderite during the depositional depositional stage, stage, which which subsequently subsequently may may be be recrystalrecrystallized during diagenesis diagenesis in in aa similar similar manner manner to to that that of of primary primary biogenic magnetite. biogenic magnetite. Siliceous Siliceous tests tests of of microorganisms microorganisms yield yield the the hydrous hydrous silica, which during deposition is almost invariably comminuted to an an opaline opaline slurry. slurry. This slurry slurry readily readily dehydrates dehydrates during during diagenesis to diagenesis to chalcedony chalcedony or or more more often often to to chert. chert. From From five five to seven seven types types of siliceous siliceous tests tests of of unicellular unicellular organisms organisms 21 �occur. occur. Usually Usually the t h e cavities c a v i t i e s are a r e filled f i l l e d with w i t h organically organically stained s t a i n e d chalcedony, chalcedony, and and often o f t e n submicron submicron sized s i z e d anhedra anhedra of of carbonate c a r b o n a t e are a r e present. p r e s e n t . The The test t e s t walls w a l l s are a r e not n o t organically organically stained; clear. Occasionally O c c a s i o n a l l y the t h e core c o r e and and s t a i n e d ; they t h e y are a r e water w a t e r clear. test t e s t are a r e recrystallized r e c r y s t a l l i z e d to t o an an optically o p t i c a l l y oriented o r i e n t e d sphere s p h e r e or or ellipsoid e l l i p s o i d of o f quartz. q u a r t z . The The tests t e s t s range range in i n width w i d t h from from 55 to to 25 microns although a l t h o u g h aa few few may may exceed exceed 50 5 0 microns. microns. PreservaPreservation t i o n of o f siliceous s i l i c e o u s tests tests occurs o c c u r s only o n l y when when they t h e y were were deposited deposited in n e v e r when when water w a t e r current c u r r e n t activity a c t i v i t y prevailed. prevailed. i n quiet q u i e t water, w a t e r , never They therefore t h e r e f o r e are a r e not n o t found found in i n association a s s o c i a t i o n with w i t h granules granules or o r stromatoljtes. stromatolites. P y r i t e may be thought t h o u g h t of o f as a s primary in i n the t h e sense s e n s e that that Pyrite it results r e s u l t s from from iron i r o n in i n the t h e water w a t e r reacting r e a c t i n g with w i t h sulphur sulphur produced produced by sulfate s u l f a t e reducing r e d u c i n g bacteria b a c t e r i a during d u r i n g decay decay of of organic o r g a n i c debris. d e b r i s . Pyrite P y r i t e occurs o c c u r s as a s discrete d i s c r e t e octahedrons o c t a h e d r o n s or or octahedrons o c t a h e d r o n s modified m o d i f i e d by aa cube, cube, as a s framboidal f r a m b o i d a l octahedra, o c t a h e d r a , or or as a s framboidal f r a m b o i d a l mats mats or o r spheres. s p h e r e s . Secondary Secondary replacement replacement pyrite pyrite formed during d u r i n g diagenesis d i a g e n e s i s is i s ubiquitous. ubiquitous. 22 �-- THE WOLF RIVER BATHOLITH BATHOLITH -- A L LATE THE WOLF RIVER ATE PRECANBRIA1 PRECAMBRIAN RAPAKIVI MPAKIVI MASSIF I NNORTHEASTERN NORTBBASTERN WISCONSIN WISCONSIN MASSIF IN L. G. G. Medaris, . Nyles, Medaris, Jr., Jr., J. L. L. Anderson, Anderson, and J. J. R B. Myles, Department of Geology Wisconsin, Madison 53706 Geology and Geophysics, Geophysics, University of of Wisconsin, 53706 ABSTRACT AESTRACT Anorogenic, epizonal batholith, epizonal ggranitic r a n i t i c rocks rocks of of the t h eWolf Wolf River River b atholith, covering an aarea of approximately 3600 square miles, miles, represent a major covering r e a of element of the t h e Precambrian Precambrian terrain t e r r a i n in i n northeastern northeastern Wisconsin. Wisconsin. This batholith, 1500 m. m. y. y. iin age, has llithologic, n age, i t h o l o g i c , mineralogic, mineralogic, b a t h o l i t h , 11150 1450 tto o 1500 chemical, and structural respect to that are a r e similar similar in i n every every respect to chemical, s t r u c t u r a l ffeatures e a t u r e s that those those of of the t h e classic c l a s s i c rapakivi rapakivi massifs massifs in i nFinland. Finland. A vvariety been distinguished, distinguished, including including ggranite, A a r i e t y of of rock rock types types have have been ranite, quartz monzonite,r rhyolite, trachyandesite, but quartz monzonite, monzonite, ssyenite, y e n i t e , monzonite, h y o l i t e , and and trachyandesite, but quartz monzonite of tthe monzonite iiss predominant, predominant, accounting accounting for f o r 87% 87% of h e exposed exposed area. A porphyritic porphyriticttexture of aalkali A e x t u r e iis s characteristic, c h a r a c t e r i s t i c , ini nwhich which phenocrysts phenocrysts of lkali feldspar f e l d s p a r and, and, to t o a lesser l e s s e r extent, e x t e n t , plagioclase and quartz quartz are a r e set s e t in i n aa medium— tto mediumo fine—grained fine-grained matrix of quartz, quartz, two feldspars, f e l d s p a r s , and mafic minerals. Rapakivi texture t e x t u r e is i s extensively developed in i n the t h e Waupaca Waupaca quartz monzonite and and occurs occurs in i n minor minor amounts amounts throughout throughout the t h e batholith. batholith. Quartz iis many llithologic units; s euhedral iin n many ithologic u n i t s ; bbiotite i o t i t e and hornblende are Quartz generally anhedral and interstitial i n t e r s t i t i a l to t o feldspars f e l d s p a r s and quartz. quartz. The The granitic g r a n i t i c rocks rocks of of the t h e batholith b a t h o l i t h tend tend to t o be be rich r i c hini nSiO SiO and alkalies, , CaO, and and MgO. TLg batho— andpoor poor in i nAl20 A120 , MgO. ~ bathoe a l k a l i e s , particularly p a r t i c u l a r l yKK0,0,and 11th l i t h has has alkaline a l k a l i n e affiniies, a f f i n i z i e s , although only only eraluminous Jeraluminous and metaluminous metalminous types have been recognized recognized so so far. f a r , Values of of normative Q—Ab—Or Q-Ab-Or for for representative r e p r e s e n t a t i v e specimens specimens plot p l o t close c l o s e to t o a low low pressure thermal trough and and minimum minimum for f o r the t h e experimental experimental "granite" "granite" system, system, with with aa slight s l i g h tdisplacement displacement towards normative Or. Or. towards Perthitic P e r t h i t i c alkali a l k a l ifeldspar feldsparisi the s t hpredominant e predominant mineral mineral in i n the t h e bathoJ.ith, batholith, accompanied quartzand andplagioclase, plagioclase, ranging accompanied bybyquartz ranging in i ncomposition composition from from An An 3 to to )tO, An Iron—richbbiotite 40, with most values falling f a l l i n g between A n 10 1 0 tto o 25. 25. Iron-rich i o t i t e and hornblende are minerals, although olivine, a r e the t h e predominant mafic minerals, o l i v i n e , clino— clinopyroxene, and pyroxene, and orthopyroxene orthopyroxene occur occur in i n monzonite monzonite and and trachyandesite. trachyandesite. Fluorite Fluorite is batholith, i s tthe h e most widespread accessory mineral in i n tthe he b a t h o l i t h , and a halogen— halogenrich biotite i s reflected r e f l e c t e d in i n high Cl C l and F F contents of of b i o t i t e and r i c h environment is hornblende. Wolf River b batholith The Wolf a t h o l i t h may have crystallized c r y s t a l l i z e d from from relatively r e l a t i v e l y dry dry granitic partial off pre-existing pre—existing g r a n i t i c magmas tthat h a t were derived by p a r t i a l melting o crustal materials, basaltic volcanics, v volcaniclastic crustal m a t e r i a l s , consisting c o n s i s t i n g of of b a s a l t i c volcanics olcaniclastic sediments, and quartz dioritic sediments, d i o r i t i c to t o granodioritic g r a n o d i o r i t i c plutonic plutonic rocks. rocks. , 23 �SUMMARY WISCONSIN SUhMkRY OOF F GLACIAL GEOLOGY GEOLOGY OF OFNORTH—CENTRAL NORTH-CENTRAL WISCONSIN D. M. Department of M. Mickelson, Mickelson, Department of Geology Geology and and Geophysics, Geophysics, University University of Wisconsin, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT ABSTRACT The The Pleistocene glacial g l a c i a lchronology chronology of of central c e n t r a land andnorthern northernWisconWisconnot not well well established. established. Early Early workers workers (Owen, (Owen, l8t7; 1847; Chamberlain, Chamberlain, 1907) outlined o u t l i n e d the t h e distribution d i s t r i b u t i o n of of glacial g l a c i a l deposits deposits and and 1882, Weidman, 1907) recognized aa presumed older o l d e r drift d r i f t outside the t h e terminal moraines of of WisWisconsin consin age. age. Hole Hole (1943) (1943) and and Thwaites (l913) (1943) concluded that t h a t the t h e older older d r i f t (Border order Drift) rift) was of of one one age age and and was deposited deposited in i n the t h e pre—Cary pre-Cary drift (pre—late ( p r e - l a t e Woodfordian) woodfordian) time. time. Radiocarbon Radiocarbon dates d a t e s (Black (Black and and Rubin, Rubin, 1968) beneath beneath the t h e Border Border Drift D r i f t in i n Wood Wood County County are a r e >>i5,O00 45,000 years years B.P. B.P. 1968) In I n southern southern and and western Wisconsin wood wood from from an an old o l d till till possible possible B. P. P. c o r r e l a t i v e with with the t h e Border Border Drift D r i f t is i s dated dated at a t about about 30,000 30,000 years B. correlative and and is i s considered considered Rockian Rockian (late ( l a t e Altonian) Altonian) age. age. The The Border b r d e r Drift D r i f t may may actually a c t u a l l y consist c o n s i s t of of 22 tills t i l l s of of differing d i f f e r i n g age. age. The till was was The lower lower till deposited by by ice i c e moving moving from from the t h e west in i n Marathon County County (LaBerge, (~a~erge, deposited 1972) 1972) and and the t h e upper upper till till by by ice i c e moving moving from from the t h e northwest northwest in i n southern southern Lincoln Lincoln and and Langlade Langlade Counties. Counties. sin s i n is is Three Three ice i c e lobes lobes built b u i l t terminal terminal moraines moraines in i n Lincoln Lincoln and and Langlade Langlade Counties Counties during during late—Woodfordian late-Woodfordian time. time. The The Wisconsin Wisconsin Valley Valley Lobe Lobe advanced advanced from from the t h e northwest northwest depositing depositing aa reddish—brown, reddish-brown, sandy sandy basal basal till. To the t h e east, e a s t , the t h e Langlade Langlade Lobe Lobe deposited deposited aa dark dark reddish—brown reddish-brown till. To basal b a s a l till till as a s ice i c e flowed flowed from from the t h e northeast. northeast. Further Further east, e a s t , the t h e Green Green Bay Bay Lobe, Lobe, advancing advancing from from the t h e east e a s t and and southeast, southeast, deposited deposited aa brown, brom, sandy, sandy, dolomitic dolomitic till. till. No No absolute absolute dates dates are a r e available, a v a i l a b l e , but but stratigraphic s t r a t i g r a p h i c and and geomorphic geomorphic evidence evidence suggests suggests that t h a t the t h e advance advance of of these t h e s e lobes lobes to t o their t h e i r terminal terminal moraines moraines was was not not contemporaneous contemporaneous as a s reported reported by by Thwaites Thwaites (1943). (1943). At At the t h e junction junction of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe and and Langlade Langlade Lobe Lobe no no strati— stratigraphic till graphic sections s e c t i o n s showing showing 22 tills t i l l s are a r e available. a v a i l a b l e . Relationships Relationships of of till fabric f a b r i c azimuths, azimuths, moraine moraine alignments alignments and and drainage drainage features f e a t u r e s indicate i n d i c a t e an an early e a r l y advance advance of of the t h e Langlade Langlade Lobe Lobe and and the t h e formation formation of of the t h e Parrish Parrish Moraine. This was was followed followed by by an an advance advance of of the t h e Wisconsin Wisconsin Valley Valley Lobe Lobe Moraine. This and was followed followed shortly shortly and the t h e formation formation of of the t h e Harrison Harrison Moraine Moraine which which was thereafter t h e r e a f t e r by by aa readvance readvance of of the t h e Langlade Langlade Lobe Lobe to t o aa position p o s i t i o n 66 miles miles short and tthe short of of its i t maximum s maximum advance advance and h e formation formation of ofthe t h eSummit SummitLake Lake Moraine. Moraine. Stagnant Stagnant ice i c eofofthe t h Wisconsin e WisconsinValley ValleyLobe Lobemay may have have been been present present during during this t h i sreadvance. readvance. To To the t h e east, e a s t , the t h e Green Green Bay Bay Lobe Lobe advanced advanced to t o its i t s maximum maximum position position and and retreated r e t r e a t e d at a t least l e a s t 20 20 miles miles before beforethe t hmaximum e maximum advance advance of of the the Langlade Bay Lobe till is stratigraphically beneath Langlade Lobe. Lobe. Green that Green Bay Lobe till i s s t r a t i g r a p h i c a l l y beneath that of of the t h eLanglade Langlade Lobe Lobe aat t lleast miles in i~from from the t h e margin margin of the the e a s t 55 miles Langlade Outwash streams h e Langlade Langlade Lobe Lobe iice c e cut c u toutwash outwash streams from from tthe Langlade Lobe. Lobe. Outwash and thet hGreen Bay and till tillofof e Green BayLobe. Lobe. 24 �A PLUTONNEAR NEARELY, ELY, MINNESOTA A LOWER LOWER PRECAMBRIAN PRECAMBRIAN LAMPROPHYRE LAMPROPHYRE PLUTON MINNESOTA M. G. M. Mudrey, ~ r .and and ' A. L. Geldon, Geldon, University U n i v e r s i t yofoMinnesota f Minnesotaand andMinnesota Minnesota G. Mudrey, Jr.1 A. L. Geological Survey. Survey. ABSTRACT ABSTRACT Oneoof bodies ooff lamprophyre One f tthe h e bbetter e t t e r exposed exposed bodies lamprophyre wwithin i t h i n tthe h e Early E a r l y PrePrecambrian Vermilionddistrict cambrian Vermilion i s t r i c t of o fMinnesota Minnesota is i s located l o c a t e d88km km northwest northwest ooff Ely, Ely, on tthe on h e north n o r t h side s i d e of o fBurntside Burntside Lake. Lake. The The ccrudely r u d e l y e elliptical l l i p t i c a l pluton, p l u t o n , about about by0.5 0.5 km, km,i is Lower Precambrian 1 km km by s situated s i t u a t e d in i nthe t h ecore coreofo a f afold f o loutlined d o u t l i n eby d by Lower Precambrian migmatizedb ibiotite amphibolite; howevert hthe migmatized o t i t e sschist c h i s t and and amphibol i t e ; however e p lpluton uton i sisvvitually itual l y 1 unmetamorphosed unmetamorphosed andand i s is d i sdiscordant c o r d a n t t otot hthe e sstructure. tructure. The has aa narrow, narrow, discontinuous discontinuousborder borderzone zoneo fofuuralitized The ppluton l u t o n has ralitized phlogopite-bearing These two two phlogopite-bearing pyroxenite p y r o x e n i t e and and an an inner i n n e r zone zone of o flamprophyre. lamprophyre. These rock types based relations, petrography, f i efield 1 d re1 a t i o n s ,petrography, rock types are a r e considered considered comagmatic comagmati c based on on Both the t h e pyroxenite p y r o x e n i t e and and the t h elamprophyre lamprophyre are are cut c u tbybynumerous, numerous, and and chemistry. Both thin adamell i t i composition, c composition,which whichcontain c o n t a i nxenocrysts xenocrysts t h i n dikes dikes of o fmonzonitic monzoni t i c to t oadamellitic of mafic minerals tthat o f the t h e same same m a f i c minerals h a t occur occur in i nthe t h epyroxenite p y r o x e n i t eand andlarnprophyre. lamprophyre. The The dikes representa al alate dikes are a r e probably probably comagmatic, comagmatic, b ubut t c ocould u l d represent t e ppink i n k lleucocratic eucocratic phaseoof adjacent VVermilion phase f tthe h e adjacent e n n i l i o n ggranite. ranite. The lamprophyre lamprophyrei is Approximately213 2/3 ooff the The s a melanocratic porphyry. porphyry. Approximately the exposed lamprophyrei sisaa bbiotite—bearing hornblendes spessartite; exposed lamprophyre i o t i t e - b e a r i n g hornblende p e s s a r t i t e ; the t h e remainremainThe sspessartite byuuralitized ing 113 is i s augite a u g i t e inokersantite. i n o k e r s a n t i t e . The p e s s a r t i t e iiss dominated dominated by ralitized i n g 1/3 with subordinatec hchloritized ddiopsidic i o p s i d i c aaugite ugite w i t h subordinate l o r i t i z e d bbiotite, i o t i t e , sericitized s e r i c i t i z e dandesine, andesine, andi interstitial and n t e r s t i t i a lpotassium potassium feldspar; feldspar; the t h e relatively re1 a t i v e l yunaltered u n a l t e r e d inokersantite inokersantite is by ddiopsidic i s dominated dominated by i o p s i d i c augite a u g i t e and and biotite b i o t i t ewith w i t hsubordinate subordinateandesine andesineand and interstitial crude subhorizontal subhorizontal llayering i n t e r s t i t i apotassium l potassium feldspar. feldspar. A A crude a y e r i n g within w i t h i n both both types ooff lamprophyre byananupward upward increase types lamprophyre i is s marked marked by increase i ning rgrain a i n ssize i z e oof f the the groundmassand and decrease phenocrysts; an groundmass decrease i n in s i size z e o of f tthe h e phenocrysts; an increase in i n amount amount of of potassiumf efeldspar potassium l d s p a r aatt the t h e expense expense ooff total t o t a l ferromagnesian ferromagnesian minerals; minerals; and and aa change change iinn the t h e compositions compositionsofo the f t hferromagnesian e ferromagnesianminerals——mainly minerals--mainly an an increase increase in i n the t h e iron/magnesium iron/magnesium rratios. atios. Calculated compositions Calculated compositions for f o r the t h erocks rocksbased basedon onmodal modal data data and and microprobe microprobe analyses analyses oof f cconstituent o n s t i t u e n t phases phases i nindicate d i c a t e tthat h a t this t h i s pluton p l u t o nmay may be be related r e l a t e d to to an alkali an an uncommon b a s a lparent, t parent, uncommon petrochemical petrochemical type type ini nLower LowerPrecambrian Precambrian a1 k a l ibasalt an terranes. terranes. The wasemplaced emplaced cooled rrapidly. The ppluton l u t o n was i nina as esemicrystalline m i c r y s t a l l i n e sstate t a t e and and cooled apidly. byeearly IInitially n i t i a l l yhigher h i g h e roxygen oxygen ffugacity, u g a c i t y , as as indicated i n d i c a t e d by a r l y ccrystallization r y s t a l l i z a t i o n of of magnetite andapparently apparently magnetite and h i ghigh h f e ferric/ferrous r r i c / f e r r o u s rratios a t i o s in i n biotite, b i o t i t e decreased , decreased Disequilibrium i s e q u i l i b r i u m ttextures e x t u r e s iindicate n d i c a t e that that somewhat somewhat d uduring r i n g c rcrystallization. ystallization. D crystallization c r y s t a l l i z a t i o nbegan beganata depth t depthand andconcluded concluded at a t shallower, shallower, synvolcanic synvolcanic depths. depths. 1Nowa tatDry DryVValley INOW a l l e y DDrilling r i l l i n g Project, P r o j e c t ,Department Department of o f Geology, Geology, Northern Northern Illinois University, DeKaib, Illinois 60115. I l l i n o i s U n i v e r s i t y , DeKalb, I l l i n o i s 25 �Mineralogical Mineralogical and and Chemical Chemical Studies Studies of Greenstones in i n Wisconsin by G. G. Mursky, G. G. Schriver S c h r i v e r and and A. A. R. R . Venditti Venditti Department of o f Geological Geological Sciences Sciences University U n i v e r s i t y of of Wisconsin—Milwaukee Wisconsin-Milwaukee Milwaukee, Milwaukee, Wisconsin ABSTRACT Central, C e n t r a l , northern n o r t h e r n and and northeastern n o r t h e a s t e r n parts p a r t s of o f Wisconsin contain volcanic—sedimentary c o n t a i n numerous belts b e l t s of of Precambrian volcanic-sedimentary sequences sequences which which are a r e commonly commonly referred r e f e r r e d to t o as a s greenstones. qreenstones. The The units u n i t s appear appear to t o be chiefly c h i e f l y of of middle Precambrian age aye and and they they have been been included included by Stockwell Stockwell (1970) (1970) in i n the t h e Southern Southern Province Province have B e l t which forms forms the t h e southern s o u t h e r n extension e x t e n s i o n of of the the o r Penokean Penokean Fold Fold Belt or 2.5 2.5 to t o 2.7 2.7 b.y. b.y. old o l d Superior Superior Structural S t r u c t u r a l Province Province of of the the Canadian Canadian Shield. S h i e l d . The The volcanic v o l c a n i c rocks in i n Wisconsin have chemical chemical c h a r a c t e r i s t i c s similar s i m i l a r to t o Archean volcanic v o l c a n i c assemblages a s s e h l a q e s of of the the characteristics S u p e r i o r Province Province and and these t h e s e similarities s i m i l a r i t i e s are a r e reflected r e f l e c t e d by the the Superior following following trends: trends: (1) The alkali—lime a l k a l i - l i m e index, index, as a s proposed proposed by by Peacock Peacock (1931), (19311, The f o r Wisconsin's v o l c a n i c rocks has a range from 59 to to for Wisconsin's volcanic 64 and and thus t h u s parallels, p a r a l l e l s , very v e r y closely, c l o s e l y , the t h e alkali—lime alkali-lime index of volcanic v o l c a n i c rocks rocks from from the t h e Superior Superior Province Province index which show show aa range ranqe from from 56 56 to t o 64 6 4 (Wilson (Wilson and and others, others, which 1965). 1965). (2) volcanic Volcanic rocks rocks from from Wisconsin Wisconsin are a r e potassium—poor potassium-poor and and compare to t o Goodwin's (1968) (1968) trend t r e n d of of potassium-poor potassium-poor compare volcanic v o l c a n i c rocks rocks in i n the t h e Superior Superior Province. Province. (3) The The Niggli N i g y l i silica s i l i c a and and total t o t a l alkali a l k a l i values v a l u e s for f o r volvolcanic c a n i c rocks rocks from from Wisconsin, when plotted p l o t t e d in i n relation relation to t o Wilson's Wilson's (1965) (1965) standard s t a n d a r d curve curve drawn drawn for f o r oceanic oceanic alkaline and orogenic calc-alkaline suites, plot alkaline c a l c - a l k a l i n e s u i t e s , p l o t on on t h e orogenic o r o q e n i c calc—alkaline c a l c - a l k a l i n e side s i d e of of the t h e standard s t a n d a r d curve curve the nearly same region r e g i o n as a s the t h e plots p l o t s for f o r the t h e volvoln e a r l y in i n the t h e same canic c a n i c suites s u i t e s from from the t h e Superior S u p e r i o r Province. Province. The greenstones ureenstones have have been been metamorphosed metamomhosed to t o greenschist areenschist facies ~ k o n n a i s s a & z eand and f a c i e s or o r -lower l o w e r amphibolite amphibolite facies. f a c i e s . Reconnaissance detailed s u l p h i d e mineralization mineralization d e t a i l e d work work has has not n o t revealed revealed any any sulphide except e x c e p t for f o r some some disseminated disseminated pyrite. pyrite. 26 �References References Goodwin, Goodwin, A. A. M., M., 1968, 1968, Evolution Evolution of of the t h e Canadian Canadian Shield: Shield: Geol. Assoc. Can. Proc., v. 19, P. -01. Assoc. Can. Proc., v . 1 9 , p. 1—14. 1-14. Peacock, Peacock, M. M. A., A., 1931, 1931, Classification C l a s s i f i c a t i o n of of Igneous Igneous Rocks: Rocks: Geology, V. 39, p. 54—67. Geology, v. 39, p. 54-67. Jour. Jour. Stockwell, Stockwell, C. C. H., H., 1970, 1970, Geology Geoloqy of o f the t h e Canadian Canadian Shield Shield (Introduction), Chapter IV in Geology (Introduction), I V i n Geology and and Economic Economic Minerals Minerals of of Canada, Canada, 5th 5 t h Ed., Ed., Department Department of of Energy, Energy, Mines, and Resources, Ottawa, Canada, p. Mines, and Resources, Ottawa, Canada, p. 44—54. 44-54. Wilson, H. D. D . B., B., Andrews, Andrews, Peter; P e t e r ; Moxham, Moxham, R. R. L., L . , and and Ramlal, Rarnlal, Wilson, H. K., 1965, Archean Volcanism in the Canadian Shield: K., 1965, Archean Volcanism i n t h e Canadian S h i e l d : Can. Can. Jour. J o u r . Earth Earth Sci., S c i . , v. v. 2, 2 , no. no. 3, 3, p. p. 161-175. 161-175. 27 �TEE IRON OREDEPOSITS DESITS AT TIE IMN ORE ATBlACK BUCKRIVER WJER FALlS, WISCONSIN, FALLS, WISCONSIN,GEOlOGY GEOLOGYAND ANDOPERA.TIONS OPEFATIONS John M. Ohison, Inland John M . Ohlson, Inland Steel S t e eCompany, l Compsw, Ishpeniing, Ishpeming, Michigan Michigan h498h9 W9 ATBAC'P Thepresence presenceofofiron iron bearing bearing rocks rocks iin the Black River Falls Falls area The n the Black Mver Attempts ttoo known since since 1839. 1839. Attempts of west-central nest-centralWisconsin Wisconsinhas hasbeen beenknown wereunsuccessful. unsuccessful. u t i l i z ethis t h i sresource resourcebefore beforethe theturn turnofofthe the centumwere utilize century 1nlandts facility, f a c i l i t y ,which whichopened opened iin n 1969, 1.969, u t i u z e s standard standard grinding grinding Inland's utilizes and nagnetic separation and mgnetic s e p m t i o n techniques. techniques. The rocks of of the the area are The rocks are aa sequence sequence of of steeply steeply dipping dipping highly highly metaaorphased sedimentsincluding includingaa thin-banded thin-banded mgnetite-quartz nagnetite-quartz metamorphased sedkmnts iron fornation. iron formtion. The The ssediments e d h e n t s l lie i e on a granite granitegneiss gneissbasement basement and intmded by by both both acid acidand and basic bssicdikes dikes.• The and are intruded %e eentire n t i r ePrecambian Ft-ecambian sequenceiis sequence s overlain w e r l a i n by by flat flatlying lyingC*mbrian Cambrian sandstones. sandstones. Water Water iiss obtained wells iinn aa concealed disobtained from from wells concealed Pleistocene Pleistocene valley valley which which was n s discovered by by geo@ysical geoaysical methods. covered methods. Plant water water circulates circulates in Plant i naaclosed closedsystem. system. Experimental Experimental ttree r e e and and grass Wisconsin gmss planting planting with with the t h ehelp helpofofthe the WisconsinDepartment Ceprixent of Natural Natural Resources, the University of ExtensionService, Service, and and the the SSoil Resources, the of Wisconsin Wisconsin Extension oil conservation Service Servicewwas started on on the the waste waste ddisposal Conservation as started i s p s a l ppiles i l e s within within a year and aa half half of of plant plant startup. %e a year and The plant plant and and waste waste disposal disposal areas were designed designed from from the the outset environmentaleffect. effect. were outset to t ohave havea aminimum minimum environmental 28 �STRUCTURAL EVOLUTION O OF STRUCTUm EVOLUTION F TEE THE DEER DEER LAKE LAKEULTRAMAFIC ULTRAMAFIC COMPLEX, COMPLEX, MINNESOTA MINNESOTA M. Ripley Ripley and Donald N. M. Davidson, Davidson, Jr., J r . , Geology Department, Department, Edward M. Edward University of Minnesota, Minnesota, Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT ABSTRACT Lake Ultramafic Ultramafic Complex Complexisislocated located 6.5 6.5 kilometers The Deer Deer Lake kilometers southsouthThe The magnetic magnetic anomaly anomaly associated a s s o c i a t e d with with this this Effie, E f f i e , Minnesota. Minnesota. The east e a s t of of Archean Complex Complex is is 13 13 kilometers long long and and 33 kilometers wide wide and and trends S. 45W.from the of Deer Lake to just n northeast o r t h e a s t of the the S. 45W.from t h e south tip t i p of t o just town of of Big Big Fork. Fork, The stratigraphic within s t r a t i g r a p h i c succession w i t h i n this t h i s Complex Complex consists c o n s i s t s of two stratiform s t r a t i f o r m differentiated d i f f e r e n t i a t e d gabbroic sills, one nonstratiform gabbroic s t r a t i f o r m sills sills s i l l and and two two locally l o c a l l y discordant discordantultrainafic u l t r a m a f i c lenses. lenses. The stratiform sill (700-1,100 m. m. thick) t h i c k ) are a r e composed composed of: of: basal b a s a l peridotite p e r i d o t i t e (160—330 (160-330 m.), m.), (700—1,100 orthopyroxene m.), gabbro 450—650 m.) 450-650 m.) orthopyroxene clinopyroxenite (less ( l e s s than 160 160 m.) plus medium— to p l u s or o r minus mediumt o fine—grained fine-grained differentiated d i f f e r e n t i a t e d felsic f e l s i c cap cap rock. rock. Zones of plumose texture all t e x t u r e have been observed o b s e ~ e dalong contacts contacts between all zones are a r e interpreted i n t e r p r e t e d as a s spinifex—like s p i n i f e x - l i k e chill c h i l l contacts contacts mafic mafic units. units. These zones r a t h e r than sequential s e q u e n t i a l contact contact metamorphic metamorphic effects. effects. rather , Deformation of the t h e Complex Complex commenced commenced with a period of of folding f o l d i n g which The axial The a x i a l plane plane produced two anticlines with an intervening syncline. two a n t i c l i n e s with an i n t e ~ e n i n gsyncline. trends of of these upright, nonpiunging, isoclinal N. 45 E. E. with upright, nonplunging, i s o c l i n a l folds f o l d s is N. Folding a a wavelength of of 1200 1200 meters meters and and an an amplitude amplitude of of 400 400 meters. meters. Folding was produced in response to the emplacement of the Zeisser's Island i n response t o t h e the Zeisser's Island Pluton located located just j u s t southeast southeast of the t h e central c e n t r a l portion p o r t i o n of the t h e Complex. Complex. Local bending of the Complex to an east—west trend around bending of t h e Complex t o an east-west t r e n d around the t h e north north end of the t h e Pluton also a l s o occurred occurred at a t this t h i s time. time. Conjugate Conjugate shear shear fractures fractures trending N. N. 20 W. W. and N. N. 80 W. W. developed in i n response to t o the t h e same NW—SE NW-SE stress s t r e s s system system which which produced produced folding. folding. The The second second stage s t a g e of deformation deformation resulted r e s u l t e d from from extensional extensional release release The with The ffaults a u l t s trend trend with the t h e development development of of normal normal faults f a u l t s and and joints. joints. W. and have minimum minimum dip dip separations separations on on the t h e order o r d e r of of 400 400 meters. meters. N. 45 W. Faulting produced 800 Longi800 meter—wide meter-wide graben graben and and horst h o r s t structures. s t r u c t u r e s . Longitudinal W.) (N. 45 W. ) release r e l e a s e joints j o i n t s are a r e believed t u d i n a l (N. (N. 45 E.) E.) and traverse t r a v e r s e (N. to t o have developed under the t h e same stress s t r e s s orientation o r i e n t a t i o n as a s the t h e normal faults. faults. Strike N. 45 E. E. trend t r e n d characterizes c h a r a c t e r i z e s the t h e final final S t r i k e slip s l i p faulting f a u l t i n g along a N. U g h t - l a t e r a l strike s t r i k e separation s e p a r a t i o n displacement offset offset s t a g e of of deformation. deformation. Right—lateral stage Renewed movement along this t h i s fault f a u l t preprenormal faults f a u l t s about about 300 300 meters. meters. Renewed sumably produced an additional a d d i t i o n a l 100 100 meters strike s t r i k e separation displacement displacement Precambrian diabase diabase dikes. dikes. of middle Precambrian 29 �THE CHEMISTRY OF THE THE PETROLOGY ETROLOGY AN]) AND CHEMISTRY THE ROUND ROUND [AKE L A E INTRUSION, INTRUSION, NORTHWESTERN NORTIMESTERN WISCONSIN WISCONSIN D. L. Roder Cameron Roder and E. N. Cameron Department of Department of Geology Geology and Geophysics Geophysics University University of of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706 53706 ABSTRACT The The Round Round Lake Lake intrusion intrusion is is aa northeast-trending northeast-trending Precambrian Precambrian mafic layered intrusion by subsurface subsurfacedrilling drilling of mafic layered intrusion found found by of an an area area ten ten miles east miles east of Hayward, Hayward, Wisconsin. Wisconsin. The The body may may be as as much much as as eight eight miles long long and two miles magnetitemiles and two miles wide. wide. Portions Portions drilled drilled consist consist of of magnetitetroctolite troctolite with with anorthositic anorthositic gabbro gabbro layers layers that that range range from from threethreefourths fourths inch inch to to more more than than eighty eighty feet feet in in thickness. thickness. Diabase Diabase interintersected sected by the the drill drill holes holes appears appears to to form form later later intrusions. intrusions. Mineral Mineral assemblages assemblages in in the the magnetite-troctolite magnetite-troctolite and and anorthositicanorthositicgabbro gabbro are are the the same, same, the the two two rock rock types types differing differing only only in in mineral mineral proportions. ilmenite, and and proportions. Plagioclase, Plagioclase, olivine, olivine, titanomagnetite, titanomagnetite, ilmenite, apatite apatite are are cumulus cumulus minerals. minerals. Clinopyroxene, Clinopyroxene, biotite, biotite, and and plagioclase plagioclase are minerals. The are intercumu.lus intercumulus minerals. The magnetite-.troctolite magnetite-troctolite averages 28 averages 28 volume volume per per cent cent plagioclase, plagioclase, 36 iron36 per per cent cent olivine, olivine, 33 33 per per cent cent irontitanium oxides, oxides, 33 per per cent cent augite augite and and biotite, biotite, and and aa trace trace of of titanium anorthositic gabbroaverages averages 66 66per per cent cent plagioclase, plagioclase, apatite. The anorthositicgabbro 22 22 per per cent cent olivine, olivine, 88 per per cent cent iron-titanium iron-titaniumoxides, oxides, '-t 4 per percent cent augite, augite, and and less less than than one-half one-half per per cent cent apatite. apatite. Titanomagnetite in in these these rocks rocks is is an an irregular irregular microintergrowth microintergrowth Titanomagnetite of ulv%pinel. of magnetite magnetite and and ulv1spinel. Ilmenite Ilmenite occurs occurs as primary granular granular aggregates, (111) lamellae lamellae in in titanomagnetite, titanomagnetite, and and as as granular granular aggregates, as as (111) aggregates aggregates around around titanomagnetite titanomagnetite grains. grains. Hercynite Hercynite is is found found as as tiny tiny "dots" "dots" in in titanomagnetite. titanomagnetite. Magnetite appears appears to to have have settled settled as as euhedral euhedral crystals. crystals. Anhedral Anhedral aggregates aggregates are are thought thought to to be be due due to to enlargement or partial recrystallization recrystallization of touching crystals after settling. settling. Only Only small-scale small-scale cryptic cryptic layering layering is is displayed displayed by by the the intrusion. intrusion. Plagioclase ranges ranges from from An51 AnS1 to to Anits, An~r,, but chemical Plagioclase but no consistent consistent chemical trend trend is is evident. evident. In X-3, anorthositic•gabbro In core core from from drill drill hole X-3, anorthositic gabbro and and magnetite-troctolite are interlayered; olivine magnetite-troctolite olivine in in anorthositic-gabbro anorthositicgabbro ranges from from P053 FoS3 to to Fo56, FoS6, whereas whereas olivine olivine in in magnetite-troctolite magnetite-troctohte ranges ranges from Fo5, Fo57 to to Fo Fo2. 2 . In In core core from from drill drill hole hole X-2, X-2, anorthositie anorthositic gabbro developed. In gabbro layers layers are are poorly poor y developed. In this this core, core, olivine olivine ranges ranges from from Fo57 of Ca4$lg3,Fel8. CaqMg37Fe18. FoS7 to to Fog1. FoS1. Augite Augite has has an an average average composition of Microprobe analysis analysis of of titanomagnetite titanomagnetite gives gives the the following followmg range range of of Microprobe composition: composition: total total iron iron as as FeO FeO 65 65 to to 7'-!74 weight 20 to to weightper percent, cent, Ti02 Ti02 20 21l per cent, cent, MgO MgO 0.5 0.5 to to 3.8 3.8 per per cent, cent,A1203 A12O3 2.3 2.3 to to 3.9 3.9 per per cent, cent, V203 V03 24 per 1.0 to to ]J3 L.3 per per cent, cent, and and Cr203 Cr203 0.1 0.1 to to 1.2 1.2 per per cent. cent. Primary Primary ilmenate ilmen~te has an an average average composition composition of of Ilmg8Hem2 Ihg8Hem2 and and contains contains up up to to S5 weight weight has per per cent cent MgO. MgO. !? Information Information at at hand indicates indicates the the presence of of sizeable sizeable concentraconcentrations tions of of iron-titanium iron-titanium oxides, oxides, but but further further exploration exploration will will be be necessary necessary to determine determine their their form, form, extent, extent, and and relations relations to to the the Round Round Lake Lake to intrusion intrusion as as aa whole. whole. 30 �UPPER MISSISSIPPI VALLEY EXPERIMENTAL UPPEX MISSISSIPPI VALLEYBASE BASEMETAL MET& DEPOSITS: DEF'OSITS: FXPERIMEIiTAL SOLUTIONS TO PROBLEMS OF ORE ORE GENESIS GENESIS SOLUTIONS TO mOBLEMS OF' B. Romberger, Romberger, Department of of Geology and Geophysics, Geophysics, University of S. B. Wisconsin, Madison, Madison, wisconsin Wisconsin 53706 Wisconsin, 53706 ABSTRACT A BSTRACT Chemical models for of base metals f o r tthe h e ttransport r a n s p o r t and deposition of in Mississippi Valley Type Deposits are studied experimentally using i n Mississippi Valley Type Deposits a r e using object is i s tto o supply evidence tto o a mineral synthesis synthesis approach. approach. The obJect support tthe hypothesis tthat have been been deposited deposited from metalmetal— support h e hypothesis h a t tthese h e s e oores r e s have containing, sulfur—deficient, chloride—rich solutions containing, s u l f u r - d e f i c i e n t , chloride-rich s o l u t i o n s entering a sulfur—containing reducing environment. Copper, iron, sulfur-containing i r o n , lead, l e a d , and and zinc zinc were synthesized together together iin molal sodium chloride chloride ssolutions olutions ssulfides u l f i d e s were n 3 molal between 200 20' and and 200°C 200° under the t h e vapor vapor pressure pressure of of water. water. Copper, iron, iron, lead, barium, and calcium were introduced a ass solid l e a d , zinc, zinc, barium, s o l i d carbonates or or The amount amountofof ssulfur soluble chlorides soluble chlorides along along with with elemental elemental ssulfur. u l f u r . The ulfur The of tthat added a l l metal. metal. The added was iin n excess excess of h a t necessary necessary tto o rreact e a c t with with all products depended dependedonont hthe of tthe products e sstarting t a r t i n g composition composition of h e experiments, experiments, but pyrite, galena, digenite, barite, were generally covellite, covellite, p y r i t e , sphalerite, s p h a l e r i t e , galena, digenite, b arite, Morphology of of some some of tthe he anhydrite, anhydrite, and and aa second second generation generation calcite. c a l c i t e , Morphology composite m metallic e t a l l i c sulfide s u l f i d e grains g r a i n s suggest suggest initial i n i t i a l rreaction e a c t i o n occurred above the indicated by by t h e melting temperature temperature of of sulfur. s u l f u r . Nonequilibrium iiss indicated with of unreacted unreactedssulfur tthe h e presence presence of u l f u r iin n tthe h e cores cores of of grains g r a i n s together with metal concentrations concentrations in i n the t h e co—existing co-existing solutions. solutions. No No metal high metal carbonates remained in i n the t h e run products. products. The sulfides s u l f i d e s showed a regular zonation in in rrelation e l a t i o n to t o the t h e un— unzoningiin terms of reacted ssulfur u l f w and and ccalcite. a l c i t e . Summarizing S m a r i z i n g t hthe e zoning n terms of paragenesis, c o v e l l i t e is i s early, e a r l y , followed followed by by galena galena and and sphalerite. sphalerite. paragenesis, covellite Pyrite F y r i t e forms before galena and s p h a l e r i t e but i t s r e l a t i o n s h i p t o s unclear. Barite B a r i t e and anhydrite form independently of of the the ccovellite o v e l l i t e iis ssulfide u l f i d e zoning, zoning, however the t h e second second generation c a l c i t e i s t h e l a s t phase galena and sphalerite but its relationship to generation calcite is the last phase whichappear appeart otocause causep precipitation, ttoo form. form. The The ffactors a c t o r s which r e c i p i t a t i o n , iin n order order of of activity, sulfur a c t i v i t y , increasing increasing pH pH of of solution, solution, importance, are: a r e : increasing sulfur and decreasing temperature. temperature. To aid a i d in i n determining tthe h e chemical conditions underwhich sulfide sulfide precipitation p r e c i p i t a t i o n took place, p l a c e , tthe h e aqueous solutions s o l u t i o n s were analyzed for f o r copper, zinc, llead, barium, and concentration of of the t h e metals metals zinc, e a d , iron, i r o n , barium, and calcium. calcium. The concentration with decreasing temperature temperature and increasing time; time; and barium decreased with that t h a t of calcium either e i t h e r increased or o r decreased, depending on the t h e starting starting variation i s a ttypical ypical v a r i a t i o n of the t h e molar ratio ratio conditions. The following is Cu:Fe:Pb:Zn iin of l1.0:1.0:1.0:1.0: .O:l.O:l.O:l.O: aatt Cu:Fe:F'b:Zn n solution s o l u t i o n aafter f t e r aa starting s t a r t i n g rratio a t i o of 200°C, 1.0:0.114:1140:360; 120°C, ~1.0:1.0:830:2280; 20O0c, ~ . 0 : 0 . ~ & : ~ 4 0 : 3 6a0at t ; 12O0C, . 0 : ~ . 0 : 8 3 0 : 2 2 8 0 and ;and at a t 25°C, 25OC, 1.0:0.15:3.3:150. The copper concentration ttypically y p i c a l l y dropped from from a few few 1.0:0.15:3.3:150. 200°C, to l000ppm t o less less 100Oppm in i n the t h e starting s t a r t i n g solution s o l u t i o n to t o less l e s s than than 55 ppm aatt 20o0C, v a r i a t i o n s are a r e consistent with the t h e paragenesis than than 11 ppm ppm at a t 25°C. 2F°C These variations not established observed in observed i n the t h e minerals. Because equilibrium was not e s t a b l i s h e d tthe he major significance s i g n i f i c a n c e of of these t h e s e data is i s to t o demonstrate relative r e l a t i v e tendencies ffor o r metal sulfides s u l f i d e s to t o precipitate p r e c i p i t a t e under under the t h e conditions conditions of of the t h e experiment. experiment. 31 �PETROLOGY OF PETROLOGY O F SOME SOME EA1LY EARLY PRECAMBRIM PRECAMBRIAN DIFFERENTIATEDULTRAMAFIC LlLTRAMAFIC BODIES BODIES DIFFERENTIATED IN I NNORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA Klaus J. Schulz Schulz and and Edward Edward M.H.Ripley, of Minnesota, Minnesota, Duluth, Duluth, Klaus 3. Ripley, University of Duluth, Minnesota Minnesota 55812. 55812. ABSTRACT Mapping iin n the t h e Newton Newton Lake Ely, Minnesota Minnesota and and Mapping LakeFormation Formationnorth north of of Ely, the t h e Deer Lake Lake Area n northern I t a s c aCounty, County, Minnesota Minnesota has l o c a t e d aa Area iin northern Itasca has located number number of of mafic—ultramafic mafic-ultramafic bodies of of Early Early Precambrian age, many many of which which are a r e differentiated. differentiated. Detailed mapping mapping of of these t h e s e bodies bodies has has shown shown Detailed that t h a t they they are a r e conformable conformable to t o the t h e surrounding surrounding country country rocks, rocks, indicating indicating they are either sills or flows. that t h a t they a r e e i t h e r sills o r flows. Country Country rocks both areas a r e a s conconrocks iinn both sist of of medasedimentary medasedimentary and r g e l y pillowed metavolcanic metavolcanic rocks. rocks. No andl alargely No sist evidence evidence for f o r contact contact metamorphism metamorphism has been been observed observed between between the t h e bodies bodies and the country rocks. and t h e country rocks. The bodies o 1,000 e e t in i n thickness thickness and and have have The bodies range range from from400 400t to 1,000ffeet lateral miles. The l a t e r a lextents e x t e n t sfrom from aa mile mile to t o several s e v e r a l miles. The rocks t h eDeer Deer rocks of the Lake Areahave havebeen beenf afaulted andt itightly while those north of Lake Area u l t e d and g h t l y folded folded while of Ely Ely are a r e faulted f a u l t e dand and only only broadly broadly folded. folded. Serpentinization S e r p e n t i n i z a t i o n and t h e r aalterlterand oother isextensive extensiveini nalla lthe l t hbodies e bodies with metamorphism generally generally of the the a t i o n is ation with metamorphism green—schist green-schist facies. facies. I n both areas, areas, bodies composed composed solely s o l e l y of of gabbro gabbro or o r peridotite p e r i d o t i t e exist, exist, In however however most most appear appear to t o be be differentiated. d i f f e r e n t i a t e d . The The typical t y p i c a l sequence sequence in i n the the is peridotite, p e r i d o t i t e , pyroxenite, pyroxenite, d i f f e r e n t i a t e d ones, ones, from from bottom bottom to t o top, top, is differentiated porphyritic p o r p h y r i t i c gabbro, gabbro, gabbro. gabbro. The The peridotite p e r i d o t i t e is i s composed composed of of rounded rounded to to euhedral euhedral olivine o l i v i n e and and rare r a r e chromite chromite surrounded surrounded by o i k i l i t i cpyroxene pyroxene by ppoikilitic and and amphibole. amphibole. At A t least l e a s t some some of of the t h e peridotites p e r i d o t i t e s contain contain both both ortho— orthopyroxene h e r z o l i t e . The The pyroxene and and clinopyroxene clinopyroxene and a s s i f i e d as andwould wouldbebec lclassified as IIherzolite. pyroxenite contains sub— pyroxenite is is in i nsharp sharpcontact contactwith withthe t h eperidotite p e r i d o t i tand e and contains subhedral h e d r a l diopsidic d i o p s i d i c augite a u g i t eand and in i nsome some cases cases also a l s o contains contains bronzite. bronzite. With Plagioclase, Plagioclase, in i nvarying varyingamounts, amounts, forms forms the t h e intercumulate i n t e r c u m d a t e phase. phase. With increasing increasing plagioclase p l a g i o c l a s e content content the t h e pyroxenite pyroxenite grades grades into i n t o porphyritic porphyritic gabbro composed composed ofofaaugite, u g i t e , plagioclase p l a g i o c l a s eand andpyroxene pyroxene phenocrysts, phenocrysts,which which gabbro are gabbro contains contains pplagioclase, a r e now now completely completely aaltered. l t e r e d . The The gabbro l a g i o c l a s e , augite, augite, t e r s t i t a l quartz quartz and and and secondary secondary aactinolite c t i n o l i t e with with varying varying amounts and amountsofofi ninterstital micrographic micrographic intergrowths. intergrowths. Cumulate Cumulate t textures e x t u r e s in i n the t h eperidotite, p e r i d o t i t epyrox— , pyroxandporphyritic p o r p h y r i t i cgabbro gabbro along along with with minor minor layering layering and and size s i z e grading grading e n i t e , and enite, i n d i c a t e that t h a t selective s e l e c t i v e crystallization c r y s t a l l i z a t i o nand and gravity g r a v i t y settling s e t t l i n gofofphases phases indicate were the the main main mechanisms mechanisms ofofddifferentiation. i f f e r e n t i a t i o n . Many Many of t h e bodies bodies examinexaminwere of the ed ed were were also a l s o found found to t ohave have complex complex chilled c h i l l e dmargins. margins. A of sulfide A ddetailed e t a i l e d study study of s u l f i d e mineralization m i n e r a l i z a t i o n in i n the t h e bodies bodies of of the the Deer Areashows showst hthat copper, and and iron i r o n sulfides s u l f i d e s are a r e conconDeer Lake Lake Area a t nnickel, i c k e l , copper, The centrated centrated in i n the t h e chilled c h i l l e d margins, margins, making making up up 22 to t o 3% 3%of of the t h e rock. rock. The 32 �basic b a s i c sulfides s u l f i d e s appear to t o have formed formed from from an immiscible Immiscible sulfide— sulfideof intrusion, oxide lliquid, i q u i d , which aatt the t h e time of i n t r u s i o n , coexisted with the the of ssulfide also silicate s i l i c a t e magma. A general llayering a y e r i n g of u l f i d e phases was a l s o found to t o exist e x i s t through through the t h e bodies bodies with with nickel n i c k e l sulf s u l f iides d e s concentrated concentrated in i n the the peridotite, pyroxenite and p porphritic p e r i d o t i t e , copper sulfides s u l f i d e s in i n the pyroxenite o r p h r i t i c gabbro gabbro u l f i d e s appear to t o have and iron i r o n ssulfides u l f i d e s in i n the t h e upper gabbros. gabbros. These ssulfides magma, p precipitating i l i c a t e magma, r e c i p i t a t i n g aass late l a t e phases been in i n solution s o l u t i o n in i n the ssilicate with the t h e intercumulus intercumulus minerals. chemical analyses of of samples from tthe bodies north north of Chemical analyses samples from h e bodies of Ely Ely show show a a bodies appear appear to The bodies t o be be general withddifferentiation. general iron i r o n enrichment enrichment with i f f e r e n t i a t i o n . The ttholeiitic h o l e i i t i c in i nnature n a t u r e and and very ssimilar i m i l a r to t o differentiated d i f f e r e n t i a t e d ultramafic ultramafic bodies age in i n Canada, Canada, Africa, Africa, and and Australia. Australia. bodies of Early Precambrian age 33 �TECTONIC HISTORY HISTORY OF OFEARLY EARLY PRECAMBRIAN PRECAMBRIAN ROCKS THE TECTONIC ROCKS IN IN THE VERMILION DISTRICT, DISTRICT, NORTHEASTERN NORTHEASTERN MINNESOTA VERMILION MINNESOTA P. P. K. K. Sims, Sims, Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul,Minnesota Minnesota55108 55108 ABSTRACT ABSTRACT The Vermilion district, ini nnortheastern The Vermilion northeasternMinnesota, Minnesota, contains contains aa sequence sequence of of complexly complexly bordered on on the the north north by by the the intertonguing volcanic volcanic and and volcaniclastic volcaniclasticrocks rocksthat thatisi sbordered intertonguing Vermilion granite—migmatite granite-migmatite massif massif and Vermilion andon on the the south southby by the the Giants Giants Range Rangebatholith. batholith. The supracrustal rocks adjacent to rocks dominantly dominantlyhave havegreenschist—facies greenschist-facies assemblages; assemblages; adjacent to the intrusive they have amphibolite—facies intrusive granitic graniticrocks rocks(Ca. (ca. 2700 2700m.y. m.y. old) old) they hove amphibolite-focies assemblages. assemblages. The supracrustal rocks rockstrend trendgenerally generally eastward, eastward, are are steeply steeply inclined, and The supracrustal andhave have and faulted. Two Twogenerations generationsofoffolds foldshave havebeen beendistinguished distinguished been complexly folded and in part of of the i n the the western western port the district. The older generation is i s represented represented by to by tight tight to that trend trend northwestward northwestward and axialsurfaces surfaces close folds that and have have planar, planar, steeply steeply inclined inclined axial and axes. The and gently—plunging gently-plunging axes. Theyounger younger generation generationfolds foldsare aresuperposed superposed on on the the older older folds of the district. folds in i n the the extreme extreme western western part of district. These These folds trend eastward eastwardand and folds trend axialsurfaces surfacesand andsteep steep plunges; plunges; they they are are accompanied accompanied by by ao have planar upright upright axial have pervasive steep steep cleavage cleavage and and associated associated lineations lineationsthat thatobscure obscuremost moststructures structures pervasive related relatedto tothe theolder olderdeformation. deformation. Judged Judgedfrom fromthe thedivergent divergenttrends trendsofofstructures structuresand and generally steep steep plunges the rocks rocks in i n the the eastern eastern part of the the district district the generally plungesof of lineations, lineations, the also also were were folded folded during during two two or or more more periods periods of deformation. deformation. Three steep fault fault systems, systems, each each of of which whichhas hasassociated associatedmylonite, mylonite,post—date post-date the the Three folding. folding. The The oldest (2) (?) faults faults have haveaa dominant dominant vertical verticalcomponent componentof ofmovement. movement. The The major major fault faultini nthis thissystem systemoccurs occursat atthe theapproximate approximateboundary boundarybetween betweenthe thelow— lowgrade supracrustal supracrustal rocks and the Vermilion Vermiliongranite—migmatite granite-migmatite massif; massif; another fault fault grade separates separates the eastern part of the the Giants GiantsRange Range batholith batholithand andassociated associatedamphibolite— omphibolitefacies facies rocks rocks from from the the supracrustal supracrustal rocks. rocks. These These faults probably have vertical movements faults probably have vertical movements of 3,000 3,000 to to5,000 5,000 feet, feet,and andappear appeartotohave havedeveloped developedlargely largelyini nresponse response to to isostatic isostatic of adjustments between crustal crustal blocks blocks having having different different rock adjustments between rock densities. densities. The younger (?) represented mainly mainly by straight, steep, (?) system system iiss represented steep, north—northnorth-northThe next younger east trending trending faults that cut cut both both the the granitic graniticrocks rocksand and the the volcanic volcanicrocks rocksand and have have east left—lateral miles. These These faults locallyare areabundant abundant left-lateral displacements displacementsof ofas asmuch much as as 44 miles. faults locally and and closely closelyspaced. spaced. Some Someofofthem themappear appeartotodisplace displacesupracrustal supracrustalrocks rocksmore more than than the the intrusive intrusiverocks, rocks,suggesting suggestingthat thatthey theypre—date pre-dote emplacement emplacementof ofatatleast leastsome some of of the the granitic granitic rocks. rocks. The youngestfaults faultsare aretranscurrent transcurrentfaults faultshaving havinghorizontal horizontalright right lateral displaceThe youngest ments. this system this systemisi sata least t least250 250miles mileslong longand andtransects transectsseveral several ments. The Themajor majorfault faultini n greenstone—granite greenstone-granite complexes. complexes. In I n northwestern northwestern Minnesota Minnesota iti tappears appears to to have have disdisplaced distinctive distinctivegravity gravityanomalies anomalies aa distance distance of about about 35 miles; miles; in i n the the Vermilion Vermilion placed district,where whereit iconsists t consistsofofseveral severalstrands, strands, iti thas hasdisplaced displacedthe the upper upper part part of of the the district, volcanicpile p i l ea adistance distanceofofabout about1212miles, miles,distorting distorting i t from a thick almond-shaped volcanic it from a thick almond—shaped lens lens to toaatenuous tenuouseast—trending east-trending mass. mass. Metamorphism, folding, and andemplacement emplacement of the the granitic graniticrocks rockswere werebroadly broadly Metamorphism, 34 �synchronous, and andoccurred occurredduring during the the Algoman Algomanorogeny. orogeny. The synchronous, The foldng foldingofofthe thesupra— supraresulting from from the the relative relative upwelling crustal rocks is attributed to to compression compression resulting upwelling convergence of of the the flanking batholiths, experiand convergence batholiths, aamechanism mechanism demonstrated demonstrated experimentally by Romberg (1967). The Vermilion massif andat at least least aa part part of of the Giants Ramberg (1967). The Vermilion massif and Giants Range batholith continued continued to rise because becauseofof their their buoyancy buoyancy after after crystallization crystalUzation Range batholith of the the granitic rocks. rocks. The Thetranscurrent transcurrent faulting faultingtook took place placeduring during aa fate latestage stage of of the orogeny, orogeny, after after the the crust crust had had attained attained sufficient sufficient strength strength to to transmit transmit regional regional related to the fracturing can compressive compressive stresses. stresses. Cataclasis Cataclasis related can account account for the the disparity between andmineral mineral ages agesi n in the the Giants Range batholith between whole—rock whole-rock and Range batholith (Prince and Hansen, Hansen, 1972). 1972). 35 �LAYEREDWMAPIC INTRUSION A KEWBENAWAN KEWEENAWAN LAYEmD I C INTRUSION NEAR NZAR FINLAND, FINLAND,LAKE LAKECOUNTY, COUNTY,MINNESOTA XIRXTSOTA R.J. R.J. Stevenson, Department Department of Geologys Geology, University of Stevensons Minnesota-Duluth, Duluth, Ninnesota-Duluth, DuLuth,Minnesota Kinnesota55812 55812 ABSTRACT ABSTRACT and one The NNE The Sonju Sonju Lake h k e Intrusion, Intrusion, four four and one half halfmiles milesNN3 Finland, has an Finland, Minnesota, Minneeota, has an exposed exposed area area of of one one and and one one intrusion isissurrounded miles • The intrusion half two and and one one half half miles. The surrounded half by two granite ,of the granophyric granite,of on three sides on three sidesby by diabase diabase and and granophyric the side is Beaver Beaver Bay Bay Complex, Complex, and and the the western western side isobscured obscured by by lamination, cryptic cryptic layering, glacial. drift. It Itshows shows igneous igneous lamination, layering, and layering, and and rhythmic rhythmic layering, and has has a a stratigraphic stratigraphic thickness thickness of of dip of approximately 3500feet feet based basedon onthe the strike strike and approximately 3500 and dip of the the rock units units comprising the intrusion intrusion igneous igneous lamination. lamination. The The rock comprising the picrite; are, from the base to the are, from the base to the top top respectively: respectively: basal basal picrite; troctolite; a gabbro; an a gabbro; an an apatite-rich ferrogabbro; an a troctolite; olivine-hedenbergite quartz-bearing diorite; diorite; a hedenbergite hedenbergite olivine-hedenbergite quarts-bearing The ferrogabbro granodiorite; granodiorite; and and a a hedenbergite hedenbergite adamellite. adamellite. The ferrogabbro contains 43.50$ SiC2. Si02. contains 19.26% 19.26s FeC FeO and and 43.50% of of glacial drift. The The compositions compositions of the the major major minerals minerals vary vary with with strati— etratigraphic height; height; they have been studied by electron electron microprobe plagioclase varies varies from An33 in and optical optical methods. methods. The plagioclase from An in the the and The piorite to to An An ininthe thehedenbergite hedenbergite adamellite. adame~lite?~ The basal picrite basal picrite to in to Fo12 3'0 in the the divine ?07 in in the basal olivine varies varies from froml#o 12 uppermost uppermost apatite—rich apatite-rich7$errogabbro. The cumulus cumulus clinopyroxene d~nopyroxene hrrogabbro. The ranges ranges from from Ca Ca Mg Ng 6Fe Fe 1 in the lowest gabbro to Ca 0Mg Mg Fe Pe injrmjiatg5ana The int?%ne%!atJ5and ferrogabbro. in the uppermoM upperno@ jatite-rich &ti&rich ferrogabb~o. The in the felsic rocks rocks have hedenbergites hedenbergites clustered felsic clustered around around Ca49Mg03Pe43. Ca49Mg03Fe48* lamination, cryptic layering, The The igneous igneous lamination, layering, and and rhythmic rhythmic P extreme iron—enrichment layering the and the extreme iron-enrichment 3' layering and establish this this intrusion trend all establish intrusion as as a a differentiated, tholeiitic intrusion of the differentiateds Skaergaard type. type. Skaergaard trend all tholeiitic intrusion of the A 36 N �THE THE PITTSVILLE PITTSVILLE (WISCONSIN) THE FORMATION FORMATION OOF F THE (WISCONSIN) MIGMATITE MIGMATITE J. E. Thresher, Department Department ooff Geography Geography and niversity o E. Thresher, andGeology, Geology,UUniversity off Wisconsin—Extension, W i scons i n-Extens ion, Madison, Madison, Wisconsin Wisconsin 53706. ABSTRACT The Pittsvi The P i t t s v ilie l l emigmatite m i g m a t i t ewas was formed formed during d u r i n g the thePrecambrian PrecambrTan by by the the iintrusion n t r u s i o n of o faahydrous hydrous granitic g r a n i t i cmagma magma into i n t o aa series s e r i e s ofo fdiabases diabases and and Duet to the hydrous hydrousnnature spatially extensive extensive b a s a l t s . Due o the a t u r e o of f t the h e ggranite, r a n i t e , spacially basalts. transport of magma into the country rock took place which hasbeen been t r a n s p o r t o f magma i n t o the c o u n t r y rock took p l a c e whichhas recordedbybyppoikiloblasts off quartz potash ffeldspar e l d s p a r wwithin i t h i n the t h e older older recorded oikiloblasts o q u a r t z and and potash rocks, and and the the presence presenceo of the ggranite. rocks, f ooriginal r i g i n a l hydrous hydrous mminerals i n e r a l s wwithin i t h i n the ranite. The observedl ilithologic The observed t h o l o g i c layering l a y e r i n g ini nthe t h emigmatite migmatitehas has formed formed axial axial planar p l a n a r to to a a series s e r i e s of o f subisoclinal s u b i s o c l i n a lnorthwest northwest plunging p l u n g i n g folds. f o l d s . Contemporaneous( (or so) w with was raneous o r nnearly e a r l y so) i t h this t h i sfolding folding wasthe t h edevelopment development of of almandine-amphibolitef afades minerals wwithin almandine-amphibolite c i e s minerals i t h i n the t h e migmatite. migmatite. Later Later more openeast-west east—west were i imprinted on tthis more open t r etrending n d i n g s usubhorizontal b h o r i z o n t a l f ofolds l d s were m p r i n t e d on his ffabric, a b r i c , and and this t h i swas was followed f o l l o w e dby bya agreenschist g r e e n s c h i s tfacies f a c i e smetamorphic metamorphic event, event, apparently a p p a r e n t l y uunrelated n r e l a t e d tto o tthe h e folding. folding. Two episodes wererecorded recorded therocks, rocks,the thef first irst Two episodes o fofj ojointing i n t i n g were w i within t h i n the of o f which which effected e f f e c t e d only o n l ythose thoseofo fPrecambrian Precambrian age. age. The The llater a t e r episode episode also also sandstonesand andi sisthus thus aatt least ffractured r a c t u r e d the the overlying o v e r l y i n gupper upperCambrian Cambrian sandstones least thesej ojoints lower Paleozoic Paleozoic in lower i n age. age. Many Many o fofthese i n t s aare r e f filled i l l e d with w i t h quartz, quartz, granite and/or cchlorite. hlorite. g r a n i t e and/or The rnigmatiteswere werel alater byaaggranitic The migmatites t e r i nintruded t r u d e d by r a n i t i c pluton p l u t o n which which is is considered be rrelated considered tto o be e l a t e d to t o the the greenschist g r e e n s c h i s t facies f a c i e smet met and and possibly possibly Several youngerggranitic Several younger r a n i t i c and and bbasaltic a s a l t i c dikes dikes tthe h e ffilling i l l i n g of o f the t h e joints. joints. crosscut the ccrystalline c r o s s c u t the r y s t a l 1 i n e rocks rocks locally. locally. The eentire The n t i r e sequence sequence is i s unconformably unconformably overlain o v e r l a i nby byupper upperCambrian Cambrian sandstones andconglomerates conglomerates which sandstones and which a r are e e sespecially p e c i a l l y pprevalent r e v a l e n t in i n the the southern the PPittsville area. southern ppart a r t oof f the i t t s v i Il earea. 37 �STRUCTURALAND ANDSTRATIGRAPHICAL STRATIGRAPHICALANALYSIS ANALYSIS OF STRUCTURAL OF THE GECO GECO SULPHIDE DEPOSIT DEPOSIT IN I N MANITOUWADGE, MANITOUWADGE, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO Jens Geology, U University Jens F. F. Touborg, Touborg, Department Department oof f Geology, n i v e r s i t y of o fOttawa Ottawa and and Departmentoof Geology,UUniversity Department f Geology, n i v e r s i t y of o f Toronto, Toronto, Ontario, Ontario,Canada. Canada. ABSTRACT ABSTRACT In area hhigh rocksc oconsisting I n the t h eManitouwadge Manitouwadge area i g h grade grade metamorphosed metamorphosed rocks n s i s t i n g ooff metavolcanic—and metasedimentary downfoldedi in metavolcanic-and metasedimentary s e rseries i e s l i lie e downfolded n a northeast northeast plunging ssyncline, plunging y n c l i n e , the t h e core core of o f which which is i soccupied occupied by by aa granodiorite g r a n o d i o r i t ebody. body. Regionalssuiphide occurs wwithin Regional u l p h i d e mmineralization i n e r a l i z a t i o n ooff stratabound stratabound nnature a t u r e occurs i t h i n aa quartz-muscovite schist quartz-muscovite s c h i s t horizon h o r i z o nalong alongthe t h econtact c o n t a coft metasedimentary—and o f metasedimentary-and ooverlying v e r l y i n g metavolcanic metavolcanic sseries e r i e s iinn the t h e upper upper part p a r t of o fthe t h esequence. sequence. The GecoCopper-Zinc-Silver Copper-Zinc-Silvers usulphide beingl located The Geco l p h i d e ddeposit e p o s i t being o c a t e d wwithin i t h i n aa synclinal s y n c l i n a l dragfold d r a g f o l d on on the t h e northeast n o r t h e a s t limb l i m b ooff the t h e syncline s y n c l i n e consists c o n s i s t s of o f aa ttabular a b u l a r body body of o f massive massive sulphides sulphides enveloped enveloped by by a a haloe haloe of o f disseminated disseminated pyrite—pyrrhotite—chalcopyrite mineralization. p y r ite-pyrrhoti te-chalcopyri t e m i n e r a l i z a t i o n . A discontinous d i s c o n t i nous zone zone ooff disseminated chalcopyri chalcopyrite—pyrrhotite—sphalerite—gahnite disseminated te-pyrrhotite-sphalerite-gahni t e mmineralization ineralization The occurs along tthe occurs along h e north n o r t h contact c o n t a c t of o fthe t h equartz—muscovite quartz-muscovite sschist c h i s t horizon. horizon. The south ccontact mineralization south o n t a c t ooff this t h i s contains contains disseminated disseminated ssphalerite phalerite m i n e r a l i z a t i o n in i n aa discontinous by magneti magnetite-chert discontinous zone zone ffollowed o l l owed by t e - c h e r t iiron r o n formation. f o r i n a t i on. The massives suiphide bodywhich whichs tstrikes east-west and andddips The massive u l p h i d e body r i k e s east-west i p s ssteeply t e e p l y to to the elongatedlenses lensesbecoming becoming successsuccesst h e north n o r t hisi scomposed composed of o f aastring s t r i n of g o5—6 f 5-6elongated plungeo of thesepparallels iively v e l y smaller s m a l l e r towards towards the t h e east. east. The The plunge f these a r a l l e l s tthe h e aaxis x i s of of the t h e dragfold. dragfold. IIn n detail d e t a i l the t h emassive massive sulphide s u l p h i d e body body cconsists o n s i s t s oof f 33 pprincipal rincipal rock types: coarseggrained rock types: 1) 1) compact compact ore: coarse r a i n e d p pyrite y r i t e rrich i c h sphalerite s p h a l e r i t e ore. ore. coarsegrained grainedppyrrhotite-chalcopyrite-sphalerite-pyriteayered ore: coarse yrrhotite-chal copyrite-sphaleri te-pyri te22)) 1layered Mg schistose ore: 3 ) schistose ore: ffine i n e grained g r a i n e dkneaded kneaded ('durchbewegte") ("durchbewegte") Mg ssilicate i 1i c a t e rich r i c h ore. ore. 3) ore These33 types types ddefine o r e of o f similar s i m i l a rcomposition composition to t o the t h e layered l a y e r e d type. type. These e f i n e aa mineralogical-textural-compositional zoningppattern the m i n e r a l o g i c a l - t e x t u r a l - c o m p o s i t i o n a l zoning a t t e r n wwithin i t h i n tthe h e lenses; lenses ; the compacttype typei siscconfined andt hthickest compact o n f i n e d t otot hthe e ccentral e n t r a l and i c k e s t ppart a r t of o f the t h e lenses, lenses, the the layered l a y e r e d ore o r e is i s arranged arranged along along the t h e north n o r t h contact c o n t a c tand and increases increases in i namount amount with with decreasingwwidth decreasing i d t h ooff the t h e lens; lens; the t h eschistose s c h i s t o s eore oredominates dominates in i nthe t h epinch—out pinch-out areas. W Within i t h i n the t h e compact compact oore r e sphalerite s p h a l e r i t e rich r i c hzones zonesare aredeveloped developed towards towards the t h e south south contact. contact. Textures iindicate Textures n d i c a t e aa metamorphic metamorphic r erecrystallization c r y s t a l l i z a t i o n of o fsulphides sulphides and and Annealingf fabrics Annealing a b r i c s exist e x i s t ini nmonomineralic monomineralic aggregates; aggregates; ppyrite yrite porphyroblasts reveal reveal aacomposite composite aggregate aggregate structure s t r u c t u r eand andare a r ecomposed composed of of 2 2 varieties v a r i e t i e s of o f pyrite; p y r i t e ; microfold m i c r o f o l dstructures s t r u c t u r e s are are characteristic c h a r a c t e r i s t i c of o f the t h e layeredlayeredand sschistose massivetypes types as aswwell and c h i s t o s e massive e l l as as the t h e disseminated disseminated types. types. silicates. silicates. 3 sets s e t s of o fsynkinematic synkinematic dyke dyke intrusions i n t r u s i o n semplaced emplaced as as Dyke chronology: chronology: 3 Dyke q u a r t z ddiorites, i o r i tes, 2) 2 ) amphibolites amphi b o l i t e s and, and, 3) 3) granodiorite g r a n o d i o r i t e and and ffollows, o l l o w s , 1) 1 ) quartz granite showdiscordant discordantr erelationships g r a n i t e pegmatites pegmatites show l a t i o n s h i p s tto o the t h e layered l a y e r e d rocks rocks None ooff these dyke dyke generageneraiincluding n c l u d i n g all a l lthe t h edisseminated disseminatedmineralized m i n e r a l i z e dzones. zones. None Dykes ooff ttions i o n s transect t r a n s e c tthe t h massive e massiveore—quartz—muscovite ore-quartz-muscovite sschist c h i s t contact. Dykes 38 �1) and and 2) 2 ) generations generations occur occur as as highly highly folded foldedboudinaged boudinaged fragments fragments wwithin i t h i n the the Significant metamorphic reaction zones are present present massive sulphide ore types. massive sulphide types. Significant metamorphic reaction zones are in-and as follows: follows: niagnetite-sulphide in-and around around the fragments fragments and and appear appear as magnetite-sulphide impregnated zones thes isilicate rock and andsphalerite sphalerite rich rims impregnated zones in inthe l i c a t e rock rims up up to t o 5" 5" rims, Zinc Within the the sulphide sulphide rims, Zinc rich around the the boudinaged boudinaged fragments. fragments. Within wide around sphalerite nearthe thessilicate sphalerite zones zones are are concentrated concentrated near i l i c a t e contact, contact, Iron Ironrich richsphal— sphale r i t ezones zones away away from his. erite from tthis. In conclusion as as a metamorphosed conclusion the thesulphide sulphidemineralization mineralizationis regarded i s regarded a metamorphosed lithological zoning in in thethe boudin—shaped The lithological zoning boudin-shaped bedded sulphide deposit. bedded sulphide deposit. The massive sulphide massive sulphideore orerepresents representsaaprimary primarystratigraphical stratigraphical configuration, Stratigraphical tops tops have have not not although although accentuated accentuated during the the deformation. deformation. Stratigraphical thedistribution distribution of However the of been determined in been determined in the theManitouwadge Manitouwadge area. area. However relatively r e l a t i v e l ycopper copper rich zones zones tto o the the north, zinc zinc rich richzones zones to t o the the south south followed by by magnetite-chert magnetite-chert iron iron formation formationdefines definesa abroad broadpattern patterncomparable comparable I tisi sproposed proposed to othersynvolcanic synvolcanicsulphide sulphidedeposits. deposits. It t o the the vertical verticalzoning zoningini nother that syncline represents represents the the refolded limbs t h a t the theManitouwadge Manitouwadge syncline limbs of ofan anoverturned overturned nappe structure with w i t hananeast—west east-west axis. axis. nappe structure 39 �THE ATIKOKAN THE ATIKOKAN IRON IRON RANGE RANGE AND AND ITS ITSIRON—COPPER IRON-COPPER MINERALIZATION MINERALIZATION dens. F. F. Touborg, Touborg, Suite S u i t e1006, 1006, 77 77Howard Howard St., St., Toronto TorontoM4X M4X IJD, lJD, Ontario O n t a r i oCanada. Canada. Jens. ABSTRACT The Atikokan Atikokan IIron The r o n Range Range iin n northwestern northwestern Ontario O n t a r i o contains containswidespread widespread magnetite—basemetal suiphide whichi sissspatially magneti te-basemetal sulphide m i mineralization n e r a l i z a t i o n which p a t i a l l y associated associated with w i t h lensoid l e n s o i dbodies bodies ofo ultrabasic—basic f u l t r a b a s i c - b a s i cigneous igneousrocks rockscomposed composed ooff pyroxenites, gabbros, amphibolites and and pperidotites. gabbros, amphibolites eridotites. The lenses, lenses, having The having a strong s t r o n g geophysical geophysical response, response, are are concordantly concordantly enclosed enclosed iinn metavolcanic metavolcanic rocks rocks of o f basaltic—andesitic b a s a l t i c - a n d e s i t i c composition composition and and 16 mmile zoneo of strikes ddefine e f i n e aa 16 i l e llong o n g zone f sstratigraphical t r a t i g r a p h i c a l continuity. c o n t i n u i t y . IItt strikes uniformly andddips The zone zonel lies i e s aa few few u n i f o r m l y eastnortheast eastnortheast and i p s ssteeply t e e p l y tto o the t h e north. n o r t h , The hundredso of whichi in hundreds f f feet e e t nnorth o r t h ooff the t h e Quetico Q u e t i c o Shear Shear S&tructure, t r u c t u r e , which n tthis h i s area area separates Archean Archeanmetavolcanic metavolcanicsseries e r i e s to t o the t h enorth n o r t hfrom fromSeine Seinemetasedimentary metasedimentary separates The impact impact ooff metamorphism area iiss low. metamorphism i nint hthe e area low. sseries e r i e s to t o the t h e south. south. The Concentrations occuri in Concentrations ooff Iron—Copper Iron-Copper m imineralization n e r a l i z a t i o n occur n ttabular a b u l a r deposits deposits up Examples are: The The Atikokan Mines-, Mines-, up ttoo 3000 3000 feet f e e t long l o n gand and50-250 50-250 wide. wide. Examples SapaweLake-, Lake—,Archibald-, Archibald—,Pattison-Roberts Pattison—Roberts and and Mark Mark prospects. Sapawe rospects. IIn n detail detail the disseminated t h e mineralization m i n e r a l i z a t i o n consists c o n s i s t sofo lenses f lensesdominated dominated by by 1) 17 massive—or massive-or disseminated magnetite minor sulphide sulphide vveinlets massive—or disseminated disseminated magnetite wwith i t h minor e i n l e t s and and 2) 2) massive-or ppyrrhotite, y r r h o t i t e , lesser l e s s e amounts r amounts of o f pyrite—chalcopyrite p y r i te-chal c o p y r i t e (.3-.6% (. 3-. 6%Copper) Copper) and and trace trace mineralized amountsoof Nickel—Cobaltbearing bearing sulphides. sulphides. The amounts f Nickel-Cobalt The m i n e r a l i z e d lenses lenses are are characterized by aa banded bandeds tstructure concordanti nintercalations c h a r a c t e r i z e d by r u c t u r e wwith i t h concordant t e r c a l a t i o n s ooff the the zonest the mineralization ultrabasic—basic host rock. u l t r a b a s i c - b a s i c host rock. Within W i t h i n pinch—out pinch-out zones he m i n e r a l i z a t i o n and and interbandedwwith tthe h e host h o s t rocks rocks become become hheavily e a v i l y interbanded i t h tthe h e surrounding surrounding volcanic volcanic rocks. Geometrically Geometrically the t h e ruagnetite-and magneti te-and ssulphide u l p h i d e lenses lenses are arranged arranged in in en—echelon sometimesw with aa complex complex en-echelon s t rstructure, u c t u r e , sometimes i t h t hthe e ssulphide u l p h i d e rich r i c hzones zones confined c o n f i n e d tto o tthe h e ffootwall o o t w a l l side; side; this t h i sfeature f e a t u r emay may be be a a possible possible iindicator ndicator ooff stratigraphical s t r a t i g r a p h i c a l tops. tops. Preliminary P r e l i m i n a r y microscopic microscopic work work reveal reveal the t h epresence presence of primary of primary magmatic magmatic ttextures e x t u r e s in i n both both the t h eoxide-and oxide-and sulphide s u l p h i d ephases. phases. Origin Available t h e mineralization mineralization O r i g i n of o f mineralization: mineralization: A v a i l a b l e data data suggest suggest 1) 1 ) the forms an an i Integrating forms n t e g r a t i n g part p a r t of o f the t h eultrabasic—basic u l t r a b a s i c - b a s i c host h o s t rocks. rocks. 22)) there t h e r e is is no evidencet to no evidence o iindicate ndicate a a possible p o s s i b l e relationship r e l a t i o n s h i p to t othe t h ebedded bedded iron i r o n formations formations Wall rock rock contained within w i t h i nthe t h eSteep SteepRock—and Rock-and Caland Caland deposits nearby. nearby. 3) Wall alteration a l t e r a t i o n isi slacking l a c k i n gapart a p a r from t fromminor minorquartz-carbonate quartz-carbonate vveining e i n i n g ooff the t h e host host There i is 4) There s no no ddirect i r e c t relation r e l a t i o nbetween between the t h e mineralized m i n e r a l i z e d uultrabasicltrabasicrock. 4) synvolcanic i intrusive! A synvolcanic ntrusive/ bbasic a s i c series s e r i e s and and the t h e Quetico Q u e t i c o shear shear sstructure. tructure. A extrusive e x t r u s i v e origin o r i g i n isi sproposed proposed for f o rthe t h estratabound stratabound ultrabasic-basic u l t r a b a s i c - b a s i c series s e r i e s and and iits t s associated associated mineralization. mineralization. 40 �GEOCHRONOLOGY PRECM4BRIANROCKS ROCKSIN IN EASTERN WISCONSIN GEOCHRONOIAGY OFOFPRECAMBRIAN WISCONSIN W. Schxnus,Department DepartmentofofGeology, Geology,University University of . Van Van Schmus, of W. RR. lawrence, Kansas, 66044 Kansas, Lawrence, Kansas,66024k Kansas, geochronological studies studies by the author, in Recent geochronological in Recent conjunction with other published and unpublished data, now conjunction permit the the delineation delineation of of major major chronologic chronologic units units for for Precambrian rocks Precambrian rocks in in eastern eastern Wisconsin. Wisconsin. The The oldest oldest rocks rocks in in the the eastern eastern part part of of the the state state are the metavolcanics, gneisses, gneisses, and intrusive rocks rocks in northeastern corner, the northeastern corner, including including the the Quinnesec Quinnesec Fm., Fm., Dunbar Gneiss, Dunbar Gneiss, Hoskin Hoskin take Lake Granite, Granite, Newingham Newingham Granodiorite, Granodiorite, and AtheLstane Athe-"Sane Quar'z QuaiJ%Monzonite. Monzonite. These These rocks rocks are are about about 1900 m m.y. whole-rock data and 1850 1850 to 1900 .y. old based on Rb-Sr whole-rock published U-Pb U-Pb zircon zircon data. data. Apparently the bulk of of the the state state is is made made up up of of metametavolcanics and volcanics and granitic granitic rocks rocks that that yield yield ages ages of of 1650 1650 to to rocks in Waushara 1700 1700 m.y. m.y. The The author author has has analysed analysed such such rocks in Waushara Co. (granites) (granites) and and to to the the south south (rhyolites), (rhyolites), and and other other workers workers have have reported reported similar similar ages ages from from near near Monico, Monico, Wausau, Wausau, and Baraboo. Baraboo. Intrusive into the 1650—1700 m.y. 1650-1700 m .y. old complex complex is is aa Intrusive large large plutonic plutonic assemblage assemblage that that is isabout about12450 1450 to to 1500 1500 m.y. m.y. old and is is now now referred referred to to as as the the Wolf Wolf River River Batholith. Batholith. It It includes a wide variety of includes of rocks rocks from from Mountain, Mountain, to to Wausau, Wausau, Point, to Waupaca and apparently is to Steven's Steven's Point, is the last major major plutonic plutonic or or metamorphic event event in in the the state, state, except except for for the the Keweenawan Keweenawan rocks rocks in in the the far far northwest. northwest. absolutely dated are Not yet absolutely are gneissic gneissic and and related related rocks in Published rocks in the the Steven's Steven's Point-Wisconsin Point-Wisconsin Rapids Rapids area. area. Published mineral ages from these rocks rocks suggest suggest they may be related mineral ages from to Resolution to the the northeastern northeastern Wisconsin Wisconsin complex, complex, or or older. older. Resolution of this problem, plus extending extending our our knowledge knowledge westward westward and and northwestward, is currently currently in northwestward,is in progress. progress. 41 �"FRMIBOIDAL" WHITEPINE, PINE, MICHIGM "ERAMBOIDAL" CHAJJCOCITE CHALCOCITE FROM FROM WHITE MICHIGAN Thomas A. A. Vogel and and Nancy Nancy Alyanak, Alyanak, Geology Geology Oepartment, Department, Michigan 48823 Michigan State S t a t e University, University,East EastLansing, Lansing,Michigan Michigan48823 ABSTRACT ABSTRACT Chalcocite with nnuclei Chalcocite with u c l e i occurs occurs throughout throughout the t h e mineralized mineralized zone zone aatt White White Pine, Pine, Michigan. Michigan. They They are a r e more more abundant abundant in i n the t h e well—laminated, well-laminated, black, black, fine—grained fine-grained lithologies l i t h o l o g i e s than than in i n the t h e massive massive lithologies. l i t h o l o g i e s . In In polished section nuclei s e c t i o n these n u c l e i are a r e either e i t h e r circular, c i r c u l a r , ellipsoidal e l l i p s o i d a l or o r con— cont o the t h e shape shape of of the t h e grain, g r a i n , with with aa median median circular c i r c u l a r diameter diameter of of four four fform on to microns microns and and aa median median ellipsoidal e l l i p s o i d a l long long axis a x i s of of eight e i g h t microns. microns. Microcrysts Microcrysts at a t least l e a s t as as small small as as 0.2 0.2 microns microns are a r e found found in i n each each nucleus. nucleus. The The nuclei nuclei are pyrite a r e similar s i m i l a r to t o the t h e framboidal texture t e x t u r e commonly observed in in p y r i t e assoassociated c i a t e d with with sediments. sediments. The The chalcocite chalcocite nuclei n u c l e i can can only only be be observed observed after after the t h e polished section s e c t i o n has been etched and stained s t a i n e d with a weak hydrochloric acid acid and and potassium ferrocyanide solution——a s o l u t i o n ~ astain s t a i n very sensitive s e n s i t i v e to t o low concentrations concentrations of of iron. iron. e l e c t r o n microscope shows that The scanning electron t h a t the microcrysts within c i r c u l a r or o r ellipsoidal e l l i p s o i d a l nucleus are a r e densely packed, a well-defined well—defined circular packed, with a few scattered s c a t t e r e d microcrysts in i n the t h e surrounding surrounding grain. grain. However, the t h e micro— microfew crysts c r y s t s are a r e less l e s s densely densely packed packed where where the t h e nucleus nucleus occupies occupies the the entire e n t i r e grain. grain All A l l gradations between between dispersed dispersed and and densely densely packed packed microcrysts a r e found. found. microcrysts are Preliminary microprobe d i c a t e s t hthat a t the u c l e i aare r e higher iron, Preliminary microprobedata datai nindicates the nnuclei higher iinn iron, potassium and carbon carbon than than the the surrounding potassium and surrounding grain. grain. Two Two origins o r i g i n s are a r e possible possible for f o r the t h e framboidal framboidal chalcocite: chalcocite: 1.) 1.) replacement of 2 . ) formation of primary framboidal framboidal chalco— chalcoof framboidal framboidal pyrite p y r i t e and 2.) cite. c i t e . We We are a r e currently c u r r e n t l y evaluating evaluating these these alternative a l t e r n a t i v e genetic models and and their t h e i r implications. implications. 42 �WISCONSIN OF LANDFORMS Na .., ii: Or- tLJ ni story irvey FII rrF F F. Su Unoron I rd Geolo irsi Hanson. Dirnotor and Stoto Genlngiot L'Fur UNIVERSITY ESTENSION, UNIVERSITY OF WISCONSIN 1971 30 Ti __ 0 UCALE OF VILEU EU �A A' lie Cassai Racine boo too 002 455 StiLES IS SCALE iuniuue Fat it] A S imL HOtFrtFTs - id 200 SL Or) _c 10 - 0 - 203 400 25 boo 500 Jr loon, In Leoal cool Sea boo Peat Fr F 'a Fr sri "r ron taboo and Adaoe toFu Eieoatian GriP Gla(n D!der at trio (OrryF (Otto) dssnsnsin V2snirainn ci oi Hordes -. DriP r data) (sisarne Seeks Mntantrri and tgnenes Boors 0rorphie imenLated ii and Graean UndiffererrlLFud h r -tamest iF Marc and Ugeenas irks toeke .1 is miii ndiI UrFjfersrtiarnd and Granite [E a - - BasalE and Gabbrn 'c P r Oornraii000 'chin For tree and Ps' 0mm Graaneitc senptnmerale) 'rotc ncr-rninuodir wirb (sandstones I-crrn',c"s tlnwennerrrn Formutioos Upper a-rd - corns with (sandstones nrA. aed shale) a-ri 5dolomite dotoir snore _55 °oncrr Oncbrinr' air Cumb i_poor Formations Jeo (dolomin) iso "mine dr Pr Ar,a? Chine Group Crrhs none and shale (snrho,crs doreen in usutnF rrsrcrr torrreratr-( ruEd rFFr Parer Fm) '0nr StS (mainly 'usr, Group Aneell Oscs'l F,rtr r--ssils some rune )dclsrnitcoirh shale) oh5 sF and ccc lanresroon with (dolomite Group Sponipea dtu, 'F dolomrtn) srd arrd (ehuls irrein Oct. Forrtiati °rrnurrorr iolrntn Mc,, S'iapaiokr--lu hdcLoortn; (oolomitu( sir Is, Si Formations lurian Furoariors II 1— a a skis' shale) dod O'i (doloroipsin rho Forrrratronn Dovoniuo S LEGEND - -1- I Co L SilLhd GO SCALE 30 1971 1)JF[°lVflLjyj1 WISCONSIN Fj• OF UNIVERSITY )s:H EXTENSION. UNIVERSITY an Geologist State and Director h( F. George 1rr::ni Hanson. 'r :r-:.n. Forli' History 'ir Geological Survey Natural s:•-•j and !YF: F WISCONSIN iF'fl In::) MAP GEOLuGIC fl-il' )l S ,.'f:s d �SHORT GEOLOGIC GEOLOGIC HISTORY HISTORY OF OFWISCONSIN WISCONSIN The bedrock separatedinto intotwo twomajor majordivisions: divisions:(1) (1) older, older, predominantly predominantly crystalline crystalline rocks rocks of of the bedrock of Wisconsin Wisconsin isisseparated Precambrian Precambrian Era; and and (2) ( 2 )younger youngerrelatively relativelyflat-lying flat-lyingsedimentary sedimentaryrocks rocksof of the thePaleozoic Paleozoic Era. Era. The Precambrian Precambrian Era Era lasted lasted from from the the time time the theearth earthcooled, cooled,over over4,000 4,000 million million years years ago, ago, until until the thePaleozoic Paleozoic Era Era which began began about 600 million years ago. ago. During During this vast period which million years period of of 3,400 3,400 million million years yearssediments, sediments, some some of of which which were rich rich in iron iron and and which which now now form formiron ironores, ores,were weredeposited depositedinin ancient ancient oceans; oceans; volcanoes volcanoes spewed spewed forth forth ash and and lava; mountains were built built and and destroyed, destroyed,and and the the rocks rocks of of the upper crust mountains were crust were were intruded intruded by by molten molten rocks rocks of of deepdeepseated origin. Only a fragmentary fragmentary record record of of these these events events remains remains but, but, as as tree treestumps stumpsattest attesttotothe thepresence presenceofofformer former forests, forests, the rocky rocky roots roots tell tell the thegeologist geologist of of the thepresence presenceofofformer formermountains. mountains.Nowhere Nowhere does does any trace trace of of the the original original crust remain, remain, and and the theoldest oldest rocks rocks yet yet found found in inthe thestate stateare areabout about2,000 2,000million millionyears yearsold. old.With Withthe theexception exception of ofthe the Upper Keweenawan formationsthat that outcrop outcrop in in the northwest, northwest, all of of these these rocks rocks have havebeen beenextensively extensively deformed, deformed, Keweenawan formations and in altered that their in many many areas areas they they are are so so highly highly altered their original original nature and and origin origin are are extremely extremely difficult difficult to interinterpret. I n the the north-central north-central part partof of the thestate statesurface surfaceoutcrops outcrops are areso sosparse, sparse, due due to to aa cover cover of of glacial glacial deposits, deposits, that In that details of the bedrock bedrock are are obscured. obscured. In In such such areas areasthe theonly onlyclues clues to t othe theunderlying underlyingrocks rocksare areobtained obtainedindirectly indirectlyby bysuch suchgeogeophysical methods as as airborne physical methods airborne magnetics. magnetics. IIn n the the past past much muchhigh-grade high-grade iron iron ore ore was was produced produced from the Precambrian Precambrian rocks of of northern northern Wisconsin, Wisconsin,and andmuch muchlow-grade low-gradeore ore("taconite") ("taconite") awaits development. work indidevelopment. Recent Recent geologic geologic work cates that that the the area areahas hasa ahigh highpotential potentialfor forfinding findingores oresofofother othermetals metalssuch suchasascopper. copper. At the the close close of of the the Precambrian Precambrian Era Eramost mostofofWisconsin Wisconsinhad hadbeen been eroded eroded to to aa rather ratherflat flatplain plainupon uponwhich which stood stood hills of more resistant rocks as those now exposed in the Baraboo bluffs. There were still outpourings of basaltic exposed in still basaltic lava lava in the the north north and and aatrough troughformed formed in inthe thevicinity vicinity of ofLake LakeSuperior Superiorininwhich whichgreat greatthicknesses thicknesses of of sandstone sandstone were were deposited. deposited. The Paleozoic Era began began with with the the Cambrian Cambrian Period, Period, the rocks Paleozoic Era rocks of which which indicate indicate that that Wisconsin Wisconsin was was twice twice subsubmerged beneath the sea. Rivers draining the land carried sediments which were deposited in the sea to form merged the sea. Rivers draining the land carried sediments which were deposited in the sea to formsandsandstone and plants plants living in the sea stone and shale. shale. Animals Animals and living in sea deposited deposited calcium calcium carbonate carbonate and built built reefs reefs to toform formrocks rocks which are magnesium-rich continued into the dolomit-a magnesium-rich limestone. limestone. These same same processes processes continued the Ordovician Ordovician Period Period are now now dolomite—a during which, was submerged submergedthree three more more times. times. Deposits Depositsbuilt built up up in in the sea which, as indicated indicated by the the rocks, rocks, Wisconsin Wisconsin was sea when when the land land was was submerged submerged were partially or or completely completely eroded eroded at at times times when when they theywere weresubsequently subsequently elevated elevated above sea level. level. During During the the close close ofof the the Ordovician Ordovician Period, Period, and and in the above sea the succeeding succeeding Silurian Silurian and and Devonian Devonian Periods, Periods, Wisconsin is believed Wisconsin is believed to have remained remained submerged. submerged. The youngest youngest rocks rocks outcropping in in Wisconsin Wisconsin are of of Devonian Devonian age age and and are areabout about350 350million million years years old. old. Absence Absence of The of If the thedinosaurs dinosaurs younger rocks makes makes interpretations interpretations of post-Devonian post-Devonian history in Wisconsin Wisconsin aa matter of of conjecture. conjecture. If younger roamed Wisconsin, as well well they they might might have some 200 million million years years ago, no trace Wisconsin, as trace of of their theirpresence presenceremains. remains.AvailAvailevidence from from neighboring neighboring areas, areas, where whereyounger youngerrocks rocksare arepresent, present,indicates indicatesthat thattowards towardsthe theclose closeof of the the PaleoPaleoable evidence some 250 million present. DurDurzoic Era, perhaps some million years years ago, ago, aa period period of of gentle uplift began which which has continued to the present. ing ing this this time time the the land land surface surface was was carved carved by rain, wind wind and and running running water. water. The final final scene scene took took place place during million years when glaciers glaciers invaded invaded Wisconsin Wisconsin from north and and The during the last million years when from the north sculptured thevalleys valleysand andleft leftaadeposit depositof ofdebris debris over over all all exexsculptured the the land land surface. surface.They Theysmoothed smoothed the thehill hilltops, tops,filled filledthe cept the southwest southwest quarter of of the theState Statewhere wherewe wemay maynow nowstill stillsee seethe theland landasasititmight mighthave havelooked lookedaamillion millionyears years ago. ago. �fI;Director si;p 5Hanson,j J•!U]%9#IC State and Geologist :' Survey,, History Natural !4[c au 'FiJOG-> d 'ge !tñJiS% Geological .!IHCOIISIfl i]1.y of University Wisconsin )I.Ii1 PtisIt uqen ds n 'H irf 'tjsoap0 pitted SLft LJSDaiflfl unpitted ne 1t)15.tJ Morn ptrnOJ9 4 or,es .YY;_JOW p'q L r ,• tR: OF dç SCALE MILES 40 p -. iHFI.Jj after 1956 Tliwaites, q Hi 1 'i• _r' n 1] DEPOSITS GLACIAL WISCONSIN F L �I SHORT S HORT HISTORY OF OF THE ICE AGE IN I N WISCONSIN WISCONSIN U 1,000,000 years ago The Pleistocene Epoch or o r "Ice "Ice Age" Age" began about 1,000,000 ago which, which, in f o u r separate separate s h o r t time time ago. ago. There were four i n terms of of geologic geologic time, time, i s a very short g l a c i a l advances advances iin n tthe h e Pleistocene Pleistocene each each followed followed by by an an inter—glacial i n t e r - g l a c i a l period period glacial is whent the The ffourth o u r t h gglacial l a c i a l stage s t a g e is i scalled c a l l e dthe t h Wisconsin e Wisconsin Stage Stage when h e iice c e receded. receded. The because wasi nint hthis that it was first studied detail. because itit was i s SState tate th a t it was first s t u d i e d iin n d etail. The gglaciers snow The l a c i e r s were were formed formed by by the t h e continuous continuous accumulation accumulation of of snow. snow. The snow i n t o ice i c e which reached a maximum maximum thickness of of almost almost two two miles. miles. The The turned into sheet spread spread over over Canada and ppart of it it flowed flowed iin general southerly southerly iice c e sheet a r t of n aa general direction d i r e c t i o n toward Wisconsin and neighboring states. states. f r o n t of the t h e advancing advancing iice c e sheet sheet had had many many tongues or o r "lobes" "lobes" whose whose The front direction wereccontrolled by tthe of tthe d i r e c t i o n and and rate r a t eofofmovement movement were o n t r o l l e d by h e topography topography of h e land land surface over by tthe surface over which which they they flowed flowed and by h e rrates a t e s of of ice i c e accumulation in i n the the different d i f f e r e n t areas from which they were fed. fed. sheet transported transported aa great rockddebris "drift". The ice i c e sheet g r e a t amount amount ofofrock e b r i s ccalled a l l e d "drift". was was "Drumlins" p i l e d up up aatt the t h e margins margins of of the t h e ice i c elobes lobestot oform form"end "end moraines". moraines". piled are of ddrift byt the a r e elongated elongated mounds mounds of r i f t which which were were molded molded by h e iice c e passing passing over over them them and hencei nindicate and hence d i c a t e tthe h e ddirection i r e c t i o n of of ice i c e movement. Some "ground Some ofoft this h i s was was deposited deposited under under the t h e ice i c etot form o form "groundmoraine" moraine"and andsome some pattern of end moraines, moraines, iin red, shows tthe was occupied occupied The p a t t e r n of n red, h e pposition o s i t i o n tthat h a t was advanced down down the t h e basin basin of of Lake Lake Michigan, Michigan, by four f o u r major ice i c e lobes. lobes. One lobe advanced Green Bay, Bay, aa third another another down down Green t h i r ddown down Lake Lake Superior and over the t h e northern peninsula The Michigan and yet a fourth of Michigan fourth entered entered the the state s t a t e from from the t h e northwest northwest corner. corner. The of "Kettle Moraine" well-known "Kettle Moraine" was was formed formed between between the t h eLake LakeMichigan Michigan and andGreen Green Bay Bay well—known lobes. As A s tthe h e ice i c e melted melted the t h e drift d r i f was t wasreworked reworked by by the t h e running running water. water. Large amountsofof sand sand and andgravel gravel were weredeposited deposited tto "outwashplains"; plains"; ppits amounts o form form "outwash i t s were were formed iin whereburied buriedblocks blocks of of ice of these are formed n tthe h e outwash outwash where i c e melted melted and and many many of are now now occupied occupied by by lakes. lakes. The action profoundly modified tthe landscape, smoothing o off a c t i o n of of tthe h e ice i c e profoundly h e landscape, f f tthe he places ititchanged changed I n some some places of hills ccrests r e s t s of h i l l s and ffilling i l l i n g the t h e valleys v a l l e y s with with ddrift. r i f t . In the of tthe Wisconsin t h e course of rivers r i v e r s forcing them to t o cut new channels such aass tthat h a t of h e Wisconsin River at a t tthe h e Dells; Dells; elsewhere it it dammed dammed the t h e valleys v a l l e y s to t o create c r e a t e lakes lakes such such as a s those those of tthe of h e Madison Madison area. area. During rrecent e c e n t years there t h e r e have been intensive i n t e n s i v e studies s t u d i e s made made of of the t h e polar polar caps, and methods have been developed for iice c e caps, f o r dating glacial g l a c i a l events events from from the the of tthe wood, bones, bones, eetc. which aare found iin many of of rradioactivity a d i o a c t i v i t y of h e carbon iin n wood, t c . which r e found n many of these these sstudies previously accepted e s u l t s of t u d i e s aare r e causing many previously tthe h e deposits. deposits. The rresults concepts to t o be changed changed or o r challenged. challenged. We thought tthat were rrather extensive gglacial W e once thought h a t tthere h e r e were a t h e r extensive l a c i a l ddeposits e p o s i t s oolder lder than Wisconsin age age in i n the t h e State, S t a t e , but but age age determinations determinations do do not not support support this. this, It was aalso thought that It l s o thought t h a t the t h e ice i c e left l e f t Wisconsin some some 20,000 20,000 years years ago ago but but aa Countywas wasburied buriedunder under an an advancing advancing iice fforest o r e s t aatt Two Creeks in i n Manitowoc Manitowoc County ce i s accumulating accumulating to t o indicate i n d i c a t e that t h a t ice ice 11,000 years ago. tongue tongue only 11,000 ago. Evidence is may have occupied the Area" of of tthe southwestern p part of t h e so—called so-called "Driftless " D r i f t l e s s Area" h e southwestern a r t of the t h e State S t a t e which hitherto h i t h e r t o has has been been held held to t o be be unglaciated. unglaciated. Most sscientists believe Most c i e n t i s t s now b e l i e v e that t h a t the t h e cause of the t h e Pleistocene "Ice "IceAge" Age" was duet to was due o vvariations a r i a t i o n s in i n the t h e solar s o l a renergy energyreaching reaching the t h eearth, e a r t h ,but buthow howthese thesemay may We haveoccurred occurredisissstill have t i l l aa matter matter of of conjecture. conjecture. W e a are r e sstill t i l l in i nthe t h eIce I c eAge Age and and it anybody's guess whether future millenia it is anybody's future m i l l e n i a will w i l l see s e e the t h e melting melting of of cities, or the regrowth coastal caps and the slow drowning of our t h e slow our c o a s t a l c i t i e s , o r t h e regrowth and and oftthe more tthe more h e inexorable inexorable advance advance of h e gglaciers. laciers. the t h e ice ice once once Prepared by tthe Natural History HistorySurvey, Survey, August August Prepared by h e University University of ofWisconsin Wisconsin Geological Geological £& Natural 19641 1964' �WiSCONSIN OF unIVERSITY A A U II Al IA OAR ._<__,1<., Spruce White Fir, Balsam FOREST BOREAL Cedar Tamarack, Spruce, Black SWAMPS CONIFER —— •—fl.l- Maple, <r— Birch Yellow Hemlock, N FOREST MESIC NORTHERN i:_ t' .', F —. Pine Red Pine, White FOREST PINE Grasses Prairie pine, Jock BARRENS PINE — r 4/ 'C<L<.. Joint, Blue Sedges, Cordgrass MEADOWS SEDGE L___J • r— <Willows, Ash Maple, Soft - HARDWOOD LOWLAND Elm - -c - Stigar Basswood, Maple, FOREST MESIC SOUTHERN Oaks Red ond Block White, FOREST OAK SOUTHERN 1 LI±J 7 t Bluestem Oak, White Oak, Bur I SAVANNA OAK -, -1";,;] Composites Bluestem, -< PRAIRIE a LEGEND 6 I r a / a S C C a L Miles at Scale 80 40 0 1965 Wisconsin of University Director L L:s4 Hanson, G.E. Survey History Natural and Geological Wisconsin 1I\L H j ccc WISCONSIN OF VEGETATION EARLY -. I f pi �INTERPRETATION OF OFTHE THEVEGETATION VEGETATIONOF OFWISCONSIN WISCONSIN about the the middle middle of of the the llast This map map iiss based on the original original land land survey survey conducted conducted about a s t cencenSurveyorswere wererequired requiredtotoplace placeaa stake stake eachhalfmile, tury. Surveyors eachhalfmile, identified identified by by notation notation of of nearby nearby trees, and and to to note note briefly briefly the the general general plant plant cover cover of of each each quarter quarter section. These records records have have been used to been to reconstruct reconstruct the the presettlement presettlement distribution distribution patterns patterns of ofplant plantcommunities communities shown shown on on the map. map. The plant communities recognized,however, however,are arebased basedon on systematic systematic studies studies of presentThe communities recognized, presentday vegetation. vegetation. The day The results results of of these these studies studiesare aresummarized summarized in a recent recent book book (J. T. Curtis, Curtis, The The Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, with Vegetation of Wisconsin, University of Wisconsin Press, 1959) in which each community, its history, history, location, location, and and relationship relationship to toother othercommunities communities and tothe tothe environment, environment, iiss considered considered Since some of the factors determining vegetation vary gradually, the vegetation vegetation itself itself in detail. in Since some of the factors determining vegetation vary gradually, the varies gradually and boundaries on the map are somewhat arbitrary. gradually and boundaries on the map are somewhat arbitrary. The vegetation vegetation of of the the state floristic provinces The s t a t e is is divided divided into into northern northern and southern southern floristic provinces by by aa line that runsinans-curve runs in an S-curvenorthwest northwestfrom fromMilwaukee MilwaukeetotoHudson. Hudson.North Northofofthis this line line the vegetation vegetation Southwest of of the the line, abroadleaf forest containing containing conifers—pines, conifers-pines, hemlock, is abroadleaf hemlock, spruces, spruces, and fir. Southwest conifers are are much much lless andare are replaced replacedby byforests forests with with several several species species of conifers e s s important important and of oaks, and by the the prairies—areas dominatedby bygrasses grasses and and tall herbs. by prairies-areas dominated herbs. Fire has has been been important important in in determining determining almost all of of the the plant plant communities communities and and their their lolothe coming of white white man, man, the the prairies (1) (1) and and the the open open woodlands woodlands burned burned almost almost cation. Before Before the coming of every year. year. Thus every Thus most most of of the the southern southern part part of of the the state s t a t ewas was covered covered with with prairie prairie or or oak oak savanna savanna (2), an orchard-like withaa few few large large bur bur or or white white oaks oaks growing in fields fields of (2). orchard-like community community with growing in of grass. grass. Only in in the the more more protected protectedplaces places did did forests forests survive. (3) but but many many were were Only survive. Some Some of of these these were were oak oak(3) sugar elm forests (4). sugar maple-basswood-slippery maple-basswood-slippery elm (4). The The lowlands lowlands were were occupied occupied by by river river bottom bottom Withsettlement, settlement, the the fires fires were (51, and and sedge sedgemeadow meadow (6). ( 6 ) . With were stopped, and the oak oak savannas savannas forest (5), of the prairies grew up dense white white oak-black oak-black oak oak forests forests found found today. today. Most Most of prairies have have been been grew up to to the dense cultivated, andat and a tpresent, present,with withthe theoak oaksavannas, savannas,are areamong amongthe therarest rarestofofour ourplant plantcommuaities. communities. In part of of the the state, aa combination In the northern northern part combination of fire and and poor poor soil resulted resulted in in the the develdevelopment of pine barrens (7) on the sandy soils, and pine forests (8) on somewhat better soils. In (8) on somewhat better soils. opment of pine barrens (7) on the sandy soils, and pine the the absence absence of of fire, fire, the the white white pine pine forests forestsgradually gradually changed changed to to the thenorthern northern equivalent equivalent of of the the sugar forests, aa community sugar maple-basswood maple-basswood forests, community containing sugar sugar maple, maple, yellow yellow birch birch and and hemlock, hemlock, with beech beech added added in in the the eastern eastern counties counties (9). (9). Also Also present present in in the the north north were were large large tracts tracts of of lowlowwith land, with with tamarack tamarack and andblack black spruce spruce bogs bogs in in the the wetter wetter areas, areas, and white cedar swamps land, swamps in drier, but still still very very moist moist habitats habitats (10). (10). In In the extreme extreme north north are local local occurrences occurrences of of the thenorthern northern but conifer by fir and spruce. conifer forest forest (11) (11) dominated dominated by A comparison comparisonofof this this map map with with maps maps ofof climate, climate, soil, and A and glacial glacial deposits deposits shows shows many many The correspondences, indicating relationships between correspondences, indicating many many relationships between vegetation vegetation and the the environment. environment. The original vegetation vegetation was was thus by the the distribution of both original thus determined determined by distribution of both climatic climatic and and soil soil factors, factors, modified modified by fire. fire. 0. G. Cottam, Cottam, 0. 0. L. L. Loucks Loucks Department of Botany Department The University of of Wisconsin Wisconsin � https://digitalcollections.lakeheadu.ca/files/original/ac9dd9c98d82d2009fc6fa2432059ff8.pdf cc4f1f23c1fae5b8a1976c91c2b31a0d PDF Text Text University of Wisconsin—Extension GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E. Ostroin, State GeoIogSt and Director GUIDEBOOK TO THE PRECAMBRIAN GEOLOGY OF NORTHEASTERN AND NORTHCENTRAL WISCONSIN 18th Ausnuul Institute on Luke Superior Geology Madison, Wisconsin, 1973 �UNIVERSITY UNIVERSITY OF OF WISCONSIN-EXTENSION WISCONSIN-EXTENSION GEOLOGICAL AND AND NATURAL GEOLOGICAL NATURAL HISTORY SURVEY SURVEY E. Ostrom, Ostrom, State State Geologist Geologist && Director Director Meredith E. GUIDEBOOK TO TO THE PRECAMBRIAN PRECAMBRIAN GEOLOGY OF NORTHEASTERN NORTHEASTERN AND AND NORTHCENTRAL WISCONSIN with Special Papers on Chronology of Precambrian Precambrian Rocks Rocks in in Wisconsin Wisconsin W.R. Van Van Schinus Schmus The Wolf River Batholith——a Batholith--a Late Late Precambrian Precambrian Rapakivi Rapakivi Massif in in Northeastern Wisconsin Wisconsin L.G. L.G. Medaris, Medaris, Jr., Jr., J.L. J.L. Anderson, Anderson, and and J.R. J.R. Myles Myles Precambrian Geology of Marathon County G.L. LaBerge LaBerge and and P.E. PE. Myers G.L. Field Trip Committee Committee C.E. C.E. Dutton, Dutton, U.W. U.W. Geological Survey Survey G.L. LaBerge, LaBerge, UW—Oshkosh; mV-Osh~osh; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. L.G. L.G. Medaris, Medaris, Jr., Jr., UW—Madison UW-Madison G. G. Mursky, Mursky, UW-Milwaukee P.E. P.E. Myers, Myers, UW-Eau mV-Eau Claire; Claire; Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Sur. Sur. W.R. Van Schmus, W.R. Schmus, University University of Kansas L.W. L.W. Weis, Weis, UW Center System-Fox Valley Valley printed in in limited limited quantities quantities for for the the 19th 19th This guidebook was printed Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. Madison, Wisconsin Madison, 1973 Available from from the the Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Wisconsin—Extension, 1815 University University of Wisconsin-Extension, University Avenue, Madison, Madison, Wisconsin Wisconsin 53706. 53706. Price: $5.00. �DEDICAT I DEDICATION This guidebook is is dedicated to to Carl E. E. Dutton Dutton in in appreciation appreciation for for his continual encouragement and and advice advice to to us us all all and and in in recognition recognition of of toward an an understanding of the the Wisconsin Precambrian. his contributions toward I �INTRODUCTION I NTRODUCT ION With the exception of early bulletins of of the the Wisconsin Wisconsin Geological Geological and Natural Natural History Survey produced between about about 1900 1900 and and 1930 1930 little little had been published on the Precambrian geology of of Wisconsin Wisconsin until until the the appearance appearance in in 1970 of of "Lithologic, "Lithologic, Geophysical, Geophysical, and Mineral Commodity Maps of of Precambrian Rocks Rocks in in Wisconsin" by by Carl Carl E. E. Dutton Dutton and and Reta Reta E. E. Bradley, which was the product of aa cooperative effort of Bradley, of the the State State Survey and and the the U.S. U.S. Geological Geological Survey. Survey. That publication is is aa compicompilation which drew together in in concise form at at aa scale scale of of 1:500,000 1:500,000 all all that was generally known about Precambrian geology of of Wisconsin Wisconsin and, and, thus, thus, served to focus focus attention on the the mineral potential of of Wisconsints Wisconsin's Precambrian rocks and and to indicate the inadequacy inadequacy of of available available geological geological and information. As aa direct consequence of the the publication publication and geophysical Information. company exploration activity increased increased markedly and and the the interest interest of of university and and survey survey geologists geologists was was revived. revived. As aa part part of of this this revival revival the the Wisconsin Wisconsin Geological Geological && Natural Natural History History Survey has initiated a program to survey and and map the the Precambrian geology geology of the state in cooperation with geologists on the the faculty faculty of of the the UniverUniversity of Wisconsin System System at at its its various various campuses. campuses. At the the present time time L. LaBerge (UW—Oshkosh), Professors Gene L. (UW-Oshkosh), Paul Myers (UW—Eau (UW-Eau Claire), Claire), and and Joe Mengel (UW-Superior) are supported by the Survey on aa part—time part-time Mengel (UW—Superior) basis during summer months to map Precambrian geology in in Wisconsin. Wisconsin. Other university geologists contributing to the program have obtained support from from various grant programs including the University—Industry University-Industry Program, the Wisconsin Alumni Research Foundation and Research Program, and from Industry. industry. The Survey will soon soon publish aa bouguer bouguer anomaly anomaly gravity gravity map map of of the the state prepared by Professors C. C. Patrick Ervin (formerly state (formerly UW—Madison, UW-Madison, now Northern Illinois (UW—Madison) at at a scale Illinois University) University) and and Sigmund Sigmund Hanuner Hammer (UW-Madison) of 1:500,000, 1:500,000, utilizing over of over 16,000 16,000 stations. stations. In In addition, addition, the Survey has begun aa program under the the leadership leadership of of Prof. Prof. John John Karl (Department (Department of Physics, Physics, UW—Oshkosh) UW-Oshkosh) to to produce an an aeromagnetic aeromagnetic map of of the the northern northern two—thirds of the the state at north—south flight two-thirds at a a north-south flight line spacing of one—half one-half mile. This study was initiated initiated by aa grant from from the the Upper Great Lakes Lakes Regional Regional Commission and has been strongly supported by aa substantial substantial grant from NL Industries Industries and and by aerial aerial photograph prints prints provided provided by by INCO. INCa. This field field guide and accompanying accompanying maps, maps, printed for the the 19th 19th Annual Institute on on Lake Lake Superior Superior Geology, Geology, will will be included in what what is Institute is hoped be aa complete series series of of Precambrian Precambrian field field guides guides and and will eventually be maps for Wisconsin Wiscsin atata ascale maps for scaleofof1:250,000, 1:250,000, published published as as Geological Geological and and Natural History History Survey Survey Information Information Circulars. Circulars. When used in in combination with the the bouguer gravity anomaly anomaly map and and the the aeromagnetic aeromagnetic map map they they will will provide aa basis for identification identification of of areas areas of of above above average average mineral mineral popotential in Wisconsin which can then be made the subject for detailed tential in Wisconsin study. M.E. Ostroin Ostrom & Director State Geologist & �SPECIAL PAPERS Chronology of Pncainbrimn Rocks by W.R. Van Schaus Wolf River Satboiith——a Lst• Precabrian Rspakivi Kant! La Wcrtheasten Wisconsin The by b.C. Medaris, Jr., J.L. Anderson, and J.R, kyle. Ptecnibrtan Geology of Marathon County by G.L. Laflerge and P.E. Myers �Superior Lake Superior u o N ....o --' "" Q Waupaca River Falls Map Symbol Age Im.y.) Chronologic Unit PALEOZOIC Keweenawan COVER 1115 .:20 Wolf River Batholith gr • •rhy• • 1500 .:50 rhy • >1500 Quartzite <1675 1675 .: 50 Central Wisconsin Complex o ~ ~ > 1500 TIgerton Anorthosite < NE Wisconsin Complex ?? o 1875 .:50 Metavolcanics and metasedi ments 1900 .: 50 Archean Complex >2500 Age uncertain or unknown I. Figure 1. Madison Miles 0 0 Kilometers Milwaukee 40 50 • = Primary age determinations Primary age WRVS 2/73 Generalized geochronologic geochronologic map mapofatPrecambrian Precambrianrocks rocksin in Wisconsin Wisconsin and Michigan. Generalized and Upper Upper Michigan. I �11 Chronology of Precambrian Rocks Rocks in in Wisconsin by W.R. Van Schmus* W.R. Geochronologic data for Precambrian rocks rocks in in Wisconsin have have existed existed for for more than aa decade, decade, but until recently the the data were limited limited to to analyses of of separate separate minerals minerals and distributed, so that analyses and were widely distributed, that exact interpretation of primary formational ages ages and and delineation of of chronologic chronologie provinces was not possible. possible. These early data were summarized summarized by by Dutton Dutton and (1970) and will not be be reviewed reviewed in in detail detail here. here. and Bradley Bradley (1970) In terms of of obtaining primary ages In terms ages of Precambrian rocks, rocks, as opposed to metamorphic ages, ages, the geochronologic methods most likely likely to to yield yield reliable results are the Rb-Sr whole-rock isochron isochron method and and U-Pb U-Pb analyses on cogenetic suites suites of of zircons. zircons. Application of these these procedures procedures to Precambrian rocks rocks in Wisconsin has recently been done by P.O. p.O. Banks (Banks (Banks and and Cain, Cain, 1969; 1969; Banks and and Rebello, Rebello, 1969; 1969; and and unpublished unpublished data), data), by Z.E. Z.E. Peterman (unpublished (unpublished data), data), Dott Dott and and Daiziel Dalziel (1972), (1972), and and by by the author Schmus, 1972, the author (Van Schmus, 1972, 1973; 1973; Thurman and and Van Schmus, Schmus, 1973; 1973; and and unpublished data). data). A A summarization summarization of of these these data data is is presented presented in in Table Table 1. 1. unpublished Based on the the available available geologic geologic and and geochronologic geochronologic data, data, aa genergeneralized chronologie alized chronologic map map has has been prepared for Precambrian rocks of Wisconsin and and Upper Upper Michigan Michigan (Figure (Figure 1). 1). A the various various A few comments on the chronologic brief discussion discussion of of their their significance significance is: is chronologie units units and and a a brief presented below, below, but space does not jermit permit detailed detailed description description or or disdiscussion. The "Pb The "Precambrian X", etc. terminology terminology used below below refers refers to to the the Xt, etc. current U.S. U.S. Geological Survey subdivisions of of Precambrian time: time: Precambrian Z, Z, base base of of Cambrian Cambrian to to 800 800 m.y. m.y. ago; ago; Precambrian Precambrian Y, Y, 800 800 to to 1600 m.y. m.y. ago; X, 1600 to ago; Precambrian X, to 2500 2500 m.y. m.y. ago; ago; and and Precambrian Precambrian W, W, oldçr than old~r than 2500 2500 m.y. m.y. Archean Complex (Precambrian (Precambrian W) The oldest rocks rocks in in the the area area are are exposed exposed in in the the northern northern part. part. In In Upper Michigan these have been shown to be 2.5 to to 2.7 2.7 b.y. b.y. old or or older older (Aldrich, 1965; Woolsey, Woolsey, 1971; 1971; Banks Banks and and Van Van Schmus, Schmus, 1971, 1971, (Aldrich, and and others, others, 1965; 1972), 1972), but no dates have been reported reported as as yet yet from from presumed presumed Archean Archean rocks rocks in northwestern Wisconsin. in These latter units unconformably underlie the metasediments metasediments and the and metavolcanics of the Gogebic Range (Aldrich, (Aldrich, 1929) 1929) and there seems little doubt that and that they they are are in in fact fact Archean. Archean. However, the southward extent of these these rocks is is not well known, known, as as outcrops outcrops are are widely scattered throughout the the area area and and lithologic lithologic correlation correlation of of PrePrecambrian crystalline rocks rocks is is risky risky at at best. best. ** Department of University of of Kansas. Kansas. of Geology, Geology, University �2 T&bl.1. 1. 'fable Sury of Primary Gscohronologio S~ of PJ-1aaI7 GeoohronologioData Datafor torPreoeabrisn PNoaabrianRocks Boob in inWisconsin. Vlnouin. Northea.tern Wisconsin Visoonsin COmplezl Compl.xz 1. Northeastern P. (rhyoiit.) Quinnl.. o VIa. (rhyolite) Quinnissc 1906 ~ 25 1805 25 11.7. ..y. Ho skinLake Iske granite granite Hoskin 1880 15 (z) (Z) Banks Banks and Cain, 1969. 1969. Dunbar .iss Dunbar gneiss 1880 2~ 15 1880 15 (Z) Bank8 and Cain, 1969. 1&69. (z) Banks 1860~ 21~l 1880 (2) Banks and Cain, Cain, 1969. (Z) BanD and 1969. 1930 2 o (Z) Aldrioh and and others, 1965. 1965. (z) Aldrich 1810 : 50 (R) Van Sebmus, Unpub.° N.vinghamgranodiorite granodiorit. Newingham "*mb.rg pink "Jllberg p1nk graniti' granit'" (Ath.lstan. quartz (Athel8tane quartsmonzonit.) IIOMOnitlO) }3 ainstte quartz JIuoinett. quartz diorits diorite Atbelatane quartz quarts monsoniti lIOn&onit. Athelotano Hoskin Lake lake granite Hoskin granite } Overall oo.slt. oompo.it..estimate: Ove1"&ll .t1lrate I :t (Z) Banks and RebellO, Rbello, 1909. (z) Bank8 and 1969. 1875 50 1875 ±~ 50 VisooMlnComplex: COmpleZI Central Wisconsin 2. Central Baraboo rWolite Baraboo rI'o1ite 1840 lMO :2 40 m.y. a.,y. (R) Dott and DaIziel, Dalziel, 1972. 1972. So, Wisconsin rbyolit.s So. Wisoonsln rbJo1ites 1665 4D 1666 :2 40 (a) (R) Wausau-Mbnioo voloanios Wausan—bnioe volcanic. 1640 4D 1840 2~ 40 (R) Petel'llllUl,Unpub.° Unpub.* (a) P.t.rman, Co. granites granites Waushapa Co. Waushera ~ 70 70 1846 1646 ± andVan VanSohlllU., Sobmus,19'7a.* 1975. 'l'hurman and (R) Thurman Vausau area Waumau areagranites granite. 1600 :t 85 85 1600 ± CR) (R) Jackson JacksonCo. Co.granit.s granite. 1690 CR) Overall composite OOIlPOsite estimate: e8t1Jla'te I 3. llna.* Thurman and Van Van SobIua, Sobaus, 1975 .'' '!'hU!'lllUl and P.t.rman, Petel'lllU'1,Unpub.* Unpub.* and P-'-run, P.teruan, 1972. 1972. (a) nKismia ..io and 1675 ± 16715 : 50 Volt Wolf River River Batholiths Batholith: Wolf Volt River-Bad River-a.d River quartz quartz monsonites IIODSOnit.s 1450 :± 30 50 lI.y. a.y. 1450 (R) Van Sobmus, Unpub. Belongia Belongia gNnite granite 1~ 1500 :t2 20 (Z) Banks, Banks, Unpzb.' Unpub.** (z) 1480 2 (a) Onpub.** CR)Van VanSohlllU., Sciu5, Unpub.' Wolf River batholith Wolt River batholithoombinad oombined Wolf River River quartz Volt quarts monzonits lIOn&onite a.d River quazo1;s monzonits lIOn&onite Red River quartz Hager complex oomplez B.longla Belongia granite viborgit. granite Vaupaca wiborgite granite Waupeoa Big Palls Big Yells med-gr. m.d-gr. granite Stevens gNnite Stevens Point Point grq gray granite Wausau oomplez Wausaueyenite syenit. complex St.tin iyenit. complex St.tin ~nite oollPlez Hogvty Hogarty hornblende hornblende granite granite Overall Overall oolllpOsit. compositee8tiDate .stimatsI 1500 ± 50 (Z) denote. zircon Zircon U-Pb U-Pb oonoordia age; (R) (R) denotes denote. tho1e-rock whole-rcok (z) denotes oonsordiaintercept intsrc.pt age; Rb-Sr Rb-Sr isochron isoobron a.gs. ~. in preparation. Sohmus, ThtmDan, Thurman, and and Peterman, ** Van Sohmus, 'etel'lDan, 1n preparation. and Banks, *" Van Sohmu., ** Medari., and 1laDU, in in preparation. preparatlon. ScLnu5, Madaris, �3 No Archean rocks rocks are are conclusively present present in in northeastern northeastern Wisconsin. Wisconsin. Although the the Quinnesec metavolcanics metavolcanics have have often often been been referred referred to to as as pospossibly being Archean, Archean, it it now seems seems probable probable that that they they are are much much younger, younger, as mentioned below. below. The lack lack of of Archean rocks rocks in in this this area area is is as will will be mentioned major geologic geologic problem, problem, for for they are exposed just to aa major to the the north in in Michigan (James, (James, and and others, others, 1961). 1961). Recent maps of of the the area area (Dutton, (Dutton, 1971, Dutton and and Bradley, Bradley, 1970) show show the the presence presence of of aa major major east—west east-west 1971, trending Formation trending fault fault system system separating strongly deformed Quinnesec Formation rocks on the south from much less less deformed Badwater Greenstone Greenstone on on the the rocks north; and this fault system may therefore north; therefore coincide coincide with with or or be be part part of of an an old old major tectonic boundary. remaining problems problems are are to to determine determine how how far far Some of the other major remaining south Archean Archean rocks rocks can be be recognized, recognized, to determine their south their ages, ages, and and to to determine the the nature of their their disappearance (burial, (burial, faulting, faulting, orogenic orogenic destruction, etc.). d~~truction, etc.). "Animikie" Metasediments and Metavolcanics (Precambrian (Precambrian X) Metagediments and These rocks represent the the major units of of sedimentary sedimentary and and volcanic volcanic origin in the northern part of of the the area area and and include include the the economically economically vital sedimentary sedimentary iron iron formations. formations. Geochronologic data (Aldrich, (Aldrich, and and others, others, 1965; 1965; Banks and and Van Schmus, Schmus, 1971, 1971, 1972) 1972) indicate indicate that that these these rocks rocks in the the Iron Iron Mountain Mountain area area are are about about 1900 1900 m.y. m.y. old. old. Banks and and Rebello (1969) obtained a 1900 million year age age for zircons from a a Quinnesec (1969) obtained a Formation rhyolite in Wisconsin, and in Wisconsin, and the the author author regards regards these these rocks rocks as as approximately, if if not not exactly, exactly, equivalent equivalent to the units approximately, units in Michigan (for (for example, the example, the Badwater Badwater Greenstone). Greenstone). No direct data exist exist for for similar similar rocks rocks from the northwestern part of the the state, state, namely the the Gogebic Range, Range, but but with the lack of any evidence to to the the contrary, contrary, the the commonly commonly used used correcorrelation with rocks rocks to to the the east east is is accepted accepted here. here. Clearly, Clearly, however, however, direct direct analytical is required. required. analytical confirmation is As with the the Archean rocks, rocks, the the maximum maximum southern southern extent extent of of these these rocks is is unknown. unknown. Northeastern Wisconsin Complex (Precambrian (Precambrian X) are exposed several gneissic gneissic In the northeastern corner of the state are and plutonic units units which are and plutonic are younger than the the Quinnesec Formation, Formation, and and in in places intrude it it (Cain, (Cain, 1964). 1964). U—Pb U-Pb ages on zircons zircons and and Rb-Sr wholerock isochrons (Table (Table 1) 1) show show that that these these rocks rocks are are about about 1875 1875 m.y. m.y. old. old. They can be traced traced southward southward for for more than than 50 50 Km. Km. south south of of the the MichiganMichiganWisconain border, Wisconsin border, but their their maximum southern southern limit limit is is not not known. known. Although these rocks rocks are important in Wisconsin, only small plutons these are important in northeastern Wisconsin, of this age exist in in Michigan (Peavy (Peavy Complex and and scattered scattered dikes dikes and and area; Aldrich, and others, others, 1965; 1965; Banks Banks and and pegmatites in the Felch Trough area; Aldrich, and Again, it Van Schmus, Schmus, 1971, 1971, 1972). 1972). Again, it appears appears that that the the E—W E-W fault fault system system be part part of of aa major major boundary. boundary. may be The westward extent of these these 1875 m.y. m.y. old rocks rocks is is also also not not known, known, but it it is is quite possible possible that that many many of of the the rocks rocks in in the the northern northern part part of of the state (north the (north and and west westof of Rhinelander) Rhinelander)are are similar similar in in age. These and and the older older rocks rocks are truncated on the south by the the the volcanic—plutonic volcanic-plutonic rocks rocks of the Central Wisconsin Wisconsin Complex, but exact the Central Complex, butthethe exactnature natureofofthe the transition transition is also unknown (intrusive, is (intrusive, fault, fault, suture suture zone?). zone?). �4 4 Central Wisconsin Complex (Precambrian (Precambrian Y) Rocks which yield Rb—Sr Rb-Sr whole—rock whole-rock ages ages of of 1650 1650 to to 1700 1700 m.y. m.y. appear appear to make up the the bulk of the the Precambrian basement basement of of Wisconsin, extending extending from Rhinelander in in the the north to to at at least least as as far far south south as as Baraboo Baraboo and and for for at least least 150 Km. Km. in at in an an east—west east-west direction direction (Figure (Figure 1). 1). These rocks rocks are are mainly volcanic, volcanic, volcaniclastic, volcaniclastic, and and associated associated granitic granitic intrusives; intrusives; the the exposures of these rocks in the the Wausau area area are are described in in aa later later section section of this guidebook. guidebook. Other areas areas of these these rocks rocks are are the the Monico area, area, the the granites granites of Waushara County and and the rhyolites to to the the south, south, the the rhyolites rhyolites underlying the quartzite at Baraboo, Baraboo, and and some of of the the rocks rocks in in the the Black Black River Falls area area (Table (Table 1). 1). Although several types types of of rock rock are are represented, represented, outcrop control control is outcrop is presently insufficient for purposes of of major correcorrelations. The full full extent of of these these rocks rocks is is unknown, unknown, particularly particularly to to the the south and west, and represents a major problem in south and west, in Midcontinent Precambrian geology. The geochronologic control on on this this complex complex to to date date is is only only by by Rb—Sr Rb-Sr whole-rock isochrons, isochrons, and and it it is is possible that that the the 1675 1675 m.y. m.y. age age given given here is a time of widespread alteration alteration of of slightly slightly older older rocks. rocks. U-Pb U—Pb zircon ages will for many of these units in the the near future future zircon ages will be be measured measured for in order order to to get get a in a better handle on the true age of these rocks and and to to look for any resolvable age age differences within the the complex. complex. Quartzites (Precambrian (Precambrian Y) Y) Dott and Dalziel (1972) (1972) have recently recently extensively extensively summarized summarized the the Precambrian quartzites in in Wisconsin. Wisconsin. The age of the quartzites is is bounded by by the the underlying underlying 1675 1675 m.y. m.y. old old rhyelite rhy~lite at at Baraboo Baraboo and and 1450 1450 to 1500 m.y. m.y. old intrusive rocks at at Waterloo (pegmatite) (pegmatite) and and at at Wausau Wausau (syenite intruding Rib Mountain Quartzite). (syenite Quartzite). (Precambrian Y) Y) Wolf River Batholith (Precambrian The youngest youngest plutonic plutonic event event in in the the state state was was the the formation formation of of aa large large It complex referred to in this guidebook as as the the Wolf River batholith. batholith. includes includes a a large variety of felsic intrusive intrusive rocks rocks which occur occur from from Mountain to to Wausau to to Stevens Stevens Point Point to to Waupaca Waupaca and and are are all all about about 1500 1500 m.y. old old (Table (Table 1; 1; Figure 1). 1). This complex is is described in in detail in in m.y. later sections of this guidebook and later and will not be elaborated on on here. here. Published mineral mineral ages ages from from several several localities localities (Bass, (Bass, 1959) 1959) indicate that this event event was was the last major thermal event in that this in Wisconsin except except for the Keweenawan activity for activity to to the the north. north. This complex is is relatively relatively well well defined defined as as to to its its areal areal extent, extent, and and it on all all sides sides by by older older units. units. However, However, the the exact exaot shape shape it is is surrounded on still needs to to be better defined, defined, and and more more U—Pb U-Pb ages ages on on zircons zircons will will have to to be determined on on individual individual units units to to fully fully tie tie down down their their absolute absolute age(s). age ( s). �5 Keweenawan Rocks Rocks (Precambrian (Precambrian Y) y) Keweenawan volcanics, volcanics, sediments, sediments, and and intrusive intrusive rocks rocks occur occur in in the but will will not not be discussed here. the northern part part of of the the area, area, but here. The age age of 1115 1115 m.y. m.y. for of for these rocks (Figure (Figure 1) 1) is is primarily based on on the the U-Pb (1963, 1972). 1972). Chaudhuri (1972) (1972) U—Pb zircon data of Silver and Green (1963, and Chaudhuri and Faure (1967, and Chaudhuri (1967, 1968) 1968) have also also reported reported Rb—Sr Rb-Sr ages ages on on similar rocks in Michigan. in Michigan. Miscellaneous The major rocks rocks included included in in this this category category are are the the granites, granites, gneisses, schists, and migmatites in central Wisconsin, gneisses, schists, Wisconsin, extending extending westward from Waupaca to Stevens Point—Wisconsin from Waupaca to Stevens Point-Wisconsin Rapids, Rapids, and and west. west. These rocks have apparently apparently been been intruded intruded by by the the 1675 1675 m.y. m.y. old old complex, and Bass Bass (1959) complex, (1959) has obtained some mineral ages ages as as old old as as Thus, it would appear 1900 m.y. these rocks. rocks. Thus, appear that that these these rocks rocks m.y. from these exact are are at at least 1900 m.y. m.y. old old and and may may even even be be Archean. Archean. Clearly, Clearly, exact determination of of the the primary ages ages of of these these rocks rocks is is important important since since it will will help help define define the minimum southern limit of sialic rocks it rocks younger than 1900 m.y. m.y. in in North North America. America. Regional Significance Significance Several major discrete igneous, Several igneous, metamorphic or sedimentary periods or events can now be recognized in in Wisconsin and and Upper Upper Michigan. Michigan. The 2500 m.y. m.y. and older rocks rocks represent the southern edge of the 2500 and older the Superior m.y. old rocks Province of of the the Canadian Canadian Shield. Shield. The 1850 to 1900 m.y. represent aa major major period period of of sedimentation, represent sedimentation, volcanism, volcanism, and and orogeny and and is considered considered by by the represent the so—called is the author to represent so-called "Penokean Orogeny" in the area Orogeny" area (Van (Van Schmus, Schmus, 1972). 1972). The 1650 to to 1700 1700 m.y. m.y. old rocks can be correlated roughly with rocks rocks of of similar similar age age in in the the Rockies and the Southwest, Rockies Southwest, although although exact correlations will need need to to await further data. In case, it await data. In any any case, it appears appears that rocks with ages ages of 1650 to 1750 m.y. m.y. comprise a a major structural structural belt from from Arizona Arizona to to Wisconsin. The 1500 m.y. m.y. old complex correlates well in in age, age, litholithologic character, to 1500 m.y. m.y. old old logic character, and tectonic setting with 1450 to plutons throughout the Southwest and plutons and volcanic and and plutonic plutonic rocks rocks in in Missouri. These rocks probably are are part of another another structural structural province province of and south of and partially overlapping the 1650 to to 1750 m.y. m.y. old old rocks rocks (Bickford and Van Schmus, Schmus, 1973). 1973). In summary, summary, it it now now appears appears that that the the various various chronologic chronologic units units In recognized in Wisconsin can be related to other rocks throughout recognized throughout North America, America, and and these these correlations may ultimately ultimately provide provide the the framework upon upon which we we can determine the detailed evolution of the framework the continent during during Precambrian Precambrian times. times. �6 Acknowledgements This work has has been largely supported by National Science Science Foundation Foundation The author gratefully acknowledges the Grants GP—1362 GP-1362 and and GA—15951. GA-15951. The cooperation of all all his his colleagues who are are mapping and and carrying carrying out out petro— petrologic studies in the area and logic studies and whose work provides the the base base necessary necessary for for sample collection and and data data interpretation. interpretation. I �7 References Aldrich, Aldrich, H.R., H.R., 1929, 1929, Geology Geology of of the the Gogebic Gogebic iron iron range range of of Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History Survey Survey Bull. Bull. 71, 71, 279 279 p. p. Aldrich, Aldrich, L.T., L.T., Davis, Davis, G.L., G.L., and and James, James, H.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from metamorphic metamorphic and from and igneous igneous rocks near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Jour. Petrology, v. v. 6, 6, p. p. 445—472. 445-472. Banks, P.O., P.O., and Cain, J.A., J.A., 1969, 1969, Zircon Zircon ages ages of of Precambrian Precambrian Banks, and Cain, Jour. Geology, granitic rocks, rocks, northeastern northeastern Wisconsin: Wisconsin: Jour. Geology, v. v. 77, 77, p. 208-220. p. 208—220. Banks, P.O., Banks, P.O., and and Rebello, Rebello, D.P., D.P., 1969, 1969, Zircon Zircon ages ages of of aa Precambrian Precambrian Geol. Soc. rhyolite, Soc. Amer. Bull., Bull., rhyolite, northeastern Wisconsin: Geol. v. 80, p. 907—910. v. 80, p. 907-910. Banks, Banks, P.O., P.O., and and Van Van Schmus, Schmus, W.R., W.R., 1971, 1971, Chronology Chronology of of Precambrian Precambrian rocks of Iron and and Dickinson Dickinson Counties, Counties, Michigan Michigan (abs.): (abs.): 17th rocks of Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. Ann. Inst. on Lake Superior Geol., Duluth, Minn., May, p. 9-10. 9-10. Banks, P.O., Banks, P.O., and and Van Schmus, Schmus, W.R., W.R., 1972, 1972, Chronology of of Precambrian Precambrian rocks of of Iron and rocks and Dickinson Dickinson Counties, Counties, Michigan. Michigan. Part II II (abs.): (abs.): Ann. Inst. 18th Ann. Inst. on Lake Superior Geology, Geology, Houghton, Houghton, Mich., Mich., May. May. Bass, M.N., M.N., 1959, Bass, 1959, Mineral age age measurements—Wisconsin: measurements-Wisconsin: Inst. of of Washington Year Book Inst. Book 58, 5~, p. p. 246—247. 246-247. Carnegie Bickford, M.E., M.E., and Bickford, and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Possible Middle and and Late Precambrian igneous arcs arcs in in the the Mid—continent Mid-continent region region of of North America America (abs.): (abs.): Program, Program, North-Central North-Central GSA GSA Meeting, Meeting, Columbia, Mo., Columbia, Mo., April. Cain, Cain, J.A., J.A., 1964, 1964, Precambrian Precambrian geology geology of of the the Pembine Pembine area, area, northeastern Wisconsin: Acad. Sd. northeastern Wisconsin: Mich. Mich. Acad. Sci. Arts, Arts, and and Letters, Letters, Papers, v. Papers, v. 49, 49, p. p. 81—103. 81-103. Chaudhuri, Chaudhuri, S., S., 1972, 1972, Radiometric Radiometric ages ages of of Keweenawan Keweenawan intrusions intrusions and extrusions in in Michigan Michigan and and adjacent adjacent areas areas (abs.): (abs.): Geol. Soc. Amer. Amer. Abstracts with Programs, Soc. Programs, v. v. 4, 4, p. p. 470. 470. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1967, 1967, Geochronology Geochronology of of the the Keweenawan rocks, rocks, White Pine, Pine, Michigan: Michigan: Econ. Geology, Geology, 62, p. v. 62, p. 1011—1033. 1011-1033. Chaudhuri, S., Chaudhuri, S., and and Faure, Faure, G., G., 1968, 1968, Rubidium—strontium Rubidium-strontium age age of of the Mt. Bohemia intrusion, the Mt. intrusion, Michigan: Michigan: Jour. v. 76, 76, Jour. Geology, Geology, v. p. p. 488—490. 488-490. Dott, R.H., Dott, R.H., Jr., Jr., and and Dalziel, Dalziel, I.W.D., I.W.D., 1972, 1972, Age and and correlation correlation of the the Precambrian Precambrian Baraboo Baraboo Quartzite Quartzite of of Wisconsin: Wisconsin: Jour. Geology, v. Geology, v. 80, 80, p. p. 552—568. 552-568. �8 Dutton, C.E., C.E., 1971, 1971, Geology Geology of of the the Florence Florence area, area, Wisconsin Wisconsin and and Dutton, Michigan: U.S. U.S. Geol. Geol. Survey Survey Prof. Prof. Paper Paper 633, 633, 54 54 p. p. Dutton, Bradley, R.E., Dutton, C.E., C.E., and Bradley, R.E., 1970, 1970, Lithologic, Lithologic, geophysical, geophysical, and and mineral commodity maps of of Precambrian Precambrian rocks rocks in in Wisconsin: Wisconsin: U.S. Geol. Survey Map set Geol. set 1—631, 1-631, with with accompanying accompanying pamphlet pamphlet (15 (15 p.). p.). James, H.L., C.L., and and Pettijohn, Pettijohn, F.J., James, H.L., Clark, L.D., L.D., Lanley, Lamey, C.L., F.J., 1961, 1961, U.S. Geol. Geology of of central central Dickinson Dickinson County, County, Michigan: Michigan: U.S. Survey Prof. Prof. Paper Paper 310, 310, 176 176 p. p. Kiemic, H., H., and Klemic, and Peterman, Peterman, Z.E., Z.E., 1972, 1972, in in Geological Survey Survey Research Research 1972. Chapter A: U.S. Geol. Geol. Survey Prof. Paper 1972. Chapter A: U.S. Paper 800—A, 800-A, p. p. 3. 3. Silver, L.T., L.T., and Silver, and Green, Green, J.C., J.C., 1963, 1963, Zircon Zircon ages ages for for middle Keweenawan Keweenawan rocks of the Am. Geophys. Geophys. Union the Lake Lake Superior Superior region region (abs.): (abs.): Am. Union Trans., Trans., v. v. 44, 44, p. p. 107. 107. Silver, L.T., L.T., and Green, Green, J.C., Silver, J.C., 1972, 1972, Time constants for for Keweenawan igneous activity activity (abs.): (abs.): Geol. Geol. Soc. Amer. Abstracts Abstracts with with Programs, Programs, v. 4, v. 4, p. p. 665. 665. Thurman, E.M., Thurman, E.M., and and Van Schmus, Schmus, W.R., W.R., 1973, 1973, Rb-Sr Rb-Sr age age of of Precambrian Precambrian volcanic and and plutonic inliers inliers in in southeastern southeastern Wisconsin Wisconsin (abs.): (abs.): Program, Program, North—Central North-Central GSA Meeting, Meeting, Columbia, Columbia, Mo., Mo., April. Van Schmus, Schmus, W.R., W.R., 1972, 1972, Geochronology of of Precambrian Precambrian rocks rocks in in the the Penokean Fold Belt subprovince subprovince of of the the Canadian ~anadian Shield Shield (abs.): (abs.): Program, Program, 18th Ann. Ann. Inst. 1nst. on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Mich., May. May. Van Schmus, W.R., 1973, Schmus, W.R., 1973, Chronology of of Precambrian Precambrian igneous igneous and and metamorphic metamorphic in eastern Wisconsin and and Upper Upper Michigan (abs.): (abs.): Program, events in 1973 Ann. Ann. Meeting Amer. Amer. Geophys. Geophys. Union, Washington, D.C., April. 1973 Union, Washington, D.C., April. Woolsey, Woolsey, L.L., L.L., 1971, 1971, A A Rb—Sr Rb-Sr geochronologic geochronologic study study of of the the Republic Republic metamorphic node, node, Republic, Republic, Michigan: Michigan: Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Kansas, Kansas, Lawrence. Lawrence. �9 t33:ir JTh f4 i:tc 2LTY y 2j; 2GIC1 1f1:i--= ii-i 4jLj yEa WOLF RIVER BATHOLITH--A LATE PRECMvIBRIAN RAPAKIVI MASSIF IN NORTHEASTERN WISCONS IN -. \2 TIlE by --:, a:: 2L J.L. Anderson*, Jr.*, 2' rf- Medaris, L.G. Myles** and J.R. C- iEE.CJL.JZINTRODUCTION LL-- aLa-aU .-: co tf •- 1L!• Classic rapakivi texture, in which grains of ovoidal alkali feldspar are mantled by plagioclase, has been described from several localities of Precambrian granite in northeastern Wisconsin (Gates, 1953; Elders, 1968), but until the present time, the regional distribution and petrologic significance of these rocks have not been Our investigation, in conjunction with chronologic fully appreciated. studies by W.R. Van Schmus (this guidebook), has established that an extensive rapakivi massif, the Wolf River batholith, underlies an area of at least 3600 square miles and represents a major feature of the This anorogenic, Precambrian terrain in northeastern Wisconsin (Fig. 1). epizonal batholith, 1450 to 1500 million years in age, consists predominantly of reddish, hypersolvus quartz monzonite and granite. In addition to the widespread occurrence of rapakivi texture, the Wolf River batholith has textural, mineralogical, chemical, and structural features that are similar in every respect to those of the classic rapakivi massifs in Finland. L t •-i&;t Li' k:y.a 4121 2 tt flCTh rjp 2!71fl ©1i -rt ras;-- tia #e :2 -it ut a?-. faa, rfl t 2UU r, :ytLr, : C:KCLiliCT.CCCiI i-Li'CfCt.CC. i-; L2tL :1r:yCiia 1j :y;,itL;y:j. r;1iC1i1C t!LtcL -LiC-r--CLi'J.c. ca aqiy-: La€'L -t iiE '5iTh-yrC aU '-U EiC LiiTT eJ' :caCyL& a1€TTICi'-2 y'iñk;I L1ra. lyai;Lt. 2ii,<: 'LirJL Ct C;iag:f, :':C'iTCtC LtC.. ::,J'.tCi'irt:C2.CCIIi, EyLa? 'i:r. flI •'CY-fl:C, 1\ t!f2T7 2T'jir :;MiC:i. C2C ta- I CCC ix rc'L;-c 2€ 1O29Lfl bxü iTnat 'Li]. ntUi C—tt2 nct- I •b - f;aLi CLE -u. -. . - UU- -z-i j•aditiCtL-• t€ CICCitC CtCiitti:LCC! LCI k.CiLC ITCaC tfi- lit 1 fr L5LitiCC.iL., 'iir:ic:a. :11Z"'2t11";f TC ;.;CT : ::rol,: :iZi1 .;yji g:aiUL'ii i:,J ii4cJsiucLi 45{j ?:U-UUL. cJ T7,r,::At :.a'::i:d •U t:: C •: t]TLC'2 : T-Lj .-Ci irCaLi? :,y., ----2 ICoILt'i C€C tttat 1'---, --, C'axiLal. aa. - L.,' LITHLOGY rtCr ±..1i.:1L'::::s€ ih- -— - - 't]'. CCC' General Characteristics liLVtJC 1ACC Cxii •iiy 'k:.C' ECliTcJ. lCJhra; ny;]i Lta'y,Li 7ç1;'T' ;-CCLi A variety of rock types have been recognized in the Wolf River batholith, including granite, quartz monzonite, monzonite, trachyandesite, syenite, and rhyolite. Quartz monzonite and granite are by far the most abundant rock types in the batholith, adcounting for 94% The predominance of alkali of the exposed area (Table 1, Fig. 1). feldspar over plagioclase in the batholith is illustrated by a plot (Fig. 2) of modal quartz, alkali feldspar, and plagioclase for representative specimens, obtained by point counts of both thin sections and stained polished surfaces of hand specimens. 2 1li-li ii-c t-a niii1 iL U a:c--.xli Li €lufrCI CE ix -uCla titi )Ei 1.. r LaU-uUSL lila t:IC.Jliuii U pta U. €L-€L 'yiyfl -. cr.. cE 2B12 1s,i'fT I tCli, - C-CT xAs?IT'r2' 'Liii i1.ii iLiT-ii ' - ] a1kaL- tzau€E Lii- ',j-c 'It,-: ar tL.2iCiiCT ruT-fT x lixvxuia, 'JL'i.- :uc'J-€l :1- iL:s uf lifC-iULihtiii.. ')2vt.1€Th p.. I 1R La TLi1--R,g-IC-9€ tu..-C C.çi-Cr xr).dt •-a :tp€E t P b.u-t:x Li'U LExy Cli ',yc.t'h •.:i -u-TxxuT'tx. CCCL. i'--n.ix 1 ILJC Cxli :xfJ.Jt '-zr:'.LiCibla-ii c-C 3€ -CT.C. itiyii:C iLiH 'r' auuTi-iCL ccxL L€Tituic Rapakivi texture is one of the most characteristic features of being most extensively developed in the Waupaca quartz monzonite, but occurring in minor amount in all of the other granite and quartz monzonite units. Equally characteristic is the development of porphyritic texture in all lithologic units of the batholith. Typically, phenocrysts1 of alkali feldspar, and to a lesser LLi&:•iuiLci 7 JULia.U. Lii" x--.,cy.i-Cl,li-: lyxaiTta ir-vrut .'UCa U: C2itT'-xfJT4T tI-LIt et311C Li-U 11CC- 'C b-a iit rCttlii,i J.CLfl.fTl rxcii,.E CIxe xrit.ciE .1LC?LiiC I I J'IZIl =itlL'L- -L . t:;rtaaa' p-CTiU.j:it:lC iLL .xj.:,f nuuiiaaCC'---ixx--- -.---.j- :€-l'1TF itl -c -i, - h-iiuci-xca.2.t- ,,.I,Cxeyftxi :t-r CE CCJ-f ui''1r 4p.iiii .iHc- :ii-.7tnt_-i irE lkui 1 -i-U; -CILL xxix- Def of Geology & Geophysics, University of Wisconsin—Madison of Geological Sciences, Univ. of California—Santa Barbara A non—genetic descriptive term, such as megacryst, might be more appropriate to describe the large alkali feldspar grains, but since phenocryst is still the term accepted by Finnish geologists, this convention will be followed here. -filL'. WLiifT 'c-a .e:''Lt :CT. 'Ii -_' Li 1 C--- aL.' -c-Sf -C it I- U-fl" fx-x.tC-x, ,LL:xi'a;y C.€-LilgiCtl. CL-Cf ,j 7: Li.. u'xlx .., taL:-Cxx€ trti., IJ'.raul. •:$p2Y vniiui xixi i.-.LL 2:Li.'litf lIC'iLC'i'C CE--x C '-,e-Li --C -a--€ fit lrxiac. Lc--ii-II E1 Ix: 'IcC ttxx Ut-Il .CC-€1Lib-iU If aiaza'n trLC-T,:J.Cs1. -'' cliaUca ** 1 Department Department . :11 :CL ** I * It_i the Wolf River batholith, �P.- 89 - 0 - ':*-- - LjLi - /F: LIMITED EXPOSURE us / - —0 / LIMITED EXPOSURE EXPLA NATION IsLofls5 granite Belongia i LtC1Ctj% 5 Wolf River granite and sd C11oT quartz monzonite 0* Red porphyritic r5CiRiser ru-p0-i:: quartz monzonite it;C- Waupaca J!&Ci wiborgite r7 CEJiUt Stevens Poist grey granite I Hay Creek C!Cifr-C:cI1CC9. quartz monzoriite, T rIi ::rIi F Hsç!s! rfr:c1Cis Hager rhyolite Hager feldspar -]-sQsC -ici5ir porphyry bxsspi'y k{wsr Ci$Clci Hager syenite Peshtigo 1q:-liL nlonzonite CiC and -:sch-'is5Ci trachyandesite i-:i!(I :i-CIIC High Falls51CiCittCi granite 1 H THE WOLF RIVER ?rk•,:BATHOLITH -4—IH1iI1H GEOLOGIC MAP OF Anorthosite :-iIC, rii5PscN], i4C tLG BY G. MEDARIS. JR J L ANDERSON, 01] [j y-y__ ':UJs AP-II Mi_t WA VANVi SCHMUS. AND J,jI:. A. MYLES 10 6 10 Ci 20 22 30 2t MILES Precambrian rocks older than 1450 —- Contact, dashed where C'6C365. 16232 46 approsimaie — Fault Mylonite 1500 M Y �4214 11 Table 1 Proportions of lithologic units in the Wolf River batholith areas only) and key to symbols used in Figures 1—7. I7717'!110 11,1rcp:4rl 21.21:. 20's. 2 :7172 07203111120i '7:'i -fl :10012. 202171:11 22; Areal extent, % .47!',47t1 :212-21:7 o Belongia • Belongia granite, coarse—grained £ Wolf River granite fine-grained 7122 71!-.1'7-'-12-!-"4.; granite, 2 7 '' 1-210,27 2120-2120 '7:2.7020 21-27207 '171 ";fl C'' and quartz monzonite 51.0 2t"'3i.101 -::'a'fl'3 21 72721172102-021,1024: (14.- Red River porphyritic quartz monzonite 20.6 Waupaca quartz monzonite (wiborgite) 10.5 721: 24 (77,1.71' 07-212110 21017; • Hager rhyolite 3.6 57 Hager feldspar porphyry 0.2 - 3-CT': 27212 11204:0177 ,!C14J 221:-i - - Hager syenite 1.9 Hay Creek quartz monzonite 0.1 '6- 21:72021'.';317. C1.-.4? 4:i$-10. •2 • • 0 '17 ";-fl:7-73:..-3 141 0114 4212'. Unit y- :r 74,7o ;lj '4' - Symbol (exposed Peshtigo trachyandesite 2'0c20T'710'2'? 0 4 32424:!370 -'4-, Peshtigo monzonite J -2041002112110 •U-31,1W7, Not Shown Stevens Point grey granite 5.0 Not Shown High Falls granite 4.0 7212 ,' 21 .102121 4: 0140)1 707102-2;- '24i l- 24 ;411'TP 21.27.121 extent plagioclase and quartz, are present in a medium— to fine—grained granitic matrix, consisting of quartz, microcline, plagioclase, and mafic minerals. In all cases, matrix plagioclase is more sodic than plagioclase phenocrysts. Quartz is interstitial to feldspars in some units, but in others, particularly in granite and some varieties of quartz monzonite, quartz displays a distinctive idiomorphic habit and apparently was one of the earliest phases to crystallize. '71100 2 — 7;; I :12:; 272-721 21-724.: 117 3-10 71721.211171 115:21123-; '2021212' TT FL p0'; 102121,1-77:21077 A-trocoao-fw 4,,•;I_1rT; - :c;:-1-:-20.1i;'o-- 212)03 1)1 1'-.r.'327:;720-07 723-0421122 421 '21if;t2152 07712!! 21JL2---L22L SI ;cnr-o$ -n .LjJ720;0 0 ,10207077> s—p ','7c7-Jt- •-0 ,L2 Z:'20J' 7!::214r44:1014 A;10:A-•: 171 10- 2121:22; 277371 274710'7721l 2-4 1112 02 21-42022 72111210('7.A:! 7:107.417 7 24Ti,; -'-,m-. - ',:'''' .',- — .-.• 7 Iron—rich biotite and amphibole are the most common mafic minerals in the batholith, although orthopyroxene, clinopyroxefle, and olivine Biotite and occur in some of the darker rocks, such as monzonite. to subhedral and occur in areas interamphibole are anhedral typically Such an occurrence stitial to feldspar and quartz. suggests that in the biotite and amphibole appeared relatively late crystallization sequence of the granitic rocks. 21 2."-0- 0100 '1:31 .02 ':20'. TI -1021. 21:1120 -:4211-.. 21 - •3o©1coosI:jf 0 --':: 20t-207044.Z0I 2-117:170 C 114q77:.12761. '3 '10 7; 0,FL0lPOl 2-20 2412" TA. 4,' 2-021 2120: 214 2-20-1 1-4 $"7--1 1ir ;7-'71211214201 -1133-11221! '20741271724214:121 34:1 217 21121 21 2021 -ro'31::-'a li 1:;':-2-c;7 1)212124 410 7024-20720 -0:. 202 aCIC-Ip 1021721 21:217717121 21212 -4, -14. 1$ 'ccoo: J, 1422 -174- 37 202101:1223 20:20 12011221! 4:i;::10 P 10111-27 Descriptions of the Lithologic Units IT Twelve lithologic units have been distinguished in the Wolf River batholith, and the following descriptions are intended to summarize only the most salient features of each unit. Actually, some lithologic units are quite heterogeneous with respect to variations in texture and grain size, and the brief descriptions given here are not intended to encompass every conceivable variant that might exist within each of the twelve units. 21321:7 41-221 1t:2a'y-:p.a21;i 202321,2121212; 2I'' 2(12:-I pL1-Lt $4 )C'1 %21';#210' 22-f • -.'- 04: --.; ç0ccJ2;E-- i4J2 IlL 211 -- 14:2 C- -21-rn4:-ap. 7t.'7TL5 421221 21.-I! 4- LIII 21-21,'. -21'tL 221 2 21 flEC 1ç42r11-2 CC -:72)121!. 01CC.L -Ca210 214 1,141 T4 flt21 7212111 2111 flafl ifl;'. ai2a'-21 2•L21 I 114212-2 21.21;t21tCC12fl 17-114-; .72-Li �12 Quartz Fl 2E / 50 50 2,• I!- /• A ----- 10 ;CttT ___ — -— T feldspar eOD[J 10 Plagioclase Figure 2. 2 Wolf Modal analyses of lithologic types from the &q;4 TP°N Xyen? :;bTLflhi. sñ2( CJ rig River batholith. u':t7cCC44q 2°-f i22 (Sbo1s listed in Table 1) -T E bCCjUAA$ ;j'it:.fl1. . This coarse—grained quartz Waupaca quartz monzonite (wiborgite). 21 CCfl resembles z2=:.;:'n rapakivi texture and closely monzonite has abundantly developed I-)ç. Approximately 70 to 80% of the:tCe;1 pink the classic wiborgite in :T Finland. pL(Civtv.I 5U2 ;L: 4i, 21i 5.0 cm in length) are mantled with ovoidal grains (1.5 to ]:i%-r:A;) alkali feldspar .tthCVTC& LCçP-J2 common. 1 to 6 mm thick, and multiple layers are a layer of 4C plagioclase LCfl (rjtC, :2 The thicker a plagioclase mantle•Ci is, the smaller and more rounded is the )LJ texture is characteristic, alkali feldspar the [ 2T- Ci in Cfl core. A porphyritic .s#_1_plagioclase, and idiomorphic quartz with the mantled feldspars, Cfl large [ <•:.LdTs microcline, plagioclase, quartz, set in a medium—grained matrix ::±:t:1 of ;o; 1U Ibiotite, and amphibole. :i C LE 4 LLifl i'an2 :i ;r p cr ]tYL : (k; fIYIii ar 5i:; IL: ro-t r. 'v: iij;•t : .D':t Wolf granite and quartz monzonite. The Wolf River granite and '! River ::.Y12;. quartz monzonite in being coarse— quartz monzonite resembles the Dt Waupaca <crIL: ovoidal alkali feldspars (1 to grained and prophyritic with prominent c :2 texture is much less abundant, 3 cm in length), except that rapakivi L f ';i ;r1TI the alkali feldspar ovoids. plagioclase rims occurring on only 3 to 10% of 2: r:• 2L1J r;zcq - ;dtr :c1 I r;icP :i rr i;fl �.11 -:1 1. 1J a 1:.4Ti1 and groundmass. fine—grained in Yi4':7CC. phenocrysts olivine feldspar — li iii L1 .. a is trachyandesite 4 40% with monzonite, the of equivalent porphyritic ::tIiI?t interstitial of traces and opaques, biotite, amphibole, The quartz. -'E•I:LYL!rC and tL1' r;:T•+:1i: clinopyroxene, orthopyroxene, olivine, amounts TP'::.'1' in subequal feldspar :):j.'jL;::o.c I slightly vp-: L and (IrU alkali and plagioclase 4;yic1 containing porphyritic, mm) (3 ?;TTiio •."° t1.1fl*.1i.] relative 11 medium-grained isT monzonIte 1J[ The minerals. Ic maf of abundance yii Zi11t1.. and quartz, of paucity color, to grey dark brown their by guished 4:. are rocks These trachyandesite. and 1° distinmonzonite Peshtigo I — T I 1 L 11R1.:i4i.Z flt.1l . : Tin.1ar7i1 T.i..T°tfl ..lt:1:t.i i:i.1 c11t 12.1r JT1 41 /-. core. the in that iJ i111:r1z) :1I9944L.trw r °T with continuity optical in is rim granophyric the in feldspar alkali °7Th II cores occur The feldspar. alkali of euhedral around quartz and spar 1j J_L ° L,C1 .4 texture, granophyric presence feld- alkaliE. of intergrowths which in of Ii 1'Lf'L CII grains LC 41 ° 1r the is granite this of feature 1.4L14..' characteristic A matrix. the in 7'ji 7't occurs ':71 r'r' n°U aInriI IC '7CILC .present. IC17rCI IC? ECIçLIIr jr'i as .j of IC clusters mineral only the is and mafic Biotite iICCI2I:LCI:t421cIcJrI:.7CI is texture rapakivi of amount minor a and boundaries, resorbed show U °0iFk-U r .3 — commonly phenocrysts quartz The in cm) 24 matrix. mm) (1 fine—grained a çL;r0 It: ; In £11 •,•0nLI7I :tM50C: IC CI°4 to (0.5 feldspar alkali ovoidal and rum) 5 to (3 quartz idiomorphic of :riLIJ is I.I "nhLn1t .11iC I-i: ii:; :CIrTrmfl of up made phenocrysts granite Inr0r':.P.=t1:I 20%) to (15tI7. fine—grained The C ' I .,1 1 1 irflll'l oi.f rOr'?). T7(,j 'oLi' 11 I't1 .:?i I 47 :° rI'4 &. t ' 1 7 Tt.tl c 4i1 CrIC IlITTI C: 1CIC are texture granophyric present. and '.: rapakivi of amounts Small — 14 IC' 21 a are in set to quartz and feldspar mm). (2 matrix medium—grained 45%) (35 sr c7IC0'CCc7II'.Ii? ICIlilfi. 21 1r0::vr.Cc7 oL1.:.rrJl a CI',ig'ICCI °LIL. alkali of phenocrysts which in texture porphyritic acquires unit zI1:1 IC',:, rT"7T some as biotite I this however, localities, mafic sole the mineral. Jt ' I ,:CI I. 41.'1; U.CIC.t 4 quartz, and feldspar and plagioclase of amounts small with idiomorphic C'AcLI floiIir'1i of [CII U subhedral .:cCc1In mm), :'IC mainly consisting to (3 even—grained alkali 5lIlT, I yi I I l::t rt7r 4.rCt4C4 1W '- U,:' ir :.J].: 7'' itiriCi CIiICt ,T7ii7t pink, i-c'rTCI7.IilThe ilc :::U°t'CVCCJLl: 5r477 €7 predominantlyT1Ct and massive, isal7CTrrrTC'I granite coarse-grained ?LIni. 0iC:iSJInr€2CY1? 07T:Irn [,.IInIC7LCi €ICC'ICLt'Iz'la variety equigranular grained variety. porphyritic fine-grained and lIt ICBelongia JICl"7'oofIn types ffCiiL €74 coarse— a exist: granite Two granite. Belongia liT tI I lIC 7111 CI'liltCJ[°'Ia 114C rock. the to fabric planar imparting ':r'Ti4 [--1iJ !71:njTIrfr'5 C' ,17 l4:2'i Xiiii.I)41 . are aligned, commonly phenocrysts feldspar The slabs. stained in 0' ,i*r_ : 417 to up n' rC.ç.', 1il1I.inCCl on 4 IlL,' the of 15% apparent are phenocrysts feldspar alkali mantles U Yr' not 4C171 €4 plagioclase discontinuous thin, although conspicuous, is texture ' ICCCt: ILU mineral, 01 4. IC '' CIT II 71141 il'27L l7CI5I 111111711 although CI CII T?1 some at Rapakivi localities. present is amphibole mafic sole the as biotite usually and predominant, is plagioclase 40 L1! C' _T "—r'l CI "11 which of feldspars, two quartz, anhedral to idiomorphic of matrix iL'Ino'1iC 1 1i C. m91Tcir: .L,IUTW.C101. 2 with mm) 2 to '14 (1 medium-grained a of consisting 80% remaining the 7jTi: 'sTh'cC ri €17 11' I0 InTL cm 14''1 rock, the of 20% about constitute size) in 2.0 to phenocrysts (0.5 o.loo1oooocrr: feldspar K%cc no L'T1CIT74404J[ ZC2t!7t alkali t411 Typically, IC:l subhedral phenocrysts. feldspar alkali t.Cl1j[CtCii i::,ti Ti .1771 :fl 711104:j::C'Ti'.T° 717 phenocrysts rather angular, and to in ovoidal, ICCITI'l than ,nT.'zo!Uj matrix proportion .'01..t CCI riI00 quartz .r,I,; Wolf and .0C'CIl; River UTL4.CI 411:711 1€174 111 contains nyCv" '1 LI Waupaca fewer unit this monzonites, 'T:i;°7rLo€ quartz porphyritic River Red LC,LiiLLCI1 In the to comparison ThJ monzonite. 0 llTr 'I • 10 Fn', CT7C CT. L I p'4 4ltt4'L 1 '€': ;4.:Tlt CC IttTIC' l. 4 .1 I::-,:.Cc:: 2 nt t'1:. In lT'r i41 r'o ., . .iiTit C: 7:711 predominant 4:11-ri 71717 CI: I 1144 11 C€1CC4 granite II 417.714 type. rock the becomes 0C1CrI.4. 'C01:nx 1c714 IC '1777141. it, 1 t'€ rr" 1411 as appearsI quartz and grains, idioblastic iron, in richer becomes r:ç'T -- TLC .121:? :,rc2€I.rnCI 1141. In 7111171 4:717111 it; .7:, :U amphibole C'1,:°° 141,': -. ;c:T14 :amount, biotite inIcdecrease and plagioclase northeast, the to Yto171I ?.;LI: monzonite, ICC..n:CUJ€Cr: quartz '7,711:2: is ff':0y$-r7114 71111 711111742 granite Belongia the with Xl'TiiiICI contact *11 the towards but 0;: :..Th:nr..LIiIIU: 2r'i'''n plagioclase, iln41C.nIT 4111.the I,14 of CI .i'0U unit River Wolf bulk The amphibole. and LI biotite, .71t.LCC:L;I IC'Ct, :mi,'C:2t °tn: l,7f.:cl:'4LrICC: interstitial 'ircTCI71IC.':I:c:I.40CIiT microcline, quartz,4lIC]71'4rli1 anhedral to subhedral of matrix grained :1 feldspar .1 €JIC7fr'[l and 'To,., Alkali Jr II'C set1111': 1'.ilrCsC 14 plagioclase CI1 a 'IL I 1L11 are phenocrysts mediumin 0 --': 1 r' CCCI 13 �14 :-:cirL:r&10154122:?1'1 222111Lc'-l'ZIIOSLI idiomorphic 0C:.*-2, I'll conspicuous The Illoco:Hager rhyolite t'-L'a-L--rlL:Lt-r contains 'L1''1L,-h2, 131-to Hager rhyolite. 1110L112112112' 51220130772101. IlSoc ;oc.:lI-.ILO-co, :1121(1 less quartz phenocrysts mm) and prominent feldspar phenocrysts -50to to 44 co] :'0311.01 1F'.,Lo :--' 0110 (3 7-tn-:.]rcrcc: :1* quartz, 701911011. feldspar, 11121.0.221.221 f1 11101 ll--15L1.-O-0 matrix (4 to mm) 170 in a '1111-f very ULIOIIfine—grained (0.1 mm) of --14 to-i5 too) '01: -:11-too The pheno— 01111,11.511713. ortcc 11-0 8/00211. con:21 7-: -- and and fL' clusters of li-tc-:. biotite, to ac I] lesser extent, amphibole. ;ooo o:f 120 "1122€: '4201911. :r7ycLito, commonly :2211201-00 0 3322111 crysts, constituting 30 CUL 0' of±2222 the rhyolite, show resorption 37 to 45% 1. :10112.lt,101 t-:-'i4I,-?11t1 of -cd 02101011102 evidence :.o2:22.(112t.80101, without : tO is The 1-105221:: rhyolite cool] homogeneous, 111 massive .1--'-12,11011 and 5-:att 11-:;:; features. :1001: is tS-co:'otto to lot; IrSc-oO:': brecciation or573112-12' pyroclastic 01- thought be intrusive, ir.ot thus 0,122 -It'f.to- and 911180 010 01' :11:1,10 activity, -1'31.1,2iD112S'1-22, rather 1-ftc-ac-c- extrusive. 1201,52112 than 111112211 0711fine— fi'-o ' :1-12.101' 100 03.0.822431 121.1 the "Cr0701111 somewhat In :ccy;f hand op8o?4-1112. specimen the Hager-- rhyolite resembles In 2212 ort c]h-oHager ,1]:cc rhyolite oIlo'o' 0 to has Sac ac much grained Itoh the :'-c±- that to-Il cicpzl-ogranite, : ---.01 ic, except :21 cOol-Il Belongia ,7119 pink, 110221111., 71I-IOF. .C'at.012:' 001be 028 101.12k-I, 4-11-411 to finer grained pii. :ish—grey, rather than 10-: tends 40'2ILILL1O-1. groundmass 3C-912.In.r111123,'211 and jlb:i:-o-':' o 5.'-I,.1-9 ci,rtc::: on a fresh surface. or- 2222220 (11Y1011'l:lIc, f.'-O-.'t I'712'51 is al somewhat The '1:10/ ' feldspar Oolon IC' porphyry '3702 Hager j;111'5.: 5ti1-7-t1ifl50 Hager feldspar porphyry. 22 o..'(' 00, I is ':3111 12210 10511-5021 -p-202t74-' :-o similar to the rhyolite, differing in that the feldspar porphyry t4.tf.:-oI22c€9* :"ft-,-OJIL.:--:, 12:12001110 0-c- 'Lbo feldspar 407 .01,5 t.1'12t110'C221-'-c1111112 001-C, >71'- n:-o o1J11lt;.tlld1 more abu:Ldant darker grey00in color and -woC contains and conspicuous 01cc-Icr .t2211 0011:22.-to LIc :-oc- ol Or is the0cr13' only oo,i-c mafic:01 mineral in 714-1:;: 1 0035' 0?1:1.' phenocrysts to1730000 quartz.- Biotite p54: -01:5122 iL-: compared 71.42-1.0porphyry. :oo.c2 705 the feldspar 11*1:1.1 Scm' SOtO and r11122011.o&, .522'07', foliate, The isOL'-217grey to 12-0 reddish—grey, 111401010 Sw 117.1"dtlt-O 131. syenite Hager syenite. 1971214.011feldspar 7-01 C o: 11:' fCctSl :0 11 Lo:lm-f porphyritic, with aligned phenocrysts (25%) of anhedral alkali >a2L I :00011 pL>cocm c-51.to C2-1"% :td7-15h5--,'v:o1t -In-I tI: SOo000: feldspars, biotite, oil Solic: rco.'c, Jr;11-015:;. -,:. 5'.l.oo=-If.'coi.clrCand 1:25cm-cr minor plagioclase 1111 a fine—grained matrix of t1b077.L11t 0011 in 01101 C-? Granophyric iL103Di'9*7'0t't'011 of '7c1,c-cochdc: . intergrowths wo-r:-:cc- rJ: 81,3121: c,:.L amounts amphibole, small of1111811011quartz. c131:11 702 1.1: and alkali feldspar 0-3102 01010 ±122 12-0111102 a.'1Y22:-38IC to some qua.tz and alkali 1142110,1.110 occur adjacent 01111:0.'- 1 feldspar 5'-,t::r:-.4l01-. 77-s'1307'C"o: 22, phenocrysts. ¶ 11 massive icr-nA :1011111.IL'-iir and This quartz monzonite is 5.100 1112,122 Id lltItC1.7'coStLO ,-1071.1-;:0i -1 Hay 17ClLc Creek quartz monzonite. ]1I1,'L .111111:123,8101': 0 (1 cm) in a 7)2:3:52210 ' 0111 14 5112 -0051212' 11017.:C-.'D 437 ..'fl'11L40 porphyritic, pink alkali feldspar'phenocryStS -1-oOp°-y'2' '21I, containing 70-0121±.--:', 'oS -.lcp.c' cc, biotite, 7711112:' 12, two too feldspars, :-00clcJo'.rtl.t 11'-fl,l medium—grained matrix mm) of anhedral quartz, :12.11101.12121*. -950-4] 401, 801011 (2 1-5111lIlkt amphibole, 01022 sphene. 'l'c-,Lct , and - 2110 1.011-LI unit *1.14- in 71,101.00-37 this have not yet studied -not 5114 '>O '.5001-:c..:' ,572 We granite. -to 5082' :,oL,OILIL1V" actually a grey 31.1:1 -x;t.o-'inorth ocr-IS Ifof ,7002201:.1:o1:,o0 50One Stevens Point is ::-01:711d collected 71.c sample detail. tloc-c.Oi., 11-c.] -21 op to-' alkali feldspar 22 Ltao'n: 17% 122c1h111t122L2-aa porphyritic quartz 10% subhedral ,1,iL:s1:1 '-cttrt about 12210:211(1 022 with 0±11 -110': 12 monzonite o:_r1 iI allotriomorphic 'IL 0 1100101 in a fine—grained pJenocrysts (0.5 to 1 cm in length) I :750 tOot-Otto , This and biotite. 711! ,:c:-±oU 1.11-1.,, 0111L7 '3:011:: c-oitsc:, plagioclase, .-.:-i1 quartz, granular 1111.1&1lCit1c matrix of '-ttc-0o. microcline, 41'20C.'91.5F' 'I,0.72 '41-123 finer grained varieties :1::f5o-o.cc'',0-.11cI 1.12 some 11.0111,of of the rocktois lithologically 2-111.111,11,1 to rook, 11'1411c.1C-J.4 cc 113' similar .'-Io-'111c1:1.t3 flo-7,"lil-T-:OlCci quartz 0,8111 River 1111.02712' porphyritic 110S12'L-S monzonite. of the -1-221 Red 0" '1'.oIt:-1h:11-'a-: 5':81911100 Stevens Point grey 21 ',i 21 ca"c. -151-1.- hetero1151125 granite High 0:1-cool t.: is rather 1-c a :'s;- 5i oil: Falls .:&-c: t-:, The High 42-S'LS,: Falls granite. 5(122: .lJ0;:1.1..771.1222I12':cLllt-I0 oo'-i22 1911, '12013,-I,1-l allotriomorphic geneous mainly ofdt medium—grained OCI'SI 01LT9* 11.01:174 011111 unit, 12227 -1 consisting octorw': oIl-Ill Shear zones 011are extensively 51.12.0 2103.01 9*-L-02011*o.1 wt1oor.. of :7.'911'1712 granular granite and quartz(19-3>1101.0-0, monzonite. 11711 other units 11 the oLir1 11111 -il:':211t 10305-1111 absent developed It'll? 0021,2107:01 outcrops, a1- feature from 12-1510 22222:1.1,0 of 18: '211.1' -1: in some -lb rcr'0" :7110024±22: Eau '-IILOOIci Claire River mylonite :0 '11c-'o,..'.7f 1712,11: :'r50 11:11 of -11.':L'klt the Wolf River exception the 11:::, catrl-:clLlLibI, with 1i',tmr batholith 'i&3,:77oo1, It is ::,.1.o1c150V uncertain 1;, .0 11? this guidebook). 1770-1'. .015 122/11121.1117zone (LaBerge, field trip locality 8, :1' -015 1210: (1 a17c1-cbS-.. 7t-I1'1:,11L11-' It' whether of the 1,12.1 batholith 022000121 I'Ll]: or lIlt" 114r I.½0:C '1-;: truly n"mCft ilL granite 01 II;111l'1.' is whether the 4111911'? High Falls part 122 :.137L&1t1b,1€02011;1 to ItoIn the 1.> '1"°111i12:. 3ii:1"11'32212.2L111-4 terrain. 0' 480- surrounding 71.0 older, it represent :5' the 1211:11 of 11 might mtgkb 0017 .c10IL::, part -: >s tac-]]' assigned to the bath— it. SOS tOlctO: 1 021-10 3:30 oso L,oliac to absence of isotopic dates it has tentatively been ooto-ptc 1,0120110 21201-so cooS tçlOIolti -.150 ol' and is spatially .10:1 1:c-cr:,'-lllm' 01-8 cool-cIlo': ,1T:8.'11L'.tO olith because it intrudes the Macaslin quartzite dli;:1,I'5bl 0-1-30:1012 -'tC-OLCIO. Ito. -oob :101410 monzonite. and Peshtigo ::l -19-12 .1, . -110.: 11c5 Ct29ttl: granite, i'oç'to..*tl- , Belongia 7;: the 1(14 —cr1 : rhyolite, related -o Hager c-tm .al,e-21 to '1 21111 �/t c-'5c-,, at.1; c-y cc;c cc'C:Ic'C'cc6 cCEcIICECcZ /Ld:,LLL -cc:. :c;:ccicc cc ,.C1 ::cc-:cc---5- To illustrate the chemical compositions of the granitic rocks, mesonorms have been calculated after the method suggested by Parslow (1969) (Fig. 4). Such a calculation takes into account the amount of potassium incorporated in biotite, thereby reducing the amount of normative Or and presumably providing a more realistic comparison of normative Q-Ab-Or with experimental data in the "granite" system. SJc-ccCc..,.C: ccL?c:.,lcccp cc,c. ic. c :c-iaccc :1;-: 2cc,:-,cccj 22-c--cU'. /p:p cc: ptc;ccc-T:cccr c::ccccct.c-i cc -'' P :1 cc-C-S -I ci 1•:as I :;:cvccc- 'cy 1c2JIC:cC,'5 cci;: cccfl c-cc::' ILL.Ii;,6;5 Ct fClC:-cC:;f.c.Lc :;c-:cc: cc-i. ,;IC:'1'. 31.;-ccc ccCci C'PL rv,cc.,mc I:; 1CTC6ttc-:e 'CC!. —25:cc:cll c,; 'c2cp.; ..:I3_':L:CC:ci. 'ZLj cc '— I cccc,irc,Li cp'.:cc;cc: L.ttXI6 c-'2J cc' ccc-: :ca'TLt:ccaci; riS4 c; "iccic ! Icc. cc: I!TCiL p,cITC. cc-.;. CttEC PLC:,' Cp; ;C:LC:C: (IN CSLC:LCC:5 l'Lc1, cclcc c['ci A Peacock plot of analyzed specimens (Fig. 3) illustrates the alkalic or aikali—calcic nature of the Wolf River batholith. Despite the alkalic affinities of the batholith, all of the lithologic units so far recognized are peraluminous or metaluminous. However, syenite and associated nepheline syenite in the Wausau area yield isotopic ages of 1450—1500 m.y. (Van Schmus, LaBerge, and Myers, this guidebook) and may represent the peralkaline complement to the peraluminous granitic rocks of the Wolf River batholith proper. PILc.cccc cc cc:' cc-c 'cYs,ccc-rm :':f'c;1C:;';c-C'c-LcccC: c; C.:LI ccc' C C:/L,IIL1'L:ciiP'JL ci ;'--;, ;'.:: 'fltcc CC:C: C:CtcL .Jccc-'C:6L .C-1; iC:177ci1: c:L:JC: clC:;1l..iC::.Ic I 'C:CJ cc:; "IL 6F1'i:C:ciYTl ccc ;c CC.IL'i C:ii,c-,L c',;:CCL.c.=.T'\a,[T PC: Cc-c Lc'ff'Ct5 I'5.c.15 5Cc S':.L °Zji TCC:LC:UtC:915' iC2-CISL" .1c. "ccc :1:'c:ccc1J PLC: cWUCJVL"1: 51 :1:5, a/c-c' ic. Bulk chemical analyses of specimens from the eastern part of the batholith, including Wolf River quartz monzonite, Belongia granite, Peshtigo monzonite, and Hager rhyolite, feldspar porphyry, and syenite have been obtained by electron probe analysis of fused rock samples, following the method described by Gulson and Lovering (1968). From the analyses listed in Table 3, it is evident that these rocks are relatively rich in Si02 and alkalies, particularly K20, and poor in A12O3, CaO, and MgO, features shared by the Finnish rapakivi granites (Sahama, 1945). ccc'.CCP leST .Y'CC'i"CI' cci "5 I-i 'ctc-c, 2C:J'. c-C: : 'CC:CPTIcC T ( C. — I L cccc'c.'.c C H' C:'c-Cc- 'C:'.'; '"1'EIP6/ 'ci cli;'; 'c--Cc sic- LT -I LI c.'-c-Ii:-', cc; IL -.1 ' cc :ccc c.c.cc.:ccpr cc-C c-CRc-c- (c c-ac-.ac-c;cc. pc'pc'c. 2L S r,,c,.Cc-1' ccc5ct'S' :C: çc6"csc-'c 'ccci: c'c' ' ;cI PC ;!.cLT'Ccrc cctccci:' ;cn 'c-cc"; tTc: c--c 5;; 5,5 Thp 'lrI.Tc-c ti i-;":.CC: ccicl.'Lc .'C: cc 'C7"Z' 'Ci-c1'fl p-C:, C:'cTC.i LC.'CC.ilT :6;Ipr'::z'c-; C'IC:PC:']C' Ic c3?SCIC7CCS Ec'PCC:IC.1L :'ctc- : 'cc-; cc 4.rCI 'ccc ic-Cc : '.5': c-cc;.i:c si:cc ROCK CHEMISTRY From published descriptions of rock types in the Finnish rapakivi massifs (Vorma, 1971) and from examination of rapakivi specimens in the petrology collection at the University of Wisconsin, it is apparent that each of the lithologic units in the Wolf River batholith corresponds to one of the distinctive rock types recognized in the Finnish occurrences. A correlation of rock types from the two regions, based on textural, mineralogical, and chemical characteristics, is given in Table 2. The only dubious correlation is that of the Hager rhyolite and feldspar porphyry with granite porphyry and quartz porphyry dike rocks. Texturally, the correlation seems to be valid, and perhaps the only difference is a higher level of emplacement for the Hager rhyolite and feldspar porphyry compared to the rapakivi dike rocks described by Vorma. p'6,:',::: p 'ip ciTc: cc- '2,TC:c-'2c- .,''ccj ','; cci. cccccPC cc "155 "S i. cc'; :,'Irc.cc':'c'.i:c' 1."cr: - C: H; ;,L',,L,'.cm 'IC Cc- ,' C:C:U'C'STC CL2tit S ic c-c. C P':.: CC:c-? (-7 I I cc- PC cc-cc "ccc:'ClCl-ccctc c-Er c': cc " A,c:T-cP,c': cc cc p PTLC:c-Cc:C:cc'c.c"- 't cc- s. :c'i-icC:'c- ccc': pip;' C:T'1cc,-: cc-c cc .,,: :1Cl;C:2cc7- p,'c,;'"c-,l' '2 -c' 'C"l." ;c-r' c-c L'icC 6):PC57 '-;'::':c'c',, 'I'P rIct'L,.6L i'' L"c- C:'pr—c-ici; Lit. 'aciccC:",ccc;c-;XL1 I'C' icc-i I1c..J'15 :'1Cc-C i'L ,,,''.:'c'Tc-cr.,,:te '1 c',. c-.:ctc,ci cc, ',Th -c-c- 'LC,-cTCPP'C:LL' P1 ]'ci',1C I/c cci L.,:m:cp.p' L..(CiPC.: cij; PC c" cc :'c.:;L; cc-cc c':c-cIcP'C ' WE c-Cc-C ci ,?,Lc;/ pc L::6;:c6 cc, ccI-cc- C: P':tJ'ic-'i icc-lIT,' '.,5 'CIT, 'c cc :cc ,,r6Cc ccc-: lcC:c';: :rc-y -'l:: c-Si. cc; ciT ccc, : 'cc-, 1,6:1:! ,;1:CCc .. cc'c'c ic-'J L'JC:c:,:cl: Sc-c-cia ic"cc: c c-Cc' ::_SIP :LlcC:1C:c 1cc'p.r c-i' P 'ccc '.. .,c- rpcp7;:i,;i:r'p':L5c. I :7PIH HH'.i sic's; ccc-.. cci fc;:mlcic-c-c:c- ;c,ii":7:ccx: c LITHOLOGIC CORRELATION OF THE WOLF RIVER BATHOLITH AND FINNISH RAPAKIVI MASSIFS LcI'Si2C:J111L 1::C:::ici Pc-c' :cac''1 pccc.:c-'.Ic-cc :tc;G1E:.ir 5,'c-'p' c'S a Cicc cc C:-i':"lC:c.C.PL :P'i"c-UC:r CfCui 'ic-C:4 Anorthosite. Anorthosite, containing plagioclase of about An 50 composition, occurs within the batholith, where it is intruded by granite (Fig. 1 and Weis, field trip locality 7, this guidebook). Interestingly, anorthosite of similar nature is associated with Finnish rapakivi, where it is also intruded by granite. A genetic relation between anorthosite and rapakivi has been suggested by Kranck (1968), among others, but some Finnish geologists believe that the spatial association is simply fortuitous and that there is no direct genetic connection (Savolahti, 1956). c:';": CC c-cc-pp 6:flC:C:'C':cIlC'C: c-i'll. cc-'PCic c-c- ,_F.cL 1'C:. i;-cc-:ci' P cc-';ccAPc ccc , ia,C PC'cUC"l c-CC:' CT,, c—-c—— " ctwc- C:T'Ic-PH A? :ci, .ccc.:cccc ucic-ciCC; nctp'-ccP I'c- J C " 6',c 'icmL,L..-,,'_Lc_', ''.2'-. 1—c—_c, - Si ClC .1CC:;' 'p c: :cc-c,'CL"P' 4-"':"'c--''4 ,•,—. C-'1'.1 ccccc' .-— 'cc-it-C.' c-nc (..'la SCCC'ST,JC.i Ic-SIC ::.cCc;c..6I ,;12T75:1',r 5:. PJ' Lc-cc'c-/ C 'p, C:.Tc-,,cC:i'iIk. 'f;CC'i'ic''' c-c ?'-'I'CLC:;''i cc-p •" ii's 4. Lj', C: "1 . cic-'c- ' L 6/'— in 15 �16 Table 2 tC.i! Correlation units in the Wolf River with onrc: those 2ar-o:- batholith rrntr O:r'-cLrct Ui -ifof1. lithologic t.n01['J-f .' nyt+ in the i5rr9t Wiborg rapakivi massif in Finland. Et n1ri :irn Er at1i :''!tAL. Wolf River batholith '.ai Wiborg rapakivi massif cr;a•r:te Peshtigo 27&II'C' monzonite Tirilite 1Ckt2C3flI :8 Waupaca quartz monzonite 'i Wiborgite -t Wolfr River izt1'C granite ;c&-t.. and quartz monzonite Pyterlite L1i 1/rL ri: Red quartz monzonite r\ct! River porphyritic Porphyritic granite :: t-•i rrttt L•L.Z'c9 -pL1T_:;r' Belongia crsgL granite, coarse—grained lilt Even—grained granite 3Jis 7 *1Ci: biotite Belongia aririCt granite, fine—grained Porphyry aplite rg aIL1c rrqy1 ( iCrp Dike granite porphyry rr:c2asaa a .e- rocks; and quartz porphyry grL';Q ja( r.rirr' Hager rhyolite and arci feldspar Z&T.t' porphyry ac Na 1: Na20 + K20 -p Ilt 2.- I lU 52 56 - CaO -— 58 6o 2 76 Sc , wt. % Si02 Fl.gur igure 3. 3' ncco1ith River atholith cloif 1ri'nz torn Ure forhpec:iraens specimenc from the Wolf grapb ftc Peaconk Peacock graph �1 17 Table 3 Bulk Chemical Analyses 66.14 0.68 1.13 13.112 51.8 1.145 r 71.14 7, o.6i :i 0.28 iy:'- nC'": '"3: 0.20 'F'"' ".cr's -A-; 0.39 69.6 %9i 'r6.2 714.5 7 6 5 9L2. Tb2 14 5: 69.6 Si02 3 :5'; 2 1 3:-c 12.1)4 1'9°J 99° IJI -r' -Sc 1)4.33 s:. i6.6 14.18 2.53 3_I 2.29 3.72 11.29 6.31 io.8 MnO o.o6 0.03 1—" 0.02 0.02 3 0.02 ;i1F.;. 0.03 ::.-:, 0.12 MgO 0.33 0.13 c_'I'-3 0.08 :5ri3 0.18 51°11 0.37 7".:;' 0.90 1.36 CaO 1.69 0.58 0.58 L 1.111 F[ 2.39 24.07' Na20 L 1.38 3.83 3.13 3.22 11.142 CI 3.3)4 3.611 11.119 1(20 5.83 5.85 5.56 6.02 '"fl-'j ., 6.28 ..-.;3 5.111 T':° .-..i 24.35 100.21 99.09 100.03 100.31 100.9)4 100.5)4 101.0)4 1- F' c-A :4. I —- ii Cc c.w 3% Wolf River ciuartz monzonite 2 ? Belongia granite, coarse, average of four analyses 3 Belongia granite, fine, average of five analyses 14 1T Hager rhyolite 5 Hager feldspar porphyry, average of three analyses ,T'31.33II33. •c;11;'rx 6 Hager syenite, average of three analyses 7 Peshtigo monzonite (c° ci: 1 11 -- Fe as Fe203 ',o. :7 F"" Total IF — * I Total CIT 1)4.3 31 "ii A" Fe203* 11.80 ti: 111.3 991 A1203 3333) .D:3,T? 9-3 73,1: :13 J:33:3 ':.3'i.73 7,33.:F3'3J,?3 tFnL;cToca 1:7 ?32c-' :cc;,cT, CiX313 co7'Fc:i: ?17700:19 5'3ç1':f33ci OX1i9t j3 :9co±935301. •33Y.3 r3v'i,:iO; Jo LI- 3F .9 �18 Q i o--:JorL8!a fC&OAt Belongia granite -5 tatr hcres granite Wolf River granite and quartz c-rr7onlt-e monzonite and 4uartz A feldspar ris cii he • feldspar Hager ffac;-er rhyolite, raritcporphyry, n-or piriTy. and syenite / -- ii- L-— - L2 Or Figure 4. . ilivar compositions of Pull of specimens spec incas from from the ih-c Wolf boll River Bulk c-orapos;tLcns hr. bat-holith in p. Ab, lb. and Or. batholith in t-crzss terms of of mesooornotI-Vi mesonormative Q, 8ourxdarycurve c-ursafor for P11 P1 BounOary = bars shown -shon: for for 1030 hu 1000 2 comnant son. comparison. batals fist-cd (Symbols listedIn inTable Table 11) - I �; TCC -'.-"Yt( 7-it F k-CELl -'C to up determined. been have 1.5% -Ci -'-'-I Cl (CCCI 11.12 7 CC CLCtLCLILI7'fliC( of ,,LIC; '7C'.If a is 7LCiLI'ICC-C- high ITT- (CT.' VCL.C:'L,.T'CkI and to up contents -IC, -Cl) 1.8% of far, So halogens. content ILCI',LCC, River C-Il. L'21fl'C7 CL characteristic ;TCLiI, the "I 7-s77[ of C 'C-CCI.C;-I 11 C!.IITL'.t .7L1112 III '- CI A '-(1 1'-CC.i Wolf batholith from biotite feature 11 - granite. Belongia YC:.7C7.i7.lL'L t(C' .T 5 IT c"CCC-Ci-'-'C YI'LIC"C 1147 IC-' .2C.1LCC-),,'C SIC, - 71121 2(9-112(12Fe+++ 4 -.1! coarse—grained the of biotite in Al octahedral for substituting 5' LkIC'Ct.CI1l of may granite 'C to -LII due iDI1Li,1)';-;'LCL. 7.7 '74t C-Cl) be -CI'4, 7-1(220 11757 CI- 7L2100;.CICY.X1Li1LI711.IL amount larger a of varieties two the from LLL7-.L7.CT'C (CC 2,'C€'2.ii'I1OI- LLI,(ILlCi7IL.CT1Li 71; C-C,C'-I'CC',.,, 4. CC' 11511C-cC"P-&, 'C3C.Tfl,-.CI Belongia biotite of content aluminum in difference The granite. :(.7,, 7,'C2;'7i2ucL11-C-LI? C-CC- T515 C '1 octahedral CLIC.CCT& IC-C CCIII 9-7.r.CCTL'C 21'L,-'0--C fine-grained the from compared when biotite with Al, C'7,IIC 'CC7TCC1C-i "II5CC5CLIL'-CC C?-CCLICCIC I '21201111 C2.(1i1'4 CL? but 'lLCI'.Ci?I[2-? 5.121 particularly aluminum, amounts small relatively of contains ' 7711L'i. LL.TCLCL '-"I' ('7 1:20 71 5,L7:.u.t I(C 2CC-c O' "CL 7'1C-0C 'C.' CC.CCcIzi.. -'CL mineral mafic sole the is which in granite, Belongia biotite grained ,p.7f -coarse— 1111-112111? 1l)C-'C.LC ('11 '1-" '1','C'5.CCCCC - LII CCII. ' River hI'7 216 P 'CCC 'CC the by is rule to exception I TI provided this An granite. Ii '0. the '1(177. 7721.'CC Hager .I-.5.7I'(' the TIC-47 C)JL7ICL.CC IC"?, LI-CCItT:' C CCI? rhyolite, quartz Wolf and monzonite, porphyritic River CC"IC(I 7217':CICCCCCC.'5r7 LIt'IC 7?- -CC' 1.i:I1Ci'2-CJCLCCCLI7,:ICILC7I some as CLI' Red the of members granite, Belongia fine—grained the such C'C5'C-711'C7. 74 211T-1,1.LILI'C.CL- 2177117CC LYfiC 'LI ?1i.I-77'C'C'l' '((PCI! lithologies k-Camphibole—free in occurring biotite aluminous most the .-i4.'7 'C'L7'YC River 'C-C,(CC-.,! I 7(7 12 .1 -CC, followed (It CLCCCCJ C.L5I,c.C-T':t:L is 117,74? ('71 by batholith, Wolf the from biotite pattern 22Tt7 This CIII CI '-21,1? a t'-. 5(C CC'? c:L' 75. "...L'LI. 7'fC"--'- as -W't-C(C 1(1-717 'C'CCIEC C-C.yC.-C21'i, well. amphibole containing rock from biotite than aluminous CCCIII CI more a as 2"CC occurs 1127 97 iCi-"kCs 177 CCC'. CC 1'?'-'? ;C( '"1(121.1 C-711'ICUIL -C' LI-CC be to tends it rock, in mineral L'-""CI-'mafic sole the C-IC?-.(1947), -2.77, 45971.C,CC-k.i 7,Cl7CI37l-iC-'CCL previously .IL2'CC.-C'C"J As 211 biotite where Nockolds C'S, by recognized L 7Cr pis 'C'I11:LkiC,C7 per C11-CCCIC LI 2,,, CI C'CC;SL!CCLI1 CLLI'CI 'CCC' formula CI?'. C-Y"' to unit. atoms 0.5 than less amounting low, '7mT ''.LLcI'©YIICC( ,i1PCC- 7L7'lç..ICCIC-ZCC ,12ITLILZ C' LI' -CTI'7?7 in :(CCIC7,CCLTCVC '11-7 01Cr Ci Al biotite octahedral monzonite, quartz porphyritic River Red and 1-1. ('1111.7? Belongia "41'CTCTLIC(l C171t CL't 3.2 'CI' C' 12192 9CS-CCICC- the "-kkC.C-'CILL .1"CII With '114; .2 - C tI 1 with granite the IL? of exception atoms. Al 3.5 to 1TI-IL'Ci1LI2-t-1Lk2 C-c'9i1C -1.1211117. CLC7CIC cl- fine—grained CSLCIC-TC,, 2CCC'L'II.C-Lbiotite contain 1721717-'. which 7.' of pecimens most granite, Belongia ranges oxygens, 0,IC.LC117 I'IC,C7 2232' 721111 CLI. 2.35 2172117-CC 11 7 -CL to 7.uCL'CI units 1all 'V .1-4,1 1,7 '7 about the 7except from CC'211C2'LCL for 3.10 C an 11 CIII- ;'H-172121 ul uCIlLfiCC,LC The 7-C basis LCICI'C'Cl anhydrous Itl?"CI.- 'LI:.CI4'k 'CCj' on7-1217 "CCLI I?.. of 22 calculated atoms, Al of number -. (CCI (:,7,IC 71-11211 'C'ICC'7 River. ;i,9.? the 41 portion 97--. granitic and '2.1.2011,,'! granite, '12'?'CL"C7 Belongia Wolf 'CCI. of Cl CILI,177213'.LC' L-1'7C -.2:117-I ,(1C1 219-C! consistently 67 -nICIT -CCCLII being CCII-177 than U&LI7C'rLIi 'Cl-CC rhyolite, Hager the (17-51 greater for -:i 90 about -7127-f':: silica—rich '7.20 C.II'CiC'Y' CCLI. ?'7175L_12-217777most 1CC-ILthe (1.7 1i, I'I'4:Y'(1 L4CC-4 'ILITt.'t :1,1 are rocks, in highest ratios Fe—Mg expected, CuI-wC39I(C,'r 11Cit..C,.CC!i'TC7'CI° IL, values 10'.." 01-25221, ..;i'CC(C 2CI,,,)"21.,L, ';"I'II(c( As to 70.1 from ranging be might 98.6. lOOxFe/Fe+Mg of 3iLI"li'"CI with ""'.CT.-LC'CLp.Ci'7. 011.772217 1 The 'TL'I'.u,, in 71121' .77 biotite '517 siderophyllite --'37(11017 tIC -C"7, 1'',I-C,JC'iLL':C and '217 C1 i' eastonite, iron—rich, is 5.7 Fig. C'.CLIT,..10T1LL-'5L 011.731 have C CLfl'LI-iC,-"T-CC'C of 1-1151111 9i-!'f( analyses 73- terms LII ,C'I-"l phlogopite, 'ICC TILCIIIC (Il)'-[ end—member 'CC plotted H -2(1,771 been in annite, ..L(', elements L1 C'4L I'7IC:"T'C'7.I eleven 122111 '97' C1'21C4' I.C means 7"ILC1'UP by 'CC-' 12277? J1f_.LE1T 'k'3,1J. analyzed the and probe, electron the of for 01(117-CC CC -22I'I'c''CC'-?C,2', 1i-.C(1''ILCCL'CCCCC'pC 47 'i'-IC(4 , CCCI! Biotite Biotite. been have specimens representative from CCII'C'C-.7, - 2 11 C.u'CCL!LC.,:p, CC:Ck19C.C-I-3 the accessory minerals. 1!1LC'. :111 and 011772'(C"Y-' 121421177 and 777' widespread 1-CC' C7-1.'I5'-k.:-1 —' most 74??' 'CCC. LIt 'CL pyroxene. 7(7, .LCCI'.i,i Fluorite of characteristic the is 7771)207 iron—rich ''Ilk and 'i..71170u7 1IY''7-C, (CC'!.-'' C'C.C CC.C..fl.,2u74'.Li(I 112.77 biotite olivine locally, and amphibole, plagioclase, (120.1(1CC-CC- smaller .L:-:L-7 :s -:sl fl'"7'-',Q' 77- 42t -11-1.2171-1-C.;: C:'.'L7 73sodic of amounts with quartz, and feldspar alkali perthitic up made are batholith 'CI 1771 (1507 C'" 1'171'T-2111k7-1'2 7r-, 717- 7721.,I1"-L,River C&,"71 .Wolf 11-I' (IT' of predominantly the ,of Rocks , 7. (9C t MINERALOGY CCLI. 219:9771 47,7. 'C17.l C' 1120 -- -1'.7--I (Luth, to respect withj7ILII7JCI21C-: saturated 1969). (12113-1120" could -_.Cc72LEC1 magma aP in -'c;11-I'C'['CC , CIa-7CC C'C..,IC 4LCI-'I72'-i conceivably under— 'CCC7LC"ci equilibria crystal—melt reflect C1"'.7C, -'ic LCL1TIC 7'ICC-CLCnLL' [ -71C77 a '1 41C5'C LCt'7''L-- 'Cs-I- rapakivi 7121>7211.15' IffCt7lLICCCl (('4121 '1;, displacement Such granites. Finnish the by 721.771711 shared -7feature ,-: 13122120 L',,'C,1-"'-C1C'C 71.112 a1 12177.21,21 corner, Or 2194. 11,21217711: -: still 917 from TI .5-C are the toward LL'1I20.'-LL'1CCL minimum C7''I:'I.C;-C granite the displaced (1Y-c' C/-C -7-TI 1 .2,'C Hager IC 7i'Ii,C.'LlC.cLI the Ci313':'c-CC'21-'of 7C calculation '('977114(7(1!,') 310117"'.-! Belongia mesonorms, rhyolite and granite 1,5-C "[(7 CC. 4C':'CIC'(L'LLIO.LLithe 1177. in 0115-77' (''2777: despite C' C feature 7 712110515 'II of C 1174 is 112117-) i3'C IC CCI amount that, by Or normative reduction .C'.77 toward 177191117 \''7'7) IC-It)-?,, 1721CC' 'C1CC' Ab—Or II along extend 'C7'Iti the significant A join. trough thermal the "7)5771 79((15C;the I'll near '017.:-?..: granitic u'C.C,,'11-7LI, -317-k-IC- 711.-'-' '17';. '7-I7- 7.1 and minimum (Cc granite plot rocks the(1-77 for Mesonorms 1121 - , 19 �Al 20 atoms 1002 1OUx 3 90 80 •4 Hager Hay Creek Peshtigo 10 100 90 • A • AAI •A As A 80 o A A Belongia S1 A A Wolf River 10 U K2Fe5A1Si5Al3020(0H) K2Fe6Si6A12020(0H) V 80 vvV V Waupac a Red River 60 40 23 20 gA •OH K2Mg5A1Si53020(0H) (.M-SA1 1:(DH).4 KMg6Si6A10000(0EI) Figure 5. FiRure a of Cumpos'Y cf Comuosition hatholith. tTL frcn from biotite cL:River Fir the Wolf ir LL7L (Symbols listed in Table 1) �21 fr i-i-U li-U)- fli- 15Ui-1 tci ThTZti'-i-iitUp Ut ; Ti-I [-i-U)-'P Si-U -Ui- _..t Ui-ill U4 .U'LJitLU the Biotite from the Wolf River batholith is similar to that Finnish rapakivi granite in displaying high Fe—Mg ratios, relatively low Al contents, especially octahedral Al, and enrichment in halogens (Simonen and Vorma, 1969). i-C Li- i-lU f7' U)lIUi-Ui5Ufl LU U r; •Q:U)i-,i-J 5 r-: -•l i-li-C Ti- U iLiSU)cU3-SlL-U) Lii-U) i--i-2 I?*81 c)iir.a U5U)UUl)'i-U LI k-i-- I i-IHLUTtC U i-i-J-U2 )fl TtitU)i U U U)flj'.L U)I2. Lii- itLUI: t-p ioi-i- ri-i- UI -U-li-f UU)UUU U -i-I 4fl2 Li-a.., Ui-U U -i-T-U U 4€LU2:UU U2t1iUU)L 'i-U Ut i-i-i- 2rim '--rU 1 LU'ti-UL ,-LLJ i-C- S A ubiquitous textural feature exhibited by the Wolf River rocks of biotite and alkali feldspar wherever phases are in contact. Configuration of the contact suggests these two at the expense of alkali feldspar, perhaps rethat biotite has grown of intensive variables during or after crystallization, flecting a change in equilibria among alkali feldspar, biotite, with a resultant change and magnetite, as studied experimentally by Wones and Eugster (1965) and Rutherford (1969). fl 'flU li-I) 5i".'i- UUU .xU:UQ :i-j. i-U)21it\J[3L • L---.1ff5 an intimate intergrowth UU[l-i-2 is i-• I -; 4liUi-U 1U)iI t.1Ul :U): U)li-i_ Cri-IlLi[ i-riI iii- :yi- SUU( i- i-i- LUlL. i-i- -TTLi-1 1Y ir&-; 1-i-) U)Uc i-UUU:flU)U2 i-U LI: 1 U'i-i-ti i-i-i-CLkçU):U)J Ui-U)fl[U iur -U ;-tp-; ;1i.U lit I _U))L2 i-i li-U E -CTU cC-fl flfl- i-U- atcLU.I.t- 14 U)ifl'i- UTU:U€ ''L 11 1 - U)li- ii: p-i-t i-i-i-i- i-.7$v- :c p Amphibole. Electron probe determinations were made for ten elements in amphibole from eleven specimens. According to the classification proposed by Leake (1968), most of the amphibole Is a hasting— sitic hornblende, with values of Ca+Na+K ranging from 2.54 to 2.71, Si from 6.33 to 6.50, and lOOxFe/Fe+Mg+Mn from 77.3 to 93.4, calculated on an anhydrous basis of 23 oxygens. In a few samples Si values around 6.6 were obtained, indicating ferroedenitic hornblende, according to Leake's classification. Like biotite, amphibole contains appreciable amounts of halogens. —r;a L.i-U)L iiC4Ui-i- - Ui-. iI[U.i- •_' U) LCi-U1I :—, rt;: Ifl:-I-:r42 i-U) .S. ii.: •1 U a:r U I. 1. U) U)12Ur •qr[U.Ui): i—U Li- U rii- zY2 - T:L4c acITr y - -U)-1 - -U)Uç ç-- i-LU) lifihili-. :JtU) Si- li-Ui U)U)ui.U)i,U 'U IEi.[U:L: cUll—Ut t' .CflU)1r )CI; Ui-1.:.fU fl UITltl CLJçJ U) iiU -IUYUU ri. TU);UUL U)'UiLU)LU- UUrU) 1jiy2t-4- Lii- i-JU) fl-l:v :i- i-•5'j1- Ui- LU atL1i-: :2.U)ILL LtYL u1it-* U)c:cUiLUU)JU) U4UkOL1 T LcL i3t nr; For comparative purposes the analyses have been plotted in terms of atomic Ca, Fe, and Mg (Fig. 6). Amphibole from the more silica—rich rocks tend to have higher Fe—Mg ratios than that from syenite and mon— zonite. Coexisting amphibole and biotite have similar Fe—Mg ratios, but generally the Fe—Mg ratio in amphibole is slightly higher than that in biotite. :1.: 11 L :_rU -UU)rL I tiIj \_41 — T1- •L;:. 2UCLL1Lt LyU [U( L SL EE U)) i-iIi--: C.U:;Uç. ULU) r; U) 1JQZtU r 21 1tyu2T':u 1i iv- 2 ) 12 çtt:. Ii(:.3U) UT.LUL I [U)UU)IU —e r-.r - cn Ca 20 Fe 80 Mg 0 Ca [U-ti 0 U Composition of amphibole from the Wolf River ct;:- (Symbols listed in Table 1) LU J -[& L {Ct t LY'; k LUT1 u: batholith. 3Tft1: a: PUETt U 6. Ca 20 Fe 50 Mg 30 c I Figure uc Ca 50 Fe 50 Mg flhc �22 41-3'5' The (13] hastingsitic hornblende in Wolf River batholith is closely '57 the 501, ;-,-. 05(17'] i 5751'. similar in chemical composition to ferrohastingsite i'7135145: 7(17:5175 1(3 41.315155555:35. from 55/57 Finnish '4530-5353/ rapakivi 'ç',7./512t*z described :.o'/ Vorma UVL(1."', and 51,551 (1969). 415375513i1 by Simonen 301137 17 'i Olivine, Anhydrous mafic minerals. 1114 '(4-414213 4144 (317(3 clinopyroxene, [0 57(I5'5513.'OU/L I orthopyroxene, 7"/3"55:../'13 /i5775; amphibole, and biotite occur in the Peshtigo 10415117513 sos 7 '5411' (151354- '13(7 .511(1, :4135(07 monzonite 4'55 trachyandesite, 57,03 (I': and 3/15113/3 and where generally surrounded pyroxene amphibole, .3775504 olivine ':7753 51/I is 04', 5(15% .5' .13/ -'13557/415,0 by 3041375 or 35111 (1't5( hiIS 21: Electron probe analyses have only been completed pyroxene, by amphibole. 0 ci:5/43(l'(; : 75/453-[5' 345-51. 3173 13221/ 53:2.3 441310 13553 (15(0' 13'(1.53 Fa for olivine one specimen, yielding an iron—rich composition 5413 L( from 115(11 01/101, 5 T31—5(1' 5 of ,,5( L'•lk'L21• 1321:ss However, it is evident from optical properties that olivine 92.2 toi1, 92.8. 'V '27' -7. 7.30751 (17 4(s-t 'IrlO,37 4101'S/D 130410 57 iron—rich from and pyroxenes as well, will prove to be 3:/3( 'sojs-ss.17: •/k•[ other 354:.': specimens, sssur.. 57trs #n 5:3 3 (1170, '241. 545(5(1.14 when analyzed 114(1' by '5717051 probe. 5 :32 electron 4'7''," ''/51, s C 17(3 '1 '2 3 C Similar olivine from green and gray varieties of Finnish 55157:414, iron—rich 5C4(11--'13t1[l53k :(11[/ 35 (15[ 5041's 1551312155 4(2.4151(1: 41 353544 rapakivi have Simonen 513 -(1553 been 1/5(41 described S1531E (1961). 414155555' by 1 416' :3.4 s The Wolf by Alkali feldspar. 441 4 River 55541. batholith ('55557 is characterized "413 1.5J:5 çsrxs13 41 1::T-1;:4; perthitic hypersolvus S and [:5113 quartz 55 which pink, 5ft/1(A554 granite (:1113 54541 monzonite, (I5,ic3/13.s in 21c:2 3/515 of perthitic alkali feldspar predominant mineral. A variety 41 5L-/k 35 is 47 the s-s :/:4513cc5C513r-1'. js:its13ci .2- LI #;T13L' patch as textures are including sss exhibited, 2147TI41 vein, and 41 tssis:21 perthites, 415 film, qLCS2 433541 i?t1 In general, alkali feldspar in granite well 7113(1 as 41 combinations 31535 51:13 55i 5/I of 13 these. 55557 1755 :/) contains larger amounts of extensively 313125 5'11133 a331431 L4/I(V 5'. perthite and 413 more i:/133 '3515 fl5.(1çi5 developed 5:4.: 553I grid r.'t:.21 twinning does alkali feldspar monzonite. 15134141 5(541135/4 35 quartz 13t41' in /i71i21T/5I than /415.13(14 311r:riy'(AL -5 513- ' ',s5. - - '13 21 i-tI— L from only To date, feldspar ''1-l21 alkali 41 'L5 /113 has 13131 been 54135 examined 41 detail 414335 13, ttXS/ 135531(5 in Hager feldspar four units, including Belongia granite, Hager rhyolite, — 141 " 'F study of porphyry, and River granite :. 45 Wolf V s:s X-ray "2112141/ 11r/' s-41s.41 and quartz 1v-: 141:15 s• sJszC2 monzonite. and Stewart nine specimens, utilizing the method described by Wright J —1 (IL _5 4 1155. 53 feldspar (1968), reveals that the host portion of peithitic alkali 41(1 41- 21 C5oiLL 53 Th7 st;-(:yssC 51415 312fl 5' in 314 these 13241 units 53P1 consists 51551335 of 27 maximum i55(7'15( microcline AYA11321 5c with 4>:• compositions ofr Or 99 22 to that yielded values of Or 95 and (1 100, ... except for (13/ two 5:/k specimens 443 97. 7 (155(215 71!3 t35735 s21 13' T35V3..•; s' — 13 i5/ 1 '1 t 11 I tt5tft5 21 . 2© samples and Perthitic 3•-. 54.55 alkali:- feldspar 12 -S1i; was hand picked L,. 5(3 four 5Tht%t TiAS Tu5 sA:cTs from for K, Na, analyzed by means of atomic absorption spectrophotometer : "55 ;5 The and Ca. -m bulk compositions of s perthite obtained lfl this fashion are -pITASISS in Or 83, 77, 76, and 72 (Fig. 7). 3Vi 0/ 54 :t32'}3 444J ?.:1;4 sits . f4; tt5554 ir . Orthoclase, and feldspar with intermediate /55k Y (:tV alkali 212,713 2T5 A7(5751L2. microcline, rapakivi (Vorma, structural states have been described from Finnish 0' 21 3.1C355/ i12121:'.:: VJUSC::..; from the Wolf River 1971), but has not Vt 1 557 yet ILAA4 1$ 15 i55J orthoclase 55 been V353(A identified However, alkali feldspar from batholith. &_,. only the more silica—rich 1[T JV•% °5JL5 lithologic units has been date, and orthoclase, :35 2154. jtes•. examined .rr((!;:p to (1:1. ic çi5 if present, would probably ::2 occur in C7 units 55 the 51; Waupaca quartz monzonite SCCCL such as 21 (wiborgite) and Peshtigo monzonite (tirilite). (V c1n/k1fl:ri t11 Li 3i.A3 L 21. s /lIAA'( 5T.ZLk Plagioclase in Plagioclase. 57 the •54 batholith 1 is relatively sodic, ,5 .y.T:5-% i:s7fl:21 ranging in composition from sodic andesine to £. albite (Table 4), 4.5 r:iç Li as 215 Within each determined by universal stage measurements. L lithologic Iw1 i1 composition on the order of unit T 4•'r::; is a3 variation tWt.:-J/kc, in plagioclase ;irv' there L2uiytL and phenocrysts are consistently more calcic anorthite, 5 to 15 mol % 2 COAC cicvJr. Act21 Slight normal zoning of phenocrysts than 1/k associated matrix grains. :.2Tzoning has2'Ttcti7 only occurs in allr units, but rL4 oscillatory 21t :L o[1t been observed in the Red River porphyritic quartz monzonite. ;:V"CW1 — I fl ncrla t ci qiz'i I L L Cz lA: irç �' ti iTii11Zi.L7ci zoned iiii ;;:c)jirc1i4 Li -LnLzr4 '[:J4ciiLLN cores. roundedzUriU enclosing overgrowths subhedral o-c to euhedral of 1c1;rtJ 11 'I'7 consisting malacon the is Zircon 1940), others, and (Tyler, variety iiff. cJ.1Ir-çci7iJ2. ' Yi'TTTLiC also I,ccI3 is ix mineral, accessory granites. rapakivi Finnish the in common btWci 'V :VtFTi. J&cj L©Lithe c€ij in Ti tions ubiquitous most the Lqc Fluorite, batholith. River Wolf cr,'-j are I TV'' ILt apatite, rutile, iT combinavarious in present sphene and allanite, i:iiTitT? magnetite, zircon,'t Fluorite, minerals. Accessory ILL I' I I - iriti1-:T TitIt •TV. - cIs'.iii 3n'ri • ilmenite, • ijh .crc:ii ij'f - • - • i' iY'TiC4ii, rapakivi LT 21ii 7..L. texture. of development i:-- LCDi iic L L'i Li may plagioclase flCtt1('7 the in role a •:iic play by feldspar alkali replacement of ti mantles of growth IL" IT pin 1ti1Cli1 c2 TSU.L yi'2 related genetically are ii that and and perthite [i -c&L:ii2-uc ic;Tj. 'i2 rLcI':PL 1 'ir.:Iic:2 that suggests observation patch of formation This plagioclase. •1Ti with continuous rjii i niair:i: tiCi r'1ii2c mantle the to similar compositionally and optically it •2i'q!cLTL 7 •nplagioclase situation this In feldspar. is perthite 1'i1I,l1i parch the in i'1iiJC •"TitTJLi P 'L1TDDL alkali mantled of core the within occurs commonly perthitebT'LIL',i Patch • Ti•c'i ic'iitIii i-i? £L. 4L i-i' "'- --- ct--irp. I :C' iiii i:pci ciit tI'I Lint L'f:CT that Lt—ic specimen. 1.7: 115d1I2iIi in fr-iiL2LL'-I phenocrysts iTiz;i'TL:c plagioclase the of part sodic most the to corresponds 9-iii77 specimen J-'iHT77,tt .97'i'27 any L:' in YM7-composition iPtitiTci' 79a has TiTit7';iri7ii that plagioclase mantle individual 'I17? tT2TT c-cLLT1Ci t2ciiTL i: 17(7 979 ii fliclIiI but Furthermore, quartz Waupaca in 23 An about (wiborgite). monzonite t2777 in ri 7XL17Xf7I -PCi 7'a has .T 9 An TIL( plagioclase ri Ci' Li' Li granite, Belongia the about ofii 1iC7tJ.t7 composition p174.9 exaniple, 'i Lc17?kFor unit. that yn-. ; '1i ULi 7-1bulk :T1 the 7C1LJC. mantle of i-:pt chemistry reflects clase IL:lJ: " ";(? lithologic c;S14c:7 ''7'1799c117 'i2 a Within l7t' IL IcLY'9LL477C the 'i given plagio— mantle of9 composition unit 9'i:L'L79''7iT 217 1717'Y it2iT:. /7 ETi13 774 TCi ' Table in listed (Symbols y-j(;9L 1);c ?1i1 i' p17Li1' C" granite porphyry. feldspar Hager and i17Ot7 WC79 4C)Composition UiTiIi'LiL4C'9 the from nPcDtej feldspar of BelongiaiL', 14 — Or -' • 'c • • •: - Figure 1. ' • Ab 23 �24 Table plagioclase from the Composition Coepoiition otofpi.agiocJ aee .Cooii the 1$ Wolf River Rrvoo batholith • -. iThcC ielc:oi.r P°l°WW i .-—-• = =_ - - - j E.oiIetdt9 3e-J.oo1oI1&. - =--•=-r••••= — — T:T'.l = .LdOt}cJ P•:loer ra,mto 1uoI1. çrot?1 IrDroo.,Io = - jFzt_ttJfl 1j Ij = = I L 0 10 30 20 )ThL rnol % •R•:riT. i±oro ?orpIh..vrLh14 Or:tIThflTO 40 Anorthite or larto graln tetrtt gfl1O Phenocrysts -oiemoero1:e or large grains Matrix grains 4 �:33114 .191' 1. 113113 :1,1c:,tL.:1111 111 131114 773.1-31 31 2.21437, 33J, 'in 1171' 1313;.: 13..$1133.9: cI7111.4, '1471 :141147.313351 155 u7--T17 71 311- 131 c31311414;lc 053.1721173:33'.- -17- 147112.3:14 1111111 14.137- :1133371317-7-353,3 2. A foliated, gradational zone about six inches thick occurs between the Hager rhyolite and feldspar porphyry. The feldspar porphyry is believed to represent a border phase of the rhyolite. 3. Dikes of Red River porphyritic quartz monzonite intrude the Wolf River quartz monzinite at several localities along the Wolf River. 4. The contact between the Wolf River quartz monzonite and Belongia granite is inferred to be gradational, because of the change in lithologic and mineralogic character displayed by the Wolf River quartz monzonite in proximity to the Belongia granite, as summarized previously. :0:3f3 32373 7 4113: tT21 2141.1211111 '11 1T1113-;'l: 31,li%1'JC5 13314 ff: 7-111 14331 1114'. :., 11 2313111 2:ThtrvlIl21l; 111 1 14117- 2111 07 111413-21141113 13 12211-171i1 3111L%;.21141 17','1131113 721 1111137-117227. 3.311112113 121 11::7c3311::6:ar T21-1313 313.1 0111L'0'2 14l,11131113 11 7-121 Ilt.131 l 41 ,L I: 121.31 :1t7 14:1' '131151: 4'15l9 11-31 14 ::14'.13721.: 1314 in 3;. 7-2212-1733 13,cll':i111 .-cin7- 72133111; :1911113313 1:11-7-3111 1117- -Lin- 71 7-' 1T. 31(4 3117 5.3113-1433) 132-143,1131 311-11L'71 111? 2'l '11 17-215313; T143T1: 12111111:1,124 '1: 7-14. 27-' :1:.%331323 cIt 3147-115 1414-l31lj 31 7121114141321 CC 1114 -lt*3(313;147 114:;:;t11. I,11& 247 c-23'7-L .317-371 23-4 1313 :312351 71.11 114.11143715 çç7-1 1:131733: 133 24 11-131:1:17- Peshtigo monzonite and trachyandesite have been intruded by dikes of Belongia granite at High Falls reservoir on the Peshtigo River and on the Oconto River near Mountain. cr;: 17 213:. 17137- -c112.711"1:lI 311; 1-::1:1113:14 :1:17-: Internal contacts of the batholith. Contacts between different lithologic units within the batholith have been found so far in only a few places, with the following relations: 514 1211 3-13371 511 22.21 31 '3111-114:; 113113 4112:-) '111111T747-'1117 .C:i'1V731141 3114, 1-33-13.2131157-211 211133.71131 ii' ,l 31 1 71:4 14:3:7-11: 3)11311 14Ll21:21: 11 7 -1:1451:3 p111c314Ii !114 '7-33l4C-247-- .tl2A1%_1l:1111434,331:r:. The second feature of importance is found at the northeastern end of the batholith, where the Belongia granite, Hager rhyolite, Hager feldspar porphyry, and Peshtigo monzonite are arranged in an arcuate pattern, perhaps reflecting their emplacement in a ring complex. Such an interpretation is supported by the distinctly por— phyritic textures and high—level characteristics of the lithologic units involved. In addition, metasedimentary rocks that occur in the postulated ring complex dip steeply and have strikes that are concordant to the arcuate arrangement of the enclosing igneous rocks. (Ring structures occurring in rocks of similar age occur in the Wausau area, N LaBerge and-Myers, this guidebook.) - _ 1 3311 5 133 2111c 21.7-. 11 1-c.31C0 p213 1147311.3111 1111. 113157-' s. inii 21 7:33 111411. 1141111 2*:2i7-.11r1437 3;3133311.1'311'3 '131111211 141,1233 : 31-7 117;:tl%-:33 43173 :21 2. 33143:' 33114111214-1' 25137.133' 2331 'Cl,clL1: y11c1T1.#c51rb-:1 721- 43-'11'': :7-: 'r :11:1211: .;-2111'13133:1331a1 112-: 11-33112i 1414 3; 11 1:.t1;14%112'J 111:31521 1(7-,.73,1117 C1413% 77- ''11:1113,3131n 1121 73 :11: 33:; L3 ..1'33'&43 7- 6314331' 7-913 21331341311,. 91432142 0-7110 .13:-i31 11:c:7115141131 J1414-7-33 112 1731; ' 3111111117-.: '11 'cii 41'1u1421'cIci1s ' 13,3373.213 1111:321:14 4 S'1:1:31: 7-311 1111-c',3$:13 41'l : r1r1n713:cj2.21z1131o 7'f"'l31r: 13; 7141311 3 73,212113 :3:-' -311111 17124:1114 l 1414113112; 127 1r::11)31,2, .3131') : 13 31; 7321114 173214 411333 114733,1314 1'.71- 17 13C.:'1-11 34 221111.11; 3737-1117213 214 2-1314 41731:12 141 1314.427- 1131131537 7133!.'131 2113111)511 14441111131414 :7-11:1:; 3123', .111723113 433'1J1!L33: 111 31,7 ,C17111'3. '77-4-141 ,141.31413', 121 321'1'137- 54111117111 ':3117-rI-Ic' 11417 137-3111111 1131:'113;1114 1214 7-3133141113317 1:1s:'t 113211 1': 1 14172 .71:13117 7-1151 . '313j% a.T13121' 1'373 212 14111311111 P*1 '$131111414 tIlt II, in 1131,k'117t I 1u211317-133'7-,L3 31"7 4;,311.ff.1'3;L :47- 7; 1131 _12412111 14-14L311 -371i3121 37 :-'lljl 41i3 331347 4131175'7"l37 4." 1111I1,.1 132113 '11413233231 322 33,13 11.11" Although structural studies of the batholith are still in progress, In two major features are readily apparent from the map (Fig. 1). the south—central portion of the batholith, the distribution of the Waupaca, Red River, and Wolf River quartz monzonites defines a major ENE trend that was previously recognized on a more local scale by Borst (1958). The contact between gneiss and Waupaca quartz monzonite probably represents the southern margin of the batholith. 1 .144:15111-53111. 1,c3::. ::( ::' sIll -12 _'&11 14 3-31 14117 14 2311 c—, ,&31 '17 r 113147- '1 1 " '113 1 '77 i11'5L147. 1121lC7-.'1,11-'331"t' 3313,' lf%-:rl,©1r, ; ,' 7-24221-2 .51411 3;':' Many of the granitic rocks in the batholith are Structure. massive, but within some units, in dikes, and near contacts, feldspar phcnocrysts may have a planar or linear orientation, presumably due Shearing is confined to well defined zones along to magmatic flow. Some of this the eastern and western borders of the batholith. emplacement of shearing may be related to the batholith, but some may be later than, and unrelated to, emplacement of the batholith (LaBerge, field trip locality 8, this guidebook). 11t13217-1374137 14;1 312-23:135333 '31,17-3r;37; '437 111'7, 'F;.,;, 314:213313 321: t'%'7-711117- "11 5151113 .14213 1331 73121713 31111-7 'c'- :113tT,) —$ LH11.34 3312 13312 37147314113 15:31 5:721-41411137 13 111 :12375 742 14 -32: . 31143 '.1311111": 11 31:111131*31111 07 5114.11113.lI113111414J21 33111 31r12115 :14:;; 7114 3111343 1.11.1 117,1 .1 r33.1.1t...23 31:; 2.112%:. 133' 12Cr,: 53' 31213,.: 32311 111 141:3191111I:111 11111111 44 11117-1137114 21' 11)51711 7-7137131:11111. 111.323-1 ''i'11 113,:53.3111:'.. 3313 -33-14;: 174311114' 111113 14 7,141:c7, 711'433311 '3' .7. :1:131116 L111'T131411-31 '?l51i'11l1114'3.in1 c.:1c1:, 14113111,231: 3113113 - 11317-17-1 .3:1: '1:1 31141s317'll 7 '1541113 14411 111 STRUCTURE AND CONTACT RELATIONS OF THE BATI-{OLITH 711,71 17, :7-171.1 1113 31747-11111737- ,1741 '077 3J1 l31tTl'7- III1I 111 37: 25 cia �26 ocarI o 070t2 of Lt bab- J! tio m::rL1.i,et: pt of In the northeastern part of External contacts of the batholith. ::.c Lcowl a the Belongia coo ac:0 a±cr•t several well exposed contacts where tioa :ttJ 0 .00 afoot a are the there 0 t batholith tLtkLc. U1t- tLOtOO.OtX0000 metasedimen—OO0 09L2 2'; and 0 LU0Z ptoP 7200 intrude metavolcanic granite and porphyry coo Hager feldspar to 2 1o!flal;1; act ri):-' sharp and discordant, and In all cases the contacts are tary rocks. 000t'0'0000 present in the intrusive rocks. ot oc3anCc1o chilled oar0ta margins are commonly 7t000ff't cotlttO : 0.11 oa iJ : fl :ia fotrof ca rco 010.0 00. the assemblages, much of &c 0 L'0rl0 WOO, basis0± oftEa000Ot textures and mineral 'o1.00o ocoka cat ha intrusion of the granitic rocks can be CO tjo ft rW 'rI 'o tooof bya contact metamorphism induced o-c,tatt totorcoçO :'f too iftiacotacy However, the discovery of 012:01 footca -. facies. fob :01-i hornblende WC coolo ltoot',i: assigned hornfelS to' the f000ti to ;a.bcLOt00 201 1.0=2010001 cto -oct o assemblage, quartz_biOtite_mUsC0vitePota5 .bbo co01t1 the lcTos;'WOtlf apparently stable tOo 0001 ;:ota2Jat410'L;;,0 rock pelitic a; specimen 01 aco'onof of ;a L 0200 metasedimentary feldspar_afldalUsite, in a folIo-pat •cLJ oootC La 0010 01W-. have been the pyroxene hornfels facies may of flo ooo.u;002sO 010it:0' .co-.oo O07 suggestsfathat conditions 0.77010 foot .o.o'01It f.o:a of roT at 07007 r:.;r Ic tO-a •ocoi'Occ 0 in the contact Scapolite to ,:cf: :; 01 is relatively abundant f cro]'L. attained 01. locally. 7114 i-ccbatholith. Ltfocf ttI; 2W the 0:; I.:oo'000,1%010102W:;at:tr-0 of metamorphic rocks,21012W attesting the halogen—rich nature t tCC00, a-ac to 0.0010: On the fiLo Co 1 2 CONCLUS IONS of cotta cot 0 oafaIltat000 been fo to point out1;the existence of toot oat till paper The7';.i purpose of this has Loot 7t ct 00201t0 tic and to describe its Woo: '0.0 zn:1 northeastern :02LI10Lmassif 701 :.:Lincart OFt4 01W- WisconSin , a major rapakivi c ;aojo-r 2W Ot 001711 o01o-7rI o in It seems appropriate, 101 characteristics. crcrcI.o?tZ ;-ofmineralOgic iLt 000ta.0200 petrologic and ffn batho— hypothesis for the origin of this 100 fLo 001 Carl of r2.cifaC-0'± i-- offer -141401NJ 01' conclusion, to o±'tr- aa working :1cn.cl aol ct: frfuture 2Woo studies. c';tai i to, direction of too-loot tO 0712W too tOo lith and to outline the blob Ci I must talCi take 7 r7' t-atLo'I I ;t coot of 0017 the Wolf batholith of 'oi.I River too- scheme 14-iY01W; Oc 0origin cot: Any forIcrthe features: 11170 'cc LC11/ into accounttOo the toOl following !. 1) 1) 2) bulk c.: of 'L 7-Abc constitute the 01,1 granite f 010Ci1 0010 05t:: 1 ocota 11' 1200-00 ,0 and hypersolvUS monzonite oct quartz the batholith, in0027102W nature, 7. c!'ZCP-IL ot 10 epizonal the batholith is io :oo,1vobtti; a'•ooa tOO batholith the tOo ta:Tho) ' oft plot itt-ct near ;!!rto. of oti the granitiC members otOfl7t a,:ft A the compositions of 00000 displaced 01 normative . 4:Q—Ab--Or, =001o1- but tot toO are Ic, terms too: a of granite minimum in t-a;ott•o o!oLo!L!lilr .0,0020 7-c toward Or, :0111 0 t'ob-t7fli feldspar by cI' alkali andratreplacement to 002202 of fcc::- to is -cct0'-011. 25- 012 c;,00c of. there extensive mantling 'P.', oligoclase, aflbote to -clILIfot 000. composition from albite to It ooocol01050I0 plagioclase 017,01200 ranging in respect 02W010t oa_with :2 -7; talc o:t to to be interstitial :ik.ill020 00010)100hydrous tend to co 001010012 mafic 177,t-tc minerals IL! quartz and feldspar, and on fo1tIo0Y 007012003 of Ltz:0 biotite ;' I cthe expense O1717'AP growth noCiCi -A .11 at Oil act.a:0101 apparent late-stage there Ut:---: is to rn-i of alkali OOILO17LIO feldspar. oil. ' 3) 4) -fl ,fl 5) P 6) t'rocoriginated from laothcJ,Of:2 may coo hoc: Wolf?:t River havecooL1oL0-lC1 or '7c'o cOt batholith ±00 oogo.ot that tcti'f the We suggest H20, initially undersaturated with :n çMtc ct0.0 0-C parent jJOi'tct magma, 01101 monzonitiC a 0 pquartz taboO 0 crustal material. .1700,12170 700=-0 i.atcaig 0117-octalpartial melting of00pre_existiflg -70l derived :'AOSd 00 .21t that was by J0L'."I1OLJ. batholith precludes I (87Sr/86Sr)0 in the 01 1002 An average of 0.705 for 0100 value Cii origin 00 000 1 0 i20tat.i 1410 with an crust but is compatible lOt :lcI1tlt 5 01, from focat older r hO 70 lOiittl,C 0' derivation granitiC ott: 50.071012 :':-OcOJOi volcanic and plutonic * atatmood° basic 0701 and intermediate lifor: .Ci,O.t!: (10 0001-0 )77 older from an terrain of 01001 --i't For example, partial Nil' eo0J-c. ±:folotllIfl. northeastern Wisconsin. 110010. 00aa in It ;1.Ot000000717'O material, as09that :oat01. 01 such 1090071 101140 (mean 020-0 granite or :7'10!L0t) Hoskin Lake 2,tLhc,000170Lc co,ast-zmonzonite 0110 -01 10 01 melting of Athelstane quartz trIo IJI cci. LII). years 141110 ,, million rIit a c:oA 10, (87Sr/SGSr)0, 0.7021) after a period of 350 , ,01" 0 Rb/Sr, 2.5; 55, ftC. ratio of 'OtCf.r 001701 of 0.714. strontium 01!.initial tot I 01 0,0-otti .710 isotope :11 07 an would produce aa :7112 rock with nIl 7 pt-cl'017' oh-ct oortaltt an abunMo northeastern 'ocotfcae$°' Wisconsin!, contains c'ao-::aiia in 'to: terrain However, the toto older fb-o'o-000T1, chemically equivalent oI-::amtsooi :01701 17th. intermediate volcanic rocks and dance of -c-I basic La boo tocO.0'lr0k'5.CL000 0100- tcfit material would 01015 tx'IlCta 00-0 'i'col .1 be of :2W,'o Rb/Sr for b-c this crustal 0101values 01200 os: plutonic rocks, 01010 00 and o'tcro f and Ot!0OI0 others, 1970). 01171 ETC.Oc 01C'I I Hart, and 1967; c.'.'21020: 00.11 others, ACt-0 17fl0fl 'jless :C than tOol 2.5t (Peterman, OIL: 77 much irtta2.Hy oa1t1J.'i toat I'll 3 ,i I I - 1702, �27 i the mean value of Rb/Sr were 0.6 or less in such crustal material, partial fusion after a period of 350 million years would yield a rock with an initial strontium isotope ratio like that in the Wolf River j .4c. icc I[ L1 ctr ccl I L-tn ic IL cc1 I N L. I cc' Ii Il') ci I 1111 1 1y '' cccc flycSc r cccc 1 I batholith. c" Lh1 If nYc cc. Future investigation of the Wolf River batholith will include: 'LCcIP.2Fc c1cS1cc ccc O©_LJ1L=iccc cic7IccnLIr -r9 F) Wc1. ccZcc4cc additional mineralogical studies that should enable us to evaluate intensive parameters, such as T, Total' H20 O2 TNcEcicccTcpcc lI -- 1j In cc1 F, and tc.n-iccFcIcL-cc and detailed chemical studies of major, minor, and trace element contents in the batholith that should provide constraints on the mode of origin of this rapakivi massif. ;cci;c;iT1zi yi iic -c *cLcr cccL-- ccjl cYtc icicc cci cIcccc1 ccc i:q,: cc 4iJfliL 1ELI c'7qI' cP4©IF: cj j:-crc2 Lc1cLc 2) Lptccc 1) �28 REFERENCES of Big Falls, ':-pc:c9.c. cC W7 Ccl 2424.1958, 12 The Granites Borst, R.I., !lm/.c,,2 9.7 4Wisconsin, •lcLc Madison. Univ. Wisconsin: 12,2. Thesis, M.S. :) 24. Wisconsin: 21cm granites of from the :2 c14c4w' -cm-22 ".2. ir242c2 Elders, \V.A., 1968, Mantled feldapars 24 .c 11 cmLc:::: 2-i 37—49. 2c2- V.- 76, p. Jour. Geol., -. ,1'.c-citccPtIL'$ of :4 perthite, p. 55—70 in c-:L. :24cc.) 7: significance 12.4. 1953, Petrogenic 2iCi] R.M., Gates, cl plagioclase: c.cm42'cHcrelationships re ccm2L. cc-; of 2c1.cc:i[ ppetrogenic .241-; Selected :r-nLcmcm (ed.) R.C. Emmons 20... ?9'2l 52. dC :ciirr0 Mem. Geol. Soc. Ccc Amer. - "• dL'AElectron .c,2:t.c', 2;; -cd: ij,ctc-: using the ,E-cm-L analysis J.F., iccmcmr.1..cS Qi21968, .24. Rock Gulson, B.L. and Lovering, LJ 2)i27 C2 cm p. 119—122. Geochim. et Cosmochim. Acta, v. 32, >22121:2:" Probe: 2. a volcanic rocks: ccm2cmcmcmcULcrC.'c2Cc:2r 'cct an modern .24'::;4 1970, cl:2- 2:Ancient cm-C. others, Hart, S.R., 52 and Lett., v. 10, p. 17—28. Earti. Plan. Sc trace element model: .:..:j2I:Lt(1y4.'24 .c.:flcwi.!cJ-r >2.7cJ..;1.- c lower I ccc' -2:24 :ccIcm-d AnorthositeS and magmas from the ;'-5. rapakivi, :124. H'C5 Kranck, E.H., 1968, k:'uct2'c72'.9d Rcc..'.:dc:. :244.7 Origin of anorthosite and 7cccmcccc (ed.) '7244 Isachsen crust, p. 93—98 :1:': inY.W. 18. C':--C i24c -l12c Univ. State New York, Mem. 11: cm .fl.,i;; cC :ncy.r:ccd.t: cc:2cc related rocks: and subcalciieroUS ccm:cm 224, .i'cm;:). calciferoUS cc of analyzed cm dcit2I'i cC Leake, B.E.,,lc:2?. 1968, A2. catalog c22;'d, Paper 98. Geol. Soc. Amer., Spec. Ccci, C..c..'t'r-. amphiboles... tR:i - 2. iidc.'\i = Si02 to NaAlSi3O8 — Si02 and KA1S13O8 —.24224 .. 'it> systems Luth, -c,. 1*22). 1969, The ..LniC, W.C., cc betweenc H2O content, p1-120, and Tota1 ' 9 t1' the relationship 20 kb and 267—A, p. 325—341. 12227 ,24'; Amer. Jour. Sci., v. in granitic magmas: '' L ).21-'' .' [ - .-,i-cc'c:cCLcomposition ccm,-:c,24tic'c and ccC >c2cccz chemical relation 241'cL•c:-. between 2-cm Nockolds, S.R., 1947, The Amer. Jour. igneous rocks: !:-244r221 cuiT:1 cI r4dL2lLkiLC2'c :: the biotite micas of '12922 in paragefleSiS c--'. 242,c., 2422, p. 401—420. -. 245, Sci., v. 224 ;u24c, 24':-24,1y Mineral. 12 Mag., cc :2.t7' 'cmiTanalyses: mJ.24cm ccc.crcm'1' c; of granitic rock '2:224 Mesonorms Parsiow, ';y>2-di"- G.R., 1969, 2. 22). 37, p. 262—269. c24-2424 v. . ].'C' >2:19 eugeosynclinal Li some 5::>'>I: -: ratios in ...]:2447', 87Sr/86Sr .2,'2i'9 1967, 2 Peterman, and others, 24±; )i9iy' Z.E., 22::'::magma 24cc dc)". cd bearing on the origin of granitic tac ic Ccc'.: 424 cr24.> and iriS their sedimentary 92CiJ'P3i].2.24 rocks . : 4.21 2; 2, p. 433—439. 2-cm24 Lett., V. '4o ccc' 2-Plan. 24:, Sc 24 rcmicc iCc belts: ':cmtc - Earth in 24. orogenic ., lIlt.". . iron biotite — ,cccmcmc2cmc'7,J1> determination of'>d2 c;2) Rutherford, M.S., 1969, An experimental 2 L, 10, 1:,,.:,. p. 381—408. cccmcmcm.449 Jour. Petrology, V. equilibria: -jC-241feldspar icm±:1;,c'''rhi:lcJ;"' alkali t'r,::24'124 4* 'cr22 its -9L'U'I'.7-1- rapakivi the chemistry of the east Fennoscafldian Cc ±2cc d%2:c!:C'7 24 ?:"'d On Sahama, T.G., 1945, 2424 136, p. 15—67. J1'.2,.'L22d. v. c;c":i Finlande, 24472, comm. ccrcm geol. >; ciC24c: Bull. graniteS 'ill,, .. Savolahti, Icr ci.'::'':l, A., Finlande, , 211'.,L ccl:. 2cm Finland: AhvenistO massif Cc: 24 :c'dtcrd ;ccc 24.' in 1214 The 1956, 114, p. 1—96. v. c 174, from rapakiVi :2cc I'cmc:224;' :7: CL Simonen, A., 1961, Olivine 2-I SN. .26. p. 371—376. v. 196, 2424 Bull. :.c"ir, geol. FcC , comm. ' FcrCHcC22 2411. •c2c,' -. Finlande, Bull. comm. ccc" geol. I �29 I 'J >? c and Vorma, A., 1969, Amphibole and biotite from rapakivi: Bull. comm. geol. Finlande, v. 238, p. 1—28. cL lEE Simorten, A., cL - c C,.71)ClfrTVEE5r 07 11) 1 ¶-c,c5 cwLc3 rTr. 1971, Alkali feldspars of the Wiborg rapakivi massif in southeastern Finland: Bull. comm. geol. Finlande, v. 246, LC::1).çY.I2., LlCC I)2t:) cdwf:L !J5LLLC7 caE: I II 1—72. 1flL '1): l_I ©ICLL p. cC7I7CCEEE L.tC[tcd5IC Vorma, A., Wones, D.R., and Eugster, H.P., 1965, Stability of biotite: Amer. Mineral., v. 50, experiment, theory, and application: 1228—1272. p. I 7)EEI diTcl.AlJ1l CilCt51)cL CLIEC d•dSl1)LCdi C CcC 1i 1Ih' I &tEEEi;IEEIk'EL I L?1) C? 7 3T57d cdi Wright, T.L.,, and Stewart, D.B., 1968, X—ray and optical study of alkali feldspar: Amer. Mineral., v. 53, p. 38—87. 51) LJiCcst rtld:;ditl 713: lJIlTl-l C 77&;J=d c,C, Cc-r.1: .1 . c1 C .cc c• L7CllC;C.1)liJ :cT df 13f0 �This page intentionally left blank �51'4.i?'71 11113132.33 >'1"" >, LI? 3fl 331 24.141111 •1'1c University of WiSCOflsln—Oshkosh University of Wisconsin—Eu Claire 1,,' '•,•i2.:327'7 324.3 of Geology, of Geology, 4121733123 377.12113131 /:. 13>33- '1 131 111)51 .17%:T :3::: Department Department '3' 23 11411201111: * 23411321113 0311 3313111413 ** Some of these problems are included as stops on this field trip. Tentative interpretations of the geology of some of these areas are presented below. However, we emphasize that the interpretations are based almost entirely on field relations, with little petrographic work, and almost no chemical or isotopic studies. Therefore, the interpretations presented here may be subject to change as additional field and laboratory studies are completed. 12143 3.'- .2'12121 4-1241 'C 111>1 133n2 4. 7151> '51,1> "1341S3 '35" :131312L .1313'' 313 (337113 133: 7,21031332733, 1132 1110102,3 14-271 ' 51-13121. 3.3" >11.14 7. (3.1 132.1711:12::: - 31 1 7.1'53 , :-n), ,'l lilt' 7.323; • 0:3:731143 773773231 37 1131 121371.73311' 7>1,2111(13' 7'1T3 '2./Cit1S''?-). 143:: 34' 117 13371233 4.113134.8 79711313 2111174-2 71 rI' 13 37.: 17713171:51 "1' 7:13 73151317135 '-1%. '1212.. 11321273. 7121273372 >' 322' 3-33.212 '3 4-'341'21j11'SL. 1211) '.591'11)732 ' 3174 '21133512121 31317 132fl33"23411 51.;'171h1.'34., 3212 172711o,21) 71217"4L ,s7 '3-13310 111111 327733127 11 42'lll32l3i'1167, .1711 "377. '31.33) '717.21: (.1%413I'711 '4 1711 '..'11,.311% 3131111 117.5 '1512117 3714; (33131'3 ',1414 133732131 41<73:; 31'31,'4313'< '251" i>7.1L71j11 16.11377 7.141 -4-1', 73314 7.721 1130 451:111.1 "11132 41211171 In 1969 the W.G.N.H.S. initiated a program of regional mapping of Approxithe Precambrian in Marathon County at a scale of 1:24,000. mately twelve minute quadrangles (about half of Marathon County) have been mapped to date. Progress reports and data maps of this work have been placed on open file by the Survey (LaBerge 1969, 1971, This field work has provided much new LaBerge and Myers 1972, 1973). data and has identified a number of problems in the area. >3>31323 1)723, 2)23)2.. 1:0 115153 1131371 '(13212273 33273312,1251 310 .33,3113,317323 732cc1J:'.': .51 i351"7',4'3) (1)" "'7.223 7 4-lfl 1'- 3, '<7121334 71,,.33131,:i 5x31%''15557f 711 333f32733<j33'17 E:3211112 :'1., '771)3312 135133175::Y 1121's17'13737(1 3122 1111:17.2, 17351772,,I713 7>7313 ;r 13 11313 77111,) 1113 '1113 33 '33251 m3 '31. ' 4i)027211Yi 1131331 2 7:73 ,i( C'23312 7 ln%2511'12':1'17. ("32. [: 1) (6<3,7 313211)33711712713' 1131 1211)7 The only comprehensive account of the regional geology of north central Wisconsin, including Marathon County was published by Weidman He recognized many of the major aspects of the geology, although (1907). his work was mainly reconnaissance in nature. The geology of the Wausau—Wisconsin Rapids area was examined in 1917 to 1921 as part of a land classification survey of the Wisconsin Geological and Natural History Survey (W.G.N.H.S.). These data are on file in Madison. An unpublished W.G.N.H.S. report by Enunons and Snyder (1944), and geo— physical studies by Vickers (1956), Allingham and Bates (1961) and Henderson, Tyson, and Page (1963) cover parts of Marathon County. Selected aspects of the geology in cntral Wisconsin were presented as the topics for field trips by Emmons (1953), LaBerge and Weis (1968) Theses prepared at the 13W—Madison and and Weis and LaBerge (1969). at 13W—Milwaukee have also dealt with certain aspects of the geology. Recent cooperative work by the U.S.G.S. and the W.G.N.H.S. to compile the geological and geophysical data on the Precambrian of Wisconsin was published by Dutton and Bradley (1970), and Dutton (1971) showed some volcanic—sedimentary belts and sulfide occurrences in Wisconsin. 1', :133211211132 112111517112 113 '.•4.l1[' 32714711' '1 .,acl '2313 13'l 31, 342123271 1P "7111L'311'1:31 "32cl. '.3 172.74 :71321) 1: 2:1"47'±5 117711 7 42t513° :1131 1.2 :' 34113: '1, 51'13'31, 71'3, L .1-141 37712 71')> 21,34',13" 713::, 31331773i '4, C 'o337- 1') i>321 2)21-' 1 74513311127 1y: 13111 >151 51:313 1 13144- ''23173.3.111711.7< 3323,131< '4 42 33123 132318 14,7: '331'3',3113'l1 4151':,1231'43.1113. ''17'4514' 13. 117.11011932 3322313104.33, ,3,,7734j(',7 Los.113.'7 .33:3371;3'3331$2371 321T :i,33,431$ .3. 3. 12:1:'. 7331131 p 1)3)3' 131>713 '33 1-'<' :1333 '213 .1)11' 77: '17.311>1): 3('312327'4 i1T' 3112111125 773 :4183 771'? 111232 233133 171.7 ±1:4 1 '4143231 14.3131 .127L1 '14 .31733'125 '71:7141s1323232 7'42113133rlhc4 23313 '3$(-' 1113231151 £311. 02'' 4.: :4. 32114$: 2.13: "L74r::r:cc'l.slIl,.''t 1.1'111'132 7)47 23113' 132 113 71132 51'1'7';,3315 >74 313332 17' '32132' 31111.7 13I1,.:''",15111123.± :I7s11c'1'E: 4)13, 3>4733 J' .1 6"3321325'4 3213'I'3(3 32'51: '133711 12.2"11 821.534 ,-,3211,11111,J ,31.•3'3314 9.1$: 711 317321313.331 3)5 I332'.13'I3lfl 2'31; 3113:3 1333 '"'1 ,,311LI1 I ';Q'33 32333213' ''1jI1It 332 71(3' 'i';,,'4 113 ';73 11:1513123 ' 13 .32 '.'7:2s37 1)1:3'l7',1$.771: —733 13.3 13'T3'1121,$ • 1$ 13713311171'323g331'l'4611517 311 '1±SLII4LI$21 14 3711.11137:32' .1370133 32:11472132 3'113 11313733. 372 .J32Jc '3312±" 3.32 - 4732313:13 1 S'co':r31i 37332 117 3'.L.127% $31351111 3'43: 41 32i"'., 4.1313711130)1.73 (13 733111111'3'3 '"tI 2'332.'71'.'l'L '%:3'"8 '1.11/' 3:313321131741 1) ,'.',119L'73113'314 117121 '1C".3333 1.1: 13" 11113(1119 33:7 ill 37) £':: 71 -- 4131:3.4-753. <10724. 121, i21231272s'1l :121::7'::c.13. "3 3273113,,7$'37 3241132 321111 '7'>(4 3013311.11 .n-62:o'c:vp' 1331-li The Wisconsin River Valley in central Wisconsin constitutes the southernmost extent of the continuously exposed Canadian Shield. Available radiometric ages indicate that these rocks are mainly of late Middle Precambrian age (Dutton and Bradley, 1970, and Van Schmus, this guidebook), yet the character of these rocks, their relationship to one another and to Precambrian rocks of other parts of the Lake Superior region has been largely unknown. '1J',,'1)7"1:3710: 52611 7:114 337 13'l 717 122(4' 33721111117174)3 311331 '333. '11112 43 14131:13 32i41712u3 72"< 327' 1:'1T4717 )'711',, 1:13111532-3334 :21230232 3111 24 323234 733') 341121- 31(30 3: 1377771.33 3312';'3' 33' 13 .l1121113321247 (1-2'$. 421-st ' :.11:%1s143113111"13 'I 134: '17131' '1331 31711) 11713111232; —>321) 31117343)12(11.2.32 11 1[11'7'; '.'4 .311121 '172321: 71313, 21151"'37I111 '131"" 7'3,<'.':2311)1:1)1323 '1" 4 '14.12/271 - 32307221' 3(33'7'251"% 2'3(32331113131151111 7721'; 4"112Th'7t 311434' 41' 11' 31'1773'34. 134227:7-1331 7>7133':14'44-,c13t113 '11214 137 3 ".7122313 '2'1'11171'211oT1371'1 32'51';5 :713111311:4131 13?:,.:, '74.33 7)1: 311,3 INTRODUCT I ON 513121331.111 Ill' Gene LaBerge* and Paul E. Myers** [7.123 7,324.211311723 751'5 11711' by 341321" PRECAMBRIAN GEOLOGY OF MARATHON COUNTY 131131'.41, M7113.;31i11'.13..'131,1 711 31 �32 General Geology .ici:' dfl!, River ifl Wolf 'fl'Y granite Q the ci;ii 'Cciatflt TLcci The Wausau region in Marathon County west of ciici1 Thi. ci.cc3. and c1 Tbv flcifltThS11%t .;:d kci4 pfl;fl:twccrc batholith is characterized by a.t. northeast—trending patchwork cci of folded hn :•a been flEfla intruded cci: cicii which have flE tc. felsic volcanic block rocks tid (?) maficci. to bjiflcflci faulted Ji ci tI cifltLfl •.c.fl.Ec events. aj:i1 deformational )fii3citfl and :cces]IflTh plutonic and :ccJ1 mylonitized during succeeding 1 iciZflL ci tJh ciciri (1) gabbro— -jC.,::Ycici generalized sequence: :i:flLfl.: The plutonic rocks were intruded in the Tkci p 'o.ci1: Li cy: i t.?'• .iwtc tti•ci i (3) quartz monzonite, flul.LCr .2 anorthosite(?), (2) diorite—quartz diorite, fl 3fl cirtflcj7cilci dia— L- Eci fiLciL by The granite isv cut ENE—trending cci and (5) granite. (4) syenites, 1flflk.3tci CtTL.JH,fl grcinit3 3S ttit; filotci Some granitic intrusions, such as the Granite Heights granite, cic.LIvfl rsTh1 ccie base cijfl.flF dikes. tflL3Lt: OLJLO fci' as indicated JL.t•C3JH•l by the fact that it has .J flfltflflflti ;icttIci b'S evidently predate this1flJ,:flfl-• sequence, t, i'h rcitz ,T-.clcirci.ci:-- plutons werefl t5.s younger :_ cicicicici been in zones along which some of the flflOi. mylonitized rfllLlbi.b .fl-fl1 y'cii- the tcici Granite flOO for O2flb' 0 cicir1i :'u -. Peterman (1970) established a 1600 m.y. age )Ci iflfrrijfl! Pcit•JLLr ficib intruded. Ibiccis TEtiui1'? 91L)3flJf rcitrci Thus, these ages ",cci' i Heights granite, and 1450 m.y. for the Wausau pluton. Ccci mci ci f0nt ton: ci! Some of the plutonic units are citLotorat 0rt , !1acJ ciiat sm are consistent with the field relations. 51'q'ci ::ii: ouiiut' cici.: contaminated and fil C'1.L' i-iltcicij cci cocii-uicibci intru.ve breccias; their contacts tend to be highly ocicot— cifluflt well— 0Th:,alflccontacts, fiCaicitci, abundant, a Strongly discordant cc zcfl:t li-yl: are cic:cic::L:: commonly mylonitized. !i&tfluit..citciflfl d1ci fl' cOcci21 , ta, t 1 ciJL metamorphic aibi- flflici of middle to high grade SflXkCI absence oriented :cEfl ru 1:Jti, and iflThtci' xenoliths, ciplcccii- cucit. icH crlitcc epizonal emplacement. cit 1Cm suggests ci ':ci: cu rafted xenoliths wallrocks except as lower nrccicicixcc: ci LJc e in a broad mylonite NE and ENE—trending shear zones appear to converge !c.flOcii' L'C a! margin to t1'c cci::r.:M ci of the Hogarty hornblende oacacJ i-iL to c:,.i1 parallel zone rc'ar near and the cciatr: western 1i.c.' bci2::JJoib) granite (Wolf River batholith). : ±C 1 'c. a- ciii -ra1- gr:tttc it: ti: !trily C rJC ' 1, flL3. ccc I 7u1] tnni-c'- Rocks L.ciC0 Volcanic i-i-X'1 i'by shear LvCL0.masses, cifliF3 generally separated boiccici2ci rccH4lfl cic cci as large Volcanic rocks occur 03JLi i-ira taaflTciLci ic air iitLl '1 Ti ci. and 'ci accici are basaltic to rhyolitic The rocks Ii-'fl volcanic ' cicici.or fihicirci, 20rci3 and/or zones plutons. nub. ra1c7-iciciLiC. and fragmental ircici- include crc. Ii-ir',pillowed, r:t Iciccic,,massive, ccci TLs The rabta mafic'7Cc: volcanics trachytic. 'ccc. less 1 i-nc. ci' Oi-ILCiLi are 'ticifldii-,. 3fr, volcanics The intermediate ctv.cc cci. iThi-i i-ccitt acicicic 1 i-Oct sediments. unitscat and associated cc ,uI ci'. Ui-i-i-, the "basaltic" varieties. rncty rEutflflTa1t chloritic and cucac more commonly fragmental than fl1 ii'CLbiat ti-cc Lob tuffOs, s, welded cclcioci'.tcifl include :CcLcsC 0 volcanics ;"i-riC cti- 0, felsic The predominantly ,,j, pyroclastic, cici'.J'Ll.fl •iThacc Ttr: nit bbas Eastt of the lJcc':.fl-' tuffs, laharscci,23.cfl'Oitu'fl and associated volcaniclastic sediments. irtilu, 'k,-:rc 3' seg00: ci'fluicilfl the volcanic i-b. cio -atciw ti- contact) in-c western.c batholith 'rC,u nrciu: the Rb."c'ci (nearer Wisconsin - £ciOci'uci 1fi1. River 'r''cflci,fl ciuci-il cdaiciii-cLbycolithologic Li'bt',j ci trends and i-fl '1evidenced chicir,t i-c' ci i-na.. .ti-2 have ments 0 ai-i northeasterly strike as :cMa:cc ''4i Land Ci1,.itOciiacci Classification Maps). Ii. b.- tacit c baciu'FlCtp WL.L1:uC cci on magnetic "lines" township maps (W.G.N.H.S. 1 -? icni:J-i-bc.-:'Ly. No 7i-• 000n'.River northwesterly. 1-4: b1ticO" trend cci'fl'ocJ is more tort: their tI—i- Wisconsin West of the i—cd, bcthe 'to volcanics cC L:i1, Tci'c nabbeen iranrecognized. ;ncntacd, stratigraphic 1Cm base to has yet 1 ci' — - .1' circcitici' a. :1 ''" i' "' '1 'lJrcrS' i-H ofcc1oan:o volcanic rocks 'Ca-ti-r :0the cnscit'tcc:u Hi cict It notycit yettcz:'cic known whether various "blocks" at is a' aoccci-n.ir. once—continuous sequence (a volcanic— :Lci,cccic' cnan.=c0'fl cci-'c. rf are segments of a ic'.adt at i-t represent different 1u000fl.iJciTit&i-Y 'Jr iTciJ to sedimentary "greenstone" belt) or whether they incicluci': occc.md1c'a'ci ni Ccc at work -T,ccic-ttccc"i,5.; c, from ci-'i-ci-' The answer may3-H not',te be forthcoming field i--i-C 0 ci'. "Ce i-fl tt't.ciLc episodes. volcanic ;J'cn'a;rtfi dismembered CLaim.alone. licor.'c: it:, Rocks Plutonic cit plutonic c. (Stop 8) 'P11: The largest mass of •tt-Lcip fl,•' :Hjifluflfl "ti-' flood Li-iCc Cflrcc1.;;ci1 Hogarty Hornblende Granite: i'nCi anCrLitt ciacoorcic acinulaL granite" to which underlies eastern itiaçc: s rccjci'ritiLe:rCc tb.: "Hogarty hornblende rocks cciatn;sci mapped isc the '-cob..': 'r t.o rnir Tigerton u-c•.u ciciZat lucc'ni-mOi-This pluton probably extends eastward to the '21:., a pLat -ci' rCca:.or Marathon Cci;:oty County. 'fltci 'ti-i-cc. to 'Ii'2H.nlcap9 lihologically coLic ccitc.a'' indistinguishable Cc.: act, 'i-r'ci- County, Anorthosite mass in Shawano is cc:a'r ibrc -H :c&at. quartz monzonite (Medaris, M uJ.[b.'mr oiccrba cicrcicin.L:1-r ci ci Wolf River ott the i-i'm ractc.' part oar-b of from the coarser 2 '-cii ticiac:'oj Itti-ccdla. locally intrudes volcanic cub :11001 L:y flTJcLi-0CL14i-? Ortu ci guidebook), and b..' .["fi,, this Anderson, and i-tb Myles, ,.ci Ti-ac :c tati-. 0': cc-l at It is nj,ri-u myionitized along the lc.ni-' Little Eau .mnaafrcErTh o.ircifit In western rocks &Uoucg its margin. cci. along 21L011'c? b.bva: Claire River. icc tn . r' ft cai �icc'!, ci.jcc'cc I', ' [1Li'i "ccc. rc' c LLTh ci' ci, 'i,ccci:.ic.ccC ,iT:' Diorite, quartz diorite, and quartz monzonite intricately intrude volcanic rocks in the region northwest of Marathon City. Alignment of metavolcanic xenoliths is northeasterly. '-cccl , ccc i", ic':' .'4.tccc.'. ccc: cISr,Sii cL,"1"c i,,., L[ccl'cLit 4LL :tLiCR: zcic',i cci' Tccii'ciccccic.;"cci ccc'.iici's'iic 5c1c tic. t,cc c'iccc'cclc Lc L.ir:ccn,cc:,.ci 'rrcicca'.i cc.'c',icc.cc,rcc,.c'cccc.c:ciL'{cc ti5 i;'i2ii c cc''.'c.cicc':ccc iccic,crclcC c2c'ci cA'c'ccccc c''[ccctui s-tic' t!C4 ccco.cc'ccci 'c1'Ei Mafic Intrusive Masses: Several small mafic bodies separated by granitic rocks occur southeast and south of Wausau. The largest mass is a gabbro body which interrupts the Eau Claire River mylonite zone near Callon. Smaller blocks of quartz diorite, gabbro, hornblendite, altered pyroxenite, and anorthosite enclosed mainly in leucogranite extend southwest from the Callon gabbro. Inclusions of pyroxenite and layered gabbro occur in diorite—quartz diorite southwest of Mosinee. It is possible that these mafic rocks are uprafted fragments of an older, subjacent, differentiated gabbro—anorthosite pluton. (Stop 11). ',LL!L cciii. cii 'c'. itc"i't cii ti,'lci'.cic'i :cc 54.c.ci'c:;c ,','T,c",yccc c,.scica 'cci5cciJ,,'cc. c cc':. c"s.q,'tccciC TO' c5'ifci. "Si,, ii". Tic: L'T 'ci:i' ccci ;C,Tccc:cc' ccc" cc'iccscTCtc7c.t UI_ ' '2Tc c.ciI:. [itci' .I'c'":c'.'A'S c .L'c'ccc,ct1t icc:' 'i''i.T_l'ictft ,dc,i'c,C .ji 'c.4't't'C it'. *"; c,:,s'c'.'c V:it's..t" '!n.:',ccct cii'St"ccc cctc'c-ccc iiccc?,_cci: ccccczcct cç..Zt r,crn.cIL"< LII c'.tt,Tc.ci :'i',SL ,c,c:c'c '4 ccc cc.tcc.c cc'. '''ccc' s'' scIc. tic::": 'cii.c'2 ,,.c!LI c4.ccC..cci "ccci "L'uii.'2.S. ic ;'- ccc' c,:5ttc 'ccii'c'i c,T;'rcc— ,,;',cRci i—4cic2cc 'tii'IctL li"l'.'ci [2 'ci'i'',ct Itcccc'briI'[C;ctc'ci .'.,c'Cl'LL ccc ii:'IIL L',,Ii',I''ccL,:'','5 Although elongated northeasterly these two alkalic plutons interrupt several major shear zones, and appear to have been "punched up" through rocks having a pronounced northeast structural grain. They are probably the roots of volcanoes, and their concentric structure must be due in part to caldera collapse. 'yccick"sic''c cc'c .c'c cccrL':,c: c'icI.cccicic..cc.cc.c ciii:': ':c;ci;ccc'.cIci, ,:. 'cc'rc.ccccc.:e'cc ',.ccTh .,c'_ cI.cc"cc ci'ccici-i ic'T' ic"cc'Lc'It' ,cirtcci'c,'icci S.t :c1'Jj(. 'C iifi'Jci tjiic.cc.[ r;',ci" :cicccL cci, i'cccidct ccct' [ccclii's .c',,cc:i?ci .1cc,!,,,, csiiyccy't ctc'I'ccH5t tic ;tccrcc ccc'.sci.'.'.c'cc oc'ci':cO.ci'Lc 1,1cic.i. ''5 'c'c'ccjcc'r'c ,.'cccc: c,.,':: The nearly contiguous, smaller (5 x mile) Stettin pluton (Stop 10) to the northwest is more alkalic and has more pronounced concentric structure. A border zone comprises gneissic nepheline syenite. A more massive intermediate zone of syenite and tabular The coarse amphibole—bearing syenite has swirled flow structures. core margin (1 mile diameter) of nepheline syenite is donut—shaped, rich in magnetite, and encloses a core of massive, gray pyroxene— amphibole syenite. .""[.cc''c [2 l]'tci"i.'CciciSL' c' Cccii c"citccl[c"-cctc:tii ci: ciit ccc''c.'cc',Ci :c ,s"is cc':: 'c,: ::,ccc.c:c :)i, i-cc'st"icc.::.3 ii 'jc •cicrcLL;.,'lcc 'ccci ccl :Pc',ic.'ccccij'c.. 'ii' cc 'cicfct'ccc cc;cCcc c5r',"c]i c'Hc cit'c'.cLl2 C'hciui.:fl.tc'cci'Tctc.,cc:-tcJcc lc:i['.c': 'cc'; ';,'1:"C'5 c..-,c"cicc .,t'-' 1:4]. SiIL. cicr'c.'t'ccc"ccuc, 'c cc =c"cccc'z' ccc ''c,c' tc[tc:'i"c C' 3 c''c4ci'c'.r ccc"' ccc cicc:'cc:cc'::ci ;' ci' c' "'cs'IRcc.ic,ci:'Li ,t'c.c4,.;L'2.cc"r ;ccIc2ci'c'c.ts ccicc,.cc'c: 1c'ci1 ii Jc t' L:,ccc,t :]L:II:L C '' ci; 'cc':: icc's cii ii'. c ' ct.Ii'.c't'i [2 The larger (17 x 8 mile) Alkalic Plutons; Wausau, Stettin: (Stop is elliptical in plan and comprises: (1) a Wausau pluton 9) hornblende-biOtite granite (Ninemile granite), core of younger intermediate zone of quartz syenite containing (2) a semicircular large lensoidal quartzite and schist xenoliths, and (3) a crescentic The southwest north rim of xenolith—rich pyroxene—amphibole—syenite. rim of the pluton is breached by the Ninemile granite which "spills out" to form a nearly circular mass to the southwest. Abundant xenoliths are found in the granite where the "xenolith circle" should Although the Ninemile granite intrudes the syenite, the contact close. In general, where the syenite intrudes between the two is gradational. it is alkalic, and where it intrudes more mafic volcanic rocks it siliceous volcanics and sediments is granitic. cs.: i.c .'-ccc.cs cc..cccc cc': "',. c..cciicc.'H1 .cs.çLcl.,.'lIc.'l iCC, cc.. cii"il:i:. ci' 'c':'c'cc.c 'it,JtLT ccci'. cclj'"cic"Icsc ',' '.' C'5 'ccc's:, ccii cccii '2" ccitT '[2. cc, 1'.'ci'C Pc ciSc" ci2icc;cc"cci': cc. cic'(VLcicCE.T ic]".'Tlt:'.it' c'Pc'.c'cc ccc.': L""i,c"tc [2.": ',c[2 ic.2jcc"ic' 'vcic:c'c.c-Lstci" 'ci ':cilI:L!:"c ciC,ci.tr ttcc'tLc";c: '.'c',i'i:: cci ;.ict, cc4c t':riC;;: tc',cci. :.;':t,,O ciSc', ut '":cc[2, [2 ciccs:i cccc'I.":c'cc'ccci ,c!,L'cii'c cc . .cuiiccc'c,$ cc . ccs.1.ç'cc cciii: ccco ci ALt' Ccci rI"cp'cc1.c'!c.'c.'i[ 'c[ccccic' ""1"'"' f -"S 'ciC,cic,','ccc: ci ,Ic ccu1cc "cc' cc.: ci,.,t'S ccr.;c', 14 .c:cc c.'flc iic';c,L'ici C iI[2Lt"V"c- .c"Itccc'tI Ci-''i[ iici..'l,c'c c-icc ci ccc. 7"c;'cCIci";..l'.Tt ccic'.cc5': 'ccici[ 'r'c,'cccc,cica:'cc' ''ccC',c'icic':.'Cci cc.' ccc; :91 cr'rc'cccc Ii ti, 'ii 'ccIccccccc.tJxc.c ii iccc':c'ci'c ccC'ii.:JY ocr 2.lfc Ac c',c,"cct ccci ccc 'cic',''ric]: Several other felsic plutons have been Other Felsic Plutons: They include the Kalinke quartz intruded into the volcanic complex. monzonite, the Granite Heights granite, which intrude volcanics north A granite and east of Wausau, and are cut by several shear zones. aplite intrusion of, as yet, undetermined size extends southwest from Marathon City. A leucocratic granite, which interrupts the Eau Claire mylonite zone and cuts gneissosity in the Hogarty hornblende River occurs south of Callon. granite, .Te,Tccci.i ccv. S :.LiT'[2cic'c'.c c',,iic cc 'c 0' 'c"' .1cc"cir-'ccccc', ,ccc.c .'Ii;cc;;':cc :'cccc'.ccc.ccrc1c,c ccc'cccc's 'cc' I,cc.,iccii c,ccc:ciic'ciJic ,"c-ci; cc,c'.cc, ':c'c'c'Ccc.,ic;'c ccii .' 4"c-n- rIicicici'Cc':c 1c2 ii4c ccccc 'c'; ''ci'c'.'ciT'c'L:] p;rccc cc. ci ccc.ccc cit 'ccc 'cc"cLt'cc'L c,t',,'.Jliccc.7S:l cA,t,.,c 'cc' ci:'c'c.[cc it'Lci cc",,cc;c:tcc'cici' cc's'cc-c c"ciicc,.,c:c' .ci[ ccccLcc,cc ccccics;cc:'c "cc" '. cicc'c'nc cc,"c:'"ci; a", 'cccc'cl "i ccci cLccii [ccc ccc:ccci,'cci': r"hii,C', ,: l'cc'ccic'ci ccc cc'cf'c'tic Ccci 'ccc'cccci ;c1i.c21'cct c.rrc'ccc''cc,c'cPci)'c cL'ci"'c,,c"C" LIt cc; 'mc,' c' ccc'ic cc:.cciccctc'L .':ccC",',c'C, cc]c1s,c,c cc', A' J,'I[ Ci's:: c'c:'r[.cc cic'cc'sccccc 33 �34 Structural i-->>'*i sn.i - Geology :575y5515c1'j, >>LCIC,naa. fcs.rsra a'. C i,1955'slfi-35-7 ti-::>> dominant Shear are the feature in Marathon County. daawdr'ar" structural 'sa' as ar-a Isls sa::- zones rocks, including 'nani:55 5535-Cit The major zones wide variety of sheared-s-sac> -> s.csan'r aa :1 si-i-is-s comprise lads si-:-ssc :aaa->>,a,s- these Nature displacement i-nt dCa; :>a.aaisaa'Ss across 1:55s3'axa of 'n-'5 can' -i-si-i. n-sal mylonites. gneisses, schists, s-s'SiaXa- and i-i-laX atlh'sa: 5-aC51-ai-i Marathon Several zones extend completely Lssi-si1-u"i-c-CCC C-Cad-a-CS. - across s-s-tiG->>--,-sasiCi shear -5 C-fti--Xzones is, :551kin'ThT's, unknown. —'cs'ss.d-sal: zone liLa. laS'S most555a557511-51a' conspicuous shear 5:55-C-Is' CiCts,>55a' :JC-1n1i-151*Lu:d County and an distancea555735ad-. beyond. The a:-. unknown which >55 155 .171: ':5: Ca' 'Jh.nis-an CLn>sr sari-a' mapped thus far is the N30°S Eau Claire River zone (Stop 8) S LIsa daC 5: 51n>5 -5-" a,t.-c3-3 marginasof ad the tdu -:'- 'Sd the -"a>>-as-- i-tugS ad-n, western is 555155 i-jars'. with, parallels, places is coincident tin plsc->>-a ,a-i-si in 355>>- and inns,>> Other C-'. h_Cr shear >neR : zones l>>55jfRiver 5551-tnPluton). lIla 59.; Hogarty hornblende 'Ksgarty dais:?-: n-Crs'agranite ;raa 55, (Wolf in Marathon -.---ar5 Ca: 55a-tdss west n-.:i-a-sc-",-- farther ;15i ta'nnd a::, present approximately trend are -s this aasnTCn:aci-a i-al.:' parallel pa's-a. -a-I to r55 sc-as: aS La-s ad an the lisa of rock affected to It vCL-::i-:r :;';a,nS County, but none appears to be equal in volume llla.sai-1:a, 5-sn: awn- n-nsa's-as-- to 5: t. Sn-annasS-a ,>>-a-arn,s Thus, intensity of >>a'>>siT">>' shearing seems to diminish C-C a5TLL,a ' 55' 'l'i' Cs ic-nC-, Cl sic--n: River d.s-ar- zone. Eau Claire 55na:l. lbs 5:Cc ' '-s front. i:lC-s batholitic westward away from tic--sri- the ::'aarrarC :;a.ay :- - 1 I - 1. and across n-i-Cc-SC las 5±1:35 Lithology rocks Ii: in s55'nr shear nsasea, zones, —a55C''j. which i-i-n-s varies along s-nC iIlssa51Lss557 of ad :sa.:'C': texture of the original Cast-inn cl tn-s an--i-CL-ass 515: -'3>5S,c 5.'>ra ristrike, is-srss" probably controlled -aiaJiy carat -:'-c-TLsic.s- by mineralogy and C ts-d li-a, is partial pressure of H2O as:: sar-ial saass -s ad 51Ctsr>>si-:'s:'ftassc rock, intensity ci> shearing, sdass--lsnS:, temperature and tntasa-S 55s' of a-s-sd, 5555 Mafic rocks are 5f-i-n ?-ssILa iSCCC_C the rock. :'a-i-i-I:n> c-as-sshiars-ns; C lsCc'i->-iad during shearing, ar.d post—shearing history of .dsrS's'g a'baa::::>> and 155: ->>'i'-sa Granitic 015.555>>' convertedCs toI sad-CL banded as amphibolites oranchioritic phyllonites. cssvsx'::-d SitS n-as: I"Cnalislc'r:tis -51111 From and CL mylonites. icnj',n-a,, Th5'35 gsan.aaan-> ;;-lha.JLcsain-aa as' a-is-a' rocks are converted to augen gneisses, phyllonites, and -ar's CsrrC-rt-n-'3 :>:-slica' I nan--5:r115'sn5553' characterized by interlensing a':,saa arssi an -u-i-rnstarts-ed :; 'n-anti--sn-i, shear zones are map scale to >ck'in: thin section, si-aL-c Cc ti-ni-cjill an-s-s-a'> slip as planes. - c-s'-- example, 5ui5'siQsS shear alIas-a zones. a':sas> For IFS-Si-n intruded Several small plutons i155>>t'uiiS have nn-ni-'-C>>i C;'., In-' Claire River zone i53':r'i- near Callon. 5' -s-S. CCI s-iar i--a' Eau gabbo and leucogranite 5c'51a"->>J-,d 5.51,,5557'alffltainterrupt 275.35 ''CL the sn-33C sass as--cl trend also occur northeast and i_Can a-; srann - -',n-sahythe 515; same 55CC - Ta'S Shear aaitln approximately s->-v n-n- with 151-a' as zones a-r'as'9 ha The'-.iraza-la Granitefls.t:.ls Heights Ida 1,5- granite s>> 'an-cadtS:'.-i"-- pluton. -Isl.s-u-o-:->::ac-s Stettin southwest -alar- discordant -CL the a,-y', -i-la--n-cc of ass-c ca--> sheaied and therefore tibaaT--n-SCaare proascii-h CC_CC-C: 5 i-;have n-2t lan-a',:: and Kalinke quartz monzonite been ulc-,an,'i--sI s-nd dali >sr,'C -55555_Ca ::r—a- lI-sasis.tC-', >a :ra-pre—shearing). 5-n-i-5'5JC5-5CL' bably (or cs.l:'1- pre—kinematic ion's:' repeatedly have been '_C 57 isas-aC 'n-5-n--as19-3lf 15 i-a tin-ass-C SOs- County aaa'Cs in Most of the Precambrian rocks Marathon 31' '5a-s Miss-isoji-;;,cali!'sc'ss: 55-.-? The differing -n-s-all.>>> :is:.iI-san.5 compositions. -s-S widely t—;s'rs"n-ar sheared and magmas of is:5'ar-'s'd -s>.l by an- l intruded a'Ca'ss'nnti ;53LsC:--?tCl'X-> aca'i-2 of 75 3135I the intrusions. 'as some -51- san:: for nibs—i as-s -5>1-s-i- channeiways ::,-.--i-Css,siCIn provided shear au-Si-Si-I evidently alCoa>>: zones -ad of the an"':. many as: asi small 51, 5 plutons 5-n t;as--a::'d and :5.>> s-1Ci-5C55I.S'i?'753'>>-'>>' cn-'355t:'C' The relationship of shearing to intrusion sad all' sn--o5isa s-ui-i(Hogarty hornblende granite) Sd -cICL5s 55 1:5' .i":ttarIs 'asn-t,t) 5,-s-ad-sI 3tti-'-n-s si--I'd the emplacement of a-I the Wolf River batholith i-he si-C 51115'? n--n-s'iPrecambrian geology ICC-a a,iss1a-:si at a>n-all JTof 5" Marathon C am—is s'f Ida -aa,>:'C ;n-rciCl>s-n-C remains one of the major problems in the resun&a.a cat: -- >55._CC u5i, County. i—:-SidLs:; -: Major 55aJa' Problems s-ca In-ma's- sCant anai-s Some the i-an morea important ones are anI 51—c Sara's of '—s-":aaa> ad- can- remain. Many major si-CL a-a problems -rcsn-n--s-Ci-r':.. discussion and sn-sal research. 5 .bsanasa:C-ta: ratIaa':L'Lasas Class :>,:>, sr's. -'>i5ai iS'-s' listed below in the hope that they may stimulate i-it ba-S balsa- S's Li Cataclasis: -i'- Lan-IS: Shear Zones — Cr: - - - 1. 5, and mapped? 'l'ci, -an-lan sacS's sariSclassified -staaaiiiIas- ars: How ass areaa-aa-c71 cataclastic rocks best 2. 5, 1155-1-35" CC dated? Can mylonites be dais: vsssLc:cflin&n-s 3. determined? .>>I5lII aaes:a,s:: c-:ot n-rrrr: 3-55 si--saC- 51 How i-sad amount of displacement 55155 and -3T5- type ia-" are 13 44. Class'? How? -, i-i- -isas-bs:nsa'fl p-': tcdcs':st'ia:dp:- between csdlsnc'n-s What, if any, are and space relationships avisthe j'e time it: nsa. Wl'at, atsiasas; a-n? ,'i-s5:'i9a,aBt'5 shearing magmatic intrusion? cbacvrlsa; and �s? ane err t older subjacent of samples ted upraf they Are variation? fC =— xenoliths Cji, 1t2At4v and orientation (:ICC ofjC Significance lithologic iCZ [ r:• ft$CCEY:1 <%-Y9 C Subvolcanic? — syenite (e.g. 7i;T !ttZ i)r,; When ' ?Ji-•i ci?1j lILCrCYqISC Ccnj intruded? syenites the were f.CtCR how and volcanics Brokaw)? near C CC 5. C 4. trachyte 7 I i—C It— and plutons between Relations comagmatic? are plutons Which iCCCCIV emplacement? of mechanisms and Depth 3. 2. C 1. i:t:C7 Geology: Plutonic 35 I �1! 36 atrSW Bates, •fl0 R.G., fl'. 1961, geophysical data and Allingham, J.W. Xfl '3Ut - "Use 34) of *t.tss%•;o. t'Zflfl ';'r geology i4tç to 4•1 interpret in Precambrian rocks of central Wisconsin": !fliS'V1'13 £.Ptrctl bV $%Y wea 1> U.S.G.S. Prof. Paper rn-cs — D—296. zt •IrJ. .(%',.; 424—D, p. °' D—292 SELECTED REFERENCES 5tF:SS.a'ffi 't1. j , L, ' %.'f Dutton, G.E., 1971, "Volcanic—sedimentary belts and sulfide —rae occur87Ps fl1'r7rC2L StCt C4fl(U U.S.G.S. Prof. Paper 750—B, p. B96—Bl00. rences in Wisconsin": r, r.oswç,s, tr : ;c.a.y rcb.a '—,;çj OtZ tn. • '°q.' •. t"i ';a'tIrtnrxrc;s Dutton, C.E.,. and '..'73SZ Bradley, R.E., 1970, geophysical, and >.E 'char "Lithologic, DLC'4Ln32 mineral commodity maps of the Precambrian of Wisconsin": U.S.G.S. 1c w:42L Arxa•nu ..f,q'g ;ta Misc. Geol. mv. Map •4gfl -15ee •"flf 1—631, :%.I4... 6C sheets. -:rj ;r ru :'wt:.jtn(, pUtfla V $ () r.qe;.p at; Emmons, R.C., Annual Tn—State3 Geological O'eQ 1953, Guidebook for 17th v, :ia( .t$q, flD4tC Field sv,.'-.xarr Conference, 11 yr p.. ,t0Ij rt4'7ii.'9 !rag r' Emmons, and F.G., fl•j Snyder, c'& 1944, y€L "A 'Ii, Structural Study of the cç Cztc.,&a R.C., xq,:iz ta•a Unpublished rept. in the files of the Wisconsin Wausau Area": i1SW% WV ;qa 4 aj; t,Wt47tttft ;'etBr.tV14 ';de.. Geol. 'TU. Survey, 'it&flS 16 p. C 'ba( a:;: t •,'( 'CT, "g'g t:\ttsc. tj) .j •. :, ': i t:b Henderson, J.R., Tyson, N.S., and map P%7I Page, 'at 'o.Qwj J.R., 1963, "Aeromagnetic rr.,:i4'rney U.S.G.S. Geophys. mv. Map GP—40l. of the Wis.": jo :qt Wausau :'sa.rajç, area, SM 49' 'SS't 'ts1 ,. :sfljr "It v' ar LaBerge, G.L.. 1969, report on P.tnnrEsJ. .acSe.t uz' the geology ".ZiGT "Preliminary a5 ma of the northern part of the en Wausau East quadrangle, .nacsfl :tth 'c,2as. Wisconsin Wis. Geol. Nat. Hist. Survey, Open File Rept., 13 p., '2s.C?3 "C map. iee ;* rnas ;ntj i:'t. t.jff f'L •'vc'- LaBerge, on mapping of i1 Precambrian geology :.qh? 1971, s25v.; Report s.r'sg co SZ'LWS$ 'GW4e.q G.L., 'ca1t "Progress Wis. Geol. Nat. in t7flcW Marathon County, Wisconsin": ELf a-a • Survey, :::Tt•sIflr3J4 'tu,c list. Open fli.J File Rept., 27 !Z p., maps. '4rc3 '?3 C.1 'Ai. L0 '.r. 'craet't, vx nrnc4w r taCaaST& tfli: UC'4Ojq n;i 4flc; '1.2? 'flL 5 LaBerge, G,L., sv 1972, "Lineainents and Mylonite Zones in the Precambrian of Wisconsin" (Abstract):t North Central Section Meeting, T2 G.S.A., DeKaib, *e.q.n.z) '•ezoa Ill. U::z*r1 't' •t .trj ts 't.St3 ''O LaBerge, G.L., "1971 %eclSord Progress t•.dej Report on .:,. Mapping t1.3E TL€T,; 4"u'f and Myers, P.E., 1972, Wis. Geol. Nat. Hist. of Precambrian Geology of Marathon County: 1;b C4taPN.Ls: J.$2t->' &.O %'.at1 fl '&.1C1s5 Survey, Open File Rept., 28 p., illus., maps. &j nd'ag bw4, c.çg 'd 4-aç "!na :. 1Ltui VII .vc flo rt LaBerge, G.L., P.E., 1973, "Precambrian Geology of tr)4flflfr( Marathon nrn..*twse. 1an and Myers, Lard sue. Wis. Geol. Nat. Hist. Survey, County; 1972 Progress Report": Sp.4 1.C-) 20.aC 4Z'a.t1 Open fl%C File Rept. (in C;) progress). 'cs.azs.c5 )T "djj 'fly W flr: ;r•i fl.1a3 ?rr, LaBerge, Ci Central ..:.t; and Weis, k"! 1968, "A• Greenstone fltLrj%S'LVaTh Belt in 'I3J4(i. G.L., '.t!Cr4 L.W., Guidebook for 32nd Annual Tn—State Field Wisconsin?": Yt33—(aZ1 ,.4t1.i.CCfliVTk )OtOflt3 aC$ t.LV, Conference, 42 p. .3 4DrdXtat) c'rq ' ''re: 'c;si Vickers, ra part of UJSttCs R.C., 1956, "Airborne .a'q.r:y,, ':t and pfl ground 1WdCUCte.F' of ;n4>s1 reconnaissance U.S.G.S. the syenite 0cm rie.I Wausau, ;utsI'r.JCT c c°u 'p Bull. nit.ts s.a complex near rgnip. Wisconsin": 1042—B, d p. 32—33. xwgna 'tn'ab1 a Weidman, bTId... geology 'Z4ni Central u4TLBt Wisconsin": çu:w.CCCTa. Cktz'ia of North t•::....;#'.•-q S., 1907, '.a.cr "The Geol. Nat. Hist. 697 p. •t$ •V1J! Survey r..t..s Bull. •IrR 0 16, 09 ;I . 'TZ '*1t 'h°1 Wis. '3;j.4 "Central Wisconsin Volcanic Weis, L.W., and Z.1Ct LaBerge, .n)'ja;s G.L., 1969, '44%tJ_ zu:awc,, 4.3VCr.s' Guidebook for 15th Annual Superior Belt": I.?:.2t.p;a3 :'a.it.t Institute rj-4n(fl w on Lake dOfl Geology, Oshkosh, Wisconsin, 30 p. VØ (.j tSo ".atcers ;•1t -— .n; ft 'u;snt: ae a... .. a ..j4uQ �This page does not have a number 1 1:500,000 scale, Wisconsin, northcentral and northeastern in terrain Precambrian the of map geologic and itinerary trip Field 2 1:250,000 scale, Wisconsin, Sheet, Mountain Iron the of map geologic Preliminary 3 1:250,000 scale, Wisconsin, Sheet, Bay Green the of map geologic Preliminary Plate Plate Plate pocket In LaBerge G.L. leucogranite and Masses Gabbroic Locality: Additional Myers P.E breccla intrusive diorite quartz Sheared 11: LocalIty Myers PE. zone pluton—wall syenite Stettin 10: Locality PE Myers Institute Technical syenlte-.Old quartz Wausau volcanics mafic 9 Locality LaBerge G.L. Rivr Wolf between Contact 8B: Park County Dells Claire Eau 8A: Locality and batholith LW Weis anorthosite Tigerton The Scftnus Va.n Schmus Van W•R• and Anderson, J.L. Jr., Medaris, R Schmus Van 7: 6: monzonite quartz porphyritic River Red The and Jr., Medaris, LG Locality LG. 5: W and Anderson, JL. Jr., Medaris, L.G monzonlte quartz River Wolf The WR Locality Locality MM Lahr, area Mountain the 3 Anderson JL. and Mylés, JR. Jr., Medaris, L•G trachyandesite Peshtigo and granite Belongia 4: of geology and porphyry feldspar and rhyolite Hager The Locality Locality JL and Myles, JR. Anderson Lahr, M.M Schmus, Van W.R. Jr.,, Medaris, L•G• monzonite quartz gray Amberg and monzonite quartz pink Athelatane 2: Locality G Hall G.I and Mursky Wisconsin northeastern in volcanics Quinessec 1: Locality Wisconsin Northcentral and Northeastern of Geology Precambrian the to Guide Field �37 L CI'C,':'i 7TCHJ Field Trip Locality 1 TITLE: Quinessec Volcanic.J in Northea;t rn Wisconsin (l'I-7J!,I C C3'CSI CC-XCk? 7 St .7;:; 'T'y CICCC,IYC.,C,:4 LOCATI( MC.: T.37N., RJOE., Marinette County IJ, " "na sec. 1, LI7tC 7',;aa.;:7t7r; Centr, AUTHORS: t,c;:'?L± .CCi. 7':,';ai,r, i"C[ 'a fI:r.17; ,;:a,1 ,'r• C"Ca. ''Ii; I,7C,C"7M: L,uZ77 Gregory Mursky, Department of Geological Sciences, UW—Milwaukee George I. Hall, Hudson Bay Mining & Smelting Ltd., Calgary '7CC, I ;:a CC KtI• ":H':aaf"7 1yT7', DATE: February 1, 1973 't 2C7'C'i1S SUMMARY OF FEATURL$: part oi Marintte County in northeastern Wisconsin Northeastern is underlain by Quinessec volcanics which consist of pillowed and •;:;: :;r,:CZJC '7., '77CC "CThCC "TC'taCQ C'C7 Cc "IC,:': :7';: CC 'CJ . ,C13C S$LCNCI, aT'tC [ YI' iC1P'4"t 1CC 'C7CL i'" •,7C [':'C '!tC '1 t 'Y'CJ' )':ICIL3E1 aC"<tIitC'T,C,C' rLiC'Ci7C I1C'CQ1C,4 S.'.ICCC' C4 vi"CC",LC1CC1a a . fragmental basalt, massiv basalts, amygdaloidal basalts, myrmekitic basalts and a very small percentage of tuffs and rhyolites (Fig. 1). The volcanics display shearing as a dominant structural feature with two distinct trends at N60°E and S6O°E and signs of regional metamorphism which varies from quartz—albite—epidote—chlorite subfacies, away from the granitic intrusions to quartz—albite—epidote—almandine subfacies near the Hoskin Lake granite (Hall, 1971). C' r 1Ia '.';:aa. •a/;!.:zc•Z. wa474t1ir2-. I'C.':z1I,:, 7C CI C': [::;:"L'1 C,7;,;,LC ., ;3,'IC'T'zJi. CICLC VT7CTCLC 'a : :;;:;: 'a C'C1 'E1?C:,,Cd Titt7 'CC'' il;: 1ia 'C CCt's''a: J7117 7 C';: C" L1• cs• '1' C'C1C tCi CcC'7XtY ;:''aI ;:,C:,;:. c_.;:01©.'11 ;,1:a::C ''' ':' a. •aicaa ttp17 'CCC17::. '.C'Ck",a,I] CLt I'i7-ç m',7 'C=; lP' 'flC1ICC "ai 7T4COLL '-'T'1 C12 jrcr'; The Quinessec volcanics have chemical characteristics comparable t:7Y'J1 ICCICfC :3CLC4C a:'7'q 'C 7u7CCvI-'. y{I• CY',TY' tI;, •'•'• C JU .CCL v'ç 'flit; CCC. :? Ct7 CC a a Y' f:a'j,,Cu;:;:CtI C4 7C7t'T'17 IaaR12T71 C'5. C' . CT'7I to the Archean volcanic assemblages from the Superior Province o the Precambrian Shield in Manitoba, Ontario, and Quebec, and thus show the WCZJ '- 'St L silica: alkali values from Quinessec volcanics, when plotted in refernce oceanic alkaline and orogenic calc— alkaline curve of Wilson (1965), plot in the same orogenic calc—al :aline wield as suites from the Superior Province (Fig. 2). iwa;: o —pa ';:'y'a '17a7 'n ©;:: I : CLL± •;:rL •.':q °9.jj7 C'CIiC_C"z.ç[ •:s-C'CCL' CT1C cY'1; i'.'C•4-'1.C cCC:iicti' ,;:,Cat ''JC7 JC iC''LC ""CiCVI,''y C'Cj, JC j :i t;1r7.C'Ja The c tion equivalent percnt of An—Ab—Or for Quinessec volcanics is quite similar to Goodwin's (1968) Archean assemblages from th Superior Province (Fig. 3). t/I'i,L7LCC 'Ci ;:tir:;r:'a IJiI;77ji C c:e Y"1 JC I II,7":i CY'R1; ?i'C;fl :,Li a;: ,c-:7t'r a CCjj (2) t'C Nili ii "c.'qa CTçi ;;t (1) 4't following similarities: : A plot o.. oxide ratios relative to stratigraphic thickness (Fig. 4) does not show any pronounced chemical trends although there appear to be three separate zone within the pillowed and fragmental basalts. c: Ca:ttc1:; :T7hCTYI,flL ::4 L: :CCC; apCC:C :::,1aCa ac.r.i. :: aiqC 7CL7 '.. L•;'..Lta, ;- .,'.CC 3C'''i' •C.:C:. :,Th:,c.'.:ia, a'p.aac. 'nz .'i'c•,.:; pc:',:C.::;:'.,ri ira tu'çc .-;r ''i C' �ii 38 -Ii 8800 7'07 - --., -- Nocra 1 177 \ 1_ £ rriC:,,, T' / — 2 — — — ,.'NtMrnet C'HIIT C ,STUDr' 'N / -) * / A 7 L_ y—1'-,, a 7\ t, toN 'N 4.*4*47* AA A A'\\,7'.-.it'- — 7-' '1H'c221J.t'C —-;,,--._ .AAT3N II 4—"ii 'Ni cons N H-— 27 - A -- - 7 7- CL 1 - ',,,_ a—-—-- - 'N—- -, -- - _1-L--7--.- Jfl=cn - - *-'7 —- -- - 10 ,L_-r-- —I — ' N' - - ;- - - 27 1— -. P.. 7-1 ;0'''7-°"--- -Nt--H, 7—- rrmI n (1 r '.j.-[\ C fl7-_° 77-- 7, 21 '- 1 i-n Li e 't,,oCit'li,'. - - 'N — -- - (7a / - -*4 2_ — 7 -"N t'Nt.,q —-_a,t Y.-:---. / 7 -t ,-i.;, lot (/ 'N N,' 27 0 '/ — 'N I - 1''N';*,/ 0 of -b • oN 17 a.- 1 N oCt— ' .-!'NL ,fi -'27-7—-- N 0.1t&_,t " A -A : s,,b —'t,-"S — A a r - r >, c I '. ( 07 'S 7- I / 'N'" 7-pLOt - - /1 17 . 'S — -- Ca-21 AREA — / 77 I là CA L4 a- 45•45- - * —---- 7--''S 'N /21. - -.7*7--f - ' 'Nk. i-'7-%_ - a VI 7-N. I LEGEND 1- Precambrian mt rusive —' L rocks 70, - - '7-.-'o 21 7-— 1i .1Fraqmenta1 7-4 I 'I volcanics 1Arnygdaloidal /LjJ basalt ara:J 6-I!77If 721/'CJIN I 0 7,-;.J-1 p o— '' "N I Myekitic C • - H —- I a -''S-— - - •.. '1d basalt -L * - - - Chr-'Nt 1-731---c' rk.,0i'Nu:.,elco Acidic volcanics 7- 0 7. 7 LCCAON MAP CE o_jbasalt U) . (1 r1 - - 0 -o Luny >, - i/f,-,ç Wi •-ns',-- — 12 -' -- Mo r,,.?te -* ---- k,om.er - - �'r\ LI I. 3',j 'C[' ''Th' C.C' Hall, 1971) 3' (After 7—U- Canadian 3 '1 the of Province Superior the in Shield. 13'22IOft J37;1-C-l,-" assemhlaes7 volcanic Archean 3'23'2L;c. three ;.122;, for trend 'uT1-2/3'33'T-C curve ri:Cj3'crr Dashed Wisconsin. (1968) Goodwin's is 333'1'.3' 3':.,-'''7 acidic County, Marinette NE in rocks volcanic -= '— 2:1523 Cation :.3'7.-( in 23' .2:1 13'-3'--23'[2percent 11,12.322 equivalent Ic 3' basic and ith—An-Or C , I 22; /\ \ \ ' I: 3. Figure \ 0 3 /C II Number Sample ,z C An /-,1'V"Ci T., G. '3'3'1;121i :1:3''121 caic—alkalifle rocks. p33'.A1 'ri13:_: (Mter Hall, :: 1971) rocks3' alkaline oceanic separating orogenic from _l 3' with made is curve standard (1965) Wilson's County, Marinette NF c WiscOnSin. — r' '1 I cI' I_ : C--— comparison 1721/ :!C " C— -'' aniilyzed and basic )'C acidic ci volcanic rocks in 3'/ ofci Plot 3'003, I3'.3' ':• I13'Gr;2. Niqqli :17 :511123:' values silica-alkali of - - - - , — —C VLj c 400 500 12' 2. 5172.3' Figure CO 4gI Sit 300 00 200 7 l0 I 7/ 4 / / /7 / / // / 20 12 > 0 / 12 CALCALKALNE ," OROGENIC 12 7-V 39 0: - 30OCEANIC ALKALINE 40- �40 40 V Si/I.E N,crn.H .: i 54- . Cl — / -. 25 0.23. 50 .5, — 75 H\ 'N'1;\l .7' 01 - I -. — N,1 - ------! 1/ : 0.3 ,0',, C .04 A' 10. / ..' H — -1 xA — C .4. /1/ /,/ A ,.' .Jo1 - - /A H / // r Ceo 0332 L.tSiUI I . 20 (I; t P. nu5' i I it .- t II -— -1 7. fly 04-." 7 --- / 00 —- 0 I '4- I c '4- 0 :: ((S 3 C. :; 5-—.,. I. •1 -o 1A C - ' I-.. C 0 // •1 0 -c /7 /7 'I 10- 7 7 —.. — 1 a.'-C'-. -' '. " • .'0.' I: -- 5 -- .7' T 1 / JL.' 0 H -- - ,±J1 Bottom Bc -1-L_ Ir tr'Sit' dItIIn 5. 5, .:''H''sv,-,I,''12 ('IL.' — - l(C7 Figure 4. ' 0)01 /I'fl( t'kr' - —- -. Tt1 0.5 0.3 V sc. Bottom '3's A55 (ion l..I ", I -t FeC) ) J '3 A 1515504: Plot of chemical 5555c/:t c- with stratigraphic d0457nS,2.C .sjI. variation 4 04552044335533555504/04 04"r:5e33335 in Ni Marinette :;1;t-5-.t Cocsit.y.. thickness 7555 hasalts NIE County, bsc/c.5T.tS ins.c '55 shows: Wisconsin. ,55..'(-5,33j/5r5 5550 JL07 zhz': 001 Generalized qeoloqv r->. Si 550455355.555 sc1s' scs's d5Ct??04*5 3 qrain size -4555.5.04 75.5,55; increase; grain size decLse; -.-- hcsc4 (i55 7 i r (EnrpBc'cT L.':3 basalts; isis Bc 55' Ct /4 shearing; porphyritic (.4 2"?'10455.a"''(S 55: basalts; CtjiL55557L 045575.A 55555 q fragmental modal StC'. iLL auartz. 55-75, 'JcS"I' (AfterssBcI, Hall, '.'s. G. I., Bc, 1971) .5 c. " Wi, I, ,_,-_., 5_ A'.' Si �41 DESCRIPTION: U l/ce n:cYk t,jc 14i.V a'oci' ri' 'u :a:aL :xn vi 'UU Massive basalts crop out to the north of myrmekitic (1) Massive basalts: basalt and comprise one unit within which there are three quartz—rich zones containing up to 10 percent of quartz grains measuring 0.15 mm in Massive basalts contain varying proportions of albite, epidote, diameter. Most of these minerals clinopyroxene, chlorite, actinolite and leucoxene. average 0.2 mm in size. Clinopyroxene is commonly altered to actinolite and plagioclase to epidote. Pyrite constitutes up to 1 percent of the rock but may occur in greater quantities in the quartz—basalt zones. :1L c : tecc1 tsa I I cLa: cc Ui tr ci c21i Ct F3eELcL1 S. - Xccii p I 'U cc. rJ c cccc/. a1: cctt'cUL UJ"c/RLtc cU eca Pitci tititre L±i-UILI. 'U a i Mctcc c'tkcc.tQ L& :crc k nc - c. :rr a-cc-i e•:c:'c cay cc.YCLC:ic ftS 134L1 irL 'U aft aagc .fctc0 cc cr .ccJLaSe i caL act iic.: c-c cUr r--eUicd cii 2eachae g cc - chsaccic sL'trect ii: cU-fl.. ratrcc tibia calLer icaci lice cc fl iL fS;.-iIi-Lf.IL-- 5rtt ataice c cc Ltii a cc U 'Ucr I rca -cc cc lUC cciiai a cc -L c'c:•H ate Ifcar UI U Ucac'U cc a a ';Lcc-c ccii at. - calU iniic-U; a'cc.ab cc;: ticac cc aa.lian cii a -racial Ha t UcccU ccc ti T1LL JUic -.leTh tS±L ace C/c. CccThL' :- cmi- icc ccc a-ta - cc-rat a t'U 1tJR -ar: t'a. 1Li ccc as::.: ;c'Ua ic: ii i;ufl9L cc :c:a cc- cit cL:-r 1: - -cc ccc cccc p1 cc-I- crit.trL cccci--: ccc- c' a iii:;' i-c U Urit ii:, hit-cc Ui 'U ccl cc-i :cycLnta_ iliac-. LL ci (2) Pillowed and fragmental basalt: Rocks to the north of massive basalts are fragmental and pillowed with well developed shearing and flow structures. The fragments are mostly angular, at times elongated, The pillows, where present, are and measure up to 5 inches in length. deformed. These rocks are made up of plagioclase phenocrysts and a groundmass consisting of epidote, actinolite, some chlorite and dm0pyroxene and occasional grains of quartz. ,- ccii :;1ccctth i-cc-cpa-c H rath -ira pUL:c-i1 aiU ci ecai'vccc ccc ar-ella (Y:i/Lc'IL_ 'IL ccalc.c ccciii ic-eU ccci i-rca i: ci cci 'U ccl -ci CC.' La.. SLLC !CtiC atiLcag --crc a cci ytmic-cacctr ccc ;PL-rgtcU -f cc Lie c cciL -cciiti :ci:ci hiU ccc L UIL 1ccckSct. t'ca-a tTI 11 LltJc -a iia'hccc iitt& I C --j.c-ac dcci :i.ILc 'Up-aL ILLC7 Ce 'U IL tm3i TLC (cjCC.?:ILtS - r:-i - cccl a1 2/c Ui iT iciacla ti-al arc etacitcaca kcic'cL La -cica lea icaraIra criiaJ. Tic (3) Amygdaloidal basalts: These rocks in hand specimen are uniformly fine grained, massive, gray in color, and contain up to 20 percent of disseminated dark green chlorite grains which measure up to mm in size. In thin sections the chlorite grains form amygdules which are Plagioclase in the form of surrounded by a fine mosaic of quartz. laths averaging 1—2 mm in length forms about 30 percent of the rock. The groundmass is composed of a fine mass of chlorite and epidote. cc Ii. cc ccc ccc ccc- icc icc ••- aac - 'c -ii- cc-. aca)r.ci/L'c aca7 yr LC-H-H c-c-ct teucia elite culcrt-cc cha acce cci cc Ian uccancre greca -U ilaccc the hr.: -ccc taLc-Ui cc Iii- claciccicita- :L.r.caJ'U'U ctcbc-clai i 1 1ccttc- nnr:ccc icuc a cacic -rtcc a CI :-ecci can a- a I Ic ccU aJjuJ:jIcc u-Y 1 - cia -ci eccacat era cicica it-c n,air,ec-LaI.. yrea:Urc nrccniti-ci-i cci La ac-a ca:cLcca-lla ecnii 'Li'; inacicica] 'U :cuut.cuThflil'l ycceacca n-cc 'U ccc arc-scec.a ::acc-L.i.-z cci c-ac- aUcta1 iat'U j:Iapa-.:cIea-e cc.tc1 ci: -ccci ace c-c-ai-acl --aria tiatacig a .lcrr.nti ear ccc "C•Cti'U a: ci i-cf cc-ecU a: 'I-c. Ua-i iac ccc rn'-: car -:r'ar a ccci c•ihc rljtflfl'Ulitcarccc cc J lr -ii (4) Myrmekitic basalts: To the north of amygdaloidal basalts the volcanics become slightly coarser grained and do not show the abundant chlorite amygdules. Under the microscope the rocks are composed of myrmekitic intergrowths of plagioclase and quartz, plagioclase laths, quartz, chlorite, epidote, and actinolite. Clinopyroxene may be present occasionally and some carbonate minerals are to be found as interstitial groundmass material. The southern contact of the myrmekitic basalts with the amygdaloidal basalts is gradational. c t cc ccc 'rica ct:ia 'C c1/.'tj c)'J1CU tU SU 'U tLcr:O Massive basalts contain isolated patches of welded ash flow tuffs and rhyolites which indicate acidic variety of volcanism in this region. The The thickness of tuffs and rhyolites is estimated at 400 feet. tend clastic with rounded quartz tuffaceous rocks to show appearance grains up to inch in diameter and cherty fragments up to 1 inch in size embedded in fine grained chloritic matrix with distinct shards which have devitrified to quartz and feldspar. The rhyolites are dark gray to black and very fine grained and contain quartz, orthoclase, cherty material and plagioclase. icc -a J ala c-cia 1 arcifc;r. bIl -b-c :r 11cr cc a -ccccL.r-ci ccc ic-acita lU i aia;yca,1c:a2.-c!L Air ccciii. tcc TcaU ccc ccci:: cii; �42 42 SELECTED BIBLIOGRAPHY 8'Liv:.t Goodwin, A.M., A0M., 1968, J!S% Evolution 'o1t'.ionof*2the •b Canadian .AU1 W4Shield: Oucihilti. 7 19, P. Canada Proc., v. Cer.&Ss .L; . 1—14. T"r.; Ct.C. Geol. Assoc. t9fl. G.I., A Study of the 'r.z?Precambrian fl3x,brtt1 Greenstones in Northeastern 6xsy a2 0,1, a 1971, J. Unpublished£.t? M.S. Thesis, tr:i.r, 'fl:t,g.Jv, Univ. Marinette County, Wisconsin: V:.nctctt; I':'jjj.b* flrcgotce Wisconsin—Milwaukee, ¶Mt' watuxMt, Wise., 'n4, ac. 80 p. kaecariu-kUvriks. Milwaukee, Hall, '*3.3, l:.tt MacDonald, Gtsj of Hawaiian rbra'.w T•cvn; Lavas: tact Origin Cct.a.ceit:.cct and Jor.z'.Id G.A., 2.JL. 1968, Composition II. In ic C1A.. Studies in R.R., Hay, R.L., Anderson, C.A., Li L., and im3 PZ'13't1D, .ntR; E.3.., 13 Volcanology, Coats, Geol. Amer. Memoir 116, ..1. p. !Lrtc.t' ed.: p. 477—522. 41''.-.t. C... . Soc. Ln td..,. 5c. A ?i3 tflTlti Wilson, H.D.B., and Archean Volcanism in the Canadian s'td others, 3*h1b. 1965, £racar. 4ssct, '1fl,fl., TIC?,3, & p. 161—175. Can..c."r Jour. Earth ttr1tt Science, ¼c1tfl?G, v. 7- 2, no. Shield: (!a isiC ', �'111101-32072quarries. rinP0Ni'L-lI: are monzonite 11:0,' (CLI 11110 0 - n:ioAmberg ,12375' of o'coon .049 0-23 areasS.1--401001-,C exposed:420 quartz extensive east, the 70. 1 7'LTU -4- About 17>77:010dates. _.t (1- isotopic 07 40701' by' indicated LJ'>--'7 70-4 UZ'LOLIO 2370: these -040;.1of. age to mile types rock 107 OLE,1101L7 I 101009 grey 4,04 i[0--0 901: 2oii::.o>oo,o:'- ,0Ci 1o .17 2,177011027175 22 relative the confirming thus monzonite, quartz Amberg of dikes 217 intruded po°i:coi:ii 0> "i÷11:,CL2i.E0TiJ C"C703177 07110. At to by is monzonite quartz 1'1tJLI pink 1tTht.7'100'[:7 Athelstane .02110017:. locality this -o%io in 't'I m.y. age. ill CLY 2o':o-p ':,[1723100LL 1670 to 0070:1 1640 being possibly ICY 04 01,1.11711711, 0:01,0-1 .$1t,:$1 younger grey 10.01117 1t10 Jon 'to0 23o' '0 .0':.is quartz monzonite Amberg the that suggest data isotopic '7700 .r7010E0 .21 10170. 2 m.y. 770' with 141-704.171 1110 0, o;17 the )SCm: 023C and Preliminary Cain Banks by given 2. ->24fl 18604-C of age (1969). 70: 171>41101 I Co7j,i407'01- (111110' 9:. 17'7 232 0 agreement 1 9IL2 good in monzonite, quartz pink Athelstane the for C 2017101>2" obtained sJtI}fr (Rb-Sr, 'UJCY'l[LO'ILOlL '1--Il-,: 7001-'> has - " '707 -1210 An m.y. 3011 isochron) CI' 0.17 age 70-0, >. been rock whole 50 ± 1810 "[2 of - '1 - ' op grey tro7artL monzonite. quartz :,co2 Amberg the ((10077017 be L14401-r2Zt1i!quartz Y.O&ol5 ¶'7"J J.04236y '7070' grey31the .iool0o?' '1. and (7-71- monzonite 92( variety, pink71170 the called Athelstane oN 0" 20'. 701-LI 971. 0.0144 -oo''rNj2 c-c L1277017'J'L177 1-4 ICLO';71'1 2>[ CoO 0211. propose we variety pink the that two the lithologies, of distribution [013 1 (Plates 79 -°Oi'0170[j 0-0107010345.1 9'; 0" 0t'7'([71]'1area geographic the of Because '2). '17 and Atheistane -7 the in in :-',-ntI being 4"-0, variety ,Costot:, pink '.distribution, 11 141171.' 101711 501>O '0 has t!C72J'1112-I 4111 U 9'. 231 of 11101 abundant ,7'.:ctc particularly wide a the 411 J'1 1042' I 04, and 1173 plutons, "OIJ O'ji'14,; 02,-2,O'n300 -'>4702711:1 7.110. 17° 0.1 -230.01: 2 270 that distinct four in occurring Amberg, of vicinity the in 4LITOTJ'011,10"-ilCo c'9 110 the oioo01mm grey 0o:o 05o11104:NL 99 040 %"4(",,'IIIL(U 10,> predominant €0is variety that established has mapping L7[0"4,;1 Field 7 were I(grey?) 0'. 1-14 ,n'c'L711012 2-0074LL'y 11047.2) 417(1 -distinguished. c'71II1I":0071194[: .0o-1 granodiorite Amberg S703L117110 separate atO 1770 and (pink) ite 10 granuI,,11.o 4L1 map a 'm:'fl'170:1,c4 .jo,74 which 0017 granite 23 170,% 27:3 t04' 711017I 1023 2Amberg on IJ.'00, presented and pink >0 of sample Amberg 't'rp 0427±701: 011:0, 4,0 103 2347--i';o (U—Pb, a ,00:: m.y. an pc'ooccoo :237:1:: Cain for zircon) 15 ± CCCI 1860 of age reported (1969) 4173 Banks .f0704" Beckman tLJ01"JG'?1110.01 ;7102,.$([4'141.1.''4114j,itN .lOfOO(1 "200112779 ((140 ,211 recognized were subsequently and (1964). and '1400 Cain by i.17'33by '- .21."OJ.2 ,:OILO.1t 710':. opo0 and (1963), so: '(Efn.C. .24227 grey '7-vo:7.1-707- Cain name the granite2oop1: varieties and pink Amberg 13,0 $:c04w-'0'7290'. originally 0d200in 70 1727fl..j LI'I'J17'>[-°' 13777> area rocks Granitic given:5 were Athelstane—Amberg1 the ' L41 DESCRIPTION: '$'L41.E-'-i-'2-2ltt 0.071372 quartz771.701 pink monzonite. 170131.1' 14 17704>023 40.7 0170.4. Atheistane into intrusive C: '7307414 41 11040,701.1 quartz are 0.'.II7 1%' grey -J1,0070'0'1'1' of 970.' monzonite Amberg Dikes 217>274-, '0 23 >7,47077(27,0 FEATURES: OF SUMMARY 1'00 1973 4,4:41 24 1972 700>07070 to March, '>C001111'25 Summer, DATE: 04 707 '1LIIO..:I5''o0 J.L. 011,207(2117,1Santa '0,1144 11(10:11270(1 -1771 Anderson, UW—Madison and Barbara; '"12077Cotter 722,73 0,70'j ''4>01 ,174'12°0Jy Corp., Lahr, M.M. 111>1" California- of 'opcq Univ. "o"7707; Myles, J.R. Colorado; 0.7 Medaris, 4"1VtC1(. 74 Van €L7.O 0007123 7-2 ':l7C'94[17'o4i o.fl Jr., - 41-123471 -"oLIlO L.G. '417 :1> UW—Madison; Kansas; of Univ. Schmus, W.R. 0 ' - AUTHORS: ., 1230 '720 sec. SW, 72 '7019,1171, R.20E., T.35N., ''741 C'T 10, County Marinette C *lUi: NW-&, LOCATION: °-: nol 01070 11111000 I 1.1110.,:Coo3ik.4 17-CO 012101-c quartz 9' :7041171: quartz 2310 2 >-fofl grey Amberg pink Athelstane monzonite and OIL monzonite TITLE: 17 2 i7'7"J7-[14137'7 Trip 171 Field Locality 43 so �44 to cra'n-g: tnc8, The Atheistane •' ?ti.rtar.squartz qta rmonzonite mennritehasana amedium— .tdtt- to coarse—grained, allotriomorphic granular contains tnC1 both biotite hornblende, grnttiisc texture, cazte, aotlafla blit.t: n:and !ctDbJSilfl4, and laSt has a a distir4ctivs distinctiveappearanze appearancedts due the;?4aGtLcS presence of pink perthitic toto VSe tH from five specimens tve pasine .i microcline and white plagioclase :L%4iC41dZiP(An fLu23—28). 2ti- 2E. Biotite ttog yielded values of lOOxFe/Fe+Mg from 71 to 78, but two other samples gave free '1 tc 10:. but ti., gavu y.eideC 'mpiUte aisSrhastingsitic iaorsgatzt'hornblende hrLh 'nieorr magnesian values of 85 said and 91. of 3? SI. Amphibole "aluts Foliation is common in this as are 'atit. as an hastingsitic hornblende. .yaattcr So acts's 4, tbta unit, recrystallization textures, such as aggregates of quartz grains aoryista.IUnt lea tn'.'a.'t, eush as s.srnstt'v e. 'vact endnmwith 'nts Saussuritizationof of;1.gtoe1.wsc plagioclase is is widespread, ''S'ep,d and a..J mosaic outlines. wunic c.t :.taa a*ssaLtrezcc epidote is usually bpdct9 43'S Jy associated with biotite and hornblende. tat flontc*rrp.nc n4.trocive •n 'stit. -/aluc. o 1cCflefZkt ot $.ct tbi sai;In hntsti: iorcts&e. ii aErcJx!? ittib bloti.u rx1 'bunfl.su's. The greyntet' quartz monzonite has a medium— kcdL'r'totc'fine—grained, fuav.znaad, ?ns Amberg 3btng rns nnvzcut.e PSLS Although hornblende few J) tto4L bovir twtdt occurs catynj in ft c.a ...fl hypidiomorphic hypi5 cnrfl to granular :'saaigir texture. tO Values of sinisrsl. Vctun samples, L1o;ite biotite is the most a4teant waCts mafic mineral. 'c. by 'ayfar tn t)as sol abundant martin. tn lOOxFe/Fe+Mg of 67 69 have been obtained C?and rn E3 Jte.ve t#sn ctcwkfor i'vrbiotite ?Co:ictfrom trri two i3 the ji, ..tflstit ;uac vcctv'.ib", toLiecSn Atheistane quartz monzonite, foliationsad and specimens. As saetnon. 4.c: in recrystallization textures common in the Amberg. Plagioclase tat nbov,. P\'aioo3 we ita.tt ! tmcn@'. tezttns b.ry,are CC!14vfl n' IJ, slip nd (An fl 22—39) is sxartrc extensively saussuritized, bsat.tt biotite is Li partially altered 39) iu y gna:c:ttzcci, to chlorite, and epidote plagioclase and with is, iS 0p2.*t* 14iis1 present t'bSift.t in :r p134.CtSta* satassociated 6rcctttsti R±1. tO CLLtZi biotite. blDt ito - I �,V 45 REFERENCES CJ[.idul! .CC r! y:' Banks, P.O., and Cain, J.A., 1969, Zircon ages of Precambrian granitic Jour. Geol., v. 77, p. 208—220. rocks, northeastern Wisconsin: T-'C ça&; - a a 3ZaC iRi1&t VVvrVy-:: :•L1.fC citA:C -: .J: - 7—14. J.A., and Beckman, W.A., 1964, Preliminary report on the Precambrian geology of the Athelstane area, northeastern Ohio Jour. Sci., v. 64, p. 57—60. Wisconsin: c:V. wViyr2;i:J t3-.r) aw V a L7V-7VVC p. #cl;lJ'C, r p.ct 3cn1V:.Cavr 1 or :.fc.TraC3Cr7 CICC C.. VVCC Cain, C C- 1963, Some problems of the Precambrian geology of a review: Ohio Jour. Sd., v. 63, northeastern Wisconsin: Cain, J.A., a �This page intentionally left blank �I 47 Field Trip Locality :771177 3 7 4Ci . 7217. . TITLE: .1:177,7.1 Belongia granite and Peshtigo trachyandesite : [7777717777177 77 774777' 77 1 777]7 '- 's771:p 774 1" LOCATION: T.32N., R.18E., Marinette County, west end of '.713? 77i:L'3.1": 77' 5r.: ,fl]7: 1, .777777, sec. 77" NW, .774 High Falls Dam 17,7] :1 t 1777 AUTHORS: Medaris, Jr., UW—Madison; J.R. Myles, Univ. of California— Santa Barbara; and J.L. Anderson, UW—Madison 77177771 °1f 7,7 .1"":77',.7] 11771"[7t7,! L.G. "7'77.I7i7.7]] 1' 7 5777777t3 DATE: 1971 and 1972 Summers, SUMMARY OF FEATURES: fl.:"" Peshtigo trachyandesite has been intruded by Belongia granite. A syenitic border phase of the Belongia occurs at contacts between granite and trachyandesite and as veinlets in the trachyandesite. .77'773 1777,7 .4,7 1"177177711.11 : '7711 77. 074(7!!I'777'7777L :7711 _•.••.1"7'[71.i77i7:7P77 2rc "l' 13:77 777 IL )7S,77:11. .72 77:77 .1777:11777.771 ''1"" 1 2777' 77 777777137717721377 7:77 '1771, .11'37i777 DESCRIPTION: Belongia granite and Peshtigo trachyandesite are in contact at but we were initially puzzled by the rather ambiguous However, after examination of thin sections, relations displayed here. chemical analysis of rock and mineral specimens, and discovery of more explicit Belongia—PeshtigO outcrops near Mountain, we believe that the Belongia granite has intruded the Peshtigo trachyandesite and that the syenitic rocks occurring here are a border phase of the Belongia. I 1'! '771.74 7771715'r.:]1i711 -'7 ''1"' .7 .1::.:. 7:7 1" L:771477727117 :714 777: .7 1:7117]. 77'I )hif' %7'.:''7r 1:) 72277 --"i"-j-L77.77 fl 71 717717717777: 17r1':ln ..7277i777...171,'7717.cL7:7'C€ .1:177.7 7)1 .7777777 57,777:7 '7'":'7c 7.777 1' 3.277]. 41 7'r.7] 71.7717 , 77 7777 577's 7772'71117771:1C1 7772 :7;7. this locality, 4"" tO.€ :r71"j0 7777." 13771 771" 7Y77 17'1]Z1.i7 7771 7717': 7 In thin section the Belongia granite is typical in appearance, consisting of euhedral to subhedral phenocrysts of alkali feldspar and quartz in a fine-grained matrix of biotite, quartz, and feldspar. Granophyric texture, a characteristic feature of the fine—grained Belongia granite, is present at the margins of alkali feldspar pheno— crysts. In contrast, the Peshtigo trachyandesite clearly shows evidence of recrystallization. Relict feldspar phenocrysts are set in a fine—grained granoblastic matrix, and the phenocrysts are surrounded by a well—defined rim that is intergrown with minerals of the matrix. In addition, anhedral poikiloblastic hornblende and biotite are scattered throughout the matrix. Thus, thin section study suggests that the Peshtigo has been recrystallized, presumably due to intrusion by the Belongia. Th7.T177': 1171:17. "775fl[ 7717 77 71773177112 7777:1777 L77 :fl 777".5.7 7["'777 .1]]; " )74fl14177 "i::7flfl 72.7.177 77 7 7771[:7 7 "L"' 7:7717 .77177'777j' 77777 13 21 27712772 7:.] 71" " 773.i77771771: :7L 71777.7777* L :777. 71.7:1fl7> . [77 :7 .777 1.7777 7: 1]: L,7]17711111717; 7 11277777 1 W.%' 77:'7.1 1]7:'77 7:2 71752 .17 •'1 771: J3.:'777 771". 777 1-:j7..;71.)7 ]77.t. c..11-:1tse.J Cc::"777]i T.7771":1 :7 ::71, .7"7L)777TI"".177#' 47 77111 :7,Ltl '77 1)7771277 17 2 :7777 5)771 •70777a'!l 777 77.7: 7. 7271] 7!1$ILTZJT'73 .771 7]12777]LItflLl7. 777 L"p: 7j7 77127.21477 c'77 711'1 771r!717"1:771.I. "1,7 57177C71321.'717T.77T7]77]1.:17:7777t 7771 777777 177,772' 2 7777 7157: 1:.7 177": 77.] 77,)*" -ij 777] 71 71717247 ,:7117'71$.C7]1 7717 751 1T\77.1.777 :7c.477t? 13 .717 ]717 7i:17"77'.121*" 7.17777.771 :]771]7ifliJ7,77, '• I LI 1177)77771 7.127 F*"V 247711€ 1.! 777 1<"L 777 7,1' LI £2 �48 If sooolttc con'ca'o to Do Lweaothe th: tctcocgla The occurrence syeniteatat contacts between Belongia ot'oi. and 5l,o(1''3'i1Ct of 33,0 1130 ?'aootlg'c. o:gc,rthat tool the Ito Peshtigo and as Peshtigo, suggest :'sii,I 543 :ijcutting ','to'nc the at- veinlets PSOJt ig'IcLc" 31 soil ai coct'iaco; t%o Fir 'Loll :a Chemical syenite phase cS of the Belongia. analyses-'o,,,:-cio'a":'o±o demonstrate 'a border to,'1oo ;l,ooo to' a 371 33 Ic is t'Ic,t of i,'30j nie4!,r::e between teI-'co-a' that ,:3 granite tYct I to La that composition ofI syenite is intermediate to'a ocopcoTttitoia tin— '1 the laic na!c'ci: , 3 Lilt Tot I -oo 0 of E' biotite t1"aI amphibole I:' 433,'a' and and trachyandesite analyses -L a tO 1), but ai'aca'noD'aioitirJ 1,9 (Table to-,':- mafic t',3333c 3:01375330 (Table reveal that To Fe—Mg St :aL:Lco ratios acoare 'Li (1.':(1,ir higher for minerals from coal 'toao 1,3 jilT:- 2) iD 101 cAlthough i,'Oli oc'aOI::'a1013o I .; granite and syenite for those from trachyandesite. 300 tiJti" .3 to than Inca :Fctr'.ooov't 010'tlL71liOtaiOili o'aY3been toot due coo ppartly cool4 to contamination development ofaDo thest-coin syenite could have cçco'at 33 :c' COOLO. 40::3 in the it': '000lL-:icof granite by in':' reaction i"ac",3or 'ttL with i33--oij5i,'o'ac't1:atotrachyandesite, perhaps reflected 00 47-0233 :' oco (1969) have occi '['.4': '-orb. a 'ta'o;tatvc :3"a:c(J,o 1: Ti02 content of the syenite (Table 1), Luth and Tuttle TaL 3Iii"L/i'ji_ :looo, in a granite DLI 'a 7 cici'S flO: shown experimentally that a syenitic border phase may form 3,1:3233 3:0303 tool: 333t4- tl"at a rot' tiC bcc'do:'t margin of '1, t'ova, 'lino cov'c,'a1iotto 5'ai'içO, 04 113(133 taicc,:'o :3 m:at,a33al, due to '.0 vapor transport of material between the crystallized 'cot' olcJLly a:-' -, to. still partially molten. 3 1-111 33:3. '30 Theinterior attot' ci.' portion, an intrusive body and the otto- oat:": 1:33: ., 113Th : fl331 53123'i'34 other o':'oi"c, Belongia iIOiL'Cv' 'a 1 coal 1,':i:t where :441301 localities Syenite hasU'o'co been observed 'ja'aor'co:I at 3-' several St-a'otts tao 03713231(1 to-i 0? 'Di':,t3o alliLlOl' 4001111 40' 1PC'(1'0'flL 'to, granite40has intruded either Peshtigo monzonite or Waupee volcanics. 030'L3' 30: 'Il,tflhiilo',I Doctirltig'; lco'30 monDi,: _.a Peshtigo on.:4L4' intrusive oa o'ic'CLT?t into For example, a clearly 1T33J'cI1.2 'a granite 03:7(1(10 to is JILt:' co:'o'pl c'. Belongia t:'at-ooc:t 33310, tiT 3 037'L':to' ''at ((1311 0307' 1:130:175 - (at the boundary between sees. zonite Mountain 133. a a arailroad aOL -i,-.ti cut near '':'tc'c.t'o in o"o.II:',,. over -ova:: -33-toogranite 7aznt to grades ::co)a::: :113,T.31N., 3 2a - R.l6E., toar'lc County), 14 and 23, 5, 1411, -' Oconto where 44 an'S " 14 sharp that lb-ta :':."icoo several inches into aa ot-a':.ita syenite zone 11 inches thick that has a "-'23,0' 18 L,n too :co,,c orCosi. contact against monzonite. 00(1,3107 0-33--o- Peshtigo Foahtig'o acoacasi,'ne . - - - :1 os:: 32' 23 7110 Jtra--O IT, Electron probe analyses of331 Belongia granite, -o'ot'o-ta 37:130and Poolct:t 1(1:03 •o:ctoco-to Belongia border phase, and Peshtigo trachyandesite 117230 Do: cog La 3-o'--do" Table 1'fc:lo 1. : - 1 31133 Si02 Ti02 1144 153' Al203 76.8 2 65.2 3 .68.3 4 57.8 0.21 0.70 0.64 '3-14 1.45 11.62 13311 15.31 141,43 14.28 16.60 Fe203* 3.20 :- . 6.67 4.48 10.80 MnO 0.03 0.02 0.05 0.12 MgO C, 13 0.10 0.57 0.63 1.36 CaO 0.75 1.52 1.74 4.07 Na20 3.16 3.66 11,13 3.76 41,434.49 K20 TO 5.15 6.69 5.73 4.35 101.02 130, 4 100.40 99.61 101.04 331,331 Total * 1 1 2 :j 3 Iii l-i' as Fe203 Total FtFe151 Total Belongia TM' 2C 7-si cng1s granite, g"iaou' <.0', tb TM 2B ,': ar in iic Po,3c'' <ki<:.Y-i,?3-.,.,0a113 Syenitic veinlet Peshtigo trachyandesite, 'TI 44-',ji,-' 'at LcOAi±,.Yc,'0 localities Ji'0335 at In-oi"co: border o':'tii,-' phase Average two coca:yooo.. analyses, Belongia '3 433 7.7 '23135 of iLt'i - 33 and 331-3 M2 near cr4 69 '1va:c. 507'L, 171.2G :0: Mountain, -S 4 33-4 Po:t'cSoci Peshtigo traco'H'ctd-oo'' trachyandesite, to, PP3 �r ;ratictf. rnn.tt: 513—548. 115, 144S. Mem. Amer. 513-tk4 p.p 113, magmas: ra4xnc granite and cqut Soc. Geol. 'wti granite with -v..tl' equilibrium in phase 't p)tas vapor hydrous Thc The 1969, o.',, 0.F., Tuttle, sa and W.C., Luth, 'c4., u.ctb, b.1. 'rico: hynct Lr br RENCE FE RE Tfl PP1 ittu. trachyandesite, Peshtigo hyeztlc tr Psuitico 2B ai e •nvhth: frar from Amphibole iii 33 from toltts Biotite i?n 44 TM nttD)et, veinlet, syenitic nctatti o's from1 Amphibole te.ptf'ace trachyandesite, Peshtigo psgi; t.1'v&&Sp' 'r ytr2.sj, PP1 13.07 3$' 8.81 33.18 32.07 32.eV 28.91 0.95 t\t LT4 0.74 ..Jt 1.06 3.85.r —— . 9.76 :.. 10.00 .0 —— l.fl 1.75 1.76 •,fl 1.33 1.45 98.18 98.51 94.5 80.8 95.1 •—-. - z ''.3 Mg + Fe Fe x 100 t caE Total a; Fe LeO as FeO • 1.59 8.37 t • 22 2B TM CL veinlet, syenitic M\I&).tfrkl from trON Biotite g:aat, granite, 85.2 93-4 96.4 0.92 3.72 3.tt 2.81 2.3' 1.92 40.97 41.40 96.22 93.54 43.4 95.72 9.12 .aC CaO MgO 0.74 —- MnO 34.96 541S6 34.4 34.98 '* Total Na20 -— —— 1.02 ipr ItS 3.23 K20 8.59 8.61 —— —— t —— —— 14.26 13.22 2 3 1•,• 5 1 Belongia Biotite lainsgLt from fr3u' igtite 2C TM 2 ts.' '5.i 34.07 34 34.17 .fl.fl 37.81 4 5 FeO* A1203 Ti02 TiG Si02 FtC2 .1 1 Peshtigo svt granite, Belongia Bc1cv.hs trachyandesite kcsht.7. tp.cl';'w&lsssatu and tw.e, phase, border :cndc: Belongia $,1tvtga gns:.ts.. amphibole and btuu.tr, Electron ¾, 2. Table Yc,tle 'ca from açb±ao.s biotite of a! PaL:flS analyses ;tct* probe :O4v,n 49 �This page intentionally left blank �ICnI CCiT 4. 201CC C of rocks. older CI:o--otcCoo:: CC. contact CC diorite quartz Hines the of Emplacement T CCC 505 and metamorphism 5. p1Cc gneiss, Macauley quartzite. and I51!C q11CC. Waupee 50CC coo and CI:;:cLt-o of i 'n5-5 CjC C-C clasts contains metasediments, metavolcanics which conglomerate, Baldwin the of deposition subsequent and Erosion Ill I 1 ::LncF -C v. s> iir.y contemporaneous). IC5Ci 2:CIT been have may 1. -;:Yr;o os:TzCCpL C5=-C4 5505 rocks. sedimentary quartz—feldspar "Cp;C1Ci:tCnCoiC:. pooo CC53I5.0CCC !4TN pzoo agglomerates and volcaniclastic, and 3P5:17 "0C0CJbCfi0C I?C'IP"Ss the t? 1531 001;. of Deposition formation, Waupee 2. rCLiCTCCCIFICrC CCCIILYIC 1:*.CCJI-:;J:L1. metamorphism. contact attendant with TC7CC5 CC0CC quartz to 5CJr2;0C2C2(C gneiss ;;CLCtCVC Macauley t5]5 the of Emplacement monzonite) (granodiorite 55050: 3. CC.OUI101111C55.C cCCCCJ Ccn ECO metamorphism andpC1 Deformation (Events 3 CCC and IF 2 T CI?C-lC;1CUC •Pco "OCCOCCOSS tuffaceous, and calcareous, s-si: , o::coopJ.. o500CCC flows volcanicC — of consisting i: CCC;: CCss5 CIIICn-5-I 1o youngest: to oldest from events, following the including "00CC 5105 CQ:CC5 515. 05 [CCC C C area, 03. preserved CC SCC0s Pis s'; history CC T :oo 0C3[inCCcC. Mountain the in Precambrian complex A AREA MOUNTAIN THE OF GEOLOGY DESCRIPTION: 5Th CC C yocovos:siffare 0CCarea 5525 Mountain 5055 •5fljp 55 theC10 of history geologic presented. j%05 " iTs I? p5±5:05-C: C 5CC are 001. 0iIL map iIT:iiT55 outlineIbCC sketch A this at illustrated the C ofr:rT1[1s,t and iCtC locality. T20,.tC.ssclfeldspar .5005 ç;- Hager and rhyolite, C5'5C.C..:C 5503 Baldwin 1: l:10flp --F po Hager iCStsy:3 conglomerate, Th; porphyry 115100551 c CCC0?2Ci CC 0111 the soI1C.1CC.54:L ;cs member upper :51 Waupee Cs:. between formation, the of Relations 5-: C .JX5. :1 Th FEATURES: OF SUMMARY 0±1:31 C3 C53, "CCSummers, 515 0151 1972 and 1971 DATE: Kansas; of Univ. ChlC" I"C"1 Lahr, "1.soo; Cotter C CT and M.M. Colorado -Corp., ''I iS0CICi5iC1I._L33L ":— Medaris, 1To_ -"_y; L.G. Schmus, Van W.R. UW—Madison; Jr., AUTHORS: .05:550 R.l6E., T.31N., 505 Oconto P110:3 County 1,- "51511 sec. OilS SE, NE-, LOCATION: 5525 15Mountain area C51CCC1 5I5 rooTs and 5i-i'5j: The 55 of geology :'o:c: P5511550:3 CS and ". 1:50.10. Hager rhyolite the porphyry 3"Ci1±5:5 feldspar TITLE: ;-iIs 55±:13[ 4 Locality •P-sp Trip P1 Field 51 �52 ". 6. H7495707)f,aJ:Ci .7,5', o'ios.t batholith OItco.asIs"Th (1450—1500 cf"1sc of the4aosf Wolf River m.y.), including H, .5nc1s0J, 7.57l5y7$),L5, 1's-Is'S Igo ,)ç71(33t Ott Hager 51'051'," syenite, Oju'tlfS. feldspar the Peshtigo monzonite, and :t'IJ .137 '.7" porphyry, 9,00 )159551:17ç0755:7,351 of xa0 Ool 0777.0 granite, son's tO with rhyolite, Belongia '2, and 75. lOs contact 1c)ltol, S metamorphism .1:)' older ..dcicr ,&557'J.Kt9'77:,51'5 Emplacement 11 : rocks. r"77''3'1 1' and 11153. steeply 2713 Waupee 0'1157'55',t.'sOi dips The 'l1710'cs formation '.111 strikes N55E. M15)507•O' about '55ss011't Ot.o':, 7-oH sot Relict llTGaO cross-stratification -3)77)3'- 555333711 '1' 370- :1' 3111W '1.7 cccfs.Loss.g ¶959 155a55'3 that graded bedding and consistently indicate 'I,7ll'075'1,0'I'L' 17'a'lst tops llTs 0: of1150053:9 beds are to to tilt the.5-cotio; north; there 1't$9. is no evidence repetition "16 01531. )1a955' for ''01 '25197:5 Hc:is of of. beds 3159 '90101199 15. 0571115 the within Waupee formation. C'r'flt CI'S, 5 15 /Ot. 51531191 has 11751 Waupee l'a'ITJSOOI formation ,sLo-a9 units ooc'ossI,s.tLrs'. The fIlLS. been i35,t")5757'5 divided offosSinto fo'•:a three (Fig. 1): 1)5 1195107 ot.55:1i3. of SI'S' metavolcanic a basal member consisting 17I1''ois aIl91a1:f'9$ £9.;-5.."OsLC-2.111.5: and llat'95. volcaniclastic 10 0jIt,L3'jLI4111-'1O meta— 1s-tS5-' 0 and sedimentary 1701 rocks, .s. .i:r: .L 515517 .9075 '91317 :o'o 1115719 1:71)517' 2'3t1J510'LsttiO'7 3,' a :nmiddle metasedimentary member, IsIS. an Ii's upper 505,105 577, the 1•''hP'S'a9omo 97i5'31-,9'.1. 995'"a,Y'T member. Within 7155711] tuffaceous metasedimeutary 0)19 'bas,sT. basal member, .111-:'5JLY-157 basalt 7r)t),51.f"7'1i75777,7 7:7357, but 71j'95j577l977.90al5 type is tHe the predominant of volcanic rock, andesite39 and so 553,'5.7171,55,9, 95,7 rhyolite 7'575:.7J 17553 LL77of 3-"'11M 53'H. occur toward the IsIt top the unit. '0091a5)5L. ll,rt5719 505 Chemical analyses of 18 specimens fo:..caa,r1c 7'''-L1' belong )1 calc—alkaline 'S's a 'IL's.volcanic 'loScolt: rocks demonstrate that :la57', the 5505)7259, to :::li053&1OI,5L.i1S sequence 61'.7617101100 )1.Ja-5 7"t9.?aO 'lOs 7,15:7 setting 7 15571,5 '1717 (Lahr, '7755 and 55557:J could have originated in an Ifs island si 1010 arc 0511:57:7 - 1972). 15 ., flC."')071,079 in formation have not been '50aup:c' .ls:-as 1395 11513'I '.1 the 'LOso Waupee IICIiU.tO 75377' evaluated 091.955077: 73 L 55S .e.1700 of completely yet because 0.1 complexities '3 lo.ç'I357._ '0.5555 introduced 5517 1710'7953050 by over11' 9523.' lapping ro),.esn0:s'caJI',:ot.'oaotlll metamorphic events. 02551 Most ,ss.jsocoLccoI specimens cOOT) display 2157710 :)0'9t7'107 9' assemblages 119515 :.os05bs.s5-os.., but characteristic of amphibolite 775555a'l 1a1'OT :3 facies '9) 57's metamorphism, ffl'.,'I:,'esso 5253 505 s :05 S:,'I garnet, 99251r17:IL, idocrase, 951-7','s occur 5j05'51,']0i05 :7'): of .a5.,7.2:0i1rs)Ls7o origin 07 contact 1:50795' .15371757 in scapolite, and 917551 andalusite 1c5715515535 metamorphic 151. rocks 11052.957rhyolite 05120112:07 a-'.1'.'.':112 ' S LOs, .11,93,1 51'-55 1591.Ca1s7'lOsSI Hager i05"15'7i 719 and of15i.lr-a7-si:5:''so.as appropriate composition near the Belongia 11 granite '2 91507 191519315's porphyry. poJ1o1'-a-r7. and feldspar 54.5tss,j/:1''701H1s Metamorphic assemblages sC71i07.,L1,a-535I' - I .Yo' 0505137'rIrtf FIELD TRIP LOCALITY Oi' '12 57t11&5.' W are 9552 tuffaceous In the woods south ofofCounty :17025 outcrops '3'S '15' '5152 of oco51 S'a.a53'j, Ccor Highway Jo. 255-1 3'S:. the upper :sLseWaupee 'Ozcspeo formation. I scoaost)'oRl , Cot On .sp,o"— member co-s 5500of c2 the :),',5 r,"i1a'J5711 a 7H50'1a9 15i517'N3,.,9 rr 351L75o1Tll 015 232 the north side 95) of the highway ", are outcrops of Baldwin conglomerate. 155' 571111 '5550 1,i,a 1 :1195'i.99 t'LaI of isiS Hager 7:55:95 consists 7150151105:112 00,'I1t1:. in .,5sli05751' 10959, prominent The highest, most outcrop area 1I.osOOr feldspar 071 this 51513.51517':53'9 porphyry, and between porphyry s7157 Baldwin iOssl7,'sr 305. '9 S l91:1tt fa57']feldspar 2T1515 10071950.) fl:. and -170-a an 501 intrusive contact l'07a55211 ,.$j)07JL base 7J115 5 '),995':' Ca.JI1L/ii0'7 On conglomerate is 9-97,1,35,7 exposed along of the '571.9 outcrop. f37,5 the 7,75'55 5' IsO a95to'10 the 1.150 southern 3a-1,-,j,,'7, :55 7'7';:177:711'5'.7551 S a,'505a5751117 97 55515s5.t 3117.11 1':571,Wf90 15157,955 north side istot)' '5577,1 of the 171 prominent outcrop a gradational contact between Hager 513:571555775115 is exposed. 512,25,'s'4'955, rhyolite feldspar porphyry Cf 'Ccilooosao' "Jr fl I SLISO and 55) 1sot1.rl.aio'rocks "3/3171]inr, metasedimentary .579 55'- : REFERENCE 77:111715.153'? of a greenstone a:o Oconto 7:173,j1595'S.'1 a lbol.. in Lahr, M.M., belt i0'1k, Precambrian .51]39s95.5'5 95, geology .1,19.: 1972, '.i1,57'.715'çj'iT eoa;c-- ''3L7;5J115O. 93'0)'i95!'s'11,17',: of County, Wisconsin and isiS the 117,15 Waupee volcanics: on'I geochemistry -50155117; ')'b"cO' Univ. i'a'yl 797j'sis,, 505555 M.S. Thesis, Wisconsin, '55'H.s')'1n7 LI, Madison. 'a I �P4/ // -. . ' 1? / P. / Jp \j r4 ( "/ /7/ \4 . A /i '-I ( - ILI 1 i-i;-' 7 ILk .1'<• - '4/ ) LL L.G.MedarJr&MJviLahr Baldwin conglomerate bc Macauley gneiss WI wm wu mgn Hines quartz diorite hqd JUM ['?IL¼ 4 LI bg Peshtigo morizonite pm 1 metasedimentary rocks metavolcanic and metasedimentary rocks ::;. tuffaceous metasedimentary rocks Waupee formation ' fl4LA!1.. ../ 4..I/;1'. i :-.-'I bg Hager feldspar porphyry Hager syenite hs hfp /)7I:4.75 Ii5r! L_ '/.fl/II/1,lp J4I., T"L4//J A/. H a..' 7 1//—/-. ://j// Mountain Hager rhyolite hr 4/'.'' J11 [7 tiar'I•t I [7 d I4/iiA] /1// 1/4 —117 hr Belongia granite bg EXPLANATION ±iL j *¼-; C,T R / 7 \/ 7:; /1/4/ I mile iL ¼ijI(4// ri 4/ 17/ If•; Tij 1 A S J. I//v hs I'.. j(( / -. / L A" j ,; ;.f/.:/,H LdhiJI.% 'I 1kv\/ D.cH (T. ¼' GEOLOGIC MAP OF THE MOUNTAIN AREA 1• j I i �This page intentionally left blank �55 Field Trip Locality 5 [17 TITLE: The Wolf River quartz monzonite t1ILL_JJT C:tCHH[1 I_• L LOCATION: Menominee County, on the 11° IL — -t IT VT — Z,? — H:. _— SE*, L sec. 22, T.28N., R.15E., of the Wolf River west bank NEQ, V IZ"'I]°( AUTHORS: L.G. Medaris, Jr., UW-Madison; W.R. Van Schmus, Univ. of Kansas; J.L. Anderson, mv—Madison; and J.R. Myles, Univ. of California- •1Ii C! H HHF4 <Jj 'C ° HL1 I ° c-HTrI - — I I — Santa Barbara l1J&flL H >(j(! j DATE: and 1972 1971 1LIIC [L 4IT°'I HHTI Summers, FHHU1H SUMMARY OF FEATURES: 1;2 (FFjj!i' Exposure of typical Wolf River quartz monzonite. rT4I ;i HLT DESCRIPTION: VJHCcYi The Wolf River quartz monzonite is the most extensive lithologic unit in the Wolf River batholith, accounting for 51% of the exposed area (see Fig. 1, page 10, this guidebook). :cc çT :I I TI .T1FIHTJH H i :• L — The quartz monzinite consists of large, pink, ovoidal alkali feldspar grains (1 to 3 cm) with a medium—grained interstitial matrix of quartz, two feldspars, biotite, and hornblende. The quartz mon— zonite is massive to slightly foliated and is cut by aplite dikes, some of which contain scattered, subhedral alkali feldspar phenocrysts. 'yHT-H[iE i1 H=1I3 C)CCI JTflT1 ''HH TcH Z:tC cq 4T'L©H t= 2Hi)II He;C5 c(qI HHItJ:HI .CCI HIP 'IHI L.V :H !F L H4 I C L ;4Q p' tJ L — II F' :H -( At several localities along the Wolf River the quartz monzonite has been intruded by dikes that resemble the Red River porphyritic quartz monzonite. Two such occurrences are well exposed at Beartrap Falls on the West Branch of the Wolf River (sec. 4, T.28N., R.l5E.) arid at Ducknest Falls on the Wolf River (sec. 27, T.30N., R.l5E.). F 1PE I (C ° ( °]i 1 IF Cc 4j1 — t7• :.:Z '1J :__L: 1 I Tj )14V C CvI&L i:;: 1 IH T1? �This page intentionally left blank �57 l.it:c Field Trip Locality T: TITLE: 6 The Red River porphyritic quartz monzonite LV' VeEV' n!I41.V'iSLVt eL'ç LOCATION: :;l :.*T1Ti °fl R.14E., Shawano County, T.27N., 2, V sec. on the Red River )çy) LV' 3IV'C Lyi; SE-, aL •IpLVI:. SW-, 37 AUTHORS: UW—Madison; W.R. Van Schmus, Univ. rV)Vi IV' L.G. Medaris, Jr., and J.L. Anderson, of Kansas; 13W—Madison 3: 3 -3rL-t uTmfl )JV DATES: Summer, 1972 LLZ1 SUMMARY OF FEATURES: V'J Exposure of typical Red River porphyritic quartz monzonite IL c:V'VLVV'I ty r)1[ V'L TT. fl.d:c r DESCRIPTION: IV' The Red River porphyritic quartz monzonite constitutes 20.6% of the exposed area of the Wolf River bgtholith and is located in an ENE-trending belt between the Wolf River quartz monzonite and the Waupaca quartz monzonite (see Fig. 1, page 10, this guidebook). ')t ç •iV' i ThLV' t)L7- V':tJ V11:rL LVV' 1V'V tT LV'4'Fli i ir — - Fl I1 —ft VD& :: j VS Cif1V2 'LIL7 4•II.E '11 1> tcCL7 At this locality the quartz monzonite consists of 10 to 20% subhedral alkali feldspar phenocrysts (0.5 to 2.0 cm in length) in a medium-grained matrix (1 to 2 mm) of idiomorphic to subhedral quartz, two feldspars, and biotite. The quartz monzonite displays a prominent foliation due to alignment of feldspar phenocrysts. çJ t. ;"zV':i' 2QVSLLtIL tLY- zci rzc1; LV') ° C)51 I i i —n nj:tccri cj ' LI I $3 'I TTi3i. LTfl- LJ H7Q7f 1'4.T 7Lta1V'fiIflC LC TL6I;=LY c 11 I €4 i)v&: �This page intentionally left blank �Dissertation. i iv .pcc...Lc I cli7Vl LiC/, 447, 4I - 1965, The Origin of the Tigerton Anorthosite. IITIL W., Cl-1c41J, L. C-.Il-: unpubi. Ph.D U. ci ycv Weis, Wis., fill-a,.- (IL.fl Reference -ccr-aiI avccc-vcc E NY. y'cc 1s14.; The most common twin is the Aibite twin. Pericline and Carlsbad twins are common, the latter has reentrant angles. External optical scatter occurs. Grain size reflects cataciastic deformation, with some outcrops, e.g. SW-, Sec.11, T27N, R11E, appearing almost layered. - --21 a- 1,1:1cc1 ILsCflacc C-nt-C-I c Ct d-yC- 411'tL)CC-Ll IltILl I Ill-till :?fii.a-fl ILl cca(a II4Cfi\C vral3cc c mc,ff'lvaw.;. cc-vt tc-;fl,; cat- rcrt-ntc'c c-cc- crr.a-: ma- t'r d-a 'cacc:ca1 - - 1fl'- l-714kC)ll 111 -q. [I 'C - 1t11-:cO1'ILLclnCI :ccw cn4 ccc a, La-trcitczcc JlaC(.)© 1-ILl The composition of the plagioclase by outcrops has a median value of An53, with only one outcrop having an average over An56 (An60). The larger common inclusions in the plagiociase are hematite, hornblende, biotite, ilmenite and magnetite. Very fine rods of these plus rutile also occur commonly in the 010 plane. C -1:15 ;fi-- 11117 CCflV II c-4;4c-a]aiI fill 9hiT .. -----Cr r'CCccc-accrC I41( 1,ji .11-I-1141".LT flC.'-iiftL)tCCll.iCCrIlr 1.-I Ti Ic'.: fl1-cr ar-;a 511:5-Il pa 71 ccv caaltC- cat iall: tilcIlla SILL l4t1c cccync city CLLLCa-l .- I aCvcc'-.'L-rcr-- a-y1 a-ILL - - 72-rn C--m:ig c- Lid pita- fill-cl cia: 111:,ILlfl t 14 a-fl TIc c-c 4p1fi.1471: 4 Tdll The Tigerton anorthosite outcrops always include granitic material. The anorthosite exposures generally are small with the largest continuous The contact with the Wolf masses exposed only about 35 meters long. River batholith is sharp, both megascopically and microscopically. C- l.-L1IL C 4llIIlLlli s-1 Cr1: 1ILfitilT1 4-c- -fit-IL? .111 pat.-: mc --fl icy c--cc -r-;nt 7ia-a-- ccc Sr Lccr;-:c-5- CCr.L!-C,IC.S, I4cc)I1IJtLcI LCt -? ll1-rcill cLttcc ducc-ca:-c cc macc-Cr ,Lt c- -I-Li- cU I cct—aa;caac 1111 'i'jj .clcCnrczv 4( ififi 'wIIc C_i.4jL :c'ca [IICLS The Tigerton anorthosite may cover 125 sq. ml. in western Shawano Most exposures are anorthosite, hornblende anorthosite, biotite anorthosite, or gabbroic anorthosite; a few are anorthositic gabbro. The plagioclase ranges from An32 to An64, with most of it An4 to An56. Grain size of the plagioclase is riab1e; 5 cm. grains are common and There is local foliation. grains up to 20 cm. occur in porphyritic parts. Biotite is second. Hornblende is the most conspicuous mafic mineral. At some localities pyroxene occurs as cores within hornblende, occaIlmenite/magnetite are common, with ilmenite sionally it is discreet. Locally, as in the SW-, NE-, Sec. 33, far more abundant than magnetite. T.28N RilE, these affect the compass. - 1'C--Pfi-dP 'lftT -cCL C 0147 C '- cc-a-c1::' c:n-::--c4crn 1r1k1 a1.c71rcL-c CflC:rT fit c-fl ?cuvfi 1tcc flalcILa -mir cc -s- CL3r1:c-; ca-c-i 71 I .rrjrcLflcC, 1 fl1 imLad I.- 71 --••c•'.1,T-fi ;ICL :1111-ca- II .11 40 lIla 47 v-IL-v1- I;LIc 711LC:L. It l- 'ta- - fl Tha-LLa-..Lr.plc :2 -: IL11 v; 1OCT11 iv 'my H ;1:;l1caifl: cc-co'rcicaa'Crl a.CflILc-1 cc Cfl l.t iltrI.II. IL? 1-IL -ca-; 1i-filc.1iCi ct-cl pcc---J- C'IfiL di -cPU Cm II- iIL-0I- ILL/v a-; l'1fi-c-LJlJtC..,-lc- It -ILlIC d-ll-t.' 11: C., I CCCII Ii CJyII13 tt:tdt.IL-'c9 ca--n vcc: -Il 210 c-ala-crap wcc-. alIt .1 : ma-arc :ra-171IL-.:l? --cc 7. c-t7 v5rycrcrcc -c-laIr 1:1: lift —flIc fl -I-fl 7a- F I?P 1a--A5.IIL am cap-ct s. 3111ilyfitLcilfl SI-Il iccr:ILC Or? Ca-a-la- I71ui cmiv Cq ILI-i'.-p Co. acILCLICL4 DE SCR I PT ION: '-c-c cLLcaI-zccrcrcc r-;r-c-c3y, - p :l.l?lIlfll- Lt--[ a-c Contact relationship of the Tigerton anorthosite. - ?S'7cfl,,:cc £4 SUMMARY OF FEATURES: -,,- 1, 7.S4aJJOIS Summers, 1962, 1963, 1972. DATES: ::cy-=crv-aw-14- ::.r,,-1l- . dd?IC/ -c a W. ;a--Il1. L. UW Center System—Fox Valley Weis, AUTHOR: pcc-c a::.:ip-[ cva-vc.xct1ta5 7'IlL.I-J 1C Art 50i1, SW--, sec. 23, T.27N., R.l2E., Shawano Co., Middle Branch Embarrass River & Co. Road J. CrC -cT m4fl Cr1a' Cram m.-ra-1rv iafi 4c NW, SW, LOCATION: 0711104 211?' iti J(?lirtj, a-kr. The Tigerton Anorthosite TITLE: Lcc-mca- -rfl;a- p407,1 Field Trip Locality 7 59 1 �This page intentionally left blank �61. 61 ;' r:iLca ctr:L,o '1 Field Trip Locality 8A TITLE: Ec1. :9.e 1 au b Eau Claire Dells County Park LOCATION: CR sec. T.29N., 7, R.1OE., Marathon County c SW-, AUTHOR: LFLtirg; UW-Oshkosh ]1 Gene L. LaBerge, DATE: i61TL iTa\ 31.1b721 Summers 1970, 1971, 1972 k ''..J1i1S J.5l AH1A: A SUMMARY OF FEATURES: i2]7s; bt izA1I ti2 D:1L :Laite Ia •iL9.:g;, Eau Claire Dells is on the western margin of the Wolf River batholith, consisting of a large expanse of relatively homogeneous "granite". This is in marked contrast to the volcanic rocks with a myriad of small plutons and large scale shearing which characterizes the geology of Marathon County mapped by LaBerge and Myers. ti;i 2' Ai Ian©b Ja ct eTk aag 1xaa a; g$gj ;a-& iLt:.ny riA by i2t :-J tztiL L(C) :tLCJ .CCRH ;cauaacti.c th;. I bt]huA ijc1i ThISCZ ra' IaL'Ltari±n C,oaarA •f gaagy a.:atEcat a3tcrc tXT CBC a arIact A major shear zone which strike approximately N30°E occurs at or near the western edge of the Wolf River batholith (informally called This shear zone is the Hogarty hornblende granite by LaBerge, 1971). particularly well exposed at Eau Claire Dells, where it is more than However, the zone has a mile wide and consists mainly of mylonite. been mapped for about 30 miles along strike, and reconnaissance to the southwest indicates that it probably continues for at least another A number of other shear zones parallel to this trend have 10 miles. The magnitude and been recognized farther west in Marathon County. number of these shear zones thus constitute a major aspect of the Precambrian geology of central Wisconsin. Cl AIaL9©11 V .t 72i icr: race Ltaa :cccta it b isad ArAc: c'c. c:'.rc;r CL raiUj La icl.IrcI•de LjC I Ac blacaIb-ci Ia; -cc-el; arAbic: I ciA re:ecIgi7i.: beea icrccc Are-i .-; cc! 1ircbac *. Ire.- at IA air. LId cIt asp-c-cl c-rIce a :c11 C I-rrAL.i-cc 1Iae at cc;iele I - 11 cr jCHCcTiHcUJ7 Eta ci; S.t$yO€;Sdl wthta- yc tcrabI3Tc2e c.cCcty tIAa : Able lad 9 ]a:JLCcga Ia ccntc 1JL -c ;cA . LTz I Ia7 il; —r bare Tb CR ciA acre Lcccc c ride-Al tbviic Re-s aç•9 ccii elI tic ceec 1 cc! JPU.c:aci-lLeIaa -cieiLcyy cC; DESCRIPTION: maccc-rely •rGii ttccccidy iii; IlIad cartacci, dcc ci:;; Li ;icii 'rr-4 Al irL Ac ?LaIcI At Eau Claire Dells county park the exposed rocks are moderately to well banded. The banding dips vertically and strikes approximately N30°E. At the Dells proper (just downstream from the highway bridge) the rocks are relatively fine grained, felsic, and homogeneous, and CL-fluid —U c1.LCRc ip Idri iCc 1 cc A It d cc bT1 f-c ,CRiLHC Icac D y-ç -j Cj91[ — AIcr; be c-:acum i:Incd ccrccc Ac ;clc-;w]c LCRLL. l 1 Irpli A caR 1-I___ cccl; Ac do not display conspicuous banding. However, further downstream (near the foot bridge) the rocks are more mafic and are more banded. Upstream from the highway bridge the rock is well banded with alternating mafic and felsic lenses and well developed quartz lenses (boudinage structures) evident near the dam. Small garnets are abundant in several zones immediately below the dam on the north side of the river. East of the swimming and picnic area are outcrops of banded amphibolite. Thus, cicpriic 1R-cCCIVelrhtdLii U cci i lb izerc;i-cl elcuic bccrAiw4igc 'ii L 11411 c Ic clIcL eCu; 4 I LLi tK2 :iJi'Gii'CClCR :i jiij lrcc-c-c-: i51C_it re tic 4 44i Lw ci cc—' C I rcuurc; la-c'c-:--iiia!,, c ICc_ 1 cc airi Ii 4uiliLc2,H - -r — I 1 — IcceciLl IcLL _c U-1i 'ci 11 TiItdV 1' i1 l111l eccA L I Ll1' -_-' it II �62 EXPLANATION FOR MAPS OF EAU CLAIRE DELLS AREA, MARATHON CO. II Scale 1:24,000 — L cd Cary drift; terminal moraine. m 2 Mylonite- and related cataclastic rocks. kqm Kalinke quartz monzonite. '1± LI'J hhg [ dJ mvJ k',j?'J,j,'2, granite. JJt,.:L' hornblende Hogarty Diabasic intrusions. 1.25 '''1 1' :":1., '±:2 and Maf Ic volcanics (locally metagabbro amphibolite). Outcrops, or outcrop areas Geological 0i'jc2'; contacts Rockpiles ' Quarries I �— 2J N6 I. — — 1 F r i ¶1 _________ I /--" , U - - 5-' - ,_" - :- LU - / 4' —— ——— —— I -' ,k7e 4':—... F ' I' I US 5' U,: U —F' ' -:; —' - II -U - 1 : I, - It/I // -s -- - - 4 - t114q -':4 ':1], Il • 44-- IC t—-_ I: - 4si - •1 • / I z 2\J - C' -I - - - �64 J1 Figure 1. j-• l3 and lens-structures in Eau Claire Delic Ba ding LÀ • - upstream fjAL. ±'om the t1t Licge brdg on CTH—Y Light gray iense% al Larker gray banded materifl 1± i rt prcb1 v boudin. quartz, i babl areqatz :;mjH Park •fic rich. :: Ltthth mafth is rrelatively structures a- aoth the banding and the lens t P fJ- tearing. thrmed as a result of sh thg hct are believ 1 to ihave L D Figure 2. Ba1d. CnJin!.g mc' ltns structures in fe]sic mylonite ±L_tJ. just downstrE?arr from dir bridge on CTH-Y. Where the rock is i more homogt --meous, the I L. banding and lens structures are less obvious, hut they are still a common featureS ktl - - I - �Lcturestru flow groundrass. ndirr - f surrou the tH of and feldspars the of most fof shape lens the :- the grained Not matrix. Felc 4. Figure fine a in "eyes" flJrkspar L .1 - ce p fracturec the that Y1 sir'± irrdu ua rt'1air pc overall or Cl De S L'ie from 'tevct' au&rtz formed lens-shaped taller grain, z River LC2 ç the f nt. JJTh t7±. Eau 'e lens . - - 30 X31 X fragments. also note and i. zone. shear Figure - - Jhe iote Nc u 3. 65 �66 tti the n-Itt IT: 'IL'aaicittlct' on the composition range from cc,'lr,'S 4ILy of nIL' the cir'n mylonitic L ciaci i'arocks :'4m- :"a4ILa ttam "basaltic" east nan C 4" the LitmCenter 'L'a'vI:';'Dells tam Inarea tans taIL Itt ti"basaltic" mta,t a a to "granitic" in and'ILant back to 'ct 'gamin ,, - j ci,r::;:m ttS':L2 Compositional acmIncn i'll' 'nau4nci ' I' downstream alongrhthis cross—section of tin the ci,caama" shear zone. ILcirn,a: tt"na'n: attiama LaS tat a'of I-isa 4' a.; 'r;:r,lmn. Inca? are variations inca. common both andacitacts across talUs thea strike the shear cltit:i:iCLL 1,t tact,": anal ". maalong , 'r,' appearance alt: character 'tint aa,ncnic' 'tr:ar"aan-m'.c':a'a and with the LIt':: result variation in I' the :a'Tata' 1 of zone nIL aa -'a:'ttti.'nLr' zcanni,LL cof the 1:'am zone. Variations aa'ci,aaadepending ILanami - na 'W4t'? upon cU whether Ct,Rt> t hydrous act-n :Yr C, 7am a an lcra also tItan' arise a ant' , eat' anhydrous ;acrla',L,:c:,m minerals Lan'aILt during i'iaairL4: ', t,,p'aJ,,, (feldspars) yam tna'tra'ti formed minerals (micas, etc.) or cn:i',r,'tatILai'a:i,tac1 'tamIli an,tIL'an, recrystallization. alt. taIL 5t 5çc laSt along it, and aititaL::the tic: Most of the Dells elsewhere act Eau tat CIClaire :- a' Cal cl,:, Itbanding itt; c-IL? ac'aaIta tIg at acatactal and 'actc atic'a,it,S' of aiRvariously -'nainacs" ILflattened Eau Claire River actually Fain, :lcIrt F. ''a' zone ?a';ta;tlIa? ,s consists IL: length IT ttgn aILS ni'::range cnsct in ft nit, material elongated ::tt,:t of na .-hrla which caL mafic tInt" canand IL' felsic at at;:rzm'a:d lenses Snnclr. Figures ansi 22 Fi':na'te 1IL and mci a ':-rtc:',c:Th'aof cL aim from more than a fraction an inch. f;ncc accca tacta amile Lit' to Microscopically cataclastic mnymlJiaja lenses. lcanams ott the ant smaller illustrate some 'l'l';raenco; - aaiLLI' oanaTLca,atI,n a: of Thus, "tb-as: maIL4 4are art tcnaa'-features, such inifS Figures 4:t'i'5t 31 and common. at SU:as asillustrated i,, tt.ttitdI La IL anti a cia ?'ni;Tc:5[ tectonically. ,,:,itt :tr}n,:c tt,i 1 i, a have 'tarn formed 'a'n Ut! t-a'agt to the rocks in this zone believed ,,cy'c are 'itt rc,nlUaL::ltmt' a-n 9::crnags: Shearing ttai7 may ;'acmctt:t produce the banding (as well as ar, cataclasis) ta:cacilaaai R't'ji from an tI't 4anILiLf aa 'antI a:c'ac zone stint ap;;:ci,aILan a: crosses 'actitac aa shear initially L,'n',o'gaa':a't''as homogeneous rock, maIL' when approaches or t,it:,mLam,,l.:: "cot-, and raIL, a cattaIL 4at,c'nc:'i '$.":nai '5 'n "L:tl,t:j:aaia,, Inca at's Lam contact between:tacontrasting lithologiesLas thetam banding may be r:na'i'nna pronounced. -Its ILLs rocks r';tim ILn'tk'c'n'n*'c This situation is ta 14::, II represented ac.,cr-'caicadT by 4; the between the ti-n evidently '"a "a latter !a'nls " ittaiat;':Ta tim-n hut tin''' road bridge damLa; upstream. anaL the titan 'IL: ''caaa and - I - �67 Field Trip Locality 8B :811 1IC'I"7j 1)1011. )ITS1I TITLE: Contact between Wolf River batholith and mafic volcanics !Y1II CtI 111 it IFi11i,1I CIlUlCIf 1C'070U 'C 11111 OCII-0L.fCtCTI k1ao': II LOCATION: I P1) IL -'r T.29N., R.1OE., Marathon County 18, sec. oqLCC1I:Ip Ct0-flUC$UII't I ej C;-. 5j3 I I N, N4, NE, AUTHOR: Gene L. LaBerge, UW-Oshkosh DATE: Summers 1971, 1972 s OF FEATURES: SUIVUVIARY The locality is typical of the contact between the Wolf River batholith (Hogarty hornblende granite) and mafic volcanics. Near the granitic rocks the greenstone has been converted to an amphi— bolite and, as at this locality, when shearing occurs the amphibolite may be well banded. Although lack of outcrops prevents determining the width of the contact metamorphic effects with certainty, it is recognizable in the field in a zone 'about one half mile wide. J.LU'0.i — CU-CI =-p•P;:: —I _ : - 8flU RC{i 1111 : ItO —' , r,_ . t"— T L-CI41 OCIl 1- I 1 St CICIL ' 4 jV •lfl :8 1 zIr;I1C'jr,J:CCplTII 1U111LIT18t- ICC -: 11C U' E C P:ICi,CIU'C 'I.lU' 8C'U-iIiCU p3 U L '—'- CII ,-CCCOfl 0€- CU' j :11 I1tI;_.CI TIll ILIfUtCI -CIp (1 71:1:111 Ci €17412 :-: TiI.11I L IC tq CCII-C I --c iwIr 1r.;iPT-173*V 1I) L1 Although the contact between the "granite" and greenstcne is poorly exposed, it was mapped on the basis of lithology of rockpiles. Rockpiles along what is believed to be the contact consist of a mixture of amphibolite (meta—greenstone), granite (commonly pegmatitic), vein quartz and in places metagabbro. Small dikes and veins of granite vein the amphibolite blocks were observed at a and quartz cutting east of the "contact zone" consisted number of places. Rockpiles granitic rocks, whereas west of the almost entirely of porphyritic "contact zone" the rockpiles and small float in fields consisted almost This change in rock entirely of slabby amphibolite and greenstone. 40 type was generally restricted to a acre (-- mile) width or less, and at least locally the change in lithology takes place on opposite sides of a creek bed. Thus even without outcrops one can locate bedrock contacts quite closely in many (but not all) areas on the basis of the lithology of rockpiles and/or float. Trenches dug for burying telephone cables were especially useful in providing information on underlying bedrock. ,I7'C7 CIIIZ CIT - I j - - TUU'"U' s- U':Ux,7UJ r' - (U' UU-L— t8IL LU U 11 ::81t 8)U't r& '1118. OCL. -y - I' - U EU1I-i UICICIU 1 tJL"I:I?cA 1 5U'1 - 1_t •3f1 — 1t tL 8 t I 7cU1:.:j: U-J1ETh:::U±DIT1t I L CI T I $Illt. —T :1i c li ;Lcn Cc::t 811711 Vfi :155I8 T &[ -Cit ;xirU tJ.E7 UI -f 'YI)i c3;ILz 1ifLt; -. 5t I r•:r i3 - 1tL ¼'LrL1CtJJI ,CU' ' 8IU7 I- 93T;dItcC-- I .CyC.! rF71I2!t2 — C' ¶1-I C i'31:c7U:15i;U214-IIi Ui Y:oU:CUvU L - L-C ;CIiLi4 1fr:c 118 8I1Ut t:1:I t5';icIv:i-:I :I7rrI 11 6Ut r- C ::: t:LX ct: rzt L;:: it if I Tr;Lez: i1ir:i:i89 :-: r a:rq z �68 '<if•'i FOR MAPS c) EXPLANATION ?.c0 :L,:J 'q AREA, fJA'SJEu1 ILP<J<2.L DELLS OF EAU CLAIRE MARATHON CO. <2<J ,i-•;<2 LIi Scale 1:24,000 5:.< <21?L7h SL moraine. Cary drift; terminal cd 1 m <2T<2 Mylonite and related cataclastic rocks. 'UT<2 kqm Kalinke quartz monzonite. hhg Hogarty hornblende granite. :i:Y•y i'l'c,v±c.. dj JD* L.1L"1<2: my .:&J=.l1 and • L i.<2.'L;< Mafic:i't2z1; volcanics (locally metagabbro amphibolite). 1 L Diabasic H intrusions. <j:c1HH ''<2<2 <22' outcrop Outcrops, or areas ,-'..- <2 Geological ':•1 c" 2' XL<2<22contacts Rockpiles ' Quarries I �1' R.IOE. I - - I0 M / hhg - my k , 19 .. V - I •1 - , I — d / — - — — C. / I / 1. d - / / '•-•-- r •,' ,' my hhg / / 29 I / m I- /1 C. — : / I. hg h i• I. ,Tr r It. 1 / , 'I I I. I 'I , i,i , , I .1. • / I,. Ir / A m / / m, — —I m '.4 / / A / A A' A 0 / A my, .-— - C- // .1••' my / / ,mv / / 1L) m m / 4- A l, (iI -- 'p — / C / / qm / A 'A , - —— / ,/ I I rtitt• .tii—z. C I PV -4 K Th 4 / f I ,1 'I K —— /' / I -I • .— C. C .• 'K : III I / •_—\ Q tr Cc 4 C I i.)C •--:-. ,;; N. R.9E. -J i1es F' / / C. •, — C -- C, N - -T-J .-- Cj CtJ I. cd ¼ It •• K S -.—- '-.4 JJ 1' "'C •\C / a::H ,$/ - A , / N. / kqm / A 1 '1 N-- - 7—. "C �70 DESCRIPTION: 5cL iLSS' au f!/ @5the Sbc contact .lLc.rttc- @rs cc ccl are coarse Outcrops of "granite" within 100 feet of St.: :1. cc cc-lcc712 ctc:c "granite" for several miles to the east. Sc N•ciT-S of the cc.c grained tcU ccitt and typical 4111 ir icc to "granite" throughout much Indeed the rock is strikingly similar T'ti fltLtt lt.TSiT-tc c::Jcc and Menominee counties to the east. 1ftIllJ .ctt. lIt cc. - valley in Shawano ck.c 55.? River of the Wolf @5 of : -. l - ' ii L- ' lcici -I con@t:,i is itiL1l1SC'f', but ? IN cit tcc' The contact hasc,:ct notb3i,fl beenLCICI@ found inci outcrop, I'!lcift cc,'i-c/ itself c:.c?r ccl itc:LI191 Y Along this valley one can -.j:citcac swamp. c'ccif.t•r under •rcrciLiLl; or Sift. a ri. valley veniently in :;c&ct icc,ccc: ::;cinc'sIlc -'c-IfS granite with abundant mafic inclusions. .iIij:Cc1.lc 11@cY¾ find blocks @5 of the tcccciiccit1 :L—i-: numerous Vi:LIV narrow liTil rsrc'cc zone evidently frccr form a very 5c"-•ct@, cy1.i±-itijJ 5 :.:- Ctc-,, however, 'ctiii ¶-5,cJ1 blocks, • -c5. The inclusion—rich -'ciii Ic-cd S t-c rcnSc@ tI,cc tcic' @'Iit. 'I and the granitic rocks on 55cr west cc the between Sc '.-iittr.ithe 55 amphibolitic ' iic.Ttiti IS : rocks on - .- r1,•c *311 5 the east. :'c'c-ticmapped ccpcJ1 all r15 rocks '?-cc'iplutonic cIt5cc. :ct± the '5t ct•cs t if also : C$flLT'J This stop is typical&cin that itt7 -,-,c5.cr.r:i'-i',r oiLcttcc-' Sr.,c :-45.:- the intrude older volcanic sequence. I 121-il is the ;L itT' iccgeneral dLfl''da area Ic this cccI dccl ci: cit. '.c,ia in 5 important ,i9cTcft1 and An interesting problem Sc-•:jt •c@;3 uc&jnrci: of :5 cS@ the Il-SLI Wolf River :1* [i; the cSc@z SI'.a shearing relationship to emplacement cr5 c± crlI.. of the 5?LciccLJ,c-cr1 cccc crc cii:' cc 'clcflcc:IS of here one can demonc:? localities ccc': S 5cc At a number of southwest ;tt, 5wi5kircJt'S?' batholith. cd'rclu21ti-I 55cdiL5lI hcti rdrcT'lT'-ji hornblende granite) has :.'i'r-.r- batholith Sn:ccS ± :1: (Hogarty -cc:t ttct 55cca' River strate that theWcI Wolf clLc:: Sc nc-c: 1cim:crgneiss, -:'.Ccc - mylonite and granite, i.ct.-i5cc gcrcc5. 51, augen ;-L.cccC ar1. gneissic -Ic produce been c,;i-ccic'cC! sheared to 'c-cic. c@iL-cill. will :-: if -R This Iproblem 123511cataclastic c-cd---?,ocd:,r-j.c i:cScon cc a¾ rather 1 -aIccI large scale. other rocks c.cclclcifL and512cc-nINatural 1:--the t@ Wisconsin :crcrcc GeologicalticS -ccc tc.c by ea mapping --:--c- as be @zclitrcl@ examined further Lnt pr.'c ccci:-:, The presence tibitI cd southwest along zone. LL:-LtLS-± this dc-ic 101 -cc History Survey continues to the c: c.'rcc' c.-.'c-tb7 1515' crocks r dcc may ct c 15115 of the batholithiC icc S'rcrii.: c±L:c.cof major s;cc-,.cT'rL.t shear zone along the front @5? @2 a ¾ cii c-tc-cticd c-c Cit-I batho— the c-cc emplacement 5la3ftLlt-tL-t of the ccJ ncc.2 cc ccinftncirc,gT'T'I indicate that cISc', the shearing is related to ccilT' crits cc-icr, cf-ic-cf which i-SlitS Lt1TT,CnCI@ along 1,-.,r,U1L L.J ±'l-ck- as iii a buttress behaved ,l' 5-ltIitlfltL 51 lith, or perhaps itc&t that 'Tcd the batholith Ni:- t@•1¾L.SL. the shearing occurred. - 1 -". �71 Field Trip Locality i±CC 9 J, iji TITLE: L-'UI Wausau quartz syenite — Old Technical Institute c- 'U-2:'CTioC.:'ojt. :iTcC0C,c',1Lc-itCIt' :i-r -'=r LOCATION: Marathon County T.29N., R.7E., 'U'U- 'U 35, 'U sec. !:fl_' NE*, 'U AUTHOR: UW—Eau Claire 0—C1T:2: Ltc-Uc- : Paul E. Myers, "I'U,:OOUiYO 'U DATE: 2:-fl February, 1973 .TTt7tJEt€.C SUMMARY OF FEATURES: c;crIIU 7n'q(U! An early, medium—grained pyroxene—amphibole quartz syenite containing NW-oriented quartzite, schist, and volcanic xenoliths is cut by coarser-grained, flow-lineated quartz syenite of similar composition (Figure 1). Average xenolith orientation here is structurally continuous with the concentric lamination of the Wausau syenite pluton whose granite core is in Ninemile Swamp 5 miles southwest of here. "Rootless", lenticular pegmatite with walls of coarse K—feldspar and cores of quartz were probably differentiated from the nearly crystallized syenite at places of greatest quartzite assimilation. Thin screens of biotite schist and quartzite were raf ted up(?) and brecciated in the viscous syenite magma (Figure 2). —"CCC IlçU4'UU.c-I CCCC1C TC05TCthC.=c-QCCCCfC CC'C'çCC2:-=TO'C'0Ci Tj ijC C i'C,C T flTh TOC2: CC t ri ' r ; tiiI ki 3'4 CCC CC CiCi:2t" tk' i J(il =ur 0 TiQi :4Io2:T i::'TCC LL 'Ito r:;mitt. i'Itt1ci ,i,'l; &\trli UC,0CCii 2:1L7 WT(1' CC - CX4TX'v22'0'L ,2: 000 ii:•::c-rc 104.T1!iX U' Lc — fl'IL''tT00ii c:iz,o.Lni0t o:2 2:0 CT:7 r,4,,)itiic-l t ''•rC',C 7CC C''Ct Ut c- I I 4 i20U,k Ci O,c-c-i[ YT'0tiit± F.T.04 'Ti C tian DESCRIPTION: 4iTP TI' fi ' 1T'1r cf iLi 4"1[I According to Weidman (1907, p. 203—208) the "Wausau-type" quartz syenite is composed of alkali feldspars (orthoclase, microcline, albite, and microperthite), barkevikite, hedenbergite, fayalite, biotite, and quartz. Accessories include fluorite, apatite, magnetite, zircon, and allanite(?). L'.tlc-.[ '--r T ti Ir ]0Iic--0act ::ti2L 0 S' c-i viJI3p;4: 0 r I iT - <) 1JT : tcCL :1 - I i(iflT0t1flT ;Y:B 4i;$ Structures and cross—cutting relations of the syenite phases exposed here typify those seen throughout the crescentic northern rim of the Wausau syenite pluton. They are listed and described below in order of decreasing age. [)1L4 0c-Ti. ..1-c- 00 ?f0T.an:1- c-c-OfI. 0.:ThflI!Jc-;t&:4= uii-ic--•o ThJDL ji4c :4: :j. r2Ii7. o-rot (LLtt -iT-i OLIL fC• c-i i0C TJ.1 i1i �72 -: II .4 I- — 1 5- 4 5 I — -5- — — ,_zl., -A" A L,:;-' --r • 1 j V ' -A I *I•-••_ • - - '-21 - — ' - I At — ' - 4- ---S -• - - C— - •'-" '1— 4A -- _••__IA - • -" - — _•', 1' -1' — - - - _•1, I -' -- -- - , / •• - - 5- : -' ' -' ': -II, -- - I - •• —- ,'4' ':4 - - ': ''4/' - '.-: ' 1, - 5-:' I-I- - --5-_k -, 15s'I -A •,, s,'I 'hi . 45-', , , — A A — I '•,5A-42-'_ - / — -, -- ' — -''2- • - I' 1 • '/4 2- -— - _;A -- - -_ - -h //5_ - - A • • 5-5- A - '—S 5- - - ' — - l.'\',', 41' • I 5- ,, '-'5- 5,5 • - - L - -• '5. • . I"1 -lw',' 4'',5-:5-5' — ' - çt5 5-ç I - I, • - I . • - 4- - '4 - • -- '-,-T:_ • -l - - ::4' : - — I — '• 7 5- I - ,::-'- • II5I 5- • ft J,_ -• •• I — -• I - 1" - -: ,-• - ' -•,•,' ••- ,. ' - I: • k ,. I T I' --. - H- -5- A_I' '.1 I,,2121'IA_ A '- :2_' ' • 9' A I 5 ''-'''-" C- - • 1 A -A5-5-' --'- P 'I 2- I 55- - -----—I A - •21:--- ---2s. .1 ' - •, '_&••*, - fl5-:4s": seams 5-2-slt4.,::LElj:l,L:5-.2-2-1I with swirled lineation and thin Amphibolite (a) xenolith •:lc:.JA,._i'1421L1b1,A,42Figure 1 Lenticular veins with - ;- A.534'P2-'5Thf"ftL-1'2- 1 1'' '11 of syenite is 'El cut by coarse pyroxene syenite (psy). c:'1,-.1tatQ ; ,,— t1LZ4-1L'-1L1_'i EHsIJA mutually crossq-:2-r- (q) show walls of K—feldspar-: (Kf) and cores of quartz 2(ICI_ Joint f'!VLt'rhI:2-Ifl',s1 intervening offset a small fault. 111 W _'-2-_ along cutting relations an1Th,C2-'VL1'2*1'th'1 15-21? '-'15- with 24 115-Al I' -1,11 amphibole. 1_s. A"' i'i- 5-s' coatings are of coarse, sodic Ah- 'f2-- 5' 4Ui - I 151,5- •, - 1. 1. 21---1H41:;2 syenite. They in2-12-il i-La xenoliths in 2-21 the :c: X'lh,!IA1'L".2i5 The oldest 15.5- cAt :'::5cIftt,: rocks :1:4::': here are '.'2 ILC21 *1 2-4,IC I meta— -:-c1,t1t-21151 amphibolitiC 1-2-21.112 4121 -: -lr,-J, schistose, clude recrystallized, 212FA!41214442 :121.1.4 thoroughly L*2-1AV' ±2,15*12-S tuff(?). unaltered felsic 5-1-2-211:5'-.L,fll22-2t45-2l 4*1*1 volcanics(?), quartzite, 'I222-2-5-A/flH' and virtually 2CsJ.A!1_i:,2-LI4)IC-I parallel to xenoliths tend 2-14: to - be .r2I1-•1*1ltl -T5-± aer,:: 5.2-2-2 of Note that long dimensions it1'2 ::i4 disparity, despite lithologic 211-152-45441 21% tIal15471.4%:, lamination and/or foliation and that, *1124121 i-Cl :*14:.6j4)Ic,1I-: -s 1:4211%' :5"a.L "grain" to distinct structural a ã.2-tlLCC ,—:ar i: -Lka±r c:52-tkP: 1117:5:2their mutual alignment imparts a 21.? :::s21.21j2, considerable 2-21 of tCi- be factor believed 14211-2112- to fa:'.tc:2, tlLc 1:2- — a the21'rJCL*1%21 enclosinghIyE21LI syenite *1l1it21L5 4' this 11545-LI pluton. rnechanisma 55-2--2122- 1:2154 :15 for '5,2-,1a-iI-211412t 42-151221 45I:215--ICç I significance in working out emplacement 2-I 2-' l-- 14 5-4 rai , 2-'- 22. ilyllIl-ib I 4.1? .-: 2-: syenite flow—laminated -1-2-C :; 21.-I quartz - -E'It1i5.5424' lensoidal 41:csm15rair.L?2- - '152-121 An early, fine—grained, .-IrC phase. —. chilled -.m15!lal 2155-2242-. may represent Ta-'--Y,C 45-Al/-C_I a I - �'3I,3L'1$ 'UI'? 377$i'35(7'3'7573 Segmented metadiabase(?) screen in flow—banded, quartz syenite. 117' 4- L4"712337—11A7-"[ 36 - 'y77'.e33-: '' 357-:cI'316P'75-17 r7nam,, rr-,---', -' — - — — 2 Of,4f • 7": Figure 7/ - — "4- 8 N - ,84 8. N • A A- — A-I — 1 t ' I '4-4 - - 8 j '4-- 4-"4-54 — a_A-' 24- -- :4 8 : -I,; :44 '448- A- —4 - 4-4 -4 x 2 -. eA— 'I :4 ' A A 41 — 2 - '4 A- A — — A — , 1 - Ar - — 31 A -- A- - 4-' 71 H : - '"'8'.I7'LJC, 33,%1. 'L31[t :7823_H'TA':A531.:Y-c':y.'':-:',':PTS- -=A-A-A--" Coarse, sodic amphibole crystallized along joint surfaces. '7/'31!, 7'7': 7'31:':L:18(:73 '' 5. 2323331':? 3. 4-5- Coarse—grained, flow—lineated pyroxene—amphibole quartz syenite cuts the fine—grained phase with sharp discordance. This unit contains irregular, lensoidal and tabular inclusions of amphi— bolite, schist, and quartzite most of which show little assimilation. Although most of these inclusions show northwesterly elongation, the enclosing quartz syenite displays highly discordant flow—lineation with swirls and eddies suggesting considerable turbulence and viscosity in the quartz syenite magma. After gaining access to the xenolith along its banding or schistosity, the magma pulled loose segments from its surface. With increasing magma/xenolith ratio the xenoliths became plastic and were strongly deformed in the flowing magma. Quartzite xenoliths appear to have been more readily plastiA screen of cized presumably because of lower melting point. schistose metadiabase(?) crosses the south end of the outcrop. Its thin western end shows plastic deformation and "pull—outs", whereas its more brittle eastern end is segmented into many angular fragments (Figure 2). '74 Late—stage, lenticular granite pegmatite veins with quartz cores probably represent residual liquid segregations along incipient contraction fractures in the already crystallized syenite. They appear to be "rootless" and of local derivation perhaps from zones of abnormally high quartzite assimilation. — — 77t11'3 8(8771-31A ,(,7'%:7 P-331'Efl': (4485 71773 "718 L'S.7'3'L811-1':': ('(In-I ç4-7171.,( '- 75 T1'871 73317 - 7'-; 3.8(17 'L571 717'445 : 357 87'71':33115 31— 33-75-1':-' :Th-i:ï. 37337' 5(4-8 -73'',':—:' 73,7131(1-5-3 .1- Th'r,l - 4-127-V-lI''1Ctt- 3:iAL3T7 37733" '174Y 'V/,J 5,877) 3T75'1Yi"L-7J ':':4d5731--114' J- L137'43 '5',:[',-'1(3 753371. 7;'PL-3': fl7, .771717 ,237331- '5 4-7'.318j8'72 -:4 :-77': 11-'73'4': '753715 1231 (81'i',1s'4'3.53 — [3-13773 53371 -3313SF ':': 7)8(t-U7 3-, 2377 75 375'7": 3'1331;3 (173 -1'& 71,7(3:44 423,.33.-3S,[717 Y'3 ':'78:-4713-37;- 1': 37" 7'3": i 37 75 -1 $771 473 -:I,3.3-$11:1M 513.1-34 3.3 33%'77'472333€': '35 3471-"':(4-' 4717 -J'U'':' --751172343 4. '3133''. 3's-s-cs,: 77:11 —:-3":x, 23823373: ,:-123721814-,': 23 4(173'A5LL 337573(757 5-34 '8718, 3-7,'!,,A-3348788 '(1'j('3-771':-_-1t7'':237'5- 5-3177 1575-Tr''33'3371'(,$ 7711":2 1323341331 731'4'C7513 (5157' '5,33 5:" °i':-:H'.: ;1-L3--'2'•':-(33.'; ,575%[771,'14- "171'%:131- ,77' C'5. 3(7-AC,- •ThtT$71'.8.33"1"4 ':711,7 23-731-'. ;38771:37(;::; 175, t,334-',7 '337733 1571', 1311-1 Sx':3 7'7'7-4'7'-131,3':'5(35 --C: ':"-k7"1":-x71- 3'l 3'317':41,?,'23 ii1i175—2 -1311 -7,31,it 73 'i771315'( 3—':-'fl 731313333:4 'I73 51 4771171' 3,7354373' 7::."iICi)'I A-r,A17'3-5 731'3271 1'i15$ 51i1J1 - C."I1375477 :':'-' 3,33, 1172171 :377758-73 48733 ;t-:-- ':':-: 175433-77'17'75 '735233-: 317(13-? --31373-5? (-Y''7' 714 ,'731-::': 71,[)-':Aç; ''5 :7'.733': ;5337735718'7'7. 4'7''5P -3: 1:15' '315 734T?j2. '73443135- :337317 ''13"73.5-53':':5 77 3313734 pa;3-7'4 a': 2317 373(3 - '7 - I - ".314-ICY 3153.73 731 L1513- — 731,11':17.'7317'I3 t,:7,'' 34 '74137 8 7'813f5 473.5 A'7'71'-'3-)'3iAA 7773 (5''337Y, 'c7L'ç83D - 5551_-1-3 7517583 73 �74 a ih* the syttitea syenites eM and It is '.s suggested that many of the structures in itt San1v. Sntfr L,.&zbr3cn .Liin1' indicate forceful, subvolcanic stS3L*a •( t? ii Ytuasu. quartz syenites of the Wausau pluton 4trIN,tULa1 aftt."'tlS .! Careful structural analysis may '22e-ILL o trz w5.uclrJs avafltt V3$tVjection of dry, viscous syenite magma. of magma flow and xenolith mixin rithi:. 1i themchanism5 ;wasntnt in time time s'ts'WRl reveal the twc instance, traLtrce, nC ?t&t' t fn.çcmwrcs fnt 1.a Do the xenoliths, for represent fragments from the magma. thvtM'vJ g :salttr& eM ta;;;. aatl J aflr during caldera collapse and later invaded fault breccia formed initially a:rLt -asvnn? by ticw,fllflA upwelling syenite magmas? t,q cvg..;tz;'rl :tat nr 2! the 3tflfl4rfl the marjn D the ntc] t;o. f wit brte3. i £:sst atE anz f;nv efl r: ,t; tt':tg *itt'D 2rrY tJJ! RE FERENCE a*rth of north iTLoraw, g..tcsL, w,The fl' nalts: Weidman, Sanluel, 1907, geology cS 'Faaa3L3Lr: central Wisconsin: £'C. Bulletin c7taat and ax! Natural Fsti..nl' History £4tctcfl Survey, !wtey1 BCLsttft XVI. Geological tV::cscs.':D Wisconsin I �uiclrYrkJ,, south. the to tc FuNiclgJNtcuru volcanics 1 ru t j Ncontiguous from derivation suggest iN mafic syenite nepheline the in auruiuui ui lenses and INuruNuisur; bands ft'NYI7 tAtut1] Mafic vr'I;rur, pluton. the of ciLL ucuuru)7113U1cuucuruizt emplacement urvt duringi-il itization itttRrNutiNiN mylon— by segmented and lenticulated locally were crystals feldspar -5 ' 2. ICL'I C contorted: strongly is syenite nepheline the in banding positional 54) ui,:iUuiLuii))YN) and clinochlore(?) iC lirY'lui JUNNNNN1L 1117 cancrinite, c-r-irNrr::Nrr tJtcu7cuuiu-I'Nb5'u Comallanite(?). thorogummite, uruyIu. (red) (N WL N apatite, r' here), cu5 fluorite, abundant (unusually I_ Yui_t zircon include Accessories Jj (lepidomelane). 1— mica brown, and (arfvedsonite) amphibole sodic ±± sodalite at::riuiuia nepheline, uiNil rc:rjoNtir1 vNINiii composed aegirine, Ltak:r±LNuj1il1r-i microperthite, anorthoclase, of mainly &NCYçJ.YiP1Nr1 is :t4a nepheline o'7N:di7-Nug here syenite k-iNN 7i2iiil Dvrrriel the N17N 235—264) T'7'7N) p. (1907, Weidman '7aaz1 '7 to According I 4 't[ 5Ni ±' c' UYTY I I t,fl .i - L ,_ 1 NI U [ '- _i2 t: l'7I :r NY location. this at N tI across east—northeasterly strikes property mine N:1a zircon tN17 abandoned the syenite N$IriN77N trtLN,JT: tabular and syenite N'7GiJZr nepheline brirrNarr contact r1ccN1tazu The !Tjr,_ LiliN ttrryrl banded J1iFilri. b between 7UN It:'ly DESCRIPTION: i:r, rI5Ier7 : (Nt$Z; ivN1:1i2lI NJJNN, near zone wall the :crrr ibe 1J. ILJ stop in is t.zNyr This pluton. the INI of edge south the 1 pyroxene s Ii (psy). syenite anorthoclase—rich of core a and 235—245) p. tite—rich 1907, (Weidman, syenite nepheline—hedenbergite—fayalite 1L magne1 Nil, -:r: caa 1:: in of rim a comprising diameter 7:i, atIl2 mile a zone core circular a (3) ' > pyroxene and amphibole vu t and lineation, flow swirled with syenite —RH — I' an (2) (lsy), syenite LjCL' pegmatitic to aplitic of zone intermediate aplitic lensoidal, La and (tsy) syenite tabular (nsy), syenite nepheline banded comprising zone wall a (1) mapping: field in distinguished were zones yr major Three zoned. concentrically a2d and northeasterly, 1L!• is J! elongate ]1LL)t. in oval pluton 'JLi.7c syenite ;7v(J!c1f Stettin S.tit7tz, The JL2tcL L:a1, 1) (Figure plan, 1,TJ 1 r lIV 1rl_ i :iaKair Ii c at 1 I i7 L ' 1b JL — 7_I' N17i=/Jcrv FEATURES: OF SUTvIMARY February, 1973 DATE: \ib,Lf1 UW—Eau Myers, E. Paul Claire AUTHOR: t>/ County Marathon XCaJtJrYs R.6E., T.29N., 22, sec. SE--, corner, NW C.T.H. '7 & Rd. Stettin7 0: LOCATION: zone 'wall tr'ita, tt!t; Stettin It• — pluton :L':N syenite TITLE: j-1!IJ Trip -H 1: I' Locality 10 jc7,r'7 Field 75 �Figure FF'/ .7/ I 76 '4-' 4-"" - ,: /7 " SYv 4--" my "4- .7/' 4-——. 'F'- tsy 1 F•" F / 7r / - / 1,7-Ft -'7 4/ 7.7.- '>' '',7 C4--- 7- -".- -' 1 1 --i-i-" 4- / / , '1/ ' 44- 1_F '/ 7-", -: 1/4- 1,, '4- 4---' i, , - , '' 4-4 2 ''j''i ,-'_f / - -. - /_ F'-. F ' F/$&f, .,. 4-''" - 4-' F" /./ ' F- -F 'FFF4- '4 / '-"F 4-7 4-' ,_e/4' /7/ '4 4/ -- 4-4- -4-' / 4/ 'F' - .4/ 4./' j ' \ /L 4-' 4-- F,4/4-f -"'"- — 4-'--F4--V4--F- ->ç4-74- - -- - -. —9 4/ "-' /4- 1 ''fl- .- -I 1.1 7' '-4- - y':- .—--",-,--.4- - 4- ' 4-—" - F' F, "7' '27"- - - - -S_,4__-,,_., '4-'F'7'4-I 7- '-74-' .# 4-1 7' 4- /4- 1/4' ,t,,,, 4. '"-F -4- cii - - - '1 —-F 4-4-,4/ -, my — '-"iFt7-,- /4-1 IF-_>,, 74- 5TTTIN L'-17'TT"7'' 7-7 4- / C 4-> 4- 77/7/ - .4-4 '"l c '.4-'..->- ,•_,,,.. - 1 ' "'-,. F .'F'47 .1 r•f$F - 1-' -' ,".77'i .; '-4-'/',.'/I - Ii ' 4-V -- —/4- 1 fv ,.' 4,,. I -' IL / /ts / -— / I C F 4- ——-—4- : 1 4 • - , :. / / 4, / 71 - - F I 7/v 7' I / ._ 4-F7. I: 4' /' ' , I - 1, >4- F.4 / 'C ,,, - ''v-1"'" /.- / F,-..: I ' F I ilL ri N / t Ii STETTIN H LIT I PWTON 4-'- " 1 I - 4/' F . 1" OF THE 4- / - ,,,,, F c7- my F H 4-/F 4-p).' MAP '.! • ,, — 'F /7 "•'-"• "S - /fr/LE - - '44/ ,,0 F I.- 4- 4-' ',, ,,/ by PE.Myers '1 ,_ Geology F'—. '4/174/4 p:'!,1,1 111:1 IF/-F) Nil '. Survey Wisconsin Geol. & Nat. Hist. 4-i I I I I 4- 973 >Hi-.ft1 Li,yI4711C EX7>PLAN ATION Qal ; LL'II r Lii tsy 1f L/4-V!U-•) A]]uvum :: (U C L I) i-fl Qgt n sy TM] p UNCONFORM TY C gr • F •I Syenitized vo]canics :'."ti,itispyroxene syenite - —7 rsyap ic/Fr /74/ .j,4, 5- 5/fl Lensoida] syenite V Granite Amphibole syenite Svenite 5'2i'- 4-/i ap]ite t-> - - 3/4/i/i Nepheline syenite 7sy - :4--n' Tabular syenite r mvb --'--F-,--. ,,F_1 is -' -½ '-,' , vo]canics Brecciated mafic 4-, F4-F., fv Felsic vo]canics'I mv I Mafic F,,• • - • volcanics a �77 2 . L.... Figure 2B Figure 2A Porphyroblastic(?) tabular syenite with mafic lenses (Fig. 2A) in a matrix of alkali feldspar and interstitial sodic pyroxene and amphibole. With increase in mafic content, the tabular syenite becomes poikil— itic (Fig. 2B) H.. -.-' ;4= 'H :•.. IJ_, ='H H' 'H' 'H 'H H'. H•'-- -'H H—•-=-'' ==; 'H -;-=. H: Ci . _;'H 'H 'H 'H E 'H H.- ii 'H "H — 'H 'H 'H- 'l 'H 'H 'H Li: 'H-: Figure 3 —— Tabuar syenite with abundant mafic lenses. Note para alignment of feldspars in maf Ic lenses and serrated margins. (3/14 x) L (A 1/ H-- 'H 'H H) - .;-..' I 'H 'H 'H 'H 21 'H Ci; amphi bole. 'Hr. 'H 1.4 'H 'H 'H -'H C') 'H 'H I,L 14 H-. H. 'H Figure —— Detail of mafic tabular syenite from NE Sec. 22, T.29N.,R 6 E, Porphyroblasts(?) of microperthite (white) Black crystals are sodic �78 ii cr Zircons ''C CL'ICCCC and I'C% some IRiCS thorogummite (C'C,C L3ltrIC II, may C collected 'CtCC :13(113 from hit: be hiitCC. pegmatitic tC).ClCIZliL'C phases of the nepheline syenite along the pit wall and west of the •C' C.. Ict-I :CC.C:LC Ctfli just iCac' (LII C.CC Please mill headframe, where a jig table was set up to separate zircons. YC(". 7ZIL.ICC,.I:j iiC'i-iizz e iiCCCIj,C iCr C-C'; it CLSAC 'ikit Cc ci r:3Ii'CC'3 'g3C(3 stay out of the building as it is very dilapitated. CCC CC. .L?.dlt:.. Lila (CC '3:3 ].:CIC C.:: ,L3 aq: liiTC':I.1 s: s ': 1 ;3 The tabular syenite itniCt a: at i.E this location (Weidman, ILIC p. 255—264) auCrLL: 1907, is pale orange with long, slender porphyroblasts (?) of zi1tCi C$cCtL: (Lilt r14 .Y&Ci'HLiC HEICYLICC(C5 ii4 C.-" HI gray micro— Smaller perthite and 2A). Ct mafic r.itti ii lenses C:31C5: (Figure :1iiCLhii1 felcspar t,:,( aadii:' laths 'C'ykLC are a,ra CLCLCiT:,I The feldspar crystals show considerable size variation pinkish. Th ii,'i- SCCC 2t1 Cm: 1a3 CcaitlI'cCtCC CC in 'Lr this All are in planar array so that the rock is banded but not Why? i1Vi.,i Cit CII, ,J5Ii71C •CiXC,CL 3:3 ThIEC.. II1[1 CacC rock. .Ctt•Ci LI' 2t31iC Some of the microperthite porphyroblasts(?) conspicuously lineated. °?CCLCdCYI (CIII'', 5C' CCIC.L (TiTiiCCi.CflCC:,l 14 iCCLLtLiCiCtC, (L1HE-i contain zoned mafic have rims. Concordant (C :3 licCi inclusions ICC. C tt[' CCC ' and tiuC'ii. some ICC C4LTCCII mafic CCC mafic lenses (altered mafic volcanic xenoliths) ciCaTiicc 131:1 are ,za composed ;c sodic atçiCa çC'CCtCE-C't: of amphibole, brown mica, and and contain perthite porphyro— i,Lt CILC't hit (-tiC green pyroxene Pfl 'CCC IlL CTC::iC.. ci-)XCL.C1 C blasts(?) of to CC similar 1LPI C'' size, L 'lE-C shape, CC and 3IC orientation CLC'IC Ci those iiCC.i4 in u:.1 the C1CC. enclosing 2ciiCtp:::C suggesting pink syenite — aii feature strongly t33CCCrL HE5r origin of ;C the Cfl7 iS r;2CCLC Ct metasomatic Tabular syenite l-mile east of here consists dominantly microperthite. C HIJ ii JargC. CiCC!CC &ii:a2c At another of crJCi'1 poikilitic and Pt33 , pyroxene 4.j c-:l sodic ;YI'C amphibole C.nj:: ti,cLnrs çoaj - (Figure 'C'tc; €1 2B). riCiJ d location 0.8 north—northwest contains C)L.LCC a°c mile i-IP CCC ::CCCCCLC of here C-C.L the LCH tabular FCCYF-C syenite C.c rCC_: Some C much more 'HEflCi C,ii( abundant: maf Ic lenses (Figure ELLcL 3). 3CCC boulders at CC this Cli. ii same location irT are composed entirely this mafic rock (Figure -i Cc 4). •2LCiC C $CCi- taL1 CCC iCLCtCC of '' - C,. L a' , e-ic 1f:"14C CC !c'-t iatty C rii Itt L j-Iir3C3ij ii rica 'CCtiC C C cfa It CC is suggested shearing C3.,th5eiFL that CViC iiUIS mylonitization J[C:C i. TC3tLZ accompanied -.rTli3..C333 CCL and Fragments forceful injection of pluton. TaTZi.tiJ subvolcanic aCCflC .:CaC ;.- the j.L Stettin XstsJ,-, syenite c:tuiitE-E iC of ?3if; mafic volcanic loose C,t7TL rocks 33CC broken rct.2C SiiCCtI from )EC2![ the €CC walls were EJ3- rafted up ZiL along £(art These fragments locally acted as them in the magma. 3C viscous C37C 'it syenite cii1t,j c4!Taa; c.rCaLii cia-iit nuclei L-4 crystallization SL1 ICc of 1:3 the C./1C syenite, itLCC to CC. have IIL2iICutt for C&itii r-. although thqy appear Considerable metasomatic alteration been resistant to assimilation. LJC%QJ T CL znC ufl54 C fl1C of the early wall zone complex Cti at ni emplacement Lii followed 1i...:.Ir7 its ri original J.: çrc;:;: as evidenced by the coarse, euhedral microperthite porphyroblasts(?). ')Cfld: 1'.th: ::1c€ Textures in poikilitic phases of the tabular syenite suggest nearly Cç7$ TC.L izCc CC.LI7 ;tc.J simultaneous crystallization of feldspars and CC2iS'LLiC 52EZC ..Ei C5TTT C Y(fl mafic minerals, :ir- although T1 the amphibole is 2L:ruDi. younger than the pyroxene. xyj. 7 iC F24. •CC !'- t :•:j ittn;9Ji a >Ij : j 1? I. :c Your ideas are solicited! These CLJL tentative SricFGC conclusions [CLCC ?7 are CC presented to stimulate discussion and debate. C. CcCt TX RE FE HENCE S L' X'S ST Emmons, R.C., V Wausau ':1: and Snyder, F.C., 1944, A structural study of the Wisconsin Geological & Natural History Survey, unpub. report. area: iC icc;1rL rj$)CrCr igxt'Q .C1t J. EZ dci :qtu Geisse, Elaine, 1951, The petrography L AF!T of the syenites, nepheline C1 sye— M.A. Thesis, nites and related rocks west of Wausau, Wisconsin: 'T t&r:u piTc; iiE7CSJ L4CC;L CC•k ICt i'&.'P Smith 4LL( College. :JC;. rr ;. C' i Turner, D.S., 1948, minerals tt- Heavy accessory t'T radioactive CQC3 511CifL and LE1PCTP13T studies of Ph.D. Dissertation, Univ. the igneous Croi rocks in the Wausau area: of IC Wisconsin. t':i* ''J1 u Weidman, Samuel, 1907, The of North Central Wisconsin: JIL geology tC1 1.ZC Geological and Natural aj, jttJi1I History j(.. EStJjI1 Survey Bulletin XVI. TLkityD .•&![• Wisconsin i ii- 2tcr;iz �l fl -.344 4747) ,4i217L 247-417.' low 2112 Ii '444 bridge -"=" 77 water. at only of times C1 . west the from it 117, 210 location this 1 the of end reached be may Note: gabbro. t1:21I17r214i.21212 :1421,17:171 ;141:7,T[4?1! 'I11'11117147 1242 4171: 171113'111I12121171L11$11 the of consolidation complete before stratification of disturbances 17 " 1717 the 11 inI layers I t121 clase r212LI in represent probably 2) Figure detail (see gabbro ij4 114'' 211 1 '44 I Di plagio- ¶ strong I 21 in crenulations discordance. with gabbro "Stair—step" $42134 2 7 1 —The c211JL IL the in banding the into cuts diorite quartz NE. strike planes 311212 3717174214 -14'2'117. 1-211) axes '21: 41274 quartz 211211? fold - 1'-1-7'44 2444444 7112)1' The are axial their and vertical, nearly diorite. 1r_ 4411714 14T77442. 2 271 11?,.i 3 was xene '247 the in incorporated then and open—folded xenolith gabbro 21214417 a in pyro— large 221274121141 At 111-1 :1: 211.prLln banding compositional I,: 3':' tl-L#. '47 1) 2-411311412: (Figure #1, Location 1 I I L14 i 1 I 'Ii1 I I 4 - 1 I 101 — 1 1-1 37.4?.' r' magma. 47 24414114412 quartz diorite 14242 —1Pj vertical AL 1414 '1 the in 4447' xenoliths of transport considerable suggests This east. 1447'(1711111 71:1:15 -441241114.7172 212I['71I14 1 4441144 411 74412 171112217 12, -- 1111444.it[2. 2412117 northat least at :7 miles 2 least and here from southwest miles 4 extends 4711112237 '11 4711171. 2711-1114 hIlt 17111:1121: 11741'5%' 121:42121714 447.1212,14 1t2444'± 371. probably which body, diorite quartz the around place in found is them of J4i44274337 4444:14.. :,L7iIt1LIrw:p 7i47'3- I none 174217 2: -.14-Tc11:l5.14 as 2141 .2412 '311 .4423115 and are 121-12±1 121442. 17242 yet xenoliths, here found types rock dominant the quartz 3-1 774T_42 17 schist, chlorite—epidote metapyroxenite, banding, showing depositional(?) 7112 in- 22 some gabbro, PyroxeneC $122 - 421 2 outcrops here. of east mile exposed 2126 are 141211440 :1141'047ItI11'444 '147424-2.2. 114441117411 21111i117 2242271721-41117 117114' 1 i-'211''2'which rocks, volcanic and diorite quartz hornblende taminated $1224471211014 2371437. 14'14.:71j1 con- 11212212224 11241211422I10 excellent between1713144211124 contact 412112122'22 sheared 1477747 the near is outcrop This 'ccl5Il 11 111L12i2H[— rir1 'It?"" 17 j'' [47117 [1717 7J.r1411A72127J[1' DESCRIPTION: 5 .17411:41714414 of .1r 2lt[11:4.147-71t:17712 stress. shearing conditions '[1714,7 different 7444±11 1l$44771i12177114 :1.1110:c41:7-1 rare 12a 1410-f.111i-liltl.±1 [1212..'.171. i-;17[2'24121t_d!C 4424 1l-7s'['L['.[i[714 compare under types rock specific of behavior to opportunity a 1 142/'7[3' branching, 1i17 zone, shear ENE.-trending :1 ' T''H ii affording thus along mylonitized 1.17-44 .[4773fl%1_ '4751741114471 :11t1 'ii:424n '42.4122112 771121: 3724 was quartz 37 747242-2 pyroxenite, gabbro, banded and schist xenoliths angular of 514,-,fl4-:44:14 221 7i=121 21114111424421344 127.174421114 quartz :3117142:i,47:71 44514'$1-41417' '14237,4 abundant, containing diorite hornblende Flow—lineated 'i,1 ' TA A 1 2717±U.L 14172 OF SUMMARY 174151444474417174 FEATURES: ;i7417i '1%:-nj--t;tFebruary, 1717-1717 1973 DATE: 4111.115 -47422s171s:ir Myers, E. Paul 211113151 Claire 1)[274'-'[4417 UW—Eau AUTHOR: R.7E. :47.4411)7 771,4 '4:444 '07sec. T.27N., 29, SE--, [1 4:110 u&14111'31 ®211'$172 at Mosinee: River 7412411'1"-111171) Wisconsin LOCATION: 7442.1(111124147 [31,fl57'711' Sheared 51t,111'112 quartz 2114127 intrusive 425-. '1.214:144.111171 breccia diorite 74 22 41 TITLE: 5i1J[. Field 37M7 Locality Trip 11 79 �1 -- LOcat°' �/ , / Ill , diorite. quartz ' / / / 1 \ " ' / in / / '' 1 i, / / I I' / _ I I '- / i / / ' NI / / , I / I v / / f \ / /1 / 'S / - / I — / 3 " / 1" / / Figure /\ I' / — I t /__.: — — / / •- :- / 'I t/ /\ / (Detail.) crenulated locally Banding quartz in gabbro pyroxene Folded — — it': U• / — r / / /, 1 / ' / diorite. Figure 2 • U_U :, •. U: 4 S / S — t I ' --- - —=-- ir— / 1; I / , , / \ maic :/ / T— i '•I 44 I U - 44 54' US — '5 '\ 4, ',,.'lI 5, .5 'S. I •• / o I / — - I A Epidote—chiorite /'L_____________—J /5incs ' — — __ U -:,-eQ / // xenolith schist I '/ I ' -—-=-- -: — ' •/,i 'A -A A I, ' 5-.-44(5-.; I 5 ) • •-•:• U, U -.c,-'4 :h-.?-H',' I I " UI s1I / U,, • •' U, 5/ A 'U •. • —4 A U ç Ii I.! I •, —,., ..A . H '.: SI U: c.,,.4' rI H '-S • - 4,, U -. •<, .tA/",,' 44- '4,2171, '4•1A -1 U- 1 U U - U •;•_•i :1 54 5- —U' 54' --U AT 45 .5-A •'"•'' • 'I . 5, U,'4 4 1* '.:- H H .. -. A - • ,U S -I A U •• • • 2 •- —I / 5, / '1 V 44. * 544'— / US. • 1': / —I 12'' 5, — I -1- 5,.,.. 4', .±... / -' U — •' I I — AlE_ TA/1 LE L 81 �82 7 H :;' L i'ittntditw Pitcc'cisa brecciatsi'tct withq!ciartc:; quartz 3tctctht intrusive Figure 4 —— Sheared alL ILLquartz wnaztc cars 'c-at I with tic-. contact lenses (cross—ruled) (crcna= ratia:2 I along aJLc'ic: the Criasas tc'wcJt 2 "Pt a, tHr!c:;te acm ccc ±;tti-,cggabbroic gt5. 'ci' it xenoliths. diorite containing ac±lPa,t criica—ra-a i.ir:li;.$ schist xenolith cc' of rtial chiorite—epidote LttItLt4@W #2(Figure 'FCUris 1) L: a dttLL'tmt-itt\ AtIt Location #2, vxlittct,:; are i:c: truncated rUt I rt,acattt4 tc; pl.a.cnttzt which is segmented ;.C.(+t cciii by shear planes by the :r.tntrJLttttgi; a2iria'r ii;:; interlensing Ia! awl ath.t'ari.nrlP (and It clear tinalP that shearing ,;,It therefore tt.ttriiftrtt claw':; 5-t. is UlLitic'r 3). 2) ±t!±Ks:ritii (Figure quartz 3;anr-ta- diorite tr,rst episodes .tmt±cn&taIt 2caw two th'crcncri - Thus, wcvl Lttintrusion. çrttittttittctquartz qiticir diorite metamorphism?) preceded 3a2r'nrcrp1i2aaU) ccc the tle snibiat cawtsainp crn..cc:;cw. development of schist contemporaneous S i t '25Iw'!LC;!ISL,i:;t:; ni:;:svalidated, rat I C atarI, Was Its.iddtcLt3 are cii shearing of r,n iLl the cit ii in The a absence -"°- cc of syenite xenoliths riP the gabbro? Ciii with folding of nii: two 'Wti 'Its 'c"t" units :Tw'Ltiiti'tage aa of the ticS PwUsy quartz diorite only cncdcc.,:;.scti indicationsciF of relative its the Lc'rJcc-c3 is qinartc satin:; it:; ctiatiStt seen in contact. nit twit snLca'nncLcs n' yt 'Pccan been since they have not yet n arc £ it'itsltw Lrwcni,i.a tact itria;t :; the intrusive breccia has been rcaran'titlP converted :.gccra 1) i 21w Lcccttcnr #3, #3, (i Figure ci Location At itt:; 'w c _ig tnt by shearing to a lensoial gneiss showing differential lenticulation 1. xenoliths with resultant length/width ratios largely litha with racai't-aicnt m:LIq'cIh!cticta ccaicicsc acacacit cclP cci cai.crvcc,ca'cjw' and segmentation of lr.awtcta, Several tt1tt crc-alLintermediate :1wcr,a.c:; St ' texture. ccc ir ic c!iofrcenctL ittI tflt.tLttdd.i Ll" and xenolith mineralogy a function Lilt a mLacc;ati,©h, Cit ctsac"acd at erc1H'Incs!. car:; stages cf of tracali xenolith Ut attenuation can be observed at this location. There stct-;ac Liatcancri. intrusive thtcctiaiLvc:3aLlitcLa!Kti between as is throughout titia thisragiani regiona ac'urizci'tc curious association It tJcct!CJlfTtitt?Jt' gmindtt 4. miia See Figure 4. aTc.Lat..i' l,tLic I -nUt tcstititi'ci' (rich (a-Icc in Ic ac-cal contacts xenoliths) and shear zones. ij'itwt 1c l' itit. bci4 mma;:'a.racl gabbro naL±tzc body ani-iccitic a ni'-fcjitcttat'it CUrl the subjacent layered cp:ca'ctz diorite .2±ctr:'te intrude lists quartz Did r' L:;1 4 j !LIt,i is this body related Li. If so, Ce H ii cvii,, and raft the xenoliths up to this level? atj,crtttosttc' :;li-'st:;.-srtcicc ± the to Tigerton anorthosite? F F - �83 Additional Locality iC L ttctYT'L'T'iiu'21 119-C TITLE: Gabbroic masses and leucogranite iiL.ILIttU .11'L7?11'T:'C '- IITTI LOCATION: sec. 31, T.28N., R.9E., Marathon County. Low and CTH J southeast of Callon. outcrops float along TLLYL. 'c:.cctL11LLCtcE'.'TI 'ZPL,IL ,: it W-, W-, '-ccc 1, L '.iLYii Cf'' C H-TC 1:-c mc 'i'i•• cTc: c'i',w AUTHOR: :: UW—Oshkosh LaBerge, L. $ DATE: Summers 1970, cr Gene 1972 SUMMARY OF FEATURES: T:T These exposures will not be visited on this trip but constitute an interesting part of the overall geology along the trend of the Eau Claire River shear zone. .3Ct:j9y I' CC T-:-'IL'H Ct ;c i'9-c LLi-.',?C1Ct2 In -Tc:-- :ttL22 "c:Ln;c 1111 iLçu,.qcT:.j- ;!:L - 1-i '3'u- IL 'iY T-:11C,: fl The Eau Claire River mylonite zone is interrupted in the vicinity of Callon by a gabbroic mass, at lest some of which appears metamorphosed (mg). Although the gabbro mass lies athwart the shear zone, it is substantially unsheared, and it contains inclusions of banded Thus amphibolite (sheared meta—greenstone?) and other sheared rocks. this mass seems to be younger than the major shearing in this area. Tc1 "11;Cti .111117111 ..L';Lm; 3CrL. :c'ti'111'tt 1-UEC CUEIa 11c.li.E ccci; , 11.i:tlc -cc TLTC1TL,TJ1LL3 3r' 1Ic'cc C-9T :±-cT, -r. -ccyç ii uLLcc: tt:LcuJ.I,L p-nL: Lr,L.c, t-Ec-:c:E U11t' 11 !TE'.c' u-.E :'•I', Ct " :;:T) '1H• T:ICI TTTIY5L I -L1 iT1'9c: ' IL:&ct_c:'J 61 611cc-cc .-Ur:uT TT1i t.t11'-.LLi.&7LLf .t'c:Ic:C EL:. ic. ,,.t- .,-rIc:tt cc tiL •'C'C CCt:4t''iYE .';,7)uC:q.:cI11CCX :-- LL! :—c ": cut': 1132. -nq u97' '1' I Southwest of the Callon area are numerous blocks of mafic rock The surrounded and intimately intruded by leucocratic granite (lg). maf Ic rocks have a range in composition, including hornblendite, gabbro, cliorite, quartz diorite; the leucogranite contains much pegmatite and graphic granite. A small altered pyroxenite (now talc-serpentine— actinolite, etc.) (ts) which outcrops near the N* corner, sec. 10, T.27N., R.8E. and a number of probably indigenous blocks of anorthosite near the SE corner sec. 8, T.27N., R.8E. may also be related to the gabbroic masses. And inclusions of pyroxenite and what appears to be layered gabbro are present in the dioritic rock in the Wisconsin River Valley at Mosinee (NW, SE-, sec. 29, T.27N., R.7E.). If all these rocks are related, it would indicate the presence of a well— differentiated mafic intrusion which was subsequently segmented and intruded by granitic rocks, mainly the leucogranite. An additional piece of this maf Ic jigsaw puzzle may be the large roadcut of grano— phyre just north of the intersection of U.S. 51 and WIs. 153 at Mosinee (near the center of SW*, sec. 28, T.27N., R.7E.). :19111 iiLi2I 'L :1:,'1'C '1'' L .''•'" flL E- ,',,bCT ,-T; 'CT T1CL. L;;ci:'.c.l1. fiI:L,i,L>n c;c c<1 )c9i:"Lm - cu -Ic: T9,IiLLT' .Lr t-L:Tii9 .JL2 C:,sL1cT :Izm i-TcUETE'.n ',.c.,m:uc .':,'€iLi'LLC:,iILI ;—cc:cct- :c; -;n Eu' ttt .n-c ;CLCIityQ T.:c:: . L9L"?LL' cTc.;cuc:. E: c-,.9c.J pc)Cc' L(T'CLL L.t' EL L'-L'.\''Li 1cLLt cci. CL pcnLc :.'1 .,nL icn C:T. i-; jCC.Li C :-Y7--L C,:Ls TUE C.'L 2tEL iTT JI i'4 -c:::Etrt, :Yi 'c-nc-cc :c-;cZ - ;i;-ci 2[P Cj- :tcI. CLt :1(J TT :Cr ju ct.' cT c<-. 'C:Iitc tTyTht. 'LLY ;TrULLt.tTLCL cu- Ti titl1-T. -1t• : )i LT tIt9tCiL- rIcv-:J ii 1 ccc:- u-nc 71,. tl'mL ': E.tCtT'V'tEL?[LtCLcCCtLr Tm f' iLH 'I .TT • uin ccLclJIYT -1I)auI uu pcLcuLtC... L .L9tO kz- I L2,itL c4LL. Li9 ?LV ; ct:cc .QYj:T tLCL. L [ccacr i99- Cc LLL H:,'41:y,, r •9u c; Ii :t �84 ,y EiE EXPLANATION JLk*17 i.711 AREA MAP FOR ict1l CALLON gal Quaternary alluvium ss Lower iLc;: PaleozoiC sandstone ig LeucocratiC granite mg 117 gabbroMetagabbro and related(?) ±7j1t• 7:Hr: diorite rocks ts Talc-Serpefltiflite m 1tL.(I :1h:iH Mylonite and:1related sheared rocks g Small granitiC bodies hhg :fl[:i.X.1 granite HogartyF, hornblende qd Quartz diorite - fv Felsic volcanics and associated volcano-genic sediments my Mafic volcanicS and associated volcano•?I& sediments jd:J-iir±b? genic 1 • granodiorite tH masses 7:.-r 'fli1 ii9: j:jTi Geologic contact Shear zone �'f"%. 31 Th! qal P - - T.28N. F IS ft 2'- 1 -, I I -. -"ml I - if! ft P ((ft "2 2 ' / I 121 / -P qI qal mg - Jl /7 - :7i[ — 2 I 2 — - 2 I 2 - "2 3 i1! -'. 7 Ig / qal( — I. itilIt -ft - 12 - t - '— ( /1 1._I 2 — 2 '1 '1k — -L / —-. "2 —. -P K- C J I ---I — . J I £ -( ig — L A -__..__m_ I / 1 - I c-s -- — - I 7 - — - I? - 2 -L'1" ç 'I 1$, - Miles — . Ig C 2 ft / / / 1. hhg 1 / I 7.. .1 I "-- LI — 11/71 SS (2( -'- : _.—-c' PU2TILI" d 1') qal -'/H 1/2TPJ -- --- T.28N. - IC mg hhg 2 - --;:. _' Jv ICI I). --='---71'---'---"=', -._i_--' -1 .1 qd / '( _4-P.1tL;._t 1 -'1-71 - —-- i7't L ,/' rng —— ILi:'& '1.41 ;Yi-..'-' a4:- 2-P ft ,/, m 7 h- . ,1-1 _D-P 'A' ¶2H ..- " ' ] - •'• 1 12 C k—I i'L .)hh94 -? (),-' ,/ '(2 p--'/' I-P - —1 ±A,;i _.71-S.LJ Ig 731 /5Ii"2 l9 :-———— —— ' — -1 lID m' ,1 '/211 1' P2 .1 / hhg '(U l\ I[o / I — —__=—tC41E —— AT Ig 1/fl -J 'U.'1 . Ig \ '9 J mg /1' 7o7'17' mg\ .' .—'----''-- '1.: 1 [ mg J 2 ft :11.11 qal — m r. — mg 2 4icti)Ec. '-.4, ,t;t+_.I_I.+4.+4* - — / '3 I -. — 11 7 A 11• 1/' ní2 ...7(2 ? my ' / /?/ ____ ___ ____ ____ ___ ____ _______ _____ E. R. C_i1Iory_\ - -— ' -' mg, .k%.:.L—II ', '11 \ 1- - Sç. - 26 25 2 - L cI9-L\ .1_i - -' qc nI \Ig) '1'tJx(/ - Alt2 / - H — ii , -- 4"—1 jH qal ,7') - — ft1 ft' 1-; " 33—-' H. - "21---'' / 15 —jI jr ft/I •.pft;q77 t1/1 -:' ' ft V - — -' — i-P'—i ii , I 1. (1 28??,/ -. 21 —--- - — —ç-—--.- T4 \m4 '- - - / A IL I'I,L I . _,Ig / 1_—- — / 11 TT — Ig I (x) 29 J-.------ ... — I" 'r - , J uit— ,LJL. /fi L' _1- ' fv —— L' 17 Li T I — " c/iT1V/ L • al 1 'N tL__—,Ia 1 / r - - ____ ________ �'c:c;y&at the -t'ii- cLL-cin. ac-c-u-scccs ccm-rcc-tc 'Ii tk F Field Ld ccc] relations a-c',ILc• suggest following sequenceccof events in the cc-: Hogarty -)d the ccc; a,;:•r1 of cc ;t-c .cc. 1) clb-c'ic'' on iY emplacement area shown theacccy;-iccc:5CLcr accompanying map: cc-cc. )iLr-cc 31 T3'ccJ-m.y. ,c-c;into the mafic volcanic hornblende granite l5OO ago vcJtcaccLc sequence; cccc-ca;cccii :C'JrJLILF uii3.@:;i9jd,.i -s: ltc-a- mylonite a-tc]cc vi: zone scc-:c 'L:c 3L:irZ 2) c;Fc•ca::L shearing 33 to t;cctcu.cFcproduce the Eau Claire River (the shearing LlFricict,acrcc:c:-i. ilL iL::F ficil:-:: rcJ ct-cd c d'-dcif't3' may be at least in part related to the emplacement of the Hogarty 3ist-L-ldd.' L c-c:• cci ,:c-cii;.5 t:.cct5 of :tc '.-i ' ,c Lac4 -c hi--c gabbroic hornblende 3) intrusion (and differentiation?) the c-iccclls granite); ccc'ca-c'ci-: d-c.r:,cb is:iLc? 'CI'') 3 iccis;s: ;"rv-:Isc:--3 ci' Fr3ii-5ThI3F5 :1, ct -u:cc mass; 4) intrustion of the leucogranite with segmentation of the &'St sr- a_ri :5,,, subsequent to emplacement I) has L -icc place Minor shearing taken gabbroic ,,3 mass. ti-s ac :gxzt.t.c ic—c the tici youngest Thus seems -Ic to be "hac the leucogranite -cccc -- cr-c cyvtcvic,ii of c the leucogranite. 3; iF tC'33 igneous rockmapped Yc2c-iic.F-t. in this FFTiL area. • iii Li? ijcc c "3 '- I P ' P : DESCRIPTION: Iiic,u-3 c-ct maf .c ,scStrvtc-3 and Low -cr' outcrops cc:,'ir-'rp aid and3iLFFs-t float of Ci leucogranite ic -'cc--S rocks c-c-icc occur Icrfor :ti,.iIic -;.c.;c ;'-J,;rc the ciclll tIc-: fields and woods along approximately a mile along c :1. in the c 1iL-cac-csCTH t3 J and xc:-c-:ic of JEt IdE5. ftJ_iLaii'cttc- zones Alternating -:31 maf c ciIc rocks -EL, T.28N., -:7. tic-iLL -;j:3zc; edge of sicsec. iiiis 31, western R.9E. iii the tci. Leucogranite is cr'.ccB&ciialong cio•ccthe lix ccroad. -cidi- iL-xsr5u;-i-c-'tx-c present and leucogranite are W1 :33ofit granite predominant rock type 2:3cvc:c1c-it-3-'t cic ii-',,'-i: in the cccc, area, cad and veins and dikes '-Zi s'cc cutting the mafic rocks were seencc atcccra1 several;Ic-ccaplaces. Lack of outcrops tIc tI--c---: :1FLi3 :tar— cc F idF- and precludes shape of the mafic zLstc-cr :3 sii the size '3lC ;Iii4, accurately 2c c—ic:-'. IF-Li.- determining I -is leucogranite. ciLa;-. 32 I3j-J.I)SU by the No clear c-c5c-c-ccc:'t a] seem to be surrounded masses, but Il-ct all tccscia. 15 ]clFcit Is ic-c--c -t.;;--'.-s-i iii.-: cc cc-Itt33 the occurrences of maf Ic rocks cutting granite were ccc-c seen. cd the c-tt - ;'i - ,Lcca il u': :/ci scr'c' c-lIt: the icc-c Ii ccccQL—ICat t-'c EL with -F--cc,:,:AIL.L- have ii :rcr-g-c The ccxc mafic rocks evidently range in composition, 1ccicc a '-cc :cccccic 5-r ;5r33r Biotite differences reflected Fr in the ferromagnesian minerals present. FtDcdWiLt, and lbLcci—lIcLtcbdIs is '3- abundant, cct -3i--Fr--! Is 7--t,-clt:1?ar-t predominant in ccc:c samples, others hornblende 3-cii iF5. in ii some iccctc iiiscc-icc5 commonly present Iiinc-Iothers Lac-ci :--t r--c'cvsca accl icc:-cfl-c-c-c1c both pyroxene and hornblende c-cc'uic occur. Quartz -"tc:Li.L,,'tCI it-c cccxc: cccLUt;usEL c'c;cc. variation Lit-c The c:-:5ctcccc extent to which cc; the compositional 'tctctcc:.,c itt-icc--c It; In the phases. 'ic-b-S blotitic fxc_'ic S.F 11cc to 1-c- partial it-aft cclc original -r-i1.c:ill cCtccFc t-i:-- ej in vii: the cc, maflc rocks reflects compositions orIs-; is due F,-s ax-sic cc-i: known. No it2cc'c;c-ac±ic petrographic work $itlc Fcc has yet c:ca-v. tV "digestion" by the Ilta ic;cxf'..-s granite is it not L77"'2cJ1c Cii -. c-cplagioclase rc;t :';,t cc: cccccsb I dcxc are arc Lcc' been done on these so compositions largely unknown. c2i,i,cc rocks, c--cctcc 'FLisi 'ccc I - i_3 3 ���� https://digitalcollections.lakeheadu.ca/files/original/e490e5cc4d21cd046bce02006cfdf9de.pdf dce4b4bbbee755b78cfd691154fc6c7f PDF Text Text University of Wizcensir,—Extsnsien GEOLOGICAL AND NATURAL HISTORY SURVEY Meredith E.Ostrom, State Geologist and Director GUIDEBOOK TO THE GEOLOGY AND MINERAL DEPOSITS OF THE CENTRAL PART OF JACKSON COUNTY AND PART OF CLARK COUNTY, WISCONSIN Prepared in cooperation with the U.S. Geological Survey and the Inland Steet Company tor the 19th Annual Institute on Lake Supetior G.otogy Madison, WisconsIn, 1973 �UNIVERSITY OF WISCONSIN-EXTENSIa1 GEOLOGICAL Afl NATURAL HISTORY SUit flY Meredith E. Ostrcn, State Geologist & Director GUIDEBOOK TO THE (ZOLOGY AND MINERAL DEPOSITS OF TH CENTRAL PART OF JACKSON COUNTY AND PART OF CURE COUNTY, WISCC*ISIN by Harry Alemic, U.S. Geological Survey, Washington, D.C. 20244 John M. Ohisan, Chief Geologist, Inland Steel Co., Ishpeming, Michigan This guidebook was printed in limited quantities for the 19th Annual Institute on Lake Superior Geology. Madison, Wisconsin Publication authorized by the Director, U.S. Geological Survey. Available from the Wisconsin Geological and Natural History Surveys University of Wisconsin—Extension, 1815 University Avenue, Madison, Wisconsin 53706. price $1.50. �GUIDEBOOK THE GUIDEBOOK TO TO THE AND MINERAL MINERALDEPOSITS DEPOSITS OF PART OF GEOLOGY AND OF THE THE CENTRAL PART OF JACKSON COUNTY COUNTYAND ANDPART PARTOF OF CLARK CLARKCOUNTY, COUNTY,WISCONS WISCONSINJJ JACKSON INlI by Harry and John Harry Klemioa" Klemi~/ and John M. M. Oh1son/ Ohlso~ IINTRODUCT NTRODUCT ION This field field trip is designed to provide an introduction to the general central part of of Jackson general geology and the economic geology of the central It includes includes aa visit visit to the Jackson County and part of Clark County. It magnetic taconite mine and County Iron Company's modern magnetic taconite mine and agglomeration plant, examination of plant, of outcropping Precambrian features, features, Upper Upper Cambrian strata, strata, and various local local physiographic physiographic features. features. will include Stops 1 through 9 (Figure 1), if if The trip will include visits visits to Stops (Figure 1), time permits. Additional places of interest interest are are shown as as localities 10 through 27 on the the maps and and are are described described briefly briefly in in the the text. text. general geology of of the northern part part of of this this area and of the The general the northern and of the the north has been been described described by by Wiedman Wiedman (1907). (1907). adjoining area to the Ostrom, Davis, Davis, and and Cline Cline (1970) have made made excellent excellent Ostrom (1966) (1966) and and Ostrom, (1970) have descriptions and correlations descriptions and correlations of of the the Upper Upper Cambrian Cambrian strata that that cover cover much of west—central west-central Wisconsin and and extend into into Jackson Jackson and and Clark (1961) discussed the clastic sedimentation Counties. Potter and Pryor (1961) of the the Paleozoic rocks of this general area of area and and noted noted the the presence presence of of phosphatic material in in the the Cambrian Cambrian rocks. rocks. The modern mining and and beneficiation facilities the Jackson facilities of of the County Iron Iron Company have have been been described described by by Skillings Skillings (1970). (1970). An occurrence of wavellite in Jackson County was described rence described by by Klemic Klemic and and Mrose Mrose (1972). The senior author is indebted to the Jackson County Iron Company for information information concerning concerning the the iron iron deposits. deposits. The cooperation and access access to their their property of many others in providing information and is gratefully acknowledged. is acknowledged. Much unpublished information information concerning the local local geology was was also also obtained from the the Wisconsin Geological Geological and and Natural History History Survey. Survey. Most of Jackson Jackson County and and parts of Clark County are in the "drift— "driftless area', but thin thin gravel gravel deposits deposits interpreted interpreted to to be be glacial glacial drift drift less area", but or outwash from glacial glacial deposits are present in many places east of the Black River. River. 11 Publication Publication authorized authorized by by the the Director, Director, U.S. U.S. Geological Geological Survey. Survey. ~/ U.S. U.S. Geological Survey, Survey, Washington, Washington, D.C. D.C. 20244. 1/ Chief Geologist, Inland Inland Steel Steel Co., Co., Ishpeming, Ishpeming, Michigan. Michigan. �2 9O0Os I1r d N (P I r 2 it S ho rtv ill e /J1c(T _ 141 rrc 1 \ atfi 1 6- eth7 2Q__. KSON / I c'°cT'r1 if 0 -18 41oj 'lL 1 23 IT Figure 1. 1. Figure S4 I I887 7 IJI (77) N Ti I i -o \ milee _44°15t=4 Field trip etops end other localities of geologic interest stops and in Jackson Jackson and end Clark C1rk Counties, in Counties, Wisconsin,. Wisconsin .. Base by U.S. Claire, 1964. 196)i. Eau Geological Survey, 1:250,000, Claire, l:2S0,000, Geological Survey, �r r 3 Exposures of Precambrian rocks in Jackson County and in the southern part part of of Clark Clark County County are are largely largely limited limited to to the the valley valley of of the the southern Black River and and its its tributaries. tributaries. A A few few mounds of Precambrian iron— ironformation and and associated associated schists schists and and some some quartzite quartzite knobs knobs occur occur as as windows in the Upper Cambrian sedimentary strata which form the the bedrock over most of of the the area. area. The exposed Precambrian rocks rocks consists consists mainly mainly of of paragneisses, paragneisses, schists, schists, phyllites, phyllites, quartzites, and, and, locally, locally, iron—formation. iron-formation. Granite and associated rhyolite and and aplitic aplitic dikes, dikes, and and gabbroic, gabbroic, dioritic, dioritic, and and doleritic dikes are are exposed in in many places. places. gneisses are are mostly mostly of of granitic granitic to to granodioritic granodioritic composition, composition, The gneisses and volcanic volcanic rocks. rocks. Thin chloritic and are metamorphosed sedimentary and layers of greenstone in in the the gneisses gneisses may may be be sills sills or or volcanic volcanic rocks. rocks. The foliation of the gneisses generally dips steeply and in some places In most most places the the gneisses are highly contorted migmatites. In the the weathered zone zone at at the the top top of of the the Precambrian Precambrian rocks rocks is is relatively relatively shallow, shallow, and or no no saprolitic saprolitic zone zone at at the the top top and it appears that there was little or of the the Precambrian Precambrian at at the the time time of of deposition deposition of of the the basal basal Upper Upper Cambrian Cambrian of sediments. age, totaling more Sandstone strata of Late Cambrian age, more than than 400 fe~t feet in thickness thickness in in places places in in Jackson Jackson and and Clark Clark Counties, Counties, rest rest unconformably unconformably in on the Precambrian Precambrian rocks. rocks. In most of the area area east of of the the Black Black River, River, however, however, the the sandstone cover cover is is less less than than 200 200 feet feet thick. thick. In In ascending order, the formations include include the Mount Simon and and Eau Eau Claire Claire order, the Cambrian formations the Mount Sandstones and and the Wonewoc and and Lone Lone Rock Rock Formations Formations of of Ostrom Ostrom (1966). (1966). units are are described described in in Figure Figure 2. 2. These units The Cambrian formations formations dip dip very very gently gently (less (less than than 10) 1°) southwest. southwest. or minor minor features features related related to to the the sedimentary processes involved Except ffor involved gradual transgression and in gradual and regression regression of of seas seas in in aa marine—shelf marine-shelf sediment zone, zone, these formations are are conformable conformable with with each each other. other. Most of the rocks cemented, very porous porous rocks are quartz arenites arenites which are weakly cemented, and permeable, permeable, and which have been intensively and intensively leached. leached. Loose sand accumulated by the disintegration of the accumulated the sandstone sandstone mantles mantles large large areas areas and conceals conceals formational formational contacts in and in most places. Deposits of river gravel derived largely from glacial deposits of the few tens of feet feet thick thick on some some terraces terraces along along north of the area are are a a few tens of the Black Black River. River. STOPS OF GEOLOGIC INTEREST STOPS STOP 1: STOP 1: Upper part of Mount Simon Sandstone. Sandstone. Location: quadrangle. West side of U.S. Black River Falls quadrangle. U.S. Rte. Rte. 12 about 500 feet north of Interstate about Interstate Rte. Rte. 94 94 (Figure (Figure 3). 3). The roadcut exposes flat—lying, medium—bedded, cross— flat-lying, thick— thick- to medium-bedded, crosslaminated, poorly poorly cemented, cemented, pale-gray pale—gray to to buff, buff, mediummedium- to to fine-grained fine—graiñed laminated, quartz sandstone with a few thin, white, clayey partings partings and thin, white, and minor �4 Upper Cambrian Cambrian formations Lone Rock Rock Formation 1966). Sandstone Sandstone Formation (Ostrom, (Ostrom, 1966). buff to to greenish-grey; greenish-gray; sandstone, sandstone, and shale, shale, huff and thinto medium-bedded, thinly crossbedded, thin- to medium-bedded, thinly crossbedded, some layers ripple ripple marked, medium- to to finesome layers marked, mediumgrained, glauconitic end grained, and micaceous, micaceous, fossiliferous; shale, buff to gray, mostly in very to gray, mostly in very thin thin erous; shale, exposed in borrow borrow pits on on layers. Unit is is well well esoosed ridgetops FEET FEET ~·~·;.:i:;;:{f~~t~:~~.ji~:~·i·;·:::: 200 ·,;':":::::;"'W.,,\(.l!II.!t~·.?\;.::> ·..·.·...::"i' .. ~·zone .:.,::.."...... Wonewoc Formation (Ostrom, 1966). Wonewoc 1966). Sandstone, white, pale-yellow to light-yellowish-brown, white, light-yellowish-brown, thick- to thicktomedium-bedded, medium-bedded,crossbedded, crossbedded, some some thin layers layers and and shalay shaley partings. partings. PredomiPredomiranges from coarse nantly medium grained, grained, but but ranges grained silty; weakly weakly cemented cemented escept except for grained to silty; thin zonesthat thatare arecemented cemented by by brown brown thin irregular irregularzones Unit forms forms bluffs iron osides. oxides. Unit Eau Eau Claire Claire Sandstone. Sandstone. Sandstone and and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to buff, mediumsandstone, to thin-bedded, croasbedded, medium- to very ~wtjA2)i~~lJ/jJ~I\1~:lil;~~~~{~::~~:~~!~~~~~~~~i~:J,~;~~~~ fine grained, some thin coquinoid layers of ·:,::•.···..,;·;,;,··:·..... :·c>::"... :.:· small brachiopods, weakly cemented, friable, except for thin irregular megular zones zones that are are locally escept cemented by iron osides; shale, light-greenish- ~~ltl'~ §ig~i~·Y:5.:;~~~:r:i:~l~.:.;: gray to buff, generally in thin partings, but locally more than 1 foot thick. Unit generally poorly esposed o C • • • • ••• .. '~ " Mount Simon Simon Sandstone. Sandstone. Sandstone and shale; shale; sandstone, pale-yellow-brown pale-yellow-brown to to white. white, thickthicksandstone, to thin-bedded, thin-bedded, crossbedded, crossbedded, mainly mainly mediummediumgrained, but ranging from grained, from pebble pebble conglomerate conglomerate in basal layer layer to to very very fine fine grained grained and and in thin basal silty, weakly weakly cemented, cemented, friable; friable; shale, shale, lightlightgray, greenish-gray, locally locally red, red, mostly mostly gray, buff, greenish-gray, foot thin partings, partings, but but locally locally more more than than 11foot in thin bluffs along along streams. streams. Unthick. Unit forms bluffs conformity at base at base -:!.f":: ;'-':~/~"~~~\to ',' ,'. ',',:: \ ; I_'~ ,-, " < ", -I: ~ A • ;, _', \,' ~ ~, ., " ,', ,,-;. ~,- ~"... , -, - < '" < v Precambrian metamorphic and igneous igneous rocks Figure 2.—Generalized stratigraphic section aection of Paleozoic 2.-Generalized stratigraphic Paleozoic aedisnentary sedimentary rocks near near Black Black River River Falls, Falls, Jackson Jackson County, CoWlty, Wia., Wis., showing showing the approximate position position of of the the wavellite wavellite occurrence. occurrence. Data from Klemic DRtA 1972. Kiemic end and Mroa8, l4roee, 1972. �5 Figure 3. Blsck Rivsr Fall. area: Stop. 1, 2, 4, 6, and localities 11, and 25. Base by U.S. Geological Survey, Black River Falls nuadrangle, 1968, 1:62,500. 10, �6 partings stained by iron oxide. The Cross—beds dip southeast. No fossils noted here. this outcrop is typical of exposures of the upper part of the Mount Simon Sandstone west of the river. These beds are about 100 the Black to 120 feet above the base of the formation as exposed near River to the northeast and to the south. The lower part of the formation in most areas has thicker bedding and in average grain size. is slightly coarser The forested mound 3. mile to the east is Tilden Mound or section u Mound. It is a motadnock of Precaubflan iron-formation, schist, and phyllite. The relief on the Precambrian surface between the top of the mound sad the surface of the Precambrian rocks on the west side of Black River is 170 feet in a horizontal distance of about 400 feet. Unfoliated Precambrian granite crops out in the river valley locally between Tilden Mound and Interstate Rte. 94. Castle Mound, $ miles to the south—southeast is Upper Cambrian sandstone. STOP 2t Precambrian monadnock of iron—formation. Location: Black River Pails quadrangle in the NE sec. 12, T. 21 N., R. 4 W. near the junction of Levis Creek Road and West Bottom Road (Figure 3). Precambrian iron-formation flanked and partially capped by remnants of the Upper Cambrian Mount Simon Sandstone extends 50 feet above the surrotmding plain that is underlain by the Mount Simon Sandstone. The surf icial part of the iron—formation contains both itagnetite and martite. The strong magnetic anomaly associated with the mound of iron—formation extends both northwest and southeast of the mound. The extent to which the magnetic anomaly at the crest of the mound has been altered by lightning strikes is an interesting question. STOP 3: Jackson County Iron Company magnetic taconite mine and agglomeration plant. Location: Hatfield SW 71—minute quadrangle, SE fr, sec. 15, P. 21 74., R. 3 W. (Figure 4). The open pit mine is at the site of iron Mound, a nonadnock of Precambrian iron—formation that fornierty extended about 150 feet above the surrounding plain. Eron Mound was flanked and partly capped by the Mount Simon Sandstone. The uppermost part of the mound was approtiraately at the altitude at which the Lau Claire Sandstone (which overlies the Mount Simon Sandstone) formerly occurred. Iron—formation here dips about iV SW and is in an interval as much as 350 feet thick. This thickness may represent an isoclinally folded unit or it may be a faulted segment of a thick formation. It extends to below 650 feet above sea level. Quartz—chlorite schists border the iron— formation. Magnetite is the predominant iron-rich mineral, but some thin layers contain abundant specular hematite. The iron—formation has Mat Sc dikes, granitic been metamorphosed to garnet—actinolite grade. or aplitic dikes, and quartz veins cut the iron—formation. A zone of tRic schist parallela the layering of the iron—formation near the center of the pit. �7 '-I I' S �S The ore averages 20 to 23 percent in recoverable iron. About 3 of crude ore are required to produce 1 ton of pellets containing 63.5 percent iron and 1 percent silica. The nagnetite and gangue minerals are so finely interlocked that in order to obtain suitable iron ore concentrates, a final grind is made to a size at which 93.5 percent of the ore will pass through a 325—mesh screen. The Tnagnetite t€ separated from the gangue minerals by magnetic separators. Twenty pounds of hen— tonite clay is added per ton of concentrate in a mixer. The nixture is fed to a balling mill in which the powdered concentrates are converted to pellets, about 85 percent of which are 3/8 to 5/8 inch in diameter, The pellets are dried and preheated and then are heated to 2500 degrees F. In this process, the nagnetite is converted to hematite, and the finished pellets become hardened enough to withstand a compression of 800 lbs. tons Pellet shipments in 1972 were 887,000 long tons. More details concerning the iron deposit and the mining, beneficiaticrn, and pelletizing of the ores, tailings disposal, water supply, and environmental factors will be discussed at stop 3. ST4W 4: Eau Claire Sandstone and Wonawoc Formation of Ostron (1966). Black River Falls quadrangle, SW fr, sec. 24, T. 21 N., Location: R. 4W. Esst end of Castle Mound, 500 feet west of U.S. Rte. 12 on Castle Mound Road (Figure 3). Castle Mound is an elongate ridge capped by the lower part of The upper part of the Mount Siron Sandstone forms the basal part of the ridge from about 880 to Wonewoc Formation of Late Cambrian age. 995 feet above sea level, and, except at the eastern end of the ridge, it is largely concealed by talus and soil derived from the overlying rocks. The Eau Claire Sandstone, which includes fossiliferous tedium— to fine—grained sgndstone, forms the strata at altitudes of 995 to 1025 feet above sea level. The fossils in the Ea Cl.tre Sandstone are snail white phosphatic brachiopod shells composed of fluorapatite. These distinctive white shells are chars.cteflstic of the Lao Claire Sandstone In the area west of the Black River. East of the river the formation has been intensively leached, and although the fossiliferous zones are present, the fossil shell remnants are generally stained by iron oxides. Commonly the shells have been coaipletely removed and are represented by empty molds in the sandstone. A noticeable anount Of glauconite is generally present in the formation. Close exaninstion Of specimens of the coquina of phosphatic brachiopod shells reveals that quartz grains in contact with the shell mates-ia]. have been partially dissolved, leaving flat surfaces that conform to the adjoining smooth shell surfaces. Empty molds of fossils also show this modification of the innermost layer of quartz grains. Remnants of the Esu Claire Sandstone capping low hills in the area to the ecist are generally stained and cemented by brown iron oxide and weather out as small platy fragments that contrast with the pale—colored and weakly cemented and nonfossilt— lerous rock of the underlying Mount Simon Sandstone. The Mount Simon sad the Wonewoc, however, also contain iron oxide—cenented layers, but these are generally inedium—grained s andstane s. �9 STOP 5: STOP 5: Lone Rock Formation of of Ostrom Ostrom (1966). (1966). 1 Black River Falls quadrangle, NW NW 4' , sec. 10, 10, T. Location: River Falls quadrangle, T. 21 21 N., N., Borrow pit on south side of Pine Creek Road Road near R. W. (Figure (Figure 5). 5). pit of R. 5 W. crest of of hill. hill. The Lone Lone Rock Formation of of Late Late Cambrian age extends from from near near the The age extends the 1120 foot foot contour to to the the crest crest of of the the hill. hill. The formation formation consists consists mainly of light brownish—gray, brownish-gray, medium— medium- to to thin—bedded, thin-bedded, medium fine— fine- to fine—grained cross—laminated fine-grained cross-laminated sandstone sandstone and and thin thin layers layers of of shale. shale. The sandstone is argillaceous and and glauconitic. glauconitic. Some beds are are abundantly abundantly fossiliferous, and trails, ripple ripple marks, marks, and and mud mud cracks cracks are are well well fossiliferous, and worm trails, in thin thin sandstone sandstone layers. layers. The rock exposed here here is is typical typical preserved in of the rock in the of the the Lone Lone Rock Rock Formation at at other "shale "shale pits" pits" near near the the crests of ridges in both the the Black Black River River Falls Falls and and adjoining adjoining quadrangles. quadrangles. The environment of deposition of the Lone Rock Formation was similar It was was one in which shallow seas to that of the the Eau Eau Claire Claire Sandstone. Sandstone. It seas transgressed over over lagoonal lagoonal areas areas and and in in which which marine marine life life flourished flourished in in transgressed Local concentrations of brachiopod the littoral and the and neritic neritic zones. zones. Local shells in coquinalike layers resulted from from the the winnowing winnowing of of sediments sediments containing abundant abundant shells shells and and shell shell fragments. fragments. chitinous The rocks have been extensively leached of calcareous and and chitinous material, leaving fossil molds. Phosphatic brachiopod shells, material, shells, however, however, have been more more resistant leaching, as white resistant to leaching, as indicated by the the remaining white brachiopod shells. shells. The sandstone and and shale of the the Lone Rock Formation are extensively used for for surfacing dirt dirt roads and for for fill fill at bridges and and culverts culverts in used roads and at bridges Jackson County because they are to erosion because they are more more cohesive cohesive and and resistant resistant to the readily than is is most most of of the readily available available rock rock of of the the underlying underlying Cambrian Cambrian sandstones in in this this general general area. area. Soil developed on on the the Lone Lone Rock Rock ForFormation is rich in potash because of the presence of glauconite and clay and is and is rich in phosphorus from marine organisms. organisms. In In comparison, comparison, poor soils occur occur on the the Wonewoc Wonewoc and and the the Mount Mount Simon, Simon, which which consist consist largely largely soils of quartz quartz sand. sand. STOP 6: STOP 6: Wonewoc Formation Formation of of °strom Ostrom (1966). (1966). Location: Black River River Falls Falls quadrangle, quadrangle, SE SE sec. 31, T. 22 22 N., N., 31, T. W. (Figure R. 5 W. (Figure 3). 3). On south side of Wisconsin Rte. Rte. 27, 27, at at roadside roadside rest area and dirt road leading leading up up hill hill to to shale shale pit. pit. t, The Wonewoc Formation is well well exposed in large roadcuts on the Rte. 27 and south side of Rte. and on the the north side side of of Interstate Interstate Rte. Rte. 94. 94. More than 100 100 feet feet of of beds beds of of the the Wonewoc Wonewoc Formation Formation are are visible visible in in the the face face than of the the large large roadcut roadcut to to the the north. north. The top top of the the formation formation is near altitude altitude 1210 1210 feet feet and and is is approximately approximately at at the the top top of of the the exposed exposed rock rock formation is is below road face. The base of the formation road level level and and is is probably near altitude 1040, 1040, at at the the base base of of the the steep steep slope slope of of the the ridge. ridge. �1.0 Figure . Creek Rod ere!* Stop . Base by U.S. Geological Survey, Black River Falls cuadrangle, 1968, 1:62,500. Pine �11 white, pale yellow to The sandstone of the Wonewoc Formation is white, to thick thick bedded, bedded, cross-laminated, cross—laminated, and and predominantly predominantly light light brown, brown, medium to coarse— to very fine—grained medium grained, grained, but includes coarsefine-grained sand and and minor amounts of of clay. clay. Some thin zones are are cemented cemented by by brown brown iron iron oxides. oxides. A large large chamiel channel in in the the sandstone sandstone is is exposed in in the the lower part of the the A The rock here here is of that Wonewoc Formation The is typical typical of that in the the Wonewoc roadcut. In some some places, places, iron—oxide throughout this general general area. area. In iron-oxide cement is is more fossils were were found found at outcrop, but but in some some places places abundant. No fossils at this this outcrop, vertical tubular markings may represent represent burrows burrows made made by by marine marine creatures. creatures. At Wildcat quadrangle, and quadrangle, and and cemented cemented by by and has been called has Humbird, in in the the southern part of Fairchild Mound east of Humbird, at several other localities, localities, variegated variegated sandstone sandstone colored colored at several iron oxide oxide is is very very distinctive distinctive in in appearance appearance and and locally locally iron "Zebra rock" rock" because because of of the the pattern pattern of of its its markings. markings. Although the the Wonewoc Formation forms bluffs and and cliffs, cliffs, the rock is is generally only weakly cemented, and and bedrock bedrock on on the the lower lower slopes slopes of of ridges hills underlain underlain by by this formation is is commonly commonly concealed concealed by by ridges and and hills this formation loose sand and and rubble from flom overlying overlying beds. beds. STOP 7: 7: Eau Claire Sandstone Sandstone and and Wonewoc Wonewoc Formation Formation of of Ostrom Ostrom (1966). (1966). STOP 35, T. Black River Falls quadrangle, SW -, sec. Falls quadrangle, SW~, 35, T. 23 23 N., N., Location: R. 55 W. (Figure (Figure 6). 6). At Silver Mound and in the field field on the southwest R. of Silver Mound. of Fossiliferous and glauconitic sandstone beds of the Eau stone stone are are well well exposed exposed in in aa small small excavation excavation on on aa prominence prominence field Mound, and loose fossiliferous fossiliferous Eau field southwest of of Silver Mound, stone occurs occurs at at an an altitude altitude of of 1025 1025 feet feet on on the the south south tip tip of of stone near the the highway. highway. Claire in in the the Claire Silver Silver SandSandMound Mound Silver Mound is is an an important important archeological archeological locality. locality. The mound is is capped by the the Wonewoc Wonewoc Formation. Formation. The lower lower part part of of the the formation formation is is largely concealed. concealed. The uppermost 100 feet or so of beds, beds, however, however, is thoroughly cemented by silica, silica, and and the the rock rock is is aa brittle brittle quartzite. quartzite. This rock was was extensively extensively used used by by prehistoric prehistoric Indians for the manufacThis Indians for the manufacture of tools tools and and weapons. weapons. Artifacts are numerous in the fields fields surrounding the part of of Silver Mound, Mound, and artifacts and and whitish whitish rounding the southern part and artifacts flakes of quartzite from this flakes this locality locality are are widespread widespread in in Jackson Jackson County. County. Similar quartzite occurs in lesser amounts miles amounts on a ridge several miles northwest of of Silver Silver Mound. Mound. The source of the the silica that that cemented the sandstone sandstone and and the the conditions conditions under under which which it it was was deposited deposited in in the the formation formation of the quartzite in this this almost isolated occurrence require require an explanation. Upper Cambrian strata of this There is no lack of silica in the the Upper this general but most most of of it form of of quartz quartz general area, area, but it is is in the the relatively inert inert form sand. Therefore, Therefore, some some local chemical environment that that differed from the the general conditions must have made silica general silica available available in in solution. solution. Perhaps the chemical the the chemical environment environment of of the the fossiliferous fossiliferous beds, beds, particularly of of the coquina layers, layers, may have been the the source source of of the the silica. silica. As previously described, the the quartz sand grains in contact with the phosphatic brachiopod described, shells have have been been partially partially dissolved dissolved into into hemispherical hemispherical forms forms having having their their shells �·OO$'G9:! '996! 'a!~ue~penu r'uadrangle, s!!ed Falls 1:62,OO. 1968, l:iw~:20!OalJ U.S. fleological ·S"n Aq by aseg Base "L 7. dOlS Stop ~ooH Rock ~oe!g Black 'AaAInS Survey, :a~.Ia pree: punai'{ Silver Mound .leAHS "9 Figure 6. e.:nj,:.!I (';1 12 �13 flat against the the shell shell surfaces. surfaces. The chemical environment environment that that flat surfaces against produced this result in the Eau Claire Claire and the Lone Lone Rock, Rock, both both of of which which produced this result the Eau and the are are fossiliferous and and contain phosphatic phosphatic brachiopods, brachiopods, would would have have made made available large quantities of of silica silica in in solution. solution. Such silica—bearing silica-bearing waters percolating from the fossiliferous fossiliferous Lone Rock Formation may have the silica silica cement cement in in the the Wonewoc Wonewoc Formation Formation at at Silver Silver Mound. Mound. deposited the Small zones of silicified sandstone a few inches thick, thick, in the Mount Simon Sandstone near its contact with the Eau Claire Sandstone have been noted in in several several places places in in Jackson Jackson County. County. STOP 8: 8: STOP Exposure showing complexities complexities of of Precambrian Precambrian rocks. rocks. This stop also provides an opportunity to also to examine examine some some economic economic uses uses of of local local geologic features problems and possibilities arising features and some of of the problems and possibilities from the pressures of demands demands for for their their use. use. Hatfield 7-i-—minute quadrangle, SE -, Location: Hatfield 7!-minute quadrangle, ~, sec. 3, 3, T. T. 22 22 N., N., R. W. At Black River, River, north of County Rte. Rte. K K and and south south of dam at at R. 33 W. Lake Arbutus (Figure (Figure 7). 7). Because of of load load limitations limitations at at the the bridge bridge over over the the canal canal at at Hatfield, Hatfield, it will be necessary to to walk about about 11 mile mile to to the the large large exposure exposure of of PrePrecambrian metamorphic immediately below the at the metamorphic rocks rocks immediately the unconformity at the the Upper Upper Cambrian Cambrian sandstone. sandstone. base of the Lake Arbutus is an an artificial artificial lake impounded behind a dam built bedrock in in the the valley valley of of the the Black Black River. River. Water level upon Precambrian bedrock in the the dam dam is is maintained maintained at at or or near near the the level level of of the the unconformity unconformity at at the top of the the the Precambrian. A A canal canal aa little little more than than 22! miles long long has been cut in the Upper Cambrian sandstone to carry water to the penpen— stocks of aa small small electrical electrical power power plant. plant. The hydraulic hydraulic head at the power plant is is nearly 100 100 feet. feet. This power plant is is an an important important local local nonpolluting source source of electric energy. energy. Lake Lake Arbutus Arbutus has has a a surface area of of slightly more more than two square miles and and is is aa popular recreation center, center, having two two county parks and and aa State campsite on its shores. on its shores. Hatfield, Hatfield, aa small resort community on the the west west side side of of the the lake, lake, is is in an an area in in which which only only about about 10 10 to to 30 30 feet of of beds beds of of Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone overlies overlies the the metametafeet morphic and and igneous igneous Precambrian Precambrian basement basement rocks. rocks. The community obtains obtains its water supply largely from wells in its in the the sandstone. sandstone. A A few wells extend into into the the Precambrian Precambrian basement basement rocks. rocks. disposed into the surficial mantle of Sewage from the the community is is disposed surficial mantle of sand and in the the upper layers layers of of the the sandstone sandstone strata. strata. Thus the the possipossibility exists for pollution of of the the water water supply. supply. Should the local local substantially, both the the amount amount of waste redemand for water increase substantially, quiring disposal and and the the possibility possibility of of pollution pollution of of the the local localgrc*ind ground waters would would also also increase. increase. Alternative sources sources of of water water and and improved improved facilities eventually be be needed. needed. facilities for sewage disposal will eventually - �14 'U . JAO CO 21 T. 22 N. 25' C" C" 0 ; 19 i- J9 \)./.;iç;// y 4O- -, HatfI) eld O7 / fl9• I /l-o ( Backw \'\ C' ) JiVt\ jJJ/ (fl I'? 1Y U(1 ¼) 18 II OA 0 OLD 897 LA V 93 ,/ 0 I 895 0 11 I Loca],i'- 200000 FEET HIGH BANK 1jii 889112$ i7,ei Pits 16 440 Locality 25 - 22'30" 900 45' Pigure Figure mile 7. 680 1810000 FEET I c.1ty 17 ° 4.2 MI. To WIS. 54 '23J 42' 30" localities 17, 17, 24, 24, and and 25. 2. Stop 8 and and localities Hatfe].d quadrangle, 1970, Base from U.S. Geological Survey, Hatfield 1970, ].: 214,000. 1:24,000. Lake Arbutu8 area: area: Lake Arbutue �15 1 The contact between the Mount Simon Sandstone and the underlying west end of the bridge where Precambrian rocks rocks is at road level level at the west mile southwest County Rte. southwest of of the the dam dam at at Rte. K K crosses the Black River Lake Arbutus. A A thick thick bed of of coarse—grained coarse-grained cross—laminated cross-laminated sandstone sandstone is is exposed exposed on on the the west west side side of of the the road, road, and and Precambrian Precambrian granitic granitic gneiss gneiss the east side side of of the the road. road. The channel of the the Black River crops out on the has been cut about about 50 50 feet feet into into the the Precambrian Precambrian rocks rocks at at the the bridge. bridge. t -' Rte. K, K, then go northeast northeast on Clay School School Proceed east on County Rte. Road about 0.2 mile to to aa dirt dirt lane lane on on the the west west side side of of the the road. road. Follow woods and dirt lane to clearing in woods and turn north on path leading down into valley. Proceed northeast northeast toward toward the the foot foot of of the the dam. dam. the river valley. This large large exposure of bedrock shows shows some some of the the complexity of the the basement rocks. rocks. Granitic and and chloritic chloritic gneisses, gneisses, schists, schists, Precambrian basement A large and greenstones trend trend northwest and and dip dip steeply steeply northeast. northeast. A northeast—trending metagabbro dike dike at east end end of of the the dam cuts cuts the the northeast-trending at the the east gneisses. Another large dike on the west side of the east channel of the river is more dioritic in in composition. composition. The intervening granite the gneisses and chloritic sills sills are are contorted contorted in in sinuous sinuous forms forms on on which which gneisses and chloritic there is is well-developed well—developed quartz quartz rodding rodding or or slickensides slickensides that that dip dip to to the the there A feet southwest of the dam a prominent siliceous east. A few hundred feet metarhyolite(?) and the adjoining gneiss are cut by a contorted mass of metarhyolite(?) dipping mafic dike or or sill. sill. An east—trending east-trending swarm of narrow steeply dipping' unfoliated siliceous siliceous and and chloritic chloritic dikes dikes cut cut all all the the other other rock rock types. types. Minor quartz—filled quartz-filled fractures fractures cut the younger dikes and the other rock units. At one place on the west side of the river a quartz vein is more than three three feet feet thick. thick. Minor amounts amounts of of pyrite pyrite are are evident in in the the rocks, and fine—grained pyrite is abundant in the youngest dike. rocks, and fine-grained pyrite is abundant in the youngest dike. STOP 9: STOP 9: Wavellite occurrence occurrence in in the the Eau Eau Claire Claire Sandstone. Sandstone. quadrangle, SW Location: Black River Falls Falls quadrangle, SW -, sec. 23, 23, T. T. 22 22 N., N., R. (Figure 8), 8), roadcut roadcut on on East East Snow Snow Creek Creek Road. Road. R. 4 W. W. (Figure t, Wavellite (Al3(P04)2(OH)35H20) (A13(P04)2(OH)3'5H20) occurs occurs as as thin thin botryoidal botryoidal crusts, erusts, small masses, and cement in the the sandstone sandstone at outcrop small spherical spherical masses, and as as cement at this this outcrop and at several other places where where this this stratigraphic stratigraphic unit unit is is exposed exposed in this general general area. area. The source of the phosphorus is believed to have been phosphatic phosphatic fossil fossil material material such such as the phosphatic phosphatic brachiopod brachiopod shells shells as the in the Eau Claire Sandstone. Sandstone. The Wonewoc Formation which crops out on the west side of the road is weakly cemented, is cemented, very porous and and permeable permeable sandstone. sandstone. It It is is coarser in grain size than the underlying rock in grain rock and and is is thoroughly thoroughly leached. leached. The Wonewoc-Eau Claire contact zone zone is is favorable favorable for the the development of aa Wonewoc—Eau perched water table in places is abundant abundant in in the the places where where shale or clay is Claire. Eau Claire. in many places in Wisconsin where the Eau Wavellite probably occurs in Claire Sandstone is is present and where conditions for movement of ground water were comparable comparable to to those those in in this this area. area. In addition, similar conIn addition, ditions for occurrences of wavellite in association with the Lone Rock Formation may exist. Wavellite, however, may may be be readily readily overlooked, overlooked, Wavellite, however, particularly icial stains of particularly in in cases cases where where it it contains contains surf surficial of iron iron oxides. oxides. �16 -I ZLji *_—:•1: - °• -.-i---- 19• 25 F IF LocalY 24 Locality 23. I 23N Ei 928 1 ' cc; 25 O1I 96 III\ EVERG EEN :T -3 'p23 \ ,** - o T.22N — M 48 13 889 f OF - POWERHO LOcZty 16 17 GreI I 21 Fj \1],'?'Locality iave1 15 .x-= Figure 8. 8. localities 12, Merrillan ares: area: Stop Stop 99 and localities 12, 15, 1', 19, 19, 20, 20, 21, 21, 22, 22, and and 27. 27. Base Base by by U.S. U.S. Geological Survey, Geological Black cuadrangle, 1968, 1968, 1:62,500. l:62,O0. Black River Falls Falls quadrangle, �17 ADDITIONAL LOCALITIES OF GEOLOGIC INTEREST INTEREST of Precambrian Precambrian rocks. rocks. Exposures of Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 15, Locality 10: Black River Falls Locality 10: T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). North of U.S. U.S. Rte. Rte. 12 at Black River T. Falls. Accessible from from east east end end of of bridge bridge crossing crossing Black Black River. River. Unfoliated jointed granite granite at at the Falls below the the dam dam appears appears Unfoliated the Falls fresh, but much of the fresh, the hornblende is is altered altered to to chlorite. chlorite. Similar granite cuts cuts iron-formation iron—formation and rocks adjoining adjoining the the iron-formation iron—formation in granite and rocks Z.E. Peterman Peterman of of the the U.S. U.S. Geological Geological Survey Survey has has deterdeterthe subsurface. Z.E. mined that that the the rubidium—strontium rubidium-strontium ratios in these granites indicate an age of years (U.S. (U.S. Geol. Geol. Survey, Survey, 1972). 1972). age of about 1,690 million years Locality 11: 11: Black River Falls Falls 15—minute 15-minute quadrangle, quadrangle, NE NE -, ~, sec. 22, the valley of Black River at T. 21 21 N., N., R. R. 44 W. W. (Figure (Figure 3). 3). In the at the the base base T. On south side of river. of river. of bluff of Mount Simon Sandstone. On Granitic gneiss and gray chloritic gneiss are cut by dolerite In In contrast to the deep channel cut cut by by the the Black Black River River in in the the Precambrian rocks Arbutus, the-channel rocks below the dam at Lake Arbutus, the· channel here here is only about only about 10 feet feet down into into the the Precambrian Precambrian rocks. rocks. The outcrops here may be concealed if if water water level level is is high. high. dikes. 15—minute quadrangle, quadrangle, NE NE ~, , sec. 30, Locality 12: Black River Falls Falls 15-minute Locality 12: T. N., R. R. 33 W. W. (Figure (Figure 8). 8). West side side of Black River near junction junction T. 22 N., Creek and and river. river. Readily accessible by road road to to canoe canoe landing. landing. of Hall's Creek bluffs leads leads to exposures exposures of of phyllite phyllite and gneiss Path to south along bluffs and gneiss beneath unconformity at at base base of of Mount Mount Simon Simon Sandstone. Sandstone. Weathered schist and and phyllite at at the the base of cliffs of Mount Simon Sandstone are are exposed a short exposed a short distance distance upstream from from the the mouth of of Hall's Hall's Creek; Creek; chloritic chloritic mafic mafic intrusive intrusive rocks rocks also also occur occur in in the the creek creek valley. valley. t, Locality Falls 15-minute 15—minute quadrangle, quadrangle, SE SE , sec. 17, Locality 13: 13: Black River Falls T. W. (Figure (Figure 8). 8). West side side of of Black River River about about 0.4 0.4 mile T. 22 22 N., N., R. R. 33 W. quarry near near river. river. southwest of power plant. plant. Abandoned quarry Strikingly contorted dark gray and and white hornblende gneiss of and a fine—grained fine-grained intrusive rock granitic to granodioritic composition and of gabbroic composition are present are exposed in the the quarry face face and and are are present in loose blocks. blocks. The composition of of feldspar feldspar augen augen in the the gneiss gneiss has has not been determined. Locality -, sec. 25, 25, T. Locality 14: 14: Hatfield 15—minute 15-minute quadrangle, quadrangle, NW NW~, T. 23 23 N., N., R. R. 33 W. W. (Figure (Figure 9). 9). West side side of of Black Black River River near near French French Island. Island. Pink granite typical of that in several several localities along along the Black River north of of Lake Lake Arbutus is is well well exposed exposed along along the the river. river. The basal beds of the the Mount Simon Simon Sandstone Sandstone crop crop out out on on the the west west side side of of the the road. road. Similar granite crops crops out out at the abutment of the abandoned bridge on the east side of of the Black River 0.2 mile mile south of Wisconsin Rte. Rte. 95 95 in the NW , in the NW~, sec. 19, 19, T. T. 23 23 N., N., R. R. 22 W. W. �18 15 17 Levis Mound I Sch . ·r l own Hall ~ 2~ ,, . ·., .~ I "Locality .. 14 ~.:~:;.' "-29 \ /. / "-/ 34 I( (, If /I If figure Figure 9. '-< .. -< L I II•• v· t.ke Arbutus Arbutu area: L.ke ( .l'Gravel Pit - ( I Localittea 14 and 15. 1. Base Locelities 14 and Baseby by U.S. U.S. Geological Geo1op,ica1 Survey, Hatfield Hatfield planimetric l98, l:1L8,000. Survey, planimetric map, map, 1958, 1:48,000. �19 Locality Locality 15: 15: Hatfield 15—minute 15-minute quadrangle, quadrangle, R. 2 W. (Figure 9). North side of of East Fork R. W. (Figure 9). east of of the the bridge. bridge. t, NW 4, T. T. 22 NW -, sec. 4, 22 N., N., of Black River River 250 feet of 250 feet Large outcrop of of granitic granitic and and migmatitic migmatitic gneiss gneiss cut cut by by maf mafic and ic and aplitic dikes. During periods of normal or low water level this outcrop is is well exposed. exposed. Quartz rodding or slickensides on minor folds folds in the the gneiss gneiss is in is similar to that in the the outcrop near near the the dam dam at at Lake Lake (Stop 8), 8), but but the the rodding rodding here here plunges plunges east east at at aa low low angle. angle. Arbutus (Stop of the mafic and aplitic dikes dikes at at this this locality locality have have The relative relative ages ages of the mafic and aplitic not been determined. Pink granite and and small aplitic dikes crop out at several several other places along along the the East Fork Fork of of the the Black Black River. River. t, 20, T. T. 23 Locality 16: 16: Hatfield 15—minute 15-minute quadrangle, quadrangle, SW SW -, sec. 20, 23 N., N., R. 1 W. (Figure (Figure 10). 10). Brushy Ridge Road. Road. R. Quartzite, a small Quartzite, probably of Precambrian age, age, is exposed in ina small roadcut tributary of of Rock Rock Creek. Creek. Quartzite roadcut on the south side of aa tributary zones in in the the Mount Mount Simon Simon Sandstone Sandstone occur occur in in aa small small knob knob on on the north zones the north side of the east-trending east—trending road 0.8 mile north side north of of this this roadcut. roadcut. t, Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE , sec. 22, Locality Locality 17: 17: Hatfield 22, T. T. 22 22 N., N., R. R. 3 W. W. (Figure (Figure 7). 7). Morrison Creek at at County Rte. Rte. K. K. Granite gneiss cut by mafic dikes is is exposed beneath the the bridge during periods of of low low or or normal normal water water level. level. Bluffs of of the the basal basal beds beds of the Mount Simon Sandstone and metamorphic and outcrops outcrops of of the the Precambrian metamorphic rocks and mafic maf Ic and and granitic granitic intrusive intrusive rocks rocks are are exposed exposed along Morrison rocks Creek to the the east of of this this locality. locality. 15—minute quadrangle, quadrangle, NW NW t, , sec. 9, 9, T. T. 21 Locality 18: Hatfield 15-minute 21 N., N., Locality 18: R. W. (Figure (Figure 11). 11). On north side of Battle Point Road. Road. R. 2 W. Precambrian quartzite is is exposed exposed in in aa small small quarry. quarry. The quartzite is is brecciated and recemented by by silica. silica. Basal sandstone of the Mount fragments of of the the quartzite quartzite at the unconformity unconformity includes fragments at the Simon Sandstone includes between the Precambrian and and the the Cambrian Cambrian rocks. rocks. Exposures of of Cambrian Cambrian rocks. rocks. t, Locality Black River -h-, sec. 19, Locality 19: 19: Black River Falls Falls 15—minute 15-minutequadrangle, quadrangle,SE SE 19, T. T. 22 22 N., N., R. R. 33 W. W. (Figure (Figure 8). 8). At bridge on on County Rte. Rte. E E crossing crossing Hall's Creek. Creek. Basal beds of Mount Simon Sandstone Sandstone are are exposed exposed near near stream stream level. level. bedded, cross-laminated, cross—laminated, medium to very coarse coarse The sandstone is is thick bedded, grained, and has at the the base the grained, has a thin pebbly layer at base in places places along the creek. �20 NEILLSVILLE 1S.4 MI. MI. TO WIS. 91S ~.~ r-ri-''l. ) / _.~~l~le Sch . "I / _. -'"- . " .1/-;... ~ _. "":' l..~ '. \, @. . 73 ........... R1W rf'o '' 44°30' 1 660000 FEET 6 5 0. BM 1005 ShortviIle 9 'v" 16 13 1--....·. '- 24 9 ",:-~,;";"",,,.lL'·~~ I •• I "--,. ":-,------.--- .. Figure 10. 10. Figure } -:- .. ,,'- mile ---.. by U.S. 3bortville Shortville area: area: Locality Locality 16. 16. Base by U.S. plazimetric map, Geologieal map, Survey, Hatfield Hatfield planimetrie Geological Survey, 1958, 1:48,000. l98, l:1.i8,000. �21 , F'1inmak r ',Flowage 36 ,.r:..-;-" ~~\~:.:. , ,-- / J f!t>:3,) .......\ \1 L I: Ii II II ft II II II II 1/ II .. ~ ~~~~~:.:_;~ f~~( "' )' vp , " /1 (~~/ / ,, >dk'2 . --' /.-9~. /; /' r, /I. ::~ l \'./ / - - :;', , ~ .... ..... _ _ :', /" ... ~ ';' 1\, \\~ 1 ~~~ {3 . t \{} ....... , ,\\.'-..,'~'.~,\ \" \.\; { \\. I.' {~ ~- ....."'\.,-:-. "- {\. '" ....... t. '.:= ~"~~~ .. .' <~ ~-, \~:-..\ /'" ;.'): . -" . 1/ /'~}/. ~ I~;~:~~~-'') :. ......._- ,\("~ ~')~~2,~ "- 5 v . I' .... ' Figure 11. 11. • Town Line Flovege area: Locality F1owge area: 18. Base by U.S. Geological Locality 18. 1958,l:Ii8,000. 1:48,000. Survey, Hatfield Hatfield planimetric planimetric map, map, 19S8, �22 Locality 20: ?, sec. 26, Locality 20: Black River Falls Falls 15—minute l5-minute quadrangle, quadrangle, NW NW~, 26, T. T. 23 23 N., N., R. R. 44 W. W. (Figure (Figure 8). 8). At park on west side of U.S. U.S. Rte. Rte. 12 at at south edge of Merrillan. Thick-bedded sandstone of the Mount Simon Sandstone is well well exposed at on Hall's Hall's Creek Creek where where there is aa scenic at the darn dam on scenic waterfall. waterfall. Locality 21: Locality 21: Black River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 30, 30, T. T. 23 23 N., N., R. R. 3 W. W. (Figure (Figure 8). 8). At Bruce Mound, in in Clark Clark County. County. Prominent cliffs of the Wonewoc Wonewoc Formation are are strikingly exposed exposed along the southwestern side side of of the the mound. mound. The Lone Rock Rock Formation Formation caps caps the mound at at the the lookout lookout tower. tower. The Eau Claire and and Mount Simon Sandstones stones are largely concealed on the the lower lower slopes slopes of of the the mound mound but but are are partly exposed exposed near near the the ski ski resort resort facilities facilities on on the the east east side side of of the the mound. Locality River Falls Locality 22: 22: Black .River Falls 15—minute 15-minute quadrangle, quadrangle, sec. sec. 22, 22, T. T. 22 22 N., N., R. R. 4 W. W. (Figure (Figure 8). 8). Along road following the top of ridge leading from West Snow Creek Road Road toward toward radio radio tower. tower. Shale pits in Lone Rock Formation have have excellent exposures exposures of of the the fossiliferous glauconite sandstone sandstone and and shaly shaly strata. strata. Locality 23: 15—minute quadrangle, quadrangle, NW~, NW , sec. 29, Locality 23: Black River Falls Falls 15-minute 29, T. N., R. R. 44 W. W. (Figure (Figure 3). 3). Roadcut on east side of Moss Hill Hill Road. Road. T. 21 N., Exposures of upper part of Mount Simon Sandstone are are capped at at an an altitude of 940 feet by the the Eau Eau Claire Claire Sandstone Sandstone which which has has thin thin layers layers of brachiopod shells. shells. A of coquina consisting of white brachiopod A similar occurrence is miles to the west. is at an altitufe altitufe of of 940 940 feet feet along along Wold Wold Road Road l-- miles Note the concentration of brachiopod shells along some of the cross It laminae. 14, T. T. 22 Locality Hatfield 15-minute 15—minute quadrangle, quadrangle, SW~, SW , sec. 14, Locality 24: 24: Hatfield 22 N., N., On northwest northwest side side of of Mollies Mollies Creek, Creek, at at sharp sharp bend bend R. R. 33 W. W. (Figure (Figure 7). 7). On about about 1000 feet feet northeast northeast of of junction of of Mollies Mollies Creek Creek and and Morrison Morrison Creek. Thin basal beds of the Mount Simon Sandstone have a thin basal basal layer of acts. The underlying Preof quartz quartz pebbles pebbles that that resemble resembleventif ventifacts. cambrian gneiss and schist is is deeply weathered to greenish—gray greenish-gray clay at the the unconformity unconformity between between the the Precambrian Precambrian rocks rocks and and the the Cambrian Cambrian at sandstone. Locality Locality 22, T. T. 22 N., Hatfield 15-minute 15—minute quadrangle, quadrangle, NE NE ~, , sec. 22, Hatfield N., On south bank of Morrison Creek about 1600 feet R. (Figure 7). 7). of feet R. 3 W. W. (Figure mouth of of Hay Hay Creek. Creek. southwest of mouth 25: 25: the Mount Simon Sandstone is is cemented Basal quartz conglomerate of the by pyrite in small about 6 inches inches thick a few feet small lenticular zones zones about feet above normal water water level. level. The streambank is is slightly overhanging in in places, places, and and careful search may be required to to find the the pyritic conglomerate. conglomerate. 1 �23 Locality 15—minute quadrangle, quadrangle, NE NE ~, , sec. 33, Locality 26: 26: Hatfield Hatfield 15-minute 33, T. T. 22 22 N., N., R. 1 W. (Figure 12). 12). Saddle Mound, Mound, north north of of Wisconsin Wisconsin Rte. Rte. 54. 54. R. W. (Figure The crest of the mound at at the lookout tower is capped by about 60 feet feet of the Lone Rock Formation. Glauconitic sandstone 60 sandstone is is well well exposed in a small small abandoned quarry near the foot foot of the tower, tower, and Ostrom's Ostrom's (1966) (1966) Birkmose Birkmose Member Member of of the the Lone Lone Rock Rock Formation Formation is is exposed exposed near the the guard rail rail several several hundred hundred feet feet east east of of the the tower. tower. steep southern slopes slopes The Wonewoc Formation is well well exposed on the steep the mound. mound. Minor amounts of weathered fossiliferous fossiliferous sandstone, sandstone, of the probably of the Eau Claire Sandstone, Sandstone, can be found found on the the spur on the northwestern side side of the the mound near near an an altitude altitude of of 1100 1100 to to 1130 1130 feet. feet. Most of of the the Eau Claire Sandstone, Sandstone, however, however, is is concealed by debris from the overlying formations, formations, and of the loose fossiliferous fossiliferous rock on and some some of the loose the lower slopes is is talus talus from from the the Lone Lone Rock Rock Formation. Formation. Holocene river river gravels. gravels. Locality 27: Falls 15-minute 15—minute quadrangle, quadrangle, SE SE ~, , sec. 20, Locality 27: Black River Falls T. T. 22 22 N., N., R. R. 33 W. (Figure (Figure 8). 8). Gravel pit on on west west side side of of Black Black River. River. gravel deposits deposits at this locality are are on aa wide wide terrace terrace Sand and and gravel at this about 20 feet feet above above river river level level and and cover an area of of more more than than one one square square about mile. The gravels include aa wide variety of siliceous igneous and rock types types and and minor minor amounts amounts of of sedimentary sedimentary rock. rock. Most of metamorphic rock the gravel gravel is is outwash from from glacial glacial deposits deposits that that are are abundant abundant to to the the the north. gravel deposits occur on the west side of the Black Similar gravel River in Clark County north of Wisconsin Rte. Rte. 95, 95, and in Jackson County as indicated on on both sides of the river south of Black River Falls, Falls, as the of these these areas. areas. the topographic maps of During construction of these deposits of Interstate Rte. Rte. 94, 94, these deposits were were important sources of sand and gravel, important gravel, and and they they currently currently supply supply local local needs. �r 24 ~(~4 Figure 12. .\ Saddle Mound: Locality 26. Base by U.S. Geological Survey, Hatfield SE quadrangle, 1970, 1:62,500. I �25 25 REFERENCES Klemic, Harry, Harry, and Mrose, Mrose, M.E., M.E., 1972, 1972, Geologic relations and X-ray X—ray Klemic, crystallography of of wavellite wavellite from from Jackson Jackson County, County, Wisconsin, Wisconsin, U.S. Geol. Geol. Survey and implications: U.S. Survey Prof. Prof. and their geologic implications: Paper 800—C, BOO-C, p. p. C53—C62. C53-C62. Ostrom, M.E., 1966, Ostrom, M.E., 1966, Cambrian stratigraphy stratigraphy in in western western Wisconsin: Wisconsin: Wisconsin Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 7, 7, 79 79 p. p. Ostrom, M.E., M.E., Davis, Davis, R.A., R.A., Jr., Jr., and Cline, L.M., L.M., 1970, 1970, Field Field trip trip Ostrom, and Cline, guidebook for Cambrian-Ordovician Cambrian—Ordovician geology geology of of western western Wisconsin: Wisconsin: Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Inf. Inf. Circ. Circ. 11, 11, 131 131 p. p. Potter, P.E., P.E., and Pryor, W.A., W.A., 1961, 1961, Dispersal Dispersal centers centers of of Paleozoic Paleozoic Potter, and Pryor, and and later clastics of the the Upper Upper Mississippi Mississippi Valley Valley and and adjacent adjacent areas: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 72, 72, no. no. 8, B, p. p. 1195—1250. 1195-1250. Skillings, DN., Jr., Skillings, D.N., Jr., 1970, 1970, Jackson Jackson County County Iron Iron Co.: Co.: Mining Rev., Rev., v. v. 59, 59, no. no. 24, 24, p. p. 1, 1, 10—14. 10-14. Skillings U.S. U.S. Geological Survey, 1972, 1972, Iron—formation Iron-formation in in Jackson Jackson County, County, Geol. Survey Prof. Wisconsin: U.S. U.S. Geol. Prof. Paper Paper 800—A, BOO-A, p. p. A3. A3. Weidman, Samuel, 1907, 1907, The The geology geology of of north north central central Wisconsin: Wisconsin: Weidman, Samuel, Wisconsin Geol. Geol. and and Nat. Nat. History History Survey Survey Bull. Bull. 16, 16, Sci. Sci. ser. ser. 4, 4, 697 p. p. 697 — � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1973 Description An account of the resource Institute on Lake Superior Geology. University of Wisconsin, Madison, Wisconsin. May 3-6, 1973. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1973 Contributor An entity responsible for making contributions to the resource J.L. Anderson C.R. Bentley Richard Berger Emmy Booy Brenton M. Hamil Ruth J. Sobanski W.F. Cannon Roger W. Cooper G.H. Dury John. C. Green E. Wm. Heinrich A.V. Heyl Robert A. Jenkins John S. Klasner Thomas R. Turner M.D. Lewan M.S. Lougheed J.J. Mancuso L.G. Megaris Jr J.L. Anderson J.R. Myles D.M. Mickelson M.G. Mudrey Jr A.L. Geldon G. Mursky G. Schriver A.R. Venditti John M. Ohlson Edward M. Ripley Donald M. Davidson D.L. Roder E.N. Cameron S.B. Romberger Klaus J. Schulz Edward M. Ripley P.K. Sims R.J. Stevenson J.E. Thresher Jens F. Touborg Thomas A. Vogel Nancy Alyanak Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/3ecd85424de1d35eb6f0359af1235823.pdf 916dcba45175acb8a04524d427dc4144 PDF Text Text �18th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY MAY 3-6, 1972 MICHIGAN TECHNOLOGICAL UNIVERSITY HOUGHTON, MICHIGAN PART I. TECHNICAL SESSIONS AGENDA and ABSTRACTS Edited by W. I. Rose, Jr. �AGENDA Tuesday May 2, 1972 8:00 a.m. Field Trip A leaves Michigan Tech Memorial Union Wednesday May 3, 1972 6:00 p.m. 7:0010:00 p.m. Field Trip A arrives back in Houghton. Institute Registration, St. Albert the Great Student Parish, MTU Campus Thursday May 4, 1972 7:3010:00 a.m. 8:00- Registration, Fisher Hall Foyer 12:00 noon General Session I, 135 Fisher Hall 1:305:00 p.m. General Session II, 135 Fisher Hall 7:00 p.m. Banquet and Address, Onigaming Supper Club Friday May 5, 1972 8:0011:00 a.m. 1:30— Penokean Session I, 135 Fisher Hall 4:45 p.m. Penokean Session II, 5:30 p.m. Departure of General Session III, 135 Fisher Hall. Field Trips B and C. from MTU Memorial Union. Saturday May 6, 1972 8:00 p.m. Departure of Field Trip D from MTU Memorial Union 6:00 p.m. Field Trips B, C. and D. arrive back in Houghton. �7 8-12 Paper No. GENERAL SESSION MAY 4, 1972 TECHNICAL SESSIONS I. Time 8:15 a.m. 34 8:0.0 a.m. 8:35a.m. 10:40 a.m. 10:20 a.m. 10:00 a.m. 18 10 8 15 9:00 a.m. 11:00 a.m. 17 6 11:20 a.m. 11:40 a.m. Co-chairmen: Ehrlich 0. Lewan M. G. Mudrey W. Weiblen J. C. Green K. G. Books P. M. T. A. Vogel R. Author(s) Robert C. Reed and Donald M. Davidson, Jr. 135 Fisher Hall (Building #15, See Map) AM Title Introductory remarks, Announcements Based on Lithologic Variation Deposition Model for the Lower Nonsuch Shale Weathering and Metasomatism of the Presque Isle Serpentinized Peridotite, Marquette County, Michigan Break for coffee Petrologic and Structural Aspects of the Gabbro Sill on Pigeon Point, Minnesota Keweenawati Lavasin Minnesota Peleomagnetic Evidence for the Extent of Lower Dimroth W. O'Hara J. Hinze Oray A. Robertson J. A. Kilburg E. N. W. E. W. Upper Precambrian Ely's Peak Basalts Petrology, Structure and Correlation of the Magnetic Reversals and Polar Shifts as Markers in a Proterozoic Time Scale The Eastern Terminus of the Lake Superior Syncline The Labrador Trough — not a Precambrian Plate Boundary �II. GENERAL SESSION 1:30 p.m. 13 4 E. Brown Author(s) Randall J. Weege and Gerald Anderson Title B. Lou gheed Co-chairmen: Iron Segregation in Precambrian Iron Formations: Effects on Sedimentary Compositions S. Geologic compilation and Nonferrous Metals Potential , Precambrian Section, Upper Michigan M. w. w. J. LeAnderson M. Lahr A. Bodwell J. J. Mancuso The Newly Compiled Geological Map of the Precambrian of Upper Michigan P. W. Ojakangas Waupee Volcanics R. Smith H. McNutt Kal 1 iokoski A. Bodwell The Geology of the Garlic River Greenstone Belt R. D. R. P. M. Clifford Cuddy' P. M. Clifford G. Nature Effect of a Rigid° Ultrebasic Sill on Deformation R. Archean Salic Volcanic Rocks at Kakagi Lake, NW Ontario - Their Physical and Chemical J. Lower Precambrian Metavolcanic-Metasedimentary Sequence, Rainy River, Northernmost Minnesota J. L. Berkley Precambrian Geology of a Greenstone Belt in Oconto County, Wisconsin, and Chemistry of the The Geology of the Deer Lake Gabbro-Peridotite Complex, Itasca County, Minnesota Formations Morphology of Magnetite in Precambrian Iron M. 1:30- 5PM Paper No. 1:50 p.m. 2 Time 2:10 p.m. 9 12 2:30 p.m. 3:10 p.m. 16 11 3:30 p.m. 2 2:50 p.m. 3:50 p.m. 19 5 4:10 p.m. 4:30 p.m. In Adjacent Rocks, Kakagi Lake, NW Ontario �III. IV. BANQUET 9:55 •a.m. 27 23 J. Naldrett, University of Toronto 7:00 p.m. May 4, 1972 Relation of Penokean Polyphase Deformation to Regional Metamorphism In the Western Marquette Range, Northern Michigan The Penokean Orogeny Title W. J. S. A. Trent F. Cannon S. S. Goldich Author(s) Co-chairmen Carl E. Dutton and Stephen C. Nordeng Penokean Tectonics in Northern Michigan V. G. G. W. B. Morey L. LaBerge R. Van Schmms Kiasner Three-phase Deformation Associated with the Penokean Orogeny, East Gogebic Range, Michigan 0. Banks Coffee and Discussion Precambrian Rocks in Minnesota Stratigraphic and Tectonic Framework of Middle Lineaments and Mylonite Zones in the Precambrian of Northern Wisconsin Dickinson Counties, Michigan, Part II Chronology of Precambrian Rocks of Iron and Short Break (10-15 minutes) P1. 8-11 A.M. Archean Ultramafic Lavas and Their Associated Nickel Suiphide Deposits" A. Onigaming Supper Club (U.S. 41 South, Houghton) ADDRESS MAY 5, 1972 PENOKEAN SESSION .1 Paper No. 25 Time 8:00 a.m. 24 26 8:50 a.m. 20 8:30 a.m. 9:20 a.m. 10:15 a.m. 28 9:40 a.m. 10:35 a.m. 11:00 a.m. �V. ____ PENOKEAN SESSION 2 and GENERAL SESSION 3 1:30-5:00 p.m. Author(s) J. W. Avery and Robert Seasor Title Geochronology of Precambrian Rocks in the Penokean Fold Belt Subprovince of the Canadian Shield Regional Relationships in the Penokean Province Stratigraphy and Sedimentation of the Espanola Formations an Early Aphebian (Middle Precambrian) Carbonate Unit. Granitic Plutonic Rocks of the Southern Province of the Canadian Shield J. T. Mengel M. E. W. H. G. Haddadin. Booy R. Van Schmus B. Stonehouse M. Young J. A. Robertson S. Goldich J. S. Stuckless Structured Clay Products Industry, Keweenaw Peninsula, Michigan J. Warren S. lvii nnesota-Wi sconsi n E. G. Winter Glacial On ft on the Mesabi Iron Range, Minnesota, Its Characteristics, Origin and Hydrologic Bedrock Morphology in the Vicinity of Portage Subsurface Geology of the Duluth Superior Area, Potential Sources of Raw Materials for the Lake, Keweenaw Peninsula, Michgan 1. Minnesota Ages of Some Precambrian Rocks in East Central Co-chairmen: 31 Paper No. 1:30 p.m. 29 Time 1:50 p.m. 33 30 2:10 p.m. 2:30 p.m. 32 3 2:50 p.m. 3:20 p.m. 21 14 4:00 p.m. 22 3:40 p.m. 4:20 p.m. Signi ficance. p �Paper THE GEOLOGY OF THE DEER LAKE GABBRO—PERIDOTITE COMPLEX ITASCA COUNTY, MINNESOTA John L, Berkley University of Missouri, Columbia ABSTRACT The Deer Lake Gabbro—Peridotite Complex is located in northern Itasca County, Minnesota, three miles southwest of Big Deer Lake. It is intruded into a terrane composed of quartzofeldspathic, tuffaceous metasedimentary rocks and pillowed metabasalts of Lower Precambrian age (Sims, et. al., 1971). In recent years the area has been investigated by several mining companies as a possible source of exploitable nickel deposits. Detailed mapping has revealed that the complex is composed of five, separate, sheet—like, basaltic intrusions, averaging approximately 700 feet in thickness, each, Magma was supplied to the area in chronologically, widely dispersed episodes, allowing time for earlier intrusions to differentiate and lithify before the emplacement of a later sheet above those already present. Observed contacts between any two sills are character— Ized by chilled dolerite against a thin zone of amphibolite, The chilled do].erite is thought to represent the parent magma, while the amphibolite is probably a result of contact metamorphism by the magma, For any given sill within the complex, a sharp contact separates the chilled dolerite from the layered sequence above which consists of, from stratigraphic bottom to top, an augite—hornblende peridotite, diopsidic or augitic pyroxenite, and gabbros of varying compositions. This layered series of rocks is a result of selective crystallization and gravity settling of phases, Typical cumulate—intercumulate textural relations as described by Jackson (1961) from the Stllwater Complex of Montana may be seen in rocks from the peridotite up to and including certain lower gabbro units. Small scale layering structures may occassionally be observed in pyr— oxeniteg and lower gabbros. Figure one shows the ideal sequence of rock types for any particular intrusion within the complex and gives the expected cumulate and intercuinulate phases for each unit, The peridotite is composed of rounded to elongate olivines surrounded poikalitically by augite, hornblende, or both, Evidence of reaction rims may be seen surrounding some olivine crystals. The peridotite grades sharply into a pyroxenit., usually composed predominately of subhedral to euhedral diopside 1 �Paper enclosed by plagioclase, diopsidic overgrowth, or oikocrysta originally of pyroxene composition but now completely altered. With increasing cumulate plagioclase content, the pyroxenite grades gradually into an augite gabbro. Upper units may exhibit a significant quartz content and micrographic intergrowth. Micro— pegatite veins cut many gabbro exposures and pegmatitic material has been observed in certain pyroxenite units as well. Post—intrusive folding in the area has deformed the formerly horizontal sills into a sequence of tightly folded anticlinee and sync].ines with axial traces trending N4OE. The complex plunges to the southwest at an undetermined magnitude. Exposure of the intrusive units is now restricted to a narrow band six miles long and a maximum of about one and one half miles wide. Metamorphic grade does not surpass lower amphibolite or hornblende hornfels facies in the rocks of the complex with most assemblages, including those of the adjacent country rocks, falling into the greenschist fades, REFERENCES CITED Jackson, Everett D.,, 1961, Primary textures and mineral associations in the ultramafic zone of the Stiliwater Complex Montana, U. S. G, S. Prof. Paper 358, 106 pp. Sims, P. K., Morey, G. B., Ojakangas, R. W., and Viswanathan, S., 1971, Geologic Map of Minnesota, Hibbing Sheet: Mimi. Geol, Survey. 1 �FIGURE I. -— — ZONE CONTACT . ZONE ULTRAMAFC ZONE GABBRO ZONES — SINGLE NONE I4ORNBLENDE AUOITE/ PLAGIOCLASE AUGITE OLIVINE- PYROXENE OIKOCRYSTS DIOPSIDE QUARTZ PYROXENE OIKOCRYSTS PLAGIOCLASE PY ROXENE AUGITE QUARTZ PHASES CUMULATE PLAGIOCLASE N ONE N ONE PHASES CUMULATE INTER — INTRUSIVE SHEET. DEER LAKE AMPHIBOLTE DOLERITE PERIDOTITE PYR OX ENI T E GABBRO CUMULATE LOWER GABBRO AUGITE GABBRO AUG ITE BEARING MEMBERS QUARTZ IDEAL STRATIGRAPHIC COLUMN FOR A COMPLEX, MINNESOTA. ETAMORPHICFAdES CONTACT FACIES BORDER SERIES LAYERED GENETIC FACIES �Paper 2 GEOLOGIC COMPILATION AND NONFERROUS METALS POTENTIAL PRECAMBRIAN SECTION, NORTHERN MICHIGAN W. A. Bodwell Michigan Technological University ABSTRACT The geology and nonferrous metal occurences of the PreCambrian section, Northern Michigan, have been compiled at the scale of 1:250,000. The map incorporates considerable new data which has become available since the previous regional map of 1936. Review of the regional geology and mineral associations indicates several geologic environments or conditions considered to have potential for mineral deposition. 1) The effective coverage of past exploration drilling in the Michigan copper district was assessed. From this data, it appears that as much as 80 - 85% of presumed favorable ground is yet to be penetrated by drilling according to criteria developed herein: a) The strata-controlled ore deposit sought has a minimum strike length of 2000 feet. b) Maps showing drill holes were reviewed and all strike segments with 2000 feet or more between drill holes were outlined. These areas were measured by planimeter and compared to total area of the favorable strata. c) All strike segments of greater length constitute untested ground. 2) A series of small felsic porphyry intrusives occurring near the base of Portage Lake lava series appear to have potential for copper sulfide deposits based on analogous features with mineralized felsic porphyry bodies on north limb of the Lake Superior syncline in Ontario. 3) A greenstone belt northwest of Marquette, Michigan exhibits certain characteristics of mineralized greenstone belts of the Canadian shield. The presence of numerous base metal occurrences and one small gold deposit suggest that significant base metal or precious metal depsoits may yet be found. �Paper 3 POTENTIAL SOURCES OF RAW MATERIALS FOR THE STRUCTURAL CLAY PRODUCTS INDUSTRY KEWEENAW PENINSULA, MICHIGAN EMMY BOOY AND MUSA S. HADDADIN Michigan Technological University ABSTRACT The Keweenaw Peninsula of Michigan was explored for potential sites for the establishment of a structural clay products plant. The most favorable location for the establishment of such an industry was in Ontonagon County, in the southwestern portion of the Peninsula. The sedimentary cover overlying the Precambrian to possibly Cambrian bedrock varies rapidly both laterally and vertically because of the conditions of deposition during the Pleistocene. In general, the average particle size decreases from North to South. Otherwise, no consistent variations were observed. Most sediments having suitable properties for raw materials for the structural clay products industry have been mapped as glacial lake sediments. An attempt was made to identify distinctive flora which might provide a mapable criterion for distinguishing between sediments for structural clay products manufacturing and those unsuitable. Although there is variation in floral assemblage with topography (e. g. well vs. poorly-drained areas) there was no distinguishable variation with sediment size. suitable Requirements for suitable materials for structural clay products include good workability, low drying and firing shrinkage, good dry and fired strengths, and good fired color. Most of the samples studied met all criteria for most structural clay products. The mineralogy of the samples did not vary appreciably in major constituents throughout the area sampled. Illite, expandable vermiculite, and chlorite were the dominant clay minerals. Quartz and feldspar were ubiquitous, while minor kaolinite, calcite, and dolomite were present in many samples. Certain fundamental soil mechanics tests were run on the materials in conjunction with the ceramiô tests performed. In general, the samples tested were relatively stable clays to silty clay soils. �Paper 3 In the area studied the most desirable location from the view- points of volume of material available and ease of transportation to markets would be in the area around Ontonagon. Most of the samples studied from this area would be useful for all types of structural clay products. �Paper 4 IRON SEGREGATION IN PRECAMBRIAN IRON FORMATIONS: EFFECTS ON SEDIMENTARY COMPOSITIONS BRUCE E. BROWN Department of Geological Sciences Milwaukee, Wisconsin ABSTRACT According to Ronov's (1964) estimates, cherty iron formations of the pre-Cambrian type were present in the amount of 15% of the total sedimentary rock volume during the time period around 2 b.y. ago. The segrega- tion of iron to this degree would seem to require significant shifts in the iron contents of other types of sediments, particularly shales. A sample mass balance calculation after the manner of Garrels and Mackenzie (1971, p. 242) illustrates this. Using a present day "average igneous rock" (Brotzen, 1966) as a source for limestone, sandstone, and shale, and considering just the total iron percent we have, after Garrels and Mackenzie (1971, p. 242): Average igneous rock Fe oxides in gms/kg 62 limestone shale sandstone 62 4 if one considers a situation where 15% by weight of the sediments are of iron formations containing 30% iron oxides, we must subtract 45 grams of iron oxide to supply this source, leaving only 17% to go into shales and sandstones. The assumption is made that iron normally going into shales (such as might happen during the weathering of a basalt today) has been diverted into iron formations. If this assumption is valid, shales formed during times when iron formations were a significant portion of the sedimentary column, should contain less iron than might otherwise be expected considering possible igneous sources. Since iron is the heaviest common element this might have implication regarding the composition, density and isostatic relationships ofrocks such as granitic gneiss formed by metamorphism of shale. �Paper 5 EFFECT OF A "RIGID" ULTRABASIC SILL ON DEFORMATION IN ADJACENT ROCKS, KAKAGI LAKE, NW. ONTARIO by R. G. Cuddy, P. M. Clifford Department of Geology, McMaster University, Hamilton, Ontario ABSTRACT The greenstones of Kakagi Lake consist of about 7500 metres of basic to acid volcanic rock, and some associated sedimentary rocks. Embedded within this assemblage are "sills" of ultrabasic material Study of the western portion of the Kakagi Lake area shows that the ultrabasic sills have a fold form of class 1-B or 1-C (cv. Ramsay; 1967 pp. 365 ff.), as revealed by thickness, measurement and isogon plots. Petrographic study of one sill (Ridler, 1966) suggests that very little strain has occurred within the sill. The rocks in contact with the sills are with very few exceptions, acid pyroclastic volcanics. They lack significant primary layering and, mechanically, form thick, rather homogeneous units. Cleavage density rises, as does consistency of orientation of cleavage, in the vicinity, and along axial surface continuationsof tight folds in the sills. Conversely, open folds in the sills are adjacent to areas of low cleavage density and locally variable cleavage orientation. In addition, fragments in the pyroclastic rocks, though flattened to lie roughly parallel to cleavage, are poorly oriented within the cleavage, a situation which suggests rather low strains within the cleavage plane compared to the high strains across it, or alternatively, a fluctuation of pyroclast long axes over 1800 in the pre-strain state. Fold axes, few in number, are everywhere of moderate to steep plunges. These features are the product of an early phase of deformation. Subsequent deformation has produced kink folds and en echelon quartz-filled gash arrays. These suggest local orientations of principal axes of stress or strain, apparently not of regional value. It is not clear from our data, or any other data available whether the granites surrounding these rocks are fully responsible for the deformation, or have merely modified a prior fold array whose axial surfaces were aligned east-west. What is clear is the marked effect of the sills with their low ductility compared to the pyroclastic rocks in which they occur. Ramsay, J. G. (1967) Folding and Fracturing of Rocks. Ridler, R. H. (1966) M.Sc. thesis (unpublished) Univ. of Toronto. �Paper 6 THE LABRADOR TROUGH - NOT A PRECAMBRIAN PLATE BOUNDARY Erich Dimroth, Service d'Exploration gologizue, Mjnistre des Richessea naturelles, Qubec ABSTRACT The boundaries between the Precambrian age provinces are the natural location where to look for Precambrian plate boundaries. This is specifically so for the .junction between the Superior and Churchill Provices, which are separated by the Circum-Ungava geosyncline. Deep erosion has removed the whole of the original geosynclinal filling in the sector between Labrador trough and Cape Smith belt, and the relations between the geosynclinal filling and its basement can be studied. Other segments of the Labrador trough are deeply enough eroded to infer the presence of a basement. At the level of the basement (that is between the Labrador trough and the Cape Smith belt) the contact between the Superior of Churchill Provinces appears to be gradational. The Archean gneisses are continuous to Ungava bay, but they give Hudsonian K-Ar ages east of line indicated in Wanless (1969). The Archean gneisses east of the age front appear to have suffered Hudsonian deformation, as indicated by the folded outline of the contact between the basement and the Lower Proterozoic sequence. Beau et al. (1963) noted that the Hudsonian biotite isograd intersects the basement-cover contact, and retrograde metamorphism has been noted in a few basement outcrops visited. It appears therefore that a Hudsonian tectonic, metamorphic and age (K-Ar) front, intersects a uniformly Archean terrain between the Cape Smith belt and the Labrador trough. The northernmost Labrador-trough and the easternmost Cape Smith belt are synclinoria plunging south-southeast and west-northwest. The Lower Proterozoic sequence of both belts, which includes very voluminous oceanic tholeiites rests on the basement gneiss with an absolutely sharp contact (Hardy, 1969; Schimann, 1972). �Paper 6 -2- In the centre of the Labrador trough a very thick sequence of oceanic tholeiite rests on continental red beds and on shallow water sediments (for example sandstone with coarse current cross-bedding, stromatolitic dolomite). Units of stromatoljtjc dolomite, of oolitic iron formation and similar shallow-water deposits is continuously exposed across the whole trough, and, in its east, mantles domes of basement gneiss. There is not a trace of a sheeted gabbro complex, and in fact the source of the basalts is still enigmatic. Only very few and generally thin gabbroic dykes intersect the sedimentary sequence and are the only possible conduits known at present. In the extreme east of the Labrador trough a metamorphosed meta-pelitic sequence, comprising interbeds of orthoquartzite, dolomitic sandstone (now diopsidequartzite), para-aniphibolite, is exposed. Arkoses, arkosic conglomerates, are present here and there and perhaps indicate the presence of occasionally emergent source areas east of the trough. According to Wanless (1970) granitoid gneisses east of the trough give at one locality a K-Ar age of 2160 m.y., that is somewhat older than the Rb-Sr age of the Labrador trough rocks (Fryer, 1971). This seems to confirm the basement nature of at least some granitoid gneisses east of the trough. There appears little doubt that the Labrador trough formed by differential subsidence and that it is not related to a continental margin existing at Lower Proterozoic time. REFER EN C ES Beall, G. H., Hurley, P.M., Fairbairn, H.W., and Pinson, W.H., Jr. (1963), Comparison of K-Ar and Rb-Sr dating in New Quebec and Labrador. Am. J. Sci., V. 261, p. 511-560. Fryer, B. J. (1971), Rb-Gr whole rock ages of Proterozoic Strata bordering the eastern part of the Superior Porvince, Canada. Geol. Soc. Amer., Abs with programs, 3, p. 574-575. �Paper 6 -3- Hardy, R.1(1969), Gologic de la re9ion du lac des Chefs, These de maitrise, non publiee; Ecol Polytechnique. Travaux sur le Department of Natural Resources, Quebec, Report S-126AF, p. 7-10. Schimann, K. (1972), Wakeham Bay In: terrain 1971. Wanless, R. K. (1969), Isotopic age map of Canada. Geol. Surv. Canada, Map No. 1259A. Published with the permission of the Minister of Natural Resources, Quebec. �Paper 7 I DEPOSITIONAL MODEL FOR THE LOWER NONESUCH SHALE BASED ON LITHOLOGIC VARIATION Robert Ehrlich and Thomas A. Vogel Geology Department Michigan State University 48823 East Lansing, Michigan ABSTRACT The White Pine copper deposit is one of the classic strata—bound Not only is the mineralization restricted to a small lower portion of the Nonesuch Shale but the vertical succession of lithologies within the mineralized section is remarkably similar in all parts of This striking similarity in vertical succession has in the the mine. past been used as a basis for assuming wide scale lateral continuity of subunits within the Lower Nonesuch Shale. This in turn led to models of deposition, diagenesis, and ore emplacement in which the layercake The aspect of the lower Nonesuch stratigraphy played a key role. purpose of this report is to integrate the observed lithologic variation into an overall depositional model for the Lower Nonesuch Shale. deposits. The lower fifty feet of the Nonesuch is composed of numerous textural modes such as graded, well—laminated, crudely laminated, fragmental, blebby, massive, etc. Various combinations of these textural elements can be found in varying proportions in each of the formal stratigraphic units and each of these (Domino, Brown Massive, etc.) have extensive lateral continuity whereas the individual textural elements included within each unit are not persistent. These lateral changes arise in three principal ways: (1) abrupt changes apparently resulting gradual and (2) from slumping and sliding of plastic sediments, and continuous changes in lithology within a major stratigraphic unit such as massive units becoming crudely laminated and then graded. Similar lateral variations can be seen with major elements within one formal stratigraphic unit varying laterally into a lithology which is a characteristic of an adjacent stratigraphic unit above or below. Most of the textural elements can be seen in varying proportions in the massive units. When observed in detail, it can be seen that there is a non—random juxtaposition of the elements; that is, certain elements tend to be adjacent to certain others. Figure 1 shows the most probable �Paper 7 PAGE 2 associations between textural elements. Elements adjacent in the diagram tend to be intimately associated with each other on a hand sample scale. Elements far apart on the diagram are rarely seen juxtaposed. Figure 1 Mutual Occurrence of Textural Elements in Massive Units Textural elements relatively closer on diagram occur together more often. ,Massive ———— Crudely Laminated ———— Graded ———— Laminated Fragmental' "Blebby ———— Crudely Laminated In these massive units the textural elements on the left side diagram (e.g., fragmental, massive, blebby) are more abundant than on the right. Because each of these elements, except those on the extremes, is associated with two others, these inter—relationships the basis for the pattern of vertical and lateral variation within massive units. of the those are the A characteristic vertical succession is from bottom to top; massive, crudely—laminated, fragmental, scoured surface, massive, blebby, crudely— laminated, graded, well—laminated. A section such as this is composed of two depositional units, each beginning with a massive textural variety Within each and terminated by a fragmental or laminated variety. depositional unit there are no sharp boundaries as one proceeds from one textural element to another, indicating that the sequence of textural elements arose from a single genetic event. The textural varieties and lateral and vertical relations observed are consistent with a depositional model involving progressive infilling of a depositional basin with coarse, denser materials being deposited over materials of low specific gravity that are mechanically weak. The pattern seen here can be understood if the effects of lateral migration and loci of sedimentation are considered as well as general infilling in the basinward direction. In general terms, the dynamic model consists of coarse—grained material deposited on muds, triggering its accompanying flow components. In the Nonesuch two modes of deposition and transport were involved in most slumps. The uppermost, least consolidated materia],, generally (1) hematite—rich, moved rapidly, partially as suspended material, partially as bonafide turbidity flow, and fanned out into a roughly lobate deposit. �Paper 7 PAGE 3 (2) The slightly more consolidated material underlying this zone, in a more reduced condition, either flowed plastically, more slowly, down the depositional slope with relatively little rotation or, if it was reasonably coherent, behaved as a rotational slump with a well—developed concave upward slip surface. Sediment that has moved further downslope is more laminar and less rotational in nature. This, coupled with longer time involved in transport, allows the previously homogenized sediment to differentiate itself with respect to grain size. The sequence, updip to downdip, is thickest, but of least lateral extent at the updip end, and thinnest (perhaps only one graded bed thick) but most laterally extensive at its downdip extremity where it fans out in an unrestricted fashion. This process model can explain the three dimensional pattern of rock variation and provides an important framework for a discussion of the origin of the other geochemical and petrological variations in the Lower Nonesuch Shale. �Paper 8 PALEOMAGNETIC EVIDENCE FOR THE EXTENT OF LOWER KEWEENAWAN LAVAS IN MINNESOTA by John C. Green Geology Department University of Minnesota, Duluth and Minnesota Geological Survey Kenneth G. Books U. S. Geological Survey Silver Spring, Maryland ABSTRACT Most of the North Shore Volcanic Group of Gehman (1958), from central Duluth northeastward to the diabase complex at Hovland (Fig. 1), is now known to be middle Keweenawan on the basis of its normal magnetic polarity (Books, 1968; Palmer, 1970; new data). Beneath (north of) the Hovland diabase and the southern prong of the Duluth Gabbro Complex in Cook County is a series of lavas, approximately 8,000—10,000 feet thick (the Hoviand and Grand Portage lavas of Green 1971) that were extruded during an earlier period of reversed polarity, and are therefore lower Keweenawan. These two units can be traced for at least 25 and probably 50 miles westward, where they are intruded by the Duluth Gabbro Complex. The Hovland lavas include many porphyritic basalts with platy plagioclase phenocrysts. These two lava units thus correlate with the lithically similar reversed "Traps of the South Range" in the Ironwood area, Michigan—Wisconsin, (Books, 1968) and with the Osler Series of Ontario (Palmer, 1970). The Grand Portage lavas are cut by a dike swarm of basalt and porphyritic basalt that also show reversed polarity and may have been feeders for the porphyritic Hovland lavas. The Grand Portage lavas rest disconformably on the Puckwunge Formation of Schwartz, 1942, an orthoquartzite that overlies the middle Precambrian Rove Slate. Although the samples showed only weak magnetization, new determinations give an unequivocal reversed polarity for the Puckwunge, and support its correlation with the lithically similar Sibley Series sandstones of the Thunder Bay district, Ontario. At the southwest end of the basin also, the Duluth Gabbro Complex intruded between lavas of normal and reversed polarity, i.e. between middle and lower Keweenawan volcanic rocks. New determinations show that most or all of the basalts at Ely's Peak (the wedge of lavas that underlie the Duluth Gabbro Complex west of Duluth) have reversed polarity, and thus correlate with the flows at Ironwood and Grand Portage. The basal pyroxene—porphyritic lavas in this unit bear a very close resemblance to the basal lavas on Lucille and Magnet Islands east of Grand Portage, further supporting this correlation; such lavas are not known from anywhere else in the North Shore Volcanic Group. Samples from the conformably underlying "Nopeining sandstone" and from the lowest flow at the "Grandview Golf Course" locality show weak magnetization and considerable scatter, but normal polarity. What is believed to be the same flow (certainly part of the same unique pyroxene—basalt flow group) 3/4 mile to the south shows reversed polarity. Although these normally polarized samples were taken at least 500 to 800 feet (structural distance) from the base of the Duluth Gabbro Complex and are not visibly recrystallized, even in thin section, it appears likely that the basalt's polarity has been inverted to �Paper 8 normal during contact metamorphism by the Duluth Gabbro Complex. No conclusions can yet be made regarding the original polarity of the sandstone; it may have been normal, thus correlating with the Bessemer Quartzite of Seaman, 1944, beneath the lowest Keweenawart flows at Ironwood, or it may also have been changed from an original reversed state, thus correlating with the Puckwunge and Sibley. Further investigations will be carried out. References Books, K. G., 1968, Magnetization of the lowermost Keweenawan lava flows in the Lake Superior area: U. S. Geol. Survey Prof. Paper 600—D, p. D248—D254. Gehman, H. M.,, Jr., 1958, The petrology of the Beaver Bay Complex [Minn.J [abs.], in Institute on Lake Superior Geology, Apr. 21—22, 1958: Minneapolis, Univ. Minn. Center Continuation Study [19581, p. 1. Green, J. C., 1971, Stratigraphy of the North Shore Volcanic Group northeast of Silver Bay, Minn. [Summary]: Inst. on Lake Superior Geology, May 5—8, 1971: Duluth, Univ. of Minn., Duluth, 1971, p. 20—22. Palmer, H. C., 1970, Paleomagnetism and correlation of some middle Keweenawan rocks, Lake Superior: Can. Jour. Earth Sd., v. 7, No. 6, p. 1410—1436. Schwartz, G. M., 1942, Correlation and imetamorphism of the Thomson Formation, Minnesota: Geol. Soc. America Bull., v. 53, no. 7, p. 1001—1020. Seaman, W. A., 1944, Summary of the geology of the Marquette iron range [Mich.]: Michigan Geol. Survey Prog. Rept. 10, p. 11—17. �a II ntrusjve rocks a L owes af Keene.wen teuas tt44t Kewn.n u&s ktween&u,an Kilo", ee's S )s _______ �Paper 9 THE NEWLY COMPILED GEOLOGICAL MAP OF THE PRECAMBRIAN OF THE UPPER PENINSULA OF MICHIGAN J. Kalliokoski and W. Bodwell Department of Geology and Geological Engineering Michigan Technological University Houghton, Michigan With the retirement of the older staff, the Department of Geology and Geological Engineering found itself in a position of requiring a mechanism whereby it could refamiliarize itself with the Precambrian geology of the Upper Peninsula, in order to identify good field-thesis problems and to become knowledgeable about the mineral potential of the region. The most direct approach seemed to be in compiling all geological data on the most suitable scale. With the help of the Institute of Mineral Research (M. T. U.) and the full cooperation of the Michigan Geological Survey, the U. S. Geological Survey, various mining companies, and land owners, this task has now been completed. The resulting map, "Precambrian Geology of the Upper Peninsula" (M. T. U. Press, Geological Series, Map 2, 1972) is on a scale of 1:250, 000. A second map "Geology of the Marquette-L'Anse Region, Michigan", (M. T. U. Press, Geological Series, Map 1, 1972) shows the available outcrop data for the "Northern Complex" on a scale of 1:62, 500. Both maps, uncolored, show the location of known base metal and precious metal showings. The 1:250, 000 map (released April, 1972) is priced at $3. 00 and the 1:62, 500 map (released in late August, 1972) is $5. 00, both including postage, prepaid. They are available from the Department of Geology and Geological Engineering, Michigan Technological University, 49931. Although the maps are complete in themselves, they represent part of the documentation for an M. S. thesis by W. Bodwell, entitled "Geologic Compilation and Non-ferrous Potential, Precambrian Section, Northern Michigan". Copies of the thesis may be obtained from the Department for the cost of reproduction. �Paper 10 PETROLOGY, STRUCTURE, AND CORRELATION OF THE UPPER PRECAMBRIAN ELY'S PEAK BASALTS JAMES A. KILBURG University of Minnesota, Duluth ABS TRACT The Upper Precambrian Ely's Peak basalts crop out in a north—south trending, wedge shaped belt in the area around Nopeming, southwest of Duluth, Minnesota. These Lower Keweenawan flows overlie the basal Upper Precambrian quartzite in the southwestern portion of the Lake Superior basin. There are about 18 individual flows totaling some 1,200 feet of thickness, the thickest flow being 125 feet thick while the thinnest is less than 10 feet thick. Many of the flows show lateral continuity, for example, one flow is traceable for about three miles along strike. Petrographically, there are three main types of flows. Five of the first six that form the basal portion are dark gray, porphyritic basalts. Of these, four contain euhedral, zoned, single and glomerophorphyritic augite phenocrysts up to 5 mm in diameter. Some ilmenite phenocrysts and some olivine pseudomorphs are also present. The groundmass contains altered plagioclase, magnetite, augite, actinolite, chlorite, and sphene. The sixth flow up from the base is a dark gray, porphyritic basalt with single and glomeroporphyritic plagioclase phenocrysts up to 7 mm in diameter; there are also occasional augite phenocrysts. The groundmass contains altered plagioclase, augite, actinolite, ilmenite, sphene, epi— dote and chlorite. The third type of flow is a dark gray, commonly ophitic, altered basalt. It consists of plagioclase, occasional olivine pseudo— morphs, actinolite after augite, augite, ilmenite, magnetite, epidote, sphene, and chlorite. Structures within the flowsinclude ropy surfaces, vesicular and amygdaloidal tops, straight and bent pipe vesicles, straight cylinder vesicles, columnar joints, and pillows in the basal flow. Several northeast trending basalt dikes cut the flows and have been deeply eroded leaving pronounced lineaments. The whole sequence has undergone regional hydrothermal metamorphism to the high zeolite—low greenschist fades. Minerals present which demonstrate this are actinolite, chlorite, and epidote. The only zeolite present is wairakite which has been discovered probably for the first time in the Lake Superior region. It is the highest temperature zeolite. Intrusion of the Duluth Complex is thought to be responsible for elevating the geothermal gradient and thus, permitting the formation of wairakite. The gabbro intrusion also contact metamorphosed the lavas to a medium grained pyroxene hornfels for a distance of up to one—fifth of a mile from the contact. �Paper 10 Pressures of metamorphism are thought to have been around 2,000 bars, although a range of pressures between 1,500—2,500 bars seems feasible. This pressure was produced by the weight of up to 30,000 feet of overlying Upper Precambrian lavas and Duluth Complex which underlie the North Shore of Lake Superior; however, as little as about 16,000 feet of overburden could have produced the minimum pressures of about 1,500 bars needed for metamorphism. Based on their distinctive petrology and reversed magnetic polarity (Green and Books, 1972), the Ely's Peak basalts appear to correlate with the basal flows at Grand Portage, Minnesota. This implies that the time of deposition at these localities was approximately the same, and the source area from which these lavas were derived was probably the same. �Paper 11 PRECAMBRIAN GEOLOGY OF A GREENSTONE BELT IN OCONTO COUNTY, WISCONSIN, AND CHEMISTRY OF THE WAUPEE VOLCANICS. Melvin M. Lahr University of Wisconsin, Madison, Wisconsin ABSTRACT Detailed mapping has been carried out in the northern half of the Mountain Quadrangle in order to establish the geologic history and evolution of a Precambrian greenstone belt and to determine the nature of volcanism. The sequence of Precambrian events was the following (oldest to youngest): 1. Deposition of the Waupee formation, including flows, agglomerates, tuffs, volcaniclastic sediments, and sandstones. 2. Emplacement of the Macauley intrusive (granodiorite to quartz monzonite). 3. 4. 5. Deformation and regional metamorphism. Deposition of the Baldwin conglomerate. Intrusion of the Hager granite and contact metemorphism of the older rocks. The Waupee formation trends approximately N450E and has a steep dip. Relic graded bedding and cross-stratification indicate that tops of beds are to the northwest. Three lithologic units have been distinguished in the Waupee formation: a basal member consisting of massive flows, volcaniclastic sediments, and minor agglomerates; a middle sandstone member with a subordinate amount of massive flows; an upper thin-bedded tuff member. Pyrrhotite mineralization is concentrated along the boundary between the basal and middle members of the formation. Sedimentary features and volcanic textures have been preserved in the Waupee formation, but recrystallization under conditions of the amphibolite facies has produced the following mineral assemblages: basic volcanic flows: plagioclase-hornblende-clinopyroxene. p1 agi ocl ase-hornbl ende-cummi ngtoni te. quartz-biotite-hornblende-plagioclase+ sedimentary rocks: epidote. quartz -microcline-biotite-mu scovite+ p1 agiocl ase. Contact metamorphism due to intrusion of the Hager granite has been superimposed on the regional metamorphic assemblages, resulting in the appearance of garnet, vesuvianite, scapolite, clinopyroxene, hornblende, and plagioclase in the metavolcanic rocks. In the aluminous metasedimentary rocks the assemblage quartz-plagioclase-alkali feldspar-muscovitebiotite-andalusite+ sillimanite has developed. �Paper 11 Eighteen samples of massive volcanic flows from the Waupee formation were fused and analyzed for nine elements (Si, Al, Ti, Fe, Mn, Mg, Ca, Na, K) by means of an electron microprobe. The majority of samples are basalts (Sio2, 46 to 51%) containing 15 to 20% A1203 and 2.0 to 5.8% Na20 + K20; a few samples are andesiEic, containing up to 6T% Si02. If the chemical compositions of the massive flow rocks have not been modified during regional metamorphism, then the Waupee volcanics can be classified as high-alumina and alkalic basalts. As yet, no tholeiitic basalts have been recognized in this area. The chemistry of the metavolcanic rocks and the nature of associated metasedimentary rocks suggest that the Waupee formation originated in an island ac environment. �Page 12 THE GEOLOGY OF THE GARLIC RIVER GREENSTONE BELT P. James LeAnderson Queen's University, Kingston, Ontario ABSTRACT The Garlic River Greenstone Belt is the Archaen greenstone belt northwest of Marquette, Michigan. It consists of a series of basalt flows, tuffs, greywackes, arkoses and iron formations formerly referred to as the "greenstone" or as Mona Schist. The belt is twenty miles wide along the southern boundary, at the contact with the Marquette Synclinorium, and extends ten miles to the north (See Fig. 1). Discernable tectonic history indicates gentle folding of the flows and sediments, followed by intrusion of quartz monzonite pegmatites, large diabase dikes and finally granodiorite pegmatites.. The flows and sediments were metamorphosed to chlorite schists and amphibolites. The chlorite and chloritic amphibole schists may represent greywackes and/or reworked or waterlain tuffs. The amphibolites are thin bedded or massive; some of the latter have pillows or relict plagioclase laths, indicating a volcanic origin. Felsic volcanics are uncommon, but form a zone of sheared rhyolitic at the east end of the Dead River Basin. Small extrusive bodies of porphyritic dacite are found throughout the chlorite and amphibole schists. tuffs (?) The Arkoses (Gar) occur commonly as thin units in the chlorite and amphibole schists, but are the dominant rock type in two areas near the northwestern boundary of the belt. Iron formation (IF) consists of thin discontinuous lenses of Neither carbonate nor sulfide facies iron formation ntagnetite in arkoses. were found. Two synclines have been mapped trending northwest—southeast and plunging southeast, one in the northwest corner of the belt and the other some six miles to the south in the central part. Additional detailed mapping may reveal other folds. Two large downfaulted basins with lower (Ar) and middle and upper (Amu) Animikie Sediments, partially covered with thick deposits of Pleistocene sand, truncate the northern and western boundaries of the belt. A third smaller basin occupies the center of the belt. In the northern part of the area two ages of felsic intrusives can be distinguished, but this distinction cannot be made southeast of the Dead River Basin. The younger intrusives are predominantly quartz monzonites, and are cut by the second set of intrusives which are weakly metamorphosed, non— porphyritic granodioritea. The felsic intrusives in the southern part are porphyritic granodiorite pegmatites. Diabase dikes consisting of unoxiented subhedral hornblende and plagioclase crystals trend east—west across the regional foliation but are not folded. They appear to belong to one set, intermediate in age between the quartz monzonite and the granodiorite. �2 Paper 12 TFie uniformity of mineral composition of the greenstones and the ubiquitous and commonly complete alteration to chlorite and sericite, makes However, the trend, from determination of the metamorphic grade difficult. predominantly pale green amphiboles to dark blue—green amphiboles, from the center to the margins of the belt, indicates that the metamorphic grade increases in the same direction from the greenschist to the amphibolite facies. Although stratigraphic and time relationships in the belt are unknown the following generalizations can be made, 1) the sediments, tuffs and lavas were deposited in shallow water, possibly subaerially, as indicated by the pillow lavas and oxide facies iron formations, 2) the series of thick and extensive metabasalts, tuffs, greywackes and rhyolites south of the Dead River Basin indicate continuous and voluminous outpourings of lava and pyroclastics, and 3) the thin discontinuous layers of basalt, greywackes, tuffs, dacites, arkoses and iron formations to the north, suggest local eruptions of short duration with frequent erosional breaks. After folding of the greenstones, magma intruded and assimilated the lower units, leading in turn to first stages of development of the The magma spread further into the greenstone and lit—par—lit gneisses (Gu), formed pegmatite dikes and sills in the nose of the northwestern syncline. This was followed by the intrusion of a series of diabase dikes; at this time the metamorphic grade reached it's peak. The area was then covered by Animikie sediments which were folded by the Penokean Event, when the structural basins were formed. The intrusion of Keweenawan dikes, followed by deposition of the Jacobaville sandstone in late Precambrian or early Cambrian times, closed the geological record, with the exception of that attributed to the Pleistocene glaciation. �GENERALIZED GEOLOGIC MAP OF THE GARLIC RIVER GREENSTONE BELT AND of Michigan. PCg Lower Precambrian Garlic River Greenstone Belt Oneiss Complex Pgn, Lower Precambrian where approximately located where approximately northern peninsula Dotted Shoet dashed located complex in the Location map of the Lower Precambrian Garlic River Greenslone Belt and the Gneisx Geologic contacts Faults VICINITY* �Paper 12 COLUMN' GEOLOGIC GENERALIZED C .00 a NE Sandstone Jacobsviile 2 a--I unconformity Dikes Diabase Keweenowan Middle and tAmu) Upper 0 Lower and N (A) Animikie (Aim) Middle 2 Reony Lower 0 Creek (Ar) Formation — Serpentinized Peridotites 2 2 Granodiorites Intrusive contact Metadiabase Dikes Intrusive contact Quartz Monzonites Intrusive contact Gu Gar — IF Z Garlic River 3 Greenstones Gri GIpa GI Gm (G) U Gneiss and Intrusive Complex (Gn) �Paper 12 Based in part on maps by Case, J.E. and Gair, J.. (i5), Gair, J.E. and Thayden, R.E. (1968), Puffett, w.P. (1969) and LeAnderson, P.J. (1969). 1Units with symbols are included on the map with Units without symbols descriptions in the text. are not included on the map due to the scale involved. 2The age is uncertain. They may be post—Anamikie and pre—Keweenewan. 3The stratigraphic succession of the units of the Garlic River Greenstone is indeterminate. BI BLIOG.APHY Case, J.1. and Gair, J.E., 1965, "Aeromagnetic Map of parts of Marquette, Dickenson, Baraga, Alger, and Schoolcraft Counties, Michigan, and its Geo1o'ic Interpretationt', U.S. Geological Survey Geophysical mv. Map GP—467 Gair, J.E. and Thayden, R.E., 1968, "Geology of the Marquette and Sands Quadrangles, Marquette County, Michian", U.S. Geological Survey Professional Paper397 LeAnderson, P.J., 1969, "The Pre—Animikie Greenstone Complex of a small area in Narquete County, "ichignn", Unpub]Jsed Msc. Thesis, Michian State University Puffett, W.P., 1969, "The Reany Creek Formation, Marquette County, Michigan", U.S. Geologicl Survey Bull. 1274—F �Paper 13 MORPHOLOGY OF MAGNETITE IN PRECAMBRIAN IRON FORMATIONS M. S. LOUGHEED and J. 1. MANCTJSO Bowling Green University, Bowling Green, Ohio ABSTRACT The morphology of magnetite in all metamorphic fades of unoxidized Precambrian iron formations in the Lake Superior region is remarkably similar. Particularly noticeable are discrete symmetrical or distorted octahedral crystals of magnetite disseminated within individual lamina of chert. Several other features are noteworthy: 1) the crystal diameters range from sub—micron to over fifty microns; 2) the concentration of crystals in a particular lamina can range from a fraction of a percent to aggregates constituting the entire lamina; 3) the invariant associate of magnetite is chert; 4) the variant associates are iron carbonate and/or iron silicate minerals; 5) the minor but not uncommon associates are minute hematite crystals as disseminated spherical clusters, and pyrite as fram— boids, octahedra, and crystal aggregates generally within laminations of digital stromatolites or in laminations of mat algae. The morphology of magnetite, its variation in grain size, and its relationship to chert (quartz) siderite, iron silicate minerals, pyrite and/or hematite indicate that it is primary and that no chemical interreactions took place during diagenesis or metamorphism even to extremely high grades. �Paper 14 SUBSURFACE GEOLOGY OF THE DULUTH-SUPERIOR AREA, MINNESOTA-WISCONSIN J. T. MENGEL, JR. University of Wisconsin, Superior ABSTRACT Study of about 300 borehole records for the Wisconsin Geological Survey indicates that the Quaternary succession in the western end of the Superior lowland consists of glacial, lake, and river deposits which record stages in the development of Lake Superior which are not presently evident in the high-level shore deposits around the rim of the basin to the west or in deeper water lake deposits to the east. Preliminary interpretation of the sequence suggests two times of deep water red clay accumulation separated by a low water stage during which sands and gravels were laid down across an unconformity. A prominent boulder bed overlies the youngest red clay deposit, suggesting a late pulse of ice development during about Nippissing time. The Duluth Complex forms the north wall of the lowland in the Twin Ports area and is found in borings along St. Louis and Superior Bays, where wells encounter the same lithologies known from surface exposures. Fluvial red clastics - mainly quartzose sandstones with limited amounts of conglomerate and shale - of the Bayfield group are unconformable on the Complex and subcrop beneath most of the plain. Throughout the subcrop the Bayfield Group is identified as a "sandstone" or "brownstone" and an aquifer. Similar red clastics underlie most of the western end of the Superior Basin and are the principal source from which the Ouaternary sediments were derived. Along the base of the South Range the red clastics are cut off by the Douglas Fault which brings the Keweenawan basalt sequence of the St. Croix Horst upward and northward over the sandstones. Basalts crop out locally along the crest of the South Range and subcrop beneath the Quaternary succession southward to the Lake Duluth beaches (elevation about 1070) and beyond. The most notable feature about the configuration of the erosion surface on which the Quaternary succession lies is the buried western extension of the major depression along the northerly shore of Lake Superior (cf. Farrand, 1969). Twenty-five to 50 feet of local relief is present on the bedrock One local high forms a prominent outcrop along the bay front at the foot of 27th Avenue West in Duluth and a belt of subsurface surface everywhere. bedrock highs are known in the northern half of 48N-13W, extending westward into the center of 48N-14W in Wisconsin. �Paper 14 2 A maximum thickness of about 600 feet of sediments are present along the axis of the north shore depression between Fond du Lac and Superior Bay and 100 to 300 feet are present under the plain as far south as the crest of the South Range. Less than a hundred feet of glacial drift overlain by clays and/or sands is present along the crest of the South Range. Glacial drift everywhere overlies the bedrock of the plain. Typically about 25 feet is present except toward the bottom of the north shore depression, where as much as 200 feet is known. The drift ranges from a silty or sandy clay to an argillaceous sand and generally contains gravel and erratic boulders. Clean sand/gravel lenses are presently locally most commonly at or near the base of the drift, and are an important source of ground water when encountered. Lake deposited stiff red clay overlies the drift and is more or less gradational with it. Along the northerly side of the St. Louis River in West Duluth, and beneath the plain to the south of Superior almost the entire Ouaternary succession is medium to stiff red brown clay containing scattered ice rafted pebbles and cobbles. Silty, sandy/gravelly layers, some of which contain small amounts of water are encountered in the clays, most comonly at depths of about 20 to 50 feet below the general level of the plain. At higher elevations i.e., about 900-1000 feet the clays are gradational with sandy materials representing shore reworking of the underlying drift and materials introduced by small tributary streams. Locally the sandy materials extend to lower elevations-lying on top of the clay sequence. Along the St. Louis River the clays are largely replaced in the stratigraphic succession by brown, poorly permeable dense argillaceous silty to sandy deposits which become coarser and cleaner and may contain gravels toward the top of the sequence. These deposits, which reach a maximum thickness of about 200 feet lie on a stiff red clay unit, which in turn rests on glacial drift deposited in the north shore depression. Deep engineering bore control is not adequate to define lateral relationships with the middle part of the clay sequence. It presently appears that there is little or no interbedding of sand and clay either in West Duluth or in Superior, suggesting the possibility of introduction of the sandy materials by ice or in part by turbidity flow or river deposition along the general trend of the north shore depression. The coarseness of the upper part of the sandy sequence, its considerable degrees of sorting, and prominent cross bedding indicate the existence of high energy conditions at the Lakehead prior to deposition of the 15 to 50 foot thick red clay which overlies the sandy unit, forming the surface of the Superior plain. The uppermost clay layer lies on an undulating surface having up to a few tens of feet of relief. Contours on the base of the clay define the north shore depression and indicate slopes toward the depression and toward Lake Superior. The clay dips beneath present water level in Howards Bay and is known beneath the younger sands and gravels of Connors Point and the outer end of Rice's Point. Both of these points are built along �Paper 14 3 the erosional zero edge of the clay as it subcrops under St. Louis Bay, suggesting that this fact may have influenced their construction. The same red clay subcrops beneath the outer end of Minnesota Point and under Wisconsin Point. This uppermost clay rests on a thin sandy or gravelly unit which overlies the main clay sequence in West Duluth and Morgan Park and conditions are similar in Superior. Prominent develop- ment of clays to elevations of about 700 feet on the Duluth hillside may indicate flooding of the plain to this level during development of the clay layer. A later very low water stage, perhaps Ferrand's (1969) Houghton Stage, allowed deep incision of drainage along the north shore depression, exposing the sandy sequence and initiating the present drainage system. A general rise in lake level toward a maximum of about 610 feet during the Nippissing Stage caused the deeper parts of the drainage to become aggraded with sandy materials and subjected the upper red clays to strong wave attack. The rise of the uppermost clay away from the north shore depression made it particularly subject to wave erosion, causing steep bluffs from the central part of the Superior Bay waterfront eastward to the present shore line of the lake. A prominent clay platform was developed offshore from the bluffs. This platform is the floor on which Minnesota and Wisconsin Point are built. It is presently blanketed by twenty to at least 70 feet of clean fine to coarse sand containing small amounts of gravel. A greater thickness of such sandy deposits may lie below present control depth under the central part of Rice's Point and the northerly third of Minnesota Point. A great number of large crystalline rock boulders occur at or near the base of these young sandy deposits under Superior Bay. Maximum boulder size recorded so far is 5 x 6 x 7 feet for one recovered during construction of the Cloquet water line. Large boulders are known throughout the length of the Superior Front Channel and the open lake shore to the southeast, their number, size and wide distribution, together with the existence of a higher lake level more or less following their deposition may suggest a late pulse of ice development. An alternative view is that they are developed by exposure of the top of the sandy unit beneath the upper red clay. This unit is known to contain boulders locally, as in the vicinity of the local bedrock high at the foot of 27th Avenue West in Duluth. However, the fact that boulders lying on a few feet of sand overlie the top of the young red clay under Connors Point suggest that ice transport may be involved. It is quite possible that some of the sand present on south shore beaches comes from exposure of the underlying sands. Much of the modern south shore sand is derived from reworking of the underlying till which is exposed along several drainages as the bedrock surface rises to the east of the Twin Ports. A period of declining lake levels during which water levels dropped from about 610 to perhaps 590 feet, witnessed the sequential development of the lake-head barriers of Grassy Point, Rice's—Connors Points, and Minnesota-Wisconsin Points (cf. Loy, 1963). All are built primarily from materials derived by the erosion of the sandy sequence of the north shore depression by the St. Louis River and by lake activity during the high waters of the Nippissing stage. The eventual decline in water level during the subsequent Algoma stage was low enough �Paper 14 4 to permit development of spruce woods rooted in the sands of what is now Allouez Bay. Later flooding, which is apparently continuing at present (cf. Moore, 1948), has led to development of organic-rich mucks, locally capped by peats as the main sediments above the most recent harbor sands. The upper parts of the organic deposits often contain sawdust, wood fragments and horse manure, a legacy of late 19th century activities in the harbor. Slag, wood derivatives, etc. of more recent origin are also present. Dredging for harbor development and slip construction have largely altered the natural stratigraphic sequence of the young sands and organic materials but the natural bottom contours, sediment types, and shore features can still be studied on the excellent 1861 chart directed by Captain G. C. Meade for the Army Corps of Engineers. REFERENCES Farrand, W. R., 1969, The Quaternary history of Lake Superior: Proc. 12th Ann. Conf. Great Lakes Res., International Assoc. Great Lakes Res., p. 181-197. Loy, W. G., 1963, The evolution of bay-head bars in western Lake Superior: Pub. No. 10, Great Lakes Res. Dir., Univ. Michigan, Ann Arbor. Moore, Sherman, 1948, Crustal movements in the Great Lakes area: Bull. Geol. Soc. Amer., 59, pp. 697-710. �Paper 15 PETROLOGIC AND STRUCTURAL ASPECTS OF THE GABBRO SILL ON PIGEON POINT, MINNESOTA M. G. Mudrey, Jr. and P. W. Weiblen Minnesota Geological Survey and University of Minnesota, Minneapolis Detailed mapping on Pigeon Point, Cook county, Minnesota, discloses petrologic and structural complexities heretofore not reported. The sill on Pigeon Point ranges in composition from a tholeiltic olivine gabbro to ilmenite gabbro, to quartz gabbro, and to potassium feldspar-bearing gabbro. The red granitoid rock above the sill is intrusive in the upper parts of the gabbro, but the origin of these red rocks by differentiation of the gabbro or fusion of the Rove sedimentary rocks is not clear. Analyses of coexisting phases in the gabbrô indicate iron— enrichment during the differentiation history of the sill. Analysis of phases also sets limits on petrogenetic relations to the Logan Intrusive Rocks, and to the Pigeon River Intru— sions of Geul. The Pigeon River Intrusions appear to have a simple direct relation; however the Logan Intrusive Rocks of Geul cannot be directly related by simple fractional crystallization to the sill on Pigeon Point. Since emplacement and cooling of the sill, faulting and fracturing on northwest and east-west trends has occurred. The northwest faulting is marked by barite—calcite veins, and the east—west direction by late olivine diabase dikes. �Paper 16 Lower Precambrian metavolcanic—metasedimentary seguence, Rainy River, northernmost Minnesota Richard W. Ojakangas University of Minnesota, Duluth ABSTRACT A thick metavolcanic—metasedimentary sequence is exposed in northernmost Minnesota, south of the Rainy River and about midway between International Falls and Baudette. The previously undescribed volcanic rocks range In composition from basalt to rhyodacite. Intermediate—felsic tuffs and agglomerates and dacitic flows and hypabyssal intrusions apparently are the dominant rock types. These rocks are intermittently exposed along the edges of two younger 200—400 ft wide diorite—gabbro dikes that trend nearly perpendicular to the northeasternly regional strike of the steeply dipping country rocks. Stratigraphic top determinations are limited to a few pillowed metabasalts. However, the scanty data indicate that the sequence may be as much as 25,000 feet thick. Massive suif ides are present in prospect pits and in drill holes in the western part of the area. References: Fletcher, G. L., and Irvin, T. N., 1955, Geology of the Emo Area: 63rd Annual Report, Ontario Department of Mines, part 5, 36 p. Ontario Department of Nines, 1967, Kenora—Fort Frances Sheet, Geological Compilation Series, Map 2115. �Paper 17 THE EASTERN TERMINUS OF THE LAKE SUPERIOR SYNCLINE ERDOGAN ORAY W. S. HINZE N. W. O'HARA Michigan Purdue University West Lafayette, Indiana Naval Weapons Center China Lake, California State Univ. East Lansing, Michigan ABSTRACT A regional gravity Investigation of the eastern portion of the Northern Peninsula of Michigan was conducted and combined with previously observed gravity stations in the Southern Peninsula of.Michigan, Beaver Island, northern Lake Huron, northern Lake Michigan and the Sault Ste. Marie area of Canada to investigate the eastern terminus of the Lake Superior syncline. The Bouguer gravity anomaly map of the eastern portion of the Northern Peninsula shows three major positive gravity anomalies. One of these anomalies trends southeast from Grand Island in Lake Superior and can traced orthwestby magnetics to the Middle Keweenawan volcanics of This anomaly represents the margin of the western limb of the Lake Superior syncline. Another positive anomaly trends south from Whitefish Point on the south shore of Lake Superior be the Keweenaw Peninsula. and is interpreted as a horst of basalts which can be traced magnetically to the Middle Keweenawan volcanics outcropping on Mamainse Point, Ontario. The eastern limb of the syncline near the eastern edge of the Northern Peninsula is also defined by a positive gravity anomaly. These three positive gravity anomalies which are associated with positive magnetic anomalies merge in the vicinity of Beaver Island in Lake Michigan and mark the termination of the Lake Superior syncline. South of Beaver Island, the Keweenawan basalts continue in a south—trending narrow belt and are expressed by the "Mid—Michigan gravity high". The Bouguer anomaly map indicates two local gravity minimums in the Whitefish Bay area on the south shore of Lake Superior. These are interpreted to result from a thick accumulation of Upper Keweenawan clastic sediments. The results of two dimensional model studies suggest that the Lake Superior syncline in the eastern portion of the Northern Peninsula consists of up to 12,000 feet of basaltic flows overlain by Upper Keweenawan clastic rocks. Two geological models can be fitted to the observed anomalies of the northern tip of the Southern Peninsula of Michigan. The basalts either extend throughout the northern tip of the Southern Peninsula where they are highly faulted into a series of horsts and grabens or they are confined to the Grand Traverse Bay area in which case pre—Keweenawan extrusives and intrusives make up the basement of the northern tip of the Southern Peninsula. �Paper 18 MAGNETIC REVERSALS AND POLAR SHIFTS AS MARKERS IN A PROTEROZOIC TIME SCALE W. A. ROBERTSON Geomagnetic Laboratory Earth Physics Branch Department of Energy, Mines and Resources Ottawa, Canada A B STRACT The construction of a useful Precambrian time-scale Fossils are scarce. Sedimentary basins are widely separated, and deposition rates may have been different from today. Small errors in radiogenic age determinations represent many millions of years. Geologists should consider the help that is presents great difficulties. becoming available from paleomagnetic sources when attempting to divide Precambrian time into useful time units. Difficulties using paleomagnetic methods of dating so far back in time are no greater than those of other methods, and have one unique advantage. The pattern of reversals of the earth's magnetic field is world-wide; it is not diachronous, and any identifiable marker horizon occurs at the same point in time wherever it is found. This is not true of polar-wandering curves, however, which apply only to their own continent. The figure shows a hypothetical reversal pattern for the earth's magnetic field, with time as abacissa. Above and below it are hypothetical movement rates, on the same time scale, of two continents, EG and AS. It is hypothetical for the Proterozoic due to lack of data, but is based on patterns emerging from Phanerozoic time. M intervals are ones of mixed polarity, whereas N and R. are of wholly normal and reversed polarity respectively. Reversal nodes marked X, between wholly normal and wholly reversed polarity intervals provide unambiguous, universal marker horizons. G nodes, where one double polarity inversion took place, give good marker horizons but may be hard to find in rock sequences. The F nodes also yield marker horizons, but may be harder to identify precisely. �Paper 18 -2— At the first and third polarity node the continents are shown as accelerating sympathetically at the time of change of reversal frequency. Further back in time they are shown as independent of each other, and more indern.dent of the polarity rhythm. Whether there are links between motions at the earth's surface and reactions at the core-mantle boundary is still an unsolved problem. In any case, the location of a pole position on the polar wandering curve of the same continent will be a measure of its age. The accuracy will be highest for rocks formed at times of rapid polar movement: conversely if a conti- nent is static relative to the pole for a long interval pole positions will not differentiate ages of rocks formed in that interval Working out the polarity scheme for a Precambrian period is a very big task. Unconformities will leave gaps that have to be filled in from elsewhere. Nevertheless a pattern is : beginning to emerge in the Hadrynian and Helikian (880-1640 m. Y.) of the Canadian Shield, although large gaps remain to be filled. An older normal interval ( 1400 m.y.) appears to be followed by a mixed interval. Then a second normal interval is succeeded by a reversed interval about 1100 m.y. ago (a potential X node). A possibly longer normal interval then appears to be followed by one of mixed polarity. It is still too early to use paleomagnetic nodes as boundaries to help form a Proterozoic time-scale, but new polar wandering and reversal pattern data are accumulating fast, and we would be wise to consider the possibility of using them to help to split the Precambrian into time strati graphic units of wide application. �Ic' 1¼. rr, WORLD -WIDE POLARITY fl C C; 4 S tt. —4 C) fl hi N 1,, z -x *3 �Paper 18 'vv'ORLJ) —WIDE C.Di /tr POLAR IT z rr —4 C) t-j N C' �Paper 18 -2SELECTED REFERENCES Cox, Allan, 1968, Lengths of geomagnetic polarity intervals. J. Geoph. Res. V. 73, p. 3247-60 Cox, A., Doell, R. R., and Dairymple, G. B. 1964, Reversals of the earth's magnetic field, science, V. 144, p. 1537-43. Gough, 0. I., Ondyke, N.D., and McElhinny, M. W., 1964, The significance of paleomagnetic results from Africa. J. Geoph. Res. V. 69, p. 2509-2519. Heirtzler, J. R., Dickson, G. 0., Herron, E.M., Pitman III, W. C., and Le Pichon, X., 1968, Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents, J. Geoph. Res. V. 73, p. 2119-36. Irving, E., and Robertson, W. A., 1969, Test for polar wandering and some possible implications. Res. V. 74, p. 1026-36 J. Geoph. McElhinny, M. W., 1971, Geomagnetic reversals during the Phanerozoic. Science, V. 172, p. 157-9. Minkovitch, D., Opdyke, N.D., Heezen, B. C., and Foster, J. H., 1966, Paleomagnetic stratigraphy, rates of deposition and tephrachronology in North Pacific deep-sea sediments. Earth and plan. Sci. 1st. V. 1, p. 476-92. Robertson, W. A., and Fahrig, W. F. 1971, The Green Logan Paleomagnetic Loop -- the polar wandering path from Canadian Shield rocks during the Neohelikian Era. Can. J. Earth Sci. V. 8, p. 1355-72. Vine, F. J.., 1968, Magnetic anomalies associated with Mid-Ocean Ridges. The History of the Earth's Crust. Ed. R. A. Phinney, p. 73-89. �Paper 19 ARCHAEAN SALIC VOLCANIC ROCKS AT KAKAGI LAKE, NW ONTARIO - THEIR PHYSICAL AND CHEMICAL NATURE by D.R. Smithl R. H. McNutt P. M. Clifford? ABSTRACT At Kakagi Lake, and Archaean (older than ca. 2500 my) supracrustal assemblage has, for its upper portion, salic volcanic rocks, approximately two thousand metres thick. These rocks are somewhat unusual , being almost devoid of outcrop-scale layering in rhyodacitic and andesitic scoriaceous breccias and having limited or crude layering in crystal tuffs. Within the fragmental rocks, there is only poor sorting of size fractions. Moreover, in any given outcrop, the accessory fragments which make up the bulk of the framework are monolithologic. Analysis of variation of maximum fragment size, and framework - matrix ratios reveal a "cryptic° macroscopic layering, not visible in individual outcrops. In addition, there are two, possibly three, areas having both large values of maximum fragment size, and a high framework matrix ratio. These areas are interpreted as projections of emission centres into the present day outcrop plane. Chemical analyses of 23 pairs of fragments and adjacent matrix show that, in general, the fragments are the richer in Si02 and perhaps Na20, with matrix the richer in total Fe and MgO. Discriminant function analysis of our data, using the four oxides mentioned, properly identifies fragments from the matrix in 80% of the samples. These pyroclastic rocks have rather strong caic-alkaline affinities, and tend to be normal or low in K)O. Normatively, matrix is: 33% basaltic, 48% andesiti, 19% dacitic; fragments are: 29% basaltic,29% andesitic, 42% dacitic. These chemical differences are echoed in thin sections. Fragments commonly have polycrystalline quartz aggregates and felspar phenocryst in a felsic background: matrix is markedly chloritic. Alteration is ubiquitous. There are no discernible chemical trends along "strike or upwards through the volcanic pile. This reinforces the evidence from physical properties-considerable thickness, lack of layering, poor sorting, monolithologic fragment 1. Texaco, Calgary, Alberta. 2. Department of Geology, McMaster University, Hamilton, Ontario. �Paper 19 —2- character locally - which indicate a pyroclastic flow origin for these rocks. Presence of a fabric possibly pseudomorphic after shard structure is further support for this interpretation. �Paper 20 Three-phase deformation associated with the Penokean orogeny, east Gogebic Range, Michigan-' by Virgil A. Trent U.S. Geological Survey, Washington, D.C. Abstract Three phases of deformation in the east Gogebic area resulted in tight folding of Precambrian X (Marquette Range Supergroup) strata followed by folding and block tilting of the Precambrian Y (lower Keweenawan) and Precambrian X (Animikie) phase of orogeny. sections during the last The deformationa]. periods are marked by coeval volcanism and by three angular unconforniities. Although the deformations may be widely spaced in time, lithology and structural morphologlj suggest that they are separate phases of a single orogenic episode. Near the east end of the Gogebic Range, Precambrian X (Marquette Range Supergroup) strata lie between tilted metamorphosed Precambrian Z volcanic rocks (lower Keweenawan) to the north and strongly meta- morphosed Precambrian W or X gneiss complex, Algoman Granite of Lawson (l9lL), and volcanic rocks (Keewatin) to the south. Three defoniiational phases can be identified in Precambrian X rocks of the eastern Gogebic Range: -'Work done in cooperation with the Geological Survey Division of the Michigan Department of Natural Resources. 1 �Paper 20 i) The earliest was folding of the Sunday Lake Quartzite, Bad River Dolomite, Palms Formation, and Ironwood Iron- Formation. Mafic lava flows intercalated with the Ironwood Iron-Formation indicate that extrusive volcanic activity preceded folding. The large Wolf Mountain anticline began to form, followed by erosion and Copps Group of Allen and unconformable Barrett (191S) and deposition of the the Tyler Formation. 2) The strongest deformational phase, the Penokean orogeny, as defined by Goldich and others (1961, p. 120-122, i6-i6o), took place at the end of Precambrian X ("Animikie") The this time. Wolf Mountain anticline was more tightly folded during event. Mafic sills, also intercalated with the Ironwood Iron-Formation were intruded syntectonicafly. The northernmost thick sill truncated by the pre-Keweenawan unconformity (Prinz, 1967), appears to be genetically related to flow breccia cropping out along its eastern margin. Erosion of these volcanic rocks, parts of the Tyler and Copps, and older rocks preceded the unconformable deposition of the oldest Keweenawan strata. 3) Post-lower Keweenawan deformation, upon which Blackwelder 638) based his original definition of the Penokean orogeny, warped and the whole Precambrian succession (191)4, p. tilted except for the Jacobsville Sandstone. folding seems to mimic major Penokean The last phase of trends of the preceding folding, especially in the area close to Lake Gogebici. Torsional basement movements related to block tilting probably contributed to the assymetry of the Wolf Mountain anticljrie. 2 �Paper 20 A large Wolf Mountain in the area. flat-lying niass of (T. 147 N., R. 1414 eflipsoidal basalt north of w.) may be the youngest volcanic rock It lies athwart the Precambrian X (.Animikie) structural trend and has not been blocktilted. The youngest major fracture in the area passes nearby, and to the southwest the fracture is filled by a thick mafic dike which I interpret to be the feeder. Two miles to the northeast, this fracture truncates the lower Keweenawan ridge. This field evidence suggests that these ellipsoidal lavas were extruded in post-early Keweenawari time and were perhaps associated with the terminal phase of folding. 3 �Paper 20 References cited Allen, R.C., and Barrett, L.P., l9l, A revision of the sequence and structure of the pre-Keweenawan formations of the eastern iron range of Gogebic (Geol. Michigan: Michigan Geol. Survey Pub. 18 Ser. l), p. 33-61; in part, Jour. Geology, v. 23, p. 689—703. Blackwelder, geologic Eliot, l91L, A summary of the orogenic epochs in the history of North America: Jour. Geology v. 22, no. 7, p. 633-65)4. Goldich, Samuel S., Nier, John H., and Krueger, Alfred 0., Baadsgaard, Halfdan, Harold W., Hoffman, 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geol. Survey Bull. 141, 193 p. Lawson, A.C., 191)4, A standard scale for the pre-Cambrian rocks of North America: Internat. Geol. Cong., 12th, Canada, 1913, Comptes rendus, p. 31i.9-370. Prinz, W.C., 1967, Pre-Quaternary geologic and magnetic map and sectioriLs of part of the eastern Gogebic iron range, Michigan: U.S. Geol. Survey Misc. Geol. mv. Map 1-1497. 14 �Paper 21 BEDROCK MORPHOLOGY IN THE VICINITY OF PORTAGE LAKE, KEAW PINSULA, MICHIGAN E. J. WARREN Department of Geology and Geological Engineering Michigan Technological University ABSTRACT Portage Lake stretches across the Keweenaw Peninsula of Michigan between Keweenaw Bay and Lake Superior. This circumstance was put to good use by the Indians and later by French voyaguers and Jesuits who used the long sinuous lake as a shortcut in their travels along the south shore of Lake Superior. Modern shipping uses the same shortcut, now known as the Keweenaw Waterway. Portage Lake has a maximum depth of about 50 feet located On the other hand, Torch in the main body of the lake. Lake, which is connected to Portage Lake by Torch Bay and a dredged ship channel, was once 170 feet deep before it was partially filled by mill tailings from various copper recovery operations. Several geologists have speculated about the origin of these unusual lakes (Martin, 1911; Scott, 1921; Hughes, 1963). However, they were handicapped by their lack of knowledge of the bedrock morphology around and under the lakes. The bedrock morphology was determined from water well and diamond drill logs and by geophysical methods. Seismic refraction profiles were run on land and on the mill tailings in Torch Lake. On the lakes, sparker and air-gun surveys were performed. Unfortunately the sparker survey lacked penetration and the air-gun profiles were rendered nearly useless by excessive reverberation. Gravity profiles were then run over Portage Lake, on ice, in an attempt to extrapolate the land based information. Interpretation of the gravity surveys, now being performed, is hampered by the large regional gravity gradient due to the Keweenaw fault (Bacon, 1966). Preliminary results indicate that both Portage and Torch Lakes lie in a complicated network of buried bedrock valleys. A water well next to the narrow northwest arm of Portage Lake reaches a depth about 380 feet below lake level and a diamond drill hole east of Hancock Michigan reaches bedrock about 280 feet below lake level. Of course, there is no assurance that either of those wells have reached the deepest part of the bedrock valley. �Paper 21 Torch Lake lies in a bedrock valley with a floor 250 feet This valley underlies the pre-. below present lake level. sent Traprock River valley to the north and continues south of Torch Lake into Portage Lake under Torch Bay. The bedrock valley under Torch Lake is also connected to Portage Lake by a bedrock valley 200 feet below lake level which parallels the Keweenaw fault and passes under the town of Dollar :ay. bedrock valley about 150 feet below lake level extends from the southeast part of the main body of Portage Lake out through Portage Fh-itry, curving to the east of the present channel. The deepest bedrock valley, however, extends south of the main body of Portage Lake under the present Sturgeon River valley where a depth L50 feet below present Lake Superior level was found. The southern extension of this deep It is interesting valley still remains to be explored. that this valley has bedrock depths on the same order as the depth of Keweenaw Bay. A bedrock valley 200 feet below lake level branches off the west side of the Sturgeon valley and passes under Otter Lake. It is probable that these buried bedrock valleys were originally a product of stream erosion. It is possible that some glacial overdeepening has taken place also, but this cannot be detexmiined until all the data is compiled and a contour map of bedrock elevations is completed. At any rate, it is apparent that the base level for stream erosion was once considerably lower than the present Lake Superior level. This discovery may have some bearing on the controversy about whether Lake Superior is mainly a result of subaerial erosion, of glacial scour, or of some combination of the two. References Bacon, L. 0., 1966, Geologic Structure East and South of the Keweenaw Fault on the Basis of Geophysical Evidence: The Earth Beneath the Continents, A.G.U. Mon. 10, pt2—55. Hughes, J. D., 1963, Physiography of a Six Quadrangle Area In the Keweenaw Peninsula North of Portage Lake: Unpublished Ph.D. Dissertation, Northwestern Univ., Evanston, Ill., 228 pp. Martin, L., 1911, Physical Geography of the Lake Superior Region: Chapt. IV in U.S.G.S. Mon. LII, The Geology of the Lake Superior Region, p85-l17. Scott, I. D., 1921, Inland Lakes of Miohigan: Mich. Geol. and Biol. Survey, Lansing, Mich., 383 pp. �,, 4/ / / I / / I F I / / ,, 6, LAKE SUPERIOR -¼ SCALE :250000 OF MICHIGAN THE KEWEENAW PENINSULA �Paper 22 GLACIAL DRIFT ON THE MESABI IRON RANGE, MINNESOTA ITS CHARACTERISTICS, ORIGIN, AND HYDROLOGIC SIGNIFICANCE'! THOMAS G. WINTER U. S. Geological Survey ABSTRACT Glacial deposits in the Mesabi Iron Range area consist ments. The basal till occurs in only a small number of mines, but they are scattered across the entire Iron Range. The is dark gray to dark greenish gray and brownish gray, sandy, silty, and is calcardous. The middle till unit, a of three major till units and associated glaciofluvial sedi- till bouldery till, is the thickest and most widespread of the three tills. It is grey, yellow, red, orange or brown, sandy, silty, contains abundant cobbles and boulders, and is non-calcareous. The till was depsoited by the Rainy lobe, which has a minimum age of 14,000 to 16,000 years before present. The surficial till was deposited contemporaneously by two minor sublobes of the same ice lobe about 12,000 years ago. The brown silty till occurs in the western and north-central part of the area. It is light to medium brown, sandy, silty, and calcareous. Red clayey till the south-central part of the area is red to reddish brown, clayey, silty, and calcareous. Stratified fluvial sediments occur within the glacial drift at many places in the Mesabi Iron Range area. These sediments, which are important aquifers, occur extensively between the three main till units. The thickest and most extensive aquifer consists of glaciofluvial sediments that lie between the surficial till and the bouldery till. The thickness of the glaciofluvial sediments is greater than 50 feet in much of the area, and the transmissivity is greater than 100,000 gallons per day per foot at a number of localities. Glaciofluvial sediments underlying the bouldery till occur largely in the western half of the area. These sediments are generally less than 50 feet thick and their transmissivity is generally less than 50,000 gallons per day per foot. Surficial glaciofluvial sediments are a source of ground water for high yield wells only in the eastern part of the area in the general vicinity of the Biwabik bedrock valley. Thickness of these sediments is greater than 100 feet in some places, but their transmissivity is generally less than 50,000 gallons per day per foot. �Paper 22 -2- The glacial drift aquifers can yield as much as 40 mgd (million gallons per day). Assuming that the ratio of area underlain by aquifer to total area is constant for the study area (about 20 percent where mapped in detail), it is concluded that as much as 80 million gallons per day could be developed from glacial drift aquifers without causing excessive water declines and depleting streamfiow. Publication authorized by the Director, U.S. Geological Survey �Paper 23 CHRONOLOGY OF PRECAMBRIAN ROCKS OF IRON AND DICKINSON COUNTIES, MICHIGAN PART II P. 0. Banks Department of GeologyCase Western Reserve University, Cleveland, Ohio 44106 and W. R. Van Schmus Department of Geology University of Kansas, Lawrence, Kansas 66044 Ertensive K-Ar, Rb-Sr, and U-Pb data available for the Precambrian rocks of Iron and Dickinson Counties, Michigan, permit considerable clarification of the chronologic development of this area. The following ares are considered well established (rounded to nearest 25 m.y.): Peavy complex 1900 m.y., Hemlock volcanics 1950 m.y., and Porphyritic Red Granite 2100 m.y. A U—Pb concordia intercept ago of 2575 ni.y. for the Norway Lake gneiss is considered minimal for this unit because of probable multiple secondary events. The pre—Animikie post—Dickinson Granite Bluffs gneiss gives an apnarent Rb—Sr whole rock age of Ca. 2700 m.y. whereas its apparent zircon U—Pb concordia intercept age is ca, 2100 m.y. This anomaly can be explained either by urusual migration of radiogenic Sr or by multi-stage Pb loss. Additional mineral analyses are in progress to resolve the issue. Our previous conclusion (Banks and Van Schmus, ILSG 1971) remains unchanged that the Animikie Series of James et al. is bracketed between 1900 and 2100 m.y. and therefore is not correlatable with the original Huronian of Ontario. Resolving the ae of the Granite Bluffs gneiss will determine whether the Dickinson Group Is or is not a candidate for correlation with the original Huronian. Additirnal data of interest include a Pb/Pb age of 2900 m.y. for detrital zircon from the East Branch arkose, and a suggestion from K—Ar h.ornblende and U-Pb apatite and sphene data that the last major metamorphism in the area occurred 1500—1600 m.y. ago. �Paper 24 PENOKEAN TECTONICS IN NORTifERN MICHIGAN by W. F. CANNON U. S. Geological Survey Washington, 2O242 D.C. ABS TRA CT The major Penokean deformation in northern Michigan occurred between 1.9 and 2.0 b.y. ago. Lower and. middle Precambrian rocks were deformed independently of, and mostly before, regional metamorphism; the deformation took place at low temperatures. The subsequent metamorphism was a low-pressure type in which andalusite was stable over a wide temperature range. The maximum confining pressure is set by the aluminosilicate triple point at about 5 kilobars (about 13 miles burial depth), but the true pressure may have been much less. Structural interpretations must be consonant with mechanisnis of rock deformation possible at low temperatures and low to moderate confining pressures. Lower Precambrian granitic rocks form the basement for the Marquette Range Supergroup in much of northern Michigan. granitic Experimental rock deformation indicates that rocks have very high strength and very low ductility under probable conditions of Penokean deformation, and kinematic interpretations of Penokean deformation must consider the probability of a strong nond.uctile basement; interpretations requiring a weak ductile basement are difficult to reconcile with the probable physical environment of deformation. The first-order regional structures in northern Michigan are uplifts of lower Precambrian rocks with middle Precambrian rocks of the Marquette Range Supergroup in intervening synclinorial basins. A wide divergence of trends for these structures suggests vertical tectonism rather than regional horizontal compression. The lower Precambrian cores of many uplifts are cut by diabase dikes. These dikes are older than the Penokean orogeny, and many are probably associated with mafic intrusive and extrusive rocks in the middle Precambrian section, yet these dikes were not externally deformed during Penokean folding; they remain planar and. largely massive. These relationships substantiate inferences from experimental rock deformation of a strong nonductile basement and strongly suggest that the lower Precambrian rocks remained rigid and were not penetratively deformed d.uring Penokean deformation. The uplifts are interpreted, as fault- bounded blocks of lower Precambrian rocks which were uplifted V The Gogebic Range is excluded from this discussion because of cnp1ications introduced by younger deformation. �Paper 24 along steep faults, many of which are steep reverse faults. The blocks may have moved either as single units or, more likely, with internal adjustments occurring along relatively narrow shear zones and parallel to dike margins. During this phase of deformation, middle Precambrian rocks were passively draped over the fault blocks, forming the presently preserved synclinal structures which occupy the relatively dow'nfaulted segments of the basament. Second-order and, smaller folds in middle Precambrian rocks indicate that these rocks have undergone substantial horizontal shortening, whereas the underlying lower Precambrian rocks have not. Furthermore, the trends of second-order and smaller folds are mostly in west and west-northwest directions and are much more uniform than trends of first-order structures (block uplifts). In some areas, second-order folds cross the trends of first-order structures at high angles. Many of these smaller folds seam to have formed independently of first-order structures, and their genetry requires a thin-skinned compressive deformation which has affected. only the middle Precambrian rocks and not the lower Precambrian basament. Many of these folds may be due to gravity sliding or spreading which, because of relatively uniform fold trends, appears to have occurred in response to a region-wide gradient. This phase of deformation must have occurred before block faulting produced sithstantial structural relief on the contact of lower and middle Precambrian rocks. The suggested sequence of events is: 1) Regional gravity sliding which produced folds in middle Precambrian rocks with west and west-northwest trends but did not deform the lower Precambrian basament rocks. This event was probably associated with early uplift of the depositional basin. 2) Uplift of fault-bounded basament blocks with widely divergent trends, accompanied by passive draping of middle Precambrian rocks and earlier gravity folds into basins or tight synclines between the uplifts. A second set of folds formed in middle Precambrian rocks in areas marginal to the uplifts. �Paper 25 THE PENOKEAN OROGEM S. S. Goldich Northern Illinois University DeKalb, Illinois 60115 ABSTRACT The Penokean orogeny (Blackwe1der, 1914) was redefined by Goldich arid others (1961) as Middle to Late Precambrian event that involved the Anuinikie Group of Minnesota and Ontario and similar rocks that were formerly assigned to the Huronian in Wisconsin and Michigan. Time limits from 1600 to 1800 ni.y. were set for the orogeny; however, Peterman (1966) showed that the metasedimentary rocks of the Cuyiina district were folded 1850 n.y. ago. New data for the Thomson Formation of east-central Minnesota give a minimum age of the folding and metamorphism of 1900 n.y. ago (Stuckless and Goldich, 1972). Thus, the Penokean orogeny is a Middle Precambrian event, using 1800 m.y. as the time boi.]ndary between the Middle and Late Precambrian (Goldich, 1968). Limiting ages have been placed on the type Huronian rocks by dating of the Nipissing Diabase in the Blind River—Bruce Mine area (Van Schmus, 1965) and of the Nipissing Diabase and Gowganda Formation at Gowganda (Fairbairn and others, 1969). The type Huronian rocks are at least as old as 2280 n.y. (Gow— ganda Formation) and were folded at least 2160 m.y. ago (Nipissing Diabase). Fryer (l97l has reported ages of 1800, 1870, and 1790 m.y. for volcanic and metasedimentary rocks from the Belcher Fold Belt, the Labrador Trough, and the Mistassini Lake area. Rb—Sr ages, however, must be used with caution. They do not necessarily date the time of deposition or of a specific metamorphic event. In Minnesota, for example, isochron ages on Aniniikian rocks range from 1900 to 1660 n.y., but all were probably deposited at essentially the same time. Considerable radiometric dating of Middle Precambrian rocks is now in progress. Until the new data from a number of laboratories are published and can be assessed, it is premature to correlate the rocks of widely separated areas of North America. References For references prior to 1969 see Goldich (1968). Fairbairn, H. W., P. M. Hurley, K. D. Card, and C. J. Knight (1969) Correlation of radionietric ages of Nipissing Diabase and Huronian metasedinients with Proterzoic orogenic events in Ontario: Canadian Jour. Earth Sci., v. 6, p. 489—497. Fryer, B. J. (1971) Rb—Sr whole—rock ages of Proterozoic strata bordering the eastern part of the Superior Province, Canada (abs.): Geol. Soc. America Abstracts with Program, v. 3, p. 574—575. Goldich, S. S. (1968) Geochronology in the Lake Superior region: Jour. Earth Sci., v. 5, p. 715—724. Canadian Stuckless, J. S. and S. S. Goldich (1972) Ages of some Precambrian rocks in east-central Minnesota: 18th Annual Institute on Lake Superior Geology, Houghton, Michigan. �Paper 26 RELATION OF PENOKEAN POLYPI-IASE DEFORMATION TO REGIONAL METAMORPHISM IN TI-fE WESTERN MARQUETTE RANGE, NORTHERN MICHIGAN John S. Kiasner Michigan Technological University Houghton, Michigan ABSTRACT Recent work at Lake Michigamme at the western end of the Marquette Trough suggests that some metamorphic minerals began to form during the early stages of Penokean deformation contrary to previous studies (Powell 1970) that suggest that regional metamorphism almost completely postdates deformation. The new studies indicate that metamorphism peaked late in the deforrna.tional sequence as shown on figure 1. F F1 F2 F Deformational events Andalusite Garnet S t.au ro lit e Actinolite Grunerite Biotite Sericite Thermal metamorphism ically shown Chlorite Fabric elements Time Figure 1, Kinematic relationship of metamorphism to deforrnationQ The deformational sequence, characterized by four phases, started with regional soft sediment deformation (F that produced a penetrative N 75° W trending foliation, th8 early stages of which can be identified as slaty cleavage (S ). Selective migration of silica (Williams 1972) during continued deformation (F1) along the early formed slaty cleavage enhanced this cleavage an formed the numerous quartz veins. The F -F1 deformational couplet produced the regional S foliation. ° ) �Paper 26 Crenulation folding (F2) of S1 foliation resulted in the formation of S2 fracture cleavage and formation of lineations (L2) due to the intersection of S1 and S2. The L2 lineations are flat lying because the strike of S2 and S1 are nearly parallel. Kink—banding (S) that affects S0, Si, 2 and L2 characterizes the last eformationai event in the area. Regional thermal metamorphism accompanied the sequence of deformation. The growth of pre-F1 andalusite porphyroblasts (figure 1) indicates that metamorphism started early in the deforinational sequence. It probably peaked between F2 and deformation as indicated by the growth of post-, pre-F2 staurolite porphyroblasts and post-F2 brown biotite and grunerite. Abundant retrograde metamorphism is shown by andalusite and staurolite porphyroblasts that have been replaced by sericite, and by garnet porphyroblasts that have been replaced by chlorite. References James, H. L., 1955, Zones of Regional Metamorphism in the Precambrian of Northern iviichigan, Bull. Geol. Soc. Am., v. 66, p. 1Li55_1483. Powell, C. McA., 1970, Relict Diagenetic Textures and Structures in Regional lVletarnorphic Rocks, Northern Michigan, North- western University Report 20, N.A.S.A. Geol. Test Site No. 126, 35 p. Williams, P. F., 1972, Development of Metamorphic Layering and Cleavage in Low Grade Metamorphic Rocks at Bermagui, Australia, Am. Jr. Sci., v. 272, p. 1—7. �Paper 27 LINEAMENTS AND MYLONITE ZONES IN THE PRECAMBRIAN OF NORTHERN WISCONSIN Gene L. LaBerge Wisconsin Geological and Natural History Survey and University of Wisconsin-Oshkosh ABSTRACT Recent geological mapping in Marathon County by the Wisconsin Geological and Natural History Survey has shown that a number of major zones of shearing cross central Wisconsin. At least 3 directions of major shearing have been recognized: N300_350E, N60°E, and N800E. The N300_350E trend is best developed in the area mapped, but reconnaissance indicates that other directions are impor- tant in other parts of the county. The major shear zones are represented by zones of mylonite and variously sheared rocks up to a mile wide. Because a number of different rock types, ranging in composition from granite to greenstone, have been granulated, mixed, and recrystallized to varying degrees to form the mylonite, the zones are lithologically variable both along and across the strike. However, they are structurally rather uniform, displaying a lensoidal structure on all scales from map scale to thin section. Indeed they seem to be composed of a myriad of overlapping lenses which show different degrees of flattening. Excellent examples of the progressive shearing of a granitic rock to produce a mylonite were observed along several of the shear zones. The best example of a mylonite zone mapped is that along the Eau Claire River in northeastern Marathon County. It has been mapped for a distance of approximately 20 miles, and almost certainly continues an additional 15 miles across the county. Furthermore, it is on a topographic lineament which can be traced across Wisconsin for at least 120 miles. At least 4 other major N300_35oE shear zones cross Marathon County, and some of these also occur on topographic lineaments 100 miles or more long. Numerous stream valleys and other topographic lineaments in northern Wisconsin are oriented approximately N30°E, and these may also represent shear zones. Significantly, the N600E and N80°E directions of shearing are also common trends of topographic lineaments. �Page 27 -2- The origin of these major shear zones is not yet certain; however, the lithologic associations in the area mapped coupled with the major shearing suggest that northern Wisconsin be part of a Precambrian subduction zone. Whatever the explanation of the shear zone, it is evident that they represent a major feature in the Precambrian of the Lake Superior region which has not previously been recognized. �—' • ,1 N ) '\ /-1e N 11 Jv 'F ' r$tt cerJf } i/f woo Fe L'.n /' • I 1r - T1 5 I. L. i11tth1r\ I - / S ibar,) -I 1! I s1o -::; ---(U 'Y t / ZL -I Po (TI ___ I 99 I I L4 Witt41 0)__fl ,NorthJ Lp (r7 aieik / _ f/ : _I LINEAMENTS AND'S POSSIBLE SHEAR ZONES IN MARATHON COUNTY T. L / / U L.—Th&/-T/r /i 7 7--MariTi1a _c) r&rrU 4:;j 29 I :; ____ �Page 27 00 C LIMIT OF OLDER DRIFT —......—LIMIT OF YOUNGER DRIFT S10. LINEAMENTS AND POSSIBLE ShEAR ZONES IN NORTHERN WISCONSIN �Paper 28 STRATI GRAPHIC AND TECTONIC FRAMEWORK OF MIDDLE PRECAMBRIAN ROCKS IN MINNESOTA G. B. MOREY Minnesota Geological Survey St. Paul, Minnesota ABSTRACT Sedimentary strata of Middle Precambrian age in Minnesota predominantly consist of argillite and graywacke with lesser amounts of iron—formation, quartzite, quartzose siltstone, limestone, and dolomite. These strata unconformably overlie folded metasedimentary and igneous rocks approximately 2,700 m.y. old; locally they also appear to unconformably overlie diabasic gabbro or diorite dikes that may be approximately 2,000 m.y. old (Hanson and Malhotra, 1971). Except for an older unnamed dolomite unit in east—central Minnesota, all the sedimentary rocks are assigned to the Animikie Group, a wedge-shaped body that thickens from less than 100 feet in the northern part of the State to at least 15,000 feet in areas 100 miles to the south. The Animikie Group comprises a single depositional event that began with well— sorted clastic detritus characteristic of a stable shelf —— Kakabeka, Pokegama, and Mahnomen Formations ——, passed through a phase of iron—formation deposition —— Gunflint, Biwabik, and Trommald Formations ——, and ended with deposition of fine sand and mud characteristic of a "deep" basin with poor circulation —— Rove, Virginia, Rabbit Lake, and Thomson Formations. Locally, the "deeper" water clastic rocks contain intercalated lava flows, thin to thick beds of pyroclastic material, and layers of carbonate— to sulfide—facies iron—formation. During or subsequent to the time of deposition, the sedimentary rocks in east—central Minnesota were folded —— perhaps more than once —— into numerous large antic lines and syndines that have many second-order folds on their limbs. The major folds are asymmetric, with steeply—dipping to locally overturned north limbs and more gently—dipping south limbs. Fold axes trend within 300 of east, and plunge from horizontal to 300 east. In addition, a part of the Thomson Formation was regionally metamorphosed to at least the lower range (staurolite and garnet) of metamorphic grade in the amphibolite facies; however, definable metamorphic isograds are not everywhere parallel to recognizable structural trends, suggesting that deformation and metamorphism were independent variables in the orogenic scheme for this region. The time of folding is unknown, but the metamorphism on the Cuyuna range has been dated at 1,850 m.y. ago (Peterman, 1966). The Animikie strata in northern Minnesota also were deformed about northeast-trending axes, although the degree of deformation and the metamorphic grade is less pronounced. In addition, these rocks appear to have been subsequently folded about north-northwest—trending axes. Available isotopic data cluster around an age of 1,650 m.y. and these data may reflect a period of mild deformation and metamorphism at that time. A variety of igneous rocks also were intruded into the sedimentary pile in east—central Minnesota. Several discrete events can be recognized, which together with the deformation and metamorphism comprise the Penokean Orogeny. These include (Woyski, 1949; Goldich and others, 1961): (1) pre—tectonic emplacement of small mafic intrusions; (2) syntectonic emplacement (1.78 — 1.63 b.y.) of intermediate—size intrusions of tonalitic to granodioritic composition -- the quartz monzonites at Warman, Isle, and Pierz, the tonalites near Hillman and Freedhem, and the gray granodorite at St. Cloud; and (3) late-tectonic to post—tectonic emplacement (1.73 1 .68 b.y.) of Woyski's "Stearns Magma Series" consisting of the augite—hornblende (red) granite at St. Cloud, the porphyritic quartz monzonte at Rockville, and other similar intermediate to silicic rocks. Lastly,rocks of the Stearns Magma Series are cut by basalt dikes which may have been emplaced during a single period, at least 1,570 m.y. ago (Hanson, 1968). — �Paper 29 GRANITIC PLUTONIC ROCKS OF THE SOUTHERN PROVINCE OF THE CANADIAN SHIELD James A. Robertson Division of Mines, Ontario Ministry of Natural Resources, Toronto *paper presented by permission of the Director, Geological Branch. AB STRACI In Ontario granitic rocks associated with the eastern portion of the Penokean fold belt comprise: (1) Archean basement; (2) early post-Huronian intrusives (= Penokean of Church, 1968), and (3) late post-Huronian intrusive ( Hudsonian of Church). Other authors eg. Stockwell (1964) have used Hudsonian and Penokean interchangeably and have not named the earlier orogenic event. The individual granitic bodies are named on Figure 1. Algoman = Archean (Robertson, 1960) granitic rocks may be divided into massive quartz monzonite and gneissic to migmatitic Bodies of quartz monzonite were formed during the terranes. Early workers placed these Kenoran orogeny circa 2,500 MY. Overprinting bodies with the "young" post-Huronian granites. of age dates becomes pronounced as the Penokean fold belt is approached (Van Schmus, 1965). 1) The Creighton and Murray Granites (Card, 1968; Ginn, 1958) They were intruded prior lie south of the Sudbury Irruptive. to the irruptive and local anomalous cutting relationships The reflect remobilisation of the granite (Hawley, 1962). granites pre-date the regional metamorphism and deformation. Gibbins et al (1971) have obtained 2,200 MY, which suggests that they are earlier than the Nipissing Diabase (2,155 MY Whether they are synchronous with the Van Schmus, 1965). earlier post-Huronian orogenic cycle or with early Huronian volcanism remains an open question (Card et al, 1972). 2) �—2— Paper29 3) The Cutler Batholith (Robertson, 1969; 1970a; Cannon, 1970) lies some eighty miles west of Sudbury and intrudes folded and metamorphosed Huronian sediments and Nipissing Diabase and is itself foliated. Age-dates (Wetherill et al, 1960; Van Schmus, 1965) indicate a minimum age of 1,750 MY with some thermal resetting at 1,350 MY. The Cutler granite is clearly synchronous with the Hudsonian orogeny. The granite is intrusive but may have been derived from Huronian rocks at depth and metasomatism may have been an important factor (Cannon, 1970). The Croker Island Complex (Card, 1965; Robertson, 1970) lies some twelve miles southeast of Cutler and comprises a circular complex of comagmatic mafic to granitic rocks accompanied by a marked magnetic anomaly. The complex postdates regional metamorphism and folding. Age-dates (Van Schmus, 1965) and paleomagnetism studies (Palmer, 1969) indicate 1,445 MY. The complex is clearly late Hudsonian. Similar magnetic anomalies under Manitoulin Island were drilled by Union Carbide. Core of granitic rock resembling that at Killarney was obtained and submitted to Van Schmus for dating. 4) Grenville Front Granites (Card et al, 1971; Frarey and Cannon, 1969; Hnderson, 1967; Quirke and Collins, 1930) are intrusive bodies in the Southern Province adjacent to the Grenville Front. To the northwest these bodies are intrusive but to the southeast they become strongly mylonitised passing into the deeper crustal granite-gneiss complex of the Grenville Province. The mylonite zone marks the Grenville Front. 5) 5a*) The Killarney batholith featured in the classical work of Quirke and Collins (1930) with a minimum age of 1,585 MY comprises porphyritic quartz monzonite. 5b*) The Lake Panache and Eden Lake Intrusives, (Card et al, 1971) range in composition from gabbro-granite with a minimum age of 1,430 M.Y. from mica. 5c*) The Chief Lake Batholith comprises quartz diorite to quartzonzonite marking the northeast continuation of the Killarney granite. Near Coniston, Phemister (in Grant et al, 1962) interpreted the rock as feldspathised sediment. Krogh (1971) indicates an initial age of 1,730 MY with some granites at 1,590 MY - 1,460 MY reflecting early movement on the Grenville Front. *Individual bodies not shown on Figure 1. �Paper 29 — — Conclusion The granitic rocks of the Ontario Sector at the Southern Province may be classified with respect to petrography, mineralogy, chemistry, isotopic composition and they can be fitted into the historical and structural scheme established by regional mapping (Robertson et al, 1969; Card et al, 1972). However, much detailed work on individual bodies remains to be done. References CannQn, W.F. (1970) Plutonic Evolution of the Cutler Area, Ontario; G.S.A., Vol. 81, p. 81-94. Card, K.D. (1965) The Croker Island Complex; No. 14. Bull. Ont. Dept. Mines, Geol. Circ. Card, K.D. (1968) Geology of Denison-Waters Area, District of Sudbury, Ont. Dept. Mines G.R. 60. Card, K.D., Palonen, P.R., and Siemiatkowska, K.M. (1971) Geology of the Louise-Eden Area, District of Sudbury; Ont. Dept. Mines and Northern Affairs, Open File Report 5065. Card, K.D. et al (1972) The Southern Province in Canada in Structural Styles in Canada, in press. Geol. Assoc. Can., Contribution to 24th mt. Cong. Montreal 1972. Church, W.R. (1968) The Penokean and Hudsonian orogenies in the Great Lakes region and the age of the Grenville Front, 14th Annual Ints. on Lake Superior Geology, p. 16-18. �Paper 29 —4— Frarey, M.J., and Cannon, R.T. (1969) Notes to accompany a map of the Geology of the Proterozoic Rocks of Lake Panache. Collins Inlet Map Areas, Ontario. Geol. Surv. Can. Paper 68-63 Gibbons, W.A., McNutt, R.H., and Adams, C.J.D. (1971) Rb-Sr Isotopic Studies of the Murray Granite, Geol. Assoc. Can. Abstracts, Sudbury 1971, p. 27-28. Ginn, RM. (1958) A Study of the Granitic Rocks in the Sudbury Area. Unpublished M0Sc. Thesis, Queen's University. Ginn, R.M. (1961) Geology of Porter Township, Ont. Dept. Mines, Geol. Rept0 No 5. Grant, J.A., Pearson, W.J., Phemister, T.C., and Thomson, J.E. (1962) Geology of Broder, Dill, Neelon and Dryden Townships District of Sudbury, Ont. Dept. Mines GR 9. Hawley, J.E. (1962) The Sudbury Ores: Their Mineralogy and Origin, Can. Mm. Vol. 7, part 1, 1962. Henderson, J.R. (1967) Structural and petrologic relations across the Grenville Province-Southern Province boundary, Sudbury, District of Ontario. Ph.D. Thesis, McMaster University, Ontario. Krogh, T.E. (1971) Isotopic ages along the Grenville Front in Ontario. Assoc. Can. abstracts Sudbury 1971. Geol. Palmer, H.C. (1969) The Paleomagnetism of the Croker Island Complex, Ontario, Canada; Can. Jour. Earth Sci., Vol. 6, p. 213-218. Quirke, T.T., and Collins, W.H. (1930) The Disappearance of the Huronian; Geol. Surv. Can. Mem. 160. Robertson, J.A. (1960) The General Geology of Part of the Blind River Area; Thesis, Queen's University, Kingston. Robertson, J.A. (1969) Geology of the Cutler Map-Area; File Rept. 5026. Robertson, J.A. (l970a) Geology of the Spragge Area; M.Sc. Ont. Dept. Mines, Open Ont. Dept. Mines, Geol. Rept. 76. �—5- Paper 29 Robertson, J.A. (1970) Geology of the Massey Area, Districts of Algoma and Sudbury; Ont. Dept. Mines Open File Rept. 5043. Robertson, J.A., Card, K.D., and Frarey, M.J. (1969) The Federal-Provincial Committee on Huronian Stratigraphy Progress Report; Ont. Dept. Mines, M.P. 31, 26p. Van Schmus, R. (1965) The Geochronology of the Blind River-Bruce Mines Area, Ontario Canada; Jour. Geol., Vol. 73, p. 755-780. Wetherill, G.W., Davis, G.L., and Tilton, G.R. (1960) Age Measurements on Minerals from the Cutler Batholith, Cutler, Ontario; Jour. Geophys. Research, Vol. 65, p. 2461-2466. Structure, metamorphism and Post-Huronian granitic intrusions of the eastern Southern Province. Fig. 1. �Paper 30 REGIONAL RELATIONSHIPS IN THE PENOKEAN PROVINCE H. B. STONEHOUSE Michigan State University ABSTRACT Investigations over the last few years in that area of the Southern Province of the North American Shield known as the Penokean Fold-Belt Subprovince, allow some of the following conclusions to be made:1. 2. Similar sequences of sediments deposited over a period of about 600 my (roughly 2.2 by to 1.6 by ago) are of predominently shallow water origin. Local tectonic activity occurred during deposition of these sediments. 3. Intrusive igneous activity during this period resulted in basic dikes and/or sills; acid intrsives are minor. 4. The regional E-W folding increases in intensity to the 5. Older geological events tend to occur in the eastern part of the region and younger ones in the west. 6. Regional tectonism was most intense at some time before south. the end of the period. Events which took place within this region during this time period are pit into the context of cause-effect relationships and a regional-time pattern; a better geological understanding results. The evidence strongly suggests that the area be re- designated as "The Penokean Province" and that the term "Penokean Orogeny" be replaced by "Penokean Tectonic Sequence". �Paper 31 AGES OF SONE PRECAi4BRIAN ROCKS IN EAST-CENTRAL NINNESOTA J. S. Stuckless Department Northern and S. S. Goldich of Geology Illinois University Illinois 60115 DeKaib, ABSTRACT The McGrath Gneiss, formerly assigned to the Penokean orogeny, l6Oo-lOO m.y. ago, was actually emplaced in a Lower Precambrian terrane during the Algoman orogeny, approximately 2700 m.y. ago. Locally the gneiss is intensively sheared. This phase of the deformation is related to epeirogeny that followed the regional metamorphism of the Middle Precambrian formations. Rb—Sr isochron studies of igneous rocks that were emplaced following folding and regional metamorphism place a minimum age of 1900 m.y. on the Mid- This age is somewhat older than the 1850 m.y. age obtained by Z. E. 'Peterman for the metasedimentary rocks of the Cuyina district and is considerably older than the previous K-Ar and Rb-Sr mica age determinations. The McGrath Gneiss appears to be extensive in east-central Minnesota; hence, it is likely that the Middle Precambrian rocks of Minnesota were all- deposited on an erosion surface developed on an Archean continental crust rather than on oceanic crust. dle Precambrian Thomson Formation. �Paper 32 GEOCHRONOLOGY OF PRECAMBRIAN ROCKS IN THE PENOKEAN FOLD BELT SUBPROVINCE OF THE CANADIAN SHIELD W. R. Van Schmus Department of Geology University of Kansas Lawrence, Kansas 66044 ABSTRACT The Penokean Fold Belt subprovince is that part of the Southern Province consisting of the folded and metamorphosed Middle Precambrian rocks which occur in an E-W trending belt running south of Lake Superior and north of Lake Huron. Included within this belt are strata of the Huronian, Marquette Range, and Animikie supergroups and associated economic deposits. For many years these rocks have been considered possible corre- latives, and the folding, metamorphism, and intrusive activity have been referred to as the Penokean Orogeny. Recent and current field and laboratory studies now show that the orogenic history of this region can not be represented by a single major orogenic episode. Instead, this portion of the North American continental plate was affected by a succession of events over the interval 2.7 to 1.1 b.y. ago. The oldest Proterozoic rocks are apparently those in Ontario, north of Lake Huron. In this area Huronian strata overlie a 2.7 b.y. old basement and are intruded by the 2.16 b.y. old Nipissing Diabase. To the west, in Upper Michigan, the Proterozoic sedimentary and volcanic rocks, the Marquette Range supergroup, are apparently younger, being between 1.90 and 2.05 b.y. old, and thus not correlative with true Huronian rocks. Farther west, in Minnesota, the Animikie rocks may be partly correlative with and partly younger than those in Michigan and Wisconsin. There have been multiple periods of intrusive, metamorphic, and tectonic activity. The oldest Proterozoic deformation apparently occurred about 2.15 b.y. ago in Ontario, affecting the Nipissing Diabase and Huronian rocks. A major episode of igneous, metamorphic, and tectonic activity occurred about 1.9 + 0.1 b.y. ago, affecting most, if not all, of the E-W trending belt from Minnesota to Ontario. This event would appear to be the one most representative of a uPenokean Orogeny.' Subsequent to the main orogenic activity several intrusive and! or metamorphic episodes have occurred, about 1.65, 1.5, and 1.3 b.y. ago. Several of these younger events may be correlated with the Middle Precambrian history of Wisconsin and the rest of the Midcontinent. Finally, much of the area was affected by Keweenawan igneous activity and associated metamorphism 0.9 to 1.2 b.y. ago. �Paper 32 -2- On the basis of present geologic and geochronologic data, it appears reasonable to interpret the Penokean Fold Belt as an orogenic belt developed along the southern edge of the Superior craton about 1.9 billion years ago. The exact nature of this structural belt and its possible relation to arc-trench sequences of present models of plate tectonics must await further work. �Paper 32 SELECTED BIBLIOGRAPHY Aldrich, L. 1., Davis, G. L., and James, H. L., 1965, Ages of Minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Jour. Petrology, v. 6., p. 447-.472. Banks, P. 0., and Cain, J. A., 1969, Zircon ages of Precambrian granitic rocks, northeastern Wisconsin: 77, 208-220. Jour. Geology, R. , 1971, Chronology of Precambrian rocks of Iron and Dickinson Counties, Michigan (Abs.). 17th Annual Institute on Lake Superior Geology, Duluth, Minn., May. Banks, P. 0. and Van Schmus, W. Bass, M. N., 1959, Mineral age measurements --Wisconsin: Inst. of Washington Year Book, 58, 246-247. Carnegie Dickinson, W. R., 1971, Plate tectonic models of geosynclines: Earth Plan. Sci. Letters, 10, 1965-174. Dott, R. H., Jr., 1969, Isotopic dating of the Baraboo and Waterloo quartzites. 15th Institute of Lake Superior Geology, Oshkosh, Wisc., p.15. Dutton, C. E. , and Bradley, R. E. , 1970, Lithologic, geophysical, and mineral commodity maps of Precambrian rocks in Wisconsin. U. S. Geol. Surv. Map set 1-631, with accompanying pamphlet (15 pp.). Fairbairn, H. W., Hurley, P. M., and Pinson, W. H., 1960, Mineral and rock ages at Sudbury-Bling River, Ontario: Geol. Assoc. Canada Proc., 12, 41-66. Fairbairn, H. W., Hurley, P. M., Card, K. D., and Knight, C. J., 1969, Correlation of radiometic ages of Nipissing diabase and Huronian metasediments with Proterozoic orogenic events in Ontario. Can. J. Earth Sci., 6, pp. 489-497. Faure, G., and Kovach, J., 1969, The age of the Gunflint Iron Formation of the Animikie Series in Ontario, Canada. Geol. Soc. America Bull., 80, 1725-1736. Goldich, S. S., Nier, A. D., Baadsgaard, H., Hoffman, J. H., and Krueger, H. W. , 1961 nology of Minnesota: Krogh T. E. , , The Precambrian geology and geochro- Minnesota Geol. Survey Bull. 41. and Davis, G. L. , 1971, the Grenville Front inter- preted as an ancient plate boundary: Washington Year Book, 70,. 239-240. Carnegie Inst. of Peterman, Z. E., 1966, Rb-Sr dating of middle Precambrian metasedi- nientary rocks of Minnesota. 1031-1044. Geol. Soc. America Bull., 77, Van Schmus, R., 1965, The geochronology of the Blind River-Bruce Mines area, Ontario, Canada: J. Geol., 73, 755-780. Woolsey, L. L., 1971, A Rb-Sr geochronologic study of the Repi.iblic metamorphic node, Republic, Michgn. Unpub. M. S. Thesis, Univ. of Kansas, Lawrence. �Paper 33 STRATIGRAPHY AND SEDIMENTATION OF THE ESPANOIA FORMATION, AN EARLY APHEBIAN (MIDDLE PRECAMBRIAN) CARBONATE UNIT GRANT M. YOUNG Department of Geology University of Western Ontario London, Ontario ABSTRACr The Espanola Formation is unique among Huronian formations in its high carbonate content. It forms part of the Quirke Lake Group, lying between the Bruce Formation (beneath) and the stratigraphically higher Serpent Formation. The Bruce Formation is mainly unstratified sandy polymictic paraconglomerate (tillite) whereas the Serpent Formation consists mainly of cross bedded felspathic quartzites. In the Quirke Lake area the Espanola Formation is divisible into three units, here called, in ascending order, limestone member, siltstone member and dolostone member. Some fifty miles to the southeast these three members can still be recognised but the central, dominantly terrigenous clastic unit, is much thicker. In the southern area there is also an additional thick upper member which displays fining upwards cycles (from conglomerate to mudstone) similar to those attributed to fluvial deposition. In the Quirke Lake area the Espanola Formation contains both intraformational and intrusive breccias. The intrusive breccias are later than some faulting and transect clastic dykes. They are considered to be downward intrusions caused by release of high pore pressure in watersaturated sediments along fissures in the already lithified Espanola Formation. The triggering mechanism for the breccias may have been earth tremors associated with early (pre-Gowganda) earth movements for the breccias appear to be spatially related to areas where there is evidence of disconformable/unconformable relations between the Gowganda Formation and older Huronian rocks. Cross bedding studies, mainly from the highest member of the Espanola Formation in the southern part of the Huronian outcrop belt, reveal a bimodal pattern with dominant modes in the south-west quadrant and towards the E.S.E. Microprobe analyses of the carbonates of the dolostone member showed that the rusty-weathering dolostones are composed of ferruginous dolomite. The Espanola Formation is interpreted as a post-glacial transgressiveregressive cycle (Fig. 1). The limestone and dolostone members are thought to be shallow water deporits while the siltstone member represents a deeper water facies (involving some turbidite transportation). The sandstone member of the southern region is thought to have been laid down from meandering streams which initiated sedimentation of the thick prograding fluvial sequence of the Serpent Formation. �0 .,-4 C. S S SQ '.4 00 00 '0 5 0 FIG. 1, F- LU 0.0 ,-l us C w C. .0 '0 NW I I (turbidite facies) SERPENT FORMATION SPACE - TINE RElATIONSHIPS DURING SEDIMENTATION OF THE ESPMTOLA FORMATION TRANSPORT DIRECTION DOMINANT SEDIMENT UPLIFT AND EROSION REGION OF CONTEMPORANEOW UPLIFT — ESPANCLA Southern limit of SUBS! DEN CE REGION ZONE OF TECTONIC Northern Limit of preserved Huronian ZONE OF TECTONIC TECTONIC HINGE ORMATION SE III • �Paper 34 WEATHERING AND METASOMATISM OF THE PRESQUE ISLE SERPENTNIZED PERIDOTITE, MARQUETTE COUNTY, MICHIGAN M. D, LEWAN Michigan Technological University ABSTRACT Presque Isle Park, Marquette, Michigan is underlain by a mass of peridotite, probably cut by Archean granite and definitely cut by a diabase dike of probable Keweenawan age. The three rock types grade upward into a complex altered zone that has variable thickness and mineralogy, depending upon the rock type it occurs on. This zone is comprised of a lower zone of dolomite-silica. and an upper zone rich in silica, which in turn is unconformably overlain by Jacobsville Sandstone. Data from major element analysis of 42 rocks, qualitative mineralogy determinations by X-ray diffraction, and field observations indicate that the peridotite has undergone three periods of alteration; 1 )early s erpentinization, 2)carbon dioxide meta somatism after emplacement, and 3)weathering after the area was exposed to surface conditions. The granite has also undurgone the same sequence of alteration with the exception that the first period of alteration was illitization. On geological and geochemical grounds the serpentinization and illitization processes could not have been contemporaneous. The forming of the silica rich weathered zone, which is best developed over the granite, is the result of weak acidic meteoric waters dissolving dolomite out of the dolomite-silica zone. Chemical and mineralogical profiles show that the removal of dolomite results in the upward concentration of residual minerals such as quartz, rutile, hematite, chlorite, and illite. The weathered zone was searched for nickel concentrations such as garnierite, but none were found. Field evidence indicates that the weathering and metasomatic alteration post-dates the intrusion of the probable Keweenawan dike and pre-dates the deposition of the Jacobsville Sandstone. Jacobsvifle Sandstone p Basal Conglomerate 8 Silica-Rich weathered zone c ° -— Dolomite-Silica zone , Diagramatical sketch(not to scale) showing the relationship between the rock units on Presque Isle.. � https://digitalcollections.lakeheadu.ca/files/original/a4db2f602031c8a408c608d8cb354236.pdf d677645b5be965a820d9bca69a888cc9 PDF Text Text ������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/b5f4086c9db7eb5ddf6d4f37b1ce7c16.pdf b1d42fe2b6fcf5b2fb62b0815cc007f1 PDF Text Text �---'--------......;;===================----------=====--------------==================.,......------'.. i" Michigan Technological University University /- ..-..;// ....::>' /tPl;SID~8;t;.~ /' ~ H'QH~A . _.'~ / ~7'" .:- .-":-'Y._~;---;;;r-;;.,.-;~--?~'-:~ - ----. --:..-- Y.~==-.:,- - _=_ -. ---._ __ HOUGHTON MI 49931 • -2< ' '1'~1J - rf'I 0'">" ~ III! :r::£'(P~ .- _.._. . . . . - .--- - ..- - . - . - . ,{'(}-(~.,c?". 'J<'£:: .f\ --' / (',{,!~,-- -~ .,~~ './ ---~. - -_. - . _ . ' - . N'-c.A ~ ~\ Seaman c···.· -' ••/ / ! --; , . .~r: ~; Mineral Museum . . .. --- (5th (5th floor) Memorial Union Union .. .,~=-'~" ::~::::-~':"'~~~:. .'.~' ~:-- - ----,- ...->--'-" / ~ —- - 1 (3rd floor) \\ / / // / r--. .. - ~f1Y- -. Geology -.—- ~~-::.~;,::;:~:~,:, * -.:• ,/ ..' ~C~ 0 ~.-:_-- - .. --7'- - " " . .. . -.., _ ...:>c.....- ~- // /' --;;.,;-. ---;.. - _~'~..rg;~.'~~~: ~_.-ifi,~.:.'~-': ~-F'i:rPJl' -~... ..e;- . ' ~ ... ?- • -~I)<0.rr - / PORTAGE LAKE / Commuter & DHH -) - _ ... - rv-l\l:rd- ~ (l"ri_,y,> 0 "'-0,,r ~ ( ,'."" f\,:,''''''- Qr4 'b-97? ?•j(4?it ,/7 r-5.jfy ,,, 5' //' - //.'/, /j1'J. HARONAVE' " - - clf i—__._ —__-'" = - - / J/ / ( /— — ,,, 5- --5 —'-_ \ -= 5J( 'n\\ \ 11 v'— r (" r -y"y' AdmInistration BuIlding Administration Building 4 ROTC ROTC BuildIng Building 5 Academic Academic Offices Offices BuIlding Building Electrical Energy Resources Resources Center Center ElectrIcal Energy 7 EERC-AE. Seaman Seaman Mineralogical Mineralogical Museum EERC·A.E. Museum (5th (5th Floor) Floor) 9 Alumni AlumniHouse-MT House-MT Fund Fund Humanities Center Center Arts and Humanities InstItute of of Mineral Mineral Research Research (Benedict (Benedict Lab) Lab) ,39- 'i\ '(! . 12 Institute CivIl-Geology Building Civil·Geology Hall 15 Fisher Hall library Forestry·lnstitute of Wood Research 19 ChemistryMetaurgyBuiing Chemistry·Metaliurgy Building MechanicalEngIneering-Engineering Engineering-Engineering Mechanics 20 Mechanical -3(Y- 24 Student Development Complex Student Development Complex Douglass Houghton Hall (DHH) Daniell Heights Housing -r4-,c' 34 Memorial Union Memorial UnionBuilding Building 37 Wadsworth Wadsworth Hall Hall \L7 -— - - I - - // rr-w-- fç,7 - FOOTBALL FIE LD -, / k/ 1 ' 9c'?1i-' /) J 14 (1 38 West West Coed Coed Hall Hall 38 39 Coed Coed Food Food Service Service 39 East East Coed Coed Hall 4t Central Heatmg Healing Plant 41 42 Physical Physical Plant Plant Storage Storage Building Building 42 Lakeside Laboratory 43 Lakeside 43 44 Storage-Service Storage-Service Building Buiiding (Pool (Pool Cars) Cars) 44 50 Gates Tennis Tennis Center Center 50 Gates 58 U.S. Forest Engineering Laboratory U.S. Forest Engineering A Visitors'Parking Parking Ares Area A Visitors )L. ç- - 9 - 40 Not appearing on on map map: Experimental Mine, Hancock Hancock Ford Forestry Center, Alberta Ford Alberta Keweenaw Research Center Center, Memorial Memorial Airport Airport Mont Ripley Ski Hill, Ripley Portage Lake Golf Course, Course, Houghton Houghton I ',S (\C'l(') '()r l ' r- (( .,.... .-,_ -( ,CY C �FIELD GUIDE TO THE GEOLOGY GEOLOGY OF OF THE THE KEWEENAW PENINSULA, PENINSULA, MICHIGAN BY J. Bornhorst Theodore J. William I. I. Rose, Rose, Jr. Jr William James B. B. Paces Department of of Geology and Geological Engineering Michigan Technological University University Houghton, Houghton, Michigan 49931 FOR SALE SALE AT: AT: E. R. R. Lauren Bookstore, Bookstore, Memorial Union E. Michigan Technological University Houghton, Michigan 49931 Houghton, Prepared as field trip trip guide guide for for the the 29th Annual Institute as aa field Annual Institute on Lake Superior Geology held held at at Michigan Michigan Technological Technolo~ical University on May 11—14, 11-14, 1983. 1983. FIRST EDITION May, 1983 May, COVER PHOTO: Miners Miners at at the the Mine(?) circa circa 1910. 1910. Baltic Mine(?) Michigan Technological University Archives and Copper Country Historical Collections. Collections. �PREFACE — It is presumptuous presumptuous for for us us to put together is based based mainly mainly on on the the work work It is to put together aa book which is of others. We have done so because hundreds of people come to of to the Keweenaw each year to to look look at at geological geological features features and and many many of of them them ask ask us us for for advice. advice. So we've tried to tried to communicate with people people who who are are doing doing serious serious geological geological field field trips. trips. This is is a first first draft of an evolving document, document, which we expect to to continually rerePlease help help us us make make it better by by suggesting changes, changes, finding finding mistakes mistakes and and Please it better vise. telling us what we've we've left left out. out. Starting with Douglass Douglass Houghton almost almost 150 years years ago, ago, dozens dozens of of geologists geologists have have contributed aa mountain of of geological on the the Keweenaw Keweenaw which which makes makes it it contributed geological information information on aa real challenge to to compile this this book. book. The greatest greatest contribution by far far has come come from from Walter Walter S. S. White, White, who who devoted devoted much of of his his professional professional career career to to Keweenawan Keweenawan whose impact geology and whose impact can can be traced traced to to virtually virtually every every page page of of this this book. book. of his his We hope that that we have faithfully faithfully transmitted his his ideas with a a fraction fraction of enthusiasm. ingenuity and enthusiasm. Houghton Houghton 30 March 1983 i1 �TABLE OF CONTENTS Page i PREFACE iii HOW TO USE THIS GUIDE GUIDE iv LIST OF OF STOPS STOPS vlii viii LIST OF MAPS ix LIST OF FIGURES xi LIST OF OF TABLES TABLES INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA 11 17 17 ROAD LOG AND STOP DESCRIPTION INDEX TO GEOLOGY ON NAPS MAPS IN IN THE FIELD FIELD GUIDE GUIDE 111 111 112 112 REFERENCES 11i i �HOW TO USE THIS GUIDE To make all the the stops stops listed listed in in this this guide guide would would take take three three days. days. If If you wish to to emphasize certain types types of of stops, stops, we we recommend recommend the the following following subsets: subsets: Suggested Stops Stops Sediments Sediments Volcanic Rocks Mineral Deposits Broad Coverage 5, 6, 8, 8, 9,. 16, 17, 17, 19, 19, 20, 20, 24 24 10, 13, 13, 16, 5, 6, 9, 10, 1, 15, 16, 16, 17, 17, 18, 18, 21 21 1, 3, 3, 11, 11, 12, 12, 13, 13, 14, 14, 15, 2,3,4,7,11,13,17,22,23 2, 3, 4, 7, 11, 13, 17, 22, 23 3, 6, 10, 10, 11, 11, 13, 13, 16, 16, 18, 18, 19, 19, 20, 20, 24 24 3, 6, Be imaginative and make up up your own own subset subset of of stops. stops. stops are are on on or or near near private private land. land. Please respect private property. property. The preMany stops Sent problems of access are minimal, but obviously we could ruin we don't don't sent problems of access are minimal, but obviously we could ruin things things if if we use low profile outdoor principles. principles. AA few few stops stops are are located located ot on old mine dumps. dumps. These can be hazardous, hazardous, especially especially where where bad bad ground ground occurs. occurs. Use common sense. sense. - have north north to to the the top top and and are are 1:24,000 1:24,000(4(4cmcmtoto1 Ikin). km). All maps have road log route on the the maps, maps, while while stars stars mark mark the the stops. stops. follow the the Dots follow Mineral collectors have long long flocked flocked to to the the Keweenaw to to collect its its unusual minerals. minerals. One of the best in the world located at this best mineral museums in world is located at the starting point point of of this field trip. trip. The Seaman Mineralogical Museum, Museum, open from 9:00—4:30 9:00-4:30 weekdays, weekdays, is is housed housed in the the EERC EERC Building, Building, Fifth Floor, in Floor, on on the the Michigan Michigan Tech Tech Campus. Campus. The mineralogical over the the Keweenaw and is collection includes includes samples samples from from all over is aa must for for all all rockhounds. rockhounds. 111 iii �STOPS LIST OF STOPS The following used to to help help you you design design your your own own field field trip trip following list of stops can be used to to see the geology of the the Keweenaw Peninsula. Peninsula. The location location of of stops stops are are shown shown in Figure la. la. The appropriate maps for for each stop and trip trip route are located in Figure Figure lb. lb. — — STOP MAP) (APPROPRIATE MAP) STOP DESCRIPTION STOP 11 (1) (1) Ophitic Scales Creek basalt flow and Keweenaw view, 7th 7th St., St., Houghton. Houghton. Waterway view, 2 2 (1) (1) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Isle Royale Mine, Dodgeville. Dodgeville. '-" 3 (2) (2) Section through a lava lava flow flow at at South South Range Range quarry. quarry. ....---4 (2) (2) Secondary minerals in in amygdaloid amygdaloid at at dump dump of of Baltic Mine. Mine. 5 5 (3) Glacial deposits on M—26 M-26 south south of of Houghton. Houghton. 6 6 (4) (4) Overlook of Keweenaw Waterway, Waterway, Houghton and the Range towns; towns; Quincy Quincy Hill, Hill, Hancock. Hancock. 7 7 (4 ) (4) Secondary minerals of amygdaloid at at dump dump of of Quincy Quincy Mine. Mine. 8 (6) (6) Flat—lying Flat-lying Jacobsville Jacobsville Sandstone Sandstone along along M—26, M-26, near Dollar Dollar Bay. Bay. 9 9 (7) (7) Hungarian Falls, Falls, near near Hubbell. Hubbell. Keweenaw Fault at Hungarian 10 10 (8) (8) Keweenaw Fault at at Natural Wall Wall Ravine, Ravine, near near Laurium. Laurium. 11 (9) (9) Secondary minerals in amygdaloid at at dump dump of of Wolverine Wolverine Mine. Mine. 12 (9) (9) Ophitic Scales Creek basalt flow, flow, at Scales Creek near Copper City. City. —- 13 ...../13 (9) (9) Lava flows flows of Portage Lake Volcanics and mineralized conglomerate with an excellent ized excellent view view of of the the central part of of the the Keweenaw Keweenaw Peninsula, Peninsula, Bumble— Bumbletown Hill. 14 (12) (12) Ophitic Greenstone flow and vein mineralogy at dump of Phoenix Mine. 15 15 (12) (12) part of of the Portage Lake Lake Section through through the the upper part the Portage Volcanics along along Eagle Eagle River. River. 16 (12) Contact between Portage Lake Volcanics Volcanics and Copper Contact Harbor Conglomerate Conglomerate at at Eagle Eagle River River Falls. Falls. ~. t/ iv �STOPS (Cont'd.) (Contld.) LIST OF STOPS STOP DESCRIPTION STOP (APPROPRIATE MAP) 17 17 (13) through the the upper upper part part of of the the Portage Portage Section through Lake Volcanics along Owl Owl Creek Creek and and amygdaloid! amygdaloid/ vein mineralogy at dump dump of of Copper Copper Falls Falls Mine. Mine. v"J.8 "18 (16) (16) Lava flows of the the Lake Shore Shore Traps Traps at at Esrey Esrey Park. Park. V19 \/19 (17) Overlook of Lake Superior Superior and and the the eastern eastern end end of of the Keweenaw Keweenaw Peninsula and outcrops of Copper the Harbor Conglomerate at at Brockway Mountain. Mountain. flO (17) (17) Copper Harbor Conglomerate Conglomerate at at Dan's Dan's Point. Point. 21 (20) (20) Diorite and granophyre stock stock at at Mt. Mt. Bohemia. Bohemia. 22 (21) Secondary mineralogy of of veins and and conglomerate conglomerate at Delaware Delaware Mine'. Mine~ The Delaware Mine is is open to to tourists for for aa fee. fee. 23 (28) Amygdaloid mineralogy of of dumps dumps at at Osceola Osceola Mine. Mine. 24 (30) at Hancock Hancock campground campground quarry. quarry. Nonesuch Shale at v �I ( I . ···i·9*··..······..·····;:;: ; ~ "'-~'L"'"alre Bailey . Eagle . . . f~~;I~.·.:::::::···:< . . . ""C~~r~·I La e M.,!dO'~ C ............ Delawar~.~.,2 ..'····· ....····· Copper Harbor 20 \ 0 " fifo" 5 IJ Eagle H ...r-nnr :._. _ - .~ .-:--~"::::~tS ~-~. Lak e Fanny Hooe Schlstter('.., •....1 (? ········\···'>... 21 = LakeV ~ Manitou Island Island ........ Phoenix .-:,., <f.2 .~.' i-~ Lake .../ "to A:::;!l\(~~:,..• o Kearsargei..,.J 1 ..i '···12 -< ~. McLain State Park McLain Park .rC"aiun;-~t·'· .f .-.,1.0... ~~ ~~ ~\ o~ C, Laurium 23*/ . Lake Linden ..... .... Scale Scale 1 0o M I 1 1 2 3 4 miles 4miles ~ Freda Atlantic South ~ ~ly ~ '" Painlsdale Pa in ed a le 12 Stopnumber number •2 Stop Figure Figure 1A: 1A: Route Route and and stop stop map map �SU ~~ \\ \ 17 o o~ 13~ ~ 23 o 12 'I-~ ... '" _0_" 27 ./' <~ t-<t-<. -.)~ ~ ~ \ o ~ c., 8 SCALE in in miles 01234 ,.... ji"Wiij o 1 2 ....., 3 p> 4 Dil2 Map number 12 ,.*" I'l + ~ " Figure 1B: 18: *'2 number Stop number Index of of 1:24,000 Index 1:24,000 scale scale maps maps �LIST OF OF NAPS MAPS Page MAP MAP 1 18 MAP MAP 2 22 MAP MAP 33 26 MAP MAP 44 31 MAP MAP 5 35 MAP MAP 6 39 MP MAP 77 42 MAP MAP 88 46 MAP MAP 9 49 MAP 10 MAP1O 60 MAP MAP 11 63 MAP 12 MAP 64 MAP13 MAP 13 71 MAP 14 MAP 74 MAP15 MAP 15 76 MAP 16 MAP 77 MAP17 17 MAP 79 MAP 18 MAP 82 MAP MAP 19 86 MAP2O t-1AP 20 87 MAP MAP 21 88 MAP 22 MAP 91 MAP MAP 23 95 24 MAP24 MAP 96 MAP25 MAP 25 98 MAP26 MAP 26 99 NAP MAP 27 100 MAP MAP 28 104 MAP MAP 29 106 MAP MAP 30 109 viii viii �LIST OF FIGURES Page vi Vi Figure 1: 1: Index map map of of route, Index route, stops and 1:24,000 scale scale maps. maps. Figure 2: 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. 2 2 Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and strati— stratigraphic column, column, western western Lake Lake Superior Superior region. region. 3 3 Generalized geologic geologic map of of the the western western Upper Upper Peninsula and stratigraphic stratigraphic section section of of the the Portage Portage Lake Volcanics. 4 4 Columnar stratigraphic Section section of of rocks rocks northwest northwest of of the Keweenaw Fault in the Calumet—Ahmeek the Calumet-Ahmeek area. area. 66 rocks Location of silicic to to intermediate intrusive rocks the Portage Lake Volcanics. in the Volcanics. 8 8 Figure Figure Figure Figure 4: 4: 5: 5: 6: 6: 7: 7: Schematic diagram showing interrelationships between northwest of of the major stratigraphic units units northwest the Keweenaw Fault in the the Keweenaw Peninsula. 10 Geologic and structure structure maps of of the the Keweenaw Keweenaw native native copper district. district. 13 and paragenesis of of secondary minerals Distribution and secondary minerals in Volcanics. in the the Portage Lake Volcanics. 14 14 Elemental mobility in in an an idealized idealized lava lava flow flow and and diagrammatic diagra~matic regional model for for metamorphism metamorphism of of the Portage Lake Volcanics. the 16 16 Figure 11: 11: Geologic cross—section cross-section for for Map Map 1. 1. 20 Figure 12: 12: Geologic profile of South Sou~h Range quarry. quarry. 21 21 Figure 13: 13: Speculative ice—marginal ice-marginal positions positions during during the the Wis— Wisconsin ice retreat. retreat. 27 Figure 14: 14: End moraine of the End the Keweenaw Bay Lobe glacier. glacier. 27 Figure Figure 15: 15: Enlarged view of ice—marginal ice-marginal positions. 28 Figure Figure 16: 16: High level drainage drainage through through the the Portage Portage Gap. Gap. 29 29 Figure Figure 17: 17: View from from Portage overlook overlook facing facing south. south. 32 32 Figure Figure 18: 18: Structures of the the Quincy Mine location. location. 36 Figure 19: 19: Geologic cross section section for for Maps Maps 4, 4, 5 and 30. 30. 37 37 Figure Figure 8: 8: 9: 9: Figure 10: 10: ix �Page Figure 20: 20: Relationships of of Jacobsville Sandstone. Sandstone. 40 21: Figure 21: Geologic sketch map of of Hungarian Falls Falls area. area. 44 Figure 22: 22: Wall Ravine. Ravine. Geologic sketch map of of Natural Wall 47 Figure 23: 23: Geologic Geologic map map and cross section, Wolverine Mine and and section, Wolverine arid cross vicinity. 51 Figure 24: 24: Thickness of of the the Kearsarge Kearsarge flow. flow. 52 Figure 25: 25: Paragenesis of secondary minerals in in the Kearsarge amygdaloid. 52 Cross section section of of Kearsarge Kearsarge amygdaloid amygdaloid showing showing the Cross the banding of of mineral assemblages. assemblages. 54 Distribution of quartz, quartz, microcline and high grade ore in in the the Kearsarge Kearsarge amygdaloid. amygdaloid. native copper ore 55 Figure Figure 28: 28: Outcrop map of of the the Allouez—Bumbletown Allouez-Bumbletown Hill Hill area. area. 57 Figure 29: 29: Map and section of the Greenstone flow between Seneca and the the Cliff Cliff Mine. Mine. 61 Figure 30; Figure 3O Map and section section of of the the Greenstone Greenstone flow flow near near Phoenix. Phoenix. 66 66 Figure Figure 31: 31: Stratigraphy of the Portage Lake Volcanics Volcanics above above the the Greenstone flow. flow. Greenstone 68 68 Plot of K20 and P205 content of 106 individual individual Portage Lake Volcanic flows flows in in stratigraphic stratigraphic order. order. 69 69 Schematic cartoon cartoonofdepositional Schematic of depositional environment environment of of the the Copper Harbor Conglomerate. Conglomerate. 83 83 Measured section of Copper Harbor Conglomerate at Dan's Dants cartoon of of the the depositional depositional environment. environment. Point and cartoon 84 84 Geologic map showing andesitic dikes near Mount Bohemia and occurrence occurrence and and paragenesis paragenesis of of secondary secondary and and opaque opaque and in the the dikes. dikes. minerals in 90 90 map and development of Sketch map of the the Keweenaw Keweenaw Fault Fault in in of Deer Deer Lake. Lake. vicinity of 93 93 Figure 26: 26: Figure 27: 27: Figure Figure 32: 32: Figure Figure 33: 33: Figure 34: 34: Figure 35: 35: Figure Figure 36: 36: Figure 37: 37: Figure 38: 38: Schematic illustration of the the funnelling effect on on Schematic illustration of funnelling effect fluids, Kingston Kingston conglomerate. conglomerate. mineralizing fluids, 102 102 Results of gravity gravity measurements across the Bear Lake on Map Map 29. 29. traverse plotted on 108 108 x �LIST OF TABLES Page Table 1: 1: Secondary minerals found found within within the the Portage Portage Lake Volcanics. Volcanics. 11 Table 2: 2: Major—element Major-element composition composition of of the the Kearsarge Kearsarge flow. flow. 51 Table Table 3: 3: Volume percent amygdule minerals from mapped assemblages shown in in Figure 26. 26. 54 Average major—element major-element composition of the the Scales Creek Creek flow. flow. 57 57 Table 4: 4: Table xi �INTRODUCTORY NOTES ON THE GEOLOGY OF THE KEWEENAW PENINSULA PENINSULA General Background The Mid-Continent Mid—Continent Rift Kansas to Lake Superior Superior Rift System extends northeasterly from Kansas to Lake It was was formed and then southeasterly through and through lower lower Michigan Michigan (Fig. (Fig. 2). 2). It formed about 1.1 1.1 to 1.2 b.y. b.y. ago ago (Keweenawan age) by by extensional extensional thinning of the the rigid rigid Precambrian Precambrian to 1.2 (Keweenawan age) thinning of Superior crustal block (Kiasner (Klasner and and others, others, 1982). 1982). Present day crustal thickness thickness the Lake Superior region, region, however, however, is is between between 40 40 and and 50 50 Km, Km, which which is is thicker thicker in the than than adjacent areas areas (Halls, (Halls, 1982). 1982). -— Peninsula is is located located on on the the margin margin of of the the Lake Lake Superior Superior Basin, Basin, The present Keweenaw Peninsula one of of the one the basins within the the Mid—Continent Mid-Continent Rift Rift System System (Fig. (Fig. 3). 3). The volcanic and sedimentary rocks rocks on the northwest side side of of the the Keweenaw Keweenaw Peninsula Peninsula generally generally dip dip toward Lake Superior and include the Portage Lake Volcanics, moderately toward Volcanics, Copper Copper Conglomerate, Nonesuch Shale Shale and and the the Freda Freda Sandstone. Sandstone. The Jacobsville Sand— SandHarbor Conglomerate, stone stone occupies the southeast side side of of much of of the the Keweenaw Keweenaw Peninsula Peninsula and and is is in in fault along the the Keweenaw Keweenaw Fault. Fault. The Jacobs— Jacobsfault contact contact with the Portage Lake Volcanics along ville Sandstone is however, it it is probably slightly younger than the the Freda Sandstone, Sandstone, however, is still most most likely upper Keweenawan in is still in age age (Kalliokoski, (Kalliokoski, 1982). 1982). At some time after the deposition of basin filling filling sediments, sediments, the Lake Superior region was was subjected to compression roughly region roughly normal normal to to the the basin basin axis. axis. These stresses in the the Keweenaw Keweenaw and and Isle Isle Royale Royale Faults, Faults, both both high high angle reverse reverse stresses re~ulted reulted in faults faults near near the margins of the the Lake Superior Superior Basin Basin (Fig. (Fig. 3). 3). This faulting steepened the dips the Peninsula Peninsula and and on on Isle Isle Royale. Royale. Definite age the dips of of strata exposed on both the relationships between between reverse reverse faulting faulting and and deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone relationships are unclear: unclear: faulting syn- or wholly post—depositional. post-depositional. faulting may may be partially syn— The Lake Superior Syncline was affected affected by aa regional regional burial metamorphic and/or hydrothermal event. event. Remobilization of many elements, elements, particularly within the the Portage Lake Volcanics, Volcanics, caused lava flow caused strong alteration of of lava flow tops tops and and interbedded interbedded concon— glomeratic units. units. Native copper deposits of the the Keweenaw Peninsula are believed to to formed wholly or in in part the deposition of of the the Freda SandSandhave formed part after after the of much or all of stone (White, (White, 1968). 1968). Paleozoic geologic geologic processes processes were were largely largely atectonic. atectonic. Sediments associated with the the Michigan basin probably once covered the the Keweenaw Peninsula, Peninsula, as evidenced by the the isolated limestone at at Limestone Limestone Mountain Mountain and and Sherman Sherman Hill, Hill, isolated occurrence of of Ordovician limestone about 20 miles south about south of Houghton. The present day landscape of the the Keweenaw Peninsula is strongly strongly influenced by Pleistocene glaciation. is glaciation. Stratigraphy The bedrock geology of the the Keweenaw Peninsula consists of five major stratigraphic units. Portage Lake Volcanics, Volcanics, Copper Harbor Conglomerate, Conglomerate, Nonesuch Shale, Shale, Freda Sandstone and Jacobsville Sandstone Sandstone (Figs. (Figs. 33 and and 4). 4). The accumulated maximum thickness of of these these units units is is over over14,000 14,000in. m. The bedrock in the Keweenaw Peninsula is unconformably capped by a variety of is of glacial glacial deposits. deposits. �2 2 A. o0 -= KM t000 1000 KM ORIENTATIONS ORIENTATIONS OF SEGMENTS SEGMENTS OF THE MIDCONTINENT RIFT RIFT B. ---1\ l. I "----... N670,E N67 E "~ f, , 1. ----,j--, , ~ 0 N38 E( i---~~ ;:'-3~'E \ , 1 j 2: Location of the the Mid—Continent Mid-Continent Rift Rift System. System. A. Major Proterozoic A. Figure 2: rifts of of North North America America (from (from Burke, Burke, 1980). 1980). B. B. Orientation of and Paleozoic rifts individual the Mid—Continent Mid-Continent Rift Rift System System (from (from Kiasner Klasner and and others, others, individual segments of the 1982). �r- lie i ~ " II iA*' I 0 - Nipigon Sand,,,,",,. o JACOBSVILLE-BAYFIELD UP UPTO TO5000'+ 500O I f Cambrian &nd _ latesa: Kewc:etUlwu 49. '9" ONTARIO '\ Coppc:r Harbor Conalomcf1ue -/'-'-, '\;Z~'-S~10' /",-, - ""~O'~';ES o Kewecnaw&.l'l voleank: s.cquence, including Portage Lake Voleanic;s ,- __ ~ FREDA SANDSTONE SANDSTONE UP TO UP 70 12,000'+ 2000+ -1030 Ma (m,n.) IO30Mo(n,n.) 0:: W 0.. 0.. 0 MINNESOTA =:l .,. aa.. :3 :::> 47. 0 o 0:: (.!) (0 « WISCONSIN o I 50 I I o 45~ 45- I .,. I 93" I i ... 10(1 0:: I~"",""ES 100 I $0 ill , I ::2: \~')(Il(')Ll£"1RES I I .,. J 85" « C-) u LU w 0:: aa.. LAKE SUPERIOR REGION—distribution of of selected selected rock units. SUPERIOR REGION-distribution units, o0 —• :° .nç•0 .0 zz I— I- z Z COPPER HARBOR CONGLOMERATE 350' 350 -7000' -7000 zz « ~ I040Mo -1040Ma zz LU w UJ w 3: LU w 0:: o0 0:: 0 o Y: LU W aa.. 11 a.. PORTAGE LAKE PORTAGE VOLCANICS 9000' 9000 -15,000'. -(5,000. ::J I (include unnamed ufl0med (Include formation in west UP) formation west U.P.) VW ·YW ThUNDER BAY THUNDER REGION REGK>N KEWEENAW 1Sl..£ ROYALE [,lK£ SUPt.RIOR S£ ct jjjp LU W 1 .J P£HIN$ULA o co :E~ VERTICAL SCALE VERTICAL EXAGGERATED EXAGGERATED SOUTH RANGE RANGE SOUTH VOLCANICS (North Shore ~ Volcanics) Volconics) G]J t'ostvolcanic rrvludrg Poslvolcamc sodimenbo sc:dimenUry rocks. rocks. including the Copper Copper Harbor Harbor Conglom.::rale Conglomerate the tntrrbnddnd volcanic sedimentary ro<:h. rnck,. InltrbeJded VOIcMic and and seJimcntary nolading the the Portage Portage Lake Lake VolcanICS 'olratncs Including Prevolcanic Pynvolcanic rocks rock, a: indrcale relative relative directions directions Arrows indicate of movement along faults BESSEMER & BESSEMER B BARRON BARRON QUARTZ lIES QUARTZITES LU w ~ LAKE LAKE SUPERIOR SUPERIOR BASIN—cross BASIN--cross section. MIDDLE - I BASEMENT PRECAMBRIAN ,v•°°: I Figure 3: 3: Simplified geologic map, map, cross—section, cross-section, and and stratigraphic stratigraphic column column of of upper upper Precambrian rocks in the western Lake Superior region (map and cross—section from rocks in Lake Superior region (map and cross-section from Huber, column from from Daniels, Daniels, 1982). 1982). Huber, 1975; stratigraphic column w �4 NE SW NATIVE COPPER < aw 2 0 2 •° . .4 EEl > wo 0a—a- .4 F MINES — 2000 —, oo —1 1000 2000 3000 — 4000 5000 €000 — Location at onion within atratigraphic anc lion Aanraalmnln upFnn limIt at apiaatn & aaa'tn Approalmate Figure lawn, lion It at A. Generalized geologic map of upper Precambrian rocks of western Upper 4: B. GeneralPeninsula, Michigan. Hatched area is represented in cross—section in B. ized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor (modified from Stoiber and Davidson, 1959). The major marker horizons and mines are shown. The dashed and dotted lines represent the approximate stratigraphic limits of secondary epidote and quartz and prehnite respectively. �Portage Lake Volcanics The Portage Lake Volcanics is a succession of more than 200 individual basaltic lava flows with a total thickness of 2500 m to 5200 m (Butler and Burbank, 1929; Huber, 1973; White, 1968) (Fig. 4). White (1960) recognized these volcanics as a thick pile of subaerial tholeiitic flood basalts. They are the product of rift zone magmatism and are comparable to the rift zones of East Africa and Iceland (Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 and 1982; White 1960 and 1972). Volcanism was apparently controlled mainly by eruptions from fissures located under Lake Superior. The Portage Lake Volcanics are others, 1982). about 1,100 m.y. old (Van Schmus and Most of the lava flows are difficult to follow laterally with confidence. The Scales Creek, Kearsarge and Greenstone flows are the best documented laterally continuous flows. The Greenstone flow can be correlated to Isle Royale (Huber, 1975; Longo, 1982). There are thin conglomerate and sandstone beds throughout the section and these are excellent marker horizons (Fig. 4). The sediment inter— beds in all but the uppermost part of the Portage Lake Volcanics have been given names and are shown on the maps included in this field guide (Fig. 5). The inter— bedded sediments make up approximately 3 to 8% of the formation (White, l971a). The conglomerates of the Calumet area the host rocks for large native copper deposits. The lithology of the conglomerates is dominated by clasts of rhyolitic volcanic rocks (Merk and Jirsa, 1982). The frequency of interbedded sediments increases in Eventually volcanism waned and sediment deposition the upper part of the formation. became dominant, the overlying Copper Harbor Conglomerate. The dominant composition of the lava flows of the Portage Lake Volcanics is tholeiitic basalt. Dikes of mafic and intermediate composition cut the volcanic pile but are as unconmion. a whole Silicjc. volcanic and subvolcanic rocks comprise less than 1% by volume of the exposed Portage Lake Volcanics (Bornhorst, 1975; Grimes, 1977; Robertson, 1974; Robertson and others, 1979). They tend to be in the lower part of the stratigraphic section in the Keweenaw Peninsula (Fig. 6). The composition of volcanic rocks of the Portage Lake Volcanics was affected by both Primary magmatic differentiation has long been igneous and metamorphic processes. recognized both within and between tholejitic flows (Broderick, 1935; Broderick and For example, the Greenstone flow, the thickest Hohl, 1935; Cornwall, l95la and b). individual flow in the formation (Figs. 4 and 5), is chemically stratified due to Copper may have conceninternal differentiation (Cornwall, l951b; Longo, 1983). differentiation trated in the pegmatitic and more importantly in the flow tops. Work by Scofield (1976) demonstrated that copper can also be concentrated in the Rose and Grimes base of individual flows by gravitational setting of magnetite. (1979) showed the existence of three magmatic cycles within the Portage Lake Vol— canics which initiate with basalts that have high incompatible element abundances. The degassing of volatiles during and after eruption in an oxidizing subaerial environment was also important in that it allowed degassing of SO2 (Cornwall, 1951c). This created a sulfur deficient environment which favored the later deposition of native copper. A third pre—metamorphic process was deuteric or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. Ljvnat and others (1976) used '3D and '3180 to show that the basalts have undergone extensive isotopic exchange with low—temperature meteoric waters prior to metamorphism/hydrothermal mineralization. After emplacement the volcanic pile was subjected to extensive low—temperature, low—pressure hydrothermal/metamorphic alteraThe Portage Lake Volcanics on the Keweenaw Peninsula are in fact a classic tion. �6 Feet FR EDA SANDSTONE ci ,.,', Lava unit 0 AND fn .. COPPER HARBOR 0 NONESUCH SHALE CONGLOMERATE 0 06 0.-A 0 00 0 12,000 c a 15,000 =- - Lava unit c 000 o — QO 4 00 0 0 0 0-0 •0 0 o00 000 00 0 •2.0 . 00 . 0 0 0 11,000 c 14,000 1. .: PORTAGE LAKE LAVA SERIES Lava unit ci :0 10000 c 13,000 . Figure Columnar stratigraphic section of rocks northwest of the Keweenaw 5: Fault in the Calumet—Ahmeek area (from White and others, 1953). The labels for units within the Portage Lake Volcanics are consistent with those used on the maps in the field guide. �C phc paf T Hancock conglomerate (No. 17) Ashbed flow pp 9000 — -— Pewabic West conglomerate (No. 16) pk Kearsarge flow pv Wolverine sandstone (No, 9) 4000- poc Old Colony sandstone (unnumbered) 3000pg Greenstone flow pa Allouez conglomerate (No. 15) 4 orta - Lak 'r,Icanics ph Houghton conglomerate (No. 14) 7000 pi Scales Creek flow psc 2000 - Iroquois flow —— = pc - conglomerate TI (No. 13) 1000P0 pkc flow Kingston conglomerate (No. 12) Pcc Copper City flow PS 5000 St. Louis conglomerate (No.6) Figure 5 continued. �8 STUDY AREA Lake Superior COPPER HARBOR INDEX MAP OF NORTHERN MICHIGAN EAGLE RIVER Fish Cove I..: LacLo_ atiot Lake Cambrian Jacobsvil le Sandstone Upper Keweenawan Precambrian loge - .-.•. . . 10 Miles Figure 6: Portage Lake Lava Series Intrusive or extrusive body Bedrock geology of the Keweenaw Peninsula showing the location of silicic to intermediate volcanic and subvolcanic rocks (from Robertson, 1975). �9 locality of abundant and widespread low temperature alteration minerals (Table 1). Penetrative deformation did not accompany the metamorphic episode and primary textures are preserved even in the most intensely recrystallized areas. Copper Harbor Conglomerate The Copper Harbor Conglomerate conformably overlies and locally interfingers with the Portage Lake Volcanics (Fig. 3). It varies in thickness from about 100 m to 1800 m. The Copper Harbor Conglomerate is a red—brown basinward—thickening wedge of volcanogenic clastic sediments. These clastic sediments fine distally and up— section. Sandstones are lithic graywackes and conglomeratesare composed of volcanic clasts with a ratio of mafic to intermediate + silicic composition of about 2:1 (Daniels, 1982). Daniels (1982) has interpreted the Copper Harbor Conglomerate as Mafic to intermediate lava flows are a prograding alluvial fan complex (Fig. 7). interbedded in the exposed Copper Harbor Conglomerate (Fig. 5). These lava flows are termed the Lake Shore Traps and occur predominantly within the middle section of the formation. Nonesuch Shale — The Nonesuch Shale is a succession of gray—black siltstone, shale and sandstone which overlies and interfingers with the Copper Harbor Conglomerate (Fig. 3). The Nonesuch has a thickness of between 40 m and 215 m. The Nonesuch was deposited in a reducing, rift—flanking lacustrine environment initiated through disruption of drainages (Fig. 7) (Daniels, 1982). This differs from the over and underlying redbeds that formed in an oxidizing environment. Freda Sandstone The Freda Sandstone is a cyclic succession of red—brown, ferruginous, sandstone The Freda and mudstone overlying and gradational with the Nonesuch Shale (Fig. 3). It is dominantly fluvial in origin with has a maximum thickness of over 3700 m. The top of this greater compositional maturity than the Copper Harbor Conglomerate. formation is not exposed. Jacobsville Sandstone The Jacobsville Sandstone is a red to bleached white succession of coarse—to—fine— grained feldspathic and quartzose sandstone with varying amounts of siltstone, shale and conglomerate which rests in fault contact with the Portage Lake Volcanics in the Keweenaw Peninsula. Elsewhere it can be found overlying Middle Precambrian basement. Jacobsville is probably slightly younger than Freda Sandstone. Jacobsville has a Sandstones are fluvial in origin whereas conmaximum thickness of over 3,000 m. glomerates are believed to be alluvial fan deposits (Kalliokoski, 1982). Structure Structure of the Keweenaw Peninsula is dominated by the Keweenaw Fault (Fig. 4), a high angle reverse fault where older Portage Lake Volcanics are thrust to the Both units are affected by this major northeast over younger Jacobsville Sandstone. the normally flat—lying Jacobsville Sandstone is often strongly tectonic feature: deformed by drag folding near the fault contact and the Portage Lake Lavas are often highly fractured. The Keweenaw Fault cuts off the base of the Portage Lake Volcanic Series along its entire strike length so that the total stratigraphic thickness �__ 10 NONESUCH SHALE DEPOSITION POSSIBLE "LAVA-DAMMED LAKE" MODEL FOR SANDSTONE FREDA STREAM BRAIDED FLUVIAL BASIN MA IN BASIN CENTRAL FLUVIO-DELTAIC 0 00 0 O - LUVIQ°Th 0 o 00 0 o° x0 x 0 0 0 0 PORTAGELAKExVOLCxANICSxxX x O 0 0 x x _— o0xxXxx XXX 0 CONGLOMERATE 0 o_—T 0 ALLUVIAL°PLAIN OCOPPER HARBOR 0 0 x 00 x - x - x : x x tINTERFLOW 0 0 SEDIMENTS X -------- ±±± RELATIVE PAL ED F LO W DIRECTIONS Figure 7: Schematic diagram showing the interrelationships between major stratigraphic units found northwest of the Keweenaw Fault in the Keweenaw Peninsula (from Daniels, 1982). x �:ii Table 1: Secondary minerals found within the Portage Lake Volcanics, Keweenaw Peninsula, Michigan (from Butler and Burbank, 1929; Stoiber and Davidson, 1959; Jolly and Smith, 1972). Widespread Minerals Locally Important Minerals Rare Minerals Laumontite Analcime Apophyllite Prehnite Sericite Atacamite Pumpellyite Orthoclase /Nicrocline Bowlingite Quartz Chalcedony Brucite Epidote Thompsonite Chlorastrolite Albite Natrolite Chrysocolla Chlorite Chabazite Cuprite Hematite Native Silver Faujasite Sphene Sulfides Fluorite Calcite Arsenides Powellite Native Copper Datolite Serpentine Heulandite Stilbite Ankerite Tenorite Sulfates Tourmaline Clay Minerals Whitneyite Wairakiite �12 The regional tectonic as well as the total displacement along the fault is unknown. context of the compressional stresses which caused development of major reverse faults is unknown at the present time, although it is probably unrelated to processes which formed the Mid—Continent rift. — The Keweenaw strata dip moderately northwesterly toward the centr of the Lake This Superior Basin and their dip angles increase toward the base of the section. is in part due to modification attributed to the Keweenaw Fault, but White (1960) has demonstrated syn—depositional downwarpage of the basin. Thus, lava flows and sediments formed wedge—shaped beds thickening basinward such that a relatively constant horizontal datum level was maintained throughout the life of the basin. Smaller scale, post—depositional folds are also present as broad synclines and anticlines (wavelengths from 5 to 10 miles) (Fig. 8). The regional context of these folds is not clearly understood, however, they appear to predate major reverse Late high angle faulting occurred throughout the area and produced several faulting. major offsets of the Keweenaw Fault. This type of fracturing and faulting is partiSignificularly abundant in the upper portion of the section northeast of Mohawk. cant deposits of massive native copper later filled many of these cross—cutting channelways (summarized from White, 1968). Mineralization and Alteration The Keweenaw Peninsula is the location of a dormant billion—dollar copper mining district. From 1845 to 1968 the mines of the Keweenaw native copper district produced about 11 billion lbs. of refined copper (Weege and Pollack, 1971). The major ore producing horizons are geographically restricted to a 45Km long belt within the Portage Lake Volcanics in the Keweenaw Peninsula (Fig. 8a). There is a close relation— ship in both time and space between native copper mineralization and alteration in the Native copper, the principal ore mineral in the Portage Lake Volcanics (Fig. 9). Keweenaw Peninsula, occurs in amygdaloidal and brecciated flow tops, interflow conglomerate units, and fracture systems (Butler and Burbank, 1929; White, 1968 and 197la). The predominant native copper deposits are lenticular blanket—like ore bodies that are found along certain stratigraphic horizons such as the tops of lava flows and conWeege and Pollack (1971) estimated that 58.5 percent of the district glomerate beds. copper production came from flow top ore bodies and 39.5 percent came from conglom— erate ore bodies. The remaining 2 percent of copper production was from fissure (or vein) ore bodies. There are three main varieties of lava flow top recognized in the Keweenaw native 1) fragmental or flow top breccia; 2) nonfragmental! cellular copper district: or vesicular basalt; 3) "scoriaceous" or flow top breccia with a sandy or silty White (1968) estimated that 21 percent of the lava flow tops in the Portage matrix. Lake Volcanics are brecciated (fragmental). These flow tops consist of a rubble of The interstices between fragments and the vesicles are vesicular and massive lava. commonly filled with secondary minerals. Most of the major flow top (amygdaloid) copper ore bodies are of the fragmental type. White (1968) has estimated that uppermost 5 to 20 percent of most individual lava flows is vesicular and contains between 5 and 50 percent vesicles which are commonly filled with secondary minerals. The abundance of amygdules decreases downward and the middle and lower parts of flows The tops of these flows are locally termed cellular are amygdule—free massive basalt. Cellular amygdaloid may have traces of native copper but and often have smooth tops. �1968). White, (from district copper native Keweenaw B. the of Folds amygdaloids. in quartz of limit northwest approximate the is line dotted The amygdaloid. (ashbed) Atlantic 7) and amygdaloid; Royale Isle 6) amygdaloid; Osceola 5) amygdaloid; Pewabic 4) amygdaloid; Baltic 3) amygdaloid; Kearsarge 2) conglomerate; Hecla and Calumet 1) production: of order in number, bold the by identified are deposits Major 1968). White, (from district copper native Keweenaw the of map Geologic A. 8: Figure 3 •l �14 Eagle Harbor Section • o,f4 FEET Top of Portage Lake Lava Seriea I Hancock Congl. 2000 I-Il I Greenstone Flow Allouez Congl. — Houghton Congi. Calumet & Hacla Congl. 0 I - I - 2000 King8ton Congl. PUMPELLY lIE ZONE Kearaarge Amyg, 4000 Scale8 Creek Amyg. 8000 Upper Limit of Zone at Dehydration Gratlot Flow Bohemia Congl. 8000 10,000 Keweenaw Fault - I EPIDOTE ZONE 12,000 Micwcline — Chlorite —— — Epidote — — — — Pumpellyite — — — Prehnite — — — Copper — — — — Datolite — — — — Silver — — — — Ankente — — Quartz — — — — — - Sericite — — — — Colcte — — Arsenides — Sulfides — .-_ — — — — — Albite — — .._ Aduloria — — — — Saponite — — — Laumontite — — Analcime — — Sulfates(barite,anhydrrte, gypsum) Figure 9: A. Distribution of secondary minerals in the Eagle Harbor section of the Portage Lake Volcanics (compiled from Butler and Burbank, 1929; Jolly, 1974; Jolly and Smith, 1972; Stoiber and Davidson, 1959; White, 1968). Location of section is between Copper Falls and Delaware Mines shown in Figure 4. B. Paragenesis of secondary minerals in the flow tops and veins (from White, 1968). Solid black symbols are the more abundant minerals. Secondary minerals shown here are nonmagmatic and not of supergene origin. �15 — A few smooth topped flows show a tendency no ore deposits are only of this type. forming what are locally for the amygduies to be laterally interconnected in bands, important host rock for ore termed "coalescing cellular amygdaloid". This is an "ScoriaceouS" amygdaloid is used locally for flow top breccia at the Quincy Mine. filled with sandy or silty in which interstices between vesicular fragments are mineralized example of The Ashbed amygdaloid is the onl-y significantly detritus. this type. — native copper deposits, Conglomerates interbedded with lava flows are host for major of copper distrifundamental control The particularly in the vicinity of Calumet. Permeability is decreased by conglomerate. bution is the permeability of the host greatly on sedimen— Localization of ore depends abundant fine detrital material. which might bedrock topography tological and environmental factors, such as the conglomthickness of influence location of a stream channel resulting in differing erate. — right deposits are tabular and commonly crosscut the bedding at nearly Large masses of native copper weighing many tons were first angles to strike. the fissure deposits. These deposits are economically much less discovered in types. important than the other Fissure Copper sulfides are a minor constituent of the system, and are found as small veins cutting the flow top native copper deposits, joint—coatings in the conglomerate units, and in association with Mt. Bohemia intrusive (Butler and Burbank, 1929; Copper sulfidesandarsenides are paragenetically Broderick, 1931; Robertson, 1975). Significant copper sulfides with minor late in flow tops and conglomerates (Fig. 9b). native copper also occur at the base of the stratigraphically higher Nonesuch Shale and top of the Copper Harbor Conglomerate (Brown, 1971) at White Pine, approximately 70 Km southwest of most of the discovered mineralization in the Keweenaw Peninsula. The solutions that formed the White Pine deposit may have been related to those which formed the deposits in the Keweenaw Peninsula (Ensign and others, 1968). Vesicular and fragmented flow tops of the Portage Lake Volcanics were prevasively altered by hydrothermal fluids, producing low temperature metamorphic mineral associations occurring as amygduie and vein fillings as well as whole rock replacements in the most permeable hOrizons. The systematic metamorphic zoning varies vertically within the volcanic pile and is equivalent to zeolite, prehnite—pumpellyite facies (Jolly and Smith, 1972; Stoiber and Davidson, 1959), and possibly lower greenschist facies (Fig. 9a). The copper deposits lie stratigraphically within the pumpellyite The copper, in the deposits, may have been leached from dehydrated lava flows zone. (epidote zone) in the deep parts of the pile and migrated up dip and precipitated in the zone of hydration where conditions were sufficiently reducing (Jolly, 1974; Scofield, 1976; White, 1968). These workers and Cornwall and Rose (1957) suggest that most of the copper was probably initially tied up in Fe—Ti oxides and their oxidation released the copper. The oxidation reactions of magnetite to hematite and pumpellyite to epidote may occur along with native copper deposition (Jolly, 1974). The intensity and degree of alteration varies as a function of position within individual flows, position in the volcanic pile, and proximity to cross—cutting fractures (Jolly and Smith, 1972). Local controls, such as pre—alteration composition, appear to govern the assemblages of final alteration products and their major—element compositions. Figure 10 shows a summary of known elemental mobilities and a schematic picture of alteration conditions. �PERMEABILITY LITHOLOGY DIA GNOSTIC MINERALOGY Added to flow top Redistributed within flow Hgh '''''' e'°r : FLOW TOP - FLOW INTERIOR Low , None —r---- Pumpellyite Epidote Metadomain - Ca Al f .. Albitized Basalt Albite Chlorite Unmetamorphosed Basalt Ca—Plagiociase 16 ELEMENT MOBILITY from Outside flow - 114 Na Clinopyrosepe Olivme Si - - 1 H2 Lost from flow top Remained Immobile — K, Fe, Ti, Mg, Zn Cu —w- Cu(s) HO—*-HO 2 (p) 2 Ni Ce) Elements Remained Immobile I. DEPTH 4. TEMPERATURE I Basal chill zone ii Least—altered flow interior lIE Amygdular flow top Arrows denote tluid movement Figure 10: A. Possible elemental mobility pattern in an idealized lava flow in the pumpellyite and epidote zones within the Portage Lake Volcanics (based on chemical data of Jolly and Smith, 1972; Jolly, 1974; Scofield, 1976; Stoiber According to Jolly (1974) Cu and H20 were derived from and Davidson, 1959). the epidote (dehydration) zone and deposited in the pumpellyite (hydration) zone. Diagrammatic regional model for the Portage Lake Volcanics showing local B. thermal/chemical gradients superpositioned on the regional geothermal gradient and showing the movement of fluids along flow tops and bottoms and through frac— tures (modified from Jolly and Smith, 1972; Scofield, 1976). �17 ROAD LOG AND STOP DESCRIPTION Mileage MAP 1 0.0 Assemble at the Memorial Union on University. Begin the field trip the northeast side of the Union. on a kame terrace to the south of the campus of Michigan Technological from the circular drive lqcated on The Michigan Tech campus is located the Portage Lake. 0.1 Right turn. 0.2 Immediately after there is a right turn on to Townsend Drive. Left turn. The Quincy Mine can be seen on the ridge on the skyline. 0.55 Left turn on Agate Street, where we go up the steep hill on the south side of the Portage. We are climbing off of the kame terrace. 0.8 Right turn on Seventh Street. 1.0 STOP 1. Scales Creek flow on Seventh Street, City of Houghton. This stop is marked by a prominent ridge of ophitic basalt, which is an outcrop of the Scales Creek flow, one of the great Keweenawan flows, which can be traced continuously for a strike length of more than 160 Km along the Peninsula. It is about 70 m thick, with an amygdaloidal top which is typically not resistent and a prominent, ridge—forming, ophitic core. The ridge at this site can be followed down hill all the way to Shelden Avenue, where it is covered by glacial deposits. It can be traced across the valley, where it passes through the Ripley School, a prominent brick building across the Keweenaw Waterway. This bearing, about N3OE, is the regional strike of the Portage Lake Volcanics which dip about 500 to the NW. Another clue to the attitude of the rocks is given by the Quincy #2 shaft house on the horizon which heads up an inclined shaft down dip along the amygdaloidal ore bodies of lava flows just over 2000 m higher in the Portage Lake section. Throughout the Portage Lake section between Baltic and Mohawk, most amygdaloidal and conglomerate zones show well developed zeolite and prehnite—pumpellyite facies metamorphism and native Cu mineralization. At this site the amygdaloids just below the Scales Creek flow are strongly mineralized. One mine, the Sheldon Columbian, operated just a few hundred m to the east in the early 1900's. This same horizon is exploited by a series of shafts called Isle Royale Mines, for several km to the SW. Stop 2 is at one of these mine dumps. The most obvious geomorphological feature here is the Keweenaw Waterway, The waterwhose origin was thoroughly investigated by Warren (1981). way formed in a fault zone like many which crosscut the Portage Lake stratigraphy. A bedrock valley, more than 200 m deep formed along the fault as a result of stream superposition through a cover of flat—lying This valley, like others on the Keweenaw, was deepened and sediments. widened by glacial erosion, in a fashion similar to the finger lake The complex glacial deposits, consisting of region of New York State. moraines, terraces, varved clays and gravels were the result of the pattern of ice retreat from the region, which had profound and complex effects on the drainage patterns. �/ 71! /, )- - II 55 NJ/' C ft7 D— G N I - -. IStOP 2• -. // / J /1 /11 i// /1 9SGIS1eYaChASHAFT —/ / Li -- d \\\\ P L - 12 p /_ - K E C •==- — I / I ' H San ds1;i one ••°' - _ji _____ C0LL6E OF MINING AND YE CN0L0G \_y' __________________ 46' SSa 907 si _________ _____ \/ I A 1/ 1059 4 +1 /1 R2 Jdevii1e - - -: . 1M7 --- L . --;•: //r '-4 / A ______ T -- — 10 II /R 567/ -7 0 607 .4- - />7) // -/ t.• I - // - H - — NC - Map4 - , — - •MAP 1 �19 1.1 Left turn on Portage Street. 1.25 Grand Portage Mine dump on left. 1.45 At this spot the Scales Creek ridge is Near the Houghton water tower. slope exposed higher on the south of the Keweenaw Waterway. There are many bald knobs with more or less east—west trending deep glacial grooves on them. To the east of the prominent ridge, there are many mine oprIings from the series of Isle Royale shafts. The Adams Township takes its water supply from these Isle Royale mines which are now filled with water, and this is the source of water for Hancock and several other towns. 1.55 Cross Sharon Avenue and continue on Portage Street east of the City of Houghton fire station. 2.15 Right turn immediately followed by a left turn so we are now on Bridge Street heading south. 3.0 Entering Dodgeville. On the right hand side of the road is one of the prominent Isle Royale mine dumps. 3.2 Center of Dodgeville. If you turn on the road to the right through the Trailer Park, there is access to the Isle Royale mine dumps from Shaft No. 4 and 5. The Isle Royale Mine is described at Stop 2, continue ahead. 3.6 Junction to the Green Acres Road and make 3.7 STOP 2. Isle Royale Shaft No. 6 a right turn. mine dump on the Green Acres Road. The Isle Royale mine worked the top of the Isle Royale flow. Production from the Isle Royale amygdaloid began in 1855, the mine closed in 1948. A total of about 350 million lbs. of refined copper was removed from this mine (Weege and Pollack, 1971). The Arcadian Mine (see Map 4) may also work the Isle Royale amygdaloid. The Isle Royale flow varies in thickness but is about 70 to 150 ft. thick and lies just below the Scales Creek flow discussed in Stop 1. It dips about 50 to 60° to the northwest (Fig. 11). A gentle fold accounts for the curvature of the flow (see Map 1), Isle Royale syncline. The flow from the top down is characterized by fragmental zone, banded amygdaloid, foot inclusion zone, The fragmental zone consists of irregular fragments and massive main trap. of amygdaloid and fine—grained basalt ranging from small grains to tabular The vesicles and spaces between the blocks several feet in long direction. secondary minerals. The banded amygdaloid is an fragments are filled with considerable area. Amygdules are commonly abundant unbroken rock body over zone a banded appearance. Below the fragat certain horizons giving this amygdaloid is the foot inclusion zone which is indemental zone or banded foot inclusion The finite patches or inclusions of amygdaloid basalt. devoid of amygdules (summarized zones grades into massive basalt practically from Butler and Burbank, 1929). �L_, I. _J —, - - Le Vc ific Ss S iac 11: Cross section A—A' on Map 1 (from White, 1956). Labels are as follows for the Pewabic West conglomerate (pp), Creenstone Portage Lake Volcanic Series (P) and its subunits: flow (pg), Allouez conglomerate (pa), Calumet and Mecla conglomerate (pc), Kingston conglomerate (pkc), National sandstone (pn), Kearsarge flow (pk), Wolverine sandstone (pw), Scales Creek flow (psc), Bohemia conglomerate (pb), St. Louis conglomerate (ps), Baltic conglomerate (pbc), and Unnamed conglomerate (pu). Figure P ...vIIIe A' �21 Butler and Burbank (1929) recognized two distinct periods of alteration. The earliest alteration was oxidation which caused the development of This oxidation could essenhematite, which produced reddened basalt. alteration shortly after eruption. tially represent deuteric The second after the period of alteration was probably flows had been tilted. This period was complex and resulted in deposition of native copper. This stage :L divisible into three substages: 1) An early stage of deposition of epidote, pumpellyite quartz, calcite, most of the native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate stage characterized by the development of sericite with quartz, calcite, anhydrite, gypsum and minor barite; 3) a final stage of copper sulfides and arsenical copper accompanied by calcite, sericite, quartz, chlorite, and specular hematite occurring in numerous veinlets. Stoiber (unpubthe following estimate of the lished data) made percentage of alteration the Isle Royale Mine: quartz, 26— minerals on dumps from four shafts of 59; calcite, 5—39; prehnite, 6—32; pumpellyite, 1—17; epidote, 1—10; sericite, 0—12; chlorite, 0—3; K—feldspar, 0—trace. This dump and the ones near Dodgeville are freshly reworked and good specimens of native copper and alteration minerals can be found. 3.9 Junction M—26 at the Copper Country Mall and you are going to make a left turn. MAP 2 5.6 Entering Atlantic Mine. 6.9 Right turn at the sign that says South Range Village Limit and drive about 150 yards into the road and walk to the right through a notch up the hill another 60 meters to Stop 3, the South Range Quarry. NW SE Felsite bed 9 IEE Fragmental amygdaloid i Non-fragmental amygdaloid 190 FEET F(a) Masve basaft PegmatEte layer (a) and zone of thin Figure 12: Geologic profile of the South Range quarry along the northeast wall (from Cornwall, 1951; White, l97lb). Location of the quarry is shown in Map 2, Sec. 17, T54N, R34W. �22 C ;: 52 // p —q w• • . njflfe San .one I �23 STOP 3. South Range Quarry. South Range quarry provides an excellent cross sectional view of a massive to amygdaloid lava flow (Fig. 12) of the Portage Lake Volcanic Series. The base of the section is a conglomerate bed, about 4 m thick; it is exposed This is overlain by an 18 m thick fine— on the main path to the quarry. grained basalt flow, followed by a 42 m thick ophitic basalt flow and finally the lower 17 m of another ophitic basalt flow. The conglomerate is well indurated and consists mostly of pebbles and cobbles of rhyolite with subordinate clasts of basaltic lava set in a sandy matrix of similar composition. The clasts are subangular to sub— The overall character is similar to the Copper Harbor Conglomrounded. This conglomerate is erate which will be seen later in the field trip. one of a number of sedimentary beds which are interbedded with the Portage This particular bed is correlatable with the National Lake lava flows. Sandstone, a marker bed in the Nass—Rockland area. The basalt flow that occupies most the quarry face has features which The characterize the thicker flows of the Portage Lake Volcanics. lower half of the flow is massive basalt, overlain by a zone with progressively smaller pegmatitic layers, topped with cellular amygdaloidal basalt, and at the top a discontinuous layer of flow top breccia (called fragmental amygdaloid). A typical pegmatitic layer, consists of 4 cm to 1.3 m core of green amygdaloidal lava surrounded by a 4—9 cm border zone at the top and bottom. The border zone is composed of a medium to coarse grained aggregate of albite/oligoclase, augite, ilmenite, and magnetite. Pegmatitic layers toward the top of the zone are more amygdaloid. Quartz, prehnite, and a green or red cherty substance occurs in flattened vesicles The pegmatitic layers are products of cooling at the top of the layer. and differentiation as it cooled (description of pegmatitic layers from Cornwall, 1951). Amygdules and interfragmental spaces are filled with Locally the basalt is quartz and prehnite containing traces of copper. intensely epidotized or prehnitized. Outside of the Quarry and to the north are a series of glacially grooved outcrops in which the exposures of the pegmatitic zones are spectacular. Take a right turn on M—26, going into the town of 7.9 Return from Stop 3. South Range. 8.4 At stop sign in South Range, take a left turn. 8.6 Right turn at the church and immediately foiJowed by a left turn as the whole road jogs to the left. 8.7 Entering the town of Baltic. 8.8 Right turn. 9.2 The main road turns to the left, we go to the right on a small paved road driving past a concrete building towards some very large mine dumps. �24 9.4 STOP 4. Baltic Shaft No. 3 Mine Dump. The Baltic, Champion, and Trimountain mines worked the Baltic amygdaloid. Total proThe Baltic Mine opened about 1898, the others opened in 1902. duction from the Baltic amygdaloid was about 1.85 billion lbs. of refined copper which was the third largest producer in the Keweenaw native copper district (Weege and Pollack, 1971). The amygdaloid was developed for about 7 Km along strike and to the 38th level in the Baltic Mine. The Baltic flow is an ophite that varies considerably in thickness but The Baltic amygdaloid in many places is 17 m is around 50—70 m thick. or more in thickness and is composed of fragmental amygdaloid, the average stoping width is about 5—8 m. However, like all fragmental amygdaloids of the district, there are significant variations, e.g. the lode can thin to only a few feet thick composed of trappy or cellular amygdaloid. The lode dips at about 70°NW (summarized from Butler and Burbank, 1929). The abundant minerals associated with copper in the Baltic amygdaloid are Copper sulfides are unusually quartz, pumpellyite, epidote and carbonate. The sulfides characteristically occur in fissures that dip 75 abundant. Most of the copper sulto 900 and strike nearly parallel with the lode. fide in the lode is chalcocite associated with iron—bearing carbonate, there is some bornite and rare chalcopyrite. Native copper is irregularly distributed through the amygdaloid ranging from minute specks to masses weighing several tons. Native copper occurs at the margins of sulfide veins and it may occur with quartz in the center of veins. Sulfides are in general paragenetically late (Fig.9h Introduction) (summarized from Butler and Burbank, 1929). The majority of the dump at this stop is amygdaloid basalt. R. E. Stoiber (unpublished) made the following estimate of the percentages of the seconcalcite, 91; quartz, 5; epidote, 3; dary minerals in the dump as a whole: Paragenetically epidote and chlorite were early minerals; chlorite, 1. calcite, quartz and native copper were intermediate; and copper sulfides Excellent specimens of chalcocite and iron—bearing carbonate were later. can be found on this dump as well as native copper. 9.4 Retrace route in Baltic. 9.9 Stop sign in Baltic, make a left turn to go back in the direction of South Range. 10.1 Right turn, immediately followed at the church by a left turn. 10.3 In the center of South Range, right hand turn off M—26. 10.8 Passing the South Range Quarry, Stop 3. 12.5 M—26 jogs to the right at the center of Atlantic Mine �25 MAP 3 14.7 STOP 5. Glacial Deposit Near Pamida The Keweenaw Peninsula has probably been modified by all of the major glacial episodes of the Pleistocene. During maximum glaciation the entire Keweenaw Peninsula is believed to have been overridden by around 3000 m of ice. The present form of Portage and Torch Lakes is related to the final retreat of the Laurentide ice sheet in the Lake Superior The final glacial advance and stillbasin (shown in Figs. 13 and 15). stand over the Keweenaw Peninsula was made by the Keweenaw Bay Lobe, marked by an end moraine of Wisconsin stage (Fig. 14) (summarized from Warren, 198]). The earliest recognized channel cut by drainage through the Portage Gap area is the Huron Creek channel (Nap 3). The channel is waterworn bedSince there is no delta at the southern end rock due to southward flow. of this channel perhaps the source of water was a large lake where glacial The drainage sediments had time to settle before the water was removed. in Fig. 16 (summarized from pattern through the Portage Gap is shown Warren, 1981). A delta kame is just west of the Huron Creek channel and is the location The sediments, in this dissected knob, show strong of Stop 5 (Map 3). evidence of being deposited by a braided stream closely associated with Extreme variations in grain size and sorting occur within a a glacier. This suggests differing flow regimes during distance of a few meters. Poorly to well—worked unconsolidated sands predominate but deposition. Numerous cut—and poorly sorted pebble conglomerates are also present. Large striated boulders of basalt within fill structures are present. from a nearby glacier. This the gravel and sand must have originated large exposure is capped by a thin (less than one meter) poorly sorted clay till which thickens rapidly to the south; it is about 7 meters thick The later unit may be a flow till(?) at the top of the nearby hill. which slumped off the nearby glacier (description by S. Beske—Diehi and S. Nordeng, Dept. of Geol. & Geol. Engrg., MTU). 15.75 Between Junction of M—26 and US—4l, so turn right on US—4l past the Mobil and Erickson gas stations. 16.2 Excellent outcrop of basalt with exposed amygdaloid on both sides of the road. 16.35 Make a left U—turn back onto US—4l going one way back through the City of 1—loughton. 16.45 Amygdaloidal basalt with pegmatitic zones at Burger King Restaurant, Shelden Avenue, Houghton. This stop is an alternate to the South Range Quarry Stop. Excellent exposures of the cellular amygdaloid and pegmatitic interior of a thin Portage Lake lava flow are found to the west of the restaurant and along Montezuma The flow top is strongly metamorAvenue, just a few steps to the north. phosed with a variety of amygdule minerals of the prehnite—pumpellyite The green color of the basalt is due to the abundance of epidote. facies. Below the amygdaloid the basalt is virtually unmetamorphosed except where thin pegmatite zones cross it. �1I 4 0 6O7 R A T ) —. 4 I '',;ee1cii:.! 1 I 4 G 26 L E — ., �1981). Warren, 1976; Kalliokoski, 14: Figure (from glacier Lobe Bay Keweenaw the of moraine End / / e 80 Kilometers es ii M 0 F 0 Prest, 1975; Huber, (from America North central from retreat ice Wisconsin the during positions ice—marginal Speculative 13: Figure 1969). 46) (Fig. 1257A). Map Canada of Survey Geological 1969, Prest, K. V. (from basin Superior Lake the readvance, or surge, ice major Note Amenca. North central from RETREAT ICE WISCONSIN in H P H B NJ' y,.,. ,.4k,.,b,,,, Sh,,..,,d. K "fl". F 40 U j' ,)" L .• •' 27 �L-\' ii) o 5t - -- - -, - - - -?-- -- S — "0A P E - ( - -' - - .— T -"i /5S5 - S jS ji - !j ' - S -- I _\ S. S SI 5—- - QS.AUL -S-j - -- S - f I -- 1 S -' '< S S I \ /55( S ) - S7 sS S - - // HURP - ( ' )•J / - / At KE - /, .S\ 55 - - : S \_S . I / S 55 / - S S MUWAUKEE - 1 5 / S q S mo0/ S - - S. I :/fj'S.S ,jS/ :-r- S - /5 - \55 I - s - / /- S -S. _S___SS S 5CHICAGO Figure 55 S S S 55S\ /,/ ...5 I 5S / / —-S Enlarged view of ice—marginal positions during Wisconsin ice retreat 15: (from Prest 1969) . Note the major ice readvance in the Lake Superior Basin and withdrawal pattern over the Keweenaw Peninsula. S. �29 LAKE / WfSHBURN // / -.5 / I/ Figure 16: High level drainage through the Portage Gap during the Washburn Stage (from Warren, 1981). �30 16.9 Right turn on US—41/M—26 and crossing the Portage Lake Lift Bridge into Hancock. The bridge was built in 1957, and is designed to accommodate Great Lakes ore boats, who prefer the Keweenaw Waterway route to rounding Keweenaw The present bridge abuts the Hancock side of point in stormy weather. the canal at approximately the site of the old Quincy Mill where the tramway descended Quincy Hill from the mines. MAP 4 17.15 Left turn on TJS—41 into Hancock. 17.35 Right turn and immediately followed by US—41 going to the left but we go straight at 17.4. 17.5 Bear to the left on White Street. 18.0 Junction between White Street and Lincoln Drive which is US—41, we take a right turn. The fenced ground near this locality surrounds an area of recently caved ground, which is thought to be related to shallow stopes of the Hancock Mine. The detection and distribution of such openings is a problem of considerable concern to local authorities, since many mines had shallow workings, since towns grew up adjacent to mines and since maps of the underground workings are incomplete and/or inaccurate. 18.3 Turn off US—41 to the right to the overlook of the Keweenaw Waterway or Portage Lake which is Stop 6. STOP 6. Keweenaw overlook near Quincy Mine. This overlook, near the crest of Quincy Hill, allows a broad overview of all the previous stops and also the best general view of the Keweenaw The features which can be seen are, from east to west (left Waterway (Fig. 17). to right): 1) On the skyline, the knobby terrane of the Huron Mountains, which lie across Keweenaw Bay. The mountains are underlain by the Archean gneisses and granites of the Northern Complex, and are the main source 2) In the forearea for the extensive deposits of Jacobsville Sandstone. ground, underlying the flat topography of Jacobsville Sandstone is clearly The Jacobsville extends from the Keweenaw fault, which crosses visible. the Waterway just east of the Michigan Tech campus, across the Keweenaw The formation is genBay and under the Huron Peninsula (Pointe Abbaye). erally flat—lying, while all of the other rocks of the Peninsula dip north3) Within the town of Houghton several westward toward Lake Superior. ridges of basalt can be traced downhill, the most prominent being the The attitude of the Scales Creek flow horizon, where Stop 1 was made. Portage Lake flows and the alternation of resistent flow interiors and interflow conglomerates with less resistent flow tops makes site investigation work critical for construction projects, to accurately determine For example, depths to bedrock and to make hydrologic interpretations. site investigations of the extensive area south of the main campus, where the Michigan Tech Student Development Complex (visible from the overlook) is now located, provided the focus of several Masterts theses for students in Geological Engineering (Stevens, 1971; Hase, 1973). A �7 dVV i / 28 fl\ / I I // 4 _0 / i I / - 0 "HH< L -' / •/ -- - R - 2Z71L 7t z / r iA .•'.<;:Ir..r /1 // (( I _,_ t! II - r • G I / •0 - / / —: / \\ I. - / I I / • // 2? // / / Wewabic h(' / -.. // ---- / NA2 I II NA6 (CH!GAN 4N/ // A2!,'ll .fl. 1/ 2 A2/ /k' / // P -___-J ;LAK/E / 1 5 !s'c , \/ // , lI i//11 !r/z"v/ >1 - • _ wJI .1 L ./.7:E MaF5 - �View from Portage overlook facing south. Notable features include: 17: 1) Huron Mountains, 2) Flat—lying Jacobsville terrain, 3A) Scales Creek flow ridge, 3B) Student Development Complex, 4A) Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale dump 114, 4C) Isle Royale dump 115, 4D) Wheelkate Bluff (Trimountain, 5) Highway M—26, 6) Contact between the Portage Lake Volcanics and the Copper Harbor Conglomerate, 7) Houghton County Courthouse, 8) Quincy Smelter, 9) Michigan Technological University Main Campus. Previous stops are located with stars and stop numbers are prefixed with an S. Figure w �33 general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, 1975) is used routinely by developers in the area. 4) On the skyline on the opposite side of the Waterway, beginning at the Houghton water tower a series of mine dumps representing the Isle This marks the Royale lodes can be seen extending into the distance. approximate route of the road between Stops 1 and 2, and shows the The knob on the skyline is Wheel— strike of the Portage Lake Lavas. kate Bluff near South Range which is one of several residual bedrock 5) The divided M—26 highhighs and is located just south of Stop 3. way is visible, traversing the glacial deposits described at Stop 5. 6) To the right, the Waterway traverses the upper contact of the Portage Lake Volcanics and the Copper Harbor conglomerate, Nonesuch Shale and Freda Sandstone. The Stop is the best single locality to observe the Keweenaw Waterway. The Waterway and the peninsula are named for an Indian word for Portage route, but to make the Waterway accessible to Lake Superior shipping, This canal work was necessary at both the northern and southern shores. The geological history of the Waterway was investwas completed in 1873. igated in detail by Warren (1981). This and other major bedrock valleys were formed by stream superposition as ancient rivers eroded through flat— But the valleys lying Paleozoic rocks into the tilted Keweenaw strata. Then the Pleistocene. were greatly deepened by glacial erosion during as the Keweenaw Bay sub—lobe retreated at the end of the Wisconsin glaciation, the Waterway allowed eastward drainage across the Peninsula to lower First, drainage occurred in the Portage Gap lake levels to the east. (between Houghton and Hancock) while a tongue of ice remained in what is As the ice retreated further, the valley now nowwestern Portage Lake. occupied by Portage Lake was formed by eastward drainage of successively Torch Lake was formed lower proglacial lakes in western Lake Superior. by a trapped block of ice which later melted in place to form the lake Warren's study includes a complete bedrock topographic map of basin. the Keweenaw and a series of maps showing the pattern of ice retreat, based on the distribution of glacial deposits. Houghton was named for Douglass Houghton, the geologist who sparked the Michigan copper mining boom by publishing his Michigan State Geologist Houghton was settled in 1852 and is the site of several Report in 1841. historic buildings, the most important of which is the Houghton County Courthouse (1887), a prominent yellow brick building with Jacobsville Sandstone facing and copper roof and a flag pole, on the hill above the main part of town. Hancock was settled in 1859. Across the road and just slightly up hill is Quincy Hill House (1871), the mine manager's house for the Quincy Mine. The Quincy No. 6 mine shaft house dominates the skyline behind the viewpoint. A map of the Quincy operations in its heyday are given in Figure 18. The inclined No. 2 shaft descends at about a 45° angle more than 3 Km (1.7 Km below the surface) making this one of North America'a deepest mines. The surface projection of the area mined is shaded on Map 4. 18.35 Right turn back on US—4l going up the hill. 18.75 Prominent outcrop of basalt with glacial grooves. �34 18.85 Right hand turn would lead to the Quincy Steam Hoist, we're in the center The Quincy Steam Hoist can be now of the Quincy Mine area (Fig. 18). visited during the summer months for a small admission charge. Inside is the largest steam mine hoist in the world. This great machine, invented by Bruno Nordberg and installed in 1920, could lift a 10 ton ore load at a rate of more than 1000 m per minute. The hoist is still in pristine condition and a full museum of the Quincy Mine is maintained inside as well. MAP 4 or 5 On the left hand side, immediately after 19.3 Turn right on Arcadian Road. the turn are some of the Quincy mine dumps, nearest Shaft No. 1. This will be Stop 7. Please respect private property signs and stay within the public right—of—way. STOP 7. Quincy Mine Dumps. The Quincy Mine worked the Pewabic amygdaloid. Production from the Quincy Mine began in 1856 and ended in 1967. Total production from the Pewabic amygdaloid was about 1 billion lbs. of refined copper, ranking fourth in the district (Weege and Pollack, 1971). Lankton and Hyde (1982) give an outstanding illustrated historical account of the history of the Quincy Mining Company which earned the name "Old Reliable" because it paid dividends so regularly. The Pewabic amygdalLoid deposit consists of a group of relatively thin flows. These basaltic flows are A geologic cross section is shown in Figure 19. Some texturally distinctly porphyritic with large feldspar phenocrysts. of the thicker flows have an ophitic texture. The tops of flows in some places are cellular whereas thick flows may be either cellular or fragmental. The amygdaloids of Pewabic flows are characteristically of a type Flows of this type typically have smooth termed ].ocally as coalescing. tops in which individual vesicles are larger than average, reaching an inch or more in diameter. VesiciLes in the same layer may coalesce to form a A series thin, jagged gash with a lateral extent of up to 12 feet or more. of such openings provided an almost continuous path for the flow of mineralizing hydrothermal solutions. Several such layers may occur in the same flow top. Where coalescing is well developed in the Pewabic amygdaloid there may be 2 to 10 layers from 3 to 5 feet thick. There is every gradation from coalesced layers of vesicles to those that show only a moderate tendency to collect in layers (summarized from Butler and Burbank, 1929). quartz is the most abundant secondary mineral assoCalcite is also abundant. ciated with native copper. Pumpellyite, epidote Laumon— and chlorite are common but not abundant and prehnite is present. tite and datolite are common in upper levels but not lower levels (summarized from Butler and Burbank, 1929). In the Pewabic lode, The majority of the dump at this stop is amygdaloidal to massive basalt. Secondary minerals in this dump are mostly quartz and calcite with lesser amounts of pumpellyite followed by epidote. Paragenetically epidote and pumpellyite seem to be early whereas quartz, calcite and native copper formed later. �__ 35 zz .../ ... V I _/ • / V ; /t \ \0. 3/ S Jl 0 I • •90:•.• — —-1 -I - - rj z / z N 7 NM j" , 4 - .v__ /' \ / I �I I J I I I :tI J ''j!J QUill~(CY MJINJE QUIENCY MI[NIE JLOCA1rJION LOCAT lION \ \ I _ ~...:r~, " HOU§JING AND HOUS]LNG AND COMMllJ:NJITY COMMUNIITY§TR1UC1r1UR1E§ STRUCTURES Co C0 f 92O R920 J 4 ClrXi5 Pdence C/zrko ~t.(Jence , 11 ff Metf,adtt Methodi.:;tG'7urd7 07urch 5tootom £7ce Mine O{flce (4 14 frank/in Franklin ichooL ochool. 7 Captaur.5 /ejidence Captalf1'.5 Re.5idence franklin Franklu7 .5dJool, icJ700l; Franklin (5 Old 1.5 Ola FranklU7 FrenkWi Franklif? (r~tl)~?) 1/. -" \..r f6 Pewdbic YcJioal ochoa, 15 Pewabic Qurncy ichoo/ QUI ncy SChool Mesnard" •••• Megn.-d -11' ~~.~~~_'~_'_~I._:-:"~"J' U~ '- ---:, \~~ r::~-,'c?::>' , .LI\D~ r;,~~:::/;:~cpJ I\~ J-1~(" G~' <S-' ;: \ .. /' '';\ '/ b;l ~' / \'1:1\ .. " ',,','1,/, \ .. '\ '~ ,~..- \ L.xe (" ,)'v , 9(8) VI \\,'I ,.~, . ~ :", ~ '\ ,®' ', . . '-<::\::i{,::;::: \ " ;. ';- .-;::~ -~_/. ." ~_. =--" ~ "'Ir)!~;'~~::[ • "' t.-" • "{"l'r J'\ : • ':". '" , "'-I' ~.~·:•. :t :, .~ •. '.. ..y~';" ;.~ ~,,"~ .~'. ~ J ',,- ~~ \0t"\' \", (/. 8 \"~ - • ""'. /\, ~.~., /' ~~. r ;' J 5inir: ,;:.O@ • ~ ••,. : ~~"~ / . .":./ ' ••• 0 ,', .. ';: . 'i' ~.- ---~ -J ' ' : . ' ' \VEl tV _ -- "'';'.', ~I)('I)'''' ~ Z ")~~ [1' •~ ,,' \: % ~~ ,~'-- ,.,~ - "I" ~ ,t; ~~ '~.~~",..~.~ ~ ~'f? ~.~ -':_. , 0®' R, .. , \Uti .. , . \ , ') fiu / " .",.. , j. 1'iin !'~inp ® #~:;~'s;ng- ~ .,. ,I Structures StructuH'.S of the the Quincy quincy 'A~G' .. h ';: ~ 'O6~/-,. '·~., ,., • .. /- • Figure 18: 18: ., . h'. i,; #.. . ~~---;- • II---~' J,:. ~, , •.•" . , . " ,®I'I. • ~ :---.-J.... ~ •. t. .... :;.:( ';:'~:\, ·1 " ~; '0\..;.), "~' " ~~i \.',' ~.~~~'i:::'--~., _~ --' .. i (~,",\~ .. /~.;/~~~,.~~I ,1r,-"\r .. ~,:,./... I -;:'1'" 'i'" . '''i;';~';cl:'' • , ',Ii', l'UI Franklin . , . , - ~ ,I, i/···' d,..... " " -![?'~' ..,.t .... ;l:~ '~~'-i.,~-",:~~"""... 6 -- , ~"" Pr I'is.,J)ir ,I .. >or ", ••h,c c- - - -. ~ (Y~'0'~0\ /~!e ,'" ',' u~ 8~~ _;t:,:~~'c~lL, N~6 ; _ , ' ~', @ ) . . W I Z . - ; - : - N 0 ? '~ -.----"'Cl.\ •• • .•~ . '"".•• , ~i~fr .. r '1'/" "J'II .. P~8bl('. •• ,-b~ ......, ~ ·~".I:.. ,I.', - ~ ,:_~. '~II '\!2~).J .... JuP<V,or"$~ '-~~> J!I ~ -______. ,;.,--::~ r'..... lt~ .•_, ~~_.:.- \ ~ ,\. ,'/ ~.~.~ ..••••·1".::"f! 4-ro CalumBt 4—eoca(umr "J,;t. ..... ~...",~" "~\"'':~'')\~;' ~. ,) , (,/",~ ~:;>{( \ :" ". ~ ':', \.-. " .... .., .. ', 5ord flaije 800rdinq ttouse /lhrth!5 OOX otDre 8. Abrth5 . Ii >;,,~/' (3. Jomei /1 Oa9r and i2w77pany fJ James, H ueaq8r cmcJ Wmp.'3ny Abrths /?;!..5ldence O<zorqe wr7e North::> .iderice •.~ -'9-~_ '., "0'., 6 =- .... ; ••-~ .,. , {i? IS Cat/)olle Olurcfiand arid Priest~ Prtest5 C.ti?olc 07urch /?Q.5idencØ R.e.:;ldence 5 9, :1' .. '. ~ . P<.-~ '.. 10 Clubhouse(öathhou5e) (l3athhouse) (0 Clubh,ue Ooctor:J Lbctcr f(e:,t.(Jence Rejtdene Dipetary DI,::;,oe=ary A9cnt5 f?e.5ldence idence k;Jent::> Z ,~ '. ~ I '----------:.~. ~;J: ~:h ~il!i t:/"2Ie' 1l: ~;H ica(e: ~ :~: 11T .~ "¥' '"F'""'C 'iIi: TT 4a:)}.~ i :1; 1um·:¥:-'.lf-----¥'-------, : r;11.. !I': Vl.U(1 • II] - , .\ I - 0 '~~•• ~ or, 'H~lJof A180 of C,e fuxaon me QlHncyMV74 kocy l.t:>cdctOn.,.no Locacror, a,ri Vte<nuy'(noC1dll} ------....... J0cation (['rom Lankton Lankton and and Tyde, Eyde, 1.982). 1982). location (crom Vnnty ( ~ ! 3 n~ a , l.v 0'> �s S' B- I I n ~l·(!,,.1 7""""- s .., c ~ 7/ 'N' J ~'C' ~ ~ "n",~ " .. .'!>'"<" ~teOa ~~ .".'_ L~ . I .J(VJ ' ~~,~eSUC; p ~ c -''' .c:= <' Copper Harbor Jacobsville -4000' I ., <P: ./ Figure 19: 19: Geological cross cross sectionfromB section from Bto to B' B' on on Map Map 30, 30, B' B' to to B" B" on on Map Map 4, 4, B" B" to to B"' B'" on on Map Map 5. 5. This This cross section section illustrates illustrates the the general general geologic geologic relationships relationships of of the the Keweenaw Keweenaw Peninsula. Peninsula. The successively by the the Copper Harbor Conglomerate, Conglomerate, the the Nonesuch Portage Lake Volcanics are overlain successively Shale and the the Freda Freda Sandstone. Sandstone. The Portage Portage Lake Lake Volcanics Volcanics are are in in fault fault (reverse) (reverse) contact contact with with the the Introduction). Labels for Jacobsville Sandstone Sandstone (see (see Fig. Fig. for the the Portage Portage Lake Lake Volcanics Volcanics (P) (P) younger Jacobsville are follows: Hancock conglomerate (phc), (phc) , Pewabic Pewabic West West conglomerate conglomerate (pp), (pp), Greenstone Greenstone flow flow (pg), (pg), are as follows: Allouez conglomerate Kear— canglomerate (pa), (pa), Calumet and and Hecla Hecla conglomerate conglomerate (pc), (pc), Kingston conglomerate conglomerate (pkc), (pkc), Kearsarge flow flow (pk), sarge (pk), Scales Creek flow (psc), (psc), Bohemia Bohemia conglomerate conglomerate (pb), (pb), St. St. Louis Louis conglomerate conglomerate (ps). (ps). W --.J �38 38 MAP 55 19.5 Entering Coburntown. Coburntown. This is is another one of the the communities that that sprung up around the the Quincy operations, operations, most of the the houses built and owned by by up Several ethnically distinct neighborhoods existed the company. Several existed "on "on the the hill" in in the the early early 1900's. 1900's. In lived on on the the In all all more than 6,000 people lived hill in in 1905. 1905. 20.45 Y in There is a Y in the road, road, we take the right hand branch which is essentially aa straight tially straight road with a sign sign saying saying Arcadian Arcadian Scenic Scenic View. View. 20.7 Passing a radio radio tower tower on on the the right. right. We are now crossing the the Scales Creek flow the top top of the small small ridge ridge (see (see Map Map 5). 5). The Arcadian Mine worked flow at at the an amygdaloid just just below below the the Scales Scales Creek Creek flow. flow. The amygdaloid may corcoran relate with the the Isle Isle Royale Royale amygdaloid discussed discussed at at Stop Stop 2. 2. North of the the road is is Shaft Shaft No. No. 11 of Mine. Stoiber (unpublished (unpublished date) date) of the Arcadian Mine. estimated the percentages of of non—metallic non-metallic secondary minerals in in the dump calcite, from Shaft No. No.11 as: calcite, 43; 43; prehnite, prehnite, 25; 25; quartz, quartz, 16; 16; K—feldspar, K-feldspar, 8; 8; epidote, epidote, 6; 6; pumpellyite, pumpellyite, 1; 1; chlorite chlorite 1; 1; and and laumontite, laumontite, trace. trace. 21.4 see the the largest largest part part of of Portage Portage Lake, Lake, Down to to the the right of of the the road road you you can can see of view is the field field of is basically Keweenaw Bay and the the Huron Huron Mountains. Mountains. Much of the flat—lying flat-lying Jacobsville terrane. terrane. 21.6 Road turns turns to to the the right right and and changes changes to to gravel. gravel. 21.8 descending off off the the Portage Lake Volcanic Volcanic Series Series across across the the Keweenaw We're descending Fault onto Jacobsville Sandstone. Sandstone. 23.0 have aa view of of the the Isle Isle Royale sands sands We are descending the the hill and and we have across Portage Lake in in Houghton. Houghton. These are tailings from the Isle Royale out and and into into Portage Portage Lake. Lake. dumps (Stop (Stop 2) 2) which were brought brought out 23.15 Junction with M—26 M-26 and and take take aa left left turn turn at at the the Portage Pottage Lake Lake Coal Coal Dock. Dock. 23.6 Entering Dollar Bay Bay on on M—26. M-26. MAP 66 25.2 of flat—lying Exposure of flat-lying cross—bedded cross-bedded redbeds of the Jacobsville Sandstone on the left hand side side of of the the road road (northwest (northwest side). side). STOP 8. 8. Jacobsville Sandstone. Sandstone. The Jacobsville Sandstone is a a fluvial fluvial succession of feldspathic feldspathic and quartzose quartzose sandstones, sandstones, conglomerates, conglomerates, siltstones, siltstones, and shales shales up to 1,000 m m thick (Fig. (Fig. 20a). 20a). There are no interbedded lava flows flows or cross—cutting cross-cutting dikes. The Jacobsville Sandstone is separated from the Portage Lake Valcanics Volcanics by the Keweenaw Fault, Fault, aa reverse reverse fault. fault. The Jacobsville Sandstone is is probably upper upper Keweenawan in in age and and may may be slightly younger than the the, Freda Sandstone. Sandstone. Current the Keweenaw Peninsula are to the northeast and east east Current directions directions in the suggests transport transport to to deeper parts parts of aa basin located located northeast of of which suggests Keweenaw Keweenaw Bay Bay (Fig. (Fig. 20b). 20b). West of Lake Gogebic thickness thickness and and current direc— directions tions suggest another deep deep part part to to the the basin. basin. East of Calumet, Calumet, near the the Keweenaw Fault (Stop (Stop 10) 10) the the Jacobsville Sandstone contains boulders of basalt which suggests a topographic topographic high in the the Portage Lake Volcanics north north of the the fault fault during during this this period period of of Jacobsville Jacobsville sedimentation. sedimentation. Metamorphosed �/ / / / ,0 /~(" / / // / .I,/""!' ... /Ci' ,;:"00' / , / /'pP .~ // /' ~ 56 / '-~~~ ..... / -....;,:~. / '086 • /// / //' // 39 // ." // II II II 1070 1070 , -I [ II II II II II II II II H \\ ,\ z , " \ 1068 ,__L_ — . II / / p- \\ H \' \\ \\ ,\. H "\\ ". —--•• , L ' p~~// ~\~. H... if] :=:;\ fr-- t1 16 II II r p N 0~ I~ 0 ,:;1'Q , '....... 0, NA/5Q .............. " II NAI3' II "'NA/5Q "" NA/3' " C'~ II :~<? H 1/ 1 0~ ....... .,,00 933 l ' ':O~ ....... CJO C, / 4, cL '\ 21 / ')0 -"',--- ""'--: ...... , . . . . ; /i /1 ~ ~\ \. 1 "( II II I I-=-- 4 A ~0 ...0 b~ --'~ , NAI7 NAI7 N-,~ Il /I It II J e~ ,~ ,000 ___ OFFSET _— OFFSET -4":t- ~0 14 i-- / KEWEENAW KEWEENAW FAULT FAULT c• \\ II .-:-1r;o.f6=====.=~ 15 N83 22 23 • 630 • : H Mill I,- 1 884 I, 'I ii I II" 'I. 913 / - "'-" '", / \. L )8 s. -T , --"J". /_-9_/ \ Stop8 602 602 \• \ "', - 0 V - II ii I, ou II * , H,;" II ,,'I; / CJ~ / ~O'" // 'so / / j .: // 668 ~ 11~ .~ /;:.~=J- ..--"--1-~~==-~;:./~ -: -- II JI-ij . - - If//// • -, ,... .~ .,;.: -:-- // // II /1I, // '1/ II // II /? /-::-~==;!/ 1, II ,726 26 / "// 11/ /,/ ,,/ ij "7 'l~' ,y 1- . 'l /,'l // 7, ~. /.1 ,'/ /1' ,,;1 ",' - "/ //' 800 :- H •- -j 4-\ Aap5 // / *0 ~0 27 62 // 26 ---- H >, \ "''-\ ,,----"'\ _ _ ;;:."'::- _F1_ \\ '\ \. '. 0,", "1L-B9~ --- ' , _ _ ,Q!=D_ M on pv, '\ ,--- ....—.. —'-.. 7 35 • 1 6 .. . MAP6 ~AAP ,,",, • �____ 40 Sandstone Thickness Current Directions 9400 Geophys. est. (ft.) 597 Weillft.l o 50 I j Km. B. A. I rocks Iron ranges 0 - 0 km mi 30 I 50 so N --...... ,. \ c. C. Figure 20: 20: Relationships of Jacobsville Sandstone Sandstone (from (from Kalliokoski, Kalliokoski, 1982). 1982). of Jacobsville Jacobsville Sandstone with minimum thickness denoted Thickness of denoted by +'. '+'. B. Current in the the Jacobsville Jacobsville Sandstone. Sandstone. C. Location of of Current directions in C. possible source areas iron formation staurolitic metasedimentary possible source areas of of iron formation and and of of staurolitic metasedimentary rocks. A. A. �41 iron-formation quartz-staurolite pebbles pebbles suggest suggest aa source source from from the the iron—formation and quartz—staurolite jacobsville Jacob sville sedimentation sedimentation was was preceded preceded by by aa long period of cratonic stability stability with with little little or or no no volcanic volcanic activity. activity. Erosion was was apparently initiated by late Keweenawan warping along the the mid—continent mid-continent rift rift system. system. The major movements on on reverse reverse faults faults were were after deposition (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). after Jacobsville deposition southeast southeast (Fig. (Fig. 20c). 20~. sandstones varies from from subarkose subarkose to to quartz quartz sublithic sublithic Lithology of sandstones arenite. There are some some beds of of arkose arkose and and quartz quartz arenite. arenite. Grain size size varies from from fine fine to to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic origin. origin. Microcline is relatively relatively unaltered unaltered and and plagioclase is is unaltered to to highly altered. altered. Other clasts clasts include: include: volcanic rocks, rocks, schist, the minerals epidote, epidote, biotite, biotite, muscovite muscovite and and chlorite. chlorite. schist, shale and the Sandstone varies in in color color from from red red to to aa cream—white cream-white or or purplish—red purplish-red color. color. The color depends on on the the alteration of of ferromagnesian ferromagnesian minerals minerals and and the the amount of iron oxide deposited deposited as as rims rims on on feldspar feldspar grains. grains. Ripple marked amount of bedding surfaces surfaces and and cross—bedding cross-bedding are are common common in in some some localities. iocalities. Sandstones are fluvial stones fluvial and conglomerates probably represent represent alluvial fan fan deposits (summarized (summarized from from Kalliokoski, Kalliokoski, 1982). 1982). At this this stop stop the the character character of of the the Jacobsville Jacobsville Sandstone Sandstone can can be be seen seen in in The exposures here can be the exposures on the left side of the road. the left side of the road. exposures here can be compared and contrasted to to Jacobsville that that will be seen at Stop 99 and Stop 10. 10. 25.9 the small small town town of of Mason. Mason. Mason was the the site site of company housing Entering the for for the Quincy mill operations operations from from 1890. 1890. 26.5 On the the right right hand hand side side of of the the road road is is an an old old dredge dredge which is is stuck stuck in in in Torch Torch Lake. Lake. This is the the C&H dredge #1, #1, built in in 1913, 1913, bought tailings in by Quincy in by in 1955 1955 and and used used until until 1967. 1967. 26.7 Now we pass pass the the remains remains of of the the main main buildings buildings of of the the Quincy Quincy Mill, Mill, built built in 1890 1890 to to accommodate accommodate steam stamps, required when when the Quincy operation operation in stamps, required the Quincy expanded to to the the Pewabic Pewabic Lode. Lode. 27.0 Along the road on the the left there there are more outcrops of flat—lying flat-lying Jacobsville Sandstone. 27.3 On the right, right, Torch Torch Lake. Lake. 27.7 On the right hand side of the the road road are tailings tailings which have been revegetated. revegetated. These tailings tailings now as we are entering Tamarack City are part of the the mill operation of the the Calumet && Hecla company mines and the the Calumet region region which have major mills located located at at Tamarack Tamarack and and Hubbell. Hubbell. 28.15 On the left hand side of the the road road are the the footings footings from from one of the the Tamarack Mills. MAP 7 28.6 On the right right hand side of the the road road are the the remains remains of a steam steam stamp stamp mill. mill. 28.7 Left turn, turn, going going up up the the hill hill toward toward Stop Stop 9. 9. Follow the paved road road which jogs a little little to to the the left left and and goes goes up up the the hill. hill. �__ _______ p 28 c/ / 5 \\ // ___ __ ___________ // i ''s / / //\ ;o367 /\' // TL 7 TL5 FaLls + 31 f I HIL / -LLVARY EM / 1 \ 36\ 42 MaD88 42 • J Cr C - Lake n en / 'S 'I I, ii' . T I \\\ \ II II II II /7 // 959 'I \ \ \ 12 1Ltp,9 . / mrs 1 \ &çubbell —;: -N ---- .. — •••S" 'so —\N ___--1-_ MapG ( MAP77 MAP \ �43 28.85 Cross the the old Copper Range Range railroad railroad grade. grade. 29.0 Sign indicating indicating Hungarian Hungarian Falls. Falls. This is is the the lower lower part part of of the the falls. falls. Continue going up the the hill, hill, straight straight ahead. ahead. 29.25 Junction of a a four—wheel four-wheel drive drive road road to to the the left. left. Stop and walk Stop here here and towards towards Tamarack reservoir/Hungarian reservoir/Hungarian Falls Falls upper upper part part where where excellent excellent exposures of of Jacobsville Jacobsville Sandstone Sandstone are are found found near near the the Keweeriaw Keweenaw Fault. Fault. STOP 9. 9. Hungarian Falls. Falls. The Keweenaw Hungarian Falls is is located located near near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 21). 21). The Fault is reverse fault Volcanics and and Fault is aa reverse fault that that juxtaposes older older Portage Lake Volcanics the In this the younger Jacobsville Jacobsville Sandstone. Sandstone. In this locality, locality, the the Keweenaw Fault presumably dips dips at at a west similar to presumably a high angle to to the west to that that illustrated illustrated in Figure 19, in 19, Stop Stop 7. 7. The The Keweenaw Fault Fault at at the surface surface varies varies from from aa single fault single fault plane to to aa more complex complex fault fault zone, zone, such such as as described described hear near Structural relationship Lac La Belle. relationship of of beds beds near near the the fault fault also varies varies from steepened also steepened dips dips to to folds. folds. In general the the dip of the the In Portage Lake Volcanics and Jacobsville Sandstone Sandstone steepen steepen appropriately appropriately as one approaches the the fault. fault. as At Hungarian Hungarian Falls the At the fault fault contact causes very little little deformation of the Jacobsville Sandstone, the Sandstone, which which is is only only tilted tilted slightly. slightly. To To the west of of the fault fault at this this site site the the Portage Lake Volcanics are unusually shallow shallow If not not viewed in the If the context of of many many other other localities, localities, the the fault fault dipping. might not might not be recognized as such such a a profound feature, feature, and could appear as a a conformable contact. contact. The the fault fault exposure The contrast contrast between between the exposure here here and and that at at the the next next stop stop (Stop 10) at at Hungarian Hungarian Falls Falls is and illusthat (Stop 10) is striking striking and illustrates of rocks rocks along along this this major major feature. feature. trates the the structural variability of The Portage Portage Lake Volcanics near the The the Keweenaw Fault at Hungarian Falls conInterbedded sists of of basaltic lava flows sists flows with interbedded interbedded conglomerate. conglomerate. sediments make make up up aa small small part part of of the of the Portage sediments the stratigraphic stratigraphic section section of the Portage Lake Volcanics Volcanics and and are found found as relatively thin thin widely separated separated beds. beds. However, in the the Keweenaw Peninsula conHowever, here and at some other localities in glomerates glomerates within the Portage Lake Volcanics are either near or at the the fault contact. fault Walking downstream downstream along along the the stream stream to to the the upper upper and and lower lower falls falls allows allows examination of good exposures of Jacobsville Sandstone with cross bedding, of Sandstone bedding, interbedded shaly shaly and and conglomeritic conglomeritic horizons horizons and and many many typical arkosic redred— interbedded typical arkosic bed sedimentary features. features. 29.25 Turn around and and go go back back down down the the hill hill to to Tamarack Tamarack City. City. 29.8 Stop sign. sign. 29.9 Entering Hubbell 30.5 On the right are Calumet & & Hecla mill buildings which have recently recently been taken over over by by Michigan Michigan Tech Tech Ventures Ventures as as aa pilot pilot plant plant location taken location for for small small industries. Torch Lake is is still on the the right with many of the the tailings tailings out in in the the lake. lake. Stamp mill mill remains are straight Stamp straight ahead. ahead. Turn left left on on M—26. M-26. �Ta arack reservoir metal gra Jacobs yule sands tone 100 feet -.- z — fIIs D fault basalt c Ong!omer Figure 21: Geologic sketch map of the Hungarian Falls area (by J.M. Robertson, 1973). Basalt and conglomerate are part of the Portage Lake Volcanics. Note that north is toward the left margin of the page. �45 31.4 Entering the town of Lake Linden. The Houghton County Historical Museum is on the right hand side of the road. The building (1917) was donated by the C&H Company to the Houghton County Historical Society in 1963. Among the best displays are scale models of underground mines and a rich photographic record of the boom copper days. 32.2 Right turn on Ninth Street (the so—called Bootjack Road) in Lake Linden. 32.35 Follow the signs to the Lakes Left hand turn at two blocks after 32.2. This is Gregory Street. Drive—In Theatre. MAP 8 33.3 On the left hand side of the road is the Lake Linden cemetery. The road heads north along the Trap Rock River Valley. On the left hand side of the road at the top of the steep slope is the Keweenaw Fault. On the right hand side of the road is a flat—lying Jacobsville terrane. The Trap Rock River follows another of the glacially eroded, deep bedrock valleys described by Warren (1981). 34.5 Pavement ends. 34.6 The gravel road bears to the right. 34.9 Cross a bridge over the Trap Rock River. 35.0 Left turn at the Trap Rock Schoolhouse. 35.0 Cross the Trap Rock River again. 35.7 Left turn on to another dirt road that begins to go up hill. 36.1 Access to the Cross the railroad grade of the Copper Range railway. Natural Wall ravine for mapping purposes can be gained by walking a couple hundred yards to the left along this railroad grade and then walking along the stream valley up toward the fault line. 36.2 Poor exposures of flat—lying conglomerate beds within the Jacobsville Sandstone on the left hand side of the road. 36.4 Stop by an old wooden sign on the left hand side of the road. 200 meters to the left (south) to the Natural Wall ravine. STOP 10. Walk about Keweenaw Fault at Natural Wall Ravine. The Natural Wall is a bed of sandstone within the Jacobsville which has a near vertical attitude and because it is more resistant, it forms a On the sides of wall which extends outward from the walls of the ravine. the ravine the lithology of the Jacobsville here includes conglomeritic The attitudes of beds in the creek beds, sandstones and shaly horizons. flat—lying to the bottom change from east, to vertical and even locally overturned as the fault is approached. An anticline in the Jacobsville trends parallel to and 300 m east of the fault. West of the fault the Portage Lake Volcanics dip to the WNW at 35—40° (Fig. 22). �__ ______________ 7- II =" 46 -': '-,-; •=/_ rN. '/ - - -- - // _.>c I 0, /ö• - 0 -o ' Co 1 0 ' -, • - (,' I \Pj II '- (O' Cog,' ,,' ,< ' -Co " ,d/ ,-; d' / C 0 // / N' 0- N LU /12'i NN "N\ N • - - p\ -, F / ,,/, - /,,' -\ \\ ci 1 // , MI I, I, - e //4' / ,,,i'</ {7iiir ,,// \-" ,/\ / /IL[=== ci C ' \ —4 'C N ' " I -> (z,I4' , ,,\ k ," ". ,/,, =====' - ) -';tiiiiit V/11 __\\ — , 0- \ i I 17 -I ;3S? __WZZ ii4t - I ' P I - < - - r"N(N - ._:;:_ 4. ITC. - ,, ' 4- 0 - ci / .7 , il? -( _o— Sly) 07 I • — 1 : -I/,wI 0- —_. II 7___ /1/1/7- Co 'C I - ;r' 0 ,/ / - - \. \ ) - -/ // - I t - , NQN ci 0 - �47 . • : -. D / N -V l 'Ii 1 SC LE n thousmds of feet 1) // GN : I CL" HEA G.. 13Wfl1V — I I 11111! 1111 1-II 1111111 U II 111111 Figure 22: Geologic sketch map of the Natural Wall Ravine. Note that north is toward the right margin of the page. 2 �48 37.95 The beginning of pavement, we are entering the town of Laurium. 38.7 Left turn which is followed immediately by a right hand turn at the next stop sign on School Street. 38.8 Turn right. Junction of School Street and Calumet Avenue, which is US—41. This is Calumet, Michigan, the center of the Michigan Copper District, and a site of the Calumet & Hecla headquarters. Here Edwin Huribut discovered the Calumet conglomerate load in the early 1860's and this Greater became the most important ore body in the whole district. Calumet (including Red Jacket, Blue Jacket, Yellow Jacket, Laurium and Among many historic Rambaultown) had a population of 33,000 in 1910. buildings here are the Calumet Theatre (1900) and the C&H Community Library Building (1898). MAP 9 40.0 Entering Centennial 40.3 On the left hand side of the road you can see the Centennial Mine After closing in 1968, this mine was dewatered in the Shaft No. 6. This operation has since been abandoned. mid—l970's by Homestake. The Centennial Mine Shaft Nos. 3 and 6 worked the Calumet and Hecla The ore body lies up dip and northeast from the main ore conglomerate. body in the C&H conglomerate mined by the Calumet and Hecla Mine in the The C&H conglomerate yielded about 4.2 billion lbs. of Calumet area. refined copper, the largest lode in th district and is over one—third of the total production from the Keweenaw native copper district (total district production of about 11 billion lbs.). The C&H lode had the highest average grade in the district of 57 lbs. of Cu per ton of rock treated (Weege and Pollack, 1971). The Calumet and Recla conglomerate can be followed along strike for more Along most of this length it is less than about 1 m thick. than 65 Km. In the Calumet area it averages over 3 m thick and tends to thicken with The bed consists of north trending thicker and thinner zones depth. representing channels. At the Centennial Mine Shaft Nos. 3 and 6 thickness is often less than 3 m and the C&H conglomerate was deposited in The pebbles in conglomerate at Centennial a tributary stream channel. The pebbles in are almost all quartz—feldspar phenocrystic rhyolite. the main channel conglomerate are a quite varied suite of rhyolite and Main and granophyre with some quartz—feldspar phenocrystic rhyolite. tributary channel conglomerates tend to be coarser and contain less fine Outside of the 5—foot thickness contours the material where thicker. bed is usually shaly or sandy. At Centennial, copper mineralization tends to occur in bands with the bed and the intensity is related to the type and amount of interstitial material and location of pinch—outs or Higher grade areas are related to conglomerate with coarse barriers. sand or small pebbles as interstitial material, especially when pebbles Evidence and sand grains are quartz—feldspar phenocrystic rhyolite. also strongly suggests that the mineralized areas follow the axis of stream channels and grade is highest adjacent to the 5—foot thickness contour where the conglomerate bed increases greatly n thickness down These pinch—outs localized ore deposition from mineralizing soludip. Sedimentological relationships are tions that were migrating up—dip. �S. Q. -.7 4i 'J. idO I I, N N k-j: IC 7 /5 "4 -'-—--- —, I( - H I, C. dew b7 �50 important in exploring the conglomerate ore bodies (summarized from Wee and Pollack, 1971). 40.6 Entering Kearsarge, Michigan. 41.1 Stone boat on the 41.3 Right turn onto Water St1 .t just before the Wolverine Market. straight ahead on the main paved road. 41.5 STOP 11 is the Wolverine Mine dumps. There are dumps both on the right and left hand side of the road. The oner on the righL hand side of the road (south), just on the other side of some old buildings, ar somewhat dangerous because of bad ground. Mining in this are.a waS Very shallow (Shaft No. 3). The dumps on the left hand side of the road appear to be (Shaft ice. 2). much safcr Park along the road and walk about 100 in to right hand side of the road. Continue the north. The Wolverine Mine is one of seven different mines that worked the Kear— Centennial, South Kearsarge, &orth Kearsa rge, Ahneek. sarge amygdaloid: Allouez, Mohawk, and Seneca. Production of copper from the Kearsarge amygdaloid began in 1887 and stopped in 1967. About 2.3 billion lbs. of ref -i:ied copper Were produced frccn the Kearsarge amygdaloid making it the second largest producer of the Keweenaw native copper district (Weege and Underground workings are continuous far more than 12 Km Pollack, 1971). and extend down dip as much as 2500 m. The Kearsarge amygdaloid is one of the best documented ore bodies in the district. The Kearsarge flow has been recognized for a distance of around 55 Kit along strike, it lies directly above the Wolverine sandstone. The flow dips between 35 and 40 degt-ees to the northwest (Fig. 23). The interior of the Jt flow is a well developed ophite with a compositi:irI shown in Table 2. has an amygdaloid top that ranges from near zero up to 10 in in thickness. Just below the amygdaloid there is a zone in which the glow is distinctly Abundance and size ol porphyritic with tabular plagioclase phenocrysts. the plagioclase phenocrysts in this zone is variable but they can make up a large percentage of the rock and can be up to 2.5 cm in length. This zone. is probably the result of plagioclise floating during in situ crystallization of the flow. The stratigraphic and textural relRtionships makes this flow wore easiiv recognized than most. The near—surface thickness of the Kearsarge flow clearly shows that the most productive area is where it is thickest (Fig. 24). The flow top in the productive ares is Individual fragments mostly a fragmental amygdaloid (flow top breccia). are generally less than 15 cm in greatest dimension and contain nwnerous small amygdules. The fragmental amygdaloid makes up the uppermost part of the flow grading downward into banded cellular atnygdaloid with arnygdules This grades downward into a zone with fewer abundant at certain horizons. and large amygdules with less tendency to be found in bands and stilt further The amygdaloid top of the Kearsarg flow in downward into massive basalt. the mined area has an average thichness of around 2 rn (summarized from Butler and B'jrbsnk, 1929). �51 I A' A C ln,IIe 4000t1 Figure 23: Geologic map and cross section showing Mine and vicinity (modified from White and others, me Mine Shaft No. 2 dump (see Map 9). Labels are (pi); Calumet and Hecla conglomerate (pc); Osceola merate (pkc); Wolverine sandstone (pw); Old Colony conglomerate (ps). Table 2: Major—element composition of the Kearsarge flow (from Stoiber and Davidson, This is a weighted average exclu1959). sive of the top 12 feet and thus represents a close approximation to the original composition of the flow. the Kearsarge flow, Wolverine 1953). Stop 11 is the Wolver— Iroquois flow, as follows: flow (po); Kingston conglo— sandstone (poc); St. Louis Weight Percent Si02 A1203 Fe203* MgO CaO Na20 1(20 Ti02 MnO H20+ H20— CO2 Total ppm Cu 48.55 16.51 11.54 6.68 9.44 2.82 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �52 300 Thickness 200 feet 100 Top of Wolverine sandstone C) CD 0 CD 0 a CD CD Butler and Burbank, 1929). Figure 24: Thickness of the Kearsarge flow (modified from from This is the near surface thickness along a strike distance of around 35 miles directly to Mandan (Map 20). The thickness is relative to the Isle Royale (Map ) underlying Wolverine Sandstone which is arbitrarily shown as horizontal. Th Chlorite Epidote Microcilne Hematite Prehnite Pumpellyite Quartz Sericite Native Copper Calcite early — TIME late Figure 25: Paragenesis of secondary minerals in the Kearsarge amygdaloid at the Wolverine Mine Shaft No. 2 (Paces and Bornhorst, unpublished data). The relationships are based on a limited megascopic and thin section study of samples from the Shaft No. 2 dump and may be modified slightly as research proceeds. The exact timing of the later minerals are difficult to determine because they do not occur together. �interior. flow Kearsarge the of outcrops find can one dumps 3 and 2 Nos. trace. quartz, and 1; Shaft the of vicinity the In prehnite, 10; epidote, 38; microcline, 51; calcite, minerals: of percentage following the estimated data) (unpublished Stoiber whole, a as dumps 2 and Nos. Shaft the For found. be can copper native with specimens Excellent 1 relationships. paragenetic their and assemblages mineral of variety a see to opportunity the have will you dump 2 No. Shaft Mine Wolverine the At trict. dis- copper native Keweenaw the in bodies ore amygdaloid of complexity the of illustration excellent an is amygdaloid Kearsarge the of area ductive pro- the within minerals amygdule of variation spatial and temporal The Bornhorst). and Paces of data unpublished of addition with 1959 Davidson, and Stoiber from summarized (mostly zones regional the within islands free prehnite and quartz are there that suggests data detailed zones. prehnite and quartz the within lies amygdaloid Kearsarge the Thus, scale regional a On mineralization. copper significant of limit the mark also may microcline of limit The boundary. zone quartz the straddle to appears ore copper richest The zones. mineral the than irregular more much is present copper native of amount The absent. is it until depth with irregularly decreases microcline of amount The depth. increasing with zone quartz the within content quartz in increase irregular an is There zone. quartz the within percent 15 about averages whole a as and depths shallower at percent 10 than less considerably is Quartz 27). (Fig. depth with vary mineralization copper native of grade and minerals amygdule the However, mineralization. copper native of grade the and banding between correlation strict no is There 25). (Fig. samples individual in seen relationships paragenetic the with consistent is This openings. remaining the in calcite of deposition finally and channel the of center the in epidote and quartz by followed channel solution the of parts outer the along first deposited been have would microcline and Chlorite channel. permeable a along moving solution hydrothermal a from minerals secondary of deposition by explained be may banding The 26). Fig. in corner wall hanging (north flow overlying the of base the in found is assemblage last The microcline. ± chlorite—calcite and epidote; ± calcite—microline calcite—epidote; quartz—epidote; microcline; ± calcite ± chlorite layer: amygdular the of top to bottom the mineral major five are from assemblages There bedding. to parallel roughly are bands The Table and 26 (Fig. 3). amygdaloid Kearsarge of bottom to top from minerals amygdule of arrangement banded a is there 3 No. Shaft Mine Ahmeek the In 25). (Fig. chlorite and calcite, copper, native quartz, are minerals formed latest the and minerals formed early are prehnite and microcline epidote, chlorite, Paragenetically spatially. and temporarily both vary assemblages mineral secondary The 1959). Davidson, and Stoiber from (summarized minerals amygdule secondary the with associated occurs copper Native sericite. and laumontite, pumpellyite, prehnite, chlorite, K—feldspar, epidote, calcite, abundant): of amounts lesser and quartz least to (most are whole, a as amygdaloid Kearsarge the in minerals filling space interfragmental and amygdule The plagioclase. replacing pseudomorphically pumpellyite fine—grained of consists basalt lyitized Pumpel— groundmass. cryptocrystalline to fine—grained a in set laths albite euhedral percent 60 about is basalt Albitized pumpellyitization. and albitization alteration: of types two by affected been has basalt top flow The oxidized. well is amygdaloid Kearsarge the in basalt The 53 �54 NORTH SOUTH Ii chlorite-mlcrocline-calcite SCALE Eli:; 10 0 3Oleet 20 copper ,, Contact between Kearsarge amygdaloid and overlying flow bottom Figure 26: Cross section of the Kearsarge amygdaloid showing the banding of amygdule mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of Shaft No. 3 (from Stoiber and Davidson, 1959). The footwall is the bottom of the Kearsarge flow. Data from the back and walls are projected to a horizontal plane. In one mapped locality Stoiber and Davidson (1959) found a laumontite—quartz—calcite zone. Amygdule mineralogy of the various zones are given in Table 3 below. Table 3: Volume percent of amygdule minerals from mapped assemblages shown in Figure 26 (from Stoiber and Davidson, 1959). Mineral Assemblage Band Chlorite Chlorite— Microcline— Calcite Microcline— Calcite Quartz— Epidote Calcite— Epidote 0—3 45—82 0—47 5—10 0—trace 0—8 0 0 Volume Percent Amydule Filling Chlorite Microcline Calcite Epidote Pumpellyite Quartz 100 0 trace 0 69—74 15—25 0—5 0—1 0 0—6 0—5 1 2 0 2 0 0—1 90—96 0 87 12 0 trace 4—9 1 2 1 �copper SCALE 2 27: 4 SENECA N K (thousands of feet) W Distribution of quartz, microcline and high grade native Microcline present on hachured side of line only -" Lower limit of microcline l?igure A Over 10% quartz on hachured side of line Upper limit of quartz Very high grade copper ore NORTH KEARSARGE AHMEEK MO H ore in the Kearsarge amygdaloid (modified from Stoiber and Davidson, 1959). The Calcite and epidote are present in all zones. Kearsarge amygdaloid dips about 35 to 40 degrees to the northwest. Data from the incline are projected to a horizontal plane. CENTENNIAL WOLVERINE SOUTH KEARSARGE �56 41.5 Continue on the same road and in the same direction as before (.isr), away from Kearsarge. 42.1 There is a dirt road junction to the right, stop here. We are now in the vicinity of Scales Creek, which is the type section of the Scales Creek flow. This Is the sane flow seen at Stop 1, about 14 miles to the south, in Houghton. STOP 12. Scales Creek. This stop gives one an opportunity to look at the Scales Creek flow, a regionally extensive basaltic flow. This is the same unit observed at Stop 1, and it has been traced for more than 150 Km along the Keweenaw. There are outcrops of the Scales Cteek flow on both sides of the main road and along Scales Creek, just to the north and paralleling the road. The Scales Creek flow Is characteristically ophitle. This flow was studied, from drill core northeast of here, by Scofield (1976). The Scales Creek The massive flow has an amygdaloidal top and base and a massive interior. interior of this flow is believed to be for the most part geochemicallv unaltered (Table 4). Mineralogically primary and secondary minerals are present. Modes estimated for the massive interior are plagioclase, 40 percent; pyroxene, 48 percent; olivine, 10 percent; and opaque oxides, 2 percent. Primary plagioclase, pyroxene, and opaque oxides can be found but olivine is pseudomorphically replaced by talc, serpentine, and/or chlorite. In the amygdaloidal flow top no primary minerals are present but all have P]agioclase is been replaced by a suite of secondary alteration products. now albite with some replacement by sericite, chlorite, and puinpellyite; clinopyroxene is replaced by chlorite; olivi.ne is replaced by chlorite, epidote and pumpellyite, and opaque oxides are altered to hematite and sphene. Scofield (1976) has studied these changes in some detail. 42.1 Turn around and retrace route back to US—4l. 42.7 Passing the Wolverine mine dumps, Stop 11. 42.9 Right turn on 115—41 at Wolverine Market. 44.2 Entering the Village of Allouez. We have an excellent view of the southeast side of a prominent ridge. This ridge is held up by the Greenstone flow which is the thickest and volumetrically Largest single flow within the Portage Lake Voicanics. It wili be seen at Stop 14. 44.4 Left turn on a paved road called Bumbletownkoad, just before a Standard gas station. 44.6 Stay on the paved road, bearing right. 44.75 STOP 13. Allouez Conglomerate and flumbletown Hill (Fig. 28). The description of this stop is modified onj.y slightly from White (1971b). The stop begins with a survey of the dumps of the Allouez conglomerate mine (1869—1392, 1300T Cu). �Table 4: Average composition of three samples from the massive part of the Scales Creek flow (from Scofield, 1976). Weight Percent 5i02 47.57 A1203 16.10 Fe203* 12.54 MgO 7.67 CaO 10.00 Na20 2.24 K20 0.29 Ti02 1.43 97.84 Total 0 1000 L Figure 28: Outcrop map of the Allouez—Bumbletown Hill area (White, 197lb). 2000 FEET �58 The lithology of the conglomerate is best studied in the dumps. The largest boulders in this conglomerate are about 2 feet in diameter, and the median size is about 3 inches. A pebble count of boulders mafic rock, more than 8 inches across gave the following results: mostly amygdaloidal, 16 percent; quartz porphyry, 36 percent; feldspar porphyry, 11 percent; granophyre, 37 percent. The greater heterogeneity of this assortment suggests a less restricted source terrane than the one that supplied the Kingston and Houghton Conglomerates in this area; the Kingston, in particular, is made up almost entirely of fragments of quartz porphyry. These dumps are well known to rockhounds as a chryso— colla locality. Thin black veinlets cutting the conglomerate are calcite full of chalcocite dust. From the dump, it is a short walk to the top of the hill, which is an area of exceptionally good exposure and provides an opportunity to see several key units of the Portage Lake Lava Series. One has a unique view of both an area of intensive mining activity and of the general physiography of the Copper Range. From here, on a very clear day, one can see Isle Royale to the northwest. The Huron Mountains lie beyond Keweenaw Bay to the southeast. Bumbletown Hill is on the southwest side of Allouez Gap, a saddle crossing the Copper Range, similar to, but much less prounounced than, the valley at Houghton—Hancock. At this gap, the strike of the lava flows swings, going northeast from about N35°E to N50°E. Fractures and minor faults associated with this bend are probably the reason for the gap. To the northwest, the land slopes off very gradually toward Lake Superior, The southeast as it does through most of the length of the Copper Range. flank of the Copper Range has a steeper slope at the skyline, more or less along the line of the Keweenaw Fault. The low—lying plain between the fault and Keweenaw Bay to the southeast is underlain by flat—lying Jacobs— ville Sandstone. Looking northeast along the strike of the Copper Range, one can see the At Bumbletown cuesta form of the ridge upheld by the Greenstone Flow. Hill, this flow is only 85 m thick; it thickens abruptly to more than 300 m at the near end of the cuesta ridge. To the right of the Greenstone ridge, the more distant hills are upheld by lavas much lower in the section; dips of bedding are steep, and cuesta forms are less pronounced. The amygdaloidal top of the Kearsarge Flow has been the principal producer in this area. The line of shafts along its outcrop is a little more than a mile southeast of Bumbletown Hill, and the bottom levels are almost vertically below the surface trace of the Houghton Conglomerate (see outThis immediate area is unique in that five different and widely crop map). separated layers have been at least modest producers, suggesting a common Stratigraphically highest is the Allouez Conglomerate; plumbing system. dumps of the old Allouez mine (1869—1892, l3,000T copper) lie along the A small headframel200m N65°E of the foot of the hill, 300 m southeast. hilltop is the Allouez No. 3 Shaft, which produced (1944—1964) about l7,000T of copper from the Houghton Conglomerate (No. 14) and 2000T copper from the Iroquois Amygdaloid, 170 m stratigraphically beneath; The large headframe 6200 feet due both were found by diamond drilling. �59 east of the hilltop serves the shaft of the Kingstone Mine; this deposit, discovered in 1962 also by diamond drilling, is in the Kingston Conglomerate (No. 12), 300 m stratigraphically above the Kearsarge Flow. The outcrops on the top and upper slopes of Bumbletown Hill represent a series of andesite flows, some slightly porphyritic. The flows range Unlike the basaltic flows found below the up to 20 m in thickness. Houghton Conglomerate, these flows are not individually very extensive; the map shows two flows pinching out within this small area. As a group, the hilltop are stratigraphically equivalent the flows in the vicinity of whose and lithologically similar to those tops were mined at the Quincy Mine, just north of Hancock. The Greenstone Flow is exposed in a series of outcrops 160—300 m southIts thick amygdaloidal top is exposed at the end east of the hilltop. of a private roadway 200 m south—southeast of the hilltop. Columnar fine—grained basalt and ophitic basalt can be seen in exposures farther down the slope. 45.05 Take a left turn on US—4l and cross into Retrace route back to US—4l. Keweenaw County from Houghton County. 45.9 Entering Ahmeek. 46.25 Junction to Cliff Drive. MAP 10 47.65 49.5 Turn left on Cliff Drive. Passing Seneca Lake on the right hand side of the road. We are driving Along the road are along strike, near the base of the Greenstone flow. several small basalt outcrops mostly on the left side of the road, At this point the Greenstone Flow abruptly thickens to nearly 400 m. It dips northward at about 25° toward the Lake Superior Syncline. This lava flow can be traced along much of the Keweenaw and has been stratigraphically and geochemically correlated with a similar unit on Isle Royale, 90 Km away on the other side of the syncline (see Fig. Thus the areal extent 3a). of this great flow exceeds 5000 and its volume is of the order of 800— 1500 Km3 according to White (1960) and Longo (1983). It rivals the composite Roza flow (Columbia R.) as the largest known lava flow on earth, The Greenstone typically shows spectacularly developed pegmatites, ophitic horizons and columnar jointed areas. A cross section of the Greenstone Flow at this locality and a map of the zone where the flow thickens rapidly The pegmatoid zone is unusually thick in the northern are in Figure 29. part of this map. The ophitic zones of the flow are relatively unaltered portions and Longo (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical similarity of the composition of the Isle Royale and Keweenaw ophitic exposures of The rapid thickening of the Greenstone here was sugthe Greenstone Flow. gested by White (pers. comm., 1982) to be caused by the separation of the upper part of the flow into multiple flow units, which appear to be separate flows. To the north the flow may be a continuous, single flow unit, while to the south it may have been made up of many flow units. �—_ . ,.// ! • • ,•//Moh /7 0 ) / ( - / •1' 2 Io / ) ) �10 I EM 0 7 SCALE 1 mile Figure 29: Map and cross section showing vertical zones within the Greenstone flow between Seneca and the Cliff Mine (from Longo, 1983). I 92 1 2 20 15 225 285 680 (feet) Thickness Vertical Scale: 1"=200' Sub-ophite Pg: 2nd Pegmatoid Zone -Sub-ophite Pg: 1st Pegmatoid Zone LOp: Lower Ophite Pg: 3rd Pegmatoid Zone UOp: Upper Ophite Mel anophyre EM: Columnar Jointed Top of Flow Vesiculated Flow Top �62 MAP 10 and 11 50.0 Crossing the Cratiot River MAP 11 50.6 52.5 We are now driving on the southeast side of a prominent ridge which is held up by the Greenstone Plow. We are at the site of the Cliff Mine which was the first mine in the district. The dumps ind old footings for the mine building are mainly on the 1.eft hand side of the road and the townsite, of which little remains, is on the right hand side of the road. optional stop where one can look at the Greenstone Flow and the Cliff Mine dumps. In this region the Creenatone Flow is mainly ophitic basalt and sometimes shows quite well dev.loped coarse columnar jointing. The Cliff Mine worked the Cliff fissure. The mine operated discontinuously from 1845 to 1887. It produced a tote] of abcwt 38 million The productive portion of the fissure lies under lbs. of refined copper. the Creenstone Flow. The Cliff fissure is nearly at right angles to the attitude of bedding and dips steeply to the east. Most of the mineralization was confined to the fissure although SOL1C amygdaloids were mineralized (Cliff Mine suinmarizedtromsutler and Burbank, 1929). Many large masses of native copper were mined from the Cliff Mine and larger masses weighed up to 100 tons. The large 100 ton mass had to be cut, by hand, into smaller pieces, it could not be blasted (Clarke, 1976). Among the fissures rhr Cliff was the In addition to native copper and silver the followmost productive of silver. caling minerals are found at the Cliff Mine (not in order of abundance): cite, epidote, chlorite, laumontite, prehnite. datolite, thomsonite, chlora— strolite, apophyllite, adularia, gypsum, sphalerite, galena, pyrite and surface oxidation minerals. This is zir 53.1 Tunction of U5—41/M—26. Turn left (north). MAP 12 53.4 Entering Phoenix 54.5 Turn left on a dirt road just before (0.1 mile) the junction between US—41 It is about 100 meters from the paved road to the base of the and M—26. Phoenix Nine dump which is Stop 14. STOP 14. Phoenix Mine and Greenstone Plow. At this stop one can look at the Phoenix Mine dump and the lower ophite of The Phoenix Mine worked numerous veins below the the Creenstone Flow. Greenstone Flow. Like the Cliff Mine discussed at mileage 52.5, the Phoenix t'Iine was one of the. eatltet mines in tze d.Lstrict and opexattd off and cc'. from 1849 to 1917. It produced a total of about 17 million lbs. of refined The Phoenix Mine also worked the Ashbed copper (Butier and Burbank, 1929). ainygdaloid where it is mineralized in the vicinity of vein copper occurrences. The Phoenix Mine dump is notable for halfbreedS (native copper plus native silver) and for spectacular secondary analcite. Other minerals reported in the Phoenix Mine ares (Clarke, 1974a) include: pumpellyite, chlorite, natrolite, chlorastrolite, and apophyllire. �It I -t- /1 -iii - I I - 'I (/ If.-r: V- - I -/2 - // // 'i \ /_ 1;' FJ 'T 'ii L7 I - - C - L -.-. - - -c C: --- - - - // - - -:--- Efri /2- - -- r - -- / -: - • / - : '\-. = — — .1 / (r / . /9GOI H ,/ /7 - - // /I- , / I /2 --r - I ' -I \ C9 �_ oo __ - - 0 '. "/ - ' w. ta - '.;:.' Phoenix Ashbed1.. - Workings ! LI9 -- 0 / - /; 4 - / - r A9i-PhoenIx Mine - K Stop 11' MAP 12 -- �54.6 Flow. Greenstonie the cross and strike to perpendicular drive River. Eagle towards M—26 on left Turn 55.0 flow. the in middle cooling slower the represent which exposures, these on found be can cm 5 to up pyroxenes individual with texture, ophitic coarse Exceptionally road. the of left the to Flow Greenstone the of Outcrops 55.4 River. Eagle along traverse a begin also can one road, the up just 15, Stop At spring. the of periods water high the in done be can't This contacts. flow many at looking River Eagle to way the all here from downstream river the follow can You pools. deep many are there locality this in and road the of site the from m 25 about is River Eagle River. Eagle along seen be can Flow Greenstone the above flows the where stop optional an is This road. the of side hand right the on pull—out a is There 55.7 downstream. or upstream either River Eagle along traverse a begin to possible is it stop this At flow. Ashbed the of north River Eagle in bend sharp very a is There flow. Ashbed the crosses River Eagle locality this In right. the on pull—out road dirt maintained poorly a is There to begin and River Eagle Cross l951b). (l951a, Cornwall by papers in described was Flow Greenstone the of differentiation of petrology and chemistry The Sn Sc 28 Zr Zn Y V Sr 195 259 92 84 14 wt.% ppm 0.14 1.2 0.4 2.1 9.9 7.8 12.8 15.1 46.7 214 104 6 8 186 1680 11 66 Rb Ni Mn La Cu Cr Ba Ti02 K20 Na20 CaO MgO FeO* A1203 Si02 is: (1983) Longo of study from determined Flow, Greenstone unaltered the of composition average The 1877—1887. from 1,000 of population a had which Phoenix, of townsite the of and flow great the of strike the of view a is there Ridge Greenstone the of top the From observed. be all can zones ophitic and subophitic pegmatoid, the cliff the along exposures the following By 30. Figure in shown ophitic lower the is zone ophitic The Flow. Greenstone the of portion ophitic the of exposure spectacular a is there where hill the of top the to climb and ahead Proceed shaft. the above just zones fissure the of one pass then and dump the over up climb must you Flow Greenstone the at look To 65 �1 mIle PHOENIX (Longo, 1983). Figure 30: Section and map of the zonation of the Greenstone flow near Phoenix, Michigan SCALE I 78 540 5 62 8 170 35 25 250 (feet) Thickness I ____. ______ Lower Ophite Vertical Scale: 1"200' Bottom of Flow LOp: Sub-ophite Pg: Pegmatoid Zone _—Pg: Pegmatoid Zone Sub-ophite C' a.' Pegmatoid Lenses with intercalated lenses of ophites and sub—ophites Sub-ophite Pg: Pegmatoid Zone Pg UOp: Upper Ophite Ml: Melanophyric Zone Top of Flow �67 STOP 15. Eagle River Eagle River, Jacobs Creek and Owl Creek each make excellent stream traverses which are regularly mapped as an introductory exercise in the Michigan Tech field camp. At this point, approximately at the Ashbed amygdaloid, a traverse along the stream north to Eagle River allows excellent observations of the upper stratigraphy of the Portage Lake Volcanics. The Ashbed is a very distinctive fragmental amygdaloid traced over a distance of almost 100 Km in outcrop and drill holes. It is the second flow top below the Hancock Conglomerate (Fig. 31 and Map 12). The amygdaloid is a jumble of amygdaloid fragments and interstitial brown, fine—grained detrital material. The secondary minerals filling the amygdaloid are calcite quartz, chlorite and minor epidote. Some vesicles contain minute Exposures of the Ashbed are found both in flecks of Cu (White, 197lb). Small mines were found along this horiroadcut and within the streambed. zon in many places, from Atlantic Mine (near Stop 3) to Copper Falls (Stop 17) The stream traverse to Eagle River traverses the section shown in Figure 31. Among the features seen in the traverse are: 1) excellent sections through individual lava flows showing amygdaloidal tops, and massive melaphyric, 2) Interbedding of sediments glomeroporphyritic or ophitic lower portions. with the lava flows, which becomes more prevalent up section. 3) The occurrences of several dikes which cut the section at low angles. These dikes make up a very small portion of the volume of the section and may be analogous to the dikes described in the Tertiary lavas of eastern Iceland by Walker (1975). If you decide to take this traverse, it's best to to wet feet and the traverse is not advisable in the just resign yourself water. spring because of high The flows just above the Greenstone Flow are compositionally different from Although they are tholeiitic basalt like most of the Portage Lake Lavas. nearly all the PLy, these rocks are distinctly higher in K20 and other inLower in the stratigraphy below the Gratiot compatible elements (Fig. 32). flow another zone of K—enriched basalts occur. This caused Rose and Crimes (1979) to divide the PLV into three cycles of basaltic lavas each of which The cycles may reflect different begins with relatively K—enriched basalts. It is interesting to note that degrees of partial melting or fractionation. one of these cycles begins after emplacement of the Greenstone Flow. 55.9 There is an outcrop of amygdaloidal basalt on the left side of the road. Further off of the road is a rock dump from the Phoenix Ashbed workings (1855—1862, 1913—1917, 400T Cu). 56.6 Entering Eagle River. On the left is the road to Five Mile Point. The stone monument is a memorial to Douglass Houghton who was the first State He did pioneering geologic studies in the Keweenaw Geologist of Michigan. He drowned off Eagle River in 1845. Peninsula. 56.8 Cross Eagle River on the Eagle River Bridge. Park NE of the bridge. �COPPER HARBOR CONGLOMERATE 68 14000 Stratigraphy of Figure 31: the Portage Lake Volcanics above the Greenstone flow in the vicinity of Eagle River and Phoenix, Michigan (from Cornwall and Wright, 1954). Melaphyre Tongue of Copper Harbor conglomerate MelophyreS 13000— Ophihc flows; thickest flow pegmatific Melaphyres flows; thickest flow pegmatitic Melaphyres; thicker flows slightly glorneroporphyritic and ophitic 12000— —Hancock conglomerate (No. 17) gygaloid}t egrained rnelaphyreo, Ashbed porphyritic Melaphyres; thicker flows glomeroporphyritic and pegmatitic melaphyres, porphyritic lomeroporphyritiC flows Upper chill zone Greenstone flow PORTAGE LAKE LAVA SERIES �• .S •5 S .•• S • • • S. S • S S I • S S S. •• S • S •S S S S. S •. •S ::, S S. S. ••S. S • S • •S • S • • 2 S S S • 1(20 3 ' S M-O 5wt% 75 50 - 25— No. S •• • S S :. S S S S S . S • S :S. S. •5 S S • S S S • S S S S • S •:. S 55S • S S S S S S. • .2 S S S S • S .3 P205 I .4 .5 GS wt% top) sampled Figure 32: Plot of K20 and P205 content of 106 individual PLV flows in stratigraphic order (1 in drill holes across the section in the vicinity of Delaware by W. S. White (pers. comm., 1976) and reported GS represents the Greenstone flow horizon, M—0 represents the melaphyre—ophite line, by Rose and Grimes, 1979. a texturally traceable line in the PLV below the Gratiot flow in this area. The stratigraphic position is plotted by flow no. and is not to scale. 75. 50 25 No. S S 1 I �70 STOP 16. Eagle River Falls. The falls occur at the contact between the top of the Portage Lake Volcanics and the base of the Copper Harbor Conglomerate. There are some spectacular If the water is low, like it is potholes that have developed on this face. sometimes in the summer, you can see ropy surfaces on flows at the top of The contact dips about 30° NNW. The contact the Portage Lake Volcanics. relationships suggest very little erosion between the flow and deposition Under the bridge one of the basalt beds of the Copper Harbor Conglomerate. can get a good view of the lithology of the lower part of the Copper Harbor It consists of mostly rhyolite pebble conglomerates but inConglomerate. cludes many sandstone and even some shaley beds. There is an optional route to Eagle Harbor via Sand Dunes Drive given after the Garden City road log. NOTE: Eagle River to Eagle Harbor via Garden City Road MAP 12 56.85 Go straight after crossing the bridge. M—26 goes to the left which is the optional route. Passing in front of the Keweenaw County Courthouse and offices. 57.1 Gitche Gumee Bible Camp, continue on paved road. 57.2 Pavement ends. MAP 13 60.2 This is the Garden City Road. Junction with paved road. Turn left towards Eagle Harbor. 60.3 Cross Jacobs Creek. 60.5 Junction of a dirt road on the left. Continue ahead on paved road. From this road, a short distance to the west, there is access into Jacobs Creek, at the site of the Arnold Mine, along the Ashbed amygdaloid. This is the end of a traverse one can make across the upper part of the Portage It is recommended to begin the traverse at the lower end Lake Volcanics. of Jacobs Creek where it crosses M—26 (Sand Dunes Drive optional route to This is a very tough traverse with many steep and dangerous Eagle Harbor). There are excellent exposures of many individual lava points within it. At the Arnold Mine, one of the nearly conformable flows along Jacobs Creek. Geologic traverses made along massive dikes is exposed in the streambed. ahead), and Jacobs Creek allow Eagle River (Stop 16), Owl Creek (Stop 17 lateral variations in the upper part of the Portage one to look in detail at Lake Volcanics. �\\\\\ 71 — 1 :,, '' \" 'I J• I \\; ' lHwtl 0 . . 4. £L - Coooer Harbor Corg!omes an k ( ' \\ i \\ - MAP 13 I - 11 k I; �72 61.2 On the left is a roadside park with a tower. From the top of this tower there is an excellent view of Isle Royale on a clear day. You can also see some of the ridge—valley topography due to the dipping lava flows and conglomerates in this part of the section. 61.9 Dirt road that slants to the right goes to the old townsite of Copper Falls. Copper Fails was settled in about 1846 and had a population of 500 in 1877. Today there are a handful of residents. 62.2 Cross Owl Creek. 62.3 Road to the right goes upstream to the dumps of the Copper Falls Mine which is part of Stop 17 described below. 62.4 If you follow this road several hundred Road to the left goes downhill. meters, you will reach the 30—mile stampsands which are the tailings dump from the Copper Falls mining operation. From this stampsand you can gain access to the bottom of Owl Creek and can begin a one—hour traverse upIf you continue upstream beyond stream to the bridge along this road. the bridge, you will reach poor rock dumped along Owl Creek from the Copper Falls mining operation. By climbing out of the creek bed, to the east, one can reach a dirt road which will come out on the main road at 62.3 STOP 17. Owl Creek — Copper Falls Mine. Owl Creek is another one of the streams that cut across the upper part of The traverse begins downstream where the base the Portage Lake Volcanics. of the Copper Harbor Conglomerate and top of the Portage Lake VoiLcanics interfinger. There are excellent exposures of interbedded conglomerate! There are sandstone and lava flows along the bed and sides of Owl Creek. several well exposed amygdaloidal flows. The Copper Falls Mining Company worked several fissures and the Ashbed The mine operated from 1847 to 1893. It produced about 18 amygdaloid. million lbs. of refined copper from the Ashbed amygdaloid and about 9 Copper Falls million lbs. from fissures, mostly the Owl Creek fissure was the only mine in the north end of the district above the Greenstorie flow that paid dividends but was not a profitable venture (summarized from Butler and Burbank, 1929). The Owl Creek vein starts near the base of the Copper Harbor Conglomerate and extends through the Portage Lake Volcanic Series, probably into the Greenstone flow. The vein was productive only in the vicinity of the Ash— bed amygdaloid. The Ashbed flows are distinctly porphyritic. The amygda— bid is scoriaceous with a notable clastic component. In some localities The mineralpebbles and boulders of amygdaboid are set in a sandy matrix. ization of the Ashbed amydgdaloid is similar to that found in other amygda— bids in the Keweenaw Peninsula. At the Copper Falls Mine the more abundant minerals are: calcite, quartz, epidote, and pumpellyite. Datolite is abundant in the Ashbed near fissures. Datolite is abundant in fissures Native copper was more abundant toward the top part of such as Owl Creek. the deposit. Other minerals reported in the Copper Falls area include: �73 laumonitite, prehnite, native silver, adularia, analcite, apophylite, faugasite, natrolite, stilbite (summarized from Butler and Burbank, The Copper Falls Mine is stratigraphically one 1929; Clarke, l974b). highest in the Keweenaw native copper district and is near the top of the pumpellyite zone (see Figs. 4b and 9a in the Introduction). MAP 14 63.75 63.85 Crossing Eliza Creek There is a dirt road that goes off to the right. From this dirt road just a few hundred meters up hill you can begin a traverse upstream on Eliza Creek to get the exposures of the Portage Lake Lava flows of this region. 64.9 We are at Eagle Harbor where we join back up with M—26. Turn right on M—26. Eagle River to Eagle Harbor via Sand Dunes Drive (M—26). MAP 12 o At Eagle River Bridge make a sharp left turn, follow M—26. 0.1 Sharp right turn. MAP 13 3.05 Jacobs Creek Falls. From this point one can begin a traverse up Jacobs Creek that ends near the Arnold Mine on the Garden City Road (mileage There are excellent exposures of the upper part of the Portage 60.5). For those who are hardy, the stream Lake Vol.canics along Jacobs Creek. offers virtually continuous exposures through thin pahoehoe flows, especially in the first several hundred meters. This is a steep and rough traverse, and should not be attempted in high water periods. 4.9 Great Sand Bay. 5.9 The Lake Shore Traps form the offshore ridge. The Lake Shore Cat Harbor. Traps are mafic lava flows interbedded with the Copper Harbor Conglomerate. MAP 14 7.8 Right hand turn by the Eagle Harbor Store. 8.0 We are at the Junction of M—26 and Garden City Road Route. Return to Main Road Log Mileage. Stay on M—26. �/ - ( I - - - C..-;. *i . etC r Lake Superior - - '"1 it /// .. ( . / ci' iI - 41" 63gke ':yh ff \ ag H / I 8/AST GUARD O8 \..( GLE HARBOR (32 S ____ - . z-- .. �75 65.0 65.75 MAP 15 66.9 67.5 67.65 The harbor at Eagle Harbor is controlled by the occurrence of units which These are basalt flows which are inter— are called the Lake Shore Traps. bedded with conglomerates of the Copper Harbor Conglomerate and form typiThere are excellent exposures of the Lake Shore cally resistant ridges. Traps that occur at the Eagle Harbor Marina and continuing along the shore through Grand Marais Harbor and into Agate Harbor and eastward through small boat from the Copper Harbor. These are accessible by canoe or winds are on—shore. Marina, but don't try it if the Junction to the left to the Eagle Harbor Marina. Continue ahead on M—26. On the right hand side you can see the offA view of Grand Marais Harbor. shore islands and ridges which are controlled by the occurrence of the Lake Shore Traps. We are driving along a conglomerate ridge. this Road passes along the shores of Lake Bailey on the right hand side of Harbor Conglomerate conglomerate ridge. The ridges throughout the Copper the valleys are underlain by the tend to be held up by the conglomerates, On conglomerate. and shaley members within the more easily eroded sandy The (on the right) is Mount Lookout. the opposite side of Lake Bailey Vol— contact between the Copper Harbor Conglomerate and the Portage Lake canics runs through the back side of Mt. Lookout. sandstone On the left hand side of the road there are exposures of the members of the Copper Harbor Conglomerate. NAP 16 69.1 69.2 69.7 70.0 Crossing the Silver River there are excellent exposures of the Copper Brock— Harbor at this locality and along the left hand side of the road up look at the Copper Harbor way Mountain. This is an optional stop to At Eagle River Falls (Stop 16) one had the opportunity to Conglomerate. At this locality look at the basal beds of the Copper Harbor Conglomerate. of the formation, just bewe are stratigraphically in the more central part (20) one low abundant interbeds of Lake Shore Traps. At an upcoming stop The formation. will get the opportunity to look at the upper part of the of other stops. lithology of the sediments here can be compared to those the summit On the south side of the road at this stop a 3 Km trail leads to in the of Mt. Lookout (Map 15), one of the most spectacular viewpoints contact The summit is located on conglomerate, but very near the Keweenaw. with the Portage Lake Volcanics. Allow at least 1½ hours. this Junction to Brockway Mountai1 Drive. We are going to come back to Go to Park. point but we are going to first take a side trip to Esrey the left on M—26. shallow dipping We are now at the shore of Lake Superior where there are approxilava flows of the Lake Shore Traps. The road follows the shore mately parallel to the strike of the lava flows. STOP 18. Esrey Park. �___ ti del4f SI. dVV\I - - _; 3 3 - I p O4 • . —:- - .. ---— - —-I i20° - — - - _- ____________ — C- ——- S I - .. -. - )) Th of magflet .— Approxtmate posItlOfl °I/ .D - 1ff yi pa qtl V �- /_ \ * I r copper Copper L - _i_=-i j' - _ : - -— rbOr. -- - - - 4-.••• - 20 ,.:—.--—:- — ., Shore TrapS. _—- ,— -A Ashbed I T1ZH hc -.-- e -TiLak •:. ! ngtOmC rate ——-— - catedbY2lrb0 _____ tl / _______ - - _ �78 The rocks cropping Out at Esrey Park are lava flows of the Lake Shore Traps. The Lake Shore Traps consist of a number of lava flows interstratified within the Copper Harbor Conglomerate. The Lake Shore Traps extend from the tip of the Keweenaw Peninsula west and south to just north of Hancock. They lie stratigraphically near the middle of the Copper Harbor Conglomerate. They consist dominantly of mafic flows similar to those of the Some intermediate compositions have also been Portage Lake Volcanics. reported. The Lake Shore Traps represent the waning stages of Keweenawan volcanism in the Keweenaw Peninsula. Several of these flows have been traced offshore by prominent magnetic anomalies. The large outcrop between the parking lot and the lakeshore is the massive interior of a fine grained basaltic flow which strikes approximately parallel to the shore. The flow's amygdaloidal top can be observed along the lakeThe metamorphic grade of these rocks is substantially shore to the east. lower than that of the Portage Lake Volcanic Series, i.e. within the zeolite zone. Note the "fresh" appearance of massive interior basalt (with olivine phenocrysts) and the low temperature amygdaloidal minerals (in order of calcite, chlorite, laumontite quartz, adularia decreasing abundance): and analcite. 70.1 Turn around and head back towards the junction of Brockway Mountain Drive. 70.9 Sharp left turn onto the Brockway Mountain Drive followed by some more exposures of the sandy conglomerate zones within the Copper Harbor Conglomerate. We will drive for several kilometers along a conglomerate ridge with many conglomerate exposures. MAP 17 75.9 At the summit of Brockway Mountain we take a right turn a short distance to the observation site. STOP 19. Brockway Mountain Viewpoint. This high conglomerate ridge reaches an elevation of over 1300 feet and is one of the best known tourist stops in the whole Keweenaw. Excellent views of the ridge and valley topography of the northern shore of the Keweenaw can be had here, because the scrub vegetation allows a 360° panorama. The conglomerate here dips at about 20° to the north. To the west the Lake Shore Traps form prominent drowned ridges in the vicinity of Esrey Park. Lake Bailey (with the small island) and Lake Upsom occupy a topographically low valley of finer grained clastic sediments within the Copper Harbor Conglomerate. Just to the south of Lake Bailey the conglomerate ridge of Mt. Lookout can be seen, marking the contact between The inland the Copper Harbor Conglomerate and the Portage Lake Volcanics. lake almost directly south is Lake Medora, and just beyond the lake is a prominent ridge which marks the stratigraphic position of the Greenstone flow. In the distance, farther to the south across Lake Medora, Mount To the southBohemia (Stop 21) with a fire tower on top can be seen. west a distant ridge with white Air Force tracking buildings on it, marks Gratiot Mountain, which is underlain by andesitic dikes and small rhyolite bodies. To the east, Copper Harbor is visible and Lake Fanny Hooe (see Map 18) which occupies the same stratigraphic horizon as Lake Bailey. Beyond Copper Harbor to the east, East Ridge, a conglomerate ridge, is To the north, on the skyline 65 Km the prominent hill on the skyline. away is Isle Royale, easily visible on a clear day. The skyline of Isle �8- Map 16 _ —-- er — -- —--- i_ I 9 ( - Dans P9int N. _J I Lake Shore Tr,ps 26 __-1 —-- — -—--—- (3 — —c- - — et L - Stop 20 —= - - I /077 — Harbor — - — : 26 - - —- 4 Su;_5Or ILake —t . — ••- -- I -- -i_s -e I'.. —. .---.. - '''c —— — p /1) ( i— ) — -I --_----- ——. — --- - '.— —— —- .•1. .f.. .••\ '.4—.. 2! ..ii&' ) :jt .SM.c14— •Q=__ aSr.'; t .-..'—- — "••• SV,.fl -—__75 :nrftt - —-;. — _ ____ �80 Royale is the Greenstone Ridge, underlain by the Greenstone flow, which is apparently a continuous unit all the way from one side of the syncline to the other. It may be the largest single lava flow on earth, with a volume of more than 1500 Km3 (Longo, 1983). 75.9 MAP 18 79.45 80.5 MAP 17 81.7 83.35 We turn to the right and follow the road straight ahead toward Copper Harbor now going downhill and continuing along the ridge with excellent views all the way down. There is a pull—out on the right hand side of the road to give an excellent Copper Harbor is controlled by view of Copper Harbor and Lake Fanny Hooe. The islands offhsore including the occurrence of the Lake Shore Traps. Porters Island are underlain by lava flows. From the Copper Harbor Marina, with a small boat you can have access to excellent exposures of the Lake Shore Traps along the edges of Copper Harbor. There are exposures of the Copper Harbor Conglomerate along the road descending into Copper Harbor. Junction at M—26, turn left. We come to the shore of the lake again at a place called the Devil's Washtub. If you stop here by the right hand side of the road and take a short walk along the conglomerate along the shore, you come to wave washed exposures of the conglomerate at the Devil's Washtub. STOP 20. Dan's Point. There is a small gift shop observation tower on the right hand side of the road. Walk just a few yards down to the shore of Lake Superior to look at the lithology of the Copper Harbor Conglomerate and the occurrence of stromatolite in well exposed and wave washed exposures. Dan's Point consists of a lakeshore outcrop of Copper Harbor Conglomerate that is characteristic of the upper two—thirds of the formation (sometimes called the Outer Conglomerate). As a whole, the Copper Harbor Conglomerate is a red—brown, basin—ward thickening wedge of volcanogenic clastics which attains a maximum thickness of 1830 m (Daniels, 1982). A coarse conglomerate facies consisting of well—rounded, poorly sorted clasts of mafic to silicic volcanic rock fragments directly overlies and locally interfingers with the lavas of the Portage Lake Volcanics (Elmore, 1981). The conglomerate facies is generally clast—supported and contains a ratio of mafic to silicic intermediate clasts of about 2:1. The Copper Harbor Conglomerate fines both distally and upsection so that sandstone interbeds become more frequent in the upper two—thirds of the formation. Sandstones are predominantly subangular to angular lithic graywackes which exhibit current—ripples, festoon trough—cross beds, parting lineations and dessica— tion features. Laminated crystalgal carbonate horizons are interbedded within the conglomeratic and sandstone facies in the upper two—thirds of the formation. Stromatolites occur as laterally—linked drapes over cobbles, as laterally—linked contorted beds in mudstone—siltstone lenses and as poorly developed mats in coarse sandstone (Elmore, 1981). �81 The depositional environment of the Copper Harbor Conglomerate has been interpreted as a prograding alluvial fan complex (Fig. 33) with proximal— to—distal braided stream and sheet flood facies on coalesced alluvial fans and sand flats (Elmore, 1981; Daniels, 1982). Isolated cryptoalgal carbonate and ooid lenses formed in shallow, medial fan lakes receiving very low rates of sediment influx (temporarily abandoned stream channels) (Elmore, 1981). Paleocurrent indicators suggest sediment transport was from the southeast to northwest indicating that a basin was located toward the center of the rift zone (Daniels, 1982). The stratigraphic section of the "Outer Conglomerate" (that part of the Copper Harbor Conglomerate above the Lake Shore Traps) exposed at Dan's Point consists of about 80—90 ft. of interbedded conglomerates and sandPredominantly clast—supported conglomerate beds consist stones (Fig. 34). of rounded, cobble—to—small boulder—sized clasts with a matrix of coarse sand—sized sub—angular grains cemented with iron oxides. Conglomerate clasts are predominantly felsic volcanics (approx. 70%) with sub—ordinate basalt, pyroclastic, plutonic and metamorphic lithic fragments. Several silty—sandstone interbeds higher in the exposed section exhibit cross— bedding, current lineations, ripple marks, parting lineation and (reduction spots along bedding. In particular one should note the white stromato— lite (genus Colleria) horizon draping cobbles about one—third of the way up the exposed section. Algal growth occurred during a period of depositional quiescence and was halted by an influx of silty material followed by renewed conglomerate deposition. Please do not remove stromatolite from the outcrop. Good specimens can be found in the pebble beach. 83.35 MAP 18 86.65 87.1 Turn around and go back toward Copper Harbor on M—26. To the left is the junction Junction, again, to the Brockway Mountain road. to the Copper Harbor Marina. Continue straight ahead on M—26 to Copper Harbor. Junction between M—26 and US—4l in Copper Harbor. out of Copper Harbor. Turn right on US—41, south Copper Harbor was suddenly a boom town in 1843, following the discovery of Porter's Island was the site of the first governcopper in the vicinity. ment land office and in 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe, to protect the miners from potentially hostile Indians. The lighthouse was built in 18o6. Fort Wilkins is now a state park with campMuch exploration activity took place in the ing facilities and a museum. fort and there are shafts and exploration pits immediate vicinity of the all along the land between Lake Fanny Hooe and the Harbor, mostly from In 1853 and for several decades thereexploration in the 1843—46 period. after mining activity took place south of the fort in a series of workings called the Clark Mine. The mineralization is of the fissure and amygdaloid type and consists of prehnite, epidote, analcite, quartz, laumontite, adularia, microcline, chlorite, datolite, calcite and several copper minerals including chalcocite, cuprite and tenorite as well as native copper. Agates are conspicuous in the amygdaloids here, and the area is well known for datolite collecting. One occurrence of manganese minerals in a fissure The manganese minerals found accounts for the name of Manganese Lake. brannite and manganite, orientite. The Estivant here were pyrolusite, of the Clark Mine lands which were deeded to Pine tract represents a part are now a nature preserve, containing some of the C&H Company in 1942 and Upper Peninsula. the last virgin pine tracts in the �L — -S. Cover P'-.. •.. . •• 963 W.AW __ -S ••. • ••- • . Copper :' - LL$i :;/ I• I /* • -, Shore p-----: •; - Lake tTTTTT+ Copp.r H - 4. • erJiarbr Lake Superior J z. HAYS — .) EXPLORATION Copper I 1 Copper Hao< _ '- .) --- ---- . !/ ;,j. �1982). Daniels, from (modified deposits stromatolitic containing lakes ephemeral shallow and deposits plain flood and stream braided fans, alluvial coalescing showing Conglomerate Harbor Copper the of environment depositional of cartoon Schematic 33. Figure — BAStNwARD 83 �I I I I I — IJj i: (T\ ; oooo00oqo;.ooy %o6,°fJ.. 0o:0 P ooj°Q4 ! I Ili. 9# I t'•' C' T rt CD C) CD CD- CD-. H- H. rtt)Q 0 o CD CD I H.t) H- t CD rl- CD CD H H- Fij 0 H. C -1 CD L) -C-- CO '-'1 CD C) CD CD- CD-. CD o '-1 oCDo CD- d 0 H. C 0 H- H- rrDrtCD '—j H- !10 00 H. H. (I) H- OC) H. rt H C o-r CD CD 0(J) H.H CD- CD CC rtH 00CC CD CD- 0HCD H- H- H- 0 0 rt H. C Hrt rt CDC) C) oCDCDCD CD CC H. 0 o o C)CDH H 0(000 0 C) CD CD OH CQ 0 H. CDHCD CD (I) H. CD rt HO -0 oCD 0 o- H. o H H H. HO 0C) 0 H- CI)—. CD c 00 (DrtC) H H. CD CCCD C CD-. C) CD CD H.CD 0 0 rt rt H- H. CD �85 Keweenaw Point, Horseshoe Harbor, East Bluff and other points of interest can be reached by taking an unmarked dirt road which goes eastward from the end of US—41. This road is rough and poorly maintained and may be followed around to Mandan. Horseshoe Harbor has excellent exposures of the Copper Harbor Conglomerate (Fig. 34). 88.2 MAP 19 91.45 MAP 20 94.3 94.55 MAP 21 97.3 MAP 20 101.4 101.6 Nice exposures of the Copper Harbor Conglomerate to the left of the road as we are going up the hill. Lake Medora on the right hand side of the road, Junction to the left to Mandan. Mandan now is only a few houses, it had 300 residents in 1910. Continue ahead on IJS—41. Road to the left. This is the entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. To visit Mount Houghton and Keweenaw point, you may exit here. Junction of the road to Lac La Belle, Turn left and continue to Stop 21 at Mt. Bohemia. If you wish to skip this stop, you may jump ahead to mileage 105.45. On the left hand side of the road is a large outcrop of amygdaloidal basalt of the Portage Lake Volcanics. These exposures are flows in the lower part of the formation below the Scales Creek flow (see Fig. 4 and in the Introduction). Dirt road turning off the main road to the left. This is STOP 21 at Mt. Bohemia, It is about one half mile walk up this road to. the summit of Mt. Bohemia; this is a four—wheel drive vehicle road. STOP 21. Mt. Bohemia. An intrusive body of diorite and granophyre crops out on the south slope of Mt. Bohemia. The majority of the intrusive body is a massive, medium— grained, miarolitic diorite. The major constituents of the diorite, are oligoclase and hornblende with lesser amounts of orthoclase, magnetite, uralitized augite, apatite, sphene, quartz, sericite, epidote, chlorite, and calcite. The later are alteration products or are introduced secondary minerals. The central core is a fine— to coarse—grained, miarolitic granophyre. The major constituents of the granophyre are albite, quartz and granophyric intergrowths of quartz and feldspar with lesser amounts of orthoclase, sericite, hornblende, apatite, sphene, magnetite and chlorite. Miarolitic cavities are lined with quartz, albite, calcite, chalcopyrite, and chalcocite (summarized from Cornwall, 1954). The Mt. Bohemia intrusive body yielded a Rb—Sr age of 1,130 ± 35 m.y. (Chauduri and Faure, 1968). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of The basalts are slightly the lower part of the Portage Lake Volcanics. metamorphosed at the contact. The intrusive body is cut by the Lac La Belle This fissure is mineralized with fissure which trends north—northwest. copper sulfides, mostly chalcopyrite and bornite and in gangue of calcite, chlorite, and quartz (summarized from Juilland, 1965). �P —— _ ( Dl / 4r? 4 — / p 6 \ / - 'P E4 ' p \ai\ L0 ON pg - - • 0 .•, ) /- .5, - /000 S — J/ .• Map 18 �''' p — • -- :TI 'I -; I ,;.. - - • '------—4\1— _j '/ K __\ / 3Yk. - Flow Sci K * Stop 21 :...' ...P 20 7 — �MAP 21 -— = - - - I —___ I V = 1 = — - -I — E) ) MF35N / —- Rv er // • ' - — t/ I 7-IS --- • • ap23 •• 'P24 Map 20 I a \ I --:- / t Ifft /080/P\ \ ---------- - :\i - .-;: - _ (1 �89 Andesitic dikes are found in the vicini.ty of Mt. Bohemia (Fig. 35a). They average about 5 m in thickness. The dikes intrude flows of the Portage Lake Volcanics, two flow tops are shown in Figure 35a as alpha and beta. The dikes and amygdaloidal flow tops carry copper sulfides. Copper sul— fides in other parts of the district are found typically as fracture fillings. Native copper is typical of amygdaloids. A variety of secondary The and opaque minerals are found in the dikes and flow tops (Fig. 35). paragenetic sequence is consistent with that for the other deposits in the district (compare Fig. 35c and Fig. 9b in the Introduction). Copper sul— The copper and sulfur in this occurrence fides are paragenetically late. is believed to be of direct magmatic origin related to the magma source that produced the andesite dikes and Mt. Bohemia intrusive body. The emplacement of flows, subconcordant faulting and chronologic sequence is: fracturing, dike emplacement, renewed movement along subconcordant breaks, regional low—grade metamorphic/hydrothermal alteration, minor folding and faulting, and sulfide mineralization (summarized from Robertson, 1975) The road Up to the summit of Mt. Bohemia crosses flows of the Portage Lake Volcanics. The diorite and granophyre intrusive complex crops out to the southeast of the summit. Intrusive stocks are not common in the Keweenaw Peninsula, Most of these occur in the lower part of the Portage Lake Vol— canics and are rhyolitic in composition. Mt. Bohemia is the only occurrence of a diorite stock in the Keweenaw Peninsula. OPTIONAL SIDE TRIP TO Lac La Belle Discussion of complex relationships along the Keweenaw Fault and the Keweenawan rhyolite bodies, Go straight ahead (south) towards Lac La O At turnoff to Mt. Bohemia. Belle down hill. O4 Junction of roads to left and right at Lac La Belle. MAP 21 To Bete Grise turn left. (See Map 22) Bete Gi se is located on the shore of Keweenaw Bay on the Keweenaw Fault. Along the shoreline east of the point where the road reaches the shore are several exposures of the Keweenaw Fault which crosses on and off These may be visited in canoe or small boat. Also shore several times. to the east are several of the rhyolite bodies which are chiefly found in the lower part of the Portage Lake Volcanics. Three tenths of a mile north of Bete Grise, four—wheel drive road continues east of the paved road to Smith's Fisheries. The road intersects the Bare Hill Rhyolite body, a shallow Beyond the end of the road at Smith's Fisheries a trail continues intrusive. eastward along the shore to the mouth of the Montreal River. From here one may traverse up river to several falls over fine outcrops of basaltic flows or continue along the shore to the Fish Cove Rhyolite, a compositionally zoned shallow intrusive (Bornhorst, 1975). Inland and not far from Bete Grise is the Mt. Houghton Rhyolite. This is an extrusive rhyolite dome �14 55 495I 18 I /48\ 43/31 \ 'i2 47 32' 46 ._—-- 34 22A7flh777/' _____jB 36< 37 6 I g8 7 25 ffflaTImffl1/7"° 4 50 Lac La Belle Fissure - 60 0 EM DIIHe —-.40 Amygdaloid - °jk \-c'-\ v-s, <j r--,1 64 I 7___2t1 Mt. Boheiat'\ .Oiorite,>vt\ \ __-c 56.54 — 61 FIRE TOWER \ 0 loo2oo Amyqdoloids and dike projected to 1300 elevation - )iogy and drQ hole locations in the Mount Bohemia area (modi - from a preliminary Calumet and ilecla Mining Company map). Secondary minerals MINERAL Chlorite Vesicle- Frocture- fillings fillings in dike matrix 0 Epio'ote Quartz 0 0 0 0 ca/cite 5cr/cite Pumpe//y/te Microc/ine o 0 - o Hem Pyri 1, Cc, su/fides Noth Copper - Common o G Minor Nonpyrogenic 0 Rare 0 —Absent Minerals in the DPis MINERAL Pyrogenic I Deuteric Hydrothermal Supergene Magnet/fe Chlorite Pumpe//ylte 3cr/cite .- 'ucrt Microc/ine Su/idj Cha/capyr,te Ga/eva 5p/,o/er,fe ——— Epidote Colch Hei I, Hematite Z Pyrite —— —— — —— ti ——-—— ——— —— P2 ietic sequence of secondary minra1s in the dikes. Pink born,te Purple born/fe Diqenife Ojucleite Cha/coc/te Hematite I.E Cove/life —-— Paragenesis of opaque minerals in dikes and flow tops at Mount Bohemia. Figure 35: Geologic map showing andesitic dikes near Mount Bohemia and occurrence and paragenesis of secondary and opaque minerals in the dikes (from Robertson, 1975). �Y) 1 I I FauI.' Creek e I', r0 Houghton ,. ,iJ \'_ �92 with prominent flow banding and block and ash flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 19). Rhyolites make up less than 1% of the mass of the Portage Lake Volcanics Considerable textural variety of as seen in outcrop on the Keweenaw. rhyolites are found including intrusive and extrusive rhyolite and even But the abundance and variety of rhyolitic boulders small ignimbrites. and cobbles within the interflow conglomerates demands that a large number of rhyolitic source areas must underly the Jacobsville south and east of the Keweenaw Fault. To Gratiot River. Turn right and proceed ahead 1.2 miles on paved road. At the west end of Lac La Belle, in the vicinity of Deer Lake, the rocks south of the Keweenaw Fault are Portage Lake basalts (Fig. 36). These rocks may represent the lowest stratigraphic horizons exposed in the The area has been studied by geological and Portage Lake Volcanics. geophysical methods by DeGraff (1976) and his model for the development It is still of this unusual feature is shown graphically in Figure 36. another example of confusing deformation which is typical of this great A traverse down the Little Gratiot River from the Lac La Belle— thrust. Gay Road crosses many outcrops of the basalts. The fault—bounded, tilted body of Portage Lake Volcanics was defined by dense array of magnetic and gravity profiles and a few key drillholes, The attitude of the beds was altered by the faulting, but the rocks, like the rest of the Portage Lake Volcanics, have normal magnetic polarity. AFTER OPTIONAL SIDE TRIP to Lac La Belle return to main road log. MAP 21 101.6 At Mt. Bohemia turnoff. 105.45 Back at the junction of US—4l, 106.5 Dirt road to the right goes to Stop 22 at the Delaware Mine. on the dirt road and follow the signs to the Delaware Mine. 106.2 STOP 22. Turn around and retrace route back to US—41. Make a left turn towards Mohawk. Turn right Delaware Mine. The Delaware Mine, first known as the Northwest Mine, has had a long and It was operated by various companies from about unprofitable history. The mi:ie mostly worked veins for mass copper. Three shafts 1847 to 1887. were opened in 1881 to mine copper from the Allouez Conglomerate (#1, #2, The Allouez Conglomerate was seen at Stop 13. Total production from #3). the Delaware Mine was about 7.5 million lbs. of refined copper. As with other vein deposits in the Keweenaw, the Delaware Mine is a notable locality for datolite. Other minerals reported from the Delaware Mine poor rock piles include (not in order of abundance): chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native silver (summarized from Clarke, 1975; Zelenka, 1978). �± \ -L Portage Lake VolcaflaS -o \ •Ro Gay Lee LaBeIle To sete Bo8e N N S S S llasalts and sandstones in a block south of the fault are exposed and overturned. l3asalts and sandstones in a block south of the fault are exposed and dip to the south. Classical fault contact between basalt and sandstone. Sandstone still exposed north of the IKeveenaw Fault. Sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Figure 36: Portage Lake Volcanics are found south of the Keweenaw Fault. At right successive cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976), P = PLy, J = Jacobsville. 11 \ Portage Lake VolcanicS 1' Mt Bohenja N Prior to faulting. �94 The Delaware Mine is open to tours for tourists during the summer months. It is owned and operated by Jack and Tom Poynter. At this stop one has the opportunity to look at the dumps from the Delaware Mine and to visit (for a fee) the underground workings. 106.35 MAP 23 109.0 Junction of Delaware Mine and US—4l. ahead towards Phoenix. Left turn on TJS—4l and continue Ahead we can see cliffs of the Greenstone flow. contact of the flow. Road nears the basal 110.3 Exposure of one of the flows beneath the Greenstone flow. 111.1 In the To the right one can see the Greenstone ridge in the background. foreground is the ghost town of Central and its associated dump piles. 111.45 Junction of paved roads to the right and left. Continue ahead on US—4l. The road to the left goes to Gratiot Lake and an Air Force Base; road to the right goes toward the ghost town of Central and the Central dump piles. The Central Mine worked a fissure vein striking nearly at right angles to bedding and dipping steeply to the east. The mine operated from 1854 to 1898 and produced about 52 million lbs. of copper. The fissure extends from just below the Greenstone flow to the Kearsarge Conglomerate. A strike fault at the Kearsarge Conglomerate offsets the vein to the west and below this it is not mineralized. The town of Central, settled in 1854, was settled mainly by Cornish immi— Although the area was mostly abandoned after the mine closed, grants. the descendants of these immigrants now living all across the country, hold a yearly reunion in July at the townsite. Later immigrant groups to the copper mining towns included: Italian, German, Croatian and Finnish people. MAP 24 112.8 Continue ahead on US—41. The road to the Junction of road to the right. right connects with an earlier part of this field trip at Jacobs Creek (mileage 60.3). 113.9 Another view of the ENE striking Greenstone flow holding up the prominent ridge. 114.6 Again another excellent view of the Greenstone flow ridge. MAP 12 115.4 Junction of M—26 and US—4l at Phoenix. There is an optional route from Phoenix to Ahmeek via US—41/M—26 given after the Five Mile Point road log. �- - - — ( I (L/ C4 ----i-I - - — .- —::; p- H. p p I 7 -- I I - 07 IL 1 ,. . - —y 24 — jge I — L — '7 :-fi0 L 2O' - J. - 1— y./ :' •O- c. . I 1 �_ ____ ___I de, • •-1-•r ,4. -— ".? ii /ç/)/11 \ I, ( // • ( - I \'\ •H \'\ .i • 1 —--\-- -, __ C _\ \\\ \\ \\ \\ \\ - -- \\ D — i4 i--, - I N -f I j 2 (fl ) \c \ LU — 1 copt 1 2 1 / ( - - C — /7 -- — - ••/// - 1 \\ '.1 1 -. - Map 1. �97 Phoenix to Ahmeek via Five Mile Point (a scenic route along the Lake Superior shore). MAP 12 115.4 Right turn toward Eagle River. 117.4 Left turn on to the road to Five Mile Point. MAPS 25 and 26 On the right hand side of the road is a turn—off to the Five Mile Point 112.2 In the front You must get permission to enter this area. lighthouse. yard of the lighthouse, there is a thin lava flow of the Lake Shore Traps with the Copper Harbor Conglomerate bed above and below it 121.5 MAP 27 126.9 Five Mile Point beach turn—off at the right hand side of the road. Along this beach there are many exposures of the Copper Harbor Conglomerate. Cross the Gratiot River. 128.45 A thin basalt flow, from a position just above the Greenstone flow, forms an outcrop here which displays a well—developed columnar jointing. The Greenstone flow itself shows spectacular columnar jointing in some areas, most notably along the Palisades shown on Isle Royale where columns 2 m In a few areas the colonade/entablature or more in diameter are found. jointing pattern described in Columbia River flood basalts is well— developed in the Greenstone. On the Keweenaw columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water—saturated when covered by the next lava flow. 128.7 Stop sign. 128.8 Another stop sign. 130.0 Right turn which is immediately followed by a stop sign in front of a Join US—4l with a right turn. Directly ahead at about 11:00 church. This is a shallow mine that worked the Kingston is the Kingston Mine. Total proConglomerate. The Kingston ore body was discovered in 1962. duction was about 20 million lbs. of copper until mining stopped in 1968 The mine was left open as a research operation (Weege and Pollack, 1971). in the late 1970's. Go straight ahead. Turn left followed in block by a right turn. The Kingston Conglomerate is stratigraphically about midway between the It is overlàirt by a Calumet Conglomerate and the Kearsarge amygdaloid. A bedding plane fault separates the over60 m thick ophitic basalt flow. The conglomerate rests on a lying basalt from the Kingston Conglomerate. The Kingston Conglomerate can be traced along scoriasceous amygdaloid. strike for over 100 Km and ranges in thickness from 0.3 to 30 m. In vicinity of the ore body it averages about 13 m. Where the bed is thick it consists of a lower layer of shale and siltstone, 10—15 cm thick and an upper congloineratic layer (summarized from Weege and Pollack, 1971). �MAP 25 M — .', ór 5 :; %0 r - - - 07/ / - / i - V ' 4 ,<' /\ �99 Fivemile Poini 6NDH / TcUAR 'I / / —- I I J Sevenmile / /• !Point V I. '1 C7 7f q Map4-'7 MAP 26 r/ �100 : 2 I? Lake Shon I,> J7 • • ( MAP 27 Ma, •./. / �The Kingston Conglomerate is typical of rhyolite pebble conglomerates. Pebbles are largely subangular to subrounded quartz—feldspar porphyry. Quartz—free porphyritic and nonporphyritic rhyolite pebbles, common in Interstitial sand other conglomerates, are not present in the Kingston. Sandstone composition is similar to the peb— and sand lenses are common. The intensity of mineralization is related to the amount of matrix bles. present which is an indication of the original permeability. The main alteration minerals are kaolinite and chlorite. Introduced calcite and copper are found as fillings in healed fractures, interstitially filling A few individual pebbles are replaced voids and replacing the matrix. Economically important copper is found as rims around clasts by copper. Matrix filling takes place along and as matrix replacement or filling. texture bands parallel to bedding. Epidote and quartz are also found as introduced minerals. Bleached rock is commonly associated with mineralization in the Keweenaw native copper district but is not present in the Kingston ore body. The abrupt thinning of the conglomerate bed localized the ore body with high grade ore nearest the pinch—out (Fig. 37) (summarized from Weege and Pollack, 197; Brumleve, 1976). PHOENIX TO AHMEEK VIA US—4l/M—26. MAP 12 O Continue straight ahead on US—4l/M—26. 0.5 Bear left on US—41/M—26. Junction of US—41 and Cliff Drive. excellent view of the Greenstone flow ridge. Another MAP 10 5.2 Lumber mill on the left side of the road. 6.0 Entering Mohawk. 6.1 On the left hand side of the road are mine dumps from the Mohawk Mine. The Mohawk Mine worked the Kearsarge amygdaloid which is described at Stop 11. 7.0 MAP 9 The hill on the skyline with the four towers on it is Bumbletowfl Hill, the location of Stop 13. 7.9 Junction of US—41/M—26 and Cliff Drive in Ahmeek. 8.0 Junction of US—4l/M—26 and the road from Five Mile Point. RETURN TO MAIN ROAD LOG MILEAGE. 130.0 Junction of US—41/M—26 and the road from Five Mile Point. 134.1 Junction of US—41/M—26 and M—2O3. �-- - - -..-, .— contact - .' ore body footwall -..' N N N N N N N N N N N N - N ' contact ha ngwall •' N N Schematic illustration of the funnelling effect on mineralizing 37: fluids causing localization of ore deposition (modified from Butler and Burbank, 1929 by Brumleve, 1976). Figure basalt ridge -— r .YfJ FI :- I! C �103 There is an optional route from Calumet to Hancock via M—203/Mctain State Park given after the TJS—41/M—26 road log. Calumet to Hancock via US—4l/M—26. 134.1 Continue straight ahead on US—41/M—26. MAP 28 134.8 Flashing light 135.7 Continue straight ahead. center of Calumet. A right turn leads to the The Osceola Mine Shaft No. 13 can be seen on Southern edge of Calumet. Follow the right hand side of the road behind the Holiday gas station. Mileage is not logged the roads on Map 28 if you wish to go to Stop 23. to this stop. STOP 23. Osceola Mine Shaft No. 6. ProThe Osceola Mine worked the Osceola amygdaloid in the Calumet area. duction from the Osceola amygdaloid began in 1879 and continued until 1920 when mining activity stopped. The mine reopened between 1925 to 193L A total of The mine reopened in 1925 and production continued until 1968. about 600 million lbs. of refined copper was removed from this mine which The amygdaloid was ranks fifth in the Keweenaw native copper district. developed for about four miles along strike and to a depth of 4,500 ft. along incline (2,700 ft. vertically) (summarized from Weege and Pollack, 1971). The Osceola flow is an ophitic basalt and varies in thickness from 35 to The thickest part of the flow, near Calumet, has been the most 210 feet. The Osceola flow has been traced from the Cliff Mine to the productive. In the Calumet area the flow strikes N35°E and dips around Arcadian. The top of the flow is a well developed fragmental amygdaloid 37°NW. consisting of well oxidized, reddish, angular fragments of vesicular lava which typically range in size from a few inches up to a foot in diameter. The lode ranged in thickness from 1 ft. up to and sometimes greater than Amygdules and the voids in the brecciated flow top are filled 60 ft. mostly with calcite, epidote, K—feldspar, chlorite, and native copper. Quartz is present in certain areas and there is also minor amounts of The fragmental amygda— prehnite, pumpellylte, laumontite, and analcite. bid is frequently interrupted by sill—like layers of dense basalt which may have been emplaced by injection of lava from the interior of the flow into the solidified, brecciated crust. These dense basalt layers proNative copper vided barriers to the movement of mineralizing solutions. in the Osceola ranges from disseminated to small masses up to an inch in diameter to large masses weighing hundreds of lbs. (summarized from Weege and Pollack, 1971; Butler and Burbank, 1929). The Osceola Shaft No. 6 is at the southwest end of the ore body and was A barrier zone is believed to have the richest part of the deposit. funnelled mineralizing solutions moving up dip resulting in the high Textures and colors characteristic of fragmental copper contents. Stoiber (unpublished data) made amygdaloid can be seen in this dump. secondary minerals in the dump as a an estimate of the percentages of �Map. - S N 104 N -1 I. .H.. t. :: ,'I -- - .1 - I' •r- - I.- •- '\_ &__ - --- - -L /\ . /Q — :1: c-.- , '1 -/1 .1 N s 42 — 1 1 L-4y'-*- - _s / /-N / ' -- -— 5/ --- /ss 0 5, 'r' -x tL - / 7l, — / H -' /,- 26- k_ __,; -I' 'V 081 A LS34 p LS33 5/5 — '3 N Q33 /: A II 1&J - :', — L312 P28 — I �105 whole: calcite, 59; microcline, 29; prehnite, 4; epidote, 1; quartz, 1; These and pumpellyite, laumontite and native copper can be chlorite, 5. found on this dump. Bleaching of the basalt in vicinity of native copper can be seen in individual specimens. 135.7 Continue ahead on US—4l/M—26 towards Hancock. No Maps Until Hancock Turn left on White Street. 145.45 Junction of White Street on the left. 145.9 Right turn on Tezcuco 146.0 Stop sign at Quincy Street. Go straight ahead through this stop sign one more block to Hancock Street where you make a left hand turn. 146.55 Middle of the Portage Lake Lift Bridge. 146.8 Junction of US—4l/M—26. Stay left on US—4l to the left past the Mobil and Erickson gas stations. 148.1 Left hand turn off Townsend Drive back into the Michigan Tech Campus. Street in Hancock. CALUMET TO HANCOCK VIA M—203/McLain State Park. O Junction US—41/M—26 and M—203 on the edge of Calumet. turn on M—203. Make a right hand No Maps Until Near McLain State Park. 0.5 Village Limit of Calumet. 2.5 Junction of road to Calumet Township Waterworks Park. 4.2 Bear right on Y 4.6 Nice view of Lake Superior. MAP 29 6.7 with Continue straight ahead. another paved road. Continue on M—203. Road to the right is Lakeshore Drive which goes to Calumet Township Waterworks Park; road to the left is Salo Road to the Bear Lake Rhyolite. The Bear Lake Rhyolite cuts the Freda Sandstone bedrock. It is the youngest known igneous activity in the Keweenaw Peninsula. The Bear Lake Rhyolite is a minimum of 1054 ± 34 m.y. years old based on a K/Ar age date (White, 1968). 7.0 Exposures of sand dunes on the right. 7.5 Bear Lake on the left hand side of the road. glacial Bear Lake Channel. Cross on top of the filled �_ __ __ 106 /('i2 (/ F •... LVA A K E T;_ r I654 eøx COAST \GUARD 7( -' 715 2 792 ( 77 Lily Pond I' I' IIv,i )_i. = TO Hahc MAP 29 1J 26 . T BI 9 i ---V( / TTi N _ af n== c/ : 25 �107 The Bear Lake Channel (Map 29) represents a deep bedrock valley, the Although the Waterway was dredged extension of the Keweenaw Waterway. to the west of McLain Park, because the distance was less, the Bear Lake Channel is a much more profound feature, with more than 600 feet The definition of this and other similar bedrock valleys to bedrock. is shown by gravity data. One such traverse, plotted on the map, is See also the discussion of the origin of the displayed as Figure 38. Keweenaw Waterway under Stops 1, 5 and 6. 8.4 Entrance to McLain State Park and the other edge of the Bear Lake Channel. Camping facilities are located here. 9.2 Continue on M—203. Road to the right is to the Coast Guard Station; road to the left is the Bear Lake Road, location of gravity traverse. 10.6 Access road to Lily Pond. At this point the End Moraine of the Keweenaw Lobe, a great mass of glacial ice which was stabilized here during the Wisconsin glaciation, is crossed. The The regional distribution of this moraine is plotted in Figure 14. positions of lobes as they retreated at the end of the Wisconsin period are shown in Figure 15. 13.5 High Point Road, continue ahead on M—203. NAP 30 16.1 Cross Swedetown Creek. To the northeast along Swedetown Creek there are If one is interested in looking in more expcsures of Freda Sandstone. detail at the Freda Sandstone, excellent exposures can be found elsewhere. In the local area excellent exposures of Freda Sandstone are present along Redridge/Freda can the shore of Lake Superior between Redridge and Freda. be reached by following the Houghton Canal Road which begins on the west side of Houghton (see Fig. 17). 16.55 Access to Hancock Campground. The Nonesuch Shale is exposed in an abanThis is Stop 24 and doned quarry located just NE of the boat launch. mileage is not logged from the main road to the quarry. STOP 24. Hancock Campground. As a whole, the Nonesuch Shale consists primarily of siltstone with subordinate amounts of shale and sandstone. It can be distinguished from the formations above and below by its generally grayish color. Most Nonesuch Lithologically is a rippled, laminated siltstone with reddish—gray partings. siltstones and sandstones of the Nonesuch are composed of around 30 to 40 The rock fragpercent rock fragments and 60 to 70 percent mineral grains. ments are mostly volcanic with a 2:1 ratio of mafic to silicic + intermediate The Nonesuch is stratigraphically between the composition (Daniels, 1982). Copper Harbor Conglomerate and Freda Sandstone (Fig. 5). It is The Nonesuch crops out around the margin of the quarry at this stop. a fine— to medium—grained, gray to reddish brown sandstone with subordinate interbedded, reddish—brown laminated siltstone and shale (Cornwall and The attitude of bedding here is about N30°E, 25°W. Wright, 1956). �108 BEAR LAKE 9 8 7 6 5 4( I 2 I I 4 6 8 0 12 14 x 0 2 -3 Q) S a) Li Results of gravity measurements across the Bear Lake Figure 38: traverse plotted in Map 29. At top is Bouguer anomaly with regional In the middle the regional trend is subtracted to get the trend. solid line which is compared with the modelled topography (X's). Below is the model of the valley and the density difference of the bedrock (Freda Sandstone) and the valley fill (Warren, 1981). �109 n 'I - • McI31fl State Park / I V I t , .,, -I - .4 • // - -- ( ; c, '-.' / 'ir •i• 0 r -• -•• —;• I• • 30 JI_1_ - - �110 16.7 Hancock Beach. 16.85 Sharp left hand turn on M—203. 17.9 Turn right on the one—way road. Junction M—203 and US—41. US—4l back to the Michigan Tech Campus Edge of Hancock. Follow south �111 INDEX TO GEOLOGY ON MAPS IN THE FIELD GUIDE Map No. — — — Quadrangle Reference 1 Chassell White, 1956 2 South Range, Chassell White & Wright, 1956; White, 1956 3 Chasseli Warren, 1981 4 Chassell, Hancock White, 1956; Cornwall & Wright, 1956a 5 Chasseil, Hancock White, 1956; Cornwall & Wright, 1956a 6 Laurium Cornwall & Wright, l956b 7 Laur ium Cornwall & Wright, l956b 8 Laur ium Cornwall & Wright, 1956b 9 Ahmeek White & Others, 1953 10 Mohawk Davidson & Others, 1955 11 Mohawk Davidson & Others, 1955 12 Phoenix Cornwall, 1954a 13 Eagle Harbor Cornwall & Wright, 1954 14 Eagle Harbor Cornwall & Wright, 15 Delaware Cornwall, l954b 16 Delaware Cornwall, l954b 17 Lake Medora Cornwall, l954c 18 Lake Medora, Fort Wilkins Cornwall, l954c; Cornwall, 1955 19 Lake Medora Cornwall, l954c 20 Delaware Cornwall, 1954b 21 Delaware Cornwall, l954b 22 Lake Medora Cornwall, l954c 23 Eagle Harbor Cornwall & Wright, 1954 24 Eagle Harbor Cornwall & Wright, 1954; Cornwall, l954a 25 Phoenix Cornwall, l954a 26 Phoenix, Mohawk, Ahmeek Cornwall, l954a; Davidson & Others, 1955; White & Others, 1953 27 Ahmeek White & Others, 1953 28 Laurium Cornwall & Wright, 1956b 29 Hancock Cornwall & Wright, 1956a; Warren, 1981 Hancock Cornwall & Wright, 1956a MTU Campus Map (Cover Page) White, 1956; Hase, 1973 1954 �____________ _____________ 112 REFERENCES Basaltic Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets: Pergamon Press, Inc., New York, 1286 p. 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Cornwall, H.R. and Wright, J.C., 1954, Bedrock geology of the Eagle Harbor quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 36. 1956a, Geologic map of the Hancock quadrangle, Michigan: U.S. Geolo— gic'al Survey Mineral Investigations Field Studies Map MT 46. 1956b, Geologic map of the Laurium quadrangle, Michigan: gical Mineral Investigations Field Studies Map MT 47. U.S. Geolo- Oronto Group, MichiDaniels- P.A., Jr., 1982, Upper Precambrian sedimentary rocks: gan—Wisconsin: Geological Society of America Memoir 156, p. 107—133. Davidson, E.S., Espenshade, G.H., White, W.S. and Wright, J.C., 1955, Bedrock geology of the Mohawk quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 54. DeGraff, J.M., 1976, Structural and age relationships of rocks associated with the Lac La Belle magnetic anomaly, Keweenaw County (M.S. thesis): Michigan Technological University, Houghton, 130 p. 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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. 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Geological Robertson, J.M., 1974, Major and minor element geochemistry of some late Precambrian dikes, Keweenaw County, Michigan (abs.): Proceedings of the 20th Institute on Lake Superior Geology, p. 27. 1975, Geology and mineralogy of some copper sulfide deposits near Mount Bohemia, Keweenaw County, Michigan: Economic Geology, v. 70, p. 1202— 1224. Robertson, J.M., Grimes, J.G. and Rose, W.I., Jr., 1979, Intermediate and silicic volcanic and subvolcanic rocks of the Portage Lake Volcanics, Michigan (abs.): Geological Society of America Abstracts with Programs, v. 11, p. 255. Rose, W.I., Jr. and Grimes, J.G., 1979, Cyclical compositional changes within flood Geological Society of basalts of the Portage Lake Volcanics, Michigan (abs.): America Abstracts with Programs, v. 11, p. 255. Scofield, N., 1976, Mineral chemistry applied to interrelated albitization, pumpel— lyitization and native copper redistribution in some Portage Lake basalts, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 144 p. Stevens, A., 1971, A study of subsurface analysis of the proposed outdoor instruction area, Student Development Complex, Michigan Technological University, Houghton Michigan Technological University, Houghton, County, Michigan (M.S. thesis): 58 p. Stoiber, R.E. and Davidson, E.S., 1959, Amygdule mineral zoning in the Portage Lake Lava Series, Michigan copper district: Economic Geology, v. 54, p. 1250—1277, 1444—1460. Van Schmus, W.R., Green, J.C. and Halls, H.C., 1982, Geochronology of Keweenawan rocks of the Lake Superior region: A summary: Geological Society of America Memoir 156, p. 165—171. Walker, G.P.L., 1975, Intrusive sheet swarms and the identity of Crustal Layer 3 in Iceland: Journal of the Geological Society of London, v. 131, p. 143—161. Warren, E.J., 1981, The bedrock topography of the Keweenaw Peninsula, Michigan (Ph.D. dissertation): Michigan Technological University, Houghton, 169 p. Weege, R.J. and Pollack, J.P., 1971, Recent developments in the native—copper district of Michigan: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 18—43. �__________ ___________ ____________ _____________ White, W.S., 1956, Geologic map of the Chassell Quadrangle, Michigan: gical Survey Mineral Investigations Field Studies Map MF 43. U.S. Geolo- 1960, The Keweenaw lavas of Lake Superior, An example of flood basalts: American Journal of Science, v. 258—A, p. 367—374. 1968, The native copper deposits of northern Michigan: ed., Ore Deposits of the United States, 1933—1967: Metallurgy and Petroleum Engineering, p. 303—325. in Ridge, J.D., American Institute of Mining, l971a, Geologic setting of the Michigan copper district: Society of Economic Geologists, Guidebook for Field Conference, Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 3—17. 1971b, Field Trip A—2 —— Houghton to Calumet via South Range quarry and Society of Economic Geologists, Guidebook for Field Conference, Eagle River: Michigan Copper District, Sept. 30—Oct. 2, 1971, p. 68—75. 1972, Keweenawan flood basalts and continental rifting: Geological Society of America Abstracts with Programs, v. 4, p. 732—734. White, W.S., Cornwall, H.R. and Swanson, R.W., 1953, Bedrock geology of the Ahmeek quadrangle, Michigan: U.S. Geological Survey Geologic Quadrangle Maps of the United States Map GQ 27. White, W.S. and Wright, J.C., 1956, Geologic map of the South Range quadrangle, Michigan: U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. 1960, Lithofacies of the Copper Harbor Conglomerate, northern Michigan: U.S. Geological Survey Professional Paper 400—B, p. B5—B8. Zelenka, B.R., 1978, The history of the Delaware Mine: Local Publication, 20 p. �i: r 2' V r 25 1. 4 14 Figure 1B: 15 r 1. 2 in mites SCALE 0 17 I r i 3 4 k12 18 12 i Stop n!Jmher Map number Index of 1:24,OOC caIe 'naps 0 r I 2 29 r 1 �'Freda McLain State Park Atlantic South Painesdale p4 Chassell Eagle rm 4 C, 0 1 4 Scate 2 o4? 3 + 4miteS Copper Harbor 12 Manitou Island Stop number Figure 1A: Route and stop map Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1972 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 3-6, 1972. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1972 Contributor An entity responsible for making contributions to the resource John L. Berkley W.A. Bodwell Emmy Booy Musa S. Haddadin Bruce E. Brown R.G. Cuddy P.M. Clifford Erich Dimroth Robert Ehrlich Thomas A. Vogel John C. Green Kenneth G. Books J. Kalliokoski James A. Kilburg Melvin M. Lahr P. James LeAnderson M.S. Lougheed J.J. Mancuso J.T. Mengel Jr M.G. Mudrey Jr P.W. Weiblen Richard W. Ojakangas Erdogan Oray W.J. Hinze N.W. O'Hara W.A. Robertson D.R. Smith R.H. McNutt Virgil A. Trent E.J. Warren Thomas G. Winter P.O. Banks W.R. Van Schmus W.F. Cannon S.S. Goldich John S. Klasner Gene L. LaBerge G.B. Morey James A. Robertson H.B. Stonehouse J.S. Stuckless Grant M. Young M.D. Lewan Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/d56384bb82b7055c0dd8947ef3feb5c3.pdf 6eac8e3073122c599c349c7c53f10d11 PDF Text Text 17TH ANNUAL 17TH A UA INSTITUTE ON LAKE SUPERIOR UPERIOR GEOLOGY MINNESOTA DULUTH, MINNESOTA MAY 5-8,1971 MAY 5-8,1971 1 -4', �TEOINICAL ThGL?J CAL SESSIONS ABSTPACFS ABSTRACfS and FIELD GUIDES GUIDES for the the 17th 17th A\'NU.t\L ANNUAl.. INSTITUTE ON ON L!\.KJ:: LKE SUPERIOR INSTITUTE SUPERIOR GEOLOGY GEOLOGY Sponsored by Sponsored UNIVEPSI1Y ; IIr-,rNESOTA,DULUTI DULUTHI UNIVEPSIfl OF OF IINNESOTA, held at held DULU'fl!, ?IINNESOTA DULUTIl, i'UNNESOTA ..lay 1971 Jay 55 -- 8, 1971 Edited D.ll. Davidson Edited by by D. D.G. Dafoy Darby D.G. J.e. Green J.C. Green J.A. Grant Grant �TABLE OF TABLE OF COYI'EN]7S CONTENTS Page No. Prtge ~~o. INSTITIJTE A!\JDLOCAL IDCAL CCLt1IflEE CCl:IMITTEE INSTI'IlJTE DIRECTORS DIRECRS AND PIJGRAt4 (TflLE of ctpirgwrS pt*R 4S1RfrtCrS) ABSFRACI'S OF OF TECIWICAL TECINICAL SESSIONS ABSTRACTS SESSIONS 11 2 2 77 FIELD FIELD TRIPS Shore Volcanic Group A - North Shore Group (Keweenawan) 73 B - Cross-Section, Precambrian Rocks, Rocks, Minnesota I'brtheastern Northeastern ~tinnesota 97 C - ~Iesabi Mesabi Range Range - Biwabik Taconite US 128 D - Vermilion District 141 �-1-1- 17th 17th Annual INSTITIITE ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE ON Sponsored by University of of Minnesota, Minnesota, [*iluth Duluth at Duluth, Duluth, Minnesota May S5 -- 8, 1971 May INSTITUTE BOARD BOARD OF OF DIRECTORS DIRECTORS INSTITUTE Laughlin Steel Steel Corp., * J. IV. W. Avery Avery (Treasurer), (Treasurer), Jones Jones &Laughlin Corp., Negaunee, Negaunee, Michigan. ilichigan. C. C. Reed Reed (Secretary), (Secretary), Michigan J'Hchigan Geological Geological Survey, Survey, ;"Iichigan. Lansing, Michigan. D. M. M. Davidson, Davidson, University University of D. of Minnesota, Minnesota, [Ailuth IW.uth Duluth, Minnesota Minnesota W. J. Hinze, State University, East W. J. Hinze, Michgian Michgian State East Lansing, Lansing, Michigan. A. B. Dickas, Dickas, Wisconsin State Superior, University, Superior, Wisconsin State University, Wisconsin. Wisconsin. G. LaI3erge, Wisconsin Wisconsin State State University, University, Oshkosh, Oshkosh, G. L. U LaBerge, Wisconsin. Wisconsin. U. W. [;1. ],V. Bartley, Bartley, Thunder Thunder Bay, Bay, Ontario Ontario ** R. * Permanent * members menvers LOCAL C(J.·tUTTEE LOCAL CCt1ITrEE Chairman: Coordinating Oiainiian: D. D. M. M. Davison Davison Arrangements Connittee: Committee: R. W. R. W. Marsden C. L.L. Matsch lttsth C. Program Program Comnittee: Coninittee: D. C. D. G. Darby Darby 3. J. C. Green Green Field Trip Committee: Conrrni ttee: J. J. A. Grant Grant A. R. R. 14. W. Ojakangas Ojakangas �-2-2- PROGRAM ~~y 4, 1971 1971 Tuesday, May 5:00 p.m. p.m. Field (North Shore Shore Volcanics) leaves Field Trip Trip A (North Volcanics) leaves Hotel liadisson Hadisson Duluth. Hotel Duluth. Wednesday, May ~,~y 5, 1971 1971 6:00 p.m. p.m. to 7:00 p.m. p.m. 7:00 p.m. 7:00 p.m. to 9:30 p.m. Field Trip A A returns to to Duluth Duluth Institute Registration Registration - Poolside, Hotel Radisson Duluth Radisson Duluth Tnursday, ~hy 6, 1971 1971 Thursday_, May 7:30 a.m. to 12:00 a.m. a.m. Registration, Superior Superior Street StreetFoyer, Foyer,Hotel IbtelDuluth Duluth �-3- SESSION S E S S ION 11 i,lorning ;lorning Thursday, l11Ursday, i.fay 1971 'ay 6,6, 1971 Symposium on Keweenawan Keweenawan Geology Geology—- Lake Superior Region Region Symposium Co-chairmen: Co-chainnen: Jack and Walter Jack Phillips and 1/alter White Page No. No. 8: 45 8:45 J. C. C. Green Green IntroductoryRemarks Remarks Introductory 9:00 IV. White Iv. & Keweenawan lVesterrunost KeweenawanStratigraphy Stratigraphy ofofTYesternimost Michigan Hichigan 71 9:20 N. K. N. K. Ih.xber Huber The Keweenawan KeweenawanGeology Geology Isle Royale, The ofofIsle ;.1ichigan Michigan 31 9:40 II. A. A. Hubbard Hubbard H. Keweenawan Geology Geology of the the Porcupine Porcupine Keweenawan ;"buntains, tuntains, Western Upper Peninsula 30 20 Others ~·,tichigan Uchigan 10:00 J. C. C. Green Green of the theNorth North Shore Shore Voltanic Vo1tanic Stratigraphy of Group Northeast Bay, 1innesota ;··linnesota Group Northeastof of Silver Bay, 10:20 R. R. N. N. Annells Armells Middle ~·liddle Keweenawan VolcanismofofEastern Eastern Lake Keweenawan Volcanism Lake Superior 7 7 10:40 A. P. Jtotsala A. P. Ruotsala Characteristicsof ofSome Some Alteration Alteration Minerals ~tinerals Characteristics Lake Lava Lava Series, Michigan Portage Lake Series, Michigan 59 11 :00 11:00 IV. T. T. Jolly W. Fades Puinpellyite Facies Zeolite and Prehnite Prehnite -- Pumpellyite Zeolite and theKeweenawan Keweenawan Basalts Northern in the Basalts of of Northern :.tichigan The Role Roleof of Volatiles Volatiles Michigan II: II: The 34 11: 20 11:20 T. A. T. A. Vogel Vogel & R.J. R.J. Chemically Zoned Native Copper Chemically Zoned Native Copper and and from White IVhite Pine Pine Michigan Michigan Rohrbacher Chalcocite from 11 :40 11:40 1!. C. C. halls H. Halls G. G. F. F. West \\Test 12:00 12: 00 DON NOON The Isle Royale Royale Fault Fault & The Mjourn for Adjourn for Lunch Lunch There 'vi1l be a lunch lunch meeting meeting of Board of the There will be of the the Board of Directors Directors in the Hotel Radisson Radisson ililuth fuluth—. - location to be be announced. announced. hotel 70 25 �-4- SESSION S E S S ION 22 Afternoon Thursday, Thursday, May 6, ~my 6, 1971 Symposium on on Keweenawan Keweenawan Geology Geology -- Lake Superior Superior Region Region Co-Chairmen: Co-01ainnen: 1:40 1:40 2:00 2:00 2:20 2:20 J. Leone K. Siiis Raymond J. Leone and and Paul K. Sims J. T. T. Mengel, Mengel, Jr.& Jr. Exploration J. Exploration Geology Geology of of Douglas Douglas County, County, R. R. A. A. Hendrickson Hendrickson Wisconsin Wisconsin D. Davidson ,Jr. D. vI. M. Davidson,Jr. Ne,.. View View of of the the Duluth Duluth Complex, Complex, A New A Minnesota B. Bonnichsen B. Bonnichsen in the the Southern Southern Part Part of of the the Hornfelses in Hornfelses Page Page No. No. 47 13 13 11 Duluth Complex, Il1luth Complex,?•linnesota Minnesota 2:40 2:40 M. M. G. G. i4idrey M.ldrey & P. W. W. Weiblen P. Reinvestigation of of "Red "Red Rocks" Rocks" in Reinvestigation in the the Pigeon Pigeon Point Point Area, Minnesota Minnesota 53 53 The Great Logan Logan Paleomagnetic Paleomagnetic Loop Loop The Great 58 58 3:00 3:00 to Coffee Break to 3:20 3:20 3:20 3:20 W. A. Robertson Ibertson W. A. W. F. F. Fahrig Fahrig W. & 3:40 3:40 A. Me.ttis A. 1'-attis Lower Lower Keweenawan Keweenawan Sediments Sediments of of the the Lake Lake Superior Superior Region Region 45 4:00 4:00 D. Myers D. ;"fyers The and Tectonic Tectonic Significance Significance The Sedimentology Sedimentology and of the Bayfield of the Bayfield Group, Group, Wisconsin Wisconsin 54 4:20 4:20 C. Merey G. B. B. ~brey Revised Keweenawan I{evised Keweenawan Subsurface Subsurface Stratigraphy, Stratigraphy, Southeastern Minnesota 50 50 4:40 H. C. Halls H. C. C. F. F. West West C. and Stratigraphy of the the Shallow Shallow Structure Structure and Lake from Seisnic Seismic Refraction Refraction Lake Superior Superior Basin Basin from Measurements Measurements 23 & ******** * * * * * * **** **** ** Evening 7:30 p.m. p.m. Banquet -- Great Hall Banquet Hall - Hotel Radisson Radisson Duluth Duluth - ADDRESS ADDRESS -- Dr. Carl Carl R. R. i\nnhausser Arrmlausser Economic Economic Geology Geology Research Research Unit Unit University University of of Witwatersrand Witwatersrand Johanneshurg, South South Africa Africa Johannesburg, �-5-5— S E S S ION 33 SESSION !trning ~'brning Friday, May 7, Friday, 7, 1971 1971 General General Session Session Co-Chaitnen: Co-Chairmen: Cedric. Cedric. L. L. Iverson Iverson and and J. J. Ka11iokoski Kalliokoski Page It. No. Page 8:40 8:40 F. C. F. C. Tan Tan 4& E. C. Perry, Perry,Jr. Jr. Implications of Carbon Carbon Isotope Isotope Ratio Ratio Variations in in Carbonates Carbonates from from the the Biwabik Biwabik Variations Iron Iron Formation, Formation, Minnesota Minnesota 64 9:00 9:00 S. Viswanathan, S. Viswanathan, Ii. C. C. Perry, E. Perry, Jr. J r. & P. Sims 4 OxygenIsotopic Isotopic Studies Studies of Oxygen of Early EarlyPrecambrian Precambrian Granitic and and Metamorphic Rocks Rocks from from the the Western Giants Range Range Batholith, WesternPart Part of of the Giants Northeastern Minnesota Northeastern Minnesota 66 9:20 G. 1. LaBerge LaBerge G. L. Some Geology of Harathon County County Volcanic of the ?larathon Some 39 Belt P. O. Banks Banks 4~ P. 0. W. Van Sc!llTlUS W. R. R. Van Schmus Rocksof of Iron Chronology of Precambrian Precambrian Rocks chronology L. L. A. A. Prince Prince 4& Geochronology of the the Giants GiantsRange P~ge Granite Granite Geochrono]ngy 57 10:20 G. Klein G. Precambrian Clastic Paleotidal Sedimentation Sedimentation Precambrian Clastic Paleotidal 36 10:40 Pt. ii!inze, Continental Continental Rifts W. Jinze, H. iiavidson,Jr. D. Daviclson,Jr. I). Iv!, & 4 R. Roy 11:00 1\la1an & It C. R. C. Malan 1]. A. A. Sterling D. 9:40 9:40 10:00 G. C. N. . I·ranson Hanson Fj and Dickinson Dickinson and 99 Counties, Michigan Michigan Thoriumin in PreDistribution of Uranium Uranium and and Thorium cambrian Rocks of of the Western cambrian Rocks Western Great Great Lakes Lakes 29 42 42 Region 11:20 20 11: N. 11[. N. Pt. O'Hara 4& w. J. I:inze Hinze Lake nichigan Michigan Aerornagnetic Aeromagnetic Survey Survey 56 56 /u An Aeromagnetic Survey Survey of Southern of the Southern ofMichigan ~lichigan Peninsula of 35 iv. 11:40 11 :40 . R. 1. L. Kellogg Kellogg 4l]" Pt. J. W. J. I-Jinze Hinze 12:00 NWN 12:00 NOON — - Lunch �-6-6- SESSION S E S S ION 44 Afternoon Afternoon 1971 Friday, Friday, I,1ay lay 7, 1971 General Session Co-Chairmen: Co-Chainnen: C. Tychsen 1'chsen Meredith F. E. Ostrom and and Paul C. Page No. Page No. 1:20 1:20 Business of the the Institute Institute &zsiness Meeting Meeting of 1:40 1:40 M. S. S. M. 2:00 2:00 J. Mancuso t,.1.ancuso J. J. J. F. Dimroth & E E. J. Chauvel .J. 2:20 2:20 W. ]Aihling W. fuhling Precambrian Iron Formation Precambrian Formation at at Copper Copper ~·ibuntain, FremontCounty CountyWyoming 1Vyoming Nbuntain, Fremont 18 2:40 E. Frodeston F. Frodeston Some Sedimentary in the the Lower Lower Sonic Sedimentary Structures in Cherty nember Fonnation: Memberofofthe the Bhvabik Biwabik Iron Formation: Cherty The Virginia Virginia Horn The Horn Area Area 32 32 3:00 G. Spencer Spencer G. Chert in Sediments Sediments Chert in 62 3:20 J. Mathersill ~bthersill Limnogeological ofThunder Thunder Bay, Bay, Limnogeological Studies of Lake Superior, Superior, Ontario Lake Ontario 51 3:40 R. Shegelski R. Shegeiski TI1e ofThunder Thunder Bay, Bay, The General General Stratigraphy Stratigraphy of Lake Lake Superior 61 4:00 4: 00 End of Technical End of TecJmical Sessions Sessions Lougheed & Hematite Pseudomorphic After After Biogenic Biogenic Pyrite in the the Negaunee Negaunee Iron Iron Formation Fonnation Pyrite in Textural Facies Facies Analysis of Precambrian Textural Precambrian Cherty Ironstones Ironstones *** * * * **** **** **** ** ** 5:00 5: 00 (Dinner and lodging are included and lodging included in the field field trip trip fee.) fee.) Departure for for Field Field Trips: Trips: Field Field Field Field Field Trip A Trip Trip BB -Trip CC -Trip UD -- North Shore Volcanic Group Volcanic Group Cross-section, Precambrian Rocks Precambrian Rocks Mesabi j\!esabi Range Taconite Range -- Biwabik Biwahik Taconite Vermilion District District Vemiilion Buses will will depart Buses depart from from Hotel Hotel Radisson Radisson Duluth. Duluth. *********** Saturday, nay May 8th, 1971 Saturday, 6:00 to to 7:00 (approx .) (approx.) REThRNOF OFALL ML FIELD RETIJRN FIELD TRIP TRIP BUSES. BUSES. 41 41 15 15 �-7- -7-- KEWEENAWAN VOLCANISM VOLCANISM OF OF EASTERN EASTERN LAKE LAKE SUPERIOR. SUPERIOR. MIDDLE KEWEENAWAN R. N. N. ANNELLS R. Geological Survey Survey of of Canada, Canada, Ottawa. Ottawa. ABSTRACT Following the study of the Michipicoten Island Island Keweenawan flows flows reported reported elsewhere (Annells, (Annells, 1970), srone type type of detailed stratigraphic/petrographic 1970), the same has been carried out on the Keweenawan volcanic rocks study has rocks of the the Mamainse Point, the east shore shore of Lake Lake Superior. Superior. Point, Alona Bay and Cape Gargantua sections on the three east east shore shore sections sections are are mostly mostly made made up up of of inafic mafic olivine—tholefite olivine-tholeiite These three types of texture, accompanied by by aa smaller smaller number number types of medium-coarse medium—coarse ophitic or diabasic texture, of fine—grained fine-grained olivine—poor olivine-poor tholeiite tholeiite flows. flows. Flows of intermediate composition composition found in these these sections sections and and the the flows flows show show little little variation variation in in mineralogy. mineralogy. were not found Small rocks occur occur interbedded interbedded with with the the Small volumes volumes of both basic and acid pyroclastic rocks flows flo\vs in the the lower part of the 14,300 foot foot Mamainse Point section, section, and and conglomerconglomerates partings showing good cross—bedding cross-bedding outcrop in in the the upper upper half half ates with with sandstone partings of this this section and in that that at at Cape Cape Gargantua. Gargantua. Evidence of the simultaneous availability of basaltic and and rhyolitic rhyolitic material material of the is is seen in the Mamainse Matnainse Point Point section; section; plugs, plugs, dykes dykes and and sheets sheets of of fine-grained, fine—grained, often flow—laminated flow-laminated and and autobrecciated leucorhyolite leucorhyolite occur occur at at all all levels levels of of this this one such intrusive sheet was found to section and one to he be composite, composite, having having aa 2—foot 2-foot basal selvage of fine—grained fine-grained basalt and and aa 50—foot 50-foot acid acid upper upper part. part. Fetrographic Petrographic similarities found found in in flows flows of of the the Mamainse Mamainse Point Point and and Cape Cape good basis basis for for lateral lateral correlation correlation of of these these two two Gargantua sequences provide aa good sequences. Near the basal unconformity of theMamainse therlamainse section section there there occurs occurs aa highhighly olivine-tholeiite flow flow crowded crowded with large large plagioclase plagioclase ly distinctive glomerophyric olivine—tholeiite laths concentrated concentrated in spherulitic clusters up laths up to to two two inches inches in in diameter diameter (Ciblin, (Giblin, 1969); aa flow flow of of exactly similar type 1969); type outcrops 40 40 miles NNW NNW along along strike strike near near the the base of the the Cape Gargantua section section (Ayres, (Ayres, 1969). 1969). Both these occurrences are assoBoth these ciated with with aa group group of olivine-tholeiite olivine—tholeiite flows ciated flows rich rich in in large large pseudomorphs pseudomorphs after after \vhich may make up up to to 35 35 per per cent cent by by volume volume of of the the rock rock in in parts parts olivine phenocrysts which of such flows This striking similarity of the flows at at Mamainse Mamainse Point. Point. This the flows flows in in the the levels of the lower levels the Mamainse Point and Cape Gargantua piles piles suggests suggests simultaneous simultaneous effusion of the the same S~le mafic magma supply supply over over aa wide wide area area to to preduce pr~duce lava lava flows flows of of sii,!lar extent to to that that of of the the Greenstone Greenstone Flow Flow of of the the Michigan Michigan Keweenawan. siIIl~Lar extent Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flo9s f1o'to.{s are are also also petrographical— petrographicalThe Mamainse Hamainse Point, ly similar to olivine—tholeiite flows ly to the the olivine-tholeiite flows forming the the basal part part of of the the Michipicoten Michipicoten Island section and it is possible that that these these latter latter flows, flows, also also cut cut by by acid acid intruintrusions, sions, may represent the the upper part of of an an extensive extensive and and largely largely uniform uniform flood flood babasalt pile whose earliest members rest rest directly directly on on the the Archaean Archaean on on the the east east shore shore of of Lake Superior. Superior. The more highly differentiated differentiated andesite andesite and and rhyolite rhyolite flows flows of of Hichipicoten Island are thus interpreted Michipicoten Island are thus interpreted as as being being of of much much later later extrusion extrusion than than the the A general increase in the deMamainse Point, Point, Alona Alana Bay Bay and and Cape Cape Gargantua Gargantua flows. flows. A flows is gree of alteration alteration of of lava lava flows is apparent apparent as as the the Keweenawan Keweenawan lava lava pile pile is is followed followed downwards of the the Michipicoten Michipicoten Island Island section section to to the the base base of of the the downwards from from the the top top of Mamainse Point Point section. section. Mamainse �-8—8— Some differences differences in general chemistry exist between flows Some flows newly newly analysed analysed from from Island and and Maniainse Mamainse Point the Island Island flows flows the Michipicoten Island Point sections; sections; 36 36 analyses of the tholeiitic trend trend of moderate iron—enrichment iron-enrichment on on an an Nfl MFA plot; plot; aa similar similar plot plot follow a tholeiltic of 46 analyses of Mamainse Point flows flows gives gives aa tholefitic tholeiitic trend trend of of high high iron—enrichiron-enrichment. References; References: Annells, R. N., N., Annells, It. 1970, geology of of Michipicoten Michipicoten Island, Island, 1970, Keweenawan volcanic geology Lake Superior Lake Superior; Program, Program, 16th 16th Ann. Ann. Inst. Inst. on. on. Lake Geol., Thunder Bay, Bay, Ont., May May 1970, 1970, 7. 7. Ceol., Ayres, L. L. D., D., 1969, 31 and 30, 30, Ranges 20 20 and and 19; 19; 1969, Geology of Townships 31 Ontario Dept. Dept. Mines Ceol. Geol. Rept. Rept. 69,38. 69,38. Giblin, P. E., E., Giblin, P. 1969, Prelim. Geol. Geol. Naps Maps 553 553 and and 555. 555. 1969, Ontario Dept. Dept. Mines, Mines, Prelim. �-9—9— CHRONOLOGY OF PRECAMBRIAN ROCKS ROCKS OF OF IRON IRON AND AND DICKINSON COUNTIES, MICHIGAN P.O. P.O. Banks Department of Geology Geology Case Western Reserve University, University, Cleveland, Ohio, 44lO6 44106 and W.R. Van Schmus W.R. Department of Geology Geology University of Kansas, Kansas, Lawrence, Lawrence, Kansas, Kansas, 6604k 66044 U—Pb analyses of cogenetic zircon suites and Rb-Sr whole rock analyses U-Pb from from selected Precambrian Frecambrian units units in Iron and Dickinson Counties, Michigan, suffice to for this classic suffice to establish an internally consistent chronology for area. Stratigraphic nomenclature used herein is adopted from from James et et al. al. (1961). (1961). Zircons from the Norway Lake Gneiss, which underlies the Dickinson Zircons from the Group, 2375 m.y., but Group, yield aa concordia intercept age of approximately 2375 Rb-Sr from the Norway Lake Gneiss do not define define an an Rb-Sr whole whole rock rock analyses analyses from isochron, and the isotopic isotopic composition composition of of Pb Pb from from separated separated feJ.dspars feldspars is isochron, is abnormal. Thus, from the Thus, we we conclude that that the 2375 m.y. m.y. "age" obtained from zircons zircons is is probably the the result result of complex metamorphism and deformation of the Norway Lake Gneiss and does not indicate indicate its its true true absolute absolute age. age. The 2375 m.y. m.y. event event that that affected the the Norway Lake Gneiss may be pre—Dickinson, pre-Dickinson, 2375 thus establishing a possible older limit for for the the age age of of the the Dickinson Dickinson Group. Group. Earlier published zircon analyses suggesting suggesting aa much greater greater antiquity antiquity for for the Dickinson Group etal., Group (2700 (2700 m.y. or more: Aldrich Aldrich et al., 1965) 1965) are are interpreted interpreted to reflect detrital detrital zircon zircon components components in in the thernetasedimentary metasedimentary gneisses. gneisses. The pre—Animikie pre-Animikie Porphyritic Red Granite, Granite, whose whose field field relation relation to to the the Dickinson Group is is uncertain, gives aa zircon zircon conoordia concordia intercept intercept age age of of approximately rock Rb—Sr approximately 2100 2100 m.y. m.y., and whole rock Rb-Sr analyses are also consistent consistent with this We interpret interpret this this age age to be post-Dickinson, thus bracketing this age. age. We the age of the Dickinson Group between 2100 2100 m.y. and, and, perhaps, perhaps, 2400 2400 m.y. m.y. , A single zircon analysis from from the Hemlock Volcanios Volcanics of of the the Animikie Animikie A but the the zircon zircon is is somewhat somewhat discordant, discordant, Series yields a Pb-Pb age of 1985 m.y., but so that that the concordia intercept intercept age is is expected expected to to be be slightly sligh~ly older older at at approximately 2000 2000 m.y. m.y. Rb-Sr whole rock analyses on the the post-Animikie post-Animikie Feavy Peavy Complex Complex yield yield Rb—Sr an age of approximately 1700 m.y. approximately 1700 m.y. However, However, previously published mineral age age determinations determinations on other post—Animikie post-Animikie units units indicate indicate that that the the Animikie Animikie Series is is definitely al., 1965). 1965). Thus, Series definitely older older than than 1900 1900 m.y. m.y. (Aldrich (Aldrich et etal., deposition of the Animikie Series appears to to be be bracketed bracketed in in the the interval interval between 2100 2100 m.y. m.y. and and 1900 1900 m.y. m.y. A A maximum age of 2100 m.y. m.y. for the Animikie Animikie Series, Series, in in conjunction conjunction with with published Rb-Sr data on on the the post—Huronian post-Huronian Nipissing Nipissing Diabase Diabase (2160 (2160 rn.y.) m.y.) and on Huronian 1-luroniansediments sedimentsthemselves themselves(2285 (2285m.y.) m.y.) (Van (Van Schmus, Schmus, 1965; 1965; Fairbairn Fairbairn et al., 1969), 1969), severely severely restricts restricts possible possible correlations correlations between the Animikie etal., Animikie Series and the Huronian formations of the North Shore of Lake Huron. Series Shore of Lake Huron. �—10— -10- References Aldrich, L.T., Davis, Davis, C.L., G.L., and and James, James, FI.L., H.L., 1965, 1965, Ages Ages of of minerals minerals from from metamorphic and and igneous igneous rocks rocks near near Iron Iron Mountain, Mountain, Michigan: Michigan: Jour. Petrology, v. ~ v. 6, 6, pp. pp. +47-472. 447-472. Fairbairn, H.W., H.W., Hurley, Hurley, P.M., P.M., Card, Card, K.D., K.D., and Knight, Knight, C.J., 1969, Fairbairn, Correlation of radiometric radiometric ages ages of ofNipissing Nipissingdiabase diabaseand and1-luronian Huronian CorrelaL on of metasedimen-ts with with Proterozoic Proterozoic orogenic orogenic events in Ontario: Can. metasediments Jour. Earth Sci., Sd., i. Jour. Earth v. 6, pp. Lt89_497. 489-497. James, ILL., H.L., Clark, Clark, L.D., Lamey, C.L., C.L., and Pettijohn, F.J., F.J., 1961, Geology Geology James, L.D., Lamey, U.S. Ceol. of central Dickinson County, County, Michigan: Michigan: U.S. Geol. Surv. Surv. Prof. Prof. 310, 176 176 p. p. Paper 310, Van Schmus, Schmus, R., R., 1965, The geochronology of the Blind River—Bruce River-Bruce Nines Mines area, area, Ontario, Canada: Canada: Jour. Jour. Ceol., Geol., v. v. 73, 73, pp. pp. 755-780. 755-780. �—11--11- HORELSES IN THE DULUTHCOMPLEX, COMPLEX,MINNESOTA MIIESOTA HORNFELSES THE SOUTHERN SOUTHERN PART PART OF OF THE DULUTH Bormichsen Bill Bonnichsen Cornell University Hornfels of feet feet in in Hornfels bodies ranging from less than an inch to thousands of dimensions are abundant in the southern part of the Duluth Complex. They dimensions are were derived from from a wide wide variety of initial rock types, types, many of which occur in the complex footwall. footwall. The The most most abundant abundant types types were derived from argillaceous ceous sediments of the Virginia Formation, Formation, mafic to intermediate volcanic rocks of Keweenawan age and various intrusive rocks indigenous to the complex. rocks complex. Others include iron iron formation, formation, quartzite quartzite and and d.ioritic dioritic rocks rocks from from the the prepreKeweenawan basement basement and. and clastic Keweenawan age. age. elastic sediments sediments of probable Keweenawan Virginia inclusions are are very very similar similar to to metamorphosed metamorphosed footwall footwall Virginia; Virginia; however, the relative relative mineral mineral proportions are hovrever, the the grain grain size size is is larger larger arid and the are slightly different. The silicate mineralogy of argillaceous inclusions inclusions inincludes coexisting cordierite, orthopyroxene, biotite, cludes cordierite, orthopyroxene, biotite, plagioclase and and potassium potassium feldspar. Minor amounts amounts of of pyrrhotite, pyrrhotite, graphite, ilmenite and and traces of chalchalgraphite, ilmenite copyrite and pentlandite are common, but olivine and and Ca pyroxene invariably but olivine pyroxene are invariably absent. Various types types of of relict relict se.imentary sedimentary structures structures are distinguishable distinguishable in all but the smallest smallest of of hornfelsed hornfelsed Virginia Virginia inclusions. inclusions. all inclusions are are characterized characterized by by their lack of of relict Volcanic hornfels inclusions their lack sedimentary structures, local round round to ellipticalplagioclase plagioclase and and Ca pyroxene structures, local to elliptical segregations that probably were segregations were amygdules amygdules and their mineralogy. They consist largely of niagneof plagioclase plagioclase and and Ca pyroxene, and normally contain abundant magnepyroxene, and tite and tite and orthopyroxene (commonly (commonly inverted invertedpigeonite). pigeonite). Olivine, brown brown hornblende, apatite, ilmenite, and and traces traces of biotite biotiteoccur occurininsome some bodies bodies but but none none apatite, ilmenite, graphite, or or more more than than traces traces of of potassium potassium are known knovm to contain cordierite, cordierite, graphite, feldspar. FeO+MgO of various The proportions of of weight weight percent percent 3102, Si0 , Al20~ and. and FeO+MgO 2 types of hornfelses hornfelses and equivalent equivalent rocks rocks are are plotted ploted in in figure figure 11 (Bonnichsen, (Bonnichsen, in prep.). A, B prep. ). The A, B and CC groups are materials from from the the Virginia Virginia Formation, Formation, vlhereas the the D, EE and and FF groups groups are are volcanic volcanic hornfelses homfelses and. and their equivalents. whereas Note Note that, that, although although both both groups groups show show considerable considerable range range in their proportion A12O3. of Si0 the Virginia materials have higher proportion of Al 0 . , SiOa, the Virginia have a higher proportion 2 2 3 The group A unmetamorphosed Virginia and and equivalent hornhomA samples are unmetamorphosed felses from the felses the footwall footwall of of the the complex. complex. The group BB samples are are from from incluinclusions vlithin within the complex. sions complex. Note their depletion in 8i0 relative to the A 5102 the A 2 group. This This suggests suggests that Si02 8i02 was lost from from the inclusions; inclusions; this this loss loss is is accompanied by a similar depletion of K20 ~O in several several samples samples and and suggests suggests loss loss of aa grantic grantic partial partial melt melt during during the the hornfelsip.g hornfelsipg process. process. The group CC samples samples are are from the margins margins of hornfels bodies and and thus thus were in in direct direct contact with with initial the the intrusive intrusive rocks. rocks. Their Their compositions compositions deviate further from from the initial deviate farther values than do those of group B; B; they are considered to be refractory resiresiduals which which had had become become nearly nearly equilibrated equilibrated with vlith the the adjoining adjoiningmagnias. magmas. Part group BBrocks feldspars and and cordierite of the the group rockscontain containtexturally texturallyinterstitial interstitial feldspars which are interpreted interpreted as as recrystallized recrystallized partial partial melts. melts. During the hornfelsing process aa melt melt with ,nth the the composition composition ofofcordierite cordieritearid, and alkali alkali feldspar evidently developed after a granitic fraction had had been been lost. lost. Hornfelses with the group C where this this later type type of melt melt C compositon are considered to have formed formed where had been lost. The formation of granitic dikes dikes and and the the production production of of abundant abundant C pyroxene are the biotite and orthopyroxene orthopyroxene at at the expense of olivine arid and Ca principal effects on the enclosing intrusive intrusive rocks assimilation rocks \vrought wrought by the the assimilation of such partial melts. �—12— -12- Si02 :7 Figure I. 'F A1203 FeO* A 00 E F. c@ 50 to 41203 AI203 V v vV v V vV to to FeOtMgO FeO+ MgO V v Group E consists of hornfelsed. basalts; they they have have bulk bulk compositions compositions that that hornfelsed basalts; show little deviation from from the the compositions compositions of of ordinary ordinary basalts. basalts. Group Group FFrocks, rocks, however, have and Si02 Si02 and and higher higher Ti0 Tb22 and and FeO have lower lower K20 and FeO contents contents than than ordinary hornfelses may have been inbasalts and and have high high Fe/Mg Fe/Mg ratios. ratios. Two of these hornfelses trusive residual residual liquids liquids which which separated separated from from trocto].ite troctolite but but the the other other one one evidently is aa hornfe].sed hornfelsed volcanic rock that that contains contains probable probable relict relictaxnygdules. amygdules. dently is volcanic rock Sample D D is is an magnetite-richbasaltic basaltic rock from an unmetamorphosed unmetamorphosed magnetite-rich from along along the the eastern margin of the complex; its Fe/Mg ratio is is like that of group F. The margin of complex; its Fe/lf~ ratio volcanic rock in group F may initially have had a composition composition similar to that that of sample D. D. If so , it material during during so, it lost lost aa substantial amount amount of granitic granitic material hornfelsing process. the hornfelsing process. in the The abundance and distribution of hornfelsed volcanic rocks in system of southern part of the complex supports the concept that an extensive system Keweenawan flows was present throughout the region and had been laid down Kew"eenawan flOivS was dOim on an erosion erosion surface surface cut cut in in the the Middle Middle Precambrian Precambrian rocks. rocks. The the Theintrusion intrusion of the an Troctolitic Series Series and accompanying crustal extension evidently broke up the volcanic volcanic rocks. rocks. As distributed throughout As a result result the the hornfelses hornfelses are are widely ddely distributed the southern half of of the the complex. complex. Many l~ of of the the large large bodies occur occur as as septum septum betvreen adjacent intrusive intrusive bodies. bodies. The great number of inclusions of various between adjacent types along the the footwall types footwall of the complex indicated that the intruding troctoconsiderable mechanical mechanical strength. strength. Evidently, litic magmas had considerable Evidently, these thesemagmas magmas were mushes were in the the form form crystal-rich crystal-rich mushesduring duringemplacement. emplacement. Ref: Bonnichsen, the Duluth Duluth Complex, Complex, St. st. Bonnichsen, B. B. (in prep.); prep.); The southern part of the Louis and Lake of Minnesota, Minnesota, Lake Counties, Counties, Minnesota; Minnesota; to to be be publ. publ. in in Geology Geolor of Schwartz commemorative volume;P.K. P.K. Sims, Sims, ed. G.M. Schw"artz connnemorative volume; �-13—13— A NEW VIEW OF THE DULUTH DULUTH CO~PLEX, COMPLEX, MINNESOTA A by Donald H. M. Davidson, Davidson, Jr. Jr. University of Minnesota, Duluth Duluth and Minnesota Geological Survey Hinnesota ABSTRACT A B S T R ACT The late Precambrian (Keweenawan) (Keweenawan) Duluth Complex is is a sequence generally discordant intrusive rocks of generally rocks extending extending northeastward northeastward from from Duluth to to 1-loyland, Hovland, Minnesota Minnesotain in a a roughly roughly crescentic crescentic configuration. The the Complex Complex is is bifurcated bifurcated on on the the east east and and south south The outcrop outcrop pattern of the by rocks rocks of the the North Shore Shore Volcanic Volcanic Group. Group. in Table 1, 1, three three rock rock series series (anorthosite, (anorthosite, As may be noted in troctolite—olivine gabbro gabbro and and felsic) troctolite-olivine felsic) constitute the the major petrologic petrologic units of the Complex. units the Complex. Anorthosite series rocks were apparently emplaced as large, crystal-liquid as crystal—liquid masses massesinin ~.,hich whichcumulus cumulusplagioclase plagioclaseisis the the prepredominant mineral. mineral. The anorthositic rocks, which form the central portion dominant rocks, t.,hich of the of the Complex, Complex, have been subsequently intruded intruded by by the the troctolite troctolite series series along the northern and western footwall footwall and and by by the the olivine olivine gabbro gabbro series series to troctolites and to the southeast. The The troctolites and gabbros gabbros are are aa sequence sequence of of genergenerally containing cumulus plagioclase and and olivine olivine and and poik— poikally layered layered rocks rocks containing ilitic pyroxenes. The The basal basal troctolite series dips gently (15°) towards dips gently (15°) towards Lake Superior, Superior, whereas whereas the Lake the attitudes of the the upper upper olivine olivine gabbro gabbro series series vary (e.g. Sawbill vary from northward dips dips of of 40° 40° (e.g. Sawbill Lake Lake area) area) to to southward southward at low Q5°) cLS°) angles angles (e.g. (e.g. along along the the Brule Brule River Prong). Felsic series at rocks are are predominantly granophyric granite which occur rocks occur as as subhorizontal subhorizontal sheet—like masses sheet-like masses above aboveboth bothmargins marginsofofthe theolivine olivine gabbro gabbro series. series. Separate minor arate minor intrusives as the Endion Sill, Sill, the the Beaver Beaver Bay Bay Complex Complex intrusives such as and to be younger than than the the Duluth Duluth Complex, Complex, and the the Hovland Complex appear to whereas only Lie the Gunflint Gunflint Prong Prong Layered Layered Complex Complex appears appears older. older. Petrologic relationships sources derived derived from from the the mantle, mantle, to to relationships suggest suggest multiple magma sources account for account for the the petrogenetic sequence of the the Duluth Duluth Complex. Complex. The Duluth Complex Complex is is coincident coincident with with the the axis axis of of the the Mid—Continent Mid-Continent Gravity High. High. Footwall shearing and the the asymmetric asymmetric position position of of the the Complex Complex with with respect respect to to the the Lake Lake Superior Superior Syncline Syncline suggest suggest Complex Complex emplacenent consanguinous emplacencnt consanguinous with with rifting. riftine. Gravity studies to to date date suggest suggest the Complex thins thins or is absent beneath Lake Lake Superior. Superior. Dominant Complex Complex the N.20E.—N.SOE.) are common fracture trends trends (N.-. (N.-~.90E. or W. W.,, ~.20E.-~.80E.) common throughout throughout 90E. or the Lake regional post—intrusive post-intrusive extension. extension. the Lake Superior area suggesting regional Significant base-metal base—metal mineralization mineralization occurs occurs within within selected Significant troctolite controls afforded afforded by by host host troctolite series series horizons horizons with local ore controls rock lithology and structural settling settling shelves. shelves. Should the proposed funnel the central complex complex be verified, subsurface subsurface funnel configuration configuration of the exploration of the the Southern Complex Complex appears appears warranted. ~varranted. �Table 1. Table 1. Summary of Principal Petrologic Series and Units, Units, Duluth Complex, Complex, Minnesota Late Minor Hinor Intrusive Complexes Felsic Troctolite— TroctoliteDuluth " G hb Duluth Complex CompleX01i Gahbro Ol l.Vl.ne ,cambrian a ro cambrian (l.ltO.2b.y.) (l.10.2b.y.) Endion Sill Sill Er.nst~ W. W. C., G., 1960, 1960, Jour. Jour. Ernst, Beaver Bay Complex Gehman, H. H. M., M., Jr., Jr., 1957, 1957~ Unpub. Unpub. Ph.D. Ph.D. Thesis, Thesis, Univ. Univ. of of Minn. Minn. Konda, T., 1970, 1970, Contr. Contr. Min. Mm. Pet., Konda, T., Pet., Vol Vol 29, 29, p. p. 338—344 338-344 Hovland Complex Hoviand Complex Jones, N., N., 1963 Unpub. Unpub. M.S. M.S. Thesis, Univ. Univ. of Minnesota Granophyric Granite and and Minor Felsic Hinor Intrusives Davidson, D. D. M., Jr., Jr., 1969, 1969, Minn. ~linn. Geol. Geol. Surv. Surv. Misc. Misc. Map Ser., Ser.~ M—7, M-7, M—8 M-8 Grout, F. F., F., and and others, others~ 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Grout, F. F., F., and and others, others, 1959, 1959, Minn. Minn. Geol. Geol. Surv. Surv. Bull. Bull. 39. 39. Grout, F. Basal Troctolite Troctolite ,1969, Minn. Minn. Geol. Geol. Surv. Surv. Rept. Rept. Inv. mv. 99 Phinney, W. C. C.,1969~ Phinney, W. 44 Bull. R. B., B., 1964, 1964~ Minn. Minn. Geol. Geol. Surv. Surv. Bull. 44 Taylor, R. Central Anorthosite Early Minor Ninor Intrusive Complexes North ~orth and Anorthosite Inclusions Bonnichsen, Bill, Bill, 1969,30th 1969,30th Annual Annual Min.Sympos.,Univ.Minn.pp.8993 ~lin.Sympos. ,Univ.Minn.pp.89-93 Bonnichsen, ,Univ.Mlnn.pp.89—93 Bonnichsen, Bill~1969~30th AnnualI'lin.Sympos. Hin.Sympos.,Univ.Minn.pp.B9-93 Bonnichsen, Bill,1969,3Oth Annual Misc. Map Davidson, D. D. }[., Jr.~ 1969, Minn. Minn. Geol. Geol. Survey Survey Misc. Hap M., Jr., Ser. 1—7, Ser. H-7~M—8 M-B Sd. Mem. Phinney, W., W., 1966, N.Y. State, State~ Mus. Mus. Sci. Hem. Vol.18, Vol.18, p.135—147 p.135-l47 1966, N.Y. Phinney, 44 Taylor~ R. R. B., B., 1964, 1964, Minn. Minn. Geol. Geol. Survey Survey Bull. Bull. 44 Taylor, Gunflint Prong Prong Sill Sill Babcock~ R.C., R.C., 1959, 1959, Unpub. Unpub. M.S. M.S. Thesis, Thesis, Univ. Univ. Wisc. Wise. Babcock, Brule Lake Sills Bull. 39. Grout and and others, 1959, 1959 ~ Minn. Hinn. Geol.Survey GeoI. Survey Bull. 39. Granoels Granofels Shore Pet., Pet.~ Vol. Vol. 1, 1, p. p. 286—303 286-303 Upper Olivine Gabbro ,e Anorthosite Anorthosite Principal References Principal Unit Series Map Ser. Ser. M—7, D.H., Jr., Jr., 1969, 1969~ Ninn. lorinn. Geol. Geol. Survey Survey Map M-7, N—8 H-B Davidson, D.M., Volcanic Volcanic Group Group Volcanics— VolcanicsUndifferentiated ;-1iddle 'Ii ddle Lower Duluth Complex Early Hinor Minor Early Intrusive Intrusive Complexes Gunflint Gunf lint Prong Layered Complex Complex Nathan~ H., 1969, 1969, Nathan, H., I I Unpub. Ph.D. Thesis, Univ. Unpub. Ph.D. Univ. Minn. Minn. I HI ~I �-15-15— TEXTURAL FACIES IRONSTONES* FACIES ANALYSIS ANALYSIS OF OF PRECAMBRIAN PRECAJfBRIAN CHEItTY CHERTY IRONSTONES* by by Erich Dimroth, Dimroth, Service de Pl'Exploration Erich Exploration geologique des Richesses Richesses Naturelles, Naturelles, Quebec, Quebec, P.Q. P.Q. Ministere des and Jean-Jacques Jean—Jacques Chauvel, Chauvel, Departement de Geologie, Rennes, France France Universite Rennes, Rennes, ABSTRACT A B S T R ACT cherty ironstones ironstones are are very very similar similar to to those those Textures of Precambrian cherty of limestones limestones (Dimroth (Dimroth 1958). 1958). Accordingly the the methods of limestone limestone petrology petrology can be applied in the the study study of of ironstones. ironstones. Ironstones can be be conceived to Ironstones to be composed of textural textural elements. elements. Textural ironstone types are defined by the the kind kind and and proportion proportion of of textural textural elements present. present. Textural facies facies types types compose compose thin thin (3 (3 feet—lOO feet-lOO feet) feet) units; they they are either texturally texturally homogeneous, homogeneous, or or are are comcomstratigraphic units; textural rock rock types types that that form form beds beds alternating alternating in in aa posed of several textural characteristic sequence. sequence. It It is to determine determine the the paleo— paleois generally possible to environment envi~onment in which the the various textural textural facies facies types types formed, formed, and and by by sections, to gain a view of of the the paleogeography paleogeography correlation of of stratigraphic sections, of the depositional basin. of the following following textural textural elements elements in in the the ironstones: ironstones: We distinguish the I I Orthochems — 1. Femicrite: A A past of fine—grained fine-grained iron iron silicate silicate (minnesotaite, (minnesotaite, Femicrite: 1. sti1pnome1ane) from iron iron silicate silicate and and iron iron carbonate carbonate stilpnomelane) or of siderite derived from muds. 2. 2. ~~trix chert; chert: Matrix 3. Cement chert: Cement chert: 3. deposition. Chert deposited as as aa silicagel silicagel matrix. matrix. after Chert that that formed between allochem allochem grains grains after chert and and cement cement chert chert can can be be distinguished distinguished only only in in some some Matrix chert hematite tones. hematite irons ironstones. II IL — Allochems 1. Pellets: particles 0.2 0.2twa. mm. across unsharply unsharply bounded, bounded, Ellipsoidal particles Pellets: Ellipsoidal 1. Pellets are interpreted as aggregated always embedded in matrix chert. Pellets are interpreted as aggregated always embedded in matrix chert. particles. with the premission of the *Published with the Deputy Minister, Department Department of Natural REsources, REsources, Quebec. Quebec. �-16—16— Entraclasts: Fragments of the unconsolidated sediment that 2. Intraclasts: that have been been redeposited. redeposited. Previously (James, (James, 1954) 1954) described from from intra— intra(large intraclasts) intraclasts) and and as as "granules" "granules" (= (= sandformational conglomerates (large sand— size intraclasts). 3. 3. Oolites and and Pisolites. Pisolites. 4. 4. Shards: Shards textures. Two sub—types sub-types predominate Shards are complex textures. (a) (accommodation (a) welded welded and and extremely extremely deformed deformed oolites oolites and and intraclasts intraclasts (accommodation shards). (b) shards fragments of oolites and and (b) shards composed mainly mainly of peeled off fragments shards). intraclasts (exfoliation (exfoliation shards). shards). types are are defined defined by the the combination combination of of textural textural elements elements Textural rock types present. Main types types are: are: I. I. Femicrites: II. II. Matrix Matrix chert: chert: Laminated or ribboned silicate—carbonate silicate-carbonate ironstones. ironstones. Lamina~ed Laminated or ribboned cherts, cherts, generally generally with pellets. pellets. III. intraclastic or or oolitic oolitic ironstones. ironstones. III. Cemented intraclastjc IV. Intraclastic or oolitic rocks with chert chert matrix. matrix. IV. V. Intrafemicrjtes: Intrafemicrites: Intraclasts embedded embedded in in aa femicrite femicrite matrix. matrix. types, particularly containing containing shard shard textures, textures, are are quantitatively quantitatively Some other types, less important. important. The paleogeographic application of the the method will be be demonstrated demonstrated at at the the example of the lower jaspilite member of the the Sokoman Sokoman Ironstone Ironstone in in the the western half of the the Labrador trough trough between between latitudes latitudes 54°45'N 54°45'N and and 55°15'N. 55°l5'N. Close to Close to the the western margin of the trough trough this this stratigraphic stratigraphic unit unit is is thickly bedded bedded finely finely intraclastic intraclastic locally represented by a massive or thickly and oolitic (facies type type 1). 1). Toward o.olitic chert chert cemented cemented hematite hematite ironstone (facies this type grades into into interbedded interbedded oolitic—intraclastic oolitic-intraclastic hematite hematite the east this ironstone with chert alternating with with laminated matrix chert cement cement or or matrix, matrix, alternating chert containing type 2). 2). This type type is is thin thin to to medium medium chert containing hematite hematite (facies (fades type bedded (2—30 (2-30 cm.) em.) andcharacteristically andcharacteristically shows shows lenticular lenticular bedding. bedding. It It grades into aa type type that that contains contains intercalated intercalated beds, beds, 2—100 2-100 cm. ern. thick, thick, basinwards into east the oolitic intra— femicrite (facies (facies type type 3). 3). Farther east intraof laminated femicrite beds are lacking in type clastic beds type 4 and finally finally type type 55 is is composed composed only only of of laminated femicrite femicrite with interbeds of of laminated laminated femicrite femicrite bearing bearing matrix matrix chert. Facies types 33 and 4 are characterized characterized by by siump slump structures structures and and Pacies types structures indicating strong synsedimentary deformation. structures deformation. Toward the the centre centre of the trough types 4 and 3 reappear, and grade into a facies containing of the types 3 reappear, and grade into a facies containing interbeds (2 cm.) em.) intraclasts intraclasts and and pisolites pisolites embedded embedded in in interbeds with very coarse (2 matrix chert chert (facies (facies type type 6); 6); the intraclasts and pisolites were very soft at time of deposition. soft deposition. Facies is tentatively interpreted interpreted as as Facies type 1 is a sand bar facies that that separates separates aa lagoonal lagoonal environment environment (not (not discussed discussed here) farther west from from the the open open basin. basin. Facies Facies type type 22 has has been been deposited deposited here) in the intratidal. intratidal and in the and shallow shallow sub-tidal sub—tidal zone zone in in the the foreshore foreshore of the sand bars. facies and and bars. Types Types 33 and 4 represent represent a relatively relatively deep deep subtidal subtidal facies �-17—17— facies zone zone 55 was was deposited deposited in in aa relatively relatively deep deep basinal basinal environment environment fades (maybe 50-100 m. water depth). Facies type 6 was likely deposited on Fades type 6 was likely deposited (maybe 50—100 m. depth). shallow sub-tidal the centre centre of the the Labrador Labrador sub—tidal shoals that extended in the trough. The coarse intraclastic and pisolitic beds may represent represent storm layers. layers. References: James, II. James, H. L., 1954: Sedimentary of iron iron formation. formation. Sedimentary facies fades of v. 49, 49, p. p. 235—293. 235-293. v. Econ. Geol., Econ. Ceol., Dirmroth, 13., 1968: Dimroth, E., 1968: Sedimentary textures, textures, diagenesis and sedimentary Ironstones. N. N. Jb. Geol. Geol. environment of certain Precambrian Eronstones. Palaeont., Abh. v. 130, 130, p. p. 247—274. 247-274. �—18— -18- IRON FORMATION At COPPER FORMATION AT COPPER PRECAMBRIAN IRON MOUNTAIN, FREMONT COUNTY, COUNTY, WYOMING MOUNTA IN, PREMONT H. Duhling, Jr. Jr. William H. Natural Resources Research Institute Institute University of Wyoming, Wyoming, Laramie ABSTRACT A B S T R ACT iron formation formation is is exposed exposed along along the the south-facing south-facing Precambrian banded iron flanks Shoshoni, in in flanks of of Copper Copper Mountain, Mountain, approximately 15 miles north of Shoshoni, northeastern Frenont Fremont County, County, Wyoming. Wyoming. The Precambrian metamorphic comcomconsists of interlayered interlayered quartzofeldspathic quartzofeldspathic gneisses, gneisses, amphibolites, amphibolites, plex consists amphibole schists, schists, peliric pelitic rocks, rocks, and iron iron formation formation into into which which granite, granite, complex pegmatite, and mafic dikes and sills have been intruded. The pegmatite, sills been intruded. has been metamorphosed to has to the the kyanite-muscovite kyanite-muscovite subfacies subfacies of of the the almanalmandine-amphibolite facies. facies. Sedimentary rocks rocks of Paleozoic or Cenozoic dine-amphibolite the Precambrian Precambrian complex complex on on all all sides. sides. age abut the The mineralogical composition of of the the iron iron formation formation is is very very simple, simple, quartz, and and any any combination combination of of blue-green blue-green hornhornconsisting of magnetite, magnetite, quartz, blend, Magnetite, in blend, grunerite, and and cummingtonite. curnrningtonite. Magnetite, in all degrees of alteration to hematite, hematite, occurs in in thin thin laminae laminae and and fine fine clusters clusters with with angular, angular, sharply embayed boundaries and as very fine fine inclusions inclusions in in quartz quartz and and amphibole grains. grains. Banding is is developed by apparent increase increase in in grain the expense expense of of quartz quartz and and amphibole amphibole grains. grains. size of the magnetite at the The iron formation, formation, interlayered interlayered with amphibolite amphibolite and and quartz-mica quartz-mica schist, is is exposed for for a distance of of about about 66 miles miles over over an an approximate approximate schist, width of of 1000 1000 feet. feet. The strike of of the the formation formation is is NN 80°E 80 0 E and and the the dip dip is to the the south. south. is 70° 700 to Liberation and concentration tests tests indicate indicate the the presence presence of of roughly roughly million iron and 22% 22% silica. silica. The The million tons tons of concentrates concentrates containing 56% iron fine magnetite in in quartz quartz and and amphibole amphibole grains grains and and the the amount of very fine amount interstitial quartz quartz in in the the magnetite-rich magnetite-rich bands bands account account for for amount of interstitial the high high silica content of the the the concentrates. concentrates. l3~ 13¾ Rail comes within ten ten miles of of the the outcrop outcrop area, area, but but Rail transportation comes the nearest markets for a blast furnace furnace feed feed are are over over 240 240 miles miles away. away. the markets for to market, market, high silica silica content, content, low low tonnage, tonnage, and and steep steep The distance to to indicate indicate that that this this iron iron formation formation has has aa questionable questionable dip combine to economic potential. potential. �-19—19— Selected References References 1. 1. Duh1ing, William William H., H., Jr, 1970, 1970, Oxide Oxide facies facies iron iron formation formation in in the the Duhling, Owl Creek Mountains, Mountains, northeastern Fremont Fremont County, County, Wyoming: unpublished MS thesis, thesis, University University of of Wyoming, Wyoming, 92 92 p. p. 2. 2. G1iozzi, James L., L., 1967, 1967, Petrology and and structure structure of of the the Precambrian Precambrian Gliozzi, James rocks the Copper Mountain district, district, unpublished unpublished PhD PhD dissertation, dissertation, rocks of the University of Wyoming, 141 141 p. p. 3. 3. Kopp, S., 1964, 1964, Reconnaissance geology geology of of metamorphic metamorphic strucstrucKopp, Richard S., tures district, Fremont County, County, Wyoming: tures of of the the Copper Copper Mountain Mining district, Compass, v. 43, p. p. 6-20. 6~20. Compass, v. 4. 4. Millgate, Mi11gate, M. M. L., L., Gliozzi, G1iozzi, James James L., L., 1966, 1966, Reconnaissance Reconnaissance of of iron iron forforin the the Copper Copper Mountain Mountain area, area, Fremont Fremont County, County, Wyoming: Wyoming: unpubmation in lished Survey of of Wyoming Wyoming files. files. lished report Geological Survey �-20- Stratigraphy of the North Shore Volcanic Group Northeast of Silver Bay, Minn. by John C. Green University of Minnesota, Duluth Minnesota Geological Survey A B S T RAe T A sequence of flows and flow vPups, totalling about 21,500 feet, makes up the northeast limb of the North Shore Volcanic Group of Keweenawan (late Precambrian) age between Tofte and Grand Portage. Exposures are generally good to excellent along the Lake Superior shore or abandoned wave-cut cliffs, and although cut by several large intrusive bodies and obscured by glacial cover over wide areas, many of these lithostratigraphic units can be traced inland from Lake Superior for many miles. Table 1 shows the informal volcanic units at the northeast limb (top of section at Tofte,base at Grand Portage); Table 2 gives the sequence (less well established because of faulting and intrusion) of the upper part of the southwest limb from Tofte as far as Palisade Head near Silver Bay. The Schroeder basalts at the top of the southwest limb are at least in part equivalent to the Lutsen basalts of the northeast limb. The basal 5,000 feet, near Grand Portage, Minn., have reversed magnetic polarity (Lower Keweenawan) whereas all the rest have normal polarity (Middle Keweenawan). The lowermost 250 feet of lavas on Lucille Island, directly overlying the basal Upper Precambrian Puckwunge Sandstone, are porphyritic melabasalts with abundant olivine and augite phenocrysts, identical to those in the same stratigraphic position at Nopeming, west of Duluth. �—2]— -2J- Table 11 Stratigraphy of (Tofte to Grand Portage) of of of Northeast Northeast Limb Linb (Tofte North Shore Volcanic Group Group (Exclusive (Exclusive of of Interf Interflow low Sediments) Sediments) Approx. Approx. - Thickness() Thickness.J ft.) Lithostratigraphic unit unit Lithic eharacter Character Lithic Top (near Tofte —- Lu Lutsen) Top (near t sen) 1020 -- Lutsen basalts olivine tholeittes tholeiites olivine basalts, olivine 160 160 Terrace Point basalt flow Thomsonite—bearing ophitic Thomsonite-bearing ophitic basalt basalt 310 310 Good Harbor Harbor Bay Bay andesites andesites brown, porphyritic andesite, brown, andesite, trachyandesite 360 flow Breakwater trachybasalt flow brown, columnar, granular trachybasalt 500 Grand I1arais Marais rhyolite flow pink, pink, red, red, gray porphyritic porphyritic rhyolite rhyolite 600 Croftville basalts various fine—grained fine-grained basalts basalts felsites Devil Track felsites aphyric flows aphyric and and porphyritic rhyolite flows Red Cliff basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Creek felsite felsite Kimball Creek pink to to tan, tan, porphyritic felsite 1800 Marr Island lavas lavas mixed tholeiitic basalt,intermediate, intermediate) tholeiltic basalt, felsic lavas felsic lavas 1000 Brule River basalts granular—diabasic granular-diabasic amygdaloidal amygdaloidal basalts basalts 3500 3500 Brule River rhyolite flow pink pink to gray porphyritic rhyolite Hoviand Hovland lavas lavas mixed porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Rock rhyolite flow red, porphyritic rhyolite red, 260 Deronda Bay andesite flow flow gray-brown, gray—brown, aphyric andesite 4500 Grand Portage basalts basalts nixed tholeiitic mixed tholeiitic to to diabasic diabasic basalts basalts Base (at Grand Portage) (at 1020 — 400-900 400—900 4000 21,430 2l~430 (est. ) (est.) �-22—22— Table 22 Stratigraphy of Upper Upper Part of Southwest Limb (Tofte (Tofte to Palisade Palisade Head) Head) of North Shore Volcanic Group to Approx. Thickness Thickness (ft.) (ft.) Lithostratigraphic unit Lithic character character 4000 Schroeder basalts ophitic olivine olivine amygdaloidal, ophitic tholeiites >300 >300 trachybasalt flow flow Manitou trachybasalt red-brown, red—brown, granular trachybasalt to basalt (at Tofte) Tofte) Top (at (more (more of the Schroeder basalts) basalts) >280 >280 Bell Harbor lavas lavas tholeiites, aphyric aphyric quartz tholeiites, trachybasalts >300 Palisade rhyolite rhyolite flow flow gray to pink, pink, porphyritic rhyolite gray to lavas Baptism River lavas mixed lavas, mostly basalts basalts Few 100's �~23-2 3— SHALLOW THE LAXE LAKE SUPERIOR SHALLOWSTRUCTURE STRUCTUREAND ANDSTRATIGRAPHY STRATIGRAPHYOF OF THE FROM SEISMIC SEISMICREFRACTION REFRACTIONMEASUREMENTS MEASUREMENTS BASIN FROM F1.C. Halls Halls and C.?. H.C. G.F. West Geophysics Laboratory, Dept. Dept. of Physics, University of of Toronto. ABSTRACT Between 1966 and 1969 thirty—three thirty-three seismic seismic refraction refraction profiles profiles were obtained in Lake Superior using aa single ship sonobuoy sonobuoy technique technique (Halls (Halls and and West, 1971). 1971). The seismic data have led led to to aa number of of conclusions conclusions concerning concerning the shallow shallow structure structure and and stratigraphy of the late Precambrian Keweenawn basin the that underlies the the lake: lake: that Faults with their bound the (1) their north north side side downthrown downthrown at at least least 1—2 1-2 1cm krn bound the north (1) Isle Royale Royale and and Michipicoten Michipicoten Island. Island. shores of Isle (2) the Keweenawan basin just just southeast southeast of of Isle Isle Royale Royale The northern limb of the (2) appears appears to to have undergone a deformation that that is is perhaps perhaps related related to to movement movement along the the Isle Isle Royale Royale fault. fault. (3) In to the the main basin between Isle Royale and the the Keweenaw Peninsula, In addition addition to (3) there the Slate Islands Islands in in the the there is is aa suggestion of of a smaller one southwest of the part of of the the lake. lake. northern part (4) (4) Cambrian Bayfield—Jacobsville Bayfield-Jacobsville sandstones sandstones appear appear Late Keweenawan or early Cambrian to underlie most of Lake Superior. Superior. Although the the site of the the lake lake is is governed governed to by the the position of the the underlying basin, the the principal principal factors factors determining determining the the size and shape of the the lake depression depression are are the the distribution distribution of of the the Bayfield— BayfieldJacobsville sandstones and their their susceptibility susceptibility to to erosion erosion compared compared with with older older rocks. rocks. (5) For those seismic profiles that have a certain degree of geological geological For those profiles that (5) control, such such as as those between Isle Royale and the control, the Keweenaw Peninsula, refraction refraction agree well with those those estimated estimated (Halls, (Halls, 1969) 1969) from from sasple sample velocities generally agree in the the laboratory. laboratory. One notable exception occurs in in those those profiles profiles measurements in that that lie just off the the Minnesota Minnesota shore. shore. Here velocities of of 55 km/s km/s are are recorded. recorded. These values are typical typical of of Freda—Copper Freda-Copper Harbor Harbor sandstones, sandstones, but but the the presence presence these rocks rocks adjacent to to the the Minnesota coast coast is is discounted discounted on on magnetic magnetic of these evidence. Instead the velocities of S5 km/s are assigned assigned to to the the North North Shore Shore volcanics that that crop crop out out along along the the mainland. mainland. The apparently low velocities of these these rocks rocks compared compared to to those those for for volcanics volcanics between Isle Isle Royale and the the Keweenaw kmfs) can be explained if Peninsula (5.7—6.2 (5.7-6.2 km/s) if the the North Shore Shore sequence sequence contains contains a greater proportion of interflow interflow sediment sediment and/or and/or amygdaloidal amygda10idal flow flow top top material. material. The seismic penetration of the (6) the refraction refraction profiles profiles was was generally generally insufficient insufficient (6) to to record the the Upper Refractor (Berry (Berry and West, 1966) 1966) with velocity 6.7± 6.7± km/s. km/s. However, one profile profile northeast of of Isle Isle Royale Royale recorded recorded aa velocity velocity of of 6.5 6.5 km/s km/s at a depth of of about about 66 km. km. This observation demonstrates the the existence existence of of Upper Upper Refractor—type Refractor-type velocities in the the marginal parts parts of the the Keweenawan basin. basin. �-24—24— References and G.F. G.F. West. West. 1966. 1966. An interpretation of the first first arrival data Berry, M.J. and of the the Lake Superior experiment experiment by by the the time—term time-term method, method, Bull. Bull. Seismol. Seismol. Soc. Amer., 56, Soc. 56, 141—171. 141-171. Halls, H.C. H.C. 1969. 1969. Compressional wave velocities of of Keweenawan rock rock specimens specimens from the Lake region, Can. Can. Jour. Jour. Earth Earth Sci., Sci., 6, ~, 555—568. 555-568. from the Lake Superior region, Halls, H.C. and and G.E. G.F. West. West. 1971. 1971. AA seismic refraction refraction survey in in Lake Lake Superior, Superior, Halls, H.C. Can. Jour. Jour. Earth Earth Sci.(In Sci. (In press). press). Can. �—25— -25- THE THE ISLE ROYALE FAULT FAULT B.C. H.C. Halls and and G.F. G.F. West West Geophysics Laboratory, Dept. Dept. of Physics, University University of of Toronto. Toronto. ABSTRACT A fault bounding the northwest shore of Isle Royale was originally postupostuA fault lated by by Irving Irving and and Chamberlin (1885) lated grounds. However, with (1885) on physiographic grounds. the exception exception of of recent recent aeromagnetic aeromagnetic studies studies (Wold and Ostenso, 1966; Hinze et the and Ostenso, al., 1966) very little extra evidence has been produced as as to to whether the the faiTt faurt al., 1966) really exists. The aeromagnetic data show a linear linear anomaly that that follows follows the the northwest shore of Isle Royale and extends eastward to to Superior Superior Shoal. Shoal. Although the sediments, it the anomaly anomaly indicates indicates aa contact contact between between Keweenawan volcanics and sediments, does or faulted faulted one one (Halls, (Halls, does not not reveal whether the contact is a stratigraphic or Evidence to 1970). to date for the so—called so-called Isle Isle Royale fault fault has therefore therefore been been 1970). rather inconclusive. This lines of evidence that that support support This paper discusses some lines the existence existence of the the fault, fault, in the the light of new magnetic and and seismic seismic data: data: the (1) (1) Seismic data (Halls (Halls and West, West, 1971) 1971) show that that the the uppermost layer that that underlies the channel north of Isle Royale and also the the region region further further northeast northeast underlies the the Slate Islands Islands has has aa velocity velocity of of about about 3.7 3.7 kin/s km/s and toward the and aa thickness of about 1—2 This seismic layer is all but continuous 1-2 km. km. This continuous with witih a similar similar one one in in eastern Lake Lake Superior can be firmly firmly identified identified as as Eayfield—.Jacobsville Bayfield-Jacobsville Superior that can sandstones. These thought to the Isle IsleRoyale Royale channel channel These rocks rocksare are thus thus thought to underlie the and if so, so, their their existence existence necessitates necessitates the the inclusion inclusion of of the the Isle IsleRoyale Royale fault fault with its downthrown downthrown side with its side to to the the north. 1970) show a remarkably (2) Paleomagnetic Books, 1968; 1968; Palmer, Palmer, 1970) Paleomagneticdata data (e.g. Books, consistent pattern pattern for for Keweenawan extrusive extrusive rocks. rocks. Whereas the the lower parts of the the volcanic sequence (such (such as as the Osler and South Range Range lavas) lavas) tend tend to to be be reversely magnetised, the upper parts such as the the Isle Isle Royale Royale and and Portage Portage Lake Lake reversely magnetised, the lavas are are normal. normal. In the the Isle Royale channel channel a linear linear magnetic anomaly anomaly (C (C in in Fig.l), Fig.l), which which is is attributed to to Keweenawan volcanics, is is strongly strongly positive positive with with an attendant minimum to to the the north, north, signifying that that the the volcanics are are normally normally an attendant magnetised. Anomaly CC continues continues beyond beyond the the channel channel to to both both the the east east and and west west where it broadens considerably considerably to to form form anomalies anomalies AA and and DD (Fig.l). (Fig.l). The sharpness and DD together together with the the seismic seismic data that the thevolcanics volcanics of anomalies A,C and data indicate that are overlain Thus north of the postulated Isle by Keweenawan are Keweenawan sedimentary sedimentary rocks. rocks. Thus the Isle If Royale fault buried, normally magnetised, Keweenawan volcanics. Royale fault there there are are buried, volcanics. the Isle Royale 'fault' 'fault' anomaly were due due to to aa stratigraphic stratigraphic contact contact the magnetic Isle between volcanics and and sediments sediments it it would imply imply that that the the sedimentary sedimentary unit unit was was sandwiched between two two thick thick sequences sequences of of normally normally magnet3sed magne~ised volcanics volcanics (i.e. (i.e. the Isle Isle Royale Royale lavas the lavas and those causing anomalies A,C A,C and and D). D). Such a sequence is of course possible but it is not a known feature feature of of Keweenawan Keweenawan stratigraphy. stratigraphy. is of course The only thick thick sedimentary unit unit that that occurs occurs in in the the Keweenawan Keweenawan volcanic volcanic sequence sequence is that is that in Michigan and Wisconsin but it lies lies between the the normal normal and and the the reversely magnetised sequence (e.g. (e.g. Meshref and and Hinze, Hinze, magnetised parts of the volcanic sequence 1970). Thus in 1970). in northern northern Lake Lake Superior Superior aa duplication duplication of of the the normally normally magnetised magnetised volcanics through movement along along the Isle Royale Royale fault fault is is favoured favoured over over aa through movement the Isle stratigraphic sequence of a sedimentary unit between between two two normal normal volcanic volcanic ones. ones. (3) of Fig.l Fig.l shows shows that that the the Isle Isle Royale Royale 'fault' 'fault' anonaly(E) anomaly (E) The magnetic map of (3) A weakening of the gradually assumes a more southerly trend trend toward toward the the west. A the gradually assumes anomaly in this anomaly this direction is more compatible compatible with the the presence presence of of aa fault fault rather rather than aa stratigraphic volcanic-sediment volcanic—sediment contact than contact (Balls, (Halls, 1970). 1970). �—26— -26- (4) Anomaly.C in Fig.l is essentially continuous continuous with aa belt of of prominent prominent the Minnesota shore before before turning turning positive anomalies that extends along much of the south and the Bayfield-Peninsula and terminating terminating in in aa hook-shaped hook—shaped anomaly over the Eayfield—Peninsula (Wold and and Ostenso, 1966). White (1966) (1966) concludes concludes that that this this anomaly is is due due to to volcanics in the upper .part sequence. The volcanics volcanics part of the Keweenawan extrusive sequence. Isle causing causing anomaly anomaly C C should should thus thus be be equivalent, equivalent, at least in part, part, to the Isle Royale lavas. lavas. Again, aa fault fault would be be necessary necessary to to explain explain the the apparent apparent of the the sequence. sequence. duplication of The foregoing foregoing observations therefore therefore all tend to to suggest suggest that that the the Isle Isle Royale fault fault does does exist. exist. A A two—dimensional two-dimensional magnetic model interpretation of the Isle Isle Royale Royale fault fault anomaly anomaly at at its its eastern end (Balls, 1970) suggests that the the (Halls, 1970) fault dips to the fault the south. south. The fault fault is is thus thus of reversad reversed type type as as its its downthrown do'~thrown side is is to to the the north. north. The displacement along along the the fault fault is is at at least least 1—2 1-2 km. km. The reversed nature the fault fault and and its itsincreasing increasingsoutherly southerlytrend trendtoward toward the the west west nature of of the that support the the idea idea initially initially raised Irving Chamberlin (1885) (1885) that (Fig.l) support raised byby Irving andandChamberlin it it is of the the Douglas Douglas fault fault in in Wisconsin. Wisconsin. is an easterly continuation of References Books, K.G. K.G. 1968. 1968. Magnetisation of the lowermost Keweenawan lava lava flows flows in in the the area, USGS Prof. Prof. Paper Paper 600—0, 600-D, 248—254. 248-254. Lake Superior area, Halls, H.C. B.C. 1970. Halls, 1970. Geological interpretation of geophysical data data from from the the Lake Lake Superior region, region, Ph.D. Ph.D. Thesis, University University of of Toronto, Toronto, 203 203 pp. pp. Halls, H.C. B.C. and G.E. West. 1971. Halls, G.F. West. 1971. A A seismic refraction survey in in Lake Superior, Superior, Can. Sci. (In (In press). press). Can. Jour. Jour. Earth Sci. O'Hara, N.W., N.W., Trow, Trow, J.W. J.W. and and Secor Secor G.B. G.B. 1966. 1966. Hinze, W.J., O'Hara, of eastern Lake Superior, Superior, AGU AGU Mono., Mono., 10, la, 95—110. 95-110. Aeromagnetic studies studies Observations on the junction between Irving, T.C. 1885. 1885. Observations Irving, R.D. R.D. and Chamberlin, T.C. the eastern eastern sandstone sandstone and and the the Keweenaw Series Series on Keweenaw Point, Point, Lake the Superior, Bull.US. Bull.US. Geol. Geol. Surv., Surv., 23, ~, 385—498. 385-498. Meshref, W.M. W.J. 1970. Meshref, W.M. and Hinze, W.J. 1970. Geologic interpretation interpretation of of aeromagnetic aeromagnetic data data in in western western Upper Upper Peninsula of Michigan, Michigan, Mich. Mich. Geol. Geol. Surv., Sun., Kept. Rept. of of lxiv., Inv., 12, 25 25 pp. pp. Palmer, B.C. and correlation correlation of of some some Middle Middle Keweenawan H.C. 1970. 1970. Paleomagnetisni Paleomagnetism and rocks, Lake Lake Superior, Superior, Can. Can. Jour. Jour. Earth Earth Sci., Sd., 7, 1410—1436. rocks, 1410-1436. l? White, W.S. W.S. 1966. 1966. Tectonics of the the Keweenawan basin, western Lake Lake Superior Superior region, region, White, USGS Prof. Prof. Paper Paper 525—E, 525-E, 23 23 pp. pp. Aeromagnetic, gravity and sub—bottom Wold, R.J. R.J. and and Ostenso, Ostenso, N.A. N.A. 1966. 1966. Aeromagnetic, sub-bottom studies in western Lake Superior, AGU Mono., Mono., 10, profiling studies Superior, AGU 10, 66—94. 66-94. �FIGURE FI GURE 89° 40' 89°20' 4a"OO' 48°OO' 88°40' $9°0O' THUNDER ---------- I 88°20 B8°0O' 88°00' BAY — ROVE FORMATION — — NORTH SHORE VOLCANICS 47° 50' a + -60$ 600 c1t:) ct=' — E ._—a.—-—ç D I F') N - V y TI V V '-I -...l SCALE V I 6 ••• i n — —, ISLE ROYALE VOLCANICS TI, 1V/ s COPPERHARBOR HARBOR CLASTICS CLASTICS COPPER 89c2O• $9000' _.- X——'-Y— X-·-··Y- 88° 40 ES MILES CONTOURS (X tOO) 100) CONTOURSIN IN GAMMAS GAMMAS 1* 88 0 20' 20' 88° 88 0 00' NORTHERLY LIMIT OF OFKEWEENAWAN KEWEENAWAN VOLCANICS VOLCANICS NORTHERLY LIMIT Total intensity magnetic magnetic map map of o tnt Total intensjty the Isle Isle Royale Royale channel. channel. Survey H. C. C. ILdIs Halls Survey by by N. F. West West in in 1966, 1966, using using aa shipborne proton precession spacing: and C. G. F. spacing: About About 33 miles. miles. N 300 c1:csjt in extreme Profile orientation: N 30 0 W., W.,except extreme northeast where it it is is more more northerly northerly 87°40' I �-28- RELIABILITY OF U-PB AGES OF SPHENE IN NORTHEASTERN MINNESOTA AND NORTHWESTE~~ ONTARIO G. N. Hanson Department of Earth and Space Sciences State University of New York Stony Brook, New York and E. J. Catanzaro Department of Geology Southampton College Southampton, New York A B S T R ACT U-Pb ages have been determined on sphenes from early Precambrian granitic rocks in relatively undisturbed areas and in a thermal aureole. The granitic bodies investigated are the Icarus pluton and the Saganaga tonalite in Ontario and the Linden Syenite and Giants Range Granite in Minnesota. A total of six sphene concentrates were analyzed. One sphene from the Linden Syenite had an unfavorable U/Pb ratio and no age could be calculated. Three sphenes from the Saganaga tonalite, the Icarus pluton, and the Giants Range Granite gave internally concordant U-Pb ages of 2710 ± 30 m.y. 'T'ivo sphenes from the Giants Range Granite and the Linden Syenite were internally discordant, but gave Pb207/Pb206 ages of 2730 and 2740 m.y., respectively. It is suggested that the discordance may be related to a relatively high uranium content in one sphene and to shearing of the host rock in the other. Sphene from near the contact of the Giants Range Granite with the 1100 m.y. Duluth complex gives internally concordant 2700 m.y. ages at 7.4 kilometers from the contact. As the contact is approached the sphene ages become internally discordant suggesting lead loss at 1100 m.y. At about one-half kilometer from the contact, where biotite and hornblende have lost essentially all of their radiogenic argon, sphene still retains about 60% of its radiogenic lead. �-29- CONTINENTAL RIFTS William J. Hinze Dept. of Geology Michigan State Univ. Donald M. Davidson Dept. of Geology Univ. of Minnesota, Duluth Robert F. Roy Dept. of Geology and Geophysics Univ. of Minnesota A B S T R ACT Comparison of late Precambrian, linear, tectonic features transecting the Mid-Continent region of the United States (e.g., the Mid-Continent and Mid-Michigan Anomalies) with relatively recent continental rift zones, such as the East African Rift System, indicates many similarities suggesting a common mode of origin. Hence, a mechanism is proposed for the development of linear Precambrian rifts and subsequent overlying sedimentary basins based upon observed geological and geophysical characteristics of modern rifts. Dissimilarities in stage of development, depth of erosion and geological age are parameters which limit the extent of comparison. Rift formation is initiated by plate splitting and subsequent upwelling of low velocity layer material into the upper mantle along the base of the crust. Although inherently denser than adj acent mantle rocks, the low velocity layer material becomes lighter and therefore rises upon partial melting and fractionation. Uplift of the earth's surface and igneous activity along pre-existing zones of weakness is associated with the vertical rise of this material, while lateral movement results in thinning and rupture of the crust producing extensional rift grabens. Subsequent magmatic activity in the rift zones results in local structural downwarping. Upon cooling, the low velocity layer residuml becomes dense and ultimately sinks into the mantle causing the uplifted rift zone to deflate. The convergent movement of adjacent mantle material into the void produced by the sinking residuum places the crust under compression, thus accounting for not only compressional features associated with rift systems, but the subsequent development of sedimentary basins over rift zones. �—30— -30- Keweenawan Geology of of the the Porcupine Porcupine Mountains, Mountains, upper Peninsula, Peninsula, Michigan Michigan Western Upper Harold A. Hubbard A. Hubbard u. Geological Survey Survey U. S. S. Geological Washington, 0. C. 20242 D. C. 20242 Washington, ABSTRACT The Porcupine Mountains, Mountains, Michigan, are are underlain by by tue the upper upper northwarLl-dipping limb of of an an overturned overturned asymmetric asymmetric anticline, antiline, not northward-dipping limb not aa dome with quaquaversal ~ua~uaversal dios dips as as usually usually shown. shown. The anticline is is faulted near its its axis1 axis, and at the southern margin the mountains mountains middle middle margin of o the diDpi1i to overturned Keweenawan volcanic rocks are thrust over over steeply steeply dipping Keweenawansedimentary sedimentaryrocks. rocks. The rocks, which upper Keweenawan The middle middle Keweenawan Keweenawan rocks, which are younger than Lava Series, can can be be divided divided into intotwo two are younger than the the Portage Porta3e Lake lake lava sequences. The Theolder older se~uence, sequence,which whichincludes inducesmost nostof of the he volcanic se~uences. volcanic of fine-grained fine-grained northward-dipping rocks the mountains, mountains, co:isists consists of rocks in the mafic to to intermediate intermediate lava lava flows flows and and two two interbedded interbedded felsic felsic lava lava flows. flows. southern felsic flow flow is is nonporphyr nonporphyritic The southern itic and and constitutes about half the outcrrp outcrop area. area. The younger younger sequence, se~uence, which which is is present present only only in in the the easternmost part part of of the the mountains, mountains, consists consists of of gently gentlyeastward eastwardand. and easternmost northeastward-dipping fine-grained and aphanitic flows flows overlain by volcanic conElonerate conglomerate and sandstone. The younger sequence se~uence is either either in fault contact or unconformable on on the the older. older. Both Both sequences se~uences are are repeao1L in part in fault slices repeated in in imbricate imbricate fault slices in inthe the southeasteru southeastern part of of the mountains. mountains. A A tear fault separates separates these rocks from the the upper Keweenawan rocks to to the the east. east. In the the Copper Harbor Conglomerate Con81omerate consists consists of of saidstone sandstone the north, north, the interbedded lavas. It appears to be conformable on middle containing interbedded lavas. It appears to be conformable on middle containing Keweenawan lavas in the lake of the Clouds valley. To the south tle Keweenawan lavas in the Lake of the Clouds valley. To the south ofo the mountains, the theupper upperKeweenawan Keweenawan rocks are folded in in an asymmetrical as~nmetrical syncline with with aa steep steep north limb. structural relIef syncline limb. The The structural reliefbets-een between the the size of and the synciline syncline is is more more than than 8000 8000 feet. feet. The size of the the PorcuPorcumountains iid sug3ests that the Keweenawan rocks of pine Mountain of western Mountain structure suggests icichiganwere were strongly st;unly folded in Michigan in post-Freda time, time, and not just just broadly warped. �—31--31- ThE KEWEENAWAN THE OFOFISLE ROYALE, MICHIGAN MICHIGfu~ KEWEENAWNGEOLOGY GEOLOGY ISLE ROYALE, N. King Huber U.S. U.S. Geological GeologicalSurvey Sury Menlo Park, California California 94025 94025 ABSTRACT A B S T R ACT Isle Royale lies on the north limb limb of the Lake Superior syncline, syncline, Royale lies and the the stratigraphic section exposed on the island is correlative correlative with the the much-studied much—studied middle middle Keweenawan Keweenawan Portage Portage Lake Lake Lava Lava Series Series and upper }ZeHr.awan Copper Harbor Conglomerate Cunglomerate on the Keweenaw Peninsula, on Keweenawan on the the south limb of of the the syncline. syncline. Dips of of the the strata strata range range from from less less than than 5Q0; 100 to over 50°; 10° side of of the the they are generally steeper on the north side the south and and average less than 20°. 20°. island than on the less than Exposures on Isle Royale indicate a minimum thickness thickness of of 10,000 10,000 feet for for the the Portage Lake Lava Series at The base feet at this this locality. locality. The baseofoftiiei the series is not exposed. exposed. As on on the the peninsula, the the series series consists consists largely largely of basaltic and andesitic lava flows, flows, with lesser amounts of of interfiow interflow sadiotaoy and tuffaceous rooks. sedimentary rocks. No felsie felsic flows flows are known from outcrops, although one has about outcrops, has been reported from diamond drilling, about 6,200 feet below the the top top of of the the lava lava series. series. The interflow clastic clastic rocks rocks do not not crop generally do crop out, out, and mast most of the individual units are are known only only from diamond drilling. drilling. Within the the lava lava series, series, which probably probably contains contains over a hundred flows flows in the the exposed section, section, certain stratigraphic units units representing flows or groups of flows flows can can be identified identified representing individual lava flows and traced on the basis and and basis of characteristic textures or structures, and relative stratigraphic stratigraphic position. position. Twelve such units have been distinguished distinguished within the the sequence and and provide stratigraphic stratigraphic and and structural structural control control for for geologic mapping. On both the Keweenaw Peninsula and Isle RoyaTh, Royale, the the Copper Copper Harbor Conglomerate is is largely derived from lowermost Keweenawan volcanic source source terranes, shed debris debris into the subsiding Lake Superior basin from from terra as, which shed opposite sides; sides; for for Isle Royale, this would be from from the the North Shore Royale, this Volcanic Group of of Gehman Gehman (1958) (1958) in in Minnesota. Minnesota. The depositional en'i:onment environment Volcano Group is is interpreted as as being one of a combination of fluvial fluvial and and lacustrine lacustrine conditions resulting in piedmont fanglomerates fanglomerates and and playa lake lake or or flood flood conditions plain deposits. deposits, Royale, various various sedimentary features On Isle Isle Royale, features indicate that that the the general direction of sediment transport was easterly, easterly, with aa range range from from northeast to to southeast. In thio this same direction the the Copper Harbor increases in Conglomerate Jr.i-eases in thickness thickness and and in in textural textural and and compositional maturity--namely conglomerate, through through aa mixture of of cobble cobble maturity——namely from a boulder conglomerate, and pebble conglomerates conglomerates and and sandstone, sandstone, to to sandstone sandstoneand andinudstone. mudstone. In a miles this distance of 20 miles this clastic wedge thickens thickens from from aa minimum minimum of of 1,500 feet feet to over 6,000 feet feet between stratigraphic marker horizons; the the top of of the the formation formation is is nowhere nowhere exposed and and the total thickness must be top appreciably greater. greater. �-3232— SOME PRIMA.RY PRIMARY SEDIMENTARY SEDIMENTARY STRUCTURES STRUCTURES IN IN THE SOME THE LOWER LOWER CHERTY CHERTY MEMBER tJfMBER OF OF THE THE BIWABIK IRON FORMATION BI~/ABIK FORMA.TION : VIRGINIA HORN HORN AREA ERIC FRODESEN Department of Geology and Geophysics Geophysics University Wisconsin, Madison, University of \.Jisconsin, Madison, Wisconsin 53706 53706 BSTRACT A B S T R ACT A The writer wri ter discovered di scoverecl and collected collected some some unusual unusua I sedimentary sedimentary oF the the Biwabik structures in the theLower Lower Cherty Cherty Member t-lember of Biwabik Iron Iron Formation Formation addition of at aa locality localitynea;r near the theMidway Midway addition of Virginia, Virginia,Minnesota. Minnesota. Polished Polished and x—radiographs overturned and and disturbed disturbed bedding bedding reresections and x-radiographs reveal reveal overturned sembling convolute—type convolute-type bedding, bedding, load load casts casts with with flame flame structures, structures, and and other structures structures characteristic characteristic of of soft soft sediment sediment deformation. deformation. SmallSmall— other scale cross-bedding cross—bedding and small small local local thrust thrust faults faults also also are are present. present. Recent experiments experi ments on on the the Formation formati on of of contorted contorted structures(McKee s truc tures (Mcl<ee and and Goldberg, show that that convolute—type convolute-type bedding bedding and and small—scale sm~ll-scale thrust thrust Goldberg, 1969) 1969) show faults, simi lar to to those those found in the Biwabik, Biwabik, can be be formed formed by by loading loading similar found in mud which was was deposited deposited on an existing existing slope slope of of 15—20 a semi—cohesive semi-cohesive mud 15-20 degrees. The The preservation of the the fine fine alternating alternatin~ dark dark and and light light laminae, laminae, small—scale small-scale cross—bedding, cross-bedding, and possible possible graded graded bedding, bedding, suggest suggest that that these wave base with only periodic these rocks rocks were deposited below wave periodic current activity. The alternation of the The the laminae laminae is is generally attributed to to seaseasonal changes{Hough, changes(Hough, 1958), or periodic periodic influxes of iron—rich and ironiron— sonal 1950), or influxes of iron-rich and impoverished impoverished layers layers due to to tectonic tectonic activity activity coupled coupled with with isostatic isostatic semi—rigid crust, crust, or or aa cornbina,tion combination oF adjustment of of a. a semi-rigid of the the two two procecess procecess (Cullen, 1963). 1963). Cullen's Cullen's idea idea that (Cullen, that banded iron iron formations formations can can he be rerell garded as as corresponding corresponding to aa syn-orogenic syn—orogenic "flysch "f1ysch' type of deposition deposition type of applications in explaining explaining some some of the structures found may have applications the structures found in in the the Lower Cherty Member. Similar sedimentary sedimentary structures structures are are found found in in the the Lower Member. Similar laminites of of documented flysch facies. The presence presence of ofallochthonous The allochthonous black chert chert pebbles pebbles within within the the beds beds poses poses aa problem as to to mode of of emplacement. Turbidity Turbidity currents, currents, subaqueous subaqueous sliding or or gliding gliding down down aa slope, slope, or or ice mechanisms have have to be ininsliding ice rafting rafting mechanisms to be voked explain their their presence presenceg voked to to exrlain If represent the the products proc'ucts of of chemical chp.mical weathering If iron iron formations formations represent under warm humid conditions in in semi—restricted semi-restricted basins, basins, then then ice ice rafting rafting under is not not aa very very likely is likely possibility. If, If, however, however, the the iron iron formations formations were were �-33—33— deposited rlepositerl in aa cool cool polar pot~rclimate climateasassuggested suggestedby bypaleonagnetic paleomagnetic data data (Symons, 1966),then thenthese thesepebbles pebblesmay may productofofice ice transport. (Symons, 1966), behe thetheproduct structures are are characteristic characteristic of Iff thesc these sedimentary sedimentary structures of the the entire entirefor— formation, and iron iron Formations general, then detailed regional mation, and formations inin ~eneral, then aa detailed regional study study could produce someenlightening enlighteningresults. results. could pro~uce SOMe refer~nces: 1'efercnces: Cul Ten,D•. U.J., 1963, Tectonic Tectonic implications implications of Cullen, J., 1963, of banded banded iron formations: formations: Jour. p.327—392. Jour. Sed. Sed. ret., Pet.,v.33, v.33, p.387-392. Gruner, J.'., Mineralogy andandgeology thethe Mesabi Gruner, J.l !.,l96, 1946, i~ineralogy geologyofof MesabiRange: Range: Office of Iron Range ofthe theComisioner Commisionerofof Iron RangeResources Resources and and t Rehabilitation, rehabilitation, St. Paul, Paul, tlinn. f1inn& 127 ppe 127 Pp. Gundersen, J.N., end Schwartz, 196Z, The geology geologyof of the metaGundersen, J.N., and G.M. G.M. Schwartz, 1962, The metamorphosedRi\-.abik SiwabikIron IronFormation, Formation,Eastern Eastern~lesabi Mesabidistrict, district, morphosed Minnesota:Minn. Minn.Geol. Geol.Sur. Stir. Bull. Bull. 43, Minnesota: 43, 137pp. l37pp. resh_waterenvironment environmentofofdeposition deposition of of PreHough,J.L., J.L., 1958, Yough, 1958, Fresh-water Precambrian iron formations: p. 41t+_1130. cambrian iron formations: Jour. Jour.Sed. Sed. Pet., Pet.,v.28, v.l8, p. 414-430. James, H.L., 1966, Chemistry of of the J~mes, H.L., 1966, Chemistry the iron—rich iron-rich sedimentary sedimentary rocks: rocks: 'J.S).S. Prof. Paper (-4O41, 6lpp. IJ.S.G.S. Prof. Paper 440-Iy" 61pp. Mcee, ~1c:\ee, E.fl., on formation formation of of conE.0., and and M. M. Goldberg, Goldberg, 1969, 1969, Experiments Experiments on torted Bull., v.80, torterl structures structures ininmud: mud: G.S.A. G.S.A. Bull., v.BO,p.23l—24-+. p.23l-244. Symons, P.T.A., 1966, A peleomagnetic paleomagneticstudy study on on the the Gunflint, Gunflint, Mesabi, Symons, ~.T.A., 1966, A Mesabi, and Cuyuna the Lake Lake Superior Superior Region; Region: and Cuyunairon iron ranges ranges in in the Econ. Econ. Geol., Geol., v.G1, v.61,p.p.1336—1361. 1336-1361. hite, \.'hi te, [l.A., [l.A., 1954, Thestratigraphy stratigraphy and 195 1f, The and structure of ofthe theMesabi ~1esabi Minnesota: ]{angc, ta: Minn. Hinn. Geol. Ceoi. Sur. Sur. Bull. Bull. 38, 38, 92pp. 92pp. Range, fHnneso �-34—34— ZEOLITE AND AND PREHNITE—PUELL?ITE PREHNITE-PUMPELLYITE FAdES FACIES IN INTHE THE KEWF.ENAWAN KEHEENAHAN BASALTS OF NORTHERN HICH:LGAN ROLE OF OF VOLATILES VOLATILES OF NORTHERN MICHIGANII: II: THE THE ROLE Wayne WayneT.T. Jolly Jolly ofSaskatchewan Saskatchewan University of Saskatoon, Canada Saskatoon. Canada ABSTRACT A B S T RAe T Keweenawpeninsula, peninsula, ~lichigan, :Iichigan. The lava flows flows of of the the Ke\\'eena,\v Thetholeiitic tholeiitic lava have undergone underone metamorphism of the the zeolite ite have metamorphism of zeoliteand andprehnite—punpelly prehnite-pumpellyite facies. the latter, fractures and upper flow flO\\1 contacts contacts latter, rocks rocks along along fractures facies. In In the been transformed have been transformed to to monomineralic monomineralic rocks rocks (metadomains) (metadomains) corposed composed of either pumpellyite pumpellyite or or epidote, epidote, depending depending on on stratigranhic stratiranhic position of position metadomains are are enriched enriched in in CaO CaO and and /\1')03 A1,O retitive in the pile. These metadomains relative to their their unaltered unaltered basalts basalts through of pre-existlnG pre—exiting plagio— to through albiti.zation albitization of plagioclase. Bulk compositions of the the altered altered parts parts of of the the flows, flows, deduced deduced re through ,veighted weighted averages averages of of the through the rock compositions, compositions, are sinilar similar to to ti1e parental basaits. parental basalts. Thus, Thus, little or no material was was added added from from extraneous extraneous sources. This metamorphic differentiation occurred occurred as as aa result result of of migration of of both both volatile volatile and non-volatile components over short and non—volatile components over Calcium distances through aa fluid fluid pressure pressure gradient zradient with \vi thr'f< r f<P total t l' Calciumalinninum silicates silicates were were formed formed preferentially preferentially near rupture alwninum rup~S~e zones, zones, at its its lowest lowest levels. levels. Theoretical considerations suggest where PP was at differentiation ofofessentially homogeneous that mdamorphic metamorphic differentiation essentially homogeneous bodies bodie~ of of rock thim P l' During the theKeweenawan Ke\\1eenaHan rock may mayoccur occuronly onlywhen whenPf Pfisisless less tian metamorphic event, dehydration. As As aa metamorphic event,the the rocks rocks underwent underwentext~g~rve etensve dehydration. depth from result, secondary phases phases decreases decreases with uith depth result, water content content of of secondary from water—rich or more) more) to water—acor epidote water-rich chlorites chlorites and and zeolites zeolites (1120=12% (H 0=12% or to '\-later-poor 2 (H about 2%). 2%). At lowest exposed levels levels P02 P0 may have have reached reached levels levels (HO0 about 2 2 sutficient sufficient to to subdue formation of pumpellyite in in favor favor of of pistacitic pistacitic epidote. PCOZ was very low 10\\1 during during the the peak peak of of the the metamorphic metamorphic event. event, Co2 �—35— -35AN AN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY C1" GF THE THE SOUTHKciilJ PENINSULA OF MIOsiIGAN MI~dIGAN PENINSULA OF SOUTHE Richard L. J. Hinze L. Kellogg and William 3. Geology Department of Geology Michigan State University Lansing, Michigan Hichigan East Lansing, ABSTRACT A B S T R ACT Only fragmentary direct information is is available on on the the basement basement complex underlying the Phanerozoic sediments of of the the Michigan Michigan Basin Basin because of the the limi;ed limited and poorly distributed basement basement drill drill tests. tests. To supplement this limited limited information information a a regional regional aeromagnetic survey has has aeromagnetic survey been of of thethe Southern Peninsula. Approximately 17,000 17,000 miles of beenconducted conducted Southern Peninsula. Approximately total magnetic intensity total intensity data data were were recorded recorded along along north—south north-south flight flight lines spaced at lines at three three mile intervals. intervals. A hasement A basement configuration map prepared prepared from from magnetic magnetic depth depth estimates estimates and basement basement drill drill tests and tests confirms that the basement surface surface under under the the Southern Peninsula of Ni Michigan has the the form form of of an an oval oval depression depression reachreachiar has ing aa maximum maximum depth depth of of approximately 15,000 feet ing feet below sea sea level level on on the the western shore shore of of Saginaw Saginaw Bay. Bay. A A basement high underlies the the Howell Howell .Anticilne and Anticline roughly north-south and aa roughly north—southstriking strikingregional regional basement basementtrough trLg plunges into into the boundarypoint poin of of Indiana, Ohio, plunges the basin basinfrom from the thecommon common boundary Ohio, and iIichigan Ilichigan to to the the vicinlty vicinity of 42°30'N. The map map shows a broad basement north\-lest in in the the extreme extreme southwest southwest corner corner of of the the platform striking northwest peninsula. Interpretation of the :esidual =~sidual aeromagnetic aeromagnetic map map in in conjunction conjunction with with geologic and other regional geophysical data seologic and other data from from the the Southern Southern PeiLtsula Peninsula and indicates that that the the basement basement of of the the :1ichigan Hichigan Basin has and adjacent areas indicates geologic history. history. Several Several basement provinces are are defined had a a complex complex geologic basement provinces defined on the basis of magnetic and and isotope isotope of magnetic and gravity gravity anomalies, anomalies, lithologies lithologies and ages of samples obtained from basement drill holes, and extrapolation of samples obtained from basement drill holes, and extrapolation of of known Precambrian geology from the the margin of of the the basin. basin. The Penokean province can be traced from into the can be from northern northern Nichiga Michigan and and Wisconsin Wisconsin into the area the northern the Southern Southern Peninsula. Peninsula. In this area the province province northern portion portion of the is characterized is characterized by east—southeast east-southeast striking striking anomalies. anomalies. Central and southwestern Michigan Michigan isis underlain rocks correlating correlating underlain primarily primarily by by felsic felsic rocks with the the Central Province. Basement rocks in Basement rocks in southeastern southeastern ~lichigan, Michigan, which which strike strike generally generally north—northeast are interpreted as as mafic mafic and and felsic felsic gneisses and north-northeast are interpreted amphibolites. amphiboli tes. They are correlated correlated with the the Grenville Grenville province province which \vhich is bounded on the west is on the west by by aa line line extending extending south-southwest south—southwest from from Saginaw Bay to south to Michigan— to west \vest of the the HowellAnticline HowellAt,ticline and and then then du.e du.e south to the MichiganOhio boundary. A A Keweenawan rift rift zone zone characterized characterized by by mafic mafic intrusives, intrusives~ extrusives and uplifted uplifted gneisses gneisses transects irom the the extrusives transects the the Peninsula from ic.neousactivity activity area to southeastern Traverse Bay Bay area southeasternMichigai Nichigan. Keweenaean Ke\veenmVan igneous mayalso also be be reflected reflected ininthe may thenumerous numerous local local magnetic magnetic anomalies anomalies in -• southwest whichoccur occuralong alongnorthvest norLn'eststriking strikingtrE!lllds treds whith soutlHvest Mi-htgan Nichigan which \vhich the regional pattern. parallel the regional gravity gravity anomaly anomaly pattern. �-36—36— PRECAMBRIAN CLASTIC CLASTIC PALEarIDAL SEDTI1ENTATION PRECAMBRIAN aarna SEDENTATION GEORGE deVRLES KLEIN GEORGE deVRIES Dept. of Geology, Univ.ofofIllinois, Illinois, Urbana, Dept. of Geology, Univ. Urbana, Illinois, Illinois,61801 61801 ABSTRACT ABSTRACT The Lm;er Fine-grained of Scotland Scotland and and The Precanbrian Precrbriari Lower Fine-grained Quartzite Quartzite of both both the Precaubrian Precanbrian Sterling Sterling Quartzite and and Precanbrian Preccmbrian part part of the the Wood Canyon Formation easternCalifornia California and are Wood Canyon Formation of of eastern and Nevada Nevada are characterized by primary primary sedimentazy sedimentary features which are characterized by features which are indicC'ltive indicative of sediment transport and and deposition deposition by bytidal tidal currents. sediment transport currents. Sedimentary structures structureswhich which occur occur in these these formations fonnations are are grouped grouped into sty seven which are produced by seven associ~tions associations which am produced by seven sevenphases phasesofof tidal tidal sediment sediment transport: transport: ASSOCIATION 1: 1: Cross-stratification sets, Cross-stratificationorganized organized into into herringbone herringbone sets, with bipolar-bimodal bipolar—bimodal orientation;parallel parallellaminae; laninae; these these features with orientation; features indicate indicate tidal tidal current current bedload bedload transport transport with with bipolar bipolar reversals reversals of of flow directions directions (Reirieck, flow (Reineck, 1963). 1963). ASSOCIATION 2: Reactivation surfaces:Multimodal Multimodalfrequency frequencydistribdistribASSOCIATION 2: Reactivation surfaces: utions of cross-strata utions cross-strataset setthickness thicknessand andofofdip dipangles; angles;unirnodal unimodal orientation of directional directional current orientation of current structures structures parallel parallel to to basin basin topographic strike; producedbybytime—velocity t:ime-veloci ty assymetry assymetry of of topographic strike; allallproduced tidal tidal current current flow flow (Klein, (Klein, l970a3. 1970a). ASS<X;IATION 3: Interference ripples; superposition ASSOCIATION 3: Interference ripples; superpositionofofcurrent current ripples ripples at 900 crests and at 90 0 and and 1800 180 0 on on crests and slip slipfaces facesofofdunes, dunes,sand sandwaves waves and and internal cross-strata; cross-strata;"B-C" "B-C" sequences sequences ClIf of cross-strata cross-strata overlain overlain by by micro-cross-laninae; highly-variant highly-var! antorientation orientation of of current current ripples; micro-cross-lcminae; all late-stage emergence runoff prior prior to all produced produced by by late-stage emergence runoff to anergence emergence of of an intertidal flat (Klein,1963,1970a,l970b). an intertidal flat ~Klein,1963,1970a,1970b). ASSOCIATION It: 4: Cross-stratification with flasers fla.sers and and clay clay drapes; drapes; Cross—stratification with flaser bedding; flaser bedding; lenticular lenticular bedding; bedding; "tidal "tidalbedding'; bedding"; convolute convolute bedding; all all produced alternation bedding; produced by by al terna.tion of ofbedload bedloadand and suspension suspension sed:imentation associated alternating bedload bedload and and slack-water slack-water sedimentation associated with with alternating tidal current tidal currentflow flow(Reineck (Reineckand andWunderlich,l968a,1965b; Wunderlich,1968a,1968b; Wunderlich, Wunderlich, 1970).• 197Q) ASSOCIATION 5. \lJashout structures, structures,sane sanefilled filled with mUd-chip with mud—chip ASSOCIATION 5. Washout conglanerates; rill casts; all allproduced produced by by tidal tidal scour scour conglctnerates; rill marks; marks;flute flute casts; (Van Straaten,1954; Straaten,l951j; Reineck, (Van Reineck, 1967; Klein,1970a). �—37— -37- ASSOCIATION 6: 6: MUdcracks; Mudc racks; mt intraformational conglanerates; rafo tin ational congicrie rates; birdseye structure; allproduced producedby byexposure exposure and and evaporation (Shinn,1968). stricture; all, Tracks and and trails; trails; burrowing burrowing structures, "escape" ASSOCIATION 7: Tracks structures,"escape burrows; all all produced burrowingorganisns orgaxüausadapted adaptedtotoaa tidal tidal burrows; produced by by burrowing regime (Rhoads,1967; (Rhoads,l967; Remneck 1968). Reineck and others, others, approximatedin in these Precanbrian paleotidal paleotidal ranges can be be approximated ranges can similar to rock units units finn rock from analysis of fining-upward sequences similar date, Late those occurring in in prograding prograding tidal copstlines. COAstlines. To date, Precambrian paleotidal ranges from from 0.3 paleotidal ranges 0.3 to to 13.0 meters meters have been measured. This Late measuitd. This Late Precanbrian Precaubrianpaleotidal paleotidal range rangevariation variation is tidal less than thRn the theknown known variation variation measured measured along along Holocene Holocene tidal ranges fran fran 00 to to 17.5 17.5 meters). meters). Perhaps coasts (variation of tidal ranges Precambri~n range variation is not greatly greatly difforent different is not Precanbripn paleotidal range fran present-day present-day variation. If further work substantiates such Precambrian, it a a limited paleotidal paleotidal range range variation variationfruit fram the Precambrian, poses critical critical problems poses problems for various various geophysical geophysical pxtblms problens that that have have been and age earth-moon systan. systen. beenproposed proposedfor forthe the origin origin and age of of the earth-noon REBERENCES REFERENCES CITED intertidal zone sediments: Jour. Klein, C.deV,1963, G.deV,1963, Bay Bay of of Plindy Fundy intertidal Jour. Sedimentary Sedimenta~ Petrology, Petrology, v. v. 33, 33, p. 844-854 8tb—85t -——,l97Oa, dynanics of intertidal sand ---,1970a, Depositional and dispersal dYnanics sand bars: Jour. Sdimentary S~dimentar,yPetrology, Petrology, v.v.140, 40, p. p. 1095-1127. --—,1970b, Tidal Quartzite -- The Lower ---,1970b, Tidal origin of of aaPrecambrian Precambrian Quartzite Pinc—grairdQuartzite Quartzite (Dalradian) (Dairadian)ofof Isl~; Islay. Scotland: Fine-grained Scotland: Jour. Jour. Sedimentary Sedimentary Petrology, Petrology, v.v.140, 40, p.p.973—985. 973-985. Reineck, H.E., H.E., 1963, un Bereic;h der sudliche Nordsee: Reineck, 1963, Sedimentgefuge Sedimentgefuge im Bereich der Nordsee: Abh. ~enckenbergischen SenckenbergischenNaturfor. Naturfor.Gesells. Gesells. No. 5O5, p. p. 1-138. Abh. No. 505, 1-138. --—,1967,Layered Layeredsediments sediments tidal flats, flats, beaches ---,1967, ofoftidal beaches and and shelf bottoms, p. 191-206: in Lauff, p. 191-206: in Lauff, (hR., G.H., Editor, Editor,1967, 1967,Estuaries: Estuaries:Am. Am. Assoc. Assoc. Adv. Sci. Sci. Pub. Pub. No. No. 83. 83. Reineck, H.E., and WUnderlich, H.E., and Wunderlich,F,F,1968a, 1968a,Classification Classification and and origin origin of flaser 99-1014. fiaserand and lenticular lenticularbedding: bedding:Sedimentology, Sedimentology, v. v. U, ll,p.p. 99-104. ---, &, ---, &, ---, ---,1968b, 1968b, Zeitmessugnen Natur und und ZeitanessugnenananGezeitenschichten: Gezeitenschichten: Natur Musetun, v. Museum, v. 97, 97, p. p. 193—197 193-197 Reineck, H.E., H.E., Dorjes, Dorjes, J, J, Gadow, Garlow, 5, S, and and Hertwick, 0,1968, S3dimentologie, Reineck, 0,1968, Sadiznentologie, Faunenzoniening and Faunenzonierung und Faziesabfolge vor vor der der Ostkuste Ostkuste der der inneren inneren Jeutschen Deutschen Bucht: Bucht: Senck. Senck. Lethaea, Lethaea, v.v.149, 49, p. 261-309 261-309 �-':;8—L8— Rhoads, D.C.,1967, and subtida subtidal D.C.,1967, Biogenic Biogenic reworking reworkingofofintertidal intertidal, and sediments in in Bamstable sediments BarnstableHarbor Harborand and Buzzards Buzzards Bay, Bay, Massachusetts: Massachusetts: Jour. Jour. Geo1or, Geology, 'r. v. 75, p. 461-476. t. b61—L76. E.A.,],968,Practical Practicalsignificance significance of of birdseye birdseye structure structure in in Shinn, E.A.,1968, carbonate rocks: rocks: Jour. Sedimentary Petrology, v. v. 38, carbonate Sedimentar,y Petrology, 38, p. p. 215—223. 215-223. Van Straaten, Van Straaten, L.M.J.U., L.N.J.tJ., 1954, 195h, Sedimentology Sedimento1o'ofof Recent Recenttidal tidal fla.t flat and the thePsamnites Psanmitesdu duC0ndroz Condroz (Devonian): (Devonian): Cleol. Geol. en en deposits and Mijnb., v. i6, Mijnb., v. 16, 25-47. p. 25-217. Wunderlich, F,1970, envirornent ofofthe T1NellenkopfschenWunderlich, F,1970, Genesis and and environment the "Nellenkopfschenschichten Il(Lower sian, EInsian,Rheinian RheinianDevonian) Devonian) at at locus locus typicus typicus in in schichten"(Lower canparison ecinparisonwith withmodern modem coastal environments enviroanents of the Cern GeImclTI n Bay: Bay: Sedimentary Petrology, Petrology, v. 240, Jour. Sedimentar,y 40, p. 102-130. 102-130. �-39—39— GEOLOGYOF OF THE SOME GEOLOGY THE 'ARATHON MARATHON COUNTY COUNTY VOLCANIC VOLCANIC BELT BELT by Gene L. L. LaBerge Wisconsin Geological Survey and and Department of Geology Geology Wisconsin State University Oshkosh, Wisconsin Oshkosh, ABSTRACT ABSTRACT The area east The east of Wausau in Marathon County consists consists largely largely of of rocks which range range in in composition composition from from basaltic basaltic to to rhyolitic. rhyolitic. volcanic rocks The rocks are mainly to the southeast and and the the rhyolitic rhyolitic rocks rocks The basaltic rocks to top of the sequence is northwest: northwest; to the the northwest, northwest, suggesting suggesting that that the the top of the however, however, no no definite definite evidence evidence of of stratigraphic stratigraphic top top \vas was found. fond. Trachytes are a1.. so present edge of of the the napped mapped area. area. Sedimentary are also pr?sent at at the the northwestern northwestrn edge rocks rocks are virtually virtually absent. absent. The volcanic rocks The rocks have been intruded by v;rious various sized masses of of gabbro, and syenite. syenite. There appears appears to to have been been gabbro, diorite, granite, and several ages of granitic intrusion. intrusion. Available radiometric ages ages indicate indicate are late late Middle Niddle Precambrian. Precambrian. that the rocks arc Structurally, the the area is is characterized by at least least two two directions directions Structurally, of large large scale faulting faulting with with niajor major fault faultzones zonestrending trendingapproximately approximately N8O°E to to N60°E. 1180°£ ~~60°E. The \vhich also shows shows up on the aeronagnetic aeromagnetic The faulting, faulting, which up well well on map many of mapcovering coveringthe the area area mainly mainly west west of of Wausau, Wausau,has hasresulted resalted in many of the lithologli units units being in Perhaps the lithologic in fault fault contact. contact. Perhaps the most significant fault zone is is the the N300E N3OF trend fault zone trend whiàh which has has produced produced aa zone zone nearly nearly aa mile mile in the the Eau Eau Claire Claire River River valley in in which mylonite mylonite is is aa major major rock rock wide in This zone truncates type. This truncates the N8O°E—N60°E N800E-N600E trend trend more prevalent prevalent to to the the ,,,,est. west. The current napping project, The current mappins project, funded funded by the the Wisconsin Geological Geological S"rvey, has Survey, revealed significantly significantlymore morevolcanic volcanicrocks rocksthan than shownOLI on has revealed areare shown Weidinan's 1907 map. \veidman's 1907 map. This This has has important importantimplications implicationsfor formineral min al exploration A previously unreported gold prospect, on tion programs. A on which mining attempted about 1920, 1920, is is probably probably the the most most interesting interesting locality locality from from was attempted an economic point point of of view. view. References Dutton, E. (1970) Dutton, C. C. B. E. and and Bradley, Bradley, R. R. E. (1970) "Lithologic, and "Lithologic, Geophysical, and ;·lineral :•lineralCommodity CommodityHaps MapsofofPrecambrian Precambrian Rocks Rocks in in Wisconsin"; Wisconsin"; U.S.G.S. Miscellaneous Geologic InvestigationsMao Map 1-631. Geologic Investigations 1—631. Henderson, J. J. IL, Henderson, R., Tyson, Tyson, ;i). R. (1963) "Aeromagnetic N. S., S., and Page, Page, J. 3. R. (1963) "Aeromagnetic Map of the Wausau Area, Wisconsin"; Map of Wisconsin"; U. U. S. G. G. S. Geophysical Investigations Map Map CP—40l. GP-40l. Laberge, G. U. and l,Jeis, LaBerge, G. 1. L. W. Iv. (1968) Central Weis, L. (1968) "A 'A Greenstone Greenstone Belt Belt if in Central Wisconsin?", Guidebook Guidebook for for 32nd 32nd Annual Annual Tn—State Tri-State Geological Geological Field Field Wisconsin?, Conference. �—40— -40- Weidman, S. S. (1907) (1907) The The Geology Geology of of North North Central Wisconsin; Wisconsin; Wisconsin Geological and Natural History History Survey Survey Bulletin Bulletin 16. 16. Weis, L. W. W. and and LaBerge, LaBerge, C. G. L. 1. (1969) (1969) "Central Wisconsin Volcanic Volcanic Belt," Belt," Weis, L. Guidebook for 15th Annual Institute Institute on on Lake Lake Superior Superior Geology. Geology. �—41— -41- HEMATITE PSEUDOMORPI-1IC AFTER BIOGENIC BIOCENIC HE~1ATITE PSEUDOMORPHIC AFTER PYRITE IN INTHE THENEGAUNEE NEGAUNEE IRON IRONFORMATION FORMATION N. M. S. S. Lougheed and J. J. 3. J. Nancuso Mancuso Bowling Green State University, Green, Ohio 43403 43403 University, Bowling Green, ABSTRACT A B S T R ACT Spherules (limonite), ranging in diameter from from Spherules of of hematite (limonite), 5 microns microns to to 20 20 microns microns but generally of similar size in each each as disseminated disseminated octahedral octahedral crystals crystals particular population, as well as of pseudomorphic hematite occur in in many laminations laminations of of the the Negaunee Negaunee iron formation. formation. Mineral associations associations include include chert, chert, magnetite, magnetite, iron iron carbonate, silicates. A A common associate is is fossil fossil fila— filacarbonate, and iron silicates. A tentative conclusion based on two mat algae. algae. A two microprobe mentous mat Thermal experiments carbon in the filaments. filaments. Thermal analyses indicates indicates carbon in the result considerableremoval removal of the filamentous material suggesting suggesting result ininconsiderable the presence presence of both both amorphous amorphous carbon carbon and and graphite. graphite. Framboidal pyrite with diameters ranging from 55 microns to to 20 20 microns sedi— nlicrons and and pyrite octahedra, octahedra, occurring in two two unconsolidated sediinents with contrasting contrasting environments, environments, one one aa Pleistocene fresh ments with fresh water water lake deposit, deposit, the lake the other a Recent marine tidal tidal lagoon, unequivocally unequivocally demonstrate their their biogenic biogenic origin. origin. Paleozoicanalogs analogsofofsomewhat somewhatsimilar similar lithology lithology to to iron iron formation formation P-Jzoic the following associations: carbonate, biogenic biogenic euhedral euhedral the following associations: chert, carbonate, pyrite, biogenic framboidal pyrite, framboidal pyrite pyrite 55 microns microns to 20 microns microns in diameter, diameter, to 20 sparce euhedral magnetite microflora. magnetite and and fossil fossil microfcunz: microfauna and/or microflora. the biogenic biogenic origin origin of of pyrite. pyrite. They further demonstrate the have A finely laminated A finely laminated chert chertcarbonate carbonatespecimen specimen from from the thePennsylvanian Pennsylvanian formation, Texas, Texas, clearly shows the Dimple formation, the transition transition of of biogenic biogenic pyrite to pseudomorphic hematite hematite (limonite) (limonite) by by oxidation. oxidation. features are These various various features are illustrated by photomicrographs phbtomicrographs to to that the support the the hypothesis hypothesis that the spherules spherules of of hematite (limonite) (limonite) possibly other other hematite hematite in in the theNegaunee Negaunee iron formation formation are pseudomorphic after biogenic biogenic pyrite, pyrite, and together pseudomorphic after together with the the presence presence of the bio~enic bio3enic (in part) genesis of probable probable algal algal mat mat strongly strongly support the (in part) of the Negaunee Negaunee iron formation. of iron formation. and and �—42— -42- DISTRIBUTION OF URANIUM URANIUM AND AND THORIUM THOP.IUM IN PRECAMBRIAN PRECAMBRIAN ROCKS RE GION ROCKS OF OF THE THE WESTERN WESTERN GREAT GREAT LAKE: LAKE: RE3ION by Roger C. Roger C. N~alan and and David Sterling Malan David1_A Sterling ommission, Grand Thiorado U.S. Atomic Energy Energy :::ommission, Grand Junction, Junction,:::olorado U.S. Atomic AE<:::;TRACT AECTRACT 1 Prospecting during during the the 1950 1950's resulted in Prospecting s resulted in the the discovery discovery of of several several uranium and thorium prospects in Precambrian rocks in the westuranium and thorium prospects in Precambrian rocks in the westeconomic deposits ern Great Lakes Lakes region region of of the the United United States. States. No No economic deposits ern Great were delHeated the few few small small exploration efforts that were delineated by by the exploration efforts that were were underunderSince then exploration for for radioradiotaken. Since then there there has has been been very very little little exploration active minerals minerals in active in that that region. region. In Wisconsin Wisconsin and and inin upper upper Michigan, Michigan, Lower, Lower, Middle, PreIn Middle, and and Upper Upper Precambrian silicic cambrian silicic and and hyperalkalic hyperalkalic plutonic plutonic rocks rocks contain contain anomalous anomalous In upper amounts of upper Michigan, Michigan, amounts of disseminated disseminated radioactive radioactive minerals. minerals. In the Middle Middle Precambrian Animikie Series contains uranium uranium veins veins in in the Precambrian Animikie Series contains slate, monazite placers placers in in conglomerate, conglomerate, and and irregular concentraslate, monazite irregular concentrations utanium in iron iron formation adjacent to to slate. tions of of Ul anium in formation adjacent slate. These These prosprospects do do not of uranium uranium or or thorium thorium that that pects not contain contain important important reserves reserves of are at present are economically economically mineable mineable at present but but some some may may contain contain large large long-range, low low-grade resources. long-range, - grade re sources. For Forexample, example, limited limited sampling sampling indicates that that masses masses of indicates of silicic silicic igneous igneous rocks rocks in in northeastern northeastern WisWiscousin may contain contain 50 50 to to lOO 100parts parts per per million consin may million uranium. uranium. This This is is greater than than the the uranium uraniumcontent content in inany any of of about about 250 250 bulk samples greater of igneous rocks rocks that analyzed in in aa recent of igneous that have have been been analyzed recent study study of of the the distribution of uranium rocks in in the the distribution of uranium and and thorium thorium in in Precambrian Precambrian rocks western United United States. potentially great great low-grade low-grade resource resource of of western States. AA potentially thorium may thorium may exist exist in in the the monazite monazite placers placers in inAnimikie Animikie conglomconglomerates in erates in the the Marquette Marquette Range, Range, upper upper Michigan. Michigan. In other other areas areas of of the the world, world, stratiform stratiformuranium uraniumdeposits depositsin inMiddle Middle In Precambrian Precambrian coarse coarse clastic clastic sediments sediments are are of of major major importance. importance. The world's world's greatest resource of uranium is is in The greatest known known resource of uranium in basal '::asal conconglomerates of the Middle Middle Precambrian Huronian Series glomerates of Precambrian Huronian Series in the Elliot Lake Blind River Elliot Lake -- Blind River district district in in southern southern Ontario. Ontario. Important stratiform uranium deposits deposits have have not not been been discovered discovered in in the the stratiform uranium Animikie Series which is in Animikie Series which is in part part correlative correlativewith withthe theHuronian; Huronian; �________ -4343— however, however, limited limited sampling sampling ia L.1. the the iviarquette Ivlarquette Range, Range, upper upper Michigan, Michigan, indicates that anomalous anomalous amounts indicates that amountsofofuranium uraniumare are present present in in coarse coarse clastic facies. Also in the the Animikie Animikie in the Also uranium/thorium uranium/thorium ratios in elastic Blind River Marquette Range and in the Huronian in the Elliot Lake River Marquette Range and in the Huronian in the Elliot Lake -- Blind More study area increase increase in in descending descending stratigraphic stratigraphic positions. positions. More study of of area the distribution of uranium the distribution of uranium and and thorium thorium in in the the Animikie Animikieisis warranted. warnnted. CELECTED REFERENCES :ELECTED REFERENCES T.llsley, ':llsley, C. C.T., T., Bills, Bills, C. C. W. W., Some geoand Pollock, Pollock, J.W. J. W.,, 1958, Some chemical methods of uranium exploration, exploration, in inSurvey Survey of of Raw Raw chemical methods Materials Resources: Materials Resources: United United Nations, Nations, New New York, York, Proc. Proc. Second Second lnternat. Conf. Energy, 1958, v. 2, Internat. Con£. Peaceful Peaceful Uses Uses Atomic Atomic Energy, 1958, v. 2, p. p. 126-130. , James, H. James, H. L., L.,1958, 1958,Stratigraphy Stratigraphyofofpre-Keweenawan pre-Keweenawan rocks rocks in in parts parts of Northern Michigan: Michigan: U. U. E E Geol. Geol. Survey Survey Pro£. Paper314-C, 314-C,42 42 p. p. of Northern Prof. Paper King, J. W., W.,1960, 1960,Report Reportofofexamination, examination,Little Little WolfMining Mining&& MinMinKing, Wolf erals, Inc., erals, Inc.,Anklam AnklamProperty PropertyBig BigFalls, Falls,Waupaca WaupacaCounty, County, WisconWisconsin: file rept. sin: U.S. U. S. Atomic Atomic Energy Energy Comm. Comm. open open file rept. Malan, C., and and Sterling, Sterling, D. Do A., A.,1969, 1969,An Anintroduction introduction to to the the disdisMalan, R. R. C., tribution thorium in in Precambrian Precambrian rocks tribution of of uranium uranium and and thorium rocks including including the the results results of of preliminary preliminary studies studiesin inthe thesouthwestern southwesternUnited United States: States: U.S. U.S. Atomic Atomic Energy Energy Comm. Comm. AEC-RD.-9, AEC-RD-9, 54 54 p., p., open open file. file. Roscoe, Roscoe, S. S. M. M., 1969, 1-luronian Huronian rocks conglomerates rocks and anduraniferous uraniferous conglomerates Canadian shield; shield: Geol. Geol. Survey Survey Canada Paper 68-40. 68-40. in the Canadian , Stead, F. F. W., F. J., Stead, W., Davis, Davis, F. J., Nelson, Nelson, R. R. A., A., and and Reinhardt, Reinhardt, P. P. W., W., 1950, Airborne Airborne radioactivity radioactivity survey survey of of parts parts of 1950, of Marquette, Marquette, DickDickinson, and open— inson, and Baraga Baraga Counties, Counties, Michigan: Michigan:U.S. U. S.Geol. Geol.Curvey :urvey openfile map. file map. Vickers, R. of t>-e te Goodrich Vickers, R. C., C.,1956a, 1956a,Geology Geology and and monazite monazite content content of Goodrich Quartzite, Quartzite, Palmer Palmer area areaMarquette Marquette County, County, Michigan: Michigan: U.S. U. S. Geol. Geo!. Survey Bull. Bull. 1030-F. Survey 1030-F. 1956b, Ai Airborne rborne and and ground groundreconnaissance reconnaissanceofofpart partof of the the ----syenite complex near near Wausau, Wausau, Wisconsin: U.S. syenite complex U. S. Geol. Geol. Survey Survey Bull. 1042-B. �Is.. .c g (/) • lii,Oll.tsdiI ~~ - o o a "'" o I :;= g;;'~~ ~~ ~~ O4! 4 l5S 50565' 8 fl. I 4515 il 0 - V t;%,ir III 1545_C1 •'l'' C E] ~i !: .. ~ (~ ?:t,"t.i. ;'''° Ui,iii,soolli,,t. ltl - ~ ~ u~ C C ~ ~ / I / o o Ul '" ~ I 50 146104Sre,,t.4 dtstil. ~ 15 ~ 0 5, SOlO. 444 isosaStis is C.sbi,en yl.'.!.o.; C154401ltUt,11.pi.o I Slot 05 II S •l 545' !!611 11,41. ~~ ~ ., -:0440,' ~ 0 =;;; fl - Jiddn IIfIJqn,e'd D ii ! :.~ ! I i f : c . 'iii 0 c 0 ~ '" ~ .. --., , I 1 I I I '"." c I I I 1 I Lakes fll*!6441r4!llt 4.11 c ~ 0 . '" Greet n n• . < '. • : 0; .! 3<" Sec horn I-I £!,oe.,, #•flsI 44144!, lId Ut SO IMi ~ i~ — ,__— <D~ • :;;. .i E~ .. ~'ii - ;; : ., co Precambrian, s ! 0.- ;. ~ bi 'I,. - i'I": -,..- ~ <; Map - -- ~i: . ~ i u ";; "0 0 0 GaochronoIoic ~ :;. ~ ood . . I:,':?. : ~~ ;:; Geologic . (I,le,n QIfl4. t15 .44 ~ D I ." ~ I G.n,,oIIzeo ! Kt#,.lIk,Ic,t!ee C $!l afl'I,!L. ;; - '" '" I '" 2 ;.: en. —4 ''6 .; 35 i ! 111111_LI . ~:. I ~ t I •.l.ih C—i,. . A ~ ~ = mj, , -44- ~ ~ ~ ~ .;, I a. II: " C 0 ~ ..J ~ C> ~ . q: u e0 " ~ ~ :E Q. 0 '"u0 C> '" " I ~ ~ c 0 <9 0 "" 0 0 <9 ... 00 ~ ~ �-45—45— LOWER KEWEENAWAN KEWEENAWAN SEDIMENTS THELAKE LAKE SUPERIOk SUPERIOR REGION LOWER SEDHlENTS OFOFTHE REGION Allen F. Mattis Mattis Allen F. Department Department of Geology Geology of Minnesota, Hinnesota, Duluth Duluth University of A B S T RAe T ABSTRACT Lower Keweenawan sediments directly directly underlie underlie the the Keweenawan Keweenawan Studies of the quartz— volcanic series in the the Lake Superior Superior region. region. quartzvoi:anic rich Puckwunge Formation (Minnesota) rich (Minnesota) and the Bessemer Formation Formation (Michigan (Michigan and Wisconsin), Wisconsin), which include thin section petrography, heavy mineral and mineral analysis, and measurement of paleocurrent indicators, indicators, provide provide new new data data analysis, and Keweenawan events. events. on Lower Keweenawan The Puckwunge Formation of Cook Cook County, County, northeastern northeastern Minnesota, Minnesota, from is exposed along along aa 25 25 mile mile belt belt extending extending westward westward from is LT.termittently intermittently exposed Pigeon Point on Lake Lake Superior. Superior. Although the lower contact contact of this this formation is is not exposed, exposed, outcrops of of the the formation formation thicken thicken from from 30 formation feet on Grand Portage Island to to over 100 100 feet feet in in the the westernmost \vesternmost feet of basal conglomerate exposures. Fifteen feet feet-of conglomerate exposed exposed on on Grand Grand Portage Portage exposures. Island contains flat flat chips chips and pebbles of of argillite argillite and and slate, slate, probably probably Island derived from the underlying Rove Rove Formation, Formation, and and rounded rounded pebbles pebbles of of feldspar content quartzite. Thin section examinutioi examination indicates indicates total total feldspar content quartzite. ranges from 20 percent percent in the eastern exposures to only a trace in the western outcrops. Unit Unit quartz is the dominant quartz uype, type, with up up to to Zircon, apatite,and apatite, and 20 percent polycrystalline polycrystalline quartz quartz being beingpreseriI. present. Zircon, with tourmatourma— epidote are the the common common nonopaque nonopaque accessory accessory heavy heavy ininerais, minerals, with line also the outcrop belt. also present in the central portion of the to only a trace in the Nopeming, just just west of of Duluth, Duluth, 25 25 feet feet of of quartzite quartzite and and quartzquartz-At Nopeming, conglomerate are •:->.oosed }T the basal (?) quartzite-pebble are exposed bere&: beneath quatnJte—pebble conglomerate (?) Keweenawn Keweenawan flow over a distance distance of of half half aa mile. mile. In the the sand—sized sand-sized fractions, unit quartz quartz is is the LUe dominant dominant quartz quartz type, tye, with polycrystalline fractions, unit polycrystalline also preseit. present. Zircon is the principal nonopaque accessory heavy quartz also is the amounts of of a;atite apatite and and tourmaline tourmaline present. present. Gravity mineral, with minor amounts and magnetic suggest the the presence presence of of aa tabular, tabular, and magnetic profiles profiles across across the the area na suggest dike—like dike-like mafic body beneath the the Puckwunge exposures exposures at at Nopeming; Nopeming; aa greater degree of recrystallization in in the the lowermos: lowermost sediments sediments may may be be related to related to this this probable intrusive. intrusive. and and The Bessemer :-:ohigai-r BessemerFormation Formationof of Hichigan and Wisconsin lHsconsin is intermittently intermittently exposed :nile belt belt extending extending eastward exposed along along aa 40 mile eastward from from >leflen, ~le~len, Wisconsin. formation is is over 150 The fonnation 150 feet thick thickwhere where both both the the upper upper i-td and lower lower contacts are are visible. visible. A contacts A basal conglomerate contains rounded pebbles pebbles of basal conglomerate contains rounded quartz, qu;E2ite, quartzite, flint, flint, and and jasper jasper in in aa qnartzite rruartzite matrix. matrix. In the the sand—si-:d qunrtz is sand-sized fractions, fractions, unit unit quartz is the dominant dominant quartz type, type, with polycrystalline quartz quartz also also present. present. The average total feidsrar feldspar content content is less than than 10 10 percent. percent. Zircon is is the tlte dominant nonopaque nccesscry accessory h!avy withapatite, apatite, rutile. rutile, and heavy hliner&I, ltlineral, \vith and tourmaline tourmaline also also present. presenL �—46— -46- sediments along both limbs the lower lower IKeweenawan Keweenawan sediments Exposures of the the Lake SuperiorSync:ine Synclinesuggest suggestthe thedeposition depositionofof aa thin thin sheet of the Lake Superior sheet of sediment throughout throughout the region. The cross-bedded, rippie—mariced, ripple-marked, of sediment the region. The cross—bedded, of Hell well rounded well sorted sorted quartz—rich quartz-rich sediment sediment composed composed of rounded grains suggests aa shallow shallow water waterenvironment. environment. Cross-bedding, mark, Cross—bedding,ripple ripple mark, in these these sedimentary sedimentary rocks rocks indicate indicate and parting lineation measurements in sediment transport, transport, with the the sediments sediments a general southerly direction of sediment being derived from the the Pre—Keweenawan Pre-Keweenawan rocks rocks to to the the north. north. Thus, Thus, these these Lower Keweenawan sediments were probably deposited deposited during during the the northward transgression of of aa sea into into the transgression the region, region, and were apparently the the final final region prior to to formation formation of of sediment deposited in the Lake Superior region the Lake Superior Syncline. Syncline. �—47— -47- EXPLORATION GEOLOGY GEOLOGY OF OF DOUGLAS DOUGLAS COUNTY, COUNTY, w::scoNSIN WISCONSIN by Joseph T. T. Mengel, Mcnge1, Jr., Jr., Professor and Ronald A. A. Hendrickson Department of Geology Geology Wisconsin State University, University, Superior, Wisconsin 54880 54880 and and and Natural Natural History History Survey, Survey, Madison Madison 53706 53706 Wisconsin Geological and ABSTRACT A B S T R ACT The oldest bed rock units in Douglas County are are the the Keweenawan Keweenawan basaltic fissure flows flows of the St. St. Croix horst south south of the line lin~ Brule, raple, Wentworth, Wentworth, South Range, Brule, Maple, Range, Pattison State Park, Park, Patzau. Patzau. These flows flows have a N6OE3SS N60E35S attitude along tha the north margin margin of of the the horst and N5OE15S N50E15S along along the the south. south. They are intruded by "red "red rock" .95 b.y. b.y. and and by aa gabbro gabbro mass mass in in 32—48N— 32-48Nin 15-47N-13W,K/Ar l5—47N-13W,K/Ar dated at .95 12W. l2W. flows occur again south of the line Totagatic River— Basaltic flows RiverOunce Creek where the attitude is N4SE3ON N45E30N and and there there are are extensive extensive conglomerate lavas. conglomerate and sandstone interbeds with the lavas. Native copper ides are copper and and copper copper suif sulfides are found found in in ainygdaloidal amygdaloidal horizons and along fractures wherever the the Keweenawan Keweenawan lavas lavas outcrop. outcrop. Almost all lava outcrop is within the the following following limits: limits: (1) A a,uth of of the the line Brule—Patzau A 22 mile wide wide band band south Brule-Patzau (2) (2) A nile wide band north of A 22 mile of the the line line Winnebaujou—St. Winnebaujou-St. Croix River in 43N-14w 44N-13W 43N—14W and 44N—13W (3) (3) 43N-15W The NW half of 43N—1SW (4) (4) The south half of 44N-15W 44N—l5W and SW quarter 44N-14W 44N—14W (5) (5) The NE quarter of 45N—l2W 45N-12W (6) The SE haf half of of 43N—1OW, 43N-lOW. especially especially along along the the valley valley of of Dingle Creek in sections 12 and 13 where an an extensive extensive section is exposed the last last century and a half the properties During the half the properties listed below have all all been the have the locus of shafts and/or test test pits and and drilling drilling for for copper in in the the lavas. lavas. �—48— -48- Location Property Nature NE 12—43N—1OW l2-43N-lOW Weyerhauser Amygdaloid Ainygdaloid and and in assoc. sediments SW 28—43N—1OW 28-43N-lOW Williams Ashbed amygdaloid NW 6—43N—13W 6-43N-l3W Superior Copper Mines C.F. C.F. Irving Mon 5, 5, pI. 25 p1. 25 8—43N—13W SW 8-43N-l3W Copper Mine Dam (? ) Ainygdaloid Amygdaloid (?) SE 34—44N—J.4W SE 34-44N-l4W Nowell (Crotty Brook Arnold) ArnoL) Nowell (Crotty Brook (? ) Anygdaioici Amygdaloid (?) SE 14—44N—13W SE l4-44N-l3W Aac ía Arnold Amygdaloid Amygdaloi<l 7N—liJ NE 31-4 3l-47N-l4W Culligan Amygdaloid SE 28—47N—14W 28-47N-l4W Bardon Amygdaloid Amygdaloid('l) () SW l4-47N-l4W 1447N—14W SW Copper Creek Creek Cc1:ier Amygdaloid NE 8—47N—13W 8-47N-l3W Fond Fond du Lac Lac Amygdaloid SE 2—47N—l3W 2-47N-l3W Starkweather Wisconsin Edwards Zdwards NWdip dip 75 NW NE strike 75 Centerll—47N—13W ll-47N-l3W Amnicon Center Fissure vein vein4—6' 4-6' wide wide Narrow steeply dipping Narrow steeply dipping vein Houghton Amygdalcid Amygdaloid NE 8—47N—12W 8-47N-l2W Badger Amygdaloid Nnygdaloid (?) NW NW 1O—47N—12W lO-47N-l2W Chippewa Fractured Fractured Amygdaloids Amygdaloids St 1O—47N—12W SW lO-47N-l2W Copper King King Amygdaloid (?) (?) Amygdaloid 23--48N--lOW NE 23-48N-lOW Cascade Amygdaloid (?) (?) Miygdaloid NE NE Percival, Jr. Jr. Percival, Amygdaloid NE NE 27-48N-lOW 27—48N—1OW Percival Veinlets ininamygdaloid amygdaloid NW NW 28—48N—1OW 28-48N-lOW Astor Amygdaloid SE 29—48N—12W 29-48N-l2W Mrnicon Amnicon Amygdaloid (?) Mtygdaloid SE SE 34-48N-l3W 34—48N—13W Catlin Amygdaloid 4—47N-12W 4-47N-l2\.J 24-48N-lO\.J 24-48N—lOW �—49— -49- The the The U. U. S. S. Bureau of Mines Mines reported on extensive tests of the Property in 1947 and the the Chippewa Chippewa Property Property in in 1955. 1955. Weyerhauser Property The Keweenawan Oronto Group occupies the the Lake Superior Superior syneline syncline of the Croix River. Resouth of the line lineWinneboujou, Hinneboujou, Solon SolonSprings Springs—- St. Croix Shale, and portedly the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, the Nonesuch Nonesuch Shale, and the the Prospecting in Freda Sandstone units are all present in this area. Prospecting Freda Sandstone units are all present in this area. the the syncline syncline has has centered centered on on attempts attempts to tolocate locatea acopper—bearing copper-bearing facies facies of the the Nonesuch Nonesuch Shale, but but has hasbeen beenhampered hampered by by complete complete absence absence of outcrop except the St. St. Croix River Valley. Valley. except along the lower portion of the Conglomerates in: NWNW NWNW 10— 10Conglomerates have have been reported from exploration tests in: half lO—45N—1OW, 44N-llW, SW corner 3l—44N—1OW, 3l-44N-lOW, WW half 10-45N-lOW, SWSW SWSW l6—45N—llW, l6-45N-llW, NE 27—45N-lOW, NENE 34—45N—llW, 10—46N—llW, NESE 25—46N—11W; NE corner corner 27-45N-lOW, NENE 34-45N-llW,SESE 10-46N-llW, NESE 25-46N-llW; Shale rrom from.near center of 34-47N-llW; Sandstone NE 3-45Nnear thethe center of 34—47N—llw; andand Sandstone fromfrom NE 3—45N— NWSWll-46N-lOW, ll—46N—lOW, W Whalf half 15—47N—1OW, lOW, SW SW 8—46N—lOW, 8-46N-lOW, NWSW l5-47N-lOW, SE SE19—47N—1OW. 19-47N-lOW. Waterwells do estimated 200 200 foot foot depth depth of of sandy sandy Waterwells donot not penetrate penetrate the estimated overburden in this area. overburden in this References Grant, Grant, U. U. S., S., 1901, 1901, Preliminary Preliminary Douglas County, Wisconsin: Douglas 6, 55 p. p. 6, 55 report on the the copper—bearing copper-bearing rocks of report Wisc. Wise. Geol. and and Nat. Nat. Hist. Hist. Surv. Surv. Bull. Bull. Holliday, it. W., Holliday, R. W., 1955, Investigation Investigation of of Chippewa Chippewa copper—nickel copper-nickel prospect prospect near Rockmont, Rockmont, Douglas County, County, Wisconsin: Wisconsin: U.S. Bur. Mines Rept. Rept. U.S. Bur. mv. 5114, Inv. 5114, 11 11 p. p. Irving, R. R. Do, D., 1883, 1883, Copper-bearing Copper—bearIng rocks Irving, rocks of Lake Superior: Superior: Mon. 5, 5, 464 464 p. p. Geo1. Survey Mon. Ceol. U. S. S. U. ,p Smith, N. H. C., 1947, 1947, Copper deposits of Douglas County, County, Wisconsin: U.S. Bur. 4088, 7 7 p. p. Bur. Mines MinesRept. Rept. Inv. mv. 4088, Sweet, F. E. T., 1880, Geology Geology of in T., 1880, of the the western western Lake LakeSuperior Superiordistrict district in Geology of Wisconsin 1873—1879: 1873-1879: Wisconsin Wisconsin Geol. Geol. Survey, Survey, v. v. 4, 4, p. 305-362. 305—362. �-50—50-REVISED KEWEENAWAN KEWEENAWAN SUBSURFACE SUBSURFACE STRATIGRAPHY STRATIGRAPHY SOUTHEASTERN MINNESOTA SOUTHEASTERN B. Morey B. Morey Minnesota Geological Survey Minnesota Geological Survey Minneapolis~ Minnesota Minnesota Minneapolis, G. G. ABSTRACT TheMid-continent Mid—continent Gravity High themajor majortectonic tectonicfeature feature of of the The Gravity High is isthe the Detailed geophysical northern mid-continent mid-continent region. region. Detailed geophysical surveys surveys over over the the 600 600 northern mile-long consists mainly mainly of ofa asequence sequence of babamile—longbelt belt show showthat that the the structure consists saltic lava blocks that are saltic lavaflows flowswhich whichform formsteep—sided steep-sided blocks are an an average average of about about 40 miles wide wide and and several several miles miles thick. Clastic rocks 40 miles rocks occur occur in flanking flanking babaBecause much much of of sins and in grabens grabens and the blocks. blocks. Because sins and andaxial axial basins basins on on top top of of the the structure isis covered rocks, little little is is known the covered by by Paleozoic Paleozoic rocks, knownabout about the the rocks rocks However, the the Paleozoic away outcrop area area around around Lake Lake Superior. Superior. However, awayfrom from their their outcrop cover is is relatively southeastern severaldrill drill holes cover relativelythin thinin in southeasternMinnesota, Minnesota, and and several holes Of particular particular have penetrated considerable thicknesses strata. Of have penetrated thicknesses ofofIceweenawan Keweenawan strata. rocks which whichflank flank and andoverlie overlie the interest here here are are the the sedimentary sedimentary rocks the St. Croix Croix an uplifted upliftedbasalt basaltblock blockin in southeasternMinnesota. Minnesota. horst, an southeastern Keweenawan sandstone shalehave havebeen beenknown known fromthe thesubsurface subsurfacefor for aa Keweenawan sandstone andand shale from Because ofoftheir red color, color,they theyhave havebeen been grouped grouped together together ununhundred years. Because hundred their red der the Red Red Clastic Series, Series, aa"temporary" IItemporaryllname name proposed proposed by der the byHall Hall and and others others in 1912. Mooney Mooney and Geophys. Res., Res., v. v. 75, 75,p.p. 5056-5086) have have 1912. andothers others (1970, (1970, J. J. Geophys. 5056—5086) subdivided number of and concluded concluded that sevsevsubdivided these these rocks rocks into aa number of seismic seismic units, and eral of already named of their theirsubdivisions subdivisionscould couldbebecorrelated correlatedwith with already named formations. formations. A detailed detailed petrographic petrographic study study of Ii,000 4,000 feet feet ofofdiamond diamond drill drillcore corefrom froma number a number thepresence presence leastthree threelithologically lithologically of localities localitieshas hasdemonstrated demonstrated the of of atatleast distinctintervals intervals whichmore—or-less more-or~less correspond correspond to seismic units. Therefore, distinct which to seismic it will be be recommended in prep.) it will recommended (Morey, (Morey, in prep.) that thatthe theterm termRed Red Clastic Clastic Series Series be be abandoned andreplaced replacedby by aa more moresuitable suitable nomenclature. nomenclature. Accordingly, Accordingly, three three abandoned and formations be recognized: recognized: (1) Hinckley Sandstone, Sandstone, a abuff tan rock rock conconformations will will be (1) Hinckley buff to to tan taining 95 (2) Fond du Lac Lac Formation, Formation, consisting consisting of 95 percent percent or or more more quartz. quartz. (2) Fond du intercalated intercalated moderate moderate red red shale shale and and sandstone sandstone containing containing 6o 60 percent percent quartz, 30 30 percent orthoclase, orthoclase, microcline microcline and and sodic sodic plagioclase, plagioclase, and 10 percent percent"granitic" "granitic" percent and 10 rock fragments. fragments. (3) (3) An An as as yet yet unnamed unnamed formation, consisting ofofdark darkreddish— reddishformation, consisting brown mudstone containing plagioclase brown mudstoneand andsandstone sandstone containingvariable variable amounts amountsofofquartz, quartz, plagioclase of intermediate intermediate composition, composition, and and aphanitic aphanitic igneous igneous rock rock fragments. fragments. The The first first two formations are known known from two formations are fromsurface surface exposures, exposures,however howeverthethethird third formation formation is confined sub—surface. confined entirely entirelytotothe the sub-surface. A stratigraphic stratigraphic analysis A analysis indicates indicates that that in in the the flanking flanking basins, basins, the the ununnamedformation formationisisoverlain overlain by by the du Lac LacFormation, Formation,which whichininturn turn is gradanamed the Fond Fond du gradationally tionallyoverlain overlainbybythe theHinckley HinckleySandstone. Sandstone. On the horst, horst,the theunnamed unnamed On top top of of the formation overlies formation overl ies basaltic basalticrocks rocksand and is locallyoverlain overlainbybyHinckley HinckleySandstone; Sandstone; is locally at places, places, aa regolith regolithasasmuch much as as 100 100 feet thick thickseparates separates the the two two formations. formations. Either the the Fond Fond du du Lac Lac Formation Formation was was wasnever neverdeposited depositedonontop topofof the the horst, ororwas removed prior to to Hinckley removed prior Hinckley deposition. Any attempttoto explain explain the the geologic geologic evolution evolution of of this structure Any attempt structuremust must take take thesestratigraphic stratigraphic relationships. into account account these relationships. �-51—51— LIMNOGEOLOGICAL STUDIES OF THUNDER THUNDER BAY, BAY, STUDIES OF LAKE LAKE SUPERIOR, ONTARIO ONTARIO J. S. Mothersil1 Mothersill S. LAKEHEAD UNIVERSITY LAICEHEAD ABSTRACT A B S T R ACT studies were carried carried out out in in Thunder Thunder Bay, Bay, Limnogeological studies Lake Superior during the the 1970 1970 field field season. season. Ponar grab samples and Ph1eger taken at one hundred and forty—seven forty-seven and Phleger cores were taken stations stations on a 1.5 mile grid for geochemical and mineralogical In addition three echo sounding traverses analyses. In three echo traverses were carried out using an an MS MS 26F 26F metric metric echo echo sounder. sounder. Thunder Bay which is partly silled to to the the south south by an an east—northeast trending horst from Victoria Island east-northeast Island to to Spar Spar Island basins. Recent sediments sediments which Island contains contains three separate basins. bay—floor grade from a thin cover the bay-floor thin veneer of of sand, sand, less less than than centimeters thick, thick, to clay—silts, up to 14 33 centimeters to aa sequence of clay-silts, meters thick, thick, in in the the central central parts parts of of the the basins. basins. Tight foldfoldclay-silts in in the the deepest deepest part part of of the the central central ing of the Recent clay—silts basin is probably caused caused by by gravity gravity slumping. slumping. Geochemical investigations the bottom-sediments investigations of of the bottom—sediments show that there appears to towards negative Eh and low pH values in the the to be be aa tendency tendency towards deep—water areas. deep-water areas. In the the vicinity of the Kaministikwia Delta anomalous Eh and pH measurements were recorded recorded which were were anomolous probably caused by industrial pollutants entering entering the the bay bay from from the the Kaministikwia River. River. overlie Pleistocene Pleistocene The Recent sediments unconformably overlie varved sediments of undetermined thickness. The Recent clay— thickness. claythe Pleistocene varved sect±on sectton each each form form aa silt section and the typical thin upper typical syndiagenetic sequence with a relatively thin oxidized zone (initial (initial stage) stage) and and aa lower lower reduced reduced zone zone (early (early burial stage). stage). The oxidized zone zone is is caused caused by by the the dissolved dissolved oxygen in the the trapped trapped waters of of the the upper upper layers layers of of sediment sediment and the the action of of aerobic aerobic bacteria. bacteria. The depletion of oxygen results results in the the underlying reducing reducing zone zone with anaerobic anaerobic and aa sharp sharp increase increase in in pH. pH. conditions and �—52— -52- REFERENCES Bissell, H. H. J., 1959, 1959, Silica in sediments of of the the Upper Upper Paleozoic of the the Cordilleran Cordilleran area. area. Spec. Publ. Spec. Pubi. of Soc. Soc. Econ. Econ. Paleontologists and of and Nineralogists, Mineralogists, 7, pp 150—185. 7, 150-185. Dapples, E. E. C., 1962, 1962, Stage of diagenesis in in the the developdevelopment of sandstones. sandstones. Bull, Bull, Ceol. Soc. Geol. Soc. Am., Am., 73, 73, pp 913—934. 913-934. pp Emery, Emery, K. K. 0. O. and and Rittenberg Rittenberg S. S. C., C., 1952, 1952, Early diagenesis of California Basin sediments in in relation to to origin of oil. Bull. Am. Am. Assoc. Assoc. Petrol. oil. Bull. Petrol. Geologists, Geologists, 36, 36, pp 735-806. pp 735—806. Larsen, C. Larsen, G. and and Chilingar Chilingar C. G. V., V., 1967, 1967, Introduction. Introduction. In In Diagenesis in in sediments. sediments. Univ. Univ. of of Southern Southern California, Los Angeles, Angeles, pp pp 1—17. 1-17. W. H., H., 1942, 1942, The rate of deposition of of sediments: sediments: Twenhofel, W. a major factor connected with aiteration alteration of Jour. Sedimentary sediments after deposition. deposition. Jour. 12, pp pp 99—110. 99-110. Petrology, 12, Changes produced by microC. E., E., 1942, 1942, Changes ZoBell, C. organisms in in sediments sediments after after deposition. deposition. Sedimentary Petrology, 12, 12, pp pp 127—136. 127-136. Jour. �—53— -53- REINVESTIGATIONOF OF "RED "RED ROCKS" REINVESTIGATION ROCKS" IN THE THE PIGIY)N POINT AREA, PIGEON AREA, MINNESOTA MINNESOTA C. M::drey, Jr., and and P. P. W. W. Weiblen Weiblen M. G. Mudrey, Jr., Minnesota Geological Survey Survey and University of Minnesota, Minneapolis ABSTRACT ABSTRACT Keweenawan granitic rocks rocks of reddish reddish color color as as exemplified exemplified by the "red rocks" rocks" of the the Pigeon Point, Cook Cook County, County, area area are are divisible into red quartzites, quartzites, porphyritic red red rocks rocks and and granular granular with this this division division reduces the problem red rocks. rocks. Retnapping Remapping with problem of of excess granophyre abundance associated with the the Pigeon Pigeon Point Point sill. sill. Reddish quartzites quartzites contain abundant recrystallized quartz Reddish quartz iicrstitial sericite—biotite feldspar— with minor minor interstitial sericite-biotite and granophyric feldsparquartz intergrowths. A faint foliation A faint foliationdefined defined by by biotite biotitelinea— lineation and tion quartzite inclusions inclusions and relict relict bedding bedding can be discerned in quartzite found in intermediate rock rock of dioritic dioritic composition. composition. Porphyritic red rock displays euhedral feldspar feldspar phenocrysts in a granophyric quartz—feldspar quartz-feldspar groundmass. groundmass. This rock type cuts Miaro— the Pigeon Point gabbro. Miarothe Rove formation and and intrudes the litic cavities are found filled with calcite and zeolite minerals. cavities zeolite Granular and feldspar feldspar Granular red rock contains granoblastic quartz and tic groundmass groundinassof of quartz quartz and and feldspar feldspar with with minor set in a granophy granophyric minor sericite-biotite and epidote. epidote. sericite—biotite and and rounded grains or sphene and Phase relations relations and overgrowths on quartz suggest suggest that that aa sedimentary parentage is is possible, possible, however intrusive intrusive relations relations on on Pigeon Point require that the granular red rocks rocks must must have have been been a crystal mush. Point area area in in excess excess The abundance of red rock in the Pigeon Point of that to be expected by differentiation has been noted since of that since 1893, the eastern eastern exposures exposures of of 1893, and is is part of a reinvestigation of the Keweenawan rocks rocks in in Minnesota. �—54— -54- THE SEDIMENTOLOGY AND TECTONIC SIGNIFICANCE THE SIGNIFICANCE OF OF THE THE BAYFIELD GROUP, GROUP ~ WISCONSIN HISCONSIN AND MINNESOTA MINNESOTA Wallace Darwin Darwin Myers, Myers~ II II University of Wisccnsin Wisconsin ABSTRACT ABSTRACT A study of the mineralogical and A and physical physical characteristics characteristics of of the the Bayfield Group was made to determine 1) 1) depositional depositional environment, environment, paleogeography, and source terrane paleogeography, terrane during during Bayfield Bayfield time, time, 2) 2) the the of the nature of the contact contact of ofthe theBayfield BayfieldGroup Group with with the the older olderOronto Oronto Group, Group, and and 3) 3) the early of the the Douglas Douglas fault. early history of fault. study included included detailed detailedmapping mapping of of Bayfield Bayfieldand andOronto Oronto Field study Group rocks outcrops, the lithology lithology Group rockstotoestablish establishthe thelocation locationofof all all outcrops, and stratigraphy of of all stratigraphic and stratigraphy all formations, formations, the the geographic geographic and and stratigraphic distribution distribution of of sedimentary structures and the the structural relationships relationships between rock rock bodies. bodies. Analyses of rock rock specimens specimens in in the the laboratory laboratory included 1) 1) petrographic study of the the bulk bulk mineralogy mineralogy and and textural textural characteristics of sandstone specimens, 2) 2) x—ray x-ray diffraction diffraction study study of of the the clay mineralogy of shale beds and and chemical chemical analyses analyses of of the the boron boron conconcentration of the clay mineral illite, 3) 3) x—radiography x-radiography study study of of the the sedimentary structures, structures~ and and 4) 4) internal stratification of selected sedimentary statistical study of directional sedimentary structures. structures. Petrographic studies of Bayfield Bayfield Group Group sandstones sandstones indicate indicate that that constitutes approximately approximately 80 80 percent percent of of framework framework grains, grains, that that quartz constitutes the feldspar population is dominated dominated by microcline, microcline, and and that that Bayfield Bayfield the feldspar Group sandstones sand·stones are are better better sorted sorted and and exhibit exhibit aa higher higher degree degree of of rounding than than the the Freda Freda Sandstone of the the Oronto Oronto Group. Group. The high compositional compositional and and textural textural maturity The high maturity of ofthe theBayfield BayfieldGroup Group suggests that that the suggests the source source area area for forthese thesesediments sediments was was not not aa simple simple volcanic terrane. Petrographic Petrographic data that the the Bayfield Bayfield and and volcanic data indicate indicate that Freda possibly recycling of of the the Freda Freda Freda sandstones sandstoneshad hada asimilar similar source; source; possibly Sandstone was an an important important source source of of sediments sediments during during Bayfield Bayfield time. time. The Tl~ sedimentary structures of the the Bayfield Group are those which are typically developed in fluvial are fluvial environments, environments~ including including trough trough cross— crossbedding, current ripple marks, sandstones, mudcracks, bedding, marks, channel sandstones, mudcracks, and associated structures. structures. The stratification and bed forms forms of the the Bayfield Group are Group are characteristic of those those formed formed in in the the upper upper part part of of the the lower— lowerwith modern alluvial (Harms and and Fahnestock, Fahnestock, 1965). 1965). By analogy ,.,ith alluvial flow regime (Harms channels channels the the general geologic setting of of the the Bayfield Bayfield Group Group can can be be inferred to to have been an alluvial plain plain characterized characterized by by loz—gradient, 100.,-gradient, perennial streams. streams. The strong N40°E N400E trend trend of of trough trough cross— crossmeandering, perennial bedding indicates was from the indicates the the direction of sedimentary transport transport was the southwest to the the northeast. This inference is is supported supported by the the orientation tion of parting lineation and and current current ripple ripple marks. marks. �—55— -55- the Bayfield and and Oronto Oronto Groups Groups is is not not exposed; exposed; The contact of the petrographic data provide~he provide the clearest evidence of the petrographic the nature of of this this boundary. On the the basis of the the high compositional compositional and and textural textural maturity maturity boundary. Group sandstones, exhibited by Bayfield Group sandstones, it it is is suggested suggested that that these these elastics represent represent a new cycle of sedimentation in clastics in the the synclinal synclinal Lake Lake This interpretation is supported by the contrasting Superior basin. basin. This supported the contrasting clay mineralogy mineralogy of the two sequences (illite— clay (illite- and and chlorite—rich chlorite-rich Oronto Oronto rocks, but kaolin—rich rocks, kaolin-rich Bayfield Bayfield rocks). rocks). compelling evidence evidence that:the that: the Douglas Douglas fault fault was was active active There is no compelling during Bayfield time. time. Conglomerates are are known known at at only nittytwo two exposures exposures of the Douglas Douglas fault, the fault, and in each case their their distribution distribution is is restricted restricted to to the zone immediately adjacent the adjacent to to the the fault. fault. Furthermore, Furthermore, the conglomconglomerates do do not not resemble true tectonic conglomerates either erates either texturally texturally or or compositionally. Additional evidence is provided by the the orientation orientation of directional sedimentary structures structures at at the the Douglas Douglas fault fault localities. localities. These structures which include include parting parting lineation and and cross-bedding, cross—bedding, show show structures which no apparent relation to the Douglas fault. to the fault. Thus, Thus, there is no geologic evidence of major faulting faulting during during Bayfield, Bayfield, or or at at least least Orienta, Orienta, time. time. �—f LAKE LAKE MICHIGAN MICHIGAN AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY by W. O'Hara Norbert W. Great Lakes Research Division University of Michigan Arbor, Mi Michigan Ann Arbor, chigan William J. J. Hinze Hinze Department of Geology Michigan State University East Lansing, Lansing, Michigan Michigan E;t ABSTRACT A B S T R ACT The Precambrian Precambrian basement basement complex complex beneath beneath Lake Lake Michigan, Michigan, which which lies lies on the western western and and northern northern flank flankofofthe thePaleozoic PaleozoicMichig.E.n Michigan Basin, Basin, is is only known from a few widely scattered basement drill holes around the scattered drill holes around the perimeter of of the Lake and and aa single single drill drill hole hole -ithin within the Lake Lake on on 3eaver Beaver Nevertheless, the basement geologyof of Lake LakeMichigan MichiganisissignifisignifiIsland. Nevertheless, basement geology cant frameworkofofthe theMidcontinent Midcontinentandand critical to cant to the the Precambrian Precambrian framework is iscritical to the extrapolation extrapolation of ofbasement basement structural structural trends trendsfrom from Lake Lake Superior, Superior, orth— Northinto the fill this ern Michigan, and Wisconsin into theMichigan Michigan Basin. Basin. To To fill thisgap gap an an em Michigan, and aeromagneticsurvey surveyconsisting consistingof of 7,000 7,000 miles miles of of total aeromagnetic total magnetic magnetic intensity were collected along flight traverses separated data were separated by by six six mile mile intervals. intervals. traverses were were flown flown over over northern northern Lake Lake Michigan in aa general northFlight traverses east direction and over southern Lake Lake Michigan in in aa northwest northwest direction. direction. The residual total magnetic intensity map map prepared from from the the collected To general the magnetic data exhibits three regional regional magnetic magnetic positives. positives. In anomalies are related in in aa direct direct manner manner to to gravity gravity anomalies anomalies on on the the periperimeter of the Lake. Lake. The strikes northwest northwest from from the the The southernmost southernmost positive postive :rikes Michigan shore from from +2° 42 0 to 13° 43 0 30'N. 30'N. This anomaly is associated with aa positive and and local local magnetic magnetic positives positives extend— extendsoutheast striking gravity positive icLg across southwestern southwestern Michigan Michigan and northeastern ing across northeastern Indiana Indiana into into Ohio. Ohio. It It is gravity and and magnetic magnetic anomaly anomaly in in northeastern northeastern is on strike with the positive gravity Indiana which has been found found by basement basement drilling drilling to to be be underlain underlain by by basalts basalts similar to Keweenawan flows flows of of the Lake Lake Superior Superior region. region. The central central regional positive, which is made up of several individual anomalies, roughly easteast— anomalies, strikes strikes roughly 450 0 0 t140 The northern components west across ·the Lake between 44 and 45 15'N. The northern components of the l5'N. this anomaly can be traced into into Wisconsin and and across across the southern southern Peninsula Peninsula this of Lchigan except where they are transected by the Mid—Michigan rift Michigan except where they are transected by the Mid-Michigan rift zone. zone. trends are believed to be assrciated with the the Penokean basement basement provprovThese trends associated with ince. A A marked regional magnetic anomaly minimum striking east-west east—west occurs occurs to the north of the regional regional positive. positive. The anomaly is on on strike strike with the the felsic felsic rocks of the Mountain—Amberg Mountain-Amberg area area of of Wisconsin Wisconsin which which is is also also charcharacterized by magnetic magnetic minimums. minimums. The minimum reappears reappears east east of of the the Mid—Michi— Mid-Michigan rift rift zone anomaly and and strikes strikes east—southeast east-southeast across across to to Lake Lake Huron. Huron. The The northern regional positive magnetic anomaly anomaly strikes strikes north—south north-south from from Traverse Traverse where it it bifurcates bifurcates with with one one limb limb extending extending Bay to north of Beaver Island where north—northwest through Lake north-northwest Lake Superior Superiortotothethe Keweenawanbaa basalts Keweenaw Keweenawan alts ononKeweenaw Point. The other limb the eastern eastern portion of of the the Northern Northern Point. limb continues continues into the Peninsula of Michigan and another another segment segment of of this this branch branch connects connects to to the the Keweenawan flows on Mamainse Point. flows on Mamainse Point. In the the Traverse Bay area the regional connects to the positive becomes becomes strongly negative and connects the south with the the midmid— Michigan gravity and and magnetic magnetic anomaly. anomaly. �-57—57— GEOCHRONOLOGY OF THE GIANTS RANGE GRANITE L. A. PRINCE FRECE AND L. A. AND G. G. N. N. HANSON HANSON State University of New York Stony Brook, N. N. Y. Y. 11790 ABSTRACT A B S T R ACT Seven whole rock samples of two—mica, two-mica, foliated foliated quartz ~uartz monzonites monzonites from the central part of the Giants Range Granite, Granite, north of Hibbing, Hibbing, Minnesota, give aa Rb—Sr Rb-Sr isochron isochron age age of of 2670 2670 1) and a 3r87/Sr86 ± 65 m.y. (Rb (Rb 87 x 10yr _1) Sr 87 /Sr 86 initial initial 87 AS A == 1.39 x i0'11 yr ratio ratio of 0.7002 ± 0.0019 0.0019 at at the 95% confidence level. level. Epidote, plagioclase, potassium feldspar, biotite—chiorite, apatite plagioclase, feldspar, biotite-chlorite, apatite and and muscovite separates from one of these whole rock samples give muscovite separates samples give mineral —whole rock ages ranging from 2350 m.y. for epidote -whole ages ranging from 2350 m.y. for epidotetoto26140 2640 m.y. m.y. for muscovite. mineral—whole rock ages muscovite. The lowered mineral-whole ages suggest suggest that at least least one event event occurred after intrusion of the granite, at granite, but that that the individual mineral phases the phases were not completely homogenized homogenized with Sr 87 /Sr 86 ratios. ratios. The 2350 m.y. epidote-rock respect to their 5r87/5r86 m.y. epidote—rock age age probably is is a maximum for the time of the last last event. event. The mineral data provide no conclusive evidence for for the sequence se~uence of of events after intrus on, but are not inconsistent events intrusion, inconsistent with aa regional regional low-grade low—grade metamorphism at around 1600 m.y. This is in agreement with U—Pb U-Pb data data on on sphene sphene This whole rock age is Giants Range Granite which suggest suggest an an age age of of and zircon from the Giants 2700 for hornblende from from the the Giants Giants 2100 m.y. n.y. and also with K-Ar K—Ar ages for Range Granite which generally generally are are 2600—2100 2600-2700 m.y. m.y. These ages ages however are older than most of the Rb—Sr Rb-Sr and and K—Ar K-Ar ages ages for for biotite biotite however are which range from 2260—2630 2280-2630 m.y. m.y. The age of the post-kinematic post—kinematic Linden Linden Syenite Syenite just just to to the the north north also also limits limits the the age ae of the syn— syn?b207_Pb2u6 data on sphene to late—kinematic late-kinematic Giants Giants Range Range Granite. Granite. Pb207_Pb206 sphene and aa Rb-Sr b—Sr mineral—whole mineral-whole rock rock isochron isochron with with an an initial initial ratio ratio of 0.7009£-0.0004 suggest an age for the Linden Syenite Syenite of of about about 0.1009±O.000b 2700 m.y. 2100 m.y. 87 /Sr 86 initial The low Sr initial ratios from from both the the Linden Linden Syenite Syenite Sr87/5r86 and the the Giants Giants Range Granite suggest suggest aa source source with aa low low Rb/Sr Rb/Sr and ratio, perhaps mantle, and and it is is unlikely that appreciable appreciable ratio, perhaps the mantle, mixing with preexisting continental crust crust took place. place. �—58— -58- THE GREAT GREAT LOGAN PALEOHAGNETIC PALEOMAGNETIC LOOP —- THE POLAR THE WANDERING PATH FROM FRaN CANADIAN SHIELD ROCKS ROCKS DURING DURING THE THE HELIKIAN HELIKIAN ERA ERA by W. A. W. A. Robertson }{obertson Geomagnetic Laboratory Energy,Mines Energy,I'Iines & & Resources Resources Ottawa, Ottawa, Ontario w. F. Fahrig H. Geological Survey of Canada Ottawa, Ontario Ottavla, ABSTRACT ABSTRACT Normally magnetized dykes dykes and reversely reversely magnetized sills sills of of Neohelikian age age near the the north west take Superior Superior form form west shore of Lake two distinct distinct paleomagnetic groups groups with mean pole positions of two 179W, 35N, 179\\1, 35N, and 140W, 47N 47i'J respectively. respectively. Thermal and and alternating alternating field field paleomagnetic studies studies and and the study of magnetic properties and opaque opaque minerals minerals indicate that and that directions directions of magnetization of of these rocks were acquired at at the the time time of of their their intrusion. intrusion. Field these rocks evidence indicates indicates that evidence that the the reversely magnetized sills are older than the normally magnetized magnetized dykes than the normally dykes and radiogenic age determinations indicate intrusion between 1000 1000 and and 1100 1100 m.y. m.y. ago. ago. These pole pole positions, positions, together with those for the These the Franklin Franklin intrusions pole pole at at l67E-08N, 167E—08N, assigned age 675 m.y., the intrusions 675 m.y., the Abitibi dykes, the NacKenzie MacKenzie dykes, at at 134W. 134W, 27N, 27N, assigned aged 1150 m.y. m.y. and the Igneous events, at Igneous at 171W, l71W, 4N, 4N, assigned assigned age age 1200 1200 iu.y. m.y. are are used used to to define Logan's Loop, the pole pole took took in in Neohelikian Neohelikian define Loop, the the path path that. that the time to the Canadian Shield. Shield. Other poles well defined defined time relative to magnetically, but less well dated, magnetically, dated, from from rocks rocks of of this this era era fit fit the curve quite well. the of available that the available data data supports supports the the hypothesis hypothesis that the Analysis of relative polarmovement movement that gave rise Logan's Loop Loop was was prerelative polar that gave rise totoLogan's preceded and followed follmved by vis a vis ceded and by polar stability vis vis North America, quite rapid rapid during during the the forforwhereas polar movement may have been quite The depositional environment of Neohelikian the loop. loop. The Neohelikian mation of the rocks of the Canadian Shield should be tested tested against against their their rocks of the probable paleolatitude as probable as indicated by the the 5 key points on Logan's Logan's Loop. �—59— -59- CHARACTERISTICS CHARACTERISTICS OF SOME SOME ALTERATION MINERALS, MINERALS, PORTAGE FJRTAGE LAKE LAKE LAVA LAVA SERIES, SERIES, MICHIGAN MICHIGAN A. A. P. p.RUOTSALA RUOTSALA Michigan Technological University Michigan Technological ABSTRACT Many silicate, carbonate, Many silicate, carbonate, and and oxide oxide minerals minerals are are associated associatedwith with copper mineralization mineralization in the Portage Series and copper in the Portage Lake Lake Lava Lava Series and associated associated conglomerates. complete listing listing was was published published by Butler and and Burbank'. Burbank l • conglomerates. AA complete Amygdule studied by Amygdulezoning zoningpatterns patterns associated associated with with mineralization mineralization were studied 2 Stoiber and and x-ray x-ray diffraction Stoiber and Davidson Davidson .. Chemical and diffraction studies studies are are being being carried out out at atMichigan Michigan Technological Technological University on on a continuing continuing basis. carried basis. In the the past -'n, In past some some of of these these studies studies were weresupported supportedby bythe theCalurnet Calumet Divisi Divisi:::n, Universal Universal Oil Oil Products Products Company. Company. Epidote isis characterized characterized by Epidote by wide wide ranges ranges in in unit unit cell cell dimensions. dimensions. In general, general, epidotes epidotes from from amygdaloids amygdaloids have have larger larger unit unit cell cellvolumes volumes than than those those from conglomerates. congloITlerates. Calcites wide ranges ranges inin trace trace element composition, especially especiaiy Calcites show show wide eleITlent cOlnposition, in Mg, and and Mn. Mn. There is a a positive positive correlation correlation bebeThere is in concentration3 concentratiois of Fe, Fe, Mg, tween Mncontent contentand andcopper copperITlineralization mineralizationininthe theKearsarge Kearsargeamygdaloid, amygaloid, and tween Mn and therefore is potentially potentially useful useful as as an an exploration exploration tool therefore is tool in in the the district. district. 3 in many ITlany forms and at virtually every every stage sh.ge of of the the Chlorite occurs in forms and sequence in alteration sequence in the the district. district. An An interesting interesting occurrence occurrence is is as an essentially pure essentially pure clay clay mineral ITlineral in inthe the fault faultgouge gouge in in the the Allouez Allouez Gap Gap Fault Fault This is and of the the Kingston Kingston Mine4. Mine~. This is one one of of the the few, few, if if not not and hanging hanging wall wall slip of the the only only occurrence occurrence of of pure pure clay clay chlorite chloriteknown, known. It essentially of of It consists consists essentially In ITluch much of ofthe thehanging hangingwall wallslip, slip, chlorite chlorite is is intimately the type Ub lIb polytype5. polytype 5 . In intiITlately absorption properties (plastic and and liquid liquid mixed with hematite. The The water water absorption properties (plastic liITlits) greaterfor for chlorite-hematite chlorite-heITlatite mixtures mixtures than than for for pure pure chlorites, chlorites, limits) are; are greater suggesting the the pas possibility of SOITle some ITlixed mixed layering layering of of chlorite chlorite and suggesting sibility of and hematite. heITlatite. References Cited Cited 1. Butler, Butler, B. B. S., S.,and andW. W.S.S.Burbank Burbank(1929) (1929) The The copper copper deposits deposits of of U. S. Geol. Geol. Surve., Surve., Prof. Prof. Paper Paper144, 144, 238 238 pp. pp. Michigan. U.S. 2. Stoiber, R. E. E.and andE.E.S.S.Davidson Davidson(1959) (1959)Amygdule AITlygdule mineral mineral zoning zoning in Stoiber, R. the Portage the Port age Lake Lake Lava Lava Series, Series, Michigan. Michigan. Econ. Econ. Geo!. v. 54, Geo. v. 1444-1460, p. 1250-1277 and p. 1444-1460. p. 1250-1277 �-60—60— 3. Ruotsala, P., S. S.C. C.Nordeng, Nordeng,and andR. R. 3.J.Weege Weege(1968) (1968) Trace Ruotsala, A. A. P., Trace elements the elements in in accessory accessory calcite -- aa potential exploration tool in the Michigan Copper District. District. Cob. of Mines MinesQuart., Quart., Jour., Jour., Michigan Copper Colo. School School of (International Geochemical Exploration v. 64, 64, p. p. 451-455. 451-455. (International v. Symposium) 4. Ruotsala, Ruotsala, A. A. P. P. (1968) (1968) Clay Clay alteration alteration associated associated with with mineralization mineralization Clays and and Clay ClayMin., Mm., v. in Michigan Copper v. 16, 16, in the Michigan Copper District. District. Clays p. 400-402. p. 400-402. 5. Brown, B. Brown, B. E.,, E., and and S. S. W. W. Bailey Bailey(1962) (1962) Chlorite Chlorite polytypism. polytypism. Am. ,v. 47, Am. Mineral. Mineral.,v. 47, p. p. 819-850. 819-850. �—61— -61- THE THE GENERAL GENERAL STRATIGRAPHY STRATIGRAPHY OF OF THUNDER THUNDER BAY, BAY, LAKE LAKE SUPERIOR SUPERIOR R. J. J. Shegelski LAKE-lEAD UNIVERSITY LAKEHEAD ABSTRACT A B S T R ACT Petrographic studies of the sediments taken from from Thunder Bay Bay combined with x-ray diffractometer analysis have indicated indicated distinct lithologic types in the the bottom sediments sediments of of Thunder Thunder Bay. Bay. Stratitypes in graphic correlation correlation of of thc the bottom bottom sediments sediments from from Thunder Thunder Bay Bay has has the aid aid of of echo echo sounding sounding traces. traces. These traces been developed with the boundaries, nature and thickness indicate the boundaries, thickness of the various litholithofacies. facies. The sediments in in Thunder Thunder Bay Bay can can be be divided divided into into five five categories; categories; (1) (2) Weathered Weathered Varved Clay, (1) Varved Clay, Clay, (2) Clay, (3) (3) Intermediate Intermediate Clay, Clay, (4) Upper Upper Deltaic Sediment, Sediment, (5) Sediment. The Varved (4) (5) Upper Upper Trough Sediment. Clay is overlain is of Post Post Valders Valders glacial glacial origin origin and and is is disconformably discoi:fom*Lj overlain by the Weathered and Intermediate Intermediate Clays. Clays. The latter are are products products of weathering of of the the older older Varved Varved Clay. Clay. The Intermediate Clay is conformably overlain overlain by by Upper Upper Deltaic Deltaic and and Upper Upper Trough Trough Sediment. Sediment • conformably The .T he latter units are sediments sediments derived derived dominantly dominantly from from the the Kaministikwia Kaministikwia River. River. Thin Thin iron iron and and manganese manganese beds beds are are formed formed through through diagenetic diagenetic solution, upward migration, migration, and precipitation at solution, at a chemical chemical interface interface in the Upper Sediments. Sediments. �—62— -62- CHERT IN SEDIMENTS SEDIMENTS by G. G. Spencer Spencer Duluth, Minnesota A B S T R ACT ABSTRACT silica solution solution becomes becomes supersuperAmorphous silica is produced when aa silica some silicates silicates are are dissolved dissolved saturated and a precipitate forms or when some in acids. In the silica is is in a colloidal form and remains remains In either case case the so for long periods of of time. time. Eventually crystallization begins, begins, and heating the substance can speed up the the process to to aa great great extent. extent. In In natural conditions conditions opal opal is is the the first first step step followed followed by by chalcedony chalcedony and and finally cristobalite. All of these finally these forms forms of silica silica have have been been termed termed chert. Chert has·long has long been regarded as a chemical precipitate. Chert precipitate. This is sufficient to to explain explain hot hot spring spring deposits deposits and and hydrothermally hydrothermally view is deposited chert or opal opal near near the the surface. surface. Cooling volcanic waters become supersaturated with silica silica in in solution solution and and amorphous amorphous is is deposited deposited as as a sinter or in in thin thin layers. layers. There are, are, however, many other other environments environments in in which which chert chert is is found found such as: as: a) a) b) c) c) d) d) e) e) f) f) g) black slate with chert lenses or beds limestones limestones with chert nodules or joint joint fillings fillings bedded cherts containing sponge spicules cherts spicules or Radiolaria Radiolaria chert stringers in oxidized sulphides sulphides chert stringers and crusts in fillings of vesicles in in lava lava flows flows agate fillings oxide granules chert chert as as a a matrix for iron oxide opal or chert chert replacing organic matter The author author ascribes chert to to the the decomposition decomposition of of clays, clays, detrital detrital In acid environsilicates, ash or sand grains in in carbonates. carbonates. In silicates, volcanic ash ments alumina alumina and and alkalies alkalies are are removed removed and and aa silica silica gel gel is is left. left. In alkaline waters waters silica is dissolved and and is deposited deposited in in aa more more neutral neutral zone or will replace a dissolving particle such such as as organic organic matter. matter. The relative solubility solubility of of alumina and alkalies compared to relative and alkalies to silica is is the the determining factor. factor. iturata (1946) investigated investigated many many silicates silicates ,vhich which produced gels when i'lurata (1946) \<Then treated with acid. He alumina ratio ratio of 1:1 or or treated with Hefound foundthat that aa silica silica totoalumina 2:3 was Other silicates silicates prpduced was conmion common toto gel forming silicates. Other produced silica gel forming particles larger than than colloidal size or were not not affected affected by by acids. acids. Any particles silicate structure from from which alumina has has been been removed removed is is halfway halfway along along to chert. to becoming chert. In and silicate iron formations formations mixed with ,.,rith quartz, quartz, minerals In carbonate carbonate and become unstable when when the the temperature temperature is is raised raised and is removed from from the the and CO, CO. is point sediment. The ionization ionization of at whicli ,..d lich Doint of \vater water increases increases up up to to 230° 23°CC at silica both in in quartz and silicates becomes hecomes increasingly incren3in~ly soluble. soluble. Sand grains such as as grains in oolites oolites might might dissolve and secondary silicates such �-63—63— minnesotaite and and stilpnonielone stilpnomelone would appear. appear. Chert in this this case case is is minnesotaite clearly clastics clearly diagenetic diagenetic and and came came from from aa breakdown of original elastics even if the the original texture texture remained remained the the same. same. formations would appear to to be be examples examples of of late late Precambrian iron formations they would also contain contain early early diagenetic diagenetic silica silica diagenetic chert although they as well. as Silica content is these rocks because Silica and and iron iron oxide content is higher in these of the the loss loss of carbon dioxide, dioxide, water, water, and small small amounts amounts of of alkalies alkalies in in solution. �—64— -64- IMPLICATIONS OF CARBON ISOTOPE RATIO VARIATIONS IN IN CARBONATES CARBONATES FROM THE BIWABIK BIWABIK IRON FORMATION, FORMATION, MINNESOTA F. C. C. Tan and E. F. E. C. C. Perry, Jr. Jr. Minnesota Geological Survey Survey University of Minnesota Minneapolis, Minnesota 55455 Minneapolis, 55455 ABSTRACT A B S T R ACT Carbon isotope ratios from carbonates of of the the Biwabik Biwabik Iron—formation Iron-formation obtained from core samples of Mesabi Deep Drilling Drilling Project Project (Pfleider (Pfleider and and others, 1968) 1968) show the following significant features. others, features. 13 (1) SC SC13 values values of of carbonates carbonates associated associated with with magnetite magnetite from holes holes (1) 5 and 7 show a range of from —7 -7 to to —19 -19 per nil mil (relative (relative to to aa Cretaceous Cretaceous belemnite standard standard calcite calcite PDB) PDB) in in comparison comparison with with1he he carbonates carbonates from from is strongly correlated the magnetite-free (0 to SC 13 is the magnetite—free horizons horizons (0 to -7 —7 per per mil). mu). with magnetite magnetite content content in in hole hole 7. 7. 13 (2) The Gc SC13 values values of of carbonates carbonates from magnetite and non—magnetite (2) The non-magnetite horizons of hole 2 with one exception, do not show1ignificant horizons of hole 2 with one exception, do not show1~ignificant difference difference range of from in contrast with holes holes 55 and and 7. 7. They exhibit a SC from —7 -7 to to —19 per -19 per mU.. mil. 13 (3) values do do not not show show any any significant significant stratigraphic stratigraphic (3) The The bC C13 values correlation correlation with with tlia the percent iron. iron. (4) between (4) There There appears appears to to be be a correlation between individual members of of the the Biwabik Biwabik Iron—formation. Iron-formation. 13 C1-3 values and the ~C the 13 In explaining the observed correlation between magnetite and and the the 13 values based on our SC our preliminary preliminary results, results, we we proposed proposed (Perry (Perry and Tan, 1970) that that aa diagenetic diagenetic oxidation—reduction oxidation-reduction reaction reaction producing producing permitted exchange exchange between between organic organic carbon carbon and and magnetite from hematite permitted carbonate carbon reservoirs: reservoirs: r 44FeO bFeO +CO 6 Fe 22033 +C + C(organic)~f----~~Fe 33044 + CO 22 (organic) (1) (1) 12 13 C1202 Fec 0 C 0 + FeC3O3 2 3 (2) (2) < 12 13 cC1-3O 0 + + FeC2O3 Fec 0 2 3 recent detailed detailed studies studies have have strengthenI~ strengthen our Our recent our previous previous observaobservavalues (—18 tion on hole 7 but have found anomalously low SC (-18 per per nil) mil) tion from from the the non-magnetite non—magnetite horizons of hole 22 (Lower (Lower Slaty Slaty Unit). Unit). These anomalous values may be related related to to metamorphic metamorphic reactions reactions accompanying accompanying the intrusion of the the the Duluth Complex because hole 22 is is located located near near metamorphic zone zone (1) (1) of French French (1968). (1968). C13 values Our observation that that there is a correlation between ~el3 and the and the individual members of the Biwabik Iron—formation Iron-formation would suggest suggest l3 variations that SC1-3 variations are are depositional depositional or or early early diagenetic diagenetic features features that the the ee and bear no relationship relationship :o ~o the the genesis genesis of of niagnetite magnetite (model (model above). above). The �-65—65— l3 values may be explained by the differences in IC13 bC the variable variable contributions contributions of organic carbon and oceanic bicarbonate to of to the the depositional depositional or or diagenetic environments. environments. 13 SC13 values of We are currently investigating the theoC of co—existing co-existing graphite-tarbonate pairs and oxygen isotope fractionation graphite-carbonate fractionation between between cocoquartz—magnetfte at various stratigraphic existing quartz-magnetite stratigraphic levels levels of of holes holes 22 and 7 to to see if they have different diagenetic diagenetic or metamorphic metamorphic histories. histories. Co—existing quartz—carbonate oxygen isotope Co-existing quartz-carbonate isotope fractionation fractionation In in samples samples from hole 2 compared to that that in in holes 55 and and 77 suggests suggests that that the the post— postdepositional history of these these two two areas areas is is indeed indeed different. different. References rrench, B. B. French, M. , (1968) Progressive contact metamorphism of the M., the Biwabik Biwabik Iron—formation, Mesabi Mesabi Range, Ninnesc:a, Minn. Minn. Geol. Iron-formation, Range, Minnesota, Geol. Surv. Surv. Bull. Bull. 45, 45, Univ. Univ. of Minn., Minneapolis. Ninneapolis. Tan, F. Perry, E. E. C.C., Jr., and Tan, F. C., C., Significance of carbon carbon isotope isotope Perry, , Jr., variations in carbonates from from the the Biwabik Biwabik Iron—formation, Iron-formation, Minnesota. Minnesota. symposiumononthe thegeology geology and and genesis genesis of International symposium of Precambrian Precambrian iron/manganeseformation formationand andore oredeposits, deposits, Kiev, Kiev, 1970 1970 (In (In Press). iron/manganese Pfleider, E. E. P., P.,Morey, Morey, C. G. B., B., and and Bleifuss, Bleifuss, F. R. L. L. (1968) Mesabi deep deep drilling project, project, progress report repo~t no. no. 1, 1, Minnesota Ninnesota section, section,AIME AIME forty— fortymeeting, Dniv. Univ. of Ninn., Minn., Minneapolis. Minneapolis. first first annual meeting, �—66— -66- Oxygen isotopic studies of Early Early Precambrian Precambrian granitic granitic and and metamorphic rocks from from the the western western part part of of the the Giants Range batholith, Northeastern Northeastern Minnesota Minnesota S. Viswanathan, Viswanathan, E.C. s. E.C. Perry, Jr., Jr., and and P.K. P.K. Sims, Sims, Minnesota Geological Survey, University of Minnesota, Geological Survey, University of Minnesota, Minneapolis, Minnesota 55455 55455 ABSTRACT A B S T R ACT objectives: (1) demonstrate that that oxygen oxygen The paper has two main objectives: (1) to to demonstrate isotope geochemistry is a valuable tool tool in in elucidating elucidating granite granite petrogenesis, petrogenesis, provided it is is integrated integrated with with detailed detailed field field and and laboratory laboratory studies, studies, and and (2) to to give give values values for~(018/016)guartz for f(O18/016)qrtz in (2) in the the Early Early Precambrian Precambrian granitic granitic and metamorphic metamorphic rocks, which are rather scarce and rocks, data for wnich scarce in in the the literature. literature. Geologic mapping of of aa 500—square 500-square mile mile area area in in the the western western part part of of the the 2.1 b.y. b.y. old Early Precambrian Giants Range batholith of 2.7 of northeastern northeastern Minnesota has revealed eleven eleven distinct distinct granitic granitic phases phases (Sims (Sims and and others, others, 1970). 1970). Field observations, petrography, petrochemistry, petrochemistry, and and trace trace element element geochemistry suggest that that five five of of the the phases phases are are magmatic, magmatic, four four are are metasomatic, metasomatic,_ and two are anatectic. anatectic. r 18 16 The ~O 10 ratios of quartz separated from from 28 28 rocks, relative relative to to meIo'8/o'6 Standard Mean Ocean are presented presented in in the the accompanying table. Ocean Water Water (SNOW), (SMOW)Jare table. The values are consistent with the the postulated postulated genetic genetic grouping grouping for for the the Early Precambrian granitic succession. succession. The following following conclusions conclusions can can be be drawn from the the data: data: (1) Values of of 9 to to 10 permil are characteristic of relatively (1) Values relatively uncontaminated, probable mantle—derived uncontaminated, mantle-derived granites granites and and granodiorites. granodic~ites. These tharhave been reported for are consistent with the the S(O18/ol6quartz ~(018/016)quartz values values that-have granites, granodiorites, granodiorites, and and tonalites, tonalites, which which range range from from about about plutonic granites, 9 to to about 11 permil (Taylor, (Taylor, 1968, 1968, p.34). p.34). (2) several special special (2) Values Values greater greater than 10 permil require one of several explanations, such such as: as: 18 (a) syntexis of large amounts amounts of of 0018—rich -rich country rocks rocks (a) into a primitive or first—cycle first-cycle granitic granitic magma magma 18 18 (b) co-mingling co—mingling of an 0 -enriched —enriched magma and a primitive (b) or first first cycle granitic magma 18 (c) of 0018_ sediments (c) anatexis of —rich rich sediments �—67— -67- 18 (d) potash metasomatisin metasomatism of of aO'8—rich -rich sediments sediments (d) potash (e) recrystallization (treptomorphisin) (treptomorphism) of of (e) simple recrystallization relatively 018_ 018—rich clastic sediments such such as r ich elastic arkoses and graywackes, which thereby thereby assume assume aa granitic fabric and composition (f) recrystallization recrystallization of of granites granites under under shearing and (f) aplogranites, accompanied by crushing to produce aplogranites, late—tectonic metasomatism in mobile zones late-tectonic (g) post-consolidation post—consolidation eataclasis, cataclasis, and and other other (g) episodes which which facilitate facilitate exchange exchange metamorphic episodes origin and granitic rocks rocks of of magmatic magmatic origin and between granitic between through a pore—fluid pore-fluid medium medium 018_ O'8—rich r ich country rocks through (h) post-consolidation (h) post—consolidation endoblastesis/autometamorphism endoblastesis/autometatOrphism involving 018018—enriched enr iched fluids (i) processes such as imbibition (i) as petroblastesis and imbibition in which the the participants are are O'8—rich 018_r ich sediments sediments and 018-enriched fluids 018—enriched fluids (j) selective (j) selective exchange between granitic intrusions and 018_ host rocks rocks O'8—rich r ich host (k) tectonic tectonic styles styles of of emplacement, emplacement, whether whether synkineinatic, synkinematic, (k) post-kinematic or late—kinematic, late-kinematic, and and post—kinematic 18 (1) early segregation of aO'8—depleted -depleted minerals which (1) in O'8—enrichment 018- enr ichment in in late late granitic granitic differentiates. differentiates. results in (3) in granitic rocks of anatectic origin origin are nearly nearly (3) The The values values observed in identical to to those those of of their their source source rocks. rocks. They are either low or high such granitic granitic rocks rocks were were formed formed from from O'8—poor 018_poor or or depending on whether such OIS_rich 018_r ich sources, respectively. respectively. The values will be grossly grossly different different only only if: if: (i) the the anatectic anatectic melt melt undergoes undergoes subsequent differentiation, differentiation, and (ii) (i) (ii) the the consolidated anatectic melt is subjected to to later later metasomatism metasomatism (see (see data data under "C" "e" and "0 (2)", of of table). table). "D (2)", (4) The main main intrusive phases of (4) The of granites granites and and granodiorites granodiorites of of maginatic magmatic origin have values nearly identical to those of their satellitic phases identical to those of their satellitic phases (sve (sve data under "A" "A" of of table). table). Interestingly, Interestingly, a value of 9.2 9.2 permil permil was obtained for for a leucogranite (satellitic (satellitic late—magmatic late-magmatic differentiate) differentiate) that that transgresses an 018—rich Ol8_r ich metasedimentary host host rock rock having having aa value value of of 12.4 12.4 transgresses perinil. permi!. This result indicates that there indicates that there was was hardly hardly any any oxygen oxygen communication differentiate and and its its alB-rich o8—rich late-magmatic differentiate between the satellitic late—maginatic metasedimentary metasedimentary host host rock. rock. This is is in in sharp sharp contrast contrast to to the the conclusion conclusion of of Shieh and Taylor (1969, (1969, p.353) p.353) who report report that: that: "Samples "Samples from from tiny tiny intrusive intrusive bodies and dikes and from the marginal portions portions of of most most of of the larger plutons 18 /0 16 ratios igneous rocks have unusually high 0 018/016 ratios relative to "normal" "normal" igneous rocks from from �—68— -68- the central portions of plutons. This is interpreted interpreted to to be the the result result of large-scale large—scale oxygen isotopic essentially molten of isotopic exchange exchange between between essentially molten igneous igneous rock and metasedimentary country country rock, rock, either either through through aa medium medium of of aqueous aqueous 1I fluids or or by by contamination contamination with with xenolithic xenolithic blocks blocks of of country country rock. rock." fluids (5) The The sequence: sedimentary (5) sedimentary parent parent ——)' -~ partially partially granitized sediment --~granitic —>-granitic rock progressive sediment rock of of metasomatic metasomatic origin origin reflects a progressive decrease in the 018/016 0 18 /0 16 ratio, and and encompasses encompasses only only aa narrow narrow range range of of 11 to 2 permil, and (6) Global comparisons of oxygen isotopic isotopic ratios ratios from from granitized granitized 18 /0 16 ratios of the sequences should not not be attempted, attempted, unless: unless: Ci) sequences (i) the 0018/016 parent rocks of two widely separated separated granitized granitized sequences sequences are are comparable, comparable, and (ii) their geological settings are nearly identical. (ii) are nearly identical. 18 16 Problems involving a possible time—dependence time-dependence of of the the 018/0 0 /0 16 ratios in in minerals from from specific specific rock—series, rock-series, representing representing the the entire entire geological geological column, column, are under study by one one of of us us (Per;y). (PerJY). Ref e—ences cited References Shieh, Y.N. Y.N. and H.P. Taylor, Shieh, Taylor, Jr. Jr. (1969): Oxygen and hydrogen isotope isotope studies studies in the the Santa Santa Rosa Rosa Range, Range, Nevada Nevada and and other other areas: areas: of contact metamorphism metamorphism in Contr. Mineral. and Petrol., v.20, p.306—356. Contr. Mineral. p.306-356. Sims, P.R. P.K. and and others others (1970): (1970): Geologic Geologic map map of Minnesota, Ribbing Hibbing Sheet Sheet Sims, (scale 1:250,000): 1:250,000): Minn. Minn. Geol. Geol. Survey, University of of Minnesota, Minneapolis. Minneapolis. Taylor, H.P. Jr. Taylor, H.P. Jr. (1968): (1968): The oxygen oxygen isotope isotope geochemistry geochemistry of of igneous igneous rocks: rocks: Contr. Mineral. p.1-71. Contr. Mineral. and Petrol., v.19, p.'—71. Other useful References Allison, 1.5. I.S. (1925): (1925): The The Giants Giants Range Range batholith batholith of of Minnesota: Minnesota: Jour. Jour. Geology, Geology, v.33, p.488—508. p.488-508. v.33, Goldich, S.S. S.S. and others (1961): (1961): The Precambrian Precambrian geology geology and and geochronology geochronology of Minnesota; Minn.Geol. Minn.Geol. Survey Bull.41, University University of of Minnesota, Minnesota, Minneapolis, p.62—65. p.62-65. �-69—69— Table .{'* b(O 18 /0 16 ratios of of quartz in Early Precambrian granitic )SMOW ratios SNOW and metamorphic metamorphic rocks from the western part of the and the Giants Range batholith batholith of Northeastern Minnesota Range (perlil) (perilil) Average (permil) A. Rocks of magmatic origin: origin: (1) Granodiorites Granodiorites (main (1) (main intrusive intrusive phase, phase t two two samples) samples) 9.4 —- 9.9 (2) Leucogranodiorite Leucogranodiorite (satellitic (2) (satellitic phase of of (1), (1). one one sample) sample) 9.7 9.7 9.8 9.8 (3) Granites Granites (main (main intrusive phase, phase t (3) two two samples) 9.5 9.5 —- 9.6 9.6 (satellitic phase phase (4) Leucogranites (satellitic of (3), (3)t two two samples) samples) 9.2 —- 9.6 9.4 10.7 -— 11.4 10.9 10.9 B. Rocks ~~.Rocks of metasomatic origin: origin: (1) (five samples) samples) (1) Granites (five 10.2 (2) Aplogranite (one (2) (one sample) sample) (3) Partially granitized (3) volcanogenic metasediments (three samples) (three samples) 10.4 — 10.4 - 12.5 11.1 11.1 9.2 9.2 —- 10.1 10.1 9.6 9.6 c. C. Rocks of anatectic anatectic origin: origin: (derivatives of relatively relatively alB_poor source rocks) rocks) 0'8—poor source (1) Quartz tonalites (four (four samples) samples) (1) (2) K-feldspathized K—f eldspathized tonalite tonalite (2) (one sample) 12.1 12.1 D. D. Parent volcanogenic metasediments metasediments of: of: (1) B (four (four samples) samples) (1) Group Group B 11.1 — 1l.1 - 12.9 12.2 �—70--70- ZONED NATIVE NATIVE COPPER CrIEHICALLY COPPER AND A<\lD CHALCOCITE CHALCOCITE FROM FRaN CHEMICALLY ZONED WHITE PINE, NICIIIGAN WHITE PINE, MIChIGAN T. A. A. Vogel Geology Department Michigan ~ichigan State State University University East East Lansing, Lansing, Michigan and T. T. J. J. Rohrbacher Staff Geologist Staff \'~ite White Pine Copper Company Pine, Michigan \.Jhite White Pine, tHchigan ABSTRACT A B S T R ACT A the copper ore are minerals at at White ~.Jhite Pine, A microprobe study of the Hichigan, has shown that that zoned copper—mineral copper-mineral grains occur in in the the Michigan, has This zoning is ore-bearing of the the Nonesuch Nonesuch Shale. Shale. This is developed develofled ore—bearing horizons of in the most type of in both both chalcocite chalcocite and and native native copper, copper, and and the most prominent type zoning is zoning is iron enrichment towards to\vards the the edge edge of of the the grain. grain. Some chalcocite grains grains are are highly highly zoned, chalcocite zoned, containing about about four four times times as as as in much iron (at least the edge of of the the grain grain as in the the core. core. least 10%) 10%) on the iron (at Aluminum, magnesium siliconshaH showthe thesame sametype typeofof zoninf, zoning, hut Aluminum, magnesium andand silicon hut are to a lesser extent. are developed to extent. copper grains are also zoned respect to iron, Many native native copper grains arewith also zoned with respect to iron, with the edge of the iron wi th the edge of the grain grain containing containing about about twice t\<7ice as as much much iron (about 1%)asas the the core. an enrichenrich(about 1%) core. All zoned zoned copper copper minerals show show an ment of iron iron towards of the ment of towards the the edge edge of the grain; grain;however, ho\·7ever, both both within ,·7ithin and and between between samples, samples, the the amount amountofofzonin~ zoningand andthe therelative relative proportion proportion This variation zoned to unzoned grains highly variable. varia1)le. This variation does c:oes of zoned to unzoned grainsisis highly not appear to be be controlled controlled by by the the major majorlitholof,ic lithologic variAtions variations in not appear to in the ore ore zone, zone, but but may be controlled controlled by uy subtle differences in lithology or by environmentrttat the the time variations in by variations chemical environment time of of in the local chemical deposition. Any Any j:lotlel modelofof'1re 're Genesis genesis must must take take into account account the the occurrence, occurrence, minerals. distribution and and type distribution type of of zoning in in these these copper copper minerals. �—71— -71- STRATICRAPHY OF KEWEENAWAN KEI.vEENAWAN STRATIGRAPHY OF WESTERNMOST i-JESTERN}[OST MICHIGAN HICHIGAN W. S. Wtite W. S. i-n1i te U. S. Geological u. Survey Agriculture Research Center Center Beltsville, Naryland Beltsville, Maryland E. R. R. Brooks E. Department of Earth and Physical Science Science California State State College College Hayward, California Hayward, H. 3. A. A. Hubbard U. S. S. Geological Survey Survey U. Washington, D.C. D.C. Robert F. Robert F. Johnson 449 Boynton Avenue Berkeley, Berkeley, California J. T. J. T. Wilband iVilband University of Toledo Toledo Uepartment Department of Geology Geology Toledo, Ohio ABSTRACT A B S T R ACT surveysprovide provideaa skeletal skeletal Recent geologic geologic and and aeromagnetic aeromagnetic surveys fracieworkfor forthroughgoing throi:ghgoing stratigraphiccorrelations correlations of framework stratigraphic of the the Keweenawan rocks rocks of westernmost westernmost Michigan. Michigan. The stratigraphy of the the middle and upper Kel.".eenawan Fceweenawan rocksofof the the Keweenaw Peninsula has rocks Keweenaw Peninsula long been known in in great great detail, detail,thanks thanks to tothe thelarge largeamount amount of of drill—hole and drill-hole and surface geologic information. information. The recent recent work perpermits certainty, mits certain certain key key horizons horizons to to be be traced, traced, with with moderate moderate certainty, westward into Wisconsin. Wisconsin. Stratigrapitic relationships relationships for for the the middle middle and and upper upper Keweenawan Keweenawan Stratigraphic rocks best shown rocks are best shown in a longitudinal stratigraphic section section drawn drawn rocks and having along strike of of the the middle middle Keweenawac Keweenawan rocks along the general strike most striking striking base the Nonesuch Nonesuch Shale rlA.tum plane. The The most base of the Shale as as aa datum (1) The predominantly features of such such aa diagram diagram are the the following: following: (1) TIle predominantly features of basaltic Portage Lake Lake Lava Lava Series Series maintains maintains aathickness thicknessofof10,000— 10,000basaltic Portage 12,000 from 1-loughton Houghton to tothe near 12,000 feet feet from theJHack BlackRiver Riverand andisis thinnest thinnest near the Ontonagon Ontonagon River. IItt is isabout about 8000 8000 feet thick thick atatthe theMontreal Montreal River. (2) (2) An An unnamed lenticular unnamed lenticularunit, unit,10,000 10,000feet feetthick thick at at the Liver on Presque Presque Isle River River and and pinching pinchinp, out out near near the the Ontonagon River on the the and the the Montreal Montreal River River on on the the west, west, lies liesabove above the thePortage PortageLake Lake east and Lava Series Series and and below below the the predominantly sediientary sedimentaty Copper Copper Harbor Harbor Conglomerate. to fine— Conglomerate. The The unit is mainly mainly composed composed of fineunit is of thin thin aphanitic to grained andesitic andesitic flows flm,s and and contains contains minor rhyolite rhyolite and and intermediate intermediate rocks, the top. top. It to represent represent accumulation rocks, particularly near the It seems seems to \Vithin fe\.". miles of aa volcanic center south of of the the Porcupino Porcupine within a few center south Mountains. (3) HarborConglomerate Conglomerate less than than 500 500 feet feet f·jountains. (3) The The Copper Copper Harbor is isless thick over over the thick tile thick part of the theunnamed unnamed unit, unit,and and4000—5000 4000-5000 feet thick near the tIle pinchouts pinchouts of of tile theunnamed unnamed unit. combined thickthickthick near unit. (4) The combined ness of of tue tlle three three units units suggests sugr,ests aa strongly strongly asynnetric asymmetric basin, basin, deepening from aa minimum minimum near more than 25,000 25,000 deepening from nearthe the Ontonagon OntonagonRiver River to to more feet between the the next next feet between the Black Blackand andPresque PresqueIsle IsleRivers, Rivers, and and then, then, in in the 15 than 10,000 10,000 feet the 15 miles miles toto the the \Vest, west, thinning thinning rapidly rapidly toto less less than feet at at the Montreal These findinf's findings reinforce reinforce the hontreal River. These the concept concept that that the themiddle middle rather than Keweenawan Ke\VeenaVlan lavas lavas accumulated in separate tectonic tectonic basins basins rather in aa single single large large one. one. the �-72—72— The Ke,,,eenawan lavas, so-called South South Trap Trap The lower lower Keweenawan lavas, !'"hich which form form the the sc—called Range, lie beneath the the Portage Portage Lake Lake Lava Series, Series, from from lie unconfonnably unconforably beneath &hich they differ in in lithology, lithology, metamorphic grade, ("hich they differ grade, and magnetic properties. The feet consists consists predominantly of very properties. The lowennost lowermost 5000 feet thin basalt the next 4000 feet feet mainly to thin basalt flows, flows, and and the next 4000 mainly of aphanitic to The uppermost fine-grained flows flows of intermediate intermediate composition. composition. The uppermost part fine—grained of this sequence is iseverywhere everywhere concealed concealed by by the the Jacobsville JacobsvilleSandstone Sandstone this sequence or deep deep overburden, overburden, but inferred from from gravity gravity and and magnetic magnetic data data or but is is inferred This lower is lC,000 to to consist consist largely largely of of felsic felsic flows. flows. This lower sequence sequence is 10,000 and uncertainty and perhaps perhaps20,000 20,000feet feetthick, thick, the the difference difference reflecting reflecting uncertainty about the location location of about the of the the top. top. The rocksare are more metamornhosedthan than the middle The lower lm"er Keweenawan Keweenm"an rocks more metamorphosed middle Their metamorphic grade appears metamorphic grade appears to to increase increasewestward westl,vard— Keweenmvan. Keweenawan. actinolite is actinolite found in Hisconsin but is is rare rare near near Ironwood. Ironwood. is found Wisconsin but Kenneth Books Hooks has found that that the the lower and middle Keweenaw€n Keweenawan rocks also also differ differ from rocks from one another in in magnetic magnetic direction. direction. In contrast contrast with with the the belts belts of of middle middle and and upper upper Ke,,,eenal,van Keweenawan rocks, roes, In dips of of bedding bedding generally generally decrease decrease !"'ith with stratirraphic dips stratigraphic depth in in the lower Keweenawan Ke\veenawan belt. belt. If If this this represents represents soutlnvard southward thickening thickening rather rather than Lian folding, folding, it it suggests suggests that that the the axis axis of of the the lower Keweenal,van Keweenawan basin lay lay to to the the south. south. �-73—73— THE NORTH SHORE SHORE VOLCANIC GROUP GROUP May 5 and 8, 1971 by Prepared by C. Green John C. University of Minnesota, Minnesota, Duluth Minnesota Geological Survey �—74--74- Croup The North Shore Volcanic Group John C. C. Green Introduction Previous Work Hork and and Acknowledgments. Acknowledgments. Detailed mapping of the Minnesota A. S. E. Sandberg's Sandberg's study study (1938) (1938) of of the the shore of Lake Superior began with A. Grout and Schwartz (1939) section between Duluth Duluth and and Two Two Harbors. Harbors. Grout (1939) and and (1957) studied the the intrusions intrusions and and flows flows in in eastern eastern Lake Lake County; County; Gehman (1957) the lakeshore Two Harbors Harbors and and Split Split Rock Rock Grogan (1940) (1940) mapped the lakeshore between Two River; Schwartz (1949) River; (1949) studied the Duluth Duluth area; area; and and Grout Grout and and others others (1959) (1959) mapped most of of Cook Cook County. County. Most of of the the data data reported reported in in this this account derive from studies by the account the writer who, starting starting in in 1965, 1965, has has mapped the shoreline between Silver Bay and Grand Grand Portage, Portage, with conconsiderable reconnaissance inland (Green, (Green, 1966; 1966; 1968a; 1968a; 1968b; 1968b; 1970). 1970). The report does, however, however, also also lean lean considerably considerably on on Grout Grout ~ etal. report does, al. (1959) (1959) and, for for the Duluth-Two Duluth—Two Harbors area, on and, on Sandberg Sandberg (1938). (1938). The field field studies have have been supported by the studies the Minnesota Geological Geological Survey, Survey, and and most of the laboratory studies have been supported by the National studies the Science Foundation. Sincere gratitude for for this this support is is extended extended to to both agencies. agencies. The writer's ideas ideas have benefitted benefitted from from discussions discussions with many other geologists rocks, esoecia11y esnecially many other geologists concerned concerned with with Keweenawan Keweenffivan rocks, including Bill Jr., H.H.Hubbard, including BillBonnichsen, Bonnichsen, D. D. M. M. Davidson, Davidson, Jr., Hubbard, C. G. B. B. Morey, Horey, W. W. C. C. Phinney, Phinney, ·P. W. Weiblen, and and W. W. S. White. P. W. S. White. Regional Setting. "North Shore has been ~egional Setting. The name "North Shore Volcanic Volcanic Group" Group" has been used used et al. al. (1961) (1961) for by Goldich et for the the lavas lavas and and interbedded sediments of Late Precambrian. rocks, as well Precambrian age in northeastern Minnesota. These rocks, as and sedimentary sedimentary rocks rocks in in the the as all all other Late Precambrian volcanic and district, have traditionally been called"Keweenawad'by called "Ke~veenffiolan" by Lake Superior district, rocks exposed on the general lithic and structural correlation with rocks and paleomagnetic Keweenaw Peninsula of Michigan, Michigan, but recent radiometric and investigations as \-lell indicate that that aa more more precise precise investigations as well as geologic mapping indicate stratigraphic stratigraphic framework framework is is needed needed to to adequately adequately describe describe the the complex complex events and and deposits deposits in in this this area. area. series of Late Precambrian events In (Grand Portage In the the northeast northeast corner corner of of }linnesota Minnesota (Grand Portage area) area) the the lowest lowest Upper Precambrian flows which in flows overlie a thin quartzite (Puckwunge) (Puckwunge) \.;rhich 1.n turn turn overlies, overlies, apparently disconfornably, disconformably, the the shales shales and and graywackes graywackes Of 6f the Middle Precambrian Rove Formation;here hereboth both sequences sequencesstrike strike nearly the Rove Formation; nearly east—west and dip at approximately 10° east-west 100 to to the the south. south. At the the southwest southwest end of the basin immediately west west of miles away), of Duluth (155 (155 miles away), the lowest lowest Upper Precambrian flows flows also conformably conformably overlie thinquartzite quartzite (Puckoverlie aa thin (Puck— wunge?) which there there overlies the the vertically folded slates and metagray— metagraywackes of the the Middle }tiddle Precambrian Thomson Formation, Formation, which is is correlated with the the Rove. Rove. Here the flows flmols strike north and dip dip at at about about 25° 25 0 to the unconformity here here reflects and subsesubseeast. The angular angular unconformity reflects the the diastrophism and quent the Penokean Penokean orogeny, orogeny, which which evidently evidently did did quent erosion associated with the the northeastern northeastern corner corner of of the the state. state. Across the the axis of the the not affect the flows Lake Superior Syncline in northern Wisconsin and Michigan the lowest flows �MINNESOTA \-n I ONTARIO J) I I \ '—-7 - rHCVL AND EARLY PRECAMBRIAN GRAND M AR A IS LEGEND LUTSEN JOFTE uACONITh INTRUSION S i., '\~r KEWEENAWAN INTRUSIONS Wf0J KEWEENAWAN LAVAS "'to FIELD TRIP STOP I -....J U' \Jl I ITLC MARAIS MARAIS ER BAY JBEAVER BAY BAY LAKE SUPERIOR SCALE ° ! •O HARBORS WISCONSIN MINN. 10 20 Miles MICHIGAN 30 40 �—76— -76- conformably overlie aa similar similar quartzite (Uessemer) that in in turn overlies overlies quartzite (Bessemer) Middle Precambrian shale and and graywacke with only only minor discordance. discordance. These quartzites have always been referred to as as Lower Lower Keweenawan, Keweenawan, but but no no radiometric age determinations are are available available and and they they may may be be much much older older than the volcanic volcanic rocks rocks of of the the iCeweenaw Keweenaw Peninsula. The North Shore Volcanic Group is cut The cut by aa. great great variety variety of of intrusive intrusive rocks rocks that are are also also of of Late Late Precambrian Prec&~brian age. age. These range range from from the the great great Duluth Complex, Complex, dominated by anorthositic and and troctolitic troctolitic rocks, rocks, to to smaller sills, sills, stocks, stocks, dLkes, dikes, and irregular plutons of of diabase, diabase, 'crro— ferroabbro, trachybasalt, granocdorite, an gabbro, troctolite, troctolite,syenogabbro, syenogabbro, trachybasalt, granodiorite, and. Someofofthese thesebodies bodiesalso also cut cut the the older graoQphyric, adamellite. Some older rocks rocks grarophyricadanellite. to the to the north, north,northwest northwestand andwest west of ofthe themain mainLate LatePrecambrian Precambrian outcrop outcrop area of Cook Countyand andthe the Thunder BayDistrict District area (e.g. (~.g. the the Logan intrusives intrusives of Cook County Thunder Bay of Ontario). of Ontario). Paleonagnetism and Age. Recent paleomagnetic studies studies (Dubois, Paleomagnetism Recent paleomagnetic (Dubois, 1962; 1962; Beck Deck that two and Lindsley, Lindsley, 1969; 1969; Books, Books, 1968; 1968; Palmer, 1970) 1970) have have shown shmm that two reversals of magnetic polarity occur within reversals 'loTi thin the Late Late Precambrian Precambrian volcanic volcanic rocks of the Lake Superior The 1m-rest lowest strata stnta show 'nor'ial" rocks Superior district. district. The shoYr "normal" (north—seeking) polarity polarity similar to to orientations orientations in the underlying (north-seeking) underlyinp; Middle Precambrian rocks, rocks, but but this this group group of of rocks rocks has has not not been been recognized reconized in Precambrian Minnesota. Keweenawan Books (1y68) (l9~8) has ha.s proposed that the Lover Lower —- Middle ~eweenawan Books boundary be redefined the second reversal where redefined at at the second macnetic magnetic reversal where rocks rocks of normal polarity. The North reversed polarity aresucceeded succeeded by by rocks of' of normal North po]arity are Volcanic Group Groupcontains containsatatthe the ba.se base of of the Shore Volcanic t~e section section atatGrand Grand Portage Portage about 5000 feet feet of lavas lavas tnat that show reversed polarity, and and are are thus thus Lower Lower Keweenawan magnetically defined. defined. The thick wedge of flows Keweenawan asasmagnetically The thick wedge of flows west west of Duluth that underlie ut overlie the Puckwunge Duluth that underlie the theDuluth Duluth Complex Complex but Pucki-runge (?) (?) quartzite have quartzite but on on have not not been beenadequately adequatelytested testedinin the the laboratory, laboratory. hut regional magnetic magnetic maps maps give aa negative negativemagnetic map;neticanomaly anonaly which which implies implies regional reversed polarization. Furthermore reversed polarization. very similar to Furthermorethey theyare arelithically lithically very reversed-polarity lavas of of Grand Grand Portage. Portage. The the reversed—polarity The remainder remainder of of the ::orth North Shore Volcanic Volcanic Group polarity, Grouphas hasnormal normalmagnetic magnetic polarity,similar similar to to the bulk bulk of of the the associated associated intrusive intrusive rocks rocks and and to to the the rocks rocks of the Keweenaw Peninsula. Only available on on rocks rocks Onlylimited limited radiometric radiometric age age determinations determinations are are yet yet available of al. (1961) of the the North North Shore Shore Volcanic Volcanic Group. Goldich Goldich ~~ (1961) found aa !! ~~. 1.1 ±± 0.1 b.y. 1.1 intrusive rocks rocks of of the the Duluth Duluth Complex Complex b.y. age for associated intrusive and K/Ar K/Ar methods, and and Silver Silver and and Green Green (1963) (1963) found found an an isotopic isotopic by Rb/Sr and age age of 1.125 by U/Pb isotopes in in zircons zircons of of both both lavas lavas and and intrusive intrusive rocks rocks and Mellen, Mellen, Wisconsin Wisconsin areas. areas. Paure Faure et al. al. (1969) (1969) determined determined from the Duluth and the age of the Endion sill, sill, which cuts cuts the flows flows at at Duluth, Duluth, as as 1.092 1.092 b.y., b.y., the age and that that of of the the Duluth Duluth Complex Complex .at at Duluth Duluth as as 1.115 1,115 b.y. b.y. by by the theRb/Srmethod. Rb/Srmethod. However, all of these sampled rocks rocks are in areas of normal magnetic However, rr..agnetic polarity polarity, to the the age so no data are available available as as to a~e of the Lower Keweenawan lavas lavas of, of, for for Grand Portage Portage area. area. Hanson and Malhotry (1970) (1970) have recently instance, the Grand a 1.380 b.y. (K/Ar) of aa "Logan "Logan Intrusive' Intrusive" in in southern southern Ontario, Ontario, found a b.y. age (K/Ar) indicate the the possible possible age age span span of of the the Lower Lower Keweenawan. Ke'lveena"ran. Isotopic which may indicate studies over over the the range range of of Upper Upper Precambrian Precambrian rocks rocks iii in the district district are are U/Pb studies currently in in progress. progress. �—77— -77- Structure Structure The Group is is that that of of aa The general structure of the North Shore Volcanic Group great nest of dishes tilted tilted gently gently to to the the southeast into ofmshes into Lake Lake Superior. Superior. endthe thestrata strata at at the strike slightly At the the northeast northeast end the base base strike slightly north north of of west and dip about about 10—12° 10-12° south, south,whereas whereasatat the the southwest southwest end, end, 155 155 miles miles away, they strike north and and dip about 25° east. east. In between the strikes strikes c-raually converge convergealong alongthe theshore shoreof of Lake LakeSuperior Superiorasashigher higher stratigraphic stratigraphic gradually levels are reached, reached, until flows strike to the the shore shore in in the the levels are until the the flows strike parallel parallel to vicinity southwestern vicini ty of ofSchroeder, Schroeder, Torte, Tofte,and andi,utsen Lutseninin southvresternCook Cook County. County. Herethe the highest highest stratigraphic stratigraphic units are the dip Here are exposed, exposed, and and the dip is approxiapproximately 12° to the southeast. southeast. The lavas lavas are The are intruded by a great variety and bulk of intrusive intrusive rocks, rocks, including several large large diabasic diabasic sills sills at at Duluth, Duluth, the the Beaver Beaver Bay Bay Complex, Complex, includim several the 1-iovland andReservation ReservationRiver River diabase diabase complexes complexes and and the the Logan intrusions. the Hovland and intrusions. Where Hhere these intrusions are are discordsnt discordant and and abundant abundant they they have have deformed deformed the the lavas considerably, lavas considerably, with local strongly divergent strikes and and steep steep to to overturned dius. dips. Along with the thick glacial cover inland, inland, they they have have also made made difficult difficult to to impossible impossible the the long-distance long-distance tracing tracing of of stratigraphic major flows or or groups roups of in the the lava lava series. series. Several Several maj or flows of similar similar flows, flovrs, units in however, can be traced inland from the lakeshore for however, can be for at at least least 15 15 to to 25 25 miles. miles. Faulting is COffi.J;lon in the flows flows near the areas of abundant intrusions intrusions (such (such is common as from Silver ~jilver Bay Day to to Little Little:iarais). :'1arais). These faults appear to to be be of of minor as displacement and are are :r.lostly mostly transverse and steeply dipping with no displacement no strongly strongly preferred strike or displacennnt, displacemnnt, but aa few few longer lon~er strike—faults strike-faults have have been been found, one one of which probably extends for found, for at least five five miles. thickness of the has been measured and and estimated estimated by by The thickness of the lava succession has feet between and Split Split ~)andberi!, and Gror-an Grof.\an (l90) (19)j·0) as as 23,148 behreen Duluth Duluth and Sandberg (19::38) (1938) and 23,lB feet Rock complex) by adding Pock River (the (the beginning beginning of of the the Beaver nay Bay intrusive complex) Whether the lakeshore. ~TIether the individual individual flow thicknesses thicknesses intersected along the lakeshore. j.ile at at Split Split Rock Rock River Biver is this conforms to the is not not this conforms the true true thickness of the pile Northeast of the Beaver Bay Complex about 5000 lmovn. Hortheast 5000 feet feet of of lavas lavas are are known. estimated recent mapping to form the lakeshore section section between between 'ilver Silver estimatcd from recent Rortheast of and Lutsen, where Bay and the uppennost flows at 'T'ofte. IJortheast Tofte uppermost flows at °ofte. Bay the flows are are parallel to the shore, lavas totalling about about 16,500 16,500 feet feet the flows have River diabase diabase near near }iovland. Hovland. Below been measured measureddovn downtotothe the Reservation Reservation River have been (northeast of) this is an older section of about 5,000 feet of (northeast of) this is an older section of about 5,000 feet of lavas, lavas, for for total on on this thislimb limb of ofabout about 21,500 21,500 feet. a total Estimate50f volcanic volcanic thicknesses thicknesses by by constructing constructing cross—section cross-section profiles Estimateof profiles give between between 11,000 Tofte, above above the the Duluth Duluth Complex, give 11,000and and18,000 18,000feet feet at at Tofte, depending 20°. Although Although the the average average on ass~~ed assumed dips dips between 12° and 20°. deDendng on is very little control on dips near dip at Tofte is about 12°, there is very little control on dips near the the at Tofte is about 12°, dip flow contacts. contacts. base section as as the thefew fe,., inland inland outcrops outcrops rarely rarelyexpose expose flow base of of the section northeast at at the theCascade Cascade River, River, about about 15,000 15,000 feet feet of of lavas lavas above above Farther northeast of 12°; another the Duluth Duluth Complex Complex are calculated with an average dip of 12°; another are calculated with an average dip lies beneath thick section, section , possibly possibly as much much as thick, here here lies beneath thick as as 5,000 5,000 feet feet thick, '. the Complex. Complex. ~ �—78--78- GenerallDesptiq Description, The North Shore Volcanic Group bears many resemblances, both physically physically and chemically, to plateau lava sequences of various geologic geolo~ic ages. ages. Similarities to the Tertiary Tertiary plateau plateau lavas lavas of of eastern eastern Iceland Iceland are are to the particularly particularly striking. striking. The lavas lavas are almost entirely subaerial, subaerial, showing showing highly vesicular (now (nmr amygdaloidal) amygdaloidal) upper portions and and massive interiors, interiors, and.various various types types of of jointing, jointing, surface surface features, features, and and textures textures depending depending and on their specific composition. composition. Evidence of submarine extrusion extrusion is is almost almost Portage and entirely limited to the at Grand Portage and at the base of the section both at Nopeming, west west of Duluth, the lowest flow Duluth; at at Nopeming, flow is is piflowed pillowed and and on on Portage Island the lowest flow shows shmrs spheroidal spheroidal forms that could could Grand Portage possibly be pillows, but excellent, excellent, thick—rinded, thick-rinded, vesicular vesicular pillows pillows constitute the lakeward side of the island aa few constitute aa flow flow on the few flows flmrs above above of the the section. section. Unequivocal hut but less well—formed well-formed pillows and and the base of pillow-breccia have been seen seen only only rarely rarely higher higher in in the the section. section. These pillow—breccia could or stream stream beds beds on on the the lava lava surface. surface. The could have have formed in local lakes or flows tabular, and since some individual flows flows are are in general tabular, flows or or flow flow groups groups can can be traced along strike for at least 20 miles, the general general impression is is that that of of aa broad, terrain. In contrast contrast broad, rather flat volcanic terrain. to clear to the the situation situation in in eastern eastern Iceland, Iceland, however however (Walker, (Walker, 1964), l96), no no clear evidence of volcanic centers, representing shield or composite evidence composite volcanoes White contemporaneous with the plateau volcanism, has yet been found. found. \'mite contemporaneous (1960) on to some Keweenm-ran (1960) has has drm-rn drawn attenti attention to the the remarkable remarkable extent extent of some Keweenawan flows (especially in Michigan) Michigan) and with ample justification flows justification calls calls them flood basalts. basalts. Interflow sediments of the the section. section. They Interfiow sediments make make up up aa minor minor part (l—3) of -part (1-3%) are principally red, cross—bedded sandstones, that occur sporadically are red,cross-beddedsandstones, sporadically as as beds aa few few inches inches thick thick between flows, flows, but but aa few fe"T local local accumulations accumulations of of over 100 feet feet are are found. found. Conglomerate is is rare. rare. Some Some sand has has filtered down into down into cavities cavities in the upper unper parts of flows, f10vs, and and also also forms forms aa matrix for flow—top breccia for flow-top breccia in in others. others. These sediments appear a.ppear to have been deposited by occasional temporary streams winding across the volcanic surface. There is is little evidence evidence of of erosion. erosion. Pyroclastic deposits deposits are are but welded tuff and mixed sand and extremely scarce, scarce, but and shards shards have been the Cascade IIiver River in Cook County (Johnson reported from the (,Tohnson and and Foster, 1965) 1965) and basaltic to to andesitic flow top breccia, is is present present andesitic breccia, breccia, other than flow in a few localities. , exception of of aa high high potassium potassium content content in in some some oaf mafic With the exception ic and intermediate abundance of of rhyolite, rhyolite, the the compositions compositions of of the the lavas lavas members and the relative abundance are also also very very similar to those those of plateau lava series in Iceland and are and elsewhere. vhere. characteristics and and abundance abundance of of the the Table 1 shows the general characteristics major types. types. The most abundant general type is is olivine olivine basalt 'basalt of of several several varieties; varieties; important, and distinctive variety is is mottled mottled (ophitic), (ophitic), one widespresd, widespread, important, and is is similar similar to to what what has has been called olivine tholeiites in other areas. and areas. Rough columnar These typically have ropy surfaces and and were very fluid. fluid. col~~nar joints are Other olivine olivine basalts basalts are with diabasic are common. common. Other are coarser, coarser, some i-rith and some ,.ith with other other characteristic characteristic textures. textures. In the Tofte—Lutsen Tofte-Lutsen area, area, high in the section, is a group in of olivine base.1ts th abundant, abundant, small basalts "ri with (1-3 phenocrysts or or crystal crystal clots. clots. At section (1—3 nun) mm) bytownite' bytownit&phenocrysts At the base of the section both t at Duluth Duluth and and on on Lucille Lucille Island Island east east of of Grand Grand Portage Portage are are distinctive distinctive basalts basa.lts that contain abundant phenocrysts, 2—3 2-3 mm across, across, of of augite augite and and �_____ ______ TABLE 1 Generalized Characti±ritics Characteristics of of Major Major Lava Lava Types Types of of North North Shore Shore Volcanic Volcanic Group Group ___ ~ I Wt % % Si02 Si0 2 -_ -_. ' --~ ,. --...--.......... I 2 ·~"-··""'''''''·~''-'''''''''''-''''-'''~~··i''''~· Wt %% MgO -..---~.--'.<.~."'-"'.' .. _ ..•,,_'__ "~_ _~ 46-49 1 0.1-0.5 I ~ ~--~·_""""~:~'.....,-'T-'·_.-.~ ~ · I{ Andesite— t"P. Intermediate Andesit~:i Intermediate Trachyandesite Quartz Tr~rtz Latite L~~ Quartz Quartz Tholelite I ~- " - - - - " , .. , . • .~-w••• _ -" ~".~~~ ••• ~.-+,~. Wt %%1(20 K 0 -, Tholei te I Olivine :ic 1 Olivine Characteristic Tholeilte Characteri~~~i~te 4,,52-57 52-57 50—51 50-51 ! 0.6-0.9 ~'~l.·.~ ~ol.AA' .!::..~< 1-,,•• 1,--.' •• _.,,-, 1 ."~.- ~"'-" ·~·~,.._'S...·_"' 5.9:6.8 5. 9-6 . 8 1 I I __ "',.. ,""~ ••• .,J • • • • ~ ~ I • , 1 Very fine— finet Very fine— finegrainS, inter— l grained, inter~ grained, granular. Some pot— { granular. commonly porphyritic (plag., ~ flow structure, ~ phyritic , ..1 augite) (plag., fine oxidationoxidation— i, fine banding Ophitic Occasionally Occasionally porphyritie porphyritic (plagioclase) --------.--.--------!..-----~---~-~t~:~~~~-.-~--+----~ 72—75 72-75 2.8—5.0 2.8-5.0 3.9—6.2 3,.9-6.2 r '_<'~~', 0.9- 1 • 9 ,.,--,~ <J .. _ _ ;· ·",· P _ > ' _ • - . _• •- ~ ~ , " ' _ ••.•• -:... . < - I aphanitic~ . aphanitic, mostly pot— porphyritic (plag., (plag.,. augite, 01.) augite, oh) . . _ _~--~ .- 0.0—0.4 0.0-0.4 ,,,n"~"·.·~,.,-.•~,,·,,,. ,'-~.~ ..,< , .• ~"'_'_, .I •... , < •• ,, ..•, .•--.- .. --. aphanitic aphanitic to to felsitic;aphyric felsitic; aphyric or porphyritic (plag., orthoclase, (plag., ) quartz, mag., pyrox.) pyrox. occas. spherulitic ~.--_ _,--.;,::::~:lt::l~~~.~ . . - — J 62—65 62-65 ._- ! : Thickness, Thickness, feet feet Range '- --.--.,,' j'" -" I ' l \ Textures t ': - 1.9—2.7 1.9-2.7 .•Y. _ _ w .• .• ~yolite ithyolite ..~~~'-~·~~,.. ..,..-".-·.-'''' --..~•...".-.-...."....-.~...,.--~ -"'. ~~-~"~---'-'-'-~---~ _.V·_·__ 1 I 4. 3-5. 9 1. 9-4 . 5 11:9—4.5 ~ ~;~'-<'~~""_ '"-->-"'"'-'~/"""~-"';""'~1--~-'>""'.w.".>--."'-•.,./A~_~C'~~'_"h,,·_, t-'_.,··",._·.·r;.,,·~ . ,..'.,. ".~., !I' __ . Quartz Quartz Latite Latite I' . 50-1300 50—1300 perhaps 3500 3500 1 2 0 ' " · ·_..5 . 0=500 ..·· 50—500 120 — ···------struc~~:-t:=-:-:py--i~c==~=tc=:=::--i·:::=:- -====:-c'oIiIIDo~ .'.. -- ]- -~ >100 <1 to >100 ~." ·I6~46 10—40 ·"' ' 30—150 30-150 ~ -,·--···l 'so 80 - 1 50—240 50-240 ~ i 1". . var:Gibier' varIable 80—200 80-200 - Structures smooth, ropy flow tops oi;ti';;- jointing j vesicular wrinkled scoriaceous rubble scoriaceous, rubbly vesicular, rolled, flow—banded platy, sub—horizontal big columns in thick irejilai tâ ,'~~~~~:~:h~:i~~~~~l ··t-~~~:i~:}~::T.::-t~~~ii,irreg;;i;r-ts~if;~~~;~g;;iarh~~~~;!!~:~~l - sheeted tops[" small, irregular small, 1rregiIar subhorizontal, flows platy .. round stretched 'o"r" or ···... i . stretched, round vesic1es round or 1rregu1ar stretched ...._,··_- . stretched or round round ~ ~--_ ·-··-~·i ~ ~ -14 ,-- ,-- - - ~ . _·--_····_..·. ~."i'----. __ -- -.~~- - - ~~"Q ~ .,~_.-.. '".~-~--'very_fluid Other ! very fluid 1 more viscous ~ brown—weathering brown-weathering I few flow : pink, pink, red, red, or more_viscous contacts exposedt exposed light Characteristics ;omewhat variable variable contacts Characteristics J, pipe amygdules some contain tomewhat light gray gray at at base ~ ~ more more 1(20, K20, ! segregation veins, l segregation veins, i Kspar; ~ vesicle cylinders quartz, agate agate vesicle cylinders ~: quartz, I common in cavities l common in cavi ties' columnar centers ve·si-~i;;~·_ -·--l--·;(;~d·-~-;· 'i;~~g~i~·~+·;t~et"~h'ed --- ~-. -"'-'--- -----..- 1 I i ~ ~~ ---.. -.-.-.. -.. -".. ! - i l··.-,-.----- .- . -.- ---,.. l Ksr I Ij --+;tretch~d· O~.. t"';~~:iche~f I I I I f. ~~~:~·ched·: - " " - . _.. • -,- - �—80— -80- (serpentinized) olivine: olivine: these these are are particularly unusual unusual in (serpentinized) in having ferromagnesian instead of of plagioclase plagioclase phenocrysts. phenocrysts. Another moderately abundant and distinctive distinctive rock rock ty-pe type is tholeiite" which is is is the the "quartz tholeiite fine grained grained and and slightly slightly more more siliceous siliceous and and viscous viscous aphanitic or very fine The quartz—tholeiites than the olivine olivine basalts. basalts. The quartz-tholeiites characteristically characteristically have a rubbly or brecciated top with the highly vesicular vesicular fragments fra~ments set set in in aa matrix of washed-in washed—in red sand sand or or occasionally occasionally calcite calcite and and zeolites. zeolites. They also ~ thick, along subhorizontal subhorizontal also commonly commonly show narrow oxidation bands, bands, 1-3 mm flowage planes. planes. This quartz—tholeiite quartz-tholeiite grades grades into into more more potassium—rich potassium-rich varieties (trachybasalt, (trachybasalt, trachyandesite) that that can can be be distinguished distin~uished only only by chemical analysis and and microscopic study; study; patches of of interstitial interstitial KK feldspar are are present present in these these rocks feldspar rocks but are invisible in in hand specimen. speci~en. Intermediate varieties are are nearly all all porphyritic with plagioclase, plagioclase, augite, ausite, magnetite, and in some magnetite, SOTIe specimens iron—rich iron-rich olivine olivine phenocrysts; phenocrysts; they they have have the compositions of andesites, trachyandesites, and the and intermediate intermediate quartz quartz Most are aphanitic, but one latites. Most one unusual flow, flow, here here called called the the Manitou Manitou trac~ybasalt, is exceptionally thick (at (at least least 300 300 feet) feet) and and granular, granular, traciybasalt, is for 55 miles although it it originally continued continued for an an and can be traced for These flows in both both directions. directions. 'I'hese flows are commonly cOTlJ1!1only brown or unknown distance in red and irregularly jointed jointed or with platy,subhorizontal joints. joints. The felsic The felsic lavas lavas are anomalously abundant abundant for for aa simple simple differentiation differentiation series from aa basaltic basaltic parent parent magma. mae;m.a. They are red, pink, or or light li~ht gray. gray, These flows composition of of quartz quartz latites. lati tes. 'l'hese flows tend to be much and have the composition thicker than the other other types: types: the thickest is is 1300 feet, feet, aa few few miles ~iles east east of Grand Marais; Marais; the 3500' 3500' Brule Flyer River rhyolite rhyolite west of of Hovland Hovland may may be aa lava dome. dome. Their top surfaces are mostly strongly strongly flow—banded, flow-banded, vesicular, vesicular, and. contorted, b~t but not not brecciated, brecciated, and and their their bases bases are are cornmonly commonly flow-banded flow—banded and contorted, brecciated. Spherulites are are occasionally occasionally present. present. Jointing Jointin~ and locally brecciated. ranges across in the thickest flows flows to sub— subranges from large columns 44 feet across horizontal platy joints; joints; small tectonically—produced tectonically-produced parallel fracture fracture sets a a few mID ccooling joint joint fragments fra~ments into into sets mm apart commonly break up the ccooling felsites are are porphyritic, with ,-rith quartz quartz and and small pieces. Most of the felsites feldspar feldspar phenocrysts (oliogclase—andesine (oliogclase-andesine and/or orthoclase) orthoclase) but but some some are only weakly porphyritic porphyritic or or arhyric. aphyric. Poikilitic quartz surrounding are stout stout alkali—feldspar alkali-feldspar laths ("snowflnke ("snowfla1:e texture:) texture';) is is aa common common microscope texture in the thicker thicker flows. flows. Even these siliceous siliceous lavas lavas have have evidently evidently flowed great distance; distance; one one lava lava or or ffow flowed aa great ..J..mr group group can can be be traced traced for for at B.t least 23 miles miles \-lest west from the Devil Track Fiver, least River, Grand Grand Marais (see (see man, Man, fig. 1). fig. 1). Alteration The lavas lavas have been strongly stronlJ,ly but irregularly irrerularl;v affected affected by b;f secondary secondary solutions that have deposited denosi ted low—temmerature lml-temner?ture minerals in in vesicles, vesicles> solutions fractures, and other some of the minerals of fractures, other cavities, cavities, and and -altered altered sot'!.e of the the no fresh fresh olivine divine has lavas themselves. For instance, instance, no has been been detected detected in in any of of the the lavas, lavas, although although it it is is common the intrusive diabases. any co~mon in the diabases. A zonation of of this alteration alteration is is anparent; anparent; at at Duluth Duluth and and at R.t Grand Granel broad zonation of the the ~round~ass groundmass Portage (in (in the lower lower parts parts of of the the lava lava section) section) r'uch ~uch of has been been converted convertedtoto actinolite actinolite (although many larger pyroxene has (althoup::h nan'.' laT£ser aurites aur.j te:=> are unaffected) unaffected) and has been been saussuritized. saussuritized. [ere Iere also andsome SOIne plagioclase plar:ioclase has also the minerals characteristicallyquartz, quartz, prehnite, prehnite, calcite, calcite, the arnygdule amygdule p.dnerals areare characteristically �-81—81— epidote, and chlorite, epidote, chlorite, the the same basic assemblage as as is is found found in in the the Porta~e Lav~ Series Keweenaw Peninsula (Stoiber (Stoiber and and Davidson, Davidson, Portage Lake Lake hava Series on the Keveenaw 1959). In and northeast of Duluth K—feldspar K-feldspar is is also also occasionally occasionally found, found, In arid laumontite becomes becomes abundant. and laumontite in the section section variouS various zeolites, zeolites, Higher in along with vith calcite, caThite, are are dominant dosnant except along except In in the the quartz quartz tholeiites tholeiites and similar agate, crystalline quartz and and chlorite chlorite are are common. common. similar lavas levas where aaate, The most most abundant abundant zeolites The zeolites are are laumontite, stilbite, heulandite, thorrsonite and scolecite scolecite but but analcite, analcite, natrolite, natrolite, mesolite, mesolite, mordenite, thomsonite and apotbvllite have also and apophyllite ~lso been found. Saponite is is common in olivine basalts. Andradite carnets garnets have been discovered in in several several localities localities amydules and andveins veinsfrom froma awide widerange range lavatypes tres (basalts in ~!'lY8dules of of lava (basalts to rhyclites) and and levels levels in rhyolites) in the the sequence, sequence, and and traces traces of ofnative nativecopper copper have have been found foundininseveral severallocalities. localities. Thus the secondary zonation in in the been Thus the secondary zonation :rorth Shore Grout spans spans both both the deeper—level, iTorth Shore 1oThanic Volcanic Group deeper-level, higher—temperatre higher-temperature tyte of the Keweenaw Peninsula and the higher—level, cooler tyte charactertype of the lCe,.,eenaw Peninsula and the higher-level, cooler type characteristic of istic of the the icuer Imler parts partsof ofthe theTertiary Tertiaryplateau plateau lavas lavas of of eastern eastern Iceland Iceland as described upper, zeolite—free is as described by by Walker 'ilalker (1960). (1960). Walker's Halker' s uDper, zeolite-free zone zone is apparently not represented representedinin Hinnesota. innesota. According Accordingtotohis his estinates, estirsates, the apparently not the presently exposed top of the exposed top the section sectionon onthe theLake Lake Sunerior Superior shore shore could could have have been anrrcxirratel'r 5,000 5,000 feet feet below the surface surface during been approximately belm., the during mineralization. Althoughdetailed (tetal led1-Tork workhas hasnot notyet yet been been done, done, no JUthou~h no clear clear cross—cutting cross-cutting relations of' to stratigraph the relations of zeolite zeolite zones zones to stratirr,raphywithin witp_~~ thelavas lavashave havebeen been recocnized. hut reco~nized, but the theevident evidentUpper Upper Precambrian, Precambrian, nostvolcanic postvolcanicunconformity unconformity ;·rhi-chch;;robe.bly Shore must mineralization, wit' probablyfollm.,s followsthe the~Torth lorth Shore must have havepostdated postdated the the mineralization, since it it does since does crosscut the zeolite ZGolite zones. zones. It should be be stressed, It stressed, however, however, that none of the flows flows has has been been entirely entirely in fact, converted to to secondary secondary minerals. In fact, the the plaioclase plagioclaseand and augite augite are are tynic8,11yunaltered unalteredororonly onlylocally locallyaltered altered mostmafic maficand andintermediate intermediate tvicall'r in in most has typically typically rocks. althour:h no no fresh olivine olivine has has been been discovered, discovered. There There h~s rocks, although been sore oxidation oxidation of of the the opsnue minerals, especially especially of of nagnetite, been sor.e opaque minerals, magnetite, and and interrsediate and ni~eonite is iscoirnonly com~only oxidized borders. In many nany intermediate and pi'eonite oxidizedatat its its borders. felsic lavas, plarioclase pladoclasephenocrysts phenocrysts have have been been albitized and/or zeolitized: zeolitized; felsic lavas. albitized and/or Fresh, undevitrified volcanic some could be be deuteric. deuteric. Fresh, volcanic someofofthis this alteration alteration could glass present in in occasional samples, r,lass is is still still present occasional samples,notably notably inina abasalt basaltfrom fromabout about t"m r'liles r10uth of Brule River. River. two miles ,{est west of of the mouth of the the Prule Etnra•iv The Thias of of the ;orth The lavas !.JorthShore ;3horeVolcanic VolcanicGroup Group can can be be conveniently conveniently divided lithostratipTanhic units unitsof ofcoherent coherent petrographic petrographic divided into into several several lithostratir'ranhic character the basis of character nrimarily nrimarily on on the of exposures exposures at or or near nearthe theLake L~ke Superior Superior shore. Hany of these shore. these units can ca,n he be traced traced for for aDoconsiderable considerable distance distance inland, but interruntions and structural structural corwlicatipns complicatiens by by intrusive intrusive bodies bodies inland, buU nterruntions and as well lacial denosits as \·rell -as as ;o;lacial denosi tsprevent prevent the thereconstruction reconstructionof' of aacomplete, complete, conconp • tinuous sequence. ofJoclear tinuous sequenc cleartrend trendofofconnositional compositionalchange chanF':e is isevident evidentfrom from base to top; at the base to top; in in fact, fact,although althou~hthe themost r'lost ferrora-'nesian ferro~arrnesinn lavas lavas occur occur at the base, flows, in in the Tofte—Lutsen area,are areentirely entirely olivine olivine ~ase, the the unnermost u:!Jnermost flmrs, Tofte-Lutsen area, oasalts. It basa,lts. It should 3hould be be kept kent in in rind r;ind also also that that aamajor ma,jor stratigraphic stratigraphic break break. mayoccur occurbeheween the Grand GrandPortap-e Portagelava lavasection section (sho'ing f:lay t"teen the (shO\.,ing reversed reversed magnetic magnetic polo.ri ty) and and the llig-her strnta. polarity) the lhgher strata. qir Table lists the To.ble 22 lists the informal informal stratigraphic strntif.rcmhic units unitsnroposed proposed for for the the northeast limb liMb (Torte (Tofte to toGrand Gr8.nd Portage) Porta,g;e) forth ~JorthShore ;3horeVolcanic Volcanic Group, Group, with "lith estimated thicknesses thicknesses and and ~eneral characters,and and Table Table 33 their estimated general lithic lithic characters, Ltivessimilar sinlar data p:ives data for forthe thesouthwest southwest limb. limb. 'I'his tabledepends depends largely largely This latter latter table on the work (1038) and and Grogan Grogan(1940), (iqito), penclin.Q; pending restudy. restudy. on the "lork of of Sandberrr Sandberr:: (1°38) �—82— -82- Table 22 Stratigraphy of of Northeast Limb (Tofte-Grand (Tofte-Grand Portage) Portage) North Shore Volcanic Group (Exclusive of interflow sediments) (Exclusive of sediments) Approx. Approx • ..IhiCkness(ft. ThigkneaL&Q) Lithostratigraphic Lithostratigraphic unit unit Lithic character character Lutsen basalts divine basalts, olivine basalts. olivine olivine tholeiites tholeiites 160 Terrace Point basalt flow flow thomsonite—bearing ophitic ophitic basalt thomsonite-bearing 310 Good Harbor Bay andesites brown, porphyritic porphyritic andesite, brown. trachyandesite 360 Breakwater trachybasalt flow flow brown, brown, columnar, columnar,granular granular trachybasalt 500 Narais rhyolite Grand Marais rhyolite flow flow pink, red, gray pink, gray porphyritic porphyritic rhyolite 600 Croftville basalts various fine-grained fine—grained basalts Devil Track felsites aphyric and porphyritic rholite rholite fJows flows Red cliff basalts basalts amygdaloidal, amygdaloidal, ophitic olivine basalts 1300 Kimball Creek felsite pink to to tan, tan, porphyritic porphyritic felsite felsite 1800 Marr Island Island lavas tholeiitic basalt, basalt, intermediate, intermediate, mixed tholeiitlc felsic felsic lavas 1000 Brule River basalts granular-diabasic granular—diabasic basalts 3500 Brule River fhyolite fhyolite flow pink to to gray porphyritic porphyritic rhyolite rhyolite (est.) 4000 (est.) Havland lavas Hovland lavas mixed porphyritic porphyritic basalt, basalt, trachybasalt, trachybasalt, rhyolite 200 Red Red Rock rhyolite flow flow red. red, porphyritic porphyritic rhyolite 260 Deronda Bay andesite andesite flow flow gray-brown, aphyric aphyric andesite andesite gray—brown, Grand Portage basalts basalts mixed tholeiltic tholeiitic to to diabasic diabasic basalts basalts Top 'fop 1020 1020 1020 400—900 400-900 4500 Base �—83— -83- Table 33 Generalized Stratigraphy of Southwest Limb (Tofte—Nopeming) (Tofte-Nopeming) North Shore Volcanic Group Group (exclusive (exclusive of interflow sediments) Approx. TbLekness_'ft) Thickness (it) Lithostratigraphic Unit Lithic character Tp 4000 Schroeder basalts ainygdaloidal ophitic ophitic olivine olivine tholeiltes amygdaloidal tholeiites >300 > 300 Manitou trachybasalt flow flow red—brown granular trachybasalt to red-brown to basalt (more of of the the Schroeder basalts) (more > 280 > 280 > 3CC' > 3CO few 100's few — — mostly quartz tholeiites, other other basalts Palisade rhyolite rhyolite flow flow gray to pink, gray to pink, porphyritic rhyolite Baptism River lavas mixed lavas, mostly basalts basalts — Beaver Beaver Bay intrusive complex — basalts, one felsite mixed basalts, felsite River basalts basalts Gooseberry River 3200 — Bell Harbor lavas lavas -- —. LaFayette Bluff, Bluff, Silver Silver Creek Creek Cliff Cliff intrusions intrusions — — — 1025 fine—grained basalts Two Two Harbors fine-grained "melaphyres", "melaphyres", some quartz tholeiites 1615 Larsmont ophitic ophitic basalts basalts amygdaloidal ophitic basalts. amygdaloidal ophitic olivine divine basalts. — — Knife River River diabase intrusion — Knife — — — — — 4930 Sucker River basalts mixed basalts, basalts, mostly ophitic 4400 Lakewood basalts mixed basalts, mostly non—ophitic non-ophitic — 3600 3600 — mixed basalts, basalts, andesites, andesites, felsites felsites Lakeside lavas lavas — diabase sill sill — Endion diabase — Endion — Leif Erickson Park lavas lavas 2560 — Lester River diabase diabase sill sill — Lester — Duluth Complex — Duluth — 2300 Nope'iuingbasalts basalts Nopeming Base Puckwunge Sandstone Sandstone Puckwunge — — mixed basalts, basalts, andesites andesites — porphyri tic meLbasalts, melc.basal ts, diabasic diabasic porphyritic basalts basalts �_____ —84--84- References Beck, M. 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Survey Survey Bull. Bull. 39, 39, 163 163 p. p. County, Minn.: Minn. Hanson, C. G. N., N., and and Maihotra, Malhotra, R., R., 1970, 1970, K—Ar K-Ar ages ages of of mafic mafic dikes dikes in in northeastern northeastern Hanson, (abs.): Program, Program, 16th Ann. lnst. on Lake Minnesota (abs.): Ann. Inst. Lake Superior Geology, Geology, Thunder Thunder Bay, Bay, Ontario, p. p. 19. 19. Johnson, C. C. H., and and Foster, Foster, R. R. L., L., 1964, 1964, Contaminated Contaminated Precambrian Precambrian ash—flow ash-flow cuff, tuff, Johnson, Cascade River, River, Minnesota Minnesota (abs.): (abs.): Geol. Geol. Soc. Soc. Amer. Amer. Special Special Paper Paper 82, 82, p. p. 102. 102. Palmer, Palmer, H. H. C., C., 1970, 1970, Paleomagnetism and and correlation correlation of of some some Middle Middle Keweenawan Keweenawan rocks, Lake Lake Superior: 6, p. rocks, Superior: Can. Can. Jour. Jour. Earth Earth Sci., Sci., v. v. 7, 7, No. No.6, p. 1410—1436. 1410-1436. across Keweenawan lavas at Duluth, Minnesota: Sandberg, A. A. E., E., 1938, Section across Minnesota: Geol. Soc. Geol. Soc. Amer. Amer. Bull., Bull., v. v. 49, 49, p. p. 795—830. 795-830. >i. 1949, The The geology geology of the Schwartz, G. G. 1'1., 1949, the Duluth metropolitan area: area: Mfnn. Hinn. Geol. Survey Survey Bull. Bull. 33, 33, 136 136 p. p. Geol. �—85— -85- page 22 Silver, L. L. T., T., and and Green, Green, J. J. C., C., 1963, Silver, 1963, Zircon ages for for Middle Keweenawan rocks rocks of the Amer. Geophys. of the Lake Superior Region (abs.): (abs.): Amer. Geophys. Union Trans., Trans •• v. v. 44, 44, p. 107. p. 107. Stoiber, R. S., 1959, 1959, Amygdule Amygdule mineral mineral zoning in the Stoiber, R. E., E.• and and Davidson, Davidson, E. E. S., Portage Lake lava series, series, Michigan copper district: district: Econ. Econ. Geol. Geol. v. v. 54, 54, p. 1250-1277. p. 1250—1277. Walker, G. G. P. P. L., 1960, 1960, Zeolite zones and dike distribution in relation to the structure basalts of eastern Iceland: structure of the basalts Iceland: Jour. Jour. Geology, v. 68, 68, p. p. 515—528 515-528 1964, Geological investigations in eastern Iceland: Iceland: Bull. Bull. Voic., Vole., v. 27, 27, — - - , 1964, p. 351-363. p. 351—363. �—86— -86- Field Trip Trip A A Field The North North Shore Shore Volcanic Volcanic Group Group Leader: Leader: John C. C. Green Green University of Minnesota, ~finnesota, Duluth are intended intended to give aa broad broad picture picture of of The stops stops described below are to give the the chemical, chemical, petrographic, and and structural varieties varieties of of lavas lavas of of the the Group, Group, some representative exposures of of the the minor minor intrusions intrusions that that cut cut the the flows, flows~ and the general structural characteristics characteristics of of these these Upper Upper Precambrian Precambrian racks. rocks. The area northeast of of Silver Silver Bay, Bay~ where where Green Green has has done done most most of of his his work, work, is is stressed. The trip excludes the the Duluth Complex, Complex, aspects aspects of of which which have have been been or are covered elsewhere (GSA Guidebook, ILSG 1968 Guidebook, Guidebook, and Field Field (GSA 1956 Guidebook, Trip BB of this program). of this program). Many more stops are listed below than will be possible to examinein but they included for examine in a one—day one-day trip, trip, but they are included for the benefit of those those who can can visit or or revisit revisit the the area area at at aa later later time. time. The U.S.G.S U.S.'G.S 7 1/2 minute quadrangle name nameisis given given for for each The stops stops which 7 1/2 minute quadrangle each stop. The which are planned as as a minimal frameworkfor forField Field Trip Trip A are designated planned minimal framework A are designated with with an an asterisk after are listed listed for asterisk afterthe thenumber. number. Mileages Mileages are fordistances distancesbetween between easily identifiable along USUSHighway for easily identifiablepoints points along Highway 61 61 (not (not cumulative cumulative mileage mileage for wholetrip)~ trip), for thethe U.S.A.fCanada whole for travel traveleither eithersouthwest southwest (starting (startingatat u.S.A./Canada or northeast Midway border—- Pigeon River: left—hand left-hand column) column) or northeast atatthe the ~fidwayRoad, Road, border (St. Louis Louis Co. Co. 13), 13),Nopeming, Nopeming,WESt west of of Duluth: Duluth:right—hand right-hand column). column). Mileages are in for side trips tripsoff offHwy Hwy 61 in parentheses parentheses or or not not given. given. All All stops stops are are for side 61 are shown on 1. Descriptions between stops stops are are written written for for southwestward southwestward shown on Fig. Fig. 1. The total total distance travel. The distancecovered covered isisapproximately approximately160 160 miles mileseach eachway. way. travel. stops volcanic volcanic structures are well well preserved. preserved. Visitors Visitors are are At At several several stops structures are destroying them, urged to refrain refrainfrom from loosening, loosening~removing removing or otherwise otherwise them~ urged since they they constitute irreplaceable evidence for for flow flow direction, direction, etc., etc., constitute irreplaceable since and valuable teaching students and teachingfeatures featuresfor for local local students and future future visitors. visitors. and are are valuable GoingGoing SW SW NE 7.4 -0:0 7.4 0.0 3.7 3.7 3.7 Minnesota—Ontario (Pigeon Start of Trip River, Minnesota-Ontario (Pigeon Point, Point, Trip A A -— Pigeon River, Travel SW along flat post—glacial lake bed, Minn. quad.). SW along flat post-glacial bed, — Mich. quad.). Minn. then rise rise along along shoulder shoulder of ofa alarge large NE-trending dike then NE—trending dike of of the Several road Keweenawan road cuts cuts ininMiddle MiddlePrecambrian Precambrian IceweenawanLogan LoganIntrusions. Intrusions. Several Excellent views Rove Formation shales small branch dikes. Excellent views cut by small branch dikes. Rove Formation shales Pigeon from parking rest rest areas areastotothethe Wauswaugoning Bay, Bay, Pigeon easteast overover Wauswaugoning from parking (Rove Fm. Point (thick (thickcomplex complex Keweenawan Keweenawan sill)~ Susy Islands (Rove Fm. and and sill), Susy flo's), Hat Lower Royale(Keweenawan (Keweenawan flows), Hat Point Point Lower Keweenawan Keweenawanflows), flows), Isle Isle Royale with Mount Mount Josephine (Logan dike). Josephine (Logan At Stop 1. Logan Formation (Grand (Grand Portage Portage quad.) quad.) At Logandik~ dike and and Rove Roc Faauction Stop 1. the top of the the rise riseisisa adeep deepcut cuttrirough through the the thick thickKeweenawan Keweenawan the top Farther oint. diabase dike that forms Mt. Josephine and Hat Point. Farther forms Mt. Josephine and flat diabase dike that the are good cuts in the Rove down the highway the southwest are good cuts in the Rove highway to down the Formation which is here dominated by graywacke. which is here dominr4lc-J by graywacke. Formation �—87— -87- Going SW Going NE (At the the base base of of the the slope slope an an interesting interesting detour detour can can be be (At to Grand Grand Portage Chippewa village and bay and made to to the the SE to SE Grand Portage National National Monument. Monument. The base of the Upper Precambrian sequence forms forms Grand Portage Island. Island. Continue out the west end of the the village to to Highway Highway 61). 61). 7.4 7.4 0.0 0.0 14.8 basalts, Grand Portage (Grand Stop 2.* Basal Lower Keweenawan basalts, (Grand At the top of the next rise (at the Junction Portage quad.). the top the rise (at the Junction Portage quad.). of Cook Co. Co. 17) 17) are are low cuts exposing basalts near or at of at the the These basalts base of the Keweenawan reversed reversed polarity polarity sequence. sequence. have aa somewhat somewhat diabasic texture and have been strongly though have though not not completely retrograded to prehnite—pumpellyite prehnite-pumpe11yite facies facies minerals. Amygdules contain weathered agate, Amygdu1es agate, prehnite, and and epidote. epidote. The basal Upper Uppe~ Precambrian sandstone sandstone (Puckwunge) (Puckwunge) underlies underlies the the gentle slope to the the north but is is not exposed exposed at at the the highway. highway. It It can be seen by bushwhacking about about 1/4 1/4 mile to to the the NNW. NNW. It is is aa clean-looking, somewhat feldspathic feldspathic quartz sandstone, sandstone, in in marked marked conconclean—looking,somewhat trast to low sandstones to the the red, red, immature, immature, volcanic volcanic interf interf10w sandstones above. above. The anC all the is underlain lowland beyond beyond is underlainby bythe theRove RoveFm. Pm.,, and the ridges ridges are are held up held up by by large large Logan Logan dikes. 3.0 11.9 Stop Stop 3. 3. Tholeiitic basalt and and porphyry porphyry dike dike (Grand (Grand Portage Portage quad.). quad.). unmaintained little Walk or drive off off Highway Highway 61 61 on on an an inconspicuous, inconspicuous,unrnaintained branch on the lake side to to an an old cabin cabin site site at at aa small small cove cove (1/8 (1/8 mile). On RR (SW) (SW) is the the basal, massive portion portion of of aa fine—grained fine-grained the Lower Keweenawan Grand Grand Portage Portage lavas. lavas. On tholeiitic basalt of the the the L is a thick, thick, compound dike dike of of porphyritic porphyritic trachybasalt trachybasalt that that trends E A large swarm of similar dikes is E into into lake. lake. A is present present in in this studied. They are are unusually unusually rich rich ji in Fe and K. K. this area and is being studied. 3.7 3.7 11.1 Stop 4. 4. Stop Red Rock rhyolite rhyolite (Mineral Center Center quad.). quad.). At Deronda to the the SE SE to to the the breccia—rubble breccia-rubble base base of of Bay the beach leads out to feet) porphyritic porphyritic rhyolite rhyolite flow flow which which is is the the aa thick (over (over 600 feet) uppermost flow found to to show show magnetic reversal reversal by by Books Books (1968). (196 8 ). More scenic exposure can can be seen seen by climbing climbing up up the the ridge ridge and and walking out to to the the point point on on the the open open lake. lake. Less scenic but more accessible exposure is in in a road road cut cut 1/2 1/2 mile mile beyond. beyond. 4.6 10.2 Stop 5. 5. Reservation River Diabase and and abandoned abandoned beach beach ridges. ridges. (Mineral Center quad.) quad.) At the the top top of the the next rise rise is the the eastern edge of the extensive Reservation River River diabase diabase complex: complex: one characteristic phase phase is is exposed exposed here here that that shows shows faint faint banding banding on on sonic surfaces. Lcrge some Large gravel the lowland lowland to to.the northeast, gravel pits pits in n the the northeast, mined out for the the new highway, highway, were large abandoned beaches of late postglacial Lake Lake Superior. Superior. Excellent Excellent smaller, smaller, later ridges can still still be be seen seen on on aa little little track that that goes goes to to the the lake lake shore shore can the base base of of the from the the slope. slope. �—88— -88- Going Going Going Going SW NE SW 9.0 9.0 5.8 10.0 il.8 14.8 --00 0.0 4.0 ----". 0.0 4.8 0r 0.0 0.0 10.6 10.6 Cross Reservation River and out of Grand Portage Indian Indian Slope is is at at contact contact of of Reservation River diabase Reservation. Slope complex and lavas (a (a rhyolite rhyolite here). here). 6.* Hovland porphyry Stop 6.* porphyry lavas. lavas. (Hoviand (Hovland quad.) Opposite aa on the lake side are exposures of a remarkable house the remarkable porphyritic trachyandesite lava flow with platy plagioclase phenocrysts up to 10 cm em across. across. By following following the the low scarp to to the the NE behind aa house (private (private property) two two flows flows can can be be ueen, ~een, the the top top of of the the one being vesicular and showing a slightly uneven crust. lower one crust. These are near the the base of of the the Middle Keweenawan Keweenawan (normal (normal polarity) polarity) lava sequence, sequence, and and are are assigned assigned to to the the Hovland Hovland lavas. lavas. They are are here cut by a large large dike, dike, at at least 22 miles long, long, of brown elinopyroxenephenocrysts, phenocrysts, that that also trachyandesite with with small. small.elinopyroxene crops out across across the the road. road. Highway descends to to old old lake—bed lake-bed flat; flat; then, then, past past Big Big Bay, Bay, rises onto higher higher ground ground of of Hovland Hovland Diabase Diabase complex. complex. Cross Flute Reed River, River, pass pass through village of Hovland at Chicago Bay, Bay, and and up onto aa large large sill—like sill-like body body of of syenogabbro. syenogabbro. Many road road cuts; cuts; some some show good foliation of of plagioclases, plagioclases, dipping dipping gently gently S. S. Syenogabbro, basalt pillow-breccia, pillow—breccia, and rhyolite at Brule Stop 7. 7. Syenogabbro, Brule River (Marr River (Marr Island quad.). Opposite Naniboujou Lodge, Lodge, park in in lot of Judge Hagney tmgney State State Park. Park. Walk up trail, trail, cross rivet river on footbridge, footbridge, Take care and follow fisherman's W bank. bank. Take care -— and follow fisherman's trail and bushwhack up W steep and unstable slope in in places. places. At footbridge footbridge is is medium—grained, medium-grained, foliated syenogabbro of of "Hovland "Hovland diabase diabase complex." complex." This is cut by basalt dike, dike, then gives way to a rather coarse—grained coarse-grained basalt aa later basalt lava with chlorite chloritescraps scrapsand andamygdules. mnygdules. Soon overlain by by Soonthis this is is overlain basaltic—scoriaceous tuff—breccia. basaltic-scoriaceous tuff-breccia. After a short short gap gap in in exposure, exposure, steep bank resumes resumes which is made of basalt pillow—breccia, steep pillow-breccia, with altered volcaniclastic matrix. This is is one of the the few few places places where evidence for evidence for underwater extrusion can can be seen seen in in the the North Shore Shore Volcanic Group (others (others are are on on Grand Grand Portage Portage Island Island and and WWof of Duluth Duluth in the Lower Lmyer Keweenawan). Keweenawan). Farther upstream this this can can be be seen seen to to overlie the altered, altered,flow—banded flow-banded and rled top top of aa very very large porphyricic porphyritic and styi swirled rhyolite the Bride Brule has has cut cut aa deep deep gorge gorge above. above. rhyolite flow through which the Return by fisherman's trail tr~il at at top top of of bank. bank. After crossing After crossing the the Brule (Arrowhead) (Arrowhead) River, River, the the highway rises rises over and cuts cuts through through three three hasalts basalts of of the the Brule Brule River River group, group, then then crosses a porphyritic trachyandesite trachyandesite or or intermediate intermediate quartz quartz latite latite the }larr Island lavas lavas at at Paradise Paradise Beach. Beach. AA few few more low low cuts cuts of of of the Marr Island this mixed group are this are passed passed in in next next 33 miles. miles. 3.8 3.8 5.8 Stop 3•x Stop 8.~ Porphyritic ~arr Island Islan~ Porphyritic intermediate intermediate quartz cuartz latite latite of p Marr lavas one one mile mile past past Cook Co. lavas Co. 14 (Kadunce (Kadunce Creek quad.) quad.) Two large road cuts cuts on N. thick, intermediate intermediate quartz latite latite road N. side of a thick, K 0) plagioclase, ferroaugite, and rare lava (62% (62% SiO Si0 , 4.1% K 0)with with plagioclase, ferroaugite, and rare 2 2 ex-olivine ana magnetie magnetitephenocrysts. phenocrysts. Contacts not exposed. exposed. ex—olivine an , �-89—89-Going SW Going NE 1 1/2 miles to the the west at Kadunce Creek (Kodonce (Kodonce River) River) miles to State Park a thick porphyritic felsite is exposed, especially especial~y in in a deep dl~ep and narrow canyon that begins about 1/8 mile upstream upstream from highway highway -— this this is part of the from the Kimball Kimball Creek Creek felsite felsite group, group, also exposed in Kimball and Cliff creeks farther also farther west. west. Excellent wave—cut cliffs abandoned wave-cut cliffs of of Nipissing Nipissing stage. stage. 7.3 3.2 3.2 Stop 9. 9. Olivine basalts of of Red Red Cliff Cliff series series (Kadunce (Kadunce Creek Creek quad.). quad.). Just past large gravel pit and and creek creek gully, gully, highway highway rises rises onto onto aa series flows totalling totalling between between series of of 5 or 6 ophitic olivine basalt flows 400 and 900 feet feet in thickness. thickness. Amygdules contain contain saponite,laumontite, saponite,laumontite, calcite, quartz, calcite, quartz, and and agate. agate. Plagioclase phenocrysts have floated floated to to top 0.5% K20. K 0. top in some, some, sunk to to bottom bottom in in others. others. 47% Si02 Si0 , 0.5% 2 2 Past Durfee Creek (near (near top of Red Cliff basalts) highway (and (and cliff) pass onto Devil Devil Track Track felsite felsite group, group, here here composed composed Nipissing cliff) of two thick flows. of flows. 9.6 1.0 Stop 10.* Felsite of Devil Track sEries, series, at promontory of of abandoned abandoned Nipissing wave—cut wave-cut cliff. cliff. N N side of highway, 0.85 0.85 miles west of of Pink, nonnon— or weakly porphyritic Durfee Creek (Kadunce (Kadunce Creek Creek quad.). quad.). Pink, rhyolite K20) slabby jointing rhyolite or quartz latite (72% (72% SiO Si0 2 , 5.5% K 0) with with slabby jointing 2 Bushwhack?ng along old cliff to E and faint flow—banding. flow-banding. Bushwhacking E for 1/4 1/4 mile one eventually passes down down into into vesicular, vesicular, locally locally spherulitic spherulitic and flow banded top top of a porphyritic flow flow of of similar similar composition. composition. and flow These two two flows flows total total about about 1020 1020 feet feet in in thickness. thickness. Five Mile (Guano) Rock, Rock, aa mile mile out out in in Lake Lake Superior, Superior, is ~uano) is made of diabase. , 10.6 0.0 0.0 3.7 Track~. upstream Cross Devil Track River. This cuts a deep gorge just upstream felsite flow. flow. Continue on Hwy 61 into Grand Marais, or or in the upper felsite alternatively turn turn off just before rise on small side road alternatively road (Cook (Cook Co. Co. 87) Stop 11. 11. 87) toward toward lake lake to to Croftville settlement and optional Stop (off Hwy 61) 61) (off (1.3) _~~ (0.0) (0.0) (0.45) Stop 11. Spherulitic hasal phase, phase, Grand Marais rhyolite, Croftville Croftville Stop 11. (Grand quad.) Drive about 1.1 mile along Nipissing terrace terrace (Grand Marais Marais quad.) over (about 0.45 mi. from WWend this road). road). over Croftville Croftville basalts basalts (about mi. from end of this Private Property. ?roperty. Ask permission at at the the house hous~ in in birches birches on on lake lake side, beach-back. Slabby, Slabby, spherulitic spherulitic side, exwline examine outcrops outcrops at at modern modem beach—back. red rhyolite rhyolite is is exposed here (73.4% (73.4% SiO SiO , 4.65% K20) K20) that that contains contains red hedenbergie, ex—fayalite and magnetite andesine-oligoclase and rare hedenbergite, ex-fayalite and magnetite andesine—oligoclase and rare Nearby is cross—bedded, calcite—cemented interflow sand. phenocrysts. cross-bedded, calcite-cemented interflow sand. phenocrysts. Strata have been steeply tilted tilted by diabase diabase intrusions. intrusions. Continue on on road until until it it re—joins re-joins Hwy Hwy 61. 61. Croftville road , (0.45) (0.0) (0.0) (2.1) (2.1) Continue SW SW to to Grand Grand Marais. Marais. (off Hwy H'YY 61) 61) Stop 12. 12. Breakwater trachybasalt (Good (Good Harbor Bay Bay quad.). quad.). Drive to E end of Grand Marais harbor. harbor. Tombolo to Coast Coast Guard Guard Station at E here is is made by gravel bar connecting mainland to to resistant resistant island and and ledges ledges of of aa massive, massive, locally locally columnar-jointed, columnar—jointed, porphyritic porphyritic trachybasalt or basalt with small phenocrysts of of plagioclase, plagioclase, augite, augite, trachybasalt and rare olivine. olivine. It 360 feet feet thick. thick. It It is not known It is is about 360 this is is a big flow certain whether this flow or sill; to to the the west is is has has for certain aa sharp, sharp, chilled basal contact contact against against felsite felsite but but its its top top is covered. covered. It It becomes amydgaloidal and zeolitized zeolitized near near contact is �Going SW Going —90— -90- NE its to be be aa flow. flow. As can be seen seen from from its top and is assumed to point, it it forms forms one of the the major major strike—ridges strike-ridges of of vantage point, "Sawtooth Range" Range" to to the the west (as (as does the the big "thomsonite "thomsonite sta~ting Good Harbor Harbor Bay). Bay). The harbor at Grand Marais Harais starting at Good probably eroded from from rhyolite. rhyolite. 3.7 0.0 0.0 9.2 this this the the flm.," flow" is is lint Trail Trail Highway 61 passes corner corner of of harbor, harbor, near near start start of of Gunf Gunflint (Cook Co. Co. 12). (Cook Then highway rises rises to W W past a good norphyritic porphyritic rhyolite rhyolite cut cut (Breakwater trachybasa1t trachybasalt cuesta cuesta ahead), ahead), then then onto higher level (Breakwater down across the the Breakwater Breakwater trachybasalt trachybasa1t and and across across Fall Fall River River back down (Rosebush Creek). About 1 mile past this this creek, low low road road cuts cuts start start in two two thick porphyritic trachyandesite trachyandesite to to andesite andesite flows flows (55% (55% Si02, 5i0 , 2 phenocrysts and and 2.7% K K 0) 0) with small plagioclase and clinopyroxene phenocrysts 2 ahead is vesicular-rubble is held up by Terrace Point vesicuar—rubble tops. Big cuesta ahead Continue across thomsonite-bearing basalt basalt flow. flow. Continue across Cut Cut face (Good (Good thomsonite—bearing Harbor) Creek. Creek. 5.2 3.9 Stop 13.* Thomsonite—bearing low sediments (Good Stop Thomsonite-bearing basalt, basalt, interf interflow (Good Bay quad.). quad.). In this this large road cut one of the major cliff Harbor Bay formers (130') section of formers of of the the "Sawtooth "Sawtooth Range" Range" overlies a thick (130') interf low sediments. The Terrace Point basalt is dominantly a interflow sediments. The Point massive, massive, fine—grained, fine-grained, ophitic basalt that that characteristically characteristically contains contains thomsonite its lengthy exposure (including (including in thomsonite in amygdu1es, amygdules, but hut in its this cut) cut) several several flow units units of of varying character show complex this relations with the major, massive relations massive part part of of the the flow. flow. The interfiow interflow sediment Is is here mainly thin—bedded thin-bedded siltstone siltstone shale, but by walking up up the the bed of of Cutface Cut face Creek Creek at at and silty shale, the bottom bottom of of this hill one passes the this hill passes outcrops of the the basal contact contact the amygdaloidal—scoriaceous amygdaloidal-scoriaceous top top of of of the sediments resting on the an flow and wellan andesite andesite flow and eventually reaches large banks cut into well— bedded sandstone showing abundant ripple ripple marks. marks. 9.2 — 0.0 0.0 16.9 0.5 0 5 16.4 16 4 cuts of the the complex complex upper upper parts parts of of the the Highway 61 passes low cuts Terrace Point flow complex, complex, with big cuesta cuesta on this this flow flow visible visible ahead, ahead, then then at at jct. jct. of of Cook Cook Co. Co. 7 passes into coarse—grained coarse-grained olivine olivine passes into basalt of the the Lutsen Lutsen basalt basalt series. series. Cross Cross Cascade River in State Park. Park. Trail up W W side provides access to to good good river river outcrops outcrops of of Terrace Point thomsonite thomsonite basalt, basalt, the the underlying underlying sandstones, sandstones, and and several andesite flows flows of of the the Good Good Harbor Harbor Bay Bay series. series. Drive past Cascade Lodge. Lodge. Stop 14* Cascade (Deer Cascade olivine olivine basalt basalt of of Lutsen basalt basalt series (Deer Yard Lake quad.). 0.5 miles W. W. of of Cascade Cascade River. River. Shore outcrops of aa thick (100 more), relatively of (100 feet feet or more), relatively coarse—grained coarse-grained olivine basalt this Cascade—Lutsen Cascade-Lutsen area. area. basalt of a distinctive group in this Segregation cylinders cylinders up up to to 6" 6" or so so in Segregation in diameter and segregation lenses lenses or sills can can be be seen seen within within this this flow. flow. Highway continues continues on on long long straight straight stretch roughly parallel parallel to strike of Lutsen basalts, topmost series of the the North North Shore Shore to basalts, topmost Volcanic Group. Group. Pass Pass through Lutsen village (big (big ridges rid?,es to to W held up W up by Leveaux trachybasalt trachybasa1t sill), sill), to to Poplar River. Rive~, �—91— -91- Going SN SW 9.3 Going NE ---7.1 Stop 15. 15. Poflyritic Porphyritic olivine basalts of Lutsen series series (Lutsen (Lutsen Poplar River. River. Watch Hatch your step step -- dangerous. Private land. land. quad.), Poplar Several flows flows of a distinctive ophitic olivine basalt characterized characterized by abundant small small(1—3 (1-3nun) mm) blocky bytownite phenocrysts are are exposed exposed by the Poplar from Poplar River River at at Lutsen Lutsen Resort, Resort, up up through through an an frcrnthe the mouth mouth of the canyon to to the the highway bridge bridge and upstream to left bend impassable canyon (1/10 highway). Take fisherman's fisherman's trail trail on on WWside. side. This (1/10 mile nile from highway). flow Ilprimitive" composition composition (lowest (lowest K, K, highest highest Mg) Mg) ?low type type has has the the most most "primitive' Si02, 0.l2I K20). L bend in river , 0.12% K20). At of the North Shore lavas (1+7% (47% Si0 2 it overlies breccia-rubble breccia—rubble top of aa basaltic andesite andesite flow; flow; red red sand sand has been washed into all the interstices between the lava blocks, has lava a typical situation. situation. 12.3 4.6 Leveaux —- Onion HtIl=Stop 16. Leveaux_ porphyry !411. Eill (Tofte Mtn. trachybasalt trachlbasalt porphyry SWof of Poplar Poplar R.. at slight L quad. ) . 2.5 mi. R•..at L bend cross cross Rollins Rollins quad.). ml. SH Creek and irnediately immediately turn up U. U. S. S. Forest Service gravel road road (No. 336). Continue on it it as as it contours back to SW, then then cuts cuts up up (No. 336). OnionRiver Mvergap gapininbig big ridge ridge held held up up by by aa big big trachybasalt into Onion into porphyry sill. sill. This sill forms forms Leveaux Mtn., the high ridge ridge with a fire tower a fire tower on on it ittotothe theSW, SW, and and comes comes out to the lake lake shore shore to to form the islands at Taccnite Harbor SN of Tofte. Its contacts at Taconite Harbor SH .of Tofte. contacts are are not exposed but it it crosscuts crosscuts the the lavas. lavas. Park as near as as possible possible to the S S corner corner of of the hill hill on on the the NE NE side side of of the the gap, gap, and and bushwKack bush~ack a short distance N n to to· the the steeper, steeper, rocky rocky rise. rise. Here the lower lower part exposed fine—grained, pigeonite-augite pigeonite—augite trachytrachy— of the sill sillis is exposed—- a fine-grained, to trachyandesite. trachyandesite. Farther up up the Glope slope aa bit bit abundant abundant large large basalt to (1 blockylabradorite labradorite phenocrysts phenocrystsappearroruptly; appeartruptly; they appear to (1 cm) cm) blocky to floated. This porphyritic phase forms have floated. forms the upper part of of the the throughoutits its extent. extent. sill throughout 16.9 2.... 0.0 0.0 ---12.1 Continue SW svr past Tofte. pastSawbill SawbillTrail Trail (Cook (CookCo. Co.2)2)atat village village of Tofte. Town Town park park on on lake lake shore 0.3 0.3mi. mi.SW SW of ofEdgewater Edgewater Motel Motel has has good good exposures of of thin-bedded thin—beddedophitic ophiticolivine olivine basalts. basalts. DO DO NOT exposures NOT DESTROY DESTROY FEATURES. These the top top of the section section of the orth NorthShore Shore FEATI.ffiES. Theselie lie at at the Volcanic Group. 10.1+ 10.4 anorthosite in diabase (Tofte Stop 17. 17. Carlton Peak ?lloythosite (Tofte quad.) 1.7 1.7 mi. mi. jet., opposite opposite large large Superior Superior National National Forest Forest SW of Sawbill Trail jct., Sign, Sign, turn up road of Erie Mining Co. Co. to large quarry in in side side of of Carlton Peak, anorthosite xenoliths xenoliths in in Peak, which is held up by massive anorthosite intrusion. Private Property. Property. The The complex complex rela.tions relations a gabbroic intrusion. between the the anorthosite anorthosite and and various various phases phases of of olivine olivine gabbro gabbro are are well well 1.7 exposed. 2.5 9.6 Stop 18. Thin—bedded ophitic olivine tholeiites of Thin-bedded of Schroeder Schroeder 18. basalts, Temperance Temperance River River (Tofte (Tofte quad.). quad.). Park at State Park lots, lots, walk down down trail to bridge near near river river mouth. mouth. Note excellent erosional Several thin flows flows or flow units, with ropy ropy surfaces, surfaces, pipe pipe potholes. anygdules amygdules and lensing lensing shape shape are are well well exposed exposed here. here. If more time is is available, walk up NE side of river above available, above highway to to the the main main gorge gorge where the river river has has cut cut aa very very deep deep and and narrow narrow slot slot with with larger larger into thicker olivine olivine basalts. basalts. Warning: people have have been been potholes into Warning people killed trying trying to to jump jump across. across. Large joint joint columns colUmns visible visible on on trail trail killed cylinders are are present in in thicker thicker flows. flows. and overlooks, overlooks, and vesicle cylinders �—92— -92- Going SW SH Going 3.8 3.8 NE 8.3 8.3 9.14 2.7 Drive SW SI'! through Schroeder and and Taconite Taconite Harbor Harbor (power (power pellet shipping facility of plant and taconite pellet shipping facility of Erie Erie fining Mining Co.) Co.) with occasional occasional low low cuts cuts of of ariygdaloidal amygdaloidal or ophitic olivine olivine tholeiite. tholeiite. Stop 19*. 19*. Thin—bedded Thin-bedded ophitic ophitic olivine olivine tholeiite tholeiite of of Schroeder Schroeder basalts basalts at Sugar Loaf Point (Little at (Little Marais Marais quad.). quad.). Private property. property. Drive down side road (just (just opposite gravel gravel road road from from uphill) uphill) at at Consolidated Consolidated Paper Co. storage and and handling handling facility. facility. Drive down to cove, cove, Co. pulpwood pupwood storage end ask ask permission permission to towalk walk onpoint opoint at and at office. office. Notice great old Walk around pine boom—logs to raft raft pulpwood pulpwood across cross lake. boom-logs used to lake. Halk Excellent exarrioles Sugarloaf Point clockwise clockwise from from end end of of beach. Excellent examples up) and thicker flows flmv units units (6" (6" and up) flo1>ls of ophitic "olivThe " olivine of thin flow tholeiites ,It with ropy ropy surfaces, surfaces, bent bent pipe pipe amyvdules, amye:dules, and and clastic clastic tholeiites," dikes dikes where sand was washed into into open open ;oints joints in in the the tops tops or of flows. flows. not remove or destroy structures! On On the the sides sides of Please do not destroy these thes~_Et~.~ures! the high high knob at the end can the can be seen seen vertical vertical tube—like tube-like concentrations concentrations arnydules ("vesicle of amygdules ("vesicle cylinders") cylinders") in in the massive Massive Imler lower nart tart of the topmost flow. flo",. 11.77 11. 0.14 0.4 12.1 0.0 0.0 11.0 Cross Cook/Lake Cook/Lake County County line. line. Ophitic olivine!-holeii:~s, tholeiites, Ma! !-S.?-chY.Easalt., tracybasalt, and Qphiti c_ olivine ~If~it0l.! strike—fault, Caribou River River (Little (Little ~larais arais quad.) strike-fault, Caribou quad.) Park Caribou Park at Caribou Falls State Park 1°t side of the the hip-;h,.,ray highway and "Talk walk ut Falls lot on the HH side up the (Between the the highway highway and Lake Lake is is private property including trail. (Between typical ophitic falls over typical ophitic olivine olivine basalts). basalts). In In the river riverand and aiocg alonr; the trail are a few outcrops the outcrops of the red red volcanic volcanic breccia breccia and and basalt basalt that underly the "Manitou "lvlanitou trachybasalt," then then at at aa LL bend bend is is the the NE— NEmost outcrop of most of the the trachybasalt. trachybasalt. lis ap]Jroaches the falls falls As the trail anproaches the river has the has cut through aa thick section section of of volcanic volcanic breccia, breccia, nut but aa large strike-fault intervenes between this and and the the typical typical ophitic ophitic large strike—fault olivine thoeiites (flio2=5-.7%, oli vine tholeiites (Si02==45-47%, K the cli f f Torn tt:e :20=o.3_o.5z) 20"'0. 3-0.5%) that form over which the the river river fells. fa.lls. Several flovs, 10-30' each, Several flows, 10—30' each, are visible in the the cliff each with a massive lower part and in and an an amygdaloidal amygdaloidal and and slabbv-jointed top. slabby-jointed These nearly all allthe thelavas lavasbetween between Theseare are typical tynical of nearly 1:ittle arais Little Maraisand andLutsen, Lutsen, the uppermost sequence sequence of of tbe the North North Chore Shore the uppermost Volcanic Group. Group. Stop Stop 20. 20. cli' 2.2 8.8 8.8 Dri ve SW, 8\1, cross cross anitou ~ftanitouRiver, River,'.rhich lIhi ch has Drive has cut cut aa deep deep f!;orge aorge throup;h throu'h drift and olivine basalts (trail in State State Land Land accessible accessible drift (trail up up streaxn stream. in on SW S1:T side via via gravel gravel pit pit road), road). Commercialized has Cornniercializedgonre gorge dmmstrear'l downstrean has falls, sea arches. falls, Continue LW bend at at Little Little I·,farais Marais R. . SH almost to to I? H bend 14.5 4.5 6.5 6.5 Stop 21. 21. Manitou trachsasait (Little Stop !5~j.~.sm !-!_a~J1_x.:!?~a1.!-. (Littlei'larais Marais quad.). quad.). Turn 'I'urndo'.in down road at Ben Fenstad's Fenstad's Resort, Resort. Private ask permission Private nrqperty; property; ask for entry at for at office. office. Continue down to lakeshore, bearing bearinp. left left to to end of driveway dri vevay loop at at fishhouse. fishhouse. here here at B.t the the end end of of the the slit slin is is exposed the base of an 1arre larp,e flow flow of of granular granular trachvbasalt, trachybasalt, at at least least 300' rLles lonp" long, that forns ofth~SDreledges t1roreledges Croa 300' thick and 55 miles forms !'uch much of fro~ breakwater on, HE of M8ni this breaki-mter on, both SW G\l and and tIE tou FLyer. Pi vel". It contains contains Menitou Si022 and 2.3% about 52% 52;~ Si0 K2 (), and and has has labradorite. labradorite, augite, aup.;i te, and and 2.3 K20, and abundant ahundant KK feldspar feldspar and and altered rare olivine phenocrysts and pigeonite piGeoni te in in the the groundviass. groundmass. higher hip:,her in in the flow fIm, it it is is coarser— coarser- �—93— -93- Going SW Going SE HE grained, less less potassic and Its top is grained, and less less porphyritic. porph~ritic. Its is not exoosed. It overlies overlies aa sequence of interLedded eXDosed. It interbedded basalts and red red volcanic volcanic breccia breccia or or conglorierate. conglomerate. high ridge inland is held up by Continue Li ttle 'arais. ~1arais. High Continue S\J SW past Little a thick intrusive diabase sill containing a thick intrusive diabase containin~ some anorthosite blocks. blocks. 8.0 8.0 9.1 9.1 2.6 Stop 22.* .iartz tholeii tholejite—trachybasalt, Kennedy Landing 22. * QJ.artz te-trachybasalt, Kennedy (Finland quad.) quad.) Good cuts for for about about 1/3 mile through throu~h several several typical auartz quartz tholeiites tholeiites to to trachybasalts. trachybasalts. They show the the charcharacteristic fine-grained, fine—grained, aphyric anhyric texture, texture, oxidation lamellae, and acteristic and scoria-rubble feldspar scoria—rubble tops. They contain interstitial alkali feldspar and about about 51-53% 5l—53 5102 and Si02 and and up up to to 2% 2% K20. K20. Red sand, sand, locally cross— crossbedded, fills the interstices between fragments. fragments. Large knob knob bedded, fills is made of the thickest of of these flows. flows. overlooking the bay is 7.8 7.8 Stop 23. in ~y~nogllR..br~; syenoabbro; overturned Anorthosite in 23. ** An_,?rth,?sitE:. ove!:turned lavas l~vas (Illgen City quad.). quad.). After crossing crossing Kennedy Creek Creek come come to to deep deep vertical cut cut in an irregular discordant intrusion intrusion (part (part of of Beaver Beaver Bay complex) Day complex) of altered syenogabbro that contains contains aa great, great, massive massive of rather After examining this, walk block of rather pure pure anorthosite. anorthosite. After examining this, walk or drive SW drive SW downhill cut that sequence of of downhill to to lower cut that is is composed of a sequence several basaltic basaltic lavas lavas with an interflow sediment bed — several - all all of which which have been overturned, overturned, probably as as aa result result of of forceful forceful intrusion intrusion of nearby diabases. These basalts show show aa variety variety of of structures, structures, including at the NE end end some some including some some lobes lobes that that look like pillows and at red scoria,-rubble scoria—rubble that that is is characteristic of the top part of the red fine—grained tholeiites, tholeiites, basaltic andesites, fine-~rained andesites, and trachybasalts. trachybasalts. 11.0 42 0.0 0.0 0.0 It.9 ~ Continue to Ulgen lilgen City, City, ~ Lc•• •with Rte.ito Continue SW to Tith Minc. Minn. Rte. -.l to Ely. Ely. Just .Just to NE are cuts cuts in in quartz tholeiite flows, flows, to to SW SW cuts cuts in in altered rhvolite. rhyolite. 0.45 0.45 4.5 24.* Stop 21~. Palisade .!1~_a~ Head P.s>E1?-~)'Ti pohyritic Stop * ~~~isad~, tic:: rhyolite, rhyolite" Shovel Shovel Point Point (Illgen (Ingert City quad.3. quad.). 0.45 0.b5 mile SW SW of of Illgen Illgen City City jct., jet., or or 0.145 0.45 mile NE of Baptism River, River, search for NE for unmafled unmarked trail leading leading to to shore shore Here is at Shovel Point in at in Baptism Baptism 9. R. State State Park. Park. Here is well exposed the upper-middle upper—middle part of porphyritic rhyolite rhyolite the of the the thick thick (>300'? (>30d: porphyritic (quartz (quartz latite) latite) that that also also forms forms Palisade Palisade Head to to the the SW and the road cuts at at Tllgen III~en City. City. Take care on on clifftop. clifftop. View to SW over underlying lavas ("Baptism ( "Baptism basalts") basalts ") and and some some mafic mafic intrusive intrusive bodies, bodies, to Palisade Palisade Head. Head. Follow trail down dipslope to end end and and corner: view TIE toward overlying overlying quartz quartz tholeiite flows. NE corner: NE toward flows. Return on sa1Ie same trail trail _._----~ Drive Head (big (big hill hill with with Drive 811 SW across across Baptism !liver River to Palisade head radio beacon). 2.1 2.7 (Iliren joint (Tity quad.). quad.), Stop 25. 25. Palisade Drive up up Palisade Head Head rhvolite r1yaUiq. (Illgen City narrow, winding road--C,ju;t'" road (just past--Palisade past Palisade Creek) Creek) to to top top of of cliff cliff next to raOio careful — columns are radio beacon. beacon. ,9areful - joint colwnns are se-narating separating Excellent views from rest of of hill. hill. ~xcellent views to to .N, ~, NE, SE, SE, SW. SW. Ridges to �—94— -94- Goin,:?; GoinI SW Going NE "[IT, NE aie B,Te held up by intrusions intrusions of of Beaver Beaver Bay Bay complex. complex. Up Up N. lakeshore to NE is columnar—jointed columnar-jointed Shovel Point, Point, made made of of same same rhyolite flow, is smoke from Taconite Harbor flow, and far far beyond is plant and and Carlton Canton Peak power plant Peak anorthosite anorthosite knob knob at at Tofte. Tofte. To S across lake lake are are Apostle Apostle Islands Islands and Bayfield Peninsula, Wisc. across Wise. To SW is Reserve Mining Co. Co. taconite plant at at Silver Silver Bay Bay and and humpy humpy Palisades made of thick, por— topography of Beaver Beaver Bay Bay complex. complex. Palisades porrhyolite with quartz quartz and and feldspar feldspar phenocrysts, phenocrysts, flow— flowphyritic rhyolite banded at the base. Return to to highway. highway. 1.9 4.9 0.0 0.0 0.0 0.0 i1.8 14.8 0.4 l.3 14.3 0.14 at Silver Bay, 2.15 ml. mi. to traffic light light at Bay, site of Drive 2.75 Co. 's taconite plant where where about about 100,000 100,000 tons of ' Reserve Mining Co.'s rock from the eastern eastern Mesabi Mesabi Range Range are are processed per day. day. Stop 26. 26. Anorthosite in in diabase diabase of of Beaver Beaver Bay Bay complex, complex, Silver Silver (Silver Bay Bay 15' 15' quad.). quad.). Stop at road cut cut directly directly opposite opposite Bay (Silver the main building taconite plant (after building of of the the Reserve Reserve Mining Mining Co. Co. 's 's taconite (after Here several large blocks of anorthosite the' 2nd lights). anorthosite the traffic lights). 2nd are in the Beaver Beaver Bay Bay are included in diabase, a typical assemblage in complex. Large patches of of interstitital, interstitital, poikilitic poikilitic olivine olivine occur occur in anorthosite. No definite source source for for the the in some parts of the anorthosite. Small red red veins veins and and dikelets dikeletsofof"granoph~y'.(e" "granophe" anorthosite is is known. Small cut the diabase and and anorthosite. anorthosite. across Beaver Beaver River River to to Beaver Beaver Bay. Bay. Continue SW 2.8 miles across 3.2 3.2 11.6 Stop 27. St,up 27. Beaver Beaver Bay ferrogabbro and and Black Black_ Bay_ gabbro (names (names after y ferrogabbro Gebman) Gehman) of Beaver Bay Bay complex complex (Silver (Silver Bay Bay 15' 15' quad.). quad.), Drive or down to shore shore on on gravel gravel road road opposite opposite the the main main restaurant restaurant In tn walk down Beaver Beaver Bay. Bay. Walk E E through woods across little little point point to to shore shore ledges. These are well-foliated ferrogabbro of of the the Beaver Beaver Bay Bay well—foliated ferrogabbro Ferrogabbro, one one of of two similar similar plugs plugs in in this this area. area. On walking NE along the shore, the contact contact with an an enclosing enclosing ring—dike ring-dike of of Black Black Bay Bay Gabhro Gabbro is reached; reached; such rings rings surround both ferrogabbro is ferrogabbro plugs. plugs. It is rather It is inhomogeneous and locally contains very abundant apatite. inhomogeneous apatite. The The ophitic ophitic Beaver River Gabbro can can be seen farther shore below some some farther along the the shore cabins. Return to to highway. highway. - Continue SW through Beaver Bay complex; complex; most outcrop outcrop is of is of coarsely mottled, mottled, ophitic olivine gabbro ("Beaver ("Beaver River River Gabbrot' Gabbro" of of Gehman), Gehman), well well seen seen opposite opposite Kings's Kings's Landing 3 miles miles from from Landing Marina Marina 3 Beaver Beaver Bay. Bay. After 2.2 more miles road road branches to to Split Split Rock Rock Lighthous,buil on Lighthouse,built on anorthosite anorthosite in in diabase. diabase. At Day Hill Hill (parking (parking At Day and 1.0 mile beyond, is and trail), trail), 1.0 is last exposure of Beaver Bay Bay complex. Re—enter volcanics, continue 5.14 5.4 miles to to Gooseberry Gooseberry complex. Re-enter volcanics, continue Falls State Park. Park. 114.8 14.8 0.0 0.0 0.0 13.1 l3.i Stop 28. Stop 28. Smooth—surfaced Smooth-surfaced olivine olivine basalt, Gooseberry Falls Falls State basalt, Gooseberry State Park Park (Split Rock Point quad.). ~Split Rock P6int quad.). Below highway bridge are good exposures, highway bridge are good exposures, in. and between falls, of Columnar—Jointed olivine ln, and between falls, of columnar-jointed olivine basalt basalt lavas lavas with with ainygdalojdal tops, tops, and amygdaloidal and smooth, gently gently billowing billowing surfaces. surfaces. Continue SW through Castle Danger (2.L Continue (2.4 mi.), across Crow Crow Creek Creek ml.), across (a diabasic diabasic intrusion intrusion here (a returns soon soon to to SW SWat here returns at deeply deeply weathered weathered Lafayette Lafayette Bluff), Bluff), through through Encampment Encampment Porest owned old— oldForest(privately (privately owned growth forest with growth forest with summer to to Silver tni~~ summerhomes) homes) SilverCliff Cliff(anothp~ (anoth' +1I41- �Going NE Going SW SW —95— -95- intrusion) to outskirts of Two Harbors. gabbroic intrusion) 12.7 0.5 Stop 29. 29. Quartz tholeiite basalt, Two Harbors city park (Two (Two Stop Just before entering town, Harbors town, turn turn toward toward lake lake at at I:arbors quad.). quad.). Drive past Burlington Wa—Ke—Ya Motel. road to to city city camp camp ground and and Wa-Ke-Ya Burlington road Bay, and up up aa hill. hill. Park at hilltop picnic area, walk walk EE to to shore, shore, Bay, and then S. S. Well exposed contact between amygdaloidal, amygdaloida1, weathered weathered then (ex—laumontite) top of of one basalt and massive basal part of an (ex-laumontite) top analyzed fine—grained, fine-grained, aphyric quartz tholeiite tholeiite (50% (50% 5102, Si02, 0.6% K20). Local thin sand lenses near and and at at contact; contact; traces traces of of Cu have been been found. found. The tholeiite shows shows occasional small small quartz— quartzagate and chlorite amygdules amygdu1es and and typical typical incipient incipient sheeting— sheetingfractures with thin .of this this thick thick thin bands bands of of oxidation. oxidation. Upper Upper zonezone' ,of tholeiite can be examined to to S. S. toward toward power power plant; plant; it it becomes becomes rubbly, vesicular, brecciated, with abundant rubb1y, vesicular, abundant laumontite. laumontite. Return to Hwy 61. 13.1 0.0 0.0 20.6 20.6 20.6 0.0 0.0 0.0 5.9 (3.0) (3.0) (3.0) Continue SW to traffic light in in Two Harbors. Harbors. At west end of town town take express highway highway to to Duluth. Duluth. Many cuts cuts of basalts and minor diabase intrusions. At-about At- about 17.7 11.7 miles Moose Moose Mtn. is is seen seen inland, inland, held up by Lester River diabase sill. sill. At 20 20 miles jct. jet. with old old St. Louis Louis Co. Co. 61), 61), and and at at 20.6 20.6 miles miles Lester Lester River River Hwy 61 (now (now St. either continue continue straight on Hwy bridge. Just beyond, beyond,either Hwy 61 61 (London (London Rd.) Rd.) direct to downtown 6 miles ahead, ahead 9 or or turn turn uphill uphill on on Minn. Minn. 23 23 (60th Ave. Ave. E) E) across ItR tracks to to Superior Superior St; St; go left. (60th RR tracks left. Stop Stop 30. 30. Tischer Creek felsite felsite and and Endion Endion sill, sill, Congdon Congdon Park Park (Duluth quad.). Examine outcrops beneath bridge; then then walk walk up up on WWside side of of creek. creek. There are some some impassable impassable trail that starts on places where you must climb climb up up to to aa bank—top bank-top trail trail on on WWside. side. part of of section cuts cuts through orange, foliated foliated felsite felsite with with Lower part through orange, flow inclusions, Clut by two two flow structure, structure, quartz veinlets, occasional inclusions, out by or three basaltic basaltic dikes. dikes. Upstream at top of of steeper steeper part part of of gorge gorge the stream cuts down into red granophyre top top of of Endion Endion sill. sill. Upcuts gradually gradually down down into into intermediate, intermediate, then then gabbroic gabbroic stream the creek cuts rocks of main part of Endion sill. rocks of Endion sill. At Vermilion Road bridge (second (second bridge above Superior St.) St.) still still in in lower—middle lower-middle part part of of sill; sill; return via trail trail or Congdon Congdon Parkway Parkway on on W. W. side. side. See Ernst, Ernst, 1960. 1960. Continue SW on Superior St. St. over rise rise held held up up by by Endion Endion Sill. Sill. 5.0 5.0 0.9 0.9 5.9 5.9 0.0 0.0 0.0 0.0 11.2 11.2 Stop 31. 31. Basaltic-andesitic interflow sandstone, sandstone, Leif Leif Basaltic—andesitic lavas, interflow Erickson Park, Duluth Duluth (Duluth (Duluth quad.). quad.). At lath 10th Avenue E. E. turn turn off off Superior St. Road at at Leif Leif Erickson Erickson Park. Park. St. toward lake to London Road I Walk over footbbridge footbbridge near near "viking "viking ship" ship' to t shore. shore. Weakly por— porphyritic basalt or basaltic basaltic andesite andesite ledges ledges behind behind stage. stage. Rubbly Rubbly (weathered?) (weathered?) top top to to NE NE is is directly overlain by a thick thick cross—bedded cross-bedded sandstone, that is is cut cut by by aa small small dike dike at at NE NE sandstone, strongly epidotized, that more flows end of beach. Several more flows exposed along shore shore to to SW. SW. anc Superior Superior Street, Street, downtown downtown Duluth. Duluth. Lake Avenue and (approx.) ~approx.) 1L 11-22 approx.)) :approx. o. a 0.0 Drive SW on Hwy 61 past Point of Rocks Rocks through Duluth Complex Thomson Hill Hill to to Nopeming. Nopeming. Turn R R at (St. Douis 13), up Thomson at Midway Midway Road Road (St. Louis ~o. o. 13), drive uphill about 0.9 mi. mi. almost almost to to top top of of rise. rise. �—96— -96- Stop 32. 32. Basal (Puckwunge?) (Puckwunge?) sandstone, basal basalts of of Lower Lower Keweenawan Ke\veena\van ('Grandview ("Grandview Golf Course" locality, locality, Esko Esko quad.). quad.). Drive or walk E E on road toward toward Cloquet Cloquet city city water supply supply tank tank on on hill. Pass low outcrops of vertical Thomson slate slate and and graywacke graywacke (Middle Precambrian: more are exposed (Middle exposed on on rise rise and and roadcuts roadcuts to to N.). At slope, go either RR or LL along along base of of slope slope to to outcrops outcrops N.). At slope, of basal Upper Precambrian quartzite and and conformably conformably overlying mafic, porphyritic basalt with small augite mafic, augite and and altered altered olivine olivine to rocks rocks on Lucille Island Island at at Grand Grand Portage. Portage. phenocrysts identical to Note pillows subtly outlined by small vesicles and and color color zones. zones. �—97-. -97- TO THE GUIDE TO THE PRECAMBRIAN PRECAMBRIAN ROCKS ROCKS OF NORTHWESTERN COOK COUNTY COUNTY AS EXPOSED ALONG ALONGTHE THE GUNFLINT GUNFLINT TRAIL AS EXPOSED Prepared by by Paul Paul W. \~. Weiblen Department of Geology and and Geophysics Geophysics University of Minnesota Hinnesota Minneapolis, Minnesota Minneapolis~ G. B. Horey G. B. Morey Minnesota Geological Survey Survey University of Minnesota Minnesota St. Paul, Minnesota '1. G. Mudrey H. G. Minnesota Geological Survey Survey University of of Minnesota Minnesota St. Paul, Paul, Minnesota �—98— -98- Geology of Northwestern Cook County, County, Minnesota INTRODUCTION An exceptionally complete complete Precambrian section is exposed in the vicinity of the the Cunf Gunflint County. lint Trail Trail in in northwestern northwestern Cook County. Rocks Precambrian age, age , represented by a volcanic Rocks of Early Precambrian succession and the the Saganaga Granite, are are unconformably unconformably overlain by by the the Middle Middle Precambrian Precambrian Animikie Animikie Group,coiLsisting Group, cOllsisting of of A low anglular unconformity the Rove Fotmations. Fo~ations. A the Gunflint and Rove separates strata from from the the nverlying f1verlying Puckwunge Puckwunge separates the t-1iddle Middle Precambrian strata Rocks Formation of Late Precambrian Precambrian age. age. The Logan Intrusive Intrusive Rocks and the Duluth Duluth Complex, Complex, which which intrude intrude and and truncate truncate the the Middle Middle Precambrian Precambrian the strata, strata, comprise comprise the the major major part part of of the the Upper Upper Precambrian Precambrian section. section. However, However, possible remnants remnants of the North Shore Volcanic Group occur at the top of Duluth Complex at Complex rocks. rocks. The geology of the area was summarized in 1959 by Grout and Because geologic mapping mapping since since 1962 has has considerably considerably reBecause revised the the geologic history of the the area, area, and because much of of this this work is is as yet unpublished, unpublished, aa comprehensive comprehensive summary summary is is presented here. This discussion is meant to to provide a framework for the the specific aspects of the the geology geology which which the the chosen chosen stops stops illustrate. illustrate. others. Lower Precambrian Introduction The Lower Precambrian rocks rocks in Cook County are the eastern extension of the Vermilion greenstone greenstone belt belt (Sims (Sims and and others, others, 1971, 1971, has shown that the district contains many in press). Gruner (1941) (1941) has major longitudinal longitudinal faults faults that that divide divide it it into into long long segments segments or or belts, belts, each with distinct distinct characteristics. characteristics. They cannot be connected stratigraphically with each other in in any any simple simple way. way. One segment segment extends from from Gabimichigami Lake Lake across across the the Gunflint Gunflint Trail Trail (Fig. (Fig. 1). 1). It It includes aa metavolcanic assemblage consisting consisting of of metabasalt, metabasalt, metaandesite, tuff, hornblende andesite porphyry, porphyry, metaandesite, agglomerate and tuff, metagraywacke and and slate. the Saganaga Saganaga and intercalated metagraywacke To the north, north, the slate. To Granite has has intruded and and metamorphosed metamorphosed the thevolcanic volcanicsuccession; succession; it it is overlaintotothe thesouth south youngerrocks rocksofofMiddle Hiddleand andLate LatePrecambrian Precambrian is overlain bybyyounger age. �-99—99— The metavolcanic assemblage constitutes constitutes aa homoclinal homoclinal sequence sequence towardwhat whatGruner Grtinerinferred inferredtoto be be the the axis \"hich dips dips southward southward toward which Pillow—topdirections directions of aa southeastward—plunging of southeastward-plunging synclinorium. Pillow-top indicate that thatthe thesequence sequence alsO also becomes becomes stratigraphically stratigraphically younger younger the south. However, However, some pillows pillm"s top top to to the the north north indicating indicating to the folding, but but poor exposure exposure precludes precludes detailed evaluation of the folding, structure. wasthought thoughttoto separate separate the Previously, an an unconformity unconformity was the mafic and rocks; thus thus the thesuccession successionwas was subdivided subdivided mafic and more morefelsic felsic rocks; metabasaltswere werereferred referredtoto as as part part of into two two formations. formations. The The metabasalts of the Ely whereasthe themore morefelsic felsicvolcanic volcanic and andclastic clastic the Ely Greenstone Greenstone whereas rocks \Vere placed placed within within the theKnife KnifeLake LakeGroup. Group. Recent mapping mapping rocks were (Fiorey andothers, others, 19(9) 1969) has has sho\Vn shownthese theset\VO twolithologies lithologies to (i-iorey and to be be other parts parts of district gradational, and gradational, an(~ nappin mapping in other of the the Vernilion Vermilion district (lorey 1968; 1971, (~Iorey and and others, others,1970; 1970;Green, Green, 1970; 107(); Sims Sims and and others, others, 1968; 1971, in press) has shown shm.;n that that specific specific rock rock types types are are not not diagnostic diagnostic particular strati~raphic stratigraphichorizon horizon—i.e., any particular - i.e., lithologic lithologic units units therefore no formal are formal stratigraphic stratigraphic are not not time-stratigraphic time—stratigraphic units units -— therefore used for for these nomenclature is is now no\V used these rocks. rocks. of Descriptive Stratigraphy Descriptive Stratigraphy Volcanogenic Rocks Volcano;;enic Detailed mapping in the Long Island Lake quadrangle, Detailed mappinR in the Lonfl Island Lake quadrangle, reconnaissance reconnaissance as far west \"est as Va>' Fay Lake Lake in the the Cillis GillisLake Lake quadrangle, quadrangle, and and as far Gruner's area have have indicated that the thevolcanigenic volcani8enicsequence sequence Grunerts Hark work in in the area indicated that of approximately 60 percent inetabasalt metabasalt and fragconsists of and associated frag— mental rocks, 30 percent netnandesitic agglomerate, conglomerate, tuff, mental rocks, 30 percent metaandesitic agglomerate, conglomerate, tuff, and flows, and and slate. slate. and flows, and 10 10 percent intercalated intercalatednetagraywacice metagraywacke and mappin rr.appin,~ IjuLLaaLs.st±1psis!; percent ofofthe :i.eta_~~i1.sa-h.~~_?.~(LQ.~sg ..0at~_~.t ro_c±,-s_: Over 95 95 percent themeta— metabasalt is basalt is extrusive; extrusive; there thereare areseveral severaltabular tabularbodies bodiesofofmetadiabase, metadiabase, rLall to too small at aa scale of to show shmv at of 1:24,000. 1:24,000. Nany Manyofof the the metabasalts exhibit pillow exhibit pillm-J structure. The pillows pillo\Vs are are as as much as as three three feet feet in in diameter, but many diameter, manyhave havebeen beendeformed deformedsosothat that they they are are now no\V two two or three three times times as as long lonf, as as they they are are wide. \"ide. Chilled rinds rindsare arewell—developed 1vell-developed and as much much I1Sasone-half inch thick: in and are are as one—half inch thick:typically typicallythey theyare are lighter lighter in color than interiors. Inter-pillm" color than the the dark dar:( green green or ordark darkgreenish—gray fJreenish-Rray interiors. Inter—pillow material locally material locally is iswell welldeveloped developed and and co!nists con~ists of of tuffaceous tuffaceous material material cEtert, chert, or or pillow—rind pillm,,-rind fragments. fragments. Themetabnsalts metaasalts shot: intense retrograde retrograde alteration; alteration; many The shoH intense many thin thin sections sections are nre nearly nearlyopaque. opaque. Recognizable Recognizable minerals include minerals includerelict relict augite augite and anu calcic cnlcic plagioclaso, plagioclase, and and secondary secondary sodic sodic plagioclase, plagioclase, actinolice, chlorite, actinolite, chlorite, epu'ote, epidote, calcite, calcite,quartz, quartz,leucoxene, leucoxene, and opaques. Property of oj C. C. Patrick Ervin Ervi n �—100— -100- The tabular bodies of metadiabase have have aa relict relict poikilitic poikilitic texture texture -— actinolite pseudomorphs after augite -— and a mineralogy much like that that of of the the metabasalts. Thin beds and mineralogically immature immature meta— metabeds of texturally and clastic rocks are locally intercalated intercalated with the the metabasalt. metabasalt. Several beds are crudely graded and have a texture suggestive of a pyroclastic a pyroclastic Most layers, layers, however, however, appear to be epiclastic with with pebblepebble— Most to be origin. to silt-size silt—size clasts of locally derived to derived metadiabase metadiabase in in aa finer—grained finer-grained matrix of chert, chert, plagioclase, plagioclase, hornblende, hornblende, chlorite, chlorite, and and sericite. sericite. Hornblende andesite prophyry and and related related rocks: rocks: There are two two types of hornblende-biotite hornblende—biotlte phenocryst bearing types bearing rocks. rocks. Both are light light greenish—gray greenish-gray in in color. color. One type type lacks lacks internal internal structure. structure. The ground plagioclase, lesser biotite, opaques opaques and and mass consists of plagioclase, lesser amounts amounts of biotite, rare secondary calcite. calcite. The other type type has similar rare quartz and secondary phenocryst and groundmass mineralogy mineralogy but but is is composed composed of of angular angular to to rounded, cobble—s,'ze clasts and and is is inferred inferred to to be be aa volcanic volcanic breccia rounded, cobble-s~ze clasts or agglomerate. Metagraywacke and and slate: slate: In the vicinity of Fay Fay Lake in in the the Gillis Lake quadrangle, quadrangle, the volcanic rocks inter— Gillis the felsic felsic volcanic rocks apparently interfinger, meta— finger, or are infolded with agglomerate agglomerate or conglomerate, conglomerate, metagraywacke, and and slate. slate. Amphibolites: The metamorphic effects of of the the Saganaga Saganaga Granite Granite metabasalts becomes becomes apparent apparent only only within within several several hundred hundred feet feet on the the metabasalts of the contact. contact. Away from from the the contact, contact, the the metabasalt contains incipient hornblende; hornblende; nearer the becomes granular granular incipient the contact, contact, the the rock rock becomes and consists of hornblende and and and calcic calcic plagioclase; plagioclase; at at the the contact, contact, the rock is strongly strongly schistose. schistose. The the The schistosity parallels the granite contact, contact, as does does a well—developed well-developed foliation foliation within within the the granite. granite. Saganaga Granite General General Statement: Statement: The Saganaga Saeanaga Granite Granite (A. (A. Winchell, Hinchell, 1888) 1888) (Fig. 1) 1) is is aa late-kinematic late—kinematic composite intrusion emplaced (Fig. arouno emplaced around 2,700 m.y. m.y. ago in older volcanic rocks rocks and and the the Northern Northern Light Light Gneiss. Gneiss. Inch— Inch- to foot—sized foot-sized inclusions inclusions of of both both rock rock types found in in the the types are are found granite. granite. The main phase, phase, which comprises comprises 85 85 percent of the the outcrop outcrop percent of area, "quartz—eye hornblende—bjotjte area, is is aa medium—graineci medium-grained "quartz-eye" hornblende-biotite tonalite. tonalite. Other Other phases phases include: include: 1) border phase, phase, found found along aloTIC' the the southern southern 1) a border margin of the the batholith margin of batholith and and along along the the base base of of a roof roof"pendant of pendant of the the Northern Northern Light Light Gneiss; Gneiss; 2) 2) aa younger younger fine—grained fine-grained tonali te which ,vhich tonalite lacks conspicuous lacks conspicuous tquartz_eyes?T; "quartz-eyes"; 3) 3) aa coarse—grained coarse-grained biotite—fluorite— biotite-fluoritebearing bearing granodiorite; granodiorite; and and 4) 4) aa quartz—feldspar quartz-feldspar pegnatite pegmatite which which occurs occurs as veinlets as three three feet as veinlets as as much much as feet wide wide in in the main phase. the main phase. �—101--101- Hain Phase: This "quartz eye"-bearing :iain This phase phaseisis aa "quartz eye"bearing tonalite containing 20 20 percent 1-6 percent percent percent quartz, quartz, 60 percent oligoclase, 1—6 microcline, up to 8 percent biotite, 6 percent hornblende, and microcline, to 8 6 percent hornblende, and 1-4 epidote. Other minerals include clino—pyroxene, clino-pyroxene, 1—4 percent epidote. muscovite, chlorite, muscovite, chlorite, sphene, sphene, apatite, apatite, zircon, zircon, calcite calcite and and opaque opaque oxides. Cataclastic deformation of the the tonalite tonalite· is is indicated indicated by by strong undulose extinction and granulation of strong of the the quartz quartz and and abunabundant mortar and mylonite mylonite zones. zones. dant Phase: The border phase is is aa quartz quartz bearing, bearing, hornblende hornblende Border Phase: diorite that that is gradational with the the "quartz—eye" "quartz-eye" tonalite. tonalite. This diorite is well developed along the phase is the southern southern edge edge of of the the batholith batholith in in feet wide, the is as much as as 1000 feet the Long Long Island Island Lake Lake quadrangle quadrangle where it is and Moose Bay area in Ontario where and in the Noose ,,,here it it is is found found along along the the roof pendant of the the Northern Northern Light Light Gneiss. Gneiss. Foliations Foliations underside of a roof rock are everywhere similar, in and in in the the country rock everYWhere similar, in the the border phase and and it is inferred that that the the border phase phase was was produced produced by by partial partial assimilation country rocks of mafic composition composition (Halford, (Halford, 1969). 1969). assimilation of of country Younger Tonalite: Tonalite: A A tonalite characterized characterized by by aa lack lack of of "quartz—eyes," aa fine—grained "quartz-eyes," fine-grained equigranular texture, texture, and and abundant abundant hornblende and biotite biotite crops out in the the Horseshoe Horseshoe Island Island area area of of hornblende crops out Saganaga Lake. Lake. This tonalite tonalite is is not not sheared sheared which ,,,nich indicates indicates that that it the main phase. phase. it was was emplaced after deformation of the Internal Structure: Structure: Linear structural elements marked by an an alignment "quartz eyes" and/or elongate hornblende grains grains are are alignment of 'quartz in the the border border phase. phase. Lineations in in the the border border well developed only in phase plunge gently southeastward. southeastward. In contrast, contrast, lineations in in the the main phase are are random. random. Structure All the minor structural elements elements in in the pre—Saganaga rocks rocks in in All the minor the pre-Saganaga the plunging the Long Long Island Island Lake Lake quadrangle reflect a southeasterly plunging synclinorium. synclinorium. In northwesterly-trending fault fault in addition, addition, a major, major, northwesterly—trending (Lookout Fault, Sims Sims and others, (Lookout Fault, others, 1969) 1969) separates rocks rocks showing showing no no metamorphic effect of of the the Saganaga SaganagaGranite Granitefrorn.those from;those that that do. do. The metamorphic effect fault is is marked marked by by aa topographic low fault 1m" developed in in aa breccia breccia zone zone as much as 50 feet as feet wide. wide. The breccia consists consists of highly sheared metabasalt in aa matrix of massive quartz quartz and and calcite. calcite. Fracture cleavage is is present present throughout the cleavage the area and and commonly commonly parallels parallels the the Fault. Southeastward Lookout Fault. formed by by bedding/ bedding/ Southeastward plunging plunging lineations lineations formed cleavage intersections developed. These lineations intersections are locally well developed. are consistent are consistent in orientation with mineral lineations lineations developed developed in in the amphibolites itself; obviously obviously all all of of these these the amphibolites and in the granite itself; structures tectonic event. event. structures are related to the same tectonic �—102— -102- related to to the the final final The Lookout Fault also apparently was related the Saganaga Saganaga Granite. Granite. Previously it was assumed emplacement of the (Grout, (Grout, 1936) 1936) that that the the granite granite was was emplaced emplaced into into its its present present position via a west\vard westward rotation rotation of about about 700 70° about about aa north—south north-south that the the eastern part part of of the the granite granite and and the the axis. This implies that represent roots roots of the Light Gneiss Gneiss represent the batliolith batholith that thatwere wereonce once Northern Light However,Goldich Goldichand andothers others (1968) as much as 25 miles deep. However, (1968) have have as much as 25 miles deep. that the granite was originally intruded at a shallow depth— suggested that the granite was at a depthan observation more consistent consistent with with the the regional regional Abukurna Abukuma greenschist facies (Mudrey, 1969) to its present present facies metamorphism metamorphism (Mudrey, 1969) -— and brought to relative position position by by dominantly vertical movements along several relative several westerly-trending border faults. faults. The granite—greenstone granite-greenstone contact contact westerly—trending border mapped by Harris (1968) (1968) on the the north shore shore of of Saganaga Saganaga Lake Lake was was interpreted to be the interpreted to be the northern border fault, fault, and it is here inferred inferred that the that the Lookout Fault is is its its southern southern analog. analog. The block block was was emplaced emplaced during during E8~ly E:ly Precambrian The Precambrian time, time, in in as as much as as detritus now found found in the the Knife Knife Lake Lake Group Group of of Gruner Gruner (1941) (19/+1) was derived there has derived from Granite. Although from the Saganaga Saganaga Granite. Although there has been been later t.,as movement on the the Lookout Fault, Fault, it it is is dominantly dominantly aa Lower Lower Precambrian Precambrian structure. MIDDLE ~UDDLE PRECAMBRIAN PRECANBRI!u~ Introduction Gunflint and and '\ove Rove Formations The Animikie Groun Group consisting of the the Gunflint comprises These rocks the entire this area. comprises the entire Middle :oliddle Precanibrian Precambrian inin this area. These rocks unconformably overlie Lower Lm.,er Precambrian rocks rocks and and in in turn turn are are intruded intruded and truncated truncated by gabbroic rocks rocks of Niddle i'·liddle Keweenawan KeweenaT,oJan age. age. The time time of Animilcie !mimikie deposition deposition has has not not been completely completely documented. documented. Hurley and iron— that deposition of the and others (1962) have have suggested suggested that the ironothers (1962) 6 io6 Although this years. formation around 1,900 1,900 ±± 200 xx 10 this K—A K-A formation occurred occurred around age includes age includes an an arbitrary and perhaps unnecessary unnecessary correction correction of of 20 20 percent assumed assumed argon argon loss, loss, it it nevertheless nevertheless has has been been widely widely quoted quoted In contrast, contrast, Faure Faure and and Kovacg Kovac (1969) in the literature. In (1969) obtained obtained aa Rb-Sr age of 1,685 ±± 24 x 10 years years from from the the Rb—Sr tvhole-rock whole—rock isochron age Gunflint Iron—formation. Iron-formation. They interpret interpret this this age age to to be be the the time time of diagenesis, however, similartotoother otherages agesobtained obtainedfrom from rocks rocks however,itit is similar Misra and Faure metamorphosed during the the Penokean orogeny. orogeny. Later Nisra Faure (1970) Iron-formation (1970) showed showed that that argillite argillite from from thr2e three Gunflint Gunflint Iron—formation . .1.7 localities Rb-Sr ages ages that that decrease from from "'.... 1.7 b.y. at the eastern localities have have Rb—Sr end to to 1.2 b.y. b.y. near... near ... the the western.. \vestern ... variation of of . this systematic variation apparent ages may be related to metamorphic effects caused by Keweenawan apparent ages may related to effects caused by Keweenawan . . ".'. Thus there diabase sills. sills •••• there is uriequivical depositional age for for is no no unequivical these rocks. b.y. at the eastern . �-103—10 3— Descriptive Stratigraphy Gunflint Iron—formation Iron-formation The Gunflint Iron—fori:iation crops out out in in aa northeasterly— Iron-formation crops northeasterlytrending belt Superior to trending belt that thatextends extendsfrom fromThunder Thunder Bay Bay on on Lake Lake Superior a point it is point in inMinnesota Minnesota 12 12 miles miles west west of Gunflint Gunflint Lake Lake where where it is truncated by the truncated the Duluth Duluth Complex. Complex. In Canada Canada the iron—formation is In the iron-formation is only slightly, slightly, if at at aF., al:_, metamorphosed and consists of silica, much of of which \"hich is is chalcedonic, chalcedonic, Consequently, Goodwin iron oxides, oxides, iron carbonates, iron carbonates, and and greenalite. greena1ite. Consequently, (1956) recognized six six sedimentary sedimentary facies facies which which serve serve to (1956) recognized to subdivide In Minnesota theoriginal oriina1 the iron-formation fourmembers. members. In Hinnesota the iron—formation into into four nature of metamorphism by the nature of the iron-formation is is -obscured obscured by TIetamorphism the the iron—formation Duluth Complex. The carbonates and greenalite are replaced by Complex. carbonates and greenalite are replaced by amphibole, amphibole, pyroxene, fayalite, and locally by garnet and pyroxene, fayalite, and and other silicates. In In addition, addition, many of the the small—scale small-scale sedimentary sedimentary textures textures have have been been almost completely completely destroyed; destroyed; however larger larger structures, structures, and especially complex bedding bedding relationships relationships are are still still preserved. preserved. Therefore the the four—fold nomenclatural nomenclatural scheme -— originally four-fold in the the Biwabik Biwabik originally outlined in Iron-formation (Wolff, (Holff, 1917) 1917) and and later later extended extended to to the the Gunflint Gunflint Iron— IronIron—formation retained by Morey and others formation (l3roderick, (Broderick, 1920) by 1'1orey and (1969) others (1969) 1920) -— ,vas was retained Accordingly, four because it it emphasizes various bedding aspects. aspects. Accordingly, members are recognized; members recognized; Lower Cherty, Cherty, Lower Lower Slaty, Slaty, Upper Upper Cherty, Cherty, Slaty. Although the do not and Upper Upper Slaty. the boundaries of of these these members members do coincide coincide witll those recognized recognized by by Goodwin Goodwin (1956), (1956) , the with those the two two schemes schemes can be equated equated \vith withonly onlyslight slight difficulty. difficulty. Lo\ver ChertLMemhe.r: Cherty Hember: Lower The Lo,ver is isthin, The Lower Cherty ChtertyNember Member thin, ranging in thickness Feldspathic quartzite quartzite that thickness from from 15 15 to to 45 45 feet. that contains contains feet. Feldspathic granite cobblesisis present present locally locally at at Lie granite and and greenstone greenstone cobbles the base base of of the the formation; these beds beds are are equivalent equivalenttotoGoodwin's CoodHin' s basal basalconglomerate conglomerate formation; member. AA persistent persistent magnetite-rich, magnetite—rich,silicate-bearing silicate—bearingunit unit five five to Feet thick occurs 15 feet occurs within IVithin this thismember member and an excellent and serves serves as as an marker—horizon. marl(er-horizon. :Iost commonly it liesdirectly directly uponbasement basement rocks, rocks, :c'st commonly it lies upon but loc<llly locaii.v it it overlies overlies either eitherthe thefeldspathic feldspathicqtiartzite quartziteorora chert— a chertcemented fragr.ents of cemented conglomerate conglomerate containing contctininr, frctgments algal structllres; in of algal structures; itit in is overlain overlainbyhya massive, a massive,chert—rich, chert-rich,magnetite—poor magnetite,-poor unit about about turn is 15 feet thick. 15 feet thick. ' \ Lower-,:,?-latY---l~~emher: Slaty Member: This This member memberisis8080toto 95 95 feet feet thick. The Lower lOHennost, magnetite-free 10 is a ablack, black,thin—bedded thin-bedded lowermost, nearly nearly magnetite—freo 10feet feet is argillitecomposed conlposcd dominantly dominantly of derived material. It argillite of volcanically volcanically derived It is equivalent equivalent to to the the intermediate InterPlcdi"tc slate slate on on the the 'esahi ;lesabi range range and and to to is the lower the lOh·er tuffaccous tuffaceous shale shale f,icies fD-cLcs ininCanada. l,<ln"da. The beds beds immediately aove the Intermediate .:1iJove tile IntenneJiate slate massive and clierty cherty and and resemble resemble slate are massive the upper upor aert the part of of the the lower LOIver Cherty ;'[e1l1her. This unit passes passes abruptly ahruptly Chcrty :-;ember. ipuird into cherty uith spilrse sparse inagnetite interuTl\!;]rd into cherty si.licate-hci1rini; beds ':lith magnetite inters iJ.icate— carjn beds calated calateJ with \vi til aa few fe\\' thinly—laminated tilinly-la:ninated silicate—rich silicate-rich beds. heels. The The remaining 50 feet is is ai1 thiin—bndciel laminatedrock rockcontaining containingvarious varioussilicates silicates thin-beJded totolill\linated and percent magnetite. and Cro from 20 2C to 35 35 percent map;netite. AA few fe'" cherty-silicate cherty—silicate beds, definitely amount are elefillitely subordinate subordinate in in illllount this interval. interval. are intercalated intercalated in in this �—104— -104- Upper Cherty Cherty Member: Member: There is is a complete complete gradation gradation between between The Upper Cherty the Lower Slaty and and Upper Upper Cherty Cherty Members. Members. Cherty Member, Member, the The lower as defined, is approximately 50 50 feet thick. thick. The 10loJer as presently defined, cherty layers part to lenticular lenticular cherty layers part consists of irregularly bedded to intercalated with thinly—laminated thinly-laminated silicate—rich silicate-rich layers layers that that increase increase in abundance abundance upward. upward. Thin irregular layers of magnetite are are common common in in the cherty beds near the the bottom of of the the member, member, but but become become less less abundant upward. upward. The top top of the the member—equivalent member-equivalent to to Goodwin's Goodwin's abundant upper algal chert facies—is facies-is characterized characterized by by several granular granular chert conglomerate fragments, fragments, chert beds beds containing algal structures, conglomerate and abundant magnetite. Upper Member: The Upper Slaty Slaty Member is is approximately approximately Upper Slaty S1ay Member: Thick lenticular chert chert beds beds with disseminated disseminated few tens tens of of feet, feet, but magnetite characterize characterize the the lower lower few but most most of of the the member consists consists of a thin—bedded thin-bedded to to laminated laminated quartz—silicate quartz-silicate rock rock thinly laminated layersofofgraphitir:: graphiticargillite, argillite, interbedded with with thinly laminated layers and pure chert. chert. The and one onetoto two twoinch inchthick thick beds bedsofof relatively relatively pure upper 10 feet feet is nearly magnetite free free and and consists consists of of limestone limestone and chert interbedded interbedded with with argillite. argillite. 150 feet thick. thick. 150 Rove Formation Rove Formation gradationally overlies The Rove overlies the the Cunflint Gunflint Iron— Ironformation and is intruded by Logan Intrusive formation Intrusive Rocks Rocks and and truncated truncated detailed description of Duluth Complex. Complex. A A detailed of the the formation formation by the Duluth is presented is presentedby byMorey Morey (1969). (1969). In In the the Long Long Island Island Lake, Lake, Gunflint Gunflint Lake, and Hungary Hungary Jack formation Lake, Southlake, and Jack Lake Lake quadrangles, quadrangles, the formation is characterized by by intercalated black to to grayish grayish black, black, locally locally is characterized intercalated black carbonaceous argillaceoussiltstone siltstone and fine-grained carbonaceousargillite, argillite, argillaceous and fine—grained gray\oJacke. In the silt silt sandstone beds becomecoarse— coarsegraywacke. In general the andand sandstone beds become formation. In grained, thicker, thicker, and and more more abundant abundant upward in the formation. tn are several addition, there are several lenses lenses and and irregular irregular bodies bodies of of limelimeaddition, there dolomite, and chert and a number of of calcite—dolomite calcite-dolomite con— constone, dolomite, cretions of of various shapes and sizes, similar cretions similar to to those those described described in the the formation by by Tanton (1931) (1931) and and Moarhouse Moorhouse (1963) (1963) scattered scattered near the the base base of the the formation. formation. Horey deep Morey(1969) (1969)has hassuggested suggestedthat thatdeposition depositionstarted started in aa deep basin in inwhich which fine—grained fine-grained sediment sediment accumulated accumulated under under reducing reducing conditions. The The siltstone siltstone and conditions. andsandstone sandstonebeds beds contain containmany many primary primary sedimentary structures indicative indicative of of turbidite sedimentary structures turbidite deposition. deposition. There is of this this type is also also evidence evidence of of an an increase increase infrequency infrequency of type of of deposition upward in in the the section. section. The graY\oJackes contain abundant abundant framework framework The graywackes grains grains of of quartz, quartz, feldspar feldspar and and Igranitici "granitic"rock rockfragments fragments indicative indicative of a granitic source area. source area. Sedimentary structures including cross— crossbedding and various kinds of of sole sole marks marks indicate indicate that that sediment sediment transport dominantly dominantly was \oJas from from north north to to south. south. These observations observations and the gray\oJacke mineralogy the the graywacke mineralogyled led Horey Morey(1969) (1969)toto conclude concludethat that the source terrane now exposednorth north of of the source area area was was the the Lower Lower Precambrian Precambrian terrane now exposed the outcrdp area of outcrop of the theRove Rove Formation. Formation. �—105— -105- Structure The Animikie SE Animikie strata strata form form aa homocline homocline that that dips dips 10°-15° 1O—l5° SE except where intrusive bodies and and secondary secondary structures structures have have disdisFor example, example, complex folding torted the beds. For torted or disturbed the commonly zones adjacent to to many of of the the Logan Logan commonly occurs occurs in narrow zones Intrusive is most likely related related to to the the forceful forceful ememIntrusive Rocks Rocks and and is the sills into into restricted restricted space. space. There is aa fairly fairly placement of the regular as much as 600 60° near the the Duluth Duluth Complex. Complex. regular increase increase in dip dip to as is most likely likely pre—Duluth pre-Duluth Complex Complex in in age. age. However, this structure is However, in the the Animikie Animikie strata strata inakestecognition makestEcognition of Lack of marker beds in faults northwesterly- and and northerly— northerlyfaults difficult; difficult; however, however, a number of northwesterly— trending faults have been mapped. mapped. trending faults faults have displacements displacements of of less less than than 50 50 feet; feet; however, however, Most faults the Lookout Lookout fault has aa displacement displacement in the the iron—formation iron-formation of fault has of at at least least 200 200 feet. feet. All All faults faults so sofar farrecognized recognizeddisplace displaceLogan Logan Intrusive rocks, Intrusive Complex; thus thus rocks, but but none extend into the Duluth Complex; movement apparently apparently occurred in Middle Middle Keweenawan Keweenawan time time prior prior to to movement of the the Duluth Duluth Complex. Complex. The fault fault pattern is similar emplacement of to 1960; Goodwin, Goodwin, 1960) 1960) near ,.,hat what can to that that in Canada (Moorhouse, (Moorhouse, 1960; be inferred inferred to to be the the northern the Lake northern hinge hinge of of the Lake Superior syncline. syncline. TIlis structure must have formed at least in prior to emplacement part prior to emp1acenen.t This must at least in of the Duluth Duluth Complex. Complex. Hovement during Keweenawan Keweenawan time time duplicates duplicates Movement on the Lookout fault during iron—formationwest westofofthe theGunflint Gunflint Trail, Trail, and the iron-formation and aanortherly— northerlytrending segment of fault separates separatesthe the iron-formation into two two trending segment of the the fault iron—Formation structurally distinct terranes. structurally terranes. East of the Gunflint Trail, Trail, the the rocks dip dip gently southward; southward; accordingly the outcrop area Animikie rocks of relatively wide most of of the apparent of the the iron—formation iron-formation isis relatively wide and and most apparent irregularities mappattern patternresult result fromthe the super-position irregularities ininthethemap from super—position of aa rugged rugged topography on gently—dipping gently-dipping strata. strata. The south side side of fault is is upthrown, upthrown, and and the the Anirnikie Animikie strata on this of the the Lookout fault side outcrop belt. belt. side dip dip steeply and thus form a narrow outcrop A also can can be be recognized. recognized. Just A number of smaller structures also east of Gunflint Trail Trail the the iron—formation iron-formation and of the Gunflint andthe thesills sills are folded into anticline with with a a steeply steeply into a southeasterly plunging anticline dipping north limb limb and a gently dipping dipping south south limb. limb. This structure post-Logan in age has an anticlinal axis which which is obviously post—Logan into the the trace trace of of the the Lookout Lookout Fault. Fault. projects into Metamorphism i'letamorphism In the the Animikie Animikie rocks no textural or or atineralogic mineralogic In rocksthere there is is no evidence for aapervassive metamorphism evidence pervassiveregional regional metamorphism beyond beyond minor minor of the the clay—size clay-size detritral frac'don. The The obvious recrystallization of detritral. fraction. the Animikie strata are are associated in the Animikie strata associated with with the the metamorphic effects in emplacement of the Duluth Complex and Logan Intrusive Rocks of Middle Ke,,,eenawan Keweenawan age. �—106— -106- The contact contact aureole aureole of of the the Duluth Complex has has not been studied in detail in in the the Gunflint Gunflint Trail Trail Area. Area. Preliminary work in in the the Gunflint Iron—formation shows there are a number of metamorphic Iron-formation there are a of facies similar to those those described from from the the Biwabik Bh\Tabik Iron—formation Iron-formation facies by French (1968) (1968) and and Bonnichsen Bonnichsen (1969). (1969). Unmetamorphosed iron— ironformation like that described by Goodwin Good\vin (1956) (1956) is is found found in in Minnesota Hinnesota lint and North Lakes. only in in aa small small area area between between Gunf Gunflint Lakes. There the the iron-formation consists of chert, chert, iron iron carbonates, carbonates, greenalite, greenalite, abundant abundant iron—formation amounts of finely disseminated hematite, and and traces traces of of magnetite. amounts However, lint Lake, Lake, the the iron-formation iron—formation has has been been metamorphosed metamorphosed However, west of of Gunf Gunflint and three three metamorphic zones zones have been distinguished distinguished by hy changes changes in in mineralogy along tI tie strike of the the formation formation toward tm'Jard the the Duluth Duluth Complex. Complex. Zone 1, 1, or slightly metamorphosed iron—formation, iron-formation, occurs occurs in in the the area immediately west of Gunflint Lake. It consists of quartz, iron of Gunflint Lake. It consists quartz, iron carbonates, greenalite, minnesotaite, and carbonates, and stilpnomelane. stilpnomelane. FinelyFinely— divided hematite hematite occurs occurs in the divided the east east end of the zone, ZOne, hut but disappears mid—way in mid-way in it. it. Disseminated Disseminated and and interlocking grains of magnetite are are abundant, especially as abundant, as rims rims around around granules. granules. This part of of the the iron— i ronformation is much like like that that described described by by French French (1968) (1968) in in 'unmetaniorphosed "unmetamorphosed" formation is Biwabik Iron—formation. Iron-formation. Zone 2, moderately metamorphosed iron—formation, Zone 2, or moderately iron-formation, is is about about 1.2 miles wide and extends to to within \vithin 0.3 0.3 miles miles of of the the Duluth Duluth Complex. Complex. GruneriteGrunerite— cummingtonite, hornblende and actinolite, cummingtonite, actinolite, as well as as quartz and magnetite map,netite As in characterize this this zone. zone. As in zone zone 1, 1, much of the the magnetite is is between hetHeen 0.002 and in diameter; and 0.02 0.02 mm in diameter; a a size—range size-range similar to to that that observed in various other other Lake Lake Superior Superioriron—formations. iron-formations. S:'1all-scale pre-metAmorphic Small—scale pre—metamorphic sedimentary structures such such as as granules granules and andoolites oolites are sedimentary structures are partly partly destroyed, destroyed, but primarystructures structuresand andbeddinr, bedding featuresarearelittle little but larger—scale larger-scale primary features affected. Zone 3, or orhighly highlymetamorpl-iosed metan,orphosed iron-formation, iron—formation,occurs occurs adjacent to the and is is characterized the Duluth Duluth Complex Complex and characterizedby bya awholly ",hollymetamorphic metamorphic fabric. The The rock composed chiefly quartz, magnetite, magnetite,iron—rich iron-rich fabric. rock is is composed chiefly of quartz, euliedraloror suhl1edral subliedral grains pyroxenes, and Very commonly, commonly, eultedral (.~rains pyroxenes, and fayalite. fayalite. Very of are poikilitically poikilitically enclosed 'Tithin large large silicate silicate grains; of magnetite magnetite are Ptlclose.d \orithin (~rains; they are of of essentially they are essentially the the same Si1Iile size size as in inthe thelower lOHer grade grade rocks. rocks. However a significantpart partofoftile themagnetite ragnetite is is extensively Hmvever a significant extensively recrystallized, recrystallized, .-:IS and grains as as aa millimeter and grains as much much <18 millimeter in in diameter diiwleter are arc concentrated concentrated along along Actinolite bedding planes. planes. Actinoli bedding te isiscommon cor:lJl1on in magnetite—rich rnagm~ti te-rich layers, layers, and and both prograde and retrograde cummingtonite :Ls±un(lantly oresent. In pro~rade and retro0rrtde cummin;>:tonitc is -:hundnntly nresent. In general this this zone zone is is very very similar similar to tothat thCltdescribed de~;cribedinin thetheJ)unka Dunka!~oiver Piver area on the the I'lesabi :olesabi range ranre by by Bonnichsen nonnicbsen (1)69). (l,)6~l). area on contactt aureole o0 fthe l\Tork on on the contnc theDuluth lluluthComplex Complex in Preliminary work RoveFormation Formationindicates indicates aa complex mixtureofof rock rock tyPes Rove complex mixture tyoes suggesting sUfgcstinR partial melting, and textural textural variations variations due to original original partial meltint, and and mineral mineral and due to Tue met"mop)!losed metamorphosedrocKs rocks :HC are netainorphilari. The inhornogenities and degree degree of of liletamorr1dsr,l. inhoinogenities and commonly layered Individual layers layers commonly layeredane! andhave haveil agranohlastic granoblastic texture. texture. Individual contain; 1) hiotite and contain; 1) cordierite corcJieriteand and Iyperstliene hynersthene with '\Tith minor loinor biotite and ilmenire, ilmenite, hiotite, and plagioclase, hiotite, and ilmanite, ilmenite, J) aur-ite, hypcrsthene, plagioclase, 3) augite, 2) hypersthene, plagioclase ±± minor olivine, ilmentte, or 1+) 4) hvperstliene, plagioclase olivine, biotite, biotite, and "at! ilmeni.t0., hypersthe.ne, contact plagioclase, K—feldspar, andbiotite. hiotite. Calcareous K-feldsrar, and Calcareous beds GeJs near ncar the contact have aa skarn—minera.logy consisting wollastonite,diopsi<le, diopside, tremolite, tremolite, have skarn-mineralogy consisting of of lvollastonitc, fromtile the contflct contact - and piece to and p:arn0.t. Away AI<7ay frol'l nnd from fron plnee to eLace Dlace and 8rossularite grossularite garnet. the the �—10 7— -107- distance varies varies from several tens to several hundreds of feet this from several feet — this distance or may most peletic rocks are are rich rich in in biotite, and and cordierite cordierite may mayor may not be present. present. The Logan Intrusive Intrusive Rocks Rocks also also have have metamorphosed metamorphosed the the Gunf Gunflint lint and Fonnations. The width of the metamorphic aureoles are related related and Rove Formations. to sill sill thicknesses and range from less than to than one foot foot to to more than than 30 30 Gunflint Iron—formation feet. In In the the Gunflint Iron-formation it is difficult difficult to to recognize recognize unique metamorphic assemblages mineral assemblages adjacent adjacent to to sills. sills. In zone 2, 2, mineral assemblages characteristic of zone 3 occurs in assemblages in aureoles around around the the sills. sills. Similarly In in zone zone 1, ininnesotaite, minnesotaite, which which is is characteristic characteristic of of zone 2 to the the sills. sills. metamorphism is found next to In the Rove Formation Fonnation thick thick sills have assemblages assemblages that that can can be be In the assigned to to the the pyroxene—hornfels pyroxene-hornfels facies facies whereas whereas thinner thinner sills sills have have assemblages characterisitc of the assemblages the hornblende—hornfels hornblende-hornfels facies. facies. Locally 1969) and chloritoid (Grant, andalusite (Morey, (Horey, 1969) (Grant, 1971) 1971) have have been been identified identified in certain beds. beds. UPPER PRECAMBRIAN Introduction In northeastern Minnesota two In two units are are recognized recognized in in the the Upper Upper Precambrian: the Lower Lower Keweenawan represented by the Puckwunge the Formation and and the Formation the Middle Keweenawan which consists consists of of the the Logan Logan Intrusive Intrusive Rocks, the the North Shore Volcanic Group (Green, Rocks, (Green, this this volume), and and the the Duluth Complex. Complex. Puckwunge Formation Fonnation The Puckwunge Formation consists consists of conglomerate conglomerate and and sandstone sandstone which unconformably North unconfonnably overlie the Rove Formation Fonnation and underlie the the North Shore Volcanic Group. The type locality was described by N. N. N. H. Winchell Winchell (1897) on Sec. 25, 25, T. T. 64 N., N., R. R. 33 B. E. where about about 18 18 (1897) on the the Stump Stump River in Sec. feet of section is feet is exposed. exposed. Exposures Exposures of of similar similarlithology lithologyare arefuund in frnind in the Grand Portage area (Grout (Grout and and others, 1959). 1959). the If these these isolated exposures are equivalent to to the the Sibley Sibley Series Series If in Canada (Tanton, in (Tanton, 1931) 1931) they represent represent aa period of sedimentation sedimentation around around period of 1376 *± 36 m.y. m.y. ago (Franklin Kustra, 1970) 1970) followed by possible possible 1376 (Franklin and Kustra, followed by uplift and erosion prior to to the the onset onset of of volcanic volcanic activity activity in in Middle Middle Keweenawan time. time. Intrusive Rocks Rocks Logan Intrusive The sills was was applied applied to intrusive The name name Logan Logan sills to tabular, tabular, diabase intrusive rocks in the Rove Formation rocks in the Rove Formation(Lawson,. (Lm"rson, 1893, 1893, p. 48). Similar intrusive p. 48). Similar intrusive in Animikie formations are Animikie and and Lower Lm.,rer Keweenawan Keweenawan formations are currently referred to as Logan referred to as Logan Intrusive Rocks. Rocks. As As now now defined, defined, they they include include sills and dikes of sills and dikes of diabasic diabasicgahhro gabbrowhich which range range in in measured measured age age from from rocks rocks 1300 n.y. ~300 m.y. (hanson (Hanson and and [alhotra, Ha1hotra, 1971) 1971) to to 963 963 m.y. m.y. (Franklin, (Franklin, cited cited Ln Hanless Wanless and In and others, others, 1970, 1970, p. 57). Thus the Logan Intrusive Rocks, Rocks, 57). Thus the Logan Intrusive p. �—108— -108- North Shore Shore Volcanic Group Group may may units of the Duluth Complex, Complex, and the the North have overlapping time—stratigraphic time-stratigraphic relationships. relationships. rocks In County the the predominant exposed volume volume of of the the Logan Logan rocks In Cook County from the sill-like, and and the the present sawtooth smvtooth topography topography results results from the is sill—like, The the inclined inclined sills sills and and Rove Rove Formation. Formation. The differential erosion of the feet sills and sills range range in in thickness thickness from from aa fe\v few feet feet to to over over aa thousand thousand feet and thick sills for several several miles. miles. In In three three sills can be mapped along strike for dimensions dimensions they they form form aa boXtVork boxwork pattern, pattern, their their emplacement emplacement having having been been ~ntro11ed fault plane connections connections between nntrolled by bedding, bedding, joint and possibly fault sills sills but but in in the the Grand Grand Portage Portage in in northeastern northeastern Cook Cook County County area area there there and extent are extent to to the the are major major northwest-trending northwest—trending dikes dikes comparable comparable in in size size and sills (Grout and Schwartz, Schwartz, 1933, P. p. 36—59). 36-59). sills (Grout Early detailed studies the Logan Intrusive studies of of the the petrogenesis petrogenesis of the Rocks were primarily restricted to to the the sill sill on on Pigeon Pigeon Point Point (Bayley, (Bayley, Reinvestigation of 1893; Daly, 1917; 1917; Grout Grout and and Schwartz, Sch\vartz, 1933). 1933). Reinvestigation of these these 1893; Daly, rocks currently in in progress follmving generalized descripdescriprocks is is currently progress and the the following textures, and is based the unpublished work of tion of of textures, and mineralogy mineralogy is based OIl on the of J. A. A. Grant, Grant, E. E. Mathez, Mathez, G. G. B. B. Morey, N. N. Mudrey and and P. P. Weiblen. Weiblen • J. margins, fine— .Texture: T exture: Rock types types include aphyric chilled margins, fine- to medium-grained diabase with ophitic clinopyroxene enclosing plagioclase, medium—grained diabase clinopyroxene enclosing plagioclase, porphyritic diabase with plagioclase plagioclase phenocrysts, phenocrysts, plagioclase plagioclase cumulates, cumulates, margins form sharp contacts and granophyre. Chilled margins contacts with with country country rocks. rocks. Clino— from fine fine to to medium medium toward toward the the center center of of sills. sills. ClinoDiabase grades from remains ophitic even though the the grain size changes changes and enclosed pyroxene remains plagioclase crystals rarely rarely exceed exceed 55 mm rom in in length. length. Plagioclase phenocrysts as 10 10 cms ems long long in in thick thick sills. sills. Diabasic crysts however however are as much as rocks with plagioclase plagioclase phenocrysts phenocrysts grade grade into into accumulations of essentially rocks with accumulations of Such accumulations are found coarse-grained plagioclase. Such found in in the the upper upper coarse—grained plagioclase. to the the parts of some large sills and their origin has been attributed to floating of of plagioclase (Grout floating (Grout and and Schwartz, Schwartz, 1933, 1933, p. p. 50). 50). M1neraly: Minor olivine is found Mineralogy: found in the the lower part of of some Plagioclase as small grains grains enclosed in Plagioclase both both as as phenocrysts phenocrysts and as pyroxene is generally highly highly seriticized. seriticized. Clinopyroxene is is altered altered to to amphibole within single oikocrysts. oikocrysts. The The remnant remnant pyroxene varies varies in composition from pigeonite through augite and has a mottled birefringence which resembles resembles that that of of the the complex complex lunar lunar pyroxenes. pyroxenes. Ilmenite lirnenite and and minor minor magnetite appear at distinct horizons in in some some sills. sills. The is The ilmenite is commonly skeletal. skeletal. Minor interstitial interstitial quartz quartz is is characteristic characteristic of of much of of the the diabase. diabase. Biotite is is ubiquitous ubiquitous in the diahase diabase and texturally appears to appears to be of both igneous and and metamorphic metamorphic origin. origin. Granophyric intergrowths the diabase \vhere intergrowths are are common common in in the the upper upper part part of of the where they impart a pink mottling which can can be be recognized recognized In in hand hand specimen. specimen. Separate impart a Separate o~currences of granophyre in mappable units are rare, rare, except for for the the occurrences Pigeon Point sill (Mudrey P~geon (Hudrey and and Weiblen, Weib1en, 1971). 1971). sills. sills. �-109—10 9— Structure: In Structure: the Duluth Complex truncates the the various various In plan view the along strike strike at at aa low low angle angle (Fig. (Fig. 3). 3). Where exposed, the the Logan sills along base of the Duluth Complex dips gently southward, southward, whereas whereas both both the dips gently country rocks rocks may may dip dip as as much much as as 60° 60° to the south. south. Logan sills and country Drilling in in the the vicinity vicinity of of the the contact contact indicates indicates that that the the base base of of the the Drilling Complex steepens to as much as 60° and levels levels off off to to about about 30° 30° 11 km. km. This structural structural configuration configuration is i down-dip (Johnson, 1970, 1970, p. p. 82). 82). This down—dip (Johnson, zuch like that Mancuso and Dolence (1970) the East much that described by Hancuso (1970) in the ?Iesabi district. They suggested that Mesabi district. that the the emplacement emplacement of the Duluth that area was in part controlled controlled by by aa pre—Complex pre-Complex structure. structure. Complex in that :1inor hydrothermal hydrothermal mineralization mineralization is is found found within within >inera1ization: Mineralization: Hinor the Logan Intrusive Rocks. The mineralization is probably similar similar to to the the important occurrences occurrences the Thunder Thunder Bay Bay silver silver deposits, deposits, but nO no commercially important Island where where aa shaft shaft was was sunk have been found found in in Minnesota. Minnesota. On Susie Island along a fracture zone filled with calcite-barite and lesser amounts along a fracture zone filled with calcite—barite and lesser amounts of of quartz, bornite, bornite, chalcocite, chalcocite, chalcopyrite, chalcopyrite, pyrite, pyrite, covellite covellite and and quartz, malacite, malacite, ore was recovered which which contained 6.22 percent copper and At Loon trace trace amounts of silver silver (Grout (Grout and 1933, p. p. 64). 64). At and Schwartz, Schwartz, 1933, Lake, R. S. Blankenburg Blankenburg has has investigated investigated aa prospect prospect in in aa quartz-calcite quartz—calcite Lake, vein that that contains arsenopyrite with minor cobalt cobalt (Johnson, (Johnson, 1968). 1968). Duluth Complex consists of a variety The Duluth Complex consists of a variety of of anorthositic, anorthositic, troctolitic, troctolitic, granodioritic, and and granophyric granophyric rocks rocks which which crop out in in an an arcuate arcuate belt belt granodioritic, crop out A brief review from the Gunflint Trail (Fig. (Fig. 1). 1). A review of of from Duluth Duluth to to east east of of the the early literature literature and and recent work up to to 1969 1969 is is given given by by Phinney Phinney the of subsequent subsequent mapping and study of of the northeastern (1969). The results results of limb of the the Complex Complex are are presented by by Nathan Nathan (1969), (1969), Morey Horey and and others (1969), Johnson Q970), and Davidson Davidson (1970). (1970). (1969), Johnson a970), and Nathan (1969) mapped aa layered series of sheet—like (1969) mapped sheet-like intrusions intrusions across across the Gunflint, and Hungry Hungry Jack Lake quadrangles (Fig. (Fig. 2). 2). To the Gunflint, South Lake and the west, west, in in the the the Long Island quadrangle, Nathan's Nathan's layered layered series series is is truncated the Tuscarora Intrusion and and other other associated associated rocks. rocks. truncated by by the Nathan Layered Series of Nathan The layered layered series series extends extends from from the the east east edge edge of of the the Hungry Hungry Jack The Jack Lake quadrangle across across the South Lake quadrangle and into into the Gunflint \vhere it it is is truncated truncated by by the the Tuscarora Tuscarora Intrusion. Intrusion. This Lake quadrangle where truncation is is marked by an irregular northwest trending trending scarp scarp (Fig. (Fig. 3). 3). truncation For the most part, part, the the series series consists consists of of aa sequence sequence of of conformable conformable For the most The sheets thicken sheets 15-25° to to the the south. south. The sheets having having a regional dip of 15—25° to west and and are are locally locally interrrupted interrrupted by by minor minor crosscutting stockstock— to the the west and dike—like dike-like bodies. bodies. On the the east side of the Hungry Jack Lake Lake quadrangle aa nortlnvest northwest trending trending fault fault offsets offsets the the series series with with an an unknown unknown quadrangle amount of amount of displacement, displacement, but but as as much much as as 140 140 feet feet of of vertical vertical displacement displacement northeast side side is is inferred of the the northeast inferred (Fig. (Fig. 3). 3). �-110—110— The series consists consists of of troctolitic, troctolitic, gabbroic, gabbroic, and and associated associated felsic rocks. rocks. Several of the major units represent represent uniqud unique occuroccurrences in the the Duluth Complex of oxide—rich rences oxide-rich gabbros gabbros and and two—pyroxene two-pyroxene gabbros. For the most part, fine—grained fine-grained rocks rocks are are not not chilled chilled margins but occur principally as or inclusions inclusions as separate intrusions intrusions or of mappable size. size. Planar orientation of of minerals is is common, cornman, indicating flow flow or or crystal crystal setting. setting. Differentiation resulting resulting from from these processes can be demonstrated within some some units, units, however however the the layered series does not form form aa regular regular stratigraphic stratigraphic sequence. sequence. Intrusive relationships for 27 different units were established for 27 different units established using cross-cutting cross—cutting structures, structs, fine—grained using fine-grainedmargins, margins, inclusions inclusions and thermal effects, effects, the latter being principally aa development development of dark clouded plagioclase near intrusive intrusive contacts, contacts, Nathan (1969, (1969, p. 99). On the basis of field field relationships, relationships, mineralogy, and and composicomposip. 99). tion, tion, Nathan concluded the 27 27 units could could be be combined combined into into eight eight cogenetic cogenetic groups. groups. Detailed rock descriptions and interpretations interpretations are are given given by by Nathan (1969, (1969, p. p. 38—185) 38-185) and are are summarized summarized here here using using his his nomennomenclature. The descriptive rock rock names have have several several textural textural prefixes prefixes clature. that that characterize the primary mineral assemblages. assemblages. AA size size classclassification for these rocks, rocks, based on on visually—estimated visually-estimated mean mean grain grain diameters, is: diameters, is: >10 mm, mm, very coarse—grained; coarse-grained; 4—10 4-10 mm, rnrn, coarse—grained; coarse-grained; 1—4 mm, mm, medium-grained; medium—grained; 1/2—1 1-4 1/2-1 mm, fine—grained; fine-grained; <1/2 <1/2 mm, mm, very very fine— fineA 'granular' grained. fabrics are are recognized. recognized. A "granular" rock has Four basic fabrics grained. If elongate elongate grains grains are present and only equidimensional equidimensiona1 minerals. minerals. If are randomly oriented, the the rock is is "decussate," "decussate," if if the the grains grains define define aligned, the a plane, plane, the rock rock is "foliated," "foliated," and and if if the the grains grains are are aligned, the rock l'lineated. II All rocks rocks are named by the the characterizing characterizing rock is is "lineated." primary mineral assemblage, assemblage, in in order order of of increasing increasing abundance; abundance; the the primary mineral assemblage assemblage refers refers to to early early crystallizing crystallizing phases phases in in Modes are indicated by sub— contrast to to late late interstitial interstitial phases. phases. Modes subIf scripts. If a significant part of the the primary assemblage assemblage was was scripts. transported in the magma the rock rock is is referred referred to to as as an an allocrystallate, allocrystallate, aa cumulate cumulate being a special special case case in in which gravity gravity settling settling has has occurred. occurred. being a Rocks formed formed by crystallization in in place place are are called called autocrystallates. autocrystallates. Rocks Thus a Subscripts are used to to indicate modal composition. composition. Thus a descriptive descriptive Subscripts fine— rock name name for for aa troctolite troctolite formed formed by by gravity gravity settling settling could could he he aa fineinter— grained foliated olivine20—plagioclase70 cumulate with minor 01ivinezo-plagioclase70 cumulate \-lith minor interstitital augite5and augitesand oxides5. oxides S • Group 11 da The oldest unit (da) (da) in in the the layered layered series series now now appears appears in the upper part of the the section section as as dilated dilated septa septa as as It is is 8a fine-grained fine—grained foliated much as as 200 200 feet feet thick. thick. It much cumulate with with minor minor pigeonite9 —plagioclase63 cumulate 01ivine~s-plagioclase63 pigeonite 9 olivine which are and aug1te are also also cumulus cumulus in in the the middle middle of of and aug?e the unit. unit. ~his unit grades grades into into aa 1,000 foot—thick foot-thick his unit the sheet of foliated augite15—pigeonite26 augiteIS-pigeonite26of medium-grained, medium—grained, foliated A very fine—grained piagioclase cumulate (dh). (dh). A fine-grained plagioclase59curnulate S9 ollvine1 —augite27—plagioclase61 rock olivine o-augite27-plagioclaseGl rock (dc) (de) occurs occurs as as sizes near the base of masses o9 ~f various shapes and Slzes of masses the layered layered series. series. Nathan speculated that that it might the represent aa chilled margin of the represent the Group 1 intrusive intrusive rocks. - db db dc de �-111—111— Groip22 Group dg the major part of of the group comprises comprises the major oxide—rich oxide-rich part the This group The main unit layered series. unit (dg) (dg) is a a coarse—grained coarse-grained series. —augite —olivine foliated ilmenite—titanomagnetite foliated ilmenite-titanOmagnetitell-augitel~-olivineI4­ plagioclase cumulate. Within tff~s unit unit fe efollowing followrng plagioclase S66crystallization appears: (1) (1) ilmeniteilmenite— sequence of of5crystallization olivine-plagioclase; (Z) ilmenite—titanomagnetite—olivine— ilmenite-titanomagnetite-olivineolivine—plagioclase; (2) augite—plagioclase; and finally augite-plagioclase; finally (3) (3) apatite—pigeonite— apatite-pigeonitetitanomagnetite-ilmenite-olivine-augite-plagioclase. titanoinagnetite—ilmenite—olivine—augite—plagioclase. dd de Very fine—grained fine-grained foliated foliatedolIvine—oxide—augite—plagioclase olivine-oxide-augite-plagioclase Very plagioclase (dd) and (dd) and fine—grained fine-grained granulo—decussate granulo-decussate augite augite— - plagioclase (de) rocks occur in in unit (de) rocks occur unit dg dg as as inclusions inclusionsasasmuch much as as 400 400 A number of mappable units are across. A are gradational gradational feet across. with (1) at at the the base base of of the the complex, (1) complex, a fine— fine- to coarse— coarsegrained decussate decussate augite—olivine—plagioclase augite-olivine-plagioclase autocrystallate autocrystallate (df) grades into rocks rocks having a texture texture and and mineralogy similar (df) to that unit dg,and may may be the to that in unit the base of the the cumulates cumulates of of Unit df unit dg. dg. Unit df shows sulfide mineralization mineralization similar similar to to unit ttf ttf of of the the Tuscarora Tuscarora Intrusion Intrusion (Johnson, (Johnson, 1970, 1970, p. p. 68). 68). unit dg: dg: unit df df di dj dj dk Groyp3 dm din (2) A fine-grained, fine—grained, olivinezo-plagioclase66-olivine20 olivine2Q—p1agioclase6—o1ivine90 (Z) A cumulate with minor miner augite5-oxide4-pigeon~te4-apatiEel augite —oxide4—pigeonie —apatite1 cumulate with within unit * fine—grained, as aa thin thin sheet sheet ,vitfiin unit dg. dg. (3) (3) A fine-graine4, occurs as autocrystallatee decussate, oxide2 —augite28—plagioclase decussate, oxideZ3-augite2S-plagioclase45 autocrystallat 5 containing minor livine2 olivine and and apatite2 apatite tntrudes intrudes unit dg and and Z z is (4) Unit Unit dg is presumed to to be aa late late differentiate differentiate (di). (di). (4) grades upward into 100—200 grades 100-ZOO foot—thick foot-thick discontinuous discontinuous sheets sheets of coarse—grained, foliated pigeonite4—titanomagnetite4— of coarse-grained, foliated pigeonite -titanomagnetite 4 4 augite6—plagioclase83 cumulatescontaining minor potass~um potassium augite -p1a gioclase cumulates containing minor S3 6 feldspar2 fine—grained granular feldspar and and quartz1 quartz (dj). (dj). A fine-grained granular 2 l plagioclase, quartz, orthoclase orthoclase rock rock (dk) (dk) occurs occurs as as dikes dikes cutting rocks. cutting other Group 22 rocks. Unit din, the upper upper part part of the dm, the the layered layered se•:ies, se~ies, is a 2,000 foot—thick 2,000 foot-thick sheet of coarse—grained coarse-grained decussate decussate pigeonite11—augite24--plagioclase59 pigeonite13-augite24-~lagi~clase59autocrystallates and cumu1aes cumulates containing conta~n~ng minor nanor oxides2, oX~desZ' quartz2 quartz 2 and potassium potassium feldspar1. feldspar . This unit is thought thought to to This unit l have been emplaced along along foliation planes planes and thus thus to have dilated dilated the the earlier earlier units. units. Variations in in grain grain size and and modal mineralogy suggest suggest th.t that this this unit unit may be a multiple intrusion. intrusion. A A related related intrusion intrusion may be be dl c..ll dn do do geonite unit dl, aa inedluin—grained medium-grained decussate decussate pi pigeonite17— 17 augite20—plagioclase50 rock containing augite20-plagioclase60 containing minor oxide, oxide, quartz, which occurs occurs as quartz, and and potassium feldspar, feldspar, ''''hich as a small stock about 1—1/2 1-1/2 miles stock about milesacross acrossininthe the central central part of the Hungry Jack quadrangle. quadrangle. Another related related intrusive granular oxide19— oxide intrusive unit unit is is aa fine-grained fine—grainS granular 19 plagioclase41—augite4 rock (dxi) which occurs occurs as aa plagio~lase4l-a~gite40 rocl~ (dn) 1vhich sheet 6 sheet 6 feet thick tlack anI and 4 mlles the northern miles long in the the part of Souti of the South Lake quadrangle. quadranp;le. Felsic dikes which intrure were given given aa separate separate designation intrude unit unitdcL dm \vere designation (do) (do) and may represent a a late—stage late-stage differentiate of of unit unit dj dj or partially fused fused country country rock rock (Nathan, (Nathan, p. p. 115). 115). �-112—112— Group 44 dp dq Group 55 dr ds Group 66 dt du dw The next intrusive unit unit (dp) (dp) occurs occurs as as aa concordant concordant as 1,200 feet feet thick thick between bet'}7een units units dg dg and and sheet as much as It is is aa fine—grained db. It fine-grained foliated augite32—plagioclase58 augite32-plagioclaseS8 andtrace trace amounts cumulate with olivine3—hypersthene.7 olivine -hypersthene"? and amounts of oxides. Plagioclase augite occur in aa granular oxides. Plagioclase and ~nd augite occur in granular fabric, hyperstheneas as as pheno— hypersthene as oikocrysts, oikocrysts,and andolivine olivine phenocrysts. of late-stage late—stageinterstitial interstitial material crysts. The absence absence of material suggests the suggests the unit unit formed by flow flow or or crystal crystal settling settling with exchange exchange between between the the magma magma and andthe the inner cumulus cumulus melt. Near melt. Near the the top top of of unit unitdp, dp,a 100—foot—thick a 100-foot-thick sheet of medium—grained foliated olivine17—plagioclase83 of medium-grained foliated olivine17-plagioclase83 cumulate gradational with with unit dp. dp. cumulate(dq) (dq)isis gradational In the southwestern lint Lake southwestern part part of of the the Gunf Gunflint Lake quadrang!le quadrangiLe pyroxene-plagioclase and and aa heterogeneous assortment of pyroxene—plagioclase olivine-plagioclase olivine—plagioclase rocks rocks possibly possibly related related to to unit unit tta tta of the Tuscarora Intrusion truncate truncate the the layered layered series. series. of the A typical example is a medium—grained A medium-grained decussate decussate tironals5— tironals S ollvine5—augite 5—plagioclase75 autocrystallate (dr). olivines-augitelS-plagioclase75 autocrystallate (dr). Near the the base base of o the layered series a medium-grained Near medium—grained foliated augite1 —plagioclase77 rock foliated augite17-plagioclase77 rock with minor minor oxide3— oxide 3 pigeonite and olivine oivine (ds) pigeonite? and (ds) is is intruded intruded as as aa sheet sheet 300 feet feet chick hick between 300 between units units df df and and dg. dg. Unit ds ds is is highly altered with montmorillonite montmorillonite after after plagioclase, plagioclase, and and amphibole amphibole and chlorite after after pyroxene. pyroxene. Locally chalcopyrite and and bornite occur within interstitial, chalcopyrite interstitial, altered pyroxene. pyroxene. A number of oxide—rich A oxide-rich stock— stock- and and dike—like dike-like bodies bodies 3/4 miles miles across the Complex Complex across occur near the base of the in the South Lake Lake quadrangle. quadrangle. Nathan recognized recognized four four varieties: varieties: (1) olivine (1) medium-grained medium—grained granular olivine16— oxide73 rocks oxide amount of of plagioclase plagioclasel6 and and 73 rocks with a minor amount augite (dt). augite (dt). The ilmenite andtitanomagnetite anddtanomagnetite occur occur as the latter generally has has exsolved exsolved as primary primary phases; phases; the coarse ilmenite lamellae with intra—titanomagnetite coarse intra-titanomagnetite granules which have in in turn turn exsolved exsolved to to a a fine fine reticulate reticulate intergrowth of magnetite magnetite and and hercynite.(')On hercynite.C)On Little Iron Little Iron Lake in the South Lake quadrangle quadrangle aa medium-grained mediunv-grained granular plagioclase 1—oxide24—olivine gra~ular,plagioclase 1-oxide -olivine (du) rock rock (du) 24 49 having minor hypersttene hyperstLne and hav1ng m1nor 1/2 mile mile and augite augite forms fogs aa 1/2 long composite sheet long sheet within unit dt.G)A coarse--grained coarse-grained unit dt.(3)A granular plagioclase8—oxide23_pjgeonjt2, granular plagioclase -oxide -pigeonite -augite —augite '· i nor8 olivine I' ,23 44 rock rock containing minor m 0 1Vlne occurs as as 24small con t a1n1ng inalldisdi cordant cordant masses in the the South South Lake Lake quadrangle. quadrangle. UI) (4) Two Two occurrences of a coarse—grained occurrences coarse-grained decussate decussate oxide oxide —_ augite31_p1agioc 't l ' 1ase 10mapped a~g1,e3l-~ ag10c autocrystallate (dw) (dw) were wer0mapped S5 autocrystallate within wlth1n unit unlt dg. dg. This unit exhibits an amphibole an amphibole alteration alteration similar similar to to that that in in unit unit ds, ds but but is is conconsidered sidered to to be be part part of of group 5 rocks b;cause of its its group 5 rocks because of large oxide content. content. �-113—113— Groupj dx dy dy dz Group 88 daa dmaa Several fine—grained Several fine-grained decussate rocks occur as as discontinuous thin sheets discontinuous sheets along the base of the the comcomand dikes dikes higher higher in in the the plex and as small stocks and section. represent either either fused fused fractions fractions section. They may represent country rock rock or contaminated contaminated melts, but but all all are are of country They consist to be intrusive. They consist of: of: (1) (1) fine— finethought to grained -augite 2-plagioclase66 grained decussate decussate oxide oxide7—augite2plagioclase66 7 olivine -quarrz and and potassium1 potassluffi 1 rock having minor olivine2—quartz2 2 (2) fine-g~ained fine—grained decussate decussate oxide oxideçfeldspar (dx); (dx); (2) —augite31—plagioclase55 autocrystallate hypersthene -augite -plagioclase autocrystal1ate hypersthone SS (dy); and and (?Y (~t fine—grained fine-g1~inedaugite3—oxide9 augite -oxide g decussate 3 quartz10—orthoclase15—hornblende29—plagioclase34 rock quartzlO-orthoclaselS-hornblende29-p1agioclase34 rock (dz).. (dz) The youngest intrusive unit within the layered series 1—1/2 miles dikes and and stocks stocks as as much much as as 1-1/2 occurs as dikes across the Hungary Jack Lake quadrangle. This unit, unit, across in the inedium-grained granular granular quartzls-alkali quartz18—alkali feldspar feldspar77 aa medium-grained oxide2 (daa), rock ,vitl, (daa) , truncates truncates rock with minor augite and oxide 2 1 unit din. unit dm. Across an an interval at the the inerval over a mile wide at there is is aa prog,ressive progressive increase in end of of unit unit din, dm, there in east end the amount amount of of late stage interstitial material that the that has has a composition similar to to unit unit daa. daa. This unit unit (dmaa) (dmaa) might be aa late late stage stage differentiate differentiate ofofdin. dm. Nathan found however that hm-lever that unit unit dx dx has has been been intruded intruded and and altered altered by by daa. daa. n Therefore, unit daa Therefore, it itisispresumed presumed that thatdin dm was \Vas cold cold when ,vhen unit daa was intruded and that that the the gradational zone zone represents represents melt from daa daa that that was introduced introduced into into unit unit dm. dm. Intrusion and and Associated Associated Rocks Rocks Tuscarora Intrusion In the Long Island quadrangle (Fig. the Long (Fig. 2) 2) a a sequence of rock types common to to other appear in in the other parts partsofofthe theDuluth DuluthComplex Complex appear the following following succession away succession away from the base: (1) (1) aa fine-grained augite from the fine—grained poikilitic augite gabbro (tp), (tp), (2) (2) aa fine-grained (hornfels) (th), (th), fine—grained granoblastic gabbro (hornfels) (3) (ttf-ttm), (4) (4) interlayered interlayered (3) aa finefine— to to medium-grained medium—grained troctolite (ttf—ttm), troctolite and troctolite and poikilitic gabhro gabbro (tta), (tta), (5) (S) anorthositic anorthositic gabbro gabbro (ag), (ag), (6) ferrograndiorite ferrograndiorite (tg), (6) (tg), (7) (gr), and (7) (7) metamorphosed (7) granophyre granophyre (gr), flows (:mv). (kmv). Although the the outcrop pattern suggests aa simple differentiated differentiated layered sequence, the stratigraphic position of units tp, tp, ag, tg and gr layered sequence, the of units ag, tg have not been unequivocally established. established. Hm.;rever, ttm, and and However, units ttf, ttn, are clearly clearly parts a separate troctolite intrusion that that truncates tta are parts of of a part layered series series (Fig. (Fig. 3). 3). part of of Nathan's layered ynits ttm,tL,ad ttf, and tta: The unit of the Tuscarora Intrusion The main unit Units tta: is aa niedium—grained medium-grained troctolite (ttm, Fig. is troctolite (ttrn, Fig. 2), 2), consisting consisting of of 6S-70 65—70 percent and 10-lS 10—15 percent cumulus percent cumulus plagioclase (An (An 56 S-60)' and cumulus divine amouns 09 ol~vine (Fo0). (F~50). Relative amoun~s of poikilitic augite and iron—titanium iron-titanium oxides oXldes varies varles locally. locally. Orthopyroxene mantles olivine and and occurs occurs in in simplectic plagioclase. Biotite biotite is associated with sitaplectic intersrowth intergrowth with plagioclase. tile oxides. Planar orientation of of plagioclase and modal— modalthe iron-titanium iron—titanium oxides. layering are are locally locally well—developed well-developed and and mutually concordant. concordant. mineral layering poikilitic �-114-114— The troctolite grades into The into an an upper upper unit unit which which consists consists of of interlayered poikilitic augite gabbro and and troctolite (Fig. 3). 3). troctolite (Fig. The poikilitic augite augite consists consists of of about about 70 70 percent percent plagioclase plagioclase 15—20 percent augite, (An SO - 60 )' 15-20 augite, 5—10 5-10 percentilmenite percent ilmenite and and is is medium— med1um- to coarse—grained coarse-grained with withwell well developed developedaugite augite orthocrysts orthocrysts as much as 1—1/2" across. The as much as 1-1/2 across. The troctolite \vithin the the layered layered troctolite within interval interval is similar to to that that in in unit unit ttm. ttm. Contacts Contacts between between layers layers are generally generally sharp sharp and and in in general gener& conformable are conformable with with layering layering in in the the troctolite. troctolite. Interlayering of several several inches inches Interlayering occurs on a scale of to to several feet, feet, and is undulatory with wave lengths lengths of of ten to twenty twenty ten to feet feet and amplitudes of two two to to three three feet, but the the gross gross structure structure feet, but is nearly flat—lying. is flat-lying. 11 A belt of fine—grained Unit ttp; ttp: A fine-grained rocks rocks occur occur beneath beneath unit unit ttf. It ttf. It consists consists of fine— fine- to medium—grained medium-grained augite augite troctolite troctolite with 60—70percent percentcumulus cumulusplagioclase plagioclase (An50), with 60-70 (An ), 5-10 cumulus 5—10 percent cumulus 50 olivine percentpoikilitic poikilitic augite, .5—10 ~livin~ (Fo35), (F~35)' 15—20 ~5-20 perce~t augite, 5-10 percent . iron—titanium oxides, minor orthopyroxene-plagioclase orthopyroxene—plagioclase simplect1te. simplecite. 1ron-t1tan1um oX1des, and mlnor As yet the upper contact As contact of tins this unit unit has has not not been been observed observed and and it it is not clear from outcrop data is data if if it it is is aa separate separate intrusion intrusion or the the basal unit of the the overlying overlying rocks. rocks. Johnson (1970, (1970, p. p. 76) 76) concluded concluded from from drill drill core data that that it is is aa separate separate intrusion. intrusion. Unit th: th: Several areas of fine—grained, fine-grained, granoblastic granoblastic gabbro gabbro consisting of 50 to 60 percent short tabular tabular plagioclase, plagioclase, 30 30 to to 40 percent rounded rounded augite, augite, minor minor subhedral subhedral iron—titanium iron-titanium oxides, oxides, olivine, and and blades of biotite are olivine, are exposed exposed on on topographic topographic highs. highs. These rocks however rocks may be a remnant remnant capping over the the troctolite; troctolite; hOlvever there is no noticeable chilling of of the the troctolite troctolite next next to to the the there is hornfels and they they more likely likely represent represent large large inclusions. inclusions. Unit ap; ag: A break in in plagioclase plagioclase content content separates separates A distinct distinct break units tta tta and and ag. ago Unit ag ag — - an anorthositic gabbro— - contains 75 units anorthositic gabbro 75 to contrast to the 85 (in to the 50 50 to to 70 70 percent percent S5percent percentplagioclase plagioclaseAnAn5560 ( 55 60 Plagioclase is phase, and and interinterof is the the only only cumulus cumulus phase, of unit unit tta). tta). Plagioclase stitialminerals, minerals,occurring occurring in invarious various proportions proportions are are augite, augite, stitial olivine, and iron texture. Orthopyroxene olivine, and iron oxides oxidesinin aa poikilitic poikilitic texture. occurs in in siciplectic occurs sil:lplec tic intergrowth intergrm-Jth with W'i th late—stage late-stage plagioclase. associatedwith \'liththe theiron—titanium iron-titanium oxides. oxides. Planar Biotite isisassociated orientation of orientation of plagioclase plagioclase is is developed developed locally. locally. At At the the top top of of unit ag, quartz quartz and and potassium potassium feldspar unit ag, feldsparoccur occurinterstitially. interstitially. Tue flat—lyingoutcrop outcroppattern patternofof the the ferrogranodiorite ferrogranodiorite (tg) The flat-lying (tg) and granophyre concordant with \vithin the the and granophyre(gr) (gr) isis concordant with the the structure structure within troctolite (ttm) troctolite (ttm) and and the the anorthositic anorthositicgalibro gabbro could could be be just just another another part of the layered intrusion. IImvever some field evidence contrapart of the layered intrusion. however some field evidence contradicts this interpretation. interpretation. llornfels Hornfels inclusions inclusions and and sulfide sulfide mineralmineraldicts this ization are are found found in at several several localities localitiesalong along the the contact contact ization in unit unit tta tta at with unit ag. ago Thus the troctolite may be intrusive into the the Thus the intrusive into anorthositicgabbro gabbro as asininthe the GabbroLake Lake quadrangle quadrangle (Green (Green and and anorthositic Gabbro Phinney (1969) (1969)has hasextended extendedthe theolder older anorthositic anorthositic others, 1966). 1966). Phinney gabbro from from the Gabbro Lake quadrangle eastward the Gabbro eastward and and this this extension extension projects toward toward unit unit ag. ago Thus TIluS unit ag ag may be aa thin thin wedge wedge of of an an In this anorthositic gabbro. gabbro. In this case, units units areally extensive older anorthositic fg to the the troctolite troctoliteand and intruded intruded fg and and gr gr could could be either related to the ancirthositic gabbro or or aa differentiated differentiated part into the anorthositic gabbro part of of the the anorthositic gabbro. gabbro. anorthositic �-115—115— Unit f: This unit is restricted Unit fg: restricted to to aa topographically topographically high high area in the southwest corner of the the Long Long Island Island Lake Lake quadrangle quadrangle southwest corner (Fig. 3). 3). It medium-grained ferrogranodiorite which contains (Fig. It isisa amedium—grained ferrogranodiorite which 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, 50 to 60 percent cumulus plagioclase, 10 to 15 percent amphibole, minor clinopyroxene, amounts of potassium minor clinopyroxene, and and varying varying amounts of quartz, quartz, potassium anorthositic feldspar, and magnetite. Contacts with the underlying anorthositic gabbro and overlying granophyre are are gradational gradational over over tens tens of of feet. feet. The former former could replacement by by intrusive intrusiveferrograno— ferrogranocould represent replacement diorite or or differentiation differentiation within within the the anorthositic anorthositic gabbro. gabbro. Further diorite study is needed to the stratigraphic stratigraphic relationships. relationships. is needed to clarify clarify the i the Unit Unit gr: The ferrogranodiorite grades grades into into and is cut The ferrogranodiorite and is cut by by It consists It consists of of quartz, quartz, The texture texture ranges plagioclase, potassium plagioclase, potassium feldspar and and magnetite. magnetite. The ranges from from granophyric granophyrictoto granitoid. granitoid. fine- to medium—grained medium-grained granophyre. fine— granophyre. Unit kmv: kmv: The The granophyre granophyre intrudes intrudesblack black fine-grainedmeta— metafine—grained volcanic rocks whch whch are remnants of ofMiddle Middle volcanic rocks are interpreted interpreted totobeberemnants groundmassisishighly highlyaltered. altered. Acicular Keweenawan The groundmass Keweenawan flows. flows. The blades of ilmenite and plagioclase plagioclase phenocrysts blades ilmeniteare arecommon common and phenocrysts are are clouded similar intruded rocks rocks in layered series. clouded similar to to intruded it'. the the layered series. the the Mineralization: Two Two types types of mineralization are found in Duluth Complex 1m., grade gradecopper—nickel copper-nickel Duluth Complexininthis this area: area: (1) (1) low concentrations are associated associated with with the the basal basal rocks concentrations are rocks of of the the Tuscarora Intrusion and Tuscarora the layered series series intrusions intrusions and several of the (Johnson, 1970), (2) Ilmenite— and and titanomagnetite-rich titanomagnetite—rich rocks (Johnson, (2) Ilmeniterocks occr occur in in several several units units of of Nathan's Nathan's layered layered series. series. With \-lith regard regard to to the the mineralization, the the unpublished unpublished Ph.D. Ph.D. thesis (1970) warrants warrants special special mention. mention. The thesis thesis thesis of of Johnson (1970) summarizes the the results results of summarizes of an an exploration program conducted by the Cleveland—cliffs the Cleveland-Cliffs Iron IronCompany Company and and the Amerada-Hess Amerada—Hess Corporation Company from from 1966 1966 to to 1969. 1969. This program ass~ssed This assessed the economic potential of the base of the Duluth potential of the base of the Duluth Complex in in aa 38 38 km corridor along the Gunflint Trail adjacent adjacent to to the the Boundary Boundary Waters Waters Canoe Canoe Area. Area. The drilling program (10 (10 holes) holes) provides provides an unique opportunity opportunity to to assess assess the the effects effects of of drilling drillingononthe thearea area comparison with with other other inin comparison activities activities such such as as logging logging and and recreation. recreation. More importantly the the rereMore importantly lease lease of of geophysical, geophysical, drill drill core, core, and assay data, data, along along with Johnson's Johnson's study represents represents a study a major contribution by by aa mining company company to to the the concern for for the the environment of the the area. area. The The correlation correlation of of geogeophysical and physical and drill drill core core data, data, discussed below, makes makes possible possible aa discussed below, more accurate accurate evaluation more evaluation of of mineral mineral resources adjacent areas areas resources in in adjacent and in other and in other areas areas of of similar similargeology geology using using less less expensive expensive and and disruptive disruptive preliminary preliminary investigations. investigations. Coç—Nicke1_Iinera1izatjon: ~0J?E.£!:.-Nickel ~'lineralization: Discontinuous gossan Discontinuous areas areas of gossan and visible sulfide and visible sulfide mineralization min~r-;li~-ation ,.,ithin have been been mapped mapped within unit ttf ttf have across the across the Long Long Island Island quadrangle. quadrangle. Similar Similar isolated isolatedexposures exposures have have been found in in unit tta atat the been.found unit tta thecontact contact with with anorthositic anorthositic gabbro. gabbro. The The sulfide assemblage, consisting sulflde assemblage, consisting of pyrrhotite and and minor minor of chalcopyrite cI:alcopyrjte,pyrrhoi, pentlandjte occurs occursinterstitially interstitially to plagioclase pentlandite plagiocla~e and and olivine. Because Because of the size of of the of the smaller smaller grain grain size the troctolite troctolite a a distinct distinct interstitial interstitial texture, texture, like like that thatfound found in the sulfide sulfide mineralization mineralization in in the Kawishiwi in the the iCawishiwi area in the Gabbro area in tQe Gabbro Lake Lake quadrangle, quadrangle, is not apparent apparent ininhand handspecimen. specimen. is not �-116—116— Drilling across across the the quadrangle quadrangle (Johnson, 1969) has has indicated indicated aa Drilling (Johnson, 1969) tabular, tabular, possibly continuous volume of of low low grade grade ore ore (0.3% (0.3% combined combined copper-nickel) about 50 feet thick thick in in the the unit unit ttf. ttf. A A thinner thinner 10—20 10-20 copper—nickel) foot-thick zone, 50—100 50-100 feet feet above above the the lower lower mineralized mineralized zone, zone, has has foot—thick zone, aa higher combined copper—nickel copper-nickel content content that that approaches approaches one one percent percent 84). The mineralization can be correlated3with correlated with a (Johnson, p. 84). the order of 700 x 10 3 ohmcentimeters detectable resistivity anomaly on the in the troctolite (ttf, (ttf, ttm). ttm). Mineralization: The primary titanium titan1um oxide oxide phases phases Titanium Mineralization: ) and titanomagnetite are i].menite ilmenite solid 0 -MgTi0 solid solution solution (Fe (Fe20 —MgTiO -FeTi0 —FeTiO3) 3 3 2 3 (Fe304—Fe (Fe 0 -Fe 2TiO Ti0 4). ). Subsolidus exsoLtion exsolution as fiasresulted resulted in in the the complex complex 3 4 intergrosAhs âescribed intergrowEhs described above. Johnson (1970, (1970, p. p. 87) 87) estimates estimates that that Ti Ti recovered recovered from from ilmenite ilmenite in In unit unit ttf ttf in in the the Tuscarora Intrusion Intrusion could add $1.50 per ton to to sulfide ore ore from from this this unit. unit. The largest titanium concentrations at Little Little Iron Iron Lake Lake in in the the Gunflint Gunflint Lake Lake at exposures in the the South South Lake Lake quadrangle. quadrangle. do not exceed occurrences at the surface do however are in units dt and du quadrangle quadrangle and and other other isolated isolated Unfortunately, most of these Unfortunately, these about 35 feet feet in maximum about dimension. A large low—grade A low-grade titanium titanium resource also is contained within unit dg (Fig. unit (Fig. 3). 3). Oxide—rich Oxide-rich layers as much as as 5 feet feet thick are common, common, although individual layers seem seem too too thin thin and and discontinuous discontinuous to be mined separately. Unit dg should he to be considered considered in its its entirety for commercial evaluation with the the potential of of developing a very large tonnage tonnage of of low—grade low-grade ore. ore. The unit is very heterogeneous and and exposures are scarce and discontinuous, so only widespread field exposures and discontinuous, systematic drilling will reveal reveal which which parts parts have have the the greatest greatest promise. promise. �_____ _____, -117—117— References Cited Bayley, Bayley, W. W. S., S., 1893, The eruptive and and sedimentary rocks on Pigeon Point, their contact contact phenomena: phenomena: U. U. S. S. Geol. Geol. Point, Minnesota, Minnesota, and their Survey Bull. Bull. 109, 109, 121 121 p. p. Bonnichsen, Bill, 1969, 1969, Metamorphic Metamorphic pyroxenes pyroxenes and and amphiboles amphiboles in Bonnichsen, Bill, the Biwabik Iron—formation, Iron-formation, Dunka Dunka River River area, area, Minnesota: Minnesota: Mineralog. Soc. Soc. America, America, Spec. Spec. Paper Paper 2, 2, p. p. 217—239. 217-239. Broderick, M., 1920, Economic Broderick, T. T. M., Economic geology geology and and stratigraphy stratigraphy of of the district, Minnesota: Econ. Econ. Geol., v. v. 15, 15, the Gunflint Gunflint iron district, p. 422-452. p. 422—452. Daly, R. A., 1917, The geology geology of of Pigeon Pigeon Point, Point, Minnesota: Minnesota: Daly, R. A., 1917, Jour. Science, ser. sere 4, 4, v. V. 43, 43, p. p. 423—448. 423-448. Jour. Amer. Davidson, D. D. M., M., Jr., Jr., 1970a, 1970a, Geologic Geologic map map of of Kawishiwi Lake Davidson, quadrangle, Minnesota (with (with discussion): discussion): quadrangle, Lake and Cook Counties, Minnesota Minn. Geol. Hinn. Geol. Survey Misc. Nisc. Map Nap 7. 7. l970b, Geologic map of Perent Lake quadrangle, ____ , 1970b, quadrangle, Lake Lake County, County, Minn. Geol. Survey Misc. (with discussion): discussion): Minn. Survey Misc. Map Map 8. 8. Minnesota (with Faure, G. G. and and J. J. Kovach, Kovach, 1969, 1969, The The age age of of the the Gunflint Gunflint Iron Iron Formation Formation Faure, Geol. Soc. of the the Animikie Series Series in in Ontario, Ontario, Canada: Canada: Geo!. Soc. America Bull., v. v. 80, 80, p. P. 1725-1736. 1725—1736. Bull., Franklin, J. R. Kustra, Kustra, 1970, Franklin, J. N., M., and and C. C. R. 1970, Proterozoic rocks rocks in in the the Thunder Bay area: Field trip trip guide for the the 16th 16th Ann. Ann. Meeting Meeting Inst. Inst. on Lake Superior Geology, p. p. 49—68. 49-68. French, B. H., N., 1968, 1968, Progressive Progressive contact contact metamorphism metamorphism of of the the Biwabik French, B. Minn. Geol. Iron—formation, Mesabi Range, Minnesota: Iron-formation, Hesabi Range, Minnesota: Minn. Geol. Survey Survey Bull. Bull. 45, 45, 103 103 p. p. Goodwin, A. 1'1.,1956, N., 1956, Facies Fades relations Goodwin, A. relations in in the the Gunflint Gunflint Iron Iron Formation: Formation: Econ. Geology, Geology, v. v. 51, p. p. 565—595. 565-595. Econ. 1960, Gunflint Iron Iron formation formation of of the the Whitefish Whitefish Lake Lake area: area: - - - , 1960, Ont. Onto Dept. Dept. Mines, Hines, v. v. Grant, Grant, J. J. A., A., 1971, 1971, Geology Geology of of the the northern northern part part of of Gunfl:;.nt Gunfl.nt Lake Lake quadrangle: P. K. Sims and quadrangle~: in in Summ. Sunun. of Fieldwork, Fieldwork, 1970: 1970: P. K. J. ~~estfall Westfall eds.: J. eds.: Minn. fHnn. Geol. Geo!. Survey Survey Inf. Inf. Circ. Circ. 8, 8, p. p. 20. 20. Green, the Gabbro Green, J. J. C., C., 1970, 1970, Lower Lower Precambrian Precambrian rocks rocks of of the Gabbro Lake quadrangle, quadrangle, northeastern Minnesota: Minnesota: Minn. Hinn. Geol. Geo!. Survey Survey Special Pub. Pub. 13, 96 96 p. p. Green, C., W. Green, J. J. C., U. L. L. Phinney, Phinney, and and P. P. W. U. Weiblen, Weiblen, 1966, 1966, Geologic map of Cabbro Gabbro Lake quadrangle, Lake Lake County: County: Minn. Geo1. Survey Survey Misc. Misc. Minn. Geol. 'tap 2. :'lap 2. Grout, 1933, Contact Minnesota Grout, F. F. F., F., 1933, Contact metamorphism of the slates of of Ninnesota by granite and and by gabbro gabbro magmas: Geol. Geol. Soc. Soc. America America Bull., Bull., V. 44, p. p. 989—1040. 989-1040. v. 44, �_____ -118—118— , 1936, Structural features features of the Saganaga Granite of Hinnesoto. :1thnesot --Ontario: Ontario: 16th Internat. Geo1. Cong., Cong., Rept. Rept. 1, 1, p. p. 255—270. 255-270. Internat. Geol. Grout, F. F. F., F., R. R. P. P. Sharp, Sharp, and and G. G. H. M. Schwartz, Schwartz, 1959, 1959, The The geology geology of of Grout, Minn. Geol. Survey Cook Survey Bull. Bull. 39, 39, 163 163 p. p. Cook County, County, Minnesota: Minnesota: Minn. Grout, F. F. F., F., and G. Grout, C. M. M. Schwartz, Schwartz, 1933, 1933, The geology geology of of the Rove Rove fonnation in northeastern northeastern Minnesota: Hinnesota: formation and associated intrusives in Minn. Geol. Geo1. Survey Survey Bull. Bull. 24, 24, 103 103 p. p. Gruner, J. J. 14., W., Gruner, 1941, Structural geology of the the Knife Knife Lake Lake area area of of northeastern Minnesota: Minnesota: Geol. Geol. Soc. Soc. America America Bull., Bull., v. v. 52, 52, p. 1577—1642. 1577-1642. p. Halford, C. C. R., R., 1969, 1969, Petrography and structure of the Saganaga Halford, Granite, Saganaga-Northern Light Light Lakes Lakes Area, Area, Minnesota—Ontario: Minnesota-Ontario: Granite, Saganaga—Northern unpub. S. Thesis, of N. N. Y. Y. at at Stony Stony Brook, Brook, 7lp. 71p. unpub. ~1. M. S. Thesis, State Univ. of Hanson, R. Malhotra, Malhotra, 1971, Hanson, G. G. N., N., and R. 1971, K—Ar K-Ar ages of mafic dikes and evidence for low—grade low-grade metamorphism metamorphism in in northeastern northeastern Y.innesota: Hinnesota: Geo1. Soc. Soc. America America Bull., Bull., in in press. press. Geol. Harris, F. F. R., area, District Harris, R., 1968, 1968, Geology af the Saganagons Lake area, of Thunder Bay: Bay: Ont. Onto Dept. Dept. Mines Rept. Rept. 66, 66, 30 30 p. p. P. M., H. H. W. W. Fairbairn, Fairbairn, W. H. H. H. Pinson, Pinson, and and J.J. flower, Hower, 1962, 1962, Hurley, P. Unmetamorphosed minerals the Gunflint fonnation used to to minerals in the Gunflint formation test the age of the the Animikie: Animikie: Jour. Jour. Geol., Geol., v. v. 70, 70, p. p. 489—492. 489-492. Johnson, Johnson, R. R. G., G., 1968, 1968, Copper—Nickel Copper-Nickel mineralization in the the basal Duluth >1. A case study: S. Gabbro complex, complex, northeastern Minnesota: Minnesota: A study: unpub. unpub. M. S. Dniv. of of Iowa, Iowa, 91 91 p. p. Thesis, Univ. - _____, 1970, Economic geology of aa portion portion of of the the basal basal Duluth Duluth Complex, Complex, northeastern northeastern Minnesota: Minnesota: unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Dniv. of of Iowa, Iowa, 136 136 p. p. Lawson, C., 1893, sills of the northwest north\-rest coast of Lawson, A. A. C., 1893, The 1accolithic laccolithic sills Lake Superior: Superior: Ninn. Geol. Nat. Nat. lUst. Hist. Survey Survey Bull. Bull. 8, 8, p. p. 25—48. 25-48. Minn. Geol. Mancuso, D., and J. Dolence, 1970, 1970, Structure of of the Duluth gabbro compic complE Mancuso, J. J. D., J. D. D. Dolence, the Babbitt area, in the area, Minnesota (abst.): (abst.): in 16th Ann. Ann. Inst. Inst. Lake Lake Superior Geol., Geo1., p. p. 27. 27. Misra, Misra, A., A., and G. G. Faure, Faure, 1970, Restudy Restudy of the the age age of of the the Gunflint Gunflint FormaFonnation of of Ontario, Ontario, Canada (absr.): tion (abst.): in Soc. America abstracts abstracts in Geol. Geol. Soc. with programs programs for for 1970, 1970, north—central north-central section, section, v. v. 2, p. 398. 398. 2, p. Hoorhouse, W.W. Moorhouse, W.W., 1960, Gunflint Iron Iron Range in in the the vicinity vicinity of of Port Port Arthur, Arthur, Ontario: Ont. Dept. Ontario: Ont. Dept. Mines, Hines, v. v. ,pt. 7, p. p. 1—40. 1-40. pt. 7, , , ____, 1963, 1963, Concretions from the Animikie of of the the Port Port Arthur Arthur region, region, Ontario: Ontario: Proc. Proc. Geol. Geol. Assoc. Assoc. Canada, Canada, v. v. 15, 15, p. 43-59. p. 43—59. Morey, 1969, The geology of the Middle Precambrian Rove Morey, C. G. B., B., 1969, Fonnation Rove Formation In northeastern Minnesota: in l'linnesota: Ninn. Geol. Survey Special Pub. 7, 62 p. p. Minn. Ceol. Pub. 7, �-119—119— Morey, and P. P. K. K. Sims, Sims, 1970, 1970, Morey, G. G. B., B., J. J. C. C. Green, Green, R. R. W. W. Ojakangas, Ojáangas, and Stratigraphy of the the Lower Lower Precambrian Precambrian rocks theVermilion Vermilion rocks in the Minn. Geol. district, northeasternMinnesota: Minnesota: Minn. Geol. Survey Survey Rept. Rept. district, northeastern Inv. 14, 33 33 p. p. mv. 14, and U. Piorey, G. B., B., P. P. W. \v. Weiblen, D. H. H. Anderson, Anderson, 1969, 1969, Morey, C. J. Papike, and Weiblen, J. J. Geologic map of Long Island Island Lake Lake quadrangle, quadrangle, Cook Cook County, County, Minnesota: Minn. Minn. Geol. Geo1. Survey Survey open open file file map. map. Mudrey, 21. Hudrey, H. G., Light Gneiss, Gneiss, Northern Northern C., 1969, 1969, Petrology of the Northern Light Light Lake, Lake, Thunder Bay district, Light district, Ontario, Canada: Canada: unpub. unpub. M.S. M.S. Thesis, North. Ill. Ill. Univ., Dniv., 66 66 p. p. Thesis, North. Mudrey, >1. r1udrey, H. G., Reinvestigation of of "red "red rocks" rocks" G. , and P. P. hi. N. lveiblen, Weiblen, 1971, Reinvestigation in the in the Pigeon Point area, area, Minnesota (abst.): (abst.): in 17th Ann. Ann. Inst. on Lake Superior lnst. Superior Geol. Geol. Nathan, Nathan, Ii. H. D., portion of of the the Duluth Duluth Complex, Complex, 0., 1969, 1969, The geology of aa portion County, unpub. unpub. Ph.D. Ph.D. Thesis, Univ. Dniv. of of Ninn., Minn., 198 198 p. p. Cook County, Phinney, W. C., 1969a, the Gabbro Phinney, W. C., 1969a, The The Duluth Complex in the Gabbro Lake quadrangle, 11innesota: Minnesota: Minn. quadrangle, Minn. Geol. Geol. Survey Survey Rept. Rept. trw. lnv. 9, 9, 20 20 p. p. Phinney, N. W. C., C., 1969h, 1969b, Geology Geology of of Central Central part part of of Duluth Duluth Complex; Complex; Phinney, P. K. in Summary of Fieldwork Fieldwork 1969: 1969: P. K. Sims and and I. I. Westfall, Westfall, eds.: eds.: t-~inn. Minn. Geol. Geol. Survey Survey Inf. Inf. Circ. Circ. 7, 7, p. 2 18. Sims, P. P. K., B. Morey, R. Sims, K., G. G.B. R. w. l.v. Ojakangas, and N. W. L. L. Griffin, 1968, 1968, Preliminary geologic map of the the Vermilion Vermilion district district and and adjacent adjacent areas, northern ttinneso ta: lirin. Geol. areas, Ninnesota: ;1inn. Geo1. Survey Survey Misc. Map Hap N—S. H-5. Sims, Sins, P. P. 1(., K., G. C. B. B. Morey, Morey, and and J. J. C. C. Green, Green, 1969, 1969, The The potential potential for for ne~v in Minnesota: Ninnesota: 30th Ann. Ann. Mining Hining Symposium, Symposium, new mineral discoveries in Univ. of Uinn., Dniv. ~1inn., p. p. 75—87. 75-87. Tanton, Tanton, T. T. L., L., 1931, 1931, Fort Fort William and and Port Port Arthur, Arthur, and and Thunder Cape mapmap— areas, district, Ontario: Ontario: Geol. CeoI. Survey Survey Canada Canada Mem. Mem. areas, Thunder Bay district, 167, 222 1G7, 222 p. p. Wanless, IL hlanless, R. K., K., IL R. U. D. Stevens, Stevens, G. G. R. and R. R. N. N. Dalablo, Da1abio, 1970, 1970, R. Lachance, Lachance, and Age ages, z\gedetenninations determinations and and geological geological studies studies K-Ar K—Ar is6topic istopic ages, Report 9: 9: Geol. Geol. Surv. Surv. Canada Canada Paper Paper 69—2A, 69-2A, 78 78 p. p. Report Winchell, 1888, Report Winchell, A. A., 18$8, Report of of aa geological survey in ~linnesota Minnesota during the season of 1887: the season of 1887: tlinn. Minn. Geol. 16th Ann. Ann. Geol. Nat. Nat. Hist. lust. Survey, 16th Rept., p. 336—337. 336-337. Rept., p. , 1897, Some· Some new features _____ , 1897, features in the the geology of northeastern northeastern Minnesota: Minnesota: Amer. v. 20, 20, p. p. 41—51. 41-51. Amer. Geologist, Geologist, v. Wolff, \-101ff, J. J. F., F., 1971, 1971, Recent Recent geological geological developments on the the Mesabi Mesabi iron iron developments on range: Amer. Inst. Inst. Min. Mm. Engs., range: Trans. Trans. Amer. Engs., V. 56, p. p. 142—169. 142-169. v. 56, �-120—120— FIELD FIELD TRIP TRIP GUIDE GUIDE TO TO THE THE PRECAMBRIAN PRECAMBRIAN ROCKS, ROCKS, ~UL' i'u.._ •• _ .. _ COOK COUNTY ALONG THE GUNFLINT TRAIL Stop 1 End of Trail Campground -- Main Phase of Saganaga Granite the Saganaga Granite Granite at at this this stop stop is is aa The main phase of the medium—grained medium-grained hornblende—"quartz—eyet' hornblende-"quartz-eye" tonalite tonalite having quartz2o— quartZ20plagioclase (An27)60_lO—hornblende6—microljne3_5 (An27)60-70-hornblende6-microline3_S and and accessory accessory biotite, chlorite, chlorite, epidote, epidote, sphene, sphene, apatite, apatite, allanite allanite muscovite, biotite, and magnetite. magnetite. The apparent lineation of of the the "quartz—eyes" "quartz-eyes" is is 25_300 ENE. 25-30° ENE. This structure is is parodied in in the the hornblende—biotite hornblende-biotite inclusions. inch-sized inclusions related to to These inch--sized inclusions are are probably related the the south south of of Seagull Seagull Lake. Lake. the greenstones to the The bay leading north to Saganaga Lake was The Has considered considered by by Grout (1936) (1936) to to be aa shatter shatter zone. zone. It It is here interpreted as as a fault in the granite. fault the granite. At this stop, aa minor secondary secondary east— eastnortheast and epidote epidote northeast trending foliation is marked by shears and veinlets, and and may be related related to to faulting. faulting. veinlets, Stop 22 Gunf lint Trail Trail near near the the Campground —- Lamprophyre dike in Saganaga Gunflint Granite larnprophyre dike at this stop is is 50 SO feet feet wide, tv-ide, and and can can be be The lamprophyre traced to to the north shore of Saganaga Lake where it it is is found found to to cut cut the northern boundary fault fault (Harris, (Harris, 1968, p. p. 21). 21). This observation the sets aa 10lv-er lower age sets age limit for faulting and uplift uplift to to the the west Hest for for the the Goldich and others (1961, p. 52) date the biotite Saganaga Granite. Granite. (1961, p. S2) date the biotite (KA—70B)fromasmall (KA-70B)from a small island island to to the the north north at at 1.75 1. 7S h.y. b.y. Sundeen (1936) (1936) reviewed reviewed the the petrography petrography of of the the larnprophyre lamprophyre dikes the Saganaga Lake are.a and found biotite, biotite, hornblende, dikes in the Lake area and the mafic phenocrysts in a groundmass of of either either and pyroxene pyroxene as as the plagioclase or This dike dike contains contains plagioclasesoplagioc1ase5— plagioclase or "orthoclase. "orthoclase"11 This pyroxenel5_20—pyroxenei5_20—biotite513 pyroxenelS-20-pyroxeneI5_20-biotiteS_IO and and hornblende5. hornblendes. Accessory Accessory minerals include minerals include quartz, quartz, apatite, apatite, magnetite, chlorite, chlorite, carbonate, carbonate, sphene, pyrite, pyrite, zircon, sphene, zircon, serpentine, serpentine, talc talc and perovskite. perovskite. Stop 3a Stop Saganaga Saganaga Granite Granite -— Border Phase The strongly foliated foliated hornblende diorite diorite exposed exposed at at this this stop stop is typical typical of the border phase of the the Saganaga Granite. Granite. The foliation is of the is defined defined by by aa layering characterized by various proportions is proportions of of dark dark and light minerals; it is is nearly vertical and strikes N70°W. N70oW. Elongate and light minerals; it the foliation foliation plane plane define define an an elongate elongate hornblende needles within the ilneation lineation that that plunges gently gently to to the the east. east. A A transition from the border to the the main phase involving involving an an 'quartz—eye' structure structure increase in quartz - with tv-ith the the development development of of "quartz-eye" -— and aa decrease in hornblende can be seen in in a number of of outcrops outcrops lint Trail Trail to to the on either side of of the the Gunf Gunflint the north of of this this stop. stoP. �—121— -121- Stop 3b 3b Ietabasalt and associated rocks Netabasalt rocks vicinity of of this this stop, stop, vaguely pillowed meta— metaIn the general vicinity basalt thin-bedded to to laminated pyroclastic pyroclastic material material typical typical basalt and thin—bedded of the the mafic the volcanic succession succession are are exposed. exposed. Layering of nafic part of the is is nearly vertical and strikes in in aa northwesterly northwesterly direction. direction. Fracture Fracture cleavage direction cleavage also also is is near near vertical and strikes in a northeasterly direction parallel to to the the trace of the the Lookout Lookout fault. fault. The mafic cut by byconformable conformable layers layers of offine—grained fine-grained mafic rocks rocks are cut graphic feldspar granite. Locally graphic feldspar a thin layer of iron-formation Locally a thin layer of iron—formation overlies the older composed and chert chertunconformably unconformably overlies composedofof magnetite magnetite and rocks. Iron-rich the lower lower part the Cunflint Gunflint Iron—richstrata stratatypical typical of of the part of the Iron—formationare are exposed exposedon on the the steep north—facing Iron-formation north-facing slope immediately immediately to the to the south south of of these theseexposures. exposures. Stopj4 Stop lint Iron-formation Iron—formation Rock Trail Trail—- metamorphosed Gunf Gunflint Along Magnetic Rock Along of Zone 22 Thin-bedded, Thin—bedded, fine—grained, fine-grained, chert—axnphibole—inagnetitebearing chert-amphibole-magnetite-bearing strata assigned to to the upper part of of the the Lower Lower Slaty Slaty member member are are exposed along Magnetic Rock Rock Trail Trail at at this this locality. locality. These exposures are the transition between moderately and and strongly strongly metamorphosed metamorphosed are near the iron-formation; small, poorly developed developed pyroxene pyroxene porphyroblasts porphyroblasts iron—formation; small, can be be seen,pecially seen,especiallyinin moremassive massive beds beds at the the top of of the the thethemore member. Along to the thesouth, south,the theiron—formation iron-formation is Alongthe thepower powerline linetrail trail to locally with beds at 15°. locally deformed deformed with beds dipping dipping northward northward at 15°. Approximately7575feet feetfarther farther to Approximately to the thesouth southa anorthwesterly— northwesterlytrending, medium-grained medium—grained diabase diabase sill sill cuts cuts slaty slaty iron—formatin. iron-formatin. Approximately 200 feet the slaty to Approximately 200 feet to to the the south south the slaty beds beds again dip dip to the south south and coarse-grained, magnetite-rich the and are are interlayered interlayered with with coarse—grained, magnetite—rich cherty beds. beds. On the same knob, knob, algal chert—bearing chert-bearing beds characteristic of the Upper Cherty Member also of also are are exposed. exposed. Stop 55 Along the Kekabeic Kekabeic Trail Trail—- Metamorphosed Gunflint Iron—formation Iron-formation at at Zone 3. The Kekabeic oror less base of of the the Gunflint Gunflint The KekabeicTrail Trailmore more lessparallels parallels the the base Iron—formationand andthe thenorth-facing north—facing slopeimmediately immediately southofofthe thetrail trail Iron-fornlation slope south The iron—formation contains exposures exposures of ofthe theLower Lower Slaty SlatyMember. Hember. The iron-formation everyhas been extensively metamorphosed and now consists where in this this area has of various quartz—cummingtonite—grunerite—fayalite— various assemblages assemblagesofof quartz-cun~ingtonite-grunerite-fayalite­ magnetite and magnetite andquartz—cummingtonite—grunerite—pyroxene—magnetite. quartz-cummingtonite-grunerite-pyroxene-magnetite. �-122—122-are in Test along the the Trail. Trail. IIost Host are iI:. the the lowe.: 10HE;:: Test pits can be seen along magnetite-rich the Lower Lower Cherty Cherty Member. Member. Various sulfides, sulfides, magnetite—rich part of the especially pyrrhotite, the magneti:e. magnetL:e. pyrrhotite, also are associated with the Stop 66 rail cut -— Basal Contact of the dIe Duluth Along the Paulson Mine Mine railcut Complex. Complex The Paulson Mine railcut railcut exposes exposes the the base base of of the the Duluth Duluth Complex Complex from the from the Kekabeic Trail to to the Tuscarora Lodge Lodge road, road, aa distance distance of of about 1—1/4 1-1/4 miles. Contacts between bet\veen beds of of the the Upper Upper Cherty Cherty Memhe: Hembe:.: of the Gui-if Gunflint Iron-formation lint Iron—formationand andfine-grained fine—grained poikilitic poikilitic augite augite troctolite, troctolite, unit unit tp tp of the Duluth Complex, are are exposed exposed at at the the west west end of the the railcut. railcut. Also at the the west end end truncation truncation of of aa thin thin sill sill of the Logan Intrusive Intrusive Rocks Rocks can can he be seen. seen. About half—way half-l'1ay along along the the railcut, railcut, argillite and graywacke of the the Rove Rove Formation Formation are are in in contact contact The contact aureole here is ,-lith the the base base of of the the Duluth Duluth Complex. Complex. The is with narrow with no visible recrystallization recrystallization of of Rove Rove Formation Formation rocks rocks except within a few few feet feet of of unit unit tp. tp. This is inferred to to be aa 100—1,000 feet. reflection of the the thickness thickness of unit unit tp tp 100-1,000 feet. The dip lint and and Rove Rove Formation Formation varies varies from from 15-60° 15—60° to to the the south of the Gunf Gunflint along this part of of the the contact. contact. Stop 7a 7a Scenic overlook overlook on on the the Gunf Gunflint lint Trail above above Gunf Gunflint lint Lake -— Copper— Coppernickel mineralization at at the the base base of of the the Tuscarora Tuscarora Intrusion Intrusion The base of unit unit ttf of the the Tuscarora Intrusion Intrusion is is exposed exposed on on the northeast side lint Trail Trail at the side of of the the Gunf Gunflint the overlook. The fine— fineto mediuin—grairied troctoliteshows shows no no regular regular increase increase in grain medium-grained troctolite grain size size away away from a contact with unit tp tp and and the the upper upper part part of of aa Logan Logan sill. sill. Visible chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, pentlandite occur occur interstitial interstitial and olivine olivine in in the the troctolite. troctolite. This is a typical typical to plagioclase and of the example of the copper—nickel copper-nickel mineralization of of unit unit ttf, ttf, which which was was found by by Cleveland-Cliffs Cleveland—Cliffs Iron Company (in found (in five five holes holes along along the the base base of the Complex) to of the Complex) to occur constantly in aa 150 feet feet thick thick interval interval near near the base of unit unit ttf. ttf. The combined nickel—copper nickel-copper content content is is about about the 0.3 percent in this this interval. interval. A A slightly richer richer zone zone 10 10 to to 20 20 feet feet thick was was intercepted about about 50—150 50-150 feet above the the lower lower zone. zone. Stop7b Stop 7b 2000 feet northeast Rocks and 2000 feet northeast of of Stop 7a -— Logan Intrusive Rocks the the Rove Formation Thin bedded argillite is is exposed exposed on on the the north north face face of of aa ridge ridge capped by diabase. diabase. The argillite is recrystallized recrystallized to to aa biotite— biotitean interval interval of of aa few few inches inches at at the the contact. contact. bearing hornfels over an is typical typical of fine— fine- to to medium—grained medium-grained diabase diabase in in thin thin The diabase is sills the lower lower parts parts of of thick thick sills. sills. sills and in the �—123— -123- Stop 88 Northwest arm of Poplar Lake on the the Gunflint Trail At this stop stop typical exposures and and intrusive intrusive relationships relationships of of At this four of Nathads Nathans units units will be be examined. examined. On the the north north side side of of the the unit unit df, df, a fine—grained fine-grained decussate augite—olivine—plagioclase augite-olivine-plagioclase rock rock the Tuscarora Intrusion intrudes (troctolite) similar to unit ttf ttf of the intrudes (troctolite) unit dc, aa very veryfine—grained fine-grained granular granularolivine—augite—plagioclase olivine-augite-plagioclase rock whichmay mayrepresent representa achilled chilled margin marginofof the the oldest rock (gabbro) (gabbro) which unit of About 50 feet (da). About feet north of the the Trail Trail of the layered series (da). at the east end of the northwest arm of Popular Lake, at the east the north~vest Lake, a small small mass of unit dt, dt, aa medium—grained medium-grained granular granular olivine olivine oxide oxide rock, rock, occurs occurs within unit unit dc. dc. A A small isolated exposure of of unit unit ds ds with with uncertain uncertain contact contact relationships occurs occurs between units dc dc and and df df about about 500 500 feet feet Lake and and 400 400 feet feet north north of of the the Gunflint Gunflint Trail. Trail. northwest of Popular Lake South of of the the Gunflint Gunflint Trail there are exposures of of the the large large oxide— oxiderich sheet sheet unit dg (coarse—grained, foliated oxide, augite, olivine, dg (coarse-grained, foliated oxide, augite, plagioclase rock). plagioclase Stop 9 Sto2j Gunflint Trail Trailsouth southofofBear BearClub ClubLake Lake— - Late granitic granitic rocks rocks Cunflint of the theDuluth DuluthComplex Complex Unit daa, daa, a medium-grained quartz-feldspar rock, rock, is is medium—grained granular quartz—feldspar as aa dike on the the north north side side of exposed as dike in in unit unit dm dm on of the the Gunflint Gunflint Trail. Trail. The mainmass massofofdaa daaoccurs occurssouth southofofthe th Trail 1—1/2 The main Trailasasa astock stock 1-1/2 miles miles across. Unit dm, across. dm, aa cumulate cumulate sheet sheet ofofpigeonite—augite—plagioclase pigeonite-augite-plagioclase rockhas hasvisible visibleinterstitial interstitial quartz rock quartz and and alkali alkali feldspar feldspar in in an an This interinteraureole much as wide around daa. This aureole as much as 11 mile mile wide aroundthe the stock stock of daa. stitial material is interpreted as as replacement associated with the intrusion of unit daa. daa. stitial �This page intentionally left blank �"-"'; ADA ~ N A D A c '''L, . ./I '1''''-,t-'-"~)(. _/ <.~~,;t? x" I 'bJ I u : ST. LOUISI St LOUIS ' x. >. )( Ely. xLAKEx Marais X r AN AT ON P LANATION E E XP IKg XX I [+++ + +++J K xx )( xx xx Duluth Duluth Compte. Complell . O~ so' +)" ~~{ SlIver '" ~ '\. Bo.y ~V 0"" .c: U, '9'" <I)", to -" ~~ -c C ..r="c Zo 4? .!:! > 'C :'2 ::;; y.,e a. a :::> ""'" :.;;; 'E E 'c C <X cr INDEX MAP Figure 1 L 0 o 1 I 10 1O 20 ! I C A A L E if s S e 3Orniles 30 miles I ~{ 4? C 2 N V'1 Mci ic intrusive nt, usive rocks Mafic rocks ci rIrirt Shore of North Shore I , 1/7"-: N I // I ? Ettrus,ve Extrusive rocks rocks rongrnq ranging in from olilJine diem. in Composition composition from bosolr totile and basalt to quartz Quartz lotite local rhyolite tocot rt.yolite [02 4cg lite and Argillite cnd Groywocke Groywacke in Cook Rove Fm. includes Rove Fm. in Cook County County C ~ to ond and Vrginio Virginiaand andI horneon Thomson Fm. Fms. St. Louis Louis County .. in in St. County VO S/ I /-' I Lrl ~ ron —Fottitoijon Iron - Formation ncluces Gunflint C u,f tilt in Cook includes Cook County and B'wo bitt in in St. cnd Biwabik Louis County County SI. Louis o l'iitiu Undiv dod ided >lap showing the geologic 1ap of of northeastern northeastern Hinnesota Minnesota showing settinE of Cook County setting County and and the the location location of of Figure Figure 2. 2. C c: ,,=! n .0 E "'C" 4? .t'" a- �I ~) SAGANAGA ISAGANAGA GRANITE 4800730 —H— CANADA ~ + 0 CMATION AN ROVE FORMATION ANO INTRUSIVE ROCKS LOGAN INTRUSIVE ROCKS df L ds — I i-a I-' Gunflint dq tta I dp db dm -~ ag ~f9+ DULUTH WLUTH COMPLEX LAYERED SERIESOF OF NATHAN NATH\ LAYERED SERIES dm + da DIAGRAM BLOCK 0 dgL--------- DULUTH COMPLEX TUSCARORA INTRuSION '~f\ N 0' Trail BLOCK A DIAGRAM DIAGRAM + B • dm + do Quadrangles Studied Field trip hip stop Field stop seA L E Contact o Fault 3 2 4 = t> ~ ~ 5 mi. .~'*'tl) ~~ ",0", " " ~<b s-v G.:J BWCA boundary boundary BWC.A ~ .'" V ~'(§q, c§'t:: ;§ %o3T•3O' Figure 22 Figure I I Generalized geologic map map of part of of northwestern northwestern Cook Cook County. County. The The Gunflit-it Gunflint Iron-formation is is stippled. stippled. Only the the major units units of of the the Layered Layered Series Series of of Iron—formation in the the Duluth Duluth Complex Complex are are shown. shown. The area designated designated df df also also includes includes Nathan in dc,de,dk,ds,du,dy,dx, and dz; similarly ds dc,de,dk,ds,du,dy,dx, ds includes includes dc,de,dg,dk,dt,du,dv,dw; dc,de,dg,dk,dt,du,dv,dw; dg includes dc,dd,dh,di,du,dv,dt, dc,dd,dh,di,du,dv,dt, and dz; dz; dp dp includes dg,dj,and dg,dj,and dq; dq; db db includes includes (Nathan, 1969). da,dd, da,dd, and dm; dm; and and dm dm includes includes da,dd,de,dn,do, da,6j,de,dn,do, and dx. dx. (Nathan, I I I I I I I I I I I I I I I I I -,'" '" "-~~ ","''I 0/' �SAGAN.GA &EANtTS\ MET *VOLC ANICS LGI.JNFLINT lION FM. M El A V Ot C A N I C S FL I N1,\ .106 A N .IOVE ff N. M. dy I t-' tv ---J I in a \ \ 'I.-~-"'----- \\ \ \\ \ , Ii iJlm,l 0 o md 9r \ ------- -, .)l Figure 33 'I ,fg ' , II \ ~ lmile I dm —1900 -1900 / og 1900 C190° 1100 1700 1700 db 1500 I Soc 1500 A B 300FEET FEET 1300 ~1 FfET L_L-----------.... 1 300 300 EE1 diagrams showing showing the the irif inferred Block diagrams erred geologic geologic relationrelationships of of rock units in the ships the Long Island Lake and Gunflint Gunflint Lake quadrangles quadrangles (location Lake (location of diagrams shown in Figure 2). 2). f �-128—12 8— Mesabi Range Magnetite Hesabi Nagnetite Taconite 8, 1971 1971 May 8, by by R. R. W. W. Narsden Harsden Minnesota, Duluth University of Hinnesota, Duluth, Ninnesota Hinnesota �—129— -129- MESABI RANGE RANGEFIELD FIELD TRIP MESABI INTRODUCTION at the Mineinin Virginia, Virginia, The MesabiRange Rangefield fieldtrip trip starts at The Mesabi the Auburn Auburn Mine Minnesota andproceeds proceedsto to the Erie Minnesota and Erie Mine Mine near near Aurora, Aurora, the theReserve ReserveMine Mine at Babbitt and and ends ends at at the the Dunka Dunka Pit theeast eastend endofof MesabiRange Range at Babbitt Pit atat the thethe Mesabi near Birch trip isisdesigned show near Birch Lake. Lake. The The trip designedtoto showthe themetamorphic metamorphic changes changes the Biwabik iron iron formation formation caused caused by by the the intrusion intrusion of of the the Duluth Duluth in the Complex. The trip plan is shown on the index index map. The Mesabi esabi Range The Range trip trip is is made made possible possible by by the the cooperation cooperation of of the the Minnesota Ore Operations, United United States States Steel Steel Corporation, Corporation, the the Erie Erie other inforMining Company and Reserve Mining Company. Maps and and the Reserve and other Leaders for each part of furnished by the the mining mining companies. companies. Leaders mation were furnished the trip are are shown in the trip trip log. log. Stop 1. 1. Stop AUBURN MINE Leader: Wayne L. L. Plummer The accompanying map, section section and description description of the The accompanying map, stratigraphic sequence gives the geologic geologic setting setting of of the the Auburn Auburn Mine. Mine. The unit numbers shown shown on on the the stratigraphic stratigraphic sequence sequence are are painted on on the the rock rock to to aid recognition recognition of the the horizons. The upper part of the Pokegama quartzite and the Cherty, Lower Lower Slaty and 145 3*5 feet feet of the the Upper Upper Cherty Cherty Lower Cherty, members of the Biwabik formation members formation are are exposed. exposed. Oxidized and partly partly leached Biwabik formation is exposed on on the the west west pit wall wall and the Upper Slaty member and leached Virginia pit formations are exposed in north are exposed in the the slump slumpstructure structure at at the north end end of of the the pit. pit. �44 E S C' RESERVE <4 CQ(\ -1 0÷ I I-. f-' w o0 #9 I 1- Os ,Figure .Figure 11 INDEX MAP INDEX MAP OF THE OF THE MESABI DISTRICT DISTRICT,, MINNESOTA MESABI I I �---ex---• I f-' GRANITE Figure 22 Figure MESABI RANGE RANGE IRON FORMATIONS IRON ( BLACK BLACK AREAS AREAS ARE ARE DIRECT—SHIPPING DIRECT-SHIPPING ORE ORE BODIES BODIES)) U) W I-s f-' I �-132—132— AUBURN MINE MINE AUBURN The is isone the The Auburn AuburnMine Nine oneofofa agroup groupofofopen openpits pits located located near the city of Virginia, Minnesota. It city of Virginia, Minnesota. It was was originally developed as asan anunderground underground originally developed mine by the during the and promine by the Minnesota Minnesota Iron IronCompany Company durin?, theperiod periodfrom from1894—1902 1894-1902 and duced 2,143,000 2,143,000tons tons of of ore prior 1902 duced prior totoclosing closingin in 1902when whenownership ownership passed passed to the Oliver Iron Mining Nining Company, Steel 'Cor'CorOliver Iron Company,a asubsidiary subsidiaryofof United United States States Steel poration. Reopened as an poration. an open by Oliver in in 1951, 1951, the mine produced an openpit pit by 11,219,000 tons tons of of ore ore by by the the end end of of 1969 1969 when whenthe themine minehecirne became additional 11,219,000 inactive because the remaining ore is is under under the the approach approach traccs tracks totothe theViridrtia Virr,inia rescreening plant plant located located just just west west of of the the nine. mine. Most of the the crushing and rescreening open pit ore was loaded loaded by by electric electric shovels shovels into into side side dump dump cars cars and and hauled hauled to to the plant by electric locomotives, but in the plant in the the last last few few years, years, ore ore from from the the lower benches benches was was loaded loaded into into trucks, trucks, hauled hauled to to aa stockpile stockpile beside beside the the track track lower in the the upper part of the in the pit and reloaded into into railroad railroad cars. cars. The Auburn Auburn Nine and other former Oliver Iron }Iining Mining Company mines mines on the Mesabi Ran?,e Rance are are the Mesabi Mine now operated by U. S. S. Steel Steel Corporation, Corporation, Minnesota Minnesota Ore Ore Operations. Operations. The rocks rocks exposed in the the mine starting startin~ at at the the bottom bottom are arc the the the lower lower three three members members of of the the Biwabik Biwabik iron iron formation: formation: Pokegama Quartzite and the Lower Cherty, Cherty, Lower Slaty Slaty and and part part of of the the Upper Upper Cherty. Cherty. These dip dip from from degrees to to 20 20 degrees degrees to to the the northwest northwest as as the the formation formatcy lies north 5 degrees lies on on the the north side of the gently southwestward plunging Eveleth anticline and the center center fold known as the fold the Virginia Virginia Horn. Horn. formed in the Biwabik formation formation by removal The Auburn ore body was formed leaving less less of silica from iron bearing rock by leaching ground waters, waters, leaving soluble iron iron Oxides. oxides. The The ore body follows formation for ore body follows drnvn downthe thedip dipof of the the formation for fissure scarcely 50 about 3000 feet. as a aSlr::. small fissure 50 feet feet about 3000 feet. Beginning as at the the southwestern southwestern part part of of the the mine, the the ore ore body gradually gradually widens wide at toward the the northwest into a larger larger trough trough with with aa maximum maximum width width of of about about toward 500 feet. feet. In the the vertical walled fissure fissure at at the the southwestern southwestern end end of of the the mine, mine, the ore the ore extends extends from from slightly slightly above above the the Quartzite Ouartzite (here (here reduced reduced to to aawhite wite sand) feet of the Lower sand) through through 115 115 feet of the Lower Cherty Cherty member, memher, whereas whereas near near the the west west end end of the mine, the ore extends extends to depth of of about about 260 260 feet feet from from the the surface surface of the mine, the ore to aa depth Duetoto the the leaching to contact. Due leaching of to the the Lower Lower Cherty-Lower Slaty contact. silica, ore zones zones are commonly slumped into structures resembling synclinal structures resembling folds. folds. Where slumping occurs adjacent to to taconite taconite walls, walls, sltnp slump faults faults may ii silica, occur. Glacial deposits deposits consisting of reddish—gray—brown reddish-fray-brown till containing containinff numerous boulders boulders of of granite granite and and greenstone greenstone covered covered the the entire entire area area to numerous to aa depth of 10 to to 35 35 feet. feet. years An earth slide in the northwestern bank of the mine several years was stabilized stabilized with with aa rock fill which now covers covers much much of of previously ago was fill which previously exposed exposcd formation formation in in this this area. area. �-133—13 3— I I I I I I I I ROUCHLEAU MINE VIRGIJ1IIA I --l-- I ------ I I I I -j-----t---- ! i I I I " \/Jf'~O~ ~Oo @ V CRUSHER SCREENING -L __ PLANT --- \ \ RIqQ: \ .::>(( \ \ \---_--I \ Figure 33 Figure ~ II1- GEOLOGIC MAP AND VICINITY VTCINITY GEOLOGTC MAPOF OF AUBURN AUBURNMJr~E M:rE AND �-134-134— Table 11 Table STRATIGRAPRIC SEQUENCE G'mATIGRAPHIC SEQUENCE IN THE THEBIWABflC BIWABIK ThON IRONFORMATION FORMATION AUBURN ICIE AUBURN KmE Thickness 'l'h1ckness in feet1 in teet l UPPER CHERTY MEMBER 16.22 Jaspery, algal chert (G 16. Jaspery, conglorieratic conglomeratic and and algal submember I) (a and S $ submember x) 15. 14. 14. 13. 13. 12. 10 (eat.) (est.) Covered Covered interval interval 10 (est.) (eat.) Nodular hematitic chert chert. beds interbedded interbedded with with laminated hematite-eilicate-magnetite beds hematite-silicate-magnetite 48 48 +1' +f Laminatedhematite-uilicate-magnetite heniatite-ailicate-magnetite beds with subordinate Laminated jaspery chert beds Jaspery beds and and lenses 31 Jaspery, conglcaneratic chert beds with subJaspery, conglomeratic chert beds interbedded interbedded with ordinate laminated laminated heinatite-ailicate-magnetite hematite-silicate-magnetite beds beds 28 liberty taconite taconite with magnetite Cherty with thin thinirregular irregular magnetitebeds, beds,mqgfl* magneanddisseminated disseminated 'retite tite mottles mottles and mBgnetite 16_ _--=~ ....,;;1;;,;;6 143 LUiQER $LATY MEMBER3 11. U. 10. silicate magnetite Laminated silicate magnetite taconite taconite with withsubordinate subordinate silicate chert chert lenses lenses silicate Laminated non-magnetic silicate taconite, part. Laminated non-magnetic silicate taconite,fissile fissile in in part. 6' of fissile fissile"intermediate "intermediate slate" slate" at atbottom bottan (a (G and S 6' of submember Q) 6ubmember Q) 101 .....37 3;.;7_--=~ 138 ER LC1WER CHERTY MEMBER LO CHERTY Cherty with irregular irregularrnngnetite magnetite beds. Upper Upper 10' liberty taconite taconite with has silicate rich has dark-colored dark-colored silicate richbeds beds instead instead of ofmagnetite magnetite beds, ng base of lower indefinite beds, mak4 making lower slaty slatysomewhat somewhat indefinite 37 37 8. Mottled with chert "pebbles" and and Mottled silicate-magnetite silicate-magnetite chert with abundant coarse coarse granules. abundant U 11 7. 7. Cherty taconite with with thick thick (i"±) (1 t)magnetite magnetite beds beds and and mottles mottles liberty 84 9. 9. 6. 1f Mottled cherty very irregular irregularmagnetite magnetite Mottled cherty taconite taconite with with thin, thin, very beds. 14 5." Thick jaspery chert beds beds interbedded interbedded with with varying varying proporproporThick 5. tions of of thin, thin,regular regularlaminated lBDlinatedinngnetite-hematite-. magnetite-hemat1te-s1l1cateilicate- carbonate carbonate beds beds.• 66 �-135—135— Thlckneoo Thickne on l feet1 in feet (ConYd) Ldwer Cherty Member Member (Cont'd) Lover Cherty Fflyft, 'rhi c k henicstitic hem~~ti tic chert beJa beis with witb subordinate sulJordinate laminated laminated zonos. Seineclastic elastic sand sand grains grains near zones. Some near bottcn. bottan. Much carbonate. 8a Jaspery, ehert with subordinate Jaspery, conc'lomeratic conglomeratic and algal chert subordinate laminated zones. lnminnted zonea. Sand graino graino common. common. 4:4 2. z. l'lassivechlorit1c chioritic (or (or hematitic) hematitic) sandstone sandstone l-lilsslve 8 8 1. 1. Jaspery, Juapcry, conglomeratic and algal algal 4.. 3. chert 4 4: 236 Total thickness exposed Total, 5I7 Base not exposed Base exposed P0iGAl4A QUARTZ ITE ** ** * ** * * * ** 1. 1. Units 15 and onbank bankbetween betweentruck truckroed road,and andrailroad railroad near entrance Units and 16 measured measured on entrance to pit. pit. Units measured on on SW bank, at at BE end end,ofof pit. pit. Remainder measured. to Units 11 - 5 measured S\rl bank, measured above railroad. above railroad. 2. Unit correspondtoto numbers numberspainted paintedon onthe the walls walls of the Unit nwubers numbers correspond theAtthun Auburn Mine Mine and and are not Intended intended to be a new stratigraphic stratigraphic system. system. 3. 3. exists The lower lower slaty-upper slaty-upper cherty cherty contact contact is 1s not not well—marked, well-marked and and disagreement disagreement exists to its its position. position. as to ** ** ** ** ** * * orebody bodyisis of of the fissure or The Auburn Auburn ore or trough trough type type and and its and its location and 0 W, 400 W, nearly nearly appear to be controlled controlled by set striking strikingabout aboutNN 40 orientation appear to be by aa fracture set at right At the SE of the the mine at right angles angles to to the the strike strikeofofthe theiron ironformation. formation. At SE end. end. of mine the trough is only from the the quartzite quartzite through trough only 50' 50' wide wide and and the theore oreextended extended upward upward from through about about U5' ofofthe At the the northwest end the the trough trough 1s is 500 115' theLower LowerCherty Chertymember. member. At northwest end 500 feet feet wide wide and and ore ore occurs occurs for about about 260 Z60 feet feetfrcmt fran the the Lover Lower Slaty-Lcwer Slaty-Lower Cherty Chertycontact contact to to the Exceflent examples examplesofofore oreslump slumpstructures structurescan canbebeseen seenin in the the ends of the outcrop. Excellent eDds ot pit, pit, especially especiallyatatthe thenorthwest northwestend.. end. �-136— -136- Mine sLown ERIE MINE MINE —- The stops in inthe theErie Erie Mineare are shownon onthe theaccompanying accompanying map. The Erie geologists designate units in in the the Biwabik Biwabik formation formation as follows: A—F A-F G-O G—O P—Q P-Q R—W R-W Leader: Stop 2. 2. Upper Upper Lower Lower Slaty member — - .av. 110' 110' av. Cherty member - avo 185' 185' Slaty member — - av. avo 105' Cherty member — - av. avo 125' Forrest W. W. Boyce Bovee Erie —- Pit 1 West This stop the upper part part of the the Lower Lower Cherty member This stop is is in the (units are are designated TT and and SS layers layers by by Erie). Erie). The Biwabik (units formation is is composed composed of of tine fine Stilpnomelane, Stilpnomelane, I!innesotaite, Minnesotaite, magnetite and cherty quartz and contains bands, mottles quartz and contains bands, mottles and and blotches blotches of' of pink to yellow carbonate. carbonate. Stop 3. 3. Erie Pit 2 West This stop stop is is in in middle to to upper upper part part of of the the Upper Upper Cherty Cherty with the the member and the lower part of the Upper Slaty member (F) (F) with in this this pit pit are algal layer (I) (I) well exposed. exposed. (Units (Units in are designated (Upper Slaty), G, G, H, H, I, I, JJ and and KK by by Erie). Erie). A A diabase sill about about F, (Upper feet in thickness occurs near the bottom of 33 feet of the the exposed exposed iron iron formation in the KK layer. layer. Some green green mottles mottles of of cuminingtonite cummingtonite occur in the I J layer layer and and carbonate carbonate mottles mottles in in the the KK layer. layer. Stop Stop 4. . Erie Pit Pit 33 This stop is in in the western part part of of Pit Pit 33 in T, S. S. and BR of the the Lower Lower Cherty Cherty member. member. The layers in the middle part of rock is a cherty, silicate silicate taconite taconite with with layers layers of of cummingtonite. cummingtonite. Stop 5. Stop 5. Erie Pit Pit 33 This stop stop is is in the the eastern part of pit 33 in the T, CS and R F in about about the the same same stratigraphic stratigraphic layers of the Lower Cherty member in zone as as stop stop 4. 4. Much of the chert in the Biwabik formation formation has has gone to form form actinolite actinolite and and cumniingtonite. cummingtonite. The rock is termed taconite. Locally pyrrhotite occurs occurs in in the the a magnetite-silicate magnetite—sflicate taconite. iron formation. formation. �ERIE MINING COMPANY COMPANY ERIE MINING Of MAP OF E-1835.2 E— 1835 • 2 PLANT 8 MINE AREAS AREAS & MINE LEGEND o CRUSHER CDCOAR COARSE CRUSHER ®FINE FINE CRUSHER CRUSHER ® @ CONCENTRATOR CONCENTRATOR ® .j)PELLET @ PELLET PLANT ® ® ® LOADING LOADING POCIET POCKET ®STOCKPILE STOCKPILE ® CD GENERAL SHOPS SHOPS .1; ADI.IINISTRATION AOMINISTRATION BUILDING S I I-' La) LV ....... I AREA I S Figure 44 Figure Plan of of Erie Pit Plan Erie Pit — �—138— -133- RESERVE MINING COMPANY COMPANY Minil1g Company Company mine mine is is situated situated in in aa zone zone with ~vith aa The Reserve Miniqg considera~le considerable range in mineralogy and texture texture shown shown by by the the Biwabik Biwabik formation. formation. The The Reserve Reserve geologists geologists designate designate units units of of the the Biwabik Biwabik formation as follows: follows: A—G A-G 11—0 H-O P—Q P-Q R-V H—V Stop Stop 6. Upper Upper Lower Lower 100130 av.—120 Slaty member member -— 100'-130' av.-120 Cherty 120—160' av.—140 Chertymember member—- 120-160' av.-140 Slaty member —- 75—120' 75-120' av.'90 av.-90 Cherty member — - 30'-50' av.-30 30'—50' av.—30 Reserve Mine Mine (Peter Mitchell HitcheEMine) Hine) Leader: James James i1. W. Emanuelson Emanuelson This sstop is in This top is in the the western ~ves tern part part of of the the mine, mine, northwest of of Crusher No. No.22 in the the middle middle part partofofthe theUpper UpperCherty Chertymember member in in the J, KK and rock is silicate taconite with J, and L L zones. zones. The The rock is aamagnetite magnetite—- silicate abundant cuznnhingtonite. cummingtonite. Stop Stop 7. 7. Reserve Mine Mine This stop is in same general stratigranhic stratigraphic zone zone as as stop stop 6. 6. with Hith The rock rock is layers from from FF to 00 exposed. exposed. The is aamagnetite—quartz—silicate magnetite-quartz-silicate taconite with and garnet. garnet. There taconite with hedenbergite, hedenbergite, ferro—hypersthene, ferro-hypersthene, and There are local local areas areas of of pegmatite. pegmatite. Stop 8. 8. Dunka Pit The Dunka Erie ['lining Mining Company Company isissituated Dunkapit pit of of the Erie situated near near the eastern end of the Rangewhere wherethe the Bhvabik Biwabik formation formation is eastern end of the Hesabi Nesabi Range by the theDuluth DuluthComplex. Complex. This Hill show show the upper upper This stop will, intruded by part of the part Upper Cherty the Upper Upper Slaty Slaty the Upper Cherty member, member,the thelower lowerpart part of of the member,and and gabbro gabbro of of the member, the Duluth DuluthComplex. Complex. The is composed composed of magnetite, hedenbergite, hedenbergite, The taconite taconite is of quartz, quartz, magnetite, fayalite with with andradite andradite garnet garnet and and locally locallysome some hessingerite hessingerite fayalite The contains suiphides, sulphides, chalcopyrite chalcopyrite and and Thegabbro gabbroininthis this area contains pyrrhotite with pyrrhotite with pentlandite. pentlandite. The iron iron formation formation and andgabbro gabbrowill willbe be observed observedinin the the pit pit and The and in north of of the the pit. pit. in outcrops outcrops north �— -' __I / / ea _I - —— __i SCALE SCALE IN IN MILES MILES —11 4 0 5 2Z 5 / / / / / I I tO / / 'sTrOe,. stnva / I /8 /& 8/~ "E i/l '7 '2OA f/~ STAfiC) "I<c 0: I~ " "/>c / 460 400 / I I I I I (.0 '0 / I I / / / / / - -&try / p -— 2C • 0 SCA.E SC --' AtFtPC i.E iS 5ØS StS?iOeiCO AT iJJ) FT iNT€vSiS SIRS DPI ROADS C IAD DPI F Lint STh YISG co-s5i0$i SHO_ O&nI. ms •PT OLJTLIIA • S Off _ _N PIT Oln'LJNE,I.S - ';"b6 ZC = SCALE ,", 2000' JAN 196~ JQ'I . . . . 10A- I Figure Figure 55 Plan of Plan of Reserve Reserve Mine Mine �lL ERIE ERIE MINING MINING COMPANY COMPANY HOYT PLANT HOYT LAKES LAKES PLANT PLANTSITE TO TO DUNKA DUNKA PIT PIT AREA AREA Figure 6 U, DUNKA PIT BABBITT / ¶ '\ y/ ~ --- C -- 01 \J c:> I I-' ...... o0 .pI RESERVE MINING co. CRUSHER No.2 AREArJ ,, . ., , . , r-. :' ~ l P P L SIT E r-- ) ~ ( I I �—141— -141- of the Metavolcanic— Geology of the Vermilion MetavolcanicMetasedimentary Belt, Belt, Northeastern Minnesota May 8, 1971 Prepared by R. R. \v. U. Ojakangas, Ojakangas, University University of of Ninnesota, iinnesota, Duluth, Duluth, and and Ninnesota Geological Survey P. P. K. Sims, Sims, Minnesota Geological Survey, K. Survey, Minneapolis, Minneapolis, Minnesota C. G. B. Norey, Morey, Hinnesota Minnesota Geological Survey B. Survey Minneapolis, Minneapolis, Minnesota J. J. C. C. Green, Green, University University of of Minnesota, Minnesota, Duluth, Duluth, and Minnesota Geological Survey �—14 2— -142- Guide to Metavolcanicto the the Geology of of the Vermilion Metavolcanic— Belt; Northeastern Minnesota Metasedimentary Belt; INTRODUCTION The The Vermilion district is is a a belt of metavolcanic-metasedimentary metavolcanic—metasedimentary rocks rocks more than 100 100 miles long long and and as as much much as as 20 20 miles miles wide. wide. It is is bordered on on the the north north and and south south by by younger younger granitic granitic batholiths batholiths (Fig. (Fig. 1) 1) of Algoman Algoman (Kenoran) (Kenoran) age. age. The region is typical of Lower Precambrian (>2,500 greenstone—metasediment--granite complexes complexes of of the the Superior (>2,500 m.y.) greenstone-metasediment-granite province. metavolcanic—metasedimentary sequence constitutes a complex The metavolcanic-metasedimentary volcanic pile, pile, characterized characterized by interfingering of lithologies and local local volcanism. Most of the the metasediinents metasediments are composed of of repetitions of volcanism. volcanic detritus, detritus, and probably include volcaniclastic and and epiclastic rocks. Numerous Numerous coeval and younger igneous rocks rocks occur locally within the sequence. sequence. The stratified sequence was metamorphosed and and deformed deformed before before and and during emplacement of the bordering granitic rocks rocks of the the Giants Range and the the Vermilion Vermilion batholith. batholith. Pervasive greensehist greenschist facies facies batholith and assemblages were developed except adjacent to the the intrusive bodies where metamorphism attained aniphibolite amphibolite grade. Deformation consisted consisted of of two two metamorphism attained major foldings foldings and and of of later later faulting faulting on on aa major major scale. scale. STRATIGRAPHY ST RATIGRAPHY The metavolcanic and metasedimentary rocks rocks are are assigned assigned to to five five The oldest oldest formation, (Morey and and others, others, 1970). 1970). The formation, the the Ely formations (Morey is overlain Greenstone overlain Creenstone -— composed mainly of mafic mafic metavolcanic metavolcanic rocks rocks -— is stratigraphically in the west by the Lake Vermilion Formation and locally, locally, the Soudan Iron—formation, Iron-formation, and in the central part by the the Knife Lake Group (Figs. (Figs. 22 && 3). 3). Both the Lake Vermilion Formation and the Knife Lake Group Group are composed mainly of intermediate—felsic the Knife intermediate-felsic pyro— pyroand volcanogenic volcanogenic sandstones. sandstones. The Newton Lake Formation, Formation, clastic deposits and a younger mafic to to intermediate-felsic unit, overlies the a intermediate—felsic metavolcanic unit, Knife Knife Lake Lake Group Group in the the central part part of of the district and interfingers with it to the east (Fig. it (Fig. 3). 3). A A generalized and idealized pre—deformational pre-deformational stratigraphic sequence the western part part of the district is shown in sequence for for the figure 4. 4. Ely Greenstone Greenstone Ely Greenstone, Greenstone, as as redefined redefined (?Iorey (Horey and others, 1970), 1970), is is an The Ely an elongate body of dominantly mafic metavolcanic rocks, rocks, on the the average 2—4 2-4 miles miles wide, wide, that that extends from the vicinity of Tower eastward to to distance of of about about 40 40 miles miles (Figs. (Figs. 22 && 3). 3). Pillowed or or Moose Lake, aa distance lavas and metadiabase dominate dominate the the formation. formation. massive metabasaltic lavas pyroclastic Pillowed lavas of andesitic comnosition, composition, interinediate—felsic intermediate-felsic pyroclastic �-143—14 3— ic—intermediate epiclastic epiclastic deposits, deposits, chert chert and banded deposits, maf mafic-intermediate iron-formation, tuff (?) (?) comprise comprise the the iron—formation, and siliceous carbonaceous tuff remainder. Andesite and and dacite dacite porphyry porphyry are are conmion common hypabyssal hypabyssal intrusive rocks. rocks. The green color of most of of the the rocks rocks is is due due to to abundant secondary chlorite and green amphibole. abundant amphibole. at about The ruaxinul maximum exposed estimated at about exposedthickness thicknessofofthe the Ely Ely is is estimated feet; the are consistently to the 15,000 feet; the tops tops of of separate separate flows flows are consistently to the north, north, as indicated by by pillows. pillows. as indicated Soudan Iron—formation Iron-formation The The Soudan Iron—formation, Iron-formation, the the thickest thickest and and most most continuous continuous banded iron-formation iron—formation in in the the sequence, sequence, extends extends from from Tower Tower and and Soudan Soudan eastward eastward for a a distance of about 16 miles (Fig. (Fig. 2). 2). for In In the the Tower-Soudan Tower—Soudan area area it it is is ov~rlain overlain directly directly by by intermediate— intermediatefelsic volcaniclastic rocks of the felsic the Lake Lake Vermilion Vermilion Formation, Formation, whereas whereas east east (Fig. 2) 2) it it is is overlain directly by at least 7,000 7,000 feet feet of Armstrong Lake (Fig. of metavolcanicrocks rocks with with lenses of mafic—interinediate mafic-intermediate metavolcanic lenses ofofbanded bandediron— ironThus, the formation, which are are assigned assigned to to the the Ely Ely Greenstone. Greenstone. Thus, the Soudan, Soudan, which represents a time—stratigraphic time-stratigraphic unit, unit, is is a useful indicator of the the essential contemporaneity contemporaneity of of intermediate-felsic intermediate—felsic volcanism in the west west essential in the (Lake Vermilion Vermilion Formation) Formation) and and mafic mafic volcanism in the east (Ely (Lake (Ely Greenstone). The Soudan Iron—formation, as redefined 1910), The Iron-formation, as redefined (Morey (Morey and others, others, 1970), consists of several several types of ferruginous ferruginous cherts cherts that consists of types of that are interbedded meta— with fine—grained fine-grained carbonaceous carbonaceous and and sericitic sericitic tuffs tuffs (?) (7) and local metabasalt; all are are intruded intruded by by metadiabase metadiabase and and dacitic dacitic porphyries. porphyries. The thickness thickness of of the the formation formation has has not not been been determined determined accurately accurately because because probably is of complex folding, folding, but probably is less than 1,000 feet. feet. It It should be noted that the in the Ely the iron—formation iron-formation in Ely trough trough (Reid, (Reid, 1956), 1956), which which has has yielded hematite iron iron ore, ore, probably yielded large quantities quantitiesofofhigh—grade high-grade hematite probably is is not equivalent equivalent to to the Soudan Iron—formation. Iron-formation. The high—grade high-grade hematite ores that that were the Soudan Iron—formation Iron-formation at at Soudan (Klinger, (Klinger, ores were mined in the 1956) and and in in the the banded banded iron-formation iron—formation at at Ely Ely (Machamer, 1968) are are 1956) (Machamer, 1968) considered to to have been formed formed by by hydrothermal hydrothermal processes processes (Gruner, (Gruner, 1926). 1926). FO~lation Lake Vermilion Formation In the extreme the district ~Fig. 2), 2), the Lake In the extreme ~~estern western part part of of the district (Fig. Vermilion Formation Formation overlies theEly ElyGreenstone Greenstone or orthe theSoudan Soudan overlies either either the Iron—formation. Until recently these strata were assigned to the Iron-formation. the Knife Lake Lake Group. Group. They were reassigned (Morey (Morey and others, 1970) to to the Lake Vermilion Formation because they the they are not demonstrably concontinuous the Knife tinuous with with strata strata exposed exposed in in the the type type area of of the Knife Lake, Lake, in the eastern part part of of the the district. district. formation which has has been The Lake Vermilion is aa heterogeneous formation divided (Morey (Morey and and others, others, 1970) into four fourinformal informal members — - a fe1dspathic 1910) into members feldspathic quartzite member, member, member, a metagraywacke-slate metagraywacke—slate member, member, a volcaniclastic member, and a mixed metagra~vacke-felsic metagraywacke—felsic conglomerate conglomerate member. member. �—144— -144- The feldspathic quartzite member, member, composed dominantly of -ts volcanogenic minerals and and rock rock fragments fragments of of dacitic dacitic composition, composition, is in at the the fold fold nose nose southwest southwest of of Tower Tower in contact contact with with the the Ely Ely Greenstone Grenstone at (Fig. 2), than the the metagraywacke-slate as indicated indicated (Fig. 2), and and is is older than metagraywacke—slate member, as by graded graded beds. beds. The metagraywacke-slate metagraywacke—slate member, member, which Is is areally area11y the most extensive member, overlies the the Ely Greenstone locally, locally, as as member, directly overlies the south south limb limb of of the the fold fold at at Tower, Tower, but but for for the the most most 'part ,part Is is in in contact contact on the with the the older quartzite. The graywacke graywack~generally generally are well bedded and commonly are are graded; graded; like like the the feldspathic feldspathic quartzite, quartzite, they they consist consist mainly mainly commonly of volcanogenic volcanogenic debris. debris. A A chioritic chloritic facies occurs on on the the shores shores of of the the fades occurs eastern part part of of Lake Lake Vermilion, Vermilion, but but aa biotitic biotitic facies, fades, containing containing scattered scattered amphibole, amphibole, is is dominant dominant elsewhere. elsewhere. The member contains several interbedded lenses of metabasalt that that are are sufficiently sufficiently large large to to be be shown sho\vu on on figure figure 2. 2. The volcaniclastic member is is of interest because it was interp:eted inter~~eted previously to 1903) related to to be mainly aa conglomerate (Clements, (Clements, 1903) to the the Laurentian orogeny. Instead, it it is orogeny. Instead, is dominantly tuff tuff and and agglomerate agglomerate of of dacitic composition, with lesser lesser dacitic dacitic lavas, lavas, banded banded iron—formations, iron-formations s and euxenic black black slates. slates. Locally, Locally, dacite porphyry intrudes the the various rock types. The agglomerates, agglomerates, which which are are interbedded with tuffs, types. The interbedded with tuffs, consist consist cobbles and boulders in a of sub—rounded sub-rounded felsite felsite to to felsite felsite porphyry cobbles and boulders txotic rock fragments, fine-grained matrix of similar similar composition. composition. Exotic fragments, mainly fine—grained iron-formation and greenstone, constitute constitute only only one one or or two two percent of the the iron—formation rock. metagraywacke—felsic conglomerate member, member, which occupies The mixed metagraywacke-felsic occupies an of about about 30 square miles miles on the south limb of the of an area of 30 square the south limb of the fold fold south of Tower, interfingers with and and is is stratigraphically stratigraphically overlain overláin by the meta— Tower, interfingers with the metaIt consists consists of of a graywacke-slate member member (Fig. (Fig. 2). 2). It a maximum of about graywacke—slate 10,000 feet feet of to mafic rocks, felsite felsite flows, flows, several several of felsic felsic to mafic volcaniclastic volcaniclästic rocks, types and metagraywacke metagraywacke (Griffin, (Griffin, 1969; 1969; types of of cong1.omerates conglomerates and agglomerates, and Griffin and Morey, 1969). 1969). The thickness thickness of the the Lake its constituent constituent Lake Vermilion Formation and its members is poorly known because of complex complex folding and faulting faulting and and rather poor exposures. exposures. In the the Tower quadrangle, quadrangle, the quartzite member is estimated to to be the volcaniclastic member is be 1,500-2 1,500—2,000 feet thick and the t OOO feet metagraywacke—slate to be a maximum of about about 4,000—5,000 4,000-5,000 feet feet thick. thick. The metagraywacke-slate to is at at least least 3,000 3,000 feet feet thick thick and and is is probably probably much much thicker. thicker. member is Knife Lake Group Rocks of the Knife Knife Lake Group directly overlie the Ely Greenstone Rocks from the vicinity of Ely, Ely, where the the Knife Knife Lake Lake terminates terminates against against aa fault, fault, from The Knife Group, as eastward to to Moose Moose Lake Lake (Fig. (Fig. 3). 3). The Knife Lake Group, as redefined eastward (Morey consists dominantly of graywacke, gra~vacke, slate, slate, and and (Morey and and others, others, 1970), 1970), consists lava phyllite but includes includes substantial amounts amounts of pyroclastic rocks, rocks, lava flows, and and conglomerates. conglomerates. Gruner (1941, (1941, p. p. 1624) estimated that that the the flows, 15,000 the eastern end of the district district is about 15,000 feet feet Knife Lake near the thick, but this figure may be conservative. conservative. thick, but this �—145— -145- Newton Lake Formation The Newton Lake Lake Formation Formation was was mapped mapped earlier earlier (Clements, (Clements, 1903) 1903) as Ely Greenstone, but has been renamed (Morey as Ely Greenstone, (Morey and and others, others, 1970; 1970; Green, Green, l970)because it is stratigraphically younger 1970)because younger than than the the Knife Knife Lake Lake Group Group (Fig. the north north by by the the Vermilion (Fig. 3). 3). The formation formation is is truncated truncated on the fault and and along along strike to fault to the the northeast by granitic rocks rocks of of the the Vermilion batholjth. batholith. At its its western extremity, extremitYt near near :olf Wolf Lake, Lake, the the is truncated truncated by by aa fault fault (Fig. (Fig. 2). 2). formation is The western western part part of of the Lake formation formation is is composed principrinciThe the Newton Lake pally of of mafic mafic volcanics volcanics and and the the eastern eastern part part of of intermediate-felsic intermediate—felsic pally members,t which interfinger in volcanic members in the the vicinity vicinity of of Newton Newton Lake. Lake. volcanic member member consists consists dominantly dominantly of of metabasalt metabasalt and and metameta— The mafic volcanic andesite and fine—to—coarse—grained fine-to-coarse-grained andesite lavas lavas,t some some of of which are pillowed, and metadiabase and tuff tuff or tuff—breccia. tuff-breccia. Several small bodies of serpen— serpentinized peridotite are are associated spatially with the tinized the metabasalt metabasalt and and metadiabase. Small Small lenses lenses of of siliceous siliceous marble marble and and banded banded iron-formation iron—formation in the the formation. formation. The felsic member, east east of of Newton Newton Lake, Lake t occur locally in is composed composed of of felsic—intermediate is felsic-intermediate volcanics, dominantly dominantly tuff—breccia tuff-breccia deposits and and lesser lesser flows. flows. At places, metabasalt is is interbedded interbedded with the dominantly felsic volcanics. the Intrusive Rocks Five activity are are recognized recognized in in the the Five distinct distinct episodes of intrusive activity region. In In order age, from from oldest to to youngest, youngest, these these are are order of of inferred age, (1) synvolcanic have aa (1) synvolcanic bodies, bodies, including including hypabyssal porphyries, which have metadiabase and and metagabbro, metagabbro, and serpentinized wide range of composition, composition, metadiabase serpentinized peridotite (2) lamprophyres and related related hornblende—bearing hornblende-bearing rocks, rocks, (3) (3) peridotite,t (2) plutonic plutonic rocks rocks of of the the Giants Giants Range Range and and Vermilion Vermilion batholiths, batholiths, which which are are syntectonic, (4) altered diorite—gabbro diorite-gabbro which forms forms large large dikes dikes that that are are syntectonic, (4) post-tectonic, (5) basalt, basalt, which forms forms small, small, discontinuous, discontinuous, scattered scattered post—tectonic, and (5) dikes. In the Saganaga Granite of Winchell (1888) (1888) at at the the eastern eastern In addition, addition, the end of the district (Fig. end (Fig. 1) in age age to to the the 1) is is approximately equivalent in rocks of the rocks the two two batholiths batholiths and and intrudes intrudes the the older older rnetavolcanics metavolcanics (Grout, (Grout, 1929; and Goldich, Goldich, 1970). 1970). 1929; Hanson and The rocks of The plutonic plutonic rocks of the the Vermilion Vermilion and and Giants Giants Range Range batholiths batholiths proprofoundly affected the the volcanic—sedimentary volcanic-sedimentary sequence. sequence. Granitic rocks rocks of of the the foundly on the the south, south, irregularly irregularly intrude intrude the the composite Giants Range batholith, on sequence or are in fault contact contact with it, it, and and have have cut cut out out an an unknown unknown amount amount of section at Where the granite is at the the base base of of the the Ely Ely Greenstone. Greenstone. ~~ere is not in in fault with the the lower-grade lower—grade volcanic-sedimentary volcanic—sedimentary rocks, rocks, it it has has normal normal fault contact contact with to the the older older strata, strata, with with the the development development of of intrusive relationships to amphibolite-facies to the the contact. contact. The Vermilion amphibolite—facies assemblages adjacent to batholith, on on the the north side the district, transects the the upper side of of the district, transects upper stratistrati— graphic part of the the supracrustal sequence. sequence. This leucocratic biotite biotite granite granite includes wide wide zones of abundant inclusions of biotite schist includes zones of schist and and amphibolite amphibolite STRUCTURE The metavolcanic metavolcanic and rocks dominantly constitute a and metasedimentary rocks homoclinal, northward—younging homoclinal, northward-younging sequence sequence in in the the central central part part of of the the district, district, �-146—146-whereas they are faulted in in the the western western and and are both complexly folded folded and and faulted eastern parts. parts. Deformation was not pervasive, pervasive, and and primary primary structures structures Graded bedding and other primary features remain in most of of the the rocks. rocks. Graded features remain in the the graywacke—slate gray\vacke-slate successions, and and pillow pillow structu:es structu::es and and variolites are remarkably well preserved in the mafic metavolcanic remarkably preserved in the mafic metavolcanic rocks. rocks. At places, however, hmvever, a penetrative penetrative deformation, deformation, mainly mainly shearing, shearing, has has obliterated the the bedding. bedding. the western part of the area the the rocks rocks are are complexly complexly folded folded as as In the aa result two distinct episodes of deformation. deformation. The younger folds folds and and result of of two aa pervasive accompanying cleavage largely largely obscure obscure the the older older folds, folds, alalthough though the the older folds folds were important in in determining determining the the distribution distribution of the rocks. rocks. Detailed studies in in the the Tower quadrangle quadrangle and and adjacent adjacent areas areas (Hooper and Ojakangas, Ojakangas, 1971) 1971) indicate that (Hooper and that the metasedimentary strata, strata, and to to aa lesser degree the metavolcanic rocks, rocks, first first were ,,,ere folded folded on on west'iVestThese (F1) folds were tight to isoclinal, had northwest-trending axes. axes. (fo ) folds tvere tight to isoclinal, had northwest—trending l steep axial axial planes, planes, and probably had gentle or steep or moderate moderate plunges. plunges. Major ~lajor fold axes, axes, as as determined by consistently facing fold facing or or opposing opposing tops tops of of beds, beds, were spaced from from 700 700 to to 1,500 1,500 feet feet apart. apart. The younger (F2) (F ) folds, folds, which 2 most of comprise most of the mappable ones, ones, are are strongly strongly asymmetric asymmetrlc and and have have In most most of of the area the (F2) steep axial planes that that trend trend eastward. eastvlard. In (F ) folds folds 2 are dominantly Z—folds, are Z-folds, and the the northwest—trending northwest-trending limbs limbs are are two two or or more more times longer than the southwest—trending southwest-trending limbs; limbs; plunges plunges are are generally generally times of aa pervasive, pervasive, mild, mild, axial axial plane plane cleavage cleavage with with steep. The intersection intersection of In biotitebiotite— and higher—grade to F2 fo fold fold axes. axes. In higher-grade rocks, rocks, bedding is parallel to 2 to the the cleavage—bedding cleavage-bedding intersection. intersection. new minerals minerals are aligned parallel to In joints, In the the Tower Tower area, area, several several nearly nearly vertical vertical structures structures -— faults, faults, joints, and third deformation deformation displace displace the the cleavage cleavage of of the the F2 F and kink bands of a third 2 deformation. High—angle faults High-angle faults of two two trends, trends, longitudinal longitudinal and and transverse, transverse, break break the metavolcanic—metasedimentary sequence the metavolcanic-metasedimentary sequence into into aa number number of of blocks blocks or or segments and separate it in part from from the the marginal batholithic batholithic rocks. rocks. segments The Vermilion fault fault (Sims (Sims and and others, 1968), 1968), aa longitudinal longitudinal fault fault with with an inferred length of 300 300 miles (Sims, (Sims, 1970) 1970) generally generally separates separates the the Vermilion batholith and associated amphibolite facies facies schists schists from from lower— lm"ergrade rocks of of the the district. district. The directioncl the the horizontal horizontal The amount and directionof component of of movement component movement is not known, known, but but possibly possibly is is several several miles. miles. The vertical displacement is inferred to be on the order of a mile, bring displacement is inferred to on the order of a mile, to to bring higher-temperature-facies higher—temperature--facies rocks rocks on on the the north north against against lower-temperaturelower—temperature— facies facies rocks rocks in in the the district. district. Other longitudinal faults, faults, some some of which ,,,hi-ch appear to to be be strands strands from from the the Vermilion fault, fault, slice the the northern part part of the district into of into separate separate segments. segments. The transverse transverse faults faults trend trend northeastward or north—northeastward north-northeastward and have have dominantly dominantly left left lateral lateral displacements; the principal faults displacements; faults of this this Set set have have measureable measureable displacements 3-4 miles (Griffin (Griffin and and Morey, ~1orey, 1969). 19(9). displacements of of about 3—4 The The major faults faults of the area are expressed expressed commonly commonly as as narrow, narrow, Where exposed, linear topographic depressions. depressions. I,'here exposed, they are are seen seen to to of wide zones of crushed crushed and and altered altered rock rock or or of of intensely intensely consist either of silicified and altered altered rocks. rocks. �-147—14 7— Selected References Clements, J. ri., U., 1903, C1e~ents, J. 1903, The Vermilion iron—bearing iron-bearing district district of of Minnesota: Minnesota: U. S. U. S. Geol. Geol. Survey Survey Mon. Hon. 45, 45, 463 463 p. p. Coldich, S. S. S., S., Nier, Nier, A. A. 0., 0., Baadsgaard, Baadsgaard, Ha1fden, Halfden, Hoffman, Hoffman, J. J. H., H., and and Goldich, Krue;er, H. U. The P:ecambrian geology and geochronology Krueger, H. IV., 1961, The P::ecambrian and geochronology of of ilinnesota: dinnesota: [inn. Hinn. Geol. Geol. Survey Survey Bull. Bull. 41, 41, 193 193 p. p. , Green, C., 1970, 1970, Lower Precambrian rocks rocks of of the the Cabbro Gabbro Lake Lake quadquadGreen, J. J. C., rangle, rang1e, northeastern northeastern Minnesota: }1innesota: :--1inn. Geol. Survey, Survey, Spec. Spec. Pub. Pub. Minn. Geol. ser., ser., SP—10, SP-10, 96 96 p. p. Griffin, L., 1969, Embarrass quadrangle, quadrangle, St. St. Louis Louis County, County, Minnesota: Minnesota: Griffin, ,~. U. L., Minn. Ceol. ~Hnn. Geol. Su—vey Su-vey Misc. Misc. Map Hap Sec., Ser., MaD Map M—6. 1'1-6. Griffin, Griffin, U. IV. L., L., and and ?torey, !'forey, G. C. B., 8., 1969, 1969, The The geology geology of of the Isaac Lake Minn. Geol. Survey, quadrangle, quadrangle, St. St. Louis County, County, Minnesota: Hinn. Survey, Special Pub. SP-8, 57 57 p. p. Pub. Ser., SP—B, Grout, F. Grout, F. F., F., 1929, The Saganaga Saganaga granite granite of of Minnesota—Ontario: Minnesota-Ontario: Jour. Jour. Geology, Geology, v. v. 37, 37, p. p. 562—591. 562-591. Gruner, .3. Gruner, J. W., The Soudan Formation and a new suggestion as to to the the U., 1926, The Econ. Geol., v. 21, p. 629—644. oriign of the the Vermilion iron iron ores: ores: Econ. 21, p. 629-644. Cruner, .3. Gruner, J. W., W., 1941, 1941, Structural geolony geology of of the Knife Lake area of northeastern Minnesota: Geol. Soc. Hinnesota: Geol. Soc. America Bull., Bull., v. 52, 52, p. p. 1577—1642. 1577-1642.' Hanson, G. G. N. N. and and Go1dich, Goldich, S. Hanson, S. S., S., 1970, Early Early Precambrian Precambrian geology geology of of the Saganaga-Northern Light Inst. the Saganaga—r4orthern Light Lakes Lakes area, area, Minnesota-Ontario: Minnesota—Ontario: Inst. Sup. Geology, Geology, Proc. 16th 16th Ann. Ann. Mtg., Mtg., Thunder Thunder Bay, Bay, Ontario, Ontario, Lake Sup. p. 18. p. 18. Hanson, C. R., 1971, 1971, K-Ar K—Ar ages ages of of mafic mafic dikes and Hanson, G. N. N. and and >Lalhocra, Nalhotra, R., evidence for low—grade lOVT-grade regional metamorphism metamoJ.Tphism in in northeastern northeastern evidence for :linriesota: Hinnesota: Geoi. Soc. Soc. America Bull. Bull. (in (in press, press, March March issue). issue). Ceol. Hooper, Vermilion [looper,Peter Peter and and Ojakangas, Ojakangas, R. R. W., U., Multiple Multinle deformation deformation in the Vermilion district, Minnesota: district, Hinnesota: Can. Can. Jour. Jour. Earth Earth Sci. Sd. (in (in press, press, April April issue). issue). Klinger, Klinger, F. F. L., L., 1956, 1956, Geology Geology of of the the Soudan Soudan mine mine and and vicinity; vicinity; Guide Guide book book Series, Series, Precambrian ef of northeastern Minnesota: Geol. Geol. Soc. Soc. America, America, Ninneapolis, Heeting, p. p. 120—134. 120-134. Minneapolis, Minnesota Meeting, iachmner, J. F. Machamer, J. F., 1968, Geology the iron are the Geology and and origin of of the ore deposits deposits of of the mine, Vermilion district, Minnesota: Zenith mine, Ninnesota: Minn. Minn. Geol. Geol. Survey Survey Spec. Spec. Pub., SP—2, Pub., SP-2, 56 56 p. p. , Ojakangas, Ojakangas, 11. R. U., W., Sims, Sims, P. & Hooper, P. K., K., & Hooper, Peter, Peter, 1971, 1971, Geology of the Tower Tm.,rer Quadrangle: Quadrangle: !'linn. Geol. Survey Survey (In (In preparation). preparation). Minn. Geol. Reid, 1. I. L., L., 19 1956, l:Zeid, S6, Ceolo1y Geo1of-y of the the Ely Ely Trough: Trough: Guidebook Series, Series, Precambrian of northeastern Minnesota: Geol. of Soc. America, Minneapolis Hinneapolis meeting, meeting, Geol. Soc. i,. 135—148. TJ. 135-148. �—14 8— -148- Sims, P. 1970, Geologic Geologic map map of Minnesota: P. IC., K., 1970, Minn. Geol. Survey Survey Misc. Map Set., Misc. Ser., Map M—l4. M-l4. Sims, Morey, C. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. W., W., and and Griffin, Griffin, N. W. L., L., 1968, 1968, Preliminary geologic map of of the the Vermilion Vermilion district district and and adjacent adjacent areas, areas, northern Minnesota: Minn. Geol. Geo1. Survey Survey Misc. Misc. Map Map Ser., Ser., Map Map M—5. M-5. Sims, Morey, G. Sims, P. P. K., K., Morey, G. B., B., Ojakangas, R. R. N., W., and and Viswanathan, Viswanathan, S., S., 1971, 1971, (in press), press), Geologic Map of Minnesota, Hibbing (in Hibbing Sheet: Sheet: Minn. Geol. Geol. Survey. Survey. Winchell, H. H. V., V., 1888, 1888, Report Report of of observations observations made made during during the the summer summer Winchell, Minn. Geol. (northern Minnesota); Minnesota): Minn. Geol. Survey Survey Ann. Ann. Rept. Rept. v. v. 16, 16, of 1887 (northern p. p. 395—478, 395-478, map. map. �F L A NJ ATION EXPLANATION cc o C, ~ c~ "-' -'=' ~ E D ° :::) 0C l::~~:1 3: { cC, 0 V ~ 0 ill U "-' ill 3: Duluth Duluth 0:::'" ~f N I Complex a. CO o ~ ~ -0 E -o-'=' -o ::J 0 Virg1nia Vrqinio <..? "'~'l Q... and Formations Rove ill I f-' C « Bv,::uk and Biwabik and Gunflint Gunflinl fornialions Iron — - formations ~ C co o ~+++++J Gions Giants r:''",; ;->~, 'I '] "::~;::::'7·{~::/,--- Range Range Granile Granite Vermilion GronLte Granile , / t,/~'-J = co o — -'=' E Saganaqa Sagona go o S u ~ Granite Q... Q; 3: o ---.J ~Sif epiclastic, volconiclastic undivided epiclastic, volcaniclastic sedlmenlary rocks, extrusive mafic sedimentary rocks, extrusive rocks, and and lhe te igneous rocks, Soudan Iron Iron -—formation tormotion (sit), (sit) mainly greensch;st focies greenschist facies o0................ jO '0 IIoowiiIl 20 I SCALE 5 CAL E 30 Miles 3OMiies J5 E o u 1: "-' & 0::: '0 I �-\0 92°00' 92°45' 90°45' -«) o o co co CANADA "" Area. of <:r p1a.te I I-' lJl o0 °Cook. I + + + + + + + + + + + + + cr + + + + + + + + + + + + Location + + ,'i' ,.'" Map ~qj~ + 'vI;;) (:)~ .",o," ~"r.o~' ~<> ~(:) ",,'0 ::<,,<6 <0(:) 'vC::; ~r:'JQ., 4..':::J'::;''v~ + T + + ., L- ..., L < ,.. "7 .t.. ~ L ? V A 7 90°45' 7 7 1\ ~'" ;, 1'\ \'" L r I< ,o,<> r- ~ L 'e- ~$"~ " "," <§> ~C?it' C)<..J,9.; .~ '<f -,J ,} v'" ~ "o,~ .,.. «J~ ~ ~ ,>'> ,o, »' '" 92°45'00" ~ 92°00' ,,<I;> o,<> ,,1$ '0'" <'¢~~~ ~l>~'v 'v~& <Q~~ J> "", ,'> o,'> ,,«. .J,.<:i <¢",,, o," . . . e,r::),.,."<> .. v'" -~ 'e- '" 92°00'00" ~ Index I "," v'" ~;§' '\:t''''' + Figure 1. 1. Figure 92°00'00" to quadrangles stud ied Generalized the Vermilion (Morey & 1970) Generalized geologic map map of of the Vermilion district, district, Minnesota Minnesota (Morey & (thers, cthers, 1970) i I I I i I I i I I I �C PL LA AN NA ATTI10 N E )C XP ON foijli North of at Vernii/ioii Vermilioll foull I'..... ... '1 Range Granite Range Grande G,onis Glonts Ver ni lion Gronile Bionic Biollle Schisi 5chiSl Newton Lake Lake Farmolion Formal ion Newton undivided undivIded Vif.:::: . ~v.gs. vii Amphibolile Amphibolite —7-———-—vmv vmv vgv YQ vq c LLake oice .2 .D E 3 ~ Q.. 5 .':'.':'." :"> . Verm,tion Vermilion Knit Knife Lake Lake vVm vvm Group (undivided) For molio n Formation vgs, meiagroywocke metagraywacke member member quorrziie vg. quartzite member member v q, vgv, mi xed metogroywacke metagraywacke - felsic felsic vg v, mired I I-' conglomerate member conglomerate member vvtn, vaiconicMsic member member vvm, volcaniclastic bonded iron -- formation vif > banded vlf cmv. dominantly dominantly melobasoli metabasalt and and vmv, metod i a baaso S8 meladiab V1 I-' I - format On Soudan Iron Iron -formation Soudon dominantly domlnontly jaspiiite jospilite, jasper, and cherl chert osper and -- cit Ely Greenstone Greenstone e9, domlnontly menobosoltic metabasaltic eg, dominantly p i ilowed flows and metaandesitic meiaandesitic pillowed and 'nlern,ediate composition and Intermediate composi lIon pyrociostic pyroc lost\c depOsits deposits elf, banded bonded Iron Iron -formation - formation 9it, Corroci, dotled where wiere inferred nte- 'Cd Contact, dotted Vault Faull,• oared dotted where where o '"' 22 inferred 4 5S 6 8 CAL E CAL E loMites �-g 92'30' 92°3 H '7 W R~7W' 9j '45' 92'00' H IS W R~-4VV B. '3"W -0 o Zoo ooZ II"'" "'"II (j) (j) ID f-< f-< Z I'l ton (j) f-< ..4 ,v_t —c a Z zZ (II C -. (j) ID (II Jwtfl okes (j) / I-f-< log1e' b V1 N: t-: 1 'V '< c-..Lake z z (H ft 6 ... : : : Z o(j) · · b H W R t~ 7 7"'V\T Z ,/ ri7' · ·. . . . . .. . .. . . . . . . . . . . · · ·· Figure 2. 2. I .. .. . . . .. . ... .. . . .. .. .. . ............................................................... . 92*30 92'30' I ::::..................... :::::::::::::::: ::::::: ~ . . . .. . 0 a is w 16VV R 0 0 0 -J ~-~-= R . .. 91045 of the the western western part part of Geology of of Vermilion Vermilion district, district, Minnesota Ninnesota (Norey (Norey &&others, others, 1970). 1970). j I I I b -J 92' 92° 15' '5 p o(j) 0 0 n law 8W ~5""N I I I II-' LI I �I I C L AN AT S ON Sc P L A N A T I O N E E X Ou'''''' 1 Cornplt. '-'-' -', - ' , -'" Sno"~OA'" Lo_" "e,,"""O~ StOel und,·•• ded ,,,,I"don Lii LLL G'Qn,'e o~~'O'ed ~(~,~,~ ro. .... ,on La •• formot,on molK: ,Olcon,e nm" mtmatl nh, Itl$,(· ,nl.rmed·"·" .....x:on..: mem!>e< oom'l'Io<"ly fe pyroelau,e (nf,) of ~.c:-"",ermed>o'. ond ,oc.~ ~,m,lc, I.~~.' lIo .. ~ eompc~",on Kn,lt 'm~. dom,nonlly mtlO\l,ay .. o~'. 0"<:1 $101., 'm~. ~m'l'Ianuy m.,'otO~O,1 dom.non", .okon.elo~"t 'oe. 01 '0 ,nr.rmtd,ol. tompo~,"OI'l Ow. Ely .\!. Itl~,~ Gr.el'l~lol'le dJm,nonl" ..,.lotlO$Olh( p,llo".d and .... 'e'm.d'O'. (O""O'O$,I,on Oy'OCIO$I..: d.PO~,I$ ""eloonde~,''': SC £ seA L S. = ~ : 4 t . . . . ;} . . - - 2 - o..._.__ • ~ Ofl<l £E I f-J Ui lJl I G,o"p S.—. La~e hi W ~.,~~...tl - I - F _~M,l~ �- 4 ,e; - - / - - —— — t\ - —— c — —- N .--.--- / / -:- -- 'F !)y/ - / / / 7 Figure 3. 3. I I / G eology of the the central Geology central part part of of the th e Vermilion district , Minnesota M'l.nnesota (Morey Vermilion district, (Morey & & others, others , 1970). 1970). I — I I I �—155— -155- E E w W 0 - C? ...... z::::;. 13 ./ '- /=:::> " ~ / " L:) c=r ' ,;' .. . .• 12 / "/ "- I \ ,;' " .... / / ....... ,;' " "- / / .. j . . .. 0[77: 00 00 .,j . . o 0 " "- "- "/ "- / I 0I- 1. 0 .,.. .,.. ..... •Q ,;' " 6 ..... I' "- ./ ...... Fe1dspathic quartzite quartzite Feldspathic agglomerate Dacite agglomerate I' \. Graywacke-slate Graywacke—slate I I " / / ,;' ./ ... ,;' \. / / \. , " / I' .... Dacite tuff Daci te porphyry Dacite Iron—formation Iron-formation Basalt—andesite Basalt-andesite GENERALIZED AND IDEALIZED IDEALIZED PRE—DEFORMATIONAL PRE-DEFOID1ATIONAL VOLCANIC VOLCANIC PILE, PILE~ WESTERN VERHILION VERMILION DISTRICT of \. / Figure 4. 4. (Not (Not to to scale. \. 3 ,;' ,- \ / \. \ '- \. ,;' 0 0 " Numbers indicate approximate stratigraphic stratigraphic positions positions Numbers field trip stops.) stops.) field trip 2 " �—156— -156- VERMILIONDISTRICT DISTRICT FIELD FIELD TRIP VERMILION INTRODUCTION This field field trip trip is is designed to be a one—day one-day trip, trip, starting starting near near Ely Ely Representative outcrops of most and ending aa few miles west of Tower. few miles west of Tower. of the the major rock rock types types in in the the Vermilion Vermilion district district are are included. included. Most stops are in in the the Lake Vermilion Formation, Formation, the the Ely Ely Greenstone, Greenstone, and and the the Soudan Iron—formation. Iron-formation. None are in the the Knife Lake Lake Group because because good good exposures are not easily accessible; accessible; however, however, the the Knife Knife Lake Lake rocks rocks are are to those those in in the the Lake Vermilion Formation. Forma.tion. similar to Stop 1 Any several roadcuts Any of several roadcuts 2—10 2-10 miles South of Ely Ely on Hwy. Hwy. 1. 1. Giants Range bathalith batholith Most abundant facies in in this this area area ('Farm C'Farm Lake Fades' Facies" of of Green, Green, 1970) 1970) is is medium—grained, medium-grained, porphyritic porphyritic hornblende—biotite hornblende-biotite quartz—poor quartz-pooradainellite adamellite with K-spar phenocrysts. phenocrysts. Hornblende and K—spar K-spar are are commonly con~only aligned aligned in in flow flow pink K—spar structure. Monzonitic, granodioritic, granodioritic, and and dioritic dioritic phases phases also also occur; occur; all all have been cut by shear shear zones zones locally. locally. Stop 22 South of Ely on Hwy 1. Outcrops under powerline pmverline on EE side of Hwy 1, l, 1.4 1. 4 Outcrops under mi. mi. S of junction junction with Hwy Hwy 169. Ely Greens Greenstone tone of a within the Dacitic to to andesitic, andesitic, pillowed lavas characteristic characteristic of a zone zone within the Ely trendsE—W E-W south shapes show show tops face face Greenstone that that trends south of of Ely. Pillow shapes Ely Greenstone are cut These volcanics volcanics are north, as as in in most most of of the the formation. formation. These cut by aplitic north, dikes to the the Giants Giants Range Range batholith; the hidden hidden contact in related to batholith; the contact lies lies in dikes related the the slope slope to to the the southwest, southwest, and and granite granite outcrop outcrop can can be be seen seen near near the the base base of the slope. slope. of Ely. 14. at curve about 0.25 Stop 3 Roadcuts Roadcuts on on Hwy Hwy 169, at 0.25 ml. mi. W. of Ely. StoRj Ely Ely Greenstone of the Creenstone Pillmved metabasalt that that is is typical typical of of the the màflc mafic lavas lavas of the Ely Ely Greenstone Pillowed The pillow structures is exposed in road road cut cut on on north north side of highway. higlmay. The pillow structures have have side of is exposed in somewhat drawn smoothly tops, nearly flat flat bases, and and are are somewhat drawn out out in in smoothly rounded tops, of an vertical an inch inch thick. thick. The The Thechilled chilled rinds rinds are are aa fraction of vertical dimension. The and SE and face U., dip pillmv structures strike strikeapproximately approximately N.20° N. 20° Eo, dip 800 80° SE., face pillow , southeastward. southeastward. The long subparallel to to the the The long dimension dimensionofofthe the pillows pillows is is subparailel in~ersection cleavageand andbedding beddingand andplunge-s plunges steeply steeply northeastward. northeastward. intersection ofofcleavage �—15 7— -157- The exposures are on the the northwest limb limb of of aa tight tight syncline, syncline, the the axis axis The Ely trough contains an through the the Ely Ely trough. trough. trough contains an of which passes through iron—formation that was largely altered to hematite, and which was iron-formation that was was aa substantial source of of direct—shipping substantial direct-shipping hematite ore. ore. On the the south side of highway, fine—to—medium—grained fine-to-medium-grained metadlabase metadiabase is is exposed in road cut and on on hill to to south. south. The metadiabase intrudes and and crosscuts the the pillowed metabasalt. AA contact can can be seen seen in in the the southern southern part part of the tile crest crest of of the the hill. hill. 4. About 2.5 mi. \oJ of Stop 33 on Hwy Hwy 169, turn turn NN (right) (right) on on road road to to Burntside Burntside Stop 4. ml. W Lodge (Co. 88). Continue on road past bridge over Burntside River (Co. 88). Burntside River and and About 1.4 miles past Van Vac road (on (on left). left). About past junction with Van Vac road Stop in about 0.2 miles road, (on curve) curve) on on private private road. road. Stop road, turn left (on north on private road, road, at at curve curve to to right. right. Newton Lake Formation Formation Serpentinized metaperidotite metaperidotite and and associated associated gabbroic gabbroic rocks rocks are are exposed exposed Serpentinized from base of hill northward to from to crest. crest. It is about 150 Serpentinized peridotite is is exposed at base of hill. It 150 feet thick, is nearly black, black, and contains some feet thick, is some poikilitic poikilitic augite. augite. Iniinediately northofofserpentinized serpentinizedperiodite periodite and and apparently apparently gradational gradational Immediately north into it it is is aa coarse-grained coarse—grained hypersthene (?) into (?) gabbro, which grades in turn into a gabbro (higher The gabbro appears to into (higher on on hill). hill). The to have some some crude crude compositional layering and is in part diabasic. diabasic. On crest of hill, hill, part of the the gabbro (or (or diorite) diorite) contains contains coarse, coarse, radiating radiating pyroxene pyroxene crystals, crystals, as much as an as an inch inch long. long. There is some interstitital quartz and feldspar granophyric material in this this phase of the the rock. rock. Pyrite is widely scattered through the the gabbroic gabbroic rocks. rocks. ultramafic-mafic body at this stop is near the the southwestern end of an The ultramafic—mafic at this stop is intrusive sheet that that is about 3.5 3.5 miles long long and and 1,000 1,000 feet feet or or more more thick, thick, and which underlies little little Long Long Lake. Lake. The sheet appears appears to be a differbody, from peridotite at entiated body, at the the base base to to gabbro gabbro at at the the top. top. North of the eastern end end of of Little Little Long Long Lake, Lake, aa small small body body of of serpentinized serpentinized of the eastern peridotite, peridotite, within within metadiabase, metadiabase, is is exposed exposed in in aa roadcut roadcut along along the the Echo Echo Trail. The top top of the body is truncated truncated by by the the Vermilion Vermilion fault. fault. Stop 55 Roadcut about Roadcut about 13.0 13.0 miles miles W W of of Ely Ely and and about about 2.5 2.5 mi. ml. W W of of Eagle's Eagle's Nest Nest Lake road (Co. (Co. 408) 408) on on Hwy H\vy 169. 169. Other outcrops of of similar similar rocks rocks are are also also present along the the highway. highway. Soudan Iron—formation Iron-formation and cross—cutting cross-cutting dacite. dacite. Roadcut Roadcut in Soudan Iron—formation. Iron-formation. A quartz—feldspar quartz-feldspar (dacite) (dacite) A porphyry dike and Ely Creenstone Greenstone are exposed exposed at at east east edge edge of of outcrop. outcrop. The iron-formation is The iron—formation is composed composed of of interlayered interlayered red red and and white white chert chert and and opaque iron iron oxide that plunge oxide layers; layers; it it is is deformed into into drag drag folds folds that plunge 0 500_600 50 -60 0 N.E. Beyond a covered interval interval of of 0.1 0.1 miles miles to to the the east, east,the the �-158iron-formation thin to thick, thick, black, black, red and and white chert chert iron—formation consists consists of of thin beds interlayered with black black argillaceous argillaceous beds beds that that contain contain abundant abundant veins, veins, stringers, and and beds beds of of euhedral euhedral pyrite. pyrite. The beds trend trend about about N.85° and W. N.85° W. and dip dip 80°N. 80 o N. This is representative of the This dacite the felsic felsic volcanic volcanic rocks rocks which apparently provided the the detritus detritus for for most most of of the the sedimentary sedimentary and tuffaceous tuffaceous rocks rocks of the the district. district. Stop 66 Outcrop just W W of Stuntz Bay road road at at crest crest of of Soudan Soudan Hill, Hill, at at the the N, N. edge edge Soudan, 1,000 ft ft E. E. of Soudan Soudan mine. mine. Conserve this this outcrop. outcrop. of village of Soudan, Soudan Iron—formation Iron-formation This is much—visited classic This is a much-visited classic exposure exposure of of folded folded Soudan Soudan Iron—formation Iron-formation comprised of alternating beds of hematite and and jasper. jasper. The nearby Soudan mine was opened opened in in 1884, 1884, and and operated operated continuously continuously until until 1962. 1962, when when it it was was deeded to to the the state state by by U. U. S. S. Steel for for the development of of Tower—Soudan Tower-Soudan State State It was was the the first first iron ore mine in Minnesota; 15.5 million tons Park. It tons of of high grade grade ore ore (63—66% (63-66% Fe) Fe) were were shipped. shipped. Most of the small folds Host folds are the the result result of of the the second second deformation deformation in in the area, and these (F2) the area, (F ) folds folds plunge to to the the east east at at steep steep angles. angles. However, 2 evidence of an earlier set of folds is is provided provided by by structures structures such such as as these in the the sketches below. below. F1 fold axis Fl /" F2 F fold axis axis 2 F F INTERFERENCE INTERFERENCE PATTERNS PATTERNS F1 AND AND F2 l 2 Approximate F1 F FOLD MODIFIED BY BY F2 F 1 DEFORMATION 2 N N 1 H One Foot Foot Approximate Scale Scale �-159—159— Stqpl Several outcrops outcrops on peninsula in Lake Vermilion, east of Several of McKinley Bay, I Bay, E and W W of development development road. road. Lake Vermilion Formation, Lake Formation, Volcaniclastic Member White Hhite dacitic tuff, tuff, white dacitic dacitic agglomerate, agglomerate, black black carbon— carboniferous (?) slate graywacke, all all of of the the volcani— volcaniiferous (?) slate and minor chloritic graywacke, clastic member, are interbedded interbedded in in this this area. area. The westernmost exposures member, are of the the Soudan Iron—formation Iron-formation also occur here. here. Good exposures of the the agglomerate are best reached by boat; therefore, agglomerate boat; therefore, we shall shall only only see see some some large glacial glacial erratics of this rock rock type type which are are virtually virtually in in place. place. The dacitic tuff tuff is is very very difficult difficult (arid (and commonly commonly impossible) impossible) to distinguish from from dacite dacite flows. flows. Study of thin sections is is usually necessary to to resolve resolve the the question. question. It comfort to know that It is is some some thmfort (1903) and numerous other workers had had similar similar difficulties. difficulties. Clements (1903) three main components components —- dacitic The tuff is composed of three dacitic volcanic rock fragments, and volcanic volcanic quartz. quartz. Recrystallization Recrystallization causes causes fragments, plagioclase, and the volcanic volcanic rock fragments the fragments to appear as a fine—grained fine-grained quartz— quartzplagioclase plagioclase matrix. matrix. stop Stop 88 Large mi. WW of of Tower Tower on on Hwy Hwy 169, 169. roadcuts 0.3 mi. Lake Vermilion Fornation, Formation, Felds feldspathic athic Quartzite Quartzite Member Member This is a a limonite—stained limonite-stained exposure of the the conglomeratic conglomeratic facies facies This is of the the feldspathic feldspathic quartzite quartzite member. member. Bedding and clasts clasts are are best observed on the the glaciated surface at at the the western end end of of the the south south roadcut. Pyrite and pyrrhotite are are the the major major sulfides sulfides present, present, and and to have replaced replaced slaty slaty fragments fragments .in ,in the the conglomerate. conglomerate. Most appear to clasts clasts are volcanic rocks, rocks, probably mostly dacitic. dacitic. The matrix is is the strong Stop 10. 10. Note the similar to the feldspathic quartzite of Stop development development of F2 lineation which ~vhich plunges easterly easterly at at about about 600. 60°. ~t.-<?.p_J_ 5t229 Small outcrop SS of thvy Hwy 169, 169, in and across ditch, ditch, 1.1 mi. WW of of Tower. Tower. (optional) Lake Vermilion Vermilion Formation, Lake formation, FeljIiicQuartzite feldspathic ~uartziteMember Member feldspathic quartzite Lapilli (?) in the basal part of of the the feldspathic Lapilli tuff tuff (?) This is the This is the only exposure of this this rock rock type type in in the the immediate immediate it appears appears to area; it to be transitional in in texture texture between between the the dacitic dacitic tuffs and dacitic agglomerates. tuffs ap,glomerates. newiber. melilber. �-160- Note: Stop 10 South of the highway in the woods on West Two Rivers is tte folded western end of the Ely Greenstone. The fold nose points W but the fold plunges E at about 55°. This is an antiformal mass cored by older, mafic volcanics whose fold axis plunges toward the older rocks the wrong way. Some small folds at Stop 11 exhibit the same structure. Roadcuts N & S of Hwy 169, 1.85 mi W of Tower. Lake Vermilion Formation, Feldspathic Quartzite Member Feldspathic quartzite is an unfortunate choice of field terms, as the rock is largely composed of plagioclase and volcanic rock fragments with only minor large quartz grains (see below). Faint bedding and lamination are visible on some parts of the outcrop, and a sericitic phyllite band occurs on the north cut. At the east end of the south cut, felsic volcanic fragments up to an inch in diameter are visible. The 20 ft.-thick dike of diabasic gabbro at the tvest end of the outcrop is the youngest rock in the area. It has a minimum K-Ar age of 1570 m.y., and similar dikes a few miles away have ages of 1520 and 1685 m.y. (Hanson & Malhotra, 1971). The dike exhibi~s excellent chilled contacts and some inclusions of the quartzite. The feldspathic quartzites contain 20-30% plagioclase; 15-30% felsic volcanic rock fragments; 30% fine recrystallized quartz and plagioclase which probably represents, in large part, recrystallized volcanic rich fragments, plagioclase and quartz; 5-10% micaceous matrix; and 5-10% quartz, including some quartz which is definitely of volcanic origin. �—161— -161- -.l1.Long Long roadcut roadcut SSof of Hwy H\vy 169, 169, 2.5 Z. 5rid. mi. WW of Tm.]er. Conserve these these folds. folds. Tower. Conserve Stp_11 _~t...2.E .. jjrwacke—Slate Vermilion_Formation Lake Vermilion Formation, Metagraywacke-Slate Member (The composition Strongly and slate. slate. (The Strongly folded biotitic metagraywacke and this rock is is described at at Stop Stop 12, lZ, where the rocks of this where the rocks are are evenly evenly bedded folding results from two and relatively undeformed.) The The complex folding two deformations, as described in in the the text text accompanying accompanying this this tions, as sketched below and as described Some geologists have speculated that field trip trip log. log. Some that the the folding folding is is soft soft sediment deformation, deformation, rather than than tectonic. tectonic. However, these these stnictures structures are are unique unique in in the the area, area, this this exposure exposure is is located located near near aa major major anticlinal anticlinal axis, well—preserved sedimentary structures axis, and well-preserved structures nearby nearby are are not not chaotic. chaotic. the excellent excellent grading. grading. Note the Approximate N i One Foot F1 F fold fold axis l Approximate Scale ·····e 5Q0 50° axial plunge OVERTURNEJ) F2 FOLD FOLD OV ERTU R.:\IED F2 F1 FOLD F2 CLEAVAGE FOLD ANT) A..~D FZ P2 cleavage fold axis 1 / -7 F F FOLD 1ODIFIED BY fOLD MODIFIED HY FF Z 2 1 DkFORMATION. DEFORMATION. F2 Cleavage FZ ~ o• F 2 cleavage --"EYE STRUCTURE" t1EYE STRUCTURE" DUE DUE TO TO EROSION EROSION OF FOLDS WHICH OF FFI FOLDS I-.THICH WERE I-.TERE DEFOR1€1) DEFORMED BY FOLDS. BY FF FOLDS. Z �-162—162— 'I •. -. C Stop 12;Lposure ExposureNJNWof of bridge bridge across across Pike Pike 169. .r:S'Y (Junction of of Co. Co. 77 Hwy 169. (Junction 77 and ... this outcrop. Please conserve conserve this River on Co. Co. 77, 77, 0.55 0.55 mi mi NN of of River an Hwy 169 is 2.4 miles W of Tower). Hwy 169 is 2.4 miles W of Tower). .;: Lake Lake Vermilion Formation, Formation, Metagraywacke—s]ate Metagraywacke-Slate Member Member This This is is an an exposure exposure of of biotitjc biotitic metagraywacke metagraywacke and and slate, slate having having excellent grading. excellent grading. Two-thirds the 200 200 graywacke beds beds on Two—thirds of the on ~his this exposure are are graded and nine percent of the exposure the 100 beds are are 100 siltstone siltstone beds graded. Beds here here are are thin, graded. Beds thin, but graywacke beds beds are are as as much much as as 12 12 feet feet thick. North—trending kink North-trending kink bands bands were formed formed by by the the latest latest (F (F )) deformation. Small Small scale scale faults faults are are common. A NNE-trending fault with 1000 feet feet A NNE—trending fault with aiout aout 1000 of of left—lateral left-lateral displacement displacement forms the S side forms the side of the river channel at this locality, locality, and extends for this for several several miles miles to to the the north north and and south. south. The biotitic biotitic graywackes graywackes contain contain 10-20% l0—20 plagioclase; The plagioclase; 15-25% 15—25% felsic felsic volcanic rock fragments; 30—50% fine recrystallized rock fragments; 30-50% fine recrystaliized quartz and and plagio— plagioclase which probably represents, clase which represents, in large large part, part, recrystallized volcanic volcanic rock fragments, plagioclase, and rock fragments, and quartz; quartz; 2-5% 2—5% quartz, quartz, and and 10-15% lO—15 biotitic matrix. matrix. Stop 13 Exposures N of Hwy 169 on Co. Co. 77, 77, at Gruben's Resort Resort on Exposures about 10 mi N (Optional) (Optional) Arrowhead Point. Point. Best exposures are are just just EE of of wooden wooden bridge bridge to to Isle Isle of Pines. Pines. Lake Vermilion Vermilion Formation, Formation, Hetagr~acke-Slate Metagrywacke—Slate Member Lake i'lember Exposures Exposures of chloritic graywackes of this locality, pillowed greenstones of this locality, slate. This is near the axis This locality is is an ENE—trending (F2) is an ENE-trending (F 2) anticline, anticline, the the the west although the beds at the fold the west the beds at fold and slates. Both east and west are are interbedded interbedded with the the graywacke— graywackethe Arrowhead Point Point fold. fold. This of the axis axis of of which ,,,hich plunges plunges steeply steeply to to nose are younger to the are younger to the east. east. The 40-50% plagioclase (albite—oligoclase), (albite-oligoclase), The chloritic gra~vackes graywackes contain 40—50% 20—25% felsic volcanic rock fragments, 20-25% felsic volcanic fragments, 10—20% 10-20% chioritic chloritic matrix, matrix, 2—6X 2-6% quartz, quartz, some of of which which is some is definitely of volcanic origin. origin. Roadcuts bet\veen between lanes of Hwy 169 on "Confusion Stop 14 Roadcuts "Confusion Hill" Hill" (the (the Continental Continental (Optional) Divide) N of Virginia and about 23 23 miles WW of of Tower. Tower. (Optional) Divide) about about 3 mi N Giants Giants Range Granite the south edge of the This the complexity complexity of of the the south This exposure illustrates the Giants Range A gray gneiss contaLning containinh ailiphiholite amphibolite gray granite granite gneiss Rangebatholith. batholith. A inclusions cut by by diorite, diorite,and andminor minor pink pink granites granites cut cut the theabove above rocks. rocks. inclusions is is cut At top of of the the exposure exposure between het\\'een the tHO lanes of of the thehichway higlmay are At the the top the ttro remnants of mafic remnants of LOvIer LowerPrecanlHian Precanl,rianthinly thinly bedded bedded sediments sediments (tuffaceous?), (tuffaceous?), mafic lapilli tuffs (?y, and massive massive amphibolites. lapilli tuffs (fl, �� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1971 Description An account of the resource Institute on Lake Superior Geology. University of Minnesota, Duluth, Minnesota. May 5-8, 1971. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1971 Contributor An entity responsible for making contributions to the resource R.N. Annells P.O. Banks W.R. Van Schmus Bill Bonnichsen Donald M. Davidson Jr Erich Dimroth Jean-Jacques Chauvel William H. Duhling Jr J.C. Green H.C. Halls G.F. West R. Roy Harold A. Hubbard H. King Huber Eric Frodesen Wayne T. Jolly Richard L. Kellogg William J. Hinze George deVries Klein Gene L. LaBerge M.S. Lougheed J.J. Mancuso Roger C. Malan David A. Sterling Allen F. Mattis Joseph T. Mengel Jr Ronald A. Hendrickson G.B. Morey J.S. Mothersill M.G. Mudrey P.W. Weiblan Wallace Darwin Myers Norbert W. O'Hara L.A. Prince G.N. Hanson W.A. Robertson W.F. Fahrig A.P. Ruotsala R.J. Shegelski G. Spencer F.C. Tan E.C. Perry Jr P.K. Sims S. Viswanathan T.A. Vogel T.J. Rohrbacher W.S. White Robert F. Johnson E.R Brooks J.T. Wilband Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English