74 10 13233 https://digitalcollections.lakeheadu.ca/files/original/44dd6753bf6d405f82fdd2013485235c.pdf 85b48ae95ebbb0ab28ef6a43599bb2a8 PDF Text Text �TECHNICAL SESSIONS TECHNICAL SESSIONS AND AND ABSTRACTS ABSTRACTS FOR FOR THE THE 31ST ANNUAL 31ST ANNUAL INSTITUTE ON INSTITUTE ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY HELD HELD AT INN OF INN OF THE THEWOODS WOODS KENORA, ONTARIO KENORA, ONTARIO MAY 9, 1985 MAY 8,8,9, 1985 WITh ThE IN CO-OPERATION CO-OPERATION WITH THE RES GEOLOG KENORA OFF RESIDENT IDENT GEOLOGIST I ST OFFICE, ICE,KENORA AND ThE AND THE ONTARIO GEOLOGICAL SURVEY, ONTARIO GEOLOGICAL SURVEY, ONTARIO MINISTRY NATURAL RESOURCES ()TARIO MINISTRY OFOF NATURAL RESOURCES PROGRAM CHAIRMAN EDITOR PROGRAM CHAIRMAI'.1AND AND EDITOR C, BLACKBURN C. E.I -BLACKBURN �1 a TABLE OF CONTENTS TABLE OF CONTENTS INSTITUTES LAKE SUPERIORGEOLOGY, 1955 1986 a, , , ,,.., , , , ., , , ii, ,a, ,.a, a,. , , , , 11 CONSTITUTION ThEINSTITUTE INSTITUTEON ONLAKE LAKE SuPIoR GEOLOGY CONSTITUTION OFOFTHE SUPERIOR GEOLOGY ..., , , , ,.. , , .,... , , , , , iii1 SAM ~ L D I C H MEDAL :AWARDGUIDELINESAND : AWARD GUIDELINES AND RECIPIENTS ~ C I PENTS I ,.,.,,..,,,,.,, , ,,,, ,, ,, , , , , , , v SAMGOLDICHMEDAL vi REPORT OFOF THE THE 19814 1984CHAIRMAN CHAIRMAN , l , l a , , , , l , l , , , , , , , , , , , , , , , , , , , ., ,..•.•.. ,,,,,, REPORT BOARD OF OF DIRECTORS DIRECTORS111111 l l l . l ~ . , l m lliii,,.. l ~ ~ l l Il lull.... ~ l , , , l llillIllIlli . l l , u , ~ , , , ...... , , , , , s ,viii v~i ,i ,1, , , , 1111 BJiRD LOCAL COtTITTEE COMMITTEE l l l l l l l l ~ l , ~ ~ l l l l l l l , l l l ~ l l , , l l s l u ~ . , . l , , l l l , , , ,i x, , , I_.oca_ BESTSrI.JDE!'rr STUDENTPAPEI PAPERCOtYv1ITfEE COWITTEE~ 6 ~ l , l o l B , . l l l l , l ~ , , , , , , ~ , ~ , , , ,I,x s , l , ~ , BESI ix GOLDICH NDAL.. MEDAL CoIT'1Ir'rEE COMMITTEE OL.DICl—1 FIELDTRIP TRIPlEADERS LEADERS ,,, l1l ,,l l, l , , l . , l l ~ l ~ , , , m l . ~ . l l , , , m , l l , ~ ~ ~ ixi, x, , ~ 8 ~ ~ o , , , SESSION CHAIRMEN1111111 . l , l l l l . l l , l l ~ ..... l l l l o......... l l l l ~ m all...... l l , . l l ~ l .. l , ... , , , l... ~ ~., ~ lx, , , , , o SESSION CI—IAIRr1EN x, i GOLDICH r"EDAI... MEDAL RECIPIENT . l B l , l . , ,,,,,... l l l l l l , ,1l , , l l , l l . , , ~ , l l , s. , ,... , ~ ,,1 , , ii , , , , ,Xl IECIPIENr ........, ANNUAL SPEAKER. , l l l , B ~ , l , l , , , , . l , , l l , , , , , , , , , , , , , , , , , , , , ~ x, i NUAL.. BANQUET BANQuET SPEPI(ER /i'i TECHNICALSESSIONS l l.. ,. ,.1aI . . l l , , s . l l l . . , l l , l ~ l m , l , l l ~ ~ , , Xii ,x li i, ~ ~ ~ ~ TECI—INICPJ... SESSIONS l . . l l . xiii x i 11 SESSION SESSION11 ONLAKE SUPERIOR GEOLOGY, 1955 TO TO 1986 INSTITUTES ON 11 a . • • a . • • a . . • • . . ~• . , F IEL...IJ , a ,, , . ~ • a , • , . , . . . . . . . . . . . . . . . • I I I I I I I I I I . . , . . . . . , , , 8. t . 8, • . • . . . • , , .~ , ,. ,~. ., . ~• . l , . . . . . . . . , , . • . . a . . . . . ,. 8 . . . . . . . . I I I I I I I I . a a . . • . • . , , . .8 , .~ ~ . . . . . I I . I I I I , . . , , , . ,. , . . , . l. , a , . . . . 3oL..IJICI—1 . I I • , . l . ,. ~ . . LX , ~ , ~ l l m ~ , , , 8 , , , . a . . • a . a a . i . a i . . . . I I I I I I I a . I . , , . . , . . I I I I I I I I I I . , I I I I I I . u I I I . , a . . a I I I I I I I , ~ . , .1 ,. 1• , . , .1 ., 1. .. 1 . , ., .. 1. ,. 1 . 1 ., .l 1. , . , . , ., 1. 1. 1. 1 . . .1 ,• 1 1 , 1 a , ,, 1. 1. * 1 , ,, ,, * , , # ,, SESSION SESSION33 ,a . a. , SESSION SESSION SESSION44 SESSION 22 ., , l , l . , , , 1 1 , , 1 1 l •l l l a l . ~i , . . , , , l l. l, , .l .l l. ' ., , ,, , , . . . . p a . ~ a 8a a a se a ~ ,i a l p , il i ., , , a il ,a al i , i ,l .@ i, a . l a a ., a u ,l . xi_r xiv 1 i, i, ,i , . , ,. ai ,a , a* ,i ,a , . , , , , , * , i i i . . p .a . , a p a l p i ~ , p p p p ~a p 8 i p 1. . ., ., , . ., .l .l ., ., .l l l . l . , . , . , . , a , , . l . l , l , l. ,. ,. ,. l. l, l. l. ,. l. ,. l. ,. l. * I , l l I, III POSTER PRESENTATIONSIIIIIIIIt l l , l . l l l , 111111 lllll,..la , , ,IiIaI , , , ,a l l ItlIllIllIll ll,,,,l,m l l ,I, , , ABSTRACTS /BSTRAC1'S POSTER PRESEI'1TA1"IONS I I I xv ~ ~ ~ ~ ~ a xvi xvi xvi 1 I xx xx . ., . , . l l l l s , , , t l , ~ ~ m , , ~ ~ ~ , ~ l . ,l ,. l , , , ,. l, l. l. l . , m , , ., ,l . l . , . , l, , l. l. ~ . l, ,• ,a lp •. .l . l . l . 8 . l . l t. m COVER COVER PHOTO; PHOTO; Sultana S u l t a n a Mine Mine (circa ( c i r c a1898) 1898) ; C o u r t e s y of o f Lake Lake of o f the t h e Woods Woods Courtesy Mueseum, Mueseurn, Kenora Kenora 1 ~ l ~ �INSTITUTES INSTITUTES ON LAKE LAKE SUPERIOR GEOLOGY INSTITUTE NUMBER 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 DATE DATE 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 ii PLACE Minneapolis, M i n n e a p o l i s , MN Houghton, MI MI East E a s t Lansing, L a n s i n g , MI MI Duluth, D u l u t h , MN MN Minneapolis, M i n n e a p o l i s , MN MN Madison, WI WI Port P o r t Arthur, A r t h u r , Ont. Ont. (Thunder (Thunder Bay) Bay) Houghton, MI MI Duluth, D u l u t h , MN MN Ishpeming, Ishpeming, MI MI St. S t . Paul. P a u l . MN MN Sault S a u l t Ste. S t e . Marie, M a r i e , MI MI East E a s t Lansing, L a n s i n g , MI MI Superior, S u p e r i o r , WI W I Oshkosh, Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN D u l u t h , MN Houghton, MI MI Madison, WI WI Sault S a u l t Ste. S t e . Marie, M a r i e , Ont. Ont. Marquette, M a r q u e t t e , MI MI St. S t . Paul, P a u l , MN MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, Milwaukee, WI WI Duluth, MN D u l u t h , MN Eau Eau Claire, C l a i r e , WI WI East MI E a s t Lansing, L a n s i n g , MI International I n t e r n a t i o n a l Falls, F a l l s , MN MN Houghton, Houghton, MI MI Wausau, Wausau , WI W I Kenora, Kenora, Ont. Ont. Hosted by by Wisconsin Wisconsin GS GS ?II'J �______________________________________ CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Article A r t i c l e II Name P The name of of the t h e organization o r g a n i z a t i o n shall s h a l l bbe e the t h e "Institute " I n s t i t u t e on Lake Superior Superior Geology. ' I Article A r t i c l e II I1 Objectives Objectives The objectives o b j e c t i v e s of o f this t h i s organization o r g a n i z a t i o n are: are: A. A. B. B. C. C. Article A r t i c l e III 111 To provide whereby geologists provide a a means whereby g e o l o g i s t s in i m the t h e Great G r e a t Lakes region region may exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To promote b better understanding of etter u nderstanding o f the t h e geology g e o l o g y of o f the t h e Lake Superior Superior region region To plan p l a n and conduct c o n d u c t geological g e o l o g i c a l field f i e l d trips. trips. Status Status of of organization No part part o f the t h e income o f the the o r g a n i z a t i o n shall s h a l l inure i n u r e to t o the t h e benefit b e n e f i t of of In any member or o r individual. individual. I n tthe h e eevent v e n t of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the organization o r g a n i z a t i o n shall s h a l l be b e distributed d i s t r i b u t e d to to (some ttax (some a x free f r e e organization). organization), [To Federal State [To aavoid void F e d e r a l and S t a t e income taxes, t a x e s , the t h e organization o r g a n i z a t i o n should should be o r 'educational" " e d u c a t i o n a l " but b u t also a l s o "non—profit."] "non-profit."] b e not n o t only o n l y "scientific" " s c i e n t i f i c " or 290,01, ssubd Minn. u b d , 44 Minn. Stat. S t a t . Anno. Anno. 290.01. If EE 29OO5(9) ' 2 90.05(9) 1954 Internal I n t e r n a l Revenue Code s. s o 50l(c)(3) 5Ol(c) ( 3 ) Article A r t i c l e IV IV Membership The membership of o f the t h e organization o r g a n i z a t i o n shall s h a l l consist c o n s i s t of o f the t h e board b o a r d of of directors. directors. b e permitted p e r m i t t e d to t o attend a t t e n d and and participate p a r t i c i p a t e in in Any geologist g e o l o g i s t interested i n t e r e s t e d shall s h a l l be and vvote meetings o t e aat t tthe h e aannual nnual m eetings. Article A r t i c l e VV Meetings Meetings The organization year, o r g a n i z a t i o n shall s h a l l meet once once a y e a r , preferably p r e f e r a b l y during d u r i n g the t h e month of of April. A p r i l . The place p l a c e and exact e x a c t date d a t e of of each e a c h meeting m e e t i n g will w i l l be b e designated d e s i g n a t e d by by tthe h e bboard o a r d of o f directors. directors. Article A r t i c l e VI VI Directors D irectors The board b o a r d of o f directors d i r e c t o r s shall s h a l l consist c o n s i s t of o f the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer and the t h e last l a s t three t h r e e past p a s t Chairmen; Chairmen; but b u t if i f the t h e board b o a r d should s h o u l d at a t any any time t i m e conconsist by rreason s i s t oof f lless e s s tthan h a n ffive i v e ppersons, e r s o n s , by e a s o n oof f uunwillingness n w i l l i n g n e s s or o r inability inability of o f any of o f the t h e above persons p e r s o n s to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies v a c a n c i e s on on the the board b o a r d may be filled f i l l e d by the t h e annual a n n u a l meeting m e e t i n g so s o as to t o bring b r i n g the t h e membership of o f the t h e board b o a r d up up to t o five f i v e members. members. Article A r t i c l e VII VII - Officers O fficers The officers o f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e a Chairman and and aa Secretary— SecretaryTreasurer. Treasurer. A. B. B. Article VIII A r t i c l e VIII The Chairman shall s h a l l be b e elected e l e c t e d each e a c h year y e a r by the t h e board b o a r d of o f directors, directors, who shall s h a l l give g i v e due d u e consideration c o n s i d e r a t i o n to t o the t h e wishes w i s h e s of o f any any group group that t h a t may may be b e promoting p r o m o t i n g the t h e next n e x t annual a n n u a l meeting. m e e t i n g . His H i s term t e r m of o f office o f f i c e as a s Chairman Chairman will w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of o f the t h e annual a n n u a l meeting m e e t i n g over o v e r which which he he preprewill orr when his ssides ides o h i s successor s u c c e s s o r shall s h a l l have h a v e been b e e n appointed. appointed. He w i l l then then serve member of s e r v e for f o r aa pperiod e r i o d oof f three t h r e e yyears e a r s aass a a member o f the t h e board b o a r d of o f directors. directors. His The Secretary—Treasurer S e c r e t a r y - T r e a s u r e r shall s h a l l be b e elected e l e c t e d at a t the t h e annual a n n u a l meeting. meeting. H is term orr u until t e r m oof f ooffice f f i c e shall s h a l l bbe e two two yyears ears o n t i l his h i s successor s u c c e s s o r shall s h a l l have have been b e e n appointed. appointed. Amendments Amendments T h i s constitution c o n s t i t u t i o n may be b e amended by a majority m a j o r i t y vote v o t e of This of those t h o s e persons p e r s o n s who who a r e personally p e r s o n a l l y present p r e s e n t at, a t , participating p a r t i c i p a t i n g in, i n , and voting v o t i n g at a t any any annual annual are meeting m e e t i n g of of the t h e organization. organization. 111 iii - �BY -LAWS —LAWS II.. Duties D u t i e s of of the t h e Officers O f f i c e r s and and Directors Directors A. It I t shall s h a l l be the t h e dutyof d u t y o f the t h e Chairman Chairman to: to: 1. 1. 22.. 33.. B. It I t shall s h a l l be the t h e duty d u t y of the t h e Secretary—Treasurer S e c r e t a r y - T r e a s u r e r to: to: 1. 1. 2. 2. 3. 3. C. II. II. III. Preside P r e s i d e at a t the t h e annual a n n u a l meeting. meeting. Appoint all needed for organization Appoint a l l committees needed f o r the the o r g a n i z a t i o n of of the the annual a n n u a l meeting. meeting. organization and Assume complete responsibility r e s p o n s i b i l i t y ffor o r the the o r g a n i z a t i o n and of the meeting ffinancing i n a n c i n g of t h e aannual nnual m e e t i n g over o v e r which he he presides. presides. Keep accurate a c c u r a t e attendance a t t e n d a n c e records r e c o r d s of of all a l l annual a n n u a l meetings. meetings. of aall meetings of, Keep aaccurate c c u r a t e rrecords e c o r d s of ll m eetings o f , and correspondence correspondence between, the between, t h e board of of directors. directors. Hold all a l l funds f u n d s that t h a t may may aaccure c c u r e aass profits p r o f i t s from from annual a n n u a l meetings meetings orr field and tto make tthese o f i e l d trips t r i p s and o make h e s e funds f u n d s available a v a i l a b l e for f o r the the organization o r g a n i z a t i o n and operation o p e r a t i o n of of future f u t u r e meetings m e e t i n g s as a s required. required. It be duty of tthe of d directors plan I t shall shall b e the the d u t y of h e bboard o a r d of i r e c t o r s to to p l a n locations locations of meetings and to organization o f aannual nnual m e e t i n g s and t o aadvise d v i s e on tthe he o r g a n i z a t i o n and financing financing of all of a l l meetings. meetings. Dues and Expenses Expenses 1. 1. There shall s h a l l be b e no no regular r e g u l a r membership membership dues. dues. 2. 2. Registration meetings R e g i s t r a t i o n fees f e e s for f o r the t h e annual annual m e e t i n g s shall s h a l l be b e determined determined by the t h e Chairman in i n consultation c o n s u l t a t i o n with w i t h the t h e board b o a r d of of directors. directors. It recommended tthat be k kept I t is sstronglr t r o n g l y recommended h a t tthese h e s e be e p t at at a a minimum to to encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. Rules R u l e s or o r Order Order Rules The rules r u l e s contained c o n t a i n e d in i n Robert's Robert's R u l e s of of Order O r d e r shall s h a l l govern govern this this organization o r g a n i z a t i o n in i n all a l l cases c a s e s to t o which which they t h e y are a r e applicable. applicable. IV. IV. Amendments These by—laws by a majority by-laws may be b e amended by a m a j o r i t y vote v o t e of of those t h o s e persons p e r s o n s who are participating a r e personally p e r s o n a l l y present p r e s e n t at, at, p a r t i c i p a t i n g in, i n , and voting v o t i n g at a t any any annual annual meeting m e e t i n g of of the t h e organization; o r g a n i z a t i o n ; provided p r o v i d e d that t h a t such s u c h modifications m o d i f i c a t i o n s shall shall not with n o t conflict conflict w i t h the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted a d o p t e d or o r subsequently subsequently amended. iv �SAM SAM GOLDICH GOLDICH HEDAL MEDAL Preamble Preamble The The Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology was was born b o r n on on or o r around around 1955, 1955, as a s documented documented w i l l be be held h e l d in i n 1981. 1981. The The Institutes Institutes by the t h e fact f a c t that t h a t the t h e 27th 2 7 t h annual annual meeting meeting will by are a r e exemplary exemplary in i n their t h e i r continuing c o n t i n u i n g objectives o b j e c t i v e s of o f dealing d e a l i n g with w i t h those t h o s e aspects a s p e c t s of of geology the geology that t h a t are a r e related r e l a t e d geographically g e o g r a p h i c a l l y to t o Lake Lake Superior; S u p e r i o r ; of o f encouraging e n c o u r a g i n gthe discussion d i s c u s s i o n of o f subjects s u b j e c t s and and sponsoring s p o n s o r i n g field f i e l d trips t r i p s which which will w i l l bring b r i n g together together geologists g e o l o g i s t s from from the t h e academia, academia, government government surveys, s u r v e y s , and and industry; i n d u s t r y ; and and of o f maintaining maintaining an exceedingly e x c e e d i n g l y informal i n f o r m a l but b u t highly h i g h l y effective e f f e c t i v e mode mode of o f operation. operation. an During During the t h e course c o u r s e of o f its i t s existence e x i s t e n c e the t h e membership membership of o f the t h e Institute I n s t i t u t e (that ( t h a t is, i s , those those geologists g e o l o g i s t s who who indicate i n d i c a t e an an interest i n t e r e s t in i n the t h e objectives o b j e c t i v e s of of the t h e I.L.S.G, I.L.S.G. bybyattending) attending) h a s become become aware aware of o f the t h e fact f a c t that t h a t certain c e r t a i n of o f their t h e i r colleagues c o l l e a g u e s have have made made particularly particularly has noteworthy and m meritorious of noteworthy and e r i t o r i o u s ccontributions o n t r i b u t i o n s tto o tthe h e improvement o f understanding u n d e r s t a n d i n g of of "Lake Superior" S u p e r i o r " geology geology and and its i t s mineral m i n e r a l deposits. deposits. "Lake was made made by by I.L.S.G. I.L.S.G. to t o Sam Sam Goldich Goldich in i n 1979 1979 for f o r his h i s many many The exemplary exemplary award award was The contributions c o n t r i b u t i o n s to t o the t h e geology geology of o f the t h e region r e g i o n extending e x t e n d i n g over o v e r about a b o u t5050years. years. Award Guidelines Guidelines Award The by the Board oof Directors, The medal medal shall s h a l l be be awarded awarded annually a n n u a l l y by t h e Board f D i r e c t o r s , II,L.SG., . L . S . G . , to t o aa geologist g e o l o g i s t whose whose name name is i s associated a s s o c i a t e d with w i t h aa substantial s u b s t a n t i a l sustained s u s t a i n e d interest i n t e r e s t in, i n , or or aa major major contribution c o n t r i b u t i o n to, t o , the t h e geology geology of o f the t h e Lake Lake Superior S u p e r i o r Region. Region. 1) 1) s h a l l appoint a p p o i n t the t h e Nominating Nominating Committee. Committee. The Board Board of o f Directors,I.L.S.G. D i r e c t o r s , I . L .S. G . shall 2) 2 ) The Their T h e i r annual annual nominee nominee will w i l l be be voted v o t e d on on at a t the t h e annual annual business b u s i n e s s meeting. meeting. The The i n i t i a l appointment appointment will w i l l be be of o f three t h r e e members, members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one initial for f o r two, two, and and one one for f o r one one year, y e a r , the t h e member member with w i t h the t h e briefest b r i e f e s t incumbency incumbencytot obebe chairman. After A f t e r the t h e first f i r s t year y e a r the t h e Board Board of o f Directors D i r e c t o r s shall s h a l l appoint a p p o i n t at a t each each chairman. I n the t h e third t h i r d year year s p r i n g meeting meeting one one new new member member who who will w i l l serve s e r v e for f o r three t h r e e years. y e a r s . In spring t h i s member member shall s h a l l be be the t h e chairman. chairman. The The Committee Committee membership membership should s h o u l d reflect r e f l e c t the the this main membership. main fields f i e l d s of o f interest i n t e r e s t and and geographic g e o g r a p h i c distribution d i s t r i b u t i o n of o f I.L.S.G. I .L.S.G. membership. The Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall s h a l l select s e l e c t the t h e medalist m e d a l i s t and and will will 3) 3) The make make its i t s recommendation recommendation to t o the t h e Board Board of o f Directors D i r e c t o r s by by November November 1 1of o f that t h a tyear. year. The Board Board of o f Directors D i r e c t o r s normally n o r m a l l y will w i l l accept a c c e p t the t h e nominee nominee of o f the t h e Committee, Committee, The will inform tthe medalist immediately, and will will inform he m e d a l i s t immediately, w i l l have have one one medal medal engraved engraved a p p r o p r i a t e l y for f o r presentation p r e s e n t a t i o n at a t the t h e May May meeting. meeting. appropriately 4) 4) I t is i s recommended recommended that t h a t the t h e Institute I n s t i t u t e set set aside a s i d e annually a n n u a l l y from from whatever whatever sources, sources, It such such funds funds as a s will w i l l be be required r e q u i r e d to t o support s u p p o r t the t h e continuing c o n t i n u i n g costs c o s t s of o f this t h i s award. award. 5) 5) April A p r i l 4, 4 , 1981 1981 J. J . Kalliokoski, K a l l i o k o s k i , Chairman Chairman Bill B i l l Cannon Cannon Fred Fred Kehienbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky RECIPIENTS RECIPIENTS 1979 Sam Sam Goldich Goldich 1979 Dutton 1981 Carl C a r l Dutton 1981 1982 Ralph Ralph Marsden Marsden 1982 1983 1983 Burton Burton Boyum Boyum 1984 1984 Richard R i c h a r d Ojakangas G j akangas 1985 1985 Paul Paul Sims Sins v �REPORT OF THE REPORT OF THE CHAIRMAN CHAIRMAN ONON LAKE SUPERIOR 330th 0 t hINSTITUTE INSTITUTE LAKE SUPERIORGEOLOGY GEOLOGY 1984 The AnnualI Institute was hheld The 330th 0 t h Annual n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology was e l d AApril p r i l 24-28, 24-28, 1984 aatt the 1984 t h e Holiday H o l i d a y Inn I n nofo Wausau, f Wausau, Wisconsin. Wisconsin. Conference Conference rregistration e g i s t r a t i o nwas was 220, 220, including i n c l u d i n g professional p r o f e s s i o n a l geologists g e o l o g i s t sand and students. s t u d e n t s . The The program program cconsisted o n s i s t e d ooff one pre-meetingand andtwo twop opost-meeting one pre-meeting s t - m e e t i n g f i efield l d t trips r i p s and and two two days days ooff technical technical two-dayoor pre-meetingt rtrip The two-day r pre-meeting i p I to t o show show ffeatures e a t u r e s of o f the t h eDunbar Dunbar gneissgneisspapers. The andaassociated ggranitoid r a n i t o i d dome dome and s s o c i a t e d EEarly a r l y PProterozoic r o t e r o z o i c vvolcanic o l c a n i c rocks r o c k s in i n northeastern northeastern Wisconsin, Wisconsin, led l e d by by P.K. P.K. Sims, Sims, K.J. K.J. Schulz, Schulz,and andZ.E. Z.E. Peterman, Peterman, had had approximately approximately 60 Thepost-meeting post-meetingt rtrip II "Early 60 pparticipants. a r t i c i p a n t s . The i p 11 " E a r l y Proterozoic P r o t e r o z o i c Tectonostratigraphic Tectonostratigraphic Terranes ooff the Region', led Terranes t h e Southern Southern Lake Lake SSuperior u p e r i o r Region", l e d by by D.K. D.K. Larue, Larue, had hadapproximately approximately 25 pparticipants, of the 25 a r t i c i p a n t s , and and field f i e l dtrip t r i III p "Geology 111 "Geology o f tWausau h e WausauSyenite S y e n i t eComplex", Complex", led led by P.E. had aapproximately 12pparticipants. The ttechnical by P.E. Myers, Myers, had p p r o x i m a t e l y 12 a r t i c i p a n t s . The e c h n i c a l sessions sessions Onef full cconsisted o n s i s t e d ooff 51 51 papers, papers, of o f which which 13 13 were were poster p o s t e r presentations. p r e s e n t a t i o n s . One u l l day day of of devotedt to paperson ont hthe Proterozoic tthe h e technical t e c h n i c a l sessions sessions was was devoted o papers e EEarly arly P r o t e r o z o i c ooff the the Lake SSuperior Proceedingsoof conferencewere wereppublished f tthe h e conference u b l i s h e d i in n ffour our Lake u p e r i o r region. r e g i o n . Proceedings separate volumes; volumes;a abstracts andeach eacho foft hthe separate b s t r a c t s and e f ifield e l d trip t r i pguidebooks. guidebooks. The annual banquet banquetwas wash held onAApril The annual e l d on p r i l 26th, 26th, 1984, 1984, and and was was attended a t t e n d e d by by approximately 100people. people.WWilliam F. Cannon Cannonp rpresented qualifications i 11i a m F. e s e n t e d t h ethe qua1 i f i c a t i o n s ooff the the a p p r o x i m a t e l y 100 Goldich Medal rrecipient, G o l d i c h Medal e c i p i e n t , and andthe t h eMedal Medal was was presented presented to t oRichard R i c h a r dOjakangas Ojakangas by by SamGGoldich. banquetaddress address"The "TheOre OreMMetals Earth Sam o l d i c h . The The banquet e t a l s i in n E a r t h History H i s t o r y " was was presented by Dr. Charles The address addressccontained by Charles Meyer Meyer of o f Sedona, Sedona, Arizona. A r i z o n a . The o n t a i n e d aa wwealth e a l t h ooff information i n f o r m a t i o n on on tthe h e nature n a t u r e and and eevolution v o l u t i o n ooff ore o r e deposit d e p o s i t types. types. Two paper awards awardsoof $150.00 each eachwere wereppresented Two sstudent t u d e n t paper f $150.00 r e s e n t e d t this h i s year, y e a r , one one each each for Christopher A. Scholz, Scholz, ffrom f o r poster p o s t e r and and oral o r a l presentation. presentation. C h r i s t o p h e r A. r o m t the h e UUniversity n i v e r s i t y ooff Minnesota-Duluthr ereceived award Minnesota-Duluth c e i v e d t hthe e award f o for r t hthe e bbest e s t pposter o s t e r ppresentation r e s e n t a t i o n f for o r his h i s paper paper "Late L a t e and and Post—glacial P o s t - g l a c i a l LLacustrine a c u s t r i n e Sediment Sediment DDistribution i s t r i b u t i o n in i nWestern Western Lake Lake Superior Superior SeismicRReflection Beck, ffrom University ffrom r o m Seismic e f l e c t i o n PProfiles", r o f i l e s " , and and Warren Warren Beck, r o m tthe he U n i v e r s i t y of of Cities, Minnesota-Twin C i t i e s , received r e c e i v e d the t h e best b e s t student s t u d e n t oral o r a l presentation p r e s e n t a t i o n for f o r hhis i s paper paper "Nd and 'Nd and Sm Sm I Isotopic s o t o p i c Studies S t u d i e s of o fthe t h eQuinnesec Quinnesecand andHemlock Hemlock Formations Formations in i n Northeastern Northeastern Wisconsin and and Adjacent Adjacent Michigan'. awards were were ppresented Wisconsin Michigan". The The awards r e s e n t e d by by Val Val W. W. Chandler, Chandler, Chairman Chairman ooff the t h eStudent StudentPaper PaperAwards Awards Committee. Committee. The Boardo of The Board f DDirectors i r e c t o r s oof f tthe h e IInstitute n s t i t u t emet met on on April A p r i l 26, 26,1984. 1984. Present Present at at G.L. (Chairman),T.T.J. Southwick, G.L. LaBerge LaBerge (Chairman), J. Bornhorst, B o r n h o r s t , D.L. D.L. Southwick, F.W. Cambray, Cambray,P.E. P.E.Myers, Myers,J .3.KKalliokoski a l l i o k o s k i (Secretary-Treasurer) ( S e c r e t a r y - T r e a s u r e r ) and and C.E. C.E. Blackburn Blackburn F.W. (incoming Boardt otook (incoming Chairman Chairman ffor o r 1985). 1985). The The Board o k t hthe e f following o l l o w i n g action: action: the t h e meeting meeting were: were: 1. Accepted Accepted t hthe e i invitation n v i t a t i o n by by Charles Charles Blackburn B l a c k b u r n ooff the the Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey to t o hold h o l dthe t h e1985 1985meeting meeting iinn Kenora, Kenora, Ontario. Ontario. 2. T e n t a t i v e l y accepted accepted t the h e iinvitation n v i t a t i o nof o fthe t h eWisconsin Wisconsin Tentatively Geological G e o l o g i c a l Survey Survey tto o hold h o l d the t h e1986 1986 meeting m e e t i n g in i nWisconsin. Wisconsin. vi �3. A motionby by KKalliokoski, byBornhorst, Bornhorst,t hthat A motion a l l i o k o s k i , second second by a t ffor or ffinancial i n a n c i a l reasons reasons tthe h e Institute I n s t i t u t ediscontinue d i s c o n t i n u e paying p a y i n g the the expenses expenses o of f t the h e rrecipient e c i p i e n t of o fthe t h eGoldich G o l d i c hMedal. Medal. Passed unanimously. Passed 4. Conference per Conference r eregistration g i s t r a t i o n should s h o u l d include i n c l u d e aa $1.00 $1 -00 per person charge tto person charge o maintain m a i n t a i n the t h e Goldich G o l d i c hMedal Medal account. account. The fundswwill i l l be be used used tto o strike s t r i k ethe t h emedals medals as as the the The funds need need aarises. rises. 5. 5. Replace Buchhei t on on the t h eGoldich G o l d i c hAward AwardCommittee Cornrni t t e e Replace Richard Richard Buchheit W i l l a r d Bodwell Bodwell with w i t h another another Member Member ffrom r o m IIndustry. n d u s t r y . Willard Comittee agreed agreed tto o serve serve a three-year t h r e e - y e a r term. term. The The Comrni t t e e ffor or 1985wwill 1985 i l l be be William W i l l i a mF.F.Cannon Cannon (U.S.G.S.), (U.S.G.S.), Chairman; Chairman; M.F. M.F. Kehlenbeck, Kehlenbeck, and and Bodwell. Bodwell. 6. Send Senda al ilist 6. s t of o f recipients r e c i p i e n t sofo fthe t h eGoldich G o l d i c hMedal Medal to t o the the incoming Chairman Chairmant otobe be i included incoming n c l u d e d iinn the t h e Proceedings Proceedings vvolume. o l ume . I would advice I would llike i k e to t o extend extend aa bit b i tofo hard—earned f hard-earned a d v i c e t otof ufuture t u r e IInstitute nstitute Chairmen. The The hhigh abstract i g h ccost o s t of o f printing p r i n t i n gand andbinding binding a b s t r a cvolumes t volumesand andguidebooks guidebooks necessitates we do donnot n e c e s s i t a t e s tthat h a t we o t pprint r i n t many many e extra x t r a ccopies o p i e s ( (II did). did). IIn n doing d o i n g so so we we ttie ie up tthe w i l not l n obe t berecouped. recouped. up h e IInstitut&s n s t i t u t e ' sresources resources in i n printing p r i n t i n gcosts c o s t s that t h a tprobably p r o b a b l y will So my mya advice So d v i c e i sis tto o print p r i n tonly o n l ya afew fewdozen dozen extra e x t r acopies copiesofo the f t h eguidebooks guidebooks and and abstracts. a bstracts. Serving a major S e r v i n g as as Institute I n s t i t u t eChairman Chairman has has been been a major learning l e a r n i n g experience. experience. It I thas has beenbboth Thewwillingness been o t h aa llot o t of o fwork work and and very very rewarding. rewarding. The i l l i n g n e s s ooff colleagues c o l l e a g u e s in in the Superior t h e Lake Lake S u p e r i o r rregion e g i o n tto o serve serve on on the t h e various v a r i o u s committees, committees, chair c h a i r sessions, sessions, lead lead field grateful myjob j o bmuch much easier, e a s i e r , and and IIam am g r a t e f u l for f o rthe t h ecooperation cooperation f i e l dtrips, t r i p setc., , e t cmade . , mademy off so o so many many i individuals. ndividuals. Respectfully submitted, Respectful l y submitted, / Gene L. LaBerge Gene L. LaBerge Chairman Annual I I.L.S.G. Chai rman 330th 0 t h Annual .L.S.G. Oshkosh, WI WI Oshkosh, May 21, 21, 1984 May 1984 vvii ii - �INSTITUTE BOARD OF DIRECTORS DIRECTORS ResidentResident Geologist, Ministry C . E. E . B1ackbu, Blackburn, G e o l o gofi sNatural t , M i Resources, n i s t r y o f N a t u r a l Resources, C. Robertson S St., Ontario, 808 Robertson t . , Kenora, Kenora, O n t a r i o , P9N 3X9 3x9 (1985) (1985) L. LaBerge, Department o off Geology, G. L G. . LaBerge, Geology, University U n i v e r s i t y of o f Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, 54901 54901 (1984) (1984) T. J . Bornhorst, Bornhorst, Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, T. J. Michigan Technological University, U n i v e r s i t y , Houghton, Houghton, Michigan, Michigan, 49931 49931 (1983) (1983) Southwick, Minnesota Geological Survey, 2642 DD.. LL. . Southwick, 2642 University U n i v e r s i t y Avenue, Avenue, St. S t . Paul, P a u l , Minnesota, Minnesota, 55114 55114 (1982) F. W. Cambray, Cambray, Department of o f Geology, Michigan State S t a t e University, University, F. W. East E a s t Lansing, Lansing, Michigan, 48824 48824 (1981) (1981) J. J . Kalliokoski, K a l l i o k o s k i , Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological Technological University, Michigan, 49931 499 31 Michigan U n i v e r s i t y , Houghton, Houghton , Michigan, (Secretary-Treasurer) ( S e c r e t a r y- T r e a s u r e r ) C o p i e s of o f the t h e abstract a b s t r a c t and field f i e l d guidebook guidebook Copies v o l u m e s may be b e purchased p u r c h a s e d from: from: volumes N.M. M.M. Kehienbeck Kehlenbeck D e p a r t m e n t of o f Geology Geology Department L a k e h e a d University University Lakehead Thunder Bay, Bay, Ontario Ontario PTV P7V 5E1 5E1 Costs: Costs: Abstracts $ 5.00 Abstracts $5.00 Field Field G u i d e b o o k $10.00 $10.00 Guidebook ((plus p l u s $2.00 $ 2 . 0 0 postage p o s t a g e and handling h a n d l i n g charges) charges ) c h e q u e s payable p a y a b l e to: to: Make cheques I n s t i t u t e on o n Lake Superior S u p e r i o r Geology Geology Institute viii viii �LOCAL COMMITTEE COMMITTEE LOCAL C. C. E . Blackburn: Blackburn: E. C . Beard: Beard: R.R. C. J . Parker: Parker: J. Conference Conference Chairman, Chairman, and and Technical Technical Sessions Sessions a Treasurer Treasurer Registration Registration C. C. C . Storey: S t o r e y : Poster P o s t e r Session Session C. M. M. R. Hailstone: Hailstone: R. Field F i e l d Trip T r i p Logistics Logistics All A l l at a t Ministry M i n i s t r y of o f Natural Natural Resources, Resources, 808 808Robertson RobertsonStreet, Street, Kenora, Ontario Ontario Kenora, BEST STUDENT STUDENTPAPER PAPER COMMITTEE COMMITTEE BEST - Gene LaBerge, LaBerge, Chairman, Chairman, Department Department of of Geology, Geology, University U n i v e r s i t y of o f Wisconsin Wisconsin, Gene Oshkosh, Wisconsin Wisconsin Oshkosh, Graham Borradaile, B o r r a d a i l e , Department Department of o f Geology, Geology, Lakehead LakeheadUniversity, University, Graham Thunder Bay, Bay, Ontario Ontario Thunder S c h u l z , United United States S t a t e s Geological Geological Survey, Survey, Klaus Schulz, Klaus Reston, Virginia Virginia Reston, GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE GOLDICH W. W. F. F. Cannon, Cannon, Chairman, Chairman, United United States S t a t e s Geological Geological Survey, Survey, Reston, Virginia Virginia Reston, M. M. M. M, Kehienbeck, Kehlenbeck , Department Department of o f Geology, Geology, Lakehead LakeheadUniversity, University , Thunder Bay, Bay, Ontario Ontario Thunder Willard W i l l a r d Bodwell, Bodwell, Resource Resource Exploration, Exploration, Marquette, Marquette, Michigan Michigan FIELD TRIP TRIP LEADERS LEADERS FIELD R. Melling, Melling, Ottawa-Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, Studies, David R, David Carleton C a r l e t o n University, U n i v e r s i t y , Ottawa, Ottawa, Ontario Ontario Watkinson, Watkinson, Ottawa-Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, Studies, Carleton C a r l e t o n University, U n i v e r s i t y , Ottawa, Ottawa, Ontario Ontario DavidI-I. H. David John C. Davies, Davies, Ontario O n t a r i o Geological Geological Survey, Survey, 77 77Grenville G r e n v i l l eSt., St., John C. Toronto, Toronto, Ontario Ontario P. P . Mark Mark Smith, Smith, Ontario O n t a r i o Geological Geological Survey, Survey, 77 77 Grenville G r e n v i l l e St., St., Toronto, Toronto, Ontario Ontario Charles Charles E. E . Blackburn, Blackburn, Ministry M i n i s t r y of o f Natural Natural Resources Resources 808 808 Robertson Robertson St., S t . , Kenora, Kenora. Ontario Ontario ix �Gary P. P . Beakhouse, Beakhouse, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 Grenvi 1 l e St., St. , Grenville Ontario Toronto, O ntario Glen W W. Ontario Grenville St., . JJohns, ohns, O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G renville S t., Toronto, Toronto, Ontario Ontario Grenville Fred WW. Breaks, O Ontario . Breaks, n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G r e n v i l l e St., St., Fred Toronto, Toronto, Ontario Ontario K . Poulsen, Poulsen, Geological G e o l o g i c a l Survey Survey of o f Canada, Canada, 601 601 Booth Booth St., St., Howard K. Ottawa, Ontario Ontario Don A. A. JJanes, a n e s , Ministry M i n i s t r y of o f Natural N a t u r a l Resources, Resources, Court Court House House Building, Building, Sioux S i o u x Lookout, Lookout, Ontario Ontario Richard C. C. Beard, Beard, Ministry M i n i s t r y of o f Natural N a t u r a l Resources, Resources, 808 808 Robertson Robertson St., St., Kenora, Kenora, Ontario Ontario SESSION CHAIRMEN CHAIRMEN Richard WW. Ojakangas, Geology Department, Richard . Ojakangas, Department, University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth, Duluth, Minnesota Grenville John Wood, Wood, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , 77 77 G r e n v i l l e St., St. , Toronto, Toronto, Ontario Ontario LeRoy Warren, Warren, Department of o f Natural N a t u r a l Resources, Resources, Hibbing, Hibbing, Minnesota Joop Langelaar, L a n g e l a a r , Norontex Exploration E x p l o r a t i o n Ltd., L t d . , Bedworth Bedworth Road, Road, Dryden, Ontario Dryden, Ontario Henry Lepp, Macalaster Department, Macalas t e r College College Lepp , Geology Department, St. S t . Paul, P a u l , Minnesota Mcllwaine, Ministry William 1-I. H. Mcllwaine, M i n i s t r y of o f Northern Northern Affairs, A f f a i r s , 435 435 James St. S t .South, South, William Thunder Bay, Bay, Ontario Ontario Everett, JJack ack E v e r e t t , Consulting C o n s u l t i n g Geologist, G e o l o g i s t , 1015 1015 North North Shore Shore Drive, Drive, Duluth, Duluth , Minnesota Michael Michael EE. . Cherry, C h e r r y , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, 77 77 Grenville G r e n v i l l e St., St., Toronto, T o r o n t o , Ontario Ontario x �GOLDICI-1 MEDAL RECIPIENT RECIPIENT GOLDICH MEDAL Paul Paul K. K . Sims Sims United U n i t e d States S t a t e s Geological G e o l o g i c a l Survey, S u r v e y , Denver Denver Federal F e d e r a l Centre, Centre, Denver Colorado Colorado ANNUAL BANQUET BANQUET SPEAKER SPEAKER Grant G r a n t M. M. Young, Young, Department Department of o f Geology, Geology, University U n i v e r s i t y of o f Western Western Ontario, Ontario, London, London, Ontario Ontario xi �TECHNICAL SESSIONS TECHNICAL SESSIONS A s t e r i s k denotes student s t u d e n t papers papers Asterisk Speakers Speakers are a r e underlined underlined xii �SESS S E S S ION I O N 1 1 Morning Wednesday, May 8 , 1985 1985 May 8, Co-chairmen: Co-chairmen: Jack Everett Everett and and Henry Henry Lepp Lepp 8:15 8:15 8:20 8:20 Opening Opening Remarks Remarks * T. Chartier Chartier * 8:40 8:40 9:00 9:OO * * 9:20 J. J . J. J . Mancuso Mancuso & C. C . W. W . Schick Schick Unconformity-type Unconformity-type uranium mineralization mineralization at a t the t h e Groveland Groveland Iron I r o n Mine, Mine, central central Dickinson County, County, Michigan. Michigan. C. L. L. Reichhoff Reichhoff Geology Geology of o f aa Lower Lower Proterozoic Proterozoic volcaniclastic v o l c a n i c l a s t i c sequence, sequence, Marathon County, Wisconsin. Wisconsin. J. J. G. G. 9:40 The the The texture t e x t u r e and and mineralogy mineralogy of o f the Lake Ellen E l l e n kimberlite, k i m b e r l i t e , Crystal C r y s t a l Falls, Falls, Michigan, Michigan, U. U . S. S . A. A. S. S. Kiasner Klasner 5 L, L o LaBerge LaBerge P. P. A. A. Nielsen 10:00 10: 00 Structural S t r u c t u r a l geology geology and and kinematics kinematics of of Early E a r l y Proterozoic P r o t e r o z o i c shear s h e a r zones zones in in central c e n t r a l Wisconsin. Wisconsin. Metamorphism Metamorphism of o f the t h e Dunbar Dunbar Gneiss Gneiss and associated a s s o c i a t e d supra-crustal s u p r a - c r u s t a l rocks: rocks: northeastern n o r t h e a s t e r n Wisconsin, Wisconsin, U. U. S. S . A. A. Coffee. Coffee. G. G. M. M. Young Young 6 H. W. W. Nesbitt Nesbitt Major Major element element geochemistry geochemistry of o f the the Gowganda Gowganda Formation, Formation, Ontario. Ontario. R. R . C, C. Johnson Documentaion Documentaion of o f aa subaqueously subaqueously emplaced emplaced volcanic v o l c a n i c horizon h o r i z o n in i n the t h e upper upper Portage Portage Lake Volcanics, Keweenaw Keweenaw Peninsula, Peninsula. Michigan. Michigan. 11:20 11:ZO J. J. Kalliokoski Kalliokoski & B. E . J. J. Welch Welch Caliche C a l i c h e paleosol p a l e o s o l in i n the t h e lower lower part p a r t of o f the the and Hecla Conglomerate, Centennial Calumet Calumet Conglomerate, Centennial Mine, Calumet, Calumet, Michigan. Michigan. 11:40 11:40 W, W. C. C. Hood Hood E& P. P . J. J. Vanstone Vanstone Economic Economic geology geology of o f the t h e rare r a r e element element pegmatites p e g m a t i t e s at a t Lilypad Lilypad Lake, Lake, northern n o r t h e r n Ontario. Ontario. 10:40 10~40 1-I. 11:00 11:OO 12:00 12 : O O * * Lunch. Lunch. xiii xiii �S E S S ION I O N SESS 22 Afternoon Aft e rn o on Wednesday, Wednesday, May May 8, 8 , 1985 1985 Co-Chairmen: Co-Chairmen: R. R. W. W . Ojakangas Ojakangas and and John John Wood Wood 2:OO 2:00 R. R. L. L . Morton, Morton, D. A. A. Groves, Groves, & D. J. NI. M. Franklin Franklin J. Volcanic V o l c a n i c stratigraphy s t r a t i g r a p h y and and nature n a t u r e of of t h e semi-conformable semi-conformable alteration a l t e r a t i o n zone zone the beneath b e n e a t h the t h e Mattabi M a t t a b i massive massive suiphide sulphide deposit, d e p o s i t , Sturgeon S t u r g e o n Lake, Lake, Ontario. Ontario. 2 :20 2:20 M. M. M. M. Kehienbeck Kehlenbeck Structure S t r u c t u r e of o f the t h e Beardmore-Geraldton Beardmore-Geraldton f o l d belt. belt. fold 2 :40 2:40 3:OO 3:00 M. J. J. Lavigne Lavigne Geological G e o l o g i c a l setting s e t t i n g of o f gold g o l d mineralization mineralization i n Beardmore-Geraldton. Beardmore-Geraldton. in P. P . W. W. Fralick F r a l i c k && B. NI. M. Scott Scott B. Controls C o n t r o l s on on the t h e genesis g e n e s i s of o f epigenetic epigenetic auriferous a u r i f e r o u s vein v e i n systems systems in i n Archean Archean chemical-siliciclastic c h e m i c a l - s i l i c i c l a s t i c submarine submarine fan fan deposits, d e p o s i t s , Geraldton G e r a l d t o n area, a r e a , Ontario. Ontario. NI. Coffee. Coffee. 3:20 3:20 3:50 3:50 H. H. G. G . Clark Clark Preliminary P r e l i m i n a r y metallogenic m e t a l l o g e n i c subdivision s u b d i v i s i o n of of the t h e Lake Lake of o f the t h e Woods Woods metavolcanicmetavolcanicmetasedimentary metasedimentary belt, b e l t , northwestern n o r t h w e s t e r n Ontario. Ontario. 4 : 10 4:10 M. M. G. G. Parr Parr 5 C . Boben Boben C. The The geological geological mineralization mineralization Mine, Mine, District District 44:30 : 30 :50 44 :50 *J J . Stix Stix B. B. A. A. Brown Brown setting s e t t i n g of o f gold gold observed o b s e r v e d at a t the t h e Scramble Scramble of o f Kenora, Kenora, N. N . W. W. Ontario. Ontario Volcanic V o l c a n i c facies f a c i e s of o f the t h e Andre: Andre": Bay Bay area, area, Lake Lake of o f the t h e Woods, Woods, Ontario. Ontario. The The deformational d e f o n n a t i o n a l history h i s t o r y of o f Archean Archean greenstones g r e e n s t o n e s in i n the t h e Central C e n t r a l Lake Lake of o f the the Woods Woods area, a r e a , northwestern n o r t h w e s t e r n Ontario. Ontario. xiv �SESS S E S S IION O N 3 Morning Thursday, May 9, 9 , 1985 1985 Co-chairmen and LeRoy LeRoy Warren Warren Co-chairmen:: Joop Langelaar and Opening Remarks Remarks 8:15 8:20 J. J. V. V. C. C. Green Green ?S W. W. Chandler Keweenawan dikes d i k e s of o f Minnesota. Minnesota- 8:40 M. M. GG. . Mudrey ?S PP.. E. E. Myers Myers Proterozoic P r o t e r o z o i c diabase d i a b a s e dike d i k e swarms swarms in in Wisconsin. 9:00 T. T. B. B. Hoist, Hoist, E. E . E. E . Mullenmeister J. C. & J. C. Green Keweenawan structural s t r u c t u r a l features f e a t u r e s at at tthe h e base of o f the t h e Duluth Complex Complex in i n the the near Dunka Pit Pit n e a r Babbitt, B a b b i t t , Minnesota. 9:20 9:40 D. M Miller * J . D. iller J. T. Wilband Magmatic pprocesses r o c e s s e s during d u r i n g the the Midcontinent Rift Midcontinent R i f t interval i n t e r v a l in i n northern northern Michigan: chemical and isotopic isotopic constraints. constraints. Coffee. 10:00 10:40 Petrogenesis P e t r o g e n e s i s ooff anorthositic a n o r t h o s i t i c rocks rocks of of the t h e Duluth Duluth Complex. Complex. D, G. W. Davis F R. Edwards Evolution of igneous complex complex o f an an Archean igneous from h high i g h precision p r e c i s i o n U-Pb U-Pb geochronology: geochronology : tthe h e Kakagi Lake Lake area, a r e a , N. N . W. Ontario, Ontario. 11:00 J. J . A. A. Percival Percival Metamorphism and and plutonism p l u t o n i s m in i n the the Quetico belt, b e l t , N. N . W. W. Ontario. Ontario. 11:20 R, H. Sutcliffe R. H. Sutcliffe well-preserved ell-preserved Mulcahy Lake Lake gabbro: gabbro : a w Archean layered l a y e r e d intrusion. intrusion. 11:40 D. D. A. A. Morrison Morrison W. W. C. C. Phinney, Phinney, F& E. Maczuga ft. The Mulcahy Lake gabbro and related related intrusions. intrusions. 12:00 Lunch. xv a �U SESSION S E S S I O N 4 4 Afternoon Thursday, May May 9, 9 , 1985 1985 Co-chairmen: Co-chairmen: i:30 1:50 . W.H. Cherry W. H . Mcllwaine M c I l w a i n e and and M.E. M E. C herry EE. . 00. . Owens E& J. Bornhorst T. J. J• D. *J. D. Vervoort Vervoort Geology Geology ooff Precambrian-hosted Precambrian-hosted precious precious metal metal prospects p r o s p e c t s in i n the t h e Fire F i r e Center Center and Holyoke mines area, a r e a , Marquette Marquette County, County, Michigan. Geology of o f the t h e Jap J a p Lake Lake area a r e a of o f the the eastern northeastern e a s t e r n Vermilion Vermilion district, district, n ortheastern Minnesota. 2:10 R. L L. R. . Bauer Multiphase fold f o l d geometry geometry along a l o n g the the ssoutheastern o u t h e a s t e r n margin of o f the t h e Vermilion Vermilion Granitic G r a n i t i c Complex, Complex, northeastern n o r t h e a s t e r n Minnesota. Minnesota. 2:30 T. L. T. L. Lawler & J . M. M. Seliner Sellner J. Ranier, Minnesota, Mineral potential R a n i e r , Minnesota, potential evaluation: e v a l u a t i o n : ooutcrop u t c r o p sampling, s a m p l i n g , geophysics geophysics and soil s o i 1 geochemistry. geochemistry. 2:50 D. D. Ela & The significance of strain The s i g n i f i c a n c e of s t r a i n ppatterns a t t e r n s in in deciphering d e c i p h e r i n g the t h e deformational d e f o r m a t i o n a l history h i s t o r y of of Archean rocks r o c k s in i n the t h e Vermilion Vermilion district, district, Minnesota. P. P. Ifudleston ifudleston 3:10 3:lO Coffee C offee 3:35 3 : 35 Announcement of o f best b e s t student s t u d e n t papers. papers. 3:40 3 :40 M. M. T. T. Corkery Stratigraphic S t r a t i g r a p h i c and structural s t r u c t u r a l evolution evolution off the o t h e Cross Lake supracrustal s u p r a c r u s t a l belt b e l t in in nnorthwestern o r t h w e s t e r n Superior S u p e r i o r Province, P r o v i n c e , Manitoba. Manitoba. 4:00 4:OO E. E. P. Moreton & P. R. Gerber R. Stratigraphy hydrothermal alteration S t r a t i g r a p h y and hydrothermal alteration Archean structural s t r u c t u r a l zone, zone, the the iin n an Archean Katisha K a t i s h a Lake Lake area, a r e a , Wabigoon Wabigoon Subprovince, Subprovince, N.W. Ontario. N.W. Ontario. 4:20 4 :20 B. B. J. J . Christie Christie & C. J. C. J. Hodgson Alteration A l t e r a t i o n and with w i t h a sheeted sheeted Red Lake Mine, Mine, 4:40 P. P. M. M. Berger, Berger, J . M. M. Dixon E& J. H. H. Helmstaedt Structural S t r u c t u r a l geology ooff nnorthern o r t h e r n Dome and southern s o u t h e r n McDonough Townships, Red Red Lake, Lake, Ontario. O ntario. xvi gold g o l d mineralization m i n e r a l i z a t i o n associated associated veinlet v e i n l e t zone zone at a t the t h e Campbell Balmertown, Balmertown, Ontario. Ontario. �U POSTER PRESENTATIONS Tuesday, May May 77 Wednesday, Wednesday, May 88 Thursday, T h u r s d a y , May May 99 4:00 - 110:00 0 : 0 0 p.m. p.m. 8:15 8 : 1 5 -- 5:00 p.m. 8:15 8 : 1 5 -- 5:00 5 : 0 0 p.m. I C. Anderson C. Correlation C o r r e l a t i o n of o f nnearly e a r l y continuous c o n t i n u o u s magnetic magnetic pprofiles r o f i l e s to t o lithology:case 1 i t h o l o g y : c a s e histories. histories. T. Anderson DD. . T. Remote sensing s e n s i n g application a p p l i c a t i o n in i n the t h e Cameron Cameron Lake Area, Ontario. A r e a , N.W. Ontario. T. T. Age of o f copper c o p p e r mineralization m i n e r a l i z a t i o n in i n the t h e flow flow tops t o p s of o f the t h e Portage P o r t a g e Lake Lake Lava Lava Series Series determined d e t e r m i n e d by paleomagnetic p a l e o m a g n e t i c methods. methods. D. Browning, D. S. S. Beske-Diehi, Beske-Diehl, J. J . Diehi, Diehl, 6 T. T. J. J. Bornhorst Bornhorst *G. T. Burgess *G. Chemical characterization Chemical c h a r a c t e r i z a t i o n and ppetrogenesis etrogenesi s Keweenawan d diabase off N Northern ooff Keweenawan i a b a s e dykes o orthern Michigan. KK.. D, D . Card Card Decade of o f North American Geology Geology (D-NAG) (D-NAG) geological g e o l o g i c a l and tectonic t e c t o n i c maps maps of o f the t h e southsoutheastern e a s t e r n Canadian Canadian Shield. Shield. Corfu FF. . C orfu & G,. M M,. Stott G Stott U-Pb U-Pb geochronology geochronology and tectonic t e c t o n i c history h i s t o r y of of the t h e Shebandowan belt, b e l t , northwestern n o r t h w e s t e r n Ontario. Ontario. FF.. GG,. G. G. R. R. Corfu, Corfu, P.o Beakhouse, P M. S Stott M. t o t t F15 H. S Sutcliffe H. utcliffe U-Pb U-Pb geochronology geochronology and tectonic t e c t o n i c history h i s t o r y of of the t h e Winnipeg River R i v e r granitoid g r a n i t o i d terrain, t e r r a i n , northnorthwestern w e s t e r n Ontario. Ontario. distri- . Crissman *S. EE, Geochemical Geochemical constraints c o n s t r a i n t s on on the t h e REE REE d i s t r i bution b u t i o n in i n the t h e Neguanee Iron I r o n Formation Formation of o f the the Empire Mine, Mine, Palmer, P a l m e r , Michigan. Michigan. R. M. M. Easton R. Easton Anomalous radiometric r a d i o m e t r i c ages a g e s from from the t h e Superior Superior Province, P r o v i n c e , Ontario: O n t a r i o : sense? s e n s e ? or o r non-sense? non-sense? T. Fitz T. Fitz & J. J . C. C . Green Green Large ignimbrites i g n i m b r i t e s in i n the t h e Keweenawan North Shore S h o r e Volcanic V o l c a n i c Group Group in i n Cook Cook County, County, Minnesota. Minnesota F4 J. W. Gell Geochemistry of M i l l Group: Group: the the o f the t h e Powder Powder Mill earliest e a r l i e s t lavas l a v a s of o f the t h e Midcontinent M i d c o n t i n e n t Rift R i f t in in Michigan. H. P. P . Gilbert Gilbert Stratigraphic S t r a t i g r a p h i c evolution e v o l u t i o n of o f the t h e Island I s l a n d Lake Lake ggreenstone r e e n s t o n e belt, b e l t , Manitoba. Manitoba. JJ.. K. K . Greenberg GreenbergF4S B, A. B. A . Brown Brown The central c e n t r a l Wisconsin Wisconsin Archean Archean block: b l o c k : new new eevidence v i d e n c e suggests s u g g e s t s a partially p a r t i a l l y reworked reworked granite/ granite/ W. Johns GG. . W. Facies F a c i e s interpretation i n t e r p r e t a t i o n of o f the t h e Berry Berry River R i v e r formation, formation, Lake of o f the t h e Woods. Woods. greens errane . g r e e n s ttone o n e tterrane, xvii �U ** W. J. W. J . Johnson Johnson T. T. The p petrology The e t r o l o g y and sedimentation s e d i m e n t a t i o n of o f the the Lower Proterozoic P r o t e r o z o i c Barron Barron Quartzite, Quartzite , nnorthwestern o r t h w e s t e r n Wisconsin. Wisconsin. Lawler F S LL.. Lawler Ranier, Minnesota, mineral R a n i e r , Minnesota, m i n e r a l potential potential sampling, g geophysics eevaluation: v a l u a t i o n : ooutcrop u t c r o p sampling, eophysics and soil s o i l geochemistry. geochemistry. J. J . NI. M. SSeliner ellner * E. The ppetrology e t r o l o g y of o f the t h e Longnose Peridotite Peridotite i t s relationship r e l a t i o n s h i p to t o the t h e Duluth Duluth ddeposit e p o s i t and its Complex. K. Lin$cheid R. Lundy * J. J . R. Minor folds f o l d s in i n the t h e Soudan Soudan Iron I r o n Formation, Formation, northeastern n o r t h e a s t e r n Minnesota. Minnesota. * D. D. MacTavish MacTavishF16 R. JJ. R. . Dutka The Atikokan cobalt—base c o b a l t - b a s e metals-platinum metals-platinum group elements e l e m e n t s project. project. A. A. * M. P. P. McDermott Chemical ccharacterization Chemical h a r a c t e r i z a t i o n ooff the t h e Unnamed Formation, Formation, aa ccentral e n t r a l vvolcanic o l c a n i c complex ooff Keweenawan age. age. * 0. D. R. R. D. D. H. H. L. B. L . B. K. K. H. H. Melling, M elling, Watkinson, Watkinson, Choriton, C horlton, Poulsen Poulsen The influence i n f l u e n c e of of shear s h e a r zone zone geometry geometry and and mineralization vvein e i n pparagenesis a r a g e n e s i s on gold-pyrite gold-pyrite m ineralization at a t Cameron Lake, Lake, northwestern n o r t h w e s t e r n Ontario. Ontario. 6 F1 E. E. Mulienmeister, Mullenmeister, T. B. Hoist, T. B. Hoist, 6 J. J . C. C . Green Green Structural S t r u c t u r a l analysis a n a l y s i s ooff the t h e nnortheastern ortheastern basal Mesabi Range Range and adjacent adjacent b a s a l Duluth Complex. B. Paces 6 B. T. T. J. Bornhorst Bornhorst Geology and geochemistry of o f lava l a v a flows flows within within the t h e Copper Harbor Conglomerate, Conglomerate, Keweenaw Peninsula, P e n i n s u l a , Michigan. Michigan. H. H. C. C. Palmer PalmerF16 The paleomagnetism of M i l l Group: Group: o f the t h e Powder Powder Mill with iits t s rrelevance e l e v a n c e tto o ccorrelation orrelation w i t h oother ther Keweenawan sequences and to t o tectonic t e c t o n i c developdevelopment of the t h e South South Range. Range. F1 J. J. F1 H. C. C. Halls H. ** E. EE.. Peterson Peterson The tectonic t e c t o n i c significance s i g n i f i c a n c e of o f the t h e Porphyritic Porphyritic Granite, Red G r a n i t e , Dickinson County, County, Michigan. Michigan. A. Ross * B. A. Ross Petrogenesis P e t r o g e n e s i s of o f the t h e Bardon Bardon Peak Peak peridotite, peridotite, Duluth Complex. * Platinum element m minerals P l a t i n u m group element i n e r a l s in i n the t h e Duluth Complex. T. T. Sabelin Sabelin W. A. W. A . Schieiss, Schleiss, T. J . Bornhorst, Bornhorst, T. J. A. P. Ruotsala A. P. Ruotsala P. M. M. Smith Smith P. 6 F1 vein mineralization wall A sstudy t u d y ooff v ein m i n e r a l i z a t i o n and w a l l rock alteration Mine, Keweenaw a l t e r a t i o n at a t the t h e Delaware Delaware Mine, County, County, Michigan. Michigan. The geological g e o l o g i c a l setting s e t t i n g at a t the t h e Duport Duport Mine, Mine, Cameron Island, I s l a n d , Shoal Shoal Lake. Lake. xviii xviii �U M. M. Swan, Swan, BB.. Keith, Keith, M. G. Parr M. G. Parr M. S. S. KK. . Thomson S DD. . Gliddon FT J. J. L . Welsh L. * S. S. FF. . Wright * 6 FT Magma series s e r i e s and and their t h e i r relationship r e l a t i o n s h i p to to greenstone g r e e n s t o n e gold g o l d metallogeny m e t a l l o g e n y in i n the the Lake Superior Lake S u p e r i o r Region. Region. The 1-lemlo Hemlo b abaritic r i t i c hhorizon; o r i z o n ; aa ppossibly ossibly ssyngenetic y n g e n e t i c Archean barite b a r i t e occurrence. occurrence. Preliminary geology P r e l i m i n a r y iinvestigations n v e s t i g a t i o n s iinto n t o tthe he g eology of o f the t h e Giants G i a n t s Range Range Complex, Complex, VirginiaVirginiaBiwabik area, Biwabik a r e a , N. N . E. E . Minnesota. Minnesota. Strain S t r a i n patterns p a t t e r n s in i n the t h e Kiruna K i r u n a district, district, northern n o r t h e r n Sweden; Sweden ; implications i m p l i c a t i o n s for for Proterozoic P r o t e r o z o i c deformation. deformation. xix �ABSTRACTS ABSTRACTS xx �U CORRELATION CORRELATION OF OF NEARLY NEARLY CONTINUOUS CONTINUOUS MAGNETIC MAGNETIC PROFILES PROF1LES - TO LITHOLOGY LITHOLOGY --CASE CASE HISTORIES HISTORIES TO I DR. CHRIS ANDERSON, DEPT. OF EARTH SCIENCES UNIVERSITY OF MANITOBA, WINNIPEG AA RESEARCH RESEARCH PROJECT P R O J E C T RELATING R E L A T I N G LITHOLOGY L I T H O L O G Y TO TOMAGNETIC MAGNET1 C MEASUREMENTS ALONGP PROFILES MEASUREMENTS ALONG R O F I L E S WWITH I T H AA STATION S T A T I O N SPACING S P A C I N G OF OF THE THE ORDER ORDER OF OF ONE ONE METRE METRE HAS HAS BEEN B E E NCONDUCTED CONDUCTED BY B Y THE T H EAUTHOR AUTHOROVER OVER PROJECTS HAVE H A V E BEEN B E E N COMPLETED COMPLETED AT A TA ANUMBER NUMBER T H E LAST L A S TDECADE. D E C A D E , PROJECTS THE OF AND P PATENTS OBTAINED OF LOCATIONS L O C A T I O N S ACROSS ACROSS CANADA CANADA AND ATENTS O B T A I N E D ON ON INSTRUINSTRUM E N T A T I O N FOR FOR R A P I D DATA D A T A ACQUISITION. ACQUISITION. MENTATION RAPID IN THIS (1) THE IN THIS PRESENTATION PRESENTATION RESULTS RESULTS WILL WILL BE BESHOWN SHOWN FROM FROM (1) THE FALCON FALCONLAKE LAKESTOCK, STOCK) BETWEEN BETWEEN THE THE INTERMEDIATE INTERMEDIATE INTRUSIVE INTRUSIVE AND AND THE HOSTRROCKS, (2) THE THE METAVOLCANIC METAVOLCANIC HOST O C K S / (2) THE EUCLID EUCLID LAKE LAKECHROMITE CHROMITE DEPOSIT D E P O S I T WITH W I T H THE T H E PROFILE P R O F I L EDATA D A T ACOVERING C O V E R I N G METAVOLCANICS1 M E T A V O L C A N I C S , MAFIC, MAFIC, AND ULTRAMAFIC INTRUSIONS# AND AND (3) (3)THE THEBIRD BIRD RIVER RIVER SILL SILL WHICH WHICH AND ULTRAMAFIC INTRUSIONS, THESE IS AALAYERED LAYERED BASIC BASIC TO T OULTRAMAFIC ULTRAMAFIC INTRUSIVE. INTRUSIVE, THESE SITES SITES IS ARE ALL ALLLOCATED LOCATEDININSOUTH—EASTERN SOUTH-EASTERN MANITOBA, MAN ITOBA, ARE THESE VARIATIONS OF THESE DATA DATA SHOW SHOW VARIATIONS OF BOTH BOTH POSITIVE POSITIVE AND ANDNEGATIVE NEGATIVE VALUES UP UP TO T OSEVERAL SEVERALTHOUSAND THOUSANDGAMMAS GAMMAS (NANO (NANO TESLAS) TESLAS)WITH WITH SOME SOME VALUES ANOMALY WIDTHS ONLY AA FEW FEWMETRES, METRES. THESE THESE VARIATIONS VARIATIONS CAN C A N BE BE ANOMALY WIDTHS OF ONLY RELATED R E L A T E D DIRECTLY D I R E C T L Y TO T O THE T H EOBSERVED OBSERVED LITHOLOGY. LITHOLOGY1 1 �U REMOTE SENSING --- APPLICATION APPLICATION IN I NTHE THECAMERON CAMERON LAKE LAKE AREA, AREA, N.WONTARIO N W ONTARIO -- -REMOTE_SENSING DR. D.T. ANDERSON, DEPT. OF EARTH SCIENCES UNIVERSITY OF MANITOBA, WINNIPEG THE LAKE AREA THE CAMERON CAMERON LAKE AREA IS IS OF OFCONSIDERABLE CONSIDERABLE INTEREST INTERESTBECAUSE BECAUSEOF OF A VARIETY VARIETY THE T H E ACTIVE A C T I V E REGIONAL R E G I O N A LGOLD GOLD EXPLORATION E X P L O R A T I O N BEING B E I N G CARRIED C A R R I E D OUT. OUT, A OF HAS NORTHERN OF TECHNIQUES TECHNIQUES HAS BEEN BEEN APPLIED APPLIED ININPARTS PARTSOFOF NORTHERNMANITOBA MANITOBA WHEREBY AND GEOPHYSICAL WHEREBY SSPECTRAL P E C T R A L AND G E O P H Y S I C A L REMOTE REMOTE SENSING S E N S I N G DATA D A T A HAVE H A V EBEEN BEEN INTEGRATED WITH GEOLOGYT OTOAASSIST INTEGRATED W I T H MAPPED MAPPED GEOLOGY S S I S T IIN N THE T H E INTERPRETATION I N T E R P R E T A T I O N OF OF THE T H E STRUCTURE STRUCTURE AND AND LITHOLOGY L I T H O L O G Y OF OF AN AN AREA. AREA, A A SIMILAR SIMILAR PROCEDURE PROCEDURE HAS HAS BEEN BEEN APPLIED APPLIED TO TOTHE THECAMERON CAMERON LAKE LAKE To TOTHIS T H I SEND, E N DTHE / T H AVAILABLE E A V A I L A B LAERIAL E A E R I APHOTOGRAPHS L PHOTOGRAPHSHAVE H A V EBEEN BEEN THE AVAILABLE AVAILABLE EXAMINED E X A M I N E D AND AND AAPHOTOLINEAMENT P H O T O L I N E A M E N TTREND TRENDMAP MAPPRODUCED. PRODUCED, THE AREA. AREA. GEOPHYSICAL G E O P H Y S I C A L SURVEY SURVEY DATA D A T A HAVE H A V E BEEN B E E N EXAMINED E X A M I N E D AND ANDAN ANANALOGOUS ANALOGOUS LINEAMENT LINEAMENT TREND TRENDMAP MAPPRODUCED. PRODUCED, MULTISPECTRAL MULTI SPECTRAL AND AND MULTITEMPORAL MULTITEMPORAL LANDSAT DATA LANDSAT DATA HAVE HAVE BEEN BEEN EXAMINED EXAMINED USING USING BOTH BOTHTHE THEPHOTOGRAPHIC PHOTOGRAPHIC IMAGERY AND TTHE YET IMAGERY AND H E DIGITAL D I G I T A LINFORMATION, I N F O R M A T I O N ,AND AND Y EANOTHER T ANOTHERANALOGOUS ANALOGOUS TREND-LINE MAP MAP PRODUCED. PRODUCED, THESE THESE THREE THREE LINEAMENT LINEAMENT MAPS MAPS HAVE HAVE BEEN BEEN TREND—LINE SUPERIMPOSED ON ONE ONE ANOTHER/ ANOTHER, AND S U P E R I M P O S E D ON AND UPON UPON THE T H E AVAILABLE A V A I L A B L EGEOLOGICAL GEOLOGICAL IT CAN MAPS OF OF THE T H E AREA, AREA, IT CAN BE B ESEEN SEEN THAT T H A T AAHIGH H I G HDEGREE DEGREE OF OF USEFUL USEFUL MAPS TH Is STUDY STUDY CONSISTED CONS IS T E D OF OF CORRELATION C O R R E L A T I O N EXISTS E X 1 S T S BETWEEN BETWEEN THESE T H E S E DATA. D A T A , THIS "MANUAL" "MANUAL" CORRELATION CORRELATION OF OF THE THE DATA, DATA, BUT BUTAUTOMATIC AUTOMATIC CORRELATION CORRELATION SHOULD AALSO L S O BBE E POSSIBLE. P O S S I B L E , TIME TIME AND AND EQUIPMENT E Q U I P M E N T CONSTRAINTS C O N S T R A I N T S PREPRESHOULD CLUDED CLUDED DDIGITAL I G I T A L CORRELATION C O R R E L A T I O N AAT T TTHIS H I S TIME. TIME. THE VALUE VALUE OF OF SUCH SUCH INTEGRATION INTEGRATION LIES IN THE THERAPID RAPIDOVERVIEW OVERVIEW THE LIES IN THAT IS IS POSSIBLE. POSSIBLE. THAT THE THE CLOSE CLOSE CORRELATION CORRELATION SUGGESTS SUGGESTS THAT THAT SPECTRAL SPECTRAL AND AND GEOPHYSICAL G E O P H Y S I C A L REMOTE REMOTE SSENSING E N S I N G INTERPRETATION I N T E R P R E T A T I O N MAY MAY GIVE G I V E VALUABLE VALUABLE INSIGHTS I N S I G H T S INTO I N T OEXPLORATION E X P L O R A T I O NMETHODOLOGY, METHODOLOGY, EVEN E V E N IN I NTHOSE THOSEAREAS AREASWHERE WHERE IT DETAILED MAPPING IS IS NOT DETA ILED GEOLOGICAL GEOLOG ICAL MAPPING NOT AVAILABLE. A V A ILABLE , FURTHERMORE, FURTHERMORE, MAY MAY DIRECT D I R E C T THE T H E GEOLOGICAL G E O L O G I C A L MAPPING M A P P I N G TO T O CRITICAL C R I T I C A LAREAS AREASWHERE WHERE THE THE ELUCIDATION E L U C I D A T I O N OF OF THE T H E STRUCTURAL STRUCTURAL STYLE S T Y L E MIGHT M I G H T MOST MOST READILY R E A D I L Y BE BE DERIVED, DERIVED. 2 �Multiphase Fold Geometry Along the the Southeastern Southeastern Margin of the the Vermilion Vermilion Granitic Granitic Complex, Complex, Northeastern Northeastern Minnesota University of Missouri, Columbia, Robert L. L. Bauer, Department of Geology, University Columbia, MO 65211. 6521 1. The Archean schist and migmatites the migmatites along the southern margin of the Vermilion Granitic Complex (VGC), (VGC), south south of of the the Lac Lac La La Croix Croix Granite, Granite, have have undergone three three periods of regional regional folding folding which are are differentially differentially developed developed and decipherable in in various portions portions of of the the terrane. terrane. A pervasive pervasive S1 S foliation foliation 1 in the schist is generally parallel parallel to bedding (S0) ( S ) except in the hinges of 0 rare minor Fl Fl folds. folds. Local graded bedding indicates indicates a downward—eastward downward-eastward structural facing in in the the S2 S foliation. foliation. We have interpreted interpreted this this facing facing and 2 reversals in facing in the Vermilion district to be a result of regional Ft Fl folding folding (Bauer and Hudleston, Hudleston, 1982). 1982). produced the the most most prominent prominent fold fold structures structures (F2), (F2), including including aa major major D produced e s t e r t Y plunging antiform along the the boundary of of the the Vermilion Cranitic Granitic westerly Complex and the the Vermilion Vermilion district district to to the the south. south. This east—west east-west trending trending boundary, marked strike-slip and dip—slip dip-slip faulting on the Vermilion and marked by strike—slip Haley faults, faults, follows follows the the axial surface surface trace trace of of the the antiform. antiform. Large-scale Large—scale parasitic folds folds on on this this structure structure are invariable invariable of of SS symmetry symmetry in in the the southern southern VGC and and occur occur on on the the northern northern limb limb of of the the antiform. antiform. These folds folds are are F2 folds of Z symmetry that occur in the Vermilion district on correlated with F 2 the southern limb limb of the the antiform. antiform. The orientation of F2 lineations are L lineations F fold fold hinges and coaxial L2 are 2 2 relatively constant in the VGC along the boundary with the Vermilion district, district, but in in the the Burntside Burntside Lake area, area, large—scale large-scale F2 F parasitic parasitic folds folds are are strongly strongly 2 noncylindrical, and and FF and noncylindrical, and L2 L vary vary from from SW SW to to NE NE plunging plunging within within the the local local S 2 2 axial surface. surface. This local noncylindricity is attributed to a combination of: (1) pre-F2 pre—F2 reorientation of S S0 and S1 S by intrusion of the Burntside tonalite, tonalite, 0 F2 synformal folding induced in part by gravitational and (2) to late—stage late-stage F 2 subsidence around a dense dense amphibolite amphibolite body. body. In the Norwegian Bay Haley and and Vermilion Vermilion faults, faults, Bay block, block, bounded bounded by by the the Haley F2 folds have been refolded by a doubly plunging, east—west—trending regional F east-west-trending 2 F3 fold cored by the F the Wakemup Bay Bay tonalite. tonalite. Northwesterly Northwesterly plunging, plunging, F3, F3 3' conical folds folds just just north of the the Vermilion fault fault also also fold fold large—scale large-scale F2 F 2 antiforms and synforms but are not associated associated with emplacement of granitic antiforms plutons such such as as the the Wakemup Wakemup Bay Bay stock. stock. Relationships between folding and the various granitic rocks rocks of of the the region indicate that the Burntside tonalite was emplaced prior to region to the the initiation of D D2; the Lac La Croix Granite was syn—D2; and the Wakemup Bay syn-D 2 2 but tonalite was emplaced post—D2, post-D but pre—D3. pre-D ' 2' 3' ' REFERENCES Bauer, R.L. R.L. and and Hudleston, P.J., P.J., 1982, 1982, F1 F recumbant recumbant folding folding in in the the western western Bauer, 1 Vermilion greenstone-granite terrane, terrane, NE NE Minnesota: Minnesota: Ann. Inst. Inst. Lake Lake Vermilion greeristone—granite Superior Geol., 28th, 28th, Proc., Proc., p. p. 4. 4. �U STRUCTURAL STRUCTURAL GEOLOGY GEOLOGY OF OF NORTHERN NORTHERN DOME DOME AND AND SOUTHERN MCDONOUGH RED LLAKE, SOUTHERN MCDONOUGH T OTOJNSHIPS, W N S H I P S , RED A K E , ONTARIO ONTARIO h Paula P a u l a M. M. Berger, B e r g e r , J. J . M. M. Dixon, D i x o n , and a n d H. H . Helmstaedt, H c l m s t a e d t , Department D e p a r t m e n t of o f Geological Geological S c i e n c e s , Queen's Q u e e n ' s University, U n i v e r s i t y , Kingston, K i n g s t o n , Ontario Ontario Sciences, and southern southern McDonough within Northern Northern Dome D o m e and McDonough TTownships, o w n s h i p s , within the Lake "greenstone" "greenstone"belt belt of the Red Red Lake of northwestern northwestern Ontario, O n t a r i o ,were were mapped scale with ongeological geological structures. structures. mapped on on a a 1:1000 1 : 1 0 0 0 scale with emphasis emphasis on Mafic Mafic to to ultramafic ultramafic metavolcanic rnetavolcanic rocks, r o c k s , felsic felsicmetavolcanic metavolcanic to to metavolcaniclastic metavolcaniclastic rocks, rocks, and and clastic clastic totochemical chemical metasedimentary greenschist grade, metasedimentary rrocks, o c k s , metamorphosed metamorphosed totogreenschist g r a d e , occur occur within supracrustal rrocks within the the area. area. These These supracrustal o c k s are are crosscut crosscut by by felsic felsic to tointermediate intermediate intrusives, intrusives, the the largest largestbeing being the the Planar, occur in in nearly nearly all P l a n a r , penetrative penetrative fabric fabric elements e l e m e n t s occur all exposures. cleavagei sisparallel parallel or exposures. This T h i s cleavage or at at a a low low angle angle to to contacts contacts oof f the the granitoid granitoid batholiths batholiths surrounding surrounding the the belt. belt. McKenzie Island Stock. McKenzie Island Stock. In and In the the study study area a r e a the the fabric fabricdips dipssteeply steeply andchanges changes gradually gradually and continuously in in strike and continuously strikefrom fromsoutheast southeastnear nearCochenour Cochenour to to northeast cleavageresulted resulted from northeast near near Slate S l a t e Bay. Bay. The T h e cleavage from bulk, bulk, inhomogeneous shorteningininaahorizontal horizontal direction, inhomogeneous shortening d i r e c t i o naccompanied , accompanied by by near—vertical near-vertical extension. extension. Competency contrastsbetween betweenrock rocktypes typesresulted resulted in in the Competency contrasts the development different structures. cleavageiis development o fofdifferent structures. The T h e cleavage s axial axial planar metasedimentary rnetasedimentary layers. layers. In In planar to to folds foldswithin withinthe the contrast, metavolcanic contrast, the thecleavage c l e a v a g e within withinthe the metavolcanicand andmassive massive metasedimentary unitsiis metasedimentary units s crosscut crosscut by by conjugate conjugate sets s e t s of o fshear shear fractures. shear fracture fracture planes fractures. The T h e shear planes maintain maintain aa constant constant orientation orientation of o f30° 3 0  from from the t h e penetrative, penetrative, flattening flattening fabric fabric and exhibit right—lateral and exhibit right-lateral slip s l i p along along the t h e clockwise c l o c k w i s e striking striking fracture left—lateral slip fracture planes planes and and left-lateral slipalong alongthe thecounterclockwise counterclockwise striking and fractures fractures striking fracture fractureplanes. planes. The T h e sshear h e a r zzones o n e s and fromed in a environment fromed in a ductile ductiletot obrittle—ductile brittle-ductile environmentsubsequent subsequent to to the the formation formation of o fthe t h ecleavage cleavage but butduring duringthe t h esame same deformational deformational event. Narrows,the theleft-lateral, left—lateral, northeast-striking northeast-striking event. Near Near PPost o s t Narrows, fracture several meters—wide fractureset setis iexpressed s expressedasas several meters-wideshear shearzones zones in in the the metavolcanic metavolcanic rocks. rocks. Pressure shadows garnets near s h a d o w s around around contact—metamorphic contact-metamorphic garnets near the Island Stock, the McKenzie McKenzie Island S t o c k , and and shear s h e a r zones z o n e s through through the the stock stock indicate that ititintruded thethedeformational indicate that intruded prior priortotoororearly earlyinin deformational history. history. Bedding iis s subparallel subparallel to tothe thecleavage c l e a v a g eexcept excepton onand and Bedding southeast Island where bedding sstrikes southeast of o f McKenzie McKenzie Island where bedding t r i k e s northeast northeast and and the the cleavage cleavage southeast. southeast. This T h i s geometry, g e o m e t r y , along along with with aa younging reversal a change c h a n g e in t r i k e ,suggests suggests the the younging reversal without without a in sstrike, presence deformational folds. folds. pre-"main-stage" deformational presence oof f early, e a r l y ,pre—"main—stage" All earlier earlierstructures structuresare a r ecrosscut crosscut by by a a second second brittleAll brittleductile ductile to to brittle brittleconjugate conjugate fracture fracture set. set. The T h e bisectrix of bisectrix of the acute acute angle angle between t r i k e s north north to to the betweenthe theconjugate conjugatepair pairsstrikes north—northeast. north-northeast. These These fractures occur throughout entire fractures occur throughout the the entire belt in strike. belt without without a a significant significantchange change in strike. 4 �U The The Deformational Deformational History History of of Archean Archean Greenstones Greenstones in in the Central Central Lake Lake of of the the Woods Woods Area Area Northwestern Northwestern Ontario Ontario Bruce Bruce A. A. Brown Brown Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey 1815 1815 University University Avnue Avnue Madison, Madison, Wis, Wis. 53705 53705 Four Four distinct distinct deformational deformational events events have have been been identified identified in in the the Archean Archean greenstones of the the Central Central Lake Lake of of the the Woods area area of of northwestern northwestern Ontario. Ontario. These These events represent represent distinct distinct stages stages in in the the tectonic tectonic evolution evolution of of the the region region during during Archean Archean time. time. The The first first stage stage (D1) (Dl) produced produced upright, upright, isoclinal isoclinal folds folds (F1) (Fl) which which have shallowly shallowly plunging plunging to to nearly nearly horizontal horizontal axes, axes, and and aa penetrative penetrative axial axial planar foliation foliation (S1). (S,). F1 Fl folds folds are are expressed expressed as as large large scale scale planar anticlines anticlines and and synclines synclines traceable traceable across across much much of of the the adjacent adjacentregion. region. D1 Dl was was accompanied accompanied by by regional regional greenschist greenschist facies facies metamorphism metamorphism (M1). (MI), The (D,) produced produced steeply steeply plunging plunging folds folds and and aa complex complex The second second stage, stage, (D2) D, deformation deformation was was aa complex complex event. event. The D2 pattern of of ductile ductile shear shear zones. zones. The Style, Style, orientation, orientation, and and intensity intensity of of development development of of D2 D2 structures structures vary vary widely widely throughout throughout the the area. area. At aa given given locality, locality, it it is is common common to to find find more more than than one generation generation of of D2 D2 structures structures developed, developed, such such as as F2 F, folds folds suggesting that that stress stress overprinting aa D2 D, cataclastic cataclastic zone zone and and vice vice versa, versa, suggesting orientation and conditions conditions of of deformation deformation varied varied through through time time during during the the D event. event. Whereas Whereas D1 Dl structures structures were were uniformly uniformly developed developed across across the the D2 region, region, D2 D, structures structures are are most intensely intensely developed developed in in the the eastern eastern part part of of the the area, area, adjacent adjacent to to large large and and small small granitic granitic plutons. plutons. The The D3 D3 deformation deformation produced produced kink kink bands bands which which are are distributed distributed throughout throughout the the area, area, and and clearly clearly overprint overprint D1 Dl and and D2 D, structures structures and and fabrics. D4 D4 produced produced faults faults marked marked by by cataclastic cataclastic zones zones which which cross cross both both fabrics. the the greenstones greenstones and and the the adjacent adjacent granitoid granitoid rocks. rocks. D1 Dl and and M1 MI apparently apparently represent represent early early regional regional tectonism tectonism and and cannot be equated equated with with granitoid granitoid emplacement. emplacement. D2 D, and and localized localized contact contact cannot metamorphism metamorphism are are interpreted interpreted to to be be the the result result of of diapiric diapiric emplacement emplacement of of the the granitoid batholiths batholiths flanking flanking the the area area and and smaller smaller plutons plutons within within the the area. area. granitoid The complex complex geometry geometry and and sequence sequence of of D2 D, structures structures is is attributed attributed to to The continually continually changing changing deformational deformational conditions conditions during during the the rise rise and and expansion expansion of of these these intrusive intrusive bodies. bodies. The The origin origin of of D3 D, is is obscure, obscure, but but these these structures structures the result result of of regional regional stress stress imposed imposed during during the the late late stages stages of, of, or or may be the following pluton pluton emplacement. emplacement. D4 is is attributed attributed to to adjustment adjustment faulting faulting following which restored restored isostatic isostatic equilibrium equilibrium following following the the widespread widespread granite granite which emplacement during during the the D2 D, event. event. emplacement 5 �U I Copper Mineralization Topso foft ntue Lae Aje t h s F Flow l o ~To.1~ e P Portaje o r t a ~ eLas: A j e oof f Co->,?er M i n e r a l i z a t i o n in i n ti-ic Lava Series ~ y Paleomajnetic P a l e o i - n a j n e t i c Metuods MecnoJs Lava S e r i e s Determined D e t e r m i n e d oy "I Tim T i m D. D. Browninj, B r o w n i n g , Sue S u e BesKe—Diehi, B a s & ? - D i e h l , Jim J i m Diehl, D i e n l , and a n d Theodore T h e o d o r a J. J. Bornnorst Geol. Geol. B o r n n o r s t (Dept. ( D e p t . of of G e o l . and and G e o l . Enjrj., E n j r j . , Micnijan M i c n i j a n Tecunolojical Te~~nolojicdl University, M I 49931) 49931) U n i v e r s i t y , Houjhton, H o u g d t o n , MI Native N a t i v e ccooper o p p e r nmineralization i n e r a l i z a t i o n in i n tue t o e Portaje P o r t a g e Lake L a k e Lava L a v a Series S e r i e s occurs occurs wituin Ru—Sr w i t n i n amy-jdaloidal a i n y j i J a l o i d a l aand n d ~orecciated r e c c i a t e dttops o p s of o f lava l a v a flows. flows. RJ-Sr iatinj Jatinj mineralization oe aaround ± 1155 i-la r o u n J 11,051 , 0 5 1 +, Ma iindicates n d i c a t e s tthe h e aaje j e oof f m i n e r a l i z a t i o n tto o ae (Paces, .S.I. aaostract, o s t r a c t , 11984) 9 8 4 ) aas s compared c o m p a r e d to t o the t n e 1,110 1 , 1 1 0 Ma Ma aje a j e of of ( P a c e s , LL.S.I. The ineriors contain concaL-i majnatitc ,,-~djnecicz eextrusion. xtrusion. The relatively r e l a t i v a l ~uunaltered n a l t e r e d fflow l o w interiors whereas i s common common in i n the t n e mineralized m i n e r a l i z e d flow f l o w tops t o 2 s (Scofield, (Scofizld, w n e r e a s hematite h e m a t i t e is Pu.D. thesis, P'1.D. t h e s i s , M.T.U. M.T.U. 1976). 1 9 7 6 ) . The T h e remanent r e m a n e n t direction d i r e c t i o n associated a s s o c i a c e d witn irfici-i majnetite i s acquired a c q u i r e d during d u r i n g the t h e cooling c o o l i n g and a n d solidification s o l i d i f i c a t i o n of o f the tne tthe he m a g n e t i t e is magnetic e pparallel a r a l l e l tto o tthe h e eearth's arth's m a g n e t i c ffield i e l d ppresent r e s e n t at at llavas a v a s aand n d sshould n o u l d soe Dunn; tnat t n a t time. tine. D u r i n g mineralization m i n e r a l i z a t i o n of o f the t h e flow f l o w tops, t o p s , tne t n e orijinal orijinal Therefore, majuetite J i a g n e t i t e was altered a l t e r e d to t o secondary s e c o n d a r y hematite. hel-natite. T h e r e f o r e , the t n e primary .pri/nary remanence ~e r e m a n e n c e aacjuired c q u i r e d during d u r i n g the t h e solidification s o l i d i f i c a t i o n of o f tue t n e lavas l a v a s would w o o l J ue destroyed d e s t r o y e d and a n d replaced r e p l a c e d ooy y another a n o t h e r representing r e p r e s e n t i n g the t h e mineralization mineralization The ppurpose s t to o ddetermine e t e r i a i n e t the h e r relative e l a t i v z t itLe . a e of of eevent. vent. The u r p o s e oof f tthis n i s sstudy t u d y iis tue copper mineralization oy comparing the remanent directionu of t n a copper m i n e r a l i z a t i o n s y comparing t n e r e n a n e n t d i r a c t i o n s of mineralized m i n e r a l i z e d flow f l o w tops t o p s witn w i t n the t h e unaltered u n a l t e r e d flow f l o w interiors. interiors. Preliminary P r e l i m i n a r y tthermal h e r m a l ddemagnetization e m a g n e t i z a t i o n results r e s u l t s reveal r e v e a l two distinct Jistinct remanent r e m a n e n t directions, d i r e c t i o n s , one o n e associated a s s o c i a t e d with w i t n the c n e initial i n i t i a l cooling c o o l i n j of of rue m e represent llava a v a (magnetite ( m a g n e t i t ecomponent) c o m p o n e n t ),, and a n d another a n o t h e which r w h imay c h may r s 2 r tue e s ecopper n c t i i a co^,-)er mineralization m i n e r a l i z a tevent i o n e(hematite v e n t ( hcomponent). e m a t i t e c o m p o n e n t ) . Both Boch snow similar similar However, the declinations d e c l i n a t i o n s of o f around a r o u n d 295 295 degrees. degrees. However, t h e hematite n e m a t i t e component coia.ponant t o 10 10 cconsistently o n s i s t e n t l y eexnibits x n i o i t s ssteeper t e e p e r iinclinations n c l i n a t i o n s oon n the t n e oorder r d e r of o r 5 to degrees ÷33 ddegrees +40 ddegrees d e j r e e s (approximately ( a p L - i r o x i i n a t e l y +33 e g r e e s aand n d +40 e j r e e s inclination inclination directions Tuese respectively) r e s a e c t i v e l y ).. T nese d i r e c t i o n s aare r e consistent c o n s i s t e n t with v i t n the c n e directions predicted . p r e d i c t e d using u s i n g the t n e North N o r t h American A m e r i c a n polar p o l a r wander w a n d e r patn p a t i 1 for f o r Keweenawan Kaweznairfan t h e nematite n e m a t i t e cannot c a n n o t easily e a s i l y ue Je aage j e roccs. r o c i < s . The steeper s t e e p e r inclinations i n c l i n a t i o n s in i n the explained oy ttectonic prior e x p l a i n e d oy e c t o n i c ttilting i l t i n j towards t o w a r d s the t h e ppresent r e s e n t tilt t i l t direction 2 rior There mineralization. tto o m ineralization. T h e r e are a r e two t w o ppossiule o s s i o l e alternative a l t e r n a t i v e explanations e x p l a n a t i o n s of of (1) The The rrelatively tuese tiiese results. results. (1) e l a t i v e l y ssteep t e e p inclinations i n c l i n a t i o n s seen s e e n within w i t n i n the tiis Jmineralized i i n e r a l i z e d flow f l o w top t o p may may oc the t h e result r e s u l tof02polar p o l a rwander w a n d e wriich r w n i c n sug s u gjests jasts uetween time o e t w a e n tue tne some ppaleomagneticaily a 1 e o m a : j n e t i c a l l . y ssignificant i g n i f i c a n t pperiod e r i o d of o f time extrusion e x t r u s i o n of o f the t n e lavas l a v a s and a n d mineralization. mineralization. ( 2 ) The hematite hematite (2) crystallization, mineraliziation, may hhave i n e r a l i z i a t i o n , may a v e occurred o c c u r r e d over over a c r y s t a l l i z a t i o n , hhence e n c e tthe he m Ion; t i m e starting s t a r t i n g soon s o o n after a f t e r the t n e extrusion e x t r u s i o n of o f tue t n e lavas. lavas. l o n g pperiod e r i o d of o f time The hematite would tthen e aan n aaverage v e r a g e oof f tthe n e sshort—term hort-cera h e m a t i t e reinanence r e m a n e n c e would h e n soe changes magnetic c h a n g e s in i n the t h e eartu's eartn's m a g n e t i c ffield i e l d (secular ( s e c x l a r variation) v a r i a t i o n ) over o v e r tnat tnat On the time. t h e other o t n e r hand, n a n d , the t h e magnetite m a g n e t i t e remanent r m a n e n t direction direction -period > e r i o d of o f time. time on o n tue tile secular s e c u l a r variation v a r i a t i o ncurve c u r v euccause Jecause would represent represent a a point p o i n t in i n time At A t tthis n i s point point ttue n e lava l a v a cooled c o o l e d in i n aa relatively r e l a t i v e l y sshort n o r t period p e r i o d of o f time. tine. de do d o not n o t have h a v e adejuate a d e q u a t einformation i n f o r ~ i a t i oto nt ocuoose c n o o s euetween ~ecw/een iin n our o u r study, s t u d y , we tthese h e s e alternative a l t e r n a t i v e explanations. explanations. 6 �U CHEM I CAL CHARACTER LZAT ON AND IS OF CHEMICAL CHARACTER LZ AT IION AND PETROGENES PETROGEMES IS OFKEWEENAWAN KEWEEI'JAW AN DIABASE D I ABASE DYKES DYKES OF O F NORTHERN NORTHERN MICHISAN I 1 I. CH I GAN Gregory T. Durqess Department Uep<artm(ant oof f Geological Geological Sciences, Universy Sciiancaa, Michigan M i c h i g a n State State U n i varss b y East E a s t Lansing, L a n s i n g , Michigan M i c h i g a n 48824 48824 age Michigan, <ago diabase d i a b a s e dykes dykes of o-f Northern Northern M i c h i g a n , which which iintrude ntrude and Proterozoic metasediments, and early early Proterozoic metasadiments;, can be ha can subdivided into eastern and s u b d i vi. ded into e a s t e r n (Saraga (Baraga and Marquette M a r q u e t t o Cots.) Ca '5.) and western western (t3ogebic Thirty—four samples fourteen dykes i n the the (Goqebic Co.) swarms. Thirty-four samples +:rom Â¥fro "Fourteen dykes in east in e a s t and and twenty—two twenty-two samples samples rorn f r o m thirteen t h i r t e e n dykes dykes i n the the? west wore were Keweenawan Kewemawan Archean Archean basement basement analyzed analyzed, widest w i d e s t dykes dykes were were sampled sampled several s e v e r a l times t i m e s from f r o m the t h e chil:1 c h i l l marqin nargin are the a r e some subtle s u b t l e changes in i n the t h e major major oxides, o x i d e s , Â¥(Â¥r from the chill but c h i l l margin margin to t o the t h e interior, interior, b u t these t h e s e changes changes are a r e small s m a l l and a n d have have no no trends. and olivine consistent Quartz which consistent trends. Quarts d i v i n e thaieiites, tholeiites, which p l o t as as plot separate on TTi02 vsP205 P2O diagrams s e p a r a t e cclusters l u s t e r s on i02 vs diagrams similar s i m i l a r to t o those t h o s e noted n o t e d by by (1980) Wilband and are in In t h e east. ea'st. In Wilband and Wasuwanich Wasuwanich ( 1 9 8 0 ),, a r e recognized recognized i n the to dykes addition in found i n the the addition t o these, these, dykes a4 o f basaltic b a s a l t i c andesite a n d e s i t a are <are found western Although swarm. the western Although t h e TiO9—P,O TiOz-PzOs p l o t of of t h i s swarm swi'arm is i:::Â¥ plot this linear, it clustering east. linear, i t lacks l a c k s the t h e bimodal bimodal c l u s s t e r i n g noted n o t a d in i n the the east Characteristic C h a r a c t e r i s t i c major major oxide o x i d e abundance abundance ranges r a n g e s in i n the t h e bimodal bimodal clivine al i v i ne? i.(—2.:V., 13—iSV., MgO 7-El.!%, 7—8.X, Na20: 'rio2 tholeiites h o l e i i t e ' s are a r e A1203: 41203: 13-19X, MqO; l. A - 2 . 3 ' / . , 'TiQ2: and 0.5--1.5%, P2O: P205: 0.0—0.i6X, 0.05-0.167., and ffor o rthe t hquartz e q u tholeiites a r t z t h are oleiitare A1203: Al203; t2—1Y., Ti02: MqO: 3.7—7V., 3 . 7 - 7 % , Na2O Na2Q:2—2.8"/., 2-2.87., Ti02: 1.2—3.9X, 1.2-3.97., P205; 0,ti—O%. 0.15-a,,57.. 12-16%, MgO F'2O Sased the Based on geochemical geochemical grounds, grounds, t h e eastern e a s t e r n swarm 'swarm may have have been bean derived d e r i v e d from f r o m two two mantle m a n t l e sources s o u r c e s which which varied v a r i a d in i n depth d e p t h and and trace trace element content. The swarm may have content. The western western have formed formed by by +ractional fractional crystallization a Further c r y s t a l li s a t i o n a$ of a less l e s s varied v a r i e d source. source. Further interpr-otatiana interpretations based oS that t h a t data. data, baaed on trace t r a c e element data d a t a are a r e pending pending acquisition a c q u i s i t i o n o4 The The inwards. inwards. There There 7 �U Ii DECADE OF O FNORTH NORTHAMERICAN AMERICANGEOLOGY GEOLOGY(D-NAG) (D-NAG)GEOLOGICAL GEOLOGICAL r)ECADE A N D TECTONIC MAPS O F THE SOUTHEASTERN CANADIAN SHIELD; AND TECTONIC MAPS OF THE SOUTHEASTERN CANADIAN SHIELD; 588 Booth Booth St., St., Ottawa, O t t a w a ,Ontario, O n t a r i o ,K1\ K1A OEQ K.D. Card, C a r d , Geological Geological Survey Survey of of Canada, Canada, 588 K.D. OEL 1:5 million million sscale c a l e geological geological and e c t o n i c compilations compilations of of the t h eArchean Archean 1:5 and ttectonic Superior Province and surrounding P r o t e r o z o i c orogens r e v e a l s o m e lithological, Superior Province and surrounding Proterozoic orogens reveal some lithological, s t r u c t u r a l , m e t a m o r p h i c , and geochronologic p a t t e r n s t h a t bear on t h e tectonic tectonic structural, metamorphic, and geochronologic patterns that bear on the evolution of of this this part p a r t of of the t h eCanadian CanadianShield. Shield. evolution Superior Province Province has has northern northern(Pikwitonei, (Pikwitonei,Minto) Minto)and andsouthern southern(Minnesota (Minnesota Superior River Valley) high-grade gneiss regions c h a r a c t e r i z e d by t h e p r e s e n c e of granulites: granulites: River Valley) high-grade gneiss regions characterized by the presence of o n e of t h e s e ( M R V ) has rocks older t h a n 3.5 Ga. Between t h e high-grade regions one of these (MRV) has rocks older than 3.5 Ga. Between the high-grade regions a r e a l t e r n a t i n g , east-west trending belts o r subprovinces whose s u p r a c r u s tal are alternating, east-west trending belts or subprovinces whose supracrustal c o m p o n e n t s a r e dominated by metavolcanics o r by m e t a s e d i m e n t s . T h e components are dominated by metavolcanics or by metasediments. The metavolcanic-rich belts b e l t s(Abitibi, (Abitibi, Wabigoon, Wabigoon, etc.) a r e characterized c h a r a c t e r i z e dby bysinuous, sinuous, metavolcanic-rich etc.) are metamorphosed komatiitic-tholeiitic, calc-alkalic, and r a r e alkalic volcanic metamorphosed komatiitic-tholeiitic, caic-alkalic, and rare alkalic volcanic s e q u e n c e s with with volcanogenic volcanogenic cclastic l a s t i c and and chemical c h e m i c a l sediments. sediments. Intervening Intervening sequences m e t a s e d i m e n t a r y subprovinces (Quetico, Pontiac, etc.) consist mainly of of turbiditic turbiditic metasedimentary subprovinces (Quetico, Pontiac, etc.) consist mainly w a c k e and p e l i t e metamorphosed at g r a d e s ranging f r o m low greenschist upper wacke and pelite metamorphosed at grades ranging from low greenschist tot o upper amphibolite, and locally, g r a n u l i t e facies. Supracrustal s e q u e n c e s a r e c u t by amphibolite, and locally, granulite facies. Supracrustal sequences are cut by a b u n d a n t plutonic plutonic rocks, rocks, including including tonalitic t o n a l i t i c gneiss, gneiss, quartz q u a r t z diorite, diorite,and and abundant trondhjemite, younger granodiorite batholiths, and still younger g r a n i t e and and syenite syenite trondhjemite, younger granodiorite batholiths, and still younger granite plutons. Plutonic Plutonic rocks rocks that t h a tmay m a y represent r e p r e s e n tbasement b a s e m e n tto t othe t h esupracrustals s u p r a c r u s t a l s are are plutons. known in e w localities. Zircon dating dating demonstrates d e m o n s t r a t e sthat t h a tvolcanic, volcanic,plutonic, plutonic, known in only only aa ffew localities. Zircon deformational, and and metamorphic m e t a m o r p h i c episodes episodes of of relatively r e l a t i v e l y brief brief duration duration were were deformational, essentially synchronous synchronous over o v e r large l a r g e parts p a r t s of of Superior Superior Province, Province, but but there t h e r e are are essentially d e t e c t a b l e d i f f e r e n c e s in t h e a g e s of e v e n t s f r o m o n e a r e a t o a n o t h e r . In t h enorth north detectable differences in the ages of events from one area to another. In the (Sachigo, Uchi) major volcanism and plutonism o c c u r r e d b e t w e e n 3.0 and 2.3 G (Sachigo, Uchi) major volcanism and plutonism occurred between 3.0 and 2.8 Gaa 2.75 and and 2.7 2.7 Ga. Ga. InInthe t h esouth s o u t h(Abitibi, (Abitibi,Wawa, Wawa,Wabigoon) Wabigoon)major major and again again between b e t w e e n2.75 and volcanism and plutonism o c c u r r e d f r o m 2.75 t o 2.66 Ga. T h e c o n t e m p o r a n e i t y of of volcanism and plutonism occurred from 2.75 to 2.66 Ga. The contemporaneity short-lived m a g m a t i c episodes along t h e l e n g t h s of t h e s e belts s e e m s c o n s i s t e n short-lived magmatic episodes along the lengths of these belts seems consistentt with aa subduction-dominated subduction-dominated tectonic t e c t o n i cregime r e g i m efor f o rthe t h eSuperior SuperiorOrogen. Orogen. with L a t e tectonic t e c t o n i chistory historyofofSuperior SuperiorProvince Provincewas wasdominated d o m i n a t e dby by faulting. faulting. Late D e x t r a l t r a n s c u r r e n t f a u l t s trending EW a n d NW and sinistral f a u l t s trendingNE ME Dextral transcurrent faults trending EW and NW and sinistral faults trending f o r m subprovince boundaries in p a r t , as d o NE and EW trending thrusts. T h e most form subprovince boundaries in part, as do NE and EW trending thrusts. The most n o t a b l e product product of of faulting, faulting, the t h eKapuskasing Kapuskasing structural s t r u c t u r a lzone, zone, exposes exposes granulites granulites notable considered t o r e p r e s e n t lower c r u s t brought t o s u r f a c e along major YE trending considered to represent lower crust brought to surface along major NE trending f a u l t s that t h a t transect t r a n s e c tthe t h eeast-west east-westsubprovinces. subprovinces. faults Superior Province, Province, representing representing part p a r t of of aapreviously previously more m o r e extensive e x t e n s i v eArchean Archean Superior C r a t o n , i s bisected and surrounded by P r o t e r o z o i c orogens. The Early P r o terozoic Craton, is bisected and surrounded by Proterozoic orogens. The Early Proterozoic fold b e l t s (Ungava, Penokean) display lithological and t e c t o n i c zonation c o nsistent fold belts (Ungava, Penokean) display lithological and tectonic zonation consistent with t h e operation of p l a t e t e c t o n i c processes. with the operation of plate tectonic processes. 8 �— — a 0 2 r, C -V m oO 0 — o o — — — a 2 ; aV3 wan .o •a '— — — 0 on CV z C CVQ Ca—— .C - I0' 0 00> o30° - 31 < 0< r C) C) IC I Ir rT, Iz I C 0 0 N 0 m -I 0 -V 2 0 m C) m — — V t > C) I V �U THE TEXTURE TEXTURE AND AND MINERALOGY MINERALOGY OF OF THE THE LAKE LAKE ELLEN ELLEN KINBERLITE KIMBERLITE THE CRYSTAL FALLS, FALLS, MICHIGAN, MICHIGAN, USA USA CRYSTAL By Torrie Torrie Chartier Chartier By Michigan Technological Technological University University Michigan Houghton, MI MI Houghton, March, 1985 1985 March, H. Spence Spence The Lake Lake Ellen Ellen kimberlite kimberlite (figure (figure 1) 1) was was discovered discovered by by William William H. The and Klaus J. Schultz in 1966 and was described physically by Cannon and and Klaus J. Schultz in 1966 and was described physically by Cannon and Mudrey (1981). (1981). Hearn and the mineralogy mineralogy and and concluded concluded Mudrey Flearn and McGee McGee (1983) (1983) studied studied the that the mineral assemblages show equilibrium compositions of mantle that the mineral assemblages show equilibrium compositions of mantle 7 0 0 - 1 3 0 0 ~and and ~ at at depths depths derived inclusions inclusions were were formed formed at at temperatures temperatures of of 700—1300°C derived of 55-160 km, within the stability field of diamond. of 55—160 km, within the stability field of diamond. This isolated isolated kimberlite kimberlite occurence occurence has has raised raised considerable considerable interest interest This in view view of of the the widespread widespread discoveries discoveries of of diamonds diamonds in in the the glacial glacial overburden overburden in This has has prompted prompted kimberlite kimberlite exploration explorationin inthis thisregion. region. in Wisconsin. Wisconsin. This in Specimens from from six six represenative represenative sites sites on on the the Lake Lake Ellen Ellen kimberlite kimberlite diatreme diatreme Specimens were studied studied in in hand hand specimen specimenand and thin thin section texture and and were section for for diagnostic diagnostic texture mineralogy. The The characteristic characteristic features featureswere were then thenphotographed. photographed. The The purpose purpose mineralogy. was to to search search for for distinct distinct kimberlite kimberlitefacies faciesin inthe thebody. body. was The Lake Lake Ellen Ellen kimberlite kimberlite is is aa breccia breccia consisting consisting of of crustal crustal and and mantle mantle The derived xenoliths. Crustal xenoliths are most abundant and consist of derived xenoliths. Crustal xenoliths are most abundant and consist of Ordovician limestone limestone and and metamorphic metamorphic clasts clasts of of biotite biotite and andtalc talcschist. schist. Ordovician A smaller fraction of the xenoliths are of highly altered possible eclogitic A smaller fraction of the xenoliths are of highly altered possible eclogitic melilitic clasts now pseudomorphs of calcite. nodules and possible nodules and possible melilitic clasts now pseudomorphs of calcite. Around the the xenoliths, xenoliths, the the kimberlite kimberlite matrix matrix consists consists of of two two distinct distinct Around sizes of of olivine olivine grains: grains: small small (.5mm), (.5mm), rounded rounded to to subangular subangular grains grains in in sizes (.5-2mm), subhedral subhedralto toeuhedral euhedralxenocrysts. xenocrysts. The The the groundmass groundmass and and larger larger (.5—2mm), the fine grained grained olivine olivine is is usually usually completely completely replaced replaced by by calcite, calcite, serpentine serpentine fine and minor minor chlorite, chlorite, which which occurs occurs in inaa clastic clasticgroundmass of still still finer—grained finer-grained and groundnass of lithic clasts are coated alteration minerals. Some olivine xenocrysts and alteration minerals. Some olivine xenocrysts and lithic clasts are coated with a fine-grained magmatic kimberlite rind interpreted to be autolithic. with a fine—grained magmatic kimberlite rind interpreted to be autolithic. The only onlyniagmatic magmatic texture texture recognized recognized in in this this body body occur occur in in these these rinds. rinds. The The most most common common unaltered unaltered primary primary minerals minerals are are ruby—red ruby-red pyrope pyrope garnet, garnet, The ilmenite, and occasionally olivine, phlogopite and microscopic magnesium magnesium ilmenite, and occasionally olivine, phiogopite and microscopic apatite. None None of of the the specimens specimens showed showed pyroxene pyroxene minerals. minerals. Secondary Secondary apatite. minerals which commonly mask the primary mineralogy include serpentine (optically (optically minerals which commonly mask the primary mineralogy include serpentine identified as as antigorite), antigorite), calcite, calcite, phlogopite, phlogopite, chlorite, chlorite, and and microscopic microscopic identified millerite (NiS) (NiS) in incalcite. calcite. millerite The Lake Lake Ellen Ellen kimberlite kimberlite can can be be classified classified as as aa serpentine—carbonate serpentine-carbonate The kimberlite breccia according to the Skinner and Clement (1979) classification classification kimberlite breccia according to the Skinner and Clement (1979) scheme. Because of the lack of distinquishing features, the body is scheme. Because of the lack of distinquishing features, the body is interpreted to represent a single breccia phase. interpreted to represent a single breccia phase. 10 �U 48 N Lake Superior f Lake Ellen Kimberlite \ I A . . 46 N Lake bwisconsin 100 I______( Urn 88W 90 W Figure Figure 1. 1. Location Location map map for for the the Lake Lake Ellen Ellen kimberlite. kimberlice. -- REFERENCES REFERENCES Cannon, Cannon, W.F,, W.!?,, and and Mudrey, Mudrey, M.G., M.G., 1981. 1981. The The potential potential for for diamond—bearing diamond-bearing kimberlite kimberlite in in Northern Northern Michigan Michigan and and Wisconsin. Wisconsin. Geol. Geol. Survey Survey Circular Circular 862. 842. McGee, E.D,, and Hearn, Beam, B.C., McCee, E.D., B.C., Jr., Jr., 1983. 1983. Lake Lake Ellen Ellen kimberlite, kimberlite, Michigan, Michigan, USA, USA, USGS USGS Open—File Open-File Report Report 83—156. 83-156. Skinner, E.M.W. and and Clement, Clement, C.R., Skinner, E.M.W. C.R., 1979. 1979. Mineralogical Mineralogical classification classification of of southern southern African African kimberlites. kimberlites. Proceedings Proceedings of of the the 2nd 2nd International International Kimberlite 1:129-139. Kimberlite Conference, Conference, Vol. Vol. 1:129—139. 11 �U MINERALIZATION ASSOCIATED ALTERATION AND GOLD MINERALIZATION ASSOCIATED WITH WITH AA SHEETED SHEETED VEINLET VEINLET ALTERATION ZONE AT THE CAMPBELL RED LAKE MINE, MINE, BALMERTOWN ONTARIO ONTARIO Christie, B.J. Christie, B.J. and and Hodgson, Hodgson, C.J. C.J. Department Department of Geological Geological Sciences, Sciences, QueenTh Queen's University University Kingston, K7L 3N6, 3N6, Canada. Canada. Kingston, Ontario, Ontario, K7L The ore bodies at the Campbell Campbell Mine occur occur in in aa volcanic volcanic complex complex that that is composed of massive to pillowed basalt, basalt, with with lesser lesser andesite andesite and and rhyolite. These units are intruded rhyolite. intruded by by concordant concordant sills sills ranging ranging from from ultramafic to gabbroic ultramafic gabbroic in in composition. composition. The ultramafic lithologies lithologies and and flanking flanking zones of alteration are termed "altered "altered rock" rock" because because of of the the uncertain origin origin of some of these these petrologically petrologically distinctive distinctive rock rock bodies. bodies. In several several localities localities where there there is is aa well well developed developed cleavage, cleavage, the the unit is "altered rock" These veinlet zones". zones". These "altered rock" unit is characterized characterized by by "sheeted "sheeted veinlet zones are are broadly cleavage sub— zones broadly lenticular lenticularininshape shapeand andconsist consistofof cleavage subveinlets parallel stockwork, gold free, free, quartz—carbonate quartz-carbonate ±Â chlorite chlorite veinlets parallel to stockwork, cm wide. averaging about wide. They are typically spaced at 2.5 2.5 to 10 10 cm averaging about 1 cm basalt—ultramafic intervals. Most "sheeted veinlet zones" extend from basalt-ultramafic intervals. contacts into contacts into the the ultramafic ultramafic rock. rock. However some, some, such such as as the the 1958W 1958W "sheeted veinlet zone", are entirely within 'sheeted within the the "altered "altered rock" rock" unit. unit. These veinlet zones zones are thought to have formed formed by by extension extension normal normal to to the cleavage, cleavage, and by a process of incremental incremental opening opening and and simultaneous simultaneous outward growth of mineral fibres along the the vein—wallrock vein-wallrock contact. contact. Overprinting Overprinting the the veinlet zones zones are are small small pod pod or or pipe—like, pipe-like, subvertically orientated and often subvertically often spectacular spectacular high high grade grade gold gold bearing bearing siliceous replacement siliceous replacement zones. zones. These replacement replacement zones zones are are rich rich in in quartz, quartz, fuchsite, fuchsite, pyrite and native native gold, gold, ±k sphalerite sphalerite ±k arsenopyrite arsenopyrite ±k stibnite stibnite ±Â molybdenite. molybdenite. alteration—mineralization types occur in association A wide variety of alteration-mineralization with with the the "sheeted "sheeted veinlet veinlet zones". zones". The objective of this study study was to to petrologically and chemically characterize characterize these these and and investigate investigate their their relationship relationship to to the the gold. gold. The type of alteration alteration developed developed here, here, as as in in most gold gold deposits, deposits, depends depends on on the the nature nature of of the the host host rock. rock. In general general alteration in basalts is is much less carbon carbon dioxide dioxide rich rich than than that that in in the the "altered 'altered rock" due to the higher higher initial initial calcium, calcium, magnesium, magnesium, and and iron iron content of the the "altered "altered rock". rock". The The earliest type type of alteration alteration occurring occurring in in the the basalts basalts involves involves alkali depletion alkali depletion and and aluminium aluminium enrichment. enrichment. It is characterized characterized by by the the minerals garnet, garnet, biotite, andalusite, andalusite, chloritoid, chloritoid, sericite sericite and and magnesium magnesium chlorite, and appears appears to be spatially spatially related related to to the the basalt—"altered basalt-"altered chlorite, rock" contacts. contacts. The alteration alteration bears bears no no known known relationship relationship to to gold gold mineralization. mineralization. Synchronous with the early alteration alteration of basalts basalts is is aa chlorite—biotite—carbonate c h l o r i t e - b i o t i t e - c a r b o n a t e alteration alteration in in the the "altered "altered rock" rock" unit unit which which is characterized by the minerals chlorite, chlorite, biotite, biotite, coarse coarse grained grained carbonate, carbonate, and locally, locally, fine fine grained grained quartz—carbonate. quartz-carbonate. It can occur occur anywhere anywhere in in the "altered rock" rock" unit unit and and also also bears bears no no known known relationship relationship to gold mineralization. mineralization. Superimposed on these early alterations Superimposed alterations are are three three alteration alteration types types which which are are associated associated with with gold gold mineralization. mineralization. The The first first is is aa buff—brown buff-brown siliceous siliceous alteration alteration of of basalts basalts that that occurs occurs near the the basalt—"altered basalt-"altered rock" rock" contact. contact. It is characterized by the the characterized by 12 12 �U minerals minerals quartz, quartz, carbonate, carbonate, pyrite, pyrite, chlorite chlorite and and sericite, sericite, and and has has an an average average gold gold content content of of about about 1000 1000p.p.h. p.p.b. The unit. The other other two two alteration alteration types types occur occur in in the the "altered "altered rock" rockf1 unit. One One is is aa pistashio—green pistashio-green alteration alteration characterized characterized by by the the minerals minerals quartz, 100 cm cm wide wide quartz, carbonate, carbonate, sericite, sericite, and and pyrite. pyrite. It It occurs occurs as as 50 50 —- 100 envelopes on on 20 20 —- 30 30 cm cm wide, wide, banded auriferous auriferous quartz—carbonate quartz-carbonate veins. veins. envelopes The The The The average average gold gold content content of of this this alteration alteration type type about about is is 350 350 p.p.b. p.p.b. other that overprints overprints the sheeted veinlets, other is is aa silic:Lfication silicification that veinlets, and and consists consists of of quartz, quartz, minor carbonate, carbonate, minor minor biotite, biotite, minor minor chlorite, chlorite, pyrite pyrite and and locally locally gold, gold, arsenopyrite, arsenopyrite, sphalerite, sphalerite, stibnite stibnite and and molybdenite. molybdenite. The The alteration alteration occurs occurs in in small small pods pods or or pipe—like pipe-like bodies bodies and and is is probably probably fault fault controlled- In In some some areas areas gold gold grades grades in in silicified silicified "altered "altered or fracture fracture controlled. or rock" rock1'exceed exceed 15 15 ounces ounces per per ton. ton. Most Most of of the the alteration alteration and and mineralization mineralization associated associated with with "sheeted "sheeted veinlet veinlet zones" zones1'occurs occurs in in strongly strongly deformed deformed rocks rocks in in close close proximity proximity to to the the The contact, and fault or fracture zones basalt—"altered rock" contact. basalt-"altered rock" contact. The contact, and fault or fracture zones appear to have provided provided channelways channelways for for the the hydrothermal hydrothermal fluids fluids responsible responsible for for the the formation formation of of the the various various auriferous auriferous and and nonauriferous nonauriferous alteration—mineralization alteration-mineralization types types found found in in the the study study area. area. �PRELIMINARY METALLOCENIC SUBDIVISTON OF THE LAKE OF THE OODS METAVOLCANIC—METASEDIMENTARY BELT NORTHYiSTERN ONTARIO HilL CLARK CONSULTING GEOLOGIST 201 MELLICK AVENUE KENORA, ONTARIO Potential for gold and base metals within the Lake of the Woods east trending metavolcanic-metasedimentary belt Northwestern Ontario, has been shown by past exploration activity. This paper will summarize current planetary evolutionary hypothesis and past exploration work to develop a workable metallogenic subdivision of the area. The many 1970's saw the development of plate tectonic theory and geologists attemping to fit this type of dynamic system into Archean crustal mechanics. During the 19801s geologists are exploring the solar system by satellite. This activity may have impact of the same magnitude as plate tectonics on geologic an thinking. Planetary exploration has given us clues to the processes Heat flow rates, volcanic early Precambrian time. active in complexes on Mars and Jupiter's Red Spot as a heat transfer mechanism have been instrumental in rethinking Archean crustal evolution. Vertical tectonics and mantle plumes may hold the key to unlocking the mechanisms in operation during this period in georecently until time. Metavolcanic-metasedimentary belts logic have been viewed as simply a mixture of rock types: today we may view them as the end result of these processes. Examples will he brought forth for examination to help develop a metallogenic pattern. The Lake of the Woods metavolcanic—metasedimentary area can be viewed as east trending lithological belts, each with a distinct metailogeny. Internal structure may be one of the many features which provide evidence for this subdivision. The Lake of the Woods belt is represented by two base metal areas, two gold areas and apparently unmineralized area. Boundaries to these areas are an. marked by structural deformation zones or batholithic intrusions. Implications for mineral exploration in the Wabigoon Metavolcanic-metasedimentary belt and all other such belts in the Superior Province are highly significant. Planetary information and its effect on metallogenic subdivisions may give the exploration geologist a rational way of determining exploration targets in the Precambrian Shield of Canada. Following this rationale, the Lake of the Woods area may contain a gold camp, which at the turn of the century produced 55% of Ontario's gold, and a base metal area which have both been over looked until recently by explorationists. 14 �U geochronology andt etectonic g e o c h r o n o l o g y and c t o n i c hhistory i s t o r y ofofthe t h eShebandowan Shebandowan bbelt, elt, northwestern n o r t h w e s t e r n Ontario. Ontario. U-Pb F. F. Corfu, C o r f u , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, c/o c / oDepartment Department of o f Mineralogy Mineralogy and 100 QQueen's Park, Toronto, and Geology, Geology, Royal Royal Ontario O n t a r i o Museum, Museum, 100 u e e n ' s Park, Toronto, Ontario, O n t a r i o ,Canada CanadaM5S M5S2C6 2C6 G.M. 77 GGrenville G.M. SStott, t o t t , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, 77 r e n v i l l e Street, Street, Toronto, M5S 1B3 16'3 T o r o n t o , Ontario, O n t a r i oCanada , CanadaM5S The Shebandowan ThunderBay, Bay, eexhibits The Shebandowan b e belt, l t , wwest e s t oof f Thunder x h i b i t s evidence evidence for f o r two two major m a j o r periods p e r i o d s of o f deformation. d e f o r m a t i o n . The The ffirst i r s t period, p e r i o d ,which which caused have accompanied caused rregional e g i o n a l folding f o l d i n g across a c r o s sthe t h ebelt, b e lmay t , may have accompanied initial i n i t i adevelopment l development of of aa granitoid g r a n i t o i dcomplex complex to t o the t h e south. s o u t h . The The second produceda ar eregional second produced g i o n a l t rtranspression a n s p r e s s i o n aacross c r o s s t hthe e nnorthern o r t h e r n hhalf alf of w h i c h reflects r e f l e c t sa amajor m a j o rshortening s h o r t e n i n gacross a c r o s s the t h e Quetico Quetico be1 twhich o f the t h e belt metasedimentary metasedi'mentary s usubprovince b p r o v i n c e t otot hthe e nnorth o r t h and and ddextral e x t r a l shearing shearing along andssedimentary a l o n g the t h e Quetico Q u e t i c o Fault. F a u l t . Igneous Igneous and e d i m e n t a r y a activity, c t i v i t y , which which accompanied succeeded one accompanied o or r succeeded one o rort hthe e o other t h e r oof f these t h e s e deformation deformation periods, p e r i o d s , permit p e r m i t us us tto o set s e t absolute a b s o l u t e time t i m e constraints c o n s t r a i n t s on on this this sequence of events. sequence of events. The The sstratigraphy t r a t i g r a p h y ooff the t h e 9reenstone r e e n s t o n e bbelt e l t was was nnot o t ddated a t e d ddirectly, irectly, but Maf ofor but a a zircon z i r c o n age age of o f 2732 2732 +1U "'"1 Ma r aaqquartz-feldspar u a r t z - f e l d s p a r pporphyry o r p h y r y ssill ill -2 sets s e t s a minimum minimum d adate t e f o for r t hthe e eextrusion x t r u s i o n ofof iits t s host h o s t volcanic v o l c a n i c rocks rocks 8 north n o r t h ofofMiddle M i d d l Shebandowan e Shebandowan Lake. Lake. The d e f o r m a t i o n (D1) (Dl)preceded preceded or o r coincided c o i n c i d e d with wi h The ffirst i r s tperiod p e r i o dofofdeformation the t h e intrusion i n t r u s i o nofothe f t hShebandowan e Shebandowan Lake Lake pluton p l u t o n dated d a t e d at a t2696.1 2696.1 t 2 . i -2.3 Ma. Ma. This T h i s pluton p l u t o n appears appears to t o have have been been formed r i o r tto o the t h e extrusion extrusion formedp prior of anda1alkalic o f "Timiskaming—type" " T i m i skami n g - t y p e " c acaic-alkalic l c-a1 k a l ic and k a l ic pyroclastic p y r o c l as t i c rocks rocks and alluvial-fluvial and tthe h e ddeposition e p o s i t i o n oof f aassociated s s o c i a t e d a1 l u v i a l - f l u v i asedimentary l s e d i m e n t a r y rocks. rocks. This T h i s late l a t e supracrustal s u p r a c r u s t a l sequence sequence ooccurs c c u r s ssouth o u t h oof f tthe h e pluton p l u t o n in i n two two parallel groups that t h a tunconformably u n c o n f o r m a b l y ooverlie v e r 1 i e older 01 d e rKeewatin Keewati n volcanic vol cani c para1 l e l groups rocks. rocks. A A maximum maximum d adate t e f ofor r t hthe e ddeposition e p o s i t i o n oof f the t h e sediments sediments is is established Ma ffor or a a quartz-phyric quartz-phyric e s t a b l i s h e d by b y aa zircon z i r c o n age age of o f 2704.1 2704.1 + 1 - 8 Ma -1.6 trondhjemitic t r o n d h j e m i t i c clast c l as tini a n conglomerate, a conglomerate. A A trachytic t r a c h y t i c pyroclastic p y r o c l as t i c b r e c c i a from f r o m tthis h i s "Timiskaming-type" " T i m i s k a m i n g - t y p e " ssuite u i t e yyields i e l d s aa zircon z i r c o n age age of of breccia 2689.3 Ma, Ma, wwhich h i c h s slightly l i g h t l y but b u t significantly s i g n i f i c a n t l ypostdates p o s t d a t e s the the 2689.3 T!; crystallization c r y s t a l 1 iz a t i oof n othe f t Shebandowan h e Shebandowan Lake Lake pluton. p l uton. All A l l ofo the f t h eabove aboveunits u n i t shave havebeen been affected a f f e c t e d by b ythe t h esecond second period period of deformation d e f o r m a t i o n (D2). ( D ? ) . The The Burchell B u r c h e l l Lake Lake pluton, p l u t o n ,ananundeformed undeformed circular c i r c u l a r stock s t o c k of o fgranitic g r a n i t i to c t trondhjemitic o t r o n d h j e m i t i composition, c c o m p o s i t i o n ,postdates postdates the and appears appearst otobe beone oneofofaa sset t h e D2-deformation D2-deformation eevent, v e n t , and poste t of o f posttectonic t e c t o n i c plutons p l u t o n s wwithin, i t h i n , and and ssouth o u t h ofof tthis h i s belt. be1 t . Preliminary Preliminary zircon z i r c o n and and ttitanite i t a n i t e data d a t a from f r o m this t h i s intrusion i n t r u s i o nindicate i n d i c a t ean anage age of of 2684 2684 +Ol oMa. Ma. Because Because o f oft hthe e r erelatively l a t i v e l y large l a r g e error e r r o r the t h e age age is is -7 indistinguishable i n d i s t i n g u i s h a b l e from f r o m that t h a tofo the f t hdeformed e deformed"Timiskaming-type' "Timiskami n g - t y p e " volcanic v o l c a n i c rocks. r o c k s . Considering C o n s i d e r i n g ttheir h e i r errors, e r r o r s , the t h etwo twoages ages allow a1 l o w f o r aamaximum maximum t time i m e span 10 Ma o r "Timiskaming-type' " T i m i s k a m i n g - t y p e " volcanism, volcanism, for spanooff 10 Maf for D2-deformation andi nintrusion of the D2-deformation and t r u s i o n of t h e Burchell B u r c h e l l Lake Lake pluton. pluton. 15 �U This T h i s data d a t a indicate i n d i c a t e aa relatively r e l a t i v e l rapid y r a p i succession d s u c c e s s i o n of o fevents, events, between 2700and and2680 2680MaMa ago,i nincluding between aabout b o u t 2700 ago, c l u d i n g i nintrusion t r u s i o n of o f major major plutons, p l u t o n s , erosion, e r o s i o n ,sedimentation s e d i m e n t a t i o nand andvolcanism v o l c a n i s mand andaamajor m a j o r(D2) (DA d e f o r m a t i o n event. e v e n t . The The D2-deformation D 2 - d e f o r m a t i o n event e v e n t corresponds c o r r e s p o n d s to to deformation widely w i d e l y recognized r e c o g n i z e d late 1a t eArchean Archean crustal c r u s t a lshortening s h o r t e n i n gmanifested mani f e s t e d as as zones zones of o f transpression t r a n s p r e s s i o nnear n e a rsubprovince s u b p r o v i n c e boundaries, b o u n d a r i e s , major major s h e a r zones zones and t e ffaults a u l t s that t h a tborder b o r d e rand and transect t r a n s e c t the the shear andl alate subprovinces, andsshallowly-plunging s u b p r o v i n c e s , and h a l l o w l y - p l u n g i n g u upright p r i g h t f folds o l d s tthat h a t refold refold e a r l ie recumbent r recumbentstructures s t r u c t u r e sthroughout t h r o u g h o uthe t t hmetasedimentary e metasedi m e n t a r y earlier mineralization Go1 d m i n e r a l i z a t i o n i is s related r e 1 a t e d locally l o c a l l y to t othe the s u b p r o v i nces . Gold subprovinces. D2-deformation andr eregionally D 2 - d e f o r m a t i o n and g i o n a l l y tto o the t h e crustal c r u s t a l shortening s h o r t e n i n gevent; event; its i t sage ageisi sthus t h u sclosely c l o s e lbracketed y b r a c k e t e by d b the y t h presented e p r e s e n t e dU-Pb U-Pb data. data. Survey. Published with Pub1 i shed w i t h permission p e r m i s s i o n ooff the t h e Director, D i r e c t o r ,Ontario O n t a r i oGeological Geol o g i c a lSurvey. 16 �U andt etectonic U-Pb geochronology geochronology and c t o n i c hhistory i s t o r y of o f the t h e Winnipeg Winnipeg River River granitoid terrain, northwestern Ontario. g r a n i t o i d t e r r a i n , northwestern O n t a r i o . FF.. Corfu, Corfu, Ontario O n t a r i o Geological Geological Survey, Survey, do c/oDepartment Department of of Mineralogy Mineralogy and Geology, Royal 100 QQueen's and Geology, Royal Ontario O n t a r i o Museum, Museum, 100 u e e n ' s PPark, a r k , TToronto, oronto, Ontario, O n t a r i o ,Canada CanadaM5S M5S 2C6 2C6 Beakhouse,OOntario GeologicalSurvey, Survey,7777Grenvi Grenville GG.P. . P . Beakhouse, n t a r i o Geological l i e SStreet, treet, Toronto, Ontario, O n t a r i oCanada , CanadaM5S M5S 1B3 1B3 G.M. Grenville G.M. SStott, t o t t , Ontario O n t a r i o Geological Geological Survey, Survey, 77 77 Grenvil l e Street, Street, Toronto, T o r o n t o , Ontario, O n t a r i oCanada , CanadaMSS M5S 1B3 1B3 Grenville RR.H. . H . SSutcliffe, u t c l i f f e ,Ontario O n t a r i oGeological Geological Survey, Survey, 77 77 Grenvi 1 l e Street, Street, Toronto, Ontario, O n t a r i oCanada , CanadaM5S M5S 1B3 1B3 geochronological i t a n i t e and and PPreliminary r e l i m i n a r y U—Pb U-Pb geochronologi c a l d a tdata a f o rfor z i zircon, rcon, t titanite monazite fromt the WinnipegRiver Riverg rgranitoid monazi t e from h e Winnipeg a n i t o i d tterrain e r r a i n indicate i n d i c a t ea acomplex complex and history. and pprotracted r o t r a c t e d ggeological e o l o g i c a l hi story. Gneissic and ffoliated G n e i s s i c and o l i a t e d tonalites t o n a l i t e sfrom fromthe t h Cedar e CedarLake, Lake, Daniels DanielsLake Lake and Kenora Kenoraa rarea and e a a r eare i n tintrusive r u s i v e i ninto, t o , oor r ccontain o n t a i n iinclusions n c l u s i o n s oof f highly highly The ttonalite onal i t e fragmented, volumetrically fragmented, vol umetri cal l yminor minorsupracrustal s u p r a c r u s t a lsequences. sequences. The in Lake aarea Ma;t this i n the t h e Cedar Cedar Lake r e a yyields i e l d s aa zzircon i r c o n age age ooff about about 3170 3170 Ma; h i s is is the t h enorthern n o r t h e r n Superior Superior t h e ooldest l d e s t reliable r e l i a b l e zircon z i r c o n age age yyet e t identified i d e n t i f i e d ini nthe old, tonalites A tonalite tonal i t efrom fromKenora Kenora is i sabout about 2880 2880 Ma Ma 01 d , whereas whereas tonal i tes Province. A iinn the t h e Daniels Daniels Lake Lake area a r e a are a r eabout about2840 2840and and 2710 2710 Ma Ma oold. l d . These new new ddata, a t a , together t o g e t h e r with w i t h previously p r e v i o u s l ypublished p u b l i s h e dages agesofof3000-3040 3000-3040 Ma Ma at Ma Kenorassuggest a t Lac Lac Seul Seul and and 2830 2830 M a aat t Kenora u g g e s t t that h a t tonalite t o n a l i t eplutoruism piutonism took during aatt least took place p l a c e during l e a s t 55 periods. periods. Regional tectonics Regional t e c t o n i c s and and metamorphism metamorphism aare r e cconstrained o n s t r a i n e d by by ages ages on on llate a t e granitoid g r a n i t o i dintrusives i n t r u s i v eand s andmetamorphic metamorphic rocks: rocks: 1) andr eregional nappe-1 i ke s tstructures r u c t u r e s and g i o n a l uupright p r i g h t ffolding o l ding 1 ) Local Local nappe—like observed Kenorap post-date observed e east a s t oof f Kenora o s t - d a t e t hthe e f foliated o l i a t e d Daniels Daniels Lake Lake ttonalite onali t e at Ma,bbut a t 2710 2710 Ma, u t iis s older o l d e r than than the t h e crosscutting c r o s s c u t t i n g Lount Lount Lake Lake batholith batholith This h i s period p e r i o d of of deformation deformation to t o the t h e north n o r t h previously p r e v i o u s l ydated d a t e data 2702 t 2702Ma. Ma. T metamorphism iiss essentially e s s e n t i a l l ycoeval coevalwith withregional regional metamorphism in i n Kenora Kenora dated d a t e d at at about 2710MMa ana amphibolite andwith witht hthe e iintrusian n t r u s i o n of of about 2710 a bybyz izircons r c o n s i ninan m p h i b o l i t e and marginal ggranodiorite, i n t r u s i o nemplaced empl aced into i n t o the the ranodiori t e , a a sheet-like sheet-1 i ke intrusion tthe h e marginal subprovince subprovince iinterface n t e r f a c eata Kenora t Kenoraabout about2705 2705Ma Ma ago. ago. 2) follows regional 2 ) Late Late doming doming follows r e g i o n a l deformation. deformation. In the t h e Kenora Kenora area area the age of doming is constrained by titanite ages which t h e age of doming i s c o n s t r a i n e d by t i t a n i t e ages which iindicate ndicate 2700-2690 Ma Ma ago. ago. Doming Doming i in n the the ccooling o o l i n g tot obelow belowabout about500°C 500 C ata t2700-2690 Cedar Lakea rarea was Cedar Lake e a was e i either t h e r r erelated l a t e d tto o or o r post-dated p o s t - d a t e d aa late l a t ephase phase of o f aa protracted p r o t r a c t e d granulite g r a n u l i t efacies f a c i e metamorphic s metamorphic history hi s t o r yrecorded recorded by by metamorphicz izircons mafic ggranulite metamorphic r c o n s i nin aa mafic r a n u l i t e and and by by monazite monazite in i n aa Titanite i t a n i te ages ages of of ttonalite o n a l i t e and and aa granodiorite g r a n o d i o r i t eata about t about2680 2680Ma. Ma. T 2600-2590MMa CedarLake Lakea rarea showt hthat 2600-2590 a i nint hthe e Cedar e a show a t t this h i s crustal c r u s t a lsegment segment remainedaat muchl olonger than iin n g e r than n the t h e Kenora Kenora region. region. remained t eelevated l e v a t e d temperatures temperatures much Publishedwwith permissionofof tthe i t h permission h e Director, D i r e c t o r , Ontario O n t a r i oGeological Geological Survey. Survey. Published 17 17 �U STRATIGRAPHIC AND STRUCTURAL EVOLUTION STRATIGRAPHIC AND STRUCTURAL EVOLUTIOM OF THE THE CROSS CROSSLAKE LAKESUPRACRUSTAL SUPRACRUSTAL BELT BELT IN NORTHWESTERN SUPERIOR PROVINCE, IN PflDVINCE, MANITOBA MANITOBA Timothy Corkery, Corkery, Manitoba Department Department of Energy and M. and Mines, Mines, Geological Geological M. Tinothy Services Branch, Branch, Winnipeg, Winnipeg, Manitoba. Manitoba. The Archean supracrustal Lake—Pipestone Lake area supracrustal belt belt in the Cross Lake-Pipestone area contains contains evidence evidence of of two two distinct distinct episodes: episodes: an early period dominated by mafic volvolcanism, canism, followed by plutonic intrusion; intrusion; aa second second period period of of uplift, uplift, erosion erosion and deposition of subaerial—fluvial subaerial-fluvial dominated dominated sediments. sediments. These observations observations indicate that the development of the Cross Lake supracrustal supracrustal belt belt is is similar similar in character to other greenstone greenstone belts in the northern Superior Superior Province Province where where the dominantly volcanic succession succession (Hayes (Hayes River River Group) Group) is is unconformably unconformably over— overby a succession succession of dominantly sedimentary rocks (Oxford lain by (Oxford Lake Lake Group, Group, Island Lake Lake Group). Group). The early supracrustal supracrustal rocks rocks comprise comprise aa sequence sequence dominated dominated by by pillowed pillowed and and massive metabasalt flows flows with subordinate subordinate amoeboid amoeboid pillow pillow breccia. breccia. Near the the basalt sequence plagioclase plagioclase phyric massive and pillowed top of the basalt pillowed basalts basalts metasediments and occur. occur. Mafic volcanic metasediments and minor minor greywacke greywacke metasediments metasediments occur occur within the within the sequence. sequence. The early supracrustal supracrustal rocks rocks are are extensively extensively intruded intruded ultramafic sills sills and and dykes. dykes. On Pipestone Pipestone Lake, Lake, aa large large layered layered by mafic to to ultramafic anorthosite—gabbro anorthosite-gabbro complex complex contains contains titanium—vanadium titanium-vanadium enriched enriched magnetite— magnetiteilimanite layers. illmanite layers. These rocks rocks were intruded intruded by tonalite tonalite (U/Pb (U/Pb age age 2712 2712 Ma). Ma). overlying the early supracrustal Unconformably overlying supracrustal rocks rocks and and tonalite tonalite is is aa generally fining upward sequence sequence of metasediments. metasediments. Thickly Thickly bedded alluvial alluvial fan conglomerates conglomerates and high high energy energy fluvial fluvial sandstones sandstones up up to to 1500 1500 mm thick thick form form the base of the the sequence. sequence. Up to 250 250 m of thickly thickly bedded bedded sandstone sandstone and and thinly thinly bedded siltstone—sandstone siltstone-sandstone grade grade upward upward into into aa thin thin siltstone—shale siltstone-shale at at the the top of the metasedimentary sequence. sequence. Deformation Deformation and and metamorphism metamorphism occurred occurred concomitant concomitant with with development development of of major batholithic terrains terrains north north and south south of of the the supracrustal supracrustal belt. belt. Linear Linear to arcuate tectonic zones, zones, from 50 m to 100 100 m thick, thick, form form boundaries boundaries which which divide divide the supracrustal supracrustal belt into into aa series series of of blocks. blocks. Within these these tectonic tectonic Typically one zones zones both ductile ductile and brittle brittle features features are are abundant. abundant. Typically one to to meter thick shear zones occur at irregular seven meter irregular spacing, spacing, becoming becoming more more abundant abundant as as the the boundary boundary is is approached. approached. The rock rock between between the the shears shears ranges ranges from slightly deformed to completely transposed into into the the shear shear direction direction in in metathe boundary zone. zone. In these areas early mafic volcanic rocks rocks and and late late meta— sedimentary rocks rocks may be be tectonically tectonically interlayered. interlayered. Within Within the the blocks blocks original stratigraphic stratigraphic relationships relationships are are retained. retained. However, However, the the degree degree of of deformation and the grade of metamorphism varies from deformation from block block to to block. block. 18 �U - . GEOCHEMICAL CONSTRAINTSO NONTHE THEREE REEDDISTRIBUTION GEOCHEMICAL CONSTRAINTS I S T R I B U T I O N IN [N THE THE NEGAUNEE AT THE NEGAUNEE IRON I RON FORMATION FORM A T I ON AT THE EMPIRE EMPI RE MINE, M I ME, PALMER, PALMER, MICHIGAN M I CH I (?AN Susan Susan S. E. Crissman Cr- is'smari Department D e p a r t m e n t of raf Geological Geol a q i c a l Sciences, S c i e n c e s , Michigan M i c h i qan Stat State - 'm . - University U r i i vor?!:i fcy East Lansing, I 48824 East L a n s i n g , PI:[ 49824 I The The approximately approximately 2. 1 Ga 2.1 Ga old old Neqaunee Meqauriee Iron I r o n Formation F o r m a t i o n at at the the Empire Michigan Empire-? Mine M i n e near n e a r Palmer, Palmer, M i c h i g a n provides p r - a v i d o s an .an ex cel:lent, cili2eil: •cziient, albeit complex, of rock types to investiqate the elemental campl e x 7 spectrum spectrum of rock types to i n v e s t i g a t e the elemental distribution distribution and t y p i c a l Superior'-t:yp Superior--fcypo and (nineraloqical m i n e r a l ( ~ g i c a 1 variations variations o-f aa typical of This iron 1i m b of t t 7 a i r o n formation, 'formation. Thiia orebody o r e b o d y is i s located l o c a t e d on on the the s o u t h a a s t 1i(Th Marquette sync and sm is (eh Mi'arquotte s y n c11 i nnor o r iium u r n,, and metamarphi motamorpliiwn i5 minimal minimal c h , Ior . o ri ito ko facies).  ¥ f a d e s ) It I t precipitated p r e c i p i t a t e d dominantly dominantly a s a chert-siderite, c h e r t - s i d e r i t e , and and ehowo shows as extensive The alterations e x t e n s i v e replacement. replacement. The major m a j o r diagenetic diaqenetic a1 tor at ion:^ are r-;\re chert c h e r t to ta magnetite, and With magnetite, and siderite s i d e r i t e to t o magnetite m a g n e t i t e and and ankerite anherite, W it h postmetamorphic oxidation, magnetite post-metamorphic oxidation, magnetite2 was was replaced r e p l a c e d by b y martite, m a r t i t e , and and the t h e carbonates c a r b o n a t e s altered a l t e r e d to t o hematite h e m a t i t e or o r goethite. qoethite. The objective this investigation is the th a The a b j a c t i v e of of this investigation i s to t o evaluate ovalui-aka crystallochemical/environmental affecting controls the PEE crystallochemical/anvironmental controls a f f e c t i nq t h fc-a distribution in these pr-ecipitates.. distribution i n t h e s e low l o w temperature t e m p e r a t u r e chemical chemical p r - e c i p i kat(:-;s. Forty—five drill core Forty-five drill c o r e samples samples ffrom r o m the the* Empire E m p i r e Mine M i n e are are; b:i.nc:; beinq examined. They represent examined. r e p r a < 3 ~ ~five f ri ~v te facies f a c i e s distinguished d i a t i n q u i shed according i ~ ~ ~ ~ r to -to d the it h~e i q major mineral assemblaqe: chert, carbonates, ma j a r mineral chert, c a r b o n a t e ' s , maqnetite m a q n o t i te rich r ic h ore, ore, Siamo and interbeds. It is Siamo slate, slate, and clastic clastic interbeds, It i s anticipated i ~ r i t i c i p a t e d that that correlations reflect, c o r r e l a t i o n s of o? the t h e trace t r a c e elements e l e m e n t s with w i t h mineralogy f n i n e r a l a q y will w i l l r e " f 1 a c t the the influence i n f l u e n c e of a? partitioning p a r t i t i o n i n g coefficients c o e f f i c i e n t s on an the t h e REE REE distribution. distritautian, Seyeral significant correlations between trace! Several significant c o r r e l a t i o n s exist exist b e t w e e n the t h e trace elements, major The is elements, m a j o r oxides, o x i d e s , and and mineralogy. mineralogy. The LREE/HREE LREE/HREE ratio ratio i s highly h i g h l y antipathetic a n t i p a t h e t i c to t o siderite, s i d e r i t e , MqO, MqO, MnO MnO and and 002; C02; less l a s s so 'so with w i t h CaD. Can. The The correlation c o r r e l a t i o n with w i t h siderite s i d e r i t e agrees a g r e e s with w i t h what is i s expected w : p s c t e d based b a s e d on on crystallographic 1980). c r y s t a l l o g r a p h i c controls c o n t r o l s (Morgan (Morgan & Wandless, Wandless, 1980). T h e r e is is aa high high There positive REE with w i t h Ti02 T i 0 2 and and A1203. A1203, ' T h i s c:an can be p o s i t i v e correlation c o r r e l a t i o n of o-f the t h e REE This be interpreted i n t e r p r e t e d to t o mean that t h a t the t h e lanthanides l a n t h a n i d e s were were adsorbed a d s o r b e d onto o n t o detrital dstrital minerals, which m i n e r a l s , such such as as chlorite, chlorite, w h i c h were w e r e deposited d e p o s i t e d with w i t h the the chemical chemical precipitates. Europium Fe3+ ~ ~ 3 . 4and and . precipitates. E u r o p i u m correlates c o r r e l a t e s negatively negatively with with positively p o s i t i v e l y with w i t h Fe2+ Fez+ (e.g., (a.g., siderite). siderite). T h i s is i 5 consistant c a r i s i - i i t a n t with with bl-ii,:.? This h:? reducing proposed r e d u c i n g conditions conditions p r o p o s e d for ? o r the t h e precipitation p r e c i p i t a t i o n of of primary primary siderite, the s i d e r i t e , and and argues a r g u e s for for t h e presence p r e s e n c e of o f Eu2+ Eu2+ in i n the t h o basin b a s i n water. water. It It was w a s expected e x p e c t e d that t h a t the t h e diaqenetically d i a q e n e t i c a l l y enriched e n r i c h e d maqnetite m a q n e t i t e would w o u l d have h a v e aa negative n e g a t i v e correlation c o r r e l a t i o n with w i t h the t h e LREE/HREE LREE/HREE ratio r a t i o because b e c a u s e the t h e stability stability of complexes o f HREE'-carhonate HREE-carbonate compl e x e s exceeds e x c e e d s that t h a t of oS LREE—carhonate LREE-carbonate complexes compl e x e ~ s in iron'-transportinq (Graf, in i r - a n - t r a n s p o r t i n g ssolutions olutions (Graf, 1'984). 'The apparent a p p a r e n t LPEE LREE 1984). The enrichment in interpreted enrichment i n magnetite m a g n e t i t e is i s i n t e r p r e t e d to to t h a t the t h e HREE, 1-IREE, iiff mean that m o b i l i z e d during d u r i n g diagenesis, d i a g e n e s i a , were w e n s not n o t deposited d e p o s i t e d with w i t h the t h o iron. iron. mobilized Morgan, Morgan, J.W. J.W. distribution distribution soutast and and in i n 04: t Wandless, G.A., 19QO, R a r e earth earth el ctnent Wandless, G.A., 1990, Rare cioment some h y d r o t h e r m a l minerals: m i n e r a l '5: ovidorico far some hydrothermal evidence fr v o l " 4 4 , p.973-9S0. p . 9'73--980. c r y s t a l l o g r a p h i c control. c o n t r o l . Geochim. Geochim. Cosmochim., Cosmochim. , vol.44, crystallographic LL. Jr., 1984, valley—type J.L. Jr., 1*?Q4, Effects E f ? o c t s of of Mississippi Mississippi v a l Ilay-type mineral m i n o r ail izati ~ a t ion o non on REE REE patterns p a t t e r n s of a+ carbonate carbonate;! rocks r o c k s and and minerals minerals, Viburnum southeast Missouri. Viburnum trend, trend, southeast Missouri. Jour. t3oa.L s y vai.92, Jour. Geol. vol.92, p 3(:)7-324. p. 307-324. (3ra+ Bra+ . 19 �U Evolution E v o l u t i o n of o f an anArchean Archean igneous igneous complex complex ffrom r o m hhigh i g h precision p r e c i s i o n U-Pb U-Pb geochronology: N. W . Ontario. Ontario. geochronol ogy: tthe h e Kakagi Kakagi Lake Lake aarea, r e a , N.W. D.W.DDavis, Departmento of Geology,UUniversity D.W. a v i s , Department f Geology, n i v e r s i t y ooff Toronto, Toronto, Toronto, T o r o n t o , Ontario, O n t a r i o ,M5S M5S1A1 1A1 G.R. Departmentooff Earth G.R. Edwards, Edwards, Department E a r t h and and Atmospheric Atmospheric Science, Science, York York University, U n i v e r s i t y , 4700 4700 Keele K e e l e Street, S t r e e t ,Downsview, Downsview, Ontario, O n t a r i o ,M3J M3J 1P3 1P3 High on 10 Archean H i g h precision p r e c i s i o n U-Pb U-Pb ages ages determined d e t e r m i n e d on 10 rocks r o c k s from from the t h e Archean complex surrounding the Kakagi Lake area give a detailed c o m ~ l e xs u r r o u n d i n g t h e Kakagi Lake a r e a g i v e a d e t a i l e d ppicture i c t u r e of of igneous igneous eevolution, v o l u t i o n , ddefining e f i n i n g aa time t i m e span span oof f aatt least l e a s t 32 32 Ma Ma ffor or Ma The eearliest a r l i e s t age age is i s 2731.7 2731.7 ÷ 4.0 Ma developmentooff the development t h e complex. complex. The - 2.9 ffrom r o m aanalysis n a l y s i s ooff zircon z i r c o n and and baddeleyite b a d d e l e y i t e iin n aa gabbro gabbro iintruding n t r u d i n g the the This Katimiagamak Katimiagamak Group. Group. T h i s is i s the t h e oldest o l d e s tknown known unit u n i t in i nthe t h ecomplex complex and rrepresents ane pepisode and e p r e s e n t s an i s o d e o fofh ihigh g h i riron o n t tholeiitic h o l e i i t i cvolcanism. v o l c a n i s m . AA sslightly l i g h t l yyounger y o u n g e r age age of o f 2727.7 2727.7 ±Â 1.1 1.1Ma Ma from from a a dacite d a c i t e in i nthe t h eDash Dash Lake aarea Lake r e a pprobably r o b a b l y r represents e p r e s e n t s t hthe e bbeginning e g i n n i n g oof f ffelsic e l s i cvolcanism volcanism age ooff 2723.2 Maon onaa ttonalite An age 2723.2 ± 11.8 . 8 Ma o n a l i t e gneiss gneiss in i n the t h ecomplex. complex. An from the interior of the Sabaskong Batholith is indistinguishable f r o m t h e i n t e r i o r o f t h e Sabaskong B a t h o l i t h i s i n d i s t i n g u i s h a b l e Ma) from phaseo of f r o m tthe h e age age ooff a a massive massive bborder o r d e r phase f t the h e bbatholith a t h 0 1 it h (2724.4 (2724.4 Ma) and showsnonoe vevidence an oolder and shows i d e n c e o fofi ninheritance h e r i t a n c e ffrom r o m an l d e r sialic s i a l i component: c component. A phaseoof Kakagis sill A pegmatite p e g m a t i t e phase f tthe h e lowermost lowermost Kakagi i l l was was dated d a t e d at at Ma, wwhich maybebeo only 2724.8 2 - 5 Ma, h i c h may n l y sslightly l i g h t l y younger y o u n g e r than t h a n the t h e age age - 2.3 ooff intermediate i n t e r m e d i a t e volcanism v o l c a n i s m in i nthe t h eKakagi KakagiLake LakeGroup. Group. This T h i s iis s similar similar to t o the t h e age age of o fthe t h eSabaskong Sabaskong Batholith B a t h o l i t hand anddemonstrates demonstrates simultaneous simultaneous mafic m a f i c and and ffelsic e l s i c plutonism p l u t o n i s m as as well w e l l as as approximate a p p r o x i m a t e ssimultaneity i m u l t a n e i t y of of tonalitic t o n a l it i cplutonism p l u t o n i smini the n t hSabaskong e Sabaskong Batholith Bath01 it h and and intermediate intermediate vvolcanism o l c a n i s m in i n the t h eKakagi Kakagi Lake Lake Group. Group. Ma f from An age age ooff 2711.1 r o m aa ddacite a c i t e occurring o c c u r r i n g above above the the An 2711.1 ÷ 1 - 3 Ma ' 1-8 ' '- 1.L Kakagi Lake Group Groupshows showsa a13 13Ma Mat i time gapi in developmentofof the Kakagi Lake m e gap n development the ageoof oneoof volcanic phases The age f one f tthe h e ooldest l d e s t tonalitic t o n a l i t i cphases v o l c a n i c ppile. i l e . The Ma, Ma, wwhile h i l e tthe h e llatest atest of the of t h e Aulneau Aulneau BBatholith a t h o l i t h is i s2716.8 2716.8 g r a n o d i o r i t e phase phase is i s dated d a t e d at a t2709.6 2709.6 +t 3.9 3.3 Ma. Ma. T h i s shows shows granodiorite This 1.5 -— 1.5 that t h a t the t h e bulk b u l k of ofthe t h eAulneau Aulneau Batholith B a t h o l i t hwas was probably p r o b a b l y intruded i n t r u d e d over over a Maand andi nindicates a time t i m e span span ooff about about 77 Ma d i c a t e s t that h a t felsic f e l s i cvolcanism v o l c a n i sm above KakagiLake Lake Group t e p lplutonic u t o n i c aactivity ctivi t y above t hthe e Kakagi Group i s is c o ecoeval v a l w i twith h 1a late iinn the t h e Aulneau Aulneau BBatholith. atholith. The between The cconformable o n f o r m a b l e r erelationship 1 a t i o n s h i p between a1 all 1 oof f tthe h e vvolcanic o l c a n i c units uni t s showst hthat wasa ar erelatively shows a t rregional e g i o n a l ddeformation e f o r m a t i o n was l a t i v e l y late l a t eevent e v e n t and and nnot o t due due tto o iintrusion n t r u s i o n of o f the t h e large l a r g e batholiths, b a t h o l i t h s ,which w h i c h occurred occurred The end endoof dduring u r i n g volcanism. v o l c a n i s m . The f rregional e g i o n a l deformation d e f o r m a t i o n iinn the t h e area area g i v e n by b y the t h e ages ages ooff two two late l a t e tectonic t e c t o n i cplutons, p l u t o n s ,the t h eHeronry Heronry is i s given Lake Lake sstock, 1.2Ma Ma Lake sstock t o c k and and the t h e Stephen Stephen Lake t o c k , dated d a t e d at a t 2701.0 2701.0 ±z 1.2 and 2699.2 2699.2± 1.9 1.9 Ma, Ma, rrespectively. espectively. and g-9 �U Ii U-Pbaanalyses sphenei ninf ofour U-Pb n a l y s e s o of f sphene u r oof f the t h e samples samples i indicates n d i c a t e s variable variable age iiss from amountso of amounts f rresetting. e s e t t i n g . The The ooldest l d e s t sphene sphene age f r o m the t h eHeronry H e r o n r y Lake Lake agei is from the the  1.6 1.6 Ma), Ma), whereas whereas the t h e youngest y o u n g e s t sphene sphene age s from sstock t o c k (2699,2 (2699.2 ± Sabaskong (2673.7 ±6.6 6.6Ma), Ma),t the samplemost mosts strongly Sabaskong g ngneiss e i s s (2673.7 h e sample t r o n g l y aaffected ffected by by diapirism. diapirism. The duet oto ddiapiric The ddata a t a ssuggest u g g e s t t hthat a t rregional e g i o n a l deformation d e f o r m a t i o n ooccurred c c u r r e d due iapiric The ccentres of tthis rremobilization e m o b i l i z a t i o n ofof sslightly l i g h t l y older o l d e r batholiths. b a t h o l i t h s . The e n t r e s of his two of rremobilization e m o b i l i z a t i o n are a r e likely l i k e l ytot be o be twogneiss g n e i s sdomes domes near n e a r the t h e mouth mouth of Theseappear appeart otohave havebeen beenareas areas Sabaskong o fofr erelatively latively Sabaskong Bay. Bay. These llong-lived o n g - 1 i v e d heat h e a t flow f l o w as asindicated i n d i c a t e dbyb ythe t h younger e y o u n g e rsphene sphene ages. ages. 21 �ANOMALOUSRADIOMETRIC RADIOMETRICAGES AGESFROM FROMTHE THESUPERIOR SUPERIORPROVINCE, PROVINCE, ONTARIO: ANOMALOUS SENSE? NON-SENSE? SENSE? or o r NON-SENSE? R.M. Easton R.M. Easton PrecambrianSection, Section,OOntario Geological Survey, 77 77 G Grenville Precambrian ntario G e o l o g i c a l Survey, renville 1B3 Street, M5S S t r e e t , Toronto, Toronto, Ontario O n t a r i o M5S 1B3 Precise U-Pbzzircon agesoobtained P r e c i s e U-Pb i r c o n ages b t a i n e d oover v e r tthe h e llast a s t 55years y e a r s by byT.E. T.E. Krogh Kroghand and co-workers have pprovided co-workers at a t the t h eRoyal Royal Ontario O n t a r i oMuseum Museum have r o v i d e d aa chronologic c h r o n o l o g i c frameframe- work work ffor o r examining examining t the h e eevolution v o l u t i o n ooff individual i n d i v i d u a lgreenstone greenstone belts b e l t s and and the the sub-provincesooff tthe al. (1984) sub-provinces h e Superior S u p e r i o r Province P r o v i n c e iinn Ontario. O n t a r i o . Krogh Krogh eet t a1. (1984) summarizet hthe summarize e r eresults s u l t s oof f tthis h i s work. work. IIn n this t h i s paper, paper, the t h e significance s i g n i f i c a n c e of of anomalously youngand ando old Rb-Sr, KK-Ar andAAr-Ar age ddeterminations - A r and r - A r age e t e r m i n a t i o n s from from the the anomalously young l d Rb-Sr, Superior Provincei is assessedi nin1ilight S u p e r i o r Province s assessed g h t ooff the t h e work work of o f Krogh Krogh eett al. a1. (1984) (1984) and aa rrecent of geochronologic and e c e n t ccompilation o m p i l a t i o n of geochronologic ddata a t a ffor o r Ontario O n t a r i o (Easton, (Easton, 1985a). 1985a). In cases,i tit i is I n some some cases, s now now ppossible o s s i b l e t otoi ninterpret t e r p r e t tthe h e ssignificance i g n i f i c a n c e ooff radioradiometric m e t r i c ages ages hitherto h i t h e r t oregarded regarded as as curiosities. curiosities. IIn n the t h e Superior S u p e r i o r Province, Province, Rb-Sr, K-Ar 100 tto younger tthan Rb-Sr, K-Ar and and Ar-Ar A r - A r ages ages are a r e commonly commonly 100 o 150 150 Ma Ma younger h a n ccorresorrespondingU-Pb U-Pbz izircon ages;a ac hcharacteristic e.g. the ponding r c o n ages; a r a c t e r i s t i c ooff other o t h e r orogens, orogens, e.g. the Archean Slave P Province Orogen (Bear (Bear PProvince). Archean Slave r o v i n c e and and the t h e Proterozoic P r o t e r o z o i cWopmay Wopmay Orogen rovince) . Anomalous ages those 50Ma Mayounger younger Anomalous ages a r are e those t hthat a t a are r e >>50 o roro lolder d e r t hthan a n t hthe e ttypical ypical 2500 tto Maages ageso obtained by~b-Sr, Rb-Sr,K-Ar K-Ar and andAAr-Ar methodsf ofor Superior 2500 o 2600 2600 Ma b t a i n e d by r - A r methods r S uperior Superior Province anomalous ages Province Province rocks. rocks. S uperior P r o v i n c e anomalous ages f a fall l l i into n t o three t h r e e categories: categories: 1) ageswhich whiche xexhibit 1 ) Reset Reset ages h i b i t ddistinct i s t i n c t associations a s s o c i a t i o n s or o r trends. t r e n d s . These These include: include: a) boundaries,p particularly r e s e t ages ages present p r e s e n t along a l o n g subprovince subprovince boundaries, a r t i c u l a r l y K-Ar K-Ar a ) reset iisotopic s o t o p i c systems. systems. b) b ) reset r e s e tages ages near near province p r o v i n c eboundaries, boundaries, including i n c l u d i n both g b o tRb—Sr h Rb-Sr and and Ar Ar ages (e.g. resetting ages (e.g. r e s e t t i n gofofSuperior S u p e r i oand r andSouthern SouthernProvince P r o v i n c eages ages along a l o n g the the Resetting up ttoo 100 Grenville e s e t t i n g may may ooccur c c u r up 100 km km from f r o m the t h e boundary. boundary. G r e n v i l l e Front). Front). R 1800-1850 Structural t h ca. e ca. 1800-1850Ma MaKenyon Kenyon S tructural cc)) zones zones of o f reset r e s e tages, ages, e.g. e.g. the Zone Sachigo Subprovince. Subprovince. Zone iinn the t h e Sachigo d) agesaassociated d ) excess excess AAr r ages s s o c i a t e d wwith i t h f faulting a u l t i n g or o r major m a j o r geological geological sstructures, t r u c t u r e s , e.g. e.g. the t h eKapuskasing Kapuskasing Structural S t r u c t u r a l Zone. Zone. cases, tthe 2) Isolated r e s e t t i ngisi commonly I n many many cases, h e cause cause ooff the t h e resetting s commonly 2) I s 0 1a t e d reset r e s e tages. ages. In a recognized time a local l o c a l geologic g e o l o g i c ffeature e a t u r e tthat h a t was was nnot o t recognized a tatt hthe e tim e of ofi ninitial itial This K - A rages ages determined determined in in h i s situation s i t u a t i o napplies a p p l i e stot omany many of o fthe t h eK-Ar sampling. T tthe h e late l a t e 1950's, 19504s, early e a r l y 1960's. 1960's. 3) 3 ) Possible P o s s i b l e primary p r i m a r y ages ages that t h a t are a r eassociated a s s o c i a t e d with w i t hmagmatic magmatic events. events. These include: in c l ude : aa)) ages ages ooff carbonatite c a r b o n a t i t e complexes complexes wwithin i t h i n the t h e Superior S u p e r i o r Province, Province, which which correspond tto correspond o the t h e time t i m e ofo fmajor m a j o rmagmatic, magmatic, volcanic v o l c a n i cand andmetamorphic metamorphic events events in i n the t h e mid-continent m i d - c o n t i n e n t region r e g i o n of o f North N o r t h America, America, or o r major m a j o r structural s t r u c t u r a l zones, zones, or o r both b o t h (Figure ( F i g u r e 1). 1). whicha rare bb)) ages ages oof f iisolated s o l a t e d pplutonic l u t o n i c bodies bodies which e l olocally c a l l y nnot o t ssignificant, ignificant, but showr eregional b u t which which show g i o n a l ttrends r e n d s ((Figure F i g u r e 1). 1). Ages Ages wwithin i t h i n t hthe e f first i r s t and and third t h i r d category c a t e g o r y are a r e particularly p a r t i c u l a r l ynoteworthy, noteworthy, in in that agesc cluster t h a t the t h e observed observed ages l u s t e r aat t intervals i n t e r v a l s which which correlate c o r r e l a t e with w i t hchronologic chronologic tterranes e r r a n e s recognized recognized eelsewhere l sewhere i in n North N o r t h America America ((Figure F i g u r e 1). 1 ) . Although A1 though not not directly d i r e c t l y affected a f f e c t e dby bythese these events, events, the t h e Superior S u p e r i o r Province P r o v i n c e locally l o c a l l yprovides provides T h i s should s h o u l d be be considered considered aa record r e c o r d of of North N o r t hAmerican American magmatic magmatic episodes. episodes. This when when i ninterpreting t e r p r e t i n g future f u t u r e geochronologic geochronologic data data from from the t h e region. region. Easton, R.M., 1985a, GeochronologyCCompilation Easton, R.M., 1985a, Geochronology o m p i l a t i o n f ofor r OOntario; n t a r i o ; Ontario O n t a r i o GeolGeological o g i c a l Survey Survey Open Open FFile i l e Report Report and and 66 Preliminary P r e l i m i n a r yMaps. Maps. Easton, R.M., 1985b, 1985b,DDistribution Easton, R.M., i s t r i b u t i o n oof f chronologic c h r o n o l o g i c tterranes e r r a n e s iin n the t h e Grenville Grenville 22 �U Province, Eastern EasternNorth NorthAmerica; America; Geol. Geol. Assoc, Assoc. Can. Can. Abstracts, Abstracts, v.v. 10. 10. Province, F., 1984, Implications of precise U-Pb Krogh, T.E., Davis, D.H., and Corfu, F., 1984, I m p l i c a t i o n s o f p r e c i s e U-Pb Krogh, T.E., Davis, D.W., and Corfu, of the Superior Province; Geol. d a t i n g f o r t h e geological e v o l u t i o n o f t h e Superior Province; Geol dating for the geological evolution Assoc. Can. Can. Abstracts, 9, p.p. 79. 79. Assoc. Abstracts, v. v. 9, Van Schmus, M.R. and Bickford, M.E., 1981. Proterozoic P r o t e r o z o i cchronology chronologyand and ME., 1981. Van Schmus, W.R. and Bickford, A. Kroner, North America; in A. Kroner. e v o l u t i o n o f t h e mid-continent region, North America; i n evolution of the mid-continent region, , PrecambrianPlate P l a t eTectonics, Tectonics, Elsevier, El s e v i e r ,p.p.261-296. 261-296. e d i t . Precambrian edit., . based anomalous Figure 1: 1:Chronologic Chronologic history h i s t o r y of of the t h e Superior SuperiorProvince Province basedonon anomalous Figure K - A r and andRb-Sr Rb-Sr ages ages compared compared w i t h other o t h e r North NorthAmerican American data. data. K-Ar with AGE AGE Mo ininMo 10001000— I200 I 200 - 1400 1400 - 1600 1600 1800 800 2000 2000 - - - 2200 2200 2400 2400 2600 2600 - L^ 1 - typical R b - S r , re-setting /meto.event event re—sefting/meta. mogmotic event event mogmatic *'bused U-Pb Pbzircon zirconages ages based onon U- 23 I �U The Significance of Strain The Strain Patterns Patterns in in Deciphering Deciphering the Deformational History of Archean ~ r c h e a nRocks - ~eformatizal Vermilion ~District, Minnesota in the Vermilion i s t r i z ,Minnesota by Dan Ela and Peter Peter Hudleston Hudleston Department of Geology & Geophysics, University of of Minnesota Minneapolis, 55455 Minneapolis, MN 55455 The Vermilion district of of northern northern Minnesota Minnesota comprises comprises an an E—W E-W trending trending belt belt of multiply deformed sedimentary and volcanic rocks rocks of of Archean Archean age. age. The The district is separated from from the the higher—grade higher-grade rocks rocks of of the the Vermilion Vermilion Granitic Granitic Complex to to the the north north by by the the Vermilion Vermilion fault, fault, which which has has aa large large component component of of dextral strike—slip strike-slip movement. movement. An early nappe—forming nappe-forming event event was was followed followed by by aa second phase of deformation deformation which produced produced all all of of the the measured measured strain, strain, cleavage, cleavage, measurements in the lower—grade and lineations. lineations. Strain measurements lower-grade sedimentary sedimentary rocks rocks reveal reveal a complex pattern of deformation, deformation, which can can be be used used to to infer infer the the tectonic tectonic history of of the the belt. belt. The Magnitude and and symmetry symmetry of of strain strain in in the the rocks rocks varies varies in in parallel parallel bands. bands. The symmetry of the the strain strain varies from from constrictional constrictional to to flattening flattening in in ENE—trending ENE-trending bands which tend tend to to be lensoid lensoid in in map view, view, and and which which are are oblique oblique to to the the trace trace of the the ESE—trending ESE-trending Vermilion Vermilion fault. fault. The largest measured strains strains consistently consistently occur near the the Vermilion Vermilion fault. fault. Flattening strains strains also also predominate predominate adjacent adjacent to to the fault, then change symmetry several times times to to finally finally become become homogeneous homogeneous in in symmetry (constrictional), (constrictional), orientation, orientation, and and magnitude in in the the southern southern part part of of the district. district. The maximum extension of all samples showing constrictional extension directions directions (x) ( X ) of strain, plunge east at at angles angles between between 30 30 and and 65°. 65'. X in samples showing showing flatflattening strain plunges east or west, but near the the Vermilion fault fault all all plunges plunges are are west or more steeply east than than they they are are in in constrictional constrictional samples. samples. The maximum ( Z ) plunges plunges consistently less than 25° 25O to to the the north north or or shortening direction (z) south. south. A number of features in the the rocks indicate indicate aa large large component component of of dextral dextral simple shear in in the the deformation deformation history. history. The significance significance of of the the strain strain patterns patterns is is not not clear. clear. The alternating constrictional and flattening flattening zones zones preclude preclude their their origin origin by by homogeneous homogeneous coaxial coaxial strain or progressive simple simple shear. shear. These strain strain variations also also require require aa The model which can satisfy satisfy compatibility compatibility constraints constraints and and space space considerations. considerations. The area of consistent constrictional constrictional strains strains in in the the south south may may represent represent one one regional component of of the the strain. strain. Spatial correspondence of the the flattening flattening strains with the Vermilion fault fault suggests that that aa simple simple shear shear component component was was modified model of transpression added in in that that area. area. A modified transpression may explain explain how how H— Eby a concomitant inhomoge— plunging X axes are are reoriented reoriented to to become become W—pluriging W-plunging by inhomogeneous progressive Less progressive simple simple shear shear which which is is clearly clearly shown shown in in the the rock rock fabrics. fabrics. Less than vertical plunge of the some component component of of oblique oblique the X axes may necessitate some motion on on the the fault. fault. A second zone of flattening flattening strain strain may have have formed formed in in aa strain field which is reflected in in a smaller smaller dextral dextral strike—slip strike-slip fault, fault, or or it it may reflect reflect strain strain accommodation accommodation around around the the more more competent competent greenstone greenstone and and iron— ironformation coring the major anticlinal anticlinal structure structure in in the the area. area. 24 �U The The relatively relatively homogeneous homogeneous deformation deformation in in the the constrictional constrictional zones zones surrounded surrounded by by more more highly highly sheared sheared and and flattened flattened zones zones suggests suggests aa large—scale large-scale ana— analogue of of the the fabric fabric of of mylonite mylonite zones. zones. The The anastomosing anastomosing geometry geometry of of such such zones zones logue serves to to satisfy satisfy compatibility compatibility conditions conditions and and room room problems. problems. Such Such patterns patterns serves have have been been modelled modelled theoretically theoretically and and require require similar similar anastomosing anastomosing behavior behaviorinin the third third dimension dimension to to explain explain the the juxtaposed juxtaposed variations variations in in strain strain magnitude magnitude and and the symmetry. Similar Similar variations variations in in strain strain have have been been predicted predicted in in simple simple shear shear symmetry. 'b' direction direction to to give give an an overall overall flattening flattening regimes, with with extension extension in in the the 'b' regimes, strain. Perturbations Perturbations of of the the shear shear produce produce local local zones zones of of constrictional constrictional strain strain strain. at an an angle angle to to the the shear shear plane plane consistent consistent with with the the angle angle that that the the boundaries boundaries of of at zones zones of of constrictional constrictional and and flattening flattening strain strain in in the the Vermilion Vermilion district district make make with the the Vermilion Vermilion fault. fault. with In In aa general general way way the the strain strain patterns patterns observed observed in in the the Vermilion Vermilion district district can can be reasonably reasonably explained explained by by aa history history of ofN—S N-S shortening shorteningaccompanied accompaniedbybyinhornoge— inhomogebe neous dextral dextral simple simple shear shear which found found its its last last expression expression as as the the Vermilion neous fault. The The variations variations of of strain strain may may be be aa consequence consequence of of variations variations in in the the fault. relative relative intensities intensities of of shortening shortening and and shear, shear, large large perturbations perturbations of of the the shear) shear. or the the influences influences of of other other structures. structures. or 25 — �U in the the Keweenawan Keweenawan i\orth North Shore Large Large Igniinbrites Ignimbrites in Shore Volcanic Volcanic Group Group in in Cook Cook County, County, Minnesota Minnesota Thomas Thomas Fitz Fitz (Dept. (Dept. of of Geology, Geology, University University of of Minnesota—Duluth, Hinnesota-Duluth,Duluth, Duluth, MN 55812) MN 55812) Dr. Dr. John John C. C. Green Green (Dept. (Dept. of of Geology, Geology, University University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812) 55812) Two Two thick thick and extensive extensive volcanic units units were studied in in the the North horth Shore Shore Volcanic Volcanic Group Group in in south—central south-central Cook Cook County, County, Minnesota. Minnesota. The The Kimball Kirnball Creek Creek quartz quartz latite latite is is 335 335 mm thick, thick, strikes strikes approximately approximately east—west, east-west, dips dips 10 10 degrees degrees south south and and can can be be traced traced 29 29 km krn along along strike strikebut but is is truncated truncated by by Lake Lake Superior Superior north—east north-east of of Grand Grand Marais. Marais. It It can can be be subdivided subdivided into into two two subunits subunits based based on on the the percentage percentage of of plagioclase plagioclase phenocrysts, phenocrysts, the the lower lower unit unit being being the the more more highly highly porphyritic. porphyritic. This This is is overlain overlain by approximately approximately 245 m of ophitic olivine olivine basalt flows flows of of the the Red Red Cliff Basalts (Green, 1972) and the 225 m thick Devil Track rhyolite. Cliff Basalts (Green, 1972) and the 225 m thick Devil Track rhyolite. The The Devil Devil Track Track rhyolite rhyolite can can be be traced traced 35 35 km km along along strike strike from from near near the the western end of Pike Lake eastward to the shore of Lake Superior western end of Pike Lake to the shore of Lake Superior where where it it too too extends extends an an unknown unknown distance distance under under the the lake. lake. Depending Depending on on assumptions assumptions as as to its its original original extent, extent, this unit appears to contain between 160 160 and 500 500 cu. cu. km km of of rhyolite. rhyolite. Closely Closely spaced spaced vertical vertical and and horizontal horizontal joints joints cause cause the the rocks rocks to to be be easily easily eroded eroded resulting resulting in in poor poor exposure exposure and and concealed concealed contacts. contacts. Texturally Texturally the the rocks rocks are are aphanitic, aphanitic, holocrystalline holocrystalline and and largely largely lack lack devitrification devitrification features. features. No No pyroclastic pyroclastic textures textures have have been been found. found. The The rocks rocks are are dominated by anhedral anhedral orthoclase orthoclase and platy, platy, randomly randomly oriented quartz quartz crystals crystals that that were were originally originally tridymite. tridymite. Tabular, Tabular, 1—2 1-2 mm rnm quartz quartz crystals, crystals, also also pseudomorphs pseudomorphs after after tridymite, tridymite, are are present in in some some small small cavities. There There are are some some oxidized oxidized pseudomorphs pseudomorphs of of clinopyroxene clinopyroxene but but cavities. blocky, blocky, subhedral subhedral magnetite magnetite is is the the dominant dominant primary primary mafic mafic mineral. mineral. It It is is partially partially weathered weathered to to hematite hematite giving giving the the rocks rocks their their red red color. color. The The lack lack of of flow flow banding banding and and vesicles, vesicles, the the very very large large volumes volumes and and aspect aspect ratios ratios (length/thickness) (length/thickness) of of 90 90 and and 160 160 for for the the Kimball Kimball Creek Creek and and Devil Track units respectively, suggest an origin by pyroclastic flows rather rather than than lava lava flows flows (Walker, (Walker, 1973). 1973). The The interpretation interpretation of of these these units units is that they were deposited by large, hot pyroclastic flows that deposited by large, hot pyroclastic flows that crystallized after emplacement similar similar to the rhyolitic tuffs tuffs of the San Juan region of of Colorado Colorado (Lipman, (Lipman, 1975a). 1975a). The The crystallization crystallization of of tridymite tridymite and orthoclase orthoclase destroyed destroyed any any pyroclastic pyroclastic textures. textures. The The tridymite tridymite subsequently subsequently inverted inverted to to quartz quartz during during burial. burial. Green, Green, John, John, C., C., 1972, 1972, North North Shore Shore Volcanic Volcanic Group. Group. In In Sims, Sims, P.K. P.K. and Morey, G.B. G.B. eds. eds. Geology Geology of of Minnesota: Minnesota: A Centennial Centennial Volume. Volume. Morey, Minnesota Minnesota Geological Geological Survey. Survey. Lipman, Lipman, P.W., P.W., 1975a, 1975a, Evolution Evolution of the Platoro Platoro caldera caldera complex complex and related volcanic volcanic rocks, rocks, Southeastern Southeastern San San Juan Juan Mountains, Mountains, Colorado: Colorado: U.S. U.S. Survey Prof. Prof. Paper Paper 852, 852, 128 128 p. p. Geol. Survey Walker, R. Soc. Soc. Land. Lond. A. A. Walker, G.P.L., G.P.L., 1973, 1973, Lengths Lengths of of lava lava flows. flows. Phil. Phil. Trans. Trans. 8. 274, 107—118. 107-118. 274, 26 �U CONTROLS ON THE GENESIS GENESIS OF OF EPIGENETIC EPIGENETICAURIFEROUS AURIFEROUS CONTROLS ON THE V E I N SYSTEMS SYSTEMS IN I NARCHEAN ARCHEAN CHEMICAL—SILICICLASTIC CHEMICAL-SILICICLASTIC SUBMARINE SUBMARINE VEIN FAN FAN DEPOSITS, DEPOSITS, GERALDTON GERALDTON AREA, AREA, ONTARIO ONTARIO andScott, S c o t tBrian, , B r i a nM. , M.Department Department F r a l i c k , Philip, P h i l i pW. , W.and Fralick, of University, o f Geology, Geology, Lakehead Lakehead U n i v e r s i t y , Thunder Thunder Bay, Bay, Ontario, O n t a r i o ,P7B P7B5El 5E1 In 1 9 2 0 ' s and and 30's 3 0 ' s aanumber number of o f occurrences occurrences of o f gold g o l d bearing bearing I n the t h e 1920's q u a r t z vein v e i nsystems systems were were discovered d i s c o v e r e d ini nthe the Beardmore-Geraldton quartz BeardmoreGera1dton Greenstone BBelt e l t nnorth o r t h of o f Lake Lake Superior. S u p e r i o r . Most Most vein v e i n systems systems are a r e located located Greenstone proximal with t o east—west east-west t rtrending e n d i n g f fault a u l t zones zones w i t h mineralization m i n e r a l iz a t i o n proximal to localized l o c a l i z e d in i n drag d r a g folds f o l d s and and ddilated i l a t e d ffractures r a c t u r e s iin na a variety v a r i e t y of o f rock rock t y p e s . Auriferous A u r i f e r o u s vein v e i nsystems systems and and associated a s s o c i a t e d replacement replacement sulphides s u l p h i d e s in in types. oxide Rock o x i d e facies f a c i e s iron i r o nformation f o r m a t i o nwere werestudied s t u d i e datathe t t hHard e Hard Rockand and MacLeod—Cockshutt Mines and Solomon's SolomontsPPillars MacLeod-Cockshutt Mines p l uplus s t hthe e MMcLellan c L e l l a n and illars occurrences occurrences tto o gain g a i n information i n f o r m a t i o n on on the t h e mineralization m i n e r a l iz a t i o nprocess. process. In In addition a d d i t i o n the t h e depositional d e p o s i t i o n a lenvironment environment of o f the t h e I.E. I . F .and andassociated associated siliciclastics belt. s i l i c i c l a s t i cwas s wasinvestigated i n v e s t i g a t e dthroughout t h r o u g h o u t the t h egreenstone greenstone be1 t. The (less The ooxide x i d e ffacies a c i e s LF. I.F. forms formsthin thin ( l e sthan s t h a5n mm) 5 mm)laminae laminaeand and packages packages ooff laminae laminae interbedded i n t e r b e d d e d with w i t h and and sometimes sometimes forming f o r m i n g the t h e EE d i v i s i o n of o f DE DE tturbidities. u r b i d i t i e s . The The cchemical-siliciclastic h e m i c a l - s i l i c i c l a s t i csuccessions successions are are division organized o r g a n i z e d into i n t oupward upward coarsening c o a r s e n i n g and and thickening t h i c k e n i n gpackages. packages. Both Both chemical chemical and and cclastic l a s t i c components components r represent, e p r e s e n t , i in n varying v a r y i n g proportions, p r o p o r t i o n s , deposition deposition from from dilute d i l u t esediment sediment gravity g r a v i t yflows f l o w sand andrainout r a i n o ubelow t belowstorm s t o r mwave wave base. base. The I.F. was was deposited d e p o s i t e d in i nshore shore The sstratigraphic t r a t i g r a p h i c succession succession indicates i n d i c a t e s I.E. proximal p r o x i m a l interchannel i n t e r c h a n n e lareas areason ona asubmarine submarine fan f a nforming f o r m i n gthe t h subaqueous e subaqueous o f aa fan f a ndelta d e l t asystem. system. p o r t i o n of portion ZONES OF IRON FORMATION ACCUMULATION OVERBAN}< VERBANK FLOW FLOW INACTIVE CHANNEL ACTIVE CTIVE CHANNEL CHANNEL Paleogeography Beardmore-Geraldton during off the Paleogeography o of f t the h e Beardmore-Geral d t o n a rarea ea d u r i n g ddeposition eposition o the As coarse eclastics As time t i m e progressed progressed tthe h e coarse lastics prograded southwardwidening wideningt hthe prograded southward e bbraidplain. raidplain. sedimentary sedimentary assemblage. assemblage. 27 I �U The veining event occurred concomitant with fol lowing aa The veining event occurred either either concomitant with or or following regional epi sode of deformation. Auriferous mineral i zation . F . is is regional episode of deformation. Auriferous mineralizationinin II.F. spaci a1 ly and probably genetical ly re1 ated t o extensive wall -rock spacially and probably genetically related to extensive wall-rock a1 terationincluding includingcarbonatization carbonatizationand andsulphidation. sul phidation.The Themineralogy mineralogy alteration of the occurrences indicates they were deposited from sulphide of the occurrences indicates they were deposited from sulphide rich, rich, alkaline tot oneutral neutralH20-C02 H20-C02 solutions. solutions. Under Under these these conditions conditions the the gold gold alkaline may have from depth depth by byreduced reduced sulphur sulphurcomplexes complexesand and may have been been transported transported from precipitated during wall-rock alteration of the I . F . b y b o t h a pH precipitated during wall-rock alteration of the I.F. by both a pH change and ZFe304 6Au(HS)y + +66H ~ '26FeS 6FeS2 ++ 8H 8Hz0 6Au change and the the reactions: 2Fe 0 ++ 6Au(HS)-T 0 +t6Au 34 2 ->2 2 22 t 4H2 2FeAsS t FeS2 t 4H20 t Z A u . Fe3O4 t 2Au(AsS2) Fe304 + 2Au(AsS2) + 4H2 2FeAsS + FeS2 + 4H20 + 2Au. + 28 �EARLIEST GEOCHEMISTRY OF G EOCHEMISTRY O F THE T H E POWDER MILL M I L L GROUF' GROUP: THE THE E A R L I E S T LAVAS LPiVAS THE THE NIL) M I D CONTINENT CONTINENT RRIFT I F T IN I NMICHIGAN MICHIGAN Jies W. OF OF Sell Sci ences, Michigan State Uni off G versi Department o Geological Dapar-tment o o l o q i c a l Science's, M i c h i gan S t a k e U r i i v e r - s i b1yy East E a s t Lansing, L a n s i n g , Michigan M i c h i g a n 48824 4Sf.324 etruded Powder Miii heo e;~:ti"nded M i 11 Group Group represents r e p r e s e n t ! %the t h 'first '~ f i r s t lavas l a v a s to to b Upper Midcontinent the development the; development oo f the the M i d c o n t i n e i n t Rift R i - F t in i n U p p e r vlichjqan. M i c h i qan. unique opportunity to These Keweenawan cenawan age age lava l a v a f1ows l a w s provide provide a u nique a ppartuni t y to one o$f the planet's oldest examine tthe h e iinitial n i t i a l eruptives eruptives ffrom rom one o the? planet's o l d e s t and and examine is(a exposed largest l a r - q e s t preserved pr-oaerved ri r i ft t systems. systems. The Powder Powder- Miii M i l l Group Gr-oup i o x posed southern qn over an area ovesr an a r e a of o f about a b o u t 160 160 km, km, +rom from s o u t h e r n Houqhton Houqhtori Courty, C o u n t y , Mi lvll:hi c h i q<,iri Mth:Lqan. Wisconsin, to Grandview, t.a Grandview, W i s c o n s i n , and is i s centred c e n t r e d around around IIronwood, ronwaod, IPlichiq<an, has IIts t s ttotal o t a l tthickness hickness h a s been estimated e s t i m a t e d at a t about a b o u t 6100 6100 m. m, Group is The Powder Mill M i l l i s divided d i v i d e d into i n t o two t w o Formations: F o r m a t i o n s : the t h e S:Lemns Siemens The lowermost Siemens C Creek Creek and the lowermost tthe he kesek t h e Kallander Kallander Creek. The 1300 rnm 0.6 of tthin and aandesite iows Formation about F o r m a t i o n represents represents a bout 1300 h i n bbasalt a s a l t and n d o s i t o flow:^ The overlying which w h i c h are a r e generally g e n e r a l l y less l e s s than t h a n 15 15 m m thick. thick, o v e r ly i ng Kallander Kal lander believed be about although only Formation Creek F ormation iis s b e l i e v e d tto o b e a b o u t 4500 m thick thick a lthough only Creek average The about a b o u t 1200 1200 m m is i s exposed. e:<posed. The a v e r a g e flow f l o w thickness t h i c k n e s s is is about a b o u t 25 2'5 m. mu (Hubbard,, els:Lte 'flows basalt These flows rrange a r i q e ffrom ram b a s a l t to t o quartz—bearing q u a r t z - b e a r i ng felsita (1-Iubbi'ar-d Powder Mill off 1975). All exposures the 1775) A ll e xposures o the Powder M i 11 Group west of o-f the t h e Keweenaw Ksweeriaw Lposures near vertical Fault F a u ldip t dip n ear v e r t i c a l and toward toward tthe h e northwest. northwo:st. Expaiuurc?!:ion a n tthe he east side east s i d e of o f the t h e Keweenaw Keweenaw Fault F a u l t are a r e flat f l a t lying. lying. by Wilband Preliminary Mill Group P reliminary iisotope s o t o p e work work on the t h e Powder Powder M i l l Group by W ilband of 0.7042+/— with an an isochran ((1984) 1.984) yyielded i e , l d e d .an isochrqn w ith an iinitial87Sr/SóSr nit1,all~~Sr/8a 6+~ ~0 .7043 + / off 1209 +/— 36 Ma. 4 0.0003 and an age o 1209 + / - 36 Ma. M a j o r element e l e m e n t data data from fr-cam 46 0.0003 and an age Major SiO' samples have been collected. Ranges o4 some sample's h a v e been c ollected. Ranges o af some oxides o x i d e s are: are; SiO12 18—4%. 70—48%; MqO 13—< 1"!.; CaO 1 1—< 1%; Al20, 16—10%; FeO 70-48Z;MgO 13-<17.;CaO 11-<17.;Al$):-!; 16-10%;FeQ (total FFe) o ) la-47.. There There a h high positive CaO. T h e r e is i s ia igh p o s i t i v e correlation c o r r e l a t i o n between b e t w e e n MqO MqG and and CaQ. Theres is i s also a h high negative correlation Al$z. a lso a igh n egative c o r r e l a t i o n between MqO MgO and and Al20,. Nine eighteen N i n e of o'f the t h e sampled lavas l a v a s are a r e olivine o l i v i n e tholeiites t l i o l e i i t e s and and e i q h t a e n are are quartz tholeiites. types byy A duality q uarts tholeiitas. duality oof lava lava t y p e s was was recoqnized recoqnized b Wilband Wasuwanich Portage W i l b a n d and W i ~ s ~ w a n i c(1980) h ( 1 9 8 0 ) in i n the t h e overlying overlying P o r t a q e Lake L a k e Lavas L a v a s and and These dykes tthe h e Keweenawan Keweenawan diabase d i a b a s e dykes. dykes. d y k e s are a r e believed be1 i e v e d to t o he he 'feeders -feeders both the This f'for ar both t h e Portage P o r t a g e Lake L a k e Lavas L a v a s and and the the? Powder Powder Miii M i l l Group. Group. T his duality in MgO v. TiO' d u a l i t y is i s also a l s o recognized recognized i n plots p l o t s o4 of MqO T i O z and A12(::):3 Ai1O', : F'205 for TTi02 iOz : P ~ d s 'For tthe h e Powder M i l l T r a c e element e l e m e n t data datia will will Mill Group. Trace be collected b e c o l l e c t e d to t o substantiate s u b s t a n t i a t e these t h e s e trends. trends. The during during . (total : Hubbard H. Hubhard H. A. A. ((1975) 1975) Lower c a n i c rocks r o c k s a-f M i c h i qiiin and Lower Koweenawan Keweenawan vol, volcanic of Michigan and W i s c o n s i n . U.S. U. S. c3eol, Geol S urvey J o u r . Research R e s e a r c h 3, 3 , 5Zc?--'-J4 J. Wisconsin. Survey Jour. 529—541, Wilband Age and and ssource of vvolcanics associated W i lbi31id J.T. J.T. ((1984) 1 9 8 4 ) Age o u r c e vvariation a r i a t i o n o-f o l c a n i c % (sissoci dtad with Keweenaw R w i t h Keweenaw i f t i n g . Trans. T r a n s . Am. Am. Geophys. Beophys. Union U n i a n 65, 6 5 , 1122. 1122Rifting. W i l b a n d J.T. J.T. and and Wasuwanich Wasuwanich F. F. Wilband ((1980) 1780) M o d e l s of a-f basalt b a s a l t petroqenesis: ptsti*-aqariei~'i.s: Models Lower Lower Keweenawan i abase ddikes i k e s and and Middle M i d d l eKeweenawan Keweeriawan Portage P o r t a g eLak:e Lake Keweenawand diabase L a v a s , Upper i c h i q a n . CContrib. antrib. M ineral. P atrol. 7 5 , 3t95-406,, Lavas, Upperl lMichigan. Mineral. Petrol. '75, 395—4O. 29 - - -- �U h STRATIGRAPHIC EVOLUTION EVOLUTION OF OF THE THE ISLAND ISLAND LAKE LAKE GREENSTONE GREENSTONE BELT. BELT, STRATIGRAPHIC MANITOBA MANITOBA 555-330 Graham Graham Ave.. Ave., Paul Gilbert. Gilbert, Geological Geological Services Services Branch. Branch, 555—330 Paul 4 E 3 Winnipeg, Manitoba. R3C Winnipeg. Manitoba. R3C 4E3 H. H. The Island Island Lake Lake greenstone greenstone belt belt in in the the northwestern northwestern The Superior Province consists of a lower, subaqueous, Superior Province consists of a lower, subaqueous. volcanosedimentary section section (Hayes (Hayes River River Group), Group), unconformably unconformably volcanosedimentary overlain by by fluvial fluvial deposits deposits and and younger younger turbidites turbidites (Island (Island Lake Lake overlain Group). The Hayes River Group was subjected to pre-Island Lake Group). The Hayes River Group was subjected to pre—Island Lake Group deformation, deformation, metamorphism, metamorphism, and and plutonism plutonism and and was was probably probably Group subaerially eroded before deposition of the younger sedimentary subaerially eroded before deposition of the younger sedimentary rocks. rocks. - Coarse volcanic volcanic breccia breccia and and relatively relatively shallow—water, shallow-water, Coarse vesicular basalt basalt in in the the eastern eastern part part of of the the belt belt suggest suggest aa more more vesicular proximal environment environment than than the the area area further further west. west. The The abandoned abandoned gold gold proximal mine in the the eastern eastern part part of Island Lake Lake occurs occurs at at aa mine in of Island volcanic/sedimentary interface within within the the Hayes Hayes River River Group. Group. volcanic/sedimentary interface Silicification and carbonatization are more widespread in this area Silicification and carbonatization are more widespread in this area than further west. Carbonatization may be partly related to than further west. Carbonatization may be partly related to possible sedimentary carbonate units (e.g. at the gold mine) but is possible sedimentary carbonate units (e.g. at the gold mine) but is 0.5 km of the Norrie Island carbonatite. This also extensive within also extensive within 0.5 km of the Norrie Island carbonatite. This intrusion, which which is is associated associated with with carbonatized carbonatized peridotite peridotite and and intrusion, intrusive breccia breccia containing containing mafic/ultramafic mafic/ultramafic clasts, clasts, is is emplaced emplaced intrusive close to to the the contact contact between between the the Hayes Hayes River River and and Island Island Lake Lake Groups Groups close in aa possible possible graben—like graben-like structure. structure. A zone of ultramafic in of A zone ultramafic intrusions extends extends through through the the central central part part of of the thegreenstone greenstonebelt, belt, intrusions and aa porphyritic porphyritic peridotite peridotite sill sill occurs occurs close close to to the the south south margin margin and of the the belt. belt. Regional Regional isoclinal isoclinal folding folding has has affected affected both both the the Hayes Hayes of River and and Island Island Lake Lake Groups Groups and and major major faults faults are are inferred inferred where where River stratigraphic discontinuities occur across the axial traces of some stratigraphic discontinuities occur across the axial traces of some folds. folds. 30 �U KEWEENAWAN KEWEENAWAN DIKES OF MINNESOTA John Green, Geology John C. Green, Geology Dept., Dept., Univ. of of Minn., Minn., Duluth, Duluth, MN MN 55812 55812 University Ave., St. Val W. Chandler, Chandler, Minn. Minn. Geol. Geol. Survey, Survey, 26)42 2642 University St. Paul, Paul, MN MN 551114 55114 Keweenawan dikes, many many of which were probably feeders for plateau basalt lavas, lavas, are concentrated in several swarms in northeastern Minnesota. Minnesota. Their Their general general trends trends probably probably show show the the direction directionof' of tensional tensional stress stress at different times and in different areas as the Midcontinent Rift system system evolved, evolved, and their their compositions compositions give give an an idea idea of of the the magmas magmas available available from from melting melting of of the the subcontinental subcontinental mantle mantle as as the the rift rift progressed. progressed. Time relations relations are inferred both from crosscutting intrusive intrusive relations studies of of polarity and pole relations and and from from paleotnagnetic paleomagnetic studies pole progression progression along the the Late Late Proterozoic Proterozoic track track (Halls (Halls and and Pesonen, Pesonen, 1982). 1982). The two oldest oldest swarms swarms show show reversed reversed polarity. polarity. The The Carlton Carlton County County swarm outcrop, trending swarm contains contains143 43 dikes dikes known known from outcrop, trending rather rather uniformly uniformly ~ 3 0 ~They . are found in the St. St. Louis Louis River River valley valley from from Carlton Canton and and N3O°E. Cloquet east through Duluth, and through the Jay Cooke State Park area west of Duluth, they cut the Lower Proterozoic Thomson Formation and some of the reversed - polarity lavas at Ely's polarity (R) (R) Keweenawan lavas Ely's Peak Peak beneath beneath the the Duluth Duluth Complex. Complex. Fe—rich basalt similar in composition to They are mostly rather evolved, Fe-rich many North Shore Volcanic Group (NSVG) (NSVG) lavas and the Columbia River plateau plateau basalts. basalts. A few normally polarized (N) (N) dikes, dikes, evidently evidently younger, younger, also occur in this same area, and several large N dikes with similar trend appear dramatically dramatically on on aeromagnetic aeromagnetic maps maps (Chandler (Chandler 1983). 1983). The The reversed reversed swarm shows a paleomagnetic pole position that closely corresponds corresponds to that previously determined by others for reversed lavas in Cook County and Logan Logan sills sills in in the the Thunder Thunder Bay Bay district. district. The occurrence occurrence of of large large RR dikes dikes up to 8 lavas or Duluth Duluth Complex 8 km km west west of of the the nearest nearest Keweeriawan Keweenawan lavas Complex suggests suggests that the R Ely's Ely's Peak basalts or their equivalent probably covered a considerably considerably wider wider area area before before Late Late Keweenawan Keweenawan erosion. erosion. - Another group of reversed reversed dikes dikes is is the the Grand Grand Portage Portage swarm swarm (Green, (Green, the coastal coastal zone zone of of northeastern northeastern Cook Cook 1981) which which is best exposed in the County Portage. They cut the reversed—polarity reversed-polarity Counìty from from Hovland Hoviand to to Grand Portage. Keweenawan lavas, lavas, the the Puckwunge Puckwunge Sandstone, Sandstone, and the underlying underlying Lower Lower Keweenawan Proterozoic Proterozoic Rove Rove Formation. Formation. At least 20 dikes are known, known, ranging from 1 to 145 thick;about about 30% 3O are 45 mm thick; are over over 10 10 mm thick. thick. They trend trend E.-W E-W to and to ENE and dip steeply steeply N. N. These These too too have have rather rather Fe—rich Fe-rich evolved evolved compositions. compositions. Several are plagioclase-porphyritic plagioclase—porphyritic and they were probably feeders for the Grand Portage Portage and and Hoviand Hovland lavas. lavas. 1 is found found in in the the Grand A major group of normally polarized dikes also is intrusions Portage area; these have been referred to as the Pigeon River intrusions by Geul Geul (1970). (1970). Consisting Consisting of at least 30—35 30-35 dikes, dikes, (most (most in in Canada) Canada) this this group contains contains many very large large ones ones over over 100 100 mm thick thick (some (some up up to to 500 500 m). m). trend N65 ~ E6 but but5 aa few few ~ are are transverse transverse with with N30—5 ~ 3 0 W- strikes. strikes. 5 ~ Most trend Several can can be be followed followed for for 15—20 15-20 km. km. They cut the Rove Fm, Several Fm, reversed Keweenawan lavas, Keweenawan lavas, and Logan Logan sills. sills. This This group group is is on on the the whole whole considerably more magnesian and primitive geochemically than the RR swarms swarms described, and represents represents aa major major tapping tapping of of new new mantle mantle melt melt after after just described, pole reversal. reversal. the R-È RN pole 31 �_____ I In 1I basalt dikes are known, all N, which In the City of Duluth about 44 cut cut the the Duluth Duluth Complex Complex and and the the NN lavas lavas above above it. it. Their Their trend trend is is variable variable but most are are N—S N-S with with aa 750 7 5 WW dip. dip. The The compositions compositions of of 10 10 analyzed analyzed samples ranges ranges from from fairly fairly primitive primitive to to more more evolved, evolved, but samples but generally generally are are not not as as Fe—rich Fe-rich as as the the RR dikes dikes of of Carlton Carlton County. County. Sixteen Sixteen N dikes south of Babbitt cut the Duluth Complex and trend transverse transverse to to the the general general rift, rift, about about N52 N52 ÷+ 15 1 5 WW (Morey (Morey and and Cooper, Cooper, Their 1976). Their extent extent is is not not well well defined defined nor nor is is their their chemistry. chemistry. Another Another 16 dikes between Ely and Moose Lake Lake in in the the Fernberg Fernberg Trail Trail area area (Green (Green et et al., Archean rocks rocks northwest northwest of of the the base base of of the the Duluth Duluth Complex. Complex. 1966) cut cut Archean al., 1966) Their Their polarity polarity is is not not established. established. Most NW; Most strike strike either either NN 65—70°E 65-70'~ or or NW; the the longest longest can can be be traced traced for for 10 10 km. km. These These have have aa range range of of basaltic basaltic compositions compositions rather rather like like those those of of the the Duluth Duluth area. area. The The 62 62 Minnesota Minnesota Keweenawan Keweenawan basaltic/diabasic basaltiddiabasic dikes dikes so so far far analyzed analyzed show show aa wide wide range range of of compositions compositions within each swarm, swarm, reflecting reflecting those those of of the the overlying overlying lavas. lavas. However, However, in in contrast contrast to to the the dikes dikes of of Michigan Michigan and Wisconsin, Wisconsin, there there is is aa preponderance preponderance of of more primitive primitive compositions compositions in in the N N group, group, and of of dikes dikes richer richer in in Fe, Fe, Ti, Ti, K, K, and and PP in in the the RR group. group. This This study study has has been supported in in part by the MNDNR Lithogeochemistry Lithogeochemistry Project. Project. References References Chandler, V. W., W., 1983, Aeromagnetic Aeromagnetic Map Map of of Minnesota: Minnesota: Carlton Canton and and Pine Pine Chandler, V. Counties., Counties., Minn. Geol. Geol. Survey, Survey, St. St. Paul. Paul. Geul, Geul, J. J. J. J. C., C., 1970, 1970, Geology Geology of of Devo Devo and and Pardee Pardee Townships, Townships,Ontario OntarioDept. Dept. Mines Mines Geol. Geol. Rept. Rept. 87 87 Green, J. J. C., C., 1981, 1981,Geol. Geol. Soc. Soc. Amer. Amer. Abstracts Abstracts with with Programs, Programs,v. v. 13, 13, p. p. Green, 271. 271. 9- Phinney, Phinney, W. W. C., C., and and Weiblen, Weiblen, P. P. W., W., 1966, 1966, Gabbro Gabbro Lake Lake Quadrangle, Quadrangle, Minn. Minn. Geol. Geol. Survey Survey Misc. Misc. Map Map M—2. M-2. Halls, Halls, H. H. C. C. and and Pesonen, Pesonen, L. L. J., J., 1982, 1982, Paleomagnetism Paleomagnetism of of Keweenawan KeweenawanRocks, Rocks, in in Geol. Soc. Soc. Amer. Amer. Memoir Memoir 156, 156, p. p. 173—202. 173-202. - Morey, G. G. B. B. and Cooper, Cooper, R. R. W., W., 1976, 1976, Bedrock Bedrock geologic geologic map of of Hoyt Hoyt Lakes Lakes — Money, Kawishiwi Kawishiwi Area, Area, St. St. Louis Louis and and Lake Lake Counties, Counties, NE NE Minn. Minn. Minn. Minn. Geol. Geol. Survey Survey open—file open-file map. map. 32 I I �i I Wisconsin Archean Block: Block: The Central Central Wisconsin Archean The New Evidence Suggests Suggests aa Partially Partially Reworked Reworked Granite/Greenstone Granite/Greenstone Terrane Terrane 3. J. K. K. Greenberg and and B. B. A. A. Brown Brown Wisconsin Geological and and Natural History History Survey Survey 1815 University Avenue Madison, WI 53705 1 A recently area of of central central Wisconsin, Wisconsin, which which includes includes most most of of Wood Wood recently mapped area and Portage counties, is typified by syn— and syn- to late—kinematic late-kinematic granitoid granitoid plutons plutons which intrude a predominantly volcanic volcanic terrane. terrane. The geology of this region is is analogous to granite/greenstone terranes common in in Archean shield shield areas areas and and analogous central Wisconsin area area was previously previously thought thought to to some younger provinces. provinces. The central of an extensive basement of Archean gneiss consist of gneiss overlain by by Proterozoic Proterozoic volcanic rocks and intruded and deformed around volcanic around 1850 1850 Ma. These These basement basement gneisses were were grouped with other gneisses in gneisses in southeastern southeastern Minnesota and and the the VaLley and and interpreted interpreted to to constitute constitute aa distinct distinct Archean Archean gneiss gneiss Minnesota River Valley provi;ce, separated from a granite/greenstone province, granite/greenstone terrane terrane to to the the north north by by aa major tectonic boundary. Our work in in central central Wisconsin suggests suggests that that the the two two major major lines lines of of evidence formerly used to infer terrane9*in in central central infer the the existence existence of of aa "gneiss "gneiss terrane" Wisconsin, age and and 1ithology;probably lithology,probably do do not not support this interpretation. Of Wisconsin,age the several available ages on Archean units, many are are younger younger than than similar similar rocks in southern southern Minnesota Minnesota or or nàrthern northern Wisconsin. Wisconsin. Most recent U/Pb dates from central Wisconsin are in in the range 2.5 2.5 to to 2.7 2.7 Ga, similar similar to to the the age age of of the proposed proposed granite/greenstone terrane in in northern northern Wisconsin and and Michigan. Michigan. Many of the newly designated designated Archean Archean units units and and other other potentially potentially Archean Archean units units are metavolcanic and metasedimentary lithologies, lithologies, such such as as those those exposed exposed at at DuBay in Portage County (interbedded Lake DuBay (interbedded felsic felsic and and mafic rocks) rocks) and and along along the Black River in in Jackson County (Algoma—type (Algoma-type iron iron formation formation and and amphibollte). amphibolite). There are numerous plutons plutons of of either either granite—granodiorite—tonalite granite-granodiorite-tonalite or or tonalite—hornblende diorite—gabbro tonalite-hornblende diorite-gabbro exposed in in the the area. area. Only a few ages are available for these rocks, but they are are generally generally thought thought to to be be early early Rock fabric and Proterozoic. Proterozoic. and contact contact relationships relationships indicate indicate that that the the intrusions were were syn to late kinematic, kinematic, commonly with massive cores and intrusions foliated margins. margins. The intrusive intrusive contacts contacts with volcanic—sedimentary volcanic-sedimentary country country rocks are extremely extremely complex. complex. Many rocks rocks previously previously mapped mapped as as diorites, diorites, gneisses, and syenites are actually contaminated—assimilated contaminated-assimilated contact contact lithologies. lithologies. Beyond the foliated foliated pluton—margins pluton-margins there there are are zones zones of of fine—grained and/or fine-grained gray "diorites" **diorites** and/or mixed mafic—felsic mafic-felsic rocks——texturally rocks--texturally "gneisses" "gneisses" with alternating bands of of granitic granitic and and mafic minerals. Where gneissic in aspect, these mechanically-mixed mechanically—mixed lithologies lithologies are are nearly nearly identical identical from the the plutons, plutons, in appearance with dated Archean gneisses. gneisses. Further away from only dikes and stringers of intrusive intrusive material are are present present in in the the country country rocks and intensity of metamorphism and and deformation deformation commonly commonly decreases. decreases. I I �I The presence of of Proterozoic Proterozoic gneissic gneissic zones zones in in central central Wisconsin Wisconsin has has possible possible tectonic implications implications for for at at least least some some of of the the Archean Archean and and supposed supposed Archean gneisses. gneisses. Geochronology and and geology geology have have been been thus thus far far unsuccessful unsuccessful in in specifying the timing at at which which these these rocks rocks became became gneisses. gneisses. In only a few few (Linwood and cases (t.inwood and Pittsville) Pittsville) are are the the gneissic gneissic structures structures almost certainly pre—Penokean. pre-Penokean. In other cases, Proterozoic tectonism tectonism probably probably converted converted Archean granite/greenstone granite/greenstone lithologies lithologiesinto intogneisses gneissesand andamphibo].ites. amphibolites. Orientations of minor folds folds and and foliations foliations vary vary widely widely throughout throughout the the area which has aa general general east—west east-west structural structural grain. grain. These structures and foliation within the plutons are generally parallel parallel near near the the pluton pluton contacts. contacts. Regional structural trends are reoriented within aa few few kilometres kilometres of of the the 1.5 1.5 Wolf River batholith, aa 9000 Ga Wolf 9000 km2 anorogenic anorogenic granite granite complex. complex. Metamorphism throughout throughout the the area area is is generally generally low low grade, grade, except except in in the the older older gneisses, gneisses, near the Wolf River batholith, and and in in some some other other contact contact zones zones where where middle antphibolite—facies amphibolite-facies rocks rocks occur. occur. Very low low grade grade Baraboo Baraboo interval interval metasedimentary metasedimentary rocks rocks (1760 (1760 to to 1630 1630 Ma) Ma) tend to reflect the composition of granite/greenstone granite/greenstone units units which they they apparently Ferruginous quartzite, apparently overlie overlie in in much of of central central Wisconsin. Wisconsin. Ferruginous quartzite, chert, argillite, and fuchsitic quartzite are are in in contact contact or or are are near near mafic and and metasedimentary rocks exposed near felsic ultramafic Equivalent metasedimentary felsic ultramaf Ic lithologies. lithologies. plutons and volcanic rocks are commonly lighter plutons lighter colored colored and and more sericite—rich. sericite-rich 34 �I Keweenawan Structural Structural Features Features at at the the Base Base of of the the Duluth Duluth Complex Complex in in the the Keweenawan Dunka Pit near Babbitt, Minnesota Dunka Pit near Babbitt, Minnesota U TIMOTHY B. B. HOLST, HOLST, EUGENE EUGENE E. E. MULLENMEISTER, MULLENMEISTER, JOHN JOHN C. C. GREEN, GREEN, Department Department of of TIMOTHY Geology, and Natural Resources Research Institute, University of Geology, and Natural Resources Research Institute, University of Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812, 55812,and and PAUL PAULW. W. WEIBLEN, WEIBLEN, Minnesota Department of Geology and Geophysics, University of Minnesota, Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota Minnesota 55i55 55455 Minneapolis, number of of faults faults and and folds folds affect affect Animikie Animikie Group Group Rocks Rocks of of the the AA number northeastern Mesabi Mesabi Range (Mullenmeister (Mullenmeister and and others, others, this this volume). volume). northeastern Range Several of of these these are are found found in in the the Dunka Dunka Pit Pit region. region. In In addition addition to to these these Several there are are structures structures found found in in Animikie Animikie Group Group rocks rocks in in the the Dunka Dunka Pit Pit in in there close proximity proximity to to the the Duluth Duluth Complex Complex that that are are found found nowhere nowhere else else in in the the close northeastern Mesabi Mesabi Range. Range. These features features include include tight tight to to isoclinal isoclinal northeastern These small-scale folds folds (amplitudes (amplitudes and and wavelengths wavelengths aa meter meter or or less), less), and and some some small—scale unusual, undulatory sub-horizontal faults, faults, here here termed termed detachment detachment unusual, undulatory sub—horizontal features features. . The small—scale small-scale folds folds occur occur in in the the cores cores of of larger—scale larger-scale folds folds The (amplitudes on the order of ten meters) and associated with the detachment (amplitudes on the order of ten meters) and associated with the detachment features, in in the the upper upper plate. plate. Fold Fold vergence vergence and and attitude attitude is is quite quite features, variable. The folds always occur within the uppermost Biwabik Formation variable. The folds always occur within the uppermost Biwabik Formation (the "A" "Av layer layer of of Erie Erie Mining Mining Company) Company) or or the the lower lower portion portion of of the the (the Virginia Formation. Formation. In In the the cores cores of of the the small—scale small-scale folds folds there there is is aa Virginia well-developed axial—planar axial-planar foliation foliation in in the the calcite calcitematrix. matrix. well—developed The detachment detachment features features are are well—defined well-defined faults, faults, which which have have variable variable The dips (usually (usually shallow) shallow) and and can can be be traced traced for for up up to to tens tens of of meters meters across across dips the pit pit wall. wall. The lower lower plate plate rocks rocks are are typically typically undeformed undeformed or or may may the The contain aa broad broad gentle gentle anticline, anticline, and and are are generally generally of of the theUCtI llClllayer layer of of contain the upper upper portion portion of of the the Biwabik Biwabik Formation. Formation. The The upper upper plate plate rocks rocks are are the typically strongly strongly folded, folded, and and consist consist of of the the "A" "Attlayer layer of of the the upper upper typically Biwabik, or or the the base base of of the the Virginia Virginia Formation. Formation. Thus Thus the the detachment detachment Biwabik, features are are observed observed to to remove remove stratigraphy stratigraphy in in each each case. case. Eight Eight such such features detachment features features have have been been defined defined to to date. date. detachment The proximity proximity of of the the small—scale small-scale folds folds and and detachment detachment features features to to the the The Duluth Complex and their absence elsewhere, and the axial-planar foliation Duluth Complex and their absence elsewhere, and the axial—planar foliation in the the recrystallized recrystallized calcite calcite hornfels hornfels establishes establishes the the age age of of these these in structures as Keweenawan (syn-intrusion). structures as Keweenawan (syn—intrusion). features could could be be the the result result of of aa regional regional compression, compression, although although These features These this seems least likely. The detachment features cut out stratigraphy in this seems least likely. The detachment features cut out stratigraphy in the manner of the listric normal faults of the Basin and Range, and may be the manner of the listric normal faults of the Basin and Range, and may be the result result of of aa regional regional extension, extension, perhaps perhaps associated associated with with mid—continent mid-continent the rifting during the emplacement of the Duluth Complex. The folds are then then rifting during the emplacement of the Duluth Complex. The folds are interpreted as as having having formed formed under under local local compression compression in in the the overriding overriding interpreted plate of of the the detachment detachmentfault. fault. Alternatively, Alternatively, these these features features could could be be the the plate result of of body body forces forces (gravity) (gravity) forming forming slumps slumps at at the the country country rock—magma rock-magma result interface at at the the time time of of intrusion. intrusion. interface 35 n �ECONOMIC ECONOMIC GEOLOGY GEOLOGY OF OF THE THE RARE RARE ELEMENT ELEMENT PEGMATITES PEGMATITES AT AT LILYPAD LILYPAD LAKE, LAKE, NORTHERN NORTHERN ONTARIO ONTARIO Hood, Hood, William William C., C., W.C. W.C. Hood Hood Geological Geological Consulting, Consulting, P.O. P.O. Box 1AO; Vanstone, Vanstone, Box 1026, 1026, Lac Lac du du Bonnet, Bonnet, Manitoba, Manitoba, ROE ROE lAO; Peter J., J., Tantalum Tantalum Mining Mining Corp., Corp., P.O. P.O. Box Box 2000, 2000, Lac Lac du du Peter Bonnet, Bonnet, Manitoba, Manitoba, ROE ROE lAO 1AO The The tantalum tantalum potential potential of of the the Lilypad Lilypad Lake Lake pegmatite pegmatite field field was was recognized recognized in in 1979 1979 during during an an exploration exploration program program by by Tantalum Tantalum Mining Mining Corporation Corporation of of Canada Canada Ltd. Ltd. Exploration Exploration for for tantalum tantalum and and other other rare rare metals metals was was prompted prompted at at that that time time by by strong strong demand demand and and rising rising prices. prices. Previous Previous exploration exploration of of these these pegmatites pegmatites had had concentrated concentrated mainly mainly on on lithium lithium mineralization. mineralization. Bedrock geochemical geochemical surveys, surveys, using using lithium lithium as as the the pathfinder pathfinder Bedrock element, element, were were successful successful in in locating locating several several mineralized mineralized pegmatite pegmatite dikes. dikes. Geological Geological mapping mapping to to determine determine the the extent, extent, orientation, and and structural structural environment environment of of these these pegmatites pegmatites orientation, was was followed followed by by drilling drilling to to evaluate evaluate their their size sizeand andgrade. grade. albiteThe best best tantalum tantalum mineralization mineralization was was found found to to occur occur in in albiteThe enriched enriched dikes dikes occupying occupying late— late- to to post-tectonic post-tectonic fracture fracture systems. systems. The The limited limited tonnage tonnage of of these these pegmatites, pegmatites, subeconomic subeconomic tantalum tantalum grades, grades, and and falling falling tantalum tantalum prices prices caused caused abandonment abandonment of of the the project project in in 1982. 1982. Several geological geological characteristics characteristics of of the the Lilypad Lilypad Lake Lake Several pegmatite pegmatite field field provide provide important important guidelines guidelines for for exploration exploration of of pegmatite—hosted pegmatite-hosted rare rare metal metal deposits. deposits. In In common common with with several several other other pegmatite pegmatite districts districts in in the the Superior Superior Province, Province, the the T.1ypad T.i-lypadpegmatites pepatites occur occur on on the the margin margin of of the the English English River River gneissic gneissic belt, belt, suggesting suggesting aa genetic genetic link link to to the the sedimentary sedimentary gneisses gneisses of of this this terrain. terrain. Although Although zoning zoning within within the the Lilypad Lilypad pegmatite pegmatite field field is is not not well-defined, well-defined, it it is is believed believed that that the the tantalum-bearing dikes dikes occupy occupy upper upper marginal marginal positions positions within within tantalum-bearing the the field. field. Detailed Detailed chemical chemical data data is is not not yet yet available available from from these these pegmatites, pegmatites, but but their their mineralogy, mineralogy, including including pollucite, pollucite, lepidolite, lepidolite, colored colored tourmalines, tourmalines, and and fluorite, fluorite,indicate indicateaa high high degree degree of of magma magma fractionation. fractionation. 36 �_____ _____ I FACIES INTERPRETATION F THE OF THE THE WOODS WOODS INTERPRETATION O OF THE BERRY BERRY RIVER RIVER FORMATION LAKE OF Johns, Precambrian J o h n s , G.W., G.W., P r e c a m b r I a n Geology G e o l o g y Section, S e c t i o n , Ontario O n t a r l o Geological G e o l o g I c a l Survey, S u r v e y , Toronto. Toronto. The T h e Berry B e r r y River R l v e r formation f o r m a t l o n (Warciub ( W a r c l u b group) g r o u p ) occurring o c c u r r l n g along a l o n g Long L o n g Bay and and Lobstick L o b s t l c k Bay Bay IInn tthe h e Lake L a k e of o f the t h e Woods Woods area a r e a is Is a 2 km hlck s e q u e n c e oof f ccaIc a l c alkaline alkal lne d a c l t e pyroclastlc pyroclastlc a 2 km tthick sequence dacite rrocks. ocks. Sub units u n l t s within w l t h l n the t h e sequence s e q u e n c e were w e r e deposited d e p o s l t e d by b y a variety v a r l e t y of o f volcanic v o l c a n l c processes. processes. Sub Fades F a c l e s mapping m a p p l n g and a n d the t h e development d e v e l o p m e n t of of a a fades f a c l e s model m o d e l has h a s allowed a l l o w e d assessment a s s e s s m e n t of o f base b a s e metal metal potential. potential. The formation f o r m a t l o n was deposited d e p o s l t e d by b y two t w o phases p h a s e s of o f volcanism. volcanism. The o l d e r event e v e n t has has aa base b a s e of of The The older r e d e p o s l t e d ttuff uff o verl aln b y p r o x l m a l tto o d l s t a l ccoarse o a r s e and f lne p y r o c l a s t i c rocks r o c k s Including l n c l udlng redeposited overiain by proximal distal and fine pyroclastic he p r o x l m a l tto o ddistal l s t a l ppyrodlastlc y r o c l a s t l c ffades a c l e s on on the t h e west west unlts o a s h flow f l o w tuft. tuff. units off ash Overlying tthe proximal a r e redeposited r e d e p o s l t e d coarse c o a r s e pyroclastic p y r o c l a s t l c rocks r o c k s with w l t h interbedded l n t e r b e d d e d wackes. wackes. On the t h e east e a s t the t h e proximal p r o x lmal are tto o d lstal p y r o c l a s t l c rocks r o c k s were w e r e intruded l n t r u d e d by by subvolcanic s u b v o l c a n l c rocks. rocks. A thick t h l c k ash a s h flow f l o w tuft t u f f unit unit distal pyroclastic associated IIs s a s s o c l a t e d with w i t h this t h l s younger y o u n g e r event. event. O u t w a r d from f r o m the t h e subvolcanlc s u b v o l c a n l c rocks r o c k s and overlying overl ylng Outward tthe h e ash a s h flow f l o w tuft t u f f are a r e proximal p r o x l m a l coarse c o a r s e pyrociastlc p y r o c l a s t l c rocks. rocks. r o x l m a l tto o d l s t a l deposition d e p o s l t l o n facies facles v a r l e s ffrom rom d e b r l s flows f l o w s Iin n tthe he The The extensive pproximal distal varies debris e a s t , doubly d o u b l y graded g r a d e d subaqueous s u b a q u e o u s pyrociastic p y r o c l a s t l c flows f l o w s and a n dfal f a 1I—out I - o u t units u n l t s in I n tthe h e central c e n t r a l portion, portion, east, tto o debris d e b r l s flows f l o w s in I n the t h e west. west. D e b r l s flows f l o w s are a r e massive, m a s s l v e , Indistinctly l n d l s t l n c t l y bedded, b e d d e d , in I n tthe h e east east Debris and Subaqueous uff a n d poorly p o o r l y bedded b e d d e d in I n the t h e west. west. S u b a q u e o u s pyrociastic p y r o c l a s t l c flows f l o w s are a r e doubly d o u b l y graded g r a d e d with w l t h aa ttuft br.ccia The b r e c c l a base b a s e overlaln o v e r l a l n by b y thickly t h l c k l y laminated I a m l n a t e d tufts. tuffs. T h e tal f a l l -i—out o u t uunits n l t s cconsist o n s l s t of o f thinly thinly bedded horizons. p u m l c e o u s lap l a pliii f l l l tuft t u f f horizons. b e d d e d tufts t u f f s and a n d pumiceous lnterbedded with deposition lnterbedded w i t h tthe h e pproximal r o x l m a l tto o ddistal lstal d e p o s l t l o n ffades a c l e s are a r e conformable, conformable, discontinuous f low tuffs d l s c o n t l n u o u s massive m a s s l v e quartz—feldspar q u a r t z - f e l d s p a r and a n d feldspar f e l d s p a r porphyry p o r p h y r y ash a s h flow t u f f s with w i t h varied varled grain a rrange of quartz/feldspar g r a l n size, size, a ange o f q u a r t z / f e l d s p a r phenoclast p h e n o c l a s t ratios, r a t l o s , and and horizons h o r l z o n s of o f llithic l t h l c ciasts. clasts The distal The d l s t a l rredeposited e d e p o s i t e d ffades a c l e s Is I s reworked r e w o r k e d tuft, t u f f , lapilli l a p l l l l tuft, t u f f , heterol h e t e r o lithic l t h l c debrIs d e b r l s flow f low and Epiclastic a n d laher l a h a r with w l t h interbedded l n t e r b e d d e d wacke. wacke. E p l c l a s t l c teldspathic f e l d s p a t h l c wacke and a n d quartz—feldspar q u a r t z - f e l d s p a r wacke Wac k e Iis s ccorrelative o r r e l a t l v e with w l t h the t h e pyroclastic p y r o c l a s t l c deposits. d e p o s It s The eastern The e a s t e r n portion p o r t l o n of o f the t h e Berry B e r r y River R l v e r formation f o r m a t l o n Iis s vvent e n t ffades a c l e s chaotic, c h a o t l c , massive, masslve, quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y containing c o n t a l n l n g rafts, r a f t s , blocks b l o c k s and a n d xenol x e n o l liths t h s oof f ppyroclastic y r o c l a s t l c material. Outward O u t w a r d ffrom r o m tthe h e vvent e n t ffades a c l e s is I s the t h e proximal p r o x l m a l depositional d e p o s l t l o n a l ffades a c l e s coarse c o a r s e homolithic homo1 l t h l c pyroclastic ground The surge p y r o c l a s t l c rrocks o c k s with w l t h tthin h l n lnterbedded lnterbedded g r o u n d surge s u r g e or o r cloud c l o u d surge s u r g e tufts. tuffs. The surge deposits s h a l l low o w wwater a t e r environment. d e p o s i t s ssuggest uggest p y r o c l a s t l c flow f l o w deposition d e p o s l t l o n Iinn a shal pyroclastic environment. pml Point Bay Group Group I::i.I Warciub WarclubGroUp Group .-:-J Snake snakeBay BayFormation Fornation Granitoids ,j Granltoids -- BERRY RIVER FORMATION FORMATION UNITS OLDER UNITS OLDER diabase dike ashflow flow tuffs tuffs Jash fades — fault -vent vent facies proximal deposition (shallow (shallow water) -proximal — ldhk9Ic contact lithologic contact proximal—dIstal deposition (component of redeposition) redeposition) proximal-distal deposition -— stratigraphic distal redeposition distal redeposition stratigraphiccontact contact 0 1 2 3 4 5 fades boundary facies boundary 2__J epiclastic facies I .. ..... 23 - . .. kll01~1€atr • + •++ * I I I I I �I of aa Subaqueously Subaqueously Emplaced Emplaced V Volcanic Horizon Documentation of olcanic H orizon iin n tthe h e Upper Portage P o r t a g e Lake Volcanics, Volcanics, Keweenaw Peninsula, P e n i n s u l a , Michigan. Michigan. Rodney C. C . Johnson (Dept. (Dept. of of Geol. Geol. and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological University, U n i v e r s i t y , Houghton, MI M I 49931) 49931) The Portage P o r t a g e Lake Volcanics V o l c a n i c s are a r e a series s e r i e s of of subareal s u b a r e a 1 flood f l o o d basalts b a s a l t s in i n which which to to date This d a t e no subaqueous igneous igneous activity a c t i v i t y has h a s been been documented. documented. T h i s paper p a p e r documents documents horizon within tthe h e eexistence x i s t e n c e oof f aa hhyaloclastic yaloclastic h orizon w i t h i n the t h e Portage P o r t a g e Lake Volcanics Volcanics (Figure 1). This minimum lateral ). T h i s hhorizon o r i z o n hhas a s aa minimum l a t e r a l extent e x t e n t along a l o n g strike s t r i k e of of (Figure 1 aapproximately p p r o x i m a t e l y 24 km from Owl Creek in i n the t h e northeast n o r t h e a s t to t o Seneca Seneca Lake Lake in i n the the southwest ppart of the Peninsula southwest a r t of t h e Keweenaw P e n i n s u l a and a thickness t h i c k n e s s of of between between 10 m. 1 0 and and 20 20 m. The hyaloclastic h y a l o c l a s t i c horizon h o r i z o n typically t y p i c a l l y lacks l a c k s any any textural t e x t u r a l homogeneity homogeneity either either vertically orr h horizontally of more more tthan few m nters. vertically o o r i z o n t a l l y oover v e r ddistances i s t a n c e s of h a n aa few e t e r s . In I n general, generaly tthe h e hhyaloclastic y a l o c l a s t i c hhorizon o r i z o n lies l i e s anywhere between two two textural t e x t u r a l end end members——a members--a Pillowed ppillowed i l l o w e d lava l a v a sequence and a true t r u e hyaloclastite. hyaloclastite. P i l l o w e d lava l a v a sequences s e q u e n c e s are are vesicular composed oof f eelliptical l l i p t i c a l to t o amoeboid v e s i c u l a r pillows. p i l l o w s . Vesicles V e s i c l e s are a r e commonly commonly cconcentric o n c e n t r i c and occasionally o c c a s i o n a l l y form form pipes. p i p e s . These pillows p i l l o w s frequently f r e q u e n t l y exhibit e x h i b i t chill chill hyalocalstite margins or o r "rinds", " r i n d s 1 ' , concentric c o n c e n t r i c cracks c r a c k s and and radial r a d i a l joints. j o i n t s . The h yalocalstite composed of of vvesicular, iis s composed e s i c u l a r , angular a n g u l a r fragments. f r a g m e n t s . Fragments Fragments rrange a n g e in i n size s i z e from blocks aash—sized s h - s i z e d to t o "rinds" " r i n d s " and b l o c k s from pillows. p i l l o w s . The smaller s m a l l e r fragments f r a g m e n t s are are frequently is f r e q u e n t l y ffinely i n e l y fractured f r a c t u r e d resembling r e s e m b l i n g perlitic p e r l i t i c texture. t e x t u r e . The hyaloclastite h y a l o c l a s t i t e is p r e h n i t e , epidote, e p i d o t e , microcline, microcline, very v e r y colorful c o l o r f u l due to t o the t h e secondary s e c o n d a r y minerals: m i n e r a l s : prehuite, native cchlorite, h l o r i t e y calcite, c a l c i t e , quartz, q u a r t z , and n a t i v e copper. copper. Field F i e l d work was conducted conducted at a t outcrops o u t c r o p s on o n Owl O w l Creek, C r e e k , near n e a r the t h e Copper Copper Falls F a l l s Mine, Mine, pillowed with and on Eagle E a g l e River. R i v e r . The outcrop o u t c r o p oon n Eagle E a g l e River R i v e r is is a a p i l l o w e d lava l a v a ssequence equence w ith p i l l o w s are a r e approximately a p p r o x i m a t e l y 50 50 cm cm in i n diameter, diameter, hhyaloclastite y a l o c l a s t i t e draped on o n top. t o p . The pillows have w well have e l l developed chill c h i l l margins that t h a t are a r e accentuated a c c e n t u a t e d by by red r e d oxidation, o x i d a t i o n , sparse sparse concentric O w l Creek Creek is is c o n c e n t r i c vvesicles, e s i c l e s , and contain c o n t a i n few pipe p i p e vesicles. v e s i c l e s . The outcrop o u t c r o p on o n Owl a p pillow—bearing i l l o w - b e a r i n g hyaloclastite. h y a l o c l a s t i t e . Pillows P i l l o w s range r a n g e in i n size s i z e from from 10 1 0 cm cm up u p to t o 11 mm and and Pillows occur are unoriented are u n o r i e n t e d in i n aa matrix m a t r i x of of hyaloclastite. hyaloclastite. P illows o c c u r singularly s i n g u l a r l y or o r in in iinterdigitated n t e r d i g i t a t e d masses. They generally g e n e r a l l y exhibit e x h i b i t well w e l l developed developed chill c h i l l margins, margins, concentric c o n c e n t r i c vvesiculation, e s i c u l a t i o n , concentric c o n c e n t r i c cracking, c r a c k i n g , radial r a d i a l joints, j o i n t s , and and occasionally occasional~y iinternal n t e r n a l cavities. c a v i t i e s . The hyaloclastite h y a l o c l a s t i t e occasionally o c c a s i o n a l l y exhibits e x h i b i t s crude c r u d e layering l a y e r i n g and and hyaloclastite Owl grading. wl g r a d i n g . An accurate a c c u r a t e estimation e s t i m a t i o n of o f the t h e thickness t h i c k n e s s oof f the the h y a l o c l a s t i t e oon n O Creek was n not o t possible p o s s i b l e since s i n c e the t h e horizon h o r i z o n is i s cut c u t by by aa fault. fault. The hyaloclastic h y a l o c l a s t i c horizon h o r i z o n has, h a s , in i n the t h e past, p a s t , been been included i n c l u d e d in i n aa unit u n i t called c a l l e d the the Ashbed, a frequently Ashbed includes Ashbed, f r e q u e n t l y mined horizon. h o r i z o n . The Ashbed i n c l u d e s rocks r o c k s that t h a t have been with ccharacterized h a r a c t e r i z e d aas s aa ppyroclastic y r o c l a s t i c flow flow w i t h scorreaceous, s c o r r e a c e o u s , highly h i g h l y oxidized, o x i d i z e d , and and ffrequently r e q u e n t l y welded textures. t e x t u r e s . Thus, Thus, as a s currently c u r r e n t l y shown shown on o n published p u b l i s h e d geological geological maps the i s sometimes sometimes the t h e pyroclastic p y r o c l a s t i c horizon h o r i z o n and and sometimes sometimes the the t h e Ashbed is E a g l e River R i v e r both b o t h horizons h o r i z o n s occur o c c u r with w i t h the t h e pyroclastic pyroclastic hhyaloclastic y a l o c l a s t i c horizon. h o r i z o n . On Eagle Ashbed and the t h e stratigraphically s t r a t i g r a p h i c a l l y separatal separated hhorizon o r i z o n identified i d e n t i f i e d aass the t h e Ashbed hyaloclastic h y a l o c l a s t i c horizon h o r i z o n unrecognized. unrecognized. The hyaloclastic d e s c r i p t i o n by Huber h y a l o c l a s t i c horizon h o r i z o n may crop c r o p out o u t on o n Isle I s l e Royale. Royale. A description (1975) of of aa ppyroclastic Ashbed and a picture (1975) y r o c l a s t i c uunit n i t ssimilar i m i l a r tto o tthe h e Ashbed p i c t u r e suggests s u g g e s t s it i t may may be the be t h e hyaloclastic h y a l o c l a s t i c horizon. h o r i z o n . The stratigraphic s t r a t i g r a p h i c position p o s i t i o n of of the t h e Isle I s l e Royale Royale unit unit of tthe horizon/Ashbed oon n the t h e Keweenaw Peninsula. Peninsula. iis s ssimilar i m i l a r tto o tthat h a t of h e hhyaloclastic y a l o c l a s t i c horizonfAshbed Although not Royale uunit may be be ccorrelatable with n o t seen s e e n by the t h e author a u t h o r tthis h i s IIsle s l e Royale n i t may orrelatable w ith the hyaloclastic on the h y a l o c l a s t i c horizon horizon o n the t h e Keweenaw Peninsula. Peninsula. 3388 I �I The presence p r e s e n c e of of the t h e hyaloclastic h y a l o c l a s t i c horizon h o r i z o n is i s significant s i g n i f i c a n t in i n that t h a t it it confirms confirms of aa body of of w water tthe h e eexistence x i s t e n c e of a t e r concurrent c o n c u r r e n t with w i t h volcanism. volcanism. T his m i g h t be This might consistent with Livnats (1983) (1983) hypothesis, h y p o t h e s i s y based based on o n oxygen oxygen isotope i s o t o p e data, d a t a y that that consistent w i t h Livnat's which m mineralized Lake V Volcanics were ssea water, tthe h e ffluids l u i d s which i n e r a l i z e d tthe h e PPortage o r t a g e Lake o l c a n i c s were ea w a t e r y aat t least least orr n not of w water iin n part. p a r t . However, However, whether o o t the t h e body of a t e r related r e l a t e d to t o the t h e hyaloclastic hyaloclastic horizon i s not n o t known. known. h o r i z o n was sea s e a water w a t e r or o r fresh f r e s h is I I I I I I I Figure F i g u r e 1. 1. Approximate location l o c a t i o n of of hyaloclastic h y a l o c l a s t i c horizon horizon l i n e ) and g e n e r a l i z e d stratigraphy s t r a t i g r a p h y near n e a r Eagle E a g l e River. River. (dashed line) generalized References: References : Hubery N . K e Y 1973, USGS Prof. P r o f . Paper P a p e r No. No. 754—C, 754-Cy p. p. C1—C32. Cl-C32. Huber, N.K., L i v n a t , A. 1983 Ph.D. Ph.D. Dissertation, D i s s e r t a t i o n , University U n i v e r s i t y of of Michigan, Michigany Livnat, A., 1983, 225 .p. 225 p. I I I I I I I 39 I I I �I ot 'Pne Petrology Petroloqy and and Sedimentation Sed~mentatlon ot tne tile iower Lower Proterozoic Protero~olc The Barron Barron tjuartzite, uuaxtzlte, Northwestern Aortnwestern Wisconsin hlsconsin University at ot dendy Jo Jo Johnson Johnson (Dept. (Dept. of of Geology, Geo.Logy,University Wendy Minnesota—Duluth, innesota 55812) Pilnnesota-Duluth, Duluth, Uuluth, Yiinnesota 55812 ) The The Barron Barron Quartzite Quartzite of of northwestern northwestern Wisconsin Wisconsin is is aa fine—grained, fine-grainedf quartz—cemented, quartz-cemented, butt butt to to red rea quartz quartz arenite arenlte with xlth scattered scattered quartz quartz pebbles pebbles and and aa thin thin basal basal quartz-pebble quartz-pebble thickness of of the the Barron Barron is 1s at at least lsast 225 2 2 5 inI I ~ conglomerate. Tne Tne thickness conglomerate. shown by drill core) and may be greater than 400 in. (as shown by drill core) and may be greater than 400 m. (as ?iafic dikes dlkss cut cut the the Barron Barron Uuartzite Quartzite out out are are as as yet yet undated. unaated. £4afic The Quartzite The primary primary framework framework component component of of the the Barron Barron Quartzite is common common quartz quartz (75%). ( 7 5 % ) . Polycrystalline Polycrystalline quartz quartz (grains [grainswitn vi1cr-i is component crystals), crystals), stretched stretched polycrystalline polycrystalline quartz quartz to 55 component 22 to (composites (composites of o numerous, numerous, suctured suctured crystals), crystals), recrystallized recrystallized quartz quartz (grains (grains made made up up of of numerous, numerous, small, small, polygonal polygonal crystals) 16% crystals) and and vein vein quartz.together quartz.togethermake make up up approximately approximately L6% of framework framework grains. grains. Multicycle ~ulticyclequartz quartz grains grains (common (common of quartz continuous of quartz grains grains which which have haveoptically optica~ly continuousoveryrowttis overgrowtt~s of quartz by other other quartz that that have have been been abraded abraded and and surrounded surrounded by overgrowths) are are also also present. present. Chert Cnert and and iron—formation iron-fornatlon overgrowths) rock rock fragments fragments occur occur but but are are rare. rare. Feldspar Feldspar is is absent. absent. Quartz Quartz cement, cement, which which occurs occurs as as optically optically continuous continuous overgrowths overgrowths on on quartz quartz grains, grains, is is common common (approximately (approximately9%) 9%) and and hematite hemstite cement cement constitutes constitutes less lessthan than1%. 1%. The The heavy heavy mineral suite suite is is composed composed almost ,almostentirely entirely of of rounded rounded zircon zircon mineral with with minor minor rounded rounded tourmaline tourmaline and and rutite, rutile, and and minor minor magnetite. magnetite. AA possible possible depositional depositional environment environment for for the the Barron aarron Quartzite plain which braidedal.LuviaJ. alluvial plain wnlch was was superseded supe~seded Quartzite is isaabraided by aa marine inarine shelf shelf environment. environment. Paleocurrent Paleocurrent data data are are by pattern towards variable. Most Nost localities localitiesshow showa auniiuodai. unlmodal pattern towards variable. the tne south, south, indicating indicating sediment sediment transport transport from from north north to to south. however, fiowever, polymodal polyinodal and and bimodal—bipolar bimoaal-9ipolar patterns patterns are are south. also present present at at some some outcrops. outcrops. AA unimodal unimodal pattern pattern probably probably also indicates environment while indicates aa fluvial fluvlal depositionai. dspositlonal environment while aa bimodal-bipolar bimoual-bipolar pattern pattern could could suggest suggsst aa tidally-influenced tidally-lnfluenceu marlne depositional depositional environment. environfuent. marine The The Barron Barron Quartzite Quartzite is is probably correlative correlative with with several quartzites in In the the iake L ~ K S several of of the tne other other Precambrian Precambrian quartzites Superior region, region, including including the the Baraboo, Baraboo, Sioux, Slouxf Flambeau, Flambeau, Superior Quartzites. Ot Ot these, these, the tne Baraboo Baraboo is 1s waterloo,and and£4cCaslin ~tlcCaslinQuartzites. aterloo, the the best best dated, dated, probably probably having havlng been been deposited deposited between between 1760 L760 and 1630 Lb30 Ma ~4a(Van (VanSchinus, Schmus, 1978; Van Schmus Schmus and and Bickiord, Bickiorci, and l98L). 1981.). N.K., l97Bf Geochronoiogy Geochronology of of the the southern southern Van Schmus, Schmus, W.R., Van 1978, Wisconsin rhyolites rhyolites and and granites: granitss: Geoscience Geoscience Wisconsin, hisconsln, Wisconsin v. 2, 2, p. p. 19—24. 19-24. v. 40 �I Schmus, 'PJ.L<.~ W.R., aand 1q81, PProtrozoic n d Sicktord, i c k k ~ r dij.E., q~. E . , 1981, rotsrozoic Van Schmust c n r o n o l o g y and a n d evolution evolution o of tne tilemicicontinent m i c i c o n t ~ n e n tregion rsgion crironology in Kroner, North A . * ed., ed.* Precambrian P r e c a m b r ~ a nelate Plate N o r t h America: in K r o n e r , A., Tectonics, * l ' e c t o n i c s t Elsevier, ~ l s e v G r *New Sew york, YorK* p. p . 261—296. 261-296. I I I I I I I I I I •1 I •1 I 41 I I I �and Hecla Hecla Conglomerate, Conglomerate, Caliche Paleosol P a l e o s o l in i n the t h e Lower Lower Part P a r t of of the t h e Caluinet Calumet and Mine, Calumet, Centennial Mine, Calumet, Michigan J. Kalliokoski J. K a l l i o k o s k i and Edwin J. J. Welch (Dept. (Dept. of Geol. Geol. and and Geol. Geol. Engrg., Engrg., University, M I 49931) 4993 1 ) Michigan Technological U n i v e r s i t y , Houghton, Houghton, MI The Calumet Calumet and Hecla Conglomerate, Conglomerate, a Keweenawan Keweenawan interfiow i n t e r f low sedimentary sedimentary unit unit about 1.1 b.y. b.y. in tthat h a t is i s about i n age consists c o n s i s t s aatt the t h e Centennial Mine of of aa felsitic felsitic upper p part and of of about about 1—2 of siltstone conglomerate upper a r t and 1-2 m of s i l t s t o n e and shale s h a l e along along the t h e base base fine—grained sediments there 1A). In I n these t h e s e fine-grained t h e r e is i s a complex complex sub—mature sub-mature (Figure 1A). profile represented by an upward increase ccaliche a l i c h e ssoil oil p r o f i l e represented i n c r e a s e in i n calcite c a l c i t e and and corresponding changes in corresponding i n ccalcite a l c i t e structures s t r u c t u r e s (Figure ( F i g u r e 1B) (Welch, (Welch, 1977). 1977). There is is All aalso l s o ccaliche a l i c h e ccalcite a l c i t e in i n the t h e felsitic f e l s i t i c conglomerate. conglomerate. A l l of of this t h i s calcite c a l c i t e predates predates period of of rregional tthe h e period e g i o n a l eepidote p i d o t e aalteration l t e r a t i o n as a s demonstrated on parts p a r t s of of the the 35—level where where tthis has been altered 35-level h i s ccalcite a l c i t e has a l t e r e d to t o epidote. epidote. Introduced ccalcite weight percent Introduced a l c i t e vvaries a r i e s from about 50 tto o 60 weight percent in i n some some upper layers of tthe weight p percent l a y e r s of h e bbasal a s a l uunit n i t to t o 10 weight e r c e n t and less l e s s in i n faintly f a i n t l y veined mudstone (Figure (Figure 1B). 1B). The introduced calcite c a l c i t e occurs in i n an upward grading grading microscopic v veinlets, sequence aas s microscopic e i n l e t s , thin t h i n rims on basalt b a s a l t clasts, c l a s t s , 33 cm cm oval o v a l nodules, nodules, horizontal h o r i z o n t a l lenticles l e n t i c l e s that t h a t may represent r e p r e s e n t coalesced coalesced and and flattened f l a t t e n e d nodules, nodules, K—fabrici is multi—generation veinlets, multi-generation v e i n l e t s , and and as a slayers l a y e r with s withK—fabric. K-fabric. K-fabric s the the designation with d e s i g n a t i o n ffor o r calcite—rich c a l c i t e - r i c h llayers ayers w i t h ffloating l o a t i n g clasts, c l a s t s ,produced produced by by under shallow overburden conditions replacement ccalcite a l c i t e under c o n d i t i o n s (Gile ( G i l e et e t al., a l . , 1965). 1965). overlain The above ttextural e x t u r a l sequence is is o v e r l a i n locally l o c a l l y by a second second similar s i m i l a r sequence. sequence. major features IIn n tthin h i n ssections e c t i o n s tthe h e major f e a t u r e s are a r e the t h e partial p a r t i a l to t o complete complete textural textural replacement of of feldspar replacement f e l d s p a r by calcite c a l c i t e and the t h e corresponding relative r e l a t i v e increase i n c r e a s e in in the proportions of the the p r o p o r t i o n s of t h e quartz q u a r t z and opaque components, components, and and the t h e exfoliation e x f o l i a t i o n of of biotite b i o t i t e cclasts l a s t s and clay c l a y chips c h i p s by introduced introduced calcite. c a l c i t e . Textures and and structures structures suggesting carbonatization c a r b o n a t i z a t i o n at a t a shallow depth are a r e the t h e K—fabric, K-fabric, and and aa soil soil mjcroreljef m i c r o r e l i e f structure s t r u c t u r e —— a llocal o c a l aantiforinal n t i f o r m a l f flexure l e x u r e iin n ccalichefied a l i c h e f i e d shale. shale. Subsequent Subsequent compaction is i s suggested by the t h e lensoid l e n s o i d shape shape of of calcite c a l c i t e nodules, n o d u l e s , and and wrinkles in i n vertically v e r t i c a l l y oriented o r i e n t e d calcite c a l c i t e veinlets. veinlets. -- The fine—grained fine-grained basal b a s a l unit u n i t has undergone undergone chemical chemical alteration a l t e r a t i o n during during ccarbonatization a r b o n a t i z a t i o n under ambient surface s u r f a c e conditions c o n d i t i o n s so s o that t h a t aa soil s o i l forming forming process process However, in and a profile p r o f i l e can can be identified. i d e n t i f i e d . However, i n the t h e conglomerate the t h e ccalcite alcite occurs o c c u r s in i n a less—recognizable less-recognizable form. form. White sparry s p a r r y calcite c a l c i t e rims pebbles pebbles and and fills fills interstices pebbles, i n t e r s t i c e s between p e b b l e s , generally g e n e r a l l y along subhorizontal s u b h o r i z o n t a l zones zones (Figure ( ~ i g u r elB). 1 ~ ) . This texture This t e x t u r e resembles resembles that t h a t described d e s c r i b e d by Gile G i l e and others o t h e r s (1966) (1966) as a s an an iintermediate n t e r m e d i a t e stage s t a g e of of caliche c a l i c h e in i n gravelly g r a v e l l y soils. s o i l s . Such cemented gravel g r a v e l can can be be unit described of it i t occurs in i n the t h e lower lower fine—grained fine-grained u nit d e s c r i b e d also a l s o as a s calcrete. c a l c r e t e . A bed of ((Figure F i g u r e IB). 1B). These kinds of of calcite—cemented calcite-cemented conglomerates conglomerates have have been been reported reported from an area a r e a that t h a t extends from 30 km km east e a s t of of Centennial Centennial (Davidson (Davidson et e t al., a l . , 1955) 1955) about 20 20 kkm southwest of of C Centennial, m southwest e n t e n n i a l , and are a r e very common in i n the t h e Copper Copper Harbor Harbor tto o about Conglomerate both on the (Wolff and and Huber, Huber, 1973). 1973). t h e peninsula and on Isle I s l e Royale Royale (Wolff Because nnative copper is abundant in Because a t i v e copper i s nnot o t abundant i n calcite—rich c a l c i t e - r i c h portions p o r t i o n s of of conglomerates, conglomerates, tthere h e r e is i s tthe h e ssuggestion u g g e s t i o n tthat h a t the t h e quantity q u a n t i t y and distribution d i s t r i b u t i o n of of native n a t i v e copper copper in in and H H conglomerate may may have been controlled tthe h e CC and c o n t r o l l e d by a pre—existing p r e - e x i s t i n g pedogenic pedogenic ccalcite. alcite. New analysis ked ssparry a n a l y s i s on on aa hand—p hand-picked p a r r y cca cite l c i t e from from aa calcite c a l c i t e rich r i c h layer l a y e r in i n the the +20.9; <S basal C: b a s a l unit u n i t gave gave values v a l u e s ((d 0: +20.9; C: —1.0) -1.0) that t h a t are a r e indistinguishable indistinguishable obtained by Livnat (1983) on all from tthose h o s e obtained a l l types t y p e s of of calcites c a l c i t e s in i n the t h e Portage Portage Lake Volcanics and and the t h e Copper Harbor Conglomerate. Conglomerate. He concluded that t h a t the the ranges in ccajites a l c i t e s had had undergone undergone homogenization homogenization and and that t h a t their t h e i r narrow ranges in C v values a l u e s denoted a CO2 CO source source from from either e i t h e r single s i n g l e magma or o r from from two two sources, sources, 2 one aa Precambrian Precambrian limestone. limestone. This probably probably was was the t h e caliche. caliche. 42 - �_________ ________ _________ _______ ________ _________ ___________ _________ The caliche c a l i c h e is i s interpreted i n t e r p r e t e d to t o have developed developed in i n slowly s l o w l y aggrading a g g r a d i n g sediments sediments This h i s ttook o o k place p l a c e during during were deposited tthat h a t were d e p o s i t e d on a basalt—floored b a s a l t - f l o o r e d fluvial f l u v i a l plain. plain. T of sslope of tthe tthe h e initial i n i t i a l sstages t a g e s of l o p e rreversal e v e r s a l of h e lava l a v a pplain, l a i n , ffrom r o m southerly s o u t h e r l y to to highly c a r b o n a t e accumulation in i n sediments sediments rrequires equires a h i g h l y seasonal seasonal northerly. n o r t h e r l y . Such carbonate and rrepresents about 15,000 y years e a r s of of weathering. weathering. ttemperature e m p e r a t u r e oor r ttropical r o p i c a l cclimate l i m a t e and e p r e s e n t s about paleolatitude been rreported The corresponding c o r r e s p o n d i n g Keweenawan p a l e o l a t i t u d e hhas a s been e p o r t e d tto o be about 30 degrees d e g r e e s north. north. o _io e0Ocp IIIIl l ?? - IIIIl l I1 c • 0 w 1•L• a, Ca a, E 2 a, - -— - - 'I—Il' 11-111 II — — a, o0 60 wt.% CALCITE CALCITE Generalized G e n e r a l i z e d ssections e c t i o n s at a t the t h e base b a s e of of tthe h e Calumet Calumet and Hecla Conglomerate. A,, stratigraphy; A s t r a t i g r a p h y ; thickness t h i c k n e s s about about 1.5 m; m; B, B , Modes of of occurrence o c c u r r e n c e of of calcalcite c i t e ((unpatterned). u n p a t t e r n e d ) . Numbers Numbers denote denote morphologic sstage t a g e of of the t h e caliche; caliche; calcite c a l c i t e abundance by chemical analysis. analysis. . A I I I I I I I I I B I References References Davidson, of the Davidson, E.S. E.S. and others, o t h e r s , 1954, Bedrock geology of t h e Mohawk Quadrangle, U.S. Geol. Michigan: U.S. Geol. Quadrangle Quadrangle Map Map GQ54, GQ54, scale s c a l e 1:2400. 1:2400. master L.H. and others, G i l e , L.H. o t h e r s , 1965, 1965, The K horizon: horizon: a m a s t e r soil s o i l horizon h o r i z o n of of carbonate carbonate Gile, Soil accumulation: S o i l Science, S c i e n c e , v. v. 99, 9 9 , p. p. 74—82. 74-82. Gile, Gile, L.H. and o others, genetic L.H. t h e r s , 1966, Morphological and g e n e t i c sequences in i n carbonate carbonate accumulation in i n desert d e s e r t soils: s o i l s : Soil S o i l Science, S c i e n c e , v. v. 101, 1 0 1 , p. p. 347—360. 347-360. Livuat, Alexander, 1983, Metamorphism and copper m mineralization i n e r a l i z a t i o n of of the t h e Portage Portage L i v n a t , Alexander, unpub. Ph.D. Univ. of Lake Lava Series, S e r i e s , northern n o r t h e r n Michigan: Michigan: unpub. Ph.D. thesis,. t h e s i s , Univ. of Mich., Mich., Arbor, 270 Ann Arbor, 270 p. p. 1 1 I 1 Origin of the mudstone at Welch, Edwin JJ., . , 1977, 1977, O r i g i n of t h e caliche—bearing c a l i c h e - b e a r i n g mudstone a t the t h e base b a s e of of the Calumet and and Hecla Hecla Conglomerate, Conglomerate, C Centennial Mine, Houghton Houghton County, County, MichiMichit h e Calumet e n t e n n i a l Mine, Unpub. M.S. M.S. thesis, Mich. Tech. Tech. Univ., Univ., Houghton, Houghton, M Mi, gan: Unpub. t h e s i s , Mich. i , 53 p. p. R.G., and Huber, 1973, The Copper Harbor Conglomerate (middle (middle Wolff Wolff,, R.G., Huber, N.K., N.K., 1973, U.S. Keweenawan) on Isle i t s regional r e g i o n a l implications: i m p l i c a t i o n s : U.S. Keweenawan) I s l e Royale, Michigan Michigan and and its Geol. Geol. Sur. Sur. Prof. P r o f . Paper 754—B, 754-B, p. p. B1—B15. B1-B15. LU i I �- STRUCTURE OF OF THE THEBEARDMORE BEARDMORE - GERALDTON GERALDTON FOLD FOLD BELT BELT STRUCTURE M. M. M. Kehienbeck Kehlenbeck M. Department Department of of Geology Geology Lakehead University University Lakehead BetweenBeardinore Beardmore and and Geraldton, Geraldton, complexly complexly folded foldedArchean ArcheanrnetametaBetween sedimentary and and metavolcanic metavolcanic rocks rocks form form an an intervening intervening terrain terrain bounded bounded sedimentary thethe Wabigoon on the thenorth northand and south south by by structures structuresofof Wabigoonand and Quetico Quetico subsubon provinces respectively. respectively. provinces The Beardmore Beardmore — Gerald.ton Geraldton fold belt is divisible into several The narrow, east-west east-west trending trending segments, segments, based based on on the the structural structural facing facing narrow, Structural facing facing directions directions are are either either east east or or direction of of folds. folds. Structural direction Depending on fold hinge line orientations, folds face upward, west. Depending on fold hinge line orientations, folds face upward, west. Where the the structural structuralfacing facing is is upward, upward,individual sideways,or or downward. downward. Where individual sideways, Where the the structural structural facing facing folds are are either either anticlines anticlinesor orsynclines. synclines. Where folds is antiformal is downward, downward, these these structures structuresare are synformal synformal anticlines anticlines or or antiformal Sideways structural structural facing facing is is associated associated with with neutral neutral folds. folds. synclines. Sideways synclines. Because Because of of variations variations in in structural structural facing facing within within and and between between narrow narrow segments, segments, the the fold fold belt belt as as aa whole whole represents represents aa disrupted disrupted and and discontinuous stratigraphy. stratigraphy. Discontinuities Discontinuities separating separating distinctive distinctive discontinuous segments segments are are zones zones of of pronounced pronounced shearing shearing which which are are coplanar coplanarwith with the the axial schistosity schistosity of ofthe thedominant dominantfolds. folds. axial Documented Documented reversals reversals in in the the structural structural facing facing direction direction between between the the segments segments of of the the fold fold belt belt suggest suggest that that the the last last folding folding episode episode Although no no refolded refolded occurred in in rocks rocks which which had had been been previously previously folded. folded. Although occurred folds folds were were observed observed in in outcrop, outcrop,the the presence presence of of an an earlier earlierschistosity schistosity has has been been recorded recorded in in several severalthin thin sections sectionsfrom from widely widely separated separatedlocalities. localities. The The second second folding folding was was in in response response to to an an inhomogeneous inhomogeneous fold-forming fold-forming shear component component accompanied accompanied by by aa homogeneous homogeneous compressive compressive strain. strain. The The shear shear shear component component formed formed folds folds of of various various amplitudes amplitudes and and wavelengths wavelengths with with shear shear planes planes everywhere everywhere parallel parallel to to the the axial axial surface surface of of these these folds. folds. Fold Fold hinge hinge lines lines parallel parallel the the intersection intersection of of the the shear shear planes planes and and the the surfaces undergoing undergoing folding. folding. Where Where the the shear shear direction direction lies lies in in the the surfaces surfaces surfaces undergoing undergoing folding, folding, no no folds folds developed developed although although the the rocks rocks show show strain component evidence of of internal internaldeformation. deformation. The The homogeneous homogeneous strain component evidence and. preserved preserved the the similar similarfold foldforms. forms. acted normal normal to the theshear shearplanes planesand acted Maximum extensive extensive strains parallel the shear shear direction, direction, and and shear shear disdisMaximum continuities continuities are are most most evident evident in in fold fold hinge hinge zones zones and and less less so so on on fold fold limbs where where the the layering layering and and axial axial planar planar schistosity schistosityare are commonly commonly subsublimbs parallel. parallel. - fold belt is divisible into several strains parallel the - The structural history Beardinore The structural historyofofthe the Beardmore - Geraldton Geraldton fold foldbelt beltmay may be summarized as follows: be sunuriarized follows: DDeformationand and metamorphism metamorphism of of sedimentary sedimentary and and volcanic volcanic rocks rocks Deformation D1 1 axial producing, at in part, part,folds foldsand and an an accompanying accompanying axial producing, at least least in tectonics including planar schistosity. schistosity. Gravity Gravity tectonics including thrusting thrusting planar may havebeen beenresponsible responsiblefor forthe the inversion inversion of of portions may have portions of of the stratigraphy. stratigraphy. the Development of similar folds by inhomogeneous shear and homohomoD2 D,, Development of similar folds by inhomogeneous shear and geneous strain strain in in surfaces surfaces of of variable variable orientation. orientation. Shear geneous Shear discontinuities discontinuities became became locally locally coneentrated concentrated as as shear shear zones zones in thin thin competent competent layers. layers. Large Large scale scale transposition transposition of of in individual, individual, shear shear zone zone bounded bounded segments segments led led to to the the disruption disruption of of the the stratigraphy stratigraphy of of the the fold foldbelt. belt. 44 I �I III I Geraldton I I I I Je/,j0 Structural facing_ of dominant folds upward 0 1Km sideways downward Eastern portion portion of of the the Beardmore—Geraldton Beardmore-Geraldton fold fold belt. belt. Eastern Individual segments segments reflect reflect variations variations in in the the plunge plunge Individual direction of of hinge hinge lines lines and and the the structural facing of of structural facing direction folds. The The segments segments are are separated separated from from each each other other fclds. by shear shear discontinuities. discontinuities. by 45 I I I I I I 1 I I I I �I STRUCTURAL STRUCTURAL GEOLOGY GEOLOGY AND AND KINEMATICS KINEMATICS OF OF EARLY EARLY PROTEROZOIC PROTEROZOIC SHEAR SHEAR ZONES ZONES IN I N CENTRAL CENTRAL WISCONSIN WISCONSIN . .- a. Klasner, Western Department Geol ogy, Western Illinois I 1 1 i noi s Department of o f Geology, Klasner, S. Macomb, inois 6145 and and G. G. L. L. LaBerge, LaBerge, Department Department Illin o i s 61455 Universi ty, Macomb Ill University, of University of Wisconsin, Oskosh, Oskosh, Wisconsin Wisconsin 54'701 49O1 f Wisconsin, o f Geology, Geology, U nivers t y o I J J. and in March C l a i r e Dells, Dells, March Rapids, Rapids, and Athens Athens in Rocks Rocks at a t Eau Eau Claire lend W i s c o n s i n have numerous 1 end c e n t r a l Wisconsin numerous structural s t r u c t u r a l features f e a t u r e s that that central themselves a n a l y s i s of o f the the nature n a t u r e and and kinematics k i n e m a t i c s of ot themselves to t o field f i e I d analysis deformation. At deformation. At EAU CLAIRE CLAIRE DELLS DELLS deformation d e f o r m a t i o n has has produced produced aa in p a r t i a l 1 y developed developed sigmoidal s i g m o i d a l pattern p a t t e r n in i n foliation f o l i a t i o n trends trends in partially finally foliations are progressively overprinted and which ENE ENE $01 i a t i ons a r e p r o g r e s s i v e l y o v e r p r i n t e d and f i na1 1 Y which Strain NNE foliation. replaced r e p l a c e d by by the NNE foliation. S t r a i n features f e a t u r e s in i n the the Dells Dells horizontal WNW elongation zone show zone show vertical vertical e l o n g a t i o n and and WNW horizontal shear crenulation Kink K i n k bands bands and andc r e n u l a t i o n folds f o l d s of o f foliation foliatian compression. Xenoliths indicate multiple i n d i c a t e mu1 o f intensely intensely t i p l e periods p e r i o d s of o f deformation. deformation. Xenol i t h s of deformed rock r o c k in i n the t h e Wolf Wolf River R i v e r batholith b a t h o l i t h near near the the Dells D e l l s suggest suggest deformed the deformation that d e f o r m a t i o n at a t the the Dells Del 1 s . predated p r e d a t e d intrusion i n t r u s i o n of of the that Structural batholith. batholith. S t r u c t u r a l measurements measurements near near MARCH MARCH RAPIDS RAPIDS indicate indicate from is separated the gneiss that tonal i t i c that tonalitic g n e i s s at at t h e rapids rapids is separated from metasedimentary and and metavolcanic m e t a v o l c a n i c rocks r o c k s to t o the the north n o r t h by by aa zone zone of of metasedimentary Foliation i n t e n s e brittle b r i t t l e deformation. deformation. F o l i a t i o n at a t MMarch a r c h Rapids Rapids south s o u t h of of intense folds Axes the the breccia b r e c c i a zone strikes s t r i k e s WNW and and dips d i p s steeply steep1 y N. N. Axes of of f a 1 d5 the fol iation plunge steeply to the E as do the long axes in in f o l i a t i o n plunge steep1 y t o the the l o n g axes of of The foliation shaped ellipsoidal shaped clasts c l a s t s in i n the the gneiss. gneiss. f o l i a t i o n and and E— Eellipsoidal open t r e n d i n g fold f o l d axes axes were were refolded r e f o l d e d into i n t o steep s t e e p N—plunging N-plunging open trending Foliation folds. folds. F o l i a t i on north n o r t h of o f the t h e breccia b r e c c i a zone zone strikes s t r i k e s ENE ENâ and dips dips doo the Folds steeply s t e e p l y S. S. F o l d s in i n bedding b e d d i n g plunge 300to 3 @ t o the the EE as asd the lorg long Foliation axes of o f ellipsoidal e l l i p s o i d a l clasts. clasts. F o l i a t i o n has has been been deformed deformed by by kink kink in ATHENS At ATHENS conspicuous conspicuous foliation fol iation i n felsic f e l s i c mylonite myloni t e bands. At Its strikes s t r i k e s NE NE and and dips d i p s steeply s t e e p l y NW. NW. I t s orientation o r i e n t a t i o n differs d i S f e r s from from The orientations structural o t h e r rocks r o c k s in i n the the region. region. The structural o r i e n t a t i o n s in i n all a1 1 other structural s t r u c t u r a l relationship r e 1 a t i onshi p between between nearby nearby bedded bedded rocks r o c k s and and mylonitic my1 on i % i c shear shear foliation f o l i a t i o n is i s nearly n e a r l y identical i d e n t i c a l with w i t h aa ductile d u c t i l e shear shear zone zone on on Foliation 1 highway S. highway U. U. S. 51near near Brokaw. Brokaw. F o l i a t i o n in i n mmetavolcanic e t a v o l c a n i c rocks rocks south s o u t h of of the the Athens f i t h e n s shear shear zone zone strikes s t r i k e s ENE ENE and and dips d i p s steeply s t e e p l y NW. NW. F o l d axes axes i n this t h i s region r e g i o n plunge gently gent1 y ENE ENâ and and the the X X axes axes of of Fold in gneiss ellipsoidal clasts Migmati ellipsoidal c l a s t s are nearly n e a r l y vertical v e r t i c a l.. M i g m a t itic tic g n e i s s at at Goodrich has Gaodrich Dells, Dells, 7 - m i l e s north n o r t h of o f Athens, has an an ENE— ENEabout 7—miles trending, v e r t i c a l foliation f o l i a t i on and and SW—plunging SW-pl ungi n g folds. $01 d5. t r e n d i n g , nearly near1 Y vertical - zones oof A l l three t h r e e areas a r e a s are a r e characterized c h a r a c t e r i z e d by by 1 l i ninear e a r zones f intense intense All d e f o r m a t i o n that t h a t diverge d i v e r g e trom f r o m the the regional r e g i onal structural s t r u c t u r a l fabric and +abr i c and deformation t h a t separate s e p a r a t e regions r e g i o n s with w i t h different d i f f e r e n t structural structural pictures. Eau that pictures. Eau C l a i r e Dells D e l l s and and Athens are a r e ductile d u c t i l e shear shear The March March Claire zones. The i t is i s possibly p o s s i b l y aa Rapids area a r e a is is a a zone zone of o f brittle b r i t t l e deformation; deformation; Rapids it ductile—brittle These shear d u c t i 1 e-br i t t l e zone zone of o f shear. shear. shear zones zones are a r e believed be1 i eved to ta have resulted r e s u l t e d from f r o m stresses s t r e s s e s that t h a t were were different d i f f e r e n t from t r o m those those that have that the regional r e g i o n a l structural s t r u c t u r a l fabrics f a b r i c s in i n the the three t h r e e areas. areas. produced the 46 -1 1 �GEOLOGICALSETTING SETTING OF GEOLOGICAL OF GOLD GOLD MINERALIZATION MINEFL4LIZATION IINN BEARDMORE-GERALDTON BEAJUMORE-GERALDTON LAVIGNE, Ministryofof Natural Natural Resources, LAVIGNE, M . JM.J., ., Ministry RED RED LAKE, Ontario is typical for most Archean greenstone belts, hosted by almost all lithologic is As A s is t y p i c a l f o r most Archean greenstone b e l t s , gold gold mineralization mineralization is hosted by almost a l l l i t h o l o g i c iin n the t h eBeardmore-Geraldton Beardmore-Geraldton camps camps is associations ccannot types, t h u s specific s p e c i f i c llithological i t h o l o g i c a l associations a m o t be used as as types, thus denominator. This fundamental genetic feature common a of is genetic f e a t u r e aa comon Archean gold mineralization. The host rocks Archean gold mineralization. The host rocks represent represent aabroad broadspectrum spectrum of time and and events, events, from from the t h eoldest o l d e s tvolcanic volcanicand andsedimentary sedimentary of geologic geologic time rocks Uniform gold ddistribution rocks to t o the t h eyoungest youngest Archean Archean intrusions. intrusions. Uniform gold istribution suggest that iin n all a l llithologic l i t h o l o g i ctypes types suggest t h athe t t hmechanism e mechanismof ofgold goldconcentration concentration processes associated is independent of tthe h e processes associated with with tthese h e s e rocks. It suggest that t h a t a ssingle i n g l e process process was was active a c t i v ethroughout throughout does, however, suggest t h e b e l t and a f f e c t e d a l l l i t h o l o g i e s uniformly on a regional s c a l e . each lithology on lithology responded ddifferently However, on a local l o c a l scale s c a l e each ifferently However, This process . This process affected a f f e c t e d young young intrusions i n t r u s i o n s which which post post t o t h e process. In date date the t h e supracrustals supracrustals and and subsequent subsequent iisoclinal s o c l i n a l folding. folding. I n Geraldton, Ckraldton, f i e l d r e l a t i o n s h i p s have c l e a r l y established t h a t t h e r e l a t i v e timing of those those hydrothermal process mineralization, p r o c e s s sresponsible responsible ffor o r gold mineralization, with respect t o t h e host rocks, w e r e t h e l a s t events i n t h e evolution The formation formation of of supracrustals of t h e greenstone b e l t . The s u p r a c r u s t a l swas was succeeded succeeded by tthe h e following sequence of events; isoclinal i s o c l i n a l folding, folding, regional felsic magniatic activity dextral d e x t r a l shear, mafic magmatic magmatic activity, activity f e l s i c magmatic a ctivity Dextral and finally f i n a l l y gold gold mineralization. mineralizatione Dextral shear shear was an an ongoing ongoing process process from to the from its its onset thru ko t h e last l a s t stages s t a g e s of of gold gold mineralization. mineralization. The common denominator The comon tto o all a l l gold mineralization in in high strain, tthis h i s belt b e l t is is tthe h e association association with zones of high s t r a i n , regional extent. iin n extent. This entire e n t i r e greenstone e l t has undergone pronounced greenstone bbelt d e x t r a l d u c t i l e shear. This has produced t h e r a t h e r unique l i n e a r , E-W trending volcanic This is E-W trending volcanic and and sedimentary sedimentary bbelts. elts. This is distinct d i s t i n c t from from lower strain s t r a i n greenstone belts b e l t s iin n which llithologic i t h o l o g i c packages do do not have regional preferred orientation. orientation. The present configuration of the can only of t h e belt b e l t can only be be produced produced as a s the t h e result r e s u l t of extremely extremely high high The stress. stress. The E-W E-W trending contacts c o n t a c t s between all a l l major lithologic lithologic units of high u n i t s are a r e zones of high strain. strain. Zones of of high high strain s t r a i n also a l s o occur Zones is found within these t h e s e llithologic i t h o l o g i c packages. packages. mineralization is Gold mineralization exclusively exclusively within within these t h e s e zones of high s t r a i n . I n Geraldton, Geraldton, these these In zones aalso l s o contain an anomalously anomalously high proportion proportion of both f e l s i c mafic and maf It appears ttherefore h e r e f o r e tthat h a t strain s t r a i n induced i c iintrusives. ntrusives permeability and hydrothermal hydrothermalaactivity permeability focused focused rnagmatic magmatic and c t i v i t y which which resulted resulted and mineralization. These zones of high sstrain iin n aalteration l t e r a t i o n and mineralization. train a re are easily all e a s i l y identified; identified; a l l primary volcanic, igneous and sedimentary sedimentary ttextures e x t u r e s have have been eeither i t h e r modified o bliterated. These zones zones orr o obliterated. also by tight may a l s o be identified i d e n t i f i e d by t i g h t repeated h e presence presence repeated folding and tthe of an high proportion of intrusions. an anomalously high IIn n conjunction intrusions. of high with t h e i d e n t i f i c a t i o n of high strain, s t r a i n , the t h e presence presence of of hydrothermal hydrothermal alteration, a l t e r a t i o n , serve to t o identify i d e n t i f y areas areas with with high high gold gold potential. potential. It is the belt and affected all lithologies uniformly on a regional scale. to the process. field relationships have clearly established that the relative timing with respect to the host rocks, were the last events in the evolution of the greenstone belt. , dextral ductile This has produced the rather unique linear, zones of high strain. . It felsic with the identification n 47 �I RANIER,MINNESOTA,NINERAL OUTCROP R4NIER,MINNESOTA,MINERAL POTENTIAL POTENTIAL EVALUATION: EVALUATI0N:OUTCROP SAMPLING, SAMPLINGy GEOPHYSICS GEOPHYSICS AND AND SOIL SOIL GEOCHEMISTRY GEOCHEMISTRY The i s located l o c a t e d east e a s t of of International I n t e r n a t i o n a l Falls, F a l l s y Minnesota, Minnesota, The Ranier Ranier area a r e a is just j u s t south s o u t h of of the t h e Canadian Canadian border. border. Outcrops Outcrops in i n the t h e area a r e a display d i s p l a y many many of of the same structural, lithologic and metamorphic characteristics as t h e same s t r u c t u r a l y l i t h o l o g i c and metamorphic c h a r a c t e r i s t i c s a s large large Canadian Canadian gold gold deposits. d e p o s i t s . At A t Little L i t t l e American American Island I s l a n d 500 500 tons t o n s of of gold gold bearing bearing rock was mined and milled in 1894, which would be ore grade at present rock and m i l l e d i n 1894, which would be o r e grade a t p r e s e n t day day prices. prices. Very low low frequency frequency electro—magnetic electro-magnetic traverses t r a v e r s e s at a t Little L i t t l e American d i s t i n c t i v e profile. p r o f i l e . The profile p r o f i l e defines d e f i n e s silicification silicific~tion I s l a n d y map aa distinctive Island, show aa vague vague indication i n d i c a t i o n of of Magnetometer observations o b s e r v a t i o n s show in i n aa fault f a u l t zone. zone. Magnetometer geologic units. u n i t s . These These characteristic c h a r a c t e r i s t i c VLF—EM VLF-EM profiles p r o f i l e s are a r e repeated r e p e a t e d at at geologic s e v e r a l locations. l o c a t i o n s . Detailed D e t a i l e d induced induced polarization p o l a r i z a t i o n surveys, s u r v e y s y coincident coincident several with w i t h VLF—EM VLF-EM surveys, surveys* define d e f i n e structural s t r u c t u r a l features f e a t u r e s and locate l o c a t e near surface surface disseminated disseminated sulf s u l fides. i d e s . Refraction R e f r a c t i o n sismic s i s m i c profiles p r o f i l e s tested t e s t e d one one such such structural s t r u c t u r a l feature f e a t u r e and and clearly c l e a r l y mapped mapped aa fault f a u l t zone. zone. They They also a l s o help help interpret i n t e r p r e t I.P. I.P. results. results. One mineral One of of the t h e goals g o a l s of of this this m i n e r a l potential p o t e n t i a l evaluation e v a l u a t i o n is i s to t o compare three These three three t h r e e geochemical geochemical sample sample media media over over gold gold bearing b e a r i n g lithologies. l i t h o l o g i e s . These vegetation; "Ao" (humus) horizon, and "A1" soil horizon. media media are: a r e : v e g e t a t i o n ; "Aott (humus) h o r i z o n , and "Altt s o i l h o r i z o n . A limited l i m i t e d number of of samples samples from from all a l l three t h r e e media media correlate c o r r e l a t e to t o help h e l p locate locate These are defined areas of interest and select drill sites. a r e a s of i n t e r e s t and s e l e c t d r i l l s i t e s . a r e d e f i n e d by by anomalous anomalous samples as a s high high as a s twenty twenty times times background. background. samples Two diamond drill d r i l l holes h o l e s confirm confirm structures, s t r u c t u r e s * silicification s i l i c i f i c a t i o n and and Mineralization M i n e r a l i z a t i o n is i s indicated i n d i c a t e d by assays a s s a y s of of short s h o r t core c o r e interinters e c t i o n s with w i t h anomalous anomalous gold gold content. c o n t e n t . These These include i n c l u d e one one six s i x inch inch interintersections DDH RR—1 RR-1 of of 3.56 3.56 ppm ppm gold. gold. The fault f a u l t structure s t r u c t u r e defined d e f i n e d by by s e c t i o n from from DDH section The DDH RR—2. RR-2. The highest highest r e f r a c t i o n seismic s e i s m i c methods methods was was further f u r t h e r tested t e s t e d by by DDH refraction gold gold assays a s s a y s for f o r this t h i s hole h o l e were located l o c a t e d in i n intersections i n t e r s e c t i o n s flanking f l a n k i n g the the indicated i n d i c a t e d fault f a u l t zone. zone. s u l f iides. des. suif Mineral potential Ranier area a r e a include: include: p o t e n t i a l evaluation e v a l u a t i o n methods methods for f o r Ranier (1) (1) a literature l i t e r a t u r e search; s e a r c h ; (2) (2) geophysical and and geochemical geochemical surveys surveys of of aa known m mineralized of these i n e r a l i z e d area; a r e a ; (3) (3) extension e x t e n s i o n of t h e s e surveys along a mapped area a r e a of of interest; i n t e r e s t ; (4) (4) tests t e s t s of of geophysical geophysical data d a t a with with outcrop outcrop and and collaborating c o l l a b o r a t i n g geophysical geophysical methods; methods; (5) (5) drill d r i l l holes h o l e s with with assays. a s s a y s . This This evaluation e v a l u a t i o n indicates i n d i c a t e s an an area a r e a of of excellent e x c e l l e n t precious p r e c i o u s metal metal mineral mineral potential. potential. If i t can can be obtained o b t a i n e d from from the t h e D.N.R. D.N.R. Minerals Minerals I f more information is i s desired, d e s i r e d , it MN 55746, phone phone (218) (218) 262—6767. 262-6767. D i v i s i o n y P.O. P.O. Box Box 567, 567y Hibbing, Hibbing* MN Division, By: T. T. L. L. Lawler Lawler J. J. M. M. Sellner Sellner 48 I �The Petroloov of the Lononose F'eridotite ERIC K. LINSCHEID (Department o-f Geology University of Minnesota Duluth, Duluth, MN 55812) The Longnose Peridotite deposit is a funnel shaped. titani-Ferous oxide rich layered ultramafic body located .E. of -4oyt Lakes Minnesota. The Peridotite lies 780m 8 km. above cese c- the atidge ver Troctolite——a basal vdde Proterozoic intrusion of the Troctolitic Series in the Duluth Eight units were distinguished in mapping the Complex. They range in surrounding, country rocks of the deposit. composition from troctolitic anorthosite to feldspathic dunite with anorthositic troctolite to troctolite being the most The units trend N.E and dip 10—25 degrees to the abundant. S.E.. youngin;. eastward. This trend is concordant with the VirQinia formation—Partridge River Troctolite contact. No contact was seen between the country rocks and the Longnose These strata are stratigraphically hich in the Feridotite. Frtride River Troctolite, which has been postulated to have formed b multiple intrusion of magma from the S.E. along the lower Froterozoic Virginia contact and middle Froterozoic North Shore Volcanic group. The deposit is t'tear dropu in plan view trends N.W.—S.E.. In long by 90m. to 488 m. wide. and is approximately Th2m the longitudinal section it forms an asymmetrical funnel; contact on the N.W. dips approximately 15—20 degrees to the 5.E., and the contact on the SE. dips approximately 70 degrees to the N.W.. The Peridotite appears to be layered with an outer shell of relatively oxide poor clinopyroxenite and an inner core of layeredq anomously rich ilmenite—magnetite duniteq peridotite. and picrite. with massive oxide zones occurring within some of the dunitic zones, the largest of which is 40m. Troctolitic anorthosite inclusions are common. thick. The dunitic zones are weakly to strongly serpentinized with minor secondary magnetite hematite, chlorite, talc and carbonate. The clinopyroxenite zone consists a-f titanaugite to hornblende, actinolite—tremolite. and and Fiagiociase may be altered to chlorite or clay. The talc. slightl-i altered oxides remain unaltered except for some occasional minor The Peridotite is ridden with near (nartltizatlor: of magnetite. vertical fractures which commonly nave slickensides. limenite and magnetite constitute the bulk of the ore combined) ulvspinel?. mineralogy with minor (less than Ilmenite—magnetite ha1copyrite, and an isotropic grey mineral. most commonly occur in a broken net—textured fashion, but may also be disseminated or massive. The contacts between these 5 tex -ures sequence can be gradational or sharp. The crystal I i zati on between ilmenite and rnagnetite varies within and i �I between units where either may be cumulate and the other interstitial or both may be cumulate in relation tD the silicate minerals_ Ilmenite exsolution lamellac commonly occur along octahedral cleavage in magnetite. An isotropic grey mineral (spinel?) commonly occurs in both ilmenite and magnetite. In magnetite it can -form along cleavage or as vermicular intergrowth with ilmenite alonq magnetite—ilmenite grain boundries. Ilmenite may contain faint white bands which are interpreted to be ulvospinel. Chalcopyrite is the major sulfide mineral averaging 1. or interstitial The troctolitic anorthosite inclusions appear to be Partridge River Troctolite which were raf ted upon intrusion o-f the Lorignose Peridotite into the Duluth Complex. 50 �Minor EQL F o l d s iu n the I r o nEQtQO.L F%rfiatiAnL !ua tfl Soudan .ici Northeastern Minnesota Northeastern Minnesota Geology (Department James R.. James R. (Department of of Geology University Uni v e r s i t y of o f Minnesota, Minnesota, Minneapolis. Minneapol i s . MN MN Lundy, Lundy, I and Geophysics, and Geophysics, 55455) 554 I part an Minor Minor folds f o l d s in i n the t h e Soudan Soudan Iron I r o n Formation F o r m a t i o n (SIF), (SIF), p a r t a-f of an terrane Archean greenstone/granite greenstone/granite t e r r a n e in i n northeastern n o r t h e a s t e r n Minnesota, Minnesota, Archean Previous have been been exmamined exmamined in i n detail. detail. P r e v i o u s work work suggests suggests the t h e preprehave This sence a llarge sence a-f of a a r g e recumbent recumbent nappe nappestructure.. structure. T h i s structure s t r u c t u r e and and associated a s s o c i a t e d minor folds f o l d s (Fl) ( F l ) have have been been redeformed redeformed during d u r i n g aa second second This tectonic t e c t o n i c event event (F2). (F2?. T h i s study s t u d y attempts a t t e m p t s to t o elucidate e l u c i d a t e the t h e geogeoboth metry and and nature n a t u r e (soft—sediment ( s o f t - s e d i m e n t or o r tectonic?) t e c t o n i c ? ? of o f folds f o l d s of of both metry with generations, w i t h a particular o a r t i c u l a r emphasis emphasis on on trying t r y i n g to t o understand understand generations, the early better b e t t e r the t h e nature n a t u r e of c l y folds f o l d s and and the t h e large l a r g e nappe—].ike nappe-1 ike study The structure. The SIF is especially a l l y useful u s e f u l for f o r this t h i s sort s o r t of of study structure of composition s i n c e it i t is i s made made up up a-f UT .Llayers d y e r -a o f ddifferent ifferent c o m p o s i t i o n and and comsince petence that t h a t became became folded f o l d e d on on a a small s m a l l scale s c a l e during d u r i n g both b o t h deforma— deformapetence tional t i o n a l events.. events. ranging wide variety v a r i e t y of o f fold f o l d shapes shapes is i s observed, r a n g i n g from from AA wide similar, broad warpings of the layering to concentric, broad warpings o f t h e l a y e r i n g t o c o n c e n t r i c , s i m i l a r , and and chevihevthese Using r o n shapes.. shapes. Using appropriate a p p r o p r i a t e quantitative q u a n t i t a t i v e techniques, techniques, these ron Fl shapes shapes are a r e described d e s c r i b e dini ndetail.. detail. F l folds f o l d s tend t e n d to t o be be of o f Class C l a s s 1C 1C F2 with o r Class C l a s s 22 shape, shape, w i t h wide wide variations v a r i a t i o n s in i n interlimb i n t e r l i m b angle. angle. F2 or folds consistent f o l d s tend t e n d to t o be be Class C l a s s 1C 1C in i n shape, shape, with w i t h -fairly fairly c o n s i s t e n t orienorienWhite t a t i o n s and and a much much narrower range range in i n interlimb i n t e r l i m b angle.. angle. White tations cherty l a y e r s consistently c o n s i s t e n t l y behaved behaved more more competently c o m p e t e n t l y than t h a n lean lean cherty layers j a s p e r or o r jaspilite layers. j a s p i 1it elayers.. jasper Detailed D e t a i l e d mapping mapping and and measuring measuring of o f fold f o l d axes, axes, axial a x i a l surfaces, surfaces, and other o t h e r structural s t r u c t u r a l elements has has been been done done in i n an an outcrop o u t c r o p showing showing Fl fine exceptionally f i n e fold f o l d interference i n t e r f e r e n c e patterns p a t t e r n s of of F l and and F2.. F2. exceptionally and F i e l d relationships r e 1a t i o n s h i p s suggest suggest sheath sheath folds f o l d s are a r e present, present, and that that Field of Fortuitous in t h e y are a r e Fl Fl i n age.. age. F o r t u i t o u s XV XY and and XZ X Z cross—sections cross-sections of they VZ and sheaths, and intersections i n t e r s e c t i o n s a-f o f fold f o l d axes axes on on opposite o p p o s i t e sides s i d e sa-f of YZ sheaths, cross—sections c r o s s - s e c t i o n s of o f sheaths sheaths suggest suggest that t h a t high h i g h strains s t r a i n s were were suffered suffered Shear direction during d u r i n gFl.. Fl. d i r e c t i o n during d u r i n g Fl F l is i s more more difficult d i f f i c u l t to t o assess assess t o movements movements during d u r i n g F2. F2. due to ' I , M Several lines l i n e s of o f evidence evidence seem seem to t o support s u p p o r t earlier e a r l i e r views v i e w s that that arose the l a r g e fold fold a r o s e at a t least l e a s t in i n part p a r t due due to t o downslope downslope soft— softlarge the wide variety This sediment sediment movement.. movement. T h i s evidence evidence includes: includes: v a r i e t y of o f fold fold non—uniform style s t y l e and and orientation o r i e n t a t i o n of o f Fl F l folds; folds; non-unif orm distribution d i s t r i b u t i o n of of the intrafolial nature these F l folds; folds; intrafolial n a t u r e of of t h e s e folds; folds; t h e likely likely Fl strains sheath folds development of of f o l d s and and associated a s s o c i a t e d high h i g h shear strains development during Fl. d u r i n g Fl. i 51 1 I I �I Unconformity-Type Uranium Uranium Mineralization Mineralization at at the the Groveland Groveland Unconformity—Type Iron Mine, Mine, Central Central Dickinson Dickinson County, County, Michigan Michigan Iron Joseph J. J. Mancuso Mancuso && Charles Charles W. W. Schick Schick Joseph Bowling Green State University Bowling Green State University Bowling Green, Green, Ohio Ohio 43403 43403 Bowling significant radiometric radiometric anomaly anomaly and and uranium uranium AA significant mineralization were detected immediately beneath the mineralization were detected immediately beneath the unconformity between Cambrian sandstone and underlying Lower unconformity between Cambrian sandstone and underlying Lower Proterozoic metasediments and metadiabases at the Groveland Proterozojc metasediments and metadiabases at the Groveland Iron Mine, Mine, Dickinson Dickinson County, County, Michigan. Michigan. Chemical Chemical analyses analyses of of 23 23 Iron samples taken from 0.1 to 1.0 meters below the unconformity samples taken from 0.1 to 1.0 meters below the unconformity yielded uranium uranium values values ranging ranging from from 0.8 0.8 to to 28.0 28.0 ppm. ppm. yielded (Background averages approximately 2 ppm.) This uranium (Background averages approximately 2 ppm.) This uranium mineralization can can be be compared compared to to the the unconformity—type unconforrnity-type uranium uranium mineralization ore deposits deposits in in the the Athabasca Athabasca Basin Basin of of Northern Northern Saskatchewan. Saskatchewan. ore The Groveland Groveland Iron Iron Mine Mine is is located located 16 16 miles miles northeast northeast The of Iron Iron Mountain Mountain in in Central Central Dickinson Dickinson County, County, Michigan. Michigan. The The of Lower Proterozoic Proterozoic rocks rocks of of the the Groveland Groveland Mine Mine area area are are found found in in Lower the Felch Felch Trough, Trough, and and are are bounded to to the the north north and and south south by by the Archean gneisses granites. The The rocks rocks in in the the trough trough consist consist Archeari gneisses and granites. of amphibolite, garnet mica schist, iron formation, marble and of amphibolite, garnet mica schist, iron formation, marble and quartzite which strike approximately E-W and dip nearly quartzite which strike approximately E-W and dip nearly vertically. These These metasediments metasediments were were folded, folded, faulted, faulted, intruded intruded vertically. by both granitic and gabbroic rocks and metamorphosed to the by both granitic and gabbroic rocks and metamorphosed to the b.y.). amphibolite facies during the Penokean Orogeny (1.85 amphibolite facies during the Penokean Orogeny (1.85 b.y.). Flat lying lying Upper Upper Cambrian Cambrian sandstone sandstone and and Pleistocene Pleistocene glacial glacial Flat drift overlie the Precambrian rocks. The sandstone is the the drift overlie the Precambrian rocks. The sandstone is Miner's Castle Member of the Munising Formation which is the Miner's Castle Member of the Munising Formation which is the upper member of the Upper Cambrian Lake Superior Sandstone upper of the Lake Superior Sandstone Group. Group. The Lower Lower Proterozoic Proterozoic rocks rocks underwent underwent extensive extensive erosion erosion The and weathering weathering after after the the Periokean Penokean Orogeny to the the and Orogeny and and prior prior to deposition of of the the Cambrian Cambrian Sandstone. Sandstone. The The weathering weathering produced produced deposition paleoregolith that that is is up up to to 30 30 meters meters thick. thick. The The most most aa paleoregolith important mineral mineral changes changes were were alteration alteration of of feldspars feldspars and and important mafic minerals minerals to to illite, illite, kaolinite kaolinite and and chlorite. chlorite. Analysis Analysis of of mafic the paleoregolith paleoregolith immediately immediately below below the the unconformity unconformity yielded yielded the 0.5% reductant reductant calculated calculated as as organic organic values ranging ranging from from 0.1 0.1 to to 0.5% values carbon. carbon. As aa working working hypothesis, hypothesis, the the following following genesis genesis is is As proposed: Oxidizing ground waters, carrying uranium in proposed: Oxidizing ground waters, carrying uranium in solution in in the the UU +6 +6 state state which which was was derived derived from from weathering weathering of of solution local Archean granite and gneiss highlands, passed through the local Archean granite and grieiss highlands, passed through the oxidized Upper Upper Cambrian Cambrian sandstone sandstone aquifer aquifer without without reaction. reaction. oxidized However, the altered basement rocks below the unconformity However, the altered basement rocks below the unconformity presented aa major major break break in in structure, structure, mineralogy mineralogy and and chemistry chemistry presented +6 and aa sudden sudden decrease decrease in in porosity porosity and and permeability. permeability. The The UU +6 and in the the oxidized oxidized fluids fluids reacted reacted with with the the reductant reductant in in the the in regolith immediately immediately below below the the unconformity unconformity reducing reducing the the regolith + 4 state state which which was was deposited deposited as as uraninite. uraninite. uranium to to the the UU +4 uranium 52 I �I Ii THE ATIKOKAN COBALT-BASE METALS-PLATINUM GROUP ELEMENTS PROJECT A.D. MacTavish MacTavish and and R.J. R.J. Dutka Dutka A.D. Ministry M i n i s t r y of of Natural Natural Resources, Resources, 435 James St. S t . South, Thunder Thunder Bay, Bay, Ontario Ontario p r o j e c t was initiated i n i t i a t e d in i n May, May, l98L 1984 to t o examine and document document The project the ccobalt, o b a l t , base metal p l a t i n u m group element element occurrences occurrences in i n the the the metal and platinum A t i k o k a n Area, Area, to t o study s t u d y in i n detail d e t a i l the t h e most significant s i g n i f i c a n t of o f these these occuroccurAtikokan rences and to t o stimulate s t i m u l a t e exploration. e x p l o r a t i o n . The detailed d e t a i l e d research r e s e a r c h will w i l l attempt attempt t o ooutline u t l i n e tthe he g e o l o g i c a l and t r u c t u r a l ssetting, e t t i n g , oore r e and s ilicate to geological and sstructural silicate p e t r o l o g y , petrochemistry p e t r o c h e m i s t r y and and potential p o t e n t i a l of o f the t h e occurrences. occurrences. petrology, I n i t i a l reconnaisance sampling, sampling, assaying a s s a y i n g and and geological g e o l o g i c a l mapping mapping Initial done during d u r i n g the t h e l98L 1984 field f i e l d season season and concentrated c o n c e n t r a t e d on on three t h r e e locations: locations: were done the Finlayson Area, the the F i n l a y s o n Lake Area, t h e Sapawe Sapawe Lake—Plateau Lake-Plateau Lake Lake Area, Area, and and the the Crooked Pine Pine Lake Lake Area. Area. This T h i s work has revealed r e v e a l e d the t h e presence presence of o f five five p r e l i m i n a r y 'deposit' ' d e p o s i t ' or o r 'occurrence' ' o c c u r r e n c e ' types. types. They were determined on on the the preliminary b a s i s of o f lithology, l i t h o l o g y , structure basis s t r u c t u r e and associated a s s o c i a t e d suiphide s u l p h i d e mineralogy, m i n e r a l o g y , which which m i g h t host h o s t cobalt, c o b a l t , base metal or o r platinum p l a t i n u m group group mineralization. mineralization. might 1) 1) 'The Quetico 'The Q u e t i c o Fault—Hosted F a u l t - H o s t e d Intrusions' I n t r u s i o n s ' contain c o n t a i n significant significant cobalt, c o b a l t , copper and nickel n i c k e l sulphides s u l p h i d e s closely c l o s e l y associated a s s o c i a t e d with w i t h disseminated disseminated to magnetite within t o massive m a g n e t i t e lenses lenses w i t h i n sheared, sheared, syntectonic s y n t e c t o n i c gabbroic g a b b r o i c to t o ultraultramafic m a f i c intrusive i n t r u s i v e rocks. rocks. A similar s i m i l a r potential p o t e n t i a l for f o r cobalt, c o b a l t , copper copper and and nickel nickel should exist within exist w i t h i n other o t h e r intrusions i n t r u s i o n s of o f this t h i s type. type. The The possibility p o s s i b i l i t y of of platinum p l a t i n u m group group enrichment enrichment is i s high h i g h in i n the t h e presence presence of o f copper copper and and nickel nickel sulph s u l p h ides. ides. I Quetico 2) 2 ) 'The 'The Q u e t i c o Intrusions' I n t r u s i o n s ' are a r e mafic maf i c to t o ultramafic u l tramaf i c bodies bodies exhibiting e x h i b i t i n g high h i g h local l o c a l concentrations c o n c e n t r a t i o n s of o f copper, copper, nickel, n i c k e l , cobalt, c o b a l t , platinum platinum and and palladium. p a l l a d i u m . The base base metals m e t a l s occur o c c u r in i n disseminated d i s s e m i n a t e d pods pods of o f chalcopyrite, chalcopyrite, pyrite p y r i t e and and pentlandite. p e n t l a n d i t e . The, The, as as yet y e t unidentified, u n i d e n t i f i e d , platinum p l a t i n u m group group minerals minerals are with a r e probably p r o b a b l y closely c l o s e l y associated associated w i t h the t h e chalcopyrite c h a l c o p y r i t e and and pentlandite. pentlandite. The The potential p o t e n t i a l for f o r base matal and platinum p l a t i n u m group group mineralization m i n e r a l i z a t i o n in i n these these o t h e r similar s i m i l a r bodies b o d i e s is i s high h i g h and should s h o u l d be be investigated i n v e s t i g a t e d further. further. and other 3) 3) The The deformed, deformed, banded chert c h e r t and iron-rich i r o n - r i c h chemical metameta- sediments sediments of o f the t h e Finlayson F i n l a y s o n Lake Lake Area locally l o c a l l y contain c o n t a i n copper, copper, cobalt c o b a l t and and minor ( ? ) sulphides. s u l p h i d e s . The The sulsulm i n o r zinc z i n c and and silver s i l v e r within w i t h i n primary p r i m a r y exhalative e x h a l a t i v e (7) phides, composed of of pyrrhotite, p y r r h o t i t e , pyrite, p y r i t e , chalcopyrite c h a l c o p y r i t e and and sphalerite, s p h a l e r i t e , are are phides, f i n e to t o coarse-grained, t o nodular, n o d u l a r , and d i s s e m i n a t e d to t o massive fine coarse-grained, banded to disseminated in i n appearance. 14) Shear zones and quartz q u a r t z veins v e i n s throughout throughout the the 4) and and 5) 5) Shear A t i k o k a n Area Area exhibit e x h i b i t localized l o c a l i z e d disseminated d i s s e m i n a t e d copper, copper, lead l e a d and and zinc z i n c minerminerAtikokan alization. a l i z a t i o n . Auriferous A u r i f e r o u s quartz q u a r t z veins v e i n s generally g e n e r a l l y have have associated a s s o c i a t e d base base metal metal m i n e r a l i z a t i o n occurring o c c u r r i n g either e i t h e r as semi-massive semi-massive lenses lenses or o r as as disseminated disseminated mineralization blebs. b l e b s . Cobalt was observed in with i n association association w i t h a possible p o s s i b l e splay s p l a y fault fault of o f the t h e Quetico Q u e t i c o Fault F a u l t Zone. Zone. D e t a i l e d research research is i s planned planned during d u r i n g 1985 1985 on on the t h e Quetico Q u e t i c o Intrusions Intrusions Detailed and and the t h e Quetico Q u e t i c o Fault-Hosted F a u l t - H o s t e d mafic m a f i c bodies. bodies. Reconnaisance Reconnaisance work will w i l l be be done done in i n the t h e Calm Calm Lake Lake Area, Area, the t h e Lumby Lumby Lake—Old Lake-Old Man Man Lake Lake Belt, Be1 t, and and portions p o r t i o n s of of the t h e Shebandowan Shebandowan Area. Area. 53 I �: CHEMICAL CHARACTERIZATION OF CHEMICAL O F THE THEUNNAMED UNNAMED FORMATION FURMATT.ON KEWEEMAWAM AGE A A CENTRAL VOLCANIC VOLCAN IC COMPLEX COMPLEX OF O FKEWEENAWAN Michael M i c h a e l Patrick P a t r i c kMcDermott McDormatt Science::; M i c h i g a n SState tate U n i v e r s i t y , Department o'f o-f Goloqical s o l o q i c a lSc:iences Michigan University, 49524 East Lansing MI. East L ansing M I . 48824 The unique Tho Unnamed Formation F o r m a t i o n provides provides a u n i q u e opportunity o p p o r t u n i t y to t o study s t u d y the the Proterozoic evolution off a e volution o a P r o t e r o s o i c volcanic v o l c a n i c system system tthroughout hrouqhout iits t's; Iwaning nning Formation off the the Keweenawan Keween<aw<an stages. o r m a t i on i s tthe h e youngest o Unnamed F stages. The Unnamed a sequence of subaerially I t iiss a si-ibaori a l 1y extruded c^~t+-udeid v o I c a r i i c s in i n Michigan. Michigan. voicanics lava and quartz—porphyry i ell ssite, a n d e s ite, to, fe ite, and quarts-porphyry l a v a ffl l aows ws i n tnterbedded e r b e d d a d with w i t h andesi subordinate sedimentary -Â¥subordinat s e d i m e n t a r y rocks. r o c k s . The The upper upper 770 770 m m a-f o f the t h e Formation F o r m a t i o n fforms arms Mountains. R Regionally Porcupine tthe h e uplands uplands o o f the the P o r c u p i n e Mountains. e g i o n a l l y the t h e the t h e Formation Formation measurable at iiss a v o l c a n i c p i l e which r e a c h e s i t s maximum maximum thickness t h i c k n e s s (neiasur<able at tthe h e surface s u r f a c e a-f o-f 2400 m m in i n the t h e Bergland B e r g l a n d and and Thomaston Thomaston quadrangles, quadrangles, Itt wedges km. south s o u t h of o f the t h e Porcupine P o r c u p i n e Mountains. I wodqos out o u t in i n the tho about about 8 km. and Greenland q quadrangle Greenland u a d r a n g l e to t o tthe h e east east and in i n the t h e Little L i t t l e Girl G i r l Point Point quadrangle west. q u a d r a n g l e to t o the t h e west. Portage The Unnamed Formation with underlying The Unnamed F o r m a t i o n is i s con-formable con-formabla w i t h tthe h e under1 yinq P ortage (PLL) series iti tbyb ydi'f'ferences di++or-cincss Lake Lava (PLL) s e r i e s and and is i s distinguishable d i s t i n g u i s h a b l efrom -from PLL are iin n rock r o c k type. t y p e . The The ma-fic mafic PLL a r e predominantly p r e d o m i n a n t l y basalts, b a s a l t s , whereas whereas those those grained and contain greater off o tthe h e Unnamed Formation F o r m a t i o n are a r e finer finer g r a i n e d and c o n t a i n a qr-eator off felsic The Harbor proportion porphyritic p roportion o p o r p h y r i t i c and and a felsic rrocks. ocks. The Copper Harbor with, the Conglomerate Conformably overlies, and con-formably o verlies, and iis s interbedded intorbodclod w ith, the? Formation 197). Unnamed F o r m a t i o n (Hubbard (Hubbard 1975) There major element element vvariation There iis s a large l a r g e spectrum spectrum a-F o f major a r i a t i o n within w i t h i n the the Silica content, which vvaries 49 to rrocks ocks o o-f the t h e Formation. S ilica c o n t e n t , which a r i e s f rfrom o m 45.8 t o '7 76 7., intermediate, X , can be used to t o discriminate d i s c r i m i n a t e basic, basic, intermediate3, and and acidic a c i d i c ;'flows. Â¥flows P2O On a-ff other CaD '-liD2 — P$g tthe he b asis o o t h e r c h a r a c t e r i s t i c oxidea, CaO TiClz basis MnO, and strong and tthe h e Na,O/K,O Na$I/KzO ratio, tthere here iiss a a s t r o n g dichotomy between + intermediate i n t e r m e d i a t e 'flows flows and a cidic f1ow<->. IIn n the the' between the t h e basic basic + and acidic iows. 'former former group he Na20/K2O r a t i o increases i n c r e a s e s tto o a m a x i , m u m which group tthe a maximuñ NaO/K.,O corresponds to to a a S i 0 2 content content o-f 65X, t h i s ratio r a t i o decreases decreases of 7., whereas this with increasing Major with increasing s i l i c a content i n the a cidic rrocks. ocks. Major acidic element modeling adequately model i n g cannot a d e q u a t e l y explain e x p l a i n these t h e s e oxide o x i d e abund<anc(as on the the abundances on basis a-F crystal -fractionation data basis o f crystal fractionation models. A l t h o u g h ttrace r a c e element element data models. Although are not complete, it are n o t complete, i t is i s suggested that that crustal m o l t i n g would crustal melting would betat best e x p l a i n the t h e origin o r i g i no-f o f the t h e acidic a c i d i c-flows. Â¥flows explain is It a volcanic pile which reaches its . characteristic oxides, - ratio, ratio silica content in the H. A. A. ( 1975) Lower Id. (197) and Wisconsin. and Wisconsin. U.S. U. 5 . Seal. Beol Hubbard Hubbard  - ¥ Kcaweenawan volcanic rocks M i c h i gan Keweenawan volcanic rocks of Michigan . Survey Survey Jour. J o u r . Research Research 3, 3, 329—41. 529-541 o 54 1 �I ZONE GEOMETRY GEOMETRYAND ANDVEIN VEIN PARACENESIS THE INFLUENCE THE INFLUENCE OF OF SHEAR SHEAR ZONE PARAGENESIS ON ATCAMERON CAMERON LAKE, LAKE, ON GOLD-PYRITE MINERALIZATION MINERALIZATIONAT NORTRWESTEIN NORTHWESTERN ONTARIO. . D.R. Poulsen3. D.R. ~Melling1, e l l i n ~D.H. D.H. l , wWatkinson', a t k i n s o n l , L.B. L.B. Chorlton2, c h o r l t o n 2 ,and andK.H. K.H. P oulsen 3 I The history h i s t o r y of of gold gold exploration e x p l o r a t i o n in i n the t h e Kenora—Fort Kenora-Fort Frances Frances area area Activity of n northwestern of o r t h w e s t e r n Ontario O n t a r i o dates d a t e s back back to t o the t h e mid—1800's. mid-1800's. A c t i v i t y peaked peaked between 1890 55 percent p e r c e n t of of 1890 and and 1910 1910 when when the t h e area a r e a accounted accounted for f o r over o v e r 55 Ontario's total Ontario's t o t a l gold g o l d production. production. Although the t h e area a r e a hosts h o s t s no no presently presently producing t h e recent recent i s again a g a i n high h i g h in i n view v i e w of o f the p r o d u c i n g gold g o l d mines, m i n e s , optimism o p t i m i s m is Cameron Lake Lake gold g o l d rush. rush. l o c a t e d 80 km south—southeast s o u t h - s o u t h e a s t of of The Cameron Cameron Lake Lake gold g o l d deposit, d e p o s i t , located Kenora, was Kenora, w a s originally o r i g i n a l l y discovered d i s c o v e r e d iin n 1960 1960 by by prospectors p r o s p e c t o r s working working for for Low gold with t tthat h a t ttime i m e ccoupled oupled w i t h aa ccomplex omplex Noranda Mines. Mines. Low g o l d pprices r i c e s aat subsurface s u b s u r f a c e geometry and poor poor outcrop o u t c r o p exposure exposure discouraged discouraged investment investment Four and dewelopment. F o u r separate s e p a r a t e diamond d i a m o n d drilling d r i l l i n g programs p r o g r a m s were were a n d development. conducted on the property prior to the discovery of a major conducted t h e p r o p e r t y p r i o r t o t h e d i s c o v e r y of a m a j o r zone z o n e of of gold Nuinsco/Lockwood joint 1983 by by the t h e Nuinsco/Lockwood j o i n t venture. venture. g o l d mineralization m i n e r a l i z a t i o n in i n 1983 Proven a t that t h a t time t i m e totaled t o t a l e d 1,287,000 1,287,000 tons t o n s grading g r a d i n g 0.154 0.154 P r o v e n reserves r e s e r v e s at oz/ton o z l t o n Au, Au, including i n c l u d i n g 807,000 807,000 tons t o n s grading g r a d i n g 0.194 0.194 oz/ton o z l t o n Au. Au. The Cameron Lake gold i s situated s i t u a t e d near near the t h e stratigraphic stratigraphic g o l d deposit d e p o s i t is ttransition r a n s i t i o n between b e t w e e n aa lower, l o w e r , mafic maf i c volcanic v o l c a n i c succession s u c c e s s i o n (Rowan (Rowan Lake Volcanics) mixed m mafic pyroclastic V o l c a n i c s ) aand n d aan n uupper p p e r mix-ed a f i c tto o ffelsic, e l s i c , ppartly artly p yroclastic ssuccession u c c e s s i o n (Cameron (Cameron Lake Lake Volcanics), V o l c a n i c s ) , but b u t within w i t h i n the t h e latter. latter. The and ooccurs deposit d e p o s i t is is epigenetic, e p i g e n e t i c , sstructurally t r u c t u r a l l y ccontrolled o n t r o l l e d and c c u r s in i n sheared sheared mafic maf i c metavolcanic m e t a v o l c a n i c rocks r o c k s adjacent a d j a c e n t to t o the t h e sheared s h e a r e d intrusive i n t r u s i v e contact contact with The sshear zone hhosting s i l l . The h e a r zone o s t i n g tthe h e ggold o l d ddeposit e p o s i t iis s aa w i t h a metagabbroic metagabbroic sill. dextral bbrittle—ductile, rittle-ductile, d e x t r a l strike s t r i k e slip s l i p system s y s t e m with w i t h an a n attitude a t t i t u d e of of 315/700 W and aa displacement Ore 315170' W and d i s p l a c e m e n t vector v e c t o r pitching p i t c h i n g 5' W. W. Ore sshoots h o o t s pitch pitch There w i t h i n the t h e plane p l a n e of of the t h e shear s h e a r zone. zone. T h e r e is is aapproximately p p r o x i m a t e l y 700 70' WW within Cameron Lake Shear llimited i m i t e d evidence e v i d e n c e to t o suggest s u g g e s t tthat h a t tthe h e Cameron S h e a r Zone Zone is is rrelated e l a t e d to t o the t h e regionally r e g i o n a l l y prominent prominent Pipestone—Cameron Pipestone-Cameron Fault. Fault. Three ddistinct have been been recognized recognized cutting Three i s t i n c t vveining e i n i n g eepisodes p i s o d e s have c u t t i n g the the mafic ccarbonatized arbonatized m a f i c metavolcanic metavolcanic rocks r o c k s of of the t h e Cameron Cameron Lake Lake Shear Shear Zone: Zone: early, veins (i) e a r l y , barren b a r r e n extensional e x t e n s i o n a l qquartz—carbonate u a r t z-carbonate v e i n s which have have (i) been buckled; buckled; major ((ii) i i ) aa m a j o r ssystem y s t e m of o f gold—bearing g o l d - b e a r i n g pyritic, p y r i t i c , quartz q u a r t z breccia breccia veins; veins ; (iii) ( i i i ) llate a t e cross—cutting c r o s s - c u t t i n g quartz—carbonate—chlorite—hematite—gold, quartz-carbonate-chlorite-hematite-gold, en—echelon en-echelon extension e x t e n s i o n veins. veins. ( i i ) breccia b r e c c i a veins v e i n s has has been been previously previously The significance s i g n i f i c a n c e of of the t h e stage s t a g e (ii) underestimated. They underestimated. They rrepresent e p r e s e n t aa s specific p e c i f i c oore r e ttype y p e wwhich h i c h ggenerally enerally The other, ggrades r a d e s greater g r e a t e r than t h a n 0.19 0.19 oz/ton o z l t o n Au. Au. o t h e r , lower lower grade g r a d e ore o r e type, type, consists c o n s i s t s of of pervasively p e r v a s i v e l y altered a l t e r e d carbonate—sericite—pyrite carbonate-sericite-pyrite rich rich phyllonitic Cameron Lake p h y l l o n i t i c rocks r o c k s and a n d occupies occupies a a large l a r g e volume v o l u m e of of the t h e Cameron Lake Shear Zone enveloping the t h e breccia b r e c c i a veins. veins. O I i I �I The The transition t r a n s i t i o n from f r o m ductile d u c t i l e cleavage c l e a v a g e development d e v e l o p m e n t to t o brittle brittle processes p r o c e s s e s within w i t h i n the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is i s manifested m a n i f e s t e d in i n the the formation f o r m a t i o n of of veins v e i n s and a n d vein v e i n breccias. b r e c c i a s . The The change c h a n g e from f r o m ductile d u c t i l e to to brittle b r i t t l e behavior behavior may be be the t h e result r e s u l t of of local l o c a l increases i n c r e a s e s in i n hydrothermal hydrothermal fluid f l u i d pressure p r e s s u r e which w h i c h facilitates f a c i l i t a t e s brittle b r i t t l e deformation d e f o r m a t i o n and a n d vein vein formation f o r m a t i o n by by reducing r e d u c i n g the t h e effective e f f e c t i v e normal normal stresses. s t r e s s e s . The The phyllonitic phyllonitic rocks s i n k for f o r the t h e gold—bearing g o l d - b e a r i n g fluids, f l u i d s , while w h i l e the t h e breccia breccia r o c k s formed f o r m e d aa sink veins v e i n s formed formed major major conduits c o n d u i t s enhancing enhancing fluid f l u i d circulation. circulation. The The localization l o c a l i z a t i o n of of economic economic quantities q u a n t i t i e s of of gold gold along a l o n g the t h e Cameron Cameron Lake Lake Shear Shear Zone Zone corresponds corresponds to t o the t h e development development of of oblique, o b l i q u e , secondary, secondary, At dextral, A t the the d e x t r a l , bedding—controlled b e d d i n g - c o n t r o l l e d sympathetic s y m p a t h e t i cshear s h e a r zones. zones. confluence s t e e p l y pitching, p i t c h i n g , dilatent dilatent t h e s e two t w o shear s h e a r systems s y s t e m s aa steeply c o n f l u e n c e of of these zone z o n e was w a s created c r e a t e d in i n which w h i c h ascending a s c e n d i n g hydrothermal h y d r o t h e r m a l . solutions solutions p r e c i p i t a t e d gold. gold. The The shear s h e a r zone zone model model serves s e r v e s to t o explain e x p l a i n the t h e complex complex precipitated subsurface s u b s u r f a c e geometry g e o m e t r y of of the t h e deposit, d e p o s i t , as a s well w e l l as as the t h e existence e x i s t e n c e of of hanging h a n g i n g wall w a l l and a n d footwall f o o t w a l l zones z o n e s on on either e i t h e r side s i d e of of the t h e main m a i n zone z o n e of of g o l d mineralization. mineralization. gold 1 Ottawa—Carleton Ottawa-Carleton Centre Centre for f o r Geoscience Geoscience Studies, S t u d i e s , Carleton C a r l e t on University, University, Ottawa, Ontario. Ontario. Ottawa, * Mineral M i n e r a l Deposits D e p o s i t s Section, S e c t i o n , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Toronto, Toronto, Ontario. 2 Ontario. Economic Economic Geology Geology and and Mineralogy Mineralogy Division, D i v i s i o n , Geological G e o l o g i c a l Survey Survey of of Canada, Ottawa, Ottawa, Ontario. Ontario. Canada, 56 �PETROGENESIS OF OF ANORTHOSITIC ANORTHOSITIC ROCKS ROCKS OF O F THE THE DULUTH DrJLUTH COMPLEX COMPLEX PETROGENESIS I James D. Miller, M i l l e r , Jr., Jr., Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University ~niversity Ave., St. St. James D. Ave., Paul, P a u l , Minnesota 55114 55114 The mafic m a f i c plutonic p l u t o n i c rocks r o c k s of of the t h e Middle Middle Proterozoic P r o t e r o z o i c Duluth Duluth Complex Complex in in northeastern >85%) n o r t h e a s t e r n Minnesota Minnesota include i n c l u d e aa wide wide variety v a r i e t y of o f plagioclase-rich p l a g i o c l a s e - r i c h (P1 ( P l >85%) rocks r o c k s belonging b e l o n g i n g to t o the t h e early—formed e a r l y - f o r m e d Anorthositic A n o r t h o s i t i c Series, S e r i e s , as a s well w e l l as a s younqer younqer rocks r o c k s dominated by troctolite t r o c t o l i t e and and olivine o l i v i n e gabbro g a b b r o (Troctolitic ( T r o c t o l i t i c Series). Series). Understanding U n d e r s t a n d i n g the t h e petrogenesis p e t r o g e n e s i s of o f the t h e anorthositic a n o r t h o s i t i c rocks, r o c k s , which which could c o u l d not n o t have have crystallized i s requisite r e q u i s i t e to t o understanding u n d e r s t a n d i n g the the c r y s t a l l i z e d directly d i r e c t l y from from basaltic b a s a l t i c liquids, l i q u i d s , is origin o r i g i n of of the t h e Duluth D u l u t h Complex. Complex. Field, F i e l d , petrographic, p e t r o g r a p h i c , and and petrochemical p e t r o c h e m i c a l studies s t u d i e s of of the t h e Duluth Duluth Complex Complex in i n the t h e Snowbank Snowbank Lake Lake quadrangle q u a d r a n g l e have h a v e been been useful u s e f u l in i n characcharacterizing t e r i z i n g the t h e kinds k i n d s of o f anorthositic a n o r t h o s i t i c rocks r o c k s that t h a t are a r e present p r e s e n t and and in i n establishing establishing their t h e i r genetic g e n e t i c relationship r e l a t i o n s h i p to t o one one another a n o t h e r and and to t o the t h e younger younger Troctolitic T r o c t o l i t i c Series Series rocks. rocks. . — The compositi~n, The major major anorthositic a n o r t h o s i t i c rock r o c k types t y p e s are a r e distinguished d i s t i n g u i s h e d by by modal modal composition, plagioclase p l a g i o c l a s e grain g r a i n size, s i z e , and and olivine o l i v i n e habit h a b i t (granular ( g r a n u l a r vs. v s . poikilitic; p o i k i l i t i c ; Miller M i l l e r and and Weiblen, 1 9 8 2 ) . Field F i e l d observations o b s e r v a t i o n s of of complex complex internal i n t e r n a l structures s t r u c t u r e s (based ( b a s e d on on Weiblen, 1982). lamination) l a m i n a t i o n ) and intrusive i n t r u s i v e and and stratiform s t r a t i f o r m contact c o n t a c t relationships r e l a t i o n s h i p s imply imply that t h a t the the Anorthositic A n o r t h o s i t i c Series S e r i e s rocks r o c k s formed formed from from diverse d i v e r s e magma magma types t y p e s during d u r i n g at a t least l e a s t three three major major stages s t a g e s of o f episodic e p i s o d i c intrusion. i n t r u s i o n . Reported Reported here h e r e are: a r e : 1) 1 ) what are a r e believed b e l i e v e d to to be b e the t h e physical p h y s i c a l and and chemical c h e m i c a l characteristics c h a r a c t e r i s t i c s of of the t h e magmas magmas that t h a t produced produced the the suite s u i t e of o f anorthositic a n o r t h o s i t i c rocks r o c k s and and how how these t h e s e characteristics c h a r a c t e r i s t i c s changed changed over o v e r the the intrusive 2 ) the t h e presumed presumed difference difference i n t r u s i v e history h i s t o r y of o f the t h e Anorthositic A n o r t h o s i t i c Series; S e r i e s ; and and 2) between between the t h e magmas magmas that t h a t produced produced the t h e Anorthositic A n o r t h o s i t i c Series S e r i e s and and the t h e younger younger Troctolitic T r o c t o l i t i c Series. Series. All All A n o r t h o s i t i c Series S e r i e s magmas magmas were were intruded i n t r u d e d into i n t o subvolcanic s u b v o l c a n i c chambers chambers at at Anorthositic depths d e p t h s of of about a b o u t 5—10 5-10 km km as a s crystal c r y s t a l mushes mushes containing c o n t a i n i n g as a s much much as a s 50 50 percent percent intratelluric Consequently, i n t r a t e l l u r i c plagioclase. plagioclase. C o n s e q u e n t l y , the t h e sequential s e q u e n t i a l intrusions i n t r u s i o n s of of these these viscous v i s c o u s magmas magmas considerably c o n s i d e r a b l y disrupted d i s r u p t e d the t h e internal i n t e r n a l structure s t r u c t u r e of o f previous p r e v i o u s crystal crystal accumulations. a c c u m u l a t i o n s . The The compositional c o m p o s i t i o n a l range r a n g e of o f complexly complexly zoned, zoned, intratelluric i n t r a t e l l u r i c pla— plagioclase g i o c l a s e (An (An 50—70) 50-70) is i s the t h e nearly n e a r l y same same for f o r all a l l anorthositic a n o r t h o s i t i c rock r o c k types. types. Textural, T e x t u r a l , modal, modal, and and mineral m i n e r a l compositional c o m p o s i t i o n a l data d a t a imply imply that t h a t the t h e compositional compositional diversity 1 ) in in d i v e r s i t y of o f the t h e plagioclase-laden p l a g i o c l a s e - l a d e n magmas magmas varied v a r i e d in i n two two general g e n e r a l ways: ways: 1) their and oother t h e i r MgO/MgO-4-FeO MgO/MgO+FeO ( I('mg') m g ' ) c ocomposition m p o s i t i o n and t h e r ccompositional o m p o s i t i o n a l pparameters a r a m e t e r s indicaindicat i v e of o f the t h e degree d e g r e e of o f differentiation; d i f f e r e n t i a t i o n ; and and 2) 2 ) in i n degree d e g r e e to t o which which the t h e magmas magmas were were tive olivine—saturated. olivine-saturated. I n general, g e n e r a l , olivine—undersaturated o l i v i n e - u n d e r s a t u r a t e d magmas magmas were were more more difdifIn ferentiated f e r e n t i a t e d (i.e., ( i . e . , lower lower tmg') I m g g ) than t h a n those t h o s e with w i t h olivine o l i v i n e on on the t h e liquidus l i q u i d u s upon upon intrusion. i n t r u s i o n . Most Most of o f the t h e compositional c o m p o s i t i o n a l diversity d i v e r s i t y was was apparently a p p a r e n t l y aa primary p r i m a r y characcharact e r i s t i c of o f the t h e Anorthositic A n o r t h o s i t i c Series S e r i e s magmas magmas as a s they t h e y were were intruded i n t r u d e d into i n t o the t h e Duluth Dull~th teristic Complex Complex as a s opposed opposed to t o having h a v i n g resulted r e s u l t e d from from differentiation d i f f e r e n t i a t i o n within w i t h i n the t h e Complex Complex chambers. chambers. The earliest e a r l i e s t stage s t a g e of o f Anorthositic A n o r t h o s i t i c Series S e r i e s magmatism magmatism produced produced medium— medium- to to The medium-coarse-grained troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s and and poikilitic p o i k i l i t i c olivine o l i v i n e anortho— anorthomedium—coarse—grained site. s i t e . These These early e a r l y magmas magmas had had the t h e highest h i g h e s t average a v e r a g e 'mg' Imgg composition c o m p o s i t i o n (25—30 (25-30 mole%) mole%) and and varied v a r i e d in i n the t h e degree d e g r e e to t o which which they t h e y were were olivine—saturated o l i v i n e - s a t u r a t e d upon upon intrusion. intrusion. O l i v i n e - s a t u r a t e d magmas magmas crystallized c r y s t a l l i z e d granular g r a n u l a r olivine o l i v i n e interstitial i n t e r s t i t i a l to t o pla— plaOlivine-saturated g i o c l a s e in i n troctolitic t r o c t o l i t i c anorthosite, a n o r t h o s i t e , whereas whereas those t h o s e that t h a t were were undersaturated u n d e r s a t u r a t e d in in gioclase olivine o l i v i n e produced produced poikilitic p o i k i l i t i c crystals. c r y s t a l s . Poikilitic P o i k i l i t i c olivine o l i v i n e probably p r o b a b l y formed formed by by r a p i d growth qrowth after a f t e r magmas magmas became became supersaturated s u p e r s a t u r a t e d with w i t h olivine o l i v i n e to t o the t h e extent extent rapid 57 I �I necessary n e c e s s a r y to t o nucleate n u c l e a t e crystals. crystals. In I n ccontrast o n t r a s t to t o the t h e early e a r l y stage, s t a g e , main stage stage magmas produced g a b b r o i c rock rock types. types. produced generally g e n e r a l l y coarser c o a r s e r grained g r a i n e d and and more more gabbroic Although the t h e average a v e r a g e 'mg' Img1 composition of of the t h e main stage s t a g e magmas was lower, lower, the the Although degree d e g r e e of of olivine o l i v i n e saturation s a t u r a t i o n was was similar s i m i l a r to t o that t h a t in i n the t h e early e a r l y stage s t a q e magmas. magmas. l a t e stage s t a g e magmatism, magmatism, olivine—undersaturated o l i v i n e - u n d e r s a t u r a t e d magmas magmas decreased d e c r e a s e d in i n relative relative During late abundance abundance such such that t h a t predominantly predominantly troctolitic t r o c t o l i t i c anorthosite a n o r t h o s i t e was was produced. produced. The The modal compositions compositions of of many many of of these t h e s e late l a t e stage s t a g e troctolitic t r o c t o l i t i c anorthosites a n o r t h o s i t e s approach approach t h o s e of of "normaF' "normal" troctolite t r o c t o l i t e (P1 ( P l <85%) < 8 5 % )implying implying a decrease d e c r e a s e in i n the t h e amount amount of of pla— plathose gioclase g i o c l a s e initially i n i t i a l l y entrained e n t r a i n e d in i n the t h e magmas. magmas. Moreover, Moreover, these t h e s e magmas maqmas were more c o n s i s t e n t l y saturated s a t u r a t e d with w i t h both both olivine o l i v i n e and and plagioclase p l a g i o c l a s e upon upon intrusion i n t r u s i o n into i n t o the the consistently Duluth Duluth Complex. Complex. The The late l a t e stage s t a g e Anorthositic A n o r t h o s i t i c Series S e r i e s magmatism magmatism is i s interpreted i n t e r p r e t e d to to be transitional t r a n s i t i o n a l to t o those t h o s e events e v e n t s which which produced produced the t h e Troctolitic T r o c t o l i t i c Series. Series. Petrochemical P e t r o c h e m i c a l data d a t a from from both b o t h rock rock series series of of the t h e Duluth Duluth Complex Complex and and from from aa v a r i e t y Keweenawan Keweenawan mafic volcanics v o l c a n i c s imply imply that t h a t the t h e parent p a r e n t magmas magmas were were derived d e r i v e d by by variety system fractionation f r a c t i o n a t i o n of of more more primitive p r i m i t i v e magmas magmas in i n mid— mid- to t o lower lower crustal crustal open system magma maqma chambers chambers (15—40 (15-40 km). km). Although Although Anorthositic A n o r t h o s i t i c Series S e r i e s magmas maqmas were were enriched enriched with w i t h plagioclase p l a g i o c l a s e crystals c r y s t a l s and and were, were, on on average, a v e r a g e , more more compositionally c o m p o s i t i o n a l l y evolved evolved than Troctolitic magmas, both than T r o c t o l i t i c Series S e r i e s magmas, ~ 0 t hseries s e r i e s were derived d e r i v e d from from the t h e same same primary primary magma Its composition can can be be approximated approximated by by tthe high-LU oohmaqma type. type. I t s composition h e pprimitive r i m i t i v e high-A1 livine v i n e tholeiites t h o l e i i t e s of o the t h e North Shore Shore Volcanic Volcanic Group Group (Green, (Green, 1981) 1981) and and is i s similar similar to t o MORE MORB except e x c e p t that t h a t it it is i s considerably c o n s i d e r a b l y enriched e n r i c h e d in i n incompatible i n c o m p a t i b l e elements. e l e m e n t s . Major Major element e l e m e n t data d a t a indicate i n d i c a t e that t h a t chinopyroxene c l i n o p y r o x e n e and and spinel, s p i n e l , in i n addition a d d i t i o n to t o olivine o l i v i n e and and p l a g i o c l a s e , were important i m p o r t a n t fractionating f r a c t i o n a t i n g phases, phases, as a s would would be be expected e x p e c t e d under under plagioclase, deep Kb). P l a g i o c l a s e was enriched e n r i c h e d in i n the t h e early e a r l y magmas magmas d e e p crustal c r u s t a l pressures p r e s s u r e s (5—10 (5-10 Kb). Plagioclase in i n part p a r t because of of the t h e effect e f f e c t of of pressure p r e s s u r e on on the t h e buoyancy buoyancy of of plagioclase p l a g i o c l a s e in in mafic m a f i c magmas. maqmas. AA decrease d e c r e a s e in i n the t h e amount amount of of entrained e n t r a i n e d plagioclase p l a g i o c l a s e and and aa trend trend p r i m i t i v e magma compositions with w i t h time time may may be related r e l a t e d to t o aa decrease decrease toward more primitive i n the t h e depth d e p t h of of source s o u r c e magma magma chambers chambers and and aa decreases d e c r e a s e s in i n the t h e residence r e s i d e n c e time time of of in primary magma in the crust, respectively. i s consistent c o n s i s t e n t with w i t h crustal crustal magma i n t h e c r u s t , r e s p e c t i v e l y . T h i s is This attenuation a t t e n u a t i o n as a s rifting r i f t i n g progressed. p r o g r e s s e d . The The transition t r a n s i t i o n from from Anorthositic A n o r t h o s i t i c to to Troctolitic T r o c t o l i t i c Series S e r i e s magmatism is i s comparable comparable to t o that t h a t observed observed at a t modern modern rift rift systems systems where the t h e rate r a t e of of spreading s p r e a d i n g increases i n c r e a s e s (Flower, (Flower, 1984). 1984). M i l l e r , J.D. J . D . and and Weiblen, Weiblen, P.W., P.W., 1982, 1982, 28th 28th I.L.S.G., I.L.S.G., p. 26. 26. Miller, p. Green, 1981, J.C., 1981, Basalt & s a l t Volcanism Volcanism Study Study Project, P r o j e c t , LPI, LPI, p. p. 30. 30. Green, J.C., Flower, Flower, M.F.J., M.F.J., 1984, 1984, Geology, Geology, v. v. 12, 12, p. p. 651. 651. 58 �I ALTERATION IIN STRATIGRAPHY AND ABD HYDROTHERMAL HYDROTHERMAL ALTERATION N AN AXARCHEAN ARCHEAN STRUCTURAL STRUCTUU STRATIGRAPHY SUBPROVINCE, N.W. N.W. ONTARIO LAKE AREA, AREA, WABIGOON WABIGOON SUBPROVIWE, ONTARIO ZONE, THE THE KATISHA KATISHA LAKE ZONE, W. Toronto Toronto Moreton, E.P., Esso Minerals Minerals Canada, Canada, 120 120 Adelaide Adelaide St. S t . W. Moreton, E.P., Esso M5W 1V9; lV9; and and Gerber, Gerber, R. R. Department Department of of Earth E a r t h Sciences, Sciences, University U n i v e r s i t y of of MSW \ Waterloo, Waterloo, Ontario N2L 3G1 The Katisha Lake area (92 30'OO" — 49 22'OO"), displays an a n exceptionally exceptionally I discrete well preserved Archean stratigraphic section comprising five discrete volcanic episodes centered around a major uplift zone. This tectonic tectonic rusive zone was the focus for associated shear zone development, intrusive activity and hydrothermal alteration. The basal b a s a l portion p o r t i o n of o r the t h e stratigraphy s t r a t i g r a p h y comprises the t h e Wapageisi wapageisi Lake Lake Group Group of of tholeiitic t h o l e i i t i c basalts b a s a l t s overlain o v e r l a i n by by heterolithic h e t e r o l i t h i c breccias, breccias, intruded l a y e r e d gabbro sill i n t r u d e d by a layered s i l l and capped by quartz q u a r t z porphyritic p o r p h y r i t ic f e l s i c volcanics. v o l c a n i c s . Uplift U p l i f t and and erosion e r o s i o n prior p r i o r to, t o , and and during d u r i n g the t h e capping caP P ~ % felsic The felsic f e l s i c volcanism, volcanism, led l e d to t o production p r o d u c t i o n of of an an angular a n g u l a r unconformity. unconformity. The -----7 - - 2 - - 0.. ---- L -aI -n- e Group n 2--*L<--l.-<,.*<,. overlying conglomerate, U V ~ L A Y A U Stormy ~~ L U S U I Y Lake W L U U ~ comprises G U U I ~ L A Z . C Z . a thin LUAU basal L J ~ z . polymictic p~ u~ A y ~ L L A L LuLLglomerate9 overlain o v e r l a i n by some some 500 m m of of dacitic d a c i t i c breccias, b r e c c i a s , followed followed by.a b y . a thick t h i c k sequence sequence A f t e r dacitic d a c i t i c volcanism, volcanism, aa series s e r i e s of of of of polymictic p o l y m i c t i c conglomerates. conglomerates. After vertical, v e r t i c a l , conjugate, c o n j u g a t e , ductile d u c t i l e shear s h e a r zones zones trending t r e n d i n g 120 120 and 180 180 formed formed Widespread carbonate c a r b o n a t e veining v e i n i n g and and in i n the t h e Wapageisi w a p a g e i s i Lake Lake Group Group rocks. -rocks. Widespread alteration a l t e r a t i o n occurred occurred in i n and and adjacent a d j a c e n t to, t o , these t h e s e shear s h e a r zones. zones. Synchronous Synchronous carbonate alteration non—shear! a l t e r a t i o n in i n the t h e Stormy Lake Group consisted c o n s i s t e d of of non-shear/ vein related areas of widespread pervasive carbonate—pyrite v e i n r e l a t e d a r e a s of p e r v a s i v e c a r b o n a t e - p y r i t e and and magnetite— magnetiteA series of composite, mafic to t o ultramafic ultramafic chiorite—pyrite c h l o r i t e - p y r i t e alteration. a l t e r a t i o n . A s e r i e s of composite, dykes dykes intruded i n t r u d e d into i n t o the t h e shear s h e a r zones zones during d u r i n g active a c t i v e carbonate c a r b o n a t e alteration alteration maybe maybe related r e l a t e d to t o subaqueous subaqueous trachy—basalt t r a c h y - b a s a l t flows flows which which extruded, e x t r u d e d , as a s part part of of the t h e Stormy Stormy Lake Lake Group, Group, some some 600 600 mm above above the t h e active a c t i v e shear s h e a r zones. zones. Later Later silicification with py, aasp silicification w i t h aassociated s s o c i a t e d py, s p and Au overprinted o v e r p r i n t e d the t h e carbonate— carbonatebearing b e a r i n g zones. zones. East—west East-west trending t r e n d i n g dextral d e x t r a l fault f a u l t zones zones with w i t h associated associated quartz of Stormy Lake Group sedimentation q u a r t z diorite d i o r i t e dykes marked the t h e end of s e d i m e n t a t i o n and maybe associated a s s o c i a t e d with w i t h batholith b a t h o l i t h emplacement emplacement and northward tilting t i l t i n g of of the the e n t i r e package. package. Late L a t e northeasterly n o r t h e a s t e r l y trending t r e n d i n g sinistral s i n i s t r a l faults f a u l t s associated associated entire with w i t h the t h e Manitou Fault F a u l t system system to t o the t h e west w e s t cut c u t all a l l the t h e above above rock rock types types and structures. structures. T I a •1 I I i I �THE THE MULCAHY MULCAHY LAKE GABBRO GABBRO AND AND RELATED RELATED INTRUSIONS INTRUSIONS ! Houston, Houston, TX, Houston, TX; TX; David DavidE.E.Maczuga, Maczuga,LEMSCO, LEMSCO, Houston, TX, 77058 77058 1 Donald Donald A.A. Morrison M o r r i s o n and and William W i l l i a m C. C. Phinney, Phinney, SN4 SN4 NASA/Johnson NASAIJohnson Space Space Center, The Mulcahy Lake gabbro gabbro is mafic The Mulcahy Lake i s a 63 63 square square km km llayered ayered m a f i c intrusion i n t r u s i o n which which resembles The intrusion resembles the t h e Skaergaard Skaergaard iinn many many respects. respects. The i n t r u s i o n iiss centered aatt 93.25W and49.35N, 49.35N,about about5050km kmsouthwest southwesto fofDryden Drydena tatt hthe southwestern llimits 93.25W and e southwestern imits of gabbroi nintrudes basaltic o f Eagle Eagle Lake. Lake. The The gabbro t r u d e s basal t i c t to o ssiliceous i 1iceous units u n i t s of o fthe t h eLower Lower Lake greenstone greenstone bbelt. Wabigoon Wabigoon SSeries, e r i e s , part p a r t of of the t h eCrow CrowLake—Savant Lake-Savant Lake elt. Two mafic be represented representedi nin tthe m a f i c to t o siliceous s i l i c e o u ssequences sequences may may be h e volcanics. volcanics. lliorites Diorites and ggranodiorites of the and r a n o d i o r i t e s of t h e Atikwa A t i kwa batholith b a t h o l it hintrude i n t r u d eboth b o t hgabbro gabbro and and volcanics.. v o l c a n i cs. Zircon my. (1). Z i r c o n from from the t h e gabbro gabbro yield y i e l d aaU/Pb UIPb age age of o f2733.2 2733.2 ÷1.01—0.9 +l.O/-0.9 my. ( 1 ) . PreviPreviously published zircon data (2) indicate crystallization of the batholith o u s l y p u b l i s h e d z i r c o n d a t a ( 2 ) i n d i c a t e c r y s t a l l i z a t i o n o f t h e b a t h o l i t h at at 2731.8 +1.61—1.3 2732.3+ I+1— .GI-1.3 my.my. t oto2732.3 - 2.9 2.9 my.,my., oneone t o to f i vfive e mmillion i l 1i o n years years at a tmost most 2731.8 +l The younger than than the younger t h e gabbro. gabbro. The vvolcanics o l c a n i c s vary vary from-2743 from-2743 to t o 2735 2735 my. my. approxiapproximately Sm—Nd analyses show gabbrowas wasdderived from aa source m a t e l y ((2). 2). Sm-Nd analyses show t h athat t t hthe e gabbro e r i v e d from source The i initial d e p l e t e d in i n light l i g h t rare r a r e earth e a r t h elements elements (1). (1). The n i t i a l SSr r ratio r a t i o of o f the the depleted gabbro i is s 0.7007, 0.7007, cconsistent o n s i s t e n t wwith i t h other o t h e r intrusives i n t r u s i v e s and and extrusives e x t r u s i v e s from from the the gabbro Wabigoon andQ uQuetico subprovinces, Wabigoon and e t i c o subprovinces, i n cincluding l u d i n g t hthe e AAtikwa t i kwa bbatholith, a t h o l i t h , and and sugsuggestive Rbddepletion g e s t i v e of o f aa moderate moderate Rb e p l e t i o n iin n the t h e source source compared compared t otot hthe e AAbitibi. bitibi. The iintrusion km The n t r u s i o n consists c o n s i s t s of o f aa llower o w e r and and middle m i d d l e zone zone each each about about two two km thick, t h i c k , aaone one km km thick t h i c kupper upper zone zone and and marginal marginal zones zones ooff variable v a r i a b l e thicknesses. thicknesses. The lower Each zoner erepresents Each zone p r e s e n t s a ad idistinct s t i n c t cooling c o o l i n g and and fractionating f r a c t i o n a t i n g regime. regime. The and mmiddle zonesf fractionated and i d d l e zones r a c t i o n a t e d from from the t h e floor f l o o upward r upwardwhereas whereas the t h e upper upper zone zone towards ffractionated r a c t i o n a t e d from frcin tthe h e roof r o o f downward downward towards t h ethe i n tinterior e r i o r oof f tthe h e intrusion. intrusion. Marginal zonesf rfractionated fromt hthe towardt hthe Marginal zones a c t i o n a t e d from e wwalls a l l s toward e i interior. n t e r i o r . The The primary primary phasesaare pyroxenes i including n c l u d i n g pigeonite, p i geoni t e , hornblende hornblende and and oxides. oxides. phases r e pplagioclase, l a g i o c l ase, pyroxenes Olivine t h e . b a s e ofo fthe t h elower lowerzone zoneand and i-n i-n the the O l i v i n e occurs occurs iin n ultramafic u l t r a m a f i c units u n i t s ata tthe-base upper zone, zone,i in upper n 'iron—rich i r o n - r i c h UUnits n i t s aatt the t h e top t o p of o fthe t h elower l o w e rzone, zone, and and -in i n a meterthick The oxides t h i c k marker marker horizon h o r i z o n near near the t h e base base of o f the t h e middle m i d d l e zone. zone. The oxides a re are chromite Plagioclase, chromi t e tto o chromian chromian sspinel p i n e l and and later 1a t e r magnetite. magneti t e . P I a g i o c l a s e , pyroxenes pyroxenes and and olivine Hornblende andmagneti magnetite 01 iv i neform formcumulates. cumulates. Hornblende and t e aare r e iritercumulus i n t e r c u m u l us phases. phases. The and fractionation The bbulk u l k composition composition is i s tholeiitic t h o l e i i t i c and f r a c t i o n a t i o n ffollows o l l o w s an ronan iiron— enrichment t trend r e n d wwith ith a a decreasing decreasing Mg/Mg+Fe r a tratio i o w with i t h sstratigraphic t r a t i g r a p h i c height height enrichment Mg/Mg+Fe andaa rrelatively and e 1 a t i v e l y constant constant ssilica i 1 ica content. content. Reversals iinn the Reversals t h eMg/Mg+Fe Mg/Mg+Fe r ratio a t i o in i npyroxenes pyroxenes and and concomitant concomitant changes changes in in showt hthat zoner erepresents oother t h e r phases phases show a t t hthe e mmiddle i d d l e zone p r e s e n t s an an i n influx f l u x o of f rrelatively elatively p r i s t i ne liquid l i q u i dfollowing f o 1 1 owingnearly n e a r l ycomplete complete fractionation f r a c t i o n a t i o n of o f the t h e pre-existing p r e - e x i s t i ng pristine liquid l i q u i dini nthe t h echamber. chamber. S m a l l e r sscale c a l e rreversals e v e r s a l s wwithin i t h i n tthe he m i d d l e zone self Smaller middle zonei titself i n d i c a t e further f u r t h e r introduction i n t r o d u c t i o n of of liquid l i q u i dasasthe t h emiddle m i d d l e zone zone m e l t ccrystallized. rystallized. indicate melt The betweenzones zonesa rare The ccontacts o n t a c t s between e c ccomplex i n ~ex l in interleavings t e r l e a v i nqs o of f ffractionated r a c t i o n a t e d and and less 1ess ffractionated r a c t i o n a t e d assemblages. assemblages. Relatively byccrystallizael a t i " e l y dense dense 1liquids iquid"s produced produced by r y s t a l 1 izapast ttion i o n near near the t h ewalls w a l l s(as ( a sliquid l i q umoved i d moved p a sthem) t them)appear appeartot have o havebeen beenconvected convected downward t oto form anomalously f fractionated r a c t i o n a t e d horizons h o r i zons in i n the t h e middle m i d d l e zone zone and and downward form anomalously possibly as we1 well. possi b l y the t h e lower lower zone zone as 1 Dike—like D i ke-1 ike uultramafic l t r a m a f i c cumulates cumulates ooff 01 i v i n e and and pyroxenes w i t h minor olivine with plagioclase p l a g i o c l a s e and and cchromite h r m i t e ooutcrop u t c r o p iin n Straight S t r a i g h t Lake, Lake, south south ofo fthe t h eMulcahy MulcahyLake Lake gabbro. Similar gabbro. S i m i l a r cumulates cumulates occur occur iin n the t h e upper upper zone zone of o f the t h e gabbro. gabbro. These 1latter a t t e rcumulates cumulates contain c o n t a i ncumulus cumul us chromian chrcini an sspinel p i n e l and and intercumulus intercumul us magnetite. magneti t e . The presence presenceofof i intercumulus The n t e r c u m u l u s mmagnetite a g n e t i t e i n dindicates i c a t e s t hthat a t t the h e ultramafics u l t r a m a f i c s are are co-magmatic presence ooff chrome—rich speciesi in co-magmatic wwith i t h the t h e gabbro. gabbro. The The presence chrome-rich species n both b o t h the the Straight and Mulcahy Lake S t r a i g h t Lake and u l t r a m a f i c s alike a1 ike suggests aa correlation correlation Lake ultramafics between tthe between h e two. two. IIff so, so, both b o t h tthe h e ffloor l o o r and and the t h e roof r o o f of o f the t h e intrusion i n t r u s i o n are are c h a r a c t e r i z e d by h e presence f uultramafic l t r a m a f i c cumulates p r e s e n t i n g t hthe e f first irst characterized by tthe presenceo of cumulatesr erepresenting productsofofc rcrystallization e i ninitial i t i a l liquid. 1i q u i d . products y s t a l 1iz a t i o n o foft hthe 6600 . �I Layered iintrusions n t r u s i o n s closely c l o s e l yresembling resembl i n g the t h eMulcahy Mulcahy Lake Lake gabbro gabbro in i n bulk bul k Layered composition, crystallization c r y s t a l 1i z a t i o nsequences sequences and and which which are a r e identical i d e n t i c a l in i n stratistrati- g r a p h i c age e nnorthern o r t h e r n pperiphery e r i p h e r y ofof tthe h e AAtikwa t i kwa bbatholith a t h o l i t h at a t Trap Trap graphic ageoccur occuronont hthe Lake, Nabish 80 km. km. (Chroniite (Chromite is i s aa Nabish Lake Lake and and Denmark Denmark Lake, Lake, aa distance d i s t a n c e of of 80 prominent phasei nin tthe Lake uultramafic). prominent phase h e Trap Trap Lake l t r a m a f i c ) . These These mmafic a f i c iintrusions n t r u s i o n s reprerepresent sent centers c e n t e r s of o fbasaltic basal t i niagmatism c magmatism active a c t i v esimultaneously, simultaneously, presumably presumably during during the t h e waning waning stages stages of development development of the t h eCrow CrowLake—Savant Lake-Savant Lake Lake greenstone greenstone belt. The belt. The aactivity c t i v i t y ofofthe t h mafic e maficcenters c e n t e rwas s waseclipsed e c l i p s e dbybyemplacement emplacement ooff the the batholith. b a t h o l it h . The development development ofof caic—alkaline calc-a1 k a l ine liquids l i q u i d smust musthave haveaccompanied accompanied The the succeeded onaavvery t h e mafic m a f i c magmatism magmatism o rorsucceeded i t iton e r y sshort h o r t time t i m e scale. scale. A A ddirect i r e c t petrogenetic p e t r o g e n e t i c link l i n kbetween between the t h egabbro gabbro and and the t h e intruded i n t r u d e d volcanics volcanics has has not n o t been been demonstrated. demonstrated. The The gabbro gabbro is i s somewhat somewhat f rfractionated a c t i o n a t e d compared compared to to intruded basal t s which which have have llight i g h t rare r a r e earth e a r t h element e l ement depleted d e p l e t e d patpati n t r u d e d pillow p i 1 l o w basalts terns. Isotopic terns. I s o t o p i c signatures s i g n a t u r e s allow a1 low aa co—magmatic co-magmatic relationship r e 1 a t i o n s h i p but b u t do do not not require r e q u i r e one. one. Whether gabbro and andi its Whether oor r nnot o t the t h e Mulcahy Mulcahy Lake Lake gabbro t s companion companion i intruntrui t i a1 representatives representatives s i o n s represent r e p r e s e n t end i n in t h ethe v ovolcanic l c a n i c c ycycle c l e o rorininitial sions endmembers members of o f aa plutonic p l u t o n i c cycle c y c l e petrogenetically p e t r o g e n e t i c a l l y ddistinct i s t i n c t from from the t h e former former is i s an an interestinteresting (3). i n g question q u e s t i o n (3). (1) ( 1 ) Morrison M o r r i s o n D., D., Davis DavisD.W., D.W., Wooden Wooden J.L., J.L., Bogard BogardD.D., D.D., Maczuga Maczuga D.E., D.E., Phinney Phinney W.C. and Ashwal AshwalL.D., L.D., 1985, Age of of the W.C. and 1985, Age t h e Mulcahy Mulcahy Lake Lake iintrusion, n t r u s i o n , NW NW Ontario, Ontario, and implications and imp1 i c a t i o n s for f o r the t h e origin o r i g i nofofgreenstone—granite greenstone-grani t e belts. be1t s In I n press, press, Earth Earth and Planet. Sci. D.W., and Planet. Sci. Letts. L e t t s .(2)( 2Davis C.E. and andKrogh Krogh T.E., T.E., 1982, 1982, ) Davis D.W., Blackburn BlackburnC.E. Zircon ages from from tthe Lakes area, area, Wabigoon Z i r c o n U—Pb U-Pb ages h e Wabigoon-Manitou Wabi goon-Mani t o u Lakes Wabi goon subprovince, subprovi nce , . northwest Ontario, CanadianJour. Jour.EEarth Sci. 19 northwest O n t a r i o , Canadian a r t h Sci. 19 p. p. 264. 264. (3) ( 3 )Davis DavisD.W. D.W. and and Edwards G.R., 1983, Edwards G.R., 1983, Zircon Z i r c o nU—Pb U-Pb ages ages from from the t h e Kakagi Kakagi Lake Lake area, area, Wabigoon Wabigoon Subprovi nce, northwest n t a r i o , Canadian Canadian Jour. arth S c i 19 19 p. p. 1235. 1235. Subprovince, northwest OOntario, Jour. EEarth Sci. . I I I I •1 I I 61 i I �I Volcanic Volcanic stratigraphy and nature of the the semi—conformable semi-confarmable alteratioin zone beneath the the Mattabi massive suiphide sulphide deposit, Sturgeon Lake, Ontario Morton, Department Department of of Geology, Geology University L. Morton, University of o+ Minnesota— MinnesotaL Duluth, Duluth Minnesota, Di-iluth, Duluth, Minnesota, 55812 55812 Groves, Newmont Exploration Ltd., Ltd. Duluth, D. A. . Groves, D. Newmont Exploration Duluth. Minnesota Minnesota 3. J. M. M. Franklin, Geological Geological Survey of Canada, Canada, 601 601 Booth Booth St., St.! Ottawa, Ontario R. hyalotuffs4 Subaerial and shallow shallow subaqueous subaqueous ma-Fic maf ic hyalotuf f s, lava lava and flow breccias, breccias, and and felsic lava flows and flows and pyroclastic flow and and fall fall deposits form a 2 pyroclastic 2 km k m thick succession beneath beneath the Mattabi Mattabi massive sulphide deposit. succession deposit. The The lowermost part o-F the succession succession is is composed composed of of massive and of the and flows and and flow flow breccias breccias which which are amygdaloidal ma-Fic maf ic flows interlayered with with repetitive sequences sequences of thinly bedded pillow lavas and hyaloclastites are absent felsic tuff; pillow absent from from this succession. this succession. Amygdaloidal Amygdaloidal felsic f elsic lavas lavas overlie over1 ie the the mafic maf ic flow succession succession and and are local1 locally capped by by a coarse explosion flow y capped believed to have initiated breccia. This breccia is believed initiated a a period period of ma-fic hydrovolcanic activity activity which which produced produced ash—laden of mafic hydrovolcanic ash-laden falls, surges, surges, and flows; these deposited thin to to thickly thickly Periods of water exclusion resulted in bedded hyalotuffs. bedded hyalotuf f s. in the formation of of scoria—rich scoria-rich beds. beds. These eruptions cone and and represent represent aa submergent submergent constructed aa tuf-f tuff cone hydrovolcanic cycle. cycle. Pyroclastic the immediate mine Pyroclastic flow flow deposits deposits -form form the -Footwall strata strata and and include include a) a) massive massive basal basal and overlying footwall These bedded bedded ash tuffs, and b) b) massive massive pumiceous pumiceous units. units. These deposits overlie overlie and and are are intercalated intercalated with with the thema-Fic mafic hyalotuf-f sequence. hyalotuf f sequence. The volcanic rocks beneath the the Mattabi deposit deposit have have hydrothermal alteration alteration and undergone hydrothermal and subsequent subsequent regional regional greenschist Within the the footwall greenschistmetamorphism. metamorphism. Within footwall volcanic volcanic sequencefour four chemically mineralogically sequence chemical 1 y and and mineralogical ly distinct alteration types types have have been been defined: defined: iron least altered, iron carbonate—chlorite, chioritoid, carbonate-chlorite, chloritoid, and sericite. sericite. Least Least altered rocks have been affected primarily by regional greenschist greenschist thus the freshest rocks rocks to ta be be facies metamorphism and are thus found in the area. area. They are largely largely confined to to mafic mafic flows flows hyalotuffs. Iron chloritoidand hyalotu-ffs. Iron carbonate-chlorite carbonate—chlorite and and chloritoid— type alteration form a widespread, semi—conformable semi-conformable zone zone beneath beneath the Mattabi Mattabi deposit; these these assemblages assemblages are are largely largely confined to t o felsic felsic pyroclastic pyroclastic flows flows and and lavas. lavas. Chloritoid Chioritoid believed to have formed formed from the interaction of iron—rich is believed iron-rich chlorite and a hydrous aluminum silicate silicate during during metamorphism. metamorphism. Sericite—type Sericite-type alteration envelopes and/or and/or crosscuts crosscuts the the earlier alteration. It I t is is semi— semiearlier iron carbonate-chlorite carbonate—chlorite type alteration. and is is most most abundant abundant within within conformable to stratigraphy and -felsic pyroclastic pyroclastic flow flow deposits. felsic An An alteration model is is proposed proposed in in which which seawater, seawater, trapped within within a thick, thick, submerged pile of mafic lava trapped lava flows flows and breccias, breccias, was heated and heated by by the Seidelman Beidelman Bay intrusion. intrusion. 6622 �I Thin, Thin, impermeable impermeable felsic f e l s i c lava l a v a fflows lows o v e r l i e the t h e mafic mafic overlie succession and and produced produced aa cap cap to t o the t h e hydrothermal h y d r o t h e r m a lreservo:ir. reservoir. High fluid f l u i d temperatures and low low water/rock w a t e r / r o c k ratios r a t i o s within w i t h i n the the rreservoir e s e r v o i r resulted r e s u l t e d in i n the t h e formation f o r m a t i o n of o f aa fluid f l u i d rich r i c hini nFe., Fe, Mn, Na, Na, and, and, presumably, Mn, presumably, C02. C 0 2 . The The C02 C 0 2 is i s believed b e l i e v e d to t o have have been derived d e r i v e d from f r o m diagenetic d i a g e n e t i c carbonate. carbonate. Deep-seated tectonism t e c t o n i s m within w i t h i n the t h e volcanic v o l c a n i c pile p i l e produced produced Deep—seated high—angle h i g h - a n g l e faulting f a u l t i n g which allowed a l l o w e d the t h e sudden sudden release r e l e a s e of of ffluids l u i d s from f r o m the t h e reservoir. reservoir. M i g r a t i o n of o f the t h e fluids f l u i d s through through Migration permeable pyroclastic p y r o c l a s t i c rocks r o c k s resulted r e s u l t e d in i n base—fixing b a s e - f i x i n g reactions reactions and the t h e formation f o r m a t i o n of o f the t h e semi—conformable, semi-conformable, ankerite—chlorite ankerite-chlorite alteration a l t e r a t i o n zone. zone. The fluids f l u i d s boiled b o i l e d as as they t h e y neared neared the the seafloor s e a f l o o r , and and siderite s i d e r i t e was was deposited d e p o s i t e d throughout t h r o u g h o u t the t h e rocks rocks Suiphide beneath the t h e discharge d i s c h a r g e area. area. S u l p h i d e minerals m i n e r a l s then then accumulated Later, accumulated on on the t h e seafloor. seafloor. L a t e r , near surface s u r f a c e interaction interaction off felsic o f e l s i c rocks r o c k s and warm seawater at a t high h i g h water/rock w a t e r / r o c k ratios ratios produced the t h e sericitic s e r i c i t i c alteration a l t e r a t i o n assemblage. assemblage. I I I I I I I •1 I 63 I I �STRUCTURAL ANALYSIS RANGE AND AND ADJACENT ADJACENT BASAL BASAL DULUTH DULUTH ANALYSIS OF THE NORTHEASTERN MESABI RANGE COMPLEX EUGENE MULLENMEISTER, MULLENMEISTER, TIMOTHY TIMOTHY B. B. HOLST, HOLST, JOHN JOHN C. C. GREEN, GREEN, Department Department of of Geology, Geology, and Natural Resources Research Research Institute, Institute, University University of of Minnesota Minnesota Duluth, Duluth, W. WEIBLEN, WEIBLEN, Department of of Geology Geology and and GeophyGeophyDuluth, Minnesota 55812, and PAUL W. sics, sics, University University of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 I I Information Information on the the structural structural geology geology of of the the Biwabik Biwabik Iron Iron Formation Formation (BIF) (BIF) and and the base of the Duluth Complex for this poster poster session has been been compiled from state geological geological maps, maps, mining company company maps, maps, structure structure contour contour maps maps based based on on drill hole hole data, data, drill core logs and field observations. observations. The The data data covers covers aa mi. long portion of the northeastern northeastern Mesabi Range 24 mi. Range of of Minnesota, Minnesota, extending extending from the Embarras (T59N, RI6W), R16~),to to the the Dunka Dunka Mine Mine on on the the Embarras mine west west of of Aurora Aurora (T59N, south south side of Birch Lake Lake (T61N, (T61N, RI2W) ~ 1 2 and ~ and ) the the adjacent adjacent Duluth Duluth Complex Complex to to the the southeast. A total total of 31 31 faults faults in in the the BIF BIF and and 16 16 faults faults in in the the base base of of the the Duluth Complex Complex and several several folds folds are are inferred. inferred. Both the the BIF BIF and and Duluth Duluth Complex Complex are affected by six six of of the the faults. faults. Displacement along the faults, faults, fold amplitude and wavelength wavelength were estimated estimated from from the the structure structure contour contour maps. maps. ft. in Displacements along faults occurring in the iron formation range from 7 ft. the Peter Peter Mitchell Mine to to 450 450 ft. ft. along along the the Siphon Siphon Fault Fault west west of of the the Spring/Siphon SpringISiphon Mine. Mine. The displacement displacement is is greater greater than than 80 80 ft. ft. along along seven seven of of the the faults faults and 50 50 ft. or or less less along along the the remaining remaining 24. 24. N8OE) in the BIF, the downthrown For nine northeast—trending northeast-trending faults (N1OE (N10E to N80E) side is is to to the the southeast southeast for for five five and and to to the the northwest northwest for for three three with with one one unknown. 20 northwest—trending northwest-trending faults faults (N15W (N15W to to N5OW), N~OW),the the downthrown downthrown side side unknown. For 20 is divided evenly to to the the northeast northeast for for 10 10 and and to to the the southwest southwest for for'10. 10. There There are two N-S faults, one with N—S trending faults, with the east side down and one with the west side down. down. A total total of 16 16 faults faults give give aa cumulative cumulative east east side side down down displacement displacement side 1222 ft. ft. and and 14 14 faults faults give give aa cumulative cumulative west west side side down down displacement displacement of of of about 1222 about 705 ft. about 705 ft. Folding occurs in the iron formation formation north of Aurora and to the east through the Wentworth anticline north north of of Aurora Aurora trends trends generally generally E—W E-W for for Wentworth Mine. A broad anticline approximately It has an amplitude amplitude of about mi. about 150 150 ft., ft., and and aa map map distance distance approximately 44 mi. from from crest crest to to trough trough of of its its attendant attendant syncline syncline to to the the north north of of about about 0.5 0.5 mi. mi. The anticline anticline flattens flattens out out for for about about 1.0 1.0 mi. mi. west west of of the the Knox Knox Mine. Mine. It It is is apparent again east of the Knox Mine and continues for about 2.5 2.5 mi. mi. on a general general E—W E-W trend trend through through the the Wentworth Wentworth Mine. Mine. The amplitude amplitude increases increases to to 250 250 ft. and the map distance from crest to trough decreases to 600 ft. at the WentWent— E—W, it is offset to worth Mine. Mine. Although the general trend of the anticline is E-W, the north in several places giving it it aa sinuous sinuous axial axial trend. trend. Only one structure, structure, the the Siphon Siphon Fault, Fault, is is observed observed to to affect affect the the stratigraphic stratigraphic thickness of Animikie Animikie Group Group rocks. rocks. It trends N40W a vertical vertical displacedisplaceN4OW and has a ment of about about 450 450 ft., ft., down down to to the the northeast. northeast. There is an abrupt decrease decrease in in thickness of the Lower Cherty Member of of the the BIF from from west west to to east east across across the the fault, from 140 fault, 140 ft. west of the the fault fault to to 60 60 ft. ft. east east of of the the fault. fault. The The Lower Lower continues to thin gradually to the east until it disappears completely Cherty continues near the the south south side side of of Birch Birch Lake. Lake. The fault fault corresponds corresponds to a lithologic lithologic boundary in the Archean basement between Knife Lake Group metamorphosed metamorphosed sedimentary volcaniclastic rocks to the the east. east. and volcarticlastic rocks to to the the west west and and Giants Giants Range Granite Granite to 64 I �Displacement along faults occurring in the Duluth Complex is estimated for 11 11 of the 16 16 faults faults and range range from from 11 ft. in the Dunka to 360 360 ft. ft. at at the the Minnamax Minnamax Dunka Mine to faults and Project. displacement is greater than 100 ft. for five of the faults Project. The displacement 30 30 ft. or less less for for the the remaining remaining six. six. For nine northeast trending trending faults faults (NO5E (N05E to to ~ 5 5 in ~ )the the Duluth Duluth Complex, Complex, the the N55E) downthrown side is to the southeast for four, four, to the northwest for three and (N30~ to N5OW), ~ 5 0 the the ~ ) ~ unknown for two. two. For six northwest trending trending faults faults (N3OW unknown for to downthrown side is is to to the the northeast northeast for for four four and and to to the the southwest southwest for for two. two. downthrown side There is one N—S N-S trending trending fault fault with with the the west west side side down. down. The east east side side down down displacement for six six of of eight eight faults faults totals totals an an estimated estimated 630 630 ft. ft. The west side side displacement for down displacement displacement for for five five of of six six faults faults totals totals an an estimated estimated 650 650 ft. ft. Undulations at the base of the Duluth Complex are shown by structure contour maps in the Dunka Dunka Mine and and the the Minnamax Minnamax Project Project area. area. An antiform antiform structure structure begins at the northwest end of the Minnamax Project and trends S4OE S40E for about At this point the trend changes N70E for for about about another another 2.5 2.5 mi. mi. The The mi. At changes to to N7OE 0.5 mi. attendant synform to the north is parallel to the antiform structure for about 1.5 mi. mi. to the east and changes 1.5 changes to to a N—S N-S trend trend over over the the next next 0.7 0.7 mi. mi. The maximum mum amplitude amplitude of of this this antiform antiform structure structure is is about 350 350 ft. ft. with aa map distance distance from E—W trending from crest crest to to trough trough of of 1500 1500 ft. ft. Several E-W trending undulations undulations occur occur at at the the southeast southeast end end of of the the prospect. prospect. They can be traced for for about about 2000 2000 ft. ft. Axnpli— Amplitudes range N70W range from from 100 100 ft. ft. to to 450 450 ft. ft. with with aa wavelength wavelength of of 900 900 ft. ft. A N7OW trending antiformal antiformal structure structure occurs occurs in in the the Dunka Dunka Mine Mine area. area. It has an ampliampliof about 550 ft. ft. and and coincides with with an an anticline anticline observed in outcrop of the tude of underlying BIF in underlying in the the Dunka Dunka Mine. Mine. The highest grade of sulfide sulfide mineralization mineralization in the area area is is associated associated with with this this structure. structure. The pattern pattern of faulting faulting appears appears to to be be Archean basement basement litholbgies. litholbgies. affected by Archean All seven faults faults occurring in the BIF over an 11 mile stretch from the Siphon Siphon Fault to the east end of the Peter Mitchell Mine trend to the northwest. Here Here in the Dunka MineMine to theto eastthe the iron formation overlies Archean granite. and in the Dunka east the iron formation overlies Archean granite. and The northwest northwest trend is still present east of the Peter Mitchell Mine into into the Dunka Mine but it becomes more complicated where the BIF is intruded by the Duluth Complex. West of Duluth of the the Siphon Siphon structure, structure, the the dominant dominant northwest northwest fault fault patpattern is present present but complicated complicated by by aa northeast northeast component. component. Here the iron iron forfortern mation is folded and overlies Archean Knife Lake Group metamorphic rocks. This This indication indication that the style of deformation was controlled to some degree by the basement rocks rocks was suggested suggested earlier earlier by by White White (1954). (1954). • Co., Reserve Mining Co., Co., LTV Grateful appreciation appreciation is extended to Erie Mining Co., Corp., U.S. U.S. Steel corp. corp. and and Bear Bear Creek Creek Mining Mining Company Company for providing access steel Corp., mine properties and and to the Minnesota Minnesota Department Department of Natural Resources to data and mine for providing funding and data for for this this project. project. White, D.A., 1954, 1954, The The Stratigraphy Stratigraphy and and Structure Structure of of the the Mesabi Mesabi Range, Range, White, D.A., Minnesota: Minn. Geol. Survey 38, 92 92 pp Survey Bull. 38, •1 I 65 I �I Proterozoic Proterozoic Diabase Diabase Dike Dike Swarms Swarms in in Wisconsin Wisconsin M.G. M.G. MUDREY, MUDREY, Jr. Jr. (Wisconsin (Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 1815 1815 University University Avenue, Avenue, Madison, Madison,Wisconsin Wisconsin53706> 53706) P.E. MYERS, (Department (Departmentof of Geology, Geology,University UniversityofofWisconsin—Eau Wisconsin-EauClaire, Claire, P.E. MYERS, Eau Claire, Claire, Wisconsin Wisconsin 54701) 54701) Eau I Regional geologic geologic mapping mapping and and analysis analysis of of regional regional aeromagnetic aeromagnetic maps maps Regional have identified identified two two areas areas of of mafic mafic dike dike swarms swarms in in Wisconsin: Wisconsin: (1) (1) aa central central have Wisconsin area, area, and and (2) (2) aa northern northern area area adjacent adjacent to to Keweenawan Keweenawan intrusive intrusive Wisconsin suites. There There appears appears to to be be little littledifference differenceininmajor majorelement elementchemistry chemistrybebesuites. tween the the two two swarms, swarms, although although the the northern northern swarm swarm and and some some of of the thecentral central tween swarm dikes dikes have have been been weakly weakly metamorphosed. metamorphosed. swarm The The dike dike swarm swarm in in central central Wisconsin Wisconsin is is defined defined principally principally from fromregional regional aeromagnetic aeromagnetic maps and and generally generally trends trends east east to to northeast. northeast. Individual Individual dikes dikes are are identified identified by by strong strong magnetic magnetic lows lows that that can can be be traced traced for forover over 260 260km tanand and continue beyond beyond the the limits limits of of the theavailable availableaeromagnetic aeromagnetic data. data. The The swarm swarm is is continue at at least least 120 120 km km wide wide and and is is lost lost at atits itssouthern southernmargin marginby by the thelimits limitsof of aero— aeromagnetic coverage. coverage. Isolated Isolated outcrops outcrops of of this this swarm swarm are are known known to to the the south. south. magnetic Some Some individual individual dikes dikes exceed exceed 80 80mm ininwidth. width. Where Where sampled, sampled, these these large large dikes dikes are are dominantly dominantly olivine olivine gabbro gabbro to to anorthositic anorthositic troctolite troctolite and and are are continental continental tholeiite, based based on on major major element elementchemistry. chemistry. In In detail, detail, the the dikes dikes can can be be diditholeilte, vided vided into into aa suite suite rich rich in in iron iron and and titanium titanium with with aa strong strong reversed reversed magnetic magnetic polarity polarity anda a n d amore moreaverage averagecontinental continentaltholeiite tholeiitesuite suitewith witha aweak weaknormal normalpopolarity signature. signature. Alteration Alteration is is minimal. minimal. Most Most of of the the recognized recognized swarm swarm is is larity hosted in in Proterozoic Proterozoicrock. rock. hosted The The northern northern dike dike swarm swarm is is defined defined from from outcrop outcrop with with supplemental supplemental defi— definition from from regional regional aeromagnetic aeromagnetic data. data. Aeromagnetic Aeromagnetic data data are are not not as as useful useful nition in in defining defining the the extent extent of of this this swarm swarm because because of of the the proximity proximity to to strongly strongly magmagnetized Keweenawan Keweenawan intrusives. intrusives. The The swarm swarm generally generally trends trends northwestward northwestward and and netized does not not appear appear to to be be as as continuous continuous as as the the central central swarm. swarm. Some Some individual individual does dikes dikes appear appear to to be be offshoots offshoots of of the theKeweenawan Keweenawan Mellen Mellenand andMineral MineralLake Lakeintruintrusive suites suites and and related related rock. rock. Locally Locally some some of of these these dikes dikes are are altered altered to to sive uralite and and chlorite, chlorite, probably probably by by subsequent subsequent metamorphism metamorphism of of the the adjacent adjacent uralite gabbroic complexes. complexes. AA few few dikes dikes cut cut the the Mellen Mellen granije. granite. gabbroic Another Another older, older, poorly poorly defined defined set set of of diabase diabase dikes dikes is is known known in in the the cencentral area, area, and and is is known known to to cut cut the the 1,760 1,760 Ma Ma rhyolite rhyolite and and granite granite in in southern southern tral Wisconsin. This This suite suite is is metamorphosed metamorphosed to to hornblende—chlorite—biotite hornblende-chlorite-biotite assemassemWisconsin. blages, has has aa weak weak tectonic tectonic fabric, fabric, and and is is calc—alkaline calc-alkaline in in composition. composition. Some Some blages, individual analyses analyses contain contain nepheline nepheline in in the the norm. norm. This This sodic sodic series series may may oc— ocindividual cupy the the same same fracture fracture system system as as the the younger, younger, fresher fresher swarm, swarm, but but generally generally cupy appears to to have have aa more more northwesterly northwesterlytrend. trend. appears Other Other post—Penokean post-Penokean dikes are are known known and and include include aa weakly weakly tectonized tectonized an— andesitic desitic suite suite in in the the Penokean Penokean orogen orogen and and aa granitic granitic suite suite in in southern southern Wis— Wis- consin. consin. event event. . These These are are probably probably related related to to the the 1,760 1,760 Ma Ma post—Penokean post-Penokean magmatic magmatic 66 a �I few diabase dikes are are known known in in the the area area between between the the northern northern and and cencenThis area area is is well well covered covered by by detailed detailed aeromagnetic aeromagneticsurveys; surveys;how-however, no strong magnetic magnetic lineaments are recognized, suggesting suggesting that that no magne distinctive swarm tically distinctive swarm exists. exists. A tral swarms. swarms. 6 6 Paleozoic cover cover 55 Keweenawan terrane terrane 4 4 Proterozoic anorogenic plutonic Proterozoic rock == Wolf River sequence rock sequence 3 3 Proterozoic quartzite = Baraboo Baraboo Proterozoic sequence sequence N I Proterozoicmetavolcanic metavolcanicand andplu-.plu2b Proterozoic Wisconsin inagmatic magmatic tonic rock == Wisconsin terraae terrane 2a Proterozoic Proterozoic metasedimentary metasedimentary rock rock == Proterozoic epicratonic Proterozoic epicratonic cover cover 1 Archean Archean terrane terrane I. A Sb2 Si02 Tb2 Ti02 A1203 A1203 FeOv FeOT MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 P205 '2O5 49 2.3 13.8 14.6 0.2 5.1 8.6 2.7 1.1 0.4 49 1.4 13.6 11.7 0.2 5.9 9.0 3.2 0.9 0.1 I C B 51 1.0 16.4 8.8 0.2 6.3 8.6 3.2 1.2 0.3 high-Fe-Ti dikes, dikes, reverreverA avg. of 55 high—Fe-Ti sly polarized polarized(incl. (md. Rib sly Mountain). Rib Mountain). 8 B avg. of 66 low low Fe—Ti Fe-Ti dikes, dikes, weakly weakly reversely (?) ( ? ) polarized polarized normally and reversely (incl.Monico, Monico, Morse, Morse, Biron, Biron, Dudley). Dudley). (mci. C avg. of S5 sodic sodic dikes, dikes, weakly weakly po— polarized (incl. (mci. Montello, larized Montello, Prairie Prairie . Dell) Dell). I 1 I 67 I I I �U # METAMORPHISM METAMORPHISM OF OF THE THE DUNBAR DUNBAR GNEISS GNEISSAND AND ASSOCIATED ASSOCIATEDStJPRA—CRUSTAL SUPRA-CRUSTAL ROCKS: ROCKS: NORTHEASTERN NORTHEASTERN WISCONSIN, WISCONSIN, USA USA PETER PETER A. NIELSEN NIELSEN (Division (Division of of Science, Science, University University of of WisconsinWisconsin- Parkside, Parkside, Box Box 2000, 2000, Kenosha, Kenosha, WI WI U.S.A. U.S.A. 53141 53141 The The Quinnesec Quinnesec Formation Formation crops crops out out in in northeastern northeastern Wisconsin Wisconsin and and surrounds surrounds the the core core zone zone of of the the Dunbar Dunbar dome. dome. Metamorphic Metamorphic grade grade varies varies across across the the structure structure and and decreases decreases away away from from the the contacts contacts with with the the Dunbar Dunbar Gneiss Gneiss and and its its late late stage stage intrusive intrusive components. components. The Ic to The Quinnesec Quinnesec Formation Formationis is dominantly dominantlymaf mafic to felsic felsic volcanics volcanics and and volcaniclastics volcaniclastics (Schulz, (Schulz,1984). 1984). Local Local occurrances occurrances of of restricted restricted basin basin sediment sediment are are present present and and have have been been explored explored for for massive massive sulfide sulfide mineralization. mineralization. Their Their high high sulfide sulfide and and graphite graphite contents contents have have resulted resulted in in aa poor poor outcrop outcrop record, record, but but samples samples were were obtained obtained from from several several drill drill cores cores from from the the West West Bass Bass Lake Lake area area of of Florence Dunbar Gneiss Gneiss Florence County. County. The The supra—crustal supra-crustal rocks rocks and and the the Dunbar record record a a similar similar sequence sequence of of fabric fabric development development and and late late stage stage vein vein emplacement. emplacement. The The supra—crustal supra-crustal sequence sequence Is is characterized characterized by by prograde prograde metametamorphic morphic assemblages assemblages including: including: 1- biotite biotite -- garnet garnet — plagioclase plagioclase - quartz quartz + cordierite cordierite in in metameta1sediments sediments 2- garnet garnet — hornbJ.ende hornblende — plagioclase plagioclase ±+ quartz quartz in in metabasalts metabasalts 2— and, and, 3- diopside diopside — tremolite tremolite — calcite calcite + quartz quartz in in marbles. marbles. 3— - - - - - - Late Late stage stage metamorphic metamorphic effects effects are are present present in in most most samples. samples. most prevalent alteration includes: most prevalent alteration includes: garnet -à biotite biotite ++ chlorite chlorite garnet -+ cordierite pinite cordierite -+ Ñ pinite ++ sericite sericite 3- hornblende hornblende Ñ>— biotite biotite ++ actinolite actinolite ++ chlorite chlorite 3and, and, — epidote 4- Plagioclase Plagioclase Ñà epidote ++ albite albite 4- The The 1122— Beds Beds enriched enriched in in SS have have pyrite pyrite ++ pyrrhotite pyrrhotite ++ cha].copyrite chalcopyrite and show show a a loss loss of Fe Fe from from the the silicate silicate phases phases due due to to suifidation sulfidation reactions. reactions. The The supra—crustal supra-crustal sequence sequence and and the the Dunbar Dunbar Gneiss Gneiss are are cut cut by late late stage stage pegmatites pegmatites and and quartz-tourmaline quartz-tourmaline veins. veins. In In thin thin section, section, an an S1 S foliation foliation defined defined by by biotite biotite Is is parallel parallel to to bedding bedding planes planes (S0). ( S ) . Retrograde Retrograde biotite biotite defines defines a weak S2 S2 foliation foliation which by up up to to a which is Is inclined to to S, S by 900. Deformation 9 0 ' . Deformation of the the Quinessic Quinessic Formation Formation probably probably corresponds corresponds to to D2 and D4 D, (Sims (Sims et et al, all 1984) 1984) an in the the Dunbar dome. dome. Dunbar prograde metamorphic metamorphic assemblages assemblages restrict restrict peak peak metametaThe prograde The morphic conditions conditions to to 500—550°C 5 0 0 - 5 5 0 ~at at ~ low low to to intermediate intermediate morphic lithostatic pressure. pressure. Based Based on on the the abundance abundanceof of graphite graphitearid and lithostatic pyrite +÷ pyrrhotite, pyrrhotite, PH H and CO2 Con and and 0 << 'total H S were (at (at least major components components In in the fluid H2S least locally) locahy) major 68 phase. phase. 68 total I I �I The ranges in composition composition from The Dunbar Dunbar Gnei.ss Gneiss ranges from granite—grano— granite-granodiorite diorite to to biotite biotite tonalite, tonalite,and and locally locallycontains containsabundant abundantniafic mafic inclusions inclusions (Schulz (Schulzet et al, al, 1984). 1984). In In many many outcrops, outcropsfthe the gneiss gneiss grades grades into into migmatite. migmatite. The The similarity similarity between between the the deformational deformational and and metamorphic metamorphic histories histories of of the the Quinnesec Quinnesec Formation Formation and and the the Dunbar Dunbar Gneiss Gneiss suggests suggests that that they they were were coeval. coeval. The The lower lower metamorphic metamorphic grade grade recorded recorded in in the the Quinnesec Quinnesec Formation Formation is is attributed attributed to to aa smaller smaller extent extent of of erosion erosion due due to to higher higher density. density. The The core core of of the the Dunbar Dunbar dome dome was was formed formed at at the the peak peak of of metamorphism metamorphism by by bouyant bouyant emplacement Dunbar Gneiss. Gneiss. The The emplacement of of the the hotter hotter and and lower lower density density Dunbar time time required required to to form form the the Dunbar Dunbar Gneiss Gneiss protolith, protolithfthe the Quinessic Quinessic Formation Formation and and their their deformation deformation and and metamorphism metamorphism was was on on the the order order of of 30 30 million million years years (Sims (Simset et al, all1984) 1984). Schulz, Schulzf K.J., K e J a 1984, f1984f Volcanic Volcanic rocks rocks of of northeastern northeastern Wisconsin, Wisconsin,in: in: Guide Guide to to the the Geology Geoloqy of of the the Early Early Proterozoic Proterozoic Rocks Rocks in in 1 ThirtiethAnnual Annual Northeastern Wisconsin, Field Trip 1, Thirtieth Institute Institute on on Lake Lake Superior Superior Geology, Geology, p. p. 51-81 51-81 Schulz, Schulzf KJ., K ; J aSims, fSimsfP.K., P.K.#and andPeterman, Peterman#Z.E., Z . E q f1984, 1984,Geochemistry Geochemistrv of of the the Dunbar Dunbar Gneiss Gneiss Dome, Dome, N.E. N.E. Wisconsin, isc cons in^ in: in:Guide Guideto to the thl Geology the Early Early Proterozoic Proterozoic Rocks Rocks in in Northeastern Northeastern Geoloqy of of the Wisconsin, Field Trip Trip 1, 1, Thirtieth Thirtieth Annual Annual Institute Institute on on Wisconsin, Field Lake Superior Superior Geology, Geology,p. P O24—42 24-42 Lake Sims, Sims, P.K., P.K.# Peterman, Peterman#Z.E., Z.E.fand and Schulz, SchulzfK.J., K.J.,1984, 1984#Dunbar DunbarGneiss Gneiss -- Grani.toj.d Granitoid Dome, Dome, in: in: Guide Guide to to the the Geology Geology of of Early Early Proterozoic Rocks Rocks in in Northeastern Northeastern Wisconsin, WisconsintField FieldTrip Trip1,1 , Proterozoic Thirtieth Annual Annual Institute Instituteon on Lake Lake Superior SuperiorGeology, Geologytp. p . 1-23 1-23 Thirtieth I •1 I 69 1 I I �PRECAMBRIAN—HOSTED PRECIOUS METAL PROSPECTS GEOLOGY OF PRECAMBRIAN-HOSTED PROSPECTS IN I N THE THE AREA, MARQUIZTTE MARQUETTE COUNTY, FIRE CENTER AND HOLYOKE MINES AREAy COUNTYy MICHIGAN MICHIGAN Bornhorst (Department (~e~artmen oft Geology and and Geological Geological Eric 0. Owens and Theodore J. of E r i c 0. J . Bornhorst E n g i n e e r i n g , Michigan T e c h n o l o g i c a l University, U n i v e r s i t y y Houghton, Houghtony Michigan 49931) Engineering, Technological 2 During the t h e summer of o f 1984 1984 aa 66 km2 km area, a r e a , located l o c a t e d about about 19 19 km km northwest n o r t h w e s t of of Marquette, M a r q u e t t e y Michigan was geologically g e o l o g i c a l l y mapped at a t aa scale s c a l e of of 1:2,400. 1 : 2 y 4 0 0 . Mapping included of T49N, R27W and the i n c l u d e d aall ll o f section s e c t i o n 35, 3 5 , T49Ny t h e top t o p part p a r t of of section s e c t i o n 2, 2 y T48N, T48Ny R27W, including R27W, i n c l u d i n g the t h e inactive i n a c t i v e Fire F i r e Center C e n t e r gold g o l d mine and Holyoke silver s i l v e r mine. An of about about 30% ooutcrop u t c r o p ddensity e n s i t y of 30% allowed a detailed d e t a i l e d analysis a n a l y s i s of of the t h e field f i e l d geologic geologic relationships of aa sequence of r e l a t i o n s h i p s of of metamorphosed Archean and Lower Proterozoic Proterozoic volcanic, v o l c a n i c y sedimentary s e d i m e n t a r y and and intrusive i n t r u s i v e rocks. r o c k s . From oldest o l d e s t to t o youngest, y o u n g e s t , the t h e Archean metavolcanic m e t a v o l c a n i c units u n i t s are: a r e : pillowed p i l l o w e d basalt b a s a l t flows, f l o w s y a schistose s c h i s t o s e pyroclastic p y r o c l a s t i c horizon, horizony banded iron banded i r o n formation, f o r m a t i o n y and laminated l a m i n a t e d phyllitic p h y l l i t i c and schistose s c h i s t o s e volcanics v o l c a n i c s and and sediments. i s in i n fault f a u l t contact c o n t a c t with w i t h aa tectonized t e c t o n i z e d breccia b r e c c i a of of s e d i m e n t s . The latter l a t t e r unit u n i t is possible Archean—age; this unit p o s s i b l e Archean-age; this u n i t could c o u l d be lower lower Proterozoic P r o t e r o z o i c in i n age. a g e . The Archean metavolcanics m e t a v o l c a n i c s and and metasediments are a r e intruded i n t r u d e d by by gabbro gabbro and and rhyolite r h y o l i t e porphyry porphyry dikes of probable d ikes o f p r o b a b l e Archean age; a g e ; field f i e l d evidence e v i d e n c e indicates i n d i c a t e s the t h e rhyolite r h y o l i t e porphyry porphyry is is u n i t s described d e s c r i b e d above above are a r e overlain o v e r l a i n by by lower lower the t h e younger of o f the t h e two. two. The bedded units Proterozoic of section s e c t i o n 35, 35, P r o t e r o z o i c slates s l a t e s and and phyllites. p h y l l i t e s . Near the t h e northern n o r t h e r n boundary of of the lower Proterozoic Michigamme Formation is in fault q u a r t z i t e o f t h e lower P r o t e r o z o i c Michigamme Formation i s i n f a u l t contact c o n t a c t with with quartzite East—west trending Archean Archean ppillowed i l l o w e d bbasalt a s a l t flows. f l o w s . East-west t r e n d i n g Middle Proterozoic P r o t e r o z o i c diabase diabase dikes d i k e s of of Keweenawan age a g e intrude i n t r u d e the t h e Archean rock rock units. units. of The strike strike o f the t h e Archean and Lower Proterozoic P r o t e r o z o i c units u n i t s is i s approximately a p p r o x i m a t e l y N60°W ~ 6 0 ' ~ e x p o s e d y contacts c o n t a c t s between units u n i t s are a r e near n e a r vertical v e r t i c a l and and commonly commonly tto o N70°W. ~ 7 0 ' ~ . Where exposed, show eevidence v i d e n c e of o f faulting f a u l t i n g and and shearing. s h e a r i n g . Foliations F o l i a t i o n s are a r e manifested m a n i f e s t e d by by slaty s l a t y and and phyllitic and schistosity both p h y l l i t i c ccleavages l e a v a g e s and s c h i s t o s i t y in in b o t h the t h e Archean and Lower Proterozoic Proterozoic Except in Formation, rrocks. o c k s . Except i n the t h e Michigamme F o r m a t i o n y strike s t r i k e and dip d i p of of foliations f o l i a t i o n s (and (and bedding) bedding) are a r e generally g e n e r a l l y N60°W ~ 6 0 'to t o~ N75°W ~ 7 5 'and and ~ are a r e near n e a r vertical. v e r t i c a l . Evidence Evidence of of intense intense and shearing ddeformation e f o r m a t i o n and s h e a r i n g include i n c l u d e phaccoidal p h a c c o i d a l and schistose s c h i s t o s e structures, s t r u c t u r e s y tight tight ffolds, o l d s y ttransposed r a n s p o s e d layering l a y e r i n g and folded f o l d e d quartz q u a r t z lenses, l e n s e s y and boudinage. boudinage. These rocks rocks have been subjected s u b j e c t e d to t o greenschist g r e e n s c h i s t facies f a c i e s metamorphism. Mineralization zonesy M i n e r a l i z a t i o n occurs o c c u r s primarily p r i m a r i l y in i n quartz q u a r t z veins v e i n s and and in i n silicified s i l i c i f i e d shear s h e a r zones, and ttends be sspatially with and e n d s tto o be p a t i a l l y associated associated w i t h the t h e rhyolite r h y o l i t e porphyry dikes d i k e s and and banded banded ore minerals iron i r o n formation. f o r m a t i o n . Primary o re m i n e r a l s are a r e dominated by widespread pyrite p y r i t e with with minor occurrences o c c u r r e n c e s of o f chalcopyrite, c h a l c o p y r i t e , galena, g a l e n a y and and sphalerite. s p h a l e r i t e . No vvisible i s i b l e gold g o l d was was found. The main non—metallic n o n - m e t a l l i c alteration a l t e r a t i o n minerals m i n e r a l s include i n c l u d e nearly n e a r l y ubiquitous ubiquitous quartz, q u a r t z y locally l o c a l l y intense i n t e n s e sericite, s e r i c i t e y chlorite c h l o r i t e and biotite. b i o t i t e . Late L a t e stage s t a g e carbonate carbonate and q quartz—carbonate and u a r t z - c a r b o n a t e vveins e i n s cross c r o s s cut c u t all a l l previous p r e v i o u s mineralization. m i n e r a l i z a t i o n . The Fire Fire Center mine consisted of vertical C e n t e r ggold o l d mine consisted o f two v e r t i c a l shafts, s h a f t s y both b o t h located l o c a t e d on o n the t h e same same rhyolite r h y o l i t e porphyry dike. d i k e . The south s o u t h shaft s h a f t was sunk sunk along a l o n g the t h e sheared, s h e a r e d * silicified silicified with while north abbro* w h i l e the the n o r t h shaft s h a f t was apparently a p p a r e n t l y sunk sunk along a l o n g the t h e contact contact ccontact ontact w i t h ggabbro, with w i t h schistose s c h i s t o s e basalt. b a s a l t . The Holyoke silver s i l v e r mine was aa horizontal h o r i z o n t a l tunnel t u n n e l about about 550 feet h o s t rocks r o c k s are a r e silicified, silicified f e e t long l o n g dug in i n aa N19°E ~ 1 9 direction. 'd i~r e c t i o n . The host carbonatized, brecciated carbonatized, b r e c c i a t e d and schistose s c h i s t o s e metavolcanics m e t a v o l c a n i c s and and metasediments, metasediment~~ minor banded iron iincluding n c l u d i n g minor i r o n formation. f o r m a t i o n . Evidence to t o date d a t e suggests s u g g e s t s that that mineralization m i n e r a l i z a t i o n was probably p r o b a b l y epigenetic. epigenetic. 70 �I Geology And Geochemistry of of Lava Lava Flows Flows Within Within the t h e Copper Copper Harbor Harbor nd Geochemistry Conglomerate, Conglomerate Keweenaw Keweenaw Peninsula, P e n i n s u l a Michigan Michigan J. J . B. B. Paces and T. T. J. J . Bornhorst B o r n h o r s t (Department (Department of of Geology Geology and and Geological Geological E n g i n e e r i n g * Michigan Technological T e c h n o l o g i c a l University, U n i v e r s i t y * Houghton, Houghton, Michigan Michigan Engineering, 49931 49931) The Keweenawan Copper Harbor Conglomerate is i s aa rift—related, r i f t - r e l a t e d basin—ward basin-ward thickening t h i c k e n i n g succession s u c c e s s i o n of of terrestrial, t e r r e s t r i a l * coarse— c o a r s e - to t o fine—grained f i n e - g r a i n e d clastic clastic which interfinger with ssediments e d i m e n t s which interfinger w i t h and conformably overlie o v e r l i e the t h e Portage P o r t a g e Lake Lake Volcanics V o l c a n i c s (Daniels, ( D a n i e l s 1982). 1982). Northeast N o r t h e a s t of of Calumet, Calumet Michigan, Michigan* the t h e middle middle , portion p o r t i o n of o f the t h e Copper Harbor Conglomerate includes i n c l u d e s aa succession s u c c e s s i o n of of lava lava flows f l o w s known collectively c o l l e c t i v e l y as a s the t h e Lake Shore Shore Traps T r a p s (Lane, ( L a n e * 1911). 1911). T h i s unit unit This has h a s a strike—length s t r i k e - l e n g t h of o f over o v e r 90 90 km and and was deposited d e p o s i t e d in i n aa basin. b a s i n . The thickest t h i c k e s t section s e c t i o n (approx. ( a p p r o x . 600 m) is i s located l o c a t e d between between Copper Copper Harbor Harbor and and the the eeastern a s t e r n end of o f the t h e Keweenaw Peninsula. P e n i n s u l a . The Lake Shore Shore Traps T r a p s are a r e of of petrologic p e t r o l o g i c importance importance because b e c a u s e they t h e y represent r e p r e s e n t some some of of the t h e youngest youngest volcanic volcanic material m a t e r i a l erupted e r u p t e d throughout t h r o u g h o u t the t h e Lake Superior S u p e r i o r Basin. Basin. A Traps end of of tthe A 594 594 m section s e c t i o n through t h r o u g h the t h e Lake Shore T r a p s aatt tthe h e eeastern a s t e r n end he t o t a l of of 31 3 1 individual i n d i v i d u a l lava lava Keweenaw Peninsula P e n i n s u l a was mapped in i n detail. d e t a i l . A total flows f l o w s were identified i d e n t i f i e d (flow ( f l o w 11 at a t base, b a s e * 31 3 1 at a t top). t o p ) . Flow tthickness h i c k n e s s varies varies 4.4 tto 42.4 m m w with m. A 27 from 4.4 o 42.4 i t h aan n average a v e r a g e of o f 18.3 18.3 m. 27 m thick t h i c k interflow interflow conglomerate bed bed is conglomerate i s ppresent r e s e n t between flows f l o w s 10 1 0 and 11. Individual I n d i v i d u a l flows f l o w s show of o other ffeatures e a t u r e s ttypical y p i c a l of t h e r Keweenawan sub—aerial s u b - a e r i a l flood f l o o d basalts b a s a l t s including: including: amygdaloidal b o t t o m s * massive m a s s i v e flow f l o w interiors, i n t e r i o r s * vesicular, v e s i c u l a r y smooth, smoth* a m y g d a l o i d a l flow f l o w bottoms, pahoehoe pahoehoe flow f l o w tops t o p s and fragmental, f r a g m e n t a l * rubbley r u b b l e y flow f l o w tops. t o p s . Many flows f l o w s also also exhibit lower pportkn e x h i b i t vvertically—oriented e r t i c a l l y - o r i e n t e d vvesicle e s i c l e ccylinders y l i n d e r s iin n t the h e lower o r t i o n of of the the and thin, discontinuous, thin* d i s c o n t i n u o u s y horizontally—oriented, h o r i z o n t a l l y - o r i e n t e d * pegmatoid pegmatoid fflow l o w interior i n t e r i o r and layers upper Zeolite—grade i s common commn in in l a y e r s in i n the the u p p e r portions. portions. Z e o l i t e - g r a d e alteration a l t e r a t i o n is permeable permeable flow f l o w tops t o p s but b u t is i s minimal to t o non—existent n o n - e x i s t e n t in i n most most flow f l o w interiors. interiors. Geochemically, G e o ~ h e m i c a l l ythe t~h e Lake Shore Shore Traps T r a p s exhibit e x h i b i t tholeiitic t h o l e i i t i c evolutionary evolutionary AFM, nnormative, and iimmobile ttrends r e n d s oon n AFM* o r m a t i v e * SSi02, i 0 2 , and m m b i l e ttrace r a c e eelement l e m e n t ddiscrimination iscrimination plots. In plots. I n ggeneral, e n e r a l * lavas l a v a s become more evolved e v o l v e d from from the t h e base b a s e upwards. upwards. The lowest fflows l o w s (1, ( 1 , 2, 2, 3 4 ) are a r e Fe—rich F e - r i c h olivine o l i v i n e tholeiitic t h o l e i i t i c basalts b a s a l t s (47—50 (47-50 lowest 3,* and and 4) wt. w t . % Si02), S i 0 2 ) * followed f o l l o w e d by Fe—rich F e - r i c h olivine—bearing, o l i v i n e - b e a r i n g * tholeiitic tholeiitic b a s a l t i c - a n d e s i t e s with w i t h 50—53 50-53 wt. w t . %% Si02 S i 0 2 (flows ( f l o w s 5—22) 5-22) and tholeiitic tholeiitic basaltic—andesites t . % (flows ( f l o w s 23—31). 23-31). aandesites ndesites w i t h Si02 S i 0 2 oof f 54—58 54-58 w with wt. IIn n tthin h i n section, s e c t i o n * all all with rrocks o c k s aare r e largely l a r g e l y aaphyric phyric w i t h oonly n l y small s m a l l amounts of of plagioclase plagioclase phenocrysts. phenocrysts Groundmass i n e r a l s in i n the t h e basalts b a s a l t s include i n c l u d e 35—40% 35-40% plagioclase plagioclase Groundmass m minerals (An45-65; 15-252 clinopyroxene c l i n o p y r o x e n e (Wo (An4565), 15—25% (Wo3040, Fe/Mg 10—20% FefMg == 40—50), 40-50) 10-20% olivine olivine 3 0-40 * (Fo460), and and5—10% 5-10%Fe—Ti Fe-Ti oxides o x i d e s(mineral ( m m e r a l composition c o m p o s i t i o n determined d e t e r m i n e d by by (Fo4p-60 eelectron l e c ron m i c r o p r o b e ) . Groundmass m i n e r a l s in i n the t h e andesites a n d e s i t e s are a r e 40—50% 40-502 microprobe). minerals plagioclase (An5), 10—20% p l a g i o c l a s e (An 10-202clinopyroxene c l i n o p y r o x e n e (Wo3040, (Wo30-40 Fe/Mg FefMg == 30-40) 30—40), 5-15% 5—15% orthopyroxene, o r t h o p y r o x e n e 5—10% Fe—Ti Fe-Ti oxides o x i d e s and and 5—10% 5-10% late—stage l a t e - s t a g e intergranular intergranu l a r K—feldspar. K-feldspar. D e v i t r i f i e d intersertal intersertal g l a s s is i s ppresent r e s e n t in i n aall l l massive low Devitrified glass massive fflow interiors Diktytaxitic i n t e r i o r s (10—20%). (10-202). D i k t y t a x i t i c cavities c a v i t i e s are a r e common commn in i n most most flows. f l o w s . Flows 1 2 and 1 3 * located l o c a t e d just j u s t above the t h e interflow i n t e r f l o w conglomerate, c o n g l o m e r a t e , contain c o n t a i n distinct distinct 12 and 13, pphenocrysts h e n o c r y s t s oof f hhighly i g h l y rresorbed e s o r b e d plagioclase p l a g i o c l a s e and and quartz. quartz. . !%%! when Most major and and trace t r a c e eelements l e m e n t s show ccoherent o h e r e n t ppatterns a t t e r n s oof f vvariation a r i a t i o n when K20y pplotted l o t t e d versus v e r s u s stratigraphic s t r a t i g r a p h i c height. h e i g h t . Generally, G e n e r a l l y * SiO A1203* Na20, Na O y K20, Si0, A1203, and Rb increase i n c r e a s e from bottom to t o top t o p of o f the t h e sequence, s e q u e n c e * s hereas e r e a s FeO, F ~ oMgO, ~ ~ CaO, CaOy M ~ o , 71 rI1IIu!' I �I Ti02, P205, V, CafAl, Ca/Al, Cr, C r y Ni, N i , and Sr S r decrease. d e c r e a s e . Though these t h e s e trends t r e n d s apply apply to the succession general, i o n in in g e n e r a l y in i n particular, p a r t i c u l a r y numerous inconsistencies i n c o n s i s t e n c i e s rule rule out p a t t e r n s . The flows f l o w s below and and above above the the o u t simple s i m p l e evolutionary e v o l u t i ol~a r y patterns. conglomerate be grouped grouped ttogether : r a t e ccan a n be o g e t h e r oon n the t h e basis b a s i s of of repeating repeating iinterbedded n t e r b e d d e d conglomc Also, orr anomalous trends. A l s o y the t h e two two flows f l o w s (12 ( 1 2 and and o anomalous chemical—stratigraphic chemic: 3 1 - s t r a t i g r a p h i c trends. above tthe conglomerate aare anomalous w with high :he conglomerate r e anomalous i t h particularly particularly h igh 113) 3 ) ddirectly i r e c t l y above Si, K,y Rb and Zr Al, low A l , Fe, F e y Ca, Ca, Ti, T i , V and and P. P. As A s aa whole, whole, the t h e Lake Lake Si, K Z r and an(1 low Shore Traps a ~ sare a r e geochemically Eeoc:hemically more evolved than t h a n the t h e Portage P o r t a g e Lake Lake Volcanics Volcanics ..- - T -r-c which are a r e almost almost exclusively e x c l u s i v e l y hi—Al hi-A1 olivine o l i v i n e and and hypersthene h y p e r s t h e n e tholeiitic tholeiitic b a s a l t s . For similar s i m i l a r Si02 SiO contents, c o n t e n t s , the t h e Lake Shore Shore Traps T r a p s contain contain basalts. 2 substantially Ti, A 1 and and Ni N i (large (large l e s s Al s u b s t a n t i a l l y more T i , V, V , P, P y Zr, Z r y and Y and and less compositional c o m p o s i t i o n a l gaps). g a p s ) . A continuum exists, e x i s t s y however, however, for f o r Fe, F e y Mg, Mg, Ca, Cay Ca/Al, CaIAl, Cr, C r , total t o t a l alkalis, a l k a l i s * and and Rb. Rb. - - Qualitative Q u a l i t a t i v e petrogenetic p e t r o g e n e t i c interpretation i n t e r p r e t a t i o n of of the t h e present p r e s e n t geochemical geochemical data data suggests s u g g e s t s that t h a t crystal c r y s t a l fractionation f r a c t i o n a t i o n exerts e x e r t s at a t least l e a s t aa partial p a r t i a l control c o n t r o l over over magma ccompositions Traps. tthe h e magma o m p o s i t i o n s oof f tthe h e Lake Shore T r a p s . Major and trace t r a c e element element geochemical trends p l a g i o c l a s e and and t r e n d s suggest s u g g e s t that t h a t clinopyroxene, c l i n o p y r o x e n e , Fe—Ti Fe-Ti oxide, o x i d e , plagioclase Zircon eventually also apatite phases. a p a t i t e were significant s i g- n i f i c a n t fractionating fractionating p h a s e s . Z i r c o n e v e n t u a l l y a l s o - However, in reached r e a c h e d the t h e saturation s a t u r a t i o n limit. l i m i t . However, i n addition a d d i t i o n to t o fractionation, f r a c t i o n a t i o n , some some Petrographic and m major ttrace r a c e and a j o r eelements l e m e n t s aalso l s o suggest s u g g e s t open system behavior. behavior. P etrographic and geochemical geochemical eevidence and v i d e n c e ssupports u p p o r t s the t h e occurrence o c c u r r e n c e of o f upper u p p e r crustal crustal 1 2 and and ccontamination o n t a m i n a t i o n oof f several s e v e r a l lava l a v a flows f l o w s of of the t h e Lake Shore S h o r e Traps (flows ( f l o w s 12 t0 1 3 ) . Within the t h e remaining r e m a i n i n g flow f l o w succession, s u c c e s s i o n , magma magma mixing m i x i n g may may be be required r e q u i r e d to 13). , -,--two ---- geocnemxaL .--.,.- : - . * the eexplain x p l a .m adifferences l r r e r e n c e s in I n fractionation r r a~c c-l o- n.-a cLl .o -n - trends c&r e~ n a-s -between DeLween Lne LWO geochemical The petrogenetic groups: g r o u p s : lower lower flows f l o w s (1—9) (1-9) and and upper u p p e r flows f l o w s (16—31). (16-31). petrogenetic relationship r e l a t i o n s h i p between the t h e Lake Shore Traps T r a p s and the t h e Portage P o r t a g e Lake Lake Volcanics V o l c a n i c s is is ccurrently u r r e n t l y under investigation. investigation. . . . P ? - - L - L #- Reference Reference Daniels, 1 9 8 2 y Geol. Geol. Soc. SOC. Amer. Amer. Mem. Mem. 156, 156, p. p. 107—133. 107-133. D a n i e l s , 1982, Lane, Lane, 1911, 1 9 l l y Mich. Mich. Geol. Geol. Surv. Surv. Pub. Pub. 6, 6 , 983 983 p. p. 72 �I: PALEOMAGNETISM OF THE THE POWDER THE PALEOMAGNETISM POWDER MILL GROUP: ITS ITS RELEVANCE RELEVANCE TO TO CORRELATION CORRELATION THE WITh OTHER 'TECTONIC DEVELOPMENT DEVELOPMENT OF THE WITH OTHER KEWEENAWAN KEWEENAWAN SEQUENCES SEQUENCES AND AND TO TO*TECTONIC THE SOUTH SOUTH RANGE MNGE H.C. Palmer1and H.C. Palmer1and H.C. Halls. Halls. 22 p! m The Keweenawan Powder Powder Mill Group crops out as a 150 km—long dominantly The Keweenawan 150 km-long east—west striking belt in Xichigan Michigan and Wisconsin. A east-west A primary primary Keweenawan Keweenawan reverse magnetization has reverse magnetization has been been isolated isolated after after extensive extensive AF AF and and thermal thermal demagnetization demagnetization from 33 sites distributed along a strike length of 100 km W, 39°N, This reverse reverse magnetization magnetization yields yields aa pole pole (142 (142~~4, 39'~~ within the within the belt. belt. This A956.O°) which subset of of these these Ag5=6.00) which plots plots close close to to the the apex apex of of the the Logan Logan Loop. Loop. A subset within the reversely magnetized sites sites from from localties localties within the outcrop outcrop belt belt having having E—W E-W yield a a pole pole (147OW, (147°W, 42'~~ 42°N, Ag5=6.40) A956.4°) which which is is within within the the cluster cluster of strike yield Mellen Complex Complex other other reversely reversely magnetized magnetized Keweenawan Keweenawan paleopoles. paleopoles. Mellen ENE—trending segments within within magnetizations and Powder Mill magnetizations from ENE-trending dominantly E-W E—W trending the dominantly trending outcrop belt suggest suggest that that these these segments segments have have undergone counterclockwise undergone counterclockwise rotations. rotations. Normal magnetizations have been isolated isolated at at four four sites. sites. Poles Poles derived derived from from these these sites sites also also plot plot on on the the western arm western arm of of the the Logan Logan Loop. Loop. The The normal normal magnetizations magnetizations are are in in sites sites near sequence but the distribution of these near the the base of the stratigraphic sequence sites is not stratigraphically stratigraphically continuous. continuous. This This lack lack of of stratigraphic stratigraphic persistence, persistence, together together with aa higher higher metamorphic metamorphic grade grade at at the the normally normally magnetized sites, magnetizations are sites, lead us to believe that the normal magnetizations secondary. The The polar signature signature and the reversal stratigraphy stratigraphy of the Powder secondary. to those those of of other other Keweenawan Keweenawan volcanic volcanic sequences. sequences. Mill Group Group are are similar similar to (1968, 1972) 1972) which which led led to to the the belief belief that that The The paleomagnetic paleomagnetic results results of of Books Books (1968, Traps (Powder the South Range Traps (Powder Mill Group) ~roup)were were older older than than other other Keweenawan Keweenawan volcanic volcanic sequences sequences are are no no longer longer valid. The eastern eastern arm arm of of the the Logan Logan Loop Loop is undefined by Keweenawan Keweenawan data. data. I References: References: I K.G., Magnetization Keweenawan lava flows in the Lake of the lowermost Keweenawan Books, Books, K.G., Superior Superior area, area, U.S. Geological Geological Survey, Survey, Professional Professional Paper Paper 550—D, 550-D, p.D117—D124, p.Dll7-Dl24, 1968. 1968. Books, K.G., K.G., Paleomagnetism Books, Paleomagnetism of of some some Lake Lake Superior Superior Keweenawan Keweenawan rocks, rocks, U.S. U.S. Geological Survey, Geological Survey, Professional Professional Paper, Paper, 760, 760, 42 42 p., p., 1972. 1972. Department 1 1 Department of of Geophysics, Geophysics, University University of of Western Western Ontario, Ontario, London, London, Ont. Ont. F I I 2 Department 2 Department of of Physics, Physics, University University of of Toronto, Toronto, Erindale Erindale Campus, CampuslMississauga, MississaugalOnt. Ont. T I 73 1 I I ! �I THE GEOLOGICAL GEOLOGICAL SETTING SETTING OF OFGOLD GOLO MINERALIZATION MINERALIZATION OBSERVED THE OBSERVED N.W. ONTARIO ONTARIO AT THE THE SCRAMBLE SCRAMBLE MINEy DISTRICTOF OFKENORA, KENORAyN.W. AT MINE, DISTRICT P A R R Y M.G. u a r t z TTower, o w e r y 33451 3 3 4 5 1 Stransky S t r a n s k y Rd., RdeYEvergreen, E v e r g r e e n yCO C O80439 80439 PARR, M.G.( Q(Quartz U.S.A.) U.S.A.) BOBEN, (Dept.o fofGeol. Geol.&&Geol. Geol.EEngrg., BOBENy C. C. (Dept. n g r g e Y MMichigan i c h i g a n TTechnological e c h n o l o g i c a l Univ., UnivaY Houghton, M I 49931) 49931) Houghtony MI The The Scramble S c r a m b l e GGold o l d MMine, i n e y l located o c a t e d tten e n kilometres k i l o m e t r e s east e a s tofo Kenora, f K e n o r a swas was originally bybythe o r i g i n a l l developed y d e v e l o p e dini nthe t h elate l a t1890's e 1890's t h Scramble e S c r a m b l eGold GoldMining Mining Company L Limited i m i t e d and n t e r m i t t a n t lto y t1914 o 1914 y t hCanadian e C a n a d i a nHomestake Homestake Company and i intermittantly bybthe Gold Gold Mining M i n i n g Company Company Limited. L i m i t e d . Although A1 though a shaft s h a f t was was excavated excavated to t oabout about seventy seventy metres metres there t h e r e isi sno norecord r e c o r dofoproduction f p r o d u c t i obeyond n beyondbulk bu1 ksampling samplingand and mill m i l l testing. testing. The The ddeposit e p o s i t is i slocated l o c a t e data the t t h northwest e n o r t h w e send t endofothe f t hWabigoon e Wabi goonVol Vo1caniccani c- Plutonic Pl u t o n i c Belt Be1twithin w i t h imetavolcanics n m e t a v o l c a n i cand s andmetasediments metasediments which w h i c h outcrop o u t c r o p in i n aa northeast n o r t h e a s ttrending t r e n d i n gwedge wedge extending e x t e n d i n gfrom f r o mLake Lakeofofthe t h eWoods. Woods. North N o r t h of of this of the R i v e r Subprovince S u b p r o v i nce wwhilst h i 1s t t h i swedge wedge are a r e the t h e gneisses g n e i sses of t h e English E n g l is h River southeast area iis southeast oof f tthe h e area s the t h e Island I s l a n d Lake Lake ddiorite, i o r i t e y aa unit u n i tofo fthe t h eDryberry Qryberry Batholith Subprovince. Bath01 i t hwhich which ini nturn t u r nis ipart s p aof r t the of tWabigoon h e Wabigoon Subprovi nce. The Scramble Minei sisu underlain The S c r a m b l e Mine n d e r l a i n p predominantly r e d o m i n a n t l y b yby t h tholelitic o l e i i t i c pillowed pillowed flows, and occasional o c c a s i o n a l ffelsic elsic f l o w s yminor m i n o r mafic m a f i c tuffaceous t u f f a c e o u s units, u n i t s , exhalites e x h a l it e s and units u n i t s (see (see diagram diagram of of the t h estratigraphic s t r a t i g r a p h i csuccession). succession). All A11 the t h e volcanics volcanics on on the t h e property p r o p e r t y face f a c e and and dip d i p to t o the t h enorthwest. n o r t h w e s t . Foliation F o l i a t i o n tends t e n d s to to subparallel and aalso dips s u b p a r a l l e l bedding bedding and lso d i p s steeply s t e e p l y to t o the t h enorthwest. northwest. Deformed Deformed pillows, p i 11owsy shearing s h e a r i n g and and shear shear folding f o l d i n g occur occur throughout t h r o u g h o u t the t h eproperty p r o p e r t yand and are a r e well w e l l exposed e x p o s e d at a t the t h e mine m i n e site. site. Q u a r t z - t o u r m a l i n e veins v e i n s both both Quartz—tourmaline concordant andddiscordant concordant and i s c o r d a n t t oto ffoliation o 1 ia t i on are a r eubiquitous. u b i q u i t o u s . Nowhere Nowhere on on the the p r o p e r t y has has there t h e r e been been observed i q n i f i c a n t alteration a l t e r a t i o ndue due property observedany anyareas areaso fofs significant either e i t h e rtot oa primary a p r i m a r volcanogenic y volcanogenichydrothermal hydrothermal system s j s t e m or o r tot oa asecondary secondary shear shear zone zone related r e l a t e dhydrothermal hydrothermalsystem. system. Detailed D e t a i l e d studies s t u d i e s of o f the t h e nature n a t u r e ofofthe t h egold g o l dmineralization m i n e r a l i z a t i oare n a runderway e underway but as yet incomplete. Observations made to date, based on b u t as y e t i n c o m p l e t e . O b s e r v a t i o n s made t o d a t e y based on detailed detailed sampling mappingof oft hthe zonealong alongs tstrike, sampling and and mapping e oore r e zone r i k e , iindicate n d i c a t e that t h a t aa high high percentage p e r c e n t a g e ofof tthe h e ggold o l d i is s within w i t h i n the t h e exhalite e x h a l i t e unit. u n i t . This T h i s could c o u l dbe be either e i t h e r as as very v e r y fine f i n e grained g r a i n e d free f r e e gold g o l d or o r tied t i e dup upwith w i t hsuiphides. sulphides. Visible observed V i s i b l e gold g o l d has has been been observed i n int hthe e s isilicia l i c i a flooded f l o o d e d ffelsic e l s i c unit u n i t just just northeast n o r t h e a s t of of the t h e shaft. s h a f t . Since S i n c e tthe h e ggold o l d ccontent o n t e n t ofoft the h e f felsic e l s i c unit u n i t is is generally g e n e r a l l y less l e s s than than200 200 ppb ppb is i swould would appear appear that t h a t the t h eenriched e n r i c h e d values values in in the t h e felsic f e l s i cunit u n i are t a r edue due to t oremobilization r e m o b i l i z a t i o n of o fsilica s i l i c and a andgold g o l dunder under particular cartoon). p a r t i c u l a structural r s t r u c t u r acontrols l c o n t r o (see l s (see cartoon). Trace Trace chemistry c h e m i s t r y carried carried out on on twelve t w e l v e selected s e l e c t e dmineralized m i n e r a l i z e dsamples samples from from the t h e ore ore zone zone indicate i n d i c a t ea a out typical c go1system. d system. t y p i c a l tholeiitic t h o l e i 1 t igold Genesis ooff the t h e gold g o l d mineralization m i n e r a l i z a t i o nas asinferred i n f e r r e from d from o u t c r o pmapping mapping isi s Genesis outcrop summarized as ffollows. s u m m a r i z e d as o l l o w s . Pillowed P i l l o w e d flows f l o w s followed f o l l o w e d by b y mafic m a f i c tuffs t u f f sand and felsic auriferous f e l s i cvolcanism volcanism with w i t h distal d i s t a tuffs l t u f fand s and a u r i f e r o u schemical chemical precipitates precipitates s i l l yaa I n t r u s i o n of e l s i c sill, Intrusion of aa ffelsic possible p o s s i b l e feeder f e e d e r to to a a stratigraphically s t r a t i g r a p h i c a l l yhigher h i g h e rfelsic f e 1 s icentre, c c e n t r ecauses y causes remobilization r e m o b i l i z a t i o nofo fgold. g o l d . Finally, F i n a l l y ydeformation, d e f o r m a t i o n y regional r e g i o n a l folding f o l d i n gand and s h e a r i n g along a l o n g iinterflow n t e r f l o w boundaries b o u n d a r i e s rresults e s u l t s in i n small s m a l l scale s c a l e folding folding shearing w i t h i n the t h e interflow i n t e r f l o wunit u n iand t andmajor m a j o r remobilization r e m o b i l i z a t i o n of of gold g o l d and and silica silica within are a r epreserved preservedby byrenewed renewed mafic m a f i cvolcanism. volcanism. into i n t odilatent d i l a t e nzones t zones within w i t h i nthe t h ecompetent competent felsic fe1 s i cunits. units. 74 ~ �Stratigraphic column, Scramble Mine, showing gold distribution with respect to rock types. —S -S —.—- 50 E gold) fran — -S SS of charts dsto nmssive silica pzds in diiatanl mxxhng (+ with Iling by silica A cartoon of the structural elements observed at the Scramble Mine site. folds throuejsut thterflcs umeterial. z N — flow . pillowed tuft nmafic barren exhali te felsic unit exhalite tuff mnafic barren flow pillowed — — — — — — — — — — — — — ,— — — I I • Ui felsic mstits lmmlricate stacking of camçetmemt / — — .— — —. — — — — — — — —S - _ �METAMORPHISM AND N.W. ONTARIO METAMORPHISM AND PLUTONISM PLUTONISM IN IN THE THE QUETICO BELT, N.W. :John John A. A. Percival, Percival, Geological Geological Survey Survey of of Canada, Canada, 588 588 Booth Booth Street, Street, Ottawa, KIA0E4 OE4 Ottawa, Ontario OntarioKIA Reconnaissance study of 350 350 km km of strike length length of of the t h e1200-km-long 1200-km-long Quetico Quetico belt belt Reconnaissance of strike reveals reveals regional regional patterns patterns of of metamorphism metamorphism and and plutonism. plutonism. Located Located between between the the Wabigoon and h e Quetico belt consists consists of of aa marginal marginal Wabigoon and Wawa Wawagreenstone-granite greenstone-granite belts, belts, tthe metasedimentary metasedimentary schist schist unit unit and and an an interior interior complex complex of of metasedimentary metasedimentary schist schistand and gneiss rocks. Metamorphic gneiss and plutonic plutonic rocks. Metamorphic grade in marginal pelitic schists varies varies from from aa chlorite-muscovite chlorite-muscovite zone zone at at the t h e outer outer margin margin to t oaagarnet-sillimanite garnet-sillimanite zone zonetoward toward the the interior. Common Commonassemblages assemblages of of garnet-andalusite garnet-andalusite throughout throughout the t h emarginal marginal unit unit and and in in interior. the t h e interior interiorininthe t h eLac LacLa L aCroix Croixarea a r e aindicate indicatelow-pressure low-pressuremetamorphism metamorphism(bathozone (bathozone2). 2). Assemblages of and rare r a r ekyanite kyanitesome some60-150 60-150 km km east e a s tof ofLac L a cLa La Assemblages of staurolite-sillimanite and Croix conditions. Mineral Mineralassemblages assemblagesin in peraluminous peraluminous granitoid granitoid Croix suggest suggest bathozone bathozone 33 conditions. leucosome, and plutons plutons also also vary vary regionally regionally along alongstrike. strike. Sillimanite, leucosome, dykes and Sillimanite, in in association association with with garnet garnet and and muscovite, muscovite, isis common common in the t h e west; west; cordierite cordieriteisispresent presentonly only t o the t h eeast. east.Leucosome Leucosomeininmigmatites migmatitesisismainly mainlyintrusive intrusivein in the t h ewest westand andlocally locally derived derived to in east. These Thesefeatures featurestogether togethersuggest suggesta adeepening deepeninglevel levelof of erosion erosion from from west west to to in the t h e east. east. east. Two large plutonic complexes complexes characterize t h e interior interior of of the t h ewestern westernQuetico Quetico Two characterize the belt: the t h eVermilion Vermilion complex complex of Minnesota Minnesota and h e Quetico Park complex complex of The belt: and tthe of Ontario. Ontario. The Vermilion complex consists consists mainly mainly of of biotite granite Vermilion complex granite and and leucogranite leucogranitewith with metasedimentary schist schist inclusions. inclusions. A A zonation zonation in in plutonic rock types characterizes the metasedimentary characterizes the Quetico width. Peraluminous Quetico park park complex complex across iits t s 20-50 20-50 km km width. Peraluminous white granite of of the the Sturgeon Lake Lake hatholith batholith occurs in in the t h e centre c e n t r eof ofthe t h ecomplex complexand andisisflanked flankedby bysmall small Sturgeon 10-km-wide) plutons plutons of of pink pink biotite biotite ±+ magnetite magnetiteleucogranite, leucogranite,rarely rarely'with withinclusions inclusionsof of (( 10-km-wide) monzonite-diorite-hornblendjte. monzonite-diorite-hornblendite. Small small-(( 55km) km) plugs plugs of diorite-monzonite cut c u tmarginal marginal metasedimentary metasedimentaryschists. schists. composite section sectionthrough throughthe t h ebelt beltshows showssteeply steeplyinward-dipping inward-dipping margins marginsand and AA composite tadpole-shaped plutoris plutons derived source in in the t h e centre c e n t r eand and tadpole-shaped derived from from a metasedimentary source tonalitic rocks rocks of of the t h e greenstone-granite greenstone-granite terranes terranestoward toward the t h emargins. margins. AAback-arc back-arc basin basin tonalitic environment environment is is postulated postulated to t o account account for forearly earlydevelopment developmentof of an a nelongate elongatesedimentary sedimentary trough trough characterized characterizedby by high high heat heat flow flow which which led to t o later l a t e r deep deepcrustal crustalmelting meltingand and magma magma rise to t o high high structural structural level. level. Underplating Underplatingby bymafic maficmagmas magmaspossibly possibly contributed contributed to t o heat h e a t transfer transfer from from the t h e mantl mantlztot othe t h elower lowercrust. crust. 76 �1' The Tectonic Tectonic Significance Significance of of the t h ePorphyritic PorphyriticRed Red Granite, Granite, The Dickinson Dickinson County, County, Michigan Michigan EDWARD PETERSON,Department Department of of Geological EDWARD E.E. PETERSON, Geological Sciences, Michigan Michigan State State University, East EastLansing, Lansing, MI M I 48824-1115 48824-1 115 University, The The Porphyritic Porphyritic Red Red Granite Granite isisexposed exposed near near Feich FelchininDickinson Dickinson County, County, at1970 1970Ma Ma old old Michigan and by the t h e Rb/Sr RbfSr whole whole rock rock method method at Michigan and has has been been dated dated by (Van Schmus, per. Comm.). (Van Schmus, Comm.). Strain Strain studies studies using using the t h e grain grain center c e n t e r method method of of Fry Fry (1979) and h e deformed Talbut (1982) (1982) indicates two episodes episodes of of (1979) and tthe deformed dike dike method method of of Talbut deformation. deformation. The Thefirst firstisisan a nintrusive intrusivedeformation deformationcontrolled controlledby by the t h egeometry geometry of of the pluton appears tto be a regional pluton while while tthe h e second second appears o be regional deformation. deformation. New New major major element analysisindicates indicatest thha/2) granite has element chemical chemical analysis granite ~ has aa low low structural structural water water a 1.3, and and iti t isisnormative normative quartz quartz high K20 K 2 0content, content,Al/(Na+K+ Al/(Na+K+ 12) == 1.3, content, aa high chemical trends trends aare with Ssaturated. These S- or o r A-type A-type granites; granites; These chemical r e consistent consistent with however, major a t a cannot differentiate between them. them. however, major element element ddata differentiate between The The granite granite is composed composed of potassium potassium feldspar feldspar megacrysts megacrysts with with lesser lesser The The feldspar feldspar megacrysts,quartz, megacrysts,quartz, and and biotite are a r e all a l l elongated elongated within within the t h e foliation. foliation. The The biotite biotite defines a well developed LSfabric fabric where where tthe foliation is everywhere developed LS h e foliation everywhere parallel to to amounts of of quartz, quartz, biotite, biotite, and and magnetite magnetite ininthe t h egroundmass. groundmass. amounts I the t h e pluton's pIutonls margin margin and and the t h e lineatiori lineation is is steeply plunging. plunging. These These are a r every very common common features features among among diapiric structures. A Relative strain strain was was determined determined using using the t h e grain grain center c e n t e rtechnique techniqueof ofFry Frywhich which This study shows shows the the records records the t h e shape shape and and orientation orientation of of grain grain distributions. distributions. This The strain pattern pattern long axes of of the long axes the feldspar feldspar megacrysts megacrysts are a r esteeply steeplyplunging. plunging. The indicates plane planestrain strain(X1>A, (A >A == 1 >> XA 3) 3) at the t h e margin margin but but becomes becomes constrictional constrictional indicates diapiric structures 3) just inward. (+>A2 == AA3) inward? Modeled %odeled diapiric structures (Dixon, (Dixon, 1975) 1975) and and many many (A1>A2 natural deformed xenoliths xenoliths (Schwerdtner (Schwerdtner et et al., a!., 1983; 1983; Pitcher and and natural examples examples using using deformed 1 I i9 Berger, 1972) wide zone zone ofofvery verystrong strongmarginward marginward flattening flattening 1972) display display a wide narrow neutral surface, and a weak constrictional strain > weak strain toward toward A > AA ),1, aa (x (A = A, the in inthet hPorphyritic t h e midle. m i d l e . The 3Thedifferent differentpattern p a t t e r of n ofstrain strain e PorphyriticRed RedGranite Granitemay may be due ttoo the methods used in in measuring measuring strain strain in in tthat methods used h a t its i t s geometry geometry isis controlled controlled by the t h e growth patterns of of the t h e feldspars feldspars. fl Both Both the t h e pluton pluton and and its i t s associated associated pegmatites pegmatites show show signs signs of of aa post-intrusive post-intrusive deformation. m wide wideeast-west east-west left lateral deformation. A A large 25 m lateral shear shear zone zone occurs occurs in in the the southern southern part while while smaller smaller shear shear zones zones(3-40 (3-40 cm c m wide) wide) are a r ecommon common in in several several northeastern region region of of the The northeastern t h e pluton pluton displays displays fabric fabric crenulations crenulations and and areas. The highly highly contorted dikes with with steeply steeply plunging plunging fold axis. A strain analysis using deformed metadiabase dikes (Talbot, 1982) 1982) which which have have using deformed dikes (Talbot, intruded intruded the t h e pluton pluton were were used used to t orecord record the t h epost-intrusive post-intrusive deformation. deformation. These These dikes ccut u t across the t h e pluton's plutonls fabric and have foliations oblique oblique tto o their margins. margins. This oblique foliation foliation is produced by layer parallel shearing as the t h e dike dike rotates r o t a t e sin in This oblique produced by pole of of the response tto o tthe h e strain strain within within the t h e country country rock. rock. Connecting Connecting tthe h e pole the response margin stereonetproduces producesan a napproximation approximation of of margin tto o ' the t h e pole pole of of the t h efoliation foliationon onaastereonet t h e structural structural movement movement path. path. The The coherent coherent pattern pattern displayed displayed by by these these paths paths the have found on on tthe dikes to to decribe decribe tthe have been been used used with with lineations lineations found h e dikes h e type of of strain strain plunges to the south while plunges steeply t o t h e south while and the t h e strain strain axes. axes. This Thisanalysis analysisindicates indicatesAA A is gently plunging A plunging tto o the t h e northeast. northeast. AAcompanion companion study study using using Proterozoic-X Proterozoic-X diles a similar similar style of of d i t e s in in the t h e basement basement rocks rocks adjacent adjacent to t o the t h e pluton pluton suggests suggests a deformation. deformation. This This style in in the t h e Felch Felch area a r e a contrasts contrasts with with that that found found to t o the t h e north north I I �in in the theMarquette, Marquette,Michigan Michiganregion regionwhere wherethe t h ebasement basementhas hasbehaved behaved rigidly rigidly A (Myers, 1984). 1984). The The general general trend trend of ofthe t h ecompression compressionaxis axisisisthe thesame, same,however. however. (Myers, and 2 show the results of these strain studies for the granite 1 and 2 show t h e results of these strain studies for the graniteand and Figures Figures 1 basement rock, respectively. respectively. basement , There have have been been several several recent recent studies studies which which suggest suggest the t h e chemistry chemistryand and There mineralogy of granites are a r e functions functions of of their theirtectonic tectonicsetting setting(Chappel (Chappeland and mineralogy of granites al., 1984). 1984). Major Major element e e m e n t chemical chemical White, 1974; 1974; Pitcher, Pitcher, 1984; 1984; Pearce Pearce et a!., White, analysis analysis indicates the t h e granite granite isisstrongly stronglyperaluminous, peraluminous, has has aa high high 1(20 K 2 0 and and low low H 2 0 content, content, and and isis normative normative quartz quartz saturated. saturated. These These are a r e characteristic of of H20 Hercynian S-type (continental.collision~ (continental, collision)and andanorogenic anorogenic!l-type A-type (continental (continental rift rift Hercynian S-type or intraplate) intraplate) granites. granites. Major Major element element data d a t a of of these these two twotypes typesisisequivocal; equivocal; or however, however, they they strongly strongly contrast contrastwith withthe t h e1820-1840 1820-1840 Ma Maold oldgranites granitesofofWisconsin Wisconsin K 2 0content. content. CaO,MgO, MgO, A1203, A1203, and and higher higher K20 by their theirlower lowerCaO, by The Ma aage for tthe The 1970 1970 Ma g e for h e Porphyritic Porphyritic Red Red Granite Granite suggests suggests iitt may may be be related related t o the the formation formation of ofthe t h eFeich Felchtrough. trough. In In this thiscase case the t h epluton plutonmay mayrepresent represent aa to rifttype typegranite granitesubsequently subsequentlyintruded intrudedbybydiabase diabasedikes. dikes. These These dikes dikes intruded intruded rift this Ma (Sims (Sims et et this region region up up until untildeposition depositionofofthe t h eMichigamme MichigammeFormation Formationata t1900 1900Ma collision. al., from rift rift tot o collision. al.,1980). 1980). This Thiswould would suggest suggest a very short time t i m e sequence sequence from Figure 1 X1: ?3= 64/177 Figure F i g u r e 22 X1 11=68/168 681168 15/303 X2, 5/277 i2= 51277 20/39 A3 %= 21/10 21/10 REFERENCES REFERENCES Two contrasting contrasting granite granite types. types. B. W. W. and and White, White, A. A. 3.J. R., R., 1974. 1974. Two Chappell, B. Chappell, Pacific Geology, Geology, 2:173-174. 2:173-174. Pacific Finite strain strainand andprogressive progressive deformation deformation in in models models ot of Dixon, 3.3. M., M., 1975. 1975. Finite Dixon, diapiric 24. diapiricstructures. structures.Tectonophysics, T e c t o n o p h y ~ i 28:89-1 c s28:89~ 124. Random point point distributions distributions and and strain strainmeasurement measurement ininrocks. rocks. N., 1979. 1979. Random Fry, N., Fry, T e c t o n ~ p h y s i c60:89-105. s60:89~ 105. Tectonophysics, Structural analysis analysis of of foliated foliatedProterozoic Proterozoicmetadiabase metadiabase Myers, G. G. A., A., 1984. 1984. Structural Myers, M > 9 Thesis, Thesis, dikes in in the t h e Marquette-Republic Marquette-Republic region region of of northern northern Michigan. Michigan. M>S> dikes Michigan S t a t e University, 78p. Michigan State University, 78p. A,; Harris, Harris, N. N. B.B. W.; W.; and and Tindle, Tindle, A. A. G., G., 1984. 1984. Trace Trace element element Pearce, 3.I. A.; Pearce, discrimination diagramsfor for tthe discrimination diagrams h e tectonic tectonic interpretation interpretation of of granitic granitic rocks. rocks. Jour. Petrology, Petrology,2 25(4):956-983. 3our. 5(4):956 -983. Pitcher, W. W. 5., Set 1984. 1984. Granite Granite type type and and tectonic tectonicenvironment, environment, in Mountain Mountain Pitcher, Building Processes, Processes, Hsu, Hsu, K. K. 3.3. (ed.). (ed.). Acad. cad. Press, Press, London, London, United United Kingdom, Kingdom, Building p. 19-40. 19-4D. p. study of of Pitcher,,'*W.S.S. and and Berger, Berger, A. A. R., R., 1972. 1972. The The geology geology of of Donegal: Donegal: aa study Pitcher,W. granite, emplacing and ing. Wyley 435p. granite.e'mplacing and unroof unroofing. Wyley Interscience, Interscience,London, London,435p. Sims, P. P. K.; K.; Card, Card, K. K. D.; D.; Morey, Morey,G.G.B.B.and andPeterman, Peterman,Z.2.E., E.,1980. 1980. The The Great Great Sims, Lakes Lakes tectonic tectonic zone zone - a a major major crustal crustal structure structure in in central c e n t r a lNorth North America. Arnerica. Geol. kc. Amer. Amer. Bull., 13uIl., part part1,1,91:690-698. 91:690-698. Geol. Soc. Schwerdtner, W, and Sutcliffe, Sutcliffe, R. R.H., H., 1983. 1983. Strain Strain patterns patterns of of Schwerdtner, W. M.; M.; Scott, G. M. and cresentic cresentic granitoid granitoid plutons plutons inin the the Archean Archean greenstone greenstone terane terane of of Ontario. Ontario. Jour. Struct. Struct.Geol., Geol.,5:419—430. 5:419-430. :Jour. Obliquely foliated foliateddikes dikesas a sdeformed deformedincompetent incompetent single single Talbot, C. C. 3., I.,1982. 1982. Obliquely Talbot, layers. Bull., 93:450—460. layers*Geot. G ~ oSoc. LSot*Amer. Amera Bull*, 93:450-460* - 78 �I GEOLOGY OF A LONER PROTEROZOIC VOLCANICLA$TIC 3EQUENCE MARATHON COUNTY, vICON3IT Cohn o± ColinL.L.Reichhoff Reichhoff(Dept. (~ept. ofGeology, Geology,University University of of Minnesota— Ninneso taDuluth, I-QT 55812) 55812) Duluth, Duluth, Duluth,MN Geologic Geologic mapDing map~ingof of approximately auproximately21 21 km^ just just north north of of Wausau, Vausau, Wisconsin Wisconsin has has aided aided in in interpreting interpreting the the depositional depositional environment environment of of aa sequence sequence of of dominantly dominantly felsic—intermediate felsic-intermediate volcanic volcanic rocks rocks and and the the associated associated volcaniclastic volcaniclastic rocks. rocks. This This at—1860 m.y. (Van Schmus, 1980) m . y . (Van Schmus, 19SO) and and sequence has been dated at--1860 sequence has been dated lies lies in in Central Central Wisconsin disconsin near near the the southern southern margin margin of of the the exexnosed Lower Lower ProterozoiC Froterozoic volcanic—plutonic volcanic-plutonic belt. belt. These These rocks rocks posed have have been been metamorphosed metamorphosed to to lower lower greenschist greenschist facies facies and and are are generally generally only only mildly mildly deformed, deformed, dipping dipping to to the the west west at at 1O_300. 10-30". The The volcanic volcanic succession succession consists consists of of rhyodacitic rhyodacitic to to andesitic andesitic flows, flows, pyroclastic pyroclastic flows flows and and intrusives. intrusives. Volcanic Volcanic and and pyropyroclastic clastic textures textures are are locally locally well well preserved preserved and and include include perlitic perlitic cracks, cracks, devitrified devitrified shards shards and and pumice pumice fragments, fragments,and and fiamme fiamme within welded welded tuffs. tuffs. Massive Massive to to amygdaloidal amygdaloidal basalt basalt flows flows are are within minor minor components components of of the the sequence. sequence. Volcaniclastic Volcaniclastic sedimentary sedimentary rocks rocks represent represent aa major major portion gortion of of the the exposed exposed section section and and exhibit exhibit aa wide wide variety variety of of textures. textures. These These sedimentary sedimentary rocks rocks include include massive massive to to laminated laminated argillites argillites and and siltstones, siltstones, possibly possibly of of lacustrine lacustrine origin, origin, which which exhibit exhibit graded graded bedding bedding and and soft soft sediment sediment (including (includingdewatering) dewatering)deformdeform"Red beds" bedsv consisting consisting of of interbedded interbedded volcanic volcanic sandstones sandstones ation. "Red ation. and The and conglomerates conglomerates are are •present "present but are are poorly poorly exposed. exposed. The dominant crossdominant epiclastic epiclastic rock rock is is aa dark, dark, greenish—black, greenish-black,crossbedded bedded volcanic volcanic sandstone sandstone with with discontinuous discontinuous interbeds interbeds of of conglomerate, conglomerate, composed composed mainly mainly of of locally locally derived derived volcanic volcanic pebbles clasts of of quartzite quartzite and and tonalite. tonalite. pebbles but but also also including including clasts These These cross—bedded cross-bedded sandstones sandstones and and interbedded interbedded conglomerates conglomeratesare are interpreted interpreted as as fluvial fluvial deposits. deposits. This intermediateThis succession succession is is interpreted interpreted to to represent represent an an intermediate— source facies facies (Fisher (Fisher and and Schmincke, Schmincke, 1984) 1984) characterized characterized by by source rocks rocks formed formed by by pyroclastic yy-roclastic flow, flow, lava lava flow, flow, airfall, airfall, and and their their reworked products. products. The The tectonic tectonic interpretation interpretation is is based based on on reworked Dickinson's Dickinsonls(1974) (1974) model model of of magmatic magmatic arcs. arcs. This This model model places places volcanic intermediate-felsic composition compositionin inan anarc arc volcanic rocks rocks of of intermediate—felsic having having continental continental affinities affinities (crustal (crustalthickness thickness>15—20 >I 5-20 km). km). Using Using this this model, model, the the described described sequence sequence would would represent represent rocks rocks deposited deposited in in an an intra—arc intra-arc basin basin (graben) (graben) and and characterized characterized by by volcaniclastic volcaniclastic red red beds, beds, subaerial subaerial tuffs, tuffs, lacustrine lacustrine deposits deposits and conglomerates. conglomerates. and i I I P1 �U RJFiRN CS 3 i c k i n s o n , .R., ;/.R., 1974, 1 9 7 4 , Sedimentation S e d i m e n t a t i o n within w i t h i n and and beside b e s i d e ancient ancient Dickinson, modem, magmatic n a g m a t i c arcs. a r c s . In: In: JJott, Uot-b, JJr., r . , 3.5. Shaver, and modern P.H. and Shaver, 2.E. , eds., e d s . , Iiodern ?,iodern and n c i e n t ggeosynclinal e o s y n c l i n a l ssedimentation, edimentation, R.H., and aancient soc. 'ubl. p. P u b l . 19, 1 9 , p. p. 230—239. 230-239. i5oc. Econ. Econ. Paleont. P a l e o n t . Liineral. i - i i n e r a l . SSp. Fisher, Schmincke, H.-U., H.—U., 1984, F i s h e r , R.V. R.V. azid and Schmincke, 1 9 8 4 , Pyroclastic P y r o c l a s t i c Rocks. Rocks. Springer—Verlag, S p r i n g e r - V e r l a g , Berlin, B e r l i n , Heidelberg, H e i d e l b e r g , New York, York, Tokyo, Tokyo, 472p. Van Schmus, W.R., W.R., 1980, 1 9 8 0 , Chronology Chronology of of igneous i g n e o u s rocks r o c k s associated associated with w i t h the t h e Penokean Orogeny in i n Wisconsin. ',!/isconsin. Geological G e o l o g i c a l 3ociety Society of of America Special S p e c i a l Paper P a p e r 182, 1 8 2 , p. p. 159—168. 159-168. 80 �PETROGENESIS PETROGENESIS OF OF THE THE BARDON BARDON PEAK PEAK PERIDOTITE, PERIDOTITE,DULUTH DULUTHCOMPLEX COMPLEX BRIAN A.A. ROSS, f Geology n i v e r s i t y of o f Minnesota, Minnesota, MinMinBRIAN ROSS,Dept. Dept.oof Geologyand andGeophysics, Geophysics,UUniversity  neapolis, MN An An area area of of 55455 - 2.5 2.5 sq. sq. km mappedalong alongthe thebasal basal contact contact of Complex km was was mapped o fthe theDuluth Duluth Complex Three bands bands of unlayered unlayered around Peak, southwest off Duluth, Bardon Peak, southwest o Duluth, Minnesota. Minnesota. Three around Bardon gabbro paralleling gabbro p a r a l l e l i n gthe thecontact contactwere were located l o c a t e dini nananextensive extensivesequence sequence of o f rhythrhythnearest the the basal The band band ooff gabbro gabbro nearest basal contact is is m i c a l l y layered layered ttroctolites. r o c t o l i t e s . The mically interpreted ononthe wall magma i n t e r p r e t e dtot obebea amarginal marginalphase, phase, which which crystallized crystallized the w aof l l the o f the magma chamber. chamber. The The other two two bands bands of' o f gabbro gabbro possess possess ggradational r a d a t i o n a l lower lower contacts contactsand and sharp contacts wwith the host sharp upper upper contacts i t h the host troctolites, t r o c t o l i t e s and , andare arehypothesized hypothesized to t obe be The layers l a y e r s of o fgabbro gabbro and and underlying underlying layers l a y e r s dipping dipping east east ata tapproximately approximately 28°. 280. The troctolite macro—rhythmic t r o c t o l i trepresent e represent macro-rhythmic layers l a y e r sformed formedby byreplenishment replenishmentofomagma f magma in i naa sill—shaped chamber,wwith higher crystal sill-shaped chamber, i t h f rfractionation a c t i o n a t i o n and and higher c r y s t a lgrowth growth rates r a t e sresponrespons i b l e for f o rformation formationof' o fthe thegabbro. gabbro. sible The increasei in The increase n ccrystal r y s t a l growth growth rates r a t e s is is hypothesized be the the rresult hypothesized t to o be e s u l t of o f an an increase increase in i n the the amount amount oof f vvolatiles, o l a t i l e s , through through diffusion magma from dewatering dewateringoof country rock basalts. d i f f u s i o ninto i n tthe o the magma chamber chamber from f country basalts. Also the Bardon BardonPeak Peak areawere werei r irregular bodies ooff peridotite Also mapped mapped i ninthe f i efield l d area r e g u l a r bodies peridotite are circular Most ooff the bodies bodies are circular found iinn both both the the troctolite t r o c t o l i t eand andgabbro gabbro units. u n i t s . Most found in andare areooften contact wwith i ngeometry, geometry, and f t e n i in n gradational g r a d a t i o n a l contact i t h their t h e i r host host rock. rock. Dike— Dike- like not disrupt l i k eperidotite p e r i d o t i t ebodies bodieswere were found found which which ccut u t but b u t do do not d i s r u p t layering l a y e r i n g in i nhost host petrographic ttextures The petrographic e x t u r e s and and ccrystallization r y s t a l l i z a t i o nsequence sequence of o fthe thepen— perit r o c t o l i t e . The troctolite. primary ddifThe primary ifdotite and d o t i t e were were markedly markedly ddifferent i f f e r e n t from from the the troctolite troctolite andgabbro. gabbro. The ferences are the the mafic mafic minerals minerals eexhibit ferences are x h i b i t an an interlocking i n t e r l o c k i n gtexture, t e x t u r e ,and andplagioclase plagioclase i s always always anhedral anhedral and t e r s t i t i a l to t othe theother otherminerals. minerals. is andi ninterstitial 81 ItI twas wasdetermined determined I �the oolivine the pperidotite tthat h a t the the compositions compositions oof f the l i v i n e and and clinopyroxene clinopyroxene i in n the eridotite ccrystallized r y s t a l l i z e dfrom fromaamagma magma t hthat a t was l i g h t l y more more ffractionated r a c t i o n a t e d than than the melt melt wass slightly Compositionsofofthe the pplagioclase Compositions l a g i o c l a s e iin n the the which formed formedthe thet troctolite which r o c t o l i t eand andgabbro. gabbro. peridotite MnAncontents p e r i d o t i t ewere were found found to t o contain contain significantly s i g n i f i c a n t l higher y higher contentsthan thanplagio— plagio- clase clase iin n the the troctolite t r o c t o l i t eand andgabbro. gabbro. It I twas was concluded concluded tthat h a t the peridotite p e r i d o t i t ewas was formedby byaavvolatile—rich metasomatizingmelt meltt hthat replaced pplagioclase formed o l a t i l e - r i c h metasomatizing a t replaced l a g i o c l a s e iin n the the host rock with host w i t h olivine o l i v i n eand andclinopyroxene. clinopyroxene. Additionally, A d d i t i o n a l l y , iti tisi hypothesized s hypothesized that that the source source of o f the t h emetasomatizing metasomatizing melt melt was was intercumulus intercumulus melt, melt, which whichhad hadbeen been fluxed by volatiles v o l a t i l e sfrom fromdewatering dewatering of' o f the t h e country country rock. rock. fluxed by The metasomatizing metasomatizing The andand moved ffluid l u i d isi senvisioned envisionedtot ohave havebeen beenlocalized l o c a l i z e dini a n dilation a d i l a t i zone, o n zone, movedupward upward forming pipe—shaped peridotite iinn channeiways channelways forming pipe-shaped p e r i d o t i t e bodies. bodies. As from two drill d r i cores l l cores fromthe theWater Water Hen Hen intrusion, i n t r u s i o n , aalayered layered As aa ppart a r t of o f this t h i sstudy, study, two mafic mafic intrusion i n t r u s i o nalong along the thebasal basalcontact contactofofthe theDuluth DuluthComplex Complex south south of of Hoyt Hoyt Lakes, Lakes, Minnesota, Minnesota, were were examined. examined. Themany manys isimilarities the pperidotite The m i l a r i t i e s between between the eridotite coresand andaat BardonPeak Peak suggest thep eperidotite iinn the the Water Water Hen Hen cores t Bardon suggest t h athat t the r i d o t i t e i in n the Water Hen Heni nintrusion by a replacement Water t r u s i o n may may have have aalso l s o been been produced produced by replacement process. process. 82 ! 1 I �U Platinum Group Group Element Element Minerals Minerals in Platinum in the the Duluth Duluth Complex Complex TATIANA SABELIN SABELIN (Mineral (MineralResources ResourcesResearch Research Center, Center,University Universityof of TATIANA Minnesota,Minneapolis, Minneapolis,MNMN55455) 55455) Minnesota, Platinum Platinum group group element element (PGE) (PGE) minerals minerals with with trace traceamounts amountsof ofAu Auand andAg Ag from the the Duluth DuluthComplex Complexare aredescribed. described. The The minerals minerals were were found foundat at two two from different locations locations within within oxide-rich oxide-richportions portions of ofaadrill drillcore. core. The The different PGE minerals occur in an oxide( 65%)-plagioclase( 25-30%)-olivine( 5%) PGE minerals occur in an oxide( 65%)-plagioclase( 25-30%)-olivine( 5%) host and and an an olivine( olivine( 40%)-oxide( 40%)-oxide( 30%)-plagioclase( 30%)-plagioclase( 25%) 25%) host. host. TitanifTitanifhost erous magnetite magnetite is is the the dominant dominant oxide oxideand and is isassociated associatedwith withminor minorherhererous cynite and and ilmenite. ilmenite. Sulfide Sulfide mineralization mineralization in in these these rocks rocks is is minor minor cynite and is is primarily primarily of of the the finely finelydisseminated disseminatedtype. type. Chalcopyrite, Chalcopyrite, bornite bornite and and pentlandite pentlandite are are the the main main sulfide sulfidephases. phases. and The PGE PGE minerals minerals were were identified identifiedby by energy energy dispersive dispersivex-ray x-rayanalysis analysis The (EDS) (EDS) using using both both an an electron electron microprobe microprobe and and aa scanning scanning electron electron micromicroscope. They and two twolocked lockedcomcomThey consist consist of of five five monomineralic monomineralic grains grains and scope. posite grains. grains. EDS EDS spectra spectra were were collected collected from from each each of ofthe theindividual individual posite mineral grains grains and and from fromnumerous numerous points pointswithin withinthe thecomposite compositegrains. grains. mineral Approximate compuApproximate chemical chemical compositions compositions of of the the phases phases were were obtained obtainedby by computor-processing tor-processing the the net net peak peak counts counts of of the the elements elementspresent present in ineach each spectrum. The The analyses analyses were were then then correlated correlated with with published published microprobe microprobe spectrum. data on on PGE PGE minerals minerals in in order order to to identify identify the the phases. phases. The The mineral mineral names names data proposed proposed in in this this paper paper are are pending pending positive positive identification identificationby by quantitaquantitative analysis. analysis. tive The olivine-oxide-plagioclase The five five monomineralic monomineralic grains grains occur occur in in the the olivine-oxide-plagioclase They They are are subsubTwo hedral hedral to to euhedral euhedral and and range range in in size sizefrom from2x5 2x5to to 34x36 34x36micrometer. micrometer. Two grains grains are are associated associated with with magnetite, magnetite, chalcopyrite, chalcopyrite,bornite bornite and and silicate silicate The alteration products. products. One One grain grain occurs occurs as as an an inclusion inclusionin inilmenite. ilmenite. The alteration fourth fourth grain grain forms forms aa composite composite sulfide sulfide grain grain (70xl6 (70x16 micrometer) micrometer) with with The pentlandite, bornite and and chalcopyrite chalcopyrite and and occurs occurs in in plagioclase. plagioclase. The pentlandite, bornite Pt-Fe Pt-Fe alloy alloy is is distinguishable distinguishable from from the the sulfides sulfides in in reflected reflectedlight light The four four grains grains microscopy by by its its high high reflectivity reflectivity and and white white color. color. The microscopy have similar compositions and consist mostly of Pt with minor Fe have similar compositions and consist mostly of Pt with minor Fe and and The fifth fifth grain grain is is aa Ru Ru sulfide sulfide with with lesser amounts amounts of of Pd, Pd, Cu Cu and and Ni. Ni. The lesser It has has aa high high reflectivity reflectivity and and is is 0s and and traces traces of of Ir Irand andFe. Fe. It minor Os minor The mineral mineral resembles resembles laurite laurite in in both both its its comcomwhite with with aa grey grey tint. tint. The white The 10x20 10x20 micrometer micrometer grain grain is is euhedral euhedral position and and optical opticalproperties. properties. The position and occurs occurs as as an an inclusion inclusionin in plagioclase. plagioclase. and rock. Four Four of of the the five five grains grains consist consist of of aa Pt-Fe Pt-Fealloy. alloy. rock. The The composite composite grains grains were were found found in in the the oxide-plagioclase-olivine o x i d e - p l a g i o c l a s e - o l i v i n e host. host. measure l3x5 and and occur inand a Fe-Mg-Al-Si The grains grains measure 13x512x8 andmicrometer 12x8 micrometer occur in a Fe-Mg-Al-Si The alteration product associated with biotite and plagioclase. alteration product associated with biotite and plagioclase. One One grain grain consists of Pt-Fe alloy and three compositionally distinct Pd phases. distinct Pd phases. consists of Pt-Fe alloy and three compositionally EDS of the minerals indicate the presence of the presence following of the following EDS spectra spectra ofPd the Pd minerals indicate the elements elements (not (not listed listed in in order order of of abundance): abundance): Pd-Pt-Fe-Cu-Ni-Sn-Bi-As, Pd-Pt-Fe-Cu-Ni-Sn-Bi-As, Pd-Pt-Cu-Sn-Bi Pd-Pt-Cu-Sn-Biand and Pd-Fe-Sn-Bi-As. Pd-Fe-Sn-Bi-As. The The Pt-Fe Pt-Fe alloy alloy is is compositionally compositionally similar similar to to the the other other Pt-Fe Pt-Fe alloy alloy grains grains found found and and constitutes constitutes 85% 85% of of interthe grain. grain. The The second second grain grain contains contains very very fine-sized fine-sizedcomplex complex interthe Six phases phases were were identified identified by by EDS EDS growth of of numerous numerous PGE PGE minerals. minerals. Six growth 83 I 1 I �! analysis. analysis. The The texture t e x t u r e of o f the t h e grain g r a i n indicates i n d i c a t e s the t h e presence presence of o f additional additional phases phases but b u t they they were were too t o o fine-grained f i n e - g r a i n e d to t o be be resolved r e s o l v e d by by the t h e scanning scanning The phases phases identified e l e c t r o n microscope. microscope. The i d e n t i f i e d in i n this t h i s grain g r a i n are a r e an an Ir-Rh Ir-Rh electron sulfarsenide or irarsite, two Pt sulfarsenides with significant s u l f a r s e n i d e o r i r a r s i t e , two Pt s u l f a r s e n i d e s w i t h s i g n i f i c a n t Fe Fe and and Os 0 s and and traces t r a c e s of of Ag Ag (one (one of of which which also a l s o contained contained Pd Pd and and trace t r a c e amounts amounts of of Au), and traces t r a c e s of of Pd, Pd, Rh Rh and and Ag, Ag, A s and Au), aa Pt-Fe-Os Pt-Fe-0s phase phase with with minor minor Cu Cu and and As Pd arsenide a r s e n i d e with with Fe, Fe, Cu, Cu, Sn Sn and and Sb, Sb, and and aa Pd-Pt-Pb Pd-Pt-Pb arsenide. a r s e n i d e . Ag Ag may may aa Pd be be present p r e s e n t in i n the t h e Pd Pd minerals minerals as a s well w e l l but b u t was was difficult d i f f i c u l t to t o detect d e t e c t due due to to peak overlap o v e r l a p in i n the t h e EDS EDS spectra s p e c t r a for f o r Pd Pd and and Ag. Ag. Similarly, S i m i l a r l y , Au Au in i n other other peak Pt P t minerals minerals may may not n o t have have been been detected d e t e c t e d because because of o f peak peak overlap o v e r l a p for f o r Pt Pt and Au. Au. and This i s the t h e second second reported r e p o r t e d occurrence occurrence of of PGE PGE minerals minerals in i n the t h e Duluth Duluth This is Complex Complex and and the t h e first f i r s t identification i d e n t i f i c a t i o n of of Pd, Pd, Ir, I r , Ru, Ru, and and Os0 s - and and RhRhb e a r i n g phases. phases. This This find f i n d is i s also a l s o significant s i g n i f i c a n t because because the t h e minerals minerals bearing d e s c r i b e d here h e r e occur occur in i n rock rock containing c o n t a i n i n g disseminated disseminatedsulfides. s u l f i d e s . The The described sperrylite s p e r r y l i t e reported r e p o r t e d previously p r e v i o u s l y (1) (1) was was found found in i n massive massive sulfide s u l f i d e ore. ore. Considerably Considerably more more mineralogical m i n e r a l o g i c a l work work is i s required r e q u i r e d to t o evaluate e v a l u a t e the the potential p o t e n t i a l of of the t h e Duluth Duluth Complex Complex as a s aa producer producer of of platinum platinum group group metals. metals. The flotation flotation is also a l s o needed. needed. The The evaluation e v a l u a t i o n of o f ore o r e recovery recovery procedures procedures is The Of particular p a r t i c u l a r conconresponses responses of o f PGE PGE minerals minerals have have not n o t been been documented. documented. Of cern of alloys, a l l o y s , expecially e x p e c i a l l y of o f iron-platinum, iron-platinum, c e r n are a r e the t h e floatabilities f l o a t a b i l i t i e s of which may may not n o t be b e as a s floatable f l o a t a b l e as a s sulfides, s u l f i d e s , arsenides a r s e n i d e s and and sulfarsenides. sulfarsenides. which References : References: 1) 1) Ryan, P.J. P . J . and and Weiblen, Weiblen, P.W., P.W., 1984, 1984, Pt Pt and and Ni N i Arsenide Arsenide Minerals Minerals in in Ryan, •Duluth Duluth Complex Cabs), ( a b s ) , Ann. Ann. Inst. I n s t . Lake Lake Superior S u p e r i o r Geol., Geol., 30th, 30th, Wausau, Wisconsin, Wisconsin, 58-60. 58-60. Wausau, 84 I l �U AA Study Study Of Vein Mineralization and and Wall Rock Rock Alteration Alteration at at the the Delaware Delaware Mine, Mine, Keweenaw Keweenaw County, County, Michigan Michigan W.A. W.A. Schleiss, Scnleiss, T.J. T.J. Bornhorst, Bornhorst, and and A.P. A.P. Ruotsala Ruotsala (Dept. (Dept. of of Geol. Geol. and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological Technological University, University, Houghton, MI 49931) 49931) Houghton, MI 1 The Delaware Delaware Mine is is located located in in the the northern northern half half of of the the Keweenaw Keweenaw The Peninsula of of Upper Upper Michigan. Michigan. It opened in in 1848 1848 and and is is one one of of the tne Peninsula oldest oldest copper copper mines mines in in the the Michigan Michigan Native Native Copper Copper District. District. Mining Mining originally orii-jinally centered on a mass copper—oearing copper-ocarina fissure fissure known known as as the the Stoughtenourgh Stoujhtenourgh vein vein and and later later production production was was from from the the Allouez Allouez Conglomerate, Conglomerate, a copper—bearing copper-oearing conglomerate conglomerate which is is cut cut oy oy the the Stoujhtenourgh. The The mine closed closed in in 1887 1887 and and remained remained so so until until 1977 1977 Stoughtenurgh. when Tom Poynter Poynter purchased purcnased the the mine and reopened reopened the the first first level level for for public tours. tours. public The The mine was geologically mapped at at aa scale scale of of 1:1080. 1:1080. The The Allouez Allouez Conglomerate Conglomerate is is an an 88 meter thick stratified stratified conglomerate conglomerate consisting consisting of of rounded to suoangular suangular peübles peooles and and coooles coooles of of mostly mostly rhyolite rhyolite and and rarely rarely amygdaloidal amygdaloidal oasalt. oasalt. Exposed in in two two crosscuts crosscuts oelow oelow the the Allouez Allouez are are two two thin thin oasalt basalt flows. flows. The The Greenstone Greenstone Flow Flow is is stratigraphically stratigraphically above aoove the the conglomerate conglomerate but but not not exposed exposed in in the tne mine. ,nine. These These rocks rOCKs generally generally strike strike E—W E-W and and dip dip 25 25 degrees degrees north. north. Numerous Numerous mineralized tension tension fractures fractures with with generally generally northerly northerly strikes strikes and and near near vertical vertical dips dips transversely transversely cut cut the the oeds. oeds. Stereographic Stereographic projection of poles to planes for for the tne fractures fractures indicate indicate that tnat the the major stress stress field, field, sigma sigma one, one, was was approximately approximately N—S, N-S, parallel paragenetic sequence sequence parallel to to the the tension tension fractures. fractures. The general paragenetic for mineralization in the fractures fractures is, oldest oldest to to youngest: 1) 1) drusy drusy suohedral suonedral to anhedral anhedral grains grains of quartz; 2) euhedral eunedral to to anhedral anhedral microcline; muscovite, in part replacing microcline; 3) 3) fine fine •;rained grained muscovite, re,~lacing microcline; microcline; 4) native native copper; copper; 5) 5) coarse coarse grained grained anhedral anhedral calcite; calcite; and and 6) 6) rare rare copper sulfide. sulfide. copper Fluid inclusion inclusion studies studies of calcite calcite from from eleven eleven veins were were conducted conducted to constrain constrain the the temperature temperature of of the the mineralizing mineralizing fluids. fluids. Homogenization temperatures temperatures of 136 inclusions inclusions ranged ranged from from 80 80°C —Analyzed inclusions were 280°c uncorrected uncorrected for for pressure. pressure. inclusions were isolated, isolated, 280°C, did not follow oovious fractures, and showed follow oovious fractures, showed no evidence evidence of of necking necxing peas: down. A histogram suggests two and possioly three temperature peai<s: down. (A) (B)160—200 160-200C C(?) ( ? ),, and and (C) (C) 230—260°C. 230-260 C. Fluid inclusion inclusion (A) 110—130°C, 110-130 C, (B) homogenization homogenization temperatures temperatures must must oe oe corrected corrected for for pressure. pressure. Livnat's Livnat's (1983) inferred inferred pressure pressure of of 1.5 1.5 ko k for thispart this0part of of the the strafigraphic straigraphic column column yields yields aa pressure pressure correction correction of of +125 +I25 (peak C 325—385 325-385 C). C). The The pressure of pressure corrected corrected temperature temperature for for peak C seems seems too too high high in in light light of wall rock rock alteration alteration mineralogy, mineralogy, Livnat's (1983) (1983) prooaole prooaole temperature temperature of of lode lode copper copper mineralization, mineralization, and and comparison0to comparison to calcites calcites in in Tertiary Tertiary veins C are This veins where where temperatures temperatures ranging ranging from from 230—260 230-260'~ are common. common. This suggests perhaps little suggests that that the the pressure pressure was was less less than than 1.5 1.5 ico ko and perhaps little if if any pressure oressure correction correction is is needed. needed. At the present time time no no firm firxi conclusions conclusions can can oe oe drawn drawn from from the the fluid fluid inclusion inclusion data. data. Wall rock rocK adjacent adjacent to to veins veins is is mildly mildly to to intensely intensely chloritized, chloritized, sericibized, Plagioclase in in oasalt oasait is is sericitized, carbonatized, carbonatized, and and silicified. silicified. Plagioclase generally aloitized out where the oy veins veins plagioclase plagioclase the basalt oasalt is is cut cut by 85 I �iis s aaltered l t e r e d to t o sericite s e r i c i t e and and chlorite. chlorite. O l i v i n e is i s wholly w n o l l y or o r partly partly Olivine altered Interstitial a l t e r e d to t o serpentine. serpentine. I n t e r s t i t i a l material m a t e r i a l in i n the t h e oasalt o a s a l t (glass?) (glass?) has h a s oeen e e n predominantly p r e d o m i n a n t l y altered a l t e r e d to t o chlorite, c h l o r i t e , or o r replaced r e p l a c e d oy oy minor minor amounts of Rhyolite veins o f calcite. calcite. R h y o l i t e cclasts l a s t s in i n cconglomerate o n g l o m e r a t e adjacent a d j a c e n t to to v eins and ssilicified, with ttend e n d tto o ooe e lless e s s aaltered, l t e r e d , ddominantly o m i n a n t l y ccaroonatized a r o o n a t i z e d and ilicified, w ith calcite c a l c i t e and quartz q u a r t z filling f i l l i n g minute m i n u t e voids v o i d s and and fractures f r a c t u r e s in i n the t h e clasts. clasts. The rhyolite moderately r h y o l i t e cclasts l a s t s aare r e aalso lso m o d e r a t e l y tto o intensely i n t e n s e l y sstained t a i n e d with with a coating Samples o of wall c o a t i n g of o f iron i r o n oxide. oxide. Samples f w a l l rock r o c k taken t a k e n pperpendicular e r p e n d i c u l a r to to t h e vveins e i n s from f r o m ddirectly i r e c t l y aadjacent d j a c e n t tto o and p to t o aa maximum of o f one o n e meter meter the and uup away were cchemically of h e m i c a l l y aanalyzed n a l y z e d ffor o r aa ssuite uite o f 23 2 3 elements e l e m e n t s in i n order o r d e r to to determine All l l analyses a n a l y s e s were were d e t e r m i n e element e l e m e n t mooility m o o i l i t y during d u r i n g alteration. alteration. A Element m moollity ccorrected o r r e c t e d for f o r volume changes. changes. Element o o i l i t y calculations c a l c u l a t i o n s indicate indicate that were m massively a s s i v e l y aadded d d e d tto o 0ooth 0 t h rhyolite r h y o l i t e and oasalt oasalt t h a t Cu and and Ca were adjacent mineralizing a d j a c e n t to t o the t h e vveins e i n s ooy y the the m i n e r a l i z i n g fluids. f l u i d s . This T h i s is i s consistent consistent with w i t h the t h e formation f o r m a t i o n of o f calcite c a l c i t e and and native n a t i v e copper c o p p e r or o r copper c o p p e r sulfide. sulfide. K and Mg Mg w were generally most altered ere g e n e r a l l y aadded d d e d ooy y the t h e fluid f l u i d to t o tthe h e most a l t e r e d rock r o c k and were incorporated i n c o r p o r a t e d into i n t o sericite s e r i c i t e and and chlorite, c h l o r i t e , respectively. respectively. Na was was massively depleted m assively d e p l e t e d from f r o m the t h e rhyolite r h y o l i t e and and ddepleted e p l e t e d only o n l y in i n tne t n e most a l t e r e d obasalt a s a l t ddirectly i r e c t l y aadjacent d j a c e n t tto o tthe h e vvein; e i n ; Na removed oy the the altered Na was was removed Na depletion solution. s o l u t i o n . Na d e p l e t i o n prooably p r o o a o l y reflects r e f l e c t s the t h e breakdown breakdown of of Ni was m mobile was oonly pplagioclase. lagioclase. N i was o o i l e oout u t was n l y rredistriuted e d i s t r i o u t e d within w i t h i n the the Ba, Y Y, V, and Ti conglomerate. , Zr, Zr, V, T i were w e r e relatively relatively c o n g l o m e r a t e . The elements e l e m e n t s Ba, immocile during Att the immooile d u r i n g alteration. alteration. A t h e ppresent r e s e n t time t i m e a model is i s oeing minj developed of d e v e l o p e d to t o ddetermine e t e r m i n e the t h e nnature ature o f the t h e hydrothermal h y d r o t h e r m a l system s y s t e m for f o r vein vain mineralization i l l allow a l l o w for f o r a comparison comparison m i n e r a l i z a t i o n at a t the t n e Delaware D e l a w a r e Mine. Mine. T his w This will with w i t h the t h e more economically e c o n o m i c a l l y significant s i g n i f i c a n t lode l o d e deposits. deposits. Reference R eference . . Livnat, (Ph. D. D. D Dissertation), L i v n a t , A., A., 1983, 1 9 8 3 , (Ph. i s s e r t a t i o n ) , University U n i v e r s i t y of of Michigan, Michigan, Ann Arbor, 2 2 5 p. p. A r o o r , 225 86 1 �I I THE GEOLOGICAL GEOLOGICAL SETTING SETTINGATATTHE THEDLTPORT DUPORT MINE, MINE, CAMERON CAMERON ISLAND, ISLAND, THE SHOAL LAKE LAKE SHOAL Smith, P.M., P.M., Mineral Mineral Deposits DepositsSection,. Section,.Ontario Geological Smith, Ontario Geological Survey, Toronto Toronto Survey, The Ouport Mine Mine has has been been explored explored and and developed developed several several The Duport times since since its its discovery discovery in in 1896. 1896. Recent Recent drilling drilling has has times increased increased the the reserves, reserves, now now estimated estimated 1,927,000 1,927,000 tons tons grading grading 0.30 ounce ounce Au Au per per ton ton over over 9.75 9.75 feet feet (Northern (NorthernMiner, Miner , 0.30 October October 13, 13, 1983). 1983). Recently Recently an an 1l85m 1185m decline declinehas has been been driven driven to intersect intersect the the two two main main mineralized mineralized zones zones at at three three to levels. levels. limb of of aa northwest-trending northwest-trending Located on on the the western western limb rocated anticline, anticline, the the deposit deposit is is hosted hosted by by tholeiitic tholeiitic and and komatiitic komatiitic basalts basalts and and by by ultramafic ultramafic flows/sills. flows/sills. The Themafic mafic volcanics volcanics are are overlain overlain to to the the west west by by aa series seriesof of andesitic andesitic and and felsic felsic flows flows and and tuffs. tuffs. The The volcanic volcanic package package has has been been intruded intruded west west of of the the deposit deposit by by the the Snowshoe Snowshoe Bay Bay grano3iorite granodiorite hatholith, batholith,arid and immediately immediately to to the the east east by by the the Stevens Stevens Island Island diorite. diorite. Late Late felsic felsic and and mafic mafic dikes dikes cut cut all all lithologies. 1-ithologies.The The regional regional metamorphic metamorphic grade grade is is upper upper greenschist to to lower lower amphibolite amphibolite fades; facies;however, however,mineral mineral greenschist assemblages in in close close proximity proximity to to the the ore ore zones zones are are assemblages indicative of of lower lower greenschist greenschist grade grade metamorphism. metamorphism. indicative The mine mine lithologies lithologies consist consist of of metahasalt, metabasalt, metapyroxenite, metapyroxenite, The and varieties varieties of of chlorite chlorite schist. schist. Lithologies Lithologies close close to to the the and ore zones zones are are anomalous anomalous in in chlorite, chlorite, talc, talc, sericite, sericite, ore hiotite, biotite, epidote, epidote, carbonate, carbonate, magnetite, magnetite, and and pyrite; pyrite; the the ore ore zones zones themselves themselves are are quartz quartz and and suiphide sulphide rich rich and and contain contain varying amounts amounts of of feldspar, feldspar, muscovite, muscovite, sericite, sericite, pale—brown pale-brown varying biotite, biotite, epidote, epidote, carbonate carbonate and and chlorite. chlorite. The The two two main main ore ore zones, the the East East and and Main Main zones, zones, lie lie within within aa zone zone which which has has zones, recorded intense intense defocmation, deformation, the the Duport nuport Deformation Deformation Zone Zone recorded (DDZ). The DDZ DDZ is is aa reverse reverse fault fault system, system, several several hundred hundred (DDZ) . The metres 75 metres wide, wide, trending trending northeast, northeast, and and dipping dipping about about 75 degrees northwest. northwest. From From east east to to west west the the DDZ DOZ is is degrees characterized characterized by by chlorite—talc-carbonate chlorite-talc-carbonate schist schist and and amphibolite, grading grading to to zones zones of of actinolite—chiorite— actinolite-chloriteamphibolite, sericite schist schist and and finally finally to to basalt basalt breccia. breccia. Deformation Deformation sericite styles styles reflect reflect these these transitions, transitions, ranging ranging from from ductile ductile in in the east east to to brittle brittle +/— +/- ductile ductile in in the the west. west. Gold Gold is is hosted hosted the by well—defined well-defined quartz— quartz- and and sulphide—rich sulphide-rich zones. zones. It Itdisplays displays by strong association association with with arsenopyrite, arsenopyrite, but but is is also also found found aa strong with with pyrite, pyrite, pyrrhotite pyrrhotite and and chalcopyrite. chalcopyrite. There There are are are are least two two ages ages of of pyrite; pyrite; the the younger younger containing containing inclusions inclusions least of gold, gold, while while the the older older is is plated plated by by gold. gold. The The ore ore zones zones of show aa pronounced, pronounced, hut but discontinuous discontinuous sulp'nide—silica sulphide-silica show layering. Commonly Commonly aa well—developed well-developed biotite biotite (+/— ( + / - pyrite) pyrite) layering. halo halo surrounds surrounds the the ore, ore, and and in in places places extends extends past past ore ore lens lens terminations. terminations. In In general general the the ore ore parallels parallels the the schistosity, schistosity, I 1 �hut but locally locally it it fills fills branching branching interconnecting interconnecting fractures fractures and and does not not form form discrete does discrete zones. zones. Where Where felsic felsic dikes dikes intersect intersect ore-bearing system, system, dike margins are are brecciated brecciated to to the ore—bearing rnylonitized and and are are replaced replaced by by quartz, quartz,suiphides sulphidesarid and gold. gold. mylonitized suggested that that the the ore ore zones zones are are Recent underground work has suggested not continuous continuous as as previously previously believed, believed, rather rather they they are are aa not iT i: series of enechelon, enechelon, almond-shaped almond-shaped lenses, lenses, which which step step le let in the horizontal in the the in horizontal sense sense and and up up and and into into the the footwall ootwall in verical ver ical sense. sense. The The extensive extensive deformation, deformation, associated associated pervasive pervasive alteration, alteration, suggest that that the the ore—bearing ore-bearing zones zones and vein orientations, suggest are structurally structurally controlled. controlled. It It is is proposed proposed that that ore ore is is are hosted hosted by zones zones of of high high permeability, permeability, either either by by brittley brittley deformed felsic felsic dikes dikes or or by by permeable permeable channels channels created created by by deformed brittle brittle failure failure within within basalt, basalt, and and concentrated concentrated into into openings created created by by movement movement over over irregular irregular fault fault planes. planes. openings 88 I - I �VOLCANIC VOLCANIC FACIES FACIES 0 OFF THE THE ANDREW BBAY AY AREA, AREA, LAKE 0OF F THE WOODS, WOODS, ONTARIO ONTARIO JJohn ohn Department Department University University Toronto, Toronto, M5S M 5S Stix Stix of Geology o f Geology of o f Toronto Toronto Ontario Ontario 1A1 1A1 Basalt lava B asalt 1 ava fflows l o w s aand n d iintermediate n t e r m e d i a t e to to felsic felsic p yroclastic pyroclastic rrocks ocks o off Archean agee ccrop outt o onn eeither off aann eeast-trending i t h e r sside id e o a s t - t r e n d i n g ssyncline y n c l i n e in i n Andrew Andrew Archea n ag r o p ou I Bay, 2 20km Ontario. 0 kmsouth-southeast s outh-southeast of o f Kenora, Kenora, O n t a r i o . The basaltic b a s a l t i c assemblage assemblage reachess 55.4km pyroclastic reache . 4 k m in i n thickness thicknes s north n o r t h of o f Andrew Andrew Bay, Bay whereas tthe h e pyroclas ti c km oof km tthick rrocks o c k s ooverlie v e r l i e 00.9 . 9 km f bbasalt a s a l t aand n d aare r e uup p tto o 11.7 . 7 km h i c k ssouth o u t h oof f Andrew Andrew Bay. Massive aand pillowed basalts products off non-explosive volcanism, re p roducts o Bay. Massive nd p illowed b a s a l t s aare whereas whereas tuffs, t u f f s , lapilli l a p i l l i tuffs, t u f f s , and a n d debris d e b r i s flows f l o w s represent r e p r e s e n t products p r o d u c t s of of eexplosive x p l o s i v e volcanism. volcanism. , The tuffs deposits The t u f f s aand n d llapilli a p i l l i tuffs t u f f s aare r e massive d e p o s i t s that t h a t ccontain o n t a i n up o up tto 407.c crystals volume.Thes These rocks fragments, some which 40% r y s t a l s b by y volume. e rock s c carry a r r y l lithic i t h i c fragments , som e oof f which may orr flow-banded have may be b e welded tuffs tuffs o f low-banded lavas l a v a s that that h a v e been been transported t r a n s p o r t e d from near-ventt aareas. Many of presence off r e a s Many o f the t h e least-altered l e a s t - a l t e r e d tuffs t u f f s indicate i n d i c a t e the the p resence o near-ven pumice iin betweenc crystals rrelict e l i c t pumice n tthe h e iinterstices n t e r s t i c e s between r y s t a l s and lithic 1i t h i c fragments. Thee presenc presence pumice provides evidence Th e oof f pumic e provide s evidenc e ffor o r contemporaneous contemporaneous eexplosive xplosive volcanism By analogy modern-day environments, the v o l c a n i s m aand n d sedimentation. sedimentation. By analogy with withmodern-day the were el i likely marine 1 environmen environmentt bu butt n aa sshallow hallow m a r i n e tto o ssubaeria ubaeria 1 k e 1 y e rerupted u p t e d i in ttuff u f f sswer deposited marine environment environment below wave wave bbase d e p o s i t e d iinn aa marine a s e . The variable v a r i a b l e crystal crystal contentt of andd the high-temperaturee iindicators conten o f the t h e tuffs t u f f s an t h e lack l a c k of o f high-temperatur n d i c a t o r s iin n tthe he deposits magmatic aand/or post-magmatic loss mplies (1) ( 1 ) magmatic n d / o r post-magmatic loss o ine v itric d e p o s i t s iimplies off ffine vitric materia emplacementt aass resedimented deposits hott a n d (2) (2 ) emplacemen resedimente d d e p o s i t s rrather a t h e r than t h a n as a s ho m a t e r i a 1land pyroclastic p y r o c l a s t i c flows. f lows. . debris are The d ebris flows are heterolithic, poorly-sorted, heterolithic, poorly-sorted, and matrix-supported. and matrix-supported. They ccan an b normally-graded They bee ungraded, normally-graded,, rreversely-graded eversely-graded ffor o r tthe h e ccoarse o a r s e ffraction, raction, w i t h subrourided s ubrounded to t o subangular with one metre diameter. No bedding s i z e s to to o ne m e t r e in i nd i a m e t e r . No cclasts l a s t s of o f aall 1 1 sizes - iiss observed iinn these t h e s e breccias. b r e c c i a s . The The poorly-sorted, p o o r l y - s o r t e d , uunstratified n s t r a t i f i e d nnature a t u r e of o f the t h e deposits deposits i n d i c a t e s emplacement emplacemen t as a smass mas sflows flows• The d e b r i s flows f l o w s may indicates debris may have aa sshallow hallow marine to t o subaerial s u b a e r i a l volcanic v o l c a n i c provenance provenance but b u t subaqueous subaqueous depositional depositional marine setting. The rounding aand off c clasts, heterolithic nature eterolithi c n a t u r e of o f tthe s e t t i n g . The n d reworking o l a s t s ,h he 11 point point rrocks, o c k s , aand n d ppresence r e s e n c e oof f eessential s s e n t i a l pumice tthat h a t aappears p p e a r s vvesiculated e s i c u l a t e d aall ttoo aann oorigin r i g i n bby y sshoaling h o a l i n g tto o ssubaerial u b a e r i a 1 eexplosive x p l o s i v e eruptions. e r u p t i o n s . However, tthe he debris d e b r i s flows f lows rest r e s t upon upon a partly p a r t l y pillowed p i l l o w e d platform p l a t f o r m and and aare r e iintimately ntimately aassociated ssociate d w i t h turbidite t u r b i d i t e beds Thi s implies i m p l i e s the th e h eterolithi c m a t e r i a 1 has ha s with beds. This heterolithic material b e e n mixed aand n d ttransported r a n s p o r t e d into into d eeper w a t e r by mass fflow low p rocesses. been deeper water processes. . . , I n sum, the t h e bbasalts a s a l t s wer r u p t e d aand nd d e p o s i t e d subaqueously In weree eerupted deposited subaqueously, whereas tthe h e ppyroclastics y r o c l a s t i c s probably e r e eerupted r u p t e d iin n aa sshallow h a l l o w marine marine to t o subaerial s ubaerial probably wwere environmen t bu t d e p o s i t e dsubaqueously. subaqueously p y r o c l a s t i c s are a r e complexly environmentbutdeposited The pyroclastics iinterbedded n t e r b e d d e d aand n d eexhibit x h i b i t rrapid a p i d ffacies a c i e s changes. y r o c l a s t i c ddeposits e p o s i t s may changes. The The ppyroclastic may become more proximal west, vent-fades nott becom e mor e proxima 1 tto o t the h e west , bubut t s usubaerial b a e r i a 1 vent-f a c i e s r rocks o c k s aare r e no present p r e s e n t in i n this t h i s area. area. . fl n     89 1 I �U MULCAHY LAKE GPBBRO: MULCAHY LAKE GABBRO: WELL-PRESERVED ARCHEAN ARCHEAN LAYERED LAYERED INTRUSION INTRUSION AA WELL-PRESERVED Sutcliffe, S u t c l i f f e R.H., , R.H., Precambrian P r e c a m b r i a nGeology Geology Section, S e c t i o n , Ontario O n t a r i oGeological Geological Survey, S u r v e y , 77 77 Grenville G r e n v i l l e Street S t r e e t Toronto Toronto e we Mulcahy Mulcahy Lake Lake gabbro q a b b r o is is an a n iron—rich, i r o n - r i c h , tholeiitic t h o l e i i t i c layered layered intrusion 4 5 km km southwest s o u t h w e s t of of i n t r u s i o n located l o c a t e d in i n the t h e Wabigoon Wabiqoon Subprovince S u b p r o v i n c e 45 Dryden, Dryden, Ontario. O n t a r i o . The The gabbro q a b b r o is is one o n e of o f several s e v e r a l mafic m a f i c to t o ultra— ultramafic maÂi c intrusions i n t r u s i o n s which which are a r e intrusive i n t r u s i v e into i n t o tholeiitic t h o l e i i t i c to t o calc— calcalkaline a l k a l i n e metavolcanics m e t a v o l c a n i c s around a r o u n d the t h e periphery p e r i p h e r y of o f the t h e Atikwa— AtikwaLawrence w e l l preserved preserved Lawrence granitoid g r a n i t o i d batholith. b a t h o l i t h . The The exceptionally e x c e p t i o n a l l y well nature n a t u r e of o f the t h e Mulcahy Mulcahy gabbro g a b b r o makes makes it i t an a n ideal i d e a l location l o c a t i o n to t o study study the t h e relationship r e l a t i o n s h i p of o f mafic m a f i c plutonism p l u t o n i s m with w i t h crustal c r u s t a l development d e v e l o p m e n t in in the t h e Archean. Archean. The The intrusion i n t r u s i o n has h a s aa thickness t h i c k n e s s of o f 77 km km and and is is composed composed of o f three three zones are the t h e result r e s u l t of o f distinct distinct z o n e s and and aa marginal m a r g i n a l facies f a c i e s which which are cooling c o o l i n g regimes r e g i m e s and and fractionating f r a c t i o n a t i n g systems s y s t e m s (Morrison ( M o r r i s o n et e t al., al., 1982). 1 9 8 2 ) . The The lower l o w e r and and middle m i d d l e zones z o n e s represent r e p r e s e n t separate s e p a r a t e magma magma pulses p u l s e s which which crystallized c r y s t a l l i z e d from from the t h e bottom b o t t o m upward upward and and are are characterized c h a r a c t e r i z e d by by iron i r o n enrichment e n r i c h m e n t trends. t r e n d s . These T h e s e zones zones are are dominated d o m i n a t e d by b y orthopyroxenes o r t h o p y r o x e n e s and and plagioclase p l a q i o c l a s e cumulates. c u m u l a t e s . The The lower lower zone z o n e has h a s aa stratigraphy s t r a t i g r a p h y defined d e f i n e d by by the t h e appearance a p p e a r a n c e of o f cumulus cumulus phases o r t h o p y r o x e n e - p l ag i o c l a s e ,clino— cl inop h a s e s in i n the t h e following f o l l o w i n g order: o r d e r : orthopyroxene—plagioclase, pyroxene, p y r o x e n e , inverted i n v e r t e d pigeonite, p i g e o n i t e , magnetite m a g n e t i t e and and olivine. o l i v i n e . The The middle middle zone s i m i l a r stratigraphy s t r a t i g r a p h y but b u t in i n addition a d d i t i o n contains c o n t a i n s aa 20 20 zone has h a s aa similar meter meter thick t h i c k layer l a y e r of o f olivine o l i v i n e — clinopyroxene c l i n o p y r o x e n e — plagioclase plaqioclase cumulate lower part p a r t of o f the t h e middle m i d d l e zone zone and and c u m u l a t e which which occurs o c c u r s in i n the t h e lower can c a n be b e traced t r a c e d for f o r the t h e full f u l l 10 1 0 km km length l e n g t h of o f the t h e intrusion. intrusion. The is not n o t clearly c l e a r l y related r e l a t e d to to The upper u p p e r zone z o n e of o f the t h e Mulcahy Mulcahy gabbro q a b b r o is the t h e sequence s e q u e n c e in i n the t h e lower lower and and middle m i d d l e zones. z o n e s . These T h e s e rocks r o c k s are are interpreted i n t e r p r e t e d to t o represent r e p r e s e n t aa roof r o o f zone zone of o f mafic m a f i c to t o intermediate intermediate volcanic v o l c a n i c or o r subvolcanic s u b v o l c a n i c protolith p r o t o l i t h which which has h a s been b e e n metamorphosed metamorphosed to to aa pyroxene p y r o x e n e hornfels h o r n f e l s and and partially p a r t i a l l y melted. m e l t e d . Sills S i l l s ranging r a n g i n g in in composition c o m p o s i t i o n from from peridotite p e r i d o t i t e to t o gabbro g a b b r o and and granite g r a n i t e intrude i n t r u d e the the hornfels h o r n f e l s of o f the t h e roof r o o f zone. zone. The The iron—rich i r o n - r i c h nature n a t u r e of o f the t h e Mulcahy Mulcahy gabbro q a b b r o indicates i n d i c a t e s that t h a t the the magma was fractionated f r a c t i o n a t e d prior p r i o r to t o emplacement emplacement into i n t o the t h e metavolcanic metavolcanic magma was sequence. s e q u e n c e . Late L a t e peridotitic p e r i d o t i t i crocks, r o c k s ,occuring o c c u r i n qalong a l o n gzones z o n e s of of deformation d e f o r m a t i o n in i n the t h e vicinity v i c i n i t y of o f the t h e Mulcahy Mulcahy gabbro, g a b b r o , contain contain cumulate c u m u l a t e magnesian m a g n e s i a n olivine o l i v i n e and and chromite c h r o m i t e which which crystallized c r y s t a l l i z e d from from aa more more primitive p r i m i t i v e magma. magma. These T h e s e rocks r o c k s do d o not n o t appear a p p e a r to t o be b e part p a r t of of the t h e Mulcahy Mulcahy gabbro g a b b r o cumulate c u m u l a t e sequence, s e q u e n c e , however, however, they t h e y are are interpreted i n t e r p r e t e d to t o be b e derived d e r i v e d from from aa common common parental p a r e n t a l magma. magma. Although A l t h o u g h no no rocks r o c k s from from the t h e Mulcahy Mulcahy gabbro g a b b r o clearly c l e a r l y represent represent l i q u i d compositions, c o m p o s i t i o n s , the t h e sequence s e q u e n c e of o f cumulate c u m u l a t e phases p h a s e s provides provides liquid information i n f o r m a t i o n on o n the t h e density d e n s i t y relationships r e l a t i o n s h i p s of o f the t h e liquid. liquid. F r a c t i o n a t i o n of o f olivine o l i v i n e from from the t h e magma magma results r e s u l t s in i n aa decrease d e c r e a s e of of Fractionation density d e n s i t y of o f the t h e residual r e s i d u a l liquid. l i q u i d . If I f the t h e peridotites p e r i d o t i t e s are a r e olivine olivine cumulates c u m u l a t e s from from aa parental p a r e n t a l magma, magma, then t h e n the t h e magma magma pulses p u l s e s forming forming t h e lower lower and and middle m i d d l e zones zones may may represent r e p r e s e n t liquids l i q u i d s at a t or o r near n e a ra a the density d e n s i t y minimum. minimum. Further F u r t h e r fractionation f r a c t i o n a t i o n of o f plagioclase p l a q i o c l a s e and and p y r o x e n e , as a s developed d e v e l o p e d in i n the t h e lower l o w e r and and middle m i d d l e zones, z o n e s , causes c a u s e s the the pyroxene, density d e n s i t y of o f the t h e residual r e s i d u a l liquid l i q u i d to t o increase. i n c r e a s e . This T h i s apparent apparent c o n t r o l of o f density d e n s i t y on o n the t h e emplacement emplacement of o f the t h e two two magma magma pulses pulses control s u g g e s t s that t h a t crustal c r u s t a l filtering f i l t e r i n g has h a s restricted r e s t r i c t e d the t h e access a c c e s s of o f more more suggests primitive p r i m i t i v e magmas magmas to t o high h i g h crustal c r u s t a l levels. levels. T h e s e density d e n s i t y relationships r e l a t i o n s h i p s and and the t h e regional r e g i o n a l geology g e o l o g y suggest suggest These the P o n d i n g of o f mantle m a n t l e derived derived t h e following f o l l o w i n g sequence s e q u e n c eof o f events: e v e n t s : 1)1 ) Ponding p a r e n t a l magma magma at a t the t h e base b a s e of o f the t h e crust. c r u s t . 2) 2 ) Fractionation F r a c t i o n a t i o n of of parental o l i v i n e lowering l o w e r i n g the t h e density d e n s i t y of o f the t h e liquid l i q u i d allowing a l l o w i n g gabbro gabbro olivine plutons p l u t o n s to t o rise rise through t h r o u g h the t h ecrust. c r u s t . 3) 3 ) uplacement Emplacementof o f granitoid granitoid magmas magmas which which are a r ederived d e r i v e d from from melting m e l t i n g of o f crustal c r u s t a lrocks r o c k s with w i t h the the heat magmatism. 4) 4 ) uplacement Emplacement of o f late late maÂi cmagmatism. h e a t source s o u r c e provided p r o v i d e d by by mafic peridotitic p e r i d o t i t i c dikes d i k e s and and sills s i l l s along a l o n g fault f a u l t zones. z o n e s . This T h i s process process implies imp1 ies that t h a t mafic maÂi c metavolcanic m e t a v o l c a n i c rocks r o c k s in i n the t h e Wabigoon Wabiqoon Subprovince Subprov i n c e a r e underlain u n d e r l a i n by by less less dense d e n s e material m a t e r i a l and and may may also alsoexplain e x o l a i n the the are p a u c i t y of o f magnesian m a g n e s i a n basalts b a s a l t s and and komatiites k o m a t i i t e sin i n the t h e region. region. paucity - - - M o r r i s o n , D.A., D.A., Ashwal, Ashwal, L.D., L.D., Henry, Henry, D.J., D . J . , Maczuga, Maczuga, D.E., D.E., and and Morrison, Phinney, P h i n n e y , W.C., W.C., 1982, 1982, The The Mulcahy Mulcahy Lake Lake layered l a y e r e d norite, n o r i t e , 12th 1 2 t hLunar Lunar Lunar and and Planetary P l a n e t a r y Science Science and Planetary P l a n e t a r y Science S c i e n c eConference, C o n f e r e n c e ,Lunar and Institute, I n s t i t u t eHouston. , Houston. 90 90 �I MAGMA MAGMA SERIES AND AND THEIR THEIR RELATIONSHIP RELATIONSHIPTOTO GREENSTONE GREENSTONE GOLD GOLD METALLOGENY METALLOGENY IIN N THE THE LAKE LAKESUPERIOR SUPERIORREGION REGION Evergreen, COCO80439 M.M. (MagmaChem (MagmaChem Expl. Expl. Inc., Inc., 6949 6949Highway Highway 73, 73, Suite S u i t e10,10, Evergreen, 80439 SWAN, M.M. SWAN, U. S.A.) U.S.A.) KEITH, Inc., 10827 10827So. So.551st St., Suite KEITH, S.B. S.B. (MagmaChem (MagmaChem E x pExpi. l . Inc., 1 s t St., S u i t e202, 202, Phoenix, AZ AZ85044 85044 U.S.A.) U.S.A.) Phoenix, PARR, M.G. ( Q u a r t z Tower, Tower, 33451 33451 Stransky s t r a n s k y Rd., Rd., Evergreen, Evergreen,CO CO 80439 80439 U.S.A.) U.S.A.) PARR, M.G. (Quartz I Metal M e t a l and a n d trace t r a c e element e l e m e n t content c o n t e n t of o fgreenstone g r e e n s t o n e gold g o l d deposits d e p o s i t sofofthe t h Lake e Lake Superior S u p e r i o r Region R e g i o n ddisplay i s p l a y clear c l e a r empirical e m p i r i c a l relationships r e l a t i o n s h i p swith w i tmagma h magma series series chemistry c h e m i s t r y of o f spatially s p a t i a l l yand andtemporally t e m p o r a l l yrelated r e l a t e digneous igneousrocks. rocks. These These empirical empirical upon r e l a t i o n s h i p s , along a l o n g with w i t h similar s i m i l a empirical r e m p i r i c arelationships l r e l a t i o n s h i pbased s based upon aa worldworldrelationships, wide w i d e data d a t a base b a s e ooff 2500 2 5 0 0 mmineral i n e r a l ddeposits, e p o s i t s , is i s the t h e basis b a s i sfor f oa r afundamentally f u n d a m e n t a l l new y new petro—chemical rocks associated p e t r o - c h e m i c a l sserial e r i a l classification c l a s s i f i c a t i o of n oigenous f igenous r o c kand s and a s s o c i a t eco—genetic d co-genetic mineral m i n e r a l deposits d e p o s i t sthat t h a has t hasserious s e r i o u smineral m i n e r a expi l e x porati l o r a ton i o nas a swell w e l as l asearth e a r t hmodel model imp1 i c a t i o n s . According A c c o r d i n g tto o the t h e magma magma sseries e r i e s cclassification, l a s s i f i c a t i o n , gold go1 d deposits d e p o s i t s of of implications. the be ggrouped t h e Lake L a k e Superior S u p e r i o r Region R e g i o n ccan a n be r o u p e d i into nto 4 4 distinct d i s t i n c magma t magma series: s e r i e s : 1)1 ) magnesian, 2)2) calcic, c a l c i c , 3)3) calc—alkalic c a l c - a 1 k a l i cand and 4) 4) nepheline nephel i n e normative n o r m a t i v e alkalic a1 k a l i c(See (See rnagnesian, F i g u r e 1). 1). Less L e s s fundamental f u n d a m e n t a l breakdowns b r e a k d o w n s can c a n be be made made based b a s e d upon upon ddepositional epositional Figure vein vs. chemical sediment). e n v i ronment (e.g. v e i n vs. c h e m i c a l sediment). environment (e.g. The The notion n o t i o n of o f magma magma sseries eries — - aa ssuite u i t e of o f co-magmatic co-magmatic igenous igenous rocks r o c k s linked l i n k e dby by I differentiation s t h core e c o r concept e concept d i f f e r e n t i a t i o ntot an o aninitially i n i t i ahomogeneous l l y homogeneous mafic m a f i c parent p a r e n t - -isi the u p o n wwhich h i c h t the h e magma s e rseries i e s c l aclassification s s i f i c a t i o n i is s bbuilt. uilt. upon magma Before B e f o r e serial serial classification c l a s s i f i c a t i o n isi sattempted a t t e m p t e d spilitization s p i 1 it i z a t i o nand/or a n d / o r phyllic p h y l l i c and and argillic argilli c hydrothermal + CaO h y d r o t h e r m a l alteration a1 t e r a t i o are n a rfilteredout e f i l t e r e dby o uuse t b y of u sthe e o fA12O3/Na2O t h e A1 2 0 3 / N a T+0 K20 t K20 + CaO vs. Si02 SiO, variation v a r i a t i o ndiagram d i a g r a m (See (See Figure F i g u r e 2). The cclassification l a s s i f i c a t i o n first i r s divides t divides vs. 2). The igneous i g n e o u s rock r o c k series s e r i e sinto i n t2 o fundamental 2 f u n d a m e n t amegaseri l m e g a s e res i e s based b a s e d on on their t h e i aluminum r a1 uminurn 2). A A given g i v e n rrock o c k ssuite u i t e is i s thus t h u s first f i r s determined t d e t e r m i n e d to t obe be c o n t e n t (See (See Figure F i g u r e 2). content a1 u m i n u m - r i c h (peraluminous) ( p e r a l u m i n o u s ) oro raluminum—poor a1 u m i n u m - p o o r (metaluminous). ( m e t a l u m i n o u s ) . After A f t e r the the aluminum—rich megaseries igneousr o rock megaseries i sis ddetermined, e t e r m i n e d , t hthe e igneous c k i s isf ufurther r t h e r cclassified l a s s i f i e d iin n terms t e r m s ooff its its a1 k a l i n i t into y i n one t o one f 1magma 4 magma series. s e r i e s . In I n addition a d d i t i o n to t oconventional c o n v e n t i o n a l petropetroalkalinity of o14 chemical c h e m i c a l ccriteria, r i t e r i a ,these t h e s e series s e r i e s are a r e defined d e f i n e d by b y aa ppriori r i o r i "off " o f fplot" p l o tempi " e m prical irical knowledge knowledge aabout b o u t mmetal e t a l ccontents o n t e n t s oof f ttemporally e m p o r a l l y and and spatially s p a t i a l l yassociated a s s o c i a t e d mineral mineral systems. mineral alkalinity s y s t e m s . IIntegration n t e g r a t i o n ooff metal m e t a l cchemistry h e m i s t r y oof f m i n e r a l ddeposits e p o s i t s wwith i t h a1 kal i n it y aspects allows a s p e c t s of o f associated a s s o c i a t e d magma magma s eseries r i e s a1 l o w s t the h e ddetermination e t e r m i n a t i o n of of the t h e overall overall The sseries e r i e s aare r e ffurther u r t h e r divided d i v i d e d into into m e t a l l o g e n i c bias b i a sofo fthe t h emagma magma series. s e r i e s . The metallogenic subseries uponooxygen, s u b s e r i e s based b a s e d upon x y g e n , wwater a t e r aand n d i iron r o n content c o n t e n t of o f the t h emagma magma series. series. Additional A d d i t i o n a l divisions, d i v i s i o n s , that t h aof t orock f r o csystems, k s y s t e m s is , iaccomplished s a c c o m p l i s h e dby b yuse use of o f the the Differentiation T h o r n t o n and a n d Tuttle T u t t l e (1960) ( 1 9 6 0 ) to t o determine d e t e r m i n e levels l e v e l s of of D i f f e r e n t i a t i o nIndex I n d e xofo fThornton differentiation d i f f e r e n t i a t i o nwithin w i t h ian magma a magma series, s e r i e s , tot ointegrate i n t e g r a tconventional e c o n v e n t i o n a rock l r o c knames names to to the t h e magma magma s eseries r i e s c classification l a s s i f i c a t i o n and and to t o refine r e f i n ethe t h emetallogenetic m e t a l l o g e n e t i cbias b i a of s oaf magma a magma series s e r i e s to t othe t h esystem s y s t e m level. l e v e l .Once Once the t h e serial s e r i a geochemical l g e o c h e m i c a l character c h a r a c t e r of o f the the associated any aassociated a s s o c i a t e d magma magma s eseries r i e s i is s determined d e t e r m i n e d any s s o c i a t e d oore r e ddeposit e p o s i t can can be be further further c l a s s i f i e dini terms n t e r mof s oits f iemplacement t s emplacement e n v i ronment. classified environment. By classifying c l a s s i f y i n ggold g o l ddeposits d e p o s i t sofothe f t hLake e Lake S u p e r i oRegion r Region a c c o r d i n to g tmagma o magma By Superior according series, to t40 elements s e r i e s , their t h e ibulk r b u lmetal k m e t aand l a ntrace d t r a celement e e l e m e ncontent t c o n t e nup t up o 40 e l e m e n t scan c a nbe be p r e d i c t e d . These These eelements l e m e n t s a rare e l ilisted s t e d in i n the t h e Table Table below b e l o w by by gold g o l d deposit d e p o s i t type. type. predicted. Means and h e s e eelements l e m e n t s f for o r each each ggold o l d system system ttype y p e will w i l l be be presented presented Means andranges rangeso foft these a t the t h eposter p o s t e rsession. session. Also, Also, ore o r eand andgangue gangue mineralogy, m i n e r a l o g y , wall w a l l rock r o c k alteration, alteration, at element e l e m e n t zoning, z o n i n g , geophysical g e o p h y s i c a l ccharacteristics h a r a c t e r i s t i c s and and ultimately u l t i m a t e l yengineering e n g i n e e r i n gand and 9' 1• I �economic parameters l s o be be predicted p r e d i c t e d from from magma magma chemistry. chemistry. In I n gréenstone greenstone economic parameterscan canaalso g o l d exploration e x p l o r a t i o n greenstone greenstone belts be1 t s can can be be subdivided s u b d i v i d e d according a c c o r d i n g to t o magma magma sseries e r i e s to to gold predict p r e d i c t which w h i c h terranes t e r r a n e s are a r e capable c a p a b l e of o f hosting h o s t i n g aa given g i v e n gold g o l d deposit d e p o s i t type. t y p e . The The immediate i m p l i c a t i o n for f o r gold g o l d exploration e x p l o r a t i o nini nthe t h Lake e LakeSuperior S u p e r i o rRegion Region iiss that that immediate implication t h mineral e m i n e r aexploration l e x p l o r a t i o process, n process, save save tthis h i s practical p r a c t i c aapproach l a p p r o a c hcan canstreamline s t r e a m 1 inethe moneyand andu lultimately ttime i m e and and money t i m a t e l y iincrease n c r e a s e ggold o l d ddeposit e p o s i t discovery d i s c o v e r y rates. rates. KIRKLAND -- MAIN '-BREAK TYPE -,+BREAK TYPE I 0 + o PtRLUMWIOU$ s-.. C'J 1WAU10U$ z I ,t,O.l., VtTALUM•NOU* -J Ut ru ALRALtC STOt4OLV o LU -J C K70—Si02 K 0-SiO variation diagram diagram showing showing approximaTe approximale cFemicat i gneous rocks rocks associated associated with with czemica? position posit ion for for igneous 9oId deposit in the the Lake Lake Superior Superior region. gold deposit types types in Figure F i g u r e 11 Wt.% SiC2 A/CNK VAR VARIATION AICNK I AT I ON 2DLGRAM AGRAM FOR FOR WORLDWIDE WORLDW I DE IGNEOUS I GNE9US ROC<S 2OCKS Figure Figure 2 2 Tab 1e Tab1 e CHEMICAL NATURE F THE LAKE SUPERIOR REGION CHEMICAL NATURE OF OF GOLD GOLD DEPOSITS DEPOSITS O OF REGION Elements E I ements Elements Elements Nagma Vagma Series Series Magnesian Series Vagnesian Series In Commonly Enriched In y Enriched Common1 Mineral Deposit Type Type Mineral Deposit Homes take Homestake (Chem in is—Omega) (Cheminis-Omega) Catcic Calcic Series Series Timmns Timmins and and Grass Grass Valley Valley (La (La Maque) Maque) CaIc—alkal Ic Calc-alkalic Series i es Ser Hemlo and Hemlo and Red Lake Lake Au, Ag, Aul Agl Ni, Nil Cu, Cul Cr, Cr, Fe, Fel Mg, Mgl W, Wl (Cc, (ColZn, Zn, B) 6) Pb, Pbl U, U l Th, Thl Sn, Sn, Be, qe, Zr, Y, Li, Hg, Li, Hg, Nb, Nb, Zr, Y, Fe, Zn, Fel Au, Aul Ag, Agl Cu, Cul B, Bl Znl Pb, Nil W, W, Pb, C, Cl Co, Co, Ni, Platinoids, Platinoidsl Se, SelCd, Cdl Mn, Li Sl Mnl Li (Cr, (Cr, Mo, Mop As), ,4s), S, K, Kl Mg, Mg1 Na Na U, Th, Thl Rb, R b l Ce, CelBe, Be, Hg, Nb, Ba, F, F, Nb, Hg, Sb, Sb, Ba, Fe, Cu, Zn, Aul Fe, Cu, Znl Pb, Pbl Ag, Agl Au, Sb, Hg, S, Ba, W, Sbl 4 1 S I Ba1 W I Mo, b l Re, Rel Mn, Mnl (As, (AslSe, SelTi), TI), Ni, U, V i l Cr, Crl Sn, Snl F, Fl 9, Th, Ti, Thl Til B, Bl Li, Li, Be, 3e, Ba, Ba, Y, Y, Nb, Ta, Ta, platinoids), Na (Co, platinoids), (Col Va K K Nephel Nephe I i me ne Normative Normative Alk&ic Alkal ic Series Series Au, Aul platinoids, platinoidsl Cu, Cu, Pb, Pb, Zn, Ag, Mo, Znl Mop Ye Te (LREE (LREE Nb, Rb, Vb, Rb, La, La, Te, Tel Co, Co, Ni, Ni, Kirkland Kirk land Lake Lake Main Main Break Break K, Sr, Ba U l F, F, W, W, K, Srl Ba ,As) As) U, 92 Commonly DeQIeTed H Ta Ta Hg, Sb, TI, Mg (3, 5) �I I BARITIC HORIZON; THE (LEMLO ENL3 3ARIri'IC HORIZON; AAPOSSIBLY POSSIBLYSYNGFNETIC SYNGENETICARCHEAN ARCHEAN BARITE BARITE THE OCCURRENCE OCCURRENCE Thomson, K. and and Gliddon, Thomson, K. Gliddon, D., D . , Department Department of ofGeology, Geology,Lakehead Lakehead U n i v e r s i t y , Thunder Thunder Bay, Bay, Ontario, O n t a r i o f P7B P7B 5El 5El University, AA baritic b a r i t i c horizon horizon occurs occurs within w i t h i n Archean Archean supracrustal s u p r a c r u s t a l rocks rocks of of the t h e Hemlo Hem10 area, a r e a , northwestern northwestern Ontario, O n t a r i o , which which exhibits e x h i b i t s characteristics c h a r a c t e r i s t i c s that t h a t suggest suggest aa svngenetic i s likely. l i k e l y . This This baritic b a r i t i c unit u n i t crops c r o p s out o u t in i n 44 or o r 55 s y n q e n e t i c origin o r i g i n is locations km east e a s t of of the t h e town town of of Marathon, Marathon, and and appears appears l o c a t i o n s situated s i t u a t e d 55 to t o 13 13 km to t o parallel p a r a l l e l the t h e regional r e g i o n a l stratigraphy, s t r a t i g r a p h y , occurring o c c u r r i n gbetween betweenpillowed pillowedinafic mafic metavolcanics metavolcanics to t o the t h e south s o u t h and and intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics p y r o c l a s t i c s and and metasediments The barite b a r i t e ia isthinly t h i n l y laminated laminated to t omassive massive metasediments to t o the t h e north. n o r t h . The and i s generally g e n e r a l l y interlaminated i n t e r l a m i n a t e d wIth w i t h chert, c h e r t , pyrite p y r i t e and/or and/or carbonate, carbonatef and is forming aa unit u n i t 11to t o 22 mm thick t h i c k which which is i s conformable conformable with w i t h the t h e associated associated forming rock rock units. u n i t s . Rock Rock lithologies l i t h o l o g i e s associated a s s o c i a t e d with w i t h the t h e baritic b a r i t i c unit u n i t include include deep w a t e r i s t a m e d basin-type basin-type sediments s e d h e n t s (pyritiferous ( p y r i t i f e r o u s graphitic q r a p h i t i c schists schists deep water/starved and and DE Dl7 turbiditic t u r b i d i t i c siltstones), s i l t s t o n e s ) , siltstones s i l t s t o n e s with w i t h green qreen mica—rich mica-rich (rip—up?) (rip-up?) clasts, c l a s t s , metapelites, m e t a p e l i t e s , green green mica mica schists, s c h i s t s , sericite s e r i c i t e schists, s c h i s t s , biotite— biotiteamphibolite amphibolite schists, s c h i s t s f mafic mafic metavolcanic metavolcanicflows flowsand andfragmentals., f r a q m e n t a l s , aa very very thin t h i n tuffaceous t u f f a c e o u s unitM u n i t * and and quartz-feldspar q u a r t z - f e l d s p a r porphyry porphyry dikes. d i k e s . Although Althouqh these these rock l i k e l y been been transposed transposed relative r e l a t i v e to t o one one another, a n o t h e r , their their rock units u n i t s have have likely persistent s u g g e s t s that t h a t their their p e r s i s t e n t presence presence at a t all a l l the t h e barite b a r i t e occurrences occurrences suggests i s real. real. a s s o c i a t i o n with w i t h the t h e barite b a r i t e is association In I n comparing comparing the t h e characteristics c h a r a c t e r i s t i c s of of the t h e Hemlo Hem10 baritic b a r i t i c horizon horizon with with those t h o s e of of other o t h e r documented documented Paleozoic Paleozoic to t o Archean Archean syngenetic syngenetic and and epigenetic epiqenetic barite it becomes becomes evident e v i d e n t that t h a t the the b a r i t e occurrences occurrences throughout throughout the t h e world, worldf it Hemlo Hem10 occurrence occurrence more more closely c l o s e l y resembles resembles syngenetic synqenetic than t h a n epigenetic epiyenetic deposits. d e p o s i t s . These These characterIstIcs c h a r a c t e r i s t i c s include: include: regional r e g i o n a l and and local l o c a l conformaconformab i l i t y of of the t h e bariti'c b a r i t i c uunit nit w i t h associated a s s o c i a t e d lithologies; l i t h o l o g i e s ; lateral lateral bIlity with continuity c o n t i n u i t y of 8 km; km; associated a s s o c i a t e d deep of the t h e baritic b a r i t i c horizon of possibly possibly 8 water/starved w a t e r l s t a r v e d basinb a s i n ? type type sedimentary sedimentary units u n i t s and and pillowed pillowed mafic mafic meta— metavolcanics; v o l c a n i c s ; thinly t h i n l y laminated laminated to t o thinly t h i n l y bedded bedded character c h a r a c t e r of of the t h e barite b a r i t e and and of i n t e r l a m i n a t i o n with w i t h chert, c h e r t " pyrite p y r i t e and and carbonate; c a r b o n a t e ; and and the t h e presence presence of interlamination rip—up rip-up clasts c l a s t s of of green green mica schist s c h i s t in i n sjltstones s i l t s t o n e s which stratigraphically stratigraphically o v e r l y the t h e baritic b a r i t i c unit. unit, overly I 'I I I '1 �U Geology of of the the Jap Jap Lake LakeArea Area of ofthe the Geology Eastern EasternVermilion VermilionDistrict, District,Northeastern NortheasternMinnesota Minnesota MinnesotaJEFFERYD. D. VERVOORT VERVOORT (Dept. (Dept.of ofGeology, Geology,University Universityof ofMinnesota— JEFFERY Duluth,MN. MN. 55812) 55812) Duluth, The Jap Jap Lake Lake area, area,located locatedat at the the eastern eastern end end of of the the Vermilion Vermilion The districtin innortheast northeastMinnesota, Minnesota, contains contains .a.a volcanic—sedimentary volcanic-sedimentarysuccession succession district typical of of many many Archean Archean greenstone—granite greenstone-granitecomplexes complexes of of the theCanadian Canadianshield, shield, typical as Proterozoicseen seen as well well as as lithologies lithologiesrepresentative representativeof ofthe thelower lowertotomiddle middle Proterozoic elsewherein in northern northernMinnesota. Minnesota. elsewhere Structurally, Structurally,this this Archean Archean sequence sequencerepresents representsthe thesouthern southern limb limb of ofaa The large antiform. antiform. The bedding bedding trends trends NW—SE NW-SE and and stratigraphic stratigraphicindicators indicatorsgive give large SW. The The lowest lowest stratigraphic stratigraphic unit, unit, here here named named the the Jap Jap Lake Lake topsto tothe theSW. tops Volcanic unit, unit, consists consists of of massive massive and and pillowed pillowed tholeiitic tholeiitic basalts basalts locally locally Volcanic intercalated with with thin thin mafic mafic tuffs, tuffs, pillow pillow breccias breccias and and hyaloclastites. hyaloclastites. intercalated Numerous mafic mafic to toultrarnafic ultramafic sills sills are are regularly regularly interlayered interlayered with with the the Numerous The basalts and and are are apparently apparently penecontemporaneous. penecontemporaneous. The base base of of this this unit unit has has basalts been intruded intruded and and apparently apparently removed removed by by the the 2.7 2.7 Ga Ga Saganaga Saganaga Tonalite. Tonalite. been Capping the the thick thick greenstone greenstone unit unit locally locally are are caic—alkaline calc-alkaline dacitic dacitic lava lava Capping The flowsand and an an associated associatedfragmental fragmental unit. unit. The entire entire volcanic volcanic sequence sequenceis is flows then overlain overlain by by aa thick thick blanket blanket of of volcanogenic volcanogenicsediments sediments and and later later capped capped then in the the early early Proterozoic Proterozoic (2.O (-2.0Ga) Galbybythe theGunflint GunflintIron IronFormation Formationand and Rove Rove in Intruding sequenceis isthe the Intruding the the top top of of this thissequence greywackesof ofthe theAnimikie AnimikieGroup. Group. greywackes Keweenawan Duluth Duluth complex complex (1.1 (-1.1 Ga). Gal. Keweenawan 17 samples samples from from the the Jap Jap Lake Lake Volcanic Volcanic Chemical analyses analyses performed performed on on 17 Chemical unit indicate indicate that that these these rocks rocks range range in in composition compositionfrom from high—Mg high-Mg tholeiitic tholeiitic unit basalts to to ultramafic ultramafic komatiltes komatiites as as defined defined by by the the Jensen Jensen cation cationdiagram diagram basalts to rocks are characterized by moderate (Jensen, 1976). 1976). These rocks are characterized by moderate to high high MgO% MgO% These (Jensen, (7-115 in in the the basalts basalts to to 20—32% 20-32% in in the the peridotite peridotite sills) sills) and and low low Ti02 Ti02 (7—11% The (0.6-1.0% in in the the basalts basalts to to O.3—O.k% 0.3-0.4% in in the the peridotite peridotite sills). sills). The (0.6—1.0% characterized by low Al203 (2-7%), high Mg values ultramafic sills are also characterized by low A1203 (2-7%), high Mg values are also ultramafic sills (-74 to ratios (0.9 (0.9 to to 3.1) 3.1) and and high high Ni Ni (700—1100 (700-1100ppm) ppm) (..71 to -831, .83), high CaO/A1203 CaO/Al203 ratios and Cr Cr contents contents (2300—3500 (2300-3500ppm). ppm). and Contact Contact metamorphism metamorphism has has been been locally locally moderate moderate to to severe severe in in the the Jap Jap Lake area. area. Adjacent to to the the Saganaga Saganaga batholith batholith hornblende hornblende hornfels hornfels facies facies Adjacent Lake plagioclase ++ assemblages can can be be seen seen in in the the basalts basalts (now (now hornblende hornblende ++ plagioclase assemblages biotite) as as well well as as in in the the peridotites peridotites (now (now tremolite tremolite ++ talc talc ++ secondary secondary dusty magnetite magnetite ++ chlorite chlorite ++ serpentine serpentine ++ calcite). calcite). forsteritic olivine olivine ++ dusty forsteritic Adjacent to to the the Duluth Duluth complex, complex, pyroxene pyroxene hornfels hornfels facies facies assemblages assemblages are are seen seen Adjacent biotite) in the the basalts basalts (augite (augite ++ plagioclase plagioclase ++ hornblende) hornblende) and and in in the the iron iron formation formation in (fayalite ++ hedenbergite hedenbergite ++ ferrohypersthene ferrohypersthene ++ magnetite magnetite ++ grunerite). grunerite). (fayalite Metamorphic Metamorphic effects effects from from the the Duluth Duluth complex complex can can be be seen seen as as far far as as 3000 3000 feet feet (map distance) distance) away away from from the the contact. contact. (map Based on on field, field, petrographic petrographic and and geochemical geochemical evidence, evidence,the the following following Based the archean volcanic—sedimentary pile. model is proposed for the origin of the archean volcanic-sedimentary pile. origin of the model is proposed for Tholeiitic basalts basalts were were erupted erupted subaqueously subaqueously at at significant significant water water depths depths and and Tholeiitic subsequently subsequently intruded intruded by by thin thin synvolcanic synvolcanic mafic mafic to to ultramafic ultramafic sills sills at at 94 94 , �I I shallow levels levels in in the the volcanic volcanic pile, pile, as as evidenced evidenced by by the the common common occurrence occurrence of of shallow quench textures textures on on the the sill sill margins. margins. The The cessation cessation of of tholeiitic tholeiitic volcanism volcanism quench also signalled signalled the the end end of of subaqueous subaqueous eruptions. eruptions. When When volcanism volcanism resumed resumed it it also be all had aa decidedly decidedly different different character: character: all later later eruptions eruptions appear appear to to ,be had subaerial and and have have caic—alkaline calc-alkaline affinities, affinities, possibly possibly signifying signifying genesis genesis in in subaerial an island island arc arc setting. setting. This largely largely dacitic dacitic volcanism volcanism is is believed believed to to be be This an genetically related related to to the the intrusion intrusion of of the the Saganaga Saganaga batholith, batholith, which which not not genetically for the felsic flows, but also was presumably only served served as as the the magma magma source source for the felsic flows, but also was presumably only responsible for for the the uplift uplift of of the the overlying overlying volcanic volcanic pile. pile. This This was was followed followed responsible by by rapid rapid erosion erosion and and deposition deposition of of the the thick thick pile pile of of volcanogenic volcanogenic sediments. sediments. I References References Jensen, L. L. S., S., 1976, 1976,AA New New Cation Cation Plot Plot for for Classifying Classifying Jensen, Subalkalic Volcanic Volcanic Rocks, Rocks, Ont. Ont. Dept. Dept. Mines, Mines, Misc. Misc. Paper Paper Subalkalic I 66, 17 17 p. p. No. 66, No. I 1 I I I I 'I I 1 95 i I �PRELIMINARY PRELIMINARY INVESTIGATIONS INVESTIGATIONSINTO INTO THE THE GEOLOGY GEOLOGY OF OF THE THE GIANTS GIANTS RANGE RANGE COMPLEX, COMPLEX, VIRGINIA-BIWABIK VIRGINIA-BIWABIK AREA, AFEA, N.E. MINNESOTA MINNESOTA James James L. L. Welsh Welsh Gustavus Gustams Adoiphus Adolphus College College St. MN 56082 56082 St. Peter, Peter, MN Geologic Geologic mapping mapping in in the the highlands highlands of of the the Giants Gi.antsRange Range Complex, Complex, from from east east of of Hwy. Hwy. 53 53 north north of of Virginia Virginia to to Hwy. Hwy. 135 135 north north of of Aurora, Aurora, has mignatitic wiit, unit, and has identified identified two two distinctive distinctive units: an older migmatitic aa younger younger hornblende-bearing hornblende-bearingunit. unit. The Hwy. 53 53 north The migmatite migmatite is is well well exposed exposed in in roadcuts roadcuts along along Hwy. of Virginia. Virginia. Four of Four separate separate phases phases within within this this body body have have been been identified: medium-grained, gneissic identified: 1) 1) pink to to grey, grey, medium-grained, gneissic biotite biotite tonalite; tonalite; 2) 2) agmatitic aptitic amphibolite amphibolite inclusions inclusions within within the the tonalite tonalite host; hornblende leucotonalite leucotonalite dikes which which host; 3) 3) mediuin-grained medium-grained hornblende crosscut 4) later later minor minor aplitic aplitic crosscut both both the the tonalite tonalite and and inclusions; inclusions; and and 4) banded amphibolitic amphibolitic gneiss gneiss marks marks the the southern southern dikes dikes and and veinlets. veinlets. AA banded migmatite Within the the area area mapped, mapped, the the migmatite boundary boundary of of the the migmatite. migmatite. Within occurs occurs only only in in the the Lookout Lookout Mountain Mountain area. area. The in the the mapped area area is is comprised comprised of of The remainder remainder of of the the Complex Complex in These rocks rocks are are pink pink to to grey, grey, mediummedium- to to hornblende-bearing hornblende-bearingrocks. rocks. These coarse-grained, coarse-grained,weakly weakly to to moderately moderately foliated, foliated, commonly commonly porphyritic, porphyritic, and and range range in in composition composition from from granodiorite granodiorite to to diorite, diorite, with with quartz quartz Amphibolite inclusions inclusions monzodiorite monzodiorite being being the the dominant dominant lithology. lithology. Amphibolite The hornblende hornblende bearing bearing unit unit is is clearly clearly are are common common within within these these rocks. rocks. The Along the the southern southern intrusive intrusive into into the the banded banded amphibolite amphibolite gneiss. gneiss. Along margin margin of of the the body body these these rocks rocks are are in in contact contact with with greenstone. greenstone. This not exposed, relatively sharp and is probably This contact, contact, though though not expased, is is relatively aa fault. fault. Foliations within both units are concordant, concordant, trending east by Foliations within Folding has been recognized with northeast. northeast. Folding has been recognized within within the theInigmatite, migmatite, with fold axes and mineral lineations plunging moderately to the east. fold axes and mineral lineations plunging moderately to the east. Hornblende Hornblende in in the the hornblende-bearing hornblende-bearing pluton appears to be similarly similarly aligned. As As structures structures in in the the greenstone greenstone have have aa similar similar trend, trend, aligned. the the fabric fabric in in the the plutonic plutonic rocks rocks is is interpreted interpreted to to be be tectonic. tectonic. 96 �I. MAGMATIC PROCESSES DURING THE MIDCONTINENT RIFT INTERVAL. IN NORTHERN MICHIGAN. CHEMICAL AND ISOTOPIC CONSTRAINTS John 1. Wilband I Department of Geological Sciences, Michigan State University East Lansing, Michigan 48924 C"1.3—0.9 Ga) rocks of the Lake Superior region The Keweenawan are preserved as several spacially and temporally separate plateau flood eruptions and/or related subvolcanic complexes. This magmatic activity was associated with the development of the Midcontinent Rift gravity anomaly, hence "the with its pronounced system CMCR) Midcontinent Gravity high". Michigan, two of these flood—type plateaus centers can be In which records the first CPMG) distinguished. the Powder Mill Group erupted lavas with eruptive centers near the Wisconsin—Michigan border, and the Portage Lake Lavas CPLLS) and overlying "un—named which records the abrupt formation" see McDermott, this program) cessation of rift related volcanism. Two dyke swarms which intrude Archean basement and early Proterozoic sedimentary basins, and small plug—like bodies, are the only exposed subvolcanic Keweenawan rocks similarities, the tholeiitic Based on petrochemical in Michigan. dykes are believed to b feeders for the overlying lavas of the PMG and PLLS. New data from the PMG yield an iiochron with 57Sr/56Sr — 0.7043 +/— 0.0003 and an age of 1209 +/— 136 Ma. The PLLS, which have eruptive centers to th northeast of the PMG, consist of two Colivine and of tholeiitic distinct, but intercalated, batches quartz) magma. Derivation of one batch from the other by micing or fractional crystallization modeling cannot adequately explain the element abundances. Two isochrons with similar ages were obtained for each batch. olivine tholeiite yielded an age of 1013 +/— 274 Ma and 875r/56Sr — 0.7029 and 1026 +/— 191 Ma with +/— 0.0006; 875r/56Sr — 0.7036 +/— 0.0005 for the quartz tholeiite. The "un—named" formation, with its high percentage of evolved rocks which include high potassium rhyolites and intercalated basaltic and andesitic flows, has a major element distribution which has an abrupt change at 65% silica. The origin of the acidic flows is melting than by fractional most easily explained by crustal crystallization of parent tholeiite magma. Petrochemical and isotopic data are interpreted to mean that the heat source which generated the PMG lavas moved notheastward relative and to the crust with time to produce the younger PLLS. The chemical isotopic duality of the PLLS suggest that proximal, but separated. magma chambers existed at this time, possibly derived by partial melting of REE undepleted upper mantle at different depths. 1 I I I I �. i: QIcI STRAIN PATTERNS .IN THE KLRUNft DISTRI-CT.9 NORTHERN SWEDEN;IMPLICATIONS IMPLICATIONS .....-- ...- --...- FOR .- .- .- FROTEROZOIC PROTEROZOIC -- .- --- -- DEFORMATION DEFORMATION .- .- --Stephen Stephen F. F. Wriqht, Wriqht, Dept. of Geology &St Geophysics, Geophysics, University University of of Minnesota, Minneapolis, MN MN 55455 55455 Early Early to to middle middle F'roterozoic Proterozoic supracrustal rocks occupy occupy aa supracrustal rocks large large area area o-f of northern the north north by by rocks rocks of of northern Sweden Sweden bordered bordered on the an an Archean Archean gneissic terrane terrane and and on on the the west west by by the the Caledonide Caledonide frontal frontal thrust. thrust. The Kiruna Kiruna district district includes includes broad broad belts belts of of The and metamorphosed metamorphosed supracrustal supracrustal rocks rocks composed composed of of bimodal bimodal deformed and volcanics, NE volcanics, volcaniclastic volcaniclastic sediments, sediments, and and quartz quartz arenites.. arenites. A NE striking striking eastern eastern belt, belt, hosting the the iron iron and and sulfide sulfide ores, ores, and aa NW NW striking striking western western belt belt are are symmetrically symmetrically disposed disposed about about an an apparently apparently younger, younger, unfoliated granite granite in in aa manner manner typical typical of of classic classic granite/greenstone qranite/greenstone terranes. terranes. fabric and and ininStructural fabric duced strains strains are inhomogeneously developed and are are attributed to to single major major phase phase of of deformation deformation —- the the Svecokarelian Svecokarelian oroqeny. orogeny. a single Extensive structural Extensive structural work work in in the the supracrustal rocks supracrustal rocks surrounding surroundinq the central granite has revealed the the following signisignificant 1..) Cleavage in in rocks rocks of of the eastern and f icant relationships: relationships: 1.) Cleavage and western belts is is steep and aligned roughly N—S N-S somewhat somewhat parallel parallel with 2..) Cleavage in rocks with the the granite granite boundaries. boundaries. 2 . ) Cleavage rocks north north and and south south of of the the granite granite is is also also dominantly dominantly aligned aligned N—S, N-S, oblique oblique to to the 3..) Bedding/cleavage Bedding/cleavage and and minor fold symmetry the granite granite borders. borders.3.) symmetry in in the the eastern eastern and and western, western belts belts both both indicate indicate structural structural vergence towards the granite (i.e. bedding dips away vergence towards the granite (i.e. dips away from from the the granite 4..) granite and and cleavage cleavage is is always always steeper steeper than than bedding). bedding). 4. ) E—W E-W shear shear zones zones with with dextral symmetry symmetry are are developed developed south south of of the the granite. 5.) Stretching ^i. ) Stretching lineations, lineations, minor minor fold fold axes, axes, and and granite. bedding/cleavage intersection plunge intersection lineations lineations congruously congruously plunqe moderately to t o steeply steeply to t o the the south south along along the the eastern eastern margin margin of of the 6.) the granite. granite. 6 . ) Facing directions are are consistently consistently away away from from the the central central granite. granite. These These structures structures suggest suggest E—W E-W shortening shortening concomitant concomitant with with large large wavelength wavelength buckling. buckling. Strain Strain measurements measurements were made made in in aa variety variety of of lithologies litholoqies bounding 1..) bounding the the central central granite granite and and reveal reveal the the following: followinq: 1.) AA considerable considerable heterogeneity heterogeneity o-f of strain strain magnitude magnitude between between the the varying varying lithologies lithologies ranging from highly strained schistose schistose conconglomerates glomerates to t o nearly nearly undeformed undeformed major major magnetite magnetite ore ore bodies. bodies. 2. 2.) Higher Higher strain magnitudes in in the the eastern belt than than in in the the western western and 3.) and southern southern belt. belt. 3.) Strain symmetry symmetry close close to t o plane plane strain. strain. 4..) Maximum shortening shortening strains strains (Z 4.) Maximum ( Z axes) are are dominantly dominantly E—W. E-W. 5. ) 5.) Maximum Maximum elongation elongation strains strains (X ( X axes) axes) plunge steeply steeply south south in in the the eastern Elongation strains eastern and and southern southern belts. be1 ts. strains plunge plunge northward northward in in the the western western supracrustal supracrustal belt. belt. The The strain strain patterns, patterns, structural structural symmetry, symmetry, and and distribution distribution strain strain intensity intensity just described described are are inconsistent inconsistent with with an an origin origin dominated dominated by by granite granite diapirism. diapirlsm. It is is proposed instead It instead that that deformation was was regionally regional 1y extensive extensive producing producing large large scale scale folds folds cored by syn—intrusive syn-intrusive granites and a regionally homogenous homogenous of of 98 �I strain strain Heterogeneities field. field. Heterogeneities are are thought thought to to result result -from -From the the large ductility contrasts contrasts in in the the supracrustal supracrustal rocks r o c k s and and the the large influence of large, newly intruded intruded granite granite bodies. bodies. SuperSuperlarge, stiff, sti-ff, newly is position position of of late late flattening flattening strains strains due due to to diapir diapir ballooning ballooninq is possible. possible. B1 . 7 q I I I I I I I I I I I I I I I �Element Geochemistry Geochemistry ooff the t h eGowganda Gowganda Formation, Ontario Major Element Formation, Ontario YOUNG, G.M. H.W.H.W. Department of of Geology, U nUniversity i v e r s i t y ooff YOUNG, G.M.and andNESBITT, NESBITT, Department Geology, Western Ontario, London, Western Ontario, London, Ontario O n t a r i oN6A N6A 5B7 5B7 Over 200 major major element ,most ooff which Over 200 element analyses analyses,most which are a r e new,are newyare available Formation,a dominantly gglaciogenic avai 1a b l e from from the t h eGowganda Gowganda Formation ,a dominantly l aciogeni c sedimentaryuunit sedimentary n i t forming forming part p a r t of o fthe t h eHuronian HuronianSupergroup. Supergroup. Most Most of of these analysesare arefrom fromd idiamictite anda argillites. a m i c t i t e mmatrix a t r i x mmaterials a t e r i a l s and rgillites. these analyses Deposition Formation and succeedi succeeding Huronian D e p o s i t i o n of o f the t h eGowgnada Gowgnada Formati on and ng Huroni an fforormations took took pplace under cconditions so tthat mations l a c e under o n d i t i o n s ooff regional r e g i o n a l subsidence subsidence so hat they preservedb oboth mainf ofold andi nin rrelatively t h e y aare r e preserved t h i nint hthe e main l d b belt e l t and e l a t i v e l y stable stable sshelf h e l f areas areas to t o the t h e north. n o r t h . There There are are three t h r e emain main areas areas of o f preservation preservation of Formation;t hthe BruceMines, Mines, Cobalt Cobalt and and W Whitefish o f the t h eGowganda Gowganda Formation; e Bruce h i t e f i s h Falls Falls areas. chemicalddata from tthe Whitefish areas. Most Most ooff the t h e new new chemical a t a aare r e from he W h i t e f i s h Falls F a l l s area, area, which had hadaamore moreb abasinal than tthe which s i n a l s setting e t t i n g than h e other o t h e r two. two. The averagemajor majorelement elementcomposition composition matrix The average o fofd diamictite iamictit e m a t r i x materials materials and and aargillites, r g i l l i t e s , giving g i v i n g equal equal weight w e i g h t tto o aall l l three t h r e e areas, areas, is i s as as follows;follows:Si02 1. 2. Ti0, Ti02 64.41 0.63 59.62 0.70 A1203 FeO FeO A12O3 Fend3 MnO MnO Fe203 15.08 2.08 17.28 2.94 3.58 5.06 MgO MgO CaO CaO Na20 Na20 0.08 3.13 1.53 4.46 0.09 3.27 1.07 3.88 K20 K20 P205 LO1 P205 LOl 1.84 0.14 2.84 0.16 2.71 3.03 analysesoof 1. is i s the t h e average average ooff 102 102 analyses f ddiamictite i a m i c t i t e matrix m a t r i x material. material. 105analyses analyseso fofa rargillites. 2. iiss the t h e average average oof f 105 gillites. With tthe exceptionooff CaO, CaO,which whichi sisddepleted With h e exception e p l e t e d i nint hthe e ddiamictites, i a m i c t i t e s , the the average composition of the diamictite matrix material corresponds losely average composi t i o n of t h e d i ami c t i t e m a t r i x m a t e r i a1 corresponds cclosely al.(1967) tto o the t h e estimate e s t i m a t e by by Shaw Shaw eet t a1. (1967) of o f the t h e average average composition composition ooff the the Archean basement Ontario. A Archean basement i ninp apart r t oof f Ontario. A similar,but s i m i l a r , b u t weaker, weaker, CaO-depletion CaO-depletion on on Archean basement iiss evident e v i d e n t ini nPleistocene P l e i s t o c e n etills t i l deposited l s deposited Archean basement ini nthe t h esame same region. The Cobalt Cobaltddiamictites and FeO FeOr erelative The i a m i c t i t e s are a r e enriched e n r i c h e d in i n CaO CaO and l a t i v e tto o the the average Gowganda anda rare depletedi nin Na Na90. average Gowganda d i adiamictite m i c t i t e and e depleted 0. DDiamictites i a m i c t i t e s from from the the Bruce Mines Minesarea areashow showr erelative Bruce l a t i v e depletion d e p l e t i o n ini nCaO CaO an an6FeO FeOand and are a r eNa90Na 0enriched. apparentwhen when thee enriched. SSimilar i m i l a r ppatterns a t t e r n s aare r e apparent t h ethe a r gargillites i l l i t e s oof f these areas comparedw iwith averagea rargillite areas aare r e compared t h t hthe e average g i l l i t e composition. composition. These These rresults esults are geology and and suggest suggest tthat a r e compatible compatible with w i t h the t h eobserved observed basement basement geology h a t the the chemical compositiono foft hthe matrix materials, chemical composition e d diamictite iamictite m atrix m a t e r i a l s , and and tto o a lesser lesser extent, be be used asaspeovenance e x t e n t , of o f the t h eargillites, a r g i l l i t emay s , may used peovenance indicators. i n d i c a t o r s . The The chemical composition composition ooff the Formation chemical t h e Gowganda Gowganda Formation i nint hthe e WWhitefish h i t e f i s h FFalls alls area mixed provenance provenancew iwith area suggests suggests aa mixed t h c contributions o n t r i b u t i o n s from from both b o t h regions. regions. Comparison averageGowganda Gowganda andddiamictite Comparison o foft hthe e average a r gargillite i l l i t e and i a m i c t i t e matrix matrix compositioni nindicates composition d i c a t e s d edepletion p l e t i o n i nins silica i l i c a (grain ( g r a i n size s i z e effect) e f f e c t ) and and the the mobile elementsCa Caand andNaNa i nint hthe e aargillites. r g i l l i t e s .Comparison Comparison of o f the t h e average average m o b i l e elements Gowganda with Gowganda a r argillite g i l l i t e composition composition w i t h that t h a t ofo the f t h eaverage averageAphebian Aphebian shale shale andGarrels, Garrels,1980, 1980,t to exclude data data from ((modified m o d i f i e d from Cameron Cameron and o exclude from the the Gowganda Formation) Gowqanda Formation) i n dindicates i c a t e s t hthat a t t hthe e 1latter a t t e risi much s muchmore more chemically chemically altered, Ti02 andand K20K20 and depleted a l t e r e d , being beingricher r i c h e in r i 5i02, n Si02, TiO2 and d e p l e t e din iCaO n CaOand andNa20. N ~ ~ o . 100 �I A index ooff alteration Young, A chemical chemical index a1 t e r a t i o n(CIA (CIAofoNesbitt f N e s b iand t t and Young,1982) 1982) was usedt to determinet the degreeoof weatheringi in was used o determine h e degree f weathering n tthe h e diamictite diamictite matrix m a t r i x materials m a t e r i a l sand and argillites a r g i l l i t eofs the o f Gowganda t h e GowgandaFormation. Formation.These These results r e s u l t s are a r einterpreted i n t e r p r e t e dtot indicate o i n d i c a tthat e t hthe a t tGowganda h e GowgandaFormation Formation in in the t h e southern southern part p a r t of o f the t h eHuronian Huronian outcrop o u t c r o p belt b e l t contains c o n t a i n s evidence evidence of of two major gglaciations by ddeposits an iinterglacial two major l a c i a t i o n s separated separated by e p o s i t s oof f an nterglacial period. period. References References Cameron, E.M. and and Garrels, Garrels, R.M. R.M. 1980. 1980. Geochemical Geochemical composition composition of o fsome some Cameron, E.M. Precambrian shales from Precambrian shales from the t h e Canadian Canadian Shield. S h i e l d.Chemical ChemicalGeology, Geology, v.28, p.181-197. p.181-197. v.28, Nesbitt, 1982. EEarly N e s b i t t , H.W. G.M. 1982. a r l y Proterozoic P r o t e r o z o i c climates c l i m a t e s and and H.W. and and Young, Young, G.M. plate chemistryoof p l a t e motions motions inferred i n f e r r e d from from major major element element chemistry f llutites. utites. Nature v.299, v.299, p.715—717. p. 71 5-71 7. Nature Shaw, D.M., RReilly, Shaw, D.M., e i l l y , G.A., G.A., Muysson, Muysson, J.R., J.R., Patterden, Patterden,G.E. G.E. and andCampbell, Campbell, F.E. F.E. 1967. 1967. An An estimate e s t i m a t e of o f the t h e chemical chemical composition composition of o f the the Canadian Precambrian Can.Jour. Jour.EEarth Canadian Precambrian S hShield. i e l d . Can. a r t h SSci. c i . v.4, v.4, p.829p.829853. 853. 1 I I I I I I 101 1 I I � https://digitalcollections.lakeheadu.ca/files/original/19e8abd9f1d6118035330430ab25f1cd.pdf e628cabb0aec31c93e60e9feb4cbf6e7 PDF Text Text Institute on Lake Superior Geology Thirty-First Annual Meeting KENORA, Ontario 1985 FIELD TRIP GUIDEBOOK �INSTITUTE INSTITUTE ON ON LAKE SUPERIOR GEOLOGY LAKE SUPERIOR GEOLOGY 31ST 3 1 sANNUAL ~ANNUAL MEETING MEETING KENORA, 1985 FIELDTRIP FIELDTRIP GUIDEBOOK GUIDEBOOK edited edited by GP G oP Beakhouse . Beakhouse R e s i d e n t Geologist Geologist Organized in i n conjunction c o n j u n c t i o n with w i t h the t h e Kenora Resident Organized Office O f f i c e and and the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey �Copies of C opies o f the t h e abstract a b s t r a c t and field f i e l d guidebook guidebook volumes v o l u m e s may be b e purchased p u r c h a s e d from: from: M..M. M.M. KKehlenbeck ehlenbeck Department D e p a r t m e n t of o f Geology Geology Lakehead University University Thunder Bay, Bay, Ontario Ontario P7V 5E1 5E1 Costs: C osts: $5.00 Abstracts Abstracts $ 5.00 Field F i e l d Guidebook Guidebook $10.00 $10.00 ((plus p l u s $$2.00 2 - 0 0 postage p o s t a g e and handling h a n d l i n g charges) charges) Make cheques c h e q u e s payable p a y a b l e to: to: Institute I n s t i t u t e on o n Lake Lake Superior S u p e r i o r Geology The contributions The c o n t r i b u t i o n s oof f the t h e following f o l l o w i n g tto o the t h e production p r o d u c t i o n oof f this this volume aare volume r e gratefully g r a t e f u l l yacknowledged: acknowledged: whod rdrafted -— Barbara B a r b a r a Moore, Moore, who a f t e d mmost o s t o foft the h e ffigures i g u r e s and and designed d e s i g n e d the the ccover over Melenchenko, who who ttyped manuscript — - Anna BBranicky r a n i c k y aand n d JJoyce o y c e Melenchenko, y p e d tthe he m anuscript who pproof—read mostoof — Chris - C h r i s Drimmie, Drimmie, who r o o f - r e a d most f tthe h e volume volume Mary-Lynne Stuart -— Mary-Lynne S t u a r t and and Renate R e n a t e Aukstakalnis, Auks t a k a l n i s ,who who advised a d v i s e d on on of various v a r i o u s aspects aspects o f the t h e reproduction r e p r o d u c t i o n of o f this t h i s volume. volume. Deformed COVER PHOTO: PHOTO: Deformed mmafic a f i c d dike i k e ccutting u t t i n g 2.85 2.85 Ga Ga Wabigoon—Winnipeg River ggneissic n e i s s i c tonalite t o n a l i t e in i n the t h e Wabigoon-Winnipeg River ssubprovincial u b p r o v i n c i a l interface I n t e r f a c e zone, z o n e , Keewatin, K e e w a t i n , Ontario Ontario 11 �Preface Preface Kenor'a, Annual Institute K e n o r a , hhost o s t oof f tthe h e 331st 1 s t Annual I n s t i t u t e on o n Lake Lake Superior Superior Geology, G e o l o g y , is i s situated s i t u a t e d at a t the t h e north n o r t h end end of o f Lake Lake of o f the t h e Woods. Woods. It It is i s especially e s p e c i a l l y appropriate a p p r o p r i a t e that t h a t Kenora K e n o r a host h o s t the t h e 1985 1985 meeting m e e t i n g on on the t h e centenary c e n t e n a r y of o f Andrew Andrew Lawson's Lawson's first f i r s t publication p u b l i c a t i o n on on the t h e Lake Lake of of the t h e Woods area; a r e a ; he h e identified i d e n t i f i e d many many of o f the t h e problems p r o b l e m s we we are are debating a s aa classical c l a s s i c a l Archean Archean d e b a t i n g today t o d a y and and established e s t a b l i s h e d the t h e area a r e a as terrane. t e r r a n e . AA brief b r i e f summary summary of o f the t h e regional r e g i o n a l geologic g e o l o g i c setting s e t t i n g of of the the Kenora Kenora area, a r e a , based b a s e d on on the t h e discussions d i s c u s s i o n s in i n the t h e field f i e l d guides g u i d e s and and the the references r e f e r e n c e s cited c i t e d therein, t h e r e i n , follows. follows. Kenora i s located l o c a t e d within w i t h i n the t h e southwestern s o u t h w e s t e r n part p a r t of o f the the Kenora is Superior S u p e r i o r Province P r o v i n c e of o f the t h e Canadian C a n a d i a n shield. s h i e l d . The The Superior S u p e r i o r Province Province has h a s been b e e n subdivided s u b d i v i d e d into i n t o east—west e a s t - w e s t trending t r e n d i n g subprovinces s u b p r o v i n c e s consistconsisting i n g of o f greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes t e r r a n e s (Shebandowan—Wawa, (Shebandowan-Wawa, Wabigoon, Wabigoon, Uchi Uchi and and Sachigo S a c h i g o Subprovinces), S u b p r o v l n c e s ) , metasedimentary m e t a s e d i m e n t a r y gneiss g n e i s s terranes terranes (Ear M a n i g o t a g a n and and Quetico Q u e t i c o Subprovinces) S u b p r o v i n c e s ) and and bath— bath( E a r Falls F a l l s —- Manigotagan olithic o l i t h i c terranes t e r r a n e s (Winnipeg ( W i n n i p e g River R i v e r and and Berens B e r e n s River R i v e r Subprovinces). Subprovinces) * The The town town of o f Kenora K e n o r a lies l i e s on o n the t h e interface i n t e r f a c e between b e t w e e n the t h e Winnipeg Winnipeg River R i v e r and and Wabigoon Wabigoon subprovinces. subprovinces. The suprac r u s t a l The western w e s t e r n Wabigoon Wabigoon Subprovince S u b p r o v i n c e comprises c o m p r i s e s aa supracrustal assemblage a s s e m b l a g e of o f predominant p r e d o m i n a n t metavolcanic m e t a v o l c a n i c and and subordinate s u b o r d i n a t e meta— metasedimentary s e d i m e n t a r y rocks r o c k s and and granitoid g r a n i t o i d intrusions, i n t r u s i o n s , some some of o f batholithic batholithic dimensions. d i m e n s i o n s . Stratigraphic S t r a t i g r a p h i c analysis a n a l y s i s of o f the t h e rock r o c k sequences s e q u e n c e s within within the was aa t h e western w e s t e r n Wabigoon Wabigoon Subprovince S u b p r o v i n c e suggests s u g g e s t s that t h a t there t h e r e was consistent c o n s i s t e n t evolution e v o l u t i o n through t h r o u g h time t i m e with w i t h initial, i n i t i a l , quiescent, quiescent, submarine, s u b m a r i n e , mafic, m a f i c , tholeiltic t h o l e i i t i c volcanism v o l c a n i s m followed f o l l o w e d by by more more silicic, silicic, submarine c a l c - a l k a l i n e pyroclastic p y r o c l a s t i c volcanism v o l c a n i s m and and s u b m a r i n e and and subaerial, s u b a e r i a l , calc—alkaline related r e l a t e d clastic c l a s t i c sedimentation. s e d i m e n t a t i o n . More More than t h a n one o n e such s u c h cycle c y c l e may may be be present. p r e s e n t . Available A v a i l a b l e high h i g h precision p r e c i s i o n U—Pb U-Pb zircon z i r c o n geochronology geochronology suggest s u g g e s t that t h a t volcanism v o l c a n i s m and and plutonism p l u t o n i s m were w e r e synchronous s y n c h r o n o u s and a n d took took place p l a c e over o v e r aa relatively r e l a t i v e l y short s h o r t time t i m e interval i n t e r v a l between b e t w e e n 2755 2755 and a n d 2695 2695 Ma. Ma. The The metallogeny me t a l l o g e n y of o f the t h e western w e s t e r n Wabigoon Wablgoon Subprovince Sub p r o v i n c e is is diverse. d i v e r s e . Massive M a s s i v e sulphide s u l p h i d e deposits d e p o s i t s such s u c h as a s those t h o s e at a t South South Sturgeon S t u r g e o n Lake Lake and and numerous numerous gold g o l d deposits d e p o s i t s have h a v e received r e c e i v e d the t h e most most attention. a t t e n t i o n . Exploration E x p l o r a t i o n ffor o r gold g o l d mineralization m i n e r a l i z a t i o n has h a s recently recently intensified s i g n i f i c a ndiscovery t d i s c o v e r at y aCameron t Cameron i n t e n s i f i e d ini nthe t h ewake wake of o fa asignificant Lake0 Other Lake O t h e r types t y p e s of o f potentially p o t e n t i a l l y economically e c o n o m i c a l l y significant significant deposits d e p o s i t s include i n c l u d e disseminated d i s s e m i n a t e d copper c o p p e r and/or a n d / o r molybdenum, molybdenum, rare rare metal m e t a l pegmatites, p e g m a t i t e s , building b u i l d i n g stone s t o n e and and industrial i n d u s t r i a l minerals. minerals. Our Our perception p e r c e p t i o n of o f the t h e terrane t e r r a n e lying l y i n g to t o the t h e north n o r t h of o f the the Wabigoon Wabigoon Subprovince S u b p r o v i n c e has h a s changed changed dramatically d r a m a t i c a l l y within w i t h i n the t h e past p a s t ten ten years. a s the t h e English E n g l i s h River R i v e r Subprovince, Subprovince, y e a r s . This T h i s area, a r e a , referred r e f e r r e d to t o as is i s now now known known to t o consist c o n s i s t of o f two two different d i f f e r e n t types t y p e s of o f terrane t e r r a n e for for which separate s e p a r a t e subprovince s u b p r o v i n c e status s t a t u s has h a s been b e e n proposed; p r o p o s e d ; aa northern northern which s u p r a c r u s t a l domain domain (Ear ( E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n Subprovince) S u b p r o v i n c e ) and and aa supracrustal southern s o u t h e r n plutonic p l u t o n i c domain domain (Winnipeg ( W i n n i p e g River R i v e r Subprovince). S u b p r o v i n c e ) . The The Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n Subprovince S u b p r o v i n c e consists c o n s i s t s predominantly p r e d o m i n a n t l y of of turbiditic t u r b i d i t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s which which have h a v e been b e e n highly h i g h l y metametamorphosed morphosed and and partially p a r t i a l l y melted. m e l t e d . The The Winnipeg Winnipeg River R i v e r Subprovince Subprovince contains p r e - t e c t o n i c gneissic gneissic c o n t a i n s three t h r e e principal p r i n c i p a l rock r o c k suites; s u i t e s ; pre—tectonic granitoid g r a n i t o i d rocks, r o c k s , pre— p r e - to t o syn—tectonic s y n - t e c t o n i c sodic s o d i c plutons p l u t o n s and a n d late— l a t e - to to post—tectonic p o s t - t e c t o n i c potassic p o t a s s i c plutons. p l u t o n s . Subordinate, S u b o r d i n a t e , amphibolitic a m p h i b o l i t i c to to iii �granulitic, g r a n u l i t i c , predominantly p r e d o m i n a n t l y metavolcanic, m e t a v o l c a n i c , supracrustal s u p r a c r u s t a l inclusions inclusions aare r e ppresent r e s e n t in i n all a l l three t h r e e suites s u i t e s but b u t are a r e most m o s t abundant a b u n d a n t in i n the the gneissic g n e i s s i c rocks. rocks. In I n ccontrast o n t r a s t to t o tthe h e tightly t i g h t l y clustered, c l u s t e r e d , relatively r e l a t i v e l y young young ages ages of the Wabigoon Subprovince, Winnipeg River Subprovince o f t h e Wabigoon Sub p r o v i n c e , Winnipeg R i v e r S u b p r o v i n c e plutonism plutonism spanned 6 0 0 Ma Ma (2560 ( 2 5 6 0 to t o 3168 3168 Ma). Ma). Many of o f the t h e younger y o u n g e r rocks rocks s p a n n e d 600 appear These a p p e a r to t o represent r e p r e s e n t reworking r e w o r k i n g of of older o l d e r rocks. rocks. T h e s e relation-relationSubsships h i p s hhave a v e bbeen e e n interpreted i n t e r p r e t e d in i n terms t e r m s of o f the t h e Winnipeg River R i v e r Sub— pprovince r o v i n c e representing r e p r e s e n t i n g a basement b a s e m e n t complex complex that t h a t existed e x i s t e d prior p r i o r to to The interface Wabigoon Subprovince S u b p r o v i n c e volcanism v o l c a n i s m and and plutonism. plutonism. The interface between b e t w e e n the t h e two two subprovince s u b p r o v i n c e has h a s stratigraphic s t r a t i g r a p h i c(unconformable) ( u n c o n f o r m a b l e ), ttectonic, e c t o n i c , metamorphic m e t a m o r p h i c and and intrusive i n t r u s i v e aspects a s p e c t s and and defies defies a simplistic s i m p l i s t i c interpretation. interpretation. iv �CONTENTS CONTENTS Preface Preface Contents C ontents The Cameron Lake The L a k e Deposit D e p o s i t (D.R. ( D . R. Melling M e l l i n g and and D0H, D.H. Watkinson) Watkinson) Introductory I n t r o d u c t o r y Discussion Discussion Field F i e l d Guide Guide References R eferences Geologic G e o l o g i c Setting S e t t i n g and and Style S t y l e of o f Gold Gold Mineralization Mineralization Lake Woods aarea Davies, PM0 Smith, r e a ((J,C JoCoD a v i e s , P,M. Smith, iin n tthe he L a k e oof f t the h e Woods and CC.E . E . Blackburn) Blackburn) and Introductory I n t r o d u c t o r y Discussion Discuss ion Field F i e l d Guide Guide References R eferences Geological G e o l o g i c a l Relationships R e l a t i o n s h i p s in i n the t h e Vicinity V i c i n i t y of o f the the Wabigoon W a b i g o o n - Winnipeg W i n n i p e g River R i v e r Subprovincial S u b p r o v i n c i a l Interface Interface in Kenora area i n the the K enora a r e a (G.P ( G . P o Beakhouse) Beakhouse) IIntroductory n t r o d u c t o r y Discussion Discussion Field F i e l d Guide Guide References References Appendix Append ix A Volcanic V o l c a n i c Facies F a c i e s Interpretation I n t e r p r e t a t i o n of o f the t h e Berry B e r r y River River Formation (G.W. Johns) Johns) F o r m a t i o n (G.W. IIntroductory n t r o d u c t o r y Discussion Discuss ion Field F i e l d Guide Guide References R eferences Granitoid G r a n i t o i d Related R e l a t e d Mineralization M i n e r a l i z a t i o n in i n the t h e Dryden D r y d e n Area A r e a (F.W. (F.W. Breaks, R.C. BBeard, . A . Janes, J a n e s , RH. K.H. Poulsen) Poulsen) B r e a k s , R.C. e a r d , DDA. Discuss ion IIntroductory n t r o d u c t o r y Discussion Field F i e l d Guide Guide References R eferences V iiii ll v v 1 2 2 5 5 1 1111 13 13 1144 26 26 56 56 599 5 60 60 7788 96 9 6 101 101 105 105 106 106 131 131 153 153 157 157 158 158 170 170 185 185 �Deposit The Cameron Lake Lake Deposit IIntroductory n t r o d u c t o r y Discussion Discuss i o n and a n d Field Field Guide Guide 31st Annual Institute 3 1 s t Annual I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology Kenora, K e n o r a , Ontario Ontario by D.R. D.R. Melling Mellinq D,H. D. H. Watkinson Watkinson Ottawa-Carleton O t t a w a - C a r l e t o n Centre C e n t r e for for Geoscience G e o s c i e n c e Studies Studies Carleton C a r l e t o n University University Ottawa, O t t a w a , Ontario Ontario K1S 5B6 5B6 �2 INTRODUCTION INTRODUCTION Lakeg ogold o c a t e d in i n northwestern northwestern The Cameron Cameron Lake l d d edeposit p o s i t isis llocated Ontario I t was was originally originally O n t a r i o about a b o u t 80 8 0 km km south—southeast s o u t h - s o u t h e a s t of o f Kenora. K e n o r a - It by two prospectors p r o s p e c t o r s working w o r k i n g for f o r Noranda N o r a n d a Mines Mines ddiscovered i s c o v e r e d in i n 1960 by Lowg ogold (Hunter ( H u n t e r et e t al., a l . , 1984). 1984 ) . Low l d p rprices i c e s aat t that t h a t time t i m e coupled c o u p l e d with with o m p l e x ssubsurface u b s u r f a c e ggeometry e o m e t r y aand n d poor p o o r ooutcrop u t c r o p exposure exposure a ccomplex Four discouraged d i s c o u r a g e d investment i n v e s t m e n t and and development. development. F o u r separate s e p a r a t ediamond diamond c o n d u c t e d on o n the t h e property p r o p e r t y prior p r i o r to t o the the d r i l l i n g programs p r o g r a m s were conducted discovery two d i s c o v e r y of o f aa major m a j o r zone z o n e of o f gold g o l d mineralization m i n e r a l i z a t i o n in i n 1983 1983 by b y two junior mining junior m i n i n g companies, c o m p a n i e s , Nuinsco N u i n s c o Resources R e s o u r c e s and a n d Lockwood Lockwood Proven Petroleum. t i m e totaled t o t a l e d 1,287,000 1 , 2 8 7 , 0 0 0 tons tons P etroleum. P r o v e n reserves r e s e r v e s at a t that t h a t time grading g r a d i n g 0.154 0 . 1 5 4 oz/ton o z / t o n Au, Au, including i n c l u d i n g 807,000 8 0 7 , 0 0 0 tons t o n s grading g r a d i n g 0.194 0.194 oz/ton o z / t o n Au Au (Nuinsco ( N u i n s c o Resources R e s o u r c e s Limited, L i m i t e d , 1983). 1983) drilling REGIONAL GEOLOGIC SETTING AND ITS ITS BEARING B E A R I N G ON GOLD MINERALIZATION Cameron western i e s in i n the the w e s t e r n portion p o r t i o n oof f the t h e Archean Archean Cameron Lake Lake llies Savant (Trowell S a v a n t Lake—Crow Lake-Crow Lake Lake metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y belt b e l t (Trowell The rregion by the et e t al., a l s f 1980), 1 9 8 0 ) . The e g i o n is is ddivided i v i d e d ggeologically e o l o g i c a l l y by t h e north— northwestsoutheast wes t - s o u t h e a s t trending, t r e n d i n g , northeast—dipping n o r t h e a s t - d i p p i n g Pipestone—Cameron P ipestone-Cameron Southwest Fault 1). S o u t h w e s t oof f tthe h e ffault a u l t lies l i e s the t h e north— n o r t h - to to F a u l t (Figure ( F i g u r e 1). east—facing, Kakag i Lake Lake greenstone g r e e n s t o n e terrain t e r r a i n (KLGT) (KLGT) (Schwerdtner (Schwerdt n e r e a s t - f a c i n g , Kakagi al., 1979) eet t a!.,, 1 9 7 9 ) aand n d tto o tthe h e nnortheast o r t h e a s t tthe h e ssouth—facing o u t h - f a c i n g Iowan Rowan Lake Lake is a a major m a j o r zone z o n e of of ggreenstone r e e n s t o n e terrain t e r r a i n (RLGT). (RLGT). The T h e fault f a u l t is ddeformation e f o r m a t i o n and a n d ddisplacement i s p l a c e m e n t which w h i c h strikes s t r i k e s over o v e r 100 1 0 0 km km in i n aa Exposure of the fault in nnorthwest—southeast o r t h w e s t - s o u t h e a s t direction. direction. E x p o s u r e o f t h e f a u l t i n the the Cameron Lake area is poor, often e i n g oobscured b s c u r e d bby y lakes l a k e s and a n d low low Cameron L a k e a r e a i s p o o r , o f t e n bbeing Correlation swampy depressions. depress ions C o r r e l a t i o n of o f lithologies l i t h o l o g i e s across a c r o s s the t h e fault, fault aalthough l t h o u g h suspected, s u s p e c t e d , has h a s not n o t been b e e n possible p o s s i b l e (Trowell (Trowell et e t al., a l . , 1980). 1980). The geology g e o l o g y of of the t h e RLGT RLGT is i s dominated d o m i n a t e d by b y the t h e Shingwak S h i n g w a k Lake Lake The fold Anticline. A nticline. f o l d hhas a s aa east—northeast e a s t - n o r t h e a s t trending t r e n d i n g axial a x i a l surface surf ace Based and and pplunges l u n g e s steeply s t e e p l y towards t o w a r d s the t h e southwest s o u t h w e s t (Kaye, ( K a y e , 1973). 1973). B a s e d on on field mapping field m a p p i n g and a n d lithogeochemical l i t h o g e o c h e m i c a l analyses, a n a l y s e s Blackburn B l a c k b u r n and and Hailstone H a i l s t o n e (1984) ( 1 9 8 4 ) have h a v e shown s h o w n that t h a t the t h e RLGT RLGT may be b e subdivided s u b d i v i d e d into into All the A l l rrocks o c k s hhave a v e been been t h e Powan Rowan Lake Lake and a n d Cameron Cameron Lake Lake Volcanics. Volcanics. The metamorphosed t o greenschist—facies g r e e n s c h i s t - f a c i e s assemblages. assemblages T h e Powan Rowan Lake Lake m e t a m o r p h o s e d to Volcanics V o l c a n i c s form form a a thick t h i c k ppredominantly r e d o m i n a n t l y ppillowed, i l l o w e d , subaqueous s u b a q u e o u s mafic maf i c flow f l o w ssuccession u c c e s s i o n in i n the t h e core core of o f the t h e Shingwak S h i n g w a k Lake Lake Anticline. Anticline. These by the mixed T h e s e rrocks o c k s aare r e ooverlain v e r l a i n by t h e Cameron Lake Lake Volcanics, Volcanics, a a m ixed succession s u c c e s s i o n of o f ssubaqueous u b a q u e o u s ppillowed i l l o w e d and a n d massive mass i v e mafic maf i c flows, f l o w s , and and South intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics. pyroclastics. S o u t h oof f the t h e fold f o l d axis a x i s top top ddeterminations e t e r m i n a t i o n s ddefine efine a a ssteeply t e e p l y ddipping i p p i n g homocline h o m o c l i n e facing f a c i n g southsouthward. Subvolcanic sills were emplaced i l l s were e m p l a c e d at a t all a l l levels l e v e l s in i n the the S u b v o l c a n i c gabbroic gabbroic s Felsic t o folding. folding. F e l s i c porphyry p o r p h y r y sills s i l l s and a n d dikes, dikes, sstratigraphy t r a t i g r a p h y prior p r i o r to monzonite aand n d quartz quartz m o n z o n i t e sstocks t o c k s intrude i n t r u d e all a l l the t h e earlier e a r l i e r strata. strata. Blackburn and Hailstone (1984) have shown that the B l a c k b u r n a n d H a i l s t o n e ( 1 9 8 4 ) h a v e s h o w n t h a t t h e lower lower is ttholeiitic mostly ssuccession u c c e s s i o n (Rowan (Rowan Lake Lake Volcanics) V o l c a n i c s ) is h o l e i i t i c aand nd m o s t l y rather rather magnesium—rich, m a g n e s i u m - r i c h , while w h i l e the t h e upper u p p e r succession s u c c e s s i o n (Cameron ( C a m e r o n Lake Lake Volcanics) t o caic—alkaline c a l c - a l k a l i n e varieties. varieties V o l c a n i c s ) includes i n c l u d e s both b o t h tholeiitic t h o l e i i t i c to The most most ssignificant within i g n i f i c a n t ggold o l d ooccurrences c c u r r e n c e s aare re w i t h i n the t h e Cameron Cameron Lake Lake The Volcanics t o be b e associated associated V o l c a n i c s (Blackburn ( B l a c k b u r n and a n d JJanes, a n e s , 1983) 1 9 8 3 ) and and tend t e n d to with Several w i t h zones z o n e s of o f high h i g h strain. strain. S e v e r a l oof f these t h e s e occurrences o c c u r r e n c e s are are Two ssuch o r near n e a r gabbroic—volcanic g a b b r o i c - v o l c a n i c contacts. contacts. u c h gold— goldssituated i t u a t e d at a t or bearing, to b e a r i n g , hhigh i g h sstrain t r a i n zones, z o n e s , previously p r e v i o u s l y unnamed, unnamed, are a r e referred r e f e r r e d to a . �______ 3 + ++ : NOLAN ,+ + LAKE + + STOCK -I-t + + + + + + + + + + •+ + + + + + + + + + + + + + • + MIDDLE MIDDLE TO TOLATE LATEPRECAMBRIAN PRECAMBRIAN(PROTEROZOIC) (PROTEROZOIC) MAFIC MAFICINTRUSIVE INTRUSIVEROCKS ROCKS diabase diabase 00 1 1 - + + + + + + )+ + + 1 + + 22 kilometres kilometres gold occurrence occurrence AAgold EARLY EARLYPRECAMBRIAN PRECAMBRIAN(ARCHEAN) (ARCHEAN) LATE FELSIC INTRUSIVE LATE FELSIC INTRUSIVEROCKS ROCKS granite, granodiorite, granodiorite. diorite, diorite, monzodiorite, monzodiorite,monzonite, monzonite, quartz quartzmonzonite monzonite granite, EARLY EARLYFELSIC FELSICINTRUSIVE INTRUSIVEROCKS ROCKS [7''j feldspar porphyry, quartz porphyry, quartz—feldspar feldspar porphyry, quartz porphyry, quartz-feldspar porphyry porphyry MAFIC MAFICINTRUSIVE INTRUSIVEROCKS ROCKS IIJffJIjJJJJJ gabbro, quartzgabbro, gabbro,pyroxenite, pyroxenite, peridotite, peridotite, diorite gabbro, quartz diorite FELSIC FELSICTO TOINTERMEDIATE INTERMEDIATEMETAVOLCANICS METAVOLCANICS 1"""""")I rhyolite rhyolite, rhyodacite rhyodacite, dacite dacite,tuff tuff, lapilli—tuff lapilli-tuff, crystal crystallaptIli—tuff Iapilli-tuff,tuff—breccia tuff-breccia MAFIC MAFICMETAVOLCANICS METAVOLCANICS basalt,andesite andesite(pillowed (pillowedand and massive),pillow pillow breccia, tuff. lapilli-tuff,tuff—breccia tuff-breccia basalt, massive), breccia, tuff, lapilli—tuff, Figure Figure 1: 1: Geology G e o l o g y of o f the t h e Cameron Cameron Lake L a k e area a r e a (modified ( m o d i f i e d after a f t e r Kaye, Kaye, 1973). 1973). �4 here here a s the t h e Cameron Cameron Lake Lake and a n d nte MonteCristo C r i s t oShear S h e a rZones. Zones. as p r e s e n t l y the t h e principal p r i n c i p a l targets t a r g e t s for f o r exploration. exploration. presently These T h e s e are are THE GEOLOGY GEOLOGY OF O F THE THE CAMERON CAMERON LAKE LAKE GOLD GOLD DEPOSIT DEPOSIT THE The Cameron Cameron Lake Lake d e p o s i t is situated s i t u a t e d on o n the t h e north n o r t h shore s h o r e of of The m northwest of the point of about 700 Cameron Lake ( F i g u r e 1 ) a b o u t 700 m n o r t h w e s t o f t h e p o i n t o f Cameron Lake (Figure 1) a t the t h e Nuinsco N u i n s c o bush b u s h camp. camp. The T h e rocks r o c k s hosting h o s t i n g the the d e b a r k a t i o n at debarkation d e p o s it are a r e composed composed of of mafic maf i c volcanics v o l c a n i c s consisting c o n s is t i n g predominantly predominant1y deposit o f fine f i n e grained g r a i n e d pillowed p i l l o w e d and a n d massive m a s s i v e flows f l o w s with w i t h minor m i n o r occurrences occurrences of of t o felsic f e l s i c pyro— pyroo f pillow p i l l o w breccia b r e c c i a interlayered i n t e r l a y e r e d with w i t h intermediate i n t e r m e d i a t e to c l a s t i c rocks. r o c k s . Two Two gabbroic g a b b r o i c sills s i l l s intrude i n t r u d ethe t h eintermediate i n t e r m e d i a t earid and clastic ffelsic e l s i c pyroclastic p y r o c l a s t i c rocks. r o c k s . Quartz—feldspar Q u a r t z - f e l d s p a r porphyry p o r p h y r y sills s i l l s and and a r e also a l s o present. present. d i k e s are dikes The is located l o c a t e d within w i t h i n the t h e Cameron Cameron The Cameron Cameron Lake Lake gold g o l d deposit d e p o s i t is Lake Lake Volcanics V o l c a n i c s near n e a r the t h e contact c o n t a c t with w i t h the t h e underlying u n d e r l y i n g Powan Rowan Lake Lake It occurs in sheared mafic volcanic rocks adjacent I t o c c u r s i n s h e a r e d ma i c v o l c a n i c rocks a d j a c e n t to to V o l c a n i c s . Volcanics. t h e highly h i g h l y deformed d e f o r m e d intrusive i n t r u s i v e contact c o n t a c t with w i t h aa gabbroic g a b b r o i c sill. s i l l . The The the shear the Cameron Cameron Lake Lake gold g o l d deposit d e p o s i t is is aa brittle— brittles h e a r zone z o n e hosting h o s t i n g the ductile, d u c t i l e , dextral d e x t r a l strike—slip s t r i k e - s l i p system s y s t e m with w i t h an a n attitude a t t i t u d e of o f 315/700NE 315/700NE Its a n d aa maximum maximum strike s t r i k e length l e n g t h of o f over o v e r 1,000 1 , 0 0 0 m. m. Its width w i d t h varies varies and f r o m 11 1 1 mm to t o6 600 m. mo from Two Two planar p l a n a r fabrics f a b r i c s may be b e seen s e e n within w i t h i n the t h e zones z o n e s of o f high high strain; t o the t h e shear s h e a r zone, z o n e , and a n d aa planar planar strain; a a cleavage c l e a v a g e parallel p a r a l l e l to mineral m i n e r a l alignment a l i g n m e n t (flattening ( f l a t t e n i n g plane p l a n e foliation) f o l i a t i o n ) inclined i n c l i n e d at a t angles angles l e s s than t h a n 4450 5 0 to t o tthe h e sshear h e a r zzone o n e à The T h e intersection i n t e r s e c t i o n of o f these these less foliations f o l i a t i o n s defines d e f i n e s aa lineation l i n e a t i o n which w h i c h pitches p i t c h e s 85°E 850E within w i t h i n the the s h e a r zone. zone. T h i s l i n e a t i o n is p e r p e n d i c u l a r t o t h e i n f e r r e d shear displacement pitches 50W wwithin i t h i n tthe h e shear s h e a r plane. plane. d i s p l a c e m e n t vector v e c t o r which which p i t c h e s 50W T h r e e distinct d i s t i n c tveining v e i n i n g episodes e p i s o d e s have h a v e been b e e n recognized r e c o g n i z e d in i n the the Three c a r b o n a t i z e d rocks r o c k s of o fthe t h Cameron e Cameron Lake Lake Shear S h e a r Zone: Zone: carbonatized e a r l y , barren, b a r r e n , extensional, e x t e n s i o n a l quartz—carbonate quartz-carbonate stage i) early, v e i n s which w h i c h have h a v e been b e e n buckled; buckled; veins s t a g e ii) ii) major system s y s t e m of o f gold—bearing, g o l d - b e a r i n g , pyritic, pyritic, aa major stage q u a r t z - r i c h breccia—veins b r e c c i a - v e i n s (315/70°); ( 3 l5/7O¡ ; quartz—rich aa late s t a g e iii) iii) l a t e group g r o u p of o f cross cross cutting c u t t i n g en e n echelon echelon stage extension e x t e n s i o n veins v e i n s (360/900) ( 3 6 0 / 9 0 0 ) which w h i c h are a r e composed composed o f quartz—carbonate—chlorite—hematite—gold. q u a r t z - c a r b o n a t e - c h l o r i te-hemat i t e - g o l d of The ssignificance i g n i f i c a n c e of o f the t h e stage s t a g e (ii) ( i i ) breccia—veins b r e c c i a - v e i n s has h a s been been The p r e v i o u s l y underestimated. u n d e r e s t i m a t e d . They T h e y represent r e p r e s e n t aa specific s p e c i f i c gold—beargold-bearpreviously i n g rock r o c k type t y p e ata Cameron t Cameron Lake Lake which w h i c h commonly commonly c contains o n t a i n s ggreater reater ing o z / t o n Au. An. Pervasively P e r v a s i v e l y altered a l t e r e dcarbonate—sericite— carbonate-sericitet h a n 0.3 0 . 3 oz/ton than pyrite l a r g evolume v o l u m e of of the the p y r i t e rich r i c hphyllonitic p h y l l o n i t i rocks c r o c k which s w h i c hoccupy o c c u p y aa large lower Cameron Lake h e a r Zone n v e l o p e t the h e breccia—veins b r e c c i a - v e i n s are Cameron LakeSShear Zoneand andeenvelope are lower is readily g r a d e . This T h i s subdivision s u b d i v i s i o n of o f gold—bearing g o l d - b e a r i n g r orock c k t ytypes p e s is readily grade. visible diamond v i s i b l eini nsurface s u r f a c exposures e e x p o s u r e sofo fthe t h deposit e d e p o s iand t and d i a m o n d drill drill deposit is This lineation is perpendicular to the inferred stage i) . core. core. T h e breccia—veins b r e c c i a - v e i n s are h a r a c t e r i z e d bby y angular, a n g u l a r , often often The areccharacterized elongate e l o n g a t e fragments f r a g m e n t s oof f altered a l t e r e d basalt b a s a l which t w h i c h range r a n g efrom f r o m 1 mm mm to to g r e a t e r than t h a n 30 3 0 cm cm in i n size. s i z e . Breccia Breccia fragments f r a g m e n t s may may be b e in i n contact contact greater 1 or o r separated s e p a r a t e d by b y aa vein v e i n matrix m a t r i x (10 ( 1 0 to t o 50%) 5 0 % )of o f quartz, q u a r t z , carbonate, carbonate, a n d plagioclase. p l a g i o c l a s e . Commonly Commonly groups g r o u p s of o f fragments f r a g m e n t s can c a n be b e fitted fitted and t o g e t h e r like l i k e pieces p i e c e s in i n aa jigsaw j i g s a w puzzle. p u z z l e . Pyrite P y r i t e rarely r a r e l y exceeds exceeds together 5% 5 % and and is i s concentrated c o n c e n t r a t e d within w i t h i n the t h e fragments f r a g m e n t s and and forms f o r m s narrow narrow �5 envelopes Gold has e n v e l o p e s surrounding s u r r o u n d i n g the t h e breccia—veins. breccia-veins. h a s been b e e n seen s e e n in in hand as inclusions i n c l u s i o n s within w i t h i n pyrite pyrite h a n d sample s a m p l e and a n d polished p o l i s h e d thin t h i n section s e c t i o n as grains t o pyrite pyrite g r a i n s and and as a s free f r e e gold g o l d within w i t h i n the t h e matrix m a t r i x interstitial i n t e r s t i t i a l to grains. Minor ( l e s s than t h a n 1%) 1 % ) chalcopyrite c h a l c o p y r i t e and a n d rutile f u t i l e are a r e also also grains. M i n o r (less present. present. The The transition t r a n s i t i o n from f r o m cleavage c l e a v a g e development d e v e l o p m e n t to t o brittle b r i t t l e processes processes is manifested m a n i f e s t e d in i n the t h e formation formation w i t h i n the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is within of t o brittle brittle o f veins v e i n s and a n d vein—breccias. vein-breccias. The change c h a n g e from f r o m ductile d u c t i l e to The behavior b e h a v i o r may may be b e the t h e result r e s u l t of o f local l o c a l increases i n c r e a s e s in i n hydrothermal hydrothermal fluid f l u i d pressure p r e s s u r e which w h i c h f facilitated a c i l i t a t e d brittle b r i t t l edeformation d e f o r m a t i o n and a n d vein vein formation by rreducing t r e s s e s . The The f o r m a t i o n by e d u c i n g t the h e eeffective f f e c t i v e normal n o r m a l sstresses. phyllonitic p h y l l o n i t i c rocks r o c k s formed f o r m e d aa sink s i n k for f o rthe t h egold—bearing g o l d - b e a r i n g fluids, fluids, while b r e c c i a veins v e i n sformed f o r m e d major m a j o r conduits c o n d u i t s enhancing e n h a n c i n g fluid £ u i d w h i l e the t h e breccia cc iirc r c ul u l aatt iion. on. The The llocalization o c a l i z a t i o n of o f highly h i g h l yanomalous a n o m a l o u s quantities q u a n t i t i e s of o f gold g o l d along along the LakeS hShear Zoneisisr related e l a t e d to t o the t h e development d e v e l o p m e n t of of t h e Cameron Cameron Lake e a r Zone oblique, o b l i q u e ,secondary, s e c o n d a r y ,bedding—controlled b e d d i n g - c o n t r o l l e d sympathetic s y m p a t h e t i c shear s h e a r zones zones (275/700N) This (275/70ON).. T h i s is i l l u s t r a t e d o n aa dipping d i p p i n g longitudinal longitudinal section Note the t h e 7OOJ 7 O W pitch pitch s e c t i o n compiled c o m p i l e d from f r o m drilling d r i l l i n g (Figure ( F i g u r e 2). 2 ) . Note of o f the t h e gold g o l d shoots, s h o o t s , and a n d the t h e periodicity p e r i o d i c i t y of o f the t h e high h i g h grade g r a d e zones. zones. Figure i s aa simplified s i m p l i f i e d stereographic s t e r e o g r a p h i c projection p r o j e c t i o n of o f the t h e Cameron Cameron F i g u r e 33 is Lake Lake Shear S h e a r Zone Zone and a n d the t h e oblique, o b l i q u e , bedding—controlled, b e d d i n g - c o n t r o l l e d , sympathetic sympathetic splays. s p l a y s . The T h e pitch p i t c h of o f the t h e deposit, d e p o s i t , as a s defined d e f i n e d by by drilling, d r i l l i n g , is is coincident c o i n c i d e n t with w i t h the t h e intersection i n t e r s e c t i o n of o f the t h e these t h e s e two two shear s h e a r systems. systems. The t w o shear s h e a r systems s y s t e m s and and the t h e deposit d e p o s i t is is T h e relationship r e l a t i o n s h i p between b e t w e e n the t h e two illustrated i l l u s t r a t e d diagramatically d i a g r a m a t i c a l l y in i n Figure F i g u r e 4. 4. I t serves s e r v e s to t o explain explain It the w e l l as as t h e complex c o m p l e x subsurface s u b s u r f a c e geometry g e o m e t r y of o f the t h e gold g o l d shoots, s h o o t s , as a s well the t h e existence e x i s t e n c e of o f hanging h a n g i n g wall w a l l and a n d footwall f o o t w a l l zones z o n e s on o n either e i t h e r side side of A t this t h i s stage s t a g e the the o f the t h e main m a i n zone z o n e of o f gold g o l d enrichment. e n r i c h m e n t . At periodicity p e r i o d i c i t y of o f the t h ehigh h i g hgrade g r a d egold g o l dpods p o d s can c a n not n o t be b eadequately adequately explained. explained is illustrated on . FIELD F I E L D TRIP TRIP STOPS STOPS At A t this t h i s stop s t o pwe w ewill w i l examine l e x a m i n e excavated e x c a v a t e d exposures e x p o s u r e s (Figure ( F i g u r e5) 5) of o f the t h egold—bearing g o l d - b e a r i n g rrocks o c k s typical t y p i c a l of o fthe t h eCameron Cameron Lake Lake deposit. deposit. Emphasis w i l l be b e placed p l a c e d on o n the t h e following f o l l o w i n g aspects a s p e c t s of o f the t h e deposit: deposit: E m p h a s i s will 1) 1) 2) 2) 3) 3) K i n e m a t i c indicators i n d i c a t o r s useful u s e f u l in i n the t h e determination d e t e r m i n a t i o n of of Kinematic sense s e n s e of o f shear s h e a r (cleavage, ( c l e a v a g e , lineation, l i n e a t i o n , rotation r o t a t i o n and a n d foldfolding i n g of o f passive p a s s i v e and a n d nonpassive n o n p a s s i v e markers, m a r k e r s , minor m i n o r folds, folds, enechelon e n e c h e l o n veins); v e i n s ); Vein andi tits V e i n pparagenesis a r a g e n e s i s and s rrelation e l a t i o n to t o alteration, a 1 t e r a t i o n , gold gold deposition d e p o s i t i o n and a n d deformational d e f o r m a t i o n a l procesess p r o c e s e s s within w i t h i n the t h e shear shear zone; zone; Shear S h e a r zone z o n e geometry g e o m e t r y and a n d its i t s influence i n f l u e n c e on on gold g o l d deposition deposition and and exploration e x p l o r a t i o nmethods. methods. Discovery D i s c o v e r y Outcrop: O u t c r o p : This T h i s is is the t h e locality l o c a l i t ywhere where the was discovered. d i s c o v e r e d . The The outcrop outcrop t h e original o r i g i n a gold l g o l dshowing s h o w i n g was isis within w i t h i n the t h emain m a i n shear s h e a r system s y s t e m and and consists c o n s i s t s primarily primarily of o f pervasively p e r v a s i v e l y carbonatized c a r b o n a t i z e d pillowed p i l l o w e d basalt, b a s a l t , the t h e least least deformed d e f o r m e d of o f which w h i c h indicates i n d i c a t e s an anoverturned o v e r t u r n e d succession success ion STOP STOP A. A. topping A t the t h e southern s o u t h e r n edge e d g e of o f the the t o p p i n g toward t o w a r d the t h e south. s o u t h . At exposure is the t h e sheared s h e a r e d intrusive i n t r u s i v e contact c o n t a c t with w i t h the the e x p o s u r e is �6 feet F i g u r e 2: 2: Figure Longitudinal L o n g i t u d i n a l section s e c t i o n dipping d i p p i n g 65°N 65ON from f r o m the t h e baseline. baseline. Contours represent the value of grade times thickness C o n t o u r s r e p r e s e n t t h e v a l u e o f g r a d e t i m e s thickness (eg. ( e g . 0.2 0. 2 oz/ton o z / t o n Au Au over o v e r 50 5 0 feet f e e t == 10). 1 0 ) . The T h e contours contours are 7 5 drill d r i l l hole h o l e piercing piercing a r e based b a s e d on o n approximately a p p r o x i m a t e l y 75 points points. . �7 CAMERON LAKE SHEAR ZONE 3 15/65'- 70 S Figure F i g u r e 3: 3: Simplified S i m p l i f i e d stereographic s t e r e o g r a p h i c projection p r o j e c t i o n illustrating i l l u s t r a t i n g the the coincidence c o i n c i d e n c e of o f the t h e pitch p i t c h of o f ore o r e shoots s h o o t s with w i t h the t h e line line of o f intersection i n t e r s e c t i o n of o f the t h e Cameron Cameron Lake L a k e shear s h e a r zone z o n e and and bedding b e d d i n g controlled c o n t r o l l e d shear s h e a r zones. zones a Figure F i g u r e 4: 4: Diagramatic Diagramatic representation r e p r e s e n t a t i o n of o f the t h e spatial s p a t i a l relationship relationship between b e t w e e n ore o r e shoots s h o o t s and a n dthe t h enorth—west n o r t h - w e s t trending t r e n d i n gCameron Cameron Lake east a s t trending trending L a k e sshear h e a r zone z o n e and a n d north—east n o r t h - e a s t t to o e bedding b e d d i n g plane p l a n e shears. shears. �Figure 5: Local geology of discussed in the IÑ Cameron Lake gold deposit with the locations of outcrops text. the TI IÑ 0 m u-i a.' 0 i= >1 m c 0 .d �9 ffootwall o o t w a l l gabbro g a b b r o sill. s i l l . To the t h e north n o r t h is is a a tthin h i n interfiow interflow sedimentary unit (passive marker) which has s e d i m e n t a r y u n i t ( p a s s i v e m a r k e r ) w h i c h h a s been b e e n folded folded Several into i n t o the t h e plane p l a n e of o f the t h e shear s h e a r zone. zone. S e v e r a l early, e a r l y , stage stage markers) extension (i) ( i) e x t e n s i o n vveins e i n s (nonpassive (nonpass ive m a r k e r s ) are a r e present p r e s e n t in in this All t h i s exposure. exposure. A l l of o f these t h e s e have h a v e been b e e n shortened s h o r t e n e d and and Three buckled, b u c k l e d , commonly commonly ddisplaying i s p l a y i n g Z—fold Z - f o l d geometry. geometry. Three stage (ii) gold—bearing breccia—veins are present, one s t a g e ( i i ) g o l d - b e a r i n g b r e c c i a - v e i n s a r e p r e s e n t , one of o f which w h i c h i illustrates l l u s t r a t e s aa distinct d i s t i n c tbrecciated b r e c c i a t e d texture t e x t u r eand and howrrapidly Note how a p i d l y these these ggeometric e o m e t r i c ffit i t of o f fragments. f r a g m e n t s . Note swell. ttypes y p e s of o f veins v e i n s pinch p i n c h and a n d swell. This North STOP B. STOP B. N o r t h Trench: Trench: T h i s ooutcrop, u t c r o p , excavated e x c a v a t e d in i n 1984, 1984, is c r i t i c a l in i n terms of of understanding u n d e r s t a n d i n g the t h e geometry g e o m e t r y of of is critical Att the the t h e deposit. depos it. A t h e western w e s t e r n end e n d of o f this t h i s exposure e x p o s u r e the the intersection i n t e r s e c t i o n between b e t w e e n the t h e main m a i n shear s h e a r system s y s t e m (Cameron (Cameron Lake Lake Shear may bbe S h e a r Zone) Z o n e ) aand n d tthe h e bbedding—controlled e d d i n g - c o n t r o l l e d ssplays p l a y s may e clearly IItt is is at a t this t h i s intersection i n t e r s e c t i o n where w h e r e the t h e most most c l e a r l y seen. seen. dilatant, d i l a t a n t , permeable p e r m e a b l e conditions c o n d i t i o n s were developed d e v e l o p e d which which facilitated f a c i l i t a t e d the t h e migration m i g r a t i o n of o f the t h e gold—bearing gold-bearing hydrothermal The lline h y d r o t h e r m a l fluids. fluids. The i n e oof f intersection i n t e r s e c t i o n defines defines as defined d e f i n e d by b y drilling d r i l l i n g for for tthe h e ppitch i t c h oof f the t h e gold g o l d sshoots h o o t s as The 1 0 0 0 m. m. The large, l a r g e , sstage t a g e (ii), ( i i ), breccia b r e c c i a vein v e i n here here oover v e r 1000 The averaged 0 . 273 oz/ton o z / t o n Au Au over o v e r 22 2 2 channel c h a n n e l samples. samples. T he a v e r a g e d 0.273 is ccut u t bby y an a n array a r r a y oof f north—striking, n o r t h - s t r i k i n g , late, late, bbreccia—vein r e c c i a - v e i n is Note ( i i i ),, eenn eechelon c h e l o n eextension x t e n s i o n veins. veins. Note the the sstage t a g e (iii) bbarren, a r r e n , unaltered u n a l t e r e d bbull's u l l ' s nose n o s e structure s t r u c t u r e developed d e v e l o p e d east east of o f the t h e confluence c o n f l u e n c e of o f the t h e sympathetic, s y m p a t h e t i c , bedding—plane bedding-plane shear s h e a r and a n d the t h e main m a i n structure. structure. STOP C. Vic's The C. V i c ' s trench: trench: The extension e x t e n s i o n of o f the t h e large large breccia—vein b r e c c i a - v e i n s e e n i n t h e l a s t o u t c r o p is e x p o s e d i n t h i s t r e n c h b u t i t s s t r i k e is now p a r a l l e l t o t h a t o f t h e main m a i n sshear h e a r system. s y s t e m . To the t h e ssouth o u t h of o f the t h e breccia—vein breccia-vein occur maÂi c o c c u r relatively r e l a t i v e l y unaltered u n a l t e r e d and a n d undeformed u n d e f o r m e d mafic volcanics v o l c a n i c s and and to t o the t h e north, n o r t h , gold—bearing g o l d - b e a r i n g pervasively pervasively altered, a l t e r e d , phyllonitic p h y l l o n i t i c rocks. rocks, seen in the last outcrop is exposed in this trench but its strike is now parallel to that of the This STOP D. NC—19 trench: D c NC-19 trench: T h i s eexcavated x c a v a t e d exposure e x p o s u r e consists consists of c u t by zones z o n e s of o f cleavage cleavage o f relatively r e l a t i v e l y unaltered u n a l t e r e d basalt b a s a l t cut which w h i c h provide p r o v i d e aa small s m a l l scale, s c a l e , but b u t barren b a r r e n example e x a m p l e of t h e intersection t w o sshear h e a r systems s y s t e m s similar s i m i l a r to t o that t h a t seen seen i n t e r s e c t i o n of o f two Note the iin n the t h e north n o r t h trench. trench. Note t h e collar c o l l a r of o f DDH DDH NC—19, NC-19, 1 9 8 1 , which w h i c h intersected i n t e r s e c t e d 31.6 3 1.6 feet f e e t of o f 0.327 0. 327 ddrilled r i l l e d in i n 1981, is exposed e x p o s e d in i n Vic's Vic's o z / t o n Au (up ( u p dip d i p extension e x t e n s i o n of o f which w h i c h is oz/ton ttrench) r e n c h ) . Two distinct d i s t i n c t cleavages c l e a v a g e s and and the t h e lineat l i n e a t ion ion b e seen s e e n in i n this this pproduced r o d u c e d by b y their t h e i r intersection i n t e r s e c t i o n may may be ooutcrop. utcrop. of the . This IIsland s l a n d Trench: Trench: T h i s ooutcrop u t c r o p cconsists o n s i s ts of of basalt b a s a l t cut c u t by by aa small s m a l l quartz—feldspar q u a r t z - f e l d s p a r porphyry porphyry ddike i k e typical t y p i c a l of o f those t h o s e intersected i n t e r s e c t e d during d u r i n g drilling. drilling Although A l t h o u g h these t h e s e ddikes i k e s are a r e commonly commonly altered, a l t e r e d , they t h e y may may postdate Note the the p o s t d a t e the t h e formation f o r m a t i o n of o f the t h e gold g o l d deposit. deposit. ( i ) extension e x t e n s i o n vein v e i n which w h i c h has h a s been b e e n buckled buckled eearly, a r l y , sstage t a g e (i) (ii) aand n d rotated, r o t a t e d , and a n d the t h e fine—grained f i n e - g r a i n e d siliceous, s i l i c e o u s , stage s t a g e (ii) STOP E. STOP pillowed pillowed �10 b r e c c i a - v e i n eenveloped n v e l o p e d b ybya ap pyritic y r i t i c aalteration 1 t e r a t i o n halo. halo. breccia—vein STOP F. F. Blood B l o o d trench: t r e n c h : At A t this t h i s location l o c a t i o n we w e will w i l l examine examine STOP exposures e x p o s u r e s of o f weakly w e a k l y altered a l t e r e d and a n d cleaved c l e a v e d massive m a s s i v e and and p i l l o w e d b a s a l ts This outcrop, i n t e r p r e t e d to occur pillowed w i t h i n the t h e main m a i n shear s h e a r system, s y s t e m , does d o e s not n o t display d i s p l a y the the within pervasive p e r v a s i v e iron i r o n staining s t a i n i n g produced p r o d u c e d by b y the t h e weathering w e a t h e r i n g of of carbonates c a r b o n a t e s characteristic c h a r a c t e r i s t i c of o f the t h e outcrops o u t c r o p s tot othe t h eeast. east. However, H o w e v e r , even e v e n at a t this t h i s distance d i s t a n c e (approximately ( a p p r o x i m a t e l y 100 1 0 0 feet feet along isolated a l o n g strike) s t r i k e ) from f r o m the t h e centre c e n t r e of o f the t h e deposit, d e p o s i t , isolated stage ( i i ) brecciaveins b r e c c i a - v e i n s and andareas a r e a sofo f disseminated disseminated s t a g e (ii) pyritic p y r i t i c alteration a l t e r a t i o n are a r e found f o u n d suggesting s u g g e s t i n g that t h a t the the potential p o t e n t i a l for f o r additional a d d i t i o n a l economic e c o n o m i c gold g o l d occurrences o c c u r r e n c e s along along the t h e Cameron Cameron Lake Lake Shear S h e a r Zone Zone is is high. high. basalts. . This outcrop, interpreted to occur STOP G. G. Gabbro G a b b r o trench: t r e n c h : In I n this t h i s trench t r e n c h the t h e gabbroic qabbroic STOP sill s i l l which w h i c h occurs o c c u r s in i n the t h e footwall f o o t w a l l to t o the t h e deposit d e p o s i t isis Carbonate e x p o s e d . Note Note the t h e presence p r e s e n c e of o f quartz q u a r t z eyes. eyes Carbonate exposed. alteration a l t e r a t i o n and a n d incipient i n c i p i e n t shearing s h e a r i n g occur o c c u r on on the the northeastern n o r t h e a s t e r n edge e d g e of o f the t h e outcrop o u t c r o p indicating i n d i c a t i n g proximity p r o x i r n i t y to to the t h e footwall f o o t w a l l shear s h e a r zone z o n e and and the t h e mafic m a f i c volcanic v o l c a n i c hosts h o s t s toto t h e deposit. d e p o s i t . On On the t h e southeast s o u t h e a s t edge e d g e of o f the t h e outcrop o u t c r o p is is aa the contact c o n t a c t between b e t w e e n the t h e gabbro q a b b r o and a n d mafic m a f i c volcanics. v o l c a n i c s . This This is interpreted i n t e r p r e t e d as a s aa small s m a l l lobe l o b e of o f gabbro qabbro e x p o s u r e is exposure related t o the t h e larger l a r g e r (over ( o v e r 100 1 0 0 foot f o o t thick) t h i c k ) gabbro g a b b r o sill sill r e l a t e d to located l o c a t e d immediately i m m e d i a t e l y to t o the t h e south. south. . STOP H. H e Hunters H u n t e r ' s trench: t r e n c h : This T h i s exposure e x p o s u r e of o f sheared s h e a r e d and and STOP altered is considered c o n s i d e r e d representative representative a l t e r e d quartz—eye" " q u a r t z - e y e " gabbro g a b b r o is of o f the t h e barren b a r r e n footwall f o o t w a l l shear s h e a r zone z o n e encountered e n c o u n t e r e d during during Note Note the t h e development d e v e l o p m e n t of o f aa green g r e e n mica mica drilling drilling associated Th is green q reen a s s o c i a t e d with w i t h the t h e carbonate c a r b o n a t e alteration. a l t e r a t i o n . This mica mica is i s tentatively t e n t a t i v e l y interpreted i n t e r p r e t e d as a s aa chromium—bearing chromium-bearing phyllosilicate p h y l l o s i l i c a t e resulting r e s u l t i n g from f r o m the t h e alteration a l t e r a t i o n of o f the the gabbro g a b b r o which w h i c h contains c o n t a i n s an a n unusually u n u s u a l l y high h i g h primary p r i m a r y chromium chromium On the t h e southern s o u t h e r n margin m a r g i n of o f the t h e outcrop o u t c r o p are are c o n t e n t c On content. contacts c o n t a c t s with w i t h both b o t h unaltered u n a l t e r e d pillowed p i l l o w e d basalt b a s a l t and and sheared sheared intermediate i n t e r m e d i a t e pyroclastics. pyroclastics. I . Controversy C o n t r o v e r s y trench: t r e n c h : This T h i s outcrop o u t c r o p consists c o n s i s t s of of STOP I. STOP intermediate i n t e r m e d i a t e pyroclastics p y r o c l a s t i c s and and fine—grained f i n e - g r a i n e d bedded bedded Graded sediments G r a d e d bedding b e d d i n g indicates i n d i c a t e s an a n overturned overturned sediments. s u c c e s s i o n facing f a c i n g south. s o u t h . The T h e strike s t r i k e of o f this t h i s unit u n i t is is the the succession s m e as a s the t h e bedding—controlled, b e d d i n g - c o n t r o l l e d , sympathetic s y m p a t h e t i c splay splay same exposed o r e shoot shoot e x p o s e d in i n the t h e north n o r t h trench t r e n c h which w h i c h controls c o n t r o l s the t h e ore g e o m e t r y . Note Note the t h e thin t h i n mafic maf i c dikes d i k e s intruded i n t r u d e d along along geometry. b e d d i n q planes. planes bedding . ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The study s t u d y of o f gold g o l d mineralization m i n e r a l i z a t i o n in i n the t h e Cameron Cameron —- Rwan Rowan Lakes Lakes The b e l t is is part p a r t of o f an a n M.Sc. PI. S c . thesis t h e s i s by b y David David R. R. Tvlelling Mell i n q in i n progress progress belt at a t Carleton C a r l e t o n University, U n i v e r s i t y , under u n d e r the t h e supervision s u p e r v i s i o n of o f David David H. H. W a t k i n s o n and and Lesley L e s l e y B. B . Chorlton. C h o r l t o n . The T h e authors a u t h o r s express e x p r e s s their their Watkinson gratitude K. Howard Howard Poulsen P o u l s e n and a n d Lesley L e s l e y B. B . Choriton C h o r l t o n for f o r their their g r a t i t u d e to t o K. d i r e c t i o n in i n the t h e field f i e l d and a n d for f o r reviewing r e v i e w i n g this t h i s contribution. contribution. direction �11 Funding provided F u n d i n g for f o r this t h i s project p r o j e c t is is in i n ppart art p r o v i d e d by b y Ontario Ontario Geoscience G e o s c i e n c e Grant G r a n t Award #193 # I 9 3 to t o David David H. H. Watkinson, W a t k i n s o n , and a n d through through the The t h e generosity g e n e r o s i t y of o f Nuinsco N u i n s c o Resources R e s o u r c e s Limited. Limited. T h e authors a u t h o r s would would also a l s o like l i k e to t o thank t h a n k Laird L a i r d Tomalty T o m a l t y and a n d Vic V i c Pitrie P i t r i e of o f Nuinsco Nuinsco Resources R e s o u r c e s Limited L i m i t e d for f o r providing p r o v i d i n g the t h e excavated e x c a v a t e d exposures. exposures. REFERENCES REFERENCES Blackburn, B l a c k b u r n , C,E. C . E . and a n d Janes, J a n e s , D.A., D.A., 1 9 8 3 , Gold Deposits D e p o s i t s in in 1983, N o r t h w e s t e r n Ontario; O n t a r i o ; pp.194—210, . 1 9 4 - 2 1 0 , in i n The Geology G e o l o g y of o f Gold G o l d in in Northwestern Ontario, A. C. Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey O n t a r i o , edited e d i t e d by b y A.C. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 10, 278p. 27 8p. Blackburn, B l a c k b u r n , C.E. C . E . and a n d Hailstone, H a i l s t o n e , M.R., M à § R . 1983, 1983, The Geological Geological Environment E n v i r o n m e n t of o f Gold Gold Mineralization, M i n e r a l i z a t i o nCameron—Iwan , Cameron-Rowan Lakes, Lakes, N.W. Paper Presented N.W. OOntario; ntario; P aper P r e s e n t e d at a t the t h eGeoscience G e o s c i e n c e Research Research Seminar, 6 - 7 , 1983, 1 9 8 3 , Toronto, T o r o n t o , Ontario, O n t a r i o , 13p. 13p. S e m i n a r , December December 6—7, Hunter, and A. D., Curtis, C u r t i s , L.W., L.W. a n d Melling, M e l l i n g , D.R., D. R. , 1984, 1984, The Cameron Cameron H u n t e r A.D., Lake Lake Gold Gold Deposit, D e p o s i t , N,W. N.W. Ontario: O n t a r i o : Pioneering P i o n e e r i n g in i n aa Dormant Dormant Gold Gold Camp; (Abstract) ( A b s t r a c t ) CIM C I M Bulletin, B u l l e t i n , Volume V o l u m e 77, 11,Number Number 863, 8 6 3 , p.60. p.60. Kaye, L., 11973, Rwan Lake Kaye, L., 9 7 3 , Rowan Lake Area, A r e a , District D i s t r i c t of o f Kenora; K e n o r a ; Ontario Ontario Division P.831, Geol. Ser., D i v i s i o n of o f Mines, M i n e s , Preliminary P r e l i m i n a r y Map Map P. 83 1 , G eol. S e r . , scale scale 1 inch i n c h to t o 1/4 114 mile. m i l e . Geology G e o l o g y 1972. 1972. Nuinsco N u i n s c o Resources R e s o u r c e s Limited, L i m i t e d , 1983, 1983, Annual A n n u a l Report R e p o r t to t o Shareholders; Shareholders; 1 6p. 16p. 1 Schwerdtner, W.M., D., Schwerdtner, W .M., SStone, tone, D . , Osadetz, O s a d e t z , K., K., Morgan, M o r g a n , 3. J. and a n d Stott, Stott, G.M., G.M. , 1979, 1 9 7 9 , Granitoid G r a n i t o i d Complexes Complexes and a n d The The Archean A r c h e a n Tectonic Tectonic Record R e c o r d iin n The The Southern S o u t h e r n PPart a r t of o f Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; Canadian Canadian Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , Volume Volume 16, 1 6 , p.1965—1977. p . 1965-1977. Trowell, T r o w e l l , N.F., N. F . , Blackburn, B l a c k b u r n , C.E. C ÃE. and a n d Edwards, E d w a r d s , G,R., Go R . , 1980, 1980, Preliminary P r e l i m i n a r y Synthesis S y n t h e s is of o f the t h e Savant S a v a n t Lake—Crow Lake-Crow Lake Lake Metavolcanic—Metasedimentary Metavolcanic-Metasedimentary Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario, O n t a r i o , and and its i t s Bearing B e a r i n g upon upon Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i o Geological Geological Survey, Accompanied S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 30p. A c c o m p a n i e d by b y Chart C h a r t A. A. �Geologic Setting S e t t i n g and and Style Style of of Gold Gold Mineralization M i n e r a l i z a t i o n in in the t h e Lake Lake of of The Woods Woods Area Area Introductory I n t r o d u c t o r y Discussion and and Field Field Guide Guide 31st 3 1 s t Annual Annual Institute I n s t i t u t e on on Lake Lake Superior Superior Geology Geology Kenora, Kenora, Ontario Ontario by 3,C. J . C . Davies Davies 411 41 1 Garrison Garrison Crescent Crescent Saskatoon, Saskatoon, Saskatchewan Saskatchewan P.M. P.M. Smith Smith Ontario O n t a r i o Geological Geolog i c a l Survey Survey 77 7 7 Grenville G r e n v i l l e St. StToronto, Toron t o , Ont. On t . C.E C cE Blackburn Blackburn Resident Resident Geologist Geologist Office Of % i c e Ministry M i n i s t r y of of Natural Natural Resources Resources 808 8 0 8 Robertson Robertson St. StKenora, Kenora, Ontario Ontario �14 SETTING REGIONAL GEOLOGIC GEOLOGIC SETTING --INTRODUCTION - - -,- Recent R e c e n t geological g e o l o g i c a l syntheses s y n t h e s e s (Trowell ( T r o w e l l et e t al a l 1980; 1 9 8 0 ; Blackburn B l a c k b u r n et et aL, a l . , 1985) 1 9 8 5 ) of o f the t h e western w e s t e r n Wabigoori Wabigoon Subprovince S u b p r o v i n c e of o f northwestern northwestern Ontario o tthe h e ggeneral e n e r a l cconclusion o n c l u s i o n that t h a t within w i t h i n the the O n t a r i o have h a v e led l e d tto 'greenstone" is aa general g e n e r a l chroriologic c h r o n o l o g i c pprogression rogress ion " g r e e n s t o n e " belts b e l t s there t h e r e is from mafic, from m a f i c , platformal p l a t f o r m a l volcanic v o l c a n i c sequences s e q u e n c e s upward upward into i n t o interinterClastic mediate t o felsic, f e l s i c , more pyroclastic, p y r o c l a s t i c , volcanic v o l c a n i c sequences. sequences. C las t i c m e d i a t e to with aand n d chemical c h e m i c a l ssediments e d i r n e n t s are a r e commonly commonly a associated ssociated w i t h the t h e upper upper These ssequences. equences. T h e s e ssyntheses y n t h e s e s hhave a v e i in n ggeneral e n e r a l bbeen e e n ccarried a r r i e d oout u t east east of rrecent oof f Lake Lake oof f the t h e Woods, Woods, wwhere h e r e c continuity o n t i n u i t y of e c e n t 1/4 1/4 mile m i l e geoqeologic mapping logic m a p p i n g bby y the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y hhas a s enabled enabled In stratigraphic s t r a t i g r a p h i c correlation c o r r e l a t i o n between b e t w e e n individual i n d i v i d u a l areas. areas. I n the the Woods (Figure 1 1 , two t w o areas a r e a s in i n which which nnorthern o r t h e r n ppart a r t oof f Lake Lake oof f the t h e Woods ( F i g u r e 1), mapping ddetailed etailed m a p p i n g hhas a s been b e e n done, d o n e , , oone n e in i n the t h e northwest, n o r t h w e s t , and a n d centred centred on Shoal Bigstone on S h o a l Lake, L a k e , aand n d the t h e oother t h e r in i n the t h e northeast n o r t h e a s t around a r o u n d Bigstone is presently Bay, are Bay, a r e separated s e p a r a t e d bby y aa central c e n t r a l area a r e a that t h a t is p r e s e n t l yunmapped. unmapped. Within t w o areas a r e a s the t h e general g e n e r a l sequence s e q u e n c e outlined outlined W i t h i n each e a c h oof f these t h e s e two above 1983): a b o v e hhas a s been b e e n demonstrated d e m o n s t r a t e d (Blackburn ( B l a c k b u r n and a n d Janes J a n e s 1983): correlation c o r r e l a t i o n oof f ssequences e q u e n c e s between b e t w e e n the t h e two t w o areas a r e a s has h a s not n o t yet y e t been been cconclusively o n c l u s i v e l y demonstrated. demonstrated In Crowduck Lake—Rush Lake-Rush Bay I n tthe h e nnorthwest, o r t h w e s t , tthe h e eeast—trending a s t - t r e n d i n g Crowduck fault f a u l t zone z o n e sseparates e p a r a t e s two t w o volcanic v o l c a n i c sequences s e q u e n c e s that t h a t can c a n be be ttentatively e n t a t i v e l y correlated, c o r r e l a t e d , notwithstanding n o t w i t h s t a n d i n g lack l a c k of o f geochronologic geochronolog i c Att Shoal iinformation, nformation. A S h o a l Lake a a lower lower mafic, m a f i c , tholeiitic t h o l e i i t i c volcanic volcanic sequence s e q u e n c e occupies o c c u p i e s the t h e core core of o f the t h e Gull G u l l Bay—Bag Bay-Bag Bay Bay anticline, a n t i c l i n e , and and is ssucceeded is u c c e e d e d upward upward oon n either e i t h e r limb l i m b by b y intermediate i n t e r m e d i a t e to t o felsic felsic At A t High High Lake, L a k e , north n o r t h of o f the t h e fault f a u l t zone, z o n e , aa ppyroclastic y r o c l a s t i c sequences. sequences. overlain lower rnafic m a f i c sequence s e q u e n c e is is o v e r l a i n unconformably u n c o n f o r r n a b l y by b y aa clastic clastic sedimentary ( Crowduck Lake Lake Group). Group). s e d i m e n t a r y ssequence e q u e n c e (Crowduck IInn tthe h e northeast, n o r t h e a s t , around a r o u n d Bigstone B i q s t o n e Bay, Bay,. recent r e c e n t mapping m a p p i n g has has demonstrated d e m o n s t r a t e d that t h a t a lower lower sequence s e q u e n c e of of mafic, maf ic, tholeiitic tholei itic core oof vvolcariics, o l c a n i c s , t that h a t llie i e iin n tthe h e core f aa bbroad r o a d ssouthwest o u t h w e s t plunging plunging are aantiform, ntiform, a r e overlain o v e r l a i n by by a a felsic f e l s i c to t o intermediate i n t e r m e d i a t e pyroclastic pyroclastic sequence e t al., a l . , 11985). 9 8 5 ) . Further F u r t h e r to t o the t h e north n o r t h in i n the the s e q u e n c e (Ayer ( A y e r et vicinity v o l c a n i c sequence s e q u e n c e that t h a t is is probably probably v i c i n i t y of o f Kenora, K e n o r a , aa mafic maf i c volcanic correlative with correlative w i t h that t h a t at a t Bigstone B i g s t o n e Bay, Bay, has h a s been b e e n isoclinally isocl i n a l l y folded f o l d e d about a b o u t nnortheast o r t h e a s t ttrending r e n d i n g axes. axes. Following F o l l o w i n g aare r e more more ddetailed e t a i l e d ddescriptions e s c r i p t i o n s of o f individual ind i v id u a l w i l l be b e visited v i s i t e d on o n the t h e field field ssub—areas, u b - a r e a s , aall l l except e x c e p t one o n e oof f which w h i c h will is included i n c l u d e d because b e c a u s e of o f its i t s key key ttrip: r i p : the t h e Shoal S h o a l Lake area a r e a is situation s i t u a t i o n in i n understanding u n d e r s t a n d i n g Lake Lake of o f the t h e Woods Woods stratigraphy, s t r a t i g r a p h y , and and t. tthe h e position p o s i t i o n of o f gold g o l d emplacement e m p l a c e m e n t wwithin i t h i n iit. - HIGH H I G H LAKE General G e n e r a l geology, g e o l o g y , adapted a d a p t e d from f r o m Davies Dav ies (1965), ( 1 9 6 5 1 , is is illustrated illustrated The ooldest 2. The l d e s t rrocks, ocks, a a thick t h i c k sequence s e q u e n c e of o f basaltic basaltic iin n Figure F i g u r e 2. and mmafic flows f l o w s and a f i c ssubvolcanic u b v o l c a n i c i intrusions, n t r u s i o n s , have h a v e been b e e n intruded i n t r u d e d by by r a n o d i o r i t e , porphyritic p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d by porphyry porphyry t o n a l i t e , ggranodiorite, dikes. d i k e s . The T h e granitic g r a n i t i c complex c o m p l e x extends e x t e n d s west w e s t for f o r at a t least l e a s t 50 5 0 km km and, and, especially is characterized c h a r a c t e r i z e d by by e s p e c i a l l y in i n Manitoba, M a n i t o b a , the t h e dominant d o m i n a n t phase p h a s e is tonalite, �A Figure tH :1 —i HH" 1: A \ '/ 4 \ ?M?èrs / / 5I — Ar 0 lADY Figure2o 4 5 •A -- / - r - /1 'A / //-A/ I I j/, A o- - a' 4 - I — S / 'A 18athO!k L h MA4A'j Ar /4 - 7 Jot 0Figure3 K IA /// / ( WsI 'p/'4 4 /s,A AY/ / / /1/) 4t t H±1 \ A" / - C fT A I 'I Fig4 A I,? A I• / / /I / / I / / / '\ A"AA '1 AZ rugure5 Z - / )(AAAA A,AAAAAA-A / A / I ) / / A / / I 7 7- Figure 6 FI - T / / / — Dl c [ EARLY PAEAMRDIAN MIDDLE lOCATE PREY DMDAIAN PRECAMBRIAN CENOZOIC PHANEIIOZOIC h ^ J3 -^ -3 u IÑ (S n3 General geology of the Lake of the Woods Area (modified from Blackburn, 1981). 'A c Ui �91 OQ0 °O 0 . I Road Lake Shoal o + 4- )Oo C +D hO + + + + + + + + + + + + + 4 ++ + + + + + + f + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + .,++..++,+t+;+++ * + + + + + + Cl) + a — + xx \XX x x .CDOOOD) -." \x\x XXXX \xxx + + + + o O9 + + '+4' 4'-I + CD D + ++++++++++++ + +Ffl+ + + + CD ++ iU) f • + ++ + +-f + + + + C) I +nl -f + + + + + ('1++ ..+ + + + — CD _ +++ 0 V $ C) b O 3o.o 'N .m...:.:.:..:.. + oo -n Q.C)D) + .... CD nO o() + ° -. oj ++ c1;: 0O,Oo00 L \xxxx \xx \xxx + X xxxx\X X X (D X XXXXX\X ::::::::::::::::::X x xxxxxx'\ X + x X x X X x x o IÑ 0 + 11\i (1\1 3. l( c2:J 0g Ni E;;x:r# P-ij �17 euhedral e u h e d r a l microcline m i c r o c l i n e phenocrysts. p h e n o c r y s ts a At A t High High Lake, L a k e , large l a r g e basaltic b a s a l t i c blocks b l o c k s are a r e enclosed e n c l o s e d in i n and a n d cut cut by b y the t h e porphyritic p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d related r e l a t e d dikes, d i k e s , and a n d are a r e interinterpreted t o be b e roof r o o f pendants p e n d a n t s in i n aa subvolcanic s u b v o l c a n i c intrusion. intrusion. The non— nonp r e t e d to The porphyritic p o r p h y r i t i c granodiorite q r a n o d i o r i t e locally l o c a l l y contains c o n t a i n s abundant, a b u n d a n t , small, s m a l l , round round mafic i t is is typically t y p i c a l l y less l e s s deformed d e f o r m e d than t h a n the the m a f i c inclusions; i n c l u s i o n s ; it porphyritic i t is is yyounger, o u n g e r , intruding i n t r u d i n g and and p o r p h y r i t i c granodiorite, g r a n o d i o r i t e , suggesting s u g g e s t i n g it deforming S u t h e r l a n d and a n d Colvine Colv i n e d e f o r m i n g the t h e porphyritic p o r p h y r i t i c granodiorite. g r a n o d i o r i t e . Sutherland (1979) ( 1 979 ) concluded c o n c l u d e d that, t h a t , although a 1 t h o u g h it it is is ppossible o s s i b l e that t h a t the t h e two t w o were were intruded i n t r u d e d in i n distinct d i s t i n c t events, e v e n t s , the t h e similar s i m i l a r composition c o m p o s i t i o n of o f both both rocks r o c k s suggests s u g g e s t s that t h a t they t h e y were more likely l i k e l y separate s e p a r a t e pulses p u l s e s of o f the the same s a m e intrusive i n t r u s i v e event. event. Both B o t h the t h e basalt b a s a l t and and the t h e porphyry p o r p h y r y are a r e overlain o v e r l a i n unconformably unconformably by Conglomerate, Crowduck Lake Lake Group. Group. C o n g l o m e r a t e , sandsandb y sediments s e d i m e n t s of o f the t h e Crowduck stone, s t o n e , greywacke, g r e y w a c k e , argillite a r q i l l i t e and a n d chert c h e r t have h a v e an a n apparent a p p a r e n t thickness thickness of 2 0 0 0 metres. metres. o f 2000 Tight T i g h t folding f o l d i n g of o f both b o t h the t h e sediments s e d i m e n t s and and felsic f e l s i c volcanics v o l c a n i c s is is associated a s s o c i a t e d with w i t h faulting f a u l t i n g and a n d shearing s h e a r i n g that t h a t extend e x t e n d into i n t o the t h e grano— granodiorite. d i o r i t e . The T h e over—all o v e r - a l l pattern p a t t e r n of o f both b o t h folds f o l d s and and faults f a u l t s indicates indicates dextral f a u l t s . , Within W i t h i n the the d e x t r a l movement along a l o n g the t h e east—trending e a s t - t r e n d i n g faults. porphyritic s e t of o f fractures f r a c t u r e s trends t r e n d s east— eastp o r p h y r i t i c granodiorite g r a n o d i o r i t e aa second s e c o n d set northeast. northeast. Mineralization is largely l a r g e l y confined c o n f i n e d to t o fractures f r a c t u r e s in i n the the M i n e r a l i z a t i o n is porphyritic t o shears s h e a r s in i n both b o t h the t h e adjacent adjacent p o r p h y r i t i c granodiorite g r a n o d i o r i t e and a n d to basalt b a s a l t and and the t h e overlying o v e r l y i n g conglomerate. c o n g l o m e r a t e . Molybdenite M o l y b d e n i t e and a n d chalco— chalcopyrite, a r e widely w i d e l y distributed d i s t r i b u t e d in i n the the p y r i t e , in i n trace t r a c e amounts, a m o u n t s , are porphyritic p o r p h y r i t i c granodiorite; g r a n o d i o r i t e ; they t h e y are a r e more more highly h i g h l y concentrated, c o n c e n t r a t e d , with with quartz, t o east—trending e a s t - t r e n d i n g faults, f a u l t s , and a n d are are q u a r t z , in i n shear s h e a r zones z o n e s adjacent a d j a c e n t to accompanied is also a l s o associated a s s o c i a t e d with w i t h pyrite, pyrite, a c c o m p a n i e d by b y minor m i n o r gold. g o l d . Gold G o l d is chalcopyrite and pyrrhotite in shears at or near the contact c h a l c o p y r i t e a n d p y r r h o t i t e i n s h e a r s a t o r n e a r t h e c o n t a c t with with basalt, b a s a l t , and and in i n quartz q u a r t z lenses l e n s e s and and irregular i r r e g u l a r masses m a s s e s in i n porphyry, porphyry, basalt b a s a l t or o r conglomerate c o n g l o m e r a t e where w h e r e there t h e r e are a r e complex c o m p l e x areas a r e a s of of competency A l l these t h e s e mineralization m i n e r a l i z a t i o n types t y p e s will w i l l be be c o m p e t e n c y contrast. c o n t r a s t . All illustrated 1, 22 and a n d 3). 3 ) . Pedora Pedora i l l u s t r a t e d by by field f i e l d trip t r i p stops s t o p s (Stops ( S t o p s 1, (1976) ( I 976 ) has h a s suggested s u g g e s t e d that t h a t mineralization m i n e r a l i z a t i o n is is arranged a r r a n g e d about a b o u t the the s o u t h e r n , non—porphyritic n o n - p o r p h y r i t i c granodiorite q r a n o d i o r i t e phase p h a s e in i n aa zonal z o n a l pattern, pattern, southern, and a n d that t h a t the t h e mineralizing m i n e r a l i z i n g fluid f l u i d may may have h a v e originated o r i g i n a t e d from f r o m the the southern s o u t h e r n phase. phase. SHOAL LAKE SHOAL LAKE - - General G e n e r a l geology, g e o l o g y , adapted a d a p t e d from f r o m Davies D a v i e s (1983), ( 1 983 ) , is is illustrated illustrated in Figure 3. i n F i g u r e 3. Tholeiitic T h o l e i i t i c basalts, b a s a l t s , interlayered i n t e r l a y e r e d with w i t h mafic maÂi c and and u l t r a m a f i c sills s i l l s and and minor m i n o r komatiitic k o m a t i i t i c basalts, b a s a l t s , are a r e overlain o v e r l a i n by by ultramafic calc—alkaline t o felsic f e l s i c pyroclastics. pyroclastics. Overlying c a l c - a l k a l i n e intermediate i n t e r m e d i a t e to Overlying these is an a n upper u p p e r sequence s e q u e n c e of o f mafic m a f i c flows f l o w s with w i t h some some felsic felsic t h e s e is volcanic s i l l - l i k e body body of o f anorthositic a n o r t h o s i t i c gabbro g a b b r o to to v o l c a n i c lenses. l e n s e s . AA sill—like diorite d i o r i t e (the ( t h e Stevens S t e v e n s Island I s l a n d Diorite) D i o r i t e ) lies l i e s near n e a r the t h e top t o p of o f the the tholeiitic The tthickness t h o l e i i t i c sequence. s e q u e n c e . The h i c k n e s s of o f the t h e northwest—facing n o r t h w e s t-f a c i n g volcanics is estimated e s t i m a t e d to t o be b e 9000 9 0 0 0 metres. metres. v o l c a n i c s is The The Canoe Canoe Lake L a k e stock s t o c k of o f altered a l t e r e d quartz q u a r t z diorite d i o r i t e terminates, t e r m i n a t e s , to to t h e southwest, s o u t h w e s t , against a g a i n s t the t h e tholeiitic t h o l e i i t i c basalts, b a s a l t s , and a n d aa major m a j o r anti— antithe dine i t . The The fresher f r e s h e r Snowshoe Snowshoe Bay Bay grano— granoc l i n eextends e x t e n d s southwest s o u t h w e s t from f r o m it. it d i o r i t e intruded i n t r u d e d the t h e intermediate i n t e r m e d i a t e to t o felsic f e l s i c sequence; s e q u e n c e ; it diorite continues c o n t i n u e s an a n unknown unknown distance d i s t a n c e into i n t o Manitoba M a n i t o b a and a n d is is of o f batholithic batholithic �+ + + + + + + + + + + + + + • __— + V ÷ + + + -- y/ "'i - 3: • / / —) / -. / / VOV V VVVV + + + • — • + + + + + + + + + + + -- + + V — •••. + + + + + + + + + + + + + + + + + + + + + + + + + + ÷ + + + + ÷ + + + + + + + + + + + + + + + + + + + + + + + + + + + , + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ± + + + + + DlORlTE÷÷÷÷ + 1- + + * + + + + + + + + + + • ++ + + + + ÷ + v + + + + + + + + VV + VV + +++++++÷v VV + 2 + yyyy • VV + + + + + + + VVV : •,pc vYI__ Labyrinth Bay V VVVVVVV VVVVV OJ ::::::::::: + ++ + V + + + + 1- + + ••••,• + + + • + + + + + + + + + + + /'vvvvvvv + vvvvvv vvv + + + ÷ + +::: ' vI'vv + + + + +—* I- V + ÷ + + +' vv + + + + + + MINE+÷11+÷++÷+÷+/ .÷ + + + + + + + + *f+ + + + + V'- v + i" VV4VVVvv + + + + + / + + + + + + + + + V + + + + + + + + + + + S.. S7 Ptarmigan Bay upper volcanic rocks LIII middle cac—akahne intermediate and felsic volcanic rocks lower tholeiiflc to komatiitic mafic volcanic rocks and sills 0 + + •:•. VVV V + + + + + + + + + + + CANOE LAKE ++++++++++ + + MIKADO + + + + v• v VVV• vv V + vvvvvvvvv VVV VV VVV + + MINE vv OLYMPI V VV VV v V 0VVV VVV VVVV vSvvvV VV VVVV VVVVV vvvv VVV + + + + + + + + Echo Bay T. Geology of the Shoal. Lake area (modified from Davies and Smith, 1984). • [ij granitic intrusive rocks Figure / / / // / + + + + Day VV+++ vV Clytie vv VV • gold occurrence diorite, quartz duorite, gabbro, anorthositic gabbro —i,' / / ///1 ,> , / GRANODlORITE,/,', '/# // / — / RUSH BAY FAULT /. / CEDAR ISLAND MINE ShoalLake + + + 7 SNOWSHOE .47 + :+ + + ÷ + + + + + + + + r-4 + + — ::GROWDUCK LAKE ay �19 dimensions. d imens i o n s . In I n much much of o f the t h e Shoal S h o a l Lake L a k e area a r e a the t h e principal p r i n c i p a l foliation £0 i a t i o n direction North i s east—northeast. east-northeast. N o r t h of o f the t h e lake l a k e the t h e foliation foliation d i r e c t i o n is bends east as the Crowduck Lake—Rush Bay dextral fault is b e n d s e a s t a s t h e Crowduck Lake-Rush d e x t r a l f a u l t zone z o n e is approached. a p p r o a c h e d . Within W i t h i n aa "shadow " s h a d o w zone" z o n e " southwest s o u t h w e s t of o f the t h e Canoe C a n o e Lake Lake stock, v o l c a n i c s are a r e not n o t foliated, f o l i a t e d , but b u t aa series s e r i e s of of s t o c k , the t h e mafic ma i c volcanics east—southeast e a s t - s o u t h e a s t faults f a u l t s with w i t h aa large l a r g e vertical v e r t i c a l component c o m p o n e n t of o f movement has These are h a s offset o f f s e t the t h e volcanic v o l c a n i c stratigraphy. stratigraphy. T h e s e faults f a u l t s are interpreted i n t e r p r e t e d to t o be b e related r e l a t e d to t o emplacement e m p l a c e m e n t of o f the t h e Canoe C a n o e Lake Lake stock. Faults stock. F a u l t s with w i t h vertical v e r t i c a l displacement d i s p l a c e m e n t have h a v e also a l s o been b e e n interinterpreted p r e t e d to t o coincide c o i n c i d e with w i t h the t h e north n o r t h and and south s o u t h contacts c o n t a c t s of o f the the Snowshoe f a u l t i n q parallel p a r a l l e l to t o volcanic v o l c a n i c strati— stratiS n o w s h o e Bay Bay pluton; p l u t o n ; some faulting graphy q r a p h y may also a l s o be b e attributed a t t r i b u t e d to t o emplacement e m p l a c e m e n t of o f the t h e pluton. pluton. Most gold g o l d occurrences o c c u r r e n c e s are a r e in i n the t h e tholeiitic t h o l e i i t i c sequence. s e q u e n c e . Those Those associated a s s o c i a t e d with w i t h the t h e east—southeast e a s t - s o u t h e a s t faults f a u l t s typically t y p i c a l l y consist c o n s i s t of o f aa chioritic Silici— c h l o r i t i c shear s h e a r zone z o n e within w i t h i n which w h i c h aa felsite f e l s i t e dike d i k e occurs. occurs. Silicification, or lenses, l e n s e s , is is f i c a t i o n , commonly commonly in i n the t h e form f o r m of o f quartz q u a r t z veins v e i n s or accompanied a c c o m p a n i e d by b y pyrite, p y r i t e , traces t r a c e s of o f base—metal b a s e - m e t a l suiphides, s u l p h i d e s , and a n d rare rare visible v i s i b l e qold. g o l d . Some Some gold g o l d was w a s produced p r o d u c e d from f r o m fracture f r a c t u r e zones z o n e s of o f this this type a t the t h e Olympia O l y m p i a and a n d Cedar C e d a r Island I s l a n d Mines. Mines. t y p e at South—southeast S o u t h - s o u t h e a s t fractures f r a c t u r e s developed d e v e l o p e d near n e a r the t h e margin marg i n of o f the the Canoe At its intrusion. intrusion. A t the t h e Mikado Mikado Mine, Mine, C a n o e Lake L a k e stock s t o c k following f o l l o w i n g its gold i s associated a s s o c i a t e d with w i t h quartz q u a r t z veins v e i n s and a n d stringers s t r i n g e r s in i n such s u c h aa g o l d is fracture crosses basalt b a s a l t and a n d a thick t h i c k dike d i k e of o f quartz quartz f r a c t u r e which w h i c h crosses diorite. d i o r i t e . Pyrite, P y r i t e , chalcopyrite, c h a l c o p y r i t e , tetradymite t e t r a d y m i t e and a n d bismuthinite b i s m u t h i n i t e also also occur o c c u r in i n the t h e quartz. quartz. Fault F a u l t and a n d shear s h e a r zones z o n e s parallel p a r a l l e l to t o volcanic v o l c a n i c stratigraphy s t r a t i g r a p h y are are mostly m o s t l y narrow n a r r o w and a n d quartz q u a r t z veining v e i n i n g within w i t h i n them t h e m is is similarly s i m i l a r l y narrow narrow and a t the t h e Duport D u p o r t Mine M i n e is is much much wider, wider, a n d discontinuous. d i s c o n t i n u o u s . The T h e fault f a u l t at and a n d gold g o l d occurs o c c u r s with w i t h quartz q u a r t z in i n zones z o n e s where w h e r e competency c o m p e t e n c y contrast contrast accompanied a c c o m p a n i e d by b y brittle b r i t t l e fracturing f r a c t u r i n g resulted r e s u l t e d in i n greater q r e a t e r permepermeability There a b i l i t y (Smith ( S m i t h1984) 1 9 8 4 ). T h e r e is is a a strong s t r o n g association a s s o c i a t i o n of o f gold gold with it also a l s o occurs o c c u r s as as free f r e e grains g r a i n s associated associated w i t h arsenopyrite, a r s e n o p y r i t e , but b u t it with w i t h pyrrhotite, p y r r h o t i t e , pyrite p y r i t e and a n d chalcopyrite. chalcopyrite. . ECHO, CLEARWATER EC H O ,- ..-PTARMIGAN PTARMIGAN AND AND-------CLEARWATER BAYS BAYS 4 . - No N o recent r e c e n t systematic s y s t e m a t i c mapping m a p p i n g of o f this t h i s area a r e a has h a s been b e e n carried carried out ( 1 9 3 6 9 , but b u t it it is is ppossible o s s i b l e that t h a t most m o s t of of o u t since s i n c e that t h a t of o f Thomson Thomson (1936), the a r e equivalent e q u i v a l e n t to t o the t h e calc—alkaline c a l c - a l k a l i n e felsic felsic t h e vvolcanic o l c a n i c rocks r o c k s are sequence s e q u e n c e of o f Shoal S h o a l Lake. Lake. s e q u e n c e and a n d upper u p p e r mafic maÂi c sequence The The ddominant o m i n a n t sstructural t r u c t u r a l feature f e a t u r e is is the t h e Crowduck Crowduck Lake—Rush Lake-Rush Bay fault f a u l t zone z o n e in i n which w h i c h the t h e volcanic v o l c a n i c rocks r o c k s are a r e strongly s t r o n g l y to t o intensely intensely foliated. Carbonate is abundant, a b u n d a n t , bbut u t only o n l y in i n aa few f e w places p l a c e s is is foliated. C a r b o n a t e is there t h e r e evidence e v i d e n c e of o f much much mmobilization o b i l i z a t i o n oof f ssilica. i l i c a . Where Where deformation deformat ion has h a s been b e e n greatest, g r e a t e s t , thin t h i n quartz q u a r t z veinlets v e i n l e t s and a n d lenses l e n s e s occur o c c u r and a n d fine fine pyrite is disseminated d i s s e m i n a t e d in i n the t h e schists, s c h i s t s , but b u t only o n l y minor m i n o r amounts a m o u n t s of of p y r i t e is gold g o l d have h a v e been b e e n found. f o u n d . The T h e zone z o n e has h a s been b e e n traced t r a c e d to t o the t h e east e a s t at at least l e a s t as a s far f a r as asthe t h esouth s o u t hshore s h o r eofo fthe t h Northern e N o r t h e r nPeninsula: P e n i n s u l a : Ayer Ayer (1984) ( 1 9 8 4 ) has h a s recently r e c e n t l y suggested s u g g e s t e d its i t s continuation c o n t i n u a t i o n right r i g h t across across the the northern n o r t h e r n part p a r t of o f Lake Lake of o f the t h e Woods Woods to t o Andrew Andrew Bay. Bay. Around t o felsic f e l s i c pyroclastics pyroclas tics Around Clearwater C l e a r w a t e r Bay, Bay, intermediate i n t e r m e d i a t e to predominate p r e d o m i n a t e and a n d are a r e interlayered i n t e r l a y e r e d with w i t h basalt b a s a l t and and overlain o v e r l a i n by by fine fine clastic c l a s t i c sediments. sediments. e a s t - s t r i k i n g synclinal s y n c l i n a l axis a x i s lies l i e s along along An east—striking �20 tthe h e bbay, a y , and e l l - d e v e l o p e d ffoliation o l i a t i o n is is w i t h i n 330 0 degrees d e g r e e s of of and aa w well—developed within number oof eeast. a s t . AA number f qquartz—porphyry u a r t z - p o r p h y r y ddikes i k e s aalso l s o trend t r e n d east, e a s t , possibly possibly Quartz marking f n a r k i n q zones z o n e s of o f shearing. shearing. Q u a r t z veins v e i n s are a r e mainly m a i n l y in i n areas a r e a s of of iintermediate n t e r m e d i a t e llapilli—tuff a p i l l i - t u f f aand n d ttuff—breccia, u f  £ - b r e c c i a eespecially s p e c i a l l y in i n the the K e n r i c i a Mine Mine (Stop ( S t o p 44 on vvicinity i c i n i t y of o f the t h e former f o r m e r Kenricia on the t h e field f i e l d trip) trip). North 1 7 , foliated f o l i a t e d basalt basalt N o r t h oof f the t h e ppyroclastics, y r o c l a s t i c s , and a n d Highway 17, It with is iin outcrops o u t c r o p s over o v e r aa width w i d t h of o f i000m. 1000m. I t is n ccontact ontact w i t h granitic granitic may bbe rrocks o c k s tto o the t h e nnorth, o r t h , aand n d may e eequivalent q u i v a l e n t to t o the t h e tholeiitic tholeiitic sequence s e q u e n c e of o f Shoal S h o a l Lake. Lake. KENO RA KENORA A wedge—shaped w e d g e - s h a p e d area a r e a of o f volcanic v o l c a n i c and a n d sedimentary s e d i m e n t a r y rocks r o c k s extends extends northeast main n o r t h e a s t from f r o m the the m a i n body body oof f supracrustal s u p r a c r u s t a l rocks r o c k s in i n the the vicinity of Kenora K e n o r a (Figure ( F i q u r e 4). 4). IIntensely n t e n s e l y ddeformed e f o r m e d gneisses q n e i s s e s lie lie v i c i n i t y of tto o the t h e nnorthwest, o r t h w e s t , aand n d to t o the t h e east e a s t aare r e ggranitoid r a n i t o i d sstocks t o c k s which w h i c h may Tholeiitic be b e related r e l a t e d to t o the t h e Dryberry D r y b e r r y batholith. batholith. T h o l e i i t i c basalts b a s a l t s are are overlain o v e r l a i n by by fine—grained f i n e - g r a i n e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastics, pyroclas tics, which w h i c h are a r e in i n turn t u r n overlain o v e r l a i n by b y clastic c l a s t i c sediments. s e d i m e n t s . A gabbroic g a b b r o i c sill sill lies l i e s near n e a r the t h e top t o p of o f the t h e basaltic b a s a l t i c sequence. sequence, The principal p r i n c i p a l direction d i r e c t i o n of o f faulting, f a u l t i n g , the t h e weak to to strong strong foliation, and the trace of fold axes are all approximately f o l i a t i o n , and t h e t r a c e of f o l d axes a r e a l l approximately Att pparallel a r a l l e l to t o wedge boundaries b o u n d a r i e s and and converge c o n v e r g e to t o the t h e northeast. northeast. A the northwest side of the wedge mafic rocks are highly deformed t h e n o r t h w e s t s i d e o f t h e wedge m a f i c r o c k s a r e h i g h l y d e f o r m e d metamorphosed aand nd m e t a m o r p h o s e d bbut u t elsewhere e l s e w h e r e primary p r i m a r y features f e a t u r e s are a r e largely largely An ooval monzonite, ppreserved. reserved. An v a l sstock t o c k oof f pporphyritic o r p h y r i t i c qquartz uartz m o n z o n i t e . which which llies i e s on on tthe h e trace t r a c e of o f the t h e Airport A i r p o r t Anticline, A n t i c l i n e , is is only o n l y weakly weakly foliated. foliated. All A l l tthe h e known vvolcanic—hosted o l c a n i c - h o s t e d q gold o l d ooccurrences c c u r r e n c e s eexcept x c e p t one o n e are are are associated with quartz veins or silicified i n bbasalt a s a l t and a n d a r e a s s o c i a t e d w i t h q u a r t z v e i n s or s i l i c i f i e d in Fractured mineralized l i e in in sshears. hears. F r a c t u r e d aand nd m i n e r a l i z e d felsite f e l s i t e dikes d i k e s which w h i c h lie The mineralized ssheared h e a r e d basalt b a s a l t have h a v e also a l s o been b e e n investigated. investigated. mineralized zones z o n e s trend t r e n d northeast n o r t h e a s t and and are a r e interpreted i n t e r p r e t e d to t o be be related r e l a t e d to to Tourmaline movement along near—vertical axial planar shears, T o u m a l i n e and and movement a l o n g n e a r - v e r t i c a l a x i a l p l a n a r s h e a r s minor a r e associated a s s o c i a t e d with w i t h most most quartz q u a r t z veins; v e i n s ; chlorite, chlorite, m i n o r suiphides s u l p h i d es are hiotite, b i o t i t e , carbonate c a r b o n a t e and a n d suiphides s u l p h i d e s are a r e common common in i n the t h e sheared sheared basalt. basal t. o c c u r r e n c e s in i n the t h e Island I s l a n d Lake Lake quartz q u a r t z diorite d i o r i t e are are Gold occurrences Most of the mineralization with shearing. Most o f t h e m i n e r a l i z a t i o n is is iin n or or aassociated ssociated with shearing. Gold is near quartz veins which occupy zones of dilatancy. n e a r q u a r t z v e i n s which o c c u p y z o n e s o f d i l a t a n c y . Gold is with aassociated ssociated w i t h ppyrite, y r i t e , especially e s p e c i a l l y along a l o n g minor m i n o r ffractures r a c t u r e s in i n the the Dike—like quartz and the host diorite or quartz diorite. D i k e - l i k e bodies bodies q u a r t z a n d t h e h o s t d i o r i t e or q u a r t z d i o r i t e . e nnear e a r mmineralized i n e r a l i z e d a nand d s isilicified l i c i f i e d sshears h e a r s at at oof f ultra—mylonite u l t r a - m y l o n i t e l ilie three t h r e e ooccurrences. ccurrences Stop S t o p 5 on on the t h e field f i e l d trip t r i p illustrates i l l u s t r a t e s the t h e former f o r m e r type, t y p e , while while is hosted by the Island Lake mineralization at Stop 6 m i n e r a l i z a t i o n a t S t o p 6 is h o s t e d by t h e I s l a n d Lake quartz quartz diorite. diorite. . . BIGSTONE BAY Tholeiitic with T h o l e i i t i c basalts b a s a l ts w i t h an a n eestimated s t i m a t e d thickness t h i c k n e s s of o f 8000m 8000m are uunderlie n d e r l i e Bigstone B i g s t o n e Bay Bay aand nd a r e broadly b r o a d l y folded f o l d e d about a b o u t the t h e Hay Island Island �Fiqure 4: Geology of the Kenora area (modified from King, 1983). �22 Antiform A n t i f o r m (Figure ( F i g u r e 5). 5 ) . Mafic M a f i c and a n d ultramafic u l t r a m a f i c sills s i l l s or or flows, f l o w s , which which lie l i e near n e a r the t h e top t o p of o f the t h e sequence, s e q u e n c e , are a r e exposed e x p o s e d on o n the t h e south s o u t h limb limb of o f the t h e fold f o l d and a n d on o n the t h e northwest n o r t h w e s t limb l i m b near n e a r the t h e fold f o l d nose. n o s e . The The inafic by iintermediate t o felsic f e l s i c pyroclastics pyroclas tics r n a f i c r rocks o c k s aare r e ooverlain v e r l a i n by n t e r m e d i a t e to and a n d flows f l o w s which w h i c h occupy o c c u p y the t h e core core of o f the t h e Sultana S u l t a n a syricline; s y n c l i n e ; the the syncline t ohave h a v e been b e e n refolded refolded s y n c l i n e and a n d oother t h e r parallel p a r a l l e l folds f o l d sappear a p p e a r to about a b o u t the t h e Hay Hay Island I s l a n d Antiform. Antiform. G r a n o d i o r i t e of o f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h occupies o c c u p i e s the t h e core core of of Granodiorite the B a s a l t s typically t y p i c a l l y show show little l i t t l e change c h a n g e in i n texture t e x t u r e or or t h e antiform. a n t i f o r m . Basalts The Quarry grain g r a i n size s i z e adjacent a d j a c e n t to t o the t h e contact, contact. Q u a r r y Island I s l a n d stock, stock, which w h i c h intruded i n t r u d e d the t h e top t o p of o f the t h e basalt b a s a l t sequence, s e q u e n c e , similarly s i m i l a r l y shows shows no no contact medium—grained i t consists c o n s i s t s oof f m e d i u m - g r a i n e d quartz q u a r t z diorite diorite c o n t a c t effects; e f f e c t s ; it with w i t h aa central c e n t r a l core core of o f porphyritic p o r p h y r i t i c granite g r a n i t e in i n the t h e northeast n o r t h e a s t part part of of Quarry Q u a r r y Island I s l a n d and a n d western w e s t e r n part p a r t of o f Sultana S u l t a n a Island. Island. On the t h e northwest n o r t h w e s t limb l i m b of o f the t h e antiform, a n t i f o r m , virtually v i r t u a l l y all a l l of o f the the gold to g o l d occurrences o c c u r r e n c e s are a r e associated a s s o c i a t e d with w i t h shear s h e a r zones z o n e s parallel p a r a l l e l to v o l c a n i c stratigraphy. s t r a t i g r a p h y . Quartz Q u a r t z veins v e i n s with w i t h pyrite, p y r i t e , many of o f which which volcanic contain s w e l l or or occur o c c u r as as c o n t a i n tourrnaline, t o u r m a l i n e , ttypically y p i c a l l y ppinch i n c h and a n d swell en—echelon e n - e c h e l o n lenses l e n s e s in i n the t h e chlorite c h l o r i t e schists. s c h i s t s . Visible V i s i b l e gold g o l d is is This erratically e r r a t i c a l l y distributed d i s t r i b u t e d in i n the t h e quartz. quartz. T h i s type t y p e will w i l l be b e viewed viewed a t Stop S t o p 77 on on the t h e field f i e l d trip. t r i p . On On the t h e south s o u t h limb, l i m b , the t h e volcanics volcanics at In vary v a r y in i n strike, s t r i k e , especially e s p e c i a l l y near n e a r the t h e granodiorite g r a n o d i o r i t e contact. contact. I n the the southeast s o u t h e a s t part p a r t of o f Bigstone B i g s t o n e Bay Bay and and extending e x t e n d i n g east e a s t to t o the t h e Islet Islet Lake Lake area, a r e a , several s e v e r a l east—southeast e a s t - s o u t h e a s t trending t r e n d i n g shears s h e a r s dip d i p south s o u t h and and show s h o w evidence e v i d e n c e of o f reverse r e v e r s e slip; s l i p ; the t h e shears s h e a r s are a r e carbonatized c a r b o n a t i z e d and and contain c o n t a i n pyrite p y r i t e and a n d narrow n a r r o w auriferous a u r i f e r o u s quartz q u a r t z veins. veins Several S e v e r a l old o l d workings w o r k i n g s are a r e in i n silicified s i l i c i f i e d and a n d carbonatized carbonat ized shears t o foliation f o l i a t i o n in i n the t h e intermediate i n t e m e d i a t e pyro— pyros h e a r s which w h i c h are a r e parallel p a r a l l e l to A t Middle M i d d l e Island I s l a n d aa shaft s h a f t was was sunk s u n k on o n aa strongly strongly e l a s t i c s . At clastics. carbonatized is associated a s s o c i a t e d with w i t h galena. galena. c a r b o n a t i z e d zone z o n e in i n which w h i c h gold g o l d is The T h e only o n l y important i m p o r t a n t gold g o l d production p r o d u c t i o n in i n the t h e Bigstone B i g s t o n e Bay Bay area area was west e s t sside i d e of o f Sultana S u l t a n a Island, I s l a n d , which which was aat t the t h e Sultana S u l t a n a Mine Mine oon n tthe he w Here operated 1 8 9 1 to t o 1906. 1906. Here gold—bearing g o l d - b e a r i n g vveins e i n s hosted h o s t e d by by o p e r a t e d from f r o m 1891 s h e a r e d quartz q u a r t z diorite d i o r i t e and a n d porphyritic p o r p h y r i t i c granite g r a n i t e of o f the t h e Quarry Quarry sheared most pproductive Island r e p o r t e d to t o have h a v e been b e e n most r o d u c t i v e aatt the the I s l a n d stock s t o c k were reported t w o intrusive i n t r u s i v e rocks. rocks. c o n t a c t between b e t w e e n the t h e two contact a -WITCH -- BAY Pillowed massive P i l l o w e d and and m a s s i v e tholeiitic t h o l e i i t i c basalts b a s a l t ~in i n the t h e Witch W i t c h Bay Bay area area were intruded i n t r u d e d by b y layered l a y e r e d sills s i l l s of o f peridotite p e r i d o t i t e to t o leucogabbro, l e u c o q a b b r o , and and the been t h e ssequence e q u e n c e hhas as b e e n folded f o l d e d about a b o u t east—trending e a s t - t r e n d i n g axes a x e s (Figure (Figure Intermediate 6) I n t e r m e d i a t e and a n d felsic f e l s i c volcanics v o l c a n i c s overlie o v e r 1 i e the t h e mafic maÂi c rocks. rocks. 6). Granodiorite G r a n o d i o r i t e of o f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h cross—cuts c r o s s - c u t s this t h i s regional reqional f o l d structure. structure. fold Gold occurrences o c c u r r e n c e s are a r e in i n carbonatized c a r b o n a t i z e d shear s h e a r zones z o n e s iin n bbasalt. asaltis hosted h o s t e d by b y silicified s i l i c i f i e d and a n d pyritiferous p y r i t i f e r o u s schist s c h i s t or or by by The gold g o l d is The quartz t o 20 2 0 percent p e r c e n t sulphides. s u l p h i d e s c At A t the the q u a r t z veins v e i n s containing c o n t a i n i n g up up to Wendigo lie W e n d i q o mine m i n e and a n d Stella S t e l l a occurrence, o c c u r r e n c e , the t h e mineralized m i n e r a l i z e d shears s h e a r s lie stratigraphically s t r a t i g r a p h i c a l l y below b e l o w t hthe e p peridotitic e r i d o t i t i c bbase a s e o of f aa ssill. i l l . The The t o be b e at at a a ssimilar i m i l a r stratigraphic stratigraphic W i t c h Bay Bay ooccurrence c c u r r e n c e appears a p p e a r s to Witch The sshearing level. h e a r i n g is is believed b e l i e v e d to t o be b e related r e l a t e d to t o competency competency level. contrast s i l l . Two of o f these t h e s e deposits deposits c o n t r a s t between b e t w e e n the t h e basalt b a s a l t and and the t h e sill. will w i l l be b e seen s e e n on o n the t h e field f i e l d trip t r i p at a t Stops S t o p s 88 and a n d 9. 9. . �23 *** + top from grading piflow top shaft location * * shear zone and/or lineament anticline syncline + ii diabase *+ grariitoid intrusiois+. mafic intrusions ++ wacke felsic metavolcanics mafic * * * 01+2 Blindf old * DRYBERRY ++ (++ BATHOLITH Lake+*+*+*+c+# * Oblong + Lake+. top8 Figure F i g u r e 5: 5: Geology Bay aarea G e o l o g y of of the t h e Bigstorie B i g s t o n e Bay r e a (modified ( m o d i f i e d from f r o m Ayer, Ayer, 1984). 1984). �Figure 6: a.' ^-1 3 Geology of the Witch Bay area (modified from Davies and Smith, 194). �25 The T h e Wendigo W e n d i g o Mine Mine produced p r o d u c e d gold q o l d and a n d silver s i l v e r from f r o m 1936 1 9 3 6 to t o 1943 1943 and a n d copper c o p p e r during d u r i n g part p a r t of o f that t h a t period. p e r i o d . The T h e average a v e r a g e gold g o l d content content o r e was was 0.33 0 . 3 3 ounces o u n c e sper p e rtori. t o n . The T h e main m a i n quartz q u a r t z vein v e i n is is o f milled m i l l e d ore of in i n aa carbonatizecl c a r b o n a t i z e d cchloritic h l o r i t i c sshear h e a r zzone o n e which w h i c h sstrikes t r i k e s easterly e a s t e r l y and and d i p s steeply s t e e p l y north. n o r t h . The T h e vein v e i n was was up u p to to 75 7 5 cm cm wide w i d e but b u t averaged averaqed dips 30 c m , and a n d contained c o n t a i n e d up up to t o 50 5 0 percent p e r c e n t sulphides s u l p h i d e s (pyrite, (pyrite, 30 cm, p y r r h o t i t e and a n d chalcopyrite) c h a l c o p y r i t e ) as a s stringers s t r i n g e r s and a n d small s m a l l masses m a s s e s which which pyrrhotite are a r e concentrated c o n c e n t r a t e d at a t edges e d g e s of o f veins. veinsa CONTROLS ON MINERALIZATION MINERALIZATION CONTROLS ON ------------- Recent R e c e n t work w o r k by b y Davies D a v i e s and a n d Smith S m i t h (1984) ( 1 9 8 4 ) has h a s shown s h o w n that t h a t in i n the the q e n e r a l Lake L a k e of o f the t h e Woods Woods area: area: general 1 . The T h e majority m a j o r i t y of o f gold g o l d occurrences o c c u r r e n c e s are a r e hosted h o s t e d by b y tholeiitic tholeiitic 1. basalts s t r a t i g r a p h i c a l l y below below felsic f e l s i c volcanic volcanic b a s a l t s that t h a t occur o c c u r stratigraphically sequences sequences The T h e major major past—producing p a s t - p r o d u c i n g mines m i n e s (eg. ( e g . Wendigo) W e n d i q o ) and a n d the t h e recently recently active a c t i v e Duport D u p o r t property p r o p e r t y occur o c c u r near n e a r the t h e top t o p of o f this t h i s tholeiitic tholeiitic where preliminary p r e l i m i n a r y data d a t a indicate i n d i c a t e aa higher h i g h e r iron i r o n magnesium magnesium s e q u e n c e , where sequence, ratio. ratio. 2. 2. All A l l of o f the t h e occurrences o c c u r r e n c e s are a r e associated a s s o c i a t e d with w i t h faults f a u l t s or o r shear shear Most gold production has come from shears which Most g o l d p r o d u c t i o n h a s come f r o m s h e a r s w h i c h are are zones. zones. nearly n e a r l y parallel p a r a l l e l to t o volcanic v o l c a n i c stratigraphy. stratigraphy. 3. 3. 4. Hydrothermal H y d r o t h e r m a l solutions s o l u t i o n s were were rich r i c h in i n silica s i l i c a and a n d carbon carbon 4. most were were enriched e n r i c h e d in i n sulphur, s u l p h u r , potassium p o t a s s i u m and a n d boron. boron. d i o x i d e , and a n d most dioxide, Gold 5. G o l d may may have h a v e been b e e n carried c a r r i e d as a s aa sulphur s u l p h u r complex c o m p l e x in i n these these 5. solutions: its precipitation may have been enhanced by combining s o l u t i o n s : i t s p r e c i p i t a t i o n may h a v e b e e n e n h a n c e d b y combining sulphur s u l p h u r with w i t h iron. i r o n . If I f such s u c h conditions c o n d i t i o n s prevailed, p r e v a i l e d , iron—rich iron-rich basalts may have been the preferred site f o r gold g o l d deposition. deposition. b a s a l t s may h a v e b e e n t h e p r e f e r r e d s i t e for LE DGEM ENTS ACKNOWLE ACKNOW DGEMENTS Thanks t o : Bernard B e r n a r d Guarnera G u a r n e r a of o f Boise Boise Cascade Cascade T h a n k s are a r e due d u e to: Corporation, t o work work on o n the t h e Scramble S c r a m b l e property p r o p e r t y and and C o r p o r a t i o n , for f o r permission p e r m i s s i o n to for r e l e a s e of o f geological g e o l o q i c a l maps, m a p s , and a n d to t o Mike Mike Parr P a r r for for f o r the t h e release stimulating s t i m u l a t i n g discussion d i s c u s s i o n of o f the t h e epigenetic e p i q e n e t i c versus v e r s u s syngenetic synqenetic evidence a t the t h e Scramble; S c r a m b l e ; numerous n u m e r o u s students s t u d e n t s from f r o m the t h e University University e v i d e n c e at of Manitoba who under the direction of Lorne Ayres and o f M a n i t o b a who u n d e r t h e d i r e c t i o n o f Lome A y r e s a n d Bill Bill Brisbin, B r i s b i n , have h a v e cleared c l e a r e d outcrop o u t c r o p over o v e r many many years y e a r s at a t the t h e Conglomerate Conqlomerate Zone Zone unconformity; u n c o n f o r m i t y ; and a n d to t o Mike Hailstone H a i l s t o n e for f o r his h i s enthusiastic enthusiastic work Wajax pump pump during d u r i n g preparation p r e p a r a t i o n for f o r this t h i s field f i e l d trip. trip. w o r k with w i t h aa Wajax �26 ThE THE -- ------- IINTRODUCTION NTRODUCTION FIELD --TRIP TRIP field The f i e l d ttrip r i p route r o u t e utilizes u t i l i z e s existing e x i s t i n g roads r o a d s and a n d highways, highways, is designed d e s i g n e d to t o examine e x a m i n e major m a j o r aspects a s p e c t s of o f Lake Lake of of the t h e Woods aand n d is gold g o l d occurrences o c c u r r e n c e s without w i t h o u t going g o i n g onto o n t o the t h e lake l a k e itself. itself. 1, the t h e trip t r i p commences commences near n e a r the the On the t h e afternoon a f t e r n o o n of o f Day Day 1, Manitoba t o vview i e w sseveral e v e r a l ooccurrences c c u r r e n c e s within w i t h i n and a n d marginal marginal M a n i t o b a border, b o r d e r , to It tto o tthe h e High H i g h Lake Lake stock. stock. I t then t h e n pproceeds r o c e e d s east e a s t along a l o n g Highway Highway 17 17 (Trans Canada Highway) ttowards (Trans C a n a d a Highway) o w a r d s Kenora, K e n o r a , with w i t h one o n e stop s t o p along a l o n g the the r e c e n t past—producers past-producers way at a t the t h e Kenricia K e n r i c i a Mine, Mine, one o n e of o f the t h e more recent iin n the t h e area. area. On the 2, we w e will w i l l examine e x a m i n e aa number number of of t h e morning m o r n i n g of o f Day Day 2, mafic lowermost ma i c volcanics v o l c a n i c s of o f the t h e Kenora Kenora ooccurrences c c u r r e n c e s within w i t h i n the t h e lowermost 2, occurrences o c c u r r e n c e s are a r e viewed v i e w e d near near aarea. r e a . On the t h e afternoon a f t e r n o o n of o f Day Day 2, These Witch W i t c h Bay, Bay, including i n c l u d i n g the t h e former—producing f o r m e r - p r o d u c i n g Wendigo Wendigo Mine. Mine. These occurrences l i e in i n the t h e upper u p p e r part p a r t of o f the t h e lower lower mafic m a f i c volcanics, volcanics, o c c u r r e n c e s lie near with predominantly n e a r the t h e ccontact ontact w i t h the t h e ooverlying v e r l y i n g ccalc—alkaline, a l c - a l k a l h e f predominantly pyroclastic p y r o c l a s t i c suite. suite. DAY -- 1 1 Proceed P r o c e e d west w e s t from f r o m McLeod McLeod Park P a r k (Husky ( H u s k y the t h e Muskie) M u s k i e ) in i n Keriora Kenora along Highway 17 to the Shoal Lake Road turn off, a distance t o t h e S h o a l Lake t u r n o f f , a d i s t a n c e of of a l o n g Highway The 444 4 km. T h e Trans T r a n s Canada C a n a d a Highway runs r u n s parallel p a r a l l e l to, t o , and a n d in i n general general t o the t h e ssouth o u t h oof, f , the t h e boundary b o u n d a r y between b e t w e e n the t h e Wabiqoon Wabigoon and and jjust u s t to English E n q l i s h River R i v e r Suhprovinces. Subprov i n c e s Proceed Turn T u r n left l e f t (south) ( s o u t h ) on o n the t h e Shoal S h o a l Lake Lake road. road. P r o c e e d 2.8 2 . 8 km to to From this Laker oroad, the t h e High H i g h Lake a d , a aggravel r a v e l rroad o a d oon n t the h e rright. ight. From t h i s point point 3 . 2 km km aalong l o n g tthe h e ggravel r a v e l road r o a d to t othe t h eEvenlode E v e n l o d e molybdenite molybdenite pproceed r o c e e d 3.2 off Eco Explorations Eco E x p l o r a t i o n s LLtd. t d . aatt the t h e east e a s tend end of o fHigh H i q h Lake. Lake. pproperty roperty o . MINE STOP --1 EVENLODE EVENLODE MOLYBDENITE-GOLD MINE (F i(Figure g u r e 77)) --MJLYBDENITE—GOLD ----1 a Att the A t h e Evenlode E v e n l o d e property p r o p e r t y aanumber number of o f molyhdenitemolybdenitebearing quartz veins occur within ductile b e a r i n g q u a r t z v e i n s o c c u r w i t h i n d u c t i l e shear s h e a r zones z o n e s in in H i g h Lake Lake ssubvolcanic ubvolcanic tthe h e pporphyritic o r p h y r i t i c pphase h a s e of o f the t h e High The iintrusion. ntrusion. The vveins e i n s contain c o n t a i n low l o w to t o trace t r a c e amounts a m o u n t s of of ggold old. Four F o u r vveins e i n s of o f molybdenite—bearing r n o l y b d e n i t e - b e a r i n g qquartz u a r t z have h a v e been been The major identified i d e n t i f i e d on o n this t h i s property. property. The m a j o r ssurface u r f a c e and and work hhas 1 or No. No. 1 uunderground n d e r g r o u n d work a s bbeen e e n ddone o n e on o n the t h e Main, Main, or vein, v e i n , the t h e most recent r e c e n t work being b e i n g by b y Eco Eco Molybdenite Molybdenite The hheadframe Mines Ltd. t o 1982. 1982. The e a d f r a m e is is still still Mines L t d . from f r o m 1980 1 9 8 0 to standing, but the mill was removed from the site s t a n d i n g , b u t t h e m i l l was removed f r o m t h e s i t e in in 1984. 1 9 8 4. "The main 'The m a i n vein v e i n is is associated a s s o c i a t e d with with a a sstrong t r o n g shear shear zone z o n e striking s t r i k i n gabout a b o u tN.800W, N . ~ O ~ W and a, n d dipping d i p p i n g about a b o u t 80°N 8 0 0 ~in in its i t s central c e n t r a lportion, p o r t i o n ,but b u tmore more shallow s h a l l o w to t o the t h e east e a s tand and west. Obliteration development west. O b l i t e r a t i o n of o f feldspar f e l d s p a rphenocrysts, p h e n o c r y s ts , development of sericite, and minor silicification occur a d j a c e n t to to o f s e r i c i t e , a n d m i n o r s i l i c i f i c a t i o n o c c u r adjacent tthe h e shear s h e a r zone z o n e in i n which w h i c h qquartz u a r t z vveins, e i n s , lenses l e n s e s and and �_____ ______ _______ 27 + + + t + + -- + + + + , High High Lake Lake + + + + + + + + + + + + + + + + + + + + ÷ + + / + + + +' ++ + , , , - Figure F i g u r e 77 ; , , ' + + + -'+ + + + + + \\trench-4- + + + + + + + _+++ + + —_4 + + + + + + + + + + + + + + + + + + + + + -4- + + + + + + + 4- + + + + + + •-4- + + + + + + + + + + + + + + + + + + + + + + + + 4- + + + + + + + ÷ + + + + + --÷ + + + + + 1__ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - + 4-J porphyritic granodiorite j-j basalt B " 'C' . — Stop 1 development muck -.... Geology o f the t h e Evenlode E v e n l o d e Molybdenite—Gold M o l y b d e n i t e - G o l d Mine Mine (after ( a Ât e r G e o l o g y of company company plans, p l a n s ,Assessment A s s e s s m e n tFiles F i l e sKeriora) Kenora) - + + + + tonallte and granodlorlte _—projection of veins to surface metadiabase 'ocations I + + + ÷ + 4- + + + + + 4- + + + ÷ + + + + + + + + + + + + + +4- + + ÷ + + + +,V —+++•+ + + + + +7 + + ++ +4+ + + + + + + + + + + 4- + + + + + + ÷ + + + + + + + + + + + + + + 4:++ + + - + + + + + + + + + +++ + + 4- + + +_•-+- + + + + 4- + + + + ++ +.+ +.++ + + + + + + + 4- - + + + +_--, 4-:÷ + + + + + ÷ + 4- + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - + + + + + + + + \\ ++ + + + + + + + + + + + +\\ + + +'— + + + + + + + + 4- + + + ,pI—( w + + ± 4- + , , + + %f,-i ++ + : + - + +-+ + +,+ -+ + ,+ ++ +'+ + ++ ÷÷ + + -'+ + ÷shaft + -+ + +-V++ + + - + + +_ p 1— 4-/7+ 4 + 4- +.+ + + + + + + + + ++ ++ + + + + + + + +IjI, + +__.—-..+ ' + + + + + + �28 stringers s t r i n g e r s are a r e found. f o u n d . The T h e shear s h e a r zone z o n e has h a s been b e e n traced t r a c e d for for about a b o u t 2300 2 3 0 0 feet, f e e t , the t h e eastern e a s t e r n 1600 1 6 0 0 feet f e e t being b e i n g that that 'Drill— portion 'Drillp o r t i o n containing c o n t a i n i n g mineralized m i n e r a l i z e d quartz quartz.. indicated i n d i c a t e d ore' o r e ' over o v e r aa length l e n g t h about a b o u t 1200 1 2 0 0 feet...., feet.. r across across an a n average a v e r a q e width w i d t h of o f 4.7 4 . 7 feet, f e e t , and a n d to t o an a n average a v e r a g e depth d e p t h of of 508 5 0 8 feet, f e e t , has h a s been b e e n calculated c a l c u l a t e d at a t about a b o u t 126,000 1 2 6 , 0 0 0 tons tons grading p.51 ) . g r a d i n g 0.68 0 . 6 8 percent p e r c e n t molybdenite" m o l y b d e n i t e " (Davies, ( D a v i e s , 1965, 1 9 6 5 , p.51). Bulk B u l k sampling s a m p l i n g gave g a v e aa higher h i g h e r grade g r a d e (0.87 ( 0 . 8 7 percent percent molybdenite) 0.5 m o l y b d e n i t e ) and a n d 0.015 0 . 0 1 5 ounces o u n c e s of o f gold g o l d per p e r ton t o n (about ( a b o u t 0.5 grams g r a m s of o f gold g o l d per p e r tonne). tonne). The No. 2 2 vein v e i n ssystem, y s t e m , to t o the t h e southwest, s o u t h w e s t , trends trends T h e No. northeast n o r t h e a s t and a n d consists c o n s i s t s of o f one o n e dominant d o m i n a n t quartz q u a r t z vein v e i n and and several s h e a r zone z o n e 30—80 3 0 - 8 0 feet feet s e v e r a l subsidiary s u b s i d i a r y veins v e i n s within w i t h i n aa shear t r a c e d for f o r 700 700 w i d e . The The dominant d o m i n a n t vein, v e i n , which w h i c h has h a s been b e e n traced wide. feet, " is reported r e p o r t e d to t o average a v e r a q e 0.47 0 . 4 7 percent p e r c e n t molybdenite molybdenite f e e t , "is 2.2 foot f owidth, o t w with i d t hgold , waveraging i t h g o l .02—.05 d averaging .02-.05 o v e r aa 2.2 over The ounces is o u n c e s per p e r ton" t o n " (Davies, ( D a v i e s , 1965, 1965,, p.51) 0.51). T h e vvein e i n is The poorly be vvisited. p o o r l y exposed e x p o s e d a and n d wwill i l l nnot o t be isited. The No. N o . 33 vein vein strikes s t r i k e s northwest n o r t h w e s t and and dips d i p s 450 4 5 0 to t o 800 8 0 ^ northeast, n o r t h e a s t , with w i t h an an estimated 1 - 2 ppercent e r c e n t molybdenite. molybdenite. A A shaft s h a f t was was e s t i m a t e d grade g r a d e of o f 1—2 sunk fromiitt covers s u n k nnear e a r this t h i s vein v e i n arid a n d muck muck from c o v e r s the t h e vein vein completely. completely. . .. . .. Locality L o c a l i t y AA An An ooutcrop u t c r o p oof f unaltered u n a l t e r e d granodiorite, granodiorite, ----porphyry phase t y p i c a l oT the t h e p o r p h y r y p h a s e of o f the t h eHigh H i g h Lake Lake €TTT intrusion, occurs close to the road at the entrance to i n t r u s i o n , o c c u r s close t o t h e r o a d a t t h e e n t r a n c e t o the t h e property. p r o p e r t y . The T h e rock r o c k is is characterized c h a r a c t e r i z e dby b yrounded rounded quartz q u a r t z and a n d subhedral s u b h e d r a l plagioclase p l a g i o c l a s e phenocrysts p h e n o c r y s ts in i n an an aphanitic a p h a n i t i c matrix. matrix. main is exposed Locality L o c a l i t y BB The The m a i n vvein e i n is e x p o s e d iin n a a trench t r e n c h through through -----w h i c h a small s m a l l stream s t r e a m drains. drains. which £4olybdenite—bearing M o l y b d e n i t e - b e a r i n g quartz quartz occurs o c c u r s in in a a silicified s i l i c i f i e d shear s h e a r zone z o n e in i n which w h i c h the the was accompanied a c c o m p a n i e d by by d e s t r u c t i o n of o f feldspar f e l d s p a r pphenocrysts h e n o c r y s ts was destruction s e r i c iitt ii zzat a t iion. on. seric vei Locality A ffourth o u r t h vein, v e i n , between b e t w e e n the t h e No. No. 2 2 and a n d No. N o . 33 L o c a l i t y CC A G f n a s " been b e e n uncovered u n c o v e r e d in i n the t h e north n o r t h part p a r t of of a a 60 6 0 mm t r e n c h . The The 'vein' ' v e i n g strikes s t r i k e sabout a b o u tN1O0W. ~ 1 0 0 ~ddips i.p s ssteeply teeply trench. w e s t and a n d consists c o n s is ts of o f aa shear s h e a r zone z o n e in i n which w h i c h there t h e r e are are west narrow, is n a r r o w , discontinuous d i s c o n t i n u o u s quartz q u a r t z veins. v e i n s . Pyrrhotite P y r r h o t i t e is Assay associated a s s o c i a t e d with w i t h the t h e molybdenite. molybdenite. A s s a y data d a t a for f o r the the vein v e i n are a r e not n o t available. available. From the t h e Evenlode E v e n l o d e property p r o p e r t y return r e t u r n 2.2 2. 2 km km along a l o n g the t h e High H i q h Lake Lake The q r a n o d i o r i t e and road. T h e road r o a d ppasses a s s e s first f i r s t through t h r o u g h porphyritic p o r p h y r i t i c granodiorite and road. At then is cut c u t by b y porphyry. porphyry. A t the t h e northernnorthernt h e n through t h r o u g h basalt b a s a l t which w h i c h is most point p o i n t in i n the t h e road, r o a d , aa small s m a l l amount a m o u n t of o f gold g o l d and a n d silver s i l v e r was was recovered r e c o v e r e d from f r o m irregular i r r e g u l a r zones z o n e s of o f quartz q u a r t z exposed e x p o s e d in i n pits p i t s just just The north n o r t h of o f the t h e road. road. T h e surface s u r f a c e geology g e o l o g y here h e r e demonstrates d e m o n s t r a t e s the the Stop complexity c o m p l e x i t y of o f the t h e basalt—porphyry b a s a l t - p o r p h y r y relationship. relationship. S t o p near n e a r the the From the gate; t o the t h e north n o r t h is i s porphyry. porphyry. t h e parking p a r k i n g point point g a t e ; outcrop o u t c r o p to metrest to walk o aa fflagged l a g g e d ttrail, r a i l , and a n d south s o u t h on on the the w a l k east e a s t about a b o u t 120 1 2 0 metres t o Stop S t o p 2. 2. t r a i l to trail �29 STOP_2 STOP --- 2 THE BASE B A S E OF THE CROWDUCK LAKE LAKE GROUP: GROUP: THE THE UNCONFORMITYANDTHE CONGLOME~TEZONE" GOLD PROSPECT " --PA-------- At A t tthis h i s stop s t o p aa rather r a t h e rspectacular s p e c t a c u l a rexposure e x p o s u r e of o f the the unconformity t h e base b a s eofo fthe t hCrowduck e C r o w d u c k Lake L a k e Group G r o u p is is u n c o n f o r m i t y aatt the in i n close c l o s e proximity p r o x i m i t y to t o aa minor m i n o r but b u t structurally structurally significant s i g n i f i c a n t gold g o l d occurrence, o c c u r r e n c e , the t h e Conglomerate C o n g l o m e r a t e Showing. Showing. Locality B a s a l t , and a n d porphyry p o r p h y r y dikes d i k e s related r e l a t e d to t o the the L o c a l i t y A Basalt, iiTgfTLakeintrusion, a r e present p r e s e n t in i n the t h e western w e s t e r n part p a r t of of H i g h L a k e i n t r u s i o n , are this outcrop area and are overlain unconformably by t h i s o u t c r o p a r e a and are o v e r l a i n unconformably by sediments The s e d i m e n t s of o f the t h e Crowduck C r o w d u c k Lake Lake Group. Group. T h e sketch s k e t c h map by by Beakhouse ( t h i s volume, v o l u m e , p.86) p.86 ) illustrates i l l u s t r a t e s three three B e a k h o u s e (this sedimentary s e d i m e n t a r y units u n i t s that, t h a t , over—all, o v e r - a l l , show s h o w coarsening coarsening upward, s i l t s t o n e s and and thinly t h i n l y bedded bedded u p w a r d , from f r o m cherty c h e r t y siltstones sandstones s a n d s t o n e s at a t the t h e base, b a s e , through t h r o u g h pebbly p e b b l y sandstone s a n d s t o n e into into conglomerate. In addition, massive to thickly bedded conglomerate. I n add i t i o n , m a s s i v e t o t h i c k l y bedded sandstones s a n d s t o n e s occur o c c u r iin n the t h e north n o r t h part p a r t of o f the t h e outcrop o u t c r o p area. area. Relationships a r ecomplicated c o m p l i c a t e d by by R e l a t i o n s h i p s between b e t w e e n tthese h e s e units u n i t s are syn—depositional t h e original o r i g i n a l highly highly s y n - d e p o s i t i o n a l erosion e r o s i o n and a n d by the irregular i r r e g u l a r surface s u r f a c e upon u p o n which w h i c h deposition d e p o s i t i o n occurred. occurred. Noteworthy N o t e w o r t h y features f e a t u r e s at a t the t h e surface s u r f a c e of o f the t h e unconformity unconformity include; most notably i n c l u d e ; aa regolith, r e g o l i t h , most n o t a b l y developed d e v e l o p e d above a b o v e aa porphyry p o r p h y r y dike; d i k e ; possible p o s s i b l e evidence e v i d e n c e of o f syn—depositional syn-depos i t i o n a l faulting f a u l t i n g at a t the t h e southern s o u t h e r n contact c o n t a c t of o f the t h e porphyry p o r p h y r y with with basalts; b a s a l t s ; local l o c a l provenance p r o v e n a n c e of o f basaltic b a s a l t i c clasts c l a s t s in i n aa lens lens of o f conglomerate. conglomerate. The conglomerate is characteristically c h a r a c t e r is t i c a l l y heterolithic; h e t e r o l i t h ic; c o n g l o m e r a t e is porphyry clasts are predominant and conspicuously p o r p h y r y c l a s t s a r e p r e d o m i n a n t and c o n s p i c u o u s l y larger larqer than a n d felsic felsic t h a n oother t h e r types, t y p e s , which w h i c h include i n c l u d e mafic maf i c and volcanics, v o l c a n i c s , chert c h e r t and a n d iron i r o n formation. format ion. Soft—sediment deformation Sof t - s e d i m e n t d e f o r m a t i o n s t rstructures u c t u r e s i in n tthe h e finer finer sedimentary s e d i m e n t a r y rocks r o c k s include i n c l u d e slump s l u m p folds, f o l d s , load l o a d casts, c a s t s , and and flame f l a m e sstructures. tructures. is at a thigh h i g h angles a n g l e s to tobedding, b e d d i n g , and a n d parallel parallel F o l i a t i o n is Foliation to Minor t o clast c l a s t elongation e l o n g a t i o n and a n d fold f o l d axial a x i a l planes. planes. M i n o r folds folds show s h o w geometry g e o m e t r y similar s i m i l a r to t o regional—scale r e g i o n a l - s c a l e folding. folding. Quartz Q u a r t z and a n d qquartz—tourmaline u a r t z - t o u r m a l i n e v e veinlets i n l e t s f ifill l l fractures fractures in some l a s t s . The T h e vveinlets e i n l e t s are a r e oblique o b l i q u e to to i n s o m e pporphyry o r p h y r y cclasts. foliation f o l i a t i o nand a n dcommonly commonly pproject r o j e c t into i n t o the t h econglomerate conqlonerate matrix, c l e a r l y indicating i n d i c a t i n g their t h e i r late l a t e emplacement. emplacement. m a t r i x , clearly this point we return to the road, walk west to the gate and From t h i s p o i n t w e r e t u r n t o t h e r o a d , w a l k west t o t h e g a t e a n d south s o u t h 20m 20m t through h r o u g h t the h e bbush u s h tto o the t h e open o p e n outcrop o u t c r o p area. area. Locality PROSPECT L o c a l i tB y CONGLOMERATE B CONGLOMERATE PROSPECT ( F(Figure i g u r e 8) 8) ----- An embayment An embayment o f of t hthe e b basal a s a l cconglomerate o n q l o m e r a t e aat t this this location 1 5 m and a n d is is l o c a t i o n has h a s an a n average a v e r a g e width w i d t h of o f about a b o u t15m exposed exposed over The conglomerate o v e r aa length l e n g t h of o f 95m. 95m. c o n g l o m e r a t e is is enclosed e n c l o s e d t o t h e s o u t h , w e s t a n d n o r t h by f o l i a t e d b a s a l t and a n d consists c o n s i s t s of o f subrounded s u b r o u n d e d clasts c l a s ts in i n aa strongly s t r o n g l y foliated foliated to the south, west and north by foliated basalt �Filire B: 0Q 00 IKE 00 30 o metres ic QOC ROAD 0 Q of ooQooOa0 Q o oo0oo —— — — S Geolo'iy of the Canqiornerate Zone coil Pros[)ec (adapt.l from Davie , 1965). B trench stop location - GATE U �31 dark d a r k wacke w a c k e matrix. m a t r i x . Clasts C l a s t s are a r e mostly m o s t l y quartz q u a r t z porphyry porphyry and a n d granodiorite, q r a n o d i o r i t e , with w i t h lesser l e s s e r amounts a m o u n t s of o f feidsoar felds~ar p o r p h y r y and a n d mafic maÂi c volcanics, v o l c a n i c s , all a l l of o f which w h i c h may may have h a v e been been porphyry locally There is no n o distinct d i s t i n c t bedding, bedding, l o c a l l y derived. derived. T h e r e is although c l a s t size s i z e in i n general g e n e r a l increases i n c r e a s e s to to the t h e west. west. a l t h o u g h clast Clast C l a s t elongation, e l o n g a t i o n , which w h i c h is is slightly s l i g h t l y greater g r e a t e r near near contacts is parallel p a r a l l e l to t o the t h e east—trending east- t r e n d i n g c o n t a c t s with w i t h basalt, b a s a l t , is foliation; r a t i o s are a r e about about f o l i a t i o n ; average a v e r a g e width: w i d t h : length: l e n g t h : depth d e p t h ratios 1:2. 1 : 2 . 55:4. : 4. The ggeometric e o m e t r i c and a n d spatial s p a t i a l relationships r e l a t i o n s h i p s between b e t w e e n the the conglomerate c o n g l o m e r a t e and a n d basalt, b a s a l t , combined c o m b i n e d with w i t h the t h e strong strong east—trending eas t - t r e n d i n g foliation, f o l i a t i o n , suggest s u g g e s t that t h a t the t h e embayment embayment of of sediments s e d i m e n t s may may have h a v e been b e e n modified m o d i f i e d by b y tight t i g h t folding f o l d i n g about about a ssynclinal y n c l i n a l axis a x i s plunging p l u n g i n q 650 6 5 0 in i n an a n easterly e a s t e r l y direction. direction. Quartz Q u a r t z is is mainly m a i n l y present p r e s e n t as as lenses, l e n s e s , thin t h i n veins v e i n s and and irregular masses which w h i c h cut c u t across foliation, £0 i a t i o n , especially especially i r r e g u l a r masses in Quartz a l s o occurs o c c u r s in in i n the t h e vicinity v i c i n i t y of o f the t h e pit. pit. Q u a r t z also tension c l a s t s and a n d in i n aa t e n s i o n fractures f r a c t u r e s in i n aa few f e w granitic g r a n i t i c clasts porphyry p o r p h y r y dike d i k e in i n schistose s c h i s t o s e basalt b a s a l t at a t the t h enorth n o r t h edge e d q e of of the t h e outcrop. outcrop. P y r i t e is p r e s e n t i n p o c k e t s i n t h e irregular o f quartz q u a r t z and a n d as as disseminations d i s s e m i n a t i o n s in in i r r e g u l a r masses of quartz q u a r t z veins v e i n s and a n d along a l o n g slip s l i p and a n d foliation f o l i a t i o n planes, planes, especially e s p e c i a l l y in i n the t h e conglomerate c o n g l o m e r a t e matrix. matrix. M i n o r tourmaline tourmaline Minor is is also a l s o associated a s s o c i a t e d with w i t h the t h e quartz. quartz. The was the t h e source s o u r c e of o f aa 76 7 6 ton t o n bulk b u l k sample s a m p l e from from T h e pit p i t was which 0. 14 oz. o z . per p e r ton t o n was was w h i c h an a n average a v e r a g e gold g o l d recovery r e c o v e r y of o f 0.14 obtained o b t a i n e d in i n 1939. 1939. Extensive E x t e n s i v e drilling d r i l l i n g and a n d channel channel sampling was undertaken u n d e r t a k e n in i n 1944, 1 9 4 4 , but b u t only o n l y 11 1 1 core core s a m p l i n g was samples s a m p l e s of o f greater g r e a t e r than t h a n 1.5m 1.5m length l e n g t h had h a d gold g o l d assays assays exceeding The erratic 0.08 oz o z per p e r ton. ton. e r r a t i c nature n a t u r e of o f the the e x c e e d i n g 0.08 i s demonstrated d e m o n s t r a t e d by b y aa 1.8m 1.8m intersection intersection m i n e r a l i z a t i o n is mineralization which w h i c h assayed a s s a y e d 1.48 1 . 4 8 ounces o u n c e s of o f gold g o l d per p e r ton t o n (Davies, ( D a v i e s , 1965, 1965, p . 335) 5). p. The T h e presence p r e s e n c e of o f gold g o l d in i n quartz q u a r t z which w h i c h cuts c u t s across across foliation, f o l i a t i o n , indicates i n d i c a t e s the t h e late— l a t e - or o r post—tectonic p o s t - t e c t o n i c timing timing of o f mineralization. mineralization. Pyrite is present in pockets in the Return R e t u r n to t o the t h e Shoal S h o a l Lake Lake road, r o a d , turn t u r n left l e f t (north), ( n o r t h ) , and a n d proceed proceed about a c r o s s outcrops o u t c r o p s of of a b o u t 150m. 150m. Walk east e a s t along a l o n g aa trail t r a i l across conglomerate c o n g l o m e r a t e to t o the t h e Arsenic A r s e n i c Zone. Zone. - STOP 33--ARSENIC ZONE 9) ZONE GOLD PROSPECT PROSPECT (Figure (Figu ------GOLD --- The Arsenic A r s e n i c Zone Zone is is so s o called c a l l e d not n o t because b e c a u s e arsenic arsenic a major m a j o r component c o m p o n e n t but b u t because, b e c a u s e , of o f nine n i n e zones z o n e s explored explored by b y Electrum E l e c t r u m Lake Lake Gold G o l d Mines M i n e s Ltd. L t d . around a r o u n d 1960, 196 0, it i t was was the the only was identified. A t this this o n l y one o n e it-i i n w hwhich i c h a rarsenopyrite s e n o p y r i t e was i d e n t i f i e d . At occurrence, is associated a s s o c i a t e d with w i t h quartz q u a r t z that t h a t contains contains o c c u r r e n c e , gold g o l d is t o u r m a l i n e , pyrite, p y r i t e , arsenopyrite a r s e n o p y r i t e and a n d minor m i n o r pyrrhotite. pyrrhotite. tourmaline, The T h e quartz q u a r t z is is in i n irregular i r r e g u l a r veins v e i n s which w h i c h occur o c c u r in i n aa complex c o m p l e x of o f porphyry p o r p h y r y and a n d felsic f e l s i c pyroclastics p y r o c l a s t i c s or o r flows, flows, near p r o m i n e n t hill h i l l of of n e a r the t h e north n o r t h side s i d e of o f aa prominent conglomerate. A s at a t the t h e previous p r e v i o u s stop, s t o p , the t h e occurrence occurrence c o n g l o m e r a t e . As is is close c l o s e to t o the t h eunconformity u n c o n f o r m i t y at a tthe t h ebase b a s eofo the f t hCrowduck e Crowduck is is �Figure 9: Geology of the Prsenic Zone gold prospect N) w �33 Lake L a k e Group. Group. The relationship r e l a t i o n s h i p bbetween e t w e e n the t h e conglomerate c o n g l o m e r a t e and a n d the the The felsic is ddifficult i f f i c u l t to to f e l s i c volcanic v o l c a n i c and a n d sub—volcanic s u b - v o l c a n i c rocks r o c k s is ddetermine. etermine. IIn n aa pprevious r e v i o u s interpretation i n t e r p r e t a t i o n (Davies, ( D a v i e s , 11965) 965) was ssuggested were all iit t was u g g e s t e d that t h a t the t h e ffelsic e l s i c rocks r o c k s were a l l porphyry porphyry as aan n eeast—trending a s t - t r e n d i n g ddike, i k e , aand n d younger y o u n g e r than than tthat h a t ooccurred c c u r r e d as greywackes were identified i d e n t i f i e d north n o r t h and a n d south s o u t h of o f it. it. g r e y w a c k e s that t h a t were The The conglomerate c o n g l o m e r a t e in i n turn t u r n was was considered c o n s i d e r e d to t o be b e younger younger than I t was also a l s o noted n o t e d (Davies, (Davies, t h a n the t h e porphyry p o r p h y r y dike. dike. It was not n o t satisfactory, satisfactory, 11965) 9 6 5 ) tthat h a t this t h i s interpretation i n t e r p r e t a t i o n was since t o grade g r a d e into i n t o the the s i n c e the t h e greywacke g r e y w a c k e appeared a p p e a r e d to cconglomerate. onglomerate. O u r recent r e c e n t mapping m a p p i n g has h a s shown s h o w n that t h a t the t h e "porphyry "porphyry Our dike" d i k e " cconsists o n s i s t s of o f at a t least l e a s ttwo t w ophases p h a s e s of o f porphyry, p o r p h y r y , and a n d aa The pyroclastic unit. T h e ccontact o n t a c t between b e t w e e n the t h e main m a i n porphyry porphyry aand n d the t h e conglomerate c o n g l o m e r a t e aappears p p e a r s to t o be be an a n unconformity, unconformity, a n d G). G) aalong l o n g which w h i c h sshearing h e a r i n g has h a s occurred o c c u r r e d (Localities ( L o c a l i t i e s AA and This main This m a i n pphase h a s e oof f the t h e porphyry p o r p h y r y is is similar s i m i l a r to t o porphyry porphyry iidentified d e n t i f i e d eelsewhere l s e w h e r e as a s ppart a r t of o f the t h e High H i g h Lake L a k e stock. stock. A small s m a l l ooutcrop u t c r o p of o f pyroclastics p y r o c l a s t i c s (Locality ( L o c a l i t y E) 3 ) is is probably probably associated a s s o c i a t e d with w i t h this t h i s main m a i n porphyry p o r p h y r y phase. phase. E l s e w h e r e in in Elsewhere the i m i l a r transitions t r a n s i t i o n s from f r o m felsic felsic t h e High H i g h Lake L a k e area a r e a ssimilar porphyry composition p o r p h y r y iinto n t o pyroclastics p y r o c l a s t i c s of o fthe t h same e samecomposition s u p p o r t t h e i n t e r p r e t a t i o n t h a t t h i s p o r p h y r y is a ssub—volcantc u b - v o l c a n i - c intrusion. intrusion. D i k e s of o f porphyry p o r p h y r y clearly c l e a r l y cut cut Dikes main—phase tthe he m a i n - p h a s e pporphyry o r p h y r y (Locality ( L o c a l i t y F), F ) , but b u t the t h e timing t i m i n q of of t o deposition d e p o s i t i o n of o f the the ttheir h e i r eemplacement m p l a c e m e n t relative r e l a t i v e to conglomerate is not n o t clear. clear. c o n g l o m e r a t e is T h e hhighly i g h l y laminated, l a m i n a t e d , fine f i n e grained g r a i n e d grey q r e y rocks r o c k s on on the the The north C ) , formerly formerly n o r t h sside i d e oof f the t h e porphyry p o r p h y r y (Locality ( L o c a l i t y C), as ggreywacke iidentified d e n t i f i e d as r e y w a c k e (Davies, ( D a v i e s , 1965), 1 9 6 5 ) , are a r e here here mylonite t o be be a m y l o n i t e zone. zone. The m y l o n i t e may 'nay The mylonite cconsidered o n s i d e r e d to t o the t h e north. n o r t h . This T h i s mylonite mylonite uunderlie n d e r l i e the t h e swampy area a r e a to zzone o n e is i s pprobably r o b a b l y aassociated s s o c i a t e d with w i t h the t h e dominant d o m i n a n t easterly easterly trending trendinq faults. The T h e ggold—bearing o l d - b e a r i n g quartz q u a r t z veins v e i n s occupy o c c u p y fractures f r a c t u r e s that that clearly post—date: the main phase porphyry within which c l e a r l y p o s t - d a t e : t h e main p h a s e p o r p h y r y w i t h i n which they B, D D aand n d F); F); t h e y are a r e dominantly d o m i n a n t l y ddeveloped e v e l o p e d ((Localities L o c a l i t i e s B, some pebbles p e b b l e s and and tthe h e Sedimentary s . e d i m e n t a r y rocks, r o c k s , within w i t h i nwhich w h i c h some b o u l d e r s c o n t a i n l a t e f r a c t u r e s t h a t have been f i l l e d by quartz n d H); n d tthe h e late l a t e porphyry porphyry q u a r t z veins v e i n s (Localities ( L o c a l i t i e s A aand H); aand D , E and a n d F) F) . T h e i r rrelative e l a t i v e age a g e with with ddikes i k e s (Localities ( L o c a l i t i e s D, Their respect i s unknown. unknown. r e s p e c t to t o the t h e mylonite m y l o n i t e is Geometry G e o m e t r y oof f the t h equartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s is is complex, complex, and However, a n d hhas a s not n o t been b e e n analyzed a n a l y z e d in i n detail. detail. H o w e v e r , there there t o bbe e ttwo w o ddominant o m i n a n t trends t r e n d s within w i t h i n the t h e main nain aappear p p e a r to pporphyry, o r p h y r y , one o n e northerly, n o r t h e r l y , the t h e other o t h e r southeasterly. s o u t h e a s t e r l y . These These a t Locality L o c a l i t y D. D. ddominant o m i n a n t trends t r e n d s are a r e especially e s p e c i a l l y evident e v i d e n t at Within W i t h i n tthe h e conglomerate, c o n g l o m e r a t e , qquartz—filled u a r t z - f i l l e d f fractures r a c t u r e s in in ppebbles e b b l e s and a n d boulders b o u l d e r s show s h o w consistent c o n s i s t e n t orientation o r i e n t a t i o n within within individual i n d i v i d u a l ooutcrops, u t c r o p s , but b u t this t h i s varies v a r i e s from f r o m outcrop o u t c r o p to to outcrop ( s e e Localities L o c a l i t i e sAA and a n d H). H). o u t c r o p (see IInn ssummary, u m m a r y , gold g o l d at a t the t h e Arsenic A r s e n i c Zone Zone is is contained contained within were emplaced e m p l a c e d into into w i t h i n qquartz—tourmaline u a r t z - t o u r m a l i n e v veins e i n s tthat h a t were pyroclastic unit. . support the interpretation that this porphyry is faults. boulders contain late fractures that have been filled by . �34 f r a c t u r e s developed d e v e l o p e d by b y brittle b r i t t l e failure f a i l u r e in i n felsic felsic fractures porphyry t o an an p o r p h y r y and a n d associated a s s o c i a t e d rocks, r o c k s , marginal m a r g i n a l to east—southeast—trending e a s t - s o u t h e a s t - t r e n d i n g mylonite m y l o n i t e zone. zone. ---- C r o w d u c k Lake Lake polymictic p o l y m i c t i c conglomerate, conglomerate, L o c a l i t y AA Crowduck Locality coriEflTg c o n t a i n i n g clasts c l a s ts of o f predominant p r e d o m i n a n t porphyry, p o r p h y r y , minor m i n o r dacite, dacite, and is in i n contact c o n t a c t with w i t h porphyry. porphyry. a n d rare r a r e basalt b a s a l t and and chert, c h e r t , is A narrow n a r r o w unit u n i t of o f inter—bedded i n t e r - b e d d e d sandstone s a n d s t o n e and a n d conglomerate conglomerate with 1-2 cm cm pebbles p e b b l e s lies l i e s immediately i m m e d i a t e l y adjacent a d j a c e n t to t o the the w i t h 1—2 The porphyry. The contact c o n t a c t with w i t h the t h e porphyry p o r p h y r y is is sharp s h a r p and and porphyry. A quartz q u a r t z vein v e i n occupying o c c u p y i n g aa fracture f r a c t u r e in i n the the sheared. A sheared. porphyry p o r p h y r y extends e x t e n d s aa few f e w centimetres c e n t i m e t r e s into i n t o the t h e sediments. sediments. Larger a t this t h i s locality l o c a l i t y show show L a r g e r conglomerate c o n g l o m e r a t e clasts c l a s ts at quartz—tilled q u a r t z - f i l l e d tension t e n s i o n fractures f r a c t u r e s that t h a t extend e x t e n d into i n t o the the matrix, m a t r i x , indicating i n d i c a t i n g their t h e i r late l a t e development. development. Locality Q u a r t z - t o u r m a l i n e veins v e i n s with w i t h associated associated L o c a l i t --y BB Quartz—tourmaline p y r ite,rrhotite, i t e , p y r r h o t i t e and , a n dminor m i n o rarsenopyrite a r s e n o p y r i t e occupy o c c u p y aa Other shear s h e a r zone z o n e trending t r e n d i n g 1400 1 4 0  in i n porphyry. porphyry. O t h e r veins v e i n s occur occur in i n minor m i n o r fractures. fractures. Locality M y l o n i t i z e d porphyry p o r p h y r y underlies u n d e r l i e s the t h e north north L o c a l i t y CC Mylonitized Strike slop s o f -ofEhe f i e outcrop o u t c r o p ridge. ridge. S t r i k e is is about a b o u t 1300, 1300, dipping d i p p i n g steeply s t e e p l y northeast. northeast. quartz—tourmaline vveins, A b u n d a n t quartz-tourmaline e i n s , showinq showinq L o c a l i t y D Abundant Locality_D two?5iinent m z e n t orientations, o r i e n t a t i o n s , one o n e approximately a p p r o x i m a t e l y north, n o r t h , the the other t w o phases p h a s e s of o f porphyry. p o r p h y r y . AA o t h e r southeast, s o u t h e a s t , occur o c c u rwithin w i t h i ntwo mafic v e r y narrow narrow m a f i c unit, u n i t , possibly p o s s i b l y aa dike, d i k e , parallels p a r a l l e l s and and very Grab in i n part p a r t follows f o l l o w s the t h e contact. contact. G r a b ssamples a m p l e s obtained o b t a i n e d from from the 1 0 oz oz t h e southeast s o u t h e a s t end end of o f these t h e s e outcrops o u t c r o p s contain c o n t a i n up u p to t o 10 per p e r ton t o n Au. Au. Locality C o n t a c t trending t r e n d i n g 1050 1 0 5 0 between b e t w e e n aa porphyry porphyry L o c a l i t y EE Contact a T R TiTfTyroclastic - ~ c f ~ y r o c l a s tphase ipch a s e of o f the t h e early e a r l y porphyry. p o r p h y r y . AA number number of o f clasts c l a s t s in i n the t h e pyroclastic p y r o c l a s t i c unit u n i t are a r e elongated elongated (1380) parallel ( 1 38O) p a r a l l e l to t o foliation f o l i a t i o n in i n the t h e conglomerates c o n g l o m e r a t e s and and Note quartz the m y l o n i t e zone. zone. q u a r t z veins v e i n s both b o t h in i n the the the mylonite porphyry p o r p h y r y and and the t h e pyroclastics. pyroclastics. Locality L o c a l i t y FF Two late l a t e porphyry p o r p h y r y dikes d i k e s intrude i n t r u d e the the The hhighly main—phase m a i n - p h a s e porphyry. porphyry. i g h l y irregular i r r e g u l a r nature n a t u r e of o f the the unconformity is seen s e e n here, h e r e , with w i t h aa deep d e e p embayment e m b a y n e n t of o f both both u n c o n f o r m i t y is wacke t h e conglomerate c o n g l o m e r a t e a nand d a ab abasal s a l wacke t oto a rargillite g i l l i t e unit unit the into into a a valley v a l l e y in i n the t h e porphyry. porphyry. -F---4- - Locality L o c a l i t y GG The T h e unconformity u n c o n f o r m i t y between b e t w e e n the t h e main—phase main-phase 7änd Crowduck Lake sheared, porpH'yFy'and Crowd uck conglomerates Lake c o n g l o m e r a t eis s is s h e a r e d , but but clasts c l a s t s of o f porphyry p o r p h y r y derived d e r i v e d in i n place p l a c e are a r e identifiable i d e n t i f i a b l e in in Note the t h e basal b a s a l part p a r t of o f the t h econglomerate. conglomerate. Note the t h e sigmoidal, s igmoidal, quartz—filled q u a r t z - f i l l e d t tension e n s i o n ffractures r a c t u r e s in i n the t h e contact c o n t a c t zone. zone. Locality Locality ----lor?ate c o n q l o m e r a t e is is seen s e e n at a t aa very v e r y shallow s h a l l o w angle a n g l e to to H H Weak bedding b e d d i n g in i n the t h e Crowduck Crowduck Lake Lake �35 foliation. foliation. N a r r o w quartz q u a r t z veins v e i n s cut c u t conglomerate c o n g l o m e r a t e in i n two two Narrow d o m i n a n t trends, t r e n d s , one o n e at a t 0850, 0 8 5 0 , another a n o t h e r at a t 1300. 1300. Unlike dominant Unlike A , where w h e r e clasts c l a s t s are a r e large, l a r g e , and a n d quartz q u a r t z veins v e i n s are are L o c a l i t y A, Locality ddominantly o m i n a n t l y confined c o n f i n e d to t o the t h e clasts, c l a s t s , the t h e clast c l a s t size s i z e here here is is ssmaller m a l l e r and a n d veins v e i n s cut c u t clasts c l a s ts and and matrix. matrix. From S t o Highway H i g h w a y 17. 17. At t o p 33 pproceed r o c e e d north n o r t h on o n Shoal S h o a l Lake L a k e road r o a d to Stop At t h e highway, h i g h w a y , tturn u r n rright i g h t (east) ( e a s t ) aand n d ccontinue o n t i n u e for f o r about a b o u t 30 3 0 km to to the is t h e Kendall K e n d a l l Inlet I n l e t Road. Road. F o r the t h e first f i r s t 11 11 km krn the t h e highway h i g h w a y is the For a p p r o x i m a t e l y pparallel a r a l l e l to t o regional r e g i o n a l foliation f o l i a t i o n and a n d passes p a s s e s throuqh through approximately T h e highway h i g h w a y crosses crosses v o l c a n i c rocks r o c k s (mainly ( m a i n l y felsic f e l s i c pyroclastics) pyroclastics) volcanic The ggranitic r a n i t i c rocks r o c k s for f o r the t h e next n e x t 10 1 0 km and a n d for f o r the t h e remainder r e m a i n d e r it i t is is iinn w e l l - f o l i a t e d basalts b a s a l t s and and intermediate i n t e r m e d i a t e to t o felsic f e l s i c tuff—breccia. tuff-breccia. well—foliated i g h t (south) ( s o u t h ) oon n the t h e Kendall K e n d a l l Inlet I n l e t Road and a n d proceed p r o c e e d south south T u r n rright Turn km to Kenricia ffor o r aabout b o u t 2 km t o the t h e vicinity v i c i n i t y of o f the t h e old old K e n r i c i a Mine. Mine. . . STOP 4. GOLD MINE_(Figure_10) 4. ---KENRICIA MINE ( F i q u r e 1 0 ) ------- Gold—bearing G o l d - b e a r i n g quartz q u a r t z veins v e i n s at a t this t h i s stop s t o p were were ddiscovered i s c o v e r e d in i n the t h e latter l a t t e r part p a r t of o f the t h e 19th 1 9 t h century. century. Three s u n k and a n d at a t that t h a t time t i m e the t h e property p r o p e r t y was was T h r e e shafts s h a f t s were sunk known as known as the t h e Three T h r e e Ladies L a d i e s Mine. Mine. IIn n tthe he m i d 1930's 1930's mid ssubstantial u b s t a n t i a l tonnages t o n n a g e s of o f gold g o l d ore o r e were were outlined o u t 1 i n e d by by Development ddrilling. rilling. D e v e l o p m e n t pproceeded r o c e e d e d on o n three t h r e e levels l e v e l s and and a a mill was constructed. During m i l l was c o n s t r u c t e d . D uring a a one—year o n e - y e a r period, p e r i o d , 2533 2533 oounces u n c e s oof f gold g o l d and a n d 521 521 ounces o u n c e s of o f silver s i l v e r were were recovered, recovered, ore and a n d the t h erecovery r e c o v e r y were were bbut u t bboth o t h tthe h e grade g r a d e of o f the t h e ore The mine bbelow e l o w eexpectations. xpectations. T he m i n e cclosed l o s e d in i n 1940. 1940. The is mainly m a i n l y underlain u n d e r l a i n by by intermediate i n t e r m e d i a t e to to T h e aarea r e a is f e l s i c llapilli—tuff a p i l l i - t u f f aand n d tuff—breccia, t u f f - b r e c c i a , having h a v i n g a combined combined o 3000 3 0 0 0 m, m , and a n d these t h e s e are a r e overlain o v e r l a i n by by at at tthickness h i c k n e s s of o f 200 200 tto lleast e a s t 800 800 m of o f fine f i n e pyroclastics p y r o c l a s t i c s and a n d related r e l a t e d sediments. sediments. An east—trending C l e a r w a t e r Bay e a s t - t r e n d i n g syncline s y n c l i n e extends e x t e n d s through t h r o u g h Clearwater and a n d the t h e entire e n t i r e section s e c t i o n from f r o m the t h e boundary b o u n d a r y of o f the t h e Wabigoon Wabiqoon Subprovince S u b p r o v i n c e to t o Clearwater C l e a r w a t e r Bay, B a y , which w h i c h includes i n c l u d e s about a b o u t 1000 1000 m oof f foliated f o l i a t e d basalt b a s a l t at a t the t h e base, b a s e , is is bbelieved e l i e v e d to t o be be ssouth o u t h facing. facing. The T h e principal p r i n c i p a l lithologies l i t h o l o g i e s on o n the t h e peninsula p e n i n s u l a where w h e r e the the veins v e i n s are located l o c a t e d are a r e tuff; t u f f , lapilli—tuff, l a p i l l i - t u f f , and and c l a s ts within within a a dark dark ttuff—breccia, u f  £ - b r e c c i a containing c o n t a i n i n g ddacitic a c i t i c clasts matrix. i s moderate m o d e r a t e to t o strong, s t r o n g , trending t r e n d i n g east east matrix. F o l i a t i o n is Foliation aand n d ddipping i p p i n g near n e a r vertical. vertical. C l a s t s are a r e aligned a l i g n e d within within Clasts the plane t h e foliation  £ 0 i a t i o n plane. Seven S e v e n qquartz u a r t z vveins e i n s hhave a v e bbeen e e n ddiscovered, i s c o v e r e d , although a1 though most N o . 11 and a n d No. No. 3 m o s t of o f the t h e work w o r k was w a s concentrated c o n c e n t r a t e d on o n the t h e No. 3 veins. All veins. A l l oof f the t h e vveins e i n s contain c o n t a i n carbonate c a r b o n a t e and a n d most ccontain o n t a i n black b l a c k tourmaline. tourmaline. M i n e r a l i z a t i o n consists c o n s i s t s of of Mineralization minor m i n o r pyrite p y r i t e and a n d chalcopyrite c h a l c o p y r i t e with w i t h traces t r a c e s of o f galena q a l e n a and and ( 1 9 3 7 ) has h a s described d e s c r i b e d three three nnative a t i v e gold. gold. Thomson (1937) ggenerations e n e r a t i o n s of o f quartz q u a r t z iin n the t h e No. No. 3 e i n ; qquartz—carbonuartz-carbon3 v vein; aate t e veins v e i n s are a r e cut c u t by by sugary, s u g a r y , faintly f a i n t l y bluish b l u i s h quartz q u a r t z in in which w h i c h tourinaline t o u r m a l i n e aand n d ssulphides u l p h i d e s ooccur c c u r along a l o n g thin thin felsic . �36 metres Kendall Inlet Clearwater Bay Lake of the Woods Figure F i g u r e 10: 10: Location at the Locat i o n of of gold—bearing g o l d - b e a r i n g vveins e i n s at theKenricia Kenricia Gold Gold Mine. Mine. �I 37 fractures, and these are cut by glassy white iuartz. largely restricted to the sugary quartz. Quartz veins in the Kenricia Mine area occur within zones where there has been a strong component of shear. These zones are parallel, or slightly oblique to regional foliation and contain concentrations of quartz, carbonate, tourmaline and biotite. Gold is restricted to quartz veins and to immediately adjacent altered wall GoLd is rocks. Here the lapilli—tuff is moderately IefocnedTith clasts elongate parallel to foliation. Locality A. vein has been traced for 475 m It is best exposed at the east end of the trenches where it is in contact with highly sheared wall rock. Fragments of wall rock are found throughout the vein but are concentrated near the margins. Quartz varies from suqary and white to coarse and clear; minor sulphides, tourmaline and hiotite are present in both types. The host schists contain up to 3% fine disseminated pyrite, are strongly silicified and are cut by quartz—carbonate veinlets. Coarse biotite is common at margins of the veinlets and alsd as flakes which cut across foliation and clast boundaries in th& host rocks. Analyses of sugary quartz, wall—rock schiat and clear quartz showed the gold content to be 310 ppb, 260 ppb and 505 ppb respectively. A second sample of clear quartz contained 855 ppb gold. Locality B. The No. 1 ffiirg5raximam width of 1.3 m. Some 20 m south of No. vein is an outcrop of strongly foliated dacitic lapilli—tuff. The rock is essentially a quartz—sericite—biotite—carhonate schist and contains rare broken remnants of sodic oliqoclase. An analyzed sample contained 3 ppb gold. 1 Locality D. At this locality several veins, E3TTEEWéTy known as No. la vein, comprise less tnan 30% of a zone of sheared dacitic lapilli—tuff. Bluish—white sugary quartz lies within the east—trending foliation plane as well as northeast—trending fractures, and encloses numerous fragments of wall rock. Veinlets of tourrnaline cross the quartz. The host schists contain carbonate and 3% euhedral pyrite. A sample of vein material contained 3590 ppb qold, and the pyritiferous schist contained 540 cob gobi. Return to Kenora. En route we will pass exposures of foliated volcanics and volcanogenic sediments. DAY 2 Proceed 5. 3 km east along Hiqhway 17 from the Thurist In formation Centre, to the junction of the Jones Road. Felsic pyroclastic �38 rocks r o c k s are a r e interlayered i n t e r l a y e r e d with w i t h basalts b a s a l t s near n e a r the t h e town, t o w n , hut b u t much much of of At the A t the the t h e route r o u t e passes p a s s e s through t h r o u g h massive, m a s s i v e , pillowed p i l l o w e d basalts. basalts. Highway 17 —- Jones J o n e s Road Road intersection, i n t e r s e c t i o n , quartz q u a r t z monzonite m o n z o n i t e with w i t h large large H i g h w a y 17 euhedral e u h e d r a l microcline m i c r o c l i n e megacrysts m e q a c r y s t s lies l i e s at a t the t h e southern s o u t h e r n edge e d g e of o f an an o v a l stock. s t o c k . Turn T u r n left l e f t (northeast) ( n o r t h e a s t ) on o n the t h e Jones J o n e s Road. R o a d . This This oval gravel g r a v e l road r o a d crosses c r o s s e s the t h e eastern e a s t e r n edge e d g e of o f the t h e quartz q u a r t z monzonite monzonite stock s t o c k up up to to the t h e railroad r a i l r o a d crossing c r o s s i n g and a n d then t h e n passes p a s s e s through t h r o u q h massive massive Proceed t o foliated f o l i a t e d basalt. basalt. P r o c e e d 1.6 1 . 6 km km beyond b e y o n d the t h e railroad r a i l r o a d crossing, crossing , to turn t u r n left l e f t (north) ( n o r t h ) on o n dirt d i r t tracks t r a c k s through t h r o u g h open o p e n clearings c l e a r i n g s and a n d then then west west through t h r o u q h light l i g h t bush b u s h to t o the t h e Scramble S c r a m b l e Gold G o l d Mine M i n e (total ( t o t a l distance distance 1 . 1 km km from f r o m the t h e Jones J o n e sRoad) R o a d. ) . The T h e dirt d i r t track t r a c k crosses crosses the t h e axial axial o f 1. Qf trace t r a c e of o f the t h e northeast—trending n o r t h e a s t - t r e n d i n g Airport A i r p o r t Anticline. Antic1ine. 1 STOP 55 SCRAMBLE STOP SCRAMBLE GOLD GOLD MINE M I N E (Figure ( F i g u r e 11) 11 ) --------------- Gold G o l d was was discovered d i s c o v e r e d on o n this t h i s property p r o p e r t y in i n the t h e 1890's 1890's and a n d several s e v e r a l interests i n t e r e s t s "scrambled" " s c r a m b l e d " to t o obtain o b t a i n aa working working option o p t i o n on o n it. i t . The T h e Scramble S c r a m b l e Gold G o l d Mining M i n i n g Company Company was was incorporated i n c o r p o r a t e d in i n 1897. 1 8 9 7 . Two Two shafts s h a f t s were were sunk s u n k and a n d some some underground u n d e r g r o u n d development d e v e l o p m e n t took t o o k place, p l a c e , but b u t there t h e r e was w a s no no gold g o l d production. p r o d u c t i o n . The T h e property p r o p e r t y lay l a y idle i d l e until u n t i l 1984 1 9 8 4 when when Boise B o i s e Cascade C a s c a d e Corporation, C o r p o r a t i o n , current c u r r e n t owners o w n e r s of o f the the property, p r o p e r t y , began b e g a n investigating i n v e s t i g a t i n g its i t s gold g o l d potential. potential. Bedrock B e d r o c k exposed e x p o s e d in i n aa recently r e c e n t l y stripped s t r i p p e d area a r e a consists c o n s is t s of o f northwest—facing n o r t h w e s t - f a c i n q pillowed p i l l o w e d basalt b a s a l t and a n d medium—grained med i u m - g r a i n e d basalts b a s a l t s that t h a t are a r e either e i t h e r subvolcanic s u b v o l c a n i c sills s i l l s or or coarser— coarserFelsite grained g r a i n e d flows. flows. F e l s i t e dikes d i k e s were were intruded i n t r u d e d into i n t o the the basalts, b a s a l ts , especially e s p e c i a l l y along a l o n g northeast— n o r t h e a s t- striking s t r i k i n g zones zones o f shearing. shearing. of Within W i t h i n the t h e stripped s t r i p p e d area, a r e a , sampling s a m p l i n g by b y Boise Boise p e r s o n n e l has h a s indicated i n d i c a t e d that t h a t gold g o l d isismore more abundant a b u n d a n t in i n aa personnel zone z o n e ssubparallel u b p a r a l l e l to, t o , and a n d immediately i m m e d i a t e l y southeast s o u t h e a s t of o f the the felsite f e l s i t e dikes. d i k e s . Our O u r ssampling a m p l i n g ssuggests u g g e s t s that t h a t gold g o l d values values a r e highest h i g h e s t (0.37 ( 0 . 3 7 oz. o z . Au Au per p e r ton t o n over o v e r 1.5 1.5m) m ) at a t locality locality are (Figure where ( F i g u r e 11) 11) w h e r e the t h e zone z o n e transects t r a n s e c t s aa felsite f e l s i t e dike. dike. The ddikes i k e s and a n d the t h e gold—bearing g o l d - b e a r i n g zone z o n e are a r e in i n aa zone z o n e of of strong is about a b o u t 20m 20rn wide, w i d e , sharply s h a r p l y bounded bounded s t r o n g shearing s h e a r i n g which w h i c h is t o the t h e northwest n o r t h w e s t (Locality ( L o c a l i t y D) D) and a n d southeast s o u t h e a s t by by to relatively r e l a t i v e l yundeformed u n d e f o r m e d ppillowed i l l o w e d bbasalts a s a l ts (Localities ( L o c a l i t i e sCCand and Remnants K). R e m n a n t s of o f mass m a s s i ive v e bbasalt a s a l t in i n the t h esheared s h e a r e d zone zone K) Major (Locality ( L o c a l i t y 3) J ) are a r e not n o tobviously o b v i o u s l y pillowed. pillowed. Major deformation within post—date deformation w i t h i n the t h e zone z o n e is is believed b e l i e v e dtot o pos t - d a t e G G . emplacement e m p l a c e m e n t o foft the h e ddikes i k e s because: b e c a u s e : the t h e dikes d i k e s themselves themselves are with a r e sheared, sheared, w i t h ffoliation o l i a t i o n in i n the t h e basalt b a s a l t cutting c u t t i n q the the dikes, d i k e s , at a t aa low l o w angle; a n g l e ; where w h e r e dikes d i k e s pass p a s s from f r o m undeformed undeformed rock r o c k into i n t o the t h e shear s h e a r zone z o n e they t h e y have h a v e suffered s u f f e r e d drag drag (Locality ( L o c a l i t y D); D ) ; ffold o l d sstyles t y l e s in i n basaltic b a s a l t i c rocks r o c k s of o f the t h e shear shear zone mimicked z o n e are are m i m i c k e d in i n the t h e narrow, n a r r o w , attenuated a t t e n u a t e d portions p o r t i o n s of of f e l s i c dikes. dikes. felsic Quartz quartz—tourmaline Q u a r t z and and q u a r t z - t o u r m a l i n e veins v e i n s occur o c c u r in i n both b o t h the the and the basalt host. been emplaced late because they fill shears in the fels ite. They d i k e s and t h e b a s a l t h o s t . T h e y commonly c o m m o n l y sshow h o w evidence evidence dikes o f folding f o l d i n g and a n d boudinage b o u d i n a q e (Localities (Localities I I aand n d 33), ) , hut b u t must nus t of have have been emplaced l a t e because t h e y f i l l s h e a r s i n t h e f e l s ite. �-----— 39 --- t- 0 0 22 - - 4 4 6 6 8 - - > 81 tuartz vein quartz vein 10 0 felsic dike felsic dike metres '' strongly stronglydeformed deformed felsic felsic dike dike brown" basalt "brown" basalt / a basalt flows flows '12 / fold style and sense F J m. sample location C Stop 5 locations -edge of deformation zone edge of deformation zone u2 .1 L ,?C^3> outcrop felsic dike -edge of Scramble deformation zone metres £ - pillow tops trenches shaft B Figure F i g u r e 1 11:: Stop 5 locations G e o l o g y oof f the t h e Scramble S c r a m b l e Gold G o l d aarea. rea. T h e aarea r e a enclosed enclosed Geology The lowermap map isisshown shown w i t h i n the t h e rectangle r e c t a n q l e in i nthe t h elower within eenlarged n l a r g e d above. above. �40 Abundant A bundant m i n o r folds f o l d s are a r e present p r e s e n t in i n the t h e shear s h e a r zone. zone. minor F2,F and These T h e s e are a r e predominantly p r e d o m i n a n t l y ZZ folds f o l d s (Localities ( L o c a l i t i e s E , F a n d G) G) Shear though t h o u g h SS folds f o l d s also a l s o occur o c c u r (Localities ( L o c a l i t i e sF Fand a n d3 J ). ). S hear ssurfaces u r f a c e s related r e l a t e d to t o the t h e development d e v e l o p m e n t of o f ZZ ffolds o l d s sstrike t r i k e at at a variety v a r i e t y of o f angles a n q l e s (approximately ( a p p r o x i m a t e l y N45°E) N45OE) but b u t are are iinvariably n v a r i a b l y ooblique b l i q u e to t o sshear—zone h e a r - z o n e boundaries b o u n d a r i e s (about ( about N52°E). N520~). Samples S a m p l e s ccollected o l l e c t e d aacross c r o s s the t h e sshear h e a r zone z o n e (1 ( 1 to t o 13, 13, Figure 1 1 ) show s h o w distinct d i s t i n c t petrographic p e t r o g r a p h i c and a n d geochemical geochemical F i g u r e 11) Relatively ( 1 aand n d 13) 13) ppatterns. atterns. R e l a t i v e l y unaltered u n a l t e r e d basalts b a s a l t s (1 contain c o n t a i n abundant a b u n d a n t hornblende h o r n b l e n d e (70—80%), ( 7 0 - 8 0 % ) , lesser l e s s e r feldspar feldspar minor ((10—25%), 1 0 - 2 5 % ) , mminor i n o r rretrograde e t r o g r a d e bbiotite i o t i t e aand nd m i n o r ilmenite ilmenite Toward aand n d carbonate. carbonate. T o w a r d the t h e centre c e n t r e of o f the t h e deformation deformation zone biotite zone b i o t i t e increases i n c r e a s e s at a t the t h e expense e x p e n s e of o f hornblende, h o r n b l e n d e , and and epidote e p i d o t e aand n d ssphene p h e n e aare r e present p r e s e n t in i nminor m i n o r amounts. amounts. Samples S a m p l e s ffrom r o m t the h e ccentral e n t r a l part p a r tare a r magnetite—bearing. e magnetite-bearing The is shown T h e ggeochemical e o c h e m i c a l p apattern t t e r n is s h o w n i in n ffigure i g u r e 12. 12. While W h i l e t the h e ppattern a t t e r n is is complex, c o m p l e x , tthere h e r e is, i s , coincident c o i n c i d e n t with with the t h e highest h i g h e s t gold g o l d contents, c o n t e n t s ,ana nincrease i n c r e a sin e iFe203, n F e 2 0 3MgO , MgO and and The K20, K20, aand n d aa decrease d e c r e a s e ini nCaO, CaO, Na20 Na2O and a n d Al203. Al2O3. The ccentral entral ppart a r t of o f the t h edeformation d e f o r m a t i o n zone z o n e is, i s , ini ngeneral, g e n e r a l marked , m a r k e d by by aan n increase i n c r e a s e in i n K20 K20 aand n d i in n t the h e ooxidation x i d a t i o n s state t a t e oof f iron. iron. . Pillowed Locality illowed L o c a l i t y AA P llavas a v a s ssoutheast o u t h e a s t oof f the t h e Scramble Scramble i d e of o f the the armatTn z o n e aare r e oobserved b s e r v e d o on n e either i t h e r sside a ^ : o r m a t i o n zone Although trail t r a i lleading l e a d i n gtoward t o w a r d the t h e airport a i r p o r runway. t runway. A l t h o u g h not not ttoo o o distinct, d i s t i n c t , tops t o p s are a r e interpreted i n t e r p r e t e d to t o be b e toward t o w a r d the the n n oorr tth h wwes e s t. t. ----- Locality P i l l o w e d bbasalts a s a l t s are a r e in i n contact c o n t a c t with with L o c a l i t y BB Pillowed E?ained c o a r s e r - g r amassive i n e d m a s mafic s i v e m a rocks f i c r o c kwith s w i t h2—3 2-3 mm mm The coarse hornblende h o r n b l e n d e porphyroblasts, porphyroblas t s , and a n d rare r a r e garnets. garnets. The coarse vvariety a r i e t y may be b e either e i t h e r coarse c o a r s e flows f l o w s or or subvolcanic subvolcanic sills. s i l l s . Pillows P i l l o w s are a r e elongate, e l o n g a t e , but b u t appear a p p e a r to t o face f a c e north. north. Several t o those t h o s e to to S e v e r a l fine—grairied f i n e - g r a i n e d ffelsic e l s i c ddikes, i k e s , ssimilar i m i l a r to be b e sseen e e n at a t the t h e Scramble S c r a m b l e shaft, s h a f t , cut c u t both b o t h rock r o c k types. types. Margins M a r g i n s of o f the t h e dikes d i k e s are a r e feathered, f e a t h e r e d , with w i t h small s m a l l shears shears displaying d i s p l a y i n g a dominantly d o m i n a n t l y dextral d e x t r a l horizontal h o r i z o n t a l component. component. Pillowed Locality L o c a l i t y CC P i l l o w e d llavas a v a s adjacent a d j a c e n t to t o the t h e stripped stripped ---. area a r e a aaroi r o u n dthe t h eScramble S c r a m b l eshaft s h a f t are a r e exposed e x p o s e d in i n aa number number Features s m a l l outcrops. outcrops. F e a t u r e s to t o oobserve b s e r v e are: a r e : distinct distinct oof f small shapes t o the the s h a p e s of o f larger l a r g e r pillows p i l l o w s indicating i n d i c a t i n g tops t o p s to with northwest; n o r t h w e s t ; smaller, s m a l l e r , amoeboid a m o e b o i d ppillows, illows, w i t h nno o cclear l e a r top top d i k e s feeding f e e d i n g the t h epillowed p i l l o w e d sequence; sequence; iindicators; n d i c a t o r s ; mafic maf i c dikes minor m i n o r ooffset f f s e t oof f pillow p i l l o w rims rims by b y shearing s h e a r i n g and a n d faulting. faulting. A felsic Locality L o c a l i t y DD f e l s i c dike d i k e is is aat t hhigh i g h aangle n g l e to to fTTatT6 F o I T Z t i oAn isharp A s h a rflexture p f l e x t u r eini nthe t h edike d i k e marks m a r k s the the nnorthwest o r t h w e s t boundary b o u n d a r y oof f the t h e Scramble Scramble deformation d e f o r m a t i o n zone. zone. Note also a l s o quartz—tourrnaline q u a r t z - t o u r m a l i n e vveins e i n s ccutting u t t i n g tthe h e ddike i k e aat t a high angle (approx. N400E) and occupying shear surfaces h i g h a n q l e ( a p p r o x . N40OE) a n d o c c u p y i n g s h e a r s u r f a c e s that t h a t extend e x t e n d into i n t o the t h e host h o s t basalt. basalt. �41 70 65 - 6055 - I... 50- Si02 I.. I 45 -J •I. 1817C 16- total iron as N Fe203 1514- A1203 13124-' 11— FeO CaO 0 ci Q. 9— 4-' 98- \ 7— 6- I 5H MgO H— E-. 43 ::AA FeO Fe203 23 Cc.'.. ...c........c: / K22 0 Au Au replicates replicates Figure F i g u r e 12: 12: "8, \ A-A B A ^*^ 00 sample number 11 sample pumber Au Au (ppb) (ppb) )6 16 ( / ' //A\\ ' ^> B F... F...• \.\.. // I BB B / NaO Na20 B B Â¥' c ......ic!% V- / \cB B / 'B / /3 DC CA B/';\ -A 22 17 17 33 66 77 88 99 10 10 80 80 2410 2410 80 80 360 3604075 4075130 130 85 85 2200 2200 75 75 75 85 2600 85 75 2600 370 5500 135 135 370 5500 125 345 345 2650 2650 125 \A-A L 11 11 12 12 13 13 4 99 77 21 21 40 40 980 980 45 45 40 40 1000 1000 5 960 960 Geochemical traverse t r a v e r s e across a c r o s s the t h e Scramble Scramble Geochemical deformation T h e location l o c a t i o n of of samples samples is is d e f o r m a t i o n zone. zone. The i l l u s t r a t e d in i n Figure Figure 11. 1 1 . Samples Samples 11 to t o 33 and and illustrated t o 13 1 3 are a r e mafic m a f i c metavolcanjc m e t a v o l c a n i c rocks; r o c k s ; 44 and and 55 6 to a r e strongly s t r o n g l y deformed deformed felsic f e l s i c dikes. dikes. are �42 -LLocalityE --o-c a l i t y E Pronounced P r o n o u n c e d Z—folding Z - f o l d i n g of o f aa tectonic t e c t o n i c fabric fabric iin n bbasaltic a s a l t i c lavas l a v a s within w i t h i n the t h e deformation d e f o r m a t i o n zone. zone. A number number a r e present p r e s e n t and a n d are a r e interpreted i n t e r p r e t e d to t o he be oof f felsic f e l s i c units u n i t s are early Fold e a r l y felsic f e l s i c dikes, d i k e s , rather r a t h e r than t h a n tuffs t u f f s or o r flows. flows. Fold axes d i f f u s e zone z o n e of o f brown—coloured brown-coloured a x e s plunge p l u n g e steeply. s t e e p l y . A diffuse basalt b a s a l t can c a n be b e traced t r a c e d toward t o w a r d Locality L o c a l i t y F. F. Locality L o c a l i t y FF S—folding S - f o l d i n g is is indicated i n d i c a t e d in i n the t h e "brown " b r o w n zone", zone", w h TEerrninates i c h t e r m i n a t e snortheastward n o r t h e a s t w a r d against a g a i n s t aa north—northeast north-northeas t ttrending r e n d i n g shear s h e a r surface. surf ace. IIntense n t e n s e 2Z—folding - f o l d i n g in i n felsic f e l s i c and and mafic is evident. e v i d e n t . Mafic M a f i c rocks r o c k s are are interpreted i n t e r p r e t e d to to ~ a f i rocks cr o c k s is Felsic be b e pillowed p i l l o w e d basalt b a s a l t flows. flows. F e l s i c units u n i t s are a r e dikes. dikes. L o c a l i t y GG A wide w i d e felsic f e l s i c ddike i k e can c a n be b e sseen e e n to t o ddip ip Locality steerthwestward Preliminary P r e l i m i n a r y grab qrab s t e e p l y n o r t h w e s t w a in r d ithe n t h eshaft. shaft samples s a m p l e s from f r o m the t h e property p r o p e r t y indicated i n d i c a t e d highest h i g h e s t gold g o l d values values within tto o be be w i t h i n rocks r o c k s aat t tthe h e sshaft, h a f t , both b o t h in i n the t h e dike d i k e and and Immediately the mafic i c volcanics, volcanics I m m e d i a t e l y southwest s o u t h w e s t of o f the the t h e ma shaft, n u m b e r of o f narrow n a r r o w quartz—tourrnaline q u a r t z - t o u r m a l i n e veins v e i n s occupy occupy s h a f t , aa number shear a t about about s h e a r surfaces s u r f a c e s in i n the t h e dike, d i k e , and a n d strike s t r i k e at N40—45°E. N 4 0 - 4 5 O ~ . This T h i s trend t r e n d is i s also a l s o seen s e e n in i n aa quartz q u a r t z vein vein within a sshear hear aalong l o n g sstrike, trike, w i t h i n the t h e bbasalts, a s a l t s , that t h a t ooccupies ccupies a zone ( Z-fold i n q ) z o n e exhibiting e x h i b i t i n g right—lateral r i g h t - l a t e r a l movement movement (Z—folding) . . . Locality L o c a l--i t y HH Two felsic f e l s i c units u n i t s interpreted i n t e r p r e t e d to t o be be dikes dikes mark margin m a r k the t h e south—east south-east m a r g i n oof f the t h e Scramble S c r a m b l e ddeformation eformation zone. 5 , Figure F i g u r e 11) 11) z o n e . One of o f these t h e s e dikes d i k e s (Sample ( S a m p l e 5, well ccontains o n t a i n s 1000 1 0 0 0 pppb p b ggold; old; w e l l aabove b o v e bbackground a c k g r o u n d vvalues a l u e s in in tthe h e basalt b a s a l t outside o u t s i d e the t h e deformation d e f o r m a t i o n zone. zone. A large l a r g e isolated i s o l a t e d quartz q u a r t z lens l e n s occurs o c c u r s here. here. is It is unclear. unclear. It could c o u l d be the t h e dislocated d i s l o c a t e d equivalent e q u i v a l e n t of o f aa wide wide quartz—tourmaline 20 metres northeast n o r t h e a s t of o f the the q u a r t z - t o u r m a l i n e vein v e i n 20 Scramble main S c r a m b l e shaft. shaft. IIn n tthe he m a i n felsic f e l s i c dike, d i k e , numerous numerous N~OOE, nnarrow a r r o w quartz—tourmaline q u a r t z - t o u r m a l i n e v veins, e i n s , sstriking t r i k i n gabout a b o u tN40°E, cross Toward c r o s s the t h e dike d i k e at a t aalow l o w angle. angle. T o w a r d LLocality o c a l i t y 3, J, nnumerous u m e r o u s examples e x a m p l e s oof f tthese h e s e can c a n be b e seen. seen. Locality L o c a l i t y II eEural ^ ^ F T e s F r U position e t u r a l p o s i t iof o n othis f t h i slens lens Examples E x a m p l e s oof f left—lateral l e f t - l a t e r a l shear, s h e a r , with with S—folds, are S -folds, a r e sseen e e n within w i t h i n the t h e main m a i n felsic felsic dike. Right—lateral dike. R i g h t - l a t e r a l sshear h e a r is is evident e v i d e n t within w i t h i n splays s p l a y s off off tthe h e ddike i k e into i n t o basaltic b a s a l t i c country c o u n t r y rock r o c k but b u t the t h e relationship relationship Deformed tto o the t h e ssinistral i n i s t r a lshears s h e a r sis iunknown. s unknown. D e f o r m e d amoehoil amoeboid ccur p i l l o w s , s i m i l a r t o t h o s e s e e n a t L o c a l i t y C , ooccur within w i t h i n the t h e Scramble S c r a m b l e deformation d e f o r n a t i o n zone, z o n e , on o n the t h e northwest northwest F r o m this t h i s point, p o i n t , looking looking sside i d e of o f the t h e main m a i n felsic f e l s i c dike. d i k e . From toward t o w a r d the t h e Scramble S c r a m b l e shaft, s h a f t , aa pronounced p r o n o u n c e d open—Z open-Z flexure flexure in is evident. evident. i n the t h e felsic f e l s i c dikes d i k e s is Locality L o c a l i t y J3 ã6Tted associated pillows, similar to those seen at Locality C, Locality Pillow L o c a l i t y KK P i l l o w lavas l a v a s ssoutheast o u t h e a s t of o f the t h e Scramble Scramble d e fition f o r m a t i ozone n z o nsuggesting e s u g g e s t i n gtops t o p stoward t o w a r dthe t h e northwest. northwest. - L -LocalityL -o c a l i .-t y L On On line OW oof Boise's l i n e 4+0 4+OOW f B o i s e ' s ggrid, r i d , aa trench trench �43 marks m a r k s the t h e location l o c a t i o n of o f an a n IP I P anomaly a n o m a l y that t h a t the t h e company c o m p a n y has has traced The geophysical t r a c e d from f r o m the t h e Scramble S c r a m b l e shaft s h a f t area. area. geophysical anomaly s t r i k e similar s i m i l a r to t o that t h a t of o f the t h e Scramble Scramble a n o m a l y has h a s aa strike deformation d e f o r m a t i o n zone. zone. . Return, t o Highway Highway 17, 1 7 , and a n d turn t u r n left(east). lef t(east) At R e t u r n , vvia i a Jones J o n e s Road, Road, to At the t h e crest c r e s t of o f the t h e first f i r s t hhill i l l which w h i c h the t h e highway h i g h w a y crosses crosses is is an an exposure e x p o s u r e of o f pillowed p i l l o w e d basalt b a s a l t with w i t h white w h i t e carbonate c a r b o n a t e filling filling inter—pillow i n t e r - p i l l o w gaps. g a p s . Reaction R e a c t i o n between b e t w e e n the t h e carbonate c a r b o n a t e and a n d the t h e basalt basalt has is cut c u t by by h a s generated g e n e r a t e d andradite a n d r a d i t e garnet g a r n e t and a n d epidote. epidote. The basalt b a s a l t is The granitic Beyond q r a n i t i c dikes. dikes. Beyond the t h e crest c r e s t the t h e outcrop o u t c r o p is is diorite d i o r i t e and and quartz q u a r t z diorite d i o r i t e of o f the t h e Island I s l a n d Lake L a k e intrusion i n t r u s i o n which w h i c h noses n o s e s out o u t aa short s h o r t distance d i s t a n c e to t o the t h e south. s o u t h . At A t the t h e Garbage G a r b a g e Dump Dump turnoff, t u r n o f f , 1.6 1 . 6 km km beyond b e y o n d the t h e south s o u t h end e n d of o f Hilly H i l l y Lake, L a k e , turn t u r n left l e f t (northeast) ( n o r t h e a s t ) and and bear m. To To the t h e left l e f t (northwest) ( n o r t h w e s t, ) , stripping s t r i p p i n g of of b e a r left l e f t for f o r 200 2 0 0 m. overburden has been carried out in the vicinity of the Silverman overburden h a s been c a r r i e d o u t i n t h e v i c i n i t y of t h e Silverman occurrence. occurrence. STOP 6A SILVERMAN ----- GOLD PROSPECT The T h e contact c o n t a c t between b e t w e e n massive m a s s i v e quartz q u a r t z diorite d i o r i t e of o f the the Island I s l a n d Lake L a k e intrusion i n t r u s i o n and a n d massive m a s s i v e basalt b a s a l t is is very v e r y near near the a r e a . The T h e contact c o n t a c t is is irregular i r r e g u l a r in i n detail, detail, t h e parking p a r k i n q area. but r e g i o n a l trend t r e n d of o f N65°E ~ 6 5 over o0v e~r aa distance d i s t a n c e of o f at at b u t has h a s aa regional least l e a s t 1.5 1 . 5 km. km. The T h e southeast s o u t h e a s t contact c o n t a c t of o f the t h e intrusion intrusion was probably p r o b a b l y fault f a u l t controlled c o n t r o l l e d and a n d post—emplacement pos t-emplacement mOvement t o the t h e fault f a u l t has h a s resulted r e s u l t e d in i n narrow narrow m o v e m e n t parallel p a r a l l e l to zones Inclusions z o n e s of o f mylonite m y l o n i t e in i n the t h e quartz q u a r t z diorite. diorite. I n c l u s i o n s of of basalt, some of o f which w h i c h have h a v e been b e e n partly p a r t l y digested, d i g e s t e d , are are b a s a l t , some locally l o c a l l y abundant. abundant. At A t the t h e Silverman S i l v e r m a n prospect p r o s p e c t aa number n u m b e r of o f shears shears trending t r e n d i n g about a b o u t N350E N35OE and a n d having h a v i n g near n e a r vertical v e r t i c a l dips digs contain c o n t a i n quartz, q u a r t z , tourmaline t o u r m a l i n e and a n d sulphides. s u l p h i d e s . The T h e main main workings 1 3 . 4 mm shaft s h a f t and a n d two t w o open o p e n cuts cuts w o r k i n g s consist c o n s i s t of o f aa 13.4 from Eron which w h i c h 184 1 8 4 tons t o n s of o f ore o r e were were shipped s h i p p e d for f o r milling m i l l i n g in in 1941. T h e average a v e r a g e gold g o l d content c o n t e n t of o f the t h e ore o r e was was 0.575 0 . 5 7 5 oz oz 1 9 4 1 . The per p e r ton. t o n . The T h e main m a i n vein v e i n was was up u p to to 50 5 0 cm c m wide w i d e but b u t was was discontinuous; d i s c o n t i n u o u s ; it i t was was emplaced e m p l a c e d within w i t h i n aa strong s t r o n g shear shear zone, a r e several several z o n e , and a n d where w h e r e the t h e main m a i n vein v e i n pinches p i n c h e s there t h e r e are parallel thin quartz veins within the shear. parallel thin quartz veins within the shear. The is sugary s u g a r y and a n d black b l a c k tourmaline t o u r m a l i n e is is T h e quartz q u a r t z is abundant locally. a b u n d a n t l o c a l l y . Pyrrhotite, P y r r h o t i t e , pyrite p y r i t e and a n d traces t r a c e s of of t o 22 percent. percent. c h a l c o p y r i t e are a r e present p r e s e n t in i n amounts a m o u n t s up u p to chalcopyrite Samples S a m p l e s of o f fresh f r e s h quartz q u a r t z diorite d i o r i t e and a n d highly h i g h l y sheared sheared quartz were q u a r t z diorite d i o r i t e adjacent a d j a c e n t to t o the t h e mined m i n e d vein v e i n were analyzed. Relative analyzed. R e l a t i v e to t o the t h e fresh f r e s h rock r o c k the t h e sheared s h e a r e d rock rock showed n e t loss l o s s of of Si02, S i O 2 , Al203, A l 2 0 3 , Na20, Na20, As, A s , Sb S b and a n d Pb, Pb, s h o w e d aa net and The g a i n of o f K2O, K20, 002 CO2 and a n d H2O. H2O. The gold g o l d content c o n t e n t of o f the the a n d aa gain fresh w a s lless e s s than t h a n 22 ppb p p b and a n d of o f the t h e sheared s h e a r e d rock rock f r e s h rock r o c k was 88 ppb. Ppb* Clearing C l e a r i n g aand n d bblasting l a s t i n g hhas a s been b e e n ccarried a r r i e d oout u t in i n the the area Here, a r e a between b e t w e e n the t h e Silverman S i l v e r - m a n vein v e i n and a n d the t h e road. r o a d . Here, quartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s occur o c c u r in i n aa swarm, s w a r m , occupying occupying shear g e n e r a l N50°E ~ 5 0 trend. t0r e~n d . Small S m a l l drags d r a q s and and s h e a r zones z o n e s with w i t h aa general . �44 Z—folds Z - f o l d s indicate i n d i c a t e dextral d e x t r a l shear. s h e a r . Their T h e i r style s t y l e and and orientation o r i e n t a t i o n is is similar s i m i l a r to t o those t h o s e at a t the t h e Scramble. Scramble. Deformation D e f o r m a t i o n continued c o n t i n u e d after a f t e r emplacement e m p l a c e m e n t of o f the t h e veins, veins, since s i n c e they t h e y are a r e themselves t h e m s e l v e s drag—folded. drag-folded. IIn n pplaces l a c e s the the vveins e i n s ooccupy c c u p y sstrong t r o n g shear s h e a r zones z o n e s aa few f e w tens t e n s of of centimetres o r the t h e shears s h e a r s themselves t h e m s e l v e s are are c e n t i m e t r e s wide, w i d e , or apparently w h i l e the t h e immediate i m m e d i a t e host h o s t diorite diorite a p p a r e n t l y unaltered, u n a l t e r e d , while Granitoid is is eenriched n r i c h e d in i n tourmaline t o u r m a l i n e and a n d silica. silica. G r a n i t o i d veins, veins, which w h i c h occur o c c u r in i n both b o t h the t h e diorite d i o r i t e and a n d basalt b a s a l t inclusions inclusions are a r e cut c u t by b y felsite f e l s i t e dikes d i k e s that t h a t have h a v e been b e e n strongly s t r o n g l y sheared sheared parallel t o their t h e i r length. length. p a r a l l e l to Return km to R e t u r n to t o the t h e parking p a r k i n g area a r e a and and ccontinue o n t i n u e northeast n o r t h e a s t for f o r 00.8 . 8 km to The trail the t h e Treasure T r e a s u r e prospect. prospect. The t r a i l is is almost a l m o s t on o n the t h e quartz quartz but ddiorite—basalt i o r i t e - b a s a l t contact c o n t a c t for f o r about a b o u t 100 100 m m northeast n o r t h e a s t of o f Stop S t o p 6, 6, b ut there is llittle i t t l e bedrock b e d r o c k vvisible i s i b l e until u n t i l the t h e Treasure T r e a s u r e prospect p r o s p e c t is is t h e r e is reached. reached . STOP 6B 6B -- - ---- - TREASURE_GOLD (Figure TREASURE GOLD PROSPECT ( F i g u r e 13) 13) - -a The T h e mine m i n e was was developed d e v e l o p e d between b e t w e e n 1891 1891 and a n d 1900, 1 9 0 0 , when two main t w o sshafts h a f t s were sunk s u n k on o n the the m a i n zone z o n e and a n d a third t h i r d on a a separate t o the t h e southeast. s o u t h e a s t . Additional A d d i t i o n a l work work s e p a r a t e zone z o n e 200 200 mm to was ddone was o n e about a b o u t 1955 1 9 5 5 when when aa small s m a l l mill m i l l was was set s e t up. up. Recorded is about a b o u t 35 35 ounces o u n c e s of o f gold. gold. R e c o r d e d production p r o d u c t i o n is Quartz Q u a r t z ddiorite i o r i t e underlies u n d e r l i e s the t h e area, a r e a , the t h e main m a i n vein vein being n o r t h w e s t of o f the t h e contact c o n t a c t with w i t h basalt. basalt. b e i n g about a b o u t 400 4 0 0 m northwest The vvein i e s at a t tthe h e hhanging a n g i n g wall w a l l of o f aa shear s h e a r zone z o n e which which The e i n llies strikes s t r i k e s from f r o m N350E ~ 3 to ~5 and t o 5N50°E ~ a n~d0 dips d i p~s about a b~o u t 750 75O Thevvein's width is about a b o u t 15 1 5 cm, c m , but but nnorthwest. orthwest. The e i n ' s average average w i d t h is iitt widens w i d e n s to t o 60 6 0 cm cm and and iin n places p l a c e s pinches p i n c h e s out out Tourmaline is common common a nand d p pyrite y r i t e is is a a minor minor ccompletely. ompletely. T o u r m a l i n e is constituent. Gold constituent. G o l d ooccurs c c u r s aas s ffine i n e grains g r a i n s and and is also also l i p surfaces. surf aces ssmeared m e a r e d oon n sslip IItt has h a s been b e e n reported r e p o r t e d (Joop ( J o o p Langelaar, L a n g e l a a r , personal personal communication, c o m m u n i c a t i o n , 1 91983) 8 3 ) t hthat, a t , iin n the t h e main m a i n sshaft, haft, a a series series ooff qquartz u a r t z veins v e i n s is is present p r e s e n t at a t the t h e footwall f o o t w a l l of o f the t h e shear shear These t o the t h e hanging—wall hanging-wall zzone. one. T h e s e vveins e i n s are a r e at a t an a n angle a n g l e to manner ' f o l d e d ' in i n aa m a n n e r indicating i n d i c a t i n g normal normal vvein e i n but b u t are a r e 'folded' movement oon o h have a v e l ilittle t t l e llateral ateral n tthe h e sshear h e a r pplane, l a n e , aand n d s so The continuity. were either e i t h e remplaced emplaced continuity. T h e ffootwall o o t w a l l veins v e i n s were eearlier a r l i e rthan t h a nthe t h ehanging—wall h a n g i n g - w a l l vvein, e i n , or or both b o t h were were eemplaced m p l a c e d simultaneously s i m u l t a n e o u s l y within w i t h i n aa fault f a u l t zone z o n e and a n d its its associated a s s o c i a t e d pinnate p i n n a t e fractures. fractures. The main to curve c u r v e westward w e s t w a r d at a t its i t s south south m a i n vein v e i n appears a p p e a r s to end, e n d , and a n d possibly p o s s i b l y to t o terminate t e r m i n a t e against a g a i n s t aa mylonite m y l o n i t e which which t o the t h e southeast. southeast. T he sstrikes t r i k e s N65°E ~ 6 5 and a0n d~ dips d i p s 750 7 5 0 to The Chemical mylonite c m to t o 33 m. m. C hemical m y l o n i t e has h a s aa width w i d t h of o f from f r o m 10 10 cm aanalyses n a l y s e s of o f the t h e mylonite m y l o n i t e indicate i n d i c a t e that, t h a t , relative r e l a t i v e to t o the the enclosing more e n c l o s i n g quartz q u a r t z diorite, d i o r i t e , the t h e mylonite m y l o n i t e contains c o n t a i n s more ssilica i l i c a (69.5% ( 6 9 . 5 % vs v s 62.2%) 6 2 . 2 % ) and and soda s o d a (4.05% ( 4 . 0 5 % vs v s 3.35%) 3. 3 5 % )and and carbonate c a r b o n a t e (1.28% ( 1 . 2 8 % vs v s 0.13%), 0. l 3 % ) , but b u t contains c o n t a i n s less l e s s of o f other other metal oxides o x i d e s (notably ( n o t a b l y iron i r o n and a n d magnesium) m a g n e s i u m ) and and trace trace is less Theggold metals. m etals. The o l d ccontent o n t e n t oof f both b o t h rocks r o c k s is less than t h a n 22 . �45 3 1 - a Outcrop ~ u c k pile Granodiorite Mylonite Pit Quartz vein metres Figure 13: Figure 13: Geologyofof the the Theasure Geology Treasure gold gold occurrence. occurrence. �46 ppb. P P ~ Replicate R e p l i c a t e analyses a n a l y s e s of o f aa chip c h i p sample s a m p l e across a c r o s s 23 2 3 cm cm of of the main vein showed the gold content to be erratic t h e main v e i n showed t h e g o l d c o n t e n t t o b e e r r a t i c AA grab ( f r o m 20 2 0 ppb ppb to t o 17.7 1 7 . 7 ppm). ppm) g r a b sample s a m p l e of o f the t h e vein vein (from averaged a v e r a g e d 50 50 ppm ppm Au Au and a n d of of the t h e footwall f o o t w a l l schist s c h i s t about a b o u t 90 90 ppb Au. Au. Another A n o t h e r sample s a m p l e of o f the t h e mylonite m y l o n i t e near n e a r the t h e shaft shaft ppb 1 2 ppb ppb Au. Au. All A l l samples s a m p l e s contained c o n t a i n e d less l e s s than than c o n t a i n e d 12 contained ppm silver. silver. 22 ppm . Return R e t u r n to t o the t h e highway highway and and turn t u r n left l e f t (southeast) ( s o u t h e a s t ) for f o r aa distance d i s t a n c e of of 1 . 6 km. km. All A l l of o f the t h e highway highway cuts c u t s are a r e in i n basalt. b a s a l t . Thrn T u r n right right 1.6 (southwest) m , where where aa s o u t h w e s t ) down down aa cottage—access c o t t a g e - a c c e s s road r o a d for f o r about a b o u t 200 200 m, t r a i l leads l e a d s south s o u t h to t o the t h e Pine P i n e Portage P o r t a g e Mine. Mine. trail STOP 77 PINE PINE PORTAGE PORTAGE GOLD GOLD MINE MINE (Figure ( F i g u r e 11) 14) STOP Originally O r i g i n a l l y discovered d i s c o v e r e d in i n 1882, 1 8 8 2 , the t h e Pine P i n e Portage P o r t a g e mine mine gained i t s abundant a b u n d a n t visible v i s i b l e gold. gold. g a i n e d early e a r l y recognition r e c o g n i t i o n for f o r its m i l l had had been b e e n built b u i l t on o n an an W i t h i n 33 years, y e a r s , aa stamp s t a m p mill Within intermittent stream and some underground development was i n t e r m i t t e n t stream and some u n d e r g r o u n d d e v e l o p m e n t was c a r r i e d out. o u t . Since S i n c e that t h a t time t i m e the t h e property p r o p e r t y has h a s been been carried explored e x p l o r e d several s e v e r a l times. times. The i s hosted h o s t e d by by west—facing, w e s t - f a c i n g , north—northnorth-northThe prospect p r o s p e c t is east e a s t trending, t r e n d i n g , pillowed p i l l o w e d and and massive m a s s i v e basaltic b a s a l t i c flows, f l o w s , and and lies less than 50 m east of the steeply dipping contact l i e s l e s s t h a n 50 m e a s t o f t h e s t e e p l y d i p p i n g c o n t a c t o f the t h e Dryberry D r y b e r r y granodiorite g r a n o d i o r i t e batholith. b a t h o l i t h . The The of granodiorite is massive to weakly f o l i a t e d and and contains contains g r a n o d i o r i t e i s m a s s i v e t o weakly foliated Granitic dikes in t h e basalt basalt f e w basaltic b a s a l t i c inclusions. inclusions. G r a n i t i c d i k e s i n the aa few a r e rare. rare. are Vein i n f i l l s aa strongly s t r o n g l y sheared s h e a r e d and and faulted faulted V e i n material m a t e r i a l infills i s at a t least l e a s t 3.5 3 . 5 mm wide. wide. Near Near the t h e inclined inclined z o n e which which is zone shaft s h a f t the t h e vein v e i n strikes s t r i k e s approximately a p p r o x i m a t e l y north n o r t h and and dips d i p s from from N65° ~ 6 to t o5 75°E; 7 5~ O ~ it ; i t has h a s been b e e n traced t r a c e d north n o r t h about a b o u t 200 200 mm where where it i t curves c u r v e s slightly s l i g h t l y to t o the t h e east. e a s t . The The main m a i n vein v e i n follows follows the t h e well—defined w e l l - d e f i n e d hanging h a n g i n g wall w a l l of of the t h e zone z o n e and and has h a s an an irregular i r r e g u l a r footwall f o o t w a l l contact c o n t a c t and and is i s commonly commonly wider w i d e r where where t h e footwall f o o t w a l l amphibolite a m p h i b o l i t e is i s brecciated. b r e c c i a t e d . The The vein vein the consists c o n s i s t s of o f discontinuous d i s c o n t i n u o u s lenses l e n s e s of of quartz, q u a r t z , with with carbonate c a r b o n a t e and and inclusions i n c l u s i o n s of o f schist. s c h i s t . An An old o l d assay a s s a y plan plan shows shows that t h a t the t h e mineralized m i n e r a l i z e d section s e c t i o n had had aa maximum maximum width width o f up up to t o 55 m. m. of Along the t h e hanging h a n g i n g wall w a l l there t h e r e is i s aa zone z o n e of o f fault fault Along gouge g o u g e several s e v e r a l centimetres c e n t i m e t r e s wide, w i d e , characterized c h a r a c t e r i z e d by by a b u n d a n t clay c l a y minerals. m i n e r a l s . No No ssilicification i l i c i f i c a t i o n of o f this t h i szone zone abundant was was detected d e t e c t e d and and only o n l y low low gold g o l d contents c o n t e n t s were w e r e found. found. Relative byt hthe e f i n e d by e rrotation o t a t i o n of o f aa R e l a t i v e movement movement i sisddefined well—developed "3"f ofoliation "C" w e l l - d e v e l o p e d "S1' l i a t i o n iinto n t o the t h e plane p l a n e of o f the t h e"C" foliation f o l i a t i o nindicating i n d i c a t i nreverse g r e v e r movement s e movement(Simpson (Simpson and and 1 9 8 3 ). Later L a t e r "S"—shaped "S"-shaped t etension n s i o n ggashes a s h e s indicate indicate Schmid, 1983) Schmid, normal movement;t hthis mayhhave n o r m a l movement; i s may a v e r eresulted s u l t e d ffrom r o m rrelaxation elaxation o f applied a p p l i e d stress. s t r e s s . Quartz Q u a r t z post—dates p o s t - d a t e s the t h e major m a j o r period period of of o f movement, movement, occupying o c c u p y i n g structures s t r u c t u r e s parallel p a r a l l e l to t o the t h e "C" "C" fabric f a b r i c as a s well w e l l as a s the t h e tension t e n s i o n gashes. sashes. Pyrite P y r i t e is i s the t h e principal p r i n c i p a l sulphide. s u l p h i d e . Chalcopyrite, Chalcopyrite, . �47 / / / /- '+4-4+ +,_++ 1 7+ ++ /+ I \------ /I'I /-----+ I / + + --.-. ----\ -1 1 H ' Tailings1 / / \ \ - Geological Geologicalcontact contact Liii Basalt Outcrop Open cut Eu Muck 1 Figure Figure Granite Hornblende—chlorite schist 14: 14: Muck trench Foliation, Foliation, dip dip Pine Portage Prospect Prospect Pine 0 • 20 mstres Geology Geology of o f the the Pine Pine Portage P o r t a g e gold gold occurrence. occurrence. 40 I + + + + L.._—J shack —— + + + ++ ++ + Core _— + + + j11 / (. + + �48 ggalena a l e n a and a n d sphalerite s p h a l e r i t e are a r e present p r e s e n t in i n lesser l e s s e r amounts a m o u n t s and and tthere h e r e is is rare r a r e pyrrhotite, p y r r h o t i t e , twinned t w i n n e d ilmenite, ilmenite , arsenopyrite, a r s e n o p y r i t e , covellite c o v e l l i t e and a n d gold. g o l d . The T h e main m a i n gangue gangue minerals m i n e r a l s are a r e quartz, q u a r t z , ankerite, a n k e r i t e , calcite, c a l c i t e , and a n d mica mica and and Fine c l a y minerals. minerals. F i n e qold g o l d (less ( l e s sthan t h a n20 2 0microns) m i c r o n s ) is clay found f o u n d iin n tthe h e gangue g a n g u e a and n d a sasi inclusions n c l u s i o n s i in n ppyrite; y r i t e ; coarser coarser The ggold o l d is is erratically e r r a t i c a l l y distributed. distributed. T h e larger l a r g e r pyrite pyrite ggrains r a i n s are a r e zoned z o n e d and a n d in i n places p l a c e s enclose e n c l o s e silicates, silicates , Sphalerite ppyrrhotite, y r r h o t i t e , sphalerite s p h a l e r i t e or or chalcopyrite. chalcopyrite. S p h a l e r i t e is is Tellurium ggenerally e n e r a l l y found f o u n d in i n ribbons r i b b o n s of o f mafic ma i c schist. schist. T ellurium ( Forsgren hhas a s bbeen e e n ddetected e t e c t e d by b.y microprobe m i c r o p r o b e aanalysis n a l y s i s (Forsgren The 1980); present. 1 9 8 0 ) ; calaverite c a l a v e r i t e(AuTe2) ( A u T e 2 ) may may bbe e p resent. The most most characteristic h e high high c h a r a c t e r i s t i c f e a t u r e o f t h e m i n e r a l i z a t i o n is tthe t w i c e the t h e ggold o l d content; c o n t e n t ; most ssilver i l v e r content, c o n t e n t , being b e i n g about a b o u t twice g o l d occurrences o c c u r r e n c e s iin n the t h e Kenora K e n o r a aarea r e a hhave a v e aa ssilver ilver gold content c o n t e n t which w h i c h is is near n e a r or o r below b e l o w detection d e t e c t i o n limits. limits T h e ffault a u l t with w i t h which w h i c h the t h e Pine P i n e Portage P o r t a g e prospect p r o s p e c t is is The aassociated s s o c i a t e d extends e x t e n d s iinto n t o the t h e Dryberry D r y b e r r y batholith. bath01 i t h . Mineralization to M i n e r a l i z a t i o n may be b e largely l a r g e l y restricted r e s t r i c t e d to Forsgren irregularities i r r e g u l a r i t i e s in i n the t h e fault f a u l t plane. plane. F o r s g r e n (1980) ( 1 980 ) cconcluded o n c l u d e d that t h a t "this " t h i s epigenetic, e p i g e n e t i c , sheared s h e a r e d fissure f i s s u r e vein v e i n is is thought t h o u g h t to t o be b e the t h e result r e s u l t ooff wall w a l l rock r o c k alteration a l t e r a t i o n and and he aa is proposed p r o p o s e d to t o be llateral a t e r a l secretion. s e c r e t i o n . The T h e vein v e i n is rredistribution e d i s t r i b u t i o n ooff host h o s t rock r o c k chemistry c h e m i s t r y with w i t h induced induced Ca2, z 0 and a n d S. S. Meteoric water may he be the the vvolatiles olatiles C 0 2 , HHO ssource o u r c e of o f these t h e s e volatiles." volatiles feature of the mineralization is - ." Return R e t u r n aalong l o n g the t h e trail t r a i l which, w h i c h , in i n part, p a r t , coincides c o i n c i d e s with w i t h the the At northward A t the t h e highway, highway, n o r t h w a r d extension e x t e n s i o n of o f the t h e Pine P i n e Portage P o r t a g e fault. fault. across a c r o s s from f r o m the t h e road r o a d leading l e a d i n g to t o stop s t o p 7, 7, iirregular r r e g u l a r lenses l e n s e s and and vveins e i n s of o f tourmaline t o u r m a l i n e and a n d pyrite—bearing p y r i t e - b e a r i n q quartz q u a r t z occur o c c u r in i n the the The basalts. b a s a l ts The contact c o n t a c t oof f the t h e basalts b a s a l t s with w i t h the t h e Dryberry Drybe r r y well is w e l l eexposed x p o s e d in i n a hhighway i g h w a y cut, c u t , 350m 350m ssoutheast o u t h e a s t of of ggranodiorite r a n o d i o r i t e is Continue this e a s t for f o r 7.2 7 . 2 km to t o the t h e junction j u n c t i o n of o f Highway Highway t h i s point. point. C o n t i n u e east 71 5. 5 km to t o Rushing R u s h i n g River R i v e r Provincial Provincial 71 aand n d then t h e n turn t u r n right r i g h t (south) ( s o u t h ) 5.5 Fromhhere it is Park. is a further f u r t h e r 6.4 6 . 4 km km tto o the t h e turnoff t u r n o f f onto o n t o the the Park. From e r e it Witch A l l of o f the t h e rocks r o c k s along a l o n g the t h e route r o u t e thus t h u s far, f a r , and and W i t c h Bay Bay Road. R o a d . All kmaalong Witch BayRRoad, for f o r the t h e first f i r s t 55 km l o n g t the he W i t c h Bay o a d , a rare e p part a r t oof f the the The Dryberry o f the t h e Witch W i t c h Bay Bay Road Road is is D r y b e r r y batholith. batholith. T h e second s e c o n d 55 km of within w i t h i n bbasalts a s a l t s which w h i c h are a r e the t h e approximate a p p r o x i m a t e stratigraphic s t r a t i q r a p h i c equivalent equivalent At of a t the t h e Pine P i n e Portage P o r t a g e Mine. Mine. At a a junction j u n c t i o n about a b o u t 10 10 km km o f those t h o s e at from f r o m Highway Highway 71, 7 1 , turn t u r n to t o the t h e right r i g h t and a n d continue c o n t i n u e 300 300 mm to t o the t h e site site of o f the t h e former f o r m e r shaft s h a f t and a n d mill m i l l of o f the t h e Wendigo W e n d i g o Gold G o l d Mine. Mine. . THE WENDIGO GOLD-COPPER GOLD—COPPER MINE STOP STOP 88 THE M I N E (Figure_15) ( F i q u r e 15 Gold G o l d was was first f i r s t discovered d i s c o v e r e d on o n the t h e property p r o p e r t y in i n 1899, 1899, Work when an 18m shaft was sunk on the main vein. a n 18m s h a f t was s u n k o n t h e m a i n v e i n . continued c o n t i n u e d during d u r i n g the t h e next n e x t year y e a r and a n d about a b o u t 1000 1 0 0 0 tons t o n s of of The mine gold—copper o r e were were milled. milled. The m i n e lay l a y idle i d l e until until g o l d - c o p p e r ore when iit was re—examined t was r e - e x a m i n e d by b y Wendiqo W e n d i q o Gold G o l d Mines Y i n e s Ltd. Ltd. 11933 9 3 3 when O v e r tthe h e next n e x t ten t e n yyears e a r s considerable c o n s i d e r a b l eunderground u n d e r g r o u n d and and Over was mine ssurface u r f a c e work work w a s ddone o n e b before e f o r e t the he m i n e cclosed l o s e d i in n eearly arly Total 11943. 943. T o t a l production p r o d u c t i o n from f r o m the t h e property p r o p e r t y was was 67,000 6 7 , 0 0 0 oz oz �49 Las La 3.11. — — .— Gaqe• t.ak. 7 - — — — —— — - /• _V V — — /477 7— —V s7 — — 7——— 2 —— ., — .&I = = ?- -¥à ## A /// /// /// — — — -> ———-— —— — I shaft shaft I1 Basalt Basalt building building swamp swamp gravel gravel road road geological geotogical contact contact lault fault area area of of outcrop outcrop anticline. anticline,syncline synctine pillow pillow lacing facing 22 Porpbyritic Porphyritic Basalt Basalt 33 LeucocratiC Leucocratic t3abbro Gabbro 44 Melanogabbro Melanogabbro 5 S @ Field Field stop stop location location 00 -' dragf old dragfokj weak foliation foliation(inclined, (inclined. vertical, dip dip unknown) unknown) strong strong foliation foliation(inclined, (inclined, vertical, vertical, dip dip unknown) unknown) F i g u r e 15: 15: Figure Pendotfie Penctotite 190 100 200 200 metres Surface S u r f a c e geology g e o l o g y of of the t h eWendigo Wendigo Gold Gold Mine. Mine. 300 300 �50 of o f gold, g o l d , 14,762 1 4 , 7 6 2 oz o z of o f silver s i l v e r and and 1,886,246 1 , 8 8 6 , 2 4 6 pounds p o u n d s of of copper c o p p e r from f r o m 206,054 2 0 6 , 0 5 4 tons t o n s milled, m i l l e d , establishing e s t a b l i s h i n g the the Wendigo W e n d i g o as a s the t h e largest l a r g e s t past p a s t producer p r o d u c e r in i n the t h e western western Wabigoon Subprovince. S u b p r o v i n c e . Average A v e r a g e grade g r a d e of o f ore ore milled m i l l e d was was 0.33 0 . 3 3 oz o z of o f Au/ton. Au/ton. Wendigo Wendigo Mine Mine lies l i e s on o n the t h e south s o u t h limb l i m b of o f the t h e Hay Hay Island and 6) 6 9 within w i t h i n mafic maÂi c volcanics volcanics I s l a n d antiform a n t i f o r m (Figures ( F i g u r e s 55 and t o ultraznafic u l t r a m a f i c sills. s i l l s Metamorphic . M e t a m o r p h i c grade g r a d e is is a n d mafic maf i c to and Analogies lower lower ggreenschist r e e n s c h i s t facies. facies A n a l o g i e s between b e t w e e n the the stratigraphy s t r a t i g r a p h y here h e r eand a n data the t t hDuport e D u p o rMine t Mineon onShoal S h o a lLake Lake can twoo occur closet oto tthe op of c a n be be drawn; d r a w n ; t the h e two c c u r close h e .top o f aa lower lower mafic maÂi c volcanic v o l c a n i c cycle. cycle. Felsic F e l s i c pyroclastic p y r o c l a s t i c rocks r o c k s are a r eexposed e x p o s e d south s o u t h of o f the the mine m i n e aalong l o n g tthe h e north n o r t h shore s h o r e of o f Witch W i t c h Bay. Bay. The The felsic felsic rocks t o sericite sericite r o c k s are a r e intensely i n t e n s e l y deformed, d e f o r m e d , commonly to Only rarely schist. r a r e l y are a r e good g o o d relic r e l i c primary p r i m a r y textures textures schist. is the the locus l o c u s of o f an an p r e s e r v e d . The The ffelsic e l s i c sequence s e q u e n c e is preserved. extensive Bay—Witch Bay ffault e x t e n s i v e fault f a u lsystem, t s y s t e mthe , t Andrew h e Andrew Bay-Witch Bay ault zone z o n e (Figure ( F i g u r e 5), 5 1 , which w h i c h Ayer A y e r (1984) ( 1 9 8 4 ) suggests s u g g e s t s is is the the extension Lake—Rush Bayd dextral e x t e n s i o n of of the t h eCrouck Crowduck Lake-Rush Bay e x t r a l ffault ault zone z o n e (Davies ( D a v i e s and and Smith, S m i t h , 1984). 1 9 8 4 ) . The T h e ffault, a u l t , therefore, therefore, may extend e x t e n d from f r o m Indian I n d i a n Bay Bay of o f Shoal S h o a l Lake Lake to t o Witch W i t c h Bay Bay of of may Lake L a k e of o f the t h e Woods, Woods, aa distance d i s t a n c e of o f over o v e r 70 7 0 km. km. The mine The m i n e ssite i t e is i s primarily p r i m a r i l y underlain u n d e r l a i n by by porphyritic porphyritic and equigranular e q u i g r a n u l a r basalt, b a s a l t , which w h i c h has h a s been b e e n intruded i n t r u d e d by by gabbro s i l l s . Pillows P i l l o w s are a r e observed observed g a b b r o and a n d peridotite p e r i d o t i t e sills. locally l o c a l l y in i n tthe h e basalts, b a s a l t s , bbut u t ttop o p ddeterminations e t e r m i n a t i o n s are a r e often often Composition questionable. Compos i t i o n varies v a r i e s from f r o m tholeiite t h o l e i i t e to to questionable. high—iron is an an h i g h - i r o n tholeiite. t h o l e i i t e . The The porphyritic p o r p h y r i t i c basalt b a s a l t is excellent marker horizon, massive excellent m arker h o r i z o n , and a n d overlies o v e r l i e s the the m ass i v e basalt. basalt. Pillows observed near t h e s h a f t a r e a i n d i c a t e This tops is aa Mg—tholeiite M q - t h o l e i i t e and and t o p s to t o the t h e north. north. T h i s bbasalt a s a l t is characterized c h a r a c t e r i z e d by b y up up to t o20% 2 0 % white w h i t e feldspar f e l d s p a r phenocrysts phenocrysts less than t h a n 2.5 2.5 cm c m in i n diameter. diameter. less Much of o f thet hproperty e p r o piseunderlain r t y is by u ngabbro d e r l aand i n by g a b b r o a n d peridotite i t e c o mthick, p r i s idifferentiated n g t h i c k , sills. d i f f e r e n t i a t e d sills. p e r i d o tcomprising Fine—grained F i n e - g r a i n e d peridotite p e r i d o t i t e lies l i e s at a t the t h e base b a s e of o f some some sills sills The directly d i r e c t l y overlying o v e r l y i n g the t h e porphyritic p o r p h y r i t i c basalt. basalt. The eridotite, w e r i d o t i t e , where w h e r e less l e s s altered, a 1 t e r e d , is is composed composed principally principally of o f serpentine, s e r p e n t i n e , talc t a l c and a n d magnetite. m a g n e t i t e . Peridotite P e r i d o t i t e is is commonly overlain o v e r l a i n by by melagabbro m e l a q a b b r o transitional t r a n s i t i o n a l to to The m melagabbro is locally l o c a l l y magnetic m a g n e t i c and and leucogabbro. e l a g a b b r o is leucogabbro. displays more commonly commonly is is non— nond i s p l a y s rhythmic r h y t h m i c layering, l a y e r i n g , but b u t more Amphibole magnetic m a g n e t i c and a n d massive. massive. A m p h i b o l e has h a s replaced r e p l a c e d original original pyroxene. f e l d s p a r : p y r o x e n e ratio r a t i o was was close close p y r o x e n e . The T h e original o r i g i n a l feldspar:pyroxene to t o 50:50. 50:50. In I n places p l a c e s the t h e leucogabbro l e u c o g a b b r o is is porphyritic, porphyritic, containing c o n t a i n i n g feldspar f e l d s p a r phenocrysts p h e n o c r y s t s up up to t o 33 cm in i n diameter, diameter, similar t o those t h o s e observed o b s e r v e d within w i t h i n the t h e porphyritic p o r p h y r i t i c basalt; basalt; s i m i l a r to C o a r s e r peridotite p e r i d o t i t e occurs o c c u r s as a s dikes d i k e s and and as a s narrow n a r r o w layers layers Coarser in cores oof f the t h e ssills, i l l s , ssuggesting u g g e s t i n g that t h a t the t h e ssills i l l s may i n the t h e cores consist t h a n one o n e cycle. c y c l e . This T h i s peridotite p e r i d o t i t e locally locally c o n s i s t of o f more than Coarse displays d i s p l a y s excellent e x c e l l e n t rhythmic r h y t h m i c layering. layering. C o a r s e peridotite peridot ite dikes d i k e s and/or a n d / o r sills s i l l s intrude i n t r u d e the t h e host h o s t volcanics v o l c a n i c s in i n aa few few places. places. . Pillo observed near the shaft area indicate �51 Several S e v e r a l tight, t i g h t , east e a s t trending, t r e n d i n g , west w e s t plunging p l u n g i n g folds folds have h a v e been b e e n identified i d e n t i f i e d by b y means m e a n s of o f the t h e reversal r e v e r s a l of of differentiation s i l l s , and a n d by b y limited l i m i t e d top top d i f f e r e n t i a t i o n trends t r e n d s in i n the t h e sills, determinations Basalt B a s a l t located l o c a t e d within within d e t e r m i n a t i o n s in i n the t h e basalts. b a s a l ts. the t h e anticlinal a n t i c l i n a l cores c o r e s of o f these t h e s e folds f o l d s is is strongly s t r o n g l y foliated foliated to This is most noticeable n o t i c e a b l e in i n the t h e vicinity v i c i n i t y of of t o sheared. sheared. T h i s is the c l o s e to t o Gagne G a g n e Lake Lake where w h e r e wide wide t h e main m a i n shaft s h a f t and and close sections Notably, a r e strongly s t r o n g l y sheared. sheared. Notably, s e c t i o n s of o f basalt b a s a l t are strong is apparently a p p a r e n t l y absent a b s e n t from f r o m the t h e gabbro gabbro s t r o n g deformation d e f o r m a t i o n is bodies. The bodies. T h e texture t e x t u r e of o f the t h e leucocratic l e u c o c r a t i c gabbro g a b b r o shows shows virtually v i r t u a l l y no n o strain, s t r a i n , and a n d while w h i l e some some strain s t r a i n is is evident evident within i t does does w i t h i n both b o t h the t h e peridotite p e r i d o t i t e and a n d the t h e melagabbro, m e l a g a b b r o , it not n o t appear a p p e a r sufficient s u f f i c i e n t to t o be b e consistent c o n s i s t e n t with w i t h the t h e tight tight folding. folding. Gold G o l d mineralization m i n e r a l i z a t i o n is is restricted r e s t r i c t e d to to zones z o n e s of of silicification, s i l i c i f i c a t i o n , notably n o t a b l y to t o four f o u r east—trending e a s t - t r e n d i n g steeply steeply north—dipping n o r t h - d i p p i n g veins. v e i n s . All A l l the t h e veins v e i n s were were examined e x a m i n e d while while the mine the m i n e was was in i n operation, o p e r a t i o n , but b u t production p r o d u c t i o n was was restricted restricted to Veins t o the t h e No. N o . 11 vein. vein. V e i n s 2, 2 , 3 aand nd 4 4 are a r e located l o c a t e d about about 460 The e a s t of o f the t h e main m a i n shaft. shaft. T h e attitudes a t t i t u d e s of o f the the 460 mm east veins are slightly s l i g h t l y discordant d i s c o r d a n t to t o the t h e enclosing e n c l o s i n g lava lava v e i n s are flows The f l o w s (Figure ( F i g u r e 16) 16 ) . The veins v e i n s occupy o c c u p y aa zone z o n e about a b o u t 50 50mm w i d e w h i c h e x t e n d s to t h e p e r i d o t i t e c o n t a c t t o t h e north. They are north. a r e found f o u n d within w i t h i n both b o t h porphyritic p o r p h y r i t i c and and massive m a s s i v e b a s a l t , much o f w h i c h is l a r g e l y a l t e r e d t o chlorite schist. The s o u t h ( o r e p r o x i m a l ) s i d e o f t h e a l t e r e d to t o aa soft soft p e r i d o t i t e s i l l h a s b e e n i n t e n s e l y altered "talcy" Chlorite " t a l c y " rock. rock. C h l o r i t e schist s c h i s t proximal p r o x i m a l to t o the t h e main m a i n ore ore zone z o n e is is enriched e n r i c h e d in i n carbonate c a r b o n a t e and a n d quartz, q u a r t z , and a n d contains contains abundant minor a b u n d a n t epidote e p i d o t e and a n d zoisite-, zoisite, m i n o r ssphene, p h e n e , and a n d lesser lesser amounts a m o u n t s of o f clinozoisite, c l i n o z o i s i t e , opaques o p a q u e s and and sericite. sericite. The The No. No. 1 vein, v e i n , which w h i c h strikes s t r i k e s N8O0E ~ 8 0 and a0n d~ dips d i p s about about 790 7 9 0 to t o the t h e north, n o r t h , maintains m a i n t a i n s an a n average a v e r a g e width w i d t h of o f 30 30 cm, cm, pinching p i n c h i n g and a n d swelling s w e l l i n g to t o aa maximum maximum width w i d t h of o f 76 76 cm. cm. Quartz Q u a r t z contains c o n t a i n s pyrite, p y r i t e , pyrrhotite p y r r h o t i t e and a n d chalcopyrite. chalcopyrite. Locally, Little L o c a l l y , sulphide s u l p h i d e exceeds e x c e e d s quartz. quartz. L i t t l e of o f the t h e vein vein material m a t e r i a l is is presently p r e s e n t l y exposed. e x p o s e d . Thomson Thomson (1936) ( 1 936 ) estimated estimated that, t h a t , throughout t h r o u g h o u t the t h e mine, m i n e , half h a l f the t h e vein v e i n material m a t e r i a l is is sulphide, s u l p h i d e , a n d t h a t t h e s c h i s t i m m e d i a t e l y ad j o i n i n g t h e quartz In commonly well w e l l mineralized m i n e r a l i z e d with w i t h sulphic3es. sulphides. In q u a r t z isiscommonly g e n e r a l , s u l p h i d e s a r e i n s t r e a k s and l e n s e s w h i c h p a r a l l e l t h e s h e a r i n g . Milky—white, M i l k y - w h i t e , unmineralized unmineralized quartz q u a r t z veins, v e i n s , containing c o n t a i n i n g traces t r a c e s of o f ankerite, a n k e r i t e , may may be b e seen seen on a n d underground, u n d e r g r o u n d , locally l o c a l l y crosscutting c r o s s c u t t i n q the the o n the t h e surface s u r f a c e and mineralized t w o generations g e n e r a t i o n s of of m i n e r a l i z e d quartz, q u a r t z , indicating i n d i c a t i n g two silicification. s i l i c i f i c a t i o n . Faulting F a u l t i n g has h a s been b e e n observed o b s e r v e d in i n places, places, but b u t offsets o f f s e t s are a r e restricted r e s t r i c t e d to t o aa few f e w metres. metres. Petrographic P e t r o g r a p h i c work w o r k ccarried a r r i e d out o u t ini n1934 1 9 3 4and a n d1935 1935 (Canada ( C a n a d a Department D e p a r t m e n t of o f Mines M i n e s and a n d Resources, R e s o u r c e s , 1936) 1 9 3 6 ) showed showed native n a t i v e g o l d t o b e p r e s e n t as r e l a t i v e l y c o a r s e q r a i n s within w i t h i n grey g r e y translucent t r a n s l u c e n t quartz: q u a r t z : pyrite p y r i t e and a n d chalcopyrite chalcopyrite are a r e the t h e dominant d o m i n a n t sulphides, s u l p h i d e s , with w i t h minor m i n o r amounts a m o u n t s of of pyrrhotite, p y r r h o t i t e , s p h a l e r i t e , a n d a r s e n o p y r i t e . Brownell Brownell (1943) ( 1 9 4 3 ) noted n o t e d distinct d i s t i n c t mineralogical m i n e r a l o g i c a l changes c h a n g e s in i n the t h e vein vein . wide which extends to the peridotite contact to the basalt, much of which is largely altered to chlorite schist. The south (ore proximal) side of the peridotite sill has been intensely 1 and that the schist immediately adjoining the general, suiphides are in streaks and lenses which parallel the shearing. gold to be present as relatively coarse qrains sphalerite, and arsenopyrite. �Fiqure 16: Geoloqy of the 500 level of the Wendiqo Gold Mine (after Brownell, 1943). 1Ñ b IÑ c 1) 3 a2 0 u V IÑ 8 0 er-1 G- T? s c IÑ 01 N) �53 w h i c h were directly d i r e c t l y related r e l a t e d to t o aa sudden s u d d e n decrease d e c r e a s e in i n gold gold which content; c o n t e n t ; in i n the t h e upper u p p e r levels l e v e l s of o f the t h e mine, m i n e , gold g o l d was was accompanied a c c o m p a n i e d by b y pyrite p y r i t e and a n d chalcopyrite, c h a l c o p y r i t e , whereas whereas below below the is the t h e ddominant o m i n a n t sulphide s u l p h i d e and and t h e 335m level l e v e l pyrrhotite p y r r h o t i t e is a r e much much lower. lower. B r o w n e l l (1943) ( 1 9 4 3 ) suggested suggested ggold o l d contents c o n t e n t s are Brownell that t h a t this t h i s relationship r e l a t i o n s h i p is is essentially e s s e n t i a l l y temperature temperature ddependent, e p e n d e n t , ie. i e . pyrrhotite p y r r h o t i t e is is normally n o r m a l l y deposited d e p o s i t e d at at hhigher i g h e r temperatures t e m p e r a t u r e s than t h a n pyrite, p y r i t e , chalcopyrite c h a l c o p y r i t e and a n d gold. gold. Hee concluded H c o n c l u d e d that, t h a t , below b e l o w the t h e 335m 335m level, l e v e l , no n o additional additional ore might o re m i g h t be b e expected. expected. The is characterized c h a r a c t e r i z e d by b y intense i n t e n s e deformation d e f o r m a t i o n and and T h e area a r e a is l i e s within w i t h i n the t h e influence i n f l u e n c e of o f the t h e Andrew Andrew pprobably r o b a b l y lies Bay—Witch Since B a y - W i t c h Bay Bay fault f a u l t zone. zone. S i n c e the t h e rock r o c k assemblage a s s e m b l a g e is is heterogeneous, h e t e r o q e n e o u s , most of o f the t h e strain s t r a i n was was taken t a k e n up u p by b y the the least ( i . e . massive m a s s i v e and a n d porphyritic porphyritic l e a s t competent c o m p e t e n t rocks r o c k s (i.e. The contrasting bbasalt). asalt). The c o n t r a s t i n q competencies c o m p e t e n c i e s oof f the t h e two t w o major major rrock o c k types t y p e s (intrusive ( i n t r u s i v e vs v s extrusive) e x t r u s i v e ) resulted r e s u l t e d in i n zones z o n e s of of dilatancy d i l a t a n c y being b e i n g created c r e a t e d along a l o n g the t h e contact c o n t a c t between b e t w e e n the the These ttwo w o units. units. T h e s e zones z o n e s of o f dilatancy d i l a t a n c y acted a c t e d as a s permeable permeable cchanneiways h a n n e l w a y s along a l o n g which w h i c h hydrothermal h y d r o t h e r m a l fluids f l u i d s moved upwards. The upwards. T h e vertical v e r t i c a l zonation z o n a t i o n noted n o t e d by b y Brownell B r o w n e l l (1943) ( 1 943 ) may represent r e p r e s e n t two t w o ddistinct i s t i n c t sstability t a b i l i t y fields f i e l d s with w i t h the t h e 335 335 m level l e v e l corresponding c o r r e s p o n d i n g to t o the t h e stability s t a b i l i t y field f i e l d boundary. boundary. Locality_A This h i s locality l o c a l i t y is is sslightly l i g h t l y east e a s t of o f the t h e map map L ocality A T -bbounda7and o u n d a r y a n dshows s h o w srelatively r e l a t i v e l y undeformed u n d e f o r m e d porphyritic porphyritic bbasalt. asalt. Locality_B Locality B -- Relatively R e l a t i v e l y undeformed u n d e f o r m e d massive m a s s i v e basalt. basalt. Slightly Locality L o c a l i t y CC S ----l i g h t l y elongate e l o n g a t e ppillows i l l o w s within w i t h i n fine— fineCompare dgrainedTsalt. rained basalt. C o m p a r e this t h i s ooutcrop u t c r o p with w i t h more—deformed more-deformed rrocks o c k s which w h i c h will w i l l be b e seen s e e n later. later. Locality D L ocality D A t h i s outcrop o u t c r o p of o f highly h i g h l y deformed deformed Att this pporphyrTEtc o r p h y r l t i c bbasalt, a s a l t , remnant r e m n a n t feldspar f e l d s p a r phenocrysts p h e n o c r y s ts are are is rich r i c h in i n carbonate c a r b o n a t e and and bbarely a r e l y recognizable. recognizable. T h i s rock r o c k is This fine f i n e pyrite. pyrite. ---7- Locality BE From L o c a l i t yt h e oold ld m i n e ssite, i t e , follow f o l l o w the t h e trail t r a i l to to From the mine t h e wpassing e s t p a s s iover n g o vvarieties e r v a r i e t i eof s ochlorite f c h l o r i t eschist s c h i s t which which tTt A t this this hhave a v e undergone u n d e r g o n e various v a r i o u s degrees d e g r e e s of o f deformation. deformation. At l o c a l i t y , vvirtually i r t u a l l y undeformed u n d e f o r m e d pillowed p i l l o w e d porphyritic porphyritic locality, From make w e will will m a k e aa bbasalt a s a l t faces f a c e s north. north. From this t h i s point p o i n t we sill. ttraverse r a v e r s e north n o r t h across a c r o s s the t h e differentiated d i f f e r e n t i a t e d sill. Locality Locality ------ FF On tthe On h e north n o r t h sside i d e of of a a valley, v a l l e y , which w h i c h is is Ttertgd i n t e r p r e t to e d be t o bunderlain e u n d e r l a i by n b ytalc t a l cschist, s c h i s t , peridotite peridotite l i t t l e sign s i g n of o f deformation d e f o r m a t i o n and a n d is is ddisplays i s p l a y s little rrepresentative e p r e s e n t a t i v e of o f the t h e fine—grairied, f i n e - g r a i n e d , bbasal a s a l pportion o r t i o n oof f the the sill. ddifferentiated i f f e r e n t i a t e d sill. ----- Locality Melagabbro Locality G G M e l a q a b b r o in i n these t h e s e outcrops o u t c r o p s is enerally is qgenerally magnium rich, magnesium r i c h ,and a n dlocally l o c a l l y contains c o n t a i n s segregations, segregations, �54 iinclusions n c l u s i o n s or or veinlets v e i n l e t s of o f leucogabbro. leucoqabbro. foliation f o l i a t i o n is is evident. evident. IIn n pplaces l a c e s aa weak weak These are Locality L o c a l i t y HH T h e s e rrocks ocks a r e representative r e p r e s e n t a t i v e of o f the the I T r ' ~ ~ ~ zzone f o n~ e a bbetween e1 t w e e n melagabbro r n e l a g a b b r o and a n d leucoqabbro. leucoqabbro. Feldspar—actinolite is close c l o s e to t o 50:50, 5 0 : 5 0 , and a n d the the F e l d s p a r - a c t i n o l i t e ratio r a t i o is rock r o c k is is generally g e n e r a l l y massive, m a s s i v e , showing s h o w i n g little l i t t l e sign s i g n of of sstrain. train. Between L o c a l i t y II B e t w e e n localities l o c a l i t i e s H and a n d I, I , coarse c o a r s e feldspar feldspar Locality within p h e n o c r w s ooccur c c u r locally locally w i t h i n the t h e leucogabbro, leucoqabbro, indicating maf i c i n d i c a t i n g the t h e top t o p oof f the t h e first f i r s t ultramafic u l t r a m a f i c to t o mafic cycle. c y c l e . Primary P r i m a r y layering l a y e r i n g within w i t h i n outcrops o u t c r o p s of o f coarse coarse melagabbro m e l a q a b b r o and a n d peridotite p e r i d o t i t e can c a n be b e observed o b s e r v e d at a t this this llocal o c a l iity. ty. -TTeucogabbro. i n t r u d e s leucogabbro. At A t this t h i s location l o c a t i o n aa coarse coarse peridotite p e r i d o t i t e dike dike Contacts C o n t a c t s are a r e sharp s h a r p and and serpentine s e r p e n t i n e fills f i l l s fractures f r a c t u r e s in i n the t h e adjacent a d j a c e n t gahbro. qabbro. Locality L o c a l -i t y 3J Locality_K R e t u r n to t o the t h e mine m i n e site, s i t e , passing p a s s i n g over over L o -c a l i t y K Return df6med,pillowed, e f o r m e d , p i l l o w e dporphyritic , p o r p h y r i t i cbasalt b a s a l t and a n d chlorite chlorite The schist. schist. T h e oonly n l y present p r e s e n t exposure e x p o s u r e of o fthe t h emain m a i nWendigo Wendigo Here, the u n f o r t u n a t e l y , quite q u i t e poor. poor. Here, t h e chlorite chlorite v e i n i s , unfortunately, be examined e x a m i n e d further, f u r t h e r , as as there t h e r e are a r e several several sschist c h i s t can c a n be The ggood o o d vertical v e r t i c a l exposures e x p o s u r e s in i n the t h e general g e n e r a l area. area. The aadjacent d j a c e n t muck—pile m u c k - p i l e contains c o n t a i n s the t h e last l a s t material m a t e r i a l taken t a k e n from from the mine, t h e 335 3 3 5 mm level. level. the m i n e , and a n d probably p r o b a b l y caine c a m e ffrom r o m below the vein is, Return Highway 771, making R e t u r n tto o Highway 1, m a k i n g one o n e additional a d d i t i o n a l stop s t o p along a l o n g the t h e way. way. At At a a distance d i s t a n c e of o f 3.2 3. 2 km from f r o m the t h e road r o a d junction j u n c t i o n south s o u t h of o f the the Wendigo mill W endigo m i l l site, s i t e , turn t u r n sharp s h a r p left l e f t (north) ( n o r t h ) onto o n t o aa forest—access fores t-access Approximately a l o n g this t h i s road r o a d aa widening w i d e n i n g occurs o c c u r s at at a rroad. oad. A p p r o x i m a t e l y 500 5 0 0 m along A trail bend: is tthe h e ffinal i n a l sstop t o p on o n the t h e field f i e l d trip. trip. t r a i l leads leads b e n d : this t h i s is 0 m to t o Kite K i t e Lake, L a k e , and a n d half h a l f way way along a l o n g this t h i s trail t r a i l are are nnorth o r t h about a b o u t 660 the workings the w o r k i n g s ooff Witch W i t c h Bay Bay Gold Gold Mines M i n e s Ltd. Ltd. - STOP BAY GOLD--PROSPECT -- 99-----WITCH --- BAY The The ggeology e o l o g y in i n the t h e vvicinity i c i n i t y of o f Kite K i t e Lake L a k e has h a s not not Based it bbeen e e n mapped in i n detail. detail. B a s e d oon n aeromagnetic a e r o r n a q n e t i c data d a t a it would w o u l d aappear p p e a r that t h a t the t h e principal p r i n c i p a l lithologic l i t h o l o g i c units u n i t s of o f the the Wendigo ( i e . basalt, b a s a l t , gabbro g a b b r o and a n d peridotite) peridotite) , W e n d i g o mine m i n e area a r e a (ie. east—northeast eextend x t e n d eas t - n o r t h e a s t as a s far f a r as a s tthe h e ccentral e n t r a l ppart a r t of o f Kite Kite Lake, L a k e , where w h e r e they t h e y terminate t e r m i n a t e against a g a i n s t granodiorite g r a n o d i o r i t e of o f the the Dryberry D r y b e r r y bbatholith. ath01 i t h . Fine—grained F i n e - g r a i n e d basalt b a s a l t underlies u n d e r l i e s an a n area a r e a south s o u t h of o f Kite Kite Near the Lake. Near t h e ssouthernmost o u t h e r n m o s t tip t i p of o f Kite K i t e Lake L a k e an an L ake. b r e c c i a , from f r o m one o n e to to e a s t - s t r i k i n g zone z o n e of o f schist s c h i s t and and breccia, east—striking 7Q0, two metres wide t w o metres w i d e and a n d ddipping i p p i n g south s o u t h at a t from f r o m 550 5 5 ^ to t o 70^, contains c o n t a i n s some carbonate c a r b o n a t e and a n d one o n e or or more more quartz q u a r t z veins v e i n s and and The lenses l e n s e s with w i t h aa maximum width w i d t h of o f 45 45 cm. cm. T h e qquartz u a r t z is is fractured, f r a c t u r e d , encloses e n c l o s e s minor m i n o r silicified s i l i c i f i e d basalt, b a s a l t , and and ccontains o n t a i n s aabundant b u n d a n t cchalcopyrite h a l c o p y r i t e and a n d pyrite p y r i t e in i n and a n d near near , �55 some s o m e of o f the t h e fractures. fractures. T h e mineralization m i n e r a l i z a t i o n and a n d its its The stratigraphic position is similar to that at the s t r a t i g r a p h i c p o s i t i o n is s i m i l a r t o t h a t a t t h e Wend Wend igo. iqo. Two sshafts a p a r t have h a v e been b e e n sunk s u n k on o n the the h a f t s about a b o u t 30 30 m apart zone. c h i p sample s a m p l e across a c r o s s 50 5 0 cm c m of o f the t h e mineralized mineralized z o n e . A chip quartz a t the t h e east e a s t shaft s h a f t assayed a s s a y e d 1.93 1 . 9 3 ounces o u n c e s of of q u a r t z vein v e i n at gold g o l d per p e r ton. t o n . A third t h i r d shaft s h a f t was put p u t down down a a further f u r t h e r 75 75 m to t o the t h e east. e a s t . A fourth f o u r t h shaft s h a f t was w a s sunk s u n k on o n aa separate s e p a r a t e zone zone approximately t o the t h e southwest. s o u t h w e s t . The T h e zone z o n e is i s not not a p p r o x i m a t e l y 100 100 mm to exposed, material e x p o s e d , but but m a t e r i a l on o n the t h e dump indicates i n d i c a t e s that t h a t it it is is carbonatized, c a r b o n a t i z e d , sheared s h e a r e d basalt b a s a l t with w i t h minor m i n o r quartz q u a r t z and a n d with with chalcopyrite, c h a l c o p y r i t e , pyrite p y r i t e and a n d pyrrhotite. pyrrhot ite. �56 References References Ayer, J.A., 198)4, Bay A Area, J.A., 1 9 8 4 , GGeology e o l o g y oof f tthe h e BBigstone i g s t o n e Bay r e a , District D i s t r i c t of of Ayer, Kenora; p.19—224 i in Summary oof Ontario K e n o r a ; p.19-24 n Summary f FFieldwork, i e l d w o r k , 11984, 984, O n t a r i o GeoGeological l o g i c a l Survey, S u r v e y , Edited E d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R.B. Barlow, A. C . Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, B a r l o w , aand n d A.C. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 119, 1 1 9 , 309p. 309p. Gil, Ayer, J.A., G i l , K.M., K.M., McCurdy, M., M., and a n d assistants, a s s i s t a n t s , 1984, 1984, A y e r , J.A., Precambrian P r e c a m b r i a n Geology G e o l o g y of o f the t h e Bigstone B i g s t o n e Bay Bay Area, A r e a , Northern N o r t h e r n Part, Part, Kenora Scale 1: 1 5 840 840 or or 1 1 inch i n c h to t o 1/4 1/4 K e n o r a District D i s t r i c t (52 ( 5 2 E/9). E/9). S c a l e 1:15 mile. m ile. Ayer, Gil, .A., G i l , K.M. K.M. McCurdy, McCurdy, M., PI., and and assistants, a s s i s t a n t s , 1984, 1984, A y e r , JJ.A., Precambrian P r e c a m b r i a n Geology G e o l o g y of o f the t h e Bigstone B i g s t o n e Bay Bay Area, A r e a , Southern S o u t h e r n Part, Part , Kenora Scale K e n o r a District D i s t r i c t (52 ( 5 2 E/9). E/9). S c a l e 1:15 1 : 1 5 840 840 or or 1 1 inch i n c h to t o 1/4 1/4 mile. mile. Blackburn, Ontario C. E . , 1981, 1 9 8 1 , Kenora—Fort K e n o r a - F o r t Frances F r a n c e s sheet. sheet. Ontario B l a c k b u r n , G.E., Geological Survey, G eological S u r v e y , Geological G e o l o g i c a l Compilation C o m p i l a t i o n Series, S e r i e s , Map 2443, 2 443, sscale c a l e 1:253,440. 1 : 253,440. Blackburn, W.D., Breaks, .D., B r e a k s , F.W., F.W., Davis, D a v i s , D.W., D . W . , Edwards, Edwards, B l a c k b u r n , G.E., C.E., Bond, Bond, W G.R., Trowell, 1985, G . R . , Poulsen, P o u l s e n ,K.}-I., K.H., T r o w e l l , N.F. N.F. and and Wood, Wood, J., J., 1 985, Evolution Volcanic—Sedimentary E v o l u t i o n oof f Archean Archean V o l c a n i c - S e d i m e n t a r y Sequences S e q u e n c e s of o f the the Western W e s t e r n Wabigoon Subprovince S u b p r o v i n c e and and its i t s Margins: M a r g i n s : AA Review; Review; in in Evolution E v o l u t i o n of o f Archeari A r c h e a n SSupracrustal u p r a c r u s t a l SSequences, e q u e n c e s , Edited E d i t e d by by Ayers, Ayers, L.D., Thurston, L.D., T h u r s t o n , P.C., P.C., Card, C a r d , K.D., K . D . , and a n d Weber, Weber, W., W . , G.A.O. G.A.C. sspecial p e c i a l Paper P a p e r 28. 28. Brownell, 1943, .M., 1 9 4 3 , Wendigo Gold Mines Ltd., L t d . , Assessment A s s e s s m e n t Files, Files, B r o w n e l l , GG.M., Kenora. Kenora. Blackburn, B l a c k b u r n , G.E., C. E., and a n d Janes, J a n e s , D.A., D. A . , 1983, 1 9 8 3 , Gold Gold Deposits D e p o s i t s in in Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; p.194—210 p.194-210 in i n The The Geology G e o l o g y of o f Gold Gold in in Ontario, A. C. Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, O n t a r i o , edited e d i t e d by A.C. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 1 0 , 27Bp. 278p. and Canada Department D e p a r t m e n t of o f Mines Mines and and Resources, R e s o u r c e s , 1936, 1 9 3 6 , Ore Ore Dressing D r e s s i n garid Metallurgical M e t a l l u r g i c a l Investigation I n v e s t i g a t i o n No.621; No.621; Investigations I n v e s t i g a t i o n s in i n Ore Ore Dressing D r e s s i n g and and Metallurgy, M e t a l l u r g y , Jan.—Jun., J a n . - J u n . , 1935, 1 9 3 5 , p.103—il6. p.103-116. Davies, 1965, D a v i e s , JJ.C., .C., 1 9 6 5 , Geology G e o l o g y of o f the t h e High High Lake—Rush Lake-Rush Bay Bay Area, Area, District D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Department D e p a r t m e n t of o f Mines, M i n e s , Geological Geological Report R e p o r t 141, 4 1 , 557p; 7 p ; 2 maps, 1 1 inch i n c h to t o 1/2 1 / 2 mile. mile. Davies, J. C . , 1983, 1 9 8 3 , Gold Deposits D e p o s i t s of o f the t h e Lake Lake of o f the t h e Woods Woods Area, Area, D a v i e s , J.C., K e n o r a District; D i s t r i c t ; p.241-245 i n Summary Summary of o f Field F i e l d Work, Work, 1983, 1 9 8 3 , by by Kenora p.241—245 in Geological tthe h e Ontario Ontario G e o l o g i c a l Survey, S u r v e y , edited e d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R. B. Barlow, B a r l o w , and and A.C. A . C . Colvine, C o l v i n e , Ontario O n t a r i o Geological Geological Survey, Miscellaneous S urvey, M i s c e l l a n e o u s Paper P a p e r 116, 1 1 6 , 3l3p. 313~. Davies, . C . and and Smith, S m i t h , P.M., P.M., 1984, 1 9 8 4 , The Structural S t r u c t u r a l and and D a v i e s , JJ.C. Stratigraphic S t r a t i g r a p h i c Control C o n t r o l in i n the t h e Lake Lake of o f the t h e Woods Woods Area; A r e a ; p.l85—193 p.185-193 ~f' Fieldwork, F i e l d w o r k , 1984, 1 9 8 4 , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, iin n Summary if Edited Owen L. L. W White, R.B. Barlow, B a r l o w , and and A.O. A.C. E d i t e d by by John J o h n Woods, Wood, Owen h i t e , R.B. Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 119, 119, 3 09~ 309p. Forsgren, F o r s g r e n , F.M., P.M., 1980, 1 9 8 0 , AA study s t u d y of o f the t h e Pine P i n e Portage P o r t a g e Prospect, Prospect , Kenora K e n o r a District, D i s t r i c t , Ontario, O n t a r i o , Unpublished U n p u b l i s h e d B.Sc. B. Sc Thesis, T h e s i s , University University of o f North N o r t h Dakota. Dakota. King, H. L., 1983, 1 9 8 3 , Precambrian P r e c a m b r i a n Geology, G e o l o g y , Kenora—Keewatin K e n o r a - K e e w a t i n Area, Area, K i n g , H.L., Eastern Part E astern P a r t (NTS (NTS 52 E/163W) E/1 6SW) Kenora K e n o r a District, D i s t r i c t , Ontario; O n t a r i o ; Ontario Ontario Geological G e o l o g i c a l Survey, S u r v e y , Preliminary P r e l i m i n a r y Map ? k p P.2618, P.2618, scale s c a l e 1:15,840 1 : 1 5 , 8 4 0 or o r 11 inch i n c h to t o 1/4 1 / 4 mile. mile. . �57 Pedora, P e d o r a , J.M., J . M . , 1976, 1 9 7 6 , Mineralization M i n e r a l i z a t i o n of o f the t h eHigh H i g hLake Lake Pluton P l u t o n and and Unpublished M.Sc. Adjacent n p u b l i s h e d M. Sc. Thesis, T h e s i s , University University A d j a c e n t Country C o u n t r y Rocks; Rocks ; U oof f Manitoba, M a n i t o b a , Winnipeg, W i n n i p e g , Manitoba. Manitoba. Simpson, and Schrnid, Scbmid, S.M., S.M., 11983, Evaluation of . and 9 8 3 , An An E valuation o f Criteria C r i t e r i a to to Simpson, CC. GSA Bull., Deduce the t h e Sense S e n s e of o f Movement Movement in i n Sheared S h e a r e d Rocks. Rocks. Bull., V.94, p.1281-1288, p.1281—1288, 11 11 figures, f i g u r e s , November November 1983. 1983. V.94, Smith, S m i t h , P.M., P.M., 1984, 1 9 8 4 , The Geological G e o l o g i c a l Setting S e t t i n g of o f the t h e Duport D u p o r t Mine, Mine, Cameron Island, I s l a n d , Shoal S h o a l Lake; L a k e ; p.194—200 p.194-200 in i n Summary Summary of o f Fieldwork, Fieldwork, Ontario Geological 11984, 984, O ntario G e o l o g i c a l Survey, S u r v e y , Edited E d i t e d by by John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R.B. Barlow, B a r l o w , and and A.C. A . C . Colvine, C o l v i n e , Ontario O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 119, 1 1 9 , 3O9p. 309~. Sutherland, and C Colvine, The G Geology .G., and o l v i n e , AA.C., .C., 11979, 9 7 9 , The e o l o g y and and S u t h e r l a n d , II.G., A r m , Canoe Canoe Lake, L a k e , and a n d High H i g h Lake Lake M i n e r a l i z a t i o n of o f the t h e Pickerel P i c k e r e l Arm, Mineralization Bodies; of Work, 1979, b y the the B o d i e s ; pp.233—243 . 2 3 3 - 2 4 3 in i n Summary o f Field F i e l d Work, 1 9 7 9 , by Ontario Geological Survey, by V. V.G. Mime, G. M i l n e , O.L. O.L. White, White, Ontario G eological S u r v e y , eedited d i t e d by R.B. Barlow, R.B. B a r l o w , and and C.R. C . R . Kustra, K u s t r a , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 90, 9 0 , 245p. 245~. Thomson, Thomson, J.E., J . E . , 1936, 1 9 3 6 , Gold deposits d e p o s i t s on o n the t h e Lake Lake of o f the t h e Woods; Woods; Ont. Dept. O nt. D e p t . Mines, M i n e s , Annual Report R e p o r t for f o r 1935, 1 9 3 5 , Vol.44, V o l . 4 4 , Pt.4, Pt.4, pp.29-47. .29-47. Thomson, JJ.E., Thomson, . E . , 1937, 1 9 3 7 , Geology G e o l o g y of o f the t h e North N o r t h Central C e n t r a l Part P a r t of o f the the Lake of the Woods, Kenora District, Ontario: Ontario Lake o f t h e Woods, Kenora D i s t r i c t , O n t a r i o : O n t a r i o Department 4 5 , Part Part D e p a r t m e n t of o f Mines, M i n e s , Annual Annual Report R e p o r t for f o r 1936, 1 9 3 6 , Volume 45, p.1—43, Accompanied by 45b, scale 1:63,360 or 1 inch 3 , p.1-43, Accompanied by Map 4 5 b , s c a l e 1 : 6 3 , 3 6 0 o r 1 i n c h to to 3, 1 mile. 1 mile. Trowell, G . R . , 1980, 1980, T r o w e l l , N.F., N.F., Blackburn, B l a c k b u r n , C.E. C.E. and and Edwards, Edwards, G.R., Crow Lake Lake Meta— MetaIreliminary r e l i m i n a r y Synthesis S y n t h e s i s of o f the t h e Savant S a v a n t Lake Lake —- Crow volcanic, v o l c a n i c , Metasedimentary M e t a s e d i m e n t a r y Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario, O n t a r i o , and and its its bearing b e a r i n g upon Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 3Op. 30p. �Geological G e o l o g i c a l Relationships R e l a t i o n s h i p s in in the t h e Vicinity V i c i n i t y of of the t h e Wabigoon W a b i g o o n —- Winnipeg W i n n i p e g River River Subprovincial S u b p r o v i n c i a l Interface I n t e r f a c e in i n the t h e Kenora K e n o r a area1 area1 Introductory I n t r o d u c t o r y Discussion D i s c u s s i o n and a n d Field F i e l d Guide Guide 31st 3 1 s t Annual I n s t i t u t e o n Lake S u p e r i o r G e o l o g y Kenora, K e n o r a , Ontario On t a r i o Annual Institute on Lake Superior Geology by G.P. G. P. Beakhouse Beakhouse Precambrian P r e c a m b r i a n Geology G e o l o g y Section Section Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey 77 7 7 Grenville G r e n v i l l e Street Street Toronto, T o r o n t o , Ontario Ontario M5S M5S 1B3 133 1 This T h i s guide g u i d e is is published p u b l i s h e d with w i t h the t h e permission p e r m i s s i o n of o f the t h e Director Director of o f the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey 1 �60 * THE THE RELATIONSHIP RELATIONSHIP OF OF SUPRACRUSTAL SEQUENCES SEQUENCES TO BASEMENT COMPLEX COMPLEX IIN N THE THE WESTERN WESTERN ENGLISH ENGLISH RIVER RIVER TO AA BASEMENT S UB PROVINCE * SUBPROVINCE* This T h i s introductory i n t r o d u c t o r y statement s t a t e m e n t is is a a modified m o d i f i e d vversion e r s i o n of o f aa paper p a p e r of of p u b l i s h e d eelsewhere l s e w h e r e ((Beakhouse B e a k h o u s e 1985) 1985). It is is t h e s a m e t i t l e published intended i n t e n d e d as a i n t r o d u c t i o n t o t h e r e g i o n a l c o n t e x t o f t h e f i e l d t r i p area. the sairte title It as a introduction to the regional context of the field trip area. . ABSTRACT ABSTRACT T h r e e ddistinctly i s t i n c t l y different d i f f e r e n t types t y p e s of o f terrane t e r r a n eare a r erecognized recognized Three within within and a n d immediately i m m e d i a t e l y adjacent a d j a c e n t to t o the t h e English E n g l i s h River R i v e r Sub— Subprovince. t e r r a n e forms f o r m s the t h e Uchi U c h i and and province. G r e e n s t o n e - t o n a l i t e terrane Greenstone—tonalite W a b i g o o n Subprovinces S u b p r o v i n c e s whereas w h e r e a s the t h e Ear Ear Falls F a l l s -— -- Mariigotagan M a n i q o t a g a n belt belt Wabigoon (EFMB) (EFMB) and a n d Winnipeg W i n n i p e g River R i v e r belt b e l t (WRB) (WRB) of o f the t h e English E n g l i s h River R i v e r Sub— Subprovince a r e paragneiss p a r a g n e i s s and a n d batholithic b a t h 0 1 i t h i c terranes, t e r r a n e s , respectively. respectively. p r o v i n c e are The T h e EFMB EFMB is is a major, m a j o r f linear l i n e a r sedimentary s e d i m e n t a r y basin b a s i n with w i t h detritus detritus d e r i v e d in i n adjacent a d j a c e n t terrains t e r r a i n s from f r o m laterally l a t e r a l l y equivalent e q u i v a l e n t volcanic volcanic derived rocks r o c k s and a n d granitic g r a n i t i c rocks. r o c k s . The T h e greenstone—tonalite g r e e n s t o n e - t o n a l i t e -- paragneiss paragneiss interface r e p r e s e n t s a facies f a c i e s change c h a n g e between b e t w e e n fundamentally fundament a l l y i n t e r f a c e represents different d i f f e r e n t depositional d e p o s i t i o n a l environments. environments. I n the t h e WRB, WRB, rare r a r e remnants remnants In of o f aa predominantly p r e d o m i n a n t l y volcanic v o l c a n i c supracrustal s u p r a c r u s t a l sequence s e q u e n c e occur o c c u r as as inclusions within metamorphosed inclusions w i t h i n hhighly ighly m e t a m o r p h o s e d and a n d deformed d e f o r m e d plutonic plutonic rocks Field F i e l d relationships r e l a t i o n s h i p s and a n d geochronological geochronolog ical r o c k s (orthogneiss). (orthogneiss) i n v e s t i g a t i o n s indicate i n d i c a t e that t h a t orthogneiss, o r t h o g n e i s s , together t o g e t h e r with w i t h certain certain investigations sodic ' K e n o r a n t volcanism v o l c a n i s m in i n the the s o d i c plutons, p l u t o n s , predate p r e d a t e widespread w i d e s p r e a d 'Kenoran' Wabigoon t o the t h e south. s o u t h . The T h e relatively r e l a t i v e l y potassic potassic W a b i g o o n Subprovince S u b p r o v i n c e to c o m p o s i t i o n and a n d slightly s l i g h t l y elevated e l e v a t e d Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s of of composition l a t e plutons p l u t o n s from f r o m the t h e central c e n t r a l axis a x i s of o f the t h e WRB W R 3 suggest s u g g e s t that t h a t they they late are a r e derived d e r i v e d from f r o m this t h i s earlier e a r l i e r crust. crust. V o l c a n o - p l u t o n i c activity, a c t i v i t y , perhaps p e r h a p s analogous a n a l o g o u s to t o that that Volcano—plutonic observed o b s e r v e d in i n the t h e greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes, t e r r a n e s , was was initiated i n i t i a t e d prior prior to 3 . 0 Ga G a and a n d led l e d to t o the t h e development d e v e l o p m e n t of o f aa 'pre—Kenoran' ' p r e - K e n o r a n t sialic s i a l ic t o 3.0 microcontinent m i c r o c o n t i n e n t now now represented r e p r e s e n t e d by b y the t h e WRB. WRB. S y n c h r o n o u s developdevelopSynchronous ment m e n t of o f volcano—sedimentary v o l c a n o - s e d i m e n t a r y sequences s e q u e n c e s in i n greenstone—tonalite greenstone- tonal ite t e r r a n e and a n d greywacke—turbidite g r e y w a c k e - t u r b i d i t e sequences s e q u e n c e s in i n paragneiss p a r a g n e i s s terrane terrane terrane o c c u r r e d adjacent a d j a c e n t to, t o , and a n d in i n part p a r t on, o n , this t h i s earlier e a r l i e r crust. c r u s t . This This occurred e a r l i e r crust c r u s t was greatly g r e a t l y thinned, t h i n n e d , or o r absent, a b s e n t , beneath b e n e a t h much much of of the the earlier Wabigoon W a b i g o o n subprovince. s u b p r o v i n c e . The T h e interfaces i n t e r f a c e s between b e t w e e n different d i f f e r e n t terranes terranes represent r e p r e s e n t either e i t h e r facies f a c i e s transitions t r a n s i t i o n s (EFMB—Uchi) (EFMB-Uch i ) or o r unconformities unconformities WRB-EFMB and a n d WRB—Wabigoon) WRB-Wabigoon) that t h a t are a r e loci l o c i for f o r subsequent subsequent (WRB—EFMB d e f o r r n a t i o n a l and a n d igneous i g n e o u s processes p r o c e s s e s that t h a t obscured o b s c u r e d the t h e primary primary deformational relationships r e l a t i o n s h i p s between b e t w e e n different d i f f e r e n t terranes. terranes . . �61 INTRODUCTION The was ffirst T h e English E n g l i s h River R i v e r bbelt e l t was i r s t ddefined e f i n e d as as a a ssubprovince u b p r o v i n c e of of the t h e Superior S u p e r i o r Province P r o v i n c e by b y Wilson W i l s o n and a n d Brisbin B r i s b i n (1963). (1 963). More recent recent mapping, ggeologic eologic m a p p i n g , particularly p a r t i c u l a r l y Project P r o j e c t Pioneer P i o n e e r (Manitoba ( M a n i t o b a Mines Mines and M c R i t c h i e and and Weber, W e b e r , 1971 1971)) and B r a n c h and a n d University U n i v e r s i t y of o f Manitoba; M a n i t o b a ; McRitchie Branch Operation Falls O p e r a t i o n Kenora Kenora — - Ear Ear F a l l s (Ontario ( O n t a r i o Geological G e o l o g i c a l Survey; S u r v e y ; Breaks Breaks shown that eett al. a l . 1978), 1 9 7 8 ) , hhas a s shown t h a t the t h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e is is with aactually c t u a l l y ccompound, ompound, w i t h tthe h e Ear E a r Falls Falls — - Manigotagan M a n i g o t a g a n belt b e l t in i n the the b e l t in i n the t h e south s o u t h (Beakhouse ( B e a k h o u s e 1977; 1977; nnorth o r t h and a n d the t h e Winnipeg W i n n i p e g River R i v e r belt Breaks B r e a k s and a n d Bond, Bond, 1977). 1 9 7 7 ) . Breaks B r e a k s et e t al. a l . (1978) ( 1 9 7 8 ) refer r e f e r to t o these these a s the t h e Northern N o r t h e r n Supracrustal S u p r a c r u s t a l domain d o m a i n and a n d Southern S o u t h e r n Plutonic Plutonic bbelts e l t s as Regional domain, (see d o m a i n , respectively. respectively. R e g i o n a l ggeophysical e o p h y s i c a l investigations i n v e s t i g a t i o n s (see references r e f e r e n c e s in i n Beakhouse B e a k h o u s e 1977) 1 9 7 7 ) have h a v e added a d d e d important i m p o r t a n t information i n f o r m a t i o n on on the t h e tthird h i r d ddimension i m e n s i o n and, a n d , oon n the t h e basis b a s i s oof f a re—evaluation r e - e v a l u a t i o n of o f geoqeopphysical h y s i c a l ddata, a t a , Hall H a l l and a n d Brisbin B r i s b i n (1981) ( 1 981 ) suggested s u g g e s t e d that t h a t these t h e s e belts belts The sshould h o u l d be b e elevated e l e v a t e d to t o subprovince s u b p r o v i n c e status. status. T h e Ear Ear Falls F a l l s —Maniqotagan Winnipeg River M a n i q o t a g a n aand nd W innipeg R i v e r bbelts e l t s rrepresent e p r e s e n t two t w o fundamentally fundamentally different t o here h e r e as as d i f f e r e n t types t y p e s of o f "high—grade" " h i g h - g r a d e " terrane, t e r r a n e , referred r e f e r r e d to paragneiss Both are p a r a q n e i s s and a n d batholithic b a t h o l i t h i c terrane, t e r r a n e , respectively. respectively. B o t h are ddistinctly i s t i n c t l y ddifferent i f f e r e n t from f r o m greenstone—tonalite g r e e n s t o n e - t o n a l i t e or o r low—grade low-grade which Wabigoon tterranes erranes w h i c h ooccur c c u r in i n the t h e adjacent adjacent W a b i g o o n and a n d Uchi U c h i sub— subpprovinces r o v i n c e s (Figure ( F i g u r e 1). 1). This T h i s paper p a p e r will w i l l discuss d i s c u s s the t h e nature n a t u r e of o f these t h e s e two t w o types t y p e s of of ''high—grade' h i g h - g r a d e ' tterrane e r r a n e and a n d their t h e i r associated a s s o c i a t e d supracrustal s u p r a c r u s t a l rocks r o c k s and and ttheir h e i r relationship r e l a t i o n s h i p to t o each e a c h other o t h e r and a n d the t h e adjacent a d i a c e n t greenstone— qreenstoneEmphasis ttonalite o n a l i t e terranes. terranes. E m p h a s i s is is placed p l a c e d on o n the t h e broad b r o a d relationships relationships between b e t w e e n the t h e various v a r i o u s supracrustal s u p r a c r u s t a l assemblages a s s e m b l a g e s and a n d aa large l a r g e basement basement complex The c o m p l e x that t h a t pre—dates p r e - d a t e s some some of o f these t h e s e supracrustal s u p r a c r u s t a l rocks. rocks. T he English E n g l i s h River R i v e r Subprovince, S u b p r o v i n c e , together t o g e t h e r with w i t h adjacent a d j a c e n t parts p a r t s of o f the the Wabigoon 1 ) , is is W a b i g o o n and a n d Uchi U c h i greeristone—tonalite g r e e n s t o n e - t o n a l i t e SSubprovinces u b p r o v i n c e s (Figure ( F i g u r e 1), unique u n i q u e in i n that t h a t all a l l 3 types t y p e s of o f terrane t e r r a n e and a n d all a l l possible possible combinations c o m b i n a t i o n s oof f interfaces i n t e r f a c e s between b e t w e e n these t h e s e terranes t e r r a n e s are are rrepresented. epresented. LITHOLOGIES LITHOLOGIES T h e rocks r o c k s in i n the t h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e can c a n be b e broadly broadly The ggrouped r o u p e d into i n t o 77 suites. suites. IIn n aapproximate p p r o x i m a t e oorder r d e r of o f decreasing d e c r e a s i n g age age t h e s e are a r e (1) ( 1 ) high—grade h i g h - q r a d e supracrustal s u p r a c r u s t a l (predominantly ( p r e d o m i n a n t l y meta— inetathese volcanic) v o l c a n i c ) remnants; r e m n a n t s ; (2) ( 2 ) oorthogneiss; r t h o q n e i s s ; ((3) 3 ) pparagneiss; a r a q n e i s s ; ((4) 4 ) internal internal ( 5 ) ssodic o d i c plutons; p l u t o n s ; ((6) 6 ) ppotassic o t a s s i c plutons; p l u t o n s ; (7) (7) ggreenstone r e e n s t o n e belts; b e l t s ; (5) mafic w i l l be b e described d e s c r i b e d only only m a f i c plutons p l u t o n s (Figure ( F i g u r e 2). 2). L i t h o l o g i e s will Lithologies briefly, b r i e f l y , more complete c o m p l e t e lithologic l i t h o l o g i c descriptions d e s c r i p t i o n s are a r e presented p r e s e n t e d by by Breaks e t al. a l . (1978) ( 1 9 7 8 ) and a n d Beakhouse B e a k h o u s e (1983). (1983). B r e a k s et Supracrustal Remnant' Suite Suite S u p r a c r u s t a l Remnant The T h e oorthogneiss r t h o g n e i s s ssuite, u i t e , and a n d to t o a lesser l e s s e r extent e x t e n t the t h e plutonic plutonic suites, s u i t e s , contain c o n t a i n minor, m i n o r , widely w i d e l y distributed, d i s t r i b u t e d , highly h i g h l y metamorphosed metamorphosed These and r a r e sedimentary s e d i m e n t a r y inclusions. inclusions. T hese a n d ddeformed e f o r m e d volcanic v o l c a n i c and a n d rare o r disruptdisruptiinclusions n c l u s i o n s aare r e usually u s u a l l y ssmall m a l l (<20m) ( < 2 0 m ) and a n d ddiscontinuous i s c o n t i n u o u s or Where the t o 1 km km thick t h i c k and a n d 55 km km long. long. the eed, d , bbut u t can c a n be b e up u p to inclusions i n c l u s i o n s ooccur c c u r in i n orthogneiss, o r t h o g n e i s s , intrusive i n t r u s i v e contact c o n t a c t relationships relationships indicate most i n d i c a t e tthat hat m o s t ssupracrustal u p r a c r u s t a l rremnants e m n a n t s are a r e older o l d e r than t h a n the the o r t h o g n e i s s (Gower, ( G o w e r , 1978; 1 9 7 8 ; Gower G o w e r and and Clifford, C l i f f o r d , 1981; 1981 ; ttonalitic o n a l i t i c orthogneiss However, Beakhouse, B e a k h o u s e , 1983; 1 9 8 3 ; Beakhouse B e a k h o u s e et e t al. a l . 11983). 983). H o w e v e r , some some 1 �62 / / God's Lake Ear Falls— Manigotagan Manitoba fl 1 FTfl1 1 0 100 200 kilometres F i g u r e 1: 1: Figure Map Map illustrating i l l u s t r a t i n g the t h e distribution d i s t r i b u t i o n of o f various v a r i o u s types t y p e s of of terranes t e r r a n e s in i n the t h e western w e s t e r n Superior S u p e r i o r province. province. Greenstone—tonalite t e r r a n e s include i n c l u d e the t h e Sachigo, Sachigo, G r e e n s t o n e - t o n a l i t e terranes Uchi, U c h i , Wabigoon Wabiqoon and and Wawa Wawa subprovinces. s u b p r o v i n c e s . The The Ear Ear Falls—Manigotagan a n d Quetico Q u e t i c o subprovince subprovince b e 1 t and F a l l s - M a n i q o t a q a n belt a r e paragneiss p a r a g n e i s s terraneS. t e r r a n e s . The The Berens ! 3 e r e n s River River are subprovince s u b p r o v i n c e and and Winnipeg W i n n i p e g River R i v e r belt b e l t are are b a t h o l i t h i c terranes. terranes. batholithic �_____ _____ 63 945 92 + * * + 4- + * * + *4- * + + 20 10 0 + * * + * * * * * * * + + * * * * * * * * * + * * * * * * * * * * I 30 I +kilomelres + + + + + 40 * * * -I- + + + + I + * + 50 I + + + * 4- * -' * * * * * + + * * + * * * + + * + * * * * * * * + + + * + * * + * + ''-l ',—'_/ + + + + - - /_\ + - - +1 + '- + ++ ::::I + — USA 51 ++:I4-I:I:Y * * +++++*+++*++*+ ::. ÷ + + * + + ++ ++ + + -51 + + * ::T + + Ear FaHs-Manigotagai • I;—. 4:::::.::::::: 5O + C-v i-'kk-(+ * + + + - + * + * * + * \S-\* + + + + * * * * + 4- + + + * * * * * + + 4- + + 4- * + ®c + + + / * * * * * * +*++ + + Quetico Th________ I granitoid rocks mafic plutonic rocks :--. -] metasedimentary rocks felsic metavolcanic rocks gneissic granitoid rocks [-J mafic metavolcanic rocks (unsubdivided) ::::: potassic plutonic rocks --J sodic plutonic rocks Figure F i g u r e 2: 2: + - 1 G e o l o g i c map of o f part p a r t of o f the t h e western w e s t e r n Superior S u p e r i o r province orovince Geologic including anigotaqan, i n c l u d i n g pparts a r t s oof f the t h e Uchi, U c h i , Ear E a r Falls F a l l s —- M Manigotagan, Winnipeg W i n n i p e g River, R i v e r , Wabigoon W a b i q o o n and a n d Quetico Q u e t i c o subprovinces. subprovinces. The i s ccompiled o m p i l e d pprimarily r i m a r i l y from f r o m Ferguson F e r g u s o n et et T h e ggeology e o l o g y is al. a l . (1970), ( 1 9 7 0 ) , Blackburn B l a c k b u r n (1981) ( 1 9 8 1 ) and a n d Breaks B r e a k s et e t al. a l . (1978). (1978). �64 . iinclusions n c l u s i o n s may be tectonic t e c t o n i c inclusions i n c l u s i o n s of o f younger y o u n g e r units. units M-phibolite Arnphibol i t e inclusions i n c l u s i o n s predominate. predominate. Some i n c l u s i o n s are a r e volcanic volcanic Some inclusions as as indicated i n d i c a t e d bby y tthe h e local l o c a l ppresence r e s e n c e oof f hhighly i g h l y ddeformed e f o r m e d pillow pillow In sstructures t r u c t u r e s. I n places p l a c e s the t h e pillowed p i l l o w e d units u n i t s are a r e interlaye i n t e r l a y e rred e d with with s i m i l a r , massive m a s s i v e amphibolites a m p h i b o l i t e s and and ccompositionally o m p o s i t i o n a l l y and a n d texturally t e x t u r a l l y similar, with w i t h coarse—grained c o a r s e - g r a i n e d amphibolites, amph i b o l i t e s , probably p r o b a b l y representing r e p r e s e n t i n g aa s e q u e n c e of o f massive m a s s i v e and a n d pillowed p i l l o w e d basaltic b a s a l t i c flows f l o w s and a n d related related sequence gabbro g a b b r o sills. sills. On h e oother t h e r hhand, a n d , many f the t h e inclusions i n c l u s i o n s are are On tthe many oof m a s s i v e amphibolite a m p h i b o l i t e of o f uncertain u n c e r t a i n origin. origin. o f these these massive Some of inclusions are mineralogically inclusions a re m i n e r a l o g i c a l l y and a n d texturally t e x t u r a l l y similar s i m i l a r to t o the the Others, a l s o be b e volcanic. volcanic. O t h e r s , however, however, vvolcanic o l c a n i c amphibolite a m p h i b o l i t e and a n d may may also s i l l s and a n d dikes. dikes. rrepresent e p r e s e n t ddisrupted, i s r u p t e d , younger y o u n g e r gabbroic g a b b r o i c sills Felsic F e l s i c volcanic v o l c a n i c rocks r o c k s have h a v e not n o t been b e e n conclusively c o n c l u s i v e l y identiidentiThe a primary primary f e l s i c vvolcanic o l c a n i c rocks r o c k s may be a ffied. ied. T h e ppaucity a u c i t y oof f felsic feature r may f l e c t ttheir h e i r less less f e a t u r e oof f this t h i s early e a r l y volcanism v o l c a n i s m oor mayr ereflect rrefractory e f r a c t o r y nature n a t u r eduring d u r i n gsubsequent s u b s e q u e n tmetamorphism m e t a m o r p h i s m aand n d ppartial artial melting al. Sedimentary et a l . 1983). 1983). S e d i m e n t a r y uunits n i t s aare r e rare r a r e and and m e l t i n g ((Beakhouse B e a k h o u s e et t o thick-bedded t h i c k - b e d d e d arkose a r k o s e and a n d greywacke, g r e y w a c k e , with with ccomprise o m p r i s e medium— m e d i urn- to interlayered c a l c - s i l i c a t e layers. layers. T hin-bedded , i n t e r l a y e r e d pelitic p e l i t i c and a n d calc—silicate Thin—bedded, is recognized ooxide—facies x i d e - f a c i e s iiron r o n formation f o r m a t i o n is r e c o g n i z e d on o n the t h e south s o u t h shore s h o r e of of tJmfreville U m f r e v i l l e Lake L a k e and a n d in i n the t h eCedar C e d a r Lake L a k e area a r e a(Westerman, ( W e s t e r m a n , 1977; 1977; Beakhouse, B e a k h o u s e , 1983). 1983). The widespread a s inclusions i n c l u s i o n s in in T he w i d e s p r e a d ddistribution i s t r i b u t i o n and a n d occurrence o c c u r r e n c e as old o l d tonalites t o n a l i t e s (discussed ( d i s c u s s e d below) b e l o w ) suggests s u g g e s ts that t h a t the t h e volcanic volcanic a m p h i b o l i t e , the the m e t a s e d i m e n t a r y , and a n d possibly p o s s i b l y many of o f the the amphibolite, metasedimentary, massive mass i v e amphibolite amph i b o l i t e inclusions i n c l u s i o n s are a r e remnants r e m n a n t s of o f an a n old, o l d , largely largely vvolcanic, o l c a n i c , supracrustal s u p r a c r u s t a l sequence. sequence. T h i s sequence s e q u e n c e may may have h a v e been been This ssimilar i m i l a r to t o the t h e greenstone g r e e n s t o n e terranes t e r r a n e s of o f the t h e better b e t t e r preserved p r e s e r v e d Uchi Uchi and a n d Wabigoon W a b i g o o n S Subprovinces, u b p r o v i n c e s , a nand d a appears p p e a r s to a v e been b e e n coextensive coextensive to hhave with Winnipeg It is tthe w i t h the the W i n n i p e g River R i v e r belt. belt. It is h e eearliest a r l i e s t sstage t a g e in i n the the development The d e v e l o p m e n t of o f the t h e belt. belt. T h e less l e s s abundant a b u n d a n t metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y inclusions i n c l u s i o n s in i n the t h e younger y o u n g e r plutonic p l u t o n i c suites s u i t e s may may hhave a v e been b e e n derived d e r i v e d either e i t h e r from f r o m this t h i s older o l d e r supracrustal s u p r a c r u s t a l sequence s e q u e n c e or or from f r o m aa younger y o u n g e r sequence. sequence. . Orthogneiss O r t h o g n e i s s Suite Suite The 2 ) is c o m p o s i t i o n a l l y and and T h e orthogneiss o r t h o g n e i s s suite s u i t e (Figure ( F i g u r e 2) is a a compositionally F els i c t e x t u r a l l y hheterogeneous e t e r o g e n e o u s assemblage a s s e m b l a g e of o f layered l a y e r e d gneisses. gneisses texturally Felsic pplutonic l u t o n i c components c o m p o n e n t s ppredominate r e d o m i n a t e aand n d uundeformed n d e f o r m e d i intrusive n t r u s i v e rocks rocks aand n d iinclusions n c l u s i o n s oof f supracrustal s u p r a c r u s t a l rocks r o c k s are a r e aa minor m i n o r component. component. T h e gneissic g n e i s s i c phases p h a s e s range r a n g e in i n composition c o m p o s i t i o n from f r o m quartz q u a r t z diorite diorite The to o m e d i u m - g r a i n e d , bbiotite i o t i t e or o r hornblende— hornblendet o granite. granite. F i n e - tto Fine— medium—grained, biotite b i o t i t e tonalitic t o n a l i t i c gneiss g n e i s s is is tthe h e ooldest l d e s t pplutonic l u t o n i c component c o m p o n e n t and and This was ccontains o n t a i n s inclusions i n c l u s i o n s of o f the t h e older o l d e r supracrustal s u p r a c r u s t a l sequence. sequence. T h i s was intruded wide i n t r u d e d bby y a w i d e variety v a r i e t y of o f fine—grained f i n e - g r a i n e d to t o pegmatitic, p e g m a t i t i c , quartz quartz ddioritic i o r i t i c to t o ggranitic r a n i t i c pphases, h a s e s , in in w h i c h the t h e ggneissosity n e i s s o s i t y rranges a n g e s from from which t o strongly s t r o n g l y developed, d e v e l o p e d , and a n d by b y mafic m a f i c dikes. d i k e s . The T h e mafic m a f i c dikes dikes w e a k l y to weakly metamorphosed t o amphibolite a m p h i b o l i t e facies; f a c i e s ; they they aare r e ddeformed e f o r m e d aand nd m e t a m o r p h o s e d to iintruded n t r u d e d many f the t h e ppost—tonalite o s t - t o n a l i t e ggranitoid r a n i t o i d phases p h a s e s but b u t are are many oof iintruded n t r u d e d by b y others. others. The T h e yneissosity g n e i s s o s i t y is is a a result r e s u l t of o f ppost—emplacement o s t - e m p l a c e m e n t deformation deformation metamorphism aand nd m e t a m o r p h i s m which w h i c h affected a f f e c t e d the t h e supracrustal s u p r a c r u s t a l remnants, r e m n a n t s , the the various v a r i o u s granitoid g r a n i t o i d phases, p h a s e s , and a n d the t h e mafic maÂi c dikes. d i k e s . Another A n o t h e r effect e f f e c t of of metamorphism was the t h e ddevelopment, e v e l o p m e n t , in i n many of o f the t h e rock r o c k units, units, tthe he m e t a m o r p h i s m was . �65 of o f concordant, c o n c o r d a n t , discontinuous, d i s c o n t i n u o u s , leucocratic l e u c o c r a t i c anatectic a n a t e c t i c lenses l e n s e s that that are l e s s than t h a n 1 cm c m thick. thick. compos i t i o n of o f these these a r e commonly commonly less The composition lenses is aa function f u n c t i o n of o f source s o u r c e rock r o c k composition c o m p o s i t i o n and a n d degree d e g r e e of of l e n s e s is melting. a r e quartz q u a r t z dioritic d i o r i t i ctot otonal t o n a litic itic m e l t i n q . Common Common associations a s s o c i a t i o n s are l e n s e s in i n amphibolite, a m p h i b o l i t e , tonalite t o n a l i t e to t o granodioritic g r a n o d i o r i t i c lenses l e n s e s in in lenses tonalitic t o granitic g r a n i t i c lenses l e n s e s in in t o n a l i t i c gneiss, g n e i s s , and a n d granodioritic q r a n o d i o r i t i c to granitoid g r a n i t o i d gneiss. qneiss. The variable v a r i a b l e degree d e g r e e of o f gneissosity g n e i s s o s i t y development d e v e l o p m e n t in i n the t h e post— postThe g r a n i t o i d phases, p h a s e s , and a n d the t h e differing d i f f e r i n g age a g e relationships relationships t o n a l i t e granitoid tonalite between b e t w e e n these t h e s e phases p h a s e s and a n d the t h e mafic maÂi c dikes d i k e s indicate i n d i c a t e aa considerable considerable t o and a n d during d u r i n g the the a g e span s p a n of o f granitoid g r a n i t o i d emplacement e m p l a c e m e n t prior p r i o r to age deformation. d e f o r m a t i o n . Pegmatitic P e g m a t i t i c and a n d aplitic a p l i t i c granitic g r a n i t i c dikes d i k e s and a n d plugs plugs that are t h a t postdate p o s t d a t e major m a j o r deformation d e f o r m a t i o n are a r e also a l s o common. common. They T h e y are probably p r o b a b l y temporally t e m p o r a l l y and a n d genetically g e n e t i c a l l y related r e l a t e d to t o the t h e potassic potassic plutonic p l u t o n i c suite. suite. The The complex c o m p l e x nature n a t u r e of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e results r e s u l t s from f r o m the the intimate i n t i m a t e admixture a d m i x t u r e of o f these t h e s e variably v a r i a b l y deformed d e f o r m e d rock r o c k types. types. Heterogeneity H e t e r o g e n e i t y is is manifest m a n i f e s t on o n two t w o scales. s c a l e s . On On the t h e outcrop o u t c r o p and a n d hand hand specimen s p e c i m e n scale s c a l e the t h e distinctive d i s t i n c t i v e layered l a y e r e d appearance a p p e a r a n c e is is aa consequence 1 ) primary p r i m a r y sedimentary s e d i m e n t a r y and a n d volcanic v o l c a n i c layering layering c o n s e q u e n c e of: o f : 1) (minor) ( m i n o r ), , 2) 2 ) transposition t r a n s p o s i t i o n of o f originally o r i g i n a l l y discordant d i s c o r d a n t structures structures into by intense i n t e n s e deformation, d e f o r m a t i o n , similar s i m i l a r to to i n t o essential e s s e n t i a l parallelism p a r a l l e l i s m by that t h a t described d e s c r i b e d by b y Myers M y e r s (1978), ( 1 9 7 8 ) , 3) 3 ) pre—emplacement p r e - e m p l a c e m e n t anisotropy anisotropy such s u c h as a s layering l a y e r i n g and a n d foliation f o l i a t i o n controlling c o n t r o l l i n g the t h e geometry g e o m e t r y of of intrusive i n t r u s i v e phases, p h a s e s , and a n d 4) 4 ) recrystallization r e c r y s t a l l i z a t i o n and a n d partial p a r t i a l melting me1 t i n g synchronous s t r e s s resulting r e s u l t i n g in in s y n c h r o n o u s with w i t h layer—normal, l a y e r - n o r m a l , principal p r i n c i p a l stress foliation f o l i a t i o n and a n d lenses l e n s e s of o f anatectic a n a t e c t i c melt m e l t being b e i n g oriented o r i e n t e d parallel p a r a l l e l to to layering. layering. AA larger l a r g e r scale s c a l e layering, l a y e r i n g , metres metres to t o hundreds h u n d r e d s of o f metres metres thick, thick, is is defined d e f i n e d by units u n i t s characterized c h a r a c t e r i z e d by particular p a r t i c u l a r assemblages a s s e m b l a g e s such such as a m p h i b o l i t e or o r granitoid g r a n i t o i d gneiss g n e i s s + anatectic anatectic a s tonalite t o n a l i t e ++ amphibolite layers. a r e not n o t continuous c o n t i n u o u s along a l o n g strike. strike. l a y e r s . These T h e s e units u n i t s are 1 -4- Paragneiss Paragneiss Paragneiss P a r a g n e i s s that t h a t is is composed c o m p o s e d principally p r i n c i p a l l y of o f plagioclase, ?lag ioclase , quartz q u a r t z and a n d biotite b i o t i t e with w i t h common common almandine a l m a n d i n e garnet g a r n e t and a n d minor minor s i l l i m a n i t e and a n d muscovite m u s c o v i t e is is the t h e dominant dominant K - f e l d s p a r , cordierite, c o r d i e r i t e , sillimanite K—feldspar, rock r o c k type t y p e of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a q a n belt. b e l t . In I n many many places places original t o 70 7 0 cm cm thick, t h i c k , can c a n be b e recognized recognized o r i g i n a l sedimentary s e d i m e n t a r y bedding, b e d d i n g , 55 to by b y variations v a r i a t i o n s in i n mineralogy, m i n e r a l o g y , texture, t e x t u r e , and a n d susceptibility s u s c e p t i b i l i t y to to anatexis. a n a t e x i s . The T h e bedding b e d d i n g is is particularly p a r t i c u l a r l y well w e l l defined d e f i n e d by b y inter— interlayered l a y e r e d fine— f i n e - to t o medium—grained, m e d i u m - g r a i n e d , granoblastic g r a n o b l a s t i c yneiss g n e i s s representing represent inq psammite p s a m m i t e of o f probable p r o b a b l e greywacke g r e y w a c k e composition, c o m p o s i t i o n , and a n d medium medium to to coarse—grained, coars e - g r a i n e d , porphyroblastic p o r p h y r o b l a s t i c gneiss g n e i s s representing r e p r e s e n t i n g semipelite s e m i p e l i t e or or siltstone. s i l t s t o n e . The T h e reversal r e v e r s a l of o f grain g r a i n size s i z e with w i t h the t h e psammite p s a m m i t e being being finer f i n e r grained g r a i n e d than t h a n semi—pelite s e m i - p e l i t e isis aa consequence c o n s e q u e n c e of o f metamorphic metamorphic recrystallization. N o r m a l graded g r a d e d bedding b e d d i n g is is recognized r e c o g n i z e d rarely r a r e l y by by r e c r y s t a l l i z a t i o n . Normal progressive p r o g r e s s i v e changes c h a n g e s in i n the t h e abundance a b u n d a n c e of o f biotite b i o t i t e and a n d garnet g a r n e t which which r e f l e c t original o r i g i n a l variations v a r i a t i o n s in i n clay c l a y content c o n t e n t (Van ( V a n de d e Kamp Kamp and and reflect Beakhouse, Other O t h e r sedimentary s e d i m e n t a r y structures s t r u c t u r e s such s u c h as a s cross— crossB e a k h o u s e , 1979) 1979) bedding b e d d i n g and a n d slump s l u m p structures s t r u c t u r e s are a r e rarely r a r e l y preserved. p r e s e r v e d . Pegmatitic Pegmat i t i c leucosome l e u c o s o m e originating o r i g i n a t i n g from f r o m the t h e partial p a r t i a l melting m e l t i n g of o f these t h e s e gneisses gneisses is i s abundant a b u n d a n t and and widely w i d e l y distributed. d i s t r i b u t e d . Metamorphic M e t a m o r p h i c mineral mineral assemblages a s s e m b l a g e s and a n d partial p a r t i a l melting m e l t i n g indicate i n d i c a t e widespread, w i d e s p r e a d , upper upper . . �66 amphibolite a i n p h i b o l i t e facies f a c i e s metamorphism m e t a m o r p h i s m (McRitchie ( M c R i t c h i e and a n d Weber, Weber , 1971b; 1971 b; Freund F r e u n d aand n d Turnock, T u r n o c k , 1971; 1 9 7 1 ; Harris, H a r r i s , 1976) 1 9 7 6 ) and a n d local l o c a l low l o w pressure pressure granulite f a c i e s conditions c o n d i t i o n s (Thurston ( T h u r s t o n and a n d Breaks, B r e a k s , 1978). 1978). g r a n u l i t e facies Because metamorphic B e c a u s e oof f the the m e t a m o r p h i c grade, g r a d e , the t h e sedimentology s e d i m e n t o l o g y of o f the the paragneiss p a r a g n e i s s progenitor p r o g e n i t o r is is difficult d i f f i c u l t to t o decipher, d e c i p h e r , but b u t van v a n de d e Kamp Kamp and a n d Beakhouse B e a k h o u s e (1979) ( 1 9 7 9 ) considered c o n s i d e r e d that t h a t the t h e paragneiss p a r a g n e i s s represents represents turbidites t u r b i d i t e s deposited d e p o s i t e d below b e l o w wave w a v e base. b a s e . The T h e provenance p r o v e n a n c e is is also also difficult d i f f i c u l t to t o resolve r e s o l v e because b e c a u s e the t h e primary p r i m a r y depositional d e p o s i t i o n a l mineralogy mineralogy must m u s t be b e inferred i n f e r r e d from f r o m metamorphic m e t a m o r p h i c mineral m i n e r a l assemblages a s s e m b l a g e s and and The c h e m i c a l compositions. compositions. The chemical c h e m i c a l and a n d mineralogical m i n e r a l o g i c a l composicomposichemical tion is ssuggestive u g g e s t i v e of o f immature immature t i o n of o f the t h e least l e a s t rnigmatitic m i g m a t i t i c pparagneiss a r a g n e i s s is sediments s e d i m e n t s (van ( v a n de d e Kamp Kamp and a n d Beakhouse, B e a k h o u s e , 1979). 1 9 7 9 ) . These T h e s e authors authors suggested s u g g e s t e d that t h a t relatively r e l a t i v e l y direct d i r e c t derivation d e r i v a t i o n from f r o m felsic f e l s i c volcanism volcanism explains e x p l a i n s certain c e r t a i n of o f the t h e chemical c h e m i c a l attributes a t t r i b u t e s of o f the t h e paragneiss. paraqneiss. Breaks e t al. a l . (1978), ( 1 9 7 8 ) , on o n the t h e other o t h e r hand, h a n d , argued a r g u e d that t h a t trace trace B r e a k s et element materials e l e m e n t abundances a b u n d a n c e s rrequire e q u i r e aa vvariety a r i e t y oof f ssource ource m a t e r i a l s ; high h i g h Cr Cr and a n d Ni N i reflect r e f l e c t mafic maÂi c or o r ultramafic u l t r a m a f i c sources s o u r c e s and a n d elevated e l e v a t e d Ba B a and a n d Rb Rb felsic f e l s i c sources. sources. The T h e interfaces i n t e r f a c e s with w i t h the t h e adjacent a d j a c e n t Winnipeg W i n n i p e g River R i v e r belt b e l t on on the the south s o u t h and a n d the t h e Uchi U c h i Subprovince S u b p r o v i n c e on o n the t h e north n o r t h are a r e modified m o d i f i e d by by faults f a u l t s and a n d plutonic p l u t o n i c activity, a c t i v i t y , but b u t primary p r i m a r y stratigraphic s t r a t i g r a p h i c relationrelationships some areas. a r e a s . In I n the t h e Rice Lake L a k e area area s h i p s have h a v e been b e e n preserved p r e s e r v e d in i n some of a r e considered c o n s i d e r e d to t o be, b e , in i n part, p a r t , aa o f Manitoba, M a n i t o b a , the t h e paragneises p a r a g n e i s e s are lateral l a t e r a l facies f a c i e s equivalent e q u i v a l e n t of o f the t h e Edmunds Edmunds Lake L a k e Formation F o r m a t i o n of o f the the Uchi M c R i t c h i e and a n d Weber, Weber, 1971b) 1971 b ) U c h i Subprovirice S u b p r o v i n c e (Campbell, ( C a m p b e l l , 1971 1971;; McRitchie In Ontario, In O n t a r i o , Thurston T h u r s t o n and a n d Breaks B r e a k s (1978) ( 1 9 7 8 ) noted n o t e d that t h a t the t h e paragneiss paraqneiss is is sstratigraphically t r a t i g r a p h i c a l l y equivalent e q u i v a l e n t to t o Cycle C y c l e II volcanic v o l c a n i c rocks r o c k s in i n the the Cerny Confederation a r e a of o f the t h e Uchi U c h i Subprovince. Subprovince. C e r n y et e t al. al. C o n f e d e r a t i o n Lake L a k e area ( 1 981 ) recognized r e c o g n i z e d a assimilar i m i l a r rrelationship e l a t i o n s h i p on o n tthe h e south s o u t h sside i d e of o f the the (1981) Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n b e 1belt t wwhere h e r e t hthe e p paragneisses a r a q n e i s s e s aare r e postulated postulated to t o be b e stratigraphically s t r a t i g r a p h i c a l l yequivalent e q u i v a l e n ot t othe t t hFlanders e F l a n d e rLake s L a k eFormation Format i o n Metaconglomerates in b e l tofo fManitoba. Manitoba. Metaconglomerates i n the t h e Bird B i r d River R i v e r greenstone g r e e n s t o n e belt o c c u r in i n both b o t h the t h e Edmunds Lake L a k e and a n d Flanders F l a n d e r s Lake L a k e Formations F o r m a t i o n s and and occur locally l o c a l l y at a t other o t h e r places p l a c e s near n e a r the t h e margins m a r g i n s of o f the t h eEar E a rFalls— Fallsb e l t (e.g., ( e . g . , Breaks B r e a k s et e t al., a l . , 1978), 1 9 7 8 ) , and a n d contain c o n t a i n aa M a n i g o t a g a n belt Manigotagan variety d e r i v e d from f r o m mafic maÂi c to t o felsic f e l s i c volcanic v o l c a n i c units, units, v a r i e t y of o f clasts c l a s ts derived mafic maÂi c to t o felsic f e l s i c plutons, p l u t o n s , and a n d sedimentary s e d i m e n t a r y units u n i t s including including ferruginous metasediments f e r r u g i n o u s cchemical hemical m e t a s e d i m e n t s ((Bateman, B a t e m a n , 11939 9 3 9 ; Breaks B r e a k s et e t al. a1 These 1978; 1 9 7 8 ; Cerny C e r n y et e t al. a l . 1981 1981 ; Campbell, C a m p b e l l , 1971 1971). ). T h e s e stratigraphic stratigraphic relationships more that m o r e proximal p r o x i m a l facies f a c i e s of o f the t h e paragneiss paragneiss r e l a t i o n s h i p s ssuggest u g g e s t that may v o l c a n o - s e d i m e n t a r y sequences sequences may occur o c c u r in i n the t h e greenstone—belt, g r e e n s t o n e - b e 1 t , volcano—sedimentary flanking f l a n k i n g the t h e Ear E a r Falls-Manigotagan F a l l s - M a n i q o t a g a n belt. belt. was apparently a p p a r e n t l y the t h e adjacent adjacent T h e provenance p r o v e n a n c e of o f the t h e paragneiss p a r a g n e i s s was The greenstone—granitoid g r e e n s t o n e - g r a n i t o i d terranes t e r r a n e s and a n d was was variable v a r i a b l e in i n composition, compos i t i o n , although a 1 t h o u q h volcaniclastic v o l c a n i c l a s t i c metasediments m e t a s e d i m e n t s may may be be regionally r e g i o n a l l y or or locallocally l y dominant d o m i n a n t (cf. ( c f Ojakangas, O j a k a n g a s , 1985). 1985). . . e B e 1 ts I n t e r n a l Greenstone G r e e n s t o n e Belts Internal Two Two relatively r e l a t i v e l y well w e l l preserved p r e s e r v e d greeristone g r e e n s t o n e belts be1 ts occur o c c u r entireentirely within ly w i t h i n the t h e English E n g l i s h River R i v e r Subprovince, S u b p r o v i n c e , along a l o n g the t h e boundary boundary between Manigotaqan belts. b e t w e e n the t h e Winnipeg W i n n i p e g R i v e r a n d Ear F a l l s - Manigotagan The Bird B i r dRiver R i vgreenstone e r g r e e nbelt, s t othe n elarger b e l and t , better t h e lpreserved a r g e r and b e t t e r preserved The of mafic to felsicr metavolcanic o f thet htwo e tbelts w o comprises b e l t s comprises n a f i c t o f rocks, e l s i c metavolcanic rocks, mafic cclastic l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s and a n d maf i c to t o ultramafic u l t r a r n a f i c intrusions intrusions River and Ear Falls - belts. �67 (Davies ( ~ a v i e et se t al. a l . 1962; 1 9 6 2 ; Karup—frloller K a r u p - M o l l e r a nand d Brurnmer 971; T r u e m a n 1975; 1975; Brummer 11971; Trueman Cerny C e r n y et e t al. a l . 1981). 1981 ) R e g i o n a l m e t a m o r p h i c g r a d e i n c r e a s e s o u t ward Regional metamorphic grade increases outward f r o m greenschist g r e e n s c h i s t to t o almandine—amphibolite a l m a n d i n e - a m p h i b o l i t e as a s the t h e belt b e l t grades g r a d e s into into from paragneiss M a n i g o t a g a n belt b e l t (Butrenchuk (Butrenchuk p a r a g n e i s s of o f the t h e Ear E a r Falls F a l l s —- Manigotagan 1970) 1970). c l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are F e l s i c metavolcanic m e t a v o l c a n i c and a n d clastic Felsic more abundant a b u n d a n t than t h a n in i n most most greenstone g r e e n s t o n e belts b e l t s of o f the t h e Wabigoon W a b i g o o n and and more u t tthis h i s may e f l e c t the t h e relatively r e l a t i v e l y small s m a l l size size U c h i SSubprovinces, u b p r o v i n c e s , bbut tJchi may rreflect of o f the t h e greenstone g r e e n s t o n e belt b e 1 t and and partial p a r t i a l engulfment e n g u l f m e n t by by younger y o u n g e r plutons plutons rather r a t h e r than t h a n any a n y primary p r i m a r y ddifferences. ifferences O t h e r greeristone g r e e n s t o n e bbelts, e 1 ts , Other h o w e v e r , ddo o llack a c k iintrusions n t r u s i o n s comparable c o m p a r a b l e tto o tthe h e layered, l a y e r e d , Cr-enrichCr-enrichhowever, ed Bird R i v e r s i l l . The T h e Separation S e p a r a t i o n Lake L a k e greenstone g r e e n s t o n e belt b e l t is is mainly m a i n l y massive m a s s i v e and and pillowed f l o w s with w i t h subordinate s u b o r d i n a t e qabbro q a b b r o and a n d peridotite peridot ite p i l l o w e d metabasalt m e t a b a s a l t flows i n t r u s i o n s and a n d oxide—facies o x i d e - f a c i e s iron i r o n formation; f o r m a t i o n ; metamorphic m e t a m o r p h i c grade g r a d e is is intrusions amphibolite a m p h i b o l i t e facies f a c i e s (Beakhouse, ( B e a k h o u s e , 1975). 1 9 7 5 ) . The The belt b e l t is is in i n fault fault contact c o n t a c t with w i t h paragrieiss p a r a g n e i s s tto o tthe h e north n o r t h and a n d the t h e southern s o u t h e r n margin marg i n is is aa 1 to t o 22 km km wide w i d e migmatitic m i g m a t i t i c zone z o n e with w i t h younger y o u n g e r plutons. plutons. Numerous N u m e r o u s gabbro, g a b b r o , and a n d iron i r o n formation f o r m a t i o n rafts r a f t s are a r e widely widely distributed d i s t r i b u t e d in i n the t h e younger y o u n g e r plutonic p l u t o n i c suites, s u i t e s , but b u t are a r e especially especially abundant a b u n d a n t along a l o n g the t h e north n o r t h margin m a r g i n of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t east east of o f Separation S e p a r a t i o n Lake L a k e where w h e r e they t h e y may may be b e an a n extension e x t e n s i o n of o f the the Separation a r e a south south S e p a r a t i o n lake l a k e greenstone g r e e n s t o n e belt, b e l t , and a n d in i n the t h e Sand S a n d Lake L a k e area of o f the t h e Separation S e p a r a t i o n Lake Lake belt. b e l t . These T h e s e rafts r a f t s lack l a c k the t h e intense intense deformation t h a t characterizes c h a r a c t e r i z e s the t h e early early d e f o r m a t i o n and a n d partial p a r t i a l anatexis a n a t e x is that supracrustal remnants. s u p r a c r u s t a l remnants. As A s noted n o t e d previously p r e v i o u s l y the t h egreenstorie—belt g r e e n s t o n e - b e 1 t sequences s e q u e n c e s appear a p p e a r to to be b e stratigraphically s t r a t i q r a p h i c a l l y equivalent e q u i v a l e n t to t o the t h e paragneisses p a r a g n e i s s e s of o f the t h e Ear Ear Falls—Manigotagan F a l l s - M a n i g o t a g a n belt b e 1 t (Cerny ( C e r n y et e t al., a 1 , 1981) 1981 ) and a n d to t o greenstone— greens tonebelt b e l t sequences s e q u e n c e s of o f the t h e tichi U c h iSubprovince. S u b p r o v i n c e . Contacts C o n t a c t s between b e t w e e n the the b e 1 t - p a r a g n e i s s assemblage a s s e m b l a g e and a n d the t h e older o l d e rorthogneiss— orthoqneissg r e e n s t o n e belt—paragneiss greenstone supracrustal s u p r a c r u s t a lremnant r e m n a n t assemblage a s s e m b l a g e have h a v e not n o t been b e e n observed. o b s e r v e d . However, However, a s w i l l b e d i s c u s s e d l a t e r , t h e r e l a t i v e a g e s o f t h e two assemblages a s s e m b l a g e s ccan a n be b e deduced d e d u c e d ffrom r o m iindirect n d i r e c t field f i e l evidence d e v i d e n c and e a n geo— d qeochronoloqic c h r o n o l o g i c data. data. . . ed Bird River sill. 1 . as will be discussed later, the relative ages of the two Plutonic P l u t o n i c Rocks Rocks e l s i c plutonic p l u t o n i c suites, s u i t e s , sodic s o d i cand a n d potassic, p o t a s s i c ,underlie u n d e r l i 80% e 80% Two f felsic Two of o f the t h eWinnipeg W i n n i p e g River R i v e r belt b e l t and and 50% 5 0 % of o f the t h e western w e s t e r n English E n g l i s h River River Subprovince p l u t o n scommonly commonly intruded intruded S u b p r o v i n c e (Figure ( F i g u r e 2). 2 ) . Potassic P o t a s s i cplutoris adjacent t h i r d (mafic) ( m a f i c ) suite s u i t e is is not n o tabundant. abundant. a d j a c e n t sodic s o d i c plutons. p l u t o n s . AA third The t w o settings: s e t t i n g s : 1)1 ) intruded i n t r u d e d into into T h e sodic s o d i c suite s u i t e occurs o c c u r s in i n two orthogneiss a n d 2) 2) o r t h o g n e i s s near n e a r the t h e margins m a r g i n s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt, b e 1 t , and as a s diapiric d i a p i r i c intrusions i n t r u s i o n s into i n t o the t h e paragneiss p a r a g n e i s s of o f the t h e Ear E a r Falls F a l l s —Manigotagan M a n i g o t a q a n belt. b e l t . The T h e sodic s o d i c suite s u i t e includes i n c l u d e s quartz q u a r t z diorites, diorites , tonalites t o n a l i t e s and a n d granodiorites q r a n o d i o r i t e s that t h a t are a r e commonly commonly recrystallized r e c r y s t a l l i z e d and, and, in some cases, c a s e s , deformed. d e f o r m e d . Primary P r i m a r y igneous i g n e o u s textures t e x t u r e s are are i n some recognizable r e c o g n i z a b l e but b u t are a r e commonly commonly modified m o d i f i e d by by the t h e development d e v e l o p m e n t of o f aa foliation f o l i a t i o n or o r lineation. l i n e a t i o n . Weakly W e a k l y yneissic g n e i s s i c fabrics f a b r i c s are are present present locally, to l o c a l l y , near n e a r contacts, c o n t a c t s , and a n d probably p r o b a b l y originated o r i g i n a t e d in i n response r e s p o n s e to laminar l a m i n a r flow f l o w during d u r i n g emplacement e m p l a c e m e n t although a l t h o u g h certain c e r t a i n units u n i t s appear a p p e a r to to pre—date p r e - d a t e deformation. deformation. The is most m o s t abundant a b u n d a n t in i n the t h e west—central w e s t - c e n t r a l part part T h e potassic p o t a s s i c suite s u i t e is of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t where w h e r e it i t forms f o r m s large l a r g e batholiths batholiths �68 (Figure ( F i g u r e 2). 2). IIt t aalso l s o ooccurs c c u r s aas s sstocks, t o c k s , ddikes i k e s and a n d sills s i l l s throughout throughout ett al., a l . , 1978). 1 9 7 8 ) . This T h i s suite suite tthe h e English E n g l i s h River R i v e r Subprovince S u b p r o v i n c e (Breaks (Breaks e includes late i n c l u d e s ggranodiorites r a n o d i o r i t e s and a n d granites g r a n i t e s that, t h a t , except e x c e p t near n e a r late ffaults, a u l t s , lack l a c k the t h e ssecondary e c o n d a r y recrystallization r e c r y s t a l l i z a t i o n foliation foliation Primary ccharacteristic h a r a c t e r i s t i c of o f the t h e sodic s o d i c suite. suite. P r i m a r y planar p l a n a r and a n d linear linear a r e rare r a r e but b u t well w e l l preserved. preserved. fflow l o w sstructures t r u c t u r e s are Inclusions a r e found f o u n d in i n the the I n c l u s i o n s of o f virtually v i r t u a l l y every e v e r y older o l d e r suite s u i t e are potassic p o t a s s i c suite s u i t e but b u t individual i n d i v i d u a l units u n i t s are a r e characterized c h a r a c t e r i z e d by b y specific specific Potassic aassemblages s s e m b l a g e s of o f inclusions. inclusions. P o t a s s i c plutons p l u t o n s in i n the t h e Winnipeg Winnipeg River a r e characterized c h a r a c t e r i z e d by b y arnphibolite, a m p h i b o l i t e , oorthogneiss r t h o g n e i s s and and R i v e r belt b e l t are t o granodioritic granodioritic vvariously a r i o u s l y recrystallized r e c r y s t a l l i z e d quartz q u a r t z dioritic d i o r i t i c to inclusions Ear Falls Falls i n c l u s i o n s whereas w h e r e a s the t h e relatively r e l a t i v e l y small s m a l l plutons p l u t o n s in i n the t h e Ear — Manigotagan - M a n i g o t a g a n belt b e l t contain c o n t a i n variously v a r i o u s l y digested d i g e s t e d paragneiss paragneiss iinclusions. n c l us ions a FOR 'PRE-KENORAN' CRUST IIN THE WINNIPEG WINNIPEG RRIVER BELT EEVIDENCE V I D E N C E FOR 'PRE-KENORAN' CRUST N THE I V E R BELT The i s the t h e culminating c u l m i n a t i n g Archean A r c h e a n orogenic oroqenic T h e Kenoran K e n o r a n Orogeny O r o g e n y is It was eevent v e n t in i n the t h e Superior S u p e r i o r Province. Province. It w a s ooriginally r i g i n a l l y ddated a t e d as a s the the pperiod e r i o d between b e t w e e n 2390 2 3 9 0 Ma and a n d 2590 2 5 9 0 Ma (Stockwell, ( S t o c k w e l l , 1964) 1 9 6 4 ) based b a s e d on on These K - A r mineral m i n e r a l ages. ages. T h e s e ages a g e s are a r e now widely w i d e l y regarded r e g a r d e d as as K—Ar representing r e p r e s e n t i n g minimum cooling c o o l i n g ages a g e s and a n d the t h e age a g e and a n d definition d e f i n i t i o n of of ( e .g. Gower Gower and and t h e orogeny o r o g e n y has h a s been b e e n revised r e v i s e d repeatedly r e p e a t e d l y (e.g. the Clifford, ( 1 9 7 7 ) concluded, concluded, C l i f f o r d , 1981, 1 9 8 1 , Harland, H a r l a n d , 1983). 1 9 8 3 ) . Goodwin (1977) largely l a r g e l y oon n the t h e basis b a s i s of o f U—Pb U-Pb zircon z i r c o n ages, a g e s , that t h a t most m o s t metavolcanic metavolcanic metasedirnentary western aand nd m e t a s e d i m e n t a r y r rocks o c k s oof  tthe he w e s t e r n SSuperior u p e r i o r Province P r o v i n c e were were Ma, were were subsequently s u b s e q u e n t l y deformed deformed ddeposited e p o s i t e d between b e t w e e n 2710 2 7 1 0 and a n d 2760 2 7 6 0 Ma, metamorphosed aand nd m e t a m o r p h o s e d by by the t h e Kenoran K e n o r a n orogeny o r o g e n y and a n d had had been b e e n intruded i n t r u d e d by by Recent late— l a t e - or o r post—tectonic p o s t - t e c t o n i c plutons p l u t o n s by b y 2660 2 6 6 0 Ma. Ma. R e c e n t U—Ph U-Pb zircon zircon ddata a t a from f r o m the t h e western w e s t e r n Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e (Hart ( H a r t and a n d Davis, D a v i s , 1969; 1969; Davis D a v i s eet t aal l . 1982; 1 9 8 2 ; Davis D a v i s and a n d Trowell, T r o w e l l , 1982; 1 9 8 2 ; Davis D a v i s and a n d Edwards, Edwards, with 1982; Blackburn e t al., a l . , 11984) 9 8 4 ) aagree gree w i t h this t h i s conclusion, c o n c l u s i o n , and and 1982; B l a c k b u r n et indicate i n d i c a t e tthat h a t vvolcanic o l c a n i c and a n d associated a s s o c i a t e d plutonic p l u t o n i c activity a c t , i v i t y here here t i m e interval i n t e r v a l of o f 2703 2 7 0 3 to t o aapparently p p a r e n t l y ooccurred c c u r r e d over o v e r the t h e restricted r e s t r i c t e d time 2755 Ma, and a n d that t h a t post—tectonic p o s t - t e c t o n i c plutons p l u t o n s were w e r e emplaced e m p l a c e d by b y 2695 2695 2 7 5 5 Ma, This is a useful u s e f u l standard s t a n d a r d against a g a i n s t which w h i c h to t o evaluate e v a l u a t e isotopic isotopic Ma. T h i s is Winnipeg aages g e s from f r o m the the W i n n i p e g River R i v e r belt b e l t because b e c a u s e of o f the t h e high h i g h precision precision a g e s and a n d the t h e proximity p r o x i m i t y to aand n d consistency c o n s i s t e n c y of o f the t h e ages t o the t h e Winnipeg Winnipeg River R i v e r belt. belt. Goodwin (1977) Ma) Lac L a c Seul Seul Goodwin ( 1 9 7 7 ) also a l s o recognized r e c o g n i z e d an a n older o l d e r (>3000 ( > 3 0 0 0 Ma) metaeevent, v e n t , and a n d ssubsequent u b s e q u e n t work w o r k has h a s recognized r e c o g n i z e d metavolcanic m e t a v o l c a n i c and a n d meta— pplutonic l u t o n i c rocks r o c k s intermediate i n t e r m e d i a t eini nage a g between e b e t w e e n2760 2 7 6 0and a n d3000 3 0 0 0Ma Ma (Nunes ( N u n e s a and n d TThurston, h u r s t o n , 11980; 9 8 0 ; BBeakhouse, e a k h o u s e , 1 91983; 8 3 ; C oCorfu r f u e teta al., l . , 1985). 1985). These a g e s complicate c o m p l i c a t e Goodwin's G o o d w i n ' s two—fold t w o - f o l d d distinction istinction T h e s e intermediate i n t e r n e d i a t e ages and Province, a n d ssuggest u g g e s t tthat, h a t , in i n some some parts p a r t s of o f the t h ewestern w e s t e r n Superior Superior P rovince, ccrustal r u s t a l evolution e v o l u t i o n may have h a v e proceeded p r o c e e d e d semi—continuously s e m i - c o n t i n u o u s l y for f o r 400 4 00 To facilitate Ma. f a c i l i t a t e ddiscussion i s c u s s i o n the t h e terms terms 'Kenoran' ' K e n o r a n ' and a n d 'pre— 'preKenoran' K e n o r a n ' are a r e used u s e d informally i n f o r m a l l y here h e r e to t o refer r e f e r to t o rocks r o c k s younger y o u n g e r and and It Ma. I t iis s eemphasized m p h a s i z e d that t h a t these these oolder, l d e r , respectively, r e s p e c t i v e l y , than t h a n 2760 2 7 6 0 Ma. terms a are terms r e adopted a d o p t e d for f o r convenience c o n v e n i e n c e only o n l y and a n d without w i t h o u t any a n y intent i n t e n t to to fformally o r m a l l y re—define r e - d e f i n e the t h e Kenoran K e n o r a n Orogeny. Orogeny. Field F i e l d Evidence Evidence The T h e oorthogneiss r t h o g n e i s s suite s u i t e intruded i n t r u d e d the t h e older o l d e r supracrustal supracrust a l remnant p h a s e s of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e predate predate r e m n a n t suite s u i t e and a n d most phases �69 the t h e plutoriic p l u t o n i c suites. s u i t e s . The T h e orthogneiss o r t h o g n e i s s is is interpreted i n t e r p r e t e d to t o be b e older older a n d Wabigoori Wabigoon t h a n the t h e paragneiss, p a r a g n e i s s , internal i n t e r n a l greenstone g r e e n s t o n e belts b e 1 ts and than s u b p r o v i n c e volcanism v o l c a n i s m based b a s e d on o n several s e v e r a l indirect i n d i r e c t field field subprovince relationships. relationships. 1) T h e orthogneiss o r t h o g n e i s s is is cut c u t by b y mafic ma i c dikes d i k e s (Bald, ( B a l d , 1981). 1981 ) Some 1) The Some of (6 o f these t h e s e dikes, d i k e s , such s u c h as a s those t h o s e in i n the t h e Tannis T a n n i s Lake L a k e area a r e a (6 o n Fig. F i g . 2), 2 ) , may may be b e feeders f e e d e r s to t o Kenoran K e n o r a n volcanism v o l c a n i s m (Clark ( C l a r k et et on al. a l . 1981), 1 9 8 1 ) , although a l t h o u g h Gower Gower (1978) ( 1 9 7 8 ) has h a s noted n o t e d that t h a t some some dikes d i k e s in i n the t h e Kenora K e n o r a area a r e a are a r e caic—alkaline c a l c - a l k a l i n e and a n d are are probably p r o b a b l y not n o t related r e l a t e d to t o the t h e basal b a s a l tholeiitic t h o l e i i t i c volcanism v o l c a n i s m in in the t h e adjacent a d j a c e n t Wabigoon W a b i g o o n Subprovince. Subprovince. 2) 2 ) Polymictic P o l y m i c t i c conglomerate c o n g l o m e r a t e at a t Perrault P e r r a u l t Lake L a k e in i n the t h e Winnipeg Winnipeg River R i v e r belt b e l t contains c o n t a i n s massive m a s s i v e and a n d foliated f o l i a t e d plutonic p l u t o n i c clasts clasts (Breaks e t al. a l . 1978). 1 9 7 8 ) . It I t is i s unlikely u n l i k e l y that t h a t the t h e foliated foliated ( B r e a k s et plutonic p l u t o n i c clasts c l a s t s were were derived d e r i v e d from f r o m syrivolcanic s y n v o l c a n i c plutons, plutons, and, a1 t h o u g h it i t cannot c a n n o t be b e established e s t a b l i s h e d that t h a t these t h e s e clasts c l a s ts a n d , although were were derived d e r i v e d from f r o m the t h e orthogneiss, o r t h o g n e i s s , they t h e y do d o demonstrate demonstrate the t h e existence e x i s t e n c e of o f an a n elevated e l e v a t e d granitoid g r a n i t o i d terrane t e r r a n e prior p r i o r to to the l a t e plutonism. plutonism. t h e late 3) 3 ) In I n the t h e western w e s t e r n end e n d of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n belt, belt, orthogneiss cores of o f antiforms a n t i f o r m s and and o r t h o g n e i s s occupies o c c u p i e s the t h e cores structurally s t r u c t u r a l l y underlies u n d e r l i e s the t h e paragneiss p a r a g n e i s s representing r e p r e s e n t i n g aa possible p o s s i b l e basement—cover b a s e m e n t - c o v e r relationship r e l a t i o n s h i p (Ermanovics ( E r m a n o v i c s et e t al., al., 1979). 1 9 7 9 ) . However, H o w e v e r , tectonic t e c t o n i c juxtaposition j u x t a p o s i t i o n of o f these t h e s e units u n i t s is is also In a l s o possible. possible. I n the t h e Cedar C e d a r Lake L a k e area, a r e a , Westerman W e s t e r m a n (1979) ( 1 979) considered cores of of c o n s i d e r e d that t h a t the t h e Twilight T w i l i g h t paragneiss p a r a g n e i s s in i n the t h e cores domal d o m a l structures s t r u c t u r e s is is aa result r e s u l t of o f subhorizontal s u b h o r i z o n t a l tectonic tectonic interleaving i n t e r l e a v i n g of o f basement b a s e m e n t and a n d cover c o v e r sequences. sequences. 4) 4 ) The T h e earliest e a r l i e s t deformation d e f o r m a t i o n that t h a t affected a f f e c t e d the t h e orthogneiss o r t h o g n e i s s in in the t h e Cedar C e d a r Lake L a k e area a r e a may may not n o t be b e present p r e s e n t in i n the t h e Twilight Twilight paragneiss p a r a g n e i s s (Westerman, ( W e s t e r m a n , 1977) 1 9 7 7 ) implying i m p l y i n g that t h a t the t h e tonalites t o n a l ites were were emplaced e m p l a c e d and a n d deformed d e f o r m e d prior p r i o r to t o the t h e deposition d e p o s i t i o n of o f the the paragneiss p a r a g n e i s s progenitor. p r o g e n i t o r . Similarly, S i m i l a r l y , deformation d e f o r m a t i o n in i n the the paragneisses p a r a g n e i s s e s of o f the t h e Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n belt b e l t appears a p p e a r s to to be b e less l e s s complex c o m p l e x than t h a n in i n adjacent a d j a c e n t orthogneiss. o r t h o g n e i s s . However, However, it i t must m u s t be b e stressed s t r e s s e d that t h a t the t h e apparent a p p a r e n t differences d i f f e r e n c e s in in structural s t r u c t u r a l complexity c o m p l e x i t y of o f paragneiss p a r a g n e i s s and a n d orthogneiss o r t h o g n e i s s could could also a l s o be b e the t h e result r e s u l t of o f differing d i f f e r i n q ductility d u c t i l i t y contrasts c o n t r a s t s and and rheologic same deformation d e f o r m a t i o n event. event. r h e o l o q i c states s t a t e s during d u r i n g the t h e same The T h e field f i e l d relations r e l a t i o n s outlined o u t l i n e d above a b o v e give g i v e inconclusive i n c o n c l u s i v e results results about b e 1 ta b o u t the t h e age a g e relationships r e l a t i o n s h i p s between b e t w e e nthe t h egreenstorie g r e e n s t o n e belt— paragneiss p a r a g n e i s s assemblage a s s e m b l a g e aand n d tthe h e orthogneiss. orthogneiss. A t the present state o f k n o w l e d g e a1 t e r n a t i v e e x p l a n a t i o n s are p o s s i b l e f o r a l l o f t h e field f i e l drelations, relationa s , common a commonsituation s i t u a t i oin n isuch n s u ccomplexly h c o m p l e x l deformed y deformed t e r r a n e s . In I n spite s p i t e o f t h e s e p r o b l e m s , t h e f i e l d relations r e l a t i o n s can c a n be be interpreted t o indicate i n d i c a t e that t h a t the t h e orthogneiss o r t h o g n e i s s is is older o l d e r than t h a n the the i n t e r p r e t e d to greenstone g r e e n s t o n e belt—paragneiss b e 1 t - p a r a q n e i s s assemblage a s s e m b l a g eand a n disispre—Kenorari. pre-Kenoran. This This interpretation is supported s u p p o r t e d by b y geochronologic q e o c h r o n o l o g i c data. data. i n t e r p r e t a t i o n is . At the present state of knowledge alternative explanations are possible for all of the terranes. of these problems, the field Geochronological G e o c h r o n o l o g i c a l Evidence Evidence AA direct d i r e c t approach a p p r o a c h to to establish e s t a b l i s h the t h e existence e x i s t e n c e and and distribution d i s t r i b u t i o n of o f pre—Kenoran p r e - K e n o r a n crust c r u s t is is the t h e isotopic i s o t o p i c dating d a t i n q of o f those those rocks r o c k s interpreted, i n t e r p r e t e d , on o n the t h e basis b a s i s of o f field f i e l d relationships, r e l a t i o n s h i p s , to t o be b e the the oldest o l d e s t in i n aa particular p a r t i c u l a r area. a r e a . Supracrustal S u p r a c r u s t a l remnants r e m n a n t s are a r e difficult difficult �70 to to ddate a t e isotopically i s o t o p i c a l l y because b e c a u s e most most are a r e mafic m a f i c volcanic v o l c a n i c rocks. rocks. Rubidium — strontium s t r o n t i u m investigations i n v e s t i g a t i o n s oof f ssuch u c h rocks r o c k s are a r e hampered h a m p e r e d by by Rubidium a ssmall m a l l range r a n g e in i n Rb/Sr Rb/Sr which w h i c h limits l i m i t s precision, p r e c i s i o n , susceptibility s u s c e p t i b i l i t y to to open o p e n system s y s t e m behaviour, b e h a v i o u r , and a n d by b y low l o w Rb/Sr Rb/Sr which w h i c h results r e s u l t s in i n aa very very sslight l i g h t increase i n c r e a s e in i n initial i n i t i a l Sr Sr isotopic i s o t o p i c composition c o m p o s i t i o n for f o r meta— metaZircons are not a common primary morphically rotated isochrons. morphically rotated isochrons. Z i r c o n s are n o t a primary mineral be of of m i n e r a l in i n mafic m a f i c volcanic v o l c a n i c rocks r o c k s and, a n d , if i f present, p r e s e n t , they t h e y may may be metamorphic Zr derived d e r i v e d from f r o m the t h e alteration a l t e r a t i o n of of m e t a m o r p h i c origin o r i g i n with w i t h Zr ppyroxene y r o x e n e to t o amphibole. amphibole. Granitoid a r e more G r a n i t o i d ggneiss n e i s s components c o m p o n e n t s oof f the t h e orthogneiss o r t h o g n e i s s are appropriate a p p r o p r i a t e for f o r Rb—Sr Rb-Sr and a n d U—Pb U-Pb zircon z i r c o n investigation i n v e s t i g a t i o n —- - they t h e y may be relatively younger than the supracrustal remnants and b e r e l a t i v e l y y o u n g e r t h a n t h e s u p r a c r u s t a l r e m n a n t s a n d the the m e l t i n g of of ttonalite o n a l i t e gneiss g n e i s s but b u t they t h e y could, c o u l d , if i f derived d e r i v e d from f r o m the t h e melting ssuch u c h rocks, r o c k s , hhave a v e Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s that t h a t reflect r e f l e c t the the ccrustal r u s t a l residence r e s i d e n c e history h i s t o r y of o f their t h e i r precursor. p r e c u r s o r . The T h e rock r o c k type t y p e that that has a t t e n t i o n is is the t h e fine—grained f i n e - g r a i n e d tonalite tonalite h a s received r e c e i v e d the t h e most attention Radiometric ggneiss n e i s s component c o m p o n e n t of o f the t h e orthogneiss. orthogneiss. R a d i o m e t r i c dating d a t i n g of o f such such rocks is not without problems but they are amenable to a variety r o c k s is n o t w i t h o u t p r o b l e m s b u t t h e y a r e a m e n a b l e t o a v a r i e t y oof f types t y p e s of o f Rb—Sr Rb-Sr and a n d U—Pb U-Pb zircon z i r c o n investigation i n v e s t i g a t i o n (Beakhouse ( B e a k h o u s e 1983). 1983). The aavailable The v a i l a b l e ggeochronoloqical e o c h r o n o l o g i c a l ddata a t a for f o r the t h e orthogneiss o r t h o g n e i s s and and Winnipeg ssodic o d i c pplutons l u t o n s from f r o m the the W i n n i p e g River R i v e r belt b e l t sugqest s u g g e s t that t h a t these these rrocks o c k s aare r e sslightly l i g h t l y to t o ssignificantly i g n i f i c a n t l y oolder l d e r than t h a n volcanism v o l c a n i s m and and 'Pre—Kenoran' plutonism 3). ) 'Pre-Kenoran' p l u t o n i s m iin n the t h e Wabigoon W a b i g o o n SSubprovince u b p r o v i n c e ((Figure Figure 3 att Sen S e n Bay Bay on o n eastern e a s t e r n Lac Lac Seul Seul ttonalites o n a l i t e s hhave a v e been b e e n recognized recognized a (Krogh Tannis K r o g h e t a l . 1976a) 1 9 7 6 a ) ,, T a n n i s Lake Lake ( (Clark C l a r k eet t aal., l . , 1981; 1981 ; D.W. D.W. Davis, D a v i s , personal p e r s o n a l communication, c o m m u n i c a t i o n , 1983), l 9 8 3 ) , in i n the t h e Kenora K e n o r a area area ((Beakhouse, B e a k h o u s e , 1983) 1 9 8 3 ) aand n d hhave a v e been b e e n interpreted i n t e r p r e t e d (from ( f r o m combined c o m b i n e d U—Pb U-Pb zircon z i r c o n aand n d Rb—Sr Rb-Sr isotopic i s o t o p i c sstudies) t u d i e s ) to t o be b e present p r e s e n t in i n the t h e Cedar Cedar Lake L a k e area a r e a (Beakhouse, ( B e a k h o u s e , 1983). 1 9 8 3 ) . Rb—Sr Rb-Sr whole w h o l e rock r o c k ages a g e s tend t e n d to t o be be U—Pb zircon yyounger o u n g e r than t h a n U-Pb z i r c o n ages a g e s for f o r the t h e same s a m e units u n i t s and a n d the t h e poorer poorer Rb/Sr ages a g e s limits pprecision r e c i s i o n of o f the t h e Rb/Sr l i m i t s their t h e i r usefulness u s e f u l n e s s in i n inter-sub— inter-subPreliminary 3 other o t h e r localities localities pprovince r o v i n c e correlation. correlation. P r e l i m i n a r y ddata a t a from from 3 (Kenora, Daniels Cedar U—Pb zircon (Kenora, D a n i e l s Lake, Lake, C e d a r Lake) L a k e ) have h a v e minimum U-Pb z i r c o n ages ages rranging a n g i n g from f r o m 2837 2 8 3 7 to t o 3168 3 1 6 8 Ma Ma (Corfu ( C o r f u et e t al., a l . , 1985). 1985). IIn n aaddition, ddition, D.W. D.W. Davis D a v i s (personal ( p e r s o n a l communication, c o m m u n i c a t i o n , 1985) 1 9 8 5 ) has h a s determined d e t e r m i n e d aa age for a granitoid boulder in a conglomerate minimum a g e f o r a g r a n i t o i d b o u l d e r i n a c o n g l o m e r a t e near n e a r the the Winnipeg W i n n i p e g River—Wabigoon R i v e r - W a b i g o o n iinterface n t e r f a c e in i n the t h eSioux S i o u x Lookout L o o k o u t area a r e a of of 22897 8 9 7 Ma. Ma. The U—Pb T h e U-Pb z i rzircon c o n g egeochronological o c h r o n o l o q i c a l d adata t a ( (Figure F i g u r e 33) ) suggest suggest that River t h a t although a 1 t h o u g h the t h e Winnipeg Winnipeg R i v e r bbelt e l t had h a d aa more more protracted protracted hhistory i s t o r y than t h a n the t h eWabigoon W a b i g o o n SSubprovince, u b p r o v i n c e , t there here a r e some some ssimilarimilarare Mostl late— ities. Most a t e - a nand d p opost—tectonic s t - t e c t o n i c g r granitic a n i t i c pplutons l u t o n s iin n the the Winnipeg Ma and a n d 2705 2 7 0 5 Ma Ma W i n n i p e g RRiver i v e r belt b e l t were w e r e emplaced e m p l a c e d between b e t w e e n 2660 2 6 6 0 Ma This with w i t h tthe h e more more hhighly i g h l y ddifferentiated i f f e r e n t i a t e d granites g r a n i t e s emplaced e m p l a c e d llast. ast. T his with ccompares o m p a r e s ffavourably avourably w i t h the t h e age a g eofo f2695 2 6 9 5Ma Ma for for a a post—tectonic post-tectonic pplutori l u t o n (the ( t h e Taylor T a y l o rLake L a k e stock) s t o c k )from f r o mthe t hWabigoon e W a b i g o o n Subprovince Subprovince e t al. a l . 1982). 1 9 8 2 ) . Tonalitic T o n a l i t i c phases p h a s e s of o f the t h e granitoid g r a n i t o i d gneiss gneiss ((Davis D a v i s et ccomponent o m p o n e n t oof f the t h e oorthogneiss r t h o g n e i s s from f r o m the t h e Cedar C e d a r Lake L a k e area a r e a apparently apparently crystallized c r y s t a l l i z e d at a t approximately a p p r o x i m a t e l y tthe h e same same ttime i m e as a s volcanic v o l c a n i c and and tonalitic t o n a l i t i cplutons p l u t o n in s ithe n t Wabigoon h e W a b i g o o nSubprovince S u b p r o v i n c e but b u thave h a v emodel model Sr Sr iisotope s o t o p e iinitial n i t i a lratios r a t i o (approximately s ( a p p r o x i m a t e l y0.704) 0. 7 0 4 ) that t h a t ssuggest u g g e s t that that melting they t h e y ooriginate r i g i n a t e from f r o m the the m e l t i n g oof f oolder l d e r crust c r u s t (Beakhouse ( B e a k h o u s e 1983). 1983). This T h i s period p e r i o d of o f melting, m e 1 t i n g , crystallization c r y s t a l l i z a t i o n and a n d associated a s s o c i a t e d metametamorphism is broadly b r o a d l y equivalent e q u i v a l e n t to t o aa period p e r i o d of o f volcano-plutonic volcano-plutonic m o r p h i s m is . et al. ities. �- = 1 Late- tto o Post—Tectonic Post-Tectonic Plutons Plutons Late— • . > 0) a) .2C Pre- tto o Syn—Tectonic Syn-Tectonic Plutons Plutons Pre— < . . a+ conglomerate near near interface interface -ø-Tonalite Tonalite boulder boulder from conglomerate ,- .Late— -oLate- to t o Post—Tectonic Post-Tectonic Pluton Pluton . •Â +  c  0 0 +a .-D) n ;  *  -0 L I 1 2600 2600 2700 2700  -1 1 Pre- tto o Syn—Tectonic Syn-Tectonic Plutons Plutons Pre— Rocks Metavolcanic Rocks 2800 2800 1 I 2900 2900 3000 3000 I 3100 3 100 Time (Ma) (Ma) Time Figure Figure 3: 3: Summary Summary of o f U—Pb U-Pb z i zircon r c o n g geochronoloqy e o c h r o n o l o q y a available v a i l a b l e for f o r the t h eWinnipeq W i n n i p e g River R i v e r—Where Wahiqoon W a b i q o o n ssuhprovince u b p r o v i n c e area. area. W h e r e error e r r o r bars b a r s are a r e not n o t visible v i s i b l e they t h e y are a r e contained contained Symbols within w i t h i n the t h e size s i z e of o f the t h e symbol. symbol. S y m b o l s with w i t h arrows a r r o w s indicate i n d i c a t e minimum minimum Data Krogh Davis (207Ph/206Pb) Data are a r e from from K r o g h eet t aal. l . ((1976a,b), 1976a,b), D a v i s aand n d E&wards dwards ( 2 0 7 ~ b / 2 0 6 ~ bages. a)q e s . Beakhouse (1982), Davis e t al. a l . (1982), (1982), B e a k h o u s e (1983) ( 1 9 8 3 ) and and (1982), D a v i s aand n d Trowell T r o w e l 1 (1982), ( 1 9 8 2 ) , Davis D a v i s et Corfu C o r f u et e t al. a l . (1985) ( 1 9 8 5 ) with w i t h additional a d d i t i o n a l unpublished u n p u b l i s h e d data d a t a from f r o m F. F. Corfu C o r f u (personal (personal communication, c o m m u n i c a t i o n , 1985) 1 9 8 5 ) and a n d D.W. D.W. Davis D a v i s (personal ( p e r s o n a l communication, c o m m u n i c a t i o n , 1985). 1985) . �72 activity a c t i v i t yini nthe t hWabigoon e ~ a b i g o o Subprovince. nS u b p r o v i n c e . Metamorphic M e t a m o r p h i c zzircons i r c o n s from f r o m aa Kenora K e n o r a aarea r e a ttonalite o n a l i t e gneiss g n e i s sformed f o r m e d somewhat somewhat eearlier arlier (approximately M a , Beakhouse B e a k h o u s e 1983) 1 9 8 3 ) but b u t it i t is i s not n o t clear c l e a r if if a p p r o x i m a t e l y 2790 2790 Ma, this t h i s represents r e p r e s e n t s aa discrete d i s c r e t emetamorphic m e t a m o r p h i c eevent v e n t oor r a a single, single, protracted p r o t r a c t e d metamorphic m e t a m o r p h i c event. e v e n t . The T h e crystallization c r y s t a l l i z a t i o nage a g e(U-Pb (U-Pb zircon) of this t h i ssame s a m etonalite t o n a l i t gneiss e g n e i s(approximately s ( a p p r o x i m a t e l2830 y 2830Ma) Ma) is is z i r c o n ) of s i g n i f i c a n t l y older o l d e r than t h a n th t hvolcano—plutoriic e v o l c a n o - p l u t o n i c aactivity c t i v i t y in i n the the significantly Wabigoon W a b i g o o n S Subprovince u b p r o v i n c e b u but t n onotso t s o oold l d as a s the t h e "Lac " L a c Seul S e u l event" event'' (Goodwin ( G o o d w i n 1977). 1977). Sodic S o d i c ssuite u i t e plutons p l u t o n s in i n the t h eWinnipeg W i n n i p e g River R i v e r bbelt e l t are are c o n c e n t r a t e d along a l o n g the t h e northern n o r t h e r n and a n d southern s o u t h e r n marg m a r g i ins n s of t h e belt belt concentrated of the and a n d spatial s p a t i a l association a s s o c i a t i o n of o f sodic s o d i cplutons p l u t o n s and a n d orthogneiss o r t h o g n e i s s is is especially e s p e c i a l l y evident e v i d e n t along a l o n g the t h e southern s o u t h e r n margin. m a r g i n . Breaks B r e a k s et e t al. al. (1978; ( 1 9 7 8 ; 1981) 1 9 8 1 ) ppoint o i n t oout u t that t h a t the t h e sodic s o d i c suite s u i t e grades g r a d e s imperceptibly imperceptibly into i n t o orthogneiss o r t h o g n e i s s and and that t h a t the t h e former f o r m e r suite s u i t e "has " h a s evolved e v o l v e d over o v e r aa relatively These r e l a t i v e l y long l o n g period p e r i o d of o f intrusion". intrusion". T h e s e authors a u t h o r s consider consider that t h a t one o n e of of the t h e oldest o l d e s t dated d a t e d units u n i t s in i n the t h e Winnipeg W i n n i p e g River R i v e r belt, belt, the t h e tonalite t o n a l i t e gneiss g n e i s s of o f the t h e Sen Sen Bay Bay Complex, C o m p l e x , which w h i c h is is more more than than 3008 3 0 0 8 Ma Ma (Krogh ( K r o q h et e t al. a l . 1976a) 1 9 7 6 a ) is is aa sodic s o d i c pluton, p l u t o n . The T h e Dalles Dalles granodiorite g r a n o d i o r i t e has h a s aa minimum minimum (2O7Pb/206Pb) ( 2 0 7 ~ b / 2 0 6 ~ bzircon z) i r c o n age a g e of o f 2762 2762 Ma Ma (Beakhouse 1983) that is slightly older than Wabigoon Subprovince ( B e a k h o u s e 1983 ) t h a t is s l i q h t l y o l d e r t h a n ~ a b i q o o ns u b p r o v i n c e volcanism v o l c a n i s marid a n d plutoriism p l u t o n i s m (Figure ( F i g u r e 3). 3 ) . Although A l t h o u g h there t h e r e is is aa gradation b e t w e e n some some sodic s o d i c plutons p l u t o n s and and orthogneiss, o r t h o g n e i s s , many many sodic sodic g r a d a t i o n between plutons intruded orthogneiss at their present crustal levels. p l u t o n s intruded orthoq neiss at t h e i r p r e s e n t c r u s t a 1 l e v e l s . In I n the t h e sodic s o d i c suite s u i t e there t h e r e is is an a n apparent a p p a r e n t discrepancy d i s c r e p a n c y between between isotopic ages and field relationships. Identical i s o t o p i c ages and f i e l d r e l a t i o n s h i p s . I d e n t i c a l Rb—Sr Rb-Sr isochron isochron ages a g e s of o f 2630 2630 Ma Ma are a r e reported r e p o r t e d for f o r the t h e Dalles D a l l e s and and Melick M e l i c k sodic sodic plutons p l u t o n s from f r o m the t h e Kenora Kenora area a r e a(Wooden (Wooden 1978). 1 9 7 8 ) . The The emplacement e m p l a c e m e n t of of the t h e Dalles D a l l e s granodiorite g r a n o d i o r i t e is is responsible r e s p o n s i b l e for f o r the t h e last l a s t major major deformational d e f o r m a t i o n a l event e v e n t in i n the t h e Kenora K e n o r a area a r e a (Gower (Gower 1978; 1 9 7 8 ; Gower Gower and and Clifford C l i f f o r d 1981) 1 9 8 1 ) and and this, t h i s , combined c o m b i n e d with w i t h the t h e Rb—Sr Rb-Sr geochronologic geochronologic data, d a t a , suggests s u g g e s t s that t h a t this t h i s batholith b a t h o l i t h was was emplaced e m p l a c e d to t o its i t s present present crustal c r u s t a l level l e v e l during d u r i n g the t h e Kenoran K e n o r a n orogeny. o r o g e n y . The T h e minimum minimum U/Pb U/Pb zircon z i r c o n age a g e of o f 2762 2 7 6 2 Ma Ma (Beakhouse, ( B e a k h o u s e , 1983), 1 9 8 3 ) , however, h o w e v e r , indicates i n d i c a t e s pre— preKenoran K e n o r a n crystallization. c r y s t a l l i z a t i o n . Field F i e l d relationships r e l a t i o n s h i p s for f o r the t h e Melick Melick pluton p l u t o n are a r e also a l s o at a t variance v a r i a n c e with w i t h the t h e apparently a p p a r e n t l y young young Rb—Sr Rb-Sr age age and a n d suggest s u g g e s t that t h a t this t h i s unit u n i t was was emplaced e m p l a c e d relatively r e l a t i v e l y early e a r l y in i n the the deforniational Kenora d e f o r m a t i o n a l hhistory i s t o r y oof f tthe he K e n o r a area a r e a (Gower (Gower and a n d Clifford Clifford 1981 1981 ) . Taken T a k e n together, t o g e t h e r , the t h e evidence e v i d e n c e suggests s u g g e s t s that t h a t some some sodic sodic plutons p l u t o n s are a r e slightly s l i g h t l y to t o considerably c o n s i d e r a b l y older o l d e r than t h a n 'Kenoran' 'Kenoran' volcano—plutonic v o l c a n o - p l u t o n i c activity a c t i v i t y in i n the t h e Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e and a n d are are similar s i m i l a r in i n age a g e to t o the t h e enclosing e n c l o s i n g tonalite t o n a l i t e gneisses. g n e i s s e s . Upward Upward mobilization m o b i l i z a t i o n of o f these t h e s e plutons p l u t o n s took t o o k place p l a c e during d u r i n g the t h e Kenoran Kenoran orogeny o r o g e n y and a n d is is responsible r e s p o n s i b l e for f o r the t h e intrusive i n t r u s i v e contacts c o n t a c t s and and the the last l a s t major m a j o r deformational d e f o m a t i o n a l event. e v e n t . The The Dalles D a l l e s batholih, b a t h o l i t h , in in particular, p a r t i c u l a r , has h a s many many of o f the t h e attributes a t t r i b u t e s of o f aa classical c l a s s i c a l mantled mantled gneiss g n e i s s dome dome (Eskota ( E s k o l a 1948). 1 9 4 8 ) . Kroner K r o n e r et e t al. a l . (1981) ( 1 9 8 1 ) describe d e s c r i b e aa similar s i m i l a r relationship r e l a t i o n s h i p for f o r tonalitic t o n a l i t i c gneisses g n e i s s e s from f r o m Finland. Finland. Deformational t o those t h o s e in i n the the D e f o r m a t i o n a l fabrics f a b r i c s and a n d structures s t r u c t u r e s similar s i m i l a r to orthogneiss o r t h o g n e i s s are a r e preserved p r e s e r v e d in i n some some of o f the t h e smaller s m a l l e r plutons, p l u t o n s , as a s for for example e x a m p l e the t h e Melic M e l i c c tonalite, t o n a l i t e , but b u t are a r e rare r a r eini nlarger l a r g e rplutons. p l u t o n s . The The absence a b s e n c e of o f early e a r l y eformational d e f o r m a t i o n a l fabrics f a b r i c s may may reflect r e f l e c t their their obliteration o b l i t e r a t i o n duriig d u r i l g upward upward mobilization m o b i l i z a t i o noro rlack l a c kofo fgrieissic gneissic �73 development d e v e l o p m e n t in i n the t h e interior i n t e r i o r of o f large, l a r g e , relatively r e l a t i v e l y homogeneous homogeneous b a t h o l i t h s that t h a t acted a c t e d as as buttresses b u t t r e s s e s against a g a i n s t which w h i c h deformation deformation batholiths took t o o k place. place. Geochemical Geochem i c a l Evidence Ev i d e n c e The The geochemical g e o c h e m i c a l characteristics c h a r a c t e r i s t i c s of o f the t h e potassic p o t a s s i c plutonic plutonic rocks r o c k s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t support s u p p o r t the t h e interpretation i n t e r p r e t a t i o n that that pre—Kenoran p r e - K e n o r a n crust c r u s t was was extensive. extensive. T h e predominant p r e d o m i n a n t plutonic p l u t o n i c rocks rocks The of o f shield s h i e l d areas a r e a s are a r e tonalite t o n a l i t e and a n d related r e l a t e d rocks r o c k s (quartz ( q u a r t z diorite, diorite, trondhjemite a n d low—K l o w - K granodiorite; g r a n o d i o r i t e ; Glikson G l i k s o n 1979). 1 9 7 9 ) . Burke B u r k e and and t r o n d h j emite and Kidd ( 1 9 7 8 ) suggest s u g g e s t that t h a t granites g r a n i t e s are a r e rare rare in i n the t h e Superior Superior K i d d (1978) Province; P r o v i n c e : aa generalization g e n e r a l i z a t i o n that t h a t reflects, r e f l e c t s , in i n part, p a r t , the t h e emphasis e m p h a s is that t h a t has h a s been b e e n placed p l a c e d on o n greenstone—tonalite q r e e n s t o n e - t o n a l i t e terranes. terranes. L a t e - and and Late— post—tectonic p o s t - t e c t o n i c granodioritic g r a n o d i o r i t i c to t o granitic g r a n i t i c plutonic p l u t o n i c rocks r o c k s are are abundant a b u n d a n t in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. Typical T y p i c a l geochemical g e o c h e m i c a l characteristics c h a r a c t e r i s t i c s of o f Archean A r c h e a n plutonic plutonic r o c k s of o f tonalitic t o n a l i t i c affinity a f f i n i t y include i n c l u d e low l o w K20, K20, Rb, R b , K20/Na20, K20/Na20, Rb/Sr Rb/Sr rocks and a n d Sr S r isotope i s o t o p e initial i n i t i a l ratios r a t i o s with w i t h moderately m o d e r a t e l y enriched e n r i c h e d LREE LREE and and depletion d e p l e t i o n in i n HREE HREE and a n d YY (Glikson ( G l i k s o n 1979). 1 9 7 9 ) . Such S u c h characteristics c h a r a c t e r i s t i c s are are explained e x p l a i n e d by b y partial p a r t i a l melting m e l t i n g of o f aa metamorphically m e t a m o r p h i c a l l y transformed transformed tholeiitic t h o l e i i t i c basalt b a s a l t at a t mantle m a n t l e or o r lower lower crustal c r u s t a l depths d e p t h s (Hanson ( H a n s o n and and Qldich G o l d i c h 1972: 1 9 7 2 : Arth A r t h and a n d Hanson H a n s o n 1972, 1 9 7 2 , 1975; 1 9 7 5 ; Glikson G l i k s o n 1979). 1 9 7 9 ) . In In contrast, t h e potassic p o t a s s i c Lount L o u n t Lake L a k e batholith, b a t h o l i t h , from f r o m the t h e central central c o n t r a s t , the axis a x i s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t has h a s relatively r e l a t i v e l y higher h i g h e r K20, ~ ~Rb, R b0, , K20/Na20, K 2 0 / N a 2 0 f Rb/Sr R b / S r arid a n d Sr Sr isotope i s o t o p e initial i n i t i a l ratios, r a t i o s , variable v a r i a b l e but but generally moderate g e n e r a l l y high h i g h LREE LREE aabundances b u n d a n c e s aand nd m o d e r a t e to t o high h i g hYYabundances abundances (Beakhouse geo— ( B e a k h o u s e 1983). 1 9 8 3 ) . Other O t h e r potassic p o t a s s i cplutons p l u t o n are s a reven e e v emore n more geochemically Lac du d u Bonnet B o n n e t ppluton; l u t o n ; Cerny C e r n y eet t al. al. c h e m i c a l l y eevolved v o l v e d ((e.g., e . g . , Lac 1981). 1981 ) . Certain C e r t a i n younger y o u n g e r plutonic p l u t o n i crocks r o c k (Dalmein, s ( D a l m e i nMpagenie , M p a g e n i e and and Sicunusa S i c u n u s a —- types) t y p e s ) from f r o m the t h e Kaapvaal K a a p v a a l craton c r a t o n of o f South S o u t h Africa A f r i c ahave have geochemical g e o c h e m i c a l ccharacteristics h a r a c t e r i s t i c s (Condie ( C o n d i e and a n d Hunter H u n t e r 1976) 1 9 7 6 ) ssimilar i m i l a r to to the t h e potassic p o t a s s i c suite s u i t eplutons. p l u t o n s . These T h e s e ccharacteristics h a r a c t e r i s t i c s are a r e not not compatible with compatible w i t h the t h e origin o r i g i n postulated p o s t u l a t e d for f o r tonalites t o n a l i t e s and a n d are a r e more more compatible c o m p a t i b l e with w i t h partial p a r t i a l melting m e l t i n g of o f pre—existing p r e - e x i s t i n g sialic s i a l i c crust. crust. The T h e initial i n i t i a l Sr S r isotopic i s o t o p i c composition c o m p o s i t i o n of o f the t h e Lount L o u n t Lake Lake batholith ( . 7 0 2 2 to t o .7044; . 7 0 4 4 ;Beakhouse ~ e a k h o u s1983) e 1 9 8 3 ) is is higher h i g h e r than t h a n that that b a t h o l i t h (.7022 considered considered 'normal' ' n o r m a l ' for f o r 2.7 2 . 7 —- 3.0 3. 0 Ga G a tonalites t o n a l i t e s (Peterman ( P e t e r m a n 1979). 1979). Such S u c h initial i n i t i a l ratios r a t i o s are a r e compatible c o m p a t i b l e with w i t h these t h e s e 2.63 2 . 6 3 —- 2.70 2 . 7 0 Ga Ga plutons p l u t o n s being b e i n g derived d e r i v e d from f r o m the t h e partial p a r t i a l melting me1 t i n g of o f aa source s o u r c e that that is is 200 2 0 0 to t o 400 4 0 0 Ma Ma older o l d e r having h a v i n g Rb/Sr R b / S r ratios r a t i o s comparable c o m p a r a b l e to t o those t h o s e of of tonalitic t o n a l i t i c gneisses g n e i s s e s from f r o m the t h e orthogneiss o r t h o g n e i s s suite s u i t e (Beakhouse ( B e a k h o u s e1983). 1983). The T h e production p r o d u c t i o n of o f large l a r g e volumes v o l u m e s of o f such s u c h magmas magmas implies i m p l i e s extensive extensive pre—existirig p r e - e x i s t i n g ssialic i a l i c crust c r u s t in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. BOUNDARY BOUNDARY PROBLEMS PROB LEM S primary nature of the t h e interfaces i n t e r f a c e s between b e t w e e n different different The The p r i m a r y n a t u r e o f t e r r a n e sare a r eofofundamental f f u n d a m e n t a limportance i m p o r t a n c efor f o development r d e v e l o p m e n t ofo fmodels models terranes for f o r Archean A r c h e a n crustal c r u s t a l evolution. e v o l u t i o n . These T h e s e iinterfaces n t e r f a c e s aare r e loci l o c i for for f a u l tting i n g and a n d iintrusive n t r u s i v e activity a c t i v i t y because b e c a u s e the t h e interfaces i n t e r f a c e s represent represent faul r e g i o n a l scale s c a l e discontinuities d i s c o n t i n u i t i e s in i n density, d e n s i t y , ductility d u c t i l i t yand and regional rheology; r h e o l o q y ; the t h e younger y o u n g e r events e v e n t s obscure o b s c u r e the t h e primary p r i m a r y stratigraphic stratigraphic relationships. t al. a l . 1978: 1 9 7 8 : Stone Stone r e l a t i o n s h i p s . The The Sydney S y d n e y LLake a k e FFault a u l t ((Breaks B r e a k s eet 1977) 1 9 7 7 ) forming f o r m i n g the t h e north n o r t hboundary b o u n d a r yof o fthe t hEar e E aFalls—Manigotaqan r Fa1 l s - Y a n i g o t a q a n belt isone o n e of o f the t h e largest l a r g e s tof o f the t h einterface i n t e r f a c efault f a u l systems. t s y s t e m s . This This b e l t is �74 Smaller fault f a u l t zone z o n e is is up up to t o 1 km wide w i d e and a n d has h a s numerous n u m e r o u s splays. splays. Smaller Stratigraphic fault a r e recognized r e c o g n i z e d along a l o n g other o t h e r interfaces. i n t e r f aces. S tratigraphic f a u l t zones z o n e s are relations a t the t h e interfaces i n t e r f a c e s can c a n be b e deciphered d e c i p h e r e d only o n l y where w h e r e fault fault r e l a t i o n s at and This a n d intrusive i n t r u s i v e activity a c t i v i t y were w e r e relatively r e l a t i v e l y minor. minor. T h i s can c a n be b e done done d i r e c t l y oonly n l y at a t the t h einterfaces i n t e r f a c ebetween s b e t w e e nthet hEar e E aFalls—Manigotagan r Falls-Manigotagan directly pparagneiss a r a g n e i s s and a n d the t h e Uchi U c h i Subpovince S u b p o v i n c e oon n t the h e nnorth o r t h and a n d the t h e Bird Bird River R i v e r internal i n t e r n a l ggreenstone r e e n s t o n e belt b e l t on o n the t h e south. south. The subprovince T h e contact c o n t a c t between b e t w e e n the t h e Uchi U c h i greenstone—tonalite g r e e n s t o n e - t o n a l i t e subprovince and as aa lateral lateral a n d Ear E a r Falls—Manigotagan F a l l s - M a n i g o t a g a n paragneiss p a r a g n e i s s originated o r i g i n a t e d as facies f a c i e s change c h a n g e between b e t w e e n fundamentally f u n d a m e n t a l l y different d i f f e r e n t depositional depositional The The ddistribution i s t r i b u t i o n of o f these t h e s eenvironments e n v i r o n m e n t s was was eenvironments. nvironments eestablished s t a b l i s h e dby b y2959 2 9 5 9Ma Ma ((the t h e aage g e oof f tthe h e ooldest l d e s t cycle c y c l e in i n the t h e Uchi Uchi belt; b e l t ; Nunes N u n e s a and n d T Thurston, h u r s t o n , 1 1980) 9 8 0 ) a nand d p epersisted r s i s t e d f for o r aat t least l e a s t 200 200 This Ma. T h i s implies i m p l i e s that t h a t the t h e subprovinces s u b p r o v i n c e s of o f the t h e western w e s t e r n Superior Superior Province a r e primary p r i m a r y features f e a t u r e s representing r e p r e s e n t i n g different d i f f e r e n t volcanic v o l c a n i c and and P r o v i n c e are sedimentary s e d i m e n t a r y environments e n v i r o n m e n t s and a n d are a r e not n o t aa consequence c o n s e q u e n c e of of ddifferential i f f e r e n t i a l uplift. uplift. The T h e nnature a t u r e oof f the t h e interface i n t e r f a c e between b e t w e e n the t h e Winnipeg W i n n i p e g River River bbatholithic a t h o l i t h i c terrane t e r r a n e and a n d the t h e adjacent a d j a c e n t Ear E a r Falls—Maniqotagan Falls-Manigotaqan paragneiss t e r r a n e s cannot c a n n o t be be p a r a g n e i s s and a n d Wabigoon W a b i g o o n greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes However, ddetermined e t e r m i n e d directly. directly. H o w e v e r , based b a s e d on o n both b o t h inconclusive i n c o n c l u s i v e field field ddata a t a and a n d more conclusive c o n c l u s i v e geochronologic q e o c h r o n o l o g i c data d a t a these t h e s e interfaces i n t e r f a c e s can can The t o be b e unconformities. unconformities. T h e Winnipeg W i n n i p e g River R i v e r —bbe e interpreted i n t e r p r e t e d to a pportion Wabigoon W a b i g o o n interface, interface, a o r t i o n oof f which w h i c h is i s the t h e subject s u b j e c t of o f this this ffield i e l d trip t r i p is i s discussed d i s c u s s e d more more fully f u l l y below. below. A first A f i r s t sstep t e p in i n understanding u n d e r s t a n d i n g the t h e nature n a t u r e of o f interfaces i n t e r f a c e s is i s to to define d e f i n e the t h e properties p r o p e r t i e s that t h a t distinguish d i s t i n g u i s h the t h e subprovinces s u b p r o v i n c e s and and As discussed llocate o c a t e the t h e transition t r a n s i t i o n on o n aa geologic g e o l o q i c map. map. As d i s c u s s e d above, a b o v e , the the Winnipeg W i n n i p e g River R i v e r belt b e l t differs d i f f e r s from f r o m the t h e Wabigoon W a b i g o o n subprovince s u b p r o v i n c e in in lower, p proportion 1 ) lower. r o p o r t i o n oof f s supracrustal u p r a c r u s t a l rrocks, o c k s , 22) ) ggenerally enerally hhaving a v i n g aa 1) 3 ) higher h i g h e r proportion p r o p o r t i o n of o f granite g r a n i t e in in hhigher i g h e r metamorphic m e t a m o r p h i c grade, g r a d e , 3) rrelation e l a t i o n to t o tonalite, t o n a l i t e , 4) 4 ) older o l d e r age a g e and a n d 5) 5 ) contrasting c o n t r a s t i n g structural structural Defining sstyle. tyle. D e f i n i n g the t h e position p o s i t i o n of o f this t h i s transition t r a n s i t i o n on o n the t h e ground g r o u n d is is not n o t aa trival t r i v a l problem. p r o b l e m . Between B e t w e e n Kenora K e n o r a and a n d the t h e Manitoba—Ontario Manitoba-Ontario pprovincial r o v i n c i a l boundary, b o u n d a r y , where w h e r e we w e will w i l l be b e examining e x a m i n i n g the t h e interface, interface, there is a a vvery e r y sharp s h a r p contact c o n t a c t between b e t w e e n older o l d e r gneisses g n e i s s e s of o f the the t h e r e is Winnipeg W i n n i p e g River R i v e r belt b e l t and a n d lavas l a v a s and a n d sedimentary s e d i m e n t a r y rocks r o c k s of o f the the Although meaningful Wabiqoon W a b i g o o n subprovince. subprovince. Although a a m e a n i n g f u l lithologic l i t h o l o g i c contact contact ccan a n be b e ddrawn r a w n on on a a map, m a p , the t h e metamorphic m e t a m o r p h i c transition t r a n s i t i o n (over ( o v e r 100—1000 100-1000 m)) is m i s not n o t sso o abrupt a b r u p t and a n d ddeformation e f o r m a t i o n associated a s s o c i a t e d with w i t h the t h e interface interface persists p e r s i s t s an a n unknown, unknown, but b u t significant s i g n i f i c a n t (<2 ( < 2 km) km) distance d i s t a n c e to t o the the north n o r t h and a n d south s o u t h of o f the t h e contact. contact. Between Vermilion B e t w e e n Kenora K e n o r a and and V e r m i l i o n Bay Bay the t h e location l o c a t i o n of o f the t h e interinterMost face f a c e is i s more uncertain. uncertain. Most workers w o r k e r s have h a v e placed p l a c e d the t h e sub— subprovincial p r o v i n c i a l boundary b o u n d a r y along a l o n g the t h e north n o r t h edge e d g e of o f the t h e Vermilion V e r m i l i o n Bay Bay This is based b a s e d largely largely ggreenstone r e e n s t o n e belt. belt. T h i s pposition o s i t i o n oof f the t h e interface i n t e r f a c e is on v o l c a n i c remnants r e m n a n t s within w i t h i n the the o n the t h e observations o b s e r v a t i o n s that t h a t 1 ) no volcanic Winnipeg W i n n i p e g River R i v e r belt b e l t are a r e comparable c o m p a r a b l e to t o the t h e Vermilion V e r m i l i o n Bay Bay green— greenterms of o f size s i z e and a n d degree d e g r e e of o f preservation p r e s e r v a t i o n and a n d 2) 2 ) tthe he sstone t o n e belt b e l t in i n terms llobate o b a t e fform o r m oof f the t h e Dryberry D r y b e r r y batholith b a t h o l i t h to t o the t h e south s o u t h of o f the the Vermilion V e r m i l i o n belt b e l t is is typical t y p i c a l of o f that t h a t observed o b s e r v e d for f o r batholiths b a t h o l i t h s within within Wabigoon Two observations tthe he W a b i g o o n subprovince. subprovince. o b s e r v a t i o n s suggest s u g g e s t that t h a t the the Vermilion V e r m i l i o n Bay Bay belt b e l t and a n d Dryberry D r y b e r r y batholith b a t h o l i t h could c o u l d be b e placed p l a c e d within within Winnipeg Firstly, tthe he W i n n i p e g River R i v e r belt. belt. F i r s t l y , the t h e Dryberry D r y b e r r y batholith b a t h o l i t h is is 1 . 1 ) �75 similar s i m i l a r to t o the t h e potassic p o t a s s i c plutons p l u t o n s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt, b e l t , and and Wabigoon uunlike n l i k e oother ther W a b i q o o n ssubprovince u b p r o v i n c e bbatholiths, a t h o l i t h s , in i n terms t e r m s of of magnetic aaeromagnetic e r o m a q n e t i c signature, signature, m a g n e t i c susceptibility s u s c e p t i b i l i t y and a n d perhaps perhaps Secondly, ( H a l l , 1968; 196 8 ; Beakhouse, B e a k h o u s e , 1977). 1977) S e c o n d l y , an an llithology i t h o l o g y (Hall, amphibolitic a m p h i b o l i t i c "tail" " t a i l " extending e x t e n d i n g off o f f the t h e west west end e n d of o f the t h e Vermilion Vermilion Bay ggreenstone belt Winnipeg e l t is is folded f o l d e d along a l o n g with with W i n n i p e g River R i v e r belt belt Bay reenstone b gneisses l a r g e recumbent r e c u m b e n t structure s t r u c t u r e in i n the t h e Silver S i l v e r Lake L a k e area area g n e i s s e s into i n t o aa large ((Beakhouse B e a k h o u s e et e t al. a l . 1983). 1983). The T h e position p o s i t i o n of o f the t h e subprovince s u b p r o v i n c e interface i n t e r Âace between b e t w e e n Vermilion Vermil ion Breaks Bay and i s controversial. controversial. B r e a k s et e t al. a l . (1978) ( 1 978) a n d Sioux S i o u x Lookout L o o k o u t is locate l o c a t e the t h e subprovincial s u b p r o v i n c i a l boundary b o u n d a r y at a t the t h e sedimentary—volcanic sed imentary-volcanic Although some ccontact o n t a c t resulting r e s u l t i n g in in a a highly h i g h l y irregular i r r e g u l a r contact. contact. A l t h o u g h some of o f these t h e s e metasediments m e t a s e d i m e n t s are a r e highly h i g h l y metamorphosed m e t a m o r p h o s e d and a n d partially partially melted b e correlated c o r r e l a t e d with w i t h the t h e Warclub W a r c l u b Group G r o u p which w h i c h can c a n be be m e l t e d they t h e y can c a n be traced t r a c e d well w e l l into i n t o the t h e Lake L a k e of o f the t h e Woods Woods qreenstone g r e e n s t o n e belt b e l t (Trowell (Trowel1 must et e t al., a l . , 1980). 1 9 8 0 ) . The proposed p r o p o s e d boundary boundary m u s t therefore, t h e r e f o r e , at a t some some e t al. a l . 1978) 1 9 7 8 ) cross cross ppoint o i n t (not ( n o t illustrated i l l u s t r a t e d on o n the t h e map map of o f Breaks B r e a k s et An sstratigraphy. tratigraphy. An alternate a l t e r n a t e interpretation i n t e r p r e t a t i o n is i s that t h a t the t h e sub— subprovincial l i e s between b e t w e e n these t h e s e supracrustal s u p r a c r u s t a l rocks r o c k s and a n d the the p r o v i n c i a l boundary b o u n d a r y lies Unfortunately, granitoid is g r a n i t o i d rocks r o c k s to t o the t h e north. north. U n f o r t u n a t e l y , this t h i s contact c o n t a c t is poorly p o o r l y exposed. exposed. The T h e ssignificance i g n i f i c a n c e oof f the t h e ddiscussion i s c u s s i o n above a b o v e is i s not n o t simply s i m p l y to to point p o i n t out o u t that t h a t further f u r t h e r investigations i n v e s t i g a t i o n s are a r e required r e q u i r e d to t o ellucidate ellucidate Rather, tthe h e nnature a t u r e and a n d position p o s i t i o n of o f the t h e subprovincial s u b p r o v i n c i a l boundary. boundary. Rather, iit t sserves e r v e s to t o emphasize e m p h a s i z e that t h a t subprovince s u b p r o v i n c e interfaces i n t e r f a c e s must m u s t be be regarded a s imprecisely i m p r e c i s e l y bounded b o u n d e d zones z o n e s rather r a t h e r than t h a n aa line l i n e on o n aa r e g a r d e d as Within map. W map. i t h i n these t h e s e interface i n t e r f a c e zones z o n e s processes p r o c e s s e s characteristic c h a r a c t e r i s t i c of of either e i t h e r ssubprovince u b p r o v i n c e may operate o p e r a t e in i n addition a d d i t i o n to t o processes p r o c e s s e s uniquely uniquely t o the t h e interface i n t e r f a c e (eg. ( e g . faulting f a u l t i n g and a n d associated, associated, rrelated e l a t e d to ttectonically e c t o n i c a l l y controlled, c o n t r o l l e d , epiclastic e p i c l a s t i c sedimentation) sedimentation) Assuming A s s u m i n g the t h e argunents a r g u m e n t s presented p r e s e n t e d above a b o v e are a r e correct c o r r e c t and a n d the the Winnipeg be1 t represents r e p r e s e n t s an a n extensive e x t e n s i v e tract t r a c t of o f pre—Kenoran pre-Kenoran W i n n i p e g River R i v e r belt sialic s i a l i c crust c r u s t and a n d the t h e deposition d e p o s i t i o n of o f supracrustal s u p r a c r u s t a l sequences s e q u e n c e s in i n the the Wabigoon s i a l ic W a b i q o o n subprovince s u b p r o v i n c e post—date p o s t - d a t e the t h e formation f o r m a t i o n of o f this t h i s sialic ccrust, r u s t , there t h e r e are a r e two t w o alternate a l t e r n a t e interpretations i n t e r p r e t a t i o n s for f o r the t h e nature n a t u r e of of One alternative tthe h e interface. interface. a l t e r n a t i v e is i s that t h a t the t h e interface i n t e r f a c e is is a a tectonic t e c t o n i c contact c o n t a c t and a n d the t h e subprovinces s u b p r o v i n c e s were juxtaposed j u x t a p o s e d after a f t e r their their Alternatively, Wabigoon sequences fformation. ormation. A l t e r n a t i v e l y , the the W a b i g o o n ssupracrustal u p r a c r u s t a l sequences l i k e l y against, a g a i n s t , this this ccould o u l d have h a v e been b e e n ddeposited e p o s i t e d upon, u p o n , or o r more likely sialic s i a l i c crust c r u s t in i n which w h i c h case c a s e aa major m a j o r unconformity u n c o n f o r m i t y occurs o c c u r s within w i t h i n the the interface The l a t t e r interpretation i n t e r p r e t a t i o n is is supported s u p p o r t e d by by the the i n t e r f a c e zone. zone. T h e latter ppossible o s s i b l e ppresence r e s e n c e oof f feeder f e e d e r ddikes i k e s in i n the t h e Tannis T a n n i s Lake L a k e area a r e a and, and, more convincingly, by tthe c o n v i n c i n g l y , by h e presence p r e s e n c e oof f aan n ancient a n c i e n t boulder b o u l d e r in i n aa Davis, cconglomerate o n g l o m e r a t e nnear e a r Sioux S i o u x Lookout L o o k o u t (D.W. (D.W. D a v i s , personal personal ccommunication, o m m u n i c a t i o n , 1985). 1 9 8 5 ) . Clearly, C l e a r l y , intense i n t e n s e deformation d e f o r m a t i o n has h a s been been superimposed minor major s u p e r i m p o s e d on o n this t h i s unconformity u n c o n f o r m i t y and and m i n o r oor r m a j o r ddislocations islocations hhave a v e ooccurred c c u r r e d along a l o n g it. i t . It I t is is aalso l s o possible p o s s i b l e that t h a t the t h e Winnipeg Winnipeg River R i v e r tterrane e r r a n e could c o u l d have h a v e bbeen e e n jjuxtaposed u x t a p o s e d ((by b y t the h e ccbs l o s iing n g of o f an an oocean??) c e a n ? ? ) against a g a i n s t the t h eWabigoon W a b i q o o n subprovince s u b p r o v i n c e during d u r i n g volcanism v o l c a n i s m and and ssedimentation e d i m e n t a t i o n aand n d tthat h a t the t h e unconformable u n c o n f o r m a b l e r relationship e l a t i o n s h i p applies a p p l ies Wabiqoon. oonly n l y to t o the t h e youngest y o u n g e s t sequences s e q u e n c e s in i n tthe he W abiqoon. . . SUMMARY SUMMARY OF OF GEOLOGICAL G E O L O G I C A L RELATIONSHIPS RELATIONSHIPS Field, F i e l d , geochronobogical g e o c h r o n o l o q i c a l and a n d geochemical g e o c h e m i c a l evidence e v i d e n c e suggest s u g g e s t aa �76 c o m p l e x geologic g e o l o g i c history h i s t o r y spanning s p a n n i n g at a t least l e a s t 500 5 0 0 Ma. Ma. The T h e earliest earliest complex i s deposition d e p o s i t i o n of o f aa supracrustal s u p r a c r u s t a l sequence s e q u e n c e preserved p r e s e r v e d as as e v e n t is event i n c l u s i o n s in i n younger y o u n g e r plutonic p l u t o n i c rocks. r o c k s . The T h e rock r o c k types t y p e s in i n this this inclusions association a r e broadly b r o a d l y similar s i m i l a r to t o those t h o s e in i n the t h e better b e t t e r preserved, preserved, a s s o c i a t i o n are b e l t s , although a l t h o u g h felsic f e l s i c metavolcanic m e t a v o l c a n i c units u n i t s have have y o u n g e r greenstorie g r e e n s t o n e belts, younger n o t been b e e n identified i d e n t i f i e d conclusively. conclusively. not Tonalite T o n a l i t e gneiss g n e i s s of o f the t h e orthogneiss o r t h o g n e i s s suite s u i t e and a n d certain c e r t a i n of o f the the r e oolder l d e r tthan h a n 'Kenoran' ' K e n o r a n ' volcanism v o l c a n i s m in i n the t h e Wabigoon Wabigoon s o d i c plutoris p l u t o n s aare sodic More data d a t a are a r e required r e q u i r e d to t o establish e s t a b l i s h whether w h e t h e r these these S u b p r o v i n c e . More Subprovirtce. were all a l l formed f o r m e d 1) 1 ) during d u r i n g aa 3.0 3.0 —- 3.1 3.1 Ga Ga event e v e n t (Goodwin (Goodwin t o n a l i t e s were tonalites 1977) o r 2) 2 ) semi—continuously s e m i - c o n t i n u o u s l y from f r o m 3.1 3. 1 Ga Ga until u n t i l the t h e Kenoran Kenoran 1 9 7 7 ) or some tonalites t o n a l i t e s in i n the t h e Winnipeg W i n n i p e q River River o r o g e n y . The T h e antiquity a n t i q u i t y of o f some orogeny. b e l t suggests s u g g e s t s deposition d e p o s i t i o n of o f the t h e oldest o l d e s t supracrustal s u p r a c r u s t a l rocks r o c k s took took belt The p l a c e prior p r i o r to t o 3.0 3.0 Ga. Ga. T h e tonalitic t o n a l i t i c gneiss g n e i s s and a n d sodic s o d i c plutons plutons place a r e geochemically g e o c h e m i c a l l y similar s i m i l a r to t o rocks r o c k s of o f tonalitic t o n a l i t i c affinity a f f i n i t y that that are occur b a s a l t s of o f the t h e younger y o u n g e r green— greeno c c u r in i n bi—modal b i - m o d a l association a s s o c i a t i o n with w i t h basalts stone—torialite s t o n e - t o n a l i t e tterraries e r r a n e s aand n d ooriginate r i g i n a t e ffrom r o m the t h e partial p a r t i a l melting me1 t i n g m e t a m o r p h o s e d tholeiitic t h o l e i i t i c basalt. basalt. metamorphosed t o the t h e paragneiss p a r a g n e i s s in i n the t h e Ear Ear Falls—Manigotagan Falls-Maniqotaqan T h e precursor p r e c u r s o r to The b e l t was was deposited d e p o s i t e d synchronously s y n c h r o n o u s l y with w i t h volcano—sedimentary volcano-sedimentary belt time s e q u e n c e s in i n the t h e adjacent a d j a c e n t greenstone—tonalite g r e e n s t o n e - t o n a l i t e terranes. t e r r a n e s . The T h e time sequences resolved. i n t e r v a l over o v e r which w h i c h tthis h i s sedimentation s e d i m e n t a t i o n occurred o c c u r r e d iis s not not resolved. interval Volcanism a r e acommenced commenced by b y 2959 2959 V o l c a n i s m in i n the t h eUchi—Confederation U c h i - C o n f e d e r a t i o n Lakes L a k e s area SedimentMa aand n d ccontinued o n t i n u e d for for 220 2 2 0 Ma Ma (Nunes ( N u n e s and a n d Thurston T h u r s t o n 1980). 1980). SedimentMa ation a t i o n occurred o c c u r r e d synchronously s y n c h r o n o u s l y with w i t h the t h e oldest o l d e s t volcanic v o l c a n i c cycle cycle 1 9 7 8 ) and a n d probably p r o b a b l y continued c o n t i n u e d during durinq ( T h u r s t o n and a n d Breaks B r e a k s 1978) (Thurston d e p o s i t i o n of o f the t h e younger y o u n g e r volcanic v o l c a n i c cycles c y c l e s (P.C. ( P . C . Thurston T h u r s t o n 1982, 1982, deposition The p e r s o n a l communication). communication) T h e detritus d e t r i t u s for for the t h e paragneiss paragneiss personal was apparently a p p a r e n t l y derived d e r i v e d externally e x t e r n a l l y from f r o m flanking f l a n k i n q green— greenp r e c u r s o r was precursor s i a l i c microcontinent, m i c r o c o n t i n e n t , now now s t o n e terranes t e r r a n e s and a n d possibly p o s s i b l y from f r o m aa sialic stone represented r e p r e s e n t e d by by the t h e Winnipeg W i n n i p e g River R i v e r belt; b e l t ; they t h e y were were deposited d e p o s i t e d from from water. The The provenance provenance t u r b i d i t y currents c u r r e n t s in i n relatively r e l a t i v e l y deep d e e p water. turbidity i n c l u d e d felsic f e l s i c volcanics v o l c a n i c s which w h i c h are a r e locally l o c a l l y or o r regionally regionally included predominant, p r e d o m i n a n t , felsic f e l s i c plutonic, p l u t o n i c , mafic m a f i c volcanic v o l c a n i c and a n d pre—existing pre-ex is t i n g (see s e d i m e n t a r y units. u n i t s . Crustal C r u s t a l structure s t r u c t u r e perturbations p e r t u r b a t i o n s (see sedimentary references r e f e r e n c e s in i n Beakhouse B e a k h o u s e 1977) 1 9 7 7 ) are a r e aa manifestation m a n i f e s t a t i o n of o f the t h e tectonic tectonic r e g i m e associated a s s o c i a t e d with w i t h basin b a s i n development. development. regime The Ma, T h e major m a j o r thermotectonic t h e r m o t e c t o n i c event e v e n t between b e t w e e n 2660 2 6 6 0 and a n d 2760 2 7 6 0 Ma, resulted in the t h a t culminated c u l m i n a t e d with w i t h the t h e Kenoran K e n o r a n orogeny, oroqeny, r e s u l t e d i n t h e that g e n e r a t i o n of o f large l a r g e volumes v o l u m e s of o f felsic f e l s i c plutonic p l u t o n i c rocks r o c k s in i n all a l l sub— subgeneration p r o v i n c e s of o f the t h e western w e s t e r n Superior S u p e r i o r Province. P r o v i n c e . Plutonic P l u t o n i c rocks r o c k s of of provinces t h e greenstone g r e e n s t o n e subprovinces s u b p r o v i n c e s are a r e dominantly d o m i n a n t l y tonalitic t o n a l i t i c in in the composition c o m p o s i t i o n and a n d probably p r o b a b l y originated o r i q i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g of of were only o n l y slightly s l i g h t l y older o l d e r than t h a n the the m a n t l e derived d e r i v e d basalts b a s a l t s that t h a t were mantle p l u t o n s (Hanson ( H a n s o n and a n d Goldich, G o l d i c h , 1972; 1 9 7 2 ; Arth A r t h and a n d Hanson, H a n s o n , 1972, 1 9 7 2 , 1975; 1975; plutons G l i k s o n , 1979). 1 9 7 9 ) . In I n contrast, c o n t r a s t , geochemical g e o c h e m i c a l evidence e v i d e n c e indicates indicates Glikson, that t h a t the t h e extensive e x t e n s i v e potassic p o t a s s i c plutoriic p l u t o n i c rocks r o c k s in i n the t h e Winnipeg W i n n i p e g River River belt o f rocks rocks b e l t could c o u l d not n o t have h a v e originated o r i g i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g of d e r i v e d from f r o m the t h e mantle m a n t l e during d u r i n g the t h eKerioran K e n o r a n orogeny. o r o g e n y . Instead I n s t e a d they they derived apparently a p p a r e n t l y originated o r i g i n a t e d from f r o m the t h e partial p a r t i a l melting m e l t i n g or or upward upward q r e e n stonem o b i l i z a t i o n of o f aa "pre—Kenoran" " p r e - K e n o r a n " volcano—plutonic, v o l c a n o - p l u t o n i c , greenstone— mobilization t y p e , association. association. type, . �77 IMPLICATIONS FOR FOR CRUSTAL CRUSTAL EVOLUTION EVOLUTION The e o l o g i c a l history h i s t o r y spanning s p a n n i n g 500 5 0 0 Ma Ma T h e recognition r e c o g n i t i o n oof f a ggeological pposes o s e s certain c e r t a i n constraints, c o n s t r a i n t s , and a n d many questions, q u e s t i o n s , for f o r crustal crustal evolution The e v o l u t i o n in i n the t h e western w e s t e r n Superior S u p e r i o r Province. Province. T h e limited, lirnited, rreliable e l i a b l e geochronological q e o c h r o n o l o q i c a l data d a t a suggests s u g g e s t s semi—continuous s e m i - c o n t i n u o u s activity activity during d u r i n g this t h i s 500 5 0 0 Ma Ma interval i n t e r v a l rather r a t h e r than t h a n two t w o "accretion "accretion super—events" s u p e r - e v e n t s " (Goodwin, ( G o o d w i n , 1977). 1977). Sialic unknown eextent was a s ppresent r e s e n t prior p r i o r to t o the the S i a l i c ccrust r u s t oof f unknown xtent w ddeposition e p o s i t i o n of o f 'Kenoran' ' K e n o r a n ' supracrustal s u p r a c r u s t a l sequences s e q u e n c e s but b u t the t h e role r o l e of of The i s unclear. unclear. The tthis h i s ccrust r u s t in i n ssubsequent u b s e q u e n t crustal c r u s t a l evolution e v o l u t i o n is pre—Kenoran s i a l i c crust c r u s t has h a s been b e e n reworked r e w o r k e d and a n d intruded i n t r u d e d and and p r e - K e n o r a n sialic ddismembered i s m e m b e r e d bby y extensive e x t e n s i v e Kenoran K e n o r a n felsic f e l s i c plutons p l u t o n s derived d e r i v e d from f r o m the the melting ppartial artial m e 1 t i n q oof f ggreenstone—tonalite r e e n s t o n e - t o n a l i t e assemblages a s s e m b l a g e s of o f the t h e earlier earlier These ccrust. rust. T h e s e oolder l d e r vvolcanic o l c a n i c rocks r o c k s may be b e analogous a n a l o g o u s to t o the t h e better better preserved, p r e s e r v e d , pre—Kenoran p r e - K e n o r a n volcanic v o l c a n i c cycles c y c l e s now now recognized r e c o g n i z e d in i n green— greensstone t o n e belts b e l t s elsewhere e l s e w h e r e in i n the t h e Superior S u p e r i o r Province P r o v i n c e (Nunes ( N u n e s and a n d Wood Nunes 11980; 980; N u n e s and a n d Thurston T h u r s t o n 1980). 1980). T h e paucity p a u c i t y of o f mantle m a n t l e derived derived The Kenoran K e n o r a n volcanic v o l c a n i c aand n d pplutonic l u t o n i c r rocks o c k s i nint the h e ccentral e n t r a l ppart a r t of o f the the WRB were nnot o t emplaced e m p l a c e d tthrough h r o u g h tthe h e older older WRB s u suqgests q q e s t s t hthat a t t these h e s e rrocks o c k s were The c r u s t i n t h i s region. T h e presence p r e s e n c e of o f mafic m a f i c dikes d i k e s near n e a r the the southern s o u t h e r n margin m a r g i n oof f the t h e WRB, WRB, ppossibly o s s i b l y representing r e p r e s e n t i n g feeders f e e d e r s to to Kenoran K e n o r a n volcanism, v o l c a n i s m , aand n d tthe h e ooccurrence c c u r r e n c e oof f aan n ancient a n c i e n t granitoid granitoid Lookout bboulder o u l d e r in i n aa conglomerate c o n g l o m e r a t e near n e a r Sioux Sioux L o o k o u t i implies m p l i e s t that h a t the the may yyounger o u n g e r s usupracrustal p r a c r u s t a l s sequences e q u e n c e s may b e ,be, i n in p apart, r t , eensialic n s i a l i c bbut u t the the present p r e s e n t jjuxtaposition u x t a p o s i t i o n oof f relatively r e l a t i v e l y oolder l d e r and a n d younger y o u n g e r sequences sequences The may also a l s o be b e tectonic. tectonic. T h e ppaucity a u c i t y oof f ggranitoid r a n i t o i d rocks r o c k s originating originating from f r o m the t h e anatexis a n a t e x i s of o f sialic s i a l i c crust c r u s t in i n the t h e Wabigoon W a b i q o o n subprovince subprovince ssuggests u g g e s t s that t h a t a Winnipeg W i n n i p e g River R i v e r belt—type b e l t - t y p e basement b a s e m e n t complex c o m p l e x is is aabsent b s e n t or o r greatly g r e a t l y thinned t h i n n e d bbeneath e n e a t h tthis h i s area. area. The T h e rrecognition e c o g n i t i o n oof f lateral l a t e r a l facies f a c i e s relationships r e l a t i o n s h i p s between between greenstone g r e e n s t o n e and a n d paragneiss p a r a q n e i s s sequences s e q u e n c e s establishes e s t a b l i s h e s the t h e contemporacontemporanneity e i t y oof f tthese h e s e terranes t e r r a n e s and a n d implies i m p l i e s that t h a t the t h e belt—like, b e l t - l i k e , sub— subpprovince r o v i n c e structure s t r u c t u r e oof f the t h e western w e s t e r n Superior S u p e r i o r Province P r o v i n c e is is aa primary primary characteristic The c h a r a c t e r i s t i c and a n d not n o t aa consequence c o n s e q u e n c e of o f differential d i f f e r e n t i a l uplift. uplift. The ppattern a t t e r n of o f pre—existing p r e - e x i s t i n g sialic s i a l i c nuclei n u c l e i and a n d younger, y o u n g e r , coeval, coeval, interdigitating is i n t e r d i g i t a t i n g volcanic v o l c a n i c arcs a r c s and a n d sedimentary s e d i m e n t a r y basins b a s i n s is geometrically, g e o m e t r i c a l l y , though t h o u g h not n o t necessarily n e c e s s a r i l y genetically, g e n e t i c a l l y , analaqous a n a l a g o u s to to modern m o d e r n plate p l a t e tectonic t e c t o n i c regimes. regimes. crust in this region. ACKNOWLEDGMENTS ACKNOWLEDGMENTS L.D. R.H. McNutt, M c N u t t , P.C. P.C. Thurston T h u r s t o n and a n d an an L.D. Ayres, A y r e s , F.W. F.W. Breaks, B r e a k s , R.H. anonymous c r i t i c i s m at a t different different a n o n y m o u s reviewer r e v i e w e r ooffered f f e r e d constructive c o n s t r u c t i v e criticism sstages t a g e s in i n the t h e preparation p r e p a r a t i o n of o f the t h e paper p a p e r from f r o m which w h i c h the the introduction was modified. modified. P.C. T h u r s t o n also a l s o reviewed r e v i e w e d the the i n t r o d u c t i o n was P.C. Thurston W.C. revised r e v i s e d version v e r s i o n and a n d the t h e road r o a d log. log. W . C . Brisbin B r i s b i n visited v i s i t e d the t h e High High Lake-Tannis L a k e - T a n n i s Lake L a k e aarea r e a stops s t o p s with w i t h the t h e author a u t h o r and a n d shared s h a r e d his his The cconsiderable o n s i d e r a b l e understanding u n d e r s t a n d i n g of o f the t h e geology g e o l o g y of o f this t h i s area. area. T he i s ggrateful r a t e f u l to t o M. M. Sweeny who assisted a s s i s t e d in i n the t h e preparation preparation aauthor u t h o r is oof f stops s t o p s and a n d legions l e g i o n s of o f University U n i v e r s i t y of o f Manitoba M a n i t o b a field f i e l d school school students Barbara s t u d e n t s who stripped s t r i p p e d most of o f the t h e moss m o s s at a t stop s t o p 4. 4. B a r b a r a Moore patiently p a t i e n t l y and a n d skilfully s k i l f u l l y drafted d r a f t e d the t h e final f i n a l figures. figures. �78 ROAD LOG LOG AND DESCRIPTION DESCRIPTION OF OF STOPS STOPS ROAD 0.0 km W e will w i l l proceed p r o c e e d west west on on highway h i g h w a y 17 17 from f r o m Husky H u s k y the the We Muskie M u s k i e in i n the t h e town t o w n of o f Kenora. Kenora. En r o u t e t o t h e first En route to the first stop, is parallel p a r a l l e l to, t o , and a n d lies l i e s 1 to t o 22 kilo— kilos t o p , highway h i g h w a y 17 1 7 is metres south s o u t h of, o f , the t h e Wabigoon W a b i g o o n -- Winnipeg W i n n i p e g River R i v e r inter— interface f a c e (Figure ( F i g u r e 4). 4 ) . Moderately M o d e r a t e l y to to intensely i n t e n s e l y flattened f l a t t e n e d and and l i n e a t e d metavolcanic m e t a v o l c a n i c rocks r o c k s and a n d granitoid g r a n i t o i d rocks rocks lineated a r e exposed e x p o s e d in i n road r o a d cuts c u t s along along ( W i n n e t k a Lake L a k e stock) s t o c k ) are (Winnetka 1 this t h i s route. route. 2.5 km Junction J u n c t i o n with w i t h highway h i g h w a y 596 596 10.0 km Junction J u n c t i o n with w i t h highway h i g h w a y 641 64 1 11.2 km Junction J u n c t i o n with w i t h Kenora K e n o r a bypass bypass 23.7 km Junction For km we w e will will J u n c t i o n with w i t h Pye's P y e ' s Road. Road. F o r the t h e next n e x t 9.1 9 . 1 km traverse t r a v e r s e the t h e elliptical e l l i p t i c a l Winnetka W i n n e t k a Lake L a k e stock s t o c k that t h a t lies lies along a l o n g the t h e Wabigoon W a b i g o o n -- Winnipeg W i n n i p e g River R i v e r interface. i n t e r f a c e . This This stock s t o c k is is compositionally c o m p o s i t i o n a l l y zoned z o n e d with w i t h aa granite g r a n i t e to t o grano— granodiorite core and a n d aa hornblende h o r n b l e n d e diorite d i o r i t e rim r i m (Davies, (Davies, d i o r i t e core 1965) i t s elliptical e l l i p t i c a l geometry g e o m e t r y is, i s , in i n ppart, a r t , aa 1 9 6 5 ) and a n d its consequence c o n s e q u e n c e of o f post—crystallization p o s t - c r y s t a l l i z a t i o n deformation deformation (Brisbin, ( B r i s b i n , 1981). 1981 ) . 32.8 km The T h e contact c o n t a c t of o f the t h e Winnetka W i n n e t k a Lake Lake stock s t o c k with w i t h enveloping envelopinq Wabigoon m e t a v o l c a n i c rocks r o c k s is is exposed e x p o s e d in in W a b i g o o n subprovince s u b p r o v i n c e metavolcanic low l o w outcrops o u t c r o p s on on the t h e south s o u t h side s i d e of o f the t h e highway. highway. 35. 1 km 41.3 km Junction J u n c t i o n with w i t h the t h e Rush Rush Bay Bay Road Road Junction is J u n c t i o n with w i t h the t h e Royal R o y a l Lake L a k e Road. R o a d . The T h e first f i r s t stop s t o p is on the north side of the highway just beyond this o n t h e n o r t h s i d e o f t h e highway j u s t beyond t h i s unction. jj u nction. The series T h e lithologic l i t h o l o g i c diversity d i v e r s i t y of o f the t h e Keewatin K e e w a t i n series metavolcanic met a v o l c a n i c and a n d metasedimentary m e t a s e d i m e n t a r y rocks r o c k s cannot c a n n o t be be adequately a d e q u a t e l y represented r e p r e s e n t e d oon n t this h i s ffield i e l d trip. t r i p . Stops S t o p s 1A 1A and a n d 18 1B aare r e included i n c l u d e d t to o iillustrate l l u s t r a t esome some of o f the t h e factors factors which w h i c h ccomplicate o m p l i c a t e i interpretation n t e r p r e t a t i o n of o f these t h e s e rocks. rocks. 41.35 km Keewatiri K e e w a t i n sseries e r i e s Pillow P i l l o wLava Lava Outcrop s ign O u t c r o p oon n tthe h e north n o r t h side s i d e of o f the t h highway e h i g h w a y below b e l o w the t h e sign for f o r the t h e Royal R o y a l Lake L a k e Resort. Resort. In I n this t h i s outcrop o u t c r o p we w e will w i l l examine e x a m i n e aa ffine i n e grained, g r a i n e d , buff b u f f to to light l i g h tgreen g r e e nweathering, w e a t h e r i n g ,feldspar—phyric f e l d s p a r - p h y r i c pillowed p i l l o w e d flow. flow. STOP STOP 1A 1A In plagioclase I n thin t h i n section s e c t i o n the t h e rock r o c k consists c o n s i s t s of o f plagioclase phenocrysts up to 2 mm in longest dimension i n aa finer finer p h e n o c r y s t s u p t o 2 rnm i n l o n g e s t d i m e n s i o n in grained g r a i n e d matrix m a t r i x consisting c o n s i s t i n g of o f feldspar, f e l d s p a r , quartz, quartz, actinolite, I t is is difficult d i f f i c u l t to to a c t i n o l i t e , biotite b i o t i t e and a n d epidote. e p i d o t e . It estimate proportions of quartz and feldspar but veins estimate proportions of and feldspar but veins and a n d diffuse d i f f u s e patches p a t c h e s of o f quartz q u a r t z suggest s u g g e s t the t h erock r o c khas h a s been been ss iilicified. licified. �- — LIII EllllfflJ EE MINOR FOLD AXFS AND MINERAL LINEATIONS s 65 us Fiqure 4: T5uuS - -— UT UK LAKI N1F4BO Figure S _FLLANE U H - - — - 8 and 11 are outlined. BATHC)L ITH I 11111 WINNIPEG RIVER GRANITOID BELT I of figures 5, Geologic map of the Wabigoon—Winnipeg River interface between the Manitoba— Ontario border and Vermilion Bay (from Beakhouse et al., 1983). The location 1 Is... Figure - WABIGDON BELT METAVOLCANICS AMPI-IIBOLITE INCLUSION ZONES LCUNT LAKE INCLUSIONS) WITH GRANITE INTERLAYERS METASEDIMENTS AND DERIVED MIGMATITE TONALITE GNEISS (± S%AMPHIBOLITE TONALITE BATHOLITHPLUTON — LATE TECTONIC GRANODIORITE TO GRANITE INTRUSIONS_LATE TECTONIC UNMETAMORPHOSED MAF1C INTRUSIONS_POST TECTONIC 4O 2Okrr �80 I ::* = T Stop I 10 I-.. 0 - -:-:::--f:—:-- - + - = + CR0 GROUP Clastlc MetasedlmentaryRocks Rocks - C R O W DWOUCK UCK GROUP Metasedimentary A . Clastic u ZLI 3 00 $2 unconformity unconform~ty Hlgh Lake L a k e Porphyry Porphyry Intrusion lntrus~on High intrusive contact contact Mafic Maflc Intrusive lntruslve Rocks Rocks intrusive lntruslve contact contact The * T h e relative relative age a g e of of felsic felsic intrusive rocks that that intrude Intrude the basement basement complex complex with with respect to to the the older older z 1;; CWQ* ::--: Clastic Rocks ClastlcMetasedimentary Metased~mentary Rocks + 3; lntermed~ateto Felsic Felslc Metavolcanic Metavolcanic Rocks Rocks I 3 a Intermediate Rocks v V _j Mafic M aMetavolcanuc f ~ cMetavolcan~c Rocks w faulted faulted unconformity unconform~ty 0 4 LUhfflhlL aLate FelsicIntrusive Intrusive Rocks' Rocks t e Felslc Early Early Felsic Felslc Intrusive lntrus~veRocks Rocks' Basement Complex >yrn , Complex :gj s Figure g u r e 5: 5: x unconformity unconform~tyand and Wabigoon Wab~goon subprovince subprovmce lithologies litholog~es is I S not not known known. ** Rocks in the **Rocks the Keewatin Keewatin Series Series are are subdivided subdivided lithologically lithologically and and the the order order does does not not imply imply age age relationships. relationships. Geologic G e o l o g i c map of o f the t h e Tannis T a n n i s Lake—High L a k e - H i g h Lake L a k e area area generalized g e n e r a l i z e d from f r o m Davies D a v i e s (1965) ( 1 9 6 5 ) with w i t h additional additional information i n f o r m a t i o n oon n tthe h e ddistribution i s t r i b u t i o n of o f the t h e basement basement The complex c o m p l e x from f r o m Bald B a l d (1981). (1981 ) . T h e location l o c a t i o n of o f this t h i s map map is is illustrated i l l u s t r a t e d in i n figure f i g u r e 4. 4. �81 A chemical c h e m i c a l analysis a n a l y s i s of o f this t h i s rock r o c k (sample ( s a m p l e 84GPB8010, 84GPB80101 appendix) i s ddifficult i f f i c u l t to t o interpret i n t e r p r e t due d u e to t o this this a p p e n d i x ) is alteration. Elements alteration. E l e m e n t s whose w h o s e abundance a b u n d a n c e may not n o t be be pprofoundly r o f o u n d l y affected a f f e c t e d bby y this t h i s alteration a l t e r a t i o n suggest s u g g e s t that t h a t the the is not n o t simply s i m p l y aa r o c k was was geochemically g e o c h e m i c a l l y evolved e v o l v e d and a n d is rock silicified Relative s i l i c i f i e d basalt. basalt. R e l a t i v e to t o tholeiitic t h o l e i i t i c basals b a s a l s from from tthe h e area a r e a (samples ( s a m p l e s 83GPB323, 83GPB3231 84GPB8007 84GPB8007 and a n d 84GPB8009) 84GP58009) lower C Co, Cr, oI C r I Ni N i and a n d Ti T i and a n d higher h i g h e r Zr Z r and and tthis h i s rrock o c k hhas a s lower LREE. T h e fractionated f r a c t i o n a t e d REE pattern p a t t e r n (Lan/Ybn ( L a n / Y b n = 77)) is The is These aalso l s o distinctive. distinctive. T h e s e ccharacteristics h a r a c t e r i s t i c s are a r e similar s i m i l a r to to those t h o s e of o f certain c e r t a i n basaltic b a s a l t i c andesites a n d e s i t e s from f r o m the the Confederation C o n f e d e r a t i o n Lake L a k e belt b e l t (eq. ( e q . samples s a m p l e s 439 439 and a n d 448; 448; Thurston T h u r s t o n aand n d FFryer, r y e r I 11983) 9 8 3 ) hhaving a v i n g SSiO i O ? contents c o n t e n t s of of The aapproximately p p r o x i m a t e l y 55 5 5 percent. percent. T h e relative r e l a t l v e significance s i g n i f i c a n c e of of pprimary r i m a r y abundances a b u n d a n c e s and a n d geochemical g e o c h e m i c a l mobility m o b i l i t y accompanyaccompanyiing n g ssecondary e c o n d a r y aalteration 1 t e r a t i o n in i n ddetermining e t e r m i n i n g the t h e observed observed ccompositions o m p o s i t i o n s and a n d apparent a p p a r e n t calc—alkaline c a l c - a l k a l i n e affinity a f f i n i t y of of This is poorly p o o r l y constrained. constrained. T h i s poses poses a a problem problen tthis h i s rock r o c k is mafic iin n ccomparing o m p a r i n g the t h e cchemistry h e m i s t r y oof f m a f i c and a n d intermediate intermediate dikes d i k e s that t h a t cut c u t an a n interpreted i n t e r p r e t e d basement b a s e m e n t complex c o m p l e x to t o the the north n o r t h with w i t h that t h a t of o f the t h e flows f l o w s which w h i c h they t h e y may be b e feedinq. feedinq. 41.8 4 1 - 8 km STOP lB Series Metasedimentary 1B Keewatin Keewatin S eries M e t a s e d i m e n t a r y Pocks Rocks Outcrop O u t c r o p on o n the t h e north n o r t h side s i d e of o f the t h ehighway highway Thin metasedimentary Metasand— t o medium medium bbedded edded m e t a s e d i m e n t a r y rrocks. ocks. M etasandT h i n to metasiltstone sstones t o n e s predominate p r e d o m i n a t e but but m e t a s i l t s t o n e and a n d meta—argillite meta-arg i l l i t e (the ( t h e llatter a t t e r ooften f t e n ddisrupted) i s r u p t e d ) are a r e common in i n parts p a r t s of o f the the outcrop. Graded i s recognizable r e c o q n i z a b l e locally. locally. outcrop. G r a d e d bedding b e d d i n g is Although d e p o s i t e d in i n aa sedimentary sedimentary A l t h o u g h these t h e s e rocks r o c k s were deposited environment they are probably closely r e l a t e d to t o felsic felsic e n v i r o n m e n t t h e y a r e p r o b a b l y c l o s e l y related vvolcanic o l c a n i c activity. activity. Throughout much of T h r o u g h o u t much o f the t h e ooutcrop, u t c r o p I foliation f o l i a t i o n (mineral (mineral foliation s aatt a high hiqh f o l i a t i o n and a n d fflattening l a t t e n i n g of o f ffragments) r a g m e n t s ) iis angle a n g l e tto o bedding, b e d d i n g I mimicking m i m i c k i n g t the h e rregional e g i o n a l scale scale 1 9 6 5 ) . In In sstructure t r u c t u r eover o v e rmuch much of o f the t h e area a r e a (Davies, ( D a v i e s I 1965). intensely i n t e n s e l y ddeformed e f o r m e d zones, z o n e s I bedding b e d d i n g is i s transposed t r a n s p o s e d so s o as as The tto o bbe e essentially e s s e n t i a l l y parallel p a r a l l e l to t o the t h e foliation. foliation. The foliation i s parallel p a r a l l e l to t o the t h e axial a x i a l plane p l a n e of o f aa f o l i a t i o n is megascopic m e g a s c o p i c fold f o l d at a t the t h e crest c r e s t of o f the t h e roadcut. roadcut. 443.35 3 . 3 5 km JJunction u n c t i o n with w i t h Shoal S h o a l Lake L a k e Road Road 44.1 4 4 . 1 km JJunction u n c t i o n with w i t h Gundy Lake L a k e Road Road — - tturn u r n nnorth o r t h on o n Gundy Lake r e s e t odometer o d o m e t e r to t o 0.0. 0.0. L a k e Road Road —- reset 3.1 km 3.1 South t u r n lleft eft S o u t h Shore S h o r e Road junction j u n c t i o n —- turn 33.5 . 5 km Powerline P ower1i n e 44.05 . 0 5 km P i u t e Lake L a k e Road Road junction junctio— n - turn t u r n right riqht Piute 4.6 km km The Wabigoon Causeway C a u s e w a y a at t eend n d oof f Tannis T a n n i s Lake. Lake. The W a b i g o o n —Winnipeg W i n n i p e g River R i v e r iinterface n t e r f a c e lies l i e s along a l o n g the t h e south s o u t h shore s h o r e of of �82 Tannis Tannis ( F i g u r e 5). 5) T h e outcrop o u t c r o p on on the t h e north n o r t h side side Lake (Figure The ( w e s t side s i d e of o f road) r o a d ) consists c o n s is ts of o f foliatfoliato f the t h e causeway c a u s e w a y (west of s i m i l a r to t o those t h o s e at a t the the e d tonalite t o n a l i t e cut c u t by b y mafic m a f i c dikes d i k e s similar ed next stop n e x t stop a 5.05 5 . 0 5 km h Junction J u n c t i o n —- turn t u r n left left 5.15 5. 1 5 km km STOP w i t h Mafic Ma i c Dikes. Dikes. STOP 22 Tonalite T o n a l i t e with Outcrop on the west side of the O u t c r o p o n t h e w e s t s i d e o f t h e road. road. The principal p r i n c i p a l rock r o c k type t y p e in i n the t h e outcrop o u t c r o p is is aa fine f i n e to to medium medium grained, g r a i n e d grey, g r e y I strongly s t r o n g l y lineated l i n e a t e d biotite biotite tonalite. Clark tonalite. C l a r k et e t al a 1 (1981) ( 1 981 ) ddetermined etermined a a Rb—Sr Rb-Sr whole whole rock r o c k isochron i s o c h r o n age, a g e I based b a s e d on o n regional r e g i o n a l sample s a m p l e selection, selection, .0014). Recent 150 of -7028 .0014). R e c e n t U—Pb U-Pb o f 2950 2950 1 5 0 Ma Ma (Ri ( R i == .7028 zircon z i r c o n geochronology q e o c h r o n o l o g y on o n aa sample s a m p l e selected s e l e c t e d from f r o m this this outcrop o u t c r o p confirms c o n f i r m s the t h e antiquity a n t i q u i t of o f this t h i s unit u n i t and and indicates a minimum minimum (2O7Pb/2OPb) indicates a ( 2 0 7 ~ b / 2 0 P b ) age a g e of o f 3028 3 0 2 8 Ma Ma (D.W, ( D e w e Davis, D a v i s , 1984 1 9 8 4 personal p e r s o n a l communication). communication) The T h e tonalite t o n a l i t e here h e r e is is relatively r e l a t i v e l y "clean" " c l e a n " arid a n d contains contains only o n l y aa few f e w inclusions i n c l u s i o n s of o f massive m a s s i v e amphibolite a m p h i b o l i t e of of indeterminate origin. These amphibolite inclusions indeterminate origin. T h e s e a m p h i b o l i t e i n c l u s i o n s are are more discontinuous than more d i s c o n t i n u o u s t h a n the t h e mafic m a f i c dikes d i k e s cutting c u t t i n g the the outcrop o u t c r o p and a n d have h a v e subtle s u b t l e differences d i f f e r e n c e s in i n composition c o m p o s i t i o n and and texture but the possibility that they represent t e x t u r e but t h e poss i b i l i t y t h a t they r e p r e s e n t disrupted d i s r u p t e d dikes d i k e s cannot c a n n o t be b e totally t o t a l l y discounted d i s c o u n t e d on o n this this outcrop. Elsewhere, amphibolite inclusions with outcrop. Elsewhere amphibol i t e i n c l u s i o n s with calc—silicate calc-s i l i c a t e pods p o d s aand n d hhighly i g h l y sstretched t r e t c h e d pillows pillows demonstrate d e m o n s t r a t e aa vvolcanic o l c a n i c oorigin r i g i n for f o r some s o m e of o f the the inclusions i n c l u s i o n s and a n d provide p r o v i d e evidence e v i d e n c e for f o r pre—3.0 p r e - 3 . 0 Ga Ga volcanism v o l c a n i s m in i n the t h e Winnipeg W i n n i p e g River R i v e r belt. belt. The T h e tonalite t o n a l i t e is is cut c u t by b y deformed, d e f o r m e d f equigranular e q u i g r a n u l a r and and porphyritic (plagioclase phenocrysts) p o r p h y r i t i c ( p l a g i o c l a s e p h e n o c r y s t s ) amphibolitic amphibolitic mafic is not n o t well well m a f i c dikes. d i k e s * The T h e age a g e of o f the t h e mafic m a f i c dikes d i k e s is constrained c o n s t r a i n e d except e x c e p t that t h a t they t h e y are a r e younger y o u n g e r than t h a n the the tonalite G a ) and a n d older o l d e r than t h a n the t h e last l a s t deformation deformation t o n a l i t e (3.028 ( 3 . 0 2 8 Ga) and a n d certain c e r t a i n of o f the t h e variously v a r i o u s l y deformed d e f o r m e d granitic granitic pegmatite The p e g m a t i t e dikes. dikes. T h e age a g e of o f these t h e s e intrusive i n t r u s i v e phases p h a s e s and and deformation d e f o r m a t i o n is is not n o t constrained c o n s t r a i n e d here h e r e but, b u t , by b y analogy analogy with a r e a s in i n the t h e Winnipeg W i n n i p e g River R i v e r belt, b e l t f the t h e dikes dikes w i t h other o t h e r areas are a r e thought t h o u g h t to t o be b e older o l d e r than t h a n 2.7 2 . 7 Ga. G a . The T h e age age constraints c o n s t r a i n t s and a n d proximity p r o x i m i t y to t o the t h e Wabigoon W a b i g o o n subprovince subprovince metavolcanic r n e t a v o l c a n i c rocks r o c k s here h e r e led l e d to t o the t h e suggestion s u g g e s t i o n that t h a t the the dikes d i k e s cut c u t an a n older o l d e r basement b a s e m e n t complex c o m p l e x and a n d fed f e d Keewatin Keewatin series s e r i e s volcanism v o l c a n i s m (Bald, ( B a l d 1981; 1981 ; Clark C l a r k et e t al, a1 I 1981). 1981 ) Modal Modal and a n d chemical c h e m i c a l analyses a n a l y s e s of o f the t h e tonalite t o n a l i t e (sample (sample 321A) 3 2 1 A ) and a n d equigranular e q u i q r a n u l a r mafic m a f i c dike d i k e (sample ( s a m p l e 321B) 3 2 1 B ) are are presented p r e s e n t e d in i n the t h e appendix. appendixo x . , . P r o c e e d back b a c k towards t o w a r d s the t h e highway h i g h w a y for Proceed f o r 1.05 1 - 0 5 km km to t o the t h e junction j u n c t i o n with with the t u r n right r i g h t (west) t h e Piute P i u t e Lake L a k e Road Road —- turn ( w e s t ) —- proceed p r o c e e d 0.55 0 . 5 5 km. km. STOP W a b i g o o n —- Winnipeg W i n n i p e g River R i v e r Contact Contact STOP 33 Wabigoon The The Wabigoon-Winnipeg W a b i g o o n - W i n n i p e g River R i v e r contact c o n t a c t in i n this t h i s area area corresponds c o r r e s p o n d s to t o aa linear l i n e a r topographic t o p g r a p h i c depression d e p r e s s i o n and and �83 exposures e x p o s u r e s oof f the t h e contact c o n t a c t are a r e not n o t abundant. abundant. T h e outoutThe crops c r o p s on o n the t h e road r o a d immediately i m m e d i a t e l y before b e f o r e we w e stop s t o p and a n d most most oof f those t h o s e to t o the t h e north north o f the t h e road r o a d are a r e fine f i n e to t o medium of grained, g r a i n e d t foliated f o l i a t e d to t o gneissic, g n e i s s i c , dominantly d o m i n a n t l y tonalitic tonal itic rrocks o c k s cut c u t by b y mafic m a f i c dikes d i k e s (Figure ( F i g u r e 6). 6 ). T h e ooutcrops u t c r o p s to to The tthe h e ssouth o u t h oof f the t h e road r o a d cconsist o n s i s t oof f fine f i n e to t o medium grained, g r a i n e d amphibolitic a m p h i b o l i t i c mafic m a f i c volcanic v o l c a n i c rocks r o c k s with with interbedded i n t e r b e d d e d chert—magnetite c h e r t - m a g n e t i t e iron i r o n formation. formation. Some Some hhighly i g h l y ddeformed e f o r m e d pillow p i l l o w structures s t r u c t u r e s are a r e present p r e s e n t on o n the the The medium mafic llargest a r g e s t outcrop. outcrop. T he m e d i u m ggrained rained m a f i c rocks r o c k s may rrepresent e p r e s e n t sills s i l l s or o r transposed t r a n s p o s e d dikes. dikes. t h i n tuffaceous tuffaceous A thin near of hhorizon o r i z o n ooccurs ccurs n e a r the t h e north n o r t h side side o f the t h e thicker t h i c k e r iron iron formation f o r m a t i o n unit. unit. The mafic The m a f i c ddikes i k e s ccutting u t t i n g the t h e larger l a r g e r tonalite t o n a l i t e outcrops outcrops nnorth o r t h oof f the t h e road r o a d are a r e atypical a t y p i c a l in i n terms terms of o f their their The ccomposition o m p o s i t i o n and a n d heterogeneity. heterogeneity. T h e banding b a n d i n g and a n d calcic calcic ppods o d s within w i t h i n them t h e m resembles r e s e m b l e s those t h o s e associated a s s o c i a t e d with with metavolcanic m e t a v o l c a n i c amphibolite i n c l u s i o n s in i n the t h e Winnipeq Winnipeg a m p h i b o l i t e inclusions River R i v e r belt. belt. T hese m a f i c units u n i t s are These mafic a r e subparallel s u b p a r a l l e l to t o the the foliation f o l i a t i o n in i n the t h e tonalite t o n a l i t e but b u t at a t one o n e contact c o n t a c t (Figure ( F i g u r e 6) 6) aa low l o w angle a n g l e discordance d i s c o r d a n c e is is noted. noted. T h e relationships relationships The developed d e v e l o p e d in i n the t h e last l a s t stop s t o p description d e s c r i p t i o n and a n d context c o n t e x t in in highly w h i c h these t h e s e unusual u n u s u a l dikes d i k e s occur o c c u r affords a f f o r d s aa highly which It iinterpretive n t e r p r e t i v e though t h o u g h plausible p l a u s i b l e explanation. explanation. I t is is cconceivable o n c e i v a b l e that t h a t these t h e s e dikes d i k e s are a r e feeding f e e d i n g flows f l o w s within w i t h i n aa few metres (in deformed ( i n the the d e f o r m e d state) s t a t e ) of o f where w h e r e we we f e w tens t e n s oof f metres are is rreasonable a r e observing o b s e r v i n g them. them. IItt is e a s o n a b l e to t o expect e x p e c t that that tthe h e pprocesses r o c e s s e s (autobrecciation, ( a u t o b r e ~ c i a t i o ninteraction i~n t e r a c t i o n with w i t h sea sea water) w a t e r ) that t h a t produce p r o d u c e "volcanic" " v o l c a n i c " structures s t r u c t u r e s and and alteration a l t e r a t i o n iin n flows f l o w s would w o u l d pproduce r o d u c e s isimilar m i l a r ffeatures e a t u r e s in in tthe h e upper u p p e r pportions o r t i o n s of o f venting v e n t i n q dikes. dikes. The River T h e aactual c t u a l contact c o n t a c t between b e t w e e n the t h e Winnipeg Winnipeg R i v e r bbelt e l t and and Wabigoon W a b i g o o n s subprovince u b p r o v i n c e is not Immediately n o t exposed e x p o s e d here. here. Imnediately north n o r t h oof f the t h e road r o a d is i s a small s m a l l outcrop o u t c r o p of o f highly h i g h l y sheared sheared mafic m a f i c rock r o c k cut c u t by b y at a t least l e a s t one o n e deformed d e f o r m e d mafic m a f i c dike. dike. IItt i s not n o t known known if i f the t h e sheared sheared m a f i c rock r o c k is i s a flow f l o w or or is mafic dike. The highly dike. T he h i g h l y ssheared h e a r e d nature n a t u r e of o f this t h i s rock r o c k and a n d the the n e g a t i v e topographic t o p o g r a p h i c expression e x p r e s s i o n of o f the t h e contact c o n t a c t suqgests suqgests negative tthe he p r e s e n c e of o f aa fault. fault. Eoes t h i s fault f a u l t represent r e p r e s e n t aa presence Does this major dislocation d i s l o c a t i o n that t h a t juxtaposes j u x t a p o s e s two t w o unrelated unrelated a s s e m b l a g e s , at a t least l e a s t one o n e of o f which w h i c h is is allochthonous a l l o c h t h o n o u s or or assemblages, ddoes o e s iitt represent r e p r e s e n t a aminor m i n o r (or ( o rmajor) m a j o r )adjustment a d j u s t m e n t along along an a n original o r i q i n a l unconformity? unconformity? R e t u r n to t o Highway H i g h w a y 17 17 —- tturn u r n left l e f t (east) ( e a s t ) —- pproceed r o c e e d 0.75 8 . 7 5 km to to Return the Shoal the S h o a l Lake L a k e Road Road— pproceed r o c e e d south s o u t h on o n the t h e Shoal S h o a l Lake L a k e Road Road for for 22.9 . 9 km — turn t u r n rright i g h t (west) ( w e s t ) onto o n t o narrow n a r r o w road r o a d —- pproceed r o c e e d 0. k m west west 0.3 km oonn the t h e narrow n a r r o w road r o a d—- the t h e exposures a t s t o p 4 a r e located a p p r o x i m a t e l y 30 metres s o u t h o f t h e r o a d . exposures at stop 4 are located approximately 30 metres south of the road. STOP H i g h Lake L a k e Unconformity Unconformity STOP 44 High metabasalts e r i e s are are IIn n tthis h i s ooutcrop, utcropt m e t a b a s a l t s oof f tthe h e Keewatin K e e w a t i n sseries cut c u t bby y pporphyry o r p h y r y ddikes i k e s rrelated e l a t e d to t o the t h eHigh H i g h Lake Lake intrusion i n t r u s i o n and a n d both b o t h are a r e unconformably u n c o n f o r m a b l y ooverlain v e r l a i n by b y the the �84 fine to medium grained mafic roc with epidote pods chert-magnetite iron formation metabasah ..................................,.,,..,.,. . ... . ..... ....... .............. ..................... mafic dikes tonalite slightiywdiscordant c o n t a c t 1 - 0 5 10 15 20 metres Figure 6: 6: Figure G e n e r a l i z e d outcrop o u t c r o p map map of t o p 3. 3. Generalized of sstop �85 m e t aased sed im e n t a r y rrocks o c k s oof f the t h eCrowd Crowd uuck c k ggroup r o u p (Figure ( Figure met imentary 7). 7). The m e t a b a s a l t s (most (most oof f which w h i c h aare r e pillowed) p i l l o w e d ) and and The metabasalts High H i g h Lake Lake pporphyry orphyry d i k e are a r e exposed e x p o s e d on o n the t h e western w e s t e r n edge edge dike of o f the t h e outcrop. outcrop. I n this t h i s outcrop, o u t c r o p , the t h e Crowduck Crowduck group g r o u p is is divisible d i v i s i b l e into into In f o u r units u n i t s that t h a t reflect r e f l e c t aa general g e n e r a l coarsening c o a r s e n i n g upwards upwards four 7 ) Stratigraphic S t r a t i g r a p h i c relationships r e l a t i o n s h i p s are are t r e n d (Figure ( F i g u r e 7) trend c o m p l e x , however, h o w e v e r , because b e c a u s e many units u n i t s were were eroded e r o d e d prior prior complex, to t o or o r concomittant c o n c o m i t t a n t with w i t h deposition d e p o s i t i o n of o f overlying o v e r l y i n g units. units. Such w e l l displayed displayed S u c h scouring s c o u r i n g relationships r e l a t i o n s h i p s are a r e well immediately i m m e d i a t e l y east e a s t of o f the t h enorthernmost n o r t h e r n m o s t exposure e x p o s u r e of o f the the porphyry Near l o c a l i t y , the t h e effect e f f e c t of of p o r p h y r y dike. dike. N e a r this t h i s same locality, local l o c a l provenance p r o v e n a n c e in i n the t h e conglomeratic c o n g l o m e r a t i c facies f a c i e s is is illustrated by aa lense i l l u s t r a t e d by l e n s e oof f conglomerate c o n g l o m e r a t e richer r i c h e r in i n mafic mafic volcanic v o l c a n i c clasts c l a s t s than t h a n the t h e remainder r e m a i n d e r of o f the t h e outcrop. outcrop. Throughout most of o f the t h e conglorneratic c o n g l o m e r a t i c facies f a c i e s in i n this this T h r o u g h o u t most outcrop, o u t c r o p , clasts c l a s t s of o f the t h e porphyry p o r p h y r y predominate p r e d o m i n a t e and a n d are are conspicuously c o n s p i c u o u s l y larger l a r g e r than t h a n the t h e other o t h e r clast c l a s t types t y p e s which which include i n c l u d e relatively r e l a t i v e l y abundant a b u n d a n t mafic m a f i c to t o felsic f e l s i c volcanic volcanic rocks r o c k s and a n d minor m i n o r chert, c h e r t , iron i r o n formation f o r m a t i o n and a n d massive massive sulphides. s u l p h i d e s . The T h e thin t h i n to t o medium medium bedded b e d d e d sandstone—siltsandstone-siltstone s t o n e sequence s e q u e n c e exposed e x p o s e d near n e a r the t h e unconformity u n c o n f o r m i t y in i n the the eastern e a s t e r n part p a r t of o f the t h e large l a r g e outcrop o u t c r o p display d i s p l a y spectacular spectacular soft s o Ât sediment s e d i m e n t deformation d e f o r m a t i o n structures s t r u c t u r e s including i n c l u d i n g slump sl ump folds, f o l d s , load l o a d casts c a s t s and and flame f l a m e structures. structures. AA regolith uck group r e g o l i t h is is developed d e v e l o p e d beneath b e n e a t h the t h e Crowd Crowduck g r o u p and and is is most apparent a p p a r e n t in i n the t h e porphyry p o r p h y r y unit. unit. I t is is not n o t clear clear It how much of o f the t h e irregular i r r e g u l a r nature n a t u r e of o f the t h e unconformity unconformity surface t o pre—Crowduck p r e - C r o w d u c k group group s u r f a c e can c a n be b e attributed a t t r i b u t e d to topography. The topography. The presence p r e s e n c e of o f clasts c l a s ts with w i t h exposed exposed cross—sectional c r o s s - s e c t i o n a l areas a r e a s in i n excess e x c e s s of o f one o n e square s q u a r e metre metre clearly c l e a r l y requires r e q u i r e s at a t least l e a s t local l o c a l steep s t e e p gradients g r a d i e n t s to t o have have been mimics b e e n present. p r e s e n t . The T h e geometry g e o m e t r y of o f the t h e unconformity u n c o n f o r m i t y mimics the t h e pattern p a t t e r n displayed d i s p l a y e d by the t h e regional r e g i o n a l folding f o l d i n g with with east—west uck e a s t - w e s t ax ax ial i a l pplanes l a n e s that t h a t deforms d e f o r m s the t h e Crowd Crowduck group. g r o u p . The The orientation o r i e n t a tofi ofoliation n o f fino this l i a outcrop t i o n iisn t h i s o u t c r o p is approximately a p p r o x i m a t e l y p a r a l l e l t o t h e s e a x i a l p l a n e s and is markedly m a r k e d l y ddiscordant i s c o r d a n t to t o bedding b e d d i n g in i nthe t h Crowduck e Crowd uck group. group. These T h e s e observations o b s e r v a t i o n s suggest s u g g e s t that t h a t at a t least l e a s t part p a r t of o f the the irregularity i r r e g u l a r i t y of o f the t h e unconformity u n c o n f o r m i t y is is aa consequence c o n s e q u e n c e of of post—Crowd p o s t - C r o w d uuck c k deformation. d e f o r m a t i o n . In I n the t h e southwestern s o u t h w e s t e r n part p a r t of of the s il ts t o n e s of of t h e outcrop, o u t c r o p , thinly t h i n l y bedded b e d d e d sandstones s a n d s t o n e s and a n d siltstones the t h e Crowduck Crowduck group g r o u p overly o v e r l y the t h e regolith r e g o l i t h above a b o v e the the porphyry p o r p h y r y dike d i k e and a n d butt b u t t up up against a g a i n s t the t h e adjacent a d j a c e n t Keewatin Keewatin series s e r i e s metabasalt. m e t a b a s a l t . Similar S i m i l a r units u n i t s immediately i m m e d i a t e l y overlying overlying the t h e metabasalt m e t a b a s a l t are a r e several s e v e r a l metres metres sstratigraphically t r a t igraphically above a b o v e tthe h e base b a s e of o f the t h e sequence s e q u e n c e over o v e r the t h e porphyry p o r p h y r y unit. unit. Does Does this t h is represent r e p r e s e n t pre—Crowduck pre-Crowd uck topography t o p o g r a p h y or or prog p r o g rressive e s s i v e syn—depositional s y n - d e p o s i t i o n a l faul f a u lting? ting? Quartz Q u a r t z and a n d quartz—tourmaline q u a r t z - t o u r m a l i n e veins v e i n s cut c u t the t h e conglomerate conqlornerate and and in i n the t h e vicinity v i c i n i t y of o f the t h e High H i g h Lake Lake stock s t o c k are are associated a s s o c i a t e d with w i t h gold g o l d mineralization m i n e r a l i z a t i o n (Davies, ( D a v i e s , 1965). 1965). Locally, L o c a l l y , the t h e veins v e i n s appear a p p e a r to t o be be confined c o n f i n e d to t o porphyry porphyry clasts s u g g e s t i n g pre—erosional p r e - e r o s i o n a l veining v e i n i n g but b u t when when c l a s ts suggesting parallel to these axial planes and is �____ 86 conglomerate pebbly sandstone i.:: pebbly sandstone massive t o thickly thicklybedded b e d d e dsandstone sandstone massive to thinly bedded sandstone and siltstone thinly bedded sandstone and siltstone — — — — — unconformity I High Lake porphyry . . . intrusive intrusive contact • contact mafic metavolcanic rocks mafic metavolcanic rocks (pillowed and massive) ''i-iÑi (pillowed and massive) S K E E W A T I N SERIES KEEWATIN SERIES o 5 10 15 20 metres regolith original topography or syn—depositional faulting? F i g u r e 7:7: Fiqure Generalized outcrop o u t c r o p map map of of stop s t o p4.4 . Generalized I clasts �27 examined most oof e x a m i n e d in i n ddetail e t a i l most f these t h e s e have h a v e 'tails' ' t a i l s ' that that project p r o j e c t into i n t o the t h e matrix. matrix. Some vveins e i n s are a r e continuous c o n t i n u o u s and and The T h e concentration c o n c e n t r a t i o n of o f this this cclearly l e a r l y post—depositional. post-depositional veining v e i n i n g in i n porphyry p o r p h y r y clasts c l a s t s is i s interpreted i n t e r p r e t e d to t o be b e due d u e to to hheterogeneous e t e r o g e n e o u s ddeformation e f o r m a t i o n arisinq a r i s i n g from f r o m the t h e differing differinq mechanical m e c h a n i c a l properties p r o p e r t i e s of o f the t h e various v a r i o u s types t y p e s of o f clasts clasts aand n d matrix. matrix. The Crowduck T he C r o w d u c k ggroup r o u p hhas a s no n o obvious, o b v i o u s , ddirect i r e c t relationship relationship However, tto o the t h e Wabigoon—Winnipeg W a b i g o o n - W i n n i p e g River R i v e r interface. interf ace. H owever, when vviewed when i e w e d from from a a regional r e g i o n a l perspective, p e r s p e c t i v e , many Temiskaming—type t o be be T e m i s k a m i n g - t y p e supracrustal s u p r a c r u s t a l sequences s e q u e n c e s do d o appear a p p e a r to spatially s p a t i a l l y associated a s s o c i a t e d with w i t h subprovince s u b p r o v i n c e interfaces. i n t e r f aces. Other s i m i l a r sequences s e q u e n c e s occurring o c c u r r i n g near n e a r an an O t h e r examples e x a m p l e s oof f similar Rainy iinterface n t e r f ace iinclude n c l u d e tthose h o s e aat t R a i n y Lake, L a k e , Beardmore— BeardmoreGeraldton This G e r a l d t o n and a n d Kirkland K i r k l a n d Lake. Lake. T h i s observation o b s e r v a t i o n may may l a t e r tectonic t e c t o n i c activity activity rreflect e f l e c t the t h e concentration c o n c e n t r a t i o n of o f later and a n d associated a s s o c i a t e d tectonically t e c t o n i c a l l y controlled c o n t r o l l e d sedimentation s e d i m e n t a t i o n at at ssubprovince u b p r o v i n c e interfaces. interfaces. . Return east o hhighway i g h w a y aand n d pproceed roceed e a s t to t o the t h e jjunction u n c t i o n oof f highway h i g h w a y 17 17 R e t u r n tto and a n d 596 5 9 6 in i n the t h e town t o w n of o f Norman Norman (between ( b e t w e e n Keewatin K e e w a t i n and a n d Kenora)— K e n o r a ) - set set t o zero z e r o —- tturn u r n north n o r t h on o n 596. 596. oodometer d o m e t e r to 1.5 1 . 5 km Junction t u r n right right J u n c t i o n —- turn 1.6 1 . 6 km STOP 55 Marginal M a r g i n a l Granodiorite G r a n o d i o r i t e Unit Unit Wee will W w i l l stop s t o p near n e a r the t h e crest c r e s t of o f the t h e hill h i l l and a n d walk w a l k north north We on t o the t h e shores s h o r e s of o f Darlington D a r l i n g t o n Bay. Bay. We o n Highway 596 596 to will w i l l examine examine a a series s e r i e s of o f outcrops o u t c r o p s which w h i c h provide p r o v i d e aa This cross—section c r o s s - s e c t i o n of o f the t h e Marginal M a r g i n a l Granodiorite. Granodiorite. T h i s unit unit is i s continuous c o n t i n u o u s along a l o n g the t h e contact c o n t a c t between b e t w e e n metavolcanic metavolcanic Wabigoon rrocks o c k s oof f the the W a b i q o o n ssubprovince u b p r o v i n c e and a n d tonalitic tonalitic gneisses 3 0 km km g n e i s s e s of o f the t h e Winnipeg W i n n i p e g River R i v e r belt b e l t for f o r at a t least l e a s t 30 Along ((Figure F i g u r e 8). 8). A l o n g this t h i s length l e n g t h its i t s width w i d t h ranges r a n g e s from from less metres to l e s s than t h a n 100 1 0 0 metres t o approximately a p p r o x i m a t e l y 700 7 0 0 metres but but The metres i s typical. typical. T h e width w i d t h of o f the t h e unit u n i t here h e r e is is 2200 00 m e t r e s is aapproximately p p r o x i m a t e l y 350 metres metres and a n d displays d i s p l a y s relationships relationships i t s length. length. ttypical y p i c a l oof f the t h e unit u n i t along a l o n g its Figure IIn n the t h e first f i r s t ooutcrop u t c r o p at a t the t h e top t o p of o f the t h e hill h i l l (5A.; (5A; F igure 9) w e can c a n observe o b s e r v e the t h e sharp s h a r p contact c o n t a c t between b e t w e e n the the 9 ) we Keewatin The K e e w a t i n metavolcanics m e t a v o l c a n i c s and a n d Marginal M a r g i n a l Granodiorite. Granodiorite. T he most m o s t striking s t r i k i n g textural t e x t u r a l characteristic c h a r a c t e r i s t i c of o f the t h e grano— qranois the t h e presence p r e s e n c e of o f subhedral s u b h e d r a l to t o lenticular, lenticular, ddiorite i o r i t e is microcline They ppoikilitic oikilitic m i c r o c l i n e megacrysts. megacrysts. T h e y have h a v e some some characteristics c h a r a c t e r i s t i c s of o f both b o t h phenocrysts p h e n o c r y s t s and a n d porphyroblasts porphyroblasts magmatic bbut u t are a r e interpreted i n t e r p r e t e d to t o be b e late late m a g m a t i c megacrysts. megacrysts. Locally, l a t e blastic ' e l a s t i c growth g r o w t h or or L o c a l l y , eevidence v i d e n c e for f o r ssome o m e late microcline oovergrowth v e r g r o w t h oof f m i c r o c l i n e is is evidenced e v i d e n c e d by b y the the coexistence c o e x i s t e n c e of o f augen a u q e n and a n d subhedral s u b h e d r a l megacrysts. megacrysts. T he The is hhomogeneity o m o g e n e i t y oof f the t h e granodiorite g r a n o d i o r i t e in i n this t h i s outcrop o u t c r o p is ttypical y p i c a l oof f that t h a t ddisplayed i s p l a y e d along a l o n g strike s t r i k e in i n the t h e southern southern one t o the t h e Keewatin Keewatin o n e third t h i r d of o f the t h e unit u n i t adjacent a d j a c e n t to metavolcanic m e t a v o l c a n i c rocks. rocks. As A s we w e proceed p r o c e e d down the t h e hill h i l l we w e will w i l l briefly b r i e f l y examine e x a m i n e aa �+ + + Marginal Megacrystic Granodiorite [ffffffffff[ Mixed Gneissic Tonalite—Granitic Pegmatite Gneissic Tonalite LII1 Diorite Rat Portage Bay fault Mafic Metavolcanic Rocks L::III Clastic Metasedimentary Rocks I Intermediate to Felsic Metavolcanic Rocks Lake of the Woods I1IU' Geologic map of the Keewatin area (simplified from Gower (1978) with minor revisions). The location of this map is illustrated in fiqure 4. Dalles Batholith (tonalite to granodiorite) Figure 8: + .••. Proterozojc Duabase Dikes LIII Lulu Lake Granodiorite kilometres gtO' Bay ti,* . co �Figure 9: metres 100 200 + + + + + + + + + + + + + + + + + + —\ — -, \/ + + + + + + + + + + + + + + + + + + + + + + + Keewatin + 5D + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + -c-- + + + + + + + Winnipeg River + + + + + Geologic map of the Darling ton Bay bridge area illustrating the locations of stops 5 and 6. Refer to figure 8 for the location of this map. o Darlington Bay —— I + I"--1 banded gneissic tonalite with amphibolite enclaves mixed gneissic tonalite — granite pegmatite + ÷] marginal megacrystic granodiorite Wabigoon Subprovince metavolcanic rocks I, — '•. l_ �90 series s e r i e s of o f outcrops o u t c r o p s (SB, ( 5 B f CC and a n d D, D f Figure F i g u r e 9) 9 ) which which illustrate a c r o s s the t h e unit. u n i t . Note Note the the i l l u s t r a t e the t h e changes c h a n g e s across variable v a r i a b l e intensity i n t e n s i t y of o f fabric f a b r i c development, d e v e l o p m e n t f local local development b a n d e d character c h a r a c t e r (best ( b e s t seen s e e n in in d e v e l o p m e n t of o f aa banded outcrops 5i3 and a n d 5D) 5 D ) and a n d increasing i n c r e a s i n g abundance a b u n d a n c e of of o u t c r o p s 5B amphibolite seains a m p h i b o l i t e inclusions i n c l u s i o n s and a n d secondary s e c o n d a r y rnicrocline m i c r o c l i n e seams and a n d megacrysts. m e g a c r y s t s . Depending D e p e n d i n g on o n water water level, l e v e l , one o n e can c a n see see the t h e transition t r a n s i t i o n from f r o m Marqinal Marq i n a l Granodiorite G r a n o d i o r i t e to t o granitic granitic pegmatite—tonalite g n e i s s complex c o m p l e x in i n the t h e outcrops o u t c r o p s on on p e g m a t i t e - t o n a l i t e gneiss the t h e shore s h o r e of o f Darlington D a r l i n g t o n Bay Bay (outcrop ( o u t c r o p SE, 5Ef Figure F i g u r e 9). 9 ) . We We will w i l l examine e x a m i n e aa better b e t t e r exposure e x p o s u r e oof f this t h i s ccontact o n t a c t llaterin ater 'in t h e day. day. the AA modal m o d a l and a n d chemical c h e m i c a l analysis a n a l y s i s of of aa sample s a m p l e from f r o m outcrop outcrop Zircoris 5D i s presented p r e s e n t e d in i n the t h e appendix. appendix. Zircons 5D (sample ( s a m p l e 313) 3 1 3 ) is a p r e l i m i n a U—Pb r y U-Pb s e p a r a t e d from f r o m this t h i s sample s a m p l e yield y i e l da preliminary separated zircon 9 1 7 Ma Ma ((Corfu C o r f u eet t aal., l . , 1985) 1985). z i r c o n age a g e of o f 2705 2 7 0 5 ++ 9/7 The T h e unusual u n u s u a l geometry g e o m e t r y of o f this t h i s unit u n i t together t o g e t h e r with w i t h its its regional r e g i o n a l context, c o n t e x t , suggest s u g g e s t it i t was was emplaced e m p l a c e d into i n t o aa zone zone t w o ccontrasting o n t r a s t i n g terranes t e r r a n e s and and o f weakness w e a k n e s s t that h a t sseparated e p a r a t e d two of that t othe t h eemplacement e m p l a c e m e n t of o f the t h eMarginal Marginal t h a t subsequent s u b s e q u e n t to granodiorite, g r a n o d i o r i t e f this t h i s contact c o n t a c t was was tectonically t e c t o n i c a l l y active. active. The is T h e nature n a t u r e of o f the t h epre—emplacement p r e - e m p l a c e m e n t zzone o n e oof f weakness w e a k n e s s is not n o t clear c l e a r and a n d the t h e granodiorite g r a n o d i o r i t e precludes p r e c l u d e s direct direct i t could c o u l d have h a v e been been o b s e r v a t i o n of o f the t h e contact c o n t a c t but b u t it observation either O K fault. f a u l t . The T h e principal principal e i t h e r an a n unconformity u n c o n f o r m i t y or s geoe v i d e n c e for f o r an a n unconformable u n c o n f o r m a b l e relationship r e l a t i o n s h i pisi geo— evidence chronological: c h r o n o l o q i c a l : tthe h e ttonalites o n a l i t e s north n o r t h of o f the t h e contact c o n t a c t are are 2,83—2.88 Ga( B(Beakhouse, 2 - 8 3 - 2 . 8 8 Ga e a k h o u s e f 1 91983; 8 3 ; C Corfu o r f u e tet aal., l . , 1985) 1 9 8 5 ) and and a r e significantly s i g n i f i c a n t l y older o l d e r than t h a n volcanism v o l c a n i s m in i n the t h e Wabigoon Wabiqoon are subprovince, s u b p r o v i n c e although a l t h o u g h metavolcanic m e t a v o l c a n i c rocks r o c k s in i n the the vicinity o f the t h e interface i n t e r f a c e have h a v e not n o t themselves t h e m s e l v e s been been v i c i n i t y of Tholeiitic dated. T h o l e i i t i c mafic m a f i c dikes d i k e s such s u c h as a s at a t Tannis T a n n i s Lake Lake dated. are a r e not n o t recognized r e c o g n i z e d in i n the t h e Keewatin K e e w a t i n area. a r e a . Some Some deformed def~rmed narrow n a r r o w mafic r n a f i c dikes d i k e s cut c u t both b o t h the t h e gneisses g n e i s s e s and a n d grano— granodiorite d i o r i t e but b u t these t h e s e are a r e not n o t voluminous v o ~ u m i n o u sand, a n d as a s noted n o t e d by by Modal and Gower G o w e r (1978), ( 1 9 7 8 ) are a r e of o f calc—alkalirie c a l c - a l k a l i n e affinity. affinity. and c h e m i c a l analyses a n a l y s e s of o f two t w o such s u c h dikes d i k e s (samples ( s a m p l e s270 270 and and chemical 272) a r e presented p r e s e n t e d in i n the the 2 7 2 ) from f r o m the t h e Darlington D a r l i n g t o n Bay area a r e a are appendix. append ix . Proceed P r o c e e d across a c r o s s Darlirigton D a r l i n g t o n Bay Bay bridge bridqe Reset odometer o d o m e t e r to t o 0.0 0 . 0 km km at a t the t h e north north Reset 0.1 0. 1 km km STOP STOP 66 end e n d of o f bridge bridge Banded Banded Tonalite T o n a l i t e Gneiss Gneiss From F r o m here h e r e we w e will w i l l walk w a l k along a l o n g the t h e roadcuts r o a d c u t s on o n the t h e east east side t o Duffus D u f f u s Road Road and a n d examine e x a m i n e some sane s i d e of o fhighway h i g h w a y 596 5 9 6 up u p to e x p o s u r e s on o n this t h i s road r o a d immediately i m m e d i a t e l y west west of o f the t h e highway highway exposures (Figure ( F i g u r e 9). 9 ) . The T h e distinctive d i s t i n c t i v e banding b a n d i n g within w i t h i n these t h e s e rocks rocks is i s interpreted i n t e r p r e t e d to t o be b e a consequence c o n s e q u e n c e of o f the t h e intense intense d e f o r m a t i o n of o f aa heterolithic h e t e r o l i t h i cplutonic p l u t o n i complex c complex deformation consisting of: c o n s i s t i n g primarily p r i m a r i l y of: - fine f i n e to t o medium medium g rgrained, a i n e d f bhiotite iotite ± k hornblende h o r n b l e n d e ttonalite onalite — to t o leuco—torialite leuco- t o n a l i t e - fine f i n e grained g r a i n e d amphibolite a m p h i b o l i t e with w i t h associated a s s o c i a t e d diorite— d iorite— �91 quartz q u a r t z diorite diorite variously - v a r i o u s l y deformed d e f o r m e d granitic g r a n i t i c pegmatite p e g m a t i t e dikes dikes —- K— K - feldspar f e l d s p a r seams s e a m s and and megacrysts megacrysts Note N o t e the t h e tight t i g h t folding f o l d i n g and a n d shallow s h a l l o w angle a n g l e discordancies discordancies in i n gneissosity. g n e i s s o s i t y . Cross—cutting C r o s s - c u t t i n g relationships r e l a t i o n s h i p s between between the t h e vvarious a r i o u s tonalite t o n a l i t e phases p h a s e s are a r e present p r e s e n t but b u t are a r e not not abundant, a n i s o t r o p y in in a b u n d a n t possibly p o s s i b l y because b e c a u s e pre—existing p r e - e x i s t i n g anisotropy the t h e rock r o c k has h a s controlled c o n t r o l l e d the t h e emplacement e m p l a c e m e n t of o f subsequent subsequent intrusive i n t r u s i v e phases. p h a s e s . Discordant D i s c o r d a n t contacts c o n t a c t s are a r e difficult difficult to t o recognize r e c o g n i z e due d u e to t o intense i n t e n s e transposition t r a n s p o s i t i o n into i n t o the the plane p l a n e of o f the t h e gneissosity. gneissosity. - 3.4 3 . 4 km km STOP M e t a v o l c a n i c Amphibolite Amphibolite STOP 77 Metavolcanic The is on o n the t h e west w e s t side s i d e of o f the t h e road road !I'he outcrop o u t c r o p is approximately metres south s o u t h of o f the t h e junction j u n c t i o n between between a p p r o x i m a t e l y 100 100 metres Highway a n d 10). 10). Highway 596 596 and a n d the t h e Kenora K e n o r a bypass b y p a s s (Figures ( F i g u r e s 88 and The The principal p r i n c i p a l rock r o c k type t y p e in i n this t h i s outcrop o u t c r o p is is aa fine fine grained, t o banded b a n d e d amphibolite. amph i b o l i t e . g r a i n e d f equigranular, e q u i g r a n u l a r massive m a s s i v e to In I n lakeshore l a k e s h o r e exposures e x p o s u r e s 1 to t o 22 km km east e a s t of o f here h e r e on on the the Winnipeg W i n n i p e g River R i v e r system, s y s t e m f such s u c h banding b a n d i n g can c a n be be clearly clearly shown shown to t o represent r e p r e s e n t highly h i g h l y flattened f l a t t e n e d pillow p i l l o w structures. structures. Also diagnostic of a volcanic origin Also d i a g n o s t i c o f a v o l c a n i c o r i g i n are a r e the t h e presence presence of to o f calc—silicate c a l c - s i l i c a t e pods p o d s and and bands b a n d s that t h a t are a r e interpreted i n t e r p r e t e d to be b e metamorphosed m e t a m o r p h o s e d seawater s e a w a t e r alteration a l t e r a t i o n phenomena. p h e n o m e n a . With With the t h e exception e x c e p t i o n of o f the t h e example e x a m p l e discussed d i s c u s s e d at a t stop s t o p 3. 3 . such such calcium—rich c a l c i u m - r i c h mineral m i n e r a l assemblages a s s e m b l a g e s have h a v e not n o t been b e e n noted noted within a m p h i b o l i t e s for f o r which w h i c h aa mafic m a f i c dike d i k e origin o r i g i n can can w i t h i n amphibolites be demonstrated. b e demons t r a t e d . Concordant C o n c o r d a n t sheets s h e e t s of o f medium medium grained g r a i n e d biotite b i o t i t e tonalite tonalite constitute 25 percent of the outcrop. A narrow, A n a r r o w , fine fine c o n s t i t u t e 25 percent of t h e outcrop. grained g r a i n e d diabase d i a b a s e dike, d i k e f interpreted i n t e r p r e t e d to t o be be of o f Middle M i d d l e to to Late 1i t h o l o g i e s L a t e Precambrian P r e c a m b r i a n age, a g e crosscuts c r o s s c u t s all a l l other o t h e r lithologies in i n the t h e outcrop. outcrop. 1 3.5 3 . 5 km km Kenora K e n o r a bypass bypass 4.35 4 . 3 5 km km Amphibolitic A m p h i b o l i t i c metabasalt m e t a b a s a l t with w i t h pegmatite p e g m a t i t e dikes dikes (alternate ( a l t e r n a t e stop) stop) 4.9 4 . 9 km km STOP STOP 8A. 8 A . Pegmatite P e g m a t i t e —- Tonalite T o n a l i t e Gneiss G n e i s s Complex Complex We W e will w i l l stop s t o p at a t aa road r o a d into i n t o aa gravel g r a v e l pit p i t on on the t h e north north side s i d e of o f the t h e highway. highway. Outcrops O u t c r o p s on on the t h e south s o u t h side s i d e of o f the t h e road r o a d consist c o n s i s t of of tonalite g n e i s s with w i t h minor m i n o r ainphibolite a m p h i b o l i t e enclaves e n c l a v e s and and t o n a l i t e gneiss abundant a b u n d a n t pegmatoid p e g m a t o i d phases. p h a s e s . The T h e deformed d e f o r m e d pegmatoid pegmatoid rocks r o c k s occur o c c u r as a s concordant c o n c o r d a n t to t o sub—concordant s u b - c o n c o r d a n t sheets s h e e t s that that t o alkali a l k a l i granite g r a n i t e to to r a n g e in i n composition c o m p o s i t i o n from f r o m granite g r a n i t e to range microcline m i n o r quartz. q u a r t z . The The latter l a t t e r composition c o m p o s i t i o n is is m i c r o c l i n e 5 minor not n o t that t h a t of o f aa magmatic m a g m a t i c rock r o c k and and it i t is is likely l i k e l y that t h a t some some or o r all a l l of o f these t h e s e pegmatoid p e g m a t o i d phases p h a s e s are a r e generated g e n e r a t e d by by vapour v a p o u r phase p h a s e transfer t r a n s f e r and a n d metasomatism m e t a s o m a t i s n rather r a t h e r than than crystallized from silicate melts. Some c r y s t a l l i z e d f r o m s i l i c a t e me1 ts Some phases, phases however, h o w e v e r f do d o have h a v e granitic g r a n i t i c minimum minimum melt m e l t composition c o m p o s i t i o n and and it i t is is not n o t unreasonable u n r e a s o n a b l e to t o expect e x p e c t that t h a t the t h e presence p r e s e n c e of o f aa . �92 ++ + mixed gneissic tonalltegt-anit~cpegmatite gneissic tonalite amphibolite ( m e t a b a s a l t ) + -1 + + Figure F i g u r e 10: 1 0 : Geologic G e o l o g i cmap map of of an anarea a r e aalong a l o n Highway g Highway596 596 between between the the Rabbit Rabbit Lake Lake ffault a u l t and and the t h e Dalles D a l l e s batholith b a t h o l i t h with w i t h the the locations l o c a t i o n s of of stops s t o p s 77 and and 8. 8 . Refer R e f e r to t o figure f i g u r e 88 for f o r the the location l o c a t i o n of of this t h i smap. map. �93 vvapor a p o r pphase h a s e ccould o u l d initiate i n i t i a t e partial p a r t i a l melting m e l t i n g of o f the the The microcline ttonalite. onalite. T h e ggeometry e o m e t r y oof f the the m i c r o c l i n e rich r i c h phase phase ranges a n 2 swell r a n g e s from f r o m continuous c o n t i n u o u s planar p l a n a r sheets s h e e t s to t o pinch p i n c h and swell sheets s h e e t s to t o isolated i s o l a t e d microcline m i c r o c l i n e megacrysts. megacrysts. A number n u m b e r of of uundeformed n d e f o r m e d ggranitic r a n i t i c pegmatite p e g m a t i t e dikes d i k e s which w h i c h exhibit exhibit a r e present p r e s e n t in i n the the ccompositional o m p o s i t i o n a l and a n d textural t e x t u r a l zonation z o n a t i o n are outcrop. outcrop. STOP 8B. Standing 8B. S t a n d i n g oon n the t h e south s o u t h lip l i p (but ( b u t not n o t to t o close close are tto o the t h e edge e d g e —- there there a r e ddangerous a n g e r o u s overhangs) o v e r h a n g s ) of o f the the gravel w e s t of o f the the g r a v e l pit p i t approximately a p p r o x i m a t e l y 100 1 0 0 metres west turn—off, s e e on o n the t h e opposite o p p o s i t e side s i d e of o f the t h e pit pit t u r n - o f f I oone n e can c a n see D a l l e s bbatholith a t h o l i t h (furthest ( f u r t h e s t away), a w a y ) I in in eexposures x p o s u r e s oof f the t h e Dalles m e t a b a s a l t unit u n i t (Figure (Figure ccontact o n t a c t with w i t h an a n amphibolitic a m p h i b o l i t i c metabasalt Near the t h e bbottom o t t o m oof f the t h e pit p i t the t h e amphibolite a m p h i b o l i t e unit unit 110). 0 ) . Near is i s in i n contact c o n t a c t with w i t h pegmatite—tonalite p e g m a t i t e - t o n a l i t e gneiss g n e i s s such s u c h as as seen This s e e n in i n the t h e outcrops o u t c r o p s discussed d i s c u s s e d above. above* T h i s thin thin (approximately m e t r e s ) amphibolite a n p h i b o l i t e unit u n i t is is ( a p p r o x i m a t e l y 100 1 0 0 metres) laterally l a t e r a l l y ppersistent e r s i s t e n t for f o r approximately a p p r o x i m a t e l y 15 1 5 km k~ along a l o n g the the Dalles D a l l e s —- gneiss g n e i s s ccontact. ontact. A ssimilar i m i l a r amphibolite a m p h i b o l i t e unit u n i t occurs o c c u r s around a r o u n d the t h e Herb H e r b Lake Lake The ppluton l u t o n 38 3 8 km to t o the t h e east—northeast e a s t - n o r t h e a s t of o f here. here. T h e Herb Lake many oof L a k e ppluton l u t o n hhas a s many f the t h e ccharacteristics h a r a c t e r i s t i c s of o f the the Dalles D a l l e s bbatholith a t h o l i t h and a n d the t h e ggneisses n e i s s e s and a n d amphibolites amphibolites are r e ddeformed e f o r n e d into i n t o a large, l a r g e I recumbent, recumbentI aaround r o u n d tthis h i s unit unit a domed upwards nnappe—like a p p e - l i k e structure s t r u c t u r e domed u p w a r d s by b y the t h e Herb H e r b Lake Lake One ssample pluton e t al., a l . I 1983). 1983). One a m p l e from f r o m the the p l u t o n (Beakhouse ( B e a k h o u s e et rroot o o t zone z o n e oof f this t h i s complex c o m p l e x in i n the t h e Daniels D a n i e l s Lake L a k e area a r e a has has to that 1985) a similar age (2837 Ma, Corfu et al., a s i m i l a r a g e ( 2 8 3 7 MaI C o r f u e t a l . I 1 9 8 5 ) t o t h a t of of This the t h e banded b a n d e d tonalite t o n a l i t e gneisses g n e i s s e s in i n the t h e Kenora K e n o r a area. area. T his rraises a i s e s the t h e possibility p o s s i b i l i t y that t h a t the t h e 2.83—2.85 2 . 8 3 - 2 . 8 5 Ga G a grieisses gneisses in the Kenora area may be in large part allochthonous. be i n l a r g e p a r t a l l o c h t h o n o u s . i n t h e Kenora area 9.8 9 . 8 km Diorite STOP 99 ((optional) optional) D i o r i t e Intrusion I n t r u s i o n Breccia Breccia — - PPsuedo— suedocconglomerate onglomerate Outcrop O u t c r o p oon n the t h e north n o r t h side s i d e of o f the t h e highway highway This T h i s intrusion i n t r u s i o n bbreccia r e c c i a contains c o n t a i n s abundant a b u n d a n t fragments fraqments rrepresenting e p r e s e n t i n g a wide w i d e range r a n g e of o f rock r o c k types t y p e s and a n d resembles r e s e m b l e s aa Mafic M a f i c to t o ultramafic u l t r a m a f i c fragments fragments cconglomerate. onglomerate. Enclaves ppredominate. redominate. E n c l a v e s of o f similar s i m i l a r lithologies l i t h o l o g i e s are are common common in i n ddioritic i o r i t i c phases p h a s e s of o f the t h e Trout T r o u t Lake L a k e pluton p l u t o n to to Intermediate the t h e west w e s t and a n d may be b e cognate c o g n a t e inclusions. inclusions. Intermediate tto o ffelsic e l s i c fraqments f r a q m e n t s are a r e also a l s o present p r e s e n t and a n d probably probably The matrix rrepresent e p r e s e n t accidental a c c i d e n t a l inclusions. inclusions. T he m a t r i x of o f the the breccia b r e c c i a is i s a medium grained, g r a i n e d I equigranular, e q u i g r a n u l a r I hornblende hornblende diorite. ' d iorite. 110.8 0 . 8 km kn Sandy S a n d y Lake Lake 12.0 1 2 . 0 km JJunction u n c t i o n —- ccontinue o n t i n u e straiqht s t r a i g h t ahead a h e a d on o n Hiqhway H i q h w a y 596 596 115.95 5 . 9 5 km STOP 10 STOP 10 ((optional) o p t i o n a l ) Megacrystic M e g a c r y s t i c Grariodiorite Granodiorite We will examine low W e w i l l e x a m i n e low roadcuts r o a d c u t s occurring o c c u r r i n g on o n both b o t h sides s i d e s of of the road. t h e road. The made to T h e sstops t o p s made t o this t h i s point p o i n t are a r e not n o t truly truly �Figure 11: t 0 ''S (O rr —•l CD II I—ri (I • :1) c Ci) 0 (Ic3 0 (1 ct CD 11D i—a 0 CD —• r•—i• (I HQ G e o l o g i c map o f t h e T r o u t Lake a r e a ( f r o m B e a k n o u s e , 1 9 8 3 ) i l l u s t r a t i n g t h e l o c a t i o n s o f s t o p s 10 a n d 1 1 . T h e l o c a t i o n o f t h i s f i g u r e is i l l u s t r a t e d i n f i g u r e 4. 0 o 0 0 0 0 III 11111 11111.11111 11111 II.: 11111 IIIIIIIII 0 00000000000 0 11111 0 11I 1111i1i1 Ililililil 1I1i1i1I III 1 II II 11 I1I1I' IllIllIlIllIll II!IIIIIIIIIIIIIIIIIIIIII 00°::°O00°o:0° 0 0 000 :000 0 0• ::: o000::: 00 ::.iIiIiIiI :::.:.i II 11111 IiI: I II III:I:I" II91I1I1I1y1i1I1I1y1I1I1I1II III 1111111111 1111111111111111111111I111111111i11 IIIIIIIIIiIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIItIIII III I: II II I il I I I I IIIIIII 0 : I 1 (I) . 11 CD 5 Q— (t — + . _ E r CD Z C rc r -_________________ II IIII ililil .IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IhIhIhIhIhIIIhIhIhIhIhIhIhIhIhIhIhIhIIIIthIhIIII IIIIIIJIIIIIIIIIIIIIIIIIIIIIIII1.IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII III1II.'.I III 1 1 ihihii IIhIIhIIhIhIhIhIhIhIhIhIhIhIhIhIhIIIhIIIIIhIhIhII I1I1III 0 0 :I: 11111 ..ihIhi'ihi'ihihihihihiIhih. 11111I.:.:.:..:.;.OIIIIIIIIIIIIIIIIIIIIIIIIIIII I ''—' ' _______________ 1I1I'I'i riihihihihihihihihihihihihihihihihiIhiII IIIIIII...........\IC.l)IIIIIIIIIIIIIIIIIIIIIIIIIIIII HHHI ::::::::::::IIIHIIIIIIIIIIIHIIIIIIIIII hIhIIIhIhIhIIIhIIIIIIIhIhIhIhIhI iII:i II III IIL 00 0IIIIIIIIIIIIIIIIIIIIIIIII II1IIIIIII1IIl1III1II1l1I1i1I1I1IIII1IIIIII1I1III1II1I1I1 00000 Oo 0 0000 F) — _____ �95 r e p r e s e n t a t i v e of o f the t h e nature n a t u r e of o f the t h e Winnipeg W i n n i p e g River River representative as b e l t . This T h i s reflects r e f l e c t s the t h e emphasis e m p h a s i s of o f the t h e field f i e l d trip t r i p as belt. w e l l a s l o g i s t i c a l c o n s i d e r a t i o n s and t h e d e s i r e t o well as logistical considerations and the desire to k e e p field f i e l d trip t r i p participants p a r t i c i p a n t s awake. a w a k e . When When considering considering keep regional t h e W a b i q o o n W i n n i p e g R i v e r i n t e r f a c e f r o m the Wabigoon—Winnipeg River interface from aa regional i t is i m p o r t a n t t o k e e p i n m i n d t h at p e r s p e c t i v e perspective it is important to keep in mind that r e l a t i v e l y h i g h l y g e o c h e m i c a l l y e v o l v e d , m a s s i v e , late late relatively highly geochemically evolved, massive, t o p o s t t e c t o n i c g r a n i t i c r o c k s p r e d o m i n a t e i n t h e to post—tectonic granitic rocks predominate in the t o their their W i n n i p e g River R i v e r belt, b e l t , in i n marked m a r k e d contrast c o n t r a s t to Winnipeg p a u c i t y i n t h e W a b i g o o n s u b p r o v i n c e . paucity in the Wabigoon subprovince. l a t e plutonic plutonic Many of o f the t h e granodiorites q r a n o d i o r i t e s within w i t h i n the t h e late Many c o m p l e x e s a r e c h a r a c t e r i z e d by t h e p r e s e n c of complexes are characterized by the presencee of m i c r o c l i n e m e g a c r y s t s s u c h as a r e a b u n d a n t i this microcline megacrysts such as are abundant inn this o u t c r o p . This p a r t i c u l a r u n i t i s , h o w e v e r , a t y p i c a l in in outcrop. This particular unit is, however, atypical a r e a b u n d a n t i n p a r t s o f t h a t a m p h i b o l i t e i n c l u s i o n s that arnphibolite inclusions are abundant in parts of ( i n contrast contrast t h e unit u n i t and a n d both b o t h hornblende h o r n b l e n d e and a n d biotite b i o t i t e (in the t o b i o t i t e a l o n e i n most g r a n o d i o r i t e s ) a r e p resent. to biotite alone in most granodiorites) are present. T h e s e d i f f e r e n c e s , t o g e t h e r w i t h its a s s o c i a t i o n with w i t h aa These differences, together with its association ma i c p l u t o n ( F i g u r e 1 1 ) , s u g g e s t it may h a v e a mafic pluton (Figure 11), suggest it may have a d i f f e r e n t origin. origin. different 19.35 19.35 1 1 (optional) ( o p t i o n a l ) Trout T r o u t Lake L a k e quartz q u a r t z diorite diorite STOP 11 STOP 'The o u t c r o p o n t h e e a s t s i d e o f t h e r o a d c o n s i s t s o f The a r t z d diorite i o r i t e to to i n h o m o g e n e o u s h ohornblende—biotite r n b l e n d e - b i o t i t e q uquartz inhomogeneous d i o r i t e containing a wide v a r i e t y o f i n c l u s i o n s which a r e a l l more maÂi c t h a n t h e h o s t . The The nature n a t u r e of of the the . e n c l a v e s f o r m a c o n t i n u u m f r o m s h a r p l y b o u n d e d enclaves form a continuum from sharply bounded i n c l u s i o n s t o d i f f u s e l y bounded i n c l u s i o n s to d i f f u s e m a f i c rich r i c h patches. p a t c h e s . It I t is is not n o t clear c l e a rhow how much much of o f the the mafic a n d represent r e p r e s e n t disrupted d isrupted a m p h i b o l e could c o u l d be b e xenocrystic x e n o c r y s t i c and amphibole u l t r a m a f i c enclaves. e n c l a v e s . AA sample s a m p l e from f r o m this t h i s outcrop o u t c r o p yields yields ultramafic a U-Pb z i r c o n a g e o f 2 7 0 0 2 M a ( B e a k h o u s e 1 9 8 3 ) a U—Pb zircon age of 2700 ± 2 Ma (Beakhouse 1983). . outcrop on the east side of the road consists of diorite containing a wide variety of inclusions which are all more mafic than the host. inclusions to diffusely bounded inclusions to diffuse * R e t u r n to t o the t h e junction j u n c t i o n of o f Highway Highway 596 596 and a n d the t h e Kenora K e n o r a bypass b y p a s s —Return t u r n west w e s t (right) ( r i g h t ) on o n the t h e bypass b y p a s s and a n d proceed p r o c e e d 5.7 5 . 7 km km and a n d stop s t o p just just turn b e f o r e t h e b r i d g e o v e r t h e o l d M i n a k i Road a n d t h e r a i l r o a d before the bridge over the old Minaki Road and the railroad tracks. tracks. STOP 12 1 2 Marginal M a r g i n a l Granodiorite G r a n o d i o r i t e -- Tonalite T o n a l i t e gneiss g n e i s s contact contact STOP O u t c r o p o n b o t h s i d e s of t h e r o a d c o n t a i n t h e c o ntact Outcrop on both sides of the road contain the contact b e t w e e n t h e M a r g i n a l g r a n o d i o r i t e a n d w e l l b a n d e d between the Marginal granodiorite and well banded 8 ) . The T h e south s o u t h end e n d of of the the t o n a l i t i c yneiss g n e i s s (Figure ( F i g u r e 8). tonalitic o u t c r o p consists c o n s i s t s of o f intensely i n t e n s e l ysheared s h e a r e dmegacrystic megacrys t i c outcrop g r a n o d i o r i t e containing c o n t a i n i n g aa few f e w flattened f l a t t e n e damphibolite amphibolite granodiorite i n c l u s i o n s and a n d highly h i g h l y deformed, d e f o r m e d , discordant d i s c o r d a n leuco— t leucoinclusions ttonalite o n a l i t e dikes. d i k e s . The The north n o r t h end e n d of o f the t h e outcrop outcrop t o n a l i t e —- quartz quartz c o n s i s t s of o f banded b a n d e d amphibolite a m p h i b o l i t e —- tonalite consists d i o r i t e gneiss. g n e i s s . Sills S i l l s of o f highly h i g h l y deformed, d e f o r m e d , megacrystic megacrys t i c diorite g r a n o d i o r i t e are a r e difficult d i f f i c u l t to t o recognize r e c o g n i z e but b u t occur occur granodiorite t h r o u g h o u t much much oof f the t h e outcrop o u t c r o p but b u t decrease d e c r e a s e in in throughout a b u n d a n c e tto o the t h e north. north. abundance H i g h w a y 17, 1 7 , turn t u r n east e a s t and a n d return r e t u r n to to C o n t i n u e on on Kenora K e n o r a bypass b y p a s s tot oHighway Continue Kenora. Ken ora. �96 Re R e ferences ferences Arth, A r t h , J.G. J . G. and a n d Hanson, H a n s o n , G.N., G. N. , 1972. 197 2. Quartz Q u a r t z diorites d i o r i t e s derived d e r i v e d by by partial p a r t i a l melting m e l t i n g of o f eclogite e c l o g i t e or o r amphibolite a m p h i b o l i t e at a t mantle m a n t l e depths: depths: Contributions C o n t r i b u t i o n s to t o Mineralogy M i n e r a l o q y and p . 161 -174. a n d Petrology, P e t r o l o g y , 37, 3 7 , p.161—174. Arth, J . G . and a n d Hanson, H a n s o n , G.N., G.N., 1975. Geochemistry G e o c h e m i s t r y and and origin o r i g i n of of A r t h , J.G. 1975. the t h e early e a r l y Precambrian P r e c a m b r i a n crust c r u s t of o f northeastern n o r t h e a s t e r n Minnesota: Minnesota: G e o c h i m i c a et e t Cosmochimica C o s m o c h i m i c a Acta, A c t a , 39, 3 9 , p.325—362. p . 325-362. Geochimica Bald, R. C. , 1981. 1 9 8 1 . Petrogenesis P e t r o g e n e s is of o f Early E a r l y Archean, A r c h e a n , gneissic gneissic B a l d , R.C., tonalite t o n a l i t e —- granodiorite g r a n o d i o r i t e from f r o m the t h e English E n g l i s h River R i v e rsubprovirice, subprovince, Gundy Gundy Lake Lake area, a r e a , northwestern n o r t h w e s t e r n Ontario: O n t a r i o : Unpublished U n p u b l i s h e d M.Sc. M. S c . thesis, t h e s i s , University U n i v e r s i t y of o f Manitoba, M a n i t o b a , l2Opp. 120pp. Bateman, B a t e m a n , J.D. J . D. , , 1939. 1 9 3 9 . Geology G e o l o g y and a n d gold g o l d deposits d e p o s i t s of o f the t h e Uchi—Slate Uch i - S l a t e L a k e s area, a r e a , Ontario O n t a r i o Department D e p a r t m e n t of o f Mines, M i n e s , Volume Volume 48, 4 8 , part p a r t 8, 8, Lakes p. p . 11—43. -43. Beakhouse, B e a k h o u s e , G.P., G . P . , 1975. 1975. The T h e English E n g l i s h River R i v e r subprovince: s u b p r o v i n c e : Centre C e n t r e for for Precambrian P r e c a m b r i a n Studies, S t u d i e s , 1975 1 9 7 5 Annual A n n u a l Report, R e p o r t , 51—66. 51-66. Beakhouse, B e a k h o u s e , G.P., G.P. , 1977. 1977. AA subdivision s u b d i v i s i o n of o f the t h e western w e s t e r n English English R i v e r subprovince: s u b p r o v i n c e : Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , 14, 14, River 1481—1489. 1 4 8 1 -1 489. Beakhouse, G. P a , 1983. 1 9 8 3 . Geological, G e o l o g i c a l , geochemical g e o c h e m i c a l and a n d Rb—Sr Rb-Sr and and B e a k h o u s e , G.P., U—Pb U-Pb zircon z i r c o n geochronological g e o c h r o n o l o g i c a l investigations i n v e s t i g a t i o n s of o f granitoid granitoid rocks r o c k s from f r o m the t h e Winnipeg W i n n i p e g River R i v e r belt, b e l t , northwestern n o r t h w e s t e r n Ontario O n t a r i o and and southeastern Ph .D. thesis, thesis , s o u t h e a s t e r n Manitoba: M a n i t o b a : unpublished u n p u b l is hed Ph.D. McMaster McMaster University, U n i v e r s i t y , Hamilton, H a m i l t o n , Ontario. Ontario. Beakhouse, B e a k h o u s e ,G.P. G.P. , 1985. 1985. The T h erelationship r e l a t i o n of s hsupracrustal i p of s u p r a c r u s t a l s e q u e n c e s to t o aa basement b a s e m e n t complex c o m p l e x in i n the t h e western w e s t e r n English E n g l i s h River River sequences subprovince. s u b p r o v i n c e . In, I n , Ayres, A y r e s ,L. L. D. D. Thurston, T h u r s t o n , P.C., P . C . , Card, C a r d ,K.K.D. D. and and Weber, Weber , W., W. , eds. e d s .: : Evolution E v o l u t i o n of o f Archean A r c h e a n supracrustal s u p r a c r u s t a l sequences, sequences, G e o l o g i c a l A s s o c i a t i o n o f C a n a d a , S p e c i a l P a p e r 2 8. Beakhouse, B e a k h o u s e , G.P. G.P. , , Stott, S t o t t , G.M., a n d S u t c l i f f e , R.H., R.H., 1983. 1983. Geological thet hKenora—Cedar G e o l o g i c a l Studies S t u d i e sini n e K e n o r a - C e d a r Lake Lake Area; A r e a ; p.5—10 p . 5 - 1 0 in in Summary Work, 11983, by the Summary o fofFField i e l d Work, 9 8 3 , by t h e Ontario O n t a r i o Geological Geological Survey, S u r v e y , edited e d i t e d by b y John J o h n Wood, Wood, Owen Owen L. L. White, W h i t e , R.B. R.B. Barlow, B a r l o w , and and A.C. Colvine, A.C C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper Paper 116; 1 1 6 ; 3l3p. 313p. Blackburn, B l a c k b u r n , C.E., C. E. ,1981. 1 9 8 1 . Kenora—Fort K e n o r a - F o r t FFrances r a n c e s ssheet. h e e t . Ontario Ontario Geological G e o l o g i c a l Survey, S u r v e y , Geological G e o l o g i c a l Compilation C o m p i l a t i o n Series, S e r i e s Map , Map2443, 2443, scale s c a l e1:253,440. 1:253,440. Blackburn, B l a c k b u r n , C.E., C . E . , Bond, B o n d , W.D., W . D . , Breaks, B r e a k s , F.W., F.W., Davis, D a v i s , D.W., D . W . , Edwards, Edwards, G.R. G . R . ,, Poulsen, P o u l s e n , K.H. K . 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Manifestations M a n i f e s t a t i o n s of of recent recent reconnaissance reconnaissance i n v e s t i g a t i o n s i n t h e English River subprovince, s u b p r o v i n c e , northern n o r t h e r n Ontario: O n t a r i o : Geotraverse G e o t r a v e r s e Conference, C o n f e r e n c e , 1977, 1977, University U n i v e r s i t y of o f Toronto, T o r o n t o , p.170—211. p.170-211. Breaks, W. D . , 1981. 1 9 8 1 . Precambrian P r e c a m b r i a n geology g e o l o g y of o f the the B r e a k s , F.W. F.W. and a n d Bond, Bond, W.D., English E n g l i s h River R i v e r —- Marchington M a r c h i n g t o n Lake Lake area. a r e a . Ontario O n t a r i o Geological Geological Survey, S u r v e y , Preliminary P r e l i m i n a r y Map Map P—2293, P - 2 2 9 3 , scale s c a l e1:63,360. 1:63,360. Breaks, B r e a k s , F.W., F.W., Bond, B o n d , W.D. W . D . and a n d Stone, S t o n e , D., D . , 1978. 1978. Preliminary Preliminary geological g e o l o g i c a l synthesis s y n t h e s is of o f the t h e English E n g l i s h River R i v e r Subprovince, Subprovince, , Geological Pssociation of Canada, Special Paper 28. G.M., and Sutcliffe, . . investigations in the English River �97 northwestern northwestern Ontario O n t a r i o and and its i t s bearing b e a r i n g upon upon mineral mineral exploration: e x p l o r a t i o n : Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper Paper 72, 55p. 7 2 , 55p. Brisbin, B r i s b i n W.C., W . C . , 1981. 1 9 8 1 . The The Winnetka W i n n e t k a Lake Lake stock, s t o c k , aa deformed d e f o r m e d Archean Archean pluton p l u t o n in i n northwestern n o r t h w e s t e r n Ontario, O n t a r i o , abstract. a b s t r a c t . Geological Geological Association A s s o c i a t i o n of o f Canada, C a n a d a , Abstracts A b s t r a c t s 6, 6 , p.A—6. p.A-6. 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Summary of o f Geochronology G e o c h r o n o l o g y Studies, S t u d i e s ,1977—1979, Pye, P y e , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 92, 92, �100 p. 44 5 5p. O j a k a n g a s , R.W., R.W., 1985. 1 9 8 5 . Review R e v i e w of o f Archean A r c h e a n Clastic C l a s t i c Sedimentation, Sedimentation, Ojakangas, C a n a d i a n Shield: S h i e l d : Major M a j o r Felsic F e l s i c Volcanic V o l c a n i c Contributions C o n t r i b u t i o n s to to Canadian T u r b i d i t e and a n d Alluvial A l l u v i a l Fan—Fluvial F a n - F l u v i a l Facies F a c i e s Associations: A s s o c i a t i o n s : in in Turbidite A y r e s , L.D. L. D. Thurston, T h u r s t o n , P.C., P.C., and a n d Card, C a r d , K.D., K. D. , and a n d Weber, W e b e r , W., W., Ayres, e d s , Evolution E v o l u t i o n of o f Archean A r c h e a n Supracrustal S u p r a c r u s t a l Sequences: S e q u e n c e s : Geological Geolog i c a l eds., A s s o c i a t i o n of o f Canada, C a n a d a , Special S p e c i a l Paper P a p e r 28. 28. Association P e t e r m a n , Z.E., Z . E . , 1979. 1 9 7 9 . Strontium S t r o n t i u m isotope i s o t o p e geochemistry g e o c h e m i s t r y of o f late late Peterman, A r c h e a n to t o late l a t e Cretaceous C r e t a c e o u s tonalites t o n a l i t e s and a n d trondhjemites: t r o n d h j emites : in in Archean B a r k e r , F., F . , ed., e d . , Trondhjemites, T r o n d h j e m i t e s , Dacites D a c i t e s and and Related R e l a t e d Rocks, Rocks, Barker, A m s t e r d a m , Elsevier, E l s e v i e r , p.133—147. p . 133-1 47. Amsterdam, S t o c k w e l l , C.H., C. H . , 1964. 196 4. Age determinations d e t e r m i n a t i o n s and a n d geological geological Stockwell, Age s t u d i e s . Part P a r t II. 11. Geological G e o l o g i c a l studies: s t u d i e s : Geological G e o l o g i c a l Survey S u r v e y of of studies. C a n a d a , P a p e r 64-17 (11). Canada, Paper 64—17(11). S t o n e , D., D . , 1977. 1977. The The Sydney S y d n e y Lake L a k e fault f a u l t zone: z o n e : Proceedings P r o c e e d i n g s of o f the the Stone, 1 9 7 7 G e o t r a v e r s e C o n f e r e n c e , P r e c a m b r i a n R e s e a r c h G r o u p , 1977 Geotraverse Conference, Precambrian Research Group, U n i v e r s i t y of o f Toronto, T o r o n t o , p.94—108. p.94-108. University T h u r s t o n , P.C. a n d B r e a k s , F.W., 1978. 1 9 7 8 . Metamorphic M e t a m o r p h i c and and tectonic tectonic Thurston, P.C. and Breaks, F.W., e v o l u t i o n o f t h e U c h i E n g l i s h R i v e r s u b p r o v i n c e : i n evolution of the Uchi—English River subprovince: in M e t a m o r p h i s m i nint the he C a n a d i a n SShield, h i e l d , Geological G e o l o g i c a l Survey S u r v e y of of Metamorphism Canadian C a n a d a , P a p e r 78-1 0 , 49-62. Canada, Paper 78—10, 49—62. T h u r s t o n , P.C. P.C. and a n d Fryer, F r y e r , B.J., B. J . ,1983. 1 9 8 3 . The The gechemistry g e c h e m i s t r y of of Thurston, r e p e t i t i v e cyclical c y c l i c a l volcanism v o l c a n i s m from f r o m basalt b a s a l t through t h r o u g h rhyolite r h y o l i t e in in repetitive t h e Uchi—Confederation U c h i - C o n f e d e r a t i o n greenstone g r e e n s t o n e belt, b e l t , Canada. Canada. the C o n t r i b u t i o n s to t o Mineralogy M i n e r a l o g y and a n d Petrology, P e t r o l o g y , 83, 8 3 , 204—226. 204-226. Contributions T r o w e l l , N.F., N . F . , Blackburn, B l a c k b u r n , C.E. C . E . and and Edwards, E d w a r d s , G.R., G . R . , 1980. 1980. Trowell, P r e l i m i n a r y synthesis s y n t h e s i s of o f the t h e Savant S a v a n t Lake L a k e —- Crow Crow Lake Lake Preliminary m e t a v o l c a n i c m e t a s e d i m e n t a r y b e l t , n o r t h w e s t e r n Ontario , metavolcanic — metasedimentary belt, northwestern Ontario, and i t s b e a r i n g upon m i n e r a l e x p l o r a t i o n . O n t a r i o Geological and its bearing upon mineral exploration. Ontario Geological S u r v e y , M i s c e l l a n e o u s P a p e r 8 9 , 3 0 p . Survey, Miscellaneous Paper 89, 30p. T r u e m a n , D.L., D. L . , 1975. 1975. Bird B i r d River R i v e— r - Winnipeg W i n n i p e g River R i v e r area: a r e a : in in Trueman, Summary o f F i e l d Work, 1 9 7 5 , M a n i t o b a D e p a r t m e n t o f M ines, Summary of Field Work, 1975, Manitoba Department of Mines, R e s o u r c e s a n d E n v i r o n m e n t a l M a n a g e m e n t , G e o l o g i c a l S e r vices Resources and Environmental Management, Geological Services B r a n c h , G e o l o g i c a l P a p e r 2/75. Branch, Geological Paper 2/75. v a n de d e Ramp, Kamp, P.C. P.C. and a n d Beakhouse, B e a k h o u s e ,G.P.., G.P., 1979. 1979. Paragneisses P a r a g n e i s s e s in i n the the van Pakwash L a k e a r e a , E n g l i s h R i v e r g n e i s s b e l t , n o r t h w e s t e r n Pakwash Lake area, English River gneiss belt, northwestern O n t a r i o : Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Science, S c i e n c e , 16, 1 6 , p.1753—1763. p . 1753-1 7 6 3 . Ontario: W e s t e r m a n , C., C . , 1977. 1 9 7 7 . Tectonic T e c t o n i c evolution e v o l u t i o n of o f aa part p a r t of o f the t h e English English Westerman, R i v e r subprovince, s u b p r o v i n c e , northwestern n o r t h w e s t e r n Ontario: O n t a r i o : unpublished u n p u b l i s h e d Ph.D. Ph .D. River t h e s i s , McMaster McMaster University, U n i v e r s i t y , Hamilton, H a m i l t o n , Ontario, O n t a r i o , p.292. p . 292. thesis, W i l s o n , H.D.B., H. D. B . ,1971. 197 1. The The Superior S u p e r i o r province p r o v i n c e in i n the t h e Precambrian Precambrian Wilson, o f Manitoba: M a n i t o b a : in i n Turnock, T u r n o c k , A.C., A . C . , ed., e d . , Geoscience G e o s c i e n c e Studies S t u d i e s in in of M a n i t o b a , G e o l o g i c a l A s s o c i a t i o n o f C a n a d a , S p e c i a l P a p e r 9, 9, Manitoba, Geological Association of Canada, Special Paper p.41-49. p.41—49. W i l s o n , H.D.B. H . D . B . and a n d Brisbin, B r i s b i n , W.C., W.C., 1963. Nature N a t u r e of o f the t h e granitic granitic Wilson, 1963. c r u s t in i n the t h e Superior S u p e r i o r province: p r o v i n c e : Abstract, A b s t r a c t , Geological G e o l o q i c a l Society Society crust of America, A m e r i c a , 76th 7 6 t h Annual A n n u a l Meeting, M e e t i n g , p.180. p . 180. of W i l s o n , H.D.B. H. D . B . and a n d Morrice, Morrice, M.G., M.G., 1977. 1 9 7 7 . The The volcanic v o l c a n i c sequence s e q u e n c e in in Wilson, W.R.A., C o l e m a n , L.C. L.C. and a n d Hall, Hall, A r c h e a n shields: s h i e l d s : in i n Baragar, B a r a g a r , W.R.A., Archean Coleman, J.M., e d s , Volcanic V o l c a n i c Regimes R e g i m e s in i n Canada, C a n a d a , Geological Geological J.M., eds., A s s o c i a t i o n of o f Canada, C a n a d a , Spec. S p e c . Paper P a p e r 16, 1 6 , p.355—374. p.355-374. Association J . L . , 1978. 1 9 7 8 . Rb—Sr Rb-Sr isotopic i s o t o p i c studies s t u d i e s of o f Archean A r c h e a n rocks r o c k s of of Wooden, J.L., Wooden, t h e eastern e a s t e r n Lac L a c Seul S e u l and a n d Kenora K e n o r a areas, a r e a s , English E n g l i s h River River the s u b p r o v i n c e , Ontario: O n t a r i o : in i n Smith, S m i t h , I.E.M. I . E . M . and a n d Williams, ~ i l l i a m sJ.G., ,J . G . , subprovince, e d s . , P r o c e e d i n g s , 1 9 7 8 ~ r c h e a n G e o c h e m i s t r y F i e l d eds., Proceedings, 1978 Archean Geochemistry Field C o n f e r e n c e , University U n i v e r s i t y of o f Toronto T o r o n t o Press, P r e s s , Toronto, T o r o n t o , Ontario, Ontario, Conference, p.131-149. p.131—149. . . �101 101 APPENDIX APPEND1 X Modal and a n a l y s e s of e l e c t e d samples t h e field f i e l d trip trip Modal and chemical chemical analyses of sselected samples from the area area Table 1: Table 1: trip trip a n a l y s e s for f o r samples samples from from the the area a r e a of of the t h e field field Modal analyses -- -Metavolcanic ---~--, ~e t ~ Rocks~ l - ~ ~e s DD lices lk --- -----Winnipeg -.-Winnipe2 River ~ i v e r Belt -~elt Wabigoon Wabigoon Intermediate Intermediate 2/5 2/9 29JA 323 7 n?T2 9 0 7~ --- 3U9 3 - 312 7 2 373-------27ZS-X 272 --- - -------- 270 ---s A plagio— plag ioclase c l a s e 39.3 39. 3 K— Kfeldspar— feldsparquartz q u a r t z tr tr horn— hornblende 60.0 60.0 biotite b i o t i t e —muscovite— muscoviteepidote e p i d o t e 0.3 0.3 opaque opaque tr tr sphene 0.4 sphene 0.4 zircon —zircon apatite a p a t i t e tr tr allanite a l l a n i t e —carbonate— carbonate- 23.0 23.0 26.3 26.3 29.9 29.9 45.9 45.9 46.2 46.2 25.0 25.0 - - - 50.2 50. 2 1.2 1.2 48.6 48.6 4.55 4. — - - - - 2.0 2.0 1.6 1.6 0.3 0.3 1.4 1.4 73.7 73.7 59.0 59.0 11.2 11.2 67.7 67.7 67.5 67.5 0.4 0.4 - — — 0.3 0.3 1.2 1.2 tr tr - — — - — 0. 0.88 - tr tr tr tr - - tr tr - 0.5 0.5 - 61. 61. 11 3. 3.33 - - - 0.9 0.9 1.8 1.8 tr tr tr tr tr tr 59.4 61.9 1. 1 0.5 26.4 30.6 — 6.2 1.2 1.2 tr — 10.4 — 0.8 tr 58.9 0.3 30.5 0.9 6.9 — 66.4 6.8 71.5 69.7 2. 3 19.2 22.1 2.3 21.0 5.4 3.0 — — 5.7 0.7 0.6 1.8 2.2 0.7 — — — 1.0 — — tr tr tr tr tr tr tr tr tr tr tr tr tr — — — — — — — 0.3 - - tr tr tr tr - 1.6 1.6 0.6 0.6 - Granodiorites Granodiorites tr tr tr 71.0 71.0 0.2 0.2 0. 11 0. 0.4 0.4 - 1.2 1.2 1.8 - Tonal Tonalites ites plagioclase p l ag i o c l as e K—feldspar K-feldspar quartz quartz hornblende hornblende biotite biotite muscovite muscovite epidote epidote opaque opaque sphene sphene zircon zircon apatite apatite allanite allanite carbonate carbonate - 33.0 33.0 3.0 3.0 0.3 0.3 - Mafic Mafic -TTtT - - 31.3 31.3 — - ---- --.- 48.0 17.4 26.5 40.8 13.2 34.8 3.8 2.2 4.2 4.6 1.5 2.1 tr tr tr tr �L_c[L tt T a b l e 2: --- tiesfroin the area o the Chemical a n a l ~ s o f s e l e c t e d samples from t h e a r e a o f t h e f l e l d t r i p . 1 WINNIPEG WINNIFEG RIVER R I E R BELT BELT META.W)LCANIC METAWLCANIC Type WABIWON W I C X I O N META.OLCANIC METAKILCANIC R(EKS R E G Rock Type WINNIPEG RIVER BELT DIKE ROCKS ~ Sampl e SnipI Number umber N SIO2 5102 AI203 A'2° Fe F e203 93 Feo PeG MgO M@ c a4 CaO NaO Na9 K20 '(20 TIO2 1102 '2'5 MnO MeG 84GF- 84GFB- 323 8007 8009 54.0 51.2 15.5 1.22 9.09 4.23 9.73 2.68 0.10 1.17 0.04 0.23 13.7 1.49 50.1 14.4 2.04 9.31 .24 .76 B3GPB- CO2 820 9.67 83GF 8010 275A 279 62.5 50.2 14. 3 13. 8 51.2 13.9 2.30 8.36 8.39 0. 9 5.31 83GP8 3.96 8.00 6.86 83GP8 11.3 5.09 4.33 1.52 2.21 4.07 2.69 0.04 0.89 0.02 0.19 0.12 0.45 0.81 11.50 1.56 0.21 1.27 0.04 0.81 0.20 0.09 0. Il 0.97 0.04 0.26 0.77 0.02 0.18 0.07 0.56 0.22 0.87 0. 11 0.52 0.07 0.08 0.76 7.73 11.9 7.51 9 33 120 10 170 10 16 9) 70 90 160 16 12 13 85 67 42 20 86 Rb 8 Sr 110 8 83 LI 8 Ba Y 10. 4 1.01 16 MARGI NL GRANODR* ITE 1.93 10.8 6.64 9.74 2.26 1.30 1.19 0.04 50.9 13.6 3.02 9.96 5.78 83GFU 83GPB 83GP8 83GFB 270 272 304A 3218 50.8 14.3 54.2 55.3 12.5 13.7 2.93 2.37 5.09 4.95 9.55 7.50 10.2 8.52 1.61 9.60 6.47 11.9 0.05 0.25 0.03 0.01 0.04 0.07 0.03 0.07 0.70 0.12 0.68 0.12 0.98 0.08 0.08 1.05 0.08 0.58 0.06 0.87 0.24 0.47 0.12 1.04 0.06 0.30 92 78 155 43 129 41 253 570 89 42 133 66 22 65 69 113 98 117 <10 107 l0 <10 118 97 103 Pb <10 <10 <10 <10 <10 <10 Zn 92 82 72 82 122 91 3.71 0.21 81 69 3.41 0.85 0.19 13 95 1.55 4.49 0.20 9 125 34 81 0.73 1.12 1.45 0.43 3.42 1.29 0.05 0.25 39) 106 3.35 0.47 0.09 0.07 18 NI 1.52 1.31 0.93 120 43 0.40 1.17 18 50 2.98 2.67 5.02 1.31 0.93 0.28 0.03 120 8 16.1 1.83 80 114 72.7 16.3 1.37 610 Cu 72.1 14.5 0.38 100 22 213 72.0 14.1 1.82 6 29 73.2 15.9 1.37 0.70 0.15 0.14 125 118 64.0 0.79 0.57 0.22 0.15 22 110 22 1.06 51 10 43 94 560 105 17 20 800 8 90 24 435 20 370 155 94 35 17 183 65 43 116 13 44 10 38 <10 80 <10 76 82 65 45 <10 126 18 321A 16.1 0.43 76 3200 69.9 0.81 16 320A 12.8 3.18 11.3 5.65 10.3 1. 74 86 BSGFB 51.2 3. 53 39 650 56 770 83GPE 16.0 2. 76 0.21 83GF 63.9 2.87 12 41 310 1.78 1 55 365 83GP8 2.05 17 Ii 83GFB- 83GBP 262 2900 3.20 4.48 10.7 19 387 49 50.4 13.6 309 83GI3 312 12 304 172 20 29OA 83GfB 48 64 43 254 98 128 1 B3GPB 11 130 16 88 45 Zr Co Cr WINNIPEG RIVER BELT TONLITES ROCKS ~ ii 0.29 2.69 0.70 3.51 3.77 1.00 0.38 0.06 0.05 0.06 0.29 1.03 1.39 0.16 0.00 0.02 0.16 0.00 0.03 74.9 14.5 0.36 0.22 1.09 0.87 0.30 0.18 2.00 1.70 3.48 3.80 3.67 2.97 0.21 0.12 0.01 0.00 0.03 0.04 0.05 0.14 0.10 0.42 0.07 0.36 0.06 3.02 0.04 1.16 0.45 2.88 5.20 4.61 1.02 0.20 73.1 14.9 0.06 0.72 51 76 85 350 28 570 165 130 24 260 25 625 20 240 12 58 840 59) 6 7 6 2 3 4 225 195 180 120 90 120 95 14 6 8 <5 <5 5 <5 7 9 <5 <5 10 18 <5 10 10 7 II 25 24 8 6 6 9 <5 5 <5 5 <5 <5 10 <10 10 12 124 60 <10 34 14 41 26 22 38 44 30 59 21 21 3 31 15 43 10 28 5 55 19 1 4 315 34 660 46 250 22 380 3 11 115 6 11 41 160 La 5 3 6 15 6 4 13 9 7 51 36 4 4 Ce 12 8 13 29 13 9 10 15 12 17 74 26 55 103 53 12 8 103 Nd 9 6 10 14 9 6 tO 10 7 34 36 24 10 3 36 21 14 40 12 Sm 2 2 5 3 3 2 4 3 1 4 7 8 5 1 8 3 2 3 Sm 2 2 5 3 3 2 4 3 1 4 7 8 5 1 8 3 2 3 Eu 0.9 0.6 0.9 0. 9 0. 8 0.6 0.8 0.9 0.6 1.0 1.6 1.0 1.1 0.5 1.4 0.8 0.6 0.6 Gd 4 3 5 3 3 3 3 3 3 4 5 3 4 I 6 2 2 2 Dy 2.4 2.0 4.0 2. 3.3 2.7 1.4 1.3 2.4 2.1 0.9 1.3 0.8 2.7 1.0 0.9 0.6 1.2 2.3 4.0 2.7 1.2 1.5 2.3 2.0 1.3 1.9 2.2 1.6 3.5 Yb 2.9 1.8 1.6 0.8 4 83GFB- 83GF8 300 313 0.4 0.8 1 4 0.3 0.4 1 0.5 0.2 2 0.6 0.3 18 9 1 1 0.4 1 1.1 0.5 C) I'.) �103 100- 100- 10 Wabigoon Metavolcanics Metavolcanics Wabigoon i I x 8 3 G P B 3 2 3 ,84GPB8007, 84GPB8007,84GPB2009 84GPB2009 183GPB323, 1 I I I Lace LaCe Nd Nd l t I I SmEuGd SmEuGd Yb Yb Dy Dy 100 Lace LaCe 1 Nd Nd I Sm EuGd SmEuGd Yb Yb Dy Dy I 100- 10 - 1 Winnipeg River River Metabasafts Metabasalts Winnipeg 1 84GPB8010 • 84GPB8O1O 10 1 Winnipeg River River Dike DikeRocks Rocks Winnipeg I I 1 I I Lace LaCe I Nd Nd I I I l l SmEuGd SmEuGd I I Dy Dy F Ifl Winnipeg River Metabasalt 1 £83GPB270 •830P8272 •83GPB321B - Winnipeg River Tonalite Winnipeg River Tonalite I I I _iI___ L a c e Nd Nd LaCe I I Yb Yb l I I Dy Dy Yb Yb l I I Fe203+ FeO + Ti02 Fe203+FeO+T102 Wabigoon Metavolcanics Metavolcanics o0Wabigoon A Winnipeg River Metavolcanics Winnipeg River Metavolcanics DikeRocks Rocks o Dike 83GPB32 1B I SmEuGd SmEuGd CAcaic—alkaline calc-alkaline CA tholeiite TTtholeiite I"'/83GPB32lB see Grunsky ( 1 9 8 1) 1981) of for calculation ternary components ternary components A M A1203 MgO F i g u r e 12. 12. C h o n d r i t e normalized n o r m a l i z e d rare r a r e earth e a r t h element e l e m e n t abundances abundances Figure Chondrite and m a j o r e l e m e n t t e r n a r y c l a s s i f i c a t i o n d i a g r a m f o r samples and major element ternary classification diagramss for samples from t h e f i e l d t r i p a r e a . from the field trip area. �V o l c a n i c FFades acies AA Volcanic IInterpretation n t e r p r e t a t i o n of o f the t h e Berry B e r r y River R i v e r Formation1 Formation1 I n t r o d u c t o r y Discussion D i s c u s s i o n and a n d Field F i e l d Guide Guide Introductory 31st A n n u a l I n s t i t u t e o n L a k e S u p e r i o Geology 31st Annual Institute on Lake Superiorr Geology K e n o r a , O n t a r i o Kenora, Ontario by G.W. Johns Johns G.W. P r e c a m b r i a n G e o l o g y Section Section Precambrian Geology O n t a r i o G e o l o q i c a l Survey Ontario Geological Survey 7 7 G r e n v i l l e S t. 77 Grenville St. T o r o n t o , O n t . Toronto, Ont. 1B3 N5S 1B3 M5S 1 This T h i s guide g u i d e is is published p u b l i s h e d with w i t h permission p e r m i s s i o n of o f the t h e director d i r e c t o r of o f the the 1 O n t a r i o Geological G e o l o g i c a l Survey. Survey. Ontario �106 INTRODUCTION INTRODUCTION -Edy Theof s t uArchean d y o f A r cpyroclastic h e a n p y r o c l a s rocks t i c r o c khas s h aevolved s e v o l v e d from f r o m aa simple o the t h e ternary t e r n a r y classifica— classificas i m p l e tuff—agqloinerate t u f f - a g g l o m e r a t e ssubdivision u b d i v i s i o n tto tions N o w I an a n important i m p o r t a n t tool tool t i o n s oof f Fisher F i s h e r (1966) ( 1 9 6 6 ) and and Schmid Schmid (1981). ( 1 9 8 1 ) . Now, in Archean i n the t h e sstudy t u d y oof f A r c h e a n ppyroclastics y r o c l a s t i c s iis s ffades a c i e s analysis a n a l y s i s (Ayres, (AyresI Tasse 11977; 977; T a s s e eett aal., l e I 1978 1 9 7 8 and and Lichtblau L i c h t b l a u and and Dimroth, D i m r o t h I 1980). 1 9 8 0 ) . This This field  i e l d trip t r i p will w i l l examine e x a m i n e a deformed d e f o r m e d amphibolite a m p h i b o l i t e metamorphic m e t a m o r p h i c grade grade Archean A r c h e a n ssubaqueous u b a q u e o u s ppyroclastic y r o c l a s t i c sequence s e q u e n c e (the ( t h e Berry B e r r y River River formation) which formation) w h i c h tthe h e aauthor u t h o r hhas a s ssubdivided u b d i v i d e d iinto n t o vvolcanic o l c a n i c ffades. acies. The The purpose p u r p o s e oof f this t h i s field f i e l d trip t r i p is i s to t o examine e x a m i n e the t h e evidence evidence for  £ o the t h e subdivision s u b d i v i s i o n of o f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n (Warclub ( W a r c l u b group) group) into volcanic IIt t iis s iimportant m p o r t a n t to t o sstudy t u d y Archean A r c h e a n pyro— pyrointo v o l c a n i c facies. facies. clastic f a c i e s model, m o d e l , when when c l a s t i c rocks r o c k s using u s i n g facies f a c i e s analysis a n a l y s i s because b e c a u s e aa facies w i l l lead l e a d to t o an a n understanding u n d e r s t a n d i n g of o f volcanic v o l c a n i c stratigraphy stratiqraphy ddeveloped, e v e l o p e d I will and ddepositional and e p o s i t i o n a l environment e n v i r o n m e n t and and thus t h u s the t h e placement p l a c e m e n t of o f known known o r e bodies. bodies. vvolcanogenic o l c a n o g e n i c ore The wasooriginally T h e formation f o r m a t i o n was r i g i n a l l y described d e s c r i b e d during d u r i n g aa 33 year year 1:15,840 detailed 1 : 1 5 I 840 d e t a i l e d mapping m a p p i n g programme programme c carried a r r i e d out o u t by b y the t h e Ontario Ontario Results Geological G e o l o g i c a l Survey. Survey. R e s u l t s of o f this t h i smapping m a p p i n g (Johns ( 3 J o h n sand a n d Richey, RicheyI 1982; 9 8 4 ) are are 1 9 8 2 ; Johns J o h n s and and Davison, D a v i s o n I 1983 1 9 8 3 and a n d J o h n s e t a l a I 11984) maps from aavailable v a i l a b l e as a s preliminary p r e l i m i n a r y maps f r o m the t h e Office O f f i c e of o f the t h e Mining Mining Additional Recorder, R e c o r d e r I Ministry M i n i s t r y of o f Natural N a t u r a l Resources, R e s o u r c e s I Kenora. Kenora. Additional were ccarried out arried o u t dduring u r i n g the t h e summer of o f 1984 1984 and a n d the the iinvestigations n v e s t i g a t i o n s were A preliminary facies p r e l i m i n a r y version v e r s i o n of o f the t h e model model f a c i e s model m o d e l was was developed. developed. iis s ooutlined u t 1 i n e d in i n Johns J o h n s (1984). ( 1984). The The Berry B e r r y River R i v e r formation f o r m a t i o n occurs o c c u r s 48 4 8 km southeast s o u t h e a s t of o f Kenora Kenora a n d 2) 2 ) outcropping o u t c r o p p i n q along a l o n g the t h e shore s h o r e of o f Long b n g Bay Bay and and ((figures f i g u r e s 1 and The fformation Lobstick i s ppart a r t oof f the the L o b s t i c k Bay, Bay, Lake Lake of o f the t h e Woods. Woods. The o r m a t i o n is Warciub W a r c l u b group, q r o u p I aa predominantly p r e d o m i n a n t l y metasedimentary m e t a s e d i m e n t a r y sequence, s e q u e n c e I found f o u n d in in the western the w e s t e r n portion p o r t i o n oof f the t h e Archean A r c h e a n Wabigoon subprovince s u b p r o v i n c e of o f the the Superior S u p e r i o r Province. Province. Johns et al., 1 SUPERIOR PROVINCE PROVINCE The of comprised o f Archean A r c h e a n age a g e rocks r o c k s with with The Superior S u p e r i o r Province, P r o v i n c e I comprised regional r e g i o n a l easterly e a s t e r l y trending t r e n d i n g structures, s t r u c t u r e s , extends e x t e n d s in i n Ontario O n t a r i o from from the t h e Manitoba M a n i t o b a border b o r d e r east e a s t to t o the t h e Quebec Q u e b e c border b o r d e r and and is i s overlairi o v e r l a i n to to by P Paleozoic t o the t h e south s o u t h by b y Proterozoic Proterozoic tthe h e nnorth o r t h by a l e o z o i c ssediments e d i m e n t s and a n d to The S Superior metasediments m e t a s e d i m e n t s and a n d metavolcanics. metavolcanics. The u p e r i o r Province P r o v i n c e has h a s been been subdivided s u b d i v i d e d into i n t o subprovinces s u b p r o v i n c e s based b a s e d on o n differences d i f f e r e n c e s in i n structural structural e t al., a l . , 1970). 1970). sstyles t y l e s and a n d lithology l i t h o l o g y (Stockwell ( S t o c k w e l l et These t e n d e n c y to t o decrease d e c r e a s e in i n age age T h e s e subprovinces s u b p r o v i n c e s show some tendency ffrom r o m north n o r t h to t o south s o u t h (Krogh ( K r o g h and and Davis, D a v i s I 1971 1 9 7 1 and a n d Krogh Krogh et e t al., al., and aare t o as a s the t h e Sachigo S a c h i g o subprovince, s u b p r o v i n c e I Berens Berens 11984) 9 8 4 ) and r e rreferred e f e r r e d to subprovince, River u b p r o v i n c e I Uchi Uchi subprovince, s u b p r o v i n c e , English E n g l i s h River R i v e r subprovince subprovince River s n t o the t h e Ear E a r Falls F a l l s—- Manigotagan M a n i g o t a g a n ssubprovince u b p r o v i n c e and and the the ((subdivided s u b d i v i d e d iinto Winnipeg W i n n i p e g 2River i v e r subprovince, s u b p r o v i n c e I Beakhouse, B e a k h o u s e I 1977), 1977 ) IWabigoon Wabigoon subprovince, Q u e t i c o subprovince s u b p r o v i n c e and and Abitihi A b i t i b i subprovince. s u b p r o v i n c e . The s u b p r o v i n c e I Quetico Berens B e r e n s River R i v e r and and Winnipeg W i n n i p e g River R i v e r subprovinces s u b p r o v i n c e s are a r ecomposed composed Ear Falls F a l l s—- Manigotagan Manigotagan ppredominantly r e d o m i n a n t l y oof f qgranitoid r a n i t o i d rocks r o c k s and a n d the t h e Ear The and Quetico s u b p r o v i n c e s are a r e metasedimentary m e t a s e d i m e n t a r y terranes. terranes The Q u e t i c o subprovinces remaining low r e m a i n i n g subprovinces s u b p r o v i n c e s are a r e characterized c h a r a c t e r i z e d by by comparatively c o m p a r a t i v e l y low metamorphic m e t a m o r p h i c grade g r a d e metavolcanics m e t a v o l c a n i c s and and subordinate s u b o r d i n a t e metasedimentary m e tased imentary rocks r o c k s intruded i n t r u d e d by by granitoid g r a n i t o i d batholiths. batholiths. . �107 Figure F i g u r e 1: 1: Location L o c a t i o n oof f Sioux S i o u x Narrows, Narrows, Ontario O n t a r i o with w i t h respect r e s p e c t to to that t h a t portion p o r t i o n of o f the t h e United U n i t e d States S t a t e s centered c e n t e r e d on on Duluth, D u l u t h , Minnesota. Minnesota. �_______ _____ ______ ________ _____ 108 * * * * * * * * + 4- * ***. * 4- * + * + + * ++:: + * + * * * * * + * * + * + * 4- .- + + * * + + * ** + * * + + * *++ — *::*+::::+45c USA ** **+ : * ++ +:::+ 51 * * :*1+>+*tI ——---- - + P4-S. * + + 'S * * * * * + + * * + + *_, * * * + + + + - _* + * * * H + + + + + * * * ** + + S.- + + + + + * + * 4- + + + + + * + + + 4- + + + + + + + * * * + + 4- + + ÷ ', + * + + + ::,* + + * + + + + + * * * + * * * * * * + + * * + + * * * * * * 4- * + + * + + + + + * * * * * + + + * * * + * + * * + •+ * + + + + + * + + + +_+ + + + 4- + * + * * * + + + * + + + + 4- + + + + + 4- + + + * + + + -'S + * + + + + * + + + * * + + + + + + + + + + * + * + + * + * + + * + * + + + + + + * + ++ granitoid rocks mafic plutonic rocks potassic pjütonic rocks 1::::::] metasedimentary rocks felsic metavolcanic rocks sodic plutonic rocks maf Ic metavolcanic rocks Lii gneissic granitoid rocks (unsubdivided) I F i g u r e 2: 2: Figure Location L o c a t i o n oof f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n with w i t h respect respect to t o the t h egeneral g e n e r a lgeology g e o l o g yofo fthe t hwestern e w e s t e rWabigoon n Wabiqoon subprovince. subprovince. �109 - WABIGOON SUBPROVINCE SUBPROVINCE --TFre-WalqooFSTTbprovince i s aeast n e a sto t t onortheast n o r t h e a s t trending trending TWbfgoöiTUbprovince is an metavolcanic—metasediment—granitoid m e t a v o l c a n i c - m e t a s e d i m e n t - q r a n i t o i d terrane. terrane. I t is is bbounded o u n d e d on on It the by Winnipeg t h e north north b y the the W i n n i p e g River R i v e r subprovince s u b p r o v i n c e and a n d on o n the t h e south s o u t h by by the It t h e Quetico Q u e t i c o subprovince. subprovince. I t is is approximately a p p r o x i m a t e l y 200 2 0 0 km in i n width w i d t h and and is i s at a t least l e a s t 700 7 0 0 km km in i n length, l e n q t h , extending e x t e n d i n g beneath b e n e a t h Paleozoic P a l e o z o i c cover cover of o f the t h e James Bay Bay lowlands l o w l a n d s and a n d Williston W i l l i s t o n basin b a s i n to t o the t h e east e a s t and and west w e s t respectively. respectively Trowell T r o w e l 1 et e t al. a l . (1980) ( 1 9 8 0 ) studied s t u d i e d the t h e Wabigoon W a b i q o o n Suhprovince Subprovince b e t w e e n Kakagi K a k a g i (Crow) ( C r o w ) Lake L a k e and a n d Savant S a v a n t Lake L a k e and a n d made m a d e the t h e following following between observations. 1) metavolcanic—metasedimentary belts observations. 1 ) TThe h e metavolcanic-metasedimentary b e 1 ts generalgenerally 2) l y face f a c e inwards. inwards. 2 ) Thick T h i c k basal b a s a l high h i g h Mg Mq tholeiitic t h o l e i i t i c basalt basalt a s e m b l a g e s occur o c c u r at a t the t h e outer o u t e r edges e d g e s of o f the t h e greenstone g r e e n s t o n e belt. belt. 3) asemblages 3) Mixed M i x e d mafic maÂi c to t o felsic f e l s i c sequences s e q u e n c e s overlying o v e r l y i n g the t h e basal b a s a l assemblage assemblage occur o c c u r in i n the t h e internal i n t e r n a l portion p o r t i o n of o f the t h e greenstone g r e e n s t o n e belts b e l t s and a n d contain contain thick t h i c k sequences s e q u e n c e s oof f ma mafic i c fflows l o w s t that h a t are a r e mostly m o s t l y toward t o w a r d tthe h e top t o p of of the 4) t h e mixed m i x e d assemblage. assemblaqe. 4 ) Clastic C l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are associated mixed mafic a s s o c i a t e d with w i t h the the m i x e d ma i c to t o felsic f e l s i c portion p o r t i o n of o f the t h e meta— metaThe volcanic v o l c a n i c sequence. sequence. T h e metavolcanics m e t a v o l c a n i c s and a n d metasediments m e t a s e d i m e n t s have h a v e been been isoclinally i s o c l i n a l l y folded f o l d e d into i n t o synforms s y n f o r m s and a n d antiforms. antiforms. Available A v a i l a b l e high h i g h precision, p r e c i s i o n , U—Pb U-Pb zircon z i r c o n geochronological geochronolog i c a l investigations metavolcanic i n v e s t i g a t i o n s oof f intermediate i n t e r m e d i a t e to t o felsic felsic m e t a v o l c a n i c rocks r o c k s in in the Wabigoon the W a b i q o o n subprovince s u b p r o v i n c e suggest s u g g e s t that t h a t volcanism v o l c a n i s m occurred o c c u r r e d over over a a limited l i m i t e d time t i m e interval i n t e r v a l between b e t w e e n 2745 2 7 4 5 Ma Ma and a n d 2703 2 7 0 3 Ma Ma (Davis ( D a v i s and and Trowell, T r o w e l l , 1982; 1 9 8 2 ; Davis D a v i s and a n d Edwards, E d w a r d s , 1982, 1 9 8 2 , Davis D a v i s et e t al., a l . , 1982). 1982). Davis D a v i s and a n d Edwards E d w a r d s (1982) ( 1 9 8 2 ) have h a v e determined d e t e r m i n e d aa U—Pb U-Pb zircon z i r c o n age a q e of of 2713.9 Ma The 6.0/-4.4 Ma ffor o r the t h e Berry B e r r y River R i v e r formation. formation. T h e Warclub Warclub 271 3 . 9 ++ 6.0/—4.4 group, River s aa part, p a r t , can c a n be be q r o u p , of o f which w h i c h tthe h e Berry Berry R i v e r fformation o r m a t i o n i is . correlated c o r r e l a t e dwith w i t hthe t hAbram e Abramgroup q r o u pini the n t hDryden—Sioux e D r y d e n - S i o u x Lookout L o o k o u t area area where w h e r e aa preliminary p r e l i m i n a r y age a g e of o f 2716 2 7 1 6 Ma Ma oon n aa tuffaceous t u f f a c e o u s unit u n i t(Don (Don Davis, D a v i s , personal p e r s o n a lcommunication, c o m m u n i c a t i o n , 1983) 1 9 8 3 ) is is similar s i m i l a r to t o that t h a t age age determined These d e t e r m i n e d ffor o r the t h e Berry B e r r y River R i v e r formation. formation. T h e s e observations observations suggest s u q q e s t that t h a tthe t h Warciub e W a r c l u bgroup q r o u pis iamong s amonqthe t hyoungest e y o u n q e svolcano— t volcanosedimentary s e d i m e n t a r y sequences s e q u e n c e s in i n the t h eWabigoon W a b i g o o n subprovince. subprovince. LONG BAY LONG BAY BAY -- LOBSTICK LOBSTICK--BAY AREA AREA -.-- The T h e Long Lonq Bay Bay —- Lobstick L o b s t i c k Bay area a r e a is is within w i t h i n the t h e western western portion i s situated s i t u a t e d between b e t w e e n the the p o r t i o n of o f the t h e Wabigoon W a b i g o o n Subprovince S u b p r o v i n c e and a n d is Savant S a v a n t Lake L a k e —- Crow C r o w (Kakagi) ( K a k a q i ) Lake L a k e area a r e a studied s t u d i e d by b y Trowell T r o w e l l et e t al. al. (1980) Woods area ( 1 9 8 0 ) aand n d tthe h e cclassical l a s s i c a l Lake L a k e oof f the t h e Woods a r e a studied s t u d i e d by b y Lawson Lawson (1885) ( 1 8 8 5 ) (Figure ( F i q u r e 2). 2 ) . The T h e metavolcanic m e t a v o l c a n i c —- metasedimentary m e t a s e d i m e n t a r y rocks r o c k s are are bounded b o u n d e d by b y the t h e Dryberry D r y b e r r y Batholith B a t h o l i t h on o n the t h e northeast n o r t h e a s t and a n d the the Aulneau The A u l n e a u Batholith B a t h o l i t h on o n the t h e southwest. southwest. T h e forceful f o r c e f u l intrusion i n t r u s i o n of of these t h e s e two t w o bbatholiths a t h o l i t h s and a n d the t h e later l a t e rinternal i n t e r n a stocks l s t o c k have s h a v eproduced produced aa complex c o m p l e x s structural t r u c t u r a l pattern p a t t e r n (Figure ( F i g u r e 3). 3). A A ggeneral e n e r a l sstratigraphy t r a t i g r a p h y has h a s been b e e n developed d e v e l o p e d ffor o r the t h e area a r e a and and is Two i s outlined o u t l i n e d in i n Figure F i q u r e 4. 4. Two s stratigraphic t r a t i g r a p h i c domains d o m a i n s occur; o c c u r ; one one southwest Zonea nand to s o u t h w e s t of o f the t h ePipestone—Cameron P i p e s t o n e - C a m e r o n F Fault a u l t Zone d t the h e oother t h e r to . the To t h e northeast n o r t h e a s t (Blackburn, ( B l a c k b u r n , 1981). 1981 ) To date d a t e no n o correlation c o r r e l a t i o n has-been has- been attempted a t t e m p t e d between b e t w e e n them. them. Southwest Zone tthe S o u t h w e s t of o f the t h ePipestone—Cameron P i p e s t o n e - C a m e r o n FFault a u l t Zone h e northeast northeast facing f a c i n g Snake S n a k e Bay Bay formation f o r m a t i o nconsists c o n s i s tof s fine— o f f i n eand - a nmediurn—grained d medium-qrained mafic f l o w s , pillowed p i l l o w e d and a n d amygdaloidal a m y g d a l o i d a l flows f l o w s with w i t h horizons h o r i z o n s of of maf i c flows, autoclastic a u t o c l a s t i c breccia b r e c c i a and a n d pillow p i l l o w breccia b r e c c i a and a n d hyaloclastite h y a l o c l a s t i t e intruded intruded �Figure 3: Simplified structural geology map of the Long Bay — Lobstick Bay area. Refer to Figure 4 for the corresponding litho—stratiqraphic map. 5-2 m c CT' 4-1 c IÑ -4 H �_____________________ + F * * + + + •.' - + +4 + + fl flrnnn + + + + + + + + + +•• + + + + + + + * + + + lflt+++*+*+l +** + iay .oup \ * + * * + * + * * + + + * + + + + / * + + + 'L_ * + + + ...... I + + Point+ + y* intermediate intrusive intrusive rocks intermediate rocks inafic mafic intrusive intrusive rocks rocks metasediments and intermediate intermediate to telsic metasediments and felsic metavolcanics metavolcanics .intermediate to intermediate felsic metavolcanics to felsic metavolcanics mafic mat ic metavolcanics metavolcanics --- + + Stock + + + + Lake + . 1. - + + Viola + ,"* + + + 1-1 + + + + + 1:.:..:.:..:.:..:1 . . . * + + + + + + * + + lithologic contact 6 6 5 8 8 7 9 10 kilometres + + + + 19seke Warc!ub4O1JP,.. * + * Figure F i g u r e 4: 4: 3 + + * 2 4 - - 2- - kilometres - , 0 fault + + + + stratigraphic stratigraphic contact + + F + + F + * * + + + * + + * + + + + + F * * * + + + f * KqukLake Stck Stratigraphic S t r a t i q r a p h i c map of of the t h e Long Lonq Bay Bay —- Lobstick L o b s t i c k Bay Bay area. area. corresponding structural ffor o r tthe h e corresponding s t r u c t u r a l interpretation. interpretation. + + * + * •.,.•• : Refer Refer to t o Figure Fiqure 33 H t-' H I-1 H I-1 �112 by b y synvolcanic s y n v o l c a n i c gabbro g a b b r o sills. sills. The supracrustal s u p r a c r u s t a l rocks r o c k s northeast n o r t h e a s t of o f the t h e fault f a u l t zone z o n e are are subdivided s ubd i v i d e d into i n t o 55 informal i n f o r m a l metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y groups groups (Figure a r e the t h e Point P o i n t Bay Bay group, g r o u p , Populus P o p u l u s volcanics, volcanics, ( F i g u r e 4). 4 ) . They T h e y are Black B l a c k Lake L a k e volcanics, v o l c a n i c s , Gibi G i b i Lake L a k e volcanics v o l c a n i c s and a n d the t h e Warciub W a r c l u b group group which w h i c h includes i n c l u d e s the t h e Berry B e r r y River R i v e r formation. formation. The is the t h e Point P o i n t Bay Bay group g r o u p which w h i c h occurs o c c u r s around around T h e oldest o l d e s t unit u n i t is the I t consists c o n s i s t s of o f mafic m a f i c and and t h e margin m a r g i n of o f the t h e Dryberry D r y b e r r y batholith. batholith. It intermediate i n t e r m e d i a t e to t o felsic f e l s i c metavolcanics m e t a v o l c a n i c s and a n d metasediments m e t a s e d i m e n t s cut c u t by by thick t o mafic maf i c sills. s i l l s . It I t is i s overlain overlain t h i c k differentiated d i f f e r e n t i a t e d ultramafic u l t r a m a f i c to by i t s base b a s e has h a s been b e e n totally t o t a l l y removed r e m o v e d by by the the b y the t h e Warclub W a r c l u b group g r o u p and a n d its intrusion Roof i n t r u s i o n of o f the t h e Dryberry D r y b e r r y Batholith. Batholith. Roof pendants p e n d a n t s and a n d xenoliths xenoliths of o f the t h e Point P o i n t Bay Bay group q r o u p are a r e found f o u n d within w i t h i n marginal m a r g i n a l phases p h a s e s of o f the the batholith. batholith. The T h e Populus P o p u l u s volcanics, v o l c a n i c s , Black B l a c k Lake L a k e volcanics v o l c a n i c s and a n d Gibi G i b i Lake Lake volcanics v o l c a n i c s are a r e all a l l younger y o u n g e r than t h a n the t h e Point P o i n t Bay Bay group g r o u p and a n d are a r e over— overlain 4 ) . Their T h e i r mutual m u t u a l stratigraphic stratigraphic l a i n by b y the t h e Warclub W a r c l u b group g r o u p (Figure ( F i g u r e 4). relationships The a r e uncertain. uncertain. T h e Populus P o p u l u s volcanics v o l c a n i c s and a n d the t h e Black Black r e l a t i o n s h i p s are Lake L a k e volcanics v o l c a n i c s are a r e predominantly p r e d o m i n a n t l y mafic maf i c metavolcanic m e t a v o l c a n i c sequences. sequences. While W h i l e both b o t h sequences s e q u e n c e s contain c o n t a i n abundant a b u n d a n t massive m a s s i v e and a n d pillowed p i l l o w e d flows, flows, the t h e Populus P o p u l u s volcanics v o l c a n i c s also a l s o contain c o n t a i n mafic maf i c pillow p i l l o w breccia, breccia, hyaloclastite, maf i c pyroclastics p y r o c l a s t i c s and a n d intermediate i n t e r m e d i a t e flows f l o w s and and h y a l o c l a s t i t e , mafic pyroclastics. The a r e composed c o m p o s e d of o f interinterpyroclastics. T h e Gibi G i b i Lake L a k e volcanics v o l c a n i c s are mediate m e d i a t e and a n d mafic m a f i c pyroclastics p y r o c l a s t i c s with w i t h minor m i n o r mafic m a f i c flows f l o w s (Trowell, (Trowell, in i n prep.). prep.). The 4 ) overlies o v e r l i e s the t h e units u n i t s discussed discussed The Warclub W a r c l u b group g r o u p (Figure ( F i g u r e 4) above is structurally s t r u c t u r a l l y and a n d stratigraphically s t r a t i g r a p h i c a l l y complex. c o m p l e x . This This a b o v e and a n d is group 7 1 km km northeast n o r t h e a s t to t o Dryden D r y d e n where w h e r e it i t can c a n be be g r o u p can c a n be b e traced t r a c e d 71 correlated c o r r e l a t e d with w i t h the t h e Abram Abram group. g r o u p . It It consists c o n s i s t s predominantly p r e d o m i n a n t l y of of metasediments m e t a s e d i m e n t s with w i t h interbedded i n t e r b e d d e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyro— pyroclastics. is e l a s t i c s . The T h e metasedimentary m e t a s e d i m e n t a r y portion p o r t i o n of o f the t h e Warclub W a r c l u b qroup q r o u p is compositionally North c o m p o s i t i o n a l l y varied. varied. N o r t h of o f the t h e Black B l a c k Lake L a k e volcanics v o l c a n i c s wackes wackes are a r e interbedded i n t e r b e d d e d with w i t h arenites a r e n i t e s while w h i l e south s o u t h of o f the t h e Gibi G i b i Lake Lake volcanics South v o l c a n i c s thin t h i n bedded b e d d e d arenite a r e n i t e and a n d siltstone s i l t s t o n e predominate. predominate. South of o f the t h e Black B l a c k Lake L a k e volcanics v o l c a n i c s wacke w a c k e predominates. p r e d o m i n a t e s . Thin T h i n beds b e d s of of magnetite a r e found f o u n d both b o t h north n o r t h and a n d south s o u t h of o f the t h e Black Black m a g n e t i t e ironstone i r o n s t o n e are Lake L a k e volcanics. v o l c a n i c s . The T h e variety v a r i e t y of o f lithologies l i t h o l o q i e s represent r e p r e s e n t various various depositional d e p o s i t i o n a l environments e n v i r o n m e n t s and a n d more more work w o r k is i s required r e q u i r e d to to reconstruct r e c o n s t r u c t the t h e paleoenvironment. paleoenvironment The T h e Berry B e r r y River R i v e r formation f o r m a t i o n (Figure ( F i g u r e4) 4 ) is i s aa 22 km krn thick thick sequence s e q u e n c e of o f intermediate i n t e r m e d i a t e to t o felsic f e l s i c pyroclastic p y r o c l a s t i c rocks r o c k s within w i t h i n the the Warclub Except W a r c l u b group. group. E x c e p t for f o r the t h e western w e s t e r n portion, p o r t i o n , the t h e formation formation faces 3 ) . It I t overlies, o v e r l i e s , with w i t h slight slight f a c e s uniformly u n i f o r m l y south s o u t h (Figure ( F i g u r e 3). unconformity, lower part p a r t of o f the t h e Warclub W a r c l u b group qroup u n c o n f o r m i t y , the t h e wacke w a c k e in i n the t h e lower and a n d is is overlain o v e r l a i n by by aa 20—100 2 0 - 1 0 0 mm thick t h i c k mafic m a f i c metavolcanic m e t a v o l c a n i c unit u n i t and and wacke e t al., a l . , 1984). 1 9 8 4 ) . The T h e isoclinally isoclinally w a c k e of o f the t h e Warclub W a r c l u b group g r o u p (Johns ( J o h n s et folded w e s t end e n d of o f the t h e formation f o r m a t i o n appears a p p e a r s to t o both b o t h overlie o v e r l i e and and f o l d e d west grade g r a d e laterally l a t e r a l l y into i n t o the t h e wacke w a c k e of o f the t h e Warclub W a r c l u b group. g r o u p . The T h e beddinq bedding and £0 i a t i o n planes p l a n e s have h a v e near—vertical n e a r - v e r t i c a l dips d i p s throughout t h r o u g h o u t the the a n d foliation strike s t r i k e length. length. . BERRY BERRY RIVER FORMATION FORMATION -- RIVER ThEting h e s e t t iof n g the o t tBerry h e B e rRiver r y R i v eformation r f o r m a t i o has n h a sbeen b e e noutlined outlined in I t is i s aa distinct distinct i n the t h e previous p r e v i o u s section s e c t i o n and a n d shown s h o w n in i n Figure F i g u r e4.4. It �113 u n i t of of subaqueously s u b a q u e o u s l y deposited d e p o s i t e d pyroclastics p y r o c l a s t i c s 20 2 0 km km long l o n g and a n d 22 km km unit thick. Rock thick. Rock units u n i t s were were mapped using u s i n g the t h e size s i z e classification c l a s s i f i c a t i o n of of Fisher ( 1 966 ) , making m a k i n q note n o t e of o f volcanic v o l c a n i c structures s t r u c t u r e s and a n d textures. textures. F i s h e r (1966), The T h e predominant p r e d o m i n a n t clast c l a s t and a n d matrix m a t r i x lithology l i t h o l o g y is i s both b o t h quartz— quartzfeldspar f e l d s p a r porphyry p o r p h y r y and a n d feldspar f e l d s p a r porphyry p o r p h y r y of o f dacite d a c i t e to t o rhyolite rhyolite composition. c o m p o s i t i o n . Thin, T h i n , fine—grained, f i n e - g r a i n e d , metasedimentary m e t a s e d i m e n t a r y horizons horizons composed c o m p o s e d of o f reworked r e w o r k e d pyroclastic p y r o c l a s t i c material m a t e r i a l are a r e interbedded i n t e r b e d d e d with with the t h e pyroclastics. p y r o c l a s t ics Size S i z e classification c l a s s i f i c a t i o n and a n d sorting s o r t i n g alone a l o n e did d i d not n o t provide provide sufficient s u f f i c i e n t information i n f o r m a t i o n to t o properly p r o p e r l y subdivide s u b d i v i d e the t h e sequence. sequence. Volcanic t o size s i z e and a n d sortsortV o l c a n i c textures t e x t u r e s and a n d structures, s t r u c t u r e s , in i n addition a d d i t i o n to ing, were used to develop subunits within the formation, i n g , were u s e d t o d e v e l o p s u b u n i t s w i t h i n t h e f o r m a t i o n , as a s outoutlined These l i n e d in i n Table T a b l e 1. 1. T h e s e subunits s u b u n i t s consist c o n s i s t of o f diagnostic d i a g n o s t i c vertical vertical sequences s e q u e n c e s of o f rock r o c k types t y p e s (after ( a f t e r Fisher, F i s h e r , 1966) 1 9 6 6 ) and a n d primary primary structures s t r u c t u r e s which w h i c h permit p e r m i t definition d e f i n i t i o n of o f distinct d i s t i n c t depositional depositional events. For events. F o r example, e x a m p l e , using u s i n g the t h e model m o d e l of o f Fiske F i s k e and a n d Matsuda M a t s u d a (1964, (1964, . their t h e sequence s e q u e n c e oof f primary p r i m a r y sstructures t r u c t u r e s expected e x p e c t e d in i n aa t h e i r Figure F i g u r e 66)) ,, the subaqueous m a s s i v e lower lower portion, p o r t i o n , which which s u b a q u e o u s ppyroclastic y r o c l a s t i c flow f l o w are: a r e : aa massive fines terms of o f non—vesicular n o n - v e s i c u l a r material m a t e r i a l and a n d an a n upper upper f i n e s upward u p w a r d in i n terms laminated t w o portions p o r t i o n s are are l a m i n a t e d portion, p o r t i o n , which w h i c h also a l s o fines f i n e s upward. u p w a r d . The The two often d o u b l y graded g r a d e d sequence. sequence. o f t e n referred r e f e r r e d to t o as a s aa doubly Examination E x a m i n a t i o n of o f aa sequence s e q u e n c e in i n the t h eBerry B e r r y River R i v e r formation formation mapped y r o c l a s t i c bbreccia r e c c i a wwith i t h ttuff u f f interbeds i n t e r b e d s in i n aapurely purely mapped asasp pyroclastic size s i z e and a n d sorting s o r t i n g classification c l a s s i f i c a t i o n (Fisher, ( F i s h e r , 1966) 1 9 6 6 ) outlined o u t l i n e d the the following f o l l o w i n g vertical v e r t i c a l sequence s e q u e n c e from f r o m base b a s e to t o top: t o p : 2.5 2 . 5 mm of o f homolithic homolithic c l a s t s ) pyroclastic p y r o c l a s t i c breccia b r e c c i a grading g r a d i n g inin( q u a r t z - f e l d s p a r porphyry p o r p h y r y clasts) (quartz—feldspar to t o lithic l i t h i c lapilli l a p i l l i tuff; t u f f ; clasts c l a s t s are a r e subangular s u b a n g u l a r and a n d quartz—feldspar quartz-feldspar tuff i s then t h e n overlain o v e r l a i n by b y 33 mm of o f moderately moderately t u f f matrix m a t r i x supported; s u p p o r t e d ; this t h i s is sorted, b e d d i n g is is s o r t e d , thickly t h i c k l y laminated l a m i n a t e d quartz q u a r t z feldspar f e l d s p a r tuff; t u f f ; bedding distinct d i s t i n c t and a n d regular r e g u l a r in i n this t h i s portion. portion. T h i s coarse coarse to t o fine fine This sequence s e q u e n c e is is then t h e n overlain o v e r l a i n by b y another a n o t h e r similar s i m i l a r assemblage. a s s e m b l a g e . The The above a b o v e vertical v e r t i c a l sequence s e q u e n c e of o f primary p r i m a r y structures s t r u c t u r e s and a n d rock r o c k type type compares ( 1 9 6 4 ) model m o d e l and a n d the the c o m p a r e s favourably f a v o u r a b l y with w i t h Fiske F i s k e and a n d Matsuda's M a t s u d a ' s (1964) sequence s e q u e n c e is i s most m o s t likely l i k e l y aa subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flow f l o w (Figure ( F i g u r e 5). 5). Individual I n d i v i d u a l subunits s u b u n i t s cannot c a n n o t be b e traced t r a c e d beyond b e y o n d single s i n g l e outcrops outcrops but b u t they t h e y do d o form f o r m unique u n i q u e packages p a c k a g e s that t h a t can c a n be b e traced t r a c e d for f o r considerconsiderable a b l e distance. d i s t a n c e . Subunits S u b u n i t s representing r e p r e s e n t i n g aa single s i n g l e depositional depositional process s u b a q u e o u s pyroclastic pyroclast ic p r o c e s s include i n c l u d e debris d e b r i s flow f l o w deposits, d e p o s i t s , subaqueous flow f l o w deposits, d e p o s i t s , block b l o c k and a n d ash a s h flow f l o w deposits, d e p o s i t s , fall—out f a l l - o u t tuff tuff deposits d e p o s i t s and a n d lapilli l a p i l l i tuffs t u f f s and a n d ash a s h flow f l o w tuff. t u f f . Table T a b l e 1 lists l i s t s the the criteria c r i t e r i a used u s e d to t o identify i d e n t i f y subunits s u b u n i t s within w i t h i n the t h e Berry B e r r y River River formation, f o r m a t i o n , and a n d aa brief b r i e f description d e s c r i p t i o n of o f each e a c h subunit s u b u n i t in i n the the formation is listed 1i s t e dbelow. below. f o r m a t i o n is 1 Debris Debris Flow F l o w Deposits D e p o s i t s (Stop ( S t o p 7) 7) Debris D e b r i s flow f l o w deposits d e p o s i t s within w i t h i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n are are compositionally c o m p o s i t i o n a l l y bimodal b i m o d a l (clasts ( c l a s t s of o f feldspar f e l d s p a r porphyry; p o r p h y r y ; quartz— quartzfeldspar f e l d s p a r porphyry) p o r p h y r y ) to t o heterolithic, h e t e r o l i t h i c , (clasts ( c l a s t s of o f feldspar f e l d s p a r porphyry; porphyry; quartz—feldspar q u a r t z - f e l d s p a r porphyry; p o r p h y r y ; fine f i n e grained g r a i n e d massive m a s s i v e intermediate intermediate volcanics; v o l c a n i c s ; felsic f e l s i c volcanics; v o l c a n i c s ; mafic maÂi c volcanics v o l c a n i c s and a n d sediments) sediments) matrix t o lapilli l a p i l l i tuffs. t u f f s . These T h e s e subunits subunits m a t r i x supported s u p p o r t e d tuff t u f f breccias b r e c c i a s to are a r e thick, t h i c k , massive, m a s s i v e , and a n d poorly p o o r l y bedded. b e d d e d . The T h e matrix m a t r i x in i n any a n y one one location t o the t h e majority m a j o r i t y of o f framework framework l o c a t i o n corresponds c o r r e s p o n d s in i n composition c o m p o s i t i o n to clasts. c l a s t s . The T h e debris d e b r i s flow f l o w deposits d e p o s i t s are a r e mostly m o s t l y tuff—breccia t u f f - b r e c c i a to to �T a b l e 1: -Table 1: Berry River Subunits_jdentified S u b u n i t s i d e n t i f i e d iin n tthe he B erry R i v e r formation f o r m a t i o n aand n d their t h e i r characteristics. characteristics. Flow Deposits D eposits Subaqueous S ubaqueous Pyroclastic P y r o c l a s t ic Flow F l o w Deposits Deposits Block B l o c k and and Ash Flow Ash Flow Depos D e p o sits its Fall F a l l Out Out Deposits D eposits Ash Flow Tuff T uff Reworked Debris D ebris Flow F l o w Deposits Deposits Bedd B e d d ing ing md i n distinct istinct ddistinct istinct distinct distinct ddistinct istinct aabsent bsent distinct distinct Grain! G rain/ clast c l a s t size size ccoarse oarse coarse coarse to t o fine fine ccoarse oarse to fine fine medium to fine fine coarse coarse to fine fine Sort S o r ti i fly ng poor poor moderate m oderate to t o poor poor ppoor oor moderate m o d e r a t e to to good good moderate to m o d e r a t e to ppoor oor mod m o dera e r att ee to t o good Grad G r a d ing ing aabsent b s e n t to to normal normal nnormal o r m a l and and rreverse everse aabsent b s e n t to to normal normal normal norm a 1 to to reverse reverse absent absent nnormal ormal Composition Composition to bbimodal i m o d a l to hheterol e t e r o l iithic thic bbimodal imod a 1 homolithic homo1 it h i c bimodal b imod a 1 qquart u a r t zz— feldspar feldspar pporphyry orphyry Pumice Pumice no yes yes yes Anyn g ulual ar rit A i t yy s uubround bround ssu ubround bround s ubang uular s ubang lar to t o angular angular ssubround u b r o u n d to to subany s u b a n g ular ular gas g a s escape escape features features rregularity e g u l a r i t y of of bbedd e d d ing i ng Subunit S ubunit Characteristics C haracteristics Debris D ebris 1Ñ I-' H h ' Unique U n i q u e features features ddouble o u b l e grading grading yes S s ubang uull aarr heterol h e t e r o l ithic ithic no no ssubround u b r o u n d to to rround ound iinterbedded nterbedded with w i t h wacke wacke �115 lapilli—tuff, l a p i l l i - t u f f , but b u t tuft t u f f in i n gradational g r a d a t i o n a l contact c o n t a c t with w i t h the t h e coarse coarse part p a r t of o f debris d e b r i s flow f l o w deposits d e p o s i t s forms f o r m s aa fine—grained f i n e - g r a i n e d top t o p in i n distal distal debris d e b r i s flow f l o w deposits. deposits. T h e debris d e b r i s flows f l o w s described d e s c r i b e d here h e r e are are The similar s i m i l a r to t o those t h o s e described d e s c r i b e d by b y Tasse T a s s e et e t al. a l . (1978) ( 1 9 7 8 ) in i n the t h e Abitibi Abitibi ss uubprov b p r o v iince. nce. Subaqueous a n d 11) 11) S u b a q u e o u s Pyroclastic P y r o c l a s t i c Flow F l o w Deposits D e p o s i t s (Stops ( S t o p s 99 and Subaqueous S u b a q u e o u s pyroclastic p y r o c l a s t i c flow f l o w deposits d e p o s i t s similar s i m i l a r to t o those those o r i g i n a l l y described d e s c r i b e d by by Fiske F i s k e and a n d Matsuda M a t s u d a (1964) ( 1 9 6 4 ) occur o c c u r in i n the the originally Berry B e r r y River R i v e r formation. f o r m a t i o n . Massive, M a s s i v e , compositionally compos i t i o n a l l y homolithic h o m o l i t h i c to to bimodal, b i m o d a l , tuft t u f f breccia b r e c c i a bases b a s e s are a r e overlain o v e r l a i n by b y caps c a p s of o f thickly thickly laminated o r quartz—feldspar q u a r t z - f e l d s p a r crystal c r y s t a l tuft. tuff T h e massive massive l a m i n a t e d feldspar f e l d s p a r or The portion p o r t i o n of o f the t h e flow f l o w is i s graded g r a d e d and a n d the t h e thickly t h i c k l y laminated l a m i n a t e d tuffs t u f f s are are subtly s u b t l y graded. graded. T h e s e subunits s u b u n i t s are a r e distinctly d i s t i n c t l y bedded b e d d e d with w i t h wellwellThese preserved p r e s e r v e d base b a s e and a n d upper u p p e r contacts. contacts. . Block B l o c k and a n d Ash Ash Flow F l o w Deposits D e p o s i t s (Stops ( S t o p s 33 and a n d 7) 7) AA block b l o c k and a n d ash a s h flow f l o w deposits, d e p o s i t s , aa product p r o d u c t of o f explosive explosive volcanism, v o l c a n i s m , consists c o n s i s t s of o f unsorted u n s o r t e d ash a s h deposits d e p o s i t s containinq c o n t a i n i n g large, large, generally g e n e r a l l y non—vesicular, n o n - v e s i c u l a r , jointed j o i n t e d cognate c o g n a t e blocks b l o c k s which w h i c h can c a n exceed exceed 55 m m in i n diameter d i a m e t e r (Fisher, ( F i s h e r , 1982). 1 9 8 2 ) . Block B l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s in in the c pyrot h e Berry B e r r y River R i v e r formation f o r m a t i o nare a r ethickly—bedded, t h i c k l y - b e d d e d , homolithic h o m o l i t h i pyro— clastic e l a s t i c breccias b r e c c i a s that t h a texhibit e x h i b i tgrading. g r a d i n g . Thin T h i n tuff t u f f zones z o n e s are are occasionally as part o c c a s i o n a l l y preserved p r e s e r v e d as p a r t of o f these t h e s eblock b l o c k and a n d ash a s h flow flow deposits. d e p o s i t s . These T h e s e ttuff u f f zones z o n e s represent r e p r e s e n t either e i t h e r ash a s h cloud c l o u d deposits deposits or o r ground g r o u n d surge s u r g e deposits. d e p o s i t s . The T h e depositional d e p o s i t i o n a l characteristics characteristics displayed terms of o f the the d i s p l a y e d by b y these t h e s e deposits d e p o s i t s can c a n be b e explained e x p l a i n e d in i n terms depositional e t al. a l . (1973). (1973). d e p o s i t i o n a l model m o d e l proposed p r o p o s e d by b y Sparks S p a r k s et Fall—Out 11) F a l l - O u t Deposits D e p o s i t s (Stop ( S t o p 99 and a n d 11) Fisher F i s h e r and a n d Schmincke S c h m i n c k e (1984, ( 1 9 8 4 , their t h e i r Figure F i g u r e 7—1) 7-1 ) outlined o u t l i n e d the the characteristics c h a r a c t e r i s t i c s of o f submarine s u b m a r i n e fall—out f a l l - o u t tephra. t e p h r a . Characteristics C h a r a c t e r i s t i c s of of the t h e deposits d e p o s i t s formed f o r m e d in i n such s u c h an a n environment e n v i r o n m e n t preserved p r e s e r v e d in i n the the A r c h e a n are: a r e : thickness t h i c k n e s s of o f single s i n g l e layers l a y e r s commonly commonly less l e s s than t h a n 50 50 cm; cm; Archean sorting s o r t i n g good g o o d to t o poor; p o o r ; plane p l a n e parallel p a r a l l e l beds; b e d s ; normal n o r m a l gradinq g r a d i n q from from crystal c r y s t a l and a n d lithic l i t h i c rich r i c h bases b a s e s to t o shard s h a r d rich r i c h tops; t o p s ; and a n d grading grading may may be b e inverse i n v e r s e if i f pumice p u m i c e is is present. present. Fall—out a r e thick thick F a l l - o u t deposits d e p o s i t s in i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n are sub—units t h i c k l y laminated l a m i n a t e d to t o thinly t h i n l y bedded bedded s u b - u n i t s of o f interbedded, i n t e r b e d d e d , thickly crystal c r y s t a l tuft t u f f and a n d pumice p u m i c e crystal c r y s t a l lapilli l a p i l l i tuft. t u f f . Although A l t h o u q h bedding beddinq is i s regular r e g u l a r and a n d distinct, d i s t i n c t , contacts c o n t a c t s between b e t w e e n individual i n d i v i d u a l beds b e d s are are gradational. i s recessively r e c e s s i v e l y weathered w e a t h e r e d and a n d darker d a r k e r than than g r a d a t i o n a l . The The pumice p u m i c e is the t h e crystal c r y s t a l matrix. matrix. Ash Ash Flow F l o w Tuff T u f f Deposits D e p o s i t s (Stops ( S t o p s 44 and a n d 10) 10) Ross Ross and a n d Smith S m i t h (1961) ( 1 9 6 1 ) have h a v e defined d e f i n e d ash a s h flow f l o w tuft t u f f as a s consolconsolidated i d a t e d deposits d e p o s i t s of o f volcanic v o l c a n i c ash a s h resulting r e s u l t i n g from f r o m the t h e ash a s h flow flow eruptive e r u p t i v e process. p r o c e s s . They T h e y define d e f i n e the t h e ash a s h flow f l o w process p r o c e s s as a s aa turbuturbulent l e n t mixture m i x t u r e of o f gas g a s and a n d pyroclastic p y r o c l a s t i c materials m a t e r i a l s of o f high h i q h temperature temperature ejected e j e c t e d explosively e x p l o s i v e l y from f r o m aa crater c r a t e r or o r fissure, f i s s u r e , that t h a t travels t r a v e l s swiftswiftly l y down down the t h e slopes s l o p e s of o f aa volcano v o l c a n o or o r along a l o n g the t h e ground g r o u n d surface. surface. Ash Ash flow f l o w tuft t u f f deposits d e p o s i t s of o f varied v a r i e d thicknesses t h i c k n e s s e s are a r e found found throughout t h r o u g h o u t the t h e Berry B e r r y River R i v e r formation. f o r m a t i o n . They T h e y are a r e massive, m a s s i v e , homohomogeneous, fine—grained quartz—feldspar porphyry. Minor variations p o r p h y r y . M i n o r v a riations geneous, f ine-grained quartz-f eldspar �116 116 ERUPTIVE ERUPTIVE EVENTS EVENTS . - end! DEPOSITS DEPOSITS z mudstone mudstone 0 I— .0 ci turbidity turbidity currents, currents, fine fine ash, ash, minor minor pumice pumice lapilli lapilli LU 33- 0 LU I- z , - pumice pumice lapilli, lapilli, fine fine crystals crystals -J C S 0 0 LU subaqueous pyroclastic flow dense d e n s e fragments, fragments, large large crystal crystal fragments fragments . - A beginning \ pumice pumice fragments fragments in in ash a s hand and crystal c r y s t a l matrix matrix z 0 0 aLU 0-J LU lithic lithic and and pumice pumice fragments fragments fine fine ash ash F i g u r e 5: 5: Figure Schematic S c h e m a t i c drawings d r a w i n g s of o f aa submarine s u b m a r i n e eruption eruption producing p r o d u c i n g subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows, f l o w s , and and subsequent s u b s e q u e n t appearance a p p e a r a n c e of o f the t h e deposits d e p o s i t s of o f such s u c h an an eruption e r u p t i o n (Easton ( E a s t o n and a n d Johns, J o h n s , in i n press). press). C) is C) Beginning B e g i n n i n g of o f eruption. e r u p t i o n . Vesiculating V e s i c u l a t i n g magma magma is Some erupted e r u p t e d into i n t o sea s e a water. water. Some fine f i n e ash a s h may may be be deposited d e p o s i t e d near n e a r the t h e vent. vent. Submarine B) B ) Climax C l i m a x of o f eruption. eruption. S u b m a r i n e eruption e r u p t i o n column column c a r r i e d much much ddebris e b r i s hhigh i g h into i n t o suspension. s u s p e n s i o n . Sorting Sorting carried splits s p l i t s the t h e debris d e b r i s into i n t ovarious v a r i o u s fractions. fractions. Buoyant Buoyant pumice d e n s e fragments, f r a g m e n t s , llarge a r g e crystals c r y s t a l s and and p u m i c e f floats; l o a t s ; dense settle around the compact c o m p a c t ppumice u m i c e l lapilli a p i l l i s e t t l e a r o u n d t h e vent, v e n t , and and a r e transported t r a n s p o r t e d llaterally a t e r a l l y in i n aa subaqueous subaqueous are Most flow. Most aash s h remains r e m a i n s in i n suspension. suspension. pyroclastic -p -y r o c l a s t i c flow. Steady pyroclastic of eruption. A) A ) End End o f e r u p t i o n . S t e a d y p y r o c l a s t i c flow f l o w ceases ceases as a s amount a m o u n t of o f erupted e r u p t e d material m a t e r i a l decreases d e c r e a s e s and a n d is is Later replaced r e p l a c e d by b y turbidity t u r b i d i t y current c u r r e n t flow. flow. Later turbidity currents contain finer and less t u r b i d i t y c u r r e n t s c o n t a i n f i n e r a n d l e s s dense d e n s e ash ash t h a t has h a s settled s e t t l e d from f r o m suspension. suspension. that As A s shown s h o w n in i n the t h e right—hand r i g h t - h a n d side s i d e of o f the t h e figure, f i g u r e , an an important i m p o r t a n t characteristic c h a r a c t e r i s t i c of o f subaqueous s u b a q u e o u s pyroclastic pyroclastic Each deposits d e p o s i t s are a r e their t h e i r doubly—graded d o u b l y - g r a d e d nature. nature. E a c h bed bed is graded, and the beds at the base of the is g r a d e d , a n d t h e b e d s a t t h e b a s e o f t h e sequence sequence contain c o a r s e r and a n d denser d e n s e r ash a s h than t h a n the t h e beds b e d s at a t the the c o n t a i n coarser Modified from Fiske and top t o p of o f the t h e sequence. sequence. M o d i f i e d from F i s k e and Matsuda M a t s u d a (1964) ( 1 9 6 4 ) and a n d Fiske F i s k e (1969). (1969). > C/) C/) �117 w i t h i n aa thicker t h i c k e r layer l a y e r indicates i n d i c a t e s deposition d e p o s i t i o n by b y aa number n u m b e r of of within separate s i n g l e cooling c o o l i n g unit. unit. s e p a r a t e events e v e n t s forming f o r m i n g aa single Petrography Petrography T h i n section s e c t i o n examination e x a m i n a t i o n of o f finer f i n e r grained g r a i n e d portions p o r t i o n s of o f the the Thin t o various v a r i o u s degrees d e g r e e s and a n d much f o r m a t i o n shows s h o w s recrystallization r e c r y s t a l l i z a t i o n to formation a 1 t e r a t i o n with w i t h secondary s e c o n d a r y carbonate, c a r b o n a t e , sericite s e r i c i t e and a n d epidote. e p i d o t e . The The alteration a n g u l a r i t y of o f ash—sized a s h - s i z e d crystals c r y s t a l s and a n d lithic l i t h i c fragments f r a g m e n t s can c a n often often angularity be b e observed o b s e r v e d but b u t generally g e n e r a l l y the t h e recrystallization r e c r y s t a l l i z a t i o n and a n d schistosity schistosity has destroyed all primary features. has destroyed a l l primary features. Geochemistry G e o c h e m i s t r y oof f the t h e Berry B e r r y River R i v e r Formation Formation Table l i s t s 20 2 0 whole w h o l e rock r o c k analyses a n a l y s e s of o f finer f i n e r grained grained T a b l e 2 lists clastic c l a s t i c samples s a m p l e s of o f the t h e Berry B e r r y River R i v e r formation f o r m a t i o n carried c a r r i e d out o u t by b y the the Geoscience G e o s c i e n c e Laboratories, L a b o r a t o r i e s , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto. Toronto. According A c c o r d i n g tto o the t h e AFM AFM t ternary e r n a r y ddiagram i a g r a m oof f Irvine I r v i n e and a n d Baraqar B a r a q a r (1971) (1971) arid a n d the t h e Al—Fe—Ti—Mg Al-Fe-Ti-Mg m o l emolecular c u l a r p r o proportion p o r t i o n t eternary r n a r y ddiagram i a g r a m of of (1976), ( 1 9 7 6 ) , tthe h e ppyroclastic y r o c l a s t i c rocks r o c k s have h a v e caic—alkalic c a l c - a l k a l i c affinities a f fi n i t i e s (Figure T h e single s i n g l e high—magnesium h i q h - m a g n e s i u m tholeiitic t h o l e i i t i c basalt b a s a l t is is from from ( F i q u r e 6). 6 ). The the t h e thin t h i n metavolcariic m e t a v o l c a n i c unit u n i t capping c a p p i n g the t h e formation. formation. T h e clasclasThe sification s i f i c a t i o n schemes s c h e m e s of o f Irvine I r v i n e and a n d Baragar 2 ) and and B a r a g a r (1971) ( 1 9 7 1 ) (Table ( T a b l e 2) Jensen J e n s e n (1976) ( 1 9 7 6 ) (Figure ( F i g u r e 6) 6 ) respectively r e s p e c t i v e l y class c l a s s the t h e samples s a m p l e s as a s dacite dacite and rhyolite. No discernable trend was noted in the major and r h y o l i t e . No d i s c e r n a b l e t r e n d was n o t e d i n t h e m a j o r element The e l e m e n t chemistry c h e m i s t r y with w i t h respect r e s p e c t to t o stratigraphic s t r a t i g r a p h i c height. height. The close c l o s e c l u s t e r i n g o f t h e p o i n t s p l o t t e d i n F i g u r e 6 may i n d i c a t e a similar s i m i l a r magma magma s source o u r c e f for o r aall l l the t h epyroclastic p y r o c l a s t i csub—units. sub-units Figure F i g u r e 66 includes i n c l u d e s an a n AFM AFM t ternary e r n a r y diagram d i a g r a m (Irvine ( I r v i n e and and Baragar, B a r a g a r , 1971) 1 9 7 1 ) and a n d an a n Al—Fe—Ti—Mg Al-Fe-Ti-Mg molecular m o l e c u l a r proportion p r o p o r t i o n ternary ternary diagram (Jensen, 1976) of metasedimentary and metavolcanic d i a g r a m (J e n s e n , 1976 ) o f m e t a s e d i m e n t a r y a n d m e t a v o l c a n i c rocks rocks from f r o m the t h e rest r e s t of o f the t h e Warclub W a r c l u b group g r o u p within w i t h i n the t h e Long Long Bay Bay —- Lobstick Lobstick Bay Bay area. a r e a . Data D a t a for f o r these t h e s e plots p l o t s are a r e found f o u n d in i n Johns J o h n s (in ( i n prep) prep). These T h e s e plots p l o t s are a r e included i n c l u d e d to t o allow a l l o w comparison c o m p a r i s o n between b e t w e e n the t h e Berry Berry River R i v e r formation f o r m a t i o n and a n d the t h e metasediments m e t a s e d i m e n t s and a n d metavolcanics m e t a v o l c a n i c s of o f the the rest r e s t of o f the t h e Warclub W a r c l u b group group Jensen Jensen clustering of the points plotted in Figure 6 may indicate a . . FACIES FAC I E S MODELS MODELS Historically, H i s t o r i c a l l y , mapping m a p p i n g of o f Archean A r c h e a n pyroclastic p y r o c l a s t i c rocks r o c k s has has supplied d a t a to t o understand u n d e r s t a n d complex c o m p l e x stratigraphy. stratigraphy. s u p p l i e d insufficient i n s u f f i c i e n t data Figure s h o w s that t h a t the t h e complexity c o m p l e x i t y of o f volcanic v o l c a n i c stratigraphy stratigraphy F i q u r e 77 shows depends d e p e n d s on o n the t h e location l o c a t i o n of o f the t h e section. s e c t i o n . Mapping M a p p i n q by b y clast c l a s t size size parameters p a r a m e t e r s only o n l y will w i l l not n o t prove p r o v e useful u s e f u l in i n developing d e v e l o p i n g map map units u n i t s and and facies It f a c i e s models. models. I t is i s ddifficult i f f i c u l t to t o compare c o m p a r e ancient a n c i e n t and a n d modern modern pyroclastic p y r o c l a s t i c sequences s e q u e n c e s without w i t h o u t aa clear c l e a r idea i d e a of o f stratigraphy s t r a t i g r a p h y and and using u s i n g facies f a c i e s analysis a n a l y s i s aa stratigraphic s t r a t i g r a p h i c context c o n t e x t can c a n be b e developed. developed. Discrete D i s c r e t e packages p a c k a g e s of o f pyroclastic p y r o c l a s t i c subunits s u b u n i t s can c a n he b e traced t r a c e d and and correlated c o r r e l a t e d allowing a l l o w i n g for f o r the t h e development d e v e l o p m e n t of o f facies f a c i e s models. models. Through T h r o u g h development d e v e l o p m e n t of o f stratigraphy, s t r a t i g r a p h y , facies, f a c i e s , and a n d subunits s u b u n i t s within within Archean A r c h e a n pyroclastic p y r o c l a s t i c sequences s e q u e n c e s comparisons c o m p a r i s o n s can c a n be b e made with w i t h other other Archean pyroclastic sequences and they can then be compared A r c h e a n p y r o c l a s t i c s e q u e n c e s a n d t h e y c a n t h e n b e c o m p a r e d with with younger y o u n g e r pyroclastics p y r o c l a s t i c s thus t h u s assisting a s s i s t i n g in i n the t h e development d e v e l o p m e n t of o f paleo— paleoenvironmental e n v i r o n m e n t a l models m o d e l s for f o r Archean A r c h e a n volcanism. volcanism. Facies are based on a number F a c i e s a r e b a s e d o n a n u m b e r of o f parameters p a r a m e t e r s described d e s c r i b e d in in Fisher and Schmincke (1984): position relative to source, F i s h e r a n d S c h m i n c k e ( 1 9 8 4 ) : p o s i t i o n r e l a t i v e t o source, environment e n v i r o n m e n t of o f deposition d e p o s i t i o n and a n d primary p r i m a r y composition. composition. A - �Si02 52 55 55 500 4 I IÑ Proximal Distal 3 0 -4'44 CCJ w c E-i 0 Ll X !a '^ Tuft Ash Flow 0 3 4 Proximal "3 -4 E "3 0 Ll 0 Distal X 4 w &-i w c El Tuft Ash Flow .^ "3 r-1 E "3 Â¥4J 0 -4 L-i 0 X in Distal Proximal— Dacite 84 70 4 40 430 .-- 75 49 2 45 305 6 3 414-1 CCJ w 3 c El Tuft Ash Flow Rhyolite . 5 7 10 8 8 6 360 0.54 0.06 1.00 99.45 0.12 0.44 0.03 17.90 0.42 1.02 0.55 1.67 5.33 1.86 0.37 0.04 69.10 IÑ "3 Proximal Dacite 45 36 4 30 355 5 6 7 17 9 7 6 260 30 45 40 35 285 5 6 14 6 7 5 35 810 0.95 0.03 1.70 99.44 0.01 0.86 0.06 0.92 1.23 0.41 3.03 4.49 2.01 0.36 0.08 68.10 16.90 93.94319 49. 43213 83-GWJ 4172 Dacite Proximal Ash Flow IÑ Dacite 28 45 20 35 370 4 18 8 5 5 60 270 0.96 0.04 1.90 99.63 0.01 1.43 0.04 0.72 1.30 0.73 5.10 4.16 0.73 0.34 0.07 67.40 16.60 93.94560 83-GWJ 4173 49.42902 - -—- 4._______ 0.63 0.06 1.10 99.48 0.00 0.87 0.03 17.30 0.77 1.17 0.76 4.03 4.04 1.00 0.29 0.03 68.50 0 4 w tn w c E-i Tu f f a u [fl c 11 "3 .-I u u > tn 0 "3 Facies 0 Dacite 24 65 2 30 370 4 6 13 15 17 7 1 350 0.62 0.07 1.20 99.44 0.00 0.71 0.05 2.55 6.05 1.08 0.42 0.06 1.53 0.80 66.40 18.30 0.80 93.99126 49.42917 93.94431 662 82-GWiJ -3' Vocanic ... 12 4 5 8 320 0.32 0.07 1.00 99.29 0.02 0.65 0,06 0.33 0.03 1.61 2.27 4.90 0.34 0.34 0.95 70.30 17.10 93.98581 611 49. 44484 82-GWJ 0 in Dacite 48 45 2 35 490 5 12 28 8 5 320 0.98 0.12 1.60 99.86 0.01 1.06 0.05 16.80 0.73 1.39 0.49 2.34 4.95 1.32 0.29 0.03 69.30 93.94540 601 49. 44003 82-GWJ coin CM -7 Dacite 45 7 38 35 420 9 10 6 9 370 98.53 0.11 1.60 0.44 0.01 1.06 0.07 4.52 1.38 0.29 0.06 3.78 0.76 1.85 0.40 67.70 16.10 -G NJ Proximal Rhyodacite 45 32 22 125 60 3 51 6 10 8 620 0.05 1.20 99.55 1.51 0.01 0.18 0.04 0.08 0.81 2.95 1.26 1.87 73.20 16.50 0.33 0.89 0.37 93.94582 49. 42833 4174 83-GWJ in m ^' Irv me and Baragar rock name Andesite . 6 12 16 8 10 320 98.66 1.02 0.11 2.90 0.01 1.92 0.06 0.39 2.58 0.95 5.17 4,44 1.98 0.35 0.08 61.20 18.40 49.43382 93.97664 82 491 49. 43269 m Zr Zn I V Rb Sr Pb Sc Nd Ni Nb Li Co Cr Cu Ba Be Ce Total H20 LOl U20 S CO2 MnO P205 Ti02 1(20 MgO CaO Na20 FeO A1203 Fe203 94.12201 WElAJ -c Lonq itude i n h a ) 169 0 49. 48657 0 J 82-GWJ E Latitude A 81 -GWJ E c-0 5 0 2054 49.45833 94.07147 Q-GO 81 -GWJ 2050 O a No. Chemical analyses of samples from the Berry River formation (Geoscience Laboratories, Ontario Geological Survey, Toronto). The Irvine and Baragar (1971) rock name and the volcanic facies designation are at the bottom of the table. HI-AJ Sample Table 2: in (N 4 .ft "3 E 0 Ll & x .1-i "3 E Ll & 0 3 3 -4 E Ll & 0 0 2 .^ AJ in & 3 3. 3 3. Â¥ & I.- "3 .-I E "3 à n in & Co �Table Table 2 2 cont. cont. SSample a m p l e No. No. Latitude Latitude Lon2itude --o n g i t u d e L Si02 Si02 A1203 A1203 Fe203 Fe203 FeO MgO M gO Ca0 cao Na20 Na 20 K20 K20 Ti02 Ti02 p205 P 2° MriO MnO cCO2 o2 sS H^o"*" H20 H20 H20" LOl LO1 Total Total Ba Be Be Ce Ce Coo C Cr cr cCuu Lii L Nb Nd Nii N Pb Pb sScc Sr sr 83-GWJ 4176 49. 442677 49. 2677 993.95789 3 . 9 5 78.9 . 49. 43636 93.93486 67.10 67.10 50.20 14.50 68.90 0.644 0.6 1.85 1. 8 5 00.83 .83 3.09 3.09 44.60 .60 2.08 2.08 00.36 .36 0. 10 0. 10 00 05 05 1.34 1.34 00.02 .02 00.92 .92 0.06 0.06 22.20 .20 999.04 9.04 1.84 0.82 1.44 16.00 16.00 580 580 1 75 75 66 66 5 5 10 10 88 1 93 16.50 8.43 0.78 3.41 3.87 1.74 0.39 0.08 0.03 0.72 5.56 10.20 2 98 0.15 1.27 0. 12 0.18 2.00 0.21 0.01 0.86 0.06 1.30 99.61 1. 10 0.06 2.70 98.80 390 90 1 55 83—GWJ 5282 83—GwJ 5283 83—GWJ 49. 43636 49. 44095 93 .9287393.99055 66.00 15.80 1.57 69.30 15.70 0.29 5286 49. 44597 83-GWJ 5294 49. 44426 93.9892493.98683 66.30 16.90 0.53 65.40 17.80 1.11 1.65 2.13 1.65 1.78 1.41 1.30 0.60 4.71 4.72 1.30 0.45 1.19 3.78 4.81 1.94 0.41 3.77 5.06 1.29 0.40 0. 13 0.06 1.56 0.01 0.75 0.05 1.80 99.51 320 3.80 3.61 1.37 0.40 0.08 0.05 0.30 0.02 1.07 0.09 1.20 99.51 0. 10 0.08 1.06 0.01 0.08 0.05 0.56 0.02 1.70 98.96 0.06 0.01 0.78 0.04 0.60 99.27 64.80 6 4.80 64.10 0.82 0. 82 00.28 .28 3.36 3. 36 44.68 .68 1.86 1. 86 0.41 0.4 1 0.08 0.08 0.03 0.03 0.54 0.54 0.01 0.01 0.73 0.73 0.02 0.02 1.20 1 .20 100.08 1 00.08 1.58 1. 58 0.83 0 .83 5.14 5. 14 4.80 4 .80 1.59 1.59 0.42 0 .42 00.09 .09 0.10 0. 10 2.02 2 .02 00.01 .01 00.77 .77 00.07 .07 2.40 2. 40 999.76 9.76 0.96 16.30 1 6 . 30 1.24 1 .24 0.07 3.26 0.01 1.08 0.03 4.10 99.76 55 45 45 110 7 6 7 5 5 77 11 11 88 6 6 7700 6 1100 32 32 1144 6 6 1 204 64 7 10 7 10 7 6 5 26 16 6 38 30 16 9 12 10 10 7 5 7 7 6 6 6 10 12 8 35 35 5 5 6 45 4 4 315 3 15 30 30 5500 47 13 444 4 32 23 4 4 5 5 5 310 205 430 305 305 385 40 30 45 8 38 70 40 40 40 55 60 45 48 44 14 26 50 0. 38 0. 14 60 7 ---. 3.16 4.10 65 7 6 0.52 4.85 940 37 11 15.20 1.90 3350 50 44 ZZrr 70.00 70.00 16.80 1 6.80 0.47 0.47 380 3 80 111 110 49. 4369 93.9842193.00328 330 55 143 49. 44200 83—GwJ 5297 320 364 36 4 4455 50 49. 44313 93.98486 83—GWJ 5296 240 135 235 21 83—GWJ 5295 1 45 50 50 4400 yY Zn Zn 83—GWJ 5279 .96 184 vV ii KlJ 83—GWJ 4177 49.42537 2 35 55 4 360 36 0 400 /0 40 30 50 50 22 56 56 355 3 D 46 IIrv r v i me ne n1d an Ba B a rrag a g aarr rock rock Dacite D acite Basalt Dacite B asalt D acite (tholei ( t h o l e i itic) itic) Psh A s h Flow Flow Puuff ff T Prox P r o x iimal mal Dacite Dacite Dacite D acite Dacite Dac ite Dacite D acite Dacite Dacite Prox P r o x iimal mal —Distal -Dis t a 1 Ash A s h Flow Flow Puff Tuff Ash A s h Flow Flow Tuff Tuff Dacite Dac ite Dacite Dac ite nname ame Vo V ocan c a ni i cc Faci F a c i es es Prox P r o x imal imal P r o x iimal m a l Prox P r o ximal— imalProx Distal D is t a1 Ash A s h Flow Flow Puff T uff Ash A s h Flow Flow Tuff Tuff H H �FEO(TOTAL) Point No. No. Sample No. No. Sample 1 810WJ-2044 8 1 G W J - 2 0 4 4 lnt..Tuff Int..Tuff 1 8 1 G W J - 2 0 4 5 Wacke,Felcf Wacke,Feld. 22 81GWJ—2045 A 3 3 81GWJ-2049 8 1 G W J - 2 0 4 9 Int.,Tuff lnt.,Tuff 8 1 G W J - 2 0 5 1 WackeFefd Wacke.Feld. 4 81GWJ-205i FEOFE2O3+Tl 5 BIGWJ—2053 8 1 G W J - 2 0 5 3 Porph.Feld. Porph..Feld. 8 1 G W J - 2 0 5 5 Porph.,Qtz/Feld Porph.,Qtz/Feld. 6 81GWJ—2055 8 1 G W J - 2 0 4 8 Arenite Arenite 7 8IGWJ—2048 88 82GWJ—ooo 8 2 G W J - 0 0 0 8 Iflt.,Tuff lnt..Tuff 99 82GWJ—069 8 2 G W J - 0 6 9 1 Wacke Wacke 1 0 82GWJ-0092 8 2 G W J - 0 0 9 2 Wacko Wacke 10 Warciub Group CALC-ALKALINE NA2Ot K20 FEO(TOTAL) B A Point No. MOO MGO AL203 Sample No. 81GWJ-2050 8 1 G W J - 2 0 5 0 Int.,Tuff Int..Tuff 8 1 G W J - 2 0 5 4 Porph..Qtz/Feld. Porph..Otz/Feld. 22 81GWJ—2054 Int.,Tutf 3 3 82GWJ0169 82GWJ-0169 Int..Tuff 8 2 ~ w J - 0 4 9 1 Tuft T u f f Breccia Breccia 4 82GWJ0491 1 1 FEO+FE203-.TI THOLEIITIC Berry River Formation 55 82GWJ-0601 8 2 G W J - 0 6 0 1 Tuft Tuff 66 82GWJ—061 8 2 G W J - 0 6 111 Porptt,Feld. Porph..Feld. 77 82GWJ0662 8 2 G W J - 0 8 6 2 Lapilli L a p i l l i Tuft Tuff 8 8 836WJ—4 8 3 G W J - 4 1172 72 Porph.,OtZ/Feld. Porph.,Qtz/Feld. 99 83GWJ4 8 3 G W J - 4173 1 7 3 fnt.Tutt Int.,Tuff 10 1 0 83GWJ5279 8 3 G W J - 5 2 7 9 tnt.,Tuft Int..Tuff 11 1 1 830WJ—5282 8 3 G W J - 5 2 8 2 Porph..OtZ/Feld. Porph..Qtz/Fald. 12 1 2 836WJ—5283 8 3 G W J - 5 2 8 3 tnt.,Tuft Int.,Tuff 13 1 3 83GWJ-5286 8 3 G W J - 5 2 8 6 Tutt,Fetd. Tuff,Feld. 14 1 4 83GWJ—5294 8 3 G W J - 5 2 9 4 Tutf Tuff 15 1 5 83GWJ5295 8 3 G W J 5 2 9 5 Int.,Tutf Int..Tuff 16 1 6 83GWJ-5296 8 3 G W J - 5 2 9 6 TuttFeld Tuff,Feld 17 1 7 83GWJ—5297 83GWJ-5297 Porph.,Qfz/Feld. Porph.,Qtz/Feld. 18 83GWJ4174 18 8 3 G W J - 4 1 7 4 Tuft Tuff 19 83GWJ4176 19 8 3 ~ ~ ~ - , 4 1Tuft T7 u f6f Broccia Breccia 20 3GWJ4177 20 8 3 ~ ~ ~ - 4Mafic 1M 7a f i7cFfow Flow AL203 F i g u r e 6: 6: Figure A FM ternary t e r n a r y diagram d i a g r a m (Irvine ( T r v i n e and and Baragar, B a r a q a r , 1971) 1971 ) and and Al—Fe—Ti—Mg Al-Fe-Ti-Mq molecular molecular AFM p r o p o r t i o n ternary t e r n a r y diagram d i a q r a m (iensen, ( J e n s e n , 1976) 1976 ) of o f wackes w a c k e s and and pyroclastics p y r o c l a s t i c s from from proportion the t h e Warcluh W a r c l u b group g r o u p (top) ( t o p ) and and Berry B e r r y River R i v e r formation f o r m a t i o n (bottom). (bottom). H N) �121 A B I c#..41YE A B I C Figure F i g u r e 7: 7: stratigraphy s t r a t i g r a p h y will will comprise c o m p r i s e rrelatively elatively Continuous layers continuous layers stratigraphy s t r a t i g r a p h y of of mixed mixed layers l a y e r s and and lenticular l e n t i c u l a r units units stratigraphy s t r a t i g r a p h y of of llenticular e n t i c u l a r units units S t r a t i g r a p h i c sections s e c t i o n s through t h r o u g h aa volcano volcano Stratigraphic illustrating of i l l u s t r a t i n g the t h e continuity c o n t i n u i t y and a n d complexity c o m p l e x i t y of sstratiqraphy t r a t i g r a p h y in i n different d i f f e r e n t sections. sections. �122 P o s i t i o n Relative R e l a t i v e to t o Source Source Position F i s h e r and a n d Schmincke S c h m i n c k e (1984) ( 1 9 8 4 ) have h a v e subdivided s u b d i v i d e d this t h i s parameter parameter Fisher into: i n t e r m e d i a t e - s o u r c e facies f a c i e s and a n d distant distant i n t o : near—source n e a r - s o u r c e facies; f a c i e s ; intermediate—source These are relative terms and distance values vary with terms a n d d i s t a n c e v a l u e s v a r y with f a c i e s . T h e s e a r e r e l a t i v e facies. t o p o q r a p h y , eruption e r u p t i o n strength, s t r e n g t h , subaerial s u b a e r i a l vs. v s . subaqueous subaqueous topoqraphy, e n v i r o n m e n t etc.. e t c . . Williams W i l l i a m s and a n d McBirney M c B i r n e y (1979) ( 1 9 7 9 ) have h a v e provided provided environment terms; central c e n t r a l facies f a c i e s (0.5—2 ( 0 . 5 - 2 km km n u m e r i c a l estimates e s t i m a t e s for f o r these t h e s e terms; numerical f r o m vent); v e n t ) ; proximal p r o x i m a l facies f a c i e s (5—15 ( 5 - 1 5 km km from f r o m vent) v e n t ) and a n d distal d i s t a l facies facies from ( g r e a t e r than t h a n 5—15 5-15 km km from f r o m vent). v e n t ) . Providing P r o v i d i n g allowances a l l o w a n c e s are a r e made made (greater f o r differences d i f f e r e n c e s in i n method m e t h o d of o f deposition d e p o s i t i o n and a n d in i n the t h e mode mode of of for preservation, p r e s e r v a t i o n , these t h e s e concepts c o n c e p t s can c a n be b e applied a p p l i e d to t o Archean A r c h e a n pyrolastic pyrolast ic d e p o s i t s (Table ( T a b l e3). 3 ) . The T h e products p r o d u c t s listed l i s t e d in i n table t a b l e 33 for f o r each each deposits facies/zone f a c i e s / z o n e can c a n be be related r e l a t e d to t o aa large l a r g e central c e n t r a l vent v e n t composite composite v o l c a n o (Figure ( F i g u r e8). 8). volcano E n v i r o n m e n t of o f Deposition Deposit i o n Environment This T h i s method m e t h o d of o f facies f a c i e s analysis a n a l y s i s considers c o n s i d e r s all a l l physical, physical, chemical c h e m i c a l and a n d geological g e o l o g i c a l features f e a t u r e s that t h a t affect a f f e c t deposition. d e p o s i t i o n . Such Such t o be b e fully f u l l y exploited e x p l o i t e d in i n studies s t u d i e s of of f a c i e s models m o d e l s have h a v e yet y e t to facies A r c h e a n pyroclastic p y r o c l a s t i c rocks. r o c k s . The T h e facies f a c i e s model m o d e l of o f the t h e Berry B e r r y River River Archean formation l a t e r attempts a t t e m p t s to t o postulate p o s t u l a t e an a n environment e n v i r o n m e n t of of f o r m a t i o n presented p r e s e n t e d later depos ition. deposition. P r i m a r y Composition Composition Primary I n complex c o m p l e x aareas, r e a s , such s u c h as a s near n e a rvent, v e n ta , petrologic—chemical a petrologic-chemical In s e d tto o separate s e p a r a t e assemblages a s s e m b l a g e s into i n t obroad broad a p p r o a c h may may be approach be uused compositional t o aid a i d the t h edetermination d e t e r m i n a t i o n of of c o m p o s i t i o n a l ccategories a t e g o r i e s to s t r a t i g r a p h i c relationships. r e l a t i o n s h i p s . Note Note hhowever o w e v e r t hthat a t iif f this t h i s were were the the stratigraphic s o l e approach a p p r o a c h here h e r e then t h e n the t h e entire e n t i r e Berry B e r r y River R i v e r formation f o r m a t i o n would w o u l d be be sole classed a s one o n e facies f a c i e s (Figure ( F i g u r e 6); 6 ) ; calc—alkaline c a l c - a l k a l i n e dacite. dacite. c l a s s e d as --- FACIES------MODEL FOR FOR THE THE BERRY BERRY RIVER RIVER FORMATION FORMATION FACIES MODEL Figure F i q u r e 44 portrays p o r t r a y s the t h e stratigraphic s t r a t i q r a p h i c setting s e t t i n g of o f the the Various f o r m a t i o n within w i t h i n the t h eLong Long Bay—Lobstick Bay-Lobs t i c k Bay Bay area. a r e a . Various formation Subunits a r e shown shown in i n Figure F i g u r e 3. 3. S u b u n i t s based based s t r u c t u r a l complications c o m p l i c a t i o n s are structural u p o n rrecognition e c o q n i t i o n of o f depositional d e p o s i t i o n a l processes p r o c e s s e swere were erected e r e c t e d within within upon t h e formation f o r m a t i o n as a s previously p r e v i o u s l y described. d e s c r i b e d . These T h e s e subunits s u b u n i t s were were the categorized c a t e g o r i z e d in i n terms terms of o f distance d i s t a n c e from f r o m source, s o u r c e , environment e n v i r o n m e n t of of deposition d e p o s i t i o n and a n d degree d e g r e e of o f reworking r e w o r k i n g based b a s e d on o n primary p r i m a r y structures structures a n d lithological l i t h o l o g i c a l association. association. and The t w o episodes e p i s o d e s of of T h e Berry B e r r y River R i v e r formation f o r m a t i o n developed d e v e l o p e d during d u r i n g two e x p l o s i v e volcanism. v o l c a n i s m . The The first f i r s t episode e p i s o d e resulted r e s u l t e d in i n subaqueous subaqueous explosive deposition d e p o s i t i o n of o f the t h e proximal—distal p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s along a l o n g with with t h i n ash a s h flow f l o w tuffs t u f f s (Figure ( F i g u r e 9). 9 ) . During D u r i n g the t h e second s e c o n d episode episode thin involving same volcano v o l c a n o (Figure ( F i g u r e 6), 6 ) , eruptions e r u p t i o n s may may have h a v e been been i n v o l v i n g the t h e same subaerial s u b a e r i a l but b u t deposition d e p o s i t i o n was was subaqueous s u b a q u e o u s in i n the t h e proximal p r o x imal d e p o s i t i o n facies. f a c i e s . AA thick t h i c k ash a s h flow f l o w tuff t u f f is is also a l s o associated a s s o c i a t e d with with deposition 9 ) . AA subvolcanic s u b v o l c a n i c quartz—feldspar quartz-feldspar t h i s eruptive e r u p t i v e event e v e n t (Figure ( F i g u r e 9). this porphyry was intruded i n t r u d e d into i n t o the t h e vent v e n t complex c o m p l e x of o f the t h e proximal proximal p o r p h y r y was Adjacent t o this t h i s is i s aa facies f a c i e s of o f reworked reworked d e p o s i t i o n facies. facies. A d j a c e n t to deposition c o a r s e to t o fine f i n e pyroclastics p y r o c l a s t i c s interbedded i n t e r b e d d e d with w i t h and a n d prograding p r o g r a d i n g into into coarse w a c k e s of o f an a n epiclastic e p i c l a s t i c facies f a c i e s (Figure ( F i g u r e 9). 9). wackes - . �123 Table T a b l e 3: 3: P r o d u c t s associated a s s o c i a t e d with w i t h the t h e four f o u r main m a i n volcanic v o l c a n i c facies facies Products o f aa central c e n t r a l vent v e n t as a s shown s h o w n in i n Figure F i g u r e 8. 8 . Johns J o h n s et e t al. al. of ( 1 9 8 3 ) . Adapted A d a p t e d from f r o m Williams W i l l i a m s and and McBirney M c B i r n e y (1979). ( 1 979). (1983). VENT FACIES FACIES VENT (0.5-2 ( 0 . 5 - 2 km from f r o m vent) vent ) dikes, d i k e s , sills s i l l s and and domes domes co—ignimbrite its c o - i g n i m b r i t e depos d e p o sits Depositional phreatomagmatic Depositional p h r e a t o m a g m a t i c deposits deposits talus t a l u s breccia, b r e c c i a , megabreccia megabreccia PROXIMAL FACIES FACIES (2—15 ( 2 - 1 5 km from f r o m vent) vent) air a i r fall f a l l deposits d e p o s i t s (tuffs) (tuffs) pyroclastic p y r o c l a s t i c flows flows subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows flows lava l a v a flows f l o w s and and domes domes Depositional Depos i t i o n a l 1 Lahars Lahars Recognizable as pyroclastics pyroclastic R e c o g n i z a b l e a s p y r o c l a s t i c s p y r o c l a s t i c flows flows tuffs tuffs Red epos e p o sii tted ed Red Recognizable R e c o g n i z a b l e as a s volcanic v o l c a n i c sediments s e d iments debris d e b r i s flows flows arenites wac wac kkes es DISTAL D ISTAL FACIES FACIES (>5—15 0 5 - 1 5 km from f r o m vent) vent) air a i r fall f a l l deposits d e p o s i t s (tuffs) (tuffs) pyroclastic p y r o c l a s t i c flows flows subaqueous s u b a q u e o u s pyroclastic p y r o c l a s t i c flows flows lava l a v a flows flows Depos iitional tional Redeposited Redeposited / c 11ah a haarr ss Recognizable as pyroclastics pyroclastic R e c o g n i z a b l e a s p y r o c l a s t i c s p y r o c l a s t i c flows flows ( tufts tuffs ,debris flows arenites Recognizable R e c o g n i z a b l e as a s volcanic v o l c a n i c sediments sediments wac Wac kkes es ss il il ts ttones ones EPICLASTIC FACIES FACIES Redepos it e d Redeposited Tal T a l us us debris d e b r i s flows flows sediments s e d iments in i n crater c r a t e r lakes l a k e s (active, ( a c t i v e , extinct) extinct) perched ponds (Santiaguito) perched ponds ( S a n t i a g u i t o ) alluvial a l l u v i a l fans f a n s (Caribbean) (Caribbean) �Figure 8: Principal facies variation in volcanic rocks related to a large central vent Central zone is also known as the vent facies. composite volcano. Epiclastic facies can occur in all three zones. Products of each Easton and Johns (in press) modified zone/facies are listed in Table 3. from Williams and McBirney (1979). .4 1) T-4 d e n M4J4-1U.4 d r r - 1 Ul M -1-1 -1-1 IÑà a w s H �125 D e s c r i p t i o n of o f Volcanic V o l c a n i c Facies F a c i e s Components Components Description Each volcanic v o l c a n i c facies f a c i e s within w i t h i n the t h eBerry B e r r y River R i v e r formation f o r m a t i o n has h a s aa Each u n i q u e character, c h a r a c t e r , as a s described d e s c r i b e d below. b e l o w . Figure F i g u r e 10 10 illustrates i l l u s t r a t e s the the unique v a r i o u s s t y l e s o f d e p o s i t i o n f o r t h e f a c i e s o f t h e B e r r y R i v e various styles of deposition for the facies of the Berry Riverr f o r m a tion. ion. format D i s t a l Deposition D e p o s i t i o n Facies F a c i e s (Stops ( S t o p s 99 and and 11) 11 ) P r o x i m a l —- Distal Proximal The d e s i g n a t i o n p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s does d o e s not not The designation proximal—distal deposition facies iindicate n d i c a t e aa facies f a c i e s progressing p r o g r e s s i n g from f r o m aa proximal p r o x i m a l setting s e t t i n g to t o aa distal distal setting. I t instead i n s t e a d refers r e f e r s to t o aa facies f a c i e s association a s s o c i a t i o n without without setting. It s u f f i c i e n t d i s t i n c t p r i m a r y f e a t u r e s w h i c h p e r m i t a s s i g n m e n t to to sufficient distinct primary features which permit assignment o n e e n v i r o n m e n t . T h e r e f o r e t h i s f a c i e s r e p r e s e n t s b o t h p r o x i m al one environment. Therefore this facies represents both proximal and d i s t a l e n v i r o n m e n t s . I t is a u n i t f o r m e d by d e p o s i t i o n and distal environments. It is a unit formed by deposition d i r e c t l y from f r o m the t h e volcano v o l c a n o without w i t h o u t significant s i g n i f i c a n t reworking. r e w o r k i n g . The The directly p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s ex t e n d s t h e l e n g t h o f t h proximal—distal deposition facies extends the length of thee f o r m a t i o n (Figure ( F i g u r e 9). 9 ) . While W h i l e the t h e eastern e a s t e r n and and western w e s t e r n portions p o r t i o n s are are formation s i m i l a r , t h e c e n t r a l p o r t i o n is o f a d i f f e r e n t n a t u r e . similar, the central portion is of a different nature. w e s t the t h e deposits d e p o s i t s are a r emassive, m a s s i v e , interbedded, interbedded, I n the t h e east e a s t and and west In p o o r l y s o r t e d , c o a r s e , med ium and f i n e , c o m p o s i t i o n a l y homopoorly—sorted, coarse, medium and fine, compositionallyl homo— l i t h i c to t o bimodal b i m o d a l debris d e b r i s flows. f l o w s . The The bedding b e d d i n g planes p l a n e s between between d e p o s i t s are a r e generally g e n e r a l l y indistinct i n d i s t i n c t indicating i n d i c a t i n g rapid r a p i d accumulation. accumulation. deposits I n t e r b e d d e d w i t h t h e s e m a s s i v e d e p o s i t s a r e d i s c o n t i n u o u s ash ash Interbedded with these massive deposits are discontinuous f l o w t u f f . T h e s e d i s c o n t i n u o u s t u f f s a r e i n s i m i l a r s t r a t iflow tuff. These discontinuous tuffs are in similar strati— g r a p h i c p o s i t i o n s ( F i g u r e 9 ) i n d i c a t i n g e i t h e r e r o s i o n a f t er graphic positions (Figure 9) indicating either erosion after d e p o s i t i o n o r t o p o g r a p h i c c o n t r o l o f d e p o s i t i o n . F i g u r e 1 0, deposition or topographic control of deposition. Figure 10, A i s a s k e t c h o f t h e s e d e p o s i t i o n a l e v e n t s . s t a g e stage A is a sketch of these depositional events. The central c e n t r a l portion, p o r t i o n , particularly p a r t i c u l a r l y south—southwest s o u t h - s o u t h w e s t of o f Berry Berry The Lake c o n s i s t s o f d o u b l y g r a d e d s u b a q u e o u s p y r o c l a s t i c f l o w Lake consists of doubly graded subaqueous pyroclastic flow ( s e e Figure F i g u r e 5), 5 ) , massive m a s s i v e coarse c o a r s e and and medium medium clast c l a s t sized sized d e p o s i t s (see deposits d e b r i s f l o w d e p o s i t s , t h i c k l y l a m i n a t e d t u f f s and p u m i c e o u debris flow deposits, thickly laminated tuffs and pumiceouss l a p i l l i - t u f f fall—out f a l l - o u t deposits d e p o s i t s and a n d massive m a s s i v e tuffs t u f f s (see ( s e e Figures F i g u r e s 18 18 lapilli—tuff a n 1 9 , S t o p 9 and F i g u r e 2 0 , S t o p 1 1 ) . T u f f s d e p o s i t e d b y a s h an 19, Stop 9 and Figure 20, Stop 11). Tuffs deposited by ash l i t h o l o g ies f l o w mechanisms m e c h a n i s m s are a r e interbedded i n t e r b e d d e d with w i t h these t h e s e lithologies. Bedding flow Bedding t o d i s t i n c t . The p l a n e s b e t w e e n a l l u n i t s a r e g e n e r a l l y s h a r p planes between all units are generally sharp to distinct. The d e p o s i t s a r e c o m p o s i t i o n a l l y homo1 i t h i c t o b i m o d a l , m a t r i x deposits are compositionally homolithic to bimodal, matrix i s aa s u p p o r t e d and a n d show s h o w normal n o r m a l and a n d reverse r e v e r s e grading. g r a d i n g . Pumice P u m i c e is supported common c o n s t i t u e n t i n t h e f i n e r d e p o s i t s . F i g u r e 10 s t a g e BB outoutcommon constituent in the finer deposits. Figure 10 stage llines i n e s the t h e mechanism m e c h a n i s m of o f deposition d e p o s i t i o n for f o r this t h i s portion p o r t i o n of o f the the is in i n aa shallow s h a l l o w basin basin p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s which w h i c h is proximal—distal w i t h i n the t h e more more massive m a s s i v e units. units. within lithic . F l o w Tuff T u f f Deposits D e p o s i t s (Stop ( S t o p 10) 10) Ash Flow Ash Ash f l o w t u f f o c c u r s a s d i s c o n t i n u o u s units u n i t s within w i t h i n the the Ash flow tuff occurs as discontinuous p r o x i m a l d i s t a l d e p o s i t i o n f a c i e s and a s a t h i c k c o n t i n u o u s unit unit proximal—distal deposition facies and as a thick continuous b e t w e e n t h e p r o x i m a l d i s t a l and p r o x i m a l d e p o s i t i o n f a c i e s between the proximal—distal and proximal deposition facies ( F i g u r e 9). 9 ) . The The ash a s h flow f l o w tuff t u f f deposits d e p o s i t s are a r e massive, m a s s i v e , broken b r o k e n and and (Figure t o f e l d s p a r e u h e d r a l c r y s t a l s u p p o r t e d q u a r t z f e l d s p a r t u f f euhedral crystal supported quartz—feldspar tuff to feldspar tuff. D i s t i n c t lithic l i t h i c clast c l a s t rich r i c h zones z o n e s of o f the t h e base b a s e or o r pumiceous pumiceous tuff. Distinct were n o t o b s e r v e d i n t h e t h i n n e r u n i t s . C l astic u p p e r p a r t s upper parts were not observed in the thinner units. Clastic were n o t e d i n t h e t h i c k e r u n i t i n d i c a t i n g t h e p o s sibility z o n e s zones were noted in the thicker unit indicating the possibility z o n e s , discontinuous d i s c o n t i n u o u s along along o f several s e v e r a l events. e v e n t s . These T h e s e clastic c l a s t i c zones, of s t r i k e may may represent r e p r e s e n t the t h e base b a s e of o f ash a s h flow f l o w deposits. d e p o s i t s . The The lack l a c k of of strike d i s t i n c t b e d s may b e a c c o u n t e d f o r by r a p i d a c c u m u l a t i o n o f distinct beds may be accounted for by rapid accumulation of were s e v e r a l ash a s h flows f l o w s cooling c o o l i n g as a s one o n e unit. unit. M i n o r lithic l i t h i c lapilli l a p i l l i were several Minor n o t e d t h r o u g h o u t t h e t h i c k c o o l i n g u n i t . T h e s e a s h f l o w t u f f s noted throughout the thick cooling unit. These ash flow tuffs �( Bj? Figure 9: Long +++1Granitoids ñt I 0 * 1 — + .ong Bay / + - — + + 3 + + :: 4 +............. kilometres 2 :++++++++ +++++I I epiclastuc tacies H :1 distal redeposition 5 + + + + + ++++++++** ++ :+::::+ * + * + + + ++ —--— stratigraphic contact facies boundary diabase dike fault lithologic contact +++::::j ash flow tuffs vent facies r proximal deposition (shallow water) y///////proximal—distal deposition (component of redeposition) L BERRY RIVER FORMATION O: C 0 4 r - f 0) ( 0 ( 0 C O U > I-) Vent facies is a subvolcanic quartz—feldspar porphyry intrusive into the base of a volcano. Proximal deposition facies is composed of coarse Schematic diagram of the facies distribution of the Berry River formation. Snake Bay Formation Warclub Group L. '±' Point Bay Group OLDER UNITS w.0 a o o + homolithic pyroclastics. Proximal—distal deposition facies contains a Distal redeposited and epiclastic variety of pyroclastic deposit types. facies are derived from the previous facies. e U4Ju-i en en a a q I\j H �127 were were deposited d e p o s i t e d during d u r i n g stage s t a g e A, A, B and a n d C, C , Figure F i g u r e 10. 10. Proximal P r o x i m a l Deposition D e p o s i t i o n Facies F a c i e s (Stops ( S t o p s 3, 3 , 4, 4 , 77 and and 8) 8) The proximal p r o x i m a l deposition d e p o s i t i o n facies f a c i e s occurs o c c u r s at a t the t h e east e a s t end e n d of o f the the The Berry B e r r y River R i v e r formation f o r m a t i o n nnorth o r t h oof f Lobstick L o b s t i c k Bay Bay aand n d iin n tthe h e central central part 9). I t isi composi— s composip a r t of o f the t h eformation f o r m a t i o nwithin w i t h i nLong Long Bay Bay (figure ( f i g u r e 9). It tionally t i o n a l l y homolithic h o m o l i t h i c pyroclastic p y r o c l a s t i c breccia b r e c c i a to t o tuff t u f f brecc.ia b r e c c - i a with with mostly quartzm o s t l y quartz—feldspar q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts l a s t s and a n d the t h e matrix m a t r i x isisquartz— feldspar f e l d s p a r tuff. t u f f . The The facies f a c i e s represents r e p r e s e n t s aa proximal p r o x i m a l environment e n v i r o n m e n t and and direct d i r e c t deposition d e p o s i t i o n by b y volcanic v o l c a n i c processes. processes. This f a c i e s is is composed composed of o f matrix m a t r i x supported, s u p p o r t e d , thickly—bedded, thickly-bedded , Th i s facies l a p i l l i s t o n e to t o pyroclastic p y r o c l a s t i c breccia b r e c c i a deposited d e p o s i t e d by b y the t h e block b l o c k and and lapillistone ash e t al. a l . 1973). 1 9 7 3 ) . Bedding B e d d i n g planes p l a n e s range range a s h flow f l o w process p r o c e s s (Sparks, ( S p a r k s , et from t o sharp s h a r p indicating i n d i c a t i n g rapid r a p i d accumulation. accumulation. Thin f r o m gradational g r a d a t i o n a l to Thin tuff t u f f beds b e d s separate s e p a r a t e some some block b l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s and a n d grain grain size s i z e gradations g r a d a t i o n s occur o c c u r within w i t h i n these t h e s e beds. beds. T h e s e thin t h i n tuff t u f f inter— interThese beds b e d s are a r e the t h e surge s u r g e deposit d e p o s i t portion p o r t i o n of o f block b l o c k and and ash a s h flow f l o w subsubunits. u n i t s . Thin T h i n tuffs t u f f s overlying o v e r l y i n g the t h e main m a i n body b o d y of o f the t h e block b l o c k and and ash ash flow f l o w deposits d e p o s i t s exhibit e x h i b i t grain g r a i n gradation, g r a d a t i o n , suggesting s u g g e s t i n g they t h e y are are products p r o d u c t s of o f cloud c l o u d surge s u r g e deposition d e p o s i t i o n rather r a t h e r than t h a n ground g r o u n d surge s u r g e (stop (stop 3). 3 ) . Primary P r i m a r y features f e a t u r e s such s u c h as a s gas g a s escape e s c a p e structures s t r u c t u r e s are a r e found found within w i t h i n block b l o c k and a n d ash a s h flows f l o w s (stop ( s t o p 7). 7 ) . These T h e s e features f e a t u r e s are a r e limited limited to t o the t h e top t o p of o f cooling c o o l i n g units. units. Figure and DD outline o u t l i n e the t h e depositional d e p o s i t i o n a l environenvironF i g u r e 10 1 0 stages s t a g e s CC and ment m e n t envisaged e n v i s a g e d for f o r this t h i s facies. facies. Vent V e n t Facies Facies Vent t o the t h e eastern e a s t e r n end end of o f the the V e n t facies f a c i e s rocks r o c k s are a r e restricted r e s t r i c t e d to Berry is represented represented B e r r y River R i v e r formation f o r m a t i o n (figure ( f i g u r e 9). 9 ) . The The vent v e n t facies f a c i e s is by b y aa subvolcanic s u b v o l c a n i c quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y intrusion i n t r u s i o n cutting c u t t i n g the the proximal p r o x i m a l deposition d e p o s i t i o n facies. f a c i e s . Portions P o r t i o n s of o f the t h e porphyry p o r p h y r y are are massive, o r brecciated. b r e c c i a t e d . The The c l a s t i c or m a s s i v e , while w h i l e others o t h e r s are a r e subtly s u b t l y clastic porphyry is similar s i m i l a r in i n petrography p e t r o g r a p h y to t o the t h e clasts c l a s t s of o f the t h e proximal proximal p o r p h y r y is deposition d e p o s i t i o n facies. f a c i e s . Rafts R a f t s and a n d xenoliths x e n o l i t h s of o f the t h e proximal p r o x i m a l unit u n i t are are found f o u n d within w i t h i n the t h e vent v e n t facies f a c i e s intrusive. intrusive. The The similarity s i m i l a r i t y between b e t w e e n clasts c l a s t s of o f the t h e proximal p r o x i m a l deposition deposition facies w e l l as a s the t h e presence p r e s e n c e of o f rafts r a f t s and and f a c i e s and and the t h e porphyry p o r p h y r y as a s well xenoliths was emplaced e m p l a c e d into i n t o the t h e lower lower x e n o l i t h s suggests s u g g e s t s that t h a t the t h e porphyry p o r p h y r y was part p a r t of o f aa growing g r o w i n g volcanic v o l c a n i c edifice e d i f i c e and and may may have h a v e been b e e n the t h e magma magma chamber c h a m b e r feeding f e e d i n g the t h e block b l o c k and a n d ash a s h flows f l o w s overlying o v e r l y i n g the t h e thick t h i c k ash ash flow f l o w tuff t u f f (Figure ( F i g u r e 10, 1 0 , Stage S t a g e D). D). Distal D i s t a l Redeposited R e d e p o s i t e d Facies F a c i e s (Stops ( S t o p s 6, 6 , 99 and a n d 11) 11) Rocks Rocks of o f the t h e distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s occur o c c u r in i n two t w o strati— stratigraphic g r a p h i c positions. p o s i t i o n s . They T h e y are a r e found f o u n d at a t the t h e base b a s e of o f the t h e Berry B e r r y River River formation f o r m a t i o n south—southwest s o u t h - s o u t h w e s t of o f Berry B e r r y Lake Lake and a n d north n o r t h of o f Mist M i s t Inlet Inlet and M i s t Inlet I n l e t (Figure ( F i g u r e9). 9 ) . The The a n d at a t the t h e top t o p of o f the t h e formation f o r m a t i o n in i n Mist distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s exhibits e x h i b i t s primary p r i m a r y structures s t r u c t u r e s and and rock rock associations t y p i c a l of o f aa distal d i s t a l environment. e n v i r o n m e n t . Evidence Evidence a s s o c i a t i o n s (Table ( T a b l e 3) 3 ) typical for f o r re—working r e - w o r k i n g is i s shown shown on o n Table T a b l e 1.1 . South—southeast S o u t h - s o u t h e a s t of o f Berry B e r r y Lake Lake the t h e distal d i s t a l redeposited r e d e p o s i t e d facies facies has ( s e e Figure F i g u r e 18, 1 8 , Stop S t o p 99 and and Figure F i g u r e 20, 2 0 , stop stop h a s varied v a r i e d thickness t h i c k n e s s (see 11) 1 1 ) and and consists c o n s i s t s of o f moderately m o d e r a t e l y sorted, s o r t e d , thin t h i n to t o thick t h i c k bedded, bedded, cross c r o s s bedded, b e d d e d , graded g r a d e d reworked r e w o r k e d tuffs t u f f s and a n d lapilli l a p i l l i tuff. t u f f . Evidence Evidence �128 Stage AA Stage -- sea mad lev< Sea ource volcanic slope T7 active a volcanism volcanism m c slope \ active active faulting/slumping -7 active faulting/slumping P turbidity current tufts Warclub group metuseduments source aulcanic volcanic vent vent source Plinian type Eruptions Plunuan type Eruptions f pyroclastic flows flows and and tufts tuffs pyroclastuc StageBB Stage - -0 0 /-/ '-'-, ii sea lev fallout tephra Warclub group metaseduments StageCC Stage - -'' P ,- source volcanic volcanic vent vent source Phnian ttype y p e eruptions eruptions Pluniun block and ash f l o ws block and ash flows ash flows flows ash ciubgroupmefa5edim' J- - / - 7 n r^ , Stage D StageD source volcanic volcanicvent vent source Plinian ttype y p e eruptions eruptions Plinuan block and and ash ash flows flows block block and ash flow epiclastic facies �123 Figure F i g u r e 10: Stage A: S t a g e A: Stage S t a g e B: B: P r o p o s e d model o r the t h e development d e v e l o p m e n t oof f the t h e Berry Berry Proposed modelf for River R i v e r formation. formation. P r o x i m a l—- Distal D i s t a l Deposition D e p o s i t i o n Facies: F a c i e s : Debris D e b r i s flows flows Proximal and and ttuffs. uffs. A vvolcanic o l c a n i c eedifice d i f i c e is is constructed c o n s t r u c t e d by by explosive explosive A vvolcanism. olcanism. B u i l d i n g and and ooversteepening v e r s t e e p e n i n g oof f the t h e cone cone Building rresults e s u l t s in i n slumping s l u m p i n g of o f coarse c o a r s e pyroclastic p y r o c l a s t i c material material i n t o aa basin b a s i n in i n the t h eunderlying u n d e r l y i n g sediments s e d i m e n t s of o f the the into Warciub W a r c l u b ggroup. roup. IInterbedded n t e r b e d d e d t tuffs u f f s in i n this t h i ssequence sequence aare r e ddeposited e p o s i t e d ffrom r o m ffine i n e aash s h cclouds l o u d s eelutriated l u t r i a t e d ffrom rom less violent violent tthe h e turbulent t u r b u l e n t mass f l o w s and and from from less mass flows eruptions. A l t h o u g h these t h e s e thickly t h i c k l y bedded bedded deposits deposits eruptions. Although tthin h i n llaterally, a t e r a l l y , they t h e y do d o not n o t appear a p p e a r to t o grade grade laterally. laterally. T h e s e deposits d e p o s i t s are a r e best b e s t exposed e x p o s e d at a t the t h e east e a s t and and These w e s t ends e n d s of o f the t h e Berry B e r r y River R i v e r formation. formation. west PProximal r o x i m a l — ~Distal i s t a lDeposition D e p o s i t i o n Facies: Facies: Subaqueous Subaqueous P y r o c l a s t i c Flow Flow Deposit D e p o s i t and and Fall—Out F a 1 1-Out Deposits Deposits Pyroclastic The growing g r o w i n g edifice e d i f i c e approaches a p p r o a c h e s sea s e a level. level. The eeruption r u p t i o n ppattern a t t e r n changes c h a n g e s from f r o m single, s i n g l e , violent violent eexplosive x p l o s i v e events e v e n t s to t o a relatively r e l a t i v e l y continuous c o n t i n u o u s series series These oof f explosions e x p l o s i o n s that t h a t wane wane in i n energy. energy. T h e s e eruptions eruptions by Fiske Matsuda aare r e ssimilar i m i l a r to t o those t h o s e ddescribed e s c r i b e d by F i s k e and and M atsuda (1964) r o d u c i n g ddoubly o u b l y graded g r a d e d subaqueous subaqueous ( 1 9 6 4 ) pproducing which ppyroclastic y r o c l a s t i c flow f l o w ddeposits eposits w h i c h fill fill a a sshallow hallow basin b a s i n in i n the t h e underlying u n d e r l y i n g massive m a s s i v e deposits. deposits. The becomes ssubaerial eeruptive r u p t i v e ccolumn o l u m n becomes u b a e r i a l and and fine f i n e ttephra ephra ffalls a l l s oout u t tthrough h r o u g h air a i r and and water, w a t e r , producing p r o d u c i n g thin t h i n to to thick Thin l a p i l l i tuff. tuff Thin t h i c k bedded bedded tuff t u f f and and pumiceous p u m i c e o u s lapilli bbeds e d s oof f ash a s h flow f l o w tuff t u f f and and lapilli l a p i l l i tuff t u f f were were deposited Slumping from d e p o s i t e d at a t this t h i s time. time. Slumping from the t h e edifice edifice also massive, a l s o produced produced m a s s i v e , medium to t o coarse c o a r s e debris debris flow f l o w deposits. d e p o s i t s . These T h e s e deposits d e p o s i t s are a r e confined conÂi n e d to t o the the ccentral e n t r a l pportion o r t i o n of o f the t h eBerry B e r r y River R i v e r formation f o r m a t i o n and and aare r e bbest e s t exposed e x p o s e d between b e t w e e n Highway Highway 71 71 east e a s t to t o the the Berry B e r r y River. River. Proximal Deposition Proximal D e p o s i t i o n Facies: Facies: B l o c k and and Ash Ash flow flow Block Deposits D e p o s i t s and and Ash Flow Flow Tuffs Tuffs The voluminous v o l u m i n o u s eruptions e r u p t i o n s producing p r o d u c i n g the t h e proximal— proximaldistal d i s t a l deposition d e p o s i t i o n facies f a c i e s rocks r o c k s deflate d e f l a t e the t h e magma chamber resulting chamber r e s u l t i n g in i n local l o c a l volcano—tectonic v o l c a n o - t e c t o n i c subsubHomolithic, massive ssidence. idence. H omolithic, m a s s i v e block b l o c k and and ash a s h flow flow A ddeposits e p o s i t s were deposited d e p o s i t e d within w i t h i n the t h e depression. depression. massive ssequence e q u e n c e of o f thick, thick, m a s s i v e ash a s h flow f l o w tuffs, t u f f s , forming forming a a cooling c o o l i n g unit u n i t were were erupted, e r u p t e d , perhaps p e r h a p s subaerially, s u b a e r i a l ly, from This f r o m the t h e vent. vent. T h i s ddepression e p r e s s i o n later l a t e r becomes becomes the the ccenter e n t e r of o f renewed renewed vvolcanism o l c a n i s m in i n a shallow s h a l l o w water env e n v iironment. ronment P r o x i m a l Deposition D e p o s i t i o n Facies F a c i e s and and Redeposited R e d e p o s i t e d Facies Facies Proximal While W h i l e explosive e x p l o s i v e eruptions e r u p t i o n s continue c o n t i n u e to t o build b u i l d the the edifice e d i f i c e aa subvolcariic s u b v o l c a n i c qquartz—feldspar u a r t z - f e l d s p a r pporphyry o r p h y r y body iintrudes n t r u d e s the t h e base. base. The eruptions e r u p t i o n s produce p r o d u c e subaerial s u b a e r i a l block b l o c k and and ash a s h flow flow ddeposits e p o s i t s that t h a t prograde p r o q r a d e laterally l a t e r a l l y into i n t o aa shallow shallow water w a t e r environment. environment. S u r g e ddeposits e p o s i t s are a r e recognized r e c o g n i z e d between b e t w e e n block b l o c k and and ash ash Surge p r o x i m a l deposits d e p o s i t s extend ex t e n d aa fflow l o w deposits. d e p o s i t s . these These proximal f a i r ddistance i s t a n c e from the t h e vent v e n t as a s the t h e eruptions e r u p t i o n s were were fair subaerial s u b a e r i a l and and more more violent. violent Reworking oof f these t h e s e ddeposits e p o s i t s and and underlying u n d e r l y i n g units units Reworking r e s u l t e d in i n production p r o d u c t i o n of o f the t h e coarse c o a r s e distal distal resulted epiclastic r e d e p o s i t e d facies f a c i e s rocks r o c k s and and the t h e lateral l a t e r a l epiclastic redeposited ffacies a c ies wackes. wackes E r o s i o n and and ddegredation e g r e d a t i o n of o f the t h e subaerial s u b a e r i a l ediface ediface Erosion p r o d u c e the t h e overlying o v e r l y i n g wacke wacke of o f the t h e Warclub W a r c l u b group. group. produce - . Stage C: S t a g e C: Stage S t a g e D: D: . . . �130 for for reworking r e w o r k i n g in i n this t h i s portion p o r t i o n of o f the t h e facies f a c i e s include i n c l u d e the t h e moderate moderate sorting s o r t i n g and a n d presence p r e s e n c e of o f subrounded s u b r o u n d e d quartz q u a r t z and and feldspar f e l d s p a r crystals crystals a n d lithic l i t h i c clasts. c l a s t s . Along Along the t h e basal b a s a l contact c o n t a c t of o f this t h i s facies f a c i e s thin thin and beds west (see (see b e d s show s h o w evidence e v i d e n c e for f o r prograding p r o g r a d i n g from f r o m both b o t h east e a s t and and west 1 8 , stop s t o p 9). 9). F i g u r e 18, Figure N o r t h of o f Mist M i s t Inlet I n l e t at a tthe t h etop t o pofo the f t hBerry e B e r r yRiver R i v e rformation formation North 9 ) distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s rocks r o c k s consist c o n s i s t of o f interbedd— interbedd( F i g u r e 9) (Figure The ed, t o tuff. tuff. The presence p r e s e n c e of of e d , heterolithic, h e t e r o l i t h i c , graded g r a d e d tuff t u f f breccia b r e c c i a to volcanic v o l c a n i c clasts c l a s t s found f o u n d in i n the t h e Berry B e r r y River R i v e r formation f o r m a t i o n indicates i n d i c a t e s that that this i s associated a s s o c i a t e d with w i t h the t h e prograding p r o g r a d i n q Berry B e r r y River River t h i s facies f a c i e s is formation. formation. Evidence Mist Inlet I n l e t area a r e a includes: i n c l u d e s : sub— subE v i d e n c e for f o r reworking r e w o r k i n g in i n the t h e Mist round t o round r o u n d clasts, c l a s t s , poor p o o r to t o moderate m o d e r a t e sorting, s o r t i n g , normal n o r m a l grading, grading, r o u n d to heterolithic h e t e r o l i t h i c nature n a t u r e and and presence p r e s e n c e of o f wacke wacke interheds. i n t e r b e d s . This T h i s tuff tuff to t o pyroclastic p y r o c l a s t i c breccia b r e c c i a unit u n i t is is heterolithic, h e t e r o l i t h i c , poor p o o r to t o well w e l l sorted sorted c l a s t s . Wacke Wacke beds b e d s are a r e interbedded interbedded a n d graded g r a d e d with w i t h subrounded s u b r o u n d e d clasts. and with ( s e e Figure F i g u r e 16, 1 6 , stop s t o p 6). 6). w i t h these t h e s e reworked r e w o r k e d pyroclastic p y r o c l a s t i c rocks r o c k s (see Figure F i g u r e 10 1 0 stage s t a g e DD outlines o u t l i n e s the t h e model m o d e l for f o r the t h e deposition d e p o s i t i o n of of t h e s e rocks. rocks. these E p i c l a s t i c Facies Facies Epiclastic Quartz—feldspar Q u a r t z - f e l d s p a r wackes w a c k e s interdigitate i n t e r d i g i t a t e with w i t h and and overlie overlie proximal—distal p r o x i m a l - d i s t a l deposition d e p o s i t i o n facies f a c i e s rocks r o c k s in i n the t h e western w e s t e r n portion p o r t i o n of of The the t h e Berry B e r r y River R i v e r formation f o r m a t i o n (Figure ( F i g u r e 9) 9) west west of o f Mist M i s t Inlet. Inlet. The wackes t o very v e r y thick t h i c k bedded, b e d d e d , graded g r a d e d (AE (AE Bouma Bouma sequence) sequence) w a c k e s are a r e thick t h i c k to They a n d moderately m o d e r a t e l y sorted. sorted. They resulted r e s u l t e d from f r o m both b o t h reworking r e w o r k i n g of of and pyroclastic p y r o c l a s t i c deposits d e p o s i t s and a n d from f r o m the t h e distal d i s t a l turbiditic t u r b i d i t i c deposition deposition of D). o f block b l o c k and a n d ash a s h flows f l o w s (Figure ( F i g u r e 10, 1 0 , stage s t a g e D). SUMMARY SUMMARY The T h e Berry B e r r y River R i v e r formation f o r m a t i o n has h a s been b e e n placed p l a c e d in i n aa facies facies During context c o n t e x t and a n d as a s such s u c h aa stratigraphy s t r a t i g r a p h y has h a s been b e e n developed. developed. During the w e will w i l l examine e x a m i n e the t h e evidence e v i d e n c e for f o r the t h e proximal— proximalt h e field f i e l d trip t r i p we distal d i s t a l deposition, d e p o s i t i o n , proximal p r o x i m a l deposition, d e p o s i t i o n , ash a s h flow f l o w tuff t u f f and and distal distal r e d e p o s i t i o n facies. facies. redeposition MENTS ACKNOWLEDGEMENTS ACKNOWLEDGE T h e a u t h o r ggratefully r a t e f u l l y acknowledges a c k n o w l e d g e s the t h e assistance a s s i s t a n c e received received from P.C. Thurston and R.M. Easton and M. Easton in the discusf r o m P.C. T h u r s t o n and R.M. E a s t o n and M. E a s t o n i n t h e discussions s i o n s leading l e a d i n g to t o development d e v e l o p m e n t of o f the t h e model m o d e l and and reading r e a d i n g this this m a n u s c r i p t . Draughting D r a u g h t i n g and and setting s e t t i n g of o f the t h e figures f i g u r e s was was skillfully skillfully manuscript. Anna Branicky patiently done by Barb Moore and Krys Gil. Anna B r a n i c k y p a t i e n t l y did d i d the the d o n e b y B a r b Moore a n d Krys G i l . t y p i n g , re—typing, re- t y p i n g , re—re—typing re-re- t y p i n g typing, TTifhor .... �131 FIELD FIELD TRIP TRIP GUIDE GUIDE The The field f i e l d trip t r i p is i s designed d e s i g n e d to t o be b e completed c o m p l e t e d in i n one o n e day d a y with with 11 1 1 stops; s t o p s ; 44 on o n Lake Lake of o f the t h e Woods Woods and a n d 77 with w i t h road r o a d access. a c c e s s . Figures Figures 11 1 1 aand n d 12 1 2 show s h o w the t h e locations l o c a t i o n s of o f the t h e stops. stops. The w i l l commence commence with w i t h stop s t o p 33 but b u t if if T h e 1985 1 9 8 5 I.L.S.G. I.L.S.G. trip t r i p will conditions a n d 22 will will c o n d i t i o n s do d o not n o t permit p e r m i t the t h e use u s e of o f boats b o a t s then t h e n stops s t o p s 1 and be The b e visited. visited. The road r o a d guid•e q u i d - e sstarts t a r t s aatt the t h e Sioux S i o u x Narrows N a r r o w s bridge b r i d g e in in the t h e village v i l l a g e of o f Sioux S i o u x Narrows N a r r o w s on o n Highway Highway 71, 7 1 , 60 6 0 km km south s o u t h of of Highway Highway 17. 17. 1 1) 1) 2) 2) 3) 3) 4) 4) Several S e v e r a l points p o i n t s should s h o u l d be b e made made regarding r e g a r d i n g the t h e area: area: Lake Lake of o f the t h e Woods can c a n be b e treacherous t r e a c h e r o u s with w i t h respect r e s p e c t to to navigation It n a v i g a t i o n and and weather. weather. I t is i s advisable a d v i s a b l e to t o have h a v e aa navigation n a v i g a t i o n map of o f the t h e lake l a k e published p u b l i s h e d by b y the t h e Canadian C a n a d i a n Hydro— Hydrographic g r a p h i c Service, S e r v i c e , Department D e p a r t m e n t of o f Fisheries F i s h e r i e s and a n d the the Environment. These Environment. T h e s e maps are a r e readily r e a d i l y available a v a i l a b l e from f r o m local local outfiters. outfiters. The kccess Road" Roa& used i s aa "Forest " F o r e s t Access u s e d by b y heavy heavy The Maybrun Maybrun Road Road is trucks. w e l l off o f f the t h e right r i g h t of o f way. way. t r u c k s . Please P l e a s e park p a r k well Outcrops wet. O u t c r o p s are a r e slippery s l i p p e r y when when wet. This T h i s is is WOOD WOOD TICK TICK country. country. �paved paved highway highway -==== gravel road road -- geologic contact contact . - - fault/hneament faultAineament @ A field trip trip atop stop location location boat boat launch launch Early Precambrian Precambrian AA- mafic to to intermediate intermediate metavolcanics metavolcanics B -- intermediate Intermediate metavolcanics metavolcanics C-- metasediments metasediments C DD- ultramafic intrusive Intrusive rocks rocks E maticintrusive Intrusive rocks rocks E -—mafic F -- intermediate Intermediate to to felsic fel8ic intrusive intrusive rocks rocks Late Late Precambrian Precambrian G maf Icintrusive intrusive rocks(diabase) rocks(diabase) G -- mafic Pro vncIaI Park bet Launch Regina Bay Figure F i q u r e 11: 11: Navigation N a v i g a t i o n g guide u i d e t otot hthe e f ifield e l d ttrip r i p stop s t o p locations l o c a t i o n s in i n the t h e eastern e a s t e r n part p a r t of o f the the field f i e l d trip t r i p area. area. N-) �-paved highway -- ==--== gravel road - --(Z) A geologic contact faultllineament field trip stop location boat launch :arly Precambrian -mafic to intermediate metavokanici i- intermediate metavoicanics - metasediments 1-ultramafic intrusive rocks - mafic intrusive rocks -intermediate to felsic intrusive rock Figure F i g u r e 12: 12: Navigation N a v i g a t i o n guide g u i d e to t o the t h e field f i e l d trip t r i p stop s t o p locations l o c a t i o n s in i n the t h e western w e s t e r n part p a r t of of the the field trip area. f i e l d t r i p area. w �134 0.0 0.0 km km South S o u t h end end of o f the t h e Sioux S i o u x Narrows N a r r o w s Bridge B r i d g e on o n Highway Highway 71 71 (Figure ( F i g u r e 11). 11). Drive D r i v e south s o u t h on o n Highway Highway 71 71 through t h r o u g h Sioux S i o u x Narrows N a r r o w s for f o r 8.2 -8.2 km t o the t h e Gaudry G a u d r y Road. Road. km to - 8 . 2 km km 8.2 Gaudry G a u d r y Road Road (see ( s e e Figure F i g u r e 13 1 3 for f o r stop s t o p locations) l o c a t i o n s ) Turn T u r n left left o n t o the t h e Gaudry G a u d r y Road Road and and drive d r i v e towards t o w a r d s the t h e Whitefish W h i t e f i s h Bay Bay onto Indian Village . 9 km. I n d i a n Reservation Reservation V i l l a g e ffor o r -0.-.-0.9km. 9. 1 km kin 9.1 Park STOP 1: 1: STOP P a r k above a b o v e the t h e gravel g r a v e l pit p i t on o n the t h e left l e f t side s i d e of of the t h e road r o a d and and walk w a l k to t o outcrop o u t c r o p 'A' ' A ' (Figure ( F i g u r e 13). 13). Formation: Formation: Lithology: Lithology : Setting: Setting: Snake S n a k e Bay formation formation Mafic Maf i c metavolcanics metavolcanics Strike—southeast, dip-vertical, S t r i k e - s o u t h e a s t , dip—vertical, top—northeast. stratigraphic st r a t i g r a p h i c t o p - n o r t h e a s t F e a t u r e ( s ) : Feeder F e e d e r dike, d i k e , hyaloclastite, h y a l o c l a s t i t e , pillows. pillows. Feature(s): . The T h e best b e s t exposures e x p o s u r e s are a r e in i n the t h e cut c u t between b e t w e e n the t h e two two The feeder outcrops o u t c r o p s where w h e r e the t h e gravel g r a v e l has h a s been b e e n removed. removed. feeder d i k e ? in i n Figure F i g u r e 14, 1 4 , strikes s t r i k e s at a t 125° 1 2 5 0 and a n d dips dips dike, It vertically. I t consists c o n s i s t s of o f two t w o symmetrical s y m m e t r i c a l pparts; a r t s ; aa vertically. marginal m a r g i n a l zone z o n e chilled c h i l l e d against a g a i n s t the t h e country c o u n t r y rock r o c k and a n d aa central c e n t r a l zone z o n e chilled c h i l l e d against a g a i n s t the t h e marginal m a r g i n a l zone. zone. The is 77 cm thick t h i c k with w i t h aa 1.5—2.0 1 . 5-2.0 cm cm The marginal m a r g i n a l zone z o n e is thick t h i c k ddarker a r k e r coloured c o l o u r e d chilled c h i l l e d zone z o n e against a g a i n s t the t h e country country Concave c m apart apart rock. C o n c a v e up, u p , sub—parallel, s u b - p a r a l l e l , fractures f r a c t u r e s 1—7 1-7 cm rock. occur within this zone and dip 20 degrees into the o c c u r w i t h i n t h i s z o n e a n d d i p 20 d e q r e e s i n t o t h e o u t c r o p . These T h e s e fractures, f r a c t u r e s , 0.2—1 0.2-1 cm c m thick t h i c k in i n the t h e center center outcrop. are a r e carbonate c a r b o n a t e filled f i l l e d and a n d rarely r a r e l y occur o c c u r in i n the t h e central central The central zone. c m wide, w i d e , has h a s aa zone. c e n t r a l zone, z o n e , approximately a p p r o x i m a t e l y 44 cm The dike 2 mm chilled c h i l l e d margin m a r g i n against a g a i n s t the t h e marginal m a r g i n a l zone. zone. dike can 2 6 rn m tto o the t h e southeast. southeast. c a n be b e traced t r a c e d for f o r 26 The The The ddike i k e formed f o r m e d iin n two t w o stages. stages. The ffirst i r s t stage stage Reactivation f r o z e as a s a massive m a s s i v e fine f i n e grained g r a i n e d dike. dike. Reactivation froze magma f o r c e d new new magma t h rthrough o u g h t h the e c ecenter n t e r o of f tthe h e old o l d dike dike forced The fractures in the older marginal zone. producing producing f r a c t u r e s i n t h e o l d e r m a r g i n a l zone. The orientation o r i e n t a t i o n of o f the t h e fractures f r a c t u r e s indicates i n d i c a t e s that t h a t magma movement (in ( i n present p r e s e n t orientation) o r i e n t a t i o n ) had had an a n upward upward vector vector perpendicular p e r p e n d i c u l a r to t o the t h e fracture f r a c t u r e system. system. The is a a brittly b r i t t l y fractured, fractured, T h e host h o s t of o f the t h e feeder f e e d e r dike d i k e is The massive, m a s s i v e , fine—grained, f i n e - g r a i n e d , mafic m a f i c metavolcanic. metavolcanic. The carbonate—filled t h e r e is is c a r b o n a t e - f i l l e d fractures f r a c t u r e s may be b e early e a r l y —- there little l i t t l e evidence e v i d e n c e of o f penetrative p e n e t r a t i v e deformation d e f o r m a t i o n within w i t h i n the the The exposure outcrop. outcrop. e x p o s u r e on o n the t h e north n o r t h side s i d e of o f the t h e gravel gravel is fine f i n egrained g r a i n e dmafic m a f i cflows f l o w swith w i t hvery v e r ylarge l a r g eameboid ameboid p i t is pit shaped crn tthick h i c k selvages s e l v a g e s and and chilled chilled s h a p e d pillows p i l l o w s with w i t h1—2 1-2 cm (smile; m a r g i n s that t h a t have h a v e carbonate c a r b o n a t e filled f i l l e d concave c o n c a v e (smile) margins A 70 ccm fractures. fractures. A 70 m t hthick i c k hhyaloclastite y a l o c l a s t i t e to t o pillow pillow within b r e c c i a (Carlisle, ( C a r l i s l e ? 1963) 1 9 6 3 ) zone z o n e ooccurs ccurs w i t h i n the the breccia m e gapil a p i l l low o w ssequence. equence. meg Stratigraphically S t r a t i g r a p h i c a l l y overlying o v e r l y i n g the t h e megapillows m e g a p i l l o w s (east (east e n d of o f outcrop) o u t c r o p ) fine—grained, f i n e - g r a i n e d , massive m a s s i v e fflows l o w s hhave a v e tthick, hick, end b r i t t l e f r a c t u r e s f i l l e d w i t h s o Ât b l a c k ( o x i d i z e d r e d ) brittle fractures filled with soft black (oxidized red) �135 - 0 <^0 gravel pit 100 200 ----- gravel pit road B Figure F i g u r e 13: 13: field trip atop Locations o f field f i e l d trip t r i p Stop S t o p number number 1(A) 1 ( A ) and Stop Locations of and Stop nnumbers u m b e r s 2(8, 2 ( B , CC and a n d D) D) center massive flow massive flow I Figure F i g u r e 14: 14: FEEDER FEEDER DIKE DIKE I S k e t c h oof f the t h e ma i c feeder f e e d e r dike d i k e at a t Stop S t o p 1 (A (A o Sketch mafic onn Figure F i q u r e 13). 1 3 ) . The ddike i k e is i s bilaterally b i l a t e r a l l y symmetrical symmetrical t w o periods p e r i o d s of o f magma magma emplacement. emplacement. f o r m i n g during d u r i n q two forming 1 �136 hematitic hematitic mud and and scattered s c a t t e r e d carbonate c a r b o n a t e filled f i l l e d amygdules amygdules less l e s s than t h a n 44 mm mm in i n diameter. d i a m e t e r . AA sample s a m p l e of o f the t h e hematitic hematitic fracture f r a c t u r e filling f i l l i n g contained c o n t a i n e d 0.05—0.50 0.05-0.50 percent p e r c e n t copper c o p p e r as as well w e l l as a s greater g r e a t e r than t h a n 10 1 0 percent p e r c e n t iron i r o n (30 ( 3 0 element element quantitative q u a n t i t a t i v e spectrographic s p e c t r o g r a p h i c analysis a n a l y s i s by b y the t h e Geosciences Geosciences Laboratory, L a b o r a t o r y , Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto). Toronto) . 0.0 0.0 km km 0.24 0 . 2 4 km km 0.39 0 . 3 9 km km Return R e t u r n to t o vehicles v e h i c l e s and and drive d r i v e towards t o w a r d s Highway Highway 71 71 (Figure (Figure 13) m. 1 3 ) for f o r 240 2 4 0in. Turn T u r n at a t first m t l left e f t and and drive d r i v e to t o the t h e "Y" "Y" junction j u n c t i o n about about 150 rn. 150 m. If I f road r o a d (Figure ( F i g u r e 13) 1 3 ) is is blocked, b l o c k e d , park p a r k here h e r e taking t a k i n g care care not to block access to the sewage pond (follow your n o t t o b l o c k a c c e s s t o t h e sewage pond ( f o l l o w y o u r nose) o r road r o a d to t o gravel g r a v e l pit. pit. n o s e ) or STOP STOP 2: 2: Walk Walk through t h r o u g h the t h e gravel g r a v e l pit p i t to t o outcrop o u t c r o p BB (Figure ( F i g u r e 13). 1 3 ) . This T h i s is is an a n ongoing o n g o i n g (1985) ( 1 9 8 5 ) operation o p e r a t i o n and and if if the is active a c t i v e at a t the t h e time t i m e of o f your y o u r visit v i s i t please p l e a s e seek seek t h e pit p i t is permission t o enter. enter. p e r m i s s i o n to STOP STOP 2B: 2B : Formation: F o r m a t i o n : Snake S n a k e Bay Bay formation formation Lithology: Maf i c metavolcanics metavolcanics L i t h o l o g y : Mafic Setting: Strike—southeast, d i p - v e r t i c a l , strati— stratiSetting: S t r i k e - s o u t h e a s t , dip—vertical, graphic g r a p h i c top—northeast. top-northeast. Feature(s): F e a t u r e ( s ) : Flow F l o w contact, c o n t a c t , pillows, p i l l o w s , hyaloclastite, h y a l o c l a s t i t e , auto— autoclastic breccia c l a s t i c breccia At A t this t h i s stop s t o p we w e will w i l l examine e x a m i n e an a n east—south—easterly east-south-easterly striking v a r i e t y of of s t r i k i n g mafic m a f i c flow f l o w that t h a t displays d i s p l a y s aa variety structures. s t r u c t u r e s . The The flow f l o w grades g r a d e s from f r o m aa massive, m a s s i v e , fine—grain— fine-qrained, crystalline base through poorly defined pillows e d , c r y s t a l l i n e b a s e t h r o u g h p o o r l y d e f i n e d p i l l o w s into into aa hyaloclastite h y a l o c l a s t i t e to t o broken b r o k e n pillow p i l l o w breccia b r e c c i a top t o p (Figure (Figure 15). mm carbonate c a r b o n a t e filled filled 1 5 ) . Amoehoid Amoeboid pillows p i l l o w s rimmed rimmed with w i t h 1 mm amygdules a m y g d u l e s appear a p p e a r 1.3 1 . 3 mm below b e l o w the t h e flow f l o w top. t o p . The The pillows pillows grade g r a d e sharply s h a r p l y into i n t o aa variable v a r i a b l e thickness t h i c k n e s s of o f hyaloclastite hyaloclastite and and broken b r o k e n pillow p i l l o w breccia. b r e c c i a . The The pillow p i l l o w breccia b r e c c i a contains contains irregular < 6 4 mm mm in i n aa fine— finei r r e g u l a r pillow p i l l o w fragments f r a g m e n t s generally g e n e r a l l y <64 grained g r a i n e d chioritic c h l o r i t i c matrix. m a t r i x . The The elongation e l o n g a t i o n of o f pillows p i l l o w s and and embayment embayment of o f hyaloclastite h y a l o c l a s t i t e 30° 30 to t o bedding b e d d i n g represents r e p r e s e n t s aa flow t o the t h ewest—northwest w e s t - n o r t h w e s t ((right r i g h t to to f l o w front f r o n t advancing a d v a n c i n g to l e f t on figure 15). The issharp s h a r pand and T h e contact c o n t a c t with w i t h the t h e overlying o v e r l y i n g flow f l o w is irregular. The base is a 2 cm very fine vesiculated irregular. The b a s e i s a 2 c m v e r y f i n e v e s i c u l a t e d zone 6 0 cm cm to t o 1 mm massive m a s s i v e portion p o r t i o n grading grading z o n e overlain o v e r l a i n by by aa 60 into poorly i n t o coarse c o a r s e hyaloclastite—broken h y a l o c l a s t i t e - b r o k e n pillow p i l l o w breccia b r e c c i a —- poorly formed f o r m e d pillows p i l l o w s that t h a t have h a v e been b e e n sheared s h e a r e d and and carbonatized. carbonatized. 1 left on figure 15). 1 STOP STOP 2C: 2C : Figure F i g u r e 13 1 3 Outcrop O u t c r o p "C" "C" Formation: F o r m a t i o n : Snake S n a k e Bay Bay formation formation Lithology: Maf i c Metavolcanics Metavolcanics L i t h o l o g y : Mafic Setting: Strike—southeast, Setting: S t r i k e - s o u t h e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i top c t o— p - northeast northeast Feature(s): F e a t u r e ( s ) : Pillows, P i l l o w s , radiating r a d i a t i n gamygdules, a m y g d u l e s , epidote epidote alteration. a 1t e r a t i o n . �Figure 15: 4-1 a -1-1 a 0 IÑ 0 3 U-li) 4-1 0900 1200 The flow direction hyaloclastite, broken pillow breccia Sketch of the mafic flow top at Stop 2(B on Figure 13). is from right to left. Flow top breccia flow massive overlying massive flow I.. w IÑ C-> (1) - 4 IÑ w e 4-1 0 �139 STOP STOP 3: 3: Lobstick L o b s t i c k Bay. Bay. This T h i s stop s t o p is i s the t h e larger l a r g e r of o f two two l i t t l e islands i s l a n d s 20 20 m from f r o m the t h e mainland m a i n l a n d (Figure (Figure little 11). 11). Formation: Formation: Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x imal Deposition Depos i t i o n Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Feature(s): F e a t u r e ( s ) : Block B l o c k and a n d ash a s h flow; f l o w ; massive m a s s i v e portion p o r t r i o n and and cloud c l o u d surge s u r g e top. top. Massive, m a t r i x supported s u p p o r t e d pyroclastic p y r o c l a s t i c breccia b r e c c i a with with M a s s i v e , matrix subangular s u b a n g u l a r quartz—feldspar q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts l a s t s ini nquartz— quartzfeldspar f e l d s p a r tuff t u f fmatrix m a t r i xhave h a v e poorly p o o r l y defined d e f i n e d contacts. contacts. Essential cm and and minor minor E s s e n t i a l porphyry p o r p h y r y clasts c l a s t are s a r10—30 e 10-30 cm accidental a c c i d e n t a l mafic maÂi c cclasts l a s t s are a r e smaller. s m a l l e r . The The fine f i n e tuff tuff matrix m a t r i x increases i n c r e a s e s slightly s l i g h t l yini nabundance a b u n d a n c e toward t o w a r d the t h e top. top. A A 21 21 cm c m tthick h i c k quartz—feldspar q u a r t z - f e l d s p a r t tuff u f f bed b e d occurs o c c u r s on o n the the south s o u t h side s i d e of o f the t h e island i s l a n d between b e t w e e n two two pyroclastic p y r o c l a s t i c breccia breccia units u n i t s (Photo ( P h o t o 2). 2 ) . The The base b a s e of o f the t h e tuff t u f f is i s medium medium to t o fine fine grained g r a i n e d and and has h a s pronounced p r o n o u n c e d laminae. laminae. On On the t h e basis b a s i s of o f lack l a c k of o f bedding b e d d i n g in i n the t h e coarse coarse units, u n i t s , homolithic h o m o l i t h i c subangular s u b a n g u l a r clasts c l a s t s and and poor p o o r sorting sorting this t h i s sequence s e q u e n c e is i s interpreted i n t e r p r e t e d as a s aa block b l o c k and and ash a s h flow. flow. The The thin t h i n tuff t u f f interbed i n t e r b e d based b a s e d on o n the t h e association a s s o c i a t i o n with w i t h the the block b l o c k and a n d ash a s h flows f l o w s and and the t h e gradational g r a d a t i o n a l contact c o n t a c t with w i t h the the underlying u n d e r l y i n g breccia b r e c c i a is is interpreted i n t e r p r e t e d to t o be b e aa cloud c l o u d surge surge deposit. deposit. Overlying O v e r l y i n g the t h e tuff t u f f with w i t h aa sharp s h a r p but b u t irregular irregular contact i s aa similar s i m i l a r block b l o c k and and ash a s h deposit. deposit. c o n t a c t is . 400 400 mm east e a s t of o f Stop S t o p 33 (Figure ( F i g u r e 11). 11) S t o p on o n aa Stop long l o n g outcrop o u t c r o p sloping s l o p i n g steeply s t e e p l y inland. i n l a n d . This T h i s outcrop o u t c r o p has has moss moss on o n it i t and and can c a n be b e very v e r y slippery. slippery. STOP 4: STOP 4: Formation: Formation: Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x i m a l Deposition Deposition Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical , Feature: Feature: top—south top-south Pumice P u m i c e in i n ash a s h flow f l o w tuff tuff stratigraphic stratigraphic Irregular c l a s t s of o f aa variety v a r i e t y of o f sizes sizes I r r e g u l a r chloritic c h l o r i t i c clasts (Photo ( P h o t o 3) 3 ) occur o c c u r near n e a r the t h e topographic t o p o g r a p h i c top t o p of o f the t h e ooututcrop. c l o t s , interpreted interpreted c r o p . These T h e s e quartz—feldspar q u a r t z - f e l d s p a r phyric p h y r i c clots, to t o be b e pumice, p u m i c e , occur o c c u r in i n aa fine—grained, f i n e - g r a i n e d , massive m a s s i v e quartz— quartzfeldspar f e l d s p a r tuff. t u f f . Two Two pumice p u m i c e bearing b e a r i n g horizons h o r i z o n s occur o c c u r in in zones z o n e s of o f silicification s i l i c i f i c a t i o n marked m a r k e d by by thin t h i n quartz q u a r t z veinlets. veinlets. Subtle S u b t l e lithic l i t h i c clasts c l a s t s are a r e seen. s e e n . The The pumice p u m i c e occurs o c c u r s in i n the the upper portion of two tuff u p p e r p o r t i o n o f t w o t u f f beds b e d s (units). ( u n i t s ) . Alteration A l t e r a t i o n to to chlorite c h l o r i t e and and silicification s i l i c i f i c a t i o n may may be b e pre—metamorphic. pre-metamorphic. �14 0 Photo 1: 1: Photo Cored Cored bomb bomb found found in i n aa 44 mm thick t h i c k mafic mafic breccia b r e c c i a at at Stop 2D. 2D. AA tuff t u f f accidental a c c i d e n t a l clast c l a s t is i s armored armored with w i t h aa Stop t h i n rim r i m of of amygdaloidal amyqdaloidal mafic mafic magma. magma. thin Photo 2: 2: Photo Cloud Cloud surge s u r g e tuff t u f f between between two two pyroclastic p y r o c l a s t i c breccias breccias The tuff is the upper portion 3. The t u f f i s t h e upper p o r t i o n of of aa a t Stop Stop 3. at Stratigraphic top is to b l o c k and and ash ash flow. flow. S t r a t i g r a p h i c top is t o the the block left. left. �141 Photo P h o t o 3: 3: Irregular I r r e g u l a r shaped s h a p e d pumice p u m i c e in i n aa quartz—feldspar q u a r t z - f e l d s p a r ash ash flow f l o w tuff t u f f at a t Stop S t o p 4. 4. T h e pumice p u m i c e now now consists c o n s i s t s of of The q u a r t z and a n d feldspar f e l d s p a r phenocrysts p h e n o c r y s t s in i n aa chloritic chloritic quartz matrix. matrix. (L -J I Photo 4: P h o t o 4: I Gas Gas escape e s c a p e structure s t r u c t u r e in i n the t h e upper u p p e r portion p o r t i o n of o f aa series s e r i e s of o f block b l o c k and a n d ash a s h flow f l o w deposits d e p o s i t s at a t Stop S t o p 7. 7. S t r a t i g r a p h i c top t o p is is towards t o w a r d s the t h e narrow n a r r o w apex a p e x of o f the the Stratigraphic triangular shaped feature. t r i a n g u l a r s h a p e d f e a t u r e . Gas G a s streaming s t r e a m i n g has has altered t o chlorite c h l o r i t e thus t h u s enhancing e n h a n c i n g the the a l t e r e d the t h e matrix m a t r i x to clasts c l a s ts . �142 STOP STOP 5: 5: A p p r o x i m a t e l y 22 km west w e s t of o f Stop S t o p 44 on o n the the Approximately l a k e s h o r e at a t the t h e west end e n d of o f Roberts R o b e r t s Lodge Lodge near n e a r the t h e boat boat lakeshore dock. dock. T h i s stop s t o p at a t the t h e end e n d of o f Roberts R o b e r t s Road Road may be be This reached Please 11). Please r e a c h e d by b y vehicle v e h i c l e from f r o m Highway Highway 71 71 (Figure ( F i g u r e 11). get g e t permission p e r m i s s i o n from f r o m the t h e lodge l o d g e for f o r this t h i s stop. stop. Formation: Formation: Lithology: Lithology : Setting: Setting: Feature: Feature: Berry B e r r y River R i v e r formation formation Mafic metavolcanics, Maf i c m e t a v o l c a n i c s , wacke wacke Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Top T o p of o f Berry B e r r y River R i v e r formation formation The T h e Berry B e r r y River R i v e r formation f o r m a t i o n culminated c u l m i n a t e d in i n aa 20—100 20-100 mm thick The t h i c k unit u n i t of o f mafic maf i c pillowed p i l l o w e d flows. flows. T h e outcrop o u t c r o p on o n the the north is fine—grained f i n e - g r a i n e d porphyritic porphyritic n o r t h side s i d e of o f the t h e dock d o c k is (plagioclase) mafic ( p l a g i o c l a s e ) ma i c flow f l o w with w i t h poorly p o o r l y developed d e v e l o p e d pillows. pillows. Remnant pillow selvages are seen here. Better p i l l o w s e l v a g e s are s e e n h e r e . B e t t e r developed developed pillows p i l l o w s are a r e found f o u n d in i n outcrops o u t c r o p s among among the t h e cabins. cabins. The cm tthick The overlying o v e r l y i n g wackes w a c k e s have h a v e40—90 40-90 cm h i c k graded graded beds. Grain is well w e l ldeveloped d e v e l o p e d with w i t h 1 mm mm beds. G r a i n ggradation r a d a t i o n is subrounded feldspars and quartz grains in s u b r o u n d e d f e l d s p a r s a n d q u a r t z g r a i n s i n aa bbiotite i o t i t e rich rich matrix These cm t thick h i c k aargillite r g i l l i t e top. top. These m a t r i x grading g r a d i n g into i n t o 4—5 4-5 cm wackes, w a c k e s , based b a s e d on o n the t h e character c h a r a c t e r of o f the t h e grains, g r a i n s , represent represent reworking r e w o r k i n g and a n d redeposition r e d e p o s i t i o n of o f the t h e Berry B e r r y River R i v e r formation. formation. 1 STOP 6 : This T h i s location l o c a t i o n in i n Mist M i s t Inlet I n l e t is i s approximately approximately STOP 6: 11.5 1 1 . 5 km west w e s t of o f Stop S t o p 55 (Figure ( F i g u r e 12). 12). Berry B e r r y River R i v e r formation formation Distal D i s t a l redeposited redeposited Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, stratigraphic s t r a t i g r a p h i c top—south top-south Feature(s): H e t e r o l i t h i c volcaniclastics, v o l c a n i c l a s t i c s , wackes wackes F e a t u r e ( s ) : Heterolithic Formation: Formation: Facies: F a c ies : Setting: Setting: The T h e coarse coarse volcanics v o l c a n i c s (Figure ( F i g u r e 16) 16 ) are a r e clast c l a s t supported supported 1.7 1.7 —- 4 m thick, t h i c k , predominantly p r e d o m i n a n t l y ungraded u n g r a d e d and and contain contain clasts o f feldspar f e l d s p a r porphyry, p o r p h y r y , intermediate, i n t e r m e d i a t e , mafic maÂi c and and c l a s ts of felsic Size i s noted noted f e l s i c metavolcanics m e t a v o l c a n i c s and and wacke. wacke. S i z e grading g r a d i n g is in Clasts, some beds. beds. C l a s t s , allowing a l l o w i n g for f o r deformation, d e f o r m a t i o n , are are i n some subrounded. The signs subrounded. s i g n s of o f reworking r e w o r k i n g (i.e. ( i.e. compositional compositional difference d i f f e r e n c e between b e t w e e n matrix m a t r i x and and clasts, c l a s t s , rounding r o u n d i n g of of clasts, heterogeneity of clast type and to c l a s t s , h e t e r o g e n e i t y o f c l a s t t y p e and the t h e ungraded u n g r a d e d to poorly p o o r l y graded g r a d e d nnature a t u r e oof f t the h e uunit) n i t ) ssuggests u g g e s t s t this h i s is i s aa debris d e b r i s flow f l o w (lahar) ( l a h a r )(c.f. ( c . f Fisher . F i s h eand r a nSchmincke, d S c h m i n c k e , 1984). 1984). The interbedded feldspar tuffs a r e thinner t h i n n e r bedded bedded The i n t e r b e d d e d f e l d s p a r t u f f s are than t h a n the t h e coarse c o a r s e volcaniclastics v o l c a n i c l a s t i c s and a n d contain c o n t a i n occasional occasional lithic l i t h i c clasts. clasts. Dark Dark grey, g r e y , fine f i n e grained, g r a i n e d , argillaceous a r g i l l a c e o u s wacke wacke and and lighter l i g h t e r grey g r e y feldspar f e l d s p a r and and quartz—feldspar q u a r t z - f e l d s p a r wacke wacke units units have h a v e variable v a r i a b l e bed bed thickness. thickness. The T h e heterolithic h e t e r o l i t h i c nature, n a t u r e , degree d e g r e e of o f sorting, s o r t i n g , and and rounding w e l l as a s the t h e wacke interbeds i n t e r b e d s suggest s u g g e s t the the r o u n d i n g as a s well volcaniclastics v o l c a n i c l a s t i c s have h a v e been b e e n reworked r e w o r k e d and and redeposited. redeposited. Provenance P r o v e n a n c e of o f the t h e unit u n i t was w a s the t h e underlying u n d e r l y i n g and and lateral lateral parts p a r t s of o f the t h e Berry B e r r y River R i v e r formation. formation. beds beds �143 MIST INLET: LAKE LAKE OF OF THE THE WOODS WOODS ............................................................... .................................................. wacke -....................................................................... a r g i l l a argillaceous c e o u s wacke o~l-feldspar tuff —feldspar tuff 0 0 - 0 0 o 0 O"Oo 0 0 0 0O.O OOOo.o 0 0 0 0 O O " O ~ o ~ O OoOoo 0 0 0 O 0 O 0 O 0 0 hert —tuft tuff breccia, breccia, upward tto o lapilli tuff fines upward wacke wacke metres metres - 10 n 10 - 88 tuff. tuff -argillaceous wacke rgiIIaceous wacke ........................ —lapillistone Ia liii st o tie ::::jjJ._Iapillistone 0 - 44 -2 1tuff . . . . . . . . . . . . '.— - 66 wacke wacke - 00 '—wacke -pyroclastic breccia breccia to t o tuff tuff —pyroclastic -feldspar tuff feldspar tuff A ~-pyroclastic breccia pyroclastic breccia A 0 A ;>:.:::::::.:.:.:.:.:.:.:.:.:.:.>>~.:.:.:.:.:.:.:.:.:.:.;*;;?>::::: :>::i^::&:k:&<^:^:::;^;:^cc:; -wacacke k e with with thin thin pyrociastic pyroclastic b r e c c i a horizons horizons breccia -feldspar tuff feldspar tuff pyroclastic breccia -pyroclastic breccia e wwacke acke -feldspar tuff '—feldspar tuff --wacke cke ..................... ...................................... ...& ..iS....ia,:....si....g...?........ :.... ............................ ......... .::x ........::.: ................................ .....:.:.......:.:.........................:: .:.x<.:.:.:.~.~z,.x<~.:.~ o oo A A Fiqure F i g u r e 16: 16: o O 0 Columnar C o l u m n a r mmeasured e a s u r e d s esection c t i o n ffrom r o m aa sshoreline h o r e 1 i n e outcrop outcrop in i n the t h e distal d i s t a lredeposited r e d e p o s i t e d facies f a c i e s at a tStop S t o p66 in i n Mist M i s t base ooff the is at Inlet. I n l e t . The The base t h e column c o l u m n is a t the t h e north n o r t hend end of the outcrop area. of t h e o u t c r o p a r e a . �144 Return R e t u r n tto o vvehicles e h i c l e s for f o r the t h e remainder r e m a i n d e r of o f the t h e field field The road r o a d log l o g will w i l l start s t a r t from f r o m the t h e north n o r t h end e n d of o f the the Sioux S i o u x Narrows N a r r o w s Bridge. Bridge. From the t h e north n o r t h end e n d of o f the t h e Sioux S i o u x Narrows N a r r o w s Bridge B r i d g e proceed proceed north krn to t o the t h e Maybrun Maybrun Road. Road. n o r t h on o n Highway 71 7 1 for f o r 10 10 km Figures F i g u r e s 11 1 1 arid a n d 12. 12. Turn T u r n right r i g h t (east) ( e a s t ) on o n the t h e Maybrun Maybrun Road Road for f o r 4.9 4 . 9 km. km. This This mileage STOP 88 aand is STOP n d wwe e wwill i l l r return e t u r n t otoi tito s o please please m i l e a g e is remember the t h e location. location. C o n t i n u e for for a a further f u r t h e r 0.6 0.6 km Continue ----km (Figure — ( F i g u r e 11). 11). trip. trip. 0.0 0 . 0 km km 10 krn 1 0 km 1 5 . 5 km km 15.5 - STOP 7: 7: (Figure ( F i g u r e 11) 1 1 ) is is aa large l a r g e area a r e a of o f outcrops o u t c r o p s on o n the the STOP left l e f t (north ( n o r t h side s i d e of o f the t h e road) r o a d ) (Figure ( F i g u r e 17). 1 7 ) . Please P l e a s e park park off i t is is used u s e d by b y large l a r g e trucks t r u c k s to t o haul h a u l pulp pulp o f f the t h e road r o a d as a s it wood. Berry B e r r y River R i v e r formation format ion Proximal P r o x i m a l deposition deposition Strike S t r i k e east, e a s t , dip—vertical, dip-vertical , stratigraphic s t r a t i g r a p h i c tops—south tops-south Feature(s): F e a t u r e ( s ) : Block B l o c k and a n d ash a s h flows, f l o w s , debris d e b r i s flows, f l o w s , lahars, lahars, gas g a s escape e s c a p e structures structures Formation: Format i o n : Facies: Facies : Setting: Setting: Figure F i g u r e 17 17 shows s h o w s the t h e location l o c a t i o n of o f outcrops o u t c r o p s as a s aa litho— lithologic l o g i c map and a n d separately s e p a r a t e l y the t h e interpretation i n t e r p r e t a t i o n of o f the the depositional were deposited deposited d e p o s i t i o n a l mechanism. mechanism. T h e pyroclastics p y r o c l a s t i c s were The as The a s block b l o c k and a n d ash a s h flows, f l o w s , debris d e b r i s flows f l o w s and a n d lahars. lahars. The lahars were deposited d e p o s i t e d in i n aa channel c h a n n e l within w i t h i n debris d e b r i s flows flows l a h a r s were (Figure ( F i g u r e 17). 17). The west end e n d of o f Figure F i g u r e 17 17 are a r e medium medium to to T h e units u n i t s at a t the t h e west coarse c o a r s e pyroclastics p y r o c l a s t i c s which w h i c h are a r e homolithic h o m o l i t h i c (quartz— (quartzfeldspar m a t r i x supported, s u p p o r t e d , poorly poorly f e l d s p a r porphyry p o r p h y r y clasts), c l a s t s ) , matrix sorted Up U p to t o 8—10 8-1 0 percent p e r c e n t pumiceous p u m i c e o u s lapilli lapilli s o r t e d and a n d graded. graded. occur Evidence o c c u r in i n units u n i t s at a t the t h e western w e s t e r n end. end. E v i d e n c e bearing b e a r i n g on on the 1 ) gas g a s escape escape t h e origin o r i g i n of o f these t h e s e units u n i t s includes: i n c l u d e s : 1) structures 4 ) ; 2) 2 ) their t h e i r homolithic, h o m o l i t h i c , poorly p o o r l y graded graded s t r u c t u r e s (Photo ( P h o t o 4); and 3 ) the t h e presence p r e s e n c e of of a n d poorly p o o r l y bedded b e d d e d character c h a r a c t e r and a n d 3) pumice. p u m i c e . The The above a b o v e are a r e consistent c o n s i s t e n t with w i t h these t h e s e units u n i t s being being deposited m e c h a n i s m s (c.f. ( c .f Sparks Sparks d e p o s i t e d by b y block b l o c k and a n d ash—flow a s h - f l o w mechanisms et e t al., a l . , 1979). 1979). A gas g a s escape e s c a p e structure s t r u c t u r e (Photo ( P h o t o 4) 4 ) is i s crudely crudely triangular t r i a n g u l a r in i n shape s h a p e with w i t h the t h e apex a p e x towards t o w a r d s the t h e strati— stratigraphic The m matrix g r a p h i c top. top. a t r i x has h a s been b e e n altered a l t e r e d to t o chlorite, chlorite, due t o gas g a s streaming, s t r e a m i n g , and a n d the t h e subround s u b r o u n d clasts c l a s t s enhanced. enhanced. d u e to Other O t h e r areas a r e a s of o f chlorite c h l o r i t e alteration, a l t e r a t i o n , though t h o u g h not n o t as a s well well defined d e f i n e d as a s Photo P h o t o 4, 4 , have h a v e been b e e n interpreted i n t e r p r e t e d as a s gas q a s escape escape structures. structures The presence p r e s e n c e of o f the t h e gas g a s escape e s c a p e structures s t r u c t u r e s and and pumice pumice indicates were deposited deposited i n d i c a t e s that t h a t these t h e s e block b l o c k and a n d ash a s h flows f l o w s were in i n a shallow s h a l l o w water w a t e r proximal p r o x i m a l environment. environment. In I n the t h e central c e n t r a l and a n d eastern e a s t e r n part p a r t of o f the t h e outcrop o u t c r o p area area one t o finer f i n e r heterolithic h e t e r o l i t h i c pyro— pyroo n e observes o b s e r v e s aa transition t r a n s i t i o n to clastics The e l a s t i c s with w i t h thinner, t h i n n e r , better—developed b e t t e r - d e v e l o p e d bedding. bedding. The . �H Ui F i g u r e 17: 17: Figure The outcrops Sketch of the thet hMaybrun S k e t c h of t h e outcrop o u t c r o p area a r e aata Stop t S t o7 p on 7 on e MaybrunRoad. Road. The o u t c r o p s were were The located l o c a t e d using u s i n gpace paceand andcompass compass methods. methods. The ppatterned a t t e r n e d iinterpretation n t e r p r e t a t i o n of of d e p o s i t i o n a l mechanisms in i n the t h e upper upper left l e f t portion p o r t i o n is is of of the t h e same same area a r e a as a s the the depositional o u t c r o p map. map. outcrop �146 most most common common clasts c l a s t s are a r e quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y with with with w i t h minor m i n o r siltstone s i l t s t o n e clasts c l a s t s in i n the t h e northern—most n o r t h e r n - m o s t outoutcrop c r o p (Figure ( F i g u r e 17). 17 ) . S u b r o u n d e d ^ fine—grained f i n e - g r a i n e d crystalline crystalline Subrounded, mafic t o the t h e block b l o c k and and r n a f i c clasts c l a s t s also a l s o occur. occur. I n contrast c o n t r a s t to In a s h - f l o w s , sorting s o r t i n g is is good g o o d to t o poor p o o r and and graded g r a d e d beds b e d s are are ash—flows, common. The bedding, b e d d i n g , sorting, s o r t i n g , and a n d heterolithic h e t e r o l i t h i c nature nature of were deposited d e p o s i t e d by by o f these t h e s e subunits s u b u n i t s indicate i n d i c a t e that t h a t they t h e y were debris d e b r i s flows f l o w s (c.f. ( c . f . Fisher F i s h e r and a n d Schmincke, S c h m i n c k e , 1984). 1984). T h r e e coarse c o a r s e volcaniclastic v o l c a n i c l a s t i c units, u n i t s , each e a c h with w i t h aa silt— siltThree stone s t o n e top t o p were deposited d e p o s i t e d in i n aa channel c h a n n e l within w i t h i n the t h e debris debris flows They f l o w s (Figure ( F i g u r e 17). 17). T h e y are a r e unsorted, u n s o r t e d , heterolithic h e t e r o l i t h i c with with elongate, c l a s t s are a r e fine— f i n e - and and e l o n g a t e , subangular s u b a n q u l a r clasts. clasts. Most clasts medium—grained med i u m - g r a i n e d mafic maÂi c metavolcanics m e t a v o l c a n i c s with w i t h approximately a p p r o x i m a t e l y 55 percent p e r c e n t white w h i t e aphanitic, a p h a n i t i c , felsic f e l s i c lapilli l a p i l l i throughout. throughout. The The matrix m a t r i x is is aa feldspar—hornblende f e l d s p a r - h o r n b l e n d e "tuff". "tuff" felsic The felsic clasts c l a s t s disappear d i s a p p e a r towards t o w a r d s the t h e top t o pand and the t h ematrix m a t r i xbecomes becomes aa light l i q h tbrown brown silty s i l t yarenite a r e n i t ewith w i t hcobbles c o b b l e sofo fsubround subround quartz—bearing The unsorted, q u a r t z - b e a r i n g pyroxene p y r o x e n e gabbro. qabbro. u n s o r t e d , hetero— heterolithic l i t h i c nature n a t u r e of o f the t h e volcaniclastic v o l c a n i c l a s t i c and and the t h e presence p r e s e n c e of of the t h e siltstone s i l t s t o n e top t o p suggests s u g g e s t s these t h e s e subunits s u b u n i t s are a r e lahars. lahars. The The tuffaceous t u f f a c e o u s matrix m a t r i x of o f the t h e southernmost s o u t h e r n m o s t lahar lahar contains c o n t a i n s rounded r o u n d e d quartz—bearing q u a r t z - b e a r i n g mmafic a f i c cclasts l a s t s and and quartz—feldspar is rusty, rusty, q u a r t z - f e l d s p a r pporphyry o r p h y r y cclasts. l a s t s . This T h i s llahar a h a r is weathering with weathering w i t h disseminated d i s s e m i n a t e d ppyrite y r i t e and and has has cross—cutting These T h e s e features f e a t u r e s suggest suggest veinlets c r o s s - c u t t i n g cherty c h e r t y veirilets. hot h o t emplacement e m p l a c e m e n t and a n d early e a r l y alteration. a l t e r a tion. The T h e complexity c o m p l e x i t y present p r e s e n t at a t this t h i s stop s t o p shows s h o w s that t h a t even even though t h o u g h aa single s i n g l e facies f a c i e s has h a s been b e e n assigned a s s i g n e d many many depositional d e p o s i t i o n a l processes p r o c e s s e s have h a v e occurred o c c u r r e d within w i t h i n this t h i s one one facies. facies. . . 0.0 0.0 km km T u r n around a r o u n d and a n d proceed p r o c e e d west west on o n the t h e Maybrun Maybrun road r o a d to t o STOP STOP Turn 88 (you remember tthe 0.6km. ( y o u remember h e sspot?) p o t ? ) aapproximately p p r o x i m a t e l y 0.6 km. 0.6 0.6 km km STOP STOP 8: 8: (Figure ( F i g u r e 11). 11 ). the t h e road. road. - F l a t outcrop o u t c r o p on o n the t h e north n o r t h side s i d e of of Flat Facies: Facies : Setting: Setting: Berry B e r r y River R i v e r formation formation Proximal P r o x i m a l deposition deposition Strike—east, S t r i k e - e a s t , dip—vertical, dip-vertical, Feature: Feature: top—south top-south Pyroclastic magma matrix matrix P y r o c l a s t i c breccia b r e c c i a with w i t h mafic ma i c magma Formation: Formation: stratigraphic stratigraphic Homolithic H o m o l i t h i c pyroclastic p y r o c l a s t i c breccia b r e c c i a with w i t h subangular subangular quartz—feldspar q u a r t z - f e l d s p a r porphyry p o r p h y r y clasts c l a s t s has h a s aa matrix m a t r i x of o f fine fine quartz—feldspar Locally magma occurs o c c u r s as as q u a r t z - f e l d s p a r tuff. tuff. L o c a l l y mafic maf i c magma discontinuous d i s c o n t i n u o u s blebs b l e b s with w i t h chilled c h i l l e d margins m a r g i n s wrapping w r a p p i n g around around clasts; c l a s t s and a n d tuffaceous t u f f a c e o u s matrix m a t r i x have h a v e been b e e n bleached bleached c l a s t s ; clasts for c m adjacent a d j a c e n t to t o the t h e mafic m a f i c magma. magma. The The outcrop outcrop f o r about a b o u t 1 cm has t o have h a v e formed f o r m e d by b y intrusion i n t r u s i o n of of h a s been b e e n interpreted i n t e r p r e t e d to rnafic magma iinto maÂi c magma n t o uunconsolidated n c o n s o l i d a t e d felsic f e l s i c pyroclastic pyroclastic breccia. breccia. This t o the t h e conclusion c o n c l u s i o n that that T h i s interpretation i n t e r p r e t a t i o n leads l e a d s to mafic maÂi c magmatism m a q m a t i s m must m u s t have h a v e been b e e n concomitant c o n c o m i t a n t with w i t h the the 1 �147 f e l s i c magmatism magmatism producing p r o d u c i n g the t h e Berry B e r r y River R i v e r formation. formation. felsic C o n t i n u e west west for f o r 2.6 2 . 6 km km toward_Highway t o w a r d H i q h w a y -71 resetting resetting Continue 71 o d o m e t e r a tat t h ethe B e r rBerry y R i v e rT7ET3. bridge. odometer Continue w e s t ffor o r -11.3km . 3 km Continue west -- 0 . 0 km km 0.0 B e r r y River R i v e r bridge. bridge. Berry 1 . 3 km km 1.3 STOP 99 (Figure ( F i g u r e 11 11 aand n d 12): 1 2 ) : included i n c l u d e d are a r e outcrops o u t c r o p s on o n both both STOP i s b u i l t up and t h e s i d es s i d e s of o f the t h e road. road. The r o a d sides The road is built up and the sides a r e soft s o f t so so care c a r e must m u s t be b e taken t a k e n while w h i l e parking. p a r k i n g . Watch Watch for for are l o g g i n g trucks! trucks! logging B e r r y River R i v e r formation formation Berry P r o x i m a l d i s t a l and i s t a l redeposited redeposited Proximal—distal andddistal dip-vertical S t r i k e - s o u t h e a s t , dip—vertical Strike—southeast, s t r a t i g r a p h i c top—southwest top-southwest stratigraphic C o n t a c t with w i t h the t h e Warclub W a r c l u b group g r o u p wackes, wackes , F e a t u r e ( s ) : Contact Feature(s): Formation: Formation: Facies : Facies: Setting: Setting: f a l l - o u t deposits, d e p o s i t s , subaqueous s u b a q u e o u s pyroclastic pyroclast ic fall—out f l o w s , double d o u b l e grading. grading. flows, The ccontact o n t a c t of o f the t h e base b a s e of o f the t h eBerry B e r r yRiver R i v e r formation formation The e x p o s e d in i n 22 outcrops outcrops a n d wackes w a c k e s oof f the t h e Warclub W a r c l u b ggroup r o u p is and is exposed m aapart p a r t oon n tthe h e north n o r t h side s i d e of o f the t h e road. road. Measured 30 in 30 Measured s e c t i o n s o f these t h e s e exposures e x p o s u r e s are a r e shown shown in i n the t h e center c e n t e r and and seEfönsöf A thin zone of distally A t h i n zone o f d i s t a l l y r i g h t columns c o l u m n s oof f Figure F i g u r e 18. 18. right r e d e p o s i t e d , reworked r e w o r k e d tuff t u f f separates s e p a r a t e s the t h e wacke wacke from f r o m the the redeposited, Note that t h a t detailed detailed p r o x i m a l - d i s t a l facies f a c i e s rocks. rocks. proximal—distal Note c o r r e l a t i o n cannot c a n n o t be b e made made between b e t w e e n these t h e s e two t w o closely closely correlation s p a c e d outcrops o u t c r o p s (Figure ( F i g u r e 18). 18). spaced is aa generalized g e n e r a l i z e d section s e c t i o n of of F i g u r e 19 19 (left ( l e f t column) c o l u m n ) is Figure A t h i c k l y t h e outcrop o u t c r o p on o n the t h e south s o u t h side s i d e of o f the t h e road. road. the A thickly t o thin t h i n bedded b e d d e d sequence s e q u e n c e of o f crystal c r y s t a l tuff t u f f and and l a m i n a t e d to laminated p u m i c e - c r y s t a l lapilli l a p i l l i tuff t u f f exhibits e x h i b i t s poorly p o o r l y defined defined pumice—crystal m u t u a l contacts. contacts. mutual to The distinct d i s t i n c t but b u t poorly p o o r l y defined d e f i n e d beds b e d s are a r e moderate m o d e r a t e to The w e l l sorted s o r t e d and and may may have h a v e been b e e n deposited d e p o s i t e d by by continuous continuous well f a l l - o u t through t h r o u g h water. water. fall—out O v e r l y i n g the t h e fall—out  £ a l l - o u deposits d e p o s i t s are a r e interbedded, interbedded, Overlying d o u b l y graded g r a d e d pyroclastic p y r o c l a s t i c flows, f l o w s , tuffs t u f f s and and wacke. wacke. These doubly These s o u t h e a s t on o n both b o t h sides s i d e s of o f the the a r e best b e s t exposed e x p o s e d 180 1 8 0 inm southeast are road. The right r i g h t column c o l u m n (Figure ( F i g u r e 19) 1 9 ) is i s aa generalized generalized road. The s e c t i o n of o f this t h i sexposure. exposure. section A t this stop the fall-out deposits underlie the c o a r s e r flow f l o w deposits. deposits coarser At this stop the fall—out deposits underlie the . 3.5 3.5 km km 0 . 0 km 0.0 km 1.9 1.9 km km Drive Drive - f o r 2.2 2 . 2 kin km to t o Highway H i g h w a y 71. 71. for Highway 71" Highway 71 R o b e r t sRoad Road 1.9km 1.9.- km T u r n lleft e f t and a n d drive d r i v e tot oRoberts Turn --STOP 10 10 (Figures ( F i g u r e s 11 1 1 and a n d 12). 1 2 ) . The The outcrop o u t c r o p is is on o n the the STOP n o r t h w e s t side s i d e of o f Highway Highway 71 71 opposite o p p o s i t e Roberts R o b e r t s Road. Road. northwest i s on o n aa curve c u r v e so so please p l e a s e park p a r k on o n Roberts R o b e r t s Road. Road. T h i s stop s t o p is This Formation: Formation: Facies : Facies: B e r r y River R i v e r formation formation Berry Ash fflow l o w tuff tuff Ash �Figure 18: • massive tuff reworked quartz feldspar 2m im 0 I— <r.2 Cr . o u > cc 2mquarzcrystai tu f 00000 o lapilli tuft — 2 0— r2 >2 0. n > z 0 >- ?i.0 x cc lapilli tuff oo ::::.:......... oL 0çQC °oOO1 a c0 c ro°0o1 OQ °4m tuft breccia 0 tuft breccia arenite reworked tuft reworked tuff 0.2-6cm discontmuous beds 575m wacke 30m <w 0 00000 lapilli tuff BERRY feldspar crystal 00 BERRY R VER o0 00 0 matrix RIVER FORMATION FORMATION 0 00000000 redeposition lapilli tuft redeposition reworked tufts 00 o prograding reworked tuffs distal source silty tuff distal source chert thinly laminated cc reworked tuft bleached contact chert . reverse graded --. BERRY RIVER FORMATION tuft indistinct beds 6cm reworked lithic-crystal tuft 1 2cm beds lithic lapilli tuft reverse graded lithic lapilli crystal tuft reworked tuft matrix recessive pumice zone reworked tuft bleached contact wacke-argillite found along the Maybrun Three measured sections from separate outcrops outcrops. The contact with Warciub qroup wackes is exposed in all lack of ioad. redeposited facies and the Note the varying thickness of distal The centre and correlation in the proximal—distal facies volcaniclaStics. right—side measured sections are from Stop 9. ath BERRY RIVER FORMATION primary deposition proximal t o distal tacies BERRY RIVER FORMATION redeposition, reworked tuff distal source WARCLUB GROUP P - 3 en (D .. rr �Figure 19: 4 ____ _________ _______ _________ ________ _____ _________________ __________ ___________ __________ ______________ ___________ .• •. ..Do I 149 \ C ____________ ______________________ __________ .:Oo tuff breccia- breccia massive homolithic o9 lapillituff oo p o o.Q tu ff lapilli tuft & tuft —:—:——:— lapilli tuft recessive clasts •:j tuft o pyroclastic breccia bimodal magnetite 0 c' ç tuft breccia pyroclastic breccia homolithic crystal-lithic lapilli tuff - thickly laminated tuft breccia tuft wacke & argillite c' o00 -0- ° -0 °o porphyryclasts quartz-feldspar tuffbreccialapilli tuft - -:.:y.-y.: tuff poorly laminated 0 0 — 2 E0 -— O 'o° tuft breccia- reworked thickly laminated tuft lapilli tuft °o0 • siltstone reworked tuft oO not to scale BERRY RIVER FORMATION tuff breccia lapilli tuft iyroclastic beccia \ o0Oi doubly graded not to scale • 0j)0000 ———,.—— :—:—:—:—: I —:—:—:—:— 2-3%bluequa'rtz —— I I I tuft-lapilli tuff tuft I 5% blue quartz I I i I \ 180m pumice Ii thu. - api I tu 0 -0 -._____ thin dark and light bed I I _—_——_—_ recessive clasts :—:——:—: lapilli tuft — :::::::::::::::::::::::: E —:—:—:—:— o——— c —:—:—:—_— 0 IapiII tuft tuft recessive _—_—_—_—_ pumice — ____ 0 primary deposition, subaqueous pyroclastic flows, proximal to distal faces Two generalized sections from two outcrop areas along the Maybrun road at Stop 9. Rocks in the left column overlie the sections on the center and right side of Figure 18 and the right column stratigraphically overlie rocks described in the left column. Fallout deposits progress up into a mixed assemblage of pyroclastic flow deposits, tuffs and wackes. r r 3 P W r-i I à ‘ ' c I-'-(D r+l--m1-- m x mr-iLQ m 0 0 t-tlm n o ; z r r 3 0)QJ rrrr LQoa �150 Strike—east—southeast, Settinq: S etting: S t r i k e - e a s t - s o u t h e a s t , dip—vertical dip-vertical Feature(s): Crystal F eature(s): C r y s t a l (quartz—feldspar) ( q u a r t z - f e l d s p a r ) tuff, t u f f , lithic lithic ci ts c l aass ts Anhedra A n h e d r a of o f quartz q u a r t z vary v a r y in i n size s i z e and and proportion p r o p o r t i o n across across the t h e ooutcrop, u t c r o p , whereas w h e r e a s euhedral e u h e d r a l to t o subhedrai s u b h e d r a l feldspar feldspar phenocrysts p h e n o c r y s t s do d o not n o t vary v a r y stratigraphically. stratigraphically. The pheno— phenocrysts c r y s t s are a r e supported s u p p o r t e d in i n a very v e r y fine—grained f i n e - g r a i n e d quartzo— quartzor e l i c t ash a s h matrix. matrix. M i n o r subrounded s u b r o u n d e d lithic lithic ffeldspathic e l d s p a t h i c relict Minor clasts This c l a s t s are a r e found f o u n d throughout. throughout. T h i s sstop t o p is i s just j u s t north n o r t h of of Pipestone—Cameron tthe he P i p e s t o n e - C a m e r o n Fault F a u l t and a n d much much of o f the t h e "ciastic" "clastic" of i s structural. structural. The vvariation ariation o f phenocryst phenocrys t ttexture e x t u r e is rratios, a t i o s , tuffaceous t u f f a c e o u s character c h a r a c t e r and and clastic c l a s t i c horizons horizons indicate was ddeposited i n d i c a t e that t h a t the t h e unit u n i t was e p o s i t e d by b y the t h e ash a s h flow flow mechanism. mechanism. There much ddebate T h e r e hhas a s bbeen e e n much e b a t e (not ( n o t quite q u i t e physical) p h y s i c a l ) as as to t o what w h a t this t h i s outcrop o u t c r o p represents. r e p r e s e n t s . What do d o you you think? think? 00.0 . 0 km Drive b a c k to t o the t h e Maybrun Maybrun Road ----1.9 1 . 9D r i v e north n o r t h on o n Highway 71 back kin. km A- 1.9 1 . 9 km . STOP 11 1 1 (Figure ( F i g u r e 12). 1 2 ) . This T h i s is is a a spectacular s p e c t a c u l a r outcrop o u t c r o p on on west e s t side s i d e of o f the t h e highway h i g h w a y opposite o p p o s i t e Maybrun Maybrun Road. Road. tthe he w Berry B e r r y River R i v e r formation formation Distal D i s t a l redeposited; r e d e p o s i t e d ; proximal—distal proximal-distal ddeposition eposition Strike—southeast, Setting: S etting: S t r i k e - s o u t h e a s t , ddip—vertical, i p - v e r t i c a l , strati— stratigraphic g r a p h i c tops t o p s folded f o l d e d at a t the t h e north n o r t h end e n d and and south s o u t h at a t the t h e south s o u t h end. end. Feature(s): Reworked tuffs, t u f f s , double d o u b l e grading, g r a d i n g , reverse r e v e r s e and and F e a t u r e ( s ) : Reworked normal n o r m a l grading grading Formation: Formation: Facies: F a c ies : Figure 20 is measured i s aa m e a s u r e d ssection e c t i o n sstarting t a r t i n g at a t the the F i g u r e 20 small s m a l l outcrops o u t c r o p s in i n the t h e ditch d i t c h just j u s t north n o r t h of o f the t h e main main eexposure. xpos u r e The T h e base b a s e of o f the t h e section s e c t i o n is is folded f o l d e d wackes w a c k e s and and pyro— pyroeclastics l a s t i c s of o f the t h e Warclub W a r c l u b group. group. The T h e distal d i s t a l redeposited r e d e p o s i t e d facies f a c i e s consists c o n s i s t s of o f folded, folded, The reworked bedded, b e d d e d , reworked r e w o r k e d tuff t u f f and a n d lapilli l a p i l l i tuff. tuff. reworked s u b r o u n d grains g r a i n s and a n d aa higher h i g h e r biotite biotite ppyroclastics y r o c l a s t i c s have h a v e subround matrix ccontent o n t e n t in i n the the m a t r i x than t h a n the t h e non—reworked n o n - r e w o r k e d material. material. This T h i s higher h i g h e r biotite b i o t i t e content c o n t e n t gives g i v e s the t h e weathered w e a t h e r e d surface surface a a brownish—buff b r o w n i s h - b u f f colour. colour. Three are T h r e e ddepositional e p o s i t i o n a l events e v e n t s not n o t seen s e e n at a t Stop S t o p 9 are The ppresent r e s e n t here. here. The first f i r s t unit u n i t (Figure ( F i g u r e 20) 2 0 ) above a b o v e the the reworked i s massively m a s s i v e l y bedded b e d d e d feldspar f e l d s p a r and and quartz— quartzr e w o r k e d tuffs t u f f s is Based feldspar f e l d s p a r crystal c r y s t a l tuffs. tuffs. B a s e d upon u p o n hiotite b i o t i t e content c o n t e n t and and angularity a n g u l a r i t y of o f phenoclasts p h e n o c l a s t s these t h e s e are a r e not n o t reworked. reworked. is the The second the s e c o n d depositiorial d e p o s i t i o n a l eevent v e n t (Figure ( F i g u r e 20) 2 0 ) is 5 ssubunits u b u n i t s of o f doubly d o u b l y graded, g r a d e d , subaqueous subaqueous ddeposition e p o s i t i o n of of 5 Each ppyroclastic y r o c l a s t i c flows. flows. Each hhave ave a a coarse c o a r s e clastic c l a s t i c base base t o tuff t u f f and/or a n d / o r laminated l a m i n a t e d tuff. tuff. ffining i n i n g south s o u t h to The third w a s the t h e deposition d e p o s i t i o n of of The t h i r d event e v e n t (Figure ( F i g u r e 20) 2 0 ) was . �________ 151 000 o00 0000 0 11Dm— cover cover lam prophyre lamprophyre bedded quartz-feldspar tuff, tuft, normal normal and andreverse-graded reverse-graded pumice pumice horizons, horizons homolithic homolithictuft tuffbreccia, breccia,massive massive tuff tuffbreccia, breccia, massive tuft, thinnly thinnly laminated tuft massive tuff, laminated tuff 10Dm— fault fault Primary deposition, fall fall deposits, deposits, note note presence presence of pumice pumice arc prophyre homolithic homolithic lapilli lapilli tuft tuffgrading gradinginto into thinnly thinnly laminated laminated tuff tuff 9Dm — 1 pyroclasticbreccia into homolithicpyroclastic brecciagrading grading into homolithic thickly thickly laminated laminated tuff Zff/7Z>E 8Dm-____ lamprophyre lamprophyre tuff tuff breccia, breccia, thin tuff tuff on on top top (homolithic) (homolithic) lam prophyre lamprophyre Primary Primary deposition, deposition,subaqueous subaqueous pyroclastic pyroclastic flows, proximal proximal to to distal distal facies facies -L OOO L)p 7Dm— p•zQp z C tuff grading into into tuff tuff )heterolithic) tuff breccia breccia qradinq (heterolithic) lani prophyre lamprophyre lapilli lapilli tuff tuffto t otuff tuffbreccia breccia - 0 UU- quartz-feldspar quartz-feldspar tuft, tuff,massive, massive,homogeneous homogeneous > >. 6Dm — : :: ::: reldspathic ~eldspathictuff, tuff,massise,laminated massive,laminated : ::: ////////// lam prophyre Iamprophyre quartz-feldspar quartz-feldspar tuft, tuff,massive massive Primary deposition, tuffs tufts prograding prograding distal distal source source I I U- tuff tuffbreccia brecciagrading grading into into thickly thickly laminated laminated tuffs tuffs 5Dm— lapilli laoilli tuft tuff feldspathic tuft feldspathic tuff reworked tuff, tuft, laminated laminated /////// lam prophyre Iamprophyre reworked reworked tuff, massive,laminated tuff,massive, laminated lam prophyre Iamprophyre 4Dm — reworked reworked tuff, tuff,massive, massive,laminated, laminated, -r cross-bedded, cross-bedded,graded graded Redeposition, Redeposition, reworked reworked tuffs, tuffs,distal distalsource source reworked reworked tuft, tuff lapplli lapilli tuft, tuff eldspathic 'eldspathic wacke w k k e (folded) (folded) 3Dm — 000 0000 00 0 0 0 2Dm— 0 1:.......... : :I .......... 1: 1: 1: I - 1Dm— 10m cover .°. lithic Iithic lapilli Iapilli tuff tuff (folded) (folded) feldspathic feldspathic wacke wacke quartz-feldspar quartz-feldspar porphyry porphyry feldspathic feldspatliic wacke wacke 0 Figure F i g u r e 20: 20: - feldspathic tuff, crystal crystal lithic lithic tuff, tuft, feldspathic tuff, lithic crystal crystal tuft tuff A m e a s u r e d ssection e c t i o n from f r o m Stop S t o p111 1ono nHighway H i g h w a y 71 71 A measured opposite The o p p o s i t e the t h eMaybrun M a y b r u n Road. Road. T h e bbasal a s a l portion p o r t i o n of of the r e s t of o f the the t h e section s e c t i o n has h a s been b e e n folded f o l d e d and a n d the t h e rest section s e c t i o n faces f a c e s south. south. T h e base b a s e of o f the t h e measured measured The s m a l l outcrops o u t c r o p s exposed e x p o s e d in i n the the s e c t i o n includes i n c l u d e s the t h e small section ditch d i t c h north n o r t h of o f the t h e main m a i n exposure. exposure. T h i s section section This includes Warclub a r c l u b group; g r o u p ; reworked r e w o r k e d tuffs t u f f s in i n the the includes W distal t u f f s , subaqueous subaqueous d i s t a l redeposition r e d e p o s i t i o n facies; f a c i e s ; tuffs, pyroclastic p y r o c l a s t i c flow f l o w and a n d fallout f a l l o u t deposits d e p o s i t s in i n the the proximal—distal p r o x i m a l - d i s t a l facies. facies. �152 thin t h i n bedded b e d d e d fall f a l l out o u t tuffs t u f f s and a n d lapilli l a p i l l i tuff t u f f and a n d tuff tuff breccia b r e c c i a deposited d e p o s i t e d by b y the t h e pyroclastic p y r o c l a s t i c flow f l o w mechanism. mechanism. T h e fall—out f a l l - o u t deposits d e p o s i t s have h a v e normal n o r m a l and a n d reverse r e v e r s e graded graded The pumice p u m i c e and a n d normal n o r m a l graded g r a d e d tuffs. tuffs. Here Here fall f a l l out o u t deposits d e p o s i t s overlie o v e r l i e subaqueous subaqueous a t Stop S t o p 99 they t h e y underlie u n d e r l i e them. them. p y r o c l a s t i c flows f l o w s whereas w h e r e a s at pyroclastic This T h i s is i s indicative i n d i c a t i v e of o f the t h e difficulty d i f f i c u l t y in i n attempting attempting pyroclastic p y r o c l a s t i c stratigraphy s t r a t i g r a p h y in i n the t h e Archean. Archean. TIME TIME FOR FOR AA BEER BEER �153 Re R e ferences ferences Ayres, A y r e s , L.D., L.D., 1977. 1 9 7 7 . Importance I m p o r t a n c e of o f stratigraphy s t r a t i g r a p h y in i n Early Early Precambrian C y c l i c Volcanism V o l c a n i s m at a t Setting Setting P r e c a m b r i a n Volcanic V o l c a n i c Terranes: T e r r a n e s : Cyclic Net N e t Lake, L a k e , Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; p.243—264 p. 2 4 3 - 2 6 4 in i n Volcanic Volcanic Regimes W. R.A. 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U—Pb U-Pb Zircon Z i r c o n Ages Aqes from f r o m the the D a v i s , D.W. Eastern Crow Lake L a k e Metavolcanic—Metasedimentary Metavolcanic-Metased imentary E a s t e r n Savant S a v a n t Lake L a k e —- Crow Belt, B e l t , Northwest N o r t h w e s t Ontario; O n t a r i o ; Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Science, Science, Volume 19, p.868—877. Volume 1 9 , p . 8 6 8 - 8 7 7 . Easton, E a s t o n , R.M., R.M., 1984. 1984. Reconstruction R e c o n s t r u c t i o n of o f Precambrian P r e c a m b r i a n Volcanoes V o l c a n o e s —- AA Review R e v i e w of o f the t h e Canadian C a n a d i a n Literature; L i t e r a t u r e ; P164—212 P 1 6 4 - 2 1 2 in i n Growth G r o w t h and and Evolution w i t h Implications I m p l i c a t i o n s for for E v o l u t i o n of o f Volcanic V o l c a n i c Edifices E d i f i c e s —- with Precambrian P r e c a m b r i a n Volcanoes V o l c a n o e s edited e d i t e d by b y R.M. R.M. 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Submarine S u b m a r i n e Equivalents E q u i v a l e n t s of o f Ash Ash Flows in the Tokiwa Formation, F l o w s i n t h e T o k i w a F o r m a t i o n , Japan; J a p a n ; American A m e r i c a n Journal J o u r n a l of of Science, S c i e n c e , Volume Volume 262, 2 6 2 , p.76—106. p.76-106. Irvine, T.N. and Baragar, G u i d e to t o the t h e Chemical Chemical I r v i n e , T.N. a n d B a r a q a r , W.R.A., W.R.A., 1971. 1 9 7 1 . AA Guide Classification Canadian C l a s s i f i c a t i o n of o f the t h e Common Common Volcanic V o l c a n i c Rocks; R o c k s ; Canadian Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , Volume V o l u m e 8, 8 , p.523—548. p.523-548. Jensen, L.S., 1976. A New Cation Plot for f o r Classifying C l a s s i f y i n g Subalkalic Subalkalic A New Cation P l o t J e n s e n , L.S., 1976. Rocks; Misc. Paper P a p e r66, 6 6 , 22p. 22p. R o c k s ; Ontario O n t a r i o Division D i v i s i o n of o f Mines, M i n e s , Misc. �154 Johns, Johns, G.W., Geology G . W . , in i n prep. prep. G e o l o g y of o f the t h e Long Long Bay—Lobstick B a y - L o b s t i c k Bay Bay Area, Area, Lake Woods, District L a k e oof f the t h e Woods, D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Geological Geoloqical Survey S u r v e y Open Open File F i l e Report. Report. Johns, Kakagi J o h n s , G.W., G.W., 1984. 1984. K a k a g i Lake—Rowan Lake-Rowan Lake L a k e Regional R e g i o n a l Geology; Geology; p.25—32 p . 2 5 - 3 2 in i n Summary Summary of o f Field F i e l d Work, Work, 1984, 1 9 8 4 , Ontario O n t a r i o Geological Geoloqical Survey, Wood, Owen Owen L. L. W White, RB. Barlow, S u r v e y , edited e d i t e d bby y JJohn o h n Wood, h i t e , R.B. B a r l o w , and and A.C. A. C . Colvine, C o l v i n e , Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Paper Paper 119, 1 1 9 , 309p. 309p. Johns, Good, and 1984. Precambrian G.W., Good, D.J., D.J., a n d Davison, D a v i s o n , J.G., J.G., 1984. Precambrian J o h n s , G.W., Geology G e o l o g y of o f the t h e Long Long Bay—Lobstick B a y - L o b s t i c k Bay Bay Area, A r e a , Eastern E a s t e r n Part, Part, Kenora K e n o r a District; D i s t r i c t ; Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Map Map P.2595, P. 2 5 9 5 , Geological G e o l o g i c a l Series S e r i e s —- Preliminary P r e l i m i n a r y Map, Map, scale s c a l e 1:15,840 1: 1 5 , 8 4 0 or or 1 Geology inch i n c h to t o 1/4 1/4 mile. mile. G e o l o g y 1982, 1 9 8 2 , 1983. 1983. Johns, Thurston, Physical J o h n s , G.W., G.W., T h u r s t o n , P.C. P.C. and a n d Easton, E a s t o n , R.M., R.M., 1983. 1983. Physical Volcanology: V o l c a n o l o g y : 22 Facies F a c i e s Models M o d e l s (Abstract); ( A b s t r a c t ) ; in i n Geoscience Geoscience Research R e s e a r c h Seminar, S e m i n a r , December 6—7, 6 - 7 , 1983, 1 9 8 3 , Abstracts, A b s t r a c t s , Ontario Ontario Geological G e o l o q i c a l Survey, S u r v e y , 22p. 22p. Johns, Precambrian J o h n s , G.W. G.W. and a n d Davison, D a v i s o n , J.G., J . G . , 1983. 1983. P r e c a m b r i a n Geology G e o l o g y of o f the the Long Long Bay—Lobstick B a y - L o b s t i c k Bay Bay Area, A r e a , Western W e s t e r n Part, P a r t , Kenora K e n o r a District; District; Ontario O n t a r i o Geological G e o l o q i c a l Survey S u r v e y Map P.2594, P. 2 5 9 4 , Geoloqical G e o l o q i c a l Series S e r i e s —Preliminary P r e l i m i n a r y Map, Map, scale s c a l e 1:15,840 1 : 1 5 , 8 4 0 or o r 1 inch i n c h to t o 1/4 1 /4 mile. mile. Geology G e o l o g y 1982. 1982. Johns, Precambrian J o h n s , G.W. G.W. and a n d Richey, R i c h e y , Scott, S c o t t , 1982. 1982. P r e c a m b r i a n Geology G e o l o g y of o f the the MacQuarrie M a c Q u a r r i e Township T o w n s h i p Area, A r e a , Kenora K e n o r a District; D i s t r i c t ; Ontario Ontario Geological G e o l o g i c a l Survey S u r v e y Map Map P.2498, P. 2 4 9 8 , Geological G e o l o g i c a l Series S e r i e s —Preliminary Scale P r e l i m i n a r y Map. S c a l e 1:15,840 1 : 1 5 , 8 4 0 or o r 1 inch i n c h to t o 1/4 1 / 4 mile. mile. Geology G e o l o g y 1981. 1 9 8 1. Krogh, Zircon U—Pb Ages K r o g h , T.E. T.E. and a n d Davis, D a v i s , G.L., G. L., 1971. 1 9 7 1. Z i r c o n U-Pb Ages of o f Archean Archean Metavolcanics M e t a v o l c a n i c s in i n the t h e Canadian C a n a d i a n Shield; S h i e l d ; Carnegie C a r n e g i e Institute Institute Yearbook, Y e a r b o o k , Vol.70, V o l . 7 0 , p.241—242. p . 241-242. Krogh, Implications D a v i s , D.W. D.W. and a n d Corfu, C o r f u , F., F . , 1984. 1984. I m p l i c a t i o n s of of K r o g h , T.E., T.E. , Davis, Precise P r e c i s e U—Pb U-Pb Dating D a t i n g for f o r the t h e Geological G e o l o g i c a l Evolution E v o l u t i o n of o f the the Superior S u p e r i o r Province; P r o v i n c e ; Geological G e o l o g i c a l Association A s s o c i a t i o n of o f Canada Canada Abstracts, A b s t r a c t s , Vol.9, V 0 l . 9 , p.79. p.79. Lawson, Report L a w s o n , A.C., A . C . , 1885. 1885. R e p o r t on o n the t h e Geology G e o l o g y of o f the t h e Lake Lake of o f the the Woods Region R e g i o n with w i t h Special S p e c i a l Reference R e f e r e n c e to t o the t h e Keewatin Keewatin (Huronian?) ( H u r o n i a n ? ) Belt B e l t of o f Archean A r c h e a n Rocks; Rocks ; Geological G e o l o q i c a l and a n d Natural Natural History H i s t o r y Survey S u r v e y of o f Canada, C a n a d a , Annual A n n u a l Report, R e p o r t , 1885, 1 8 8 5 , Vol.1, V o l . 1 , Pt.C., Pt C., 1 1 1 15 1 5 ip. 1p. . Lichtblau, Stratigraphy A. P. and a n d Dimroth, D i m r o t h , E., E . , 1980. 1980. S t r a t i g r a p h y and and Facies Facies L i c h t b l a u , A.P. at a t the t h e South S o u t h Margin M a r g i n of o f the t h e Archean A r c h e a n Noranda N o r a n d a Caldera, C a l d e r a , Noranda, Noranda, In Current Quebec. Quebec. In C u r r e n t Research R e s e a r c h Pt.A, P t . A , Geological G e o l o g i c a l Survey S u r v e y of of Canada, C a n a d a , Paper P a p e r 80—lA, 80-1A, p.69—79. w.69-79. Ash Flow Ross, a n d Smith, S m i t h , Robert R o b e r t L., L., 1961. 196 1. Flow Tuffs: Tuffs : R o s s , Clarence, C l a r e n c e , S. S . and Their G e o l o g i c a l Relations R e l a t i o n s and a n d Identification, Identification, T h e i r Origin, O r i g i n , Geological United G e o l o g i c a l Survey S u r v e y Professional P r o f e s s i o n a l Paper P a p e r 366, 3 6 6 , 8lp. 8 1p. U n i t e d States S t a t e s Geological Schmid, Descriptive Schmid , R., R . , 1981. 1981. D e s c r i p t i v e Nomenclature N o m e n c l a t u r e and a n d Classification C l a s s i f i c a t i o n of of Pyroclastic P y r o c l a s t i c Deposits D e p o s i t s and a n d Fragments: F r a g m e n t s : Recommendations R e c o m m e n d a t i o n s of of the the IUGS Subcommission S u b c o m m i s s i o n on o n the t h e Systematics S y s t e m a t i c s of o f Igneous I g n e o u s Rocks; Rocks ; Geology, G e o l o g y , Volume Volume 9, 9 , p.41—43. p.41-43. The Ground Sparks, S p a r k s , R.S.J., R . S . J . , Self, S e l f , S., S . , and a n d Walker, W a l k e r , G.P.L., G.P. L., 1973. 1973. Ground Surge S u r g e Deposit: D e p o s i t : AA Third T h i r d Type T y p e of o f Pyroclastic P y r o c l a s t i c Rock; Rock; Nature, Nature, Volume Volume 241, 2 4 1 , p.63—64. p.63-64. Stockwell, S t o c k w e l l , C.H., C . H . , McGlynn, McGlynn, J.C., J . C . , Emslie, E r n s l i e , R.F., R.F., Sanford, S a n f o r d , B.V., B.V., �155 Norris, Donaldson, N o r r i s , A.W., A.W., D o n a l d s o n , J.P., J . A . , Fahrig, F a h r i g , W.F. W.F. and a n d Currie, Currie, K.L. K. L. 1970. 1 9 7 0 . Geology G e o l o g y of o f the t h e Canadian C a n a d i a n Shield, S h i e l d , in i n Geology G e o l o g y and and Economic E c o n o m i c Minerals M i n e r a l s of o f Canada, C a n a d a , edited e d i t e d by b y R.J.W. R.J.W. Douglas, Douglas , Geological G e o l o g i c a l Survey S u r v e y of o f Canada, C a n a d a , Economic E c o n o m i c Geology G e o l o g y Report R e p o r t No.1, No. 1 , 838p. 838p. Tasse, T a s s e , N., N . , Lajoie, L a j o i e , 3., J . , and a n d Dimroth, D i r n r o t h , E., E . , 1978. 1978. T h e Anatomy A n a t o m y and and The Interpretation I n t e r p r e t a t i o n of o f an a n Archean A r c h e a n Volcaniclastic V o l c a n i c l a s t i c Sequence, Sequence, Noranda N o r a n d a Region, R e g i o n , Quebec; Q u e b e c ; Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Science, Science, Volume V o l u m e 15, 1 5 , p.874—888. p.874-888. Trowell, Geology i n prep. prep. G e o l o g y of o f the t h e Gibi G i b i Lake L a k e Area, Area, District District T r o w e l l , N.F., N.F. , in of o f Kenora; K e n o r a ; Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Open Open File F i l e Report. Report. Trowell, B l a c k b u r n , C.E., C.E. , and a n d Edwards, E d w a r d s , G.R., G.R., 1980. 1980. T r o w e l l , N.F., N.F. , Blackburn, Preliminary Synthesis of the Savant Lake — C r o w Lake Lake P r e l i m i n a r y S y n t h e s i s o f t h e S a v a n t L a k e - Crow Metavolcanic M e t a s e d i m e n t a r y Belt, B e l t , Northwestern N o r t h w e s t e r n Ontario; Ontario; M e t a v o l c a n i c—- Metasedimentary and a n d its i t sBearing B e a r i n g upon u p o n Mineral M i n e r a l Exploration; E x p l o r a t i o n ; Ontario O n t a r i oGeological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 3 0 p . Accompanied A c c o m p a n i e d bby y Chart Chart A. A. Williams, W i l l i a m s , H., H., and a n d McBirney, M c B i r n e y , A.R., A.R., 1979. 1 9 7 9 . Volcanology; V o l c a n o l o g y ; Freeman, Freeman, Cooper C o o p e r and a n d Co., Co., San S a n Francisco F r a n c i s c o379p. 379p. �Granitoid G r a n i t o i d Related Related Mineralization M i n e r a l i z a t i o n in i n the the Dryden D r y d e n Area Area I n t r o d u c t o r y Discussion D i s c u s s i o n and and Field F i e l d Guide Guide Introductory 31st 3 1 s t Annual A n n u a l Institute I n s t i t u t e on on Lake Lake Superior S u p e r i o r Geology Geology Kenora, Ontario Kenora , Ontario by F.W. F.W. Breaks Breaks 110 110 Chan Chan Cresent Cresent f i a s k a t o o n , Saskatchewan Saskatchewan Saskatoon, S7K S7K 5N8 5N8 R.C. R.C. Beard Beard Ministry M i n i s t r y of o f Natural N a t u r a l Resources Resources 808 8 0 8 Robertson R o b e r t s o n St. St. Kenora, K e n o r a , Ontario Ontario D.A. D. A. Janes Janes Resident R e s i d e n t Geologists G e o l o g i s t s Office Office Ministry M i n i s t r y of o f Natural N a t u r a l Resources Resources P.O. P.O. Box Box 309 309 Sioux S i o u x Lookout, L o o k o u t , Ontario Ontario K.H. K . H . Poulsen Poulsen Geological G e o l o g i c a l Survey S u r v e y of o f Canada Canada 601 Booth St. 601 Booth S t . Ottawa, O t t a w a , Ontario Ontario K1A K I A 0E8 OE8 �158 GENERAL GENERAL GEOLOGY This T h i s field f i e l d trip t r i p examines e x a m i n e s the t h e diverse d i v e r s e granitoid q r a n i t o i d rocks r o c k s and and a s s o c i a t e d mineralization m i n e r a l i z a t i o n in i n the t h e Dryden D r y d e n area. a r e a . The T h e rocks r o c k s of o f this this associated area to a r e a are a r e transitional t r a n s i t i o n a l from f r o m the t h e Wabigoori Wabigoon Subprovince S u b p r o v i n c e northward n o r t h w a r d to t h e Southern S o u t h e r n plutonic p l u t o n i c domain d o m a i n (Winnipeg ( W i n n i p e g River R i v e r terrane) t e r r a n e ) of o f the the the English A l l field f i e l d stops s t o p s will w i l l be b e made within w i t h i n aa E n g l i s h River R i v e r Subprovince. Subprovince. All b o u n d a r y z o n e l i m i t e d b y t h e Wabigoon F a u l t on t h e s o u t h and by b y aa boundary zone limited by the Wabigoori Fault on the south and line marking line m a r k i n g the t h e maximum extent e x t e n t northward n o r t h w a r d of o f abundant abundant supracrustal 1 ). T h e precise p r e c i s e position p o s i t i o n of o f the the s u p r a c r u s t a l rocks r o c k s (Figure ( F i g u r e 1). The subprovince is debatable d e b a t a b l e and a n d is is largely largely s u b p r o v i n c e boundary b o u n d a r y within w i t h i n this t h i s zone z o n e is dependent s t r u c t u r a l or o r metamorphic m e t a m o r p h i c criteria criteria d e p e n d e n t on on the t h e lithological, l i t h o l o g i c a l , structural used u s e d to t o define d e f i n e it it but, b u t , for f o r the t h e purposes p u r p o s e s of o f this t h i s excursion, e x c u r s i o n , it it is is sufficient s u f f i c i e n t to t o note n o t e aa number number of o f general g e n e r a l characteristics c h a r a c t e r i s t i c s of o f the the zone: zone : 1 ) I t contains c o n t a i n s aa higher h i g h e r proportion p r o p o r t i o n of o f metasedimentary m e t a s e d i m e n t a r y rocks r o c k s and and derived d e r i v e d migmatitic m i g m a t i t i c stages s t a g e s (Table ( T a b l e 1) 1 ) than t h a n is is normal n o r m a l within within the et t h e main m a i n mass mass of o f the t h e Southern S o u t h e r n plutonic p l u t o n i c domain d o m a i n (Breaks ( B r e a k s et al., a l . , 1978) 19 7 8 ) and a n d the t h e Wabigoon Wabigoon Subprovince S u b p r o v i n c e to t o the t h e south. south. In In the t h e Dryden D r y d e n area, a r e a , the t h e Wabigoon Wabigoon Fault F a u l t marks m a r k s the t h e southern southern extent ( Z e a l a n dGroup) G r o u p )which which e x t e n t of o f these t h e s emetasedimentary m e t a s e d i m e n t a r y rocks r o c k s(Zealand are a r e dominantly d o m i n a n t l y oof f tturbiditic u r b i d i t i c origin. origin. 2) 2 ) The The pproportion r o p o r t i o n oof f exposed e x p o s e d pplutonic l u t o n i c rrocks o c k s rrelative e l a t i v e to to supracrustal s u p r a c r u s t a l rocks r o c k sincreases i n c r e a s e northward s n o r t h w a r dand a n dnorthwestward northwestward within w i t h i n the t h e zone. zone. 3) is ppresent within 3) A A ssteep t e e p metamorphic m e t a m o r p h i c g rgradient a d i e n t is resent w i t h i n this t h i s zone: zone: low l o w ggrade r a d e aassemblages s s e m b l a g e s i ninp pelitic e l i t i c rrocks o c k s aadjacent d j a c e n t to t o the the Wabigoon d i s t a n c e of o f 77 km to to Wabiqoon Fault F a u l t give g i v e way northward n o r t h w a r d over o v e r a distance high a r e inferred i n Âe r r e d h i g h grade g r a d e assemblages. a s s e m b l a g e s . Metamorphic M e t a m o r p h i c pressures p r e s s u r e s are to t o be b e relatively r e l a t i v e l y low l o w (Bartlett, ( B a r t l e t t , 1978; 1978; Breaks, B r e a k s , 1982). 1982). 4) 4 ) A suite s u i t e of o f gneissic g n e i s s i c granitoid g r a n i t o i d rocks r o c k s which w h i c h represent represent intensely metamorphosed intensely m e t a m o r p h o s e d and a n d deformed d e f o r m e d polycyclic p o l y c y c l i c intrusive intrusive phases o f the t h e main m a i n mass m a s s of o f the t h e southern southern p h a s e s are a r e characteristic c h a r a c t e r i s t i c of plutonic p l u t o n i c domain d o m a i n bbut u t aare r e absent a b s e n t from f r o m the t h e zone z o n e under under cons c o n s iderat i d e r a t ion. ion. 5) 5 ) Metavolcanic M e t a v o l c a n i c rocks r o c k s are a r e particularly p a r t i c u l a r l y abundant a b u n d a n t in i n the t h e eastern eastern part p a r t of o f the t h e zone z o n e and a n d form f o r m parts p a r t s of o f two t w o units u n i t s which w h i c h extend extend northeastward n o r t h e a s t w a r d out o u t of o f the t h e area a r e a of o f consideration. c o n s i d e r a t i o n . The The northern n o r t h e r n unit u n i t which w h i c h extends e x t e n d s to t o Gullwing G u l l w i n g Lake Lake (Figure ( F i g u r e 1) 1) forms f o r m s aa portion p o r t i o n of o f the t h eNorthern N o r t h e r n Volcanic V o l c a n i c Belt B e l t (Trowell ( T r o w e l l et et al., a l . , 1980) 1 9 8 0 )which w h i c h comprises c o m p r i s e s aa lower lower south s o u t h facing f a c i n g mafic mafic sequence and an a n upper upper s e q u e n c e composed composed largely l a r g e l y of o f magnesian m a g n e s i a n basalts b a s a l ts and mixed m i x e d intermediate i n t e r m e d i a t e to t o felsic f e l s i c metavolcanic—metasedimentary metavolcanic-metasedimentary sequence. s e q u e n c e . The T h e second s e c o n d unit u n i t which w h i c h includes i n c l u d e s the t h e Brownridge Brownridge Volcanics 1 ) forms f o r m s part p a r t of o f the t h e Central C e n t r a l Volcanic V o l c a n i c Belt Belt V o l c a n i c s (Figure ( F i g u r e 1) which mafic w h i c h comprises c o m p r i s e s ma i c t to o intermediate i n t e r m e d i a t e flows f l o w s with w i t h local local f e l s i c flows, f l o w s , autoclastic a u t o c l a s t i c breccias b r e c c i a s and a n d thin t h i n sedimentary sedimentary intervals e t al., a l . , 1980). 1 9 8 0 ) . AA third t h i r d unit, u n i t , comprising comprising ( T r o w e l l et i n t e r v a l s (Trowell mixed t o felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s occurs o c c u r s in i n the the m i x e d mafic maÂi c to western w e s t e r n part p a r t of o f the t h e zone z o n e in i n the t h e vicinity v i c i n i t y of o f Vermilion V e r m i l i o n Bay. Bay. 1 ) It felsic GRANITOID G R A N I T O I D ROCKS ROCKS WhilTiTvidual W h i l e v i d u aintrusions l i n t r u s i o n within s w i t h i nthe t h eboundary b o u n d a r y zone zone commonly commonly display d i s p l a y internal i n t e r n a l compositional composit i o n a l variations, v a r i a t i o n s , it i t is is possible p o s s i b l e to t o subdivide s u b d i v i d e the t h e granitoid g r a n i t o i d rocks r o c k s in i n aa general g e n e r a l way way into into . - . �Figure 1: General Geology of the Dryden Area. 01 �- T a b l e 1: 1: Table CLASSIFICATION FEATURES OfiETASEDI%NTARY OFMETASEDIMENTARY MIGMATITES ENGLISH CLASSIFICATION AND GENERAL FEATURES. MwTITES ENGLISH RIVER RIVER SUBPROVINCE, SUBPROVINCEe IGMATITIC M IGMATITIC STAGE STAGE LEUCOSOME: LEUCOSOME LEUCOSOME: LEKOSOME && PALEOSOME---RATIO-- DIAGNOSTIC MIGMATITIC MIGMATITIC STRUCTURE STRUCTURE GENERAL GENERAL PROCESSES PROCESSES DOMINANT EOALNAE GENERAL GENERAL FIELD FIELD FEATURES FEATURES PrOtOProto— metatex ite m e t a t e x ite <0.11 <o- Locally L o c a l l y stromatic strcinatic Sedimentary Sed i m e n t a r y bedding b e d d i n g or or llaminae a m i n a e may show show preservation preservat ion selective' IIncipient, n c i p i e n t , 'selective' aanatexis. n a t e x i s . Metamorphic Metamorphic differentiation d i f f e r e n t i a t i o n may be be iimportant mportant Characterized C h a r a c t e r i z e d by by intercalated i n t e r c a l a t e d fg Eg and mg—cg mg-cg porphyroblastic porphyroblastic wacke and pelite p e l i t e ccnponents. mponents. Podiform Pod i f o r m and a n d lensic l e n s i c potassic potass ic lleucosonies e u c o s c i n e s eexhibit x h i b i t cconfinement o n f i n e m e n t to to pelitic p e l i t i c horizons. h o r i z o n s . Hydrothermal Hydrothermal (qtz. ( q t z - vveins) e i n s ) mobilizate m o b i l i z a t e may may be be - important. Metatexite Metatex ite Stromatic S t r o m a t i c and/or and/or Phlebitic P hlebi tic 0.11 ttoo 0.6 0. 0.6 Local m c a l to t o moderate moderate ddegree e g r e e oof f anatexis anatexis Mobilizate M o b i l i z a t e ddeveloped e v e l o p e d i in n ssitu, itu, p o s s e s s e s biotitic b i o t i t i melanosonies c melanoscines possesses along a l o n g leucosome—paleosome l e u c o s o m e - p a l e o s o m e inter— interMobilizate fface. ace, M o b i l i z a t e (without (without melanosomes) me1 a n o s o m e s ) also a 1 so commonly common 1y -IInhomogeneous nhomogeneous Diatexite Diatex ite 0.6 tto 0.6 o 0.9 Oe9 Homogeneous Homog e n e o u s Diatex D i a t e x ite ite >0.9 injected i n j e c t e d along a l o n g prevailing prevailing foliation b e d d i n g surface surface f o l i a t i o n or bedding of o f paleosome. p a l m . SSchollen c h o l l e n structure structure especially e s p e c i a l l y character— characterLocally iistic. stic. L ocally sschlienitic c h l i e r i t i c or or nnebulitic e b u l it ic A n a t e x is rrelatively elatively Anatexis extensive, e x t e n s i v e , mobilizate mobil i z a t e essentially essentially aautochthnous utochthnous Homogeneous usually usually massive, mass i v e * Locally Iocally sschollen, c h 0 1 1 e n ~ schlieritic s c h l ier it ic or nebulitic nebulitic sstructures t r u c t u r e s apparent apparent Very advanced a d v a n c e d fusion;  £ ui o n ; Very m o b i l i z a t e probably probably mobilizate a 1 lloch o c h t thonous honous al Abbreviations-fied;ji b b r e v i a t i o n s : f g - f i n e g r a i n e dmedium—rained; ; mg - m e d i u m - 2 r a i n e d ; cgc g —- ccoarse oarse grained; C gained; CII 0 - -- Q R e p l e t i c n of o f disoriented disoriented Repletion p a l e o s o m e and a n d metatexite metatexite paleosome iinclusions n c l u s i o n s and a n d melanosome melanosome clum c l u m p s is is ddiagnostic. iagnostic. - U s u a l l y hholo—leucocratic o l o - l e u c o c r a t i c and and Usually s e v e r e 1 y ssenate. eriate. R a r e 1 y more severely Rarely m a f i c variants v a r i a n t s (CI ( C I 15 tto o 30) 3 0 ) may mafic rrepresent e p r e s e n t cases c a s e s of o f complete complete aanatexis n a t e x i s eeffecting f f e c t i n g resorption resorption of o f melanosome me1 a n o s o m e component c o m p o n e n t into into magmatic m a g m a t i c phase phase C o l o u r ,Index; I n d e x ; >> - Colour t h a n ; < - less less atenthan;<— - z a t e r than than �161 three t h r e e suites s u i t e s which w h i c h reflect r e f l e c t not n o t only o n l y compositional c o m p o s i t i o n a l variations v a r i a t i o n s but but their t o other o t h e r tectonic t e c t o n i c events: events: t h e i r timing t i m i n g relative r e l a t i v e to i) i ) aa pre— p r e - to t o syn—tectonic s y n - t e c t o n i c sodic s o d i c suite suite ii) a syn—tectonic peraluminous suite i i) a syn-tectonic peraluminous s u i t e iii) i i i ) aa syn— s y n - to t o post—tectonic p o s t - t e c t o n i c potassic p o t a s s i c suite. suite. The The essential e s s e n t i a l features f e a t u r e s of o f each e a c h suite s u i t e are a r e described d e s c r i b e d below b e l o w with with reference to the plutonic rock nomenclature of Streckeisen r e f e r e n c e to t h e p l u t o n i c r o c k nomenclature of S t r e c k e i s e n (1976). (1976). Sodic S-.o d i c Suite Suite The The phases p h a s e s within w i t h i n these t h e s e intrusions i n t r u s i o n s are a r e dominantly dominantly trondhjemite t r o n d h j emite and a n d granodiorite g r a n o d i o r i t e with w i t h rare r a r e granite. g r a n i t e . The The rocks r o c k s are are quite q u i t e uniform u n i f o r m in i n composition c o m p o s i t i o n and a n d commonly commonly possess p o s s e s s aa metamorphic metamorphic foliation. The rocks r o c k s are a r e generally g e n e r a l l y medium medium grained g r a i n e d and a n d contain contain f o l i a t i o n . The biotite b i o t i t e as a s the t h edominant d o m i n a n t mafic m a f i c mineral. m i n e r a l . In I n the t h e Dryden D r y d e n area a r e a this this suite s u i t e isisrepresented r e p r e s e n t e d by by small s m a l l plutons p l u t o n s and a n d sills s i l l ssuch s u c h as a s the the G o l d l u n d ttrondhjemite rondhjemite w i t h i n the t h e Central C e n t r a l Volcanic V o l c a n i c Belt B e l tand and by by Goldlund within stocks s t o c k s such s u c h as a s the t h eLateral L a t e r aLake l U k ebody body composed composed oof f foliated foliated biotite—bearing b i o t i t e - b e a r i n g granodiorite g r a n o d i o r i t e (McCarter, ( M c C a r t e r 1980) 1980 ) and and the t h e Broadtail Broad t a i l Lake body composed composed l i a t e d bbiotite i o t i t e and and Lake body o f of m amassive s s i v e t otof ofoliated hornblende—biotite h o r n b l e n d e - b i o t i t e granodiorite. granodiorite. A - - Peraluminous P eraluminous ------.-- Suite S -uite AA dominnt d o m i n a n t granitoid g r a n i t o i d element e l e m e n t in i n the t h e Dryden D r y d e n area a r e a is is the t h e Ghost Ghost Lake Lake Batholith. B a t h o l i t h . This his peraluminous, p e r a l u m i n o u s two—mica t w o - m i c i granitoid g r a n i t o i d was was previously p r e v i o u s l y mapped, m a p p e d , in i n part, p a r t by b y Moorhouse M o o r h o u s e (1939) ( 1 9 3 9 ) and a n d Satterly Satterly (1941) ( 1 9 4 1 ) and and completely c o m p l e t e l y delineated d e l i n e a t e d by b y Breaks B r e a k s et e t al. a l . (1976) ( 1 9 7 6 ) with with more The more recent r e c e n t detailed d e t a i l e d mapped mappedcompleted c o m p l e t e dbyb yBreaks B r e a k s(1984) ( 1 9 8 4 .) The batholith 280kin2, km2f is is elongated e l o n g a t e d and a n d is is broadly b r o a d l y concordant c o n c o r d a n t with with b a t h o l i t h isis280 east t o northeasterly n o r t h e a s t e r l y striking s t r i k i n g structural s t r u c t u r a l trends t r e n d s in i n adjacent ad] a c e n t e a s t to rocks. is distinguishable d i s t i n g u i s h a b l e from f r o m virtually v i r t u a l l y all a l l other other r o c k s . The T h e batholith b a t h 0 1 i t h is plutonic u n i q u e accessory accessory p l u t o n i c masses m a s s e s in i n the t h e region r e g i o n by b y virtue v i r t u e of o f aa unique mineral m i n e r a l suite s u i t e including i n c l u d i n g muscovite, m u s c o v i t e cordierite, c o r d i e r i t e sillimanite, sillimanite, Mn—garnet, r a r e duinortierite d u m o r t i e r i t e and a n d beryl. beryl. Mn-garnet tourmaline t o u r m a l i n e and a n d rare The T h e main m a i n exposed e x p o s e d mass mass of o f the t h e batholith b a t h o l i t h covers c o v e r s a a 40 4 0 km km long lonq area a r e a between b e t w e e n Eagle E a g l e River R i v e r and a n d Ghost G h o s t Lake Lake which w h i c h contains contains inhomogeneous t o homogeneous h o m o g e n e o u s diatexite d i a t e x i t e composed composed of o f coarse c o a r s e grained grained i n h o m q e n e o u s to granite g r a n i t e and a n d granodiorite g r a n o d i o r i t e with w i t h variable v a r i a b l e contents c o n t e n t s of o f biotite b i o t i t e and and muscovite. m u s c o v i t e . The T h e western w e s t e r n two—thirds t w o - t h i r d s of o f this t h i s mass mass probably probably represents lower sstructural t r u c t u r a l level l e v e l of o f the t h e intrusion i n t r u s i o n in i n that t h a t the the r e p r e s e n t s aa lower granitoid homogeneous, less homogeneous contain c o n t a i n less l e s stourmaline t o u r m a l i n eand and g r a n i t o i d rocks r o c k s are a r eless muscovite m u s c o v i t e and a n d form f o r m ttransitional r a n s i t i o n a lcontacts c o n t a c t with s w i t migmatized h migmatized metased rocksddisplaying i s p l a y i n g aassemblages s s e m b l a g e s ttypical y p i c a l of o f the the m e t a s e d i imentary m e n t a r y rocks second s e c o n d sillimanite s i l l i m a n i t e isograd. i s o g r a d . The The eastern e a s t e r n portion p o r t i o n of o f the t h e mass mass shows it s h o w s characteristics c h a r a c t e r i s t i c s of o f the t h e upper u p p e r level l e v e l of o f the t h e intrusion i n t r u s i o n as a s it has h a s an a n abrupt a b r u p t contact c o n t a c t with w i t h metasediments, m e t a s e d i m e n t ~few f~e w sedimentary sedimentary i n c l u s i o n s f abundant a b u n d a n t muscovite m u s c o v i t e and a n d tourmaline t o u r m a l i n e (locally ( l o c a l l y1010to t o 20 20 inclusions, percent) p e r c e n t ) and a n d potassic p o t a s s i c pegmatites p e g m a t i t e s which w h i c h typify t y p i f y the t h e cupola c u p o l a zone z o n e of of batholiths b a t h o l i t h s parental p a r e n t a l to t o rare r a r e element e l e m e n t pegmatites p e g m a t i t e s (Varlamoff, (Varlamoff 1972). l i e s in i n abrupt abrupt 1 9 7 2 ) . Along Along the t h e southern s o u t h e r n contact, c o n t a c t f the t h e batholith b a t h o l i t h lies contact l o w - to t o medium—grade m e d i u m - g r a d e metasediments m e t a s e d i m e n t s with w i t h no no c o n t a c t with w i t h low— appearance a p p e a r a n c e of o f assemblages a s s e m b l a g e s of o f the t h e second s e c o n d sillimanite s i l l i m a n i t e zone z o n e in in metapelitic m e t a p e l i t i c layers l a y e r s which w h i c h militates m i l i t a t e s against a g a i n s tin—situ i n - s i t u partial partial melting n e l t i n g in i n this t h i spart p a r tofo fthe t h body. e body. . �162 Potassic P o t a s s i c Suite Suite T h i s ssuite u i t e is is represented r e p r e s e n t e d in i n tthe h e Dryden D r y d e n area a r e a by by two t w o large large Thi masses, m a s s e s I the t h e Dryberry D r y b e r r y Batholith B a t h o l i t h and and the t h e Gullwing G u l l w i n g Lake Lake Batholith Batholith The pphases (Figure ( F i g u r e 1). 1) h a s e s within w i t h i n these t h e s e bodies b o d i e s are a r e predominantly predominantly monzonites and ggranites commonly mmassive qquartz uartz m o n z o n i t e s and r a n i t e s wwhich h i c h aare r e commonly assive; homogeneous and Unlike homogeneous a n d medium to t o coarse coarse grained. grained. U n l i k e the t h e sodic sodic ssuite, u i t e l these t h e s e rocks r o c k s are a r e generally g e n e r a l l y discordant d i s c o r d a n t with w i t h their t h e i r hosts h o s t s and and dikes s i l l s of o f similar s i m i l a r composition c o m p s i t i o n may be b e very v e r y abundant a b u n d a n t in in d i k e s and a n d sills The aadjacent d j a c e n t country c o u n t r y rocks. rocks. T h e greatest g r e a t e s t volume v o l u m e of o f rock r o c k in i n these these batholithic b a t h 0 1 i t h i c complexes c o m p l e x e s characteristically c h a r a c t e r i s t i c a l l y lacks l a c k s aa metamorphic metamorphic foliation  £ 0i a t i o n aalthough 1 t h o u g h contact—parallel c o n t a c t - p a r a l l e l foliations  £ 0i a t i o n s near n e a r the t h e margins marg i n s related t o emplacement, e m p l a c e m e n t I are a r e common common features. features. r e l a t e d to -- . ECONOMIC -o l-d -D GEOLOGY Gold G ~ t s --- -Gold G o l d ccurrences o G u r r e n c e s in i nthe t h eDryden D r y d e n area a r e a are a r e concentrated c o n c e n t r a t e d in i n the the Central Volcanic Central V o l c a n i c BBelt e l t iin n the t h e eastern e a L t e r n part p a r t of o fthe t h eboundary b o u n d a r y zone. zone. IIn n aa general g e n e r a l way, wayr tthe h e ggeological e o l o g i c a l ssetting e t t i n g of o f gold g o l d mineralization mineralization is similar i n t h i s a r e a is s i m i l a r to t othat t h a in t imany n manyother o t h e rgold g o l d 1camps camps in in Someo foft the Superior S u p e r i o r PProvince r o v i n c e ( (Colvine C o l v i n e e et t aal., l m r1984). 1 9 8 4 ) . Some h e ffeatures eatures oof f this t h i s gold—district g o l d - d i s t r i c t are: are: ii)) On a r e g i o n a l s c a l e r g o l d is l o c a l i z e d a t o r n e a r a m a j o r most vvolcanic—sedimentary o l c a n i c - s e d i m e n t a r y iinterface n t e r f a c e (Figure ( F i g u r e 1) 1 ) though though m ost individual i n d i v i d u a l deposits d e p o s i t s occur o c c u r within w i t h i n volcanic v o l c a n i c and a n d granitic granitic rrocks. ocks. wide morphologies iii) i ) AA w i d e vvariety a r i e t y oof f ddeposit eposit m o r p h o l o g i e s is i s present p r e s e n t including including veins rocks I en—echelon e n - e c h e l o n vein vein v e i n s and and sstockworks t o c k w o r k s in i n volcanic v o l c a n i c rocks, arrays i n t r u s i v e bodies, b o d i e s , carbonate c a r b o n a t e zones z o n e s in in a r r a y s in i n felsic f e l s i c intrusive volcanic rocks and and silicified s i l i c i f i e d shear s h e a r zones z o n e s in in v o l c a n i c and a n d sedimentary s e d i m e n t a r y rocks tuffs t u f f s aandlavas n d ' l a v a s (Blackburn ( B l a c k b u r n and a n d Janes, J a n e s I 1983). 1983). Gold mineralization by iiii) ii) G old m i n e r a l i z a t i o n is i s hosted hosted b y sstructures t r u c t u r e s bounded b o u n d e d by b y two two major faults f a u l t s which w h i c h roughly r o u g h l y parallel p a r a l l e l stratigraphic s t r a t i g r a p h i c trends. trends. Gold—quartz iiv) v) G o l d - q u a r t z vveins e i n s post—date p o s t - d a t e a lall l rrock o c k ttypes y p e s iin n the t h e area a r e a with with tthe h e possible p o s s i b l e exception e x c e p t i o n oof f some some ppost o s t ttectonic e c t o n i c granitoid granitoid iintrusions. ntrusions. Several t o small s m a l l bodies bodies vv)) S e v e r a l ooccurrences c c u r r e n c e s are a r e spatially s p a t i a l l y related r e l a t e d to composed composed of o f quartz q u a r t z and and feldspar f e l d s p a r porphyry. porphyry. The most most ssignificant The i g n i f i c a n t occurrence o c c u r r e n c e of o f gold g o l d in i n this t h i s area a r e a is is tthe he It Goldlund I t ccomprises o m p r i s e s en e n echelon e c h e l o n sets s e t s of o f extensional extensional G o l d l u n d deposit. deposit. is broadly broadly vveins e i n s which w h i c h ttransect r a n s e c t aa body body of o f trondhjernite t r o n d h j e m i t e which w h i c h is concordant with adjacent volcanic rocks. The veins c o n c o r d a n t w i t h a d j a c e n t v o l c a n i c rocks. T h e v e i n s appear a p p e a r to t o be be tthe h e product p r o d u c t oof f hydraulic h y d r a u l i c fracture f r a c t u r e oof f the t h e intrusion i n t r u s i o n and a n d the the is llikely rrelationship e l a t i o n s h i p bbetween e t w e e n g gold o l d a nand d t hthe e g granitoid r a n i t o i d r rock o c k is ikely pass ive passiv e aand n d s isimply m p l y t hthe e r eresult s u l t oof f bbrittle r i t t l e deformation d e f o r m a t i o n oof f aa competent unit. competent u n i t . T h i s s i t u a t i o n is s i m i l a r t o t h a t a t o t h e r deposits d e p o s i t s in i n Superior S u p e r i o r Province, P r o v i n c e " most notably n o t a b l y at a t the t h e Sigma Sigma Mine, Miner An important 1983). t aal., l . , 1983) An i m p o r t a n t ffeature e a t u r e of of V a l d'Or, d 1 0 r Quebec Q u e b e c ((Robert R o b e r t e et Val is tthe Goidlund G o l d l u n d is h e ppresence r e s e n c e oof f nnumerous u m e r o u s ddikes i k e s oof f qquartz u a r t z aand n d feldspar feldspar porphyry which p orphyry w h i c h cut c u t the t h e trondhjemite t r o n d h j e m i t e but b u t not n o t the t h e gold—quartz gold-quartz In some cases cases vvein—bearing veins. e i n - b e a r i n g sstructures t r u c t u r e s in i n the t h e trondhjemite trondhjemite veins. I n some Porphyries extend ex t e n d unmineralized u n m i n e r a l i z e d into i n t o porphyry p o r p h y r y dikes. dikes. P o r p h y r i e s of o f this this type t y p e are a r e common common features f e a t u r e s of o f many many gold g o l d depos d e p o sits i t s (McIntyre, (McIntyreI Hollinqer, H o l l i n g e r D3me) D o m e ) but b u t their t h e i r genetic g e n e t i c relationship r e l a t i o n s h i p to t o gold gold mineralization m i n e r a l i z a t i o n is is poorly p o o r l y understood. understood. DosTts in this area a regional scale, gold is localized at or near a major This situation is similar to that at other �163 Mo1yiteD M o l y b d e n--i t e Depos e---p o s its its - The The Lateral L a t e r a l Lake Lake granodioritic g r a n o d i o r i t i c stock s t o c k hosts h o s t s several several occurrences its contact c o n t a c t with w i t h rocks r o c k s of o f the the o c c u r r e n c e s of o f molybdenite m o l y b d e n i t e at a t its Northern Belt. This m i n e r a l 1 z a t i o n has h a s been b e e n described described N o r t h e r n Volcanic V o l c a n i c Belt. This mineralization by b y McCarter M c C a r t e r (1980), ( 1 9 8 0 ) Colvine C o l v i n e and a n d McCarter M c C a r t e r (1977) ( 1 9 7 7 ) and and Page P a g e (1984). ( 1 984). M o l y b d e n i t e occurs o c c u r s in i n quartz q u a r t z and a n d pegmatitic p e g m a t i t i c veins v e i n s which which are are Molybdenite w e l l developed d e v e l o p e d in i n aplitic a p l i t i c dikes d i k e s which w h i c h cut c u t the the p a r t i c u l a r l y well particularly granodiorite. The 1) as a s euhedral e u h e d r a l grains g r a i n s with with granodiorite. The molybdenite m o l y b d e n i t e occurs o c c u r s i) K—feldspar i i ) as rare r a r e euhedral euhedral K - f e l d s p a r and a n d phlogopite p h l o g o p i t e in i n pegmatites, p e g m a t i t e s f ii) grains i i i ) along a l o n g vein v e i n margins, margins i v ) as a s isolated isolated g r a i n s in i n quartz q u a r t z veins, v e i n s iii) iv) grains g r a i n s in i n quartz—vein q u a r t z - v e i n stockworks; s t o c k w o r k s ; v) v ) as a s narrow n a r r o w bands b a n d s and and lenses lenses parallel t o foliation f o l i a t i o n in i n wall—rocks w a l l - r o c k s and, a n d f vi) v i ) along a l o n g fractures f r a c t u r e s not not p a r a l l e l to parallel t o foliation f o l i a t i o n in i n walirocks w a l l r o c k s (Colvirie ( C o l v i n e and a n d McCarter, M c C a r t e r 1977). 1977). p a r a l l e l to Muscovite M u s c o v i t e and a n d pyrite p y r i t e are a r e common common accessories a c c e s s o r i e s to t o the t h e molybdenite molybdenite mineralization. Colvine mineralization. C o l v i n e and a n d McCarter M c C a r t e r (1971) ( 1 971 ) relate r e l a t e the the t o aa hydrothermal h y d r o t h e r m a l system s y s t e m developed d e v e l o p e d during d u r i n g the the m i n e r a l i z a t i o n to mineralization l a t e r sstages t a g e s of o f crystallization c r y s t a l l i z a t i o n of o f the t h e Lateral L a t e r a l Lake Lake stock s t o c k while while later Page P a g e (1984) ( 1 9 8 4 ) relates r e l a t e s it i t to t o post—tectonic pos t - t e c t o n i c emplacement e m p l a c e m e n t of o f pegmatites pegmatites which t o the t h e Lateral L a t e r a l Lake Lake intrusion i n t r u s i o n and a n d controlled controlled w h i c h are a r e unrelated u n r e l a t e d to by b y the t h e nearby n e a r b y Kathlyn K a t h l y n Lake Lake Fault. Fault. -- Rare—Metal R a r e - M e t a l- Pegmatites -P e-g m aptei gt ems a t i t e ~in Rare—metal R a r e - m e t a l pegmatites i n the t h e Dryden D r y d e n area a r e a were were first first described ( 1 9 6 5 ) who who termed t e r m e d their t h e i r concentration c o n c e n t r a t i o n the the d e s c r i b e d by b y Mulligan Mull i g a n (1965) "Dryden " D r y d e n Pegmatite P e g m a t i t e Field". F i e l d 1 ' . Regional Reg i o n a l zonation z o n a t i o n within w i t h i n this t h i s field field was ( 1 9 8 0 ) as a s outlined o u t l i n e d in i n Table T a b l e 2, 21 was first f i r s t recognized r e c o g n i z e d by b y Breaks B r e a k s (1980), resulting r e s u l t i n g in i n aa subdivision s u b d i v i s i o n into i n t o two t w o distinct d i s t i n c t pegmatite p e g m a t i t e groups groups (Terminology ( T e r m i n o l o g y aafter f t e r Cerny, C e r n y f 1982, 1 9 8 2 f p.8—9) p . 8 - 9 ) at a t Mavis Mavis Lake L a k e and and Gullwing—Tot Lakes separated by a distance of 9.7 km. G u l l w i n g - T o t L a k e s s e p a r a t e d b y a d i s t a n c e o f 9 . 7 km. The The geology g e o l o g y of o f the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group Group is isdominated dominated by the Ghost Lake Batholith which represents the most by t h e G h o s t Lake B a t h o l i t h w h i c h r e p r e s e n t s t h e most plausible plausible source s o u r c e area a r e a for f o rthe t h erare—metal r a r e - m e t a l pegmatites p e g m a t i t e s based b a s e d upon u p o n the the following f o l l o w i n g ppetrologic e t r o l o g i c features f e a t u r e s and and chemical c h e m i c a l characterist-ics: characterist-ics : i) the advanced degree of geochemical fractionation t h e a d v a n c e d d e g r e e o f g e o c h e m i c a l f r a c t i o n a t i o n and and i1 difference sf 66 (Table ( T a b l e 3) 3) d i f f e r e n c e in i n plutonic p l u t o n i c units u n i t s such s u c h as a s GLB4, GLB4# 5, relative r e l a t i v e to t o the t h e main m a i n western w e s t e r n mass m a s s of o f the t h e batholith b a t h 0 1 i t h which w h i c h is is dominated d o m i n a t e d by b y plutonic p l u t o n i c unit u n i t GLB—1 GLB-1 (Breaks, ( B r e a k s in i n prep.). prep.) The The former t o exhibit e x h i b i t increased i n c r e a s e d levels l e v e l s of of f o r m e r plutonic p l u t o n i c units u n i t s tend t e n d to muscovite, with t o nil n i l biotite biotite m u s c o v i t e f tourmalirie t o u r m a l i n e aand n d ggarnet arnet w i t h ssparse p a r s e to in t o plutonic p l u t o n i c unit u n i t GLB—1; GLB-1; i n contrast c o n t r a s t to ii) i i ) sporadic p r e s e n c e of o f rare—metal r a r e - m e t a l mineralization m i n e r a l i z a t i o n (i.e. ( i .e beryl) beryl) s p o r a d i c presence within w i t h i n some some internal i n t e r n a l pegmatites p e g m a t i t e s (Dryden ( D r y d e n Airport A i r p o r t beryl beryl occurrence) t o u r m a l i n e -- quartz quartz o c c u r r e n c e ) and and in i n contact c o n t a c t pneuinatolytic p n e u m a t o l y t i c tourmaline deposits d e p o s i t s (Petrunka ( P e t r u n k a Tungsten T u n g s t e n Property P r o p e r t y at a t STOP STOP 5); 5); i i i ) contact iii) c o n t a c t metasomatic m e t a s o m a t i c selvedges, s e l v e d g e s developed d e v e l o p e d in i n mafic mafic metavolcanic m e t a v o l c a n i c host h o s t rocks, r o c k s which which exhibit e x h i b i t anomalous a n o m a l o u s trace t r a c e level level L i Cs, C s Be, B e , Rb, Rbf Sn Sn and a n d FF (Petrunka ( P e t r u n k a Thngsten Tbngsten e n r i c h m e n t in i n Li, enrichment Property P r o p e r t y at a t STOP STOP 5). 5). Significant GhostLake Lake S i g n i f i c a n t petrochemical p e t r o c h e m i c a l zonation z o n a t i o n within w i t h i n the t h eGhost Batholith B a t h o l i i h is is revealed r e v e i l e d by by ccertain e r t a i n trace t r a c e elements, e l e m e n t s f in i n particular p a r t i c u l a r B, Bf Ba, Ba Li, Li Rb, R b f Sr, S r Zr Z r and a n d REE REE ((Breaks, B r e a k s iin n pprep.). r e p . ) . Trends T r e n d s of of increasing F3, i n c r e a s i n g geochemical g e o c h e m i c a l ffractionation r a c t i o n a t i o n involving i n v o l v i n g enrichment e n r i c h m e n t of o f B, Be, with B e Ga, Ga Li, L i Nb, Nb and a n d Pb R b coupled coupled w i t h ddepletion e p l e t i o n of o f Ba, Ba Sr, S r Zr, Z r and and total t o t a l REE REE have h a v e been b e e n delineated d e l i n e a t e d within w i t h i n the t h e batholith b a t h o l i t h from f r o m the t h e main main . . �______________________________Assemblage1 _____________ 164 able 2: 22 Fable Geochemical Features Petroi P e t r o l o g i c a l and and Geochemical F e a t u r e s of of Rare-Metal—Bearing Rare-ZeLal-&ear1119 Pegsatites P e g m a t i t e s from From the t h e Dryden Dryden Field. Field.- Area/Occurrence Area/Occurrence Charactristic Charactristic Pegsatite P e g m a t i t e StructurR Structure Pegmatite P e q m a t i t e Mineral Hineral ~ s s e m b l a ~ ~ - Geochemical Aasoclation2 &.sociation2 Degree of (ate Degree OF b t e Stage Stage Replacueent bplacment Albitization A lbitization B—CBs—Cs) B-(Be-Ce) Absent Absent MaRie ~ a v i sLake u k e Pegmatit. p e g m a t i t e Group Dryden irFort Dryden AAirport occurrenm, Occurrence, Zealand x e a l a n d lbwnship mmnship Unzoned.i internal, Unmned, nternal, , barren uu.ually sually b a r r e n potassic p t ~ s i c pegmatitea Garnet +t Muscovite Garnet n u s c o v i t e +t Iburmaline m umaline + t Albite A l b i t e +t Quartz a l o c k y k—feldspar K-feldspar Q u a r t z +t Blocky + (Limegr.en t (Limegreen Beryl) mryl) Taylor Occurrence, Taylor Occurrence, Concession c o n c e s s i o n VII. V1 I , Zealand ?ownmhip Itenship zealand .arqinal m a s q i n a l to t oQost mostLaX. fah tkzoned potassic lhaoned p tdssic peqsatites p e g m a t i t e 8 developed developed Beryl (Sn—Nb>Ta— B e r y l ++lbur,salin. m u m a l i+nAlbite e + AB—Be— l b i t e 8-B-(Sn-~b>TaQuartz P)) +t Q uartz + t Graphic Graphic P K—feldspar K -feldspar + + Blocky Blocky k—feldspar R-feldapar t+ ((Colueblt. colmbite + Garnet t G a r n e t ++ Muscovite M u s c o v i t e +t Green *at ).patiits) Green te) p e t r u n k a Occurrence, Wcurrence, Petrunka Brownridge Brownridge and Zealand mmnship Zealand Townships p.g.atites Bathol B a t h o lith ith Unmned, t o u r m a l ins— ineUnmoned, toursal eenriched n r i c h e d fracture/pillow frecture/pillow ssalvage—controlled elvqemtrollad replaces.nt r e p l a c m e n t in i nBrownridg. Brownridge m i c estavolcanics metavolcsnics s.fa tIc Quartz t Plaqioclaae P l a q i o c l ~+ et Q uartz + Biot B i o t iits te ÷ + Scheel S c h e e l iit. te + + + (Pyrite 'Toursaline burmaline + ( P y r i t e ++ Holequletite Holmquia t i t o + t Fluorite?) PI w r i t e ? ) Incipient. all Incipient. % a l l pod. p a l s of of fine—grained, saccharoidal fine-grained , saccharoidsl splits a p l i t e (4 ( t Chriua Chrmium Mica ~ i c at4 Quartz W-artz + + aAlbit.) lbite) W—B—F— (Li—Sn—Be) W-B-P-(Li-Sn-Be) Ibeerved Sot C tat bservd Li— (Be—Rb-ra>Wb— Li-(&-Rb-Ta>NbB—Sn) 6-Sn) Moderate W e r a t e ddevelopeent w e l o p e n t of of aelbitization l b i t i a a t i o n (+ (t Garnet 4t Tantal T a n t a l iits t e ++ White W h i t s Beryl mryl Green *Fa.cov 7 Green s c w i t its e + t Quartz Clesv.landita) m a r t s t+ C leavelMdite) Falrservice e a i r s e r v i c e Property, Property, Brownr E x o m r i dIdge g e Township Tounship Main and sSouth u i n and o u t h Ions. an" Un zonedt to Unzoned o ccrudely rdely zoned zoned e x t e r n a l pegmatitea. peqnatitaa. externsl 4 Green Mu.cov Beryl Green H u s c w iits te Beryl + t+ Albite N b i t e 4.t Spodueens Spcdmene Contains C o n t a i n s r arandly n d m l y oriented, o r i e n t e d , Blocky Blocky K—feldspar K - f e l d s p a r +t last UstZone Zone ++ g r e e n primary p r h a r y spodLa.fle spodmene green phenocrysts p h e n o c r y ~ t s(Type (Type I1 epodtene e p c d m e m of o f H.inricfl, Heinrich, 1975) 1975) Quartz ( B l u e Apatite Apatite + t Q u a r t z t+ (Blue Garnet Garnet + t Toursaline T u t u m a l i n e4.t Tantal T a n t e l iits) te) Unmoned extetnal U nmnd ex ternal Primary sineralogy R imary m ineralcqy llarg.ly a r g e l y replaced. replaced. Bemnants Fmmndnts oof f blocky blocky k—feldspar, K - f e l d s p a r , spodue.ne. eiXdmelN, and and qquartz u a r t z sstill till discernible discernible p.geatitea pqmstltu Ta)Nb—B.— Ta>Nb-Be*B-( L(Li) i) ' Pervealve P e r v u l v e aalbitizatlon. lbitisation. Fast of mst o f peqeat p e g m a t iit. te White Beryl replaced r e p l a c e d by by 4. t White B~ryl 4. Green + rantal it. t T a n t a l i t e t Green Fascov Quartz m e c o v i its t e 4t ~ u a r t st+ C1.au.landitra C&elandi te Guliwing Lake—Itt Peqest Gullwing Iake-Tot fLake ah P w m a t its l t s Group QOuP Mica Point n ica P oint Gullwlng Lake, Gullwinq bh, rope R o wTownship lbmhip Crudely zoned, eexternal Cxudely so&, xternal potassic peq.atits ptassic m matite Muecovite Biotite Mumcwite ++ B i o t i t e ++ Albite N bite 4 t Quartz Quartz + t K—feldspar K - f e l d s p a r ++ (Molybdenits (mlybdenite Coluebite—Tantal ++ C o l m b i t - T a n t a l i t eits) ) (Nb>Ta-WO) (Nb>Ta*) Gullwinq Gullwinq Lake Iah Co.pl.x C o m p l ~external e~x t e r m 1 Green Green w'odten. m e n e +t Li— (TsCNb-Mo-Bn) (Ta(Nb—Mo—Sn) Li- Peg.atlte, P e g m a t i t e ,Webb !&bb Toimah T o m e h iipp Most ppeq.atlte. eqmatite. mt ooff dik, d i h consists c o n s i s t s of of .uBcov m u s c w iits—blot t m - b i o t i tits e peg.atltic p e g m a t i t i c granite. granite. ContaIns C o n t a i n s green g r e e n Type Wpm 1 s.podaens p o d m e n e of of B.inrlcb winrich I (1975) (1975) Muscovite t+ AAlbite Muscovite lbite + t Quartz t Blocky Blocky m artz + K—feldspar K-feldspar Albit. GreenYsaacovit. n ~ s c w i t 4et ~ l b i t4etGreen Quartz Q u a r t z +t Blocky Blocky k—feldspar K-feldnpar Incipient Incipient Moderateaalbitisation Moderate lbitization ddeveloped w e l o p a d in i n 22 sstages: tag-: I. e a r l ysediua—grained, mdium-grained, 1. early equ e q u iig g rranular anular + Biotite Tantal t ~ i o t i t4 e2 T a n t a lIts i t e +t usCOv l i u s c w iite te +Q Quartz + uarts + t Albite Albite 2. later, 2. l a t e r ,fine—gralnsd fine-grained u(apidol p i d o l Ite—Albite ite-Albite C a p l e x + Tantalit. Tantalite + t Beryl n e r y l ++ Garnet Garnet Lapidol +4 Lep1d01ite ++ Muscovite Muscwite t ClpvelapditeJ Cplez 4 it. + Clca!iteJ Coates Peqastite, CoatPaqaat it*, Webb m Township Webb mnship Peg.atlte P e g m a t i t e 215 215 5 m Southwest ooff Coates South-t coatPegmatite, P e q m a t i t e , Wsbb Webb Township m unship Tot Lake mt fake Pegsat iI tte, Pegmat e, Webbmmnship xnship Webb lUnzon.d, h z o n d , eexternal xternal potassic peq.etit• p taseic w matite Unxoned, eexternal Unmnad, xternal potas. p t a ~ sIc i cppeg.atite R3mstite -- complex C a p l e x eexternal xternal Contains peg.atlte. pegmatite. Contains pink p i n k Type Typ 2 2 spothnene epodmene off Beinrich o w i n r i c h (1975) (1975) Accessory ~ c c e s s o r ymminerals i n e r a l s pplaced l a c e d iIn n brackets. brackets. Minoreelements 22 Minor l e m e n t s pplaced l a c e d i in n bbrackets. rackets. Muecov its 4-+ A Albit. Muscovite l b i t e ++ Quartz m art; + t Graphic Graphic k-f K - f eeldBpar l d s p a r + (Molybdenite (mlybdenite Garnet 4+ Pyrite w r i t e t+ G arnet + + SSeaarskite marskite + t Sphalsrite Sphalerite Chalcopyrite + Beryl) t C h a l c o p y r i t e 4. t B eryl) nMo-e )Nb)Ta—Cu— (Nb>Ta-Cu- Muscovite 4t Albite A l b i t e +t 4 Blocky Quartz Blocky K—feldspar K-feldspar Quartz + + t (Colbite—Pantalite ( C o l m b i t e - T a n t a l i t e4.t Garnet Garnet + t Falybdenlte) mlyMenite) Nb>Ta?— (Mo) Nb>Ta?(-1 S p o d m e n e +t Pink Spodesene Pollucite Q u a r t z +t P o l l w i t e +t Quartz Albite N b i t e ++Blocky Blocky K—feldspar K - f e l d s p a r ++{(Fluorapatlte Flwrawtite 4t Garnet + Ibursaline) Garnet t mumeline) In—S-Be—RE!) Zn-840-REE) IIncipient n c i p i e n t repiscesent r e p l a c e m e n t by by fine—grsined f i n e - g r a i n e d aalbite l b i t e along along edge. Fast adgem of of K—feldspar. K-feldsparnost solybdenite mol y M e n i t e end and sarekite a m a ~ s k i associated t ea s s o c i a t e d with albitized cress IIncipient, n c i p i e n t , file—like film-like albitizatlon a l b i t i a a t i mand andaBeociated associated coiabite—tantal c o l m b i t e - t a n t a l iite t e In in with a l b i t i z e d a r e a s ccoarse u a r s e blocky b l o c & K—feldspar K-feldspar Li -Cs—Rb— Li-Cs-Rb- tensive aibitization Rtensive albitizatim developed -F-P -F+ )Ta>Nb—Be) ( ~ a > ~ b - ~ e )d w e l o w d iin n 22 sstages: tages: 1. sssccharoidsl a c c h a r o i d a l sodic sodic aplite (Blw Watite ++ Tourtualine m u m a l i n e 4 Quartz Wartz ++ ALb1t.a) Alblte) 2- tapidal u p i d o l ite—Albit. ite-Albite 2. Complex (+ (+ White mite complex Beryl B eryl + + Garnet Garnet ++ Trantalite anealite + + Sericite Sericite + + Lapidol + Quartz L e o i d 0 1 iite te + o u a r t z 4t C cl&l$ndite; split. (Blue gpatite llandite) �_______ Tablejmmy ofofP Petrol2!c GhoLBatholith. Summary e t r o l a i c Feat F e a t u r eures s o f Iof ~ t Irus r u s i Iv veP e - P hhs ~ s the t2h e GhoQ Lake B a t h o l i t h . T * 3: IIntrusive ntrusive -- P* Rock Rsk G LB—i GLB-1 Muscovite—biotite M u s c o v i t e - b i o t i t e and a n d biotite— biotitem u s c o v i t e ggranite r a n i t e and and rare rare muscovite Locally g ranodiorite. L o c a l l y cordierite— cordieritegranodiorite. bearinq beMuscovite—blotite ~ u s c o v i t e - b i o t i t e granite g r a n i t e to to g g rranod a n o d iioo rrite it e G LB -2 GLB-2 GLB—3 GLB-3 -GLB-4 G LB -4 GLB -5 GLB-5 Petroloatures IIntrusive n t r u s i v e Relations Relations e t r o l o ~ ~ u r e ~ Massive Coarse—grained M a s s i v e to t o weakly w e a k l y ffoliated. oliated. C o a r s e - g r a i n e d to to peginat itic, i t i c , inequig i n e q u i g rranular, a n u l a r generally generally pegmat . P- TE I hypidiomorphic—granular, hypidiomorphic-granularI - Mass, white—weathering w h ite-weathering aV faf fol -— occasf a1 Mass i v e t o c c a s ions-£0i a t e d fine— inedium—grained, f i n e - tto o m e d i u m - g r a i n e d I aallotriomorphic— llotriomorphic_9anular. Distinctive ranular. D g t i n c t i v e medium grey g r e y colour colour weakly foliated kMassive s % t o to weak1 y m ' i a t e d and o c c a s ~ o n a lyl lineated, medium—grained, lineated m e d i u m - g r a i n e d , allotriomorphic— allotriomorphicUniquep presence + ggranular. ranular. Unique r e s e n c e o foff fibrolite ibrolite+ + muscovite quartz quartz + m u s c o v i t e faserkiesel faserkiesel biotite granite + Muscovite ~ u s F o v i t eand a n d biotite—muscovite biotite-muscovite 5 garnet garnet ppegmatitic e g m a t i t i c leucogranite leucogcanite + + + tourmaline t o u r ~ ~i ~ n ea l garnet—muscoite— ~ S g r a i n e dg arnet-muscov itettourmaline o u r m a l i n e leucogranite leucogranite Massive to occasionT1 elayere M ~ S iSv e to o c c a ~ a l l $vaq ue layered - FTgraii granular hhypidiomorphic ypid iomorphic g ranula; - - MITe EodasionäI[y layered, ffne- trMuscov , -- l¶l\urnialine—quartz b u n n a l i n e - q u a r t z vveins eins Occurs as small O c c u r s as s m a l l masses m a s s e s and and dIkes dikes cross—cutting cross-cutting GLB—1. GLB-1. ftff and occasioT1fl TErisivereatTns No i n t r u s i v e r e l a t G MuscovTfftti muscov ~ u s c o v E e - b i te o t and i t e and m u s c oite— vitebiotite granite ggarnet arnet Mass i v e t ~ o c c a s i o n a lyl l a y e r e d I f i n e grained, usually g r a i n e d n allotriomorphic—granular, allotriomorph ic-granular usually ee3igranular 2igranular Mass Mass ive, i v e , h y p ~ o ~ p ch- qir a n u l a r w i t h distinctive d i s t i n c t i v i - randomly r a n d o m l i oriented oriinted bladed , b l a d e d rates a r 2 a trich e s r l in c h igreen n g r e e nmuscovite muscovite Massive, Mass i v e 2 y Tiypidiomorphc p * d ~ o r p h cg r a gran1ay n " m y be with aassociated ssociated w i t h fine—grained, f i n e - g r a i n e d , banded b a n d e d sodic sodic aplite. Contains o n t a i n s rare r a r e green g r e e n syngenetic syngenetic a p l ite. C beryl. beryl. Garnet—biot ii-6 m G a r nr e t - b i o t i t ite—tourfine--muscoT€e etourmaline-muscovite pegmatitic p e g m a t i t i c leucogranite leucog r a n i t e -G I J-7 ~ M u s c o vite—tourmal i t e - t o u r m a l ime n e potass p o t a s s ic ic . pegmatite p e g m a t i t e ?+garnet -garnet GLB—B GLB8 - . - --- tern ow.eas part %all veins c o n c e n t r a t e r n a r d s eastern p art Relatively ooff thost C h o s t Lake I d k e Batholith. Batholith. R e l a t i v e l ycommon common in i n metasedimentary m e t a s e d i m e n t a r y rocks r o c k s between b e t w e e n Dryden Dryden and and Thunder Featured T h u n d e r Lake. Lake- F e a t u r e d by b y locally l o c a l l y impressive impressive inetasomatic tourmaline metasomatic tourm a l i n e h a l o e s halohS2cks. i n host rp&. n i bserved. aadjacent d j a c e n t GLB—1 GLB-1 o or r 22 oobserved. GLB—3c ocontains GLB-3 n t a i n s llayers a y e r s and and small small pods ooff gradational g r a d a t i o n a l coarse— coarseraind_to_gmatiticranite grained t o m a~t i t i c r a n i t e Observed Observed as as veins v earwl w ~ e cutting c u t t i n g GLB—1 GLB-1 and a n d 2. 2. dies part ifed fy in No t e d on .on1 in eas Ghost Lake Batholith; Bath01 i t h ; intruded 7. i n t r u d e d by b GLB—6 GLB-6 and and 7. Crosscuts GLB-5 Cros r U s-cuLs yGLB-5 UI GLB-nx a n d r - cuts GLB ~r&%.-cuts Youngest Youngest g granitic r a n i t i c pphase h a s e inn Ghost Batholith. May G h o s t Lake Lake B atholith. May be be ccorrelative o r r e l a t i v e with w i t h exocontact, exocontact pegmatitic pegmat i t i c dikes d i k e s having having I ttounualine o u r m a l i n e babes h a l o e s and and zoned zoned garnet— g a r n e t - ttourmal o u r m a l me—green ine-green muscovite m u s c o v i t e dike d i k eon onHighway' Hiqhway' 17 - 17 1022 w e s t o f ~-,r ~ d & n . - Lm -- �166 northwestern n o r t h w e s t e r n mass mass of o f GLB—1 GLB-1 t o towards w a r d s t hthe e nnarrow a r r o w eeastern a s t e r n lobe lobe A t othe t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. A ssecond e c o n d ttrend r e n d of of aadjacent d j a c e n t to geochemical i s also a l s o developed d e v e l o p e d within w i t h i n the t h e batholiths batholiths g e o c h e m i c a l fractionation f r a c t i o n a t i o n is t o southwest s o u t h w e s t towards t o w a r d s plutonic p l u t o n i c unit u n i t GLB—3. GLB-3. aand n d ddirected i r e c t e d south s o u t h to T h e Mavis Mavis Lake Lake Pegmatite P e g m a t i t e Group G r o u p is is almost a l m o s t entirely e n t i r e l y contained contained The within is 8 km in i n sstrike t r i k e length l e n g t h and and w i t h i n the t h e Brownridge B r o w n r i d g e volcanics v o l c a n i c s and a n d is A well 1 . 4 km in i n breadth. breadth. w e l l developed d e v e l o p e d lateral l a t e r a l zonation z o n a t i o n of of ..8 8 tto o 1.4 The zonal is apparent a p p a r e n t over o v e r this t h i s strike s t r i k e length. length. zonal ppegmatites e g m a t i t e s is pattern p a t t e r n of o f typomorphic t y p o m o r p h i c mineral m i n e r a l assemblages, a s s e m b l a g e s internal i n t e r n a l structures, structures of a l b i t i z a t i o n and a n d characteristic characteristic ddegree egree o f replacement r e p l a c e m e n t stage s t a g e albitization geochemical g e o c h e m i c a l associations a s s o c i a t i o n s changes c h a n g e s progressively p r o g r e s s i v e l y at a t increasing increasing This ddistances i s t a n c e s from f r o m the t h e parental p a r e n t a l Ghost G h o s t Lake Lake Batholith. Batholith. T his is similar, s i m i l a r for f o r example, e x a m p l e to to ssuccession u c c e s s i o n of o f rare—metal r a r e - m e t a l ppegmatites e g m a t i t e s is that t h a t ddescribed e s c r i b e d in i n the t h e Yellowknife—Beaulieu Y e l l o w k n i f e - B e a u l i e u district d i s t r i c t (Hutchinson, (Hutchinson 1955), Preissac—Lacorne Quebec 1955) P r e i s s a c - L a c o r n e aarea r e a of of Q u e b e c (Mulligan, ( M u l l i g a n 1965), 1 9 6 5 ) and a n d the the Issia 1uvre t T b u v r e area a r e a of o f the t h e Ivory I v o r y Coast C o a s t (Varlamoff, ( V a r l a m o  £ f1972). 1 9 7 2 ) . The I s s i a eet degree w e s t to t o east e a s t in in d e g r e e of o f late—stage l a t e - s t a g e albitization a l b i t i z a t i o n increases i n c r e a s e s from f r o m west Mavis Lake tthe h e Mavis Lake Pegmatite P e g m a t i t e Group Group such s u c h that t h a t thin t h i n (1—3 ( 1 -3 mm width) width) ppegmatite e g m a t i t e ssheets h e e t s exposed e x p o s e d at a t the t h e East E a s t Zone Zone of o f the t h e Fairservice Fairservice Property e s s e n t i a l l y of o f secondary s e c o n d a r y mineral m i n e r a l assemblages. assemblages. P r o p e r t y consist c o n s is t essentially These white T h e s e mainly m a i n l y consist c o n s i s t of of w h i t e sodic s o d i c beryl beryl + + green g r e e n muscovite m u s c o v i t e ++ + cleavelandite Primary quartz quartz + c l e a v e l a n d i t e ++ ttantalite. antalite. P r i m a r y relict r e l i c t spodumene, spodumene mica, largely reen m i c a ragged ragged l a r g e l y cconverted o n v e r t e d into i n t o fine—grained f i n e - g r a i n e d albite a l b i t e ++ ggreen K—feldspar bblocky locky K - f e l d s p a r and a n d quartz quartz are nevertheless still Further rrecognizable. ecognizable. F u r t h e r west west at a t the t h e Main Main Zone Zone aalbitization l b i t i z a t i o n isismuch much less less ppronounced, r o n o u n c e d , consuming c o n s u m i n g between b e t w e e n 20 20 and a n d 50 5 0 percent p e r c e n t of o f primary primary pegmatite IIn n many instances i n s t a n c e s here h e r e the t h e albitization a1 b i t i z a t i o n appears appears p e g m a t i t e units. units directly t o aa rudimentary r u d i m e n t a r y quartz—rich q u a r t z - r i c h core core zone z o n e as a s at at d i r e c t l y related r e l a t e d to STOP STOP 4. 4. K, Cs, Sn, B,f Rb Metasomatic M e t a s o m a t i c release r e l e a s e of o f Li, Li K t C s Sn B R b and a n d FF can can ddevelop e v e l o p impressive i m p r e s s i v e endogenic e n d o g e n i c dispersion d i s p e r s i o n ppatterns a t t e r n s in i n mafic mafic metavolcanic a l b i t i z e d spodumene s p o d u m e n e pegmatites p e g m a t i t e s as as m e t a v o l c a n i c rocks r o c k s enclosing e n c l o s i n g albitized exemplified e x e m p l i f i e d by b y the t h e Main Main and and South S o u t h Zones Z o n e s of o f the t h e Fairservice Fairservice These mineralogically Property. m e s e elemental e l e m e n t a l concentrations c o n c e n t r a t i o n s are are m ineralcq i c a l l y P roperty. attributable a t t r i b u t a b l e tto o secondary s e c o n d a r y bbiotite, i o t i t e tourmaline, t o u r m a l i n e , and a n d holmquistite holmquistite w h i c h aare r e intensely i n t e n s e l y developed d e v e l o p e d within w i t h i n layers l a y e r s and a n d pods p o d s in i n proximal proximal which Five metasomatic mafic rocks. F i v e aanalyses n a l y s e s of o f these these m etasomatic m a f i c host h o s t rocks. assemblages, a s s e m b l a g e s (termed ( t e r m e d glimmerite g l i m m e r i t e in i n Russian R u s s i a n literature) l i t e r a t u r e ) from from Tot o t Lake Lake iimmediate m m e d i a t e contacts c o n t a c t s of o f Mavis Mavis Lake Lake and a n d Guliwing G u l l w i n g Lake Lake -- T Be, F,t Li, rare—metal a r e presented p r e s e n t e d in i n Table T a b l e 4. 4. B e t Cs, Cs, F Lit r a r e - m e t a l pegmatites p e g m a t i t e s are Rb aand Rb n d Sn Sn all a l l hhave a v e obvious o b v i o u s utility u t i l i t y in i n lithogeochemical l i t h o g e o c h e m i c a l surveys, surveys hhowever, o w e v e r in i n reconnaissance r e c o n n a i s s a n c e surveys s u r v e y s ddesigned e s i g n e d to t o locate l o c a t e rare—metal rare-metal pegmatite p e g m a t i t e fields, f i e l d s lithium 1i t h i u m represents r e p r e s e n t s the t h e most useful u s e f u l element element Pryslk d o c u m e n t e d several several ((Ovchinriikov, G v ~ h i n n i k o v 1976). 1~9 7 6 ) . P r y s l a k (1981) ( 1 981 ) documented impressive i m p r e s s i v e lithium l i t h i u m aureoles a u r e o l e s on on the t h e Main Main Zone Zone with w i t h the t h e largest largest by 1220 measuring 8 5 m by 1220 m and a n d containing c o n t a i n i n g maximum lithium lithium m e a s u r i n g 60 6 0 —- 1185 cconcentrations o n c e n t r a t i o n s of o f 4095 4 0 9 5 ppm. ppm. Pegmatite The Guliwing me G u l l w i n g Lake—Tot Lake-Tot Lake Lake rare—metal rare-metal P e g m a t i t e Group G r o u p (0.8 ( 0.8 2.2 tto o 2. 2 x 8.6 8 . 6 km in i n area) a r e a ) is is ssituated i t u a t e d bbetween e t w e e n the t h e northeast n o r t h e a s t end end of of mainly Guliwing G u l l w i n g Lake L a k e and a n d Tot T o t Lake and a n d is is m a i n l y confined c o n f i n e d to t o aa medium—grade, m e d i u m - g r a d e ! hhighly i g h l y deformed, d e f o r m e d southwest—striking s o u t h w e s t - s t r i k i n g mafic mafic metavolcanic m e t a v o l c a n i c uunit n i t which which envelopes e n v e l o p e s the t h e Lateral L a t e r a l Lake Lake Stock S t o c k (Breaks ( Breaks et Six e t al., al. 11978). 978). S i x rare r a r e metal pegmatites p e g m a t i t e s hhave a v e been b e e n ddiscovered i s c o v e r e d to to which ddate a t e ((Table T a b l e 22) ) w h i c h aare r e ddistinctive i s t i n c t i v e in i n sseveral e v e r a l ways from f r o m those those are, nevertheless, still . �___________ _________ S e l e c t e d themical ChemicalAnalyses1 A n a l y s e s 1 of o fMetasomatic Metasomatic S e l v a g e s Developed Developed a Selected Selvages att C o n t a c t s R a r e M e t a l P e g m a t i t s r o m t h e D r y k p e g m a t i t e F i , e l d . _—Mal Pegmatites from theDryderPegrnatiteFeld. - T a b l e 4: Table Spodumene Spod umene Pegmatite 2 P e g m a t i t e No. No. 2 Fairservice— F airserviceProperty P roperty o f Some Contacts of Some B B Be Be Cs F F Li Rb Sn Pa Nb 2 222 920 920 77650 650 6050 3790 68 <30 13 3.69% ine-holmquistite-biotite glimmerite) glimmerite) (tourmaline—holmquistite—biotite Pegmatite P e g m a t i t e No.2 No - 2 Taylor T a y l o r Beryl Beryl 5 20 5 20 1150 7250 2300 2210 762 <30 70 4.58% 18400 4600 7580 167 60 925 6.39% 5930 1900 4820 45 0 450 K20 ( tourmal Occurrence Occurrence ((biotite—rich b i o t i t e - r i c h glimmerite) qlimmerite) Gullwing G u l l w i n g Lake Lake Spoduinene Spodumene Pegmatite <5 P egmatite (biotite—rich ( b i o t i t e - r i c h gglimmerite) limmerite) lbt Lake Lake Spodumenelbt SpodumenePollucite P o l l u c i t e Pegmatite P e g m a t i t e 25 25 ((biotite—rich b i o t i t e - r i c h glimmerite) glimmerite) Gullwing G u l l w i n g Lake Lake Batholith att Batholith a STOP 6 STOP 6. N. D. N.D. 6 1140 I.-J 1122 1.60% 66 755 17,800 1400 1860 90 1010 1240 50 23.9 142 N.D. <10 N.D. 4.78% 7 3.70% 35 0.13% ( b i o t i t e - t o u r m a l me i n e glimmerite) g l immerite) (biotite—tourmal P e t r u n k a ¶Iingsten T u n g s t e n 44200 200 Petrunka P r o p e r t y at a tSTOP STOP 55 Property ((tourmaline t o u r m a l i n e +-+ bbiotite iotite met m e tasomatizeci a s m a t i z e d ppillow illow immediately sselvage e l v a g e immed iately below b e l o w scheelite—tounnaline s c h e e lite-tourmal i n e ssheet) heet) 3 3 iin n ppm u n l e s s otherwise o t h e r w i s e shown ppm unless = Not D N.D. = Determined etermined N.D. 1 3.7 N.D. �168 in i n the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t eGroup: Group: 1) Most Most ppegmatites e g m a t i t e s a are r e ssignificantly i g n i f i c a n t l y discordant d i s c o r d a n t to t o the the general 0 7 0 0 sstructural t r u c t u r a l trend t r e n d of o f host h o s t rocks. rocks. general 070° 2) Presence more P r e s e n c e of o f internally i n t e r n a l l yzoned zonedpegmatites p e g m a t i t e s exhibiting e x h i b i t i n gmore complex complex ggeochemical e o c h e m i c a l s pspecialization e c i a l i z a t i o n ii.e. .e . Li-Cs-Rb—Be--Ta>Nb Li-Cs-Rb-Be-Ta>Nb aand n d Li-Ta>Nb-Be--Mo. Li-Ta>Nb-Be-Mo. 3) no mineral i z a t ion ; no evidence e v i d e n c e oof f associated a s s o c i a t e d scheelite s c h e e l i t e mineralization; 4) absence a b s e n c e of o f tourmaline t o u r m a l i n e replacement r e p l a c e m e n t oof f host h o s t rocks, r o c k s , and and much more cconfined o n f i n e d development d e v e l o p m e n t of o f metasomatic metasomatic much more gl g l immerite i m e r i t e assemblages. assemblages. r e g i o n a l zonation z o n a t i o n of o f rare—metal r a r e - m e t a l pegmatite p e g m a t i t e types t y p e s not n o t as as 5) regional clearly c l e a r l y developed. developed. 6) parental p a r e n t a l granitic g r a n i t i c source s o u r c e area a r e a is is not n o t clearly c l e a r l y apparent. apparent. Most pegmatites p e g m a t i t e s of o f this t h i s group g r o u p are a r e oriented o r i e n t e d sub—perpendicular sub-perpendicular to t o the t h e curvilinear c u r v i l i n e a r contact c o n t a c t between b e t w e e n the t h e mafic m a f i c metavolcanic m e t a v o l c a n i c host host unit u n i t and and Lateral L a t e r a l Lake Lake Stock. S t o c k . Exceptions E x c e p t i o n s to t o this t h i s include i n c l u d e the t h e Mica Mica Point P o i n t columbite c o l u m b i t e pegmatite p e g m a t i t e (concordantly ( c o n c o r d a n t l y emplaced e m p l a c e d in i n the t h e mafic mafic metavolcanic it deflects d e f l e c t s north n o r t h to t o northeast n o r t h e a s t around around m e t a v o l c a n i c unit u n i t where w h e r e it western w e s t e r n terminus t e r m i n u s of o f the t h e Lateral L a t e r a l Lake Lake Stock) S t o c k ) and and the t h e Drope Drope 'Ibwnship Tbwnship ccolumbite—molybdenite o l u m b i t e - m o l y b d e n i t e ppegmatite e g m a t i t e exposed e x p o s e d at a t the t h e extreme extreme southern s o u t h e r n known known limit l i m i t of o f the t h e pegmatite p e g m a t i t e group. g r o u p . The The latter latter pegmatite t o foliation f o l i a t i o n of of clastic clastic p e g m a t i t e was was emplaced e m p l a c e d concordant c o n c o r d a n t to metasedimentary m e t a s e d i m e n t a r y host h o s t rocks. rocks. The The source s o u r c e area a r e a for f o r rare—metal r a r e - m e t a l pegmatites p e g m a t i t e s of o f the t h e Guliwing— GullwingTot T o t Lakes Lakes Group Group is is not n o t known known at a t present. p r e s e n t . The The Coates Coates Bay Bay Stock, Stock, located l o c a t e d near n e a r the t h e southwestern s o u t h w e s t e r n limits l i m i t s of o f the t h e pegmatite p e g m a t i t e group, group, could c o u l d represent r e p r e s e n t aa parental p a r e n t a l source s o u r c e region r e g i o n for f o r the t h e pegmatites p e g m a t i t e s but but has h a s not n o t been b e e n adequately a d e q u a t e l y studied. s t u d i e d . The The easternmost e a s t e r n m o s t part p a r t of of this this granitic pegmatitic g r a n i t i c stock s t o c k consists c o n s i s t s of o f garnet—muscovite g a r n e t - m u s c o v i t e pegmatitic leucogranite l e u c o g r a n i t e characterized c h a r a c t e r i z e d by by plumose p l u m o s eaggregates a g g r e g a t e sofo ffine—grairied fine-grained green g r e e n muscovite m u s c o v i t e and and quartz. quartz. The The relationship r e l a t i o n s h i p of o f rare—metal r a r e - m e t a l pegmatites p e g m a t i t e s of o f this t h i s pegmatite pegmatite group t o molybdenite—rich m o l y b d e n i t e - r i c h granitic g r a n i t i c pegmatites p e g m a t i t e s of o f the t h e Lateral L a t e r a l Lake Lake g r o u p to area, 4.8 km lun to t o the t h e east e a s t of o f the t h e Tot Tot lake l a k e pegmatite, pegmatite, a r e a , approximately a p p r o x i m a t e l y 4.8 is is presently p r e s e n t l y uncertain. u n c e r t a i n . Although A l t h o u g h these t h e s e molybdenite—rich molybdenite-rich pegmatites were not n o t included i n c l u d e d in i n the t h e study s t u d y of o f Breaks B r e a k s (in ( in p e g m a t i t e s were preparation) g e n e t i c relationship r e l a t i o n s h i p could c o u l d very v e r y well w e l l be b e involved involved p r e p a r a t i o n ),, aa genetic since s i n c e molybdenite m o l y b d e n i t e is is an a n accessory a c c e s s o r y in i n most most of o f the t h e rare—metal rare-metal pegmatites p e g m a t i t e s of o f the t h e Gullwing—Tot G u l l w i n g - T o t Lakes Lakes Pegmatite P e g m a t i t e Group. Group. -- Uraniferous egmatites U r a n i f e r o u s PPematites Uranium mi?Tization Uranium m i n e r a l i z a t i o within n w i t h i nthe t h eboundary b o u n d a r yzone z o n e is is concentrated c o n c e n t r a t e d in i n the t h e Vermilion V e r m i l i o n Bay Bay area. a r e a . These T h e s e occurrences o c c u r r e n c e s are are generally g e n e r a l l y concentrated c o n c e n t r a t e d along a l o n g the t h e margins m a r g i n s of o f potassic p o t a s s i c intrusions intrusions associated a s s o c i a t e d with w i t h the t h e Dryberry D r y b e r r y Batholith. B a t h o l i t h . The The mineralization mineral i z a t ion occurs coarse grained g r a i n e d to t o pegmatitic p e g m a t i t i c granitoid g r a n i t o i d rocks r o c k s and and o c c u r s in i n coarse contains c o n t a i n s uraninite, u r a n i n i t e , uranothorite u r a n o t h o r i t e and and allanite a l l a n i t e as a s common common minerals. m i n e r a l s . Most Most uuranium r a n i u m o occurrences c c u r r e n c e s i nint hthe e nnorthern o r t h e r n ppart a r t of o f the the English where E n g l i s h River a v e r Subprovince S u b p r o v i n c e occur o c c u r in i ninhomogeneous inhomogeneous ddiatexites i a t e x i t e swhere boundaries b o u n d a r i e s with w i t h supracrustal s u p r a c r u s t a l rocks r o c k s are a r e gradational g r a d a t i o n a l into i n t o pods pods of of uraniferous u r a n i f e r o u s granitoid g r a n i t o i d material. m a t e r i a l . In I n the t h e Vermilion V e r m i l i o n Bay Bay area area however, however, supracrustal s u p r a c r u s t a l host h o s t rocks r o c k s are a r e metavolcanic m e t a v o l c a n i c flows, f l o w s , tuffs tuffs and and associated a s s o c i a t e d sedimentary s e d i m e n t a r y rocks. r o c k s . Radioactive R a d i o a c t i v e mineralization m i n e r a l i z a t i o n in in this is confined c o n f i n e d to t o discrete d i s c r e t e pegmatitic p e g m a t i t i c leucocratic l e u c o c r a t i c dikes dikes t h i s case c a s e is �169 and sills s i l l s which w h i c h are a r e clearly c l e a r l y intrusive i n t r u s i v e into i n t o the t h e host h o s t rocks. rocks. and - Building B u i l d i n g Stone Stone om 1Tes soms $ i e of s the o f t hlate—tectonic e l a t e - t e c t o n i cpotassic p o t a s s i c suite s u i t e are a r e suitable suitable sources s o u r c e s of of monumental monumental and and building b u i l d i n g stone s t o n e in i n that t h a t they t h e y are are homogeneous, homogeneous, lack l a c k metamorphic m e t a m o r p h i c foliation £0i a t i o n and a n d locally l o c a l l y contain c o n t a i n few few joints. j o i n t s . The The Nelson N e l s o n Granite G r a n i t e Ltd. L t d . quarry q u a r r y near n e a r Vermilion V e r m i l i o n Bay Bay (STOP (STOP 2) 2 ) is is developed d e v e l o p e d on o n aa plug p l u g of o f granite g r a n i t e of o f this t h i s type t y p e within w i t h i n the the Dryberry 1983). D r y b e r r y Batholith B a t h o l i t h (Storey, ( S t o r e y , 1983). �170 THE THE FIELD FIELD TRIP TRIP The w i l l commence commence at a t the t h e Inn I n n of o f the t h e Woods, Woods, Kenora. Kenora. The field f i e l d trip t r i p will Proceed P r o c e e d approximately a p p r o x i m a t e l y 37 37 km km (23 ( 2 3 miles) m i l e s ) east e a s t along a l o n g the the Trans—Canada Trans-Canada Highway Highway (Hwy (Hwy 17) 1 7 ) to t o aa point p o i n t of o f intersection i n t e r s e c t i o n with w i t h the the C.P.R. r a i l line l i n e (overpass). ( o v e r p a s s ) . Proceed P r o c e e d an a n additional a d d i t i o n a l 650 6 5 0 mm east e a s t of of C.P.R. rail the s o u t h from f r o m the t h e highway h i g h w a y to to t h e overpass o v e r p a s s and a n d walk walk approximate a p p r o x i m a t e 250 250 mm south an a n area a r e a of o f stripping s t r i p p i n g and and trenching. trenching. --- STOP_1: BY BERG (HAWK N I U M OCCURRENCE OCCURRENCE STOP 1 : BYBERG_(HAWK_LAKE)_URANIUM ---. LAKE ) isU R Aconntrated UFTum Uranium mThèraITjàtion m i n e r a l i z a t i o n is c o n c e n t r a t e dini n masses masses and and 7 stringers coarse magnetite m a g n e t i t e within w i t h i n aa wedge—shaped wedge-shaped mass mass s t r i n g e r s of o f coarse of o f pegmatite p e g m a t i t e (Figure ( F i g u r e 2). 2). The pegmatites p e g m a t i t e s are a r e contained contained The within w i t h i n aa package p a c k a g e of o f mafic mafic volcanic v o l c a n i c rocks, r o c k s , now now largely largely hornblende h o r n b l e n d e schists. schists T h e s e volcanic v o l c a n i c rocks, r o c k s , along a l o n g the the These contact mass , are are very v e r y iron iron c o n t a c t with w i t h the t h e main m a i n pegmatite p e g m a t i t e mass, rich, r i c h , locally l o c a l l y magnetic, m a g n e t i c , and a n d layered l a y e r e d in i n appearance. appearance. The main m a i n showing s h o w i n g has h a s been b e e n explored e x p l o r e d by b y stripping s t r i p p i n g and and The 10 1 0 trenches, t r e n c h e s , one o n e open o p e n cut c u t 130 1 3 0 ft. f t . long, l o n g , scintillometer scintillometer surveys, s u r v e y s , and and 22 diamond diamond drill d r i l l holes. h o l e s . None None of o f the the uraniferous u r a n i f e r o u s zones z o n e s are a r e more more than t h a n 1.6 1.6 mm wide wide or o r 99 mm long. long. Earlier E a r l i e r work work by b y 3. J. Satterly S a t t e r l y of o f the t h e Ontario O n t a r i o Department D e p a r t m e n t of of 11ines Mines ssuggests u g g e s t s tthat h a t aalthough l t h o u g h aan n average a v e r a g e of o f 7 grab grab samples s a m p l e s from f r o m the t h e narrow n a r r o w magnetite—rich m a g n e t i t e - r i c h sections s e c t i o n s of o f the the pegmatite mass of of l b s U308 ~ 3 0 per 8P e r ton, t o n , the t h e main m a i n mass p e g m a t i t e ran r a n 1.9 1.9 lbs pegmatite p e g m a t i t e will w i l l probably p r o b a b l y run r u n less less than t h a n 11 lb l b U308 U308 per per ton. Ltd. in t o n . Diamond Diamond d drilling r i l l i n g by by Kerr Kerr Addison A d d i s o n Mines Mines Ltd. in 1975 1 9 7 5 iintersected n t e r s e c t e d one o n e zone z o n e that t h a t ran r a n0.41 0 . 4 1lbl U308 b U308 per p e r ton ton over b u l k sample s a m p l e collected c o l l e c t e d in i n the t h e early e a r l y 50's 50's o v e r 49 49 feet. f e e t . AA bulk had of 1.4 1.4 lbs I b s U308 U308 (chem. ( c h e m . equiv.) equiv.) had an a n average a v e r a g e content c o n t e n t of per p e r ton. ton. Uranium are Uranium minerals m i n e r a l s which w h i c h have h a v e been b e e n identified i d e n t i f i e d are uraninite, u r a n i n i t e , thorite, t h o r i t e , uranothorite, u r a n o t h o r i t e , uranophane, u r a n o p h a n e , and and B—uranotil. In I n 1977, 1977, 3. J. Douglas D o u g l a s Scott, S c o t t , formerly f o r m e r l y of of B-uranotil Eldorado material E l d o r a d o Nuclear, N u c l e a r , working w o r k i n g with w i t h magnetite—rich m a g n e t i t e - r i c h material from f r o m the t h e Byberg Byberg deposit, d e p o s i t , identified i d e n t i f i e d what what may may be b e either e i t h e r aa new new mineral m i n e r a l or or aa peculiar p e c u l i a r altered a l t e r e d allanite. allanite. Return R e t u r n to t o highway h i g h w a y and and proceed p r o c e e d eastward e a s t w a r d approximately a p p r o x i m a t e l y 43 43 km km (27 (27 miles) m i l e s ) to t o the t h e Nelson N e l s o n Granite G r a n i t e Quarry. Quarry. . . STOP STOP 2: 2: GRANITE GRANITE QUARRY QUARRY Exiiine Examine the t h e highway h i g h w a y exposures. e x p o s u r e s . The T h e "granite" " g r a n i t e 1 ' at at this t h i s locality l o c a l i t y is is distinctive d i s t i n c t i v e in i n its i t s uniform u n i f o r m pink p i n k colour, colour, consistent as c o n s i s t e n t texture t e x t u r e and a n d freedom f r e e d o m from f r o m fracturing f r a c t u r i n g as evidenced e v i d e n c e d by by the t h e highway h i g h w a y cut. cut. T h i s is i n d i s t i n c t contrast c o n t r a s t with w i t hthe t h esurrounding s u r r o u n d i n ggneissic g n e i s s i crocks r o c k sexposed exposed along It is is intrusive i n t r u s i v e into into a l o n g the t h e highway h i g h w a y on o n either e i t h e r side. s i d e . It the t h e gneissic g n e i s s i c granitoid g r a n i t o i d rocks r o c k s and and xenoliths x e n o l i t h s of o f these t h e s e can can be b e found f o u n d near n e a r the t h e contacts c o n t a c t s of o f the t h e body. body. Only Only the the central dimension s a t i s f a c t o r yasas d i m e n s i o n granite g r a n i t e due d u e to to c e n t r a l part p a r t isissatisfactory these t h e s e xenoliths. x e n o l i t h s . This T h i s granite g r a n i t e is iscurrently c u r r e n t l ybeing being quarried a s monumental monumental and and building b u i l d i n g stone s t o n e by by two two q u a r r i e d as companies, c o m p a n i e s , Nelson N e l s o n Granite G r a n i t e Ltd. L t d . on o n the t h e south s o u t h side s i d e of o f the the highway h i g h w a y and and Granite G r a n i t e Quarries Q u a r r i e s (GQI) ( G Q I ) Inc. I n c . (formerly (formerly Scotstown S c o t s t o w n Granite G r a n i t e and a n d Universal U n i v e r s a l Granite G r a n i t e Centre C e n t r e (1976) (1976 ) 7 This is in distinct �171 Byberg (Hawk Lake) Occurrence MacNicol Township District of Kenora metres I, •r 3 granitfr pegmatit - hornblende schist -Ii (metavolcanic) —I magn • • -• —'I— S —. - Geology and H.D. Figure F i g u r e 2:2: Geology G e o l o g yof o fthe t h Byberg e B y b e r gUranium U r a n i u m Occurrence. Occurrence. trench �172 L t d . oon n the t h e north n o r t h side. side. Ltd. The r a n i t e Ltd. Ltd. qquarry u a r r y was w a s first f i r s t oopened p e n e d in in The Nelson Nelson G Granite 1981, More 1981, pproducing r o d u c i n g stone s t o n e largely l a r g e l y for f o r monuments. monuments. More rrecently, e c e n t l y , hhowever, o w e v e r , the t h e pproduction r o d u c t i o n is is more evenly e v e n l y split split bbetween e t w e e n monumental monumental and construction c o n s t r u c t i o n uses. u s e s . Annual is on o n the t h e order o r d e r of o f 50,000 50,000 cubic c u b i c feet f e e t per per pproduction r o d u c t i o n is year. year. At A t the t h e present p r e s e n t time, t i m e , rough r o u g h blocks b l o c k s of o f approximately approximately 100 ccubic u b i c ffeet e e t are h i p p e d bby y ttruck r u c k to t o pplants l a n t s in i n New New 100 are sshipped Brunswick, B r u n s w i c k , Quebec, Q u e b e c , and a n d the t h e United U n i t e d States S t a t e s for f o r finishing. finishing. The company h has The a s constructed constructed a a ssmall m a l l plant p l a n t at a t the t h e quarry quarry ssite i t e so s o that t h a t sawn s a w n slabs s l a b s and a n d finished f i n i s h e d products p r o d u c t s may be be produced. produced o c k pproduced r o d u c e d in i n the t h e qquarries u a r r i e s is is pink, p i n k , medium The rrock g r a i n e d massive m a s s i v e biotite b i o t i t e granite: g r a n i t e : Modal n a l y s e s plot p l o t in in grained Modal aanalyses the close l o s e to t o the t h e ggranite r a n i t e — quartz quartz t h e ggranite r a n i t e ffield i e l d vvery ery c m o n z o n i t e boundary b o u n d a r y on the t h e Streckeisen S t r e c k e i s e n QAP QAP ddiagram. iagram. monzonite There is a a sslight l i g h t layering l a y e r i n g parallel p a r a l l e l to t o the t h e sheeting. sheeting. T h e r e is This is eevidenced by aa sslight T h i s is v i d e n c e d by l i g h t llightening i g h t e n i n g oof f the t h e ppink ink ccolour o l o u r oof f the t h e ffeldspar e l d s p a r aand n d biotite b i o t i t e is is roughly r o u g h l y aligned aligned pparallel a r a l l e l to t o these t h e s e layers. l a y e r s . Microcline M i c r o c l i n e crystals c r y s t a l s reach r e a c h up up tto o 1 cm c m in i n width w i d t h although a l t h o u g h the t h e texture t e x t u r e is is not not minor pporphyritic. orphyritic. A few few m i n o r quartz q u a r t z veins v e i n s up u p to t o 22 cm wide wide There Vertical are v e r y few f e w fractures. fractures. Vertical a r e present. present. T h e r e are very joints widely i d e l y spaced s p a c e d and in i n many parts p a r t s of o f the the j o i n t s are w outcrop Subhorizontal o u t c r o p are a r e not n o t evident. evident. S u b h o r i z o n t a l sheeting s h e e t i n g is is tthick. hick. Return highway aand R e t u r n tto o tthe h e highway n d pproceed r o c e e d through t h r o u g h tthe h e town town oof f Vermilion Vermilion Bay approximately a p p r o x i m a t e l y 27 27 km to the t h e Eagle E a g l e River R i v e r intersection i n t e r s e c t i o n (Hwy (Hwy 17 17 Continue C o n t i n u e eeastward a s t w a r d aapproximately p p r o x i m a t e l y 0.5 0.5 km krn further further and 596 ) and Hwy 596). ande xexamine aalong l o n g Highway Highway 1717and a m i n e t h the e o uoutcrop t c r o p a lalong o n g t hthe e nnorth o r t h sside i d e of of the t h e road. road. . - 1 . STOP STOP 3: - -- GHOST GHOST LAKE BATHOLITH_MIGMATITES BATHOLITH MIGMATITES relF1.zely X x i v e l yllarTzone a r g e z o n eofo t iiiiiFization m i g m a t i z a t i o n is is situated situated t o nnorthwest o r t h w e s t flanks f l a n k s oof f the t h e Ghost Ghost Lake Lake Batholith Batholith aadjacent d j a c e n t to eexhibiting x h i b i t i n g migmatitic m i g m a t i t i c sstages t a g e s (protometatexite, (protometatexite, metatexite) m e t a t e x i t e ) (Table ( T a b l e 1) 1 ) very v e r y similar s i m i l a r to t o those t h o s e encountered encountered iin n tthe h e northern n o r t h e r n ssupracrustal u p r a c r u s t a l terrain t e r r a i n of o f the t h e English English River Subprovince be1 t ) R iver S u b p r o v i n c e (Ear ( E a r Falls—Manigotagan F a l l s - M a n i g o t a q a n belt) Protometatexite Breaks ddelineated e l i n e a t e d by B r e a k s et e t àl., a l . , (1978). ( 1978). P r o t o m e t a t e x i t e is is ccharacterized h a r a c t e r i z e d by intercalation i n t e r c a l a t i o n ooff fine—grained f i n e - g r a i n e d wacke wacke and and medium—grained pelitic less than t h a n 15 15 cm cm medium-grained p e l i t i c layers, l a y e r s , usually u s u a l l y less which the iin n tthickness, h i c k n e s s , in i n which t h e ppelitic e l i t i c component contains contains sparse s p a r s e non—amalgamated non-amalgamated leucosome l e u c o s o m e patches. p a t c h e s . Note ffoliation o l i a t i o n llying y i n g aatt aan n aangle n g l e tto o bbedding e d d i n g oof f about a b o u t 20° 2 0 0 and and axial ccoplanar o p l a n a r with w i t h ax i a l ssurfaces u r f a c e s oof f small s m a l l sscale c a l e relatively relatively Development metatexite s i m i l a rtype t y p eS—folds. S-folds. Development o of f m etatex i t e oopen, p e n , similar in i n which w h i c h layers l a y e r s of o f thin t h i n hololeucocratic h o l o l e u c o c r a t i c mobilizate m o b i l i z a t e have have been b e e n iinjected n j e c t e d cconcordant o n c o r d a n t aand n d ssub—concordant u b - c o n c o r d a n t to t o bedding bedding is subordinate. Subisoclinal is subord i n a t e . S u b i s o c l i n a l to t o isoclinal i s o c l i n a S—folding l S - f o l d i n g of of is also a l s oapparent a p p a r e n tand andmay may ppelitic e l i t i cand a n dleucosome l e u c o s o m e layers l a y e r s is represent r e p r e s e n t tthe h e ffirst i r s t pphase h a s e of o f folding, f o l d i n g , although although interfering with p e n vvariety a r i e t y have have i n t e r f e r i n g relations relations w i t h the t h e more oopen A ~ �173 not n o t been b e e n observed o b s e r v e d in i n this t h i s particular p a r t i c u l a r area. a r e a . These These i s o c l i n a l folds f o l d s exhibit e x h i b i t coplanarity c o p l a n a r i t y of o f axial a x i a l planes p l a n e s and and isoclinal bedding. P o l i t i c units u n i t s are a r e characterized c h a r a c t e r i z e d by by the the b e d d i n g . Pelitic assemblage K - f e l d s p a r ++ cordierite c o r d i e r i t e ++ biotite biotite a s s e m b l a g e almandine a l m a n d i n e ++ K—feldspar + + quartz q u a r t z ++ plagioclase. p l a g i o c l a s e . Cordierite C o r d i e r i t e porphyroblasts p o r p h y r o b l a s t s can can be recognized r e c o g n i z e d as a s light l i g h t brown brown pits p i t s on o n weathered w e a t h e r e d surfaces. surfaces. Note Note also a l s o presence p r e s e n c e of o f sillimanite, s i l l i m a n i t e , mauve mauve cordierite, cordierite, and o f the t h e white white a n d rare r a r e blue b l u e dumortierite d u m o r t i e r i t e in i n some of intrusive i n t r u s i v e aanatecticmaterial. natectic material. Proceed miles) (9.25 m i l e s ) east e a s t along a l o n g Highway Highway 17b 1 7 b to t o vvillage i l l a g e of of P r o c e e d 14.8 14.8 km (9.25 Oxdrift. Oxdrift. STOP STOP 4: 4: GHOST GHOST LAKE_BATHOLITH LAKE BATHOLITH All ~igh1f7roadTeThxposures 7 a d s i d e e x p o s u r e s of o f white w h i t e granitoid granitoid ITiih rocks r o c k s between b e t w e e n the t h e Aubrey Creek C r e e k bridge b r i d g e east e a s t to t o the t h e Dryden Dryden cemetary the Ghost Ghost Lake Lake Batholith. Bath01 i t h . c e m e t a r y are a r e situated s i t u a t e d within w i t h i n the This T h i s roadcut r o a d c u t is is located l o c a t e d in i n the t h e western w e s t e r n part p a r t of of the the batholith ( F i g u r e 1) 1 ) and a n d features f e a t u r e s three t h r e e plutonic p l u t o n i c phases phases b a t h 0 1 i t h (Figure (GLB (GLB 1, 1, 2 2 aand n d 44 iin n Table T a b l e 33)) of o f this t h i s regionally r e g i o n a l l y extensive extensive S—type S - t y p e granitoid g r a n i t o i d complex. complex. Most of o f the t h e outcrop o u t c r o p consists c o n s is ts of o f inhomogeneous inhomogeneous diatexite d i a t e x i t e (GLB—1), (GLB-1 ) , characterized c h a r a c t e r i z e d by b y aa significant s i g n i f i c a n t proportion p r o p o r t i o n of o f metasedimentary m e t a s e d i m e n t a r y inclusions i n c l u s i o n s and and restite r e s t i t e (melanosome) (melanosome) patches. p a t c h e s . The latter l a t t e r may may locally locally contain significant sillimanite i g n i f i c a n t amounts amounts oof f s ill i m a n i t e and/or and/or contain s muscovite. m u s c o v i t e . These T h e s e minerals m i n e r a l s may may also a l s o appear a p p e a r within within enclosing e n c l o s i n g white, w h i t e , inequigranular, i n e q u i g r a n u l a r , medium— medium- to t o coarse— coarsegrained granite leucosome. g r a i n e d g r a n i t e l e u c o s o m e . Almandine garnet, g a r n e t , blue— bluegreen g r e e n apatite, a p a t i t e , and a n d rare r a r e deep—blue d e e p - b l u e cordierite c o r d i e r i t e may may also a l s o be be recognizable. recognizable. Dikes Dikes oof f fine—grained, f i n e - g r a i n e d , grey, g r e y , muscovite—biotite muscovite-biotite granite and coarse—grained, c o a r s e - g r a i n e d , white, white, g r a n i t e (GLB—2) (GLB-2 ) and holo—leucocratic h o l o - l e u c o c r a t i c granite g r a n i t e (GLB—4) (GLB-4) represent r e p r e s e n t later later intrusive Ghost Lake Lake Batholith. Batholith. i n t r u s i v e phases p h a s e s of o f the t h e Ghost Proceed P r o c e e d 8.8 8 . 8 km east e a s t along a l o n g Highway 17 17 to t o aa point p o i n t where it i t makes aa sharp s h a r p turn t u r n south. s o u t h . Continue C o n t i n u e through t h r o u g h Dryden Dryden for f o r 13.6 13.6 km. km. Turn Turn n o r t h on on Thunder Thunder Lake Lake Road Road and a n d continue c o n t i n u e for f o r 1.7 1.7 km. km. Turn north Turn northwest Lakea access n o r t h w e s t on on the t h e south s o u t h Ghost G h o s t Lake c c e s s r oroad, a d , t travelling r a v e l l i n g for f o r 1 ..55 km. Turn T u r n wwest e s t oon n ppoorly oorly m a i n t a i n e d ppowerline o w e r l i n e r road o a d aand n d t travel r a v e l for for maintained about km tto o point p o i n t where where road r o a d departs d e p a r t s north n o r t h from from powerline. powerline. a b o u t 1. 11 km Travel by aa ssteel 0.6 km km to t o base b a s e of o f small s m a l l ridge r i d g e marked marked by tee1 T r a v e l aa further f u r t h e r 0.6 gate g a t e (usually ( u s u a l l y locked). l o c k e d ) . Proceed P r o c e e d west west for f o r 0.27 0 . 2 7 kin km and and then t h e n turn turn south s o u t h on on one o n e of o f many many eexploration x p l o r a t i o n access a c c e s s roads r o a d s constructed c o n s t r u c t e d by by Sanmine and ttravel Sanmine EExploration x p l o r a t i o n IIncorporated n c o r p o r a t e d and r a v e l for f o rabout a b o u t0.0.37 37km. km. P r o p e r t y aaccess c c e s s rroads o a d s aare r e best b e s t travelled t r a v e l l e dby byfourwheel f o u r w h e e l drive drive Property vehicles. v e h i c l e s . Consult C o n s u l t figure f i g u r e 33 for f o r stop s t o p locations. locations. PLEASE PLEASE DO DO NOT NOT HAMMER HAMMER SURFACE SURFACE OF OF STRIPPED STRIPPED OUTCROPS. OUTCROPS. SELECT SELECT MINERAL MINERAL SPECIMENS SPEC IMENS FROM FROM LOOSE LOOSE BLASTED BLASTED MATERIAL MATERIAL ONLY. ONLY. STOP TUNGSTEN PROPERTY PROPERTY, SANMINE EXPLORATION STOP 5: 5: PETRUNKA PETRUNKA TUNGSTEN SANMINE EXPLORATION -INC. (EAST END) I N C . (EAST E N D ) f e1'iTeinera1ization z a t i ooccurs n o c c u r sini ngenerally generally "SchTeliteminerali flat—lying, undulating £a t - l y i n g , undulating . tourmaline—rich The t o u r m a l i n e - r i c h sheets. she'ets The sheets s h e e t s which which variably v a r i a b l y transect t r a n s e c t folation f o l a t i o n trends t r e n d s of o f host host �174 + + + + + + + +11+ + + + +. + + + + + + + + + + + + + + + + + + + + + + + + + + + + •¼\+ + + + + + + + + + + + +++ +++ + + +\l ++ + + ++÷++ + + ++ ÷ + + + + + + + + + + + +++ +++ ++ + +÷ + ++ + ++ + ++ + ++ + + + ++ + + + ++ + + + + + + + + ++ + + + + + ++++++ + + + + + + + + + + + + + + + + +++ + + + + +4+4. + + + + + + + ++ + + + + + + + + + + + + + + + + ++ ++ + + + + + + + + ++ +++ + + + + + + + + + + + + + 4+ + + +++++ + + + + + + + + + + + + + + +4. + GHOST LAKE BATHOLITH ++ ++ + + + + + ++ + +4+ ++ + ++ ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +.+ + + + + + + +++4. + + + ++ + + + + + + + + + + + + + + + + + ++ ++ + + + + + ++ +++++ + + ++ + + + + + + + + + ++ +++ + + + + +4. +4. + + + + + ++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ++ + ÷+++÷+ + d + + • + + + + + + + + + + + + + + + + + + + + + ++ +o___.__.__,,__,__,__ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +5 +++ +4. + + + + ++*+ + + + +i_.._+ + + + + + + + + + + + + + + + + + + + + + + '+ + ABe+ V..+ + + + + + + + + + + + + + + + +4. + + + + + + + ÷\\_.+ + + + + + + + + + ++ + + + + + + + + + + + + •\'X+++ + + ++ + ++ + ++ + +++ ++ GPO5 + + ++ + + + + + + 4. ++ + ++ + +4. + +++ + + + +4. + + + + + + +4. + + + + + +'_ + +4. + ++ + - + + +++++++ ++++++_ + + •4. _—i + + + +4. + + + + + + + + + + + + - + + +'.. + (-. I :: ZEALAND METASEDIMENTS Thunder Lake a \^+\ x x Ghost Lake Batholith and Ghost and Zealand Zealand Stock Stock Porphyritic Biotite Granodiorite Porphyritic Granodiorite and and Granite Granite Zealand Metasediments (medium Zealand (medium grade ]metawackes, metapelites, metapelites, and andmagnetite— magnetitechert iron iron formation> formation) Brownridge Volcanics (massive (massive and and pillowed pillowed mafic metavolcanics with sparse sparse felsic metavolcanic metavolcanic tuff layers) layers) • field fieldtrip tripstop stop _—j bedding 4 bedding with dip 1 Lithophile Mineral Occurrence Occurrence Lithophile Mineral 2— "Si---bedding bedding (inclined, (inclined, overturned), overturned), -ft" top (arrow) (arrow) from from grain grain gradation gradation -igo foliation with dip dip .— strike M strikeofofbanding banding in in granitic granitic rocks rocks r facing direction of lava flows as indicated 9 . shape and packing by pillow facing direction of lava flows as indicated by pillow shape and packing F i g u r e 3: 3 : Geology G e o l o g y of o f the t h eMavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. Figure Be beryllium beryllium Lii L lithiulm Ta Ta tantalum tantalum W W tungsten tungsten �175 pillowed pillowed mafic maÂi c metavolcanics m e t a v o l c a n i c s are a r e up up to to 0.3 0 . 3 mm in in thickness 1 1 and a n d 19 19 degrees. degrees. Highest t h i c k n e s s and a n d dip d i p between b e t w e e n 11 Highest t o date d a t e occur o c c u r within w i t h i n these these l e v e l s of o f scheelite s c h e e l i t e found f o u n d to levels tourmaline t o u r m a l i n e sheets s h e e t s accompanied a c c o m p a n i e d by by ancillary a n c i l l a r y amounts amounts of of biotite, b i o t i t e , quartz, q u a r t z , plagioclase, p l a g i o c l a s e , pyrite p y r i t e and and possible possible lepidolite. is l e p i d o l i t e . An An identical i d e n t i c a l mineral m i n e r a l assemblage a s s e m b l a g e is developed d e v e l o p e d on o n several s e v e r a l spatially s p a t i a l l y associated, a s s o c i a t e d , ancillary ancillary fracture s e t s with w i t h relatively r e l a t i v e l y steep s t e e p dips d i p s (69—85°) (69-85O) and and f r a c t u r e sets along a l o n g 77 mm mm —- 55 cm c m wide w i d e pillow p i l l o w selvages, s e l v a g e s , the t h e latter l a t t e r of of which which have h a v e been b e e n intensely i n t e n s e l y replaced r e p l a c e d by by tourmaline t o u r m a l i n e and and biotite t h e vicinity v i c i n i t y of o f the t h e scheelite s c h e e l i t e mineralization mineralization b i o t i t e in i n the and C s and and a n d contain c o n t a i n trace t r a c e level l e v e l anomalous a n o m a l o u s enrichment e n r i c h m e n t in i n Cs Li L i (Table ( T a b l e 4). 4 ) . Scheelite, S c h e e l i t e , up up to to 55 by by 7.5 7.5 cm cm size, s i z e , is is predominantly p r e d o m i n a n t l y anhedral, a n h e d r a l , poikilitic, p o i k i l i t i and c , ahoney—brown n d honey-brown on on clean 3. 5mmchannel channel c l e a n weathered w e a t h e r e d surfaces. s u r f a c e s . Analysis A n a l y s i s of o f aa3.5 sample s a m p l e selected s e l e c t e d from f r o m aa flat—lying f l a t - l y i n g biotite—tourmaline biotite-tourmaline sheet s h e e t containing c o n t a i n i n g the t h e highest h i g h e s t scheelite s c h e e l i t e content c o n t e n t observed observed to t o date d a t e isisgiven g i v e nbelow b e l o w (in ( i nppm ppm unless u n l e s s otherwise o t h e r w i s e stated): s t a t e d ): W Be Cs FF W Be Cs Li Sn Au Li Sn Au 950 40 9,600 193 950 45 45 40 9,600 246 246 1 9 3 <2 < 2 ppb ppb Levels of tungsten are similar to those previously Levels of tungsten a r e s i m i l a r to those p r e v i o u s l y documented d o c u m e n t e d by by Noranda Noranda Mines Mines Limited L i m i t e dwho who reported r e p o r t e d channel channel samples s a m p l e s up up to t o 0. 0. 11 percent p e r c e n tW03 WO3 (Blackburn ( B l a c k b u r n and and Hailstone, Hailstone, 1983, 1983, p.12—13) p . 12-13) and a n d Selco S e l c o Incorporated I n c o r p o r a t e d who who obtained obtained grades up to 0.09 percent Wa3 (A. Pryslak, g r a d e s up t o 0 . 0 9 p e r c e n t W03 ( A . P r y s l a k , geologist, geologist, Selco S e l c o Incorporated, I n c o r p o r a t e d , personal p e r s o n a l communication, c o m m u n i c a t i o n , 1983). 1983). Return R e t u r n to t o main main property p r o p e r t y access a c c e s s road r o a d and and travel t r a v e l west w e s t for f o r 2.3 2 . 3 km km (1.5 ( 1 . 5 miles). miles). --- - , -stop is important in that it establishes a STOP STOP 6: 6 : PETRUNKA PETRUNKA TUNGSTEN PROPERTY SANMINE SANMINE EXPLORATION EXPLORATION - TUNGSTEN -- PROPERTY, INC. —I N C . (WEST (WEST END) END) ' T hTTs T s s t o p 1s i m p o r t a n t i n t h a t it e s t a b l i s h e s a genetic g e n e t i cconnection c o n n e c t i o nofo frare—metal r a r e - m e t a l mineralization m i n e r a l i z a t i o narid and *< associated a s s o c i a t e d boron boron metasomatism m e t a s o m a t i s m with w i t h the t h e Ghost Ghost Lake Lake Batholith. Bath01 i t h . This This large l a r g e stripped s t r i p p e d outcrop o u t c r o p exposes e x p o s e s the t h e rarely rarely observed o b s e r v e d contact c o n t a c t of o f the t h e Ghost Ghost Lake Lake Batholith B a t h o l i t h with with deformed The d e f o r m e d mafic maÂi c and a n d intermediate i n t e r m e d i a t e metavolcanics. metavolcanics The by c o n t a c t a t t h e w e s t p a r t o f t h i s o u t c r o p is d e f i n e d by an t ocoarse—grained coarse-grained a n interlayering i n t e r l a y e r i nof g omedium— f medium- to almandine—muscovite—tourmaline almand i n e - m u s c o v i t e - t o u r m a l i n e granite g r a n i t e with with calc—silicate m e t a v o l c a n i c s over o v e r35 35m. m. In In c a l c - s i l i c a t e bearing b e a r i n g mafic maÂi c metavolcanics places p l a c e sa abrown brownweathering w e a t h e r i n g1—8 1-8 cm cm wide w i d e biotite—rich biotite-rich metasomatic is developed d e v e l o p e d along a l o n g the t h e contact. contact. m e t a s o m a t i c sselvage e l v a g e is About to tthe About 550 0 mmt o h e eeast a s t the t h e contact c o n t a c t isismore more abrupt abrupt and an aoutermost a n d is ischaracterized c h a r a c t e r i z eby d by n o u t e r m o zone s t z o n(1—2 e (1-2mmwide) wide) of o f green g r e e n muscovite m u s c o v i t e enrichment e n r i c h m e n t which w h i c h rreverts e v e r t s inward inward to t o aa much l e s smicaceous m i c a c e o u almandine—muscovite—tourmalirie s almandine-muscov i t e - t o u r m a l i n e much less granite. off intense g r a n i t e . Impressive I m p r e s s i v e zones zones o i n t e n s e black b l a c ktourmaline tourmal i n e deposition thet hgreen e g r e emuscovite—rich n muscovite-rich d e p o s i t i o n occur o c c u r adjacent a d j a c e n ttot o granite. most extensive e x t e n s i v etourmaline—rich t o u r m a l i n e - r i c h zone z o n e (2 ( 2mm g r a n i t e . The The most wide) w i d e ) contains c o n t a i n s radiating r a d i a t i n gsheaves s h e a v e s of o f tourmaline t o u r m a l i n ewith with individual i n d i v i d u a l crystals c r y s t a l sup uptoto8 8cm cmini nlength, l e n g t hbrown , brown weathering w e a t h e r i n g biotite, b i o t i t e , and a n d actinolite. a c t i n o l i t e . These T h e s e pneumatolytic pneumatolytic . contact at the west part of this outcrop is defined �176 ddeposits e p o s i t s exhibit e x h i b i t anomalous anomalous enrichment e n r i c h m e n t in i n Be, B e , Cs, C s , Rb, Rb, Sn, Sn, F, F , and a n d BB (Table ( T a b l e 3). 3 ) . With increasing i n c r e a s i n g distance d i s t a n c e from f r o m the the bbatholithic a t h o l i t h i c ccontact o n t a c t a ggradation r a d a t i o n of o f the t h e tourmaline—rich tourmal ine-rich zzone o n e iinto n t o aalbite—quartz—rich l b i t e - q u a r t z - r i c h ppegmatitic e g m a t i t i c pockets p o c k e t s is is obvious. obvious. A c c e s s o r y , euhedral, e u h e d r a l , light l i g h t green g r e e n beryl b e r y l up u p to to Accessory, 5.4 m iin n bbasal a s a l ssections e c t i o n s occurs o c c u r s in i n these these 5.4 xx 6.5 6.5 c cm quartz—rich q u a r t z - r i c h masses. masses. Zoned u a r t z - t o u r m a l i n e veins, veins, Zoned qquartz—tourmaline exposed l i m i t s of o f the t h e stripped s t r i p p e d outcrop, outcrop, e x p o s e d near n e a r the t h e eastern e a s t e r n limits aare r e ggenerally e n e r a l l y ssubconcordant u b c o n c o r d a n t to t o hhost o s t rock r o c k foliation £0i a t i o n and and cclearly l e a r l y emanate e m a n a t e from f r o m the t h e Ghost Ghost Lake Lake Batholith. Bath01 i t h . R e t u r n to t o south s o u t h ciost Ghost Lake Lake access a c c e s s road, r o a d , turn t u r n north, n o r t h , and and proceed proceed Return Turn 1.5 km. km. T u r n eeast a s t on aa vvery e r y inconspicuous i n c o n s p i c u o u s oold l d drill d r i l l access access ffor o r 1.5 Park road r o a d and and follow f o l l o w for f o r 0.3 0 . 3 km. km. P a r k vehicle v e h i c l e and and walk w a l k on drill d r i l l road road 215 m. m. ffor o r aabout b o u t 215 STOP STOP 7: 7: --- ---- —- MPLVIS LAKE LAKE SPODUMENE-BERY SPODtJMENE-BERYL-TANTALITE PEGMATITES MAVIS L-TANTALITE PEGMATITES --- (FTR_SWICEROPERTY,_MAIN SERVICE PROPERTY, M A I NZONK) ZONE) -(FAIR This 12i76 12 x 76 mlensoidal—shaped m i e x d a l z h a p e d pegmatite p e g m a t i t e dike dike ooccurs c c u r s in i n foliated f o l i a t e d and and gneissic g n e i s s i c mafic m a f i c metavolcanics m e t a v o l c a n i c s arid and subordinate It It s u b o r d i n a t e fine—grained f i n e - g r a i n e d laminated l a m i n a t e d metawackes. metawackes eexhibits xhibits a a vague v a g u e internal i n t e r n a l zonation z o n a t i o n which w h i c h is is generally generally not n o t apparent a p p a r e n t in i n most most rare—metal r a r e - m e t a l ppegmatites e g m a t i t e s of o f the t h eMavis Mavis Lake Pegmatite Lake P e g m a t i t e Group. Group. A A qquartz—rich u a r t z - r i c h core o n e is core zzone is irregularly i r r e g u l a r l y and a n d asymmetrically a s y m m e t r i c a l l y ddistributed i s t r i b u t e d from f r o m the t h e dike dike centre These c e n t r e to t o north n o r t h contact. contact. T h e s e pod—like p o d - l i k e ddomains o m a i n s ccontain ontain cm iinn conspicious K—feldspars t o 33 33 xx 41 41 cm c o n s p i c i o u s blocky blocky K - f e l d s p a r s up up to ccross—sectional r o s s - s e c t i o n a l area, a r e a , and minor m i n o r beryl, b e r y l , green g r e e n spodumene, spodumene, muscovite, ggreen reen m u s c o v i t e , tourmaline, t o u r m a l i n e , blue b l u e apatite, a p a t i t e , and a n d orange orange garnet. garnet. Outer margins z o n e can c a n ggrade rade O uter m a r g i n s oof f the t h e core zone indistinctly i n d i s t i n c t l y into i n t o aan n aalbite—spodumene—quartz l b i t e - s p o d u m e n e - q u a r t z pegmatite pegmatite 4 7 percent p e r c e n t quartz q u a r t z and a n d 29 29 to t o 48 48 uunit n i t containing c o n t a i n i n g 37 37 ttoo 47 ppercent e r c e n t green g r e e n sspodurnene, p o d u m e n e , t hthe e l alatter t t e r being b e i n g hhighest i g h e s t levels levels recorded r e c o r d e d for f o r aany n y ppegmatite e g m a t i t e oof f the t h e Mavis Mavis Lake Lake Pegmatite Pegmatite Group. G roup. A third t h i r d zonal z o n a l unit u n i t is is developed d e v e l o p e d along a l o n g the t h e outer outer margins m a r g i n s of o f the t h e spodumene—rich s p o d u m e n e - r i c h unit u n i t and and contains c o n t a i n s the the assemblage muscovite—spodumene—albite—quartz— a s s e m b l a g e ggreen r e e n muscov ite-spodumene-albit e-quartzK—feldspar. to 7 ppercent e r c e n t while while K-feldspar. Spodumene contents c o n t e n t s drop d r o p to those K—feldspar It t o 55 55 percent. percent. It consists c o n s is ts t h o s e oof f K - f e l d s p a r increase i n c r e a s e to of o f coarse, c o a r s e , generally g e n e r a l l y anhedral, a n h e d r a l , coalescing c o a l e s c i n g white white K—feldspars K - f e l d s p a r s with w i t h interstitial i n t e r s t i t i a l quartz—spodumene q u a r t z - s p e d umene '"pockets". pockets" Small, white S mall, w h i t e to t o bbuff u f f coloured c o l o u r e d domains d o m a i n s (up ( u p to t o 11 x 33 m) of m) o f fine—grained, f i n e - g r a i n e d , equigranular, e q u i g r a n u l a r , saccharoidal s a c c h a r o i d a 1 sodic s o d ic aplite a p l i t e are a r e sparsely s p a r s e l y scattered s c a t t e r e d throughout t h r o u g h o u t the the sspodumene—rich p o d u m e n e - r i c h zone. z o n e . These T h e s e domains d o m a i n s consist c o n s i s t of o f albite, albite, muscovite, qquartz u a r t z aand n d accessory a c c e s s o r y ggreen reen m u s c o v i t e , apatite a p a t i t e and a n d an an unidentified brown m mineral u n i d e n t i f i e d brown i n e r a l (possibly ( p o s s i b l y aa phosphate) phosphate) This This type o be b e primary p r i m a r y iin n oorigin r i g i n as as t y p e oof f aplite a p l i t e aappears p p e a r s tto contacts with contacts w i t h bounding b o u n d i n g spodumene—rich s p o d u m e n e - r i c h units u n i t s are are iinvariably n v a r i a b l y ssharp h a r p aand n d exhibit e x h i b i t nno o evidence e v i d e n c e oof f replacement replacement ttextures. e x t u r e s . At A t STOP STOP 8, 8, identical i d e n t i c a l aplites a p l i t e s are a r e clearly clearly ttransected r a n s e c t e d bby y vveinlets e i n l e t s of o f coarser c o a r s e r albite a l b i t eand and green green . . . . �177 muscovite m u s c o v i t e (best ( b e s t observed o b s e r v e d on o n wetted w e t t e d surfaces) s u r f a c e s ) which which probably t o replacement r e p l a c e m e n t stage s t a g e aplites. a p l ites p r o b a b l y relate r e l a t e to Albite—rich A 1 b i t e - r i c h replacement r e p l a c e m e n t zones, z o n e s , commonly commonly peripheral peripheral to core zones, umene t o quartz—rich q u a r t z - r i c h core z o n e s , typify t y p i f yalla lspod l spodumene pegmatites p e g m a t i t e s of o f the t h eMavis Mavis Lake Lake area. a r e a . Approximately A p p r o x i m a t e l y 10 10 percent p e r c e n t of o f this t h i spegmatite p e g m a t i t e has h a s been b e e n intensely i n t e n s e l y albitized albitized to t o the t h e point p o i n t that t h a no t novestige v e s t i g of e oprimary f p r i m a r ymineralogy m i n e r a l o g y has has survived. a r e distinctly d is t i n c t l non—equigranular, y non-equigranular , s u r v i v e d . Textures T e x t u r e s are fine f i n e to t o medium medium grained g r a i n e d and a n d involve i n v o l v e aalbite, l b i t e , quartz, q u a r t z , green green muscovite, rare m u s c o v i t e , with w i t h accessory a c c e s s o r y white w h i t e beryl, b e r y l , garnet, g a r n e t , and a n d rare ilmenite. ilmenite. Columbite is C o l u m b i t e mineralization m i n e r a l i z a t i o n in i n this t h i s pegmatite p e g m a t i t e is sporadically s p o r a d i c a l l y distributed d i s t r i b u t e d and and clearly c l e a r l y associated a s s o c i a t e d with with replacement r e p l a c e m e n t stage s t a g e albitization, a l b i t i z a t i o n , as as evidenced e v i d e n c e d by by its its restriction blocky r e s t r i c t i o n to t o albitized a l b i t i z e rims d r i mof s osome f some b l o c kK—feldspar y K-feldspar aggregates a g g r e g a t e s and a n dspodumenes. spod umenes Proceed P r o c e e d aabout b o u t 660 0 mms osouth u t h t otos side i d e oof f hhill. ill. . . TANTALITE-BEARING TANTALITE-BEARING SPODUMENE_PEGMATITE_DIKE SPODUMENE PEGMATITE D I KE -Thlo T h e - l owe w ermos r m o s t tp pàE a x oö!ThTflr t a b T F G r cat c a t i ffIT t q , 26 268 m m I l o ngg STOP 8: STOP 8: . pegmatite p e g m a t i t e dike d i k e contains c o n t a i n s sparse s p a r s e disseminated d i s s e m i n a t e d t tantalite, antalite, distributed d i s t r i b u t e d uniformly u n i f o r m l y relative r e l a t i v e to t oother o t h e rpegmatites p e g m a t i t e s in in the t h e area. area. Maximum Maximum v avalues l u e s o of f ttantalum a n t a l urn (380 ( 3 80 ppm ppm oover v e r 0.9 0.9 m) m ) and a n d Nb Nb (210 ( 2 1 0 ppm ppm over o v e r 0.9 0.9 m) m) for f o rthe t h eMain MainZone ZoneMavis Mavis Lake area pegmatites p e g m a t i t e s occur o c c u r at a t this t h i s locality. l o c a l i t . The T h e rare rare Lake area lithium l i t h i u m amphibole a m p h i b o l e holmquistite h o l m q u i s t i t e[Li2(Mg, [Li2(Mg,Fe2)3 Fe ) 3Al2Si2022 Al2Si2022 s is subtly apparent in mafic metavolcanics above (OH)2] (OH)2] is s u b t l y a p p a r e n t i n m a f i c m e t a v o l c a n i c s a b o v e the t h e upper u p p e r 50 50 degree d e g r e esouth—dipping s o u t h - d i p p i n g contact. contact. Most Most oof f this t h i s pegmatite p e g m a t i t e isiscomposed composed oof f aa K—feldspar—rich K - f e l d s p a r - r i c h z ozone n e s i similar m i l a r t to o tthat h a t ata tSTOP STOP 7 7 but b u t can can be b e distinguished d i s t i n g u i s h e d by b y the t h econspicuous c o n s p i c u o u s development d e v e l o p m e n t of o f aa symplectic s y m p l e c t i cgreen g r e e nspodumene s p o d u m e n e ++ quartz q u a r t z intergrowth. intergrowth. Slender S l e n d e r spodumene spodumene pphenocrysts h e n o c r y s t s up u p to t o 1 mm long l o n g and and 12—19 12-1 9 cm c m wide w i d e are a r e oriented o r i e n t e d approximately a p p r o x i m a t e l y normal n o r m a l to t o the t h e lower lower pegmatite p e g m a t i t e contact c o n t a c t and and contain c o n t a i nfine—grained, f i n e - g r a i n e d , equigranular equigranular quartz A 4 4 to to q u a r t z comprising c o m p r i s i n g about a b o u t 30 3 0 percent p e r c e n t of o f the t h e host. host. A 55 cm cm wide w i d e quartz q u a r t z ++ green g r e e n muscovite m u s c o v i t e ++ albite a l b i t e carapace carapace 1 surrounds surrounds most most of o f tthe h e spodumerie—quartz s p o d u m e n e - q u a r t z intergrowths. intergrowths. The The entire e n t i r e intergrowth i n t e r g r o w t h is is typically t y p i c a l l y enveloped e n v e l o p e d by by coars coars ee—grained - g r a i n e d K—feldspar. K-feldspar. This T h i s pegmatite p e g m a t i t e also a l s o contains c o n t a i n s local l o c a l development d e v e l o p m e n t of o f aa quartz—rich q u a r t z - r i c h core core (accompanied ( a c c o m p a n i e d by by blocky b l o c k y K—feldspar, K-feldspar , white w h i t e euhedral e u h e d r a l beryl b e r y l up u p to t o 5.5x7 5 . 5 ~ 7an on in i n cross—sectional cross-sectional area, a r e a , and a n d spodumene) s p o d u m e n e ) and a n d pockets p o c k e t s of o f saccharoidal s a c c h a r o i d a l sodic sodic aplite a p l i t e similar s i m i l a r to t o that t h a t at a t STOP STOP7.7. Return t o drill d r i l l road r o a d and a n d walk walk short s h o r t distance d i s t a n c e east e a s t to t o top t o p of o f hill. hill. R e t u r n to - STOP 9: STOP 9 : ALBITIZED ALBITIZED SPODUMENE SPODUMENE PEGMATITE PEGMATITE WITH WITH METASOMATIC METASOMATIC --LAYERS_DEVELOPED IN LAYERS D E V E L O P E D I N HOST H O S T RROCKS OCKS-. -- Thfs This r e l aEivi7hiEiy t i v e l y 7 i g h lalbitized y a l b i t i z e dportion p o r t i o n of o f the the same same dike d i k e as a s that t h a t observed o b s e r v e d at a t Stop S t o p8 8exhibits e x h i b i t s well' well" �178 ddeveloped, e v e l o p e d , fine—grairied f i n e - g r a i n e d ssaccharoidal a c c h a r o i d a l aalbite l b i t e and a n d quartz. quartz. Glimmerite* bands are Glimrnerite* b ands a r e apparent a p p a r e n t in i nthe t h mafic e m a f i meta— c metavvolcanics o l c a n i c s immediately i m m e d i a t e l y nnorth o r t h oof f the t h e contact c o n t a c t and and ddisposed i s p o s e d cconcordant oncordant to oliation. The l i m r n e r i t e in in to ffoliation. The ggliirunerite this t h i s case caseisischaracterized c h a r a c t e r i z e by d benrichment y e n r i c h m e nin t ibronze— n bronzeb l a c k tourmaline, t o u r m a l i n e ,and a n d sporadic sporad ic ccoloured o l o u r e d bbiotite, i o t i t e ,black A ppartial hholmquistite. olmquistite. A a r t i a l chemical c h e m i c a l analysis a n a l y s i s is i v e n in in is ggiven Table T a b l e 4. 4. Geochemical G e o c h e m i c a l profiles p r o f i l e s for f o r distribution d i s t r i b u t i o n of o f mobile mobile elements Cs, Sn aand K , F, F, Li, L i , Rb, Rb, Cs, n d Be in i n mafic mafic e l e m e n t s K, m e t a v o l c a n i c hhost o s t rocks r o c k s as as aa function f u n c t i o n of o f increasing increasing metavolcanic No. 4 , ddistance i s t a n c e from f r o m northern n o r t h e r n contact c o n t a c t of o f Pegmatite P e g m a t i t e No.4, ssituated i t u a t e d 130 1 3 0 m east e a s t of o f this t h i s stop s t o p is is given g i v e n in i n Figure F i g u r e 4. 4. Return Ghost Lake access access rroad R e t u r n tto o ssouth o u t h Ghost o a d aand n d travel t r a v e l bback a c k to t o Highway 17. t o junction j u n c t i o n with w i t h Highway 601 and a n d turn t u r n north. north. 17. P r o c e e d west to Proceed T r a v e l ffor o r 4.8 4.8 km km to t o junction j u n c t i o n with w i t h Ghost G h o s t Lake Lake Road Road and a n d turn turn Travel east. east. P r o c e e d for f o r 23.5 2 3 . 5 km and turn t u r n west w e s t on on old o l d gravelled g r a v e l l e d logging logging Proceed km. rroad o a d for f o r 1.8 1.8 km. T u r n ssouthwest o u t h w e s t on on very v e r y poor p o o r clay—surfaced, c l a y - s u r f a c e d ,abandoned a b a n d o n e d logg l o g ging ing . Turn aaccess c c e s s road r o a d and a n d travel t r a v e l ini nfour—wheel f o u r - w h e e l ddrive r i v e for f o r 1.7 1.7 km. km. Walk 4 4 0 mm nnorthwest o r t h w e s t uup p vvery e r y poor, p o o r , partly p a r t l yovergrown o v e r g r o w n logging l o g g i n g road r o a d for f o r440 tto o ttop o p oof f hill. hill. f o r aabout b o u t 260 260 m north n o r t h along a l o n g pegmatitic pegmatitic Then walk walk for r i d g e to t o base b a s e of o f outcrop o u t c r o p area area on on north n o r t h slope. slope. ddike i k e forming f o r m i n g a ridge - - zondpmatite, - -disdaiTEto aniphibolitic STOP 110:__GULLWING 0 : GULLWING LAKE SPODUMENE PEGMATITE PEGMATITE STOP ThTh T his zoned p e g m a t i t e , d-i%corea%toasphibolitic metavolcanics, att the ma ic m e t a v o l c a n i c s , is is ssituated ituated a t h e northern n o r t h e r n end of of mafic aa 412 412 mml olong, n g , ccurvilinear, u r v i l i n e a r , pegmatitic p e g m a t i t i c ggranite r a n i t e dike dike a s t . Most Most oof f this this sstriking t r i k i n gN18°q N180W and and dipping d i p p i n g 52°—72° 520-720 eeast. pegmatite b l o c k yK—feldspar K - - f e l d s p a r + quartz quartz p e g m a t i t e consists c o n s i s t s of o f a ablocky coarsestggrain aassemblage s s e m b l a g e wwhich h i c h r erepresents p r e s e n t s t hthe e coarsest r a i n ssize i z e of of A small small core A core zone z o n e of of aany n y ppegmatite e g m a t i t e iin n the t h e Dryden Dryden Field. Field. muscovite uscovite sspodumene—blocky p o d u m e n e - b l o c k y KK—feldspar--quartz—albite - f e l d s p a r - q u a r t z - a 1 b i t e ++ m occurs The coarse light—green o c c u r s at a t the t h e lowest lowest exposure. exposure. The coarse light-green randomly measure e a s u r e uup p to t o 44 r a n d o m l y ooriented r i e n t e d spodumene spodumene pphenocrysts h e n o c r y s ts m x 100 cm cm( (parallel p a r a l l e l to t o 001) 0 0 1 ) and a n d 66 xx 40 40 cm c m (normal ( n o r m a l tto o x 100 001). 001 ). Two stages s t a g e s oof f replacement r e p l a c e m e n t aalbitization l b i t i z a t i o nhave h a v e been been identified d o m i n a n t and and i d e n t i f i e d within w i t h i n this t h i s pegmatite. p e g m a t i t e . The T h e most dominant eearliest a r l i e s t cconsists o n s i s t s oof f aan n eequigranular, q u i g r a n u l a r , albite—rich albite-rich assemblage a s s e m b l a g e accompanied a c c o m p a n i e d by b y minor m i n o r quartz, q u a r t z , muscovite, m u s c o v i t e , and and remnants This T h i s albitic albitic r e m n a n t s oof f primary p r i m a r y blocky b l o c k y K—feldspar. K-feldspar replacement r e p l a c e m e n t unit u n i t closely c l o s e l y follows f o l l o w s external e x t e r n a l contacts c o n t a c t s of of Gullwing mafic u l l w i n g Lake Lake Pegmatite P e g m a t i t e aand n d those t h o s e oof f several several m afic tthe he G and intermediate and i n t e r m e d i a t e metavolcanic m e t a v o l c a n i c xenoliths. x e n o l i t h s . A variant v a r i a n t of of tthis h i s aalbitic l b i t i c aassemblage s s e m b l a g e ooccurs c c u r s near n e a r the t h e upper u p p e r pegmatite pegmatite ccontact o n t a c t and and is is ffeatured e a t u r e d bby y an a n interesting i n t e r e s t i n g bbladed l a d e d texture texture muscovite fformed o r m e d bby y rrandomly a n d o m l y ooriented, r i e n t e d , tthin h i n bbiotite i o t i t e aand nd m uscovite . ----------* Russian Russian * metasomatic term for f o r a rrock o c k resulting r e s u l t i n g from from m etasomatic t r a n s f o r m a t i o n by by outward o u t w a r d dispersion d i s p e r s i o n of o f fluids f l u i d s enriched e n r i c h e d in i n such such transformation B, Li, eelements l e m e n t s as as K, K , B, Li, Cs, C s , F, F , Rb Rb which w h i c h were were released r e l e a s e d due d u e to t o late late s t a g e albitization a l b i t i z a t i o n of o f primary p r i m a r y spodumene spodumene ++ K—feldspar K - f e l d s p a r bbearing earing stage assemblages. ass embl a g e s . �179 E a. a. C 0 4- Ca 4- C a) C.) C 0 C.) 4C ci) E ci) a) distance from contact contact (metres) (metres) Geochemical F i g u r e 4: 4: Geochemical profile p r o f i l e within w i t h i n mafic metavolcanic rocks rocks Figure adjacent a d j a c e n t to t o the t h e contact c o n t a c t with w i t h aa pegmatite pegmatite dike. dike. �180 laths l a t h s up u p to t o 10 1 0 cm. cm. Sparse S p a r s e molybdenite m o l y b d e n i t e and and platy platy columbite—tantalite c o l u m b i t e - t a n t a l i t e can c a n be b e subtly s u b t l y intergrown i n t e r g r o w n with w i t h these these micas. micas A later l a t e r replacement r e p l a c e m e n t stage s t a g e is is finer—grained f i n e r - g r a i n e d and and specifically t o the t h e spodumene s p o d u m e n e core c o r e zone. z o n e . It I t is is s p e c i f i c a l l y confined c o n f i n e d to c h a r a c t e r i z e d by b y radiating r a d i a t i n g aggregates a g g r e g a t e s of o f platy, p l a t y , white white characterized to t o light l i g h t blue b l u e cleavelandite c l e a v e l a n d i t e accompanied a c c o m p a n i e d by b y green green muscovite, l o c a l lepidolite, l e p i d o l i t e , red—brown red-brown garnet, g a r n e t , light 1i g h t m u s c o v i t e , local green g r e e n beryl, b e r y l , and and platy p l a t y tantalite. t a n t a l i t e . Endogeneous E n d o g e n e o u s aureoles aureoles involving K , F, F, Li, L i , Cs, C s , Rb, Rb, Be, B e , and a n d Sn Sn are a r e much much less less i n v o l v i n g K, extensive e x t e n s i v e relative r e l a t i v e to t o rare—metal rare-metal pegmatites p e g m a t i t e s of o f the t h e Mavis Mavis Lake Lake Pegmatite P e g m a t i t e Group. Group. However, However, intense i n t e n s e metasomatic metasomatic activity a c t i v i t y is is obvious o b v i o u s within w i t h i n 3—5 3-5 cm cm of o f the t h e pegmatite pegmatite contact c o n t a c t and a n d these t h e s e brown—weathering b r o w n - w e a t h e r i n g bbiotite—rich i o t i t e - r i c h selvages selvages contain c o n t a i n the t h e highest h i g h e s tlevels l e v e l of s oF(1.84%), f F( 1 . 8 4 % )K20(8.82%), , K20 ( 8 . 8 2 % ) , Li(1 L i ( 1 1,000 1 , 0 0 0 pprn), R b ( 7 5 8 0 pprn), T a ( 1 0 0 ppm), p p m ) , Sn(320 S n ( 3 2 0 ppm) ppm) ppm), Rb(7580 ppm), Ta(100 and ppm) found and Zn Zn (2560 ( 2 5 6 0 ppm) f o u n d within w i t h i n in i n glimmerites g l i m m e r i t e s formed f o r m e d via via replacement r e p l a c e m e n t oof f mafic maÂi c metavolcanics m e t a v o l c a n i c s in i n the t h eDryden Dryden Field Field (Breaks ( B r e a k s iin n pprep., r e p . , and and Table T a b l e 4). 4). Return R e t u r n to t o Ghost G h o s t Lake Lake road r o a d and a n d proceed p r o c e e d north n o r t h for f o r 1.8 1.8 km. km. Turn Turn e a s t on old o l d gravelled g r a v e l l e d logging l o g g i n g road r o a d and a n d travel t r a v e l for f o r about a b o u t 1 km. km. east Park P a r k vvehicles e h i c l e s and a n d walk northeast n o r t h e a s t up u p undrivable, u n d r i v a b l e , clay c l a y surface surface logging t o aa junction. j u n c t i o n . Turn T u r n north n o r t h and and l o g g i n g road r o a d for f o r 1.35 1 . 3 5 km, km, coming coming to walk walk for f o r 345 345 m. m. . 1 Th T h e zzoned o n e d 'Ibt Tb t Lake Lake rare—metal r a r e - m e t a l pegmatfEe p e g m a t i t e represents represents STOP STOP 11: 11: TOT LAKE LAKE SPODUMENE-POLLUCITE SPODUMENE-POLLUCITE PEGMATITE PEGMATITE the t h e most most easterly e a s t e r l y known known occurrence o c c u r r e n c e of o f spodumene spodumene and and greatest g r e a t e s t degree d e g r e e of o f geochemical g e o c h e m i c a l specialization s p e c i a l i z a t i o n for f o r the the Dryden 1-6 mm Dryden Pegmatite P e g m a t i t e Field. F i e l d . This T h i s northwest—striking n o r t h w e s t-s t r i k i n g 1—6 wide, w i d e , 48 48 mm long l o n g dike d i k e lies l i e s sharply s h a r p l y discordant d i s c o r d a n t to to foliation £0i a t i o n trends t r e n d s of o f mafic maÂi c metavolcanic m e t a v o l c a n i c and and meta—ultramafic m e t a - u l t r a m a f i c host h o s t rocks. r o c k s . Presence P r e s e n c e of o f pollucite poll ucite (CsAlSi2O6), ore mineral m i n e r a l of o f cesium, c e s i u m , is is a unique unique ( C s ~ l S i 2 0 6 ) ,the t h e only o n l y ore feature f e a t u r e in i n the t h e area area and, a n d , elsewhere e l s e w h e r e in i n Ontario, Ontario, is is only only known a t Lily L i l y Pad Pad Lake, Lake, near n e a r Fort F o r t Hope Hope (Wallace, (Wallace, 1978). 1978) known at This T h i s mineral m i n e r a l is is confined c o n Âi n e d to to aa small s m a l l 1 xx 55 mm pod pod near n e a r the the well—layered w e 1 1 - l a y e r e d southeast s o u t h e a s t exposed e x p o s e d end e n d as as coarse, coarse, anhedral, anhedral, masses comprising c o m p r i s i n g about a b o u t 37 37 percent p e r c e n t of o f the t h e mode, mode, w h i t e masses white and a n d filling f i l l i n g interstices i n t e r s t i c e s between b e t w e e n relatively relatively earlier—formed, s p o d u m e n e phenocrysts. p h e n o c r y s ts e a r l i e r - f o r m e d , bladed, b l a d e d , pink p i n k spodumene Spodumene Spod umene may occur o c c u r as as relatively r e l a t i v e l y coarse, coarse, randomly randomly oriented o r i e n t e d blades b l a d e s up u p to to 1 x x 14 1 4 xx 38 3 8 cm cm near n e a r the the northwestern n o r t h w e s t e r n end e n d of o f the t h e exposure. e x p o s u r e . In I n proximity p r o x i m i t y to t o the the pollucite p o l l u c i t e zone, z o n e , finer—grained f i n e r - g r a i n e d spodumene spodumene exhibits exhibits sub—horizontal s u b - h o r i z o n t a l alignment a l i g n m e n t in i n longitudinally l o n g i t u d i n a l l y oriented oriented bands b a n d s with w i t h c—crystallographic c - c r y s t a l l o g r a p h i c axis a x i sapproximately a p p r o x i m a t e l ynormal normal to t o dike d i k e contacts. c o n t a c t s . These T h e s e bbands a n d s ccontain o n t a i n about a b o u t 70 7 0 percent percent spodumene alternate t e r n a t ewith w i t halbite—quartz—green a1 b i t e - q u a r t z - g r e e n s p o d umene aand n d a1 muscovite m u s c o v i t e aaplitic p l i t i c layers l a y e r s containing c o n t a i n i n g little 1it t lspodumene. e spodumene. A A ssignificant i g n i f i c a n t portion p o r t i o n of o f the t h epegmatite p e g m a t i t e has h a s been been subjected t o late l a t e stage s t a g e fracture—controlled f racture-controlled s u b j e c t e d to albitization. a l b i t i z a t i o n . This T h i s moderate m o d e r a t e to t o intense i n t e n s e albitizatiori a l b i t i z a t i o n was was effected e f f e c t e d by by hydrothermal h y d r o t h e r m a l fluids f l u i d s emanating e m a n a t i n g from f r o m aa now now . 1 . 1 �181 quartz—filled q u a r t z - f i l l e d central c e n t r a l branching b r a n c h i n g vein v e i n system s y s t e m extending ex t e n d i n g f o r virtually v i r t u a l l y the t h e complete c o m p l e t e exposed e x p o s e d dike d i k e length. l e n g t h . Near Near for t h e northwestern n o r t h w e s t e r n end, e n d , metasomatic m e t a s o m a t i c fronts f r o n t s oriented oriented the parallel p a r a l l e l to t o thin t h i n quartz—filled q u a r t z - f i l l e d fractures f r a c t u r e s intersect i n t e r s e c t pink pink p a r t l y altering a 1 t e r i n g these t h e s e (behind ( b e h i n d the the spodurnene phenocrysts, p h e n o c r y s ts , partly spodumene front)to tantalite-rich f r o n t ) t o fine—grained f i n e - g r a i n e d green g r e e n micas. m i c a s . AA tantalite—rich zone z o n e in i n the t h e same s a m e part p a r t of o f the t h e dike d i k e exhibits e x h i b i t s spodumenes spodumenes and a n d blocky b l o c k y K—feldspars K - f e l d s p a r s that t h a t have h a v e been b e e n completely completely r e p l a c e d by b y albite—green a l b i t e - g r e e n mica m i c a (cymatolite) ( c y m a t o l i t e ) and and albite, albite, replaced respectively. - a l b i t eite rreplacement e p l a c e m e n t assemblages assemblages respectively. L e p i d o l it Lepidol it ee—alb occur o c c u r locally l o c a l l y at a t the t h esoutheastern s o u t h e a s t e r n end end of o f the t h e dike d i k e and and are a r e specifically s p e c i f i c a l l y associated a s s o c i a t e d with w i t h the t h e pollucite p o l l u c i t e zone zone where w h e r e spodumenes spodumenes are a r e clearly c l e a r l y partially p a r t i a l l y replaced r e p l a c e d by by fine—grained f i n e - g r a i n e d lepidolite. l e p i d o l ite. Beryl B e r y l is is rarely r a r e l yfound f o u n d in i nthe t h eTot TbtLake Lake pegmatite, pegmatite, occurring t o anhedral a n h e d r a l crystals c r y s t a l s (up ( u p to to o c c u r r i n g as a s white w h i t e subhedral s u b h e d r a l to 2 x 4 cm in i n cross—section) c r o s s - s e c t i o n ) in i n albitic a l b i t i c replacement replacement zones. is noteworthy n o t e w o r t h y as a s fine—grained, fine-grained, z o n e s . Holmquistite H o l m q u i s t i t e is randomly r a n d o m l y oriented o r i e n t e d acicular a c i c u l a r purplish p u r p l i s h crystals c r y s t a l s on on the the surface s u r f a c e of o f a massive, m a s s i v e , medium—grained, m e d i u m - g r a i n e d , mafic m a f i c metavolcanic metavolcanic host h o s t reentrant r e e n t r a n t near n e a r the t h e southeast s o u t h e a s t end end (best ( b e s t seen s e e n on on wetted w e t t e d surfaces) s u r f a c e s ) and a n d in i n similar s i m i l a r adjacent a d j a c e n t rocks r o c k s for for distances t o 1 m from f r o m the t h e dike d i k e contact. contact. d i s t a n c e s up u p to Return R e t u r n to t o Ghost Ghost Lake Lake Road, Road, turn t u r n north, n o r t h , and a n d travel t r a v e l for f o r7.75 7 . 7 5km km to to junction. j u n c t i o n . Turn T u r n eeast a s t along a l o n g poor p o o r gravel g r a v e l road r o a d and and travel t r a v e l for f o r5 5km km to t o junction j u n c t i o n with w i t h Kathlyn K a t h l y n Lake Lake access a c c e s s road. r o a d . Turn T u r n south s o u t h and a n d travel travel for f o r about a b o u t 3.5 3 . 5 km. km. Proceed P r o c e e d aa sshort h o r t distance d i s t a n c e along a l o n g old o l d road r o a d to to west west to t o an a n outcrop o u t c r o p area a r e a with w i t h pits p i t s and a n dana nada dit. it. 1 STOP 12: STOP 12: - LATERAL LATERAL LAKE LAKE MOLYBDENITE MOLYBDENITE DEPOSIT DEPOSIT this T h i s property p r o p e r t y is is held h e l d by b y PT ~ i d g ~ M6iybdenum ~ o l ~ b d eMines Mines n u m Ltd. Ltd. and a n d covers c o v e r s the t h e eastern e a s t e r n contact c o n t a c t between b e t w e e n the t h e Lateral Lateral Lake Lake intrusion i n t r u s i o n and and intensely i n t e n s e l y foliated f o l i a t e d metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y rocks r o c k s (Figure ( F i g u r e 5). 5 ) . The The property p r o p e r t y has h a s been been explored e x p l o r e d by by an a n adit a d i t and and extensive e x t e n s i v e diamond diamond drilling, d r i l l i n g , most most recently r e c e n t l y by b y Rio R i o Tinto T i n t o Canadian C a n a d i a n Exploration E x p l o r a t i o n Ltd. Ltd. in in 1979—80. At A t this t h i s locality l o c a l i t y the t h e intrusion i n t r u s i o n is is composed composed of of 1979-80. foliated, t o coarse—grained coars e - g r a i n e d granodiorite, g r a n o d i o r i t e , pink pink f o l i a t e d , medium medium to aplite a p l i t e and and several s e v e r a l varieties v a r i e t i e s of o f pegmatite. pegmatite. Quartz—filled Q u a r t z - f i l l e d tension t e n s i o n fractures f r a c t u r e s are a r e oriented o r i e n t e d at a t aa high h igh angle a n g l e to t o foliation f o l i a t i o n and and cut c u t all a l lof o fthe t h eintrusive i n t r u s i v phases e phases (Page, 1 9 8 4 ) . Mineralization M i n e r a l i z a t i o n consisting c o n s i s t i n gof o fmolybdenite molybdenite ( P a g e , 1984). with w i t h lesser l e s s e r pyrite p y r i t e is is preferentially p r e f e r e n t i a l l y associated a s s o c i a t e d with with late l a t e feldspar f e l d s p a r and and muscovite—rich m u s c o v i t e - r i c h intrusive i n t r u s i v e phases. phases. Molybdenite is present p r e s e n t as a s scattered s c a t t e r e d flakes f l a k e s in in M o l y b d e n i t e is muscovite—bearing and vvein m u s c o v i t e - b e a r i n g p pegmatites e g m a t i t e s and e i n quartz. q u a r t z . Pyrite Pyrite and and muscovite m u s c o v i t e are a r e common common aassociates s s o c i a t e s of o f molybdenite m o l y b d e n i t e and and rare r a r e magnetite, m a g n e t i t e , bismuthinite b i s m u t h i n i t eand a n dtourmaliri,e t o u r m a l i n e have h a v e been been reported. reported. The most recent r e c e n t development d e v e l o p m e n t on o n this t h i s property p r o p e r t y has has The most resulted r e s u l t e d in i n aa published p u b l i s h e d reserve r e s e r v e estimate e s t i m a t e of of 14,300,000 14,300,000 tons . 0 8 %M0S2. MoS2. t o n s grading g r a d i n g .08% e a s t w a r d for f o r 8.6 8.6 Return t o Kathlyn K a t h l y n Lake Lake access a c c e s s road r o a d and R e t u r n to and continue c o n t i n u e eastward 72. Turn Turn right right km w i t h Highway Highway 72. km (5.4 (5.4 miles) m i l e s ) to t o the t h e intersection i n t e r s e c t i o n with �+ + I' + + + + + + + + + •_I__ LATERAL LAKE AREA '-. tz'_;l.. I + + + + + ÷ + + + + + + + + ÷ + + + + + -.—-— + + ++ + + ++ + ++++++ Stop 1 +++++ +++ + +. + + + + + + , 7 'I,— 1+ +1 adit after Page 1984 ' \' —JI' _\ —I I I—. rocks \.> \/ EJ metavolcanic sedimentary rocks granodiorite . Mo, Py occurrence I' powerline Lake Area. Figure 5 Generalized Geology of the Lateral '-I + + '+++++++ +++++++++ ++++++++++ +++++++++++++ ++++++++++++ +++++++++ _,ç-I/ ,_- v—' H �183 ( s o u t h ) and and proceed p r o c e e d 2.7 2 . 7 km km (1.7 ( 1 . 7 miles) miles) to t o the t h e Goldiund G o l d l u n d Mine Mine (south) access road. ( w e s t ) and a n d proceed p r o c e e d along a l o n g this t h i s road road a c c e s s r o a d . Turn right r i g h t (west) approximately km (1.5 ( 1 . 5 miles) miles) to t o the t h e mine. mine. a p p r o x i m a t e l y 2.4 2. 4 km STOP 13: GOLDLUND GOLDLUND MINE MINE STOP 13: The The G o l d l u n d ~ ~ is i t o p e r a t e d by Campbell Goldl ndposit is operated by Campbell Resources and ccontains R e s o u r c e s LLtd. t d . and o n t a i n s ppublishes u b l i s h e s reserves r e s e r v e s of of 600,000 .20o oz/ton o tthe h e 8800 0 0 f ft. t . level. level. 6 0 0 , 0 0 0 t tons o n s ggrading r a d i n g .20 z / t o n t to It I t is is hosted h o s t e d by aa tabular t a b u l a r northeasterly n o r t h e a s t e r l y striking s t r i k i n g body body of of is grossly g r o s s l y concordant concordant t r o n d h j e m i t e which intrudes i n t r u d e s and a n d is trondhjemite with w i t h mixed mixed mafic m a f i c to t o felsic f e l s i cmetavolcanic m e t a v o l c a n i c rocks r o c k s (Figure (Figure . 6). 6 ) AA large l a r g ediscordant d i s c o r d a n tbody bodycomposed composed oof f quartz q u a r t z and and feldspar f e l d s p a r porphyry p o r p h y r y occurs o c c u r s in i nthe t h emine m i n earea a r e and a andnumerous numerous dikes d i k e s of o f similar s i m i l a rcomposition c o m p o s i t i o n cut c u t the t h etrondhjemite t r o n d h j e m i t e and and the t h e volcanic v o l c a n i c rocks. r o c k s . The The ore ore zones z o n e s comprise c o m p r i s e cclusters l u s t e r s of of enechelon enechelon extensional e x t e n s i o n a l veins v e i n s which which transect t r a n s e c t the the trondhjemite: these trondhjemite: t h e s e sstrike t r i k e northerly n o r t h e r l y and and dip d i p at at moderate The m o d e r a t e angles a n g l e s to t o the t h e west. west. The v e i n s a r e f r a c t i o n s o f an a n inch i n c h to t o one o n e foot f o o t wide w i d e and and occur o c c u r at a t spacings s p a c i n g s of o f inches inches to t o several s e v e r a l feet. feet. v e i n s are a r e composed composed primarily p r i m a r i l y of o f quartz, quartz, The veins ankerite a n k e r i t e and p y r i t e with minor a c t i n o l i t e , b i o t i t e , tourmaline, t o u r m a l i n e , scheelite, scheel i t e , sphalerite, s p h a l e r i t e , galena, g a l e n a , chalcopyrite, chalcopyrite, pyrrhotite, i l r n e n i t e aand n d nnativegold. a t i v e g o l d . Most Most p y r r h o t i t e , tellurides, t e l l u r i d e s , ilmenite veins haloes v e i n s are a r e enveloped e n v e l o p e d by by "bleached" " b l e a c h e d " alteration a 1 t e r a t i o n haloes within w i t h i n trondhjemite: t r o n d h j emite: these t h e s e are a r e characterized c h a r a c t e r i z e d by by enrichments e n r i c h m e n t s of o f ankerite, a n k e r i t e , albite a l b i t e and and pyrite p y r i t e but b u t their their width correlate w i d t h and a n d intensity i n t e n s i t y of o f alteration a l t e r a t i o n does d o e s not n o t correlate directly d i r e c t l y with w i t h gold g o l d contents. contents. The The mine m i n e has h a s been been developed d e v e l o p e d by b y conventional conventional underground u n d e r g r o u n d stoping, s t o p i n g ,aa decline d e c l i n efrom f r o m surface s u r f a c e and and open open cuts c u t s at a t surface. s u r f a c e . Depending, Depending, on o n the t h e status s t a t u s of o f mining mining operations o p e r a t i o n s at a t the t h e time time of of the t h e field f i e l d trip, t r i p , one o n e or or more more areas a r e a s will w i l l be b e visited v i s i t e dtot oexamine e x a m i n e the t h e host h o s t trondhjemite, trondhjemite, porphyry p o r p h y r y ddikes, i k e s , qquartz u a r t z vveins e i n s and and aalteration 1 t e r a t i o n haloes. haloes. Return R e t u r n to t o Highway Highway 72 7 2 and a n d proceed p r o c e e d south s o u t h to t o the t h e intersection i n t e r s e c t i o n with with Highway Highway 17 17 to t o Kenora Kenora via v i a Dryden Dryden and and Vermilion V e r m i l i o n Bay. Bay. veins are fractions of and pyrite with minor actinolite, biotite, �Figure : Generalized Geology of the Goldiund Mine Area. — V' % '.1 shaft dump after Page 1984 zone pit decline J porphyry !I+ +1 trondhjemite ,"I--'-,'I metavolcanic rocks — �185 REF REF ERENC ERENCES ES Bartlett, B a r t l e t t , J.R., J. R., 1978, 1 9 7 8 , Metamorphic M e t a m o r p h i c trends t r e n d s in i n the t h e metasedimentary metasedimentary rocks r o c k s north n o r t h of o f Eagle E a g l e Lake, L a k e , Ontario; O n t a r i o ; unpublished u n p u b l i s h e d B.Sc. B.Sc. thesis, t h e s is, University U n i v e r s i t y of o f Western W e s t e r n Ontario, O n t a r i o , 73p. 73p. Blackburn, C. E. and and Hailstone, H a i l s t o n e , M.R., M.R., 1983, 1983, 1982, 1982, Report R e p o r t of o f the the B l a c k b u r n , C.E. Kenora p. 1-1 9 in i n Report R e p o r t of o f Activities Activities Kenora Resident R e s i d e n t Geologist; G e o l o g i s t ; p.1—19 Regional R e g i o n a l and a n d Resident R e s i d e n t Geologists, G e o l o g i s t s , 1982, 1982, edited e d i t e d by b y C.R. C.R. Kustra, O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 107, 107, Kus t r a , Ontario 211. 21 1. Blackburn, 1983, D.A., 1 9 8 3 , Gold Gold deposits d e p o s i t s in in B l a c k b u r n , C.E., C.E., and a n d Janes, J a n e s , D.A., N o r t h w e s t e r n Ontario; O n t a r i o ; p.194—210 p . 194-210 in i n The The Geology G e o l o g y of o f Gold Gold in in Northwestern Ontario; e d . A.C. A.C. Colvine; C o l v i n e ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey O n t a r i o ; ed. Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 10, 278p. 278p. Breaks, B r e a k s , F.W., F.W., 1980, 1 9 8 0 , Lithophile L i t h o p h i l e Mineralization M i n e r a l i z a t i o n in i n Northwestern Northwestern Ontario: Rare Element E l e m e n t Granitoid G r a n i t o i d Pegmatites; P e g m a t i t e s ; p.5—9 p .5-9 in i n Summary Summary O n t a r i o : Rare of o f Field F i e l d Work, Work, 1980, 1 9 8 0 , by by the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, edited e d i t e d by b y V.G. V.G. Mime, M i l n e , O.L. 0. L. White, White, R.B. R.B. Barlow, B a r l o w , J.A. J. A. bertson, R o b e r t s o nand , a nA.C. d A.C. Colvine, C o l v i n e Ontario , O n t a r i oGeological G e o l o g i c a lSurvey, Survey, Miscellaneous M i s c e l l a n e o u s Paper P a p e r 96, 9 6 , 201p. 201p. Breaks, rare-metal pegmatites p e g m a t i t e s of o f the the B r e a k s , F.W., F.W., 1982, 1 9 8 2 , Metamorphism Metamorphism and a n d rare—metal Dryden D r y d e n area; a r e a ; p.4—12 p.4-12 in i n Stratigraphy S t r a t i g r a p h y and and Structure S t r u c t u r e of o f the the Western Wes t e r n Wabigoon Wabigoon Sub?ovince s u b p r o v i n c e and a n d its i t s margins, m a r g i n s , Northwestern Northwestern Ontario O n t a r i o ed. e d . C.E. C. E. Blackburn; B l a c k b u r n ; Geological G e o l o g i c a l Association A s s o c i a t i o n of of Canada, Field Trip guidebook No.3, Winnipeg. C a n a d a , F i e l d T r i p g u i d e b o o k No. 3, Winnipeg. Breaks, G h o s t Lake Lake area, a r e a , District D i s t r i c t of of B r e a k s , F.W., F.W., 1984, 1984, Eagle E a g l e River R i v e r — Ghost Kenora; Kenora; Ontariä O n t a r i o Geological Geological Survey, S u r v e y , Preliminary P r e l i m i n a r yMap Map P.2623, P. 2 6 2 3 , Geol. Geol. Ser., S e r . , scale scale 1 1 in i n to t o 1/2 1/2 mi. mi. Breaks, B r e a k s , F.W., F.W. , in i nprep., p r e p . ,Geology Geologyand a n dGeochemistry G e o c h e m i s t r y of o f the t h eDryden Dryden Pegmatite D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Geological Geological P e g m a t i t e Field, F i e l d , District Survey S u r v e y Geological Geological Report. Report. Breaks, B r e a k s , F.W., F.W., Bond, Bond, W.D., W.D., Westerman, W e s t e r m a n , C.J. C . J . and a n d Harris, Harris, N., N . , 1976a, 1976a, Operation O p e r a t i o n Kenora—Ear Kenora-Ear Falls, F a l l s , Dryden—Vermilion D r y d e n - V e r m i l i o n Bay Bay Sheet, Sheet, District D i s t r i c t of o f Kenora; K e n o r a ; Ontario O n t a r i o Division D i v i s i o n of o f Mines, M i n e s , Preliminary Preliminary Map Map p.1203, p . 1 2 0 3 , Geol. G e o l . Ser., S e r . , scale s c a l e 1:63,360 1:63,360 or or 1 inch i n c h to t o 1 mile. mile. Geology G e o l o g y 1975. 1975. Breaks, Bond, W.D., W. D. , Harris, Harris, N., N., Westerman, Wes t e n n a n , C.J. C. J . and and B r e a k s , F.W., F.W. , Bond, Desnoyers, D e s n o y e r s ,D.W., D.W., 1976b, 1 9 7 6 b , Operation O p e r a t i o n Kenora—Ear Kenora-Ear Falls, Falls, D i s t r i c t of o f Kenora; Kenora; Ontario Ontario S a n d y b e a c h - R o u t e Lakes Lakes Sheet, S h e e t , District Sandybeach—Rute D i v i s i o n of o f Mines, M i n e s , Preliminary P r e l i m i n a r y Map Map p.1204, p . 1204, Geol. G e o l . Ser., S e r . , scale scale Division 1:63,360 1:6 3,360 of o f 1 inch i n c h to t o1 1 mile. mile. Geology Geology 1975. 197 5. Breaks, B r e a k s , F.W., F.W., Bond, Bond, W.D., W.D., and and Stone, S t o n e , Denver, D e n v e r , 1978, 1978, Preliminary Preliminary GeologicaL G e o l o g i c a l Synthesis S y n t h e s i s of o f the t h e English Engl i s h River R i v e r Subprovince, Subprov i n c e , Northwestern Ontario and a n d its its Bearing B e a r i n g Upon Upon Mineral Mineral N o r t h w e s t e r n Ontario E x p l o r a t i o n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Paper Paper Exploration; 72, 7 2 , 54p. 54p. Accompanied Accompanied by b y Map Mapp.1972, p . 1972, Scale S c a l e1:253,440. 1: 2 5 3 , 4 4 0 . Cerny, C e r n y , P., P., 1982, 1 9 8 2 , Anatomy Anatomy and a n d classification c l a s s i f i c a t i o n of o f granitic granitic p e g m a t i t e s ; p . 1-39 i n S h o r t C o u r s e i n G r a n i t i c Pegmatites P e g m a t i t e s in in pegmatites; p.1—39 in Short Course in Granitic S c i e n c e and a n d Industry; ~ n d u s t r y ; ed. e d . P. P. Cerny; C e r n y ; Mineralogical Mineralogical Science A s s o c i a t i o n of o f Canada, C a n a d a , Short S h o r t Course C o u r s e Handbook, Handbook, V.8. V. 8. Association Colvine, C o l v i n e , A.C. A.C. and a n d McCarter, McCarter, P., P., 1977, 1 9 7 7 , Geology Geology and a n d mineralization mineralization of o f the t h e Lateral L a t e r a l Lake Lake stock, s t o c k , District D i s t r i c t of o f Kenora; K e n o r a ; p.205—208 p.205-208 ini n Summary Summary of o f Fieldwork, F i e l d w o r k , 1977, 1 9 7 7 , by by the t h e Geological G e o l o g i c a l Branch, B r a n c h , ed. ed. V.G. V. G. Mime M i l n eete tal., a 1 ,Ontario O n t a r i oGeological G e o l o g i c a lSurvey, S u r v e y , Miscellaneous Miscellaneous Paper P a p e r 75. 75. - - 1 1 . 1 �186 C o l v i n e , A.C., A.C., A.J., C h e r r y , M.E., M.E., Durocher, D u r o c h e r , N.E., M.E., Fyon, Fyon, Colvine, Andrews, A.J., Cherry, A.J., L a v i g n e , M.J. M . J . Jr., J r . , Macdonald, Macdonald, A.J., A . J . , Marinont, Marmont, S., S., A.J., Lavigne, P o u l s e n , rCH., K.H., S p r i n g e r , J.S. J.S. and and Troop, Troop, D.G., D.G., 1984, An An Poulsen, Springer, 1984, i n t e g r a t e d model for f o r the t h e origin o r i g i n of o f Archean Archean lode l o d e gold gold integrated d e p o s i t s ; Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Open Open File F i l e Report R e p o r t 5524, 5524, deposits; 84p. E.W., 1975, Economic Economic Geology and and mineralogy m i n e r a l o g y of o f petalite petalite H e i n r i c h , E.W., Heinrich, 1975, and a n d spodumene spod umene pegmatites; p e g m a t i t e s ; Indian I n d i a n Journal J o u r n a l of o f Earth E a r t h Sciences, Sciences, V.2, V.2, No.1, NO.1, p.19—29. p.19-29. Hutchinson, R.W., 1955, Regional Zonation of PPegmatites 1ss 1955, R egional Z o n a t i o n of e g m a t i t e s nnear e a r Ross H u t c h i n s o n , R.W., Lake, Mackenzie, Northwest NorthwestTrritories; Lake, District D i s t r i c t oof f Mackenzie, erritories; Geological G e o l o g i c a l Survey Survey of o f Canada, Canada, Bulletin B u l l e t i n 34. 3 4. McCarter, p., M c C a r t e r , P., 1980, 1980, Geology and mineralization m i n e r a l i z a t i o n of of the t h e Lateral Lateral Stock, D i s t r i c t of o f Kenora, Kenora, Northwestern N o r t h w e s t e r n Ontario; O n t a r i o ; unpublished unpublished S t o c k , District M.Sc. M.Sc. thesis, t h e s i s , Oregon Oregon University, U n i v e r s i t y , 141p. 141p. Moorhouse, 1939, W.W., 1939, Geology Geology of of the t h e Eagle Eagle Lake Lake Area; Area; Ontario Ontario Moorhouse, W.W., Department Department of o f Mines, Mines, Vol.48, Vol.48, pt.4, p t . 4 , p.1—31. p. 1-31. Accompanied by by Accompanied Map i n c h to t o 1 mile. Map No.48d, No.48d, Scale S c a l e 1 inch Mulligan, M u l l i g a n , Robert, R o b e r t , 1965, 1965, Geology Geology of o f Canadian C a n a d i a n Lithium L i t h i u m Deposits; Deposits ; Geological G e o l o g i c a l Survey Survey of o f Canada Canada Economic Economic Geology Geology Report Report 21. 2 1. Ovchinnikov, 1976, Ovchinnikov ,L.N., L. N., 1976, Lithogeochemical L i t h o g e o c h e m i c a l Methods Methods for f o r Prospecting Prospecting Rare—Element Rare-Element Pegmatites; P e g m a t i t e s ; Acad. Acad. Sci. S c i . U.S.S.R. U. S. S. R. Moscow, Moscow, 79pp. 79pp. Page, 1984, R.O., 1984, Geology of o f the t h e Lateral L a t e r a l Lake Lake Area, A r e a , District District Page, R.O., of of Kenora; Kenora; Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Open Open File F i l e Report Report 5518, 551 8, 17 5p. 175p. Pryslak, P r y s l a k , A.P., A. P., 1981, 198 1 , Rafter R a f t e rProject P r o j e c— t F a i r s e r v i c e option o p t i o n No.1, No. 1 , Fairservice unpublished Files u n p u b l i s h e d rreport; e p o r t ; Assessment Assessment F i l e s Research R e s e a r c h Office, Office, Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y , Toronto. Toronto. S a t t e r l y , J. , 1941, 194 1, Geology Geology of o f the t h eDryden—Wabigoon Dryden-Wabigoon aarea, r e a , Kenora Kenora District; D i s t r i c t ; Ontario O n t a r i o Department Department of o f Mines, Mines , Annual Annual Report R e p o r t for for 1941; 1941; v.50, v.50, pt.2, p t . 2 , p.1—57. p . 1-57. Accompanied by Map 5 0 e , s c ale Accompanied by Map 50e, scale 1:63,360 1 ~ 6 3 , 3 6 0or o r 11 inch i n c h to t o11 mile. Storey, S t o r e y , C.C., C.C., 1983, 1983, Preliminary P r e l i m i n a r y Report R e p o r t of of the t h e Building B u i l d i n g and and Ornamental Stone Ornamental S t o n e Inventory, I n v e n t o r y , Kenora Kenora and a n d Rainy Rainy River River Districts; Geological Districts Ontario ; Ontario G e o l o g i c a lSurvey S u r v e yOpen Open File F i l eReport R e p o r t 5446, 5 446, 143p., 14 3 p . , 20 20 tables t a b l e s and a n d 37 3 7 figures. figures. Streckeisen, S t r e c k e i s e n , A., A., 1976, 1976, To To each e a c h plutoriic p l u t o n i c rrock o c k its its proper p r o p e r name; name; Earth E a r t h Science S c i e n c e Reviews, Reviews, v.12, v. 12, p.1—33. p. 1-3 3. Trowell, T r o w e l l , N.F., N.F., Blackburn, B l a c k b u r n , C.E. C.E. and and Edwards, Edwards, G.R., G.R., 1980, 1980, P r e l i m i n a r y geological g e o l o g i c a l synthesis s y n t h e s i s of of the t h e Savant S a v a n t Lake—Crow Lake-Crow Preliminary Lake metavolcanic—metasedimentary m e t a v o l c a n i c - m e t a s e d i m e n t a r y belt, be1 t , Northwestern N o r t h w e s t e r n Ontario Ontario Lake and a n d its i t s bearing b e a r i n g upon upon mineral m i n e r a l exploration; e x p l o r a t i o n ; Ontario O n t a r i o Geological Geological Survey, S u r v e y , Miscellaneous M i s c e l l a n e o u s Paper P a p e r 89, 8 9 , 30p. 3Op. Varlanioff, N., 1972, 1972, C Central and W West African e n t r a l and est A f r i c a n rare r a r e metal m e t a l granitic granitic V a r l a m o f f , N., pegmatites, p e g m a t i t e s , related r e l a t e d aplites, a p l i t e s , quartz q u a r t z veins v e i n s and and mineral mineral deposits; M i n e r a l l i u m Deposita, Depos i t a , v.7, v. 7, p.202—216. p . 202-21 6. d e p o s its ;Mineralliuni Wallace, H., 1978, 1978, Geology of o f the t h e Opikeigen O p i k e i g e n Lake Lake Area, A r e a , District District W a l l a c e , H., of of Kenora Kenora (Patricia ( P a t r i c i a Portion); P o r t i o n ) ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Report R e p o r t 185, 185, 58p. 58p. Accompanied Accompanied by by Map Map 2379, 2379, scale s c a l e 1 inch i n c h to to 1/2 1/2 mile. mile. 1 1 - Satterly, J., 1 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1985 Description An account of the resource Institute on Lake Superior Geology. Kenora, Ontario. May 6-11, 1985. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1985 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/447a6860028737df745d7974761e2c60.pdf b1fa75cb16513474e44fbc86c5e78652 PDF Text Text ������������������������������������������������������������������������������������������������������������������ https://digitalcollections.lakeheadu.ca/files/original/a7b558dc93da691333f1e1949b8696c9.pdf 25248eb71f780870062be75615a68e26 PDF Text Text ����������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/9fc774d21baf36760c0b5db050d7509e.pdf 65fb153ecfed13c8786f579e8d9310da PDF Text Text ���The following map was omitted from the printed field guide and included as a hand out during the meeting. It has been included here in the PDF to address that omission. The file was added on May 29, 2019. ������������������������������������������������������������ Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1986 Description An account of the resource Institute on Lake Superior Geology. Wisconsin Rapids, Wisconsin. April 29-May 4, 1986. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1986 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/5112d4ee1c22ab4b1871f1e3264eeb66.pdf 46f792ea23d8305833e7bae3ed9a151f PDF Text Text r IL 1 A Fl Ti Institute on Lake Lake Superior Geology N PROCEEDINGS PROCEEDINGS and ABSTRACTS ABSTRACTS Volume Volume 33, Part Part 11 HI 33rd 33rd Annual Annual Meeting Meeting May May 12 and 13, 13, 1987 1887 I I I p r p. r t r 'It Wawa, Ontario Ontario �- ERRATA ERRATA apologies to Explorations and David Baxter. - with with.apologies to Muscocho Muscocho .. .~-- Explorations and David Baxter. .. — . . .. .. . . . ~ ~ ..~ , . ... ~ ~~~. - last last line line should should read: read: page page xii xii — - Muscocho Muscocho Explorations Explorations Ltd. Ltd. (Toronto) (Toronto) — coffee coffee breaks breaks - lines lines 5—6, 5-6, sentence sentence omitted; omitted; lines lines should should read: read: page page 77 — . ~. . .... ..... ~ - .,- - . .. - . ~ . are are quartz quartz and and carbonate, carbonate, with with lesser lesser amounts amounts of of chlorite. chlorite. The The chief chief accessory accessory sulphide sulphide mineral mineral is is pyrite pyrite with with lesser lesser amounts amounts of of pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, and and arsenopyrite. arsenopyrite. �INSTITUTE on on INSTITUTE LAKE LAKE PROCEEDINGS PROCEEDINGS GEOLOGY G EOLOGY and ABSTRACTS ABSTRACTS and 33, 33, Volume Volume SUPERIOR SUPERIOR Part Part 1 1 MEETING 33rd ANNUAL ANNUAL MEETING 33rd WAWA, WAWA, May May ONTARIO ONTARIO 12 and 12 and 13, 13, 1987 1987 Organizedbybythe theOntario OntarioMMinistry off Organized inistry o Northern Development Northern Development and and Mines: Mines : Wawa ResidentGeologist Geologist OOffice W awa Resident ffice and tthe and he Ontario Geological Ontario Geological Survey Survey ProgramChairmen Chairmenand andEditors: Editors: Program E.D. Frey E.D. Frey and and R.P. R.P. Sage Sage Vol. 33, Proceedings and and Abstracts Abstracts Vol. 33, Part Part1:1:Proceedings Part 2: Wawa Gold Field Part 2: Wawa Gold F i e l d TTrip rip Part 3: 3: Michipicoten Stratigraphy FField Michipicoten Iron I r o n Formation Formation Stratigraphy i e l d Trip Trip Part Part 4: Hemlo Gold Field Trip Part 4: Hem10 Gold F i e l d T r i p Part 5: Structural Zone 5: Kapuskasing Kapuskasing Structural Zone FField i e l d TTrip rip Part �TABLE TABLE OF OF CONTENTS CONTENTS .............................. Constitution Lake Superior Constitution of of the theInstitute I n s t i t u ton e on Lake SuperiorGeology Geology ........... By—Laws By-Laws o f oft hthe e I Institute n s t i t u t eon onLake LakeSuperior SuperiorGeology Geology ................ Sam Goldich Medal: delines Sam Goldich Medal :Award Award Gui Guide1 ines and and Recipients Recipients ............... Student Student Travel TravelAward Award ............................................. Institutes I n s t i t u t e sononLake LakeSuperior SuperiorGeology Geology ii iii iv iv v V vi vi ...................................... Vii vii Board ix Board ooff Directors Directors ............................................... Local Local Committee Committee ................................................ Best Best Student StudentPaper PaperCommittee Committee ..................................... Goldich GoldichMedal Medal Committee Committee .......................................... Field F i e l d Trip T r i pLeaders Leaders ............................................... Technical xi Technical Session SessionChairmen Chairmen ....................................... xi Goldich xi (Soldich Medal Medal Recipient Recipient .......................................... xi Banquet Speaker xi Speaker .................................................. xi Acknowledgements ................................................. xii Technical TechnicalProgram Program ................................................ xiii x i ii Abstracts Abstracts ........................................................ xxii xxi i Report Report of o fthe t h e1986 1986Chairman Chairman ix Y x x xA xi Acknowledgements i �U INSTITUTES ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTES NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 DATE - PLACE - DATE PLACE MMinneapolis, i nneapol i s ,MN MN Houghton, Houghton, MI MI East Lansing, East Lansing, MI MI Duluth, Duluth, MN MN Minneapolis, MN MN Minneapolis, Madison, Madison, WI MI Port Arthur Port Arthur (Thunder (Thunder Bay), Bay), Ont. Ont. Houghton, MI Houghton, M I Duluth, MN Duluth, MN Ishpeming, MI Ishpaning, MI St. Paul, St. Paul, MN MN Sault Ste. Sault Ste. Marie, Marie, MI MI East Lansing, East Lansing, MI MI Superior, WI Superior, WI Oshkosh, WI Oshkosh, WI Thunder Bay, Bay, Ont. Thunder Ont. Duluth, MN Duluth, MN Houghton, MI Houghton, MI Madison, WI Madison, WI Sault Ste. Sault Ste. Marie, Marie, Ont. Ont. Marquette, MI Marquette, M I St. Paul, St. Paul ,MN MN Thunder Bay, Ont. Thunder Bay, Ont. Milwaukee, WI Milwaukee, WI Duluth, MN MN Eau Claire, Claire, WI Eau WI East Lansing, East Lansing, MI MI IInternational n t e r n a t i o n a l Falls, Fa1l s ,MN MN Houghton, MI Houghton, M I Wausau, WI Wausau, WI Kenora, Ont. Kenora, Ont. Wisconsin Rapids, Wisconsin Rapids, WI WI Wawa, Ont. Wawa, Ont. Marquette,MMI I ((tentative) tentative) Marquette, Duluth, MN MN ((tentative) tentative) Duluth, 1955 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 j U U U U -ii- �CONSTITUTIONOF OF INSTITUTE ON SUPERIOR GEOLOGY CONSTITUTION ON LAKE LAKE SUPERIOR GEOLOGY Article A r t i c l e II Name of the The name of t h e organization shall s h a l l be the t h e "Institute " I n s t i t u t e on on Lake Lake Superior Superior Geology."" Geology. Article A r t i c l e II I1 Objectives Objectives The objectives o b j e c t i v e s of of this t h i s organization are: are: A. A. BB.. C. C. Article I11 A r t i c l e III To provide a means means whereby whereby geologists g e o l o g i s t s in in the t h e Great Great Lakes Lakes region region may exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To promote promote b better To e t t e r understanding understanding of of the t h e geology geology of of the t h e Lake Lake Superior Superior region. region. To plan and conduct geological field f i e l d trips. trips. Status No part of the N o p a r t of t h e income income of of the t h e organization organization shall s h a l l inure Inure to t o the t h e benefit b e n e f i t of of any member or I n the t h e event of of dissolution d i s s o l u t i o n the t h e assets a s s e t s of of the the o r individual. individual. In organization shall s h a l l be distributed d i s t r i b u t e d to to (some tax t a xfree f r organization). e e organization). [To avoid Federal Federal and and S State [To avoid t a t e income income taxes, taxes, the t h e organization organization should should be not %on-profit ."I be n o t only only "scientific" " s c i e n t i f i c " or o r "educational" "educational" but b u t also a l s o "non—profit."] Minn. Stat. Anno. 290.01, Minn. S t a t . Anno. 290.01. subd. subd. 44 w vg ' 290.05(9) 290.05(9) 1954 s. 50l(c)(3) 501(c)(3) 1954 Internal I n t e r n a l Revenue Code Code s. Article IV A r t i c l e IV Membership Membership The membership of of the t h e organization organization shall s h a l l consist c o n s i s t of of the t h e board board of of directors. directors. Any permitted to Any geologist geologist interested i n t e r e s t e d shall s h a l l be permitted t o aattend t t e n d and pparticipate a r t i c i p a t e iin n t h e annual annual meetings. meetings. and vote at a t the Article A r t i c l e VV pMeetings eetings The organization shall s h a l l meet once once aa year, year, preferably p r e f e r a b l y during during the t h e month month of of April. April. The place and exact date d a t e of each each meeting meeting will w i l l be be designated designated by by tthe h e board of of directors. directors. Article A r t i c l e VI VI Ilirectors Directors The The board board of of directors d i r e c t o r s shall s h a l l consist c o n s i s t of of the t h e Chairman, Chairman, Secretary—Treasurer Secretary-Treasurer past l a s t three three p a s t Chairmen; but if i f the t h e board board should should at a t any any time time conconand tthe h e last of less reason of of unwillingness unwillingness or o r inability inability sist of less than five f i v e persons, persons, by reason of any of of the of t h e above persons to t o serve s e r v e as a s directors, d i r e c t o r s , the t h e vacancies vacancies on on the the may board m y be filled f i l l e d by the t h e annual meeting meeting so s o as a s to t o bring b r i n g the t h e membership membership of the t o five f i v e members. members. of t h e board up to Article A r t i c l e VII Officers O fficers of tthis organizition be aa Chairman and aa SecretarySecretary— The officers o f f i c e r s of his ~ r g a n i z ~ t i osshall nh a l l be Treasurer. A. A. B. B. Article VIII A r t i c l e VIII The Chairman shall shall be elected e l e c t e d each each year by by the t h e board board of of directors, directors, who shall t h e wishes of of any group that t h a t may s h a l l give due consideration consideration to t o the His be promoting the i s term of office o f f i c e as a s Chairman Chairman t h e next next annual annual meeting. meeting. H will of tthe annual meeting meeting over over which which he he prepreh e cclose l o s e of h e annual w i l l terminate aatt tthe sides orr when h his will i l l then then sides o i s successor successor shall s h a l l have have been been appointed, appointed. He w serve for t h r e e years y e a r s as a s aa member member of of the t h e board board of of directors. directors. f o r a period of three The Secretary—Treasurer Secretary-Treasurer shall s h a l l be elected e l e c t e d at a t the t h e annual annual meeting. meeting. His His term of of o office s h a l l be two two years y e a r s or o r until u n t i l his h i s successor successor shall s h a l l have have f f i c e shall been appointed. Amendments Amendments may be be amended by by aa majority majority vvote of those those persons parsons who who This cconstitution o n s t i t u t i o n may o t e of aare r e personally present at, a t , participating p a r t i c i p a t i n g in, in, and and voting v o t i n g at a t any any annual annual meeting meatins of of the the organization. organization. —iii— �BY-lAWS BY-LAWS I. I. Duties of Duties of the t h e Officers O f f i c e r s and and Directors Directors A. A. It sshall It h a l l be the t h e dutyof dutyof the the Chairman Chairman to: to: Preside 1. 1. P r e s i d e at a t the t h e annual annual meeting. meeting. needed for of tthe 2. Appoint all a l l committees needed f o r tthe h e organization of he 2. annual annual meeting. meeting. 3. 3. Assume complete responsibility r e s p o n s i b i l i t y for f o r the t h e organization and financing of of the t h e annual annual meeting over over which which he he presides. presides. B. It It shall s h a l l be the t h e duty duty of of the t h e Secretary—Treasurer Secretary-Treasurer to: to: 1. 1. Keep accurate accurate attendance attendance records records of of all a l l annual annual meetings. meetings. Keep a accurate records of of aall meetings o of, and correspondence correspondence 2. 2. Keep c c u r a t e records l l meetings f , and between, the between, t h e board of of director8. directors. meetings 3. 3. Hold aall l l fwids funds that t h a t may accure aass pprofits r o f i t s from annual meetings or o r field f i e l d trips t r i p s and and to t o make make these these funds funds available a v a i l a b l e for f o r the the organization and operation of organization of future f u t u r e meetings as a s required. required. C. C. Li It sshall h a l l be the t h e duty of of the t h e board of of directors d i r e c t o r s to t o plan p l a n locations locations of annual meetings and to and financing of t o advise on tthe h e organization and of all of a l l meetings. meetings. m ii. 1 1. Dues and Expenses 1-4 1. 1. There shall s h a l l be no regular r e g u l a r membership membership dues. dues. 2. 2. Registration R e g i s t r a t i o n fees f e e s for f o r the t h e annual meetings shall s h a l l be determined by the in consultation c o n s u l t a t i o n with with the t h e board board of of directors. directors. t h e Chairman in It is sstrong]. t r o n g l y recommended recommended that t h a t these t h e s e be be kept kept at a t aa minimum minimum to to encourage attendance of graduate graduate students. students. III. 1 11. Rules or o r Order Order The rules Robert's Rules of of Order shall rules contained in Robert's ahall govern this this organization in i n all a l l cases cases to t o which which they they are a r e applicable. applicable. IV. IV. Amendments Aoendments These bee amended by a majority v vote These by—laws by-laws may b o t e of of those t h o s e persons who personally present present aat, voting aatt any 6annual in, and voting nUWil aare r e personally t , pparticipating a r t i c i p a t i n g in, meeting of of the t h e organization; organization; provided that t h a t such modifications shall shall not orr subsequently n o t conflict c o n f l i c t with the t h e constitution c o n s t i t u t i o n as a s presently p r e s e n t l y adopted o amended. V 4 1j -iv- �Preamble Preamble SAM GOLDICH SAM GOLDICH MEDAL MEDAL The The IInstitute n s t i t u t eononLake LakeSuperior SuperiorGeology Geology was was born born on on or o r around around 1955, 1955, as as documented by the fact that the 27th annual meeting will be held i n1981. 1981. documented by t h e f a c t t h a t the 27th annual meeting w i l l be held in TheI Institutes The n s t i t u t e s are are exemplary exemplary i nin ttheir h e i r continuing continuing objectives objectives of o f dealing dealing with those aspects of geology that are related geographically w i t h those aspects o f geology t h a t are r e l a t e d geographically to t o Lake Lake Superior; of the discussion discussion ooff subjects sponsoringf field Superior; o f encouraging encouraging the subjects and and sponsoring ield geologists from thet hacademia, w i l bring l b r i ntogether g together geologists from e academia,government government ttrips r i p swhich which will surveys, and and industry; industry; and informal but but surveys, and ooff maintaining maintaining an an exceedingly exceedingly informal highly effective mode of operation. h i g h l y e f f e c t i v e mode o f operation. Duringthe the course courseoof During f iits t s existence existence the t h e membership membership o f oft hthe e I nInstitute s t i t u t e (that (that is, those geologists who indicate an interest in the objectives i s , those geologists who i n d i c a t e an i n t e r e s t i n the objectives ooff the the I.L.S.G. by become aware I.L.S.G. by attending) attending) has has become aware o f of thethe f a cfact t t hthat a t c ecertain r t a i n oof f ttheir heir colleagues have made particularly noteworthy and meritorious contributions colleagues have made p a r t i c u l a r l y noteworthy and meritorious contributions to understandingoof 'Lake Superior" Superior" geology and i its t o the the improvement improvement oof f understanding f "Lake geology and ts mineral deposits. m i neral deposits. The exemplary exemplaryaward awardwas wasmade made I.L.S.G.t otoSam SamGoldich Goldichi nin1979 1979f ofor The by by I.L.S.G. r hhis is many contributions to the geology of the region extending over about many c o n t r i b u t i o n s t o t h e geology o f t h e region extending over about 50 50 years. years. Award Guide1 Guidelines Award ines Themedal medals hshall beawarded awarded annually Board Directors,I.L.S.G., I.L.S.G., 1) The 1) a l l be annually byby t h the e Board o f of Directors, to a geologist whose name is associated with substantial sustained interest t o a geologist whose name i s associated w i t h substantial sustained i n t e r e s t in, or in, o raamajor major contribution c o n t r i b u t i o nto, to,the t h geology e geologyofo the f theLake LakeSuperior SuperiorRegion. Region. 2) The The Board Boardoof Directors, I.L.S.G. thet hNominating 2) f Directors, I.L.S.G. shall s h a lappoint l appoint e NominatingCommittee. Committee. Their annual nominee will be voted on at the annual business The meeting. The Their annual nominee w i l l be voted on a t t h e annual business meeting. oneto serve iinitial n i t i a appointment l appointment will w i l lbe beofo three f t h r e emembers, members, one'to serve ffor o r three t h r e e years, years, one for for two, with one two, and and one one for f o rone one year, year, the t h emember member w i t h the t h e briefest b r i e f e sincumbency t incumbency After ttoo be be chairman. chairman. A f t e r the t h e first f i r s year t yearthe t h eBoard Board of o f Directors Directors shall s h a l l appoint appoint member servef ofor three years. w i lwill l serve r three years. IIn n the the aatt each each spring spring meeting meeting one one new new member whowho The Committee membership tthird h i r dyear year this t h i smember member shall s h a l l be be the thechairman. chairman. The membership shouldr reflect off should e f l e c t the t h e main main f fields i e l d s of o f interest i n t e r e s tand and geographic geographic ddistribution istribution o I.L.S.G. membership. I.L.S.G. membership. 3) The TheSoldich GoldichMedal MedalNominating Nominating Committee selectt hthe medalistand andwwill 3) Committee s h ashall l l select e medalist ill make its recommendation to the Board of Directors by November 1 of that make I t s reconmendation t o t h e Board o f Directors by November 1 o f t h a t year. year. 4) The The Board Boardoof Directors normally f Directors normally will w i l laccept acceptthe t h enominee nominee of o fthe t h eCommittee, Committee, 4) one medal wwill i l l inform informthe t h emedalist medalistimmediately, immediately,and andwill w i have l l have one medalengraved engraved appropriately appropriately for f o r presentation presentationata tthe theMay May meeting. meeting. It isi srecommended 5) It recommended t hthat a t t the h e IInstitute n s t i t u t eset setaside asideannually annuallyfrom fromwhatever whatever 5) sources, such funds as will be required to support the continuing costs ooff sources, such funds as w i l l be required t o support t h e continuing costs this award. t h i s award. April A p r i l 4, 4, 1981 1981 J. Kalliokoski J. K a l l iokoski (Chairman),. (Chairman), . Bill Fred Kehlenbeck, 8111Cannon, Cannon, Fred Kehlenbeck, Glenn Morey, Glenn Morey, Greg Mursky Greg RECIPIENTS RECIPIENTS 1979 Sam Goldich, 1981 1981Carl Carl Dutton, Dutton, 1982 1982 Ralph Ralph Marsden, 1984 Burton Burton Boyurn Sam Goldich, Marsden, 1984 Boyum 1979 1987 Henry H Halls 1984 Richard Ojakangas, 1986 G.B. Morey, 1985 Paul Sims, 1984 Richard Ojakangas, 1985 Paul Sims, 1986 G.B. Morey, 1987 Henry alls —1— �STUDENT STUDENT TRAVEL TRAVELAWARD AWARD The 1986 Board Boardoof The 1986 f DDirectors i r e c t o r s established e s t a b l i s h e d the t h eTUG ILSGStudent Student Travel TravelAward, Award, to a r c i p i t a t i o n at a t the t h e annual annual IInstitutes. n s t i t u t e s . The awards awards t o support support student student pparcipitation will be made from the accrued interest from a special w i l l be made from t h e accrued i n t e r e s t from a s p e c i a l fund fund set s e t up up for for this t h i spurpose. purpose. This This award award iis s intended intended tto o help h e l p defray d e f r a y some some oof f tthe h e direct direct travel t r a v e l costs c o s t s to t o the t h e Institute I n s t i t u t eand andincludes i n c l u d e s aa waiver waiver of o f registration r e g i s t r a t i o n fees, fees, but excludes expenses for meals, lodging, and field trip b u t excludes expenses f o r meals, lodging, and f i e l d t r i p rregistration. egistration. j j J The numberand ands isize i l l be be determined determined by by the t h e annual annual Chairman Chairman i in n consulconsulThe number z e wwill tation with the Secretary—Treasurer and will be announced at the t a t i o n w i t h t h e Secretary-Treasurer and w i l l be announced a t t h eannual annual banquet. banquet. The considered bybythe The ffollowing o l l o w i n g general general criteria c r i t e r i awill w i be l l be considered t h annual e annualChairman, Chairman, who is responsible for selection: who i s r e s p o n s i b l e f o r s e l e c t i o n : 1) The have aactive The aapplicants p p l i c a n t s must must have c t i v e resident r e s i d e n t (undergraduate (undergraduate or or graduate) students tstatus time graduate) student a t u s a tatt hthe e tim e o foft hthe e I nInstitute, s t i t u t e , ccertiertified f i e dby bythe t h edepartment department head. head. 2) 3) 4) Students whoa rare authoron oneeither an ooral Students who e t hthe e ssenior e n i o r author i t h e r an r a l or or poster paper will be given favored consideration. p o s t e r paper w i l l be g i v e n favored consideration. ItItisi sdesirable d e s i r a b l efor f o two r twooro more r more students students tto o jointly j o i n t l yrequest request travel t r a v e l assistance. assistance. iJ In I n general, general, ppriority r i o r i t y will w i l lbe begiven given to t o those those iin n the t h e Institute Institute region r e g i o n who who aare r e farthest f a r t h e s taway. away. 5) I yJ Each requests shall bemade made award request h a l l -be i ninw writing, r i t i n g , . tto o the the Each t travel r a v e l award annual Chairman, with an explanation of need, possible annual Chairman, w i t h an e x p l a n a t i o n o f need, p o s s i b l e author author status s t a t u s oorr other o t h e r ssignificant i g n i f i c a n t details. details. WI j I ME j -vi-J �—a 0> Cr mI- Coo Zr —I a' rn rID —I C-u =0 -I, -In, -10 rn Lii C) -C r GD rn Cr Cr Cr taco —. C 0. 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Cr = S Cr 0 r 1 C fl CD C.. - :5C —. -< 4fl (CZ0-CLa-u 0- — 0 0_CD V '-O)CDO 0(0 CE Cr C 0 —- CD 0) C J CL C 0- OrtCrtoO —t so= CI-"O)Ua WE 0)0 0CDI—IU)C-0)O) 00- 0 —- (0 0 CL I CD GitoGir Se Cr-n Oh Ci 0--k--CD OOiSc-tDi Di —. — S 'si CD '<r--rta0.V0-CU) fli—"(D 5(0 (0 01, Cr C- 0.0 — 0) 0 CrCD). CDSOhfrCr 0) — 0. L S — U)10CDV re Ot-tCD OS (0 0- = V i— nC mOan0) --t,CDC 5(0 0.% c-tfr'-CrOiCD O+0-I—CL 0 = • I—nCr tU)U)r0 Oh F--"2— U)OCr_C0_ COr p--(Dlt ct O"U)-OjCD (DO OCDCD c-p Gir • c-CD>c >C. — .EV1-->c 0 Cp--CDetO I-" 50i(D0t 0=9 CrU)fr- — • -1 rat0 GJ a.----0. C 0p--U)p--CDCDfl19C I I OI— CD (0 CD c i--rtOi c-p = ,c-CACD 0)OOhV - 0 COSCA 0- Or-jc-reI-c--rr(DP-EP(CWO- 0 CD—OCU) 0 OiSCn (Di--' 0 0.0 (Ii I—fiC—-rrC :rIrt00mP-. O- 0 CD >cCrCD0CLOh-r.--1 *, — Oh S — CD CD fr (00Th 90(0 CD(DOCDCDEP-V, p.-..tD-t V CC0P-CcZCrV0h CD-. 0.CDCDCD0hOt U)U)CD IO (CrCDVCDCDe+ C (0000CD U)aCDtCCc05wE PV QiP---C01rr. c-tp.—0-CV) 0.0 -, CCDCDrtflCDO-0 c-r Oh CD GD - 0) (DU) CD CA CD —0 CD E C P—i *' -rno(D-,r.--p-'--p-0) 0 (0 S i x t y papers were presented, f o r t y - t w o i n t h e t e c h n i c a l sessions and e i g h t e e n as p o s t e r s . The morning o f May 2 f e a t u r e d a s p e c i a l symposium on t h e Ray Anderson and Eva Precambrian basement o f t h e n o r t h - c e n t r a l U.S. K i s v a r s a n y i were c o - c h a i r s o f t h e symposium. Two b e s t student-paper awards o f $100 each were p r o v i d e d by d o n a t i o n s from Exxon M i n e r a l s Co. and Nekoosa Papers I n c . These generous c o n t r i b u t o r s a l s o made i t p o s s i b l e t o award e i g h t s t u d e n t g r a n t s c o v e r i n g r e g i s t r a t i o n and luncheon expenses. The student-paper awards were presented by Wayne Zwickey t o K . W . Klewin o f N o r t h e r n I l l i n o i s U n i v e r s i t y f o r h i s paper, "The P e t r o l o g y and Geochemistry o f the P o t a t o River I n t r u s i o n (Eastern M e l l e n Complex), N o r t h e r n Wisconsin" and t o A . 0. Maharidge o f Bowling Green S t a t e U n i v e r s i t y f o r h i s paper " T e c t o n i c E v o l u t i o n o f t h e F e l c h Trough." 0-' Z Cth CD CC — CD 0) Oc-rr-rtS —Izrnzr —- 0 i'0C Q0—C- 0c)CDo 'CACDCLO = CD ID U) CD O 'Ii 0 0 re CD O(D.— LID ZLD)>< CDC-.P--Lfl0 Cr-. 0- rr0CO-(D OC GD-C U)0iI--(0 i—-I--OCLrr c-t fr--—. 0 C 5= (DO ' 0. S 0 CDCDrP. U) CDC)—4 r0 p--fl. U)0 0) C U)W0 (00) OhOCOCEr U) 4,S CD c-p COrP-CD CD . Ci) il CD . • —. S O I-.-Di CD I U) err— 0 00-0I 0 • CDoOh 0 0.S U)L CD —4 05 VCD0 CDCO (DO CL —- 0 L4 'ID fr--0t) Cr0 rO.-4P- OJOiN) 0O) O Oh — c-c- 5 (0 • 0.—IC) T. OCt 0 0 LI)— Oh -O O,(Q-,5 c-tAiP-"C/)(D r 0E0i— Oi CD CflCDI—-U) OCOCD9S E • r5- CD CIDOCDCO aCD- 'c S"e '(Dc-P-CD o. CC IC) 0 c-P —4 COm0Ci rr0_C 0)<CDC.CD • 050 0CL0t. Cr C 00 oiDi CL SDi Oh (000 C • c. CD • • • 0 Cr--i ePO. Cc—pr rO.rr(0 (nO) 00 GD0 • SO fr-iCC 0. (1 50 -no = a CD — CD' 0 Cr5Cr C(Dc-t 0.-CDOE —. Cr" 0-'-,CDrtIr--" I-i = a. 0- rPC*C —CCDU) 0.P—rt 0 crc-c-.-" -, (fl-C ott oc-, 0Q1-" 00(0= • C CD. C-JO. • C) Q. • — Cr Cr rr QiCO — 0 i--C • • 0 C-a'N)O-'0 rtpI—rn— a —0LAp.-rt CD O-ZI-N) 5- N) er 0.flErtO rOi5t • et*4 tAO. 0 oDi CD 0 —. I HH < <(0 c-p 0 CO Cr C (ii i—U) c_.. —- CD C —- S i--fl etc CCDCOC CD S Cr S V (0 CArt (Fl 0. - C Di p-"roic-r I—rrEC I—U)0)U) LCD 0 U)U)0)) 0-Oh 0.0i Op-etS • C-. CD C COW — I—CD • ErrSO) rn—-rn-' ,CD • •CDO OCDOCD 0)0 -,,L (I) .—c-trr< I n view o f i t s r e l a t i v e l y h e a l t h y f i n a n c i a l s t a t u s , the I n s t i t u t e w i l l use most o f t h e i n t e r e s t income f o r s t u d e n t t r a v e l awards. A p r i m a r y o b j e c t i v e o f t h e awards w i l l be t o a t t r a c t Canadian s t u d e n t s . A committee (M. M. Kehlenbeck, C. E. Blackburn, T . J. B o r n h o r s t ) w i l l submit the g u i d e l i n e s t o the Board. CDS' 2) t o t a l $2592.34 and As o f A p r i l 22, 1986, t h e U.S. accounts o f I.L.S.G. i n c l u d e $890 i n t h e G o l d i c h Medal Fund account. The Canadian account stands a t SCAN 6,209.34. The 32nd I.L.S.G. t u r n e d over an a d d i t i o n a l $1200.00 t o t h e U.S. account. 44U)fr—ctrU) N)QiO 1) rtC0SP-l -CD-s,00 .— -._- 0m r.—o-, 0 Ci 40 CD The I n s t i t u t e Board o f D i r e c t o r s met a t noon on May 1. Board members p r e s e n t i n c l u d e d J e f f Greenberg (Chairman), Bruce Brown ( C o - c h a i r ) , J. K a l l i o k o s k i ( S e c r e t a r y - T r e a s u r e r ) , Gene LaBerge, Ted B o r n h o r s t , C h a r l i e Blackburn, and Dave Southwick. Ron Sage was a l s o p r e s e n t as the 33rd I.L.S.G. Chairman. The Board took the f o l l o w i n g a c t i o n : . S 0. — C-i CD C p—4(0 C40--0. cJnh— U) 0 CrCr00- • Di 0 Cr 0(0Cr 0(40 ECOIDO c-rt0 flI—rr rr05-i, c-on— n. r-0Lnw0_C CD tC CD 0 P-D Wa rtCDOtI —IO-C (010 c-tO- ct 0 ' fr---—-0 -tOJ (D0) 1Oh0 Oct0 - rtOrt0- N)Ci0i -0-. 00 GDCh- 0. oi-, • c-p —.Crt CD CD 0 C CD CD CDC<n —. -, Oh S-i-.Or--Oip-- I--0U) p—-<% 'XfrCD CD(D ICE ac-or—I U)-C(09o o,CrctrCU). 0 5'0 I—p... Cr5 tCpQirt CDC xP—4 —1'{P-05 O-n C —iCi -co p-o-A> O)P (DO.Cfl0.P- 0. COS Ot4C CDCDrII0i--C.ct 00 C00.It o,or' rt 00) On M a y 1 the I n s t i t u t e ' s annual banquet f e a t u r e d e x c e l l e n t food, an award "ceremony," and t h e guest speaker. The Goldich Medal was presented by the e v e r - e n t e r t a i n i n g Dick Ojakangas t o G. 0 . Morey o f t h e Minnesota G e o l o g i c a l Survey. Through the m i d s t o f some t e c h n i c a l a d v e r s i t y , John Rogers of the U n i v e r s i t y o f North C a r o l i n a shared h i s i n s i g h t s i n t o t h e "Precambrian o f Peninsular I n d i a . " I 1 CD —r '(C rP I—rtLfl 0)0) CD,CCet N) 5N) (Oct -0U) .-" 0) Girt 4.EU)OZV'%Jt c-tIC 00-U) U)C CO —4 p-i 0.—CD (sin 'O -t.-OCLCDOWZ.--. -I OtfiWet rtP-0O-055 <o-ceeo0.m z0 nr--0)p--'.COCD 0(0W.— Lflrr0.U)CD.—0 rCA OhC.-w 0)0 U) c_. C,J S c -C = c-t r — h COO) Cr >CCA—p--o I-4-,Ep—c-t —— V '<aEO,SrtOpO)CrE,N)VCDOO(D05 0Dc-j O.OQi----4 50_CrU)(D-,Oh I--S no P-CDU)(0tI-.-0. COO- (Dr. O<0 ttr W0)rt U)0CD00--0.CD0aa mr-vlsi CDSCDCO rrCi—r-r- r—--4 The 32nd meeting o f the I n s t i t u t e on Lake Superior Geology was hosted b y the Wisconsin G e o l o g i c a l and N a t u r a l H i s t o r y Survey and h e l d from A p r i l 29 t o May 4, 1986 i n c e n t r a l Wisconsin. Meeting headquarters was the Mead I n n i n Wisconsin Rapids where t e c h n i c a l sessions took p l a c e on May 1 and May 2. Conference r e g i s t r a n t s numbered 207 w i t h s t u d e n t s c o m p r i s i n g j u s t over one t h i r d o f these. Two-day f i e l d t r i p s were h e l d b o t h b e f o r e and a f t e r the meeting. The pre-meeting t r i p 1, which was l e d by J e f f Greenberg and Gordon Medaris, v i s i t e d exposures o f p l u t o n i c r o c k s a s s o c i a t e d w i t h the Wolf River b a t h o l i t h on A p r i l 29 and exposures o f Baraboo i n t e r v a l metasedimentary and igneous r o c k s on A p r i l 30. There were 38 p a r t i c i p a n t s on t r i p 1. F i e l d t r i p 2 leader Randy Maass was j o i n e d by 24 people on May 3 and May 4 t o observe s t r u c t u r a l c o m p l e x i t i e s o f Archean gneisses and E a r l y P r o t e r o z o i c metavolcanic u n i t s i n c e n t r a l Wisconsin. Separate guidebooks were p u b l i s h e d f o r each t r i p . to t1TJ i::ii-" t; t—; CC Ltt i— c ri (4 N) REPORT OF THE C H A I R M A N 32ND INSTITUTE ON LAKE SUPERIOR GEOLOGY 1986 �j 3) I.L.S.G. I.L.S.G. abstracts a b s t r a c t sare a r enow now submitted s u b m i t t e d to t o the t h eAmerican American Geological G e o l o g i c a l IInstitute nstitute for f o rinclusion i n c l u s i oinn GEOREF. i n GEOREF. 4. Starting w i l l be be Institute Institute S t a r t i n g in i n 1987, 1987, tthe h e ttitle i t l e of o f the t h e I.L.S.G. I.L.S.G. publication p u b l i c a t i o n will This title on Lake Superior Geolov ProceedinQs and Abstracts. on Lake Superior Geology Proceedinas and A b s t r a c t s . This t i t l ewill w i lappear l appear J j on on the the title on the t h e cover cover and and on t i t l epage. page. The The publication p u b l i c a t i o n will w i l also l a l sappear o appearunder under volume aa volume designation, the 33rd I.L.5.G. at Wawa will publish 33. volume d e s i g n a t i o n , the 33rd I.L.S.G. a t Wawa w i l l p u b l i s h volume 33. These i l l enable enable tthe h e IInstitute n s t i t u t e to t oapply apply ini n1988 1988 for f o ran an These sstandardizations t a n d a r d i z a t i o n s w will ISBN andthereby thereby tto recognized pperiodical. I S B N number number and o become become aa recognized eriodical. 5. Meeting notices Meeting n o t i c e s for f o r those those meetings meetings to t o be be held h e l d in i nthe t h eU.S. U.S. should shouldinclude include 'This Institute is recognized as a non—profit the statement: the statement: " T h i s I n s t i t u t e i s recognized as a n o n - p r o f i t sscientific cientific J and IRS and educational e d u c a t i o n a l organization o r g a n i z a t i o nunder underthe t h1954 e 1954 I R SRevenue Revenue Code Code S.5Ol(c)(3 S.S01(c)(3) Therefore, Therefore, aall l l ggifts i f t s to t o the the Institute Institute (Employee (Employee Indent. I n d e n t .No. No.23—7326054). 23-7326054). are a r e tax tax deductible." deductible." J 6. on the R. R. W. W. Ojakangas Ojakangas is i sthe t h enew newmember member (1986—1989) (1986-1989) on t h e Goldich GoldichMedal Medal H. Kehlenbeck. Committee, replacing N. Coamittee, r e p l a c i n g M. M. Kehlenbeck. 7. To Best Student Paper To be be eligible e l i g i b l efor f oconsideration r c o n s i d e r a t i o for n f othe r the Best Student PaperAward Award the the Starting student must be senior author and must present the paper. s t u d e n t must be s e n i o r author and must p r e s e n t t h e paper. S t a r t i n g in i n 19:97 1987 J agreed agreed to t o prepare prepare the the sample sample ccertificate. ertificate. U the the prize p r i z e will w i l lconsist c o n s i s tofo fboth b o t haacheck check and and aa ccertificate. ertificate. Gene Gene LaBerge LaBerge 8. Ron Sager ereported the 1987 1987 I Institute Ontario i l l take takeplace place Ron Sage p o r t e d t hthat a t the n s t i t u t e ini nWawé Wawa O n t a r i o wwill 9. Although wereno nocclear Although tthere h e r e were l e a r ooffers f f e r s of o f sponsorship sponsorship ffor o r the t h e 34th 3 4 t h I.L.S.G. I.L.S.G. (1988), Gene LaBerge mentioned the possibility of a proposal to hold t h e p o s s i b i l i t y o f a p r o p o s a l t o h o l dthe the (1988), Gene LaBerge mentioned meeting in Michigan's Upper Peninsula in the vicinity of the Gogebic meeting i n Michigan's Upper Peninsula i n the v i c i n i t y o f the Gogebic Boardaalso discussedthe the ppossibility meeting Range. Range. The The Board l s o discussed o s s i b i l i t yofo a f a meetingini Sudbury n Sudbury andi ninclude May May 11 11 to t o May May I15 S and c l u d e s eseveral v e r a l e xexciting c i t i n g f ifield e l d ttrips. rips. U Ontario O n t a r i o for f o r1989 1989ororbeyond. beyond. As As in i n the t h eprevious p r e v i o u sthirty—one t h i r t y - o n e years, years, this t h i year's s y e a r 'completed s completedchairmanship chairmanship how I t is i sindeed indeedwonderful wonderfultot see o see howsosomany many has has been been an an educational e d u c a t i o n a l experience. experience. It people from ddifferent canwork workt otogether the people from i f f e r e n t organizations o r g a n i z a t i o n s can g e t h e r f ofor r th e I Institute's nstitute's Perhaps the only problem of note for the 32nd I.L.S.G. success. success. Perhaps the o n l y problem o f n o t e f o r t h e 32nd I.L.S.G. was was the thepoor poor pre—meeting responset otothe thenmailed pre-meeting response a i l e d r registration e g i s t r a t i o n forms. forms. ItI tisi svery very difficult d i f f i c u l t to to estimate e s t i m a t e pparticipation a r t i c i p a t i o n in i n meals, aeals, field f i e l dtrips t r i p and s andtechnical t e c h n i c a lsessions sessions (seating), (seating), etc. without reasonable early notice of two weeks or so before e t c . w i t h o u t reasonable e a r l y n o t i c e o f two weeks or so b e f o r ethe t h emeeting. meeting. II suggest consider iincreasing suggest tthat h a t future f u t u r e local l o c a lcommittees committees consider n c r e a s i n g t the h e ddifferential ifferential between pre—meeting feesand andfees feesf for on—site between pre-meeting r e gregistration i s t r a t i o n fees or o n - s i t e rregistration. egistration. should encourage more people to preregister. s h o u l d encourage more people t o p r e r e g i s t e r . This This My thanksagain againt to maket hthe I.L.S.G. (and (and tthe 32ndI nInstitute My thanks o aall l l who who make e I.L.S.6. h e 32nd s t i t u t e in in particular) a priceless gathering of the friends of the Precambrian. p a r t i c u l a r ) a p r i c e l e s s g a t h e r i n g o f t h e f r i e n d s o f t h e Precambrian. L ee ttfully f t f u l l ysubmitted, submitted, U J K 2 rman 'r Institute Institute Madison, Madison, Wisconsi Wisconsi July, J u l y , 1986 1986 —viii— -viii- I L �INSTITUTE BOARD INSTITUTE BOARD OF OF DIRECTORS DIRECTORS R.P. Sage Sage((with E.D. R.P. w i t h E. D. Frey, Frey, Mineral Mineral 0ev. Dev. Br., Br., Wawa), Wawa), Ontario Ontario Geological Geological Survey, M Ministry andMines, Mines,7777GGrenville St., Survey, i n i s t r y of o f Northern NorthernDevelopment Development and r e n v i l l e St., Toronto, Ontario M7A 1W4 (1987) Toronto, Ontario M7A 1W4 (1987) J.K. Greenberg Geological and and Natural Natural H History J.K. Greenberg ((with w i t h B.A. B.A. Brown), Brown), Wisconsin Wisconsin Geological istory Survey, 3817 Mineral Point 53705 (1986) (1986) Survey. 3817 Mineral Point Rd., Rd., Madison, Madison, Wisconsin Wisconsin 53705 C.E. Branch,MMinistry off Northern C .E. Blackburn, Blackburn, Mineral Mineral Development Development Branch, inistry o Northern Development and Mines, P.O. Box 5160, Kenora, Ontario P9N 3X9 Development and Mines, P.O. Box 5160, Kenora, Ontario P9N 3x9 (1985) (1985) G.L. Wisconsin—Oshkosh, Wisconsin-Oshkosh, G .L. LaBerge, LaBerge, Department Department ooff Geology, Geology, University Universitybf'of Oshkosh, Wisconsin 54901 (1984) Oshkosh, Wisconsin 54901 (1984) J. Kalliokoski, J. K a l l iokoski Department , Departmentofo fGeology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Technological University, 49931 (Sectretary(Sectretary— Technological University, Houghton, Houghton, Michigan Michigan 49931 Treasurer) Treasurer) —ix— �j I LOCAL COMMITTEE LOCAL COMMITTEE Ed Frey: Conference Programand andAbstracts Abstracts Editor Editor Ed Frey: Conference Co—chairman, Co-chairman, Program Ron Sage: Conference Programand andGuidebooks GuidebooksEEditor Ron Sage: Conference Co—chairman, Co-chairman, Program ditor ta-i Tern—Ann Hoffmann (MNDM, (MNDM, Wawa): Mailingand andRegistration Registration Terri-Ann Hoffmann Wawa): Mailing Barbara Leschishin Leschishin (MNDM, Wawa):MMailing andRegistration Registration Barbara (MNDM, Wawa): a i l i n g and Wendy Wing(MNDM, (MNDM, Wawa): andRegistration Registration Wendy Wing Wawa) : D r Drafting a f t i n g and Delio Wawa):FField Delio Tortosa Tortosa (MNDM, (MNDM, Wawa): i e l d TTrip r i p Assistance Assistance Gerry (MNDM, SaliltSte. Ste.Marie): Marie): FField Gerry Bennett Bennett (MNDM, Sault i e l d Trip T r i p Assistance Assistance J Ken Card (GSC, (GSC,Ottawa): Ottawa):FField Ken Card i e l d TTrip r i p Assistance Assistance I Mike M I ke Lockwood (Univ.Western WesternOntario) Ontario): Lockwood (Univ. : FField i e l d Trip T r i p Assistance Assistance Dave Walker (MNDM, (MNDM,Toronto): Toronto): DDrafting Dave Walker r a f t i n g and and Guidebook Guidebook Preparation Preparation Krystyna Toronto): Graphics Krystyna Gil G i l (MNDM, (MNDM. Toronto): Graphics I BEST STUDENT PAPER BEST STUDENT PAPER COMMITTEE COMMITTEE A.J. A.J. J Andrews,Ontario Ontario Geological Geological Survey, Andrews, Survey, Toronto, Toronto, Ont. Ont. J.J. Consulting Geologist, Geologist, Toronto, J.J. Brummer, Brumer, Consulting Toronto, Ont. Ont. P.K. P.K. Sims, Sims, United United States States Geological GeologicalSurvey, Survey, Denver, Denver,CO CO U GOLDICH GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE W.A. Bodwell, Resource ResourceExploration, Exploration, Inc., Inc., Marquette, MI Marquette, MI W.A. Bodwell, J K.D. K.D. Card, Card, Geological Geological Survey Survey of o fCanada, Canada, Ottawa, Ottawa, Ont. Ont. R.W. Ojakangas,Dept. Dept. ooff Geology, R.W. Ojakangas, Geology, University U n i v e r s i t yofo Minnesota—Duluth, f Minnesota-Duluth, Duluth, Duluth, MN MN FIELD FIELD TRIP TRIPLEADERS LEADERS E.D. Development E.D. Frey, ~ r e yMineral ,MineralDevelopment Development Branch, Branch, Ministry M i n i s t r yofoNorthern f Northern Development and and Mines, Wawa, Wawa, Ont. Ont. T.L. Development T.L. Muir, Muir, Ontario OntarioGeological Geological Survey, Survey, Ministry M i n i s t r yofoNorthern f Northern Development and Mines, Toronto, Ont. ! and Mines, Toronto, Ont. j J I J.A. J.A. Percival, ~ e r c i v a Geological l , GeologicalSurvey Surveyofo Canada, f Canada, Ottawa, Ottawa, Ont. Ont. R.P. Development R.P. Sage, Sage, Ontario Geological Geological Survey, Survey, Ministry M i n i s t r yofoNorthern f Northern Development and Mines, Toronto, Ont. and Mines, Toronto, Ont. j Li �TECHNICAL TECHNICAL SESSION SESSIONCHAIRMEN CHAIRMEN T.J. T.J. Bornhorst, Bornhorst, Department Department of o f Geology Geology and and Geological Geological Engineering, Engineering, Michigan Technological University, MI Michigan Technological University,Houghton Houghton MI K.D. K.O. Card, Card, Geological Geological Survey Survey of o fCanada, Canada, Ottawa, Ottawa, Ont. Ont. A.M. Departmento fofGeology, Geology,UUniversity A.M. Goodwin, Goodwin, Department n i v e r s i t y oof f Toronto, Toronto, Toronto, Toronto, Ont. Ont. J.S. Geology,Western Western University, Dekalb, J.S. Klasner, Klasner, Department Department oof f Geology, I l lIllinois i n o i s University, Oekal b, IL IL G.L. of oWisconsin—Oshkosh, G.L. LaBerge, LaBerge, Department Department of o f Geology, Geology, University University f Wisconsin-Oshkosh, WI I 1 Oshkosh, Oshkosh, W I I F.R. Luther, Department of Geology, University of Wisconsin—Whitewater, F.R. Luther,Department o f Geology, u n i v e r s i t y of Wisconsin-Whitewater, Whitewater, WI Whitewater, WI R.J. R.J. Rupert, Rupert, Citadel CitadelGold GoldMines Mines Inc., Inc., Wawa, Wawa, Ont. Ont. R.H. R.H. Sutcliffe, S u t c l i f f e ,Ontario OntarioGeological GeologicalSurvey, Survey, Toronto, Toronto, Ont. Ont. i GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Henry C. Halls, Halls, Department off Geology, Henry C. Department o Geology, University U n i v e r s i t yofo Toronto—Erindale, f Toronto-Erindale, Toronto, Toronto, Ont. Ont. BANQUET BANQUET SPEAKER SPEAKER ,. 1 K. Poulsen, Geological Geological Survey Survey of o f Canada, Canada, Ottawa, Ottawa, Ont. Ont. K. Howard Howard Poulsen, —xi— �j ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS In thet hLocal Committee, thet hCo—chairmen I n addition a d d i t i o ntot othose thosecited c i t eon d on e Local Committee, e Co-chairmen wish wish to t o thank thank other other individuals i n d i v i d u a l sand andorganizations organizationswhose whose efforts e f f o r t sand andcooperacooperation apprecition t i o n have have contributed contributed to t o the t h eoperation operation of o fthe t h e33rd 33rdILSG. ILSG. Our Our apprecition also otherswho whow will ILSG i l l aaid i d the the Wawa Wawa ILSG a f tafter e r t hthis i s wwriting. riting. also goes goes tto o many many others - J Pam Aurora (MNDM—Toronto) manuscriptpreparation preparation Pan Aurora (MNDM-Toronto) — manuscript - Ann Wilson (Wawa) Ann Wilson (Wawa) —ccirculars irculars - Ann Ann May May (Wawa) (Wawa) - banquet banquet - Larry Larry Robinson Robinson and and others others of o fthe theWawa Wawa and and District D i s t r i cChamber t Chamberofo Commerce f Commerce conference conference assistance assistance Grant and sstaff Services Grant Southwell Southwell and t a f f ofo fthe theLeisure Leisure ServicesDepartment Department of o fthe theTownTown- ship ship of o f Michipicoten Michipicoten - conference conference f afacilities cilities - Township Michipicoten Council Council —use useo fofconference conference Township oof f Michipicoten f afacilities cilities - Algorna OreDDivision AlgomaSteel SteelCorporation CorporationLtd. Ltd. (Wawa) (Wawa) — f i efield l d t trip rip Algoma Ore i v i s i o n oof f Algoma assistance assistance - Bridget property access Bridget Lake LakeResources Resources Inc. Inc. (Wawa) (Wawa) — property access - CANAMAX Resources Inc. (Timmins) coffee breaks CANAMAX Resources Inc. Timmins) —coffee breaks - Citadel Inc. (Wawa) (Wawa) — f i field e l d ttrip r i p assistance assistance Citadel Gold Gold Mines Mines Inc. - Dunraine Ltd. (Toronto) Dunraine Mines Mines Ltd. (Toronto)— property propertyaccess access - Monk Gold and and Resources ResourcesLtd. Ltd. (Toronto) Monk Gold (Toronto) — property property access access - Muscocho Explorations Ltd. Ltd. (Toronto) Muscocho Explorations (Toronto)— property propertyaccess access -I j J J j J U U 1-I —xii— J �TECHNICAL TECHNICAL PROGRAM PROGRAM One Asterisk IIdentifies One Asterisk d e n t i f i e sStudent Student Papers. Papers. TwoAsterisks Asterisks IIdentify Two d e n t i f y Dual Dual (Oral (Oral & S Poster) Poster) Presentations. Presentations. Speaker/Presenter SpeakerIPresenter Underlined Underlined L I. L L 11 ft —xiii— �SESSION ONE ONE SESSION [ Tuesday Morning Tuesday Morning — May 12, 12, 1987 May 1987 i I 8:00 8:00 8:05 8:05 Allan A l l a n M. M. Goodwin Goodwin and and Ted Ted Bornhorst Bornhorst Co—chairmen: Co-chairmen: I I -- Opening Welcome Opening Welcome Conference Co—chairmen Conference Co-chairmen Greetings Development Greetings from from tthe h e Ontario Ontario Ministry M i n i s t r yofoNorthern f Northern Development && Mines Mines 8:20 K.D. K.D. Card Card Superior Province: Superior Province: the t h e product product of o fArchean Archean convergent pplate convergent l a t e tectonism tectonism 8:40 A. Turek A. Turek The meaning meaning ooff U—Pb andRb-Sr Rb—Sr agesi nin the the The U-Pb and ages Wawa area W awa area 9 :00 T.A. T. A. Vandall Vandal1 && D.T.A. D. T.A. Symons Synons Paleomagnetism Archean granitesi in Paleomaanetism o fofArchean aranites n tthe he Wawa area: definition W awa area: f u further rther de f i n i t i o n ooff the the apparent polar polar wander apparent wander path path 9 :20 R.I. Thorpe, R.I. Thor e, R.P. Sage, & J.M. J. M. Franklin Franklin F. F. Corfu Corfu && 9 :40 R.P. Sagee m . ... 10:40 11:20 11:20 11:40 12:00 precise IJ—Pb zirconage agef ofor trondhjemite AA precise 11-Pb zircon r aa trondhjem cclast l a s t ini nthe t h Dore e Coreconglomerate, conglomerate,Wawa, Wawa, Ontario Ontario coffee coffee 10:00 11:00 11:OO Leadisotope isotopeevidence evidencef ofor anoold Lead r an l d ccrustal rustal source ffor ore leads source o r many many ore leads in i nthe theWawa Wawa region reg d& . ** G.E. G .E. McGill McGill && C.H. Shrady t.H. Shrady Sequence folding, southwest Sequence o foff afaulting u l t i n g and and folding, southwest Michipicoten greenstone greenstonebbelt, Michipicoten e l t , Ontario Ontario G.E. McGill EkhmTf CC.H. H Shrady Shrad && Natureoof cleavage,f ofolding andsstrain Nature f cleavage, l d i n g and t r a i n in in tthe h e Michipicoten Hichipicoten greenstone greenstone belt, b e l t ,near nearWawa, Wawa, Ontario Ontario R.P. R. P. Bowen Bowen Geologyoof Geology f tthe h e Mishibishu Mishibfshu Lake Lake area area ** K.B. ** K.B. Heather Heather Gold mmineralization Gold i n e r a l i z a t i o n of o f the t h eMishibishu Mishi bishuLake Lake greenstone be1 beltt greenstone lunch lunch —xv— �j SESSION T TWO SESSION WO Tuesday Afternoon Afternoon Tuesday Co—chairmen: Co-chai rmen: - May 12, 1987 May 12, 1987 — j John John Klasner K l asner and andGene Gene LaBerge LaBerge U 2:00 2: OO ** E.C. ** E.C. Grunsky Grunsky Geology ooff the area, Ontario Geology the Batchawana Batchawana area, Ontario 2:20 2:20 W.T. W .T. JJolly olly Rhyolite R h y o l i t e and and basaltic b a s a l t i cvolcanism volcanism from from the the Huronian area, central Huronian ooff the t h e Thessalon Thessalon area, central Ontario Ontario 2:40 2:40 3:00 3:OO ** C. C.T. T. Barrie Barrie Geologyand ands tstructural Geology r u c t u r a l hhistory i s t o r y ooff the the Kamiskotia igneous igneous complex, complex,western westernAAbitibi Kamiskotia bitibi Subprovince, Subprovince, Ontario Ontario — "Basement—uplift" tectonics in "Basement-uplift" tectonics i nthe t h eKapuskasing Kapuskasing Structural Zone, Structural Zone, central c e n t r a l Superior Superior Province Province J.A. J.A. Percival Percival b, coffee 3:20 3 20 i Imprint of Imprint o f Archean Archean AAbitibi b i t i b i tectonics t e c t o n i c s on on the the 3:40 R.J. R.J. Shegeiski Shegelski 4:00 4:OO R.H. SSutcliffe R.H. utcliffe Contemporaneousl alate Contemporaneous t e Archean Archean mafic mafic and and granitoid Lac des des llies g r a n i t o i d magmatism magmatism i nin tthe h e Lac ies area, Wabigoon Subprovince, Ontario area, Wabigoon Subprovince, Ontario 4:20 4:ZO H.R. Williams H.R. Williams Fluid F l u i d induced induced structures structures in i nQuetico Quetico metasediments, northern northern Ontario metasediments, Ontario 4:40 4:40 ** W. ** W. Cannon, Cannon, J. Behrendt, 3. Behrendt, Fl. M. Lee, Lee, Proterozoic Lake Lake Superior Superior basin basin AA brief b r i e flook lookat aGLIMPCE t GLIMPCE D. Hutchinson, A. Green, Green, 0. ~ u t c h i n s o n ,A. C. Milkereit, C. Spencer, Spencer, B.B. M ilkereit, P. Morel, P. Morel, A. A. Davidson, Davidson, &6 D. 0. Teskey Teskey I Li s-A j j j U U U �SESSION SESSION Wednesday Morning Morning Wednesday Announcements Announcements 8:20 8:20 * — -- May 13, 13, 1987 May 1987 RoyRupert Rupertand andRichard RichardSSutcliffe Roy utcliffe Co—chairmen: Co-chairmen: 8:15 8:15 THREE THREE Conference Co—chairmen Conference Co-chairmen D.A. D.A. Baxter, Baxter, T.J. Bornhorst, 7.J. Bornhorst, && J.L. Van Aistine J.L. Van ~ lstine Geology,structure, structure, and Geology, and associated associated precious metal mineralization Archean precious metal m i n e r a l i z a t i o n of o fArchean rocks i in the vvicinity rocks n the i c i n i t y ofo fClark ClarkCreek, Creek, Marquette County, Marquette County, Michigan Michigan 8:40 8:40 R.C. R. C. Johnson, Johnson, T.J. Bornhorst, & T.J. Bornhorst, & J.L. Van Alstine J.L. Van A lstine Geology and and precious precious metal Geology metal mineraliza— mineralizaH i l l ' sLakes Lakes area, area, ttion i o n of o f the the Hill1s Marquette County, County, Michigan Marquette Michigan 9:00 9:OO T.J. Bornhorst T.J. Bornhorst && D.A. Baxter D.A. Baxter Geochemicalcharacter character ooff Archean Geochemical Archean rocks rocks from the east half of the northern from t h e east h a l f o f t h e northerncomplex, complex, upper Michigan: Michigan: aa progress progress report report upper 9:20 R.L. R. L. Bauer Bauer Refolding and andf ofold Refolding l d rreorientation e o r i e n t a t i o n during during pluton emplacement regional stress pluton emplacement i ninaa regional stress ffield, i e l d . Vermilion Vermilion granitic g r a n i t i ccomplex, complex, northeastern Minnesota northeastern Minnesota M.E. Bidwell && M .E. Bidwell R.L. Bauer R.L. Bauer two—stagesimple simpleshear shearmodel modelf ofor high AA two-stage r high fflattening l a t t e n i n g strains s t r a i n s ini nshear shear zones zones ooff the the ccentral e n t r a l Vermilion Vermilion ddistrict, i s t r i c t , northeastern northeastern Minnesota Minnesota 9:40 9:40 * coffee coffee 10:00 10:OO 10:40 11:00 D.C. Stewart && D.C. J.M. J. M. Mancuso Mancuso The "Hagar "Hagar Suite" Suite" and The and problems problems concerning and llocation tthe h e nature nature and o c a t i o n ooff the t h e northern northern boundaryo of the Wolf River River bath01 batholith ith boundary f th e Wolf I..Watkins, I Watkins, Rapakivi textures textures of Rapakivi o f central c e n t r a lMinnesota Minnesota G. Anderson, G. Anderson, && P. Erickson P. Erickson 11:20 P.A. P. A. Nielsen Nielsen 11:40 11:40 J.A. Peterson ** J.A. Peterson && C.A. Geiger C.A. Geiger 12:00 Petrologic evolution evolution ooff early Petrologic e a r l y Proterozoic Proterozoi c supracrustal rocks supracrustal rocks from from Florence Florence County, County 9 WI WI and ttheir of the and h e i r bearing bearing on on the t h e development development of the Dunbar Gneiss Dunbar The Hardwood Gneiss, a basic The Hardwood Gneiss, basictwo—pyroxene two-pyroxene ggranulite ranulite lunch lunch —xv ii— �SESSION SESSION WednesdayAfternoon Afternoon Wednesday -- May 13, 13, 1987 May 1987 M.L. Cummings M.L. Cummings Geochemistryo of Geochemistry f PProterozoic r o t e r o z o i c vvolcanic o l c a n i c hosted hosted formations in northern Wisconsin: formations i n n o r t h e r n Wisconsin: prospects prospects ffor o r gold gold mineralization mineralization D. Werbach Werbach AA rreview e v i e w ooff the t h e LaSalle LaSalle Falls F a l l smassive massive sulphide sul phide prospect prospect 2:40 R.R. Dahi, Dahl , D.H. m t k Watkinson, i n s o n , && J.J.W. W. McGoran McGoran TwoDuck DuckLake Lake Coldwell aalkaline Two I n intrusion, t r u s i o n , Coldwell lkaline complex, Ontario. Ontario. 1 1.. Geology and sstructure complex, Geology and tructure 3:00 R. Dahi, R. Dahl, D.H. m t k Watkinson, f n s o n , & JJ.W. .W. McGoran McGoran TwoDuck DuckLake Lake Coldwell a1 alkaline Two i n tintrusion, r u s i o n , Coldwell kal i n e complex, Ontario. 2. Petrology and complex, Ontario. 2. P e t r o l o g y and basebasemetal PGE geochemistry metal PGE geochemistry 2:20 * J ccoffee offee 3:20 3:40 4:00 J Ken Card Card and and Frank Frank Luther Ken Luther Co—chairmen: Co-chairmen: 2:00 FOUR FOUR * A. A . Davidson Davidson && 0. Van 0. VanBreemen Breemen Northeasternextension extensionoof Northeastern f tthe h e Proterozoic Proterozoic igneous terranes of mid—continental igneous t e r r a n e s o f m i d - c o n t i n e n t a l North North flmerica America J.F. Peterman, J.F. Peterman, Geological and and geophysical geophysicali investigation Geological nvestigation of graphite resources o f g r a p h i t e resources in i nupper upper Michigan Michigan 0. Droege, A.A.M. M. Johnson, Johnson, &i J.L. Van J.L. Van Aistine ~lstine 4:20 * 4:40 4:40 ** J.S. J.S. Springer Springer B.J. Prosen B.J. Prosen && A.M. Johnson A.M. Johnson Natural N a t u r a l brine b r i n e contamination contamination of o fgroundwater groundwater in the Keweenawan rocks of northern i n t h e Keweenawan rocks o f n o r t h e r n Michigan Michigan Mesozoicpaleogeography: paleogeography:i mimplications Mesozoic p l i c a t i o n s ffor or economic deposits north of Lake Superior economic d e p o s i t s n o r t h o f Lake Superior j -J j U -J —xviii— �C- POSTER POSTER PRESENTATIONS PRESENTATIONS May 11 11 Monday, May 12 Tuesday, May 12 May 13 13 Wednesday, Hay C.D. Anglin, J.M. Franklin, - brief MacLeod MacLeod Mine geology geology— aa b r i e f review review E.N. Berdusco E.N. Berdusco 3J.. Behrendt, Behrendt, M. M. Lee, Lee, 10:00 pan. 10:OO p.m. 5:00 5:00 p.m. p.m. 5:00 5:OO p.m. p.m. - Geochemistryo of scheelites associated with Geochemistry f scheelites with Archean gold deposits Archean gold hR. Jonasson, I.R. Jonasson, K. Bell, K. B e l l , &&E.E. Hoffman Hoffman W. W. Cannon, Cannon, -- 4:00 4:00 8:00 8:00 8:00 8: OO ** ** brief AA b r i e flook lookat aGLIMPCE t GLIMPCE 0. Hutchinson, 0. Hutchinson, A. A. Green, Green, C. Spencer, B. Milkereit, C. Spencer, B. M i l k e r e i t , P. A. Davidson, Davidson, && P . Morel, Morel, A. M. Teskey M. Teskey P.M. P. M. Eick Eick * Geochemistry andpetrography petrographyoof selected Early Geochemistry and f selected Early Proterozoic metadiabase Proterozoic metadiabase dikes from from Marquette Marquette County, Michigan County, Michigan R.E. R .E. Ernst Ernst && K. Bell K. Bell ** The great great AAbitibi The b i t i b i dyke dyke — ppetrological e t r o l o g i c a l overview overview R.J. R.J. Ferderer Ferderer && V.W. Chandler V.W. Chandler ** The The uutility t i l i t yofoWerner f Wernerdeconvolution deconvolution as as aa E.C. E. C. Grunsky Grunsky K.B. K. B. Heather Heather - geomagneticmapping mappingt otool geomagnetic o l in i n east—central east-central Minnesota Minnesota ** ** ** ** Geology ooff the area, Ontario Geology t h e Batchawana Batchawana area, Ontario Gold mineralization mineralization of Gold o f the t h eMishibishu Mishibishu Lake Lake greenstone bbelt greenstone elt M.A. JJirsa M.A. irsa Stratigraphic S t r a t i g r a p h i c evolution evolution of o f part p a r tofo fthe t h eArchean Archean M.J.P. Kuhns M.J.P. Kuhns && Applicability A p p l i c a b i l i t yofoaf sediment—hosted a sediment-hosted copper copper deposit model Solor Church model ttoo the t h eKeweenawan Keweenawan Solor Church Formation, Formation, R.J. Kuhns R.J. Kuhns metavolcanic bbelt, IItasca t a s c a County County metavolcanic e l t , northern northernMinnesota Minnesota Minnesota Minnesota G.L. LaBerge G.L. LaBerge Major llithological magmatic Major i t h o l o g i c a lunits u n i t in s ithe n t hWisconsin e Wisconsin magmatic terrane: data from fromddrill terrane: new new data r i l l cores cores G.A. G. A. Lehman Lehman U—Pb pitchblende from U-Pb d adatation t a t i o n oof f pitchblende from Dickinson Dickinson County, County, upper Michigan, Michigan, suggests suggestsr reactivation of upper e a c t i v a t i o n of Precambrianstructures structuresduring during formation formation of of the Precambrian the Michigan Basin Basin D.S. McPhee O.S. McPhee - Magnacon Project —Mishibishu Mishibishu Lake Lake greenstone greenstone Magnacon Project beltt be1 —xix— -xix- I �U - D.S. D. S. McPhee HcPhee MagmaProject Project —Michipicoten Michipicoten greenstone greenstone bbelt Magino elt J.D. MMiller, J.D. i l l e r , Jr. Jr. Bedrock geology geology ooff Keweenawan rocksi in Bedrock Keweenawan rocks n tthe he vicinity of Silver bay and Beaver Bay, v i c i n i t y o f S i l v e r bay and Beaver Bay, northeastern Minnesota northeastern Minnesota ' % - T.L. Muir T.L. Muir Stratigraphic S t r a t i g r a p h i c and and sstructural t r u c t u r a l considerations considerations on on the Hemlo gold deposit setting the Hemlo gold deposit s e t t i n g P.A. Nielsen P.A. Nielsen On thef afailure O n the i l u r e of o f the t h e midcontinent midcontinent rrift i f tsystem system to proceed to sea—floor spreading t o proceed t o sea-floor spreading W.I. Rose W.I. Rose Videof field Video i e l d trip t r i ptot othe t h eKeweenaw Keweenaw r irift ft R.J. Rupert R.J. Rupert Structural and geologyooff Citadel Structural and economic economic geology Citadel Gold Gold Mines Inc., Wawa, Ontario Mines Inc., Wawa, Ontario ' C.H. Shrady & G.E. McGill * Structural geology portion Structural geology of o f the t h esouthwestern southwestern p ortion of the Michipicoten greenstone belt, Ontario o f t h e Michipicoten greenstone b e l t , Ontario K.M. Sikkila K. M. S i k k i l a &8 W.J. Gregg U.J. Gregg * metasedi— AA sstructural t r u c t u r a l analysis analysisofoProterozoic f Proterozoic metasediments, northern Falls River, Baraga ments , northern Fa11s River, Baraga County, County, Michigan Michigan J.S. Springer J.S. Springer ** . JJ. Stevenson, Stevenson, J.M.. Mancuso, J M . , 3. Frizado, J. Frizado, Truskoski, &8 PP Truskoski, W. Kneller W. Kneller * D. D. Stone Stone T.J. Suszek T.J. Suszek &8 P.J. Meyer 'P.J. Meyer * 0. Tortosa 0. Tortosa Mesozoicpal paleogeography: implications Mesozoic eogeography: imp1 i c a t i o n s ffor or economic deposits north of Lake economic deposits north o f Lake Superior Superior j U L.A Solid S o l i d pyrobitumen pyrobitumen iin n veins, veins, Panel Panel Mine, Mine, Elliot Lake uranium district, E l l i o t Lake uranium d i s t r i c t , Ontario Ontario Geologyoof the Atikokan Geology f the Atikokan area, area, northwestern northwestern Ontario: an overview Ontario: an overview j Gravity and Gravity and magnetic magnetic evidence evidence for f o r rhomboid rhomboid sedimentary basins in the Wisconsin sedimentary basins i n t h e Wisconsinmagmatic magmatic terrane terrane U * Evidence ffor Evidence o r widespread widespread basement basement decollement decollement structures and related crustal structures and r e l a t e d c r u s t aasymmetry l asymmetryassoci— associated wwith limb ooff the ated i t h the t h e western western limb t h e inidcontinent midcontinent rift .1 Kremzargold gold deposit, deposit, District CANAMAX Kremzar D i s t r i of c t Algoma, o f Algoma. CANAMAX Resources Inc. — Kremzar Gold Mines Ltd. Resources Inc. Kremzar Gold Mines Ltd. rift G.R. G. R. Yule Yule U Reconnaissance geology gneissic Reconnaissance geology o f ofg rgranitic a n i t i c and and gneissic terrane, Wawa District terrane, Wawa D i s t r i c t R. R. Wunderman Wunderman &8 C.T. Young t.T. Young G.R. G.R. Yule Yule U . L I - U Structurally S t r u c t u r a l l y hosted hosted vein vein type type gold gold mineralization, mineralization, Goudreau—Lochalsh gold camp, Goudreau-Lochal sh go1d camp, D iDistrict s t r i c t of o f Algoma Algoma a.- It L �ABSTRACTS ABSTRACTS —xxi- �Geochemistry Geochemistrv of of Scheelites S c h e e l i t e s Associated Associated with w i t h Archean Archean Gold Gold Deposits Deoosi t s C.D. C.D. ANGLIN Survey of ANGLIN (Geological (Geological Survey of Canada, Canada, 601 601 Eooth Booth Street, Street, Ottawa, Ottawa, Ontario, O n t a r i o , K1A K I A OEB) OEB) J.N1. FRANKLIN (same) J.M. FRANKLIN (same) I.R. JONASSON I. R. JONASSON (same) (same) K. K. BELL BELL (Geology (Geology Department,Carleton Department,Carleton University, U n i v e r s i t y , Ottawa, Ottawa, Ontario) Ontario) E. E. HOFFMAN HOFFMAN (Nuclear (Nuclear Activation A c t i v a t i o n Services, Services, Hamilton, Hamilton, Ontario) Ontario) In I n the t h e study of o f gold g o l d deposits, deposits, fundamental fundamental questions questions remain remain regarding r e g a r d i n g the t h e criqin o r i g i n of o f the t h e ore—bearing ore-bearing fluids f l u i d s and and the If t h e absolute a b s o l u t e age age of o f mineralization. mineralization. I f tthe h e timing t i m i n g of of gold gold emplacement emplacement can can be be shown shown to t o be be related r e l a t e d to t o specific s p e c i f i c maymatic magmatic or metamorphic events, then very specific geological o r metamorphic events, then very s p e c i f i c g e o l o g i c a l criteria c r i t e r i a for f o r these these events events can can be be documented, documented, and and new new or or refined guidelines for exploration can be defined. To r e f i n e d g u i d e l i n e s f o r e x p l o r a t i o n can be defined. To date, date, attempts attempts to t o determine determine the t h e absolute a b s o l u t e timing t i m i n g of o+ emplacement emplacement 0+ of gold g o l d have have been been frustrated f r u s t r a t e d by by the t h e lack l a c k of o f suitable s u i t a b l e minerals minerals for f o r dating d a t i n g by by conventional conventional radiometric r a d i o m e t r i c dating d a t i n g techniques. techniques. This T h i s study study was was initiated i n i t i a t e d to t o follow f o l l o w up up aa suggestion suggestion by by Ludden common constituent constituent Ludden et. et. al. a l . (1984) (1984) that t h a t scheelite, s c h e e l i t e , aa common of o f gold—bearing gold-bearing veins, v e i n s , may may be be aa suitable s u i t a b l e mineral mineral for f o r Rb/Sr Rb/Sr and In and Sm/Nd Sm/Nd isotopic i s o t o p i c analysis. analysis. I n addition, a d d i t i o n , scheelite s c h e e l i t e may may be be suitable s u i t a b l e for f o r U/Pb U/Pb isotopic i s o t o p i c determination, determination, and and 0—isotope 0-isotope analysis. Boyle of: analysis. Boyle (1979) (1979) has has noted noted the t h e close c l o s e association a s s o c i a t i o n of scheelite s c h e e l i t e with w i t h gold g o l d mineralization, m i n e r a l i z a t i o n , and and pointed p o i n t e d out o u t that that scheelite s c h e e l i t e "occurs "occurs in i n [gold] [ g o l d ] deposits d e p o s i t s of of all a l l ages ages from from Precambrian For Precambrian to t o Tertiary". Tertiary". For this t h i s reason, reason, aa preliminary preliminary examination examination of of the t h e trace t r a c e element element and and REE REE contents c o n t e n t s of of scheelites s c h e e l i t e s from from gold g o l d deposits d e p o s i t s has has been been undertaken undertaken to to determine determine if i f the t h e levels l e v e l s of o f REE, REE, U U and and Sr S r would would be be sufficient sufficient for f o r isotopic i s o t o p i c study. study. To To date, date, more more than than 30 30 samples samples of of scheelite s c h e e l i t e have have been been collected c o l l e c t e d from from active a c t i v e or o r past p a s t producing producing gold g o l d mines mines or or prospects. 19 prospects. 19 samples samples were were analyzed analyzed for f o r their t h e i r trace trace element and rare earth element (REE) contents by element and r a r e e a r t h element (REE) c o n t e n t s by E. E. Hoffman, Hoffman. Nuclear Activation Services. All samples were associated Nuclear A c t i v a t i o n Services. A l l samples were associated spatially s p a t i a l 1y with w i t h gold, gold, and and several several contained contained native n a t i v e gold. gold. The The scheelite s c h e e l i t e samples samples typically t y p i c a l l y contain c o n t a i n several several tens t e n s of of ppm ppm of o f REE, REE, very v e r y abundant abundant strontium s t r o n t i u m and, and, in i n some some samples, samples, abundant The abundant uranium. uranium. The variation v a r i a t i o n in i n the t h e content content of of strontium strontium in i n scheelite s c h e e l i t e from from samples samples within w i t h i n aa single s i n g l e deposit d e p o s i t is i s generally g e n e r a l l y very v e r y restricted, r e s t r i c t e d , but b u t samples samples from from different different districts At d i s t r i c t s show show wide wide variations. variations. A t the t h e Sigma Sigma Mine, Mine, Sr Sr contents c o n t e n t s range range between between 100 100 and and 200 200 ppm, ppm, whereas whereas in i n Timmins Timmins scheelites s c h e e l i t e s typically t y p i c a l l y contain c o n t a i n 2400 2400 ppm, ppm, those those from from Geraldton Geraldton contain c o n t a i n an an average average of of 7i00ppm 7SOOppm and and those those from from Vellowknife Y e l l o w k n i f e are are highly The h i g h l y variable v a r i a b l e and and enriched enriched over over the t h e other o t h e r deposits. deposits. The contents S r in i n all a l l cases cases are a r e sufficient s u f f i c i e n t to t o permit permit c o n t e n t s of o f Sr —1— �U U determination d e t e r m i n a t i o n of of iinitial n i t i a l uvSr/FJtsr B'7Sr/-^eSr rratios, a t i o s , which g i v e an an which may give indication i n d i c a t i o n of of the t h e primary primary fluid f l u i d composition, composition, and andof of jnantlc mantle crustal versus c r u s t a l sources. sources. within with strontium, As w ith s t r o n t i u m , the t h e REE REE contents contents w ithin a a single single deposit d e p o s i t or o r district d i s t r i c t are a r e typically t y p i c a l l y quite q u i t e uniform, uniform, but but significant s i g n i f i c a n t variations v a r i a t i o n s exist e x i s t between between groups groups of o f deposits. deposits. Both the t h e Geraldton and and Sigma Sigma samples samples contain c o n t a i n between between 33 and and 10 ppm (avth-age 9ppm) La, La, whereas whereas tthe Timmins samples (average oof f 9ppm) h e Timmins have S r , the t h e REE: REE have 14 14 to t o 28 28 ppm ppm (average (average 23 23 ppm) ppm) La. La. As with w i t h Br, contents c o n t e n t s of o f scheelite s c h e e l i t e from from Yellowknife Y e l l o w k n i f e are a r ehighly h i g h l yvariable., variable, generally and g e n e r a l l y enriched enriched over over the t h e other o t h e r deposits. deposits. Chondrite—normalized Chondrite-normalized REE REE patterns p a t t e r n s illustrate i l l u s t r a t e two two features; 1) 1) all a l l samples samples have have aa significant significant features; positive p o s i t i v e Eu anomaly which may may indicate i n d i c a t e that t h a t Eu Eu was was transported reduced sstate 2 ) th3 the t r a n s p o r t e d iin n tthe h e reduced t a t e iin n tthe h e oore r e f fluid l u i d ; 2) PEE patterns may be be separated separated iinto two groups: groups i) samples i) samples R EE p a t t e r n s may n t o two Timmins, which have from Timmins, have a a relatively r e l a t i v e l y flat f l a t REE REE profile, p r o f i l e , with with anomaly, and ii) distinctive a d i s t i n c t i v e positive p o s i t i v e Eu ii)samples from Eu anomaly, Sigma in Sigma which display d i s p l a y a pattern p a t t e r n with with a a broad broad positive p o s i t i v e hump hump in The tthe h e intermediate i n t e r m e d i a t e REE's. REE's. The I3eraldton—Beardmore Geraldton-Beardmore samples samples show both b o t h types t y p e s of of profile. profile. interesting interesting both and heavy rrare IInn b o t h groups, groups, the t h e light light A d heavy a r e earths e a r t h s(LREE ' (LREE and HREE) HREE) have approximately and approximate1y the t h e same same chondrite—normalized chondri te-normal ized contents. Either E i t h e r the t h e samples samples with w i t h the t h e broad broad hump hump have have incorporated i n c o r p o r a t e d tthe h e 'middle" "middle" PEE REE more more efficiently e f f i c i e n t l y than than the the other group, or else the PEE compositions of the o t h e r group, o r e l s e t h e REE compositions o f t h e mineralizing m i n e r a l i z i n g fluids f l u i d s of of each each group group were were different. different. IIonic onic radius and charge conditions which controlled the PEE radius c o n d i t i o n s which c o n t r o l l e d t h e REE distribution d i s t r i b u t i o n in i n scheelite s c h e e l i t e should be be constant (with ( w i t h the the exception , and different exceptionofo fELI) Eu), and tthus hus d i f f e r e n t fluid f l u i d compositions compositions seem seem a more likely explanation off the differences likely e xplanation o the d i f f e r e n c e s in i n shape of of the the However, patterns. patterns. However, possible p o s s i b l e temperature temperature and and pressure pressure dependence of o f the t h e PEE REâ partitioning p a r t i t i o n i n g need need to t o be be considered considered further. further. J U U U j preliminary From our our p r e l i m i n a r y data, data, it i t is i s clear c l e a r that t h a t continued continued study of w i l l yield yield o f scheelite s c h e e l i t e and and other o t h e r accessory accessory minerals, minerals, will more information i n f o r m a t i o n on the t h e source source of o f mineralizing m i n e r a l i z i n g fluids f l u i d s for for gold go1d deposits. deposits. References References U Boyle, R.W., R.W., 1979; 1979; The geochemistry of o f gold g o l d and its i t s Boyle, deposits, Geological Survey deposits, Survey of o f Canada Canada Bulletin Bulletin no.280, no.280, 584p. 584p. Ludden, U.N., J.N., Daigneault, Daigneault, P., R., Robert, Robert, F., F., and andTaylor, T a y l o r , R..P., R.P., Ludden, 1984; Trace element mobility mobi 1it y in i n alteration a1t e r a t i o n zones zones associated with w i t h Archean Archean Au Au lode l o d e deposits. deposits. Economic Geology Geology v.79, v.79, no. no. 5,, p Economic 1131-1141. p 1131—1141. —2— U U �Geology andsstructural Geology and t r u c t u r a l history h i s t o r yofo fthe t h eKamiskotia Kamiskotia Igneous Complex, western Abitibi Subprovince, Igneous Complex, western A b i t i b i Subprovince, Ontario Ontario C. BARRIE (Department Geology,University University ooff Toronto, C. TUCKER TUCKER BARRIE (Department o f of Geology, Toronto, Toronto, M5S 1A1) 1A1) Toronto, Ontario Ontario M55 The The Kamiskotia Kamiskotia Igneous Igneous Complex Complex (KIC), (KIC), located located 30 30 km km west west of of Timmins, Tinunins, Ontario Ontario near near the the western western margin margin of of the the Abitibi Abitibi Subprovince, Subprovince, is is composed composed of of the the Kamiskotia Kamiskotia Gabbro Gabbro (KG), (KG), aa large large (>200 0 2 0 0 km2) km2) anorthositic anorthositic gabbroic gabbroic intrusion, intrusion, and and the the overlying overlying Kamiskotia Kamiskotia Volcanics Volcanics (XV), (KV), aa bimodal, bimodal, tholeiitic tholelitic volcanic volcanic pile pile that that hosts hosts significant mineralization 0 (>5 mu, tons significant massive massive sulfide sulfide mineralization 5 mil. tons The KIC is underlain by a Cu-Zn ore recovered). Cu-Zn ore recovered). The KIC is underlain by a 22 mm thick thick oxide—sulfide oxide-sulfide iron iron formation formation and and aa sequence sequence of of tholeiitic mafic volcanic rocks, and is intruded tholeiitic mafic volcanic rocks, and is intruded by by four four distinct distinct tonalitic tonalitic masses. masses. In In order order to to unravel unravel the the structural structural history history of of the the KIC, detailed structural mapping of penetrative and KIC, detailed structural mapping of penetrative and nonnonpenetrative penetrative fabrics fabrics is is presented, presented, along along with with preliminary preliminary U—Pb U-Pb geochronology qeochronology to to constrain constrain the the timing timing of of deformation deformation and and magmatism. magmatism. There There are are three three prominent prominent structural structural features features in in the the region. region. 1) 1 ) AA broad broad regional regional monocline monocline facing facing to to the the north north and and east east has has affected affected all all lithologies except three late tonalitic intrusions. 2) lithologies except three late tonalitic intrusions. 2 ) Contact Contact strain strain aureoles aureoles are are present present around around three three tonalitic intrusions, and extend up to tonalitic intrusions, and extend up to two two km km to to either either They are defined by a side of their contacts. side of their contacts. They are defined by a wellwelldeveloped developed flattening flattening fabric fabric parallel parallel to to the the contact contact accompanied by a strong elongation fabric accompanied by a strong elongation fabric locally. locally. There There is is evidence evidence for for overprinting overprinting of of one one contact contact strain strain A fourth tonalitic body aureole aureole on on another. another. A fourth tonalitic body located located at at the the center center of of the the KG KG does does not not have have an an associated associated contact contact strain strain aureole. aureole. It It is is characterized characterized by by clear clear magma magma mixing mixing textures textures between between tonalitic tonalitic and and gabbroic gabbroic material. material. 3) 3 ) AA predominately predominately east—trending, east-trending, non-penetrative non-penetrative fabric fabric crosscuts crosscuts stratigraphy stratigraphy and and is is pervasive pervasive throughout throughout the the region. region. this This fabric fabric is is particularly particularly well—developed well-developed in in the the felsic felaic volcanics volcanics of of the the KV. KV. +~ - 'k .' . a Preliminary Preliminary precise precise U—Pb U-Pb zircon zircon and and sphene sphene geochronology* indicates that the voluminous qeochronoloqy* indicates that the voluminous tholeiitic tholeiitic and calc-alkalic magmatism magmatism and and deformation deformation in in the the and calc-alkalic Kamiskotia Kamiskotia area area occurred occurred within within aa 15 15 Ma Ma interval. interval. Two Two samples samples from from the the KIC, KIC, aa quartz quartz pegmatitic pegmatitic gabbro qabbro from from the flow-banded rhyolite rhyolite from from the the XV KV are are coeval coeval the KG KG and and aa flow-banded at at 2705 2705 Ma. Ha. This This agrees agrees with with field field and and geochemical geochemical evidence evidence for for the the derivation derivation of of the the XV KV from from aa supracrustal supracrustal magma magma chamber chamber that that crystallized crystallized to to form form the the KG. KG. AA foliated foliated hornblende hornblende tonalite tonalite along along the the western western —3— �1-i U margin of One abraded sphene margin of the the KG is is 2697 2697 Ma. Ma. One sphene from this this sample is at 2692 fraction from is nearly concordant at 2692 Ma, suggesting a protracted cooling history, or a Ma, suggesting a protracted cooling history, or a dynamic metamorphic event 55 Ma after crystallization to reheat the reheat the sphene sphene past past its its blocking blocking temperature. temperature. AA foliated biotite tonalite from within margins of the foliated biotite tonalite within the margins KG has two nearly concordant zircon fractions KG has two nearly concordant zircon fractions at at 2692 2692 Ma. A third abraded fraction has a 207/206 age of 2926 Ma. A third abraded 2926 Ma and and is These data data can Ma is 4.6% 4.6% discordant. discordant. These can be be interpreted as as defining defining aa mixing mixing line line between between 2692 2692 Ma Ma interpreted and approximately 3500 Ma, indicating inheritance of and approximately 3500 Ma, indicating inheritance of xenocrystic zircon zircon from a much xenocrystic from a much older older crustal crustal component. component. work is Further work is in in progress progress to to analyze analyze older older zircon zircon populations, and and better better establish the evidence for very populations, old crust in the Kamiskotia area. old area. The KIC intruded into into previously existing crustal material composed of tholelitic tholeiitic mafic volcanics and an an older component, component, probably felsic During older felsic intrusive intrusive rock. rock. During the crystallization of the KG, KG, a caic—alkalic calc-alkalic tonalitic tonalltic magma was was injected into its center and mixed with the . mixed resident tholeiitic magma. Approximately 10 Ma later, resident later, a series of tonalitic intrusions were vertically emplaced intrusions into and and along along the margins of the KG, into KG, and subsequently expanded in situ to produce the well-developed well-developed flattening fabrics that characterize their contact strain aureoles. Between 2705 and 2695 Ma., Ma., a non— strain aureoles. nonpenetrative deformation event formed penetrative formed the large monoclinal structure across the Kamiskotia region. monoclinal region. Later north—south north-south compression compression formed formed the the regional regional easteasttrending, non-penetrative non—penetrative fabric. trending, fabric. With its magmatic magmatic and structural history, With history, the Kit KIC similar to several mafic intrusions that border is similar border granitoid terrane in granitoid in northwestern Ontario, Ontario, and appears Doze Lake to be comparable to the Sell Bell River and Dore Complexes in in Quebec. Bedding attitudes and structural structural are compatable compatable with predominately vertical vertical fabrics are movement of crustal material. There is little evidence movement material. There that modern day plate tectonic processes played a role role in the evolution of of the the KIC. KIC. Li j La U - U J J errors in in age age determinations are approximately +/—2 *All errors +/-2 Ma. Ages and errors will be modified as geochronologic work progresses. —4— U �Refolding andfold fold reorientation Refolding and reorientation during durin pluton regionalstress stressfield, field, pluton emplacement emplacement in ina aregional Vermilion Vermilion Granitic GraniticComplex, Complex, northeastern northeasternMinnesota Minnesota ROBERT BAUER (Department of Geology, Universityof of Missouri, Missouri, ROBERT L. L.BAUER (Department of Geology, University Columbia, Columbia, Missouri Missouri 65211, 65211, U.S.A.) U.S.A.) Archean schists and migmatites along along the the southern of the Archean schists and migmatites southern margin margin of the Vermilion southeastof of the the Lac La Croix Croix batholith batholith Vermilion Granitic Granitic Complex, Complex, southeast Lac La (LLB), undergonethree threeperiods periodsofofregional regional ductile ductile deformation. have undergone deformation. (LLB) , have Both of regional N—S Both F, F and and F F folds foldsformed formedasasa aresult result of regional N-Scompression. compression. However, F fdlds and local noncylindrical variations in ow eve?, F here f8lds and local noncylindrical variations inF9 F are are interpreted to be an indirect result of country rock interpreted here to be an indirect result of country rock teorientation reorientation during of the during the theemplacement emplacement of the LLB. LLB. F folds folds along along most most of of the thesouthern southern margin margin of of the theLLB LLB are are generally generally F cylndrical have relatively relatively constant cylindrical and and have constantSW-plunging SW-plunging hinges hinges and and east- striking in the the Burntside strikingaxial axialplanes. planes. However, However, in Burntside Lake Lake area, area, along along the the southeast margin of the LLB, large—scale F9 parasitic folds become southeast margin of the LLB, large-scale F parasitic folds become noncylindrical, noncylindrical,and andF,, F fold foldhinges hingesrange rangefrom fromSW SW to to NE NE plunging plunging within within the local F2 axial planes. In this same area, local tonalite the local Fn axial planes. In this same area, local tonaliteveins veinshave have undergone counterclockwise rotation undergone aa counterclockwise rotationproducing producingS—syninetry S-symetry drag drag patterns patterns in the local local F, in the the S. S foliation foliationcut cutby bythe theveins. veins. Both Both the F noncylindricity noncylindricity and the drag drag patterns patterns adjacent adjacenttotoveins veinsare areattributed attributed to to aa and the counterclockwise rotation of counterclockwise rotation of the thecountry countryrocks rocksalong along the thesoutheast southeast margin of the in aa continuing margin of the LLB LLB during during its itsprogressive progressiveemplacement emplacement in continuing N-S N-S compressional the LLB LLB continued, continued, aa doubly compressional regime. regime. As As emplacement emplacement ofof the doubly plunging parallel to plunging F F synform synform developed developed parallel tothe thesoutheastern southeastern margin margin of the the LLB, refolding both the earlier earlier F2 LLB, refolding both the Fn folds folds and and the the tonalite tonalite veins veins displaying displaying adjacent adjacent drag drag patterns. patterns. Other to WNW-trending axialplanes planes occur occur to to the Other F3 F3 folds folds with withW— W- to WNW-trending axial the southwest of the LLB wherethey theynoncylindrically noncylindrically refold regional southwest of LLB where regional F9 F folds 1986). The The FF folds folds(Bauer, (Bauer,1985, 1985, 1986). folds in in this thisarea areaare are interpreted interpreted to to have been reoriented reoriented to have been tothe theNW NW dJing duringemplacement emplacement of of the theLLB LLB and and then then refolded F3 during duringcontinued continuedN-S N-S regional regionalcompression. compression. refolded by by F3 These variations ininfold These variations foldgeometry geometrysuggest suggestthat thatemplacement emplacement of the theLLB LLB caused late—stagemodifications modificationsin in the regional caused late-stage regional fold foldgeometries geometriesbut butwas was not thethe N—S not responsible responsibleforfor N-Scompression compression which which caused caused the theF2 F2and and F3 F3 folds. folds. Bauer, Bauer, R.L., R.L., 1985, 1985,Geologic Geologicmap map of ofthe theNorwegian Norwegian Bay Bay quadrangle, quadrangle, St. St. Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Map Series, Map (scale == 1:24,000). Map Series, Map M—59, M-59, (scale 1:24,000). 1986, emplacement 1986, Multiple Multiplefolding foldinand andpluton pluton emplacement ininArchean Archean migmatites GraniticComplex, Complex, northeastern northeastern migmatites of of the thesouthern southern Vermilion Vermi ionGranitic Minnesota: Journal of of Earth Minnesota: Canadian Canadian Journal Earth Sciences, Sciences, v. 23, 23, p. p. 1753-1764. 1753-1764. 7 —5— �J Geology, structure, and associated precious metal mineralization of Archean rocks in the vicinity j of Clark Creek, Marquette County, Michigan D.A. BAXTER BAXTER and BORNHORST (Dept. o fofGeology D.A. andT.J. T.J. BORNHORST (Dept. Geology& &Geol. Geol. Engrg., Engrg., Michfgan Tech. Tech. U University, Michigan n i v e r s i t y ,Houghton, Houghton, MI M I49931) 49931) J .L. VAN VAN ALSTINE ALSTINE (Geological i v i s i o n ,Michigan Michigan Department Department ooff J.L. (GeologicalSurvey SurveyDDivision, M I 48909) 48909) Resources, Lansing, Lansing, MI Natural Resources, The Clark Creek Creekr region The Clark e g i o n l lies i e s within w i t h i n the t h eIshpeming Ishpeming Greenstone Greenstone BBelt e l t iin n the the nnorthern o r t h e r n portion p o r t i o n of o fMarquette Marquette County. County. This T h i s area area iiss currently c u r r e n t l y being being ttested e s t e d by by several several mining m i n i n gcompanies companies for f o r the t h epresence presence of o feconomic economic gold gold mineralization. m i n e r a l i z a t i o n . The The ooldest l d e s t rocks h e area r e ppart a r t of o f aa rocks observed observedi nin tthe area aare succesion ooff steeply s t e e p l y dipping d i p p i n gArchean Archean metavolcanics metavol cani c s known known as h e MetavolMetavolsuccesion as tthe canics canics of Silver S i l v e rMine MineLakes. Lakes. This T h i s group group was was named named ooriginally r i g i n a l l ybybyOwens Uwens lY85 (Michigan (MichiganGeological GeologicalSurvey SurveyDivision D i v i s i oReport n Report OFRand Bornhorst i n1985 and Bornhorst in OFR— 85—2; 85-2; 1985 east of the t h e Clark C l a r k Creek Creek region region 1985ILSG) ILSG)i ninan anarea areaimmediately imediately east and t o PPillowed i l l o w e d BBasalt, a s a l t , Pyroclastic, Pyrocl a s t i c , Iron I r o nFormation, Formation, and was wassubdivided subdividedi ninto and and Laminated Schist S c h i s tmembers. members. In I n 1986, 1986, Johnson Johnson and and oothers t h e r s (Michigan (Michigan Geological Survey OFR-86—2; Survey Division D i v i s i o Report n Report OFR-86-2; 1986 1986 ILSG) ILSG) rreported e p o r t e d on on an an area immediately t h ewest westwhich which contained contained foliated, f o l i a t e d ,non—foliated, n o n - f o l i a t e d , and and area imediately tot othe highly altered basalts of unknown stratigraphic relationship to the h i g h l y a1 t e r e d basal t s o f unknown s t r a t i g r a p h i c re1 a t i o n s h i p t o t n e Metavolcanics S i 1v e r Mine Mine Lakes. Lakes. Metavol canics ooff Silver J j This two areas areas and andr revision T h i s study study allows a l l o w s correlation c o r r e l a t i o n between between tthe h e two e v i s i o n ooff the the members Metavolcanicso of Lakest to members w iwithin t h i n t hthe e Metavolcanics f SSilver i l v e r Mine Mine Lakes o ((from f r o m ooldest l d e s t to to youngest): Willow Creek PPyroclastic youngest): Lower Lower Pillowed P i l l o w e d Basalt B a s a l t Member, Member, W i l l o w Creek y r o c l a s t i c and and Pillowed IIron r o n Formation Formation Member, Member, and and Upper Upper Pi1 lowed basalt b a s a l tMember. Member. The The Upper Upper Pillowed subdividedi ninto altered, P i 1lowed Basalt B a s a l t Member Member i sissubdivided t o hhighly i g h l y a1 tered, foliated, f o l i a t e dnon— , nonNumerous ffoliated, o l i a t e d , and and laminated 1aminated sschist c h i s t vvarieties. arieties. Numerous p ipillow 11ow sstructures t r u c t u r e s in in the t h e basalts b a s a l t s consistently c o n s i s t e n t l yshowed showed tthe h e ttop o p of o f beds beds to t o be be towards towards the t h e southsouthsouthwest. Wherev ivisible, andl ilithologic southwest. Where s i b l e , bedding bedding and t h o l o g i c contacts c o n t a c t s strike s t r i k ebetween between and~N75°W from NNO'W ~ O ' W and 7 5 'and ~ and d i pdip from 70"70° t o to v evertical, r t i c a l , ggenerally e n e r a l l y tto o the t h e southwest. southwest. The metavolcanics metavolcanics aare The r e iintruded n t r u d e d by by the t h eArchean Archean Metagabbro Metagabbro ooff Clark Clark Creek, Creek, which roughly roughly pparallels During the t h e Late L a t e Archean Archean the t h e area areawas was which a r a l l e l s bedding. bedding. During subjected ttoo aa period and metamorphism. subjected p e r i o d of o fintense i n t e n s edefomation deformation and metamorphism. Most Most field comes f i e l devidence evidence for f o rthis t h ievent s event comesfrom fromthe t h epresence presence of o fmappable mappable ftaults aults basedononl i lithologic based t h o l o g i c ccontact o n t a c t ddiscontinuities, i s c o n t i n u i t i e s , highly h i g h l y sheared sheared iintrusive ntrusive contacts, zoneso of contacts, and and zones f hhighly i g h l y ffoliated o l i a t e d to t oschistose s c h i s t o s ebasalts, b a s a l t s , many many of Most foliations have strikes which we interpret as shear zones. which we i n t e r p r e t as shear zones. Most f o l i a t i o n s have s t r i k e s of The Archean between N60°Wand and~N75'W 60. and and vvertical. e r t i c a l . The between N6O0W 7 5 w ' with i~t h ddips i p s between between 60 Rhyolite Intrusive of Fire Center Mine intrudes pre—existing rocks R h y o l i t e I n t r u s i v e o f F i r e Center Mine i n t r u d e s p r e - e x i s t i n g rocks in i n aa dike d i k e to t o sill—like s i l l - l i k emanner. manner. Field F i e l d relationships r e l a t i o n s h i p ssuggest suggestthat t h a these t t h e s erhyo— rhyoThe Archean rocks rocks are l i t e sare a r esyn— syn- to t o post—tectonic. post-tectonic. The Archean a r e unconformably unconformably lites Proterozoic ooverlain v e r l a i n by by quartzites q u a r t z i t e sand andslates s l a t e sof othe f t hLower e Lower P r o t e r o z o Michigamme i c Michigamme Formation. Formation wasmetamorphosed metamorphosedand andf afaulted Formati on. The The Michigamme Michi gamine Formati on was u l t e d near T h i s orogeny orogeny tthe h e end end of o f the t h eLower Lower Proterozoic P r o t e r o z o i cbybythe t h ePenokean Penokean orogeny. orogeny. This was was aalso l s o rresponsible e s p o n s i b l e ffor o r reactivation r e a c t i v a t i o nofo Archean f Archean faults f a u l t sand andminor m i n o rsecondsecondMiddle i d d l e Protero— Proteroary within a r y metamorphic metamorphic ooverprinting verprinting w i t h i n the t h eArchean Archean rocks. rocks. M diabase zzoic o i c (Keweenawan) (Keweenawan) diabase d i kdikes, e s , t ytypically p i c a l l y east—west east-west t r trending, e n d i n g , ccut u t aalll l Additional off the o t h e older o l d e r rock rock units u n i t s and and structures. structures. A d d i t i o n a l sstratigraphic t r a t i g r a p h i c details details will bepublished p u b l i s h e dini na 1987 a 1987Michigan Michigan Geological Geological Survey Survey Division D i v i s i o n Open Open FFile ile w i l lbe Report. Report. -6- U �Mineralization quartz— M i n e r a l i z a t i o n in i n the t h e region region exists e x i s t s ini ntwo twoforms: forms: 1) 1)epigeneti epigenetic quartz- carbonate—suiphi veins,and and2)2)disseminated di sseminatedsul sulphides altered carbonate-sulphide de veins, phides wwithin i t h i n a1 tered country rocks. The epigenetic quartz veins are often associated with country rocks. The epigenetic quartz veins are o f t e n associated with shear andf faults. The most most common common gangue mineralsi nin these these veins shear zones zones and a u l t s . The gangue minerals veins are carbonate,wwith amountso fofp pyrrhotite, are quartz quartz and and carbonate, i t h llesser e s s e r amounts y r r h o t i t e , chalcopyrite, chalcopyrite, and arsenopyrite. Disseminated mineralization is most prominent i in and arsenopyrite. Disseminated m i n e r a l i z a t i o n i s most prominent n the the highly altered variety of the Upper Pillowed Basalt Member but also h i g h l y a l t e r e d v a r i e t y o f t h e Upper Pillowed Basalt Member but a l s o occurs occurs This m mineralization ttoo aa much much llesser e s s e r degree degree iinn other o t h e r Archean Archean rock rock types. types. This ineralization consists of by minor minor amounts amountso fofppyrrhotite consists o f disseminated disseminated pyrite p y r i t eaccompanied accompanied by yrrhotite and chalcopyrite. The gangue minerals in the altered and chalcopyrite. The gangue minerals i n t h e a l t e r e d country country rocks rocks are are primarily Locally, galena and galena and p r i m a r i l y sericite, s e r i c i t e , quartz, quartz, chlorite, c h l o r i t e and . andcarbonate. carbonate. Locally. sphalerite are the dominant disseminated sulphide minerals. s p h a l e r i t e are thedominant disseminated sulphide minerals. 7 - A which yyielded A limited l i m i t e dnumber number of o f gold goldassays assays was was completed, completed, some some ooff which ielded anomalous values. values. The The highest highest values values were werefrom fromt hthe e hhighly i g h l y altered altered anomalous variety Member. Additional anomalous anomalous values values v a r i e t y ofo fthe t h eUpper UpperPillowed Pi1lowedBasalt Basalt Member. Additional for f o r gold goldwere were obtained obtained from from the t h eWil W i llow low Creek Creek Pyroclastic P y r o c l a s t i cand and Iron I r o nFormaFormation andBornhorst Bornhorst(1985) (1985)also also found found anomalous anomalousgold goldi in n tthis his Owens and t i o nMember. Member. Owens member which representaachemically chemicallyfavorable favorablehost host tfor member which wewe i n tinterpret e r p r e t t otorepresent or gold mineralization. An anomalouss silver obtained from An anomalous i l v e r assay assay was was obtained from an an area area gold mineralization. with enamineralization. mineralization. w i t h shear shear zone zone associated associated gal galena , —7— �Ii LI U - Mine Geology Geology - AA B Brief MacLeod Mine MacLeod r i e f Review Review N. BEROUSCO BERDUSCO E. N. E. (Algoma Ore Ore D Division, Wawa, O Ontario (Algoma i v i s i o n , Wawa, ntario P05 IKO) POS 1KO) ii located 235 235 kilometers The MacLeod MacLeod iiron The r o n oore r e (siderite) ( s i d e r i t e ) mine mine iiss located kilometers north off Wawa by highway, north kilometers n orth o Wawa by highway, n o r t h of o f Sault Sault Ste. Ste. Marie, Marie, 44 kilometers the Canadian and lies the Wawa Wawa Belt and l i e s within w i t h i n the B e l t of o f the Canadian Shield's S h i e l d ' s Superior Superior Province, downward extension extension oof the depleted depleted Helen Heln and a downward IItt iiss a f the and Province. single orebody together formed a Victoria orebodies which all V i c t o r i a orebodies which a l l together formed a s i n g l e orebody iin n The siderite—pyrite, the Helen the Helen IIron r o n Range Range (Goodwin, (Goodwin, 1964). 1964). The s i d e r i t e - p y r i t e , banded banded chert c h e r t iron i r o n formation formation is i s conformable conformable within w i t h i n underlying underlying felsic f e l s i c tuffs, tuffs, pillow lavas. overlying intermediate flows and agglomerate, and agglomerate, and o v e r l y i n g intermediate flows and p i l l o w lavas. limb of aa forms the south This continuous uninterrupted sequence This continuous u n i n t e r r u p t e d sequence forms the south limb of is overturned to the north, strikes east—west, dips syncline that s y n c l i n e t h a t i s overturned t o t h e north, s t r i k e s east-west, d i p s south an average average o off 60°and south an 60°an plunges plunges 35°east. 35Oeast. from 180 180 tto 730 meters MacLeod Mine which extends MacLeod Mine ssiderite, i d e r i t e , which extends from o 730 meters in length, 60 meters meters the shaft collar, averages 2 kilometers below below the s h a f t c o l l a r , averages 2 kilometers i n length, 60 which widens half of the mine, in width and in the east i n w i d t h and i n the east h a l f o f the mine, which widens tto o aa low iron high chert central silica maximum 150 meters, contains a maximum 150 meters, contains a low i r o n h i g h c h e r t c e n t r a l s i l i c a An average grade of from 33 tto 20 meters o 20 meters iin n width. width. An average iinn ssitu i t u grade of rrib i b from 3.86% S, Si02, 2.85% CaO, 5.60% 5.60* siderite Fe, 3.86% 5, 6.89% SiO,, 2.85* CaO, 35.3% Fe, 35.3% 6.89% s i d e r i t e iis: s: MgO, 0.70% 0.70% A1203, MgO, A 1 2 0 2.02% 2.02% Mn. Mn. the from the the s siderite contact, the descending descending order order from i d e r i t e ffootwall o o t w a l l contact, all the rocks may few meters each, o off any any o orr a may grade grade iinto a rocks nto a few meters each, l l ooff the interbanded and ffollowing ollowing interbanded cchert hert and ssiliceous iliceous ssiderite, iderite, orr dike, pyrite—argillite, p y r i t e - a r g i l l i t e , ffuchsite u c h s i t e bearing bearing felsic f e l s i c iintrusive n t r u s i v e sill sill o dike, encountering 60 60 meters ooff siliceous before 90 meters s i l i c e o u s ssiderite, iderite, before encountering tto o 90 the comon iinn the carbonated ffelsic pyroclastics. Chioritoid carbonated elsic p yroclastics. C h l o r i t o i d iiss common The massive underlying volcanics. volcanics. The massive siderite s i d e r i t e grades grades upwards upwards iinto n t o aa width and then 15 meters meters iin high high pyrite p y r i t e zone zone from from 33 tto o 15 n w i d t h and then into i n t o several several Some by upper volcanics. hundred meters of banded chert topped hundred meters o f banded c h e r t topped by upper volcanics. Some thin bands of zones in upper banded chert member contain the zones i n the upper banded c h e r t member c o n t a i n t h i n bands of The latter two minerals are also jasper, magnetite and pyrrhotite. jasper, magnetite and p y r r h o t i t e . The l a t t e r two minerals a r e a l s o not uncommon iin and they they freauently not uncommon n ssiderite i d e r i t e and f r e q u e n t l y occur occur with w i t h pyrite, pyrite, veins. Large ankerite and calcite in narrow quartz a n k e r i t e and c a l c i t e i n narrow quartz veins. Large iirregular rregular masses of masses o f metadiorite m e t a d i o r i t e generally g e n e r a l l y strike s t r i k e northeast northeast and and iintrude n t r u d e aall ll and lamprophyre dikes, rock Minor intrusions of types. rock types. Minor I n t r u s i o n s o f lamprophyre dikes, ssills, i l l s , and quartz—feldspar porphyry porphyry a are Four steeply quartz-feldspar r e also a l s o present. present. Four steeply dipping dipping diabase dikes width orebody. diabase dikes from from 10 10 tto o 20 meters meters iin n w i d t h traverse traverse the the orebody. Two iinn the the centre and one at east boundary Two c e n t r e and a t tthe h e east boundary strike s t r i k e northwest northwest while a west west boundary w hile a boundary dike d i k e strikes s t r i k e s northeast. northeast. U In In - The orebody orebody iis central offset att the east east c The s o f f s e t 107 meters meters nnorth orth a entral This east side diabase dike; dike; rrelative e l a t i v e displacement displacement iiss east s i d e northward. northward. This dike divides d ike d i v i d e s the the mine into i n t o MacLeod MacLeod West and and East. East. jj I La U II U ii U -8- U U �the Vugs of si zes are Vugs o f all a l l sizes a r e frequently f r e q u e n t l y intersected i n t e r s e c t e d especially e s p e c i a l l y iin n the in one area they are hangingwall banded chert of MacLeod East where hangingwall banded c h e r t o f MacLeod East where i n one area they are Several vugs vugs are interconnected 250 meters along strike. meters along interconnected for f o r 250 strike. Several are 10 10 to to in height and width. Most were water filled, coated with 30 meters 30 meters i n h e i g h t and width. Most were water f i l l e d , coated w ith and forms off calcite, marcasite, p pyrite and very very various assemblages various assemblages and forms o c a l c i t e , marcasite, y r i t e and galena rarely with amounts of chalcopyrite, marmatite, minute r a r e l y w i t h minute amounts o f c h a l c o p y r i t e , marmatite, galena oorr ssee len l e nii tte. e. 1961 58 The MacLeod Mine Mine has production since since 1961 and 58 has been been The MacLeod Iinn production and from all million tons of ore have been m Total ore med to 1986. m i l l i o n t o n s o f o r e have been mined t o 1986. Total o r e from a1 i 1939 since siderite three mines the same three mines iinn the same orebody orebody since s i d e r i t e mining mining began began iin n 1939 million 1939 1950, has been 8 million tons by open pit, and 79.3 1950, and 79.3 m i l l i o n has been 8 m i l l i o n tons by open p i t , 1939 surface drill hole tons from diamond d r i Il h o l e from from surface tons from underground underground since since 1949. 1949. AA diamond intersected siderite 1,200 meters below the shaft collar. i n t e r s e c t ,e d ,s. i d-e r i t e 1,200 meters below the .s h::a f t . c~ o,l l ,a r . . - . < .* . ; . .. - . ' . . .*> ... . ., , . ., . . .~~ !,* ., ..' .,< . , :. .* , ~, . .. ..... . .. . . . . . . . '< , 4 . . . , , . , .< . . - .. . . ., . . ... : : . <.,*- . . . , .~ . . , , 3 . . . . . .. .*. . < .. -. .. .", GOODWIN, GOODWIN, Range: A.M. Geochemical1 studies studies a att the the Helen Helen IIron A.M. 1964, Geochemica r o n Range: — 684 718. . . Economic Geology, Geology, Vol. Vol. 59, 59, 1964, 1964, pp. pp. - , , .- ,, . , .. . —9— . ., . ,.. <. +, ... .. . �s-I j A simple—shear model high flatteningstrains strains in A two—stage two-stage simple-shear model for for hiqh flattening in shear zonesofof the the central central Vermilion shear zones Vermilion district, district,northeastern northeasternMinnesota Minnesota U MATTHEW BIDWELL (Department Geology Geophysics, University of of MATTHEW E. E. BIDWELL (Department of of Geology andand Geophysics, University Wyoming, Laramie, Wyoming 82071) Wyoming, Laramle, Wyoming 82071 1 ROBERT BAUER (Department of Geology, University of Missouri, Missouri, Columbia, ROBERT L. L.BAUER (Department of Geology, Columbia, - of -- University Missouri 65211) Missouri 65211 ) Large—scale anastomosingshear shear zones zones up up to to 600 Large-scale anastomosing 600 meters meters wide wide deform deform basalt, tuff, lamprophyre, and graywacke in the central Vermilion basalt, tuff, lamprophyre, and graywacke in the central Vermilion district Mylonites in inthe thesbear shearz8nes zones districtjust justnorth northofofthe thetown town of of Ely. Ely. Mylonites have a relatively consistent C foliation orientation of N72 and have a relatively consistent C foliation orientation of N72E,E,6868SSand contain mineralliaeations li9eationsand nd striations stsiations with contain numerous numerous mineral with high high concentrations at S2Z S2 E, W, 56 56 and and a more more dispersed dispersed concentrations at E, 669and and544 S44W, concentration at N74 E, 33 Small-scale kinematic indicators, including concentration at N74 E, 33 Small-scale kinematic indicators, including actinolite S—C actinoliteporphyroblast porphyroblastfish, fish, S-C fabric fabricrelationships, relationships,shear shearbands, bands,and and extension with aa dextral indicatenon—coaxial non-coaxial deformation deformation with dextral extension fractures, fractures,indicate sense of shear. sense of shear. . Finite fromvariolitic variolitic pillow Finitestrain strainmeasurements measurements from pillowbasalts, basalts,agglomerate agglomerate clasts, and phenocrysts indicate large flattening strains clasts, and phenocrysts indicate large flattening strains in in the theshear shear zones (Fig. 1). of kk range from aa nearly nearly plane plane strain strain value Values of range from value of of zones (Fig. 1). Values 0.94 0.94 to to highly highlyoblate oblatevalues values of of0.06; 0.06; r rvalues values(=X/V (=X/Y+tY/Z Y/Z +1) +1) are are locally locallygreater greaterthan than15. 15. This range range in strain, strain,along alongwith withthe theabundant abundant kinematic against generation of the kinematic shear shear indicators, indicators,argues arguesagainst generationof the high high flattening flatteningstrains strainsvia viacoaxial coaxialdeformation. deformation. In In addition, addition, the the flattening flattenina strains by aa combination combination of simple strainscannot cannotreasonably reasonablybebeaccommodated accommodated by simple shear volumeloss loss - greater shear and and volume volume loss. loss. Excessive Excessive volume greaterthan than70% 70% -- is is required measured required to toattain attainthe the measured strains; strains;however, however, no no evidence evidence of of diffusive diffusivemass mass transfer transferwas was observed observed either either on on aa microscopic microscopic or or aa mesoscopic mesoscopic scale. scale. - - U Là U — Although strain path A1 though aa strain path involving involvingaacombination combination of ofprogressive progressive simple simple shear pure shear shearmay maybebecalled calledupon upon explainthe thestrain strain values shear and and pure totoexplain values in in Figure 1, we weconsider considerthe thepossibility possibilitythat thatthe thedifferential differential clustering Figure 1, clustering of of lineations striations on the CC foliation foliation and the distribution distribution of and the of lineations and and striations on the major and intermediate intermediatestrain strain axes axesininFigure Figure22isis aa result result of major and of superimposed simple shear. Possible strain paths consistent superimposed shear. Possible strain paths consistent with the the observed distribution of were observed distribution of flattening flatteningstrains strains werecalculated calculatedusing usinga atwo— twostage in which two simple simple shear shear events events with with different stage model model in which two differentdisplacement displacement vectors and displacement planes superimposed. and slightly slightlydifferent different displacement planesareare superimposed. AA difference in inthe theorientation orientationofofthe thedisplacement displacement planes planes is is required required because superimposedsimple simpleshear, sheatwith with different different shear because superimposed sheardisplacement displacement vectors planes,resultsinfinite finite plane vectors but parallel parallel displacement displacement planes,resultsin plane strains strains regardless regardless of ofthe theangle anglebetween between displacement displacement vectors. vectors. J U Relatively near plane-strain plane—strain values values obtained obtained from three Relativelylow—magnitude, low-magnitude, near three samples collected adjacent adjacent to to the mylonitic samples collected myloniticshear shearzones zones are are taken taken to to represent during the the initial initial simple represent strains astained attained during simpleshear shear event. event. An An angle the shear sheardisplacement displacementplanes planes thefirst first angle as as small snail as as 55 between between the ofofthe and secondevents events willproduce producelarge largefinite finite flattening flattening strains. and second will strains. The The best best fit usinginitial initial strain fitstrain strainpaths paths(Fig. (Fig.1)1)were were obtained obtained using strain values values ((ri) Y 1 of of 1.0 1.0 and and 2.5, 2.5, respectively, respectively,overprinted overprintedbybya asecond secondsimple simple shear shear with w i d aa -10- U �750 angle between the plane angle anglefrom fromthe thefirst first event and 1 0 ' shear shear plane event andasaa8.0 75' are angle between the as hi9h two vectors. yy values values as high as 8.0 are required required to to two displacement displacement vectors. produce the observed finite ttrains. oroduce the observed finite strains. 100 II x V I 2 3 4 5 0 7 S 5 10 11 12 13 14 15 I V z Flinn analyses Flinn plot plot of of finite finitestrain strain analyseswith withtwo two strain strainpaths paths of 1.0 and 2.5 and intervals 0.2, 0.5, 1.0, 1.5, for i 1.0 and 2.5 and 2y, intervals 0.2, 0.5, 1.0, 1.5, 2.0, 2.0, 2.5, 2.5, 3.0, 4.0, 6.0, 6.0, and and 8.0. 8.0. . , -. Figure 1. . .. '. " ,> . .. ,, ~ , a Ass aA £ ,. "' A A A A S 5.29 S •521 S —Is U.29 S Sot •18 •oe 5)0 Un S t44 •,26 •94 •.82 ..ft S S UI. A Figure Orientation of of minor minor (triangles), (triangles), intermediate (circles) Fi ure 2. 2. Orientation intermediate (circles) andma major (squares) axes finitestrain strain ellipsoids. ellipsoids. Numbers an or (squares) axes of of finite Numbers are are k values. values. -^-r —11— ~. .~. �k-J Character of Archean Rocks Rocks from Half Geochemical Character Geochemical of Archean from the the East East Half of the Northern Complex, Upper Peninsula, Michigan: of the Northern Complex, Upper Peninsula, Michigan: A Progress A Prnareqa Report Rennrt T.J. HURNHORST and and D.A. D.A. BAXTER BAXTER (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Michigan Tech. University Houghton, MI Engrg., Michigan Tech. University Houghton, MI 49931) 49931) L The granite—greenstone Archean granite-greenstone The northern northern complex complex is is an an Archeari As a terrane located in Marquette and Baraga terrane located in Marquette and Baraga Counties. Counties. As a whole, it consists of more granitoid and gneissic rocks whole, it consists of more granitoid and gneissic rocks than greenstone. greenstone. yIn 21n the the eastern eastern half half of of the complex there there than the complex of exposed Archean rocks, one—third are about 1000 km are about 1000 km of exposed Archean rocks, one-third greenstone, which which are are unconformably unconformably overlain overlain by by Proterozoic Proterozoic greenstone, The Archean of the east half consists sediments. sediments. The Archean of the east half consists of of thouthousands of meters of dominantly subaqueous, mafic to sands of meters of dominantly subaqueous, mafic to felsic felsic volcanic flows, flows, pyroclastics, pyroclastics, and and volcaniclastic volcaniclastic sediments volcanic sediments that are intruded by gabbro and rhyolite and rhyolite dikes dikes and and sills, sills, and granitoid An Bxl Archean peridotite peridotite body body and granitoid plutons. plutons. An 8x1 km km Archean was also emplaced structurally within the volcanic rocks. within the volcanic rocks. All of of these these rocks have been been subjected deforma— All rocks have subjected to to intense intense deformafades. tion and and metamorphosed to to at at least least greenschist greenschist facies. data, weighted weighted for exposed Histograms of geochemical data, area, illustrate that the greenstone greenstone belt, belt, excluding granigrani— area, Basaltic toid plutons, is weakly bimodal in in character. character. Basaltic Pyroclas— type. Pyroclaslava flows are, by far, the the dominant dominant rock rocktype. tic volcanic rocks of andesitic to dacitic composition are histograms, rhyolites are lesser in the second mode in the histograms, abundance. On a Jensen cation diagram the basaltic flows abundance. and gabbroic intrusives are tholeiitic whereas andesitic pyroclastic rocks and rhyolite intrusives are pyroclastic are calc—alkalic. calc-alkalic. The granitoid rocks are calc-alkalic calc—alkalic and on the basis of modal mineralogy range range from quartz diorite to trondhjemite. trondhjemite. Within two two sections sections of basalt, where structural structural repetirepetition may may be low, low, we looked for stratigraphic geochemical Basalts and variations but no no coherent coherent trends trends were were found. found. Basalts the gabbros which which intrude them cannot be distinguished distinguished from one another geochemically, geochemically, suggesting that they are from genetically similar or possibly the same genetically same magma source. source. AA few INAA data for the basalts basalts show relatively flat to slightly LREE depleted patterns, 55 to to 9x 9x chondrites. chondrites. The last Archean Archean magmatic event in the greenstone belt The was the intrusion of relatively tabular rhyolite bodies and granitoid plutons. plutons. There is a textural continuum between the rhyolites and granitoid rocks which is further exressed by expressed by excellent excellent chemical chemical continuity continuity on on variation variation diagrams. Thus, Thus, a close genetic link exists between the diagrams. rhyolite and granitoid intrusives. intrusives. The rhyolites are are interpreted as the late-stage, late—stage, generally more-evolved more—evolved parts of the plutons. This investigation is an outgrowth of projects partially funded by the the Michigan Michigan Geological Geological Survey. Survey. —12— J 4 — j J �.2 in 'Ii L a: 0 in -J -C in .0 ill -.4 -C a. -I-. t -C 4'4- 0 0 0 a. 0 -.-. L in 4.' aC — 0 4-' C L 0 C i- riCi .i ..-. > C Ci L to I'. h. ) 01 > J LI) in .-. U -.4 Di 0 .—. 0 a, (0 0 I. -.4 in i-s aC — 0.-. -uU cm-c..-.-— m+'-UWC in.-.o JOW4J mLW'.-D ru a-) LW a-Cs--U-0 4-' 0 .—.in W-.4 o-.-sn-.-.N 01 9-in Ut ÷'.MWW inin>WLJCin W.JmOWU >-4, -C t CUCL U.-.D'0 E0CJ SCUWOU >•' in .4 Ifl-.-.uI t')fl Lfl .1J.C00 inC-.-.t0.-. WoOm tJLn 0-.-.inLOJ.t or 00+' C E0 0 W-...(fl4J OCt CO .4-al— in u 0 — 5Jc>-.'d-iin 15th U0 0.- in -.-.E_c>-Di.. 01 a..'.-. i- 0_c4,uOm4-4L WWWin..Jcu)-4J.cO -..4UlaC4-'-..in-.-.in uiuiu.-.-.-. in.—. COQIdO COW 4-' 0.-.Lin.-i OIL-i-' .Ift U IdO u •.-.tnw u..tr 4)3 in_cu n_cm mu SC-.-. •OOC 00 U'd4,U LO —c .., 0 in..4CM-inin Was.-.-.' L —m÷.0 4-'CIdL U—i-..L .fl.-.-.-..-'D —-.-tU--.4 in4-IOW .xo.-.ina UUWIVJO -1-'---L.inid>-0W-.4C_cSLL Jinflfl_cCLCiUO L'I 4flin qdinld 15 I I LC Un flC .4in U (JO-.-. LOCO •0-i.J .-. 0.dImLin>inmininW ..i4DI5JCU 03 in inC .-..SL..thin inOiU.-.4-_cW .-.W m.-.m_cWCinIdO-1L .C-.-.-nCin L-X u .'fl.uidn fl.-.m9-c omso-.-. u •.4Din -i-iOU inn.-. .'flWI CithinIUUOfl in >.C L Cci-. .—.inn-.-.lUW.-.LIflU — -.41_cin min_c-.Juu÷.C-.4 inCi U>0WSW -..-.-.WC.-.S9- Gs nin4JD'IdLD aininmI inin-,.EUfl.!C.--. LEU -.cenuam> -i-i mu_cu 4.1 -..C 53 in L-I-J-4-' mi— 0 mm-.. wLa.>—_cc rWfl÷'WW in 4-'O mdi Ci in 1.. UCJ in>- I U - -I-' .-.0 in. in.- 4- Om LW uo - 'dOW LIVC in 0. W.. U. oc vt.sc flWL-.--iI. 4-'Wm WE Wa. X in UU OE L .c U.-' -.4.... Em 4-'.-. ---.0 4-'.C 'n--, In C D'.o .4 C_c .—. mm 0 Ci L L.-4 0 'U4-JC EmO 9-in_c -.-i.--..W U .—.u-.-. no>— aJinci DSC Cm..-' u_cm Cfl '4- S LW -i-'--.a thin CUL in-.-.in in -.4mm flu ..ifl CS os—in Q 4-'.-. 0.0 q-.to F f l s i ~hypabyssal, nafic plutonic, t r a n s i t i o n a l migmatitic rocks bounding t h e supracrustal rocks and f e l s i c stocks and b a t h o l i t h s make u p most of t h e rocks underlying the nap area. .C IflWO —i-.'--. mm L L0 0550 IAE.' -.40c 0.0'L CCL COo UUU 0>- . in-i-a-.-' -x uOJ_c cc... LOn 1._c-ia 4-'L >-in C-.-. in_c OCUC a. LL.'DiD mmmc-.-' C 4-I inO +'E>. C .0 >—W-.-i C l a s t i c metacdimentary rocks comprise 15% of t h e supracrustal rocks and range from mudstone t o conglomerate. These rocks appear t o have been deposited b y t u r b i d i t y c u r r e n t s along submarine fans. 00mm-no'.EcE3li-0 9- 0>- Qi5>4,0 L÷'Umu .44-a'D C .4-'oZcL -.40 U1UL 10>-C .X..4flin LO UD. WOid-.. C.-. 5 .4 0 .C 4, in>-Lmin 0.rU ..-.Cq-OCL moot-.. .-i-.-.SU 4U.-i inS WDCWW10 OCLmWGiL Dci U_cL_c in C_c04-GSL U>.-._cW thU in.-4 W-'U) -.-'u_c--.OW—. Cu I—vC .C.-. fl_c 0. L a0. C CLin 0 • -4-'O W9-W> — ldon-.-.o '4-fl4-'UU 0 0 Win LLWW.X —0m..cmU C h f i c a l netasedimentary rocks make u p l e s s than 1% of the supracrustal rocks and a r e t y p i c a l l y magnetitic chert or Jasper interlayered w i t h magnetitic iron-rich rocks and appear t o be The cherty associated w i t h the waning s t a g e s of a volcanic cycle. portions nay be arkosic t o wicke and s u l f i d r a r e often associated w i t h the oxide portions in varying degrees. These rocks often wxhibit t h e e f f e c t s of deformation r a t h e r dramatically. -C: .coIn-E-.-' mo mom -.-.in.. UL C 0 -..EOCUCI fl.xfl0-.-4C in in - .—.9JL_cCOC II, C inLth.i.IUEO.J au-.-.-.-.0÷i -n-.4CUinO >.Li 0E0.C_c0Suq-Oin.X .-i÷'CSs -.4 in 0. D'U*- C-.-i .49- .... .C am-... >—.C .C4'9- in Sin -rid 04-' OlE -Lin W'. floinLOldoin .-.COinJaUinC.-. .-.UaC mlnELxO 001 0 WSLW €0_c -.-iLO ininU ..JCi.xmm +'C Oinri9Win.C.CL04J L> ins...ainau inLO n—° mm w-n-..m 3÷' inaL z÷minme.x 0-...-D mu-.-. 0 o.-ain.o-.-' inmin aa,rtWoe —acm .-s0t.ca. >-0 4.1.009inDia diW OIL -_ 00 i-.Cfl 5mW ..03>-.. 1dm mxli EL_c m Di 00101—. 0.-i OJCfl_-iUin mtm -inLU L >-WC 0 L4cicC0. 4,UUIin in..-.in 0 Cm 011105 IflC inU aOCCinD LC sin .11-i-i_cS.... in .Jin OOi in.--. Proceeding upward s t r a t i g r a p h i c a l l y , t h e supracrustal rocks consist of 15% nafic metavolcanic, oassive and pillowed b a s a l t i c , and l e s s e r andmsi t i c f lous and associated breccia5 and p y r o c l a s t i c rocks. Chemically, these rocks a r e magnesium- and i r o n - t h o i e i i t i c b a s a l t s , t h o l e i i t i c andesites and calc-alkaline b a s a l t s . The iron t h o l e i i t e predominatr. Intermediatr oetavolcanic f lows and basal t s p y r o c l a s t i c s make up about 4% of t h e supracrustal rocks and c o n s i s t of t h o l e i i t i c dacites and calc-alkaline andnsitf. Felsic metavolcanic flows and p y r o c l a s t i c rocks of c a l c - a l k a l i n e d a c i t f t o r h y o l i t e composition make u p about 3% of t h e supracrustal rocks. The intmrmediate and f e l s i c metavolcanics increase in proportion west of M i s h i b i s h u Lake. inWGaWIi I. -.-.tfl -I-jOqF0 II. in -— c-. LmL 00'.- 0 C CL 03_cO -.-. 0 .-.fli>- ..-i OW mcmua-.-' 0-.4+J..45in L fl-i-'LO-.-. 'I LW_c L CL.i-'Om mci n in in CE .xWiODI mmUac-_m -.4_n_c WCCCD OlinOOc '4-0-i-aCId -riE 0-4-s S 1d5..iW.-.. LUd 0 .fl4n 0004,4, C.C'.-iflc mi—-.--.-. CL UW in—. >-. Di >-L00 ..-.a-.-. .'4inL04-' U .cin---4 W4.aCLO uSOS -.-.uuum EQ DC '-4 0L ICWEWO 0 Oc.-'.cSs u-_-_xc inWa' OC-.-.L 0L0fl0 C.',... 4-'C-C --.-.l -0 4,0 Ui_c .-. 4-. 0 •.-.0-..mu c A considerable range of mineralogy and chrmical composition i s evident in t h e q r a n i t o i d rocks. The stocks intruding the supracrustal rocks tend t o be f a i r l y uniform in composition u h i l e t h e b a t h o l i t h i c rocks bounding t h e supracrustal rocks e x h i b i t a more varied composition and may be multiple i n t r u s i o n s or the product of a d i f f r e n t i a t e d magma. - —In O.W r: 4-' • inn.n.OL m .1 - LUJ .—1 oincJ-aCO0FL-,.r _j L_J in Ln no _J J j in-id0zm in -.4 .__t_J Oa,n>n minma, a. u_cc 0 in_cO-.. ni— -ninu.--.-.-. .1mm -.-i_c w gI.-.000W uD>-+'Ww -.-.co, uci mE--.-' 0.-au-.-,C Z— -riO -..Lm.nc.c-.-a i-'Os on ..-am-.-.mmO—-at-.-. C-ia CJL.-. in.4in Etj—.-,.0.'-.-. (Eta rwus_c-.-. -nm.--i u4-.-.u-ri.-—tO-En .0 OCU—DW WidLu-.-. Idin .-. 0..-' .0 ...oo 00th oInm-nea.--.u÷.>...L-.4 .-..xm mom_c .cLmO.-mn-.-. Ocr UWIdOWL .C4.'CC-C —.we—.ina 4J>-4Jin L)a-.inLac I—004U Din UDOn C-.-.O.4-'Li-iDCinO-.-.x ou> >Dinin-ri nClOinO & 'i-CC'U>-M-WC-.. z The Hishibishu Lake Area i s located about 35 kr w i t of Maua and about 80 km southeast of Hemlo. The M i s h i b i s h u Lake supracrustal belt i s about 33 k m long and 16 km uide and i s concave t o t h e south, by felsic bounded on either end by Lake Superior, enclosed b a t h o l i t h i c c o ~ p l e x e sand l o c a l l y intruded by younger f e l s i c plutonic rocks. The r a t i o of supracrustal t o b a t h o l i t h i c rocks is 2:3. S) .J .J LU to (Ontario Beological Survey, 77 Brenville, Toronto, Ontario -UJ en —I .._J ._J �I— 1.. m 01vOLD - - >.W In t.-tfl.-'-irnoimc.,-.u — OJL -,-.-.-.>mthD .rwmon 0-0 It, 1, Smq--oo ojo in dl a0 .-..dowmmiu LN>J-,.C 0-.-.uo ndi nm..-.-. ODmOM-in 0-1.0 E03L E-e-' Ui 04-' 0C >flO•..-,. CLZ -C ma, in ainmut -u djrn>-..'-.. r—U)m.-.L .-.wn 4-.-.-.030003ffl -,-.— OIC.X ma D4-.-. uo..JWauw .iiOI—>c-.-.0 ...o i,.mco. C-.-. Em Cdi >%flDifl LI. fr) U .CW .-.0tJ 0.mmmo..-.tO 03—Ln m .••,.4 viW -..j4-3E 010mW iii 1,4-3>03.-i >.)-9--,-.m.-.a. in 1,4.5 .cn 030 D'CO 0. >-. — U inc 03 ' CCO -..Ø' t.1i9 rn.-. ai÷'.-' 40cc €-'aj040 L.,-.Lfl.--.UI .-.-.m 0mo •-.>9-mCi CLO .W n QIC0 >-m mcci L-'-' in a0'ai.3 Co ma no, c•... c — 2m r • .4.iGiJ n.m in 40 >OU .CCirio,>03k.-0 mc o-wc t,-4 m÷.mc -a-cC *L.i.3 Wcai.-. wmn'o .xa,nmW .CLDL ULIflinin..'n> 0.IJinL03 WCW LI 03OJ-,-..-.C0c .-sL,-.,--wmwuu W0lmin0La m mr—. cn 0,> Cm 0'.-. -.-.rni.Wmaj-...c 03 C.-.)0L LU .-..Cfl COIL_..40 -n—coWcm-,. .—..-. >r C o.ir.. urn ..-.uzm .' 0L.t-.-. i-sm C rnm..J.._.n,mL 0 flEm---.-. ---40-.-4 .02 caJou CLCO-i-' ..-. CD mrnunm.s-'q4rnC03 innin 0.-..cc.,-.omwn. -.-'mrnu -.-...-..E 0-fl CLEL -..mmc.4-'Co'Eu >W WWcm OWC 0-..-.-.x . -.-44fl .-..--. 0Win-..,-.EnLI3 cm a.'UI —.c 0..mn C muir-rn —.--.-.c-.-'._-_wum -... 1, C Un' ciinin CC .fl. 0J.,..4-I E-r.-.-4 iii mc .n x.-. WI. m 0-.--.-. in mDnmEc -3'n mi-sW 0 .... The s u p r a c r u s t a l r o c k s have been f o l d e d i n t o an i s o c l i n a l synformal shape about an e a s t - t r e n d i n g a x i s w i t h s e v e r a l s u b p a r a l l e l p a r a s i t i c f o l d axes on e i t h e r side. F a u l t s and l i n e a m e n t s w i t h v a r y i n g degrees o f m o v f n t d i s p l a y d along them c u t a l l Archean l i t h o l o g i e s , b o t h p a r a l l e l and t r a n s v w s e . Shearing i s most i n t e n s e near t h e l a t e stagm i n t r u s i v e b o d i r . The main H i s h i b i s h u Deformation Zone i s a composite o f smveral shear zones. Shearing i s c h a r a c t e r i z e d by an increase i n the penetrative fabric, examples o f which a r e k i n k banding i n c l u d i n g c o n j u g a t e k i n k s e t s , c o m p o s i t i o n a l banding and t h r c dimensional chevron f o l d s . in 9-00. mU..-fl 4.3 -t 0 9- (04' 0 C 40 .C I—.m_ .4-' 03 Ci In > 03 -n-a1,0>.co ida' 0' mon.mn. ••• 4.3 03.—. '-4 -S tj c3 c =i - i a C WOO 1130 WDO L 03c CL •V GJ—C-'.c--' C WD2LOA-s 1.-Did 0' E-+LO' in tiiCjOU .-.E a3.CCUL-,-... •LC Ifl..-Jmom.i-.Jwoo SC DEm Dorm+s Ill ma, 40 DO mm> cLLcO,n'Lo, OLOW 1,IS1OD c'+.O..-.ct,'* 1,-4 -.-'..-'W --.0j .0 OCOOCI-.-LLO wL.-.-.-'a-,Lm— Ca. O0'-.'a9-CD—a LW ,cCOU X>.-.-. on uu 03+2 w L 1, 0>. 1.0 111am • Lwmc L>q-nt-4inindpinain -o to 0U O3LO .C 0 C WOLdm03m+iaW 030(0 mL- C 1, 03.-it ZoOq.-.-. .0 03cm—rn .-'—-,-.uin W÷'DWL-.-.COa, CL-1,DLOc> c0-.Jm.fl-.-. ..-. -n om mOlLffl'4->-mLiUOj>. 03 LOW 0..LW..j>.. I. Cot w.-.m -..ac 'omamo.O.—. LOD -.-.X.JC OW >0 -.-.cxED'c-.. c 03 -to -.-C-,-. 0 C4.' 03m 1,flC-.-.> .'C m>->-.,-.z_o'o I. L id.--.. 4.020>-.-. -4-' -rN-LCWt-SJLLW 0m flCOIaOI-.4C toE co-ww OCO 0—4 03cm .ca, 4.CVWWDQ.UI 4-Jo, E mc ES' mu •L 4-sauna, 1, C >-m-n n4i—. 00 0..-LOJCW 01DcmWW -t D 0. a' LELW.-4ffl xrnc-or003mm 030303PICW>WL>Lu-.-'fl-O OJLSI-. —.0 mu C 01 4- DtJ.0 Iii 0-4-' m 29- -.-. rnmxo,W-,l-.-.WD'o ,.mm÷scld-.-JnrnW..-. m>— Wmc WLCWLC .0 0301 .30303005 Q..-.W0W-.-.03 fln.oEv0n'n.Lo0m -.i03 uS..-.VlWmcin r.-. LCEucL c..-Ic.mE0,-.-'m 9- 0 di 3c L -.-. L .. 01 C03..m4-'>UICn0 Lm - .D-.. 0 flin9U C m.4.soa'cJoCuc LD CCL ....c0J 0011103 a'03 ..C n03€-4c-L.'03 ... M i n e r a l e x p l o r a t i o n i n t h e area has been recorded i n assessment f i l e r e c o r d s s i n c e 1907 and i s r e p o r t e d t o have begun b e f o r e t h e t u r n of t h e century. E a r l y e x p l o r a t i o n was f o r i r o n o r e and was c o n c e n t r a t e d near t h e David Lakes area. Gold e x p l o r a t i o n occurred b e t w ~ n1937 and t h e b e g i n n i n g o f U o r l d Mar 11. A f t e r t h e war g o l d e x p l o r a t i o n resumed and w i t h o n l y b r i e f b r e a k s c o n t i n u e d u n t i l t h e present. Some base metal e x p l o r a t i o n p r o j e c t s occurred from t i m e t o ti-, however, t h e s e programs w r e n o t o f a v e r y l a r g e s c a l e . The area i s p r e s e n t l y u n d w g o i n g r e l a t i v e l y i n t e n s e e x p l o r a t i o n f o r g o l d w i t h s e v e r a l companies i n v o l v e d in property (Valuation and f e a s i b i l i t y s t u d i e s on p r e v i o u s l y d i s c o v e r e d shonings. J ) fl =3 rj 1 =J 1 .CO.-4fl >1, .I' C—. C—.lt -—mmrn.-.m vOn. 2 0 -D • L—0.3 Ee.JC ..-.u cvi UL 4.3 -.. miii -.-.WL DLWW0a-.-' ..t.XNDW mow 2.m .JL L 03010 0.-.-i.I C -s-Ix .cOmE inL..JIIi >-fl0 Cr 0.0.3jfl 9-fl -—0- E mEm.c-.-' 1, EmwrnmWo Jc..4_JLE OiO rno-.ir ..4i0 9C.3 0300103 WWW.t OIIin.4JUiW .tuUuLcO am-.-.o C u W 3,QU fl—---40C4-iGJ C4-eJWWn wOmoim-.-. .ce>-.-.zinE .—E0,03÷'cO 0 1, 0 —4 COl L--'OL--.WD mm Dc., r)-0u .EDOCCOIW muLidOL> ola,-.-.mm i-i 0303.-scm = re000i 0 1, 1. L 0 0 Inn. C 03.—.a -a a.mm-,4m 0 idCa.O -€4 mc 9-..4 CLO' Lolca, o'-mn.-. U oWEmL. .,i4J .3C030J03 .-.mac VOL -.4L 03-.-. U glnint..-..0 DL. .4-Ira, m•.-. C L on CC+'C - The physiography i s c h a r a c t e r i z e d by low t o moderate r e l i e f , commonly broken by s t m p s i d e d h i l l s and r i d g e s 30 t o 200 m high. E l e v a t i o n s range from 183 l (Lake S u p e r i o r ) t o 300 m above sea l e v e l . P l e i s t o c e n e d e p o s i t s a r e varved c l a y s w i t h l e s s e r d e p o s i t s o f sandy Recent s u r f i c i a l d e p o s i t s outwash, t i l l , g r a v e l b a r s and d e l t a s . c o n s i s t o f a mantle o f o r g a n i c d e b r i s and r e c e n t e r o s i o n a l p r o d u c t s from bedrock and g l a c i a l d e p o s i t s . CI.4-3LWD 000 -o$n a' w>uwo .atnoL L034-0300+t)034J4J n,.—...-wowm UiCC co 303001003 0-.n-fl 0D'..-'Wuu 03.,. — ..'O —.0303 .min •L -...--. —r LL r)m> in .mWr Un. c÷'m-.-.d cojuCa.-' mm o mc LU LLC LUI+'o' Cal-nOD 4-' O'-.-.a-n • ma,dlnO •'in 0C c-.. cm U-4-i Ui-i-''-. cm>-.orn Metamorphic grade i s m a i n l y low t o m i d d l e g r e e n s c h i s t rank w i t h some c o n t a c t f a c i e s t o r p h i b o l i t e rank. M i d d l e t o L a t e Archean and P r o t e r o z o i c diabase d i k e s o f a t l e a s t 3 d i f f e r e n t ages c u t a l l Archean r o c k s i n t h e M i s h i b i s h u Lake Area. Several d i a t r e m e s and e r o s i o n a l r r n a n t s o f L a t e P r o t e r o z o i c l a v a s occupy t o p o g r a p h i c a l l y low areas near t h e shore o f Lake S u p e r i o r . These r o c k s do n o t appear t o have undergone metamorphism o r s t r u c t u r a l deformation. �AA Brief B r i e fLook LookataGLIMPCE t GLIMPCE W. CANNON (USGS,Reston, Reston, VA W. CANNON (USGS, VA 22092) 22092) 3. BEHRENDT, M. LEE (USGS, Denver, CC J. BE-T. M. LEE (USGS. Denver. CO 80225) 80225) 0. HUTCHINSON (USGS, WoodsHole, Hole, MA HUTCHINSON (USGS,WOO~S MA 02543) . 0. A. B. MILKEREIT, A. GREEN, GREEN, C. C. SPENCER, SPENCER, B. MILKEREIT, P.P.MOREL, MOREL, A.A. DAVIDSON, OAVIDSON, 0. TESKEY (GSC,I1Observatory ObservatoryCrescent, Crescent, Ottawa, 0. TESKEY (GSC, Ottawa, Ont. Ont. K1A K I A 0Y3) OY3) The Great GreatLakes LakesI nInternational The t e r n a t i o n a l Multidisciplinary M u l t i d i s c i p l i n a r yProgram Programon on Crustal Evolution Evolution(GLIMPCE) (GLIMPCE) was was conceived in i nNovember November 1985 1985 ttoo coordinate researchononfundamental fundamental problems problems of of coordinate multidisciplinary mu1t i d i s c i p1inaryresearch Participants crustal c r u s t a l evolution e v o l u t i o n of o fthe t h eGreat GreatLakes Lakes region. region. P a r t i c i p a n t s include include U.S. and Canadianfederal federalgeological geological surveys, surveys, sstate U.S. and Canadian t a t e and and pprovincial rovincial GLIMPCE has has geological surveys, manyuuniversity geological surveys, and and many n i v e r s i t y geoscientists. GLIMPCE tthe h e following f o l l o w i n g principal p r i n c i p a l aims: aims: To promote cooperative research 1.. To 1 promote cooperative researchand andcommunication communicationamong among researchers researchers i in n the region, region, To advocate advocatefunding fundingoof research i in 2. 2. To f research n the region, region, and and To cooperatively cooperatively fund 3. 3. To fund large l a r g e geophysical geophysical surveys. surveys. During tthe During h e first f i r s year t yearofoGLIMPCE, f GLIMPCE, tthree h r e e large l a r g e data data sets sets were were acquired. Seismic Seismicr reflection km acquired. e f l e c t i o n profiles p r o f i l e stotalling t o t a l l i n1350 g 1350 kmwere were obtained obtained by marine marine seismic seismic surveys surveys in i nLake Lake Superior, Superior, Lake LakeHuron, Huron, and LakeMichigan; Michigan;preliminary preliminaryrresults and Lake e s u l t s are displayed displayed in i n posters posters Duringt the throughout tthis throughout h i s meeting. meeting. During h e rreflection e f l e c t i o n survey, survey, aa large large data. set of refraction and wide—angle reflection data also was data. set o f r e f r a c t i o n and wide-angle r e f l e c t i o n data also was recorded aatt on—land recordings isites placedsstrategically on-1 and recording t e s placed t r a t e g i c a l l y around around the the recorded lakes and and with w i t h lake lakebottom bottomseismometers. seismometers. Data Data were were recorded by by teams from from the the University teams U n i v e r s i t y ofo fWisconsin—Madison, Wisconsin-Madison, UUniversity n i v e r s i t y of of Wisconsin—Oshkosh, Southern University, Western Wisconsin-Oshkosh, Southern I l l iIllinois n o i s University, Western Ontario Ontario University, University U n i v e r s i t yofoSaskatchewan, f Saskatchewan, the the Geological Geological Survey Survey of of Funding Canada (GSC),and andt the Canada (GSC), h e U.S. U.S. Geological GeologicalSurvey Survey(USGS). (USGS). Funding ffor or all through tthe GSC through h e Lithoprobe Lithoprobe a l lseismic seismicwork workwas was provided provided by by the t h eGSC Program and and by L o g i s t i c a l support support was was provided provided by by the the Program by the t h eUSGS. USGS. Logistical Ontario Geological Geological Survey Survey and and the the U.S. U.S. Coast CoastGuard. Guard. IIn n another another cooperative cooperative survey, survey, a anew newaeromagnetic aeromagnetic map map of Lake Lake Huron was funds from fromthe theGSC GSCand andthe t h eUSGS, USGS, the t h eGSC GSC Huron was produced. produced. With funds conducted survey and andproduced producedthe thepreliminary preliminary map napon onddisplay conducted t hthe e survey i s p l a y in in tthe h e poster poster session. session. Seismic rreflection Seismic e f l e c t i o ndata datafrom fromLake Lake Superior Superior reveal reveal aaremarkable remarkable imageoof Keweenawan basin strongr reflecR i f Rift t basin w iwith t h strong eflecimage f tthe h e asymmetric asymmetric Keweenawan andand sedimentary ttions i o n s from from the t h e intercalated i n t e r c a l a t e d rift r i fvolcanic t volcanic sedimentary horizons horizons Beneath extendingt to two-wayt rtravel times (T) (1) of extending o two-way a v e l times o f à 7 ss (( 5 20 km). km). Beneath the western end of the lake, the crust-mantle transition is t h e western end o f t h e lake. t h e crust-mantle t r a n s i t i o n i s represented bythe the base baseoof prominentband bando fofr ereflections represented by f aa prominent f l e c t i o n s tthat hat km)t to ddips i p s to t o the t h e south south from from TT —11.5 * 11.5 s (—'38 ( - 3 8 km) o TT —14s 14 s (-'40 ( - 4 0 km) km) and beneath beneatht hthe centeroof lake iti tcould and e center f tthe h e lake couldbe beas asdeep deep as as TT 17 5s The GGrenville (—56 ( - 5 6 km). km). The r e n v i l l e Front Front at a tthe t h ewestern westernend endofo fGeorgian Georgian Bay Bay is asaa spectacular spectacularseries seriesoof dipping reflections i s imaged imaged as f eeasterly a s t e r l y dipping reflections west tthat h a t truncate truncate a nearly nearly flat f l a thorizon horizon that t h a tlies l i e to s t the o the westbeneath beneath Lake Huron Huron aatt TT — Lake <x 6 s s ( —20 4 0 km). km). A A less less prominent prominent band bandofofsub— sub—'40 km) —35 km) 10 ss ( ~ 3 km) 5 t to o T a 12 12 5s ( -40 km) hhorizontal o r i z o n t a l reflections r e f l e c t i o n sata tT T— 10 maydelineate delineatet hthe baseo fofthe thec rcrust may e base u s t i in n tthis h i s region. region. - È —15— - - ( �6.1 Superior Superior Province: Province: The The product product of of Archean Archean convergent convergent plate p l a t etectonisni tectonism U K.D. K.D. CARD CARD (Geological (Geological Survey Survey of of Canada, Canada, 588 588 Booth Booth St., St., Ottawa, Ottawa, Ontario Ontario K1A K I A 0E4) OE4) Models for the the tectonic Models proposed proposed for tectonic evolution evolution of of the theArchean ArcheanSuperior Superior Province Province (SP) can be characterized as fixist (1,2,3) involving deposition of volcanics (SP) can be characterized as fixist (1,2,3) involving deposition of volcanics and and sediments in rifts rifts of sediments in of older older sialic sialic crust, crust, followed followed by by gravity gravity driven driven vertical vertical tectonism; or mobilist (4,5,6) with convergent plate tectonism, tectonism; or mobilist (4,5,6) with convergent plate tectonism, such suchas as in in the the NW NW Pacific where ongoing accretion is the result of subduction beneath Eurasia Pacific where ongoing accretion is the result of subduction beneath Eurasia (7,8). (7,s). SP SP greenstone greenstone belts, belts, from from 3.0 3.0 to to2.7 2.7 Ga Ga (9) (9) consist consist of of lower, lower, extensive, extensive, submarine plain tholeiitic tholeiitic pillow submarine plain pillowbasalts basaltsand and komatiites, komatiites, and and upper, upper, partly partly subaerial, of calc-alkaline calc-alkaline and tholeiitic subaerial, chemically diverse diverse central complexes complexes of and tholeiitic volcanics volcanics with with turbiditic turbiditicsediments sedimentsthat thatalso alsoform formthe thelarge, large, intervening intervening metasedimentary andalluvial/fluvial alluvial/fluvial metasedimentary belts belts (10). (10). Late Lateshoshonitic/alkalic shoshonitic/alkalic volcanics volcanics and sediments unconformably overlie older volcanics in some belts. SP greenstone sediments unconformably overlie older volcanics in some belts. SP greenstone sequences donot notresemble resemblethe thefill fill of of continental continental rifts, rifts, which sequences do which commonly commonly begin begin with alluvial sediments and end with volcanics (11,12), nor do they resemble Proterozoic alluvial sediments and end with volcanics (1 1,12), nor do they resemble Proterozoic greenstones depositedon onrifted riftS sialic begin with with terrigenous terrigenous greenstones deposited sialiccust custwhich whichcommonly commonly begin sediments and end with submarine volcanics. They do resemble sequences of island island sediments and end with submarine volcanics. They do resemble sequences of arcs that vary from immmature to mature and from ensimatic to ensialic (13,14). arcs that vary from immmature to mature and from ensimatic to ensialic (13,14). SP plain accumulations may may represent represent the lower parts SP submarine submarine plain parts of of accreted accretedarcs, arcs, seamounts, seamounts, or or upper oceanic crust, whereas whereas the the complexes complexes are are the the upper upper parts parts of of mature mature arcs arcsor or oceanic oceanic islands. islands. Bimodal Bimodalcycles cyclesmay mayrepresent represent back-arc back-arc volcanism volcanism on be the the on stretched stretched continental continentalcrust crustand and late latecycles cycles in in polycyclic polycyclicbelts beltsmay may be products products of of back-arc back-arc rifting riftingand and intra-arc intra-arc wrench wrenchfaulting. faulting. Superior Superiorturbidite turbidite belts belts ma' may represent represent the the fill fillofoftrenches, trenches,intra-arc intra-arcand andback-arc back-arcbasins, basins,and and transported transported deep-sea deep-sea fans. fans. Li —I SP and later, later, sodic suites suites and SP plutonic plutonic rocks, rocks, including including early, early, in inpart partsynvolcanic, synvolcanic, sodic in those ofofPhanerozoic Phanerozoic in part partsyntectonic, syntectonic, potassic potassic suites, suites, are generally similar to to those orogens. 3.0 to to2.65 2.65 Ga Ga and, and, like likethe thevolcanics, volcanics, display display orogens. They Theyrange range in in age age from from3.0 little littleevidence evidenceofofisotopic isotopicinheritance inheritancefrom fromappreciably appreciablyolder older(>3.0 P3.0 Ga) Gal crustal crustal sources sources(15). (1 5). Plutonic-supracrustal Plutonic-supracrustal contacts contacts are are mainly mainly intrusive intrusive or or tectonic; tectonic; unconformities arerare. rare. unconformitiesare SP trends and and metamorphic metamorphic zonation may be be partly partly attributable attributable to to SPstructural structural trends zonation may early orogenesis, but are mainly the products of late, polyphase events early orogenesis, but are mainly the products of late, polyphase events that that occurred south. Major Major occurred at a tabout about2.73-2.7 2.73-2.7 Ga Ga in inthe thenorth northand and2.7-2.68 2.7-2.68 Ga Gain in the the south. north-south compression and transpression resulted in early, ductile, isoclinal north-south compression transpression resulted in early, isoclinalfolds folds and later, increasingly brittle shear zones and wrench faults. Major recumbent and later, increasingly brittle shear zones and Major recumbent folds, beenmapped mappedinin some some belts belts(16,17,18). (16,17,18). folds,thrusts, thrusts,and anddeformation deformationzones zoneshave havebeen In In the the NW NW Pacific, Pacific, terrains terrainsof of lithological, litholo ical,structural, structural,and andmetamorphic metamorphiccomplexity complexity such (8) and and Japan 3apan (19) are variably variably deformed deformed and such as as the the Philippines Philippines (8) 19) are and ? metamorphosed metamorphosed subduction subduction complexes, complexes,arc, arc, back-arc back-arc and and trench trench sequences sequenceswith with abundant of about about 300 300 M Maa through through aa complex rocks accreted accreted over over aa period of complex abundantplutonic plutonic rocks sequence evident is evident sequenceofofthrusting, thrusting,rifting, rifting, wrench wrenchfaulting, faulting,and andisoclinal isoclinalfolding. folding. ItIt is that common, that Superior Superior Province Province and and the the NW NWPacific Pacific have have many manyfeatures features in in common, including including similar similarassemblages, assemblages, structural structuraland and metamorphic metamorphic styles, styles, scales, scales, and and time time Differences of komatiites in as the the absence absence of in the the NW NW Pacific Pacificand and the the Differencessuch such as lack belts rocks theSP SPcan can lackofofpaired pairedmetamorphic metamor~hic beltsand andabundance abundance of of plutonic ~Iutonic rocksininthe probably probably be attributed to &I hotter hotterArchean Archean mantle mantleand and the the relatively relativelyshallow shallow level levelof of erosion erosion in in the the NW NW Pacific. Pacific. frames. frames. ~- —16— ~ - ~ - - - - U U �REFERENCES REFEREN ES 1) 1 WBaragar, . R .W.R.A. A . and and McGlynn McGlynn 3.C., J.C., 1976, 1976, Geol. Gaol. Surv. Surv. Can. Can. Paper Paper 76-14; 2) Young, G.M., 1978, Geoscience Canada; 2) Young, G.M., 1978, decadence Canada; 3) U). p., 1985; in GAC and o n s trh u -Thurston, 'l G C Spec. Paper 28, 343-380; 33-380; 3) Ayres, Ayret, L. D. and 4) Langford,F.F. and Morin, M.A., 1976, Am. 4) Lang1ord.F.F. and Morin, M A , 1976, Am. Jour. 3our. Sci., Sd:,276, 276, 1023-1034; 1023-1034; 5) C.E., 64-72; 5) Blackburn, C & . , 1980, 1980, Geosci. Geosci. Canada Canada 7, 7,64-72; 6) Dimroth, E., Imreh, U., Goulet, N., and Rocheleau, M., ., Imreh, L., Goulet, N., and Rocheleau, M. , 1983, 1983, Can. Can. Jour. Jour. 6) Dimroth, E Earth Sci., 20, 1374—1388; 20, 1374-1388; 7) 7) Nur, A. and Ben-Avraham, Ben-Awaham, Z., Z., 1983, 1983, Terra Terra Scientific ScientificPubl.Co., PubLCo., Tokyo; Tokyo; 8) Hamilton, W., 1979,U.S.G.S. Prof. Paper 1078, 345 p. 9; 8) Hamilton, W., 1979,U.S.G.S. 9) 9) Davis, D.W.,Corfu, D.W.,Corfu, F., F., and and Krogh, Kro T.E., L.P.1. Tech. Rept. No. NO. 86-10, 86-10, 77-79; 77-79; 10) Ojakangas, R.W., 1985, in G.A.C.Spec. Paper 28, 23-47; 10) Ojakangas, R.W., 1985, in G.A.C . 11) 11) 12) 12) 13) 13) 14) 14) 15) 15) 16) 16) 17) 17) 18) 18) 19) 19) Van Am. Assoc. Assoc. Petrol. Geol., Van Houten, F.B., F.B., 1977, 1977, Bull. Bull. Am. Geol., 61, 61, 79-99; 79-99; 12) 12) Hoffman, P.F., Nature, in preparation; Hoffman, P.F., Nature in preparation; Sylvester, Attoh, K., and K.J., in in press, press, Can. Can. 3ovr. Jour. Earth Earth Sci.; Sd.; ~.J.,Attoh,~., and Schulz, K.J., Sylvester, P.3., Ludden, iN., C.,C., 1986, Geol.Mag., 153—166; J.N., Hubert, Hubert,C., C.,Gariepy Gariepy 1986, Geol-Mae.,123, 123, 153-166; Shirey, Geochem. Cosrnochem. Acta, 50, w e y , 5.5. saand Hanson, G.N., G.N., 1986, 1986, 50, - G 2631—265 1. 2631-2651. Paulsen, K.H., G.3., Can. Jour. K.H.9 Borradaile, k-k, GJ.9 Kehlenbeck, K M k k , M.M., MA., 1980, 1980, CmJOW. EarthSci., 17, 17,1358—1369; 1358-1369; McGill, G.E. .& and Shrady, Shrady, C.H., C.H., 1986, 1986, Jour. 3our Geophys. Res., 91, 91,E281-E289; E2814289; Hubert, and Ludden, Hidden, 3.N., J.N.9 1986, 1986, in in L.P.I. L.P.I. Tech. Tech. Rept. R-t. 86-10, 86-10, 121-123; 121-123; Hubert, C. C. and Taira, 51-63, Tokyo. A., 1985, 1985,DEUP DELP Pub Pub 3, 3,51-63, Tokyo. Taira, A., -, —17— �U -I A agef ofor trondhjemitecclast A precise precise U—Pb U-Pb z i rzircon c o n age r aatrondhjemite l a s t in i nthe theDore Dore conglomerate, conglomerate, Wawa, Wawa, Ontario. Ontario. F. (Ont. Geol.Surv., Surv.,c/o do Dept. F. CORFU CORFU (Ont. Geol. Dept. of of Mineralogy Mineralogyand and Geology, Geology, Royal Royal Park, Toronto, Toronto, Ont. O n tOntario a r i o Museum, Museum, 100 100 Queen's Queen's Park, Ont. M5S M5S 2C6) 2C6) R.P. (Ont.Geol. Geol.Siirv., Surv.,77 77GGrenville r e n v i l l e St., St., Toronto, Toronto, Ont. Ont. M55 M5S 183) 103) R.P. SAGE SAGE (Ont. j Trondhjemite predo— Trondhjemite clasts c l a s t sand and boulders, boulders, set setin ian matrix a m a t composed r i x composed predo- minantly characteristic m i n a n t l y of o f volcanic v o l c a n i c detritus, d e t r i t u s ,are area a c h a r a c t e r i s t icomponent c component of o f the the Dore greenstone belt, Subpro— Dore conglomerate conglomerate in i n the theMichipicoten Michipicoten greenstone b e Wawa l t , Wawa Subprovince. and associated associated sedimentary rocks are vince. The The Dore Dore conglomerate conglomerate and sedimentary rocks are laterally interfingered with felsic volcanic rocks belonging to l a t e r a l l y i n t e r f i n g e r e d w i t h f e l s i c v o l c a n i c rocks belonging t o the the second volcanism i in the bbelt. second ccycle y c l e oof f volcanism n the e l t . These These uunits n i t s are are overlain o v e r l a i n by by aa third cycle comprising intermediate to mafic volcanic rocks. The t h i r d c y c l e comprising intermediate t o mafic v o l c a n i c rocks. The distribution clasts suggests d i s t r i b u t i o nofothe f the c l a sin t s the i n conglomerate the conglomerate suggestsa provenance a provenance from a source in the west of the belt. Blue anatase from a source i n the west of t h e b e l t . Blue anatase isi sa aunique unique feature, feature, that t h a tmay may help h e l p in i n locating l o c a t i n gthe thesource source of o fthe thetrondhjemite. trondhjemite. A attempt tto date aa trondhjemite trondhjemite cclast A previous previous attempt o date l a s t by by analysing analysing bulk bulk zircon fractions was hampered by the highly metamict, U—rich zircon f r a c t i o n s was hampered by the h i g h l y metamict, U-rich nature nature of of the the zircons zircons which which yyielded i e l d e d very very discordant discordant analyses analyses (Turek (Turek eett al. a1. 1984). the analysis i f f e r e n tapproach approach based based on on the a n a l y s i s ofo f20-1 20-1ugugsamples samples 1984). AA ddifferent of the subordinate, carefully selected and strongly abraded, of the subordinate, c a r e f u l l y selected and s t r o n g l y abraded, clear clear zircons zircons provided providedconcordant concordant and and nearly n e a r l yconcordant concordant data data which which define d e f i n e an an age of 2698 +/—2 Ma. The various fractions analyzed comprised age o f 2698 + I - 2 Ma. The various f r a c t i o n s analyzed comprised longlongprismatic, prismatic, euhedral enhedral crystals, c r y s t a l ssubrounded , subroiindedgrains grainsand andapparent apparentcores coresand and single the mmatrix of aa clast. clast. All A l lthese these analyses analyses yyield ield s i n g l e zircons zircons from from the a t r i x of indistinguishable i n d i s t i n g u i s h a b l e results r e s u l t s indicating i n d i c a t i n gthat t h athe t thetrondhjemite trondhjemitedoes does not not contain contain any any older, older, inherited i n h e r i t ecomponent. d component. U jj The +/—2Ma Maage agef ofor the ttrondhjemite The 2698 2698 +/-2 r the r o n d h j m i t e is i ssimilar s i m i l ato r tU—Pb o U-Pb dates reportedbybyTurek Turekeett a1. al. (1982, dates of of 2696 2696+/—2 +/-2 and and 2698 2698 +1—11 + / - I 1 MaMareported (1982, 1984) 1984) ffor o r felsic f e l s i cvolcanic v o l c a n i crocks rockswithin w i t h i ncycle c y c l 2. e 2Since . Sincethe theDore Dorecongloconglomerate merate iis s stratigraphically s t r a t i g r a p h i c a l l yassociated associatedwith w i t hthese these volcanic v o l c a n i crocks rocks the the overlapping agesi nindicate of volcanism overlappingU—Pb U-Pb ages d i c a t e aa very rapid r a p i dsequence sequence of volcanismand and plutonism, and sedimentation plutonism, uplift, u p l i f t erosion , erosion and sedimentationspanning spanning only o n l ya afew fewMa. Ma. The The source source ooff the t h e trondhjemite trondhjemitedetritus d e t r i t uis s unknown. i s unknown.The TheU-Pb U-Pb age age indicates that it was not derived from older sialic crust documented i n d i c a t e s t h a t it was not derived from o l d e r s i a l i c c r u s t documented in 2800—2900 t U—Pb by U-Pbages agesofofabout about 2800-2900 Ma Ma (Turek (Tiirek eett al., a1 1984). 1984). AA i nthe thebelt be1by possible source may be the granitoid terrain to the west, one p o s s i b l e source may be the g r a n i t o i d t e r r a i n t o the west, one uunit n i t of of which was dated by Turek et al. (1984) at 2698 +/—1 Ma. Alternatively which was dated by Turek e t a1. (1984) a t 2698 + / - I Ma. A l t e r n a t i v e l y ., U the represented the the rrapidly the trondhjemite .trondhjemitemay may have have represented a p i d l y uplifted up1 i f t emagma d magma chamber of cycle 2 volcanic rocks. chamber o f c y c l e 2 v o l c a n i c rocks. Turek, P.E., VanVan Schmus, W.R., A., Smith, Smith, P.E.,andand Schmus, W.R.1982. ,1982. Rb—Sr Rb-Sr and andU-Pb U-Pb ages ages Turek, A., of of volcanism volcanism and and granite g r a n i t eemplacement emplacement iin n the Michipicoten Michipicoten belt— beltWawa, Ontario. Canadian CanadianJournal Journalooff Earth Sciences, Wawa, Ontario. Sciences, 19, 19. pp. pp. 1608— 16081626. 1626 - - - - -Turek, P.E., VanVan Schmus, U—Pb Turek, A., A., Smith, Smith, P.E., andand Schmns,W.R., W.R.,11984. 984. U-Pb zzircon i r c o n ages ages and the eevolution and the v o l u t i o n of of the theMichipicoten Michipicotenplutonic—volcanic p l u t o n i c - v o l c a n i c terrane terrane of of the theSuperior Superior Province, Province, Ontario. Ontario. Canadian Canadian Journal Journal of of Earth Earth Sciences, 21, pp.457—464. pp.457-464. Sciences, 21, U di -18- u �Geochemistry Geochemistry of of Proterozoic P r o t e r o z o i c Volcanic Volcanic Hosted Hosted Iron I r o n Formations Formations in in Northern Northern Wisconsin: Wisconsin: Prospects P r o s p e c t s for f o r Gold Gold Mineralization Mineralization L. MICHAEL MICHAEL L. CUMMINGS CUMMINGS (Department (Department of of Geology, Geology, Portland P o r t l a n d State S t a t e University, University, Portland, OR 97207) P o r t l a n d , OR 97207) Iron I r o n formation formation units u n i t s were were selectively s e l e c t i v e l y sampled sampled in i n drill d r i l l cores c o r e s at a t the the Wisconsin Core Repository in Milwaukee, Wisconsin during exploration Wisconsin Core Repository i n Milwaukee, Wisconsin during e x p l o r a t i o n for for possible p o s s i b l e gold—bearing gold-bearing uunits. n i t s . The q u a r t z as as The rocks r o c k s contain c o n t a i n grunerite g r u n e r i t e + quartz + the mineral t h ecommon common m i n e r a l assemblage. assemblage. Ferro—hornblende, Ferro-hornblende. fferro—actinolite, erro-actinolite, stilpnomelane, stilpnomelane, and and sulfide s u l f i d e minerals m i n e r a l s are a r e present p r e s e n t ini nvarying varyingproportions. proportions. Most units are well—bedded and contain alternating r o n ssilicate i l i c a t eand and Most u n i t s are well-bedded and c o n t a i n a l t e r n a t i n g iiron quartz q u a r t z beds. beds. The The grade grade ofofmetamorphism metamorphism ranges rangesfrom from upper upper greenschist greenschist facies f a c i e s to t o amphibolite amphibolite facies. f a c i e s . Samples Samples were were collected c o l l e c t e d from from 99 cores c o r e s from from throughout the Northern Northern Wisconsin Wisconsin volcanic v o l c a n i c belt. b e l t . Ten throughout the Ten elements, elements, including i n c l u d i n g Au, Au, Ag, Ag, Cu, Cu, Pb, Pb, Zn, Zn, Co, Co, Ni, N i , As, A s , Ba, Ba, Mn, Mn, BB(ppm) (ppm) and and Fe Fe (%), (%), were determined for a set of 48 samples. were determined f o r a set of 48 samples. Whenever Whenever possible, p o s s i b l e , the t h e samples samples were were approximately approximately 33 mm lengths l e n g t h s of of core. core. > . Gold Gold was was detected d e t e c t e d in i n concentrations c o n c e n t r a t i o n s > .02 .02 ppm ppm in i n cores cores from from Marinette Marinette County Corporation) and Mineral County (Duva]. (Duval Corporation) and Clark C l a r k County County (North (North Central C e n t r a l Mineral Ventures). Ventures). In I n Marinette M a r i n e t t e County County the the iron i r o n formations formations are are those t h o s e associated associated with with the t h e Duvál DuvalDeposit. Deposit. Geochemical Geochemical data d a t a indicate i n d i c a t e patterns p a t t e r n s that that distinguish d i s t i n g u i s h the t h e gold—bearing gold-bearing iron i r o n formations formations from from those t h o s e in i n which which gold gold was was absent a b s e n t or o r below below detection d e t e c t i o n limits. limits. These These include: i n c l u d e : concentration c o n c e n t r a t i o n of of Cu, Cu, Zn, Zn, Pb Pb are are low low in i n all a l l iron i r o n formation formationsamples samples(Cu (Cu< <1,000 1,000 ppm, ppm, ave. ave. 208 208 ppm; ppm; Zn Zn K< 1,350 1,350 ppm, ppm, ave. ave. 180 180 ppm; ppm; Pb Pb <50 <50 ppm, ppm, ave. ave. 99 ppm), ppm), however, however, gold—bearing gold-bearing iron i r o n formations formations contain c o n t a i n Zn>Cu, Zn>Cu, they they also a l s o contain c o n t a i n detectable detectable concentrations are not not c o n c e n t r a t i o n s of of Pb; Pb; gold—bearing gold-bearing iron i r o n formations formations are distinguishable the basis b a s i s of of Co:Ni; Co:Ni; Fe Feand and Mn Mnsuggest s u g g e s tthat t h a t variations variations d i s t i n g u i s h a b l e on on the in the concentrations of both elements within the section are favorable i n t h e c o n c e n t r a t i o n s of both elements w i t h i n t h e s e c t i o n are f a v o r a b l e for f o r gold gold association, a s s o c i a t i o n , where where the theconcentration c o n c e n t r a t i o nof of both both do do not not vary vary gold gold was not detected; As concentrations ranged from 10 to 50 ppm and, was n o t d e t e c t e d ; A s c o n c e n t r a t i o n s ranged from 10 t o 50 ppm and, asas aa group, group, were were on on the t h e average a v e r a g ehigher h i g h e r in i n gold—bearing gold-bearing iron i r o n formations; formations; B Bisis elevated in gold—bearing iron formations (71 ppm ave. / e l e v a t e d i n gold-bearing i r o n formations (71 ppm ave. / 18 18 ppm ppm ave.). ave.). Fifty—three F i f t y - t h r e e additional a d d i t i o n a l samples samplesofof the t h eiron i r o nformation formationsection s e c t i o n ini n Marinette County were analyzed by instrumental M a r i n e t t e County were analyzed by i n s t r u m e n t a l neutron neutron activation. activation. Samples Samples were were prepared prepared from from sections s e c t i o n s of of core c o r e containing c o n t a i n i n g 22 to t o 55 cm cm stratigraphic thickness. s t r a t i g r a p h i c t h i c k n e s s . Twenty—eight Twenty-eight samples samples contained contained Au Au concentrations l i m i t sand andranged ranged upuptot o.15 .15 ppm. ppm. c o n c e n t r a t i o n s greater g r e a t e r than than detection d e t e c t i o n limits The Thepersistence p e r s i s t e n c eofof stilpnomelane s t i l p n o m e l a n eini nassociation a s s o c i a t i o nwith w i t hgrunerite g r u n e r i t eand and quartz theaxnphibolite amphibolite facies f a c i e s of of metamorphism metamorphism q u a r t z under under conditions c o n d i t i o n sofof the suggests s u g g e s t s aa high high alkali a l k a l i content c o n t e n t ini nthe t h eiron i r o n formation. formation. Trace Trace element element concentrations c o n c e n t r a t i o n s show showstrong s t r o n gvariability v a r i a b i l i t yamong amongsamples. samples. These These differences differences are arerelated r e l a t e d tot omineralogy mineralogy ofof the t h esample sampleand andtot othe t h eintensity i n t e n s i t yofofthe the hydrothermal hydrothermalsystem systemata tthe t h etime timeofof deposition. deposition. Volcanic. V o l c a n i c -stratigraphy s t r a t i g r a p h y suggests s u g g e s t s that t h a t the t h e iron i r o nformation formation in i n Marinette Marinette County was deposited d e p o s i t e d within w i t h i n aa local l o c a basin l basinthat t h amay t mayhave havebeen been aa caldera. caldera. County was Basalt Basalt dikes d i k e s and and sills sillswithin w i t h i nthe t h iron e i r o formation n formation were were intruded i n t r u d e d while while the the sediments were unconsolidated. unconsolidated. These sediments were These basalts b a s a l t sare a r echemically chemically distinct distinct from from basalts b a s a l t swithin w i t h i n the t h elocal l o c a lvolcanic v o l c a n i csection. section. —19— �U t.1 Two thickLake LakeIntrusion. Intrusion,Coldwell ColdwellAlkaline AlkalineCunolex. Complex. tario Two Duck Ontario 1. Geology and Structure Structure L Geology and WATKINSON (Dept.Geo1 ogy, Carleton Carleton University U n i v e r s i t y and and DAHL R,. IiEfawa—Carleton Centre oscience Studies, Ottawa-Carleton Centre f o for r Geoscience Studies, Ottawa, Ottawa, Ontario, DAHL R., WATKINSON D.H. DH .. (Dept.Geology, Ontario, 586) 586) 800—543Granvi Granville McGORAN (FleckResources Resources Ltd., Ltd., 800-543 St., Vancouver, 1l e St., McGORAN AM.J.W. (Fleck B.C., B C .,. V6C V6C 1X8) 1x8) 1(15 K1S TheColdwell Coidwell Alkaline Alkaline Complex, onthe thenorth north shore shore ooff Lake Superior, iiss The Complex, on Lake Superior, composite intrusion layeredgabbroic gabbroict oto syeni syenitic ti c aa Proterozoic Proterozoic composite intrusion o f oflayered rocks. Along Along iits occurs an an arcuate arcuatebbelt rocks. t s eastern eastern boundary boundary occurs e l t of of layered layered gabbroic rocks rocks regarded as aa single intrusive gabbroic regarded as intrusiveunit u n(CURRIE, i t (CURRIE, 1980). AA platinum—group_element(PGE) (PGE) and copper depositwas wasoutlined outlined through platinum-group-element and copper deposit 1986; WAIKINSON 1986)i in recent exploration exploration (DM1 recent (DAHL et e t aT., al., 1986; WATKINSON etetalal., ., 1986) n the sameunit. unit. Detailed mapping (1:200),structural structural analysis same mapping (1:200), analysis and and logging logging ooff new new ddrill r i l l core coreoutlined o u t l i n e da adistinct d i s t i n ccoarse—grained t coarse-grained gabbroic gabbroic tto o monzonitic intrusion, the Two Duck Lake Intrusion, cross-cutting the monzonitic intrusion, the Two Duck Lake Intrusion, cross-cutting the copper—PGE layered gabbroic unit, and corresponding layered u n i t , and corresponding ttoo the copper-PGE mineralization. Two Duck Lake Intrusion is a N—S elongated dyke—shaped mineralization. Two Duck Lake Intrusion i s a N-S elongated dyke-shaped unit, ofol3Qn maximum width, width, continuously continuouslyexposed exposed for f o r1.5km. 1.5km. It It is is f 1%maximum discordant to the large scale stratigraphy of the layered gabbro, discordant t o large scale stratigraphy o f the layered gabbro, and and to c layeri ng, and c brecci a and t o its i t mesoscopi s mesoscopic layering, andexhi e x hbits i b i t smagmati magmatic breccia and xenolithic zones along the eastern (bottom) and western x e n o l i t h i c zones along the eastern (bottom) and western (top) contacts. Along contacts. Along the t h e eastern easternboundary, boundary, the t h ecoarse—grained coarse-grained gabbro gabbro intrudes foliated mafic and felsic Archean metavolcanics, the the i n t r u d e s f o l i a t e d m a f i c and f e l s i c Archeanmetavolcanics, ffoliation o l i a t i o n of o fwhich which isi ssystematically systematically subparallel subparallel tto o the the intrusion, intrusion, suggestingthat that it it was majorf fault was intruded intruded along along aa pre—existing pre-existing -major a u l t or or suggesting Steeply shear zone. zone. This This early structure structurehas hasthen thenbeen been reactivated. reactivated. Steeply dipping ttoo the becomes nothernpart, part,the theintrusion intrusion becomes more more dipping the west west ini nthe thenothern thethe coarse—grained coarse-grained fflat l a tsouthward. southward. Several Several phases phases ooff faulting faultingaffected affected gabbroic intrusion. intrusion. They are ooff various gabbroic They are various intensity, i n t e n s i t y , and and consist consist subvertical fault, and essentially of o f aamajor majorNNE NNE subvertical andaaconjugate conjugate network network of minor andSE SEtrending trendingfaults faults and andfractures. fractures. The Therelative relative offsets offsets of minor NE ME and along these these structures structures vary strike, and along vary along along strike, andare are responsible responsible for forsome some off the the intrusion. intrusion. o the discontinuities discontinuities of o f the CURRIE ological Survey Bulletin 287, OJRRIE K.L.,K.L.,Geological Survey of ofCanada Canada Bulletin 287, 1980. 1980. McGORAN JJ.W., G.A.C.—M.A.C.-C.G.U. DM11 WATKINSON D DJL, ., WATKINSON H.,. McGORAN U . ,. UC.-MAC.-CLU. JJoint oint DAHL RP., Annual Meeting, Meeting, May May 1986, 1986,program programwith withabstract, abstract, vol.11, Annual vol.11, p.61. p.61. WATKINSON DAHL McGORAN ibid., p.142. UATKINSON O.H.,D.H.,DAHL R., R.,McSORAN J.W., LW., ibid., p.142. J U Li U U -20- j U �Tv (kick Like LakeIntrusion, Intrusion, Coldwell CoidwellAlkaline Mkaline complex. complex.Ontario. (tario.. TMD Dude II. Petrology Petrology and base-metal /P( qeochi stry IL base-metallP6E qeocheçistr R., MATKINSON OJL (Department (Departmentoof Geology, Carleton Carleton University University WHL R. f Geology, ' SWd Ottawa-Carleton Centre for Geoscience studies, and Ottawa-Carleton Centre f o r Geoscience studies, Ottawa Ottawa DAHL WATKINSON D.H. Ontario, KiS Ontario, K1S 586) 586) McGORAN J J.W. (Fleck Resources Ltd., 800—543 Granville st., st., Vancouver HcGORAN M .. (Fleck Resources Ltd., 800-543 Granville Vancouver V6C BB.C., C. ,. V6C 1X8) 1x8) Detailed carried Detai 1ed petrological petrologi ca1and andgeochemical geochemicalcross—sections cross-secti ons have have been been carried out across Lake IIntrusion out across Two Two Duck Duck Lake n t r u s i o n iin n order order to t o identify i d e n t i f y any any and geochemical ppetrological e t r o l o g i c a l and geochemical sstratigraphy t r a t i g r a p h y oor r zoning, zoning, ttheir heir and geochemical and tto relationships, and relationships, o enlighten enlighten petrological p e t r o l o g i c a l and geochemical relationships with host Archean metavolcanics on the eastern margin, relationships with host Archean metavolcanics on the eastern margin, section and Coldwell Coldwell Eastern on the the western Typical section Gabbro on western margin. margin. Typical and Eastern Gabbro consists from bottom to top of 3 main subunits. consists from bottom t o top of 3 main subunits. of L AAfine to to medium-grained fine d m - g m l n e dhornblende hornblende gabbro gabbro to to monzodiorite Monzodlorite of ophitic to poikilitic textures (plagioclase, K—feldspar, augite, o p h i t i c t o p o i k i l i t i c textures (plagioclase, K-feldspar, augite, olivine, o l i v i n e , hornblende, hornblende, bbiotite, i o t i t e . apatite, apatite, chalcopyrite, chalcopyrite, cubanite, cubanite, pyrrhotite, ± [quartz, magnetite, pentlandite, prehnite, actinolite, actinolite, pyrrhotite, [quartz, magnetite, pentlandite, prehnite, chlorite, serpentine, recrystallized chlorite, serpentine, calciteJ) calcite]) including includingnumerous numerous recrystal 1ized and and partially melted xenoliths of metavolcanic material, and numerous p a r t i a l l y me1t e d x e n o l i t h s o f metavolcanic material, and numerous granophyric pods. pods. 2. coarset otoppegmatitic ferrogabbrot otof eferrodiorite 2. A A coarse e g m a t i t i c oolivine l i v i n e ferrogabbro r r o d i o r i t e ooff ol i lvi hypididiomorphi omorphi pegmati ctictextures textures (plagi oclase, ocl ase, augite, augite, 01 v i ne, ne, hypi c tcotopegmatiti Fe—Ti—oxides, biotite, apatite, [orthopyroxene, chalcopyrite, chalcopyrite, Fe-Ti-oxides, b i o t i t e , apatite, + [orthopyroxene, prehnite, cubanite, pyrrhotite, pyrrhotite, pentlandite, serpentine, actinolite, actinolite, prehnite, cubanite, pentlandite, serpentine, chlorite, calciteJ), cross-cut by numerous podsoof cross—cut by c h l o r i t e , calcite]), numerous pods f gabbro gabbro ttoo monzodiorite occur. monzodi o r it e pegmatites pegmatites where where granophyres granophyres may may occur. coarset to verycoarse-grained coarse—grainS gabbro 33. . AA coarse o very o l olivine i v i n e gabbro t otod idiorite o r i t e wwith ith augite, olivine, hypidiomorphic poikilitic iv i ne, te, 01 textures (plagioclase, (plagioclase, augi hypi d i omorphi c t otopoi k i 1iti c textures cubanite, pyrrhotite, orthopyroxene, biotite, biotite, apatite, apatite, chalcopyrite, chalcopyrite, cubani orthopyroxene, te, pyrrhoti te, ± [K—feldspar, epidote, chlorite, chlorite, pentlandite, Fe—Ti—oxides, pentlandite, Fe-Ti -oxides, + [K-feldspar, sphene, sphene, epidote, albite, prehnite, numerous albite, prehnite, actinolite, actinolite,calcite]), calcite]),including including numerous xenoliths xenoliths and blocks ooff equigranular from and blocks equigranular fine—grainS fine-grained olivine—biotite o l i v i n e - b i o t i t e gabbro gabbro from the Eastern Mostoof theseinclusions inclusionsdid did not not suffer Eastern Coldwell Coldwell Gabbro. Gabbro. Most f these suffer L ppartial a r t i a l melting melting as as did xenoliths xenoliths in i n subunit subunit 1. The abundance of hydrous and volatile—rich minerals near the the contacts The abundance o f hydrous and volatile-rich minerals near of the intrusion and the common association of pegmatites with o f t h e i n t r u s i o n and t h e common association o f pegmatites w ith xenoliths suggest that assimilation xenoliths suggest that assimilation took took place place at a tboth botheast eastand and west west boundariesoof intrusion and boundaries f t the h e intrusion and through through the xenolithic xenolithicmaterial. material.Base— Basemetal and PGE geochemical distributions follow the petrographic metal and PGE geochemical d i s t r i b u t i o n s f o l l o w t h e petrographic zoning, iinn that zoning, t h a t they they are areconcentrated concentrated assymetrically assymetrical 1y along along the the boundaries. The asymmetry of ore concentration is attributed boundaries. The ~ S F e t r Yo f ore concentration i s a t t r i b u t e d to to the bottom bottom by by gravity ppartial a r t i a l withdrawal withdrawal of o f assimilated assimilated material material from from the and concentration concentration ooff volatile/Cu+PGE—rich towardthe the top top ooff the and volatile/Cu+PGE-rich f l ufluids i d s toward intrusion. intrusion. + —21— �U U U Northeastern Northeastern Extension Extension of of the the Proterozoic Proterozoic Igneous Igneous Terranes Terranes of Mid—continental North America of Mid-continental North America A. A. DAVIDSON DAVIDSON and and 0. 0. VAN VAN Geological Survey Geological Survey of of BREEMEN BREEMEN Canada, Canada, U (Lithosphere Canadian Shield Shield Division, Division, (Lithosphere && Canadian 588 Booth Street, Ottawa, 588 Booth Street, Ottawa, Canada Canada KLA KIA OE4) 0~4) Granites Granites and and rhyolites rhyolites ranging ranging in in age age from from 1.8 1.8 to to 1.34 1.34 Ga Ga are are known known to underlie much of mid—continental North America west of the Phaneroto underlie much of mid-continental North America west of the Phanero— zoic zoic Michigan Michigan Basin. Basin. U—Pb U-Pb zircon zircon ages ages of of similar similar rocks rocks adjacent adjacent to to the the Grenville Ma; Killarney Killarney Grenville Province Province in in Ontario Ontario (Killarney (Killarney granite, granite, 1742 1742 Ma; porphyry, porphyry, 1732 1732 Ma; Ma; Bell Bell Lake Lake granite, granite, 1470 1470 Ma) Ma) suggest suggest that that the the mid— midcontinental continental terranes terranes extend extend northeast northeast beneath beneath and and beyond beyond the the Michigan Michigan Basin. Basin. Prevalence Prevalence of of similar similar U—Pb U-Pb zircon zircon ages ages obtained obtained from from meta— metagranitoid affected by by granitoid plutonic plutonic rocks rocks southeast southeast of of the the Grenville Grenville Front, Front, affected the the interpretation that the 1.15 1.15 to to 1.0 1.0 Ga Ga Grenvillian Grenvillian orogeny, orogeny, prompts promptstheinterpretation that deformed deformed equivalents equivalents of of the the mid—continental mid-continental Proterozoic Proterozoic rocks rocks form form the the bulk of the Grenvillian crust immediately east of Lake Huron. Farther Farther bulk of the Grenvillian crust immediately east of Lake Huron. east, east, pre—1.35 pre-1.35 Ga Ga terranes terranes are are tectonically tectonically occluded occluded by by 1.28 1.28 to to 1.25 1.25 Ga Ga Grenville Supergroup volcanic and sedimentary rocks and 1.26 to 1.22 Ga Grenville Supergroup volcanic and sedimentary rocks and 1.26 to 1.22 Ga Elzevirian themselves deformed deformed and and intruded intruded by by even even Elzevirian plutonic plutonic rocks, rocks, themselves younger Grenvillian plutons. Recognition of ca. 1.65 Ga and younger Grenvillian plutons. Recognition of 1.65 Ga and 1.5 1.5 to to 1.35 1.35 Ga Ga granitic, granitic, volcanic volcanic and and anorthositic anorthositic rocks rocks on on both both sides sides of of the the Grenville Sweden, Grenville Front Front in in Labrador Labrador and and in in the the Sveconorwegian Sveconorwegian Province, Province, Sweden, attests attests to to the the widespread widespread nature nature of of igneous igneous activity activity comparable comparable in in age age and type to that which characterizes the mid—continental terranes. and type to that which characterizes the mid-continental terranes. U U z. j U -j '-S U U —22— �Geochemistry Geochemistry and and Petrography Petrography of of Selected Selected Early Early Proterozoic Metadiabase Dikes Proterozoic Metadiabase Dikes from from Marquette County, Marquette County, Michigan. Michigan. P.M. EICK (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Engrg., Michigan Michigan Technological University, Roughton, MI 49931) Technological University, Houghton, MI 49931) Early Early Proterozoic Proterozoic dikes dikes and and sills sills of metadiabase intrude the sediments of the Marquette Range Supergroup Supergroup and intrude the sediments of the Marquette Range and the Archean Granite—Greenstones throughout Marquette the Archean Granite-Greenstones throughout Marquette County, County, Michigan. Michigan. Between Between Champion Champion and and Marquette, Marquette, thirteen thirteen selected metadiabase dikes (.5—75 m wide selected metadiabase dikes (.5-75 m wide and and 44 km km long) long) were were studied. studied. One thick dike wasf .studied, - in detail for intra—intrusive intra-intrusive variations. variations. The metadiabase is is medium to coarsely crystalline, dark green to greenish black in in color, color, commonly commonly porphyritic, porphyritic, There is with ophitic to sub—ophitic textures. ophitic to sub-ophitic textures. There is 15—40% 15-40% groundmass, which is comprised of chlorite, calcite, biot— groundmass, biotite, amphiboles amphiboles and and quartz. quartz. Some sections have up to to 15% 15% large (.3—15mm) (.3-15m) phenocrystic relict plagioclase and pyrox— pyroxene crystals. They are altered with reaction rims of chlorite, hornblende hornblende (uralite), (uralite), and and biotite. biotite. The phaner— phaneritic mineral assemblage, other other than than the the phenocrysts, phenocrysts, accounts for for 35—75% 35-75% of the the rock, rock, and and is is composed composed of of the the following minerals minerals (vol. (vol. %): %): plagioclase, 18; 18; amphiboles, amphiboles, 15; chlorite, 15; calcite, calcite, 12; 12; quartz, quartz, 12; 12; pyroxene, 10; 10; biotite, 8; 8; opaques, opaques, 8; 8; apatite, apatite, 1; 1; and and sphene, sphene, 1. 1. The metamorphic grade is is low to middle greenschist facies, fades, but there there are are no foliations foliations visible visible in in hand hand specispecimens. There is extensive secondary mineral growth of mens. fibrous amphibole, felty chlorites chlorites with quartz, quartz, and and calcite calcite which is in micro—veinlets. There are multiple stages is in micro-veinlets. stages of oxy—exsolution oxy-exsolution in in titaniferous magnetites. magnetites. The The primary primary ilmenites have reaction rims of rutile and secondary conversion of the the rutile rutile to to sphene. sphene. Geochemical Geochemical data data thuggest suggest that the metadiabases are are tholeiitic in character. tholeiitic in character. The average chemical composition composition is 13.6; total total Fe Fe as as Fe FeO3, is (wt%): (wt%): Si02, 47.7; 47.7; A120.,, A1 0 13.6; 03, 17.3; 17.3; MgO, 8.3; CaO, 7.5; Na.,O, 1.9; K20, 1.3; TiO.,, 1.8; MgO, 8.3; CaO, 7.5; Na 02 3.9; K 0, 1.3; Ti0 1.3; P205, P 05, .4; PPM: V, V, 371; .4; and MnO, -0, .2. .2. In P?M: 3713 Cr, 264; 264; Nt, N?, 124; 124; Cu, 58; 58; Zn, Zn, 94; Rb, 27; 27; Zr, Sr, 337; 337; Y, Y, 24; 24; and and Zr, Zr, 134. 134. This compositional average reflects reflects the the data from from seven seven different different intrusive intrusive bodies. bodies. It should also be noted that there is is as much intra—intrusive intra-intrusive geochemical geochemical variation variation as as there there is is inter—intrusive inter-intrusive variation. variation. Further data analysis analysis is is curcurrently being performed. performed. , —23— , ~8, �- The Great Great Abitibi Abitibi Dyke petrological overview overview The Dyke — petrological J R.E. ERNST ERNST and and K. K. Sell R.E. Bell (Dept. of of Geology, Geology, Carleton Carleton University University & (Dept. & Ottawa—Carleton Centre for Geoscience Studies, Ottawa-Carleton Centre for Geoscience Studies, Ottawa, Ottawa, Ontario, Ontario, 1(15 5B6) 556) K1S The Abitibi Abitibi dyke dyke swarm, The swam, southeastern southeastern Superior Superior Province, Province, Canadian Canadian Shield, consists of at least 10 major dykes. The largest Shield, consists of at least 10 major dykes. The largest of of these, these, the Great Abitibi Dyke (GAD), is more than 600 km long, up toe0.25 the Great Abitibi Dyke (GAD), is more than 600 km long, up tor-"O.25 km wide wide and km and subvertjcal subvertical in in attitude. attitude. Previous workers have shown shown that that the age age of of the the GAD GAD and and probably probably the of the the rest rest of the swarm, swarm, is is 1.14 1.14 Ga Ga the (U—Pb data from from baddeleyite baddeleyite and (U-Pb data and K—Ar K-Ar data data from from biotite). biotite). .JJ The GAD GAD consists consists of of transitional weakly alkaline The transitional to to weakly alkaline olivine olivine gabbro gabbro to monzodiorite monzodiorite which which can be subdivided to can be subdivided into into two two compositional compositional groups groups (Unit Unit 1 (Unit 11 and and 2). 2). Rocks Rocks of of Unit 1 occur occur along along the the entire entire length length of of the the dyke, while while Unit Unit 2 rocks are are restricted dyke, 2 rocks restricted to to the the dyke dyke interior interior over over about half half of about of the the dyke dyke length. length. A Mg/ A linear linear relationship relationship between between the the Fo Fo content content of of olivines, olivines, the the Mg! (Mg + Fe) ratio of clinopyroxenes and the whole—rock Ba concentra(Mg + Fe) ratio of clinopyroxenes and the whole-rock Ba concentrations suggests suggests compositional compositional control by fractional tions control by fractional crystallization. crystallization. The range in chemistry (particularly for The range in chemistry (particularly for olivines) olivines) is is comparable comparable to to that found in large, layered, mafic bodies such as Kiglapait that found in large, layered, mafic bodies such as Kiglapait and and Skaergaard. Skaergaard. The variation in rocks can can be be modelled modelled The chemical chemical variation in Unit Unit 11 and and Unit Unit 22 rocks by fractionation of olivine and plagioclase from a magma by fractionation of olivine and plagioclase from a magma corresponding corresponding in.composition to to the most primitive, primitive, chilled—margin in.composition the most chilled-margin sample. sample. Some of these rocks could only have been derived, in in situ, if if olivine olivine and and plagioclase plagioclase settled settled out out to to deeper deeper levels levels in in the the dyke. dyke. synformal Feldspar alignment at at one one traverse traverse across across the the dyke dyke defines defines aa synforinal foliation (restricted (restricted to Unit 2) which suggests suggests that that the the dyke dyke dips dips southwards at about 75". Asymmetrical variation southwards about 75°. variation in in foliation foliation and and chemistry across across the dyke suggests suggests that that the the dyke dyke was was south—dipping south-dipping during intrusion. during intrusion. Incompatible—element spidergrams from the GAD are compared with data Incompatible-element The GAD patterns from igneous rocks of various tectonic settings. The abundances are similar and abundances similar to to those those of of Ocean Ocean Island Island Basalts Basalts and and some some Relative to these, the uncontaminated Continental Continental Flood Flood Sasalts. Basalts. Relative GAD is enriched in Ba, Eu, K, P, and Ti, Ti, and and depleted depleted in in Hf Hf and and Zr. Zr. -d The GAD GAD may may be be part part of of Lake Lake Superior Superior Keweenawan Keweenawan volcanism. volcanism. The age The and paleomagnetic signature signature of the the GAD, GAD, suggest suggest emplacement emplacement during during interval of Lake Superior Superior Keweenawan Keweenawan the lower 'narmal' 'normal' polarity interval stratigraphy. A positive Eu anomaly, anomaly, high high Al203 AlzOi and and other other aspects aspects cheistry of the GAD are similar to those of of some Lake Lake Superior Superior of the cheiatry Keweenawan volcanics. -J —24— 1 U �The U Utility The t i l i t yofofWerner WernerDeconvolution Deconvolutionasa sa Geomagnetic a GeomagneticMapping Mapping Tool in Tool i n East—Central East-Central Minnesota Minnesota R.J. (Department Geologyand andGeophysics, Geophysics,University University of R.J. FERDERER FERDERER (Department of ofGeology of MinMinnesota, nesota, Minneapolis, Minneapolis, MN MN 55455) 55455) V.W. CHANDLER (Minnesota Geological Survey, V.W. CHANDLER ( ~ i ~ e s o Geological t a Survey, St. st. Paul, Paul, MN MN 55114—1057) 55114-1057) Werner Werner deconvolution deconvolution is is an an inverse inverse magnetic magnetic modeling modeling technique technique used used to estimate position, depth, susceptibility contrast, and d i p parameters parameters t o estimate p o s i t i o n , depth, s u s c e p t i b i l i t y c o n t r a s t , and dip for f o r anomaly anomaly sources sources that t h a t can can be be approximated approximated by by thin t h i n sheets s h e e t s or o r planar planar interfaces. Related software was designed specifically for microcomi n t e r f a c e s . Related software was designed s p e c i f i c a l l y f o r microcom- puters the end end product product consists c o n s i s t s of of magnetic magnetic p u t e r s and and the source parameter source parameter maps maps plotted technique was applied to p l o t t e d at a t various various scales. scales. The tohigh—resolution high-resolution The technique was applied aeromagnetic data from east—central Minnesota flight (305 m aeromagnetic d a t a from e a s t - c e n t r a l Minnesota (305 f l i g h t lines l i n e sata 150 t 150m meant terrain samplingi intermean e r r a i n clearance, clearance, spaced m aapart p a r t with with a a 50 50 m m sampling nterspaced 400 400 m val). val). The of Werner Werner deconvolution deconvolution as a s aa structural s t r u c t u r a l and and lithologic lithologic The utility u t i l i t y of mapping mapping tool t o o l has has been been proven proven by by its its application a p p l i c a t i o n in i n areas a r e a s where where direct direct geological major syncline exist. tThe geological and and drill d r i l l hole hole information information exist. h e major syncline in i n the the North Cuyuna iron i r o n district d i s t r i c t is i s successfully s u c c e s s f u l l y represented represented by by North range range of of the t h e Cuyuna Results obtained north of tthin h i n sheet s h e e t solutions. solutions. Results obtained north of the the major major syncline syncline imply elongate, syncline. syncline. second, more more elongate, imply aa second, Along the the northeastern northeasterntwo— twoAlong thirds is represented t h i r d s of of the theSouth Southrange, range, the theiron—formation iron-formation is represented by by tthin hin sheets sheeta dipping dipping steeply s t e e p l y southeast, southeast, consistent c o n s i s t e n twith with observed observed data. data. Along the third, calculated t h e southwestern southwestern third, c a l c u l a t e d dips d i p s systematically s y s t e m a t i c a l l y change change tto o steeply steeply north. north. Northeast L a c s Lake Lake in i nthe theGlen GlenTownship Township area, area, a aknown known Northeast of of Mille MilleLacs syncline—anttcline pair is successfully represented by thin sheet solus y n c l i n e - a n t i c l i n e p a i r i s s u c c e s s f u l l y represented by t h i n s h e e t solutions bodiesaare t i o n s •. The The causative causative magnetic magnetic bodies r e ppyrrhotite y r r h o t i t e layers, l a y e r s , tthat h a t at a tone one time were considered consideredffor miningasasaa source source of of ssulfur, u l f u r , and/or and/or metametatime ware o r mining morphosed diabase morphosed diabase sills. sills. Werner deconvolution Werner deconvolution results r e s u l t s are a r e presently p r e s e n t l y being being interpreted i n t e r p r e t e d in i n areas areas of poorly understood geology. East of Mifle Lacs Lake, where several of poorly understood geology. East of Mille Lacs Lake, where s e v e r a l two—dimensional two-dimensional aeromagnetic aertmagnetic anomalies anomalies occur, occur, associated associated sheets s h e e t s and and interfaces i n t e r f a c e s have been characterized c h a r a c t e r i z e d and are are consistent c o n s i s t e n t with w i t h modern conconcepts the geology geology iin n the t h e region. region. Geologic c e p t s of of the Geologic ffeatures e a t u r e s represented represented by by these magnetite— and and p pyrrhotite—rich these results r e s u l t s may may include include magnetitey r r h o t i t e - r i c h lenses, lenses, sills sills and thrust faults. and dikes, dikes, limbs limbs of of folds, f o l d s , and and thrust faults. In has been used primarily primarily to to obtain the past, past,Werner I n the Werner deconvolution deconvolution has bean used obtain depth depth estimates estimates for f o r basins basins associated associated with with oil o i l exploration. exploration. This study study shows shows that t h a t the the technique kechnique also a l s o has great g r e a t potential p o t e n t i a l as as a mapping mapping tool t o o l for for Precambrian structural geology. Precambrian terranes terrams of of complex complex structural geology. —25— �Geology area, Ontario Geology ooff the t h e Batchawana Batchawana area, Ontario ERIC C. GRUNSKY Geological Survey,7777 St., Toronto, ERIC C. GRUNSKY ( O n(Ontario t a r i o Geological Survey, G rGrenville e n v i l l e St., Toronto, Ontario O n t a r i o M7A M7A 1144) 1W4) The The Batchawana Batchawana area a r e a has h a a been been subdivided s u b d i v i d e d into i n t o two two supracrustal a u p r a c r u s t a l and and three plutonic—gneissic, litho—tectonic domains. The two three plutonic-gneieaic, l i t h o - t e c t o n i c domaina. The twosupracrusta]. aupracrustal domains domaina are a r e predominantly p r e d o m i n a n t I y volcanic v o l c a n i c and and are a r e divided d i v i d e d into i n t o aa western v a t e r n and and an eastern domain. The plutonic terranes that enclose the supracrustal a n e a a t e r n domain. The p l u t o n i c t e r r a n e s t h a t e a c l o a e t h e a u p r a c r u s t a l rocks r o c k * has h a s been b e e n previously previously subdivided s u b d i v i d e d by by Card Card (1919) (1979) into i n t o the t h e Chapleau Chapleau Oneiss, G i r i a s . Ramsey Ramsmy Gneiss, G n e i a a , and and Algoma Algoma Plutonic P l u t o n i c domains. domains. Each Each of of these t h e s e five five litho—tectonic l i t h o - t e c t o n i c domains d o m a i n a are a r e geologically g e o l o g i c a l l y and a n d geochronologically geochrono1ogica11y distinct. d i s t i n c t . The T h e two t w o asupracrustal u p r a c r u a t a l domains d o m a i n s are a r a ddistinct i s t i n c t volcanic v o l c a n i c cycles cycles that t h a t are a r e spatially spatially separated s e p 8 r a c e d by bya amajor m a j o rtectonic t e c t o n i cevent e v e n tofof'-2715 -2715 Ma. Ma. The Tha oldest o l d e s t domain d o m a i n is i f the t h e western w e a t e r n supracrustal a u p r a c r u a t a l group g r o u p of of rocks r o c k s in in the t h e Batchawana B a t c h a w a n a greenstone" " g r e e n a t o n e " belt. b e l t . The T h e succession a u c c e a a i o n is i s principally p r i n c i p a l l y aa , homoclinal h o m o c l i n a l sequence a e q u e n c a of of submarine submarine tholeiitic t h o l e i i t i c mafic m a f i c volcanics v o l c a n i c s with w i t h minor minor intercalated i n t e r c a l a t e d sediments a e d i m e n t a and a n d felsic f e l s i c tuffs t u f f a (first ( f i r a t cycle). c y c l e ) . The The entire entire sequence a e q u e n c e defines define a a single a i n g l e volcanic v o l c a n i c cycle c y c l e and and is i s interpreted i n t e r p r e t e d as as a a mafic mafic plain p l a i n extrusive s x t r u a i v e environment e n v i r o n m e n tthat c h a t grades g r a d e * from f r o mthick c h i c k flows f l o w in i n the t h e west west with w i t h minor m i n o r intercalated i n t e r c a l a t e d tuffs t u f f a and a n d sediments a m d i m a n t i eastward e r t w a r d into i n t o aa distal distal facies f a c i e a equivalent e q u i v a l e n t containing c o n t a i n i n g more more abundant a b u n d a n t sediments. a e d i m e n t a . U/Pb U/Pb zircon z i r c o n data d a d from f e l e i c tuft t u f f in i n the t h e western w e a t e r n part p a r t of of the t h e succession a u c c e a a i o n yields y i e l d # an a n age age f r o m al felsic of o f —2729 -2729 Ma Ha (Corfu ( C o r f n and and Grunsky, Grunaky, in i n press). p r e a a ) . This T h i a sequence a e q u e n c e is i s bounded hounded to to the t h e north n o r t h by by post p o e t kinematic k i n e m a t i c intrusions i n c r u a i o n e of o f -"2668 -2668 Ha Ha and and by by gneisses g n e i e a e s of of the t h e Chapleau C h a p l x u gneiss g n e i a a domain. domain. The T h e southern s o u t h e r n part p a r t of o f the t h e sequence a e q u e n c e is is bounded bounded by by aa large l a r g e (-'2715 (-2715 Ma) Ma) granodioritic g r a n o d l o r i t i c intrusion i n t r u s i o n which predates predates the is t h e the t h e younger y o u n g e r eastern e a a t e r n supracrustal a u p r a c r u a t a l group. g r o u p . The T h e western w e a t e r n boundary b o u n d a r y is covered c o v e r e d by by Keweenawan Keweenawan volcanics v o l c a n i c aand a n dit i t is i a not n o t known known how how far f a r west w e s t the the sequence a e q u e n c e extends. e x t e n d a . The T h e eastern e a a t e r n margin m a r g i n of o f the t h e western w e s t e r n domain d o m a i n is i s bounded bounded by by aa fault f a u l t that t h a t possibly p o a a i b l y developed d e v e l o p e d around a r o u n d the t h e time t i m e of o f the t h e early early intrusions i n t r u a i o n a in i n the t h e Algoma Algoma Plutonic P l u t o n i c Domain Domain (—2715 (-2715 Ma). Ha). The e e a t e r n supracrustal a u p r a c r u a c a l domain domain (second (aecond cycle) c y c l e ) can c a n be be subdivided subdivided The eastern into i n t o an a n early e a r l y mixed mixed tholeiite—calc—alkalic t h o l e i i t e - c a l c - a l k a l i c volcanic v o l c a n i c succession a u c c e a a i o n that chat evolved c a l c - a l k a l i c environment. a n v i r o n m e n t . The The upper u p p e r part p a r t of of the the e v o l v e d upward upward into i n t o aa calc—alkalic succession a u c c s ~ s i o nis i a predominantly p r e d o m i n a n t l y tufts t u f f s and a n d sediments. a e d i m e n t s . U/Pb UIPb zircon z i r c o n age age determinations d e t e r m i n a t i o i r in i n the t h e eastern e a a t e r n supracrustal s u p r a c r u a t a l group g r o u pyield y i a l da arange r a n g eofof'—2111 -2711 to t o '-'2698 - 2 6 9 8 Ma Ha (Corfu ( C o r f u and a n d Grunsky, G r u n a k y , in i n press). p r o s ) . These T h e s e ages a g e s have h a v e been been determined d e t e r m i i r d from f r o m sites d t c in i n the t h e south a o u t h east e a a t part p a r t of of the t h e eastern e a a t e r n group. group. The The volcanics v o l c a n i c aini nthe t h enortheast n o r t h e a s tpart p a r tof o f the t h e area a r e a have h e v e been b a e ninferred i n f e r r e dto t o be b e of of approximately a p p r o x i m a t e l y the t h à same mame age a g e based baaed upon upon stratigraphic s t r a t i g r a p h i c correlations c o r r e l a t i o n s from from north n o r t h to t o south. a o u t h . The The lowest l o w e a t part p a r t of o f this t h i n succession a u c c e a s i o n is i s interpreted i n t e r p r e t e d as a s aa mafic m a f i c plain p l a i n environment e n v i r o n m e n t that t h a t evolved e v o l v e d upward u p w a r d into I n t o a shield a h i e l d volcano volcano environment e n v i r o n u n t as a a evidenced a w l d a n c e d by by the t h e increasing i n c r c a i n g component component of of calc—alkalic calc-elkalic pyroclastics p y r o c l f t i c e interbedded i n t e r b e d d e d with w i t h mafic m a f i c flows. flow. The The sedimentary a e d i m e n t a r y basin b a a i n in i n the t h e north—central n o r t h - c e n t r a l part p a r t of of the t h e belt b e l t began began as a a aa distal d i a t a l environment e n v i r o n m e n t to t o the t h e mafic m a f i c plain p l a i n volcanics v o l c a n i c a at a t the t h e base b a s e of of the the eastern e a s t e r n volcanic v o l c a n i c succession a u c c e a a i o n (second (aecond cycle). c y c l e ) . The The lower l o w e r part p a r c of of the t h e basin basin is i a comprised comprised of o f turbiditic t u r b i d i t i c sediments a e d i m e n t e of o f mafic m a f i c provenance p r o v e n a n c e with w i t h minor minor amounts amounce of o f interbedded i n t e r b e d d e d felsic f e l e i c tuffaceous c u f f a c a o u a units. u n i c a . Abundant A b u n d a n t turbiditic turbiditic sediments s e d i m e n t s interbedded l a t e r b e d d e d with w i t h conglomerates conglomerates derived d e r i v e d from f r o m the t h e pyroclastic pyroclaatic events e v e n t s to t o the t h e southeast a o u t h e e a t dominate d o m i n a t e the t h e middle m i d d l e to t o upper u p p e r part p a r c of of the t h ebasin. basin. The T h e basin b a a i n was waa probably p r o b a b l y active a c t i v e from f r o m early e a r l y in i n the t h e development d e v e l o p m à § nof o f the the eastern e a a t e r n succession a u c c e a a i o n until u n t i l the t h e onset o n a e t of o f plutonism p l u t o n i a m(-'2675 (-2675 Ma). Ha). The The southern a o u t h e r n boundary b o u n d a r y of o f the t h e sedimentary a e d i m e n t a r y basin b o i n is i a fault f a u l t bounded b o u n d e d with w i t h the the older o l d e r western w t e r n volcanic v o l c a n i c cycle. c y c l e . This T h i a fault f a u l t is i a aa major m a j o r disconformity diaconformity within w i t h i n the t h e supracrustal a u p r e c r u s t a l succession. aucceeeion. The The structural structural fabrics f a b r i c * of of the t h e two two volcanic v o l c e n i c domains domaina are a r e distinctly distinctly different. d i f f e r e n t . The The western w e a t e r n volcanic v o l c a n i c cycle c y c l e (first ( f i r a t cycle) c y c l e ) is l a only o n l y slightly alightly deformed deformed with w i t h northeasterly n o r t h e f t e r l y trending, t r e n d i n g , steeply s t e e p l y dipping d i p p i n g foliations f o l i a t i o n s and and subsequently s u b s e q u e n t l y intruded i n t r u d e d by by the t h e Griffin G r i f f i n Lake L a k e and a n d Pancake P a n c a k e Lake L a k e post— postkinematic k i n e m a t i c stocks s t o c k s (—2675 (-2675 Ma). Ha). LLarge a r g e sscale c a l e pplutonism l u t o n i a m ooccured c c u r e d aat'2715 t -2715 Ma Ma —' j J J —26— �and terminated the western western volcanic and terminated the v o l c a n i c cycle. cycle. A A major major fault/shear f a u l t l s h e a r system system bbounds o u n d s tthe h e wwestern e s t e r n volcanic v o l c a n i c domain d o m a i n and a n d the t h e sedimentary s e d i m e n t a r y basin. basin. TThis his of tthe ddisconformity i s c o n f o r m i t y wwas a s pprobably r o b a b l y active a c t i v e during d u r i n g the t h e development d e v e l o p m e n t of he sedimentary s e d i m e n t a r y basin. b a s i n . TThe h e oonly n l y known k n o w n gold g o l d occurrences o c c u r r e n c e s within w i t h i n the the ggreenstone" r e e n s t o n e " belt belt occur o c c u r in in proximity proximity to to this this fault. fault. TThe h e eastern e a s t e r n volcanic v o l c a n i c cycle c y c l e (second ( s e c o n d cycle) c y c l e ) is i s dominated d o m i n a t e d by by aa ddistinct i s t i n c t nnorthwest o r t h w e s t trending t r e n d i n g schistosity s c h i s t o e i t y in i n the t h e asouthern o u t h e r n and a n d central central domain. TTop pparts a r t s of of tthe h e domain. o p ddeterminations e t e r m i n a t i o n s in i n the t h e ssoutheast o u t h e a s t part p a r t of o f tthe he o r t h w e s t ttrending r e n d i n g zzone one bbelt e l t iindicate n d i c a t e ooverturning v e r t u r n i n g of o f the t h e ssequence. e q u e n c e . AA nnorthwest that extends extends ffrom the northern northern tto southern part part oof belt demarcates that r o m the o tthe h e southern f belt demarcates thrust. TThis aa zzone o n e oover v e r which w h i c h the t h e sequence s e q u e n c e is is thrust. h i s zone z o n e is i s ppart a r t ooff aa tightly folded syncline that extends into the north central part t i g h t l y f o l d e d s y n c l i n e that extends into t h e north c e n t r a l part of o f the the northeast—east trending trending ssyncline aarea r e a wwhere h e r e it it merges merges with w i t h aa northeast-east y n c l i n e from f r o m the the northeast group group of of volcanics. northeast volcanica. This This zone z o n e developed d e v e l o p e d in in part part due due to to active active ssubsidence u b s i d e n c e aassociated s s o c i a t e d wwith i t h aa mmajor a j o r sshield h i e l d volcano v o l c a n o environment environment accompanied by by later accompanied l a t e r contemporaneous contemporaneous tectonism—plutonism. tectonism-plutonism. to be be tthe TThe h e AAlgoma l g o a a PPlutonic l u t o n i c DDomain o m a i n aappears p p e a r s co h e ooldest l d e s t pplutonic lutonic Ma). TThis tterrane e r r a e ((—'2715 ~ 2 7 1 5 Ha). h i s ddomain o m a i n iiss ccharacterized h a r a c t e r i z e d by b y massive massive granodiorite, qquartz monzonite, end and granite granite pplutons granodiorite, u a r t z monzonite, l u t o n s wwith i t h asmall n a l I enclaves enclaves of a supracrustal of u p r a c r u s t a l mmaterial a t e r i a l situated s i t u a t e d between between the the major major intrusive i n t r u s i v e phases. phases. TThe h e ddomain o m a i n iiss distinctly d i s t i n c t l y llacking a c k i n g iinn aany n y ssignificant i g n i f i c a n t amounts a m o u n t s ooff gneiss /migmat it ics u supracrus material. gneiss/migmatitic p r a c r u a t tal a l material. 2675 GGa) (' TThe h e RRamsey a m s a y Gneiss G n a i a a DDomain o m a i n ("2675 a ) iiss ddominated o m i n a t e d wwith ith metasomatized and tec:onized equivalents (paragneiss) m e t e s o m a t i z e d a n d tec:onized e q u i v a l e n t s ( p a r a g n e i ~ a of )of the the eastern eastern 1supracrustal u p r a c r u n t a l domain. domain. TThe h e ddomain o m a i n is is ccharacterized h a r a c t e r i z e d by by linear l i n e a r zones z o n e s of of by mmassive ggneiss n e i s s intruded i n t r u d e d by a s a l v e to t o foliated f o l i a t e d felsic f e l s i c plutonic p l u t o n i c rocks. rocks. The The gneiss zzones gneiss o n e aare r e commonly c o a m o n l y gneiss g n e i s s at at the the borders borders and and migmatitic rigmatitic at at tthe he cores. TThese of aamphibolite h a à § linear l i n e a r zones tones strike s t r i k e northeasterly northeasterly and and are a r e of mphibolite cores. rank metamorphism. rank metamorphic. The T h e Chapleau C h a p l e a u Cneiss G n e i s s Domain D o m a i n is i s dominated d o m i n a t e d with with a a mixture m i x t u r e of of pparagneiss, a r a g n e i x , mmigmatite, i g m a t i t a , oorthogneiss, r t h o g n e i s s , ppegmatite, e g m a t i t e , aand n d intrusive i n t r u s i v e stocks. stocks. The T h e domain d o m a i n is i s distinctly d i s t i n c t l y more m o r e heterogeneous h e t e r o g e n e o u s relative r e l a t i v e to t o the t h e Ramsey Ramsey Gneiss G n e i s s Domain Domain and and the t h e Algoma A l g o m a Plutonic P l u t o n i c Domain. Domain. the Batchawana Batchawana Area Geology of the General CKology Qwral Keweenawan volcaniciand sediments mat ic to intermediate metavolcanics telsic to interdiate m*tavoIcSflIc3 fr—fl I I metasediments f} urpCtone plutonic and migmatituc rocks . i= late to post tectonic sauc vitrusive rocks ,,49.J metagabbro' • • s.- • J p;st Kewanawan CHAPLEAU GNEISS - MOfltflS H. DOMAIN • .. t..'.' s.dr.ntary4 2 AMSEY W'Z 1 7 — I ALGOMA PLUtONIC DOMAINS —C-- flAMSEY ONEISS -\v.vDOMAIN... 9 5 10 kulom.tres —27— 15 �j Cold M Mineralization Gold i n e r a l i z a t i o n ooff The The Mishibishu Mishibishu Lake Lake Greenstone Greenstone Belt Belt J KEVIN B. HEATHER HEATHER ((Ontario Geological Survey, Survey, 10th KEVIN B. O n t a r i o Geological 7, 10th Floor, F l o o r , 77 Crenville G r e n v i l l e SStreet, t r e e t , Toronto, Toronto, Ontario, Ontario, M7A M7A 1W4) 1W4) j The Mishibishu Mishibishu Lake Lake belt is located l o c a t e d 35 35 km km west west of o f Wawa, Wawa, Ontario Ontario The b e l t is and approximately approximately 80 km south south ooff Hemlo, Hemlo, Ontario. SO tan Deformation zones and Ontario. Deformation zones known gold gold occurrences occurrences found hhost o s t all a l l the t h e known found to t o date d a t e within w i t h i n the the Mishibishu Lake The Scuzzy Scuzzy L Little Lake (1), Granges-MacMillan Mishibishu Lake belt. b e l t . The i t t l e Lake ( I ) , Granges-MacMillan Magnacon ((3), Northwest (41, (4), h Nnichi Hollinger (6) (6) and and ((2), Z ) , Magnacon 3 ) , Northwest i c h i (5), (51, Hollinger Discovery (7) gold occurrences occurrences all Discovery (7) gold a l l occur occur within within aa lithologically l i t h o l o g i c a l l y and and structurally complex zone known as the Mishibishu Deformation Zone s t r u c t u r a l l y complex zone known as t h e Mishibishu Deformation Zone (MDZ) (Figure The N No Name Lake Lake (8) gold occurrence occurrence is 1). The o Name (8) gold is hosted hosted (MDZ) ( F i g u r e 1). within the Eagle River Deformation Zone (ERDZ), while no w i t h i n t h e Eagle River Deformation Zone (ERDZ), while no gold gold mineralization been found t h e Rook Rook Lake Lake m i n e r a l i z a t i o n hhas a s been found to t o date d a t e within within the Deformation Zone (RLDZ) (Figure 1). Deformation Zone (RLDZ) ( F i g u r e 1). The 40 40 kin long MOZ MDZ extends extends eastward eastward from from tthe East Pukaskwa The km long h e East Pukaskwa River, n north of Mishibishu, River, o r t h of Mishibishu, Mishi, Mishi, and and Katzenbach Katzenbach Lakes, Lakes, at a t which which it swings swings to t o tthe h e southeast s o u t h e a s t and and continues c o n t i n u e s to t o Lake Lake Superior Superior ppoint o i n t it 1). The MDZ MDZ v varies width from ((Figure F i g u r e 1). a r i e s iin n width from 200 ZOO tto o 500 500 mm and and is is The composed of composed o f several s e v e r a l anastomosing anastornosing shear s h e a r zones zones localized localized along along aa major major The metavolcanics metavolcanics tto of tthe volcanic-sedimentary contact. volcanic-sedimentary c o n t a c t . The o tthe h e nnorth o r t h of he MDZ cconsist MDZ o n s i s t of of massive massive to t o foliated f o l i a t e d mafic mafic to t o intermediate i n t e r m e d i a t e tuffs, tuffs, and vvolcanic The llapilli a p i l l i tuffs, t u f f s , crystal c r y s t a l tuft's t u f f s and o l c a n i c bbreccias. r e c c i a s . The metasedimentary rocks of interbedded interbedded MDZ cconsist o n s i s t of metasedimentary rocks to t o the t h e south south of o f the t h e MDZ polymictic polyinictic and and oligomictic o l i g m i c t i c conglomerates, conglomerates, wackes, wackes, quartz q u a r t z grits, g r i t s , and and Both the metavolcanic and aargillites. r g i l l i t e s . Both t h e metavolcanic and metasedimentary metasedimentary rocks rocks exhibit exhibit an iincreasing of sstrain an n c r e a s i n g sstate t a t e of t r a i n as as tthe h e MDZ MDZ is is approached, approached, with with rocks rocks within the core fo the I'VZ being intensely deformed and altered. w i t h i n t h e c o r e f o t h e MDZ i n t e n s e l y deformed and a l t e r e d . J J The MOZ MDZ is is characterized c h a r a c t e r i z e d by: by: The (a) development o of ( a ) tthe h e development f aa strong s t r o n g penetrative p e n e t r a t i v e foliation foliation (including 5, C, and C shear ( i n c l u d i n g S, C, and C' s h e a r fabrics), f a b r i c s ) , aa north-northeast north-northeast plunging stretching and asymmetric plunging s t r e t c h i n g lineation, l i n e a t i o n , syawnetric symmetric and asymmetric snail small scale scale folds f o l d s of of the t h e foliation, f o l i a t i o n , chevron chevron folds f o l d s and and cconjugate o n j u g a t e kink kink bands. bands. development o of ((b) b ) tthe h e development f vvariable a r i a b l e ddegrees e g r e e s of o f hydrothermal hydrothermal the form form of of cchloritization, h l o r i t i z a t i o n , carbonatization carbonat i z a t i o n aalteration l t e r a t i o n in i n the calcite and and aankerite), n k e r i t e ) , sericitization s e r i c i t i z a t i o n (÷ ( + green ((both b o t h calcite mica), s i l i c i f i c a t i o n , and and minor minor albitization. a l b i t i z a t ion. mica) silicification, , AA rrelatively e l a t i v e l y systematic s y s t e m a t i c ppattern a t t e r n oof f alteration a l t e r a t i o n minerals m i n e r a l s flanks f l a n k s tthe he auriferous a u r i f e r o u s zones zones within w i t h i n the t h eI'VZ. ?1. IIn n order o r d e r of o f increasing i n c r e a s i n g proximity proximity minerals tto o the t h e auriferous a u r i f e r o u s zones zones the t h e dominant dominant aalteration lteration m i n e r a l s are: are: ((1) 1 ) chlorite c h l o r i t e.s.+ ccalcite alcite - -+ ppyrite yrite (2) chlorite (2) c h l o r i t e ++ aankerite nkerite -+ ccalcite alcite + ppyrite yrite ± + + - sericite + a l c i t e + ppyrite yrite ((3) 3 ) chlorite c h l o r i t e ++ sericite ± ccalcite 4 -28- J —9 �mica ÷ + green mica + cchlorite hlorite nkerite + green + ppyrite yrite ±+ aankerite (Ll) sericite + (4) sericite Gradational ccontacts between each each of of tthese groups, Gradational o n t a c t s eexist x i s t between h e s e alteration a l t e r a t i o n groups, with tthe progression manifest manifest best mafic best within within tthe h e mafic with h e ooverall v e r a l l progression tnetavolcanic and more more ccryptically within the metavolcanic rrocks o c k s and r y p t i c a l l y within t h e metasediments. metasediments. knowngold goldoccurrences occurrences iin occurwithin within tthe AAll l l known n the t h e MDZ MOZ occur h e most most anda laltered is located l o c a t e d north n o r t h of o f the the iintensely n t e n s e l y deformed deformed and t e r e d p portion o r t i o n t hthat a t is Lake sstock, of monzonitic monzonitic tto Mishibishu Lake Mishibishu t o c k , aa llate a t e ttectonic e c t o n i c iintrusion n t r u s i o n of o quartz monzonitic composition. Both quartz—feldspar (QFP) porphyry (QFP) q u a r t z monzonitic composition. Both q u a r t z - f e l d s p a r porphyry and ffeldspar porphyry (FP) and e l d s p a r porphyry (FP) ddikes, i k e s , ttexturally e x t u r a l l y similar s i m i l a r to t o those those crosscutting the Plishibishu Lake stock, occur in close c r o s s c u t t i n g t h e Mishibishu Lake s t o c k , occur i n c l o s e proximity proximity to to of porphyry porphyry several r o t r a c t e d hhistory i s t o r y of s e v e r a l ooff the t h e gold gold occurrences. occurrences. AA pprotracted emplacement is with varying varying d degrees ddike i k e emplacement is eevident, v i d e n t , as as there t h e r e are are ddikes i k e s with egrees of alteration and deformation, ranging from weakly foliated with of a l t e r a t i o n and deformation, ranging from weakly f o l i a t e d with pporphyritic o r p h y r i t i c ttexture e x t u r e preserved preserved tto o intensely i n t e n s e l y foliated f o l i a t e d quartz q u a r t z ++ sericite ++ hhematite sericite ematite ± + ppyrite y r i t e schists. schists. - - Native gold -Native gold occurs o c c u r s ini nquartz q u a r t zveins v e i n (-4s (+ aankerite nkerite ± + aarsenopyrite r s e n o p y r i t e-4+ tourmaline + pyrite p y r i t e ±+ ggalena a l e n a i-+ cchalcopyrite h a l c o p y r i t e + ssphalerite p h a l e r i t e + tourmaline lbite + ± ± aalbite green which v vary sericite + g sericite r e e n mmica i c a +± cchlorite) h l o r i t e ) which a r y ffrom r o m several several - metres in ccentimetres e n t i m e t r e s to t o several several-metres i n width width and and are a r e several s e v e r a l tens t e n s of of metres in within zones up tto metres in metres i n llength, e n g t h , within zones up o several s e v e r a l metres i n thickness. thickness. Three ttypes mineralized q quartz Three y p e s ooff mineralized u a r t z vveins e i n s have have been been recognized: recognized: strongly boundinaged foliation—parallel pods of quartz, s t r o n g l y boundinaged f o l i a t i o n - p a r a l l e l pods of q u a r t z , laterally laterally continuous zones at aa continuous zones ooff quartz q u a r t z vveins e i n s which which ccrosscut r o s s c u t the t h e foliation f o l i a t i o n at low angle and likely occupying large shear fractures, iate quartzlow a n g l e and l i k e l y occupying l a r g e s h e a r f r a c t u r e s , l a t e q u a r t z ffilled i l l e d ffractures r a c t u r e s within within both both of o f above above vein vein types. types. between tthe majority of tthe There is is aa sspatial p a t i a l rrelationship e l a t i o n s h i p between he m a j o r i t y of he There known gold occurrences within the MOZ and major structures, commonly known gold occurrences within t h e MOZ and major s t r u c t u r e s , commonly by diabase t h e MDZ. MDZ. ffilled i l l e d by d i a b a s e dikes, d i k e s , that t h a t intersect the o Scuzzy Little (Dominion Explorers LimitedlAuj C Mishibishu Lake Greenstons Belt (T) Scuzzy UttlaLake LUalDominion Explarwi LimitadIUal MtaMUlM Lie O r ~ m l à §Â ¥ i ® Grsngss—MacMjllan(Grang,s Exploration (2) ~M~U-MMMIIIM~&M~U ~ x t ~ o f t iLimitecu umitmii an eBathelithic m ~ m Grsnltold a~r *u 4 1Rocks ~mi* Mishibishu N I ~ M N ~Lake ~akm ~ M Stock soak S Iron # 5- Lead Copper ® Tungsten Tlimtu .. Deformation 1 D d * n à ‘ t l ÃZones ZMà GJ 3 lMagnacon i ~ f l n ~ c o(Muacocho n i ~ u l c o cExplorations n o ~ x p t oufLimitedxhlj)(MI tm l~n i ti w x ~ ~ u ) ~ ~ Northwest 4 N o r t h ~ Ã(Westfield <§w n t f M dMinerals à ‘ n u a LimitedflAu) umitad~~~ul Amichi I(Westfield Minerals Umitadllml Limited)(M} s Amteill W U t f l l d MlnÈr> ® Hollinger Hollingw(Westfield IWÑtfiU Minerals M h i w ÃLimited)(Aga) UmltadlIJki) 0 Discovery Limited)(M) @ ~ i ~ o n(Westfield ~r wy u t f t aMinerals Minuall ~ u mitw~iw ® NNo @ O Name Nun* Lake LUr (Central ICWtlÈCrud,.C n i d aNoranda -N~ind8 Exploration UmitadIlJIu) Limited)(M) Eiptoratlon 8 8' —29— �Stratigraphic Archean S t r a t i g r a p h i cEvolution Evolution of of part p a r tofofthe the ArcheanItasca I t a s c aCounty County Metavolcanic Metavolcanic Belt, Belt, Northern NorthernMinnesota Minnesota MARK 057) MARK A. A. JIRSA JIRSA (Minnesota (Minnesota Geological Geological Survey, Survey, St. S t . Paul, Paul, MNMN55114—1 55114-1057) The southwestern—most ItascaCounty County metavolcanic metavolcanic belt beltis ithe s the southwestern-most exposed exposed The Itasca Archean metavolcanic terrane in the Superior Province, It Archean metavolcanic t e r r a n e i n the Superior Province. It lies l i e s4040km km west it by w e s t of of the the western western Vermilion Vermilion ddistrict, i s t r i c t , separated separated from from it by Giants Giants Range Range Granite Granite and and several s e v e r a l major major faults f a u l t s•. Rocks Rocks exposed exposed iin n the the southern southern part p a r t of of the t h e belt, belt, subject s u b j e c t of of this this in quadrangleaare i n the the Sherry Sherry Lake Lake 7—1/2—minute 7-1/2-minute quadrangle r e the the Volcanic andcclastic Volcanic and l a s t i c rocks rocks in i nthe theSherry Sherry Lake predominantly Lake area a r e a are a r e generally generallyupright uprightand andsteeply s t e e p l ydipping, dipping,with with predominantly east Locally e a s t and and southeast southeast younging younging directions. directions. Locally complex complex fold f o l d patterns patterns are the result r e s u l t of of at a t least least two two deformations, deformations, the the dominant dominant one one (D2) (D2) being being a r e the aa transpressional transpressional event. event. presentation. presentation. two Two contrasting contrasting cycles cycles of ofvolcanism volcanism and and sedimentation sedimentation exist e x i s t in i n the the Sherry Sherry Lake Lake area area (see (seefigure). f i g u r e ) . AA lower lower sequence sequence of of mafic mafic to t o felsic felsic volcanic volcanic and and clastic clastic rocks rocks capped capped by by iron—formation iron-formation is i s conformably conformably overlain predominantlyofof bbasaltic overlain by by aa second second sequence sequence composed composed predominantly a s a l t i c flows. flows. Both Both are a r e metamorphosed metamorphosed to to greenschist greenschist and, and, locally, locally, amphibolite amphibolite facies. fades. The The lower lower sequence sequence is is at a t least l e a s t 2500 2500 mm thick thick and and contains contains plagioclase— plagioclasephyric, pillowed, mafic to intermediate flows, blocky f e l s i c flows, flows, and and phyric, pillowed, mafic to intermediate flows, blocky felsic lenticular units of volcaniclastic and clastic rocks. The succession l e n t i c u l a r u n i t s of v o l c a n i c l a s t i c and c l a s t i c rocks. The succession becomes more felsic f e l s i c and and fragmental fragmental stratigraphically s t r a t i g r a p h i c a l l y upward upward becomes increasingly increasingly more (eastward), and finally passes into laminated, sulfide—, (eastward), and f i n a l l y passes into laminated, sulfide-, magnetite— magnetite- and and chert—rich andt utuff inferred to chert-rich iron—formation iron-formation and f f inferred to have have been been deposited deposited in in relatively r e l a t i d y deep, deep, quiet q u i e t water. water. The The upper upper sequence sequence is is 4000 4000 mm thick thick and and consists consists mainly mainly of of dark dark green, green, massive, In massive, pillowed pillowed basalt basalt and and rare r a r e lenses lenses of of fragmental fragmental basalt. basalt. In aa broad broad sense, senae, the the upper upper sequence sequence contains contains evidence evidence of of stratigraphically— stratigraphicallyupward upward shoaling shoaling processes. p r o o f s . The the basal basal and and central c e n t r a l parts p a r t s of of the the sequence sequence contain contain aa high high proportion proportion of of massive massive flows, flows, and and lack lack vesicles vesicles and and hyaloclastite These h y a l o c l a s t i t e units units implying implying deposition deposition in i n relatively r e l a t i v e l y deep deep water. water. These grade grade irregularly i r r e g u l a r l y to to more Bore pillowed, pillowed, vesicular vesicular and and fragmental fragmental flows flows upupward In the the uppermost upparmost part, p a r t , mafic mafic volcanism volcanism was was interrupted interrupted ward (eastward). (eastward). In by by aa pulse pulse of of dacitic d a c i t i cvolcanism volcanismand andsubsequent subsequentdeposition depositionofof a a400 400in— mthick heterolithic (dacite-dominated) conglomerate and tuff sequence. t h i c k h e t e r o l i t h i c (dacita-doalnatad) conglomerate and t u f f sequence. Dacite the northeastern northeastern basalts b a s a l t s may may Dacite porphyry porphyry dikes dikes which which irregularly i r r e g u l a r l y cut c u t the represent feeders or apophyses of this felsic volcanic source. The represent feeders o r apophyses of t h i s f e l s i c volcanic source. The dacite—bearing dacite-bearing clastic c l a s t i c sequence sequence is is overlain overlain by by fragmental fragmental basaltic b a s a l t i c rocks rocks inferred i n f e r r e d to t o have h a w been been deposited deposited in in relatively r e l a t i v e l y shallow shallow water, water, possibly possibly onto The onto the t h e flanks flanks of of ananemerging emergingfelsic f e l s i ccenter. center. The source source of of mafic mafic volcanic volcanic rocks rocks in i n the the upper upper sequence sequence may may be be represented represented by by large, large, semi— aemiconcordant concordant gabbroic gabbroic plutons plutons emplaced emplaced in i n the the lower lower sequence, sequence, and and smaller smaller mafic sills and and dikes dikes within within the t h e upper upper sequence. sequence. mafic sills AA four—stage four-stage depositional depositional model model is i s outlined outlined on on the the figure. figure. —30— 1 �SCHEMATIC STRATIGRAPHIC STRATIGRAPHIC SEQUENCE SCHEMATIC SEQUENCE Fragmental F r a g w n t a l mafic mafic volcanic volcanic rocks, rocks, rare r a r e flows flows 4 LU 0z Felsic F e l s i c volcanic volcanic breccia, breccia, conglomerate, conglomerate, tuft tuff , ,. .' .. . - . :. LU = 0' LU , . . ~ : , . ;*;. Pillowed b basalt dominant Pillowed a s a l t fflows l o w s dominant . C', . . .. .. . . .', . , ~. ----------------------- LU 0 0 = Massive b basalt flows dominant dominant Massive a s a l t flows 2. 0 LU — -c 4 0= Iron—formation and argillite interbedded with volcaniclastic ffine ine v o l c a n i c l a s t i c rocks rocks A4 1% Felsic intermediate volcanic volcanic rocks rocks and and to intermediate F e l s i c to volcaniclastic and eepiclastic ccoarse o a r s e to t o ffine ine v o l c a n i c l a s t i c and piclastic LU rocks )_ C'qAq / ..' cz$ZèjZ? LU 0 -I Mafjc to volcanic rocks rocks Mafic t o intermediate intermediate volcanic 1—soom . . DEPOSITIONAL SUMMARY DEPOSITIONAL SUMMARY 1 1 volcanism passing passing upward upward tto explosive ffelsic Mafic—intermediate volcanism Mafic-intermediate o explosive elsic and sedimentation. sedimentation. tto o intermediate intermediate volcanism volcanism and 2 2. of ffelsic volcanism (collapse?), Cessation of Cessation e l s i c volcanism ( c o l l a p s e ? ) , deepening deepening of of basin, basin, rrelative e l a t i v e tectonic t e c t o n i c and and volcanic volcanic quiescence. quiescence. 3. 3 Basin filling Basin f i l l i n g with w i t h mafic o a f i c flows. flows. • • Initial resurgence of nearby felsic source, shedding d debris ebris I n i t i a l resurgence of nearby f e l s i c source, basin. 4. flows $, l w and and water—laid w a t e r - l a d tuffs t u f t s into i n t.:o shallowing shallçylng.bÇsU . . f , . . .. . —31— , . ;.. , �Geology and Geology and Precious Precious Metal Metal Mineralization Mineralization of of the Hill's Hill's Lakes Lakes Area, Area, Marquette the Marquette County County Michigan Michigan Geol. and (Dept. of of Geol. and Geol. Geol. RR.C. .C. JOHNSON and T.J. BORNHORST (Dept. Engrg., Michigan Tech. Engrg., Tech. University, University, Houghton, Houghton, MI MI 49931) 49931) J.L. VANALSTINE (Geological J.L. (Geological Survey Survey Division, Division, Department Department of of Natural Resources, Resources, Lansing, Lansing, MI MI 48909) 48909) J j 2) The bedrock (13 km 2 ) area area including including The bedrock geology geology of of aa 55 mmi.2 i . (13 sections 3, 11, 12, 13 and 14 of T. 49 N., R. 28 W, sections 3, 11, 12, 13 and 14 of T. 49 N., R. 28 W, in in northern Marquette County, County, Michigan was mapped during the the summer of summer of 1986. 1986. Several abandoned prospects and trenches as well well as significant quartz veining and alteration are contained contained within within the the area. area. The oldest rocks in in the area are Archean tholeiitic pil— pillow basalts of the Upper low basalts of the Opper Pillowed Pillowed Basalt Basalt Member Member of of the the Hill's Lakes PyroPyro— Metavolcanics of Silver Mine Hetavolcanics Mine Lakes. Lakes. The Hill's clastic Member of the Metavolcanics of Silver Mine Lake clastic Member of the Metavolcanics of Silver Mine Lake crops out out in section 11 11 and crops in section and strikes strikes to to the the northeast northeast where where It is is composed composed of highly highly further exposures are expected. expected. It deformed, white to tan, pumiceous lapilli in a black, horn— deformed, hornblende—plagioclase—garnet, blende-plagiqclase-garnet, schistose schistose matrix and and has has aa The basalts have thickness in excess of 150 150 feet feet (46 (46 mm ). ). The been intruded by Archean gabbros gabbros and and diabase of of the the Meta— Metagabbro of Clark Creek. Creek. The mafic rocks rocks have been intruded intruded by the Archean Rhyolite Intrusive Intrusive of Fire Fire Center Mine the the Granodiorite of Rocking Chair Lakes. Lakes. The Granodiorite Granodiorite of of Rocking Chair Lakes is is generally massive, massive, tan tan to pink, and and composed of granodiorites, granodiorites, tonalites, quartz monzodiorimonzodiori— is composed Their massive massive nature, nature, association tes and quartz quartz diorites. diorites. Their with schistose amphibolite facies basalts, and the the intruintrusion along the hinge of the major fold in the area suggest in the suggest granodiorites are syntectonic. These rocks that the qranodiorites rocks are are cut cut by Archean quartz veins. The Archean units are intruded by veins. intruded by Lower Proterozoic Metadiabase and Keweenawan Diabase and and are unconformably overlain by Lower Proterozoic metasedi— metasedi- J J ments. The major major structure in the area is is a large large steeply steeply plung— plungfold. The fold symmetry is outlined by a gabbro sill sill the typigal Archean foliation in the pyroclastic pyroclastic u8it. unit. The typical in the area strikes The typical typcal Lower strikes NN 68 68 W and dips d i p s44 NN. . The Lower Proterozoic cleavage strikes strikes N 74° 74 W and and dips dips 51 51 SS. . This suggests that the Archean rocks cocks were relatively relatively unaffected unaffected by the Lower Proterozgic Proterozoic deformasion. deformation. The rhyolite dikes typically strike W, a strike subparallel strike NN 70 70 W to N 60 60 W, to the Archean foliation foliation in in the the area. area. This suggests that they intruded the axial planar foliation and, and, if if contempocontempowith the granodiorites, granodiorites, are also syntectonic. raneous with ing and -32- J �The pillowed basalts are metamorphosed from lower green— schist to upper amphibolite facies. The increase in metamorphic grade is associated with contact metamorphism related to emplacement of the granodiorite plutons. Lower greenschist facies metabasalts are characterized by chlori— te—actinolite—albite—clinozosite/epidote with minor carbonate and sericite and have relict magmatic textures. The upper amphibolite facies metabasalts are characterized by hornblende—calic plagioclase—hypersthene and are schistose. Altered basalts are found closely associated with faults The alteration forms varied retrograde and shear zones. assemblages of chlorite—albite—carbonate—epidote—sericite— quartz. The retrograde assemblages indicate that the mineralization in the area postdates the Archean metamorphism. The alteration is commonly associated with pyrrhotite and pyrite and locally is associated with quartz veins. Chal— copyrite and pyrite and occasionally sphalerite—galerza— arsenopyrite—pyrrhotite are commonly associated with the quartz veins. Several quartz veins in the area exceed 1000 ft. (300 m in width. The Cenin length and 20 ft. (6 m tral Section 14 Prospect consists of one shallow test This prospect is shaft, two pits and several trenches. located on a quartz vein hosted in altered basalts adjacent to a rhyolite dike. The dominant sulfide found at this prospect is pyrite. Within this area a limited number of gold assays were completed and several were anomalous. In addition, significant areas of alteration, numerous faults and shear zones, and several large quartz veins are favorable indicators of precious metal mineralization. ) ) —33— �-J J Rhyolite volcanism from from the the Huronian Huronian of of the the Thessalon Thessalon Rhyolite and and basaltic basaltic volcanism area, area, central central Ontario Ontario WAYNE WAYME T. T. JOLLY JOLLY (Dept. (Dept. Geol. Geol. Sci., Sci., Brock Brock Univ., Univ., St. St. Catharines, Catharines, Ont. L2S 3A1) Ont. L2S 3A1) The The bimodal bimodal Huronian Huronian volcanics volcanics of of the the Thessalon Thessalon region, region, central central Ontario, Ontario, are are composed composed of of interfingering interfingering caic—alkaline calc-alkaline rhyolite, rhyolite, tholeiitic tholeiitic basalt basalt and and andesite andesite flows, flows, and and minor minor pyroclastic pyroclastic sediments sediments The erupted in a developing continental rift zone environment. erupted in a developing continental rift zone environment. The rhyolites high-LILE, low—LREE low-LREE group group (75%) (75%) rhyolites are are subdivided subdivided into into 1) I) aa high—LILE, with Ba/La ratios greater than 50, low—LREE contents (LaN 100 - 50), SO), with Ba/La ratios greater than 50, low-LREE contents (LaN == 100 and and moderate moderate HREE HREE (ERN (ERN == 15), 15). and and 2) 2) aa low—LILE, low-LILE. high—LREE high-LREE group group (25%) (LaN == 150 150 — 200). 200). and high—LREE high-LREE (LaN (25%) with with Ba/La Ba/La less less than than 20, 20, and Batch melting calculations suggest the latter were generated Batch melting calculations suggest the latter were generated by by up up to to 20% melting in granulitic siliceous tonalite gneiss at deep levels, 20% melting in granulitic siliceous tonalite gneiss at deep levels, while while the the former former were were derived derived at at shallower shallower depths depths by by about about 30% 30% fusion fusion of of low—melting low-melting sources, sources, such such as as pegmatites pegmatites and and K—rich K-rich migmatitic aigmatitic leucogranites. leucogranites. - - Tholeiitic Tholeiitic flows flows are are subdivided subdivided into into 1) 1) an an upper upper basaltic basaltic unit, unit, characterized characterized by by lithophile lithophile element element ratios ratios approaching approaching chondritic chondritic levels 80 compared compared to to 110 110 in in chondrites), chondrites), low low REE REE and and (TiIZr == 80 levels (Ti/Zr nearly nearly flat flat HREE MUSE chondrite—normalized chondrite-normalized patterns patterns generated generated by by about about 20% 20% fusion fusion of of aa peridotitic peridotitic source, source, and and 2) 2) an an early early and and central central unit unit of of fractionated fractionated andesites andesites and and subordinate subordinate basalts, basalts, with with variable variable Ti/LILE TiILILE ratios ratios (Ti/Zr (Ti/Zr ranges ranges from from 35 35 in in early early types types to to 55 55 in in central central basalts), basalts), negative and Ti Ti anomalies anomalies on on distribution distribution diagrams, diagrams, and and high high negative K, K, Zr, Zr, and REE REE with with moderately moderately fractionated fractionated HREE HREE segments, segments, generated generated by by lesser lesser degrees degrees (from (from 10 10 to to 20%) 20X) of of perid3tite peridotite melting. melting. Garnet, Garnet, amphibole, amphibole, zircon, apacite and Ti—oxide phases remained residual in the zircon, apatite and Ti-oxide phases remained residual in the source source after but only only olivine, olivine, orthop orthop roxene, roxene, and and after generation generation of of early early flows, flows, but clinopyroxene clinopyroxene persisted persisted after after removal removal of of late late basalts. basalts. Many Many of of the the early early basalts, basalts, especially especially fractionated fractionated end—members, end-members, were were contaminated contaminated by by or or hybridized hybridized with with the the rhyolitic rhyolitic liquids liquids during during aa residence BaILa vs. vs. Rb/La RbILa ratio ratio diagrams, diagrams, residence period period at at crustal crustal levels. levels. Ba/La used contamination, reveal reveal that that basalt basalt used to to constrain constrain the the degree degree of of contamination, magma was was commonly commonly mixed mixed with with up up to to 40% 40% of of either either rhyolite rhyolite type. type. Compositions Compositions of of the the basalt basalt hybrids hybrids can can be be reproduced reproduced by by mixing mixing calculations. calculations. The The mantle mantle source source of of the the Huronian Huronian volcanics volcanics displays displays evidence evidence of of aa long All of of the the basalts, basalts, including including least least long and and complex complex history. history. All contaminated contaminated and and uncontaminated uncontaminated representatives, representatives. carry carry low low Ti Ti and and Nb Nb and high Rb, Ba, K, La, and Ce, indicating their source was hydrated and high Rb, Ba, K, La, and Ce, indicating their source was hydrated and metasomatically metasomatically enriched enriched in in tILE. LILE. Pronounced Pronounced negative negative anomalies anomalies characterize Ba, Nb, P, Ti, and HREE abundances due to withdrawal withdrawal characterize Ba, Nb, P. Ti, and HREE abundance* due to of basaltic liquids liquids prior prior to to the the metasomatic metasomatic episode, episode, probably probably during during Archean Archean time. time. U d �Applicability A p p l i c a b i l i t y of of aa sediment-hosted sediment-hosted copper copper deposit d e p o s i t model model to to the Keweenawan Solor Church Formation, Minnesota the Keweenawan Solor Church Formation, Minnesota MARY (Minnesota Geological Geological Survey, Survey, St. MARY JO JO P. P. ICUHNS KUHNS (Minnesota St. Paul, Paul, MN MN 55114) 55114) ROGER J. KUHNS (Department of Geology and Geophysics, University ROGER J. KUHNS (Department of Geology and Geophysics, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN MN 55455) 55455) Large copperddeposits Large tonnage tonnage sediment—hosted sediment-hosted s tstratiform r a t i f o r m copper e p o s i t s occur occur within within many middle to late Proterozoic basins throughout the world. Prominent many middle to late Proterozoic basins throughout t h e world. Prominent North include White Spar Lake, North American American examples examples include White Pine, Pine, Michigan, Michigan, Spar Lake, MonMonAlthough and Redstone, Redstone, NWT. NWT. Although specific s p e c i f i c processes processes of of formation formation are are ttana, a n a , and unique at each locality, these deposits share many of the unique a t each l o c a l i t y , these d e p o s i t s s h a r e many of the same same basic basic characteristics: (1) thick ( 1 ) restricted r e s t r i c t e d to t oProterozoic Proterozoic age age rocks, rocks, ((2) 2 ) thick characteristics: basina]. sequences indicative of rapid subsi—dence and sedimentation, (3) b a s i n a l sequences i n d i c a t i v e of r a p i d subsi-dence and sedimentation, (3) basic b a s i c to t obimodal bimodal volcanic volcanic association, a s s o c i a t i o n , (4) ( 4 ) thick thick 'redbed" "redbed" host h o s t rocks, rocks, and ( 5 ) "green "green beds" beds* of of marine marine or o r lacustrine l a c u s t r i n e origin. origin. Source Source rocks rocks for for and (5) copper are probably underlying basalts, but in some cases may copper a r e probably underlying b a s a l t s , but i n some cases may be be the the redheds, Deposi—tion the copper copper generally generally seems seems to t o be be redbeds, themselves. themselves. Deposi-tion of of the controlled c o n t r o l l e d by by local l o c a l reduc—ing reduc-ing conditions conditions in i n thick t h i c k redbed redbed sequences. sequences. The sequence The Solor Solor church Church Formation Formation is i s aa fluvial/alluvial f l u v i a l / a l l u v i a l redbed redbed sequence within Midcontinent rift the Iceweenawan Keweenawan Midcontinent r i f t system. system. The t h e formation formation consists consists w i t h i n the of mters of of interbedded interbedded arkosic a r k o s i c sand—stone sand-stone and and limestone. limestone. of 580 580 to t o 980+ 980+ meters Numerous the primarily primarily Numerous grayish—green grayish-green siltstones s i l t s t o n e s and and shales s h a l e s occur occur within within the redbed the presence presence of of oncolites o n c o l i t e s suggests suggests organic organic activity activity redbed sequence, sequence, and and the during d u r i n g deposition. deposition. Copper Copper staining s t a i n i n g has has been been recognized recognized in i n core core samples samples from from the the Solor Solor Church Church Formation Formation as a s well w e l l as a s in i n underlying underlying basalts. basalts. Structural S t r u c t u r a l complexities complexities within within the t h e Keweenawan Keweenawan rift—parallel r i f t - p a r a i l e l faults f a u l t a assoassociated w i t h the the Solor Solor Church Church basin basin may may represent represent basin—growth basin-growth faults. faults. c i a t e d with These These faults f a u l t s would would provide provide important important conduits conduits and and focal f o c a l points p o i n t s for for copper—bearing fluids. copper-bearing f l u i d s . Clearly the above above description d e s c r i p t i o n of of the the Solor Solor Church Church Formation Formation shows shows C l e a r l y the to environments which host known stratiform to environments which h o s t known s t r a t i f o r m copper copper deposits deposits elsewhere. Furthermore, elsewhere. Furthermore, the the Precambrian Precambrian rocks rocks of of the the Lake Lake Superior Superior region are major sources of copper (the native copper deposits region are major sources of copper ( t h e n a t i v e copper d e p o s i t s of of the the Keweenawan Peninsula Keweenawan Peninsula in i n amygdaloidal amygdaloidal basalts b a s a l t s and and conglomerates, conglomerates, and and shale—siltstone—sandstone—hosted shale-ailtatone-sandstone-hosted copper copper at a t White White Pine, Pine, Michigan). Michigan). These These examples the presence presence of of copper copper and and its its mobility n o b i l i t y in i n aa examples demonstrate demonstrate the variety v a r i e t y of of host h o s t rocks. rocks. Therefore, t h e r e f o r e , if i f aa reasonable reasonable concentrating concentrating mechamechanism nism can can be be identified, i d e n t i f i e d , the the potential p o t e n t i a l for f o r large—scale large-scale copper copper concentraconcentrations the Solor Solor Church Church Formation. Formation. t i o n s exists e x i s t s in i n the similarities similarities —35— �Major Major lithological lithological units units in in the the New Data New Data from from GENE GENE L. L. LABERGE LABERGE Wisconsin Wisconsin magmatic magmatic terrane: terrane: Drill Core Drill Core (Geology Department, UW, UW, Oshkosh, Oshkosh, Oshkosh, Oshkosh, WI WI 54901 54901 (Geology Department, and U.S. Geological Survey) and U.S. Geological Survey) More More than than 250 250 exploration exploration drill drill cores cores from from central central and and northern northern Wisconsin Wisconsin have have been been examined examined and and their their locations locations plotted plotted on on 1:250,000 1:250,000 base base maps. maps. Because Because northern northern Wisconsin Wisconsin is is characterized characterized by by extremely extremely meagre meagre outcrop, outcrop, the the data data from from these these drill drill cores, cores, in in conjunction conjunction with with the 1987), the recontoured recontoured aeromagnetic aeromagnetic map map of of northern northern Wisconsin Wisconsin (Karl, (Karl, 1987), provide provide aa significant significant improvement improvement in in the the data data base base for for inferring inferring the the regional extent of major lithologic units in the Wisconsin magmatic regional extent of major lithologic units in the Wisconsin magmatic . j J terrane. terrane The The drill drill core core demonstrates demonstrates that that northern northern Wisconsin Wisconsin consists consists of of large large areas underlain by either greenschist facies volcanic, sedimentary and areas underlain by either greenschist facies volcanic, sedimentary and plutonic plutonic rocks rocks or or by by amphibolite amphibolite facies facies quartzofeldspathic quartzofeldspathic gneisses, gneisses, amphibolites In Rusk Rusk and and Price Price count— countamphibolites and and sillimanite—bearing sillimanite-bearing schists. schists. In ies, the highly foliated amphibolite facies rocks are intruded ies, the highly foliated amphibolite facies rocks are intruded by by isotropic The potassic granites granites that that appear appear to to be be postorogenic. postorogenic. The isotropic potassic aeromagnetic map of northern Wisconsin contains several rhomboid—shaped aeromagnetic map of northern Wisconsin contains several rhomboid-shaped areas areas in in Rusk Rusk and and Price Price counties counties with with subdued subdued magnetic magnetic expression expression that that are separated by areas of similar size with high amplitude, are separated by areas of similar size with high amplitude, short short wavewavelength length anomalies. anomalies. Drill Drill cores cores show show that that the the rhomboid—shaped rhomboid-shaped areas areas are are underlain argillite and and graywacke graywacke whereas whereas the the underlain mainly mainly by by graphitic graphitic argillite magnetically magnetically high high area area are are underlain underlain by by greenschist greenschist or or amphibolite amphibolite facies facies volcanic volcanic rocks. rocks. The rhomboid—shaped rhomboid-shaped areas areas are are also also charactercharacterized ized by by gravity gravity lows lows relative relative to to the the intervening intervening areas, areas, suggesting suggesting aa horst (LaBerge and and others, others, 1986; 1986; Suszek Suszek horst and and graben graben basement basement structure structure (LaBerge and and Meyer, Meyer, this this conference). conference). Linear Linear magnetic magnetic trends trends and and the the presence presence of of highly highly foliated foliated and and flattened flattened rocks rocks along along the the margins margins of of the the rhomboid— rhomboidshaped shaped grabens grabens suggest suggest that that the the boundaries boundaries are are faults. faults. Diabase Diabase dikes dikes and and ultramafic ultramafic rocks rocks are are present present along along some some boundaries. boundaries. j The The drill drill cores cores show show that that the the Wisconsin Wisconsin magmatic magmatic terrane terrane consists consists of of numerous Tlblockstl of disparate metamorphic grade. However, numerous "blocks" of disparate metamorphic grade. However, the the strati— stratigraphic graphic and and structural structural relationships relationships between between these these blocks blocks remain remain to to be be resolved. resolved. -1 REFERENCES REFERENCES Karl, Karl, J.H., J.H., 1987, 1987, "Total "Total Magmatic Magmatic Intensity Intensity Map Map of of Northern Northern Wisconsin", Wisconsin , Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Map Map 86—7. 86-7. LaBerge, LaBerge, G.L., G.L., Klasner, Klasner, J.H., J.H., and and Suszek, Suszek, T.J., T.J., 1986, 1986, "Early "Early Proterozoic Proterozoic Horst—Graben Horst-Graben Structures Structures in in the the Magmatic Magmatic Terrane Terrane of of Northern Northern Wisconsin", Wisconsin", Abstract, Abstract, E0S, EOS, Trans. Trans. Amer. Amer. Geophys. Geophys. Union, Union, Vol. Vol. 67, 67, No. No. 44, 44, P. P. 1211. 1211. —36— �U—Pb pitchblende from from Dickinson County, U-Pb d adating t i n g o of f pitchblende County, upper upper Michigan, Michigan, suggests structures dduring suggests rreactivation e a c t i v a t i o n of o f Precambrian Precambrian structures u r i n g formation formation of of t h e Michigan M i c h i n a n Basin Basin the GEORGE LEHMAN (Minatome Corporation,Denver, Denver, Colorado GEORGE A. A.LEHMAN (Minatome Corporation, Colorado 80265) 80265) Exploratory ddrilling Exploratory r i l l i n ghas hasdelineated delineatedan an east—west east-west s tstriking, r i k i n g , north n o r t h dipping dipping degrees)b rbrittle Lake ((—60 4 0 degrees) i t t l e fault f a u l within t w i t h ithe n t hGene e Gene LakeGneiss, Gneiss,ananArchean Archean gneiss on tthe gneiss complex complex on h e north n o r t h edge edge of o f the t h eMiddle MiddlePrecambrian Precambrian Felch FelchTrough. Trough. The The bbrittle r i t t l e fault f a u l tclosely c l o s e l ycoincides coincides with, with, and and llocally o c a l l y cuts, cuts, aa mylonitic mylonitic fault t o t hdominant e dominantFelch FelchTrough Trough trend. trend. f a u l t which which in i n turn t u r nisi sparallel p a r a l l etol the Thus Precambrian Thus t the h e mmylonitic y l o n i t i c ffault a u l t isi sataleast t l e a sMiddle t Middle Precambrian ini nage ageand and the the brittle b r i t t l efault f a u l is t i younger. s younger. Pitchblende—carbonate occursasasspace spacef ifillings Pitchblende-carbonate m imineralization n e r a l i z a t i o n occurs l l i n g swhich which have have healed healed bbrittle r i t t l estructures structures within w i t h i nthe t h ehanging hanging wall w a l l and, and, less l e s s extensively, extensively, Four pitchblende the footwall of o fthe t h eeast—west east-west ffault. a u l t . Four pitchblendesamples samples were were t h e footwall analyzed U and and Pb Pb iisotopic s o t o p i c composition composition by by Teledyne Teledyne Isotopic I s o t o p i c Laboratory Laboratory analyzed ffor or U and were ccalculated denotes and tthe h e ratios r a t i o sofo206Pb*/238U f 206Pb*/238Uand and2O7Pb*/235U 207Pb*/235U were a l c u l a t e d ((**denotes are as as follows: radiogenic lead). lead). Ratios radiogenic Ratios are sample ## sample FR3 C18/4 C2/14 C3/10 206/238 2061238 .047040 .050370 .064910 .093450 207/235 2071235 .354300 .366770 .508890 .701320 Core sampleC1814 C18/4i sisconcordant, concordant,i nindicating possible m mineralization Core sample d i c a t i n g aa possible ineralization Core sample C2/14 and surface sample are normally event Core sample C2114 and surface sample FR3 FR3 are normally event at a t 317 317 m.y. m.y. discordant (assuminga as single remobilization) discordant and and (assuming i n g l e remobili zation) represent represent modification modification of "400 and—'SOO respectively. o f mineralizations m i n e r a l i z a t i o n swith w i tminimum h minimumages ages ofof-400 a n d - 5 0 0 mm.y. y . respectively. Core sample sampleC3110 C3/10 reverselydiscordant discordantand andr results modification rom m odification Core i sisreversely e s u l t s ffrom 400 m.y., m.y., again of o f mineralization, m i n e r a l i z a t i o n ,with w i ta h maximum a maximum age age of o f 400 againassuming assuming aa i n l e t s i in n core core indicate indicate Cross-cutting v eveinlets ssingle i n g l e remobilization remobilization event. event. Cross—cutting two, possibly three, three, mineralization/remobilization two, and and possibly mineral izationlremobil i z a t i o nepisodes. episodes. Concordia—discordiai nintercepts havebeen beenc acalculated employingaall Concordia-discordia t e r c e p t s have l c u l a t e d enploying l l four four An upperi nintercept of analyses and assuming assuminga as isingle remobilization. A analyses and n g l e remobilization. n upper t e r c e p t of 403 m.y. and and aa lower lower intercept 403 m.y. i n t e r c e p t ofo f4141m.y. m.y. were wereobtained obtainedusing usinga aprogram program written While w r i t t e nbybyHaxel Haxeland andWright Wright(1982, (1982,USGS USGSOpen Open File F i l eReport Report82—898). 82-898). no attempt attempt has beenmade madet otodetermune determune the data, data, the no has been thethe u nuncertainty c e r t a i n t y i nin the the ccorrelation o r r e l a t i o n ccoefficient o e f f i c i e n t of o f the t h e discordia d i s c o r d i a best best ffiti tisi s0.996 0.996 which which is is sufficiently good to support the conclusions to follow. s u f f i c i e n t l y good t o support t h e conclusions t o 400 m.y. m.y. oold wasppartly Theccalculated The a l c u l a t e d iintercepts n t e r c e p t s suggest suggest that t h a t 400 l d uranium urani um was artly remobilized between about 50 m.y. and the present, perhaps during the remobilized between about 50 m y . and t h e present, perhaps the erosion ooff Paleozoic erosion Paleozoic sstrata, t r a t a , outliers o u t l i e r sofowhich f whichoccur occurthroughout throughout the t h e area. area. Other iinterpretations Other n t e r p r e t a t i o n s include i n c l u d e episodic episodic mineralization m i n e r a l i z a t i o n ending ending at a t about about 300 m.y. m.y. oorr aa single s i n g l eepisode episode at a t500 500tot o300 300m.y. m y .which whichhas hasbeen been mobilized mobilized 300 more than once. more than once. The Felch Feicharea areai is on tthe Basin, indeed indeed iitt can can be be The s on h e margin margin ooff the t h e Michigan Michigan Basin, viewedas ason, on, oorr near, hingel line viewed near, aa north—south north-south hinge i n e between between aa sstable t a b l e shelf —37— �to the pperiodically The most t o the t h e west west and and the e r i o d i c a l l y subsiding subsiding basin basin tto o the t h e east. east. The most active period of deposition was during the Upper Silurian, averaging a c t i v e period o f deposition was d u r i n g the Upper S i l u r i a n , averaging 65 moof sedimentper perm.y., m.y.,over overt wtwice ther rate the next 65 m f sediment i c e the a t e oof f the next active a c t i v e period, period, the Misssissippian (—30 m/m.y. deposited). Note that the close t h e Misssissippian ( ~ 3 0m1m.y. deposited). Note t h a t t h e c l o s e of o f the the Silurian S i l u r i a n corresponds corresponds nicely n i c e l y with w i t hthe t h eupper upperconcordia—discordia concordia-discordia iintercept, ntercept, 405 vs. 403 m.y., and and tthe h e close close of o f the t h eMississippian Mississippiancorresponds corresponds cclosely losely 405 vs. 403 my., with the age of the one concordant sample, 310 vs. 317 w i t h t h e age o f t h e one concordant sample, 310 vs. 317 m.y. my. Therefore t is i s strongly s t r o n g l y indicated i n d i c a t e d tthat h a t the t h e space space f ifillings, l l i n g s , and and ffault, ault, Therefore i it are are Paleozoic Paleozoic in i n age age and and represent represent reactivation r e a c t i v a t i o nofo a f aPrecambrian Precambrian structure s t r u c t u r e ini nresponse response to t o the t h eformation formation ofo fthe t h eMichigan MichiganBasin. Basin. J This by Minatome Corporation, aa subsidiary This work work was was supported supported by Minatome Corporation, subsidiary ofo fCFP CFP (Total (Total Oil), O i l ) , and and Central Central Electricity E l e c t r i c i t yGreat Great Britain B r i t a i nas aspart p a r tofo a f auranium uranium exploration exploration program. program. PERIOD/EPOCH J SEDIMENTATION SEDIMENTATION RATE RATE . (meters/m.y.) (meters/m.y ) Jurassic Jurassic Pennsylvanian Pennsylvanian Mississippian Mississippian Devonian Upper Devonian — Upper — Middle Middle &8 Lower Lower Silurian — Upper Silurian Upper — Middle Middle - Lower Lower Ordivician O r d i v i c i a n— Upper Upper — Middle Middle — Lower Lower Cambrian Cambrian ----- 1.5 2.6 30.5 16.9 28.8 65.3 6.6 8.7 28.9 17.6 5.9 2.3 U/Pb U/Pb AGE AGE (rn.y.) H.Y 1 317 J 403 J -I J Li J J J -38- J U �Sequence Sequence of of Faulting Faulting and and Folding, Folding, Southwest Southwest Michipicoten Greenstone Michipicoten Greenstone Belt, Belt, Ontario. Ontario. E. . McGILL and CATHERINE H. SHRADY SERADY Dept. Dept. of Geology and Geography, Geography, GEORGE E University of Massachusetts, Amherst, MA 01003) 01003) complicated The The rocks of of the Michipicoten Michipicoten Greenstone Belt Belt record record aa complicated Our primary objective sequence of faulting, folding and intrusion. faulting, folding and intrusion. primary objective is is to determine the tectonic setting(s) settingcs) for the deposition of the the sedimensedimenThis requires tary and volcanic rocks rocks and and for for their their early early deformation. deformation. This requires determination of the structural sequence so that the effects determination of the structural sequence so that the effects of of younger younger deformation deformation can can be be removed. removed. This abstract reviews reviews the the evidence evidence pertainpertaining to this sequence in the ing the southwest southwest part part of of the the belt. belt. Localities Localities are are the text text (in (in 1 that are referenced in by letters located on Figure located Figure 1 by letters that referenced in the All localities are in Chabanel Towtiship, and all are parentheses). parentheses). localities are in Chabanel Township, and all are in or along the margins of the the fume fume kill. kill. At present, At present, we do do not not have have the the evidence evidence needed needed to to determine determine if if the the tectonic evolution evolution of the tectonic the Michipicoten Michipicoten Greenstone Greenstone Belt Belt occurred as an an essentially continuous continuous single single event event or or as aa series essentially series of of discrete discrete events events the separated by by intervals separated intervals of little little or or no no deformation. deformation. Very likely, likely, the truth lies lies between these truth these extremes. extremes. The structural structural style style did did change, change, one characterized characterized by by penetrative deformation deformation with with cleavage developfrom one stretching, to to one characterized and marked flattening and ment and marked flattening and stretching, characterized by by that appears appears to have occurred in the brittlelductile brittle/ductile transition faulting that regime. regime. We suspect suspect that that at at least least some some of of the the early early penetrative penetrative strucstructures developed in in aa single single evolving evolving event. event. The young faults faults probably probably represent discrete discrete later later events. events. The youngest major structure the Mildred structure in in the the area area we have mapped is is the late Lake fault fault (M-M'), of a a belt-wide (M-M'), one Lake one of belt-wide system system of of NNW-trending NNW-trending late faults. All rock units and major faults that intersect the Mildred Lake faults. Correlation of three fault are offset. offset. Correlation three contacts contacts and units units with with differdiffering attitudes attitudes across the fault indicates a sinistral net slip across the fault indicates a sinistral net slipofof3.2 3.2 kin. km. An unnamed fault fault (A-A') (A-A') west of of the the Magpie River River with 700 700 m of of sinistral sinistral separation separation is very likely likely aa young young NNW-trending NNW-trending strike-slip strike-slip fault fault also. also. Next oldest is (B-B"') that that strikes strikes parallel parallel to to the the strike strike is a fault fault (B—B''') of of bedding. bedding. This fault fault has caused a dextral separation separation of of diabase diabase dikes dikes of 100-200 100-200 m; m; the true net slip slip cannot cannot be be determined determined because because the the fault fault steeply dipping does not offset offset anything than steeply anything other does other than dipping diabase diabase dikes. dikes. Diabase dikes offset by this this fault fault are are commonly commonly distorted distorted as as well, well, sugsuggesting that, that, at the the level level of of modern modern exposure, exposure, deformation deformation was was in in the the brittle/ductile transition brittlelductile transition regime regime for for the the diabase. diabase. NE-trending NE-trending faults of moderate moderate apparent apparent displacement displacement (separations (separations of of 10's to 100's 10's 100's of meters) occur throughout throughout the area, but are most abundant near the dant the east east and and south south margins margins of of the the Pleistocene Pleistocene gravel gravel plain. plain. These faults probably probably occur beneath beneath the gravel as well, and and they they could could be responsible for the relative ease of erosion of the rocks beneath erosion the beneath the the Some gravel and along the Magpie River below Siderite Junction (SJ). gravel and along the Magpie River below Siderite Junction (SJ). Some Furthermore, of of these these faults faults offset offset diabase diabase dikes, dikes, generally generally dextrally. dextrally. Furthermore, faults that offset diabase dikes dextrally commonly offset faults that offset contacts in older rocks sinistrally. It is not entirely clear if this is rocks sinistrally. It is due to to a —39— �-j single post-diabase post-diabase oblique-slip oblique-slip event or to to fault fault reactivation, reactivation, but but we we suspect the the latter. latter. Because distinctive contacts in the older rocks can be NE faults faults at at the the SW SW end end of of Mildred Mildred Lake Lake be traced traced across across the the zone of NE there can be no Cc), (C), there can no major major fault fault passing passing through through that that location location (cf. (cf. "Magpie River River fault" fault" of Sage Sage et et al., al., OGS OGS Prelim. Prelim. Map Map P.2439); P.2439); instead, instead, a set of three or four four small faults faults is is responsible for for aa sinistral sinistral sepaseparation of (where the the "Magpie River fault" of about about 300 300 in m (where fault" follows follows the the river river below Siderite Junction there there is significant significant faulting faulting due due to to coincidence coincidence NE-trending faults of HE-trending faults with with older older bedding-related bedding-related faults). faults). IDiabase dikes truncate structures, and thus are truncate all thus are Diabase dikes all penetrative structures, younger than the younger the deformation deformation event(s) eventcs) responsible responsible for for the the steep steep dips, dips, metamorphism, cleavages, metamorphism, cleavages, and and strain strain that that characterize characterize the theArchean Archeaninetametasediments and metavolcanics. Major overturning occurred with or and metavolcanics. or before before the earliest resulting in in areally earliest cleavages, cleavages, resulting areally extensive extensive terranes terranes with bedding-related opposed stratigraphic tops that are juxtaposed by opposed stratigraphic tops are juxtaposed faults. These are described described in in more more detail faults. These pre-diabase pre-diabase structures structures are detail in in a companion abstract in in this this volume. volume. speculative working working hypothesis, As a somewhat speculative hypothesis, we propose propose that the earliest structures structures formed formed during during imbrication of volcanics earliest imbrication of volcanics and and poorly poorly consolidated sediments. consolidated sediments. The bewildering complexity of the the cleavages cleavages and and in part the would thus the stratigraphy stratigraphy would thus be be due due in part to the the tendency tendency for for each each imbricate slice to have its imbricate its own stratigraphy stratigraphy and and to to some some extent extent its its own own structure structure as well. well. The generally generally steep steep bedding bedding dips dips most most likely likely are are associated with aa later later but but still still pre-diabase pre-diabase NE-trending NE-trending cleavage. cleavage. In In most most places, places, the the effects effects of of younger younger faulting faulting and and diabase diabase intrusion intrusion are are relatively minor and and can can be be "removed" "removed" by by detailed detailed mapping. mapping. Unscrambling the earliest earliest events events is the the key key to to our our effort effort to to determine determine the the tectonic tectonic significance significance of of the the Michipicoten Michipicoten Creenstone Greenstone Belt. Belt. - - Early bedding-related Early bedding-related faults faults — Younger faults Younger faults -j sJ I" -J O feet 0 fast 3000 3000 1600 o 0meters (Titters 4000 B' Fig.1. Central Fig.l. CentralChabonel Chabanel Township Township —40— -40- �- Magnacon Project Mishibishu Lake Lake Greenstone Greenstone Belt Magnacon Project — Mishibishu Belt 0.5. D.S. McPHEE McPHEE (Muscocho Explorations Ltd., (Muscocho Explorations Ltd., Suite 601, Toronto, Ontario Suite 601, Toronto, Ontario 25 25 Adelaide Adelaide Street Street East, East, M5C 1Y2) M5C 1Y2) The Magnacon Project The Magnacon Project is is located located in in the the Mishibishu Mishibishu Greenstone Greenstone Belt Belt of the Superior Province, approximately 60 kilometers of the Superior Province, approximately 60 kilometers west west of of Wawa, Wawa, Ontario. Flanagan McAdam McAdam Resources Resources Inc. Inc. owns owns 50%. 50%, Muscocho Muscocho Explorations Explorations Ontario. Flanagan Limited Windarra Minerals Minerals Ltd. 25% of of the the property. property. Limited owns owns 25% 25% and and Windarra Ltd. owns owns 25% A A royalty royalty of of 3% 3% to to 5% 5% is is payable payable to to Westfield Westfield Minerals Minerals out out of of production. production. Presently, Presently, the decline, the project project is is at at an an advanced advanced exploration exploration stage stage with with aa decline, underground underground exploration exploration and and bulk bulk sampling, sampling, plus plus surface surface drilling drilling underway. underway. Auriferous hydrothermal Auriferous hydrothermal quartz quartz veins veins occur occur within within an an extremely extremely dilatant dilatant shear gold—bearing horizon is shear zone. zone. The host rock within the the gold-bearing is aa quartz— quartzsericite—ankerite +1— fuchsite fuchsite +1— +/- chlorite chlorite +1— +/- albite albite schist. schist. sericite-ankerite +/Mineralization Mineralization is is characterized characterized by by the the presence presence of of visible visible gold, gold, pyrite, pyrite, galena, Structurally, all galena, arsenopyrite, arsenopyrite, chalcopyrite chalcopyrite and and sphalerite. sphalerite. Structurally, all primary primary textures textures have have been been obliterated obliterated within within the the shear shear zone. zone. At At October October 1986, 1986, drill—indicated drill-indicated reserves reserves were were 1,032,435 1,032,435 tons tons grading grading 0.156 oz. gold per ton or 647,769 tons grading 0.219 oz. per 0.156 oz. 0.219 oz. per ton. ton. These These reserves reserves occur occur between between lines lines 79+00W 79+OOW and and 116+00W 116MOW and and to to aa depth depth of 450 feet. of 450 feet. Displayed will be map, sections map, sections and and polished specimens, specimens, photomicrographs photomicrographs of of —41— drill drill core, core, property property geology geology ore. ore. �j Magino Magino Project Project —- Michipicoten Michipicoten Greenstone Greenstone Belt Belt D.S. D.S. MePHEE McPHEE (Muscocho (Muscocho Explorations Explorations Ltd., Ltd., 25 25 Adelaide Adelaide Street Street East, East, Suite 601, Toronto, Ontario M5C 1Y2) Suite 601, Toronto, Ontario M5C 1Y2) The The Magino Magino Project Project is is aa joint joint venture venture between between Muscocho Muscocho Explorations Explorations Limited and McNellen Resources Inc. The property consists of of 55 Limited and McNellen Resources Inc. The property consists 55 claims claims located in the Goudreau—Lochalsh area, approximately 95 kilometers located in the Goudreau-Lochalsh area, approximately 95 kilometers by by road, road, northeast northeast of of Wawa, Wawa, Ontario. Ontario. The The gold gold on on the the Magino Magino property property occurs occurs mainly mainly in in aa series series of of parallel parallel quartz quartz veins veins and and alteration alteration zones zones within within aa large large mass mass of of trondhjemite trondhjemite which which intrudes intrudes aa series series of of mafic mafic flows. flows. Calculations 1986 drill drill Calculations of of drill—indicated drill-indicated tonnage tonnage at at the the end end of of the the 1986 programme programme gave gave aa total total of of 1,962,645 1,962,645 tons tons averaging averaging 0.251 0.251 oz. oz. gold gold per per ton. ton. These These preliminary preliminary reserves reserves occur occur to to aa depth depth of of 500 500 feet. feet. J The The 1986 1986 drill drill programme programme has has now now encountered encountered good good gold gold values values over over aa strike length of 5200 feet with the zones open at both ends. Although strike length of 5200 feet with the zones open at both ends. Although the the 1986 1986 drilling drilling has has been been concentrated concentrated on on the the zones zones within within the the intrusive, recent drilling has intersected additional intrusive, recent drilling has intersected additional zones zones at at or or near near the contact but within the volcanics. These will be tested in the the contact but within the volcanics. These will be tested in the current current drilling. drilling. AA decline decline ramp ramp of of 1600 1600 feet feet has has been been driven driven to to the the 200—foot 200-foot level level with with 1 drifting drifting occurring occurring on on several several gold gold zones. zones. The The display display will will consist consist of of drill drill core, core, hand hand specimens, specimens, maps maps and and drill drill sections. sections. j ii J -A -A ii -A -42- U j �Gaol .. .~ Bedrock Geology ogy of of Keweenawan ~eweenawanRocks Rocks in i n the tihe Vicinity v i c i n i t y of of Silver Silver Bay Bay and and Beaver Beaver Bay, Bay, Northeastern Northeastern Minnesota Minnesota ,..%' . & JAMES JAMES D. 0. MILLER, MILLER, JR. JR. (Minnesota (Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, MN MN 55114) 55114) Geologic Point Geologic mapping mapping in i n the the Silver S i l v e r Bay Bay and and Split S p l i t Rock ~ock Point NE NE 7.5' 7.5' quadrangles quadranglaa along along the t h e north north shore shore of of Lake Lake Superior Superior has has established e s t a b l i s h e d the the presence Middle Proterozoic (Keweenawan) presence of of a avariety v a r i e tof y of Middle Proterozoic (Keweenawan) mafic mafic plutonic plutonic and rocks amplaced emplaced in and hypabyssa]. hypabyasal rocks in a a thick thick sequence sequence of of dominantly dominantly basaltic basaltic volcanic volcanic rocks rocks of of similar The s i m i l a r age. age. The intrusive i n t r u s i v e rocks, rocks, collectively collectively assigned to the Beaver Bay complex, include at least assigned t o t h e Beaver Bay complex, include a t l e a s t three t h r e e temporally temporally distinct d i s t i n c t intrusive i n t r u s i v e suites; s u i t e s ; the t h e Lax Lax Lake Lake gabbro, gabbro, the the Beaver Beaver River River diabase, The theBeaver Beaver Bay Bay gabbro. gabbro. The complex complex aalso l s o includes includes two two diabase, and and the relatively Faulting, sills. Faulting, coeval coeval with w i t h magrnatic magmatic r e l a t i v e l y minor minor diabase diabase sills. intrusion, the sequence sequenceof of volcanic volcanicflows flowsand andminor minorinterf i n t e r f low low i n t r u s i o n , disrupted d i s r u p t e d the sedimentary rocks of the normally polarized (upper) North Shore Volcanic sedimentary rocks of the normally polarized (upper) North Shore Volcanic Group (MSVG), host h o s t rocks rocks for f o r the t h e BBC. BBC. Group (NSVG), Most range iin fromt tholeiitic Moat volcanic volcanic rocks rocks of of the theNSVG NSVG range n composition composition from holeiitic basalt to basaltic andesite, but some b a s a l t to b a s a l t i c a n d e s i t e , b u t some quartz—feldspar—porphyritic quartz-feldspar-porphyritic rhyolite r h y o l i t e flows flows also a l s ooccur. occur. Three Three ttextural e x t u r a l types types of of basaltic b a s a l t i cflows flows are are distinguished: ophitic basalt,plagioclase—porphyritic plagioclase-porphyritic o p h i t i c basalt, basalt, distinguished: ophitic o p h i t i c basalt, and Drill and intergranular i n t e r g r a n u l a r to t o intersertal i n t e r s e r t a l basalt b a s a l t and and basltic b a s l t i c andesite. andesite. Drill core c o r e (Green, (Green, 1982) 1982) and and exposures exposures to to the t h e east east of of the the field f i e l d area a r e a indicate indicate that siltstones and and sandstones sandstones and and volcanoclastic volcanoclastic t h a t interflow i n t e r f l o w arkosic a r k o s i c siltstones conglomerates conglomerates 'are a r e fairly f a i r l y common common in i n this this interval i n t e r v a l of of the the NSVG, NSVG, although although they Silver arerarely r a r e l yexposed exposedini the n the S i l vBay—Beaver e r Bay-Beaver Bay Bay area. area. Hornfels they are Hornfels of of volcanic thermal metamorphism volcanic and andsedimentary sedimentary rocks rocksresult r e s u llocally t l o c a lfrom l y from thermal metamorphism by by Beaver Beaver Bay Bay complex complex iintrusions. ntrusions. Subophitic Subophitic olivine o l i v i n egabbro, gabbro, granophyric granophyricgabbro gabbro and and gabbronorite, gabbronorite, mafic mafic granodiorite, and granophyre comprise the Lax Lake gabbro, q r a n o d i o r i t e , and granophyre comprise the Lax Lake gabbro, the the oldest oldest intrusive i n t r u s i v e rocks rocks in i n the thearea. area. Collectively, C o l l e c t i v e l y , these these rocks rocks define d e f i n e aaconcontinuous tinuous range range of of evolved evolved (Fe—Ti—rich) (Fe-Ti-rich) to t o highly highly evolved evolved (Si—K—rich) (Si-K-rich) comCOBpositions, implying a coeval evolution by differentiation. p o s i t i o n s , implying a coeval evolution by d i f f e r e n t i a t i o n . However, However, the the spatial the overall o v e r a l l shape shape s p a t i a l relationships r e l a t i o n s h i p s between between various various rock rock types types and and the of of the t h e Lax Lax Lake Lake body body are areobscured obscured by bya alack lackof of internal i n t e r n a l structures s t r u c t u r e s and and post—crystallization faulting. post-crystallization faulting. Both Both the the Lax Lax Lake Lake gabbros qabbros and and the the lava l a v a flows flows are a r e intruded intruded by by dikes dikes and and sills s i l l s of of Beaver Beaver River River diabase, diabase, typically t y p i c a l l y aa fine— fine- to t o medium—grained, medium-grained, ophitic o p h i t i c olivine o l i v i n e gabbro gabbro which which locally l o c a l l y grades grades into i n t o aa coarse—grained, coarse-grained, oxide—rich River diabases diabases aare oxide-rich ophitic o p h i t i cgabbro. gabbro. The The Beaver Beaver River r e unique unique iin n that that they they contain c o n t a i nnumerous numerous inclusions i n c l u s i o n s of of anorthosite, a n o r t h o s i t e , some some as a s much much as a s 100 100 meters meters in i ndiameter. diameter. The The inclusions i n c l u s i o n s tend tend to tobe be concentrated concentrated in i n the thelower lower parts p a r t s of of the t h e sills. sills. Typically, Typically, they they are a r e coarse—grained, coarse-grained, consist c o n s i s t almost almost entirely of calcic plagioclase (An 54—80, Morrison et al., 1983), and e n t i r e l y of c a l c i c p l a g i o c l a s e (An 54-80, Morrison e t a l . , 1983), and are Though less common, common, inclusions i n c l u s i o n s of of medium— mediuma r e commonly commonlytectonized. tectonized. Though less grained grained granite g r a n i t e and and aphanitic a p h a n i t i c felsite f e l s i t e also a l s o occur occur locally l o c a l l y in i n the t h e margins margins of both dikes and sills where they commonly are partially assimilated of both d i k e s and sills where they cormonly a r e p a r t i a l l y a s s i m i l a t e d by by the the diabase. diabase. The The basal b a s a l portions p o r t i o n s of of the the diabase diabase sills sills and and the the underlying underlying volcanics a ) granophyre granophyre dikes dikes volcanica are a r e commonly commonly intruded intruded by by thin t h i n (1(1 cm—i cm-1 m) which may have been generated by partial which nay have been generated by p a r t i a l melting melting of of the thevolcanics. volcanics. —43— �Theiron-rich iron—richBçave Beaver Bay gabbro theyoungest youngest intrusiveunit uniti in the The Bay gabbro i s is the intrusive n the area. Near the lakeshore, it consists of three zoned, elliptical-shaped area. Nur thà UAwhof, it consist* of thxà aonad, elliptical-shaped bodies which emplacedi ninthà theupper upperpart part of of aa thick w h i c h vwere m f ¥¥pUlc thickBeaver Beaver River River bodies sill. Each intrusion typically grades abruptly from a margin sill. Bxch intrusion typically grades abruptly from a marginofofcoarse— coarsegrained to commonly gabbro to to an grained topegmatitic, p w t i t i c ,van—textured, vari-taxturçd coÑonl granophyric granophyric gabbro an of interior medium—grained, well—laminated, moderately to locally locally i n t o r i o r of nÑdiua-qraLned moderçtel to wll-laminated, gabbronorite or or olivine Inclusions llayered, a y f d , gotabronorita olivine ferrogabbro ferroqabbro (Shank, ( S h m k , 1987). 1987). Inclusions of Beaver river diabase are especially common in one of the intrusions of Bçave r i v e r diab8ae a r e especially c o ~ o ni n one of the intrusions centered south of of Silver Inland, Beaver gabbro is is represented aenfrad Â¥oat SilvrBay. Bay. Inland, Beaver Bay Bay gabbro represented by an irregular—shaped intrusion of medium—grained ferrogabbro by an i r r d g u l a r - x ~intrusion of ndim-qr&inod ferroqabbro which which grades iinto was emplaced emplacedi ninthe the aaxial gradà n t o mafic oafic granodiorite granodiorif and and which which was x i a l porportion of Intrusionsofof tthis type are are ffairly Beavr River R i v r diabase diab8ae dike. dike. Intrusions h i s type airly tion of aaBeaver ccommon o~o thà area area to to the the northeast. northeast. niin n the relatively vinor minor Beaver relatively Beaver two Bay Complex intrueions intrusions are T wo Bay Complex are aa 15—20—meter—thick, aphanitic to fine—grained, intergranular diabase sill 15-20-Ñtu-thick Â¥phaniti to fim-graiifd, intargranular di-e sill ferrodiorite, Green, 1982) and aa 55-65-çeter-thick 55—65—meter—thick, 1982) and ((compositionally c o ~ p o i i t i o ~ l lfercodiorita, y Green, to mum-grained, medium—grained, hentitic-stained, hematitic—stained, slightly P1—porphyritic ophiophialightly Pl-porphyritic ffine i n e to diabasesill. sill. Petrogenetic relationships with other intrusive diçbà Petroapnatic relationships w i t h other intrusive rocks rocks uncertain, but the and texaare re u m a d h , but the ferrodiorite feeradiorite sill s i l l is is mineralogically  ¥ i o e r a ~ i c a l land texturally similar some Lax Lake gabbros and therefore may be an to t w d i ciliilu to xne Lax Lake gabbros and therefore nay be an offshoot Similarly, sills sills of of ophitic diabase are texoff are text of at that that suite. milt*. Similarly, ophitic similar to to Bkavr Beaver River River diabaae diabase and and may may bà be c comagnetic with it. tturally u r a l l y siçila o a a p t i c with it. ttic ic d this mapping Thia upping was w conducted conducted in i n conjunction conjunction with with the the U.S. U.S. Geological Geological Survey's COGDOHAP COGEOMAP program. Survey's progrç References Green, J.C., 1982, Geology Geology of of the the Milepost Milepost 7 7 Green, J.C., 1982, Minnesota: Minn. Geol. Survey, Report of Invest. H i w o t a : Wan. Gaol. Survey, Raport of Invest. area, Lake Lake area, 26, 12 p. 26, 12 County, County, Morrison, D.A. Morrison, D.A. and and others, other*, 1983, 1983, Pre—Keweenawan Pre-Kewmenaw~ anorthosite anorthosite inclusions inclusions Keweenawan the K Beaver Bay Bay and Italudi Duluth Coxplexes, Complexes, iinn the e w e l u w a n Beaver Minnesota: Hinnm8otA: Shank, S., S., Shank, Minnesota: Minifott: northeastern northeastern Geol. Soc. Am. Bull., Gaol. Soc. ta. Bull., v. v. 94, 94, p. p. 206. 206. Complex near Silver 1987, Potxoloqy Petrology of of the 1987, theBeaver Beaver Bay Bay C i ~ p l c xnear Silver Bay, Bçv GSAMÈtr Abstr. W with Programs, v. 19, 19, no. 4. GSA ith P r-, V. no. 4. —44— 4 �and SStructural on tthe Hemlo Gold Cold Deposit Deposit SStratigraphic t r a t i q r a v h i c and t r u c t u r a l CConsiderations o n s i d e r a t i o n s on h e Hemlo setting setting T.L. MUIR MUIR (Geologist, Precambrian Geology Geology SSection, Ontario Geological T.L. (Geologist, Precambrian ection, O n t a r i o Geological Survey, Toronto, Toronto, Ont., Ont., M7A 1W4). Survey, M7A 1W4). Initial of the Hemlo Gold Gold Deposit Deposit and and its I n i t i a l iinvestigation n v e s t i g a t i o n of t h e Hemlo its setting, setting, in the early 1980s, resulted in the interpretation of a relatively i n t h e e a r l y 1980s, r e s u l t e d i n t h e i n t e r p r e t a t i o n of a r e l a t i v e l y undeformed, homoclinal and undeformed, h m c l i n a l sequence sequence of of Archean Archean metavolcanic metavolcanic and metasedimentary units that contained a conformable, metasedimentary u n i t s t h a t contained a conformable, ssyngenetic yngenetic gold-bearing sinter Recently, more more detailed ((exhalative), e x h a l a t i v e ) , gold-bearing s i n t e r horizon. horizon. Recently, detailed surface mapping, drill core logging, and work in three mines, has has lled ed s u r f a c e mapping, d r i l l c o r e logging, and work i n t h r e e mines, to recognition of major lithological, structural, and alteration t o r e c o g n i t i o n of major l i t h o l o g i c a l , s t r u c t u r a l , and a l t e r a t i o n which have have introduced introduced ssignificant complications ffor ffeatures e a t u r e s which i g n i f i c a n t complications o r tthe he syngenetic model. These complications have forced a re—evaluation s y n g e n e t i c model. These complications have forced a re-evaluation of of now tthe h e setting s e t t i n gand and timing timingofofmineralization, m i n e r a l i z a t i o nand , and nowmounting mounting evidence, evidence, some of wtich is covered below, strongly supports an eepigenetic some of which is covered below, s t r o n g l y s u p p o r t s an p i g e n e t i c oorigin rigin gold deposit. ffor o r the t h e gold deposit. Nossiliceous No i l i c e o u s sinter s i n t e rhas hasbeen beenfound found ata Hemlo. t Hmlo. PPotassic otassic dominant form of the dominant form of of alteration a l t e r a t i o n of t h e mineralized mineralized metavolcanic and Some ffeatures rocks. metavolcanic and metasedimentary metasedimentary rocks. Some e a t u r e s ppoint o i n t to t o aa hydrothermal o origin with tthe is aassociated s s o c i a t e d with he hydrothermal r i g i n ffor o r the t h e barite b a r i t e tthat h a t is evidence for bedding iin ddeposit. e p o s i t . In I n any any case, case, evidence f o r bedding n tthe h e bbarite-bearing a r i t e - b e a r i n g rrocks ocks is equivocal. equivocal. is feldspathization is the f e l d s p a t h i z a t i o n is the L Gold and andmolybdenum molybdenum westernp apart Gold a r eare p r epresent s e n t i n in t hthe e western r t ofof tthe h e ddeposit eposit within to felsic felsicquartz—feldspar q u a r t z - f e l d s p a r porphyritic p o r p h y r i t i ccomplex complex within an an intermediate i n t e r m e d i a t e to and/or hypabyssal?), hypabyssal?),and andi nint the of the ((extrusive e x t r u s i v e andlor h e eeastern a s t e r n ppart a r t of t h e deposit deposit within laminated some within laminated metasediments metasediments which which show show evidence evidence of of some such, the tectono-metamorphicbanding bandingdue dueto to shearing. shearing. AAs tectono-metamorphic s such, the mineralization appearst otoccrosscut overa asstrike m i n e r a l i z a t i o n appears r o s s c u t sstratigraphy t r a t i g r a p h y over t r i k e length l e n g t h of of aa few few kilometres. kilometres. Majori isoclinal of the Major s o c l i n a l ffolding o l d i n g of the supracrustal s u p r a c r u s t a l rocks rocks has h a s taken taken place. This This is is cclearly place. l e a r l y eevident v i d e n t iin n rrocks o c k s sstructurally t r u c t u r a l l y ooverlying v e r l y i n g tthe he wtierer reclined, where e c l i n e d , antiformal a n t i f o r m a l synclines s y n c l i n e s have have been been ddelineated; elineated; Hence rocks structurally underlying the deposit have also been folded. folded. Hence rocks s t r u c t u r a l l y underlying the d e p o s i t have a l s o been the rocks hosting the mineralization have almost certainly been folded t h e rocks h o s t i n g t h e m i n e r a l i z a t i o n have almost c e r t a i n l y been folded and may be overturned. overturned. SStructurally t r u c t u r a l l y overlying o v e r l y i n g tthe h e eastern eastern may themselves themselves be part of the orebody are pelitic metasediments containing several P a r t of t h e orebodv are o e l i t i c metasediments c o n t a i n i n a s e v e r a l key key alteration/metamorphicmminerals (eg.a anthophyllite, n t h o p h y l l i t e , ccordierite, ordierite, alteration/metamo$hic i n e r a l s (eg. is aa rresult of ttight sstaurolite). t a u r o l i t e ) . This e s u l t of i g h t ffolding olding This sspatial p a t i a l association a s s o c i a t i o n is deposit deposit L is nnot which limits here; iitt is limits the t h e apparent apparent sstrike t r i k e eextent x t e n t ofoft this h i s uunit n i t here; o t aa which result of localized syngenetic alteration of sediments. r e s u l t of l o c a l i z e d syngenetic a l t e r a t i o n of sediments. L The andisis not not aa rresult The iisoclinal s o c l i n a l folding f o l d i n g ppredates, r e d a t e s , and e s u l t of, o f , dextral dextral whichisis manifest manifestas as sseveral of sstrong to intense sshearing h e a r i n g which e v e r a l zones zones of t r o n g to intense deformation, oone of which This is deformation, n e of which hhosts o s t s the t h emain main orebody. orebody. T h i s sshearing h e a r i n g is incipiently i n c i p i e n t l y developed developed locally l o c a l l ybetween between these t h e s e highly h i g h l ydeformed deformed zones, zones, and and significantly, hasaaffected least tthe s i g n i f i c a n t l y , the t h e shearing s h e a r i n g has f f e c t e d aat t least h e eearlier a r l i e r stages s t a g e s of of mineralization. m ineralization. —45— �Dislocation beddingand andi sisoclinal D i s l o c a t i o n along along bedding o c l i n a l ffold o l d limbs, limbs, by by dextral d e x t r a l and and ssinistral i n i s t r a lfaults f a u l t sresulting r e s u l t i n gfrom fromfolding f o l d i n gand/or and/or the t h edextral d e x t r a lshearing shearing andand medium—scale isevident e v i d e n tini nsmallsmallk d i u m - s c a l e sstructures. t r u c t u r e s . TThis h i s suggests suggests eevent, v e n t , is that bedding dislocation may have occurred on a mega—scale, which may may t h a t bedding d i s l o c a t i o n may have occurred on a mega-scale, which one of of tthe reasons why why sstratigraphy cannot be be matched matched cconsistently bbee one h e reasons t r a t i g r a p h y cannot onsistently major fold Considerable vertical component displacement aacross c r o s s major f o l d axes. axes. Considerable v e r t i c a l component displacement is suspected is suspected with with some some faults. faults. Transposition to folding f o l d i n g and/or a n d l o r shearing shearing is is present present T r a n s p o s i t i o n due due to particularly within noses of small— to medium—scale, p a r t i c u l a r l y within noses of small- t o medium-scale, ttight i g h t iisoclinal soclinal folds. However, the development of this feature on a f o l d s . However, t h e development of t h i s f e a t u r e on a large l a r g e scale scale has not not aaffected of tthe rocks. llikely i k e l y has f f e c t e d nnotable o t a b l e pproportions r o p o r t i o n s of h e ssupracrustal u p r a c r u s t a l rocks. This is because distinguishable lithologic units can generally be T h i s is because d i s t i n g u i s h a b l e l i t h o l o g i c u n i t s can g e n e r a l l y be some d distance ttraced r a c e d ffor o r some i s t a n c e along along strike. strike. Tectonic p pull—apart Tectonic u l l - a p a r t features f e a t u r e s due due to t o dductility u c t i l i t ycontrast c o n t r a s thave have developed The degree tto which in some tight isoclinal fold noses. o which developed in some t i g h t i s o c l i n a l f o l d noses. The degree these tectonic features sufficiently mimic primary fragmental ocks, t h e s e t e c t o n i c f e a t u r e s s u f f i c i e n t l y mimic primary fragmental rrocks, such tthat misidentification is iinevitable, is considered considered n e v i t a b l e , is such h a t ttheir heir m i s i d e n t i f i c a t i o n is minimal. Only Only one one n notable within tthe minimal. o t a b l e uunit, n i t , which which is is within h e oore r e ddeposit, e p o s i t , is is considered by considered by the t h e author author to t o be be aa possible p o s s i b l e tectonic t e c t o n i c breccia b r e c c i a due due to to Numerous units dductility u c t i l i t y contrast. c o n t r a s t . Numerous u n i t s of of deformed deformed pyroclastic p y r o c l a s t i c rocks, rocks, However, the and conglomerates conglomerates are are recognizable. recognizable. However, the vvolcaniclastic o l c a n i c l a s t i c rocks, rocks, and degree of of ttectonic and ttransposition of tthe degree e c t o n i c ffolding, o l d i n g , ddislocation, i s l o c a t i o n , and r a n s p o s i t i o n of h e rrocks ocks in precludes any any d delineation of primary growth faults so far. far. i n this t h i s aarea r e a precludes e l i n e a t i o n of primary growth f a u l t s so Possible P o s s i b l e conjugate conjugate shears s h e a r s in i n the t h e relatively r e l a t i v e l y isotropic i s o t r o ic quartz-feldspar appear, q u a r t z - f e l d s p a r pporphyritic o r p h y r i t i c complex complex appear, l o locally c a l l y a at t least, e a s t , tto o control some of of tthe mineralization These sshears are c o n t r o l some he m i n e r a l i z a t i o n and and alteration. a l t e r a t i o n . These h e a r s are likely zones of of sstrong and must must have have l i k e l y rrelated e l a t e d tto o tthe h e zones t r o n g ddextral e x t r a l sshearing, h e a r i n g , and been ccreated during a compressional event been r e a t e d during a compressional event which which involved involved pressures p r e s s u r e s and and stresses well well in excess excess of of tthose with lithostatic loading. stresses h o s e aattainable t t a i n a b l e with l i t h o s t a t i c loading. This T h i s strongly s t r o n g l y suggests s u g g e s t s that t h a t the t h e host h o s t rocks rocks must must have have been been deformed deformed and and major compressive compressive force a s eexerted. xerted. ttilted i l t e d ssubvertically u b v e r t i c a l l y bbefore e f o r e tthis h i s major f o r c e wwas The mineralization The timing timing of of m i n e r a l i z a t i o n is is thereby t h e r e b y constrained c o n s t r a i n e d to to post post deposition deposition and post folding of the host rocks. Zircon dating of several and post f o l d i n g of the h o s t rocks. Zircon d a t i n g of s e v e r a l rrocks ocks from w within and around around tthe 70 tto 90 M Ma from i t h i n and h e ddeposit e p o s i t indicates indicates a a 70 o 90 a ddifference ifference between age of of the the intermediate i n t e r m e d i a t e to to felsic f e l s i c qquartz-feldspar uartz-feldspar between tthe h e age porphyritic complex which locally hosts mineralization, and the p o r p h y r i t i c complex which l o c a l l y h o s t s the the m i n e r a l i z a t i o n , and t h e age age of major major granitic plutonism (eg. Cedar Lake Pluton) and numerous g r a n i t i c p l u t o n i a n (eg. Cedar Lake P l u t o n ) and numerous However, as as yet, ffeldspar e l d s p a r and and quartz-feldspar q u a r t z - f e l d s p a r porphyritic p o r p h y r i t i c dikes. dikes. However, y e t , no no clear between dike mineralization/ clear age age relationship r e l a t i o n s h i p between d i k e intrusion i n t r u s i o n and and m ineralization/ been established. established. aalteration l t e r a t i o n has has been ? J J j —46— �Petrologic evolution of early Proterozoic sucracnistal rocks from Florence County. WI and their bearingon onthe the d develonrent of ele- -the- Dunbar Gneiss . T . Peter of of Geology, tJW—Parkside, PeterA. A. Nielsen Nielsen(Dept. (Dept. Geology, OW-Parkside, Kenosha, Kenosha, WI) WI) 90 Kerr W samples ~ l e s obtained ~ f r a fran n & drill i l cores l - m provided & b y tbyh the e m - McGee have been Corporation petreographically. The The cores cores are are Corporation have been examined examined petreoqraphically. from restricted basins fran restricted basins with withshallow shallow water water sedinents. sediments. All All holes holes were w e r eoriented o A e n t etowards d t m - c the o n tcontact a c t - t hbetween e - d t h e the sedirrents and the Bush Lakes Granite. Samples represent upt oto300 300feet feet of of the the Bush Lakes Granite. mles represent up sedinentary sequence and show no coherent pattern of net amorphic Sedhntary sequeme and show m coherent pattern of mtamxphic grade as aa function the contact grade as function of of proximity proximity tto o the contact (the (the distance distance ranges fran 1.7 }cn to less than 100 m. ranges fran 1.7 km t o less than 100 m. The The rretasedinents range qfran franmicaceous micaceous quartz -zit- ites through timniqh marbles, graphite and sulfide sulfide rich ma&les, m t e and r i c h schists schistsand andruafic mafic volcaniclastics. Mineral aseitlages inply net amorphic conditions wlcaniclastics. Mineral asentolagw imply netamozphic conditions ranging from fran uppermost uppern'st greens chist fades facies ttoo amphibolite ranging greenschist au@iblite ffacies. ades. Assetlages include ~~ ~~garnet garnetarrphibolites, a q h i b o l i t e s , diopside dim* marbles ma&les and and biotite-garnet-cordierite—plagioclse—cpa.rtz schists. Nearly Nearly all all biotite-gamet-oordierite-plagioclse-quartz schists. samples have been affected by retrograde alteration due to fluids samples have been affected by retrograde alteration due t o fluids from the Bush fran the Bush Lake Lake Granite. Late stage stage quart veinslocally locally cut cut the Late quartz<-z-tourmalineveins the netasediitents, as et a.1., metasedtments, asoccurs occursini nthe theDunbar DmbarDone Done (Sims (Sins et al., 1985). 1985) Polyphase deformationis is evident An early early SS Polyphase deformation evident in inmost most samples. samples. An foliation bybiotite biotite is is parallel parallel to t o origional origional layerin4 layer& f o l i a t i o n defined defined by is (Sn). Retrograde biotite psoduces (S Retrograde biotite produces aa weak weak S5, ffoliation o l i a t i o n which which is in1ined to Thesefabrics fabrics & ae probably & t o Ss1by by up up to t o 90 90 w probably correlative correlative with D2 in the et al.) al.) with Dg and and D4 D4 in theDunbar Dunbar Done Done (Sims (Sirs et . Prograde minerala sasblages netamorphic Pnqrade mineral e l a g e srestrict restrictpeak peak metanorphic conditions at low conditionstot 500—550 o 500-550 at low tto o interrediate intermediatepressure pressure (4-5 (4-5 kbar). kbar) . Fluid pressure probably probablywas wasequal equalt otolithostatic lithostatic pressure; pressure; the Fluid pressure the fluid and ranged ranged from fromnearly nearlypure purewater water iin the fluidwas was heterogeneous heterogeneous and n the micaceous quartzites to micaceous quartzites t o fluid fluidwith withhigh highconcentrations concentrationsofofCO2 CO, and and 3 s in in carbonate, carbonate, graphite, graphite, and and sulfide sulfidebearing bearing layers. layers. The evolution of the done described described by by Sims et The evolution theDunbar Dunbar Gneiss done Sims et al., is sbdlar similar in (1985), is in style s t y l e to t othe thesupracnistals supmcmstalsdescribed descral., (1985), above. areas display amorphismfollowed followedbybylater later above. Both Both areas displayprograde proqradenet metanorphism retrograde net amorphism accatpanied by deformation. Sims et al. A x O g n c k metamz@lisn acaqmied by &foxmation. sins et al. (1985) show clear evidence that the Dunbar Done is a large scale (1985) s h o w d - e v i m W t h e - D o n e i s a m s d e fold-interference from fold-interference structure structureresulting resulting franpolyphase polyphasedeformation deformation and diapirism. I suggest that the two areas and that that diapirism. I suggest that the two areaswere wereco—eval co-eval and the differences in net amorphic grade between the Dunbar Gneiss and thedifferencesinmetamorphicgradebetweentheDunbarGneissand the supracrtstal rocks represent an an original original the Florence Florence County County siapracrustal rocks may may represent difference in in depth of burial burial - the having formed formedat at a depth of the Dunbar Dunbar having deeper level ~ ~ crustal M a nand dthen ~been~displaced ~ l to aa shallower c e level d t by not displaced displaced vvertically by diapirisu diapirisn while while the the supracrustals mpmxwhb were were not ertically to during D2Dnand asgreat greatananextent extent duringthe the andD4 D4 deformations. deformations. t o as - —47— o a ~ �-J lj Sims, P.K., P.K., Petennan, Petentian, Z.E., Z.E., and Schulz, KK.J., Sims. and Schulz, .J., 1985, 1985, The The Duitar Duribar Qeiss—granitoid dare: Implications for early Proterozoic W - u r a n i t o i d &me: ilmlications for earlv P ~ e m z o i c tectonic evolution tectonic evolutionofofnorthern northernWisconsin, Wisconsin, Geol. Geol.Soc. Soc. Am. am. Bull. ., 1101—1112. Bull. 96, 1101-1112. ~ ~ ~~A —I ~ U ci —I j J .3 j s-i U U -48- J �On the failure of the Midcontinent Rift System to proceed to sea—floor spreading Peter Peter A. A. Nielsen Mielsen(Departxrent (Department of Geology, Geology, University University of ofWisconsin Wisconsin Parkside, lcexsosna, iteriusna, WI WI 53141). 53141). Parkside, The system systemof of gravity gravity and anomaliesthat that extends Ole and magnetic magnetic anomalies extends from from Kansastto Superior and and then then southwards into central Kansas o Lake Lake Superior southwards into centralMichigan Michigan is one It reflects reflects aa is one of of the themost mostprominent prominent in inNorth N o r t h Anerica. America. It major geologic geologic feature feature which whichhas hasbeen beenidentified identified as as an abortive abortive major rifting craton - the rnidcontinentrift rift riftingof ofthe theNorth NorthAnerican American craton the midcontinent system Nurrerous authors authors system (ICES), @CIS), sinnarized summarizedininWold Wold&& Hinze, Hinze, 1982. 1982. Numerous haveproposed proposed that thisfeature featureisisa aresult resultofof 'activer 'active' rift ing have that this rifting processes hotspots spots intersecting intersecting the response tto o one one or more more hot the processes in response North Atrerican &&Dewey, toerican plate plateapproximately approximately1100 1100Ma Ma B.?. B.P.(Burke (Burke Dewey, Others (Tapponnier et al., al., 1982; 1973; van Schmus Hinze, 1985). Schnus &&Hinze, 1985). Others (Tacponnier et 1982; 1973; Gordon&&wHeupton, 1986)have havepresented presentedarguments argunentsthat that the the Gordon o n , 1986) tensional environtent ICRS tensional eiwironnenCrepresented representedbybythe the 1CRSmay may have have been been produced by Grerwille Orogenic Orogenic event. event. produced by the the Grenvifle - The t435is is unique uniquein in that that there The MSBS there is isno nothird thirdaim armassociated associated with with this failed RRR (Burke & &Dewey, this failed BRR triple t r i p l ejunction junction (Burke Dewey, 1973). 1973) Although true rifting rocksare are absent, absent, aa number nuiter of true riftingand andassociated associated mafic mafic rocks alkaline along thethe Coldwell Trend a l k a l b e intrusive intrusivecenters centers along Coldwall Trendmay may mark !nark the the position of this arm (Currie, 1976; Wieblen, 1982). The trace of this am (Currie, 1976; Wieblen, 1982) The trace of the potential also be be represented representedby bythe the suite suite of thirdarm armmay may also potential third north-trending mafic dikes tth are prominent north of Lake north-trmding m f l c dikes a c h are pranirmt north of Lake Superior. The presence of of a passive margin on the the w west Ole presence margin on est (receiving (receiving Belt Group andequivalent equivalent sediments) sedinents) coupled with aa continentGroup and coupled with continent collisional Grenvifle Orogeny) collisionalmargin margin on on the theeast east(the (the Grenville Orogeny) not only only prevented a sea-floor sea-floor spreading spreadingcenter centerfrom f r mdeveloping, developing, but also inhibited the developTentof of the the thirdarmof third ann of the but inhibitedthedevelopmt the conventional ' 'ERR' conventional PKR' ttriple r i p l e junction junctionfrom franforming. forming. . . Stress conditions Stress conditionsinposed imposedon onthe theNorth N o r t hAnerican Americanplate plate1100 1100Ma Ma B.?. suchthat thatgeneration generationofofa arift rift in in the B.P. were were such the direction of the the third thirdann arm of of the theideal idealERR RRR ttriple r i p l e junction junction was was prohibited prohibited (Fig. (Fig. 1) 1) and that that extension wasnot not oennitted permitted along extensionofofmore morethan than65-701cn 65-70km was alona the arms (the ?'EA mid—Michigan the two twosuccessful successful amis (the M3Aand andthe the mid-Michigan geophysical anomaly).. Global plate distribution, distribution, plate Global plate plateboundary boundary orientation, anomaly) plate boundary typeand andintxaplate intraplates&s stress distribution distribution control boundary type control whether continental continental lithosphere lithosphere can respond whether respond tto o hot hot spot spot induced induced Under unconfined. unconfined stress by stress by fonning forming an an ERR RRR t rtriple i p l e junction. Under extensional stress situations, extensional stress situations,continental continentallithosphere lithospherecan canform form an an ERRt rtriple junction in of aa hot hot spot RRR i p l e junction i n response response to t o errplacement emplacement of spot A new new divergent divergent boundary (Burke & Dewey, 1973). 1973). A (Burke & Dewey, boundary can can form form aa new new mid ocean ridge ridge system whereplate plate boundary conditions allow mid ocean system (ICR) @-%XUwhere boudary conditions This can occur when one or or more moreof of the the continued extension. This when one pre—existing plate bouxbries boundaries is is aa continentpre-existhg plate amthent-ocean ocean(C-O) (C-0) or or ocean-ocean (0-0) (0-0) comergent convergentboundary boundary(cf. (cf. the the break break up up of ocean-ocean The absence absenceof of an an oceanic oceanic free free face al.) Pangea). face (Tapponnier (Tapponnier et e t al.) Pangea) The for between for the theNorth North?aerican Americancontinent continent between1200 1200and andl000Ma lOOOMa B.?. B.P. causedthe the failure failure of the MS caused MESto t oproceed proceed to t o sea-floor sea-floor spreading. spreading. . —49— �j Burke, J.F., 1973, triple-junctions Burke, K., K., and and Des.ey, Dewey, J.F., 1973, Flute-generated Plume-generated triple-junctions Key plate Key indicators i.IXikdt0rs in inapplying applying p l a t e tectonics tectonics to t o old o l drocks, rocks, Journal Journal of 406—433 ofGeology, Geology,.J., Sl, 406-433 Currie, Sun. Currier K.L., K.L:, 1976, s 7 6 , The Sa4jne Rocks of m,Geol. -1. S-. of Canada, Can. Can. Bull. Bull. 239, 239. 229pp. 229co. Gordon, M.B., and and %I&, Herpton, M.R., M.R., 1986, 1986,Collision-induced Collision-induced rrifting: Gordon, M.B., ifting: The Riftof of North North America, Nierica, The Grenville GrenvilleOrogeny Orogeny and and the theKesceenawan Keweenawan Rift j Tectonophysics, T e c t ~ s i c s.]fl, m, , 1—25 1-25 Tapponnier, T ~ , R R., . P,Feltzer, e l t z e r , G., G., I.eoain, Wain,A.Y., A.Y., Atmijo, Annijo,R.., R., and andCobbold, Cokbld, P., tectonics in insi$its P., 1982, 1982, Propagating Propagating extrusion extrusion tectonics inAsia: Asia: New Mew insights from sinpie experiiients Geology, from siaple experimentswith withplasticine, plasticine, Geology,)aQi u,611-616 611-616 Van Scbmus,W. W.R., andHinze, Hinze,W.J., W.J., 1985, 1985, The Themidcontinent midcontinentrift rift Van Schmus, R., and system, Planet. Sci., system, kin. Arm. Rev. Rev. Earth Earth Planet. Sci., U, 13, 345—383 345-383 Wieblen, .W., 1982, intrusive rocks. -wan intrusive rocks. See SeeWold Wold & & Hinze Hinze Wieblen, PP.W., 1982, Keweenawan 1982, 1982,47—56 47-56 Wold, R.J., and V&ld, R.J., andHinze, Hiwe, W.J., W.J., editors, editors,1982, 1982,Geolocv and Tectonics 1 of the Lake Surior Basin, Geol. Soc. Mt. tn. 156 280 280 pp. s- j J J j J .4 j j -50- J �"Basement—uplift" tectonics in Structural Zone, "Basement-uplift" tectonics i n the t h eKapuskasing Kapuskasing Structural Zone, central Superior Province Superior Province J.A. PERCIVAL (Geological Survey Surveyof of Canada, 588Booth BoothSt., St., Ottawa, J.A. PERCIVAL (Geological Canada, 588 Ottawa, 0E4) Ontario KK1A I A OE4) The 500 500 km km long, long, NNE-trending NNE-trending Kapuskasing Kapuskasing uplift uplift exposes deep crustal sections The sections of of the east-west east-west striking strikingWawa-Abitibi Wawa-Abitibi and andQuetico—Opatica Quetico-Opatica belts belts of the central central Superior Province. Granulite to upper amphibolite fades rocks of the uplift uplift form form Superior Province. Granulite to upper amphibolite fades rocks of from south south to north entities: from three distinct geological-geophysical geological-geophysical entities; north the Chapleau, Chapleau, Groundhog River River and blocks. Chapleau consists of of Groundhog and Praserdale-Moosonee Fraserdale-Moosonee blocks. Chapleau block (CS) (CB) consists densegneissic gneissicand andanorthositic anorthositicrocks, rocks,with with high high seismic seismic velocities, velocities, in in the dense the upper upper amphibolite and and granulite facies, fades, metamorphosed metamorphosed at 7-9 7-9 kbar. It It is is iningradational gradational contact, across contact, across a a Conrad-like Conrad-like discontinuity, discontinuity, with with amphibolite-facies amphibolite-fades (5-6 (5-6 kbar) kbar) tonalitic rocks rocks with with lower lower seismic seismic velocity, velocity, of of the the Wawa Wawa belt to to the the west. west. In contrast, the eastern easterncontact contactofof CB CB with with the the Abitibi belt the well-defined well-defined contrast, the belt is the Ivanhoe Lake thrust, 35-3S0 NW-dipping NW-dipping Ivanhoe Lake thrust, imaged imaged by by seismic seismic reflection reflection as as a 35—38° structure. The Thepositive positivegravity gravityanomaly anomalyover overthe theblock blockisiscaused causedby bythe thepresence presence of dense surface, as as shown shown by by gravity gravity modelling modelling and and supported supported by by dense granulites granulites at surface, seismic refraction evidence which indicates anomalously thick (ca. 48 km) crust 48 seismic evidence which indicates anomalously thick beneath the structure, relative beneath the relativetot oregional regionalvalues valuesunder under 40 40 km. krn. Groundhog Groundhog River River block (GRB) consistsofof tonalitic tonalitic and Ic gneiss gneissininthe the granulite granulite ffades (7-8 kbar), kbar), (GRB) consists and maf mafic a d e s (7-a boundedononthe theeast, east,west west and andsouth southby bybrittle brittle faults. faults. It is is characterized characterized by by aa bounded arcuate gravity strong positive aeromagnetic aeromagnetic anomaly, anomaly, but but aasub—parallel, sub-parallel, arcuate avity anomaly anomaly exposing occurs up ttoo 40 40 km kin to t othe thewest. west.Fraserdale Fraserdale- Moosonee Moosoneeblock block(FMB), (FMB , exposingdeep deep levels of the diatexite and t h e Quetico Quetico belt, belt, consists consists of of paragneiss, paragneiss, diatexite and minor minor tonalitic tonalitic levels gneiss in in the granulite Thewedge-shaped wedge-shaped block block is is fault-bounded fault-bounded gneiss granulite facies facies(7-9 (7-9kbar). kbar). The and lies lies within within aa ttoo the the east east and and west, west, has has a strong strong positive positive magnetic magnetic anomaly anomaly and broad positive positive gravity anomaly. broad anomaly. AA65-km 65-km "gap" "gapnwithout withoutgranulites granulitesoccurs occursbetween between the the GRB GRB and and FMB. FMB. - 7 geological—geophysical models involving aa major Integrated geological-geophysical major SE-directed SE-directed thrust and normalmovement movementononbrittle brittle faults, faults, explain explain the thrust and later, W-side-down W-side-down normal diverse CS is is a northwest-dipping northwest-dipping tilted slab, slab, diverse characteristics characteristics of each each block: block: CB exposing an oblique obLiquecrustal crustal cross-section; cross—section;GRB GRBand andsouthern southernFMB FMBare arethrust thrust tips exposing an truncated by normal faults; an an arcuate arcuate normal fault faultcuts cutsout outgranulites granulitesininthe theGRB.GRBFMB gap; the northern FMB has pop-up geometry. The overail geometry, scale, FMB gap; northern FMB has popup geometry. The overall geometry, scale, timing and and chronology chronology of the the diverse diverse structures structures ininthe theKapuskasing Kapuskasing uplift uplift closely closely resemble those those in in Phanerozoic basement uplifts uplifts such as the Laramide province province of of resemble Phanerozoic basement such as the western western U.S.A. U.S.A. Early Early Proterozoic Proterozoiccooling coolingdates dates ininthe theKapuskasing Kapuskashg zone zone are are consistent with remote uplift effects of in the "Hudsonian" orogeny orogeny in the consistent with remote basement basement uplift of "Hudsonian" Churchill Province. Province. —51— �(j _._j 0 km 100 Granulite fades -14r j Regionalgeology geologyof of the thecentral centralSuperior SuperiorProvince Provinceshowing showingmajor major tectonic features Regional tectonic features associated with withthe theKapuskasing Kapuskasingzone, zone, a composite structure made up of the associated aand composite structure made up of the Chapleau (CB), Groundhog River (GRB) Fraserdale-Moosonee (FMB) blocks. Chapleau (CB), Groundhog River (GRB) and Fraserdale-Moosonee (FMB) blocks. TheVal Val Rita Ritablock block(VRB) bounded by by the theLepage Lepage(LF), (LF), Foxville (FF), Kineras (VRB) isisbounded The (FF), Kineras (KF)and and Saganash Saganash Lake Lake (SLF) (SLF) faults. faults. Additional Additional structures structuresFoxville indicated include the (NP) indicated include the Bad River (BRF) and Wakusimi River (WRF) faults and Ivanhoe Lake catadastic Bad River (BRF) and Wakusimi River (WRF) faults and Ivanhoe Lake cataclastic zone(ILCZ). (ILCZ). Geographical Geographicallocations locationsinclude includeCochrane Cochrane(C), (C),Chapleau Chapleau(Ch), (Ch),Hearst Hearst zone O K ) , Timmins ( 1 1 , and Wawa (W). (H), Kapuskasing (H), Kapuskasing (K), Timmins (1), and Wawa (w). c-i U I —52— �Geological Geological and and Geophysical Geophysical Investigation I n v e s t i g a t i o n of of Graphite Graphite Resources Resources in i n Upper Upper Michigan Michigan JILL JILL F. F. PETERMAN PETERMAN (Dept. (Dept. of of Mineral Mineral Economics, Economics, Michigan Michigan Tech. Tech. University, University, Houghton, Houghton, MI M I 49931) 49931 ) DAVID DAVID DROEGE DROEGE (Dept. (Dept. of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Michigan Tech. University, Houghton, MI 49931) Tech. University, Houghton, M I 49931 ) ALLAN ALLAN M. M. JOHNSON, JOHNSON, (BioSource (BioSource Institute, I n s t i t u t e , Michigan Michigan Tech. Tech. University, University, Houghton, MI 49931) Houghton, M I 49931 ) JACK JACK VAN VAN ALSTINE ALSTIME (Michigan (Michigan Geological Geological Survey Survey Division, Division, Dept. Dept. of of Natural M I 48909) 48909) Natural Resources, Resources, Lansing, Lansing, MI Graphite i n Baraga Baraga Graphite was was produced produced from from several s e v e r a l small small quarries q u a r r i e s in County, Michigan around the turn of the century for use County, Michigan around the t u r n of t h e century f o r use in i n coating coating foundry The graphite g r a p h i t e occurs occurs in i n the the and as a s aa battleship b a t t l e s h i p paint. paint. The foundry molds molds and Lower Slate Unit of the Lower Proterozoic (Proterozoic X) Michigamme Lower S l a t e Unit of t h e Loner Proterozoic (Proterozoic X) Michigamme Formation. the northern northern margin margin The strata s t r a t a crop crop out o u t sporadically s p o r a d i c a l l y along along the Formation. The of the Marquette Trough from Alberta on the west to the Hunboldt area area of the Marquette Trough from Alberta on t h e w e s t t o the Humboldt on the east, east, aa distance d i s t a n c e of of approximately approximately 50 50 km km (Klasner, (Klasner, 1972), 19721, on the (Bodwell, and Klasner Klasner 1977). 1977). Recent Recent work work by by Michigan Michigan (Bodwell, 1972), 1972), (Cannon (Cannon and Technological the Michigan Michigan Geological Geological Survey Survey Technological University University and and the established from 17% 17%to t o 30% 30%carbon. carbon. Three Three e s t a b l i s h e d that t h a t the the strata s t r a t a range range from billion tons of graphitic be contained contained in i n aa b i l l i o n tons of g r a p h i t i c material m a t e r i a l are a r e estimated estimated to t o be 1.6 km wide zone along the 50km strike length (Hwang, etal., 1986). 1.6 wide zone along t h e 50 km s t r i k e length (Hwang, %&., 1986). It I t is is known known that t h a t the the area a r e a is is structurally s t r u c t u r a l l y complex complex and and has has undergone undergone regional r e g i o n a l metamorphism metamorphism (LaRue (LaRue and and Sloss, Sloss, 1980; 1980; James, James, 1955). 1955). AA 1986 1986 literature l i t e r a t u r e search search revealed revealed scant s c a n t information information pertaining p e r t a i n i n g to to details the graphitic g r a p h i t i c slate s l a t e unit u n i t of of the the Lower Lower Michigamme Michigamme d e t a i l s of of the Formation. the Much of of the the early e a r l y prospecting prospecting work work was w a s done done prior p r i o r to t o the Formation. Much 1900's and during World War II; none of this work was published. 1900's and during World War 11; none of this work was published. Subsequent Subsequent work work in i n Baraga Baraga County County has has shown shown mappable mappable graphitic g r a p h i t i c units units (Klasner, 1972). However, detailed regional mapping (Klasner, 1972). However, d e t a i l e d r e g i o n a l mapping has has not not been been possible Core from from regional regional p o s s i b l e because because of of extensive extensive glacial g l a c i a l overburden. overburden. Core diamond drilling done in the mid 1970's for uranium exploration diamond d r i l l i n g done i n t h e mid 1970's f o r uranium e x p l o r a t i o n shows shows some some graphitic g r a p h i t i c zones. zones. This This core core was was available a v a i l a b l e for f o r study study and and was was used used to t o delineate d e l i n e a t e the t h e extent e x t e n t of of graphitic g r a p h i t i c zones. zones. During summer of of 1986, 1986, aa geophysical geophysical survey survey was was conducted conducted During the t h e summer using a VLF—EM (very low frequency electromagnetic) meter using a --EM (very low frequency electromagnetic) meter and and aa proton proton precession magnetometer. The EM readings have been correlated with precession magnetometer. The EM readings have been c o r r e l a t e d with known of unknown unknown known graphite g r a p h i t e occurrences, occurrences, and and compared compared with w i t h areas a r e a s of potential. p o t e n t i a l . Unfortunately Unfortunately the the interpretations i n t e r p r e t a t i o n s are a r e complicated complicated by by characteristics the overburden overburden and and individual i n d i v i d u a l conductor conductor response. response. c h a r a c t e r i s t i c s of of the However, However, filtering f i l t e r i n g techniques techniques combined combined with with magnetic magnetic data d a t a are a r e being being used used to t o enhance enhance the the graphitic g r a p h i t i c anomalies. anomalies. Ongoing the mineralogy, mineralogy, geology, geology, Ongoing research research involves involves study study of of the geophysical geophysical response, response, beneficiation b e n e f i c i a t i o n characteristics c h a r a c t e r i s t i c s and and economics economics of of the the graphite g r a p h i t e resource. resource. Aside Aside from from uses uses as a s an an industrial i n d u s t r i a l mineral mineral aa principle p r i n c i p l e application a p p l i c a t i o n considered considered for f o r the t h e graphite g r a p h i t e is is as a s aa reductant reductant in in steelmaking. steelmaking. —53— �I . REFERENCES REFERENCES ~, ..., ' . ~. .,., . . ~' Bodwell, w.A., W.A., (1972), Non—Ferrous Metal Bodwell, (1 972 ), Geologic Compilation and Non-Ferrous Potential, P o t e n t i a l , Precambrian Precambrian Section, Section, Northern Northern Michigan, Michigan, IM.S. [M.S. Thesis]: Thesis]: Houghton, Houghton, Michigan Tech. Tech. University, University, 73 73 p. p. Cannon, W.F. (1977), Cannon, W. F. and Kiasner Klasner J.S., J.S., (1977), Bedrock Bedrock Geologic Geologic Map Map of of Part of tthe Diorite the Southern P a r t of he D i o r i t e and Champion 7 1/2 Minute Quadrangles, Marquette County, County, M MI, U.S. Geological Survey Quadrangles, I , U.S. Survey Miscellaneous Investigations Series, Miscellaneous Investigations S e r i e s , Map 1—1058 1-1058 Scale 1:2400. 1:2400. I Hwang, J.Y., J.Y., Carlson, Carison, D D.H., Johnson, A.M. A.M. and Van A Alstine, .H., Johnson, l s t i n e , J., J., Hwang, (1986), Preliminary Investigation (19861, Preliminary I n v e s t i g a t i o n of Graphite Graphite Resources Resources in i n Michigan, Michigan, SME) AIME, AIME, N New Orleans, LA, LA, P Preprint, ew Orleans, r e p r i n t , 13 13 p. p. 115th Annual (Mtg. (Mtq. SHE) James H.L. H.L. (1955), (1955), "Zones "Zones of of Regional Metamorphism Metamorphism in i n the the Precambrian of Northern Michigan" Geol. Soc. 2\mer. Bull., V66, of Northern Michigan" Geol. Soc. h e r . Bull., V66, p. 1455-1488. p. 1455—1488. Klasner, Klaaner, J.S., J.S., (1972), (1972), Style S t y l e and and Sequence Sequence of of Deformation Deformation and and Pssociated Metamorphism Due to t o the t h e Penokean Penokean Orogeny Orogeny in i n the t h e Western Western Ketamorphism Due Associated Marquette Range, Range, Northern Michigan (Ph.D. tPh.D. dissert.]: dissert.1: Houghton, Michigan Tech. Tech. Univ., Univ., 131 131 p. p. and Stoss, LaRue, LaRue, D.K., D.K., Slosa, L.L., L.L., (1980), (19801, Early Early Proterozoic Proterozoic Sedimentary Basins of the the Lake Lake Superior Superior Region: Region: Summary. Geological of America B Bulletin, Society of u l l e t i n , Part P a r t I, V. v. 91, p. p. 450—452. 450-452. — U J J U U nj -54- U -J �The The Hardwood Hardwood gneiss, gneiss. aa basic basic two—pyroxene two-pyroxene granulite granulite J.W. J.W. PETERSON PETERSON (Department (Department of of the the Geophysical Geophysical Sciences, Sciences, University University of of Chicago, Chicago, Chicago, Chicago, IL IL 60637 60637 U.S.A.) U.S.A.) C.A. C.A. GEIGER GEIGER (Technische (Technische Universität UniversitSt Berlin, Berlin, Institut Institut für fur Mineralogie Mineralogie und und Kristallographie, Kristallographie, Ernst Ernst Reuter Renter Platz Platz 1, 1, 1000 1000 Berlin Berlin 12, 12, West West Germany) Germany) The Early Precambrain Precambrain age age outcropping outcropping in in The Hardwood Hardwood gneiss gneiss is is aa unit unit of of Early eastern—central eastern-central Dickinson Dickinson County, County, Michigan. Michigan. The The unit unit is is exposed exposed along along State State Route Route M—60 M-60 between between Foster Foster City City and and Hardwood, Hardwood, Michigan. Michigan. The The gengeneral eral lithology lithology of of the the unit unit is is described described by by James James et et al., al., 1961*, 1961*, and and consists consists of of garnet—hornblende—pyroxene garnet-hornblende-pyroxene gneiss, gneiss, plagioclase—quartz plagioclase-quartz gneiss, gneiss, hornblende—pyroxene hornblende-pyroxene gneiss, gneiss, amphibolite, amphibolite, garnet—quartz—mica garnet-quartz-mica schist, schist, and and micaceous micaceous quartzite. quartzite. This This assortment assortment of of rocks rocks is is suggestsuggestive of a supracrustal sequence. Samples containing garnet—hornblende— ive of a supracrustal sequence. Samples containing garnet-hornblendeclinopyroxene—orthopyroxene—plagioclase—quartz clinopyroxene-orthopyroxene-plagioclase-quartz have have been been examined examined petrographically, and analyzed with electron microprobe petrographically, and analyzed with electron microprobe techniques. techniques. The The pyroxenes pyroxenes have have been been previously previously interpreted interpreted as as primary primary igneous igneous crystals (James et al., 1961). High average calcium crystals (James et al., 1961). High average calcium content content of of the the clinopyroxene (> 42 mole Z Wo) as well as low average calcium content clinopyroxene (> 42 mole Z Wo) as well as low average calcium content of of the the orthopyroxene orthopyroxene (4 ( 4 33 mole mole ZZ Wo) Wo) indicate indicate aa lower lower temperature temperature (i.e. metamorphic) origin. The close textural proximity (1.e. metamorphic) origin. The close textural proximity of of the the pyrox— pyroxenes with porphyroblasts of garnet also supports a metamorphic enes with porphyroblasts of garnet also supports a metamorphic interinterpretation. pretation. Equilibrium Equilibrium assemblages assemblages of of garnet—clinopyroxene, garnet-clinopyroxene, and and orthopyroxene—clinopyroxene yield geotherinometric orthopyroxene-clinopyroxene yield geothermometric paleotemperatures paleotemperatures ranging Geobarometers ranging from from 730°—890°C. 730'-890°C Geobarometers that that utilize utilize assemblages assemblages of of garnet—plagioclase—orthopyroxene—quartz garnet-plagioclase-orthopyroxene-quartz yield yield paleopressures paleopressures greater greater than than 6.4 6.4 kbar. kbar. Garnet Garnet cores cores equilibrated equilibrated at at temperatures temperatures of o f d—'850— 850890°C, 89O0C, and and pressures pressures between between 7.4 7.4 and and 11.0 11.0 kbar. kbar. Garnet Garnet rims rims are are 16 16 mole % more depleted depleted in in caw Ca than mole ZZ richer richer in in iron, iron, and and 17 17 mole Z than garnet garnet cores. cores. These These differences differences represent represent aa re—equilibration re-equilibration in in temperature temperature down down to to 730—770°C, 730-77O0C, and and aa reduced reduced equilibrium equilibrium pressure pressure of of 6.4 6.4 to to 7.5 7.5 kbar. The presence presence of of apparently apparently metamorphic metamorphic clinopyroxene clinopyroxene and and ortho— orthokbar. The pyroxene, in conjunction conjunction with with calculated calculated temperatures temperatures and and pressures pressures of of pyroxene, in assemblages is opx-cpx-garnet-plagioclase-quartz, is assemblages bearing bearing the the phases phases opx—cpx—garnet—plagioclase—quartz, evidence evidence that that the the Hardwood Hardwood gneiss gneiss experienced experienced granulite granulite facies f a d e s metametamorphism requiring burial burial to to at at least least 25 25 km km depth. depth. morphism —— requiring -- * * James, James, H.L., H.L., Clark, Clark, L.D., L.D., Lamey, Lamey, C.A. C.A. and and Pettijohn, Pettijohn, F.J., F.J., 1961, 1961, Geology of central Dickinson County Michigan: U.S. Geology of central Dicklnson County Michigan: U.S. Geol. Geol. Survey Survey Paper Paper 310, 310, 176 176 pp. pp. —55— �Natural of Natural Brine Brine Contamination Cont-tion of Groundwater Grwater in an the t h e Keweenawan Keweenawa~ Rocks of Northern Michigan Rocks of Northern Michigan BARBARA BARBARA J. J. PROSEN PROSED (Dept. (Dept. of of Geology Geology and and Geological Geological Engineering, Engineering, Michigan Tech. University, Houghton, MI Michigan Tech. University, Houghton, M I 49931) 49931) ALLAN ALLAH M. M. JOHNSON JOHNSON (BioSource (BioSource Institute, I n s t i t u t e , Michigan Michigan Tech. Tech. University, University, Houghton, MI 49931) Houghton, M I 49931 j Former Former Michigan Michigan State S t a t e geologist, g e o l o g i s t , A.C. A.C. Lane Lane (1908) (1908) first f i r s t reported reported the presence of high concentrations of brines in the Keweenawan t h e presence of high concentrations of b r i n e s i n t h e Keweenawan rocks rocks of of Michigan. Michigan. Lane Lane coined coined the the term term "connate" "connate" to t o describe d e s c r i b e the t h e brines brines which which were were sometimes sometimes at a t concentrations concentrations greater g r e a t e r than than 15% 15%dissolved dissolved solids (150,000 mg/i) in the deep native copper mines s o l i d s (150,000 mg/l) i n t h e deep n a t i v e copper mines of of the the Portage Portage Lake Lava Series. Lake Lava S e r i e s . Less L e s s concentrated concentrated brines b r i n e s of of similar s i m i l a r composition composition have have been been encountered encountered in i n relatively r e l a t i v e l y shallow shallow water water wells w e l l s drilled d r i l l e d along along the t h e Lake Lake Superior Superior shore, shore, especially e s p e c i a l l y above above Upper Upper Keweenawan Keweenawan sedimentary sedimentary strata; strata; i.e., i.e., the t h e Nonesuch Nonesuch and and Freda Freda Formations. Formations. Working w e l l drillers d r i l l e r s in i n the t h e western western Working in i n cooperation cooperation with with water water well Upper Upper Peninsula Peninsula of of Michigan, Michigan, more more than than 100 100 brine b r i n e contaminated contaminated water water wells 37 wells wells were were sampled sampled and and analyzed analyzed wells were ware identified. i d e n t i f i e d . Of Of these, these, 37 for C l , SO4, SO4, Sr, S r , Mn, Mn, Ba, Ba, Al, Al, f o r aa number number of of cations c a t i o n s and and anions anions including including Cl, I, I, Zn, Zn, Cu, Cu, NO3, NO3, Br, B r , Fe, Fe, IC, K, Na, Na, Mg, Mg, and and Ca. Ca. The The total t o t a l dissolved dissolved solids solids ranged ranged as as high high as a s 24,000 24,000 mg/i mg/1 with w i t h an an average average value value of of 2800 2800 mg/i. mg/1. Elemental concentrations of the nine samples with chloride levels Elemental concentrations of the nine samples w i t h c h l o r i d e l e v e l s above above 1000 1000 mg/l, mg/1, in i n order order of of relative r e l a t i v e abundance, abundance, were: were: Cl, C l , Ca, Ca, Na, Ma, 504, SO4, Br, B r , Sr, Sr, Mg, Mq, Ba, Ba, and and I. I. Statistical S t a t i s t i c a l analyses analyses established e s t a b l i s h e d strong strong positive p o s i t i v e linear l i n e a r correlation c o r r e l a t i o n coefficients c o e f f i c i e n t s between between many many of of the t h e analyzed analyzed elements. elements. J 1\ number of of the the b brine A number r i n e contaminated contaminated wells wells were were situated s i t u a t e d some some distance inland from the Lake Superior shoreline. It was hypothesized hypothesized d i s t a n c e i n l a n d from t h e Lake Superior shoreline. I t was that that these these wells wells may may have have been been contaminated contaminated by by brine b r i n e migration migration along along vertical fissures which transect the Keweenawan rocks. v e r t i c a l f i s s u r e s which t r a n s e c t t h e Keweenawan rocks. To To test t e s t this this hypothesis hypothesis linearnents lineaments were were mapped mapped from from aerial a e r i a l photographs photographs and and satellite s a t e l l i t e imagery imagery and and compared compared to t o the the brine b r i n e occurrences. occurrences. Preliminary Preliminary data Geophysical field field d a t a are a r e not not adequate adaquate to t o confirm confirm this this hypothesis. hypothesis. Geophysical measurements measurements using using resistivity r e s i s t i v i t y methods methods are a r e proposed proposed to t o resolve resolve this this problem. problem. We them from W e favor favoraa model modelofof origin o r i g i nfor f o rthe t h ebrines b r i n e swhich whichderives derivesthem from the the Lake Lake Superior Superior Basin. Basin. Compaction Compaction of of t h e Keweenawan Keweenawan sediments sediments in i n the the the sediments sediments and and resulting r e s u l t i n g fluid f l u i d expulsion expulsion provides provides aa plausible plausible mechanism mechanism for f o r updip updip movement movement of of the t h e brines. brines. This This model model is i s similar s i m i l a r to to White's White's hypothesis hypothesis for f o r the t h e origin o r i g i nof of the t h enative n a t i v ecopper copperdeposits d e p o s i t sofof the the Keweenaw Keweenaw Peninsula Peninsula (White, (White, 1966). 1966). REFERENCES REFERENCES Lane, Lane, A.C. A.C. (1908), (1908),"Mine "MineWaters", Waters", Lake Lake Superior Superior Mining Mining Institute Institute Proceedings, Proceedings, pp. pp. 63—152. 63-152. White, White, W.S., W.S., (1966), (1966),"Tectonics "Tectonicsof of the theKeweenawan KeweenawanBasin: Basin: Lake Superior Region", USGS Prof. Paper 524—E. Lake Superior Region", USGS Prof. Paper 524-E. —56— Western Western j �Video yideo Field Field TriD Trio to to The The Reweenaw Keweenaw Rift Rift I. ROSE ROSE (Dept. (Dept. of of Geology Geology and and Geological Geological Engrg., Engrg., Michigan Michigan Tech. Tech. University, University,.Houghton, Houghton, MI M I 49931) 49931) W. 14. 1. 0 40 40 minute minute video video field field trip trip to to the the Reweenaw Keweenaw Peninsula Peninsula and and Isle Isle Royale Royale is is presented presented as as aa example example of of the the unique 1-n-iique ability ability of of this this median medium to to communicate communicate the the field field setting setting and and geologic geologic context context of of classical classical areas. areas. The The video video fl incorporates numerous ions incorporates aerial aerialviews viewswith with numerousground ground locat locations ItIt is meant for audiences ranging from high is meant for audiences ranging from high and and maps. maps. school erice classes t hrough geo 1 ogy graduate school earth earthSc science classes through geology graduate students whoare areinterested interested in in an an introduction introduction to students who to the the large scale flood basalt phenomena of the area arid large scale flood basalt phenomena of the area and the the Michigan CopperDistrict. District. Michigan Copper ItIt isishoped videofield fieldtrips trips will hoped that that such such video will allow allow better frequent interchange interchangeof cf field field observations better and and more more frequent observat ions among geoscient ists and educators working in areas areas ail all among geoscientists and educators working in over the world. The expansion of video systems and over the world. The expansion of video systems and the the availability of editing availability of editingsystems systems and and technical technical comniun i cat ions studentseager eagerfor for projects projects which communications students which demonstrate cornrnunicat ion communication demonstrate the the various variousadvantages advantages ofofvideo video for science purposes it forcertain certainnatural natural science purposes makes makes it possible possible for for scientists scientists with with little 1 itt le video background background to to produce produce high high quality results. The video will be run continuously quality resu.lts. The video will be run continuously during during the the poster poster session, session, with with the the author author available available for. for. quest ions and comments. quest ions and comments. —57— �-j —4 J J Structural Structural and Economic Geology Geology of of Citadel Citadel Cold Gold Mines Mines Inc. Inc. Wawa, Ontario (Citadel Gold Gold Mines Mines Inc., Inc., P.O. P.O. Box 54 J. RIJPERT RUPERT (Citadel 54 ROY J. Wawa, Ontario Ontario POS Wawa, POS 11(0) 1KO) J The Surluga Surluga and Jubilee Mines of Citadel Citadel Gold Mines Mines Inc. Inc. were were reopened reopened in in 1987. 1987. These former former gold producers producers are are both both located in or adjacent adjacent to to the the Surluga Surluga Fault Fault Zone. Zone. series of anastomosing anastomosing The Surluga Fault Zone is is defined by a series mud slips slips and breccia zones zones up to to 55 feet wide, within aa wider fault fault 50 to to 200 200 feet feet wide. It dips dips east-south-east east-south-east at 300 30 to to zone from 50 400. Slickensides consistently indicate 400. Slickensides indicate movement in a normal right lateral sense sense along along aa plunge plunge direction direction of of 15° 15' to to 200 20 south. south. The fault zone is clearly defined where intrusive intrusive dioritic unit, but cannot tuffaceous tuffaceous rocks rocks to to the the north north and and south. south. the diorities diorities are relatively fresh relatively fresh rocks. rocks. tiple tiple it crosses crosses a complex mul— mulbe readily readily traced traced into into Outside Outside the the fault fault ione, zone, J IJ J Within the the fault fault zone, zone, anastomosing anastomosing splay splay faults, faults, schist schist zones zones and quartz veins trend at a higher azimuth azimuth and have have aa lower lower dip dip angle than than the the fault fault zone zone as as aa whole. whole. Failure to recognize recognize this this relationship, and the relationship, the assumption assumption that that the the "shearing" "shearing" was was paralparallel to the fault was a major contributing contributing factor factor in in the the economic economic failure of the failure the Surluga Surluga Mine Mine in in 1970. 1970. zones and quartz veins parallel the Siliceous alteration zones the schis— schistosity tosity and and the the faults. Where siliceous siliceous alteration alteration is is most intense intense ore is is developed. developed. These ore zones zones are offset en echelon to the the left and progresssively beneath one one another another from from south south to to north. Mine isa classic The Surluga Mineisa classic example example of of en en echelon echelon dilatant dilatant zones zones related to to movement movement on on aa fault. fault. II 1, -58- J �Imprint I m p r i n t of o f Archean Archean AAbitibi b i t i b i tectonics t e c t o n i c s on on the t h e Proterozoic Proterozoic Lake Lake Superior Superior Basin Basin R.J. (EssoMinerals MineralsCanada, Canada,P.O. P.O.Box Box290, 290, Timmins, Timmins, Ontario R.J. SHEGELSKI SHEGELSKI (Esso P4N 7N6) P4N 7N6) Archean supracrustals form formssix Archean supracrustals i x lithotectonic, l i t h o t e c t o n i cvolcanic—sedimentary , volcanic-sedimentary facies associations: 1) Least differientiated consists f a c i e s associations : 1) Least d i f f e r i e n t i a tPRIMATIVE e d PRIMATIVECRUST CRUST consists of komati— of voluminous, voluminous, thick t h i c ksubmarine submarine Mg—tholeiitic M g - t h o l e i i t i c basalts b a s a l t swith w i t minor h minor komatiitic i t i clavas lavasand and ultramafic u l t r a m a f i c intrusions. i n t r u s i o n s . Flat f l a t paleotopography paleotopography ccollects ollects thin 2) The The tholeiitic t h o l e i i t iBASALT c BASALT t h i n but butextensive extensivepyritic—graphitic p y r i t i c - g r a p h i t i cmudrocks. mudrocks. 2) PLATFORM contains both minor ffelsics PLATFORM contains both MgMg andand F eFe—tholeiites, - t h o l e i i t e s , wwith i t h minor e l s i c sand and local mafic sedimentation near normal faults. upper lavas are l o c a l mafic sedimentation near normal f a u l t s . The The upper are vario— variolitic, a transition VOLCANIC COMPLEX 3) t h e CENTRAL VOLCANIC COMPLEX which which l i t i cforming , forming a t r a n s to i t i 3) o nthe t o CENTRAL contains two tthirds contains two h i r d s volume volume oof f ttholeiitic h o l e i i t i cand andcalc—alkalic c a l c - a l k a l i c basalts b a s a l t s or or andesites andesites and and one one tthird h i r dsubmergent submergent to t oemergent emergent dacite—rhyolite d a c i t e - r h y o l i t e cone cone complexes. more andemergent, emergent,ppyroclastic complexes. As As lavas lavas become become more f efelsic l s i c and y r o c l a s t i c flank flank facies f a c i e s develop develop and and fine f i n edownslope downslope into i n t o4)4)lateral l a t e rTURBIDITE a l TURBIDITEBASIN BASIN deposits deposits consisting debris and minorbut but more morel alaterally c o n s i s t i n g of o f quartzo—feldspathic quartzo-feldspathic debris and minor terally extensive deposits form form along extensive iron i r o n formations. formations. 5) RIFT RIFTBASIN—RIDGE BASIN-RIDGE deposits along lineaments as predominantly predominantlycalc-a1 calc—alkalic and1ocal locally alkalic 1ineaments as k a l i c and l y a1 ka1 i c lavas, 1avas , alluvial—fluvial a l l u v i a l - f l u v i asediments l sedimentsand and fault—bounded f a u l t-bounded t uturbidites. r b i d i t e s . 6) 6 ) CRATONIC CRATONIC NUCLEI basements telescoped versions otherl i lithotectonic NUCLEI asasbasements areare telescoped versions o f of other t h o t e c t o n i c assoassociations by sstable andi iron c i a t i o n s capped capped by t a b l e sshelf h e l f carbonates, carbonates, sstromatolites t r o m a t o l i t e s and r o n fforormations. mations. Areal Areal ddistribution i s t r i b u t i o n of o f lithotectonic l i t h o t e c t o n i c associations associations iin n the t h e Abitibi A b i t i b i terrane terrane suggests structures suggests tthat h a t earlier e a r l i e rdeposition depositionwas was favoured favoured along along regional regional structures which and recordshearing shearingasast their WNW and record h e i r latest l a t e smovements. t movements. which now now ttrend r e n d WNW This This is the i s the t h e direction d i r e c t i o nofo the f t h eboundary boundary between between t h e AAbitibi b i t i b i northern northern "internal "internal zone" southern "external "external zone". zone" and and southern zone". Possibly Possiblycontemporaneous contemporaneous ENE trendENE trend- ing i n g structures s t r u c t u r e s were were reactivated r e a c t i v a t e d and and ddilatant i l a t a n t during during later l a t e rdeposition depositionand and orogeny, and now host economic epigenetic ore deposits. Intersections orogeny, and now host economic epigenetic ore deposits. I n t e r s e c t i o n s of regional ttectonic faulto f these these two two trends trends produce produce aa regional e c t o n i c grain g r a i n of o fshear shearand and fault— bounded lozenges wwith bounded lozenges i t h apparent apparent east—west east-west eelongation. l ongat ion. Changes Orogeny produced a NNW—NNE Changes iinn regional regionalstress s t r e sduring s d u r the i n g Kenoran t h e Kenoran Orogeny produced a NNW-NNE fracture represented by by thet hMatachewan f r a c t u r eset set represented e Matachewandike d i kswarm e swarmand andKapuskasing Kapuskasing Structural Structural Zone Zone respectively. respectively. The The iinherited n h e r i t e d ENE ENE AAbitibi b i t i b i trend t r e n d controlled controlled deposition greenstone deposition of o fearly e a r l yProterozoic Proterozoic greenstonein i Wisconsin n Wisconsinand andHuronian Huronian deposition ooff the stable stab1 e shelf she1 f sedimentation sedimentation in i n Ontario. Ontario. Subsequent Subsequent deposition the Cobalt andNipissing Nipissingf lflood basaltswas wasi ninitiated Cobalt pplatform l a t f o r m and o o d basalts i t i a t e d aat t tthe h e interintersection and tthe southern termination termination of section of o fthe t h eENE tNE Huronian Huronian ttrend r e n d and h e southern o f the the NNW Matachewanddike NNW Matachewan i k e swarm. swarm. Younger analogoustrends trendse exist Younger analogous x i s t iin n the t h e Lake Lake Superior Superior basin. basin. The The Animikie Animi k i e strand byby thet hMesabi—Gunflint strand line, l i n e ,defined defined e Mesabi-Gunflint iron i r o nrange, range,trends trendsENE tNEand and is The NNW NNW f rfractures actures NNW ddilatent i l a t e n t fractures. fractures. The i s intersected intersectedby byaborted abortedNNW allowed and deposition deposition of allowed subsidence subsidence and o f the t h elacustrine—shallow lacustrine-shal lowmarine marine Sibley Sibley Group and subsequent deposition of the Nipigon—Logan sills. Group and subsequent deposition o f t h e Nipigon-Logan s i l l s . Long—lived Long-lived NNE NNE f afaults u l t s subparallel subparallel to t othe t h eKapuskasing Kapuskasing Structural S t r u c t u r a lZone Zone provided provided periodic access for alkalic intrusions such as the Coldwell complex at at p e r i o d i c access f o r a l k a l i c i n t r u s i o n s such as t h e Coldwellcomplex the t h eclose c l o s eofoKeweenawan f Keweenawan volcanism. volcanism. The The Keweenawan, Keweenawan, asast hthe e llast a s t major major extrusive e x t r u s i v e event event ini nthe t h ebasin, basin,produced produceda athick t h i c sequence k sequenceofofemergent emergent —59— �U tholeiitic The ttrace r a c e of o f the t h e axial a x i a lsurface surface t h o l e i i t i basalts c b a s a l t sand andfelsic f e l s i cextrusives. extrusives. The in i n the the western WNW easternp oportions basin as, as, respectively, western and and WNW i n in t h the e eastern r t i o n s oof f t the h e basin respectively, later l a t e rand and earlier e a r l i e r inherited i n h e r i t e d Abitibi A b i t i b istructural s t r u c t u r a ltrends. trends. The The ENE tNE AAbitibi bitib-i trend t r e n dwas was once once aain againpredominantly predominantlydilatent d i l a t e during n t d u r iKeweenawan n g Keweenawanvolcanism, volcanism, as which ooriginated trans-'AbitibiKeweenawan Keweenawan ddike i k e swarm swarm which riginated as evidenced evidenced by by the t h etrans—Abitibi from f i n a argument l argument from the t h e Aphebian Aphebian greenstone greenstone bbelt e l t axis a x i s ini nWisconsin. Wisconsin. AA final 11 byby Keweenawan of o f the t h eLake Lake Superior Superiorsyncline synclinedefined defined Keweenawan sstrata t r a t a isi sEPIE ENE U for Superior f o rAbitibi A b i t i btectonic i t e c t o n iimprint c i m p r i nint the i n t hLake e Lake Superiorbasin basinis i the s t hpresence e presence J of between o feither e i t h eENE r ENEoroWNW r WNW fault f a u l tcontacts contacts betweenArchean Archeangranite—greenstone granite-greenstone and and gneiss—amptiibolite gneiss-amphi bol i t e ccrustal r u s t a l remnants remnants wwithin i t h i n the t h e Lake Lake Superior Superior basin. bas1n. LI J U j j j j J j -60- J �Nature of Cleavage. Foldin2 and Strain in the Michinicoten Greenstone BelL Near Wawa. Ontario CATHERINE H. SHRADYand andGEORGE GEORGE McGILL (Department of E.ILMcGILL (Department of Geology Geology and Geography, Geography, University Universityof of Massachusetts, Massachusetts,Amherst, Amherst,MA MA01003). 01003). The rocks within withinthe theMichipicoten Michipicoten Greenstone Greenstone Belt Belt near near Wawa, Wawa, well exposed. exposed.This This and and the the generally low Ontario are exceptionally well metamorphic grade grade and and excellent excellent preservation preservation oof primary metamorphic f primary sedimentologicalfeatures featurespermit permit detailed detailedstructural structural analysis. sedlmentologlcal analysis. Development oof multiple phases of with associated Development f multiple of folding with associatedcleavages cleavages and shear zones zones characterizes the predominantly predominantly ductile earlier Archean deformation. These were subsequently subsequentlydissected dissected and and displaced displaced along faults faults and shear andShrady, Shrady, this this volume). volume). Strain along shear zones zones (McGill (McGlU and during the earlier earlier deformation deformation of of the the area areaisIsgenerally generallyheterogeneous heterogeneous although conglomerate conglomeratepebbles pebblesdeformed deformedvery veryearly early in in the the history of of this part strain. this part of of the theBelt Belt record record moderate, moderate, relatively relativelyhomogenous homogenous strain. Rootless tight to isoclinal Rootless tight isoclinal mesoscopic mesoscopic folds oof f probable soft sediment sediment slump origin and generally larger, meter—scale tight folds without generally larger, meter-scale tight folds without associated axial axial planar cleavage associated cleavage but of of probable probable tectonic origin are are among the oldest structures. Conglomerate oldest recogni2ed recogoiaad structures. Conglomeratepebbles pebbles lie lie within an an approximately approximately bedding bedding parallel cleavage, cleavage, the earliest earliest observed. This cleavage is only rarely rarely observed penetrative cleavage cleavage observed. cleavage is observed to to be axial planar to clastic dikes dikes parallel parallel to this be to folds. folds. The The existence oof f clastic suggests that, that, at early axial planar cleavage cleavage suggest* at least least locally, locally, this this cleavage cleavage developedin In incompletely incompletely consolidated consolidatedsediments. sediments. Mineral lineations Uneations developed principal extension and the thelong long axes axesofof deformed deformedpebbles pebblesdefine definea aNE—E NE-E principal extension within this thiscleavage cleavage plane. plane. Estimates Estimates of of the the axial axial ratios ratiosof of oblate oblate strain ellipsoids suggeststrain strain of of moderate moderate intensity intensity with little strain ellipsoids suggest little variation across faults are variation acrossthe thearea. area.Bedding—related Bedding-related faults are also also of of comparable relative relative age. age. Although Althoughthe theprecise preciserelation relation among comparable among the is not not at at present known, a early folds, folds, faults and this cleavage cleavage is of deformation deformation resulting resulting in in these structures structures isissuspected. suspected. continuum of Regionaloverturning overturning and and stratigraphic stratigraphic inversion Regional inversionsuggestive suggestive of of thrusting and with this phase and large large recumbent recumbent folds folds also is associated associated with phase of deformation. In In comparison, comparison, younger youngerdeformation deformationand andstrain strain are are o f deformation. Inhomogeneousand andhave havebad had little little effect, effect, except except locally locally (e.g. (e.g. in in shear Inhomogenwus zones) on the zones) the deformed deformed conglomerate conglomerate pebbles. pebbles. A younger, younger, generally A generallyNW—trending, NW-trending, moderately moderatelyNE—dipping NE-dipping is most most strongly developed inthe the western western and crenulation cleavage cleavage is developed in northwestern sections foldsare are rare. rare. northwestern sections of of the the area. area.Related Related mesoscopic mesoscopic folds —61— �-4 this and a NE— this and crenulating crenulatingall allprevious previoussurfaces surfacesisis a NEtrending cleavage that dips steeply SE and NW and is axial planar to trending cleavage that dips steeply SE and NW and is axial planar to folds oof opentototight tight geometry. geometry. Shear Shear zones zones parallel parallel the the axial axial surfaces surfaces folds f open of these folds. steepeningoof dipsprobably probably is is associated associated with with o f these folds. Regional Regional steepening f dips this deformation phase which appears more intensely developed in the the this deformation phase which appears more intensely developed in southern part is crenulated crenulated by by part of of the the area areamapped. mapped. This This older older cleavage cleavage is southern aa younger northeasterly trending axial planar cleavage with shallow younger northeasterly trending axial planar cleavage with shallow to moderate southeasterly southeasterly dips. dips. In Inaddition additionto tothose thosedescribed describedabove, above, are cleavages of only local development; some parallel faultsfollowed followed are cleavages of only local development; some parallel faults by diabase diabase dikes, dikes, others others are are oof variable attitude attitude and and uncertain by f variable uncertain association. association. Post—dating Post-dating The deformational deformationalhistory historyrecorded recordedby bythese thesestructural structural feautures feautures is is The more complex than previously recognized, with significant shortening more complex than previously recognized, with significant shortening and strain and shearing. and strain achieved achieved through through early earlyfolding folding and shearing. Subsequent Subsequent folding, cleavage cleavagedevelopment developmentand andassociated associatedstrain strain are are more local and folding, heterogeneousinincharacter. character. OOur observationsare are inconsistent inconsistentwith with a heterogeneous u r observations simple Archean deformational history dominated by either vertical simple Archean defarmational history dominated by either vertical motion or or horizontal compression motion compression resulting in an an uncomplicated uncomplicated suggest that that the complex nature of synclinal geometry. We We suggest complex nature of deformation in this part of the Michipicoten Greenstone Belt is more consistent with in this part of the Michipicoten Belt is more consistent with that recently documented in some other Archean terranes (e.g. the recently documented in some other Archean terranes (e.g. Barbeton Greenstone Greenstone Belt, Belt, de de Wit, Wit, 1982; 1982; the theNorseman—Wiluna Norseman-Wiluna Greenstone Belt, Martyn, 1986) and with that observedwithin within many many Greenstone Belt, Martyn, 1986) and with that observed Phanerozoic orogenic belts. Phaneroaoic belts. References Wit, M. M. J. J. 1982. Glidingand andoverthrust overthrust nappe nappe tectonics tectonics in in the 1982. Gliding de Wit, Barbeton greenstone belt, .1 Struct. 117—136. belt, J. Struct.Geol., Seol.,4,4,pp.pp. 117-136. Barbeton Martyn, J. E. 1986. Evidencefor forstructural structural stacking stacking and and repetition repetition in Martyn, J.E. 1986. Evidence the greenstones of of the Kalgoorlie district, Western Western Australia, Australia, In the Kalgoorlte district, Workshop on Tectonic Evolution of Creenstone Belts (M.J. J. de Wit Wit and Workshop on Ttctoaic Evolution of Srefastoae Btlts (M. L. D. L.P.1. TechRpt. TecftRpt. 86—10. Lunar and and L. D. Ashwal, Ashwal, eds.), cds.),pp. pp.150—152. 150-152. L.P.I. 86-10. Lunar Planetary Institute, Institute, Houston. Houston. —62— �Structural Geolov of the Southwestern Portion of the Michlnicoten Greenstone Belt. Ontario CATHERINE H. SHRADYand andGEORGE GEORGE McGILL (Department of Geology E. E.McGILL (Department Geology and Geography, University of Massachusetts, and Geography, University of Massachusetts,Amherst, Amherst,MA MA01003). 01003). The The Michipicoten ~ichipicotenGreenstone Belt Belt extends for about about150 150 kin k m ENE ENE from from the northeastern angle of Lake Superior. The eastern limit of the northeastern angle of Lake Superior. The eastern limit of the the belt belt isis the Kapuskasing zone zonethat that separates thehigh—grade high-grade Kapuskasing separatesthe theMichipicoten Michipicoten from the Abitibi Greenstone Belt. We are mapping key areas in from the Abitibi Greenstone Belt. We are mapping key areas in the the southwestern portion of the Belt at a scale of 400 = 1, tying these southwestern portion of the Belt at a scale o f 400' = I", these 4* areas Geological areastogether together with with11mIle mile== 4 " mapping mapping and andrecent recentOntario Ontario Geological Survey Surveypreliminary preliminarymaps mapsby bySage Sageand andothers. others.All Allof of our ourmapping mappingto to date has been within Chabanel Township, and most of it is in or date has been within Chabanel Township, most of is in or adjacent adjacent to to the the large large fume fume kill kffldownwind downwind from the the sintering sintering plant plant in in Wawa Wawa where where outcrops outcrops are are very veryabundant abundantand andeasily easilylocated. located. This This abstract of our ourdetailed detailed maps. maps. abstractaccompanies accompaniesaaposter posterdisplaying displayingsome some of The The rocks rocks of of our our area areamay maybebedivided dividedinto intothe thetraditional traditionallithologic lithologic types: types:rnafic—intermediate mafic-intermediate volcanics, wlcanlcs, intermediate—felsic intermediate-felsic volcanics, volcanics, clastic iron formation). clastic sediment5, sediments, and chemical chemical sediments sediments (including (including Iron formation). In In the thesouthwestern southwesternportion portionofofthe theMichipicoten MichipicotenGreenstone Greenstone Belt Belt there there is is aa northern northern(interior) (interior)terrane terraneconsisting consistingmostly mostlyof of intermediate intermediate to to mafic volcanics. These rocks dip north to northeast at intermediate mafic volcanics. These rocks dip north at Intermediate angles, angles, and are are overturned overturned (all (allindicators indicatorssuggest suggest southward southward or or southwestward southwestwardyounging). younging). Along Along the southern margin margin of of the the belt belt Is is aa thick volcanic rocks rocks with with minor iron formation that thick sequence sequence of of volcanic that youngs andhas hassteep steepnorth northororsouth southdips. dips.Between Betweenthese these youngs northward northwardand dominantly terranes isisan anextensive extensivebelt beltof of clastic clastic dominantly volcanic volcanic terranes sedimentary sedimentaryand andpyroclastic pyroclasticrocks. rocks.Much Muchof of our ourdetailed detailedmapping mapping has has been concentrated in this belt because of the abundance of good been concentrated in this belt because of the abundance of good indicators of younging younging direction, direction, and and because because cleavages cleavages generally generally are are indicatorsof better in the metasedimentary metasedimentary rocks rocks than they are batter developed developed in are in in the the rnetavolcanic metavolcanicrocks. rocks. In In the theeastern easternpart partofofChabanel Chabanel Township, Township, there there is is aa single, single, abrupt abrupt reversal reversalininyounglng younging direction direction within the sedimentary sedimentary belt belt that that Is is interpreted to be a fault (or a faulted isoclinal fold). One late fault interpreted to be a fault (or a faulted isoclinal fold). One late fault that is present present south south of of this this reversal, but thatgenerally generallyfollows follows bedding bedding Is but the Other bedding— thedisplacement displacementdoes doesnot notappear appeartotobebesignificant. significant. Other beddingrelated faults may be present but obscure due to lack of such related faults may be present but obscure due to lack of suchfeatures features as astruncation, truncation,obvious obviousshearing shearingand andlocal local stratigraphic stratigraphicinversion. inversion. Overall, thatthe thesedimentary sedimentarysequences sequences Overall, however, however, the theimpression impression isis that north and south of the one obvious younging direction reversal north and south of the one obvious younging direction reversal are arenot not severely severelydisrupted. disrupted. —63— �To the west, west, the widens rather rather To the the width width of of the the sedimentary sedimentary belt belt widens rapidly, in part due to Increasing thicknesses of Individual rapidly, in part due to increasing thicknesses of individuallithologic lithologic units, but units, but also also we w e suspect suspect due due to to fault fault imbrication imbrication (imbricatlon (imbrication is is very difficult the widest very difficult to to prove prove in in the the absence absence of of fossils!). fossils!). Within Within the widest part of and map map part of the the sedimentary sedimentary belt belt we we have have been been able able to to define define and lithologic "packages", most of which are bounded by contacts that we lithologic "packages", most of which are bounded by contacts that we believe are are early early faults, believe faults, based based on on the the presence presence of of one one oorr more more suggestive characteristics characteristics (deformed suggestive (deformed conglomerate conglomerate pebbles, pebbles, local local spaced spaced cleavages, gossans, mat ics sills, networks of quartz veins, narrow cleavages, gossans, mafics sills, networks of quartz veins, narrow linear topographic depressions,truncation truncation oof layering, oorr abrupt abrupt tops linear topographic depressions, f layering, tops reversals). In reversals). In addition, addition, the the sedimentary sedimentary belt belt appears appears to to be be separated separated from the the northern northern volcanic terrane by by aa fault from volcanic terrane fault that that we we have have been been able able to trace across almost the entire width of Chabanel Township. to almost the entire width of Chabanel Township. Tentatively, we we interpret Tentatively, interpret the the mapped mapped relationships relationships as representing representing a thrust—imbricated sequence of volcanic and sedimentary rocks, with with thrust-imbricated sequence of volcanic and sedimentary rocks, imbrication increasing increasingwestward westward within the area we have mapped. the area we have mapped. Becauseofofthe thefaulting, faulting,the theage ageofofthe therocks rocksinInthe thenorthern northern (interior) (interior) Because volcanic terrane relative to the volcanic rocks along the southern volcanic terrane relative to the wlcanic along margin of margin of the belt near near Wawa Wawa is is not not known known (no (no published published radiometric ages comefrom fromthe thenorthern northern volcanic volcanicterrane), terrane), nor do we we know the ages come sense of of relative relative movement movement across across the imbricate faults. Efforts Efforts to eliminate these uncertainties are underway. eliminate these uncertainties are underway. .1 —64— �fl Struct ural Mnal ysi s ofofPrc'terczcic MetMetasediments, ased iment s, fl Structural flnalysis Proterozoic Northern Falls Falls River. Michigan Northern River, Saraga Baraga County. County, Michigan SIRKILM arid GREGG (Dept. (Dept. of of Geology Geology and KK.M. . M. SIKKILfi. and W.W.J. J. GREGG and Geol. Gaol. Engrg., Michigan Tech. Univ., Houghton, MI 49931) Engrg., Michigan Tech. Univ., Houghton, M I 49931) The geologic geologic feature historically referred referred to The feature historically to as as the the "Baraga Basin" Basin" is is a a roughly roughly crescentic crescentic depression depression trending trending "Baraga east—west across across north-central north—central and and northeastern northeastern Baraga east-west Baraga County contains County in in the the Upper Upper Peninsula Peninsula of of Michigan. Michigan. IIt t contains deformed and and metamorphosed metamorphosed sediments sediments that that have have been deformed been correlated with correlated with the the lower lower Proterozoic ProterozoicMichigarnme Michigamme Formation. Formation, and is rocks of of the the Northern Northern Complex Complex to to and is bounded bounded by by flrchean flrchean rocks the the south south and and northeast. northeast. The The best bast exposures exposures of of the the structure structure within within the the Baraga Baraga Basin occur in the beds of the northward—flowing streams Basin occur in the beds of the northward-flowing streams draining into westernmost of these into Lake Lake Superior. Superior. The westernmost streams, the Falls River, was intensively mapped from streams, the Falls River, was intensively mapped from its its mouth in the village of L'Mnse to a terminal point mouth in the village of L'ftnw to a terminal point located located approximately one to the the south. Other Other aspects aspects approximately one mile mileupstrearii upstream to of the investigation included description of microstructural of the investigation included description of microstructural features and and geometric geometric analyses analyses of of various various elements elements cf features of the the rock fabric. rock fabric. The slates The slates and and metagreywackes metagreywackms of of the the Falls Falls River River area area are characterized by three roughly coaxial systems are characterized by three roughly coaxial systems cf of folds, folds, two of of which Style group two which are are mesoscopically mesoscopically distinct. distinct. Style group B. BI consists of a series consists series of tight to isoclinal isoclinal overturned folds folds with axes with axes that plunge shallowly to the the west—northwest west-northwest and east—southeast. Broal 1—scaleparasitic parasitic folds folds are are commonly commonly east-southeast. Small-scale associated with these The overall overall vergence vergence cf associated these larger larger folds. folds. The of the system suggests the suggests that the the field field area is is located located on on the the The axial—planar regional fold. long limb limb of of aa B1 B1 regional fold. The axial-planarfc.liati':'n foliaticm this style style group (Se) associated with this <S,) dips d i p s gently to the the southwest in in those those areas areas unaffected unaffected by by later later deformation. deformation. Microscopically, SI 5, varies in in appearance appearance from a Microscopically, well—developed continuous continuous slaty fabric well-developed fabric in in the the pelitic pelitic units units to an irregular domainal rough cleavage cleavage in in the the matrix—rich matrix-rich greywackes. In nearly nearly all all cases, cases, the mineral chlorite greywcckms. In chlorite defines the Matrix—poor varieties of defines the cleavage cleavage fabric. fabric. Matrix-poor greywacke display an an 5,—parallel SI-parallel flattening flattening of of clasts. clasts. Recrystallization textures are common in these R~crystallization textures are common in these rocks. rocks. A system of S, —parallel thrusts thrusts is is also also associated associated with this S,-parallel this style group. The fault fault zones are commonly cataclastized and style group. mineralized with quartz quartz and and carbonate. carbonate. Style group B B, considerable lateral . exhibits considerable lateral variation within the field area from north to south. To the the north, B, area from north to south. north, Em is best visualized as a series i s best series of of gentle gentle folds folds and and fabric. SI fabric. asymmetric flexures flexures in in the the previously previously existing existing 5, Fault zones zones have have also also been been visibly visibly folded folded in in some some locales. locales. trond roughly Fold axes appear to be horizontal and trend east—west. P sinuous sinuous crenulation is developed developed east-west. ft crenulation cleavage cleavage (B,) (9.) is —65— �j in the the proximity Cleavage domains in proximity of of the the B, B. hinges. hinges. Cleavage domains vary vary B. folds become tight at the Be folds become tight at the southern end is generally generally southern end of of the the survey survey line, line, and and S. S. is pervasive. Microscopically, S, is more strongly pervasive. Microscopically, Se is more strongly developed developed here than to here than to the the north, north, with with well—defined well-defined cleavage cleavage domains, domains, anastomosing and commonly commonly symmetrical symmetrical profiles. anastomosing rnorphologies morphologies and profiles. from from zonal zonal to to discrete. discrete. J — B deformation Bi deformation is is characterized characterized by by macroscopic macroscopic folds folds which overprint B, style group elements. Field evidence evidence is Field is which overprint Be style group elements. most most easily easily seen seen at at the the southernmost southernmost extent extent of of the the field field line S. cleavage cleavage line and and consists consists mainly mainly of of the the reorientation reorientationc'f of Sà attitudes. Originally east—west striking, nearly vertical attitudes. Originally east-west striking, nearly vertical crenulat ion cleavage cleavage planes planes have have been been rotated rotated more more than 70 crenulation than 70 degrees along a roughly east—west trending horizontal degrees along a roughly east-west trending horizontal axis. axis. Mesoscc'pic fold axes axes for for this this system system have have not not been Mesoscopic fold been precisely precisely located in the field. Pdditional field evidence in the field. additional field evidence in in the thefcrri form of is of a a localized localized steeply steeply dipping dipping spaced spaced cleavage cleavage CS3) (S,) is recognized outcr-ops at at the the terminus terminus of of the the survey survey line. line. recognized in in outcrops These These cleavage cleavage surfaces surfaces appear appear in in thin thin section section as as rough rough fractures and irregular fractures and irregular seams seams of of dark dark residual residual material material that that overprints overprints earlier earlier foliations, foliations, and and has has aa strike strike coincidental coincidental with with the the rotational rotational axis axis of of the the earlier earlier B, S. fabric. fabric. The operation operation of nappe—style nappe-style tectonism tectonism during during the the PenokeanOrogeny Orogenyhas hasbeen beenproposed proposed severalauthors authors in in Penokean byby several recent not be it may may not be the theonl9 onlymechanism mechanism recent years. years. fllthough Although it capable capable of producing producing the the structural structuralfeatures featuresobserved observed at at this and other locations in the Baraga Basin, it is a this locations in the Baraga Basin, it a tectonic tectonic model model that that is is consistent consistent with with known known field field evidence: evidence: 1) B fold 1) The B, fold systems systems in in the the region region display display aa vergence vergence indicative of a position on the long the long limb limb of of aa large— largescale overturned Fold scale overturned regional regional B1 Bi fold system. systems reflective limb reflçctiv of a position on the the short limb of a regional fold are not seen. of a regional fold are not seen. 2) S1—parallel thrust faults 2 ) Systems Systems of S,-pai-allel faults are are observable observable throughout the region, perhaps reflective the region, perhaps rçflectiv of of large— largescale overthrusting. scale overthrust ing. 3) 3 ) The The systematic systematic disappearance disappearance of of later—stage later-stage fold fold systems systems towards towards the the north, and and the the overall overall reduction reduction in the the intensity intensity of of deformation deformation towards towards the the north, north, is something observable on a regional scale, and reflective deform— reflective of a lateral lateral progression from a deformational foreland foreland to to aa hinterland. hinterland. 4) 4) Previous Previous work regarding multiply—deformed multiply-deformed terranes (overthrust (overthrust belts in particular) has shown that a single single progressive progressive tectonic tectonic event event can can produce produce poly— polyphase deformational deformational features features such such as as refolded refolded folds. folds. This This eliminates eliminates the the need need for for models models involving involving discrete deformat ion. discrete "pulses" "pulses" of of deformation. J J J j J -66- J -j �Mesozoic Mesozoic Paleogeography: Paleogeography: implications implications for f o r economic economic deposits north of Lake Superior deposits north of Lake Superior J. J. S. S. SPRINGER SPRINGER (Ontario (Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 5P9) 5P9) During During the t h e Mesozoic Mesozoic major major shifts s h i f t s took took place place in i n the t h e position p o s i t i o n and and attitude attitude of of the t h e North North American American crustal c r u s t a l plate p l a t e and and by by early e a r l y Cretaceous Cretaceous time time Africa Africa had had split s p l i t away away from from North North America America to t o form form the t h e Atlantic A t l a n t i c ocean. ocean. Great Great movements movements also a l s o took took place place in i n the t h e position p o s i t i o n of of magnetic magnetic north, north, influencing influencing global global weather weather patterns. patterns. For For long long periods periods the t h e Precambrian Precambrian Shield Shield stood stood as a s aa continental c o n t i n e n t a l massif massif subject s u b j e c t to t o intense intense tropical t r o p i c a l weathering, weathering, which which advanced advanced most most quickly quickly along along existing e x i s t i n g fracture f r a c t u r e zones zones or o r in i n rocks rocks of of susceptible s u s c e p t i b l e composition. composition. By late Jurassic time this process had developed a subdued By l a t e J u r a s s i c time t h i s process had developed a subdued surface surface of of advanced karst across parts of Minnesota on which quartz—feldspar advanced k a r s t across p a r t s of Minnesota on which quartz-feldspar debris, debris, supplied supplied by by the t h e granite g r a n i t e terranes t e r r a n e s of of Manitoba Manitoba and and Saskatchewan, Saskatchewan, was was slowly transported southwards across a gentle topogradient. slowly transported southwards across a g e n t l e topogradient. By By early e a r l y Cretaceous Cretaceous time time aa rapid rapid pulse pulse of of seafloor s e a f l w r spreading spreading and and renewed renewed sources of volcanism in the mantle caused rotation of the North sources of volcanism i n t h e mantle caused r o t a t i o n of t h e North American American plate. p l a t e . Mountain Mountain building building and and local l o c a l explosive explosive volcanism volcanism marked marked the western margin of the continent, whereas a shallow north—south t h e western margin of t h e continent, whereas a shallow north-south seaway seaway developed developed across across the t h e continental c o n t i n e n t a l midline. midline. Once Once again again the the Ontario Shield was a landmass Ontario Shield was a landmass upon upon which which terrestrial t e r r e s t r i a l materials m a t e r i a l s were were patchily SO* parallel p a r a l l e l now now ran ran from from about about Kenora Kenora to t o Cape Cape p a t c h i l y deposited. deposited. the The 50° Henrietta Henrietta Maria Maria and and the t h e climate climate on on the t h e eastern e a s t e r n shore shore of of the the inland inland sea s e a was was warm warm but but semi—arid. semi-arid. The The long long episodes episodes of of continental c o n t i n e n t a l weathering, weathering, the t h e subaerial s u b a e r i a l volcanism volcanism and and the t h e climate climate conditions conditions influenced influenced the t h e formation formation and and concentration concentration of of aa suite s u i t e of of economic economic mineral mineral deposits d e p o s i t s which which are a r e characteristic c h a r a c t e r i s t i c of of this this time. time. Kaolin, Kaolin, valuable valuable for f o r the t h e refractory r e f r a c t o r y properties p r o p e r t i e s of of iron—free iron-free aluminous i n addition a d d i t i o n have have aluminous materials, m a t e r i a l s , and and secondary secondary kaolins, kaolins, which which in special s p e c i a l plastic p l a s t i c properties, p r o p e r t i e s , were were formed formed worldwide worldwide in i n the t h e Mesozoic. Mesozoic. Volcanic Volcanic dusts, d u s t s , produced produced by by explosive explosive subaerial s u b a e r i a l volcanism, volcanism, have have been been subsequently weathered to special—use bentonitic clays. The hot, often subsequently weathered t o special-use b e n t o n i t i c clays. The h o t , often humid humid climate climate produced produced karst k a r s t depressions depressions filled f i l l e d with with concentrates concentrates such such as a s hematitic hematitic iron—ores iron-ores or o r carbonate—free carbonate-free clays. clays. Leaching Leaching of of carbonate carbonate from has left l e f t gravelly g r a v e l l y phosphate phosphate residues residues enriched enriched from carbonatite c a r b o n a t i t e bodies bodies has in rare earths and fluorine. i n r a r e e a r t h s and f l u o r i n e . Silica S i l i c a leaching leaching has has upgraded upgraded siderite siderite iron s o f t hematite—limonite hematite-limonite concentrate concentrate which which was w a s the t h e earliest earliest i r o n ores o r e s to t o aa soft Great Lakes iron ore. Great Lakes i r o n ore. The The common conmon theme theme of of these these deposits d e p o s i t s is is their t h e i r relationship r e l a t i o n s h i p to t o the t h e Mesozoic Mesozoic evolution of the North American Shield. evolution of t h e North American Shield. Ontario Ontario examples examples suggest suggest that that beneath beneath aa glacial g l a c i a l cover cover more more of of these these valuable valuable concentrations concentrations may may be be found and that t h a t the t h e importance importance of of this t h i s time time interval i n t e r v a l has has been been underunderfound and valued. valued. —67— �-a U Solid Pyrobitutxn Pyrobitumen iin Panel Mine, Mine, Elliot Solid n Veins, Veins, Panel E l l i o t Lake Lake Uranium Uranium District, Ontario Ratriet, Ontario JEFF STEVENSON, JOE MANCUSO, ,University,JOE HAHCUSO, JOE JOE FRIZADO, FRIZADO, Bowling Bowling Green Green JEFF State Bowling Green, Ohio 43403. State University, Bowling Green, Ohio 43403. TRUSKOSKI, Rio PPAUL AUL Â¥niUSKOSKI Rio Algom Algom Ltd. Ltd. Elliot E l l i o t Lake, Lake, Ontario Ontario P5A P5A 2K1 2K1 WILLIAM KNELLER, University of Toledo, Toledo, Ohio 43606 WILLIAM KHELLER, University of Toledo, Toledo, Ohio 43606 Globular blebs Globular blebs of o f solid s o l i d pyrobitumen pyrobitumen (thucholite (thuoholite of o f older older reports) are found in veins exposed in open stopes and r e p o r t s ) a r e found i n veins exposed i n open stopes and drifts d r i f t s in in The tthe h e Panel Panel Mine Mine in In the t h e Elliot E l l i o t Lake Lake Uranium Uranium District, District, Ontario. Ontario. The veins fill f i l l fractures fractures in i n the t h e 2.2 2.2 billion b i l l i o n year year old o l d Matinenda Matinenda veins Formation. The The blobs blebs a are mm) and Formation. r e small small (1—10 (1-10 ran) and free—form,varying free-formavarying shape from The surfaces from round round to t o disc, d i s c , twisted twisted or o r elongate. elongate. T he surfaces iin n shapa shiny and and pel-meated permeated w with Analyses show show the aare r e shiny i t h vesicles. vesicles. Analyses t h e blebs blebs be predominantly predominantly carbon with a a H/C H/C ratio r a t i o of of 0.51, 0.51, aa tto o be carbon with and aa 66 13C 13C value value of of —33°i6o(PDB). rreflectivity e f l e c t i v i t y (max (max Ro) Ro) of of 0.91%, 0.91%. and -33O/>o(PDB). j j Kaiman and and Horwood Kaimn Horuood (1976) (1976) concluded concluded that t h a t blebs blebs of of thucholite thucholite in the Milliken Mine were formed by the agglomeration and i n t h e Milliken Mine were formed by the agglomeration and polymeriztion of polymeriztion o f carbon carbon particles p a r t i c l e s from from the t h e exhaust exhaust of o f diesel diesel We propose that the pyrobitumen blebs in mining equipment. i n the the mining equipment. Me propose t h a t t h e pyrobltumen blebs Panel Mine are the result of the natural migration and maturation Panel Mine a r e t h e r e s u l t o f t h e 'natural migration and maturation of petroleum. The Precambrian petroleum migrated migrated into Precambrian petroleum i n t o the the of petroleum. The and with with ttime ffractures r a c t u r e s and i n e and and increased increased temperatures temperatures polymerization polymerization progressed and and tthe masses matured matured iinto blebs of of progressed h e ttarry a r r y masses n t o tthe h e blebs pyrobitumen. pyrobitumen. Blebs o of similar morphology morphology and and occurrence occurrence have have been been Blebs f similar reported from from fracture reported f r a c t u r e fillings f i l l i n g s in i n the the Cambrian Cambrian Bonneterre Bonneterre Formation from Magmont West West Mine Formation from tthe h e (tagmont Mine on on the t h e Viburnum Viburnum Trend, Trend, al. 1986) and in the Ordovician Missouri (Marikos,et Missouri (Marikos.et a l . 1986) and i n t h e Ordovician Trenton Trenton Formation in Both 1986). Both Formation i n Uyandot Wyandot County, County, Ohio Ohio (Haefner, (Haefner, ete tal., al., 1986). considered tto from locally l o c a l l y derived derived oil o i l that that aare r e considered o have have been been formed formed from was polymerized polymerized in was i n the t h e fractures. fractures. Based on on observations observations with with the Bued the petrographic petrogr8phie and and scanning scanning electron micrpscopes, microscopes, a paragenetic paragenetic sequence oof mineralization iin n electron f mineralization tthe h e ffractures r a c t u r e s and and the t h e occurrence occurrence of o f the t h e pyrobitumen pyrobituaen have have been been determined. Quartz Quartz was was the mineral to determined. t h e first first mineral t o crystallize c r y s t a l l i z e in i n the the followed by by a ffirst pyrite. The pyrite was ffractures r a c t u r e s followed i r s t generation pyrite. The p y r i t e was subsequently altered morphologically by partial dissolution. subsequently a l t e r a d lorphologioally by p a r t i a l dissolution. Petroleum migrated migrated iinto and wwas Petroleum n t o tthe h e ffractures n o t u r e s and u ppartially artially polymerized into polymePized i n t o blebs bleba which which were were encased e n c a ~ dby by fibres f i b r e s of o f sepiolite. sepiolite. generation ppyrite Near tthe h e end ooff sepiolite formation a second generation yrite was deposited. is in i n the t h e form form of of larger l a r g e r (5—15 (5-15 mm) was deposited. This ppyrite y r i t e is cubes. The ffact inclusions oof cubes. a c t tthat h a t tthis h i s ppyrite y r i t e contains Inclusions f and pyrobitunen pyrobitumen indicates ssepiolite e p l o l i t e and i n d i c a t e s that t h a t the t h e pyrobitumen formed formed h e same time time oorr just j u s t after a f t e r the t h e second second pprior r i o r tto o tthe h e ppyrite. y r i t e . AAtt tthe generation p pyrite formed, minor minor ppyrrhotite and galena galena y r r h o t i t e and generation y r i t e was formed, deposition began. mm) calcite c a l c i t e crystals c r y s t a l s cover cover and and deposition began. Large (5—20 (5-20 no) n tthe he overgrow the t h e blebs ooff pyrobitumen and aall l l other minerals iin fractures. fractures. —68— J J J J �The The source s o u r c e of o f the t h e organic o r g a n i c material m a t e r i a l which which produced produced the the petroleum is still in question. Willingham et petroleum is s t i l l i n q u e s t i o n . Willingham e t aal. l . (198k) (1984) ccited ited the t h e ooccurrence c c u r r e n c e of o f stratiform s t r a t i f o r m kerogens kerogens in i n the t h e Matinenda Matinenda Formation Formation Elliot Lake Region evidence for mats o of iin n tthe he E l l i o t Lake Region aass evidence f o r aancient n c i e n t mats f cyanobacteria. The other possible sources of organic material c y a n o b a c t e r i a . The o t h e r p o s s i b l e s o u r c e s o f o r g a n i c m a t e r i a l for petroleum formation f o r petroleum formation are a r e the t h e argillites a r g i l l i t e s and and siltstones s i l t s t o n e s of o f the the Mokim Formation. Mckim Format ion. REFERENCES REFERENCES Haefner, Haefner, R.F. R.F. Mancuso, Mancuso, J.J., J.J., Frizado, F r i z a d o , J.P., J.P., Shelton, S h e l t o n , K.L., K.L., and and Gregg, J.M., 1986, Crystallization temperatures and Gregg, J.M., 1986, C r y s t a l l i z a t i o n t e m p e r a t u r e s and stable stable carbon and oxygen isotopes carbon and oxygen i s o t o p e s of o f Mississippi M i s s i s s i p p i Valley—Type Valley-Type sulfides sulfides and associated carbonates, Trenton Limestone and a s s o c i a t e d c a r b o n a t e s , Trenton Limestone (Ordovician), (Ordovician), Wyandot County, Wyandot County, Ohio: Ohio: Geol. Geol. Soc. Soc. Amer. A m e r . Ann. Ann. Mtg. M t g . Abstracts Abstracts with Programs, p. 624(ab). with Programs, p. 624cab). Kaiman, S. 5. and Kaiman, and Horwood, Horwood, J.L., J.L., 1976 1976 An An unusual unusual "thucholite" " t h u c h o l i t e w from from Elliot Lake, Ontario: Ontario: Canadian Canadian Mineralogist, v. 1k, E l l i o t Lake, M i n e r a l o g i s t , v. 14, p. p. 422—428 422-428 Marikos, M.A., M.A., Laudon, Laudon, R.C. Marikos, R.C. and and Leventhal, Leventhal, J.S., J.S., 1986, 1986, Solid Solid insoluble i n s o l u b l e bitumen bitumen in i n the t h e Magmont Magmont West West Orebody, Orebody, southeast southeast Missouri: Leon. Missouri: Econ. Geology, Geology, v. v. 81, 81, No. No. 88 (in ( i n press). press). Willingham, T.O. Krinsley, Willingham, T.O. Nagy, Nagy, B. 0. and and Nagy, Nagy, L.A., L.A., K r i n s l e y , Dii. D.H. and and Mossman, D.J., 1985, Uranium—bearing stratiform organic Mossman, D.J., 1985, Uranium-bearing s t r a t i f o r m o r g a n i c matter matter in paleoplacers of the i n p a l e o p l a c e r s of t h e lower lower Huronian Huronian Supergroup, Supergroup, Elliot Elliot Lake—Blind River Lake-Blind River region, r e g i o n , Canada: Canada: Can. Can. Jour. Jour. Earth Earth Sci. S c i . 22, 22, p. p. 1930—194k. 1930-1944. —69— �j j The "Eager "Hager Suite" Suite" and Concerning the the Nature The and Problems Problems Concerning Nature and and Location Location of the the Northern Northern Boundary Boundary of of the the Wolf Wolf River River Batholith Batholith of J D.C. D.C. STEWART STEWART and and J.M. J.M. MANCUSO MANCUSO (Department (Department of of Geology, Geology, Bowling Bowling Green Green State University, University, Bowling Bowling Green, Green, Ohio Ohio 43403) 43403) State It contention of of this abstract that It is is the the contention this abstract that the the "Hager "Hager Granite Granite // Porphyry", which has previously been considered to be the Porphyry", which has previously been considered to be the northernnorthernmost unit in Wolf River most unit in the the Wolf River Batholith Batholith of of northeastern northeastern Wisconsin Wisconsin (Anderson and and Cullers, Cullers, 1978; 1978; Greenberg Greenberg and and Brown, Brown, 1984). 1984), is is neither neither (Anderson a member of the batholith, nor a granite. The northern—most member a member of the batholith, nor a granite. The northern-most member of the Wolf River Batholith is the "Belongia Granite" which has of the Wolf River Batholith is the "Belongla Granite" which has inintruded into into the the Eager-a Hager——a volcanic volcanic suite of felsic truded suite of felsic to to intermediate intermediate rocks——and into rocks-and into older older greenstones greenstones and and gneisses. gneisses. The extent extent of of the Hager Suite The the Eager Suite is is larger larger than than currently currently recogrecognized because exposures of this suite can be found nized because exposures of this suite can be found along along the the entire entire southern boundary boundary of of the Mccaslin Quartzite Quartzite in southern the McCaslin in regions regions currently currently mapped The disdismapped as as Belongia Belongia Granite Granite (Greenberg (Greenberg and and Brown, Brown, 1984). 1984). The tinction between between rocks rocks of of the Hager Suite tinction the Eager Suite and and the the Belongia Belongia Granite Granite can be made on the the basis of petrographic and/or and/or chemical chemical criteria. criteria. The felsic felsic member member of of the Hager Suite metarhyolite with with abunThe the Eager Suite is is aa metarhyolite abundant (20%) (20%) relic quartz phenocrysts that that commonly commonly display display resorpresorption embayments. The intermediate embayments. The intermediate members members of of the the suite suite show show an. an. tion increase in in mafic minerals and plagioclase and and rarely rarely contain contain the the quartz phenocrysts. Hager resorbed quartz phenocrysts. The eastern boundary of the the Eager appears to to have been intruded intruded by the the High Falls falls Granite; Granite; the the High High Falls is is currently thought thought to to be older older than than the the Hager Eager (Greenberg (Greenberg Au increase in metamorphic grade can be seen seen in in and Brown, 1984). 1984). An the pelitic components of the McCaslin Quartzite from east to west the pelitic components of the McCaslin Quartzite from east to west as the the High High Falls as Falls Granite Granite is is approached. approached. A similar gradient may be evident in the more mafic units of the the Hager Eager Suite. The boundaries, boundaries, extent The extent of of differentiation, differentiation, degree degree of of metamorphism, metamorphism, and timing of formation of the Hager Suite is being reevaluated. formation Eager Suite is Preliminary results results of of field works show Preliminary field and and chemical chemical works show that that the the Hager Eager Suite can be distinguished as a separte volcanic sequence from a separte volcanic sequence from the the other rocks knowledge of the character of this this rocks of the the region. region. A knowledge suite will be essential in in determining determining the the nature of the the northern northern boundary of the Wolf River Batholith. REFERENCES REFERENCES Anderson, J J.L. Cullers, R.L., R.L., 1978, 1978, Geochemistry Geochemistry and and evolution evolution Anderson, .L. and Cullers, of the Wolf River Batholith, a a Late Late Precambrian Precambrian rapakivi rapakivi massif massif Wisconsin, U U.S.A.: Precambrian Research, v.7, v.7, p.287—324. in north Wisconsin, .S.A.: Precambrian p.287-324. J.K. and Brown, B.A., B.A., 1984, 1984, Bedrock Bedrock geology geology of of Wisconsin: Greenberg, J.K. Northeast Sheet, Sheet, Wisc. Wisc. Geol. Nat. Hist. Surv., Surv., Regional Regional Map Map Series, Series Map No. 84—2. 84-2. —70— J �Geology Atikokan Area, northwestern Ontario: Geology of of the the Atikokan Area, northwestern Ontario: an an overview overview D. D. STONE STONE (Atomic (Atomic Energy Energy of of 601 Booth St., Ottawa, 601 Booth St., Ottawa, K1A KIA Canada Canada Limited/Geological Limited/Geological Survey Survey of of Canada, Canada, OES) OE8) Beginning Beginning late late in in the the nineteenth nineteenth century, century, geologists geologists have have more more or or less continuously studied Archean rocks in the Atikokan area, less continuously studied Archean rocks in the Atikokan area, with with The particular particular emphasis emphasis on on the the metavolcanic metavolcanic belt belt at at Steep Steep Rock Rock Lake. Lake. The first recorded survey of the area identified an unconformity overlain first recorded survey of the area identified an unconformity overlain by by conglomerate, conglomerate, dolomite dolomite and and tuff tuff formations formations along along the the northeastern northeastern These formations, margins These formations, which which comprise comprise margins of of the the Steep Steep Rock Rock belt belt (1). (I). the Rock Group, were studied extensively during the Steep Steep Rock Group, were studied extensively during open—pit open-pit mining mining of Early of the the iron iron ore ore zone zone at at the the top top of of the the dolomite dolomite unit unit (2). (2). Early workers workers thought thought that that the the Steep Steep Rock Rock Group Group was was one one of of the the youngest youngest supracrustal supracrustal sequences sequences in in the the area area (e.g. (e.g. 3), 3), but but recent recent lead lead isotope isotope studies yield an an age age of Harmion Lake tonalite Ga age age for for the the Madon Lake tonalite studies yield of 2.929 2.929 Ga Accordingly, the may be basement basement (4). (4). Accordingly, the overlying overlying Steep Steep Rock Rock Group Group may be older older than than most most metavolcanic inetavolcanic rocks rocks in in the the Wabigoon Wabigoon Subprovince Subprovince since since these Ga (5). (5). these tend tend to to be be in in the the range range of of 2.71—2.76 2.71-2.76 Ga I Three Three distinct distinct assemblages assemblages of of metavolcanic metavolcanic rocks rocks are are identified identified in in the the Steep Steep Rock Rock belt belt on on the the basis basis of of Atomic Atomic Energy Energy of of Canada Canada Limited's Limited's (AECL) mapping survey survey and (AECL) mapping and studies studies of of major major and and trace trace element element These consist of the lower lapilli tuff geochemistry. These consist of the lower lapilli tuff (ash (ash rock) rock) geochemistry. overlain by voluminous mafic pillow lavas, followed by intermediate overlain by voluminous mafic pillow lavas, followed by intermediate to to Erosion of felsic felsic flows, flows, tuffs tuffs and and breccias. breccias. Erosion of these these metavolcanic metavolcanic extrusives exposed tonalite extrusives and and exposed tonalite appears appears to to be be the the source source for for clastic elastic sediments in both the Quetico Subprovince and in narrow units sediments in both the Quetico Subprovince and in narrow units Several throughout the 1). Several phases phases of of felsic felsic the greenstone greenstone belts belts (Figure (Figure 1). plutonic and gneissic rocks occur outside of the supracrustal plutonic and gneissic rocks occur outside of the supracrustal belts. belts. Tonalitic gneisses containing Tonalltic gneisses containing thin thin amphibolite amphibolite units units are are extensive extensive in in the map area and can be correlated with the Marmion Lake tonalite the map area and can correlated with the Marmion Lake tonalite During or basement and early early supracrustal baseinent complex complex and supracrustal sequences. sequences. During immediately after the late stages of volcanism, the gneisses icoediately the stages the gneisses were Emplacement granitic intruded of granitic intruded by by several several "young" "young" tonalite tonalite plutons. plutons. Emplacement of magma, magma, such such as as the the Eye—Dashwa Eye-Dashwa pluton pluton at at 2.672 2.672 Ga, Ga, marked marked the the latest latest stage stage of of crustal crustal genesis genesis in in this this area. area. (1) (1) (2) (2) (3) (3) (4) (4) (5) (5) Smyth, H.L. 1891. 1891. American American Journal Journal of of Science, Science, 42, 42, 317—331. 317-331. Sayth, H.L. Jolliffe, Jolliffe, A.W. A.W. 1955. 1955. Economic Geology, 50, 50, 373—398. 373-398. GSC Memoir Memoir 28, Lawson, A.C. Lamon, A.C. 1912. 1912. GSC 28, 23. 23. HP 126, Davis, D.W. D.W. and Jackson, Jackson, M.E. M.E. 1985. 1985. OGS MP 126, 135—137. 135-137. Paper 28, 28, 89—123. 89-123. Blackburn, C.E. C.E. et.al. et.al. 1985. 1985. GAC Special Paper —71— �91° 45' 49000 49° 00 -4 j j j J -J fl -J —4 480 45' — 48° 4 5' ONTARIO ISTUDY AREA .1 91° 45' sr-45' Figure Figure 1: 1: Geology oof the Atikokan Atikokan area, area,northwestern northwesternOntario. tario. f the —72— �Gravity and Gravity and Magnetic Magnetic Evidence Evidence for f o rRhomboid Rhomboid Sedimentary Basins in Sedimentary Basins i n the t h eWisconsin WisconsinMagmatic Magmatic Terrane Terrane THOMAS SUSZEKand andPAUL PAULJ.J. MEYER MEYER(Department (Department o off Geology, J. J. SUSZEK Geology,UW—Oshkosh, UW-Oshkosh, THOMAS (lshkosh, M I 54901) 54901) Oshkosh, WI and PPrice Gravity and and magnetic magnetic data data from fromRusk, Rusk, Chippewa, Chippewa, Sawyer Sawyer and rice counties in counties i n northern northern Wisconsin Wisconsin indicate i n d i c a t ethe t h epresence presence of o fEarly EarlyProtero— Protero(Fig. 1) 1) zoic rhomboid rhomboid shaped shaped sedimentary sedimentary basins. (Fig. Gravity readings Gravity readings taken taken across across tthree h r e e basins, basins, the t h e boundaries boundaries of o f which which have been beendefined definedby bythe the aeromagnetic aeromagneticpattern, pattern, have have provided provideddata data ffor have or 2) twodimensional dimensional gravity g r a v i t ymodels. models. (Fig. tthe h e construction construction oftwo, o f -two,two (Fig. 2) The Ladysmith Ladysinith ggravity one basin in The r a v i t ymodel model,, which which spans spans one i nRusk Rusk and and Chippewa counties, was developed from data taken along a f t e e n mile mi1 e Chippewa counties, was developed from data taken along a f ififteen traverse w with taken aatt one thousandf ofoot traverse i t h readings readings taken one thousand o t iintervals. n t e r v a l s . This model model suggests an asymmetrical asymmetricalbasin basindeepening deepeningt otot hthe south wwith thickness suggests an e south i t h aa thickness of of approximately feet. o f sediments sediments of approximately tthirteen h i r t e e n thousand thousand feet. The Park Park FFalls The a l l s gravity g r a v i t ymodel, model, which which spans spans two two basins basins ini nSawyer Sawyer and and Price fromdata datagathered gatheredalong alongaaf fifty—four P r i c e counties, was was developed developed from i f t y - f o u r mile mile The model model of traverse wwith takenaat onehhalf mile traverse i t h readings readings taken t one alf m i l e iintervals. n t e r v a l s . The these sedimentthickness thickness ooff twelve these basins basins suggests suggests aa sediment twelve thousand thousand tto o sixteen sixteen Bothpprofiles modelsi nindicate thousand feet. feet. Both thousand r o f i l e s and and models d i c a t e t that h a t tthe h e ggravity r a v i t y highs highs correspondt to highs and and ggravity correspond o tthe h e magnetic magnetic highs r a v i t y lows lows to t o magnetic magnetic lows. lows. Drill D r i l lcore corefrom fromthese theseareas areas show show tthat h a t greenschist greenschist to t o amphibolite amphibolite grade metavolcanicand andg rgranitoid rocksuunderlie grade metavolcanic a n i t o i d rocks n d e r l i e t the h e ggravity r a v i t y highs, highs, and an'd graphitic t h e gravity g r a v i t y lows. 1ows. g r a p h i t i c argillites a r g i l l i t eand s andgraywackes graywackes underlie under1 ie the U 4 I 1 L1 LI 5 as-'I I -I I Os a — —_ J.3340k •.. • fled — a —73— I I I, I • — I fl C S N �—4 anti o.aticjn of Gravity Traverses the Sediriientary Basins(Xs) N(}RJIIWEST[RN WI SCONSIN Showipiij OF A[R(IiA(iNIJIC MAP OF A PORTION IL -, - •'.a a L_ L J_fl•.'I L L t_ I �Contemporaneous Archeanmafic niaficand andggranitoid Contemporaneous l alate t e Archean r a n i t o i d magmatism magmatism i in n the the Lac des lies area, Wabigoon Subprovince, Ontario Lac des l i e s area, Wabigoon Subprovince, Ontario Ri-I. Grenville St., R. H. Sutcliffe Sutcl i f f e(Ontario (OntarioGeological GeologicalSurvey, Survey, 917—77 917-77 Grenvil l e St., Toronto, Ontario M7A 1W4) - ""Toronto, Ontario M7A 1W4) The Lac Lac des des Ilies km north n o r t hofo fThunder Thunder Bay Bay The l e s area, area, located locatedapproximately approximately100 100km in the Wabigoon Subprovince, contains a suite of mafic to ultramafic i n t h e Wabigoon Subprovince, contains a s u i t e o f mafic t o u l t r a n a f i c Archean iintrusions n t r u s i o n s which which show show evidence evidence of o f being beingcontemporaneous contemporaneous wwith i t h llate a t e Archean tonal ite and granodiorite. The mafic to ultramafic and granitoid t o n a l i t e and granodiorite. The mafic t o ultramafic and g r a n i t o i d i intruntrusions are are emplaced emplaced gneissicb biotite formppart sions i n into t o o lolder d e r gneissic i o t i t e ttonal o n a l iite t e and and form a r t ooff tthe h e Wabigoon Wabigoon DDiapiric i a p i r i c Axis. Axis. The The t tholejitic h o l e i i t i c mafic mafic to t o ultramafic u l t r a m a f i c intrusions i n t r u s i o n s in i nthe t h earea area have have ssimilar imilar lithologic, tectonic, and metailogenic characteristics and define a a l i t h o l o g i c , t e c t o n i c , and metal logenic c h a r a c t e r i s t i c s and define circular c i r c u l a r structure s t r u c t u r eapproximately approximately 30 30 km km in i n diameter. diameter. The Lac Lacdes des Ilies The les Complex, thesei nintrusions, hostt to Pt Complex, t h the e l a largest r g e s t o fofthese t r u s i o n s , i sis host o ssignificant i g n i f i c a n t Pd, Pd, Pt mineralization as aa rresult multiple m i n e r a l i z a t i o n and and formed formed as e s u l t of o fthe t h eemplacement emplacement oof f m ultiple batches ooff magma minori nin—situ Themore moref rfractionated batches magma w iwith t h minor - s i t u f rfractionation. a c t i o n a t i o n . The actionated gabbroic rocks gabbroic rocks were were emplaced emplaced first f i r s and t andconsist c o n s iof s t plag—cpx—opx o f plag-cpx-opx and andplay— plagcpx cumulates. Theyounger youngeru lultramafic ol—cpx, cpx, cpx, cpx cumulates. The t r a n a f i c ssuite u i t e cconsists o n s i s t s ooff ol 01, , 01-cpx, cpx—opx, and cpx—opx—plag cumulates. The Tib Gabbro, the second largest cpx-opx, and cpx-opx-plag cumulates. The Tib Gabbro, t h e second l a r g e s t mafic consists ooff mafic intrusion, i n t r u s i o n , represents representsaamore more fractionated f r a c t i o n a t e dsequence sequence and and consists opx—cpx—piag cumulates grading zones cumulusa papatite, opx-cpx-plag cumulates grading t o tozones w iwith t h cumulus a t i t e , Fe—olivine Fe-olivine and magnetite. magnetite. AAll and l l of o fthe t h eintrusions i n t r u s i o nhave s havemarginal marginalzones zones characterized characterized by tthe gabbrot to hornblendite. by h e presence presence ooff hornblende hornblende gabbro o hornblendite. Late ggranitoid Late r a n i t o i d rocks rocks ranging ranging in i ncomposition composition from from hornblende hornblende t tonal o n a l i tite e tto o biotite granodiorite occupy the center of the circular structure defined b i o t i t e g r a n o d i o r i t e occupy t h e center o f t h e c i r c u l a r s t r u c t u r e defined b the Thehornblende hornblendet otonalite has ttextures by t h e mafic mafic intrusions. intrusions. The n a l i t e has e x t u r e s tthat hat indicate mixing between leucocratic tonalite and mafic magmas. These i n d i c a t e mixing between l e u c o c r a t i c tonal it e and maf i c magmas. These textures include include nnet veinedmafic maficdikes, dikes,mafic mafic" p"pillows" textures e t veined i l l o w s " i in n ttonalite, onalite, The rnixmixand hhybrid zonescharacterized characterized by by coarse, coarse, sskeletal and y b r i d zones k e l e t a l hornblende. hornblende. The ing textures occur within the tonalite pluton and at the contacts of i n g t e x t u r e s occur w i t h i n t h e t o n a l i t e p l u t o n and a t t h e contacts o f the the tonalite Mixing and and hhybridization t o n a l i t e pluton p l u t o n with w i t h the t h e mafic mafic intrusions. intrusions. Mixing ybridization appears tto widespread process process as as iindicated appears o have have been been aa widespread n d i c a t e d by by the t h edevelopment development of coarse throughoutt hthe pluton. of coarse sskeletal k e l e t a l to t o blocky blocky hornbiende hornblende throughout e t otonalite n a l i t e pluton. Breccia zones developedi in Breccia zones developed n tthe h e tonal t o n a lite i t emay may have have resulted r e s u l t e dfrom fromdegassing degassing chamberw with mafic magma magmaunderlying underlyingt the ooff aa zoned zoned magma magma chamber i t h mafic h e ggranitoid r a n i t o i dmagma. magma. Ther relationships mafic iintrusions i e s area area suggest suggest tthat h a t mafic ntrusions The e l a t i o n s h i p s iin n the t h e Lac Lac des des lIles played aa ssignificant The g r a n i t o magma i d magma genesis. genesis. The played i g n i f i c a n t role r o l eini late n l a Archean t e Archeangranitoid emplacement maficmagma magma generation ooff emplacement o f of mafic i n t ointo o l dolder e r c r ucrust s t r eresulted s u l t e d i nint the h e generation crustal mafic—felsic c r u s t a lmelts meltsand andthe t hdevelopment e developmentof ozoned f zoned m a f i c - f e l s imagma c magmachamixers. chambers. The compositions reflect between The rresultant e s u l t a n tmagma magma compositions r e f l e c mixing t mixing betweenthese theseend-members. end-members. —75— �Lead Many Ore Lead Isotope Isotope Evidence Evidence for f o r an an Old Old Crustal C r u s t a l Source Source for f o r Manv Ore Leads Leads in in the t h e Wawa Wawa Region Region R.I. R.I. ThORPE THORPE (Geological (Geological Survey Survey of of Canada, Canada, 601 601 Booth Booth St., St., Ottawa, Ottawa, Ontario Ontario [CiA 0E8) K I A OE8) 918—77 Grenville R.P. R.P. SAGE SAGE (Ontario (Ontario Geological Geological Survey, Survey, 918-77 Granville St., S t . , Toronto, Toronto, Ontario Ontario MSS M5S 1B3) 1B3) 601 Booth J.M. J.M. FRANKLIN FRANKLIN (Geological (Geological Survey Survey of of Canada, Canada, 601 Booth St., S t . , Ottawa, Ottawa, Ontario Ontario[CiA KIA OE8) OE8) Lead Lead isotope i s o t o p e analyses analyses for f o r galena galena from from deposits d e p o s i t s and and occurrences occurrences in in the because of of tthe t h e Wawa Wawa region region (Table (Table 1) 1 ) aare r e significant s i g n i f i c a n t because h e old old model model lead lead values for ages ages for f o r aa few few deposits d e p o s i t s and and the t h e high high 207Pb/201'Pb "'~b/"''~b values f o r many many of of the the in composition In these respects they are comparable specimens. specimens. I n these r e s p e c t s they a r e comparable i n composition ttoo leads from selected leads from s e l e c t e d localities l o c a l i t i e s in i n western western Superior Superior Province Province (Wabigoon (Wabigoon Subprovince) and are dissimilar to leads from Abitibi Subprovince. Subprovince) and a r e d i s s i m i l a r t o leads from A b i t i b i Subprovince. Application of Archean Application of Archean lead lead evolution evolution models models derived derived by by Thorpe Thorpe (in (in preparation) yields model lead ages greater than 2830 Ma for the preparation) y i e l d s model lead ages g r e a t e r than 2830 Ma f o r t h e 8CR BCH and and Ma .J J veins veins by by the t h e Abitibi A b i t i b i model, model, and and greater g r e a t e r than than about about 2870 2870 M a by by the the The latter model may apply because a comparable Western Superior model. Western Superior model. The l a t t e r model nay apply because a comparable Ma has zircon has been been reported reported for f o r tthe h e biotite biotite z i r c o n U—Pb U-Pb age age of of about about 2888 2888 Ma granite phase of the Hawk Lake oomplex (Turek et al., 198k), an external g r a n i t e phase of t h e Hawk Lake complex (Turek e t g . , 1984), an external pluton pluton that t h a t has h a s intruded intruded the t h e supracrustal s u p r a c r u s t a l rocks rocks of of Subcycle Subcycle 1 hosting hosting are thus old model ages a The leads with these mineralized zones. these mineralized zones. The leads with old model ages r e thus J — 1 restricted rocks aatt the r e s t r i c t e d tto o metavolcanic metavolcanic rocks t h e base base Other recognized recognized as a s the t h e oldest o l d e s t in i n the t h e region. region. Other of of the t h e section s e c t i o n that t h a t are are leads from localities leads from l o c a l i t i e s in in Sachigo property, property, Sachigo two and Subprovince, Ma, and iinn two Subprovince, also a l s o yield y i e l d model model ages ages greater g r e a t e r than than 2800 2800 Ma, cases c a s e s as a s great g r e a t as a s about about 3000 3000 Ma. Ma. Wabigoon Wabigoon Subprovince, Subprovince, and and from from the the Musselwhite Musselwhite J The The Kozak Kozak mineralization, mineralization, probably probably synchonous synchonous with with volcanism, volcanism, yields yields We and 2724 Superior) and model (W. Superior) 2724 Ma Ma ((Abitibi). Abitibi). W e model lead lead ages ages of of 2770 2770 Ma Ma (W. consider consider that that the t h e Abitibi A b i t i b i model model most most likely l i k e l y applies, a p p l i e s , but but this t h i s can can only only of model) of (W. Superior Superior model) dating. Model ages by zircon zircon dating. Model ages (W. 2657 f o r two two of of the t h e MacLeod MacLeod East East galenas galenas and and of of 2670 2670 Ma Ma Ma and and 2658 2658 Ma Ma for 2657 Ma for Leclair Township galena galena aare within aanalytical of ages for L e c l a i r Township r e within n a l y t i c a l uuncertainties n c e r t a i n t i e s of of a possibly iindicative a for plutons in area, f o r some some plutons i n the t h e area, possibly n d i c a t i v e of ggenetic enetic located The relationship. relationship. The Northern Northern Granite Granite (granitic ( g r a n i t i c gneiss) g n e i s s ) that that is is located along along the t h e northern northern boundary boundary of of the t h e greenstone greenstone belt b e l t has has aa zircon z i r c o n U—Pb U-Pb age age of of 2662 2662 ti 22 Ma, Ma, and and the t h e Troupe Troupe Lake Lake trondhjemite trondhjemlte is is apparently apparently of of the the same same age age (Turek (Turek et & al., &., 198k). 1984). be be confirmed confirmed Many Wawa region region plot p l o t well well above above tthe h e ffields i e l d s ffor or Many leads l e a d s from from tthe h e Wawa in the 2695 Superior Province massive suphide deposits with ages Superior Province massive suphide d e p o s i t s with ages i n t h e 2695 ttoo They and for 2770 2770 Ma Ma range, range, and f o r most most Superior Superior Province Province gold gold deposits. deposits. They mostly f o r Zimbabwe Zimbabwe gold gold deposits d e p o s i t s (Robertson, (Robertson, 1973; 1973; mostly lie l i e within within the t h e field f i e l d for Such 207Pb/201'Pb—enriched leads and unpublished data). l e a d s aare r e generally generally Such "'~b/"''~b-enriched and unpublished d a t a ) . high U/Pb U/Pb rratios interpreted evolved in had high that had atios i n t e r p r e t e d to t o have have evolved i n sources sources that time prior (p values) values) for f o r extended periods of of geological time p r i o r ttoo oore re have not formation, formation, sspecifically p e c i f i c a l l y iin n upper upper crustal c r u s t a l terranes t e r r a n e s tthat h a t have not been been These (e.g. Robertson, Robertson, 1973). subjected to t o high—grade high-grade metamorphism (e.g. 1973). These leads, leads, and some of those from from the t h e Wabigoon Wabigoon Subprovince, Subprovince, thus t h u s suggest suggest the the presence iin presence n these these regions of an ancient a n c i e n t lead l e a d source source of of "Minnesota "Minnesota River —76— j J �Valley—type". Wawa area Valley-type". IInn tthe h e Wawa a r e a these these leads leads aare r e from from within within or o r near near Subcycle 11 rocks. rocks. Subcycle The Th/U rratios The calculated c a l c u l a t e d Th/U a t i o s ffor o r the t h e lead lead sources sources of of the t h e Wawa Wawa region region galenas aare, with two two exceptions exceptions ((the BCH vein vein aatt aa value value of of 4.12 4.12 and and galenas r e , with t h e BCH the the epigenetic epigenetic vein vein in i n tthe h e Woman Woman River River iron i r o n formation), formation), iin n the t h e range range 4.00 The 4.00 to t o 4.07. 4.07. The uniformity uniformity in i n these these ratios r a t i o s suggests suggests that t h a t these these leads leads must must have have been been derived derived from from large l a r g e volumes volumes of of source source rocks, rocks, because because local local sources would be be expected expected to t o contribute c o n t r i b u t e leads leads with with much much more more variable variable sources would ratios. ratios. Galena Galena that, t h a t , with with calcite, c a l c i t e , pyrrhotite p y r r h o t i t e and and graphite, g r a p h i t e , occupies occupies aa late late fracture cutting ore in the Kremzar gold deposit, Goudreau area, has f r a c t u r e c u t t i n g o r e i n t h e Kremzar gold deposit, Goudreau a r e a , has a a very Assuming geologically it formed formed aatt aa geologically very radiogenic radiogenic composition. composition. Assuming it recent time, tthe calculated source source age age is r e c e n t time, h e calculated is 2680 2680 to t o 2735 2735 Ma M a if i f the t h e initial initial Pb composition of the source was in the range of the Hanson and Renabie Pb composition of t h e source was i n t h e range of t h e Ranson and Renabie compositions. compositions. Robertson, D.K., 1K., 1973, of the Earth 1973, AA model model discussing discussing the t h e early e a r l y history h i s t o r y of t h e Earth Robertson, the some Archean based on study of lead isotopes from veins in based on t h e study of lead i s o t o p e s from v e i n s i n some Archean cratons of Africa; Geochimica Acta, Cosmochimica Acta, Vol. 37, cratons of Africa; Geochimica eett Cosmochirnica Vol. 37, p. 2099—2124. p. 2099-2124. Turek, A., Smith, Turek, A., Smith, P.E. P.E. and and Van Van Schmus, Schmus, W.R., W.R., the the 1984, U-Pb U—Pb zircon ages and 1984, zircon ages and evolution of the evolution of of the t h eMichipicoten Michipicoten plutonio—volcanic plutonic-volcanic t eterrane r r a n e of the Superior Superior Province, Province, Ontario; Ontario; Vol. Vol. 21, 21, No. No. 4, 4, p. p. U57—464. 457-464. Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, Table 1. data for and occurrences occurrences Load isotope Isotope data for deposits d e p o s i t s and Table 1. Lead in the Hawa twa region In the region Property Property .1 Vein J Vein ECH BCH Vein Vein Lakemount Lakemount Lakemount Lakemount Lakemount Lakemount Kozak Kozak Edwards Edwards pros. pros. MacLeod East MacLeod East MacLeod MacLeod East East MacLeod MacLeod East East Soocana Soocana Renabie Renabie Michipicoten Michipicoten Leclair L e c l a i r Twp. Twp. Rengold Rengold Braminco Braminco pros. pros. Hanson Ranson Kremzar Kremzar Vein Vein in in Woman Woman H. R. iron formation i r o n formation Model Ages Model Ages W. Superior W. Superior Abitibi Abitibi Model Model Model Model 207Pb/ 13.584 13.617 13.666 13.653 13.681 13.208 13.957 13.953 13.979 13.972 14.241 13.343 13.546 13.565 13.472 13.48 14.921 14.947 14.940 14.939 14.949 14.402 15.077 15.006 15.033 15.014 15.194 14.484 14.657 14.642 14.532 13.595 14.625 17.419 15.123 28.867 14.814 114.52 —77— 33.391 33.477 33.462 33.455 33.494 33.083 33.699 33.723 33.789 33.774 33.991 33.216 33.394 33.272 33.336 33.35 33.448 49.105 34.422 2838 2879 Ma Ma 2879 2838 2832 2873 Ma 2873 M a 2832 2788 2829 Ma 2829 Ma 2788 2798 2838 Ma 2838 Ma 2798 2824 Ma 2783 2824 Ma 2783 2724 2770 2770 Ma M a 2724 2670 2709 2709 Ma Ma 2670 2617 2657 2657 Ma M a 2617 2618 2658 2658 Ma Ma 2618 2649 Ma 2609 2649 Ma 2609 2548 2587 Ma 2587 Ma 2548 2678 2723 2723 Ma Ma 2678 2699 2699 Na Ma 2655 2655 2670 2627 2627 2670 Ma Ma 2654 2609 2654 Ma Ma 2637 2637 Ma Ma 2591 2591 2631 2587 2631 Ma M a 2587 anomalous anomalous 2066 2107 Ma Ma M a Ma M a Ma M a Ma Ma Ma Ma Na Ma Ma Ma Ma Ma Ma Ma Ma M a Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma Ma �Reconnaissance Geology of the Reconnaissance the Granitic Granitic and and Gneissic Gneissic Terranes Terranes in the Wawa District i n t h e m DELIO TORTOSA, (Ministry DKLIO (Ministry of Northern Northern Development Development and and Mines, Mines, P.O. Box P.0. Box 530, 530, Wawa, Wawa, Ontario, Ontario,P05 POS11(0) 1KO) geological the basis On basis of reconnaissance On the reconnaissance and and detailed geological mapping the Wawa District District over over the the past two two capping completed in in the together regional lake lake sediment/water sediment/water data, years, years, together with regional data. aeromagnetic data, aeromagnetic data, and studies studies by the the Geological Geological Survey Survey of of granitic Canada, Canada, aa preliminary gelogical gelogical evaluation evaluation of of the the granitic and gneissic terranes terranes in in the the Wawa District District is is in in progress. progress. into the Wawa area The The granitoid rocks rocks in the area can can be subdivided subdivided into three three main classes classes from f n r oldest oldest to to youngest: a) a) tonalite tonalite to to from gneiss "domes" or oval oval structures structures ranging granodiorite gneiss granodiorite "domes" or ranging from massive to well-layered well—layered gneiss gneiss containing volcanicmassive to containing metavolcanic— enclaves metamorphosed to ainphibolite metasedimentary me-basedimentary enclaves metamorphosed to amphibolite grade; grade; medium—to coarse—grained granodioriteto to quartz quartz monzonite nmdium-to coarse-grained granodiorite ronzonite size; ranging from large c) ranging large plutons to to batholiths batholiths in in size; c) late late quartz quartz diorite diorite to 1.0 syenite syenite plutons. plutons. b) b) The granitoid complexes complexes of the the Wawa Wawa District District have have geological geological which are similar to those described which are similar to those described by Schwerdtner et (1979). Some Some of al. (1979). of these these include: include: Schwerdtner eta].. 1) Tonalite gneiss domes d o e s displaying displaying aa transition transition from from a coarse—grained gneissic core core to coarse-grained 1.0 a marginal zone zone composed composed of layered tonalite tonalite gneiss gneiss containing containing arcuate—shaped arcuate-shaped metavolcanic metavolcanic —metasedimentary -metasedimentary segments. segments. characteristics characteristics j to Crescent-shaped of hornblende 2) Crescent-shaped plutons plutons of hornblende diorite diorite to 2) occupying quasi-concordant quasi—concordant sites sites granodiorite occupying granodiorite between gneissic "'domes" gneissic d m s " and and adjacent supracrustal supracrustal belts. belts. quartz A large large batholith from 3 batholithranging ranginginincomposition cc~position from quartz 3) A portion the central monzonite monzonlte to to granodiorite granodioriteand and occupying occupying Â¥th central portion of the a thestudy studyarea arearepresenting representing a of the granitoid granitoid terrane terrane in inthe post-tectonic period post-tmctonic periodofofemplacement. eaiplacaiaent. 4) Evidence of high and low ductility contrast between 4) the metavolcanic—metasedimentary gneissic/layered the metavolcanic-Botasedimentary segments segments and gaeissic/layered tonalites. tonalites The arcuate—shaped metavolcanic—metasedimentary 5) 5) The arcuate-shaped met-laanic-wtasedimentary enclaves can outer perimeter of the the can be the outer perimeter of enclaves be traced traced around around the synformal— gneissic "domes' and traced adjacent to larger gneissic "domes" adjacent to larger synformalshaped shaped metavolcanic-metasedimentary ntavolcanic-ntasedimentary belts. belts. J . —78— �I I I I I geological history of the granitic and gneissic terranes The The geological history of the granitic and gneissic terranes appears tonalite appears to to involve involvm an an early earlymagmatic magmatic period period of of tonalite intrusion into metavolcanic—metasedimentary rocks under intrusion into lae-tavolcanic-motasedloantary rocks under conditions high ductility ductility contrast. contrast. This This was was followed followed by aa conditions of of high period of auto—deformation with low contrasts period of auto-deformation with low ductility contrasts and the in the the development development of of gneiss gneiss domes domes which w h i c h resulted resulted in the infolding and fragmentation of the metavolcanicinfolding and fragmentation of the aetavolcanicmetasedimentary intense, post-tectonic oe-baaedhentary belts. belts. A period period of of intense, post-tectonic felsic plutonic activity followed, forming the large plutons felsic plutonic activity followed, forming the large plutons and and "central" "central" batholith. batholith. The The arcuate arcuate and and amoeboid amoeboid shape shape of of the metavolcanic—metasedimentary such as the the lae-tavolcaaic-BetaaediBentary belts belts such as the ductility Dayohessarah greenstonebelt belt and Dayohea8arah groanstone and the theMichipicoten Michipicoten greenstone gr-tone belt deformation thebroad broadscale scale deformationwhich which resulted resulted from from belt reflect reflectthe the the early early and and late late periods periods of of felsic felsic plutonic/gneissic plutonic/gneissic diapiric diapiric activity. activity. References: References : Schwerdtner, Schwerdtner, W.M., W.M., Stone, Stone, D., D., Stott, G.M. G- M.Stott. . .-- Osadetz, Osadetz, K., K., Morgan, Morgan, J., J., and and - 1979: and 1979: Granitoid Grani-boid complexes complex& and the the Archean Archean tectonic tectonic record partof ofnorthwestern northwesternOntario. Ontario. record in in the thesouthern southern part —79— �J The and Rb—Sr ages iin The meaning meaning of o fU—Pb U-Pb and Rb-Sr ages n the t h eWawa Wawa area area A. University A. Turek Turek (Department (Department oof f Geology, Geology, U n i v e r s i t y of o f Windsor, Windsor, Windsor, Windsor, Ontario Ontario N9B N9B 3P4) 3P4) U—Pb zirconages agesf ofor U-Pb zircon r tthe h e Michipicoten Michipicotengreenstone greenstonebelt b e lappear t appearchrono— chronostratigraphically correct. The greenstone belt and surroundingggranitic s t r a t i g r a p h i c a l l y correct. The greenstone b e l t and surrounding ranitic terrane occurred at terrane evolved evolvedaround around 2888 2888 to t o2615 2615Ma Ma ago. ago. Volcanism Volcanism occurred a t 2743, 2743, 2717, datedf fall Ma. Plutonic P l u t o n i c rocks rocks dated a l l into i n t o55events; events; 3 are coeval coeval 2717, and and 2696 2696Ma. with independent w i t h the t h eabove above volcanic volcanic periods periodswhile w h i l e2 2are are independentata2668 t 2668and and2888 2888 Ma. The 2668 Ma plutonism is probably part of the Kenoran orogeny, Ma. The 2668 Ma plutonism I s probably p a r t o f t h e Kenoran orogeny, while while j j J the Maggranite maybebea ar arafter t h e 2888 2888 Ma r a n i t e may f t e r ooff older o l d e r basement basement o or r r related e l a t e d tto o older older U The Rb—Srages ages obtainedf ofor rocks iin The Rb-Sr obtained r rocks n the t h e area area have have large l a r g eage ageuncertain— uncertainties notnot make t i e sand andchronostratigraphically c h r o n o s t r a t i g r a p h i c a l l do y do makesense; sense; probably probablybecause because they they are An attempt attempt at a t unmixing unmixing are hybrid hybridages, ages, between between primary primaryand andmetamorphic. metamorphic. An these these ages ages mathematically mathematically suggests suggests 55 possible possibleevents eventsaround around 2750, 2750, 2615, 2615, J volcanism volcanism asasy eyet t n onot t i didentified e n t i f i e d i in n tthis h i s belt. belt. 2510, The f first i r s t age age is i s essentially e s s e n t i a l l yaaprimary primary age age ffor or 2510, 2410, 2410, and and2330 2330Ma. Ma. The the t h e specific s p e c i f i crocks rocksdated, dated,the t h subsequent e subsequent ages ages are a r e thought thought to t obe bethermal thermal events. events. < J j J J J J j J J —80— -J �Paleomagnetism Archeangranites granitesi in area:f further Paleornagnetism o fofArchean n tthe h e Wawa Wawa area: urther definition of the Apparent Polar Wander Path d e f i n i t i o n of t h e Apparent Polar Wander Path l.A. Yandall University Ontario, (Department of of Geophysics, Geophysics, U n i v e r s i t y of of Western Western Ontario, T.A. Vandal1(Department London, Ontario Ontario N6A N6A 5B7) 5B71 London. D.T.A. Symons (Department Geology,u University D.T.A. Symons ( ~ e p a r t m e n to fofGeology, n i v e r s i t y ooff Windsor, Windsor, Windsor, Windsor, Ontario M9B N98 3P4) Ontario 3P4) Paleomagnetic measurements have been been completed completed on on about Paleomagnetic measurements have about 500 500 specimens specimens from and and Gamitagama Archean ggranitic r a n i t i cplutons plutonsin ithe n t hMichipicoten e Michipicoten Gamitagamagreen— greenfrom Archean stone belts, The The plutons plutons had stone belts. had all a11been beendated datedbybythe t h U—Pb e U-Pb zircon z i r c o nmethod method and also. Extensive Extensive AF and thermal thermal step AF and step and iinn most most cases cases by by other o t h e r methods methods also. demagnetization analysis was used to isolate stable remanence directions, demagnetization analysis was used t o i s o l a t e s t a b l e remanence d i r e c t i o n s . The 100) defines defines the = 5°, 5*, Dm Dm == lo0) the The ffirst i r s tpaleopole paleopole(HSE) (HSE) at a t20°W, 20*W, 37°S 3 7 * ~(Dp (Dp = '-2694 Ma position of the APWP. The pole position was established -2694 Ma p o s i t i o n o f the AWP. The p o l e p o s i t i o n was established by by averaging averaging single s i n g l ecomponent component remanences remanences i isolated s o l a t e d within w i t h i nthe t h Southern e SouthernGran— Granitic Terrane, Hawk Lake Granitic Complex and the Eastern External Granite i t i c Terrane, Hawk Lake G r a n i t i c Complex and t h e Eastern External Granite rock units. units. This apparentlyrecords recordst hthe rock This remanence remanence apparently e a cacquisition q u i s i t i o n ooff the the magnetization magnetization dduring u r i n g t hthe e l last a s t intrusive i n t r u s i v e event event of o f these these adjacent adjacent plutons. plutons. The second paleopole (NM) is derived from the Northern External Granite The second paleopole (MM) i s derived f r o m t h e Northern External Granite and and tthe h e Baldhead Baldhead River River Quartz QuartzMonzonite Monzonite which which have have U—Pb U-Pb zzircon i r c o n ages ages of of 2662 Ma and 2668 Ma respectively. They yield a single component reman2662 Ma and 2668 Ma respectively. They y i e l d a s i n g l e componentreman— ence which defines defines aa paleopole paleopole ffor ence which o r the#2665 the-2665 Ma Ma position p o s i t i o nofo the f t h APWP e APWP at at 16°E, 2005 (Dp = 12°, Dtn = 18°). The third paleopole (GD) comes from the The t h i r d paleopole (GD) comes from t70, he 16*E, 20*S (Dp = 12*, Dm = 18'). NNW—trending diabasedikes. dikes. They give aa position NNW-trending diabase They give p o s i t i o n of o f57°E, 5 7 * ~ 41°N , 4 1 " ~(Dp (Dp == 7O, Om 14°) which which agrees with Dm ==14") agrees w i t h poles polesdetermined determinedfrom fromthe t hMatachewan e Matachewanand and Hearst This result r e s u l t shows shows t that h a t aa ttectonically ectonically Hearst dike d i k eswarms swarms elsewhere. elsewhere. This stable s t a b l e craton craton existed e x i s t e d since since the t h e time t i m e of o fintrusion i n t r u s i o nata2633 t 2633Ma Ma and and also also These improves tthe MaMMatachewan improves h e precision p r e c i s i o nofothe f t h2633 e 2633 a Matachewan pole p o l eon onthe t h eAPWP. APWP. These results, paleomagneticdata datafrom fromt hthe eastern sside r e s u l t s , when when compared compared t to o paleomagnetic e eastern i d e ooff the the Kapuskasing Zone, also imply a1 so imply r e l arelatively t i v e l y 1 i tlittle t l e ttectonic e c t o n i c rotarotaKapuskasing S t rStructural u c t u r a l Zone, tion Subprovinces. A b i t i b iSubprovinces. t i o n or o rtranslation t r a n s l a t i obetween n betweenthe t h Wawa e Wawa and and Abitibi —81— �j -7 Rapakivi ttextures e x t u r e s of o f central c e n t r a lMinnesota Minnesota Ivan Watkins, Paul Erickson Ivan Watkins, Garry Garry Anderson, Anderson, and and Paul Erickson (Department (Department ooff Earth Earth Science, St. Cloud State University, S t Cloud, . Cloud,MN MN56301) 56301) Science, S t . Cloud State University,St. Crystalline St. Cloud C r y s t a l l i n erock rocksamples samples were were collected c o l l e c t e d from fromthe t h emapped mapped St. Cloud red red granite. The K—spar megacrysts, about 0.5 to 3 cm across, have rims granite. The K-spar megacrysts, about 0.5 t o 3 cm across, have rims like describedr rapakivi texture. IInn aa hand hand sample sample tthere here l i k ethe t h ecommonly commonly described a p a k i v i texture. are euhedral megacrysts showing little fracturing and subhedral are euhedral megacrysts showing l i t t l e f r a c t u r i n g and subhedral or or ovoidal megacrysts extensivef fracturing, ovoidal megacrysts wwith i t h extensive r a c t u r i n g , but b u t both bothtypes types have have an an easily observable rim on about fifty percent of the megacrysts. e a s i l y observable r i m on about f i f t y percent o f t h e megacrysts. The rrim i m ooff the t h e fractured f r a c t u r e dmegacrysts megacrysts isi scomposed composed ooff K—spar K-spar ccrystals r y s t a l s not not The The i m , ini nsome some iin n optical o p t i c a l continuity c o n t i n u i t ywith w i t hthe therest r e s tofo the f t h emegacryst. megacryst. The rrim, cases, has has an anooutline cases, u t l i n e made made bybyb biotite i o t i t e that t h a t isi smostly mostlyoutside o u t s i d ethe t h eK—spar K-spar The rrim but is rrim i m but i s included included in i n small small parts. parts. The i m iiss frequently frequently made made up up of of manyccrystals with between many rystals w i t h groundmass groundmass between i n dindividual i v i d u a l c crystals. rystals. The rrim i m ooff the t h eeuhedral euhedral megacrysts megacrysts is i salso alsocomposed composed ooff K—spar K-spar ccrystals. rystals. The Its from tthe anhedralrims rimsare aret hthat I t s main main ddifferences i f f e r e n c e s from h e anhedral a t t the h e ooptical p t i c a l contincontinuity notnot as as much groundmass u i t yisi sbetter b e t t eand r and much groundmass occurs. occurs. J J J J There are are iinclusions i n both b o t hthe t h efractured f r a c t u r e dand andeuhedral euhedral megacrysts megacrysts ooff There n c l u s i o n s in The most most quartz, biotite, plagioclase, K—spar relics, and chlorite. quartz, b i o t i t e , plagioclase, K-spar r e l i c s , and c h l o r i t e . The interesting inclusion is chlorite, without any apparent fracture i n t e r e s t i n g i n c l u s i o n i s c h l o r i t e , without any apparent f r a c t u r e along along The groundmass groundmassabout aboutt hthe megacrystscontains contains quartz, quartz, which iitt could could grow. grow. The e megacrysts which biotite, plagioclase, K—spar, chlorite, and other small crystals not b i o t i t e , plagioclase, K-spar, c h l o r i t e , and other small c r y s t a l s n o t yyet et iidentified. dentified. AAtt this t h i s time time we we are are looking looking at a t rapakivi r a p a k i v i from from the t h e Wolf Wolf River River Batholith Batholith for comparison purposes. f o r comparison purposes. j J -4 j j j J -82- j J �AA review review of of the the LaSalle Pails massive L a S a l l e F a l l s massive suiphide s u l p h i d e prospect prospect DAVID DAVID WEREACH WERBACH (Dept. (Dept. of of Geology Geology Northern Northern Illinois Illinois University, DeKalb, 601155 IL "60115) U n i v e r s i t y . DeKalb, IL -- The The Lasalle L a S a l l e Falls F a l l s massive massive sulphide s u l p h i d e prospect p r o s p e c t is is located l o c a t e d at a t the t h e Lasalle L a S a l l e Pails F a l l s (Pine ( P i n e Rapids) Rapids) on on the t h e Pine Pine River, R i v e r , Florence Florence County, County, northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. The The prospect p r o a p e c t occurs occurs within w i t h i n aa graphitic gra h i t i c slate s l a t e in i n the t h e Quinnesec Quinnesec Formation Formation (Early (Early Pro-terozoic), P r o t e r o z o i c ? , nnear e a r the t h e contact c o n t a c t between between felsic tuffs to t o the t h e north, n o r t h , and and mafic mafic flows f l o w s to t o the t h e south. south. f e l s i c tuffs Topping Topping directions d i r e c t i o n s based based on on pillow p i l l o w structures s t r u c t u r e s are are equivocal e q u i v o c a l (Dutton, ( ~ u t t o n 1971). , 1971 ) . Petrographic P e t r o g r a p h i c and and geochemical geochemical analysis a n a l y s i s for f o r both both major major and trace element oxides, indicate that the Quinnesec and t r a c e element o x i d e s , i n d i c a t e t h a t t h e Quinnesec Formation i s comprised comprised of of tholeiitic tholeiitic Formation in i n the t h e study s t u d y area a r e a is basalts (some komatiitic) and calc—alkaline b a s a l t s (some k o m a t i i t i c ) and c a l c - a l k a l i n e andesites andesites and s i l l s and and volcanogenic volcanogenic and dacites, d a c i t e s , with w i t h minor minor gabbro gabbro sills sediments locally present. sediments l o c a l l y p r e s e n t . Just J u s t to t o the t h e south s o u t h of of the the prospect, p r o s p e c t , rocks r o c k s of of the t h e Dunbar Dunbar dome dome have have intruded i n t r u d e d the the Quinnesec QuinnesecFormation. Formation. All A l l units u n i t s in i n the t h e region r e g i o n have have been been metamorphosed metamorphosed to t o amphibolite a m p h i b o l i t e facies. f a d e s . AA penetrative p e n e t r a t i v e NW—SE NW-ST foliation f o l i a t i o n is i s present, p r e s e n t , along a l o n g with w i t h local l o c a l secondary secondary folds folds and and Shear s h e a r zones. zones. Secondary Secondary fold f o l d axes a x e s and and outcrop o u t c r o u data data indicate i n d i c a t e that that the t h e area a r e a has h a s been been isoclinally i s o c l i n a l l y folded, folded, possibly p o s s i b l y as as aa result r e s u l t of of movement movement along a l o n g the t h e Niagara Miagara Fault Piult Zone, which is less than two miles north. Zone, which i s l e s s than two m i l e s n o r t h . Drill D r i l l cores c o r e s from from near n e a r the t h e prospect p r o s p e c t as as well w e l l as as outcrop outcrop data approximately three miles to the northwest d a t a a u ~ r o x i m a t e l yt h r e e m i l e s t o t h e northwest indicate indicate that t h a t the t h e mafic maficand andfelsic f e l s i crocks r o c k sare a r often e o f t einter'oedcjed. n interbedded. Trace element data on units in an area Trace element d a t a on u n i t s i n an a r e a approximately ap?roximately three three miles that m i l e s to t o the t h e northwest northwest suggests s u g g e s t s the t h e possibility p o s s i b i l i t y that mineralization m i n e r a l i z a t i o n is i s greater g r e a t e r there t h e r e than t h a n at a t Lasalle LaSalle Falls. Falls. Thus the possibility exists that if there i s aa massive massive Thus t h e p o s s i b i l i t y e x i s t s t h a t i f t h e r e is sulphide s u l p h i d e deposit d e p o s i tin i n the t h e area, a r e a , it i t is i s more more likely l i k e l y to t o occur occur there. there. Dutton, C.E., 1971, 1971, Geology Geology of of the t h e Florence F l o r e n c e area, a r e a , Wisconsin Wisconsin Button, C.E., and and Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey Professional P r o f e s s i o n a l Paper Paper 633, 633, 54p. 54~. —83— �-d J F luiu idd I inndduucced e d sts tr ruuc ct tuur ree5s 1i nn Qu Q ueeiit ci coo met m e tas a see di d imen m e nt tss , Ft n o r t h e r n O n t a r i o northern Ontario H. R. R. WI WI LU LLI MIS AMS Ontario OntarioGeological GeologicalSurvey, Survey,Toronto, Toronto,M7A M7AP44. 1W4. H. Sediment dewatering dewatering and and fluidisation fluidisationphenomena, phenomena, including including pillars pillarsand andhydraulic hydraulicfracture fracture Sediment and vein structures, have been identified within low grad* metamorphosed sedimentary and vein structures, have been identified within low grade metamorphosed sedimentary strataofofthe theQuetieo h e t i d oSubprovince. Subprovince.The Thestructures structuresare arecontained containedwithin withinsize sizegraded gradedand and strata form a 60 Km thicK, s t r e p l ~ dioping, ungraded lithic and frldsptthic wackts that ungraded lithic and feldspathic wackes that form a 60 km thick, steeply dipping, probablythrust thrustimbricated, imbricated,northwards northwardsyounging ywngingsequence. sequence. These These strata strataoccur occur within withinano and probably . , southofofthe theSeardmore—Geraldton Beardmore-Geraldton Belt. Belt. south .. j — J + Earlydewatering dewateringstructures structurrsare arecommon commonwithin withinthe thesediments, sediments,such suchas flames,convolute convolute Early as flames, and pillars. The pillars are rrmarhble far their size and shape, occurring lamination, lamination, and pillars. The pillars are remarkable for their size and shape, occurring orbell—shaped bell-shaped sfructures of slightly slightly a sparabolic parabolicor as structures up up to to 22 m m across. across.Fluidisation Fluidisation of structup* and a contemporaneous doming over it,indicate indicateaa laminated strata within the laminated strata within the structure and a contemporaneous doming over it, prc-lithification age for the struetwrs. Concentration of phyllosilicates occurs both pre—lithification age for the structures. Concentration of phyllosilicates occurs both within the pillars a s cirrus-shaped wisps, and around the margins of m o s t pillars. within the pillars as cirrus—shaped wisps, and around the margins of most pillars. intermittent^structurally structurallycontrolled controlledfluid fluidflow flow throughrocks rocKsmay may also alsobe be responsible responsible Intermittent, through for the initiation of bedding concordant breccia zonrs, listric structwes, and quartz for the initiation of bedding concordant breccia zones, listric structures, and uartz or after the imposition of a weaK regional veins. Them structurts drvrloped during veins. These structures developed during or after the imposition of a weak regional dipping steeply. steeply. cleavage. Mean Mean bedding cleavage. bedding and andcleavage cleavageorientations orientations birth both trend trend easterly, easterly, dipping Quaptz-filled extension fractures along both planar fabrics represent an early tectonic Quartz—filled extension fractures along both planar fabrics represent an early tectonic by a subseauent fluid-tnhtncrd brittle failure. These veins have been deformed phase of phase of fluid—enhanced brittle failure. These veins have been deformed by a subsequent of dextral dextralductile duetileshearing shearingthat thatfocussed focussedon onweak, we&, pelitic peliticunits unitsininthe thewacke wacKe episode of episode sequence. Cutting t h i s deformation fabric are bedding-parallel breccia zones consisting sequence. Cutting this deformation fabric are bedding—parallel breccia zones consistirQ ofcentimetre, ~entimetm or~smaller, smaller,unoriented unorirnted fragments fragmrnts set f t in inaa pelitic peiiticororvein veinquart: quartzmatrtx. matrix. of or 20 c m thicK and extend for up to 20 m along bedding striKe, The breccias maybe up t o The breccias maybe up to 20 cm thick and extend for up to 20 m along bedding strue, sometimes trrminating a s quart? s subtle discontinuities. sometimes terminating as quartz veins veins or or aas subtle listric listric discontinuities. J The structures s'tmctuTMdescribed dtscribed indicate indicateaa protracted protracted history historyofofdewatering dewatering during during The t h i s enormous pile of sediment. Thev are are compaction and s u b w q w r t deformation of compaction and subsequent deformation of this enormous pile of sediment. They simxlar ~ * p u t c to u r f s found within recently drilled accre'tiorwy prisms. similar to structures found within recently drilled accretionary prisms. -J J j —84— �Evidence for Widespread Basement Decolleisent Structures and Related Crustal Asyetry Associated with the Western Limb of the Nidcontinent Rift Richard Wunderman and and Charles Charles T. T. Young Young (Dept. (Dept. of of Geology Geology and and Geol. Geol. Engrg., Michigan Technological Univ., Houghton, MI 49931) Engrg., Michigan Technological Univ., Houghton, MI 49931) long, 18 stations) stations) across the AA magnetotelluric magnetotelluric (NT) (MI) survey survey (180 (180 km km long, the exposed Midcontinent Rift Rift (MCR) (NCR) and and associated associated adjacent adjacent crust crust indicate indicate exposed Midcontinent that major south that a a major south to to southeasterly southeasterly dipping dipping conductive conductive unit unit is is present present on The conductive (WOK) margin margin in in Minnesota Minnesota [1]. [I]. The conductive on the the western western off—rift off-rift (WOR) unit beneath the WOR has been followed MT data data and and unit seen seen dipping dipping beneath the WOR has been followed in in the the MT in compatible controlled—source audiofrequency MT (CSANT) data in compatible controlled-source audiofrequency MT (Cdata [2, [ 2 , 3]. 31. The unit has been traced northern The conductive conductive unit has been traced to to the the surface surface along along the the northern edge of the McGrath Gneiss, at the southern edge of the Animikie edge of the McGrath Gneiss, at the southern edge of the Animikie basin. This basin. This suggests suggests that that the the conductive conductive unit unit correlates correlates to to Animikie Animikie basin the upper contact of this unit represents a major basin rocks, rocks, and and the upper contact of this unit represents a major decollement in which Archean Archean McGrath McGrath Gneiss Gneiss has has been been emplaced emplaced over over decollement in which Lower Proterozoic Animikie basin rocks. Near the western edge Lower Proterozoic Animikie basin rocks. Near the western edge of of the the NCR the deepening conductive unit appears to thin or die out. Thus MCR the deepening conductive unit appears to thin or die out. Thus near may either near the the western western edge edge of of the the NCR, MCR, the the inferred inferred decollemont decollemont may either attenuate, be offset by Keweenawan faults, or it may continue the attenuate, be offset by Keweenawan faults, or it may continue into into the NCR as a structure too thin or resistive to be resolved with this MCR as a structure too thin or resistive to be resolved with this method. met hod. Geologic evidence supports a decollement along the southern margin of the Aninikie basin basin consistent consistent with with the the MT MT and and CSAMT CSAMT data data and and the the the Animikie interpretation discussed above. interpretations in interpretation discussed above. Some structural interpretations the Thomson Formation Formation of of the the Animikie Animikie basin basin suggest suggest an an early early Penokian Penokian the Thomson south dipping dipping nappe fold or thrust occurs there [4, 5, 61, 6], just east just east of where the the surface surface trace trace is is observed observed in in the the CSANT CSAMT data. data. A decolle— decollement is metamorphic grade is also consistent with other observations: observations: a) metamorphic and deformation increase southwestern margin margin of the AniAni— and increase toward toward the southwestern mikie basin adjacent b) inclusions inclusions adjacent the the proposed proposed decollement decollement [71, [TI, and b) in Late— to located south and southin Lateto post—Penokian post-Penokian igneous igneous stocks stocks 171 [TI located east east of of the the surface surface trace trace of of the the decollement decollement contain contain inclusions inclusions of of rocks rocks which are petrologically similar similar to to rocks of the the Thomson Formation suggesting that these sediments are tion of of the the Animikie Animikie basin basin [71, [TI, suggesting are present present at at depth. depth. In In contrast to to the the WOR WOR where where the the decollement decollement is is the the chief chief complexity, complexity, the MT data across the MCR in (-1 in Wisconsin indiindithe eastern off—rift off-rift (EOR) cate the the crust is is lithologically and structurally complex to depths of tens tens of of kilometers. kilometers. The central central NCR MCR itself itself appears appears as as an an elongate elongate plateau or horst and MT results are consistent with a body consisting of multiple mafic mafic igneous intrusive sheet dikes overlain by a basaltic basaltic pile. Resolution of the deep roots of the NCR from the surrounding pile. the roots the MCR from the surrounding crust is is difficult with with available available data. data. Proprietary Iowa undisclosed), traverse Iowa MT data data 181 [81 (specific (specific location undisclosed), traverse the MCR NCR with one site site on on each each off—rift off-rift margin. margin. The MT data data east east and and west of of the the NCR MCR in in Iowa Iowa appear appear analogous analogous to to those those obtained obtained along along the the off—rift off-rift margins to to the the north north on on the the EOR EOR and and WOR WOR respectively. respectively. For For example, the one available site west of the rift in Iowa shows a —85— �j -j Further studies nearby nearby intrabasement intrabasement conductive conductive zone. zone. Further studies are are indicated indicated but the conductive zone could be caused by decollement in but the conductive zone could be caused by decollement in aa situation situation similar The Iowa Iowa MT MT site site east east of of the rift similar to to the the WOR WOR in in Minnesota. Minnesota. The the rift again reflects extreme crustal complexity. COCORP data in Kansas again reflects extreme crustal complexity. COCORP data in Kansas [9, 19, 10] (COK) (COK) show show a a prominent prominent continuous continuous east east dipping dipping feature feature in in the the 101 basement to to the the west west of of the the MCR MCR which which extends extends at at least least to to the the main main basement low rift axis. This structure has been interpreted as: 1) "... a rift axis. This structure has been interpreted as: 1) a low angle detachment similar to those seen in the Basin and Range..." or angle detachment similar to those seen in the Basin and Range or 2) "... a sill similar to the Duluth Cabbro in Lake Superior..." [9]. a sill similar to the Duluth Gabbro in Lake Superior. [91. 2) Again, east Again, east of of the the rift, rift, extreme extreme crustal crustal complexity complexity is is seen seen in in COK COK The LOR data [io] similar to SOR MT MT data data [lo] similar to the the EOR data discussed discussed above. above. The EOR corn— complexity is consistent with with Alpine Alpine nappes nappes or or the the roots roots of of island arcs island arcs plexity is consistent [10] in in both both the COK and [lo] the COK and the the MT MT data. data. ."... ..." .." "... decollement and and observed crustal asymmetry in MT and and COK data The decollement in the MT are here here interpreted a Penokian Penokian continental margin are interpreted to to suggest suggest that that a continental margin preceded the emplacement of of the the MCR MCR and and that that the the younger younger rift rift strucstrucpreceded the emplacement If essentially a ture is is essentially a tectonic tectonic reactivation reactivation of of this this structure. structure. If and crustal asymmetry are indeed present and and widespread widespread decollement and indeed present be quite compatible to recent models models of Phanerozoic rift this would be genesis [111. genesis [11 I. J J J References: References: 91—92. 11 Wunderman, Wunderman, R., R., 1986; 1986; 32nd 32nd Annual Annual Inst. Inst. Lake Lake Superior Superior Geol., Geol., 91-92. ElectroMagnetic Surveys Inc., 1985; Rep. 8417, v. 1, Berkeley) CA. 2 ElectroMagnetic Surveys Inc., 1985; Rep. 8417, v. 1, Berkeley, CA. 3 Lawler, T. and M. Vadis, 1986; 32nd Annual Inst. Lake Superior 3 Lawler, T. and M. Vadis, 1986; 32nd Annual Inst. Lake Superior Geol., 49. Geol., 49. 4 Rolst, 4 Holst, TT.B., .B., 1985; 1985; J. J. Struct. Struct. Geol., Geol., v. v. 7, 7, 375—383. 375-383. HoIst, T.B., 1984, Geol., v. 12, 135—138. 5 5 Holst, T.B., 1984, Geol., v. 12, 135-138. 6 Holm, D O.K., 1986, 32nd 32nd Annual Annual Inst. Inst. Lake Lake Superior Superior Geol., Geol., 32-33. 32—33. 6 Holm, .K., 1986, 7 A Centennial VolKeighin et al., 1972; in Geology of Minnesota —— 7 Keighin al., in A Centennial Vol(Sims and Morey, eds.), eds.), Minn. Minn. Geol. Geol. Surv. 240—254. ume (Sima Surv. publ., publ., 240-254. 8 Phoenix 8 Phoenix Geophysics, Inc., Inc., 1985; 1985; Nonexclusive lionexclusive Iowa Iowa Midcontinent Midcontinent Rift Rift MT Data Data and HI and 2—d 2-d Model. Model. 9 et al., al., 1984; Tectonics, v. v. 3, no. no. 3, 367-384 367—384 9 Serpa et v. 11, 11, 25—30. 25-30. 10 Brown et et al., al.. 1983; 1983; Geology, Geology, v. 11 Bosworth et al., 11 al., 1986; 1986; Eos, Transactions, American Geophysical no. 29, pp. v. 67, no. pp. 577, 577, 582—583. 582-583. Union, v. 2 F -- J j Support for for BLU: RLW: & IW, 1W, Minnesota Geol. Geol. Surv. Surv. Grant-in-aid Grant—in—aid for Support GC 6 Students, Trek and Trail Sporting Goods (winter camping equipment). ment). Acknowledgements: Dal Stanley Anderson and others Aclounrladg~ents: Stanley (consultation), (consultation), R9. . Anderson others at .5. Phoenix Geophysics, Denver (MT modeling aid); D. McDowell, at Phoenix Geophysics, Denver modeling aid); D. McDowell, J. Paces, V. Chandler, C. Morey, .5. Diehl (discussion), T. Seiss, Paces, V. G. Morey, J. Diehl (discussion), T. Seiss, Kitchen, the the Lynch Lynch family, family, and and many many others MM. . Kitchen, others (field (field work). work). -86- J J -j �Kremzar GoldDeposit, Deposit, DDistrict Kremzar Gold i s t r i c tofo Algoma f A1 goma - .CANAMAX Resources Inc. — Kremzar Gold CANAc l t d Mines Ltd.. G.R. Resources Inc.,255 255Algonquin Algonquin Blvd. Blvd. West, G.R. Yule Yule (CANAMAX (CANAMAX Resources Inc., West, Timmins, Timmins, Ontario P4N 2R8) Ontario P4N 2R8) - Drill geological reserves at the Kremzar Gold Mines D r i l indicated l indicated geological reserves a t CANAMAX t h e CANAMAX —Kremzar Mines Ltd. Ltd. gold golddeposit depositare arecalculated calculatedata932,000 t 932,000 tonnes tonnesgrading grading8.6 8.6 grams grams gold gold per on rresults per tonne tonne iinn five f i v esubparallel subparallelmineralized mineralizedzones, zones, based based on e s u l t s of of diamond recentddrill diamond ddrilling r i l l i n gprior p r i oto r t September o September1986. 1986. Aditional A d i t i o n a l recent r i l l results results to have t o the the west west confirming confirming continuity c o n t i n u i t y of of the t h e'B'' BHorizon ' Horizon havenot n o been t been included. included. In Mines, operators operators ooff the dine I n 1940, 1940, O'Brien O'Brien Gold Gold Mines, t h e then then producing producing C l i n eLake Lake Gold Mine, ooutlined tonnesoof gold m mineralization Gold Mine, u t l i n e d 64,000 64,000 tonnes f gold i n e r a l i z a t i o n grading grading 7.9 7.9 gg Au per tonne tonne iin fall1ofo f1984, Au per n 17 17 ddrill r i l lholes holesononthe t h e'New 'New Zone'. Zone'. Since Since tthe h e fa1 1984, CANAMAX's evaluation 'NewZone' Zone' gold gold bearing bearing structure CANAMAX'S evaluation o foft hthe e 'New s t r u c t u r ehas hasexpanded expanded reserves ananunderground reserves ssubstantially. u b s t a n t i a l l y . In I n the t h e fall f a lof l o1985 f 1985 underground exploration exploration program was initiated, based on drill indicated geological program was i n i t i a t e d , based on d r i l l i n d i c a t e d geological reserves reserves of of 790,000 tonnes grading grading 7.9 7.9 grams gold per off the 790,000 tonnes grains gold per tonne. tonne. Results Results o t h e underunderground programshowed showed ground eexploration x p l o r a t i o n program e x cexcellent e l l e n t c ocorrelation r r e l a t i o n wwith i t h t hthe e eearlier arlier drill d r i l lresults. results. Auriferous Auriferous quartz quartz veins veins within w i t h i nmafic maficmetavolcanics metavolcanics on on the t h eKremzar Kremzar project project are localized within NW and NE striking biotitized shear zones. a r e l o c a l i z e d w i t h i n NU and NE s t r i k i n g b i o t i t i z e d shear zones. Mineralized mainly of ized veins veins are arecomposed composed mainly o f cherty chertyblue—grey blue-grey quartz, quartz,K—spar, K-spar, and and sericite. minerals s e r i c i t e . Accessory Accessory minerals i n cinclude l u d e p y pyrite, r i t e , p ypyrrhotite, r r h o t i t e , bbiotite, iotite, chlorite, very ffine c h l o r i t e , carbonate, carbonate, and and very i n e free f r e e gold. gold. Native gold gold occurs occurs mainly mainly as as very very fine f i n e free f r e e gold gold "dust "dust clouds", clouds", as as fine f i n eindividual i n d i v i d u aspecks, l specks,and andon on the majority t h e boundaries boundaries oof f ffine i n e anhedral anhedral tto o subhedral subhedral ppyrite y r i t e grains. grains. The The m ajority of veins oblique oblique to t o the the o f the t h e gold g o l d is i srestricted r e s t r i c t e dtot 2nd o 2ndorder ordersigmoidal sigmoidal veins shear zone, tthat dip NW within w i t h i n the t h e shear shear shear zone, hat d i p vertically, v e r t i c a l l y ,and andplunge plungetot othe t h eNW zone structure. This n aa ductile—brittle d u c t i l e - b r i t t l eshear shearzone zone This deposit deposit has has formed formed iin zone structure. environment strongb but restricted wallrock aalteration. A l l obserobserenvironment wwith i t h strong ut re s t r i c t e d wallrock l t e r a t i o n . All vations from hand handsamples, samples,f r ofrom m d rdrill i l l core, core, and and from from detailed detailed vations have have been been from underground investigations. underground investigations. On displaywwill and On display i l l be be a a typical t y p i c a l section section of o f drill d r i lcore l core anditsi tcorresponding s corresponding drill d r i l section, l section,a alongitudinal l o n g i t u d i n asection, l section,and andplan p l a nofo fthe t h edeposit, deposit, as as well well as as hand hand samples. samples. * , .. . ~~ ~ + ., .., . : . .. , ,: .. ., . . .,.. , - . ! , . . . , ., . ., .. , .. —87— , , r . �j - Structurally Lochalsh S t r u c t u r a l l yhosted hosted vein vein type typegold goldmineralization, m i n e r a l i z a t i o nGoudreau , Goudreau —Lochalsh camp,DDistrict ggold o l d camp, i s t r i c tofo Algoma f Algoma J G.R. (CANAMAX Resources 255A1Algonquin Blvd. West, West, Timmins, G.R. YULE YULE (CANAMAX Resources Inc.,Inc.,255 gonquin Blvd. Timmins, P4N 2R8) Ontario PAN 2R8) Ontario J Since Resources commenced search goldmmineralizSince CANAMAX CANAMAX Resources Inc.,Inc., commenced t h e the search f o rfor gold ineralization terrane, gold a t i o n ini nthe t h eWawa Wawa greenstone greenstone terrane, gold has has been been noted noted to t o be be hosted hosted within major and minor structures transecting all lithologies, except w i t h i n major and minor structures t r a n s a c t i n g a l l l i t h o l o g i e s , except the diabase dike It also apparent tthat t h e late l a t eKeweenawan a l s obecame became apparent hat Keweenawan diabase d i k eswarm. swarm. It the Goudreau—Lochalsh area hosted the major criteria for gold deposits. the Goudreau-Lochalsh area hosted t h e major c r i t e r i a f o r gold deposits. In entered joint—venture with I n 1983 1983 CANAMAX CANAMAX entered i ninto t o jo i n t - v e n t u r e agreements agreements w i t h Algoma Algoma Steel Steel Corporation and and wwith GoldMines MinesLtd., Ltd., a Corporation i t h Kremzar Kremzar Gold a subsidiary subsidiary ofo fAlgoma Algoma Steel holdings in the Steel Corporation, Corporation, to t o explore explore their t h e i large r l a r gland e land holdings i n t Goudreau— h e GoudreauLochalsh area. CANAMAX has since defined major auriferous structures, Lochalsh area. CANAMAX has since defined major auriferous structures, responsible for the many gold occurrences of the area, which responsible f o r t h e many gold occurrences o f t h e area, which eluded eluded previous workers. previous workers. The hhistoric gold camp northernf l aflank The i s t o r i cGoudreau—Lochalsh Goudreau-Lochalsh gold camp i s is on on t h ethe northern n k oof f tthe he Wawa greenstone terrane. The lithology of the region is typically Wawa greenstone terrane. The l i t h o l o g y o f t h e region i s t y p i c a l l y Archean metavolcanicrocks, rocks,ranging rangingfrom fromf efelsic Archean metavolcanic l s i c ttoo mafic mafic composition, composition, with w i t h minor, minor, but b u t regionally r e g i o n a l l yextensive, extensive,carbonate—sulphide carbonate-sulphide iiron r o n formations formations markingt hthe majorl ilithologic marking e major t h o l o g i c contact. contact. Goldmmineralization campi sissstructurally t r u c t u r a l l y controlled c o n t r o l l e d by by the the Gold i n e r a l i z a t i o n wwithin i t h i n tthe h e camp major east-northeast east—northeasttrending, trending,low lowangle anglereverse reversef fault major a u l t system system rreferred eferred Zone, and andby by subsidiary subsidiary minor ttoo as as the t h eGoudreau Goudreau Shear Shear Zone, minor splays splays and and shear shear fractures units the the latel aKeweenawan fractures that t h a ttransect transectalla rock l l rock u n except i t s except t e Keweenawandiabase diabase dikes. LLithologies dikes. i t h o l o g i e s found found tto o host host these these gold gold bearing bearing structures s t r u c t u r e s include include mafic and andffelsic sulphide—carbonate mafic e l s i c volcanics, volcanics, felsic f e l s i intrusives, c i n t r u s i v e and s , and sulphide-carbonate iron i r o n formation. formation. J U j Hydrothermala lalteration these sstructurally Hydrothermal t e r a t i o n oof f these t r u c t u r a l l y prepared prepared conduits conduits iiss also also essential ffor Wallrockaalteration essential o r gold gold mineralization. mineralization. Wallrock l t e r a t i o n includes includes potassic potassic metasomatism theb ibiotization the mafics maficsand ands esericitization metasomatism (i.e.(i.e. the o t i z a t i o n oof f the r i c i t i z a t i o n ooff sulph— tthe h e ffelsics), e l s i c s ) , silicification, s i 1 i c i f i c a t i o ncarbonatization, , carbonatization,chloritization, c h l o r i t i z a t i o nand , and sulphdization (pyrite, pyrrhotite, chalcopyrite, arsenopyrite, and sphalerite). d i z a t i o n ( p y r i t e , p y r r h o t i t e , chalcopyrite, arsenopyrite, and s p h a l e r i t e ) . The GoudreauShear Shear Zone, a major zone low angle reverse The Goudreau Zone, a major zone o f of low angle reverse f afaulting, u l t i n g , is is host to gold deposit. deposit. Splays Splays of t othe t h eMagino—Muscocho Magino-Muscocho gold o f the t h eGoudreau Goudreau Shear Shear Zone, trending northwest at 35 — 45 degrees to the structure, host Zone, t r e n d i n g northwest a t 35 45 degrees t o t h e s t r u c t u r e , host several other occurrences, namely golddeposit deposit,, othergold gold occurrences, name1the y t hCANAMAX—Kremzar e CANAMAX-Kremzar gold These northwest northwest tthe h e Cline C l i n e Lake Lake past past producer, producer, and and the t h e Markes Markes prospect. prospect. These trending splays trending splays appear appear tot ohave havean anextensional extensional.component, component, suggested suggested by by ont hthe GoudreauShear Shear Zone, tthrust h r u s t movement movement on e Goudreau Zone, a l lallowing o w i n g f ofor r aal larger a r g e r dilat— dilatancyooff the the splays, thus witdths, witdths, and ancy splays, and and thus and therefore t h e r e f o r e tonnage tonnage ppotential. otential. Minor conjugate conjugate northeast northeast ttrending Minor r e n d i n g splay splay structures s t r u c t u r e ssuch suchas asZones Zones 22 and and 33 on tthe property are are also also auriferous. auriferous. These Theseminor minorstructures structures are on h e Kremzar Kremzar property tonnageppotential. comprescconsistantly o n s i s t a n t l y narrow, narrow, and and thus have have lower lower tonnage o t e n t i a l . AA compres— sional component may be be responsible, responsible, component ooff the t h emajor majorGoudreau Goudreau Shear Shear Zone Zone may making minorsplays splaysa at itighter structure. making t hthe e minor g h t e r structure. - J -4 —88— J �-j I C) a E ft C) a) it it LC -I-) U, 4-, -Cr- i :i r i —, :i 1 — Ji I Ci TI i±I L....1 ! I I I I I I I I I I I I I I I I I I CNC r it .r- 43 U, 4) .-. (0 0 C) 0 C )<CC) _o -c C) -c rSL 4-) 0 •!- I— (0 0' .— U1 -C C ci -w I— C) >, r 4- L (0010 it,— a) t_ it -C 4' 4-) a) 4-' r LF -C Ci 4JC,(0 4-' (0 it 4-) 3 L C) LrL 0 4-' it it -r Li—C .C I/I r- C) >, 0 U, C ro o'.o WOE 4-' C) o (I) w L a' r'--f-- C) -I-' -0-C C, C -0-c r+J a F Circa L -o (0 This e x h i b i t w i l l I l l u s t r a t e t h e s t r u c t u r a l l y c o n t r o l l e d gold minerali z a t i o n which transacts a l l t h e various l i t h o l o g i e s w i t h i n t h e gold camp and t h e r e s u l t i n g hydrothermal a l t e r a t i o n assemblages. �AUTHOR AUTHOR INDEX INDEX ........... 821 ............. . .......... ........ 5,10 3 5. 10 6,12 ............. 6. 12 .............. 151,24 .................. 1. 24 ........... 8 ....... 106,12,32 .......... 6.12. 32 .............. 13 ................ 15 ............... 16 ........... 25 ................. 18 ...... 19 .................. 20,21 20. 21 Anderson, Anderson. Gary Gary Anglin, Anglin. C.D C.D. Barrie, Barrie. C. C Tucker Tucker Bauer, Robert Bauer. Robert LL Baxter, Baxter. D.A D.A. Behrendt, Behrendt. 3J Bell, B e l l . KK Berdusco, Berdusco. E.N E.N. Bidwell, Bidwell. Matthew Matthew E. E Bornhorst, Bornhorst. T.J T.J. Bowen, Bowen. R.P R.P. Cannon, Cannon. WW Card, K.D. Card. K.D Chandler, Chandler. V.W V.W. Corfu, Corfu. FF Cummings, Michael LL Cunnings. Michael Dahl, Dahl. RR Davidson, Davidson. AA Droege, Droege. David David Eick, Eick. P.M P.M. Erickson, Erickson. Paul Paul Ernst, Ernst. R.E R.E. Ferderer, Ferderer. R.J R.J. Franklin, Franklin. J.M J.M. Frizado, Frizado. Joe Joe Geiger, Geiger. C.A C.A. Green, Green. AA Gregg, Gregg. W.J W.J. Grunsky, Grunsky. Eric E r i c CC Heather, Heather. Kevin Kevin BB Hoffman, Hoffman. EE Hutchinson, 0D Hutchinson. Jirsa, Jirsa. Mark Mark AA Johnson, Johnson. Allan A l l a nMM Johnson, R.C. Johnson. R.C Jolly, Wayne J o l l y . Wayne TT Jonasson, Jonasson. hR I.R. Kneller, Kneller. William William Kuhns, Kuhns. Mary Mary Jo Jo PP Kuhns, Roger Kuhns. Roger JJ LaBerge, LaBerge. Gene Gene LL Lee, M Lee. M Lehman, Lehman. George George AA McGill, George McGill. George EE McGoren, McGoren. J.W J.W. McPhee, McPhee. 0.5 D.S. Mancuso, Mancuso. J.M J.M. Meyer, Meyer. Paul Paul 3J MilkereTt, M i l k e r e i t . BB Miller, M i l l e r . Jr., Jr.. James James 0D Morel PP Muir, Muir. T.L T.L. 82 1 3 15 8 10 13 15 16 25 18 19 .............. ............ ............... ........... .............. ........... ........... ............. ............. ................. .............. .......... ......... ............... ............ ............ ......... ............ ........... ........... ......... ......... ........... .......... ................... ......... 39,61,63 ......... ............ ............. ............ ............ ............. ..... .................. ............... 15,22 15. 22 53 53 23 23 82 82 24 24 25 25 1,76 1.76 68 68 55 55 15 15 65 65 26 26 28 28 1 15 15 30 30 5 3,56 53. 56 32 32 34 34 1 1 68 68 35 35 35 35 36 36 15 15 37 37 39.61. 63 20,221 1 20. 41,42 41. 42 68,70 68.70 73 73 15 15 43 15 15 45 45 1 47,49 ........ 47. 49 .......... 51 ........ 5553 .......... ....... 5756 .............. ........... 5818. 18,76 .............. 76 ......... 59 39,61,6 3 ..... 39.61. 63 ........... 6515 .............. .......... 67 ......... 68 ........... 7170 ................ ........ 73 ......... 75 .......... 8115 ............... ............ 76 .......... 78 ......... 8068 ................ 6,32,53 ....... 226.32. 53 ........... ........... 81 ........... 82 20,21 ......... 8320. 21 .......... .......... 84 ...... 85 ........ 8587. 87,88 .............. 88 Nielsen, Peter Peter AA Nielsen. Percival J.A. Percival. J.4. Peterman, Jill F Peterman. Jill F Peterson, J.W Peterson. J.W. Prosen, Barbara Prosen. Barbara J. J Rose, Rose. W.I W.I. Rupert, Rupert. Roy Roy JJ Sage, R.P Sage. R.P. Shegelski, Shegelski. R.J R.J. Shrady, Catherine H Shrady. Catherine H. Sikkila, S i k k i l a . K.M. K.M. Spencer, CC Spencer. Springer, Springer. 3.5. J.S. Stevenson, Stevenson. JJeff eff Stewart, Stewart. D.C. D.C. Stone, Stone. DD Suszek, Suszek. Thomas Thomas JJ Sutcliffe, S u t c l i f f e . R.H. R.H. Symons, D.T.A. Symons. D. T.A. Teskey, 0. Teskey. D Thorpe, R.I. Thorpe. R.I. Tortosa, Tortosa. Delia Delio Truskoski, Truskoski. Paul Paul Turek, AA Turek. Van Alstine, J.L Van Alstine. J.L. Van Van Breenien, Breemen. 00 Vandall, Vandall. T.A T.A. Watkins, Ivan Watkins. Ivan Watkinson, Watkinson. D.H D.H. Werbach, Werbach. David David Williams, Williams. H.R H.R. Wunderman, Richard Wundennan. Richard Young, Charles TT Young. Yule, G.R Yule. G.R. —90— 53 55 56 57 58 59 65 15 67 68 70 71 73 75 81 15 76 78 68 80 22 81 82 83 84 85 85 � https://digitalcollections.lakeheadu.ca/files/original/c8d8c053aa0e63109723bb2132dd3fc8.pdf e87a531a6c2b257913b28ed87343a403 PDF Text Text Institute on Lake Superior Geo'ogy i r t y - T h i r dAnnUal Annual Meeting Me ThirtyThrd WAWA, ONTARR:) May 12 and 13, 19B7 GeoIogy of Ww Area God MbieraUaton Sponsored by Onlaria Ministry Ministry ofofNorthern and Wnes fi/iinics NorthernDevelopment DeIopment and OntarIo VVtw Resiclont Uoloqit U Nice Volurr)e a :: Par 2 �OF GEOLOGY O F WAWA AREA GOLD MINERALIZATION MINERAL1 ZATI ON E. D. D. Frey Frey Ontario O n t a r i o Ministry M i n i s t r y of o f Northern N o r t h e r n Development Development and a n d Mines Mines Wawa Resident s Of Office R e s i d e n t Geologist' Geologistt s £ic P.O. P . 0 . Box 530 530 Wawa, Ontario 1KO Wawa, O n t a r i o PUS POS 1KO Institute I n s t i t u t e on Lake Superior S u p e r i o r Geology 33rd Annual Meeting 3 3 r d Annual Meeting Wawa, Wawa, Ontario Ontario 11957 987 Fieldtrip F i e l d t r i p Guidebook Volume 33, Volume 33, Part P a r t 22 �FOREWORD FOREWORD T h i s guidebook guidebook is i s aa candidate c a n d i d a t e for f o r the t h e most-delayed most-delayed production production This award. award. conducted the t h e original original y e a r s have passed p a s s e d since s i n c e I conducted Three years f i e l d t r i p twice t w i c e during d u r i n g the t h e Wawa Wawa ILSG ILSG meeting. meeting. fieldtrip C i t a d e l Mine Mine The Citadel h a s test t e s t milled m i l l e d its i t s underground underground development development and and continues c o n t i n u e s to to has explore e x p l o r e on on surface. surface. C i t a d e l Gold Gold Mines Mines Ltd. Ltd. has h a s acquired a c q u i r e d the the Citadel P a r k h i l l Mine Mine and and has h a s conducted conducted extensive e x t e n s i v e surface s u r f a c e stripping s t r i p p i n g on on Parkhill that t h a t property p r o p e r t y and and surrounding s u r r o u n d i n g prospects. prospects. Ranson prospect p r o s p e c t was was The Ranson o p t i o n e d to t o FinNeth FinNeth Explorations E x p l o r a t i o n s Ltd. Ltd. in i n late l a t e 1987 1 9 8 7 and and has has been been optioned thoroughly t h o r o u g h l y sampled sampled and and evaluated. evaluated. some some of of these t h e s e new new data. data. incorporates The guidebook incorporates No changes changes have have affected a f f e c t e d the t h e other o t h e r sites sites No visited v i s i t e d during d u r i n g the t h e ILSG I L S G meeting. meeting. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I thank t h a n k Dello D e l i o Tortosa, T o r t o s a , Wawa Wawa Resident R e s i d e n t Geologist, G e o l o g i s t , for f o r providing p r o v i d i n g the the dedicated d e d i c a t e d time t i m e necessary n e c e s s a r y for f o r completion c o m p l e t i o n of of this t h i s project. proj ect. Contract Contract geologists g e o l o g i s t s Rosa Rosa Stewart S t e w a r t and and Ann Ann Wilson Wilson prepared p r e p a r e d the t h e figures. figures. Wilson Wilson reviewed r e v i e w e d the t h e text. text. Ann Ann Ron Sage, Sage, Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, also a l s o provided p r o v i d e d continued c o n t i n u e d support. s u p p o r t . Any Any rremaining e m a i n i n g eerrors rrors or o r word word fog f o g are a r emy my responsibility. responsibility. Toronto, Toronto, fieldtrip would not exist without the co-operation of the This T h i s f i e l d t r i p would n o t e x i s t w i t h o u t t h e c o - o p e r a t i o n of t h e property property owners owners and and operating o p e r a t i n g companies companies listed l i s t e d below. below. Their T h e i r open open access a c c e s s policies p o l i c i e s have contributed c o n t r i b u t e d greatly g r e a t l y to t o the t h e continuing continuing exchange of of observations o b s e r v a t i o n s and and ideas i d e a s on on Wawa geology geology and and gold gold mineralization m i n e r a l i z a t i o n that t h a t characterize c h a r a c t e r i z e the t h e Wawa Wawa exploration e x p l o r a t i o n community. community. I thank t h a n k the t h e management management and and staff, s t a f f , as a s noted, n o t e d , of: o f : Citadel C i t a d e l Gold Gold Mines Mines Ltd. Ltd. -- Roy Roy Rupert Rupert and and Alison A l i s o n Leroy; Leroy; Monk Gold Gold and and Resources Ltd.; Ltd. ; and and Bridget B r i d g e t Lake Lake Resources Resources Inc. Inc. �—2— - 2 NTRODUCTI ON ON I NTRODUCTI The fieldtrip f i e l d t r i p provides p r o v i d e s aa one one day day overview o v e r v i e w of of the t h e variety v a r i e t y of of lithological of g gold bearing quartz vein l i t h o l o g i c a l and structural s t r u c t u r a l settings s e t t i n g s of old b earing q uartz v ein m i n e r a l i z a t i o n in i n the t h e Wawa Wawa area. area. mineralization The route r o u t e traverses t r a v e r s e s the the historical h istorical g o l d mining m i n i n g area a r e a south s o u t hof ofWawa Wawa and and includes i n c l u d e s several s e v e r a l as as gold yet y e t minor o c c u r r e n c e s that t h a t are a r e of of interest i n t e r e s t for f o r their t h e i r geological geological occurrences ssetting e t t i n g (Fig. (Fig. 1). 1). 10 stops s t o p s were selected s e l e c t e d for f o r their t h e i r interest interest The 10 and large l a r g e group g r o u p accessibility. accessibility. occurrences o c c u r r e n c e s are a r e known known (Fig. (Fig. numerous additional a d d i t i o n a l gold gold However numerous 1)) and and aa comprehensive comprehensive review 1 r e v i e w of of the the local gold mineralization l o c a l lithostructural l i t h o s t r u c t u r a l relationships r e l a t i o n s h i p s of of g old m ineralization remains r e m a i n s to t o be be done. done. The mineral m i n e r a l development history h i s t o r y of of Wawa began began in i n June J u n e 1897 1897 with of Wawa Lake by by w i t h the t h e discovery d i s c o v e r y of of gold g o l d on the t h e southwest s o u t h w e s t sshore h o r e of local l o c a l native n a t i v e William W i l l i a m Teddy. Teddy. Wawa d discovery The Wawa i s c o v e r y coincided c o i n c i d e d with with the t h e Kiondike K l o n d i k e gold g o l d rush r u s h and and many many westward-bound westward-bound prospectors prospectors sstopped t o p p e d at a t Wawa on on their t h e i r steamer s t e a m e r journey j o u r n e y across a c r o s s Lake Lake Superior. Superior. The first f i r s t Wawa gold g o l d rush r u s h ended ended in i n 1906 1906 after a f t e r numerous numerous shortshortlived l i v e d mining m i n i n g developments d e v e l o p m e n t s of o f low low tonnage. tonnage. Gold exploration exploration rrevived e v i v e d in i n the t h e 1930s 1930s and and resulted r e s u l t e d in i n fifteen f i f t e e n mines mines tthat h a t produced produced tthrough h r o u g h tthe h e early e a r l y 1940s. 1940s. The total production t o t a l gold gold p r o d u c t i o n from from the t h e Wawa Wawa area a r e a has h a s been b e e n less l e s s than t h a n 200,000 200,000 ounces. ounces. The next n e x t cycle c y c l e of of gold g o l d exploration e x p l o r a t i o n was was stimulated s t i m u l a t e d by b y the the record r e c o r d high h i g h gold g o l d price p r i c e of of 1980 1980 and and the t h e Hemlo Hemlo discoveries d i s c o v e r i e s two two years y e a r s later. later. Continued C o n t i n u e d high h i g h demand and a sustained s u s t a i n e d acceptable acceptable price of eexploration has p r i c e have h a v e maintained m a i n t a i n e d the t h e level l e v e l of x p l o r a t i o n tthat hat h a s rresulted esulted in i n recent r e c e n t mine mine development development activities a c t i v i t i e s and and production p r o d u c t i o n decisions. decisions. An accidental a c c i d e n t a l result r e s u l t of of the t h e intensive i n t e n s i v e gold g o l d prospecting p r o s p e c t i n g was was �Occurrences. Gold and Geology General Area Wawa Occurrence Gold © A Mine Gold Producing Past IA Stop Trip Field v V Rocks Intrusive Mafic Rocks Metavolcanics Malic Sediments Quaternary T1 vV V \N\\\\ \\\ \\ \N\NN \N\\N\\\ v v STOCK LAKE 4vt41 vvvVvvVVVVVVV\\\\\\\\\\N\\\\\\N\N\\N N /\NN\\\\\\\N\\JV\\/,VVVVV/ -' /\N\N\N\\\\NNYvV.iV\4-VVVVVVVVV+\N\\\N\\. vVVVV\\\\\ vvvvvv\\\N. V ,Y'VVVVVVVVV VVVV V Li: Rocks Intrusive Felsic vVV VV Figure Rocks Metavolcanic Felsic Rocks Plutoruc Felsic vVVVVVVvVVV 1. Lillill VVVVVVBHOGET \VVVV - V vvV'\ \N\NNN\\ VVVVVV\\\\\NN\ v/vVv\vVvVvVVvvVVVVVvK/'P/) -vv Y -P; \JVvVvVVVVVVVYji! vVvVVVVVVV \VVVVVVVV')'/' \VVVVV vvvV:/P ,vVvv-c 1-NNNN\\N\-%\NNN\\NNwyvvV-,/ vVvvVvvVVVVVVVVVVVVVV V \V /v\,\\ VVVVVM VVVVVVV//N\N\N\N\N\\NN\N\\ \\\\ \\\\\\ CNNNN vVvvVVV\ V-VVVVVvVVvVVvVVVVV vv V VVVVVVVV jV vv V - -'/ \\\N\\ 4- 4 I + 4 1 4- 4 vvvvVV /VVVVVVV\V /vVVVVVVV 4-j 'vvVvvv\t -+VVVV4L.' yvvvv\ Superior 4 t + 4- If 4- 1 4- 4 4- 4 +4-f t f4-1 1-44-444-4 114NQ STOCK :*4-+ /_ - 4CEHIENtJAY N'"-' + + 4 j\\\ H Lake + -4- 4- 4- 4 F + + 4- 4- 1— 1— 4- 1- ,,C',. -4- 4- 1- _l- 4- - * / / 0 / // ;P_,\ "'';iP,;/ '//_J ,! - 4/—\, l/_/I\ ,\j\_ 4\)i'--ç P \ 1 4 ± 4 + 4- 4- 4- 4- 4- 4- N 4 /; 4 > A V v �—4— t h e discovery d i s c o v e r y of of iron i r o nore o r eini n1898. 1898. the I r o n mining mining became became the the Iron m a i n s t a y of of the t h e Wawa Wawa economy economy until u n t i l reduced r e d u c e d demand demand for f o r steel steel mainstay f o l l o w i n g World World War War II forced f o r c e d the t h e closure c l o s u r e of of the t h e Helen Helen and and Magpie Magpie following mines by by 1920. 1920. mines I r o n mining mining revived r e v i v e d in i n the t h e late l a t e 1930s, 1930~ prompted ~ by aa Iron prompted by provincial p r o v i n c i a l bounty b o u n t y of of two two cents c e n t s per p e r ton t o n in i n 1937 1937 and and the t h e onset o n s e t of of 11. The The open open pit p i t Helen Helen Mine Mine re-opened re-opened in i n 1939 1939 and and by by World War WarII. World 1960 had had developed d e v e l o p e d into i n t o the t h e George GeorgeW. W. MacLeod MacLeod Mine, Mine, which which 1960 c o n t i n u e s to t o operate o p e r a t e today t o d a y as a s an a nunderground undergroundsiderite s i d e r i t emine. mine. continues Modern Modern geological g e o l o g i c a l mapping mapping of of the t h e Wawa Wawa area a r e a by by the t h e provincial provincial government has h a s been been completed completed by by the t h e Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey government (Ministry ( M i n i s t r y of of Northern N o r t h e r n Development Development and and Mines) Mines) at a t aa scale s c a l e of of 1: 15, 840 (1 ( 1 inch i n c h == 1./4 114 mile). mile). 1:15,840 This T h i s work work includes i n c l u d e s preliminary preliminary maps (Sage, (Sage,ete al. t al, . , 1982a—1982d; 1982a-1982d; Massey, Massey, ete tal. a l .,, 1982a-1982c; 1982a-1982c; and and maps Mandziuk, et e t al., a l . , 1981) 1981) and and open open file f i l e reports r e p o r t s (Massey, (Massey, 1985; 1985; Mandziuk, Sage, in i n press). p r e s s 1. Sage, GEOLOGICAL SETTI NG GEOLOGI CAL SETTING Wawa Wawa is i s in i n the t h e south s o u t h central c e n t r a l part p a r t of of the t h e Michipicoten M i c h i p i c o t e n greenstone greenstone belt, b e l t , within w i t h i n the t h e Wawa Wawa Subprovince Subprovince of of the t h e Superior S u p e r i o r Province P r o v i n c e of of the the Canadian Shield S h i e l d (Fig. ( F i g . 2). 2). Canadian The The Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t is is composed composed of of supracrustal s u p r a c r u s t a l metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r yrocks, rocks, that t h a t have have been been divided d i v i d e d into i n t o three t h r e e volcanic v o l c a n i c cycles c y c l e s (Sage, (Sage, 1986). 1986). Each Each cycle c y c l e consists c o n s i s t s of of mafic m a f i c to t o felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s and and a s s o c i a t e d subvolcanic s u b v o l c a n i c intrusions. intrusions. associated The The volcanic v o l c a n i c cycles c y c l e s are are of overlain o v e r l a i n by by iron i r o n formation f o r m a t i o n or o r clastic c l a s t i c metasedimentary m e t a s e d i m e n t a r y rocks r o c k s of v o l c a n i c origin. origin. volcanic �GAMITAGAMA LAKE GREENSTONE BELT / Figure 2. General Geology of the Michpicoten Greenstone Belt MSHIBISHU LAKE GREENSTONE BELT + 4-J f ,#+/ B ELI Granitic Intrusive Rocks (internal) Metavolcanic-Metasedimentary Supracrustal Rocks L + ft 1- 4 V+ LEGEND Granite-Gness Pluflonic Rocks (external) GA EENS TO NE MICHPICOTEN (fl �—6— - 6 The mafic m a f i c volcanic v o l c a n i c compositions c o m p o s i t i o n s vary v a r y from from basaltic b a s a l t i c to to p e r i d o t i t i c komatiite k o m a t i i t e in i n the t h e oldest o l d e s t cycle, c y c l e , to t o tholeiitic t h o l e i i t i c basalts basalts peridotitic i n the t h e two two younger younger cycles. cycles. in The rrocks o c k s are a r e massive and pillowed pillowed f l o w s and minor minor accumulations a c c u m u l a t i o n s of of tuff. tuff. flows The iintermediate n t e r m e d i a t e to to ffelsic e l s i c rocks r o c k s of o f the t h e three t h r e e cycles c y c l e s are a r e pyroclastics p y r o c l a s t i c s and minor flows flows of o f rhyolite r h y o l i t e and and dacite, d a c i t e l of of caic-alkalic c a l c - a l k a l i c affinity. affinity. M i c h i p i c o t e n Iron I r o n Formation, Formationl dominated by siderite s i d e r i t e in i n the the Michipicoten Wawa area, a r e a l caps caps the t h e oldest o l d e s t volcanic v o l c a n i c cycle. cycle. The clastic elastic m e t a s e d i m e n t a r y rocks r o c k s that t h a t overlie o v e r l i e the t h e younger younger cycles c y c l e s consist c o n s i s t of of metasedimentary u n u s u a l l y well w e l l preserved p r e s e r v e d siltstones s i l t s t o n e s to t o conglomerates c o n g l o m e r a t e s that t h a t have have unusually d e p o s i t e d in i n aa variety v a r i e t y of of marine marine and and non-marine non-marine settings. settings. been deposited s t r a t i g r a p h i c thicknesses t h i c k n e s s e s of of the t h e mafic m a f i c and and felsic-intermediate felsic-intermediate The stratigraphic s e c t i o n s of of the t h e oldest o l d e s t cycle, c y c l e l in i n the t h e Wawa Wawa area, a r e a l are a r e approximately approximately sections 1800 m and and 900 900 m, ml respectively. respectively. (SageI 1986; 1986; (Sage, Sagel et e t al. a l .,, Sage, 1987; 1987; Sage, in Sagel i n press) press) Michipicoten The M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t is i s enclosed e n c l o s e d within w i t h i n Early Early P r e c a m b r i a n granitic g r a n i t i c and and gneissic g n e i s s i c rocks r o c k s that t h a t are a r e younger younger than t h a n the the Precambrian supracrustal s u p r a c r u s t a l rocks. rocks. The supracrustal s u p r a c r u s t a l rocks r o c k s have been intruded i n t r u d e d by by felsic ccoeval o e v a l tto o younger stocks s t o c k s of of a variety v a r i e t y of of intermediate i n t e r m e d i a t e to t o felsic ccompositions. ompositions. These events e v e n t s have been dated d a t e d by the t h e U-Pb zircon zircon method and rrange from 2888 2888 +1/ - 9 Ma Ma to t o 2663 2663 +/+ / - 66 Ma Ma (Turek, ( T u r e k I et et method and a n g e from aal. l., 1988; 1988; Turek, Turekl et e tal. a l ., 1990). 1 990). Michipicoten The M i c h i p i c o t e n greenstone g r e e n s t o n e belt b e l t has been metamorphosed mainly to t o greenschist g r e e n s c h i s t grade. grade. Amphibolite grade g r a d e metamorphism metamorphism has has altered a l t e r e d the t h e supracrustal s u p r a c r u s t a l rocks r o c k s along a l o n g the t h e margin of of the t h e greenstone greenstone belt b e l t and adjacent a d j a c e n t to t o the t h e larger l a r g e r intrusions. intrusions. mineralization exclusively Gold m i n e r a l i z a t i o n iis s hosted h o s t e d almost almost e x c l u s i v e l y iin n quartz quartz �— - 7— 7- v e i n s and and lenses l e n s e s or o r pods pods within w i t h i n shear s h e a r zones zones and and breccia b r e c c i a zones. zones. veins Only minor u a n t i t i e s of of gold g o l d have have been been reported r e p o r t e d from from adjacent adjacent Only minorqquantities wall wall rocks. rocks. These gold g o l d depositional d e p o s i t i o n a l settings s e t t i n g s occur o c c u r in i n aa variety v a r i e t y of of These lithologies. lithologies. T h e i r orientation o r i e n t a t i o n and and character c h a r a c t e r appear a p p e a r to t o be be Their c o n t r o l l e d by the t h e competency competency of of the t h e host h o s t rock r o c k and and its i t s behaviour behaviour controlled during d u r i n g the t h e shearing s h e a r i n g and/or a n d / o r other o t h e r deformation. deformation. Common elements e l e m e n t s of of Common t h e gold g o l d occurrences o c c u r r e n c e s are: a r e : their t h e i r lack l a c k of of preferred p r e f e r r e d host h o s t lithology, lithologyl the the t h e presence p r e s e n c e of of recrystallized r e c r y s t a l l i z e d quartz, q u a r t z l and and minor minor amounts amounts of of sulphide s u l p h i d e minerals. minerals. The presence p r e s e n c e and intensity i n t e n s i t y of of alteration a l t e r a t i o n also also appears a p p e a r s to t o be an a n important i m p o r t a n t factor f a c t o r in i n evaluating e v a l u a t i n g individual i n d i v i d u a l gold gold occurrences. occurrences. Al though tthe A 1 though h e rrelationship e l a t i o n s h i p remains unclear, unclear) significant s i g n i f i c a n t gold g o l d occurrences o c c u r r e n c e s rarely r a r e l y occur o c c u r outside o u t s i d e of of aa zone zone of of pronounced pronounced alteration. alteration. JUBILEE STOCK STOCK STOP STOP 1: 1: - - V e r t i c a l Rockcut, Rockcutl SE SE side s i d e of of Highway Highway 101, 101, High Vertical km NE from from Surluga S u r l u g a Road Road Intersection I n t e r ~ e c t i o n-2 km high-level The Jubilee J u b i l eStock e S t (Fig. o c k ( F i g . 1) 1 ) iis s aa h i g h - l e v e l subvolcanic s u b v o l c a n i c intrusion intrusion The which varies v a r i e s in i n composition c o m p o s i t i o n from from diorite d i o r i t e to t o quartz q u a r t z diorite d i o r i t e and and granodiorit e . granodiorite. It I t is i s finef i n e - to t o medium-grained, medium-grained) equigranular e q u i g r a n u l a r to to locally l o c a l l y porphyritic. porphyritic. The stock s t o c k intrudes i n t r u d e s felsic f e l s i c and intermediate intermediate fragmental f r a g m e n t a l metavolcanic m e t a v o l c a n i c rocks r o c k s of of the t h e lower l o w e r volcanic v o l c a n i c cycle. cycle. A U-Pb U-Pb z i r c o n age a g e of of 2745 2745 +/+ / - Ma Ma obtained o b t a i n e d from from the t h e stock s t o c k identifies i d e n t i f i e s it it zircon as a s coeval c o e v a l with w i t h the t h e metavolcanic m e t a v o l c a n i c rocks r o c k s of of the t h e lower l o w e r volcanic v o l c a n i c cycle cycle + / - 10 10 Ma Ma and 2749 2749 +/— + / - 22 Ma, Mal Turek, Turekl et e t al., al. (2744 +/— 1982). 1 982). ssurface u r f a c e expression e x p r e s s i o n of of the t h e stock s t o c k is i s approximately a p p r o x i m a t e l y 88 km km sq. sq. The �—8— - 8 - m a r g i n a l zones z o n e s of o f the t h e stock s t o c k form form an a n intrusive i n t r u s i v e breccia breccia The marginal contact. contact. The central i s dioritic d i o r i t i c to t o granodioritic g r a n o d i o r i t i c in in c e n t r a l stock s t o c k is i s partly p a r t l y encircled e n c i r c l e d by a massive m a s s i v e quartz-feldspar quartz-feldspar c o m p o s i t i o n and a n d is composition porphyry. p orphyry. p o r p h y r y may occupy a ring r i n g fracture f r a c t u r e associated associated The porphyry w i t h caldera c a l d e r a formation f o r m a t i o n during d u r i n g the t h e intrusion i n t r u s i o n of o f the t h e Jubilee J u b i l e e Stock. Stock. with ((Sullivan, S u l l i v a n , et e t al., al., 1985; 1985; sage, Sage, 1986 & in i n press) press) The Jubilee J u b i l e e Stock S t o c k is i s highly h i g h l y variable, v a r i a b l e , both b o t h within w i t h i n its its compositional c o m p o s i t i o n a l range r a n g e and a n d texturally. texturally. The v variability The a r i a b i l i t y is i s displayed displayed within w i t h i n small s m a l l areas a r e a s and and often o f t e n within w i t h i n individual i n d i v i d u a l outcrops. outcrops. A lso Also c o n t r i b u t i n g to t o its i t s mapping complexity c o m p l e x i t y are a r e abundant a b u n d a n t xenoliths x e n o l i t h s of of contributing metavolcanic m e t a v o l c a n i c rocks r o c k s that t h a t locally l o c a l l y comprise c o m p r i s e up to t o 50% 50% of o f the t h e intrusion intrusion and display d i s p l a y great g r e a t size s i z e variation. variation. (Sullivan, ( S u l l i v a n , et e t al. al., , 1985) 1985) The fieldtrip f i e l d t r i p will w i l l examine examine aa 100 100 m m length l e n g t h of of aa large l a r g e vertical vertical roadcut r o a d c u t of o f diorite d i o r i t e and a n d quartz q u a r t z diorite d i o r i t e on on the t h e south s o u t h side s i d e of of Highway Highway 101. 101. Annually, A n n u a l l y , renewed rock r o c k falls f a l l s provide p r o v i d e fresh fresh exposures e x p o s u r e s of o f the t h e stock s t o c k and and related r e l a t e d features: f e a t u r e s : multisized multisized xenoliths, x e n o l i t h s , quartz q u a r t z vein v e i n occupation o c c u p a t i o n of o f minor minor shears, s h e a r s , and a n d hematitic hematitic and a n d carbonate c a r b o n a t e alteration. alteration. JUBILEE J U B I L E E TUFFS TUFFS STOP 2: STOP 2: - - Roadcut and Hillside H i l l s i d e Outcrops, O u t c r o p s , SE SE side s i d e of of Highway 101, Highway 101, SW SW of o f Surluga S u r l u g a Road IIntersection ntersection - Quartz Q u a r t z feldspar f e l d s p a r crystal c r y s t a l tuffs t u f f s are a r e an a n abundant a b u n d a n t component of o f the the felsic f e l s i c metavolcanic m e t a v o l c a n i c rocks r o c k s south s o u t h of o f Wawa Wawa Lake. Lake. They consist consist mainly m a i n l y of o f fine f i n e to t o medium grained g r a i n e d quartz q u a r t z and feldspar f e l d s p a r and and minor minor quantities q u a n t i t i e s of o f sericite, s e r i c i t e , carbonate, c a r b o n a t e , chlorite, c h l o r i t e , epidote, e p i d o t e , and and biotite. b iotite. The quartz q u a r t z content c o n t e n t is i s 10% 10% to t o 15% 15% and a n d quartz q u a r t z crystals crystals �—9— - 9 - are a r e often o f t e n up up to t o 55 mm mm in i n diameter. diameter. Q u a r t z in i n the t h e tuffs t u f f s is is Quartz e n r i c h e d 33 to t o 55 times t i m e s over o v e r that t h a t of of the t h e felsic f e l s i c flows f l o w s in i n the t h e area. area. enriched L i t h i c fragments f r a g m e n t s up to t o lapilli l a p i l l i size s i z e are a r e common common and confirm c o n f i r m the the Lithic pyroclastic p y r o c l a s t i c origin o r i g i n of of the t h e tuffs. tuffs. P r e v i o u s l y , most of these t h e s e and Previously, most of o ther p o r p h y r y i t i c pyroclastic p y r o c l a s t i c rocks r o c k s of of the t h e area a r e a had been been mapped mapped other porphyryitic as a s felsic f e l s i c intrusives. intrusives. (Sage, in i n press) press) (Sage, The wavy bedding of of the t h e tuffs t u f f s visible v i s i b l e along a l o n g the t h e road r o a d dips dips gently g e n t l y away away from from the t h e Jubilee J u b i l e e Stock. Stock. t u f f s also a l s o are a r e mapped mapped as as The tuffs t o the t h e stock s t o c k and and are a r e interpreted i n t e r p r e t e d to t o be the t h e re-worked re-worked conformable to p y r o c l a s t i c products p r o d u c t s of of the t h e emplacement emplacement of of the t h e stock. stock. pyroclastic Elsewhere iin n tthe h e vicinity v i c i n i t y of of the t h e stock s t o c k polymictic p o l y m i c t i c tuff t u f f breccias b r e c c i a s are a r e more more common. common. (Sage, et 1982; Sage, (Sage, e t al., a l . , 1982; Sage, in i n press) press ) STOP STOP 3: 3: CITADEL MINE CITADEL -- South on the t h e Surluga S u r l u g a Road, Road, 1 km from iits t s Intersection Intersection with w i t h Highway Highway 101 1 0 1 -- (Fig. ( F i g . 3 The Citadel 3) was developed developed on seven C i t a d eMine l Mine ) was s e v e n levels l e v e l s to t o aa depth 687 d e p t h of of 950 950 feet f e e t in i n the t h e late l a t e 1960s 1960s and and produced produced 1,1 , 6 8 7 ounces ounces of of gold g o l d and 43 43 ounces ounces of of silver s i l v e r in i n 1968. 1968. Re-evaluation R e - e v a l u a t i o n and exploration exploration since 500 ttons of pproven s i n c e 1987 1987 has h a s yielded y i e l d e d 358, 358, 500 o n s of r o v e n and probable p r o b a b l e ore ore reserves r e s e r v e s with w i t h aa grade g r a d eofof0.0.215 215 oz. oz. Au/ton. 000 An additional a d d i t i o n a l 150, 150,000 tons Au/ton aalso have been been t o n s of of possible p o s s i b l e reserves r e s e r v e s grading g r a d i n g 0. 0. 23 2 3 oz. oz. Au/ton l s o have outlined. outlined. ((Citadel C i t a d e l Gold Gold Mines Mines Inc. Inc. , 1988 1988 Annual Report) Report) , During 1989, 1989, Citadel C i t a d e l Gold Mines Mines Inc. I n c . continued c o n t i n u e d underground operations o p e r a t i o n s tto o sample and to t o assess a s s e s s the t h e quality q u a l i t y and mineability m i n e a b i l i t y of of ore o r e reserves r e s e r v e s in i n the t h e Jubilee J u b i l e e shear s h e a r zone. zone. This T h i s work terminated t e r m i n a t e d in in September 1989 1989 and tthe h e recalculation r e c a l c u l a t i o n of of reserves r e s e r v e s is i s in i n progress. progress. �10Dm (Modified from Citadel Gold Mines nc) Figure 3. Citadel Mine Exploration and Development - Jubilee and Minto Mines Development. lOOft 0 —H--- Minto Mine (past producer) Citadel Mine (under development) �- 1111 - — Also A l s o in i n 1989, 1989, a a six s i x month long l o n g test t e s t milling m i l l i n g program p r o g r a m processed processed 5 7 , 9956 56 t o n s oof f oore r e aand n d pproduced r o d u c e d 4737 4 7 3 7 Troy T r o y ounces o u n c e s of o f gold. gold. 57, tons The ore o r e zones z o n e s occur o c c u r within w i t h i n the t h e northeast n o r t h e a s t (0200) ( 0 2 0 ) trending trending JJubilee u b i l e e shear s h e a r zone. zone. ssouth. outh. They dip d i p 30° 30 to t o 40° 40 east e a s t and a n d plunge p l u n g e to t o the the The surface s u r f a c e projection p r o j e c t i o n of o f the t h e mineralization m i n e r a l i z a t i o n within w i t h i n the the i s 1800 1800 feet f e e t long l o n g and a n d 200 200 to t o 300 300 feet f e e t wide. wide. JJubilee u b i l e e shear s h e a r is Gold is finely d i s e m m i n a t e d in i n pods p o d s and a n d lenses l e n s e s of o f quartz q u a r t z within within is finely disemminated s e g m e n t s of o f the t h e shear s h e a r zone, zone, within w i t h i n the t h e Jubilee J u b i l e e Stock. Stock. segments Ore a p p e a r s to t o be b e further f u r t h e r restricted r e s t r i c t e d to t o areas a r e a s of o f carbonatized c a r b o n a t i z e d and and appears l o c a l l y silicified s i l i c i f i e d sericite s e r i c i t e and a n d chlorite c h l o r i t e schists s c h i s t s within w i t h i n the the locally w i l l provide p r o v i d e an a n overview o v e r v i e w of o f the the J u b i l e e Stock. S t o c k . Citadel C i t a d e l geologists g e o l o g i s t s will Jubilee ccurrent u r r e n t exploration e x p l o r a t i o n and a n d development d e v e l o p m e n t plan p l a n for f o r the t h e property. property. The Minto M i n t o and a n d Jubilee J u b i l e e mines mines and a n d the t h e newly newly developed d e v e l o p e d Old O l dTom' Tom1ss Zone a re p r o g r e s s i v e l y deeper d e e p e r extensions e x t e n s i o n s of o f a south s o u t h plunging p l u n g i n g zone zone Zone are progressively o f m i n e r a l i z a t i o n (Fig. ( F i g . 33). ). of mineralization a n d Jubilee J u b i l e e mines together together The Minto and p r o d u c e d 37, 37, 6678 7 8 oounces u n c e s oof f g o l d and a n d 1, 1, 123 u n c e s oof f ssilver i l v e r bbetween etween produced gold 123 oounces 1929 and a n d 1944. 1944. STOP 4: STOP 4: JUBILEE SHEAR JUBILEE SHEAR (OLD (OLD TOM' TOM' S ZONE) ZONE) - - East E a s t side s i d e of o f South S o u t h end e n d of o f Jubilee J u b i l e e Lake, Lake, on o n lower lower Hillside, H i l l s i d e , 20 2 0 m North N o r t h of o f South S o u t h end e n d of o f llake, a k e , Surluga Surluga Road follows f o l l o w s West Shore S h o r e of o f Jubilee J u b i l e e Lake Lake -- The south s o u t h end e n d of o f Jubilee J u b i l e e Lake provides p r o v i d e s an a n excellent e x c e l l e n t perspective perspective on tthe h e eroded e r o d e d lineament l i n e a m e n t that t h a t forms forms the t h e surface s u r f a c e expression e x p r e s s i o n of o f the the JJubilee u b i l e e shear s h e a r zone. zone. An abandoned decline d e c l i n e of o f unknown depth depth meters), on tthe ((exceeding e x c e e d i n g ttwenty wenty m e t e r s ) , aand n d aage, g e , on h e ssoutheast o u t h e a s t sside i d e of of Jubilee J u b i l e e Lake was the t h e site s i t e of o f early e a r l y mining m i n i n g of of a a quartz q u a r t z lens l e n s within within �- 12 12 —- — the the Jubilee J u b i l e e shear. shear. The site s i t e provides p r o v i d e s aa good good introduction i n t r o d u c t i o n to t o the t h e character c h a r a c t e r of of the the The quartz q u a r t z veins v e i n s that t h a t are a r e typical t y p i c a l of of the t h e Wawa Wawaarea. area. F e a t u r e s to t o note note Features are a r e the t h e sharp s h a r p contacts c o n t a c t s of of the t h e veins v e i n s and and host h o s t rock, r o c k , reverse reverse fault fault movement indicators, i n d i c a t o r s , the t h e fine f i n e to t o medium medium grained, g r a i n e d , recrystallized recrystallized movement form form of of the t h e quartz, q u a r t z , the t h e general g e n e r a l scarcity s c a r c i t y of of suiphides, s u l p h i d e s , rare rare visible v i s i b l e gold g o l d on on intergrain i n t e r g r a i n boundaries b o u n d a r i e s and and adjacent ad-j a c e n t to t o suiphides, sulphides, and the t h e unusual u n u s u a l odour odour released r e l e a s e d on on breakage b r e a k a g e of of the t h e quartz. quartz. and The The l a t t e r appears a p p e a r s to t o be be characteristic c h a r a c t e r i s t i c of of gold g o l d bearing b e a r i n g quartz q u a r t z veins veins latter in i n the t h e area a r e a and and consists c o n s i s t s of of aa pungent pungent garlic g a r l i c odour, odour, possibly p o s s i b l y aa m e r c a p t a n or o r another a n o t h e r gas gas from from inclusions i n c l u s i o n s in i n the t h e quartz. quartz. mercaptan Recent Recent surface s u r f a c e prospecting p r o s p e c t i n g and and channel c h a n n e l sampling s a m p l i n g of of the t h e vein vein in i n the t h e vicinity v i c i n i t y of of the t h e decline d e c l i n ehas hasyielded y i e l d e dupuptot o0.0. 65 65 oz. oz. Au/ton Au/ton over o v e r aa width w i d t h of o f five f i v e feet. feet. The average a v e r a g e assay a s s a y result r e s u l twas was0.0.26 26 The oz. Au/ton. 02. Au/ton. The The vein v e i n strikes s t r i k e s 0200 020Âand and dips d i p s 37° 37' southeast. southeast. C i t a d e l Gold Gold Citadel Mines Mines Inc. I n c . has has identified i d e n t i f i e d the t h e vein v e i n underground underground as a s part p a r t of of the t h e Old Old Tom' Zone, tthe Tom'ss Zone, h e aapparent p p a r e n t down-plunge down-plunge extension e x t e n s i o n of of the t h e Jubilee Jubilee Mine Mine orebody orebody (Fig. ( F i g . 3). 3). STOP STOP5:5: PARKHILL PARKHILL MINE M I N E (PAST (PASTPRODUCER) PRODUCER) - Mine Mine Gate Gate is i s on on West West side s i d e of of Surluga S u r l u g aRoad, Road, of of Citadel C i t a d e l Mine Mine -- - km South South 44 km The The Parkhill P a r k h i l l Mine Mine was was the t h e largest l a r g e s t gold g o l d producer p r o d u c e r in i nthe t h eWawa Wawaarea. area. It I t produced produced aa total t o t a l of of 54,301 5 4 , 301 ounces ounces of of gold g o l d and and 2,896 2, 896 ounces ounces of of silver s i l v e r from from 125, 125, 778 ttons o n s of of ore o r e milled, m i l l e d , yielding y i e l d i n g an a n average a v e r a g e grade grade of 0. 4 3 2 oz.Au/ton. oz. Au/ton. of 0.432 The The earliest e a r l i e s t production p r o d u c t i o n reported r e p o r t e d was was 16.8 16. 8 �13 — - 13 — oz. o of f gold g o l d from from 99 tons t o n s of of ore o r e in i n 1904. 1904. Mining stopped s t o p p e d until until 1929 and then t h e n resumed resumed from from 1931 1931 through t h r o u g h 1938. 1938. P r o d u c t i o n peaked Production iin n 1935 1935 with w i t h 9, 9, 618. 618. 77 ounces e c o v e r e d from from 20, 20, 871 o n s milled. milled. ounces rrecovered 871 ttons S u r f a c e clean-up c l e a n - u p from from 1940 1940 to t o 1944 1944 yielded y i e l d e d additional a d d i t i o n a l gold. gold. Surface Mine development ) iincluded n c l u d e d 14 llevels e v e l s to to a a vertical vertical development (Fig. ( F i g . 44) depth d e p t h of o f 1,1,244 2 4 4 ft. f t .,, 30, 000 ft. 30,000 f t . of of drifting, drifting, cutting, c u t t i n g , and and 5,000 5 , 0 0 0 ft. f t . of raises. raises. fft. t. inclined i n c l i n e d shaft. shaft. 4 , 000 ft. 4, 000 ft. of cross of cross Access of a 1,877 1, 877 Access was was by way of Extensive E x t e n s i v e development in i n this t h i s style s t y l e was was ttypical y p i c a l of o f the t h e narrow-vein n a r r o w - v e i n gold g o l d mines mines of of that t h a t era. era. The property property remained r e m a i n e d dormant until u n t i l Dunraine Dunraine Mines Mines Ltd. Ltd. began a a modern modern surface surface and underground u n d e r g r o u n d exploration e x p l o r a t i o n program program in i n 1980. 1980. The main gold-bearing g o l d - b e a r i n g quartz q u a r t z veins v e i n s are a r e a series s e r i e s of of quartz quartz lenses l e n s e s of o f short s h o r t strike s t r i k e length l e n g t h (up ( u p to t o 125 125 feet) f e e t ) and and more more extensive extensive down dip d i p dimension, d i m e n s i o n , approximately a p p r o x i m a t e l yin i nthe t h eratio r a t i oofof1:1:4. 4. The quartz width q u a r t z llenses e n s e s have an a n average average w i d t h of of two feet f e e t and a maximum maximum width w i d t h of o f six s i x feet. feet. occupy a zone of of iintense They occupy a zone n t e n s e schistosity schistosity 0 0 0 that t h a t strikes s t r i k e s 090 0 9 0 and dips d i p s 30 3 0 tto o 48 4 8 to t o the t h e south, s o u t h , crosscutting crosscutting metavolcanic m e t a v o l c a n i c and and metasedimentary m e t a s e d i m e n t a r y host h o s t rocks r o c k s that t h a t strike s t r i k e 0500 050 tto o 070°. 0 70. The h o s t rocks r o c k s are a r e Jubilee J u b i l e e Tuff Tuff and a polymictic p o l y m i c t i c volcanic volcanic host breccia b r e c c i a in i n the t h e vicinity v i c i n i t y of of the t h e Jubilee J u b i l e e Stock S t o c k (Sage, (Sage, in i n press). press). Goldun Age Resources R e s o u r c e s entered e n t e r e d a joint j o i n t venture v e n t u r e in i n 1986 1986 with with Dunraine D u n r a i n e Mines Mines Ltd. Ltd. and completed an a n extensive e x t e n s i v e evaluation e v a l u a t i o n of of the the underground workings to u n d e r g r o u n d workings t o the t h e 7th 7 t h level l e v e l to t o test t e s t a proposed p r o p o s e d model model of of paleoplacer p a l e o p l a c e r gold g o l d concentration c o n c e n t r a t i o n and and to t o test t e s t the t h e potential p o t e n t i a l for f o r gold gold rrecovery e c o v e r y by stope/drift s t o p e / d r i f t washing washing and and tailings t a i l i n g s processing. processing. ttest e s t yielded y i e l d e d ore. ore. Neither N either The program iincluded n c l u d e d more tthan h a n 13,000 1 3 , 0 0 0 feet f e e t of of underground u n d e r g r o u n d diamond diamond drilling. drilling. �It, C. -, (I) C, 0 CD :IJcc CD (I) C CD a CD (I) a 0 -' Shaft, drift, and slope dimensions exaggerated for clarity (0 • ' a (Dunraine Mines Ltd. 198 1 Annual Report) :3 :3 CD 0 2 CD CD () (0 CD :3- CD C (C -fl Figure 4. Parkhill Mine - 1938 Development Plan �- 15 15 - — — Subsurface S u b s u r f a c e geology observed o b s e r v e d by by the t h e author a u t h o r to t o the t h e 3rd 3 r d level level and reported E. r e p o r t e d on on the t h e 7th 7 t hlevel l e v e lbybyJ.J.E. communication, communication, T i l l s l e y (personal (personal Tillsley s dominated by a massive, massive, fine f i n e grained grained 1987) iis t u f f , that t h a t is i s devoid d e v o i d of of sedimentary s e d i m e n t a r y structure, s t r u c t u r e , and and is is tuff, s t r a t i g r a p h i c a l l y below below massive massive to t o pillowed p i l l o w e d mafic m a f i c flows. flows. stratigraphically A A f r a g m e n t a l unit, u n i t , consisting c o n s i s t i n g of of coarse c o a r s e lapilli l a p i l l i to t o bomb bomb sizes, sizes, fragmental occurs o c c u r s at a t the t h e east e a s t end end of of the t h e mine. mine. t r a n s i t i o n of of clast c l a s t shape shape A transition to t o a flattening f l a t t e n i n g fabric f a b r i c marks marks aa high h i g h strain s t r a i n area, a r e a , possibly p o s s i b l y aa shear shear Lamprophyre of vvarious Lamprophyre d dikes i k e s of a r i o u s attitudes a t t i t u d e sare a rcommon. e common. This T h i s exploration e x p l o r a t i o n program program concluded concluded tthat h a t no no mineable mineable ore ore zone. zone. remains remains it. it. above the t h e 14th 1 4 t h level, l e v e l , although a l t h o u g h ore o r e potential p o t e n t i a l exists e x i s t sbelow below The quartz q u a r t z veins v e i n s were were well w e l l explored e x p l o r e d and and completely c o m p l e t e l y mined mined by by previous p r e v i o u s workers, w o r k e r s , leaving l e a v i n g only o n l y minor minor ppillars. illars. concluded concluded The program lso The program aalso that t h a t the t h e gold g o l d recovery r e c o v e r y potential p o t e n t i a l from from subsurface s u b s u r f a c e clean— clean- up is i s minor minor due due to t o low low volume. volume. Sampling the t h e surface s u r f a c e muck muck piles piles and tailings t a i l i n g s yielded y i e l d e d an a n average a v e r a g e of of 0.01 0. 0 1 oz.Au/ton oz. Au/ton and and aa maximum maximum of of 0.025 0. 025 oz.Au/ton. oz. Au/ton. The original o r i g i n a l fieldtrip f i e l d t r i p examined examined two two outcrops o u t c r o p s of of metagreywacke metagreywacke (water—laid ( w a t e r - l a i d ttuff?) u f f ? ) that t h a t contain c o n t a i n truncated t r u n c a t e d bedding bedding and and minor minor crossbedding. crossbedding. Recent overburden o v e r b u r d e n stripping s t r i p p i n g reveals r e v e a l s these t h e s e rocks r o c k s to to be clastic c l a s t i c metasediments or o r crystal c r y s t a l tuffs t u f f s interbedded i n t e r b e d d e d with with coarser c o a r s e r tuff t u f f breccias b r e c c i a s and and massive massive crystal c r y s t a l and and lapilli l a p i l l i tuffs. tuffs. The The gold g o l d bearing b e a r i n g silicified s i l i c i f i e d zone zone strikes s t r i k e s east, e a s t , transecting t r a n s e c t i n g the the subvertically s u b v e r t i c a l l y dipping d i p p i n g pyroclastic p y r o c l a s t i c rocks r o c k s at a t aa low low angle. angle. A late late lamprophyre dike d i k e occupies o c c u p i e s the t h e centre c e n t r e of of the t h e shear s h e a r zone zone and and has has aa fenitized f e n i t i z e d alteration a l t e r a t i o n halo h a l o parallel p a r a l l e l to t o it. it. The The zone zone of of alteration alteration consists c o n s i s t s of of replacement r e p l a c e m e n t of of quartz q u a r t z by by aa blue b l u e sodic s o d i c iron i r o n amphibole amphibole �- 16 16 —- — ( x - r a y diffraction d i f f r a c t i o nidentification identification Sage, personal personal bybyR.R.P.P. Sage, (x-ray communication, communication, STOP 6: 6: STOP I988 ) 1988). . MONK DEFORMATION DEFORMATION ZONE ZONE MONK - - Stripped Stripped Area 10 10 mm West West of of Monk Monk Access Access Road, Road, 0. 0 . 55 km km Area South of of Access Access Road Road Intersection I n t e r s e c t i o n with w i t h High High Falls F a l l s Road Road -South O b s e r v a t i o n s in i n the t h e vicinity v i c i n i t y of o f the t h e Monk Monk Prospect P r o s p e c t (see ( s e e Stop S t o p 7) 7) Observations and several s e v e r a l other o t h e r less l e s s developed d e v e l o p e d prospects p r o s p e c t s suggest s u g g e s t that t h a t the t h e area area and i s part p a r t of of aa wide wide zone zone of of highly h i g h l y strained s t r a i n e d metavolcanic m e t a v o l c a n i c rocks, rocks, is The The Monk Monk zone zone has has here h e r e named named the t h e Monk Monk deformation d e f o r m a t i o n zone zone (Fig. ( F i g . 5). 5). aa minimum minimum width w i d t h of of one one kilometre k i l o m e t r e and and aa strike s t r i k e length l e n g t h of of over over Its I t s strike s t r i k e varies v a r i e s slightly s l i g h t l y but b u t is i s consistently consistently t h r e e kilometers. kilometers. three a b o u t 1400 140 and and its i t s dip d i p is i s vertical. vertical. about The The deformation d e f o r m a t i o n zone zone will will be be examined examined at a t this t h i s site s i t e in i n order o r d e r to t o compare compare its i t s features f e a t u r e s here, h e r e , aa barren b a r r e n prospect, p r o s p e c t , with w i t h those t h o s e at a t the t h e Monk Monk Prospect, P r o s p e c t , a gold g o l d occurrence. occurrence. The deformation d e f o r m a t i o n zone zone as a s viewed viewed at a t this t h i s stop s t o p is i s characterized characterized by intensely i n t e n s e l y flattened f l a t t e n e d breccia b r e c c i a fragments fragments of of quartz q u a r t z feldspar feldspar s e r i c i t e schist. schist. sericite The The abundance abundance of of sericite s e r i c i t e suggests s u g g e s t s aa felsic felsic composition c o m p o s i t i o n for f o r the t h e protolith. protolith. ratios r a t i o s from from4:4:11to t o14: 14:1. 1. The fragments f r a g m e n t s exhibit e x h i b i t flattening flattening Both the t h e fragments f r a g m e n t s and and the t h e matrix matrix contain c o n t a i n abundant abundant euhedral e u h e d r a l feldspar f e l d s p a r megacrysts, megacrysts, 1 cm cm by by 22 mm. mm. 1 Concordant Concordant with w i t h the t h e foliation f o l i a t i o n are a r e narrow narrow zones, zones, up up to t o 10 10 cm cm wide, wide, of of foliated f o l i a t e d mafic m a f i c tuff t u f f (?), (?), a c r o s s the t h e outcrop. outcrop. across continuous continuous for f o r their t h e i r strike s t r i k e length length The tectonic t e c t o n i c preservation p r e s e r v a t i o n of of such such ustratigraphy?t " s t r a t i g r a p h y " iis s cconsistent o n s i s t e n t throughout t h r o u g h o u t the t h e deformation d e f o r m a t i o n zone. zone. Remnants of of prep r e - or o r syn-deformation s y n - d e f o r m a t i o n quartz q u a r t z veining v e i n i n g are are recorded r e c o r d e d by dismembered and and ptygmatically p t y g m a t i c a l l y folded f o l d e d narrow narrow vein vein �P++! g g a nite S mafic metavolcafliCS Figure 5. Monk Deformation Zone - Michipicoten River Area Gold Occurrences WAWA felsic metavolcaniCS felsic intrusive A prospect (orientation unknown) prospect (orientation known) deformation zone boundary (position approximate) past producing mine (orientation known) �- 18 18 —- — segments and and tear t e a r drop d r o p shaped s h a p e d quartz q u a r t z nodules. nodules. segments The nodules n o d u l e s have have The c u r v e d tails t a i l s or o r sigmoidal s i g m o i d a l shapes s h a p e s that t h a t indicate i n d i c a t e rotational rotational curved movement but b u t they t h e y do do not n o t provide p r o v i d e consistent c o n s i s t e n t kinematic kinematic movement information. information. Z - f o l d s up up to t o 20 20 cm cm amplitude a m p l i t u d e within w i t h i n the t h e sericite sericite Z-folds schist s c h i s t plunge p l u n g e 50° 5 0 to t o the t h e southeast. southeast. Intersection I n t e r s e c t i o n lineations l i n e a t i o n s in in t h e schist s c h i s t also a l s o plunge p l u n g e southeast s o u t h e a s t but b u t more more steeply, s t e e p l y , 70° the 7 0 to t o 75°. 75. Minor Minor quantities q u a n t i t i e s of o f suiphide s u l p h i d e mineralization m i n e r a l i z a t i o n accompany accompany some some of of t h e quartz q u a r t z veins v e i n s however however no no gold g o l d has h a s been been reported r e p o r t e d from from this t h i s part part the of the t h e deformation d e f o r m a t i o n zone. zone. of 7: STOP 7: STOP MONK PROSPECT PROSPECT MONK - - Total Total NW of of S Scott Trenches, T r e n c h e s , Stripping, S t r i p p i n g , and and Adit, A d i t , 300 3 0 0 in m NW c o t t Falls F a l l s -- production p r o d u c t i o n from from several s e v e r a l bulk-sampling b u l k - s a m p l i n g programs, programs, since s i n c e gold gold was was discovered d i s c o v e r e d on on the t h e property p r o p e r t y in i n 1936, 1936, has h a s been been less l e s s than t h a n 100 100 ounces. ounces. The last l a s t exploration e x p l o r a t i o n program program ended ended in i n 1987, 1987, and and the the property p r o p e r t y is i s currently c u r r e n t l y dormant. dormant. Gold Gold mineralization m i n e r a l i z a t i o n is i s concentrated c o n c e n t r a t e d in i n aa series s e r i e s of of en e n echelon echelon quartz q u a r t z veins v e i n s which which strike s t r i k e 050° 050' and and dip d i p 45° 45' northwest. northwest. Assays Assays from early e a r l y surface s u r f a c e and and recent r e c e n t subsurface s u b s u r f a c e sampling s a m p l i n g consistently consistently y i e l d e d 0. 0. 5 ounce g o l d per p e r ton. ton. yielded ounce gold Tonnage calculations c a l c u l a t i o n s are a r e not not available. available. The shallow-dipping, s h a l l o w - d i p p i n g , northeast-trending n o r t h e a s t - t r e n d i n g mineralized m i n e r a l i z e d veins veins transect transect a a zone zone of of weakly weakly mineralized m i n e r a l i z e d quartz-carbonate q u a r t z - c a r b o n a t e veins v e i n s (the (the "main m a i n zone") z o n e " ) that t h a t are a r e concordant c o n c o r d a n t with w i t h the t h e regional r e g i o n a l southeastsoutheasts t r i k i n g foliation. foliation. striking The The zone zone consists c o n s i s t s of of a a 33 to t o 44 m m wide section section of of vertical v e r t i c a l quartz q u a r t z veins v e i n s and and stringers, s t r i n g e r s , which which are a r e contained contained �- 19 1 9 —- — within w i t h i n aan n iintensely n t e n s e l y sericitized, s e r i c i t i z e d , carbonatized, c a r b o n a t i z e d , and silicified silicified host h o s t rock. rock. d e g r e e of of alteration a l t e r a t i o n obscures o b s c u r e s host h o s t rock rock The degree i d e n t i f i c a t i o n ; however property p r o p e r t y mapping mapping suggests s u g g e s t s an a n intermediate intermediate identification; t o mafic m a f i c volcanic v o l c a n i c assemblage. assemblage. to The "main " main zone" zone" and the t h e associated a s s o c i a t e d shallow-dipping s h a l l o w - d i p p i n g mineralized mineralized veins v e i n s occur o c c u r at a t the t h e apparent a p p a r e n t southwestern s o u t h w e s t e r n margin margin of of aa regional regional of intense i n t e n s e flattening f l a t t e n i n g strain, s t r a i n , the t h e Monk Monk deformation d e f o r m a t i o n zone zone (cf, (cf, zone of S t o p 6). 6). Stop SSTOP T O P 8: 8: CENTENNIAL STOCK - - Roadside Outcrop Hill H i l l 1 km km N of of High Falls F a l l s -1 The Centennial km The C e n t e n n i a l Stock S t o c k occupies o c c u p i e s 77 sq. sq. k m of of tthe h e northwest n o r t h w e s t corner corner of of Naveau Township and and adjacent a d j a c e n t McMurray McMurray Township Township to t o the t h e north north Fig. 1 & 5). 5). 1 Itt consists white I c o n s i s t s of of a grey g r e y to to w h i t e granodiorite g r a n o d i o r i t e to to t r o n d h j e m i t e , massive massive to t o weakly foliated f o l i a t e d and and medium medium to t o coarse coarse trondhjemite, grained. g rained. distinguished presence IIt t iis s d i s t i n g u i s h e d by the the p r e s e n c e of of grey-blue g r e y - b l u e to to opalescent o p a l e s c e n t quartz-eye q u a r t z - e y e phenocrysts p h e n o c r y s t s that t h a t are a r e up up to t o 33 mm mm diameter. diameter. On its i t s southwest s o u t h w e s t margin, margin, massive massive granodiorite g r a n o d i o r i t e grades g r a d e s into i n t o aa fine fine porphyry. grai g r a i nned e d graniti g r a n i t icc quartz q u a r t z-p1 - p lagi a g i oocl c l aas s e e porphyry. dikes d i k e s occur o c c u r within w i t h i n the t h e stock. stock. Graniti G r a n i t i c apli a p l i ttee Small xenoliths m)) of x e n o l i t h s (up ( u p to t o 0. 0. 5 m mafic m a f i c metavolcanic m e t a v o l c a n i c flows flows are a r e also a l s o common, common, but b u t not n o t abundant. abundant. Felsic xenoliths F elsic x e n o l i t h s have not n o t been observed, o b s e r v e d , even though t h o u g h the t h e stock stock iintrudes n t r u d e s felsic f e l s i c metavolcanics. metavolcanics. (Fig. (Fig. 66)) A series s e r i e s of of discrete d i s c r e t e shears s h e a r s strikes s t r i k e s southeast s o u t h e a s t (1400) (1 4 0 ) across a c r o s s the t h e stock. stock. They are wide) a r e usually u s u a l l y narrow (<10 ( < 10 cm cm w i d e ) zones of of iintensely n t e n s e l y foliated, f o l i a t e d , black b l a c k cataclastic c a t a c l a s t i c rock. rock. Quartz Q u a r t z eyes are are �'- — 7Q, / 0 V till Ii 45 2 cw 2 nI%tl \\ 'tIIflltt' 7/ p7 / 2 Qv 2 I // 70/ 60 1) / 1 OU.4P -- 80 1IN \ThIflhi rut //open cut Ov/ - 70 (l/llhJIIII1ENTENNiAL UV MINE 2 V 0 - 7/ I 100 ft. ft. /i 2 •75 'I meters rnc>lers 80 LAMPROPHYRE DIKE DIKE LAMPROPHYRE DIABASE DIKE DIKE DIABASE 2 Th\ 100 100 00 CENTENNIALSTOCK STOCK CENTENNIAL granodlortte granodiorite XENOLITHS MAFIC XENOLITHS MAFIC Shaft )iiPit -1'Trench -i-I / 2,1 2 Field Trip Stop '3 —— ——— 2 Figure 6. Centennial CentennialMine Mine - Surface Surface Geology Geology Figure (afterWAWA WAWA ASSESSMENT ASSESSMENT FILE FILE 'iVP 1985) (after WP NaveauNaveau-1.t. S.M SM. Sears, t985) �- 21 21 — - — preserved p r e s e r v e d within w i t h i n them them and and the t h e feldspars f e l d s p a r s are a r e fractured f r a c t u r e d and and Where they t h e y have have been been mapped mapped in i n the t h e Centennial C e n t e n n i a l Mine Mine stretched. stretched. area a r e a (Fig. ( F i g . 6) 6 ) they t h e y are a r e spaced s p a c e d about a b o u t 100 100 m apart a p a r t and and have have strike strike lengths l e n g t h s of o f several s e v e r a l hundred hundred meters. meters. is i s unknown. unknown. Their T h e i r sense s e n s e of of displacement displacement Quartz Q u a r t z veins v e i n s of of the t h e same same orientation o r i e n t a t i o n and and up up to t o aa metre m e t r e in i n width w i d t h occupy occupy portions p o r t i o n s of of several s e v e r a l of of the t h e shears. shears. These These veins v e i n s host h o s t the t h e known known gold g o l d mineralization m i n e r a l i z a t i o n within w i t h i n the t h e stock s t o c k (Fig. ( F i g . 55 6). && 6). The Centennial C e n t e n n i a l Stock S t o c k hosts h o s t s two two minor minor past p a s t producing p r o d u c i n g gold gold mines: mines: the t h e Norwalk Norwalk Mine, Mine) 60 ounces ounces (1904 (1904 & 1910), 1 9 1 0 ) 1 and and the the ounces of Centennial C e n t e n n i a l Mine, Mine) 510 ounces ounces of of gold g o l d and 30 ounces of silver s i l v e r from 8 6 1 2 tons t o n s of of ore o r e (1939) ( 1 9 3 9 ) (Fig. ( F i g . 55 && 6). 6). 8612 Both mines mines were shallow shallow operations o p e r a t i o n s with w i t h their t h e i r deepest d e e p e s t drifts d r i f t s at a t 200 200 feet f e e t and and 250 250 feet, feet) respectively. respectively. Historical H i s t o r i c a l information i n f o r m a t i o n on on these t h e s e operations o p e r a t i o n s is is sparse s p a r s e but b u t it i t suggests s u g g e s t s that t h a t mining mining ceased c e a s e d for f o r financial, financial) management, management) and/or a n d / o r labour l a b o u r reasons r e a s o n s rather r a t h e r than t h a n ore o r e depletion. depletion. Although A l t h o u g h the t h e shear-vein s h e a r - v e i n system s y s t e m of of the t h e Centennial C e n t e n n i a l Stock S t o c k has has yielded significant quantities of gold, it is analogous in n o t y i e l d e d s i g n i f i c a n t q u a n t i t i e s of g o l d ) i t i s a n a l o g o u s i n not many many r respects e s p e c t s tto o the t h e mineralization m i n e r a l i z a t i o n at a tthe t h eMagino Magino Mine, MineI in in production production near n e a r Goudreau Goudreau since s i n c e 1988. 1988. The most noteable noteable difference, d i f f e r e n c e ) in i n addition a d d i t i o n to t o gold g o l d content, c o n t e n t ) is i s the t h e absence a b s e n c e of of The Maginoo ore The Magino r e iis s within within siliceous thet hWebb s i l i c e o u s zones zones and and veins v e i n s of ofthe t h esheared s h e a r e dportion p o r t i o nofof e WebbLake Lake byssericite i t is i s accompanied accompanied by e r i c i t e and and t r o n d h j e m i t e stock s t o c k and and it trondhjemite a l t e r a t i o n in i n the t h e Centennial C e n t e n n i a l Stock. Stock. alteration potassium potassium feldspar f e l d s p a r alteration. alteration. �- — STOP 9: STOP 9: 2222 — - BRIDGET LAKE STOCK & IIRON R O N FORMATION - - Rock C u t and a n d Surface S u r f a c e Stripping, S t r i p p i n y , SE SE Side S i d e of o f Highway Highway 17, 17, Cut 112 2 kkm m S o u t h of o f Turnoff T u r n o f f to t o Wawa Wawa -South This T h i s stop s t o p displays d i s p l a y s the t h e character c h a r a c t e r of o f the t h e Bridget B r i d g e t Lake Stock S t o c k and and i t s unusual u n u s u a l intrusive i n t r u s i v e relationship r e l a t i o n s h i p with with a a magnetite-chert m a g n e t i t e - c h e r t iron iron its fformation o r m a t i o n and a n d mafic m a f i c flows. flows. IIt t iis s aalso l s o tthe he s ite o f a a high h i g h grade grade site of g old o c c u r r e n c e l related r e l a t e d to t o shearing s h e a r i n g within w i t h i n the t h e iron i r o n formation. formation. gold occurrence, The Bridget B r i d g e t Lake Stock S t o c k is i s a quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y that t h a t has has aa ssurface u r f a c e expression e x p r e s s i o n of o f about a b o u t 22 sq. sq. km. km. I t outcrops o u t c r o p s about about 6 6 km km It s o u t h of o f the t h e mouth mouth of o f the t h e Michipicoten M i c h i p i c o t e n River R i v e r (Fig. ( F i g . 1). 1). south Its Its c o m p o s i t i o n l texture t e x t u r e and a n d intrusive i n t r u s i v e relationships r e l a t i o n s h i p s here h e r e and a n d at a t the the composition, next n e x t stop s t o p suggest s u g g e s t that t h a t it i t is i s aa high h i g h level, l e v e l ) subvolcanic s u b v o l c a n i c intrusive. intrusive. The stock s t o c k consists c o n s i s t s of o f aa medium medium grained g r a i n e d feldspar f e l d s p a r porphyry p o r p h y r y with with minor m i n o r blue b l u e quartz q u a r t z eyes. eyes. The feldspar f e l d s p a r phenocrysts p h e n o c r y s t s are a r e white white andesine 1 cm in a n d e s i n e laths, l a t h s ) subhedral s u b h e d r a l to t o euhedral e u h e d r a l and a n d up to to 1 i n length, length) in i n a fine f i n e grained g r a i n e d ground g r o u n d mass mass of o f quartz q u a r t z and a n d feldspar f e l d s p a r and a n d minor minor amounts of o f chlorite, c h l o r i t e l calcite, c a l c i t e ) sericite, s e r i c i t e ) and a n d sphene. sphene. phenocrysts p h e n o c r y s t s are a r e anhedral a n h e d r a l and a n d clear. clear. The quartz quartz The porphyry p o r p h y r y texture t e x t u r e is is generally g e n e r a l l y massive m a s s i v e except e x c e p t where it i t is i s strongly s t r o n g l y foliated f o l i a t e d in i n local local sshear h e a r zones. zones. (Massey, (Massey) 1985) 1985 1 The iron i r o n formation f o r m a t i o n consists c o n s i s t s of o f alternating a l t e r n a t i n g layers l a y e r s of o f chert chert and a n d magnetite m a g n e t i t e in i n thicknesses t h i c k n e s s e s that t h a t vary v a r y from from 11 mm mm to t o 5-10 5-10 cm, cmJ aand nd up to t o >30 > 3 0 cm cm for f o r some some•chert c h e r t layers. layers. ffrom r o m 20% 20% to t o 70%. 70%. The magnetite m a g n e t i t e content c o n t e n t varies varies Grunerite as of G r u n e r i t e occurs occurs a s sspheroids pheroids o f radiating radiating ffibres i b r e s in i n some chert-magnetite c h e r t - m a g n e t i t e laminae. laminae. The iron i r o n formation f o r m a t i o n layering l a y e r i n g is i s commonly commonly contorted c o n t o r t e d into into �— - 23 23 — - complex flow(?)-folding  £ l o w ( ?- f o l d i n g or o r planar p l a n a r disruptions. disruptions. IIt t iis s concordant concordant and a n d interfolded i n t e r f o l d e d with w i t h a massive m a s s i v e mafic m a f i c flow f l o w at a t the t h e northeast n o r t h e a s t end e n d of of tthe h e roadcut. roadcut. t llies i e s ssubhorizontally u b h o r i z o n t a l l y on o n the t h e upper upper F u r t h e r ssouth o u t h iit Further surface s u r f a c e of o f the t h e porphyry. porphyry. o r p h y r y discordantly d i s c o r d a n t l y intrudes i n t r u d e s the the The p porphyry mafic m a f i c flow f l o w but b u t does d o e s not n o t display d i s p l a y a clearly c l e a r l y intrusive i n t r u s i v e contact c o n t a c t with with the t h e overlying o v e r l y i n g folded f o l d e d iron i r o n formation. formation. Coarse C o a r s e ggrained r a i n e d visible v i s i b l e gold g o l dwas was exposed e x p o s e d in i n 1981 1981 by by trenching trenching adjacent 30 mmssoutheast a d j a c e n t to t o aa pit p i of t ounknown f unknown vintage, v i n t a g e , 30 o u t h e a s t oof f the the highway. The gold g o l d occurs o c c u r s in i n aa vertical v e r t i c a l bed bed of o f sheared, sheared, rrecrystallized e c r y s t a l l i z e d chert. chert. The shear s h e a r zone z o n e is is a a few few centimeters c e n t i m e t e r s wide wide where it aand n d iis s ttraceable r a c e a b l e to t o the t h e vertical v e r t i c a l roadcut r o a d c u t where i t is i s exposed e x p o s e d in in the t h e underlying u n d e r l y i n g porphyry p o r p h y r y as a s aa zone zone of o f intense i n t e n s e foliation, f o l i a t i o n , without without ssilicification i l i c i f i c a t i o n or o r any a n y gold g o l d mineralization. mineralization. RANSON MINE RANSON M I N E (PAST (PAST PRODUCER) PRODUCER) STOP STOP 10: 10: -- km Bush Bush Roadf Road, Accesa Access Road Road B Begins End of 1. 1. 6 6km e g i n s aatt NW South Side S i d e of of Highway Highway 17, 17/ 11 kkm m S o u t h of o f Turnoff T u r n o f f to t o Wawa Wawa -- The Ranson Ranson Mine Mine (Fig. ( F i g . 7) 7 ) consisted c o n s i s t e d of of aa 200 2 0 0 ft. f t . adit a d i t along a l o n g the t h e HH vein v e i n and a n d aa stope s t o p e raise r a i s e to t o surface. surface. All A l l development d e v e l o p m e n t work and and mining m i n i n g occurred o c c u r r e d during d u r i n g aa few few months months in i n 1939. 1939. An on on site s i t e mill m i l l processed p r o c e s s e d 774 774 tons t o n s of o f ore o r e and a n d recovered r e c o v e r e d 156 156 ounces o u n c e s of o f gold g o l d for for a a grade g r a d e of o f 0.0. 20 20 oz. 02. /ton. /ton. The property p r o p e r t y was dormant d o r m a n t until u n t i l acquired a c q u i r e d by Bridget B r i d g e t Lake Lake Resources R e s o u r c e s in i n 1982. 1982. The company built b u i l t an a n access a c c e s s road r o a d and and prospected p r o s p e c t e d the t h e vein v e i n systems s y s t e m s known known from from early e a r l y records. records. Visible Visible gold was d discovered g o l d was i s c o v e r e d on o n the t h e E vein v e i n and a n d several s e v e r a l ounces o u n c e s recovered recovered from mill. f r o m hand h a n d cobbed c o b b e d samples s a m i l e s with w i t h the t h e use u s e of o f aa portable p o r t a b l e mill. In In �l/ /2 I / I / 2; 2/ / GABBRO F / •2m / —— \ dsz I \lOcm 20-30cm / \\EVf JIN '.23 B.VEIN,toocm / 0Ocm I C-VEIN / / / / m I' I / / 80cm 80co lS0c/ / / / ' // 1 --_ ,.. QFP' /0 V El raIse 30cm / I-. / -• vein I I / / GAB8RO aim —._ - ---i F/ / (WAWA ASSESSMENr FItE WPIabao 10 FinNeth Eioio,ation Inc, 3 LuLes 198?) / H VEIN Figure 7. m H.vElN;cH Ouaitz rekispar Porphyry iron Formation / /: GABERO P GEOLOGY & VEIN WIDTHS / 1L /OFF A / / I BRlDTL PESOUES INC veflohithis / MhCROGA8BAO / ?aocm IF QFP / T..1 "!jocm / F VEIN with —— '— \AICROGABBRO ero ma / 2/ () I / / MICROGAa ./ a S .-.. --.r / I / / / ' p GABORO ICROG8BR9 QFP I &I 2/ / 'MEDtUM GRAINED / GAB8RO / / '. I / / / / / ". / / / OFF / / / ".. _..f / // /'' 1-a-Si -. �— - 25 25 —- addition, a ddition, a b o u t 35 ounces were recovered r e c o v e r e d from 188 188 tons t o n s test test about milled m i l l e d by by Pamour Pamour Mines Mines Ltd. Ltd. in i n Timmins. Timmins. The veins v e i n s are a r e hosted h o s t e d by the t h e Bridget B r i d g e t Lake Stock S t o c k quartz quartz ffeldspar e l d s p a r porphyry p o r p h y r y and and gabbro g a b b r o (Fig. ( F i g . 7). 7). two stocks: stocks: o r p h y r y is i s mapped mapped as as The p porphyry a e s t e r n body of o f grey, grey, h e t e r o g e n e o u s quartz q u a r t z feldspar feldspar a w western heterogeneous porphyry p o r p h y r y that t h a t contains c o n t a i n s late l a t e phase p h a s e segregations s e g r e g a t i o n s of of finer f i n e r grained grained granite g r a n i t e and xenoliths x e n o l i t h s of of mafic m a f i c and felsic f e l s i c composition; c o m p o s i t i o n ; and and an an eastern e a s t e r n iintrusion n t r u s i o n of of similar s i m i l a r composition c o m p o s i t i o n but b u t homogeneous homogeneous and and xenolith x e n o l i t h free. free. Both porphyry p o r p h y r y stocks s t o c k s are a r e intruded i n t r u d e d by by gabbro. gabbro. The gabbro gabbro v a r i e s from a coarse c o a r s e grained g r a i n e d plagioclase-pyroxene p l a g i o c l a s e - p y r o x e n e rock r o c k to t o an an varies aphanitic, a p h a n i t i c , phenocryst p h e n o c r y s t free f r e e micrograbbro m i c r o g r a b b r o in i n chilled c h i l l e d margins near near tthe h e porphyry p o r p h y r y stocks. stocks. eastern porphyry has The e astern p o r p h y r y sstock tock h a s been intruded i n t r u d e d by numerous numerous veins v e i n s and and dikes d i k e s of of microgabbro. microgabbro. Banded chert-magnetite occurs Banded c h e r t - m a g n e t i t e iron i r o n formation formation o c c u r s along a l o n g the the northern n o r t h e r n contact c o n t a c t of of the t h e quartz q u a r t z feldspar f e l d s p a r porphyry p o r p h y r y and and along a l o n g the the margins oof gabbro andddikes within s o u t h e r n margins f g a b b r o vveins e i n s and ikes w i t h i n tthe h e eastern eastern southern p o r p h y r y stock. stock. porphyry Contacts C o n t a c t s between the t h e iron i r o n formation f o r m a t i o n and the the gabbro g a b b r o are a r e reactive r e a c t i v e and and commonly commonly show brecciation b r e c c i a t i o n of of the the magnetite m a g n e t i t e layers l a y e r s by by silica s i l i c a remobilized r e m o b i l i z e d from from the t h e cherty c h e r t y beds. beds. Chioritic C h l o r i t i c alteration a l t e r a t i o n of of the t h e porphyry p o r p h y r y is i s common common and and extensive extensive adjacent a d j a c e n t to t o the t h e gabbro g a b b r o veins v e i n s and and dikes. dikes. Carbonate C a r b o n a t e alteration a l t e r a t i o n of of the t h e host h o s t is i s pervasive p e r v a s i v e within w i t h i n the t h e auriferous a u r i f e r o u s veins. veins. Sericite S e r i c i t e is is aalso l s o abundant a b u n d a n t as a s aa coating c o a t i n g on on minor minor slip s l i p planes. planes. A penetrative 1 0 5 and and dips d i p s 80° 8 0 SW, SW, p e n e t r a t i v e cleavage c l e a v a g e strikes s t r i k e s 105° paralleling p a r a l l e l i n g the t h e gabbro-iron g a b b r o - i r o n formation f o r m a t i o n contact. contact. 0 0 0 SW, quartz q u a r t z veins v e i n s strike s t r i k e 100 100" to t o 110 110" and dip d i p 80 80" S W, Shear S h e a r zone hosted hosted �— 2266 - -— cconcordant o n c o r d a n t with w i t h the t h e trend t r e n d of of the t h e shear s h e a r zone. zone. s h e a r zone zone is is The shear 70 tto o 80 meters m e t e r s wide and and has has aa dextral d e x t r a l sense s e n s e of of motion. motion. quartz vein property The q uartz v e i n systems s y s t e m s of of the the p r o p e r t y have a minimum and an a n average a v e r a g e width w i d t h of of one one a g g r e g a t e strike s t r i k e length l e n g t h of of 1000 1000 m and aggregate meter. Two meter m e t e r widths w i d t h s are a r e common common at a t depth. depth. alteration a l t e r a t i o n is i s minimal minimal to t o absent. absent. rock Wall rock Where p r e s e n t it i t is i s sericitic sericitic present in i n the t h e quartz q u a r t z feldspar f e l d s p a r porpyhry porpyhry and and chioritic c h l o r i t i c in i n the t h e gabbro. gabbro. The The veins v e i n s occupy shear s h e a r fractures f r a c t u r e s and and many many display d i s p l a y crack-seal c r a c k - s e a l zones zones to to 15 cm wide, wide, ssuggesting 1 5 cm u g g e s t i n g multiple m u l t i p l e episodes e p i s o d e s of of hydraulic h y d r a u l i c emplacement. emplacement. Exploration E x p l o r a t i o n to t o date d a t e suggests s u g g e s t s the t h e presence p r e s e n c e of of possible possible reserves, r e s e r v e s , near-surface, n e a r - s u r f a c e , of of 10,000 10, 000 to t o 30,000 30,000 tons t o n s from from the t h e D, D, and H veins v e i n s with w i t h an a n average a v e r a g e grade g r a d e 0. 0. 2 2 to t o 0. 0. 6 6 oz. oz.Au/ton. Au/ton. E, E, Large samples from tthese vein samples from h e s e vveins e i n s and and tthe he C C v e i n have have ddefined e f i n e d tthe h e gold g o l d as as fine f i n e grained, g r a i n e d , non-uniformly non-uniformly ddistributed, i s t r i b u t e d , and and primarily p r i m a r i l y associated associated with with suiphide s u l p h i d e minerals. minerals. �— 27 REFERENCES Mandziuk, Z.L. 1981, P Precambrian geology Z. L. and Studemeister, S t u d e m e i s t e r , P.A., P. A. , 1981, recambrian g eology of the Molybdenite Lake area, covering parts of Andre of t h e a r e a , c o v e r i n g p a r t s of Andre and Bailloquet B a i l l o q u e t Townships, Townships, Algoma District: D i s t r i c t : Ontario Ontario Geological P. P.2406, 15, G e o l o g i c a l Survey SurveyPreliminary P r e l i m i n a r yMap Map 2406,Scale S c a l1: e 1: 15,840. 840. 1985, Geology Geology of of tthe Mishewawa Lake A Area, Massey, N.W.D., N. W. D. , 1985, h e Mishewawa r e a , Algoma Massey, District: D i s t r i c t : Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Open Open File F i l e Report Report 5532, 5532, 167 p. 167 p. Massey, N.W.D. 1983a, Precambrian geology N. W. D. and and Jennings, J e n n i n g s , E., E. , 1983a, g e o l o g y of of Massey, 49, Algoma Lendrum Lendrum Township Township and and parts p a r t s of of Gros GrosCap CapI.I .R. R. 49, District: D i s t r i c t : Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Preliminary P r e l i m i n a r y Map Map P. 2681, Scale P. 2681, S c a l e1:1:15, 15, 840. 840. 1983b, Precambrian geology Massey, N. W. D. and and Navratil, N a v r a t i l , S., S. , 1983b, g e o l o g y of of Massey, N.W.D. Township, Algoma District: Rabazo Township, D i s t r i c t : Ontario O n t a r i o Geological Geological Survey Preliminary 840. Survey P r e l i m i n a r yMap MapP.P.2682, 2682, Scale S c a l e1:1:15, 15,840. Massey, N. S., and JJennings, N. W.W.D. D., , NNavratil, a v r a t i l , S. , and e n n i n g s , E., E. , 1983c, 1983c, Precambrian geology g e o l o g y of of Naveau Township, Township, Algoma District: D i s t r i c t : Ontario Ontario Geological Map P. P. 2683, 15, 15,840. 840. G e o l o g i c a l Survey SurveyPreliminary Preliminary Map 2683,Scale S c a l1: e 1: 1986, S Stratigraphic Sage, R.P., R. P. , 1986, t r a t i g r a p h i c correlation c o r r e l a t i o n in i n the t h e Wawa Wawa area, area, Sage, p. 62-68 62-68 i in Volcanology and and Mineral Mineral Deposits, p. n Volcanology D e p o s i t s , edited e d i t e d by by J. J. Geological Misc. P Paper Wood and Wood and H. H. Wallace, Wallace, Ontario Ontario G e o l o g i c a l Survey Misc. aper 129, 1 2 9 , 183 p. 183 p. Sawitsky, E., Turner, J., Leeselleur, P., and Sagle, R. PP., . , Sawitsky, E . , Turner, J . , L e e s e l l e u r , P. , and S a g l e , Sage, R. E.,, 1982a, E. 1982a, Precambrian Precambrian geology of of McMurray Township, Township, Wawa Area, Algoma Algoma DDistrict: i s t r i c t : Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Preliminary 840. 2 4 4 1 , Scale S c a l e1:1:15, 15,840. P r e l i m i n a r yMap Map P. P. 2441, ----- ,, 1982b, 1982b, Precambrian geology of of Lastheels L a s t h e e l s Township, Township, Wawa Wawa Area, Area, Algoma District: D i s t r i c t : Ontario O n t a r i o Geological G e o l o g i c a l Survey Preliminary 2 4 4 2 , Scale S c a l e1: 1:15, 15,840. 840. P r e l i m i n a r yMap MapP.P.2442, Abercrombie, S., P., P . , Rebic, Rebic, ZZ., . , Abercrombie, S . , Neale, Neale, K. K. McMillan, D. D. and Calvert, 1982c, Precambrian Precambrian geology geology of of Esquega C a l v e r t , T., T. , 1982c, Township, Township, Wawa Area, Area, Algoma District: D i s t r i c t : Ontario O n t a r i o Geological Geological Survey Preliminary 2440, Scale 040. P r e l i m i n a r y Map P. P. 2440, S c a l e1:1:15, 15,040. Sage, R. R. Sage, P., Abercrombie, S., P . , Rebic, ZZ., . , Abercrombie, S., Neale, Neale, K., K . , McMillan, McMillan, D., D., Precambrian England, D. D. and Calvert, C a l v e r t , T., T. , 1982d, 1982d, P r e c a m b r i a n geology g e o l o g y of of Chabanel Township, Township, Algoma District: D i s t r i c t : Ontario O n t a r i o Geological Geological Preliminary 840. 15,840. Survey P r e l i m i n a r yMap MapP.P.2439, 2439, Scale S c a l e1:1:15, Survey Sage, Sage, R. Geology of of Chabanel, Chabanel, Esquega, Esquega, L Lastheels R. P.P., , i in n ppress, r e s s , Geology a s t h e e l s and McMurray Townships, District of Algoma: Ontario Townships, D i s t r i c t of Algoma: O n t a r i o Geological Geological Survey Open Open File F i l e Report Report 5586, 5586, 523 523 p. p. R. R. �— 28 Sullivan, Sullivan, — R.W., 1985, U-Pb zircon R . W . , Sage, Sage, R.P., R. P . , and and Card, Card, K.D., K.D., 1985, U-Pb z i r c o n age age of tthe of h e Jubilee J u b i l e e Stock S t o c k in i n the t h e Michipicoten M i c h i p i c o t e n greenstone greenstone belt 361-365 i in Geolgical e o l g i c a l Survey b e l t near n e a r Wawa, Wawa, Ontario, O n t a r i o , p. p. 361-365 n G of Canada Paper B, 637 p. of P a p e r 85-lB. 85-lB, Current C u r r e n t Research, Research, Part P a r t B, 637 p. R. P.P., and Van Van Schmus, R., Turek, A . , Sage, R. , and Schmus, W. W. R . , 1990, 1990, Advances in in Turek, A., geochronology of of the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt: belt: IInstitute n s t i t u t e on Lake Superior S u p e r i o r Geology, Geology, Proceedings P r o c e e d i n g s and and Abstracts. (in A bstracts. ( i n press) press) Turek, A . , Van Van Schmus, Schmus, W.R., W. R . , and and Sage, Sage, R.P., R. P . , 1988, 1988, Extended Turek, A., volcanism v o l c a n i s m in i n the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt, b e l t , Wawa, Wawa, Ontario: Mineralogical O n t a r i o : Geological G e o l o g i c a l Association A s s o c i a t i o n of Canada Canada -- Mineralogical Association Annual Meeting, Meeting, Program w with A s s o c i a t i o n of o f Canada Annual ith Abstracts, p. 127. A b s t r a c t s , v. v. 13, 13, p. 127. Turek, 1982, Rb-Sr Rb-Sr and U-Pb A. , Smith, Smith, P.E., P. E . , and and Van Van Schmus, Schmus, W.R., W. R. , 1982, Turek, A., ages a g e s of o f volcanics v o l c a n i c s and and granite g r a n i t e emplacement emplacement in i n the t h e Michipicoten Michipicoten belt, Wawa, Ontario: O n t a r i o : Canadian Canadian Journal J o u r n a l of of Earth E a r t h Sciences, Sciences, b e l t , Wawa, v. 19, 1 9 , p. p. 1608-1626. 1608—1626. �— - 29 29 - LIST LIST OF FIGURES Figure F i g u r e 1. 1. Wawa Area General Geology and Gold Occurrences Occurrences Figure F i g u r e 2. 2. General G e n e r a l Geology of the t h e Michipicoten M i c h i p i c o t e n Greenstone G r e e n s t o n e Belt Belt Figure F i g u r e 3. 3. Citadel C i t a d e l Mine Exploration E x p l o r a t i o n and and Development Development -- JJubilee ubilee and Minto Mines Development Development Figure 4. F i g u r e 4. Parkhill 1938 Development Plan P a r k h i l l Mine -- 1938 Plan F i g u r e 5. 5. Figure Monk Deformation Michipicoten Deformation Zone Zone -- M i c h i p i c o t e n River R i v e r Area Gold Occurrences Occurrences Figure 6. F i g u r e 6. Centennial C e n t e n n i a l Mine -- Surface S u r f a c e Geology Geology Figure 7. F i g u r e 7. Ranson Prospect P r o s p e c t -- Geology and Vein Widths � https://digitalcollections.lakeheadu.ca/files/original/0d5e2404cf86f8c0cd09e874bc54d539.pdf a1b06ae6e6d6b18fc5bcf643d4b01b57 PDF Text Text ������������������������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/9fb80bcae67b4ebd07fb14adbabd2fdd.pdf 5052087fe87fa65daa8b16946d6910cf PDF Text Text ����������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/8786c509eb186e81797fcf04ae095105.pdf 09bf7145eb17aace4568c122d2ba2511 PDF Text Text r I F F I I Institute on Lake Lake Superior Superior Geology Geol Thirty-Third Annual Meeting THE ICAPUSKASING UPLIFT: ARCHEAN GREENSTONES AND GRANULITES n 0 50 km n P a Wawa, Wawa, Ontario. Ontario Vol. Vol. 33, Part Part 55 P ii �THE THE KAPUSKASING KAPUSKASING UPLIFT: ARC-lEAN ARCHEAN GREENSTONES GREENSTONES AND GRANULITES GRANULITES 3.A. 3.A. Percival Percival Geological Geological Survey of Canada, Canada, 588 Booth Street Street Ottawa KIA OE4 0E4 Ottawa KIA Annual Institute Institute on Lake Superior Superior Geology 33rd Annual Geology Wawa, Ontario Ontario Wawa, Vol. 33, Part 55 Vol. 33, �I ' I à I I I TABLE OF CONTENTS TABLE OF CONTENTS Page h U ZI:?GEOLOGICAL ~GE~L-FRAMEWORKOFTHEKAPU~KA~INGUPLIFT PART FRAMEWORK OF THE KAPUSKASING UPLIFT Introduction Introduction RegionalSetting Setting Regional Geophysical characteristics of south-central Superior Province Geophysical characteristics of south-central Superior Province General Geology ofthe theWawa Wawa- Abitibi Abitibi Region General Geology of - - 1 1 i 1 2 Region I)1) Greenstone- Granite GraniteTerranes Terranes Greenstone 2)2 ) WawaGneiss GneissTerrane Terrane Wawa 6 6 9 9 Kapuskas'ingStructural StructuralZone Zone Kapuskasing Relationshipof ofKapuskasing Kapuskasingstructural structural zone to adjacent subprovinces Relationship zone to adjacent subprovinces Structure of the Kap~crustal crass-section Structure of the Kapuskasing crustal cross-section ATcheanevolution evolutionofofthe tileKapuskasing ingcrustal crustatstructure structure Archean Uptiftofofthe theKapuskasing Kapustasingstructure structure Uplift 3)3 ) I 13 13 21 21 25 29 32 PART II: ROAD LOG Summary Summary DayI:1: Stops Stops1-1 1-ltoto1-10; 1-18;Geology Geologyof ofthe the Wawa subprovince, Day Wawa subprovince, Wawa to C h a p k u Wawa to Chapleau Day 2: Stops2-1 2-1toto2-9; 2-9sGeology Geologyofofthe theKapuskasing Kapuskasing structural Day 2: Stops structural zone in the Chapteau-Poleyet area zone in the Chapleau-Foleyet area 34 34 34 39 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS 46 REFERENCES REFERENCES t \^ PARTI PART t Figure1 1 Figure F i r e22 Figure Figure3 3 Figure Figure44 Figure Figure5 5 Figure Figure66 Figure figure7 7 Figure Eggre88 Figure 1 1 46 LETOF OFILLUSTRATIONS BAUSTKATIONS LIST Geoiogyof of central centralSuperior SuperiorProvince Province Geology Geologyof ofthe theWawa-Chapleau-Foleyet Wawa-Chapteau-Foleyetarea area Geology Crustedthickness thicknessininthe theLake LakeSuperior Superiorarea area Crustal Bouguergravity gravitymap m p Bouguer Pressurebased basedon enhornblende hornblendeAl A1content content Pressure Geology of of the theKapuskasing Kapuskasing structural structuralzone zoneand andvicinity vicinity Geology Geologyof of the theShawmere Shawmereanorthosite anorthositecomplex complex Geology Metamorphicmineral mineralassemblages assemblagesin inthe theChapleau-Foleyet Chageau-Fokyet area Metamorphic 2 3 4 5 11 11 12 12 15 15 area 1717 �U Figure 9 Figure 10 Figure 11 Figure 12 Metamorphic reactions and P-I conditions for Kapuskasing granulites Paleo-pressure map for the Chapleau_Foleyet area Figure 13 Concorcfia diagram for zircon samples Gravity profile and crosssection for Kapuskasing zone in the Chapleau area Seismic reflection profile Figure 14 Figure 15 Restored vertical section 40Ar/39Ar age spectra Page 19 21 22 23 24 26 32 PART II Figure 22 Location of outcrops at Stop 2-5 42 3 j J �st I 8 PART ft PART b GEOLOGICAL GEOLOGICALFRAMEWORK FRAMEWORK OF OF THE THE KAPUSKASING KAPUSKASING UPLIFT INTRODUCTION The purpose purposeofofthe the trip trip is is to to examine examine the the characteristics characteristics and The and interrelationships interrelationships of of Archean high-grade gneiss gneiss terranes terranes of of the Superior Province. A Archean greenstone-granite greenstone-granite and high-grade Superior Province. A 300-km long west transect westtot oeast east transect between Wawa Wawa and Timmins, Ontario will be be used ttoo illustrate illustrateregional-scale regional-scale relationships. Figure Figure 11 shows the the major major geological features features of the theSuperior Superior Province Province and and Figure 22 traces trip route. The traces the the trip The first first day day will will be spent spent examining features features of of the the Michipicoten belt, a dominantly dominantly metavolcanic metavolcanic portion of the theWawa Wawa subprovince, subprovince, and and contact of the contact relationships between the the Michipicoten Michipicoten supracrustal supracrustal rocks and intrusions of Wawa domal gneiss gneiss tterrane. Wawa domal Onday daytwo, two,the theWawa-Kapuskasing Wawa-Kapuskasing boundary boundary will willbe be e r r a e . On examined, features of examined, as well as features of the theKapuskasing Kapuskasing structural structuralzone, zone, including including the the Shawmere anorthosite complex, high-grade gneisses, and the Ivanhoe Lake cataclastic cataclastic high-grade gneisses, zone separating zone from from those of of the Abitibi separating rocks of the the Kapuskasing Kapuskasing zone Abitibi Belt. . REGIONAL REGIONAL SETTING SETTING The Superior Province Province is is an an Archean Archean tterrane composed of of east-west east-west trending belts e r r a composed of alternate alternatevolcanic-rich volcanic-rich and and sediment-rich sediment-rich character, character,termed termedsubprovinces subprovinces(Fig. (Fig. 1). I). The continuity continuity of of the the east-west east-west belts belts is is interrupted interrupted by by aa northeast-trending northeast-trending zone zone of of highhighgrade metamorphic rocks, rocks, the Kapuskasing structural zone zone (Thurston (Thurstonet et al., al., 1977). Kapuskasing structural 1977). At its its southern end, the Kapuskasing structure is fault-bounded fault-bounded on on the the southeast southeast but but the Kapuskasing structure western contact contactisiscomplex complexand and gradational gradationalover over120 120 km to low-grade low-grade rocks of the the Michipicoten belt near near Lake Lake Superior Superior (Percival (Percivaland and Card, Card,1983; 1983;1985) 1985) (Figs. (Figs. I1and and 2). 2). The Kapuskasing Kapuskasing"high", "high",aaprominent prominentnortheasterly northeasterly gravity and aeromagnetic aeromagnetic anomaly, was interpreted indicate pronounced interpretedby byWilson Wilson and and Brisbin Brisbin (1965) (1965) tto o indicate pronounced upwarp of the the Conrad Conrad discontinuity. Bennett Bennettetetal. al.(1967) (1967)concluded concluded that that the theKapuskasing Kapuskasing structure structure is aa complex complex horst uplifted during during the Proterozoic. Proterozoic. The Theassociation associationofof1,100-1,000 1,100-1,000 Ma Ma alkalic that the alkalic rock-carbonatite rock-carbonatitecomplexes complexesled ledBurke Burkeand and Dewey Dewey (1973) (1973) tto o suggest that the Kapuskasing structure is a failed arm of the the Keweenawan Keweenawan rift structure. structure. Watson Watson(1980) (1980) Kapuskasing structure postulated postulated that thatthe theKapuskasing Kapuskasingzone zone was was uplifted uplifted during during late late Archean Archean or or early early Proterozoic sinistral transcurrent movement. transition aatt the movement. The The low-to-high-grade low-to-high-grade transition the southern of the the structure southern end of structurehas has been been interpreted interpreted as asan an oblique oblique cross-section of the crust uplifted along an east-verging east-verging thrust (Percival and Card, Card, 1983). 1983). Recent earthquakes in the region region indicate that that the thestructure structureisisstill stillactive active(Forsyth (Forsythand Morel, 1982; Forsyth et et a!., al.,1983). 1983). �-2- Figure1.1. Geology Geologyof of the thecentral centralSuperior SuperiorProvince. Province. Inset: Inset:positive positive gravity anomalies Figure gravity anomalies dark stipple b-25 mGal); limes (-25 mGal t o -35 mGal); blank (<-35 mGal). dark stipple @-25 mGal); lines (-25 mGal to -35 mGal); blank (<-35 mGal). GEOPHYSICALCHARACTERISTICS CHARACTERISTICSOF OFSOUTH-CENTRAL SOUTH-CENTRAL SUPERIOR PROVINCE GEOPHYSICAL SUPERIOR PROVINCE mapshowing showing apparent apparent crustal crustalthickness thicknessininthe theLake Lake Superior region, based on AAmap Superior region, based on seismic refraction studies, was presented by Halls (1982) (Fig. 3). These data show that seismic refraction studies, was presented by Halls (1982) (Fig. 3). These data show that �— 3— C C) C Co p1 0 4) U) p4 L b 1-i 4) t r4 C) 4-) r1 C) (Ti .1-I -p rl 4) --1 'p Cli U) C) 0 I— C) 'C a) 4.) :2 )< E o C) C) Co C o III IllIlillIjillIlIl lillillIlIl 1.17 — 111,1,1, —'t t :2 0 5 o.w c r-1 Ci, C D 0 a) a) Ct >1 Co ' CO •- w C 0 — Co Co E 0 'C) c 0 (0 C Ia) — C) — E 0) (N C Co o 0 — ct Ct 5 E 0 L. — > -C C) o c0 —t CC) ox rn Ii1'llI El! E C a) Ct Cl) .u) a) C) 0CtCOC — 0 —o — .9 — 0(0 2Co(0 0 E > 0 o c 0 (:' (0 N 0- 0 a) — C) iiiipj 0 0 .0 -o 111111r11111111,J; I.- C (0 Ct —1 �J U I Initial 1986). Ellis, and Boland 1986; West, and Northey 1985; al., et (Northey interpretation of stages preliminary in still are zone, Kapuskasing the beneath structure crustal examine to 1984 in conducted study, refraction major a of Results velocities. mantle and crustal averaging of necessity the to due partly and areas some in coverage insufficient of because partly preliminary, as thickness crustal apparent of map contour the viewed Halls east. the to km —35 to abruptly drop zone Kapuskasing the beneath range km 39 the in Values zone. Kapuskasing the of boundary eastern the with associated Moho to depth in decrease step—like a be to appears there addition, In Timmins. near km 35 to Wawa near km 45 about of values from easterly decreases Province Superior the of crust the of thickness apparent the advised. was map using in caution extreme and Halls by listed are data of Sources 1982). Halls, (after area Superior Lake the in crust the of thickness Apparent 3 Figure 1 j 2 U U 3 j -4U �-585° 470 810 Figure 4. Bouguer gravity map superimposed on simplified geology. (Gravity values in mGal), with 5 mGal Contour interval are from Earth Physics Branch maps 44078, 44084, 48078 and 48084). Checks - greenstone belts; dots -Kapuskasing unpatterned_undjyided granitoid rocks. gneiss; interpretation indicates that the crust is at least 48 km thick beneath the Kapuskasing zone and thins abruptly to about 40 km to the southeast; high seismic velocities characterize the high-grade rocks of the Kapuskasing zone (0. Northey, oral communication, 1985; Cook, 1985; Fountain and Salisbury, 1986). The Bouguer gravity anomaly map for the Wawa-Timmins region is shown in Figure 4. In general, areas underlain by metavolcanic rocks have associated positive gravity anomalies and granitoid..gneissic rocks have negative anomalies. The Kapuskasing structural zone has an assoçiate linear positive gravity anomaly extending �—6— from from James JamesBay b y in in the the north north to t o some some 50 50 km km southwest southwest of of Chapleau. Chapleau. In In the the WawaWawaChapleau.-Foleyet Chapleau-Foleyet area, the the gradient gradient isisgradual gradual on on the the west west and and abrupt abrupt on the east, east, suggesting contact between betweenthe theKapuskasing Kapuskasing zone and Abitibi Abitibi suggesting a west-dipping contact subprovince. In this thisregion, region,the thegravity gravityprofile profile(Fig. (Fig.12) 12)shows shows aa paired pairedhigh—low high-low subprovince. In anomaly. anomaly. The The trough trough of of the the low low is coincident with the fault fault at a tthe theeastern easternboundary boundaryof of the the Kapuskasing Kapuskasing zone. zone. To the north, as itit coalesces coalesces with with the the north, the thepositive positiveKapuskasing Kapuskasinganomaly anomaly broadens broadens as east-west east-west gravity gravity high high associated with with the the Quetico-Opatica Quetico-Opatica metasedimentary metasedimentary subprovince. J j 1 GENERAL GENERAL GEOLOGY GEOLOGY OF OFIL-fE THE WAWA WAWA -- ABITIBI ABITIBI REGION REGION Three Three distinct distinct types types of of terrane terraneare arerecognized recognized in inthis thispart partof ofthe theSuperior Superior Province: Province: 1) greenstone-granite greenstone-granite belts, belts, 2) 2) regions regionsdominated dominated by by orthogneiss orthogneiss in in the the amphibolite fades, facies, and 3) 3)heterogeneous heterogeneousgneisses gneisses in in the the granulite granulite to t oupper upper amphibolite amphibolite fades. facies. Differences between terranes terranes in in metamorphic metamorphic grade grade and and pressure pressure suggest suggest that that the the terrane terranetypes typesrepresent representcrustal-scale crustal-scaleniegalayers megalayers(Percival (Peruvaland andCard, Card,1985), 1985),the the components components of the the upper upper and and middle middle continental crust. crust. The TheWawa Wawaand and Abitibi Abitibi belts belts are are greenstone-granite terranes; of terrane type terranes; the theWawa Wawa gneiss terrane is an example of type 22 and zone represents type and the the Kapuskasing Kapuskasing zone type 33 terrane terrane(Fig. (Fig. 2). 2). ~ j j 4.: 1) 1) Greenstone-Granite Greenstone-Granite Terranes Terranes a The partofofthe thevolcanic-rich volcanic-richWawa Wawasubprovince, subprovince,Isiscomposed composed The Michipicoten Michipicoten belt, part mainly IC and mafic andfetsic felsiccomposition composition(Goodwin, (Goodwin, mainly of metavolcanic metavolcanicrocks rocksofofultrarnafic, ultramafic,maf 1962), with intercalated intercalated greywacke, 1962), with greywacke, conglomerate, chert chertand andiron iron formation, formation,mainly mainly siderite. as well as downward-facing downward-facing strata strata siderite. Dome Dome and basin structures structures(Goodwin, (Goodwin, 1962) 1962) as and and overturned overturned structures structures(Attoh, (Attoh, 1980) 1980)have have been recognized. recognized. Metamorphic Metamorphic grade grade ranges amphibolite facies facies (Fraser (Fraser et al., ranges from sub-greenschist sub-greenschist to amphibolite al., [978). 1978). Several Severalsuites suitesof of intrusive ranging from from peridotite peridotite to intrusive rocks rocks include include synvolcanic synvolcanic bodies ranging t o granodiorite, granodiorite, younger younger granodiorite granodiorite batholiths, batholiths, and and still stillyounger younger granite graniteand andsyenite syeniteplutons plutons (Card, (Card, 1982). 1982). The of the southern part of The supracrustal rocks ro of the the belt belt were weredivided divided into three three major (1962). A lower lower cycle, cycle, consisting of of roafic major cycles cycles by by Goodwin Goodwin (1962). rnafic and felsic felsic volcanics, volcanics, isis capped iron formation, formation, mainly mainly siderite, siderite, but with lesser pyrite-, capped by by Michipicoten-type Michipicoten-type iron U - 7 �r —7- I chert- and and graphite-rich graphite-rich rocks. rocks. The Theassociated associatedJubilee JubileeStock, Stock,aa high-level high-level subvolcanic SU~VO~C~N intrusion, was was emplaced emplaced within aa caldera caldera structure structure(Sage, (Sage, 1980). 1980). The middle cycle cyc Icvolcanics volcanicsoverlain overlain by byclastic clastic metasediments metasediments and and comprises maf comprises mafic and felsic tuffs an breccias. The breccias. The clastic clasticsediments, sediments, including including the the Doré Dor6 conglomerate, conglomerate, wacke, wacke, siltstone, siltstone, and an I crossbeddedarkose, arkose,a are thef facies equivalentsofof the the felsic felsic pyroclastics and crossbedded r e the a d e s equivalents and are formed mainly of detritus detritus eroded eroded from the t h e felsic felsic centres. centres. The Theupper upper cycle cycle comprises comprises intermediate to felsic -dacite) tuffs tuffs and quartz-feldspar porphyry. porphyry. Recent felsic (andesite (andesite -&cite) and quartz-feldspar Recent (pers.comm., comm., 1986) 1986)indicates indicatesonly onlytwo twocycles cycleswithin within tthe work by Sage Sage (pers. h e main volcanic pile. The Abitibi Abitibi subprovince The subprovince is is dominated dominated by a thick thick sequence sequence of volcanic volcanic and and I J I I I I I fl of the sedimentary rocks of t h e Abitibi Abitibigreenstone greenstonebelt belt(Jensen, (Jensen, 1981; 1981; 1985). 1985). The supracrustal successiontypically typically comprises comprisessequences sequencesofofultramafic, ultramafic, mafic, mafic, and and felsic felsic volcanics. succession volcanics. high proportion of volcanic volcanic detritus. detritus. Intercalated turbiditic turbiditicsedimentary sedimentary rocks rocks contain contain aa high In the Abitibi Abitibibelt, belt,the t h euppermost uppermostgroup, group, the t h eTimiskaming, Timiskaming,isisan anunconformity-bounded unconformity-bounded sequenceofof alkal~c alkalic volcanics and fluviatile fluviatile sediments sediments(Hyde, (Hyde,1980) 1980) localized localized along along major major sequence east-west fault east-west faultzones. zones. Large areas areas of of the Abitibi Abitibi greenstone Large greenstone belt belt are aremetamorphosed metamorphosed to t o greenschist greenschist prehnite-pumpellyite Ifacies acies rocks rocks are common common in in tthe Timminsh e Timminsffacies; a d e s ; subgreenschist, subgreenschist, prehnite-pumpellyite Rouyn area areaand andnarrow narrowaureoles aureolesofofamphibolite amphibolite ffacies rocks occur occur adjacent adjacent tto Rouyn a d e s rocks o plutonic plutonic bodies (Jolly, (Jolly, 1978). 1978). The supracrustal supracrustal rocks rocks of of the Abitibi The Abitibisubprovince subprovince display display evidence evidence of polyphase polyphase orientations. deformation in the t h e form form of of major majorand and minor minor structures structuresof ofseveral severalages ages and orientations. In the Abitibi Abitibigreenstone greenstone belt, older northerly-trending folds folds are are overprinted overprinted by by easteaststructures west trending major and minor folds, forming formingmajor major dome dome and and basin basin structures (Pyke, 1982). The Themajor majorisoclinal isoclinal folds folds with with east-west east-west striking striking subvertical (Pyke, 1982). subvertical axial axialplanes, planes, steeply-plunging minor folds, folds, subvertical axial plane foliation, foliation, and steeply-plunging minor and steeply steeply plunging plunging stretching stretching lineation lineation were were probably probably formed formed under under subhorizontal, subhorizontal, generally generally north-south north-south major compression. compression. Toward Towardtthe southernmargin marginofofAbitibi Abitibi belt the major h e southern t h e major folds are overturned northward, and and in the the adjacent adjacent Pontiac Pontiac subprovince, subprovince; folds folds are a r e recumbent. recumbent. The Cadillac-Larder Lake fault fault zone, between tthe Abitibi The Cadillac-Larder zone, which constitutes the the boundary boundary between h e Abitibi and probably has hasboth both transcurrent transcurrent and and thrust components and Pontiac subprovinces, subwovinces. orobablv comDonents of movement. Several suites of intrusive rocks in the Abitibi subprovince can be distinguished on I I of composition, composition, structural structural relationships, the basis basis of relationships, setting, setting,and andage a g e(Card, (Card, 1982). 1982). The The sills, dykes and and plutons plutons ranging rangingin in composition composition from from oldest suite includes synvolcanic sills, peridotite typically quartz diorite peridotite to t o granodiorite; granodiorite; the more more felsic intrusions aare r e typically diorite and and trondhjemite. Gneissic Gneissic plutonic plutonic rocks rocks of of tonalite tonaliteand and granodiorite granodiorite composition, composition, �—8— commonly containing amphibolitic amphiboliticenclaves, enclaves, occur occur in in the the northeastern and commonly containing and southwestern southwestern Abitibi subprovince. Massive felsic plutonic plutonic rocks rocks intrude intrude both both the the greenstones and the Abitibi subprovince. Massive felsic gneissic rocks in in the form of simple and and composite composite plutons plutons and and batholiths. batholiths. They They form several suites, suites, including including early early granodiorites, granodiorites, younger younger granite granite batholiths, batholiths, and andstill stillyounger younger syenite-diorite plutons. plutons. Contacts Contactsbetween between the theplutons plutons and and the the country country rocks rocks are are commonly concordant and and steeply steeply dipping; dipping;dominant dominanteast-west east-weststructural structural trends are commonly concordant are locally deflected about about the theintrusions. intrusions. A time framework for events events in in the theMichipicoten Michipicoten and and Abitibi Abitibi belts belts can can be be constructed U-Pb zircon dates. In the western Abitibi Abitibi belt, volcanic volcanic rocks rocks range in in constructed from from U-Pb age from Nunes and and Jensen, Jensen, 1980), with late late to 2,703 2,703 Ma Ma (Nunes and Pyke, 1980; 1980; Nunes 19801, with from 2,725 2,725 to alkaline Group) aatt 2685 Ma, Ma, and and in in the the Michipicoten Michipicoten belt, from from alkaline volcanics volcanics (Timiskaming (Timiskaming Group) 2,749 a t 2737, 2737, 2744 2744 (Turek (Turek et etal., al., 1982) 1982)and and2745 2745 2,749 tto o 2,696 Ma, with synvolcanic plutons at Ma (Sullivanetetal., al., 1985). 1985). A number numberofoflatelate- ttoo post-tectonic plutons M a (Sullivan plutons from from the the Abitibi Abitibi and Michipicoten Michipicoten belts have zircon dates dateswithin within aafew fewmillion million years yearsof of2,680 2,680(Icrogh (Krogh et et al., al., 1982; 1982;Frarey Frareyand and Krogh, Krogh, 1986). 1986). Thus Thus the themain main Abitibi Abitibi and and Michipicoten Michipicoten supracrustal supracrustal sequences sequences and and early earlyintrusions intrusionsdeveloped developed between between 2,750 2,750 and and 2,700 2,700 Ma Ma ago. The dates on volcanics and late late plutons bracket the volcanics and the age age of of deformation deformation and and regional regional metamorphism Ma ago. Major a ago. Major volcanic, plutonic, and metamorphism aatt between between 2,700 2,700 and 2,680 2,680 M tectonic tectonic events events of of relatively relatively brief brief duration durationwere wereessentially essentiallysynchronous synchronous throughout throughout the Abitibi and Wawa subprovinces, a region some 1,200 km wide. wide. The Wawa subprovinces, 1,200 km long and 200 km The lithologic and age similarities similaritiesbetween between the theAbitibi Abitibiand andWawa Wawa subprovinces subprovinces strongly strongly suggest original continuity, now structural zone. now interrupted by the Kapuskasing Kapuskasing structural Diabase dyke dyke swarms swarms of of late late Archean Archean and and Proterozoic age are present present throughout throughout the region. The Theoldest oldestdykes, dykes, the thenorth-trending north-trending Matachewan Matachewan swarm swarm of of the the Abitibi subprovince, Rb-Sr age age of of 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). NorthwestNorthwestsubprovince, have a Rb-Sr striking subprovince are are petrographically petrographically similar to t o and and have have been been striking diabase diabase dykes dykes in in Wawa Wawa subprovince paleomagnetically correlated correlatedwith withthe theMatachewan Matachewanswarm swarm(Ernst, (Ernst,1981; 1981;Ernst Ernstand and paleomagnetically Halls, subprovincesare are thus thus inferred inferred ttoo have been tectonically Halls, 1984). 1984). Abitibi Abitibi and Wawa Wawa subprovinces tectonically time. Northeast-striking Northeast-striking tholelltic tholeiiticdykes dykesare areabout about2105 2105Ma Ma old old stable cratons cratons by by this time. stable (Gates 1973);northwest northwest olivine diabase diabase dykes (Gates and and 1-lurley, Hurley, 1973); dykes (Sudbury (Sudbury swarm) swarm) are a r e about about 1250 Ma Ma old old (Van (VanSchmus, Schmus,1975); 1975);and andeast-northeast east-northeast olivine diabase diabase dykes dykes (Abitibi (Abitibi swarm) swarm) are M aold old(Lowden (Lowdenand andWanless, Wanless,1963). 1963). are approximately approximately1100 1100Ma �r 1 2) 2) 4 I I I I $ I I I I I I I The belt is intruded intruded ttoo the The Michipicoten Michipicoten belt the southeast southeast by by tonalitic tonalitic gneiss and plutons plutons of gneiss terrane terrane (Fig. 2). The consist of of aatt least of the theWawa Wawa domal domal gneiss (Fig. 2). The rocks in this region consist least four four lithologic lithologic components: components; (1) (1)hornblende-plagioclase hornblende-plagioclase ±+ clinopyroxene clinopyroxene mafic and rare rare paragneiss paragneiss xenoliths, xenoliths, ranging ranging from centimetres centimetresto totens tensofofmetres metresininmaximum maximumdimension, dimension, making most makingup up55to to 50% 50% of of individual individual outcrops, and enclosed in (2) the volumetrically most abundant abundant phase, phase, hornblende-biotite hornblende-biotite tonalitic tonaliticgneiss gneisswhich which is iscut cutby by (3) (3) concordant concordant to to discordant discordant layers layers of of foliated foliatedto t ogneissic gneissicbiotite-hornblende biotite-hornblende granodiorite, granodiorite,which whichin in turn turn are arecut cutby by (4) (4)late late discordant discordant quartz quartz monzonite monzonite pegmatite. Xenolith-rich Xenolith-rich tonalitic tonaliticgneiss gneiss units units alternate alternateon on aa 55 to to 10 10 km krn scale with xenolith-poor xenolith-poor units and can be be traced traced for for distances distances of of at a tleast least50 50km. km. Layering Layeringininmafic maficxenoliths xenolithsisislocally locallydiscordant discordant to tolayering layering in in enclosing enclosing gneiss. gneiss. Small Small folds folds of of layering layering in in tonalitic tonaliticgneiss gneiss are arecommonly commonly truncated truncated by by layers layers of of foliated foliatedgranodiorite. granodiorite. Tonalite Tonalitegneiss gneisshas hasa aminimum minimumU-Pb U-Pb zircon zirconage ageof of2707 2707 Ma, M a(Percival (Percivaland andKrogh, Krogh, Ma, partly partly reset resetby bythe theintrusion intrusionofofgranodiorite granodioritesheets sheetsata 2677 t 2677Ma 1983) 1983)(Fig. (Fig. 5). 5). The The layers layers of of granodiorite granodiorite on on the cm cm to to km km scale scale in the the gneiss gneiss terrane terrane can can be be correlated correlatedby byzircon zircongeochronology geochronologywith with discordant discordantplutons plutonsof of 2680 2680Ma Ma age age in in the the greenstone greenstone belts, belts, suggesting suggesting that that the the plutons plutons have have deep roots in the gneissic gneissic terrane. In In the the area areabetween betweenthe theMichipicoten Michipicotenbelt beltand andKapuskasing Kapuskasingzone zone (Fig. (Fig. 2) 2) the the orientation orientationof of foliation, foliation,gneissosity gneissosityand and axial axial surfaces surfacesof of small smallfolds foldspermit permitdefinition definitionof of several severalstructural structuraldomains domainscharacterized characterizedby bydomal domalgeometry geometry(Fig. (Fig. 6). 6). The Thespacing spacing of of major major domal domal or or antiformal antiformalculminations culminations is is on on the the order order of of 20 20 to t o25 25 km, km, although althoughmany many smaller smaller culminations culminations are arealso alsopresent. present.The TheHighbrush HighbrushLake Lakeand andRacine RacineLake Lakedomes domeshave have cores coresof of tonalite-granodiorite tonalite-granodioritegneiss gneisswhereas whereasthe theChaplin C h a p lLake i Lakedome domeand andMissinaibi MissinaibiLake Lake arch planar fabric fabricin in the the archhave have granitic graniticcores coresflanked flanked by by foliated foliated to to gneissic gneissic rocks. AAplanar homogeneous homogeneous granitic rocks, defined by by lenticular quartz quartz and and biotite biotitealignment, alignment,isis generally generally concordant concordant to t ogneissosity gneissosity in in mantling mantling gneiss. gneiss. The Thestructural structuraldomes domesmay maybe be related relatedtotothe theemplacement emplacementofofplutons, plutons,possibly possiblyby bydiapiric diapiricrise. rise.The TheRobson RobsonLake Lakedome, dome, adjacent adjacentto t othe theKapuskasing Kapuskasiig structural structuralzone, zone, has has aa core coreof of interlayered interlayeredmafic maficgneiss, gneiss, paragneiss paragneiss and and tonalitic tonaliticgneiss. gneiss. InIngeneral, general,asymmetric asymmetricsmall smallfolds foldsofofgneissic gneissiclayering layeringdo donot nothave have aa consistent consistent sense senseof of asymmetry asymmetrywith with respect respectto todomal domalculminations culminations and and are are therefore thereforenot notcongruent congruent with withthe thedomes. domes. Near Nearsome somedomal domal crests, crests,the theorientation orientationofofgneissic gneissiclayering, layering,small small folds are widely variable to chaotic and definee aa pattern foldsand and lineations 1 patternof ofcoalescing coalescing domes. domes. I Wawa Wawa Gneiss Terrane Terrane �- 10 - geobarometer for calc-alkaline igneous rocks is based on the Al content of hornblende (l-lammarstrorn and Zen, 1986): A P= —3.92 + 5.03 Allotal Application of the barometer to a suite of tonalites from the Wawa gneiss terrane suggests suggests that thatthe thepressure pressureofofigneous igneouscrystallization crystallizationincreases increasesfrom fromabout about55kbar kbarininthe the central over Kapuskasing 6 kbarnear nearthe the Kapuskasingzone zone(Fig. (Fig. 5). 5). These These centralpart partofofthe theterrane terranetoto over6 kbar results areintermediate intermediatebetween betweenindependent independentpressure pressureestimates estimatesfor forthe theMichipicoten Michipicoten resultsare belt basedon onsphalerite-pyrrhotite sphalerite-pyrrhotitegeobarometry geobarometry(Studemeister, (Studemeister,1983) 1983)and and beltof of2-3 2-3kbar, kbar, based for 6-8kbar kbarbased basedon ongarnet-pyroxene-plagioclase_quartz garnet-pyroxene-plagioclase-quartz forthe theKapuskasing Kapuskasingzone zoneof of6-8 barometry barometry(Percival, (Percival,1983). 1983).AAvalue valueofof8 8kbar kbarnear nearWawa Wawaisisderived derivedfrom fromaabiotite biotite tonalite tonalhewhich whichcontains containshornblende hornblende only on adjacent to contacts with amphibolite; the hornblende hornblendeisisprobably probablyxenocrystic. xenoaystic. Metasedimentary Metasedimentaryrocks rocksoccur occurini two locations in the eastern Wawa subprovince. AAdiscontinuous, discontinuous, antiformal antiformalto t odomal domalbelt beltofofparagneiss paragneisswest westofofthe theRacine RacineLake Lakedome dome may 6). maybe becontinuous continuous to t othe theeast eastwith withparagneiss paragneissofofthe theKapuskasing Kapuskasingzone zone(Figs. (Figs.22and and6). Stretched-pebble Stretched-pebble metaconglomerate metaconglomerateoccurs occursininassociation associationwith withquartz quartzwacke wackeand and amphibolite Thepolymictic polymictic(tonalite, (tonalite,granodiorite, granodiorite,metame amphibolitein inthe thevicinity vicinityof of Borden Borden Lake. Lake. The andesite, andesite,metasediments, metasediments,amphibolite, amphibolite,vein veinquartz), quartz),clast-supported clast-supported rock rockcontains contains cobbles cm)with withaaprominent prominentshallow shallow cobblesranging rangingfrom fromequant equanttotoconstricted constricted(1.5 (1.5mmx x7 7x x7 7cm) northeast plunge. In cross-section the clasts vary from equidimensional to northwestdipping ellipses. The Floranna Lake complex is a strongly lineated and foliated complex crescentic pluton plutonof ofintermediate intermediatecomposition compositionthat thatoccurs occursbetween betweenthe theRobson RobsonLake Lakeand andRacine Racine Lake medium-grained Lakedomes. domes. The Themargins marginsofofthe thecomplex complexare arefinefine-toto medium-grainedhypersthene.hypersthenebiotite contains medium-grained biotitegranite, granite,whereas whereasthe thecore core contains medium-grainedrnonzonite rnonzoniteand anddiorite dioritewith with rare raregabbro gabbroand andcoarse coarsebiotite-clinopyroxene biotite-clinopyroxene melagabbro melagabbrolayers. layers. The Theleast-deformed least-deformed interior igneous(?) interiorportions portionscontain containrelict relict igneous(?)clinopyroxene clinopyroxeneand andfeldspar feldsparaugen augenphenocrysts. pheno Migmatitic Migmatiticquartz quartzmonzonite monzonitelayers layersconstitute constituteupuptot o10% 10%ofofsome someoutcrops. outcrops.The The complex complexhas hassimilar similarstructural structuraland andlithological lithologicalcharacteristics characteristicstotocrescentic crescenticplutons plutonsofof the theWabigoon Wabigoonsubprovince subprovinceof of northwestern northwesternOntario Ontario(Schwerdtner (Schwerdtneretetal., al., 1979,1983; 1983 1979, Sutcliffe 1979). Sutcliffeand andFawcett, Fawcett, 1979). The donial region a semi-continuous Theeastern easternlimit limitofofthe the domal regionis is a semi-contin"ous zone zoneofofnorth, north, northeast easterly-dipping and northeastand andnorthwest northweststriking, striking,gently gently easterly-dippinggneissosity gneissosity andeasterlyeasterlyplunging 6)6may plunginglineation. lineation. This Thiscurvilinear curvilinearfeature feature(Fig. (Fig. ) mayrepresent revresentthe theeastern easternextremity extremity �I I I I I I I — 11 2.6 0 0 a) Ia -0 interior intermediate edge 8 S S.- I. U (3) ¼ I I a S a2E 6- (I, 0 4 (4 Lu — 0 0 • .40 •• 5 A 150 Wowa I &ne/ss Terr one 100 I I I I I - — . 50 L8r() N Structural Zone I I I I ao >' 0 Kop uskasing S 0 A.4 I p p 2 I_ '4' ---------- 0 9-1.6 C Distance Distance from from Ivanhoe Ivanhoe Lake Lake cataciastic cataclastic zone, km km Al/n A/ in Horn b/en de Barometer Hornblende Barometer ............ ...,......... .. b'} . .. . . ., Wa wa/ / 4•97 I I 0 I I 1 •1 24 0 0 I I 0--- r 0 -S. 1* I I I — to 11.0 &ne/ss V / A bit/b - V , ,. / Belt 5.1 Terrane 50 0 km Figure Figure 5.5. a)a) Plot Plotof ofhornblende hornblende composition composition vs vs spatial spatial distribution. distribution. Vertical Vertical array arrayof of points represents representswithin-sample within-sample compositional variation. Hornblende at a t far far left leftisis points variation. Hornblende probably xenocrystic, xenocrystic, from from adjacent adjacent amphibolites amphibolites of of Michipicoten Michipicoten belt. Dashed-line Dashed-line box box probably representsindependent independentpressure pressure estimates estimatesfrom fromgranulites granulitesofofthe theKapuskasing Kapuskasing zone. zone. represents b)b) Map Map showing average pressure in kbar, kbar, based based on on hornblende hornblende geobarometry geobarometry in in the theWawa-Chapleau Wawa-Chapleau area. area. �63'Oo' LEGEND Proterozoic Alkalic rock—carbonatite complex: I: Lackner Lake complex; n: Nemegosenda Lake Lake complex; comple%s: a: Shenango Shenango complex Complex 1100 t i 0 0 Ma Ma intrusions intrusions Archean I m + massive granite, granodiorite, grenodiorite, with minor minor tonalite tonalite diorite—monzonite intrusive complex; minor hornblendite, granite diorite-monzonite intrusive 2707-2668 Ma Me sequence sequence 2707—2668 foliated foliated to to flaser flaser tonalite tonalite I@ tg;4 tonalite—granodiorite tonelite-granodiorite gneiss; gneis metavolcanic metavolcanic rocks, rocks, mainly mainly metabasalt metabasait . :: ---------- ~....' - Shawmere Shawmere anorthosite anorthositecomplex: complex: metamorphosed metamorphosed gabbroic gabbroic anorthosite, anorthosite, anorthosite, anorthosite, gabbro, gabbro, minor minor tonalite tonalite pre—2765 pre-2765 Ma sequence sequence Amq gneiss: highhigh Ca,AI basaltic composition, with gneiss: Ca,AI basaltic composition, withtonalitic tonaliticleucosome ieucosome "fl-i,maficmafic lAp 0 ' / ^ 2749-2696 Ma sequence sequence 2749—2696 flaser ic tonalite flaser diorite dioritetotomat mafic tonalite— includes inciudesminor minorgabbro, gabbro .._.:j .-.--hornbiendite, granodiorite granodiorite hornblendite, "'Bsojl I metasedimentary metasedimentery rocks rocks (includes (includes metaconglomerate metaconglomerste with with tonalite tonalite cobbles zircon date date of of 2664±12 cobbles with with aa U—Pb U-Pb zircon 2664±1Ma) Ma) paragneiss- quartz-rich paragneiss— quartz—richcomposition, composition,wi with up to 15% tonalitic leucosome — fault; fault; Ivanhoe ivanhoe Lake Lake cataclastic cstaclasticzone zone Figure Figure 6. 6. Geology Geologyof ofthe theiCapuskasing Kapuskasing structural s t r u c t u r a l zone zone and and vicinity. vicinity. �I I I I I I I - I -13of of aa first-order first-order dome domeof of 75-100 75-100 km km diameter, diameter, of of which which the t h e individual individual structural structural domains domains are a r e higher-order higher-order domes domes of of similar similarscale scaleand andspacing spacingtot othose thoseofofthe theWabigoon Wabigoonsubprovince subprovince (Schwerdtner (Schwerdtner and and Lumbers, Lumbers, 1980). 1980). Dome development development can can be be temporally temporally related related to t o the the formation formation of of minor minor structures structuresin in gneiss. gneiss. The Thediscordant discordant foliations foliationsin in mafic mafic gneiss gneiss predate predate the thegneissic gneissic layering layering in the tonalite-granodiorite tonalite-granodiorite host. host. Small Smallfolds foldsof of this thisgneissic gneissiclayering layering in in turn turn predate layers. Crosscutting predate intrusion intrusion of granodiorite layers. Crosscutting pegmatite pegmatite dykes dykes and and sills are still still younger younger and are a r e probably probably the t h e same same age age as asthe thehomogeneous homogeneous plutonic plutonic rocks rocks which which locally locally have by lenticular quartz grains, have a planar planar fabric defined by grains, biotite alignment, alignment, fracture fracture cleavage, of granulation. granulation. The cleavage, or minor minor planar zones of The absence absence of aa consistent consistent sense sense of asymmetry asymmetry of small small folds with respect to t o domal domal culminations culminations and the t h e random random orientation orientation of of re-orientation of small small folds folds near dome crests argue in favour of re-orientation of of pre-existing pre-existing small small folds layering during duringthe the latest latest doming. doming. The folds and gneissic gneissic layering The quartz-lenticle foliation foliation and and fracture plutonic rocks rocks cannot cannot be be readily readily attributed attributed to fracturecleavage cleavagein inhomogeneous homogeneous plutonic to magmatic magmatic flow flow and therefore suggest suggest that that the the plutons plutons were were emplaced emplaced at their their present present structural structurallevel levelat a tsub-solidus sub-solidus temperature, possibly possibly relating to t o late l a t e diapiric diapiric rise. rise. 3) Kapuskasing Structural Zone The The Kapuskasing Kapuskasing structural zone zone comprises comprises northeast-striking, northwest-dipping northwestdipping belts tonalite, and belts of of paragneiss, paragneiss, mafic mafic gneiss, gneiss, gneissic gneissic and xenolithic tonalite, and rocks rocks of of the the Shawmere Shawmere anorthosite anorthosite complex complex (Bennett (Bennett et et al., al., 1967; 1967; Thurston Thurston et et al., al., 1977) 1977) (Figs. (Figs. 22 and and 6). 6). Migmatitic layered with with garnet, biotite, Migmatitic paragneiss paragneiss is compositionally layered biotite, quartz-rich quartz-rich and and rare rare graphitic graphitic varieties. varieties. Concordant Concordanttonalitic tonaliticleucosome leucosome constitutes constitutes up up to to 20 Ic gneiss 20 per per cent cent of of many many outcrops. outcrops. Enclaves Enclavesand andlayers layersofofmaf mafic gneiss in in paragneiss paragneiss occur occur on on the the10 10cm cm to t o 11km km scale. scale. Migmatitic Migmatiticmafic maficgneiss gneiss isis characterized characterizedby by garnetgarnetclinopyroxene-hornblende-plagioclase-quartz-ilmenite+orthopyroxenemineral mineral clinopyroxene-hornblende-plagioclase-quartz-ilmenite÷orthopyroxene assemblages assemblages and and generally contains concordant tonalitic tonalitic leucosome. leucosome. Layering, Layering, on on the the i1to t o10 10cm c m scale, scale,isisproduced produced by by variable variable proportions proportions of minerals. minerals. Table Table11presents presentstwo two sets setsof of whole-rock whole-rock analyses analyses from from adjacent adjacentanhydrous anhydrous (garnet-clinopyroxene-plagioclase(garnet-clinopyroxene-plagioclasequartz)and and hornblende-bearing hornblende-bearing layers from mafic gneiss in two different locations. locations. quartz) From From the t h e analyses analyses iti tisisunclear unclear whether whether the t h elayering layeringisisaapreserved preservedcompositional compositional heterogeneity heterogeneity or or aa product product of of metamorphic metamorphic differentiation. differentiation.The Thebulk bulkcomposition composition corresponds correspondsto t ohigh highcalcium calcium(10-15 (10-15wt% wt%CaO), CaO),high high alumina alumina(13.4-17.2 (13.4-17.2 wt% wt%A1203) AIn03) basalt basalt - I I I �- 14 Table Table 1: 1: e Si02 Si02 Ti02 1102 A1203 Whole rock chemical analyses of Whole of mafic gneiss from the the Kapuskasing Kapuskasing zone, with CIPW norms. Analyst: I: granulite layer, Analyst: R. R. Charbonneau, Charbonneau, GSC GSC Lab. 1: layer, P79-475 P79-475 CIPW norms. (Gt-Cpx-Pl-Qz, 5% 2: amphibolite amphibolite layer, P-475 (Gt-Cpx-PI-Qz, 5% Nb); Hb); 2: P-475 (Gt-Cpx-Pl-Qz, (Gt-Cpx-PI-Qz, 25% 25% Nb); Hb); 3: granulite (Gt-Cpx—Pl,trtrQz); Qz);4:4:amphibolite amphibolitelayer, layer, P79-371 granulitelayer, layer,P79—371 P79-371 (Gt-Cpx-PI, (Nb 40%, 40%, Gt Gt 15%, 15%, Cpx Cpx 15%, 15%,PI Fl20%); 20%);5:5:average averageofofthree three mafic gneisses from (Hb the the KSZ KSZ (79-84A, (79-84A, 123, 123, 299); 6: 6: high-alumina basalt basalt (Ringwood, (Ringwood,1975). 1975). 1 2 3 4 5 6 47.8 46.6 52.5 43.1 47.8 49.9 1.0 1.3 0.81 0.81 1.81 1.59 15.5 15.6 17.2 13.4 16.2 17.0 Fe203 1.3 2.2 2.2 5.7 3.4 1.5 FeO FeO 9.1 9.4 8.5 12.8 8.5 7.6 MnO MnO 0.27 0.19 0.32 0.3 0.32 0.2 MgO MgO 4.53 5.29 3.64 9.25 5.41 8.2 13.50 11.4 CaO CaO Na20 Na20 K20 K2 fl20 Co2 C02 Ni Ni Cr Total Total QZ OR AB AN DI HE EN PS P0 PA MT IL AP CC 15.4 14.2 11.2 10.0 2.0 2.4 2.8 1.6 2.3 2.8 0.25 0.41 0.12 0.58 0.33 0.2 0.5 1.1 0.3 1.6 0.8 2.3 2.0 0.4 0.1 0.6 0.014 0.014 0.0095 0.0098 0.024 0.019 0.018 0.018 0.014 0.015 100.0 1.5 1.49 17.02 32.77 11.42 12.80 6.05 7.83 1.9 1.55 0.12 5.26 100.4 2.44 20.46 30.81 11.52 10.90 3.64 3.95 3.01 3.60 3.21 1.55 0.14 4.58 100.6 100.6 100.4 CIPW CIPW Norm Norm 6.6 6.6 0.71 3.47 0.71 23.63 13.72 13.72 33.92 28.03 28.03 6.99 10.20 8.28 6.41 8.28 5.80 5.39 7.89 3.89 9.26 7.36 3.18 8.37 2.24 3.06 3.06 0.26 0.24 0.26 0.24 0.91 0.46 0.91 0.46 100.2 100.1 100.1 1.95 1.95 19.8 32.97 13.77 13'77 10.58 4.96 4.43 4.43 1.54 1.0 1.0 23.5 33.4 33.4 1-54 4.95 4.95 1.90 0.19 0.19 1.44 1.44 1.21 1.21 18.9 9.4 9.3 2.2 2.2 2.5 2.5 �t I I I I R mafic gneiss in the 95-220 and 1212(Table 1). Nickel and chromium abundances abundance5 ofof mafic gneiss aare r e in 95-220 and 190ppm ppmranges rangesrespectively respectivelyand andare arenot notdefinitive definitive in distinguishing between 190 between basaltic igneousand andmarly martysedimentary sedimentaryparentage parentagefor for the the rock rock type. type. igneous In the the area area of of Figure Figure 6, 6,four four linear, linear, northeast-striking northeast-striking bodies bodiesofof flaser-textured flaser-textured tto In o foliated diorite foliated dioriteand and mafic mafictonalite tonaliteoccur occurdominantly dominantlywithin withinparagneiss paragneiss terranes. terranes. These These ff' SHAWMERE ANORrHOSITE COMPLEX Megacrystic qabbrac anorthosile // Banded zone cpabbrO/anar I hosite/qarneti let I' I Anorthosite zone I 5 / hornbleedet / 'a Tonahtic racks Liiiilii Paraqnetss —— $ — —— km —— I I I Ia p - I I _—_—_— 1 / ____iii___ ±61r'- / / ---- — / / - / —:——7 a C' / /-';Y/ / — :Y / // // / - // / /// -: Renee / _/ / / / ,:-:i / Catty / *34B \/ a- 1 ii / /r //c/:-/// / /-/ _—_/ -/ — /1—- /— a / J-& -- - -- I I / /-:j // 7 // I',) / /-;: I / z __ / _// / / / / — Mat a yneiss. amohibolute FseIt ___I — ;;/ /ft\/// // S Luneament / ". E::E J ?- couNrAt ROCKS $ / '1- / ronalilic rocks ___ // C Border zone-am phibolite. mat'c gnetss 4à2 — - - -yI / IMd::y 3 4A / // 13.:c::_J -- —-—— / ' -: - —:—:—-- — - 8300----f ':':nFigure 7. - t' a / 8230 Geologyof of the the Shawmere Shawmereanorthosite anorthositecomplex complex (after (after Riccio, 1981 and Geology 1981 and Percival, 1981). 48 �- 16 - medium- to coarse-grained, coarse-grained, locally locally migmatitic migmatitic rocks mediumrocks consist consist of of hornblende, hornblende, biotite biotite and and per cent cent quartz plagioclase, with up to 10 plagioclase, 10 per quartz as as well well as as orthopyroxene, orthopyroxene, clinopyroxene clinopyroxene and and hornblendite and rare pyroxenite pyroxenite occur cm to garnet. Gabbro, as layers layers 10 10 cm to rare garnet. Gabbro, hornblendite and rare occur locally locally as cii thick, generally within 2 km km of of paragneiss contacts. 2 2m present south south of of the t h e main main Discrete belts of of xenolithic xenolithic and and gneissic gneissic tortalite tonalite are present and small small bodies are present present to to the north. anorthosite complex and body of the the Shawmere Shawmere anorthosite The southern southern belt belt is made up of of coarse coarse garnet-hornblende-biotite-plagioclase-quartz garnet-hornblende-biotite-plagioclase-quartz made up and garnettonalite containing enclaves of of mafic gneiss, paragneiss, hornblendite and orthopyroxene-hornblende-biotite rocks. orthopyroxene-hornblende-biotite rocks. Southwest Southwest along along this belt, garnet decreases decreases in composition is is granodioritic. granodioritic. Inclusions abundance and the composition Inclusions in this area area are are amphibolite, amphibolite, and cummingtonite-hornblende-biotite cummingtonite-hornb!ende-biotite rocks. hornblendite, and rocks. The Shawmere Shawmere anorthosite anorthosite complex (Thurston et et al., al., 1977) 1977) consists of a main main northern body, measuring 55 xx 15 km. km. The 50 km and a smaller mass, mass, measuring The bodies bodies taper to to body, 15 15 x 50 the northeast and and thus thus have haveconcordant concordantcontacts. contacts. Gneissic and southwest and Gneissic textures textures prevail in in the the outer outerportions portionsof ofthe themain mainbody, body,whereas whereas primary primaryigneous igneous minerals minerals and and textures are preserved preserved in the interior interior(Simmons (Simmons et et al., al.,1980). 1980). The Themain mainbody body comprises comprises four distinct (1)aaborder border zone zone of of distinctlithological-textural lithological-texturalunits units(Riccio, (Riccio,1981; 1981;Fig. Fig.7): 7):(1) rnigmatitic, foliated migmatitic, foliatedtot ogneissic gneissicgarnetiferous garnetiferousamphibolite, amphibolite,(2)(2)a abanded banded zone zone consisting consisting of 11 ttoo 30 30 cm-thick layers layers of anorthosite, anorthosite, gabbro, gabbro, garnet-rich, and and ultramafic ultramafic rock, rock, (3) (3)an an anorthosite zone gabbro and (14) megacrystic gabbroic gabbroic anorthosite (4)aamegacrystic anorthosite zone containing containing minor gabbro zone with plagioclase phenocrysts cm and and minor minor anorthosite, anorthositic phenocrysts to t o 50 cm anorthositicgabbro, gabbro, gabbro and andmelagabbro. melagabbro. AA 1 km km wide wide body bodyofoffoliated foliated garnetiferous tonalite tonalite is gabbro is present present within the the outcrop outcrop area of the anorthosite. anorthosite. Its Itsgenetic geneticrelationship relationshipto t othe theanorthosite anorthosite complex is not clear although although ititappears appears to tobe be temporally temporallyrelated related(Simmons (Simmonsetetal., al.,1980). 1980). southern body body consists consistsdominantly dominantly of of coarse coarse gabbroic anorthosite. The southern The orientation orientation of gneissosity and lithological lithological contacts the prominent prominent The gneissosity and contacts make make up up the east-northeast structural structural grain of the structural zone. zone. Gneissosity in all east-northeast the Kapuskasing Kapuskasing structural Gneissosity in rock types is folded or warped gently-plunging (0-25°) northeast-trending axes. warped about gently-plunging (0-25O) northeast-trending axes. The folds vary from from isoclinal "Z"sense senseasymmetry asymmetrywhen when viewed viewed toward toward isoclinalwith withconsistent consistent"Z" the east to northwest-facing northwest-facing monoclinal flexures. flexures. Axial Axialsurfaces surfacesare arerarely rarelyaccompanied accompanied by a foliation foliation defined defined by by flattened flattened quartz quartzgrains. grains. The Thetrend trendofoflineations lineationsand andfold foldaxes axesisis northeast-southwest throughout throughout this part of but plunge plunge direction direction northeast-southwest of the theKapuskasing Kapuskasing zone, zone, but varies on on aa regional regional scale scale from from dominantly dominantly southeasterly southeasterly in in the the south south tto northeasterly in o northeasterly the north. Between lineations are are within within 10° Between these these areas, areas, lineations 1O0 of horizontal horizontal and and abrupt changes plungedirection direction occur occur on on the the 100 m m scale. scale. Both Both regional regional and and local local plunge plunge changes inin plunge reversals can be be related related to aa gently gently southeast-plunging southeast-plunging warp axis. reversals can �r LI I - 17 - I A A I I I I 'A -4- -s A 'c -e A Sc "INDEX MINERAL' ISOGRADS (teeth point p up—grade) 0 A / Clinopyroxene / -f n A A Garnet — cIinopyroxene Orthopyroxene A A I 'Lfl A A 4, / 1' A A4 A n I I I I I I I I I I I . . LEGEND LEGEND 1 SYMBOLS SYMBOLS Alkalic rock-carbonotite complex Granitic Graniticrocks rocks ' Anorthositic Anorthositic rocks rocks . Retrograde Retrograde greenscllst greemctist fades facies laI Unsubdivided — Unsubdivldedgreenschist ÇMnSchist amphibolite amphibolite facies facie* supra— supracrustal crustal rocks rocks Cataclastic ASSEMBLAGES ASSEMBLAGES MAFIC(BASALTIC) (BASALTIC)GNEISS GNEISS MAFIC C HbHb-P1PI —Hb—PI CE Gt Gt-Hb-PI nfl Cpx—Hb—PI Cpx-Hb -PI ttton ton Q Gt Gt—Cpx-Hb-PI -Cpx-Hb-PI -Qz -02 GI~t—Cpx —Qz ton -CPX-Hb—PI -~b-PI -02—-ton Gt -ton Gt—Opx-Cpx-Hb—PI -0px-Cpx-Hb-PI—Qz -02-ton DIOR ITIC ROCKS ROCKS DIORITIC A Hb—Bt-PI Hb-Bt-PI -Qz -02 r A Hb—Bt Hb-Bt—P1 -PI—Qz -02—ton -ton AA Cpx-Hb—Bt Cpx-Hb-Bt—P1 -PI -02 -ton -Qz -ton AA Opx-Cpx-Hb—Bt Opx-Cpx-Hb-Bt—P1 -PI -Qz -02-ton -ton PARAGNEIS PARAGNEISSS 00 BtBt—P1 -PI —Qz±Hb -0ztHb(+sfauroliteØ) (*stniirnl~te 0) 0<SGt—Bt Gt -Bt -P1 -PI -QztHb -0ztHb AA Opx—Gpx—Hb—Pl ±Qz opx-OPX-H~-PI to2 CC Gt Gt-Hb-PI -Hb-PI ±Qz Hb-PltQz C Hb-Pl e0Opx-Bt-PI Opx-Bt -PI-Qz -02 ANORTHOSIT1C ROCKS ROCKS ANORTHOSITIC e0 GtOpxHb-PItQz Gt-Opx-Hb-PltQz ULTRAMAFIC +ULTRAMAFIC ROCKS ROCKS CCGt—Bt-PI —Qz—ton Gt-Bt-PI -02-ton± tHbHb opx-cpx-~b(+Pp (<-PI.+) Opx-Cpx—Hb 4) cM -Opx-Bt—PI -Qz—ton(+Kspe) 1 -op~-Bt-pI -O~-~O~(+KSD:È Opx-Cpx-Bt-Pl -Qz-ton zone . Figure Metamorphicmineral mineralassemblages assemblagesand andindex indexmineral mineralisograds isogradsIfor part of ofthe the Figure8.8. Metamorphic or part Chapleau-Foleyet garnet;Opx Opx- orthopyroxene; orthopyroxene;Cpx CpxChapleau-Foleyet area. area. Gt Gt- -garnet; clinopyroxene; clinopyroxene;Hb Hb- hornblende; hornblende; Bt Bt- -biotite; biotite; P1 PI- -plagiocase; plagiocase;Ksp Ksp- -feldspar; feldspar; Qz Qz- quartz; quartz;ton ton- -tonalitic tonaliticsegregations. segregations.(after (afterPercival, Percival,1983) 1983) - - - - �- 18 - Two high-grade high-grade metamorphic metamorphic zones canbe bedistinguished distinguishedininthis this part part of of the the Two Kapuskasing structural zone. zone. Assemblages characteristic of Kapuskasing structural Assemblages characteristic of aa lower-grade lower-grade garnetgarnetclinopyroxene-plagioclase zone zone are are developed developedinin mafic mafic gneiss. gneiss. Orthopyroxene, in clinopyroxene-plagioclase Orthopyroxene, present present in four areas (Fig. 8; areas in most rock types, is is diagnostic of aa higher-grade higher-grade orthopyroxene zone zone (Fig. Percival, 1983). 1983). A continuous reaction resulting resulting in of hornblende in mafic A continuous reaction in decomposition decomposition of hornblende in mafic rocks rocks to to produce garnet garnet and and clinopyroxene clinopyroxene may may be bewritten: written: hornblende plagioclase^±garne ± garnet + clinopyroxene + + quartz quartz + ll2O (1) + clinopyroxene +H 20 ornblende ++ plagioclase (1) The coexistence over large areas areas of of this divariant and tonalitic tonalitic leucosome xistence over divariant assemblage assemblage and leucosome veinlets suggests that the the reaction reaction was liquid over over aa range range veinlets suggests that was anatectic anatecticand and also also produced produced aa liquid of P-I conditions (Fig. 9): 9): hornblende ++pplagioclase garnet + ÷ clinopyroxene clinopyroxene ++ tonalite tonalite hornblende l a g i o c l a s e±e garnet (2) (2) A reaction leading leadingtto the production production of of orthopyroxene orthopyroxene in in mafic mafic rocks is: is: A possible possible reaction o the hornblende ++garnet garnete ± orthopyroxene + clinopyroxene clinopyroxene ++ H20 H20 hornblende (3) (3) The evolved evolved water would The would presumably presumably have have been been taken up by anatectic anatecticLiquids. liquids. In paragneiss, paragneiss,aare reaction producing orthopyroxene yroxen in the presence of anatectic melt is: is: . . biotite + quartz ÷ plagioc1ase orthopyroxene + gra.rtodioritic (4) ' biotite + + plagioclase^sorthopyroxene + grandioritic liquid * . - .. > ..~. .'. ..,. diagram summarizing summarizing continuous continuous reactions reactions in in the mafic - - ' - : AA P—I P-T diagram mafic system system and and apparent metamorphic conditions on various mineral geothermometers conditions based based on geothermometers and and geobarometers, is presented in Figure Figure 9. 9. Apparent Apparentpressures, pressures,based based on onNewton Newtonand and geobarometers, Perkins' (1982) (1982)garnet-clinopyroxene-plagioclase garnet-clinopyroxene-plagioclasequartz quartz barometer, barometer, are a r e plotted plotted on on aamap map Perkins' have aan averagevalue valueofof 6.3 6.3 kbar. kbar. This 10 and have n average This barometer apparently apparently in Figure 10 by 1-1.6 underestimates pressure pressure by 1-1.6 kbar (Newton (Newton and and Perkins, Perkins, 1982; 1982; Ghent et et al., al., 1983) 1983)and and hence an an average average value valueof of 7.8 7.8 kbar kbar is is suggested. suggested. Apparent temperatures, temperatures, based based on the hence Ellis garnet-clinopyroxene thermometer thermometer (Fig. 9) 9)are a r e in in the t h erange range 700700Ellis and and Green (1979) (1979) garnet-clinopyroxene 800°C. Metamorphic on water water barometry 80O0C. Metamorphic fluids fluidswere were probably probably depleted depleted in H20, H20, based based on (Percival, 1983) and the the presence presenceof of carbonic carbonic fluid inclusions 1983) and inclusions (Rudnick (Rudnick et et al., al., 1984). 1984). The assemblage assemblageaimandine almandinegarnet-clinopyroxene-plagioclase-quartz garnet-clinopyroxene-plagioclase-quartz is diagnostic The of the regional egionalhypersthene hypersthene zone zone according according to t o Winkler Winkler(1979, (1979, p. p. 260, 260, 267-268). 267-268). de de Waard Waard (1965)and andGreen Greenand andRingwood Ringwood (1967) (1967)suggested suggestedthat that this this assemblage forms as an an (1965) forms as alternative to anulite-facies toorthopyroxene-plagioclase orthopyroxene-plagioclaseduring during high-pressure high-pressure gr granulite-facies alternative metamorphism. Turner attachesaadifferent different significance significance to t o the theassemblage, assemblage, metamorphism. Turner (1981) 0981) attaches �I I I I I - 19 - 12 I 0 4 0$ I $ 9. I 0 0 I I . II 7. .0 I 0) 0) 0) .5 3 11.5 S 0 Gt-Cpx—Hb—PI—Oz Gt-Cpx- Hb-PI-Qz C 0 Ct Gt—Opx—Cpx—Hb—PI -0px-Cpx-Hb-PI 0 0 Gt—Opx—Bt—PI—Oz Gt-Opx-Bt-PI-Qz I. 4. I I S •• 0. I I S. . 0 3 I I S 0 700 800 Temperature (°C) Figure Figure 9. 9. Summary of reactions applicable to mafic Summary of mafic rocks rocks arid and metamorphic pressuretemperature temperature estimates. estimates. Temperatures Temperatures are arederived derived from from the garnet- clinopyroxene and Green, Green, 1979) 1979) and pressures from clinopyroxene thermometer thermometer (Ellis (Ellis and garnet-pyroxene-plagioclase-quartz garnet-pyroxene-plagioclase-quartzbarometers barometers(Newton (Newtonand and Perkins, Perkins, 1982). 1982). �-20regarding based ononBinns' regarding it it as as transitional transitionalfrom fromamphibolite amphiboliteto t ogranulite granulitefades fades based Binns'(1964) (1964) study. In the present study area, the location of the garnet-clinopyroxene-plagioclase study. In the present study area, the location of the garnet-clinopyroxene-plagioclase zone hornblende-plagioclase÷clinopyroxene rocks zone between between hornblende-plagioclase+clinopyroxene rocks and and orthopyroxene-bearing orthopyroxene-bearing rocks suggests suggeststhat that it it characterizes amphibolite-granulite facies transition. characterizes the the amphibolite-granulite facies transition. rocks Although is the the same that in Although the the assemblage assemblage is same as as that in the theAdirondacks Adirondacks(de (deWaard, Waard,1965) 1965) and and temperature Bohlen and Essene, 1977),the the path path of temperature conditions conditions were were similar similar(Cf. (cf. Bohlen Essene, 1977), metamorphism different. In In the the Grenville Grenville Province, Province, the the development development of of garnetgarnetmetamorphism was was different. clinopyroxene hasbeen beenattributed attributed tto isobaric cooling clinopyroxene assemblages assemblages has o isobaric cooling of orthopyroxeneorthopyroxeneand Schrijver, plagioclase granulites (Martignole 1971; Whitney, 1978) whereas in plagioclase (Martignole and Schrijver, Whitney, 1978) whereas in the the Kapuskasing Kapuskasing zone, zone, garnet garnet and and clinopyroxene formed formed during during prograde reactions. Rounded zircons of Rounded zircons of probable probable metamorphic metamorphic origin origin from from Kapuskasing Kapuskking mafic maficgneiss gneiss gave a concordant date date of of 2,650 2,650 Ma Ma and and from fromaaleucosome leucosome layer layerininparagneiss paragneiss of 2,627 2,627 Ma Ma (Percival (Percival and and Krogh, Krogh, 1983; 1983; Fig. 11). 11). Further Furtherwork workon onmetamorphic metamorphiczircon zirconhas has extended (Krogh et et al, A al, 1986). 1986). A extended the the range range of of metamorphic metamorphic dates dates to t o 2696-2616 Ma Ma (Krogh minimum age of of emplacement emplacement for foliated tonalite minimum age tonalite from from the theShawmere Shawmere complex complex is provided by by zircons (2,765 (2,765 Ma) Ma)but butthe the U-Pb U-Pb system system has has been been strongly affected affected by by the the high-grade Krogh, 1983). 1983). The rocks rocks intruded by by tthe high-grade metamorphism metamorphism (Percival and Krogh, h e tonalite tonalite are thus t h e Abitibi Abitibi and and Michipicoten Michipicoten belts. thus older older than than dated dated volcanic volcanic rocks rocks of of the Quartz-bearing gabbroic anorthosite contains contains zircon zircon with with two two habits: habits: red-stained red-stained resorbed grains with with meta-igneous meta-igneous appearance, appearance, and equant, multifaceted, colourless colourless grains of probable probable metamorphic origin. Both Bothpopulations populations have have aa U-Pb U-Pb age ageof of 2649 2649Ma Ma (3.A. Sullivan, unpublished unpublisheddata), data),interpreted interpreted as tthe (LA. Percival and R.W. R.W. Sullivan, h e time time of of metamorphic The analysis analysis of of the coarsest coarsest resorbed resorbed grains grains plots slightly slightly to the the metamorphic cooling. cooling. The right line, suggesting suggesting an an older older component. component. right of of the the2649 2649Ma Ma discordia discordia line, At least least two two swarms swarms of fresh fresh mafic mafic dykes dykes transect transect metamorphic metamorphic rocks rocks of of the the Kapuskasing zone. East-northeast-striking, Kapuskasing zone. East-northeast-striking, southeast-dipping southeast-dippingKapuskasing Kapuskasingdykes dykes are are11to to 10 m m wide, wide, sparsely sparsely plagioclase plagioclase porphyritic, porphyritic, mediummedium- to to fine-grained, fine-grained, ophitic, green-grey gabbro. Northeast-trending Northeast-trending olivine-bearing olivine-bearing dykes dykes may may belong belong to t o the the Abitibi Abitibi swarm. swarm. Several rock-carbonatite complexes Several small alkalic rock-carbonatite complexes are associated with the the Kapuskasing zone. The Kapuskasing zone. The more more northerly northerlybodies bodieshave haveK-Ar K-Ar dates datesofof1655 1655tot o1720 1720Ma, Ma, whereas those in the the south south have have dates datesof of 1050 1050to t o 1100 1100 Ma Ma (Gittins et e t al., al., 1967). 1967). Thin Thin lamprophyre dykes and andaa rare rare diatreme diatreme breccia are are associated associated with with the the complexes; complexes; lamprophyre dykes biotite biotite from fromaalamprophyre lamprophyre dyke dyke in the Chapleau-Foleyet Chapleau-Foleyet area gave a K-Ar K-Ar date date of of 1144 I144 +±31 31 Ma (Stevens eta!., e t al.,1982). 1982). 4 i 1 $ Li �r I I I I I I 1 $ I I -21 - PALEOPRESSURE PALEOPRESSURE ESTIMATES ESTIMATES Equilibria Equilibria I I I 032—8.3 / 024- ,+. 29-6.5 21 —& 53 .1W( DC 0 22— 8.i;9,9 W 06.7 enstatite=1/3 grossular ~ 6 . Anorthite+ 7Anorthite+enstatite=1/3 gross + 2/3 pyrope+quartz 0+ 2/3 pyrope+quartz (Perkins (Perkins&SNewton, Newton,1981) 1981) 2 06.7W 0 6 . 7 ~Garnet—orthopyrOXene Garnet-orthopyroxene A (Wood, (Wood,1974) 1974) 06.79 06.7~33Anorthite=grOSSUIart Anorthite=grossular+ 2 sillimanite÷ciuartz (Ghent, 1976) 07-6.7 2 0-6.2 14—' 0 10—6.6 013—4.29.9W 013-L2.9.9W >20 1 1.3,COW 17-6.5 — 48°00 - 2 1—6.7 0 Chapeat 10 0 40 I I I 6-7.3 2 3—5.4 06.7 grossular 06.7 Anorthite+diopside=2/a ~northite+diopside=~/s grossu ÷+ 1/3 pyrope+quartz V3 pyrope+quartz I I 3 1-6.00 km km Figure Figure10. 10. Paleopressure Paleopressure map Symbols represent rock map of of the Chapleau-Foleyet Chapleau-Foleyet area. area. Symbols type paragneiss; squares squares - mafic mafic gneiss; gneiss; triangles triangles - orthogneiss). orthogneiss). type (circles (circles- paragneiss; Numbers Numbers to to the the right rightofofthe thedash dashare arepressure pressure estimaters estimators(kbar) (kbar)keyed keyed to tothe the equilibrium equilibriumused used to t o derive derive the t h e value. value. The The6.3 6.3 kbar kbar reference referenceline lineisisbased based on on garnet-dinopyroxene-plagioclase-quartz equilibrium. (afterPercival, Percival,1983) 1983) garnet-clinopyroxene-plagioclase-quartz equilibrium. (after - - - RELATIONSHIP OF OFKAPUSKASING KAPUSKASING STRUCTURAL STRUCTURAL ZONE ZONE TO TOAD3ACENT ADJACENTSUSPROVINCES SUBPROVINCES RELATIONSHIP The The contact contactbetween between the theKapuskasing Kapuskasing structure structureand and Abitibi Abitibisubprovince subprovinceisis aa zone zone of faulting faultingand andcataclasis, cataclasis,the theIvanhoe Ivanhoe Lake Lake cataclastic cataclasticzone, zone, that thatseparates separates the the two two of terranes of of contrasting contrasting lithological, lithological, structural, structural,and and metamorphic metamorphic characteristics. characteristics. The The terranes �- 22 — 2O6 b 238 u 0.55 2800 1• 14 '4, 0N 2 0.50 'Ix Paragneiss Paragneiss leucosorne leucosome ( Vv Mafia Mafic gneiss gneiss (2) (2) 013 Shawmere Shawmere tonalite tonalite (3) (3) (vanttoe Ivanhoe Lake Lake ptuton pluton (4) (4) 0a Gneissic Gneissic tonalite tonalite (5) (5) v- 0¡ ' + OneissicGneissic- foliated granodiorite granodiorite (6) (6) 7 0 0.45 ZO7Pb 235u 12.0 13.0 14.0 15.0 Figure Figure 11. 11. Concordia Concordia diagram diagram with with isotopic isotopic ratios ratiosof of zircon zircon samples. samples. Ab: Ab:abraded abraded (Krogh, N: non-magnetic (Frantz); MI: magnetic at : non-magnetic MI: magnetic atj0l oside side tilt tilt (Krogh, 1982); 1982); N (Frantz); (Frantzk pr: pr: prismatic; prismatic; an: an: anhedral. anhedral. Solid Solidlines lines are areempirical empiricallead-loss lead-loss trajectories; Ma trajectories;dashed dashedline: line: hypothetical hypothetical lead-loss lead-loss trajectory trajectory(projects (projectstoto0 0Ma lower lower intercept); intercept); dash-dot line: empirical mixing xing line. line. (after (afterPercival Percivaland and Krogh, Krogh, 1983) 1983) zone zone is is defined defined in part by by positive, positive, linear north-northeast-trending north-northeast-trending aeromagnetic aeromagnetic anomalies pairedhigh high(Kapuskasing) (Kapuskasing) --low low (Abitibi) (Ab'itibi) anomalies and and coincides coincideswith withthe thetrough troughofofa apaired gravity and12). 12). gravityanomaly anomaly(Figs. (Figs.44and The Ivanhoe Ivanhoe Lake cataclastic zone is is characterized characterizedby bynarrow narrowveinlets veinletsof offinely finely The cataclastic zone comminuted rock rock which which form form discontinuous, discontinuous, randomly-oriented randomly-oriented pods pods and networks. networks. Two Two comrninuted foliatedtotomassive, massive,semi-opaque semi-opaque typesof of fault faultrocks rockscan canbe bedistinguished. distinguished. The Thefirst firstisisfoliated types mylonite, cataclasite cataclasiteand andblastomylonite, blastomylonite, partly partly or or totally totallyrecrystallized recrystallizedtot ofine finegrained grained mylonite, epidote, chlorite, chlorite, carbonate, carbonate, and and actinolite. actinolite. The Thesecond secondtype typegrades gradesfrom from cataclasite cataclasitetoto epidote, pseudotachylite with with aphanitic, aphanitic,almost almostopaque opaquematrix matrixand androunded, rounded,embayed embayed pseudotachylite monomineralic rnonomineralicporphyroclasts. porphyroclasts. �r I I o - 23 - - -5 It: .- > F 0 -to- .3c. -so- m CB - 0 10 kkrn m I I I 20 Shawmere Shawmere anorthosite anorthosite complex complex PROTEROZOIC 1100 Ma alkalic-rock complex ARCHEAN Massive granite. granodiorite (G2.70) I I I I I I 4 Ivanhoe Ivanhoe Lake cataclastic cataclastic zone zone 1 I Tonalitic gneiss (G.270) H Metavolcanic rocks (Gz2.90) Anorthositic rocks (G~2.82) (G2.82) Anorthositic rocks Kapuskasing gneisses (G2.52) Kapuskasing zone zone gneisses (G=2.82) Figure Figure12. 12. Generalized Generalized west-east west-east cross-section cross-section from fromthe theWawa Wawa domal domal gneiss gneiss terrane, terrane, through structural zone zone into into tthe Abitibi subprovince, through the t h e Kapuskasing Kapuskasing structural h e Abitibi subprovince, showing showing gross gross crustal structure. The The gravity gravity model modelbased based on on the t h e average average rock rock densities: densities: tonalitic tonaliticgneiss gneissand andgranite: granite:2.70; 2.70; metavolcanics: metavolcanics: 2.90; 2.90; Kapuskasing structural zone Kapuskasing structural zoneand and lower lower crust: crust:2.82 2.82 g/cm g/cm 3.3. The cataclastic zone The dip of the the Ivanhoe Ivanhoe Lake cataclastic zoneisisnot notwell wellconstrained constrainedgeologically. geologically. Although fault-rock veinlets are Although some fault-rock are parallel parallel to t ogneissosity gneissosity and and therefore thereforedip dipgently gently northwest, northwest, many many others others have have random random orientation. The Thejuxtaposition juxtapositionofofhigh-grade high-grade against displacement across across the the cataclastic cataclastic zone. against low-grade low-grade rocks indicates reverse displacement zone. The The associated associated paired paired gravity gravity anomaly anomaly is i s characteristic characteristic of of many many well-documented well-documented overthrust terranes terranes(Smithson (Smithsonetetal., al.,1978; 1978;Fountain Fountainand andSalisbury, Salisbury,1981) 1981) and suggests that that the the Ivanhoe cataclastic zone Ivanhoe Lake cataclastic zone is is the t h esurface surfaceexpression expression of of aanorthwest-dipping northwest-dipping thrust thrust fault fault(Fig. (Fig. 12). 12). AAshort short(10 (10km) km) seismic reflection survey survey over the zone indicates aa reflector reflectorininthe t h eappropriate appropriateposition positionwith withaatrue truenorthwesterly northwesterlydip dipofof38-40° 38-40-(Cook, (Cook,1985; 1985; Fig. Fig. 13). 13). The boundaryvaries variesinincharacter character over over its its length. length. North The Wawa-Kapuskasing Wawa-Kapuskasing boundary North of of Bonar Bonar Lake, Lake, it i t is is aafault, fault,with withdistinct distinctaeromagnetic aeromagneticexpression, expression,which whichdiverges diverges westward westward into into Wawa Wawa tonalites tonalites toward toward the thesouthwest. southwest. South SouthofofBonar BonarLake, Lake,the t h eboundary boundaryhas has T �_______________ - 24 — 24 a a LINE KAP LINE KAP - s-P. ____.i —. b — 2I -1 1sw 5 km 400? —-.-——---- :200 LINE KAP b 5.P. n_fl- 201 -1 5km W — A —C N S C — B — —— —— - A B 5.0. Figure 13. a ) Figure 13. a) Seismic reflection profile over the eastern Kapuskasing zone. The data Seismic reflection profile on left the Kapuskasing continuity of zone. reflections is are plotted with east overbecause the eastern The data are plotted with east on left Reflection because theAcontinuity better in this orientation. is likely from the Ivanhoeis Lake of reflections better in this zone; orientation. cataclastic reflections B a r e from t h e Abitibi Reflection A is within likely from the subprovince. Lake cataclastjc zone; reflections B are from within the Abitibi Ivanhoe subprovince. b) Line drawing interpretation of a ) (after Cook, 1985). b) Line drawing interpretation of a) (after Cook, 1985). �'I -25- I I I J I I I I $ gradational lithogical, structural and lithogical, structural and metamorphic metamorphic characteristics. Mafic Maficgneiss gneiss with with minor paragneiss paragneiss is typical of the minor the Kapuskasing Kapuskasing zone but also occurs in in the the Robson Robson Lake Lake dome with characteristic structural style subprovince. GarnetGarnetdome style of the the Wawa Wawa subprovince. clinopyroxene-hornblende-plagioclase assemblages are common commonhere, here, suggesting suggestingthat that the clinopyroxene-hornblende-plagioclase assemblages are metamorphic similar to that in the structural zone. zone. The metamorphic grade grade is similar the Kapuskasing Kapuskasing structural The discontinuous paragneiss paragneiss belt belt that extends 30km kminto intothe theWawa Wawasubprovince subprovince extends for for up upto t o30 discontinuous may also be be a part of lithological sequence. sequence. Tonalitic of the the Kapuskasing Kapuskasing lithological Tonalitic gneiss gneiss can be be traced eastward eastward from from the the Borden Borden Lake area, where it i t has has the the complex complex structures structures characteristic of characteristic of the theWawa Wawa subprovince, subprovince, into strongly foliated and lineated gneiss typical of the the Kapuskasing Kapuskasing zone. zone. The change in in structural structural style The change style from from domal domal in in the the eastern easternWawa Wawa subprovince subprovince to ENEbelts belts in inthe the Kapuskasing Kapuskasingstructural structural zone zonecan can be be used usedto to define define aa transitional transitional linear ENE boundary zone zone between betweenterranes terranes with with contrasting structural boundary structural styles, styles,but butno nosharp sharpline linecan can drawn on on this this bask. basis. South be drawn South of Chapleau, the orientation orientation of of gneissic gneissic layering layering changes changes eastward from horizontal horizontal near near the theHighbrush Highbrush Lake Lake dome, through a zone with a superimposed upright uprighteasterly easterly foliation, foliation, ttoo strong northeast-striking, superimposed northeast-striking, northwest-dipping northwest-dipping north-south-trending structural structural culmination coincides with with the eastern gneissosity. A north-south-trending eastern domes of of the Wawa subprovi.nce.East Eastofof the the culmination, culmination, lineations plunge plunge easterly easterly domes Wawa subprovince. toward a structural structuraldepression depression into into which which southwest-trending southwest-trending lineations of the southern southern Kapuskasingzone zonealso alsoplunge. plunge. To To the the north, lineations plunging northeasterly off the Kapuskasing plunging northeasterly the Lake arch arch appear ttoo be continuous with with northeastnortheastnortheastern flank flank of the the Missinaibi Missinaibi Lake plunging, reclined reclined folds in in tthe structural zone plunging, h e northern Kapuskasing Kapuskasing structural zone (Percival, (Percival, 1981 1981a,b). a,b). Cataclastic veinlets veinlets characterize the the faulted faulted contact contactbetween between mafic maficgneiss gneiss and and tonalitic tonalitic gneiss southwest southwest of of Kapuskasing KapuskasingLake. Lake. To To the the south, south, the the gradational nature of gneiss lithological contacts as well as the structural lithological structural and and metamorphic metamorphic continuity continuity between between high-grade gneisses gneissessuggests suggeststhat that the the contacts contacts were etablished prior tonalites and high-grade prior ttoo metamorphism and doming, doming, and and that that rock units of of the theKapuskasing Kapuskasing zone zone locally occur the Wawa Wawatonalite-granodiorite tonalite-granodiorite gneiss. gneiss. Based structurally below below the Based on on the the change change in in average rock density density across across this thisdiffuse diffusesubhorizontal subhorizontalboundary, boundary, Percival Percival(1986) (1986) suggested that it could represent an exposed mid-crustal mid-crustal (Conrad) (Conrad)discontinuity. discontinuit STRUCTURE OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CROSS-SECTION I $ The The transition from from the the Michipicoten Michipicoten belt to t o the the eastern eastern boundary boundary of the the �- 26 - 0 C 4-. 0 04a. fl-I 0 5 :::::::::::. Ct E o . V CD U, ci) 67 __:::_::.c_:c.: C s a, r ——— i! iiiiii: ::::::::::::::::::::•— —15 T::::E:::::::::: :::.. — — — .. — -. ——— a — .A>2,765 — 25 \Ivanhoe Ivanhoe Lake Lake cataciastic cataclasticzone zone Figure Figure 14. 14. Restored Restoredvertical verticalsection sectionthrough throughthe theMichipicoten Michipicotenbelt, belt,domal domalgneiss gneiss terraneand andKapuskasing Kapuskasing zone. zone. Numbers Numbersare a r ezircon zircondates dates(÷4 (54Ma) Ma)on onigneous igneous terrane and meta-igneous rocks (after Percival and Card, 1983). Kapuskasing Kapuskasing zone can be interpreted interpreted as asan anoblique oblique crustal crustal cross-section cross-section based basedon onthe the following: following: 1)1)metamorphic metamorphic grade gradeincreases increaseseastward eastwardfrom fromlow lowgreenschist greenschistfacies faciesininthe the Michipicoten Michipicoten belt belt(Studemeister, (Studemeister,1983) 1983)through through amphibolite amphibolite facies faciesin inthe theWawa Wawadomal domal gneiss gneissterrane terranetotoupper upperamphibolite amphiboliteand andgranulite granulitefades faciesininthe theKapuskasing Kapuskasing zone; zone;2)2)the the proportion proportion of of plutonic plutonicto t osupracrustal supracrustalrocks rocksincreases increaseseastward eastwardininthe theWawa Wawasubprovince; subprovince; 3)3)the theoldest oldestrocks rocks(>2,765 b2.765 Ma) Ma)are a r eininthe theKapuskasing Kapuskasing zone zone at atthe theinferred inferredbase baseofofthe the section; section;4)4)the thegravity gravityanomaly anomalycan canbebebest bestmodelled modelledbybyusing usingaawest-dipping west-dipping crustal crustalslab slab (Fig. (Fig.12); 12);and and5)5 ) rocks rockswith withseismic seismicvelocities velocities typical typicalof of the theupper uppercrust crustare a r enot notpresent present �r I -27the Kapuskasing zone. The three major terrane types recognized in the Abitibi-Wawa region can be be related region can related to t o depth depth zones zones in in the the crust crustbased based on on metamorphic metamorphic evidence evidence and and consistent seismicvelocity velocitycharacteristics characteristics of of the the crust consistent with with known known seismic crust of of the t h e Superior Superior Province. crust is of supracrustal supracrustal rocks rocks of of the the greenstone Province. Thus Thus the the uppermost uppermost crust is made made up up of greenstone belts and and discordant discordant plutonic plutonic rocks. rocks. Beneath megalayer made made up up of of variably variably belts Beneath is is aa megalayer deformed felsic felsic ttoo intermediate deformed intermediate plutonic plutonic rocks, rocks, with with large-scale large-scale domal domal geometry. geometry. With With increasing depth within within this this layer, layer, the the attitude attitude of from sub-vertical, sub-vertical, increasing depth of gneissosity gneissosity changes changes from near zone. The near greenstone greenstone contacts, contacts, to t o sub-horizontal, sub-horizontal, near near the the Kapuskasing Kapuskasing zone. The lowermost lowermost exposed megalayer is represented represented by exposed megalayer by the t h e Kapuskasing Kapuskasing zone, made made up of aa heterogeneous heterogeneous lithological assemblage assemblage aatt high metamorphic grade. grade. Moderate high metamorphic Moderate dips dips of of lithological lithological layering lower crustal crustal attitude attitude rotated layering aare r e interpreted as as the t h e dominant dominant sub-horizontal sub-horizontal lower rotated passively uplift. passively during uplift. Construction of of a generalized generalized crustal crustal cross-section cross-section (Fig. (Fig. 14) 14) requires requires several several Construction assumptions: 1)the the dip dip of of the the crustal slab is constant; 2) assumptions: 1) 2) pressure is a function of depth de so that estimates of the estimates of of metamorphic metamorphic pressure pressure can be used used to derive tthe h e thickness of section; 3) the metamorphic assemblages assemblages aare r e the product product of of aa single single metamorphic metamorphic event; event; post-metamorphic vertical displacement on faults within 4) post-metamorphic and 4) within the the section section is isnegligible. negligible. The highest-grade highest-grade assemblage from tthe area is garnet-andalusite in h e Wawa Wawa area in indicating aa maximum maximum pressure pressure of of 3.3 3.3 kb kb and and aa depth of of metagreywacke (Ayres, (Ayres, 1969), 1969), indicating about 11 km (Carmichael, (Carmichael, 1978). 11 km 1978). Similar pressures, in the t h e 2-3 2-3 kb kb range, are arebased based on on sphalerite-pyrrhotite geobarometry on rocks rocks from Gutcher Lake, 30 km km northwest of o Wawa (Studemeister, 1983). 1983). The The range range of of pressures pressures estimated estimated from Wawa (Studemeister, from the t h eKapuskasing Kapuskasing garnet-clinopyroxene-plagioclase-quartz zone, based on Newton Newton and Perkins' Perkins' (1982) (1982) garnet-clinopyroxene-plagioclase-quartz barometer, is is 5.4 5.4 to to 8.4 8.4 kb kb (average (average of of 6.3 6.3 kb, kb, Percival, Percival, 1983) 1983) but the t h e lower lower values values may may result from re-equilibration re-equilibration during during cooling. cooling. These These values values correspond ttoo depths of 18 18 ttoo km (average (average 21 21km). km). The The minimum minimumerosion-level erosion-leveldifference difference isis therefore therefore 7 km, but the 28 km the closer ttoo 15 km. The maximumdip dipestimates estimates over over aa difference is is probably probably closer 15 km. The minimum minimum and maximum 100. constantly-dipping slab 120 km long long aare constantly-dipping 120 km r e approximately 5° 5O and lo0. The dips of of post-metamorphic post-metamorphic dykes dykes in in the the Kapuskasing Kapuskasing zone zone and and eastern easternWawa Wawa providean anindependent independentestimate estimateofoft the tilt of of tthe subprovince may may provide h e tilt h e slab in this area. dykes dip dip NE NE at at 75' 75° ttoo 85° and ENE ENE Kapuskasing Kapuskasing dykes dykes dip dip SE SEaatt 70 70° ttoo 85° 85' and 85"'. Matachewan dykes ' on measurements measurements of of dykes dykeswith withvertical vertical exposure exposureininroadcuts. roadcuts. Post-metamorphic based on Post-metamorphic maf Icdykes dykesinint the Shieldgenerally generallyhave havenear-vertical near-vertical orientations, rnafic h e Shield orientations, as asdo do Matachewan Matachewan dykes in the Abitibi subprovince (Thurston et a!., 1977; Mime, 1972). The consistent nonin I I fl I pLi I I I ' �- 28 - vertical dip may thus have resulted from large-scale crustal rotation. To restore the dykes of both both swarms swarmsto to vertical, vertical, a dykes of a 14° 14O counter-clockwise counter-clockwise rotation rotation about about an an axis axis trending 038° is necessary. necessary. Thus 14°northwesterly northwesterly dip dip is is indicated indicated in in this trending 038'' is Thus aa 14" this eastern eastern area. area. The difference difference in The in dip dip estimate estimateprovided provided by by these these two twomethods methods may may be be due due to to uncertainties in the the calculations, calculations, faulty or real uncertainties in in the the data data used used in faultyassumptions, assumptions, or real differences differences in in dip dip from from east east to t o west. west. The The overall overall dip dipmust must flatten flattentot othe thenorthwest northwestand andisisreversed reversed northwest northwest of of the t h e Michipicoten h4ichipicoten belt beltwhere whereErnst ErnstU981, (1981, p. p. 87; 87; 1983) 1983) reported reported consistent consis 85° SW dipsofof Matachewan Matachewandykes. dykes. Therefore, Therefore, an an intermediate intermediate dip 85O SW dips dip value value of of 10° 10' If dips flatten perpendicular tto the fault fault was for construction construction of perpendicular o the was chosen chosen for of Figure Figure 14. 14. If dips flatten toward the the northwest, northwest, this this will will result of the toward result in in over-estimation over-estimation of of the the true true thickness thickness of the section. The generalized section section is is a a valid valid representation representation provided provided that that(1) (I)aa single si The generalized regional event affected affected all (2) late late vertical vertical regional metamorphic metamorphic event all of of these these rocks, rocks, and and (2) displacement along faults isisnegligible Wawa negligiblebetween betweenthe theIcapuskasing Kapuskasingzone zone and and eastern e displacement along faults subprovince. In subprovince. In view of of the thecomplex complex relationships relationships described described and and uncertainties uncertainties involved, involved, these simplifications simplifications may information which be these may be be unwarranted; unwarranted; however, however, the information which can can be derived from an exposed exposedcross-section cross-sectionthrough throughpart partofofthe thecrust crust is is potentially potentially valuable derived enough permit some enough tto o permit some speculation. The generalized crustal cross-section, cross-section, constructed constructedusing using aa dip dipof of10° 10' (Fig. (Fig.14), 14),has has at its upperamphibolite amphibolite tto its base base a sequence sequence ofof upper o granulite granulite facies faciesgneiss gneiss and anorthosite, unknown,and andof ofwhich whichsome some55tot o10 10km km isisexposed exposed in i the the full fullthickness thicknessofofwhich whichisisunknown, Kapuskasing zone. Structurally Kapuskasing zone. Structurallyabove aboveand and separated separated by by an an analogue analogue of the the Conrad Conra an estimated estimated 10 tto km thickness thicknessof of tabular tabular ba batholiths discontinuity (Percival, (Percival, 1986) 1986) is an o 15 km of gneissic and xenolithic tonalite. sheetsand anddeepdeepgneissic and tonalite. Massive Massivegranitic graniticrocks rocksoccur occurasassheets rooted plugs at this this structural structural level. upper 5-10 km, both both granitic granitic rocks level. In the upper 5-10 km, rocks and and plugs at gneissic migmatitic migmatitic haloes surroundthe thelow-grade low-gradeMichipicoten Michipicotenbelt. belt. The interfaces gneissic haloes surround between the the adjacent, adjacent, generally horizontal megalayers undulating surfaces surfaces with with between megalayers are undulating several kilometres kilometres of of relief, domesatatintermediate intermediate structural structural levels as gneiss gneiss domes several relief, manifest manifest as and as as intrusive intrusive bodies bodies aatt higher levels. and In the western Superior Superior Province, two seismic seismic discontinuities discontinuitiesat at16-19 16-19and and 21-22 21-22 km, define upper, km, upper, middle and and lower crust (Hall (Hall and and Brisbin, Brisbin, 1982). 1982). Using Usingthe theKapuskasing Kapuskasing model, boundary between betweenaastructurally structurally higher model, the upper upper discontinuity corresponds corresponds tto o the boundary granitoid gneissic subjacent heterogeneous heterogeneous high-grade high-grade gneiss gneiss complex, granitoid gneissic layer layerand and aasubjacent whereas the lower discontinuity, corresponding to the middle-lower crustal boundary, is �I I I I I I I -29probably aa metamorphic metamorphic isograd (orthopyroxene (orthopyroxene isograd?) within withinthe theheterogeneous heterogeneous gneiss. Woods (1985)studied studiedelectrical electrical conductivity conductivity in Woods (1985) in the theKapuskasing Kapuskasing region with with aa large-scale array. Although large-scale magnetometer magnetometer array. Although the t h elower lowercrust crustisisanomalously anomalously conductive conductive in in the area (Duncan et al., al., 1980), there is is no no conductivity conductivity anomaly associated associated with with the 1980), there (Duncan et Kapuskasing zoneofofmidmid-t otolower lowercrustal crustalorigin. origin. This was wasinterpreted interpreted tto indicate that that Kapuskasing zone o indicate the conductivity the result of in conductivity anomaly anomaly at depth depth is the & situ fluids fluids which which were were lost during uplift uplift ofofthe theKapuskasing Kapuskasing structure. Similar gravity Similar models models of mega-layered mega-layered continental continental crust crustare arebased based on on seismic seismic and and gravity data (Smithson and Brown, Brown, 1977; 1977;Berry Berryand andMair, Mair,1980). 1980). Other Other inferred inferred cross-sections (Smithson and cross-sections through the the crust crust (Ivrea (Ivrea zone, zone, Pikwitonei Pikwitoneiregion, region,Musgrave, Musgrave, Fraser Fraser ranges; ranges; Fountain Fountain and and Salisbury, haveinincommon commonaadownward downwardincreasing increasingmetamorphic metamorphic grade grade and and aa thick, thick, Salisbury, 1981)have intermediate-depth intermediate-depth amphibolite-facies amphibolite-fades section section of of quartzofeldspathic quartzofeldspathicgneiss, gneiss, corresponding gneissterrane terrane of of the Wawa Wawasubprovince. subprovince. In In the the central corresponding tto o the domal gneiss Superior Province section, intrude and and assimilate assimilate both the section, these these gneisses gneisses intrude the overlying overlying supracrustal succession successionand andparts partsofofthe theunderlying underlyingcomplex. complex. The entire section down The entire down tto o I ' I 20 addedt to the crust crust in the interval 20 km was was added o the intervalbetween between 2750 2750and and 2680 2680 Ma. Ma. The The prepreexisting as thick thick as present present continental continental crust crust existing crust crust may may have, have, but but need need not have have been been as prior to to the the major major thickening thickeningevent. event. The Thehigh highmetamorphic metamorphic grade grade in in this this older older crust crust can can be accounted accountedfor for by by burial, burial, first first by later by by intrusion intrusion of of by aa volcanic volcanic pile pile and and somewhat somewhat later tonalite tonalitesheets. sheets. ARCHEAN ARCHEANEVOLUTION EVOLUTION OF OF THE THE KAPUSKASING KAPUSKASING CRUSTAL CRUSTAL STRUCTURE STRUCTURE I The and mafic gneiss of the The oldest rocks so far far recognized, recognized, paragneiss paragneiss and gneiss of the Kapuskasing zone, aare considered part part of a sedimentary-volcanic Kapuskasing zone, r e considered sedimentary-volcanic succession succession deposited deposited $ probably also prior to and probably probably as asaastratiform stratiform body t o 2765 2765 Ma M a ago and body at a t depths depths of less less than than 20 20 km, as inferred from from the the presence presence of relict relictolivine olivine(Thurston (Thurstonetetal., al., 1977; 1977; Kushiro Kushiro I I I I prior prior to t o2765 2765 Ma Ma ago. ago. The TheShawmere Shawmere anorthosite anorthositewas was emplaced emplaced into intothis thissuccession, succession, and by Simmons et al. (1980), the intrusion intrusion may represent the As suggested suggested by Simmons et (1980), the the and Yoder, 1966). 1966). As differentiation basalt differentiationproduct productofoftholeiitic tholeiitic basaltmagmas magmaswhich whichalso also erupted erupted at a t surface. surface. Major Major eruption eruption of ofvolcanic volcanicrocks rocksand anddeposition deposition of ofsediments sedimentsoccurred occurredbetween between al.,1982) 1982)and andbetween between 2725 2725 and and 2749 and 2696 2696 Ma Ma ago in the Michipicoten Michipicotenbelt belt(Turek (Tureketetal., 2749and 2703 M Ma ago in in the western Abitibi a ago Abitibibelt belt(Nunes (Nunesand and PyRe, Pyke, 1980). 1980). The lowermost volcanics are dated by the U-Pb are generally generally mafic maficand and so so have have not been been dated U-Pb zircon method. method. �- 30 - including ultramafic, ultramafic, mafic, and trondhjemitic to Synvolcanic intrusions, including Synvolcanic to granodioritic granodioritic bodies, were intruded into into the theMichipicoten Michipicoten and and Abitibi Abitibi piles piles 2750 2750 ttoo 2700 MMa ago. Large Large volumes volumesofoftonalite tonalite intruded intruded beneath beneath and andadjacent adjacent tto the greenstone 2700 a ago. o the at this thistime. time.The Theminimum minimumage ageofof2707 2707Ma Mafor forWawa Wawa tonalite tonalh? (Fig. (Fig. 11) 11)isisgiven given by by aa belts at concordant point point and and is is therefore therefore probably close tto the age of of crystallization. nearly concordant probably close o the The tonalites tonalites could could be be the the subsurface expression expression of of magmas magmas that that produced produced &cites dacites in the The upper parts of the upper the volcanic volcanic piles. piles. Tonalite Tonaliteintrusions, intrusions,now now gneissic, gneissic, engulfed engulfed and and represented as detached fragments of the the lower lower parts parts of of the thegreenstone greenstone succession succession (now (now represented rnafic mafic xenolith trains), possible possible older, older, tonalite tonalitebasement basementenclaves enclaves(e.g. (e.g. 1-lillary Hillmy and and Ayres, 1980), 1980),and andthe thewestern western parts parts of of the Kapuskasing which extend extend into the Ayres, Kapuskasing zone which tonalite gneiss gneiss terrane. The Thetonalitic tonaliticrnagmas magmasmay mayrepresent representjuvenile juvenilemaginas magmas derived derived from the mantle, or may products of partial partial melting melting of of aa heterogeneous heterogeneous lower lower from may be the products crust similar to zone. The t o that that exposed exposed in in the the Kapuskasing Kapuskasing zone. The tonalitic tonalitic intrusions intrusions have have imposed amphibolite-facies amphibolite-facies aureoles on metavolcanic metavolcanic host host rocks; rocks; considering considering the thevolume volume imposed sufficient ttoo account for most of of tonalite, the the heat heat from fromthese thesemagmas magmas was was probably probably sufficient the metamorphism of the volcanics. metamorphism of volcanics. Tonalitic Tonaliticmagmatism magmatismthus thusmay mayhave havecoincided coincided with with regional metamorphism metamorphismand andacted actedas asthe the main mainagent agentofofheat heat transfer transfer into the upper regional upper crust (cf Wells, Wells, 1979). 1979). Isoclinally Isoclinallyfolded foldedgneissosity gneissosityininthe thetonalite tonalite demonstrates demonstrates that major (cf major deformation post-dates post-dates these these intrusions. intrusions. The age of of major deformation Abitibi and and Wawa Wawa subprovinces is closely deformation in in the the Abitibi Ma, the the approximate approximate age age of of the youngest volcanics of of the main youngest volcanics main bracketed between 2696 Ma, pile, and 2680 Ma,the the approximate approximateage ageofoflatelate- to post-tectonic plutons plutons (Frarey (Frarey and 2680 Ma, In supracrustal supracrustal rocks rocks at at high high crustal levels, this this deformation deformation produced produced Krogh 1986). 1986). In upright to vertically-plunging structural features upright vertically-plunging structural features as as well well as as thrusts thrusts and and nappe-like nappe-like structures etal., al.,1981; 1981; Gorman German et et al., al., 1978; 1978; Thurston and Breaks, Breaks, 1978). 1978). At structures(Poulsen (Poulsen et deeper structural structural levels, levels, the thedeformation deformationresulted resultediningneissosity gneissosity and and subsequent subsequent folds folds in in plutonic rock rock and and paragneiss, paragneiss, followed followedby bylater later doming. doming. Forceful emplacement of plutonic massive plutons plutons also also deflected deflected structural structural trends massive trends in in country country rock rock into into concordance concordance with with of these bodies. at 2680 2680Ma, Ma, the margins of bodies. Following Following intrusion of the the massive massive plutons at subprovinces. There there was was relative relative tectonic tectonicquiesence quiesencein inAbitibi Abitibi and and Wawa Wawa subprovinces. There is is evidence, however, of continued activity activity in in the theKapuskasing Kapuskasing zone. zone. High-grade metamorphic rocks of of the Kapuskasing yield concordant U-Pb High-grade Kapuskasing zone yield U-Pb zircon dates of 2696 Ma. U-Pb U-Pb zircon dates dates are a r e generally generally considered considered to t o record record 2696 ttoo 2616 2616 Ma. case are a r eof of metamorphic metamorphic origin. origin. the age of crystallization of of the the zircons, zircons, which which in in this this case interpretation would This interpretation would imply imply tthat h a t metamorphism metamorphism in in the t h e Kapuskasing Kapuskasing zone occurred �r I 1 I I 3 I I P I I I 2696 Ma ago,up upt to 60M Ma aftertectonic tectonic stabilization of of much much of of the the rest of 2696 ttoo 2616 2616 M a ago, o 60 a after of Superior province. A discrete burial and metamorphism metamorphismevent, event,restricted restricted tto burial and o the Superior province. Kapuskasing zone, could explain the deformed, metamorphosed metamorphosed conglomerate conglomerate cobbles cobbles from Borden Lake which which have have aa zircon zircon date date of 2664 2664 Ma Ma (Percival et al., al., 1981). 1981). However, However, Borden Lake an anomalously young zircon zircon date date of of 2552 M Ma on aa trondhjemitic trondhjemitic cobble from the anomalously young a on the weakly weakly metamorphosed Ma Doré conglomerate conglomerate near Wawa, reported by Turek et et metamorphosed >2696 >2696 M a Dore Wawa, reported by Turek al. (1984), suggests that that the date (1984), suggests date on on the theBorden Borden Lake Lake conglomerate conglomerate cobble cobble may may not represent the age of crystallization of the source source pluton. pluton. In In addition, addition, tectonic mechanisms which which could could lead lead tto of the 500 krn wide wide o deep burial of 500 km long xx 50 50 km Kapuskasing "sliver"are are unknown unknownand andseem seemt otobe beunlikely unlikelyafter after termination termination of of the major Kapuskasing "sliver" tectonism theAbitibi Abitibiand andWawa Wawasubprovinces. subprovinces. It is more likely that aa single single tectonism ininthe protracted protracted metamorphic metamorphic event eventwas wasresponsible responsible for forproducing producing the the observed observed characteristics. One must must therefore examine the assumption that zircons zircons are a r e closed closed to t o lead lead loss loss immediately following crystallization, regardless of the following crystallization, the cooling cooling history. Slowly Slowly decreasing temperatures from decreasing metamorphic temperatures from peak levels of 800°C 800° could could result result in in lead lead diffusion years after after crystallization, provided that there diffusion out out of of zircon zircon for several million million years provided that is temperature" for zircon. 50°C was was estimated is some finite "blocking "blocking temperature" zircon. AAvalue value of of 700 700 ± -+ 50° for this hypothesis ttoo explain for zircon blocking blocking by Mattinson (1978). (1978). Invoking Invoking this explain the theyoung young "metamorphic" "metamorphic" dates dateswould would allow allow aa simpler simpler geological geological history historyinvolving involving only only the the metamorphism with later fluid metamorphism at at 2700 2700 to t o 2680 2680 Ma M a with fluid circulation and and possible possible ductile shear at at depth. depth. The east-northeast structural The prominent prominent east-northeast structuraltrends trendsininthe theKapuskasing Kapuskasing zone zone are are the the result of of relatively relatively late late tectonism. tectonism. The Thestructural structuralgrain grainisisdefined defined by by the orientation orientation of inigmatitic axes. This nigmatiticand and gneissic gneissiclayering layering folded folded about aboutshallow-plunging shallow-plunging ENE ENE axes. This folding folding event event therefore therefore post-dates post-dates crystallization crystallization of of tonalitic tonaliticmelts, melts,thought thought to t ocoincide coincide with with the netamorphic peak. units that can be the inetamorphic peak. Similarly, Similarly, structurally structurally complex complex tonalitic gneiss units traced into the Kapuskasing have a strong, strong, superimposed superimposed traced from from Wawa Wawa subprovince into Kapuskasing zone have ENE ENE foliation foliation and lineation in in the theKapuskasing Kapuskasing zone zone(Percival (Peruvaland andCoe, Coe,1981). 1981). If the the correlation correlation is isvalid valid between between massive massive granodiorite dated at a t 2680 2680 ± Ma and granodiorite granodiorite -+ 3 Ma gneiss then the the ductile gneiss adjacent to to the theKapuskasing Kapuskasing zone in the Abitibi subprovince, subprovince, then strain strain occurred occurred after after2680 2680 Ma Ma but pre-dated pre-dated post-metamorphic post-metamorphic cooling. cooling. This This timing timing is consistent that sinistral sinistral transcurrent transcurrent movement consistent with with the thesuggestion suggestion of of Watson Watson (1980) 0980) that movement occurred occurredalong alongthe theKapuskasing Kapuskasing zone zone during during emplacement emplacement of of the theMatachewan Matachewandyke dyke swarm swarm at at 2633 2633 Ma Ma (Gates and Hurley, Hurley, 1973). 1973). Late Late Archean Archean deformation deformation could could have have promoted promoted resetting resettingofof2700-2680 2700-2680 Ma Ma zircons zircons to toages agesdown downto t o2616 2616Ma. Ma. �- - — 32 32 — UPLIFT UPLIFT OF OF THE THE KAPUSKASING KAPUSKASING STRUCTURE STRUCTURE The age of of uplift of the Kapuskasing constrained. Evidence Kapuskasing zone is not well constrained. Evidence of of late lateArchean Archean transcurrent transcurrentmovement movementwas wascited citedby byWatson Watson(1980) (1980) and Percival Percival and and Coe Coe (1980), however its its magnitude was probably probably small, small, judging judging by bythe the minor minor apparent apparent offset (1980), however offset of occurred aatt that of the the Abitibi-Opatica Abitibi-Opatica contact contact (Fig. (Fig. 1). I). Major Major thrusting thrusting could could also also have occurred that time, time, setting settingU-Pb U-Pb and andK-Ar K-Ar isotopic isotopicsystems systemsininthe thehigh-grade high-graderocks rocksata t2,650-2,250 2,650-2,250 Ma. Ma. Geochronological evidence indicates indicates activity activity at Ma. Three Three alkalic alkalic Geochronological evidence at 1,655-1,850 1,655-1,850 Ma. rock-carbonatite rock-carbonatite complexes complexesnear nearKapuskasing Kapuskasiighave haveK-Ar K-Ar dates datesofof1,655-1,720 1,655-1,720 Ma Ma (Gittins (Gittins et et a!., al., 1967). 1967). AAbiotite-whole-rock biotite-whole-rock Rb-Sr Rb-Sr isochron isochron from tonalite of of the the Shawmere arid others, others, 1980). 1,850Ma Ma (Simmons (Simmons and 1980). A A whole-rock whole-rock Shawmere anorthosite anorthositecomplex complexisis1,850 40Ar/39Ar analysis of blastomylonite from from the Ivanhoe Lake Lake cataclastic cataclastic zone gave aa '+o~r/^~ r of date dateof of 1,720 1,720Ma Ma (Percival, (Percival,1981; 1981;Fig. Fig. 15). 15). 3-0 25 to 2.0 0) 0l C 02 Co a a I.e 1.0 0.2 0.4 0.6 0.8 1.0 Fraction Fraction 39Ar " ~ rre'eased released Figure Figure15. 15. 40Ar/39Ar 40Ar/39Ar age agespectra spectrafor forhornblende, hornblende,plagioclase plagioclaseand andwhole-rock whole-rock separates separatesfrom fromnear near the theIvanhoe IvanhoeLake Lake cataclastic cataclasticzone. zone. Increasingly Increasinglyhigh high release releasetemperature temperature from from left lefttotoright. right.Width Widthofofbars barsare are2o-uncertainty 2uuncertainty estimates. estimates. �ii I 17 I I I I I I I I I I I I I I I -33rock-carbonatite complexes in the southern Three alkalic rock-carbonatite southern Kapuskasing Kapuskasing zone have of 1,050-1,100 Ma (Gittins (Gittins et at., K-Ar K-Ar dates of 1,050-1,100 Ma al., 1967). 1967). Plagioclase Plagioclase from from amphibolite4n amphibolite-in tthe he of tthe Ivanhoe Lake Lake cataclastic cataclastic zone footwall of h e Ivanhoe zone yields a 40Arf39Ar ^O~r/39Arplateau at at 1107 1107 Ma Ma (Fig. 15), suggestingmild mildresetting, resetting, possibly possiblydue duet otofaulting. faulting. Lower concordia intercepts intercepts (Fig. 15), suggesting Lower concordia of zircon discordia in tthe Ma (Percival (Percival and and Krogh, Krogh, 1983) 1983)may mayrelate relatetto of h e range 827-1,108 827-1,108 Ma o ago. uplift 1,100-1,000 1,100-1,000 Ma ago. events along along tthe structure with major The coincidence of Proterozoic events h e Kapuskasing Kapuskasing structure orogenic activity activity elsewhere Shield suggests suggeststhat thatt hthe structure is is an anintracratonic intracratonic orogenic elsewhere in tthe h e Shield e structure basementuplift uplift related to possibly an anearly early Proterozoic Proterozoic basement t o aa distant distant compressional compressional event, possibly collision in the Churchill Province to t o the t h e northwest northwest (Percival (Percivaland andMcGrath, McGrath, 1986). 1986). �- 34 - PART lb ROAD LOG . KAPIJSKASING UPLIFT: UPLIFT: ARCHEAN THE KAPUSKASING ARCHEAN GREENSTONES GREENSTONES AND AND GRANULITES GRANULITES SUMMARY Variousstructural structural levels within tthe Various h e central centralSuperior Superior Province Province will will be be examined examined to to demonstrate their characteristics characteristics and and interrelationships. interrelationships. Starting Startingwith with the thelowest-grade lowest-grade area, we we will will progress up-grade up-grade through an rocks in the Michipicoten Michipicoten belt of the t h e Wawa Wawa area, unbrokenoblique obliqueccrustal cross-section into tonalitic gneisses and granulites of the unbroken r Kapuskasing zone. DAYI Geology of the Geology of the Wawa Wawa Subprovince, Wawa ttoo Chapleau Chapleau in well-preserved well-preserved supracrustal rocks of of tthe h e Michipicoten Michipicoten belt The first day begins in and ends ends in in the the lowest lowest structural structural levels gneiss terrane (Fig. and levels of the the Wawa Wawa gneiss (Fig. 2). 2). Exposures Exposures near Wawa willdemonstrate demonstrate lithological, lithological,structural structural and and metamorphic metamorphic characteristics characteristics of Wawa will of the low-grade terrane. To rocks ocks and and internal low-grade terrane. To the theeast, east,the thetransition transitiontot ogneissic gneissicplutonic pi characteristics gneiss terrane will be examined. W characteristicsof of the t h eWawa STOP 1-1: 1-1: Doré STOP Dore Conglomerate Conglomerate(E. (E.and andW. W. sides sidesof of Hwy Hwy 17) 17) The Dore Doré isis aa thick, thick, coarse polymictic polyrnictic conglomerate unit tthat h a t isis overlain overlain by by The metavolcanic rocks at2696 2696 Ma Ma (Turek (Turek et et al., al., 1982) 1982)and and underlain underlain by by rocks of cycle cycle HI, 111, dated dated at older inetavolcanic metavolcanic rocks. rocks. Eastward f a d e s transition transitionfrom from Doré Dore conglomerate conglomerate older Eastward there there is is aa facies of wacke, siltstone, cross-bedded cross-bedded arkose and conglomerate called the the into a sequence of "Eleanor Slate". Slate". At this locality, coarse felsic tuff-breccias to "Eleanor t o the t h enorth north are aresucceeded succeeded southward by by aa sequence sequence of of wacke wacke (reworked (reworked tuff?) tuff?) and and Dore Doré conglomerate. conglomerate. Bedding southward Bedding and foliation dip approximately 45° 45" eastward eastward and and may may face facedownward downward (west). (west). The Dore Dare consists of of pebbles pebbles and and boulders boulders of of mafic mafic and and felsic volcanics, The volcanics, quartz quartz porphyry, iron iron formation formation and andtrondhjemite trondhjemiteininaa schistose, schistose, chloritic chloritic matrix. matrix. The The pebbles pebbles porphyry, aare r e flattened flattenedininthe thefoLiation foliation plane plane and and elongated elongated in in the the east-plunging east-plunging rodding rodding lineation. lineation. Variations in pebble pebblepacking packingand andsize sizedefine definecrude crudestratification stratification units. units. A Variations in A single trondhjemitic boulder apparent age age of of 2552 2552 Ma Ma boulder yielded discordant zircons with an apparent (Turek et et al., at., 1984), approximately 150 150M Ma youngerthan thant hthe stratigraphicage age of of the the unit unit 1984), approximately a younger e stratigraphic (Turek likely that that the source of of the based on zircon zircon dates of bracketing volcanic volcanic rocks. rocks. It is likely based trondhjemitic boulders syn—volcanic M a age. trondhjernitic bouldersand andcobbles cobblesis is syn-volcanic plutons plutonsofof2744—2735 2744-2735 Ma �r I 1-2: Helen Iron Range Section at McLeod Mine, Algoma Ore Properties Ltd. The McLeod Mineextracts extracts siderite siderite and and pyrite pyrite from from the base of the McLeod Mine the Helen Helen iron iron range. This 1800 m m thick unit of intermediate to t o felsic felsic Thisiron iron range range lies lies at a t the thetop topof of aa1800 metavolcanics metavolcanics consisting of oligomictic and polymictic breccia, thin thin bedded bedded to t o massive massive tufts, flows, and andcrystal crystal tuffs. tuffs. These tuffs, lapilli lapilli tuffs, tuffs, spherulitic spheruliticflows, flows, flow flow banded banded flows, These intermediate to felsic felsic metavolcanics metavolcanics are areintruded intruded by by gabbro gabbro ttoo quartz quartz diorite diorite dykes dykes and intermediate to sills sills that that reach reach290 290m m thickness. thickness. The intermediate intermediate to dominantly massive massive and and t o felsic felsicmetavolcanics metavolcanicsoverlie overlieaadominantly pillowed of intermediate to ed sequence of t o mafic mafic metavolcanics. metavolcanics. The The mafic to t o felsic felsic metavolcanics metavolcanics are arebimodal bimodal in in composition composition and represent the the oldest cycle cycleof ofvolcanism volcanism(Fig. (Fig. 14). 14). The The iron formation caps the first firstvolcanic volcanic cycle cyclein in the theMichipicoten Michipicoten greenstone greenstone belt belt and and from from the the stratigraphic stratigraphicbottom bottom to totop t o pconsists consistsof of five fivelithologic lithologic rock rock types types that that are are gradational gradational into into each other. Upper Upper and and lower lower contracts are sharp. sharp. From From stratigraphic stratigraphic bottom bottom to t o top top the t h eiron iron formation formation consists consists of of siderite, siderite, pyrite, pyrite, banded banded chert, chert, thin chert-wacke-magnetite, and graphite-pyrite. thin bedded bedded chert-wacke-magnetite, graphite-pyrite. AAU-Pb U-Pb isotopic isotopic age age of of approximately has been been obtained obtained from from the the crystal M a has crystal tuffs tuffslying lyingimmediately immediately below below approximately 2749 2749 Ma the the iron iron formation formation (Turek (Turek et et al., al., 1982). 1982). Overlying intermediate to Overlying tthe h e iron formation are massive massive pillowed pillowed intermediate t o mafic mafic inetavolcanics inetavolcanics of of cycle cycle two. two. The The area area of of the themine minedisplays displays numerous numerous major and minor faults, and and contains contains several a1Proterozoic Proterozoic diabase diabase dykes that strike strike northeast northeast and and northwest. northwest. Beneath areaofofapproximately approximately1800 1800mmby by 750 750 m m has has been been Beneath the theiron iron formation formationan anarea outlined outlined that that contains containschloritoid. chloritoid. These Thesecrystals crystalsare aregenerally generallyup upto t o22mm mrn in in diameter diameter and and are a r erandomly randomly oriented with with respect ttoo the schistosity. schistosity. Chloritoid Chloritoid alteration alterationoccurs occurs above above the the iron iron formation formation as aswell, well, in in less less abundant abundant quantities. quantities. The The volcanics volcanics above above and and below below the the iron iron range range are arepervasively pervasivelysoaked soakedwith with carbonate. carbonate. Carbonate Carbonatealteration alterationisisofofregional regionalextent extentand andoccurs occursin inall allrock rock types, types, volcanic, volcanic. sedimentary, sedimentary, and and intrusive. intrusive. STOP il I I I I I I I I I I I I I Spherulitic rhyolite rhyolite(100-200 (100-200 m m south south of of gate gateon onMcLeod McLeod Mine Mine road) road) Stop 1-3 1-3 Spherulitic Stop This This stop stop contains containsthe thebest bestexposure exposureofofaaspherulitic spherulitic(hollow) (hollow)flow flowbanded banded felsic felsic & . flow Mine area. area. The flow within within the the McLeod McLeod Mine The spherulitic spherulitic unit unit isis overlain overlain by by aa flow flow breccia breccia containing well well developed developed fiamme fiamme and and this this unit unit isisin in turn turnoverlain overlainby by aa massive massivetuff tuffwith with containing scattered scattered lapilli-size lapilli-size clasts. clasts. This Thisexposure exposure lies lies in in the the lower lower part of of the the felsic felsic part part of of the the �— 36 - oldest oldest cycle cycle of of volcanism. volcanism. Stratigraphic Stratigraphic tops tops are are north north and and the t h esection sectionisisoverturned, overturned, dipping along Wawa atWawa Wawa dipping south. south. Interpreted Interpretedfaulting faulting along WawaLake Lakeand andbeach beachdeposits depositsat prevent any estimate as to how far above the contact with the intermediate prevent any estimate as t o how far above t h e contact with t h e intermediate to t o mafic mafic pillowed metavolcanics this this felsic felsic section pillowed and and massive massive metavolcanics section occurs. occurs. Return Return to t o Hwy Hwy 101 101 - 00.0 km - Junction Me, Wawa. Junction of of Highway Highway IOIE 101Eand and Broadway Broadway Ave, Wawa. Proceed Proceed east east on on 00.0 km Highway Highway 101. 101. - 20.9 20.9 km -- Stop Stop 1-4: 1-k Mafic Maficgneiss gneiss - tonalite tonalitecontact contactzone zone(N. (N.and andS.S.sides sides of of Hwy Hwy101) 101) , A Ic gneiss A large large enclave enclave of of maf mafic gneiss is enclosed in and and intruded by tonalitic tonaliticgneiss gneissininaa migmatitic migmatiticzone zone marginal marginal to t o the the Michipicoten Michipicoten greenstone greenstone belt. The Thehornblendehornblendeplagioclase considered tto represent deformed, metamorphosed plagioclase gneiss is considered o represent metamorphosed Michipicoten volcanics and and metagabbro. metagabbro. In In this this exposure exposurei titisiscut cut by byearly earlytonalitic tonalitic intrusions, intrusions, llate ate aplitic apliticand and pegmatitic pegmatiticdykes, dykes, and and still stilllater latermafic maficand andlamprophyric lamprophyricdykes. dykes. The Thegneiss gneiss displays subvertical foliation, foliation, mineral displays subvertical mineral lineation, lineation,and and tight tightsteeply-plunging steeply-plunging isoclinal isoclinal minor folds. 45.1 45.1 km km Jct. Jct. Hwy. Hwy. 651. 651. Continue Continueeast. east. * , - 68.5 gneiss Budd and 68.5 km Stop Stop1-5: 1-5: Xenolithic Xenolithictonalite tonalite gneissatat BuddLake Lake(N. (N. andS.S.sides sidesofofHwy Hwy101) 101) This This complex complex outcrop outcropconsists consists of of several severalphases: phases: 1) 1) xenoliths of mafic maficgneiss, gneiss, interpreted interpreted as asrafts raftsofofthe t h eMichipicoten Michipicotenmetavolcanic metavolcanicsequence, sequence, 2) 2)gneissic gneissic tonalite tonalite with small, wispy mafic xenoliths, cut by 3) foliated to gneissic hornblende-epidote- biotite-sphene tonalite, all cut by 4) pink-white granitic pigmatite. Hornblende from foliated wt% ,41203, A1203, indicating indicating crystallization crystallization at foliated tonalite tonalite(3) (3) contains contains 10.4 10.4 wt% approximately approximately5.6 5.6 kbar kbar(Hammarstrom (Hammarstromand andZen, Zen, 1985). 1985). Continue east on 101 94.4 km Stop 1-6; Tonalite gneiss and maf Ic dykes (N. and S. of Hsy 101) Tonalite northeast-trending mafic Tonalite gneiss gneiss iiss cut by northwest- and and northeast-trending mafic dykes dykes with wit chilled dykes (Ernst and chilledmargins. margins. The Theolder oldernorthwest-striking northwest-strikingHearst Hearst dykes (Ernst andHalls, Halls,1980, 1980,1984) 1984) occur have aa similar similar trend and occur west west of of the t h eKapuskasing Kapuskasing zone. zone. The The dykes dykes have and similar similar �- r I (I I I I 1 I I I I including plagioclase plagioclase phenocrysts phenocrystsand andtholeiitic tholeiitic composition, composition, tto characteristics, including o Matachewan dykes dykes east east of of the Kapuskasing zone. The Kapuskasing zone. The Matachewan Matachewan dykes dykes have an Rb-Sr Rb-Sr Matachewan whole-rock age of 2633 ± 75 M Ma (Gates and andHurley, Hurley, 1973). 1973). Ernst and Halls (1980, a (Gates (1980, 1984) 1984) whole-rock 2633 + also reported reported similar paleomagnetic poles poles for for the two zone 50 50 km km wide wide also two swarms. swarms. InInaa zone " zone, the the Hearst dykes average average 44 m m in in width and west of the the Kapuskasing Kapuskasing zone, and have have a consistent easterly easterly dip dip of of 80 80° (Ernst, (Ernst, 1983; Percival, 1981). 1981). The Thetonalitic tonalitic gneiss is thinly thinly consistent 1983; Percival, gneiss is layered and and has hassparse sparsemafic maficxenoliths. xenoliths. Gneissosity appearstto havechaotic chaotic orientation orientation Gneissosity appears o have but is subhorizontal onaverage. average. There Thereisisevidence evidencefor forat at least least two two sets setsofof structure: structure: an an but subhorizontal on older gneissosity gneissosity is is reoriented reoriented by by younger younger subhorizontal subhorizontalfoliation foliation to t o give give complex complex patterns. sigmoidal patterns. Continue east 122.2km km Stop 1-7: 122.2 1-7: Highbrush Highbrush Lake Lake Dome Dome (N. (N.side of Hwy Hwy 101) 101) Small domes domesexposed exposedininroadcuts roadcutshere hereare aretypical typicalofof the the local local and and possibly possibly of of the the Small regional-scalestructural structural pattern. pattern. The rock type is fine-grained, fine-grained, thinly-layered thinly-layered regional-scale The main main rock biotite and biotite and hornblende-biotite hornblende-biotite gneiss gneiss with with local localaugen augen of potash potash feldspar. The outcrop outcrop consists consists of of several several domes domesor orcanoe-shaped canoe-shapedfolds foldswith withaarolling rolling easteastThe west mineral mineral and andstretching stretchinglineation. lineation. Small parts west Small intrafolial intrafolialfolds foldsare arepresent present in in some some parts as are areamphibolitic amphibolitic xenoliths, xenoliths,locally locally with with clinopyroxene. clinopyroxene. Pink Pink granitic granitic of the outcrop, outcrop, as and sills sills cut cut gneissic gneissic layering layering in in some some areas. areas. Late sub-horizontal highpegmatite dykes dykes and are common commonininthe the vicinity vicinity of strain zones zones are of the thetransition transitionzone zonebetween betweenWawa Wawa and and Kapuskasing gneisses. gneisses. Continue east - I 131.6km km - Junction Junction of of Highway andHighway Highway129. 129. Follow Follow 101E, lOlE, 129N toward Highway 101 101 and 129N toward 131.6 1 132.9 km Chapleau Stop 1-8: 1-8: Xenolithic tonalite (w. side side of of Hwy Hwy Stop tonalite with withhorizontal horizontalshear shear zones zones (W. 101—129) 101-129) 1 I I I Xenolith alignment and gneissosityhave havesub-vertical sub-verticalorientations orientations in in the the central central and gneissosity thin part of this this road-cut. road-cut. Layering Layeringbecomes becomes horizontal horizontal and and mafic mafic xenoliths xenoliths become become thin and bottom bottom of of the mafic layers in 1/2 112 m-thick horizontal horizontalshear shear zones zones near near the top and outcrop. �139.5 - — 38 — km . Junction )unction of of Highways and 129N: 129N: Proceed north km Highways 1OIE 101E and north on on Highways Highways 101-129 101-129 through Chapleau. Chapleau. Follow Follow the t h eMissinaibi Missinaibi Provincial Park Park signs north of town on gravel road. road. Proceed Proceednorth northand andeast easton onpark parkroad roadand andlogging logging roads roads leading ttoo the the Chapleau Chapleau River. River. - 178.3 FlorannaLake LakeComplex Complex Stop 1-9: 1-9: Floranna 178.3 km - Stop The Floranna Floranna Lake Lake Complex Complexisisaacomplex complexcrescentic crescentic pluton plutonofof intermediate intermediate composition. composition. The The western western margin margin consists of lineated, h e a t e d , fine fine grained grained granite granite with with orthopyroxene and and biotite. biotite. inside Inside the the marginal marginal unit is is lineated diorite diorite to t o monzonite rnonzonite containing hornblende-rimmed augenclinopyroxene clinopyroxenephenocrysts. phenocrysts. The Thecentral central part of the hornblende-rimmed augen the complex is foliated hornblende-clinopyroxene-biotitediorite, diorite, gabbro gabbroand and foliated and and lineated lineated hornblende-clinopyroxene-biotite melagabbi-o. well-exposed eastern eastern contact contact of melagabbro. The well-exposed of the thecomplex complexshows shows extremely extremely attenuated attenuatedand and contorted contortedlayering layering in in granite granite of of the thecomplex complex adjacent adjacent to t o rocks rocks of of the the Robson Lake dome dome tto the east. Robson Lake o the Clinopyroxene augen diorite-monzonite diorite-monzonite C l i p y r o x e n e augen These coarse-grained monzonite. medium- to coarse-grained monzonite. RodRodThese rocks are strongly lineated, mediumshaped shaped clinopyroxene clinopyroxene phenocrysts, rimmed rimmed by by hornblende, hornblende, make make up up some some 20% 20% of the the rock. rock. Original Originaloutlines outlines of of feldspar feldspar grains grains are arevisible visible but but these theseare arenow now polycrystalline polycrystalline aggregates. aggregates. j-y, - 179.3 - Foliated and lineated h e a t e d diorite dioritewith with gabbro gabbro and and melagabbro melagabbro layers layers Igneous clinopyroxene with with hornblende hornblende overgrowths overgrowths and and granitic leucosome leucosome layers layers are are present. present. - 183.2 Granulitegneiss, gneiss,Robson Robson Lake Lake dome dome 183.2 km - Stop Stop 1-10: 1-10: Granulite The of tthe complexisisaa foliated foliated to to augen-textured, augen-textured, The easternmost exposure of h e igneous complex xenolithic porphyritic granite granite with with leucogranite leucogranite veinlets veinlets parallel ttoo foliation xenolithic hornblende hornblende porphyritic on on the the 11 mm-2 mm-2 cm scale. scale. The Thelayering layeringisisfolded foldedabout aboutnorthwesterly-plunging northwesterly-plunging axes. axes. Parts Partsof of the theoutcrop outcropare a r efine-grained fine-grained and andmylonitic myloniticwith with highly highly attenuated attenuatedlayering. layering. To of interlayered mafic To tthe h e west, the t h e Robson Robson Lake dome consists of mafic and and tonalitic tonalitic gneiss. gneiss. Near Near the thecontact contactwith withthe theFloranna FlorannaLake LakeComplex, Complex, the t h e layering layering in in rocks in the dome concordant tto west, however, however, the the attitude attitude is dome is concordant o the contact and and dips steeply west, is horizontal Ic rocks eastin in the thecore coreof of the thedome. dome. AtAtthis thisoutcrop outcropthe themaf mafic rocks consist consist horizontal farther farther east of garnet-clinopyroxene-hornblende-plagioclase-quartzassemblages, assemblages, with with layering layering of garnet-clinopyroxene-hornblende-plagioclase-quartz defined and hornblende-rich defined by by different different proportions proportions of of minerals, minerals,including including garnet-rich garnet-rich'and hornblende-rich varieties. varieties. Concordant Concordanttonalitic tonaliticlayers layerslocally locallyhave havelarge largeclinopyroxene clinopyroxenecrystals crystalsrimmed rimmed by by hornblende, hornblende, in clots up ttoo 4 cm. The Thelayering layering isisfolded folded about about upright upright isoclinal isoclinal folds folds locally. locally. �r I I I I I I I -39inclusions of of mafic gneiss gneiss in in granite granite of granite in mafic gneiss and inclusions Small dykes of granite in indicate an indicate an intrusive intrusivecontact contactbetween betweenthe theFloranna FlorannaLake LakeComplex Complexand and Robson Robson Lake dome. The interpretation interpretation of the Lake dome, dome,which whichhas hasthe thestructural structural attributes attributes The the Robson Robson Lake of the domal gneiss gneissterrane terraneand andthe thelithological lithological characteristics characteristics of t h e Wawa Wawa domal of Kapuskasing Kapuskasing zone, is is that rocks zone underlie underlie the Wawa domal zone, rocks like likethose those exposed exposed in the the Kapuskasing Kapuskasing zone Wawa domal terrane been exposed exposedhere hereininaastructural structural culmination. culmination. terrane and and have have been Return to t o Chapleau Chapleau DAY 2 Geologyof of the Kapuskasing KapuskasingStructural Structural Zone Zone in in the the Chapleau-Foleyet Chapleau-Foleyet Area Geology In this this section we will will examine In examine the t h e rocks rocks and and structures of of the t h e Wawa Wawa domal doma' gneiss -- Kapuskasing Kapuskasingzone zoneboundary boundaryand andofofthe theKapuskasing Kapuskasingzone zoneitself itself along along gneiss Highway 101. 101. - 0.0 km km 0.0 I I I I I I I * ii. and Highway Highway 129 south south of of Chapleau. Chapleau. Proceed Junction of Highway Highway 101E 101E and Proceed east on Highway 101. 101. 2-1: Borden 13.0 km km Stop 101) Lake conglomerate conglomerate (S. (S. side of Hwy 101) 13.0 Stop 2-1: Borden Lake This outcrop outcrop consists consists of of stretched-pebble stretched-pebble metaconglornerate metaconglomerate with with aa strong rodding rodding This weak, gently gently north-dipping north-dipping foliation. foliation. The lineation and and weak, The rock rockisisaaclast-supported clast-supported conglomerate containing 10% 10%matrix matrix of of garnet-hornblende-biotite-quartz. garnet-hornblende-biotite-.quartz. The The cobbles, cobbles, conglomerate which range range up uptto m in in length, length, aare felsic metavolcanics, metasediments,granodioritegranodioriter e felsic metavolcanics, metasediments, which o 1m amphibolite, with rare hornblendite tonalite, plagioclase-porphyritic plagioclase-porphyritic meta-andesite meta-andesite and and amphibolite, and vein vein quartz. quartz. The and The metaconglomerate metaconglomerate is spatially spatially associated associated with amphibolite and and paragneissto tothe the south southon onBorden BordenLake, Lake,and andisiscut cutby bygranite, granite, however, however,tthe stratigraphic h e stratigraphic paragneiss relations of relations of the thesupracrustal supracrustal rocks rocks are areunknown. unknown. An aggegate aggegateofoftonalitic tonalitic cobbles extracted from the An cobbles extracted the metaconglomerate metaconglomerate yielded yielded Ma (Percival et et al., 1981). 1981). The The zircons zircons have have aa corroded corroded zircons dated at at 2664 2664 ±+ 12 12 M a (Percival appearanceand andproduced produceddiscordant discordantdata datapoints pointsand andhence hencet hthe interpretation of of the the data appearance e interpretation open. Rather than recording recording the the original original crystallization crystallization age of the source pluton for for is open. Rather than age of source pluton the cobbles the zircons zircons probably probablydate dateaalater later deformation-metamorphic deformation-metamorphic event. event. The cobbles the The source pluton plutonfor for the the cobbles cobblesmay maybe besimilar similart otothat that which which provided providedmaterial material for for the source Doré conglomerate. Dor6 �— 40 - Continue east on 101 Continue . .. - .. 2-2: Mafic 25.9 km Stop 2-2: 25.9 Mafic gneiss gneiss xenoliths xenoliths with with amphibolitic amphibolitic margins margins (N. (N. side of Hwy Hwy 101) 101) This exposure exposuredemonstrates demonstrates an an important important aspect aspect of between the This of the boundary boundary between Kapuskasingzone zoneand andWawa Wawagneiss gneiss terrane. Aside Asidefrom fromthe thelarge-scale large-scale structural structural Kapuskasing terrane. terrane and contrast between between the the domal domal Wawa Wawa terrane and the t h e linear linear belts beltsin inthe theKapuskasing Kapuskasing zone, intrusive relations relations are also instructive. The intrusive Theoutcrop outcropconsists consists of of two two main main components: components: (1)coarse-grained coarse-grainedhornblende-biotite hornblende-biotitetonalite, tonalite, the the dominant dominant rock rocktype type tto the west, west, and and (1) o the (2) medium mediumgrained grained mafic mafic gneiss gneiss consisting consisting of of garnet-clinopyroxene-hornblendegarnet-clinopyroxene-hornblende(2) plagioclase-quartz assemblages. assemblages. Small xenoliths of of mafic mafic gneiss gneiss in intonalite tonalite have have plagioclase-quartz Small xenoliths margins, up up tto cm thick, thick, consisting consisting of of hornblende-plagioclase. hornblende-plagioclase. Dykes Dykesofoftonalite tonalite margins, o several cm cutting mafic gneiss gneiss are are bordered bordered by mafic rock with hornblende-plagioclase hornblende-plagioclase assemblages. The assemblages. The interpretation of of age age relationships relationships is that that the thehigh-grade high-grade metamorphism that that produced the garnet-clinopyroxene assemblages in mafic gneiss metamorphism gneiss preceded the the intrusion intrusion of of tonalite. tonalite. Water preceded Water in in the the tonalite tonalitemagma magma was was presumably presumably ,. crystallization and and hydrated hydrated the the adjacent less-hydrous mafic rock. rock. released upon upon crystallization less-hydrous mafic Althoughthe the tonalite tonalite at this outcrop has not been dated, iti t probably either to Although probably belongs belongs either Ma tonalite gneiss gneiss suite suite or ttoo the 2680 group of of plutons. plutons. The high-grade the >2707 >2707 M a tonalite 2680 Ma M a group high-grade metamorphismisistherefore therefore older olderthan than 2680 2680Ma. Ma. This Thisisisininconflict conflictwith withthe thedirect direct dates dates metamorphism of metamorphic zircons from the as 2616 2616 Ma. Ma. of the Kapuskasing Kapuskasing zone that yield yield ages ages of of as aslow low as The conflict conflict has led ttoo the that the The the suggestion suggestion (Percival (Percival and and Krogh, Krogh, 1983) 1983) that the Kapuskasing Kapuskasing gneisses, although although metamorphosed metamorphosed prior prior tto 2680 M Ma ago,remained remainedat at high high temperatures temperatures gneisses, o 2680 a ago, where radiogenic lead diffused readily out of zircon until at least 2616 Ma ago. Continue east 37.0 km 37.0 2-3: Thinly-layered Stop 2-3: Thinly-layered tonalitic gneiss gneiss and diatreme diatreme breccia breccia (N. (N. side side of of Hwy Iiwy 101) 101) Fine grained grained tonalitic tonalitic gneiss Fine gneiss aatt this exposure is strongly foliated and layered on a 1-5mm mmscale scalewith withgarnet, garnet,hornblende hornblendeand andbiotite-rich biotite-richlayers. layers. Extremely Extremelyattenuated attenuated 1-5 intrafolial folds folds are are present present locally. locally. Units foliation intrafolial Units characterized characterized by by extremely planar foliation such as as this this aare relatively rare in tthe zone. Although the orientation orientation of of such r e relatively h e Kapuskasing Kapuskasing zone. Although the foliation in this exposure exposure is typical typical for for the theKapuskasing Kapuskasing zone, zone, most most Kapuskasing Kapuskasing gneisses gneisses coarse-grained and andlayered layeredwith withdistinctive distinctiveleucocratic leucocratic portions. portions. In are mediummedium- tto o coarse-grained addition, the the layering layering in in the the typical gneisses gneisses is is warped warped about about gently gently northeast northeast or or addition, southwest-plungingaxes. axes. The fine grain size and thin thin planar layering in this outcrop southwest-plunging suggest aa relatively relatively late, high-strain suggest high-strain flattening flattening or shearing shearing event. �r —41 - I? d A A thin thin diatreme diatremedyke dykeoccurs occursininthis thissame sameexposure. exposure. ItIt has has not not been been dated dated but but presumably presumably is part of of aa set set of of lamprophyre lamprophyre dykes dykes of 1100 . ~ l l 0Ma 0M aage age(Stevens (Stevens et et a!, al, 1982) 1982) that are particularly particularly common thatoccur occurininthe t h eKapuskasing Kapuskasing zone zone and and are common in the the area area between between the I I I Lackner Lakecomplexes. complexes. Both Both the the matrix matrix and fragments in the Lackner and and Nemegosenda Nemegosenda Lake the dyke dyke are be identified. identified. These are altered, altered, but but some some fragments can be These include include tonalitic tonaliticgneiss, gneiss, spinel spinel n Continue Continue east east on on Hwy Hwy101 101 lherzolite not occur occur in the Iherzoliteand and massive massive pink granite. As Asmassive massive granite granite does does not Kapuskasing zone,the thegranite granite fragments fragments are arerelatively relatively exotic. Their Kapuskasing zone, Theirsource sourcewas was probably below Kapuskasingzone, zone,possibly possiblyiningranite graniteofofthe the Abitibi Abitibi belt, below the Kapuskasing belt, which which according according to t o the the gravity gravitymodel, model, lies liesvertically verticallybelow belowatata adepth depthofof—15 -15 km. km. ' 52.1 52.1 km km Stop KapuskasingGneiss Gneiss (S. (S. side side of of Hwy Hwy101) 101) Stop 2-4: 2-4: Kapuskasing Layered ruafic in situ tonalitic tonaliticleucosome, leucosome,and and crosscrossmafic gneiss gneiss with concordant & cutting cuttingtonalitic tonaliticand andpegmatitic pegmatiticdykes. dykes. Layering Layeringononthe the5 5tot o1010cm c mscale scaleisisgiven givenby by I alternating of similar alternatinghornblende-rich hornblende-rich and and garnet-pyroxene-rich garnet-pyroxene-rich layers layers(see (see analyses analyses of layers layers in Table 1). 1). Metre-scale Metre-scale blocks blocks of mafic mafic gneiss gneiss in breccia give parts of the outcrop moutcrop aa chaotic chaoticappearance. appearance. These These structurally structurallycomplex complexpanels panelsare areseparated separated by. bym- scale high-strain high-strain zones with gently rolling, north-dipping, foliation. zones with north-dipping, pronounced pronounced foliation. Continue Continue east east on on Hwy Hwy101 101 59.8 59.8 km Stop Stop2-5: 2-5: Kapuskasing Kapuskasinggneisses gneisses (N. (N. and and S. S. sides sides of Hwy Hwy 101) 101) There are several several features features of of interest interest at this this outcrop outcrop (Fig. (Fig. 23): 23); Mafic Maficgneiss gneiss is present on the northwest side side of the the road. road. ItIt isis aa coarse coarse grained grained rock rock consisting consisting of of three threetypes types of of layers layerson on the the5-100 5-100 mm mm scale: scale: i)i)relatively relativelyanhydrous anhydrous A. I I I I I rnafic and quartz, quartz, with some mafic rock rock made made up of garnet, clinopyroxene, clinopyroxene, plagioclase and some hornblende to analyses analyses I1 && 3, 3, Table Table 1); ii) more hornblende (analogous (analogous to 1); ii) more hydrous hydrous layers layers containing containingless less garnet garnet and and clinopyroxene clinopyroxeneand and more morehornblende hornblende (analogous (analogous to t o analyses analyses 22 &&4, 4, Table Table1); I); and and iii) iii)tonalitic tonaliticleucosome leucosomelayers, layers, both both concordant concordant to t o layering layering and and transverse transverse in the amphibole-rich amphibole-rich mafic rocks. rocks. Note Note that that the thetonalite tonalitehas has no no retrogressive retrogressive effect effect on on adjacent anhydrous mafic gneiss. gneiss. The tonalitic tonalitic leucosome anhydrous mafic leucosome veinlets are are considered considered ttoo be in situ anatectic anatecticmelt meltsegregations segregationsdeveloped developed during prograde prograde metamorphic reactions of the outcrop, submicroscopic (see reaction 2). 2). In the western end of submicroscopic symplectites of orthopyroxene-plagioclase identified by form barely-visible coronas orthopyroxene-plagioclase identified by microprobe microprobe analyses, analyses, form coronas around garnet, clinopyroxene clinopyroxene and andhornblende. hornblende. Analyses Analysesofof the the symplectite symplectite minerals, at around garnet, at �-- 42 42 lower size size limit limit of of microprobe microprobe resolution, resolution, aare reported along along with with those those of of tthe tthe h e lower r e reported h e other minerals in in the the rock, rock, in in Table Table 2.2. The minerals The rock contains three three plagioclase plagioclase compositions. compositions. An39 Ana9 is present in in coronas coronas whereas worm-like worm-like intergrowths intergrowths of of An35 An35 and and An50 Anro make up tthe he matrix plagioclase. plagioclase. The mineral mineral compositions compositions yield yieldestimates estimates of of 735°C usingtthe and Green Green The 735'C using h e Ellis and (1979)garnet-clinopyroxene garnet-clinopyroxenethermometer thermometer and and 6.2 6.2 kbar kbar using usingtthe garnet-clinopyroxene(1979) h e garnet-clinopyroxene- plagioclase-.quartzbarometer barometer (Newton (Newtonand andPerkins, Perkins,1982). 1982).At Atthe thesame sametemperature temperature tthe plagioclase-quartz he and matrix matrix garnet yield 9.1 coronal minerals and 9.1 kbar kbar with tthe h e garnet-orthopyroxenegarnet-orthopyroxeneplagioclase-quartzz Newton and Perkins Perkins barometer. barometer. plagioclase-quart Newton and Kapuskasing dike Kapuskasing dike 1 B, . . A A orthopyroxeneorthopyroxeneplagioclase coronas 22Dm 0m 0 I I I orthopyroxene bearma bearing orthopyroxene metasedimentary imentary rock '7 ic and tonalitic gneiss Figure 23. 23. Location Location of of outcrops outcrops at at Stop Stop 2-5. 2-5. - A Kapuskasing Kapuskasingmafic maficdyke dykecuts cutsthe theeastern easternend endofofthe theoutcrop. outcrop. The overal overall BB.. A attitude SE although although tthe h e margin is offset by by numerous small attitudeof of the t h edyke dykeisis070/75 070175 SE sinistral faults. The Theouter outer22cm c mof of the themargin margin isischilled. chilled. Sparse Sparseplagioclase plagioclase phenocrysts phenocrysts are present in olivine-bearing gabbro. gabbro. Several in the t h e dominantly dominantly medium medium grained ophitic olivine-bearing Several dykes of of this swarm been dated by tthe dykes swarm have been h e whole-rock whole-rock K-Ar K-Ar method method and and yield yield "ages" "ages" and 3649 3649 Ma, Ma,indicating indicatingt the presence of of excess argon between 2367 2367 and h e presence (Stevens et et al., 1982). al, (1986) (1986)estimated estimated an age of 2040 2200 Ma Ma based based on (Stevens 1982). 1-lanes Hanes etet al, 2040 -- 2200 dyke and and its its baked baked country country rock. rock. ^40Ar/39Ar ~ r / ^ ~ ranalyses of a Kapuskasing Kapuskasing dyke Homogeneousmetasedimentary metasedimentary rock C. Homogeneous South of the road is a flat outcrop of medium grained rock with the h e assemblage . . �r I I I I I I I I I I I I I 1 1 I — 43 - Table 2. 2. Microprobe Microprobeanalyses analyses of minerals minerals in coronitic coronitic mafic mafic gneiss, gneiss. Stop Stop 2-5 2-5 1 2 4 3 Si02 Si02 38.01 51.57 49.06 42.29 hO2 Ti02 0.00 0.34 0.03 2.03 A1203 20.99 2.92 4.75 12.98 Cr203 0.22 0.21 0.34 0.08 28.06 11.81 31.20 18.43 0.70 0.81 13.35 1.39 0.17 9.28 8.32 0.00 11.34 22.65 11.41 0 27 0.74 0.52 1.95 Cr203 10* FeO* MnO MnO MgO MgO CaO CaO Na 0 Na20 2 K20 K2 4.11 0.00 0.08 0.00 0.69 Total Total 100.67 101.79 101.45 99.31 Si Si 2.973 1.908 1.885 6.252 Aliv Aliv 0.00 0.092 0.115 1.748 Alvi Alvi 1.935 0.035 0.100 0.513 Ti Ti 0.00 0.009 0.001 0.226 Cr c r 0.014 0.008 0.010 0.009 0.0 0.087 0.042 0.288 1.835 Mg Me 0.040 0.479 0.278 0.003 0.625 0.960 0.026 0.764 Ca Ca 0.697 0.898 0.057 1.990 0.021 2.044 1.807 Na Na 0.041 0.053 0.039 0.559 K K 0.00 0.004 0.00 0.130 3+ pe3 Fe 2÷ 2+ Fe Fe Mn Mn (0) (0) * * (12) (6) (6) (23) 1: 1: garnet; garnet; 2: 2: clinopyroxene; clinopyroxene; 3: 3: orthopyroxene; orthopyroxene;4: 4: hornblende hornblende Total Fe3 by Total iron as FeO; Fe3+ bystoichiometry stojcHiornetry Specimen Specimen also also contains contains quartz quartzand andplagioclase plagioclase(An33 Art88 in syrnplectite) symplectite) Ann8 in I 1.:jyt- mntrir. in matrix, �- 44 - z. Plagioclase garnet-orthopyroxene-biotite-plagioclase-quart garnet-orthopyroxene-biotite-plagioclase-quartz. Plagioclase occurs occursas asporphyroblasts porphyroblasts to is up uptto mm. The t o 22 cm cm and and orthopyroxene orthopyroxene is o5 5 mm. The rock rock has has the the same same mineral mineral assemblage assemblage as as high-grade in tthe zone but but lacks lacks tthe high-grade paragneiss paragneiss in h e Kapuskasing Kapuskashg zone h e migmatitic migmatitic layering layering typical typical of of paragneiss. paragneiss. Application Application of of the the garnet-orthopyroxene-plagioclase-quartz garnet-orthopyroxene-plagioclase-quartz geobarometer geobarometer yields values values in in excess excess of and Perkins yields of 11 11 kbar kbar by by both both Newton Newton and and Perkins Perkins (1982) (1982) and Perkins and and Chipera (1985) calibrations. calibrations. Chipera Interlayered mafic mafic and tonalitic gneiss D. Interlayered and tonalitic gneiss D. complex relations relations between Ic and and tonalitic tonalitic gneiss. outcrop demonstrates This This outcrop demonstrates complex between maf mafic gneiss. Isoclinal folds of of layering layering are are truncated truncated by Isoclinal folds by tonalite tonalitepods pods and and dykes, dykes, suggesting suggesting multiple multiple generations of of tonalite. tonalite. Thin generations Thinmylonite mylonite seams seams are are sub-parallel sub-parallel to t o gneissic gneissic layers. layers. Continue east 67.0 km km Stop 67.0 Stop 2-6: 2-6: Xenolithic Xenolithictonalitic tonaliticgneiss gneiss(S. (5.side sideof ofHwy Hwy101) 101) This outcrop outcrop consists consists of of mediummedium-t to coarse-grained tonalite tonalite made up of of garnet, garnet, This o coarse-grained hornblende, biotite, biotite, plagioclase plagioclase and and quartz. quartz. AA variety hornblende, variety of of xenoliths xenoliths includes includes mafic gneiss gneiss (garnet-.clinopyroxene-plagioclase-quart z),amphibolite, amphibolite,biotite-rich biotite-rich schists and spinel (garnet-clinopyroxene-plagioclase-quartz), pyroxenite. Amphibole-rich rims characterize characterize the pyroxenite. Amphibole-rich rims t h e high-grade high-grade inclusions. inclusions. Continue east 69.2 km Stop 2-7: Ivanhoe Lake cataclastic cataclastic zone 69.2 km Stop 2-7: Ivanhoe Lake zone(S. (S. side sideof ofHwy Hwy 101) 101) The outcrop outcrop is is on ont the western, high-grade high-grade side sideofoft the cataclastic zone and consists h e western, h e cataclastic The of migmatitic garnet-clinopyroxene-hornblende-plagioclase-quaitz of migmatitic mafic mafic gneiss gneiss with with garnet-clinopyroxene-hornblende-plagioclase-quartz assemblages. ItIt is assemblages. is transected transactedby by numerous numerous small fault offsets offsetsand and by by one one major major cataclasite thin section, section, this black black aphanitic material is cataclasite vein. vein. In In thin is seen seen to t o consist consist mainly mainly of (recrystallized) (recrystallized) fine fine actinolitic actinoliticamphibole amphibole and and of porphyroclasts porphyroclasts of hornblende. hornblende. AA 39 40Ar/39Ar whole-rock analysis of material from art age age plateau plateau at analysis of from this this vein vein yielded yielded an A r / Ar whole-rock 1720MMa (Fig.15). 15). On Ont hthe west side sideofoftthe outcrop aare rusty-weathering 1720 a (Fig. e west h e outcrop r e thin (3 cm) rusty-weathering lamprophyre dykes. dykes. Tonalitic by cataclasite cataclasite are of the lamprophyre Tonalitic rocks rocks cut cut by a r eexposed exposed 150 150 m north of highway on an overgrown road. Continue east �r I I U I I metavolcanics, Abitibi 2-8: Mafic km Stop 70.5 km 70.5 Stop 2-8: Mafic metavolcanics, Abitibi subprovince subprovince (N. (N. side sideof of Hwy Hwy 101) 101) on the eastern, low-grade the IL,CZ and is is the the westernmost This outcrop is on low-grade side of the ILCZ and belt. It is aa fine hornblendegrained, layered hornblendeof rnetavolcanics metavolcanics of of the Abitibi belt. fine grained, exposure of clinopyroxene rock rock with with local local rusty-weathering rusty-weathering patches. plagioclase + patches. ± clinopyroxene The structural characteristics characteristics of the east-west strike of of The structural t h e outcrop, outcrop, including including east-west isoclinal small small folds, folds,aare typical of of the the Abitibi layering, vertical dip dip and steeply-plunging steeply-plunging isoclinal r e typical Abitibi belt. Chlorite belt. Chloriteand and epidote epidote are are common common tto o tthe h e east along strike, where where the belt is wider, wider, suggesting an an easterly easterly decrease in metamorphic grade. grade. suggesting 40Ar/39Ar of hornblende hornblende and and plagioclase plagioclase from from this this outcrop outcrop by by tthe Analyses of he A ~ I A ~ method (Fig. (Fig. 15) show showaa plateau plateau for for hornblende hornblende at at 2567 M Ma and aa saddle-shaped saddle-shaped spectrum spectrum method a and plagioclase with with aa plateau plateau at 1107 Ma. The for plagioclase 1107 Ma. The plagioclase plagioclase plateau may may be due to t o argon argon loss resulting resulting from from aa mild mild thermal thermal event, event, possibly possiblyrelated related tto faulting. loss o faulting. 72.3 km km Turn main road. road. 72.3 Turn north on on logging logging road follow main side of 87.2 km km Stop 2-9: 2-9: Shawmere of road) 87.2 Shawmere gabbroic anorthosite (w. (W. side mainly coarse-grained coarse-grained gabbroic anorthosite anorthosite with The outcrop is mainly with hornblende hornblende and I I • I 1 I I I I I minerals. Ultramafic Ultramaficlayers layersconsisting consistingof of orthoortho- and andclinopyroxene clinopyroxene rare garnet as mafic minerals. with hornblende hornblende rims rims and and sparse sparse plagioclase plagioclase to 3 cm, occurs occurs in in layers layers and and pods pods up to to 44 m m with Mafic and and ultramafic ultramafic layers are structures thick. Mafic thick. are locally locally folded folded into into shallow shallow NE-plunging NE-plunging structures with aa prominent prominent lineation. lineation. One part of the with the outcrop outcrop is is a spectacular spectacular coronitic coronitic gabbroic gabbroic anorthosite with football-sized football-sized plagioclase megacysts. megacysts. Coronas Coronas have have orthopyroxene orthopyroxene or clinopyroxene cores; cores; orthopyroxene orthopyroxene has has successive successive hornblende hornblende and and pale pale garnet garnet rims; clinopyroxene clinopyroxene has has hornblende hornblenderims rims and andrare rare orthopyroxene orthopyroxene cores. cores. clinopyroxene Return to Hwy 101. km END 134.1 km END OF OF DAY DAY 2. 2. Return to t o Wawa. Wawa. �- 46 ACKNOWLEDGEMENTS Weberimproved improvedthe themanuscript. manuscript. C.W. by P.C. W. Weber Reviews by P.C. Thurston and W. C.W. Jefferson is thanked for editorial editorial revisions. revisions. . . . REFERENCES REFERENCE in the the Attoh, K., K., 1980. Stratigraphic relations of the the volcanic-sedimentary volcanic-sedimentary successions in Wawa greenstonebelt, belt, Ontario. Ontario. In Current Research, part 5 Current,Research, part A. A. 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Parallel Parallelevolution evolutionofofArchaean Archaeanlowlow-and andhigh-grade high-grade terrane; terrane; aaview view based based on on relationships relationshipsbetween betweenthe t h eAbitibi, Abitibi,Wawa Wawaand andKapuskasing Kapuskasing belts. Research, 14,14, pp.pp.315-331. belts. Precambrian Precambrian Research, 315-331. Percival, Percival, lÀ. J.A.and andKrogh, Krogh,T.E., T.E., 1983. 1983.U-Pb U-Pbzircon zircongeochronology geochronologyofofthe t h eKapuskasing Kapuskasing structural structuralzone zoneand and vicinity vicinity in in the t h e Chapleau-Foleyet Chapleau-Foleyet area, Ontario. Ontario. Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences,20, 20,pp. pp.830-843. 830-843. - �- 52 - 3.A. and and McGrath, McGrath, P.H., P.14.,1986. 1986.Deep Deepcrustal crustalstructure structure and and tectonic tectonic history of Percival, J.A. an integrated uplift of Ontario: an tthe h e northern Kapuskasing Kapuskasing uplift integrated petrological-geophysical petrological-geophysical study. study. Tectonics, Tectonics, 5,5,pp. pp. 553-572. 553-572. Percival, 3.A.., and Sullivan, Sullivan, R.W., R.W., 1981. 1981. U-Pb U-Pbzircon zircon ages ages of of tonalitic tonalitic J.A.., Lovenidge, Loveridge, W.D. W.D. and metaconglomerate cobbles and quartz monzonite monzonite from the t h e Kapuskasing Kapuskasing structural structural zone in in the the Chapleau zone Chapleau area, Ontario. Ontario. In InRb-Sr Rb-Sr and and U-Pb U-Pb Isotopic Isotopic age Studies, Report 4. In In Current Research, Research, part DartC. C. Geological GeologicalSurvey SurveyofofCanada, Canada,Paper Paper81-IC, 81-1C, pp. pp. 107107113. Percival, l.A., Stern, R.A. and Digel, M.R., 1985. Regional geological synthesis of western Superior Province, Ontario. Ontario. In Current Research, part part A. A. Geological GeologicalSurvey Survey Superior Province, of Canada, Paper 85-lA, 85-lA, pp. pp. 385-397. 385-397. Perkins, D. and and Chipera, Chipera, S.J., 5.1, 1985. Perkins, D. 1985. Garnet-orthopyroxene-plagioclase-quartz Garnet-orthopyroxene-plagioclase-quartz barometry: and tthe barometry: refinement refinement and andapplication application to t othe t h eEnglish English River River subprovince subprovince and he Minnesota River Valley. Valley. Contributions Minnesota River Contributions to t oMinerology Minerology and Petrology, 89, 89, pp. pp. 69-80. 69-80. Pine, 3. 1978. Preliminary examination of regional metamorphism Pirie, 3. and and Mackasey, Mackasey, W.O., W.O., 1978. metamorphism in parts of Quetico metasedimentary belt, Superior Ontario. In Superior Province, Province, Ontario. InGeological Geological Survey of Canada, Paper 78-10, Survey of 78-10, pp. pp. 37-48. 37-48. Poulsen, K.H., K.H., Borradaile, Borradaile, G.J. G.3. and Kehlenbeck, 198!. An Poulsen, Kehlenbeck, M.M., M.M., 1981. An inverted inverted Archeart Arche'an succession at Rainy CanadiannJournal iny Lake, Ontario. Ont JournalofofEarth EarthSciences, Sciences,17, 17,pp. pp.135813581369. Powell, R., R., 1978. geotherms. Philosophical Powell, 1978. The The thermodynamics of pyroxene pyroxene geotherms. Philosophical Transactions of the t h eRoyal RoyalSociety Societyof of London, London, A288, A288, pp. pp. 457-469. 457-469. Pyke, D.R., D.R., 1982. of the the Timmins Timminsarea, area, District District of of Cochrane. Cochrane, Ontario Pyke, 1982. Geology Geology of Ontario Geological Survey, Report 219, 219, 141 141 p. Riccio, L., of the northeastern Riccio, L., 1981. 1981. Geology Geology of northeastern portion portion of of the the Shawmere Shawmere anorthosite anorthosite complex, District of complex, of Sudbury. Sudbury. Ontario Ontario Geological Geological Survey, Survey, Open File Report 5338, 5338, 113 p. Ringwood, A.E., 1975. 1975. Corn Composition and Petrology of the Earth's Earth's Mantle. Mantle. McGraw-Hill, rtgwood, A.E., McGraw-Hill, New York, York, 618 618 p. ,. . . . . Rudnick, R.L., R.L., Ashwal, Ashwal, L. L.D. and Henry, Henry,D.J., 0.3., 1384. Rudnick, D. and 1984. Fluid Fluid inclusions inclusions in high-grade of the Kapuskasing structural zone, Ontario: metamorphic gneisses of Kapuskasing structural metamorphic fluids fluids and and uplift/erosion upliftferosion path. Contributions ContributionstotoMinerology Minerology and and Petrology, Petrology, 87, 87, pp. 399-406. 399-406. Sage, Summary Sage, R.P., R.P., 1980. 1980. Wawa Wawa area, area, District Districtof ofAlgoma. Algoma. InIn Summaryof offield fieldwork, work,1980. 1980. Edited by V.G. Mime, O.L. O.L. White, White, R.B. R.B. Barlow, Barlow, J.A. l.A. Robertson and Edited V.G. Milne, and A.C. A.C. Colvine. Colvine. Ontario Geological Survey, Miscellaneous Miscellaneous Paper 96, pp. pp. 47-50. 47-50. Schwerdtnen, W.M.and andLumbers, Lumbers,S.B., S.B.,1980. 1980. Major Major diapiric diapiric structures structures in Schwerdtner, W.M. in the t h eSuperior Superior Grenville provinces provincesofoftthe Canadian Shield. Shield. In The The continental continental Crust Crust and its and Grenville h e Canadian Mineral Deposits. Edited by by D.W. D.W. Strangway. Geological Association Association of Canada, Mineral Deposits. Edited Strangway. Geological Special Paper No. No. 20, 20, pp. 149-180. 149-180. �r I I I • I I U I I I I I U I I I I I Schwerdtner, Stone, D., D., Osadetz, Osadetz,K., K., Morgan, Morgan, 3.3.and andStott, Stott, G.M., G.M., 1979. 1979. Granitoid Schwerdtner, W.M., W.M., Stone, complexes and tthe Archean tectonic tectonic record in the complexes and h e Archean the southern southern part of of northwestern northwestern Ontario. Sciences, 16,16, pp.pp.1965—1977. Ontario. Canadian CanadianJournal JournalofofEarth Earth Sciences, 1965-1977. Schwerdtner, W.M., Stott, Stott, G.M., G.M., and andSutcliffe, Sutcliffe, R.H., R.ft, 1983. Schwerdtner, W.M., 1983. Strain Strainpatterns patternsof ofcrescentic crescentic granitoid greenstoneterrain terrainofofOntario. Ontario. Journal of Structural granitoid plutons plutons in tthe h e Archean Archean greenstone Journal of Geology, 19-430. Geology, 5,5,pp. pp.4 419-430. Sen, S.K. and and Bhattacharya, Bhattacharya, A., A., 1985. 1985. An orthopyroxene-garnet Sen, S.K. orthopyroxene-garnet thermometer and and its its application application to t othe t h eMadras Madras charnockites. charnockites. Contribution Contributionto t oMinerology Minerologyand and Petrology, Petrology, 83, 1. 83,pp. pp.64—7 64-71. Simmons, G.M., and and Lumbers, Lumbers, S.B., S.B., 1980. 1980. Geochemistry of the Simmons, E.C., E.C., Hanson, Hanson, G.N., theShawmere Shawmere anorthosite structural zone, Ontario. Precambrian Research, K anorthosite complex, complex, Kapuskasing 11, 11,pp. pp.43—71. 43-71. Smithson, S.B.and andBrown, Brown,S.K., S.K.,1977. 1977.AAmodel modelfor forlower lower continental continental crust. crust. Earth Smithson, S.B. Earth and and Planetary PlanetaryScience ScienceLetters, Letters,35, 35,pp. pp.134-144. 134-144. Smithson, S.B., Brewer, Brewer, J., 3., Kaufman, Kaufman, S., S.,Oliver, Oliver, J., 3., and andHurich, Hunch,C., C., 1978. 1978. Nature Nature of of the Smithson, S.B., Wind deep-reflection data and from gravity Wind River thrust, thrust, \Vyoming, Wyoming, from from COCORP COCORP deep-reflection gr data. data. Geology, Geology,6,6,pp. pp.648-652. 648-652. Stevens, Stevens, R.D., R.D., Delabio, Delabio, R.M. R.N. and and Lachance, Lachance, G.R., G.R., 1982. 1982. Age Agedeterminations determinationsand a Geological GeologicalStudies, Studies, K-Ar K-Ar isotopic isotopicages, ages,Report Report15. 15. Geological GeologicalSurvey SurveyofofCanada, Canada, Paper Paper 81-2, 81-2, 56 56p.p. Studemeister, Studemeister, P.A., P.A., 1983. 1983. The The greenschist greenschist facies faciesofofan anArchean Archeanassemblage assemblagenear nearWawa, Wawa, Ontario. Ontario. Canadian CanadianJournal JournalofofEarth EarthSciences, Sciences,20, 20, pp. pp. 1409-1420. 1409-1420. Sullivan, Card, K.D., K.D., 1985. Sullivan, R.W., R.W., Sage, Sage, R.P. R.P. and and Card, 1985. U-Pb U-Pb zircon zircon age age of of the the Jubilee Jubileestock stockinin the Research, part B. t h eMichipicoten Michipicotengreenstone greenstone belt belt near near Wawa, Wawa, Ontario. InInCurrent C Geological GeologicalSurvey Survey of of Canada, Canada, Paper Paper 85-IB, 85-10, pp. pp. 361-365. 361-365. Sutcliffe, studies on the Sutcliffe,R.R.and andFawcett, Fawcett,3.3., J.J., 1979. 1979.Petrological Petrologicaland andgeochronological geochro Rainy Rainy Lake Lake granitoid granitoidcomplex, complex,northwestern northwestern Ontario; Ontario;aaprogress progress report. report. In In Current Current Research, Research, part part A. A. Geological GeologicalSurvey SurveyofofCanada, Canada, Paper Paper 79-lA, 79-LA, pp. pp. 377-380. 377-380. Thompson, hompson, A.B., A.B., 1976. 1976. Mineral Mineral reactions reactions in in pelitic politicschists schistsH. 11. Calculation Calculatio of some P-T-X phase phase relations. relations. American AmericanJournal JournalofofScience, Science,276, 276,pp. pp.425—454. 425-454. Thurston, F.W., 1978. 1978. Metamorphic Metamorphic and andtectonic tectonic evol evolution of the UchiThurston, P.C. P.C. and and Breaks, Breaks, F.W., English River River subprovince. subprovince. InInMetamorphism Metamorphism ininthe t h eCanadian Canadian Shield. Shield. Geological Geological English Survey SurveyofofCanada, Canada,Paper Paper78-10, 78-10, pp. pp. 49-62. 49-62. Thurston, Thurston,P.C., P.C., Siragusa, Siragusa,G.M., G.M., and andSage, Sage, R.P., R.P., 1977. 1977. Geology Geologyofofthe t h eChapleau Chapleau area, area, Districts DistrictsofofAlgoma, Algoma,Sudbury Sudburyand and Cochrane. Cochrane. Ontario OntarioDivision DivisionofofMines MinesGeological Geological Report Report157, 157,293 293p.p. �- 514 - Turek, Smith, P.E., W.R., 1982. Turek, A., A., Smith, P.E., and and Van Van Schmus, Schmus, W.R., 1982. Rb-Sr Rb-Sr and and U-Pb U-Pb ages agesof of volcanism volcanism and granite emplacement in the Michipicoten Ontario. Canadian and Michipicoten belt, Wawa, Wawa, Ontario. Canadian lournal Journal of Earth Earth Sciences, Sciences, 19, pp. 1608-1625. 1608-1625. Turek, A., Smith, P.E. and Van Schmus, W.R., W.R., 1984. 1984. U-Pb P.E. Van Schmus, U-Pb zircon ages ages and and the t h e evolution evolution Turek, A., of plutonic-volcanicterrane terrane of tthe of tthe h e Michipicoten Michipicoten plutonic-volcanic h e Superior Superior Province, Province, Ontario. Ontario. Canadian Journal of Earth Earth Sciences, Sciences, 21, 21, pp. pp. 457-464. 457-464. Turner, Field and Tectonic Aspects. Turner, F.)., F.J., 1981. 1981. Metamorphic Metamorphic Petrology; Petrology; Mineralogical, Mineralogical$e~~.~n~Je$o,n~~,~sp^cts. Second edition. McGraw-Hill, McGraw-Hill, New New York, York, 524 524p. p. .,.z. + ~2b7b&; <;:, 5 3 ,;';<:,~, .:q Van Schinus,W.R., W.R.,1975. 1975. On Ont the age of of tthe dike swarm. swarm. Canadian Van Schmus, h e age h e Sudbury Sudbury dike Canadian Journal Journal of of Earth Earth Sciences, Sciences,12, 12,pp. pp.1690-1692. 1690-1692. Wanless, R.K., 1969. 1969. Isotopic age map Wanless, R.K., map of Canada. Canada. Geological GeologicalSurvey Surveyof of Canada, Canada,Map Map Â¥ 9- 1256A. 1256A. Watson, 3., 1980. and history of of the Kapuskasing structural zone, The origin and Kapuskasing structural zone, Ontario, Ontario, Watson, J., 1980. The Canada. Canada. Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences, 17, 17, pp. pp. 866-876. 866-876. Wells, P.R.A., P.R.A., 1979. 1979. Chemical and thermal evolution of Archean Wells, Archean sialic sialic crust, crust,Southern Southern West Greenland. Greenland. Journal Journal of of Petrology, Petrology, 20, 20, pp. pp. 187-226. 187-226. Whitney, P.R., 1978. of garnet "isograds" in granulite facies rocks of Whitney, P.R., 1978. The The significance of "isograds" in the t h e Adirondacks. Adirondacks. In Metamorphism Metamorphism in the t h e Canadian Canadian Shield. Shield. Geological GeologicalSurvey Survey of of Canada, Paper Paper 78-10, 78-10, pp. pp. 357-366. 357-366. Wilson, H.D.B.,and and Brisbin, Brisbin,W.C., W.C.,1965. 1965. Mid-North Mid-North American American ridge ridge structure structure (Abstract). Wilson, H.D.B., (Abstract). Geological Society of America, Special Special Paper Paper 87, 87, pp. pp. 186-187. 186-187. Winkler, H.G.F., 1979. 1979. Petrogenesis Petrogenesis of of Metamorphic MetamorphicRocks. Rocks. 5th 5th edition. edition. SpringerWinkler, H.G.F., SpringerVerlag, Berlin, Berlin, 1-Ieidelburg, Heidelburg, New York. York. Wood, B.)., 1974. Wood, B.J., 1974. The The solubility of alumina in orthopyroxene coexisting with with garnet. garnet. Contributions Contributions to t oMineralogy Mineralogy and Petrology, Petrology, 46, 46, pp. 1-15. 1-15. Woods, D.V.,1985. 1985. Large-scale Large-scale electromagnetic electromagnetic induction investigation of the Woods, D.V., the Kapuskasing structural In Current Current Research, Research, part partA. A. Kapuskasing structural zone, zone, northern northern Ontario. Ontario. In Geological Geological Survey Survey of of Canada CanadaPaper Paper85—lA, 85-1A, pp. pp. 533-542. 533-542. .-, .*. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1987 Description An account of the resource Institute on Lake Superior Geology. Wawa, Ontario. May 12-13, 1987. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1987 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/0ac2b7d90fa70da0fc171bbd32248ac5.pdf 10dbf180b065de6c5397d0231466198b PDF Text Text _________ Thirty-fourth Annual Meeting Marquette, Michigan Mayl2and 13, 1988 Institute on Lake Superior Geology Proceedings and Abstracts Volume 34, Part 1 22p0 LINEF,F,UNMIGRATED UNMIGRATED UNE 24p0 u 00 10 km 10km �34th ANNUAL LAKE SUPERIOR INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY INSTITUTE Proceedings and Abstracts Proceedings Abstracts Marquette, Michigan Michigan May 12 1 2 and 13, 13, 1988 1988 Organized by John Hughes, Northern Michigan University John Kiasner, Klasner, Western Illinois Illinois University University Klaus Schulz, S. Schulz, U. U. S. Geological Survey Survey Klaus Program Program Chairman Chairman and and Editor: Editor: Volume Volume 34. 34. John Kiasner Klasner John Part 1 Program Program and Abstracts Abstracts Part 2 Field Guidebooks Guidebooks COVER Seismic time section section with inset inset showing the location of line line FF in Lake Superior. Superior. The seismic seismic is from the GLIMPCE section is program in the Great Great Lakes. Lakes. S volcanics; S == sediments; sediments; V == volcanics; AP == Archean-Proterozoic AP terrane. Archean—Proterozoic terrane. �PURCHASE OF PROCEEDINGS PROCEEDINGS AND ABSTRACTS AND FIELD GUIDEBOOKS The Proceedings and Abstract and the Field Guidebooks for for the the 34th Annual Annual Institute on Lake Superior Geology may be purchased by contacting: contacting: John Kiasner Klasner Geology Department of Geology Western Illinois University Macomb, Illinois Illinois 61455 61455 PROCEEDINGS AND ABSTRACTS, VOLUME 34. 34. PART PART 11 ----------- 4OO $4.00 FIELD GUIDEBOOKS, GUIDEBOOKS, VOLUME VOLUME 34, 34, PART PART 22 - - - - - - - - - - - - - - - $5.00 $5OO Issues Issues of Proceedings and Abstracts and Field Guidebooks from from previous meetings may be purchased by contacting the Secretary— SecretaryTreasurer: Treasurer: Joe Kalliokoski Kalliokoski Department of Geology and Geological Engineering Michigan Technological University Houghton, Michigan 49931 49931 �TABLE OF OF CONTENTS CONTENTS TABLE Institutes on on Lake Lake Superior Superior Geology Geology to to 1988 1988 Institutes Constitution of of the the institute Institute on on Lake Lake Superior Superior Geology Geology Constitution By Laws Laws on on the the Institute Institute on on Lake Lake Superior Superior Geology Geology By Goldich Medal Medal Guidelines Guidelines Goldich Student Travel Travel Award Award Student 1 1 ii ii iii iii iv iv v v Board of of Directors Directors Board vi Local Committee Committee Local vi Best Student Student Paper Paper Committee Committee Best vi vi vi vi Goldich Medal Medal Committee Committee Goldich vii Field Trip Trip Leaders Leaders Field vii Technical Session Session Chairs Chairs Technical vii Goldich Medal Medal Recipient Recipient Goldich viii Banquet Speaker Speaker Banquet viii viii Acknowledgements Acknowledgements vi ii viii Report of of the the Chairs Chairs of of the the 33rd 33rd Annual Annual Institute Institute Report Calender of of Events Events Calender Abstracts Abstracts vii vi i vii viii ix ix xi1 xii xvi i i xviii �INSTITUTES ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTES INSTITUTE NUMBER NUMBER INSTITUTE DATE DATE 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1 22 3 3 44 55 66 77 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 13 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 PLACE PLACE M i n n e a p o l i s , MN MN Minneapolis, Houghton, MI MI Houghton, E a s t Lansing, L a n s i n g , MI MI East D u l u t h , MN MN Duluth, M i n n e a p o l i s , MN MN Minneapolis, Madison, W I Madison, WI P o r t Arthur, A r t h u r , Ont. Ont. (Thunder (Thunder Bay) Bay) Port M I Houghton, Houghton, MI D u l u t h , MN MN Duluth, Ishpeming, MI Ishpeming, MI S t . P a u l , MN St. Paul, MN S a u l t Ste. S t e . Marie, M a r i e , MI MI Sault E a s t Lansing, L a n s i n g , MI MI East S u p e r i o r , WI WI SuDerior, Oshkosh, WI WI O3hkosh, Thunder Bay, Bay, Ont. Ont. Thunder MN D u l u t h , Duluth, MN Houghton, MI MI Houghton, Madison, W Madison, WII S a u l t Ste. S t e . Marie, Marie, Ont. Ont. Sault M a r q u e t t e , M I Marquette, MI S t . Paul, P a u l , MN MN St. Thunder Bay, Ont. Thunder Bay, Ont. WI Milwaukee, WI Milwaukee, D u l u t h , MN MN Duluth, Eau Claire, C l a i r e , WI WI Eau E a s t L a n s i n g 241 East Lansing,, MI I n t e r n a t i o n a l F a l l s , MN MN International Falls, Houghton, M I Houghton, MI Wausau, WI WI Wausau, Kenora, Ont. Kenora, Ont. WI Wisconsin Rapids, R a p i d s , WI Wisconsin Wawa, Ont. Ont. Wawa, MI M a r q u e t t e , MI Marquette, 1 �_________________________ CONSTITUTION CONSTITUTION OF OF INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Article II Article Article II I1 Article Name Name Article Article VII VII Officers Officers The The name name of of the the organization organization shall shall be be the the "Institute "Institute on Lake Lake Superior Superior Geology." Geology." on The The officers officers of of this this organization organizationshall shall be be aa Chairman Secretary-Treasurer. Chairman and and aa Secretary-Treasurer. Objectives Objectives The The objectives objectives of of this this organization organizationare: are: A. A. The The Chairman Chairman shall shall be be elected elected each each year year by by the the board board of of directors, directors, who who shall shall give give due due consideration consideration to to the the wishes wishes of of any any group group that that may may be be promoting promoting the the next next annual annual meeting. meeting. His His term term of of office office as as Chairman Chairman will will terminate terminate at at the the close close of of the the annual annual meeting meeting over over which which he he presides presides or or when when his his successor successor shall shall have have been been appointed. appointed. He He will will then then serve serve for for aa period period of of three three years years as as aa member member of of the the board board of of directors. directors. B. 6. The The Secretary—Treasurer Secretary-Treasurer shall shall be be elected elected at at the the annual annual meeting. meeting. His His term term of of office office shall shall be be two two years years or or until until his his successor successor shall shall have have been been appointed. appointed. A. A. To To provide provide aa means means whereby whereby geologists geologists in in the the Great Lakes Lakes region region may may exchange exchange ideas ideas and and Great scientific scientific data. data. B. B. To To promote promote better better understanding understanding of of the the geology geology of of the Lake Lake Superior Superior region. region. the C. To plan and conduct geological field trips. C. To plan and conduct geological field trips. Article III 111 Article Status Status No No part part of of the the income income of of the the organization organization shall shall inure inure In the the to the the benefit benefit of of any any member member or or individual. individual. In to event event of of dissolution dissolution the the assets assets of of the the organization organization shall shall be be distributed distributed to to (some tax tax free free organizatt3iT. organization). (some (To Federal and (To avoid Federal and State State income income taxes, taxes, the the organization organization should should be be not not Only only "scientific" "scientific" or or "educational" but also "non—profit".) "educational" but also "non-profit".) Minn. Minn. Stat. Stat. Anno. Anno. 290.01, 290.01, subd. subd. 44 ht-'- I-i. ' 290.05(9) 290.05(9) 1954 (3) 1954 Internal InternalRevenue RevenueCode Codea.s.501(c) 501(c)(3) - 1-'• Article IV IV Article Article VV Article Article VI VI Article Membership Membership The The membership membership of of the the organization organization shall shall consist consist of of the board board of of directors. directors. Any geologist geologist interested interested the shall shall be permitted to to attend attend and and participate participate in in vote at at the the annual annual meetings. meetings. and vote Meetings Meetings The The organization organization shall shall meet meet once once aa year, year, preferably preferably during during the the month month of of April. April. The The place place and and exact exact date date designated by by the the board board of of of each meeting will be designated directors. directors. Directors Directors The The board of directors directors shall shall consist consist of of the the Chairman, Chairman, Secretary—Treasurer, Secretary-Treasurer, and and the the last last three three past past ChairChairmen; men; but if if the board should should at at any any time time consist consist of of less than five persons, persona, by by reason of unwillingness unwillingness or 01 or inability inability of any of the the above above persona persons to to serve serve as as directors, directors, the the vacancies on on the the board board may may be be filled by by the annual meeting meeting so as to bring the the membership membership of of the the board board up up to to five five members. members. Article Article VIII VIII Amendments Amendments This This constitution constitution may may be be amended amended by by aa majority majority vote vote of of those those persons persons who who are are personally personally present present at, at, participating participating in, in, and and voting voting at at any any annual annual meeting meeting of of the the organization. organization. �- BY-LAWS BYLAWS I. I. Duties of of the the Officers Officers and and Directors Directors Duties A. A. It shall shall be be the the duty duty of of the the Chairman Chairman to: to: It 1. 1. 2. 2. 3. 3. B. B. at the the annual annual meeting. meeting. Preside at Preside all committees committees needed needed for for the the organization organization of of Appoint all Appoint the annual annual meeting. meeting. the Assume complete complete responsibility responsibility for for the the organization organization Assume and financing financing of of the the annual annual meeting meeting over over which which he he and presides. presides. It shall shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurerto: to: It Keep accurate accurate attendance attendance records records of of all all annual annual Keep meetings. meetings. 2. Keep Keep accurate accurate records records of of all all meetings meetings of, of, and and 2. corres?ondence between, between, the the board board of of directors. directors. corresrondence 3. Hold Hold all all funds funds that that may mav accure accure as as profits profits from from annual annual 3. meetings or or field field trips trips and and to to make make these these funds funds meetings available for for the the organization organization and and operation operation of of future future available meetings as required. meetings as required. 1. 1. C. C. 11. II. Dues and and Expenses Ex-oenses Dues 1. 1. 2. 2. III. III. It shall shall be be the the duty duty of of the the board board of of directors directors to to plan plan It locations of annual meetings and to advise on the locations of annual meetings and to advise on the organization and and financing financing of of all all meetings. meetings. organization regular membership membership dues. dues. There shall shall be be no no regular There for the the annual annual meetings meetings shall shall be be Registration fees fees for Registration determined by by the the Chairman Chairman in in consultation consultation with with the the determined the board board of of directors. directors. It It is is strongly strongly recommended recommended that that the these be kept at a minimum to encourage attendance of these be kept at a minimum to encourage attendance of graduate students. students. graduate Rules of of Order Order Rules The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern The this organization orqanization in in all all cases cases to to which which they they are are applicable. applicable. this IV. IV. Amendments Amendments amended by by aa majority majority vote vote of of those those These by-laws by-laws may may be be amended These persons who are personally present at, particinating in, and and persons who are r'ersonally present at, particiating in, voting at anv annual meeting of the organization; provided voting at any annual meeting of the organization; provided that such such modifications modifications shall shall not not conflict conflict with with the the that constitution as presently adopted or subsequently amended. constitution as presently adopted or subsequently amended. iii iii �Award CudaUnes SAN GCLD:C: 4EDAL Preamble Preamble The tnszituz an wasborn born an onor o raround around The InsT:itx-:3 on l aaie k e Sueror S u p e r i o rGecloav Geoioqy as 1 9 5 5 , aas s dec-sexad 'ay the =he acz fac-: that that tne cke27th 2 7 t h annual a n n u a l meetn: neecn,; 1955, iocmentd by will w i l l be be held h e l d in i n1981. 1981. The The 1nsT:i'curss a r e exemiar'a x e n g l a r y in i n their :heir tnsttutes are continuinc c o n c i ~ u i n cx ~:ecz;es : e c i z ~ , - of e sofdealing d e a l i n g with w i t h those 3 o s e aseczs a s p e c t sofofgeology geolsqy that Si-aerier: of of en— ent h a t are a r e related r e l a c e dgeograchically ~ ~ e o g r a p n i c a . lto l t' /ocake Lake Superior courauxng =r:a i s c i s s i o n oof r sub?ec-ss p o n s o r i n g ffield ield couraging the ddiscussion sabjects and ands sonscring t r i o s whch whick will v i l lbring b r i n atocether z o a e t h e rgeologists q e o i o c i s t sfrom fromthe t h eacademia, academia, trios government sur-J-eys, and indus'czy; and of of maintaining s i a i n c a i n i n g an an government surevs, and industr'; and exceedlv e x c e e d l v informal i n 5 m a l but b u t highly h i a h l y effective e f f e c t i v e mode mode of peraelon. of ooerazion. Durina i t se:istence e x i s t e n c ethe t h rserttbership e .'nembershiu of o f the the During tthe h e course c o u r s e of of its Institute I n s - c i t u t e that k h a 'is, c i those s , t h o sgeologists e q e o l o a i s c who s who indicate i n d i c a t e an a n interest interest in i n the t h e objectives obyectiq.'es of of the t h e I.L.S.G. 1.Ii.S .G. by by attending) a t t e n d i n g ) has h a s become become aware aware of of the t h e fact S a c t that t h a t certain c e r t a i n of of their t h e i r colleagues c o l 1 e a c u e s have have made nocaworthy and and meritorious m e r i t o r i o u s contributions contributions mace particularly p a r t i c u l a r l y noteworthy to 'ake Suerior" t o the t h e iprcvement i a p r o v e z e n c of of understanding understandinu ofof"Lake Superior" geology and iits qeoloay and t s mineral m i n e r a l degosits. degosits. The I .L.S . G . to t oSam Sam Gcldich G o l d i c h in in The exemclar-. exemniary award awardwas :/as made made by by I.L.S.G. 1979 hsi smany off the 1 9 7 9 ffor or h many contributions c o n t r i b u t i o n s to t o the t h e geology geology o t h e region reuion extending 50 years. years. e x t e n d i n g over o v e r about a b o u t 50 Awrd Guidellnes 1) 1) Thu "he xmedal e d a l sshall n a l l be be awarded awarded aannually n n u a l l y by by the t h e Board 3 o a r d of of Directors, is associated 2.:. G. , to t oa ageologist q e o l o a i s twnose wnose name name is assoczated D i r e c t o r s , 1..L.3.G., subszanzal sustaned interest in, or a major con— Â¥;= --~ - -.-- u t ~ oto, n i^.e geology geoloqy ofofShe a ~ eSSueror u s e r z o r region. region. trbuton the theLtaie with :.r~^. aa s u b s z . i n i ~ ^ . lsus-ca1r.ea Lnceras-c i n , o r a ^layor con- The ofSDirectors, acoint the The 3Board o a r t 05 i r e c t o r s , I .I.L.S.C. L.3.3. s shall h a l l aoooint: the at a t the *e annual a n n u a lbusiness b u s i n e s smeeting. neecina. The The iinitial n i t i a l apointment appoinment will w i l l be be of ofthree 5 r e members, e members, one one to t o serve s e r v e for f o r three t h r e e years, y e a r s , one one for thebbrefest riefest f o r two, two, and and one a n e for f o r one one year, y e a r , the t h e rnemoer rnemner wwith i t h the incumoencv incumbency to t o be bechairman. chairman. After A f t e r the =he first f i r s t ;year y e a rthe t h eBoard 3oard of of Directors Direc-iors shall s n a i lappoint angoin-c at a teach each string s ? r i n a meeting meeting one onenew new member who member vno x iwill 1 l s serve e r v e ffor o r three t h r e e years. y e a r s . In I n the t h e third t h i r d year year this t h i smember m e m e r sshall n a l l be be the t h echairman. chairman. The The Corrittee Committeemembership membership should s h o u l d rref e f lluct e c t the t h e main main ffields i e l d s of of interest i n t e r e s - cand and geograthic geographic 2) 2) ominating i l l be b e voted voced on on !lominaci.ncCommittee. Commxtitee. Their T h e i r annual a n n u a l nominee xominee wwill distribution dis-cribuizion of of I.L.S.G. I.L.S.G. membership. niembership. Committee 3) 3 ) The The Goidich Goidzcr. :edal Medal ominating ^lom.~natina Committee shall s n a i l select s e l e c t the the medalist and w i l lmake m a k e its ~ recommendation t recormenda'c~on s tto o the t o e Board 3 o a r c of of medai~s'c anc. will Directors by Iovember !roveainer 1, L, of of that c h a t year. year. DLrec=ors by 4) 4 ) The The Board Board of of Directors D i r e c t o r s normally normally will w i l l accept a c c e p t the t h enominee nominee of w i l linform inform the t h emedalist m e d a l i s timmediately, immeaiacely, of the t h eCommittee, Comi=-cee, will an engraveda ~apropatalv and.will w i l have l have one one medal medal engraved p r o p r i a t e l yfor Sor prepresentation s e n t a t i o n at a t the t h e Iay .lay meeting. meeting. 5) 5) It I t is is recommended recommended that t h a t the the Institute I n s t i t u t e set see aside a s i d eannually annually from whatever w i l l be be required r e q u i r e d to to from w h a t e v e r ssources, o u r c e s , such such funds funds as a s will support s u p p o r t the t h e continuing c o n t i n u i n g costs c o s e s of of this t h i saward. award. April 4 , 1981 1981 A p r i l 4, J. J. Kalliokoski, K a l l i o k o s k i ,Chairman Chairman Bill B i l lCannon Cannon Fred Fred Kehlenbeck Kenienbeck Glenn Glenn 4orey Yoray Greg Greg Murskv Mursky iv �STUDENT TRAVEL TRAVEL AWARD AWARD STUDENT The 1986 1 9 8 6 Board Board of o f Directors D i r e c t o r s established e s t a b l i s h e d the t h e ILSG ILSG Student Student The T r a v e l Award Award to t o support s u p p o r t student s t u d e n t participation p a r t i c i p a t i o n at a t the t h e annual annual Travel I n s t i t u t e s . The The awards a w a r d s will w i l l be b e made made from f r o m the t h e accrued a c c r u e d interest interest Institutes. s p e c i a l fund f u n d set s e t up up for f o r this t h i s purpose. p u r p o s e . This T h i s award a w a r d is is f r o m aa special from i n t e n d e d to t o help h e l p defray d e f r a y some some of o f the t h e direct d i r e c t travel t r a v e l costs c o s t s to t o the the intended iinstitute n s t i t u t e and a n d includes i n c l u d e s aa waiver w a i v e r of o f registration r e g i s t r a t i o n fees, f e e s , but but meals, lodging, l o d g i n g , and a n d field f i e l d trip trip e x c l u d e s expenses e x p e n s e s for f o r meals, excludes s i z e w i l l b e d e t e r m i n e d by by the the r e g i s t r a t i o n . The number a n d registration. The number and size will be determined a n n u a l C h a i r m a n i n c o n s u l t a t i o n w i t h t h e S e c r e t a r y T r e a s u r e r and and annual Chairman in consultation with the Secretary Treasurer w i l l b e a n n o u n c e d a t t h e a n n u a l b a n q u e t . will be announced at the annual banquet. The following f o l l o w i n g general g e n e r a l criteria c r i t e r i a will w i l l be b e considered c o n s i d e r e d by by the the The a n n u a l Chairman, C h a i r m a n , who who is is responsible r e s p o n s i b l e for f o r the t h e selection: selection: annual 1 ) The The applicants a p p l i c a n t s 'must 'must hhave a v e aactive c t i v e resident r e s i d e n t (undergraduate (undergraduate 1) t i m e o f t h e institute, institute, o r g r a d u a t e ) s t u d e n t s t a t u s a t t h e or graduate) student status at the time of the c e r t i f i e d b y t h e d e p a r t m e n t h e a d . certified by the department head. 2 1 Students S t u d e n t s who who are a r e the t h e senior s e n i o r author a u t h o r on on either e i t h e r an a n oral o r a l or or 2) p o s t e r paper p a p e r will w i l l be b e given g i v e n favored f a v o r e d consideration. consideration. poster 3 ) It I t is is desireable d e s i r e a b l e for f o r two t w o or o r more more students s t u d e n t s to t o jointly jointly 3) r e q u e s t travel t r a v e l assistance. assistance. request 4 4) I n general, g e n e r a l , priority p r i o r i t y will w i l l be b e given g i v e n to t o those t h o s e in i n the the In I n s t i t u t e region r e g i o n who who are a r e farthest f a r t h e s t away. away. Institute 5 ) Each Each travel t r a v e l award a w a r d request r e q u e s t shall s h a l l be be made made in i n writing, w r i t i n g , to t o the the 5) a n n u a l C h a i r m a n , w i t h a n e x p l a n a t i o n o f n e e d , p o s s i b l e annual Chairman, with an explanation of need, possible a u t h o r status s t a t u s or o r other o t h e r significant s i g n i f i c a n t details. detailsauthor V �BOARD BOARD OF OF DIRECTORS DIRECTORS 1988 1988 J. J. S. Klasner (with J. D. Hughes and K. of Kiasner (with K. J. 3. Schulz), Department of Western Illinois Illinois University, University, Macomb, Illinois Illinois Geology, Western 61455 61455 1987 1987 Sage (with R. P. 'Sage (with E. D. Frey) Ontario Geological Survey, Ministry of Northern Northern Development Development and and Mines, Mines, 77 77 Grenville Grnville Street, Street, M7A 1W4 Toronto, Ontario 1W4 1986 1986 Wisconsin Geological and J. K. Greenburg (with (with B. B. A. A. Brown) Brown) Wisconsin Natural History Survey, 3817 Mineral Point Road, Madison, 53705 Wisconsin 53705 1985 1985 C. E. Blackburn, Mineral and and Development Development Branch, Branch, Ministry Ministry of of Kenora, Northern Development and Mines Mines P. P. 0. 0. Box Box 5160, 5160, Kenora, Ontario P9N 3X9 Ontario 3x9 Secratary-Teasurer Secratary-Teasurer J. Kalliokoski, Department of Geology and Geological Engineering, Michigan Technological Technological University, University, Houghton, Houghton, Michigan 49931 49931 Michigan LOCAL COMMITTEE COMMITTEE J. D. D. Hughes: Hughes: Conference Co-Chair; Conference Co-Chair; Local arrangements arrangements 3. J. S. S. Kiasner: Klasner: Conference Co—Chair; Co-Chair; Program and Abstracts Abstracts editor, editor, mailings and regitration regitration K. J. J. Schulz: Schulz: arrangements and Conference Co-Chair; Co-Chair; Field trip arrangements and field guidebook editor, banquet banquet speaker speaker BEST STUDENT STUDENT PAPER COMMITTEE COMMITTEE G. W. Adams: Adams: Exploration, Noranda Exploration, G. L. LaBerge: G. LaBerge: P. Sage: Sage: R. P. Rhinelander, Rhinelander, Wisconsin University of of Wisconsin—Oshkosh, Wisconsin-Oshkosh, Wiscons in Wisconsin Ontario Geological Geological Survey, Survey, vi Oshkosh, Oshkosh, Toronto, Ontario �GOLD1 CH MEDAL MEDAL COMMITTEE COMMI TTEE GOLDICH J. J. J. Brummer: Brummer: J. K. D. D. K, Brununer Consulting, Consulting, Toronto, Toronto, Ontario Ontario Brummer Card: Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario Ontario Card: R. J. J. Oiakarigas: Ojakangas: University Minnesota R. Uriiver3ity of of Minnesota, Minnesota, Duluth, Duluth, Minnesota FIELD TRIP TRIP LEADERS LEADERS FIELD D. A. A. Baxter: Baxter: Michigan Michigan Technological Technological University, University, Houghton, Houghton, D. Michigan Michigan J. Bornhorst: Bornhorst: Michigan Michigan Technological Technological University, University, Houghton, Houqhton, T. J. T. Michigan Michigan B. C. C. Boyurn: Boyum: B. Cleveland-Cliffs, Inc. Inc. Ishpeming, Ishpeming, Michigan Michigan Cleveland-Cliffs, A. Brozdowski: Brozdowski: Callahan Callahan Mining Mining Corporation, Corporation, Negaunee, Negaunee, Michigan Michigan R. A. R. C. Gallup: Gallup: California California Institute Institute of of Geology, Geology, Long Long Beach, Beach, C. California Ca i i for n i a W. R. R. Gregg: Gregg: Michigan Michigan Technological Technological University, University, W. Michigan Michigan € C. C. Johnson: Johnson: R. Michigan Michigan Wm. Kangas: Kangas: Wm. Houghton, Houghton, Michigan Technological Technological University, University, Michigan Houghton, Houghton, Cleveland-Cliffs, Inc., Inc., Ishpeming, Ishpeming, Michigan Michigan Cleveland-Cliffs, J. S. S. Klasner: Klasner: Western Western Illinois Illinois University University and and U. U. S. S. Geological Geological J. Survey, Macomb, Macomb, Illinois Illinois Survey, L. MacLellan: MacLellan: M. L. M. Michigan Michigan R. G. G. Reed: Reed: R. Michigan Geological Geological Survey, Survey, Michigan G. W. W. Scott: Scott: G. P. K. K. Sims: Sims: P. Michigan Technological Technological University, University, Michigan Lansing, Michigan Michigan Lansing, Callahan Mining Mining Corporation, Corporation, Callahan U. S. S. Geological Geological Survey, Survey, U. Houghton, Houghton, Neqaunee, Michigan Michigan Negaunee, Denver Colorado Colorado Denver TECHNICAL SESSION SESSION CHAIRS CHAIRS TECHNICAL R e L. L. Bauer: Bauer: R. University of of Missouri, Missouri, Columbia, Columbia, Missouri Missouri University F. W. W. Cambray: Cambray: Michigan Michigan State State University, University, Lansing, Lansing, Michigan Michigan F. W. F. F. Cannon: Cannon: W. U. S. S. U. Geological Survey, Survey, Reston, Reston, Virginia Virginia Geological J. Hinze: Hinze: Purdue Purdue University, University, West West Lafayette, Lafayette, Indiana Indiana W. J. W. M. M. M. Kehienbek: Kehlenbek: M. Lakehead University, University, Lakehead vii vii Ontario Ontario �S. S. W. Nicholson: Nicholson: W. J . M. M. J. Washington, D. D. C. C. Washington, Paces: Paces: Michigan Michigan Technological Technological University, University, Michigan Michigan D. Southwick: Southwick: Minnesota Minnesota Geological Geological Survey, Survey, D. Minnesota Minnesota Houghton, Houghton, Minneapolis, Minneapolis, GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Walter S. S. White, White, U. S. S. Geological Geological Survey Survey (retired). (retired). Medal Medal Walter U. awarded awarded by by D. D. H. M. Davidson, Davidson, Northern Northern Illinois Illinois University University BANQUET SPEAKER SPEAKER BANQUET P. F. F a Hoffman: Hoffman: P. Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario Ontario ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Several Several people people and and organizations organizations assisted assisted in in preparation preparation of of the 34th 34th Annual Annual ILSG. ILSG. Without Without their their help help the the many many tasks tasks in in preprethe paring paring this this meeting meeting could could not not have have been been done. done. We We would would like like to to thank thank the the following following people people and and organizations organizations for for their their help. help. Diana Robertson Robertson and and the the office office of of Non—Residential Non-Residential Programs Programs at at Northern Northern Michigan Michigan University University for for logistical logistical assistance. assistance. The Department Department of of Geography, Geography, Earth Earth Science, Science, Conservation Conservation and and Planning at at Northern Northern Michigan Michigan University University Planning The Department of Geology at Western Illinois Illinois University Gretchen Gretchen Kiasner Klasner for for assistance assistance in in handling handling finances. finances. Cathy McCormick and and Corrine Corrine Weaver Weaver for for help help with with typing, typing, logistics, and and mailing. mailing. logistics, Callahan Callahan Mining Mining Corporation Corporation for for assistance assistance with with field field trips. trips. Michigan Technological Technological University University for for assistance assistance with with Michigan transportation for for field field trips. trips. transportation Geological Survey Survey for for providing providing mailing mailing lists lists and and Minnesota Geological labels labels viii vili �33rdINSTITUTE IYSTITUTS ON ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 33rd WAWA, WAWA, ONTARIO ONTARIO -- 1987 1987 Lake Superior S u p e r i o r Geology Geology was was held held The 33rd 33rd meeting m e e t i n g of of the t h e Institute I n s t i t u t e on on Lake The h o s t s d by by i nWawa, Wawa, Ontario O n t a r i o from from 10 10 to t o 15 1 5 May May 1987. 1937. The meeting messing was hosted in t h e Ontario O n t a r i o Ministry M i n i s t r y of of Northern N o r t h e r n Development Devel0pmer.t and and Mines Mines -- Wawa Wawa Resident Resident the G e o l o g i s t Office O f S i c e and and the t h e Ontario O n t a r i o Geological Geologies! Survey. Survey. Technical T e c h n i c a l sessions sessions Geologist were held h e l d on on 12 1 2 and and 13 1 3 May May ini n the t h e corrnunity community arena a r e n a and and posters a o s t -^s - were were were d i s p l a y e d in i n the t h e adjacent a d j a c e n t curling c u r l i n g clubhouse. c l u b h o u s e . Registered R e g i s t e r e d attendance screndance displayed was 255, 255, including i n c l u d i n g 30 30 students. s t u d e n t s . P:e—registraticn P r e - r s g i s t r a t i m totalled t o t a l l e d 220. 220. Four Fou; crc—meeting, or?-meeting, three t h r s s repeated r e p e a t e d post p o s t meeting, meeting, and two two duolicate d u p l i c a t e field field trips o f 245 2 4 5 participants, p a r t i c i p a n t s , many many t r i p s during d u r i n g the t h e meeting m e e t i n g attracted a x r a c t s d aa total t o t a l of attending a t e n d i n 5 two two of of the t h e five f i v e individual i n d i v i d u a l tours. t o u r s . Bernie Berr.ie Schnieda:s S c h n l e d e r s became became a n excellent e x c e l l a n t substitute s u n s t i t u c s for f o r Tom Tom Muir Mui; when when illness i l l n e s s forced f o r c e d Tom's Tom's absenc2 aksencs an f:om from leadership l e a d e r s h i p of o i aa review r e v i e w of of Hemlo Henlo geclacy g e c l o c y attended a t t e n d e d by by 47. 47. John John Percival P e r c i v a l conducted c o n d u c t e d two two 2—day ?-day transects t r a n s e c t s of of the t h e Kapuskasing Xapuskasincj Structural 3t;xt'~ral f o r 40 40 visitors. v i s i t o r s . Ron Ron Sage Sage led l e d 33 3 3 participants p a r t i c i p a n t s through t h r o u g h the t h e st:a— sxaZone for tigraphy of the Michipicoten Iran Formation an two field trips, t i g r a p h y o f t h e X i c h i g i c o t s n I r o n Formation on two f i e l d t r i p s . rawa Wawa ea wasexamined examinedbyby 96 9 6 during d u r i n g two two field f i e l d trips t r i p s led led AreaGold GoldMineralitation M i n e r a l i z a t i o nwas mine of G.W. MacLead MacLeod side:ita s i d e s i t e mine of the t h e Algoma Algorra Steel Stsel Staf: of of the t h e G.W. 3d Frey. F r e y . Staff by Ed C o r p o r a t i o n hosted h o s t e d 29 29 visitors v i s i t o r s on on two two half—day h a l f - d a y tours. t o u r s . Separate S e p a r a t e guide— guideCorporation books books. were were published p u b l i s h e d for f o r three t h r e e of of the t h e field f i e l d trips t r i p s and a fourth f o u r t h is is in in p r e p a r a t i o n for f o r the t h e Wawa Wawa gold g o l d tour. t o u r . AA guidebook guidebook was was not n o t published p u b l i s h e d for for preparation t h e MacLead MacLeod Mine Mine tour. tour. the Thirty-three 29 posters p o s t e r s were were displayed displayed T h i r t y - t h r e e papers p a p e r s were were presented p r e s e n t e d orally o r a l l y and and 29 during d u r i n g the t h e technical t e c h n i c a l sessions. s e s s i o n s . K. M. Lockwood Lockwood replaced r e p l a c e d the t h e last-minute l a s t - m i n u t e cancancellation c e l l a t i o n of of two two papers p a g e r s by by R. R. Dahi, Dahl, et e t al., a l . , with wich an a n impromptu i m o r o a p t u review r e v i e w of of Fifteen chioritoid c h l o r i t o i d alteration a l t e r a t i o n in i n the t h e Wawa Wawa area. area. F i f t e e n students s t u d e n t s presented presented eight t a s k for f o r the the e i g h t papers p a p e r s and eight e i g h t posters p o s t e r s and provided provided a challenging c h a l l e n g i n g task the Best Student presented Tony Andrews Student Awards Committee, Committee. Andrews p r e s e n t e d t h e Z e s t S t u d e n t Paper Paper Student Award to t o Matthew E. E. Bidwell, B i d w e l l , Univ. Univ. of of Wyoming, Wyoming, for f o r his h i s paper p a p e r "A "A two— twostage s t a g e simple—shear s i m p l e - s h e a r model for f o r high h i g h flattening f l a t t e n i n g strains s t r a i n s in i n sshear h e a r zones of of the t h e central c e n t r a l Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesotan. MinnesotaR. R.L. R.L. Bauer, Bauer, Univ. Univ. of of Missouri, M i s s o u r i , was was co—author. c o - a u t h o r . The The Best Best Student S t u d e n t Poster P o s t e r Award Award went went to K. Sikkila, Tech. Univ., Univ., ffor A structural t o Kevin M. S i k k i l a , Michigan Tech. o r hhis i s pposter o s t e r "A structural analysis a n a l y s i s of o f Proterozoic P r o t s r o z o i c inetasediments, metasediments, >northern n o r t h e r n Falls F a l l s River, R i v e r , Ba.&&@ co—authored by by W.J. W.J. Gregg, Gregg, Michigan T6c'h. TéEñ. Univ. County, Michigantt, Michigan", co-authored Univ. Each award award consisted c o n s i s t e d of of $150.00 $ 1 5 0 . 0 0 provided p r o v i d e d from from registration r e g i s t r a t i o n fees. f e e s . Six Six students s t u d e n t s received r e c e i v e d waiver w a i v e r of of registration r e g i s t r a t i o n fee f e e and and $50.00 $ 5 0 . 0 0 each e a c h as as a Student S t u d e n t Travel T r a v e l Award. Award. These funds funds also a l s o were were provided provided by registration registration receipts. receipts. The The annual a n n u a l banquet b a n q u e t on on 12 1 2 May May at a t the t h e Union Union Hall H a l l was an a n outstanding outstanding feast, f e a s t , catered c a t e r e d for f o r 229 229 people p e o p l e by by the t h e Voyageur Voyageur Restaurant. R e s t a u r a n t . Allan Allan Goodwin presented Erindale p r e s e n t e d the t h e Goldich G o l d i c h Medal Medal to t o Henry Halls, Halls, E r i n d a l e College— ColleqeUniv. Univ. of of Toronto. T o r o n t o . The guest q u e s t speaker s p e a k e r was was Howard Howard Poulsen Poulsen; Geological Geological Survey S u r v e y of o f Canada, Canada, who who reviewed reviewed the t h e relationship r e l a t i o n s h i p between bet-ween tectonics t e c t o n i c s and gol'd g o l d mmineralization i n e r a l i z a t i o n throughout t h r o u g h o u t Canada. Canada. The ILSG ILSG Board Board of of Directors D i r e c t o r s held h e l d aa luncheon luncheon meeting meeting on on 12 1 2 May. May. In In attendance were Co-chairmen Ed Frey and Ron Sage, Bruce Bro, a t t e n d a n c e were Co-chairmen Ed F r e y and Ron Sage, Bruce Brown, Charlie Charlie Blackburn, Blackburn, Gene Gene LaBerge, LaBerqe, and and Fred Fred Kehienbeck. Kehlenbeck. Also Also present p r e s e n t were were Ted Ted Bornhorst B o r n h o r s t and the t h e 34th 3 4 t h ILSG ILSG team team of of John John Kiasner, K l a s n e r , John John Hughes Hughes and and ix �The Board Board took took the the following following action: action: Klaus Schulz. Schulz. The Klaus 1.As As of of 22 April April1987 1937 the the U.S. U.S. account account totalled 3 3 0 5 3 . 2 l and and the the 1. totalled $O63.21 Goldich Medal ?edai Fund Fund was was $1153.92. $1153.92. As As of of12 12May May 1937 1337 the theCanadian Canadian Goldich account total was $5507.51. The 33id ZL3G submittad $3839.56 account total was $5507.61. The 33rd LLSG submitted $3839.56 ($2637.55 pofit) Canadianaccount accountininDec. Dec.1937 1237and and ($2637.56 profit) totothethe Canadian C$255.00 to the Goldich Medal Fund. C$255,00 to the c-oldich Medal Fund. 2. Ted Ted 3ornhorzt 3ornnorstmoved moved that-the custodianofofthethe Canadianaccount account 2. thatthe custodian Canadian be present present at at all all businessmeetings. meetings. Motion Motion passed passed unanimously. unanimously. be business 3. Gene Gene .LeBes;e aoved that thatinterest in-rarast cc~3inedU.S. Y.S. and and 3. noved onsnthethe combined .a2er;e Canac:an ac=cui"ttsbe be used used for forStuden: SfczdentTravel TravelAwards. Awards. Motion Mocion Canadian accounts :assed unanImously. iinaninously. ItItwas wasnoted notad that that ititisisdesirable desirabletotohave have passed $ 1 0 , 2 C O . L.-. aac." account and that no meetin? shcuLd be planned $10,000. in each account and that no meeting should be planned to lose losemoney. xney. to 4. The The ILGG is aa non-profit non-profitorganization organization underU.S. U.S.law lawand anddonadona4. LLG is under tions are are tax taxdeduc:ible. deductible. This This fact factshould should be be noted notsd on tions on all all circulars for U.S. meetings. circulars for U.S. meetings. 5. There There is isno no need need to to publish publishthe theby—laws by-laws of the organization organization 5. of the foreach eachmeeting. meeting. for in 6 . Student Studentpaper pager and and poster poster awards awards should should be be $150.00 $150.00 each, 6. each, in The awards awards should be part part the currency cxzency of of the the meeting meeting site. site. The the should be Co-authored pacers now acceptable, ofthe themeeting meetingbudget. budget. Co—authored of papers are are now acceptable, provided that the student student is isthe thesenior seniorauthor. author. provided that the 7. Ted Ted Bornhorst Bornnorst and and Charlie Charlie Blackburn Blackburn prepared prepared guidelines for 7. guidelines for by the Board. Student Travel Awards that were accepted Student Travel Awards that were accepted by the Board. Klaus Schulz Schuizrecommended recommended that thenew new awards awards requirements requirementsbe be Klaus that the sent to tointerested interestedgeology geologydepartments. degartments. sent 3. The The Proceedings Proceedings and guidebooks 3. andAbstracts Abstractsvolume volumeand andfield field trip trip guidebooks now have now havevolume volumeand andpart partnumbers numberstotoallow allowproper properlibrary library indexing. The The P. P. & & A. A. title title hasbeen beenstandardized. standardized. indexing. has 9. Dr. Dr.J.J. J.J.(Joe) (Joe) Brummer, consulting consultinggeologist, geologist,Toronto, Toronto, is is the the 9. Brurtuner, W.A. Bodwell. Bodwell. new iember Medal Committee, Committee, reglacing new memberofofthe the Goldich Goldich Medal replacing W.A. be Michigan and and will The 1933 1938 iL3G meet in in Marquette, Marquetta, Michigan 10. The 10. ILSGwill will meet will be organized by John Klasner, John Hughes, and Klaus Schulz. organized by John Kiasner, John Hughes, and Klaus Schulz. The 1989 1989 ILSG in Duluth, Duluth,Minnesota Minnesota and and chaired chaired by by The LLSGwill will be be in 1990 meeting meetingmay may be be in inThunder Thunder Bay, Bay, Ont. Ont. Dick Ojakangas. Ojakangas. The The 1990 Dick 11. Gene Gene Laberqe will forthe theBest BestStudent Student 11. L1aberge willprepare preparea acertificate certificate for Poster Awards Awards and the winners. winners. The The Paper && Poster Paper and send send them them to to the certificatewill will state title of paper/poster, date, and ILSG certificate state title of paper/poster, date, and ILSG and will will signed awardcommittee. committee. The The locationand location bebesigned bybythethe award winners' names should be published in the Chairman's report. winners' names should be published in the Chairman's report. We hope hope Chairingthe the33rd 33rdILSG ILSG has has been been an an education education in in organization. organization. We Chairing thatthe theWawa Wawa meeting meeting has has demonstrated demonstrated that small communities communities with with that that small sufficient accommodations accommodations can sufficient can host host futureILSGs. ILSGs. The The absence absence of of custom custom future x x �facilities insDired innovation here, as it can elsewhere. We again thank all who rtade the Wawa rneeting possible and those who provided encouragernent and support. The ILSG is a priceless gathering of friends in the geological fraternity working in the Lake Superior Toronto, Ontario RP. Sage region. We know of no better way to keep in touch with new ideas on the region than through the ILSG. Respectfully submitted, E.D. Frey Wawa, Ontario CoChai:en, 33rd ILSG January l87 xi I-' X �CALENDER OF EVENTS EVENT'S AND PROGRAM PRE-MEETING FIELD FIELD TRIPS TRIPS TUESDAY, May 10, 1988 1988 TUESDAY, 8:00 8:OO a.m. a s m oto to 5:00 5:OO p.m. p.m. Field Trip 11 -— -- Archean geology and mineralization mineralization of of the the Marquette Greenstone Belt (day Marquette (day one of a two-day two-day field trip) trip) W?3DNESDAY. May 11, 1988 1988 WEDNESDAY. 8:00 8:OO a.m. to to 5:00 5:OO p.m. p.me -- Archean geology geoloqy and mineralization mineralization of of the the Field Trip 11 —Marquette Greenstone Belt (day Marquette ( d a y two of a two—day two-day field trip) trip) 8:00 8:OO a.m. to to 5:00 5:OO p.m. p.m. Field Trip Trip 22 —— -- Marquette Marquette Mineral District District of of Michigan: Michigan: Mining Mining history and geology GET TOGETHER TOGETHER REGISTRATION AND WELCOME GET 1988 WEDNESDAY. May WEDNESDAY, l&y JJ- 1988 4:00 to 7:00 4:OOp.m. p.m. to p.m. 7:OO p.m. Registration at the the Ramada Inn Inn Convention Convention Center Center 7:00 p.m. p.m. 7:OO Welcome get together, together, poster poster displays, displays, cash cash bar. bar- TECHNICAL TECHNICAL SESSIONS SESSIONS THURSDAY, 1988 THURSDAY. May 12, 1988 Morning Co-Chairs: Co-Chairs: Geology of the Keweenawan Rift Rift William J. J. Hinze and James James B. B. Paces Paces Welcoming remarks remarks 8:15 $:I5 a.m. a.m. F. F. G. R. C. 8:20 a.m. a.m. W. A. D. 3. J. Cannon Cannon Green Hutchinson Hutchinson Behrendt 8:40 a.m. a.m. S. W. Nicholson Nicholson Paces 3. B. Paces J . B. W. F. Cannon Cannon Variations in in structural structural style style of the the Midcontinent Rift beneath Lake Superior Superior Development of of the Midcontinent Midcontinent Lake Superior Rift in in the the Lake Superior region: Petrologic region: Petrologic and and geochemical constraints for qeochemical for aa tectonic model model xii x ii �9:00 9:OO a.m. a.m. J. J e B. B. D. D. W. Paces Paces Davis Davis 9:20 a.m. a.ma 9:20 K. W. Kiewin Klewin J. J. H. Berg Berg Chemostratigraphy of of the the lower lower division division lavas lavas of of the the Mamairise Mamainse Point Point Formation and implications implications for for rifting tectonics tectonics Coffee break break 10:00 a.m. 1O:OO a.m. 10:20 a.m* a.m. C. 10:20 J, J. M. M. precision Implications of a high precision U-Pb age dates on zircons from U-Fb from on Portage Lake volcanic ba3alts basalts on subsidence rdtes, rates, Midcontinent Rift subsidence lava flow repose periods, lava periodsp and magma macpa production rates rates P. F. G. Geophysical and petrological Ervin petrological characteristics of Olmsted Olmsted of the the Clam Clam Lake Lake constraint on a Mudrey, Jr. intrusion -— Jr. intrusion -- a on the thc time time of Keweenawan basin basin developdevelopmentt men 10:40 a,m. 10:40 a o m . R. R 6 P. P a Meyer Meyer V. Green WW.* V. Comparison Comparison of of the the Keweenawari Keweenawan and and Gregory Rifts from from the study study of teleseismic delay delay times times and Bouguer gravity 11:00 a.m, Mudrey, JJr. Midcontinent Rift model based ll:€ a - m a MM.e GG.a Mudrey, K - Hidcontinent A.* B. A B a Dickas Dickas upon Gregory Rift tectonic tectonic and and sediment sediment geometries geometr i e s 11:20 a.m. P. A. 11:20 a.m. A. Nielsen The Keweenawan Rift: a kinematic model for its its origin and evolution 11:40 1 1 ~ 4 0a.m. a-m. Lunch, Lunch- THURSDAY. THURSDAY. Afternoon Board of Directors luncheon luncheon 12.1988 12,1988 Geology of the Keweenawan Rift/Miscellaneous Co-Chairs: W. F. Cannon and S. S. W. W. Nicholson Nicholson 2:00 2:OO p.m. p.ma F. W. Cambray A tectonic model for for the the Midcontinental Rift System 2:20 2:20 p.m. p e m e M. L. Manson* Manson* H. C C. H. . Halls Halls A 2:40 2:40 Hinze p.m. W. W e 3. J. Hinze W. C. Kelly Scientific drilling into into the the Midcontinent Rift System 3:00 3:OO p.m. p .me Coffee break break submersible dive on on Superior Superior Shoals: Shoals: plans and prospects xiii x iii �3:20 p.m. p.ma V. W. R. J. 3:40 p.m. B. SainiEidukut* Sulfide mineralization and and associated associated in anorthositic anorthositic hydrous silicates in rocks from from the the Duluth Complex Complex 4:00 p.m. T. Lewchuk* Lewchuk* p.m. M. M. T. D. A. Syrnons Symons D e T. T. A. Paleomaqnetism of of the the Clay—Howells Clay-Howells Paleomagnetism carbonatite carbonatite and and Keweenawan Keweenawan motion motion on KSZ on the the KSZ 4:20 p.m. p.m. M. M. D. D. Thompson* Thompson* C. C - P. P. Ervin Ervin Refraction analysis analysis of of the the GLIMPCE GLIMPCE Refraction marine marine reflection reflection profile profile in in Georgian Georgian Bay Bay 4:40 p.m. p.m. 5:00 p.m. T. J. Boerboom Boerboom p e m &T. An An unusual unusual apatite—rich apatite-rich nelsonite—, nelsonite-, pyroxenite—, pyroxenite-, and and hornblendite— hornblenditebearing bearing intrusion intzusion of of post—Penokean post-Penokean age, age, central central Minnesota Minnesota 5:30 p.m. Cash Cash Bar Bar 6:30 p.m Banquet Banquet FRIDAYS FRIDAY, Morning Morninq Chandler Chandler Ferderer Ferderer Copper-nic!<el mineralization mineralization of of the the Copper—nickel Duluth Complex, Complex, northeastern northeastern Minnesota, Minnesota, a gravity gravity and magnetic maqnetic perspective perspective W. Michigan Michigan kimberlite kimberlite province province W. Jarvis Jarvis J. J. Kalliokoski Kalliokos~i MaY 1988 May 13. 1988 Geology mineral Geoloqy and and mineral deposits Archean rocks rocks deposits of of Archean Co-Chairs: R. R. L. L. Bauer Bauer and and M. M. M. M. Kehienbeck Kehlenbeck 8:20 8:20 p.m. p.m. T. T. J. J. Bornhorst Bornhorst An introduction introduction to to the the geology qeoloqy and and An mineral deposits deposits of of the the Archean Archean mineral Marquette Greenstone Greenstone Belt, Belt, Michigan Michigan Marquette 8:40 8:4Q a.m. a.m. G. G. B. B. J. J. W. W. R. R. A. A. A. A. S. S. B. A. B. A. Comparison of of two two parts parts of of the the Comparison Dead Dead River—Ishpeming River-Ishpeminq Greenstorie Greenstone Belt: Belt: evidence for for correlation correlation of of volcanic volcanic evidence stratigraphy stratigraphy 9:00 9:OO a.m. J. W. W. Norby Norby a.m. J. History History of of precious precious metal metal exploration/development in in the the Dead Dead exploration/development River-Ishpeming Greenstone Greenstone Belt Belt River—Ishpeming 9:20 9:20 a.m. a.m. R. R. L. L. Bauer Bauer Multiple folding folding and and regional regional fold fold Multiple patterns patterns in in the the northern northern Vermilion Vermilion granitic granitic complex, complex, NE NE Minnesota Minnesota Margeson Margeson Norby Norby Brozdowski Brozdowski Carter Carter Bouly Bouly xiv xiv �9:40 9 ~ 4 0 a.m. a.me J. R. R . Tabor* Tabor* P. J. Hudleston Hudleston Deformatign history of of the the Quetico Quetico Deformation inetasediments along along the the northern northern metasediments of the Vermilion granitic granitic margin of complex, northern Minnesota 10:00 a.m. Coffee break 10:20 a.m. B. L. Brasaemle* qeobarametry of of Stratigraphy and geobarometry Stratigraphy monzodiorites from the Giants Giants Range Range monzodiorites Minnesota Batholith, northeastern Minnesota 10:40 a.m. G. J. Hudak* The The stratigraphy stratigraphy and physical physical volcanology vo~canology associated associated with with the the F-group volcanogenic volcanogenic massive massive sulfide sulfide F—group Sturgeon Lake, Lake, northwestern northwestern deposits, Sturgeon Ontario Ontario 11:00 1l:QO a.m. a.m. W. K. M. Kehienbeck Kehlenbeck B. E. Seemayer Seemayer late Archean Archean clastic clastic sequence—fill sequence-fill A late of a fault-bounded fault-bounded basin basin structure structure of 11:20 11:2Q a.m. acme The magnetic fabric fabric and structure structure The the Quetico Quetico slates slates at at the the of the Quetico-Wabigoon interface, interface, northwest northwest Quetico—Wabigoon Ontario Ontario P. Sarvas Sarvas G. G e J. J e Borradaile Rorradaile 11:40 a.m. Lunch Lunch FRIDAY. FRIDAY, May Afternoon Afternoon 1988 Rocks/ Geology of of Early Early Proterozoic Proterozoic Rocks! Geology Miscellaneous Miscellaneous Co-Chairs: Co-Chairs: F. F. W. W - Cambray Cambray and and D. D. L. L. Southwick Southwick 1:00 1:OO p.m p - m P. P e K. K. Sims Sims K. J. J. Schulz Schulz Z. Z. E. E. Peterrnan Peterman W. R. R . Van Van Schmus Schmus Evolution of of the the Early Early Proterozoic Proterozoic Evolution Wisconsin magmatic magmatic terrane terrane of of the the Wisconsin Penokean Penokean orogen oroqen 1:20 1:20 p.m. p.me P. P. F. F. Hoffman Hoffman Animikie Animikie Group: Group: A Penokean Penokean foredeep? foredeep? 1:40 1:4O p.m. D. D. L. Southwick Southwick G. B. Morey Tectonic Tectonic imbrication imbrication and and foredeep foredeep development in in the the Penokean Penokean orogen, oroqen, development east—central east-central Minnesota Minnesota 2:00 2:QO p.m. p.m. S. S. D. D. Stahl Stah1 Early Penokean Penokean deformation deformation in in the the Early Peavy Pond Pond area, area, northern northern Michigan: Michigan: Peavy evidence evidence from from the the Michigarnme Michigamme Formation and the Peavy Peavy Pond Pond igneous igneous Formation complex complex D. J. Matty Matty 2:20 2 : 2 0 p.m. p.me J. R. R. K. K. G. S. S. W. J. J. L. L. Klasner Klasner Ojakangas Ojakangas Schulz Schulz LaBerge LaBerge for development development of of an an Evidence for Early Early Proterozoic Proterozoic overthrustoverthrustnappe nappe system system in in the Penokean Penokean orogen orogen of of northern northern Michigan Michigan xv �2:40 p.m. p.m. J. C. Palmqu.st Palmqt-'.st tectonicsArchean and Proterozoic tectonics— northern Michigan, a speculative speculative synthes is synthesis 3:00 3:OO p.m. pain. Coffee break break Coffee 3:20 3:20 p.m. G. L. L. LaBerge LaBerge p.m. G. J. J. S. S. Kiasner Klasner new look look at at The Baraboo Quartzite: Quartzite: A new an an old old problem problem 3:40 3:40 p.m. p.m. P. P. K. K. Sims Sims Z. 2 . E. E. Peterman Peterman J. Klasner J. S. Kiasner -- relevance relevance The Mountain Mountain shear shear zone zone -— The to to age age of of quartzite quartzite at at McCaslin McCaslin and and Thunder Mountains, northeastern northeastern Thunder Wiscons in Wisconsin 4:00 4:OO p.m. p.m. W. T. Jolly Jolly stratigraphy of of the the Geochemical stratigraphy Huronian Huronian continental continental volcanics, volcanics, Ontario: Relative Relative contributions contributions of of mantle mantle heterogeniety, heterogeniety, open-system open-system magmatism andcrystal crystal fusion maqmatism and fusion 4:20 4:20 p.m. A. U. U. Faister Falster p.m. A. Emplacement, mineralogy, Emplacement, mineralogy,and and internal internal evolution evolution of of a highly hiqhly evolved evolved Li-pegmatite Li-pegmatite in in Florence Florence County, County, W. W. B. B. Simmons Simmons Wiscons in Wisconsin 4:40 4:40 * * p.m. B. H. H. Boyum Boyum The origin oriqin and extent extent of of the the hard hard and and The soft soft iron iron ores ores of of the the Maquette Maquette Range, Range, Michigan Michiqan Papers Papers eligible eligible for for student student competition competition POSTER POSTER PAPERS PAPERS The The authors authors of of poster poster papers papers have have been been requested requested to to be be at at their their poster poster displays displays during during the the first first part part of of the the lunch lunch breaks breaks on on Thursday Thursday and and Friday Friday and and at at the the end end of of the the tecnical tecnical sessions sessions on on Thursday. Thursday. C. C. D. D. Anderson Anderson and and R. I?. Argenal Axgenal -— -- New New VLF-EM VLF-EM field field parameters sarameters D. A. Baxter* Baxter* and and T. T. J. J. Bornhorst Bornhorst --- Multiple Multiple discrete discreternafic mafic D. A. intrusions intrusions of of Archean Archean to to Keweenawan Keweenawan age, age, western western Upper Upper Peninsula, Peninsula, Michigan Michiqan T. T. M. M. Boduz* Bodus* and and W. W. F. F. Kean Kean --- Preliminary Preliminary paleomagnetic paleomaqnetic study study of of the the Amberg Amberg and and Atheistane Athelstane granites granites in in northeastern northeastern Wisconsin Wisconsin M. M. Cohen*, Cohen*, J. J. Mancuso, Mancuso, J. J. Frizado, Frizadol and and D. D. Stewart, Stewart, E. E. Berdusco Berdusco —— -Paragenetic Paraqenetic relationships relationships among among siderite, sideritel magnetite, magnetite, calcite, calcite, quartz, quartz, and and sulfides sulfides in in the the MacLeod MacLeod Siderite Siderite Mine, Mine, Wawa, Wawa, Ontario Ontario D. D. H. M. Davidson, Davidson, Jr. Jr. --- Precambrian Precambrian Red Red Bluff Bluff granite granite complex, complex, West Comparison West Texas: Texas: Comparison with with other other Mid—Proterozoic Mid-Proterozoic rapakivi rapakivi granites granites xvi �J. Feeny* Feeny* and and W. W. F. F. Kean Kean -- Paleornagnetism of Keweenawan age 3. of Falls Keweenawan hasalts from the TaylorPaleomagnetism Falls-St. Croix Croix area ofage basalts from the Taylor Falls—St. Falls area of Wisconsin and and Minnesota Minnesota Wisconsin - R. J. J. R. Ferderer* --.Application of Werner dec~nvolution to the Ferderer* Application of Werner deconvolution to the Penokean fold-and-thrust belt, east-central Minnesota Penokean fold-and—thrust belt, east-central Minnesota J. Fronk Fronk*and andD. D. C . Stswart -- An investigation into the chemical J. C. Stewart -— An investigation into the chemical processes causing the the formation of unakite in the Waupaca processes causing adamellite of Wisconsinformation of unakite in the Waupaca adamel].ite of Wisconsin -- T. H. M. Han Han -— Genesis Genesis and metamorphism of magnetite in Biwabic IronT. and District, metamorphism of magnetite in Biwabic Iron— Formation, Mesabi Minnesota Formation, Mesabi District, Minnesota P. P. K. Jongewaard* Jongewaard* -— -- Stratigraphy Stratigraphy and physical K. and physical footwall rocks to the the Sturgeon Sturgeon Lake footwall rocks to Lake deposits, Nki Ontario deposits, MW Ontario volcanology of the volcanology of the massive sulphide massive sulphide L. MacLellan* MacLellan* and and T. T. J. J. Bornhorst Bornhorst -- Geology, Geology, structure and M. L. M. —— structure and Marquette County, mineralization of the Reany Lake area, mineralization of the Reany Lake area, Marquette County, Michigan Michigan Mudrey, Jr., Jr., and and B. B. A. A. Brown Brown —— -- Bedrock Bedrock geology of the Mudrey, geology of the Superior map sheet, Wisconsin Superior map sheet, Wisconsin M. G.G. M. Peterson* and and C. C. A. A . Geiger -- Two generations of garnet Peterson* Geiger —— Two generations of garnet growth in the Hardwood gneiss, Dickinson County, Michigan growth in the Hardwood gneiss, Dickinson County, Michigan R . Schneiker* Schneiker* and and W. W. F. F. Kean Kean -- AA paleomaqnetic study of the R. paleomagnetic study of the Hamilton Mound area of Adams Adams County, County, central central Wisconsin Hamilton Mound area of Wisconsin J. 3. W. W. - K. J. J. Schulz, Schuiz, P. P. K. K. Sims, Sims, and and Z. Z. E. E. Peterman Peterman ——A --A post-tectonic K. post-tectonic rare-metal-rich granite in the southern complex, Upper rare—metal--rich granite in the southern complex, Upper Peninsula, Michigan Peninsula, Michigan and T. T . J. J à Bornhorst -- The Small* and Small* Bornhorst -— The Marquette County, Michigan: northern northern Marquette County, Michigan: Reany Creek Formation, Reany Creek Formation, Archean or Proterozoic? Archean or Proterozoic? P. 3. J. Wagner Wagner and and M. M. K. K. Sood Sood -— -- Geochemistry Geochemistry and petrology of the P. and petrology of the Athelstane granite, Marinette County, Wisconsin Wisconsin Atheistarie granite, Marinette County, S. M. M. Wee Wee and and J. J. T. T. Wilband Wilband -- Geochemistry and tectonic S. Geochemistry -— and tectonic significance of Early Proterozoic igneous rocks, rocks, northern significance of Early Proterozoic igneous northern Michigan and northeastern Wisconsin Michigan and northeastern Wisconsin J. R. R. 3. J. 3. * L. Welsch Welsch -— -- Preliminary Preliminary structural analysis of Archean rocks L. structural analysis of Archean rocks in the Virginia Horn area, area, northeastern Minnesota in the Virginia Horn northeastern Minnesota * Papers Papers eligible eligible for for student student competition competition xvii xvii �POST POST MEETING MEETING FIELD FIELD TRIP TRIP j,. 1988 L U 8:00 8 : O O a.m. a.m. to to about about 7:00 7:OO p.m. p.m. Field Trip Trip 33 —— -- Evidence Evidence for Early Proterozoic ?roterozoic overthrusting overthrusting in in northern northern Michigan Michigan and and Wisconsin. W i s c o ~ s i n ~This field field trip trip terminates terminates in in Iron Mountain, Mountain, Michigan, Michigan, which which has has air air service. service. The The bus bus will will return return to to Marquette. Marquette. SATURDAY. V W xviii �ABSTRACTS �NTT VLF-::J FITLD ?ATIRS by Chris :Iris rgenai P. Anderson 3. m t i e r s o n and a9fL Poger ?.ozer t i ~ ? e i ; d :innipeg, Manitoba, ,:inni?eg, Xanitoba, Canada and the The primary r a n s m i t t e r md the i ~ r i r n a r yfield f i e l d from the t h e VLF ttransmitter secondary ffield from aa conductor conductor combine combine aatt aa llocation i e l d from ocation resulting 3 ' 5 field f i e l d ellipse. e l l i ? s e . Conventional measurements mezisure~ents r e s u l t i n g in i n aa EM are with ith a r 5 of of' the t h e angle the t h e major aaxis x i s of of the t h e ellipse e I l i ; ~ s emakes w a h horizontal o r i z o n t a l plane -?lane (sometimes (sometimes called c a l l e d the t h e in-'hase in-,>base measurement) and. of tthe measurement) and tthe h e rratio a t i o of h e xminor i n o r and major mz.jor axes axes field ellise tthe c, e fielcl e l l i x eexoressed e x x e s z e 6 as a s >ercent e r c e n t(sometimes (zmetir:er called measurement). r quaem-ture ne2surene;i~ c ~ l l e ?the t h e out-of-hase out-of- ~ h a or s eoquadrature In 7lace In > l a c e of tthe h e ratio r z t i omeasurement, measurement9some sor2e systems s y s t e z s measure ::~XLIL-S tthe h e secondary secondary ffield i e l d strength s t r e n g t h which often o f t e n is i s exoressed ex~ressed as ercent above a s a2 3ercent above tthe h e primary ?rimary ffield. ield. Based on field f i e l d experience e x y e r i e n c e and model ccalculations alculations measurement of of we have found that t h a t the t h e measurement of the t h e direction d i r e c t i o n of the component of t h e hhorizontal o r i z o n t 2 1 com2onent of the t h e secondary field f i e l d gives gives a That is, good indication i n d i c a t i o n of of the t h e strike s t r i k e of of the t h e conductor. c o n 2 u c t o ~ . Yh~2.t is, without tthe h e ddirection irection w i t h o u t a secondary secondzry field f i e l d is i s at a t right risht angles a g l e s to t o the t h e direction 2 i r e c t i o n to t o the t h e VLF 7LL2 station. s t a t i o n . iith Yitk the the resence of direction will ill Yresence of a strong s t r o n g secondary field, f i e l d , the the d irection w be c controlled be o n t r o l l e d by the t h e conductor conductor and and will w i l l be be at a t right r i g h t angles anglss For nmoderate tto o the t h e strike s t r i k s of of the t h e conductor. c o n d u c t o r , For o d e r z t e secondary secongmy fields, f i e l d s * the t h e effect e f f e c t can can be evaluated e v a l u a t e d and and using u s i n g this this information c m be be calculated. ~alculate6~ i n f o r m a t i o n the t h e strike s t r i k e of of the t h e conductor conductor can This ~ roceedure ? a r t i c u l a r l y important i m ~ o r t a n tin i n areas a r e a s of of This r o c e e d u r is ei s particularly multile m u l t i 3le conductors. conductors. IIn n tthe h e ccase a s e of of three t h r e e field f i e l d vectors v e c t o r s at a t aa- station, stztion* namely, namely, the t h e Primary x i m a r y field, f i e l d , a strong s t r o n g secondary field f i e 1 2 from Troy a bed bed rock rock conductor, and a secondary field c o n d u c t o r , and f i e l d ffrom r o m overburden having q u a d r z t u r e component, con?onent, the t h e calculations c a l c u l a t i o n s and an? h a v i n s mostly a2. quadrature f r o m ffield i e l d . and ar-d model moc?el ddata a t a clearly c l e a r l y show shoi! the the rresults e s u l t s from of uusing llimitations i - ~ i t z t i o n sof s i n g tthe h e rratio a t i o data d a t a in i n interpretation. inte~~retz+ign. " of 01 >. 1 �inaii,r, th2 resu1t of uiti1e-conducor nJ effects and non— 1anar field vectors result in a triaxial field elli?soid which can be artially resolved as of the interpretation. 2 �I MULTIPLE FOLDING AND REGIONAL FOLD PATTERNS IN THE NORTHERN VERMILION GRANITIC COMPLEX, NE MINNESOTA Robert L. Department Bauer of Geology, University of Missouri Columbia, Missouri 65211, USA The western Vermilion Granitic Complex of the southwestern Quetico Subprovince is a highly deformed amphibolite facies (M1) The principal rock units are paragneiss and biotite schist that contain variable concentrations of veins and lenses of early tonalite—granodiorite and younger granite of the adjacent Lac La Croix batholith. These granitic units are interlayered with biotite schist on scales as great as several kilometers and are folded along with the schist into a series of easterly trending folds. The distribution of these folds has migmatite complex. been well established by reconnaissance geologic mapping (Southwick and Ojakangas, 1979) and more recently by regional aeromagnetic patterns (Chandler, 1983). Analysis of multiple fold geometries along the northern margin of the Vermilion Granitic Complex, in the Kabetogama and Namakan Lakes area, indicates that the large—scale regional fold patterns observed in the complex correlate with the youngest of three periods of folding. The oldest deformation produced a strong bedding—parallel foliation (el) in the schist and local sinistral/north-side—down shear parallel to S1. Well-developed asymmetric pull-apart structures in early tonalite veins parallel to bedding in the schist indicate the kinematics of shear. The second deformation generated easterly plunging F2 folds and a D2 IS fabric that locally aligns M1 sillimanite—muscovite tufts parallel to a axial plane foliation (S2) and F2 fold hinges. In the mignatitic rocks described here, the F2 folds are of S—symmetry and fold the D1 asymmetric pull—apart structures and S1 foliation. Further to the north, in the less migmatitic biotite schist north and west of Kettle Falls, the F2 folds are of Z—symmetry (Tabor, this volume) and indicate the presence of a major upright east-west—trending F2 antiformal trace along the Kabetogama peninsula between Rainey and Kabetogama Lakes. Stratigraphic tops are invariably to the north on the southern (migmatitic) limb of this major F2 structure and change to the south on the northerr limb, indicating a downward structural facing of the regional F2 antiformal syncline (Fig. 1). F2 fold axial planes, which are steeply dipping along the northern margin of the complex, dip more gently to the north as one proceeds to the south toward the more migmatitic part of the Here the F2 folds of S—symmetry are refolded by upright F3 folds of Z—symmetry on the northern limb of one of the large east-west—trending, easterly plunging antiformal structures recognized during reconnaissance mapping (Fig. 2). An intense D3 linear fabric occurs parallel to the regional F3 fold hinges, and a locally well—developed S3 crenulation foliation deforms both and the M1 sillimanite—muscovite tufts aligned in S2. complex. 3 �N- / I,/' Inf erred structure Inferred structure // / '/ / 0 / ,1 / Fig. Fig. F I, / Observed Observed rnl->tinnc;t-,Jps relationships 1 2/ Schematic Schematic cross cross section section illustrating illustrating the the relationship relationship among F2 F2 folding, folding, inferred inferred F1 Fi folding, folding, and and stratigraphic stratigraphic younging young ing among directions directions (given (givenby by bar bar and and ball ball symbols). symbols). 1l F2 F3 Fig. Fig. 22 Schematic Schematic cross cross section section illustrating illustrating the the relationship relationship between between F2 F2 and and F3 F3 folding. folding. This This section section is is south south of of the the cross cross section shown in inFigure Figure1.1. section shown 4 �U Preliminary analysis of this deformation sequence and the orientation of the structures generated suggests the following sequence of events: Northwest—directed compression resulted in early recumbent folding. Associated northwest—directed shear on the lower limb of this structure produced the asymmetric boudins with sinistral/north—side—down displacement. Continued north- to northwest—directed compression lead to F2 refolding of the lower (overturned) F fold limb and resulted in the downward—facing easterly plunging F2 folds. Progressive overturning of these F2 folds to the south (possibly during emp].acement of the Lac La Croix batholith), in a regime of continued north to northwestdirected compression, lead to F3 refolding of F2 folds about a similar easterly plunging axis. A significant feature of this sequence of deformation is its development in a relatively constant north— to northwest—directed compress ional regime. REFERENCES CITED Chandler, V.W., 1983, Aeromagnetic map of Minnesota, St. Louis County, total intensity anomaly. Minnesota Geological Survey, Aeromagnetic Map Series, Map A—2, St. Paul, scale 1:250,000. Southwick, D.L. and Ojakangas, R.W., 1979, Geological map of Minnesota: International Falls sheet. Minnesota Geological Survey, St. Paul, scale, 1:250,000. Tator, J.R., this volume, Deformation history in the Quetico metasediments along the northern margin of the Vermilion Granitic Complex, NE Minnesota. 5 �Multiple Discrete Discrete Mafic Mafic Intrusions Intrusions of of Archean Multiple Archean to to Keweenawan Age, Age, western western Upper Keweenawan Upper Peninsula, Peninsula, Michigan Michigan D.A. BAXTER and Ti. D.A. BAXTER and T.J.BORNHORST BORNHORST (Department (Department of of Geology Geology and andGeological Geological Engineering, University Houghton, MI MI 49931) 49931) Engineering, Michigan Michigan Technological Technological University The bedrockofof the the western Upper Peninsula Peninsula of of Michigan Michigan concon The Precambrian Precambrian bedrock western Upper tains gabbro and diabase intrusions of of varying age, origin, tains gabbro and diabase intrusions varying age, origin, and size. size. Previous studies assignedthese thesemafic mafic rocks, rocks, on on the the basis studies have have typically typically assigned basis of of alteration alteration and and orientation, to to one of Archean, Lower Lower Proterozoic, Proterozoic, and and orientation, of three three broad broad age agegroups: groups: Archean, Middle Proterozoic In contrast, Middle Proterozoic (Keweenawan). (Keweenawan). In contrast, detailed detailed mapping mapping by Kantor Kantor (1969) (1969) documented more more than than three three ages documented ages of mafic mafic intrusions intrusions in in the theSugarloaf Sugarloaf Mountain Mountain area, north of area, of Marquette. Marquette. In this this study, study, we we suggest suggest that at at least least six six separate separate intrusive events intrusive events occurred occurred based based on careful careful examination examination of textures, textures, mineralogy, mineralogy, and degree in hand hand sample, thin section, and degree of metamorphism metamorphism in sample, thin section, and outcrop outcrop (Figure (Figure 1). The local setting of of each The local geologic geologic setting each body body must must also also be be taken taken into intoconsideration. consideration. The oldest oldest mafic mafic intrusions intrusions in region are dike dike and and sill-like sill-like gabbro gabbro bodies bodies The in the region within the Marquette within Marquette Greenstone Greenstone Belt. Belt. The The gabbro gabbro typically typically consists consists of plagioplagioclase, amphibole, amphibole, and and varying of secondary clase, varying amounts amounts of secondary sericite sericite and retrograde retrograde rocks of of the greenstone belt are cut gabbro and volcanic volcanic rocks greenstone belt cut by by gneissic gneissic chlorite. The gabbro tonalite to to granodiorite plutons which whichare are in in turn turn cut by tonalite granodiorite plutons by thin thin discontinuous, discontinuous, tabular, amphibolite tabular, amphibolite bodies bodies such as as those those at at Wetmore Wetmore Landing. Landing. Although Although xenoliths xenoliths of greenstone belt plutons, we we interpret interpret these these tabular tabular of greenstone belt rnafic mafic rocks rocks exist exist in in the plutons, bodies as as mafic on the mafic intrusions intrusions based based on the appearance appearance of of their their margins. margins. Foliation bodies in Foliation in these dikes dikes is parallel rocks which which leads these parallel to the the surrounding surrounding gneissic gneissic rocks leads to to the the conclusion Archean deformation deformation event post-date the conclusionthat that the the dikes dikes pre-date pre-date an an Archean event but but post-date tonalite to granodiorite tonalite granodiorite plutonic plutonic activity. activity. The occurred in in aa span The next next mafic rnafic intrusive intrusive activity activity occurred span of time time bracketed bracketed by by the the Archean deformation event event and and the the deposition of the sediments of the Archean deformation deposition of sediments of the Lower Lower Proterozoic Marquette Supergroup. These dikes dikes are are porphyritic Proterozoic Supergroup. These porphyritic and typically typically trend trend north-south (±12°). (212"). They They contain contain 4i to cm (4 (4 to to 1 inch) euhedral euhedral to to subhedral subhedral to 3 cm phenocrysts phenocrysts of plagioclase plagioclase (approx. (approx. An70). Anm). The dikes dikes range range from from 9-60 9-60 meters meters (30-200 feet) feet) in (30-200 in width width and andare arevariably variablymetamorphosed. metamorphosed. Cannon Cannon (1975) (1975) noted noted that that some dikes dikes in in the Republic and cut the Archean some Republic area area are distinctly distinctly porphyritic porphyritic and the Archean granites and gneisses, but do not granites and gneisses, but not cut cut the theEarly EarlyProterozoic Proterozoic sediments. sediments. Puffett (1975) also also noted noted the the existence of coarsely porphyritic mafic mafic dikes (3975) existence of coarsely porphyritic dikes which which may may be be Archean in age. We tentatively tentatively interpret interpret these Archean age. We these porphyritic porphyritic mafic dikes dikes as as equivalent Archean Matachewan Matachewan Dike Ontario which which have have an an age age equivalent to to the Archean Dike swarm swarm of of Ontario of 2690±93 Ma (Gates and Condie and and others (1987) of 2690293 Ma and Hurley, Hurley, 1973). 1973). Condie (1987) state state that that Matachewan dikes in in Ontario Matachewan dikes Ontario cut Archean Archean lithotectonic lithotectonic trends trends and and are areconsequently consequently younger than the last event in the younger than last major major Archean Archean tectono-thermal tectono-thermal event the area. area. This is is consistent with with our our observations in the western consistent observations in western Upper Peninsula Peninsula of Michigan. Michigan. The Matachewan dikes are are cut by Matachewan dikes by both both Lower Lower Proterozoic Proterozoic and and Middle Middle Proterozoic Proterozoic (Keweenawan) diabase diabase dikes dikes on on Sugarloaf (Keweenawan) Sugarloaf Mountain Mountain (Kantor, 1969). 1969). This mafic This mafic intrusive intrusive event event may may include include some some relatively relatively non-porphyritic non-porphyritic dikes dikes as as well. well. 1 Following the deposition deposition of of most Following the most of the the Lower Lower Proterozoic Proterozoic Marquette Marquette SuperSupergroup, a swarm swarm of finefine- totocoarse-grained coarse-grained gabbro gabbro and and diabase diabase intrusives intrusives cut all all group, pre-existing These dikes dikes and and sills pre-existing rocks. rocks. These sills have have been been previously previously interpreted interpreted as as related to the 1974). Michigamme Formation Formation (Cannon, (Cannon, 1974). related the Clarksbbrg Clarksburg Member Member of of the theMichigamme They They consist consist of pyroxene/hornblende, pyroxene/hornblende, chlorite, chlorite, plagioclase, plagioclase, epidote, sericite, sericite, and and variable amounts variable amounts of secondary secondary carbonate. carbonate. Intrusive Intrusive bodies bodies range range from from 10 cm to to over 175 (6 inches over 175 meters meters (6 inches to >> 500 500 feet) thick but but orientation orientation is is highly highly variable, variable, feet) thick and therefore and therefore not not useful useful as aa tool tool for for identification. identification. These intrusions are Early Early These intrusions Proterozoic inin age age and and have during the PenoProterozoic have been been deformed deformed and and metamorphosed metamorphosed during Penokean kean orogenic orogenic event. event. 6 �____________________________ _______________________ _______________________ _______________ ________________ ______________ ___________________________ ___________________ ____________________________ _________________ In Marquette Marquette County, County, there there are are at at least least two two groups groups ofofKeweenawan Keweenawan diabase diabase In dikes. dikes. The The older older of of these these is is aa set set of of fine-grained fine-grained diabases diabases that that trend trend approxiapproximately mately north-south north-south (±15°). (215O). They commonly consist slightly altered altered pyroxene, pyroxene, They commonly consist of of slightly plagioclase, amphibole, generally less less than than 30 30 meters meters (100 (100 plagioclase, amphibole,and and chlorite, chlorite, and and are are generally feet) thick. thick. The younger younger intrusives intrusives trend trend east-west east-west (±10°), (±lo0)cross-cut cross-cut the the older older Keweenawan diabase, medium to coarse-grained, and be over over 200 200 meters meters Keweenawan diabase, are are medium to coarse-grained, and can be (600 (600 feet) thick. thick. The younger younger dikes dikes also also have have aa strongly strongly reversed reversed remnant remnant magnetization, and occasionally have a coarse-grained magnetization, and occasionally have coarse-grained granophyric granophyric interior. interior. Cannon (1975) (1975) mentioned existence of "undeformed" diabase which cut cut Cannon mentioned the the existence of "undeformed" diabase dikes dikes which folded sediments sediments of of the the Marquette Marquette Supergroup Supergroup and the Lower Lower ProteroProterothe folded and also also cut cut the zoic zoic dikes dikes and and sills sills which which intrude intrude the thesediments. sediments. We We interpret these these undeformed undeformed dikes as early early (north-south) (north-south) Keweenawan Keweenawan mafic mafic intrusions. intrusions. There There are multiple multiple ages ages of mafic mafic intrusive intrusive rocks rocks in the the western western Upper Upper Peninsula. Peninsula. We Archean mafic maficintrusives: intrusives: 1) 1) We propose propose three distinct distinct groups groups of of Archean post-plutonic/pre-deformation; and postpost-volcanic/pre-plutonic; 2) 2) post-plutonic/pre-deformation; and 3) 3) postdeformation! deformation/ pre-Early pre-Early Proterozoic Proterozoic sedimentation sedimentation (Figure (Figure 1). 1). This is is followed followed by by intrusives of Early age and and by two intrusives of Early Proterozoic Proterozoic age two ages ages of of Keweenawan Keweenawan (north-south (north-south and then the youngest Archean, the the Early Early then east-west) east-west) intrusives. intrusives. Previously, Previously, the youngest Archean, Proterozoic, and the oldest Proterozoic, and oldest Keweenawan Keweenawan (north-south) (north-south) were were combined combined together together as as the Metadiabase Metadiabase of Early Early Proterozoic Proterozoic age age (Clark (Clark and and others, others, 1975; 1975;Cannon, Cannon,1975; 1975; Cannon, Gair and Cannon, 1974; 1974; Gair and Thaden, Thaden, 1968; 1968; Puffet, Puffet, 1974). 1974). It It is not not possible possible to to base base aa field of age on the the trend field determination determination of age simply simply on trend of individual individual intrusives intrusives or the the degree degree of alteration alteration and and deformation. deformation. For example, example, aa N-S N-S trending trending dike dike which which isis known to be known to be Keweenawan Keweenawan in age age contains contains alteration alteration of the the primary primary mineralogy mineralogy to to chlorite, chlorite, carbonate, carbonate, and and sericite sericite and andhas hasweakly weakly foliated foliatedmargins margins(Owens, (Owens,1986). 1986). These are being with further These preliminary preliminary results results are being confirmed confirmed with further laboratory laboratory and and field field work. This study study was was partially partially funded funded by by aa grant grant from fromthe theMichigan MichiganGeological Geological Survey. Survey. <E-W Keweenawan Keweenawan Diabasj ~iabase] Mid Continent Continent Rifting Rifting < N-S Keweenawan Diabasel ~iabasel ..jj-S 0 0 N Penokean Penokean Orogeny Orogeny 0 Baraga L o w e Proterozoic r ProterozoicDiabas1 ~iabase) -lilLower Group Marquette Marquette Supergroup Supergroup —4 Menominee Group Chocolay Group —1Matachewan Intrusionsj 03 2 J- I Late Archean deformation and and metamorphism metamorphism _j ..cZ"Wetmore < " w e t m o r e Landing" Landing" Intrusions! ~ntrusions] 1 Tonalite toto granodiorite granodiorite 1 plutons plutons 1 -zZGabbro ~ a b b r Intrusions! ~ntrusions] o \ Marquette Marquette Greenstone Greenstone 1 1 Belt Belt volcanism volcanism 1 Figure Figure 1. 1. Schematic Schematic diagram diagram of of mafic maficintrusion intrusion relative relativechronology. chronology. 7 �REFERENCES Cannon, W.F., W.F., 1975, Bedrock Geologic Geologic Map Map of of the Republic Cannon, 1975, Bedrock Republic Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey, Survey, Miscellaneous Miscellaneous Investigations Investigations Series Series Map, 1-862. 1-862. Cannon, W.F., Map of the Cannon, W.F., 1974, 1974, Bedrock Bedrock Geologic Geologic Map the Greenwood Greenwood Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey, Survey, Geologic Geologic Quadrangle Quadrangle Map, Map, GQ-1168. GQ- 1168. Clark, L.D., and Kiasner, Map of of Clark, L.D., Cannon, Cannon, W.F., W.F., and Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock Geologic Geologic Map the Negaunee Quadrangle, Marquette Marquette County, County, Michigan: U.S. Geological SurGeological Surthe Negaunee SW SW Quadrangle, Michigan: US. vey, vey, Miscellaneous Miscellaneous Map Map Series, Series, GQ-l226. GQ- 1226. K.C., Bobrow, D.J., and Condie, K.C., Bobrow, D.J., and Card, Card, K.D., K.D., 1987, 1987, Geochemistry Geochemistry of PrecamPrecambrian Mafic Dykes of the brian Dykes from the the Southern Southern Superior Superior Province Province of the Canadian Canadian Shield, Shield, in: Mafic Dyke W.F. Fahrig Fahrig editors, editors, Geological Geological Association Association in: Dyke Swarms, Swarms, H.C. H.C. Halls Halls and and W.F. of Canada Paper 34, of Canada Special Special Paper 34, p. p. 95-108. 95-108. Gair, Gair, J.E. J.E. and and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of of the the Marquette Marquette and andSands Sands Quadrangles, Marquette Marquette County, County, Michigan: U.S. Geological Geological Survey Survey Prof. Prof. Paper 397, Quadrangles, Michigan: U.S. Paper 397, 77 pp 77 PP. Gates, Gates, T,M. T.M. and and Hurley, Hurley, P.M., P.M., 1973, 1973, Evaluation Evaluation of Rb-Sr Rb-Sr Dating Dating Methods Methods Applied Applied to Matachewan, Matachewan, Abitibi, MacKenzie MacKenzie and and Sudbury Sudbury Dike Dike Swarms Swarms in in Canada: Canada: 10, p. 900-919. Canadian Journal of Earth Canadian Journal Earth Sciences, Sciences, v. v. 10, 900-919. Kantor, J.A, Kantor J.A., 1969, 1969,Assimilation Assimilation and and Dike Dike Swarms Swarms in in the the Sugarloaf Sugarloaf Mountain Mountain Thesis, Michigan Michigan Technological Technological UniverArea, Area, Marquette Marquette County, County, Michigan: Michigan: M.S, M.S. Thesis, sity, Houghton, Houghton, Michigan, Michigan, 83 83 pp. pp. Owens, E.O., E.O., 1986, Geology and and Precious Precious Metal Metal Mineralization of Owens, 1986, Precambrian Precambrian Geology Mineralization of the Fire Center the Center Area, Area, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan TechnoTechnological University, University, Houghton, logical Houghton, Michigan, Michigan, 152 152 pp. Puffet, W.P., W.P.,1974, 1974, Geology Geology of the the Negaunee Negaunee Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: U.S. U.S. Geological GeologicalSurvey, Survey,Prof. Prof. Paper Paper 788, 788, 53 53 pp. Michigan: 8 �Preliminary Preliminary Paleomagnetic Paleomagnetic Study Study of of The The Amberg Amberg and and Atheistane Athelstane Granites Granites in in Northeastern Northeastern Wisconsin Wisconsin Theresa M. M. Bodus Bodus Theresa and and William William F. F. Kean Kean Department Department of of Geosciences Geosciences University University of of Wisconsin—Milwaukee, Wisconsin-Milwaukee, WI WI 53201 53201 The The Amberg Amberg and and Athelstane Athelstane granites granites of of Marinette Marinette County, County, Wisconsin Wisconsin have have compositions compositions which which are are similar similar to to the the Penokean Penokean granites but the the ages ages tend tend to to overlap overlap with with granites of of Northern Northern Wisconsin, Wisconsin, but the the post post Penokean Penokean granites granites of of south south central central Wisconsin. Wisconsin. In In addition, addition, the the grey grey Amberg Amberg granite granite cross-cuts cross-cuts the the pink pink Atheistane Athelstane granite granite and and gives gives an an Rb/Sr Rb/Sr age ageof of1650+m.y.a. 1650+m.y.a. This This study study was was started started to to help help define define the the chronology chronology of of the the ignious ignious intrusives intrusives and and to to determine determine if if there there is is any any similarities similarities between between the the paleopole paleopole positions positions of of these these samples samples and and those those of of the the 1760 1760 m.y. m.y. old old granites granites and and rhyolites rhyolites of of south south central centralWisconsin. Wisconsin. Ten Ten oriented oriented hand hand samples samples were were collected collected from from the the intrusives intrusives and and analyzed analyzed for for magnetic magnetic stability stability and and magnetic magnetic directions. directions. Preliminary Preliminary results results indicate indicate about about half half the the samples samples were were stable stable enough enough to to provide provide well well clustered clustered magnetic magnetic directions. directions. In In addition, Amberg and and the the addition, the the magnetic magnetic directions directions for for the the Amberg Atheistane Athelstane granites granitesare arenot notsimilar. similar. The The magnetic magnetic direction direction of of the the Amberg Amberg granite graniteseem seem to to be be associated associated with withthe the1650 1650m.y. m.y. associated overprint overprint whereas whereas the the Athelstane Athelstane pole pole positions positions may may be be associated with in.y. with either either1760 1760m.y. m.y.oror1450 1450 m.y. It It is is further further suggested suggested that that the the Amberg Amberg and and Atheistane Athelstane granites granites are are not not simply simply single single intrusives, intrusives, but but are are probably probably the the main main components components in in aa large large intrusive intrusivecomplex. complex. 9 �An Unusual Apatite-Rich Nelsonite-, Nelsonite-, Pyroxenite-, and Homblendite-Bearing An and Hornblendite-Bearing Intrusi Intrushof of Post-PenokeanAge, Age, Central Centmi Minnesota Minnesota Post-Penokean Texrence J. Boerboorn, Minnesota Geological Survey, 2642 University Ave., SL Paul, Minnesota 55414 A A small small pluglike pluglike intrusion inmsion in incentral tendMinnesota Minnesota contains containsvery veryapatite-rich apatite-richrocks rocks rangingfrom from nelsonite nelsonite (oxide-apatite (oxide-apatie rock) m k )to topyroxenite, pyroxenite*hornblendite, hornblendite*and and diorite. dionte. As As ranging judgedfrom frommagnetic magneticdata, data,the theplug plughas hasaadiameter diameterofofabout a b u t2.5 2.5km, kmvand andisisconcentrically concen~ly judged zoned Petrochemical Petrochemicaldata data indicate indicatethat thatthe theplug pius is issubalkalic s u b W c to alk1ic W c in in composition composition zoned. is characterized by atypically high values d Fev Ti* P, and H g q but is depleted and and is aracterized by atypically high values of Fe, Ti, P. and H20, but is depleted inhKK and Si. Si The l%e distinctive disthaivemagnetic magneticanomaly anomaly(Fig. (Fig. 1), I)*combined combined with rock distnbution dismbution and panems defines defies aa plug-like plug-Iike geometry geomeuyand andconcentrically-zoned concenmcally-mnedintrusion inmsion2.5 2.5km laninin patterns, diamm.It intrudes It intrudes conglomeratic rocksofofEarly M yProterozoic Proterozoicage, age,and andisislocated Iocatedalong dung diamer. conglomeratic rocks thetrace sacof of the the Great GreatLakes Lakestectonic tectoniczone, zoneqaamajor rna~ur E-NEtrending m n h gstructural smb u n c h yinin the E-NE boundary east-caml Minnesota. Mimesom This E sintrusion intrusionforms ~OITXIS oneofofmany manysharp, sharp,small s dmagnetic magnetic east-central one aresynsynano& in central central Minnesota. Mimesom Regional Regionalrelationships rehionshipsimply implythat thatthese theseplutons plutonsare anomalies in topost-tectonic p o s t m n i c with regard regard to to the the Penokean Penokm orogeny. q e n y . AAfew fewscattered scatteredoutcrops outmpsofofthe the to plutonedst, exis&and anditithas hasbeen beenintersected intmectedbyby1212drill CM holestotaling totaling250 250m, m,which which were were pluton holes drilled in the 1900s during iron-ore drilled ly early in the 1930s duxing iron-meexploration. explcmion. The type in outcrop outcrop is rtlanocradc mianocratictotomesocratic mesomaticferrodiorite; f e d o r i t e ;the the The dominant dominant rock type latter lattercontains cmtains pegmatitic pegmatiticveins veins and andanorthositic anorthositicsegregations. segregations.Hornblendite Hmblendieisis gradmad into into pyroxenite, ppxenite*which whichtogether togetherwith withnelsonite nelsoniteform fomaasignificant significantfraction hctionofof gradational theintruaion. on. Approximately AppximateIy 80% 80% of the core faxage the footageisishornblendiee/pymxenite, hornblendite/pyroxenite,10% l0 nelsonire, nelsonkvand and 10% 10% diorite. diorite-The Thenelsonite, nelsonite,pyroxenite, pymxeniteqand andhornblendite hornblenditeare arelocated located withinthe theferrodiorite femdionte in in aa horseshoe-shaped horseshoe-shapedwoe, m e *and andare areseen s e nonly odyinindrill drillcore. cores within The Theferrodiorite femdioriteisismediummedum-totocoarse-grained coarse-pined and and consists consistsdominantly dominantlyof of andesk (Anjgjo), ( b m ) ferTopargasitic ,fermpargasiuchornblende, hmblende,actinolite, actinolite9apatite, apatite*magnetite, magnetite*ilmenite, henite* andesine augite(Ca43Mg37Fej) Ca43Mg37Fe20)and andlesser lesseramounts amountsof ofalbite. dbite. Apatite Apatiteisisprominent prninentininthe the augite meladicxite, volume. Layering meIadicxite9comprising cornpising as as much as as 15% 15% of of the the modal zmdaâvolumes Layeringdefined definedby by eithercumulus c m d u s or ur flow-aligned flow-aligned plagioclase plagioclaiecrystals crystals and and by by centimeter-scale centimeter-scalemodal modal either v a r i of of~feldspar feldspar ~ and hornblende hornblendeisisconcordant c o n h t with with the the edge edge of of the the intrusion intrusionand and variations and dips dipssteeply steeplytowards towardsthe thecenter. center* Hornblendite Xmblendite and andpyroxenite pymxeniteare aredark darkgreen, green,medium mediumgrained, grained,and andequigranular. equigranuh, The tworock rocktypes typesare aregradational, pdationa17depending dependingmainly d yupon uponthe thedegree degreetotowhich whichpyroxene pymxene Thetwo hasbeen beenreplaced replaced by by hornblende hornblendeand andactinolite. a c ~ o l i t eDominant .Dominantminerals mineralsininboth bothrock rocktypes types has include includeprimary primary and andsecondary smndaxyferropargasitic ferropargasitichornblende, hornblende*augite augite(C&39Mg29Fe), (agMg~gFa), actinolixe, oxides, and apatite. a c t i n o h Fe-Ti Fe-Ti oxides* apatite. Tabular Tabularzoned m e d magmatic magmatic hornblende homblendeisiscommon, common, and dark andconsts co& ofofa red-brown a red-brownferropargasitic fmpargasiriccore corerimmed -ed by byrhythmic rhythm~c darkgreen greenand a d coIorle overgrowths ofofincreasing cmlurles avergrowths increasingactinolitic actinofiticcontent. contentTextural T e x Mevidence evidenceshows showsthat that cumulus cumulusaugite augitewas wasreplaced replacedby bymaginatically magmaticaIlyrelaxed related prismatic pismaticferropargasitic fmpargasitic hornbIeie, and and hornblede* andboth bothaugite augite andhornblende hornblendewere weresubsequently subsequentlyreplaced replacedby byfibrous fibrous actinoli~.In Inextreme extremecases casesthe therock rockisiscomposed composedofofaafelted feltedmat matofofactinolite xrholitethat thathas has actinolixe. all primary pt i m~q grain grain boundaries, boundaries-Modes Modsofofoxides oxidesrange m g efrom from10% 10%toto80%, 8Q%,and ad o b ~all obliterazed the magmatic thelatter latterrocks rocksgrade grade into intonelsonite. n e l ~ n i tVery eVery ~ minor minoramounts amountsofofinterstitial, interstitial9 mgmatic sphene andcalcite calciteare arepresent pxesentininboth bothhornblendite hmblenditeand andnelsonite. rielsorite. spheneand Black B k kand andwhite, white*strongly stronglymagnetic magneticnelsonite nebnite contains containsvariable variableamounts amountsof of chlorite. chloriteactinolite, aainolite*homblende, hmblende*and andpyroxene. pyroxene.Oxides Oxidesconsist consistofofequant equantmagneute magnetitegrains, grains, which whichcontain amainabundant abundant(111) (1 11)exsolved exsolvedlamellar lamellarilmenite, ilmenite*asaswell wellasasgrains grainsofoflate late 10 �anbedralilmenite. ilmenite.Grains Grainsofofprismatic prismaticaparite +te are arcaaprominent prominent feature of the nehmite. anhedral feature of the nenite. Thisintrusion intrusioncontains containsappreciable appreciabkapatite apatiteand andtherefore thereforeititcould couldbe be a pmi?de This a possible P. By analogy w i t h other a p ~ r i c h bodies it could also be a source @-rare saxrce of sce of P. By analogy with other apanie-rich bodies it could also be a source of rare e a r t h elemems Limited analyses of the neisonite and ppxenite show up to 15% Ti%, earth elements. Limited analyses of the lsonite and pyroxenite show up to l TiC)2, and 50% F q Q ; this implies that the plum could also be a source of these comxxiities. and 50% Fe203; this implies that the plinon could also be a source of these conodities. 15%apatite apatiteora10% 1Wofree free Akhough none noneof ofthe thematerial materialnow nowavailable availablecontains mntainsmore morethan than15% Although k n i t e not tied up in magnetite, the exking c m (7 cm per 1.5 m) was p h k i y biased ilmenite not tied up in magnetite, the exing core (7 cm per 1.5 m) was probaby biased tcnvard the theiron-rich iron-richunits. units.ItItisisalmost h o s ta acertainty certaintythat thataasimple simple drilling drilling pproam r o g mwould ~would toward imcrsect intmals of considerable apatite mntent andor zones containing econanic intersect intervals of considerable apatite content and/or zones containing econccuc beenhanced enhancedby bythe thewellwellamunts of of recoverable m v e r a b l e ilmenite. ilmenite.Exploration Explcmionwould wouldbe amounts cumrained size sizeofofthe thepluton phtonand andby bythe thefact fictthat thatititisisburied buriedby byno nomore morethan than30 3Gmmof of constrained g l a d material. glacial material. Fi-gure 1.1.Aerornagetic Ammageticmap mapofofthe thePhilbrook Philbrmkarea area(modified (modifiedfrom h mthe theMinnesotz Minnesotz Figure Gedogical Sumey, Legislative Commission on h4innesota Resources, aemmapcncmap map Geological Survey, Legislative Commission on Minnesota Resources, aeromaznenc of h e Motley 7.5 quadrangle.) showing lrxations of outcrops and d r i l l holes used i n this of the Motley 7.5 quadrangle.) showing locations of outcrops and drill holes used in this s d y Outcrops. . Outcrops;drill s;drillholes— holes-. sny. 11 �An to the Geology of the An Introduction Introduction to Geology and Mineral Mineral Deposits Deposits of the Archean Marquette Archean Marquette Greenstone Greenstone Belt, Michigan Michigan T.J. BORNHORST (Department of of Geology T.J. BORNHORST (Department Geology and Geological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, University Houghton, Houghton9 Michigan Michigan 49931) 4993 1) The Marquette Belt occupies occupies an an area area of of about Marquette Greenstone Greenstone Belt about 125 125 mi2 mi2 (325 (325 km2) km2) The geology in northern northern Marquette Marquette County, County7Michigan. Michigan. The geology is is complex. complex. The belt belt consists of of several thousand feet feet of subaqueous mafic to silicic consists several thousand subaqueous mafic silicic flows flows and and pyroclastics is dominated dominated by tholeiitic tholeiitic basalt, basalt, with with pyroclastics and volcaniclastic vokaniclastic sediments. sediments. It is rocks are are intruded a scattering scattering of of compositions compositions towards towards rhyolite. rhyolite. These These rocks intruded by by gabbro gabbro The belt and rhyolite and rhyolite dikes, and and by by granitoid granitoid plutons. plutons. The belt includes includes two two peridotite peridotite Stratigraphic correlations correlations are complicated complicated All rocks rocks are of of Archean Archean age. age. Stratigraphic bodies. All of the the belt will by the the existence existence of faults faults and and shear shear zones. zones. Stratigraphy Stratigraphy of will be be by discussed, with suggestions for improving discussed, with suggestions for improving the current current stratigraphic stratigraphic nomenclature. nomenclature. All of these All these rocks rocks have have been been metamorphosed metamorphosed from from greenschist greenschist to to amphibolite amphibolite facies vertica1 facies and subjected subjected to to multiple multiple deformation deformation during the the Archean, Archean* Near vertical dips Regionally,the the belt belt isis affected affected by dips are quite quite common. common. Regionally, by two two major major Archean Archean The Carp shear zones. zones- The Carp River River Falls Falls Shear Shear Zone Zone trends trends E-W E-W and lies lies along along the the is cut cut by by much much less less deformed deformed mafic mafic dikes dikes of of southern boundary of of the southern boundary the belt. belt- It is The full width width of of the the shear shear Archean Archean age (Baxter (Baxter and Bornhorst, Bornhorst, this this volume). volume). The zone is is unknown because part part of of itit was zone unknown because was reactivated reactivated during during the the Penokean Penokean orogeny, orogeny? juxtaposing sediments against against more more altered and juxtaposing less less deformed deformed Lower Lower Proterozoic Proterozoic sediments and The Carp Shear Zone Zone may may be be part part of of the sheared Archean rocks. rocks- The Carp River River Falls Falls Shear the sheared Archean Great Lakes Great Lakes Tectonic Tectonic Zone Zone of Sims Sims (1980, (l98Q9Geol, GeoL Soc. Sot- Amer. Amer- Special Special Paper 182, 182, p. p* second major structural structural zone, zone, Dead Dead River River Basin Basin Shear Shear Zone, Zone?trends trends 113-124). The second NW-SE and and bisects too was was reactivated reactivated NW-SE bisects the belt, belt7with with unknown unknown displacement. displacement. It too Stratigraphic correlation correlation across across this this zone zone is is tenuous. tenuous. during the during the Penokean Penokean orogeny. orogeny. Stratigraphic Of Of the the numerous numerous base base and and precious precious metal metal orebodies orebodies and occurrences occurrences known known in in Most of of the the belt, belt7 the the Ropes Ropes Mine Mine is is the the most most significant. significant. Most the occurrences occurrences are are the interpreted to be with faults faults and shear interpreted be epigenetic, epigenetic, spatially spatially associated associated with shear zones, zones, and and structures may may be important Regional structures important in in localizing localizing syn- to synto post-tectonic. post-tectonic. Regional mineralization. Precious Precious metal metal mineralization mineralization is accompanied accompanied by sulfide sulfide minerals, minerals, especially pyrite pyrite with with lesser of pyrrhotite, pyrrhotite7 chalcopyrite, chakopyrite, and and arsenopyrite, arsenopyrite, especially lesser amounts amounts of and by and by non-metallic non-metallic minerals minerals such such as quartz, quartz, carbonate, carbonate7 chlorite, chlorite, and and sericite. sericite-. The The present data data permits that there there have present permits the tentative tentative suggestion suggestion that have been been at at least least two two major pulses major pukes of of mineralization. mineralization. The potential potential for discovery discovery of of new new economic economic deposits in in the deposits the Marquette Marquette Greenstone Greenstone Belt Belt isis indicated indicated by byanomalous anomalousgeochemical geochemical Au of numerous quartz and and carbonate Au values, values, the occurrence occurrence of numerous quartz carbonate veins, veins, areas areas of pervasive alteration, areas areas of of relatively abundant faults faults and shear zones? and and the the pervasive alteration, relatively abundant shear zones, overall geologic geologic setting. setting. 12 �THE ORIGIN ORIGINAND AND EXTENT EXTENTOF OFTHE THEHARD HARDAND ANDSOFT SOFTIRON IRONORES ORESOF OF THE THE MARQUETTE MARQUETTE RANGE, RANGE MICHIGAN MICHIGAN THE BurtonH.H.Boyurn Boyum Burton 1shpeming9Michigan Michigan49849 49849 Ishpemlng, ABSTRACT ABSTRACT The Marquette D iDistrict s t r i c t i is s llocated o c a t e d iin n the the north n o r t h central c e n t r a l part p a r t ofo fthe t h eUpper UpperPeninsula Peninsula of o fMichigan Michigan as as The MarquetteMineral Mineral r e l a t i v e l yminor minoroccurrences occurrences of o f gold g o l d and and of of relatively o f Middle Precambrian age. The pprincipal rincipal m i n e r a l i z a t i o n iiss Iron i r o n with w i t h other other shown iin n Figure Figure I.I * The shown mineralization The host host rocks rocks are arefound foundini the n the Marquette RangeSupergroup Supergroup copper. The copper. Marquette Range There are are of Middle Precambrian age. There several iron-formation iron-formation memberswith w i t hthe the NegauneeIron—Formation Iron-Formation the the principal p r i n c i p a l locus locus of o fhigh h i g hgrade grade iron i r o nores. ores. several members Negaunee i s the the thickest t h i c k e s treachreachA1 though generally generally similar s i m i l a r tot othe theother o t h eiron—formations r iron-formations of o fthe t h eLake Lake Superior Superior Region, Although Region,i Itt Is i n g aa stratigraphic s t r a t i g r a p h i cthickness thickness ofofover over1,300 1,300 meters meters (3500 (3500 feet), f e e t ) , It I t differs d i f f e r salso a l s oini nthat t h aItt contains i t contains a minimum ing a minimum o f arillaceons argillaceonsoroarenaceous r arenaceous facies. facies. of The The " s o f t " ores ores are goethite, s osoft, f t , f rfriable i a b l e tto o earthy earthy oorr plastic. p l a s t i c . The The "hard" "hard1' ores ores are a r edense dense 'soft1' are hematite hematiteand and goethite, There aare r e t three h r e e ddistinct i s t i n c t structural s t r u c t u r a l locations l o c a t i o n s for f o r the t h eores, ores* The The soft s o f tones ones There t o specular specularhematite hematiteand andmagnetite. magnetite. to are found found at a t the the base base of of the the Negaunee Negaunee Iron-Formationp g e ngenerally e r a l l y i n In f a fault u l t sstructures t r u c t u r e s wwith i t h intrusive i n t r u s i v edikes; dikes;and and are Iron—Formation, on large l a r g e iintrusive n t r u s i v e ssills, i l l s , also also in i n structures s t r u c t u r e s related r e l a t e d to t o faulting. f a u l t i n g . The The hard found near t o p of o f the the on hard ores ores are are found near the the top Negaunee Iron—Formation. Iron-Formation. The The Marquette t h e Lake Lake Superior Superior Region Region to t o have have both both hard hard Negaunee Marquette Range Rangei sisthe the only only one one iInn the and soft s o f t ores. ores* and The regional regional metamorphism metamorphism has ranging l o r i t e in i nNegaunee Negaunee and u l k of of The haszones zones rangingfrom fromc hchlorite and Ishpeming, Ishpeming,where wherethe the bbulk the soft s o f t ore ore was was found, b i obiotite, t i t e , ggarnet, a r n e t * s staurolite t a u r o l i t e tto o ssillimanite. i l l i m a n i t e . Most Most o t h e hard hard ore o r e was was found found in in the found,through through off the the higher orders o f metamorphism. the higher orders of metamorphism. From 1846 t a l of 57599009119 long tons of o firon i r o ore n o rhave e have beenproduced producedand andshipped shippedfrom from From 1846through through1986 1986a at ototal of 575,900,119 long tons been the Marquette Marquette Range, Range* i including n c l u d i n g concentrates e l l e t s from from low low grade grade operations. operations. Of O f the t h e natural, n a t u r a l *high h i g hgrade grade the concentrates and andppellets ores 186,607,540 186,607*540 tons f o ofootwall t w a l l s osoft f t ore, tons were i n tIntrusive r u s i v e s isill l l structure s t r u c t u r e soft s o f tore oreand and ores tonswere were ore,54,092,030 54,092,030 tons were 6O935OS944tons were were hard hard ore. ore. 60,350,944 The extent the ores ores are l l u s t r a t e dby by their t h e i r plan p l a n and and thickness thickness as e l a t e d tto o structural s t r u c t u r a l controls. controls. The extent of of the are iIllustrated as rrelated Hypotheses oof f oorigin r i g i nare arediscussed. discussed. Hypotheses UPLANATION FGURC I •EOI.GS' UPCWIS&ø$ 9PC. 'SICA flU, .1 W((haS*l Og S dIOCIL I •**CLS.kI As •QC,I lAO, '0.1111o $1401.1. 105(1 PItt PSI '04.10 14.14(1 O W.P(* PINISIW,& t -. - Figure 1 — Generalized a l f ooff the t h e Upper Upper Peninsula Peninsula of of Michigan Michigan Figure Generalizedgeology geologyo fofthe thewestern westernhhalf 1 13 �STRATIGRAPHY AND GEOBAROMETRY OF MONZODIORITES FROM THE STRATIGRAPHY THE GIANTS RANGE BATHOLITH, NORTHEASTERN MINNESOTA BATHOLlTH, MINNESOTA of Geology Bruce L. Brasaemle, Brasaemle, Department of Geology Minnesota, Minneapolis, Minnesota, Minneapolis, MN MN 55455 and Geophysics, University of Mapping in the the northeastern part of the northeastern part the Archean Archean Giants Giants Range Range batholith batholith (in near Ely, the Bear Minnesota has Bear Island Island quadrangle), near Ely? Minnesota has revealed a suite suite of five mappable composition from mappable granitic granitic units ranging in composition from hornblende hornblende monzodiorite monzodiorite to granodiorite are comparable the Farm granodiorite (Fig. (Fig. 1). 1). These These units units are comparable toto the F a m Lake Lake facies facies of of the tlie Giants by Green Giants Range Range batholith batholith proposed proposed by Green (1970) (1970) for for granitic granitic rocks rocks in the Gabbro Gabbro Lake Lake quadrangle. All All of of the thegranitoids granitoids in the the Bear Bear Island Island quadrangle quadrangle are are generally generally mediummedium- to to coarse-grained, and variably porphyritic with microcline being the most The different are distinguished on the common type type of common of phenocryst. phenocryst. The different granitic units are distinguished on the especially modal basis of of texture texture and and modal modal mineralogy, mineralogy, especially modal abundances abundances of quartz, Contacts hornblende, and/or Contacts between between the units, where observable, andfor biotite. observable, are Dikes of the quartz monzodiorite (Agqm) gradational. (Agqm) cut the hornblende stratigraphic relations of of Agmd monzodiorite (Aghm), monzodiorite (Aghm), but but the stratigraphic Agmd to to the other units field. Nevertheless, it is plausible to could not could not be be deciphered deciphered in in the field to assume assume that that the units are genetically related. related* The The "mg' "mg"values values(Mg/(Mg+Fe)) (Mg/(Mg+Fe)) of of hornblende hornblende and/or whole rocks rocks (based (basedon on ~Fe+ e + only) +only)suggest suggest a adifferentiation differentiation sequence sequence of of the the and/or whole principal units: + Agmd Agmd + Agqm (see (see Table 1). 1). Aghm —> principal units: Aghm - Pressure determinations based on hornblende stoichiometry stoichiometry (Hammarstrom Assuming that that the and and Zen, Zen9 1986; 1986; Hollister Hollister and and others, others, 1987) 1987) are are shown shown in in Fig, F i g 1. 1- Assuming the stratigraphic and geobarometric deductions are correct, correct, two structural models The observed for the could could account account for the observed observed geologic geologic relations. The observed distribution of 1) these granitic rocks could represent: 1) the faulted record of aa composite of asymmetric folding of of such intrusion (Fig. 21, 2), or 2) intrusion (Fig. 2) a product product of asymmetric folding such an an intrusion intrusion (Fig. (Fig. less plausible becauseofof the the lack lack of Model 11 seems seems less plausible because of field field evidence evidence for for faults faults 1. faults shown other other than than the the regional regional northeast northeast trending trending faults shown in in Fig. 1. 3). References References Brasaemle, B. L., Southwick D. L., L., and Brasaemle, B, Southwick De and Sims, Sims* P. K., K., in in prep., prep., Bedrock Bedrock geologic geologic map map of of Minnesota Geological Louis County, Bear Island Bear Island quadrangle, quadrangle, St. St* Louis County7 Minnesota: Minnesota: Minnesota Geological Miscellaneous Map Map Series, Survey Miscellaneous Series, scale scale 1:24,000. 1:24,000. Gabbro Lake 1970, Lower Green, J. I. C., 1970, Lower Precambrian Precambrian rocks rocks of the Gabbro Lake quadrangle, Special Publication Minnesota Geological Survey northeastern Minnesota: Survey Special Series, SP-13, Series, SP-13. 96p. 96p. An empirical 1986, Aluminum M., and Hammarstrom, J. M., and Zen, Zen, E., E., 1986, Aluminum in in hornblende: hornblende: An empirical 1297-1313. igneous geobarometer: igneous geobarometer: American American Mineralogist, Mineralogist, v. 71, 71, p. p. 12971313. Hollister, L. S.$ S., Grissom, G. C., K., Stowell, Stowell, H. H., H., and and Sisson, Sisson, V. V. B., B ~1987, ,1987, H011ister~L. Grissom, G. C., Peters, Peters, E. Ee K., of Al Confirmation of the Confirmation of the empirical empirical correlation correlation of A1 in hornblende hornblende with with pressure American of solidification of solidification of caic-alkaline calc-alkaline plutons: American Mineralogist, Mineralogist, v. v. 72, p. p. 23 1-23 9. 231-239. 14 �Fig. Fig. 11 Schematic Schematic map map of granitic granitic units of the Giants Giants Range Range batholith batholith in in the the Bear Bear Island Island quadrangle quadrangle (modified (modified from Brasaemle, Brasaemle, and and others, in in prep.) prep.) 15 �—. — Fig. 2 Faulting Faultingof of aacomposite compositeintrusion intrusionto toaccount account for for observed observed geologic geologicrelations relationsof of granitic graniticunits. units. Fig* 3 Asymmetric Asymmetricfolding foldingof of aacomposite corn ositeintrusion intrusion Fig. to to account account for observed observed geologic geologic relations r e h o n s of granitic graniticunits. units. Table Table 1. 1. Monzodiorite Monzodioritewhole wholerock rockand andhornblende hornblendeanalyses. analyses. II Whole Rock Analyses Analyses Whole Rock Unit Samo! # Aghm 3A Oxides (wt %) 'YO) Oxides (wt Si02 ~ i 0 2' ' 56.3 Al203 17.7 A1203 17-7 Ti02 0,63 Ti02 0.63 Fe203 2.57 Fe203 FeO 3.32 FeO MnO 0.10 MnO MgO 3.38 CaO 4,93 Na20 5.40 K20 2,84 P205 0SO Total 97.67 Mg/(Mg+Fe2+) 0,645 0.645 (atomic) (atomic) Agmd 148 64,9 64-9 17.5 17.5 0,37 0-37 1.21 1.21 1.92 1.92 0.05 1.92 3.90 6.20 2.25 O1 Agqm 19 71.0 71.O 16.3 16~3 0.13 0-13 0.55 0.67 0.03 0.65 1.84 5.90 2.73 Hornblende Hornblende Analyses Analyses Aghm Aghm Agmd Agmd Agqm Agqm Unit Unit SmnIA S m e # 333A 3A 148 146 Oxides Oxides (wt (wt %) O/O) 48.21 Si02 48.21 Si02 6.88 A1203 A1203 6~88 0,94 T102 Ti02 0-94 14.34 MgO MgO 14-34 14.40 FeO FeO 14-40 0.40 MnO MnO 11.35 CaO 47.53 43.74 7.56 7*56 8.02 8-02 0.75 0-75 0.77 13.02 13~02 12.18 12.18 16.40 16.40 17.94 17.94 0.34 0.34 0.60 0.60 11,46 11.06 Na20 K20 1.36 0.68 O0 100.60 99.86 0.641 0.641 0.635 1.48 0.81 319 319 1.35 1,03 Cations Cations (based (basedon on 23 23 oxygens) oxvaens) Unit Unit ' Anhm ~ a h m~Acmd q m d"'A,m AQQ~ ampIe# 146 319 319 14 S a m ~ l e# 33A 33A Si 7.04 6.97 6.69 AI(iv) 0.93 1,03 1.31 Al(tot) 1.18 1.31 1.45 Al(vi) 0.22 0.28 0.14 Ti 0.10 0.08 0.09 Mg 3.12 2.85 2.78 Fe+2 Mn Ca Na K Mg/ (Mg+Fe) 16 1.76 0.49 1.77 0.37 0.13 1.95 0.42 1.80 0.42 0.15 0.640 0.594 2.30 0.08 1.81 0.40 0.20 0.548 �A TECTONIC TECTONIC MODEL MODELFOR FORTHE THEMID-CONTINENTAL MID-CONTINENTALRIFT RIFTSYSTEM SYSTEM A F. William William Cambray Cambray F. Department of Geological Sciences Department of Geological Sciences Michigan State University Michigan State University 48824-1l1.S East Lansing, Lansing,MI MI48824-1115 East The opening opening vector vector of of the the MRS MRS isisrestricted restricted totoananapproximate approximatenorth-south north-south direction direction The because its its Continuous continuous nature 180' of Lake because nature through through almost almost 1800 of arc arc from from Kansas, Kansas, north north to to the Lake Superior Region Region and and then then south souththrough through Michigan, Michigan, has has been beenestablished establishedby bygravity, gravity, Superior magnetic and and seismic seismic reflection reflection studies. studies. Motion Motion on on such such aa rift riftsystem systemwould would be belargely largely magnetic extensional in regions at right angles to the opening vector and increasingly transtensional extensional regions at right angles to the opening vector and increasingly transtensional as the the angle angle decreased. decreased. This Thisseems seemsto to be beborn bornout outby by the thegreater greaterwidth width of of the the basin basin in in the the as east-west trending Lake Superior portion when compared with the narrower geophysical east-west Lake Superior portion when compared with the narrower geophysical anomalies on on the the more more north-south north-south sections. sections. InInaddition, addition9the therift riftfits fitsan anasymmetric asymmetricmodel model anomalies such as as that that of ofWernicke Wernicke (1981, (1981, 1985) 1985) or Lister Lister et et al. al.(1986) (1986) in in the theLake LakeSuperior Superiorregion. region. such The south south side side appears appears to to be be the thelower lowerplate platewith with the thegreater greaterthickness thicknessand and more more complex complex The pattern of of sediments sediments close close to to that that margin. margin. The Thelower lower plate plate uplift uplift close close to to the theupper upperplate plate pattern margin described Lister et al. al. model model is is represented represented by by the the deep deep level level of of erosion erosion margin described in in the the Lister exposing the the higher higher grade grade metamorphic metamorphic rocks rocks on on the the northwest northwest exposing the Duluth Duluth Gabbro and the Finally, the MRS has been involved in a later compressional shore of Lake Superior. shore of Lake Superior. Finally, the MRS has been involved in a later compressional event. The Thevector vectorofofmovement movementfor forthis thisphase phase would would also also be be restricted restricted to toan anapproximately approximately event. north-south direction in a rigid crust. The thrusting and folding in the Lake Superior north-south direction a rigid crust. The thrusting and folding in the Lake Superior region is related related to tothis thismovement. movement. Elsewhere Elsewhere the the motion motion must must have haveinvolved involved various various region TheSt. St.Croix Croix Horst Horst and and its its continuation continuation to to the the south south could could be be amounts of transpression. transpression. The amounts described as a positive flower tested in in described flower structure structure in in this this setting. setting. The The model model can can be further tested the field field by by collecting collecting kinematic kinematic data from £ro fault surfaces surfaces and finite strain data data from from fold fold the structures. The Thedetachment detachmentfault faultshould shouldbe beexposed exposedto tothe thenorth northand andwest westof ofthe thegabbro. gabbro. structures. 17 �Variations V a r i a t i o n s in i n Structural S t r u c t u r a l Style S t y l eofo fthe t h eMidcontinent M i d c o n t j n e n t Rift R i f Beneath t Beneath Lake Lake Superior Superior USGS,Reston, Reston,VVirginia W e FF.e Cannon, Cannonp USGSu irginia AA, e G. G* Green, Green# Geological G e o l o g i c a l Survey Survey ofo fCanada, Canada, Ottawa, Ottawa9Canada Canada D, R. Hole, Massachusetts I?. Hutchinson, Hutch i n s o n #USGS, USGS8Woods Woods Hole, Massachusetts 3, J Q C. C- Behrendt, Behrendt, USGS, U%S, Denver, Denver9 Colorado Colorado W, Recent deeps eseismic Recent deep i s m i c r ereflection f l e c t i o n profiles p r o f i l e sby bythe t h eGreat G r e a tLakes Lakes Program ononCrustal Program C r u s t aEvolution l Evol u t i o(GLIMPCE) n (GLIMPCX 1 IInternational n t e r n a t i o n a lMultidisciplinary Mu1t i d i s c i p l 1 nary only nnot ot o n l y show show ddetails e t a i l s ooff the t h e deep deep sstructure t r u c t u r e ooff the t h e Midcontinent Midcontiment RRift ift beneathLake LakeSSuperior beneath u p e r i o r b but u t aalso l s o iIndicate n d i c a t e structural s t r u c t u r a l changes changes along a l o n g the the trend r i fthat t t h asuggest t suggestchanges changes iin n the t h e rifting r i f t i n gprocess. process. These new new t r e n d of o f the t h e rift data, combined an iinterpretation data, combined w iwith t h p opotential t e n t f a 1 f ifield e l d data, d a t a 8 support s u p p o r t an n t e r p r e t a t j o n of of rifting r i f t i n gand andsubsidence subsidence of o f discrete d i s c r e t eblocks b l o c k shaving h a v i n gdimensions dimensions of o f aa few few tens tens Individual I n d l v i d u a l blocks b l o c k s appear appear to t o have have flexed flexed tto o aa few few hundred hundred kkilometers. ilometers. during being d u r i n g subsidence subsidence rrather a t h e r tthan han b e i n g ccompletely o m p l e t e l y rrigid. f g l d . IInn some some areas, areasr subsidence as 10 10 km kmappears appearst otohave haveoccurred occurredppurely by ccrustal f as as much much as u r e l y by rustal subsidence oof flexing Boundariesooff tthe f l e x i n g within w i t h i n an an individual ind-ividual block. block. Boundaries h e blocks, blocks, however, however* are On sseismic a r e probably probably ffaults. aults. On e i s m i c llines, i n e s , boundaries boundarfes are a r eshown shown by by abrupt abrupt changes and/ora tattitude changes i nint hthickness i c k n e s s and/or t i t u d e oof f rrift—filled i ft-f i 1 l e dvolcanic vo1 c a n i c and and sedimentary cases, sseismic imageso of sedimentary rocks. r o c k s - In I n some some cases, e i s m i c images f t the h e ffault a u l t planes planes were obtained. obtained. were I n western western Lake Lake Superior, t h e rift r i fappears t appearsto t b.e o beananasymmetric asymmetric graben graben In Superior, the 3 0 kml e nnorth, o r t h , whereas e ccentral e n t r a l ppart art o t h e lake, lakep deepest b('30 deepest km)on ont hthe whereasi nint hthe off the tthe h e graben graben is i s deepest deepest on on the t h e south. south. AA zone zone of o f accommodation accommodation between between t h e s e two n f e r r e d aalong l o n g aa prominent f f s e t iin n the t h e gravity gravity these two grabens grabensi sis i inferred prominento offset ppattern a t t e r n extending e x t e n d i n g from from jjust u s t west west of o f Isle I s l Royale e Royaletot onear nearOntonagon, Ontonagon, Michigan. M ichigan@ The sstructure t r u c t u r e beneath beneath eastern e a s t e r n Lake Lake Superior S u p e r i o r is i smore more symmetrical, symmetrical, and and an an The area a r e a at a t least l e a s t80 80km kmwide wide appears appears to t ohave have subsided subsided uniformly u n i f o r m l yabout about15 15km, kmu w i t h little l i t t l or e ono r no t i l t i nbefore g , b e f undergoing o r e undergoing a d d i t i o n a15 l 15 more with tilting, ananadditional kmkmofo fmore complex complex subsidence. The The TThiel h i e l ffault, a u l t , aastructure s t r u c t u r elong l o n grecognized recognized from from p o t e n t i a l field f j e l ddata, data,extending e x t e n d i n gfrom fromnear n e a rMarathon, Marathon, Ontario, O n t a r i o 8 to t o near near potential Marquette, Michigan, M i c h i g a n 8isi proposed s proposed accmmodationzone zonebetween between Marquette, asas anan accommodation structures s t r u c t u r e s in i n the t h e eastern e a s t e r n and and ccentral e n t r a l lake. lake. The a t t e r n in i nBouquer Bouquer gravity g r a v i t yanomalies anomal i e s beneath beneath much much ooff the the The unusual unusual ppattern 1lake, ake, where where ttrends r e n d s ooff linear 1 ineargravity g r a v i t yanomalies anomal i e s end end abruptly abrupt1 y or o rshow show sharp sharp changes n t e r p r e t e d t to o rreflect e f l e c t the t h e outlines o u t 1 i n e s of o f discrete discrete changesi nintrend, trend,i sis i interpreted blocks b l o c k s ooff prerift p r e r i fbasement. t basement. The The Independent independent movement f tthese h e s e blocks blocks movemento of d u r i n g rrifting i f t i n g controlled c o n t r o l 1ed tthe h e tthickness h i c k n e s s o fofb abasalts s a l t s t h athat t f i 1filled l e d t hthe e r rift. if t during Detailed D e t a i l e d cconfiguration o n f i g u r a t i o n oof f tthe h e rrift, i f t ,therefore, t h e r e f o r e ,may may be be inherited i n h e r i t e d from from o l d e r structures s t r u c t u r e sini n t hArchean e Archeanand andLower Lower Proterozoic P r o t e r o z o i cbasement basement tthat h a t were were older the asf afaults rreactivated e a c t i v a t e d as u l t s dduring u r i n g r rifting. ifting. 18 �COPPER—NICKEL COPPER-NICKEL MINERALIZATION MINERALIZATION OF OF THE THE DULUTH DULUTH COMPLEX, COMPLEXf NORTHEASTERN MAGNETIC PERSPECTIVE PERSPECTIVE NORTHEASTERN MINNESOTA: MINNESOTA: AA GRAVITY AND MAGNETIC Val Val W. W. Chandler Chandler and and Robert R o b e r t J. J. Ferderer, F e r d e r e r f Minnesota Minnesota Geological G e o l o g i c a l Survey, Surveyf 2642 2642 University U n i v e r s i t y Avenue, Avenuer St. S t . Paul, P a u l r Minnesota Minnesota 55114—1057 55114-1057 It I t is i s now now generally g e n e r a l l y accepted a c c e p t e d that t h a tinteraction i n t e r a c t i obetween n betweenmagmas magmas of the t h e Duluth Duluth Complex (MiddlePProterozoic) and tthe Complex (Middle r o t e r o z o i c ) and h e sulfur—rich s u l f u r - r i c h Virginia V i r g i n i a Formation Formation (Early (Early Proterozoic) Cu-Ni sulfides s u l f i d e s near n e a r the t h e base base P r o t e r o z o i c ) played p l a y e d aa key key role r o l e in i n forming forming the t h eCu—Ni of o f the t h e complex, complex, but b u t many many details d e t a i l s regarding r e g a r d i n g their t h e i r evolution e v o l u t i o n remain remain unknown unknown (Ripley, ( R i p l e y , 1986). 1 9 8 6 ) . Gravity G r a v i t y and and high-resolution h i g h - r e s o l u t i o n aeromagnetic a e r o m a g n e t i c data d a t a are a r e useful useful i n elucidating e l u c i d a t i n g the t h e structural s t r u c t u r a l setting s e t t i n g for f o r the t h e Cu-Ni Cu-Ni sulfide s u l f i d e deposits d e p o s i t s in i n the the in Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi area. a r e a . The The sulfide s u l f i d e deposits d e p o s i t s themselves themselves generally g e n e r a l l y lack lack aa direct d i r e c t gravity g r a v i t y and and magnetic magnetic signature, s i g n a t u r e f but b u t associated a s s o c i a t e d inclusions i n c l u s i o n s of of wall wall rock, r o c k , as a s well w e l l as a s structures s t r u c t u r e s near n e a r the t h e base b a s e of of the t h e complex, complex, can c a n produce produce s t r o n g magnetic magnetic signatures s i g n a t u r e s especially e s p e c i a l l y if i f any any involve i n v o l v e the t h e Early E a r l y Proterozoic Proterozoic strong Biwabik Biwabik Iron I r o n Formation. Formation. For For example, example, contact c o n t a c t metamorphosed metamorphosed iron—formation iron-formation in i n the t h e Babbitt B a b b i t t area a r e a produces produces aa prominent, p r o m i n e n t , northeast-striking n o r t h e a s t - s t r i k i n g magnetic magnetic signature. s i g n a t u r e . AA spur—like s p u r - l i k e eastward e a s t w a r d projection p r o j e c t i o n of of this t h i s signature s i g n a t u r e reflects r e f l e c t s aa step—like s t e p - l i k e structure s t r u c t u r e in i n the t h e basal b a s a l contact c o n t a c tat a tthe t h eNIINNAMAX MINNAMAX deposit. d e p o s i t . Detailed Detailed magnetic MINNAMAX area a r e a indicates i n d i c a t e s that t h a t the t h e Biwabik Biwabik Iron Iron m a g n e t i c modeling modeling of of the t h e MINNAMAX Formation Formation thins t h i n s appreciably a p p r e c i a b l y across a c r o s s this this step—like s t e p - l i k e structure s t r u c t u r e and and ultimately ultimately pinches p i n c h e s out o u t aa short s h o r t distance d i s t a n c e down down dip d i p between between the t h e complex complex and and the the underlying i s improved improved if i f more more iron— ironu n d e r l y i n g Archean Archean granite. g r a n i t e . The The fit f i t of of the t h e model model is i s included i n c l u d e d several s e v e r a l kilometers k i l o m e t e r s farther f a r t h e r down down dip d i p along a l o n g the t h e basal basal f o r m a t i o n is formation contact. contact Several S e v e r a l kilometers k i l o m e t e r s south s o u t h of of the t h e MINNAMAX MINNAMAX deposit, d e p o s i t f well w e l l within w i t h i n the the interior i n t e r i o r of of the the complex, complexf prominent prominent magnetic magnetic anomalies a n o m a l i e s sharply s h a r p l y outline o u t l i n e an an area a r e a containing c o n t a i n i n g abundant abundant inclusions i n c l u s i o n s of of hornfelsed h o r n f e l s e d wall w a l l rock. rock. These These anomalies a n o m a l i e s demonstrate d e m o n s t r a t e that t h a t areas a r e a s of of interaction i n t e r a c t i o n between between wall w a l l rock r o c k magma maqma and and are a r e not n o t restricted r e s t r i c t e d to t o the t h e basal b a s a l contact c o n t a c t of o f the t h e complex. complex. Many Many of of the t h e sulfide s u l f i d e deposits d e p o s i t s in i n the t h e Hoyt Hoyt Lakes—Kawishiwi Lakes-Kawishiwi area a r e a lie lie along a l o n g northwest-striking n o r t h w e s t - s t r i k i n g lineaments l i n e a m e n t s observed o b s e r v e d in i n derivative—enhanced d e r i v a t i v e - e n h a n c e d gravity gravity and and aeromagnetic a e r o m a g n e t i c data. d a t a . The The lineaments l i n e a m e n t s cut c u t both b o t h the t h e complex complex and and the the surrounding s u r r o u n d i n g wall w a l l rocks r o c k s and and are a r e believed b e l i e v e d to t o represent r e p r e s e n t late l a t e Archean Archean faults faults that t h a t were were reactivated r e a c t i v a t e d during d u r i n g emplacement emplacement of of the t h e complex. complex. These These lineaments lineaments support s u p p o r t Weiblen Weiblen and and Morey's Morey's (1976) ( 1976) idea i d e a that t h a t northwest—striking n o r t h w e s t - s t r i k i n g faults faults enhanced sulfide s u l f i d e deposition, d e p o s i t i o n r either e i t h e r by by providing p r o v i d i n g conduits c o n d u i t s for f o r volatiles v o l a t i l e s or or enhanced by by enhancing enhancing wall w a l l rock r o c k interaction i n t e r a c t i o n along a l o n g fractures. fractures. G r a v i t y and and magnetic magnetic modeling modeling of o f the t h e Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi area area Gravity indicates 15O to t o the t h e southeast. southeast. i n d i c a t e s that t h a t the t h e base b a s e of of the t h e complex complex dips d i p s about a b o u t 15° The The models models indicate i n d i c a t e that t h a t in i n the t h e Hoyt Hoyt Lakes-Kawishiwi Lakes-Kawishiwi aarea r e a the t h e Biwibak Biwibak Iron Iron Formation Formation and and presumably presumably the t h e overlying o v e r l y i n g Virginia V i r q i n i a Formation Formation dip d i p subparallel subparallel to i t s subsurface s u b s u r f a c e extension. extension. t o the t h e basal b a s a l contact c o n t a c t and and may may locally l o c a l l y occur o c c u r along a l o n g its Under Under these t h e s e conditions c o n d i t i o n s magma magma ascending a s c e n d i n g along a l o n g the t h e basal b a s a l contact c o n t a c t would would have h a v e aa lengthy l e n g t h y reaction r e a c t i o n time time with w i t h the t h e Virginia V i r g i n i a Formation, Formation, which which is i s conconsistent s i s t e n t with w i t h results r e s u l t s of of sulfur s u l f u r and and oxygen oxygen isotopic i s o t o p i c studies s t u d i e s (Ripley, ( R i p l e y f1986). 1986). Model Model studies s t u d i e s south s o u t h of of the t h e study s t u d y area a r e a indicate i n d i c a t e that t h a t the t h e base b a s e of of the t h e complex complex there t h e r e dips d i p s much much more more steeply s t e e p l y and and abruptly a b r u p t l y truncates t r u n c a t e s the t h e Virginia V i r q i n i a Formation Formation (Ferderer, ( F e r d e r e r ! 1982). 1 9 8 2 ) . The The consequent c o n s e q u e n t decrease d e c r e a s e in i n reaction r e a c t i o n surface s u r f a c e of of the the 19 �Virginia V i r g i n i a Formation Formation might might explain e x p l a i n the t h e lack l a c k of of significant s i g n i f i c a n t Cu-Ni Cu-Ni sulfides s u l f i d e s in in t h e southern s o u t h e r n part p a r t of of the t h e Duluth Duluth Complex. Complexa the Acknowledgment Acknowledgment This T h i s study s t u d y was was supported s u p p o r t e d by by the t h e Legislative L e g i s l a t i v e Commission Commission on on Minnesota Minnesota Resourceso Resources, References R e f e r e n c e s Cited Cited R e J e , 1982, 19€ Gravity G r a v i t y and and magnetic magnetic modeling modeling of o f the t h e southern s o u t h e r n half h a l f of of F e r d e r e r , R.J., Ferderer, the t h e Duluth Duluth Complex, Complex, northeastern n o r t h e a s t e r n Minnesota: Minnesota: Unpublished, Unpublished, M.A. M.Ae thesis, thesisp Indiana 99 p. p. I n d i a n a University, U n i v e r s i t y , 99 Ripley, R i p l e y r E.M., E.M., 1986, 1986r Application A p p l i c a t i o n of of stable s t a b l e isotopic i s o t o p i c studies s t u d i e s to t o problems of of magmatic magmatic sulfide s u l f i d e ore o r e genesis g e n e s i s with w i t h special s p e c i a l reference r e f e r e n c e to t o the t h e Duluth Duluth Complex, 9Friedrich F r i e d r i c h and and others, o t h e r s , Geology Geology and and metallogeny m e t a l l o g e n y of of Complexr Minnesota, Minnesotar in copper c o p p e r deposits: d e p o s i t s : Berlin, B e r l i n r Heidelberg, H e i d e l b e r g r Springer—Verlag, S p r i n g e r - V e r l a g , p. p. 25—42. 25-42. Weiblen, W e i b l e n r P.W., P e w e , and and Morey, Morey, G.B., G.B.r 1976, 197€Textural T e x t u r a l and and compositional c o m p o s i t i o n a l characcharacteristics t e r i s t i c s of of sulfide s u l f i d e ores o r e s from from the t h e basal b a s a l contact c o n t a c t zone zone of of the t h e South South in Kawishiwi i n Mining Mining Kawishiwi intrusion, i n t r u s i o n r Duluth Duluth Complex, Complex, northeastern n o r t h e a s t e r n Minnesota: Minnesota: Symposium, Symposiumr 37th 3 7 t h Annual, Annual, and and American American Institute I n s t i t u t e of of Mining Mining and and Metallurgical N e t a l l u r g i c a l Engineers, E n g i n e e r s r Minnesota Minnesota Section, S e c t i o n , 4th 4 t h Annual Annual Meeting, Meetingr Duluth, Duluthr 1976, 1976, Proceedings: P r o c e e d i n g s : Minneapolis, M i n n e a p o l i s , University U n i v e r s i t y of of Minnesota, Minnesota, Continuing Continuing Education E d u c a t i o n and and Extension, E x t e n s i o n , paper p a p e r 22, 2Zr 24 24 p. p. 20 �Paragenetic Relationships Relationships Among Among Siderite, Siderite, Magnetite, Magnetite, Paragenetic Calcite, Quartz, Quartz, and and Sulfides Sulfides in in the the Macleod Macleod Siderite Siderite Mine, Mine, Calcite, Wawa, Ontario Ontario Wawa, J. Mancuso, Mancuso, J. J. Frizado, Frizado, D. D. Stewart Stewart M. Cohen, Cohen, 3. M. Bowling Bowling Green Green University, University, Bowling Bowling Green, Green, Ohio Ohio 43403 43403 E. Berdusco Berdusco E. Algoma Ore Ore Division, Division, Wawa, Wawa, Ontario Ontario POS POS 1KO 1KO Algoma The Macleod Macleod Mine Mine is is located located four four kilometers kilometers north north of of The Wawa, Wawa, Ontario Ontario and and lies lies within within the the Helen Helen Iron Iron Range Range in in the the Wawa Greenstone Greenstone Belt Belt of of the the Superior Superior Province Province of of the the Wawa Canadian Shield. Shield. The The mine mine is is an an underground underground siderite siderite mine mine Canadian that began began production production in in 1949 1949 and and has has continued continued to to the the that present. It It has produced produced an an estimated estimated 80 80 million million tons tons of of present. ore through through 1986. 1986. ore The The siderite—pyrite—banded siderite-pyrite-banded chert chert iron iron formation formation is is conformable between between underlying underlying felsic felsic tuffs tuffs and and overlying overlying conformable intermediate flows flows and and pillow pillow lavas. lavas. The The iron iron formation formation intermediate and adjacent adjacent volcanics volcanics form form the the south south limb limb of of an an overturned overturned and syncline plunging plunging approximately approximately 35 35 degrees degrees to to the the east. east. syncline The overturned overturned limb limb strikes strikes east—west east-west and and dips dips The approximately 60 60 degrees degrees to to the the south. south. The The age age of of the the iron iron approximately formation has has been been determined determined by by U—Pb U-Pb dating dating of of underlying underlying formation volcanics to to be be 2750 2750 Ma. Ma. before before present. present. volcanics The iron iron formation formation consists consists of of aa thin, thin, basal basal banded banded The chert member member (1—2m) (1-2m) overlain overlain by by the the massive massive siderite siderite chert (30-loom). The The siderite siderite member member is is overlain overlain by by massive massive (30—lOOm). (3-15111)grading grading to to aa banded banded chert chert member member several several pyrite (3—15m) pyrite hundred meters meters in in thickness. thickness. The The mine mine itself itself is is located located hundred within the the massive massive siderite siderite member. member. within Mine mapping mapping in in the the massive massive siderite siderite and and petrographic petrographic Mine analyses of of selected selected samples samples indicate indicate the the following following analyses paragenetic sequence: sequence: paragenetic 1. Magnetite Magnetite filling filling fractures fractures and and partially partially 1. replacing siderite. siderite. replacing 2. Calcite Calcite filling filling fractures fractures crossing crossing magnetite magnetite and and 2. siderite. siderite. 3. Multiple Multiple episodes episodes of of quartz, quartz, sulfide, sulfide, and and 3. tourmaline veining. veining. tourmaline The origin origin of of magnetite magnetite in in Precambrian Precambrian iron iron formations formations The has long long been been an an unresolved unresolved problem. problem. Theories Theories proposed proposed has vary from from primary primary sedimentary sedimentary through through diagenetic diagenetic and and vary metamorphic to to exhalative. exhalative. In In the the MacLeod MacLeod Mine Mine the the metamorphic magnetite is is definitely definitely secondary secondary because because it it selectively selectively magnetite replaces siderite and fills fractures. replaces siderite and fills fractures. 21 �PRECAMBRIAN RED RED BLUFF BLUFF GRANITE GRANITE COMPLEX, COMPLEX, WEST WEST TEXAS: TEXAS : COMPARISON WITH OTHER MID-PROTEROZOIC "RAPAKIVI" "RAPAKIVI " GRANITES . Donald M. M. Davidson, Davidson, Jr. Jr Department of Geology Northern Illinois Illinois University, University, DeKaib, IL 60115 60115 DeKalb, IL Red Bluff Granite Complex is exposed exposed over an area of 20 The Red 20 The square km k m in in the the Franklin Franklin Mountains, Mountains, near near El El Paso, Paso, Texas. Texas. The units and an intrudes metasedimentary RBGC RBGC intrudes supracrustal units and an ignirnbrite cap cap (Harbour, (Harbour, 1960). ignimbrite 1960). in this b.y. have been mapped ey. Seven phases phases have mapped thus thus far far in this 11 b batholith. Two early microgranite microgranite sills are spatially spatially separated separated three-phase ring ring complex complex by by aa younger 6 6 km k m from from aa three-phase younger tin—bearing tin-bearing biotite granite granite which which cores cores the the complex. complex. A riebeckite granite granite is is all aplites cut phase, although the youngest phase, cut all the although pegmatites pegmatites and and aplites units. units. granite are except the the riebeckite All phases phases except riebeckite granite are medium to to Several coarse—grained with equigranular, porphyritic textures. coarse-grained porphyritic textures. Several phases display Quartz and alkali phases display rapakivi rapakivi texture. texture. Quartz alkali feldspar feldspar riebeckite granite The constitute 90% 90 of constitute of minerals observed. observed. The riebeckite granite typically exhibits an ineguagranular, typically inequagranular, hypidiomorphic texture and and to 38%). 38). contains plagioclase plagioclase as a major major mineral mineral component component (up to contains Riebeckite crystals crystals show strongly Riebeckite strongly preferred orientations orientations and Elsewhere the unit granulated textures are observed granulated observed locally. locally. Elsewhere unit is is pegmtitic (Ray, pegmatitic (Ray, 1982; 1982; McCutcheon, McCutcheon, 1982). 1982) rapakivi granites, granites, the RBGC is is As with many mid—Proterozoic mid-Proterozoic rapakivi but marginally peraluminous (Al203>K20+CaO+Na20), but with (A1203>K20+CaO+Na20), SiO2 peralkaline tendencies. tendencies. Moreover, Moreover, the RBGC is is enriched enriched in in Si02 and strongly depleted depleted in Al2O3, Al203, MnO, MnO, MgO, MgO, and CaO CaO compared compared with with (Anderson, such bodies of similar age 1983) other such bodies of similar age (Anderson, 1983) or the the "average" a v e r a g e " granite of of Nockolds Nockolds (1978). (1978). RBGC show high K, Ba, and REE values suggestive Units of the RBGC.show derivation Plotted on a Rb/Nb—Y derivation from from aa crustal crustal source. source. Plotted on Rb/Nb-Y tectonic discrimination tectonic discrimination diagram (Pearce (Pearce and and others, others, 1984) data 1984) data for the RBGC fall fall in in the the "within "within plate" plate" field. field. However, such aa does not category does not preclude preclude aa relationship to to subducting subducting true, this may represent lithosphere. If the lithosphere. If true, this batholith represent the westernmost manifestation of of the the Grenville Grenville orogeny. orogeny. of of 22 �REFERENCES REFERENCES Anderson, Anderson, J.L., J.L., 1983, 1983, Proterozoic Proterozoicanorogenic anorogenicgranite graniteplutoriism plutonism of of North America: America: Geological Geological Society Society of of America America Memoir Memoir 151, 161, North p.133-154. p,133—154. Harbour, R.L., R.L., 1960, 1960, Precambrian Precambrian rocks rocks at at North North Franklin Franklin Mountain, Mountain, Harbour, Texas : American Association Association of of Petroleum Petroleum Geologists Geologists American Texas: Bulletin, V. v. 44, 44, p.1785—1792. p.1785-1792. Bulletin, T., 1982, 1982, Petrology Petrology and and geochemistry geochemistry of of the the T., Northern Franklin Complex, Precambrian Red Bluff Granite Complex, Northern Franklin Granite Precambrian Red Bluff unpublished Mountains, El El Paso Paso County, County, Texas: Texas: unpublished MS MS thesis, thesis, Mountains, University of of Texas, Texas, El El Paso, Paso, p.177. p.177. University McCutcheon, McCutcheon, Nockolds, S..R., S.R., and and others, others, 1978, 1978, Petrology Petrology Nockolds, Cambridge University University Press, Press, 435p. 435p. Cambridge for for Students: Students: Ray, Ray, D.R., D.R., 1982, 1982, Geology Geology of of the the Precambrian Precambrian Red Red Bluff Bluff Granite Granite 'aso Complex, Complex, Fusselman Fusselman Canyon Canyon area, area, Franklin Franklin Mountains, Mountains, El El P aso MS thesis, thesis, University University of of T Tex, County, Texas: Texas: unpublished unpublished MS ~ : o ,s County, El Paso, Paso, 295p. 295p. El and and others, others, 1984, 1984, Trace Trace element element distribution distribution discrimination diagrams diagrams for for the the tectonic tectonic interpretation interpretation of of discrimination granitic rocks: rocks: Journal Journal of of Petrology, Petrology, v. v . p.956—983. p.956-983. granitic Pearce, J..A., J.A., Pearce, 23 �GEOPHYSICAL GEOPHYSICAL AND AND PETROLOGICAL PETROLOGICAL CHARACTERISTICS CHARACTERISTICS OF OF THE THE CLAM CLAM LAKE LAKE INTRUSION--A CONSTRAINT CONSTRAINT ON ON THE THE TIME TIME OF OF KEWEENAWAN KEWEENAWAN BASIN BASIN INTRUSION--A DEVELOPMENT DEVELOPMENT C. Patrick Patrick Ervin Ervin C. Dept, of of Geology, Geology, Northern Northern Illinois IllinoisUniv. Univ, Dept. DeKalb, IL IL 60115 60115 DeKalb, F. Olmsted Olmsted James F. James Center for Earth & Env. Sci., SUNY-Plattsburgh SUNY-Plattsburgh Center for Earth & Env. Sd., Plattsburgh, NY NY 12901 12901 Plattsburgh, M.G. Mudrey, Mudrey,Jr. Jr. M.G. Wis. Wis. Geol. Geol. && Nat. Nat. Hist. Hist. Surv., Surv., 3817 3817Mineral MineralPoint PointRd. Rd. Madison, WI WI 53506 53506 Madison, The The Clam Clam Lake Lake gravity gravity and and magnetic magnetic anomalies anomalies are are associated associated gabbro, with aa layered, layered, mediummedium- to to course—grained, course-grained, mafic—rich mafic-rich gabbro, with probably probably of of Keweenawan Keweenawan age age (Mudrey (Mudrey and and others, others, 1982), 19821, intruded intruded into an an Archean Archean granite granite gneiss. gneiss. The The intrusion intrusion is is located located aa few few into kilometers kilometers south south of of the the Mellen Mellen Complex Complex and and has has been been penetrated penetrated by by two, two, nearly—coincident nearly-coincident boreholes-—one boreholes--one vertical vertical and and one one inclined inclined 65O to to NNW. NNW. 65° The The northern northern Wisconsin Wisconsin aeromagnetic aeromagnetic data data show show the theintrusion intrusion to to be be marked marked by by aa 7000 7000 gamma gamma anomaly anomaly with with aa wavelength wavelength of of only only 5.5 5.5 km, km, indicating indicating aa highly highly magnetic, magnetic, shallow shallow source. source. The The field field configuration configuration suggests suggests the the presence presence of of aa significant significantremanent remanent polarization, which has has been been confirmed confirmed by by paleomagnetic paleomagnetic analysis analysis polarization, which (Kean and and Swingen, Swingen, 1981). 1981). After After reduction—to-the-pole, reduction-to-the-pole, the the (Kean magnetic magnetic anomaly anomaly is is slightly slightly oval oval with with an an east—northeast east-northeast trending trending axis and and with with aa narrowed, narrowed, westward westward elongation, elongation, suggesting suggesting axis Model analysis analysis yields yields an an possible possible extension extension along along aa fracture. fracture. Model average average susceptibility susceptibility contrast contrast of of 0.026 0.026 cgs cgs units units for for aa source source exhibiting exhibiting surface surface relief relief and and having having aa thickness thickness significantly significantly greater greater than than its its depth depth of of burial, burial, which which is is only only slightly slightly over over 20 20 at one one point. point. mm at The The same same source source configuration, configuration, using using aa density density contrast contrast of of 0.5 0.5 g/cc, g/cc, also also yields yields aa satisfactory satisfactory fit fit to to the the residual residual Bouguer Bouguer anomaly anomaly calculated calculated from from aa small small gravity gravity survey survey made made over over the the intrusion. intrusion. Cores Cores from from both both drillholes drillholes were were sampled sampled for for laboratory laboratory analysis. Although Although the the holes holes are are only only about about 152 152 mm apart, apart, analysis. susceptibility susceptibility and and density density values values are are significantly significantly different different between between the the two, two, and and both both give give generally generally higher higher values values than than the the geophysical geophysical modeling modeling suggests suggests to to be be representative representative of of the the body. body. The The differences differences are are probably probably reflective reflective of of the the proximity proximity of of the the holes to to the the edge edge of of the the intrusion. intrusion. The The most most extreme extreme values values holes occur occur in in the the hole hole believed believed to to be be closest closest to to the the contact. contact. The The variation variation in in compositon compositon is is due due largely largely to to changes changes in in cumulate phases. phases. Oxide Oxide poor poor zones zones are are composed composed of of cumulus cumulus cumulate plagioclase plagioclase (An46-50) (~n46-50)and and clinopyroxene clinopyroxene (Wo.4l, (Wo.41, En.47, En.47, Fs.09, Fs.09, Ac.03) Ac.03) with with oxides oxides restricted restricted to to the the postcumulus postcumulus fraction. fraction. In In 24 �contrast, the the oxide—rich oxide-rich layers layers include include magnetite magnetite and and ilmenite ilmenite in in contrast, the cumulus fraction as well. Strongly oriented plagioclase Strongly oriented plagioclase the cumulus fraction as well. occurs in in both both types types of of layers layers parallel parallel to to their their boundaries boundaries and and occurs This is most obvious at about 30 to the axis of the drill core. This is most obvious the axis of the drill core. to at about 300 and quite quite striking striking in in the the oxide—rich oxide-rich layers. layers. The The orientation orientation and increases to to about about 40° 40' in in deeper deeper parts parts of of the the core, core, suggesting increases suggesting aa flattening, possibly possibly related related to to the the boundary boundary of of the the intrusion. flattening, intrusion. Major Major and and selected selected trace trace element element data data were were obtained, obtained, along along with microprobe microprobe data data of of major major mineral mineral phases, phases, to to help help characterize characterize with Ti02; however, however, no no the body. body. The The unit unit is is extremely extremely rich rich in in Ti02; the abnormal abnormal concentrations concentrations of of vanadium vanadium or or other other trace trace elements elements were were detected. detected. Banding Banding in in the the cores cores suggests suggests that that the the intrusion intrusion has has been been rotated 10° lo0 to to 20° 20 from from the the vertical, vertical, while while the the paleomagnetic paleomagnetic rotated data show show no no evidence evidence of of rotation rotation (Kean (Kean and and Swingen, Swingen, 1981). 1981). This This data implies that that the the body body was was either either (a) (a) emplaced emplaced in in aa tipped tipped implies position or or (b) (b) magnetization magnetization was was acquired acquired after after tipping. tipping. The The position mineral chemistry chemistry clearly clearly indicates indicates that that the the magnetite—ilmenite magnetite-ilmenite mineral temperature-oxygen fugacity fugacity is is subsolidus subsolidus (around (around 600°C), 600°C) which which temperature—oxygen is above the hematite and magnetite blocking temperatures. We is above the hematite and magnetite blocking temperatures. We conclude, conclude, therefore, therefore, that that the the NRM NRM was was acquired acquired when when the the intrusion intrusion was in in aa subsolidus subsolidus stage stage in in its its cooling cooling history, history, and and that that was tipping of of the the body body occurred occurred during during or or very very slightly slightly after after tipping emplacement. emplacement. This This suggests suggests that that significant significant rotation rotation and and evolution evolution of of the the Keweenawan basin basin occurred occurred in in the the middle middle Keweenawan Keweenawan during during Keweenawan emplacement emplacement of of plutonic plutonic bodies bodies and and during during extrusion extrusion of of the the lavas. lavas. REFERENCES CITED CITED REFERENCES Kean, W.F., W.F., and and Swingen, Swingen, R.A.,1981, R.A.,1981, Paleomagnetism Paleomagnetism of of aa Keweenawan Keweenawan Kean, age intrusive intrusive near near Clam Clam Lake, Lake, Wisconsin, Wisconsin, Geophys. Geophys. Res. Res. Let., Let., age v. 8, 8, p. p. 579—582. 579-582. v. Mudrey, M.G., M.G., Jr., Jr., Brown, Brown, B.A., B.A., and and Greenburg, Greenburg,J.K.,1982, J.K.,1982, Bedrock Bedrock Mudrey, geologic map map of of Wisconsin, Wisconsin, Wisconsin Wisconsin Geological Geological && Natural Natural geologic History Survey, Survey, Madison, Madison, Wisconsin. Wisconsin. History 25 �EMPLACEMENT, EMPLACEMENT, MINERALOGY, MINERALOGY, AND AND INTERNAL INTERNAL EVOLUTION EVOLUTION OF OF AA HIGHLY HIGHLY EVOLVED Li-PEGMATITE Li-PEGMATITE IN IN FLORENCE FLORENCE COUNTY, COUNTY, WISCONSIN WISCONSIN EVOLVED U. Faister, Falster, Wm. Wm. B. B . Simmons, Simmons, Dept. Dept. of of Geology Geology and and Alexander U. Alexander of New New Orleans, Orleans, Lakefront, Lakefront, New New Orleans, Orleans, LA LA Geophysics, University University of Geophysics, 70148 70148 ' Recent investigation investigation of of several several highly highly evolved evolved grariitic granitic Recent pegmatites peqmatites in in Florence Florence County, County, Wisconsin, Wisconsin, have have make make it itpossible possible to determine determine numerous numerous details details of of their their origin, origin, their their paragenesis paragenesis to and their their internal internalevolution. evolution. and One large large pegmatite pegmatite in in particular particular was was studied studied in in detail. detail* One aa with in maximum dimension, This pegmatite may exceed 300m in maximum dimension, with 300m This pegmatite may exceed thickness of of up up to to 4.5m. 4.5m. The The pegmatite pegmatite invaded invaded the the surrounding surrounding thickness heavily country rock rock concordantly, frequently frequently engulfing engulfing heavily concordantly, country tourmalinized screens screens of of country country rock rock in in the the pegrnatite pegmatite and and tourmalinized causing tourmalinization tourmalinization in in the the surrounding surrounding countr' countryrock rock as well, causing as well. 0 The The pegmatite pegmatite strikes strikes N20 ~ 200W'to to ~ N35 ~ 3 05W'and ~ and dips dips 60 60 —65 -65" in in aa westerly westerly exhibits a striking partitioning direction. This This pegrnatite pegmatite exhibits partitioning of of Mn Mn direction. and Fe Fe along along its its length. length. The The northern northern end end is is Mn-enriched Mn-enriched and and and contains tourmaline tourmaline var. var. rubellite, rubellite, lepidolite, l e p i d ~ l i t e ~spodumene, spodumene, contains and mangano—columbite/tantalite, lithiophilite, fillowite mangano-columbite/tantaliteà and fillowite lithiophilite, The southern rhodizite, besides besides quartz, quartz, microcline, microcline, and and albite. albite. The southern rhodizite, segment is is enriched enriched in in both both Mn Mn and and Fe Fe and and lacks lacks lithiophilite lithiophilite and and segment rnangan— heterosite—purpurite, fillowite, containing instead heterosite-purpurite, manganinstead containing fillowite, Spodumene mangan-huhnerkobelite(?la Spodumene occurs occurs alluaudite, and and mangan-huhnerkobelite(?). alluaudite, abundantly in in the the core core zones zones in in crystals crystals several several times times larger larger abundantly than those those from from the the northern northern segment. seqment. Rubellite Rubellite does does not not occur occur than in this this section section but but Fe—rich Fe-rich blue—black blue-black tourmaline tourmaline is is found found ininits its in place. place. The tourmaline tourmaline in in both both segments segments occur occur in in large large quantity quantity in in The the outer outer wall wall and and contact contact zone, zone, as as well well as as in in the the inner inner the lack of of tourmaline tourmaline in in most most of of the the other other intermediate zone. zone. AA lack intermediate All phosphates appear with tourmaline zones is is conspicuous. conspicuous. All phosphates appear with tourmaline in in zones the inner inner intermediate intermediate zone zone and and the the core core zone. zone. They They are are absent absent the in the the other other units. units. in From country country rock rock distortion distortion it it appears appears that that the the intruding intruding From The south—easterly direction. pegmatitic melt invaded from a south-easterly direction. The from a invaded pegmatitic melt the most likely likely source source of of this this and and neighboring neiqhborinq pegmatites pegmatites is is the most Hoskin Hoskin Lake Lake granite, granite, aa Precambrian Precambrian intrusive intrusive of of an an age age of of 1,650 1,650 million years. years. million The following following list list of of minerals minerals has has been been identified identified to to The date (EDS, (EDS,petrographically petrographically and and by by wet wet chemistry): chemistry): date . in the the Microcline-oerthits is is the the most most abundant abundant mineral mineral phase phase in Microcline-perthit The color It forms blocky grains up to 15 cm across. pegmatite. It forms blocky grains up to 15 c m across. The color pegmatite. ranges from from grayish grayish white white in in the the northern northern segment segment to to reddish reddish in in ranges the southern section, the southern section. Albite, Albite, var. var. cleavelandite, cleavelandite, evidently evidently with with low lowanorthite anorthitecontent, content, is widespread widespread and and also also forms formslate latestage stagemetasornatic metasomatic units. units. The The is color ranges ranges from from aa bluish bluish gray gray to to white white to to red red brown. brown. color 26 �Quartz, of of aa distinctly distinctly gray gray (and (and not not smoky) smoky) color color is is less less abundant than than the the feldspars. feldspars. Masses up to to several several tens tens of of centimeters occur occur occasionally. occasionally. (rubellitel occurs abundantly abundantly in in Tourmaline, variety, elbaite (rubellite) some of the the zones. zones. Deep-blue tourmaline appears appears to to be be an an elbaite elbaite var iety. variety. Spodumeme strictly S ~ o d ~ m e moccurs e strictly in in the the core core zones. zones. Crystals up to to 30 30 cm have been recovered from the core zones in in the southern segment. segment. Lepidolite Leoidolite is is abundant throughout the pegmatite and forms forms patches patches and stringers of purple to pinkish—lilac pinkish-lilac or rarely yellowish flakes (commonly (commonly around 1—2mm 1-2mm in in diameter) diameter) and and masses masses and and occasionally some coarse books books up up to to 1.5cm 1.5cm in in diameter. diameter. Polytlithionite has been identified identified from from near the spodumene core cors masses resembling topaz where it it is found in masses topaz crystals crystals in in outline, outline, thus possibly indicating complete alteration of earlier existing topaz. topaz. The size of these lumps lumps ranged from from 1cm 1cm to to 6cm, 6cm, the the color color greenish yellow. is a greenish yellow. muscovite has been tentatively identified from a patch in Lithian muscovite in where it occurs as bright golden-yellow the intermediate zone where books up to to 5mm 5mm across. across. ADatite occurs throughout the pegmatite pegmatite with the bulk Apatite bulk near the blue, the size up to 5mm in contact. The color is deep blue, in maximum contact. dimension. Apatite occurs also as the white core in dimension. in lithiophilite nodules near the the spodumene spodumene core. core. It is rimmed by lithiophilite and finally finally by by fillowite. fillowite. Lithiophilite Lithioohilite occurs in in the intermediate intermediate and core zones zones of of the the northern segment. northern segment. The size of the nodules nodules reaches reaches aa maximum maximum of of 2cm, Zcm, and generally has a tan to to salmon-pink salmon-pink color, color, in in some some cases cases rimmed by black Mn-oxides. Mn-oxides. Fillowite occurs as a light light tan tan rim rim over over lithiophilite lithiophilite nodules. nodules' Heterosite-~urourite Heterosite-purDurite of the Fe-richer Fe-richer variety was found only at purplish—brown the southern segment as nodules up to 3cm and of purplish-brown color, rimmed by a so far unidentified unidentified white white mineral mineral and be an outer layer layer of of light light blue blue tourmaline. tourmaline. Mangan-alluaudite also was only Manuan-alluaudite only found found at at the the southern southern segment. segment. olive—brown nodules up to 2cm 2cm in in diameter.Mangandiameter.ManganIt formed olive-brown huhnerkobelite occurs with mangan-alluaudite as as brownish brownish masses masses up to 1cm 1cm in in diameter. diameter. This is is the first first reported reported occurance occurance for for this Mn-rich Mn-rich variety. variety. Mangan—huhnerkobelite Mancran-huhnerkobelite occurs occurs with with mangan-alluaudite mangan-alluaudite as as brownish brownish masses up to to 1cm 1cm in in diameter. diameter. This is is the first first reported reported occurance for for this this Mn—rich Mn-rich variety. variety. 27 �Mangano—columbite Yanqano-columbite and mangano-tantalite manqano-tantalite both occur occur throughout throughout the the pegmatite in in small amounts in in crystals of reddish-black color, color, up up 2mm in in maximum maximum dimension. dimension. It is remarkable that both both occurred occurred to 2mm only mm apart in in the the same same sample. sample. Rhodizite is is probably the most remarkable mineral from from the the pegrnatite. glassy, tan colored grains up to 4mm pegmatite* It was found as glassy, 4mm near the contact contact of of the the intermediate intermediate and and wall wall zones. zones. Only Only 22 other localities produced rhodizite: the first first is is near Swerdlovskz, in the Wral Ural Mountains., Mountains., USSR, and the second is Swerdlovskz, is near Mania, Madagascar. Madagascar. The internal internal evolution is is believed to have taken taken the the following pegmatitic magma, magma, highly enriched in following path: path: The pegmatitic in volatiles, Li, Rb, Cs, B invaded invaded the country country rock rock along along bedding bedding planes and planes of of weakness. weakness. Some partial melting meltinq of of the the of country rock may also have occurred, liberating the alkalies of low meltinq melting point and and possibly possibly B. B. A thin contact contact zone z o n e up up to to e.l few mm formed first, immediately followed by a thick wall zone zone up up to 20 2 0 cm. c m * Possibly at this time an interfering influence, influence! either a fluid phase contributed by b y the country rock, or a ph/Eh differential, caused NAA caused profuse profuse crystallization crystallization of of tourmaline, tourmalineo NAA data suggest suggest that the rubellite may indeed indeed have have formed formed relatively relatively Cs. early, despite its its high Mn/Fe Mn/Fe ratio, ratio, it it is is very very low low in in Rb Rb and and Cs. These elements occur abundantly abundantly in in the the deep deep blue blue tourmaline, tourmaline, indicating a higher degree of differentiation. indicatinq differentiationm As the the intermediate zones began began E forming, magma fluxed by lithium intermediate o ~ m i n gaa~ magma prevented precipitation of tourmaline and tetraborate may have prevented inner phosphates (due (due to lack lack of of aqueous aqueous fluid), fluid). Once the inner intermediate zone began to form, form, free free aqueous aqueous fluid fluid began began to to exsolve, resulting in destabilizing of the tetraborate flux, fluxf and an2 in crystallization crystallization of large amounts of of tourmaline tourmaline and and phosphates. phosphatese The fluids enriched in Li eventually gave rise to the spodumene core and to replacement units of lepidolite and albite throughout throuqhout the pegmatite. pegmatite- Finally, escaping fluids, rich in in B, created aa tourmalizied halo in in the the surrounding surrounding country country rock. rock. miarolitic cavities in To date, no evidence of miarolitic in the pegmatite has been been found. found. , 28 �Paleomagnetism Paleomagnetisn of of Keweenawan Keweenawan Age Age Basalts Basalts From From The The Taylor Taylor Falls-St. Falls-St. Croix Croix Falls Falls Area Area of of Wisconsin Wisconsin and and Minnesota Minnesota John John Feeney Feeney and and William F e Kean Kean William F. Department Department of 05 Geosciences Geosciences University of of Wisconsin-Nil'iaukee Wisconsin-KilGaukee University Milwaukee, Milwaukee, WI WI 53201 5320 1 Ten Ten oriented oriented hand hand samples samples from from the the St. St. Croix Croix Falls Falls area area were measured measured for for magnetic magnetic characteristics. characteristics. A.F. A.F. demagnetidemagnetiwere zation zation and remanence remanence acquisition acquisition studies studies indicate indicate that that the the remanence remanence is is carried carried by by magnetite. magnetite. Most Most samples samples show show aa single single The paleopole paleopole directions directions are $re component of of magnetization. magnetization. The component predominately with latitudes latitudes ranging ranging from from S40 S40° to to ~10' Nb0 predominatelv reversed with The The basalts basalts are are probably probably middle middle Keweenawan Keweenawan in in age, age, based based on on known known reversal reversal patterns patterns for for Keweenawan Keweenawan time. time. 29 �APPLICATION OF OF WERNER DECONVOLUTION TO THE THE PENOKEAN PENOKEAN BELT9EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA FOLD-AND-THRUST BELT, R.J. FERDERER FEFUIERER (Department (Department of Geology Geology and and Geophysics, Geophysics, University University of Minnesota, Minnesota7 R.J. Minneapolis, MN 55455; Minneapolis, 55455; and Minnesota Geological Survey, 2642 University Ave., St. 55114) Ave., St, Paul, MN 55114) The geology of the Penokean orogen in east-central Minnesota has recently been reinterpreted by Southwick Southwick and others others <1988). (1988). These authors authors have have divided divided the the orogen orogen several tectonic elements, elements, including including a fold-and-thrust fold-and-thrust belt and and the main bowl bowl of the the into several Animikie basin. The fold-and-thrust fold-and-thrust belt ?At has been further further divided divided into into three three zones zones which which Animilcie basin. The The discontinuities discon~uities are defined defined by are bounded by major structural discontinuities. The are changes metamorphic grade, stratigraphy, stratigraphy, and structural structural style. changes in metamorphic defining structures structures Werner deconvolution has proven to be a useful tool for defining This inverse inverse magnetic magnetic modeling modeling associated with the Penokean fold-and-thrust belt* belt. This technique (k)or or thickness, thickness, and and dip dip estimates estimates technique yields yields position, position9depth, depth, susceptibility susceptibility contrast contrast (k) for anomaly sources by thin thin sheets sheets or or planar planar interfacesinterfaces, Results sources that can be approximated by Results the above-mentioned above-mentioned obtained within two areas areas that lie along dong two of the presented here were obtained nature. structural discontinuities, and provide new information on their name. One area studied straddles the Malmo M a h o structural discontinuity, discontinuity, a southwardsouthwarddipping dipping thrust zone zone that that separates separates the internal internal and and medial zones zones of the fold-and-thrust fold-and-thst belt. The beltThe presence presence of of this this feature featureis is strongly strongly supported supported by a magnetotelluric modeling Young, 1987). Consistent study ((Wunderman W u n d e m and Young? Consistent intermediate intemediate to steeply southward dipping along dipping thin sheet sheet solutions S O ~ ~ were O ~ obtaitied obtaified S dong the mapped location of the discontinuity discontinuity (Fig. 1). in this area (Fig I)*Depth Depth estimates estimateshave have an average average value of 95 m, m9and k estimates (calculated for a sheet thickness of 50 m) have an average value of 0.0230 cgs. cgs- The existence existence of consistent thin sheet solutions over a strike strike length of at least least implies that that the anomaly anomaly source source is related to the discontinuity, discontinuity,and and may may represent represent 40 km implies itself. Pyrrhotite-rich the fault zone itselfPynhotite-rich graphitic graphitic phyllite are common throughout the foldthrustaand-thrust n d - b s t belt and one of these units may have acted as a plane of slippage for the thrust. Alternatively, Alternatively, a layer layer of magnetite magnetite and/or pyrrhotite pynhotite may have formed formed in the the fault fault zone, zone, processes during during faulting, faulting,or or after afterdeformation* deformation. It is also associated with metamorphic processes conceivable conceivablethat that the thin sheet sheet solutions solutions represent a magnetic magnetic layer layer oriented oriented subparallel subparallel to to Formation. The presence of a northwest-trending, leftthe fault zone, within the Denham Formation. lateral strike-slip strike-slip fault fault is is also also indicated indicated (Fig. (Fig. 11b)). b)). A second second area of study lies on the boundary between the fold-and-thrust fold-and-thrust belt and and main bowl of the Animikie basin. basin. A the nuin A major major north-directed north-directed thrust is mapped in this elements mentioned area, as well as an unconformity between rocks of the two tectonic elements mentioned above. Holst Holst(1984) (1984)defined definedaa boundary boundary between between areas areas affected 'affected by one and by two major km east east of of this this area. area. The boundary was interpreted phases of folding, approximately 55 km to be the outermost limit of the hinge of a major north-directed, isoclinal, isoclinal9recumbent fold that is probably a thrust nappenappe. Southwick Southwickand and others others (1988) (1988) extended this boundary, boundaq, based on sparse sparse drilling drilling data, to the northeastern edge of the area considered here. here* 30 �Interface Interface solutions solutions were were obtained obtained north of the mapped mapped thrust fault, fault, and have have Thin sheet sheet solutions solutions were obtained over a orientations which are consistent with it. it. Thin distance along strike, north of the fault and south of the westward distance of greater greater than 15 15 km along Holst's boundary. boundary. Forward Forwardmodeling modelingwas wasperformed performedusing using both both interface interface extension of Hoist's sheet solutions solutions to establish establish which source type is more appropriate for the and thin sheet Thethin thin sheet sheet solutions solutions are are favored based on similarity between anomaly in question. The calculated calculated and and observed obsemed anomalies. anomalies. The Thethin thinsheet sheetsolutions solutionsdip dipapproximately approximately65° 650NN and and are are associated associated with with average averagedepth depth and and kk estimates estimatesof of 300 300m mand and0.0100 0.0100cgs, cgs, respectively. respectively. Because Because of the proximity of the thin sheet solutions solutions to the mapped location location of Holst's Holst'sboundary, boundary,ititisisproposed proposedthat thatthe thesheet sheetmay maycorrespond correspondto toaaunit, unit,possibly possiblyaalean lean iron-formation, located located within within the the nappe nappe hinge hinge so so that that northward northward dips dips would would be be expected. expected. iron-formation, The large large depth depth estimates estimates may may represent represent an an unconformity unconformity separating separating rocks rocks of of the the nappe nappe The h n t from from overlying overlying sediments sedimentsthat that were were derived derived from from the stacked stacked thrust thrust pile pile to to the the front south. ItItisisalso alsopossible possiblethat thatthe theupper upperportion portionof ofthe thenappe nappefront fronthas hasbeen beenfaulted faultedout, out, possibly possibly by by the thethrust thrustmapped mappedin inthis thisarea. area. For For both both of of the the areas areas considered, considered, the the absence absence of interface interface solutions solutions associated associated with thrust thrust faults faults may be be explained explained by a low susceptibility susceptibility contrast contrast between the footwall footwall and and hanging hanging wall. Except Exceptfor foriron-formation, iron-formation,most most supracrustal supracrustal rocks in the Penokean orogen wealdy magnetic. magnetic. Therefore, orogen in east-central Minnesota are weakly Therefore,strong strong susceptibility susceptibility contrasts contrastsacross acrosslow-angle low-anglefaults faultsininthese theserocks rocksare arenot notlikely. likely. Acknowledgments Acknowledgments This This research research was was funded funded by by the the Legislative Legislative Commission Commission on on Minnesota Minnesota Resources. Resources. References ReferencesCited Cited Holst, Holst, T.B., 1984, 1984, Evidence Evidencefor fornappe nappedevelopment developmentduring during the the early early Proterozoic Proterozoic Penokean Mimesota: Geology, Geology,v. v. 12, 12,p. p. 135-138. 135-138. Penokean orogeny, orogeny, Minnesota: Southwick, P.L., 1988, Geologic Southwick, D.L., Morey, G.B. and McSwiggen, P.L., Geologic map map (scale (scale 1:250,000) 1:250,000) of of the the Penokean Penokean orogen, orogen, east-central east-centralMinnesota, Minnesota,and andaccompanying accompanyingtext: text: Minnesota MinnesotaGeological GeologicalSurvey SurveyReport Reportof of Investigations Investigations37 37(in (inpress). press). Wunderman, Wunderman,R.L., R.L., and andYoung, Young,C.T., C.T., 1987, 1987,Evidence Evidencefor forwidespread widespreadbasement basement decollement decollementstructures structuresand and related related crustal crustal asymmetry asymmetry associated associated with with the the western western limb limbof of the theMidcontinent MidcontinentRift Rift(abs.): (abs.): Institute Instituteon onLake LakeSuperior superiorGeology, Geology, Proceedings Proceedingsand andAbstracts, Abstracts,v. v. 33, 33,Pt. pt. 1,1,p. p. 85-86. 85-86. 31 �• 0156 •353,2 1km II 069 and c) susceptibility contrast solutions, all obtained along the Malmo structural discontinuity. Depth estimates are in meters and susceptibility estimates are in cgs units, a •99 01 6. g Fig. 1, Werner deconvolution thin sheet; a) depth, b) dip, 069 •103 •ni•120 •96 •.Q22? S oi4• 02090 022 ?025.02b0 0302 2...1_j5BI ..os \ 3 O2O1 C °" ! b ________________________ 4 �An An investigation investigation into into the the chemical chemical processes processes causing causing the the formation adamellite of of Wisconsin Wisconsin formation of of unakite unakite in in the the Waupaca Waupaca adamellite JODY FRONK FRONK and and Dion Dion C. C. Stewart Stewart(Department (Departmentof ofGeology, Geology, JODY Bowling Bowling Green Green State State University, University, Bowling Bowling Green, Green,OH OH 43403) 43403) Unakite, Unakite, an an epidote-chlorite-rich epidote-chlorite-richred red granite, granite,is islocally locally developed developed in in the the Waupaca Waupaca ademellite, ademellite,which which is is the the southern southernmost most Inthe the pluton in in the the Wolf Wolf River River batholith batholith of of northern northernWisconsin. Wisconsin. In pluton Johnson Johnson Quarry Quarry near near the the city city of of Waupaca Waupaca the the unakite unakite occurs occursin in narrow (20 (20centimeter) centimeter)linear linearzones. zones. Forty Forty samples samples were were collected collected narrow at at regular regular one-meter one-meter intervals intervalson on two two traverses traversesrunning running perpendicularto tothese thesezones. zones. Detailed Detailed mapping mapping of of the the quarry quarry was was perpendicular used used to to establish establish the the orientation orientation of of the the zones zonesand and the thelocation locationof of each sample sample relative relative to to the the unakite unakitezone. zone. Both Both modal modal and and chemical chemical each analyses analyses were were conducted conducted on on the the rocks rocks and and their their consituent constituentminerals minerals from both both traverses. traverses. from Results Results show show that that unakite unakite occurrence occurrence is is spatially spatiallyrelated relatedto to the presence presence of of fracture fracturejoints. joints. Three Three distinct distinct zones zones are are the developed in in the the field field in in aa symmetrical symmetricalpattern pattern around around the the developed fracture joints. joints. Each Each zone zone can can be be characerized characerized by by its its mineral mineral fracture alterations and and either either the the formation formation and/or and/or disappearance disappearance of of alterations The outer most zone is represented by specific minerals. The outer most zone is represented by specific minerals. relatively relatively unaltered unaltered adamellite, adamellite,having having aa strongly strongly developed developed rapakivi rapakivi texture texture and and aa mode mode of of 17% 17% quartz, quartz, 11% 11% biotite, biotite, 62% 62% perthitic microcline, microcline, 6% 6 % plagioclase plagioclase (Ab (Ab== 93), 93), and and 4% 4% accessories accessories perthitic predominately predominately apatite, apatite, sphene, sphene,opaques opaques and and zircon. zircon. The The first first zone of of alteration alteration is is recognized recognized by by the the appearance appearance of of chlorite chlorite and and zone the progressive progressive disappearnce disappearnceof ofbiotite. biotite. The The second second zone zone is is the recognized recognized by by the the appearence appearence of of epidote epidote in in the the groundmass, groundmass,and and aa decrease in in the the amount amount of of microcline, microcline, which which becomes becomes progressively progressively decrease more red red in in handspecimen. handspecimen. The The central central zone, zone, in in the the fracture fracture more lineament, lineament, is is recognized recognized by by aa large large increase increase in in epidote epidote including including the the conversion conversion of of the the rapakivi rapakivi rims rims to to epidote, epidote, aa slight slight increase increase in plagioclase plagioclase (Ab (Ab== 99+), 99+), aa large large decrease decrease in in microcline, microcline, and and the the in conversion of of perthite perthite to to antiperthite antiperthite (bulk (bulkmineral mineral Ab=63, Ab=63, Or=36, Or=36, conversion An=l) An=1). . Mass balance balance calculations calculations using using modal modal abundances, abundances,mineral mineral Mass chemistry, chemistry, and and bulk bulk rock rock chemistry chemistry (both (bothmajor major oxides oxides and and trace trace elements) show show that that the the "unakitization" "unakitizationtl process is is accomplished accomplished by by elements) process both redistribution redistribution of of ions ions among among the the rock-forming rock-forming minerals minerals of of the the both adamellite adamellite and and the the addition addition and/or and/or subtraction subtraction of of ions ions to/from to/from the the rock by by aa hydrothermal hydrothermal fluid. fluid. Calcium Calcium is is redistributed redistributed from from rock plagioclase plagioclase to to epidote, epidote, and and is is added added to to the the rock rock by by the the fluid. fluid. Maanesium and and iron iron are are redistributed redistributed from from biotite biotite to to chlorite. chlorite. Magnesium Aluminium redistributed from from microcline microcline and and plagiolase plagiolase to to ~ l k i n i u mis is redistributed chlorite and and epidote. epidote. Sodium Sodium is is partially partially redistributed redistributed from from chlorite Potassium is is perthite perthite and and plagioclase plagioclase to to antiperthite antiperthite and and albite. albite. Potassium partially partially redistributed redistributed from from biotite biotite and and microcline microcline to to antiperthite, antiperthite, but but is is largely largely removed removed from from the the system system by by the the fluid. fluid. These These types types of of chemical chemical alteration alteration are are broadly broadly synonomous synonomous with with the the characteristics of of "propylitic "propyliticalteration". alteration". characteristics 33 �Genesis Genesis and and Metamorphism Metamorphism of of Magnetite Magnetite in in Biwabik Biwabik Iron—Formation, Iron-Formation,Mesabi Mesabi District, District, Minnesota Minnesota by by Tsu-Ming Tsu-Ming Han Han The The Cleveland—Cliffs Cleveland-Cliffs Iron IronCompany Company Abstract Abstract The The Bjwabik Biwabik iron—formation iron-formationin in the the Mesabi Mesabi District Districtextends extends east—northeast east-northeast for for contact The eastern end has been subjected to a progressive The eastern end has been subjected to a progressive contact about 120 miles. 120 miles. about Four metamorphic metamorphic metamorphism metamorphism by by the the intrusion intrusion of of the the Duluth Duluth Gabbro GabbroComplex. Complex. Four zones have have been been established established by by French French (1968) (1968) within within the the iron—formation iron-formation along along zones (Zone These zones zones are are unaltered unaltered (Zone the strike strike toward toward the the contact contact of of the the complex. complex. These the 3), and highly (Zone metamorphosed moderately 1 1, transitional (Zone 21, moderately metamorphosed (Zone 3 ) , and highly (Zone 2), transitional 1), metamorphosed (Zone (Zone W metamorphosed ). . iron-formation in in The following following diagram diagram shows shows the the mineralogy mineralogy of of the the Biwabik Biwabik iron—formation The Gabbro as a function of distance from the Duluth different metamorphic metamorphic zones zones as a function of distance from the Duluth Gabbro different contact. contact. tOO iltIl In 50 I—till ZONE 111111 0I I ZONE 4 ZONE 2 I i.. Gre.nolit. C)ianiosic — — Minnesotoite I a— U . a. Stilpnom.ton. FoIc o. 1.0 5 ai as Ñ — t3runer,te-Cummungtonite Orunentç-Cumm~nqton~t blend. Blue Blue•gr.en -green bern hornblende , Ned.nberqttt Hedenberqitt Ferroty.r3then. Foyalite i Quartz — Sideri?. — AnUritC •UI au I — — Hematite Magn.ttte ••• 111111 too 50 COlcite Calcite mmmm U... Pynt. u I.. Pyrrbef it, aaa 111111 I0 11111 l_......L_ I.0 5 Distance from f r o m Contact Contact (mtles) (miles) Distance Modified Modified from from French,(l968) French,(1968) 34 0.5 I I 0.I �This study study deals deals with with the the genesis genesis of of magnetite magnetite in in the the iron—formation, iron-formation,based based This on on its its internal internal microstructures, microstructures, and and the the effect effect of of the the progressive progressive metamorphism on on the the internal internal microstructures microstructures of of the the magnetite magnetite in in the the respective respective metamorphic metamorphic zones. zones. Polished sections sections prepared prepared from from the the magnetite—rich magnetite-rich specimens specimens of of the the iron— ironPolished formation formation were were microscopically microscopically examined examined and and reexamined, reexamined,before before and and after after an anininduced oxidation. oxidation. The The oxidation oxidation was was done done by by heating heating the the polished polished sections sections in in aa duced stagnant air air furnace furnace at at about about 300°C 300° for for three three to to four four days. days. This This oxidation oxidation stagnant process process is is rather rather selective selective and and takes takes place place along along either either or or both both the theoctahedral octahedral planes on planes or or the the preexisting preexisting structural structural weaknesses weaknesses of of the the magnetite, magnetite,depending depending on the degree degree of of metamorphism. metamorphism. the The The magnetite studied studied was was free free from from martitization, martitization, except except for for traces traces of of magnetite This magnetite occurs as granules, hematite hematite inclusions inclusions In in some someof of it. it. This magnetite occurs as granules, laminae, laminae, and and single single or or coalesced coalesced octahedra octahedra in in all all the the metamorphic metamorphic zones zones classified. classified. the induced oxidation results show the magnetite coexisting with However, the induced oxidation results show the magnetite coexisting with laylayHowever, ered type type silicates silicates oxidizes oxidizes along along the the preexisting preexisting structural structural weaknesses, weaknesses, ered whereas the the magnetite magnetite associated associated with with chain chain type type silicates silicates oxidizes oxidizes mostly mostly whereas along its its octahedral octahedral planes. planes. along In In the the unaltered unaltered and and transitional transitional zones, zones, the the hematite hematite generated generated by by the the ininduced oxidation oxidation of of magnetite magnetite outlines outlines the the size, size, morphology morphology and and microstructures microstructures duced of of the the preexisting preexisting inclusions inclusions within within the the magnetite. magnetite. These These inclusions inclusions have have been been The interpreted interpreted as as "preexisting l'preexisting hematite" hematite1' (Han (Han 1987 1987 and and 1986). 1986). The existing existing hematite inclusions inclusions observed observed in in the the magnetite magnetite before before the the induced induced oxidation oxidation are are hematite These actually actually unreplaced unreplaced portions portions of of the the preexisting preexisting hematite. hematite. These preexisting preexisting They hematite inclusions inclusions vary vary widely widely in in apparent apparent morphology. morphology. They may may be be platy, platy, hematite bladed, hexagonal, rhombohedral, colloform, wedge—shaped, and lath—shaped bladed, hexagonal, rhombohedral, colloform, wedge-shaped, lath-shaped or in in other irregular irregular forms. forms. They They exhibit exhibit various various types types of of microstructures, microstructures,such such as as other vuggy, vuggy, microgeodic, microgeodic, botryoidal, botryoidal, etc. etc. In In the the moderately moderately metamorphosed metamorphosed zone, zone, the the induced induced oxidation oxidation takes takes place place prinprincipally along along the the cleavage cleavage planes planes of of the the magnetite. magnetite. However, However, the the outlines outlines of of cipally the the preexisting preexisting hematite hematite inclusions inclusions and and their their arrangements arrangementsare are still still traceable traceable in most most of of the the specimens. specimens. in The magnetite magnetite from from the the highly highly metamorphosed zone zone oxidizes oxidizes almost exclusively exclusively The The internal internal microstructures microstructures created created by by the the preprealong along the the octahedral octahedral planes. planes. The existing hematite has been almost completely obliterated. existing hematite has been almost completely obliterated. Genetically, it it is is believed believed that that the the preexisting preexisting hematite hematite functioned functioned as as the the Genetically, principal principal nuclei nuclei responsible responsible for for the the development development of of much much of of the the magnetite magnetite in in the Biwabik Biwabik iron—formation. iron-formation. The The existing existing magnetite magnetite was was largely largely developed developed by the the bethe replacement replacement and and overgrowth overgrowth that that occurred occurred concurrently concurrently at at the the interface interface between tween the the hematite hematitenucleus nucleusand andits itsgarigue gangue host. host. The The development development varies varies in in magmagnitude from from very limited limited to to rather rather extensive, extensive, as as indicated indicated by by the the differences differences nitude in size size and morphology morphology between between the the existing existing magnetite magnetite and and its its nucleus. nucleus. In In gengenin magnetite larninae, existing eral, eral, the size, size, orientation orientation and and outlines outlines of of the the existing magnetite laminae, granules, granules, and and coalesced coalesced octahedra octahedra are are dictated dictated by by the the corresponding corresponding features featuresof of This clearly demonstrates that the magnetite is the preexisting hematite. This clearly demonstrates that the magnetite is not not preexisting hematite. the primary mineral mineral and and may may also also suggest suggest that that the the so—called so-called carbonate carbonate facies facies and and aa primary 35 �silicate facies fades either either originally originally contained contained hematite hematite or or were were oxide oxide fades facies bebemagnetitization, carbonatization, carbonatization, and fore the postdepositional postdepositional changes changes -- magnetitization, and fore the silication. silication. The The developed by overgrowth on, magnetite developed magnetite by the the replacement replacement of, of, and overgrowth on, hematite hematite centripetal ionic diffusion diffusion of Fe++ was apparently apparently the nuclei suggests that the centripetal the Iron was probably initially deposited process. Iron probably initially deposited as as aa key magnetite-forming magnetite—forming process. oxide gel ferric oxide gel associated associated with with siliceous siliceous mud. mud. This This gel gel could could have have dehydrated dehydrated to colloform layers and granules or could have crystallized to hematite cryscrysto tals with different different microstructures. microstructures. The gel could also have reacted with carsource for for the as a bon to produce produce Fe++ Fe++ which which served served as a principal principal source the magnetite magnetite development. development. The The magnitude magnitude of of magnetite magnetite enrichment enrichment was, was, of of course, course, determined determined by the Fe++ Fe++ supply which, in turn, turn, was controlled by the availability availability of of oxyoxyMagnetite development by centripetal and ferric oxide gel. gen, carbon, carbon, ferric oxide gel. centripetal difdifgen, early stages fusion fusion probably occurred occurred during during late late diagenesis diagenesis or or in in the the early stages of of regional regional metamorphism. metamorphism. References References Iron— French, B.M. B.M. 1986 Progressive Contact Metamorphism of the Biwabik IronFrench, Formation, Mesabi Range, Formation, Range, Minnesota. Minnesota. Minnesota Geological Survey Survey Bull. I5. 45. Microstruotures of Magnetite Magnetite as Guides Guides to Its Origin Origin in Some Han, T.M. Han, T.M. 1978 Microstructures Fortschritte der Precambrian Iron—Formations. Precambrian Iron-Formations. Fortschritte der Mineralogie, Mineralogie, Vol. Vol. 56, 56, p. 1O5—12. 105-142. Origin of Magnetite Magnetite in Precambrian Iron-Formations Iron—Formations of Han, T.M. (in (in press) Origin Han, T.M. Abstr. Terra Terra Cognita, Low Metamorphic Grade. Abstr. Cognita, The The Journal Journal of of the the Metamorphic Grade. 6, 1986, Union of of Geosciences, Geosciences, No. No. 3, 3, Vol. 6, 1986, p. 563. 563. European Union 36 �SCIENTIFIC SCIENTIFICDRILLING DRILLINGINTO INTOTEE THEMIDCONTINENT MIDCONTINENT RIFT RIFTSYSTEM SYSTEM William H i l l i a m j. J. Hinze(1) I?inzeO and and William W i l l i a m C. C . Kelly(2) Kelly (2) Approximately Approximately Minnesota Minnesota aa at at 100 100 geoscientists geoscientists workshop workshop entitled entitled recently recently convened convened "Scientific "Scientific in in Drilling Drilling Duluth, Duluth, of of the the of defining Midcontinent Rift R i f t System" Systemn ffor o r tthe h e purpose purpose of d e f i n i n g the t h e generic g e n e r i c and and Midcontinent s p e c i f i c scientific s c i e n t i f i c objectives o b j e c t i v e s of' of drilling drilling specific into into the Rift t h e Midcontinent Midcontinent Rift System and and to t o recommend recommend and and prioritize p r i o r i t i z e drilling d r i l l i n g sites. sites. System was was sponsored by by sponsored Deep Deep Continental Crust, Crust, Inc., Inc., Continental Observation Observation paleo-rift paleo—rift midcontinent midcontinent Sampling Sampling of of the the Earth's Earth's the t h e Department Department of of Energy Energy and and several s e v e r a l state state surveys MRC. surveys interested i n t e r e s t e d in i n the t h e MRC. old old and and This This workshop workshop , The The Midcontinent Midcontinent Rift R i f t (MCR), (MCR) an an 1100 1100 Ma Ma system system extending extending for f o r more more than than 2000 2000 km km across a c r o s s the the region, region, offers offers excellent excellent opportunities opportunities for for studying studying well as a s problems problems dealing d e a l i n g with with the the c o n t i n e n t a l rifting r i f t i n g processes processes as a s well continental e v o l u t i o n of of continents. continents. evolution The The MCR MCR is is unique unique among among rifts rifts because because it it contains m of c o n t a i n s as a s much aass 30 km o f rift—related r i f t - r e l a t e d volcanic volcanic and and sedimentary sedimentary rocis rocics Ga were were and several s e v e r a l crustal c r u s t a l provinces provinces having having aa range range in i n age age of o f about about 22 Ga and c u t by by the t h e crustal c r u s t a l disruption. disruption. cut Our direct d i r e c t knowledge knowledge oof f the t h e MCR MCR is i s largely l a r g e l y limited l i m i t e d to t o evidence evidence obtained obtained from restricted restricted from outcrops outcrops in in the the Lake Lake Superior S u p e r i o r region region and and cuttings r i f t is is c u t t i n g s obtained obtained from from widely distributed d i s t r i b u t e d drill d r i l l holes h o l e s where the t h e rift covered covered by Phanerozoic Phanerozoic by geophysical geophysical have have studies s t u d i e s and and sedimentary sedimentary rocks rocks of of the the craton. craton. However, However, drilling d r i l l i n g of of the t h e overlying overlying Phanerozoic Phanerozoic strata strata pinpointed manya rareas alongt hthe pinpointed many e a s along e l elength n g t h o foft hthe e rrift i f t where where hholes o l e s less less ( 1 ) Department Department of of Earth Earth and and Atmospheric Sciences, Purdue Purdue University, University, (1) West West Lafayette, IN I N 147907 47907 ( 2 ) Department of of Geological Geological Sciences, Sciences, (2) University MI University of of Michigan, Ann Ann Arbor, Arbor, MI 37 1006 C.C. 1006 C.C. 148109—1063 48109-1063 Little L i t t l e Building, Building, �than 5-ian 5-KIU iin n depth can bbee drilled d r i l l e d to t o adequately adequately sample sample the t h e Proterozoic Proterozoic rocks and investigate i n v e s t i g a t e their t h e i r stratigraphic s t r a t i g r a p h i c and and structural s t r u c t u r a l relationships. relationships. These relationships and the These r e l a t i o n s h i p s and t h e sampled rocks rocks can can ne De used used to t o study study the t n e two two MCR: primary scientific s c i e n t i f i c objectives o b j e c t i v e s of of' drilling d r i l l i n g into i n t o the t h e MCR: 11)) To investigate i n v e s t i g a t e the t h e physical p h y s i c a l and snd chemical chemical processes processes involved involved in in the of ccontinental rifts, sspecifically MCR; and and p e c i f i c a l l y tthe h e MCR; t h e origin o r i g i n and eevolution v o l u t i o n of o n t i n e n t a l rifts* To To 2) 2) continental continental iinvestigate n v e s t i g a t e crust crust rrifting ifting process; and mantle specifically specifically interaction interaction to to identify identify during tthe he the the mantle reservoirs r e s e r v o i r s iin n the t h e continental c o n t i n e n t a l lithosphere l i t h o s p h e r e and and the t h e asthenosphere asthenosphere that that have hzve acted acted aass sources ffor o r rift rift basalts b a s a l t s and presumably presumably reflect r e f l e c t tthe he differing d i f f e r i n g ages of of the t h e crust c r u s t and the t h e related r e l a t e d mantle. mantle. These two two primary following reasons. reasons. themes aare re pparticularly articularly attractive attractive for for tthe he First, F i r s t * they are a r e focused focused on on major major geologic g e o l o g i c problems problems broad ggeneric which can be a applied having broad e n e r i c implications, i m p l i c a t i o n s , which p p l i e d to t o the t h e study s t u d y of of rifts. oother t h e r intraplate i n t r a p l a t e rifts. Second, they Second, t h e y can be be addressed addressed only o n l y with with fresh fresh samples obtained by drilling; samples d r i l l i n g ; existing e x i s t i n g outcrops outcrops and and drill d r i l l hole hole samples samples aare r e inadequate. inadequate. initially, initially, Third, tthe Third* h e drilling d r i l l i n g program program can can be staged staged such such that that can be be made ssignificant i g n i f i c a n t pprogress r o g r e s s can made with with several s e v e r a l relatively relatively low—cost low-cost shallow to t o intermediate i n t e r m e d i a t e depth hholes, o l e s , the t h e results r e s u l t s of o f which will will serve s e r v e to t o aid a i d in i n siting s i t i n g and prioritizing p r i o r i t i z i n g possible p o s s i b l e deeper holes. holes. Fourth, Fourth* ddrilling r i l l i n g tto o achieve achieve the t h e purposes purposes of of the t h e primary primary themes themes will w i l l provide provide a basic basic framework iinto n t o which oother ther sstudies, tudies, such aass sedimentology, geophysics, geophysics, metamorphic geology, geology, fluid f l u i d chemistry and movement, movement* etc. e t c . can can / be integrated. integrated. In I n fact, f a c t , the t h e vast v a s t majority m a j o r i t y of of the t h e "secondary nsecondary science" sciencew oobjectives b j e c t i v e s aare r e really r e a l l y essential e s s e n t i a l ingredients i n g r e d i e n t s that t h a t support support the t h e primary primary themes. Fifth, wee anticipate a n t i c i p a t e that t h a t the t h e drilling d r i l l i n g environment environment of of the t h e MCR 14CR F ifth* w will w i l l be be as as benign benign as a s one one can can expect expect to t o encounter. encounter. Finally, F i n a l l y , and and most most significantly, s i g n i f i c a n t l y y tthe h e two two primary primary objectives O D J ~ C ~can, c~a nV* ~ffor oSr the t h e most most part, p a r t * be be achieved with core c o r e samples samples from from the t h e same same drill d r i l l holes. holes. 38 �We W e propose propose as a s aa first first stage s t a g e of of the t h e MCR MCR drilling d r i l l i n g program program two two 3.5— 3.5- to to J4.5—im—deep first iin 4.5-Km-deep ddrill r i l l hholes, o l e s , tthe h e first n southern Minnesota and and the t h e second second i n northern northern Kansas. Kansas. in Because Ekcause of of our our current c u r r e n t knowledge, knowledge, the t h e drilling drilling program could be initiated i n the t h e near near future f u t u r e with with minimum minimum pre—drilling pre-drilling i n i t i a t e d in studies. studies. In we recommend recommend that t h a t site s i t e selection s e l e c t i o n studies s t u d i e s begin begin in in I n addition, a d d i t i o n , we the t h e eastern e a s t e r n Northern Northern Peninsula of Michigan, Michigan, for f o r the t h e purpose purpose of of locating locating d r i l l sites sites to t o sample sample the t h e 20—km—thick 20-km-thick tholeiitio t h o l e i i t i c basalt b a s a l t section s e c t i o n in in drill eastern Lake Superior. Superior. e a s t e r n Lake 39 �ANIMIKIEGROUP: GROUP: A A PENOKEAN PENOKEAN FOREDEEP? FOREDEEP? ANIMIKIE Paul F. F. Hoffman Hoffman Geological Survey Survey of of Canada, Canada, 312-538 Booth St St., Ottawa, Ontario Ontario KIA K 1A 0E4 OE4 Geological 3 12-588 Booth ., Foredeeps (foreland (forelandbasins) basins)a rare linearasymmetric asymmetricbasins basinst hthat migrate in in front front of, Foredeeps e linear a t migrate and They develop (Fig. 1). 1). They and become become incorporated incorporated within, within, foreland foreland thrust-fold thrust-fold belts belts (Fig. of the continental thrust sheets. as a flexural flexural response response to t o loading loading of continental lithosphere lithosphere bby y thrust sheets. Many foredeeps evolve evolve from from oceanic trenches when ted ccontinental Many foredeeps when rif rifted m t h e n t a l margins margins are are drawn into into subduction subduction zones zones(Fige (Fig.219 2),but butthey theymay mayalso alsoresult result from from intracontinental intracontinental drawn thrusting. Taiwan thrusting. Taiwan Strait, Strait,the t h ePersian-Arabian Persian-Arabian Gulf, Gulf, and and the t h e Ganges Ganges River River basin basin aare re examples of active foreJeeps f o r d e e p s in in progressive progressive stages of of devlopment. examples of Active in front by by flexural flexural forebulges forebulges and and behind behind by by Active foredeeps foredeeps are bounded bounded in progradirig thrust-fold belts (Fig. Foredeep migration migratim causes causes diachronous diachronous prograding thrust-fold (Fig. 3). Foredeep of lithofacies, deposition of lithofacies, recognized recognized by by the t h efollowing following diagnostic diagnostic stratigraphic stratigraphic sequence (fig. 4): sequence (Fig. 4): (1) (1) pre-foredeep p r e - f o r d e e p deposits deposits (e.g. (e.g, passive-margin passive-margin shelf shelf sediments); sediments); (2) short-lived erosional disconformity caused by by the (2) short-lived erosional discmformity caused t h e migrating migrating forebulge; forebulge; (3) (3) transgressive outer-ramp outer-ramp (strandline (strandline ttoo foreslope) transgressive foreslope) lithofacies; lithofacies; (4) axial axial turbidites, whIch may shoal upward which m a y shoal upward tto o fluvial fluvial sediments sediments that that are a r ecommonly commmly eroded eroded away away during immediately immediatelysubsequent subsequentthrust-fold thrust-folddeformation. deformation. Foredeep outer-ramps aare during Foredeep outer-ramps re possibly caused caused by commonly broken by normal commonly broken normal faults, possibly by lithospheric lithospheric bending bending stresses. The stresses. The outer-ramp outer-ramp lithofacies lithofacies are a r e typically typically chemical, chemical, starved starved of of terrigenous terrigenous sediment, from areas of of sediment, and and the t h e axial axial turbidites turbidites are arecommonly commonly derived derived along strike from more However, m o r e advanced advanced orogeny orogeny (e.g. (eeg. foreland promontories). p r m on tories). Xowever , terrigenous terrigenous sediments in in some some foredeeps foredeeps may may be be derived derived directly directly from from tthe sediments h e foreland foreland (e.g. (e.g. Nile Nile of tthe ccone o n e of h e eastern Mediterranean). Mediterranean). The Group (Marquette (Marquette Range one of of several possible The Animikie Animikie Group Range Supergroup) Supergroup) isis me possible foredeep sequences sequencesofof Early Early Proterozoic Proterozoic aage identified in in the foredeep g e identified t h e Canadian Canadian shield shield on thwnflexed Archn crust (Hoffman, 1987). It It was was deposited deposited on cbwnflexed Archean crust between between the the (Hoffman, 1987). Penokean thrust-fold Penokean thrust-fold belt tto o the t h e south, south, related related to accretion of the t h e Early Proterozoic island-arc island-arc terrane of Wiscmsin, and and the t h e Archean Archean foreland foreland to to Proterozoic of central centralWisconsin, pre-foredeepdeposits deposits aare tthe h e north. north. Accordingly, Accordingly, t hthe e pre-foredeep r e tthe h e Milles Milles Lacs Lacs and/or and/or Chocolay groups, groups, outer-ramp outer-ramp sediments sediments are represented represented by bythe t h eMenominee Menominee Group, Group, Chocolay and and the t h e axial axial deposits deposits by by the t h eBaraga Baraga Group. Group. As As with other other Early Early Proterozoic Proterozoic foredeeps in in Canada, foredeeps Canada, the t h e Animikie Animikie Group Group is characterized characterized by outer-ramp outer-ramp ironironfformation o r m a t i m and axial tholeiitic tholeiitic volcanism. volcanism. Traditionally, tthe h e Animikie Animikie Group a s an a n evolving evolving passivepassiveTraditionally, Group has has been been interpreted interpreted as margin prism. prism. Testable margin Testable predictions predictions of of the t h e foredeep foredeep model model for for the t h eAnimikie Animikie Group Group are: (1) (1) the t h e age a g e of of Animikie Animikie Group Group deposition deposition (U-Pb (U-Pb dating of of flows oorr tuffs) should be close close to be t o that t h a t of of the t h ePenokean Penokeanorogeny orogeny(ca. (ca. 1.85 1.85Ga), Gal, and and(2) (2) the t h eAnimikie Animikie Group Group m a y be be derived derived from from the t h e Early Early Proterozoic Proterozoic arc a r c terrain terrain (U-Pb (U-Pb dating dating of of turbidites may detrital zircons detrital zircons or o r Nd-Sm Nd-Sm model model age a g e of of terrigenous terrigenous sediment). sediment). However, However, an an Archean source source terrain is Archean is not not excluded excluded in the t h e foredeep foredeep model. model. Preliminary PreliminaryNd-Sm Nd-Sm to an a n Early E k l y Proterozoic Proterozoic source source for for the t h eAnimikie Animikie Group Group turbidites turbidites ddata a t a point point to al., 1987, 1987, 1988). 1988). ( k o v i c h et a!., (Barovich References Barovich, K.M., Ekovich, K.M., Patchett, P.J., a n d Peterman, Peterman, Z., 2,1987, 1987, Origin Origin of of 1.9-1.7 1.9-1.7 Ga P.L, and Penokean continental crust of Penokean ctntinental of the t h eLake LakeSuperior Superiorregion: regim :Eos, Eos, v.68, v.68, p.1547. p.1547. Barovich, K.M., Z.E., and a n dSims, Sims, P.K., P.K., 1988, 1988, Nd Nd isotopes isotopes K.M., Patchett, P.L, P.J., Peterman, Peterman, Z.E., and tthe h e origin of 1.9-1.7 1.9-1.7 Ga Penokean Penokean continental t h e Lake Lake Superior Superior continental crust of the region: Geological region: Geological Society Society of America Bulletin, Bulletin, in review. review. Hoffman, P.F., P.F., 1987, Early Proterozoic foredeeps, foredeep Hoffman, 1987, Early foredeep magmatism, magmatism, and and Superior-type iron-formations h e Canadian Canadian shield, shield, in Proterozoic Superior-type iron-formations of of tthe Uthospheric r k e rA., A*, , ed., ed American AmericanGeophysical Geophysical Union, Union, Evolutim :~Krner, Lithospheric Evolution: Geodynamics Series, v.17, Geodynamics v.17, p.85-98. p.85-98. ., 40 �___ ____ Paul F. F. Hoffman Hoffman ANIMIKIE GROUP: A A PEPJOKEAN PENOKEAN FOREDEEP? ANIMIKIE GROUR fold-and-thrust FOREDEEP outer clS pheric ntinentol crust i i i ::::. :::: :: : mantle o an ic crust F'oceanic fold—and- I I fold-and* 00 0 100 200 300 + 4:0 with foredeeps foredeeps Fig. Fig. 1. 1. Tectonic elements associated with and nomenclature used usedininthis this paper. paper. Note the step-like and nomenclature step-like a m p The The geonormal faults forming h e outer normal forming on on tthe outer rramp. IS strictly strictly schescheof the fold-and-thrust fold-and-thrust belt is metric form of matic. — active I foredeep - II II m IIIItUlt!!IlI!tIIIlIIIlII I I initial-rif passive-margin trench-foredeep initial-riftt passive-margin trenchforedeep deposits deposits deposits deposits Fig. 2. Evolution of an an oceanic trench (A) Fig. Evolution of (A) into a foresubduction of rifted deep (B) by byattempted attempted subduction of a rif ted continental a l margin. margin. direction of direction of foredeep migration '" I.,., flexed plate foredeep deposits iron sb ssei r m j fold—and—thrust fold-and-thrust wedge wedge Foredeep migration migration causes the site s i t emarked marked by by Fig. 3. Foredeep Fig. a black triangle to t o experience uplift and erosion erosion aatt time 12, deposition deposition of of outer-ramp outer-ramp sediment aatt 13, T2, T3, deposition deposition of axial-zone axial-zone sediment sediment aatt 14, of T4, and incorporation into the the allochthonouswedge wedgeaat 15. Note actively deforming deforming allochthonous t T5. of the the progressive progressive sedimentary infilling of t h e foredeep foredeep diachronous process also in a direction with time, aa diachronous parallel to t o the the foredeep foredeep axis. axis. 41 fluvial "molasse" "molasse" m . • outer—ramp outer-romp ddeposits eposits I I 1 axial turbidites axial sequence pre-foredeep sequence stratigraphic sequences. sequences. Fig. 4. Typical foredeep stratigraphic Middle columncorresponds correspondst to site of of the black Middle column o tthe h e site black Figure 3. Paleocurrent directions directions are a r e mainly mainly triangle in Figure 3. Paleocurrent axial. �BANQUET BANQUET TALK TALK UNITED PLATES O OFF AMERICA: ORIGIN AND AND EARLY EARLY EVOLUTION EVOLUTION OF OF LAURENTIA LAURENTIA (2.0 (2.0 TO TO 1.0 Ga) 1.0 Gal F. Hoffman Hoffman Paul F. Geological SurveyofofCanada, Carda, 312-588 Booth Booth St., St., Ottawa, Ont. KIA OE4 0E4 Geological Survey The me stable Precambrian Precambrian lithosphere lithosphere of of North North America America and and Greenland Greenland (Laurentia) (Laurentia) isis weldedby byaa system of 2.0 system of 2.0 - 1.8 Ga Ga aan n aggregate aggregate of of former former microccntinents, micmcmtinents, welded The microcontinents, microcontinents, clustered clustered in in tthe colEsion (Hoffman, 1988). 1988). The h e northern na-them collision zones (Hoffman, mainly of of Archean two-thirds of of Laurentia, are composed composed mainly Archean crust. crust. The collision collision two-thirds Laurentia, are forelands have have sheif-foredeep zones (Fig. zones (Fig. 1) 1) are a r e asymmetric: asymmetric: their their forelands shelf-foredeep prisms prisms of of relatively low low metamorphic metamorphic grade, grade, deformed deformed by byearly earlythin-skinned thin-skinned thrusting thrustingarK! and subsequent thick-skinned folding; folding;their their hinterlands hinterlands have have linear calc-alkaline subsequent thick-skinned calc-alkaline and and crustal-aratectic crustal-ana t e c t i c magmatic magmatic zones, zones, and and systems systems of of obliqueoblique- and and strike-slip str ike-slip shear shear zones andlor post-collisional post-collisional indentation-extrusion indentationextrusion zones related to to oblique oblique subduction subduction and/or The inferred tectonics. The tectonics. inferred sutures sutures are arecommonly commonly cryptic, cryptic, but butthe t h eTrans-Hudson Trans-Hudson orogen preserves preserves a 400-km-wide orogen 4OO-km-wide internal zone in in Manitoba Manitoba and a n d Saskatchewan Saskatchewan that that belts of of former oceanic In northern northern Quebec, the ccontains m t a i n s belts oceanic island i s l a d arcs. In t h eforelarK! foreland of of the collision zone zone preserves preserves aa 400x80-km klippe inin which which a continentalt h e sai-ne same collision 400x80-km klippe continentalmargin is overthrust margin rift assemblage assemblage is overthrust by by transitional transitional oceanic oceanic crust, overthrust overthrust in in turn an imbricated imbricated ophiolite, ophiolite, complete complete with with "sheeted "sheeted dikes" dikesf1 and and maficmaficturn by by an al., 1988). The of the ultramafic cumulates The location location of t h e exposed exposed uitramafic a m u l a t e s (St-Onge (St-Onge et al., Precambrian shield, as as opposed opposedt to covered Precambrian Precambrian platform, platform, is apparently o tthe h e covered Precambrian shield, controlled by by tthe ccntrolled h e distribution distribution of of Archean Archean crust, crust, perhaps perhaps reflecting reflecting its i t s greater greater buoyancy due due tto depleted mantle lithosphere. lithosphere. buoyancy o aa depleted 3uvenile Proterozoic crust, composed of former Juvenile Proterozoic composed of former island island arcs a r c s and and other other oceanic oceanic crustal relics, was was accreted to t othe t h eassembled assembled microcontinents microcontinent s prior prior to t o 1.6 1.6 Ga Ga and and during western Laurentia, In western Laurentia, crust of of ca ca2.2 2.2 Ga Ga during tthe h e 1.25-1.0 1.25-1.0 Ga Ga Grenville Grenville orogeny. omgeny* In (LA.Bowring, &wring, aage g e was was accreted accreted beginning beginning about about 1.9 1.9 Ga GaininWopmay Wopmayorogen orogen(S.A. appears to unpublished data) and and appears t o be b ewidespread widespread ininthe t h parautochthonous(?) e parautochthcnous(?) Cordillera from from California California tto Alaska. In In southeastern and southern Laurentia, belts Cordillera o Alaska. Ga crust of 1.9-1.8 1.9-1.8 Ga crust were were accreted accreted in in the t h ePenokean Penokeanand andMakkovik-Ketilidian Makkovik-Ketilidian orogens, 1.8-1.7 1.8-1.7 Ga Ga crust crust in the t h e Yavapai-Central Yavapai-Central Plains Plains orogen, orogen, and and 1.7-1.6 1.7-1.6 Ga Ga orogens, crust in These belts extend in the t h eLabrador Labrador and and Mazatzal Mazatzalorogens omgens(Hoffman, (Hoffman, 1988). 1988). These extend crust for 5000 km along along strike (including Baltic equivalents) equivalents) and and total 1200 foe 5000 km (including Baltic 1200 km km in in width width south of Archean crust crust isis rrare of the t h eWyoming Wyoming province province (Fig. (Fig. 1). 1). Archean a r e tto o absent absent (Patchett about 1.7 1.7 Ga, Ga, aa possible possible sea-level sea-level highstand highstand resulted in and Arndt, 1986). 1986). Beginning Beginning about in the t h e deposition deposition of of clastic clastic sediments sediments in in widely distributed distributed cratonic basins basins (eg. (eg. Baraboo, Athabasca, Thelon, J3arabo0, lhelon, Hornby). Hornby). From at least least 1.5 1.5 to t o1.3 1.3 Ga, Ga, epizonal epizonalsyenogranite syenogranite batholiths batholiths and and layered layered gabbro gabbro From masfs and/or anorthosite anorthosite m a s g f s were wereemplaced emplaced across much of southern aand nd southeastern Laurentia. In In many many areas, areas, the t h eMiddle MiddleProterozoic Proterozoic"anorogenic" 'lanomgenict' magmatism lacks lacks associated associated rift rift faulting, thick magmatism thick alluvial alluvial sedimentation, sedimentation, and and syn-ri synqi fftt (isostatic) and and post-rift post -rift (thermal) (thermal)subsidence subsidence normally normally expected expected as asconsequences ccn sequences of lithospheric Rather than lithospheric stretching. Rather than attributing attributing the t h e magmatism magmatism to t o extensional extensional tectonism, it isis suggested above aa mantle mantle tectonism, suggested tthat h a t tthe h e then then young young Laurentia Laurentia sat above "superswell" (Pribac and Davies, superswells aare tlsuperswell'l Davies, 1987). Such Such superswells r e products products of deep deep convective upwellings, expressed as topographic ccnvective upwellings, expressed topographic and and geoidal geoidal highs highs arK! and hotspot hotspot clusters having having diameters diameterson on tthe clusters h e order order of of 5000 5000 km. km. The proposed proposed Middle Middle The Proterozoic caused thermal thermal erosion Protem zoic superswell superswell czused e m s i m of of the t h eLaurent Laurentian ian lithospheric lithospheric mantle, of mantle mantle melts melts into the continental crust, and mantle, injection injection of a n d extensive extensive crustal crustal melting. melting. Components Components of of uplift uplift were were both both temporary, temporary,due dueto t othermal thermalexpansion, expansion, and and permanent, permanent, due due to t o magmatic magmaticcrustal crustalunderplating underplating(McKenzie, (McKenzie, 1984). 1984). Only Only the the Archean cratons whose whose tectospheric tectospheric m roots Archean cratons o t s hal h d not not been been disrupted disrupted by, by, for for example, example, Early Proterozoic subduction zones remained relatively unaffected; unaf f e t e d ; Early Proterozoic crust crust was was extensively extensively remelted. - 42 �UNITED UNITED PLATES PLATESOF OFAMERICA AMERICA F. Hoffman Hoffman Paul F. Figure 1. 1. Precambrian Precambrian tectonic elements elements of of Laurentia Laurentia and and Baltica. Baltica. Uppercase FIgure Uppercase names are a r e Archean Archean provinces provinces (former (former microcontinents); microcont inent s); lowercase lowercase names names are are names Proterozoic orogens. orogens. Greenland Greenland is is restored restored prior prior to t orefting reftingfrom fromNorth NorthAmerica; America; Proterozoic Baltica possible pre-lapetus pre-Iapetus position. position. Abbreviations: Abbreviations:BH=Black BH=BlackHills; Hills; Baltica isisshown shown in in aapossible BL=Belcher foldbelt; CH=cheyenne CH=Cheyenne belt; CS=Cape CS=Cape Smith Smith belt; belt; FR=Fox FR=Fox River River belt; belt; BL=Belcher GL=Great Lakes Lakes tectonic tectonic zone; zone;GS=Great GS=GreatSlave SlaveLake Lakeshear shearzone; zone;KL=Killarney KL=Killarney GL=Great magmatic KR=Keweenawan rift; rift; MK=Makkovik MK =Makkovik magmatic zone; zone;KP=Kapuskasing K P=Kapuskasing uplift; uplift ;KR=Keweenawan orogen; orogen; MO=Mistassini-Otish MOsMistassini-Otish basins; basins; MRV=Minnesota M RV=Minnesota River River Valley Valley terrarie; terrane; SG=Sugluk terrane; THThompson SG=Sugluk terrane; TH=Thompsonbelt; belt;TS=Transscandinavian TS=Transscandinavian magmatic magmatic zone; zone;WR= WR= Winisk Winisk River River fault. fault. 43 �UNITED PLATES PLATES OF OF AMERICA AMERICA Paul F.Hoff man F.Hoffman The The protracted thermomagmatic thermomagmatic assault by by the the superswell superswell caused caused thinning thinning and weakening of much of the weakening of much of t h e Laurentian Laurentian lithosphere, lithosphere, and and has has implications implications for for injection injection of deformation in the of the t h e Mackenzie Mackenzie dike swarm, deformation t h e Grenville Grenville orogen, orogen, and and magmatism magmatisin in the t h e Keweenawan Keweenawan rift. The 1.3 1.3 Ga Ga Mackenzie Mackenzie dike dike swarm swarm presents presents problems problems in in accounting for its width (1800+ km) if caused by rifting and its length (2400+ for i t s width (1800+ km) if caused b y and its length (2400+km) km) if if caused Alternatively, hotspot. Alternatively, tthe h e dikes dikes may may represent represent leakage leakage from from caused by by aa hotspot. extensive in intrallthosçeric tralithosphericmelt-ponds melt-ponds emanating emanating from from the t h e mantle mantleupwe!ling. upwelling. Dike Dike orientation may may only record the t h e ambient ambient intraplate intraplate stress stressregime, regime, generally generally related related to forces at plate plateboundaries. boundaries. Accordingly, Accordingly, tthe h e dikes dikes may may parallel parallel forces generated generated at compressional stress trajectories generated coeval(?) orogen orogen marginal marginal to t o the the compressional stress generated by b y aacoeval(?) Beaufort Sea, inferred inferred from from seimic seimic reflect reflection profiling. Recent Beaufort Sea, ion profiling. Recent seismic seismic reflection reflect ion profiling shows that .25-1.0 Ga) t h a t much much of of the t h ecollisional collisionalGrenville Grenvilleotogen orogen(1(1.25-1.0 Gal is is thrust thrust imbricated to t o the the base base of of the t h ecrust. crust.The Theorogen orogenisisalso alsounusual unusual in in lacking lacking preserved preserved foreland foreland basins basins oorr other evidence evidence of aa flexural flexural response response to t o orogenic orogenic loading. loading. These These observations suggest aa thin lithospheric observations suggest lithospheric mantle mantle and and low low flexural flexural rigidity rigidity during during Grenvillian The rift has Grenvillian deformation. deformation. The 1.1 1.1 Ga Ga Keweenawan Keweenawan rift has an a nextraordinary extraordinary thickness (15-20 synclinal structure is is due due to t o volcanic volcanic thickness (15-20km) km)ofofbasalt basalt(its (its post-rift post-rift synclinal loading). loading). Theoretical Theoretical calculations calculations show show that t h a t magma magma generation genera tion in in rifts r i f t s isis critically critically dependent 19871, consistent with with dependent on on potential asthenosphere asthenosphere temperature t e m p e r a t u r e (White, (White, 1987), anomalously hot asthenosphere asthenosphere beneath beneath tthe anomalously hot h e rift. Among the many many unsolved unsolved problems problems regarding regarding tthe Among the h e early evolution evolution of of Laurentia Laurentia are (1) Did Didtthe Archn microcontinents common ancestry ancestry in in a r e the t h e following: following: (1) h e Archean microcontinent shave haveaacommon l a t eArchean-early Archean-early Proterozoic Proterozoic supercontinent? supercontinent? (2) (2) Did Did Laurentia Laurentia belong a late belong to to a Middle Proterozoic supercontinent tthat h a t broke broke up up prior prior to t othe t h eGrenvillian Grenvillian collision? collision? Middle Proterozoic supercontinent (3) was tthe hinterland tthat separated from (3) What What was h e Grenville Grenville hinterland h a t presumably presumably separated from Laurentia Laurentia during the t h e opening opening of lapetus? Iapetus? References Hoffman, United plates plates of of America, America, the the birth of of a craton: Early P.F., 1988, 1988, United Early Hoffman, P.F., Proterozoic Proterozoic assembly assembly and and growth growth of of Laurentia; Laurentia;Annual AnnualReview Reviewof ofEarth Eartharid and Planetary PlanetarySciences, Sciences,v.16, v.16, p.543-603. p.543-603. McKenzie, A possible possible mechanism mechanism ffor epeirogenic uplift; Nature, McKenzie, 1)., D., 1984, 1984, A o r epeirogenic Nature, v.307, v.307, p.616—618. p.616-618. Patchett, Patchett,P.3., P.J., and andArndt, Arndt,N.T., N.T., 1986, 1986,Nd Nd isotopes isotopes and and tectonics tectonicsof of1.9-1.7 1.9-1.7 Ga Ga crustal crustalgenesis; genesis; Earth Earth and and Planetary Planetary Science Science Letters, Letters,v.78, v.78, p.329-338. p.329-338. Pribac, Pribac, F., F., and and Davies, Davies, G.F., G.F., 1987, 1987, Mantle Mantle superswells: superswells: regressions regressions arid and rifts? rifts? (abstract); (abstract); Eos, Eos, v.68, v.68, p.1451. p.1451. St—Onge, S t a g e , M.R., M.R., Lucas, Lucas, D.3., D.J., Scott, Scott, D.i, D.J., and andBegin, Begin,N.3., N.J., 1988, 1988,Thin-skinned Thin-skinned imbricat ion and and subsequent subsequent thick-skinned thick-skinned folding foldingofofrift-fill, rift-fill, transitional-crust, imbrication and ophiolite suites in the t h e 1.9 1.9 Ga Cape Smith Belt, northern Quebec, Quebec, in Current Research, Part Part C; C ;Geological Geological Survey Survey of of Canada, Canada, Paper Paper 88-IC. 88-1C. In In press. Research, White, and igneous igneous underplating underplating in in sedimentary White, R.S., R.S., 1987, 1987, Volcanism Volcanism and sedimentary basins basins and and XIX General GeneralAssembly, Assembly, International International rifted continental continentalmargins margins(abstract); (abstract);XIX rifted Union of Geodesy and Geophysics, Vancouver, Union of Vancouver, v.1, v.1, p.183. p.183. 44 �THE STRATIGRAPHY AND PHYSICAL VOLCANOLOGY ASSOCIATED WITH THE F-GROUP VOLCANOGENIC MASSIVE SULFIDE DEPOSIT, STURGEON LAKE, NORTHWESTERN ONTARIO George George J. J. Hudak Hudak (Dept. (Dept. of of Geology, Geology, University University of of Minnesota Minnesota -Duluth, Duluth, Duluth, Duluth, MN MN 55812) 55812) The The F—Group F-Group volcanogenic volcanogenic massive massive sulfide sulfide deposit, deposit, situated situated 77 Km. west of the the Mattabi massive sulfide sulfide deposit deposit in in the the Archean Wabigoon Wabigoon greenstone greenstone belt, belt, is is located located within within an an intensely intensely altered altered succession succession of of mafic to felsic felsic metavolcanic metavolcanic rocks and and associated associated intrusive intrusive rocks. rocks. This This deposit deposit yielded yielded rocks nearly nearly 400,000 400,000 tons tons of of Zn-Cu—Pb—Ag Zn-Cu-Pb-Ag ore ore prior prior to to its its depletion depletion in in 1984. Detailed Detailed mapping and petrographic petrographic studies studies allow allow the the 1984. volcanic volcanic succession succession associated associated with with this this deposit deposit to to be be divided divided into into several several distinct distinct lithological lithological units. units. These These are: are: bedded, bedded, scoria—rich scoria-rich volcaniclastic volcaniclastic rocks rocks which which a) form form the the base of of the the volcanic volcanic succession succession and and are are up up to 110 110 meters meters thick: thick: to massive, massive, poorly sorted sorted mesobreccia mesobreccia deposits deposits which b) overlay overlay the the volcaniclastic volcaniclastic rocks rocks throughout throughout the the entire field field area. area. These These heterolithic heterolithic deposits deposits entire are are up up to to 150 150 meters thick thick and contain contain from from 20-70% 20-70% basaltic basaltic and and dacitic dacitic fragments fragments which appear appear to to be be derived derived from from volcanic volcanic rocks rocks which which underlie underlie the the scoria—rich scoria-rich volcaniclastic volcaniclastic rocks: rocks: a series series of of quartz quartz phyric, phyric, pumice—rich pumice-rich pyroclastic pyroclastic c) flow flow deposits deposits which which are are up up to to 110 110 meters meters thick thick and and are are locally locally interfingered interfingered with, with, and and grade grade into into the the mesobreccia mesobreccia deposits. deposits. These These pyroclastic pyroclastic flows flows and and associated form the immediate associated ash ash tuft's tuffs form immediate footwall footwall rocks rocks to to the the F—Group F-Group massive massive sulfide sulfide deposit: deposit: a 250 250 meter thick thick series series of of well well bedded ash ash and and d) quartz quartz phyric, phyric, pumice-rich pumice-rich pyroclastic flow flow deposits. To To the the east, east, these these rocks rocks host host the the Mattabi Mattabi deposits. orebody. orebody. a a series series of of more massive massive pyroclastic pyroclastic flows flows which which e) contain contain 1—6 1-6 mm diameter diameter quartz quartz and and plagioclase plagioclase crystals. These These flows flows comprise comprise the the uppermost uppermost units units crystals. associated associated with with the the F-Group F-Group orebody. orebody. The The scoria—rich scoria-rich volcaniclastic volcaniclastic rocks rocks are are the the reworked reworked equivalents cone deposit deposit located equivalents of of aa scoria scoria cone/tuft' cone/tuff cone immediately immediately east east of of the the field field area, area, and and are are believed believed to to have have been deposited deposited in in shallow shallow water. water. The The mesobreccia mesobreccia and and quartz quartz been crystal—rich crystal-rich pyroclastic flows flows are believed to represent represent deposits deposits formed formed during the collapse collapse of a caldera caldera combined with simultaneous felsic felsic volcanism. volcanism. The The F—Group F-Group massive massive sulfide sulfide simultaneous deposit was formed formed prior to a second second cycle cycle of explosive explosive volcanism that that deposited deposited the bedded, bedded, quartz-phyric, quartz-phyric, pumice-rich pumice-rich pyroclastic which host host the the Mattabi Mattabi massive massive pyroclastic flows flows and and ash ash tuft's tuffs which sulfide deposit deposit to to the the east. east. The The uppermost uppermost quartzquartz- and and sulfide plagioclase—phyric plagioclase-phyric pyroclastic flows flows represent represent the last last phase of explosive explosive volcanism volcanism associated associated with with the the caldera. caldera. 45 �MICHIGAN KINBERLITE PROVINCE MICHIGAN KIMBERLITE PROVINCE W. JARVIS W. JARVIS Jack Murphy, Murphy, Trustee, 49920 90, Crystal Crystal Falls, Falls, Michigan Michigan 49920 Jack Trustee, P.O. Box 90, J. KALLIOKOSKI KALLIOKOSKI University, Houghton, Houghton, Michigan Michigan 49931 49931 Michigan Technological Michigan Technological University, The disclosure disclosure by Mudrey (1981) by Cannon Cannon and and Mudrey (1981) of of the the presence presence of of the the The Lake Ellen kimberlite in Michigan pointed Lake Ellen kimberlite in the the Upper Peninsula Peninsula of of Michigan pointed to to the the historical diamond finds finds in Great Lakes Lakes possibility that the source of historical in the the Great possibility that the James Bay could be be other than region could than in in the the James Bay lowlands lowlands of of Ontario Ontario as as had had region Jack Murphy, been previously previouslyassumed. assumed. Jack Murphy,Trustee Trustee(Dow (DowChemical ChemicalCompany), Company), with whom whom we we are are associated, associated, has has been been actively actively exploring exploring since since 1982 1982 for for other Lake Ellen other expressions expressions of of the the Lake Ellen kimberlite kimberlite field, field, and and has has looked looked at at potential of those kimberlites kimberlites that the economic potential that have have been been found. found. This This reports on six found, which which occupy occupy a paper reports a northnorthpaper six additional additional ld.mberlites kimberlites found, west trending trending belt extending extending from from the the Powers/Hermansville Powers/Hermansville area area to to Lake Lake Ellen Ellen (Fig. (Fig. 1). 1) . WISCONSIN GEOLOGY L Pvot.rozoic granite gn.i.e I-. L Prot. matlc volcanic rocks • 463O MICHIGAN GEOLOGY x7oJ Jurassic kimb.rlltes (Sits No.) I Ordoviclan s.dHiisnts Cambrian s.dim.nts / L Prot.s.d. and Voic. rockal Amass I (iron formation solid black) ] kI Arch.an rocks —'." Fault , 'I ) 46 -T . 'i -7 -j >'i ;... V ,><r r- r'\1. lounti :s : 7 x 873O" FIG. Bedrock geology geology of of the Marquette—Iron Mountain FIG. 1. 1. ~edrock the Marquette-Iron Mountain region region of of Michigan—Wisconsin, showing bodies. the location location of kimberlite bodies. Michigan-Wisconsin, showing the ofImown known kimberlite It now generally It is is now generally accepted that thatininMichigan Michigan the thePrecambrian Precambrian Shield Shield Archean terranes is made made up up of of two two sutured sutured Archean terranes across across which which were deposited deposited is margin and lower Proterozoic Proterozoic passive passive margin and rift rift basin basin assemblages assemblages of of sedimentary sedimentary lower and and volcanic volcanic rocks, rocks, some some possibly possibly 2.1 2.1 b.y. b.y. old. old. These These rocks rocks underwent underwent aa 46 �period period of of tectonism tectonism estimated estimated at at about about 1.9 1.9 b.y., and and were were cut cut by by east—west east-west striking striking post—orogenic post-orogenic diabase diabase dykes. dykes. Thus, Thus, one one requirement requirement that that the the search search for for diamondiferous diamondiferous kimberlites kimberlites be be conducted conducted on on stable stable portions portions of of cratonic cratonic blocks blocks was was satisfied. satisfied. In the the region region of of our our kimberlite kimberlite finds finds the the structures structures in in the the Archean Archean In Proterozoic cover trend from westerly to deformed basement and basement and deformed Proterozoic cover trend from westerly to northwest northwest (Fig. 1). 1). (Fig. 73 kimberlite kimberlite intrudes intrudes flat—lying flat-lying lower lower Paleozoic Paleozoic shallow shallow The Site Site 73 The thissedimentary sedimentarycover cover sea basin basin margin margin sedimentary sedimentary rocks. rocks. At one time this sea extended to the thewest west and and northwest northwest as as evidenced evidenced by outliers outliersatatLimestone Limestone extended Palaeozoicrocks rocksin in all all the Mountain and and by by abundant abundant xenoliths xenoliths of of lower Palaeozoic the Mountain discovered discovered kimberlites. kimberlites. The The Lake Lake Ellen Ellen kimberlite kimberlite was was dated dated by by Cannon Cannon and and Mudrey Mudrey as as post post lower lower Palaeozoic Palaeozoic by by the the presence presence of of Ordovician Ordovician limestone limestonexenoliths. xenoliths. The The additional kimberlites kimberlites are are also also post post lower lower Palaeozoic, Palaeozoic, some some with with 66 additional Devonian Devonian fossils fossils (J. (J. Humi, Huml, personal personal communication, communication,1987). 1987). Macrocrystal Macrocrystal zircons zircons (3mm) (3mm) recovered recovered from from Site Site 73 73 mineral mineral concentrates concentrates have have been been dated dated at at 155 155 m.y. using using the the fission—track fission-track method method (Craig (Craig Chesner, Chesner, personal personal communication, communication, 1987) 1987) and and aa potassium—argon potassium-argon age age of of 190 190 m.y. m.y. was was obtained obtained from from phiogopite phlogopite from from the the same same kimberlite kimberlite (Craig (Craig Smith, Smith, personal personal communication,1987). 1987). Based Based on on these these age age determinations determinations and and their their similar similar communication, modes modes of of occurrence, occurrence, we we conclude conclude that that all all of of the the kimberlites kimberlites are are Mesozoic, Mesozoic, probably probably Jurassic. Jurassic. The The compositions compositions of of garnet garnet and and chromium chromium spinel spinel from from kimberlite kimberlite can can be be used used as as guides guides to to the the possible possible presence presence of of diamond diamond by by comparing comparing them them (and garnet and (and their their abundance) to to the the compositions compositions of of garnet and spinel spinel occurring occurring as as inclusions kimberlites (Gurney inclusionsinindiamond diamondand and in inknown known diamondiferous kimberlites (Gurney and Switzer, 1973; 1973; Gurney, Gurney,1984; 1984;Harte, Harte,etetal, al, 1980; Sobolev, Sobolev, et et al, al,1973; 1973; has two two proven proven parageneses: parageneses: eclogitic Sobolev,1984). 1984). Diamond Diamond has eclogiticand and perido— peridoSobolev, titic. The garnet garnet population population at at each each of of the the kimberlites kimberlites was was examined examined for for titic. The compositions kimberlitescontaining containingdiamonds diamonds compositions comparable comparable to to those those found found in in kimberlites ofaaknown known peridotitic peridotitic paragenesis paragenesis (Gurney's (Gurney'sG—10 G-10 garnets). garnets). For For the the Lake Lake of Ellen Ellen and and Bacon Bacon kimberlites, kimberlites,aapreselection preselectionofofgrains grainswas wasmade made to to ensure ensure inclusion with diamond diamond inclusion that all allcolor colorgroups groupswere were represented. represented. Garnets with that compositions, CaO and and higher higher Cr203 Cr203 than than compositions,or oreven evencompositions compositionswith withlower lowerCaO McGee has has reported reported aa similar similar the lherzolite lherzolite field, field, are are rare rare (Fig. (Fig. 2). 2). McGee the 69, 70 70 For the the Site Site 69, low low G—10 G-10 population population for for Lake Lake Ellen Ellen (McGee, (McGee,1987). 1987). For and and 73 73 kimberlites, kimberlites, only only lilac, lilac, purple purple or or mauve mauve garnets garnets were were sent sent for for with a analysis. This analysis. This produced produced aa plot plot with a bias bias toward toward garnet garnet compositions compositions However, aa large largeamount amount of of mineral mineral concenconcenfalling falling near near the the G—10 G-10 field. field. However, trate trate was was examined examined for for the the selection selection of of these these grains grains and, and, according according to to the criteria, the significant population population of the Gurney criteria, the lack of a significant of G—10 G-10 garnets garnets suggest be highly highly diamondiferous diamondiferous (Gurney, (Gurney, 1984; 1984; Boyd Boyd suggest the the pipes pipes may may not not be and and Gurney, Gumey, 1982). 1982). A Michigan kimberlites A number of ofchromium chromium spinels spinels from from each each of of the the Michigan kimberlites were -but no no spinels spinels of of diamond diamond inclusion inclusion field field compositions compositions were also also analysed analysed-but were were found. found. Literature Literature sources suggest that thatinindiamondiferous diamondiferous kimberlites, kimberlites, up up to to about about 12% 12% of of the the spinel spinel population population falls falls in in the the diamond diamond inclusion inclusion compositional field. field. compositional Based Based on on our our work work we we conclude conclude that that these these particular particular kimberlites kimberlites are are unlikely unlikely to to be be economically economically diamondiferous diamondiferous and and also, also, that that they they are are not not the the probable probable specific specific source source for for the the large large diamond diamond finds findsin inWisconsin. Wisconsin. However, in the the garnet garnet population population does does However, the the presence presence of of G—10 G-10 compositions compositions in indicate indicate that that the the source source region region for for the the kimberlite kimberlite magma magma was was within within the the diamond by diamond stability stability field field of of the the upper upper mantle, mantle, as as was was also also indicated indicated by McGee McGee and and Hearn Hearn (1982), (1982), and and that that the the potential potential for for diamonds diamonds in in other other kimberlites kimberlites in in this this area area remains remains strong. strong. 47 �Lake Ellen Site 69 (2 pipes) Bacon I :• F I.. I... I I.. ;.• I' cSo3 .1;.. .1' 4 ' It. •' t-._ 2 4 c.e S IS S I SiteTO(2 S i t e 7 0 ( 2pipes) pipes) I. 1 / 8 I I. 1 1 1 Site S i t e73 73 -.- " . * — -.-'4.-. • :.4. I 'S I, FIG. Cao v. v. Cr203 CrgOaplots plots for for selected selected garnet garnet grains grains from from each each of of FIG. 2.2. Gao the The dashed dashed lines lines correspond correspond to to the the 85 85 percentile percentile lines lines thekimberlites. kimberlites. The of Gurney. of Gurney. References References Boyd, Boyd, F.R. F.R. and and Gurney, Gurney,J.J., J.J., 1982, 1982,Low Lowcalcium calciumgarnets: garnets: keys keysto to craton craton structure structureand anddiamond diamondcrystallisation. crystallisation. Carnegie Carnegie Institute,Washington, Washington, Yearbook, Yearbook,v. v.81, 81,p.p.261—267. 261-267. Institute, Cannon, F. and Cannon,W.W.F. and Mudrey, Madrey,M.G., M.G., Jr., Jr., 1981, 1981,The Thepotential potentialfor fordiamond— diamondbearing bearing kinberlite kimberlitein innorthern northernMichigan Michigan and andWisconsin. Wisconsin. U.S. U.S. Geol. Geol. Survey Survey Circular Circular 842, 842,15 15p.p. correlation between between garnets garnets and and diamonds diamonds in in kimber— kimberGurney,J.J., J.J., 1984, 1984,AA correlation Gurney, lites, E. and lites,in inGlover, Glover,J.J.E. and Harris, Harris, P.G., P.G., eds., eds., Kimberlite Kimberlite occurrences occurrencesand and origin: origin: aa basis basis for forconceptual conceptualmodels modelsin inexploration. exploration. University University of of Western WesternAustralia, Australia,Geology GeologyDept. Dept. and andUniv. Univ. Extension ExtensionPublication. Publication. Harte, Harte,B., B., Gurney, Gurney,J.J., J.J., Harris, Harris,J.W., Jew., 1980, 1980,The The formation formation of of peridotite peridotite suite suiteinclusions inclusionsin indiamond. diamond. Contrib. Contrib.Mineral. Mineral.Petrol, Petrol,v.v.72, 72,p. p. 131—190. 131-190. McGee, McGee,E.S., E.S., 1987, 1987,Garnet Garnetxenocryst xenocrystanalyses: analyses: potential potentialfor fordiamonds diamondsin in kimberlite,north—central north-centralMontana Montanaand andthe theLake LakeEllen Ellenkimber— kimbertheWilliams Williamskimberlite, the lite, lite,northern northernMichigan. Michigan. U.S. U.S. Geol. Geol.Survey SurveyOpen—file Open-fileReport Report87—418, 87-418,1515p.p. Sobolev, N.V., 1984, 1984,Kimberlites Kimberlitesofofthe theSiberian Siberianplatform: platform: their Sobolev,N.y., theirgeologigeological caland andmineralogical mineralogicalfeatures featuresin: in: Glover, Glover,J.E. J.E. and andHarris, Harris,P.G., P.G., eds., eds., Kimberlite Kimberliteoccurrence occurrenceand and origin: origin: aabasis basisfor forconceptual conceptualmodels modelsininexexploration. UniversityofofWestern WesternAustralia, Australia,Geology GeologyDept. Dept. and andUniv. Univ. ploration. University Extension 143-166. ExtensionPublication Publication8,8,p.p.143—166. 48 �GEOCHEMICAL STRATIGRAPHY STRATIGRAPHY OF OF THE HURONIAN GEOCHEMICAL HURONIAN CONTINENTAL CONTINENTAL VOLCANICS, VOLCANICS, ONTARIO: ONTARIO: RELATIVE CONTRIBUTIONS CONTRIBUTIONS OF MANTLE MANTLE HETEROGENEITY, SYSTEM MAGMATISM AND RELATIVE HETEROGENEITY, OPEN OPEN -- SYSTEM CRUSTAL FUSION FUSION CRUSTAL Wayne T. Jolly (Department (Department of Geological Geological Sciences, Sciences, Brock Brock University, University, St. Catharines, Catharines, Ontario, Ontario, Canada Canada L2S 3A1) 3A1) L2S The 1500 1500 m thick thick sequence sequence of of Huronian Huronian flood flood basalts basalts at at Thessalon, Thessalon, Ontario, Ontario, contains interlayered low—Ti, low-Ti, enriched enriched continental continental tholeiites tholeiites and and two two distinct distinct varieties varieties of crustally crustally derived derived rhyolite rhyolite (1, (1, 2). 2). The stratigraphic stratigraphic succession succession is divided into four volcanic cycles, cycles, each each of which includes includes early early mafic mafic and late late felsic felsic phases. phases. Basalts Basalts of mafic phases phases were were erupted erupted from from aa progresprogressively fractionating, fractionating, periodically periodically replenished replenished magma source source of of the the type type O'Hara and Mathews (3), envisaged by O'Hara ( 3 ) , probably probably located located at at the the density density discondisconmarking the boundary between the tinuity marking the crust crust and lithospheric lithospheric upper upper mantle. mantle. Magmas of the the earliest earliest volcanic volcanic sequence sequence underwent underwent simultaneous simultaneous contamination contamination by siliceous, siliceous, depleted depleted material material of of lower lower crustal crustal affinities affinities and and gabbroic gabbroic fractionation with an assimilation/fractional assimilation/fractional crystallization fractionation crystallization (AFC) ( A X ) ratio ratio of 0.4. 0.4. Subsequent Subsequent cycles cycles do not display display AFC—type AFC-type contamination, contamination, suggesting suggesting that a solid basaltic layer layer formed formed at at the the top top of of the the main main tnagmatic magmatic source source body cutting cutting off contact contact with with the the lower lower crust crust (see (see also also 4). 4). Crustal Crustal fusion fusion during during the the mafic phase phase of of each each volcanic volcanic cycle cycle eventually eventually produced so much rhyolitic liquid that basalt magmas magmas no no longer longer passed passed freely freely surface; basalts are uncommon to the surface; uncommon in in felsic phases. When When present present they they predominant contaminant are are invariably invariably highly highly contaminated. contaminated. The predominant contaminant was was derived derived by an an average average of of 20% 20% fusion fusion of of high—LILE, high-LILE, relatively relativelylow—LREE low-LREEleucograriitic leucogranitic upper crustal crustal material material (1), (I), but but low—LILE, low-LILE, high—LREE high-LREE liquids liquids from from low—degree low-degree melting of depleted depleted siliceous siliceous tonalite tonalite at at deeper deeper levels levels were were also also present. present. Resulting Resulting hybrid magmas magmas form form two two mixing mixing lines lines between between basalt basalt compositions compositions and the individual individual rhyolite rhyolite types; types; basalt—rhyolite basalt-rhyolite mixing mixing ratios ratios as as high high as as 40:60 are are common common in in the the central central part part of of the the stratigraphic stratigraphic section. section. During During volcanfc cycle, cycle, rhyolites the final volcanic rhyolites were not erupted, erupted, and and crustal crustal contamination contamination became less less common, common, probably probably because because volcanic volcanic vents, vents, conduits conduits and and feeders feeders had become insulated insulated by marginal marginal chilled chilled zones, zones, as as suggested suggested elsewhere elsewhere (5) (5) The beginning of each each successive successive volcanic volcanic cycle cycle presumably presumably occurred occurred following crustal cooling during the interim, interim, and was was marked by by replenishment replenishment of the main main magma reservoir at depth and renewed renewed mafic volcanic volcanic activity. activity. Initial magmas of each cycle were relatively relatively uncontaminated, uncontaminated, but but compositions compositions of mafic end—members end-members at at any any given given Mg* Mg* became became progressively progressively less less siliceous siliceous and less enriched in in LILE LILE and and LREE LREE with with time. time. For example, example, early early flows flows display display La/Y, Sr/Y, Sr/Y, and Cu/Y Cu/Y ratios ratios of of 0.6, 0.6, 6.0, 6.0, and and 0.8 0.8 respectively, respectively, compared compared to to La/Y, 1.0, 8.0, and 2.0 in central central basalts and 1.2, 15, 15, and and 3.0 3.0 in in late late basalts. basalts. addition, absolute Ti02 content increased In addition, increased from from 0.75 to to over over 1.25%, 1.25%, while while Ti/Zr Ti/Zr ratios ratios gradually gradually rose rose from from 35 35 to to stabilize' stabilize at about 85 in in late late basalts. basalts. Enrichment Enrichment of early early basalts basalts cannot cannot be be attributed attributed to to crustal crustal contamination, contamination, since both Sr and Cu are also enriched in in these these basalts, basalts, while while compositions compositions of both upper and lower crustal crustal contaminants, contaminants, as as reflected reflected by by compositions compositions of the accompanying rhyolites, rhyolites, are highly depleted depleted in in these these components. components. Therefore, Therefore, the the variations variations are are considered considered to to reflect reflect heterogeneity heterogeneity in in the the 1-ithospheric mantle source. lithospheric mantle source. Basalts of the first volcanic volcanic cycle cycle were were composed composed of the most enriched enriched magma magma type. type. This This liquid liquid was subsequently subsequently progressively progressively diluted in the main reservoir reservoir by influx influx of aa new, new, less—enriched less-enriched magma, magma, giving giving rise to a mixing line line between between the the two two types. types. The The original original magma magma was was largely largely flushed from the system system by late late stages stages of Huronian Huronian volcanism volcanism (6). (6). 49 �Both Both basalt types types exhibit exhibit enrichment enrichment in in incompatible incompatible element element abundances, abundances, but but negative negative anomalies anomalies for for the the more more refractive refractive lithophile lithophile elements, elements,including including Nb, mantle—normalized diagrams Nb, P, P, Zr, Zr, and and Ti, Ti, and positive positive anomalies anomalies for for Sr on mantle-normalized diagrams are are features features characteristic characteristic of of islnd islnd arc arc tholeiite tholeiite basalts basalts (2). (2). It It is is suggessuggested that enrichment enrichment of the the Huronian Huronian subcontinental subcontinental lithospheric lithospheric mantle mantle occurred occurred through through ancient ancient subduction subduction of of crustal crustal material, material, probably probably during during formation formation and and consolidation consolidation of of the the continental continental crust. crust. The The Huronian Huronian basalts basalts resemble, resemble, in in both both tectonic tectonic setting setting and and geochemistry, geochemistry, widespread widespread Mesozoic Mesozoic flood flood basalts basalts erupted break—up, including the Farrar Group erupted in in association association with continental continental break-up, of of Antarctica Antarctica (7), (7), and and the the Parana Parana and and equivalent equivalent Etendeka Etendeka continental continentalbasalts basalts of of south south Brazil Brazil and and Namibia Namibia (8, (8, 9) 9) respectively. respectively. References References 1) 1) Jolly, Jolly, W. W. T., T., 1987, 1987, Can. Can. J. J. Earth Earth Sci. Sci. 24, 24, 1360—1385. 1360-1385. 2) W. T., T., 1987, 1987, Earth Earth Planet. Planet. Sci. Sci. Lett. Lett. 85, 85, 401—415. 401-415. 2) Jolly, Jolly, W. 3) and Mathews, Mathews, R. R. E., E., 1981, 1981, J. J. Geol. Geol. Soc. Soc. 3) O'Hara, O'Hara, M. M. J. J. and London London 138, 138, 237—277. 237-277. 4) 4) Huppert, Huppert, H. H. E. E. and and Sparks, Sparks, R. R. S. S. J., J., 1980, 1980, Contr. Contr. Mineral. Mineral. Petrol. Petrol. 75, 75, 279—289. 279-289. 5) 5) Cox, Cox, K. K. G. G. and and Hawkesworth, Hawkesworth, C. C. J., J., 1985, 1985, J. J. Petrol. Petrol. 26, 26, 355—377. 355-377. 6) 6 ) Jolly, Jolly, W. W. T., T., 1988, 1988, Contrib. Contrib. Mineral. Mineral. Petrol. Petrol. (in (in press). press). 7) 7) Kyle, Kyle, P. P. R., R., 1980, 1980, Contrib. Contrib. Mineral. Mineral. Petrol. Petrol. 73, 73, 89—104. 89-104. 8) 8) Petrini, Petrini, R. R. et et al., al., 1987, 1987, J. J. Petrol. Petrol. 28, 28, 701—726. 701-726. 9) 9) Hawkesworth, Hawkesworth, C. C. J. J. et et al., al., 1984, 1984, Nature Nature 311, 311, 331-335. 331-335. 50 �0 8 04 0 0 0 0 E a a 0 N a -J 0 1 0 N N 0 0 0 N E a. 8 0 0 0 C', 0 0 8 8 I', • SSau3uj 51 !UdOJ6!4OJ4S �STRATIGRAPHY STRATIGRAPHY AND AND PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY OF OF THE THE FOOTWALL FOOTWALL ROCKS ROCKS NW ONTARIO ONTARIO TO THE THE STURGEON STURGEON LAKE LAKE MASSIVE MASSIVE SULFIDE SULFIDE DEPOSIT, DEPOSIT. NW TO K. JONGEWAARD, University University of of PETER K. JONGEWAARD, PETER 55812 Minn., 55812 Minn., Minnesota-Duluth, Duluth, Duluth, Minnesota-Duluth, Sturgeon Lake Lake massive massive sulfide sulfide deposit deposit sits sits atop atop aa 66 Sturgeon volcanic and succession of xnafic to felsic succession of mafic to felsic volcanic and volcaniclastic rocks rocks of of the the Savant—Sturgeon Savant-Sturgeon Lake Lake metavolcanic— metavolcanicvolcaniclastic metasedimentary 2.1m.t. m. t. metasedimentary greenstone greenstone belt. belt. The The ore ore deposit deposityielded yielded2.1 of of high—grade high-grade Zn—Cu—Pb—Ag-Au Zn-Cu-Pb-Ag-Au ore ore from from 1974 1974 to to 1980. 1980.Despite Despite regional greenschist greenschist and and local local amphibolite amphibolite grade grade metamorphism metamorphism and and regional variable amounts amounts of of hydrothermal hydrothermal alteration, alteration, seven seven distinct distinct variable volcanic footwall succession. succession. volcanic units units have have been been identified identified in in the the footwall This subdivision subdivision is is based based on on preserved preserved primary primary textures, textures, fragment fragment This types, composition, composition, and and regional regional stratigraphic stratigraphiccorrelation. correlation. types, Mafic km, of of the the Mafic volcanic volcanic rocks rocks comprise comprise the the lowermost lowermost 33 km. footwall succession, succession, and and are are composed composed of of massive, massive, brecciated, brecciated, footwall amygdaloidal, may consist consist of of up up to to amygdaloidal, and and pillowed pillowed flows. flows. Pillows Pillows may 70% 70% rounded rounded amygdules, amygdules, indicative indicative of of shallow shallow water water extrusion. extrusion. The The mafic volcanic volcanic rocks rocks are are overlain overlain by by aa thick thick (1 (1 km.), km.), laterally laterally mafic extensive heterolithic heterolithic breccia, breccia, composed composed of of angular angular lapilli— lapilli- to to extensive block—sized mafic block-sized mafic mafic and and felsic felsic volcanic volcanic fragments fragments set set in in aa mafic matrix. This This breccia breccia is is intercalated intercalated with, with, and and overlain overlain by by aa matrix. quartz—phyric quartz-phyric pumice—bearing pumice-bearing ash—flow ash-flow tuff, tuff, which which reaches reaches aa 150 in. m. This This tuff tuff marks marks the the first first largelargemaximum thickness thickness of of 150 maximum volume eruption eruption of of felsic felsic material material in in the the succession. succession. The The ash— ashvolume flow tuff tuff is succeeded succeeded upward upward by by debris debris flow flow and and bedded bedded is flow epiclastic epiclastic deposits, deposits, which which contain contain fragments fragments of of the the underlying underlying units units as as well well as as bomb—sized bomb-sized juvenile juvenile pumice. pumice. Overlying Overlying the the debris debris flow km. sequence sequence of of massive massive to to bedded bedded flow deposits deposits is is aa thick thick 11 km. ash-flow quartz/plagioclase-phyric ash-flow tuffs. tuffs. Massive Massive quartz- and and quartz/plagioclase—phyric quartz— in thickness, whereas bedded 250m. m. in thickness, whereas bedded units units consist consist units are are up up to to 250 units m. basal basal beds beds composed composed of of crystals, crystals, of normally-graded normally-graded 10—30 10-30 in. of lithic lithic lapilli, lapilli, and and pumice pumice overlain overlain by by thinly—bedded thinly-bedded ash ash units. units. The top top of of this this sequence sequence is is the the immediate immediate host host to to the the Sturgeon Sturgeon The to tuaf Ic Thin Lake massive sulfide sulfide deposit. deposit. Thin axnygdaloidal amygdaloidal mafic to massive Lake intermediate form the the hangingwall hanginwall to intermediate lavas lavas cap the succession succession and. and form to the orebody. The The volcanic volcanic succession succession is is intruded intruded by by intermediate intermediate the orebody. 25% of of the the rocks rocks to mafic mafic sill—like sill-like bodies bodies which which comprise comprise up up to to 25% to in the the area. area. in A major major north—trending north-trending synvolcanic synvolcanic structure structure divides divides the the area of area into into two two distinct distinct stra.tigraphic stratigraphic sequences. sequences. To To the the west west of the the structure, structure, basal mafic flows flows are are overlain overlain by by the the breccia—ash— breccia-ashflow flow tuff—debris tuff-debris flow flow sequence. sequence. East East of of the the structure structure the the basalts basalts are immediately immediately overlain overlain by by fragment—poor fragment-poor ash-flow ash-flow tuffs tuffs which which are thin rapidly rapidly and and pinch pinch out out eastward. eastward. It It is is believed believed this this thin structure represents represents the the eastern eastern topographic topographic margin margin of of the the structure Sturgeon which has has been been traced westward 20 Sturgeon Lake Lake caldera. caldera which westward for for up up to to 20 km. Owing Owing to to unique unique circumstances circumstances of of regional regional deformation deformation and and km. erosion, fill and and outflow outflow facies fades resulting erosion, both intracaldera fill resulting from from caldera caldera collapse collapse can can be be studied studied in indetail. detail. The The km.thick km. thick 52 �A LATE ABCHEAN CLkSTIC SEQUCE — FILL OF A FAULT-BOUNDED BASIN ST1JCTU M.M. Kehlenbeck arid M.M. and B.E. B.E. Seemayer Seemayer Dept. of Dept. of Geology, Geology, Lakehead Lakehead University, University,Thunder ThunderBay, Bay,Ontario OntarioP7B P7B5E1 5E1 - North west of of Thunder Bay, Ontario, Ontario, the of the Thunder Bay, the Archean Archean bedrock bedrock of the North and and west Wawa subprovince includesseveral several exposures exposuresofof cl clastic Wawa subprovi nce includes a s t i csedimentary sedimentaryand and intercalated volcanic form isolated outcrop intercalated volcanicrocks. rocks. These These clastic cl a s t i csequences sequences form outcrop 80km ka long long belt b e l tfrom fromThunder ThunderBay Bay areas l e n t i c u l ashape r shapewhich whichdelineate delineateanan80 areas of of lenticular west to t oShebandowan. Shebandowan. These These rocks are arecommonly commonly designated as as aa younger younger sequence sequence compared compared to to the Archean volcanic and and sedimentary sedimentaryterrane terranew with whichthey theyare arei in contact. i t h which n contact. Archean volcanic the The terms terms "Timiskaming" "Timiskarning" or or post-Keewatin" The "oost-Keewatin" have have been been suggested suggested ffor o r these these clastic Shegeiski, a s t i csequences sequences (?lacdonald, (!4acdonald, 1938; 1938; Shegel ski, 1980). 19SO). In In most most cases cases the the cl designation of on ccertain designation of these these rocks rocksas asaayounger younger sequence sequence iiss based based on ertain lithological similarities Abitibi h establishedTimiskaming Timiskann'ng sstrata t r a t a iin n the the Abi t i bi lithological simi 1a r i t i ewith s w i t established belt (Quebec), and on structural and stratigraphic discontinuities along b e l t (Quebec), and on structural and straticraohic discontinuities along the the contacts wwith i t h "Keewatin' "Keewatin' volcanic volcanic rocks. rocks. contacts More recently Borradaile Brown (1987) (1987) have have used used the term term More recently Borradaileand andBrown "Shebandowan group" r cclastic l a s t i csedimentary sedimentary rocks rocksnear nearShebandowan. Shebandowan. Their Their work work "Shebandowan group"f ofor showst hthat rocks are are iisoclinally s o c l i n a l l yfolded foldedand and that t h a tthe thedeformation deformationwas was shows a t tthe h e rocks accompaniedbybythe thedevelopi'ient development single tectonic and magnetic ffabric. e tectonic and magnetic a b r i c . Based Based accompanied of ofa asing1 on bedding-cleavage relationships, showt hthat the folds, folds, Borraaai l e and and Brown Brown show a t the on beddi ng-cl savage re1 ationships, Borradaile wheretraceable, traceable, have east-west axi axial moderatelyt oto strongly strongly whera have east-west a1 surfaces surf aces and and moderately curved hinge n e s , and and tthat h a t locally the the folds folds developed developed iin n inverted inverted strata. strata. curved hingel ilines, They suggest a t the grouo" i s aist at l e aleast s t partly n ffault a u l t contact contact They suggestt hthat the "Shebandowan "Shebandowan group" partlyi in with w i t h the the adjacent adjacent volcanic volcanicrocks rocks("Keewatin (Yeewatin group"), group"),although although they theywere were unable unable which would wouldpermit permitdocumentation documentation relationship. tto o locate locate exposures exposures which of oft hthis i s relationship. Corfu and from rocks rocks of U-Pb ages ages from Corfu and SStott t o t t (1986) (1986) have have reported reported precise precise U-Pb the Shebandowan Theirr eresults show theclclastic rocks of of the t. Their s u l t s show t h that a t the a s t i c rocks the the Shebandowan be1 belt. a years "Keewatin" "Shebandowan group" "Shebandowan group"are areabout about40 40M Ma yearsyounger youngerthan thanthe the adjacent adjacent "Keewatiri" volcanic rocks. They They suggest r the l a s t i c rocks rocks of of volcanic rocks. suggestthe theage ageofofdeposition depositionf ofor thecclastic Tiniiskaming-type a t at 2 62689Ma. 8 9 2 ~ a . This obtained from a a l alatitic t i t i c breccia breccia Timiskaming—type Thisage agewas was obtained from reDresentativeofof calc-a1 calc-alkaline representative kal i ne to t o alkalic a1 kal i cvolcanic volcanicrocks rockswhich which are are interfingered w i terrestial t h t e r r e s tsediments i a1 sediments suggesting contemporaneous 1ateral ly interfingered laterally with suggesting contemporaneous t e cl a s t fror. from aa volcanism and volcanism andsedimentation. sedimentation.A Aporphyritic porphyritic trondhjeni trondhjemite clast conglomerate which part ofofthe theclastic c l a s tsequence i c sequence formed 2704*2Ma Ma ago ago and and conglomerate which iiss part formed 2704±2 represents age the sequence. sequence.InIn contrast, contrast, an repi-esents a maximum maximum age f o for r d deposition e ~ o s i t i o nofof the an age age of of 273353 from i l l isi a s minimum a minimin age age ffor o r aa sequence sequence ofof older 2733t3 from aa porphyry porphyry ssill older volcanic rocks the north. rocks exposed exposed t to o the 53 �The variety of The clastic clasticsequence sequence is i s composed composed ofof aa variety of rock rocktypes typeswhich which include clastic include sandstone, sandstone, ssiltstone, i l tstone,greywacke, greywacke, arkose, arkose, conglomerate, conglomerate, cl astic volcanic volcanic rocks, iron formation. rocks, and and minor minor occurrences occurrences ofof iron formation. Spatially Spatiallythese these rock rocktypes types are are intimately severaltypes typesoccur occurin in a single intimately associated, associated, and and commonly commonly several single outcrop. outcrop. Because thecomplex complex nature theirdistribution, distribution, iitt isi snot n o possible t possibletot omap map Because ofofthe nature of of their any particular rock distance in in the the field. field. any particular rock type type for any any distance In outcropsthe therecognition recognitionofof bedding beddingi is not difficult. difficult. However, In many many outcrops s not However, iti tisi typical marked in in bedding ito find to find markedvariations variations beddingattitudes a t t i tudesfrom fromone oneoutcrop outcrop s t y ~cal to to another another as as well we1 1 as as inina asingle singleexposure. exposure.These These variations variationsininbedding bedding attitudes separatedbby small faults. faults. attitudesare arecommonly commonly separated y small In sequence, In the the eastern eastern portion portion ofofthe theclastic clastic sequence,bedding beddingofofmore more consistent consistent orientation orientation can can be be traced traced in in several several outcrops. outcrops. Here Here too, local local way—up the strata strata can way-up ofofthe can be be determined determined from from graded graded beds beds and and cross-bedding. cross-bedding. Based onthese theseobservations, observations,the the rocks rocks appear appeart oto indicate indicate aa synformal Based on synformal structure structure although no fold closures observedinin the the ffield. although no closures were were observed ield. In most exposures, but particularly in those where finefine-grained grainedand and In most exoosures, b u t particularly in thosewhere semipelitic semi pel i t i c rocks rocks occur, occur, aacontinuous continuous slaty slatycleavage cleavage isi sobservable. observable. This This cleavage cleavage iiss also also present present in incoarser coarser grained grained rocks rocks where where iti tforms formsan an anastomosing pattern. anastomosi ng pattern. In outcropsofof the the clastic clastic sequence, andparticularly particularly in the In most most outcrops sequence, and the finer rocks, thethe bedding and finergrained, grained,well welllayered layered rocks, bedding andcontinuous continuouscleavage cleavagehave have been folded. In exposuresthis thissmall smallscale scalefolding folding has led to t o the the been folded. In many many exposures has led development chevron folds folds possessing narrow hinge hinge zones zonesand andstraight straight limbs. limbs. development ofof chevron possessing narrow In outcrops,polycl polyclinal hinge In some some outcrops, i nal folds folds with with multiple mu1 tip1 ehinges hingesand and non-parallel non-para1 1 el hinge lines In all lines have have developed. developed. In all cases cases these these noncylindrical noncylindrical folds foldspossess possess aa subvertical subvertical axial axialplanar planarcrenulation crenulationcleavage cleavagewhich which strikes strikesbetween between northeast northeast and northwest. In In general and northwest. general fold fold hinge hinge lines linesplunge plungesteeply steeplynorthward. northward. Although Although the folds folds are arebest bestdeveloped developed in inthe themore more laminated laminated rock rock types, clastic rocks. some unstratified types, they they are are also also present present in the the coarser coarser clastic rocks. InInsome sheets of conglomerate, the individual clasts are buckled into folds sheets of conglomerate, the individual clasts are buckled folds with with angular folds ininthe angular hinges, whereas whereas folds thematrix matrixhave havehinges hingeswhich whichare aremore morerounded. rounded. In one case, refolding refolding of of earlier about north north striking strikingaxial axialsurfaces surfaceshas has one case, earlier folds foldsabout been observed. observed. been Near the contact with of the Near the with the themetavolcanic metavolcanic rocks, rocks, many many outcrops outcrops of the clastic are cut cut by faults. These clasticsequence sequence are by faults. These structures truncate truncate the the small-scale small-scale folds and all earlier and a11 earlierstructures. structures. InIntypical typicaloutcrops outcrops several several faults of of variable patterndividing dividing the outcrop outcrop into into variable orientation orientationproduce produce an an anastomosing anastomosi ng pattern lensoidal portions variation in portions ininwhich whichprevious ?ravious structures structuresshow show marked marked variation in orientation. itI is uncommon near t inot s not uncommon tto o find earlier earlierstructures structuresinin nearorthogonal orthogonal relationships segments.Evidence Evidence faulting is re1 ationshipsbetween between adjacent adjacent fault—bounded faul t-bounded segments. forforfaulting is 54 �particularly particularlypronounced pronounced in rocks rocks of of the the western western part part of of the theclastic c l a s t isequence c sequence along the contact of the contact along the contact with with the thevolcanic volcanicsuccession. succession. Exposures Exposures of contact occur occur here the rocks markeddevelopment development myloniticschistosity. schistosity. mylonitic here and and the rocks show show aa marked of of aa evidence supports a u l t relationship relationship between between the astic Field evidence supportsthe theffault the cl clastic sequence andthe the adjacent adjacent volcanic volcanic terrane. Along sequence and Along the thewestern western and and southern southern margin, outcrops thecontact contactprovide provided idirect evidenceofoffaulting faulting in margin, numerous numerous outcrops of ofthe r e c t evidence in the mylonitic of ffault mylonitic schistosity schistositydeveloped develooed in in the the rocks. rocks. Elsewhere, Elsewhere, zones zones of ault breccia truncations of of regional regional structural structural trends distinctive brecci a and and truncations trends and and di s t i ncti ve lithologies 1i tho1 ogi es reflect ref 1ectthis t h i sdiscordant discordant relationship. re1 a t i onshi p. Internally, the rocks of the Internally, the rocks of theclastic c l a s t isequence c sequence include include aa wide wide variety of types contact with with each other in in individual types which which are are commonly commonly ininf afault u l t contact each other individual outcrops. Abundantsmall smallf afaults greatlyobl obliterate earlier i e r structural structuraland and outcrops. Abundant u l t s greatly i t e r a t e earl stratigraohic relationships. re1 ationships. Collectively Collectivelythese thesefeatures featuresmay may indicate that that the the stratigraphic clastic c l a s t i csequence sequence as as aa whole whole represents represents aa strongly stronglyimbricated imbricateddown—faulted down-faulted block. In addition f a u l t i n s , the the clastic c l a s t i csequence sequence ddiffers i f f e r s structurally addition to tr.e the faulting, from rocks. A north—southstriking striking subvertical subvertical crenulation A north-south crenulation from the metavolcanic metavolcanic rocks. cleavage scale north-plunging north-pl ungi ng folds. folds. The The structures structures cleavage iis s axial axi a1 planar pl anar to t o small small scale fold fold the thecontinuous continuous slaty slatycleavage cleavage as as well as as the the bedding. bedding. This This crenulation crenulation cleavage has not not been observedinin the the adjacent cleavage has been observed adjacent volcanic rocks. rocks. Mesoscopic foldsi in the rocks rocks of of the clastic are rare, nor n the c l a s t i csequence sequence are nor Mesoscopic folds could bedetermined determined from from systematic systematic observations observations of of could such such structures structuresbe bedding—slaty cleavagere1 relationships. beddi ng-sl aty cleavage ationshi ps. The mayreoresent representananooutlier The cclastic l a s t i csequence sequence may u t l i e r of of younger younger rocks rocks in in fault f a u l tcontact contactwith withthe thevolcanic volcanicterrane. terrane.Field Fieldobservations observationstotodate datesuggest suggest that representsthe thef filling sequence as as aa whole whole represents i l l ingofofa afault-bounded fault-bounded that the the clastic cl a s t i csequence basin structure. structure. The The tectonic tectonichistory historyofofthis t h basin i s basin i s complex mayhave have basin is complex andandmay included periods periods of of transtension transtensionand and transpression transpression which which affected affectedthe theArchean Archean included crust regionally regionallyand andclosely closely coincide with boundary betweenthe theQuetico Queticoand and crust coincide with thethe boundary between Wawa subprovi nces. Wawa subprovi nces. Borradaile, G.H., 1987. 1987. The Borradai l e yG.J. G.J. and andBrown, Brown, G.H., The Shebandowan Shebandowan Group: "Timi skami ngGroup: "Timiskaminglike"Archean Archean rocks rocks ininnorthwestern northwestern Ontario. Ontario. Canadian Canadian Journal Journal of of Earth Earth like" Sciences, 24, pp.185—188. 185-188. 24,pp. Corfu, F. and Stott, G.M., 1986. U-Pb Corfu, F. and S t o t t , G.M., 1936. U-Pb ages o r late l a t emagmatism magmatism and and regional regional ages ffor t , Superior SuperiorProvince, Province,Canada. Canada. Canadian Canadi an deformation ininthe theShebandown Shebandown Be1 deformation Belt, Journal pp.1075-1032. 1075-1032. Journal of of Earth EarthSciences, Sciences, 23, 23,pp. Macdonald, R.D., 1938. 1938. Geology Geology of Gorham Township andand vicinity. Ontario Macdonald, R.D., of Gorham Township vicinity. Ontario Department Mines, Annual AnnualReport, Report,v.v.48, 48, part part 3, Department ofof Mines, 3, 18 18 p. p. Shegelski, R.J., R.J., 1980. Shegelski, 1980.Archean Archeencratonization,emergence cratonization,emergenceand andred redbed beddevelopment, development, 1 2 , pp. pp. 331-347. 331-347. Lake Shebandowan Shebandowan area, Canada. Precambrian Lake area, Canada. Precambrian Research, Research, 12, 55 �PROTEROZOIC OVERTHRUST-NAPPE OVERTHRUST-NAJ?PE EVIDENCE FOR DEVELOPMENT OF AN EARLY PROTEROZOIC SYSTEM IN THE PENOKEAN OROGEN OF NORTHERN MICHIGAN KLASNER, J.S., 3.2., Department of Geology, Western Illinois KLASNER, Illinois University U.S. Geological Survey, Survey, Macomb, Macomb, IL IL 61455; 61455; OJAKANGAS, OJAKANGAS, R.W., R.W., and U.S. Department of Geology, University of Minnesota, Duluth Duluth and U.S. Geological Survey, Duluth, Duluth, MN MN 55812; 55812; SCHULZ, K.J., K.J.-, U.S. U.S. GeoloGeological Survey, MS 954, National Center, Reston, VA 22092; 22092; and G.L., Department of Geology, University of Wisconsin, LABERGE, G.L., Oshkosh,and U.S. U.S. Geological Survey, Oskosh, WI 54901 Oshkosh,and 54901 Evidence for development of an Early Proterozoic thrust-nappe thrust-nappe system is found in 1900—Ma 1900-Ma rocks at several localities localities in in northern northern Michigan. At Falls River in in L'Anse, north-verging, recumbently recumbently folded slates and graywackes of the Michigamme Formation Formation have have nearly nearly flat—lying, flat-lying, axial planar foliation (Sikkila, (Sikkila, 1987, 1987, and Sikkila Sikkila and and Gregg, 1987). 1987). About 20 20 km k m south of L'Anse, flat—lying flat-lying Early Early Prot— Proterozoic quartzite occurs occurs at at Canyon Canyon Falls. Falls. The quartzite is is separseparated by thrust faults from from stratigraphically higher slates, slates, phyl— phyllites, and metaqraywackes metagraywackes of the Michigamme Formation at Little 1 ites, and Mountain and Taylor Taylor Mine. Mine. Bedding at Little Mountain and Taylor Mine is overturned toward the north and has steeply south-dipping foliation (see foliation (see Fig. Fig. 1). 1). At Plumbago Creek similar overturned slates slates and phyllites have steep south-dipping foliation foliation that projects projects Archean gneiss. gneiss. A drill-hole about 10 10 km km east of Taylor beneath Archean Mine penetrates Archean gneiss. gneiss. The gneiss has shallow—dipping shallow-dipping penetrative cleavage and is is underlain by graphitic slate slate and and quartquartzite, suggesting that the gneiss was overthrust above the the slate. slate. About 110 km to the the west, west, in in Ironwood, Ironwood, Michigan, Michigan, bedding beddng in in graywacke gr~ywackeand slate slate of of the the Tyler Tyler Formation Formation is is oriented oriented N75 N75 5, E, 70°NW. 70 NW. These rocks have a prominent cleavage that that is is oriented oriented N75°,, 58°NW. broad—scale, north-dipping N75 58 NW. The Tyler are part of a broad-scale, homocline that that formed formed during during the the 1100-Ma 1100-Ma rift rift event. event. The Tyler Tyler strata are overlain overlain by by nearly nearly concordant concordant Keweenawan Keweenawan strata. strata. Reorientation Reorientation of of the the Tyler Tyler to to its its position position prior prior to toKeweenawari Keweenawan deformation shows subhorizontal bedding and gently gently south-dipping south-dipping foliation compatible with a north-verging north-verging thrust-nappe thrust-nappe system. system. Thirty km east of of Ironwood, Ironwood, hyaloc&astitgs hyalocastitgs of of the the Emporer Emporer Formation have have a foliation foliation oriented oriented N30 N30 E, E, 30 30 SE. SE. This shallow shallow south dipping foliation is characteristic of the thrusted Early Proterozoic terrane described above and is is interpreted interpreted to to have have north—verging thrust-nappe thrust—nappe system been formed by the same north-verging system that affected the the Tyler Tyler and and Michigamme Michigamme Formations Formations near near L'Anse. L'Anse. Such evidence for for north—verging north-verging thrust thrust faulting faulting was was previously recognized by Cannon Cannon and and Kiasner Klasner (1972), (19721, Klasner Klasner (1972), (19721, and Klasner Kiasner (1978) (1978) and and was wa interpreted Cannon (1973), (19731, and interpreted as a decollement. The field guide for lement. for this this meeting meeting by by Kiasner Klasner and and others, others, (1988) provides provides additional additional data on the nature of Early (1988) Early Proterozoic Proterozoic overthrusting in northern northern Michigan. Michigan. overthrusting in The data presented above span a distance of well over 100 100 km indicate that that Early Early Proterozoic Proterozoic rocks rocks from Ironwood to L'Anse and indicate 56 �and Archean gneiss of the Penokean orogen in in this region are part of a broad-scale north-vergging north-vergqinq thrust-nappe thrust-nappe system, system, probably probably the the same thrust-nappe system as that described by Hoist Holst (1984), (1984), 300 300 km to the west in in Minnesota. Minnesota. REFERENCES REFERENCES W.F., 1973, The Penokean orogeny in northern Michigan, In Cannon, W.F., In G.M. Young (ed.), GeologG.M. (ed.), Huronian Huronian stratigraphy stratigraphy and and sedimentation: sedimentation: Geological Association of Canada Special Paper 12, 12, p. p. 253-271. 253-271. J.S., 1972, 1972, Guide to Penokean Penokean deformadeformaCannon, W.F. and Klasner, J.S., tional style and regional metamorphism of the Western Marquette In W.I.Rose W.I.Rose (ed.), (ed.), Field description and road road Range, Michigan, In logs: logs: 18th Annual Institute on Lake Superior Superior Geology, Geology, Houghton, Houqhton, Mich., p.B1-B38. p.B1-B38. Mich., Holst, T.B., T.B., 1984, Evidence for nappe development during the Early Proterozoic Penokean Penokean orogeny, orogeny, Minnesota: Minnesota: Geology, v. v. 12, 12, 135-138. p. 135—138. Klasner, J.S., J.S., 1972, Style and sequence of deformation and associated metamorphism due to the Penokean orogeny in the western Marquette Michigan: PhD. dissertation, Michigan Technological Range, northern Michigan: University, Houghton, Mich., 132p. University, Mich., 132p. KLasner, J.S., J.S., 1978, Penokean deformation and associated metamorphism in the western Marquette Range, northern northern Michigan: Michigan: Geological Society Society of America Bulletin, Bulletin, v. v. 89, 89, p. p. 711—722. 711-722. Klasner, J.S., J.S., Sims, A structural traverse ing Early Early Proterozoic R.J. field guide, guide, In K.J. tute on Lake Lake Superior Superior P.R., Gregg, P.K., Gregq, W.J., W.J., and Gallup, Gallup, Christina, Christina, 1988, 1988, across a part of the Penokean orogen illustratillustratoverthrusting in in northern northern Michigan: Michigan: text and and Schulz Schulz (ed.), (ed.), Field Field guides: guides: 34th Annual InstiInstiGeology, Geology, Marquette, Mich. Mich. p. C1—C32. C1-C32. Sikkila, K.M., 1CM., 1987, A structural analysis of Proterozoic metasediments, northern Falls River, River, Baraga Baraga County, County, Michigan: Michigan: Master of of Science Science thesis, thesis, Michigan Technological Technological University, University, Houghton, Houghton, Mich. Mich. 103 p. 103 p. Sikkila, K.M. K.M. and Gregg, Gregg, W.J., W.J., 1987, 1987, A structural analysis analysis of of ProProterozoic metasediments, metasediments, northern Falls River, Baraga Baraqa County, Michv. 33, 33, igan (abs.): (abs.)/: 33rd Annual Institute Institute on Lake Superior Superior Geology, Geology, v. igan part 1, 1, pp. pp. 65—66. 65-66. 57 �2 11111, Mu.j.Iuh. 2. Mint I op lot FIGURE 1. — N20W 3 C.*p, FtIIt 'S. N ¼ BASEMENT — N16°E I I 4 I N III It — I I 4s' a.M tiPS.. t _N2OW ESitulo. Si IKIItStI.. I-. btd Slit0 • Fold ,.., Is 8.Sdiag 5, A, I 67 II II Sd SI Falsil —. l5i tC tot inie.t S $t (sUn kKOI•S F FACIIK ROOILIP 'as i ii CPOflttCTI kk k t ___Sin,ina "It.lAitst I. A structural traverse extending southward from Falls River to Covington Mich. and along highway U.S. 141 illustrating the structural relation between Falls River, Little Mountain, Taylor Mine, Plumbago Creek, Lower hemisphere Canyon Falls, and points southward. illustrate orientalion of bedding (SO), stereoplots foliation (Si), and fold axes in SO (black dots) From Klasner dnd others (1988). along the profile. See text for discussion. pI.mt.go 'S. _N30°E !j — — a a a — — — — — a — — a — a a vs r a Foil, Cise A — N2rE �CHEMOSTRATIGRAPHY OF THE LOHER DIISIOfl LAVAS OF THE MiHAINSE POINT FORMATION fiND IMPLICATIONS FOR RIFTING TECTONICS Kiewin. K l e x i n . K. K . 4. H . ,, aand n d Berg, Berg, University, U n i v e r s i t y , DeKalb, DeKalb, Ii T l J. Northern J.H. H . . , iDepartment 2 e p a r t m e n t oof f Geology, G e o l o ~ : , ~ ,N o r t h e r n I Illinois llinois b115 ball5 Detailed Detailed e a s t e r n shore shore eastern sstudy t u d y oof f eexposures x p o s u r e s of o f the t h e Mamainse M a m a i n s e Point P o i n t Formation F o r m a t i o n along a l o n g the the of o f Lake L a k e Superior S u p e r i o r in i n Ontario O n t a r i o reveals r e v e a l s at a t least l e a s t six s i x recognizable recognizable The (1973). T h e llowermost o w e r m o s t uunit n i t ( (3e ~ 3 @ mm uunits n i t s within w i t h i n the t h e Lower L o w e r Division D i v i s i o n of o f Annells A n n e l l s (1973). thick) consists of olivine—phyric basaltic and picritic flows that are heavily t h i c k ) c o n s i s t s of o l i v i n e - p h y r i c b a s a l t i c and p i c r i t i c f l o w s t h a t a r e h e a v i l y more ddissected i s s e c t e d by b y calcite c a l c i t e veins v e i n s aand n d aappear p p e a r tto o be be m o r e aaltered l t e r e d than t h a n fflows l o w s hhigher i g h e r up up (olivines ( d i v i n e s in i n this t h i s and a n d all a l l other o t h e r units u n i t s are a r e altered a l t e r e d to t o secondary s e c o n d a r y minerals). minerals). This by aa ssecond (28e mm thick) T h i s unit u n i t is i s overlaizi o v e r l a i n by e c o n d uunit n i t (5200 t h i c k ) of o f similar s i m i l a r olivineolivinephyric p h y r i c flows, f l o w s , but b u t without w i t h o u t the t h e uubiquitous b i q u i t o u s ccalcite ' a l c i t e vveins e i n s aand n d aappearing p p e a r i n g tto o be be Near less altered. altered. N e a r the t h e middle m i d d l e of o f this t h i s unit u n i t are a r e two t w o or o r three t h r e e very v e r y mafic m a f i c flows floss The that t h a t are a r e komatiitic k o m a t i i t i c in i n terms terms of o f major—element m a j o r - e l e m e n t chemistry. chemistry. T h e upper u p p e r part p a r t has has several s e v e r a l flows f l o w s that t h a t ccontain o n t a i n small s m a l l iinclusions n c l u s i o n s ((i $ 1 cm) c m j of o f wehrlite s e h r l i t e or o r spinel spinel swehrlit.e e h r l i t e ( (the t h e dolivine i v i n e aand n d ppossible o s s i b l e sspinel p i n e l are a r e altered a l t e r e d to t o secondary s e c o n d a r y mtnerals). m~nisrals:~. Overlying O v e r l y i n g this t h i s is i s the t h e third t h i r d unit, u n i t , the t h e very v e r y distinctive d i s t i n c t i v e "daisy " d a i s y stone" stone" ( 25 m This tthick). hick). T h i s unit u n i t consists c o n s i s t s of o f 2—3 2-3 thin t h i n and a n d one o n e very v e r y thick t h i c k flows f l o s s of' of pplagioclase—phyric l a g i o c l a s e - p h y r i c ferrobasalt f e r r o b a s a l t containing c o n t a i n i n g locally l o c a l l y abundant a b u n d a n t 3—cm 3-cm pla5ioclasa plasiuclass The sspherulites. pherulites. T h e ffourth o u r t h unit u n i t (5øø ($500m m thick) t h i c k ) isi scomposed c o m p o s e dof' o f olivine—phyric oli-jine-phyric Especially bbasaltic a s a l t i c and a n d picritic p i c r i t i c flows. flows. E s p e c i a l l y in i n the t h e lower l o w e r part, p a r t , this t h i s unit u n i t has h a s much much coarser c o a r s e r olivine o l i v i n e phenocrysts p h e n o c r y s t s than t h a n the t h e unit u n i t below b e l o w the t h e daisy d a i s y stone s t o n e unit u n i t < oiiiine oil.-ins Above aa transitior phenocrysts p h e n o c r y s t s in i n both b o t h units u n i t s are a r e typically t y p i c a l l y skeletal). skeletal). Abovs t r a n s i t i o n zone z o n eof' of alternating a l t e r n a t i n g olivine—phyric o l i v i n e - p h y r i c and a n d plagioclase—phyric p l a g i o c l a s e - p h y r i c flows, f l o w s , is i s the t h e t'ifth f i f t h unit unit ('4ø@ This ( - ~ 4 0m @ thick) t h i c k ) consisting c o n s i s t i n g of o f plagioclase-phyric p l a g i o c l a s e - p h y r i c basaltic b a s a l t i c flows. flows. T h i c unit u n i t is is ttopped o p p e d by the t h e uppermost u p p e r m o s t (sixth) ( s i x t h ) unit u n i t (z14•ØØ (2400 ma t thick) h i c k ) cconsisting o n s i s t i n g oof f aaphyric phyric Near N e a r the t h e base b a s e of of this t h i s bbasaltic a s a l t i c flows f l o w s interspersed i n t e r s p e r s e d with w i t h aa few f e w ophitic o p h l t i c basalts. basalts. unit u n i t is i s the t h e "basaltic " b a s a l t i c breccia" b r e c c i a " noted n o t e d by b y Annells A n n e l l s (1973). (1973). Thus T h u s far f a r we we have h a v e analyzed a n a l y z e d flows f l o u s from f r o m the t h e four f o u r oldest o l d e s t units u n i t s and a n d found found major geochemical differences between them. The basal unit is dominated m a j o r g e o c h e m i c a l d i f f e r e n c e s b e t w e e n them. T h e b a s a l u n i t i s d o m i n a t e d by by llow—Ti02 o w - T i 0 2 ((1.ø—1.b 1.0-1. 6 nwt%) t % ) bbasalts a s a l t s aand n d ppicrites, i c r i t e s , bbut u t tthese h e s e aalternate l t e r n a t e llocally o c a l l y uwith ith The high—TiOz h i g h - T i 0 2 (up ( u p to t o 2.'t 2. 4 wwt%) t % ) basalts b a s a l t s and a n d picrites. picrites. T h e second s e c o n d unit u n i t contains c o n t a i n s only only The the t h e low—TiOz l o w - T i 0 2 flows f l o w s with w i t h generally g e n e r a l l y less l e s s altered a l t e r e d chemistry. chemistry. T h e komatiitic komatiitic The mentioned MgO ccontents 18—23 wwt. fflows lows m e n t i o n e d aabove b o v e hhave a v e HgO o n t e n t s oof f 18-23 t%. T h e daisy d a i s y stone s t o n e unit u n i t is is a a very—high—Ti02 v e r y - h i g h - T i 0 2 ferrobasalt, f e r r o b a s a l t , and a n d analyses a n a l y s e s support s u p p o r t an a n accumulation a c c u m u l a t i o n model m o d e l for for The the t h e plagioclase p l a g i o c l a s e spheruljtes. spherulites. T h e oolivine—phyric l i v i n e - p h y r i c flows f l o a s above a b o v e the t h e daisy d a i s y stone stone Figures uunit n i t are a r e high—Ti02 h i g h - T i 0 2 (1.4—2,7 ( 1 . 4-2. 7 wt%) u t % ) basalts b a s a l t s and a n d picrites. picrites. F i g u r e s 1, 1, 2, 2, and . . ~ n d33 sshow h o a that t h a t except e x c e p t for f o r the t h e lowest l o w e s t unit u n i t the t h e other o t h e r units u n i t s have h a v e distinct d i s t i n c t geochemical gsochemical A ccharacteristics h a r a c t e r i s t i c s and a n d trends. trends. A plot p l o t of o f Ti02 T i 0 2 vs. vs. flow f l o w I! (Fig. ( F i g . 2) 2) rreveals e v e a l s some within oof f the t h e systematic s y s t e m a t i c iinternal n t e r n a l vvariation ariation w i t h i n uunits, n i t s , bbut u t aalso l s o tthe h e pprofound r o f o u n d aand nd aabrupt b r u p t changes c h a n g e s between b e t w e e n most m o s t of o f the t h e units. units. These T h e s e field f i e l d and a n d ggeochemical e o c h e m i c a l ccharacteristics h a r a c t e r i s t i c s hhave a v e aallowed l l o w e d uus s tto o ccorrelate orrelate this t h i s main m a i n section s e c t i o n of o f the t h e MPF MPF that t h a t starts s t a r t s at a t Mica M i c a Bay Bay with a i t h the t h e Alona A l o n a Bay Bay secsection MPF based b a s e d on o n reconnaissance r e c o n n a i s s a n c e field f i e l d and a n d compositional c o m p o s i t i o n a l examination e x a m i n a t i o nof' of t i o n of o f the t h e MPF Contrary the t h e Alona A l o n a Bay Bay section. section. C o n t r a r y to t o the t h e speculation s p e c u l a t i o n of o f Annells A n n e l l s (1973), (1q73",the the Alona A l o n a Bay section s e c t i o n starts s t a r t s high h i g h up u p in i n our o u r second s e c o n d unit u n i t (alternatively, ( a l t e r n a t i v e l y , tthe h e first first two t w o units u n i t s are a r e extremely e x t r e m e l y thinned t h i n n e d at a t Alona A l o n a Bay). Bay). IIn n aany n y eevent, v e n t , although a l t h o u g h prepreviously v i o u s l y unrecognized, u n r e c o g n i z e d , the t h e daisy d a i s y stone s t o n e unit u n i t occurs o c c u r s relatively r e l a t i v e l y near n e a rthe t h ebase b a s eof' of the t h e Alona A l o n a Bay section, s e c t i o n , and a n d it i t is i s underlain u n d e r l a i n by by the t h e low—Ti02 l o x - T i O ; olivine—phyric olivine-phyric Rare lavas l a v a s and a n d overlain o v e r l a i n by b y the t h e high—Ti02 h i g h - T i 0 2 olivine—phyric o l i v i n e - p h y r i c lavas. lavas. R a r e small small plagioclase p l a g i o c l a s e spherulites s p h e r u l i t e s are a r e present p r e s e n t in i n the t h e Alone A l o n a Bay Bay daisy d a i s y stone s t o n e unit, u n i t , but but otherwise o t h e r w i s e it i t is i s free f r e e of o f the t h e abundant a b u n d a n t large l a r g e spherulites s p h e r u l i t e s that t h a t characterize c h a r a c t e r i z e the the Mica Bay daisy Mica d a i s y stone. stone. (2a 59 �He He believe b e l i e v e that t h a t the t h e magma magma chemistry c h e m i s t r y of o f these t h e s e primitive p r i m i t i v e la;as. l a ; a s , the t h e prospro;-;rressive e s s i v e changes c h a n g e s in i n magma magma chemistry c h e m i s t r y within s i t h i n each e a c h unit, u n i t , . and a n d the t h e abrupt a b r u p t . changes changes i l l uultimately l t i m a t e l y pprovide r o v i d e iimportant m p o r t a n t sstratigraphically—controlled tratigraphicallv-controlled bbetween e t w e e n uunits n i t s wwill a n s w e r s to t o maflor m a i o r qquestions u e s t i o n s r regarding e g a r d i n g tthe h e ttectonic e c t o n i c ddevelopment. evelo~ment.m a g m a t i c e',.'oiaanswers magmatic evolittion. i o n , mantle m a n t l e structure s t r u c t u r e and a n d dynamics, d y n a m i c s , and a n d crustal c r u s t a l integrity i n t s g r i t y during d u r i n gthe t h eriftirig fifting For pprocess. rocess. F o r example, e x a m p l e , the t h e lowermost l o a e r m o s t unit u n i t contains c o n t a i n s lavas l a v a s that t h a t may have have were very v a r y rich r i c h in in o r i g i n a t e d from f r o m two t w o separate S e p a r a t e mantle m a n t l e sources, s o u r c e s , both b o t h of o f which w h i c h were originated LILE, u t oone n e (producing ( p r o d u c i n g the t h e high—Ti02 h i g h - T i 0 2 lavas) l a v a s ) richer r i c h e r than t h a n the t h e other. other. A lternaLILE, bbut Alternamagmas were were bbeing modified eing m o d i f i e d bby y ccrustal r u s t a l assimilation a s s i m i l a t i o n while while ttively, i v e l y , some s o m e of' o f t the h e magmas others o t h e r s were were not, n o t , or o r at a t least l e a s t less l e s s so. so. D u r i n g the t h e eruption e r u p t i o n of o f the t h e second s e c o n d unit, unit, During o n l y the t h e less—enriched l e s s - e n r i c h e d source s o u r c e was being b e i n g tapped t a p p e d and a n d magmas became b e c a m e progressively progressively only more m o r e primitive. primitive. PPresumably r e s u m a b l y the t h e plumbing p l u m b i n g system s y s t e m was was becoming b e c o m i n g better b e t t e r developed, developed, This aallowing l l o w i n g primitive p r i m i t i v e lavas l a v a s an a n ever—more e v e r - m o r e direct d i r e c t route r o u t e to t o the t h e surface. surface. T his was aabruptly ferrobasalts eepisode p i s o d e was b r u p t l y tterminated e r m i n a t e d bby y the t h e eeruption r u p t i o n oof f hhighly i g h l y eevolved v o l v e d ferrobasalts After fforming o r m i n g the t h e daisy d a i s y stone s t o n e unit. unit. A f t e r oonly n l y 3-4 3-4 eruptions e r u p t i o n s of o f this t h i s highly h i g h l y evolved evolved magma system less magma, aa new new primitive p r i m i t i v e magma s y s t e m took t o o k oover, v e r , erupting e r u p t i n g progressively p r o g r e s s i v e l y less primitive p r i m i t i v e lavas l a v a s ssomewhat o m e w h a t similar s i m i l a r to t o the t h e high—Ti02 h i g h - T i 0 2 laas l a v a s of o f the t h e basal b a s a l unit. unit. Because B e c a u s e it i t appears a p p e a r s difficult, d i f f i c u l t , if i f not n o t impossible, i m p o s s i b l e , to t o relate r e l a t e the t h e three t h r e e magma magma ssystems y s t e m s represented r e p r e s e n t e d by by the t h e flows f l o w s oof f the t h e ddaisy a i s y stone s t o n e and a n d the t h e units u n i t s above a b o v e and arid below, b e l o a , profound p r o f o u n d changes c h a n g e s in i n magma magma sources s o u r c e s arid a n d tthe h e crustal c r u s t a l plumbing p l u m b i n g system s y s t e m must must have h a v e been b e e n taking t a k i n g place p l a c e across a c r o s s this t h i s interval. interval. PPerhaps e r h a p s tthe h e llow—hO: o x - T i O : magma magma source l i t h o s p h e r - i c mantle. mantle. s o u r c e was lithospheric l i t h o s p h e r i c mantle m a n t l e or o r involved i n v o l v e d aa component c o m p o n e n t of o f lithospheric mark time wwhere Its I t s termination t e r m i n a t i o n ccould ould m a r k tthe h e ppoint o i n t iin n time h e r e tthe h e aasthenospheme s t h e n o s p h e r 1 . c diapir diapir This finally f i n a l l y eroded e r o d e d through t h r o u g h to t o the t h e base b a s e of o f the t h e crust. crust. T h i s would w o u l d have h a v e accelerated accelerated rifting r i f t i n g of o f the t h e crust c r u s t and a n d could c o u l d have h a v e resulted r e s u l t e d in i n the t h e disruption d i s r u p t i o nand a n dtapping t a p p i n gat' of crustal c r u s t a l magma magma chambers c h a m b e r s containing c o n t a i n i n g highly h i g h l y evolved e v o l v e d magmas, magmas, thus t h u s forming f o r m i n g the the New evolved e v o l v e d daisy d a i s y stone s t o n e unit, unit. N e w magma magma generation g e n e r a t i o n would w o u l d subsequently s u b s e q u e n t l y be b e derived derived Alternative solely s o l e l y from f r o m the t h e asthenospheric a s t h e n o s p h e r i c subeontinental s u b c o n t i n e n t a l mantle. mantle. A l t e r n a t i v e models m o d e l s are are models i l l be b e ggreatly r e a t l y iimproved m p r o v e d with xith ppossible, o s s i b l e , aand n d tthe h e cconstraints o n s t r a i n t s oon n tthese hese m o d e l s wwill Nevertheless, models Keweenaan iisotopic s o t o p i c results. results. N e v e r t h e l e s s , ddynamic y n a m i c ttectonic ectonic m o d e l s ffor o r tthe he K exeenaiian rrift i f t wwill i l l ddepend e p e n d hheavily e a v i l y oon n aaccurate c c u r a t e aand n d ddetailed e t a i l e d cchemostratigraphic h e m o s t r a t i g r a p h i c studies studies of o f the t h e erupted e r u p t e d lavas. lavas. . REFERENCE REFERENCE The 1973, Annells, .N., 1 9 7 3 , Proterozoic P r o t e r o z o i c flood f l o o d basalts b a s a l t s of' o f eastern e a s t e r n Lake L a k e Superior: Superior: The A n n e l l s , RP.,N,, Gaol. Keweenawan Keweenawan volcanic v o l c a n i c rocks r o c k s of' o f tthe h e Mamainse M a m a i n s e Point P o i n t area, a r e a , Ontario, Ontario, G eol. Surv. S u r v . Canada C a n a d a Paper P a p e r 72—10, 7 2 - 1 0 , 51 51 p. p. FIGURES NOTE FOR FIGURES 1, open Asterisks A s t e r i s k s == uunit n i t 1, o p e n squares s q u a r e s == uunit n i t 2, 2, oopen p e n triangles triangles Some of the unit stone)1 solid squares = s t o n e ) , s o l i d s q u a r e s = u n i t 4. 4. o f t h e samples s a m p l e s from from not n o t been b e e n analyzed a n a l y z e d for f o r chromium. chromium. 60 == unit unit 3 3 (daisy (daisy units u n i t s 1 and a n d 22 have have 1 �Cu 3 2 0 33 5 5P I I 1 0 Fig. a a I 0 3 15 a mu au,. 10 MgO Fig. I a %a 0 xD I 2 20 a 0 25 3 0 0 I 0 I I a. I 0 I Fig. I a 2 1000 CR Fig. 4 I 0 2 1500 — I. •1. JLD 0 1111111 I 500 1 3 2 I 0 80 go 2000 3 70 60 50 40 30 20 10 0 CU 0 -,-1 I— 0 -J IL FLOW # I 0 0.3 0.2 0 Ti02 + n - i W ^ L n r n ^ J C D t D 0 I— WI Cu 0 0 0.1 0.0 Ti02 0 0 0 0 0 0 0 0 0 w �THEBARABOO EARABOO QUARTZITE: OUARTZITE: THE ?,lE?! LOOK LOCK AT ATAN A?! OLD CLDPROBLEM PRO3LE4 A.4NEW GEYE L. L. LABERGE, LABERGE, Geol. Geol. Dept., Dept., UW—Oshkosh, UJ-Oshkosh, Oshkosh, Oshkosh, WI VI and and U.S.G.S. U.S.G.S. and and JOHN JOIIN S. S. GENE KLASNER, Geol.Dept., Dept.,Vestern WesternI Illinois SLASXER, Geol.. l l i n o i sUniv., Univ*,Macomb, Yacomb, IL I Land andU.S.G.S. U.S.G.S. i n c l u d i n g the t h e Baraboo Baraboo c e n t r a l . and and southern s o u t h e r n Wisconsin, Idisconsin, quartzires, q u a r t z i r e s , including InI n central Quartzite, Q u a r t z i t e , represent r e p r e s e n t the t h e southernmost southernmost occurence occurence of of Precambrian Precambrian rocks r o c k s in i n the the Lake Lake Superior S u p e r i o r region, r e g i o n , but but their t h e i r stratigraphic s t r a t i g r a p h i c and and tectonic t e c t o n i c relations r e l a t i o n s to t o the the sedimentary rocks r o c k s of o f the t h e iron i r o n districts d i s t r i c t s to t o the t h e north n o r t h is is uncertain. uncertain. sedimentary Originally, O r i g i n a l l y , the t h e Baraboo Baraboo Quartzite Q u a r t z i t e and and associated a s s o c i a t e d slate, slate, dolomite, dolomite, and and iron— ironwere called c a l l e d "Huronian" "Huronian" and and correlated c o r r e l a t e d with w i t hthe t h eiron—bearing iron-bearing rocks r o c k s of of formation were formation the VanHise Hise and andLLeith, t h eLake Lake Superior S u p e r i o r region r e g i o n(Weidman, (Weidman, 1904; 1904; Van e i t h , 1911; 1911; Leith, L e i t h , and and o t h e r s 1935). 1935). Subsequently, Subsequently, Dalziel Dalziel. and and Dott Dott (1970), (l97O), Smith Smith (1978), ( l 9 7 8 ) , Van Van Schmus Schmus others (1978), (1978), and and Greenberg Greenberg and and Brown Brown (1983, (1983, 1986) 1986) suggested suggested that t h a t the t h e quartzites q u a r t z i t e s in in t h e r e f o r e , substantially substantial.1.y southern southern Wisconsin Idisconsin are are younger younger than t h a n 1,760 l V 7 6 0Ma M a and, and, therefore, Deformation of of younger younger than t h a n the t h e Proterozoic P r o t e r o z o i c sedimentary sedimentary rocks r o c k stot othe t h enorth. n o r t h . Deformation the t h e quartzites q u a r t z i t e s has h a s been been attributed a t t r i b u t e d to t o aa postulated p o s t u l a t e d plate p l a t e tectonic t e c t o n i c event e v e n t that that occurred 1,630 1,630 Ma Ma ago ago and and was was buried buried beneath beneath Paleozoic P a l e o z o i c rocks r o c k s to t o the t h e south south occurred (Smith, 1978; 1978; Dott, D o t t v 1983; 1983; Cambray, Cambray, 1987). 1987). (Smith, Recent ??ecent geologic g e o l o g i c studies s t u d i e s (LaBerge (J4aBerge and and Kiasner, Klasner, 1986, 1986, and and preparation) p r e p a r a t i o n ) in in central c e n t r a l . and and southern s o u t h e r n Wisconsin 14?isconsinsuggest s u g g e s t that t h a t the t h e quartzite q u a r t z i t e occurrences o c c u r r e n c e s in i n this this area a r e a are are older o l d e r than t h a n currently c u r r e n t l y interpreted i n t e r p r e t e d and and that t h a t they they are a r e remnants remnants of of aa major south—vergent south-vergent thrust—fold t h r u s t - f o l d system. system. Our Our studies, s t u d i e s , presented presented below below and and major shown shown in i n Figures F i g u r e s 11 and and 22 suggest s u g g e s t that t h a t the t h e quartzite q u a r t z i t e was was present p r e s e n t and and was was thrust thrust southward and southward before b e f o r e 1,760 1,760 Ma, kv and probably probably before b e f o r e 1,850 1,850Ma. !la. At A t Baraboo, 3arab00, the t h e relation r e l a t i o n of of the t h e quartzite q u a r t z i t e to t o adjacent a d j a c e n t rhyolite r h y o l i t e is is Dal.zie1. and and Dott . D o t t (1970) (1970) suggested suggested that t h a t the t h e quartzite q u a r t z i t e is is problematical. Dalziel problematical. stratgraphically s t r a t g r a p h i c a l l y above, above, and and younger youn'ger than, t h a n , adjacent a d j a c e n trhyol.ite, r h y o l . i t e , which which is is inferred inferred t o be be 1,760 1,760 Ma. ?fa. However, flowever, Stark S t a r k (1930, (1930, 1932) 1932) suggested suggested that t h a t rhyolite r h y o l i t e crops c r o p s out out to on the t h e upturned upturned northern n o r t h e r n limb limb of of the t h e Baraboo 3araboo Syncline, S y n c l i n e , which which indicates i n d i c a t e s that that on t h e quartzite q u a r t z i t e is i s older o l d e r than t h a n the t h e rhyolite. r h y o l i t e . Although Although not n o t unequivocal, unequivocal., our our field fie1.d the A t Hamilton Ramilton Mounds, Younds, the the i n v e s t i g a t i o n s support s u p p o r t Stark's S t a r k ' s (1932) (1932) interpretation. i n t e r p r e t a t i o n . At investigations deformed is intruded i n t r u d e d by by an a n undeformed undeformed granitoid g r a n i t o i d dike d i k e dated dated at a t 1,764 1,764 deformed quartzite q u a r t z i t e is A t Vesper Vesper Ma, Ma, which which indicates i n d i c a t e s pre—1,764 pre-19764 Ma M a deformation deformation of of the t h e quartzite. q u a r t z i t e . At quarry, q u a r r y , quartzite q u a r t z i t e that t h a t has h a s aa steep—dipping steep-dipping tectonic t e c t o n i c fabric f a b r i c occurs o c c u r s within w i t h i n 33 min of of an a n undeformed undeformed granite g r a n i t e that t h a t is i s identical i d e n t i c a l . to t o granite g r a n i t e at a t Cary Cary Mound Yound dated dated at at 1,832 Ma; ?la; we w e infer i n f e r that t h a t the t h e 1,832—Ma 1,832-Ma granite g r a n i t e intruded i n t r u d e d the t h e already a l r e a d y deformed deformed 1,832 . q u a r t z i t e . Along Along Hamann Hamann Creek Creek in i n western western Marathon Farathon County, County, quartzite q u a r t z i t e boulders bou1.ders •quartzite. occur in i n aa conglomerate conglomerate that t h a t is is interbedded interbedded with w i t h 1,850—Ma—old 1,850-?fa-old volcanic v o l c a n i c rocks rocks occur T h i s requires r e q u i r e s the t h e presence presence of of aa 1,850—Ma 1,850-!la quartzite quartzite (LaBerge and and Myers, Hyers, 1983). 1983). This (LaBerge c e n t r a l .Wisconsin. I/isconsin. Sillirnanite—bearing S i l l i m n i t e - b e a r i n g qquartzite u a r t z i t e xenoliths x e n o l i t h sini nthe t hWausau e Vausau central pluton probably probably represent r e p r e s e n tuplifted u p l i f t ehigh—grade d high-grade basement basement rocks r o c k s that t h a t are a r e not not pluton to tunderlie of the the exposed, but but are a r einferred inferred o u n d e r l1,850—Ma—old i e 1,850-Ma-old vvolcanic o l c a n i c rrocks o c k s of exposed, r e g i o n (LaBerge (LaBerge and and Myers, ?fyers, 1984). 1984). region in in Therefore, T h e r e f o r e , the t h e availabl.e availab1.e sstratigraphic t r a t i g r a p h i c evidence evidence indicates i n d i c a t e s that t h a t the the quartzites q u a r t z i t e s in i n central c e n t r a l and and southern s o u t h e r n Wisconsin iscon cons in may be be older o l d e r than t h a n 1,850 1,850 Ma ?la (Figure 1). 1 ) . Thus, Thus, they t h e y appear appear to t o pre—date pre-date the t h e 1,850—Ma 1,850-Ha Penokean Penokean orogeny. orogeny. We ?!e (Figure suggest suggest that t h a t the t h e quartzites q u a r t z i t e s represent r e p r e s e n t remnants remnants of of aa once—extensive once-extensive sequence sequence of of Early Early Proterozoic P r o t e r o z o i c platform p l a t f o r m sedimentary .sedimentary rocks r o c k s deposited d e p o s i t e d on on the t h e passive p a s s i v e margin margin The The exact e x a c t age age of of the the of of an a n Archean Archean craton, c r a t o n , now now exposed exposed in i n central c e n t r a l . Wisconsin. l!isconsin. sedimentary sedimentary rocks rocks is i s unknown, unknown, but, b u t , inasmuch inasmuch as a s they they appear appear to t o pre—date pre-date the the Penokean Penokean Orogeny, Orogeny, they they may may be be roughl.y roughly equivalent e q u i v a l e n t to t o the t h e Marquette I l a r q u e t t e Range Fange Supergroup supergroup of of northern n o r t h e r n Michigan. Yichigan. As A s shown shown in i n Figure F i g u r e 2, 2, the t h e platform ? l a t f o r m sediments sediments 62 �are a r e interpreted i n t e r p r e t e d to t o have have been been thrust t h r u s t southward southward onto onto the t h e Archean Archean craton c r a t o n as a s it it (see collided t h e Wisconsin Visconsin Magmatic ?,lagmaticterrane t e r r a n e (see col.1.ided with the t h e island i s l a n d arc a r c rocks rocks of of the earlier e a r l i e r studies s t u d i e s of of LaBerge, LaBerge, 1986; 1986; LaBerge LaBerge and and others, o t h e r s , 1984a, 1984a, b). b). REFERENCES CITED CITED Cambray, F.W., 1987, The Cambray, F.V., The Baraboo 3araboo Syncline; The The Shape Shape and and Refolding Refolding Explained Explained as as aa Result Result of of Superposition Superposition of of Simple Simple Shear Shear on on aa Pre—Existing Pre-Existing Fold: Fold: Abstract, G. G. S. S. A., A., Minneapolis, Ninneapolis, p. p. 192 192 Abstract, Daiziel, I.V*D., and and Dott, Dott, R.H., R*H., jr. jr. 1970, 1970, Geology Geo1.ogy of of the t h e Baraboo Baraboo District, District, D a l z i e l , I.W.D., Wis.: and Nat. Nat. HHist. Survey IInfor. Circular nfor. C i r c u l a r 14, 14, 164 164 p. p. Idis* : Geol.. Geol.. and i s t . Survey The Proterozoic Proterozoic red red quartzite q u a r t z i t e enigma enigma in i n the t h e north— northDott, R.H., Jr. Jr. 1983, 1983, The Dott, R.H., G. S. A. Memoir Memoir 160. 160. central. United SStates: central. United t a t e s : Resolved by plate p l a t e collision? col.lision? G. S. A. Greenberg, J. K., K., and Brown, Brown, B.A., B-A., 1983, Middle Proterozoic P r o t e r o z o i c to t o Cambrian rocks Greenberg, J. in i n central central. Wisconsin: !$isconsin: Anorogenic Anorogenic sedimentary sedimentary and and igneous igneous activity: a c t i v i t y : Wis. Vis. Geol. Geol.. and and Nat. Hat. Hist. R i s t . Survey Survey Field F i e l d Trip T r i p Guide Guide Book Book No. 80. 8, 8 , 50 50 p. p. Greenberg, J*K., Brown, Brown, B.A., B.A., and and Medaris, Medaris, L.G. L.G. Jr., J r * ,1986, 1986,The TheWol.f Wolf River River Greenberg, J.K., Batholith 32ndAnnual. Annual. Inst. Inst. GuidebookField F i e l d Trip T r i p1,1,32nd B a t h o l i t h and and Baraboo Baraboo Interval: I n t e r v a l : Guidebook on Lake Superior Geology, b!isconsin Rapids. Rapids. Ge01.ogy , Wisconsin LaBerge, La3erge, G.L., G*L., 1986, 1986, The Proterozoic P r o t e r o z o i c Geology of of the t h e Lake Superior Region. Eegion. in 50th Annual Annual. Tn—State T r i - S t a t e Fiel.d Fie1 d LaBerge, G.L. G. L. and and Mode, Xode, 'I.N., !!.!I., Guidebook. Guidebook. 50th Conference. Conference. LaBerge, 1985, Evidence for f o r a major south—directed south-directed LaBerge, G.L., G.L., and Klasner, Kl.asner, J.S., J.S., 1986, Early G. Ear1.y Proterozoic P r o t e r o z o i c thrust t h r u s t sheet s h e e t in i n south south central central. Wisconsin: Visconsin: Abstract, A b s t r a c t , G. S. A. A. San San Antonio, Antonio, TX. TX. S. LaBerge, LaBerge, G.L., G.L*, and and Klasner, Klasner, J.S. J.S. (in ( i n preparation), p r e p a r a t i o n ) , Major Ikijor south south directed directed thrusting t h r u s t i n g of of Early Early Proterozoic P r o t e r o z o i c quartzites q u a r t z i t e s in i n south southcentral. central. Wisconsin: !!isconsin: Implications I m p l i c a t i o n s of of the t h e Penokean Penokean Orogeny. Orogeny. LaBerge, La9erge, G.L., G.L., and and Myers, Myers, P.E., P.E., 1983, 1983, The Precambrian b e c a m b r i a n geology geology of Marathon County, Vis. : Wis. Vis. Geol. Geol.. and and Nat. Hat. lUst. Hist. Survey Survey Info. Info. Circular C i r c u l a r 45, 45, 83p. 83p. County, Wis.: LaBerge, Myers, P.E., P.E., 1984, Proterozoic successions in LaBerge, G.L., G.L., and Myers, 1984, Two eearly arly P r o t e r o z o i c successions in . central c e n t r a l Wisconsin b!isconsin and and their t h e i r tectonic t e c t o n i c significance: s i g n i f i c a n c e : G. G. S. S. A. A. Bull. Full.. pp. pp. 246-253. 246—253. LaBerge, Myers, P.E., ?*E., 1984a, 1984a, The plate p l a t e tectonic tectonic LaBerge, G.L., G.L., Schulz, S c h u l . ~IC.J., ,K.J., and Myers, history Wisconsin: Abstract. h i s t o r y of of central central. IJisconsin: Abstract. 30th Annual Inst. I n s t . on Lake Superior Superior Geology, Geology, Wausau, Wausau, p. p. 25—27. 25-27. LaBerge, J., Myers, P.E., P.E., 1984b, Proterozoic Plate K. J *, and Myers, 1984b, "Early "Early P roterozoic P late G.L., Schulz, Schulz, K. LaBerge, G.L., Tectonics: G. S. S. A. A. Reno,NV. Reno ,NIT. Tectonics: Evidence Evidence from from north n o r t h central c e n t r a l . Wisconsin,"Abst. W i s c o n s i n ,"Abst C. Leith, Pre—Cambrian rocks of L e i t h , C.K., C.K., Lund, Lund, R.J., R.J., and Leith, L e i t h , AA.* 1935. 1935. Pre-Cambrian of the t h e Lake Superior region, region, with revised r e v i s e d geologic geologic maps. maps. U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper 184. 134. Smith, E.I., E.I., 1978, 1978, Precambrian Precambrian Rhyolites Rhyolites and and Granites G r a n i t e s in i n South—Central. South-Central. Smith, Wisconsin: IJisconsin: Field F i e l d Relations R e l a t i o n s and and Geochemistry: Geochemistry: Geological. GeoI.ogica1. Society S o c i e t y of of America Bulletin, B u l l e t i n , vol. vol. 89, 89, pp. pp. 875—890. 875-890. Stark, J. T., T., 1930, 1930, Pre—Cambrian Pre-Cambrian water—laid water-].aid tuff t u f f in i n the t h e Baraboo, 3arab00, Wisconsin, Wisconsin, S t a r k , J. District.: District.: Jour. Jour. Geol., Geol.., Vol. Vol. 38, 38, pp. pp. 466—471. 466-471. Stark, District, Wisconsin: !$isconsin: Jour. Jour. 1932, Igneous Igneous rocks rocks in i n the t h e Baraboo Baraboo District, S t a r k , J.T., J-T., 1932, Geol., Geol*, Vol. Vol.. 40, 40, pp. pp. 119—139 119-139 W.R., 1978, 1978, Geochronology of of southern southern Wisconsin Visconsin rhyolites r h y o l i t e s and and Van Schmus, Schmus, W.R., Van granites; p. 19—24. 19-24. Val* 2, 2 , p. g r a n i t e s ; Geoscience Geoscience Wisconsin, Visconsin, Vol.. Van Hise, use, C.R., C.R*, and and Leith, L e i t h , C.K., C.K., 1911, 1911, Geology Geology of of the t h e Lake Lake Superior ' s u p e r i o r Region. Region. U.S. U.S. Geological GeologicaT Survey Survey Monograph Konograph 52. 52. Weidman, The Baraboo Iron-Eearing Iron—Bearing District District of of V!isconsin Wisconsin: Wisconsin : :*!isconsin Weidman, S., S., 1904, 1904, .=The X i i i , 190 190 p. p Geological. and Natural. Natural Ristory History Survey Survey B Bulletin No. Xiii, GeoI.ogica1. and u l l e t i n ?To. . . 63 �__________________________________ }40 TOUATEO. ItLiUANITE.aEARIN6 QUAflT2I1 C RIB MOUNTAIN XENOUTN IN 500 MA SYENITE NAT iNTRUOBS GI1EENS0WST.ACBS I 130 MA VCS.CAMCS. PRE—1,850 Ma • - :? ... . 4.—'. .. .•-—', '. VO1.C.5N OUARTZITE PRE.OATES lOSE MA. OEFCRME0O.LAR1E ERREO 100* INTRUOEO BY U9OEFCRM*0 I5MARO VESPER QUARRY GAAMTL PRE—1,832 Ma JARTZITE AND DEFORMATION PRE-QATES 1332MA. OEFGRMEOQUM1TE INT.J0E0 BY 1154 MA . ' . INTERBEDOED WITH OEFORMED 1550 MA ° PRE-1,850 Ma • • METMIORPSW 10 SIWMANITE GRAOE PRIOR 10 1550 MA. aNR1 BA0EPS 19 CGI.C*.IERATE NAMANN CREEK L...._ — O.MR1'ZrTE OEPOSITEO AIO : -- GRAMTE. HAMILTON MOUNDS : ••-4- PRE—1,764 Ma CUAR1ZITE AND OEFORMATION PQE.OAT3 1704 MA. —Y..•.,.•_'• OEFCRMEO OUARTZTTE IS STRATIGRAP,.IICAIY 8ARABOO SYNCLINE 5*1.0W UNOEFOI1MED hOE MA YOJTE. CUANTZIT* AND OSFORMATION PRE.OATES PRE—1,76o Ma 1760M& Figure Figure 1. 1 . Location Locationmap map and and a-ge age rrelationships e l a t i o n s h i p s of o f quartzites quartzites in in central c e n t r a land andsouthern southernWisconsin. Wisconsin. QUARTZITES OF OF SOUTHERN SOUTHERN WISCONSIN WISCONSIN QUARTZITES RAEO BE A ARAB 00O Y NC N C LINE LINE SSY NECEDAH N E C E D A H HAMILTON HAMILTON MOUNDS MOUNDS QUARRY QUARRY VESPER VESPER HAMANN HAMANN QUARRY Q U A R R Y CREEK CREEK RIB MOUNTAIN MOUNTAIN I— 44'4 4AA 4. 4 A 4 1754 MA A 4 4 ARCHEAN ARCHEAN I.\ g 1532 MA 4 CONTINENTAL CONTINENTAL FORELAND - FORELAND EAU EAU PLEINE P L E I N E FAULT F A U L TZONE ZONE ACCRETED ACCRETED VOLCANIC VOLCANIC TERRAINE Figure 2. 2 . Diagramatic Djagramat,!~cross—section c r o s s - s e c t i o n of o f the the proposed proposed tectonic tectonic Figure r e l a t i o n s h i p s ofo fthe t h esouthern southernWisconsin Wisconsin quartzites. quartzites. relationships 64 �PALEOMAGNETISM O F THE TH3CLAY-HOWELLS CUY-HOmLLS CARBONATITE CAFBONATITEAND ANDKEWEENAWAN KE-ENAWAN MOTION ON PALEOMAGNETISM OF MOTION THE KSZ LewchukI M.T.# SymonsI D . T . A a I Department of Lewchuk, M.T., and Symons, D.T.A., of GeologyI Geology, University of Windsor, Windsort Windsor, Windsort Ontario, OntarioI Canada Canada N9B N9B 3P4 3P4 The Clay-Howells Clay-Howelis Complex is of i s llocated o c a t e d approximately 130 km eeast a s t of HearstI Ontario, Ontario, at a t 49950'N, 4 9  ° 5 0 ' ~82°05'W 8 2 O 0 5 ' ~within tthe he n o r t h end of h e Kapuskasing Hearst, north of tthe It (KSZ) of the t h e Superior Superior Province Province of of the t h e Canadian Canadian Shield. Shield. It S t r u c t u r a l Zone (KSZ) Structural i s a large l a r g e aviform 'U6 km2 km2 that t h a t i s composed composed dominantly dominantly of of syenite syenite is oviform pluton of "16 with with minor minor carbonatite. c a r b o n a t i t e . It I t was emplaced into i n t o an an Archean gneissic g n e i s s i c terrain terrain of of the t h e amphibolite a m p h i h l i t e to t o granulite g r a n u l i t e facies f a c i e s with with Middle Middle Precambrian Precambrian diabase diabase dikes. dikes. The complex is age (Rb/Sr 107216 Ma) n age The complex i s Late Precambrian iin (Flb/Sr 1072516 Ma) with w i t h aa relatively relatively fresh texture. f r e s h unmetamorphosed unmetamorphosed t e x t u r e . Field F i e l d and and geophysical geophysical ddata a t a iindicate n d i c a t e tthat h a t the the is complex wasprobably probablyformed formedbybyt hthe passive iintrusion complex was e passive n t r u s i o n of of several s e v e r a magmatic l magmatic pulses l a t e fault f a u l t may cut c u t the t h e northeast n o r t h e a s t corner p u l s e s with with similar s i m i l a r compositions. compositions. A late of the t h e complex. complex. Detailed of 194 Detailed AF and and thermal demagnetization of 194 specimens specimens from 21 sites sites (18 from from tthe h e iintrusion, n t r u s i o n , two from from the t h e dikes d i k e s and and one one from from the t h e host h o s t gneisses) gneisses) was completed completed using using aa CTF CTF cryogenic cryogenic magnetometer magnetometer in i n aa shielded shielded room. room. The The 18 1 8 syenite s y e n i t e sites s i t e s define d e f i n e aa consistent c o n s i s t e n t unit u n i t mean mean direction d i r e c t i o n of of 294.2°, 294.2O, 27.1° ( N == 18, 18, kk == 26,ccg5 2 6 , a g ~== 7.0) which which yields y i e l d s aa pole p o l e position p o s i t i o n of of l78.8°E, 178.8O~~ 27.1' (N 26.5°N (D == 4.1, 26.5O~ (Dp 4.11 Dm Dm == 7.6) for f o r the t h e Clay—Howells Clay-Howells Complex. Complex. AA rudimentary rudimentary contact c o n t a c t test t e s t with with the t h e three t h r e e Archean Archean ssites i t e s proved proved inconclusive. The The sscatter catter of of the t h e site s i t emeans means about about the t h e unit u n i tmean mean direction d i r e c t i o n does does not not indicate i n d i c a t e aageographgeographical alongt hthe i f any any -- did d i d not not i c a l bias b i a sso sothat t h apost—intrusive t p o s t - i n t r u s i v e movement movement along e ffault a u l t -- if produce tilting rotations. produce t i l t i n g r o t a t i o n s . The concordant concordantwith w i t hthe t h eapparent apparentpolar p o l a rwander wander The ppole o l e ffor o r the t h e intrusion i n t r u s i o nisi s path rocks of of Palmer p a t h for f o rKeweenawan Keweenawan rocks Palmer and Davis (1987). (1987). It It plots p l o t sat a tapproxapproximately 107510Ma on the the Logan Logan Loop Loop which. which is i s in i n agreement agreement w i t h the t h e Rb/Sr Rb/Sr age age 1075210~aon with of l072t16 i s that that 1072216 Ma Ma for f o r the t h e Clay—Howells Clay-Howells Complex. Complex. Therefore Therefore the t h e conclusion conclusion is the Its concordant pole pole t h e complex records r e c o r d s an untilted, u n t i l t e d f primary primary remanence. remanence. Its s i g n i f i c a n t uplift u p l i f t or o r rotation r o t a t i o n of of the t h e KSZ KSZ indicates i n d i c a t e s that t h a t there t h e r e has has been been no significant since since the t h e intrusion i n t r u s i o n of the t h e Clay—Howells Clay-Howells Complex Complex and and that that all a l l significant significant geotectonic geotectonic activity a c t i v i t y on on the t h e KSZ KSZ m.ust must ppredate r e d a t e l072tl6Ma. 1072216Ma. 65 �Geology, Structure and Mineralization Geology, Structure Mineralization of the the Reany Reany Lake Lake Area, Area, Marquette Marquette County, County,Michigan Michigan Marv L. L. MacLellan MacLellan and and Theodore Theodore J. Bornhorst Bornhorst (Department (Department of Geology and GeoMary of Geology and Geological Engineering, Engineering, Michigan Michigan Technological Technological University, University, Houghton, I-Ioughton, Michigan Michigan 49931) 49931) logical During mi2 area area of of the theMarquette MarquetteGreenstone GreenstoneBelt Belt During the the summer summer of of 1987 1987 aa 55 mi2 was was mapped mapped at at aascale scaleofof1:6000. 1:6000. This Thisarea areaincludes includesSection Section 36, 36,T49N, T49N.R27W, R27W, Section Section 31, 31, T49N, T49N, R26W, R26W, Section Section 1, 1, T48N, T48N, R27W, R27W, and and Sections Sections 6,7, 6,7, T48N, T48N.R26W. R26W. The The Reany Reany Lake Lake Area Area isis outlined outlined in in Figure Figure11below. below. 1 SI Figure 1.1. Figure Regional Regional geology geology and and location location map map of of the Reany Reany Lake Lake area. area. the 100 icc K.. This This study study was was undertaken undertaken in in order order to to extend extend detailed detailed mapping mapping of of the the northern northern Marquette Marquette Greenstone Greenstone Belt Belt to to the theeast. east.Previous Previousdetailed detailed mapping mapping has has been 1985),Johnson Johnson been done done to tothe thewest westofofthis thisarea areabybyOwens Owensand andBornhorst Bornhorst(ILSG (ILSG1985), et.al. of the units et.al. (ILSG (ILSG 1987) 1987) and and Baxter Baxter et.al. et.al. (ILSG (ILSG 1987). 1987). Nomenclature Nomenclature of units isis still still in in aaprocess process of of evolution evolution but but has has been been retained retained from from one one study study to to the the next next asas much much as as possible. possible. Figure Figure 22 shows shows the the stratigraphic stratigraphic correlation correlation of of the theunits units identified identified in in the the Reany Reany Lake Lake area. area. The The majority majority of of the thearea areaisiscomposed composed of of Archean Archean pillowed pillowed basalts basalts interbedded interbedded with two two mudflow mudflow breccias breccias and and an aniron iron formation formation and and intruded intruded by by Archean Archean gabbro gabbro and and rhyolite rhyolite dikes. dikes. Mapping Mapping in in this this area area extends extends nearly nearly 2000' 2000' lower lower into into the thesection section than thanprevious previousdetailed detailedstudies studiesdue due to to the thepinch pinchOut outofofa downfaulted a downfaultedblock blockofofMichigamme MichigammeFormation. Formation. With With the the exception exception of of the thelower lower breccia breccia member member and andthe thebottom bottomseveral several thousand thousand feet feet of of pillowed pillowed basalt, basalt, the the majority majority of ofthe theArchean Archeanvolcanics volcanics and and intrusives intrusives can can clearly clearly be be correlated correlated to the the west. west. This This isis especially especially true of of the theIron Iron Formation Formation Member Member and and the the Breccia Breccia Member Member of of Reany Reany Lake Lake which which persist, persist, relarelatively tively unchanged, unchanged, for up up to to four four miles miles totothe thewest westofofthis thisarea area(Owens (Owensand and 66 �Bornhorst, ILSG upper part part of of Bornhorst, ILSG 1985, 1985, Baxter Baxteret,al., et.al., ILSG ILSG 1987). 1987).Other Otherunits unitsinin the the upper Archean sequence vary in character. character. To the the west, west, the Archean sequence can can also also be be traced traced but but they they vary there To the there appears appears to be be aa greater greater number number of of recognizable recognizable pillow pillow structures. structures. To the west, there there is aa greater greater amount amount of of quartz quartz and and carbonate carbonate alteration alteration whereas whereas in the west, in the Reany Lake Lake area area sericite sericite and and chlorite chloriteare arecommon. common. Owens Owens and andBornhorst Bornhorst (ILSG (ILSG Reany 1985) mapped Laminated Schist Member, Member, composed composed of laminated phyllitic phyllitic and and 1985) mapped aa Laminated of laminated schistose volcanics, the Altered, Altered, and and Foliated Foliated Basalt Basalt schistose volcanics,this this isis now now correlated correlated with with the Varieties of the Pillowed Pillowed Basalt Basalt Member. Member. The Reany Lake area area includes includes aa lower lower Varieties of the The Reany breccia unit stratigraphically below called the breccia unit stratigraphically belowdetailed detailedstudies stuaiestotothe the west. west. ItIt is is called Breccia Member Bismark Creek, polymictic breccia lies along a major major Breccia Member of of Bismark Creek, a polymictic breccia which which lies NW-SE trendingshear shear zone. zone.This Thisunit unit isis truncated truncated by by gabbro and itit is uncertain NW-SE trending gabbro and uncertain whether to the west whether it continues continues to west of of the the Reany Reany Lake Lake area. area. The Archean Archean volcanic volcanic and intrusive intrusive rocks rocks are are unconformably unconformably overlain overlain by the the Reany this unit is Reany Creek Creek Formation, Formation, this is discussed discussed in detail detail by by Small Small and and Bornhorst Bornhorst (ILSG 1988).To Tothe the south south of of the the Reany Formation isis an an upfaulted block of of (ILSG 1988). Reany Creek Creek Formation upfaulted block highly basalts and and rhyolites rhyolites which which pinches pinches out out to highly foliated foliated Archean Archean pillowed pillowed basalts to the the west. The uncertain. The overlain by by slates slates of the the west. The relative relative age age is is uncertain. The entire entire area area is overlain Michigamme Michigamme Formation. Formation. All All of the the preceding preceding units units have have been been Cut cut by by Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan diabase dikes. dikes. All pre-Keweenawan pre-Keweenawan rocks rocks have have been been metamorphosed metamorphosed to to greenschist greenschist facies. facies. The Archean and is near Archean units units typically typically have have aa foliation foliation which which strikes strikes N70°W N70° and near vertical vertical to steeply steeply north dipping. dipping. The The gabbro gabbro and and rhyolite rhyolite dikes dikescommonly commonly parallel parallel this trend. generationsofof faults faults are are evident evident in in the trend. Several Several generations the Reany Reany Lake Lake area. area. The The older (Archean) faults tend tend to parallel the trend (Archean) faults parallel the trend of foliation foliation and and are are quite quite continuous. They 10-100 foot wide zones zones of very high high foliation foliation continuous. They are are marked marked by by 10-100 foot wide of very and abundant The older older faults faults are are frequently truncated or or off-set abundant alteration. alteration. The frequently truncated off-set by by later (Archean (Archean but possible possible reactivated reactivated during during the the Lower Lower Proterozoic). Proterozoic). N-S trending faults. These These younger younger faults faults are are reflected reflected by by 10-50 trending faults. 10-50 foot wide wide zones zones of of moderate to strong moderate to strong foliation foliation and and are frequently frequently marked marked by by distinct distinct ravines. ravines. Evidence favoring precious precious metal metal mineralization mineralizationinin the the Reany Evidence favoring Reany Lake Lake area area appears appears to be be less less abundant abundant than than totothe thewest. west.Mineralization Mineralization occurs occurs primarily primarily as as disseminated sulfides within altered disseminated sulfides altered Country country rocks. rocks. There There are arevery veryfew fewquartz— quartzcarbonate-sulphide veinswhich whichare are abundant abundantinin the the areas areas to the carbonate-sulphide veins the west. west. MineralizMineralization is is most most abundant abundant adjacent adjacent to to the the major major NW-SE NW-SE trending trending shear shear zones zones and and next next to or or within within the therhyolite rhyolitedikes. dikes.Metallic Metallic minerals minerals generally generally consist consist of of disseminated disseminated pyrite and and widely widely scattered scatteredchalcopyrite. chalcopyrite. This project project was was funded funded by by the theMichigan MichiganGeological Geological Survey Survey and and Michigan Michigan Technological University. University. 67 �__ tnfr4u vii I I CoieIaion cf MaØ kit$ Sodimen* Sediment, ond Volcanici Mlconb and Peroean Orogeny JLeuutv otecoic xnlq Xms }li kI L_ J Fault .kcM.i&a..sr I*1 U— lAd lAy I IMl Fot Aif j IAI IAmbi Keweenawan Diabase Diabase Keweenawan ;:sIq Michigame Formation Formation (Slates/Quartzites) (~lates/~uartzites 1 Xms/q Michigamme Reany Creek Creek Formation Formation Reany Yd AXa AXa AXs AXs AXb AXb s r Agr Ar Ag A9 %? Aga Abr Art Art 2: Apb Aba Ab f Abf Ai f Aif Amf Amf Amb Axnb Undifferentiated Undifferentiated Slates Slates Basal Conglomerate Basal Conglomerate Granodiorite of of-Rockin Chair Lakes Lakes Granodiorite Rocking Chair Intrus~veof of Fire $ire Center Center Mine Mine Rh o l ~ t eIntrusive Rhyolite ~ a g b r oof of Clark Clark Creek Cr=ek Gabbro Altered Variety Var~ety Altered Undifferentiated Foliated Foliated Pillowed Basalt Undifferentiated Highly Foliated Foliated Rhyolite Rhyolite Pillowed Basalt Highly Volcanics of of Silver Silver Mine Mine Lakes Lakes Volcanics Pillowed Basalt Basalt Member Member Pillowed Altered Basalt Basalt Variety Variet Altered A$tered and and Foliated ~ o y i a t e dBasalt Basalt Hi hly Altered Highly jormatlon Member Member Iron Formation Iron Breccia Member Member of of Reany Reany Lake Lake Breccia Breccia Member Member of of Bismark Bismark Creek Creek Breccia and Rhyolite Rhyolite and Variety Variety Figure 2. 2. Stratigraphic Stratigraphic Correlation Correlation chart chart for for the the Figure Reany Lake Lake area. area. Reany 68 �ASUBMERSIBLE SUBMERSIl3LEDWE DIVE ON ON SUPERIOR SUPERIOR SHOALS: SHOALS: PLANS PLANSAND AND PROSPECTS PROSPECTS A M.L.Manson & & H.C.Halls, H.C.Halls, Dept. Dept. of of Geology, Geology, University University of of Toronto, Toronto, Erindale ErindaleCampus, Campus, M.L.Manson Mississauga, Ontario, Canada L5L L5L1C6 lC6 Mississauga, Areview reviewisisgiven givenof ofaaplanned plannedGeological Geologicaland andGeophysical Geophysicalstudy study of of the the Superior SuperiorShoals, Shoals,Lake Lake A Superiorundertaken undertakenas aspart partof ofthe theJuly July 1988 1988Great Great Lakes Lakes Manned Manned Submersible SubmersibleProgram Program(NOAA (NOAA Superior National Underwater Underwater Research Research Program). Dives are are to tobe becarried carriedout outusing using aa NOAA NOAA 2600 2600 ftft National Program). Dives submersible for for the the purpose purpose of of orientated orientated sample samplecollection collection with, with, ititisishoped, hoped,supplementary supplementary submersible dredge sampling sampling and and photography tethered ROy, ROV, over over aa period period of of one one to to one one and and aa dredge photography from fromaa tethered A concurrent series of side scan sonar and ship-borne magnetometer surveys will half days. half days. A concurrent series of side scan sonar and ship-borne magnetometer surveys will provide important bathymetric and geological data. provide important bathymetric and geological data. The Superior Superior Shoals Shoals lie lie at at the theintersection intersection of of the theIsle IsleRoyale Royaleand andThiel Thielfaults faultsand and occur occur The about half way along the Trans-Superior Tectonic Zone defmed to the north by the Slate about half way along the Trans-Superior Tectonic Zone defined to the north by the Slate Islands crypto-explosion structure and a line of intrusive alkaline complexes. The shoals are Islands crypto-explosion structure line of intrusive alkaline complexes. The shoals are known from fromprevious previous dredging dredgingand andbathymetric bathymetric work work to to consist consistof of aa northern northern ridge ridge of of red red and and known grey sandstones sandstones and and aa southerly southerly one one composed composed of of amygdaloidal amygdaloidal basalt. Theselithologies lithologiesare are grey basalt. These consistent with with Middle Middle to to Upper Upper Keweenawan Keweenawan volcanic The shoals shoals consistent volcanic and and clastic clastic assemblages. assemblages. The 60kilometer kilometerradius radiusininLake LakeSuperior. Superior. representthe theonly onlyoutcrop outcropof ofthese theserocks rockswithin withinaa60 represent be; Priorities of the project will Priorities of the project will be; 1. To To further further understanding understanding of of the the stratigraphy stratigraphy and and structure structure of of the the eastern easternLake LakeSuperior superior 1. Basin, particularly in relation to the Trans-Superior Tectonic Zone and to recently acquired Basin, particularly in relation to the Trans-Superior Tectonic Zone and to recently acquired GLIMPCEseismic seismicreflection reflectionprofiles. profiles. GLIMPCE 2. To Toinvestigate investigateanomalous anomalouspalaeomagnetic palaeomagnetic signatures signatures suggested suggested from from crudely crudely orientated orientated 2. chips collected collected previously previously by surface scuba scuba dive. Data gained gained from from these these suggest suggest aa reversed reversed chips by surface dive. Data magnetisationfor forthe theKeweenawan Keweenawanvolcanics volcanicswith withaacurious curiousoverprint overprintof ofunknown unknownorigin originwhich which magnetisation may be be due duetotoreheating reheatingeffects effects(due (duetotointrusions intrusionsorortotooverlying overlyingnormally normallymagnetised magnetisedflows flows may similar to to those those on on Isle IsleRoyale) Royale) or ormay maybe berelated relatedtotothe theSlate SlateIslands Islandsexplosive explosive event. event. AA similar will be be aimed aimed atatresolving resolving these these questions questions and and will will further further further program program of of collection collection will further knowledge of Keweenawan faulting, alkaline complexes and diatremes in the area. knowledge of Keweenawan faulting, alkaline complexes and diatremes in the area. 3. To Tostudy studyaspects aspectsofofnative nativecopper coppermineralisation mineralisationreported reported (Kirkham (Kirkham& &Franldin Franklin1981) 1981) 3. from samples dredged by the 1980 Cousteau expedition and models of basin wide fluid motion. from samples dredged by the 1980 Cousteau expedition and models of basin wide fluid motion. Workwill willbe bedone donein in co-operation co-operationwith withR.V. R.V. Kirkham Kirkham& &J.M. J.M. Franidin, Franklin,Geological GeologicalSurvey Surveyof of Work Canada (copper mineralisation, M o c k geology), J. Klasner, Western Illinois University (rock Canada (copper mineralisation, bedrock geology), J. Kiasner, Western fflinois University (rock fabric),and andW.C. W.C. Kelly, Kelly,University U~versity of Michigan Michigan(metamorphic (metamorphicphase phaseequilibria, equilibria,fluid fluidinclusions inclusions fabric), of and stable stableisotope). isotope). and Finally, an an overview overview of ofthe themechanical mechanicalproblems problemsof ofunderwater, underwater,remote remoteoriented orientedsample sample Finally, collection will willbe be given. given. collection 69 �COMPARISON OF OF TWO TWO PARTS PAFiTS OF OF COMPARISON THE DEAD DEAD RIVER-ISHPEMING RIVER-ISHPEMING GREENSTONE GREENSTONE BELT: BELT: THE EVIDENCE EVIDENCE FOR FOR CORRELATION CORRELATION OF OF VOLCANIC VOLCANIC STRATIGRAPHY STRATIGRAPHY by by G. W. Norby, Norby, G. Bradford Bradford Margeson, Margeson, John John W. Robert A. A. Brozdowski, Brozdowski, Alan Alan S. S e Carter, Carter, Bruce Bruce A. A. Bouley Bouley Robert CALLAHAN CALLAHAN MINING MINING CORPORATION CORPORATION EXPLORATION EXPLORATION DEPARTMENT DEPARTMENT 25 25 Industrial Industrial Park Park Road Road Negaunee, 49866 Negaunee, Michigan Michigan 49866 Detailed Detailed geologic geologic mapping mapping by by Callahan Callahan Mining Mining Corporation Corporation in in the the Dead Dead River-Ishpeming River-Ishpeming Greenstone Greenstone Belt Belt has has shown shown similarities similarities in in volcanic—sedimentary volcanic-sedimentary stratigraphy stratigraphy and and intrusive intrusive events events between between I ) the the west west end end of of the the south south arm arm of of the the belt, belt, and and 2) 2) the the south south 1) half half of of the the north north arm arm of of the the belt. belt. The The west west end end of of the the south south arm arm of of the the belt belt comprises, comprises, from from WNW to to ESE, ESE, aa consistently consistently southeastward-facing southeastward-facing sequence sequence of of 1) 1) WNW pillowed to to massive massive basalt, basalt, subordinate subordinate basalt basalt tuff, tuff, associated associated pillowed hypabyssal hypabyssal gabbroic gabbroic sills sills and and dikes, dikes, and and minor minor mafic mafic graywackes; graywackes; dacite tuff, and porphyritic interlayered basalt, 2) a zone of interlayered basalt, dacite tuff, and porphyritic zone of a 2) hypabyssal 3 ) dacite dacite tuff, tuff, which which hosts hosts aa discondisconhypabyssal dacite dacite sills; sills;3) tinuous trend trend of of banded banded quartz—magnetite quartz-magnetite iron iron formation formation and and tinuous quartzose quartzose graywacke; graywacke; 4) 4) volcanic volcanic conglomerates conglomerates and and tuff tuff breccias. breccias. Fine grained grained serpentinized serpentinized peridotite peridotite strikes strikes northeast northeast and and cuts cuts Fine AA the the overall overall mafic mafic to to felsic felsic transition transition at at an an acute acute angle. angle. northeast trending trending line line of of granitoid granitoid plugs plugs intrudes intrudes the the above above northeast mafic section. section. The The extreme extreme northwest northwest and and west west parts parts of of the the mafic basalt section, section, in in proximity proximity to to the the bounding bounding granitoid granitoid terrane, terrane, basalt is is at at amphibolite amphibolite facies, facies, the the remainder remainder of of the the above above section section is is at at greenschist greenschist facies. facies. The The south south half half of of the the north north arm arm of of the the belt belt comprises, comprises, from from 1) north to to south, south, aa consistently consistently south south facing facing sequence sequence of of 1) north pillowed pillowed basalt, basalt, subordinate subordinate basalt basalt tuff, tuff, and and hypabyssal hypabyssal gabbroic gabbroic 2) aa zone zone of of interlayered interlayered basalt, basalt, mafic mafic graywacke, graywacke, sills; 2) sills; hypabyssal porphyritic porphyritic dacite dacite intrusions intrusions transitional transitional to to dacite dacite hypabyssal trend quartz—magnetite tuff, and and aa discontinuous discontinuous trend of of quartz-magnetite iron iron tuff, 3 ) dacite dacite tuff tuff and and porphyritic porphyritic hypabyssal hypabyssal dacite dacite formation; 3) formation; intrusions. An An east east trending trending line line of of granitoid granitoid plugs plugs intrudes intrudes intrusions. The northernmost part of the basalt the mafic mafic section. section. The northernmost part of the basalt section section the is is at at amphibolite amphibolite facies, facies, the the more more southerly southerly part part of of this this arm arm is is at at greenschist greenschist facies. facies. The The data data suggests suggests that that the the above above two two sequences sequences have have similar similar volcanic—sedimentary volcanic-sedimentary rock rock successions, successions, intrusive intrusive events, events, facing facing Although gradients. metamorphic directions, and and metamorphic gradients. Although minor minor directions, two sequences, differences exist exist between between the the two sequences, the the strong strong differences It is similarities suggest suggest aa common common heritage. heritage. is proposed proposed that that similarities separated sequences presently spatially these two two presently spatially separated sequences of of Archean Archean these rocks were were originally originally on—strike on-strike parts parts of of the the same same terrane terrane which which rocks has by opening opening of of the the early early has been been separated separated and and somewhat somewhat rotated rotated by Proterozoic Proterozoic Dead Dead River River Basin. Basin. 70 �Comparison Comparison of of the the Keweenaw Keweenaw and and Gregory Gregory Rifts Rifts from from the the Study Study of of Teleseismic Teleseismic Delay Delay Times Times and and Bouguer Bouguer Gravity Gravity R.P. R.P. Meyer Meyer and and W.V. W.V. Green, Green, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Wisconsin-Madison Wisconsin-Madison Parameters Parameters that that can can be be equally equally well well studied studied in in aa billion-year-old billion-year-old rift and and an an active active modern modern continental continental rift rift are are the the focus focus of of an an ongoing ongoing rift study in in the the midcontinent midcontinent Keweenaw Keweenaw rift rift in in the the vicinity vicinity of of the the PettyPettystudy Ray Ray profile profile northwest northwest of of Minneapolis Minneapolis and and in in the the Gregory Gregory rift rift in in the the region region of of greatest greatest uplift, uplift7northeast northeast of of Nairobi, Nairobi,Kenya. Kenya. The The parameters parameters being being used used are are teleseismic teleseismic delay delay times times of of near-vertically-arriving near-vertically-arriving waves waves from from distant distant earthquakes earthquakes and and Bouguer Bouguergravity. gravity. The The data data show show that that the the slope slope of of the the regression regression of of delay delay time time on on Bouguer Bouguer anomalies anomalies is is five five times times as as steep steep for for African African data data as as for for midcontinent midcontinentdata. data. Why Why are are the the seismic milligal so so much much greater greater in inAfrica? Africa? We seismic delays delays per per milligal We believe believe that that the the answer answer lies lies in in the the existence existence of of partial partial melt melt underlying underlying the the active active rift. rift. Further, Further, in in the the Keweenaw Keweenaw rift rift we we find find that that the the slope slope of of the the regression regression of of delay delay times times on on Bouguer Bouguer anomalies anomalies is is typical typical of of other other older older tectonic tectonic features, features*such suchas as the the Sierra SierraNevada. Nevada. Other significant significant results results are are that that these these rifts rifts are are asymmetric asymmetric Other features features consistent consistent with with aa model model employing employing alternating alternatinghalf-grabens. half-grabens. We We find find this this at at the the Gregory Gregory rift, rift*and and note note that that GLIMPCE GLIMPCE and and other other seismic seismic profile profile data data across across Lake Lake Superior Superior also also support support an an alternating alternating half-graben half-grabenKeweenaw Keweenawrift riftmodel. model. We We also also find find as as much much variation variation in in delay delay time time along along the the Gregory Gregoryrift riftas asacross acrossit. it. 7]. �SUPERIOR MAF' MAP SHEET, BEDROCK GEOLOGY GEOLOGY OF OF THE THE SWERIOR SHEET, WISCONSIN M.G. M.G. Mudrey, Mudrey, Jr., and and B.A. B.A. Brown, Brown, Wisconsin Geological Geological and and Natural Natural History History Survey, 3817 Mineral Point 53705, (in Survey, 3817 Mineral Point Road, Road, Madison, Madison, WI WI 53705, {in cooperation cooperation with the the U.S. Geological Survey) U.S. Geological Survey) ABSTRACT ABSTRACT Reconnaissance Reconnaissance mapping, examination examination of of newly acquired acquired drill drill core, core, and and reanalysis of geophysical data in northwestern Wisconsin is preliminary reanalysis is in U.S. Geological Survey as part of of the COGEOMAP the COGEOIYAP progress in in cooperation with the U.S. Initial work has resulted in a new new preliminary preliminary 1:250,000 bedrock bedrock Initial work program. program. units on the do not differ differ geologic geologic map. map. The The broad lithologic lithologic units the new map do significantly from those on previous maps; however, the relationship relationship and significantly Archean metavolcanic metavolcanic rock, significance rock, significance of of the the various various units units has has changed. changed. Archean granite, southwest trending trending belt south south of the Gogebic Gogebic granite, and gneiss occupy a southwest The southeast southeast corner of the corner of the map sheet is is underlain by Early Proterozoic Proterozoic Range. Range. The metasedimentary metasedimentary rock, rock, mafic mafic to to intermediate intermediate volcanic volcanic rock, rock,and and iron ironformation. formation. The Proterozoic succession succession on the Gogebic Range which is The Early Proterozoic the Gogebic is probably contemporaneous age with the rock to the southeast southeast in the Mercer Butternut contemporaneous in age area Proterozoic Keweenawan area is is in in turn turn unconformably unconformably overlain by Middle Proterozoic of the tectonic tectonic setting setting of the volcanic reevaluation of the upper Keweenawan volcanic rock. rock. AA reevaluation sedimentary separate presentation at this sedimentary rock rock succession succession is is discussed discussed in in a separate this meeting (A.B. (A.B. Dickas Dickas and and M.G. M.G. Mudrey, Mudrey, Jr.). Jr.). meeting unconformity between the The regional mconfomity the Chocolay Group (represented (represented on the Gogebic Range Range by the Menominee Group Group west Gogebic the Bad River Dolomite) and the the Menominee (represented (represented by the the Palms, Palms, Ironwood Ironwood and and Tyler Tyler Formations) Formations) is is confirmed, confirmed, suggesting suggesting regional regional folding, folding, uplift uplift and and erosion erosion during during the the Early Early Proterozoic; Proterozoic; the regional ite and and the regional unconformity unconformity between between the the basal basal Keweenawan Keweenawan Bessemer Bessemer Quartz Quartzite the the Tyler Tyler Formation Formation indicates indicates deformation, deformation, uplift and erosion prior to to Subsequently, the the units were tilted tilted to to the the north deposition of deposition of the the Bessemer. Bessemer. Subsequently, into the the Lake Lake Superior Superior syncline. syncline. into Future work will concentrate on establishing the relationship relationship between the Future the tectonic history of of the Proterozoic rock of the Gogebic Gogebic Range Range and that in tectonic the Early Proterozoic southeast corner corner of the area, south south of the intervening block block of Archean the southeast of this project is to better map map the Archean rock and rock. rock. An additional goal of the relationship relationship between the granitegreenstone granite—greenstone terrane south of Hurley clarify the and the and the gneiss gneiss exposed exposed further further to to the the southwest. southwest. 72 �MIDCONTINENT RIFT RIFTMODEL MODEL BASED BASEDUPON UPON MIDCONTINENT GREGORY AND SEDIMENTATION SEDIMENTATION GEOMETRIES GEOMETRIES GREGORY RIFT RIFT TECTONIC TECTONIC AND M.G. M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geologicaland andNatural Natural History HistorySurvey, Survey, 3817 3817 Mineral Mineral Point Point Road, Road, Madison, Madison, WI WI 53705, 53705, and and WI 54880 54880 A.B. Dickas, Dickas, University University of of Wisconsin—Superior, Wisconsin-Superior, Superior, Superior, WI A.B. ABSTRACT ABSTRACT Middle Middle Proterozoic Proterozoic tepetate—type tepetate-type sedimentation sedimentation growth growth geometries geometries on on aa major major scale scale have have been been identified identifiedwithin within the theMidcontinent MidcontinentRift Rift System System from from Lake Lake Superior Superior reflection reflection profiles profiles (GLIMPCE), (GLIMPCE), on—shore on-shore Wisconsin Wisconsin drill drill core core (Bear (Bear Creek Creek Mining MiningCo.), Co.), and and outcrop outcropanalysis. analysis. These These geometries geometries are are in in the the form form of of structurally structurally independent independent basins basins in listric movement movement along along axially—oriented axially-orientedfault fault in which which differential differential listric systems systems have have created created sedimentation sedimentation wedges wedges of of alternating alternating isopach isopach polarity. Within the the area area of of study study from from northwestern northwestern Wisconsin Wisconsin into into polarity. Within the the eastern eastern sector sector of of Lake Lake Superior Superior this this regional regional geologic geologic setting setting appears appears to to be be structurally structurally similar similar to to that that reported reported along along the the Gregory Gregory Rift Rift of of Kenya, Kenya,Africa. Africa. Midcontinent Midcontinent Rift Rift tectonic tectonic models models published published since since 1956 1956 have have emphasized emphasized aa centrally centrallypositioned positionedhorst horst bounded boundedby by parallel parallelfaults faults within within aabroader broadergraben grabenor orrift. rift. These Thesesystems systemsformed formedin inthe theinner inner border border of of flanking flankingasymmetric asymmetricbasins basinsof ofsedimentation. sedimentation. Fault Fault throws throws were were implied impliedto to have have been been equivalent equivalent resulting resulting in in supra—horst supra-horst sedimentation both parallel parallel and and sedimentationpackages packages of of similar similar thickness, thickness, both perpendicular to the rift axis. perpendicular to the rift axis. New analysis of New analysis of core, core, particularly particularly depth depth constraints constraints associated associated Orontostrata strataand andpre—Oronto pre-Orontoage agevolcanic volcanicrock, rock, principallywith with Oronto principally permits series of of permits the the portrayal portrayal of of the the Midcontinent Midcontinent rift rift trend trend as as aa series sub—basins sub-basins separated separated by by "accommodation "accommodationzones." zones." Three Three identified identified sub—basins sub-basins are are believed believed to to have have developed developed independently independently in in the the study study area area in in response response to to rift rift stress stress and and fault fault movements movements of of contrasting contrasting magnitude. magnitude. This This resulted resulted in in sedimentation sedimentationisopach isopachpolarities polaritiesthat that are are symmetric symmetricparallel, parallel, but but asymmetric asymmetricperpendicular, perpendicular,totothe therift rift axis. axis. From From west west to to east east these thesepolarity polarity orientations orientationsare aresouth southinin Bayfield Bayfield County, County,Wisconsin Wisconsin (Brule (BruleBasin), Basin), north northonshore onshoreand andoffshore offshore Ontonagon, Ontonagon,Michigan Michigan(Ontonagon (OntonagonBasin), Basin), and andsouth southoffshore offshoreMarquette, Marquette, Michigan Michigan(Manitou (ManitouBasin). Basin). AA fourth fourthbasin basin (Cariboo (Cariboo Basin) Basin) is is located located southeast southeast of of the the Manitou Manitou Basin, Basin, but but is is poorly poorly defined defined from from geologic geologic and and geophysical geophysicalconstraints. constraints. The Theaccommodation accommodationzones zones are are generally generally situated of fluctuating fluctuating sedimentation sedimentation patterns patterns and and situated within within the the region region of are arespecifically specificallyidentified identifiedby byoffsetting offsettingBouguer Bouguergravity gravitypatterns. patterns. Although Although this this Middle Middle Proterozoic Proterozoicmodel model may may not not be be representative representative of 20to to40 40m.y. m.y. developmental developmentalhistory historyofofthe theentire entire ofthe theentire entire20 length lengthof ofthe theMidcontinent MidcontinentRift Rift System, System,it itdoes doesencourage encouragedevelopment development of ofnew new models models pertinent pertinent to to rift rift evolution evolution and and the the discovery discovery of of associated associatedbase—metal base-metaland andhydrocarbon hydrocarbonresources. resources. 73 �COMPARISON AFRICANAND AND MIDCONTINENT RIFT ELEMENTS1 COMPARISON EAST EAST AFRICAN ELEMENT ELEMENT AFRICAN AFRICAN MODEL MODEL U.S. MODEL U.S. MODEL SYSTEM SYSTEM EAST AFRICAN EAST AFRICAN RIFT RIFT MIDCONTINENT RIFT RIFT MIDCONTINENT BRANCH BRANCH EASTERN EASTERN WESTERN WESTERN MID-MICHIGAN GRAVITY HIGH2 MID—MICHIGAN GRAVITY HIGH2 MID-CONTINENT GRAVITY GRAVITY HIGH2 HIGH2 ZONE ZONE CRRROUY (KENYA) (KENYA) GREGORY 500—700 500-700 km km STEFANIE (CHOW BAHIR) T.AKK SUPERIOR3 STIPRRTOR3 LAKE CENTRAL IOWA3 NORTHEASTERN KANSAS3 SOUTHERN MICHIGAW in length in length TANGANYIKA USNO—OMO—KIBISH UNIT4 UNITq 80—160 km 80-160 km in length in length L/W ratio ratio 2—4/1 L/W 2-4/1 TURKANA TURKANA SUGATA SUGATA BARINGO—BOGORIA5 BARINGO-BOGORIAS NAKURA—NAIVASHA5 NAKURA-NAIVASHA5 MAGADI-NATRON5 MAGAD I-NATRONS MANITOU ONTONAGON ONTONAGON BRULE BRULE CARIBOU CARIBOU BLOCK8 BLOCK6 width 10 km width 10kin L/W ratio ratio 4—10/1 4-10/1 RECOGNIZED RECOGNIZED RECOGNIZED RECOGNIZED - --------------- 'After rift rift Scale 1After Scale classification classification by by Rosendahi Rosendahl (1987). (1987). The The architectural elements should should be considered typical, typical, rather rather than architectural correlative, examples. correlative, examples. 2Known principally principally as as geophysical geophysical entity 3After 3After Dickas Dickas (1986) (1986) 4Fundainental rift building building block block 4Fundamental rift Keisler (1986) 5After =After Bosworth, Bosworth, Lambiase Lambiase and and Keisler (1986) 6lnfrastructure of rift 8Infrastructure of rift units units References Cited: References Cited: Bosworth, William, Joseph, and and Keisler, Keisler, Ron, Ron, 1986, Bosworth, William, Lainbiase, Lambiase, Joseph, 1986, AA new new look look at at Gregory's Rift: The The structural structural style style of of continental continental rifting: rifting: EOS, EOS, v. v. 67, 67, no. 29, 29, p. p. 577—582, 577-582, 583. 583. Dickas, A.B., A.B., 1986, Seismologic analysis of arrested stage stage development of Dickas, 1986, Seismologic the Midcontinent Midcontinent Rift: Geoscience 11, p p. v. 11, . 45—52. 45-52. the Geoscience Wisconsin, Wisconsin, v. Rosendahi, B.R., B.R., 1987, rifts with with special Rosendahl, 1987, Architecture of continental rifts reference Earth and Planetary reference to East Africa: Annual Reviews of Earth Science, v. 15, 15, p. p. 445—503. 445-503. Science, v. 74 �Isle Isle Royale Royale Flexure Flexure \ D ! ! - 4' Apostle LAKE L A K E SUPERIOR SUPERIOR —4 Ui Keween Detachment Douglas Douglas ,' hite Pine ~lexurei' I 4T ] 1 I I I / / I S F I DEPOCENTER AXIS DEPOCENTER AXIS DETACHMEN DETACHMENT 1 FAULT FAUp FLEXURE Fm p""nw 3 1 MANITOU BASIN 2 Lake Owen Detachment KM Flexure CARIBOU BASIN BASIN 50 0 ] ONTONAGON BASIN - I1 I BRULE BASIN PRE—RIFT ROCK RE-RIFTROCK SCHEMATIC -CHEMATlC CROSS CROSSSECTION SECTION I WESTERN LAKE LAKESUPERIOR SUPERIOR STRUCTURE STRUCTURE 1 �DEVELOPMENT DEVELOPMENT OF OF THE MIDCONTINENT MIDCONTINENT FUFT RIFT IN THE THE LAKE LAKE SUPERIOR SUPEFUOR REGION: FLEGION: PETROLOGIC AND A N D GEOCHEMICAL GEOCHEMICAL C O N S T U I N T S FOR MODEL CONSTRAINTS FOR A A TECTONIC MODEL S.W. Nicholson, Dept. ofofGeology, Geology, University u a i v d t y of Minnesota, Minneapolis, Minneaph, Minnesota 55455 55455 =ti and the US. Geological U.S. GeologicalSurvey, Survey,MS MS 954, 954, Reston, k t o a , Va. Va. 22092 22092 3.B.Paces, Paces, Dept. of ~ e o land o g yaGeological d Geologica~ hgineahg, Michigan TechnologicalUniversity, u a i v d t y ,Houghton, Houghton, J.B. Dept. of Geology Engineering, Michigan Technological Michigan Michigan49931 49931 W.F. U.S.UGeological Survey, MS W.F.Cannon, Cannon, S . Geological Survey, MS911, 911.Restou, Raton, Va. Va. 22092 22092 and isotopic isotopic data with Integration of new geochemical geochemical and with new new geophysical geophysical and geochronological data data for western Lake Superior provides an excellent opportunity opportunity to develop a tectonic and magmatic magmatic model model for for the the evolution evolution of of the the Midcontinent Midcontinent rift. Basalt Basaltcompositions compositionsbecame became more more primitive primitive as as the therift riftevolved, evolved,which whichsugsuggests that the theextent extentofofcrustal crustalattenuation attenuationinfluenced influencedthe the.composition composition of of the the volcanic rocks rocks that were were erupted. erupted. basaltic rocks rocks exhibited exhibited a broad variation in As the Midcontinent rift evolved, basaltic through quartz tholeiites composition, ranging from olivine through tholeiites [1,2]. [1,2]. This This discussion discussion focus on on the the North Shore volcanic group group in in Minnesota Minnesota and and the Portage will focus Portage Lake Lake volcanic for which which the most v o l c ~ group cgroup in Michigan for most complete complete chemical chemical and and isotopic isotopic data data have have been been compiled. compiled. The The older older North North Shore Shorebasalts basdts generally generallydisplay display more more chemically evolved evolved compositions compositions (Mg# (Mg# 2 440—55), showingenrichment enrichment in incomQ-551, showing patible patible trace traceelements elements[1,3]. [1,3]. Younger Younger basalts, including including most of of the the Portage PortageLake Lake volcanic group group [5] [5] and and some of of the North volcanic North Shore Shorebasalts basalts[1,2], [1,2],are areless-evolved less-evolved olivinetholeiites tholeiites(Mg# (Mg 2 65-70 65—70and andhigh highcompatible compatibletrace-element trace-element abundances). abundances). olivine The most primitive The primitive tholeiites tholeiites occur at the the top top of of the the Portage PortageLake Lakesection section and and repflood baalts basalts in the rift. Chemical resent the youngest flood Chemicalvariations variations among among basalts baalts can be attributed attributed largely largely to to crystal crystal fractionation fractionation in subcrustal subcrustal to to intracrustal intracrustal which were weresubject subject to to replenishment, replenishment, periodic periodic tapping, tapping, crustal magma chambers, which contamination, contamination,and and minor minor variations variationsin inparent parentmagma magmacomposition composition[4,51. [4,5]. Nearly one hundred Nd Nd isotopic isotopic analyses have been obtained obtained for for rocks rocks from from the North the North Shore Shore[3,6] [3,6] and the the Portage PortageLake Lake[5,7] [5,7] volcanic volcaaic groups. Despite Despite chemical values at at 1100 1100 Ma Ma cluster cluster about 0 (Fig. cal variations G a t i o n s among the the basalts, basalts,the theENd C N values ~ (Fig. 1)[3,6,8,9]. The range of values for basalts from the North Shore is from about -9 1)[3,6,8,9]. range d u e s basalts from the North Shore is from about—9 whereasbasalts basalts from from the the Portage Lake to +3.5 [3,61, [3,6], whereas Lake group group show show aa more more narrow narrow to +1.4 +1.4 [5,7]. range of values, from about —2 -2 to [5,7]. However, However, the strong strong clustering clusteringof of values around 0 implies implies that that most most of the basalts values around baalts in in the thewestern westernLake Lake Superior Superior region were derived derived from from aa similax similar mantle mantle source. source. The region were The wide wide range rangeininenriched enriched isotopic compositions for for North North Shore basalts suggests some crustal contarninasuggests some crustal contamination [10]. [lo]. The more restricted restricted composition composition of of the Portage Portage Lake Lake basalts basalts suggests suggests less involvementofofaacrustal crustal component. component. Within the Portage less involvement Portage Lake Lake group, group, the the 76 �amount of crustal component component decreases decreases upsection upsection and and virtually virtually disappears disappears dur[51. Strongly enriched Nd C N values values ~ at 1I00 Ma Maofof—13 -13 ing the the latest lateststages stagesofofrifting rifting[51. at 1100 to —16 -16 obtained Portage Lake Lake areas areas obtained for for some somerhyolites rhyolitesin inthe the North North Shore Shore and and the Portage [6,8] melting of of Archean Archean crust did did occur occur locally. locally. However, However, [6,81indicate indicatethat that partial melting rhyolites show show isotopic compositions similar basalts, which which most rhyolites similar to to those of of the basalts, suggests derivation from a similar source to that of of the thebasalts basalts[8]. [8]. reflection profiles profiles suggest suggest that that In western Lake Lake Superior, GLIMPCE GLIMPCE seismic seismic reflection the main main depositional depositional basin basin of of the the rift rift was was confined confined between between two major faults, faults, Fault on the north and the Kewmaw-Lake Keweenaw-Lake Owen Fault the Isle Isle Royale-Douglas byale-Douglas Fault Inthis thisarea, area,subsidence subsidence along dong the rift axis axis accommodated up to 30 30 on the south. In km of rift-related volcanics volcanics and sediments. sediments. The The Portage Portage Lake Lake volcanic volcanic group group in in Michigan, which which are are the the youngest youngest rift-related rift-related flood floodbasalts, basalts, lies lieswithin within this this major depositional basin. basin. However, However, the North North Shore Shore volcanic volcanic group in Minnesota Minnesota lies lies within basin (about (about 5 km deep) deep) to the northwest northwest of of the Isle Isle within a broad broad shallow shallow basin Royale-DouglasFault. Fault. This shallow basin probably probably developed during the early Royale-Douglas shailow basin developed during early stages of volcanicrocks rocksoccur occuratatthe the base base of of the North of rifting (reverse-polarity (reverse-polaxity volcanic Shore group), group), but was active at least least until until major major subsidence subsidence occurred along dong the the rift axis. axis. Hence, Hence, the North North Shore Shore and and Portage Portage Lake Lake volcanic volcanic groups were not emplaced in the same structural structural setting. setting. Integration of of these these data leads model: In the early early stages stages Integration leads to to the the following following model: of rifting, rifting, thick continental crust impeded of impeded the rapid ascent ascent of of basaltic basaltic magma magma and permitted permitted magma magma interaction interaction with with walirock. wallrock. Early Early basalts basdts preserve preserve chemical and isotopic of fractional fractional crystailization crystallization aand isotopic evidence of d ccrustal m t d assimilation assimilation enroute enroute to the plate extension, the surface. surface. As As the thecrust crustthinned thinnedduring duringcontinued continued.plate extension, magma magma established, and magmas that ascended conduits became established, ascended more rapidly had had less less opportunity opportunity for for crustal crustalinteraction. interaction.Younger Youngerbasalts basaltsshow show more more primitive primitive compocompoor isotopic isotopic evidence evidenceofofcrustal crustalcontamination. contamination. The The basin sitions and less cchemical h e m i d or in which the North North Shore Shore group group resides resides is underlain underlain by by continental crust crust which which was thinned no more than to GLIMPCE data; comthan aa few few kilometers, kilometers, according to compositions of the North Shore rocks reflect reflectsome somecrustal crustalcontamination. contamination. In Shore volcanic rocks In contrast, contrast, the the Portage PortageLake Lake group group lies at the the edge edge of of the major depositional basin beneath which which the crust crust was was greatly greatly thinned thinned or orperhaps perhapscompletely completelyseparated sepaated dikes and a d sills sills [11]. [ll].The The compositions compositions of the the youngest youngest and replaced replaced by sheeted sheeted dikes and most suggest little little or no most primitive primitive basalts basalts of of the thePortage Portage Lake Lake Volcanics Volcanic3 suggest no interaction between basaltic magma and the continental crust in which the rift between basaltic magma and continental crust which developed. developed. Thus, Thus, the thevariation &ation ininthe thechemical chemicalcha.ractertistics charactertistics of of the volcanic volcanic rocks can be used to qualitatively infer the extent of crustal attenuation. 77 �REFERENCES 1. Green, of Keweenawm Keweenawan extrusive rocks, Ri. Wold and WLffinze, 1. Green, LC., J.C., 1982, 1982, Geology Geology of extrunive rocks, h jRJ. Wold and W L h , ed., ed., Geolog GeoJm and tectonics of the the Lake Lake Superior SuperiorBasin: Baaia Geological Geological Society %ety of of America, Americb Memoir Memoir 156, 156, p. 47—55. 47-55. Baaalticvolcanvolcan2. Basaltic Volcanism Study Study Project, Project, 1981, 1981, Pre-Tertiary Pre-Tertiary continental continentalflood floodbasalts, b a d t o , th Basaltic 2. B d t i c Volcanism ism on the terrestrial urn ternatrialplanetr planet&Pergamon PergamonPress, Prezu,p.p.30—77. 30-77. 3. Brannon, Brannon?J.C., J.C.,1984, 1984,Geochemistry G e ~ c h e m i of ~ of t successive q s u 6 v elava lavaflows flowsofofthe theKeweenawa.n Xeweenawan North NorthShore ShoreVolVolGroup: St. Louis, Missoun, hub9 hhmuri, Ph.D. %D. dissertation, dissertation,312 312pp. pp. canic G m u v Washington Washington University, university, st. 4. Miller, in 4. Miller, J.D., LD., 1987, 1987, The Thegeology geology and and petrology petrology of of anorthositic anorthadticrocks KO& inthe theDuluth Duluthcomplex, complex,SnowSnowbank Lake quadrangle9 quadrangle, northeastern bar& northeastern Minnesota M n n e a o tUniversity ~UnivedtyofofMinnesota,. b f h u o t + Minneapolis, Minneapolis, Minnesota, Minnesota, Ph.D. dissertation, Ph.D. M a t i o n , 436 436 pp. pp5. Paces, Paces, LB., J.B., 1988, 1988,Geochemical Geochemical and and isotopic isotopic evaluation evaluation of of the themamgatic mamgaticprocesses, proasses, evolution evolution and mantle in lflood basalt basalt in development development of of the the major majorKeweenaw Keweauw continental continem~ t aflood mantle source murce involved inw~ l v d Univexbasin: Kmmenaw Peninsula, Peninsula, Michigan: Michigan: Michigan MichiganTechnological Tech1;ohgicd Univerhuh Portage PortageLake LakeVolcanica, Volcanica,Keweenaw ILty,Houghton, Rougliton, Mi&ga Michigan, Ph.D. dissertation mty, 6. Dosso, L., The nature of mantle: isotopic study (Sr, 6. hmo, L ., 1984, 1984, The of the the Precambrian Precambrian snbcontinental suLmntinental mantle: (Sr, Pb, the Keweenawan Xeweenawan volcanism VO~C~I&SII of the North North Shore Shore of of Lake Lake Superior: Superior: University UniversityofofMinnesota, Mhneaota, Nd) of the Minneapolis, Minnesota, Ph.D, Ph.D. dissertation, 221 221 pp. pp. bGnneapolis, Miieaota, 7. Nicholson Nichobn (in (ii prep) prep) S.W. and 1100-Ma midcontinent midcoutinent rift development: evidence 8. NIcholson, Nkhohn, S.W. and Shirey, Shirey, S.B., S.B., 1987, 1987,1100-Ma evidence from Nd of volcanic rocks, rocks, northern northern Michigan: b t o ~ i composition composition c of Keweenawan Kmeenawan volcanic Michigan: Geological G d o g i c d Society and Sr Sz isotopic of America, Abstracts with Program, v. 19, p. 788. nor 9. Paces, LB. and Bell, K., (in review), Enriched shallow lithospheric mantle beneath the Superior Province: Nd-Sr isotopic evidence from uncontaminated 1.1 Ga znidcontinent rift olivine tholeiites, t-9 Keweenaw Peninsula, Michigan: submitted Acta neweenaw remnsum, ~ ~ g aS nU D: I I U ~ ~to soGeochimica ucocxwmu et a Cosmochimica -mocnmuca t a (Sr9 10. Dosso, L., 1985, The The nature of mantle: hisotopic data (Sr, Nd, Nd, Pb) mbcontinentd mantle: t o p i c da 10. Doom, L., a~fthe Precambrian subcontinent.al on the the North Shore of of Lake Supexim. Superior. (abet.), f the (atmt.), Terra Ten aCognita, the Keweenawan Xeweenawan volcanism ~01cani.sm oof Cognita,v.5, v.5, p. 207. 20711. Lee, Milkereit, 11. Bebrendt, Bduendt9J.C., J.C., Green, Green,A.C., A.C.*Cannon, uamon,W.F., w .r Eutchinson, nusamson,D.R., UXL, M , M.W., M.w ., muereit,B., B., Agena, Agena, results ead@from W.F. WSFsand and Spencer, Spencer, C., C., 1988, 1988, Crustal Crustal structure structure of of the theMidcontinent hfidcontinent rift rift system: syatem: r GLIMPCE profiles: Geology, Geology,v.v. 1fJ9 16, p. p. 81-85. GLMPCE deep deep seismic eeismic reflection d e c t i o n profiles: - ., 20 u PORTAGE LAKE VOLCANIC8 PORTAGE VOLCANlCS NORTH SHORE VOLCANICS U' a. I' 0 10 U' m z H 0 —10 0 —6 E Nd 5 at 1100 Mi Fig. 1: 1Nd values at 1100 Ma cluster around 0 for volcanic rocks in both the Portage Lake and North Shore volcanic groups with <-. 56% Si02. 78 �Vrnric 1N RThT: A ICNETIC MT1 P ITS (IGIN Peter P e t e r A. A. Nielsen, NielsenI &parbentof of GeolcqyI WParksideIKeriosha, KenoshaIWI WI53141 53141 Departxrent Geology, UW—Parkside, The P f S ) has has been been modelled mcdelled as a passive passive The Midcontinent Midcontinent Rift Mft Systen System(ICRS) structureIoroimpactogen, r h p a c t q e n tcaused causedbybythe the Grenville Orogenyand and as as an an active, activeI or or structure, Grenvifle Orogeny p1un p l u m induced induced structure. structure. II show, showI that based on stress that based on an an analysis analysis of of the stress conditions conditions present present in in the the North North Anerican Amrican Plate Plate(NAP) OW?) from fm - 1400-1000 1400-1000 Ma Pb b.p./ b.p., - the wasananactive activerrr rrr ttriple theICRS MXS was r i p l e junction. junction. Global G l o b a l pplate l a t e distribution distributioncould could not accczidate acccmcdateunconfined unconfined extension extension of ofthe theNAP NAP and this thisprevented preventedthe theMRS M3.5 not from proceeding tto from proceeding o sea-floor spreading spreading (Figure (Figure 1). 1). The KPS no classical t h i r dam annassociated a s s m i a t e dwith with The ICRSisisunique uniqueininthat thatthere there is is no classical third it. it. Howeverf the Coldwell Trend, Trendf a series However, the Coldwell Ma alkaline intrusive intrusive seriesofof1130—1110 1130-1110 M a alkaline centers represent the the location of the the third thirdarm. arm. centers may may represent Stress distribution distributionwas was primarily primarily aa function function of of the the nature nature of of the theNorth North Stress Aitrican American Plate' Plate'ss continental continental margin margin typs typs of plate plate types as as well well aass the types boundaries boundaries present. present. The TheNAP NAP was was characterized characterized by by passive passive continental continentalmargins margins in w e s tand andnorth northand andby by an an active activecontinental continentalconvergent convergent margin =gin in i n the the i nthe t h ewest east. weremid-ocean mid-ocean ridges in in the thewest west and and Plateboundaries, boundaries, therefore, thereforeIwere east. Plate north in the east east and and southeast. southeast. These These boundary boundaq northand and aa convergent convergent boundary boundary in conditions stress field f i e l d that that was was dominantly dominantly inward inward directed directed conditions produced p r & W a stress ccipression, cmpressionfcomprised cmprisedof of west west and and northwest, northwestf directed directed capression carpression at a t its its eastern Grenvifle easternmargin margin (the (thesite siteofofthe the M l l eOrogeny), Orogeny) I eastward eastwarddirected directed ccaiipression the westernf western, passiveI passive, continent-ocean margin (site (site of conpression aat t the continent-ocean margin of Belt E!dt Group directed Group and equivalent sedinentation), sedimntation) I and andpossibly possiblysouthward -s directed compression along of aa 1200 1200 Ma Pb rrifting i f t i n g center). center) . compression alongthe the northern northern margin margin(the (thesite site of The of an The absence absence of an oceanic oceanic free free face face by by 1160 1160 Ma Pb (ocean-continent (ocean-continent or o rocean-ocean man-ocean convergent convergent margin) margin) bounding bounding the the NAP NAP coupled coupled with w i t h the the net net conpressive cmpressive stress stress fields pinned NAP, fieldseffectively effectively pinnedthe the NAPI limited l i m i t e d rifting rifting to t o65-7 65-700 kin, hf prevented the the CRS KRS from frcan proceeding p r c e d h g to t o mid-ocean mid-ocean ridge status s t a t u s and and precluded precluded the the active activestage stage of 05rifting r i f t i n galong alongthe t h eam anndefined &fined by by the theColdwell Coldwell trend. trend. The me systen system of ofgravity gravityand andmagnetic magneticanomalies a n d i e s that thatextends extendsfrom frmKansas Kansas to to Lake -s iinto n t o central mtralMichigan Michigan and and into i n t oeasterrn easternOhio Ohio Lake Superior and and then southwards isisone most prominent oneofofthe the most prcminentini North n NorthAmerica. mica. ItItreflects reflects a majorgeologic geologic a major event identified as thethe North American been identified asan anabortive a b r t i v erifting r i f t i n of g of North American event which which has been - the theCRS, K3Sfsuninarized m i z e dini nWold Wold&& Hinze, Hinze' 1982. 1982. craton craton — NUIFTOUS authors authors have have Numerous proposed this feature processes proposed tthat h a t this feature is isaaresult resultofofactive activerifting rifting processesini response n response to Plate w aroximately t oone oneor o rmore more hot hot spots spots intersecting intmeingthe theNorth NorthAmerican American Plate roximtely 1250 &&Dewey, I& b.p. b.p.(Burke (Emke Ikweyt 1973; 1973; van mnSchnius Schmus & & Hinze, 1985). 1985). Others Others 1250 to t o1100 1100Ma (Tapponnier et al., al.!1982; 1982;Gordon Gordon&& Htpton, HeqtonI1986) 1986)have havepresented presentedarguments arguments (Tappnnier et that t h a t the t h e tensional tensionalenvironment environment represented represented by by the t h eCRS MIGmay m y have have resulted resultedfrom frm the event. theGrenvifle WileOrogenic 0rcqen.i~ mt. The thethe Keweenawan The petrology petrologyand andgeochnistry geochdst.ryofof Kewemwan igneous igneous rocks, mcJcsIasasexposed exposed 1) nultiple source require that: ini nthe Lake Superior region, the Lake Superior regionf require that: 1) multiple source regions regions and contributed contributedmagma; magma; 2) 2) partial partialmelting m l t i n goccurred occurredover overaarange rangeofofdepths; ckpths; and 3)3)one sources was REE oneoro more r moreofofthe the sources was FEEundepleted. undepleted. . They were: were: Three l'hreemagma magma series s e r i e swere were proposed proposed by by Weiblen Weiblen (1982). (1982) They 1) 1) o l e i i t e (alkalic, (alkalicIhigh high Ti), T i ) Iand and alkaline C02-poor),2)2)quartz quartzt htholeiite alkaline(C02—ric.h ( a 2 - r i c h t otoC02-por) 79 �3) olivine olivine tholeiite t h o l e i i t e(low (lowalkali, alkali, high highAl). Al) . The The first firsttwo twoseries series have REE 3) have REE patterns and and initial initialSrSrratios r a t i ocompatible s compatiblewith w i t hderivation derivationfrom from aa mantle mantleplurre plume patterns The olivine olivine tholeiites t h o l e i i t ehave s have FEE source (Weiblen, (Weiblen, 1982; 1982; Wilband, Wilband, 1985). 1985) . The source REE patterns and bulk compositions which correspond closely t o mid-ocean ridge patterns and bulk coiTositions which correspond closely to mid—ocean ridge b a s a l t s (Weiblen, 1982) . basalts (Weiblen, 1982). The order order of of eirplacerrent emplacement of threemagma magma series from The of the the three series and andthe the transition transition from PEE undepleted, plume derived melts t o M3BB type melts strongly supports the REE undepleted, plurre derived malts to MDRB type malts strongly supports the hypothesis that that the theMRS 1CRS forned formed as riftsystem. system. hypothesis as an an active active rift Recent and and current current research research in i nthe thebest bestexposed exposedGrenvifle G r e n v i l l erocks rocks(Brown (Brown et et Recent al., 1986; Easton, 1986; Windley, 1986, summarized in M o o r e et a l . 1986) al., 1986; Easton, 1986; Windley, 1986, surrinarized in Moore et al. 1986) constrain stress stress distribution distribution along along aa region a r a l l e l tto o the the strike s t r i k e of of the the constrain regionpparallel Coldwell Trend, thatby by1160 1160 Ma Ma b.p. NW directed was Coldwell. Trend, and and indicate indicate that b.p. NW directed thrusting thrusting was prominent. Davidson Davidson (personal communication, 1987) suggests that these major prominent. (personal catinunication, 1987) suggests that these major NW compressional shear zones represent thrust t i v i t y that &dfted NW ccmpressional shear zones represent thruststacking stackinga cactivity that shifted SE with timedue due to t olocking lockingup upand andstepping steppingback back of of Benioff Benioff zones. zones. Any Any SE with tine sutures associated associated with with this thisactivity a c t i v i t yare arenow now cryptic. cryptic. The The timing timing of ofthis this NW sutures NW directed stress p a r a l l e l t o the Coldwell Trend and the Grenville Front provide directed stress parallel to the Coidwell Trend and the Grenville Front provide the necessary necessary stress f i e l d to t oprevent prevent any any rrifting i f t i n g along along this this possible possible third third the stress field rift arm. T h e absence of any rift-type cracking along the Coldwell trend rift arm. The absence of any rift-type cracking along the Coidwell trend strongly argues argues against r the r it is in inthe theregion region strongly againstaapassive passiveorigin originf ofor theM3^St CRS,f ofor it is parallel t o crustal thickening, that crustal flexure amd f a i l u r e should occur. parallel to cnistal thickening, that crustal flexure and failure should occur. The absence The absenceofofany anycontrols controlsononthe thedistribution distributionofof Central CentralMstasedimentary tasedirrentary Belt age age rocks rocks south south of of the theAdirondacks, Adirondacks, their spotty distribution distribution in innorthern northern Belt their spotty Quebec and Newfoundland (Figure Easton, 1986) coupled with with the the Quebec and absence absence In in Newfoundland (Figure 2,2, Easton, 1986),, coupled apparent truncation of the SE trending arm of the M3RS in the vicinity of the apparent truncation of the SE trending arm of the MS in the vicinity of the west end end of of Lake Lake Erie, and the change iin n orientation of the theGrenville G r e n v i l l eFront Front west Erie, and the change orientation of that the M3RS is not passive in origin. south of Lake Erie strongly argue south of Lake Erie strongly argue that the MRS is not passive in origin. zJsIc The Midcontinent Midcontinent Rift System was riple The Rift System wasananactive, active, plume plurreinduced inducedrrr rrr ttriple Near constant constant stress stressmagnitude magnitude and and orientation orientationfrom from the thewestern western and and junction. Near junction. northern margins margins of of the theNorth N o r t h Arterican American Plate coupled w i t h changing changing stress northern Plate coupled with stress conditionson on the theeastern easternmargin marginprevented preventedthe thearm armdefined definedby bythe theCoidwell Coldwell conditions Trend fran from rifting r i f t i n goroproducing r producingmafic maficvolcanics. volcanics. Evolving Evolving stress stressconditions conditions Trend l a t e rstopped stoppedfurther furtherrifting rifting Michigansegrrent segment and and ffinally i n a l l y along along the the later ononthethe Michigan The 1CRS Grenville Orogenyoverlapped overlapped in time, Lake Superior Superior segnent. segment. The Lake S andand thethe Grenville Orogeny in tine, The only only effect of the the but there therewas was no no genetic geneticrelationship relationshipbetween betweenthe thetwo. two. The but effect of Grenville Orogeny was t o cause the failure of the M^RS t o proceed t o sea-floor Grenville Orogeny was to cause the failure of the ICRS to proceed to sea-floor spreading. spreading. 80 �500 0 1000 kiIaI,S* ..•..•..•:;' Figure 2, fran Easton, BTtTCQAPBY BIx,IasAmY R.L., Chappel, J.F., Wrer Vriore,J.Mer J.M.,and andThompsonr Thcqson, P.H.r P.H., 1975, An Brown, R.L., Bmmr -lr J.F.# 1975# An island arc Grenvifle Province of enigmatic island arcand and ocean ocean closure in tthe h e Gremdlle southeastern Ontario, Canada, v. v. 2, Ontarior Canada, Canada, Geoscience Geoscience Canadar Zt pp. p.141-144 141-144 Burke, K.C.A. K.C.A., and and Dewey! Dewey,J.F., 1973Plume Plunegenerated generatedt rtriple i p l e junctions: junctions: Key Key Burker J.F. 1973 indicators in plate in applying -lying p l a t e tectonics tectonics to t oold oldrocks, rocksrJournal JournalofofGeology, Geolcgy, v. 86, 406—433 8Grpp. p. 406-433 Easton, R.M., Grenvifle Province, in Eastonr R.M. 1986, 1986, Geochronology ~ n 0 ofof the 1 Gmmille ~ Promhcer hMoore, Wrer J.M., J.M., Davidson,A.A., and andBBaer, A.J., Davidsonr a a r A. J. eds. eds. The The Grenville G r e m L l l e Province, Provincer Geolocical Geolcdcal Association of of Canada Canada SpecialPaper SpxialPaper 31, 3Ir pp. s.127-173 127-173 Gordon, M.B.! M.B., and andHen@onl Henpton,MM.R., 1986,Collision-induced Collision-inducedr rifting: .R. 1986r i f t i n g : The The Gordonr Grenville of North North Anerica, G r d l l e Orogeny Orcgeny and the the Keweenawan -wan R Rift i f t of Amricar Tectonophysics, v. v. 127, 127,pp.1—25 p.1-25 Tectonophy~ics~ Moore,J J.M., Davidson,A.A.,and andFaerr Baer,A.A.J., Wrer . M e r Davidsonl J e teditors, editorsr1986, 1986, The The Grerivifle Grenville Province, P r & n e r Geological Geolcgical Association of of Canada Canada Special Paper 31, 31r 358 358 pp Van Sdxnusl Schmus,W.R.r W.R.,and andHimet Hinze,W.J., W.J..,198Sr 1985,The The xnidcontinent riftsystemt systn, van midcontinent rift the Earth V. 13r 13, pp. Annual Earth and and Planetary Planetaxy Sciences, Sciencesr v. p. 345-383 345-383 Annual Reziews Reviews of the 1982 in Wieblen, P.W., intnisive rocks, K e w e n a w a n intrusive rockst 1982 in Wold, Wold, R.J., R . J e r and Wieblenr P.War 1982, 1982r Keweenawan Hinze, W.J., editors, editorsr1982, 19821Geology Wlm and and Tectonics Tectonics of the t h e Lake Lake Superior Swerior Hinzer W.J.r ir 156156 280 pp. 47-56 Basin, Geological Easi.~~ Geoloaical Society Societv of Axrica America Wmir 280pp., R. p. 47-56 Wilband, J.T., 1985, processes during during the the Midcontinent Rift 198SrMagmatic Magmatic precesses Midcontinent R ift Wilbandr J.T.l interval ininnortheastern Qienical and and isotopic isotopic constraints, intnortheasternMichigan: Michigan: Chemical constraintsr Proceedings of the the Annual Institute on Proceedings of Annual Institute onLake Lake Superior %prior Geology, Geologyr v.31,p.97 v. 31rp. 97 Windley, B.F., 1986r 1986, CCrparative of Windeyr B.Fmr a p r a t i v e Tectonics T-onics of the theWestern Western Grenville and tthe he and BBaer, A.J., eds. h t'bore, Wrer J.M., J . M e r Davidson, Davidsonl AA., e r and a a r A.J:r eds. Himalayar in Western Himalaya, The Grenville The G r e n v i l l e Province, P r & n e r Geological Geolwical Association of of Canada Canada Special SceaaI, Paper 31, 341—348 Parer 31rpp. p. 341-348 Wold,R.R.J., Geology Woldr J. and and Hinze, Hinzer W.J., W. J. editors, editorsr1982, 1982# !%elmand and Tectonics Tectonic$ of the Basin, Geological Societyof of AAnerica moir 156 cal Sccietv m e r i c a P~ITDU 156 the Lake Lake Superior Smerlor E ~SUI~ Geol 280 pp. p. 81 1986. �History History of of Precious Precious Metal Metal Ex,loration/Development Ex~loration/Develo~ment Ishpeming Greenstone Greenstone Belt Belt in the the Dead Dead River River — Ishpeming in - JOHN W. W, NORBY NORBY (Callahan (CallahanMining Mining Corporation, Corporation,Exploration ExplorationDept, Dept, JOHN 25 Industrial Industrial Park, Park, Negaunee, Negaunee, MI MI 49866) 49866) 25 - The Dead Dead River River - Ishpeming Ishpeming Greenstone Greenstone Belt Belt (DIGB) (DIGB)is is located located The in in northern northern Marquette Marquette County, County, Michigan Michigan and and is is part part of of the the Archean Archean Gold Superior Province. Province. Gold was was first first discovered discovered in in the the DIGB DIGB by by Superior Michigan's first State Douglass Houghtonl Michigan's first State geologist geologist (1837(1837Houghton, Douglass 1845)# who who panned panned the the metal metal from from an an undisclosed undisclosed location location between between 1845), silver veins veins LIAnseand and Marquette. Marquette. In In the the mid—1860s mid-1860s base base metal metal - silver L'Anse in the the middle middle DIGB DIGB were were worked worked for for their their lead, leadl needed needed in in the the in production production of of minie minie balls balls used used by by Federal Federal armies armies fighting fighting the the Civil Civil War, War, and and for for their their silver silver credits. credits. - In In 1880, 1880, Julius Julius Ropes Ropes discovered discovered the the mine mine that that was was to to bear bear his his name name in in the the southwest southwest DIGB. DIGB. From From 1882 1882 to to 1897 189'7 the the Ropes Ropes Gold Gold Mine produced produced 41,280 41,280 oz oz Au Au and and 193,500 193,500 oz oz Ag. Age Two Two other other mines mines Mine the have have recorded recorded production production from from this this era: era: the Michigan Michigan Mine Mine (875 (875 the Fire Center Mine (97 oz) in the southwest DIGB, and oz) in the southwest DIGB, and the Fire Center Mine (97 02) in oz) in the middle middle DIGB. DIGB. Numerous Numerous additional additional prospects prospects in in the the southwest southwest the DIGB were were developed developed in in the the late late 1880s 1880s and and worked worked sporadically sporadically DIGB until until the the 1893 1893 depression. depression. At At the the turn turn of of the the century, century,cyanid.cyanidization ization of of Ropes Ropes tails tails and and mill mill amalgam amalgam netted netted 2,645 2,645oz ozAu. AU* In In 1934, 1934, the the 69% 69% rise rise in in gold gold price price to to $35 $35 US US stimulated stimulated renewed activity. activity. From From that thqt year year through through 1942 1942 Calumet Calumet and and Hecla Hecla renewed Consolidated Consolidated Copper Copper Co. Co. developed developed lmT 1mT grading grading 0.13 0.13 oz/ton oz/ton Au, Aul 0.7 0.7 In oz/ton oz/ton Ag Ag in in the the Ropes Ropes Gold Gold Mine. Mine. In 1936, 1936# Norgan Norgan Gold Gold Mining Plining Co. conducted conducted aa reconnaissance reconnaissance program program throughout throughout the the belt, belt, Co. Fire Center drill test of the a 13—hole culminating in culminating in a 13-hole drill test of the Fire Center trend. trend. US gold gold The 1942 1942 War War Powers Powers Act Act halted halted the the development development of of US The properties. properties. During the the 1960s 1960s and and 70s, 70s1 .the .the DIGB DIGB was was the the subject subject of of During massive sulfide sulfide exploration, exploration, but but much much of of the the generated generated core core was was massive assayed assayed for for precious metals, metals, providing information information to to later later gold gold prospectors. Callahan Callahan Mining Corp. Corp. purchased purchased the the Ropes Ropes Gold Gold Mine Mine prospectors. in 1975. 1975. After the the US US abandonment abandonment of of the the gold gold standard standard in in 1973 1973 in of that that commodity commodity throughout throughout the the and subsequent subsequent rise rise in in price price of and decade, exploration exploration in in the the belt belt switched switched to to gold gold in in the the early early decade, 1980s. In 1983, 1983, Callahan Callahan made made the the decision decision to to mine mine the the Ropes Ropes In 1980s. The orebody, and and production commenced commenced in in September September 1985. 1985. The Ropes Ropes orebody, Gold Gold Mine Mine had had produced produced 83,671 831671 oz oz Au Au and and 113,014 113,014 oz oz Ag Ag through through the the third third quarter quarter of of 1987, 1987, bringing bringing total total precious precious metal metal production production in in the the DIGB DIGB to to approximately approximately 128,500 128,500 oz oz Au Au and and 306,500 306,500oz oz Ag. Ag. 82 , �CHRONOLOGY CHRONOLOGY Precious Precious Metal Metal Exploration/Development Exploration/Development Dead Ishpeming Greenstone Greenstone Belt Belt (DIGB) (DIGB) Dead River River — Ishpeming - 1837 - 1845 Douglass Houghton discovers Douglass Houghton discovers placer placer gold gold at at unrecorded L'Anse and and Marquette. Marquette. unrecorded location location between between L'Anse mid mid 1860s 1860s Base silver veins veins in in middle middle DIGB DIGB worked, worked, Base metal metal - silver including Silver Creek prospect including Silver Creek prospect (4 (4 shallow shallow shafts), shafts), Silver Silver Lakes Lakes mines mines (2 (2 shafts, shafts, adit, adit, winze), winze), Lead Lead pits. pits. 1864 - 1865 Holyoke Holyoke precious precious and and base base metal metal mine mine developed developed (526 (526 ft ft adit, adit, 64 64 ft ft winze), winze), no no production. production. 1880 Julius Julius Ropes Ropes discovers discovers gold gold west west of of Deer Deer Lake. Lake. 1882 — 1897 Ropes Gold and and Silver Silver Co. Co. produces produces 215,000 215,000tons tons at at Ropes Gold 0.192 oz/ton Au, 0.90 oz/ton Ag from Ropes Mine. oz/ton Au, 0.90 oz/ton Ag from Ropes Mine. 0.192 late late 1880s 1880s East—west East-west quartz quartz vein vein trend trend in in extreme extreme southwest southwest DIGB Prospects DIGB explored. explored. Prospects include include Lake Lake Superior Superior Gold, Gold, Lake Lake Superior Superior Iron, Iron, Superior, Superior, Breitung, Breitung, Grayling, Grayling, and and Mockler Mockler Brothers, Brothers, plus plus Michigan Michigan Mine. Mine. Nearby Nearby Peninsula Peninsula prospect prospect also also worked. worked. 1887 — 1894 Michigan working,^), Michigan Mine Mine in in operation operation (2,065 (2,065ft ft of of workings), produces produces 3,500 3,500 tons tons at at 0.25 0.25 oz/ton oz/ton Au. Au. 1891 — 1893 Fire 225 tons tons at at 0.43 0.43 Fire Center Center Mining Mining Co. Co. produces produces 225 oz/ton oz/ton Au Au from from Beaver Beaver shafts shafts and and Crescent Crescent tunnel. tunnel. 1899 — 1901 Corrigan, treat Ropes Ropes tails, tails, Corrigan, McKinney McKinney and and Co. Co. treat 30,000 eqv oz oz Au. Au. mill amalgam amalgam yield yield 2,645 2,645 eqv 30,000 tons tons && mill 1932 Yellow gold explored, explored, Plains glacial glacial drift drift gold Dog Plains Yellow Dog surface ft). (500ft). samples, 66 drill drill holes holes (500 bulk samples, surface bulk 1934 Michigan Mine dewatered dewatered by by Marquette Marquette Mines Mines Co., Co., Michigan Mine 500 500 tons tons milled, milled, no no recorded recorded production. production. 1934 - 1942 Calumet and Consolidated Calumet and Hecla Hecla Consolidated Copper Copper Co. Co. evaluates evaluates Ropes Ropes Gold Gold Mine, Mine, 2,550 2,550 ft ft underground underground development, development, 94 94 underground underground drill drill holes holes (10,885 (10,885 At holes on on property property ft). At surface, surface, drills drills 66 holes ft). (1,564 (1,564ft), ft), 33 holes holes east east of of Ropes Ropes (1,278 (1,278ft), ft), 88 holes holes west west of of Ropes Ropes (4,109 (4,109 ft), ft), and and 55 holes holes at at Bjork-Lundeen Bjork-Lundeen prospect prospect (2,109 (2,109ft). ft). 1936 Norgan Norgan drills drills - Gold Gold Mining Miming Co. Co. prospects prospects entire entire DIGS, DIGB, 13 13 holes holes (1,999 (1,999 ft) ft) along along Fire Fire Center Center trend. trend. 83 �- Precious Metals Exploration/Development, Exploration/Developmentt cont. cont. DIGB Precious CHRONOLOGY - DIGB CHRONOLOGY 1966 1966 Cleveland—Cliffs Iron The Cleveland-Cliffs Iron Company Company (CCI) (CCI) drill drill holes. tests tests Michigan Michigan Mine, Minet 3 holes. 1968 — 1971 explores Humble Oil and Humble Oil (later (later Exxon) explores middle middle and Exxon) sulfide, analyzes southwest southwest DIGB DIGB for for massive massive sulfide, analyzes for for Drills 2 2 holes iron precious metals. precious metals. Drills holes into into iron formation and 2 into topographic formation topographic low low (2,000 (2,000 ft). ft). 1970s (Bethlehem Steel Steel and and CCI). CCI). Beth-Cliffs JV (Bethlehem 1975 presents Ropes Resource Exploration, Resource Exploration, Inc. Inc. (REI) (REI) presents Ropes which Callahan Mining Corp. Gold Mine data data to to Callahan Mining Corp. which Arcadian Copper from purchases property property from Arcadian Copper Mine Mine Tours (owner Tours (owner since since 1955). 1955). 1972 — 1985 Superior Oil Co. Co. and and Nicor Nicor Mineral Mineral Ventures Ventures JV JV Superior Oil massive DIGB for massive prospects middle and northwest northwest DIGB several geophysical and/or geochemical sulfide, several geophysical and/or geochemical sulfide, manager thru anomalies RE1 project project manager thru 1983. 1983. anomalies drilled, drilled, REI several to switches to Emphasis switches gold that that year, yeart several Emphasis additional additional targets targets drilled. drilled. During both phases phases of of 14 holes exploration JV exploration JV drills drills 14 holes (4,700 (4#700 ft) ft) on on Holyoke Holyoke property. property. 1977 - 1981 NOMEX AU JV JV (Chevron (Chevron and CCI) CCI) explores explores southwest southwest Bjork—Lundeen prospect holes 4 DIGB, drills drills 4 holes at Bjork-Lundeen prospect DIGB, (2,729 ft) and 4 (2#729ft) 4 holes holes west west of of Ropes Ropes (1,680 (lt680ft). ft). 1979 - 1981 REI Mine, Callahan Callahan evaluates evaluates Ropes Ropes Gold Mine, RE1 project project manager. manager. Drills 18 surface holes (12,724 (12*724ft) ft) into into into IP IP anomaly anomaly (802 (802 ft), ft), plus plus 8,000 8,000 orebody and 2 into ft ft of underground underground drilling. drilling. 1984 psnt 1984 —- psnt Kerr—McGee Kerr-McGee drilling. drilling. 1983 1983 St. Joe American Corp. prospects patchwork of land in northern northern and and southern southern DIGB, DIGBt no no holes holes drilled. drilled. - 1985 1983 — 1985 1983 - psnt 1984 1984 - psnt Corp Corp prospects prospects middle DIGB, DIGB, actively actively develops production makes Callahan makes production decision, decisiont develops Callahan ft level. Ropes Gold Mine to to 900 900 ft level. Acquires and and renovates renovates iron iron ore ore flotation flotation mill mill in in Champion. Champion. for additional on Callahan Callahan prospects prospects for additional reserves reserves on Ropes property property and and in in other areas areas within hauling hauling radius radius of of Ropes Ropes mill, mill, actively actively drilling. drilling. - prospects southwest Dodge prospects Phelps Dodge southwest DIGB, DIGB, drills drills 11 Phelps hole east eas-tof of Ropes Ropes (824 (824 ft). ft). - Au, 0.28 0.28 ml' at 0.087 0.087 oz/ton Au, Callahan Callahan mills mills 1.25 mT orebody above above 1284 1284 ft ft level. level. oz/ton Ag from Ropes orebody 1985 1985 - 1986 1986 9/87 9/85 — 9/87 9/85 84 �IMPLICATIONS IMPLICATIONS OF HIGH PRECISION PRECISION U-Pb AGE AGE DATES DATES ON ON ZIRCONS ZIRCONS FROM FROM PORTAGE LAKE LAKE VOLCANIC VOLCANIC BASALTS ON MIDCONTINENT RIFT SUBSIDENCE SUBSIDENCE RATES, RATES, LAVA LAVA FLOW FLOW REPOSE PERIODS PERIODS AND AND MAGMA MAGMA PRODUCTION RATES RATES JAMES JAMES B. PACES, PACES, Dept. Dept. Geology Geology & &Geological GeologicalEngrg., Engrg., Michigan Technological University, Houghton, Houghton, MI 49931 Technological University, 4993 1 DON W. DAVIS, DAVIS, Jack Satterly Geochronology Geochronology Laboratory, DON W. Royal Ontario Museum, Queen's Park, Park, Toronto, Ontario M5S Museum, 100 Queen's M5S2C6 2C6 Recent U-Pb zircon Recent high high precision precision U-Pb zircon dating dating of of Keweenawan-aged Keweenawan-aged rocks rocks in the the western western Lake Lake Superior Superior region region has has revealed revealed that basaltic basaltic igneous igneous activity activity associated associated with with the the Midcontinent Midcontinent Rift (MCR) (MCR) was was initiated initiated around around 1109 1109Ma1. ~ a ' . Dates of similar similar quality quality which which record record the the cessation cessation of extensive extensive flood flood basalt basalt extrusion extrusion do not not exist. exist. In In this this paper, paper, we we report the upper report new new dates dates which which constrain constrain the upper age age limit limit of of MCR MCR mafic mafic volcanism, volcanism, and and use use these data to to estimate estimate rates rates of of rift-related rift-related tectonic tectonicand andigneous igneousprocesses. processes. STRATIGRAPHY The Portage Portage Lake Lake Volcanics Volcanics (PLV), (PLV), northwest northwest Michigan, Michigan, represents the youngest youngest flood basalt-filled basalt-filled portion portion of of the theMCR MCR in the region2. The thick pile (3-5 the western western Lake Superior Superior region2. (3-5 km) km) of normal normal magnetic magnetic polarity, polarity, predominantly predominantly olivine olivine tholeiite tholeiite lavas isis conformably conformably overlain overlain by Oronto Oronto Group Group sediments. sediments. lavas This sequence of rocks sequence of rocks therefore therefore records records a major major transition transition in in MCR tMCR evolution evolution from from dominantly dominantly volcanic volcanic to to sedimentary sedimentary rif riftfilling material. material. filling Figure Figure 11 shows shows generalized generalized stratigraphic relationships in the the Keweenaw Peninsula. Peninsula. Highly differentiated differentiated pegmatoid pegmatoid layers layers within within two PLY PLV flows, flows, the the Greenstone Greenstone Flow Flow and and Copper Copper City City Flow Flow (GSF (GSF and CCF CCF respectively), respectively), were were sampled sampled for zircon zircon stratigraphic horizons horizons represented represented by these these extraction. The stratigraphic flows are separated by 2600-3100 of flood basalts and minor 2600-3100 m of sediments. A single single lava lava from from aa series series of of flows flows interflow sediments. (Lake Shore Traps, LST) within the Shore Traps, the Copper Copper Harbor Harbor ConglomConglomis separated erate was was also also sampled. sampled. LST LST magmatism magmatism is separated from from the GSF 700 m m of GSF horizon horizon by approximately approximately 700 of PLY PLV lavas lavas and and 800-1000 800-1000 m of coarse coarse clastic clastic sediment. sediment. RESULTS Ages from U-Pb U-Pb data on Ages were were determined determined from on multiple multiple fracfracabraded zircon zirconseparates. separates. All data points points plot plot close close to to tions of abraded the concordia concordia curve suggesting suggesting that problems problems of lead lead loss loss and and inheritance are are minimal. minimal. Six Six zircon zircon fractions fractions from from the the two two PLY and two PLV samples samples and two fractions fractions from the the LST LST sample sample yield yield 1.3 Ma and and 1094.1 1094.1 ± 2 3.6 3.6 Ma Ma respectively respectively 1095.1 ±2 1.3 ages of 1095.1 (based on zero errors on on all (based on zero age age lower lower intercepts; intercepts; errors all data data are are quoted at at 95% 95%confidence confidence levels). levels). PLY PLV and and LST LST ages ages are are quoted unresolvable from present data. data. Within Within the PLY PLV section, section, unresolvable from the present separate ages GSF and 1.7 separate ages for for the the GSF and CCF CCF horizons horizons are are 1094.4 1094.4 ±k 1.7 and 1096.0 1096.0 ± k 1.9 1.9 Ma Ma respectively. respectively. The GSF-CCF GSF-CCF age age Ma and difference and and one one sigma sigma error error isis1.6±1.3 1.6k1.3 Ma. Ma. The age reported reported for for the the PLY PLV isisconsistent consistent with with slightly slightly older, older, reverse reverse magnetic magnetic polarity polarity lavas l a v a from from the the Black Black Bay Bay Peninsula (upper Osler Peninsula (upper Osler Group, Group, 1097.6±3.7 1097.6k3.7 Ma'). ~ a ' ) . These age age C5 Fig. Fig. 11 (1cm) (km) C., S 0 I (1094.1 3.6 a S a 0. 0. 0 0. 1 —I. GSF (1094.4 1.7) C) 0 1 (I, 0 z 0 -ii 0 > —3 w -I w CCF (1096.Otl.9) 00. Keweenaw Fault �- relationshipssuggest suggestthat that all all of of the normal relationships normal polarity flood flood basalts with the polarity basalts associated associated with the western Lake Lake Superior Superior segment segment of of the MCR western were produced produced over over aa period of 2-3 were period of 2-3 Ma. Ma. However, an an age age reported reported from from a porphyrHowever, porphyritic intrusive/subintrusive intrusive/subintrusive unit uniton onMichipi— Michipicoten Island is ~sig- ) Island (1086.5 (1086.5 +1.3/—3.0 +1.3/-3.0 ~Ma3) a is nificantly younger than than PLY nificantly younger PLV or or LST LST ages ages reported here. reported here. This This large large age age difference difference implies that either 1) implies that 1) volcanic volcanic rocks rocks in the the eastern MCR are much eastern MCR much younger younger than than those those to west, 2) 2) the Michipicoten Michipicoten Island Island the west, to the Formation represents aa much later, Formation represents later, isolated isolated magmatic episode, episode, or or 3) intrusion magmatic intrusion occurred occurred much later later than deposition much deposition of the the volcanic volcanic host rocks. RATES OF SUBSIDENCE RATES geochronologic and stratiCombined geochronologic graphic data can be used to estimate estimate minimum rates rates of rift-related minimum rift-related subsidence. subsidence. The assumption assumption underlying underlying this this calculation, calculation, maintenanceofof a near maintenance near horizontal horizontal deposidepositional surface, is is supported supported by flow morphology, primary primary slope variations4, morphology, variations4, and distributions of interf low sediments. distributions interflow sediments. An average thickness thickness of of 2850 average 2850 m between between the the GSF ens4 i n n /^~PPo-GSF and and C'F CCF b~Awnnm horizons and +ha the age &WAA&Ulm -6- differMa yields yields subsidence subsidence rates rates ence of 1.6-1.9 ence 1.6- 1.9 Ma Although higher higher rates rates of 1.5 1.5 to to 2.0 2.0 mm/yr. mim/yr. Although may occur along MCR axis, the values MCR axis, the values may occur along-the - - - -- calculated from GSF-CCF GSF-CCF data are comparcalculated from able with able with rates rates of of tectonic tectonic subsidence subsidence in in other continental continental grabens (typically (typically 1-2 mm/yr; range range of of 0.2-10 mm/yr). The mm/yr; 0.2-10 mm/yr). The large large error in the error the reported reported LST LST age age reduces reduces the the significance of of similarly calculated rates rates for significance similarly calculated PLY subsidence the GSF-LST the GSF-LST interval. interval. PLV subsidence rates rates are roughly roughly an an order order ofofmagnitude magnitude those calculated greater than greater than those calculated from Osler Osier Group Group data (0.l2-0.24 (0.12-0.24 mm/yr). mm/yr). However, 1.5-2 mm/yr subsidence over the 12-13 1.5-2 mm/yr subsidence over 12-13 Ma Ma period period of of MCR MCR magmatic magmatic activity activity (1108(11081095 1095 Ma) Ma) would would have have resulted in the accumulation of 18—26 kmof of rift-fill. rift-fill. This 18-26 km thickness added to to 8-10 thickness added 8-10 km km of of overlying overlying post—magmatic sediments5'6 post-magmatic sediment^"^ yields total totalrift— riftfill values values in in close close agreement agreement with with recent recent seismic reflection reflection results7. results7. OULU LJiU UAJ.J.&dL- LAVA IODICITY LAVA REPOSE PER PERIODICITY Average interflow Average interflow repose periods periods can can also be estimated estimated from the the GSF-CCF GSF-CCF data. data. also Up to 140 140 separate separate cooling cooling units are recogrecognizable over this stratigraphic stratigraphic interval, however the the presence however presence of of compound compound flows flows reduces this number to to approximately approximately 65-70 65-70 86 major lava major lava flows. flows. Therefore, Therefore, the the average average repose period between successive successive major eruptions eruptions is is estimated at 20-30 Ka. Somewhat longer repose repose may may typify erupSomewhat longer er'uptions separated by by interf low sedimentary tions interflow sedimentary units while units while shorter shorter repose repose periods periods may may be be typical of of the majority typical majority of of PLY PLV flows flows which which directly overlay the underlying flow top. top. RATES OF OF MAGMA MAGMA PRODUCTION Finally, magma proproFinally, minimum minimum rates rates of of magma duction have been for the duction have been calculated calculated for the CCFCCFGSF interval. interval. Total Total volume volume of eruptive eruptive products is speculative products speculative given present present expoexposure. Minimal and "probable" sure. Minimal "probable" estimates estimates of the original original areal areal extent extent of PLY PLV lavas lavas are are shown shown in Figure Figure 22 (modified (modified after afterGreen8). re en^). Constant thickness thicknessacross acrossthe the basin basin is asConstant assumed (axial (axial thickening thickening is counteracted sumed counteracted by marginal thinning). Estimates of minimal marginal thinning). Estimates minimal . and "probable" volumes for for the and "probable" volumes the GSF-CCF GSF-CCF interval are are approximately approximately 40,000 and 100,000 km3 km3 respectively respectively which 100,000 which result result in ma ma production between 2-6x10"~ magma production rates rates between 2-6x102 km4/yr. Although these km /yr. Although these values values may may be be underestimatedby byaa factor factor of of 2-5, 2-5, they underestimated they fall fall within within the the range range of of values values estimated estimated for for h-@-1^ and basaltic magma production production in in other other rift and hot spot hot spot settings settings (Iceland ~ km3/ yr; (Iceland 5xl02 5x 1o ' km3/yr; Columbia River Basalts 7x102 km3/yr; Basalts 7x10'~ km3/yr; and and Columbia River Hawaii 3-10xl02 krn3lyr)'. Hawaii 310x10-2 km3/yr)9. 5 iB'adUJ.LJ.W LJ.J.Ue.LJ.f.U Davis and Sutcliffe Sutcliffe (1985) (1985 GSA GSA Bull Bull 96: 96: 1572. 1572. 2 Green (1982) (1982) GSA GSA Mem Mem 156: 156: 47. 47. Palmer and and Davis Davis (1987) (1987) Precambrian Res Res 37: 37: 157. 157. White (1960) (1960) Am J Sci Sci 5 258A: 367. 5Daniels 258A: 367. Daniels (1982) (1982)GSA GSAMem Mem156: 156:107. 107. 6Kalliokowski GSAMem Mem 156: 156: 147. 147. '7Behrendt 6 ~ a l ~ o k o w s(1982) k(1982) i GSA ~ehrendt 8 (1988) Green (1983) (1988) Geology Geology 16: 16: 81. (1983) Tectonophysics Tectonophysics 94: 413. 9Swanson 94: 413. g~wansonat et a!. al. (1975) (1975) Am Am JJ Sci Sci 278: 275: 877. 877. I Fig. Fig. 22 'Probable" Area �- Archean and and Proterozoic Proterozoic Tectonics Tectonics - Northern Michigan A Speculative Speculative Synthesis Synthesis John Palmquist, Geology Department C. Palmquist, John C. Lawrence University, University, Appleton, WI 54912 Lawrence 54912 tectonic interpretations offered as an attempt These eclectic These eclectic tectonic interpretations are offered attempt to to Penokean orogeny call ancestry of of the the Penokean orogeny and to call attention attention to to the the Archean Archean ancestry to apparent conflicts previously published reconcile reconcile the the apparent conflicts in in previously published ideas ideas about about the the nature nature of of the the Penokean Penokean deformation deformation (vertical (vertical vs. horizontal horizontal tectonics) tectonics) and views concerns the nature concerns the the contrasting views nature of basement-cover basement-cover interaction interaction the contrasting Two (brittle ductile basement-cover (brittle basement basement blocks blocks vs. vs. ductile basement-cover relationships). Two conflicting tectonic tectonic concepts have been sets of of conflicting concepts have been presented in in both both the the sets One concerning concerning the the question district and the the region.. region. One question of of the the role role of the the district and the Penokean was it Archean Archean basement basement behavior behavior during during the Penokean - was it ductile ductile or or brittle? brittle? The second conflict has to do with with reconciliation of the The the steep steep fault fault zones zones surfaces of folds and near near vertical vertical axial axial surfaces folds and and cleavages cleavages with with the the recumbent recumbent and folding folding in in adjacent adjacent areas. areas. - Archean scenario. Archean scenario. A southern southern gneissic gneissic terrane terrane (southern (southern complex) complex) and complex) were juxtaposed northern northern greenstone-granitic greenstone-granitic terrane terrane (northern (northern complex) juxtaposed in in proto-continental collision Zone (GLTZ) (GLTZ) of of proto-continental collision to form the Great Lakes Tectonic Zone Dextral shear shear along along the the GLTZ GLTZ may have have created created aa series series of low low Sims, ( 1980). Dextral Sims, (1980). Compeau Creek pressure zones the emplacement pressure zones which which guided guided the emplacement of the the Compeau Creek plutons plutons into syntectonic syntectonic relations with the greenstones of the northern complex and southern complex. Strain in the the Archean Archean of the the southern the the gneiss gneiss of complex. Strain patterns patterns in Vermilion District, Minnesota have been shown greenstone belt of the greenstone belt of the Vermilion District, Minnesota have been shown by by convincing example Schultz-Ela example Schultz-Ela (1986) (1986) to to indicate indicate dextral dextral transpression. transpression. AA convincing pull-apart associated with the the South pluton emplaced emplaced in of a granite of a granite pluton in a pull-apart South Ainorican Shear Shear Zone Zone of of France France is given by American is given by Guineberteau Guineberteau and and others, others, (1987). (1987). were intruded multiple ages Diabase dikes Diabase dikes of multiple ages were intruded along along fractures fractures and and faults faults in in northern and southern both both the the northern southern complexes complexes as as an an accompaniment accompaniment of of regional regional the syntectonic emplacement. Later of uplift and/or and/or "relaxation" "relaxation" of the syntectonic emplacement. Later uplift remobilization remobilization of of the the complexes complexes is is indicated indicated by by the the deformation deformation patterns patterns in in dismembered and of the gneissic terrain terrain and by dismembered and contorted contorted remnants remnants of the southern southern gneissic remnants appear early The appear as diffused, early dikes dikes in in the the northern northern complex. complex. The remnants diffused, Some feldspathized feldspathized amphibolites amphibolites and schlieren schlieren in in the the Compeau Compeau Creek Creek gneiss. gneiss. Some Mona of these these amphibolite amphibolite "ghosts" "ghosts" may may represent represent incomplete incomplete assimilation assimilation of Mona schist (Stonehouse, (Stonehouse, 1970). 1970). schist rift become the the Marquette The Penokean orogeny. orogeny. The rift destined to to become Marquette began to to close'by closeby transpression synclinorium began transpression (Cambray, (cambray, 1984) 1984) along the the site site southward directed subduction under the of the the GLTZ. GLTZ. A southward subduction zone zone somewhere somewhere under the of Wisconsin juxtaposed juxtaposed the the Baraga, Baraga, Menominee present present area area of of northern northern Wisconsin Menominee and and Chocolay Groups in wedge Chocolay Groups in an an accretionary accretionary wedge (Larue and Ueng, Ueng, 1985). (Larue and Underthrusting wedge comprised Underthrusting of the the footwall footwall caused the piling up of a wedge comprised of of a a series series of thrusts, thrusts, including including the the crystalline crystalline cored cored nappe nappe preserved preserved in in the the Felch Felch District District (Maharidge (Maharidge and and others, others, 1986). 1986). As As the the thrust thrust sheets sheets advanced advanced subducting northward (the footwall may have been actively subducting relatively relatively northward (the footwall may have been actively southward), toward have been southward), toward the the foreland, foreland, their their leading leading edges edges may may have been diverted diverted diverged around topographic buttresses, buttresses, into topographic lows, into topographic lows, i.e., i.e., diverged around topographic thrusts were southern complex. complex. Where the possibly possibly the the gneisses gneisses of of the the southern Where the thrusts were thickly stacked, stacked, depressed depressed geotherms geotherms formed formed the the metamorphic metamorphic nodes nodes at at 87 �Watersmeet, Peavy Watersmeet* Peavy and and Republic Republic (Attoh, (Attoh* 1986) following following aa thermal thermal lag. lag. The The have caused northward thinning thinning of the the tectonic tectonic load would have caused thermal thermal weakness weakness toward the the foreland. The anisotropy Archean rocks to slope slope up toward foreland. The anisotropy in in the the Archean rocks to modified the transpressional the shortening transpressional tectonic averted the shortening direction direction and modified tectonic trends to trends to allow allow Penokean Penokean reactivation reactivation of of Archean Archean structures. structures. Differential Differential thermal thermal weakening weakening of of diverse diverse foreland foreland (footwall) (footwall) Archean rocks rocks would allow allow some portions the footwall to yield whereas other some portions of of the footwall to yield as as brittle brittle blocks blocks whereas other initially weaker weaker or more portions, more heated, portionsy either either initially heatedy would fail fail by foldingj foldingyplastically the hanging hanging wall plastically flowing, flowingy or melting into the wall rocks. rocks. Ellis Ellis (1988) (1988) explored foreland and explored the the idea idea that that thrusting thrusting migrates toward the the foreland and that that the the internally by analyzing footwall/foreland secton will begin begin to to deform aeform internally analyzing the the footwall/foreland secton strength of a strength a rheologically rheologically simple simple two-layer two-layer lithosphere lithosphere under under compression. compression. This This interpretation interpretation resolves resolves the the dilemma dilemma of of the the vertical vertical axial axial surfaces surfaces seen at with the seen at the the east east end end of of the the Marquette Marquette synclinoriuxn synclinorium with the horizontal horizontal axial axial basement planes planes in in the the west. west. The The evidence evidence of of aa block-like block-like behavior behavior of of the basement Klasner and the the draping draping of of the the supracrustal supracrustal rocks rocks (Marquette (Marquette and and Republic Republic -- Klasner indications of the indications of a and and Cannon, Cannon* 1974) 1974) in in seeming seeming conflict conflict with with the a ductile ductile interaction interaction of of basement basement and and cover cover (Watersmeet (Watersmeet area) may also also be resolved resolved by were raised basement (footwall) the interpretation interpretation offered offered here here -- the the basement (footwall) rocks rocks were raised through the the ductile-brittle ductile-brittle transition transition as the ductile environment from aa ductile environment through as the from orogeny. Penokean orogeny. footwall/foreland deformed deformed internally during the Penokean At the the footwall/foreland ductile east end east end of of the the Marquette Marquette synclinorium, ~ynclinorium~ ductile greenstones greenstones appear appear to to have have cover rocks interacted with the interacted with the metasedimentary metasedimentary rocks rocks because because basement basement and and cover rocks properties (Carter Where have have similar similar mechanical mechanical properties (Carter and Palmquist, Palmquisty 1986). 1986). Where stronger stronger gneisses gneisses were were uplifted uplifted en bloc bloc the the weaker, weaker* layered layered metasediments metasediments over basement blocks in are draped over basement blocks in the the fashion fashion of the Rocky Mountain are draped Laramide thrusting. In the foreland uplifts foreland uplifts associated associated with with Laramide thrusting. In the Rockies, Rockiesy basement and more homogenous homogenous crystalline crystalline basement a cooler however* a and a cooler thermal thermal however, a more behave in more uniform, structure structure caused caused the the basement basement rocks rocks to to behave in a more uniformy brittle, brittle, region, the GLTZ of block-like fashion. In the block-like fashion. In the Lake Lake Superior region, the GLTZ of the the Archean zones of weakness that localized the Marquette Marquette synclinorium foreland created zones Presumably, the vertical vertical axial axial surfaces Basin. and the the Dead Dead River River Basin. Presumablyy surfaces at the the horizontal axial surfaces east end of the Marquette synclinorium and the horizontal surfaces on on resulted from the same same north-south north-south shortening shortening event, west have the have resulted from the event* the the the west Recumbent isoclinal Penokean footwall/foreland Penokean footwall/foreland compression. compression. Recumbent isoclinal folds folds described described might be be interpreted interpreted by (Kiasner, (Klasner* 1972) at the west end of the synclinorium might Group as as these rocks escaped escaped the over of of the as the the spilling spilling over the Baraga Baraga .Group these rocks the and were flattened gravitational confinement the footwall confinement of of the footwall "jaws" "jawst' and flattened by gravitational force. force. the crust, Where the the tectonic tectonic loading has sufficiently sufficiently heated the crusty basement basement ductile along with the metasedimentary rocks became ductile gneisses have became along with the rocks gneisses have Differential mechanical susceptibility (Watersmeet node). node). Differential thermal thermal and and mechanical susceptibility in in (Watersmeet strain along ductile zones zones leaving rocks may have concentrated concentrated strain the basement the basement rocks bloc (Republic free to intermediate (Republic node). node). intermediate areas areas unaffected unaffected and and free to deform deform en & locally reset radiometric clocks conditions may locally Thus, reset radiometric clocks without without Thus, metamorphic metamorphic conditions everywhere during penetratively deforming penetratively deforming or or remobilizing remobilizing the the basement basement everywhere during the the Penokean Penokean metamorphic metamorphic event. event. 88 �REFERENCES REFERENCES Attoh*K. K. 1986, 1986* Metamorphic Metamorphic Pressures, Pressures*Temperatures Temperatures and and Early Early Proterozoic Proterozoic Attoh, Geotherms in in Northern Northern Michigan Michigan [Abstract], [Abstract]$ Thirty-second Thirty-second Ann. Ann. Inst. Inst. on on Geotherms geology*p. p. 5-6. 5-6. Lake Superior Superior geology, Lake Cambray* W.F., W.F.* 1984, 1984* Proterozoic Proterozoic Geology, Geologyy Lake Lake Superior Superior South South Shore, Shore* Cambray, Geological Geological Association Association of of Canada Canada Field Field Trip Trip Guide Guide5. 5. Carter, Carter* P.J., P.J.* and and Palmquist, Palmquist* J.C., J.C.* 1986, 1986* Strain Strain Analysis Analysis of of Deformed Deformed Archean Archean Pillow Lavas, Lavas* Mona Mona Schist, Schist* Marquette Marquette County, Countyy Michigan, Michigan* U.S.A. U.S.A. Pillow [Abstract]. [Abstract]. Thirty-second Thirty-second Ann. Ann. Inst. Inst. on on Lake Lake Superior Superior Geology, Geologyyp. p. 16. 16. Initiation Ellis*M., M a y 1988, 1988$ Lithospheric Lithospheric strength strength in in compression: compression: Initiationof of Ellis, subduction, subductionyflake flake tectonics, tectonics* foreland foreland migration migration of of thrusting, thrusting*and and an an origin origin of of displaced displaced terranes, terranes* Journal Journal of of Geology, Geologyyv. v. 96, 96,p. p. 91-100. 91-100. Guineberteau* B., B e y Bouchez, Bouchez* J. J. and and Vigneresse, Vigneresse* J., J a y 1987, 1987* The The Mortagne Mortagne Guineberteau, granite* pluton pluton (France) (France) emplaced emplaced by by pull-apart pull-apart along along aa shear shear zone: zone: granite, Structural Structural and and gravimetric gravimetric arguments arguments and and regional regional implication, implication, Geological Geological Society Society of of America America Bulletin, Bulletin*v. v. 99, 99*p. p. 763-770. 763-770. Klasner* J.S., J.S.* 1972, 1972* Style Style and and sequence sequence of of aa deformation deformation and and associated associated Kiasner, metamorphism metamorphism due due to to the the Penokean Penokean orogeny orogeny in in the the Western Western Marquette Marquette Range* northern northern Michigan Michigan [Ph.D. [Ph.D. dissertation], dis~ertation]~Houghton, Houghton* Michigan Michigan Range, Technological Technological University, University*131 131p. p. Klasner* J.S. J.S. and and Cannon, Cannon* W.F., W.F.* 1974, 1974$ Geologic Geologic Interpretation Interpretation of of Gravity Gravity Kiasner, District, Northern Western Marquette the Profiles in in the Western Marquette District* Northern Michigan, Michigan* Profiles Geological Geological Society Society of of America America Bulletin, Bulletin*v. v. 85, 85*p. p. 213-218. 213-218. An Larue* D.K. D.K. and and Ueng, Ueng, W.L., W.L.* 1985, 1985* Florence-Niagara Florence-Niagara terrane: terrane: An early early Larue, Proterozoic accretionary accretionary complex, complexy Lake Lake Superior Superior region, region* U.S.A., U.S.A.y Proterozoic Geological Geological Society Society of of America America Bulletin, Bulletinyv. v. 96, 96*p. p. 1179-1187. 1179-1187. Maharidge, Maharidge* A.D., A.D.* Mancuso, Mancuso* J.J. J.J. and and Onasch, Onasch* C.M., C.M.* 1986, 1986$ Tectonic Tectonic Evolution Evolution of of the the Felch Felch Trough Trough [Abstract], [Abstract]? thirty-second thirty-second Ann. Inst. Inst. on on Lake Lake Superior Superior geology, p. p. 53-54. 53-54. geology, Schultz-Ela, D.* 1986, 1986* Strain Strain Models Models for for the the Evolution Evolution of of- the the Vermilion Vermilion Schultz-ElayD., Ann. Inst. Thirty-second Minnesota District, District* Minnesota [Abstract], [Abstract]* Thirty-second Ann. Inst. on on Lake Lake Superior Geology, Geologyyp. p. 71-72. 71-72. Superior Sims, Sims* P.R., P.K.* 1980, 198OY Boundary between Archean Greenstone and Gneiss Terranes in Northern Northern Wisconsin Wisconsin and and Michigan, Michigan* Geological Geological Society Society of of America America Special Special Paper 182, 182* p. p. 113-124. 113-124. Paper Stonehouse, Stonehousey H.B., H.B.* 1970, 19709 Precambrian Precambrian of of the the Marquette Marquette Area, Areay Michigan, Michigan* in in Guidebook Guidebook for for Field Field Trips, Trips* Geological Geological Society Society of of America, America*North-Central North-Central Sec., Set.* Michigan Michigan Basin Basin Geol. Geol. Soc., S O C . East ~East Lansing, Lansing*p. p. 159-177. 159-177. 89 �Two of aarnet Jwo aenerations of cmrnet arowth arowthininthe theHardwood Hardwoodaneiss. aneissL Dickinson Cauntv. Ilichiaon Michiam DiekinsunCounty. 4.W. PETERSON PFTERSON (Department of the theGeophysical Qeophysiwl Sciences, SciencessUniversity Universityof Chicago, ChicagosChi -, IL J.W. (Department of Chicago, ft 60637U.S.A.) U.S.A) 60637 CA* QEIQER ( Technixhe UniversiM Berlin Ernst C.A. GEIGER (Techniache Universitat Berlin,I nstitut InstitutfW für Mineralqie Mineralogie und undKristallqraphie, Kristailogrophie, Ernst Reuter ReuW Plat2 P1aQ 1, I , 1000 1000BerlIn Berlin12, 12,West WetGermany) hrmany) The Hardwood Hardwoodgneiss gneissisisaaunit unitof ofEarly Early Precambrian Precambrian age outcropping in age outcropping ineastern—cantral eastern-central Dickinson general lithology of the described by )ames et at a]., al., D i c k i mCounty, bunty*Michigan. Michip. The Thegeneral lithdqyof theunit unitwas wus&cribd by James * 1961* pyroxene gneiss* gneiss, plagioclequartz plagioclase—quartz gneiss* gneiss, 196 1 and andconsists consistsofofgarnet— garnet- hornblende— hornblende-pyroxene hornblende— pyroxenegneiss, gneiss,amphibolite, amphibolite, garnet-quartz-sillimanite-mica garnet—quartz—sillimanite— micaschists schist,and andquartzite. quartzlte. hornblen&-pyroxene Two generations of pyroxene Two generations cd garnet garnet growth growthcan mbe bedistinguished distinguishedininthe thegarnet—hcrnblende— garnet-hurnblende-pyroxene units. anhedr& porphyroblasts porphyroblasts of garnet, units Generation Generation Iiconsists consists of of subhedral to anhedral garnet*1.0—2.5 1 .O-2.5 mm in in diameter, matrix of diameter*set set ininaafine—grained fine-grained matrix ofplagioclase plqioclaseand and hornblende. Many Many of these garnets contain rutile up to 100 100urn pmlong. long. Some &me garnets garnets contain amtain inclusions inclusionsof cpx, cpx, opx, opx, and and contain needles needles ofofrutile up to plagioclase, thoughthis this is not common. common. InclusionInclusion—free garrietshave havedistinct distinctrims. rims. h Generation II1 p?cgia3ase,though free prnets eration 1 consists, 00um wide) generation((I) rims consistssin in part, part*ofof distinct distinctrims rims(80— (80- 11OOpm wide) on the gmeration I ) garnets. garnets. These These rims contain aa band of contain of irrqularly-shaped irragularly—shaped oxide blebs blebs (5(5—10 10pm urndimensions) dimensions)which which forms forms a sharp sharp contact diffuse contact with the ant& with m n k t with the interior interior(generation (generation1)I )portion portionofofthe thegarnet garnetand anda diffus remainder garnet rim. rim. Generation remainder of the garnet Qeneration(II) (11)garnet prnetgrowth g m t hisisalso alsorepresented representedby by50— 50- 100 I 00 i.jm pm diameter geometric grains grains are commonly commonly cored coredwith with oxide oxideblebs blebssimilar similar diameter euhedral euhedral garnets. garnets. These These geometric to those rims of t h w in the rims of generation generation(I) ( I garnets. ) garnets.These Thesecores coresare are—25 -25 .Lrn pm inindiameter diameterand andconsist consistofof several m inindimension. -5 jim dimension.The Theeuhedral euhedralgernets garnetsare arecommonly mmmonlylocated located several individual individualoxide wick blebs blebs—5 around rims of larger generation relative location wound the rims uf the larger generation ((I)I )garnets. garneb. Because Bemuse of the relative laxtionof of oxide blebs the ares cores of of euhe$ral euhedral garnets garnetsand andthe therims rims of sub-8nhedrid sub—anhedralgarnets* garnets,we weinfer infer that bkbs between the that both contemporaneously,and andatataadistinctly distinctly different different time both rims rimsand and euhedr& euhedral garnets grew mtemp~ranmusly~ timethan thanthe the garnets. generation ((I)I)garnets. generation In samples, no nollarge (generation I) gamete In some same samples, a m (generation I) garnetsare arepresent. present.However, However,augen—shaped augn-shaped areas 10 euhdral euhedral garnets* garnets, eech areas (—1.5 (-1 -5 mm rnm by 1I mm) mm) are arepresent presentwhich whichcontain contain5— 5- 10 em31 150—200 150-200 .im pm butbut areare riddled inclusions in gamnets rarely cored with oxides, riled with with inclusions These pgeometric m e t r i c garnets areare rarely mred with in diameter. These of cpx, have been beenthe thelaxtions locationsof of1arq large generation generation cpx, plagioclase, phgitclasesand and hornblende. hornblenck. These These augen augem may have (I) subsequentlyrecrystallizd recrystallized to (1)gamete garnetswhich whichexperienced experiencedlater laterpenetrative penetrativedeformation deformationand and subsequently the, euhedral generation (II) gamnets. A difference In whole—rock the small, euhedral pneration ( 11) prnets. A difference in whole- rockbulk bulkcomposition cornpusitionmay m8y explain explainthe thelack lackofofoxide mi&cores. mre. Electron reveal mmpositional compositionaldifferences differencesbetween betweenthe thetexturally texturally Electron microprobe microprobe analyses reveal thermobarometry indicates equilibration equilibration defined generation(I) (I) and and(11) (II) gamete. defined generation garnets. Quantitative Quantitative thermobarometry conditions 850—950C and kbar for for generation ((I)Igarnets, 8- 111 1 kbar ) grnets,and andP—I P-T conditions mnditionsof anditions of 850-950° and 8— 650-750C (II) gamete. 650-750°and and7-8 7-8kbar kbarfor forgeneration generation (11) garnets. The recognition of two growth at least portion of The recognition two generations gmerations of garnet growth l e d records rear& one portion of the the decompression—cooling history for for this terrane, and discriminate between ~mpression-mUnghistory thishigh—grade high-gr& terrane, and may discriminate between Archean Proterozoic metamorphic Archean and Proterozoic metamorphicevents. events. * James* H.L. Clark,L.D., L.D. Lamey,C.A. Lamey, C.A. and and Pettijohns F.J., 1961, 196 I ,Geology h l a of ~ Dickinm James, H.L.,Clark, Pettijohn, F.U., of~central central Dickinson County Michigan: U.S. Geol. Survay Paper Paper3310, U.S. b l.Survey 10, 11 76 pp. 90 �SULFIDEMINERALIZATION MINERALIZATIONAND ANDASSOCIATED ASSOCIATEDHYDROUS HYDROUSSILICATES SILICATESIN IN SULFIDE ANORTHOSITICROCKS ROCKSFROM FROMTHE THEDULUTH DULUTHCOMPLEX COMPLEX ANORTHOSITIC Bernhardt Saini—Eidukat, S a i n i - E i d u k a t ? Dept. Dept. of of Geology Geology and and Geophysics, Geophysicst Bernhardt University U n i v e r s i t y of of Minnesota, Minnesota? Minneapolis, Minneapolis? Minnesota Minnesota 55455 55455 The The principal p r i n c i p a l sulfide s u l f i d e minerals m i n e r a l s in i n anorthositic a n o r t h o s i t i c rocks r o c k s of o f the the D u l u t h Complex, Complexf Minnesota, M i n n e s o t a ? are a r e chalcopyrite, c h a l c o p y r i t e t pyrite p y r i t e and and Duluth pentlandite. p e n t l a n d i t e . They They occur o c c u r as a s interstitial i n t e r s t i t i a l void—filling, v o i d - f i l l i n g ? included, i n c l u d e d ? and and fine—veini-et t y p e s ? similar s i m i l a r to t o those t h o s e observed o b s e r v e d in in f i n e - v e i n l e t textural t e x t u r a l types, troctolitic series rocks r o c k s (Weiblen (Weiblen and and Morey, Morey? 1976). 1976) t r o c t o l i t i c series A n a l y s e s of o f biotites b i o t i t e s in i n Duluth D u l u t h Complex Complex anorthositic a n o r t h o s i t i c and and Analyses t r o c t o l i t i c rocks r o c k s show show higher h i g h e r chlorine c h l o r i n e contents c o n t e n t s in i n biotites biotites troctolitic a s s o c i a t e d with w i t h sulfide s u l f i d e mineralization. m i n e r a l i z a t i o n . Substitution S u b s t i t u t i o n of o f chlorine chlorine associated ( C l ) in i n biotite b i o t i t e depends d e p e n d s on on temperature, t e m p e r a t u r e ? Cl C l activity a c t i v i t y during during (Cl) e q u i l i b r a t i o n f and a n d the t h e Mg!(Mg+Fe) Mg/ (Mg+Fe) ratio r a t i o ("mg") (llmgll) of o f the t h e biotite biotite equilibration, i s known known in i n the t h e case c a s e of of (Munoz? 1984) 1 9 8 4 .) . Only Only the t h e latter l a t t e r parameter p a r a m e t e r is (Munoz, the C l with with t h e Duluth Duluth Complex. Complex. The The expected e x p e c t e d correlation c o r r e l a t i o n of of increasing i n c r e a s i n g Cl decreasing i s observed o b s e r v e d (Table ( T a b l e 1), I ) , but b u t the t h e highest h i g h e s t Cl C l found found d e c r e a s i n g "mg" lvmgvlis also A t this t h i s point p o i n t it it is i s not not a l s o correlates c o r r e l a t e s with w i t h high h i g h sulfide s u l f i d e content. c o n t e n t . At known C l content c o n t e n t reflects r e f l e c t s dominantly dominantly aa magmatic magmatic enrichment enrichment known if i f the t h e Cl with C l when when SS was was added added to t o the the w i t h differentiation, d i f f e r e n t i a t i o n ? or o r the t h e addition a d d i t i o n of of Cl system system (Ripley, ( R i p l e y ? 1981) 1981). It I t has h a s been been proposed p r o p o s e d that t h a t Cl—complexing Cl-complexing fluids f l u i d s may may play p l a y an an important i m p o r t a n t role r o l e in i n the t h e metallogenesis m e t a l l o g e n e s i s of o f platinum p l a t i n u m group g r o u p element element (PGE) deposits d e p o s i t s (Balihaus ( B a l l h a u sand andStumpf S t u m p1, f l ? 1986; 1986; Boudreau, Boudreau? Mathez Mathez and and (PGE) McCallum? 1986) 1 9 8 6.) . Preliminary P r e l i m i n a r y analyses a n a l y s e s of of Duluth Duluth Complex Complex rocks r o c k s show show McCallum, aa correlation N i and and c o r r e l a t i o n of of enrichment enrichment of of chlorine c h l o r i n e with w i t h whole whole rock r o c k Cu, Cut Ni PGE PGE enrichment. e n r i c h m e n t . Although Although at a t this t h i s point p o i n t in i n the t h e investigation i n v e s t i g a t i o n the the role C l in i n metal m e t a l concentration c o n c e n t r a t i o n is i s equivocal, e q u i v o c a l r it it is i s hoped hoped that that r o l e of o f Cl further with w i l l provide p r o v i d e exploration e x p l o r a t i o n geologists geologists w i t h a tool t o o l for for f u r t h e r study s t u d y will t a r g e t i n g PGE PGE deposits d e p o s i t s in i n the t h e Duluth Duluth Complex. Complex. targeting . References : References: and B a l l h a u s f C.G. C.G. a n d E.F. E . F . Stumpfl, S t u m p f l ? 1986, 1986? Sulfide Sulfide Ballhaus, mineralization in the Merensky Reef: m i n e r a l i z a t i o n i n t h e Merensky R e e f : evidence evidence silicates Contr. Mm. Pet., Pet., s i l i c a t e s and fluid f l u i d inclusions. inclusions. C o n t r . Min. and a n d platinum platinum from from hydrous hydrous 94, 9 4 ? 193—204. 193-204. A . E . ? Mathez, Mathez? E.A. E - A . and a n d 1.S. I . S . McCallum, McCallumf 1986, 1986? Halogen Halogen Boudreau? A.E., Boudreau, geochemistry g e o c h e m i s t r y of o f the t h e Stillwater S t i l l w a t e r and a n d Bushveld B u s h v e l d Complexes: Complexes: evidence e v i d e n c e for f o r transport t r a n s p o r t of o f the t h e platinum—group p l a t i n u m - g r o u p elements e l e m e n t s by by Cl—rich J . Petr., P e t r . ? 27, 2 7 ? 967—986. 967-986. C l - r i c h fluids. f l u i d s . J. F—OH 1984, Munoz? J.L., J.L. 1984 F-OH and a n d Cl-OH C l - O H exchange e x c h a n g e in i n micas m i c a s with with Munoz, In: Bailey, applications to hydrothermal ore deposits. a p p l i c a t i o n s t o h y d r o t h e r m a l o r e d e p o s i t s . I n : B a i l e y ? S.W. S.W. (ed.) Micas,t Rev. (ed.) w Rev. Mineral. M i n e r a l . 13, 1 3 ? Mineral. M i n e r a l . Soc. SOC. Am., Am. Virginia, Virginia, 469-494. 469—494. Ripley, E . M m f 1981, 1981r Sulfur S u l f u r isotopic i s o t o p i c studies s t u d i e s of of the t h e Dunka Dunka Road Road Cu—Ni Cu-Ni R i p l e y f E.M., deposit, 7 6 ? 610—620. 610-620. d e p o s i t ? Duluth Duluth Complex, Complexr Minnesota. Minnesota. Econ. Econ. Geol., Geol . 76, Weiblen, Weiblenf P.W. P .W. and a n d G.B. G . B . Morey, Morey? 1976, 1976? Textural T e x t u r a l and and compositional compositional characteristics of sulfide ores from the basal c h a r a c t e r i s t i c s of s u l f i d e o r e s from t h e b a s a l contact c o n t a c t zone zone of of the South Kawishiwi intrusion, Duluth Complex, Northeastern t h e S o u t h Kawishiwi i n t r u s i o n ? D u l u t h Complext N o r t h e a s t e r n University Minnesota. M i n n e s o t a . Proc. P r o c . 37th 3 7 t h Ann. Mi Min. Symp., Symp. U n i v e r s i t y of of Minnesota. Minnesota. 91 �2 3 34.45 5.16 13.93 0.04 18.98 9.93 37.87 3.27 16.55 0.06 10.00 15.66 0.09 0.42 9.55 1 Si02 1102 Ti02 Al203 A1203 Cr203 CQ03 FeO FeOTT MgO MI0 cCaO ao Na20 Na20 K20 K20 32.48 3.33 cCls 0.19 25.88 6.39 0.05 0.33 8.93 0.46 TOTAL TOTAL 92.45 92.92 -0=Cl -O=CI 92.35 92.82 93.68 93.63 Si Si 5.36 5.46 5.61 Ti Ti Al1 A 0.41 0.61 2.80 0.02 3.57 1.57 0.36 2.89 0.01 2.51 0.01 0.11 n.d. 0.11 1.88 0.13 1.94 0.12 15.87 15.71 Cr Fe Fe Mg Mg Ca Ca Na Na K K cClI TOTAL TOTAL 14.41 n.d. 0.37 9.62 0.44 2.60 2.34 0.21 0.01 1.24 3.46 0,01 0.12 1.81 0.05 15.56 1..Analyses Table I Analyses of biotites in Duluth Complex rocks. n.d. = not detected. n.d. Numbers the basis basis of of22 220. Numbers of ions on the 0. 1. Troctolitic Troctolitic Series. Series. INCO 2B, Gabbro Lake Ql~ad. Q'iad. 1. INCO Test Pit sample 26, Anorthositic Series. Sulflde.bearing 2. Anorthositic Sulfide-bearinganorthosite. Gabbro Gabbro Lake Lake Quad., BL.27A-87 BL-27A-87 3. Anorthositic Anorthositic Series, late stage. Troctolitic anorthosite, sample 30814 308A of Miller 3. (Geology and Petrology of Anorthositic Rocks in the Duluth Complex, Snowbank Lake Quadrangle, Quadrangle, Northeastern Northeastern Minnesota. Minnesota. Ph.D. Ph.D. Thesis, 1988) 1986) 92 �I THE MAGNETIC FABRIC AND STRUCTURE OF THE QUETICO SLATES AT THE QUETICO-WABIGOON INTERFACE, NORTHWESTERN ONTARIO. PERRY SARVAS and GRAHAM .3. BORRADAILE. Department of Geology, Lakehead University, Thunder Bay, Ontario, Canada. u Recent studies of magnetic fabric in tectonites be many workers have repeatedly revealed a strong correlation between principal magnetic susceptibility directions and principal finite strain directions. These observations have led to this study of magnetic fabric in the Quetico slates to assist structural investigations. The Archean Quetico metasedimentary belt, at the interface with the Wabigoon volcanic—plutonic subprovince, is characterized by sheath—folded greywacke-slate sequences of very low metamorphic grade. The sequences show a lateral metamorphic gradient towards the center of the Quetico subprovince, where migmatites are found. The sheath folds close to the belt bounday are primary, isoclinal and are believed to result from pervasive dextral transpression of the northern margin of the Quetico subprovince. The Quetico metasedimentary rocks have a polyminerallic magnetic mineralogy, comprised of a small trace (<2 weight U of highly magnetic grains (magnetite and pyrrhotite) and a much more substantial proportion of weakly magnetic minerals Both fractions are believed to contribute (phyllosilicates). significantly to both the magnetic susceptibility and the magnetic susceptibility anisotropy of the rocks. The magnetic fabric of the Quetico slates is predominantly The minimum magnetic susceptibility tectonic in derivation. directions are consistently perpendicular to continuous cleavage These cleavage planes parallel the major structural planes. trends and metamorphic isograds, corresponding to the major episode of pervasive regional deformation/metamorphism. In places, a weak remnant sedimentological magnetic fabric is preserved. The directions of maximum and intermediate magnetic susceptibilities vary throughout the area. This may be due to the influence of the phyllosilicates on the lithological magnetic susceptibility anisotropy (phyllosilicates have an oblate magnetic susceptibility ellipsoid, with poorly defined maximum and intermediate susceptibility directions). Also, the complexities introduced from a polyminerallic magnetic mineralogy, and a subordinate sedimentological magnetic fabric, could have influenced the orientations of the principal magnetic susceptibilities. 93 �A A Paleomagnetic Paleomagnetic Study Study of of the the Hamilton Hamilton Mound Mound Area of of Adams County, County, Central Wisconsin Robert Robert Schneiker Schneiker and William F. Kean Department Department of of Geosciences Geosciences University Wisconsin—Milwaukee University of of Wisconsin-Milwaukee Milwaukee, Milwaukee, WI WI 53201 53201 The The Hamilton Hamilton Mound area area represents represents aa complex complex intrusion intrusion into into precambrian measurements were precambrian quartzites. quartzites. Magnetic measurements were made made on on the the granitic granitic intrusion, intrusion, the the complex complex mixed mixed zone zone and and the the quartizites. quartizites. The viscous to The granite granite proved proved to to be be too too magnetically viscous to provide provide reliable palemagentic reliable palemagentic directions. directions. The The magnetism in in the the quartizite appears appears to be caused by hematite, based on on A.F. A.F. and quartizite thermal demagnetization thermal demagnetization studies. studies. The The pole position position of of the the quartizite, after quartizite, after aa correction correction for for local local structure structure is is N15°, ~15O, W120°, ~ 1 2 which which 0 ~ is is similar similar to to the the position position for for the the Baraboo Baraboo type type quartzites of quartzites of Wisconsin Wisconsin and and Minnesota. Minnesota. The is The mixed zone zone has has a a magnetism which is directions are magnetite. The magnetic directions are well magnetite. The provide a provide a pole pole position position at at S20°, s20° W75°. ~ 7 5 ~This This . represent the the last represent last age age of of intrusion intrusion at at about about 94 primarily primarily carried carried by clustered clustered and and position probably position probably 1600 1600 m.y.a. m.y.a. �A POST-TECTONIC POST-TECTONIC RARE-METAL-RICH RARE-METAL-RICH GRANITE GRANITE ININTHE THESOUTHERN SOUTHERNCOMPLEX, COMPLEX, UPPER UPPER A PENINSULA, PENINSULA, MICHIGAN. MICHIGAN. SCHULZ, K.J., Survey, Reston, Reston, VA VA 22092; 22092; Sims, Sims, P.K. P.K. SCHULZ, K.J., U.S.Geologica1 U.S.Geological Survey, and Z.E., 80225. and Peterman, Peterman, Z. E., U.S.Geological U.S. Geol ogicalSurvey, Survey,Denver, Denver,CO CO 80225. We repert herein herein preliminary results We report resultsofofa geochemical a geochemical and and Rb-Sr Rb-Sr isotopic granite from the northern isotopic study study of ofaasmall smallundeforined undeformed granite from the northern part of of the Southern miles south Southern Complex, Complex, 22 miles south of ofHumboldt Humboldt in in the theUpper Upper Peninsula Peninsula of granite, which of Michigan. Michigan. The The granite, which is of of probable probable Early Early Proterozoic Proterozoic age, age, is is coinpositionally similar to composi tionally similar torare-metal-rich rare-metal -richgranites granitesand andsuggests suggests aa possible potential potential for forSn-W Sn-W (Ta-Nb) (Ta-Nb) mineralization mineral ization ininupper upperMichigan. Michigan. The granite, which wasfirst first discovered briçfly The granite, which was discovered and and bri flydescribed described by by Hoffman (1987),is roughly circular outline, about17/1/ miles Hoffman (1987) ,is roughly circular in inout1 ine, about miles in 8 diameter, diameter, and and intrudes the the Archean Archean Bell Creek Creek granite granite and an gneisses gneisses of of the Southern Thegranite granite is is generally massive, mediumSouthern Complex. Complex. The massive, finefine-toto mediumgrained equigranular to to hypidiomorphic granular, nonfoliated, nonfoliated, and light grained equigranular hypidiomorphic granular, and light red to brick brick red. red. AA prominant prominant biotite and(or) lineation 1 ineation is is red biotite foliation foliation and(or) present locally near joints are present locally near the the margins. margins. Fractures Fractures and and joints are ubiquitous ubiquitous and typically are Kand typically arecoated coated with withmicas. micas. The The mineralogy mineralogy consists of of Kfeldspar, albite, muscovite, a1 bi te,quartz, quartz,biotite, biotite, muscovite,and andaccessory accessory fluorite fluoriteand and zircon. Accessory uranothorite, col columbite, euxenite, cassiterite, Accessory uranothorite, umbi te, euxeni te, cassiterite, molybdenite, (1987). According and topaz topaz were were reported by by Hoffman Hoffman (1987). According to to the the molybdeni te, and IUGS classification of plutonic 1976), this this body body is is IUGS classification plutonic rocks rocks (Streckheisen, (Streckheisen, 1976), an a1 kal i -feldspar granite. granite. an alkali-feldspar The granite isischaracterized The granite characterizedbybyhigh highSi02 Si02(>74 (>74%), %),low lowFeO(11 FeO (<2 %), (<0.2 %) %), CaO(~0.5 (<0.5%) %), andTi02 1102(<0.02 (<0.02%) %), andnear'iiual near'eual %) , MgO MgO (<0.2 , CaO , and , and Na20 and KK,O (4-5 %) %) contents. The Na 0 and 0 (4-5 The trace traceelements elementsRb Rb (350-1000 (350-1000ppm), ppm), Pb Pb (20-70 (26-70 ppmj, ppm?, VY (28-115 (28-115 ppm), ppm), Nb Nb (35-209 (35-209 ppm), ppm), and and Ta Ta (21-36 (21-36 ppm) ppm) are are strongly (<I7ppm), ppm),BaBa(<20 (<20ppm), ppm),and andEu Eu (<0.07 (<0.07ppm) ppm) strongly enriched, enriched,and andSrSr(<17 are strongly stronglydepleted depletedcompared compared to toaverage average granites. granites.The TheREE REE have have U-shaped chondrie normalized normalizedpatterns patterns with with very large U-shaped chondrite large negative negative Eu Eu anomal i es (Eu/Eu (Eu/Eu <0.025). <O.O25). anomalies Age Age determination by by the theRb-Sr Rb-Sr method method on on three threewhole whole rock rocksamples samples defined preliminary age ageofof 1733 1733/_25 a Sr initial ratio ratio of /_25 MaMa andand a Sr initial of defined aa preliminary 1.55). Although Although this this isisa minimum about 0.81T/_0.078 0.817+/0.078 (Model (Model I,I,MSWD MSWD = =1.55). a minimum about age, granite may age, ititsuggests suggeststhat thatthe the granite mayhave havebeen beenemplaced emplaced during the the Early Proterozoic, with the Proterozoic,perhaps perhapscontemporaneously contemporaneously with the ca. ca.1760 1760Ma Ma anorogenic magmatism Wisconsin. An magmatism inin Wisconsin. An Early Proterozoic Proterozoicpost-Penokean post-Penokean age wouldbe becompatible compatiblewith withthe the lack lack of age would of penetrative penetrativedeformation deformation and and mineral alteration in this mineral alteration this granite. granite. Compositional featuresofofthe the granite granite stock stock are are similar similar to Compositional features tothose those of Sn-W mineralized kal i -feldspar granites of of the theArabian Arabian Shield Shield Sn-W mineral ized a1alkali-feldspar (Jackson Ramsay,1986) 1986)and andthe the Nigerian Nigerian Younger Granite province Younger Granite province (Jackson and and Ramsay, (Kinnaird others, 1985), 1985),and andtotothe thetopaz topazrhyolite rhyolite suite of of the the (Kinnaird and and others, Western UnitedStates States (Chri (Christiansen and others, others, 1986). Western United sti ansen and 1986). Highly Highly evolved, evolved, rare-metal-rich granite stocks, or cupolas, typically occur rare-metal -rich granite stocks, or cup01 as, typically occur in clusters clusters or linear are related related to larger lineararrays arraysthat thatcommonly commonly are larger granite granitebodies bodies as, as, for 1986).ItIt is is for example, example, in in the theArabian Arabian Shield Shield (Jackson (Jackson and and Ramsay, Ramsay, 1986). interesting to lies on tonote note that thatthe thegranite granitenear nearHumboldt Humboldt lies on the the 95 �northeastern edgeofof aa large large negative negative gravity gravity anomaly that is northeastern edge anomaly that is roughly roughly coincident coincident with withthe theRepublic Republicmetamorphic metamorphic node; node; this thisanomaly anomalyhas hasbeen been subjacent granite granitepluton pluton(Kiasner (Klasnerand and others, others, 1985). 1985). attributed totoaasubjacent Although highly greisenized rocks rocks have have not Although highly greisenized not been beenfound foundinin the the granite near trace-element-enriched nature nature and and the possible possible near Humboldt, Humboldt,its its trace-element-enriched occurrence thearea area suggests suggests this this region region occurrenceofofother other similar similar intrusions ininthe Peninsulaof of Michigan Michiganmay may containa asignificant significant potential of the the Upper Upper Peninsula contain for Sn-W for Sn-W (Ta-Nb) (Ta-Nb) resources. resources. REFERENCES REFERENCES Christiansen, E.C., Christiansen, E.C., Sheridan, Sheridan, M.F., M.F., and and Burt, Burt,D.M., D.M., 1986, 1986,The TheGeology Geology and Geochemistry Geochemistryof of Cenozoic Cenozoic Topaz TopazRhyolites Rhyolites from from the Western and Western United States: Geological States: Geological Society Society of ofAmerica America Special Special Paper Paper 205, 205, 82 8 2 p. Hoffman, M.A., M.A., 1987, Hoffman, 1987, The The Southern Southern Complex: Complex: Geology, Geology, Geochemistry, Geochemistry, Mineralogy and Mineral Chemistry Mineralogy and Mineral Chemistry of ofSelected SelectedUraniumUrani urn-and and Thorium-Rich Thori urn-Ri ch Granites: unpublished disseration, PhD di sseration, Michigan Michigan Technological Techno1 ogical unpubl i shed PhD University, 382 University, 382pages. pages. Jackson, N. N.J. C.R., 1986, 1986, Post-Orogenic Post-Orogenic Fel Felsic Jackson, J. and and Ramsay, Ramsay, C.R., sic Plutonism, Pl utoni sm, Specialization in the Mineralization and and Chemical Chemical Specialization the Arabian Arabian Shield: Shield: Transactionsof of the the Institute Institute ofofMining Transactions Mining and and Metallurgy Metallurgy (Sect. (Sect. B: B: Appl. Appl . earth earth sd.), sci.), v.v.95, 95,p. p.B83-B93. B83-B93. Kinnaird, J.A., J.A., Batchelor, Batchelor,R.A., R.A., Whitley, Whitley,J.E., J.E.,and andMacKenzie, MacKenzie, A.B., A.B., 1985, Geochemistry, Mineralization andHydrothermal HydrothermalA1Alteration of the i zati on and terat i on of 1985, Geochemi stry, Mineral Nigerian High ProducingGranites, Granites, in High Nigerian High Heat Heat Producing High Heat Heat Production Production Granites, HydrothermalCirculation Circulation and andOre OreGenesis: Genesis:Institute Institute of Hydrothermal of Mining Mining and and Metallurgy, p. p. 169-195. 169-195. Kiasner, J.S., Klasner, J.S., King, King,E.R., E.R., and andJones, Jones, W.J., W.J., 1985, 1985,Geologic Geologic Interpretation ofofGravity Interpretation Gravityand andMagnetic Magnetic Data Data for forNorthern Northern Michigan Michigan and and Wisconsin,inin Hinze, Hinze,W.J., W.J., editor, editor, The Utility ofofRegional Wisconsin, The Utility Regional Gravity Gravity and and Magnetic Anomaly AnomalyMaps: Maps: SocietyofofExploration Exploration Geophysicists, Geophysicists, p. 267-286. 267-286. Magnetic Society Streckeisen, A., Earth A., 1976, 1976,To ToEach Each Plutonic PlutonicRock Rock Its ItsProper ProperName: Name: Earth Science 12, p. 1-33. Science Reviews, Reviews, v. 12, 1-33. 96 �The Mountain Shear Zone——Relevance Zone--Relevance to age of quartzite quartzite at McCaslin and Mountain Shear Thunder northeastern Wisconsin Thunder Mountains, Mountains, northeastern Wisconsin CO 80225; 80225; P.K. SIMS SIMS and and Z.E. Z.E. PETERNAN, PETERMAN, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO P.K. J.S. KLASNER, KLASNER, Western Western Illinois Illinois University, University, Macomb, Macomb, IL IL 61455 61455 J.S. The Mountain shear zone zone is a discrete, 1- to 2.5-km-wide discrete, 1— 2.5—km—wide zone of rocks that trends N.55°—60° ~ . 5 5 ~ - 6E .0 ~and largely obliterates regional mylonitic rocks E. obliterates the regional north-trending fabrics fabrics (S0/S1) (So/Sl) in in metavolcanic rocks of early north—trending metavolcanic and granitoid rocks Proterozoic ("1860 Ma) age age (Sims (Sims and and others, others, 1986; 1986; Sims, Sims, in in press). press). An An (1860 Ma) quartz diorite diorite body (Hines Quartz Quartz Diorite) body that intruded the undeformed quartz the shear zone has a U-Pb U—Pb upper upper intercept age age of of 1812.7±3. 1812.7±3.6 Ma, Ma, which which provides provides a firm age on on the the shearing. finn minimum age A deformed within the deformed conglomerate conglomerate (Baldwin (Baldwin Conglomerate) Conglomerate) within the shear shear zone zone of granitic granitic gneiss gneiss and and metavolcanic metavolcanic rocks derived derived from the contains clasts of evolving evolving shear shear as as well as as clasts clasts of quartzite quartzite as as much as as 25 25 cm cm in in diameter diameter was the (Lahr, 1972). The source for quartzite clasts almost certainly was (Lahr, 1972). Mountains, less than 20 km to quartzite now exposed at McCaslin and Thunder Mountains, the north. Thus, Thus, inasmuch inasmuch as the Baldwin Conglomerate was deformed during the shear deformation, deformation, and prior to emplacement of the Hines Hines Quartz Diorite, Diorite, the quartzite clasts and their parent rocks are older than 1812 Ma. quartzite clasts their parent rocks are older than 1812 Ma. The quartzite at McCaslin and Thunder Mountains unconformably overlies the Waupee Volcanics (Olson, (Olson, 1984), 1984), which were deformed deformed on on northeast—trending northeast-trending fold fold axes axes and and metamorphosed quartzite was metamorphosed prior prior to to quartzite quartzite deposition. deposition. The quartzite was deformed deformed later later westward—plunging syncline into a westward-plunging syncline (Nancuso, (Mancuso, 1960). 1960). in the Lake Superior show a great disparity The quartzite quartzite bodies in Superior region region show deformation, yet yet all of them generally have have been presumed presumed to in intensity of deformation, 1981), inasmuch as the be younger than 1760 1760 Ma (see Van Schmus and Bickford, 1981), Wisconsin disconformably overlies 1760 Ma Baraboo Quartzite in southern Wisconsin rhyolite (Daiziel rhyolite (Dalziel and Dott, Dott, 1970; 1970; Van Van Schmus, Schmus, 1978, 1978, 1980). 1980). The The establishment establishment of the the quartzite at McCaslin and Thunder Mountains as being older older than than 1812 1812 Ma Ha suggests that other strongly deformed quartzite bodies, such as the Flambeau suggests Perhaps these Quartzite, 160 west, possibly Quartzite, 160 km km to the the west, possibly are are of of comparable comparable age. age. Perhaps these quartzites were deposited during a tectonically tectonically quiescent interval between quartzites "'1850 1850 Ma and and 1812 1812 Ma. Ma. Because in the north-central north—central United States may Because the quartzite quartzite bodies in differ more, and have undergone differ in in age age by as much as as 50 50 Ma, or perhaps more, different tectonic histories, histories, the term "Baraboo interval" (Dott, (Dott, 1983) should different be restricted restricted to those those quartzite quartzite bodies bodies known known to to be be younger younger than than 1760 1760 Ma. Ma. REFERENCES CITED REFERENCES CITED Dalziel, Dalziel, I.W.D., I.W.D., and and Dott, Dott, R.H., R.H., Jr., Jr., 1980, 1980, Geology Geology of of the the Baraboo Baraboo District, District, Wisconsin: Wisconsin Geological Geological and Natural History Survey Information Wisconsin: Information Circular 17, Circular 17, 164 164 p. p. Dott, Proterozoic red quartzite enigma in the northnorth— R.H., Jr., Jr., 1983, 1983, The Proterozoic Dott, R.H., Resolved by by plate plate collision?, collision?, in inMedaris, central United States: central States: Resolved Medaris, L.G., L.G., Jr., ed., ed., Early Proterozoic region: Jr., Proterozoic geology geology of of the the Great Great Lakes ~akesre~ion: Geological Society Geological Society of America America Memoir Memoir 160, 160, p. p. 129—141. 129-141. 97 �Lahr, M.M., M.M., 1972, geology of Lahr, 1972, Precambrian geology of a greenstone g r e e n s t o n e belt b e l t in i n Oconto County, Wisconsin and geochemistry of of the t h e Waupee Waupee metavolcanics: m e t a v o l c a n i c s : M.S. M.S. thesis, thesis, University U n i v e r s i t y of of Wisconsin, Wisconsin, Madison, 62 62 p. p. Mancuso, J.J., J.J., 1960, of the Mancuso, 1960, Stratigraphy S t r a t i g r a p h y and sstructure t r u c t u r e of t h e McCaslin District, District, Ph.D. Wisconsin: Ph.D. thesis, t h e s i s , Michigan State S t a t e University, U n i v e r s i t y , East E a s t Lansing, Lansing, 101 101 p. p. Olson, J.M., 1984, of the 1984, The geology of t h e llower o w e r Proterozoic P r o t e r o z o i c McCaslin Formation, Formation, Olson, J.M., northeastern n o r t h e a s t e r n Wisconsin: Wisconsin: Geoscience Wisconsin, v. v. 9, 9 , p. p. 1—19. 1-19. Sims, P.Kç P.K., iin Geologic map map of of P Proterozoic Mountain, Oconto Sims, n ppress, r e s s , Geologic r o t e r o z o i c rrocks o c k s nnear e a r Mountain, County, Wisconsin: County, Wisconsin: U.S. U.S. Geological G e o l o g i c a l Survey Miscellaneous M i s c e l l a n e o u s Investigations Investigations Series 1-1903, scale s c a l e 1:24,000. 1:24,000. S e r i e s Map 1—1903, Sims, P.K., P.K., Day, Day, W.C., W.C., and K Kiasner, J.S., 1986, Early Proterozoic Sims, l a s n e r , J.S., 1986, The E arly P r o t e r o z o i c Mountain sshear h e a r zone, zone, northeastern n o r t h e a s t e r n Wisconsin: Wisconsin: Geological G e o l o g i c a l Society S o c i e t y of of America America Abstracts with 752. A bstracts w i t h Programs, Programs, v. v. 18, 1 8 , p. p. 752. Van Schmus, Schmus, W.R., W.R., 1978, 1978, Geochronology of of the t h e southern s o u t h e r n Wisconsin rhyolites r h y o l i t e s and and Wisconsin, v. v. 2, 2 , p. p. 19—24. 19-24. ggranites: r a n i t e s : Geoscience Wisconsin, Van Schmus, W.R., 1980, Schmus, W.R., 1980, Chronology of of igneous i g n e o u s rocks r o c k s associated a s s o c i a t e d with w i t h the the Penokean orogeny iin Wisconsin, & inMorey, Morey, G.B., G.B., and and Hanson, Hanson, G.N., G.N., eds., eds., n Wisconsin, Selected of Archean gneisses S e l e c t e d sstudies t u d i e s of g n e i s s e s and and lower lower Proterozoic P r o t e r o z o i c rocks, rocks, ssouthern o u t h e r n Canadian Canadian Shield: S h i e l d : Geological G e o l o g i c a l Society S o c i e t y of of America Special S p e c i a l Paper 182, p. 182, p. 159—168. 159-168. Van Sebmus, W.R., and Bickford, M.E., 1981, Schmus, W.R., B i c k f o r d , M.E., 1981, Proterozoic P r o t e r o z o i c chronology and evolution inK Kroner, e v o l u t i o n of of the t h e Midcontinent region, r e g i o n . North America, America, & r o n e r , A., A . , ed., ed., Precambrian p plate Elsevier Scientific Publishing Precambrian l a t e ttectonics, ectonics, E lsevier S cientific P u b l i s h i n g Co., Co., Amsterdam, Amsterdam, p. p. 261—296. 261-296. 98 �EXPLANATION EXPLANATION ml PALEOZOIC PALEOZOIC (570 (570 Ma Ma and and younger) younger) !-?a) EARLY PROTEROZOIC (1600—2500 (7600-2500 Ma) CRrnbrian and.tone Cambrian sandstone MIDOLE PROTEROZOIC ( 900-1 600 Ma) Ma) MIDDLE PROTEROZOIC (900—1600 'Yi Y,i, Hager quartz porphyry quartz p o r phyr y ys, Hager Rhyolite '1,,, Hines Q u a r t z DDiorit iorlte Hines Quartz Xbc Baldwin Conglomerato High FalL Granite Quartzi te Belongia Granite 1 yw9 1 xh xq X Wolf R i v e r Granite Granite Wolf River -'—--'-- Mangerite Grani to Waupen Vo1anics Mylonite in Mourita'n sshear h e a r zone .4 Bedding $ Bedding -4 + Foliation 4 F oliation 6 // Fault Fault + —'• Geologic map GeolOgiC map Fold Fold of part of of northeastern n o r t h e a 9 t e r n Wisconsin X i s c o m i n (Compiled ( C o m p ~ l eby dbyP.1<. P.K. Sims, Slmg, 1988) 7988) OF > 99 �Evolution Evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terrane terrane of of the the Penokean Penokean orogen orogen K.J. SCHULZ, SCHULZ, U.S. U.S. P.K. SIMS, SIMS, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225; 80225; K.J. P.K. Geological Survey, Survey, Reston, Reston, VA VA 22092; 22092; Z.E. Z.E. PETERMAN, PETEEMAN, U.S. U.S. Geological Geological Geological Survey, SurveyyDenver, Denver, CO CO 80225; 80225;W.R. W.R. VAN VAN SCHMUS, SCHMUS,Department Departmentof of Geology, Geology, University University of of Kansas, Kansas, Lawrence, Lawrence,KS KS 66045 66045 The 1) is is aa major major Early Early Proterozoic Proterozoic tectonic tectonic belt belt The Penokean Penokean orogen orogen (fig. (fig* 1) along along the the southern southern margin margin of of the the Archean Archean Superior Superiorcraton. craton. It It consists consists of of aa northern continental—margin continental-margin assemblage assemblage that that overlies overlies an an Archean Archean basement basement and and aa northern southern volcanic—plutonic volcanic-plutonic (oceanic (oceanic arc) arc) assemblage, assemblage, termed termed the the Wisconsin Wisconsin southern maginatic magmatic terrane. terrane. The Ma along along the the The two two terranes terranes were were juxtaposed juxtaposed at at about about 1860 1860 Ma Niagara Niagara fault, fault, aa 10—km—wide 10-km-wide paleosuture paleosuture zone zone containing containing aa dismembered dismembered ophiolite ophiolite (Schulz, (Schulzy1987). 1987). The The Wisconsin Wisconsin magmatic magmatic terrane terrane consists consists of of two two known known subterranes subterranes separated 7-km-wide zone zone of of high high strain strain (Eau (Eau Pleine Pleine shear shear zone) zone) presumed presumed separated by by aa 7—km—wide to to be be aa paleosuture. paleosuture. The The northern, northern, and and major, major, subterrane, subterrane,which which is is exposed exposed along along aa strike strike length length of of 275 widthof of150 150kin, km, is composed composed 275 km km and and across across aa width dominantly dominantly of of greenschist—facies, greenschist-facies, and and locally, locally, lower lower amphibolite—facies amphibolite-facies volcanic volcanic rocks rocks deposited deposited in inthe the interval interval1860—1870 1860-1870Ma. Ma. These These rocks rocks are are mainly mainly calc—alkaline calc-alkaline felsic felsic to to mafic mfic volcanic volcanic rocks rocks similar similar to to volcanic volcanic sequences sequences in in recent recent island island arcs, arcs, but but include include tholeiitic tholeiitic basalt basalt compositionally compositionally similar similar to to back—arc back-arc basin basin basalts basalts and and island—arc island-arc tholeiites tholeiites(Schulz, (Schulz,1984). 1984). AA more more restricted, restricted, younger, younger, greenschist—facies greenschist-facies volcanic volcanic succession succession (1840—1850 (1840-1850 Ma) Ma) overlies overlies older older tholeiitic tholeiitic basalt basalt near near Wausau, Wausau, in in the the area area southeast southeast of of the the Athens Athens shear shear zone. zone. It It consists consists of of felsic felsic calc—alkaline calc-alkaline volcanic volcanic rocks, rocksy also also of of island—arc island-arc affinity, affinity, and and associated associated subvolcanic(?) subvolcanic(?) quartz quartz diorite diorite (LaBerge (LaBerge and and Myers, Myers, 1984). 1984). The exposed south south of of the the Eau Eau Pleine Pleine shear shear zone, zone, The southern southern subterrane, subterraneyexposed consists volcanic succession, succession, approximately low-grade felsic felsic to to inafic mafic volcanic approximately consists of of aa low—grade 1860 which unconformably unconformably overlies overlies aa possibly possibly continuous continuous Archean Archean M a old, old, which 1860 Ma basement. basement. Interlayered Interlayered with with the the volcanic volcanic rocks rocks are are ferruginous ferruginouschert, chert, quartzite, quartzite, conglomerate, conglomerate,and and carbonaceous carbonaceousargillite. argillite. The The Archean Archean gneisses gneissesare are exposed exposed widely widely in in the the major major river river valleys valleys in in central central Wisconsin. Wisconsin. AA moderately moderately widespread widespread red red alkali—feldspar alkali-feldspar granite, granite,1835 1835 Ma Ma old, oldy intrudes the volcanic rocks in the southern subterrane and the Wausau intrudes the volcanic rocks in the southern subterrane and the Wausauarea. area. It It is is cogenetic cogenetic with with two two known known small small patches patches of of rhyolite, rhyolite, welded welded tuff, tuff, and and volcanogenic volcanogenic graywacke graywacke (LaBerge (LaBerge and and Myers, Myers, 1984) 1984) which which probably probably are are caldera caldera related. related. Granitoid Granitoid rocks, rocks,mainly mainly ranging ranging in inage agefrom fromabout about1860 1860Ma Matoto1760 1760Ma, Ma, compose the Wisconsin Wisconsin magmatic magmatic compose about about one—quarter one-quarter of of the the exposed exposed part part of of the terrane. terrane. Calc—alkaline Calc-alkaline (volcanic—arc) (volcanic-arc) intrusive intrusivebodies bodies(1840 (1840MaMaand andolder) older) characterize characterize much much of of the the northern northernsubterrane. subterrane. They They are are presumed presumed to to be be of of mantle mantle origin originmodified modified by by aasubduction subductioncomponent. component. Near Near the the Niagara Niagara fault faultzone zone in in northeastern northeastern Wisconsin, Wisconsin, the the dominant dominant granitic granitic intrusive intrusive rocks rocks are are collision—zone collision-zone intrusions, intrusions,as as defined defined by by Harris Harrisand andothers others(1986). (1986). They They include include both both syn—collisional syn-collisional and and post—collision post-collision plutons, plutons, and and apparently apparently were were generated generated during during continent—arc continent-arc collision collision(-1860 (-1860Ma) Ma) from frommelting meltingofof continental They can can be be distinguished distinguished from from volcanic—arc volcanic-arc plutons plutons continentallithosphere. lithosphere. They 100 �through through their their higher higher Nb Nb and and Ta Ta values. values. The 1835 1835 Ma and the the still still younger younger 1760 1760 Ma granitic bodies are post-tectonic post—tectonic and have have characteristics characteristics of A-type A—type granites. Presumably they were derived derived as as partial partial melts melts of of evolved evolved crust. crust. Structurally, the 1860—1870 volcanic rocks rocks in in the the northern northern subterrane subterrane Structurally, 1860-1870 Ma volcanic have a dominant east-trending, east—trending, steep foliation foliation that is axial planar to tight intersection lineation; lineation; primary structures folds and a related mineral or intersection commonly commonly are are partly partly preserved. preserved. The The main main east—trending east-trending structural structural grain grain is is inferred modified inferred to have have resulted resulted from from north—south north-south collision. collision. It was modified zone, emplacement subsequently by gneiss domes adjacent to the Niagara fault zone, diverse orientation, and and discrete discrete (-1815 of granitoid bodies, major faults of diverse Ma) shear shear (ductile (ductile deformation) zones zones that that locally locally obliterate obliterate older older structures. The 1840—1850 structures. 1840-1850 Ma volcanic rocks southeast of the Athens shear zone dip steeply and are folded on northeast-trending northeast—trending axes, axes, whereas whereas the 1835 zone 1835 Ma M a volcanic rocks rocks are are virtually virtually undeformed. In In contrast, contrast, the the -1860 -1860 Ma Ma volcanic volcanic rocks rocks and and Archean Archean basement basement rocks rocksitt in the the southern southern terrane terrane have have aa nearly pervasive steep stretching lineation and accompanying mylonite that is superposed ott older Archean Archean and and Early Early Proterozoic Proterozoic structures. These These mylonitic mylonitic superposed on older structures pre-date pre—date the 1835 Ma magmatism, magmatism, and possibly resulted from arcarc— structures continent continent collision collision along along the the Eau Eau Pleine Pleine shear shear zone zone at at about about 1840 1840 Ma. Ma. summary, the Wisconsin Wisconsin magmatic magmatic terrane is aa composite composite arc arc system that In summary, records interval of calc—alkaline records a major interval calc-alkaline and tholeiitic volcanism at 1860— 18601870 restricted younger younger interval interval of of caic—alkaline calc-alkaline volcanism volcanism at at 1870 Ma and aa more restricted 1840—1850 Ma. Granitoid intrusive 1840-1850 intrusive rocks accompanied and followed the -1840 Ma Ma along the Eau volcanism. Following final assembly of the terrane at -1840 volcanism. Pleine Pleine shear shear zone, zone, intraplate intraplate magmatism magmatism in in the the south south produced produced post—tectonic, post-tectonic, possibly caldera—related caldera-related rhyolite rhyolite and and cogenetic cogenetic alkali alkali feldspar feldspar granite. granite. This This relatively local magmacism was followed by more widespread magmatism at 1760 local magmatism 1760 Ma, which which was Ma, was coeval coeval with with the theanorogenic anorogenicrhyolite—granite rhyolite-granitetuagmatisut magmatism in in southern southern Wisconsin Wisconsin (Smith, (Smith, 1983; 1983; Anderson Anderson and and others, others, 1980). 1980). REFERENCES CITED CITED Anderson, R.L., Van Schmus, .L., Cullers, Cullers, R.L.,andand Van Schmus,W.R., W.R.> 1980, 1980,Anorogenic Anorogenic Anderson, JJ.L., mid—Proterozoic of tnetaluminous andperaluminous peraluminousplutonism plutonismin in the metaluminous and the mid-Proterozoic of Wisconsin, Contributions p. Wisconsin, U.S.A.: U.S.A.: Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, v. v. 74, 74, p. 3 11-328. 11—328. 3 Harris, N.B.W., Pearce, Pearce, J.A., J.A., and and Tindle, Tindle, A.G., A.G., 1986, 1986, Geochemical Geochemical Harris, N.B.W., characteristics of collision—zone in Coward, Coward, M.P., M.P.y and and Ries, Ries, characteristics collision-zone magmatism, magmatism, & Publication A.C., eds., A.CeY eds., Collision Collision tectonics: tectonics: Geological Geological Society Special Special Publication no. lgy 19, p.p .67—81. 67-81. Myers, P P.E., Proterozoic successions successions in LaBerge, G.L., G.L., and Myers, .E., 1984, 1984, Two Early Proterozoic LaBerge, Geological Society central Wisconsin Wisconsin and their central their tectonic tectonic significance: significance: Geological Society of of America Bulletin, Bulletin, v. v. 95, 95$ p. p. 246—253. 246-253. 1984, Volcanic Volcanic rocks rocks of of northeastern northeastern Wisconsin, Wisconsin, in g Sims, Sims, P.K., P.K., Schulz, K.J., 1984, Schulz, 1C.J., Schulz, K.JeY K.J., and Peterman, Peterman, Z Z.E., eds., Guide to the geology of the Early .E., eds., Schulz, Proterozoic rocks l y 30th 30th Annual Annual Proterozoic rocks in in northeastern northeastern Wisconsin: Wisconsin: Field trip 1, Institute Institute on on Lake Lake Superior Superior Geology, Geology, Wausan, Wausau, Wisconsin, Wisconsin, 93 93 p. p. Geological 1987, an Early Proterozoic Proterozoic ophiolite ophiolite in 1987* in the the Penokean Penokean orogen: orogen: Geological Association of Association of Canada Canada Programs Programs with with Abstracts, Abstracts, v. v. 12, 12, p. p. 87. 87. Sims, Sims, P.K., P.K., 1987, 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic Proterozoic terranes terranes in in the the Great Great U.S. Lakes region——A Lakes region--A brief brief overview: overview: U .S. Geological Geological Survey Survey Bulletin Bulletin 1694—E, 1694-E, p. 56—74. 56-74. p. 101 �Smith, Smith, E.I., E.I., 1983, 1983, Geochemistry Geochemistry and and evolution evolution of of the the early early Proterozoic Proterozoic post— postPenokean Penokean rhyolites, rhyolites, granites, granites, and and related related rocks rocks of of south—central south-central Wisconsin, inMedaris, U.S.A., & Medaris, L.G., L.G., Jr., Jr., ed., ed., Early Early Proterozoic Proterozoic geology geology Wisconsin, U.S.A., of the Great Lakes region: Geological Society of America of the Great Lakes region: Geological Society of America Memoir Memoir 160, 160, p. p. 113—128. 113-128. 102 �90° 46° 45° FIGURE 1. GEOLOGIC MAP OF PENOKFAN OROGEN, EASTERN LAKE SUPERIOR REGION, FIGURE 1. GEOLOGIC MAP OF PENOKEAN OROGEN, AND WISCONSIN MAGMATIC TERMNE. SHOWING CONTINENTAL-MARGIN ASSEMBLAGE EASTERN LAKE SUPERIOR REGION, SHOWING CONTINENTAL—MARGIN ASSEMBLAGE MAGMATIC (Modified from Sims, 1987.) C r o s s h a tAND c h pWISCONSIN a t t e r n , Archean g n eTERRANE. iss; blank a r e a s , (Modified Archean Eau P lgneiss; e i n e s h eblank a r ( s uareas, ture) E a r l y P r ofrom t e r o zSims, o i c r o1987.) c k s ; â‚ Crosshatch P a l e o z o i c spattern, t r a t a . E, Early Proterozoje rocks; Paleozoic strata. zone; J , Jump River s h e a6, r zone; A, Athens s h e aE, r zone; PI, Mountain shear Eau Pleine shear (suture) zone; shear zone; A, Athens shear zone; N, Mountain shear M , I rRiver o n Mountain; M, Marquette. zone. J, I Jump zone. IM, Iron Mountain; M, Marquette. 103 �The TheReany ReanyCreek CreekFormation, Formation,Northern NorthernMarquette MarquetteCounty, County,Michigan: Michigan: Archean Archean ororProterozoic? Proterozoic? J.R. J.R. SMALL SMALL and andT.J. T.J.BORNHORST BORNHORST (Department (Department of ofGeology Geologyand andGeological Geological Engineering, Engineering, Michigan Michigan Technological Technological University University Houghton, Houghton, MI MI49931) 49931) The The Reany Reany Creek Creek Formation Formation consists consists of of aavariety varietyofofclastic clasticsediments sediments and anE-W E-Wtrending trendingelongate elongate belt, belt, less less than than 1.5 1.5km kmwide, wide, and crops crops out out ininan along along the the north north shore shore of ofthe theDead DeadRiver RiverStorage StorageBasin BasinininMarquette Marquette There are are three threestratigraphic stratigraphic units units (Puffett, (Puffett, 1969): 1969): 1) 1) aabasal basal County. There County. conglomerate composedofof an an eastern eastern lens lens in sections sections 2 and and 3,3,T48N, T48N, conglomerate composed R26W, R26W, a western western lens lens in in section section 6, 6, T48N, T48N, R26W, R26W, and and the the Breccia Breccia of of HolyHolyoke oke Mine Mine of of Owens Owens and andBornhorst Bornhorst (1985); (1985); 2) 2) aa middle middle succession succession of of slate slate and plutonic); and and 3) an upper and greywacke greywacke with with dispersed dispersed clasts clasts (dominantly (dominantly plutonic); upper unit ofofarkose, arkose,quartzite, quartzite,slaty slatygreywacke, greywacke,and andconglomerate. conglomerate. The The basal basal unit sediments overlie, or or are are in fault sediments unconformably unconformably overlie, fault contact contact with withArchean Archean To the the south, south, the the upper upper unit unit is is in in fault fault volcanic rocks rocks to to the the north. north. To volcanic Clasts were were sampled sampled throughout throughout the the contact with withArchean Archeanvolcanic volcanicrocks. rocks. Clasts contact formation formation and and include: include: granite, granite, granodiorite, granodiorite, rhyolite, rhyolite, mafic mafic volcanics, volcanics, slate, slate, and iron-formation. iron- formation. and Both Both the the age age of of the theformation formation and and its its mode mode of of origin origin have have been been debated. ItIt has hasbeen beenproposed proposed as a sArchean Archean totoLower LowerProterozoic Proterozoic in in age ageand and debated. parts parts of of itithave have been been interpreted interpreted to to be be either either tillite tillite (Puffett, (Puffett, 1969) 1969) or or aa mass flow flow deposit deposit(Mattson, (Mattson,1983). 1983). This This study study focused focused on on the the question question of of mass VanHise and Leith Leith (1911) (1911) assigned assigned the unit unit to to the age age of of the theformation. formation. VanHise the the the Upper Upper Huronian Huronian due due to tothe thepresence presence of ofiron-formation iron-formation clasts clastswhich which they thought thought to tobe beMiddle MiddleHuronian. Huronian. However, However, these these clasts clasts are are quite quite they similar similar to the the iron-formation iron-formation found found to the the north north in in the theArchean Archean stratistratigraphic and similar graphic succession succession and similar to iron-formation iron-formation within within the the Reany Reany Creek Creek W. A. A. Kelly Kelly(1936, (1936, Formation Formation as as described described by byOwens Owensand andBornhorst Bornhorst(1985). (1985). W. in in Engel, Engel, 1954) 1954) referred referred to to the theunit unitasasbeing beingTimiskaming, Timiskaming, ororsub-Huronian sub-Huronian (Archean), (Archean), in in age age based based on onlithology lithology and and on onan anangular angularunconformity unconformity Engel between between slates slates and and aaquartzite quartzitecorrelated correlatedasasLower LowerProterozoic. Proterozoic. Engel (1954) the unit unit to the (1954) assigned assigned the the sub-Huronian, sub-Huronian, but but stated stated there there was was aa Puffett (1969) (1969)named named possibility possibility that itit was was Middle MiddleororLower LowerHuronian. Huronian. Puffett the the unit, unit, Reany ReanyCreek CreekFormation, Formation, and andsuggested suggested aaLower LowerProterozoic Proterozoic age. age. However, However, he also also stated stated that that itit could could be beequivalent equivalent totothe theTimiskaming. Timiskaming. Owens (1985) favored favored an an Archean Archean age age for the Owens and Bornhorst Bornhorst (1985) the Breccia Breccia of of Holyoke Mine Mine (basal (basalconglomerate). conglomerate). At At the theHolyoke Holyoke Mine Mine Area, Area, they they Holyoke observed is deformed, and that folds observed that the the basal basal conglomerate conglomerate is deformed, and folds in in iron iron formation formation are vertically vertically plunging, plunging, a style style of of deformation deformation more more like like the the A shear shear zone zone follows follows the the basal basal Archean than than the theLower LowerProterozoic. Proterozoic. A Archean contact contact of of the the Reany Reany Creek Creek Formation Formation (Breccia (Breccia of Holyoke Holyoke Mine) for for about about 22 km is is entirely within Archean km until until i it entirely within Archeanrocks rocks(MacLellan (MacLellanand andBornhorst, Bornhorst, (1987) concluded concluded that that the Reany Finally, Weeks Weeks (1987) Reany Creek Creek this volume). volume). Finally, this Formation filled a basin as a result Formation filled basin which which was was truncated truncated as result of of Archean Archean faulting faulting along along the the Dead Dead River River Shear ShearZone. Zone. No such such dikes dikes cut cut Rhyolite dikes dikes are are common common cutting cutting Archean Archean rocks. rocks. No Rhyolite sediments age in the Geologic sediments of Lower Lower Proterozoic Proterozoic age the Marquette Marquette area. area. Geologic mapping mapping by Puffett Puffett (1969) (1969) showed showed no rhyolite rhyolite dikes dikes cutting cutting the the Reany Reany Creek In one one Two possible possible dikes dikes were were found found in in the the basal basal unit. unit. In Creek Formation. Formation. Two locality, there is aa poorly locality, there poorly exposed exposed tabular tabular rhyolite rhyolite body, .5 .5 meters meters by by 10 10 104 �meters, at at an oblique meters, oblique angle angle to to bedding. bedding. This exposure could This exposure could be be either aa dike or In another locality, or an an unusually unusually large, large, elongate elongate clast. clast. In locality, a well well exposed tabular rhyolite exposed tabular rhyolite body body cuts aa schist. schist. Identification of the parent Identification of parent to to the schist schist is is uncertain. uncertain. It may may be be Archean Archean volcanics volcanics or sediments sediments of Reany Reany Creek Formation. Formation. If Archean, Archean, the the rhyolite rhyolite and and surrounding surrounding schists schists are part part of aa fault Unfortunately, these these data data are faultbounded bounded block. block. Unfortunately, are inconclusive inconclusive with respect respect to the the age age of of the theReany ReanyCreek CreekFormation. Formation. The age of the Reany Creek Creek Formation Formation isisequivocal. equivocal. The formation formation is is The the Reany in unconformable or fault contact unconformable or contact with with Archean Archean rocks. rocks. There There is no no evidence to rule out evidence to out conclusively conclusively an Archean Archean or an an Early Early Proterozoic Proterozoic age. age. It should should not be be presumed presumed that that the the Reany Reany Creek Creek Formation Formation is is Early Early ProProterozoic in age. terozoic age. REFERENCES Engel, T. Jr. Engel, Jr. (1954) (1954) The The Stratigraphy Stratigraphy and Petrography Petrography of the the Holyoke Holyoke Meta-sediments of of the Dead [M.S. Meta-sediments Dead River River Basin, Basin, Marquette Marquette County, County, Michigan, Michigan, [M.S. Thesis]: East Lansing, Thesis]: East Lansing, Michigan Michigan State State University, University, 72p. 72p. Mattson, S.R. S.R. (1983) (1983) The The Reany Reany Creek Creek Formation: Mattson, Formation: aa Mass Mass Flow Flow Deposit Deposit of Possible Post Post Menominee MenomineeAge: Age:Proceedings Proceedingsand andAbstracts, Abstracts,29th 29th Institute Institute on on Lake Possible Superior Geology, Geology, Houghton, Houghton, MI., MI., 1983, 1983, p.27 p.27 Owens, E.O. and Bornhorst, Owens, E.O. Bornhorst, T.J. (1985) (1985) Geology Geology and precious precious metal metal mineralizmineralization of the ation the Fire FireCenter Centerand andHolyoke HolyokeMines Mines Area, Area, Marquette Marquette County, County, Michigan: Michigan: Michigan Geological Geological Survey Survey Division, Division, Department Department of of Natural Michigan Natural Resources, Resources, Open Open File File Report OFR-85-2, Report OFR-85-2, 105p. 105p. Puffett, W.P., W.P., (1969), (1969), The Reany Reany Creek Creek Formation, Formation, Marquette Marquette County County MichiMichigan, U.S. Survey Bulletin Bulletin 1274-F, 1274-F, 25 25 p. gan, U.S. Geological Geological Survey VanHise, C.R., and and Leith, C.K., VanHise, C.R., C.K., (1911) (1911) The Geology Geology of the the Lake Lake Superior Superior Region; U.S. Survey Monograph Monograph 52, 52, p. 287-288 Region; U.S. Geological Geological Survey 287-288 Weeks, V.L., (1987) (1987) Gravity Gravity and and Magnetic in the South-Central Weeks, V.L., Magnetic Investigations Investigations in South-Central Part of Part of the theIshpeming Ishpeming Greenstone Greenstone Belt, Belt, Marquette Marquette Co. Co. Michigan, Michigan, (M.S. [M.S. Thesis]: Thesis]: Houghton, Michigan University, 60 p. Houghton, Michigan Technological Technological University, p. 105 �TECTONIC TECTONIC IMBRICATION IMBRICATIONPtND AND FOREDEEP FOREDEEP DEVELOPMENT DEVELOPMENT IIN N THE THE PENOKEAN PENOKEAN OROGEN, OROGEN, EASTEASTCENTRAL MINNESOTA MINNESOTA CENTRAL G.B. Morey Morey D.L. Southwick Southwick and and G.B. D.L. Minnesota Minnesota Geological Geological Survey, survey, 2642 2642 University University Avenue, Avenue, St. st. Paul, Paul, MN MN 55114 55114 Geophysical Geophysical data d a t a (chiefly ( c h i e f l y aeromagnetic), aeromagnetic), together together with with the t h e results r e s u l t s of of scientific and industrial drilling, have led to the recognition of several s c i e n t i f i c and i n d u s t r i a l d r i l l i n g , have l e d t o t h e recognition of s e v e r a l structural s t r u c t u r a l discontinuities d i s c o n t i n u i t i e s within within the t h e Cuyuna Cuyuna iron—mining iron-mining district d i s t r i c t and and contiguous tiguous terrane t e r r a n e in i n east—central e a s t - c e n t r a l Minnesota. Minnesota. These These discontinuities d i s c o n t i n u i t i e s separate separate structural s t r u c t u r a l panels panels of of differing d i f f e r i n g stratigraphy, s t r a t i g r a p h y , structural s t r u c t u r a l style, s t y l e , and and metametabe zones zones of of thrust t h r u s t faulting. f a u l t i n g . Regionally Regionally the the morphic grade, grade, and and appear appear to t o be morphic thrust—faulted, t h r u s t - f a u l t e d , tectonically t e c t o n i c a l l y imbricated imbricated terrane t e r r a n e constitutes c o n s t i t u t e s aa fold-and— fold-andthrust t h r u s t belt b e l t that t h a t was was emplaced emplaced onto onto the the southern southern margin margin of of the t h e Superior Superior craton c r a t o n early e a r l y in i n the the deformational deformationalhistory h i s t o r yofof the t h ePenokeari Penokean orogen. oroqen. Lubricate Imbricate thrusting t h r u s t i n g and and recumbent recumbent folding f o l d i n g may may have have begun begun as a s early e a r l y as a s the the time 30—2180 m.y. in.y. and and continued continued eepisodically t i m e interval i n t e r v a l 21 2130-2180 p i s o d i c a l l y for f o r 300 300 m.y. m.y. or or more. From From south south to to north north the t h e thrust—bounded thrust-bounded structural s t r u c t u r a l panels contain more. rocks rocks metamorphosed metamorphosed at a t successively successively shallower shallower crustal c r u s t a l depth; depth; deformation deformation occurred occurred under under conditions conditions ranging ranging from from amphibolite amphibolite facies f a c i e s in i n the t h e southernsouthernmost McGrath-Little Falls F a l l s panel panel (Fig. (Fig. 1) 1 ) to t o lower lower greenschist g r e e n s c h i s t facies f a c i e s in i n the the most McGrath—Little North range range of of the t h e Cuyuna Cuyuna district. district. North Geophysical Geophysical and and drilling d r i l l i n q data d a t a also a l s o indicate i n d i c a t e that t h a t the t h e east-northeast e a s t - n o r t h e a s t strucstructural the fold—and—thrust fold-and-thrust belt b e l t are a r e overlapped overlapped unconformably on t u r a l trends t r e n d s of of the the the lower lower strata s t r a t a of of the the Animikie Animikie Group Group along along the t h e south south margin t h e north north by by the The of of the t h e main main bowl bowl of of the t h e Animikie Animikie basin basin (Fig. (Fig. 1). 1). The deformation deformation within within the t h e main main bowl bowl decreases decreases regionally r e g i o n a l l y and and systematically s y s t e m a t i c a l l y from south—southeast south-southeast to the Mesabi iron i r o n range range at a t the t h e north north margin t o north—northwest, north-northwest, until, u n t i l , along along the of the Animikie Animikie Group Group dip d i p gently gently of the t h e basin, b a s i n , the t h e unfolded unfolded basal b a s a l strata s t r a t a of of the southward southward and and rest r e s t with with angular angular unconformity unconformity on on Archean Archean basement. basement. We We interpret i n t e r p r e t the t h e main main bowl bowl of of the the Animikie Animikie basin to t o be a tectonic t e c t o n i c foredeep foredeep that t o loading loading of continental c o n t i n e n t a l crust c r u s t by t h a t developed developed as a s aa flexural f l e x u r a l response response to thrust t h r u s t sheets s h e e t s and and nappes nappes in i n the t h e fold—and—thrust fold-and-thrust belt b e l t to t o the t h e south. south. Tectonic transport t r a n s p o r twas was from from south—southeast south-southeast tto o north—northwest, north-northwest, and and the the Tectonic Animikie foredeep probably probably migrated migrated cratonward cratonward iin Animikie foredeep n the t h e same same sense. sense. and ddrilling F i n a l l y , geophysical geophysical and r i l l i n g data d a t ahave have revealed revealed two two other o t h e r basins basins Finally, f i l l e d by by sedimentary sedimentary strata s t r a t a comparable comparable to t o the t h e Animikie Animikie Group Group that t h a t lie lie between between the t h e fold—and—thrust fold-and-thrust terrane t e r r a n e of of the the Cuyuna Cuyuna district d i s t r i c t and and the t h e cratonic cratonic Archean rocks. rocks. These, These, named named the the Long Long Prairie P r a i r i e basin basin and and the the f o r e l a n d of of Archean foreland Nimrod I ) , are a r e interpreted i n t e r p r e t e d to t o be remnants remnants of the t h e formerly formerly Nimrod outlier o u t l i e r (Fig. (Fig. 1), more extensive extensive Animikie Animikie foredeep. foredeep. more filled 106 �ANIMIKIE ANIMIKIE 8ASN BASIN dikes (Early Prot,) &J Possible riftud—margin terrane .,4 Rocks of Archean age LOCATION MAP KILOMETERS 1 1.• Generalized tectonic t e c t o n i c map of of the t h e Penokean orogen orogen of of east—central east-central fold-and-thrust belt b e l t of of Early Early Proterozoic P r o t e r o z o i c age age consists c o n s i s t s of of Minnesota. A fold-and—thrust the t h e McGrath—Little McGrath-Little Falls, F a l l s , the the Moose Moose Lake Lake - Glen Glen Township, Township, and and the t h e Cuyuna Cuyuna South South range range structural s t r u c t u r a l panels; panels; the t h e panels panels are a r e bounded bounded by by structural structural discontinuities d i s c o n t i n u i t i e s inferred i n f e r r e d to t o involve involve significant s i g n i f i c a n t thrusting. t h r u s t i n g . The North range of the i s interpreted i n t e r p r e t e d as a s an an early e a r l y foredeep foredeep that t h a t has has t h e Cuyuna Cuyuna district d i s t r i c t is of the been tectonically t e c t o n i c a l l yincorporated incorporatedini nthe t hexternal e e x t e r nzone a l zone of tfold—and— h e fold-andbeen major foredeep foredeepofof Early Early PProterozoic A major r o t e r o z o i c age, age, but b u t consequent consequent t h r u s t mass. mass. A thrust t o some and perhaps much deformation in i n the t h e fold—and—thrust fold-and-thrust belt, b e l t , conconto sists of of the t h e Animikie Animikie basin, b a s i n , the t h e Long Long Prairie P r a i r i e basin, b a s i n , and and the t h e Nimrod Nimrod out— outl i e r . The sedimentary sedimentary fill f i l l of of these t h e s e basins b a s i n s rests r e s t s unconformably unconformably on on cra— craher. tonic t o n i c basement basement of of Archean Archean age age along along the t h e northwest northwest margins margins of of the the basins. basins. Figure Figure - 107 �EARLY EARLY PENOKEAN PENOKEAN DEFORMATION DEFORMATION IN INTHE THE PEAVY PEAVY POND POND AREA, AREA, NORTHERN NORTHERN MICHIOAN: UICHIOAN: EVIDENCE EVIDENCEFROM FROMTHE THEMICHIGAMME MICHIGAMMEFORMATION FORMATIONAND ANDTHE THEPEAVY PEAVYPOND PONDIGNEOUS IGNEOUSCOMPLEX COMPLEX Steven andDavidd. Davithi. flatly, Matty, Geology Dept.,Central Central Michigan Michigan Univ., Univ., Mt. Pleasant, M Steven D. D. Stahl and Geology Dept., MI 48859 48859 INTRODUCTION INTRODUCTION In areaof ofnorthern northern Michigan, the Inthe the Peavy Peavy Pond area the Early EarlyProterozoic ProterozoicMichigamme NichigammeFormation Formation (PPC). Both bythe thePeavy PeavyPond Pond igneous complex (PPC). Bothunits unitswere weredeformed deformedand and was intruded intrudedby was metamorphosed during the the Proterozoic Proterozoic Penokean Penokeanorogeny orogeny(e.g., (e.g.,Attoh, Attoh, 1984, 1984, 1986 metamorphosed during 1986a,a,b). b). Detailed structural analysis Detailed structural analysisofofthe themacroscopic macroscopic fabric fabricelements elements in i nthe the Michigamme Michigamme Formation in in and to the the PPC PPCsupports supports an anarc-continent arc—continentcollision collision model modelwith with north north over and adjacent to over south south shortening. structure isi saanorth—closing with the shortening. The Thedominant dominantPenokean Penokean structure north-closing fold fold nappe nappe with the PPC PPC iinn the core core and and the upper and and lower lower limbs limbsjuxtaposed juxtaposed by bypostnappe postnappe faulting faultingassociated associated with withthe theBush BushLake Lake (BLF). Fault (BLF). Fault OBSERVATIONS OF OF STRUCTURAL STRUCTURAL FEATURES FEATURES OBSERVATIONS For presentation, we study area area into into the following following domains: Forease ease of presentation, we have have subdivided the stud/ domains: Domain Domain I1consists consistsofofthe theMichigamme MichigammeFormation Formationnorth northofofthe theBLF BLFand andadjacent adjacenttotothe thePPC; PPC; Domain Domain 22 comprises Includesigneous igneousrocks rocksofof comprisesenclaves enclaves of Michigamme Michigamme Formation Formation within withinthe thePPC; PPC;Domain Domain33includes the the PPC; PPC; and andDomain Domain 44 contains containsrocks rocksofofthe theMichigamme MichigammeFormation Formationtotothe thesouth southofofthe theBLF BLFand and adpent totothe thePPC. PPC. adjacent Domah11 £7ffl81fl Minor structural fabric Minorfolds foldsdominate dominate the structural fabricofofthe thegreenschist greenschisttotoamphibolite amphibolitefacies faciesMichigamme Michigamme Formation north of Formationexposed exposed to the north of the the BLF. BLF. Six Sixgenerations generationsofoffolds foldsare arerecognized. recognized.The Theoldest oldest three (Fl,1,F2, three generations generations (F F2,F3) F3)predate predateregional regionalmetamorphism. metamorphism. They Theyposess posess the following of axial axial planar planar foliation; WSW—ENE 1 ) absence absence of foliation;2)2)consistence consistencewith with WSW-ENE common characteristics: common characteristics: 1) shortening; shortening; 3) 3)asymmetry asymmetryindicative indicativeofofWSW WSWtotoENE ENE overriding; overriding;4)4)quartzo—feldspathic quartzo-feldspathic layers layers defining folds; 5)5)micaceous micaceouslayers layersdefining definingClass Class33folds; folds;and and6)6)rounded roundedhinges hingesand andthe the definingClass Class 11 folds; reduction of hinge to limb limb ratio age. Fl, F 1 ,F2, F2,and andF3 F3appear appear to to be be coaxial, but but the ratiowith withdecreasing decreasing age. data not conclusive conclusivein in part part due duetototheir their insufficient insufficient number dueto totheir their reorientation reorientation data are not number but but also also due by polyphasedeformation. deformation. F 11are aretight tight to isoclinal isoclinal folds (SO). F2 folds of of beds beds (SO). F2are areclose closetoto by subsequent subsequent polyphase tight, axialsurfaces surfaces(Si (51))))folds foldsofofSO SOand and tight, shallowly shallowlytotomoderately moderatelyinclined inclined(with (withrespect respecttotoF F11axial Si. inclined (with S1.F3F3are areopen opentotoclose, close, moderately moderately to steeply inclined (withrespect respectto to Si) S1)folds foldsofofSO, SO, Si, 31and ,and F2 axial surfaces (52). (32). Younger are markedly different different from style, attitude, attitude, and geometry: apperently apperently Younger folds are fromFF11—F3 4 3 i ninstyle, and geometry: synmetamorphic almost ideal ideal chevrons chevrons (interlimb (interlimb angle synmetamorphic F4 F4 folds are almost angleclose close to 700, 70° hinge hinge region region very with axialplanar planar foliation foliation ((34) verysmall) small)ofofearly early3—surfaces 5-surfwithmoderately moderately well well developed developed axial 3-4)ini nthe the hinge. The shorteningand andnorthward northwardoverriding overriding which which iiss The sense sense ofof 3344 asymmetry indicates indicates N—S N-5 shortening (e.g. Cambray, 1978). consistent with withPenokean Penokean kinematics (e.g. consistent Cambray, 1978). Fifth striking, Fifthand and sixth sixthgeneration generationfolds foldsare areopen open to to gentle. F5 F5isi sdefined definedby byaa N8OW—N8OE N80W-N80E striking, steeply dipping dipping foliation foliation(35); (55);it isitconsistent steeply i s consistent withwith N—S N-5 shortening shortening and and is ipost—F4 s post-F4because because55 5 5isi s neither parallel paralleltoto34 3 4nor norfolded foldedby byF4. F4. F6 F6folds foldsS5; 55; this thisgeneration generationisi sconsistent consistentwith withE—W E-W neither F5and andF6 F6are areregional regionaldeformations deformationspresent presentini nseveral severalPenokean Penokeanterrenes. terranes. shortening. F5 Domarh 2 Don7ern 2 Enclaves of the the Michigamme MichigammeFormation Formationwithin within the PPC PPCare arecharacterized characterizedbby minor folds folds with with Enclaves of y minor superimposed equigranular equigranular texture texture that that isi slocally locallyfoliated, foliated.These Thesefolds foldsare arecorrelated correlatedtotoDomain Domain11 Fl, they are are similar similar in the intrusion intrusion of F 1 ,F2, F2,and andF3 F3because because they instyle. style.F FI 1—F3 -F3 therefore predate predate the of the the PPC. Domain22 Michigamme Michigammerocks rocks are are stoped stopedblocks, blocks,attitude attitude measurements measurementsof offabric fabric PPC. Because Because Domain Domain I1 surfaces surfacesmay may of Domain Domain 2 surfaces elements iinn these blocks blocks are are moat; moot; parallelism parallelism of surfaces with with Domain or fortuitous. Nonetheless, onthe the or may may not not be fortuitous. Nonetheless, the the orientation orientationofofthe thefoliation foliationsuperimposed superimposedon xenolithic xenolithicblocks blocksisi ssteeply steeplydipping dippingand andstrikes strikesN8OE—N8OW. N80E-N80W. The The equigranular texture texturewas was 108 �developed foliation developed by by contact metamorphism, metamorphism,and andthe theevent eventwhich whichproduced producedthe thelate—stage late-stage foliation postdatesPPC PPC emplacement. emplacement. postdates Doma~h33 Dornern Two BLF; one onestrikes strikes Two steeply dipping dipping foliations foliationsare arepresent presentini nthe thePPC PPCon on both both sides sides of the BLF; N8OE-.N8OW andi is crosscut by by the second, second,which whichstrikes strikes NI O—20E. On Onthe thebasis basisof ofparallelism parallelism N80E-N80W and s crosscut N10-20E. of surfaces, surfaces, the the former former isi scorrelated correlatedtotoDomain Domain I1F5 F5and andthe the letter latterisi scorrelated correlatedtotoDomain Domain11F6. F6. of Dams/# 4 Dome/n I Domain Domain 44 consists consistsofofsillimanite—grade sillimanite-grade Michigamme MichigammeFormation Formationexposures exposurestotothe thesouth southofofthe the BLF thePPC. PPC.Minor Minor folds are ubiquitous, but flattened to to tight to BLF and &adjacent p e n t totothe but they they have have been flattened to isoclinal isoclinalwith withquartzo—feldspathic quartzo-feldspathic leyers layersdefining definingClass Class 22 folds. folds. This Thisflattening flatteningmakes makes differentiation differentiationand andcorrelation correlationofofDomain Domain44folds foldsto to Domain Domain 11 Fl F 1,,F2, F2, or orF3 F3impossible. impossible. Ductile andflattened flattenedgarnets garnetsare areprevalent prevalent iin theseexposures. exposures. Estimates, that are Ductileboudinage boudinage and n these necessarily novolume volumestrain, strain, of finite necessarilylow lowand and assume no finiteextension extensionderived derivedfrom fromthe themeasurement measurementofof boudins from 75 boudins range from 7 5 to to 85 8 5percent; percent;ini nflattened flattenedgarnets garnetsthe theestimated estimatedfinite finiteextension extensionranges ranges from 95 95toto105 105percent. percent.The Themean mean finite finitestrain strainellipsoid ellipsoidIsi soriented orientedsuch suchthat: that: 1) 1 ) the the from intermediate intermediateaxis axisplunges plungesshallowly shallowlyand andtrends trendsapproximately approximatelyE—W; E-W; 2) 2)the themaximum maximumextension extension axis plunges plunges shallowly shallowly and and trends N—S; N-S; and axis and3) 3) the themaximum maximumcompression compressionaxis axisi sisnear nearvertical. vertical. The The presence presence of rolled rolledgarnets, garnets,rolled rolledboudins, boudins,and andfolded foldedboudins boudinsindicate indicatethat thatthe themechanism mechanism of deformation deformation was not pure shear instead extreme shear of shear but Instead extremesimple simple shear shearwith with near horizontal horizontal shear plane N—Strending trendingshear sheardirection. direction. This event event iiss correlative correlative totoDomain it is plane and N-S Domain11 F4 F4because because it is syn—metamorphic; asymmetry (S ( S over over N) N)are arethe the syn-metamorphic; moreover, the the closure closure direction directionand andsense sense of asymmetry same in i nboth bothdomains. domains. same INTERPRETATIONS INTERPRETATIONS The andsurrounding surrounding Michigamme Formation fold nappe nappe(recumbent (recumbent fold, The PPC and Formation define define aa Penokean Penokean fold fold, allàchthonous, extremesimple simpleshear sheari ninlower lower"short" "short or allkhthonous, extreme or"overturned" "overturned" limb limband andparasitic parasiticfolds foldsini n upper with faulted lower limbs have been documented upper "upright" "upright"limb). limb).Nappes Nappes with faulted lower limbs have been documentedelsewhere elsewhere in i n the the Penokean foldbelt belt(e.g. (e.g.Hoist, Holst, 1984), 1984), but ductle lower lower limb limb is Penokean fold but the recognition of a ductle i s apparently apparently unique juxtaposes the upper Peavy area. The ThePPC PPC is i s ininthe thecore coreofofthe thenappe nappeend and the BLF juxtaposes upper unique to to the the Peavy (Domain (Domain 1) 1 )and and lower lower (Domain (Domain 4) 4)limbs. limbs.The Theextreme extremesimple simpleshear shearassociated associated with withthe the development fold nappe nappeobscured obscuredthe theearly early fabric fabric elements — development of the Penokean Penokean fold elements in i nthe thelower lowerlimb limb - this eventsi in rocksof ofthis this limb, limb, which thisreorientation reorientationprohibits prohibitsthe therecognition recognitionofofearly earlyPenokean Penokean events n rocks comprise the exposuresinin thePeavy PeavyPond Pondarea. area. comprisethe the overwhelming overwhelmingmajority majorityofofexposures Structural Structuralanalysis analysisofofthe theMichigamme MichicjammaFormation Formationini nand andadjacent adjacentto tothe thePPC PPC indicates that the the structures compatible only structuresassociated associatedwith withthe thePenokean Penokean orogeny are compatible only with withan anarc—continent arc-continent collision similar to Cambray((1978). collisionmodel model similar tothat thatproposed proposed by Cambray 1978). Our Our work workalso also implies, implies,however, however, that previously. thatthe thepaleogeography paleogeographymust must have have been been more complex than than has has been proposed previously. REFERENCES REFERENCES Attoh, of Early Early Proterozoic Attoh. K., K.. 1984, 1984.Some Someconstraints constraintson onthe thethermal thermalceouses caouses of Proterozoic metamorphic - zones Assoc. i n & in i nnorthern northernMichigan: Michigan:Geol. Oeol. Asm.Can. Can.— Mm. Min.Assoc. Assoc.Can. Can. Ann. Ann. Meeting. Meeting. Attoh, Early Proterozoic Attoh, K., K., 11 986a, Metamophic Metamophic pressures, pressures, temperatures temperatures and and Early Proterozoic geotherms geotherms iinn northern ononLake northernMichigan: Michigan:32nd 32ndAnnual AnnualMeeting fleetingInstitute Institute LakeSuperior SuperiorGeology. Oeology. Attoh, K., 986b, Early geotherms Penokean K., 11986b, EarlyProterozoic Proterozoiccrustal crustal geothermsduring during Penokeanmetamophism metamophism ini n - northern Assoc. Min.Assoc. Asm. Can. Can. Ann. Meeting. Meeting. northernMichigan: Michigan:Geol. Oeol. Assoc.Can. Can.— Mm. Cambray, modelfor forthe theenvironment environmentofofdeposistion deposistionand anddeformation deformation Cambray, F., F., 1978, 1978,Plate Platetectonics tectonicsososaamodel of the Early Michigan: (3eol. Soc. Am. Abst. w northern flichiqan: 0eol. Soc. Am. Abst. w Prog., Procj., Earlv Proterozoic Proterozoic(Precambrian (PrecambrianX)X)ofofnorthern 10, p. p. 376. 376. j.Q., 984, Evidence B., 11984, Evidence for fornappe nappedevelopment development iinn the the Early EarlyProterozoic ProterozoicPenokean Penokeanorogeny, orogeny, Hoist, 1. B., Minnesota: Geology, J2, p. 135—138. HOISTT. 109 �DEFORMATION HISTORY OF OF THE THE QUETICO QUETICO METASEDIMENTS METASEDIMENTS ALONG THE THE NORTHERN NORTHERN DEFORMATION MARGINOF OFTHE THEVERMILION VERMILIONGRANITIC GRANITICCOMPLEX, COMPLEX,NORTHERN NORTHERNMINNESOTA. MINNESOTA. MARGIN PJ.,Dept. Dept.ofofGeology Geologyand andGeophysics, Geophysics,University UniversityofofMinnesota, Minnesota, Tabor, J.R., J.R., and and Hudleston, Hudleston, PJ., Tabor, Minneapolis, MN, MN, 55455. 55455. Minneapolis, Arnphibolite-grade(M1) (Mi)pelitic pelitic schists schists and and younger younger minor minor leucogranites leucogranites and and pegmatites pegrnatites of of the the Amphibolite-grade trending belt of Archean supracrustals supracrustals that Rainy Lake LakeDistrict District in in northern northernMinnesota Minnesota dominate dominate the E-W trending Rainy borders the the northern northern margin margin of ofthe thehigher-grade higher-grademigmatites migmatitesand andgneisses gneissesof ofthe theVermilion VermilionGranitic Granitic borders Complex of the Quetico Gneiss Belt. Belt. The (VGC),the thesouthwestern southwesternextension extension in northern northern Minnesota of The Complex (VGC), structural structuraldevelopment developmentof of the theschist schistbelt beltinvolved involvedthe thetemporal temporalpartitioning partitioningof of the the strain strainassociated associatedwith with aa dynamic both E-W dextral shear dynamic dextral dextral transpressive transpressive deformation deformation involving both shear and and N-S N-S horizontal horizontal flattening. flattening. Theearly earlystage stageof of deformation deformation involved involved two two phases phases of of pervasive pervasive folding, folding, the the first first possibly recumbent recumbent The and and nappe-like nappe-like and and the the second second upright upright and and isoclinaL isoclinal. Minor Minorfolds folds across across much much of of the the width width of of the the schist schist arepreodniinantly preodminantly F2 F2 and and of 2Z' symmetry,with withminor minor'perturbed' 'perturbed'areas, areasof of 'S' 'S' symmetry symmetryrepresenting representing belt are belt symmetry, either undulations undulations in the the hinge hinge lines lines of of minor minor F2 F2 folds folds or or major major F2 folds. folds. However, However,approaching approachingthe the either southern aredominant dominantin inthe theschists schists(Bauer, (Bauer, F2 folds folds of of 'S 'S' symmetry symmetryare southern margin of the the schist schist belt belt minor minor F2 1988), suggesting suggesting that that aa major major F2 F2fold folddoes doesindeed indeedunderlie underliethe theschist schistbelt beltwhose whosenorthern northernlimb limbforms forms 1988), much of the the width width of of the the belt. belt. Reversal Reversalininstratigraphic stratigraphictops topsfrom fromnorthnorth-totosouth-facing south-facingacross acrossthe the much northern limb of this this major major F2 F2 fold fold suggests suggests the presence of a major major F1 F i fold. fold. Minor MinorF1 FlF2 fold northern F2 fold alsosupport supportthis. this. interferencepatterns patternsalso interference Mesoand microstructural microstructural evidence evidence along along the the Rainy Lake-Seine River Fault (RLSRF), (RLSRF),the themajor major Meso- and fault fault defining definingthe the boundary boundary between betweenthe theschist schistbelt belt and andthe theRainy RainyLake LakeWrench WrenchZone Zoneto tothe thenorth, north,suggest suggest E-W E-W near-horizontal near-horizontaldextral dextralshear sheardominated dominatedthe theintermediate intermediatestage stageof ofthe thetranspressive transpressivedeformation deformationand and was localized localized into the RLSRF RLSRFasasthe theschists schistsalong alongthe thenorthern northern margin margin of of the the belt beltcooled cooledfrom from was amphibolite-to togreenschist-facies greenschist-faciesconditions. conditions. amphiboliteThe veins crosscutting Thelack lackof ofevidence evidencefor forshear, shear,the thepresence presenceofoftectonized tectonizedpegmatite pegmatiteveins crosscuttingF1F2 FlF2fold fold interference of conjugate shear shear bands bands and zones in the interference patterns patterns and the presence presence and orientation of the 110 �and pegmatites suggest the N-S leucogranites and N-S horizontal horizontal flattening flattening component component of of the thetranspression transpression the later stages of the deformation. Quartz dominated the Quartz and and calcite calcitelattice lattice preferred preferred orientation orientation (LPO) (LPO) of a ductile component component of of N-S N-S horizontal horizontal flattening flattening in in the analyses also suggest an increased dominance of RLSRF RLSRFduring duringgreenschist-facies greenschist-faciesconditions. conditions. In the center of the the schist schist belt, belt, quartz quartz LPO LPO patterns patterns suggest: 1) leucogranites and pegmatites have also experienced experienced both E-W E.W dextral 1) the schists schists bordering the leucogranites dextral N-S flattening, 2) 2) schists located away away from from the the intrusives intrusives have have experienced experienced only only E-W E.W dextral dextral shear and N-S shear and 3) the N-S horizontal flattening. Quartz the leucogranites leucogranites and and pegmatites pegmatites have experienced experienced only N-S Quartz 120 LPOpatterns patternsfrom fromthe thesouthern southernmargin margin of of the theschist schistbelt belt bordering bordering the the inigmatite migmatite terrane to the south to those measured measured along along the the northern northernmargin marginof ofthe thebelt beltininthe theRLSRF RLSRF and to those in the were similar to enveloping the margins schists enveloping margins of the the leucogranites leucogranitesand and pegmatites pegmatites in in the the center center of of the the belt, belt, indicating indicatingthe the schists to the south have also experienced experienced both both E-W E-W dextral dextral shear shear and and N-S N-S flattening. flattening. schists have also It is suggested partitioning of of strain across the width suggested that this sequence of structural structural development and partitioning consequence of the rotation of the regional kinematic framework framework of deformation deformation and and of the schist belt is a consequence in the ductility of the the schists schists and and intrusives. intrusives. Initially, while bedding was was nearneartemporal variations in horizontal, the schists accommodated the coaxial coaxial component of the transpression horizontal, accommodated the component of transpression and deformed deformed homogenously by by pervasive pervasive folding. folding. Minor homogenously Minor noncoaxial noncoaxial strain from this episode episode of the the deformation deformation is is rucorded in the asymmetric quartz LPO patterns in schists in the center of the belt. belt. Following Following pervasive pervasive recorded upright and and isoclinal isocinal F2 favorableorientation orientation to to accommodate accommodate the upright F2 folding, folding, the the schists schists were were in in aafavorable noncoaxial component component of of the the transpression. transpression. However, noncoaxial However, the schists schists were were also also cooling, cooling, and and therefore therefore hardening, such such that that E-W E-W dextral dextral shear shear was was heterogeneously heterogeneouslylocalized localizedinto intothe theRLSRF RLSRF along along the the hardening, northern margin of of the belt. Subsequently, Subsequently,the the regional regional kinematic kinematic framework framework rotated rotated such that that ductile ductile N- flattening occurred occurredinin the: the: 1) 1) RLSRF, RLSRF, 2) S horizontal horizontal flattening 2) leucogranites leucogranites and and pegmatites pegmatites and and schists schists enveloping their margins and 3) schists schists along along the the southern southern margin of the the belt belt bordering bordering the the migmatite migmatite terrane to to the south. The terrane Thebulk bulk of ofthe theschist schistbelt beltdefromed defromedby by brittle brittle faulting faulting during during this this stage stage of of the the deformation. deformation. increased ductility ductility necessary The increased necessary for for the aforementioned aforementioned areas areas to accommodate accommodate the late component component of N-S horizontal flattening was was a consequence consequence of: of: 1) 1) strain strain heating heating in in the RLSRF along along the the northern northern 111 �margin of of the schist belt, 2) contact heating supplied supplied by by the the plutons plutons in in the center of the belt and 3) margin 3) regional metamorphic heating supplied by by the the VGC VGC along the southern margin margin of of the the belt. belt. At At this this time, time, significance of the rotation of the regional kinematic framework are unclear. unclear. the reasons and tectonic significance framework are ..........this this volume. Bauer, R.L., R.L.,1988, 1988, Multiphase Multiphase folding folding , 112 �REFRACTION REFRACTION ANALYSIS ANALYSIS OF OF THE THE GLIMPCE GLIMPCE MARINE MARINE REFLECTION REFLECTION PROFILE' IN GEORGIAN GEORGIAN BAY PROFILE IN BAY Michael D. Thompson Thompson and and C. C. Patrick Patrick Ervin Ervin Dept. of Geology, Geology, N. Illinois Illinois Univ., Univ., DeKaib, DeKalb, IL IL 60115 60115 In 1986, a multichannel, marine reflection reflection survey survey was was made made along a profile across across Georgian Georgian Bay Bay and and Lake Lake Huron Huron (GLIMPCE (GLIMPCE Line Line J) employing employing a streamer streamer length length of of approximately approximately 33 km. km. Part Part of of the data within Georgian Bay, Bay, beginning with shotpoint shotpoint 1598 1598 north north of Cabot Head and and extending extending westward westward to to shotpoint shotpoint 2174 2174 north north of of Cove Island Island in in the the entrance entrance of of the the bay, bay, were were reprocessed reprocessed using using an an automatic automatic picking algorithm algorithm to to obtain obtain arrival arrival times times for for the the refracted energy. refracted energy. Both a refractor refractor offset offset correction correction and and aa lake lake bottom topography correction were incorporated into the topography correction were incorporated into the inversion inversion of the first first arrival arrival data data to to obtain obtain aa velocity—depth velocity-depth section section along along the the profile. profile. the eastern eastern portion po rtion Preliminary analysis of the data shows Prelimi nary analysis shows the to be domina dominated (<0.5') dipping (<0.5°) .ted by laterally continuous, continuous, westward westward dipping gentle dip dip is is refractors, probably of of Ordovician Ordovician age. age. The gentle fractors, probably consistent regional geologic consistent with with the theregional geologic structure, structure, and and the the computed computed velocities velocities are are within the the range range of of values values expected expected on on the the basis basis Assuming that velocities of the known known lithologies lithologies in in the the area. area. velocities on the order of 6.1 km/s mark the the top top of of the the Precambrian Precambrian 6.1 to to 6.6 6.6 km/s basement (Mereu obidon, 1971), ( ~ e r e uand Jobidon, 19711, the the interpreted interpreted velocity velocity structure beneath this portion of the the profile suggests suggests that that the the depth of the the westward deepening deepening basement basement surface surface ranges ranges from from 300 300 to 400 400 m. m. The western part of the the profile profile track track overlies overlies near—surface, near-surface, high—velocity high-velocity Silurian Silurian dolomite, dolomite, which which tends tends to to mask mask the the refractions refractions from from underlying underlying layers. layers. In this this instance, instance, refractions refractions from the Precambrian Precambrian surface surface are are not observed observed because because first arriving arriving energy energy until until•beyond 'beyond the the they do not become become the the first limits of the further problem arises arises in in the the limits the receiving receiving array. array. AA further shallow water areas where bottom sediment sediment refractions refractions are are often often absent absent due due to to the the large large source—to—first—receiver source-to-first-receiver distance distance relative to relative to the the refractor refractor depth. depth. Because refractor depths depths are are calculated cumulative fashion, fashion, lack lack of of information information for for the the calculated in in a cumulative undetected shallow layers precludes precludes calculation calculation of reliable reliable depths depths for for the the deeper deeper interfaces. interfaces. This This analysis analysis demonstrates demonstrates that that marine marine reflection reflection data data can can be reprocessed reprocessed relatively cheaply to obtain additional additional However, the information on the shallow shallow velocity velocity structure. structure. However, the technique is ineffective ineffective in the extremely extremely shallow shallow water overlying overlying the unusually—high, near—surface velocities unusually-high, near-surface velocities found found in in the the entrance entrance to the the bay. bay. REFERENCES REFERENCES CITED CITED R.F., and Jobidon, Jobidon, G., 1971, 1971, A Seismic Seismic Investigation Investigation of of Mereu, R.F., the Crust and Moho on a Line Perpendicular Perpendicular to to the the Grenville Grenville Front, Canadian Jr. of Front, of Earth Earth Sci., Sci., v. v. 8, 8, p. p. 1553—1583. 1553-1583. 113 �GEOCHEMISTRY GEOCHEMISTRY AND AND PETROLOGY PETROLOGY OF OF THE THE ATHELSTANE ATHELSTANE GRANITE, GRANITE. MARINNETTE MARINNETTE COUNTY, COUNTY. WISCONSIN WISCONSIN R. J. J. Wagner Wagner and and M. M. K. K. Sood Sood Department Department of Earth Earth Sciences Sciences Northeastern Northeastern Illinois I1 linois University University Chicago, Chicago, Illinois, Illinois, 60625 60625 The The Athelstane Athelstane Granite Granite lies lies in in the the northern northern part part of of is roughly roughly Marinette Marinette County, County, northeastern northeastern Wisconsin. Wisconsin. It is oval shaped pluton pluton that that covers covers an an area area of of 2226 mi. (585 26 mi. (585 Van Schmus km. Schmus et al., (1975) (1975) obtained obtained an an Rb/Sr Rb/Sr isotope isotope km.). age of 1810+/—50 m.y. for 1810+/-50 m.y. for the the Athelstane Athelstane Granite, Granite, and and considered it to to be a part of the the Penokean Penokean Northeastern Northeastern considered it Wisconsin Wisconsin orogenic orogenic and and plutonic plutonic complex. complex. The The Athelstane Athelstane Granite Granite has has relatively sharp sharp contact contact relations relations with with the the Quirinesec Quinnesec metavolcanics (1905+/—50 m.y.). Quinnesec metavolcanics (1905+/-SO m.y.1. Quinnesec xenoliths xenoliths in in Athelstane Athelstane are are thermally thermally altered. altered. Locally, Locally, the the Athelstane Athelstane Granite Granite is isintruded intrudedby by 1760+/—10 1760+/-10 m.y. m.y. old oldArnberg Amberg Granite Granite (Van (Van Schmus, Schmus, 1980). 1980). 9 "4. The is aa medium medium to to coarse coarse grained grained The Atheistane Athelstane Granite Granite is pink granite granite with average average modal composition composition of of microperthitic microcline (39.1%), (39.1%),Ans0-rn An20_ plagioclase microperthitic microcline plagioclase (24.9%), bluish quartz quartz (26.5%), (26.5%), biotite biotite (3.8%), (.8%), and (24.9%), bluish and hornblende hornblende (1.2%). (1.2%). Accessory Accessory minerals minerals include include apatite, apatite, sphene, and and magnetite. magnetite. Modal compositions compositions plot in in the the sphene, Granite Granite field field of of Streckeisen's Streckeisen's (1976) (1976)quartz—alkali quartz-alkali feldspar-plagioclase feldspar-plagioclase feldspar feldspar diagram. diagram. Micrographic Micrographic growths growths are are present. present. Retrogressive Retrogressive reactions reactions seen seen include include sericitization sericitization of of plagioclase, plagioclase, and and the the replacement replacement of of hornblende hornblende by by biotite biotite or or chlorite. chlorite. Major element element chemistry of the the Atheletane Athelstane rocks rocks shows shows that they they are are calc—alkaline calc-alkaline and and marginally marginally peraluminous. peraluminous. The The S102 SiQ2 varies varies between between 67 67 to to 75 75 weight weight %. %. KoO, FeO, Fed, TiO2, TiOo, 1(20, and and P205 P205 are are high, high, whereas whereas MgO, MgO, CaO CaO and and to to aa certain certain extent extent Na20, Na 0, are are low, low, when compared compared to to granitoids granitoids with similar similar is generally greater greater than than Na20, with with siTica si ica contents. contents. K20 is total alkalis alkalis (Na20+K20) (Na20+K 0 ) between between 6.1 6.1 to to 8.5 8.5 weight weight %. "is The The (K20+Na20)/CaO and Fe Fe/(FeO+MgO) < K O+Na2Q)/Ca0 and /(FeO+MgO) ratios ratios of of 1.5 1.5 to to 3.5 3.5 and and 0.75 0. 5 to to 0.86 respectIvely, respectively, are are similar similar to to anorogenic anorogenic granite, granite, but different different from from other other Penokean Penokean granites. granites. Harker Barker variation diagrams diagrams (S102 (S102 vs. other major oxides) show show aa limited role played by fractional fractional crystalization. crystalization. Both Both Zr Zr limited (130—410 ppm.) and Ba (630—2380 (130-410 ppm.) (630-2380 ppm.) ppm.) are are relatively relatively higher higher than other other Penokean Penokeangrariltes. granites. Ba—Rb-Sr Ba-Rb-Sr relations relations do do not not than show show extensive extensive effects effects of of metasomatism metasomatism or or late late fluxing fluxing of of magma 1975). magma with with volatiles volatiles (El—Bouseily (El-Bouseily and and El-Sokkary, El-Sokkary, 1975). ? Y 8 114 �Petrographic, chemical chemical (Figures (Figures 1—3), 1-31, and and field field Petrographlc, relations of of the the Athelstane Athelstane Granite Granite have have greater' greater affinity affinity to to relations anorogenic than than synorogenic synorogenicgranite graniteplutoris. plutons. Clearly, Clearly, the the anorogenic Athelstane Granite Granite is is aa late late orogenic orogenic (or (or perhaps perhaps even even post post Atheistane orogenic) intrusion intrusion that that certainly certainly did did not not originate originate during during orogenic) the main stage stage of of the the Penokean Penokean orogeny. orogeny. the Plots of of the the compositions compositions of of Athelstane Athelstane rocks rocks in in the the Plots albite-orthoclase-silica minima albite—orthoclase-sil Ica system system containing polybaric minima 19835, suggest suggest that that the the granite granite magma magma projections (Anderson, (Anderson, 1983), projections was probably probably generated generated at at approximately approximately 35 3 5 km. km. depth, depth, and and was emplaced at at about about 10 10 km. km. depth. depth. emplaced It is is therefore therefore proposed proposed that that the the Athelstane Athelstane Granite Granite It magma was was generated generated by by aa moderate moderate degree degree of of partial partial melting melting magma of crustal crustal material, material, probably probably aa mixture mixture of of Archean Archean and and of Penokean crust crust transitional transitional to to tonalite-gabbro tonalite-gabbro composition. composition. Penokean This This study study was was supported supported by by aa grant grant to to N. M. K. K. Sood Sood from from the Committee Committee on on Organized Organized Research. Research. the J. L., L., 1983, 1983, Proterozoic Proterozoic anorogenic anorogenic granite granite Anderson, J. Anderson, p. plutonism of of North North America: America: Geol. Geol.Soc. Soc.America AmericaMern. Mem. 161, 161, p. plutonism 133-154. 133-154. Anderson, J. J. L., L., and and Cullers, Cullers, R. R. L., L., 1987, 1987, Crust-enriched, Crust-enriched, Anderson, mantle-derived torialites tonalites in in the the early early Proterozoic ProterozoicPeriokean Penokean mantle—derived orogen of of Wisconsin: Wisconsin: Journal Journal of of Geology, Geology, v. v. 95, 95, p. p. 139-154. 139-154. orogen El-Bouseily, A. A. M., M., and and El-Sokkary, El-Sokkary, A. A. A., A., 1975, 1975, The The El-Bouseily, Relation Between Between Rb, Rb, Ba, Ba, and and Sr Sr in in Granitic Granitic Rocks: Rocks: Chemical Chemical Relation v. 16, 16, p. p. 207-219. 207-219. Geology, v. Geology, Streckeisen, A. A. L., L., 1976, 1976, To To each each plutonic plutonic rock rock it's it's proper proper Streckeisen, name: E. E. Sd. Sci. Review, Review, number number 12, 12, P. P. 1—34. 1-34. name: Van Schmus, Schmus, W. W. R., R., 1980, 1980, Geochronology Geochronology of of igneous igneous rocks rocks Van associated with with the the Penokean Penokean Orogeny Orogeny in in Wisconsin: Wisconsin: in in Morey, Morey, associated G. B., B., and and Hanson, Hanson, C. G. N., N., eds., eds., Selected Selectedstudies studiesofofArcheari Archean C. and lower lower Proterozoic Proterozoic rocks, rocks, southern southern Canadian Canadian Shield: Shield: Geol. Geol. and p. 159-169. 159-169. Soc. America America Spec. Spec. Paper Paper 182, 182, p. Soc. Van Schmus, Schmus, W. W. R., R., Thurman, Thurman, E. E. N., M., and and Peterman, Peterman, Z.E., Z.E., 1975, 1975, Van Geology and and Rb-Sr Rb-Sr chronology chronology of of middle middle Precambrian Precambrian rocks rocks in in Geology v. eastern and and central central Wisconsin: Wisconsin: Geol. Geol. Soc. Soc. America America Bull., Bull., V. eastern 86, p. p. 1255—1265. 1255-1265. 86, 115 �Q Figure 1 A P p 0N Figure 2 N z+ 0 N 80 55 50 55 70 75 80 S0p 3 S S Figure 3 Figure 3 £ I 0 U £ 3 2 C 5 Wl. 4n.,n 0 U thsls.n. 0 1.0 0.2 OIPw Normally. Figures Figures 1-3. 1-3. QUsrtz/(OrtftoclSss...AIbj.+Aflo,thlt,) Figure Q—A-P Diagram (modal Figure 11 is a Q-A-P (modal Quartz—Alkali Quartz-Alkali Feldepar—Plagioclase Feldspar-Plagioclase Feldspar) Feldspar) comparing comparing the the Atheistane pluton to the other Penokean plutons of northern Athelstane and northeastern northeastern Wisconsin. Wisconsin. Figure 22 is is aa plot plot of of Total Total Alkalis Alkalls (K20 ++ Na20) vs. Si02 (weight (weight %s) %s) for for the the Athelstane pluton compared to to other other Penokean Penokean plutons plutons of of shows the CIPW-normative corundum Wisconsin. Wisconsin. Figure 3 show3 corundum vs. vs. quartz/feldspar ratio for the Atheistane quartz/feldspar Athelstane pluton compared compared to to the other Penokean Penokean plutons plutons of of Wisconsin. Wisconsin. Box ABCD Is is the the zone of normal normal granltes granites (from ( f r m Fernandez—Alonso Fernandez-Alongo et et al., al., 1986). 1986). 116 �Geochemistryand and Tectonic TectonicSignificance Significance of Early Earlv Proterozoic Proterozoic Igneous Igneous Rocks. Rocks, Geochemistry Northern NorthernMichigan Michiganand and Northeastern NortheasternWisconsin Wisconsin Soo So0 Meen Meen Wee Wee and and John JohnT. T. Wilband, Wilband, Department Departmentof ofGeological GeologicalSciences, Sciences,Michigan Michigan State StateUniversity, University,East EastLansing, k i n g ,MI MI48824 48824 Early Early Proterozoic Proterozoic igneous igneous rocks rocks in northern northern Michigan Michigan and and northeastern northeastern Wisconsin consist of of a complex assemblage of of lavas, lavas, sills sills and and dikes. dikes. These Wisconsin consist complex assemblage Theserocks rocks were were metamorphosed metamorphosed atatvarying vaqing degrees degreesduring duringthe thePenokean PenokeanOrogeny Orogeny(1.82-1.85 (1.82-1.85 Ga). of the area Ga). The The tectonic tectonic evolution evolution of area has has been been attributed attributed to toplate platemargin margin processes, processes, arc-continental arc-continentalcoffision collision processes, or intracratonic intracratonicmobilization. mobilization. The the tholeiitic tholeiiticfield fieldinin an an AFM AFM diagram. diagram. A A The analyzed analyzed rocks rocks fall Within within the northern tholeiitic tholeiiticassemblage assemblageofofdike dikeswarms swarmsand andvolcanic volcanicpiles pilescontaining containingpillow pillow northern lavas (Hemlock (Hemlock and and Badwater Badwater Greenstones) Greenstones) can can be bedistinguished distinguishedfrom from aasouthern southern lavas magmatic with arc-related chemical characteristics. characteristics. Mafic magmatic assemblage with Mafic rocks rocks of the the dike dike swarms, swarms, the the Hemlock Hemlock volcanics, volcanics, and the Badwater Badwater Greenstones Greenstonesevolved evolved from from tholeiitic tholeiitic basalts basalts with with subalkaline subalkalineaffinities. affinities. Virtually Virtually all all rocks rocks plots plots within within the the subalkaline subalkaline field of the Ol-Ne-Q 01-Ne-Q diagram. The Theabsence absenceof of the thealkaline alkalinebasalt basaltfield field within within the the region region could could mean mean that thatearly earlyProterozoic Proterozoic magmas magmas were were generated generated atat relatively relatively shallow shallow depth, depth, under under the theinfluence influenceof of aa high high geothermal geothermalgradient. gradient. Based CaO/Ti02 and andA1203 A1203 vs. vs. Ti02 Ti02plot, plot, itit Based on on chemical chemical characteristics and CaO/TiO can arederivatives derivativesofofhi-Ti hi-Ti can be be sugested suggestedthat thatthe therocks rocksofofthe thenorthern northernassemblage assemb ageare MORB MORB like like tholeiites tholeiites from from relatively relatively undepleted undepleted source(s). source(s). The The elemental elemental distributions lava and and dike dikeswarms swarms in in the the northern northernassemblage assemblagehave haveled ledus ustoto distributionsof of the thelavas conclude concludethat thatthe thedikes dikesserved servedasasfeeders feederstotothe thevolcanic volcanicpiles. piles. Other data datasupport supportcontamination contamination processes. processes. For Forexample, example,ininsome somedikes, dikes, Other Si02 S O 2 and and Rb/Sr RbISrare areenriched e ~ c h eatdatthe themargins marginscompared compared to to the thecenters centersand and may may represent emplacement or or crystallization. crystallization. The The Zr/Y ratio represent assimilation assimilation during emplacement ratiofor for the ( > 10)isismuch much higher higher than thanthe themore moreprimitive primitiveflows flowsand and the supracrustal supracrustal rocks rocks (>10) dikes. dikes. Evolved Evolvedrocks rockswith withprogressively progressively higher Zr/Y ratios ratiosmay may have haveresulted resultedfrom from assimilation systems. Furthermore, assimilation within ponded magma systems. Furthemore, Ce/Yb Ce/Yb vs. vs. Ce Ceplots plots can can be beinterpreted interpretedtotorepresent representassimilation-fractional assimilation-fractionalcrystallization crystallizationrather ratherthan thansimple simple fractionalcrystallization. crystallization. Finally, Finally,ininspider spiderplots plotsofofsuite suiteaverages, averages,the thedike dikeswarms, swarms, fractional Hemlockvolcanics, volcanics, and and Badwater Badwater Greenstones Greenstonesare medistinctively distinctivelydepleted depletedininNb Nbwith with Hemlock respect Nb anomaly anomaly isis calculated calculated asas respect toto its its neighboring neighboring elements, elements, where where the the Nb Nb/chon. (Thlchon. ++ La/chon.)/2 La/chon.)/2 (Ueng (Ueng etet al., al., 1987). 1987). The The decrease decrease Nblchon. - - (Th/chon. approximates approximates an anexponential exponentialfunction functionwith withincreasing increasingdifferentiation differentiationindex. index. This This implies impliescontinuing continuingassimilation assimilationthroughout throughoutthe thedifferentiation differentiationhistory. history. The Thetectonic tectonicsettings settingsofofthe thedike dikeswarms, swarms,Hemlock Hemlockvolcanics, volcanics,and andBadwater Badwater Greenstones Greenstoneswere weretested testedbybypreviously previouslydeveloped developedtectonic tectonicdiscrimination discriminationdiagrams. diagrams. In InTi-Zr-Y Ti-Zr-Y plots lots(Pearce), (Pearce),the themajority majority of of the therocks rocksplot plotininthe thewithin withinplate platebasalt basalt field, field,and andaafairly airly large large number number in in the the calc-alkaline calc-alkaline and ocean ocean floor floor basalt region. In In Nb-Zr-Y Nb-Zr-Y plot plot (Meschede), (Meschede), the the data datamostly mostly fall fall in in the the within within plate plate tholeiites tholeiites and and PPNbapex apexmay mayreflect reflect typeMORBs. MORBs. The Thesubparallel subparallel"vertical" "vertical"trends trendsaway awayfrom fromthe theNb type the of crustal Nb. The The other other the aforementioned aforementioned assimilation assimilation of crustal rocks rocks depleted depleted in in Nb. possibility possibility is is that that the theP-type P-typeMORBs MORBscan canbe begenerated generatedbybygradual gradualdecompression decompression during duringrifling. rifting. This Thisdecompression decompressionenabled enabledconcurrent concurrentmelting meltingofofzoned zoned source sourceofof upper, upper,more moredepleted depletedmantle mantleand andlower lowerenriched enrichedmantle. mantle.InIntectonic tectonicdiscrimination discrimination diagram diagramusing usingHf-Ta-Th Hf-Ta-Th(Wood), (Wood),most mostsamples samplesfrom fromthis thisinvestigation investigationplot plotoutside outside the Ta, thetectonic tectonicfields. fields. This Thissuggests suggeststhat thatthe therocks rockshas hasbeen beencontaminated contaminatedsince sinceHf, Hf,Ta, and andTh Thare arevery verysensitive sensitivetotocrustal crustalcontamination. contamination. InInsummary, summary,there thereisisno noclear clear definition definitionof of tectonic tectonicsetting settingfor forthe theearly earlyProterozoic Proterozoicrocks rocksof ofthe thearea. area.However, However, Nesbitt),most mostofofthe thenorthern northern CaO/Ti02and andAl,O3/TiO2 A1303/Ti02vs.vs.Ti02 Ti02 plots(Sun (Sun&&Nesbitt), CaO/Ti02 plots assemblage assemblage rocks rocks äluster c uster along along an an undepleted undepleted source source trend; trend;whereas whereasthe thesouthern southern ? k' 117 �"magmatic arc" arc"rocks rocksofofthe the Quinessec Quinessecplot plot in in aa depleted source region. region. Because Because arc-related rocks are commonly commonlydepleted depletedininTTiO rocks are i 0 and are enriched in A1203/Ti02 compared to MORBs MORBs or continental continental tholeiitic tholeiitic %asalts, northern compared basalts, the the rocks rocks of of the northern assemblage assemblage are are probably probably best assigned assigned as as having having aa rift related origin. origin. Interpretations of these rocks, Interpretations of of the the chemical chemical characteristics characteristics of rocks, based on on modern modern analogs, favor an extensional analogs, favor extensional tectonic tectonic regime, regime, such such as would would develop develop by by arcarccontinent by previous previous investigaters. investigaters. continentcollision collisionprocesses processessuggested suggested by 118 �Preliminary Structural Preliminary Structural Analysis Analysis of of Archean Archean Rocks Rocks in in the the Virginia Virginia Horn area, areaI Northeastern Minnesota Minnesota J.L. WELSH WELSH (Department (Department of GeologyI J.L. Gustavus Adoiphus Adolphus College, CollegeI Geology, Gustavus St. St. Peter, PeterI1'2 MN 56082) 56082) Detailed mapping in Detailed mapping in lower lower greenschist greenschist grade grade Archean Archean rocks rocks northeastern Minnesota Minnesota (the within the the Virginia Horn area of northeastern (the defined by the unconformable unconformable superjacent prominent Z-fold 2-fold defined superjacent Biwabik Iron Formation of the Mesabi Iron Range), has Iron Fomation Iron Range)# has revealed revealed the the presence presence of of at at least least one one major major period periodof offolding folding(F].) (Fl) and and aa series northeasterly trending trending faults series of of northeasterly faults which which postdate postdate the the folding. The identified primarily primarily on folding. The fold fold event is identified the basis basis of of on the reversals folds are are reversals in in stratigraphic stratigraphic top top indicators. indicators. Minor Fl folds rare, where present they are tight to rareI but where are tight to isoclinal isoclinal in in style style and and well developed steeply steeply plunging. plunging. A moderately to well developed axial axial plane foliation foliation is is present present in in these these folded folded rocks. rocks. informally designated One prominent fault, faultI here informally designated the the Fayal Fayal fault, greenstone occupying faultI separates separates the the greenstone occupying the the ridge ridge west west of of Gilbert Gilbert with with the the greywacke—slate greywacke-slate sequence sequence present present east east of of Eveleth Eveleth (Fig.). Another Another fault, faultI here informally informally designated designated as as the the Pike Pike (Fig.) River sequence from River fault, faultI separates separates this this same same metasedimentary metasedimentary seqyence from greenstone greenstone to to the the west, westI in in the the northern northern portions portions of of the the study study The Pike. area. phyllonitic rocks area. Strongly Strongly phyllonitic rocks mark mark its its presence. presence. The Pike. River River fault fault is is more more difficult difficult to to delineate delineate to to the the south south as as it it metasedimentary sequence appears to cut into the metasedimentary sequence and and trends trends parallel parallel to to bedding. In In this this southern southern area area the the Pike Pike River River fault fault interpreted to occupy a phyllonitic zone is interpreted zone which which separates separates aa distinctive distinctive conglomeratic conglomeratic unit unit from from the the more more turbiditic turbiditic greywacke—slate between these greywacke-slate sequence. sequence. Located between these two two major faults faults occur a group group of inferred subsidiary faults, occur inferred subsidiary faultsI that that strike strike obliquely to obliquely to the the main main fault fault trend. trend. These These subsidiary subsidiary faults faults are are identified by topograhic lineaments, identified lineamentsI changes changes in in strike strike of of bedding bedding (in the easternmost easternxnost of of these these faults) faults) and and local local silicification silicification (in the and/or sericite-.carbonate alteration of the rocks and/or sericite-carbonate alteration rocks along along them. them. The The localization localization of alteration alteration zones zones along along some some of of these these faults, and the occurrence faultsI and the occurrence of abundant abundant sericite sericite and and carbonate carbonate in in many of many of the the metasedimentary metasedimentary rocks rocks suggests suggests that that large large volumes volumes of of fluids passed through through these these rocks, probably using fluids rocksI probably using the the faults faults as as conduits. Therefore these these faults faults and conduits. Therefore and their their associated associated alteration alteration zones mineral exploration zones may be useful useful guides for for mineral exploration in in the the area. area. The The Pike Pike River River fault fault lies lies essentially essentially on on trend trend with with the the Waasa Waasa fault fault further further to to the the northeast, northeastI and and thus thus could could have have regional regional significance. significance. The occurrence occurrence of of these these faults faults in in the the Archean Archean rocks rocks of of the the area area also also suggests suggests aa possible possible genetic genetic relationship Proterozoic structure relationship to to the the Proterozoic structure of of the the of of the the Virginia Virginia Horn itself. Horn itself. 119 �Vif Virginia 0 fault Eveleth El El Gilbert fault 1— —i miIes I. Sketch map Virginia Horn Horn area, area, showin showin Fig. Sketch Fig. mapofof Archean Archeanrocks rocksinin the the Virginia the distribution di j t r i bution of metasedimentary(ms) (ms)and andmetavolcanic metavol canic(mv the of metasedimentary rocks, and and major The boundary boundary shown rocks, major faults. faults. The shownininthe thevicinity vicinity (mvj of the the cities c i t i e sofofVirginia, Virginia, Eveleth,and andGilbert Gilbertmarks marks the the of Eveleth, unconformity between between the the Archean Archean rocks and the the superjacent superjacent unconformity rocks and Proterozoic rocks. rocks. Proterozoic 120 � https://digitalcollections.lakeheadu.ca/files/original/019747c29e8c82d96f5b64350c5a0b6b.pdf cb43ca8d828e1d80a5ab6c9e3009ff8a PDF Text Text Thirty-fourth Annual Meeting Marquette, Michigan May l2and 13, 1988 Institute on Lake Superior Geology Field Trip Guidebooks Volume 34, Part 2 — - —— —'—-—----:i-e-,-' — "4... �34th 34th ANNUAL ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE Field Trip Trip Guidebooks Guidebooks Field Volume Volume 34, 34, part part 22 Marquette, Marquette, Michigan Michigan May 12 12 and and 13, 13, 1988 1988 May Organized Organized By By John John Hughes, Hughes, Northern Northern John John Klasner, Klasner, Western Western Klaus Klaus Schulz, Schulz, U. U. S. S. Michigan Michigan University University Illinois Illinois University University Geological Geological Survey Survey Edited Edited by by Klaus Klaus Schulz Schulz Cover: Cover: 1 Line ScandinavianLine drawing drawing of of Scandinavianstyle style headframe headframe and and modern modern head— headframe frame at at Cleveland Cleveland Cliff's Cliff's Cliff Cliff Ishpeming, mine, iron shaft shaft iron mine, Ishpeming, Michigan. Michigan. �TABLE OF OF CONTENTS CONTENTS TABLE FIELD TRIP TRIP 11 FIELD An Introduction Introduction to to Archean Archean Geology Geology and and Precious Precious Metal Metal An Mineralization of of the the Marquette Marquette Greenstone Greenstone Belt, Belt, Michigan. Michigan. Mineralization Geological Overview Overview of of the the of of the the Marquette Marquette Greenstone Greenstone Geological Michigan Belt, Michigan Belt, T.J. Borrihorst Borrlhorst T.J. Al A1 -- Al8 A18 Geological Framework Framework of of aa Part Part of of the the Marquette Marquette Geological Greenstone Belt Belt North North of of the the Dead Dead River River Storage Storage Basin Basin Greenstone D.A. 3axter Baxter and and M.L. M.L. MacLellan MacLellan.................... D.A. A19 A19 -- A31 A31 Geology of of the the Ropes Ropes Mine Mine Geology R.A. Brozdowski. R.A. Brozdowski A32 ~ 3 —-2 A53 ~ 5 3 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological 1 to 11 Part I, Day 1 Road Log Stops 1 to 11 Stops Part I, Day 1 Road Log TJ. T.J.Bornhorst, Bornhorst,D.A. D.A.Baxter, Baxter,M.L. M.L.MacLellari, MacLellan, and and R.C. Johnson Johnson...................................... R.C. A54 A54 -- A64 A64 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological Road Log Log -- Stops Stops AA to to EE Part II, 11, Day Day 22 Road Part T.J. Bornhorst Bornhorst and and D.A. D.A. Baxter Baxter T.J. A65 A65 -- A71 A71 Geological Field Field Trip Trip to to the the Marquette Marquette Greenstone Greenstone Belt: Belt: Geological Part III, 111, Callahan Callahan Mining Mining Corporation Corporation Ropes RopesMine Mine Part Property Property R.A. Brozdowski Brozdowski and and G.W. G.W. Scott Scott....... R.A. A72 A72 - A73 A73 ................................... .................................. ..................... ............. FIELD TRIP TRIP 22 FIELD Marquette mineral mineral district district of of Michigan, Michigan, mining mining history history Marquette and geology. and geology. Burton H. H. Boyum Boyum and and Robert Robert C. C. Reed Reed....... Burton Bi Bl —- B15 B15 Marquette mineral mineral district district of of Michigan Michigan with with emphasis emphasis on on Marquette MINING HISTORY HISTORY and and GEOLOGY GEOLOGY MINING Burton H. H. Boyum, Boyum, Robert Robert C. C. Reed Reed and and Wm. Wm. Kangas Kangas Burton B16 B16 -- B33 B33 ........... ...... FIELD TRIP TRIP 33 FIELD structural traverse traverse across across aa part part of of the the Penokean Penokean orogen orogen AA structural illustrating Early Early Proterozoic Proterozoic overthrusting overthrusting in in northern northern illustrating fieldquide. Michigan: text text and and fieldcuide. Michigan: John J. Gregg Gregg and and John S. S. Klasner, Klasner, Paul Paul K. K. Sims, Sims, Wm. Wm. J. Christina Gallup Gallup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cl Cl -- C36 C36 Christina 1 �FIELD TTRIP FIELD RIP 1 1 Geological of the Geological Overview Overview of the Marquette Greenstone Marquette Greenstone Belt, Michigan Michigan T.J. Bornhorst T.J. Bornhorst Department of Geology Department Geology and and Geological Geological Engineering, Engineering, Michigan Technological University, Houghton, Michigan Technological University, Houghton, Michigan Michigan 49931 49931 INTRODUCTION The name Greenstone Belt Belt isis applied applied to to the belt name Marquette Marquette Greenstone belt of of dominantly dominantly Archean volcanic rocks rocks which which underlies underlies an an area area of of about Archean volcanic about 125 125 mi2 mi2 (325 (325 km2) km2) in in \ The belt occupies northern occupies the the eastern eastern northern Marquette Marquette County, County, Michigan Michigan (Figure (Figure 1). 1). The part of of the the northern northerncomplex, complex, an anextensive extensive terrane terrane ofofArchean Archeangranite-greenstone granite-greenstone Lower Proterozoic (750 km2) north north of of the (750 mi2; mi2; 1950 1950 km2) the Marquette Marquette trough. trough. Lower Proterozoic sediments, sediments, which fill fill the Marquette and overlie the complex, bury the Great which Marquette trough trough and overlie the complex, bury Great Lakes Lakes Tectonic Tectonic Zone, Zone, a major major regional regional Archean Archean structural structural zone zone described described by by Sims Sims (1980). (1980). The Marquette The Marquette Greenstone Greenstone Belt Belt represents represents the southwestern southwestern extension extension of the the Wawa Wawa Subprovinceof of the the Superior Province of of the Canadian Subprovince Superior Geologic Geologic Province Canadian Shield Shield as defined defined focus of of this overview (and of of the The specific specific focus overview (and the by Card Ciesielski (1986). (1986). The by Card and andCiesielski accompanyingfield fieldtrips) trips) isis the the greenstone belt, which which occupies occupiesabout about one-fifth one-fifth of accompanying greenstone belt, the entire the entire Archean Archean northern northern complex. complex. The Marquette of several The Marquette Greenstone Greenstone belt Consists consists of several thousand thousand feet of of subaqueous subaqueous These are mafic to silicic flows flows and andpyroclastics, pyroclastics, and andvolcaniclastic volcaniclastic sediments. sediments. These to silicic The belt also intruded also intruded by gabbro gabbro and and rhyolite rhyolite dikes dikes and and by by granitoid granitoid plutons. plutons. The includes two intrusive intrusive peridotite peridotite bodies, bodies, one one in in vicinity of the includes two vicinity of the Ropes Ropes Mine Mine and and All these the other other at at Presque Presque Isle. Isle. All these rocks rocks are Archean, Archean, about about 2700 2700 to 2500 2500 Ma Ma metamorphic grade grade old (Morgan (Morgan and and DeCristoforo, DeCristoforo, 1980; 1980; Trow, Trow, 1979). 1979). Their metamorphic ranges from from greenschist to amphibolite amphibolite facies facies and and they they have ranges greenschist to have been subjected subjected to to multiple deformation multiple deformation during the the Archean. Archean. There are numerous There numerous gold gold and base base metal occurrences occurrences throughout throughoutthe the belt belt (Bodwell, (Bodwell, 1972) 1972)but but the the Ropes Ropes Mine Mine is the metal the most significant most significant to date date (Brozdowski, (Brozdowski, this volume; volume; Bornhorst Bornhorst and others, others, 1986; 1986; Brozdowski and others, Archean rocks rocks are are unconformably unconformably overlain overlain by by Brozdowski others, 1986). 1986). The Archean A-i �Keweenawan EarIy Proterozoic ::i::Archean granitoids and gneiss 50 0 I km A Archean Southern Complex 'S Paleozoic Greenstofle Figure1: 1: Regional Regionalgeological geologicalsetting settingofofthe theMarquette Marquette GreenstoneBelt Beltwhich which Figure is shown in solid black. black. is shown in solid A—2 �and, in in fault faultcontact contactwith, with,Lower LowerProterozoic Proterozoicsediments. sediments. Greenstone Belt Belt was was proposed proposed for for these same The name name Ishpeming Ishpeming Greenstone same rocks rocks by by However, this this name name isis abandoned here in favor Morgan and DeCristoforo Morgan DeCristoforo (1980). (1980). However, abandoned here favor of Marquette Belt because becausethese theseArchean Archeanrocks rocksdo do not not crop crop out out in Marquette Greenstone Greenstone Belt in Ishpeming (Lower (Lower Proterozoic Proterozoicsediments sedimentscrop cropout out in in Ishpeming) whereas they they do Ishpeming Ishpeming) whereas do crop out out in the crop the City City of of Marquette. Marquette. Further, Further, the belt belt is is located located in in northern northern Marquette County. Marquette County. The rooks rooks of the the belt belthave havebeen beenstudied studiedand anddiscussed discussedby bynumerous numerousgeologists. geologists. For a historical the reader reader isis referred referred to to the work For historical background background the work of of Morgan Morgan and and based on on work work by by the author and This overview overview isis based and his his DeCristoforo (1980). (1980). This students, and and on on work (1968), Puffett (1974), (1974), Clark Clark and students, work by Gair Gair and and Thaden Thaden (1968), others (1975), Cannon and and Klasner and on the others (1975), Cannon Klasner (1977), (1977), and the geological geological studies studies summasummarized MacLellar (this (this volume). volume). rized by by Baxter Baxter and andMacLellari. STRATIGRAPHY STRATIGRAPHY As by the the literature from other As documented documented by literature from other parts parts of of the the Superior Superior Province, Province, stratigraphic correlations across across regional regionalfaults faults or or shear shear zones stratigraphic correlations zones are quite quite tenuous tenuous and and error. The stratigraphy stratigraphy of the the Marquette Marquette Greenstone Greenstone Belt Belt will will be be subject to error. discussed in two two separate parts because because the the belt belt is traversed discussed in separate parts traversed obliquely obliquely by by the the Dead Dead River 2). For purposes purposes of of description, description, River Shear Shear Zone, Zone, a probable probable major major fault fault (Figure (Figure 2). the greenstone belt has has been been subdivided subdivided into into aa northern northern and and a southern the greenstone belt southern part; part; other other faults necessitate that the the southern southern part part be be further divided faults necessitate that divided into into an an "eastern "eastern two-thirds" and aa "western two-thirds" "western one-third". one-third". Northern Part Northern The rocks of the northern The rocks of northern part of of the the belt belt have have been been described described by by Baxter Baxter and and rocks are are dominated dominated by by pillowed pillowed and and massive massive basalt basalt MacLellan MacLellan (this volume). volume). The rocks lava mudflow breccias breccias and and iron-formations; iron-formations; this thisassemblage assemblage lava flows with with interbedded interbedded mudflow These rocks are are has 2). These has been named named the the Volcanics Volcanics of Silver Silver Mine Mine Lakes Lakes (Figure (Figure 2). cut by of gabbro and all by dikes dikes and and sill-like sill-like bodies bodies of gabbro and all are cut cut by by dikes dikes of of rhyolite rhyolite A-3 ��it: u 0 a; -J z 0 E- DEAD RIVER PLUTON GRANITOID ROCKS SEDIMENTS 3 1-1 n 4 ca $ n Of. n 21-1 1 z MONA SCHIST KITCHI SCHIST PERIDOTITE z Cd z E- z u 0 n. 0 E- Cd m "3 0 E- 01 u a: u vs LIGHTHOUSE POINT MEMER Ed s Cd 2: E-i x 1-1 u 1-1 SHEARED RHYOLITE TUFF MEMBER a: I 0 I m Cd Of. AGE RELATION UNCERTAIN I Of. ARCHEAN 0 Ill I w ARCHEAN z PROTEROZOIC Q LEGEND ______ ca w Ln Ill Ill 3 E- w E- u 1-1 0 ?-i s Of. 0 Cd 2Cd a: m Of. Cd rn z Cd z ^ Cd Cd K u x 2 Cd z 4 z 0 z m x 4 1-1 1-1 0 VOLCANICS OF SILVER MINE LAKES LOWER BASALT MEMBER NEALY CREEK MEMBER Cd Ed z u z Of. Cd > 1-1 n m Ill 0 m u n 2u �Figure 2: Southern extents of the Dead River Geology of the Marquette Greenstone Belt, Michigan. and Carp River Falls Shear Zones are shown. Numbers and letters represent stops for field Cannon and Kiasner (1977), Clark and others (1975), trips (this volume). Compiled from: Puffett (1974), Bodwell (1972) and Gair and Thaclen (1968). �plutons intrude intrude the the northern northern part part of the and Granitoid plutons the and plutons plutons of of granodiorite. granodiorite. Granitoid greenstone belt to to the northeast greenstone belt northeast (see (see Day Day 2 Road Road Log, Log, Stop Stop E). E). The The granitoid granitoid rocks rocks of of the theMarquette MarquetteQuadrangle Quadrangle were were mapped mappedasasCompeau Compeau This name name has has also also been been assigned assigned more more Creek Gneiss Gneiss by Gair Gair and andThaden Thaden(1968). (1968). This recently crystallinerocks iocks in in the the region recently to similar-looking similar-looking crystalline region south south of the the Marquette Marquette trough l), and and ininessence, essence, signifies signifies "undifferentiated "undifferentiated plutonic plutonic rocks rocks of of trough (Figure (Figure 1), Creek Gneiss Gneiss should should be be used used only only in that Marquette County". County". The name name Compeau Compeau Creek that context context or prhaps, perhaps, be beabandoned. abandoned. Southern Southern Part Part The rocks of the rocks of the southern southern part part of the the belt, belt, south south of of the the Dead Dead River River Shear Shear Zone, Zone, have have been been mapped mapped by Gair Gair and and Thaden Thaden (1968), (1968), Puffett Puffett (1974), (1974), Clark Clark and and others others (1975), (1975), and Cannon Cannon and and Klasner Klasner(1977). (1977). Much Much of the the following following is is based based units (Figure (Figure 2) 2) in in the southern their work. work. The major major lithologic lithologic units southern part of of the the on their belt are: Kitchi Schist, Schist, Deer Deer Lake Lake Peridotite, Peridotite, Dead Dead River Pluton Pluton and and are: Mona Mona Schist, Schist, Kitchi other unnamed as Compeau Creek Gneiss Gneiss and and as as graunnamed granitoid granitoid plutons plutons (mapped (mapped as Compeau Creek nite). Relative The Relative age age relations relations among among these these major major lithologic lithologic units units are are uncertain. uncertain. The contact the Mona as a shear Kitchi Schists Schists was was mapped mapped as shear zone zone by by contact between between the Mona and and Kitchi top direction within a few Clark and and others others(1975). (1975). In addition, addition, stratigraphic stratigraphic top direction within few miles of the NE whereas whereas the Kitchi Kitchi Schist Schist miles of the contact contact indicates indicates that Mona Mona Schist Schist faces faces NE (1983) has has suggested suggestedthat that the the contacts contacts of of the Deer faces SE. SE. Rossell Rossell (1983) Deer Lake Lake Peridotite are structural and not Peridotite are not stratigraphic, stratigraphic, making making age age relations relations uncertain. uncertain. Although between the plutonic Although contacts contacts between plutonic rocks rocks and and volcanics volcanics rocks rocks are arecommonly commonly faults or shear shear zones, zones, the the plutonic plutonic rocks rocks in in close close proximity proximity to to the thegreenstone greenstone belt belt can be be interpreted interpreted to to intrude intrudethe thevolcanics, volcanics, based based on onsmaller smallerintrusive intrusiverelationships relationships and contact contact metamorphic metamorphic features. features. In view view of the the fact fact that thatfaults faults complicate complicate the the study study of of the the stratigraphy stratigraphy of of to resort even even the the southern southern part part of of the thegreenstone greenstone belt, belt, itit is necessary necessary to resort to to A-7 �describing describing the the stratigraphy stratigraphyofofthe theeven evensmaller smaller"eastern "easterntwo—thirds" two-thirds" and and"western "western one-third" areas. areas. of the southern The eastern eastern two-thirds two-thirds of southern part part of of the the belt belt Eastern Eastern Two-Thirds. Two-Thirds. The This name name should should perhaps perhaps be modified modified in in consists of the consists of the Mona Mona Schist Schist (Figure (Figure 2). 2). This the future future to tothe the"Mona "Mona Group" Group" because because the the Mona Mona Schist Schist can be be subdivided subdivided into into units (currently scale which which should should be elevated (currently termed termed members) members) at 1:24000 1:24000 scale elevated to to status. In addition, addition, the the rocks rocks that that are aremapped mapped asasthe theMona Mona"Schist" "Schist" formation status. have to the North have an an identifiable identifiable protolith protolith and and consequently, consequently, according according to North American American Code the parent parent lithology lithology term term should should be be used Code of Stratigraphic Stratigraphic Nomenclature, Nomenclature, the used in in for present Nevertheless, for present purposes purposes the term term Mona Mona name instead instead of of schist. schist. Nevertheless, the name Schist will be retained Schist will retained as as will will the thecurrently currentlyrecognized recognized four fourmembers: members: Lower Lower Member, Member, Nealy Nealy Creek Creek Member, Member, Sheared Sheared Rhyolite Rhyolite Tuff Member, Member, and andLighthouse Lighthouse Point Member. Member. The Lower Lower Member Member of of the theMona MonaSchist Schistconsists consists mainly mainly of ofsubaqueous subaqueousmassive massive and pillowed Day I1 Road pillowed tholeiitic tholeiitic basalt basalt lava lava flows flows (see (see Day Road Log, Log, Stops Stops 1 and 2, 2, this this volume) volume) with minor minor interbedded interbedded volcaniclastic volcaniclastic and and tuffaceous tuffaceous rocks. rocks. The member member crops crops out in in aa 25 25mi2 mi2(65 (65 km2) km2) area and and is is over over 10,000 10,000 feet feet (3300 (3300 m) m) thick, thick, top direction direction in the Stratigraphic top the Lower Lower assuming there is no assuming there no structural structural repetition. repetition. Stratigraphic Member is to the Member is the north. north. The Nealy lie the Nealy Creek Creek Member Member is considered considered to ove overlie the Lower Lower Member. Member. ItIt consists of a variety schistswhich whichcrop cropout out in in a quartz-chlorite-sericite-feldspar schists consists of variety of of quartz—chlorite-sericite-feldspar mi2 (18 (18 km2) km2) area. area. The schists schists appear to to be be mostly mostly greywacke greywacke and and shale shale (see (see 7 mi2 Day Day 11 Road Road Log, Log, Stop Stop 11, 11, this this volume), volume), but but in ingeneral general the theschistose schistose texture texture prevents member prevents recognition recognition of volcaniclastic volcaniclastic or tuffaceous tuffaceous textures. textures. This member (perhaps 3000 feet feet (1000 m) thick) thick) is the only unit in the (perhaps 3000 (1000 m) only significant significant sedimentary sedimentary unit the greenstone belt. belt. The Sheared Tuff Member Sheared Rhyolite Rhyolite Tuff Member is considered considered to overlie overlie the the Nealy Nealy Creek Creek rocks which consists of light-colored, light-colored, porphyritic porphyritic volcanic volcanic rocks which crop out out in in Member. It consists Member. A- 8 �of tabular aa 1.3 1.3 mi2 mi2(3.4 (3.4 km2) km2) area. area. The The common common lithology lithology consists consists of tabular fragments fragments of of porphyritic by fine-grained porphyritic rhyolite rhyolite surrounded surrounded by fine-grained matrix matrix of quartz, quartz, sericite sericite and and are quartz quartz and and feldspar, feldspar, and and make make up up 10 to 50 chlorite. Phenocrysts Phenocrysts are 50 percent percent of of chlorite. This the rhyolite rhyolite (Puffett, (Puffett,1974). 1974). In In some some outcrops outcrops there there are aregranitic graniticfragments. fragments. This the rock rock was was interpreted interpreted by by Puffett Puffett(1975) (1975) as asan anintensely intenselydeformed deformed pyroclastic pyroclastic deposit. deposit. The lies north north of the The Lighthouse Lighthouse Point Point Member Member lies the Nealy Nealy Creek Creek Member Member and and mi2(18 (18km2) km2)area. area. This This member member encompasses encompasses two different different crops out out in in'aa77mi2 crops relatively coarse-grained coarse-grained amphibolite, amphibolite, and and layered layered amphibolitic amphibolitic schist schist lithologies: lithologies: relatively Morgan and and DeCristoforo DeCristoforo (see (see Day Day 22 Road Road Log, Log, Stops Stops C C and and D, D,this thisvolume). volume). Morgan (1980) (1980) have have interpreted interpreted the the coarse-grained coarse-grained amphibolite amphibolite to be be gabbro. gabbro. The The layers layers in in the the layered layered amphibolite amphibolite are are interpreted interpreted as as flattened flattened pillows pillows and and the the material material between between the the layers layers isis often oftenwell-foliated. well-foliated. The The flattened flattened pillows pillows may may be due due to to that much This author author suggests suggests that much of the the deformation. This primary processes processes or to to deformation. primary flattening flattening is due due to tohigh highstrain. strain. The western western one-third one-third of the the southern southern part part isisunderlain underlain Western One-Third. One-Third. The Western by Kitchi Kitchi Schist Schist and and Deer Deer Lake LakePeridotite Peridotite(discussed (discussed under under Intrusive IntrusiveRocks) Rocks) be changed 2). The The name name "Kitchi "Kitchi Schist" Schist" should should likewise likewise be changed to "Kitchi "Kitchi (Figure 2). Kitchi Schist Schist crops crops out in in aa 12 12mi2 mi2(30 (30 km2) km2) area area and and consists consists of of Group". The Kitchi To the the east east of of the the Deer Deer Lake Lake Peridotite Peridotite itit consists consists of of dominant lithologies. lithologies. To three dominant quartz-sericite quartz-sericite phyllites phyllites and and schists, schists, commonly commonly containing containing feldspar feldspar phenocrysts phenocrysts and and lithic lithic fragments, fragments, (see (see Day Day 22 Road Road Log, Log, Stop Stop A, A, this thisvolume) volume)and andcoarse coarsebreccias breccias (see Day 22 Road Road Log, Log, Stop Stop B, B, this thisvolume). volume). The phyllites phyllites and and schists schists are areandesite andesite to dacite dacite in in composition composition and and are are interpreted interpreted as as interbedded interbedded pyroclastic pyroclastic fall and and coarse breccias breccias consist consist flow deposits, deposits, volcaniclastic volcaniclastic sediments, sediments, and lava lava flows. flows. The coarse of porphyritic porphyritic andesite-dacite andesite-dacite clasts clasts surrounded surrounded by quartz-sericite-chlorite quartz-sericite-chlorite matrix. matrix. The breccias sorted, but but locally along the the south shore of breccias are mostly mostly poorly poorly sorted, locally along of Deer Deer layering isisconspicuous conspicuous (Brozdowski, (Brozdowski, 1988, 1988, personal personal communication). communication). They They Lake layering A- 9 �are areinterpreted interpretedasassubaqueous subaqueousmudflows mudflowsand andpyroclastic pyroclastic flow flowdeposits. deposits. To Tothe the west west of ofthe theDeer DeerLake LakePeridotite, Peridotite,the theKitchi KitchiSchist Schistconsists consistsofofmafic maficvolcanic volcanicand and gabbroic gabbroic rocks rocks which whichmay mayunderlie underliethe theintermediate intermediatecomposition compositionvolcanic volcanicrocks rockstoto theeast east(Brozdowski, (Brozdowski, this thisvolume; volume;Brozdowski Brozdowski and andothers, others,1986). 1986). Stratigraphic Stratigraphictop top the direction consistently direction ininthe theKitchi KitchiSchist Schistis is consistentlysouth south(Brozdowski, (Brozdowski,1988, 1988,personal personal communication). communication). IntrusiveRocks. Rocks. The TheDeer DeerLake LakePeridotite, Peridotite,now nowpredominantly predominantlya aserpentinite, serpentinite, Intrusive mi2(5(5 km2) km2) area area (see (see Field Field Guide GuidetotoCallahan CallahanMining Mining crops out out in' i daa22mi2 crops Corporation Corporation Ropes Ropes Mine Mine Property, Property, this volume), volume), and is is surrounded surrounded by by Kitchi Kitchi Serpentine pseudomorphs pseudomorphs after olivine olivine and and pyroxene pyroxene are are Schist (Figure (Figure2). 2). Serpentine Schist Insome someserpentinite serpentinite there thereare are common and and the therock rockcontains containseuhedral euhedralmagnetite. magnetite. In common Foliated serpentinite serpentinite occurs occurs near near textures textures which which are areindicative indicative ofofcumulate cumulateorigin. origin. Foliated Near the the Ropes Ropes Mine, Mine, the theserpentinite serpentiniteisis the contacts contacts and and atatthe theRopes RopesMine. Mine. Near the Bornhorst and and altered altered also also to to aatalc-carbonate talc-carbonate rock rock(Bornhorst (Bornhorstand andothers, others,1986). 1986). Bornhorst others others (1986) (1986) interpret interpret the the Deer Deer Lake Lake Peridotite Peridotite as as an andiscordant discordantintrusive intrusivebody body with with structural structural contacts contacts whereas whereas Brozdowski Brozdowski and others others (1986) (1986) agree agree on on the theoverall overall intrusive intrusive nature nature of of the the body body but butinterpret interpretitsitscontacts contactsasasbeing beingmore moreconcordant concordant and hence hence more moresill-like. sill-like. and Where recognized, recognized, Dikes Dikes of of Archean Archean gabbro gabbro cut cut the theMona Monaand andKitchi KitchiSchists. Schists. Where these these intrusions intrusions were were mapped mapped most most commonly commonly as as metadiabase metadiabase of of uncertain uncertain age age Dikes of of rhyolite rhyolite cut cut the thebasalt basalt relations relations (Puffett, (Puffett, 1974; 1974; Gair Gair and andThaden, Thaden,1968). 1968). Dikes and and gabbro, gabbro, but but the theage agerelationship relationship between between the the rhyolite rhyolite dikes dikes and andthe thegranitoid granitoid plutons plutons is is less less clear; clear; only only aa few fewsimilar-appearing similar-appearing rhyolite rhyolite dikes dikes cut cutthe theplutons. plutons. The The textures textures of of the therhyolite rhyolitedikes dikesare areporphyritic porphyritic(most (most common), common), aphanitic, aphanitic, and and granular (least (leastcommon). common). Porphyritic Porphyritic rhyolite rhyolite is is composed composed of phenocrysts phenocrysts of of granular quartz quartz with with or or without without feldspar feldspar set setinina avery veryfine-grained fine-grainedgroundmass. groundmass. The The granular granular rhyolite rhyolite dikes dikes show show aa textural textural continuum continuum totogranitoid granitoid plutons. plutons. Undifferentiated part of of Figure 2) 2) and and the theDead Dead Undifferentiated granitoid granitoid plutons plutons (southwest (southwest part A—1O �River Pluton Pluton cut cutthe thegreenstone greenstonebelt. belt. The The Dead Dead River River Pluton Pluton isisaacomposite composite River pluton pluton and and consists consists of of granodiorite, granodiorite, diorite, diorite, and andsyenite syenite(Puffett, (Puffett,1974). 1974). The The southwestern southwestern granitoid granitoid plutons plutons have have been been poorly poorly studied, studied, but butmost mostare areprobably probably At the thePeppin PeppinProspect Prospect(3.5 (3.5 miles miles NW NW of of the theRopes RopesMine), Mine),Boben Boben granodiorite. At granodiorite. (1986) described described aa trondhjemite. trondhjemite. The The Archean Archean granitoid granitoid plutons plutons are areinterpreted interpreted asas (1986) syn- totopost-tectonic. post- tectonic. synGEOCHEMISTRY GEOCHEMISTRY There There aie are now now over over200 200major majorand andtrace traceelement elementanalyses analyses from fromthe theMarquette Marquette Most trace trace element element data data have have been been determined determined by by XRF X R Fand and GreenstoneBelt. Belt. Most Greenstone Geochemically the basaltic basaltic lava lava flows flows and and gabbroic gabbroicintrusives intrusives about 20 20 by byINAA. INAA. Geochemically about are are tholeiitic, tholeiitic, whereas whereas the the andesite andesite to to dacite dacite fragmental fragmental rocks rocks and andrhyolite rhyolite Although variable, variable, the the chemical chemical compositions compositions of of the the intrusives are arecalc-alkalic. calc-alkalic. Although intrusives basalts composibasalts and gabbros gabbros overlap overlap to the the extent extent that that they they must mustbe beconsidered considered compositionally tionally similar, similar, and and totohave havesimilar similarpetrogenetic petrogenetichistories. histories. To To demonstrate demonstrate that the the belt belt isis dominantly dominantly basalt basalt with with aa scattering scattering of of compositions compositions towards towards rhyolite, rhyolite, Bornhorst Bornhorst and and Baxter Baxter (1987) (1987) multiplied multiplied the thesurface surface area area of of each each major major unit unit of ofthe thegreenstone greenstone belt belt (as (as an anindication indication of of volume volume Of the the lesser lesser relations) relations) by by the therepresentative representativeaverage averagechemical chemicalcomposition. composition. Of number number of of silicic silicic rocks, rocks, more more compositions compositions fall near near the the andesite-dacite andesite-dacite boundary boundary than i.e., the thebelt beltisisvery verymildly mildlybimodal. bimodal. than on on either either side, side, i.e., The The few few analyses analyses of of granitoid granitoid plutonic plutonic rocks rocks suggest suggest that that the the granitoids granitoids are are calc-alkalic in in affinity. affinity. On On aa variety variety ofofcompositional compositional diagrams, diagrams, the the rhyolite rhyolite dikes dikes caic-alkalic that that cut cut the the greenstone greenstone belt belt lie lie on on similar similar trends trends with with the the plutonic plutonic rocks rocks and and The rhyolite rhyolite dikes dikes overlap overlap the the chemical chemical composition composition of the the more more silicic silicicplutons. plutons. The are parts of are interpreted interpreted as as late-stage, late-stage, generally generally more more evolved evolved parts of the the plutons plutons that that intrude the the greenstone greenstone belt. belt. intrude METAMORPHISM METAMORPHISM The The rocks rocks of of the thegreenstone greenstone belt beltwere weremetamorphosed metamorphosed from from greenschist greenschist toto A-li �amphibolite facies facies during during the Archean. During the Penokean Penokean orogeny, orogeny, the amphibolite Archean. During Archean rocks rocks were were subjected subjected to to greenschist facies metamorphism metamorphismand, and, in in areas areas of of Archean greenschist facies amphibolite facies, facies, this denoted by retrograde amphibolite this Penokean Penokean metamorphism metamorphism isis denoted retrograde assemassemblages. Archean greenschist facies facies was was elevated elevated to to the Archean regional regional greenschist the amphibolite amphibolite facies facies in relatively relatively restricted restricted areas. areas. STRUCTURE STRUCTURE Archean structural structural geology of the Marquette Archean geology of Marquette Greenstone Greenstone Belt Belt is dominated dominated by by E-W, to N-S N-S faults, faults, but but some data suggest suggest that that the the belt belt has E-W, NW-SE, NW-SE, to some data has been been subFor example, from north north of of the jected to to multiple multiple deformations. deformations. For example, from the Dead Dead River River jected Storage Basin, Johnson Johnson and and others have described Storage Basin, others (1987) (1987) have described an Archean, Archean, steeplysteeply- plunging, anticline with with dimensions on the the order of This fold plunging, synformal synformal anticline dimensions on of miles. miles. This fold requires aatt least Archean deformation. deformation. requires least two two periods periods of of Archean Similarly, the Mona-Kitchi Similarly, the Mona-Kitchi structural relationship relationship described describedearlier earlierrequires requiresatat least least two two periods periods of of Archean structural Archean deformation. The Archean Archean rocks rocks are are overlain overlain by by Early Early Proterozoic Proterozoic supracrustal supracrustal rocks rocks which which were deformed were deformed during the the Penokean Penokean orogeny orogeny (1900 (1900 to to 1800 1800 Ma). Ma). Although reactiAlthough reacti- vation of Archean Archean structures structures during during the the Penokean Penokean orogeny orogeny can can be be documented documented vation clearly, various various lines lines of of evidence evidencesuggest suggestthat thatmost mostofof the the structure structure in in the clearly, greenstone belt belt represents greenstone represents Archean Archean deformation. deformation. Local Local Faults and Shear Shear Zones Zones dips steeply; dips near In the the Marquette Marquette Greenstone Greenstone Belt Belt most most stratification stratification dips steeply; dips near The rocks are variably foliated, but but on vertical vertical (+1_be) (+/-lo0) are are quite quite common. common. The rocks are variably foliated, on both both a local local and and regional regional scale scale there there are are linear linear zones zones along along which which the foliation foliation is is better better zones of of higher These zones higher strain may may be be faults faults developed developed than than in in surrounding surrounding rocks. rocks. These Where stratigraphic stratigraphicunits unitsare are offset offset they they are mapped mapped as as faults. faults. or shear shear zones. zones. Where North North of the the Dead Dead River River Storage Storage Basin Basin many many high high strain strain zones zones are are too too small small Faults are are of of brittle-ductile brittle-ductile and and to show to show at 1:6000 1:6000 (1 inch inch equals equals 500 500 feet). feet). Faults ductile types, ductile types, and and displacement displacement may be be mostly mostly vertical. vertical. A-12 These faults faults are are also These also of �two older roughly E-W faults truncated two general general ages: ages: older roughly E-W truncated by by younger younger N-S N-S faults faults (Johnson and and others, others, 1987). 1987). (Johnson South South of the the Dead Dead River River Storage Storage Basin, Basin, Clark Clark and and others others (1975) (1975) interpreted interpreted the distinct Kitchi Kitchi and and Mona to be aa Mona Schists Schists to the contact contact between between the the lithologically lithologically distinct shear shear zone zone (Figure (Figure 2), and and contacts contacts of of the the Deer Deer Lake LakePeridotite Peridotitehave havealso alsobeen been interpreted interpreted as either either faults faults or orshear shearzones zones(Clark (Clark and andothers, others,1975; 1975;Rossell, Rossell, 1983). 1983). Regional Regional Faults Faults and Shear Shear Zones Zones The Belt is affected The Marquette Marquette Greenstone Greenstone Belt affected by by two two regional regional Archean Archean shear shear along the the entire southern Extending along southern boundary boundary of of the the greenstone greenstone zones (Figure 2). 2). Extending belt isis the the Carp CarpRiver RiverFalls FallsShear Shear Zone Zone (Puffett, (Puffett,1974). 1974). Rocks Rocks along along this shear shear zone are both both intensely intensely foliated foliated and altered altered (see (see Day Day I1Road RoadLog, Log,progression progression the full full width However, the width of the the shear shear zone zone isis from Stops Stops 11 to 3, 3, this thisvolume). volume). However, from not not known known since since a part part of ofititwas wasreactivated reactivatedduring duringthe thePenokean Penokean orogeny, orogeny, juxtaposing juxtaposing more more altered and and sheared sheared Archean Archean rocks rocks against against less less deformed deformed Early Early width of of this this zone zone is is up to exposed width to 1500 1500 ft f t (450 (450 m) m) Proterozoic sediments. sediments. The exposed as documented documented by by detailed detailed mapping mapping (Brozdowski, (Brozdowski, 1988, 1988,personal personal communication). communication). Since this shear is cut by Since this shear zone zone is by much much less less deformed deformed mafic mafic dikes dikes of of Archean Archean age age (Baxter and Bornhorst, 1988), itit must must be be Archean Archean in in age. age. This shear zone zone may may be be (Baxter and Bornhorst, 1988), part of of the theGreat GreatLakes LakesTectonic TectonicZone ZoneofofSims Sims(1980). (1980). The second cuts through second major major structural structural zone zone cuts through the middle middle of of the the greenstone greenstone belt and As and isis termed termed the the Dead Dead River River Shear Shear Zone Zone (Puffett, (Puffett, 1974) 1974) (Figure (Figure 2). 2). As recognized by Puffett Puffett (1974), the shear recognized by (1974), the shear zone zone lies lies within within the the Sheared Sheared Rhyolite Rhyolite Tuff Member of the Mona Member of Mona Schist Schist (near (near the east east end end of of the theDead DeadRiver RiverStorage StorageBasin). Basin). In this with the interpretathis area area detailed detailed gravity gravity and and magnetic magnetic data data are consistent consistent with interpretation of of aasteeply steeplydipping dippingshear shearzone zone(Weeks, (Weeks,1987). 1987). The Dead Dead River River Shear Shear Zone Zone can be be extended extended to to the the west west ititwas wasreactivated reactivated during duringthe thePenokean Penokean orogeny, orogeny, juxtaposing Archean and and Early Early Proterozoic Proterozoicrocks rocksinin aa manner manner similar similar to to the Carp juxtaposing Archean Carp Falls Shear Shear Zone. Zone. In the the west, west, the the existence existence of the the shear shear zone zone isis indicated indicated River Falls A-13 �by by well-foliated well-foliated and and altered altered Archean Archean rocks rocks along along the Archean Archean and Early Early ProteroProterozoic zoic contact contact (see (see Day Day 11 Road Road Log, Log, Stop Stop 5,5, this this volume). volume). ItIt isisproposed proposed that that the the eastward of this shear eastward extension extension of shear zone zone follows follows the Lighthouse Lighthouse Point Point Member Member of the the Mona Mona Schist Schist which which is interpreted interpreted as as having having been been subjected subjected to to high high strain strain(see (see Road Road Log Log Day Day 2, 2, Stops Stops C C and and D). D). Thus, Thus, the the Dead Dead River River Shear Shear Zone Zone represents represents aa NW-SE NW-SE trending trending fault, with with unknown unknown displacement, displacement, that that bisects bisects the the Marquette Marquette Greenstone Greenstone Belt. Belt. PRECIOUS PRECIOUS METAL 'METALMINERALIZATION MINERALIZATION Of Of the the numerous numerous base base and and precious precious metal metal occurrences occurrences in in the the belt belt(Bodwell, (Bodwell, 1972), the Ropes 1972), the Ropes Mine Mine is the the most most significant significant orebody orebody to to date date (Figure (Figure 2). 2). The The Ropes Ropes Mine Mine has has been been described described by byBornhorst Bornhorst and andothers others(1986) (1986)and andBrozdowski Brozdowski It has has been been mined mined for for Au Au and and others others (1986) (1986) and and ininthis thisvolume volumebybyBrozdowski. Brozdowski. It Metallic minerals minerals are are dominated dominated and Ag Ag and and has has aa Au/Ag Au/Ag ratio ratio of of about about 11 to to 5.5. Metallic and by by pyrite, pyrite, with with lesser lesser other othersulfides 'sulfidessuch such asastetrahedrite, tetrahedrite,galena, galena,and andchalcopyrite. chalcopyrite. Certain Certain parts parts of of the the Ropes Ropes Mine Mine show show aa good good correlation correlation between between abundance abundance of Au Au and and fine finepyrite pyrite(Brozdowski, (Brozdowski, this thisvolume). volume). Non-metallic Non-metallic alteration alteration minerals minerals are are dominated dominated by by quartz quartz and and carbonate carbonate with with varying varying amounts amounts of of sericite, sericite, chlorite chlorite talc. The The ore ore host host rock rock for for the theRopes Ropesorebody orebody isis interpreted interpreted by byBornhorst Bornhorst and talc. and others others (1986) (1986) and and Brozdowski Brozdowski and others others (1986) (1986) as as aa dacitic daciticvolcaniclastic volcaniclastic rock rock and Bornhorst Bornhorst agree agree that the Both Brozdowski Brozdowski and the within within the the Deer Deer Lake Lake Peridotite. Peridotite. Both mineralization epigenetic,but but differ differ in their mineralization isis epigenetic, their interpretation interpretation of of mechanism mechanism of of and others (1986) emplacement. Brozdowski Brozdowski and (1986) suggest suggest that precious precious metals metals were were emplacement. concentrated concentrated by hydrothermal hydrothermal fluids fluids related related to to emplacement emplacement of peridotite peridotite sills sills Bornhorst and others others (1986) (1986) suggest suggest that the the orebody orebody was was (Deer Lake Lake Peridotite). Peridotite). Bornhorst (Deer syntectonic and that that hydrothermal fluids followed followed aa zone of relatively syntectonic and hydrothermal fluids zone of relatively high high strain, strain, (this volume) volume) describes describesaa structural structural genetic Brozdowski (this genetic model model for shear zone. zone. Brozdowski a shear the Ropes orebody. Ropes orebody. Other less less important important occurrences occurrences of of mineralization mineralization present present as asdisseminations disseminations A- 14 �and in in quartz quartz veins, veins, are are associated associated with with all the the major major Archean Archean rock rock types. types. Most of the the occurrences occurrences are interpreted interpreted as as epigenetic, epigenetic, but at at some some poorly poorly studied studied localities the the mineralization localities mineralization may be be syngenetic. syngenetic. The description The description that that follows follows applies to epigenetic applies epigenetic mineralization. mineralization. Mineralization is commonly spatially associated associated with with faults and Mineralization is commonly spatially and shear shear zones, zones, and is interpreted and interpreted as synsyn- to to post-tectonic. post-tectonic. Sulfide Sulfide minerals minerals are significant significant indicators of precious indicators precious metal metal mineralization. mineralization. quartz and quartz-carbonate quartz-carbonate veins. veins. Pyrite and in Pyrite occurs as disseminations disseminations and in Pyrrhotite, chalcopyrite, Pyrrhotite, chalcopyrite, and arsenopyrite arsenopyrite are are less less abundant abundant than pyrite. pyrite. In studies studies carried carried out out atatMichigan MichiganTechnological Technological % University, no anomalous Au or or Ag Ag values were obtained obtained from from any any sample University, no anomalous Au values were sample of of rock rock and galena or quartz quartz vein vein that that was was free free of of sulfides. sulfides. Sphalerite Sphalerite and galena are found found at at some some occurrences, and these tend to occurrences, and these minerals minerals tend to be be more more commonly commonly associated associated with with anomalous Ag, whereas whereas the the yellow Abundance of anomalous Ag, yellow sulfides sulfides are associated associated with Au. Au. Abundance sulfides in a rock, as measured measured by by abundance abundance of sulfur, sulfur, isis poorly poorly correlated correlated with with sulfides in rock, as chlorite, and and sericite occur as the abundance of Au. the abundance of Au. Quartz, Quartz, carbonate, carbonate, chlorite, as wall-rock wall-rock alteration quartz and carbonate alteration minerals; minerals; quartz carbonate also also occur occur as as vein veinminerals mineralsassociated associated with precious with precious metal metal anomalies. anomalies. The that there there appear The present present data permit permit the the tentative tentative suggestion suggestion that appear to have have been at least been least two two major major pulses pulses of ofmineralization. mineralization. An early pulse An pulse resulted resulted in in pervasive quartz quartz and and carbonate carbonate alteration alteration and and was was accompanied accompaniedby by gold, gold, pyrite pyrite and pervasive other yellow sulfide minerals, and abundant other yellow sulfide minerals, and abundant chlorite chlorite and and sericite. sericite. Quartz-carbonate veins are associated with this early veins associated with early pulse. pulse. Detailed Detailed studies by by Callahan Callahan Mining Mining Corporation (Brozdowski, 1988, personal personal communication) communication) indicate indicate that significant Corporation (Brozdowski, 1988, significant occurrences of of gold mineralization with structures parallel occurrences mineralization are associated associated with parallel and and conjugate to layering conjugate layering between between rock rock types. types. A later later pulse pulse of of mineralization mineralization was was dominated by quartz-carbonate dominated by quartz-carbonate veins containing containing base metal metal sulfides sulfides (pyrite, (pyrite, galena, galena, sphalerite, with little little or or no at the sphalerite, with no Au), Au), although although the the relatively relatively abundant abundant galena galena at the Ropes Mine Mine may may be be an an exception. exception. The The extent extent of country country rock rock alteration alteration associassociRopes ated ated with this this latter latter pulse pulse may may have have been been less less than than that that associated associated with with the the earlier earlier A-15 �pulse. At At some some individual individual prospects prospects aa paragenetic paragenetic succession succession of of metallic metallic and and pulse. non-metallic non-metallic minerals minerals can be be recognized recognized within within aapulse. pulse. SUMMARY SUMMARY The The Marquette Marquette Greenstone Greenstone belt belt consists consists of of several several thousand thousand feet feet ofofsubaqueous subaqueous mafic mafic to to silicic silicicvolcanic volcanic flows, flows,pyroclastics, pyroclastics, and andvolcaniclastic volcaniclastic sediments. sediments. These These are are intruded intruded by by gabbro gabbro and and rhyolite rhyolite dikes dikes and and by by granitoid granitoid plutons, plutons, all all of ofArchean Archean The belt belt also alsoincludes includes two twoperidotite peridotitebodies. bodies. age. The age. All All of of these these rocks rocks have have been been 1 metamorphosed from greenschist to amphibolite metamorphosed from greenschist to amphibolite facies facies and subjected subjected to to multiple multiple deformation. Precious Precious metal metal mineralization mineralization is is dominantly dominantly epigenetic. epigenetic. The The Archean Archean deformation. geologic history of of the geologic history the belt belt isisobscured obscured by byunconformably-overlying unconformably-overlying Early Early Proterozoic sediments and and by deformation Proterozoic sediments deformation during during the the Penokean Penokean orogeny. orogeny. The potential potential for for discovery discovery of of new new economic economic deposits deposits of precious precious metals metals in in the the Marquette Marquette Greenstone Greenstone Belt Belt is is denoted denoted by by anomalous anomalous Au Au values, values, quartz quartzand and carbonate carbonate veins, veins, areas areas of of pervasive pervasive alteration, alteration, areas areas of of relatively relatively abundant abundant faults faults and and shear shear zones, zones, and andoverall overallgeologic geologic setting. setting. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I thank thank the the present present and andformer formergraduate graduate students students who who have have spent spent many many hours hours working on the geology of the Belt and and with working on geology of the Marquette Marquette Greenstone Greenstone Belt with whom whom I have have They include: include: D. D. Baxter, Baxter, C. C. Boben, Boben, R. R. Johnson, Johnson, M. M. had many many fruitful fruitfuldiscussions. discussions. They MacLellan, have benefited benefited from from numernumerMacLellan, E. Owens, Owens, D. D. Rossell, Rossell, and and T. T.Shepeck. Shepeck. I have Michigan Geological Geological ous Kalliokoski. The Michigan ous conversations conversations with with my my colleague, colleague, J.J.Kalliokoski. Survey, of Natural Survey, Department Department of Natural Resources Resources and the the Department Department of of Geology Geology and and Geological University have Geological Engineering, Engineering, Michigan Michigan Technological Technological University have supported supported my my D. Schueller Schueller and and D. D. program program of research research on on the theMarquette Marquette Greenstone GreenstoneBelt. Belt. D. paper was was improved improved by by Baxter provided comments commentson onaa draft draft of this Baxter provided this paper. paper. This paper the reviews reviews of of J.J.Kalliokoski, Kalliokoski,Michigan Michigan Technological Technological University, University, and and K. K.Schulz, Schulz, S. Geological Geological Survey. Survey. U. S. A-16 �REFERENCES Baxter, T.J., 1988, Mafic Intrusions of Baxter, D.A. D.A. and Bornhorst, Bornhorst, T.J., 1988, Multiple Multiple Discrete Discrete Mafic Intrusions of Archean to Keweenawan Archean Keweenawan Age, Age, western western Upper Peninsula, Peninsula, Michigan, Michigan, [abs.]: [abs.]: ProceedProceedings and Abstracts, ings Abstracts, 34th 34th Institute Institute on on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan, (this volume). volume). Boben, comparison of of three three precious Boben, C.A., C.A., 1986, 1986, Geological Geological comparison precious metal metal prospects prospects in in Marquette County, County, Michigan: M.S. Thesis, Thesis, Michigan MichiganTechnological Technlogical University, Marquette Michigan: M.S. Houghton, 77 p. Houghton, p. Bodwell, W.A., W.A., 1972, 1972, Geologic Geologiccompilation compilationand and non-ferrous non-ferrous metal potential, Bodwell, potential, Precambrian Precambrian section, section, northern Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan Technological Technological University, University, Houghton, Houghton, 106 106 p. p. 1 Bornhorst, T.J. T.J. and Baxter, character of of Archean Bornhorst, Baxter, D.A., D.A., 1987, 1987, Geochemical Geochemical character Archean rocks rocks from the the east east half half ofofthe theNorthern NorthernComplex, Complex,Upper UpperPeninsula, Peninsula,Michigan: Michigan: Institute Proceedingsand and Abstracts, Abstracts,v.v. 33, 33, part part 1, Institute on Lake Lake Superior Superior Geology Geology Proceedings 1, p. p. 12. 12. Bornhorst, T.J., T.J., Shepeck, A.W. and and Rossell, Rossell, D.M., D.M., 1986, 1986, The The Ropes Ropes gold Bornhorst, Shepeck, A.W. gold mine, Marquette County, Michigan, U.S.A.: in in MacDonald, MacDonald,A. A. J., 1., Ed., Ed., Proceedings of Marquette County, Michigan, U.S.A.: Proceedings of Gold on the the Geology of Gold, Toronto, Gold 86, an an International International Symposium Symposium on Geology of Toronto, 1986, 1986, p. p. 2213-227. 13-227. Brozdowski, R.A., Gleason, Gleason, R.J. R.J. and and Scott, Brozdowski, R.A., Scott, G.W., G.W., 1986, 1986, The Ropes Ropes Mine: Mine: A A pyritic gold deposit Archean volcaniclastic volcaniclastic rock, rock, Ishpeming, Ishpeming, Michigan, Michigan, U.S.A.: U.S.A.: pyritic deposit in in Archean A. J., in MacDonald, MacDonald, A. J., Ed., Ed., Proceedings Proceedings of Gold Gold 86, 86, an anInternational International Symposium Symposium on on the Geology of Gold, the Geology of Gold, Toronto, Toronto, 1986, 1986, p. p. 228-242. 228-242. Cannon, and Klasner, map of of the Cannon, W.F. W.F. and Klasner, J.S., J.S., 1977, 1977, Bedrock Bedrock geologic geologic map the southern southern part of the part the Diorite Diorite and andChampion Champion 77 1/2-minute 1/2-minute quadrangles, quadrangles, Marquette Marquette County, County, Michigan: U. S. Michigan: S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigation Series Series Map Map 1-1058. 1-1058. Card, K.D. of the #I. Subdivisions Subdivisions of the Superior Superior Card, K.D. and and Ciesielski, Ciesielski, A., A., 1986, 1986, DNAG DNAG #1. Province of the Province of the Canadian Canadian Shield: Shield: Geoscience Geoscience Canada, Canada, v. v. 13, no. no. 1, p. 5-13. 5-13. Clark, L.D., Clark, L.D., Cannon, Cannon, W.F. W.F. and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock geologic geologic map map of the Negaunee quadrangle, Marquette Marquette County, Negaunee SW SW quadrangle, County, Michigan: Michigan: U. S. S. Geological Geological Survey Survey Geologic Geologic Quadrangle Quadrangle Map Map GQGQ-1226. 1226. Gair, J.E. and Gair, and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of the the Marquette Marquette and and Sands Sands quadrangles, Geological Survey Professional Professional quadrangles, Marquette Marquette County, Michigan: Michigan: U. U. S. S. Geological Paper Paper 397, 397, 77 p. p. Johnson, R.C., Bornhorst, T.J. and VanAlstine, 1987, Geologic Geologic setting setting of of Johnson, R.C., Bornhorst, T.J. VanAlstine, J.L., J.L., 1987, precious metal metal mineralization mineralizationinin the the Silver Silver Creek Creek to to Island Island Lake Lake area, Marquette precious Marquette County, Michigan: Michigan Geological GeologicalSurvey SurveyDivision, Division,Department Department of of Natural County, Michigan: Michigan Natural Resources, Open-File Open-File Report Report OFR-87-4, OFR-87-4, Supersedes OFR-86-2, 134 Resources, Supersedes OFR-86-2, 134 p. Morgan, evolution of of the Morgan, P.J. P.J. and DeCristoforo, DeCristoforo, D.T., D.T., 1980, 1980, Geological Geological evolution Ishpeming Greenstone Greenstone Belt, Belt, Michigan, Ishpeming Michigan, U.S.A.: U.S.A.: Precambrian Precambrian Research, v. v. 11, p. 23-41. Puffett, W.P., of the Puffett, W.P., 1974, 1974, Geology Geology of the Negaunee Negaunee quadrangle, quadrangle, Marquette Marquette County, County, Michigan: U. U. S. Geological Professional Paper Paper 788, 788, 51 p. Michigan: Geological Survey Survey Professional p. A-17 �Rossell, D.M., 1983, 1983, Alteration Alterationofof the the Deer Rossell, D.M., Deer Lake Peridotite Peridotite near the the Ropes Ropes Mine, Marquette County, Mine, County, Michigan: Michigan: M.S. M.S. Thesis, Michigan Michigan Technological Technological University, Houghton, sity, Houghton, 83 p. Sims, P.K., 1980, and gneiss Sims, P.K., 1980, Boundary Boundary between between Archean Archean greenstone greenstone and gneiss terranes terranes in in northern Wisconsin and Michigan: Geological Society Society of of America northern Wisconsin and Michigan: Geological America Special Paper 182, 182, p. 113-124. 113-124. Trow, in the Trow, J., 1979, 1979, Final Final report report diamond diamond drilling drilling for geologic geologic information information in the Middle Precambrian basins basins in in the the western Middle Precambrian western portion portion of of northern northern Michigan: Michigan: Michigan Michigan Geological Survey, Survey, Department Departmentofof Natural Natural Resources, Resources, Open-File Open-File Report Report UDOE Geological OFR GJBX-162(79), 44 p. OFR GJBX-162(79), 44 Weeks, V., V., 1987, 1987, Gravity Gravity and and magnetic investigationsinin the the south-central Weeks, magnetic investigations south-central part part of the the Ishpeming Ishpeming Greenstone Greenstone Belt, Belt, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Houghton, Michigan ~Tchnological t k h n o l o ~ i cUniversity, aUniversity, l Houghton, 61 61 p. p. A-lB �Geological Frameworkofof aa Part of Geological Framework of the theArchean Archean Marquette Marquette Greenstone Belt North Greenstone Belt North of the the Dead Dead River River Storage Storage Basin Basin D.A. D.A. Baxter Baxter and and M.L. M.L. MacLellan MacLellan Department Department of of Geology Geology and andGeological Geological Engineering, Engineering, Michigan Michigan Technological Technological University, Houghton, Houghton, Michigan Michigan 49931 49931 INTRODUCTION INTRODUCTION The Archean Archean Marquette Marquette Greenstone Greenstone Belt Belt underlies underlies approximately approximately 125 125mi2 mi2(325 (325 km2) of northern km2) of northern Marquette Marquette County County in in Michigan's Michigan's western western Upper Upper Peninsula Peninsula / belt is divided greenstone belt divided into northern northern and and southern southern portions portions by by (Figure (Figure 1). 1). The greenstone a structural structural zone zone which which parallels parallels the the Dead Dead River River Storage Storage Basin Basin (Bornhorst, (Bornhorst, this this volume). The southern southern part of of the the greenstone greenstone belt belt and and the the metasediments metasediments of the the volume). part of the Marquette The northern northern part the Marquette Supergroup Supergroup were were mapped mapped by by the theU.S.G.S. U.S.G.S. The belt was and the remainder was partially partially mapped mapped by the the U.S.G.S. U.S.G.S. and remainder was was included included on on the the 1:60,000 compilationmap map of of the northern aim of of 1:60,000 compilation northern complex complex by by Bodwell Bodwell (1972). (1972). The aim this paper of the paper is is to to briefly briefly describe describe the the geology geology of the northern northern part of of the the Archean Archean Marquette Belt based based on on detailed Marquette Greenstone Greenstone Belt detailed mapping mapping of the the southwest southwest 25 25 mi2 mi2(65 (65 km2). km2). Archean Archean rocks rocks of the the northern northern part partconsist consist ofofdominantly dominantlysubaqueous subaqueous mafic mafic lava and pyroclastic of lava flows, flows, and minor, minor, interbedded interbedded volcaniclastic volcaniclastic and pyroclastic deposits deposits of All of of these these rocks rocks are are assigned assigned to to intermediate and iron formation. intermediate composition composition and formation. All the Yolcanics of Silver Mine Lakes, Lakes, an an informal formation name name used used to to distinVolcanics of Silver Mine informal formation guish strata from guish these these strata from the remainder remainder of the the Mona Mona Schist Schist which which is situated situated on on the the southern side of of the southern side the Dead Dead River River Shear Shear Zone, Zone, an an Archean Archean structural structural zone zone with with aa large, large, but but unknown, unknown, degree degree of ofmovement. movement. The volcanic volcanic package package has has been been intruded intruded by by gabbro gabbro and and subsequently subsequently by rhyolite rhyolite and and granodiorite granodiorite of of Archean Archean age. age. The rhyolite rhyolite is is interpreted interpreted as as aa more more evolved evolved equivalent equivalent of of the the granodiorite granodiorite to to tonalite 1987). tonalite plutonic plutonic rocks rocks (Bornhorst (Bornhorst and and Baxter, Baxter, 1987). A- 19 �T5ON T49N T48N o• 0 30 60 60 90 90 30 M iles Miles 0 o I I I 50 100 100150 150 50 I 1 I Km. Km. Regional geology geology and location location map map of of the the Figure 1.1. Regional Figure Marquette Marquette Greenstone Greenstone Belt Belt (modified (modifiedfrom from Morgan and DeCristoforo, 1980). Morgan and DeCristoforo, 1980). A-20 �VOLCANICS VOLCANICS OF SILVER SILVER MINE MINE LAKES LAKES The Volcanics 'The Volcanics of Silver Silver Mine Mine Lakes Lakes (MacLellan (MacLellan and and Bornhorst, Bornhorst, 1988) 1988) are are named for a succession of Archean Archean volcanic volcanicunits unitsthat thatcrop crop out out in in the vicinity named for succession of vicinity of and Bornhorst, Silver Mine Mine Lakes. Lakes. Detailed Detailed mapping mapping (MacLellan (MacLellan and Bornhorst, 1988; 1988; Baxter and and Silver others, and others, and Bornhorst, has distinothers, 1987; 1987; Johnson Johnson and others, 1987; 1987; Owens Owens and Bornhorst, 1985) 1985) has guished guished five members: members: Pillowed Pillowed Basalt Basalt Member, Member, Breccia Breccia Member Member of Bismark Bismark Creek, Member of of Reany Creek, Breccia Breccia Member Reany Lake, Lake, Iron Iron Formation Formation Member, Member, and the the Hill's Hill's of the Lake Pyroclastic Pyroclastic Member Member (Figure (Figure 2). 2). Relative Relative ages ages of the members members are are based based on on the presence presence of of pillows pillows as as top top indicators indicators in in the thePillowed Pillowed Basalt Basalt Member. Member. The The members are too members are too small small to to be be distinguished distinguished at at74 7+minute minutequadrangle quadranglescale scale (1:24,000). Pillowed Pillowed Basalt Basalt Member Member This member member has been been subdivided subdivided into three three varieties, varieties, normal, normal, foliated, foliated, and and contacts between between these these varieties varieties are are altered, altered, based based on on various various criteria. criteria. The contacts gradational. gradational. dark green green to green-black This variety variety is commonly commonly dark green-black in in Normal Normal Variety. Variety. This color, color, fine-grained fine-grained to to aphanitic, aphanitic, and and massive massive to to moderately moderately foliated foliated (see (see Day Day 11 Visible mineralogy mineralogy includes very very Road Road Log, Log, Stops Stops 6 and and 10, 10, this this volume). volume). Visible fine-grained and sericite, fine-grained chlorite, chlorite, very very fine-grained fine-grained plagioclase plagioclase and sericite, and rarely rarely fine-grained plagioclase plagioclase crystals crystals often show show relict relict fine-grained amphibole. amphibole. Very fine-grained Elongate, variably variably flattened pillows pillows are are found found locally locally igneous igneous microlite microlite textures. textures. Elongate, and range feet (30-250 (30-250cm) cm) inin length length and and 3-30 range from from 1—8 1-8 feet 3-30 inches inches (8-76 (8-76 cm) cm) in in thickness. Some pillows show show small small bands bands of of vesicles vesicles (1/16-1 (1/16-1 inch, 2-25 Some pillows 2-25 mm) mm) is common common to find find interpillow interpillow void void space space filled filled with with the chilled chilled margins. margins. It is along the fewplaces, places, stratigraphic stratigraphic tops tops have have been been to gray gray carbonate carbonate material. material. In aa few tan to determined cuspate pillows pillows shapes. shapes. determined from the the cuspate Quartz and quartz-carbonate veinsfrom fromless lessthan than 1/16 1/16 inch inch (2 (2 mm) Quartz and quartz-carbonate veins mm) to 99 veins can can inches (23 cm) in width width can can be be found foundthroughout throughout this this variety. variety. The veins inches (23 cm) A-21 �___________________________ Correlation of Archean Archean Units Units and Volcanic and Sedimentary Rocks Rocks Intrusive Rocks Rocks c Granodiorite Granodiorite of Rocking Rocking Chair Lakes Lakes rhyolite Intrusive Rhyolite Intrusive of of Altered Fire Center Center Mine Mine Variety I Gabbro of Gabbro of I Altered Altered 1 1 Clark Creek Creek 1 Variety 1 7 Foliated Variety Variety Highly Altered Variety Hill's L a k e Pyroclastic Pyroclastic Member Hiils Lake Member j [ Volcanics of Silver Mine Lakes Silver I Iron Formation Member Member a. P- Breccia Member Member of Reany Reany Lake Lake Breccia Member Member of Bismark Bismark Creek Creek Figure 2. A 2 A-- 222 �carry up up to to5% 5% sulfides sulfides and and there there may may be be up uptoto2% 2%disseminated disseminated sulfides sulfides in in the the carry sulfides occur occur throughout throughout much much of of this unit adjacent Disseminated sulfides unit and and adjacent basalts. basalts. Disseminated are usually usually >> 95% 95% pyrite pyrite with with minor minor amounts amounts of of chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, and and are arsenopyrite. arsenopyrite. This variety variety ranges ranges in in color color from from medium medium gray-black gray-black to to Foliated Foliated Variety. Variety. This It has has an an aphanitic aphanitic texture, texture, aaphyllonitic phyllonitic to to schistose schistose fabric, fabric, and and isis green-black. green-black. It composed dominantly of of chlorite composed dominantly chlorite with lesser lesser amounts amounts of plagioclase plagioclase and/or sericite, sericite, quartz and andqarbonate. carbonate. Some Some exposures exposures contain contain up up to to40% 40% secondary secondary carbonate carbonate quartz (ankerite) (ankerite) as as the the matrix matrix of ofbrecciated brecciated basalt. basalt. Other Other exposures exposures contain contain alternating alternating light light and and dark dark layers layers which which are are interpreted interpreted as as tectonic tectonic layering layering resulting resulting from from highly elongated elongated pillows. pillows. The The alternating alternating layers layers originated originated from from darker darkerpillow pillow highly interiors Some outcrops may may also also have have interiors surrounded surrounded by by lighter lighter colored colored pillow pillow rinds. rinds. Some originally originally been been basalt basalt tuffs and and the the layering layering may may reflect reflecthighly highlyelongated elongated lithic lithic pyrite is is found fragments. Disseminated Disseminated pyrite found throughout throughout this variçty variety and and can can occur occur fragments. locally locally in in concentrations concentrations up up toto30%. 30%. The highly highly altered altered variety variety of of the thePillowed Pillowed Basalt Basalt Highly Highly Altered Altered Variety. Variety. The Member is dark Member is dark to light light gray gray in color color and takes takes on a green green hue hue near near the the gradagradational tional contact contact with with the the normal, normal, less less altered altered variety variety (see (see Day Day 11 Road Road Log, Log, Stops Stops 44 The basalt basalt is is aphanitic aphanitic to to very very fine-grained fine-grained and andisiscomposed composed 5, this this volume). volume). The and 5, of varying varying quantities quantities of of chlorite, chlorite, carbonate, carbonate, sericite, sericite, plagioclase, plagioclase, and and quartz. quartz. The The rocks rocks are are predominantly predominantly chioritized, chloritized, with with carbonatization, carbonatization, sericitization, sericitization, and and silicification The fabric fabric varies varies from from massive massive to to very very silicification occurring occurring in in varying varying degrees. degrees. The the degree degree of of foliation in this Typically, the foliation in this variety variety is as as high high as as the the highly foliated. foliated. Typically, highly rare cases, cases, deformed deformed and andundeformed undeformed pillow pillow structures structures foliated basalt basalt variety. variety. In rare can still still be be observed observed on onweathered weatheredsurfaces. surfaces. Disseminated mineralizationisismost most abundant abundant in in this this variety Sulfide Disseminated mineralization variety of of basalt. basalt. Sulfide minerals can reach reach up to minerals can to 20 20 volume volume percent percent of of the theoutcrop, outcrop, but buttypically typicallyaverage average veins, similar similar to to those Quartz and quartz-carbonate quartz-carbonate veins, those found found in in the the 2 4 % . Quartz only 2-6%. general, both both types types of of foliated foliated variety, variety, also also occur occur in in this this variety. variety. In general, A- 23 �mineralization mineralization are are related related totowell wellfoliated foliatedstructural structuralzones. zones. Breccia Member Member of ofBismark BismarkCreek Creek Breccia The TheBreccia Breccia Member Member of of Bismark Bismark Creek Creek isislocated located along alongaamajor majorNW-SE NW-SE trending trendingstructural structuralzone, zone,the theWillow WillowCreek CreekShear ShearZone Zone(MacLellan (MacLellan and andBornhorst, Bornhorst, 1988) (see (see Day Day 11Road Road Log, Log, Stop Stop9,9,this thisvolume). volume). There There ar areatatleast leastthree threetypes types 1988) ofofclasts clastsininthis thisunit: unit:boudinaged boudinagedporphyritic porphyriticrhyolite rhyolite(similar (similartotothe theRhyolite Rhyolite Intrusive The Intrusive of of Fire FireCenter CenterMine), Mine),wispy wispygabbro, gabbro,and andboudinaged boudinagedgranodiorite. granodiorite. The clasts in shape and range from 1/2 to le&oidal to elongate elongate in shape and range from to 3/4 3/4 inches inches (1-2 (1-2 clasts are are lensoidal cm) cm) for for the thelensoidal lensoidal type, type, and and up up to to 4-6 4-6 inches inches (10-15 (10-15 cm) cm) in in width width by by 3-6 3-6 feet feet (1-2 meters) meters) ininlength lengthfor forthe theelongate elongatetype. type. Clasts Clasts are are supported supported in in an an (1-2 Both the the matrix matrix and and the therhyolite rhyolite clasts clasts contain contain up uptoto epidote-rich basaltic basalticmatrix. matrix. Both epidote-rich This unit unit isisinterpreted interpretedasasa amudflow mudflowbreccia. breccia. 5% disseminated disseminated pyrite. pyrite. This 5% Breccia Member Member of of Reany ReanyLake Lake Breccia I The The Breccia Breccia Member Member of Reany Reany Lake, Lake, best best exposed exposed near near Reany Reany Lake, Lake, isis aa breccia breccia with with aa strike strikelength length of ofatatleast least5 5miles miles(8(8kilometers) kilometers)(see (seeDay Day 1 1Road Road Log, Stop Stop 8,8,this thisvolume). volume). The The unit unitisiscorrelative correlativewith withthe theMudflow MudflowMember Member Log, described by by Baxter Baxter and andothers others(1987). (1987). The The breccia breccia clasts clasts are are white, white, gray, gray, or or described brown whereas the the matrix matrix weathers weathers to to aa brown on on both both weathered weathered and and fresh fresh surfaces, surfaces, whereas The lower lower light light green-tan green-tan color color and and isisaagreen-black green-black color coloron onfresh freshsurfaces. surfaces. The portion portion of of the theunit unitcontains containsvery veryfew fewlarge largeclasts clastsand andwas wasmapped mappedasasclast-poor, clast-poor, whereas whereas the the upper upper portion portion contains contains up up to to 35% 35% clasts clasts of of all allsizes sizes and andwas wasmapped mapped In some some exposures, exposures, there there isis second second clast-poor clast-poor zone zone as the theclast-rich clast-rich horizon. horizon. In as above the the clast-rich clast-rich zone. zone. above The The clast-poor clast-poor horizon horizon has has equant equant to to oblong, oblong, sub-angular sub-angular totosub-rounded sub-rounded grains grains of of volcanic volcanic rock rock which which rarely rarely exceed exceed 1/3 1/3 inch inch (1 (1 cm) cm)ininsize. size. The The matrix matrix is is medium medium to to fine-grained, fine-grained, intermediate intermediate totomafic maficinincomposition, composition,with withoccasional occasional The clast-poor clast-poor horizon horizon isis 1/16 to to 1/8 1/8inch inch(1-3 (1-3mm) mm)grains grainsofoffeldspar. feldspar. The 1/16 interpreted mudflow or or aa reworked reworked tuff tuff deposit. deposit. interpreted as either either aa well-sorted well-sorted mudflow A- 24 �In the horizon the the clasts clasts are matrix In the clast—rich clast-rich horizon matrix supported. supported. Shapes vary vary from Shapes highly elongate to to sub-equant and rounding highly elongate sub-equant and rounding from very very angular angular to to rounded. rounded. The The more more equant equant clasts clasts are generally generally 1/3-4 113-4 inches inches (1-10 (1-10 cm) cm) across across while while the the elongated elongated fragments can reach reach lengths of up to fragments can lengths of to 10 10inches inches (25 (25 cm). It is is important important to to note note that about of the This, coupled about 50% 50% of the clasts clasts are are white, white, gray, gray, and and black black cherts. cherts. This, coupled with with the fact fact that that aacherty chertyiron-formation iron-formation overlies overlies this this unit, unit, suggests suggests that that these these cherts cherts may may have have formed formed in in aa volcanic volcanic vent vent region region and andwere werebrecciated brecciated during duringexplosive explosive Theremaining remaining clasts clasts are are fine-grained, fine-grained, porphyritic porphyritic andesites. andesites. eruptions. lhe The matrix is very very similar similar to the the material material in in the the clast-poor clast-poor horizon. horizon. Therefore, matrix Therefore, we we t also also interpret interpret the the clast-rich clast-rich horizon horizon as as aamudflow mudflow breccia breccia deposit. deposit. Iron Formation Formation Member Member The Iron Iron Formation Formation Member, Member, which which overlies overlies the Breccia Breccia Member Member of of Reany Reany Lake, consists consists ofof gray, gray, dark dark gray, Lake, gray, to black black banded banded rock with with alternating alternating bands bands of micro-crystallinechert chertand and magnetite, magnetite,or or iron-rich iron-rich chert chert (see micro-crystalline (see Day Day 11 Road Road Log, Log, Stop 10, Stop 10, this this volume). volume). In some the unit unit is is a black, some localities, localities, the black, cherty cherty iron iron formation containing formation containing up to to 2-5% 2-5% disseminated disseminated sulfides, sulfides, mainly mainly pyrite. pyrite. These cherty layers are cross-cut which may may contain contain up up to 20% cherty layers are cross-cut by carbonate carbonate veinlets veinlets which 20% suif ides. sulfides. At Clark Clark Creek, Creek, the the iron iron formation formation is is gray gray in in color color and andshows shows very very distinctive distinctive interlayering of micro-crystalline interlayering of micro- crystalline quartz quartz and and massive massive magnetite. magnetite. This locality locality also also contains clots clots of of sulfides through the the rock, often contains sulfides scattered scattered through often associated associated with with the the carbonate veins that fill 5% carbonate veins fill tension tension gashes. gashes. The sulfides sulfides comprise comprise a maximum maximum of of 5% of the whole whole rock. rock. Hill's Hill's Lake Lake Pyroclastic Pyroclastic Member Member The Hill's of white white to tan The Hill's Lake Pyroclastic Pyroclastic isis aa breccia breccia composed composed of tan dacite dacite clasts clam in aa black in black schistose schistose basalt basalt matrix. matrix. The clasts are flattened The clasts are flattened and and give give vertical vertical The metamorphic gradeofof this this unit unit is metamorphic grade is lower lower surfaces surfaces a banded banded appearance. appearance. The clasts consist consist of plagioclase plagioclase and quartz with with minor minor hornblende, hornblende, and quartz amphibolite. The clasts A-25 �The matrix matrixisiscomposed composedofofhornblende, hornblende,plagioclase, plagioclase,biotite, biotite, sericite, and andepidote. epidote. The sericite, and garnet, garnet, with withminor minorsericite, sericite,chlorite, chlorite,tourmaline, tourmaline,and andclinozoisite/epidote clinozoisite/epidote and (Johnson and and others, others,1987). 1987). (Johnson GABBRO OF OFCLARK CLARKCREEK CREEK GABBRO The The Gabbro Gabbro of of Clark ClarkCreek Creek(MacLellan (MacLellan and and Bornhorst, Bornhorst, 1988) 1988) is is named named for for gabbro gabbro intrusives intrusives that that cut cutthe theVolcanics Volcanics of of Silver Silver Mine Mine Lakes Lakes near nearClark ClarkCreek Creek and 10, 10,this thisvolume). volume). The The gabbro gabbro isismedium medium toto (see Day Day 11Road RoadLog, Log, Stops Stops5,5, 8,8, and (see dark dark green-black green-black on on aafresh freshsurface, surface,holocrystalline, holocrystalline, medium medium to to very verycoarsecoarseThe mineralogy mineralogy is is blue-green blue-green grained, and and massive massive to tostrongly strongly foliated. foliated. The grained, amphibole, chlorite, and minor amphibole, plagioclase, plagioclase, chlorite, minor pyrite, pyrite, magnetite, magnetite, and andpyrrhotite. pyrrhotite. The The more more foliated foliated zones zones within within the the gabbro gabbro have have aamuch muchhigher higherpercentage percentage ofofchlorite chlorite which causes causes aa deeper deepergreen greencolor. color. which There There is is also also an an altered altered variety variety of of gabbro gabbro which which is is medium medium to to dark dark gray gray inin color color with with plagioclase plagioclase crystals crystals forming augens augens surrounded surrounded by chlorite, chlorite, carbonate, carbonate, This rock rock has has an an undulating, undulating, schistose schistose texture on on the the quartz, and andsericite. sericite. This quartz, foliation surface. surface. The The intensity intensity of of alteration alteration isis greater greater near near zones zones of ofintense intense foliation foliation. foliation. RHYOLITE RHYOLITE INTRUSIVE INTRUSIVE OF OF FIRE FIRECENTER CENTER MINE MINE The The Rhyolite Rhyolite Intrusive Intrusive of of Fire FireCenter CenterMine Mine(Johnson (Johnson and andothers, others, 1987) 1987)has has three three common common textural textural types types and cuts cuts the the volcanics volcanics and and the the gabbro gabbro(see (seeDay Day1 1 The first first two, two, porphyritic porphyritic and and 7, this thisvolume). volume). The Road Log, Log, Stops Stops 5,6, 5,6, and and 7, Road The third third isis aphanitic, aphanitic, but but granular, granular, are are grouped grouped together together as as the thenormal normalvariety. variety. The since itit is is typically typically altered, altered, itit isistermed termed the thealtered alteredvariety. variety. since Quartz-porphyritic Quartz-porphyritic rhyolite rhyolite is the most most common common textural textural type, type, with with anhedral anhedral phenocrysts of quartz, 1/16 1/16 to to 5/16 5/16 inches inches (2-8 (2-8mm) mm)across. across. The The other other porphyporphyphenocrysts of quartz, ritic ritic type type isisquartz-feldspar quartz-feldspar porphyritic porphyritic rhyolite, rhyolite, with with phenocrysts phenocrysts of of subhedral subhedral potassium feldspar and/or and/or plagioclase as well well as anhedral potassium feldspar plagioclase as anhedral quartz quartz of of similar similar size. size. The The matrix matrix in in both both types types isisfine-grained fine-grained totoaphanitic aphanitic and andconsists consists of of quartz, quartz, A- 26 �from dark gray Color varies varies from gray to to light light gray gray carbonate, carbonate, feldspar, feldspar, and and minor minor sericite. sericite. Color The granular granular type type isisgenerally generally light light pink pinkwith withroughly roughlyequidimensional equidimensional to to pink. pink. The quartz Disseminated quartz and and feldspar feldspar grains, grains, 1/16 1/16 to to 3/16 3/16inches inches(2-5 (2-5mm) mm)across. across. Disseminated sulfides sulfides are present present in in amounts amounts of of usually usually less less than than 1%. 1%. The The altered altered variety variety is is aalight lightgreen greentotogreen-gray, green-gray-aphanitic, aphanitic,schistose schistose rock. rock. identified in in the thefield fieldprimarily primarily by bycolor color and andlack lackofofvisible visiblegrains. grains. The The It isis identified rock is is composed composed of partially partially recrystallized recrystallized quartz, quartz, feldspar, feldspar, and and interstitial interstitial sericite sericite which may may define define aa crude crude foliation. foliation. There are are up up toto8% 8%disseminated disseminated sulfides sulfides in in which the altered altered variety. variety. the GRANODIORITE GRANODIORITE OF ROCKING ROCKING CHAIR CHAIR LAKES LAKES The Granodiorite Granodiorite of Rocking Rocking Chair Chair Lakes Lakes was was named named by by Johnson Johnson and and others others (1987) plutons which which intrude intrude the Volcanics (1987) for dominantly dominantly granodioritic granodioritic plutons Volcanics of Silver Silver intrusive contacts contacts are are often often sheared sheared Mine Mine Lakes Lakes and Gabbro Gabbro of of Clark Clark Creek. Creek. The intrusive of Fire Fire Center Rhyolite Intrusive Intrusive of Center Mine Mine is interpreted interpreted as aa and/or faulted. faulted. The Rhyolite late-stage, late-stage, more more evolved evolved equivalent equivalent of the the granodiorite granodiorite plutons plutons (Baxter, (Baxter, 1988; 1988; t Johnson 1987; Bornhorst Bornhorst and and Baxter, Baxter, 1987). 1987). Johnson others, 1987; The Granodiorite of Rocking Granodiorite of Rocking Chair Chair Lakes Lakes is medium medium gray gray to light light pink, pink, medium to coarse to allotriomorphic granular, and and is medium to coarse grained, grained, hypidiomorphic hypidiomorphic to allotriomorphic granular, composed dominantly of of granodiorite composed dominantly granodiorite with with lesser lesser tonalite, tonalite, quartz quartz monzonite, monzonite, quartz quartz monzodiorite, and quartz diorite monzodiorite, and diorite (using (using aaStreckeisen Streckeisen diagram). diagram). The The massive massive granodiorite is composed of plagioclase, K-feldspar, quartz, quartz, amphibole, granodiorite is composed of plagioclase, K-feldspar, amphibole, and minor minor more amphibole-rich amphibole-rich sericite, sericite, epidote, epidote, chlorite, chlorite, apatite, apatite, and and carbonate. carbonate. A more granodiorite, owing it's it's origin granodiorite, owing origin to the the assimilation assimilation of amphibole amphibole from from the the mafic mafic country country rocks, rocks, is typically typically aa darker gray gray in in color color and and mediummedium- to to fine-grained. fine-grained. The altered altered variety variety is red red to to orange, orange, finefine- totomedium-grained, medium-grained, and and isis cross-cut cross-cut by by foliated variety, variety, found found along along intrusive intrusive contacts, contacts, is aa stockwork stockwork quartz quartz veins. veins. The foliated mineralogy of of gray gray to black, black, fine-grained fine-grained totoaphanitic, aphanitic, schistose schistose mylonite. mylonite. The mineralogy this of plagioclase, chlorite, K-feldspar, K-feldspar, quartz, quartz, and minor this variety variety consists consists of plagioclase, chlorite, minor apatite, apatite, A-27 �sericite, and epidote sericite, epidote (Johnson (Johnson and and others, others, 1987). 1987). STRUCTURE STRUCTURE The rocks The rocks in the the northern northern part part of of the theMarquette Marquette Greenstone Greenstone Belt Belt were were affected in the Archean affected by several several deformational deformational episodes episodes in Archean and and Lower Lower Proterozoic Proterozoic The first first event event folded, folded, sheared, sheared, faulted, faulted, and andmetamorphosed metamorphosed the the (Penokean). Archean rocks of the Archean rocks the Marquette Marquette Greenstone Greenstone Belt Belt in in Archean Archean time. time. A later later event event folded, folded, faulted, faulted, and and metamorphosed metamorphosed the the Lower Lower Proterozoic Proterozoic sediments sediments and diabase diabase / of the and had had a less the Marquette Marquette Range Range Supergroup Supergroup and less definite definite effect effect on on Archean Archean minor reactivation reactivation of of Archean Archean faults faults may may have have taken rocks. Some Some minor taken place place during during between Archean Archean and and Penokean Distinguishing between Penokean metathe Penokean Penokean deformation. deformation. Distinguishing morphismisis difficult difficult since since they they are are both both greenschist facies,but but in in the Island morphism greenschist facies, Island Lake Area where Archean Archean metamorphism metamorphism reaches reaches amphibolite amphibolite facies, facies, Penokean Penokean metamormetamorArea phism is denoted and fabrics phism denoted by by retrograde retrograde assemblages assemblages and fabrics (Johnson (Johnson and and others, others, 1987). 1987). Foliations in the region Foliations in region are are defined defined by by slaty, slaty, phyllonitic, phyllonitic, and andschistose schistose cleavages and generally These cleavages cleavages generally trend trend N70°W. N70¡W These cleavages are most most prominently prominently displayed in in the lepidoblastic displayed lepidoblastic textured, mafic mafic rocks. rocks. Most in the Most foliations foliations in the Archean rocks rocks are are interpreted interpreted to to have Archean have been been formed formed during the the Late Late Archean Archean tectonic event. event. The Archean Archean rocks rocks in the the area area of of Silver Silver Mine Mine Lakes, Lakes, Clark Clark Creek, Creek, and Silver Creek lie lie on the and Silver Creek the southern southern limb limb of of aasteeply steeply plunging, plunging, synformal synformal anticline (Johnson The nose anticline (Johnson and others, others, 1987). 1987). The nose of of this this regional regional fold fold is is exposed exposed to to the of Silver Creek where where the the hinge hinge region region of of this the northwest northwest of Silver Creek this structure structure has has been been intruded intruded by the the Granodiorite Granodiorite of of Rocking Rocking Chair Chair Lakes. Lakes. There are are several generationsofof faults faults in in the region There several generations region that that faults faults probably probably formed Archean deformational deformational event. event. The oldest formed during during various various pulses pulses of the the Late Late Archean oldest faults faults in the the area area generally generally trend trend southeast-northwest southeast-northwest to east-west, east-west, are are generally generally ductile ductile in nature, nature, and and would would be be termed termed shear shear zones zones in in Ontario. Ontario. A large large structural structural zone, zone, the Dead Dead River River Shear Shear Zone, Zone, also also trends trends southeast-northwest, southeast-northwest, and and was was This zone initiated during the zone is typified typified by by steeply steeply dipping, dipping, phyllonitic phyllonitic initiated the Archean. Archean. This A-28 �to highly highly schistose schistose volcanic volcanic rocks. rocks. It originated originated as an Archean Archean ductile ductile shear shear zone zone which subsequentlyhad had aa minor minor portion portion reactivated reactivated as as aa relatively brittle fault relatively brittle which subsequently during the the Early Early Proterozoic. Proterozoic. Earlier faults and and shear are truncated, Earlier Archean Archean faults shear zones zones are truncated, and locally locally offset by by slightly slightly younger, younger, north-south north-south to to northeast-southwest northeast-southwest trending trending Archean Archean faults. faults. The deformational regimefor for these these faults faults was was relatively relatively brittle brittle in in contrast deformational regime contrast to the the older older ductile faults. faults. It is is likely likely that that movement movement along along these these faults faults took took place place in the the waning stages' stages'ofof the the Archean Archean deformational deformationalevent eventbecause becausethey theyoffset offset the the zone waning zone of highly altered basalts. highly basalts. MINERALIZATION Mineralization in the region Mineralization in region exists exists in in two two forms: forms: 1)1)disseminated disseminated sulfides sulfides within altered 2) quartz-carbonate-sulfide quartz-carbonate-sulfide veins. veins. within altered country rocks, rocks, and and 2) Disseminated mineralization most prominent prominent in in the the highly mineralization isis most highly altered altered variety of of the thePillowed Pillowed Basalt Member Member and and in in the Iron Basalt Iron Formation Formation Member, Member, but but also also occurs occurs occasionally occasionally in pyrite and sporadic other Archean Archean rock rock types. types. It consists consists of disseminated disseminated pyrite sporadic minor minor pyrrhotite and The alteration minerals in in the country alteration minerals country rocks rocks are are and chalcopyrite. chalcopyrite. The primarily primarily chlorite, chlorite, sericite, sericite, carbonate, carbonate, and and quartz. quartz. The veins of quartz of chlorite, The veins of quartz and and carbonate, carbonate, and lesser lesser amounts amounts of chlorite, are often often associated with shear zones associated with zones and and faults. faults. The chief chief sulfide sulfide mineral mineral is pyrite pyrite with with much much lesser lesser amounts amounts of chalcopyrite, chalcopyrite, arsenopyrite, arsenopyrite, and pyrrhotite. pyrrhotite. Locally, galena Locally, galena and sphalerite sphalerite are the the dominant dominant sulfide sulfide vein vein minerals. minerals. In general, general, it appears appears that that two two episodes episodes of of mineralization mineralization have have affected the the volcanicsand and intrusives intrusivesofof the the northern northern part part of the volcanics the Marquette Marquette Greenstone Greenstone Belt. Belt. The early early episode episode produced produced the majority majority of of the the disseminated disseminated mineralization mineralization and was likely likely controlled controlled by by the the location of the east-west was location of east-west trending trending faults faults and and shear shear for the the production of zones This event event was was also also responsible responsible for production of zones of intense intense zones. This carbonatization, sericitization, and chioritization. chloritization. The second second episode episode produced produced carbonatization, sericitization, primarily carbonate-quartz veins with primarily carbonate-quartz veins with associated associated galena, galena, sphalerite, sphalerite, and chalcopyrite chalcopyrite A— 29 �These veins veins are are localized localized near near the the areas areas of ofyounger, younger,north-south, north-south, mineralization. These mineralization. brittlefaults. faults. Anomalous Anomalous precious precious metal metal values values can be be found found associated associated with with both both brittle episodes of of hydrothermal hydrothermalmineralization. mineralization. episodes GEOLOGICHISTORY HISTORY GEOLOGIC The The earliest earliest event event in in the theregion region north northofofthe theDead DeadRiver RiverStorage StorageBasin Basin was was the the extrusion extrusion of of the thesub-aqueous, sub-aqueous, tholeiitic, tholeiitic, pillow pillow basalts basalts that that form formthe thePillowed Pillowed Basalt Member Member of of the theVolcanics Volcanics of of Silver SilverMine MineLakes. Lakes. The The age age of of these thesebasalts basalts isis Basalt / about about 2.7 2.7 Ga Ga based based on on the theradiometric radiometric age age dating dating of of aarhyolite rhyoliteintrusive intrusivewhich which cuts basalt basalt beneath beneath the theClark ClarkCreek CreekBasin Basin(Trow, (Trow,1979). 1979). During During eruption eruption of of the the cuts basalts, basalts, several several thin mafic mafic to to intermediate intermediate volcanic volcanic mudflow mudflow breccias breccias that that contain contain locally abundant abundant iron iron formation formation debris debris were were deposited. deposited. Continued Continued extrusion extrusion of of locally subaqueous lava lava flows flows produced produced additional additional pillow pillow basalts. basalts. The The volcanic volcanic pile pile was was subaqueous then intruded intruded by by dikes dikes and andsills sillsofofgabbro gabbro(Gabbro (GabbroofofClark ClarkCreek). Creek). The The mafic mafic then rocks deformed and and intruded intruded by by syn- to rocks were were synchronously synchronously deformed to post-tectonic post-tectonic rhyolite rhyolite and granodiorite granodiorite (2.7 (2.7 Ga). Ga). The The rhyolites rhyolites may may represent represent differentiated differentiated portions portions of of and the the granodiorite granodiorite plutons plutons (Bornhorst (Bornhorst and and Baxter, Baxter, 1987). 1987). An An episode episode of synsyn- to to post-tectonic post-tectonic hydrothermal hydrothermal alteration alteration resulted resulted in in the theprecious preciousmetal metalmineralization. mineralization. The The Late Late Archean Archean deformation deformation and and hydrothermal hydrothermal activity activity also also produced produced the the foliated foliated and and altered altered varieties varieties of of the thePillowed Pillowed Basalt Basalt Member Member of of the theVolcanics Volcanics of of Silver Mine Mine Lakes. Lakes. Silver ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The The co-operative co-operative research research effort which which made made this this study study possible possible was was funded funded by of the by the the Michigan Michigan Geological Geological Survey Survey Division Division of the Department Department of of Natural Natural Resources Resources and the the Department Department of of Geology Geology and andGeological Geological Engineering Engineering atat Michigan Michigan This paper paper has has benefited benefited from from discussions discussions with with Ted Ted Technological University. University. This Technological Bornhorst, Rod Rod Johnson, Johnson, Jo Jo Kalliokoski, Kalliokoski, and and Eric Eric Owens. Owens. Careful Careful review review of of this this Bornhorst, paper paper by by Ted TedBornhorst, Bornhorst, Jo JoKalliokoski, Kalliokoski, and andKlaus KlausSchulz Schulzare arealso alsoacknowledged. acknowledged. A- 30 �REFERENCES REFERENCES Baxter, Baxter, D.A., D.A., 1988, 1988, Geology, Geology, Geochemistry, Geochemistry, and and Hydrothermal Hydrothermal Alteration Alteration Associated with Precious in the Clark Associated with Precious Metal Metal Mineralization Mineralization in Clark Creek Creek Region, Region, Marquette Marquette County, County, Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan Michigan Technological Technological University, University, Houghton, Michigan Michigan (in (in preparation). preparation). Houghton, Baxter, Baxter, D.A., D.A., Bornhorst, Bornhorst, T.J., T.J., and and VanAlstine, VanAlstine, J.L., J.L., 1987, 1987, Geology, Geology, Structure, Structure, and Metal Mineralization Mineralizationofof Archean ArcheanRocks Rocksinin the the Vicinity Vicinity of and Associated Associated Precious Precious Metal Clark Clark Creek, Creek, Marquette Marquette County, County,Michigan: Michigan:Michigan MichiganGeological Geological Survey SurveyDivision, Division, Department of Natural Open File File Report Department of Natural Resources, Resources, Open Report OFR-87-8, OFR-87-8, 54 54 pp. pp. Bodwell, Bodwell, W.A., W.A., 1972, 1972, Geologic Geologic Compilation Compilation and Nonferrous Nonferrous Metal Metal Potential, Potential, Precambrian Precambrian Section, Section, Northern Northern Michigan: Michigan: M.S. M.S. Thesis, Thesis, Michigan MichiganTechnological Technological University, University, Houghton, Houghton, Michigan, Michigan, 106 106 p. p. Bornhorst, T.J, and Baxter, Character of of Archean Bornhorst, T.J. Baxter, D.A., D.A., 1987, 1987, Geochemical Geochemical Character Archean Rocks Rocks from the the East East Half Half ofofthe theNorthern NorthernComplex, Complex,Upper UpperPeninsula, Peninsula,Michigan: Michigan: Institute Proceedingsand andAbstracts, Abstracts,v.v.33, 33, part part 1, Institute on Lake Lake Superior Superior Geology Geology Proceedings 1, p. 12. 12. Johnson, Johnson, R.C., R.C., Bornhorst, Bornhorst, T.J. T.J. and and VanAlstine, VanAlstine, J.L., J.L., 1987, 1987, Geologic Geologic Setting Setting of of Precious in the the Silver Precious Metal Metal Mineralization Mineralization in Silver Creek Creek to Island Island Lake Lake area, area,Marquette Marquette County, Michigan: Survey Division, Division, Department Department of of Natural Michigan: Michigan Michigan Geological Geological Survey Natural Resources, Open-File Report, OFR-86-2, 134 Resources, Open-File Report, OFR-87-4, OFR-87-4, Supersedes Supersedes OFR-86-2, 134 p. p. MacLellan, M.L. and Bornhorst, 1988, Geology, Geology, Structure, Structure, and and MineralizMineralizMacLellan, M.L. Bornhorst, T.J., 1988, ation ation of of the theReany ReanyLake LakeArea, Area,Marquette MarquetteCounty, County,Michigan: Michigan:Michigan MichiganGeological Geological Survey Department of of Natural Natural Resources, Resources, Open Open File File Report, Report, (in preparaSurvey Division, Division, Department preparation). Morgan, Evolution of of the Morgan, P.J. P.J. and and DeCristoforo, DeCristoforo, D.T., D.T., 1980, 1980, Geological Geological Evolution the Ishpeming Greenstone Belt, Belt, Michigan, Michigan, U.S.A.: U.S.A.:Precambrian PrecambrianResearch, Research,v.v. 11, 11, p. Ishpeming Greenstone 23-4 1. 23-41. Owens, Owens, E.O. E.O. and and Bornhorst, Bornhorst, T.J., T.J., 1985, 1985, Geology Geology and and Precious Precious Metal Metal MineralizMineralization ation of the the Fire FireCenter Centerand andHolyoke HolyokeMines MinesArea, Area, Marquette Marquette County, County, Michigan: Michigan: Michigan Survey Division, Division, Department Department of of Natural Resources, Michigan Geological Geological Survey Resources, Open Open File File Report OFR-85-2, OFR-85-2, 105 105 p. p. Report Trow, Trow, J., J., 1979, 1979, Final Final report report on on diamond diamond drilling drilling for forgeologic geologic information information in in the Middle basins in in the western Middle Precambrian Precambrian basins western portion portion of of northern northern Michigan: Michigan: Michigan Survey Division, Division, Department Department of of Natural Resources, Michigan Geological Geological Survey Resources, Open Open File File Report Report UDOE UDOE OFR GJBX-l62(79), GJBX-162(79), 44 p. p. A-31 �Geology of of the Ropes Geology Ropes Gold Gold Mine Mine R.A. R.A. Brozdowski Brozdowski Callahan Callahan Mining Mining Corporation Corporation Exploration Exploration Dept. Dept. 25 Industrial 25 Industrial Park Park Rd. Rd. Negaunee, Negaunee, Michigan, Michigan, 49866 49866 INTRODUCTION The mine is is located in the south-west The Ropes Ropes gold gold mine located in south-west part of of the the Archean Archean Marquette Greenstone Greenstone Belt, Belt, 5.8 5.8 km km northwest of the Marquette northwest of the town town of of Ishpeming, Ishpeming, Michigan, Michigan, 43', in at latitude latitude 46° 46' 32', 32', longitude longitude 87° 87' 43', in the the Sl/2 Sl/2NW1/4 NW1/4 Section Section 29, 29, T48N, T48N, R27W, R27W, / Ishpeming Township, Township, Marquette County, Ishpeming County, Michigan, Michigan, USA. USA. The mine The mine can be be reached by by traveling from US Hwy reached traveling northward northward from Hwy 41, west west via via paved paved County County Road Road west via via unpaved 573, then west unpaved County County Road Road GCL (the (the Ropes Ropes mine mine access access road). road). 573, HISTORY Julius Ropes, Julius Ropes, a druggist druggist and and prospector prospector from fromIshpeming, Ishpeming, Michigan, Michigan, discovered discovered a gold-bearing gold-bearing quartz stringer stringer in 1880 1880 while while prospecting prospecting for asbestos asbestos and serpentine "marble"ininlow lowground groundnear near the the east east end end of of the serpentine "marble" the present-day present-day Ropes Ropes prospectingresulted resultedinin discovery discoveryofof the the outcrop Continued prospecting outcrop of the the mine property. property. Continued Ropes main ore zone 250 m m west west of of the Ropes main zone approximately approximately 250 the initial initial discovery discovery (Allen, (Allen, 1912). 1912). The original The original Ropes Ropes mine operated operated sporadically sporadically from 1882 1882 to to 1897, 1897, producing 1029 Kg Kg of of Au Au and and 2057 2057 Kg of of Ag Ag from from 195,000 195,000 tonnes tonnes of of ore. ore. The producing 1029 The property idle, except property remained remained idle, except for minor minor cyanidization cyanidization of tailings, tailings, until until Calumet Calumet and Hecla Copper Co. Co. conducted extensive surface surface and underground Hecla Consolidated Consolidated Copper conducted extensive underground exploration from from 1935 to 1942 tonnes of of ore exploration 1935 to 1942 and outlined outlined 1,393,000 1,393,000 tonnes ore averaging averaging 3.98 3.98 The relatively low grade gradeofof the the deposit at a time g/tonne Au g/tonne Au (Broderick, (Broderick, 1945). 1945). The relatively low deposit at time of controlled of controlled gold gold prices, prices, combined combined with with wartime wartime restrictions restrictions on precious precious metals metals mining, precluded precluded any any production production at at that time. Mining Corporation mining, time. Callahan Callahan Mining Corporation of Phoenix, Arizona, Arizona, purchased purchased the the property property from from Arcadian Arcadian Copper Copper Mine Mine Tours Tours in Phoenix, 1975, began began exploration explorationinin 1979, 1979,and and made madeaa decision decisiontoto develop develop the the mine mine in in mid 1975, mid began in in September 1985, and and isis now Production began September 1985, now about about 1,800 1,800 tonnes tonnes per 1984. 1984. Production day. A-32 �GEOLOGY OF SW PART PART OF OFTHE THEMARQUETTE MARQUETTEGREENSTONE GREENSTONE BELT BELT GEOLOGY OF THE SW Rocks in the Rocks in the southwest southwest part of of the the Marquette Marquette Greenstone Greenstone Belt, Belt, which which host host the the Ropes of the lower Ropes mine, mine, generally generally have mineral mineral assemblages assemblages of lower greenschist greenschist facies, facies, except except in proximity proximity to the the granitoid granitoid rocks rocks which which bound bound the the greenstone greenstone belt, belt, where where amphibolite facies rocks rocks are charamphibolite facies facies assemblages assemblages occur. occur. The greenschist greenschist facies char- acterized by a sub-vertical acterized by sub-vertical planer planer foliation, foliation, defined by by aa weak weak parallelism parallelism of of aphanitic phyllosilicate minerals, which which is commonly phyllosilicate minerals, commonly conformable conformable to flow flow margins margins in volcanic volcanic rocks, rocks, graded graded bedding bedding in in graywackes, graywackes, and and compositional compositional layering layering in units units such such as as chert-magnetite chert-magnetite iron iron formation. formation. There There are relict relict cumulate cumulate textures textures in serpentinized peridotite, pillows in basalt, serpentinized peridotite, pillows in basalt, and and bipyramidal bipyramidal and and embayed embayed quartz quartz grains, and lithic Therefore, rocks grains, lithic fragments fragments in in volcaniclastic volcaniclastic rocks. rocks. Therefore, rocks with with readily readily recognizableprimary primarystructures structuresand andtextures texturesare arereferred referredtotohere here in in by by their recognizable sedimentary or igneous names as as recommended recommendedinin the the North North American Code of of sedimentary or igneous names American Code Stratigraphic nomenclature; the the prefix "meta-" Stratigraphic nomenclature; "meta-" is is impli€d. implied. Hydrothermally altered altered rocks in in the vicinityofof the the Ropes Ropes mine mineare are referred referred to to by by their rocks the immediate immediate vicinity dominant assemblageslisted listedinin decreasing decreasingorder order of of abundance, dominant mineral mineral assemblages abundance, such as "quartz—sericite-chlorite "quartz-sericite-chlorite rock." rock." The southwest part of the to ESE, southwest part the greenstone greenstone belt belt comprises, comprises, from from WNW WNW to ESE, aa sequence of: of: (1) pillowed sequence pillowed to massive massive tholeiitic tholeiitic basalt, basalt, associated associated hypabyssal hypabyssal gabbroic gabbroic sills and dikes, dikes, and and subordinate subordinate mafic-volcanic mafic-volcanic derived derived graywackes; graywackes; (2) sills (2) an inter—layeredzone zoneofofbasalt, basalt,dacite dacitetuff, tuff,and and porphyritic porphyritic dacite dacite sills; sills; (3) (3) dacite dacite tuff tuff inter-layered with subordinate tuff breccia, with subordinate tuff breccia, which which hosts hosts banded banded quartz-magnetite quartz-magnetite iron formation formation and quartzose immediately west west of of the Ropes (4) serpentinized, serpentinized, and quartzose graywacke graywacke immediately Ropes mine; mine; (4) and talc-altered fine grained grained peridotite, peridotite, which which is carbonatized carbonatized and talc-altered in proximity proximity to to the the conglomeratesand andtuff tuff breccias brecciasofof dccitic dcitic composiRopes mine; and (5) (5) volcanic volcanic conglomerates composiRopes mine; tion. The volcanic units strike strike ENE, ENE, dip subvertically, and top consistently to the The volcanic units subvertically, and consistently to the southeast, based based on pillow southeast, pillow facing facing directions directions and and graded graded bedding bedding (Callahan (Callahan Mining Mining Corporation geologic mapping core logs). logs). The serpentinized Corporation detailed detailed geologic mapping and and drill core serpentinized peridotite has a relict, peridotite has relict, fine fine grained grained cumulate cumulate texture texture and and was was likely likely aahypabyssal hypabyssal A- 33 �sill sill complex complex emplaced emplaced within within the the volcanic volcanic section, section, based based on its its fine finegrain grainsize sizeand and local local complex complex interlayering interlayering with with the thevolcanic volcanicrocks. rocks. The The rocks rocks which which most most directly directly host host the the Ropes Ropes mine mine represent represent one one ofofsix sixknown knownlocalities localitieswhere wherevolcanic volcanic rocks rocks are are interlayered interlayered with withthe theserpentinized serpentinizedperidotite peridotite(Callahan (CallahanMining Mining Corporation Corporation detailed detailed geologic geologic mapping mapping and drill drill core core logs); logs); other othervolcanic volcanic inliers inliers may may exist exist in in poorly poorly totonon nonoutcropping outcropping low low ground ground throughout throughout the the outcrop outcrop belt belt of of the serpentinized serpentinized peridotite. peridotite. the The The Ropes Ropes mine mine isis located located to to the thesoutheast southeast of of the thebasalt-to-dacite basalt-to-dacite transition transition The zone 1). The zone and and the the layers layers of ofbanded bandediron ironformation formationand andgraywackes graywackes(Figure (Figure1). , Ropes gold gold deposit depositisishosted hostedbyby quartz-sericite-chlorite rock interpreted asas Ropes quartz—sericite—chlorite rock interpreted hydrothermally altered dacite dacite tuff on hydrothermally altered on the thebasis basis ofofthe theprogressive progressivedevelopment development of of This alteration alteration gradationally gradationally replaces replaces and and pervasive pervasive quartz quartz and and sericite sericitealteration. alteration. This finally finally totally totally pseudomorphs pseudomorphs feldspar feldspar phenocrysts, phenocrysts, matrix feldspar, feldspar, and and felsic felsiclithic lithic fragments fragments in the the tuffs tuffsasasthe theRopes Ropesmine mineisisapproached approached from fromthe thewest. west.Similar Similar less less mobile mobile trace trace element element abundances abundances and and similar similar chondrite-normalized chondrite-normalized rare rare earth earth patterns dacite tuff patterns between between unaltered unaltered (except (except for for greenschist greenschist facies facies metamorphism) metamorphism) dacite to thethe quartz—sericite-chlorite quartz-sericite-chlorite rock rock which which hosts hosts to the thewest westofofthe theRopes Ropesmine mineand and the the Ropes Ropes deposit deposit also also provides provides evidence evidence for foraacommon commonorigin origin(Callahan (CallahanMining Mining Corp., unpublished unpublished data). data). Corp., GEOLOGY GEOLOGY OF OF THE THEMINE MINEAREA AREA There There are are four four main main rock rock types types within within the the immediate immediate mine mine area area: (1) (1) Fine Fine grained the ore zones, quartz-sericite-chlorite rock rock encloses encloses the zones, strikes strikes N70°E N70° and and dips dips grained quartz-sericite-chlorite This rock rock type type is is bounded bounded to the the north north and and south south by, by, (2) (2) fine fine steeply south. south. This steeply grained, grained, carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock which which isismassive massivetotocompositionally compositionallylayered layered quartz-sericite-chlorite rock rock and and the the The quartz-sericite-chlorite on aascale scaleofofseveral severalmillimeters. millimeters. The on carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are are locally locally complexly complexly interlayered, interlayered, particularly particularly Contacts between between the two two rock rock 1, 2, 2, 3). 3). Contacts within and west west of the the mine mine (Figures (Figures 1, within The carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock is is flanked flanked types are are generally generally sharp. sharp. The types A- 34 �'-4 U II L± - E1 Ti EXPLANATION FOR FIGURE 1 Basalt tuff Basalt (includes pillowed and glomerophyric basalt) Fine-grained mafic intrusions Graywacke and siltstone Banded quartz-magnetite iron formation Dacite tuff, tuff breccia and flows, minor andesite flows; altered to quartz-sericite-chlorite rock in mine area Compositionally layered to massive carbonate-quartz chlorite rock Carbonate-talc rock Carbonatized, serpentinized peridotite N Ct, Serpentinized fine-grained peridotite Ill LI : JHIH Quartzite Graywacke Geology v r -. JJpdip projection to surface of orebodies Shaft Fault (dotted where inferred) Field trip stop Paved road Unpaved road inferred) Contact (dotted where Symbols �a Figure 1. Geologic Map of the Ropes Mine area. Explanation on preceding page. �EXPLANAT ION EXPlANATION ELEVATION (ft.) ELEVATIO Serpentinized finefineSerpentinized IH I Ii 1400 grained peridot peridotite, grained ite, locally carbonatized carbonatized locally Carbonate-talc Carbonate-talc rock rock Compositionally Compositionally layered to to massive massive layered carbonate-quartzcarbonate-quartzchlorite chlorite rock rock 1200 LI 1000 I Quartz-sericiteQuartz-sericitechlorite rock rock chlorite Orebody Orebody >2 gg Au/tonne Aultonne >2 800 Mine Levels Levels Mine L 600 L L 400 Scale Scale 100 100 L 200 200ft. ft. 0 61 m. 200 100 L 61 rn. 200 ft. L Sea Sea Level Leva 0 Figure 2.2. Figure Ropes Ropes Mine Mine 600 600 EE Cross-Section Cross-Section looking SS 80° 80' WW looking — 200 400 A-37 �Scale 61 m. -H 200 ft. Figure 3. Geologic plan maps of the Ropes Nine. See Fig. 2 for explanation. �successively,on onboth both the the north north and and south successively, south sides, sides, by, (3) (3) fine fine grained, grained, massive massive to to moderately foliated, foliated, carbonate-talc carbonate-talc rock, rock, and and (4) fine moderately fine grained, grained, totally totally serpentinized serpentinized peridotite retains aa relict cumulate peridotite which which commonly commonly retains cumulate texture after after original original olivine olivine This rock is is carbonatized carbonatized to varying varying degrees degrees near near its its contacts contacts and lesser lesser pyroxene. pyroxene. This between the carbonate-quartz-chlorite Contacts between carbonate-quartz-chlorite rock rock with with the the carbonate-talc carbonate-talc rock. rock. Contacts and the carbonate-talc rock and and the and the carbonate-talc carbonate-talc rock, rock, and between between the carbonate-talc rock serpentinized peridotite are generally over one to serpentinized peridotite generally gradational gradational over to several several meters. meters. The preservation of relict relict feldspar and lithic and the total The preservation of feldspar and lithic clasts, clasts, and total thickness thickness of quartz-sericite-chlorite rock, rock, increases gradationally westward westward from from the Ropes quartz-sericite-chlorite increases gradationally Ropes main main ore zone (Figure 1) 1) over over aa distance of several hundred meters meters into into aa large body of of ore zone (Figure distance of several hundred large body dacite that has dacite has moderately moderately aligned aligned twinned twinned plagioclase plagioclase phenocrysts, phenocrysts, bipyramidal bipyramidal quartz, and volcanic quartz-sericite-feldspar-chlorite quartz, volcanic rock fragments fragments in in an an aphanitic aphanitic quartz-sericite-feldspar-chlorite matrix characteristic matrix characteristic of of aacrystal—lithic crystal-lithic tuff. The dacite dacite locally locally contains contains intervals intervals of lapilli-sized lapilli-sized'fragments. fragments. rock isis restricted largely The carbonate—quartz-chlorite carbonate-quartz-chlorite rock largely to the thin intervals intervalsup uptoto 22 m m thick the mine mine area area (Figure (Figure 1), l), although although thin thick occur occur up to to The thickest 400 m west west of the the Ropes Ropes main main ore ore zone. zone. The thickest intervals intervals of carbonate-talc carbonate-talc 400 rock rock occur occur within within the mine mine area area (Figure (Figure 1); 1); however, however, thin intervals intervals of talc-rich talc-rich rock at the contacts rock occur occur at numerous numerous localities localities at contacts of, and and also also in, in, serpentinized serpentinized Serpentinized peridotite peridotite peridotite away peridotite away from the the mine mine area area(Rossell, (Rossell,1983). 1983). Serpentinized occurs up to to 2 km of the and up km northeast northeast of the Ropes Ropes mine mine and up to to 55 km km southwest southwest of the the occurs up mine in aa northeast mine northeast trending trending set set of of outcrops, outcrops, approximately approximately 600 600 m wide wide (Clark (Clark et.al., 1975). et.al., 1975). MAJOR ROCK ROCK TYPES TYPES IN IN THE ROPES MAJOR ROPES MINE MINE PROPERTY PROPERTY Quartz-Sericite-Chlorite Rock Quartz-Sericite-Chlorite Rock The main The main host host for gold gold is is light light green, green, massive massive to slightly slightly foliated, foliated, fine fine This rock rock isis up grained, up to 40 40 m m grained, quartz-sericite-chlorite quartz-sericite-chlorite rock with with relict relict clasts. clasts. This thick on on the 800 toward the the surface and toward the east thick 800 Mine Mine Level, Level, but but narrows narrows toward surface and toward the to less than than 6 m m thick. thick. to less is complexly It is complexly interlayered interlayered with carbonate-quartz-chlorite carbonate-quartz-chlorite A-39 �rock, rock, especially especially west west of the the Ropes Ropes main main ore ore zone zone (Figure (Figure 1) 1) and and in inthe themine mine and3). 3). The The rock rock has has equant equant quartz quartz grains grains 50 50 toto100 100microns microns inin (Figures 22 and (Figures diameter diameter in in aarandomly randomly oriented oriented totomoderately moderately aligned aligned sub-20 sub-20 micron micron quartz, quartz, sericite, and and minor minor chlorite chloritematrix. matrix. Randomly Randomly oriented oriented totomoderately moderatelyaligned, aligned, I1 toto sericite, 22mm, mm, angular, angular, rectangular rectangular mats mats of of sub-10 sub-10 micron micron sericite sericite and andminor minorquartz quartzare are enveloped enveloped in this this matrix matrix and and have have an anexternal external habit habitvery verymuch muchlike likethe theplagioclase plagioclase phenocrysts phenocrysts in the the thicker, thicker, more more massive, massive, lateral lateral equivalent equivalent of of this this rock rock This textural textural change change isisgradational gradationaleastward eastward immediately west west of of the themine. mine. This immediately toward toward the the orebody orebody over over aa distance distance of of aafew fewhundred hundred meters meters and andisischaracterized characterized by by increasing increasing alteration alteration of of the theplagioclase plagioclase phenocrysts phenocrysts to to sericite sericite and andan anincrease increase in in the the abundance abundance of of quartz quartz and and sericite sericite ininthe thematrix, matrix,with witha acorresponding corresponding quartz-sericiteTherefore, the the sericite-rich sericite-rich mats mats in in the thequartz-sericitedecrease in in feldspar. feldspar. Therefore, decrease chlorite pseudomorphs after afterplagioclase plagioclase chlorite rock rock of of the themine mineare areinterpreted interpretedasaspseudomorphs constituteup up to to 20 The sericite sericite pseudomorphs pseudomorphs constitute 20 percent percent of of the the rock. rock. phenocrysts. The phenocrysts. mm inindiameter diameterand andcomposed composed ofofmicrocrystalline microcrystalline aggreaggreUncommon clasts, clasts, I1 to to 22 mm Uncommon gates gates of of quartz, quartz, may mayrepresent represent pseudomorphs pseudomorphs of of quartz quartz phenocrysts phenocrysts which which now now exhibit exhibit subgrain subgrain development, development, or or alternatively, alternatively, some some may may be bechert chertfragments. fragments. Chlorite-quartz Chlorite-quartz fragments, fragments, which which may may be be more more mafic mafic volcanic volcanic rock rock fragments fragments or or pseudomorphed mafic mineral occur less in the rock. pseudomorphed mafic mineral phenocrysts, phenocrysts, occur less commonly commonly in rock. Chlorite componentofof the the rock Chlorite is generally generally a subordinate subordinate component rock at less less than than 10% 10% and and occurs occurs both dispersed dispersed in the the matrix matrix and and locally locally as as coarser coarser laths laths which which define define aa slight foliation. foliation. Ferroan Ferroan dolomite dolomite is locally locally a minor minor component component of the the matrix. matrix. slight The rock rock isislayered layered locally locally with with 55 mm mm thick, thick, planer, planer, sericite-rich sericite-rich and andalternate alternate The more chlorite—rich chlorite-rich laminae. laminae. more Gold Gold abundance abundance is generally generally greatest greatest where where very very fine to to aphanitic aphanitic pyrite pyrite to 8% 8% of the the rock, rock, quartz quartz and and sericite sericite are are most most abundant, abundant, and and chlorite chlorite comprises 55 to comprises is does not not apply apply in in the case is least least abundant abundant (this generality generality does case of of the the chloritic, chloritic, pyritic, pyritic, farthest farthest eastern eastern rim rim of of the the Ropes Ropes main main ore ore zone, zone, as asdiscussed discussed in in the the subsequent section section on on"The "TheOrebodies"). Orebodies"). Rock with with greatest greatest gold gold abundance abundance subsequent A-40 �contains contains only only trace trace amounts amounts of of carbonate, carbonate, compared compared with higher higher but but still stillminor minor concentrations of carbonate quartz-sericite-chlorite concentrations of carbonate in less less auriferous auriferous parts parts of of the thequartz-sericite-chlorite Fine pyrite, pyrite, 50 50 to to 100 100 microns microns in in diameter, diameter, is is dispersed dispersed in the the rock rock matrix matrix rock. rock. Fine and and is and less less commonly commonly within within the the sericite sericite pseudomorphs pseudomorphs after plagioclase plagioclase and is not not confined confined only only to to quartz quartz veinlets veinlets or or totofoliation foliationplanes. planes. Coarser Coarser pyrite, pyrite, 0.5 0.5 to to I1 mm mm in in diameter, diameter, occurs occurs near near quartz quartz veinlets veinlets and and also alsoalong along chioritic chloritic foliations. foliations. This This relatively relatively coarse coarse pyrite is is enclosed enclosed locally locally by by quartz quartz over-growths, over-growths, and and isis occasionally pulled apart along Rock characterized characterized by by only only coarser coarser occasionally pulled along the the foliation. foliation. Rock less than than 11 mm Quartz veinlets veinlets less mm thick thick comprise comprise up up to to several several pyrite pyrite is is not not ore. ore. Quartz percent Quartz in in the theveinlets veinletscommonly commonly percent of the the rock rock and andare arerandomly randomly oriented. oriented. Quartz Rock outside outside of of the theore orezones zones has has undulatory undulatory extinction extinction and and local local mortar mortar texture. texture. Rock is is characterized characterized by by <2% <2% very very fine fine pyrite. pyrite. Carbonate-Quartz-Chlorite Carbonate-Quartz-Chlorite Rock Rock Carbonate-quartz-chlorite Carbonate-quartz-chlorite rock rock envelopes envelopes the afore-mentioned afore-mentioned quartz-sericitequartz-sericite- chlorite with it, particularly chlorite rock rock and and isis complexly complexly interlayered interlayered with particularly toward toward the the west west carbonate-quartz-chlorite rock rock contains contains end of of the theRopes Ropesmine mine(Figure (Figure1). 1). The The carbonate-quartz-chlorite end abundant abundant ferroan ferroan dolomite, dolomite, and and lesser lesser quartz quartz and andchlorite. chlorite. Minor sericite sericite occurs occurs in some and minor some specimens, specimens, and minor talc talc in others, others, but but these these two two minerals minerals are aregenerally generally quartz-sericite-chlorite rock rock are aresharp; sharp; Contacts with with the the quartz-sericite-chlorite mutually exclusive. exclusive. Contacts however, minerals are are present present in in the however, minor minor carbonate carbonate minerals the quartz-sericite-chlorite quartz-sericite-chlorite rock rock near carbonate-quartz-chlorite rock, rock, and and minor minor sericite sericite isis near its its contacts contacts with with the the carbonate-quartz-chlorite present present in in the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock near its its contacts contacts with with the the quartzquartz- this rock rock contains contains up up to 150 Typically, this 150 ppb ppb Au. Au. sericite-chlorite sericite-chlorite rock. rock. Typically, Quartz-rich Quartz-rich parts parts of of the thecarbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are arelocally locally slightly slightly pyritic pyritic and contain contain up to to 1 ppm ppm Au. Au. The carbonate-quartz-chlorite layered on on aa carbonate-quartz-chlorite rock is is commonly commonly compositionally compositionally layered Layering is defined defined by by scale of several several millimeters, millimeters, but but locally locally isismassive. massive. Layering parallel, parallel, fine to to medium medium grained, grained, white white carbonate carbonate laminae, laminae, chlorite chlorite foliation, foliation, and and A-41 �quartz-chlorite-rich laminae. quartz-chlorite-rich laminae. with carbonate-talc with carbonate-talc rock. rock. The rock rock is is increasingly increasingly talcose talcose toward toward the the contact contact Coarse grained, barren, barren, white white dolomite dolomite veins veins up up to to 55 Coarse grained, thick cut across of the rock. cm thick across all other other features features and and comprise comprise <1% ~ 1 %of rock. Carbonate- quartz-chloriterock rockoccurs occursnot notonly onlyininthe themine, mine,but butalso alsoininaa layer layer up up to to 60 quartz-chlorite 60 m thick on on the north l), where where itit contains contains thin thin layers layers of of thick north side side of of the the mine mine (Figure (Figure 1), the the other three three main main rock rock types. types. Serpentinized Peridotite Perdotite and Carbonate-Talc Serpentinized Carbonate-Talc Rock Rock The interlayered The interlayered quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock are bounded bounded on the the north north and andsouth south by bysill-like sill-like masses masses of ofserpentinized serpentinized peridotite. There are several peridotite bodies bodies within within the There several smaller smaller serpentinized serpentinized peridotite carbonate-quartz-chlorite rockon on the the north north side carbonate-quartz-chlorite rock side of the the Ropes Ropes mine. mine. The larger larger of these peridotite masses massesforms formsthe the north north wall wall of of the Ropes these minor minor serpentinized serpentinized peridotite Ropes mine The rock 1, 2). 2). The rock is dark dark gray gray to to green, green, fine finegrained grainedserpentine serpentine mine (Figures (Figures 1, containing lesser talc talc and and carbonate, containing lesser carbonate, and minor minor chlorite, chlorite, with with accessory accessory chromite chromite Commonlyitit has has aa relict texture of of 1 to and magnetite. to 33 mm mm serpenserpenmagnetite. Commonly relict cumulate cumulate texture 1 tine pseudomorphs after olivine olivine and and pyroxene, pyroxene, which which are are surrounded surrounded by by rims rims of of pseudomorphs after talc and although locally locallythe the rock rock isis dark dark green, talc and carbonate, carbonate, although green, felted felted textured textured serpentine. The serpentinized toward its serpentinized peridotite peridotite isis increasingly increasingly carbonate—rich carbonate-rich toward borders, although borders, although relict texture texture isiscommonly commonly continuously continuously preserved. preserved. Au abundance isis typically typically less less than than 30 30 ppb ppb in the the serpentinized serpentinized peridotite, peridotite, even even in abundance close close proximity proximity to the the mine. mine. Massivetoto well well foliated, foliated, gray gray to to dark dark green, Massive green, very fine fine grained grained carbonate-talc carbonate-talc rock occurs around the margins 3). The rock occurs around margins of serpentinized serpentinized peridotite peridotite (Figures (Figures 1, 2, 2, 3). carbonate-talc rock rock has contacts over over one one to several carbonate-talc has gradational gradational contacts several meters meters with with serpentinized peridotite peridotiteand and with with talc-rich talc-rich parts of serpentinized of the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock. The in the The carbonate carbonate mineral mineral in the carbonate-talc carbonate-talc rock rock is is dominantly dominantly ferroan ferroan ranges from from <30 <30 ppb ppb to approxiAu abundance abundance ranges approxidolomite with minor dolomite minor magnesite. magnesite. Au mately ppb in the mately 100 100 ppb the carbonate-talc carbonate-talc rock. rock. A- 42 �The The spatial spatial association association of carbonate-talc carbonate-talc rock rock with with the the margins margins of of serpentinserpentinized ized peridotite, peridotite, the thegradational gradational contacts contacts with with serpentinized serpentinized peridotite, peridotite, and and the the similar similar less less mobile mobile trace trace element element composition composition of the the carbonate-talc carbonate-talc rock rockand and serpentinized with regard regard to Cr serpentinized peridotite, peridotite, especially especially with Cr content, content, suggests suggests that that the the carbonate-talc carbonate-talc rock rock isisthe thealtered alteredmargins marginsofofserpentinized serpentinizedperidotite peridotitemasses. masses. SUMMARY OF OF MINERAL MINERALCOMPOSITION COMPOSITION SUMMARY Minerals Minerals in in rock rock samples samples from from selected selected traverses traverses across across and along along the the strike strike of of Although detailed detailed the Ropes Ropes deposit deposit were wereanalyzed analyzedby byelectron electronmicroprobe. microprobe. Although the mineral is not dealt mineral chemistry chemistry is dealt with with here, here, aa brief brief summary summary of ofgeneral general trends trends isis included included in in this thisfield fieldguide guide(Callahan (CallahanMining MiningCorporation, Corporation, unpublished unpublished data). data). Chlorite Chlorite occurs occurs in in nearly nearly all all rock rock types, types,but butitsitscomposition compositionand andabundance abundance In general, general, the the Fe/Mg Fe/Mg ratio ratio ofofchlorite chloriteincreases increases toward toward the the center center are variable. variable. In are of of the thequartz-sericite-chlorite quartz-sericite-chlorite rock rock and andaway awayfrom fromserpentinized serpentinized peridotite. peridotite. The The chlorite rocks and clinochlore chlorite isis mostly mostly sheridanite sheridanite in inthe thequartz—sericite-chlorite quartz-sericite-chlorite rocks clinochlore in in the other other major majorrock rocktypes. types. the Talc Talc increases increases in iron iron content content from from serpentinized serpentinized peridotite peridotite toward toward quartzquartzTalc sericite-chiorite quartz-sericite-chlorite rock rock itself. itself. Talc sericite-chlorite rock, rock, but isis absent absent in inthe thequartz-sericite-chlorite compositions show aa narrow compositions show narrow range, with with an an Fe/(Fe+Mg) Fe/(Fe+Mg) cation cation ratio ratio between between 0.0 0.0 and 0.11, 0.1 1, centered centered atat0.05. 0.05. and Sericite Sericite is restricted restricted mostly mostly to the the quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and is is minor minor inin carbonate—quartz-chlorite rock,where wherethese these two two rocks rocks are are in carbonate-quartz-chlorite rock, in contact. contact. The The sericite sericite is is an an FeFe- and andMg-bearing Mg-bearing muscovite, muscovite, with with FeO FeO and and MgO MgO contents contents of of as asmuch much asas The sum sum of of Mg+Fe Mg+Fe cations cations in the the sericite sericite structural structural formula, formula, several wt.% wt.% each. each. The several on 22oxygens, oxygens, isisbetween between 0.4 0.4 and and1.2 1.2cations, cations, centered centered atat0.6 0.6cations. cations. on the the basis basis of of 22 No in the rocks No consistent consistent trends trends in in sericite sericite composition composition were were recognized recognized in rocks of of the the mine. Ropes mine. Carbonate are common to all rocks Carbonate minerals minerals are common to rocks and are are dominantly dominantly low low iron iron Low iron iron dolomite dolomite is aa minor minor component component in in dolomite and and lesser lesser pure pure dolomite. dolomite. Low dolomite A— 43 �quartz-sericite-chlorite quartz-sericite-chlorite rock, rock, but but isis aamajor majorcomponent component in in the theother otherthree threemajor major rock types types atatthe theRopes Ropesmine. mine. Calcite Calcite isisminor minorininquartz-sericite-chlorite quartz-sericite-chlorite rock. rock. rock Magnesite Magnesite is is commonly commonly a major major component component of of the theserpentinized serpentinized peridotite peridotite and andthe the Serpentine isis major major ininthe theserpentinized serpentinizedperidotite. peridotite. carbonate-talc rock. rock. Serpentine carbonate-talc Disseminated Disseminated chromite chromite is minor minor in in the theserpentinized serpentinized peridotite peridotite and andcarbonate-talc carbonate-talc rock. rock. The The differences differences ininmineral mineralcomposition composition probably probably reflect, reflect, in inlarge largepart, part,original original differences differences in in bulk bulkcomposition composition between between serpentinized serpentinized peridotite peridotite and and the thedacitic dacitic volcaniclastic protolith protolith of of the thequartz-sericite-chlorite quartz-sericite-chlorite rock. rock. Talc Talc and andchlorite chlorite volcaniclastic compositions compositions are more more Mg-rich, Mg-rich, and and Mg-carbonate Mg-carbonate minerals minerals are are also also more moreabunabundanttoward towardthe theserpentinized serpentinizedperidotite. peridotite. dant STRUCTURE STRUCTURE The The dominant dominant structural structural element element in the the Ropes Ropes mine mine area area is is aaN70°E N70° subsubvertical vertical foliation foliation defined defined by by the thealignment alignmentofofaphanitic aphaniticphyllosilicate phyllosilicate minerals, minerals, The overall overall strike strike which which isis generally generally parallel parallel to to the thelayering layeringbetween betweenrock rocktypes. types. The A slight, slight, of of the theRopes Ropesmain mainore orezone zonealso alsonearly nearlyparallels parallelsthis thisfoliation. foliation. A sporadically and is sporadically present present sub-vertical sub-vertical second second foliation foliation strikes strikes N45°E N45OE and is defined defined by by generally generally slightly slightly coarser coarser grained grainedphyllosilicate phyllosilicatelaths. laths. Several Several ore-related ore-related structural structural elements elements characterize characterize the the Ropes Ropes deposit: deposit: 1)1)aa series series of of N55°E N55OE to to N65°E N65OE striking, striking, vertically vertically dipping, dipping, steeply steeplywestward westward plunging, plunging, auriferous auriferous quartz quartz vein-dominated vein-dominated pods pods occur occur progressively progressively further east east in in occur at, at, or south successively deeper levels of the the mine. mine. These These pods pods occur south of, of, the the successively deeper levels south crypticzones zonesofofsignificantly significantlyhigher higher south side side of of the theRopes Ropesmain main ore orezone; zone; 2)2)cryptic grade grade Au Au mineralization, mineralization, defined defined solely solely on the the basis basis of of assay assay data, data,are arecontained contained more more centrally centrally within within the the Ropes Ropes main main ore orezone. zone. The The middle middle parts parts of of these these higher higher grade trend of the grade zones zones strike across across the overall overall N80°E N80"E trend the orebody orebody ininen-echelon en-echelon fashion fashion at at approximately approximately N55°E, N55OE, while while the extremities extremities of these these higher higher grade grade transverse N70° trend, trend, thus thus forming forming aalow lowangle anglesigmoidal sigmoidal transverse zones zones have have a nearly nearly N70°E A- 44 �pattern across the ore zone This pattern pattern can can best at the pattern across the zone (Figure (Figure 5). 5). This best be recognized recognized at 250 ft. ft. elevation in the the mine, the east east end end of 250 elevation in mine, toward toward the of the the Ropes Ropes main main ore ore zone zone (Figure 3). 3). Both Both of the the above above structural structural elements elements can can be be regarded regarded as asextensional extensional features. features. The quartz pods are are evidence of silica The quartz vein dominated dominated pods evidence of silica addition addition in incipient incipient voids. voids. The higher zones within within the the main main ore ore zone, The higher grade grade transverse transverse zones zone, while while not strictly strictly veins, may have have been been zones of increased veins, nonetheless nonetheless may zones of increased permeability permeability to ore ore fluids. fluids. A comparison with shear shear zone zone models models presented presented in in Ramsay and Huber (1983) comparison with Ramsay and (1983) demondemon- strates strates that the the above above structural structural elements elements are best best interpreted interpreted as as extensional extensional features, features, and and that that the the rocks rocks containing containing the the Ropes Ropes deposit deposit can can be be considered considered to to represent aa structural some degree degree of of simple shear, with aa represent structural setting setting involving involving some simple shear, Figure 55 compares compares the the component of of positive volume change change in in the shear component positive volume shear zone. zone. Figure theoretical orientation orientation of of extensional extensionalvein vein arrays arrays developed developedinin aa shear theoretical shear zone zone as aa result of positive in aa shear _result positive volume volume change change in shear zone zone with with the theobserved observed geologic geologic relations of ore related relations of related structural structural elements elements at the the Ropes Ropes mine: mine: ititisisgeometrically geometrically correct that en-echelon 45' to to correct en-echelon fissure fissure systems systems will always always make make angles angles of less less than than 450 the trend trend of of the theshear shearzone zoneinincases caseswhere wherepositive positive volume volume change change isis involved involved relationshipsatat the the Ropes Ropes mine mine between between the the two (ibid). The observed observed geometric geometric relationships two ore related above, and and the shear related structural structural elements elements discussed discussed above, shear zone zone "walls" "walls" (the nonfoliated serpentinized peridotite), peridotite), are are consistent consistent with with the the required nonfoliated serpentinized required acute acute angle angle of shear required relative relative sense sense of shear in in the the present present day dayhorizontal horizontal relationship. The required plan view view of of the WSW and and south south plan the Ropes Ropes mine mine area area is, is, therefore, therefore, north north side side to tothe theWSW the midpoints of the midpoints of the side side to the the ENE, ENE, as as illustrated illustrated in in Figure Figure 5. 5. Connecting the quartz vein vein dominated dominatedpods podsatat the the Ropes Ropes mine mine gives givesthe the true true sense sense of of shear shear in in the quartz third dimension as lying lyingalong alongaaline lineoriented orien.eddown downtotothe the ENE ENE and and up up to to the third dimension as considerationofof the the plan WSW (Figure (Figure 5). WSW 5). A simultaneous simultaneous consideration plan and and long long section section views views necessitatethat that the the south south side side of of the zone necessitate zone had had an an ENE ENE and and downward downward net net compocomponent while the the north nent of movement, movement, while north side side of the the zone zone had had aaWSW WSW and upward upward net net component component of movement. movement. A-45 �R o o e s Production S h a f t \ .E .*l.-Northwes+ 2 Ore Zone Major Gold Gold Ore Ore Types Types Major 1. 1. Light Light green green to to tan tan quartz-sericite quartz-sericiterock, rock,with with lenses lensesof of light light gray gray cherty cherty quartz quartz rock rock containing containing pyrite-tetrahedriteChalcO pyrite-tetrahedrite-chalcopyrite-galena. Pyrite Pyrite content content of of this this ore ore type type does does not not pyrite-galena. correlate with with gold gold grade grade correlate 2. Light Light green green quartz-sericite-chloritepyrite quartz-sericite-chlorite-pyriterock. rock. Good Good 2. correlation Au grade. grade. correlation between between fine-grained fine-grained pyrite pyrite content content and and Au 3. Dark Dark green green quartz-chlorite-pyrite quartz-chlorite-pyriterock. rock. Consistently Consistently high high 3. fine-grained fine-grained pyrite pyrite content content and and high high gold gold grade. grade. 4. Figure 4. Figure Ropes Ropes Mine Mine long-section long-section looking looking NN 100 lo0 WW A - 446 6 A- �_____ A A A B ELANATION w near vertical vertical foliation foliation near of Ropes Ropes orebody orebody outline of outline 9-> Au zone of of higher-grade higher-grade Au zone mineralization mineralization L— contact between between serpentinized serpentinized contact component) component) (with down down (with component component) arrow in in plan plan arrow view projection projection view of plane of of plane of shear shear true sense senseof of shear sheardetermined determined true by connecting midpoints of by connecting midpoints of extension views extension views verticalprojection projectionof of quartz quartz vertical vein-dominated pods (extension vein—dominated pods (extension veins) onto ontothe the plan plan view view veins) quartz-vein dominated dominated pods pods quartz—vein projected onto ~ 8 long 0 ~ projected onto N80°E long section section (with up up (with 0 <\s maximum stretch stretch direction direction maximum (vein (vein opening opening direction) direction) <y 7 peridotiteand and dacite daciteCuff Cuff (with (wi~h peridotite associated rocks) rocks) associated strike of of layering layeringin in rocks rocks strike Figure5: 5: Figure Schematic structural structural diagrams diagrams of of the the Ropes Ropes Mine Mine Schematic A is plan view, inset after Ramsay and Huber, A is plan view, inset after Ramsay and Huber, 1983, Figure Figure 3.21A; 3.21A; BB is is N80°E N 8 0  °vertical vertical long long section sectionview view 1983, A-47 �THEOREBODIES OREBODIES THE The The Ropes Ropes mine mine main main ore orezone zone isissteeply steeplydipping, dipping, 335 335mmininmaximum maximumstrike strike length, length, 12 12 m m ininaverage averagethickness, thickness, and and 600 600 mmininpresently presentlydefined defineddown-dip down-dip occurswithin withinthe thequartz-sericite—chlorite quartz-sericite-chlorite rock, rock, and andisis 4). ItItoccurs extent (Figure (Figure4). extent characterized The total total characterized by by disseminated disseminated pyrite pyrite with with only onlyminor minorquartz quartzveins. veins. The stated stated property property tonnage, tonnage, including including historic historicproduction production through through1987 1987and andgeologic geologic Based on on reserves, reserves, is is approximately approximately 2.5 2.5 million million tonnes tonnes at 3.25 3.25 g/tonne g/tonne Au. Au. Based available from the the upper available information information from upper third of of the the Ropes Ropes main main zone, zone, the the Ag Aggrade grade 12g/tonne. g/tonne. estimated at at 12 isis estimated The The Ropes Ropes main main ore ore zone zone can can be be divided divided longitudinally longitudinally into into three three major major ore ore types of the types based based on on the the physical physical characteristics characteristics of the ore, ore, as as illustrated illustrated ininFigure Figure4.4. In In plan plan view, view,these theseore oretypes typesform formcrescent—shaped, crescent-shaped, concentric shells, shells, with with the the convex convex side side of each each ore ore type type toward toward the the east east and and the theconcave concave side side toward toward the the of the west. The The convex-to-the-east convex-to-the-east geometry geometry of the ore ore type type zones, zones, along along with with an an west. overall cutoff of Au and a sharp overall gradual gradual western western cutoff Au mineralization mineralization and sharp eastern eastern cutoff, cutoff, suggests that the suggests that the flow flow vector vector for for the themineralizing mineralizing fluids, fluids, relative relative to to the the present-day present-day surface, surface, may may have have been been upwards upwards from the the deep, deep, southwest southwest end end of of the the deposit deposit toward toward the the shallower shallower northeast, northeast, high high grade grade keel keel of of the thedeposit. deposit. The The Ropes Ropes main main ore zone zone is is cut cut by by an aneast-striking, east-striking, southsouth- dipping, dipping, low low Offset of of units units across across angle reverse reverse fault fault zone zone at at the the 900 900 mine mine level level (Figure (Figure 2). 2). Offset angle the greater atat the the south south side side of of the the mine the fault fault zone zone is is generally generally greater mine than than at the the north north orebody thins thins down down dip toward toward the fault fault zone, zone, but but thickens thickens below below it. it. The orebody side. The side. Several bodies exist exist on the Several other gold-mineralized gold-mineralized bodies the Ropes Ropes property. property. The The Northwest ore zone is a small Northwest ore zone is small ore zone zone to to the the northwest northwest of of the theRopes Ropes main main ore ore Significant intersections intersections of gold-mineralized gold-mineralized rock, rock, comparable comparable in in zone (Figure (Figure 4). 4). Significant zone grade grade and and width width to to the theRopes Ropes main main ore orezone, zone, have have been been encountered encountered in in deep deep drilling 370 370 m m below below the theRopes Ropesmine mine1284 1284level level(Callahan (CallahanMining Mining Corporation Corporation news release, release, July July 20, 20,1987). 1987). news In general, general, most most gold gold occurs occurs associated associated with sub-100 sub-100 micron micron sized sized pyrite pyrite A-48 �which the mass which is is dispersed dispersed throughout throughout the mass of the the quartz-sericite-chlorite quartz-sericite-chlorite rock, rock, as as well well as as on on fractures, fractures, foliations, foliations, and andalong alongquartz quartzveinlets. veinlets. However, However, in in certain certain ore ore types types the the modal modal abundance abundance of pyrite pyrite does does not not show show aastrict strictcorrelation correlationwith withgold gold grade 4). Native Native gold, gold, of of variable variable fineness, fineness, occurs occurs as as grade (see (see explanation, explanation, Figure Figure 4). approximately approximately 3 to to 10 10 micron micron sized sized grains grains ininthe thefollowing followingspecific specificsites: sites: 1)1) attached attached to the the surface surface of of the the fine fine grained grained pyrite, pyrite, 2) 2) included included as as fine fine blebs blebs within within the the fine fine grained grained pyrite, pyrite, 3) 3) on on fractures fractures within within the fine fine grained grained pyrite, pyrite, and 4) 4) at at grain boundaries boundaries of of fine fine grained grained quartz quartz and andsericite. sericite. A A volumetrically volumetrically minor minor grain amount amount of coarse coarse free free gold gold occurs occurs on on fractures fractures in in quartz quartzstringers stringers and andlenses. lenses. Silver Silver occurs occurs as electrum, electrum, native native silver, silver, argentiferous argentiferous tetrahedrite, tetrahedrite, argentiferous argentiferous galena, and and rare raredyscrasite. dyscrasite. galena, Pyrite over 95% 95% of of the metallic Pyrite comprises comprises over metallic minerals minerals in the the flotation flotation mill mill concentrate, galena, argentiferous argentiferous concentrate, followed followed by by chalcopyrite chalcopyrite at at1%. 1%. Argentiferous galena, , tetrahedrite, magnetite, and and rutile rutile are present tetrahedrite, sphalerite, sphalerite, hematite, hematite, magnetite, present in in trace trace amounts. amounts. Fine Fine grained, grained, white white to to light light gray gray sugary-textured sugary-textured auriferous auriferous quartz quartz veins veins are are concentrated at and and south concentrated at south of the the extreme extreme south south side side of of the the Ropes Ropes main main ore orezone. zone. Individual quartz veins veins are are rarely rarely up up to Individual quartz to aa meter meter thick, thick, but butcollectively collectively these these veins, veins, interlayered with quartz-sericite-chlorite rock, form form pods pods up up to aa maximum quartz-sericite-chlorite rock, maximum of of 88 interlayered with m thick thick and and 30 30 m m ininstrike strikeand andplunge plungeextent. extent. The pods pods strike strike approximately approximately N65°E, compared to to the the N80°E overall trend trend of of the Ropes N65OE, compared N8VE overall Ropes main main ore ore zone, zone, plunge plunge steeply further east east at deeper steeply to the the west, west, and and occur occur progressively progressively further deeper levels levels of the the Ropes Ropes mine, mine, as as discussed discussed in in the thesection sectionon on"Structure". "Structure". Accessory minerals in in these Accessory minerals these quartz quartz pods pods include: include: pyrite, pyrite, minor minorargentiferous argentiferous tetrahedrite and chalcopyrite, and rare free tetrahedrite galena, galena, and chalcopyrite, and free gold, gold, molybdenite, molybdenite, and and dyscrasite. Trace tourmaline tourmaline and native native Ag Ag were were reported reported by byBroderick Broderick(1945). (1945). dyscrasite. These contain 44 to to 77 g/tonne g/tonne Au Au and andapproximately approximately 20 20 g/tonne g/tonne Ag. Ag. These pods pods typically typically contain Although these pods pods are are higher higher than than average grade ore, ore, the the higher Although these average grade higher grade grade parts parts of of the quartz-sericite-chlorite rock ore ore of of the Ropes quartz-sericite-chlorite rock Ropes main main ore ore zone zone are are not not zoned zoned A-49 �about about the thepods; pods; rather, rather, the thehigher highergrade gradeparts partsofofthe themain mainore orezone, zone,characterized characterized by bydispersed dispersed pyrite, pyrite, occur occur more more centrally centrally within within the the trend trendofofquartz-sericitequartz-sericiteestimatedthat thatthe theexisting existingand andmined minedout outpods podsconstitute, constitute,inin chloriterock. rock. ItItisisestimated chlorite 5%ofof the the ore oreatatthe theRopes Ropesmine. mine. total,approximately approximately5% total, DISCUSSION DISCUSSION The Theserpentinized serpentinized peridotite peridotite bodies bodies have have contact contact relations relations with with the thebordering bordering and and interlayered interlayered volcanic volcanic rocks, rocks, as as well well as as internal internal relict relict fine finegrained grainedigneous igneous texture, consistent consistent with withtheir theirintrusion intrusionasashypabyssal hypabyssalsills. sills. Serpentinization Serpentinization texture, preserved preserved igneous igneous textures, textures, and and was was most most like'y likelyatatnear nearconstant constantvolume volume(Best, (Best, This constant constant volume volume serpentinization serpentinization process process would would have havenecessarily necessarily 1982). This 1982). released The released large large amounts amounts of MgO MgO and and Si02 Si02 to to the thesurrounding surrounding rocks rocks(ibid). (ibid). The voluminous voluminous carbonate-quartz-chlorite carbonate-quartz-chlorite rocks, rocks, which which bound bound and and are areinterlayered interlayeredwith with the the Ropes Ropes gold gold deposit, deposit, are arecomprised comprised primarily primarily of of weakly weakly ferroan ferroan dolomite dolomite and and Their origin origin could could conceivably conceivably be attributed attributed to to such such aarelease release ofof lesser quartz. quartz. Their lesser MgO of the MgO and and Si02 Si02 during during serpentinization serpentinization of the peridotite peridotite enclosing enclosing the trend trend of of volcanic rocks rocks at at the theRopes Ropesmine. mine. volcanic The The Ropes Ropes orebodies orebodies are are overall overall tabular, tabular, stratiform stratiform and andstratabound strataboundalteration alteration zones as dacite tuff quartz-sericite-chlorite rock rock interpreted interpreted as tuff on on the thebasis basis of of zones in in quartz-sericite-chlorite relict relict fragmental fragmental crystal-lithic crystal-lithic textures textures preserved preserved in and and near near ore. ore. These These pseudomorphs pseudomorphs are clearly clearly gradational gradational to feldspar feldspar phenocrysts phenocrysts and and lithic lithicfragments fragments in tuffs tuffswest west ofofthe theRopes Ropesmine. mine. Additionally, Additionally, the the mine mine rocks rocks have haveabundances abundances in Gold of of less less mobile mobile trace trace elements elements indicative indicative of of aadacitic daciticcomposition. composition. Gold mineralization at the the Ropes mine is is restricted to these mineralization at Ropes mine restricted to these rocks, rocks, and itit appears appears that that these receptive host host for K20 K20 these originally originally feldspar-rich feldspar-rich rocks rocks provided provided a chemically chemically receptive and and Au Au bearing bearing solutions, solutions, which which altered altered the the feldspar feldspar totosericite. sericite. Possibly, Possibly, either either better better permeability permeability in the the tuffs tuffs relative relative to to the thedense densecrystalline crystalline peridotite, peridotite, or or else else aa ductility ductility contrast contrast between between the the volcanic volcanic rocks rocks and andperidotite, peridotite, facilitated facilitated The bounding bounding peridotite peridotite near near the the preferential focussing focussing of of ore orebearing bearingsolutions. solutions. The preferential A- 50 �mine and appears to have mine isisextensively extensively carbonatized carbonatized and appears to have been been aa sink sink for forC02, CO2, possibly contained contained in in the thesame sameAu-bearing Au-bearing solutions. solutions. possibly Certain structural elements elementssuch such as as aa series of quartz Certain ore—related ore-related structural quartz vein vein dominated dominated pods pods south south of the the Ropes Ropes main main ore ore zone, zone, and andtransverse transverse zones zones of of higher higher gold grade grade in in the theRopes Ropesmain mainore orezone, zone,have havegeometric geometricrelations relationsconsistent consistent with with gold an an origin origin as asextensional extensional features features in inaashear shearzone zonewith withpositive positivevolume volumechange. change. Structural Structural elements elements indicate indicate that that the the net netcomponent component ofofmovement movementduring duringsome some stage stage of of gold gold mineralization mineralization was was north north side side up up totothe theWSW WSW and andsouth southside sidedown down to the theENE, ENE,relative relativetotothe thepresent-day present-day ground groundsurface. surface. Furthermore, Furthermore, the the overall overall to concentric, to the east of the major concentric, convex convex to east geometries geometries of major ore ore types types in in the theRopes Ropes main main ore ore zone, zone, combined combined with with the the gradual gradual western western cutoff cutoff ofofgold goldmineralization mineralization and and sharp sharp eastern eastern cutoff cutoff in in front front ofofthe thehigh highgrade gradeeastern eastern"keel" "keel" of of the thedeposit, deposit, suggests that the flow suggests that flow vector vector for for mineralizing mineralizing fluids, fluids, relative relative to to the the present present day day surface, surface, may may have have been been upwards upwards from from the the deep deep southwest southwest part of of the the deposit deposit toward the the shallow shallow eastern eastern high high grade gradeedge. edge. toward Timing Timing of of gold gold mineralization mineralization can be be demonstrated demonstrated as being being later later than than deposition deposition of the the volcanic volcanic rocks rocks which which host host the the Ropes Ropes deposit, deposit, because because alteration alteration associated associated with with the Ropes Ropes deposit deposit affects affects the the serpentinized serpentinized peridotite, peridotite, which, which, on on the the basis basis of of relict relict fine finegrained grainedigneous igneous texture texture and andinterlayering interlayering with with the thevolcanic volcanic rocks, rocks. appears appears to be be aahypabyssal hypabyssal sill sill complex, complex, and, therefore, therefore, intrusive intrusive into into the the of the Emplacement of the peridotite peridotite may may have have been beenpreferentially preferentially volcanic section. section. Emplacement volcanic controlled by an controlled by an early-formed early-formed structure structure which which appears appears to have have exerted exerted aa control control on on the the original original distribution distribution of of volcanic volcanic and and sedimentary sedimentary units: units: the the peridotite peridotite occurs occurs at at or or near neara amajor, major,partially partiallyinterlayered interlayeredtransition transition between between basalt basalt and anddacite dacite This transition transition is is accompanied accompanied by aa zone zone of of sedimentary sedimentary units units pyroclastic rocks. rocks. This pyroclastic including banded banded iron iron formation formation and andquartzose quartzosegraywackes. graywackes. This This major major transition transition including in the by sediments, could represent represent aa break the volcanic volcanic section, section, accompanied accompanied by sediments, could break or or zone zone of flexure of the flexure which which controlled controlled the position position of the interface interface between between the the two two partly partly Such aa boundary boundary between between contrasting contrasting contemporaneous major volcanic volcanic facies. facies. Such contemporaneous A-51 �volcanic volcanic facies facies may may have have been been controlled controlled by aa zone zone of of crustal crustalweakness weakness which which facilitated facilitated intrusion intrusion of upper upper mantle mantle derived derived peridotite, peridotite, as as well well as as provided provided aa conduit The trend trend of ofvolcanic volcanic rock rock which which conduit for forfocussing focussinggold goldbearing bearingsolutions. solutions. The hosts hosts the Ropes Ropes deposit deposit is near near this this transition, transition, and and strikes strikes away away from from the thetransition transition at at an an acute acuteangle. angle. The The Ropes Ropes environment environment may may represent represent a splay splay or or second second order order of ore types structure structure off off the the more more major major break. break. The The observed observed zoning zoning of types at at the the Ropes is consistent consistent with with fluid fluid flow from Ropes mine, mine, as as discussed discussed previously, previously, is from the the direction direction of of the the inferred inferred major major break break to to the the west west of of the theRopes Ropes mine, mine, toward toward the the Persistent or recurrent recurrent movement movement along along the inferred inferred major major present-day ENE. Persistent present-day ENE. structure structure which which controls controls the distribution distribution of major major volcanic volcanic fades, facies, could could have have provided action to assist provided a seismic seismic pumping pumping action assist in moving moving large large volumes volumes of mineralmineralcould also also account account for for the ore Such movement movement could ore related related ized ized hydrothermal hydrothermal fluid. fluid. Such structural observed in in the structural elements elements observed the Ropes Ropes main main ore ore zone, zone, which which indicate indicate relative relative movement during at least movement during least part part of ofthe thegold goldmineralizing mineralizingprocess. process. CONCLUSIONS CONCLUSIONS Gold at the Ropes Gold mineralization mineralization at Ropes mine mine occurs occurs primarily primarily with with fine fine grained grained pyrite rock interpreted interpreted as as altered quartz-sericite-chlorite rock altered dacite tuff. tuff. pyrite dispersed dispersed in quartz-sericite-chlorite The may represent represent aa splay off aa more The Ropes Ropes environment environment may splay off more major major early early formed formed structure basalt structure which which controls controls the distribution distribution of the the two two major majorvolcanic volcanic facies: facies: basalt dacite pyroclastics. pyroclastics. The The serpentinized serpentinized peridotite, peridotite, as as well well as as gold gold bearing bearing and dacite solutions, may have have used solutions, may used this this structure as as aa conduit. conduit. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The author author thanks thanks Glen Glen Scott, Scott, Ropes Ropes mine mine Chief Chief Geologist, Geologist, who who was was instruinstru- mental much of of the mental in defining defining mappable mappable units units and compiling compiling much the geology geology at the the paper benefited benefited from from editing editing and and revision revision by by Klaus KlausSchulz, Schulz, Ropes mine. mine. This paper Geological Survey. Survey. U.S. Geological A-52 �REFERENCES Allen, of Michigan Allen, C., C., 1912, 1912, Mineral Mineral Resources Resources of Michigan with statistical statistical tables tables of of production and and value production value of mineral mineral products products for 1910 1910 and and prior prior years: years: Michigan Michigan Geological and and Biological Survey, Publication Publication 8, p. Geological Biological Survey, p. 365-366. 365-366. Best, M.G., M.G., 1982, and metamorphic W. H. H. Freeman Freeman and Best, 1982, Igneous Igneous and metamorphic petrology: petrology: W. Company, San San Francisco, Company, Francisco, p. 398-399. 398-399. M., 1945, Geology of of the Ropes 1945, Geology Ropes Gold Gold Mizie, Mice, Marquette Marquette County, County, Broderick ,, M., Michigan: Economic EconomicGeology, Geology,v.v.40, 40, ## 2, p. p. 115-128. 115-128. Michigan: Clark, L.D., map of Clark, L.D., Cannon, Cannon, W.F., W.F., and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock geologic geologic map the Negaunee Negaunee SW SW Quadrangle, Quadrangle, Marquette Marquette County, Michigan: Michigan: U.S. U.S. Geological Geological SurSurvey, Map Map ##GQ-1226, GQ-1226, Scale Scale1:24000. 1:24000. Ramsay, J J.G., and Huber, .G.,and Huber, M., M., 1983, 1983, The techniques techniques of modern modern structural structural Ramsay, geology, v. 1: Strain Strain analysis: analysis: Academic AcademicPress, Press,Inc., Inc., Orlando, Orlando, Florida, Florida, p. p. 48-50. 48-50. v. 1: % Rossell, D.M., 1983, 1983,Alteration Alterationofofthe the Deer Deer Lake Lake Peridotite Peridotiteinin the the vicinity of Rossell, D.M., vicinity of the Ropes the Ropes Mine, Mine, Marquette Marquette County, County, Michigan, Michigan, (unpublished (unpublished M.S. M.S. thesis): thesis): Michigan Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 83 p. Technological p. A-53 �Geological Geological Field Field Trip to to the theMarquette Marquette Greenstone Greenstone Belt: Belt: Part Part II Day Day 11Road RoadLog Log- - Stops Stops 11toto1111 T.J. T.J.Bornhorst, Bornhorst,D.A. D.A.Baxter, Baxter,M.L. M.L.MacLellan, MacLellan, and andR.C. R.C.Johnson ~ohnson* Department Department of ofGeology Geologyand andGeological GeologicalEngineering Engineering Michigan MichiganTechnological Technological University UniversityHoughton, Houghton,Michigan Michigan49931 49931 *Currently with *Currently withKerr-McGee Kerr-McGeeCorporation Corporation NOTE: on the NOTE: Additional Additional information information on the geologic geologic setting setting of the the field field trip tripstops stopsmay may be be found foundininpapers papersbybyBornhorst Bornhorstand andbybyBaxter Baxter&&MacLellan MacLellanininthis thisvolume. volume. Refer totoFigure Figure1:1:Route Routeand andStop StopMap Map Refer Mileage Mileage 0.0 0.0 Ramada Inn, Inn, Marquette Marquette StartDay Day1 1 -- Ramada Start Assemble at at the the entrance entrance of ofthe theRamada RamadaInn. Inn. From From the theRamada Ramada Inn Innturn turn Assemble right (west) to Washington Street and proceed toward junction with U.S. right (west) to Washington Street and proceed toward junction with U.S.41. 41. At At At 6.4 6.4 mi, mi, 1.3 mi, mi, turn turnright right(west) (west)totoU.S. U.S.4141and andproceed proceedtoward towardNegaunee. Negaunee. At 1.3 pull off offtotothe thetight lightshoulder shoulderalongside alongsideofofoutcrops. outcrops. pull 6.4 6.4 Stop11 -- Pillowed Pillowed Basalt Basalt Stop The The dominant dominant volcanic volcanic lithologies lithologies in the the Marquette Marquette Greenstone Greenstone Belt Belt are are massive massive and pillowed pillowed tholeiitic tholeiitic basalt, basalt, the the massive massive variety variety appearing appearing to to be be more more abundant At this this abundant perhaps perhaps because because typical typical mossy mossy outcrops outcrops may may obscure obscure the thepillows. pillows. At stop stop are are excellent excellent three threedimensional dimensional views views of ofrelatively relativelyundeformed undeformedpillowed pillowed basalt. basalt. The in shape with dimensions around 1'1' X X 4' The pillows pillows are ellipsoidal ellipsoidal in shape with dimensions around 4' X X 5'; 5'; attitude attitude Cusps on on pillows pillows indicate indicate of of bedding bedding strikes strikesapproximately approximately E-W E-W and anddips dips85°N. 85ON. Cusps There are arealso alsocharacteristic characteristicradial radial that that here here stratigraphic stratigraphic top top is is to to the thenorth. north. There fractures fractures and and interpillow interpillow void void spaces spaces filled filled with with quartz quartzand andcarbonate. carbonate. This This locality locality was was mapped mapped most most recently recently by by Puffett Puffett(1974) (1974)asasLower LowerMember Member Location: NW+, NWi, section section 20, 20, T48N, T48N,R26W. R26W. of the theMona MonaSchist. Schist. Locaticn: of At 7.6 7.6 mi, mi, pass pass the the road road totoMarquette MarquetteCounty County Continue west west on on U.S. U.S. 41. 41. At Continue At 8.6 8.6 mi, mi, large large outcrop outcrop on on opposite opposite side side of of highway highway (south) (south) is is Stop Stop 22 Airport. At Airport. (for (for safety safety proceed proceed 0.1 0.1 mi mi west, west, make make aa U-turn U-turn just just before before the the Carp Carp River, River, and and proceed east to outcrop; when finished finished proceed proceed east east 0.05 0.05 mi, mi, make make aa U-turn proceed east outcrop; when U-turn to to U.S. 41 41 west). west). U.S. A-54 �ARCHEAN ARCHEAN PROTEROZOIC [ r ++++++ DEAD RIVER PLUTON GRANITOID ROCKS 1 SEDIMENTS I I U. I 03 z Cd "I E- M E- +I >-i 0 >< x a; n Cd a. 4 Cd x 01 BASALT MEMBER z (Xl tn VOLCANICS OF SILVER MINE LAKES LOWER NEALY CREEK MEMBER SHEARED RHYOLITE TUFF MEMBER LIGHTHOUSE POINT MEMER MONA SCHIST KITCHI PERIDOTITE AGE RELATION UNCERTAIN I LEGEND a. w �"-4 C) -H z (I) 0 4-i (ID 1J 4-i z 0 4-i 'Ii cj 4-i C A-56 �Stop Deformed Pillowed Pillowed Basalt Stop 22 -- Slightly Deformed 8.6 The vertical The vertical road cut cut consists consists of of slightly slightly deformed deformed pillowed pillowed basalt. basalt. Pillow rinds rinds are not not easily easily visible visible in the the vertical vertical face face but but are aremore moreconspicuous conspicuous on on the the are flattened glacially polishedsurface surfaceon on the the top top of the glacially polished the outcrop. outcrop. Pillows Pillows are flattened and and rinds rinds have have feathered feathered edges; edges; bedding bedding strikes strikes roughly roughly E-W. E-W. Foliation strikes strikes N86°W N86OW dips 84°S. 84's. Quartz Quartz and carbonate carbonate veins veins containing containing aa few percent percent euhedral euhedral and dips Flat-lying fractures fractures are filled filled dominantly dominantly with with pyrite parallel pyrite parallel this foliation. foliation. Flat-lying carbonate. This was mapped most recently recently by by Puffett (1974) This locality locality was mapped most (1974) as the the Lower Lower Member of the Member the Mona MonaSchist. Schist. Location: Location: SW+, SWi, section section 28, 28, T48N, T48N. R26W. R26W. Proceed west west on on U.S. U.S. 41 41 and and at at 8.75 Proceed 8.75 mi cross cross bridge bridge over over Carp River. River. At 9.3 mi, 9.3 mi, pull pull off off to tothe theright rightshoulder shoulderalongside alongside aa number number of of small smalloutcrops. outcrops. Deformed .Archean Volcanic Stop Volcanic Rocks Rocks Stop 33 -- Deformed-Archean 9.3 The rocks The rocks in this this road road cut cuthave havea awell-developed well-developed close-spaced close-spaced foliation foliation (N75-88°W, dip dip 70-89°S) which produces (N75-88OW, 70-89"s) which produces a slate-like slate-like appearance. appearance. These rocks These rocks are There are two two lithologies lithologies in within Archean Carp Carp River River Falls Falls Shear Shear Zone. Zone. There within the Archean this outcrop: outcrop: chlorite chlorite schist schist from from aabasaltic basaltic parent, parent,and andquartz—sericite quartz-sericite schist schist from from The quartz-sericite schist isis aa tabular a rhyolitic rhyolitic parent. parent. The quartz-sericite schist tabular shaped shaped body body near near the the center center of the the outcrop, outcrop, and and isis probably probably aa dike dikebased based on onanalogous analogous lithologies lithologies to the the north. Near end of the Near the extreme extreme eastern eastern end the outcrop outcrop are are probable probable pillow pillow rinds rinds which suggest suggest the the basalt of the which basalt parentage parentage of the chlorite chlorite schist. schist. Flat—lying fractures, fractures, Flat-lying similar to to Stop Stop 2, 2, are present present in the the basalts basalts but not not in in the therhyolites. rhyolites. similar This most recently recently by by Puffett (1974) This locality locality was was mapped mapped most (1974) as Undifferentiated Undifferentiated Greenstone. Location: Location: S+, S+, section section 29, T48N, T48N, R26W. R26W. 10.2 mi, enter enter City City of of Negaunee Negaunee and and continue continue Proceed west Proceed west on U.S. U.S. 41. 41. At 10.2 At 13.8 mi, traffic light through Negaunee on U.S. 41 and towards Ishpeming. At 13.8 mi, traffic light at at through Negaunee U.S. 41 and towards Ishpeming. 41, turn right right (north) (north) to to County County Road Road junction of County junction County Road Road 573 573 and and U.S. U.S. 41, on left, stay 14.2 mi, pass pass cemetery cemetery on stay on on main main road, road, now now called called Deer Deer Lake Lake 573. 573. At 14.2 At 14.9 14.9 mi, mi, Deer Deer Lake Lake is is visible visible on on right, right, continue continue ahead ahead on on main main road. road. Avenue. At At 16.7 mi, junction with Cooper Lake Road Road on on left, left, stay At 16.7 mi, junction of County County Road Road 573 573 with Cooper Lake stay on on At 17.5 mi, gravel road to to the the Ropes Mine on on the the left left (the 17.5 mi, gravel road Ropes Mine (the field field trip will will 573. At 573. A- 57 �stop stop at at Ropes Ropes on onDay Day 2), 2),continue continueon on573. 573. At At 22.4 22.4 mi, mi, at atY-intersection, Y-intersection, go go left left to At 27.7 27.7 mi, mi, to the the North North Dead Dead River River Road; Road; road road turns turns to to gravel gravel atatthis thispoint. point. At the Archean rocks rocks of of the theClark ClarkCreek Creekarea. area. At At 28.8 28.8 mi, mi, the hills hills on on the theright rightare areArchean cross cross bridge bridge over over the the Dead Dead River; River; Archean Archean rocks rocks of of the theSilver SilverCreek Creek area areaare are exposed exposed in the the steep steeptopography topography ahead. ahead. At At 28.95 28.95 mi, mi, intersection intersection of of North North Dead Dead River River Road Road and and Silver Silver Lake Lake Road, Road, proceed proceed right right (east) (east) on on North North Dead Dead River River At 30.2 30.2 mi, mi, outcrops outcrops of ofMichigamme Michigamme Formation Formation in in roadbed. roadbed. At At 30.8 30.8 mi, mi, Road. Road. At At 31.1 31.1 mi, mi, turn turn left left totodirt dirtroad roadtowards towardsGrigg Grigghunting hunting cross cross over over Silver Silver Creek, Creek, At camp. At At 31.4 31.4 mi, mi, park park atathunting hunting camp camp and and walk walk about about 400 400 'eet feetN20-25°E N20-25OE camp. from the cabin to the Silver Creek prospect located on the side from the cabin to the Silver Creek prospect located on the side of of the thevalley. valley. 31.4 31.4 Stop44—- Silver Silver Creek Creek Prospect Prospect Stop The The The Silver Silver Creek Creek Prospect Prospect consists consists of of several several shallow shallow shafts shafts and and trenches. trenches. The prospect by aa quartz vein (up (up to to 4 ftf tthick) prospect is dominated dominated by quartz and and carbonate carbonate vein thick)which which contains contains galena galena and sphalerite sphalerite as the the major major sulfides, sulfides, lesser lesser amounts amounts of of pyrite pyrite and and chalcopyrite, and trace chalcopyrite, and trace amounts amounts of arsenopyrite arsenopyrite and and pyrrhotite. pyrrhotite. Pyrite Pyrite replaces replaces 120 ppm ppm Ag Ag and and one of A mineral mineral separate separate of galena galena contained contained 120 of pyrrhotite. pyrrhotite. A sphalerite contained less less than than 1 ppm yellowsulfide sulfideseparate separate(chalcopyrite, (chalcopyrite, sphalerite contained ppm Ag. Ag. AAyellow pyrite 180 ppb ppb Au. Au. AAgrab grabsample sample of of white whitemassive massive pyrite and and pyrrhotite) pyrrhotite) contained contained 180 quartz quartz vein vein from from the the rock rock piles piles at at this this prospect prospect contained contained 38 ppb Au Au and and 44ppm ppm Ag. Ag. The vein vein isishosted hosted by byaltered alteredpillow pillow basalt. basalt. The This by Johnson This locality locality was mapped mapped most most recently recently by Johnson and others others (1987) (1987) and is is designated as the Highly designated as Highly Altered Altered Variety Variety of of the the Pillowed Pillowed Basalt Basalt Member Member of of the the N E k section 25, 25, T49N, T49N. R2SW. R28W. Location: NE+, Volcanics of Silver Mine Mine Lakes. Lakes. Location: Volcanics of Silver Proceed back to to North River Road Road and and turn left Proceed back North Dead Dead River left (east) (east) at at 31.5 31.5 mi. mi. At At 31.8 31.8 mi, mi, turn left left and and proceed proceed to to dirt dirtlogging logging road, road, turn turn right rightand andfollow followlogging logging At 32.1 32.1 mi, mi, park, park, continue continue walking walking on on dirt dirt road road about about950 950 road north, north,0.O5mi. 0.05mi. At feet (generally up slope) (generally up slope) to Stop Stop 5a; 5a; cross cross altered altered rhyolite rhyolite at about about 700 700 feet. feet. 32.1 32.1 Stop 5 -- Section Section 30 Alteration Alteration Zone Zone Stop This This area is very very close close to the the Dead Dead River River Shear Shear Zone, Zone, an Archean Archean zone zone of Alteration intensity intensity varies varies from outcrop outcrop to to outcrop, outcrop, strain and and deformation. deformation. Alteration high strain Chlorite is is ubiquitous ubiquitous throughout throughout the the as as does does the the dominant dominant type type of of alteration. alteration. Chlorite alteration alteration zone, zone, whereas whereas sericite sericite and carbonate carbonate are are locally locally abundant abundant alteration alteration this zone Alteration along along this zone is interpreted interpreted to to be be synchronous synchronous with with the the products. products. Alteration A- 58 �The stop has been been divided divided into three three parts parts which which will will be be described described deformation. The separately. This locality most recently recently by by Baxter locality was was mapped mapped most Baxter and others others (1987) (1987) and lithologies are are designated designated as as the the Highly lithologies Highly Altered Altered Variety Variety of the the Pillowed Pillowed Basalt Basalt Memb'r of of Clark Member of the the Volcanics Volcanics of Silver Silver Mine Mine Lakes, Lakes, Gabbro Gabbro of Clark Creek, Creek, and and Location: NW+, section 30, T49N, Rhyolite Intrusive Intrusive of of Fire Center Rhyolite Center Mine. Mine. Location: NWi, section T49N, R27W. R27W. 5a. The 5a. The Cliff Cliff Outcrops Outcrops This set of outcrops rocks and and intrusives of altered This outcrops contains contains altered altered gabbroic gabbroic rocks intrusives of altered on the south outcrop on south side of the the valley valley isis mainly mainly altered altered rhyolite porphyry. porphyry. The outcrop gabbro gabbro with with a fault-bounded fault-bounded block block of of altered altered rhyolite, rhyolite, which which strikes strikesapproximately approximately N50° dips 750 75O to the east, east, along along the the eastern eastern contact. contact. The western western contact contact of N50°E and dips this rhyolite block has has aa similar strike and and aa dip of this rhyolite block similar strike of about about 40° 40Âtowards towards the the east. east. The maximum east-west thickness thicknessofof the the rhyolite rhyolite block block isis 50 50 feet. Mineralization The maximum east-west is concentrated along the the faulted contact is concentrated along contact between between the altered altered gabbro gabbro and and altered altered rhyolite. Pyrite is the Pyrite the dominant dominant sulfide sulfide phase, phase, with with arsenopyrite arsenopyrite and and chalcopyrite chalcopyrite outcrop on on the the north north side side of The small small outcrop of the the occurring in much occurring much lesser lesser amounts. amounts. The valley is a slightly valley is slightly less less altered altered example example of the the gabbro. gabbro. 5b. The Hillside 225 feet feet east 5b. Hillside Outcrop Outcrop (about (about 225 east of 5a) 5a) These outcrops outcrops are are located locatedalong alongthe the north north side side of of the These the valley valley on aa gently gently Near the the south south end of of upward hill, and upward sloping sloping hill, and are are mainly mainly highly highly altered altered basalt. basalt. Near the outcrop the outcrop is aa rhyolite rhyolite porphyry porphyry contact contact trending trending about about N10°W NlWW and dipping dipping 50° 50' east. This is is aa good good location location to to observe observe quartz-carbonate quartz-carbonate veining veining along along the the contact contact between rhyolite between rhyolite and altered altered basalt. basalt. Between this this outcrop outcrop and and Stop Stop 5c 5c there are Between are several several smaller smaller outcrops outcrops on the the north and south with rare north south side of of the the valley valley of of predominantly predominantly altered altered basalts basalts with rhyolite dikes. dikes. A- 59 �5c. 5c. The The Island Island Outcrop Outcrop (about (about 225 225 feet east east of of 5b) 5b) This is in the This outcrop outcrop is the middle middle of of the thevalley valley which which isisotherwise otherwise outcrop-free. outcrop-free. The entire outcrop outcrop is highly highly altered altered basalt basalt with with the exception exception of the the western western 1/4 1/4 which is is cut by which by rhyolite. rhyolite. Proceed back back toto North North Dead Dead River River Road Road and and turn turn left (east) Proceed (east) at 32.3 32.3 mi. mi. At 34.3 mi, mi, bridge 34.3 bridge over over Clark Clark Creek, Creek, park park near near bridge. bridge. Across Across the Clark Clark Creek Creek bridge, the the road bridge, road is is known known as as Red Red Road. Road. 34.3 Stop Stop 6 (optional) (optional) -- Pillowed Basalt and and Rhyolite Rhyolite The outcrops directly beneath beneaththe the western westernside sideofof the the bridge The outcrops directly bridge are predompredom- are vertical inantly Archean Archean pillowed pillowed basalt. basalt. These These pillows pillows are vertical and and show show younging younging direction toward S30¡W S30°W. A A fault contact direction toward contact (seen (seen when when the water water level level isis low) low) juxtaposes aa rhyolite rhyolite porphyry porphyry on on the the east against juxtaposes against the pillow pillow basalt basalt on the the west. west. A few normal toto the the main main fault fault show of the few small small (inch (inch scale) scale) zones zones normal show shearing shearing of gives the the rhyolite This structural structural interleaving interleaving gives rhyolite a basalt basalt into the the rhyolite. rhyolite. This feet to the pseudo-pillowed appearance. The large large cliff, cliff, visible visible about about 1500 1500 feet the north north pseudo-pillowed appearance. The of of the the bridge, bridge, is is the the type type locality locality for for the the Gabbro Gabbro of of Clark Clark Creek. Creek. This locality locality was was mapped mapped most most recently recently by Baxter Baxter and and others others (1987) (1987) and and contains Member of of the Volcanics of Silver contains the the Pillowed Pillowed Basalt Basalt Member Volcanics of Silver Mine Mine Lakes Lakes and and Rhyolite Intrusive Intrusive of of Fire Rhyolite Fire Center Center Mine. Mine. Continue north on Red Continue north Red road. road. low relief outcrops. low outcrops. 35.0 35.0 Location: SE+, section section 29, T49N, Location: SE4, T49N, R27W. R27W. At 35.0 mi, pull off to At 35.0 mi, pull off to the the right right shoulder, shoulder, near near Stop 7 (optional) Stop (optional) -- Granular rhyolite These outcrops are are along along the the upward upward slope slope on on the the east east side side of the These outcrops the road. road. Even this rock Even though though this rock is is holocrystalline, holocrystalline, itit has has been been included included with the the other other rhyolites based on on its similar rhyolites based similar major major and and trace trace element element chemical chemical composition, composition, e.g., e.g., calc-alkaline rhyolite on aa Jensen calc-alkaline rhyolite Jensen diagram. diagram. The granular granular rhyolite rhyolite Consists consists of microcline and albite, albite, but is microcline and is now now moderately moderately altered altered to to sericite, sericite, Quartz, quartz, and and minor minor Some sulfide sulfide mineralization mineralization can can be be found in epidote chlorite. Some in localized localized zones zones epidote and chlorite. A- 60 �of of the theoutcrop, outcrop, mainly mainly on on the thesouth southside. side. This This locality locality was was mapped mapped most most recently recently by by Baxter Baxter and andothers others(1987) (1987)asas NWi. section 28, 28, T49N, T49N,R27W. R27W. Location: NW+. Rhyolite Rhyolite Intrusive Intrusive of Fire Fire Center Center Mine. Mine. Location: Continue Continue north north on on Red Red road. road. At At 35.05 35.05 mi. mi. cross cross Deer Deer Creek Creek and turn turn right right (east) after the the bridge tridge to aa dirt At 35.35 35.35 mi, mi, cross cross Deer Deer Creek Creek (east) immediately immediately after dirtroad. road. At at the the top of aa hill, At 35.5 35.5 mi, mi, 3-way 3-way irtersection intersection at hill, take take road road to tothe theright. right. again. again. At At At 36.0 36.0 mi, mi, flat flat area areaisispart partofofthe theClark ClarkCreek Creekbasin basinconsisting consistingofofLower Lower Proterozoic Formation;prominent prominentoutcrops outcropson on the the left are Proterozoic Michigamme Michigamme Formation; are Archean Archean At 36.6 mi, pull over to small side road on the right and walk about200 200 rocks. At 36.6 mi, pull over to small side road on the right and walk about rocks. feet southwest to outcrops on small knob. feet southwest to outcrops on small knob. 36.6 36.6 - Stop Stop 88 - Breccia Breccia This This outcrop outcrop is is the the best bestknown knownexposure exposure of ofa amember memberwhich whichgeomorphologigeomorphologiStratigraphic top is is towards towards the thesouth-southwest, south-southwest, cally cally tends tends to to form form aadepression. depression. Stratigraphic member consists consists of at at consistent consistent with nearby nearby pillowed pillowed basalt basalt top top indicators. indicators. This member The lowest lowest part of of this this member member isis interpreted interpreted least least three three lithologic lithologic breccia breccia units. units. The to to be be aasubaqueous subaqueous pyroclastic pyroclastic and/or and/or fine-grained fine-grained mudflow mudflow deposit, deposit, devoid devoid of of Above this is is aa breccia breccia with with aalarge largeproportion proportion of offragments fragments large large fragments. fragments. Above representing The majority majority of of fragments fragments are are representing a wide wide range range ofoflithologies. lithologies. The heterolithologic heterolithologic porphyritic porphyritic volcanic volcanic rocks rocks of of probable probable andesite andesite composition, composition, now now extensively These fragments fragments are equant equant to to slightly slightly elongate elongate and and extensively altered. altered. These are of iron-rich The other other fragments fragments are iron-rich chert chert which which sub-angular to to sub-rounded. sub-rounded. The sub-angular occurs from equant occurs in shapes shapes ranging ranging from equant to highly highly elongate, elongate, with with angular angular to to breccia is interpreted interpreted as as aa subaqueous subaqueous mudflow, mudflow, of sub-angular edges. edges. This breccia relatively An unbrecciated unbrecciated cherty cherty iron-formation iron-formation overlies overlies relatively near-vent near-vent facies facies origin. origin. An this breccia, the chert chert clasts must have have been breccia, consequently consequently the clasts must been derived derived from prepreexisting existing chert deposits deposits that formed formed in in aaless lessstable stableenvironment. environment. This member member has has undergone undergone a relatively relatively large large amount amount of of strain, strain,demonstrated demonstrated are many many replacement replacement by flattened flattened clasts, clasts, compared compared to to adjacent adjacent members. members. There are pods, of mainly pods, consisting consisting of mainly pyrite, pyrite, throughout throughout the the member member indicating indicating hydrothermal hydrothermal alteration. alteration. The large large outcrops outcrops to the the south south of of the the breccia breccia member member are are of ofrelatively relatively A-61 �This showsaa wide wide range range of of grain due to This gabbro gabbro shows grain size, size, probably probably due unaltered gabbro. unaltered gabbro. the localized which produced produced finer-grained finer-grained zones the localized fault movement movement which zones within within the the overall coarse-grained overall coarse-grained rock. rock. This locality was mapped most recently recently by by Baxter This locality was mapped most Baxter and others others (1987) (1987) and and contains the the Breccia Member of of Reany contains Breccia Member Reany Lake Lake of the the Volcanics Volcanics of of Silver Silver Mine Mine Lakes and and Gabbro of Lakes of Clark Clark Creek. Creek. Location: SW+, section 27, 27, T49N, SWi, section T49N, R27W. R27W. Location: Retrace route to to Red Red road Retrace route road at first first Deer Deer Creek Creek bridge bridge and turn turn right right (north) (north) on the the main main gravel/dirt gravel/dirt road road and and at at 41.3 41.3 mi mi turn turn right Continue on right at 38.0 38.0 mi. mi. Continue (south) to gravel At 46.3 mi, turn turn left (east) to dirt road, (south) gravel County County Road Road 510. 510. At 46.3 mi, (east) to road, the the Park near and walk walk 1200 1200 feet feet east east on on the road, Holyoke Holyoke Trail. Park near intersection intersection and road, then then 160 160 feet southeast southeast to Stop Stop 9. 9. 49.5 49.5 Stop 99 Stop -- Breccia These outcrops, located located along along the the extension of the These outcrops, extension of the Willow Willow Creek Creek Shear Shear Zone, Zone, The matrixconsist of aa breccia matrixconsist of breccia member member interbedded interbedded with with pillowed pillowed basalt. basalt. The supported breccia consists consists of of several several types types of of flattened to 1:20) supported breccia flattened clasts clasts (1:10 (1:lO to 1:20) in aa basaltic matrix. basaltic matrix. The margins of some clasts are are feathered. The clasts The margins of some clasts feathered. The clasts vary vary in size size from lensoidal 1/5 inch inch fragments to 44 inch wide feetlong long fragments. fragments. fragments to wide and and 66 feet from lensoidal 115 Clast types Clast types include include rhyolite, rhyolite, gabbro, gabbro, and and granodiorite. granodiorite. The rhyolite The rhyolite clasts clasts are are porphyritic with 20% phenocrystsinin aa fine-grained, porphyritic 20% plagioclase plagioclase phenocrysts fine-grained, quartz, quartz, plagioclase, plagioclase, and chlorite chlorite matrix. matrix. The granodioritic granodioritic clasts are porphyritic porphyritic with with40% 40%plagioclase plagioclase phenocrysts in in fine-grained, phenocrysts fine-grained, quartz quartz and and chlorite chlorite groundmass. groundmass. The gabbro gabbro clasts clasts are are medium-grained, sub-ophitic sub-ophitic with with plagioclase, plagioclase, chlorite chlorite and and amphibole. amphibole. The matrix medium-grained, matrix of the of mainly chlorite and and epidote epidote with with up to 5% pyrite. pyrite. of the breccia breccia consists consists of mainly chlorite to 5% This breccia breccia is interpreted interpreted as as aa subaqueous subaqueous mudflow mudflow which which has has undergone undergone a high high amount amount of strain. strain. This locality This locality was was mapped mapped most most recently recently by by MacLellan MacLellan and and Bornhorst Bornhorst (1988) (1988) and is of Bismark Creek of of the Volcanics of is designated designated as the the Breccia Breccia Member Member of Bismark Creek Volcanics of Location: SE+, SEk section section 31, 31, T49N, T49N, R26W. R26W. Silver Mine Lakes. Silver Lakes. Location: Continue south on County 48.4 mi, mi, pull pull off off to to right rightshoulder shoulder Continue south County Road Road 510. 510. At 48.4 Be careful, careful, this (outcrops on on other other side of (outcrops of road). road). Be this road road is heavily heavily traveled traveled at times. A-62 �51.4 Basalt, and and Gabbro Gabbro Stop 10 -- Iron-Formation, Basalt, Stop This outcrop outcrop consists consistsofof iron iron formation formationinin contact contacttoto the the north north and south with This between the the massive massive basalt. basalt. To the the west west the the basalt basalt is is cut cut by by gabbro. gabbro. The contact between iron-formation is is approximately approximately 55 basalt basalt and gabbro gabbro follows follows the the highway. highway. The iron-formation exclusively of of fine, black feet thick thick and andtrends trendsN30°W. N30°W It is is compcsed compcsed almost almost exclusively black chert which To the west which contains contains scattered scattered magnetite magnetite grains grains and abundant abundant pyrite, pyrite. To west of this is generally layered with with 1/2 inch this locality, locality, the the iron-formation iron-formation member member is generally layered inch chert and and magnetite magnetite bands. bands. Although the magnetite content can can be highly Although the magnetite content highly variable, the iron-formation variable, iron-formation produces produces aa strong strong magnetic magnetic signature. signature. dark green to dark to black, black, fine-grained fine-grained and and relatively relatively non-foliated. non-foliated. The basalt basalt is is The gabbro The gabbro is is medium-grained, ophitic ophitic to to sub-ophitic, sub-ophitic, and is medium-grained, is composed composed of equigranular equigranular amphiamphibole, plagioclase bole, plagioclase and chlorite. chlorite. This locality was mapped mapped most most recently recently by by Puffett (1974) This locality was (1974) as the the Lighthouse Lighthouse A more Point of the of uncertain more Point Member Member of the Mona Mona Schist Schist and and Metadiabase Metadiabase of uncertain age. age. A satisfactory correlation isis with with the Pillowed satisfactory correlation Pillowed Basalt Basalt and Iron Iron Formation Formation Members Members of of the Volcanics of Silver Mine Lakes Lakes and and the the Gabbro Volcanics of Silver Mine Gabbro of Clark Clark Creek Creek as as mapped mapped Location: SE+, SEi, section 5, 5, one mile mile to to the theeast eastby byMacLellan MacLellanand andBornhorst Bornhorst(1988). (1988). Location: T48N, T48N. R26W. R26W. 48.8 mi, mi, intersection intersection with with North North Continue Continue south on County County Road Road 510. 510. At 48.8 At 50.6 mi, pull off to right At 50.6 mi, pull to right Basin Road and pavement begins, Continue south. Basin Road and pavement begins, continue south. Walk east east across shoulder, just just before across road road shoulder, before going going downhill downhill and and across across a bridge. bridge. Walk along an an abandoned along abandoned portion portion of 510 510 to to small small outcrops. outcrops. 53.6 Stop Stop 11 (optional) (optional) -- Archean greywacke This outcrop of black, This outcrop consists consists of black, quartz-feldspar-sericite-chlorite quartz-feldspar-sericite-chlorite schist with with This rock rock is interpreted interpreted as as minor minor disseminated disseminated pyrite; pyrite; foliation foliation trends trends westerly. westerly. This greywacke. This extends eastward eastward for for 8 miles This particular particular member member extends miles and and represents represents The the only the only major major sedimentary sedimentary unit within within the the Marquette Marquette Greenstone Greenstone Belt. Belt. The member consists consists of of greywacke member greywacke and slate. slate. A- 63 �This This locality locality was was mapped mapped most most recently recently by Puffett Puffett (1974) (1974) as as the theNealy Nealy Creek Creek Location: Sf, Si,section section 10, 10,T48N, T48N,R26W. R26W. Member of of the theMona MonaSchist. Schist. Location: Member Continue Continue south south on on County County Road Road 510. 510. At At 50.85 50.85 mi, mi, cross cross bridge bridge over over the the At 52.9 mi, bear left and at 53.0 mi, turn left(east) (east) Dead Dead River RiverStorage StorageBasin. Basin. At 52.9 mi, bear left and at 53.0 mi, turnleft and to to the the east east end endofofCounty CountyRoad Road502. 502. At At 53.6 53.6 mi, mi, turn turn left left (east) (east) to to U.S. U.S. 41 41 and return return to to the theRamada Ramada Inn InnininMarquette. Marquette. END END OF OF DAY DAY 11 Acknowledgements and References References in Day Acknowledgements and Day 22 Road Road Log. Log. A- 64 �Geological Field Trip Trip to to the Marquette Belt: Part II Geological Field Marquette Greenstone Greenstone Belt: I1 Day Day 2 Road Road Log Log -- Stops Stops A to EE T.J. T.J. Bornhorst Bornhorst and and D.A. D.A. Baxter Baxter Department Department of of Geology Geology and andGeological Geological Engineering Engineering Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 NOTE: The field field trip trip for forDay Day22includes includes aalate latemorning morning to to afternoon afternoon stop stop at at the the NOTE: The There is aa separate separate guide, guide, Part Part III, 111,authored authored by byBrozdowski Brozdowski and and Ropes Mine. Mine. There Ropes Additional information on on the thegeologic geologic of Callahan Callahan Mining Mining Corporation. Corporation. Additional Scott of setting of the setting of the field field trip trip stops stops may may be be found found in in the thepaper paperby byBornhorst Bornhorst (this (this volume). volume). Refer Refer to to Day Day 11Road Road Log, Log, Figure Figure 1:1: Route Route and and Stop Stop Map Map Mileage Mileage Start Start Day Day 22 -- Ramada Ramada Inn, Marquette Marquette 0.0 Assemble at the the main Assemble at main entrance entrance of the the Ramada Ramada Inn. Inn. Turn Turn right right out out of of the the parking to U.S. parking lot of of the the Ramada Ramada Inn Inn to toWashington Washington Street Street to U.S. 41 and and then then west west At 13.8 13.8 mi, mi, turn turn right right (north) (north) at at traffic traffic light light to toCounty County Road Road towards Ishpeming. Ishpeming. At towards At 14.75 14.75 mi, mi, pull pull off off to to the theright rightshoulder shoulder 14.6 mi, mi, hairpin hairpin turn turn left. left. At 573. 573. At 14.6 alongside of of outcrops. outcrops. alongside 14.75 14.75 Stop Stop A -- Schist Schist These These rocks rocks are foliated foliated quartz-sericite quartz-sericite schists schists with with angular angular carbonate carbonate clots clots rocks are are N70° and dips dips 84°S. 84OS. The rocks Foliation strikes N70°W scattered throughout throughout them. them. Foliation intermediate (dacite) arid and have rocks intermediate in composition composition (dacite) have a calc-alkalic calc-alkalic affinity. affinity. These rocks are interpreted interpreted totobebesubaqueously subaqueously deposited deposited volcaniclastic volcaniclastic sediments sediments or orpyroclastic pyroclastic deposits, and are are an important of the the southwestern part of of the deposits, and important component component of southwestern part greenstone belt. belt. This locality most recently recently by by Clark locality was was mapped mapped most Clark and others others (1975) (1975) as as the the Kitchi Location: NW+, NWL section 34, 34, T48N, T48N,R27W. R27W. Kitchi Schist. Schist. Location: 14.9 mi, mi, Deer Deer Lake Lake is is on on right. right. At Continue NW NW on County County Road Road 573. 573. At 14.9 15.55 mi, pull pull off to 15.55 mi, to the theright rightshoulder shouldernear nearglacially glaciallypolished polished surface. surface. 15.55 15.55 Stop Stop B -- Breccia Breccia The breccia outcrop and and on the The breccia is exposed exposed in aa glacially glacially polished polished outcrop the lake lake shore. shore. A-65 �On Onthe thepolished polished surface, surface, the the clasts clasts vary vary from from 10" 10" X X 14" 14" down down to to the the size size of ofthe the matrixgrains. grains. Larger Larger clasts, clasts, up to to 2' 2, XX4'4'inincross crosssection, section,are arepresent present ininthe the matrix lakeshore shoreoutcrops. outcrops. Clasts Clasts greater greater than than 1/2" 1/2" make make up up about about 20% 20% of of the therock rockand and lake thereisisananobvious obviousstratification stratificationininclast clastsize. size. Shape Shape of of clasts clastsvaries variesfrom from there Theclasts clastsare areandesite-dacite andesite-dacite(near (nearcompositional compositional very-angular totorounded. rounded. The very-angular division) division) inincomposition compositionwith withsmall smallchemical chemicalvariation variationbetween betweenindividual individualclasts clasts studiedtotodate. date. This This breccia breccia isisinterpreted interpretedasasa asubaqueously subaqueouslydeposited depositedmudflow mudflow studied breccia. breccia. This Thislocality locality was was mapped mapped most most recently recently by byClark Clarkand andothers others(1975) (1975)asas Location NE+, N E k section section33, 33,T48N, T48N.R27W. R27W. agglomerate facies facies of of the theKitchi KitchiSchist. Schist. Location agglomerate At 17.5 17.5 mi, mi, turn turn totoleft lefton ongravel gravelroad road toto Continue on onCounty CountyRoad Road573. 573. At Continue See Field Field Trip TriptotoCallahan CallahanMining MiningCorporation CorporationRopes RopesMine Mine the Ropes RopesMine. Mine. See the Property (this (thisvolume). volume). Property At 34.2 34.2 mi, mi, enter entercity cityofofMarquette Marquette Retrace route routeback backtowards towardsMarquette. Marquette. At Retrace and and atat34.5 34.5 mi, mi,make makeaaleft leftturn turnononWashington WashingtonStreet Street towards towards the the Ramada Ramada Inn. Inn. At At 34.95 34.95 mi, mi, turn turn left left totoRublein Rublein Street Street and and at at 35.1 35.1 mi, mi, turn turn right right totoRidge Ridge Pull over over and and park park atat35.3 35.3mi, mi,near nearsmall smalloutcrops outcrops on onright rightshoulder. shoulder. Street. Pull Street. Stop CC (optional) (optional) -- Schists Schists Stop 35.3 35.3 AA small small roadcut roadcut on on the thesouth southside sideofofRidge RidgeStreet Streetexposes exposeswell-foliated well-foliated Foliation strikes strikes roughly roughly E-W E-W and and dips dipsvertical. vertical. On On the the chlorite-sericite schists. schists. Foliation chlorite-sericite north north side, side, about about 200 200 feet feet through through the the trees, trees, there thereisisa aclearing clearingwith withglacially glacially polished outcrops. outcrops. On On the the way way totothe theclearing clearingthere thereare arelayered layeredamphibolitic amphibolitic polished A banded, banded, tabular tabular body body ofofquartz-sericite quartz-sericite schists D). A schists (discussed (discussed further at at Stop Stop D). schist schist is is well well exposed exposed at the the clearing; clearing; this is is interpreted interpreted as as aa rhyolite rhyolite dike. dike. The The contorted contorted banding banding is either either due due to to primary primary flow flow banding banding and/or and/ordeformation. deformation. We We consider consider the the latter latterinterpretation interpretation the themost mostlikely. likely. This This locality locality was was most most recently recently mapped mapped by Gair Gair and and Thaden Thaden (1968) (1968) as as the the Location NE+, NEi, section section 22, 22, T48N, T48N, Lighthouse Lighthouse Point Point Member Member of of the theMona MonaSchist. Schist. Location R25W. R25W. A-66 �Continue Continue east east on Ridge Ridge Street Street and at at 35.4 35.4 mi, mi, turn turnright righttotoLincoln LincolnAvenue. Avenue. Continue straight straight on on At Washington At 35.5 35.5 mi, mi, turn turnleft leftatattraffic trafficlight lightto to WashingtonStreet. Street. Continue Washington Street past past the the Ramada Ramada Inn, Inn, from 36.1 Washington Street 36.1 mi mi until until 36.6 36.6 mi, mi, where where At 37.1 37.1 mi, mi, Washington Street ends at Washington Street at Lake LakeStreet. Street. Turn Turn left left on onLake LakeStreet. Street. At make make aa right right turn turn atatthe theentrance entrancetotothe theMaritime Maritimemuseum museum and andcontinue continue on onroad road to to the the Coast Coast Guard Guard Station Station and and park.. park.. 37.25 37.25 D -- Lighthouse Lighthouse Point Point Member Member Stop D Stop You from the U.S. You must must obtain obtain permission permission from U.S. Coast Coast Guard to to visit visit this this locality. locality. No rock rockhammers hammersallowed!! allowed!! No Excellent on Lighthouse Lighthouse Point Point provide provide a view Excellent shoreline shoreline exposures exposures on view of of Archean Archean We will will walk walk around around the the point point noting noting the thelocalities localities shown shown and and Proterozoic Proterozoic rocks. rocks. We in detail This area area was was most most recently recently mapped mapped in detail by Gair Gair and and Thaden Thaden on Figure Figure 2. 2. This on (1968) as the Lighthouse Point Member Member of of the Mona (1968) as Lighthouse Point Mona Schist Schist cut by by Early Early ProteroProteroLocation: NW+, NWL section 24, 24, T48N, T48N,R25W. R25W. zoic zoic and and Keweenawan Keweenawan diabase diabase dikes. dikes. Location: Stop Stop Dl. Dl. Archean, (basaltic) schist schist isis cut by Archean, thinly thinly layered, layered, amphibolitic amphibolitic (basaltic) by aa tabular, tabular, porphyritic porphyritic rhyolite rhyolite dike dike trending trending roughly roughly parallel parallel to to the t h elayering. layering. The The layers layers on on Lighthouse Point, as aa whole, Lighthouse Point, whole, strike strike approximately approximately E-W E-W and and dip dip70°N. 70°N This This layered layered schist schist was was mapped mapped by Gair Gair and and Thaden Thaden (1968) (1968) as as the the Lighthouse Lighthouse Point Point The layers layers in in the the schist schist are areinterpreted interpreted asasflattened flattenedpillows pillows (basalt). (basalt). Member. Member. The The mechanism of flattening could be be primary, primary, but but we interpret mechanism of flattening could interpret high high strain strain as as the the most most important important means means of of flattening. flattening. The The rhyolite rhyolite is is interpreted interpreted as as an anlate-tectonic late-tectonic rhyolite dikes dikes in in the greenstone belt are more Archean dike. dike. Some Some rhyolite greenstone belt more strained strained than than others. others. The are cut by The Archean Archean rocks rocks are by two two N-S N-S trending trending diabase diabase dikes that are are metamorphosed to greenschist greenschist facies facies and and are are distinctly metamorphosed to distinctly younger younger than the the layered layered and Thaden Thaden (1968) (1968) interpreted interpreted these these dikes dikes as as Early Early amphibolite-grade amphibolite-grade schist. schist. Gair and However, Baxter Baxter and Bornhorst Bornhorst (1988) (1988) suggest suggest these these porphyporphyProterozoic Proterozoic in in age. age. However, ritic ritic dikes dikes are are Archean Archean in in age, age, correlative correlative with with the theMatachewan Matachewan dike dike swarm swarm in in Ontario. Ontario. A- 67 �EXPLANATION EXPLANATION Keweenawan Keweenawan @Diabase Diabase ProterOzoiC proterozolc Diabase Diabase Archean Archean9 ? Gabbro Gabbm Rhyolite UhyoIitO Archean Archean Ala Layered L a y e r e dAmphlbolitic AmphiboliticSchist Schist — Contact Contact -----Fault Fault Pd Ag Ar 0 I 50 50 100 100 I ftf t If Ala F i g u r e2:2: Figure Geology Geology of of Lighthouse L i g h t h o u s e Point, P o i n t , Marquette, M a r q u e t t e , Michigan. Michigan. Modified Modified slightly s l i g h t l y from from detailed d e t a i l e d map map by by Gair G a i r and and Thaden (1968). ( 1 9 6 8 ) . Numbers Numbers at a t localities l o c a l i t i e s described described Thaden i n text. text. in A-68 �Walk over ridge ridge to to other side A relatively relatively unmetamorphosed, unmetamorphosed, Walk over side of of the the point. point. A E-W diabasedike dikecrops cropsout out along along the the crest crest of of the E-W trending trending Keweenawan Keweenawan diabase the ridge. ridge. Stop Stop D2. D2. There There are are bodies bodies of of comparatively comparatively massive, massive, fine fine to tomedium-grained medium-grained (Archean?) (Archean?) body must must have have been been gabbro within within the the layered layered amphibolilic amphibolilic schist. schist. This body relatively late-tectonic due due to to the relatively late-tectonic the lack lack of of foliation/strain foliation/strain as as compared compared to the the amphiboliticschist schistand and gabbro gabbro are are cut cut by aa Layered amphibolitic surrounding layered layered schists. schists. Layered metamorphosed metamorphosed (Proterozoic?) diabase dike. dikeStop D3. D3. Intense Intense foliation foliation has has obliterated obliterated layering layering at this this location; location; interpreted interpreted as as aa higher higher strain strain zone zone within within the the layered layered amphibolitic amphibolitic schist. schist. Stop Stop D4. D4. Layered schist is cut Layered amphibolitic amphibolitic schist cut by by aametamorphosed metamorphosed (Proterozoic?) (Proterozoic?) diabase diabase dike and and layered layered amphibolite amphiboliteschist schistare arecut cut by by a thin, dike. The metamorphosed metamorphosed dike thin, relatively E-W trending trending diabase diabase dike dike of Keweenawan The relatively unmetamorphosed, unmetamorphosed, E-W Keweenawan age. age. The metamorphosed diabasedike dike isis offset offset by aa small metamorphosed diabase small NW-SE NW-SE trending trending fault. fault, Retrace Retrace route back back to to Lake Lake Street. Street. At 37.4 37.4 mi, mi, turn turn right right totoLakeshore Lakeshore Blvd. Blvd. and proceed 38.2 mi, mi, junction junction proceed along along the the lakeshore lakeshore towards towards Presque Presque Isle Isle Park. Park. At 38.2 with Fair Fair Avenue, Avenue, stay stay on on Lakeshore Lakeshore Blvd. Blvd. and at at 38.7 38.7 mi, mi, Lakeshore Lakeshore Blvd. Blvd. joins joins Pine 38.8 mi, mi, excellent excellent view view of active active iron iron ore ore docks docks and and Presque Presque Isle Isle Pine Street. Street. At 38.8 (an Archean, Archean, serpentinized serpentinized peridotite peridotite unconformably unconformably overlain overlain by by Jacobsville Jacobsville 39.3 mi, mi, turn turn left lefttotoHawley Hawley Street Street before before power power generating generating plant. plant. Sandstone). At 39.3 Sandstone). At 40 40 mi, mi, turn turn right right(north) (north)totoCounty County Road Road 550. 550. At 43.6 43.6 mi, pass pass turnoff turnoff to to Sugarloaf Mountain overlook overlook (requires (requires climb climb along along aa maintained Sugarloaf Mountain maintained trail trail with with steps). steps). At 43.8 on both 43.8 mi, mi, large large granitoid granitoid gneiss gneiss outcrops outcrops on both sides sides of the the road. road. At 44.9 44.9 mi, pathway to to Harlow Harlow Lake, Lake, into into a mi, turn turn right right towards towards the the lakeshore, lakeshore, opposite opposite pathway small parking area. area. small 44.9 Stop E£ -- Plutonic Plutonic rocks rocks at a t Wetmore Wetmore Landing Landing Stop Walk around the the gate gate and and down down aa dirt road Walk around road to to the thelakeshore lakeshore and and proceed proceed east. east. Walk SE along along the the road Walk SE road above above the the beach beach totolarge largerounded roundedwave-washed wave-washed outcrops outcrops to view of granitoid view features features characteristic characteristic of granitoid rocks rocks which which intrude intrude the the volcanic volcanic rocks rocks A-69 �of the theMarquette MarquetteGreenstone GreenstoneBelt. Belt. of The dominant dominant rocks rocks are aregneissic gneissictonalite tonalitetotogranodiorite. granodiorite. These These plutonic plutonicrocks rocks The are are cut cut by bytonalite tonalitedikes dikesofofvarying varyingage, age,by bymafic maficdikes dikes(amphibolite), (amphibolite), and and by by The mafic mafic dikes dikes are are irregular irregular in in plan plan view view and and veins of of quartz quartzofofvarying varyingage. age. The veins are deformed deformed(Baxter (Baxter and andBornhorst, Bornhorst,1988). 1988). Ductile Ductile to to brittle brittle shear shear zones zones cut cut the the are rocks; epidote epidote isis associated associated with with the the brittle brittleshears. shears. These These outcrops outcrops display display the the rocks; complex history history experienced experienced by by the thegranitoid granitoid rocks. rocks. These These features features are are often often complex obscured obscured in inmore moretypical typicalmoss-covered moss-covered outcrops. outcrops. This This locality locality was was most most recently recently mapped mapped in in detail detail by by Gair Gairand andThaden Thaden(1968). (1968). Location: SE+, SEi7section section 29, 29, T49N, T49N,R25W. R25W. Location: Return to toRamada Ramada Inn. Inn. Return END OF OFDAY DAY 22 END ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This field field trip tripwould would not notbebepossible possiblewithout without support supportby bythe theMichigan Michigan Geological Survey, Department Department of of Natural Natural Resources Resources and and the Department Geological Survey, Department of of Geology University for an Geology and Geological Geological Engineering, Engineering7 Michigan Michigan Technological Technological University an This field field guide guide on-going on-going program program of of research research on on the theMarquette Marquette Greenstone Greenstone Belt. Belt. This has has benefited benefited from fromreviews reviews by byJ.J.Kalliokoski, Kalliokoski,Michigan MichiganTechnological Technological University, University, and K. K.Schulz, Schulz7U. U.S.S.Geological GeologicalSurvey. Survey. and REFERENCES REFERENCES Baxter, Baxter, D.A. D.A. and and Bornhorst, Bornhorst, T.J., T.J., 1988, 1988, Multiple Multiple Discrete Discrete Mafic Mafic Intrusions Intrusions of of Archean Archean to to Keweenawan Keweenawan Age, Age7western western Upper UpperPeninsula, Peninsula7Michigan Michigan[abs.]: [abs.]: ProceedProceedings ings and and Abstracts, Abstracts, 34th 34th Institute Institute on onLake LakeSuperior Superior Geology, Geology7Marquette, Marquette, Michigan Michigan (this volume). volume). (this Baxter, Baxter, D.A., D.A.7 Bornhorst, Bornhorst, T.J., T.J., and and VanAlstine, VanAlstine7J.L., J.Le71987, 19877Geology, Geology7Structure, Structure, and Metal Mineralization Mineralizationofof Archean Archean Rocks Rocks in in the and Associated Associated Precious Precious Metal the Vicinity V i c i ~ i t yof of Clark Clark Creek, Creek7Marquette Marquette County, County,Michigan: Michigan: Michigan MichiganGeological Geological Survey Survey Division, Division7 Department of Natural Open File File Report Department of Natural Resources, Resources7 Open Report OFR-87-8, OFR-87-8, 54 54 p. p. Clark, Clark7L.D., L.D., Cannon, Cannon7 W.F., W.Fe7and and Klasner, Klasner, J.S., J.S., 1975, 1975, Bedrock Bedrock Geologic Geologic Map Map of of the the Negaunee Negaunee SW SW Quadrangle, Quadrangle, Marquette Marquette County, County7Michigan: Michigan: U.S. U.S. Geological Geological SurSurvey, vey7Miscellaneous Miscellaneous Map Map Series, Series, GQ-1226. GQ- 1226. A-70 �Gair, J.E. and Gair, and Thaden, Thaden, R.E., R.E., 1968, 1968, Geology Geology of the the Marquette Marquette and and Sands Sands Quadrangles, Marquette County, Michigan: Quadrangles, Marquette Michigan: U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 397, 397, 77 p. p. Johnson, R.C., R.C., Bornhorst, T.J., and VanAistine, Johnson, Bornhorst, T.J., VanAlstine, J.L., J.L., 1987, 1987, Geologic Geologic Setting of Precious Metal Mineralization Mineralizationinin the the Silver Creek to Island Precious Metal Silver Creek Island Lake Lake Area, Area, Marquette Marquette County, Michigan Geological Geological Survey Survey Division, Division, Department Department of of Natural County, Michigan: Michigan: Michigan Resources, Open File File Report OFR-86-2, 134 Resources, Open Report OFR-87-4, OFR-87-4, Supersedes Supersedes OFR-86-2, 134 p. p. MacLellan, M.L. M.L. and and Bornhorst, T.J., 1988, MacLellan, Bornhorst, T-J., 1988, Geology, Geology, Structure, and and MineralizMineralization Reany Lake LakeArea, Area,Marquette MarquetteCounty, County,Michigan: Michigan: Michigan Michigan Geological Geological ation of the the Reany Survey Division, Department Departmentofof Natural Natural Resources, Resources,Open OpenFile File Report Report (in (in preparaSurvey Division, preparation). Puffett, W.P,, W.P., 1974, 1974, Geology Geology of the the Negaunee Negaunee Quadrangle, Quadrangle, Marquette Marquette County, County, Michigan: U.S. 788, 53 53 p. p. Michigan: U.S. Geological Geological Survey, Survey, Professional Professional Paper Paper 788, A-71 �Geological Field Trip Trip to the Belt: Geological Field the Marquette Marquette Greenstone Greenstone B e k Part III I11 Callahan Callahan Mining Mining Corporation Corporation Ropes Ropes Mine Mine Property Property R.A. R.A. Brozdowski Brozdowski and G.W. G.W. Scott Scott Callahan Callahan Mining Mining Corporation Corporation Exploration Exploration Dept. Dept. 25 25 Industrial Industrial Park Park Rd., Rd., Negaunee, Negaunee, Michigan, Michigan,49866 49866 NOTE: Additional information informationononthe theRopes RopesMine Minemay maybe be found found in in the paper NOTE: Additional paper by by Brozdowski Brozdowski in this this volume. volume. STOP STOP 1. le (Outcrop (Outcrop is 225 m west west of of the the intersection intersection of of the theRopes Ropesmine mineaccess access road road with road curves to south with the the paved paved highway: highway: Park where where access access road curves to south and and walk walk the the Julius Ropes Ropes made made final final 40 40 m m west west along along the the cut cut line line totoa asmall smallprospect prospect pit). pit). Julius his of gold his initial initial discovery discovery of gold at or or near near this this spot spotinin1880, 1880,and andsubsequently subsequently discovered the Ropes main ore ore zone The outcrop outcrop in the the pit pit isis discovered the Ropes main zone 250 250 m to to the the west. west. The a fine quartz-sericite-chlorite rock with with fine grained, grained, massive massive to to moderately moderately foliated, foliated, quartz-sericite-chlorite I abundant abundant 0.2 mm mm quartz quartz grains grains and and 11 -- 22 mm rectangular rectangular mats mats comprised comprised of of aphanitic The aphanitic sericite sericite in aa matrix matrix of of aphanitic aphanitic quartz, quartz, sericite, sericite, and andchlorite. chlorite. The sericite sericite mats mats are are interpreted interpreted asaspseudomorphs pseudomorphs after afterfeldspar feldsparphenocrysts, phenocrysts,because because progressively more sericite sericite altered progressively more altered feldspar feldspar phenocrysts phenocrysts are observable observable in in this this same same feldspar remains remains rock rock type type as as the the Ropes Ropes mine mine isisapproached approached from from the thewest. west. No feldspar the north Toward the north side side of the the pit pit isiswell well foliated foliated within within or east east of of the the mine. mine. Toward quartz-sericite quartz-sericite rock rock in in contact contact with with massive, massive, rusty rusty brown brown weathering weathering carbonatecarbonatequartz rock rock with with white whitecarbonate carbonate veins. veins. 2. STOP 2. to a letter (105 According to letter written written (105 m at at azimuth azimuth 285 285 degrees degrees from from stop stop 1). 1). According by by Julius Julius Ropes Ropes in in 1890, 1890, these these two two small small quarries quarries were were excavated excavated in the the late late 1880's to provide provide carbonate carbonate flux flux for for a nearby 1880's to nearby iron iron ore ore blast blast furnace. furnace. The north north wall wall of both both quarries quarries is is aafine finegrained, grained,well wellfoliated, foliated,light-green light-green carbonate-talc carbonate-talc rock Massive, rock with with lenses lenses of of blue-green blue-green talc talc and and white whitecarbonate carbonateveins. veins. Massive, carbonate-quartz rock occurs occurs toward toward the the south south ends ends of of the eastern carbonate-quartz rock eastern walls walls of of both both A-72 �serpentinized peridotite peridotite crops crops out uphill quarries. quarries. Brown Brown weathering, weathering, carbonatized, carbonatized, serpentinized uphill from the the quarries. quarries. from STOP STOP 3. 3. (Park (Park across across highway highway from from Ropes Ropes mine mine access access road, road, follow follow path pathsoutheastward southeastward peridotite at at this locality The serpentinized serpentinized peridotite locality has has aa well well to shore shore of of Deer Deer Lake). Lake). The developed fine grained texture of of 3-5 3-5 mm mm serpentine pseudomorphs pseudomorphs after after developed fine grained cumulate cumulate texture and lesser lesser pyroxene. pyroxene. The rock rock has has curvilinear curvilinear fracture fillings fillings of olivine and asbestos. chrysotile asbestos. STOP 4, 4. Examine drill core core and and hand of various various types types of of ore and Examine drill hand specimens specimens of and major major types types of wall wall rock rock from from the theRopes Ropes mine mine property. property. View View geologic geologic maps maps of Ropes Ropes mine mine area area and and geologic geologic plans plans and and cross cross sections sections of of Ropes Ropes mine. mine. A-73 �Field Field Trip Trip No. No. 22 Marciuette Mineral District District of of Michicran Michian Marouette Mineral Mining Minincr History History and andGeolociy Geolocrv by Burton Boyum Burton H. Boyum Mining Mining Department, Department, Retired Retired Cleveland-Cliffs, Cleveland-Cliffs, Inc. Inc. and and Robert Robert C. C. Reed Reed Michigan Michigan Geological Geological Survey Survey May, May, 1988 1988 �MARQUETTE MARQUETTE MINERAL MINERAL DISTRICT DISTRICT OF OF MICHIGAN MICHIGAN MINING HISTORY HISTORY AND AND GEOLOGY GEOLOGY MINING Introduction Introduction Welcome to to the the Marquette Marquette Mineral Mineral District District situated situated in in Welcome Marquette County County and and the the eastcentral eastcentral part part of of Baraga Baraga County County in in the the Marquette Upper Peninsula Peninsula of of Michigan Michigan (Figure (FigureA)! A)! This This district district was was the the Upper first of of the the iron iron "ranges" "ranges" of of the the Lake Lake Superior Superior region region to to be be first developed mid-1800ts,and and hosts hosts the the only only iron iron mines mines still developed in in the the mid-1800's, still active in in the the Upper Upper Peninsula, Peninsula, the active the Empire Empire and and Tilden TildenMines. Mines. The The Marquette Marquette Mineral Mineral District District also also contains contains the the only only operating operating gold gold mine in in the the U.S. U.S. portion mine portion of of the the Lake Lake Superior Superior region, region, the the Ropes Ropes Mine, and and has has known knowndeposits depositsof of copper. copper. Mine, The The dominant dominant geologic geologic feature feature of of the the district district is is the the Marquette Marquette trough which which contains contains rocks rocks of of the the Marquette Marquette Range Range Supergroup, Supergroup,an trough an Early Proterozoic Proterozoic sequence sequence of of mostly mostly sedimentary sedimentary and and lesser lesser Early volcanic volcanic rocks rocks deposited deposited unconformably unconformably on on Archean Archean greenstones greenstones and and gneisses of of the the Superior SuperiorCraton. Craton. The The Marquette Marquette Range Range Supergroup Supergroup gneisses consists of of four four groups groups (Cannon (Cannon and and Gair, Gair, 1970), 1970), from from oldest oldest to to consists youngest, the the Chocolay, Chocolay, Menominee, Menominee, Baraga, Baraga, and and Paint Paint River River Groups. Groups. youngest, The three three oldest oldest are are preserved preserved in in the the Marquette Marquette trough, trough, wereas wereas the the The Paint River River Group Group is is found found only only in in the the Iron Iron River-Crystal River-Crystal Falls Falls Paint District to to the the southwest.The southwest.The rocks rocks of of the the Supergroup Supergroup record record aa District progressive progressive change change intectonic intectonicconditions conditionsfrom from aa stable stable craton craton (Chocolay (Chocolay Group) Group) through through aa sedimentary sedimentary basin basin with with mild mild tectonism tectonism (Menominee Group) Group) to to aa highly highly active active tectonic tectonic basin basin (Baraga (BaragaGroup) Group) (Menominee as the the long—stable long-stable Superior Superior Craton Craton was was reactivated reactivated at at the the onset onset of of as the Penokean Penokean Orogeny. Orogeny. The The time time of of deposition deposition of of the the Supergroup Supergroup is is the still poorly poorly constrained, constrained, but but deposition deposition probably probably commenced commenced about about still 2.1 2.1 b.y. b.y. and and was was terminated terminated with with the the Penokean Penokean Orogeny Orogeny about about 1.85 1.85 b.y. (Morey, (Morey,1983). 1983). Keweenawan Keweenawan dikes dikes cut cut rocks rocks of of the theSupergroup, Supergroup, b.y. and the the Jacobsville Jacobsville sandstone, sandstone, of of probable probable Keweenawan Keweenawan age, age, and and and lower lower Paleozoic Paleozoic sedimentary sedimentary rocks rocks unconformably unconformably overlie overlie units units of of the Supergroup locally. the Supergroup locally. Pleistocene Pleistocene sand, sand, gravel, gravel, silt, silt, till, till, and and clay clay were were deposited deposited over over the the district district about about 10,000 10,000 years years ago ago during during retreat retreat of of the the last last Outwash deposits deposits of of silt, silt, sand, sand, and and gravel gravel preserved preserved glaciers. Outwash glaciers. Quaternary Quaternary trees, trees, mostly mostly spruce, spruce, in in the the Tilden Tilden Mine Mine Gribben Gribben Basin Basin Buried Forest Forest near nearPalmer. Palmer. The The remains remains of of more more than than 100 100 trees trees are are Buried preserved with with their their roots rootsin in place. place. Carbon Carbon 14 14 dates dates on on material material preserved from from these these trees, trees, which which have have as as many many as as 150 150 growth growth rings, rings, range range This indicates indicates the the recession recession of of the the y.B.P. This from 9545 9545 to to 10,230 10,230y.B.P. from Valders (Great (GreatLakean) Lakean) glacier glacier(Hughes, (Hughes,1979). 1979). Figure Figure BB shows shows aa Valders cross section section of of the the Gribben Gribben Basin Basin forest. forest. cross Economic Considerations Considerations Economic The The principal principal mineralization mineralization of of the the Marquette Marquette Mineral Mineral District District Total has has been been iron, iron, with with some some manganiferous manganiferousiron ironore. ore. Total shipments shipments of of iron iron ore ore through throughDecnither, December, 1987 1987 were were 590,776,442 590,776,442long longtons. tons. The The the Empire and the Tilden, two two active active iron iron mines mines of of the the district, district, the Empire and the Tilden, each each mine mine taconite taconite type type ore ore in in open open pit pit operations, operations, and and through through the the produce a high grade produce a high grade use of concentrators and pellet plants, use of concentrators and pellet plants, product. Shipping Shipping ports ports for for the the taconite taconite pellets pellets are are Marquette Marquette and and product. Escanaba. Escanaba. B-2 �General Geology ofMichfgan o f Michigan's's Upper Upper Peninsula. Figure A B—3 Figure A �NMU C.rt a r lLob. Ltb. 1978- J.M. 1 SLF SLF Figure B section of of Gribben Gribben Basin Basin Buried Buried Forest. Forest, Paltner Palmer % showing showing cross. cross,section The Reoessiøn of the Valders Glacial Ice, dtring time of Marquette-Munising MoZ'ai Ca,ra 9,925 years B P. 5. •' • • • ... . •* sit S....' •tt• St.. S..b SS ••,••• ' 5 S * S • *' : •.'..: : : S • S • •:. : • S _• - •.. :: •:•e, : %*•t4: •It 55. 55 *5 • • • ,.* • • It.tSi*.s. . . • :. - • •. . • ....t_O.r.. • • • S . . SAN0 . • . • . . ....... -: . • . , ' • •'.' ..0._,.5*,_..t.5, .'etS•5 •• •s''0 •5.....;,., * •.%•. •1• •S • • ''. •'•S .•. s. .. • •*h..5. ' • • •iUNDERLYING • •5 . _...s •Ss.•t St :......,..,5 • IS • Si S v •• • ; ........ .55,. .••t......•. • •••• • •• •,• • • ••1• •. ,•...•• •. ••••t 5 %• • . • • • • • • •S5•• • S. ••••• •••S•••S••S• SO • • I 5 • f.:. — ._..0.s •• •5 • Ste •__• . • _ • •• • • • •e . • • : • • •a • . •• : • . ..• •.e • •.• — ." • s__S.... • it •• • •.. • •.... ••• •• 0.•..• ,•°.° •• • I•,e •5tS5 ,.• S • •_t _.S ••, . • ..-_*•.•• Prepared by John D.Jughes, Northern Michigan University,, 1979 r'±gure B .5 . ORGANIC LAYER._L:. — e—. . • •. .... • • • — • . .. �The The greater greater part part of of the thedistrict's districttsiron ironore orehas hascome comefrom fromthe the Negaunee Iron—Formation Iron-Formationof ofthe theMenominee MenomineeGroup. Group. The The Negaunee, Negaunee! one one Negaunee worldlhas hasaamaximum maximum of the the thickest thickestiron-formations iron-formationsof of the the world, of stratigraphicthickness thickness of of over over1,300 11300meters meters (3,500 (31500feet) feet)in in stratigraphic Negaunee and and Ishpeming. Ishpeming. Some Some iron iron ore ore was was produced produced also also from fromironironNegaunee formation, formationlof of unknown unknown stratigraphic stratigraphiccorrelation correlationto to the theNegaunee Negaunee Iron-Formationlin in the the samller samller Gwinn Gwinn District District to to the the south, southland and Iron-Formation, from the the Bijiki Bijiki Iron-Formation Iron-Formationof ofthe theBaraga BaragaGroup. Group. from Today, Todayltaconite taconiteisisthe theonly onlyore oretype typebeing beingmined.. mined. (The (Theterm term taconiteoriginated originatedin inMinnesota, Minnesota,on onthe theMesabi Mesabi Range, Rangelafter afterState State taconite Geologist N.H. N.H. Winchell Winchell proposed, proposedlin in1884, 1884#that thatthe theiron-formation iron-formation Geologist was of of"Taconic ttTaconic Agett. ) However, Howeverlin in the the past, pastlthe the major ma2or iron ironores ores was Age".) were direct direct shipping shippingor ornatural naturalores oresof of two twomain main varieties. varieties. One were Onewas was ttsofttt ore composed composed of of soft, soft, friable, friablelearthy earthy or or semi—plastic semi-plastic "soft" ore ore hematitelmartite martiteand andgoethite. goethite. The The other other was was "hard" Ithardt8 orecomposed composed hematite, is of dense, denselcompact compactspecular specularhematite hematiteand andmagnetite. magnetite. "Ore" IfOrett is of defined defined as as aa mineral mineral or or minerals minerals from from which which aa metal metal or ormetals metalscan can be mined mined at at aa profit. profit. be natural ores ores were were found found in in three three distinct distinct structural structural The natural The settings. The The soft soft ores ores were were found found in in synclines synclinesand and in infault fault settings. structures structures at at the the base base of of the the Negaunee Negaunee Iron—Formation, Iron-Formationland and in in fault fault structures structures on on the the intrusive intrusive sills sills in in the the upper upper portion portion of of the the Negaunee Iron—Formation. Iron-Formation. The The hard hard ores ores were were found found generally generally at at the the Negaunee Quantitatively, the total top of the Negaunee Iron-Formation. Quantitativelyl the total top of the Negaunee Iron-Formation. footwall long footwall soft soft ores ores shipped shipped from from the the district district was was 186,607,540 1861607f540 long tons, long tonslthe the total total sill sill soft soft ores ores shipped shipped was was 54,092,030 5410921030 longtons, tonsf and the the total total hard hard ores ores was was 60,350,944 6O135OI944 long tons. tons. Maximum Maximum thickness thickness and long of of the the footwall footwall soft soft ore ore was was 80 80 meters meters (260 (260feet) feet) normal normal to to the the bedding; (100feet) feet) bedding; maximum maximum thickness thickness of of the the hard hard ore ore was was 30 30 meters meters (100 (see (see cross cross sections, sectionslFigures FiguresCCand andD). D). The The Marquette Marquette Range Range is is the the only only iron iron range range in in the the Lake Lake Superior Superior Region Region to to have have extensive extensive deposits deposits of of both both hard hard and and soft soft iron ores. ores. The The spatial spatial distribution distribution of of these these two two ore ore types types along along iron the the range range appears appears to to correlate correlate with with the the grade grade of of metamorphism metamorphism of of the host host rocks. rocks. The The soft soft ores ores are are found found mostly mostly in in the the chlorite chlorite the grade grade rocks rocks in in the the Negaunee Negaunee and and Ishpeming Ishpeming area, area, and and the the hard hard ores ores mostly mostly in in higher higher grade grade rocks rocks (ie. (ie.biotite, biotitelgarnet, garnetlstaurolite, staurolitefto to sillimanite sillimanite grade) grade) of of the the Republic Republic metamorphic metamorphic node node (James, (Jamesf1955; 1955; see Figure Figure E). E) see Two Two principal principal hypotheses hypotheses have have been been advanced advanced for for the the formation formation of hypothesis of the the direct direct shipping, shipping! natural natural ores; ores; the the "cold-water" ttcold-watertt hypothesis (VanHise (VanHise and and Bayley, Bayleyl 1897), 1897)f and and the the hydrothermal hydrothermal hypothesis hypothesis (Grunerl1930). 1930). Today, Todayl most most company company geologists geologists favor favor aa (Gruner, hydrothermal hydrothermal origin origin for for both both the the soft soft and and hard hard iron iron ores. ores. ~htoricalSummary summa& Historical The The extensive extensive copper copper deposits deposits of of the the Keweenawan Keweenawan Peninsula Peninsula were were worked over 5,000 worked by by the the ancients ancient;-over if000 years years ago ago and and were were known known to to the the European European explorers, explorerslmissionaries missionariesand and fur furtraders. traders. The The iron iron deposits deposits were were not not known known to to the the Europeans, Europeansf although although some some were were known known to to the the native native Americans Americans who who were were very very superstitious superstitious about about them. them. The The Marquette Marquette Range Range was was the the first first of of the the region's regiontsiron iron ranges ranges The discovery was made by government to be be discovered. discovered. The discovery was made by government surveyors surveyors to The survey survey subdividing subdividing the the land land into into townships townships of of 36 36 square squaremiles. miles. The inventor of of party, partyf under under Deputy Deputy Land Land Surveyor, Surveyorl William William Austin Austin Burt, Burtf inventor . (See (See Figure F i g u r e E-1) E-1) B- 5 �MARQUETTE IRON IRON MARQUETTE 1 GENERALIZED RANGE — - MICHIGAN MICHIGAN RANGE LONGITUDINAL FIGURE SECTION 4 — - N—S N - S CROSS CROSS SECTION SECTION ONE MILE ONE M I L E EAST E A S T OF OF WEST WEST LINE LINE OF OF R.26W R.26W GENERALIZED FIGURE FIGURE LOOKING WEST REv,5c, lq7c #9 D D c �__ MAP MAP SHOWING SHOWING NODES NODES AND AND ZONES ZONES OF OF PENOKEAN REGIONAL REGIONALMETAMORPHISM METAMORPHISM PENOKEAN EXPLANATION EXPLANATION I...] Blotite Blothe zone zone Chloritezone zone ChIert• StauroUte zone Garnet Gornet zone zone Silllmanlte zone zone Sillimanite KEWEENAWAN KEWEENAWAN Marquette ROCKS ROCKS Grovelond Groveland Mine Mim I0 10 I 1 a * . 00 tO II I 10 Figure EE Figure 20 MILES 20 KILOMETERS Modifiedfrom fromJames James (1955) (1955)and and Cannon Cannon (1973) (1973) Modified FLORENCE �G . Matthews, Matthews, Sr., Sr., Frank G. Memorial Fund **HISTORICAL NOTES ** NUMBER ONE * * HISTORICAL NOTES NUMBER ONE ******* The Historical Notes are are prepared prepared to honor the Historical Notes the memory m e m o y of oj Frank G. G. Matthews, Matthews, Sr., Sr., enthusiastic enthusiastichistorian historianand andcollector coilectorof oflore loreof ofearly early iron iron mining mining and and charcoal charcoaliron iron making making of of Michigan's Michigan's Upper UpperPeninsula. Peninsula. ******* FRANK G. G.MATTHEWS. MAmHEWS, SR. SR. FRANK BURT'S SOLAR COMPASS COMPASS used that number 9428X 9428Xfor for his his invention. It was first used year by by him himand and by by his hisson sonAlvin, Alvin,also alsoaasurveyor. surveyor.Here Here year was was his his original originaldevice device attached attached to tothe thestandard standard field field compass of of the the day. day. The Solar Solar Compass Compass of William William Austin Austin Burt Burtrevolurevolutionized tionized the the early early land land surveying surveying and land subdivision by providing providing aa true true north-south north-south direction. direction. Prior Prior to to this this invention, invention, the the surveyor surveyor was was completely completely dependent dependent upon the magnetic magnetic compass, compass, which which could could be beunreunreliable liable due due to to the the local local magnetic magneticcharacter characterof of the the earth earth in the the area area being beingsurveyed. surveyed. in William William Austin AustinBurt BurtofofMt. Mt.Vernon, Vernon,Michigan, Michigan,had had been been appointed appointed aa Deputy Deputy Land Land Surveyor Surveyor for for the the Federal 1834he he surveyed surveyed an an Federal Government Government inin1833. 1833.In In1834 area north of of Milwaukee Milwaukee ininWisconsin WisconsinTerritory. Territory. The The area had local local magnetic attraction attractioncausing causinggreat great diffidifficulty in in surveying surveying for for Burt Burtand andother othersurveyors. surveyors. In In 1835 he he worked worked on a model of his his solar solar compass. compass. then then variation referred to as aa "variation referred to "variation apparatus" apparatus" or or "variation compass." compass." Variation Variation referred referred to to the the amount amount of of differdifference in in degrees degrees between between true true north north and andmagnetic magnetic north. 26, 1836 1836 he received received patent patent north. On On February February 26, THE SUN DIAL DIAL To understand understand how how Burt's Burt's Solar SolarCompass Compass works, works, itit is helpful helpful to to think think of ofthe thesun sundial, dial,which whichmost mostpeople people is is an an ancient ancient device device and and has has have seen. The The sun sun dial dial is many forms. But But the the simple simple garden garden variety variety has has aa dial dial with the the hours hours marked marked on itit and and an an arm arm (called (called aa with "gnomon," from from the theGreek Greekmeaning meaning one one who who knows knows or or indicates) indicates) that that casts casts aashadow shadow read read on on the the hour hour the sun sun dial dial has hasbeen beencorrectly correctlymade madeand and circle. If the circle. correctly oriented, oriented, the the time. time. At At correctly the shadow shadow will will tell the noon, noon, the sun is in in aa true true north-south north-south line line called called the the "meridian." "meridian." one had had aa portable portable instrument instrument and and knew knew the the So, if one time, time, it could could be be oriented oriented to to indicate indicatethe themeridian meridian (provided the sun is is shining shiningor or at at least leasthazy hazy enough enough to to create shadows). This was the heart of Burt's Burt's genius. genius. Burt's Original Solar Attached to a Compass 3-8 Figure E— �the Solar Solar Compass, Compasston on September September 19, 19! 1844, 1844! was was running running the the township township the line line between between Range Range 26 26 West West and and 27 27 West West south south of of Teal Teal Lake Lake in in what what is now now the the City City of of Negaunee. Negaunee. They They noted noted that that their their magnetic magnetic is compass compass pointed pointed south south in in this this area. area. Burt Burt directed directed his his party party to to look and look around around and and they they found found "spathose ltspathose and magnetic magnetic ores ores abunding". abundingl1. However, HoweverI news news of of this this discovery discovery was was overshadowed overshadowed by by the the rush rush for for copper copper in in the the Keweenaw. Keweenaw. In In fact, fact! the the first first iron iron mining mining company company to to operate operate in in the the region, region, the the Jackson Jackson Mining Mining Company, Companyf organized organized on on July July 23, 23! 1845 1845 in in Jackson, Jackson! Michigan, Michigsnl went went to to the the Upper Upper Peninsula Peninsula looking looking for for cooper cooper and and other other base base metals, metals! and and was was persuaded persuaded to to look look for for iron iron by by aa half-breed, half-breed! Louis Louis Nolan. Nolan. Although Although Nolan Nolan could could not not find Gesick" find the the exposures exposures of of iron iron ore, ore! the the local local chief chief "Marji tlMarji Gesickt1 finally finally led led them them to to the the east east shore shore of of Teal Teal Lake, Lake! in in what what is is now now Negaunee. This This location location was was federal federal permit permit Number Number 158, 158! and and was was Negaunee. secured secured by by the the Jackson Jackson Mining Mining Company Company as as Permit Permit Number Number 593, 593! Section Section 1, lt Township Township 47 47 North, North! Range Range 27 27 West, West! on on October October4, 4! 1845. 1845. Their Their intent made intent was was not not to to ship ship iron iron ore, ore! but but to to ship ship iron iron "blooms" llbloomsll made from (Spanish) from charcoal charcoal forges forges of of the the "Catalan" tlCatalanll (Spanish) style style like like those those used time! and and used used in in Europe Europe used in in New New York York and and New New England England at at that that time, for over over 2,000 2t000years. years. They They built built aa townsite townsite on on the the Carp Carp River, River! for along along with with aa dam dam and and the the Forge. Forge. The The first first iron iron blooms blooms were were made made on on February was February 10, lol 1848, 1848! and and "mining" tlminingtl was by by gathering gathering high high grade grade lumps lumps of of ore ore found found on on the the surface surface at at the the Jackson Jackson Mine. Mine. It It was was tough tough going going for for them them and and for for the the other other charcoal charcoal iron iron operations operations that that followed followed them. them. It It soon soon became became apparent apparent to to the the managements managements of of the the mining mining companies, companiest that that the the future future of of the the iron iron industry industry lay lay in in shipping shipping iron iron ore ore rather rather than than the the charcoal charcoal iron iron blooms. blooms. However, However! the the iron iron bloom bloom industry industry limped limped along along in in the the Upper Upper Peninsula Peninsula until until 1898; 1898; over over 1.8 1.8 million million long long tons tons of of processed processed iron iron had had been been shipped shipped from from the the Upper Upper Peninsula. Peninsula. The July! 1849. 1849. The The first first The port port of of Marquette Marquette was was founded founded in in July, iron iron ore ore shipped, shipped! on on July July 7, 7! 1852, 18521 consisted consisted of of six six barrels. barrels. The The opening opening of of the the Sault Sault St. St. Marie Marie locks locks in in June, June! 1855 1855 was was aa great great boon boon to to both both the the infant infant iron iron and and infant infant copper copper mining mining ventures. ventures. Allof the the first first mines mines were were open open pit pit operations operations and were were in All- of in hard iron iron ores. ores. The The hard hard ores ores cropped cropped out out on on hilltops hilltops and and also also hard contained contained enough enough magnetite magnetite to to deflect deflect the the magnetic magnetic compasses compasses where where way! followed followed by by the the Cleveland Cleveland concealed. The The Jackson Jackson Mine Mine led led the the way, concealed. Mines Mines at at the the east east side side of of Ishpeming Ishpeming (Jasper (Jasper Knob), Knob)! the the Humboldt, Humboldtl Republic, Mines on on the the main main Marquette Republicl Champion Champion and and Michigannue Michigame Mines trough, trough! and and the the Isabella Isabella Mine Mine on on the the Cascade Cascade Range. Range. The The first first underground underground mines mines opened opened in in 1868 1868 as as the the miners miners followed followed the the iron iron ore ore in in depth. depth. The The soft soft ores ores in in Negaunee Negaunee were were found found first first at at the the Negaunee Negaunee Mine Mine in in 1873. 1873. The The soft soft iron iron ores ores did did not not crop crop out out because because they they were were easily easily eroded eroded and and were were covered covered by by However! some some soft soft ores ores came came up up varying amounts amounts of of glacial glacial drift. drift. However, varying to ledge ledge surface. surface. to Crude Crude geophysics geophysics by by magnetic magnetic compass compass and and the the dip-needle dip-needle helped helped The diamond diamond drill drill was was developed developed in in locating locating the the iron iron ore ore bodies. bodies. The in in 1876 1876 and and first first employed employed on on the the Marquette Marquette Range Range in in1879. 1879. B- 9 �Mining Mining towns townssprang sprangup uparound aroundthe themines minesin inwhat whatwere weretermed termed fllocations~.Many Many towns townswere were developed developedby by the themining miningcompanies, companies, "locations". with with homes homes and and "boarding—houses" wboarding-houses"subsidized subsidizedby by the thecompanies companiesto to attractemployees. employees. There There was was aa parallelism parallelism between between the thecopper copper attract mining mining companies companiesand and their theirpaternalistic paternalisticefforts effortsto toobtain obtain employees and and retain retainthem, them,and andthe theiron ironmining miningcompanies. companies. Foremost Foremost employees among the the copper copper companies companies was was Calumet Calumet and and Hecla Hecla Consolidated Consolidated among Copper Copper Company Company while while the the foremost foremost iron iron company company was was the the Cleveland Cleveland Iron Iron Mining Mining Company Company (from (from1891 1891 it it was was The The Cleveland-Cliffs Cleveland-CliffsIron Iron Company). C.& C . & H. H. built built the the first firs: hospital hospital in in Calumet Calumet before before the the Company). company paid paid its itsfirst firstdividend. dividend. Cliffs Cliffs also also pioneered pioneered company company company houses,hospitals, hospitals,and andvisiting visitingnurses. nurses. They They had had the the first first houses, pension pension plan plan in in the the Lake Lake Superior SuperiorRegion, Region, the the first firstsafety safety department,and and employed employed thefirst firstcompany companygeologists. geologists. department, the ~ihincrMethods ~ethods Mining On the the Marquette Marquette Range, Range, by by the the 1880's 1880fsalmost almost all all production production On came from from underground undergroundmines. mines. In 1n the the hard hard ore ore mines mines the theprincipal principal came method method was was open openstoping stoping(a (astope stopeis isaa Cornish Cornishword word for foraaroom) room)by by the "room "room and and pillar" pillarwmethod. method. Very Very little little timber timber was was employed employed for for the sloping, ground support. support. In In the the soft soft ore ore mines mines there therewas wassublevel sublevelstoping, ground sublevel sublevel caving, caving,square squareset setmining, mining,and andtop topslicing. slicing. Much Much later, later, the the concept concept of of block block caving caving was was introduced introduced and and used used extensively. extensively. Much Much timber timber was was used used for for ground ground support support in in the the soft soft ore ore mines mines and and One wag said "the best forests of Michigan in the copper mines. "the best forests of Michigan One wag said in the copper mines. are underground." underground. If are The The choice choice of of the the mining mining method, method, and and the the use use of of wood wood or or steel steel supports supports related related directly directly to to the thegeologic geologicconditions. conditions. The The hard hard ores ores were were "competent" NcompetentNand and would would support support an an open open span, span,while while the the soft ores ores did did not not have have that that strength. strength. Other Other factors factors such such as as soft jointing, jointing, ground ground water, water, and and depth depth from from the the surface surface all all entered entered into into both both safety safety considerations considerations and and contamination contamination of of leaner leanermaterial material affecting the the ore ore grade. grade. affecting B-lU �Metallurgical Beneficiation Metallurqical Beneficiation For two two generations, generations, the the Marquette Marquette Range Range iron iron ore ore that that was was For mined and and shipped, shipped, or or used used in in the the charcoal charcoal iron iron industry, industry, was was rich, rich, natural, direct-shipping natural, direct-shipping materials. materials. Both the company the mining company officials and officials and government government geologists geologists recognized recognized that that the the iron— ironformations formations contained contained rich rich bands bands of of iron iron minerals. minerals. The question question was, how how to to separate separate these these bands from the waste or gangue was, materials, materials, essentially essentially the the chert chert or or siliceous siliceous bands. bands. "wellM from from the the Latin) Latin) is is the the process process Beneficiation (to make "well" Beneficiation (to or processes processes used to or to separate separate the the valuable valuable material material from from the the gangue gangue and generally generally consists consists of of several several steps. steps. First First is is to to crush crush and and "liberatew the the valuable valuable grind the the feed feed material material fine fine enough enough to to "liberate" materials, making making them them essentially essentially free free of of the the gangue. gangue. The The next next materials, step step is is to to collect collect and and separate separate the the two two materials materials into into aa "concentrate" of the valuable material from worthless material, wconcentrateN from the the worthless material, the latter the latter called called the the "tails" "tailsw or or "tailings". "tailingsw. The "feedw or or crude crude The "feed" material "headsw. material is is called called the the "heads". This This beneficiation beneficiation process process (or (or processes) processes) is is termed termed "concentrationw. There are are three three principal principal means means of of concentration: concentration: "concentration". There gravity, magnetic, The gravity, magnetic, and and chemical/physical. ~hemical/~hysical~ The gravity gravity process process utilizes the utilizes the differences differences in in specific specific gravity gravity of of the the ore ore minerals minerals in in contrast to This might be contrast to the the gangue. gangue. This be done done with with jigs, jigs, tables, tables, heavy heavy media, media, or or siphonsizers, siphonsizers, to to name name aa few. few. Magnetic Magnetic separation separation applies principally applies principally to to magnetite. magnetite. Chemical/physical seperation separation utilizes utilizes principally principally flotation, flotation, but but could could include include electrostatic electrostatic separation. separation. Flotation Flotation uses uses the the surface surface response response of of various various reagents reagents to to various various minerals. minerals. It possible, in "floatw the the ore ore minerals, minerals, or or It is is possible, in some some instances, instances, to to "float" to float float the the gangue gangue minerals. minerals. It It is is also also possible, possible, in in some some instances, use a instances, to to use a differential differential float float to to separate separate various various ore ore minerals minerals from from one one another. another. Neaaunee Concentrating Concentratinq Works Works Negaunee The The first first commercial commercial concentrating concentrating plant plant on on the the Marquette Marquette Range built on on the the lands lands of of Range was was the the Negaunee Negaunee Concentrating Concentrating Works Works built It used the jaspilite from the North Jackson the Jackson Mine. the Jackson Mine. Jackson Mine, Mine, paying paying aa royalty royalty of of 45 45 cents cents aa ton. ton. The The company, company, organized organized 1881, built a plant 183 feet wide and in 1881, feet long, long, 116 116 feet feet wide and 113 113 feet feet It had a high (nine (nine stories), stories), on on aa rock rock ridge ridge towards towards Teal Teal Lake. Lake. It a 600 horsepower horsepower boiler, 600 boiler, aa boiler boiler house, house, and and an an engine engine house. house. It It In its "CornishN rolls, rolls, and and rotary rotary jigs. jigs. In its first first used aa jaw jaw crusher, crusher, "Cornish" year of year of operation, operation, 1882, 1882, the the plant plant produced produced and and shipped shipped 1,177 1,177 tons tons Production increased of of concentrates. concentrates. Production increased to to 10,394 10,394 tons tons in in 1883. 1883. The The plant plant did did not not operate operate in in 1884 1884 and and 1885, 1885, and and it it closed closed in in 1886, 1886, years ahead years ahead of of its its time. time. Edison's EdisonlsMill, Mill, Humboldt Humboldt The second The second concentrating concentrating plant plant was was built built by by Thomas Thomas A. A. Edison. Edison. He He had patented patented his his electromagnetic electromagnetic separator separator in in 1880 1880 (U.S. (U.S. Patent Patent Number Number 228,329 228,329 on on June June 1, 1, 1880 1880 (see (see Figure Figure F)), F)), after after his his research research Edison looked in in 1879. 1879. Edison looked around around the the iron iron districts districts of of the the United United States States for for an an area area with with magnetic iron iron ores ores and and heard heard of of the the Sampson Sampson Mine (also known known as as the the Edwards Edwards or Mine at at Humnbolt Humbolt (also or the the Argyle Argyle Mines). Mines). He worked with with Walter Walter S. Mallory to to construct construct the the Concentrating Concentrating Plant using magnetic ores and lean ores mined by the Plant using magnetic ores and lean ores mined the Sampson Sampson Edisontsseparator separator was was different different from from the the separators separators of of personnel. Edison's personnel. B-li �(NoModel.) ~ode'l.) (No T.A. A .EDISON. EDISON. T. K a g n e t i c Ore-Separator. Ore-Separator. Magnetic Patented P a t e n t e dJune J u n e 1,1, 1880. 1880. No. 228,329. 228.329. No. y.2. =— — - t: L awn S..r a. B—12 Figure FigureFF �the time timein inthat thatit ithad hadno nomoving movingparts. parts. It It consisted consisted of of aa feed feed the hopper, aa gate, gate,the theunipolar unipolarnon-contact non-contactelectromagnet, electromagnet,aa hopper, partition, partition,and and bins bins for forthe themagnetic magnetic concentrate concentrateand andfor forthe thewast wast material. material. The 1889as asthe theEdison Edison The plant plant was was built built in in 1888 1888and and operated operatedin in1889 Iron Concentrating ConcentratingCompany. Company. It It had had aa Gates Gates jaw jaw crusher, crusher,two two 16 16by by Iron 30 30 Cornish Cornish rolls, rolls,and and screens screenssizing sizing the the feed feed to to20 20mesh, mesh,aagrain grain size for forliberation. liberation. The The iron iron concentrate concentrate analyzed analyzed 62 62to to68 68 size percentiron. iron. The The start—up start-up had had the the usual usual problems problemssuch suchas as percent breakdowns breakdowns of ofthe theprimary primarycrusher crusherand and learning learningthat that20 20mesh meshwas wasnot not fineenough enoughfor forliberation. liberation. The The intermediate intermediateproduct product Edison Edison called called fine nmugwumpw. The The plant plant burned burned in inDecember, December,1890 1890and andwas wasnot notrebuilt. rebuilt. "mugwump". He He said said "Well, "Well, its its all all gone, gone, but but we we had had aa hell hell of of aa good good time time spending it" itN(his (hisinvestment)! investment) ! spending The The third third mill mill to to open open was was that that of of the the Republic RepublicReduction Reduction Company in in1888 1888and and1889; 1889;it itwas wassold soldinin1891. 1891. The Company The Michigamme Michigamme Mine Mine used aa Swedish Swedish"Wenstroin" "Wenstrom" electromagnetic electromagnetic separator separatorstarting startingin in used 1889. Although Although early early results results were were encouraging, encouraging,the theplant plant closed closedin in 1889. 1892. 1892. Minnesota Concentrating ~oncentratina Efforts Minnesota Efforts After After these these early early efforts efforts at at concentration concentrationin in Michigan, Michigan, the the scene shifted shiftedto toMinnesota. Minnesota. In In 1902, 1902, the the first first concentrating concentrating plant plant scene was was built built at at the the west west end end of of the theMesabi Mesabi Range Rangeand and used used the theBiwabik Biwabik Iron-Formationfor forore. ore. Various Various plants plants followed, followed, using using gravity gravity Iron—Formation Professor Edward Edward W. W. Davis, Davis, of of the the vwash-oresw Professor methods on on the the "wash—ores" methods Minnesota Minnesota Mines Mines Experiment Experiment Station, Station,pursued pursued aa vigorous vigorousresearch research program program on on the the magnetic magnetic concentration concentrationof of the themagnetic magnetic portion portionof of the Biwabik Biwabik Iron-Formation, Iron-Formation,starting startingin in1914. 1914. The The Reserve Reserve Mining Mining the Company Company was was organized organized to to mine mine the the magnetic magnetic iron—formation iron-formationand and to to use Davis' Davistideas ideasfor forconcentration. concentration. The The plant plant operated operated in in the the use 19201s,but but closed closed due due to to two two principal principal problems: problems: (1) (1)the the 1920's, difficulty difficulty of of drilling drilling blast blast holes, holes, and and (2) (2)the the high high cost cost of of concentration concentration while while competing competing with with low low cost, cost, open open pit pit mined mined natural natural . . ores. ores. The The idea idea was was revived revived in in the the 1940 1940 by by Professor Professor Davis, Davis,who who had had continued to to work work on on the theproblem. problem. The The Reserve Reserve Mining Mining Company Company was was continued reorganized reorganized and and their theirfirst firstplant plantconuuenced commenced operations operations after afterWorld World I1 on on the the "taconite" '%aconitet'iron-formation. iron-formation. Shortly Shortly after, after, the the fine fine War II War grained grained concentrate concentrate was was agglomerated agglomerated or or pelletized pelletized at at Reserve Reserve Mining. Mining. Michicran Low Low Grade Grade Ores Ores Michigan During During World World War War II, 11, Cleveland Cleveland Cliffs Cliffs investigated investigated various various low low grade grade iron—formations iron-formations that that could could be be amenable amenable to to commercial commercial concentration. The The research research was was directed directed into into two two areas: areas: (1) (1) the the concentration. Bijiki Bijiki Iron—Formation Iron-Formation west west of of Michigamme, Michigamme, and and (2) (2) the the hard hard ore ore jaspilite jaspilite iron-formation iron-formationat at the theold old hard hard ore oremines. mines. The tested well of Michiganune Michigamme tested well in in terms terms of of heavy heavy The Ohio Ohio Mine Mine west west of The opening opening of of two two open open pits pits and and the the media concentration. concentration. The media construction construction of of aa concentrator concentrator started started in in 1951. 1951. The The first first concentrates concentrates were were produced produced in in May, May, 1952. 1952. The The plant plant operated operated until until September, long tons tons of of September, 1960 1960 producing producing aa total total of of 747,729 747,729 long concentrate. This This is is not not significant significant by by today's today's standards, standards,but but it it concentrate. marked marked aa dramatic dramatic shift shift from from underground underground mining mining to to the the new new era era of of open pit pit mining mining and and concentration. concentration. open B-13 �- The The jaspilite, jaspilite, or or "jasper" "jasperN as as Cliffs Cliffs called called it, it, was was being being investigated at at the the Humboldt Humboldt and and Republic Republic Mines. Mines. The investigated The mode mode of of concentration was was to to float float the the specular specular hematite hematite and and magnetite magnetite in in concentration fatty acids. acids. The The Humboldt Humboldt plant plant was was built built in in 1952 1952 as as aa joint joint fatty venture of of Ford Ford Motor Motor Co. Co. and and Cliffs, Cliffs, the the same same year year the the Ohio Ohio Mine Mine venture opened. The The first first concentrates concentrates were were produced produced in in 1954, 1954, but but no no form form opened. of agglomeration agglomerationwas was used. used. of Work Work had had gone gone ahead ahead at at the the Republic Republic Mine Mine and and its its first first concentrates concentrates ere wereproduced producedin in1956, 1956,using using the the same same flow flow sheet sheet as as the Humboldt Humboldt Mine. Mine. The The Republic Republic Mine Mine concentrates concentrates were were shipped, shipped, the starting starting also also in in 1956, 1956, to to Eagle Eagle Mills, Mills, east east of of Negaunee, Negaunee, to to aa This plant had its Straight Grate Plant to be pelletized. Straight Grate Plant to be pelletized. This plant had its share share of of problems, and and Cliffs Cliffs looked looked to to aa different differentprocess. process. problems, Cliffs Cliffs worked worked with with Allis-Chalmers Allis-Chalmers Manufacturing Manufacturing Co. Co. of of Milwaukee Milwaukee to to adapt adapt the the Grate-Kiln Grate-Kiln process, process, used used in in making making cement, cement, to produce produce iron iron concentrates. concentrates. This This was was aa first first in in the the world-wide world-wide to iron ore ore technology. technology. This Humbolt This process process was wasfirst firstapplied appliedatatthe theHuiubolt iron Mine with with two two identical identical "lines" "lineswin in1960. 1960. AA second second plant plant was was Mine started at at the the Republic Republic Mine Mine in in 1962. 1962. started The The Empire Empire Mine, Mine, south south of of Negaunee Negaunee and and west west of of Palmer, Palmer, was was aa magnetite rich rich iron-formation. iron-formation. Test Test work work included included the the development development magnetite of autogenous autogenous grinding grinding (self (self grinding) grinding) mills mills and and aa combination combination of magnetic separation separation and and gravity gravity methods. methods. Later, Later, flotation flotation was was magnetic added as as the the final final step. step. The The concentrates concentrates were were pelletized pelletized by by the the added The first concentrates and pellets were ACL Grate-Kiln system. The first concentrates and pellets were ACL Grate—Kiln system. produced in in December, December, 1963. 1963. produced The The Pioneer Pioneer Pellet Pellet Plant Plant was was started started in in 1964 1964 to to pelletize pelletize Mather Mine Mine underground underground ores. ores. This This improvement improvement in in product, product, Mather appealed appealed to to the the steel steel plants plants and and resulted resulted in in keeping keeping this this last last underground mine mine operating operating until until 1979. 1979. underground The Tilden Tilden Mine Mine had had been been an an open open pit pit operation operation producing producing aa The special special grade grade of of iron—formation iron-formation called called siliceous siliceous ore ore for for use use in in the the open-hearth furnace. furnace. Years Years had had been been spent spent on on metallurgical metallurgical open—hearth "break through" through" occurred occurred in in April, April, 1967 1967 from from aa research. But But aa "break research. joint joint research—development research-development venture venture of of Cliffs Cliffs and and the the U.S. U.S. Bureau Bureau of of The mode of concentration developed Mines at Minneapolis. The mode of concentration developed was was Mines at Minneapolis. "selective flotationH to to recover recover the the non—magnetic non-magnetic "selective flocculation flocculation flotation" The plant and pit were built in hematite and goethite. The plant and pit were built in1972-1974. 1972-1974. hematite and goethite. The first first pellets pellets were were produced produced in in December, December,1974. The 1974. The The initial initial pit pit and and plant plant at at the the Tilden Tilden Mine Mine was was sized sized at at 4.0 4.0 million million long long tons tons of of pellets pellets per per year, year, and and was was known known as as Tilden Tilden I. I. Provision Provision had had been been made made in in the the design design for for doubling doubling the the capacity capacity to to 8.0 8.0 million million tons tons per per year, year, or or even even to to 12.0 12.0 million milliontons tonsper peryear. year. The I1 and and it it commenced commenced The decision decision was was made made to to build build Tilden Tilden II operations in in 1979. 1979. operations The Empire Empire Mine Mine had had had had aa similar similargrowth. growth. Empire The Empire II started started in in 1963, 1963, Empire Empire II I1 in in 1966, 1966, Empire Empire III I11 in in 1974, 1974, and and Empire Empire IV IV in in 1980. 1980. This This brought brought the the annual annual capacity capacity of of each each plant plant to to 8.0 8.0 million million tons tons ftstandbytf per year. year. The The Republic Republic Mine Mine pit pit and and plant plant have have been been on on aa "standby" per basis since since1983. 1983. basis Pellet Pellet shipments shipments for for1987 1987were: were: 7,417,703 long long tons tons Empire Empire Mine Mine 7,417,703 Ti1n Mine 4,458,620long longtons tons Tilc'en Mine4,458,620 B— 14 �In the Tilden In 1987 1987 the Tilden Mine faced faced economic economic necessities necessities and and quality quality product review, review, and and concluded concluded that that aa new new open open pit pit source source of of magnetic ore magnetic ore needed needed to to be be developed developed to to replace replace the the present present open open pit pit mining of mining of hematite hematite and and goethite goethite material. material. A source source of of magnetic magnetic material was material was known known on on the the Cliffs Cliffs Drive, Drive, and and necessary necessary permits permits are are being sought. being sought. The Gogebic Gogebic Range, Range, the The the last last iron iron range range found found in in the the Upper Upper Peninsula, Peninsula, was was the the first first closed, closed, followed followed by by the the Menominee Menominee Range, Range, the Marquette Marquette Range Range active leaving today only the active in in the the Upper Upper Peninsula. Thus, the Marquette Range is Peninsula. Thus, the Marquette is still still alive alive and and continuing, 144 continuing, 144 years years after after its its discovery. discovery. 3-15 �Institute Institute of of Lake Lake Superior Superior Geology Geoloay FIELD FIELD TRIP TRIP No. No. 22 Marquette Marquette Mineral Mineral District District of of Michigan Michigan with with emphasis emphasis on on MINING HISTORY HISTORY and and GEOLOGY GEOLOGY led led by Burton Burton Boyumu Boyum Robert Robert C. C. Reed Reed and and Win. Kangas Wm. Kangas May, May, 1988 1988 The The KEY KEY MAP, MAP, Figure Figure 1, 1, provided provided through through the the courtesy courtesy of of Cleveland-Cliffs, Cleveland-Cliffs, Inc. Inc. B- 16 �H I— Witch LOh. \. CS 4 "I' lop.. DHfL.â. Key Map SiII Soft Ore STATE OF MICHIGAN No. 2 — May, 1988 FootwaII Soft Ore .MAP LOCATION to Field Trip Hord Ore Marquette Iron Range Figure I Sold Nit.. 0 SCALE 2 IN MILLS 1 3 Lok# S&.•fs•r �••1 AcJ<ermanlith.3?9.BtOadWay NY. VIEW VIEW NEAR NEAR CARP CARTRIVER, RIVER.LAKE LAKE SUPERIOR. SUPERIOR B-18 Figure Figure 22 �I k r / B-19 Figure Figure 33 �STOP 11 (Fig. (Fig. 22 and and 3)-3)-- MARQUETTE MARQUETTE HARBOR HARBOR STOP The The port port city city of of Marquette Marquette was was established established July July 10, 10, 1849, 1849, as as Worcester, the the name name of of the the home home city city of of Mr. Mr. Waterman Waterman A. A. Fisher, Fisher, aa Worcester, Figure textile mill mill owner owner of of Worcester, Worcester, Massachusetts. Massachusetts. Figure 22 shows shows aa textile scene of of the the harbor harbor in in 1851, 1851, taken taken from from Foster Foster and and Whitney Whitney (1851). (1851). scene Figure Figure 33 shows shows the the charcoal charcoal bloomery bloomery of of the the Marquette Marquette Iron Iron Company Company and aa part part of of the the community community in in 1852, 1852, as as seen seen from from Ripley's RipleytsRock. Rock. and This This is is the the oldest oldest known known photograph photograph of of Marquette, Marquette, as as the the name name was was changed in in 1851. 1851. changed Mr. Fisher Fisher was was the the principal principal financer financer of of the the Marquette Marquette Iron Iron Mr. Company, which which was was promoted promoted by by Mr. Mr. Robert Robert Graveraet. Graveraet. Although Although the the Company, company had had no no mines, mines, it it built built aa charcoal charcoal iron company iron bloomery bloomery on on the the shore of of Lake Lake Superior, Superior, using using ore ore from shore from the the Jackson JacksonMine. Mine. Previously, in in 1847, 1847, the the Jackson Jackson Mining Mining Company Company had had constructed constructed aa Previously, building in in this this area area for for both both aa habitation habitation and and aa storehouse. storehouse. The building The eastern backers backers of of the the Marquette Marquette Iron Iron Company Company soon soon lost lost interest interest in in eastern the venture venture and and they they sold sold out out to to the the Cleveland Cleveland Iron Iron Mining Mining Company Company the in 1853. 1853. The The plant plant was was destroyed destroyed by by fire fire in in 1853 1853 and and was was not not in rebuilt rebuilt because because the the Cleveland Cleveland Iron Iron Co. Co. was was putting putting its its emphasis emphasis on on shipping shipping ore ore promoted promoted by by the the start start of of construction construction of of the the Sault Sault Ste. Marie Marie (SOO) (SOO) Locks Locks Agitation Agitation had had gone gone on on for for years years to to build build Ste. locks at at the the SOO, SOO, because because all all passengers passengers and locks freight had to portage and freight had to portage around the the rapids rapids each each way. way. On On August August 26, 26, 1852, 1852, U.S. U.S. President President around Millard Fillmore Fillmore signed signed aa bill bill authorizing authorizing the the construction construction of of Millard locks and and aa canal. canal. locks The The first first water water was was let let into into the the system system on on April April 19, 19, 1855, 1855, but but vessel to to lock there were were leaks leaks to to be be reparied. reparied. The The first. first vessel lock through through there was on wIllinoisn,going going "upbound", ttupboundtt, on June June 18th. 18th. The The was the the steamer steamer "Illinois", brigantine "Columbia" flColumbiaHcarried carried the the first first cargo cargo of of iron iron ore, ore, brigantine in amounting to to 132 132 tons, tons, "downbound" ttdownboundtt in August, August, 1855. 1855. Thus, Thus, amounting Marquette became became the the first first iron iron ore ore port port in in the the Great Great Lakes. Lakes. AA Marquette total total of of 1447 1447 tons tons of of iron iron ore ore was was shipped shipped from from Marquette Marquette Harbor Harbor in in that first first year, year, all all by by the the Cleveland Cleveland Iron Iron Mining Mining Company. Company. that The The Cleveland Cleveland Iron Iron Company Company built built its its first first ore ore dock dock in in 1855. 1855. The The Lake Lake Superior Superior Iron Iron Company, Company, Samuel Samuel P. P. Ely, Ely, Agent, Agent, built built their their ore dock dock next next to to them them in in 1857, 1857, but but used used aa radically radically different different ore The Lake Superior Iron Co. dock was 25 feet above design. The Lake Superior Iron Co. dock was 25 feet above the the design. "pocketsNto to hold hold the the ore ore and and chutes chutes to to drop drop the the ore ore water and and had had "pockets" water onto onto the the deck deck or or into into the the hold hold of of vessels. vessels. This This was was the the first first ore ore dock with with pockets pockets built built in in the the world! world! dock . . STOPS 22 (Fig. (Fig. 4)--KONA DOLOMITE DOLOMITE and and COPPER COPPER MINERALIZATION MINERALIZATION STOPS This This is is the the middle middle member member of of the the Chocolay Chocolay Group. Group. It It is is crystalline essentially essentially aa fine fine to to medium medium grained, grained, pink pink to to gray, gray, crystalline siliceous siliceous dolomite dolomite with with some some interlaminated interlaminated argillaceous argillaceous and and Hematite staining staining locally locally gives gives the the rock rock aa arenaceouaphases. phases. Hematite arenaceou pinkish to to reddish reddish hue. hue. Locally, Locally, there there are are large large domal domal algal algal pinkish structures in in the the Kona. Kona. One One classic classic locality locality alongside alongside U.S. U.S. structures Highway 6, T47N, T47N, R24W, R24W, has has been been visited visited by by countless countless Highway 41, 41, in in Section Section 6, geologists; we have have chosen chosen this this series series of of exposures exposures to to geologists; however, however, we show the the algal algal structures. structures. show B-20 �JS JS • JACOBSVILLE JACOBSVILLE SANDSTONE SANDSTONE _UflCOflfOrmity — .Unconformity. SS SS •= SIAMO SIAMO SLATE SLATE Loke ' I MARQUETTE MARQUETTE SYNCLINORIUN SYNCLINORIUM AQ AQ • AJI8IK AJIBIK QUARTZITE QUARTZITE WS WS • WEWE WEWE SCHIST SCHIST KO K O •= KONA KONA DOLOMITE DOLOMITE MQ MQ Superior = MESNARD MESNARD QUARTZITE QUARTZITE EL E L • =ENCHANTMENT ENCHANTMENT LAKE L A K E FM. FM. _Unconformity_ AJnconformity. CCG= COMPEAU COMPEAU CREEK CREEK ONEISS GNEISS CCGa MS MONASCHIST SCHIST M S •* MONA STRATIGRAPHICCONTACT CONTACT --—. STRATIGRAPHIC - - - 44_, Js __-__— '.-' —, lCD —. FAULT CONTACT FAULT CONTACT — . -'. — — — j4tc—:— — FIGURE 44 FIGURE G E N E R A L GEOLOGY G E O L O G Y OF OF GENERAL E A S T E R N PORTION P O R T I O N OF O F THE THE EASTERN MARQUETTE M A R Q U E T T E SYNCLINORIUM SYNCLINORIUM STOP 2 0 t 2 k- After Gair Gatr and and Thadan, Taylor,p972 1972 After Thad.n, 1968, 968. Toylor �Copper Mineralization: Mineralization: A.R. A.R. Renfro Renfro wrote wroteininEconomic EconomicGeolociy, Geoloqv, Copper (1974): "Recently "Recently discovered sedimentary sedimentary and geochemical geochemical processes processes of coastal coastal Sabkhas Sabkhas provide provide the the foundation foundation for for aa hypothesis hypothesis that that of successfully successfully explains explains the the genesis genesis of of these these (copper) (copper) deposits". depositstt. "Coastal sabkhas sabkhas are are evaporite evaporite flats flats that that form form along along the the subaerial subaerial "Coastal landward margins margins of of regressive regressive seas. seas. Because Because of of their their unique unique landward position, coastal coastal sab]thas sabkhas are subsurface flow flow of of position, are nourished nourished by subsurface landward-migrating, Fh-high pH pH sea sea water water and and by by seawardseawardlandward-migrating, low low Eh-high migrating, migrating, high high Eli-low Eh-low pH terrestrial terrestrial water. water. Commonly Commonly they they are are bordered bordered on on the the seaward seaward side side by by intertidal intertidal mudflats mudflats nad nad lagoons lagoons that are are carpeted carpeted by by leather-like leather-like mats mats of of sediment-binding, sediment-binding, bluebluethat green green algae. algae. Fetid Fetid ooze ooze consisting consisting of of interbedded interbedded decaying decaying algae algae and and detrital detrital sediment sediment occurs occurs immediately immediately beneath beneath the the living living algal algal "Coastal sabkhas sabkhas and and their their related related evaporite evaporite facies facies prograde prograde mat." "Coastal seaward seaward across across adjacent adjacent algal-mat algal-mat facies. facies. Upon Upon banal, barial,the the algalalgalmat mat facies facies becomes becomes saturated saturated with with hydrogen hydrogen sulfide sulfide generated generated by by anaerobic bacteria. bacteria. Concurrently, Concurrently, the the trailing, trailing, landward landward edges edges of of anaerobic elastics of of coastal sabkhas sabkhas are are buried buried by by prograding prograding ternigenous terrigenous clastics coastal the desert. desert. As As sabkhas sabkhas migrate migrate basinward, basinward, terrestrial—formation terrestrial-formation the water water eventually eventually must must pass pass upward upward through through the the buried, buried, strongly strongly reducing reducing algal—mat algal-mat in in order order to to reach reach the the surface surface of of evaporation." evaporation.If "Terrestrial-formation wTerrestrial-formationwater water initially initially has has low low pH pH and and high high Eh, Eh, and and thus thus can can mobilize mobilize and and transport transport trace trace amounts amounts of of such such elements elements as as copper, copper, silver, silver, lead, lead, and and zinc. zinc. As As terrestrial—formation terrestrial-formation water water passes passes through through the the hydrogen hydrogen sulfide-charged sulfide-charged algal-mat, algal-mat, its its load load of of solute solute metals metals is is reduced reduced and and precipitated precipitated interstitially interstitially as as sulfides." sulf ides." The ides in in the the Kona Kona dolomite dolomite are bornite, bornite, chalcopyrite, The suif sulfides chalcopyrite, Estimates suggest suggest aa potential potential of of 250 250 million million tons tons of of and pyrite. pyrite. Estimates and mineable material. material. This This potential potential was was not not recognized recognized until until about about mineable 1896. Early Early prospectors prospectors in in the the area area included included Julian JulianCase, Case,J.M. J.M. 1896. Wilkinson, and and Andrew Andrew Pings. Pings. Interest Interest in in the the Longyear, James James Wilkinson, Longyear, sulfide mineralization in sulfide mineralization in the the Kona Kona died died out out by 1898, 1898, but but was was renewed renewed in in the the 1970's, 1970fs,with with drilling drilling and and mapping mapping by by several several groups. groups. Mineralization Mineralization is is not not readily readily seen seen in in place, place, but but diamond diamond drill drill core core and and hand hand specimens specimens will will be be shown. shown. 5)--MORGAN STOP STOP 33 (Fig. (Fig. 5) --MORGAN FURNACE FURNACE As As noted noted in in the the Introduction, Introduction, many many of of the the early early developers developers of of the the Marquette Marquette Iron Iron Range Range had had the the concept concept of of shipping shipping the the iron iron as as blooms blooms rather rather than than as as ore. ore. As As is is typical, typical, commercial commercial development development The Iron Iron sprang were developed. developed. The sprang up up along along the the railroads, railroads, as as they they were Mountain Mountain Railroad Railroad was was incorporated incorporated February February 22, 22, 1855 1855 and and commenced commenced operations operations in in 1857. 1857. It It was reincorporated reincorporated February February 6, 6, 1857, 1857, as as the the Marquette and later later as as the the Marquette, Marquette, Marquette and and Ontonogan Ontonogan Railroad, Railroad, and Houghton Houghton and and Ontonogan Ontonogan Railroad Railroad (M.H.& (M.H.& 0.), O.), followed followed by by the the Duluth, Duluth, South South Shore Shore and and Atlantic Atlantic Railroad Railroad (D.S.S.& (D.S.S.& A.); A.); it it is is now now known known as as the the Soo Soo Line Line Railroad. Railroad. AA Mr. Mr. Schweitzer Schweitzer started started aa grist grist mill mill along along the the line line some some eight eight miles west west of of Marquette Marquette in in aa favorable favorable location location adjacent adjacent to to the the Little Little Carp Carp River River (later (later renamed renamed Morgan Morgan Creek). Creek). Mr. Mr. Cornelius Cornelius Donkersley, Donkersley, active active in in the the railroad, railroad, felt felt this this was was aa good good site site for for aa The Ely family of Rochester, New York, wealthy charcoal charcoal furnace. furnace. The family Rochester, York, wealthy flour flour milling people, people, had taken taken an an interest interest in in the the Marquette Marquette Range Range B- 22 �Morgan in 1$83. MorganFurnace. Furnace.Built Built in 1S63. Figurn 5 B-23 Figure Figure 55 �in the the early early 1850's. 1850's. They They encouraged encouraged Donkersley Donkersley and and financed financed the the in development. The The good good friend friend and and legal legal counsel counsel for for the the family family was was development. Lewis Henry Henry Morgan. Morgan. From From the the beginning, beginning, Morgan Morgan had had advised advisedthem, them, Lewis and he he also also invested invested in in the the development. development. Starting Starting in in1856, 1856, and Donkersley had had cleared cleared the the land land and and built built houses houses for for his his workers. workers. Donkersley The Morgan Morgan Iron Iron Company Company was was incorporated incorporated July July 1, 1, 1863, The 1863, and and had had an an initial capitalization capitalization of of $50,000, $50,000, made initial made up up of of 2,000 2,000 shares shares at at $25 $25 each. The The Ely Ely family family joined joined Morgan Morgan in in this this venture. venture. Annual Annual each. production for for the the company company was was (in (intons): tons): production 1863 337 1868 4023 4023 1873 6324 6324 1873 1868 337 1863 1864 4023 4023 1869-out of of blast blast 1874 1874 5973 5973 1869—out 1864 1875 1865 3489 3489 1870 5952 5952 1875 5377 5377 1870 1865 1876 1866 3749 3749 1871 4755 4755 1876 3278 3278 1871 1866 663 1877 1867 5057 5057 1872 4356 4356 1877 663 1872 1867 Total production production of of 57,573 57,573 tons tons Total Lewis Lewis H. H. Morgan Morgan is is noteworthy noteworthy not not only only for for his his role role with with the the railroads and and with with the the furnace furnacecompany, company,but but also alsoas asaanaturalist. naturalist. railroads He spent spent aa number number of of summers summers on on the the Marquette Marquette Range Range observing observing the the He beaver. His His treatise, treatise, "The "The American American Beaver", Beaveru,was was remarkable, remarkable, and and beaver. established him him as as an an authority authority whose whose works works are arestill stillrespected. respected. established STOP 4--MICHIGAN 4--MICHIGAN IRON IRON INDUSTRY INDUSTRY MUSEUM MUSEUM STOP This is This is the the newest newest of of the the State State of of Michigan Michigan historical historical museums museums outgrowth of of aa community community effort effort dating dating back back to to 1973. 1973. AA and is is the the outgrowth and Michigan Michigan non-profit non-profit corporation, corporation, the the Carp Carp River River Forge Forge Bi-Centennial Bi-Centennial Park, organized organized an an effort effort to to honor honor the the Carp Carp River RiverForge. Forge. It Park, It raised raised In time, it joined money and and purchased purchased land land for forthis thispurpose. purpose. In time, it joined money forces with with the the Bureau Bureau of of History, History,Michigan Michigan Department Departmentof ofState, State, forces and had had the the cooperation cooperation of of The The Cleveland-Cliffs Cleveland-Cliffs Iron Iron Company. Company. The and The result became became this this Museum. Museum. Ground Ground breaking breaking was was in in July July 1986 1986 and and result dedication of of the the museum museum took took place place on on May May 16, 16,1987. 1987. dedication A. Tour Tour of of Museum Museum and and Rest Rest Stop. Stop. A. B. Convene Convene in in Frank Frank G. G. Matthews, Matthews, Sr. Sr. Memorial Memorial Museum Museum B. Remarks Remarks by by Tom Tom Friggens, Friggens, Director, Director, followed followed by by aa brief brief audial-visual program. program. audial—visual C. Solar Solar compass compass demonstration demonstration (rain (rainor or shine). shine). C. The The Historical Historical Introduction Introduction has has already already commented commented on on William William Austin Burt Burt and and his his solar solarcompass. compass. Attached NotesAttached is is Historical Historical NotesAustin Number One, One, which which provides provides more more detail. detail. Also Also demonstrated demonstrated is is aa sun sun Number dial dial compass, compass, probably probably more more used used by by field field geologists geologists than than the the Solar Solar Compass. Compass. STOP 55 (Fig. (Fig.6)--NEGAtJNEE 6)--NEGAUNEE HIGHWAY HIGHWAY CUT CUT STOP This This series series of of road road cut cut exposures exposures along along U.S. U.S. Highway Highway 41 41 contains, over a short distance, the Mesnard Quartzite, contains, over a short distance, the Mesnard Quartzite, basal basal to to the Ajibik Quartzite, Quartzite, basal basal to to the the Menominee Menominee the Chocolay Chocolay Group; Group; the the Ajibik Group; Group; and and the the Siamo Siamo Formation, Formation, the the middle middle member member of of the the Menominee Menominee To the northwest, along the north side of the hill is To the northwest, along the north side of the hill is aa Group. Group. thin (one (one meter) meter) basal basal conglomerate. conglomerate. The The Kona Kona Dolomite Dolomite pinches pinches out out thin just to to the the east east of of these these exposures. exposures. just The The Mesnard Mesnard Formation Formation is is aa thick, thick,vitreous vitreous quartzite, quartzite, Numerous generally generally light light gray, gray, but but sometimes sometimeswith with shades shadesof ofpink. pink. Numerous veins and ripple ripple marks marks and and veins of of quartz quartz and and hematite hematite cut cut the the bedding, bedding, and This is is the the only only member member of of the the crossbedding are are also also present. present. This crossbedding D - �B-25 Figure 6 85 J% - - .- .;'S• --. ... -— 4 q — •.: ., C' ... . faA- — —-... 3 67 :f iç 6 50 - mn p95' I I I 0 — - — - I 8 ks I38' 'Lii1 r • ;) ... NPC ms 80 .- -. %_' ml 1 — A / SS —: - / -' — ' _4.4;-/99 j I Q - 2 -/ . '. - o - - -. flO N 45 ..- .s -4— ,,. 1 mm __ • COJNTY i3 ( 13M FIGURE 6 — -. J%8¼ . :< APR PORT •1I MING : .— bi . .. 83_4zrn 'jr- I ,'-----z - 8 —' kd 87_( md 6re' , ms 4 /, 6O) / Mi1 507 — ) * /f1 - — / 80X- e1;— '. 9 ç"8O8ft4 _ ? e sJ1'; ' '- J/ /4O8, . :.. —.-..- k -. r7L 25 - ' ______ �Chocolay Group Group to tobe be found foundthis thisfar farwest. west. Perhaps Perhaps the the other other Chocolay members were were eroded eroded here here before before deposition depositionof ofthe theMenominee MenomineeGroup, Group, members or they they were were not not deposited deposited this this far far west west from from their their principal principal area area or of deposition. deposition. of The Ajibik Formation Formationis is found The Ajibik found in in the the next next series seriesof of outcrops outcrops to the thesouth. south. It It is is massive massive quartzite quartzite with with minor minor amounts amountsof of to argillaceousand and conglomeratic conglomeraticmaterial. material. In In appearance, appearance,the the Ajibik Ajibik argillaceous resemblesthe the Mesnard Mesnard Quartzite. Quartzite. Present Present in in the the quartzite quartzite is is aa resembles distinctive concentric concentric staining staining similar similar to to Liesegang Liesegang rings. rings. Also distinctive Also present locally, locally,are aredistinctive distinctivegreenish greenishgranules. granules. present The Siamo SiamoFormation Formationconsists consistsof of dark dark gray gray to to light lightgray gray The argillite,slate, slate,graywacke graywackeand andquartzite. quartzite. Slaty Slaty cleavage cleavageis is argillite, common to to conspicuous. conspicuous. Locally, Locally, there there are are carbonate carbonate rich rich layers layers common and beds beds of ofconglomerate. conglomerate. Also clasticdikes dikescomposed composed Also present present are are clastic and of material material similar similarto tothe thegraywacke graywackebeds. beds. The of The contact contactof of the the Siamo Formation Formation with with the the Negaunee Negaunee Iron Iron Formation Formation is isnot not exposed exposed Siamo here, but but it it lies liesjust just south south of of the the Negaunee Negaunee Branch Branch Bank. Bank. here, Also of of interest interestis isthe the Miners' Miners1Park Parkwith with the thepyramidal pyramidal Also monument located located on on the the west west side side of of U.S. U.S. Highway Highway 41. 41. The The monument monument monument was erected erected originally originally by by the the Jackson Jackson Iron Iron Mining Mining Company Companyin in1905 1905 was before the the company company was was sold sold to, to, and and assimilated assimilatedinto, into,the the before Cleveland-CliffsIron IronCompany. Company. Because Because the the monument monument was was erected erected Cleveland—Cliffs "Cornish Town", Townw,now now an an area area of of potential potential subsidence subsidence from from first in in "Cornish first the Shaft, the deep deep underground underground mining mining of of the the Mather Mather Mine Mine "B" l@Btt Shaft,it it was was taken apart, apart, each each stone stone marked, marked, moved, moved, and and reassembled reassembled on on the the taken present site siteby by Cleveland—Cliffs, Cleveland-Cliffs,at atits itsexpense. expense. present STOP 6--BURT 6--BURTSURVEY SURVEYMARKER MARKER (NE (NECORNER, CORNER,SECT.1, SECT.1,T47N, T47N,R27W) R27W) STOP This This brief brief stop stop is is adjacent adjacent to to the the Don Don Tresedder Tresedder Insurance Insurance Agency, 109 109 U.S. U.S. 41 41 W. W. at at the the northeast northeast corner corner of of the the section sectionwhere where Agency, William William Austin Austin Burt Burt commenced commenced his his survey survey of of the the Town Town Line Line between between Ranges 26 26 and and 27. 27. On On the the morning morning of of September September 19, 19, 1844, 1844,he he and and his his Ranges party party went went south south and and discovered discovered the the first first iron iron ore ore of of the the Marquette Marquette Range. The The marker marker was was erected erected by by the the Marquette Marquette County County Historical Historical Range. Michigan's Sesquicentennial. Sesquicentennial. Society in in 1987 1987 as as part part of of Michigan's Society STOP STOP 77 (Fig. (Fig. 7)--RAILWAY 7)-RAILWAY STREET STREET UNOXIDIZED UNOXIDIZED IRON-FORMATION IRON-FORMATION This This series series of of railroad railroad cuts cuts is is ideal ideal to to examine examine the the unoxidized, unoxidized, primary, primary, cherty, cherty, iron iron carbonate carbonate iron—formation. iron-formation. Structurally, Structurally, it it is is located located in in the the faulted faulted section section that that passed passed It is is on on the the north north through through the the Negaunee Negaunee Mine Mine Number Number Three ThreeShaft. Shaft. It dipping limb limb of of the the Athens Athens Enginehouse EnginehouseAnticline. Anticline. dipping Although Although this this section section is is unoxidized unoxidized except except for for recent recent alteration, Several alteration, it it lies lies just just above above aa high high grade grade iron irondeposit. deposit. Several thin intrusivescan can be be seen seenin in this thisexposure. exposure. thin sill—like sill-like intrusives Worthy Worthy of of note note is is the the westward westward plunging plunging zone zone of of gypsum; gypsum; the the Figure 77 shows shows the the structure structure gypsum gypsum was was formed formed after after the the iron iron ore. ore. Figure of of the the zone zone in in plan, plan, together together with with an an east-west east-west longitudinal longitudinal section, looking looking north. north. The The ore-enrichment ore-enrichment extended extended down down the the section, syncline through the the Tracy Tracy Mine, Mine, the the Lucky Lucky syncline from from the the Regent Regent Group, Group, through The Lucky Lucky Star Star Star Star and and Athens Athens Mines, Mines, to to the the Bunker Bunker Hill Hill Mine. Mine. The "Orebody" and ItOrebodytt and the the first first three three levels levels of of the the Athens Athens Mine Mine were were never never mined mined because because of of their their high high sulfur sulfur(gypsum) (gypsum)content. content. The The enrichment enrichment under under the the railway railway street street was was also also high high in insulfur. sulfur. This This B-26 �FIGURE FIGURE 77 PLAN MAP MAPAND ANDCROSS CROSS SECTION SECTION -- STOP STOP 77 PLAN PLAN PLAN MAP MAP -\ '' '. Unoxidized Iron - Formajion - LONGITUDINAL LONGITUDINAL CROSS CROSS SECTION SECTION- LOOKING LOOKINGNORTH NORTH Lucky Lucky Star StarMine Mine Athens Mine Mine Athens k. - Iron- Format/on Formation Iron High Sulfer BOre" $iamO for a B-27 D-II'c Figure Figure 77 �condition condition existed existed also also in in the the upper upper levels levels of of the the Mather Mather Mine. Mine. The The post-ore post-ore interstitial interstitial fillings fillings of of gypsum, gypsumf calcite, calcitefand and sometimes sometimes dickite dickite and(or) and(or) halides halides have have been been found found on on the the Gogebic Gogebic Range, Rangefat at Elyf Minnesota, Minnesotafand and at at the the the Zenith Zenith Mine Mine in in the the Ely Ely trough trough at at Ely, the Steep Rock Rock Mine Mine at at Atikokan, AtikokanfOntario. Ontario. The The latter latter mine mine also also had had Steep some arsenic arsenic minerals. minerals. some STOP STOP 8--JACKSON 8--JAC?<SONGROVE: GROVE: PASTY PASTY LUNCH LUNCH AND AND REST REST STOP STOP The Pasty, Pastyf as as aa meal, mealf is The is aa Cornish Cornish traditional traditional miner's minerfslunch. lunch. It was was developed developed as as aa "package" ffpackageff that the the miner miner could could take take underunderIt that ground and and even even reheat reheat with with aa candle candleunder underhis hisshovel! shovel! It ground It continues continues to to be be aa favorite favorite around around the the world world wherever wherever the the Cornishmen Cornishmen have gone. gone. have STOP 8--SOUTH 8--SOUTH JACKSON JACKSON MINE: MINE: MAGANESE MAGANESE MINERALS MINERALS STOP The The South South Jackson Jackson Mine Mine Pit Pit is is in in aa completely completely different different geologic geologic setting setting from from that that of of the the North North Jackson Jackson Mine. Mine. The The latter latter mine was was in in high high grade grade hard hard ore. ore. The The South South Jackson Jackson Mine Mine was was in in mine intermediate oref like like that that intermediate (iron (ironcontent) content) grade, gradefsoft softore. ore. This This ore, of of the the Lucy Lucy Mine Mine to to the the east, eastf was was high high in in manganese, manganesef principally principally as as The ores ores from from these these mines mines were were the the only only manganite and and pyrolusite. pyrolusite. The manganite There ones ones on on the the Marquette Marquette Range Range to to be be high high in in manganese manganese There were were exotic exotic manganese manganese minerals minerals found found at at the the Champion Champion Mine, Minef such such as as manganiferous manganiferous garnets, garnetsfbut but The The Champion Champion Mine Mine was was in in aa different different geologic geologic setting, settingf both both structually structually and and in in terms terms of of metamorphic metamorphic . grade. grade. . I STOP 10--JASPER 10--JASPER KNOB. KNOB, ISHPEMING ISHPEMING STOP This This is is aa wonderful wonderful exposure exposure of of Jaspilite Jas~ilite(the (the miners' minersfhard hard ore jasper). jasper). Note Note the the complex complex folding folding in in the the jaspilite jaspilite and and the the ore To the the south south and and west west were were irregular irregular replacement replacement by by the the hematite. hematite. To lenses of of high high grade grade hard hard ore. ore. lenses To Inclinef To the the north north are are the the hard hard ore ore open open pits pits of ofthe theIncline, Sawmill, SawmillfSchoolhouse Schoolhouse and and Little LittleMountain MountainMines. Mines. The The first first mining mining The hard hard here here was was in in 1848 1848 by by the the Cleveland Cleveland Iron Iron Mining Mining Company. Company. The ore, oref which which continued continued along along the the pitch pitch of of the the synclinal synclinal axis axis that that passes under passes under the the City City of of Ishpeming, Ishpemingfwas was followed followed underground underground in in the the Cliffs Shaft ShaftMine. Mine. Cliffs The iron—formation The iron-formation characteristically characteristically has has alternating alternating thin thin -or black black beds beds and and lenses lenses of of steel-gray, steel-grayfdark-blue-gray, dark-blue-grayfdark-gray, dark-grayfor specular specular hematite hematite and and bright-red bright-red hematitic, hematiticf fine—grained, fine-grainedfcherty cherty quartzite. Beds Beds commonly commonly range range in in thickness thickness from from aa fraction fraction of of aa quartzite. millimeter centimeters, and and fine fine internal internal laminations laminations millimeter to to about about 22 centimeters, can be be seen seen in in the the thicker thicker layers. layers. Specularite Specularite plates plates are are strongly strongly can oriented oriented parallel parallel to to bedding bedding in in the the hematitic hematiticlayers. layers. Excellent Excellent colored colored illustrations illustrationsof of this this have have been been published publishedin inU.S. U.S. Geological 28. Geological Survey Survey Monograph Monograph 28. Folds Folds having having drag drag folds folds on on their their limbs limbs and and themselves themselves being being drag drag folds folds on on the the limb3 limbs of of aa still still larger larger fold fold are are strikingly strikingly shown shown in most most exposures. exposures. Fold Fold axes axes are are horizontal horizontal to to gently gently plunging. plunging. in In In cross cross section section the the south south limbs limbs of of individual individual anticlinal anticlinal drag drag indicating that that the the folds folds commonly commonly are are longer longer than than the the north north limbs, limbsf indicating major major synclinal synclinalaxis axispasses passessouth southof ofJasper JasperKnob. Knob. - B-28 �Small breccia breccia zones zones occur occur in in the the iron—formation iron-formation at at this this Small locality. Along Along them, themt the the comparatively comparatively brittle brittle reddish reddish cherty cherty locality. (jasper) layers layers in in particular, particulart have have been been fragmented. fragmented. Fractures Fractures (jasper) have been been healed healed mainly mainly by by crystalline crystalline hematite. hematite. Some have Some of of the the , breccia zones breccia zones may may correspond correspond in in orientation orientation to to axial axial plane plane cleavage. cleavage. Two Two principal principal theories theories have have been been advanced advanced for for the the origin origin of of jaspilitic iron—formation iron-formation at atJasper JasperKnob. Knob. One the jaspilitic the One theory theory advocates advocates oxidation of of aa siderite-chert siderite-chert iron-formation oxidation iron-formation during during the the postpostNegaunee erosional erosional interval interval and and its its recrystallization recrystallization to to Negaunee specularite—quartz specularite-quartz during during the the Early Early Precambrian Precambrian Penokean Penokean orogeny orogeny and metamorphism. metamorphism. This This theory theory would would account account for for the the patches patches of of and jaspilite in in carbonate—facies carbonate-facies iron—formation iron-formation which which are are present present near near jaspilite ast for for example, exampletin in the the Cliffs Cliffs Shaft Shaft contacts between between the the two two rocks rocks as, contacts Mine about about 1/2 112 mile mile northwest northwestof ofhere. here. The The second second theory theory advocates advocates Mine primary origin origin for for the the iron iron oxide, oxidef either either as as depositional depositional aa primary diagenetic modification modification of of hematite or or as as magnetite magnetite derived derived by by diagenetic hematite depositional oxides. oxides. The The rock rock here here resembles resembles megascopically, megas~opically~ depositional particularly particularly in in the the very very even even bedding, bedding! magnetite-rich magnetite-rich facies facies of of iron-formation rather rather than than hematitic hematitic facies, fadesf that that is is iron—formation characteristically characteristically irregular irregular bedded bedded and and oolitic. oolitic. STOP 11--CLIFFS 11--CLIFFS SHAFT SHAFT MINE, MINE, ISHPEMING ISHPEMING STOP The and Shafts The distinctive distinctive obelisk obelisk style style headframes headframes of of "A" ffAff and "B" ftBft Shafts were 191gf replacing replacing the the original original wooden wooden headframes headframes were built built in in 1919, erected when when the the shafts shaftswere were sunk sunkin in1873. 1873. The The shaft shaft sections sections show show erected Their tgoarff. Their ultimate ultimate depth depth was was 1250 1250 feet feet that both both shafts shafts cut cut "oar". that shaft from surface. surface. "C" ftCtf shaft was was sunk sunk in in 1954 1954 to to replace replace the the two two from smaller smaller shafts shafts for for more more efficient efficient hoisting hoisting of of the the ore. ore. The The Koepe Koepe hoisting hoisting system system used used in in this this shaft shaft was was the the first first such such installation installation Ifendlessrope" ropetfsystem system in the the Western Western Hemisphere. Hemisphere. It It features features an an "endless in with the the hoist hoist in in the the top top of of the the headframe. headframe. with The Minet closed closed in in December, Decembert1967, 1967#had had the the The Cliffs Cliffs Shaft Shaft Mine, longest longest production production life life of of any any mine mine in in the the Lake Lake Superior Superior region region (1848-1967). It It produced produced 28,960,406 28,96Of4O6long long tons tons of of high high grade grade hard hard (1848—1967). ore. Its Its greatest greatest year year of of production production was was 1942 1942 when when 747,564 747!564 tons tons of of ore. and ore were were shipped. shipped. The The "room ffroom and pillar" pillartfworkings workings present present under under the the ore town town of of Ishpeming, Ishpemingtextend extend to to 1250 1250 feet feet below below the the collar collar of of the the shafts in in the the deepest deepest (15th) (15th)level. level. shafts STOP STOP 12--SOUTH 12--SOUTH PINE PINE STREET, STREET, ISHPEMING ISHPEMING As As noted noted in in the the Introduction, Introductionfthere there are are two two structural structural locations locations for for the the soft soft iron iron ore. ore. The The ores ores in in Negaunee Negaunee and and along along the the north north rim rim in in Ishpeming Ishpeming and and the the North North Lake Lake District District are are all all on on The second second location location the footwall footwall of of the the Negaunee Negaunee Iron IronFormation. Formation. The the The mines mines here here is is in in fault fault structures structures on on the the big big intrusive intrusivesills. sills. The were were the the Lake, Laket Lake Lake Angeline, Angelinet Section Section 16, lGf Holmes, Holmest and and Salisbury Salisbury Lake Angeline Angeline is is aa natural natural expression expression of of the the basin basin in in which which Mines. Lake Mines. The lake lake was was the Lake Lake and and Lake Lake Angeline Angeline deposits depositswere were found. found. The the pumped pumped out out in in 1890 1890 to to permit permit mining mining the the soft soft ore ore on on the the lake lake bottom. These These ores ores were were very very high high grade, gradet and and had had extensive extensive bottom. botryoidal botryoidal and and mammilary mammilary hematite hematite and and goethite goethite with with numerous numerous vugs. vugs. The Minet at at the the west west end end of of Lake Lake Angeline, Angelinelhad had both both The Section Section 16 16 Mine, B- 29 �hard ore ore (above) (above)and and soft soft ore ore (below) (below)in in direct direct contact contact with with one one hard another. another. These mines mines were were the the first first on on the the Marquette Marquette Range Range to to use use These electricity electricity for for electric electric for for underground underground locomotives, locomotivestlights, lightst slusherstand and pumps. pumps. It It was was here here also also that that Cliffs Cliffs voluntarily voluntarily slushers, introduced the the eight eight hour hour work work shift shiftin in1892. 1892. introduced STOP 13--HUMBOLDT 13--HUMBOLDT MINE: MINE: EDISON EDISON HISTORICAL HISTORICAL MARKER MARKER STOP This stop stop is is at at the the historical historical marker marker erected erected by by the the Marquette Marquette This County Historical Historical Society Society in in 1987 1987 for for the the Sesquicentennial Sesquicentennialof of County Michigan. Michigan. This This series series of of hard hard ore ore mines mines operated operated from from 1865 1865 to to 1892 1892 and and from 1908 1908 to to 1917, 1917t producing from producing 1,368,546 1t368t546tons tons of of hard hard ore ore from from both both open pit pit and and underground undergroundoperations. operations. The The Humboldt Humboldt Mine Mine was was open Michiganlsfirst firsttaconite taconite type type open open pit, pittconcentrator Michigan's concentratorand and pellet pellet plant operation. operation. It It was was in in production production from from 1954 1954 to to 1970, 1970tshipping shipping plant 9t433t305 long tons tonsof of concentrates concentratesand andpellets. pellets. 9,433,305 long STOP 12 12 (Fig. (Fig. 8)--REPUBLIC 8)--REPUBLIC MINE MINE OPEN OPEN PIT PIT STOP The The Republic Republic Mine Mine was was opened opened in in 1870 1870 as as aa series seriesof of hard hard ore ore open pits, pitst but but followed followed the the near near vertical vertical dipping dipping beds beds of of the the open Negaunee Iron Iron Formation Formationinto intounderground undergroundoperations. operations. The The Pascoe Pascoe Negaunee 4t000feet feet deep deep (2,910 (2t910feet feet shaft was was an an inclined inclined shaft shaft some some 4,000 shaft vertically) gradethard hard hematite hematite and and magnetite magnetite ore ore to to vertically) with with high high grade, depthtin in aa host hostof ofjaspilite. jaspilite. From From 1872 1872 to to 1926, 1926tthe the that depth, that Republic long Republic Mine Mine shipped shipped 8,563,170 8t563t170 long tons tons of of hard hard ore. ore. It It began began as as taconite type type operation operation in in 1956, 1956tbut but closed closed in in 1983 1983 and and is is on on aa taconite llstand-byll basis. "stand—by" basis. The the The Republic Republic pit pit is is distinctive distinctive for for its its "high *'highwall", wallllt the contact of of the the upper upper portion portion of of the the iron-formation iron-formation with with the the contact metadiabasesill. sill. The The contact contact of of the the Negaunee Negaunee Iron Iron Formation Formation and and metadiabase the overlying overlying Goodrich Goodrich Quartzite Quartzite was was marked marked by by an an extensive extensive the jaspilite. This conglomerate made made up up of of jaspilite. This conglomerate conglomerate was was higher higher in in conglomerate titanium than than the the underlying underlyingNegaunee NegauneeIron IronFormation. Formation. titanium developedtmining mining the the iron—formation iron-formationfrom from As the the open open pit pit was was developed, As footwall to to the the conglomerate conglomerate and and Goodrich Goodrich Quartzite Quartzite the metadiabase metadiabase footwall the hangingwall, hangingwall, numerous numerous underground underground workings workings were were encountered. encountered. These These openings openings were were filled filled with with broken brokencrude crudeore oreso sothe thedrills, drillsttrucks, trucks, and shovels shovels could could work work with with safety. safety. and STOP 15--HIGHWAY 15--HIGHWAY M-95 M-95 ROAD ROAD CUTS: CUTS: MICHIGAMME MICHIGAMME FORMATION FORMATION STOP Tightly Tightly folded folded schist schist of of the the lower lower slate slate member member of of the the Michigamme Michigame Formation Formation is is exposed exposed in in aa roadcut roadcut on on the the east east side sideof of The rock rock here here highway highway M—95 M-95 near near the the axis axisof ofthe theRepublic Republicsyncline. syncline. The is is iron—rich iron-rich metasediment, metasedimentt now now consisting consisting of of biotite—garnetbiotite-garnetamphibole amphibole schist schist that that contains contains aa few few inch-thick inch-thick layers layers of of impure impure Although the the rocks rocks are are in in the the sillimanite sillimanitezone zoneof of quartzite. Although quartzite. metamorphism, metamorphismt sillimanite sillimanite is is not not present present here here because because of of the the lack lack foldsthaving having Minor folds, of appropriate appropriate aluminous aluminoussource sourcematerials. materials. Minor of amplitudes amplitudes much much greater greater than than wavelengths wavelengths and and greatly greatly attenuated attenuated limbs, limbstare are common common and and reflect reflect the the geometry geometry of of the the major major syncline syncline whose whose preserved preserved keel keel is is deeper deeper than than it it is is wide wide at at this this point point and and noncylindbecomes deeper deeper to to the the northwest. northwest. Folding Folding is is markedly markedly noncylind— becomes rical at at outcrop outcrop scale; scale; domains domains of of homogeneous homogeneous strain strain are are commonly commonly rical B- 30 �FIGURE FIGURE 88 GEOLOGY GEOLOGY OF OF THE THEREPUBLIC REPUBLIC MINE MINE AREA AREA a-. 530 000 ,000 , 36 3t s. / ./ / - B-31 _s Fiqure E'iqure g8 / �only aa few few square squarefeet. feet. Most Most minor minor folds folds plunge plunge northwest northwest in in only accordance accordance with with the the regional regional synclinal synclinal axis, axist but but plunges plunges vary vary from from about 15° 15O SE SE to to 600 60 tq NW. about (1to to33 inches) inches) outcroptaa thin thin (1 Near the the north north end end of of the the outcrop, Near quartzite bed bed is is repeated repeated many many times timesby by ninor minor folds. folds. Axes quartzite Axes of of adjacent adjacent folds folds only only aa few few inches inches apart apart have have plunges plunges that that diverge diverge by by This 6 0 ' . This noncylindrical noncylindrical geometry geometry may may be be aa result result of of an an as much much as as 600. as earlier earlier fold fold set set in in the the sedimentary sedimentary rocks rocks that that formed formed prior prior to, tot and and was was strongly strongly overprinted overprinted by, byt the the folding folding which which formed formed the the Republic Republic . sync1 sync 1 ine me. STOP 16 16 (Fig. (Fig. 9)--GREENWOOD 9)--GREENWOOD RESERVOIR RESERVOIR STOP The The Greenwood Greenwood Reservoir Reservoir is is aa prominent prominent new new land land feature feature created created in in 1973 1973 by by the the Tilden Tilden Mining Mining Company Company to to provide provide aa constant constant source source of of water water for for the the concentrating concentratingplant plantrequirements. requirements. The The water water surface surface approximates approximates1,400 lt4O0acres. acres. The The Reservoir Reservoir area area is is open open to to the the public public for for fishing, fishingtboating, boatingt hiking, hikingtand and other other recreational recreational activities. The The agreement agreement with with the the Michigan Michigan Department Department of of Natural Natural activities. Resources thatt at at all all times, timest the the discharge discharge downstream downstream to to Resources provides provides that, the the Middle Middle Branch Branch of of the the Escanaba Escanaba River River will will be be at at least least three three times times the the minimum minimum low low flow flow observed observed by by stream stream gauging gauging over over many many multipart An interesting interesting feature feature of of the the system system is is the the multiport years. An years. discharge discharge system system in in which which any any combination combination of of four four vertically vertically arranged arranged ports ports may may be be utilized utilized to to mix mix waters waters of of varying varying temperatures and and oxygen oxygen content. content. temperatures The The two two principal principal granitic granitic units units forming forming the the Archean Archean Southern Southern 8A (Fig.9) (Fig.9) Compeau Compeau Creek Creek Complex will will be be seen seen here. here. Near Near point point BA Complex Gneiss is is exposed exposed in in aa large large roadcut. roadcut. The The Compeau Compeau Creek Creek Gneiss Gneiss is is Gneiss generally generally mediummedium- to to coarse-grained coarse-grained and and mostly mostly granodiorite granodiorite or or tonalite. It It is is characteristically characteristically both both compositionally compositionally and and tonalite. structurally Heret it it varies varies from from structurally heterogeneous heterogeneous at at outcrop outcropscale. scale. Here, massive massive rocks rocks with with faint faint banding banding or or schleiren schleiren expressed expressed by by variations variations in in percentage percentage of of mafic mafic minerals, minerals, mostly mostly biotite, biotite, to to Clots of of biotite biotite are are common common and and in in rather well well foliated foliated gneiss. gneiss. Clots rather Relict garnet garnet cores cores can can be be places are are aligned aligned in in the the foliation. foliation. Relict places found in in some some clots. clots. Toward Toward the the northeast northeast end end of of the the road road cut, cuttthe the found Compeau Compeau Creek Creek Gneiss Gneiss is is cut cut by by aa nearly nearly vertical vertical dike dike of of Early Early Proterozoic metadiabase. metadiabase. Proterozoic of We hope hope that that you you have have found found this this "sampler" ltsamplerll of This ends ends our our trip. trip. We This the the Marquette Marquette Mineral Mineral District Districtof of interest. interest. B-32 �559 ''f__5_ ) -Wbcg - 30 _j54O Xnic FIGURE 9 A PORTION OF THE GREENWO( 7 MINUTE QUADRANGLE SHOWING THE LOCATION OF STOP 17 Figure 9 �FIELD FIELD TRIP TRIP 33 A STRUCTURAL STRUCTURAL TRAVERSE TRAVERSE ACROSS A PART PART OF TUE THE PENOKEAN PENOKEAN OROGEN ILLUSTRATING ILLUSTRATING EARLY IN NORTHERN NORTHERN MICHIGAN: MICHIGAN: EARLY PROTEROZOIC PROTEROZOIC OVERTHRUSTING OVERTHRUSTING IN TEXT AND FIELD FIELD GUIDE GUIDE TEXT by JOHN KLASNER, Department JOHN S. S . KLASNER, Department of of Geology, Geology, Western Western Illinois Illinois University and U. S. Geological Survey, Macomb, IL IL 61455 61455 University and U. S. Geological Survey,Macornb, PAUL PAUL K. K. SIMS, SIMS, U. S. Geological Geological Survey, Survey, Box Box 25046, 25046, Denver Denver Federal Federal Center, 905, Denver, Denver, CO CO 80225 80225 Center, MS 905, Geological Department of Geology and GREGG, WILLIAM J. GREGG, Department of Geology Geological J. MI Engineering, Michigan Technological University, University, Houghton, Houghton, MI 49931 49931 CHRISTINA CHRISTINA GALLUP, GALLUP, Department Department of of Geological Geological and and Planetary Planetary Science, Science, California CA 91125. 91125. California Institute Institute of of Technology, Technology, Pasedena, Pasedena, CA C-i �INTRODUCTION INTRODUCTION The Early Early Proterozoic Proterozoic Penokean Penokean orogen orogen is is one one of of several several The major orogenic orogenic belts belts in in the the North North American American craton craton that that developed developed major between about about 1.95 1.95 and and 1.85 1.85 Ga Ga (Hoffman, (Hoffman, 1988). 1988). Rocks Rocks of of the the between orogen are are exposed exposed in in Michigan, Michigan, Wisconsin, Wisconsin, and and Minnesota Minnesota (Fig. (Fig. orogen 1) and and extend extend eastward eastward into into the the Lake Lake Huron Huron area area (Sims, (Sims, et et al. al. 1) 1981), and and westward westward in in the the subsurface subsurface into into Iowa Iowa and and Nebraska Nebraska 1981), (Sims and and Peterman, Peterman, 1986). 1986). The The southern southern boundary boundary is is not not exposed exposed (Sims inasmuch as as it it is is overlapped overlapped by by Phanerozoic Phanerozoic platform platform sedimentary sedimentary inasmuch rocks. The The Penokean Penokean orogen orogen is is intruded intruded by by 1.76 1.76 Ga Ga anorogenic anorogenic rocks. rhyolite granite granite which which is is exposed exposed in in Wisconsin. Wisconsin. rhyolite The Penokean Penokean orogen orogen consists consists of of aa northern northern assemblage assemblage of of The sedimentary and and bimodal bimodal volcanic volcanic rocks rocks of of the the Marquette Marquette Range Range sedimentary Supergroup in in Michigan Michigan (Cannon (Cannon and and Gair, Supergroup Gair, 1970) 1970) and and equivalants equivalants in in Minnesota, Minnesota, the the Animikie Animikie Group Group and and Mills Mills Lacs Lacs Group Group deposited deposited on on aa continental Archean Archean margin margin and and aa southern southern terrane terrane' composed composed continental mainly of of Early Early Proterozoic Proterozoic caic-alkaline calc-alkaline plutonic plutonic rocks rocks termed termed mainly The the Wisconsin Wisconsin magrnatic magmatic terrane terrane (Sims, (Sims, 1987 1987 and and in in press). press). The the Minnesota, in recognized magmatic arc terrane has not been recognized in Minnesota, has not been terrane arc magmatic although it it may may occur occur in in the the subsurface subsurface in in southeastern southeastern Minnesota. Minnesota. although The Niagara fault fault zone zone is is aa brOadly broadly arcurate arcurate convex convex Niagara The as much as 10 km northward systems systems of of faults faults and and shears, shears, as much as 10 km wide, wide, northward that separates separates the the continental continental margin margin assemblage assemblage and and Wisconsin Wisconsin that It magmatic terrane terrane (Fig. (Fig. 2). 2). It contains contains flattened flattened , steeply steeply maginatic dipping rocks rocks that that have have prominent prominentstretch stretchlirieations lineations parallel parallel to to dipping , dip dip (Ueng (Ueng and and others, others, 1984; 1984; Sedlock Sedlock and and Larue, Larue, 1985; 1985; and and Sims Sims and and others, 1985), 1985), and and it it is is interpreted interpreted by by the the above above authors authors to to be be others, In the surface surface expression expression of of aa 1850 1850 My My old old suture suture zone. zone. In the northeastern Wisconsin Wisconsin all all of of the the components components of of an an ophiolite ophiolite northeastern assemblage, although although dismembered, dismembered, occur occur near near the the suture suture zone zone assemblage, 1987a). (Schulz,1987a). (Schulz, Following the the initial initial suggestion suggestion of of Van Van Schmus Schmus (1976), (1976), Following several authors authors (Cambray, (Cambray, 1978; 1978; Larue Larue and and Sloss, Sloss, 1980; 1980; Greenburg Greenburg several and Brown, Brown, 1983; 1983; Anderson Anderson and and Black, Black, 1983; 1983; Schulz, Schulz, 1983, 1983,1984; 198-2; and Schulz and and others, others, 1984; 1984; LaBerge LaBerge and and others, others, 1984; 1984; Sims Sims and and Schulz 1984; Klasner Klasner and and others, others, 1985; 1985; Sims Sims and and others, others, 1985; 1985; Peterman , 1984; Peterman Klasner and and Attoh, Attoh, 1986; 1986; Schulz, Schulz, 1987a, 1987a, b; b; and and Sims Sims and and others, others, Klasner tectonic proposed a plate-tectonic scenario for the 1987) have proposed a plate-tectonic scenario for the tectonic have 1987) evolution of of the the Penokean Penokean foldbelt foldbelt in in northern northern Michigan Michigan and and evolution Wisconsin. Although Although they they differ differ in in detail, detail, these these authors authors suggest suggest Wisconsin. that evolution evolution of of the the orogeri orogen began began with with rifting rifting accompanied accompanied by by that and Marquette the troughs (such as formation of basins and troughs (such as the Marquette and basins and formation of the Archean Archean Republic troughs) troughs) along along the the passive passive margin margin of of the Republic followed was This in northern Michigan. by Superior craton craton in northern Michigan. This was followed by Superior with south, the crust to subduction of of oceanic oceanic crust to the south, with ultimate ultimate subduction collision of of arc-related arc-related volcanic volcanic and and plutonic plutonic rocks rocks with with the the collision Archean continental continental margin. margin. Archean , consequence consequence of of the the accretion accretion of of arc-related arc-related crust crust to to of rocks the Superior Superior craton, craton, widespread widespread deformation deformation of rocks of of the the the continental margin margin as as well well as as of of the the magmatic magmatic arc arc is is to to be be continental As As aa C— 2 �EXPLANATION EXPLANATION n Ma and and younger) younger) PHANEROZOIC (600 (600 Ma PHANEROZOIC Sedimentary Sedimentary strata strata MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC (900—1600 (900-1600 Ma) Ma) Mafic Mafic igneous igneous and and sedimentary sedimentary rocks rocks of of Midcontinent Midcontinent rift rift system system (1000—1200 (1000-1200 Ma) Ma) Anorogenic Anorogenic anorthosite anorthosite and and rapakivi rapakivi granite granite (1480—1500 (1480-1500 Ma) Ma) EARLY EARLY PROTEROZOIC PROTEROZOIC (1600—2500 (1600-2500 Ma) Ma) n Granitoid Granitoid rocks rocks (1760—1800 (1760-1800 Ma) Ma) Volcanic Volcanic and and graaitoid granitoid rocks rocks of of Wisconsin Wisconsin magmacic magmatic terrane terrane (1815-1890 Ma) Ma) (1815—1890 -1 Marquette Range Range Super— SuperStratified Stratified rocks rocks of of Animikie Animikie basin; basin; Marquette - ground ground and andAnimikie Animikieand andMil].e Mille Lacs Lacs Groups Groups ARCHEAN A R C W A N (2500 (2500 Ma Ma and and older) older) A Greenstone—granite Greenstone-granite terrane terrane (2600—2750 (2600-2750 Ma) Ma) A n Gneiss Gneiss terrane terrane(2600—3550 (2600-3550Ma) Ma) A Extra-Superior gneiss gneiss and and schist schist (2500—3000 (2500-3000 Ma) ~ a ) Extra—Superior -.--- Great Lakes Lakes tectonic tectonic zone; zone; dots, dots, buried buried trace trace C-4 �480 48° 440 FIGURE 1. 1. Generalized Generalized geologic cjeologic map map of of the the Lake Lake Superior S u ~ ? r j . ~ > region rregion FIGURE units of of the thePeriokean Penoksan orogen o r o p n and and adjacent adjacent areas. aress. showifiq rock rock units showing Xodified from from Morey Morey and znd others others (1982). (1982). Modified C- 5 �FIGURE 2. Map of the eastern part of the Lake Superior region showing e:tent of the Early Proterozoic contlnental-margLn assemblage and Wisconsin rnagrnatic terrane of the Pnokean oroen. Archean rocks are patternd. Stippled area snows location of traverse in this field guidee. IM = iOfl Mountain; M = Marquette. C-6 �expected. In this this guidebook, gui6ebookf we we examine examine evidence evidence from from northern northern In expected. Michigan showing showing that that there there was was extensive extensive overthrusting overthrusting on on the the Michigan continental margin margin during during the the accretionary accretionary event. event. We We examine examine the the continental for overthrusting overthrusting along along aa north-south north-south structural structural evidence for evidence traverse (Fig. (Fig. 2) 2) extending extending from from Falls Falls River River southward southward across across the the traverse and Michigame basin, basinf Arnasa Amasa uplift, and Feich Felch trough-Calumet trough-Calunet trough trough uplift, Michigamrne resion to to .the Niagara fault fault zone zone which which lies lies along along the the the Niagara region fi?ichiqan/~$isconsin border. Michigan/Wisconsin border. This guidebook guidebook is is mainly mainly the the outgrowth outgrowth of of field field work work and and This related related synthesis synthesis done done during during 1986 1986and and 1987. 1987. Critical Critical areas areas for for examination were were selected selected from from several several excellent exc2llent published published examination geological maps maps and and papers papers in in the the south south (principally (principally James James and and geological 1968; Bayley and others, 1966; James and others, othersf 1961; James and othersf 1968; Bayley and othersf 1965; 1961; others, by This Duttonf 1971). 1971). This was was followed, followedf where where appropriate, appropriatef by Dutton, detailed structural structural studies studies in in the the north, northf mainly mainly done done by by Kiasner Klasner detailed previously and Gallup. Gallup. In this this part part of of the the area area previously mapped mapped by by In and and Cannon and Kiasner (see for example mainly W. F. Cannon and Klasner (see for example Cannon and mainly W. F. Cannon Kiasner, Klasnerf 1972; 1972; Kiasner, Klasnerf 1972; 1972; Cannon, Cannonf 1973; 1973; Kiasner, Klasnerf 1978), 1978), field field of addition involved refinement and the work principally principally involved refinement and the addition of new new work detailed observations. observations. Gregg's Greggls work work has has been been in in the the Baraga Baraga detailed basinf primarily primarily northeast northeast of of the the area area covered covered in in this this report. report. basin, 1987 and Sikkalaf 1987 and Sikkala Sikkala and and Detailed studies studies at at Falls Falls River River ( Sikkala, Detailed Greggf 1987), 1987)f however, howeverf mark mark the the northern northern end end of of the the traverse traverse in iil Gregg, the area area of of this this report. report. the , ( GENERAL GEOLOGY GEOLOGY GENERAL of the the Marquette Marquette Range Range Supergroup Supergroup Stratigraphic units units of Stratigraphic (Cannon and and Gair, Gairf 1970) 1970) are are listed listed in in Table Table 1. 1. The The Marquette Marquette (Cannon Range unconformably Range Supergroup Supergroup consists consists of of three three groups groupswhich whichlie lieunconforrnably abovef or or in in fault fault contact contact with, withf underlying underlying Archean Archean greenstone— greenstoneabove, granite or or gneiss. gneiss. The The rocks rocks occupy occupy broad broad open open basins, basinsf such such as as granite fault-bounded troughs troughs the Michigamme Michigamme basin basin or or relatively relativelynarrow, narrowf fault—bounded the such as as the the Marquette Marquette and and Republic Republic troughs troughs (Fig. (Fig. 3). 3). An An such apparently thick thick sequence sequence of of metavolcanic metavolcanic rocks, rocksf the the Hemlock Xeinlock apparently Formztion (see (see Cannon Cannon and and Klasner, Klasnerf 1975 1975 and and Foose, Foasef 1980) 1980) lies lies Formation along the the west west side side of of the the Amasa Amasa uplift. uplift. As As discussed discussed below below , we we along tentatively tentatively interpret interpret this this apparently apparently large large thickness thickness of of volcanic volcanic rocks as as resulting, resultingf at at least least in in part, part, from from tectonic tectonic stacking stacking rocks It should be the Early Protrozoic overthrusting event. during the Early Prot.~rozoic overthrusting event, It should be during noted noted that that the the Michigamme Michigamme Formation Formation is is informally informally divided divided into into an an Member Formation upper and and lower lower slate slate member member by by the the Bijiki Bijiki Iron Iron Formation Nember upper (see Table Table 1). 1). The The lower lower slate slate member member is is the the dominant dominant lithology. lithology. (see evidence for overthrusting is found Much of of the the evidence for overthrusting is found in in the the upper upper Much slate member member (dominantly (dominantly graywacke graywacke ) member member of of the the Michigamrne Michigamme slate Formation. Formation. , ) Archean Archean rocks rocks of of northern norkhern Michigan PTichigan and and Wisconsin Wisconsin have have been divided divided by by Sims Sims (1980) (1980)into into aa granite-greenstone granite-greenstone terrane terrane been (2600 -- 2700 2703 Ma) Ma) on on the the north north and and aa gneiss gneiss terrane terrane (2600 (26CO -- 3550 3550 (2600 Ma) on on the the south. south. The The boundary boundary between between these these two two terranes terranes has has Ma) been In the the study stuZy area, areaf it it been named named the the Great Great Lakes Lakes tectonic tectonic zone. zone. In is oriented oriented eastward eastward and and lies lies roughly roughly along along the the Marquette Narquette trough trough is (Fig. 3). 3). The The Penokean Penokean foldbelt foldbelt is is localized localized along along the the GLTZ, GLTZ, (Fig. The The C- 7 �___________ ____________ ___________________ . .TABLE TABLE II Michigamme Michiqamme Basin Basin paint Paint Felch-Calumet Felch-Calumet trough trough Iron Iron River River syneline svncline Fortune Fortune Lakes Lakes Slate Slate Stambaugh Stambauqh Formation Formatior Hiawatha Hiawatha Graywacke Gravwacke Riverton Riverton Iron— 1ro& Formation F o m a tion Dunn Dunn Creek Creek Slate Slate River River Group Group Saraga Baraqa __________________ Badwater Badwater Greenstone Greenstone Bedwater Bedwater Greenstone Greenstone ichigamme ichiqanme Formatjo, Formatit flichigamme Nichiqannne Slate Slate Michigamme M i c h i g a m Slate Slate 3ijik. ijiki Iron— IronAinasa Amasa Formation Formation Hemlock Formation Hemlock Formation Formation FormationMember Member :larksburg larksburg Volcanics VolcanicsMember Member ;reenwood reenwoodIron— IronFormation FormationMember Hear oodrich ite oodrichQuartz Quartzite ' Group Group - LOCAL UNCONFORMITy UNCONFORMIT' LOCAL — UNCONFORMITY UNCONFORMITY OR DISCONFORMITY — - I4enominee Menomine{ Group Group Marquette Marquette EARLY PROTEROZOIC PROTEROZOIC EARLY Range Range Negaunee Neqaunee Iron— IronFormation Formation Siamo Siamo Slate** Slate** ,. Ajibik Ajibik Quartzite Quartzite Vulcan Vulcan IronIronFormation Formation Felch Felch Formation Formation Supergroup supergroup - — UNCONFORMITY UNCONFORMITY Chocolay Chocolay Not present Not -present Saunders Saunders Formation Formation Grou Group p - ARCHEAB ARCHEAN - Granite ranite — Gneiss Gneiss Randville Randville Dolomite Dolomite Sturgeon iturgeon Quartzite Quartzite Fern 'ern Creek Creek Formation Formation - —- UNCONFORMITY UNCONFORMITY — — UNCONFORMITY— UNCONFORMITY UNCONFORMITY UNCONFORMITY Gneiss Gneiss greenstone reenstone * Upper Upper slate slate member of the the Michigamme Michiqamme Forma.ion F0rma:ion lies above above the the Bijiki Bijiki lies Member and and the the lower lower slate slate member member of of the theMichiganune Michiqame lies lies below below it. it. Member ** Possibly Possibly present present in in the the subsurface subsurfaceof ofthe theMichigalume Michiqamme basin. basin. * ** C-B — - Iron Formation Formation Iron — - �Fkld trip stops \ Thrust fault & Geologic contact Fault of unknown dip block h u- upthrown 1 Strike ond dip direction of foliation Intrusive rocks P= Peavy metamorphic node &= I 8 3 4 Mo gronlte ;J:;erento i ted Point River Group 0 Undifferentiated Barago Group rocks. Includes undifferentiated Bodwater ond Hemlock volconic units Undifferentiated Menominee ond Chocoloy Group rocks @ J z Undifferentiated qronitoid gneiss ond Dickinson Group metoconglomero 0 a a 5 0 0 5 0 Miles I 0 Kilometem FIGURE 3. Geologic map of the study area showing major structural and location of structural location of field stops: features, c-c' is part of the 8); 3—B' Fig. 6) and profiles A—A' (Fig. 9) which lies along a line connecting A composite profile (Fig. Features discussed in the text include A4 = ±-rnasa uplift, to C'. Canyon Fa)ls, CT = BB = Baraga basin, BL = 3ush Lake Fault, CF Calumet trough, DD =Dunbar dome, FR = Falls River location, FT = Feich trough, MB = Michigamme basin, MT = Marquette troi;gh, NC = flO(i, northern complex, TM = Taylor Mine, P = Peavy metamorphiclocain Creek. RT =RepubliC trough. AA is ti and PC = Plunjbaqo of the the granitic granitic intrusion intrusion dated dated at at 1824 1824 Ma Ma (Z.E. (z.E. Peterman, Peterman, perspersof onal onal communication). communication). From From Cannon Cannon (1983) (1983) and and Dutton Dutton and and Linebaugh Linebauqh (1967) (1967). C-9 - - �. deformation which appears appears to to have have played played aa role role in in the the style style of of deformation which North of of the the GLT7J, GLTZr Early Proterozoic Prt7tsroz~ic of Early Early Proterozoic Proterozoic stata. stata. North of strata are are only only gently gently deformed, deformedr whereas whereas south south of of it it Early Zarly strata The traverse traverse described described Proterozoic Proterozoic strata strata are are intensely intensely deformed. deformed. The intensely in in this this guidebook guidebook lies lies mostly mostly south southof ofthe theGLTZ, GLTZ,in in the the intensely Here, Early deformed part part of of the the Penokean Penokean foldbelt. foldbelt. Herer Early Proterozoic Proterozoic deformed strata overlie overlie block block faulted faulted Archean Archean rocks rocks (Cannon (Cannon and and Klasner, Klasner, strata 1972 and and Cannon, Cannonr1973). 1973). 1972 At least least four four regional regional metamorphic metamorphic aureoles aureoles (James, (Jamesl 1955) 1955) At Attoh were formed formed during during the the Penokean Penokean orogenic orogenic event event (Fig. (Fig. 4). 4). Attoh were and Vander Vander Muelen Muelen (1984) (1984)and and Kiasner Klasner and and Attoh Attoh (1986) (1986)argue argue that that and thickening, crustal by were caused tke metamorphic metamorphic aureoles aureoles were caused by crustal thickeningr the possibly due due to to tectonic tectonic stacking stacking associated associated with with overthrustirig overthrustirq possibly during the the Penokean Penokean accretionary accretionary event. event. during c chlorite C chlorite biotite bb biotite 9 garnet ggarnet S - 40 km 40 km s Staurolite Paleozojc Paleozoic Rocks Rocks Peavy Node Node Watersmeet Node Florence Node Node Florence -' F1232E 4. 4. Location Location of of metamorphic netamorphic aureoles aureoles in in northern northsrn Michian bfichiqsn FItrn2 (after James, Samesl1955). 1955). (after Structzral studies stusies (Cannon (Cannon and and Kiasner, Klasner? 1972; 1972; Klasner, Klssnsr, Structural and Klasner, 1978) have shown Early 1972; Cannon, Cannon? 1973; 1973; and Klasnerr 1978) have s h ~ i ~that that n Early 1972; subjected to at least Proterozoic ?rotsrozoic rocks rocks in in northern northern Michigan Michiqan were wers subject& to ~t lsast ( F l ) ws K Z S thin thin thrse periods peri~As of of deformation. defornatici-i. The The first first event event (Fl) three strata resulted in shortening of Early Proterozo1c skinned znd resulted in shortening of Early ProtsrazoiL? strata and skinned widespread widespread west-northwest-trending w e s t - n t ~ r t h ~ c t ? s t - t r ~ f i d' i ~ g and development development of of az and c-10 C10 �block str~ctural fabric(Fig. (Fiq.3). 3 ) . The The second second event evsnt (F2) (F2)involved inv~lve5 block structural fabric structural formation of Archean basement rocks and uplift of Archean basement rocks and formztion of structural of uplift features infoicling features such such as as the theMarquette Karquetteand andRepublic Republictroughs troiighsand an2 infolding of Early Early Proterozoic Proterozoic strata strata into intothe thetroughs. troughs. Larue Larue and and Sloss Sloss of (1980) have have shown shown that that the the troughs troughs actually actually started started to to form form (1980) earlyf during during deposition deposition of of the the sediments, sediinents, and anZ before before Fl Fl early, deformation. Kiasner Klasner (1972, (1972, 1978) 1978) noted notsd aa third, third, late late stage, stags, deformation. brittle deformational deformational event event (F3) (F3) in in the the northern northern part part of of the the brittle Michigamme Michigamme basin basin and and suggested suggested that that it it could could have have been been caused caused by by late block block uplift uplift of of Archean Archean basement. basement. Petrofabric Petrofakric studies studies late (Klasnerf 1972, 1972f 1978) 1978) showed showed that that regional regional metamorphism metamorphisin in in this this (Kiasner, part of of northern northern Michigan Michigan peaked peaked after after Fl Fl deformation, deformation, about about the the part tine of of F2 E'2 deformation. deformation. time Uplift Basin Basin Uplift + 47 Trends Trends of of first first order order structures structures ---- Trends Trends of of second second order structures Paleozoic Rocks 0 0 20 20 miles miles L FIGURE 5. 5 . General General trends trends of of first first and and second second order or6er structures structures in iz FIGURE narthern Michigan Michigan (from (fromCannon, Cannon, 1973). 1973). northern Cancon (1973) (1973) divided Zivided the the regional regional structures structures in in northern northern Cannon ichigan Xichiganinto into"firsts' "first"and and "second'1 "secon~"order order features fsatures (Fig. ( F i q . 5). 5 ) . First First af orientations arier,tations and a n 6 are .3rs ordsr structures structxres have hs-~e aa wide wide range r m q e of order of and block uplift uplift s n ddoming Samincj(Sims (Sins and znd others, others, 1$84a) :-S84a) (2f relste6 to to block related order st.ractu2s structures have ths Archean Archsan crust. S2cond ordsr have a z regular rsqilai-westx?stthe crust. Second of and are related to the Fl shortening trend Early northwest trenz an6 are relstd ta the Fl shortsning of Early northwest C-li �Proterozoic Proterozoic strata. strata. PREVIOUS EVIDENCE EVIEENCE FOR FOR THRUSTING THRUSTING OF OF EARLY EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS PREVIOUS The The dichotomy dichotomy in in style style of of deformation deformation between bstween Early Early Proterozoic Proterozoic rocks rocks and and underlying underlying Archean Archean rocks rocks led led Cannon Cannon and and Klasner (1972), (1972) Kiasner Klasner (1972), (1972) Cannon Cannon (1973), (1973) and and Kiasner Klasner (1978) (1978) Kiasner to to suggest suggest that that aa decollement decollement exists exists between between them. them. They They suggested that the shortening of suggested that the shortening of Early Early Proterozoic Proterozoic strata strata relative Archean rocks rocks was was caused caused by by gravity gravity relative to to underlying underlying Archean sliding off slizing off an an ancestral ancestral Penokean Penokean mountain mountain range range in in the the south. south. They They (in (in particular particular Kiasner, Klasnerf 1972, 1972, 1978) 1978) suggested suggested that that Fl Fl deformation deformation occurred, occurredf in in part, partf while while the the sediments sediments were were unconsolidated; unconsolidated; however, howeverf this this postulate postulate is is no no longer longer tenable, tenabler and and it it appears appears that that the the Fl Fl deformational deformational event event involved involved solid solid rocks. rocks. \ Recently, Recently, Hoist Holst (1982, !1982r 1984) 1984) identified identified Early Early Proterozoic Proterozoic structures Similarly, structures in in eastern eastern Minnesota. Minnesota. Similarlyf Maharidge ?.laharidge (1986) (1986) proposed proposed that that the the Felch Felch trough trough area area of of northern northern Michigan ?!ichicjan (Fig. (Fig. 2) 2) represents represents aa crystalline-core crystallice-core nappe nappe feature. feature. He He based basez this this interpretation interpretation on on reexamination reexamination of of sedimentary sedimentary rock rock outcrops outcr~ps in in the the Feich Felcb.trough trough area, areaf previously previously mapped mapped by by James Janes and znd others others (1961), (196llf and and on on microstructural microstructural analysis analysis of of hand hand specimens specimens from from the the region. region. Later, Later, Sims Sims and and others others (1987) (1987)tentatively tentatively suggested sucjgested that that the the Felch Felch trough trough area area may may represent represent the the core core of of aa northnorthverging verging nappe nappe thrust thrust structure, structuref but but this this interpretation interpretation remains remains equivocal; equivocal; and, andf as as discussed discussed below, belowr although although we we cannot cannot rule rule out out the the presence presence of of aa nappe, nappet we we think think that that Felch Felch trough trough area area may may be be part Structural part of of aa south-verging south-vergingbackthrust. backthrust. Structural studies studies underway underway in in this this region rsgion should should permit permit resolution resolution of of this this problem problem in in the the near future. near future. nappe nappe On On the the other other hand, handf Sikkala Sikkala (1987) (1987) and and Sikkala Sikkala and and Gregg Gregg have identified (1987) (1987) have identified recumbent recumbent folds folds and and aa probable probable nappe nappe structure structure in in slate slate and and graywacke graywackeof of the theMichigamrne Michigame Formation Formation at at Falls Falls River River near near L'anse. Ltanse. Similarly, Similarlyf Van Van Roosendaal Roosendaal (1985) (1985) mapped mapped large l a ~ g e scale scale westwest- northwest northwest trending trending thrust thrust systems systems in in slates slates and and graywackes graywackes of of the the Baraga Baraga basin basin (Fig. (Fig. 3) 3) northeast northeast of of Falls Falls River. River. Evidence Evidence for for Early Early Proterozoic Proterozoic overthrusting overthrusting has has recently recently been been found found by by Xlasner Klasner and and others others (1988, (l98Bf in in press) press) in in several several places About Xichigan. About 120 120 km km west west of of the the traverse traverse places in in northern northern Michigan. shown shown in in Figures Figures 22 and and 3, 3 f Early Early Proterozoic Proteroz~icslate slate and and graywacke graywacke of of the the Tyler Tyler Formation Formation (Baraga (BaragaGroup) Group) near near Ironwood, Ironw006~Michigan Xichigan and an6 metavolcanic metavolcanic rocks rocks of of the the Emperor Emperor volcanic volcanic complex camplex at at nearby nsarby Wolf Xolf Mountain eastXountain have have aa penetrative penetrative foliation foliation that that strikes strikes roughly rou~hly 2astwest west and, and, when when corrected corrected for for rotation rotati~ndue due to to deformation deforriiationin in the the the the ca ca 1.1 1.1 Ga Ga Midcontinent MidcontinentRift, Riftf dips dips gently gently south. soath. This This suggests suggests that that these these rocks rocks may may have have been been involved involved in in az thrust, thrustt or or thrustthrust- nappe nappe event event similar similar to to that that mapped mapped about about 100 100 km km west west in in Minnesota Ninnesota by by Holst Holst (1984) (1984)and and at at Falls Falls River River by by Sikkala Sikkala 1987 1987 and and Sikkala (1987). Sikkala and and Gregg Gre~g (1987). Klasner Klasner and and others others (in (inpress) press) also also C-12 �presented evidence to show show that Archean crust is locally involved in the overthrust overthrust event. event. hole about about six six kilometers kilometers east east A drill hole of Canyon Falls in in the the northern northern complex complex (Fig. 3) penetrzted of Canyon (Fig. penetrated 3) underlying sheared gneiss and underlying sheared slate slate and and quartzite, quartzitef all of which which have low dipping foliation. The slate have low dipping foliation. The slate and and quarzite quarzite are are interpreted interpreted to to be be Early Early Proterozoic Proterozoic in in age. age. Similar Similar carbonaceous carbonaceous Taylor Mine and quartzite slate occurs at Taylor quartzite at at nearby nearby Canyon Canyon Falls. Falls. These These relationships suggest that that Archean gneiss gneiss was was thrust thrust over over relationships suggest the the Early Early Proterozoic Proterozoic slate. slate. Earlier nearer to Earlier studies studies in in both both Michigan Michigan and and Wisconsin, Wisconsin, nearer to zonef support support the the idea idea of of overthrusting overthrusting on on the the the Niagara fault fault zone, continental margin. Bayley and James and others continental margin. and others others (1966), (1966)f James others foliations (1961)f and Bayley (1959) (1959) mapped local local subhorizontal subhorizontal foliations (1961), Michigamme Formation, the Michigamme in the Formationf especially especially in in the the region region between in stops Fault. Ueng stops 99 and and 13 13 (Fig. (Fig. 3) just north of the Niagara Niagara Fault. Ueng and others (1984) (1984) attributed this this foliation foliation to to vertical vertical uplift uplift of of Archean However, we attribute attribute the Archean basement. basement. Howeverf we the subhorizontal subhorizontal foliation foliation to thrust thrust faulting, faultingf as as discussed discussed in in some some detail detail below. below. the continent-arc Finally, thrusting resulting Finallyf thrusting resulting from from the continent-arc fault. has also affected rocks collision rocks south south of the the Niagara Niagarz fault. collision has Sims and others From From geologic geologic mapping mapping and and geochemical geochemical evidence, evidence, Sins others (in (in press) have concluded that chemically chemically dissimilar dissimilar rocks rocks in in the the juxtaposed by Dunbar area (Sims (Sins and others, othersf 1985) 1985) have have been juxtaposed Dunbar area thrust faulting faultinq and and related related deformation; deformation; and this interpretation interpretation accords accords with an earlier earlier interpretation interpretation of Klasner and Osterfeld Osterfeld dome modelling that the Dunbar is from gravity from gravity modelling that the Dunbar dome is (1984) (1984) the a consequence of thrusting along allochthonous, either as allochthonousf either as consequence thrusting along the south—dipping Niagara fault south-dipping fault or a subsidiary subsidiary fault. fault. OVERTHRUSTING ALONG THE EVIDENCE FOR OVERTHRUSTING THE STRUCTURAL STRUCTUXAL TRAVERSE TRAVEXSE Geologic mapping detailed structural Geologic napping and detailed structural observations observations at at demonstrate several field localities localities in in the the study study area area demonstrate several selected field moderate-scale thrust thrust faults faults and small to the existence of small to moderate-scale the existence of locally related recumbent recumbent folds. folds. These These features features are are particularly particularly well well exposed at Little Mountain (field (field stop 2) near the northern foliation and and related related the traverse, traversef and subhorizontal subhorizontal foliation end of the end overturned overturned to recumbent recumbent folds folds are are present present at at several several localities, localitiesf especially, as especiallyf as mentioned mentioned above, abovef at Falls River (field (field stop stop 1), lIf 12, and in the broad area area encompassed encompassed by by stops stops 9, g f lZf and 13 13 (see (see and thrusts aad and these observationsf observations, larger—scale thrusts From these From lar9er-scale below) below). possibly can possibly nappes nappes can be inferred inferred where where permissive permissive structural structural features observed in mzpped features are observed in the the rocks rocks and/or where where previously previously mapped faults are better better interpreted interpreted as as thrusts. thrusts. . Proterozoic deformation in To illustrate illustrate the style of Early Pr~terozoic in in northern Michiganf we have compiled compiled the the geologic geologic map ma? shown shown in northern Michigan, sections Figure 3 and Figure and. have constructed c~nstructedtwo two interpretive interpretive cross cross sections 3 on Figure and The thrust system depicted (Figs. 6, (Figs. 6: and 8). The systen depicted on Fiqure 33 8). displays an overall northward sense Zisplays an overall northward sense of of structural structural vergence. ver9er~ce. C-13 �A Folio Criol 2 Lulls MOOOIOIA Cr1811 PlombogO 3 Conon Foils s. HEAN BASEMENT N16E I 4 I 6 III II I I .101. . P.. I. $• 6 7 1 '1 '11 II &. t)ii 11 7I JLt Fold 008$ S 'U.. IA A' SLCTIOO OlIN S. of the profile between stops are shown by arrows at top of figure. S1,ocm,,oc. 00,0,60 iTc toc.Iofl000 IN 0010 CoOls 100(06 IlflCII005 1.00106 (So) 0111$ OTIflh500PIIIC Smucamot 00IIOTOTI005 Ill I $hl.Sl80 b.ddhlq Foliolioul S So BiddIng Note field stop localities. Structural profile A--At. FIGURE 6. stereoplots Lower hemisphere location. for See Figure 3 foliation (Si), ard fold illiitrate orientation of bedding (SO), Directions of each segment axs (black dots) along the traverse. 2. Toylor Mill. '5. LI 2- I �The style style of of deformation deformation in in the the Michigarnme Kichigamme basin basin is is The Structural (Fig. 6). A—A' illustrate6 on on section ssction A-A' (Fig. 6 ) . Structural data 6ata in in illustrated primarily the the upper u 2 p r slate slate member member of of the the Michigainme Xichigznine Formation Forination primarily along along this this profile profile suggests suggests that that the the Early Early Proterozoic Proteroz~icrocks rocks were were of ~ r i 6eform~d as as part p~rt of an an irnbricate iribricate thrust thrust system. systan. As As shown shown on deformed not Figure 6, 6, there there does d~es not seem ssem to to be be much much involvement involvement of of the the Figure Archean rocks rocks in in the the thrusting. thrusting. Structural Structural relationships relationships at at Archean Plumb.go Creek, and Canyon Falls (Fig. Taylor Mine, Ninef Plumb?-goCreekf and Canyon Falls (Fig. 3), 3If however, however, Taylor was some some involvement involverent of of the the basement b~sernsntin in the the indicate that that there there was indicate lies quartzite flat-lying Falls Canyon thrusting. At Canyon Falls flzt-lying quartzite lies At thrusting. on Archean Archean basement basement and and has has only only minor minor evidence evisence of of uriconformably on unconformably km to to Yet at at Taylor Taylor Mine, :4ine, about about 55 km Early Proterozoic Proterozoic deformation. deformation. Yet Early the north, northf Early Early Proterozoic Proterozoic slates slates are are overturned overturned toward towarc? the the the and have have steep steep south south dipping dipping foliation foliation as as shown shown in in Figure Ficpre north and north penetratively At Plumbago Creek, 1.6 km south of Taylor Mine, 7. At Plumbago Creekf 1.6 km south of Taylor Xinet penstratively 7. deformed deforned Early Esrly Proterozoic Proterozoic phyllite phyllite has has aa south-dipping south-dipping foliation foliation data, These structural projects beneath Archean gneiss. which projects beneath Archean gneiss. Thess structural datz, which when plotted plotted on on the the elevation elevation profile, profile, as as shown shown on on Figure Figure 6, 6, when indicate that that there thsre was was some sone involvement involvement of of basement bassinent rocks rocks in in indicate Because 2ecause of of Early Proterozoic Proterozoic overthrusting ovsrthr~stinqin in this this region. rsgion. Early difficult will difficult access, zccessf outcrops outcrops at at Plumbago ? L i ~ m b ~Creek Creek g~ will not not he he visited. vtsited. Taylor Mine Mine? is is an an alternate alternate stop. stop. Taylor SOUTH SOUTH Field stop stop area area Field KORTH NORTH 200 feet o i • SCLE :j N\ I Keweenawan Keweenawan diabase dike diabase ---- -- - dike -..- Folded Folded sandy sandy N Cherty iron iron Cherty formation fortnatiofl 't laver layer Slack Black slate slate with with Si Sl foliation foliation Orientation Orientation of cleavage cleavage of -Y Core core hole hole showing ~howinq core core dips dips Struck~ral cross cross section section in in the the Taylor 76i~e s r s a Structural Ta-lasnd 's t y- l earea r Jj1fl on Fig. 3) showing Sl fcliatici~ c,f on Fia 3) dezornation. DiamonS drill-hole data are frmi Ford ~ o t o r C ~ m p any deformat ion D iamond dri11ho1e data a re f ram Fod tar ( A f h r Klssrxr, 1 9 7 2 1 . FIGTJRE FIGURE 7. 7. (location (locaLlon - 23 2a . C- 15 �_____________ The main main feature feature illustrated illustrated on on section sectionB-B' B - B t (Fig. (Fig. 8) 8 ) is Ts The that the the large large apparent a2parent thickness thickness of of Hemlock Hemlock volcanic volcanic rocks rocks (see (se that 1980) along along the the west west side si6e of of the the Amasa A m s a uplift uplift may, msyr in in Fooser 1980) Foose, partr be be accounted accomted for for by by tectonic tectonic stacking. stackinq. Structural Structural data dsta at st part, alternate field field stops stops 7a 7a and and 7h 7b lend lend support support for for the the idea idea of of alternate At stop 7a mafic volcar..c tectonic thickening of the Hemlock. At stop 7a mafic volcariic Hemlock. tectonic thickening of the rocks are are intensely intsnsely deformed defornsd and and have have aa prominent prominent foliation foliation that that rocks Stretch 3. Figure on shown 3. Stretch is oriented nortkdestward, as shown on Figure as northwestward, oriented is lineations on on the the foliation foliation surfaces surfaces plunge plunge steeply steeply toward toward the the lineations slet west. At At station station 7b 7b axes axes of of small small drag drag folds folds in in siliceous siliceoas slat.? west. plunqe gently gently northwestward northwestward and and their their Z-shape 2-shape symmetry s-pmetryindicates indicates plunge northeastward sense sense of of vergence. vergence. Thinly Thinly layered layere6 tuff tuff at at aa northeastward oriented is a1Qrnate 8 has a penetrative foliation that is orisnted 8 has a penetrative foliation that altrnate stop N55 W, L?, 60 60 SW, S7J, and and other other outcrops outcrops in in the the region region have have similarly similarly N55 oriented foliations. foliations. Taken Taken together, together, these these and and other other outcrops outcrops on on oriented the west west side side of of the the Amasa Amasa uplift uplift indicate indicate that that tectonic tectonic stacking stackiii~ the could have have significantly significantly thickened thickened the the Hemlock Hemlock volcanic volcanic pile. pile. could is not resolved The nature nature of of the the stacking, stacking, however, however, is not resolved at at this this The B-8' (Fig. (Fig. 8) 8 ) suggests suggests that that it it is is an an imbricate imbricate time. Profile Profile B-B' time. may represent thrust fan. fan. Alternately, Alternatsly?the the Arnasa Amzsa uplift zay represent aa domed Zoined thrust Either style of deformation would account fr the far ths Zuplex system. Either style of defornation w o ~ l Z zccocnt duplex system. apparent. the and rocks volcanic s ~ ? z r e~*. thick szction of Hemlock volcanic rocks sn2. the Hemlock of section thick structural discordance discordance between between the the Michigamme NichigxixneFormation Foriaationand an3 the the structural (1980). :Iemlock volcanic volcanic pile pile as as pointed pointed out out by by Foose Foose (1980). Hemlock ....N2OE B J\ 2000 2000 --e 0 I'= xx xxx xxx 0 I000 1000 x 0o O- IIH.m1o L flZ— Rocks Rocks ofof - Baraga Bamga Group Group '—— Badwater Bodwatet Miiigamme Michigomme I L ARCHEAN ARCHEAN Randvilla Rondvlile 0and Rocks ofof Menominee ~enominea Rocks 00 rOUOS Chocolay OCOI ØY GGroups 00 a * Drag Drag Fold FOI~ SmIles 5 miles y 55kilometers kilometers Basemeift Basement Gneiss Gneiss \ Fault FOUI~ Structural profile B—B'. Note drag fold from stop 7. Rou;hly 20 times vertical exageration. See Figure 3 for location. FIGURE 8. C-16 �In particular, particularr either either system system would would explain explain the the structural structural In discordance between between the the Hemlock Hemlock and and the the magnetically magnetically mapped mapped iron iron discordance fornation that that lies lies just just above above the the contact contact in in the the Michigamrne Michigamme formation Formation. We We interpret interpret the the Michigamme Michigamme Formation Formation to to be be separated separated Formation. from the the Hemlock Hemlock Formation Formation by by aa thrust thrustfault. fault. The The configuration configuration from of the the magnetically magnetically mapped mapped iron iron formation formation mimics m.imics the th2 of Inasmuch configuration of of the the thrust thrust fault. fault. Inasmuch as as the the western western edge edge configuration of the the Hemlock Hemlock volcanic volcanic pile pile is is covered, coveredr this this fault fault is is inferred inferred of and was was not not observed observed in in the the field. field. and The The rocks rocks that that lie lie in in the the region region between between the the Bush 8ush Lake Lake fault fault north-verging the 3) are part of 3) are part of the north-verging and the Niagara fault (Fig. Niagara fault (Fig. and the thrust system system described described above, above, but but the the exact exact nature nature of of the the thrust Maharidge's (1986) thrusting in this region remains problematic. Maharidge's (1986) thrusting in this region remains problematic. interpretation interpretation that that the the Feich Felch trough trough is is part part of of aa nappe nappe structure structure also, it cannot be discounted at has not been proven, butr alsor it cannot be discounted at this this has not been proven, but, Early and Archean show that both time. Our recent recent studies studies show that both Archean and Early Our time. Proterozoic rocks rocks possess possess aa prominent prominent low-dipping low-dipping foliation foliation that that Proterozoic is superimposed superimposed upon upon aa steeply-dipping steeply-dipping foliation foliation in in the the Archean Archean is rocks (see (see field field stops stops 10 10 and and 11). 11). Also, Alsor in in this this region region there there is is rocks firm evidence evidence for for southwest southwest verging vercjing thrusting thrusting in in rocks rocks of of both both firm the Feich Felch and and Calumet Calumet troughs. troughs. We We tentatively tentatively interpret interpret the the the south-verging structure structure as as being beincj formed formed due due to to south—directed south-Zirectsd south-verging backthrusting caused by by ramping ramping of of the the north-verging north-verging thrust thrust caused backthrusting faults. Best evidence evidence for for this this southward southward vergence vergence is is found found at at Best faults. stops 9, g r 11, llr 12, 12r and and 13. 13. We We will will visit visit stops stops 9, g r 11, llfand and 12 12 but but stops we will will most most likely likely not not visit visit stop stop 13, 13ran an alternate alternate stop, stopr because becauss we of difficult difficult access. access. of composite section section (Fig. (Fig. 9) 9 ) along along the the length length of of the the AA composite structural traverse traverse summarizes summarizes our our current, currentr and and as as yet, yetr structural tentativer interpretation interpretation of of the the style style of of deformation deformation that that tentative, This interpretation is consistent occured in northern Kichigan. This interpretation is consistent in northern Michigan. occured with aa fore1.nd forelan6 thrust thrust system system as as depicted Zepicted in in the the model zodel of of an an with The idealized orogen by Hatcher and Williams (1986). idealized orogen by Hatcher and Williams (1986). The idealized idealized orogen consists consists of of aa foreland foreland overthrust overthrust belt, beltr an an overthrust overthrust orogen metamorphic core complex that may include ophiolites metamorphic core complex that may include ophiolites and and thrusted thrusted crystalline basement basercient rocks, rocksr and and an an accreted accreted plutonic/volcanic plutonic/volcanic crystalline terrane. Part Part A-A' A-A' of of the the composite composite section section marks marks the the foreland foreland terrane. tectonism thin-skinned overthrust belt belt which which involves involves thin-skinned tectonisn with with overthrust relatively of basement basement rocks rocks in in the the thrusting thrusting relatively little little involvement involvement of (note these these comments comments apply apply to to the the area area close close to to this this traverse, traverse, (note Early and the the amount anount of of basement basement involvement involvenent in in Early Proterozoic Proterozoic and overthr~sting may may change change along along the the strike strike of of the the Penokean Penokesn overthrusting orogen). Telescoped Telescoped and and foreshortened foreshortened Early Early Proterozoic Proterozoic strata strata orogen). are ars separated separated from from basement basement rocks rocks along along aa basal basal detachment detachment fault. fault. (1987) Nd isotope isotope studies studies by by Barovich Barovich and and others, others, (1937) indicate indicats that that Nd the southern southern half half of of this this terrane terrane was was derived derived from from the the Wisconsin Wisconsin the magmatic terrane terrane to to the the south, southr thus thus supporting supp~rtiricj the the idea idea of of magmatic northward tectonic tectonic transport transport of of at at least least aa part part the the Michigamme Michigamme northward Formationr and and explaining explaining the the presence presence of of deep deep water xater turhidite turbidite Formation, deposits on on the the continental continental margin. margin. deposits which Section B-B' B-B' marks marks the the Amasa Amasa uplift uplift area, arear which is is Section defamation between thick-skinned basement-involved transitional between thick-skinned basement-invalved defamation transitional �N S MARGINAL MARGINAL BASEMENT BASEMENT ARCH ARCH A AA I Michlgamme Basin Basin Michigomme Foreland Thrust Thrust Foreland I 'S Baraga Baraga Group Group Rocks x X . — — XX - Felch Felch - Calumet Calumet Imbricate Imbricate Thrust Thrust Belt Belt ——— ——— GL I Uplift Uplift Amaso Amasa — — X X x' ARCHEAN Hemlock Hemlock ~ e n o m inee nee Menomi VolcafliCS volcanics Chocolav && Chocolav Group Group ' -.- —GL X \- & 0 a 10 Ground Ground level level - Bush Bush Lake Lake Fault Fault - NF -- i.l10 Miles a Fault Fault - GL GL 81 BL o Wisconsin Wisconsin Accreted Accreted Magmatic Magmatic Arc Arc XXX XXX Accreted Accreted Volcanic Volcanic Plutonic && Plutonic Rocks Rocks Rocks ~ocks i' a' B' c LIB Niag4ra Niagara Fault Fault Km Composite st.ructuralprof profile C o m p o s i t e st.ruct.ura~1 i 1 e 1ong lt3ng line 1ineconnecting connecting to C' C ' (in c,n Figure? 3 . See See text tsxt for for discussion. dj.scussion. Figure 3. to FIGIJRE 9. 9. FIGUflE <: A X �to the the south south near near the thecontinental continentalmargin, marginf and and the the thin-skinned thin-skinned to tectonism tectonism of of the the foreland foreland thrust thrust belt belt to to the the north. north. Tentatively, Tentatively, we consider consider the the Amasa Amasa uplift uplift as as having having behaved behaved as as aa stable stableblock block we consisting of of an an Archean Archean core core and and aa large large volcanic volcanic pile pile over over consisting which less less competent competentrocks rocksof of the thecontinental continentalmargin marginwere werethrust. thrust. which The thrust thrust system system refracted refracted upward upward from from the theArchean Archeanbasement basement on on The the south south so so that that it it is is largly largly confined confined to to supracrustal supracrustal Early Early the Proterozoic strata strata north north of ofthe theuplift. uplift. Proterozoic Part Part C-C' C-C' on on Figure Figure 99 marks marks the the crystalline crystalline metamorphic metamorphic core core complex sytem sytem of of Hatcher Hatcher and and Williams Williams(1986). (1986). It It consists consistsof of an an complex imbricate, piggy piggy back-type back-type of of crystalline crystalline thrust thrust sheet sheetwhich which is is imbricate, bounded on on the the south south by by the the Niagara Niagara fault faultzone zoneand and on on the the north north bounded by the the Bush Bush Lake Lake Fault Fault(Fig. (Fig. 3). 3). The The Bush Bush Lake Lake Fault Fault appears appears to to by system. It have been a key feature in evolution of the thrust system. It been a key feature in evolution of the thrust have trend which between structures on the north marks a boundary between structures on the north which trend boundary marks a northwest northwest and and those those on on the the south south which which trend trend east-west east-west (see (see Fig. Fig. and 1984 (Attoh and Vander Muelen, isograds 3). Metamorphic isograds (Attoh and Vander Muelenr 1984 and Metamorphic 3). is south side the that indicate Klasner and Attoh, 1986) indicate that the south side is Klasner and Attoh, 1986) which along fault to be a major upthrown. We We interpret interpret it it to be a major fsult along which upthrown. crystalline rocks rocks of of the the continental continental margin margin were were thrust thrust upward upward crystalline and over over the the Amasa Amasa uplift. uplift. and Rocks of of the the Wisconsin Wisconsin magmatic magmatic terrane, terrane, south south of of the the Rocks Niagara Niagara fault fault zone, zone, have have been been accreted accreted to to the the continental continentalmargin. margin. macjmatic Nd Nd isotope isotope data data indicate indicate that that the the volcanic volcanic rocks rocks of of the the magmatic terrane represent represent new new Early Early Proterozoic Proterozoic crustal crustal material material terrane (Barovichand and others, others, 1987). 1987). Klasner Klasner and and Osterfeld Osterfeld (1984) (1984) and and (Barovich Sims and and others others (1984b, (1904b, 1985) 1985) suggested suggested that that the the magmatic magmatic rocks rocks Sims of northeast northeast Wisconsin Wisconsin are, aref in in part, partf allochthonous. allochthonous. Klasner Klasner and and of others (1985, (1985, page page 284) 284) and and Klasner Klasner and and Attoh Attoh (1986) (1986) inferred inferred others that the the actual actual edge edge of of the the continental continental margin margin is is cryptic, cryptic, and and that p~ssibly buried buried beneath beneath the the allochthonous allochthonous magmatic magmatic terrane terrane in in possibly terrane is northern Wisconsin. Wisconsin. The The Wisconsin Wisconsin magrnatic magmatic terrane is equivalent equivalent northern to to the the accreted accreted volcanic/plutonic volcanic/plutonic terrane terrane of of Hatcher Hatcher and and Williams William Schulz crust. oceanic contain slivers of (1986)r which can contain slivsrs of oceanic crust. Schulz which can (1986), northeast in assemblage an ophiolite (1987b) has identified an ophiolite assemblage in northeast identified has (1987b) Xisconsin. wisconsin. The geology geology of of the the Early Early Proterozoic Proterozoic continental continental margin margin The consistent is Michigan younqer assemblage of of northern northern Michigan is consistent with with younger assemblage Atlantic-type (passive) (passive) margins margins (Nelson (Nelsonand and others, others, 1982) 1982) as as Atlantic-type represented in in the the Ouachitas, Ouachitas, New New England England Appalachians, Appalachiansr Tibetan Tibetan represented They have Hiinalayas, and and Oman Oman Mountains. Nountains. They have in in common common an an inboard, inboard, Himalayas, allochthonous foreland foreland thrust thrust belt, belt, and and an an outboard outboard imbricate imbricate allochthonous thrust thrust system system involving involving crystalline crystalline basement basement rocks. rocks. AGE AGE OF OF THRUSTING THRUSTIEG AA minimum minimum age age for for the the overthrusting overthrusting is is 1824 1824 ±+ 2.6 2.6 Ma, Ma, which which granite pluton is aa U—Pb U-Pb zircon zircon intercept intercept age age on on an an undeformed undeformed-granite pluton is that intrudes intrudes Badwater Badwater Greenstone Greenstone at at locality locality AA on on Figure Figure 55 (Z. (Z. that E. Peterman, Peterman, written written communication, communication, 1987). 1987). AA possible possible maximun imximum E. 17 Ma; Ma; two two splits splits of of apatite apatite from from iron iron formation formation age is is 1929 1929 ++ 17 age uriderlying the tEe Michigamme Hichigainme Formation Formation in in the the Earaga Earaga basin basin yield yield underlying �lead-lead 17 Ma lead-lead ages ages of of 1929 1929 ±+ 17 Ma CR. (R. E. E. Zartman, Zartman, written written communication, communication, 1987). 1987). The het thrusting thrusting occured occured within within the the interval interval 1930 1930 to to 1824 1824 Ma. Ma. Data from from northeastern northeastern Wisconsin, Wisconsin, within within the the Data Wisconsin Wisconsin magmatic magmatic terrane, terrane, is is consistent consistent with these these constraints constraints and further further refine refine the the age age limits. limits. dome, deformed In the Dunbar Dunbar dome, granitoid granitoid rocks rocks have have U-Pb U-Pb zircon zircon ages ages of of ca ca 1860 1860 Ma, Ma, whereas whereas an an undeformed, post-tectonic granite granite has has an an age age of of 1835 1835 ±+ 66 Ma (Sims (Sins undeformed, and and others, others, 1985). 1985). These data data suggest suggest collision collision along along the the These Niagara fault fault zone zone occured occured about about 1850 1850 Ma. Ma. Probably Probably the the thrusting thrusting Niagara in in the the continental continental margin margin assemblage assemblage occurred occurred approximately approximately contemporaneous with or or slightly slightly later later than than collision. collision. contemporaneous FIELD FIELD STOPS STOPS AND AND ROAD ROAD LOG LOG The The structural structural traverse traverse across across northern northern Michigan Michigan starts starts in in L'Anse, L'Anse, Michigan and and ends ends near near Florence Florence , Wisconsin. Wisconsin. Eighteen Eighteen stops stops are are shown shown on on Figure Figure 33 but, but, because because of limited limited time time and and difficult difficult access access to to several several of the the localities, localities, only only eight eight to to ten ten of them Localities them will will be be visited. visited. Localities 2b, 2b, 7a, 7a, and and 7b, 7b, will will not not be be visited visited and and localities localities 2a, 2a, 8, 8, and 13 13 are are alternate alternate stops, stops, which which , will be be visited visited only only if if time time permits. permits. Road Road logs logs are are not not given given for for the the alternate alternate stops, stops, but but their their location location is is given given by by section, section, township, township, and and range. range. ROAD LOG Follow Follow highway U. S. S. 41 41 west west from from Marquette Marquette to to L'Anse. L'Anse. ROAD LOG Proceed Proceed west west through through L'Anse L'Anse to to bridge bridge over over Falls Falls River River on on U. U. S. S. 41. Park 41. Park in in the the pulloff pulloff area area on on the the north north side side of of the the highway highway between between the the RR RR tracks tracks and and the the bridge. bridge. Numerous STOP STOP 1-FALLS 1-FALLS RIVER. RIVER. Numerous outcrops outcrops are are present present along along Falls Falls River Structures River on on both both sides sides of of the the highway. highway. Structures consist consist of of northward—verging, small-scale1 folds with northward-verging, small-scale, recumbent recumbent folds with subhorizontal subhorizontal axial-plane axial-plane foliation foliation indicating indicating nappe—thrust nappe-thrust style style of deformation deformation in in this this area. area. ROAD ROAD LOG. LOG. From From the the parking parking lot lot area area for for stop stop 1, 1, follow follow U. U. S. S. 41 41 east east for for 2.6 2.6 miles. miles. Turn Turn west west on on Golf Golf Course Course Road Road and and drive drive 1.75 1.75 miles Follow miles to to the the cul-de-sac cul-de-sac at at the the end end of of the the road. road. Follow footpath footpath to It to Little Little Mountain. Mountain. It is is about about a 15 15 minute minute walk walk to to the the too to? of of the the mountain; mountain; be sure sure to to follow follow left left forks forks of of the the main, main, well well worn worn path. Path path. Path extends extends around around the the southwest southwest corner corner of of the the mountain mountain where where it it turns turns sharply sharply toward toward the the east east up up the the south south flank flank of of the the mountain. Follow mountain. Follow path path to to the the highest highest point point on on the the mountain. mountain. From From this this vantage vantage you you can can see see the the Keweenaw Keweenaw Peninsula Peninsula of of the the Midcontinent Midcontinent Rift Rift System System to to the the north-northwest north-northwest and and the the Archean Archean terrane terrane of of the the northern northern complex complex (Fig. (Fig. 3) 3) to to the the east-southeast. east-southeast. The of the the The low low lying lying area area to to the the south south is is underlain underlain by by rocks rocks of Michigamrne Michigamme basin. basin. Outcrops STOP STOP 2-LITTLE 2-LITTLE MOUNTAIN. MOUNTAIN. Outcrops at at the the highest highest point point on on Little Little Mountain Mountain consist consist of of an an unfoliated unfoliated (ca (ca 1.1 1.1 Ga) Ga) Keweenawan Keweenawan diabase diabase Grading dike dike and and graded graded beds beds of of metagraywacke. metagraywacke. Grading is is expr2ssed expressed by by presence presence of of foliation foliation in in the the finer finer grained grained bed bed tops. tops. The The beds beds face face toward toward the north north and and dip dip steeply steeply south, south, indicating indicating that that they they are are overturned overturned toward toward the the north. north. �4., LITTLE MOUNTAIN, MOUNTAIN. BARAGA BARAGA COUNTY, COUNTY, Mt. MI. LITTLE corner of FIGURE 10 10. Field Field sketch sketch mao map of of the the northeast northeast corner of FIGURE for thrust faulting. Mountain Mountain showing showing evidence evidence for thrust faulting. Little Littls sketch map, map, shows shows the the nature nature of of structural .?t~ii~tar5l Figure 10, 10, aa sketch Figure Here, kcre, deformation deformation near near the the northeast northeast corner corner of Little Little Mourt1n. Mountsin. overturned graded beds of inetagraywacke strike east--west sixilar overturned graded beds of netagr&ywacke strike east--west similar and dip dip steeply steeply south, south, as as does does Si 31 foliation. foliation. In In several several places places and bedding has has aa convoluted convoluted appearance, appearance, indicative indicative of of irtene intense bedding zones deformation. Deformed zones of of concretions concretions crudely crudely define define Deformed deformation. bedding. The long long axes axes of of the the concretions ~oncretio~isplunge plunge steeply steeply The bedding. southwest, indicating indicating extension extension in in this this direction. direction. old Fold ages axes southwest, easternrsz the On a bench at clung& gently aently towardthe toward the west. west. O n a bench at the easternrms:. plunge W.. oriented edge of of the thft mountain mountain similar similar graded graded beds beds are are oriented N(0 NEC*X: edge I T C- 21 �5 7 570NW, Looking and ~ are are ~ upright. upright. ~ Looking west west from from the the bench, bench, the the and intensely intensely deformed deformed beds beds of of an an overlying overlying thrust thrust can can be be seen seen in in the the Tectonic three-meter-high cliff. cliff. Tectonic striations striations can can be be found found on on the the three-meter-high underside of narrow narrow overhangs overhangs on on the the cliff cliff face face aa few few meters meters to to underside The the north north and and west. west. The striations, striations, along along with with northward northward the overturning of of bedding bedding indicate indicate that that the the hanging hanging wall wall of of the the overturning The thrust moved moved northeastward. northeastward. The total total thickness thickness of of the the thrust thrust thrust fault fault zone zone at this locality is aameter meter or or less. less. The The thrust thrust fault fault About can be traced traced down down the the east east flank flank of of Little Little Mountain. Mountain. About 100 100 can meters south south and and two two benches benches down down the the flank flank of of the the mountain mountain aa meters glacially-gouged, glacially-gouged, upright upright bed bed of of metagraywacke metagraywacke which which lies lies beneath beneath It the fault fault observed observed above above is is well well exposed. exposed. It too too has has deformed deformed the concretions concretions whose whose long long axes axes plunge plunge southwest. southwest. The The main main point point at at this this stop stop is is that that Little Little Mountain Mountain probably probably an an erosional erosional remnant remnant of of an an allochthonous allochthonous sheet sheet of of rocks rocks that that has been been thrust thrust northeastward northeastward as as part part of of an an imbricate imbricate thrust thrust has Further system. Further studies studies at at Little Little Mountain Mountain are are needed needed to to fully fully system. document the nature and style of deformation here. document the nature and style of deformation here. is is ROAD LOG LOG Return Return to to the the vehicle vehicle by by walking walking north north and and west west around around ROAD the north north side side of of Little Little Mountain Mountain to to the the intersection intersection of of the the the Turn path. Turn right right (east) (east) on on the the path and and return return to to Golf Golf Course Course path. Follow Road. Follow the the road road eastward eastward to to the the intersection intersection of of Golf Golf Road. Course Course Road Road and and and and U. U. 5. S. 41. 41. Turn Turn right richt (south) (south)on on U. U. S. S. 41. 41. Located ALTERNATE ALTERNATE STOP STOP 2a-TAYLOR 2a-TAYLOR MINE. MINE. Located in in the the NW NW 1/4 1/4 sec. sec. 9, 9, T49N, T49N, R33W, R33W, graphitic graphitic slate slate and and ironiron- formation formation of of the the Michigamme Michigamme Formation near near the the mine mine have have been been folded folded about about aa penetrative penetrative Formation axial-plane south-dipping, axial-plane foliation foliation (see (see Fig. Fig. 7). 7). Keels Keels of of south-dipping, rootless folds folds in in the the graphitic graphitic slate slate indicate indicate that that bedding bedding has has rootless been transposed transposed parallel parallel to to foliation, foliation, and and that that the the beds beds are are been overturned to the the north. north. An An unfoliated unfoliated Keweenawan Keweenawan diabase diabase dike dike overturned Style slate. the ironcuts the graphitic graphitic slate. Style of of folding folding in in the the iron— cuts formation can can be be seen seen in in aa roadcut roadcut about about 30 30 meters meters north north of of the the formation dike. dike. Similar steeply steeply south-dipping south-dipping foliation foliation occurs occurs in in Early Early Similar Proterozoic phyllite about about 22 km km to to the the south south at at Plumbago Plumbago Creek Creek Proterozoic (2b, Fig. 3). 3). The The phyllite phyllite is is exposed exposed in in aa creek creek bed bed at at the the base base (2b, by Archean underlain facing slope that is steep north of a steep north facing slope that is underlain by Archean a of gneiss. Thus, Thus, it it appears appears that that the the foliation foliation in in the the phyllite phyllite dips dips gneiss. beneath the gneiss, suggesting that the gneiss is thrust beneath the gneiss, suggesting that the gneiss is thrust over over the the phyllite. phyllite. ROAD LOG. LOG. From the the intersection intersection of Golf Golf Course Course Road Road and and U. U. S. S. 41 41 ROAD Between drive drive 7.6 7.6 mile mile south south on on U. U. S. S. 41 to Canyon Canyon Falls Falls Park. Park. Between Alberta U. S. S. 41 41 and and Canyon Canyon Falls Falls Park Park the the highway highway passes passes over over Alberta on on U. which is (Fig. 3) the northern northern complex complex (Fig. 3) which is an an the west west end end of the the Follow uplifted block block of of Archean Archean basement basement rock. rock. Follow the the nature nature path path from the parking parking lot lot at at Canyon Canyon Falls Falls Park Park westward westward for for about about 10 10 from the minutes minutes along along Sturgeon Sturgeon River River to to the the Falls. Falls. Proceed Proceed to to the the northnorthNo south oriented cliff cliff face face in in back back of of the the fence. fence. No need need to to walk walk up the the steps steps in in the the cliff cliff face face for the critical critical information information at at up this this stop stop is is visible visible in in the the cliff cliff face. face. �STOP 3-CANYON 3-CANYON FALLS. FALLS. At this this stop stop subhorizontal subhorizontal Early Early At STOP ripples prominent interference Proterozoic quartzite contains prominent interference ripples quartzite contains Proterozoic that appear appear to to be be unaffected unaffected by by Early Early Proterozoic Proterozoic deformation. deformation. •that Close examination examinationof of the thecliff cliffface, face, however, however, reveals reveals that that thin thin Close pelitic layers layers intercalated intercalated between between the the uartzite quartzitebeds bedshave have aa pelitic 27SW. SW. Also, Also, tectonic tectonic penetrative foliation foliation oriented oriented N85°W, N 8 9 W, 27 penetrative 20 striations on on the the quartzite quartzite beds beds are are oriented oriented '2 toward toward NlO°E. N10 E. striations Clearly the the quartzite quartzite has has been been transported transported some some unknown unknown distance distance Clearly northeastward (based (based on on the the north north sense senseof of vergence vergence found found in in northeastward less the by taken up was previous outcrops). Deformation was taken up by the less Deformation outcrops). previous shaly layers; layers;the the more more competent competent quartzite quartzite beds beds appear appear competent shaly competent to have have undergone undergone little, little, or or no, no, internal internal deformation, deformation, but but to detailed petrofabric petrofabric studies studies are are needed needed to to confirm confirmthis. this. detailed As shown shown on on Figure Figure6, 6, the the flat-lying flat-lying quartzite quartzite at at Canyon Canyon As Falls must must lie lie beneath beneath one one or or more more thrust thrust faults faults that that intensely intensely Falls deformed Early Early Proterozoic Proterozoic strata strata at at Taylor Taylor Mine Mine and and Plumbago Plumbaao deformed Creek. Also, Also, elevation elevationdata, data, together together with with structural structural data data at at Creek. these three three localities localitiesnecessitate necessitatelocal local involvement involvementof of Archean Archean these basement rocks rocks in in the the overthrusting. overthrusting. basement Return to to Canyon Canyon Falls FallsPark Parkparking parkinglot. lot. Drive Drive south south on on ROAD LOG LOG Return ROAD U. S. U. S. 41 for 3.0 miles to the intersection with highway U. S. 41 for 3.0 miles to the intersection with highway S. U. 141/28. Turn right right (west) (west)on on highway highway 141/28 141/28 and and follow follow it it for for Turn 141/28. 4.1 miles. miles. Turn south southon on U. U. S. S. 141 141 and and drive drive 4.1 4.1 miles miles to to atop Turn 4.1 4. 4. Numerous outcrops outcrops of of the the upper upper slate slats member member of of the the Numerous 141 south of Covington. S. U. S. 141 south of Covington. Michiganune Formation occur along Formation occur along U. Michigamxne field We have have selected selectedaa few fewof of the the more more informative informative outcrops outcropsas as field We 5 , 6, 6,and and 77on on Figure Figure6). 6). stops (4, (4,5, stops STOP 4-U. 4-U. S. S. highway highway 141. 141. Located Located on on the the east east side side of of the the STOP stop consists of thick beds of graywacke that this stop consists of thick beds of graywacke that are highway, this are highway, graded and and have have flame flame structures structures at at some some bed bed contacts. contacts. graded across (SO)is is Penetrative foliation0refracts foliationrefrac~s across bedding. bedding. Bedding Bedding (SO) Penetrative SW. SW, and cleavage H, 20° 20 SW, cleavage (Si) (Sl)N75°W, N~!?W, 4cf 4CfSH. generally oriented oriented N62 N62 W, generally Lineations formed formed by by the the intersection intersection of of cleavage cleavage and and bedding bedding Lineations Numerous Numerous concretions concretions form form strain strain plunge 140 14 toward toward S83°W. S83 W. plunge ellipses with with the the axes axes of of maximum maximum elongation elongation that that plunge plunge ellipses generally 540 54O toward toward S36°E. ~36¡~ generally At this this outcrop outcrop bedding bedding (SO) (SO)dips dips only only moderately moderately toward toward the the At as bedding marked variations in the orientation of in the orientation of bedding as south, but marked variations but south, one as outcrops can be seen in other well as cleavage (Sl) can be seen in other outcrops as one cleavage (Si) as well U. S. S. highway highway 141. 141. Ne We mainly mainly used used these these proceeds south southalong alongU. proceeds variations in in structure structure to to locate locate the the position position of of thrust thrust faults faults variations shown on on Figure Figure6. 6. shown ROAD LOG. LOG. ROAD Proceed Proceed south south on on U. U. S. S. 141 141for for2.4 2.4 miles. miles. 5-U. S. S. 141. 141. AA long long outcrop outcrop of of thick-bedded thick-bedded graywacke graywacke is is STOP 5-U. STOP beds Graded present on on the the west west side side of of the the highway. highway. Graded beds strike. strike. present and are are nearly nearly vertical; vertical; foliation foliztion is is subparallel sabparallel rouqhly N67oW, N67oM, and roughly C- 23 �•to to bedding. bedding. At At the the north north end end of of the the outcrop outcrop bedding beddin5 is is overturned overturned toward toward the the north. north. ROAD LOG ROAD LOG clearly clearly Proceed south south on on U. U. S. S. 141 141 for for 3.4 3.4 miles. miles. Proceed STOP STOP 6-TRACY 6-TRACY CREEK. CREEK. Examine outcrops outcrops on on both both sides sides of of the the Examine highway highway which which consist consist of of graded graded graywacke graywacke beds. beds. Folds Folds in in be-Jding be3ding (SO) have have axes axes that that plunge plunge gently gently toward toward the the 0northwest. northwest. (SO) Refracted, N86 E, E, 85CSE. 8 9 SE. Refracted, penetrative penetrative Si Sl foliation foliation is is oriented oriented N86 Concretions tend tend to to lie lie in in the the bedding bedding plane. plane. Some concretions, concretions, Concretions Some however, however, have have been been partly transposed transposed so so that that their their long long axes axes are are partly partly parallel parallel to to bedding and and partly partly parallel parallel to to foliation. foliation. Many Many have have been been deformed deformed so so that that their their long long axes axes are are completely completely parallel to This parallel to foliation. foliation. This outcrop outcrop shows shows the the style style of of deformation deformation in in the the slates slates and and metagraywackes metagraywackes of of the the Michigarnne Michigamne Formation. S. 141 141 traverse traverse Formation. Some Some outcrops outcrops on on this this part part of of the the U. S. have 6. A completely completely have two two foliations foliations as as shown shown on on Figure Figure 6. A different, different, north north dipping dipping foliation foliation will will be be seen seen at at the the next next stop. stop. ROAD ROAD LOG. LOG. Proceed south south on on U. U. S. S. 141 141 for for 1.0 1.0 mile. mile. Proceed STOP 7-U. S. S. 141. 141. Most features features in in this this long long outcrop outcrop of of black black STOP 7-U. Most slate slats and and metagraywacke metagraywacke on on the the east east side side of of the the highway highway indicate indicate aa. southward southward sense sense of of thrusting, thrusting, completely completely opposite opposite to t.o that that observed Figure sketch observed at at all all previous previous stops. stops. Figure 11 11 is is aa sketch illustrating illustrating the the types types of of features features observed observed along along the the length length of of the and 9. 9. At point p i n t 55 the outcrop. outcrop. Most significant significant are are points points 55 and Most At small small drag drag folds folds indicate indicate aa southward southward sense sense of of vergence. veqencs. This This southward southward sense sense ofo f -vergence vergence is is confirmed confirmed by by several several other other features features in in this this outcrop outcrop and and indicates indicates backthrusting backthrusting at at this this location. meter-wide zone zone of of siginoidal sigmoidal quartz veins at point point 99 location. AA meter-wide veins at is is one one of of the the more more striking striking features features in in this this outcrop. outcrop. The The sigrnoidal sigrrioidal shape shape of of the the quartz quartz veins veins suggests suggests down-to-the--north down-to-the-north normal normal faulting, faulting, opposite opposite the the sense sense of of movement movement observed observed at at point point 5. The 5. The structure structure at at point point 99 may may be be aa late late feature feature related related to to post-thrusting post-thrusting uplift upliftof ofthe theAniasa Amasa dome. dome. Such Such uplift uplift would would cause cause rotation rotation of of pre-existing pre-existing features, features, but but the the amount amount of of rotation rotation is is not not known. known. We We interpret interpret the the backthrusting backthrusting at at this this locality locality to to be be caused caused abrupt abrupt change change in in dip dip of of the the thrust thrust sytem sytem as as it it ramps ramps off off the the north north edge edge of of the the Amasa Amasa uplift uplift (see (seeFig. Fi9. 6). 6). by by an an ROAD ROAD LOG. LOG. Proceed south south on on U. U. S. S. 141 141 for for aa distance distance of of 23 23 miles miles Proceed S. 141 141 with with U. U. S. S. highway highway 22 at at the the west west end end to the the junction junction of of U. S. to of of Crystal Crystal Falls, Falls, Michigan. Michigan. On On this this segment seqmit of of the the traverse, traverse, the the highway highway passes passes over overthe thewest westflank flankofofthe thaAinasa Amasa uplift. Turn left (east) U. S. S. 141/2 141/2 and and follow follow it it to to the the center center of of Crystal Crystal (east) on on U. Falls, Falls, where where the the highway highway intersects intersects MM 69. 69. This is is at at the the This intersection intersection of of Superior Superior and and Fifth Fifth street, street, near near the the U. 3. S. S . Post Post Office To proceed proceed to alternate alternate stop stos 8, turn Office in in Crystal Crystal Falls. To Falls. to turn - 8, east to stop stop 99 proceed proceed south southon n U. east on on MM 69. 69. To To continue continue on to TJ. . S. uplift. Turn left 2/141. 2/14l. C-24 �STOP STOP 77 C a — C • • •• N g! 4 —U 0 ...- NORTH NORTH : '8 • V o 0 a a •U 2U •6 C V 0 V 0 0 V I-I-I 00 I 10 10 meters meters FIGURE 11. 11. Sketch Sketch of FIGURE 7, east east side side of of roa road, of roadcut roadcut at at stop stop 7, showing location location and and attitude showing attitude of of some some key key structural structural features. features. This ALTERNATE STOP STOP 8-OLD 3-OLD M69. M69. This stop stop is is located located in in the the NW MW 1/4, 1/4, ALTERNATE 20, T43N, R31W, about 500 meters east of the bridge over sec. 20, T43N, about 500 meters east of the bridge over the the sec. Micigamme0River K i ~ ~ i g a m m e R i v on eon r Old Old MM 69. 69. Here Here thinly thinly layered layered tuff, tuff, oriented oriented N20 W, 50 50 Sw, SW, has has aa penetrative penetrative Si Sl foliation foliation oriented oriented NG5CW, N S ~ W , N2j W, This 79 79 SW. SW. This northwest—trending northwest-trending foliation foliation is is characte;istic characteristic of of the the structural structural fabric fabric in in the the region region (west (west side side of of the the Amasa Amass uplift), 3. uplift), as as shown shown on on Figure Figure 3. Falls, To ROAD LOG. LOG. To reach reach stop stop 99 from from the the center center of of Crystal Crystal Falls, ROAD proceed S. 2/141 2/141 for for roughly roughly 66 miles, miles, to to the the road road on on proceed south south on on U. U. S. the the east east to to Horse Horse Race Race Rapids Rapids and and Iron Iron County County Airport. Airport. Turn Turn left left (east) (east) and and follow follow this this road road for for 3.5 3.5 miles miles to to parking parkinq area area at at Horse Race Race Rapids. Rapids. Follow Follow path down down slope slope to to plentiful plentiful outcrops oiitcr~ps Horse along alone the the river. river. This This outcrop outcrop area area is is south south of of gush 3usl-1 At A t this this locality locality graded graded beds beds (SO) (SO) of of face face south, south, and and form forn aa system systsm of of folds axial—plane foliation (1). folds that have a subhorizontal axial-plane (.^1). Fcld Fcld foliation Si Sl foliation has has been been axes in in SO SO plunge plunce gently gently westward. westward. axes refolded n ~ - i r lcoaxial ycoaxialwitli with refolded in in some some places places on on fold fold axes axes that thatare arenearly Syntectonic the fid foldaxes axes in in SO. SO. Syntectonic quartz quartz veins veins occur occur in in the the axes axes STOP STOP 9-HORSE RACE RACE RAPIDS. RAPIDS. Lake Lake Fault Fault (see ( s e e Fig. Fig. 3). 3). graywacke qraywacke stratigraphically stratigraphically C-25 �of of We some folds. folds. We interpret interpret this this outcrop outcrop to to be be part part of of the the some south-verging backthrust backthrust system, system, the the same same as as that that found found in in the the south—verging Feich trough area (see 3). Felch Trough—Caluinet Trough-Calumet trough (see Fig. Fig. 3). Return ROAD LOG. LOG. Return to to the the intersection intersection of of the the Horse Horse Race Race Rapids Rapids ROAD Turn highway road with with U. U. S. S. highway 2/141. 2/141. Turn left left onto onto U. U. S. S. 2/141 2/141 and and road Turn proceed proceed east east for for 18.9 18.9 miles miles tc to the the intersection intersection with with MM 95. 95. Turn 95 and follow follow 10.2 10.2 miles miles to to the the intersection intersection left (north) (north) on M 95 left with with County County Road Road 569 569 which which goes goes eastward eastward to to Feich, Felch..MI. MI. Follow Follow CO CO 569 569 east east through through Feich Felch for for 14.9 14.9 miles miles to to stop stop 10 10 (about (about 1.5 1.5 miles miles west west of of the the village village of of Foster Foster City). City). Mile Map of east 12. east end of Felch Felch trough trough (adapted (adapted from from James Jaws FIGURE 12. FIGURE and others, others, 1961) 1961) showing showing locations locations of of stops s t q s 10 10 and and 11. 11. Small Small and lower hemisphere stereoplots show show orientation low-dippin5 nl hemisphere stereoplots orientation of low-dippinç Shoj steep foliation; large large lower lower hemisphere stereoplot shows s t a e p (Sa) (Sa) foliation; foliation in in Archean Archean gneiss. gneiss. Black Black dots dots in in the the stereoplcts stereoplcts show show foliation orientation by the intersectio' intersecticn oof 3a an>-"! and r^-1. orientation of lineatior formed by f 3.3 Black Black dots dots outside outside the the stereoplots stereoplots show show location location of of outcrops. outcrops. 1 C- 26 �STOP 10:_CO STOP 10LCO 569. 569. Granitoid gneiss on the north side of the road distinct foliations. has The has two two distinct foliations. The steeper steeper foliation,0 foliation, herein herein is an Archean fabric fabric that strikes strikes about about N85 called Sat W , and called Sa, N85W, dips nearly subnearly vertical (see (see large large stereoplot stereoplot on on Fig. Fig. 12). 12). A subhorizontal foliation foliation (Si), (Sl), expressed by0aligned byaligned zones zones and and clots clots of biotite, biotite, is oriented about about Nb N10 W, W, 25 25Nfl. NE. Gneissic foliation foliation Gneissic and fold axes axes in in gneissic gneissic foliation foliation in in Archeari Archean rocks rocks throughout and throughout the Felch trough trough region are steep. the Felch region are The nearly nearly flat lying steep. The flat lying penetrative Si foliation is found throughout penetrative Sl foliation throughout the the Feich Felch trough trough area, area, as shown shown on on Figure Figure 12, 12, but but because because the the Archean Archean fabric fabric (Sa) (Sa) is generally more prominent, it it is is difficult difficult to to recognize recognize Si Sl (for (for example, example, climb climb to the large large outcrop outcrop area in in back of of the the roadcut roadcut Si on this The and look for Sl this nearly nearly horizontal horizontal surface). surface). The small small stereoplots 12 shows shows that that the the Si Sl foliation foliation is is irregular irregular stereoplots on Figure 12 Si also exists in Early in in orientation. orientation. The next stop stop shows shows that Sl Proterozoic rocks. Proterozoic rocks. ROAD LOG. LOG. Turn around at stop 10 and proceed west on CO 569 for miles to the intersection Proceed 6.7 miles 69. Proceed south south 6.7 intersection with Old Old M 69. (left) (left) on M69 for only 0.25 miles miles to to the the bridge. bridge. STOP 11-OLD 11—OLD M 69. Figure i3A isaa geologic showing aa STOP 69. Figure 13A is geologic map showing to south of roughly sequence north to south of roughly vertically bedded sequence from from north Randville Dolomite sandwiched between Sturgeon Quartzite and Randville Dolomite sandwiched between Sturgeon Quartzite Archean gneiss Archean gneiss blocks. blocks. The fact fact that the the stratigraphically stratigraphically older older dolomite indicates quartzite quartzite lies north of the dolomite indicates that that the the section section faces southward. faces southward. Also, bedding in the dolomite on the north side side the river of river dips dips steeply steeply north north suggesting suggesting slight slight overturn overturn of of of the south. bedding the south. bedding toward toward the The dolomite dolomite has has a subhorizontal subhorizontal foliation (Si) foliation (Sl) that is is axial axial planar planar to to small small folds folds in in it. it. the Archean Archean gneiss There are There are two distinct foliations foliations in in the gneiss The south of the the river. river. The steep steep dipping Archean Archean foliation foliation (Sa) (Sa) is is the crosscut by by low-dipping Early Proterozoic Proterozoic foliation foliation (Sl), the crosscut (SI), foliation as found Randville same subhorizontal is in the same subhorizontal foliation as is found in the Randville have note that the dolomite does not a steep Dolomite, but note that dolomite does not have a steep Dolomite, foliation. foliation. in Our interpretation interpretation of the Our the structure structure at at stop stop 11 11 is is shown shown in We suggest cross section section A-A' (Fig. (Fig. 13a). 13a). suggest that that the the Archean Archean cross gneiss has been thrust above the Sturgeon Quartzite and Ra-ndville Randville thrust'above Sturseon Quartzita Dolomite, Dolomite, which which are are exposed as aa window window in in the the Archean thrust thrust indicates southward sheet. Southward facing stratigraphy sheet. Southward facing stratigraphy indicates southward vergence The the Sl Si vergence in in the thrust thrust system. system. The thrusting thrusting created created the subhorizontal foliation in both Early Proterozoic subhorizontal foliation Proterozoic and and Archean Archean rocks, rocks, but the the steep steep Sa Sa fabric fabric occurs occurs only only in in the the Archean Archean gneiss. gneiss. Figure Figure 13D 13B shows shows the the thrust thrust system system in in aa broader broader perspective, perspective, and provides provides additional additional key key evidence evidence for for southward southward vergence vergence in in the Felch the Felch trough trough area. area. Although the the exact exact configuration configuration of of the thr fold which thrust faults faults is not known thrust known at at this this time, time, the drag drag fold which cross shown on occurs in in Sturgeon Sturgeon Quartzite, Quartzite, as as diagrarnatically diagramatically shown on cross The section B-B', unequivocally indicate section B -B', indicate southward southward vergence. vergence. mu lac west of the profile at the drag fold actually occurs about a mile west see it same same structural structural position position along along the the fault. fault. We We will not not see it �______ B B XX XX X X X X X X XXX X X X XXX XXX .m45?. • XXX XX X X X Xn XU X X •V .• X - x x x x x I- ä 2000 felt 30cm 500meters meters 500 00 'I I 0.6 cm XX X Cover 1000 I 0 0 0 feet feet 00 XXX X X - Sondstone x 1!' )C XX )( XX red ounger x x x XXX x x x xXX) x x X XXX o X X x X X X Cover A A XXX X XXX XXA A- I 300 300meters meters 00 Drag folds AA /North North 9 B 7,A 7, A' / •1 d m Strike Strike and and Younger sandstone sandstone Younger > 'a Randviile Dolomite Dolomite Randville vulcan Iron Iron Fm. Fm. Vulcan V I Strik, Strike and and dip dip of af bedding bedding Sense sense ofof vergence vergence pP' Thrust / Thrust fault fault Sturgeon Ouartzlte Quartzite Sturgeon Ix dip dip ofof foliation foliation Archean gneiss gneiss Archean Outcrop Outcrop 4 Fault Fault and and sense ofof movement movement sense FIGERE 13. 13. Geologic Geologic maps maps in in area area of stop 11 (adapted from James FIGURE Map and others, others, 1961). 1961). Map AA and and geologic qeologic cross Gross section seciion shows shoiis the thc and and gneiss Archean structural relationship relationship between between Archean gneiss and Tarly Ezrly structural :.:as Z and xu? Prctsrozoic Sturgeon Sturgeon Quartzite Quartzits and Xandville Dolomite. Map Prcterozoic andville Dolomit€. of location (note cross section is of a larger area structural cross section is of a largsr area (note l~cction of structural These maps show that low-dipping fnliation map A and drag fald). These maps show that low-dig~inq fzliation map A and drag fold). ~herezs occurs in in both both Archean Archeari and and Early Early Proterozoic Proterozoicrocks, rocks: whereas (Sl) occurs (Si) Archean ( Z s )occurs occurs only only in in the the Archean gnei.;s. gneiss. the steeper steeper foliation foliation (ca) the T h s maps nass and an2 cross cross sections sections also also present prssent evidence evidencefor for soi.:thward s~1:thmrZ The Sse text text for for further furtherdiscussion. fiiscussion. structuralvergence. vergeiice. See structural C- 28 �because of of difficult difficult access access to to the the outcrops. outcrops. because In summary, summary, several key points can be be made made from from this this stop: stop: In points can 1) Sa fabric is found only only in in Archean Archean rocks rocks (and (and not not in Sa fabric 1) in Early Proterozoic rocks)f thereby proving proving an Archean Archean age age for for Sa. Protérozoic thereby rocks), Sa. 2)Sub-horizontal Sl fabric is founG and Early Si 2)Sub-horizontal found in both Archean and it is is not not older Proterozoic rocks, thereby that it Proterozoic rocks, thereby proving that older than than Proterozoic age. age. 3) Thrust vergence is is toward the the south south in in Early Proterozoic the the Felch Felch trough trough area. area. ROAD ROAD LOG. LOG. Turn around and return return to to intersection intsrsection of of Old Old 69 69 and and CO CO 569 (a (a distance distance of of 0.25 0.25 miles). miles). Turn Turn left le2t (west) (west) on on 569 569 and and follow it follow it for 8.2 miles miles to to intersection intersection with with MM 95. 95. Turn left Turn left 5.4 miles miles to to Steele (south) on on M 95 and follow follow it it for for 5.4 (south) Steele Road (Swanson Road Road on on right). right). left on on Steele Steele Road Road and and follow follow it it (Swanson Turn left to "THE STEELE FARM" to "THE STEELE end of of road. road. After checking with FARM" at end After checking with residentsf go through through gate gate to to field field on on the the east. east. Outcrops Outcrops are are in in residents, go the southern the southern part the field about about 400 east of of the the part of of the 400 m east farmhouse. farmhouse. This outcrop STOP 12-STEELE 12-STEELE FARM. FARM. outcrop of Michigamme Michigamme Formation Formation is is in in the Calumet Calurnet Trough (Fig. the Trough (Fig. 3). Here graded gradsd beds (SO) of Here beds of 3). (SO) .rnetagraywacke, metagray~acke~ now quartz—sericite-biotite quartz-sericite-biotite schist, schist! have a have a prominent that refracts prominent subhorizontal subhorizontal foliation foliation (SJ.) tha& across ref racts across (Si) bedding. Si is oriented axial bedding. Sl is oriented roughly roughly N90 N90 E, E, 25 25 SE, SE, and is is axial folds in to the metagraywacke metagraywacke that plunge gently planar to folds in the that plunge gently northwest. northwest. Bedding strikes strikes roughly roughly east east and dips dips steeply steeply south. south. metagraywacke indicate indicate Graded beds and flame flame structures structures in in the the metagraywacke that stratigraphic stratigraphic facing that facing is is toward toward the the south. south. Both SO and and Si Sl have been have been refolded with a steeper steeper foliation foliation (S2) (S2) that that strikes strikes N40°E. approximately ~ surfaces approximately 4 0 ~ Also, Alsof ~ . crinkle crinkle folds folds on on the the Si Sl surfaces indicate indicate post-Fl post-Fl folding. folding. summary, this outcrop indicates In summary, indicates that that there there is is aa prominent prominent subhorizontal foliation foliation in the Calurnet strata in subhorizontal Michigamme strata Calumet in Michigarnme in the bedding trough. Sedimentary structures indicate that faces trough. Sedimentary structures indicate that bedding faces This toward toward the the south. south. This implies implies that that SO SO has has been been rotated rotated toward the south that the the Calumet trough is is a south—verging the south and and that Calumet trough a south-verging structure. structure. Return ZOAD LOG. LOG. Return to to MM 95 95 and and turn turn left left (south). (south). The turn t u m to to ROAD alternate stop stop 13 13 is is 1.0 1.0 mile south south of of Steele Steele Road Road on on MM 95 9 5 at at the the intersection 14 95 95 with with Sportsman Sportsman Club Club Road. Road. Turn left left (east) (east) intersection of M on Sportsman S~ortsnanClub Club Road. Road. This a large outcrop area area of of ALTERNATE STOP the ALTEFUJATE STOP 13. 13. This is is a lsrcje outcrop the Michigamme Formation in the Calumet trough Michigaame trough located locatsd in in the the E1/2, E1/2, sec The sec 21, 21f T41N, T41?Jf R28W R28X at at a sharp sharp bend in in the the Sturgeon Sturgeon River. Riwr. The rocks here are now are metagraywacke, metagra~wacke~ now schist schist and and phyllite. phyllits. They have have subhorizontal a sub?iorizontal foliation foliation (Si) (Sl) which which is is axial axial planar p l a n ~ rto to numerous numerous a drag folds Sil draq folds in bedding beddin9 (SO), (SO)f which which indicate indicate south south vergence. vergsnce. S foliation forms a gently undulating surface surface which, which, in in places, placzsf has has been fol6ed folded with with an an S2 S2axial axialplane planethat thatstrikes strikes northwest i andnd is northvest steeply dipping. dipping. steeply Like the the strata strata at at stop stop 12, 12f this outcrop outcrop also also shows that the Calumet trough trough is is a south south verging verging structure. structure. �To reach stop 14 from the intersection of Steele Road ROAD LOG. and M 95, proceed south on M 95 for a distance of 4.8 miles to Turn right and proceed west S. 2/141. the intersection with U. 2/141 for approximately 11 miles to the center of the on U. S. town of Florence, Wisconsin. Turn left (south) on County Road N the center of Florence and proceed south for 3.3 miles to the in Turn right on CO D and go 1.3 intersection with County Road D. Follow this "Site 34". miles west to a gravel road labelled road for 3.4 miles to the Pine River dam. From the parking lot fence near the dam walk onto the dam embankment to a chain link Turn that blocks access to the discharge flume from the darn. fence left and walk down the embankment next to the chain link for about 400 feet (130) meters to outcrops along the river. STOP 14-PINE RIVER FLOWAGE. This outcrop lies within the Niagara foliated fault zone. The rocks here consist of strongly been Primary layering has chloritic-garnetiferous schist. Dextral drag folds in the transposed parallel to Si foliation. which are transposed layering have steeply plunging axes, xes parallel to mineral lineations on the foliation surfaces of gaximum elongation in deformed concretions plunge 60 toward s80 W, parallel to the mineral lineation. completely deformation shown in this outcrop is The previous outcrops. A different from that seen in the lacking as is any evidence for a foliation is subhorizontal Rather, these highly strained southward structural vergence. rocks have an Si foliation that dips steeply south, as do the As defined by Ueng and others elongation (stretching) axes. this stop lies within the Florence-Niagara terrane, (1984), steeply which is characterized by a west-northwest—trending, south-dipping foliation that contains a prominent south—plunging Similarly oriented structures occur in stretch lineation. volcanic rocks of the Wisconsin magmatic terrane on the south margin of the Niagara fault zone, a few miles south of the Pine River dam (Sims and others, 1985). The structural fabric in this region reflects overthrusting of the Wisconsin magmatic terrane from the southeast onto the continental margin. ACKNOWLEDGEMENTS F. Cannon, benefited from conversations with W. L. LaBerge, B. W. Ojakangas, Z. E. Peterman, and K. J. Schulz G. It also benefited from critical who toured with us in the area. Z. IL Peterman provided the Foose and T. Off ield. reviews by N. Dale Beaver drafted the geochronological data on the granite. illustrations. This guide 0-30 �REFERENCES REFERENCES R., and Black, Black, R. R. A., A., 1983, 1983, Early Early Proterozoic Proterozoic Anderson, R. R. fl., and Anderson, development development of of the the southern southernArchean Archean boundary boundary of of the the Superior Superior province province in in the the Lake Lake Superior Superior region region (abs.): (abs.): Geological GeologicalScoScciety iety of of America America Abstracts Abstractswith with Programs, Programs,v.15, v.15, p.515. p.515. K., and Vander Vander Muelen, Muelen, M. M. 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D., Lamey, Lamey, C. A., and and Pettijohn, Pettijohn, F. F. J., J., Geology of central central Dickinson Dickinson County, County, Michigan: Michigan: U. U. S. S. Geology Geological Geological Survey Survey Professional Professional Paper Paper 310, 310, l76p. 176p. L., Dutton, H. Dutton, C. E., Pettijohn, Pettijohn, F. F. J., J., and and Weir, Weir, K. K. L., L., H. 1968, 1968, Geology and ore deposits of the the Iron Iron River-Crystal River-Crystal Falls Falls U. S. S. Geological Geological Survey Survey district, Iron Iron County, County, Michigan: Michigan: U. district, Professional Paper Paper 570, 570, 134 134 p. p. Professional James, James, �Klasner, Klasner, J. J. S., S., 1972, 1972, Style Style and sequence sequence of of deformation deformation and and metamorphism due associated metamorphism due to to the the Penokean Penokean Orogeny Orogeny in in the the western Marquette Range, DissertaRange, northern Michigan: Ph. D. 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S., 1984, 1984, The The volcanic-plutonic volcanic-plutonic terrane terrane of of nornorthern thern Wisconsin: implications implications for for Early Early Proterozoic Proterozoic tectonism, tectonisin, Lake of Canada Canada Lake Superior Superior region region (abs.): (abs.): Geological Geological Association Association of Abstracts with with Programs, Programs, v.9, v.9, p.103. p.103. R. L., and Larue, Larue, D. K., 1985, 1985, Fold Fold axes axes oblique oblique to to the the regional plunge and Proterozoic Proterozoic terrane terrane accretion accretion in in southern southern Lake Lake Superior Superior region: region: Precambrian Precambrian Research, Research, v.30, v.30, pp.249-262. pp.249-262. Sedlock, Sedlock, K. M., 1987, Sikkala, Sikkala, K. M., 1987, A structural structural analysis analysis of of Proterozoic Proterozoic rnetasediments, northern Falls Falls River, River, Baraga County, metasediments, northern County, Michigan: Michigan; University, Technological University, Master of of Science Science Thesis, Thesis, Michigan Michigan Technological Houghton, Houghton, MI, MI, 103 103 p. p. Sikkala, K. M., M., and Gregg, Sikkala, Gregg, W, J., J., 1987, 1987, A structural structural analysis analysis of of Proterozoic metasediments, metasediments, northern Proterozoic northern Falls Falls River, River, Baraga Baraga County, County, Michigan Michigan (abs.): (abs.): 33 33 Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, v. 33, 33, part 1, 1, pp. 65—66. 65-66. Sims, P. K., K., 1980, Sims, 1980, Boundary between Archean greenstone greenstone and and gneiss gneiss terranes terraries in in northern Wisconsin Wisconsin and and Michigan: Michigan: Geological Geoloqical SocSociety of America America Special Soecial Paper Paper 182, 182, pp.113-123. pp.113-123. Proterozoic 1987, P. K., K., 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic P. terranes -- AA brief overview: overview: U. U. S. S. terranes in in the the Great Great Lakes Lakes region region -U. S. Geological Geological Survey Survey Bulletin Bulletin 1964, 1964, pp. pp. 56-74. 56-74. Sims, Sims, �Sims, Sims, P. P. K., K., Card, Card, K. K. D., D., and and Lumbers, Lumbers,S.S.13., B . , 1981, 1981, Evolution Evolution of of Early Proterozoic Proterozoic basins basins in in the the Great Great Lakes Lakes region, region, in in Early F. H. H. A. A. Campbell Campbell (ed.), (ed.), Proterozoic Proterozoic basins basins of of Canada: Canada: GeolGeolF. Geological Geological Survey Survey of of Canada Canada Special Special Paper Paper 81-10, 81-10, pp. pp. 379379397. 397. P. P. K., K., and and Peterman, Peterman, Z. Z. E., E., 1984, 1984, A partisan partisan review review of of the the Proterozoic geology geology of of Wisconsin Wisconsin and and adjacent adjacent Michigan Michigan Early Early Proterozoic (abs.): 30th 30th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, (abs.): Wausau, Wisconsin, pp. 73-76. Wausau, Wisconsin, pp. 73-76. Sims, Sims, and and Peterman, Peterman, Z. Z. E., E., 1986, 1986, The The Early Early Proterozoic Proterozoic major buried structure Central -- AA major buried structure in in northnorthCentral Plains Plains orogen orogen —— central central United United States: States: Geology, Geology, v. v. 14, 14, pp. pp. 488-491. 488-491. Sims, P. P. Sims, K., K., Sims, K., Peterrnan, Peterman, Z. E., Prinz, Prinz, W. W. C., C., and and Benedict, Bened-ict,F. I?. C., C., Sims, P. P. K., 1984a, Geology, Geology, geochemistry, geochemistry, and and age age of of Archean Archean and and Early Early 1984a, Proterozoic Proterozoic rocks rocks in in the the Marenisco-Watersmeet Marenisco-Watersmeet area, area, northern northern Michigan: Michigan: U. U. S. S. Geological Geological Survey Survey Professional Professional Paper Paper 1292—A, 1292-A, pp. Al-PAl. A1-A41. pp. Peterman P. K.., K.., Peterman Z. Z. E., E., and and Schulz, Schulz, K. K. J., J., 1985, 1985, The The P. Early implications Dunbar gneiss-granitoid gneiss-granitoid dome; dome; implications for for Early Dunbar Proterozoic Proterozoic tectonic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: GeoloGeological gical Society Society of of America America Bulletin, Bulletin, v.96, v.96, pp.1101-1112. pp.llO1-1112. Sims, Sims, P. P. K., K., Peterman, Peterman, Z. Z. E., E., Kiasner, Klasner, J. J. S., S., Cannon, Cannon, W. VJ. F., F., and and Schulz, Schulz, K. K. J., J., 1987, 1987, Nappe Nappe development development and and thrust thrust faulting faulting in the the upper upper Michigan Michigan segment segment of of the the Early Early Proterozoic Proterozoic in (abs.): Geological Geological Society Society of of America America AbsAbsPenokean orogen orogen (abs.): Penokean tracts with with Programs, Programs, v.19, v.19, p. p. 246. 246. tracts Sims, Sims, K., E., 1984b, 1984b, Guide Guide to to K., Schulz, Schulz, K. K. J., J., and and Peterrnan, Peternan, Z. Z. E., in northeasten rocks Proterozoic the Early Geology of of the Early Proterozoic rocks in northeasten Geology Wisconsin: Wisconsin: Field Field Trip Trip 1, 1, 30th 30th Annual Institute Institute on on Lake Lake Superior Superior Geology, pp.1-50. pp.1-50. Geology, Sims, P. P. Sims, W. P. P. K., Schulz, Schulz, K. K. J., J., Peterman, Peterman, Z. Z. E., E., and and Van Van Schmus, SC~MIIS, W. R., in in press, press, Wisconsin Wisconsin magmatic magmatic terrane, terrane, Lake Lake Superior Superior region, region, in in J. C. C. Reed Reed Jr. Jr. and and others others (eds.), (eds.),Precambrian-conterrninous Precambrian-conterminous Uniited States: States: Geological Geological Society Society of of America, America, The The geology geology of of Uniited North North America, America, v. v. C-2. C-2. Sims, Sims, Ueng, W. W. L., L., Larue, Larue, D. D. K., Sedlock, Sedlock, R. L., L., and and Kasper, Kasper, D. D. A., A., Ueng, 1984, 1984, Early Early Proterozoic Proterozoic tectonostratigraphic tectonostratigraphic terranes terranes of of the the southern southern Lake Lake Superior Superior region: region: Field Field Trip Trip Guide Guide with with summary, sun-iinary, Field Field Trip Trip 2. 2. 30th 30th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Geology, 23p. 23p. Van Roosendaal, Roosendaal, D. D. J., 1985, 1985, An An analysis analysis of of rock rock structures structures and and strain strain in in cleaved cleaved pelitic pelitic rocks, rocks, East East Branch Branch of of the the Huron Huron River, River, Baraga Baraga County, County, Michigan: Michigan: Master Master of of Science Science Thesis, Thesis, Michigan Houghton, MI, MI, 82 82 p. p. Michigan Technological Technological University, University, Houghton, �I I Van Van Schmus, Schmus, W. W. R., R . , 1976, 1976, Early Early and and Middle Middle Proterozoic Proterozoic history history of of the the Great Great Lakes Lakes Area, Area, North North America: America: Philosophical Philosophical Transactions Transactions of of the the Royal Royal Society Society of of London, London, A280, A280, pp.605-628. pp.605-628. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1988 Description An account of the resource Institute on Lake Superior Geology. Marquette, Michigan. May 12-13, 1988. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1988 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/2e727a9fa1fcd2d0abc22690e75dbf6d.pdf a1564fefb4944bae6ad3d41031638cc2 PDF Text Text INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY PROCEEDINGS MAY M A Y 1989 1989 VOLUME 35 VOLUME 35 i Part 1. 1. Abstracts Abstracts 35th 35th Annual Annual Meeting Meeting May 3-6, 3-6, 1989 1989 held at Duluth, Minnesota 55812 Duluth, Minnesota 55812 �Organizing Committee, 35th Annual Annual Meeting, Meeting, ILSG ILSG (1989) (1989) Richard W. W. Ojakangas, Ojakangas, Dept. Dept. of of Geology, Richard Geology, University of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 John C. Green, Dept. of of Geology, University of Minnesota-Duluth, Duluth, MN MN 55812 Green, Dept. Geology, University Minnesota-Duluth, Duluth, 55812 Timothy B. Hoist, Holst, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812 55812 Timothy B. Program Chair Chair and and Abstract Abstract Editor: Editor: John Program John C. C. Green Green Guidebook Editor: Timothy Guidebook Editor: Timothy B. B. Hoist Hoist Volume 35 Parts 1 1 and Volume 35 consists consists of Parts and 2: 2: 1: Abstracts 1: 2: Field Trip Guidebooks Guidebooks Published and Distributed by Published and by Institute on Lake Lake Superior Superior Geology Geology J. Kaiiiokoski, J. Kalliokoski, Secretary/Treasurer SecretaryITreasurer Dept. of Geological Geological Engineering, Engineering, Geology Geology and and Geophysics Geophysics Dept. University Michigan Technological University Houghton, Houghton, Michigan 49931 49931 ISSN 1042-9964 1042-9964 ISSN �35th 3 5 t hANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Proceedings P r o c e e d i n g s and and Abstracts Abstracts D u l u t h , Minnesota Minnesota Duluth, May and 5, 1989 1989 May 44 and Organized O r g a n i z e d by by Richard Ojakangas,UUniversity R i c h a r d WW. . Ojakangas, n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth John C. Green, Green, UUniversity n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth John C. Timothy Timothy B.B. HHoist, o i s t , University U n i v e r s i t y of o fMinnesota, Minnesota, Duluth Duluth Program Chairmanand and EEditor: Program Chairman ditor: Volume Volume 35. 35. John John C. C . Green Green Part P a r t 11Program Program and and Abstracts Abstracts Part P a r t 22 Field F i e l dTrip T r i Guidebooks p Guidebooks COVER COVER A n t i c l i n ein iThomson n ThomsonFormation F o r m a t i o nataThomson t Thomson Anticline dam dam nnear e a r Thomson, Thomson, Minnesota. M i n n e s o t a . View View from from e a s t bank bank oof f S t . Louis L o u i s River, R i v e r , looking looking east St. west. Wendell Wendell Wilson W i l s o n 5/30/1968 5/30/1968 �PURCHASE O OF AND ABSTRACTS ABSTRACTS AND AND FIELD PURCHASE F PROCEEDINGS PROCEEDINGS AND FIELDGUIDEBOOKS GUIDEBOOKS The andAAbstract andt the The PProceedings r o c e e d i n g s and b s t r a c t and h e FField i e l d Guidebooks Guidebooks ffor o r the t h e 35th 3 5 t hAnnual Annual Institute I n s t i t u t eononLake LakeSuperior S u p e r i o Geology r Geology may may be be purchased purchased bby y ccontacting: ontacting: John C. C. Green Green John Department of Geology Department of Geology University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth Duluth, D u l u t h , Minnesota Minnesota 55812 55812 PROCEEDINGS VOLUME 35. PART PART 11 ------------------ $5.00 PROCEEDINGS AND AND ABSTRACTS, ABSTRACTS, VOLUME GUIDEBOOKS, VOLUME VOLUME 35, PART 22 ............................ $5.00 FIELD GUIDEBOOKS, 35, PART Issues I s s u e s of o f Proceedings Proceedings and and Abstracts A b s t r a c t s and and Field F i e l dGuidebooks Guidebooks from f r o m previous previous meetings maybe bepurchased purchasedbybyc contacting meetings may o n t a c t i n g tthe h e Secretary-Treasurer: Secretary-Treasurer: Joe KKalliokoski Joe al l i o k o s k i Department and GGeological Department ooff Geology Geology and e o l o g i c a l Engineering Engineering Michigan Technological University M i c h i gan Techno1 ogi cal U niversity Houghton, Houghton, Michigan M i c h i g a n 49931 49931 �TABLE OF OF CONTENTS CONTENTS Institutes I n s t i t u t e sononLake LakeSuperior S u p e r i o rGeology Geology to t o 1989 1989 Constitution Lake C o n s t i t u t i o n of o f the t h eInstitute I n s t i t u ton e on LakeSuperior S u p e r i o rGeology Geology By-Laws ont hthe By-Laws on e IInstitute n s t i t u t eon onLake LakeSuperior S u p e r i o rGeology Geology Goldich G o l d i c h Medal Medal Guidelines Guidelines Student S t u d e n t Travel T r a v e l Award Award i i ii ii iii iii ivv i v Boardooff Directors Board Directors vvii LLocal o c a l Committee Committee vvii Best B e s t Student S t u d e n t Paper Paper Committee Committee vvii Goldich Go1 d i ch Medal Medal Committee Committee vvii Goldich G o l d i c h Medal Medal Recipient Recipient vii Banquet Banquet Speaker Speaker vvii ii Acknowledgements vii vii Report R e p o r t oof f tthe h e Chairs C h a i r s ooff the t h e 34th 3 4 t h Annual Annual I Institute nstitute Calender C a l e n d e r of o f Events Events Poster P o s t e r Papers Papers Abstracts Abstracts viii v i ii x xxvi vi xXviii v i ii �INSTITUTES INSTITUTESON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE NUMBER INSTITUTENUMBER DATE DATE PLACE PLACE 1 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 Minneapolis, M i n n e a p o l i s , MN MN Houghton, MI MI 1 22 33 44 55 66 7 7 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 30 30 31 31 32 32 33 33 34 34 35 35 East E a s t Lansing, L a n s i n g , MI MI Duluth, D u l u t h ,MN MN Minneapolis, M i n n e a p o l i s ,MN MN Madison, Madison, WI WI Port P o r t Arthur, A r t h u r , Ont. Ont.(Thunder ( T h u n d e rBay) Bay) Houghton, MI Houghton, MI Duluth, D u l u t h , MN MN Ishpeming, MI Ishpeming, MI St. S t . Paul, P a u l ,MN MN Sault MI S a u l t Ste. S t e . Marie, M a r i e , MI East E a s t Lansing, L a n s i n g , MI MI Superior, S u p e r i o r , WI MI Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN D u l u t h ,MN Houghton, MI MI Madison, Madison, WI MI Sault S a u l t Ste. S t e . Marie, M a r i e , Ont. Ont. Marquette, MI M a r q u e t t e , MI St. S t . Paul, Paul MN , MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, WI Milwaukee, WI Duluth, D u l u t h ,MN MN Eau Claire, Eau C l a i r e , WI MI East E a s t Lansing, L a n s i n g , MI MI International I n t e r n a t i o n a l Falls, F a l l s MN , MN Houghton, MI Houghton, MI Wausau, Wausau, WI MI Kenora, Kenora, Ont. Ont. Wisconsin Wisconsin Rapids, R a p i d s , WI W I Wawa, Wawa, Ont. Ont. Marquette, M a r q u e t t e , MI MI Duluth, D u l u t h ,MN MN �___________________________ CONSTITUTION OF CONSTITUTION OF INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Article Article II Name Name Thename name The o f of t hthe e o rorganization g a n i z a t i o n s hshall a l l b be e t hthe e " I"Institute nstitute Article A r t i c l e VI VI on Lake Superior on Lake S u p e r i o r Geology." Geo 1 o g y . " Article A r t i c l e II I1 Objectives Objectives Theoobjectives The b j e c t i v e s oof f tthis h i s organization o r g a n i z a t i o n are: are: A. 0B.. C. Article III A r t i c l e 111 To pprovide wherebyg geologists To r o v i d e aa means means whereby e o l o g i s t s iin n the the Great G r e a t Lakes L a k e s region r e g i o nmay may exchange exchange ideas i d e a s and and scientific s c i e n t i f i c data. data. To ppromote To r o m o t e bbetter e t t e r uunderstanding n d e r s t a n d i n g oof f tthe h e geology g e o l o g y ooff the t h e Lake Lake Superior S u p e r i o r region. region. To pplan andcconduct To l a n and o n d u c t g egeological o l o g i c a l f i field e l d ttrips. rips. Article A r t i c l e VII VII Directors D irectors The bboard The o a r d oof f ddirectors i r e c t o r s shall s h a l l consist c o n s i s tofo the f t h Chairman, e Chairman, Secretary-Treasurer, andt hthe S e c r e t a r y - T r e a s u r e r , and e l last a s t three t h r e e past p a s t ChairChairmen;bbut t h e board b o a r d should s h o u l d aatt any any ttime i m e cconsist o n s i s t of of men; u t iiff the lless e s s than t h a n five f i v epersons, p e r s o n s , by b y reason r e a s o n of o f unwillingness unwillingness oorr inability i n a b i l i t yofoany f anyofothe f t habove e abovepersons p e r s o n s to t o serve serve as directors, as d i r e c t o r s , the t h evacancies v a c a n c i e s on onthe t h eboard b o a r dmay may be be filled as ttoo bring f i l l e dbyb ythe t h eannual annual meeting m e e t i n g so so as b r i n g the the membershipo of membership f tthe h e bboard o a r d uup p ttoo five f i v emembers. members. Officers icers Off - The The oofficers f f i c e r s of o f this t h i s organization o r g a n i z a t i o n shall s h a l l be b e aa Chairman i r m a n and and aa Secretary-Treasurer. Secretary-Treasurer. Cha A. Status S tatus Noppart No a r t ooff the t h e income income oof f tthe h e organization o r g a n i z a t i o n sshall h a l l inure inure tto o the t h e benefit b e n e f i t ofo fany a n ymember member oor r iindividual. n d i v i d u a l . IIn n the the eevent v e n t oof f dissolution d i s s o l u t i o n the t h e assets a s s e t s of o f the t h e organization organization sshall h a l l be b e ddistributed i s t r i b u t e d to to (some (some t atax x ffree r e e oorganization). rganization). ((To T o aavoid v o i d Federal F e d e r a l and and State S t a t e income income ttaxes, a x e s , the the oorganization r g a n i z a t i o n should s h o u l d be b e not n o t only o n l y " sscientific c i e n t i f i c " oorr "educational " e d u c a t i o n a l " bbut u t aalso l s o "'non-profit.') non-profit.") B. Minn. M i n n . Stat. S t a t . Anno. Anno. 290.01, 2 9 0 . 0 1 , subd. subd. 44 ' 290.05(9) 290.05(9) 1954 1954 Internal I n t e r n a lRevenue Revenue Code Code s. s . 5501(c)(3) 01(c)(3) Article A r t i c l e IV IV Article A r t i c l e VV Membership Membership The membership o n s i s t of of The membership o f oft hthe e o rorganization g a n i z a t i o n sshall h a l 1 cconsist Any ggeologist interested e o l o g i s t interested tthe h e board b o a r d oof f ddirectors. i r e c t o r s . Any in sshall h a l l be b e permitted p e r m i t t e d to t o attend a t t e n d and and pparticipate a r t i c i p a t e in and vote at the annual meetings. and v o t e a t t h e a n n u a l m e e t i n g s . Meetings Meetings The The oorganization r g a n i z a t i o n shall s h a l l meet meet once once aa yyear, e a r , preferably preferably The pplace during d u r i n g the t h e month m o n t h oof f AApril. p r i l . The l a c e and and eexact x a c t date date of o f each each meeting m e e t i n g wwill i l l be b edesignated d e s i g n a t e d by b y the t h e board b o a r d of of directors. directors. Article VIII A r t i c l e VIII The Chairman Chairmans shall The h a l l bbe e eelected l e c t e d each each year y e a r by by the t h e board b o a r d oof f directors, d i r e c t o r s , who who shall s h a l l give g i v edue due cconsideration o n s i d e r a t i o n to t o the t h e wishes w i s h e s of o f any any group group that t h a t may may be be promoting p r o m o t i n g the t h e next n e x t annual annual m e e t i n g . His H i s term t e r m of o f office o f f i c easasChairman Chairman meeting. will w i l l terminate t e r m i n a t e at a t the t h e close c l o s e of o fthe t h eannual annual meeting which m e e t i n g oover ver w h i c h hhe e ppresides r e s i d e s or o r when when his his successor s u c c e s s o r sshall h a l l have h a v e been been appointed. a p p o i n t e d . He He will w i l l then t h e n serve s e r v e for f o r aaperiod p e r i o d of o f three t h r e eyears years as a as a member member o foft hthe e bboard o a r d oof f ddirectors. irectors. The SSecretary-Treasurer The e c r e t a r y - T r e a s u r e r sshall h a l l be b e elected e l e c t e d at at His the t h e annual a n n u a l meeting. meeting. H i s tterm e r m oof f ooffice ffice shall s h a l l be b e two two years y e a r s oor r until u n t i l his h i ssuccessor successor shall s h a l l have have been been appointed. appointed. Amendments Amendments This majority b eamended amended bby y aa m ajority T h i s constitution c o n s t i t u t i o nmay may be who aare r e personally personally vvote o t e of o f those t h o s e persons p e r s o n s who i n , and and voting v o t i n g at a tany any ppresent r e s e n t aat, t , participating p a r t i c i p a t i n g in, organization. meeting aannual nnual m e e t i n g oof f tthe h e organization. �BY-LAWS I.I. Duties D u t i e s of o f the t h e Officers O f f i c e r sand and Directors Directors A. ItI tshall s h a l be l bethe t h eduty d u t yofothe f t h Chairman e Chairman to: to: 1. 1. 2. 2. Preside P r e s i d e at a t the t h eannual annual meeting. meeting. Appoint A p p o i n t all a l lcommittees committees needed needed f for o r tthe h e organization o r g a n i z a t i o n of o f the t h eannual annual meeting. meeting. 3. 3. B. ItI tshall s h a l be l bethe t h eduty d u t of y othe f t hSecretary—Treasurer e S e c r e t a r y - T r e a s u r e r to: to: 1. 1. 2. 2. 3. C. Assume Assume c ocomplete m p l e t e r e responsibility s p o n s i b i l i t y ffor o r the t h e organization o r g a n i z a t i o n and and financing financing of o f the t h eannual annual meeting m e e t i n g over o v e r which w h i c h he he presides. presides. Keep Keep aaccurate c c u r a t e aattendance t t e n d a n c e r erecords c o r d s oof f aall l l annual annual meetings. meetings. Keep of all correspondence Keep aaccurate c c u r a t e rrecords e c o r d s of a l lmeetings m e e t i n g sof, o f and , and correspondence between, between, tthe h e bboard o a r d oof f ddirectors. irectors. Hold H o l d all a l l funds f u n d s that t h a tmay may accure a c c u r e as as profits p r o f i t sfrom fromannual annual meetings m e e t i n g s or or field f i e l dtrips t r i p and s andtot make o make these t h e s e funds f u n d s available a v a i l a b l e for f o r the t h e organization organization and and ooperation p e r a t i o n of o f future f u t u r emeetings m e e t i n g s as as required. required. It I tshall s h a l lbe bethe t h e duty d u t y of o f the t h e board b o a r d of o f directors d i r e c t o r s to t o plan p l a n locations l o c a t i o n s of of annual meetings andt otoaadvise ont hthe andf ifinancing annual m e e t i n g s and d v i s e on e oorganization r g a n i z a t i o n and n a n c i n g oof f all all meetings. meetings. II. 11. Dues and and Expenses Expenses Dues 1. 1. 2. 2. There There shall s h a l l be beno noregular r e g u l amembership r membership dues. dues. Registration R e g i s t r a t i o n fees f e e s for f o rthe t h eannual annualmeetings m e e t i n g s shall s h a l lbe bedetermined d e t e r m i n e d by b y the the Chairman Chairman i nin cconsultation o n s u l t a t i o n wwith i t h tthe h e board b o a r d ooff directors. d i r e c t o r s . It I t is i sstrongly strongly recommended be kkept recommended t hthat a t t hthese e s e be e p t aatt aa minimum minimum tto o encourage encourage attendance a t t e n d a n c e of of graduate g r a d u a t e students. students. III. 111. R u l e s of o f Order Order Rules The The rrules u l e s contained c o n t a i n e d iin n Robert's R o b e r t ' s Rules R u l e s oof f Order Order sshall h a l l govern govern tthis his organization o r g a n i z a t i o n in i n all a l lcases cases to t owhich w h i c h they t h e y are a r e applicable. applicable. IV. IV. Amendments Amendments These maybebeamended amended These bby—laws y - l a w s may b y by a maamajority j o r i t y v ovote t e oof f those t h o s e persons persons who who are are personally annual p e r s o n a l l y present p r e s e n t aat, t , participating p a r t i c i p a t i n gin, i nand , andvoting v o t i n at g aany t any annualmeeting meeting of modifications o f the t h e organization; o r g a n i z a t i o n ; provided p r o v i d e d tthat h a t such such m o d i f i c a t i o n s sshall h a l l nnot o t cconflict onflict with presently w i t h the t h e constitution c o n s t i t u t i oas n as p r e s e n tadopted l y a d o p t eor d osubsequently r s u b s e q u e n t lamended. y amended. 111 �Award Guidelines Award G uidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble The The IInstitute n s t i t u t eononLake LakeSuperior S u p e r i oGeology r Geologywas was born b o r non onoro around r around1955, 1955,asasdocumented documented by by the t h e fact f a c t that t h a tthe t h e27th 2 7 t hannual annual meeting m e e t i n g wwill i l l be be held h e l d ini n1981. 1981. The The IInstitutes nstitutes a r e exemplary e x e m p l a r y i in n ttheir h e i r continuing c o n t i n u i n g objectives o b j e c t i v e s of of dealing d e a l i n g with w i t hthose t h o s e aspects a s p e c t s of of are g e o l o g y tthat h a t are a r e related r e l a t e dgeographically g e o g r a p h i c a l l y to t oLake Lake Superior; S u p e r i o r ; ofo fencouraging e n c o u r a g i n g the the geology discussion andssponsoring d i s c u s s i o n oor r ssubjects u b j e c t s and p o n s o r i n g f i efield l d t trips r i p s which w h i c h wwill i l l bring b r i n g together together geologists and i industry; g e o l o g i s t s from f r o m the t h eacademia, academia, government government ssurveys, u r v e y s , and n d u s t r y ; and and of of maintaining an eexceedingly informal m a i n t a i n i n g an xceedingly in f o r m a l bbut u t hhighly i g h l y effective e f f e c t i v e mode mode ooff operation. operation. During membership D u r i n g tthe h e ccourse o u r s e oof f i its t s existence e x i s t e n c e tthe h e membership o f of t h ethe I n Institute s t i t u t e ( t(that h a t iis, s, those whoi nindicate t h o s e ggeologists e o l o g i s t s who d i c a t e anani ninterest t e r e s t i in n tthe h e oobjectives b j e c t i v e s oof f the t h e I.L.S.G. I.L.S.G. by by attending) aware a t t e n d i n g ) has has become become aware o f of t h the e f afact c t t hthat a t ccertain e r t a i n of o f their t h e i colleagues r c o l l e a g u e shave have made p particularly a r t i c u l a r l y noteworthy n o t e w o r t h y and and m e r i t o r i o u s contributions c o n t r i b u t i o n s to t othe t h eimprovement improvement of of made meritorious understanding Superior" and i its u n d e r s t a n d i n g oof f "Lake "Lake S u p e r i o r " geology g e o l o g y and t s mineral m i n e r a l deposits. deposits. The awardwas wasmade made I.L.S.G. tto The eexemplary x e m p l a r y award byby I.L.S.G. o Sam Sam GGoldich o l d i c h iin n 1979 1979 ffor o r his h i smany many contributions 50 years. years. c o n t r i b u t i o n s to t othe t h egeology g e o l o g y of o fthe t h eregion r e g i o nextending e x t e n d i n gover o v e rabout about 50 Award Guidelines Award G uidelines medals shall be awarded awarded Board 1 ) The The medal h a l l be a nannually n u a l l y b yby t h the e Board of of D iDirectors, r e c t o r s , I .I.L.S.G., L . S . G . , to to 1) a geologist namei sIsa associated substantial g e o l o g i s t whose whose name s s o c i a t e d w iwith t h a as u b s t a n t i a l ssustained u s t a i n e d i ninterest t e r e s t in, in, or o r aa major m a j o r contribution c o n t r i b u t i o n to, t o ,the t h egeology g e o l o g y ofo fthe t h eLake LakeSuperior S u p e r i o r region. region. Boardoof Directors, 2) 2 ) The The Board f D i r e c t o r s , I.L.S.G. I.L.S.G. shall s h a appoint l l a p p o i nthe t t hNominating e N o m i n a t i nCommittee. g Committee. Their T h e i r annual annual nominee nominee wwill i l l be be voted v o t e d on on at a tthe t h eannual annualbusiness b u s i n e s s meeting. m e e t i n g . The The initial w i l be l beofothree f t h r e members, e members, one one tto o serve s e r v e for f o r three t h r e e years, y e a r s , one one i n i t i a appointment l a p p o i n t m e n t will for with f o r two, two, and and one one for f o rone oneyear, y e a r ,the t h emember member w i t h the t h e briefest b r i e f e s incumbency t incumbency to t o be be chairman. chairman. After A f t e r the t h e first f i r syear t y e a the r t h eBoard Board of of Directors D i r e c t o r s shall s h a l lappoint a p p o i n t at a teach each spring member s p r i n g meeting m e e t i n g one one new new member whowho w i lwill l s eserve r v e f ofor r tthree h r e e years. y e a r s . In I n the t h e third t h i r d year year this Committeemembership membership t h i smember member sshall h a l l be be the t h echairman. chairman. The The Committee s hshould o u l d r ereflect f l e c t the the main main ffields i e l d s of o f interest i n t e r e sand t andgeographic g e o g r a p h i c distribution d i s t r i b u t i o nofofI.L.S.G. I.L.S.G.membership. membership. 3 ) The The G o l d i c h Medal o m i n a t i n g Committee s h shall a l l s eselect l e c t t hthe e m e d a l i s t and ill 3) Goldich Medal NNominating Committee medalist and wwill make Boardo of make i its t s recommendation recommendation t otot hthe e Board f DDirectors i r e c t o r s by by November November 1,1,o of f tthat h a t year. year. 4) Directors w i l accept l a c c e p tthe t h enominee nominee of of the t h eCommittee, Committee, 4 ) The The BBoard o a r d oof f D i r e c t o r s normally n o r m a l l y will will one medal w i l linform i n f o r mthe t h emedalist m e d a l i simmediately, t i m m e d i a t e l y ,and andwill w i have l l have one medalengraved engraved appropriately a p p r o p r i a t e l y for f o rpresentation p r e s e n t a t i o nata the t t h May e Maymeeting. meeting. ItI tisi srecommended recommended t hthat a t tthe h e Institute I n s t i t u t eset s e aside t a s i d eannually a n n u a l l yfrom fromwhatever whatever sources, suchf ufunds i l l be be rrequired e q u i r e d tto o support s u p p o r t tthe h e ccontinuing o n t i n u i n g ccosts o s t s oof f this this sources, such n d s asasw will 5) 5) award. April A p r i 14,4,1981 1981 J. J. Kalliokoski, K a l 1 i o k o s k iChairman , Chai rman Bill B i l Cannon l Cannon Fred F r e d Kehlenbeck Kehlenbeck Glenn Glenn Morey Morey Greg Greg Mursky Mursky iv �STUDENT STUDENT TRAVEL TRAVEL AWARD AWARD The 1986 1986Board Boardo of The f DDirectors i r e c t o r s established e s t a b l i s h e d the t h e ILSG ILSG Student S t u d e n t Travel T r a v e l Award Award to to The awards awards wwill i l l be bemade made ssupport u p p o r t sstudent t u d e n t pparticipation a r t i c i p a t i o n aatt the t h e annual annual IInstitutes. n s t i t u t e s . The accruedi ninterest fund sset up ffor This ffrom r o m tthe h e accrued t e r e s t ffrom r o m aa sspecial p e c i a l fund e t up o r this t h i s purpose. purpose. T his awardi is some award s iintended n t e n d e d t oto hhelp e l p ddefray e f r a y some o f oft hthe e d idirect r e c t t rtravel a v e l ccosts o s t s tto o the the institute i n s t i t u t eand and includes i n c l u d e s aa waiver w a i v e r of o f registration r e g i s t r a t i o nfees, f e e sbut , b uexcludes t e x c l u d e sexpenses expenses for for numberand ands isize meals, andf i field meals, l lodging, o d g i n g , and e l d t trip r i p registration. r e g i s t r a t i o n . The The number z e wwill i l l be be annual Chairman Chairmani nincconsultation with ddetermined e t e r m i n e d bby y tthe h e annual onsultation w i t h the t h e Secretary S e c r e t a r y Treasurer Treasurer and wwill i l l be beannounced announced aatt the t h e annual annual banquet. banquet, and The considered The ffollowing o l l o w i n g general g e n e r a l ccriteria r i t e r i awill w i be l l be c o n s i d e r e dbyb ythe t h annual e annualChairman, Chairman, who who i is s responsible r e s p o n s i b l e ffor o r the t h e selection: selection: have aactive 11)) The The aapplicants p p l i c a n t s must must have c t i v e resident r e s i d e n t (undergraduate ( u n d e r g r a d u a t e oorr ggraduate) r a d u a t e ) s student t u d e n t s tstatus a t u s a tatt hthe e t itime m e o of f t hthe e i institute, nstitute, ccertified e r t i f i e dbybythe t h edepartment d e p a r t m e n t head. head. whoa rare oneeither an ooral 22) ) Students S t u d e n t s who e t hthe e s senior e n i o r aauthor u t h o r on i t h e r an r a l or or poster i l l be be given g i v e n favored f a v o r e d consideration. consideration. p o s t e r paper paper wwill 33)) IItt isi sdesirable d e s i r a b l e for f o rtwo two or o r more more sstudents t u d e n t s t otoj jointly ointly request r e q u e s t ttravel r a v e l assistance. assistance. 44)) IIn n general, g e n e r a l , ppriority r i o r i t y will w i l lbe begiven g i v e n to t o those t h o s e in i n the the IInstitute n s t i t u t eregion r e g i o nwho who are a r e farthest f a r t h e s taway. away. 5) be made madei ninwwriting, 5 ) Each Each ttravel r a v e l award award rrequest e q u e s t sshall h a l l be r i t i n g , to t o the the annual Chairman,wwith an eexplanation annual Chairman, i t h an x p l a n a t i o n of o f need, need, possible possible author a u t h o r sstatus t a t u s oor r oother t h e r ssignificant i g n i f i c a n t details. details. V �BOARD BOARD OF DIRECTORS DIRECTORS 1989 1989 R.W. Ojakangas Ojakangas( w(with J.C. Green andT.B. T.B. Hoist), R.W. i t h J.C. Green and H o i s t ) , Department Department of o f Geology, Geology, University U n i v e r s i t y of of Minnesota, Minnesota, Duluth, D u l u t h ,Duluth, D u l u t hMinnesota , Minnesota55812 55812 1988 1988 J.S. K l a s n e r (with ( w i t hJ.D. J.D.Hughes Hughes and and K.J. K.J. Schulz), S c h u l z ) ,Department Department of o fGeology, Geology, J.S. Klasner Western l i n o i s University, U n i v e r s i t y ,Macomb, Macomb, IIllinois l l i n o i s61455 61455 WesternI lIllinois 1987 1987 R.P. Sage E.D. FFrey), Ministry R.P. Sage ( (with w i t h E.D. r e y ) , Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey, M i n i s t r y of o f Northern Northern Development andMines, Mines,7777GGrenville Development and r e n v i l l e Street, S t r e e t , Toronto, T o r o n t o ,Ontario O n t a r iM7A o M7A1W4 1W4 1986 1986 J.K. Greenburg Geological andNNatural History J.K. Greenburg ((with w i t h B.A. B.A. Brown), Brown), Wisconsin Wisconsin G e o l o g i c a l and atural H istory Survey, Survey, 3817 3817 Mineral M i n e r a l Point P o i n tRoad, Road, Madison, Madison, Wisconsin Wisconsin53705 53705 Secretary-Treasurer Secretary-Treasurer J. Kalliokoski, J. K a l l i o k o s k i ,Department Department ofo fGeology Geology and and Geological G e o l o g i c a l Engineering, Engineering, Michigan M i c h i g a n TTechnological e c h n o l o g i c a l University, U n i v e r s i t y ,Houghton, Houghton, Michigan M i c h i g a n 49931 49931 LOCAL COMMITTEE LOCAL COMMITTEE R.W. R.W. Ojakangas: Ojakangas: General Chairman General Chairman J.C. J.C. Green: Green: ProgramChairman; Chairman;Program Programand andA bAbstracts Program s t r a c t s eeditor ditor T.B. Hoist: T.B. Hoist: Field andf i efield F i e l d Trip T r i p Chairman; Chairman; FField i e l d ttrip r i p arrangements arrangements and l d t trip rip guidebookeeditor guidebook ditor BEST STUDENT BEST STUDENT PAPER PAPER COMMITTEE COMMITTEE J.S. J.S. Kiasner: Klasner: WesternI lIllinois Western l i n o i s University, U n i v e r s i t y , Macomb, Macomb, I lIllinois linois Ray Anderson: Ray Anderson: Iowa GGeological Survey, Iowa Iowa e o l o g i c a l Survey, Iowa CCity, i t y , Iowa Iowa Keith K e i t h Laskowski: Laskowski: Newmont Newmont E xExploration, p l o r a t i o n , LLtd., t d . , Duluth, D u l u t h , Minnesota Minnesota GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE JJ.J. . J . Brummer: Brummer: Brummer Brummer C Consulting, o n s u l t i n g , TToronto, o r o n t o , Ontario Ontario M.G. Mudrey, JJr.: M.G. Mudrey, r . : Wisconsin Wisconsin Geologic G e o l o g i c and and Natural N a t u r a l History H i s t o r ySurvey, Survey, Madison, Madison, Wisconsin R.W. Ojakangas: R.W. University U n i v e r s i t y of of Minnesota-Duluth, M i n n e s o t a - D u l u t h , Duluth, D u l u t h , Minnesota Minnesota vi �GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT Jorrna Jorma KKalliokoski, a l l i o k o s k i , Michigan M i c h i g a n Technological T e c h n o l o g i c a l University U n i v e r s i t y (Professor ( P r o f e s s o rEmeritus). Emeritus). Medal by M.G. M.G. Mudrey, Mudrey,JJr., Medal awarded awarded by r . , Wisconsin Wisconsin Geological G e o l o g i c a l and andNatural Natural H i s t o r ySurvey Survey History BANQUET BANQUETSPEAKER SPEAKER S.F. S.F. Sawkins, Sawkins, University U n i v e r s i t y of o fMinnesota, Minnesota, Twin Twin Cities, C i t i e s , 'Ore "Ore genesis genesis models models for for volcano-plutonic v o l c a n o - p l u t o n i c arc a r csystems: systems: an anagnostic a g n o s t i cview viewofo the f t h conventional e c o n v e n t i o n awisdom l wisdom" ACKNOWLEDGMENTS ACKNOWLEDGMENTS Several p e o p l e and and oorganizations r g a n i z a t i o n s aassisted s s i s t e d iinn preparation p r e p a r a t i o n of o fthe t h e35th 3 5 t hAnnual Annual Several people Without their help the many tasks in preparing this meeting could ILSG. W i t h o u t t h e i r h e l p t h e many t a s k s i n p r e p a r i n g t h i s m e e t i n g c o u l d not not ILSG. have been been done. done. The The three t h r e e of o f us us(R.W. ( R . W . Ojakangas, Ojakangas, J.C. J.C. Green, Green, and and T.B. T.B. Holst) Hoist) have would would llike i k e to t othank thank the t h e following f o l l o w i n gpeople people and and organizations o r g a n i z a t i o n s ffor o r their t h e i r help. help. Mary Nash, EExecutive Geology,UUniversity Mary Nash, x e c u t i v e SSecretary, e c r e t a r y , Department Department oof f Geology, n i v e r s i t y of of Minnesota-Duluth, Minnesota-Duluth, for f o r handling h a n d l i n g finances f i n a n c e s and and other o t h e r aspects. aspects. Joan Secretary, Geology, UUniversity Joan Hendershot, Hendershot, SSenior enior S e c r e t a r y , Department Department ofof Geology, n i v e r s i t y of of Minnesota—Duluth, Minnesota-Duluth, f for o r various v a r i o u s tasks. tasks. Avis A v i s Hedin, Hedin, Principal P r i n c i p a lSecretary, S e c r e t a r y ,College C o l l e g e ofofScience Science and and Engineering, E n g i n e e r i n g , University University of o f Minnesota-Duluth, M i n n e s o t a - D u l u t h , ffor o r typing typing. Linda L i n d a Solcich, S o l c i c h . Radisson Radisson Hotel, H o t e l , Duluth, D u l u t h , for f o rmeeting m e e t i n gsite s i t earrangements. arrangements. John Klasner, Departmento fofGeology, Geology, Western 11 1Illinois i n o i s UUniversity, n i v e r s i t y , for f o r mailing mai 1i n g John K l a s n e r , Department Western l is t sand andadvice. advice. lists Graduate University Graduate sstudents t u d e n t s aat t U n i v e r s i t y of o f Minnesota-Duluth, M i n n e s o t a - D u l u t h , for f o r performing p e r f o r m i n g tasks, tasks, including i n c l u d i n g mailing m a i l i n gbrochures brochures and and projection. projection. Numerous company personnel Numerous company personnel f o r for c ocooperation o p e r a t i o n on on f i efield l d t trips. rips. University r aassistance s s i s t a n c e wwith i t h transportation. transportation. U n i v e r s i t y of o fMinnesota—Duluth, Minnesota-Duluth, f ofor Everyone else. else. Everyone vii �34TH ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Marquette, Michigan, Marquette, M i c h i g a n , 1988 1988 The annual mmeeting The 334th 4 t h annual e e t i n g oof f tthe h e Institute I n s t i t u t eononLake LakeSuperior S u p e r i o rGeology Geology was was held held May10-14, 10-14, 1988, 1988, iinn Marquette, ffrom r o m May Marquette, Michigan. M i c h i g a n . The e e t i n g was o - h o s t e d by by The m meeting was cco-hosted Northern M ichigan U n i v e r s i t y , the t h eU.S. U.S. Geological G e o l o g i c a lSurvey-Branch Survey-Branch of o f Eastern Eastern Northern Michigan University, Mineral andWestern Western M i n e r a l Resources, Resources, and I l lIllinois i n o i s University. U n i v e r s i t y . The The many s k s i ninvolved v o l v e d iinn manyt atasks t h e planning, p l a n n i n g , preparation, p r e p a r a t i o n ,and andconducting c o n d u c t i n g of of the t h emeeting m e e t i n gwere were shared shared by by the the the John KKlasner servedasasggeneral chairman; Klaus Klaus SSchulz cco-hosts. o-hosts. John l a s n e r ooff WIU W I U served e n e r a l chairman; c h u l z oof f the the USGS banquet NMU took took USGS a r arranged r a n g e d f ofor r t hthe e ffield i e l d trips t r i p and s and banquetspeaker; speaker;John JohnHughes Hughes ofo fNMU ccare a r e of of local l o c a larrangements. arrangements. T e c h n i c a l ssessions e s s i o n s and h e banquet banquet were e l d aatt the the Technical and tthe werehheld RamadaI nInn on May May 12 12 and Ramada n on and 13. 13. AA ttotal o t a l of o f 245 245 persons persons registered r e g i s t e r e d for f o r the t h e meeting. meeting. T h i r t y - s e v e n oral o r a l presentations p r e s e n t a t i o n s were were scheduled, scheduled, but b u t two two had had to t o be be cancelled cancelled Thirty-seven becauset hthe were unable unable tto Nineteen because e ppresenters r e s e n t e r s were o attend. attend. N i n e t e e n poster p o s t e r papers papers were were andt hthree ppresented r e s e n t e d and r e e d different i f f e r e n t field f i e l d trips t r i p were s wereconducted. conducted. Newdevelopments developmentsf rfrom New o m s seismic e i s m i c sstudies t u d i e s in i n Lake Lake Superior S u p e r i o rbyb ythe t h GLIMPLE e GLIMPLE program n f o r m a t i o nfrom f r o ma aDOSECC DOSECC workshop h e Keweenawan Keweenawan R Rift ift m e r i t e d aa program and and iinformation workshopon on tthe merited sspecial p e c i a l full f u l day l daysession s e s s i o nononMay May12, 12, on onthe t h e"Geology "Geology ofo fthe t h eKeweenawan Keweenawan RRift." ift.'' Also, A l s o , half h a l fday daysessions s e s s i o n son onMay May 13, 13, were were devoted devoted to t o the t h e"Geology "Geology and and Mineral Mineral Deposits Rocks"and and"Geology "GeologyofofEEarly Rocks..." D e p o s i t s ooff Archean Archean Rocks" a r l y PProterozoic r o t e r o z o i c Rocks Poster paperscovered covereda av avariety respectively. respectively. P o s t e r papers r i e t y oof f ttopics. opics. ...I1 two-dayt trip AA ttotal o t a l of o f 151 1 5 1 persons persons e nenrolled r o l l e d f ofor r f ifield e l d ttrips. rips. A A two-day r i p on on the the "Archean Geologyand andMMineralization Belt" A r c h e a n Geology i n e r a l i z a t i o n ooff the t h e Marquette M a r q u e t t e Greenstone Greenstone B e l t " conducted conducted bby y 1. T . Bornhorst B o r n h o r s t of o fMichigan M i c h i g a n Technological T e c h n o l o g i c a l University U n i v e r s i t yand andR.A. R . A . Brozdowski Brozdowski and and G.W. SScott The ppre-meeting G.W. c o t t of o f Callahan C a l l a h a nMining M i n i n gCompany Company pproved r o v e d vvery e r y popular. p o p u l a r . The re-meeting version people v e r s i o n oof f this t h i s trip t r i pfilled f i l l ewith d w iSO t h 50 p e o p l eand and the t h e leaders l e a d e r s kindly k i n d l y agreed agreed to to conduct Twenty-nine conduct iitt for f o r2828persons personsafter a f t ethe r t hmeeting e m e e t i n gononMay May14 14and and 15. 15. Twenty-nine persons bybB. Boyum, persons pparticipated a r t i c i p a t e d in i naaspecial s p e c i a trip l t r conducted i p conducted y B. Boyum,R.R .Reed, Reed, and and William on "The "TheMMarquette W i l l i a m Kangas Kangas on a r q u e t t e M Mineral i n e r a l D District, i s t r i c t , Mining M i n i n g History H i s t o r yand andGeology." Geology." " A Structural S t r u c t u r a l Traverse T r a v e r s e Across Across aa P a r t of of A l s o , 44 44 persons persons eenrolled n r o l l e d i in n aa ttrip r i p on on "A Also, Part the OrogenI l lIllustrating t h e Penokean Penokean Orogen u s t r a t i n g Overthrusting O v e r t h r u s t i n g ini nNorthern N o r t h e r nMichigan" M i c h i g a n "conducted conducted C. Gallup wasaa cco-author by by J. Klasner, K l a s n e r , P. P.Sims, Sims, and andWilliam W i l l i a mGregg. Gregg. C. G a l l u p was o - a u t h o r oof f tthis his trip t r i p but b u t could c o u l d not n o t attend. attend. Don Davidson Davidson of AA ttotal o t a l ofo 163 f 163people peopleattended a t t e n d e dthe t h eannual annualILSG ILSGbanquet. banquet. Don of Northern N o r t h e r n IIllinois l l i n o i sUniversity U n i v e r s i t presented y p r e s e n t e dthe t h eGoldich G o l d i c h Medal Medal to t o Walter W a l t e r White W h i t e of o f the the USGS manyy years USGS f ofor r hhis i s many e a r s oof f sstudy t u d y of of and and excellent e x c e l l e n tcontributions c o n t r i b u t i o nto s Keweenawan t o Keweenawan P.F. Hoffman g e o l o g y . P.F. Hoffman ooff the t h e Geological G e o l o g i c a l Survey Survey of o fCanada Canada regaled r e g a l e d the t h e banquet banquet geology. audience anooverview early audience wwith i t h an v e r v i e w o foft hthe e t etectonic c t o n i c eevolution v o l u t i o n oof f Laurentia L a u r e n t i a dduring uring e arly and middle Proterozoic and m iddle P r o t e r o z o i c time. time. Inasmuch ILSG encourages t student Inasmuch asast hthe e ILSG t r itries e s t to o encourage u d e n t p aparticipation, r t i c i p a t i o n , both b o t h in in attendance a t t e n d a n c e aat t tthe h e Institute I n s t i t u t eand and presentation p r e s e n t a t i o n of o f papers, papers, we we provided p r o v i d e d ffinancial inancial assistance Waiver ooff a s s i s t a n c e to t o several s e v e r a lstudents s t u d e n t sand andgave gave two two best b e s tpaper paperawards. awards. Waiver rregistration e g i s t r a t i o nfee f e ewas was given g i v e n to t o 17 17 students s t u d e n t s who who aapplied, p p l i e d , and and 13 13 ooff the t h e 17 17 students students were aalso from aa sspecial were l s o ggiven i v e n ssmall m a l l ($20-$4O) ($20-$40) t rtravel a v e l aassistance s s i s t a n c e from p e c i a l fund f u n d set s e t aside aside awardoof $150was wasp rpresented ffor o r this t h i spurpose. purpose. An An award f $150 e s e n t e d t otoBBernhardt e r n h a r d t SSaini-Eidukat a i n i - E i d u k a t of of the Geophysics,UUniversity t h e Department Department ooff Geology Geology and and Geophysics, n i v e r s i t y of o f Minnesota-Minneapolis Minnesota-Minneapolis a $150 a $150award awardwas was given g i v e n to t oPeter P e t e rJongwaard Jongwaard of of ffor o r the t h e best b e s toral o r apresentation l p r e s e n t a t i oand n and tthe h e University U n i v e r s i t y of o fMinnesota-Duluth M i n n e s o t a - D u l u t h ffor o r the t h e best b e s t poster p o s t e r paper. paper. The ILSG ILSGBoard Boardoof Directors The f D i r e c t o r s luncheon luncheon meeting m e e t i n g was was held h e l d at a tthe t h eRamada Ramada Inn I n n on on was attended a t t e n d e d by b y C. C . Blackburn, Blackburn, B. 0 . Brown, Brown, J. Greenburg, Greenburg, J. J. Hughes, Hughes, J. J. May May 13. IIttwas Kalliokoski, M.M. Kehlenbeck, Kehlenbeck, J. J. Klasner, K l a s n e r , R. R. Ojakangas, Ojakangas, R. R . Sage, Sage, and and K. K . Schulz. Schulz. K a l l i o k o s k i , M.M. The ffollowing The o l l o w i n g items i t e m s of o fbusiness b u s i n e s swere were discussed: discussed: viii �- - Review Review ooff minutes m i n u t e s from f r o m 33rd 3 3 r d ILSG. ILSG. No No changes. changes. -- - Treasurer's T r e a s u r e r ' s report r e p o r t by by J. J. Kalliokoski, K a l l i o k o s k i Treasurer , T r e a s u r e rofofthe t h eAmerican American Account, Account, the the -balance b a l a n c e iin n the t h e general g e n e r a l account a c c o u n t as as of o f April A p r i l2,2,1987 1987was was $3,065.21. $3,065.21. The Goldich had aa bbalance M.M. Kehlenbeck, Kehlenbeck, Treasurer M.M. Treasurer G o l d i c h Medal Medal Funds Funds had a l a n c e of $1,153.92. $1,153.92. Account, rreported 1988. ooff the t h e Canadian Canadian Account, eported a a balance b a l a n c e of $9,664.88 $9,664.88 as as of o f May May 12, 12, 1988. - - R.W. i n dindicated i c a t e d t h that a t t hthe e UUniversity n i v e r s i t y oof f Minnesota, u l u t h w will i l l host host R.kJ.Ojakangas Ojakangas Minnesota,DDuluth -— tthe h e 35th 3 5 t h ILSG. ILSG. He He wwill i l l serve s e r v e as aschairman. chairman. - - J. K l a s n e r reported r e p o r t e d tthat h a t mailing m a i l i n g lists l i s t sare are o u t - o f - d a t eand andthere t h e r eare a r names e names J. Klasner out-of-date -whoa rare ooff many many p people e o p l e onon t h ethe l i slist t who e nono l o nlonger g e r a f faffiliated i l i a t e d wwith i t h t hthe e I Institute. nstitute. J. Kalliokoski J. K a l l i o k o s k i volunteered v o l u n t e e r e d t to o uupdate p d a t e t hthis i s l ilist s t and and fforward o r w a r d i it t to t o the the Minnesota Surveywhere wherei tit iiss kept. kept. M i n n e s o t a GGeological e o l o g i c a l Survey --—- M.G. r . of o f the t h e Wisconsin W i s c o n s i n Geological G e o l o g i c a l and and Natural N a t u r a l History H i s t o r y Survey Survey has has M.G. Mudrey, Mudrey,OJr. aagreed g r e e d tto o serve s e r v e on on the t h eGoldich G o l d i c hMedal MedalCommittee. Committee. He He rreplaces e p l a c e s K.D. K.D. Card Cardwho who finished f i n i s h e d his h i sterm t e r mon onthe t h ecommittee. committee. The 334th would nnot been ppossible The 4 t h ILSG ILSG would o t have have been o s s i b l e without w i t h o u t the t h ehelp h e l pof omany f manymembers. members. IIn n particular, p a r t i c u l a r ,the t h esuccess success of o fthe t h emeeting m e e t i n g is i slargely l a r g e l ydue duetot othe t h numerous e numerous high high Numerous members qquality u a l i t y papers papers presented p r e s e n t e d both b o t h orally o r a l l yand and as as poster p o s t e r papers. papers. Numerous members kkindly i n d l y agreed a g r e e d to t oserve s e r v eas asSession S e s s i o n Chairs, C h a i r s , Student S t u d e n tPaper Paper Judges, Judges, Goldich Goldich Committee Members,F Field Actually Committee Members, i e l d TTrip r i p Leaders Leaders and and Board Board ooff Directors D i r e c t o r sMembers. Members. A ctually tthe h e Institute I n s t i t u t eisi a s continuum, a continuum,with w i t heach eachmeeting m e e t i n g built b u i l tupon upon the t h e work work of o f previous previous organizers o r g a n i z e r s and and tthe h e willingness w i l l i n g n e s s of o fmembers members tto o serve s e r v e as as hosts h o s t s and and oorganizers r g a n i z e r s of of future f u t u r e meetings. meetings. We We t hthank a n k a lall l ffor o r their t h e i r help h e l p with w i t h this t h i syear's y e a r ' smeeting. meeting. Respectfully R e s p e c t f u l l y submitted, submitted, J. Hughes Hughes J. Klasner Klasner K. Schulz Co-hosts CO-hosts 34th 3 4 t h ILSG ILSG ix �CALENDAR OF OF EVENTS EVENTS AND PROGRAM PROGRAM WEDNESDAY, MAY MAY 33 FIELD TRIPS TRIPS 1, 22 FIELD departs from from Radisson, 8:00 8:00 a.m. a.m. Field Field Trip Trip 11 (North (North Shore Shore rhyolites, rhyolites, Minnesota) Minnesota) departs Radisson, upper upper level. Green. Will return return in in evening; evening; dinner (Dutch) (Dutch) en route. route. level. Leader: Leader: J.C. Green. 8:00 a.m. Field Field Trip Trip 22 (Penokean (Penokean structural structural terranes terranes in in East-Central East-Central Minnesota) Minnesota) departs departs 8:00 Radisson, level. Leader: T.B. T.B. HoIst. Hoist. Will return return in time time for for dinner dinner in in Radisson, lower level. Duluth. Duluth. 6:00 p.m. to to 9:00 9:00 p.m. p.m. Registration, Registration, Radisson Radisson Hotel, Hotel, Duluth Duluth 7:00 p.m. p.m. to to 10:00 10:OO p.m. p.m. Welcome Welcome get-together get-together and and cash cash bar, bar, Radisson Radisson Hotel. Hotel. x �TECHNICAL PROGRAM PROGRAM THURSDAY, THURSDAY. MAY 44 Morning 8:00 a.m. Welcome and and introduction introduction 8:00 a.m. Midcontinent Rift Session Session Chairs: A.B. Dickas and J.D. Miller, Miller, Jr. Jr. 8:10: James D. Miller, Miller, Jr. Jr. James Geology of the the Beaver Beaver Northeastern Minnesota Minnesota 8:30: Eric A. Jerde Jerde North Shore Hypabyssat rocks of the North Hypabyssal rocks Shore of Lake Superior: evidence for for polybaric Lake Bay Complex, fractionation in the Midcontinent Midcontinent Rift Rift 8:50: 850: Mark J. Severson Severson "Stratigraphy" 'Stratigraphy" and and general general geology of aa Intrusion, portion of the Partridge Partridge River River Intrusion, Duluth Complex, Minnesota Minnesota 9:10: Karl E. Seifert Seifert Pluton: two intrusions intrusions The Mineral Lake Lake Pluton: rather than a layered complex? rather layered complex? 9:30: Mudrey, Jr. Jr. Michael G. Mudrey, Albert B. 6 . Dickas Dickas Fundamental unit unit differentiation differentiation of of the Fundamental middle Proterozoic Proterozoic Midcontinent Midcontinent Rift Rift System, System, North America America 9:50: Coffee Break Break 10:30: McGinnis Lyle D. McGinnis Faulting in Possible in aa Possible Late-Stage Thrust Faulting Keweenawan-Age Keweenawan-Age Accommodation Zone Zone beneath Lake Superior Superior 10:50: J. Kalliokoski Kalliokoski Jacobsville Sandstone and Tectonic Tectonic Activity Activity 11:10: G. Wilson Campbell Craddock clastic dikes dikes as as Keweenawan Keweenawan Mafic and clastic in indicators Huron paleostress in the Huron Mountains, Michigan Michigan 11:30: Thomas Suszek Petrography Petrography *By title only: Susanne 'By Susanne Th. Th. Schmidt Schmidt John C. C. Green Green 11:50: 1 1:SO: and Sedimentation of the Middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) Nonesuch Nonesuch Formation, Formation, Western Western Lake Lake Superior Superior Region, Region, Midcontinent Rift Zone Midcontinent Zone Metamorphic zonation in the the North North Shore Shore Volcanic Group, Group, Minnesota Minnesota Lunch Break Break xi �THURSDAY, MAY 4 THURSDAY, Afternoon Afternoon 1:30 to 2:30: Poster Poster session, session, Viking Viking Room Room Oral Session, Session, Mostly Mostly Economic Economic and and Quaternary Quaternary Chairs: Penelope Morton and Chairs: and David David Groves Groves 2:30: John S. S. Mothersill Mothersill James Fraser Fraser The paleomagnetic paleomagnetic record of Late Late Glacial Glacial and Post Post Glacial Glacial sediments sediments of of Lake Lake Superior Superior 2:50: Gary N. Meyer Gary Meyer Northern Glacial Glacial geology of of Northern mineral exploration exploration applications applications 3:10: E.R. Koopman, E.R. Koopman, B. Dube B. J.M. Franklin J.M. Franklin K.H. Poulsen Poulsen M.R. M.R. Patterson Patterson Deformation of of the Lyon Deformation Lyon Lake Lake massive massive suiphide sulphide deposit, Wabigoon Wabigoon subprovince, subprovince, Northwestern Ontario, Canada Canada 3:30: Coffee Break Break 3:50: Robert J. Horton Horton Robert Minnesota: Minnesota: The mining and and geologic history history of the the The Islet mine, and aa conceptual conceptual ore Silver Islet mine, and ore genesis model for the genesis the deposit deposit 4:10: Mark L. Nebel Nebel and polygenesis Metamorphism Metamorphism and polygenesis of ore ore deposits: an an example from from the the Madem Madem Lakkos PB-ZN-AG-AU deposit, deposit, Greece Greece 4:30: Mark Smyk the West Geology of the West Dead Dead Horse Horse Creek Creek rare metal metal occurrences, diatreme-hosted diatreme-hosted rare Schreiber-Hemlo district, Ontario Ontario 4:50: End of Session Session * * * * * * * * * * * * 5:00-7:00 5:OO-7:00 Cash Cash bar bar 7:00: 7:OO: Banquet Banquet Kalliokoski, Michigan Presentation of Goldich medal medal to to J. Kalliokoski, Michigan Technological Technological Presentation of the Goldich University, University, by M. M. G. G. Mudrey, Mudrey, Jr. Jr. Frederich J. (Sam) Frederich J. (Sam) Sawkins, Sawkins, University University of of Minnesota, Minnesota, Twin Twin Cities Cities "Ore genesis genesis models models for for volcano-plutonic volcano-plutonic arc arc systems: systems: An An agnostic agnostic view of of "Ore the conventional conventional wisdom" wisdom" xii xii Speaker: �FRIDAY, MAY 5 FRIDAY, Morning Morning Mostly Proterozoic Proterozoic R. W. W. Ojakangas Ojakangas Chairs: Val W. Chandler Chandler and A. 8:00: 8100: Gene L. L. LaBerge LaBerge structure and Tectonic Tectonic implications implications of the structure and stratigraphy of quartzites in in Central Central and and Southern Wisconsin Wisconsin 8:20: Bruce A. Brown Brown Significance argillites, and and Significance of conglomerates, conglomerates, argillites, in the Baraboo and dirty sandstones in and of Southeastern quartzites Southeastern Waterloo Wisconsin 8:40: Jeffrey K. K. Greenberg Greenberg Encore: The Proterozoic Proterozoic Baraboo Baraboo interval interval -- Encore: composition composition data et al. al. 9:00: 9:OO: Chan Lung S. Chan Paul E. Myers Myers Paleomagnetic studies of of Wausau Syenite Paleomagnetic studies Syenite Complex and Wissota Complex Wissota Dam Mafic Mafic Dike Dike 9:20: 9:20: Tern Terri Patton Patton M.K. Sood M.K. Sood B. Biddulph Biddulph Petrogenetic evolution of the Proterozoic Petrogenetic evolution Proterozoic Wausau igneous complex, complex, Wisconsin Wisconsin 9:40: 9140: Coffee Break Break 10:10: 1O:lO: Theresa M. Bodus Bodus William F. F. Kean Kean Preliminary paleomagnetic paleomagnetic survey survey of the Preliminary metasediments and metasediments and metavolcanics metavolcanics of of the Niagara Fault Niagara Fault system system in in Florence County, County, Wisconsin 10:30: M. Bodus Bodus Theresa M. Keith A. Sverdrup Sverdrup Preliminary magnetic survey of the Preliminary magnetic the Niagara Niagara in Florence, Forest, fault system system in Florence, Forest, and and Marinette counties, Wisconsin Wisconsin 10:50: 10150: Dennis J. Bebel Bebel A ground A ground resistivity technique for locating locating buried Precambrian fracture aquifers aquifers in in buried Precambrian basement, Central Central Wisconsin Wisconsin 11:10: 11:lO: Timothy Holst Timothy B. HoIst in Minnesota The The Penokean Penokean orogeny orogeny in Minnesota and and A comparison Michigan: A comparison of the upper Michigan: structural geology geology of of the structural the Michigamme Michigamme and and Thomson Formations Formations 111:30: 1:3O: Lunch Break Break Xlii xiii �FRIDAY, MAY MAY 55 Afternoon Afternoon 1:30 to 2:30: 1130 2130: Poster Session, Viking Room Room Oral Session, Session, Mostly Mostly Archean Archean M.A. Jirsa Jirsa and Steven A. Hauck Chairs: Chairs: M.A. Hauck 2130: 2:30: David L. L. Southwick Southwick Bryan Schaap Schaap Val W. Chandler Chandler Multiple Archean Archean terranes in SW Multiple SW MinnesotaMinnesotathe old gray gneiss she ain't what gneiss ain't what she she used used to be be 2:50: 2150: Stephen J. J, Schaefer Schaefer A comparison comparison of two two Archean Archean ultramafic pyroclastic rock units, Northwestern pyroclastic Northwestern Ontario Ontario 3:10: 3110: James L. L. Welsh Welsh Archean rocks Strike-slip faulting rocks in in the the Strike-slip faulting in in Archean Virginia Horn Horn area, area, N.E. N.E. Minnesota: implications implications for the origin origin of the Virginia Horn structure structure 3:30: 3130: Coffee Break Break 3150: 3:50: Mark A. Jirsa Jirsa Stratigraphic and and structural structural evolution evolution of of the Stratigraphic the Northmetavolcanic belt, NorthNorthern Itasca Northern ltasca metavolcanic Central Minnesota Minnesota 4:10: 4:lO: Roger Kuhns Kuhns an indication of as an tectonic environment environmentfor for the the central of tectonic central part of Belt, Greenstone Belt, the Hemlo-Heron Hemlo-Heron Bay Bay Greenstone Ontario Ontario 4130 4:30 William F. F. Read Read possibly two, One, possibly two, impact craters under under One, DePere, Wisconsin, DePere, Wisconsin, discovered discovered via water Basalt geochemistry Basalt well logs logs and and drill drill cuttings cuttings End of Session Session 4:50 4150 * ** * * * ** * * xiv * * ** �SATURDAY, MAY 6 SATURDAY? FIELD TRIPS 3,4 3,4 7:00 a.m. 7100 a.m. Field Field Trip Trip 33(Mellen (MellenComplex, ComplexlWisconsin) Wisconsin) Departs Departs from from liadisson Radisson upper upper level. level. Leaders: Karl Seifert, James Olmsted, Olmstedl Ken Klewin. Klewin. (Vans will return return to Duluth). Duluth). structural settings, settings, (Archean gold gold occurrences Field Field Trip 4 (Archean occurrences and and their structural J. Welsh, Minnesota) departs from Radisson, Leaders: J. D. England, England, D. D. Minnesota) departs Radissonl upper upper level. level. Leaders: Welsh, D. Groves? Levy? P. Hudleston, Hudlestonl D. Southwick, Southwickl R. Bauer?W. Ulland. Ulland. (Vans will return return to to Groves, E. E. Levy, R. Bauer, Duluth). Duluth). 8:00 8100 a.m. xv �POSTER PAPERS PAPERS Authors are requested to be on hand Authors are requested to hand at at their their posters posters during during the the special special poster poster Friday, and sessions sessions from from 1:30 1:30 to 2:30 2:30 Thursday Thursday and and Friday, and other other times times when when convenient. convenient. 1. of the I . Adams, Adamsf D.C., D.C., and and Young, Young, C.T., C.T., Magnetotelluric Magnetotelluric investigation investigation of the contact contact in northeastern northeastern between the Duluth between the Duluth Complex Complex and and the the Animikie Animikie Basin Basin in Minnesota. Minnesota. 2. Belden, 2. Beldenl J., Anderson, Anderson* G., Geland and Watkins, Watkins* I., I.* Zircons Zircons of the the St. St. Cloud Cloud Red Red and and Reformatory Reformatory Granites. Granites. 3. Block, Block, D.P., D.P., and andCavaleri, Cavaleri,M.E., M.E.,Petrogenesis Petrogenesis and andgeochemistry geochemistry ofofrhyoUtes rhyolites from the Chengwatana Chengwatana Volcanic Volcanic Group, Group, Mid-Continent Mid-Continent Rift Rift System. System. 4. Buchheit, Buchheit, R.L., R.L.?Malmquist, Malmquistl K.L., K.L., and and Niebuhr, Niebuhr, J.R., J R 1Glacial Glacialdrift driftgeochemistry geochemistry for strategic strategic minerals, minerals, Lake Lake County, Countyl Minnesota. Minnesota. 5. Cannon, 5. Cannon* W.F., W.Fe1Schulz, Schulz, K.J., K.J., Hinze, Hinze* W.J., W.J., and and Green, Green, A.G., A.G.,Precambrian Precambrian terranes defined by seismic terranes beneath beneath northern northern Lake Lake Michigan Michigan defined seismic and and gravity gravity analysis. analysis. 6. Chandler, Chandler, V.W., V.W., and and Schaap, Schaap, B.D., B.D., New New Bouguer Bouguer gravity gravity anomaly anomaly map map of of Minnesota. Minnesota. 7. 7. Pierre, and and Smith, Dods, S.D., Dods, S.D., Hinze, Hinze, W.J., W.J., Keating, Keating, Pierre? Smith, J.G., J.G., Magnetic Magnetic and and gravity maps of of Lake Lake Huron. Huron. 8. Hinze, W.J., W.J., Ravat, Ravat, D.N., D.N., McGinnis, McGinnis, L.D., L.D., Cannon, Cannon, W.F., W.F., Milkereit, Milkereit, B., B., Sexton, Sexton, J.L., and Wang, Structure J.Le1 Wang, H.F., H.Fa1 Structure of the the Midcontinent Midcontinent Rift Rift System System in in eastern eastern Preliminary results results from from the the 8-sec reflection Lake Superior: Superior: Preliminary reflection seismic data and gravity and and magnetic magnetic anomalies. anomalies. 9. Holm, 9. Holml D.K., D.K., and and Selverstone, Selverstone, J., J., Preliminary Preliminary constraints constraints on on the the P-T P-Tevolution evolution of the Penokean Penokean orogeny: orogeny: east-central Minnesota. Minnesota. 10. Horton, 10. Hortonl R.J., R.Js1and and Smith, Smith, B.D., B.D., Geophysical Geophysical investigations, investigations, International International Falls and Roseau Roseau quadrangles, quadranglesl Minnesota-Ontario. Minnesota-Ontario. of the M.A., Stratigraphic M.A., Stratigraphic and structural structural evolution evolution of the Northern Northern Itasca ltasca metavolcanic belt, north-central north-central Minnesota. Minnesota. 11. I I. Jirsa, Jirsa, 12. Kehlenbeck, M.M., and and Cheadle, Cheadle,S.P.? S.P.,Gravity Gravitysurvey surveyofof aa portion Kehlenbeck, M.M., portion of of the the Quetico and Wawa Wawa subprovinces subprovinces near Thunder Bay, Bay, Ontario. Ontario. xvi �13. 13. Kucks, Kucks, R.P., R.P., Chandler, Chandler, V.W., V.W., Dods, Dads! S.D., S.D., Ervin, Ervin, C.P., C.P., Hood, Hood,P., P.,McConnell, McConnell, anomaly maps K., and Teskey, Teskey! D., D., Potential-field Potential-field anomaly maps of of the Lake Lake K., Superior region. region. Superior 14. 14. MacArthur, MacArthur, J.H., J.H., and and HoIst, Holst, T.B., T.B., Deformation Deformation in the the Archean Archean Knife Knife Lake Lake Group, Group, Ensign Ensign Lake Lake area area of of northeastern Minnesota. Minnesota. northeastern the the eastern eastern Vermilion Vermilion District, District, Characterization Characterization of of the the graphite graphite occurrences occurrences in in the the and western western Penokean Penokean orogen. orogen. southern and 15. McSwiggen, McSwiggen, P.L., P.L., 15. 16. 16. 17. 17. Mudrey, Mudrey, M.G., M.G., McGinnis, McGinnis, L.D., L.D.! Ervin, Ervin, C.P., C.P., Nyquist, Nyquist, J.E., J.E., Dickas, Dickas, A.B., A.B., of the and Sexton, J.L., Structure Morey, Morey! G.B., G.B., Green, Green, A.G., A.G.! and Sexton, J.L., Structure of the Midcontinent Midcontinent Rift Rift System System from from 8-sec 8-sec reflection reflection seismic seismic data data in in Lake Superior. Superior. western Lake Chacko, Chacko, T., T., and and Kuehner, Kuehner, S.M., S.M., Petrographic Petrographic and and near Republic, iron-formation lens of isolated microprobe study study of isolated iron-formation lens near Republic! microprobe Peterson, J.W., Peterson, Michigan: aasearch searchfor forhigh-grade, high-grade,pre-Penokean pre-Penokeanmetamorphism. metamorphism. 18. Reich, Reich, Laura, Laura, Kean, Kean, W., W., and andSverdrup, Sverdrup,K., K.,Preliminary Preliminarygeomagnetic geomagnetic model model the St. St. Croix Croix Horst HorstininPolk PolkCounty, County,Wisconsin. Wisconsin. of the 19. Schulz, Schulz, K.J., K.J., and and Sims, Sims, P.K., P.K., Implications Implications of of igneous igneous rock rock geochemistry geochemistry inin Penokean orogen orogen for metallogeny metallogeny and and tectonic tectonic setting: setting: A A the Penokean synthesis of recent recent data. data. 20. Setterholm, Setterholm, 0., D., and and Hammond, Hammond, R.H., R.H., Manganese Manganese potential potential of the the Cretaceous Cretaceous rocks flanking flanking the the Sioux Sioux Ridge, Ridge, Minnesota Minnesota and and South South Dakota. Dakota. 21. Sims, Simsl P.K., P.K., New New bedrock bedrock geologic geologic map map of of Precambrian Precambrian rocks, rocks, eastern eastern Lake Lake Superior region, region! Wisconsin Wisconsin and and northern northern Michigan. Michigan. 22. Small, in vicinity vicinity of the Small, J.R., J.R., and and Bornhorst, Bornhorst, T.J., T.J., A geological geological investigation investigation in the contact! northern northern block block of the the Marquette Marquette volcanic-plutonic contact, Greenstone Belt, Belt, Michigan. Michigan. 23. 23. Smith, Smith, B.D., B.D., Labson, Labson, V.F., V.F., and and Horton, Horton, R.J., R.J., Airborne Airborne geophysical geophysical surveys surveys Effie-Coon Lake Lake complex, complex, Minnesota. Minnesota. of the Effie-Coon and magnetic data over 24. 24. Sverdrup, Sverdrup, K.A., K.A., and and Kean, Kean, W.F., W.F., Gravity Gravity and magnetic data over the the Fault, S.E. S.E. Wisconsin. Wisconsin. Waukesha Fault, xvii xvii �ABSTRACTS ABSTRACTS �MAGNETOTELLURIC INVESTIGATION MAGNETOTELLIJRIC INVESTIGATION OF OF THE THE CONTACT CONTACT BETWEEN BETWEEN THE IN NORTHEASTERN MINNESOTA MINNESOTA DULUTH COMPLEX AND ANIMIKIE BASIN IN CL, Young, Young, C. C. T. T. (Department (Department of of Geological Geological Adams, Donald C., Engineering, Geology and Geophysics, Geophysics, Michigan Michigan Technological University, University, Houghton Houghton MI, MI, 49931) 49931) Technological Magnetotelluric profiling profiling was was used used to to investigate investigate the the resistivity resistivity contrast contrast of of the the contact contact between between the the Animikie Animikie Basin and Duluth Duluth Complex Complex in in Northeastern Northeastern Minnesota. Minnesota. Data Data at eight eight sites, sites, during during June June and and July July 1988, 1988, were collected at alonq a Northwest Northwest to to Southeast Southeast 37 along 37 km k m line line (Figure (F1qur.e 1) 1) approximately approximately perpendicular perpendicular to to the the contact. contact. Preliminary one one dimensional modeling modeling and and interpretation interpretation of the data indicate indicate that that the the electrical electrical contact contact has has the the shape of a half graben sloping east and stepping to t o a depth of 15 km within the the field field area area (Figure (Figure 2). 2 ) . The The form form of of the the contact between the Duluth Complex and the the Animikie Basin Basin agrees with vith the the half half graben interpretation interpretation of of Weiblen Weiblen and Morey 1980 1980 and approximate depth to to the the contact contact determined by Frederer 1982. 1982. The The Duluth Duluth Complex Complex has has an an apparent apparent resistivity resistivity of of 10,000 10,000 to to 60,000 60,000 ohm ohm meters, meters, while while the the Animikie Basin and 255 255 ohm ohm Basin has has apparent apparent resistivities resistivities of of 33 and meters apparent meters and the the Giants Giants Range Range Granite Granite has has aa apparent resistivity resistivity of of 600 600 to to 3000 3000 ohm ohm meters. meters. The The field field work work was vas supported supported by by aa grant grant from from the the Minnesota geological qeological survey. survey. REFERENCES Frederer, Robert J. (1982): (1982): Gravity And And Magnetic Magnetic Modeling Modeling Of Of Robert J. The Duluth Duluth Complex, Complex, Northeastern Northeastern Minnesota, Minnesota, M.S. M.S. Thesis, Indiana Indiana University, University, 99 99 pages paqes Weiblen, Weiblen, Paul Paul W., W., Morey, Morey, G. G. B. B. (1980): (4980): A Summary Summary Of Of The The Stratigraphy, Petrology, Petrology, And Structure Structure Of Of The Duluth Duluth Complex, American American Journal Journal Of Of Science, Science, v. v. 280-A, 280-A, pp 88— 88133 133 �- • AURORA AURORA 47 47 30' 30' 91130 J45• 92100' 115' • HOYT H O Y T L LAKE AKE 01.0 02.5 02.0 05.0 03.5 N SCALE SCALE 1:384615 11384615 15' — (15' 92(00' 15' 1 130' I 46' FIGURE 11 LOCATION MAP MAP o* C 1.0 2.0 2:5 2.5 STATION S TATION 3 . 0 3.5 4.0 3.0 5.0 5.U 6.0 6 .0 AB ----E z I DC DC \ 10• 10GRG GRG 0 w 20 20- 600 6 0 0 --3000.n.m 3000~m GAG i AB-ANIMIKIE BASIN AB-ANIMIKIE BASIN DC-DULUTH COMPLEX DC-DULUTH COMPLEX GAG-GIANTS GRG-GIANTS RANGE RANGE GRANITE GRANITE SCALE 1:393701 SCALE 1:393701 FIGURE 2 MODEL INTERPRETATION INTERPRETATION 2 �TECHNIQUE FOR AQUIFERS IN A GROUND RESISTIVITY RESISTIVIlY TECHNIQUE FOR LOCATING LOCATING FRACTURE FRACTURE AQUIFERS I N BURIED BURIED PRECAMBRIAN BASEMENT, CENTRAL CENTRAL WISCONSIN Dennis J. J . Bebel, Bebel, Department of of Geology, Northern Illinois I l l i n o i s University, University, DeKaib, DeKalb, IL IL Decreases in Decreases i n aapparent p p a r e n t resistivity r e s i s t i v i t y have been recognized through through comparative measurements of ground ground resistivity r e s i s t i v i t y taken t a k e n above above and and below below the the water table t a b l e located l o c a t e d within w i t h i n buried b u r i e d crystalline c r y s t a l l i n e basement. basement. These decreases decreases have been interpreted i n t e r p r e t e d to t o indicate i n d i c a t e zones zones of of high h i g h fracture f r a c t u r e porosity p o r o s i t y and and therefore water volume allowing t h e r e f o r e increased i n c r e a s e d water a l l o w i n g for f o r greater g r e a t e r electrical electrical cconductivity. o n d u c t i v i t y . The survey method might provide a tool t o o l for f o r locating l o c a t i n g water water well w e l l drilling d r i l l i n g sites s i t e s in i n crystalline c r y s t a l l i n e basement. basement. Vertical A Lee array a r r a y was utilized u t i l i z e d during d u r i n g trial t r i a l surveys. surveys. V e r t i c a l electrical electrical soundings were were conducted at a t points p o i n t s along a l o n g the t h e survey traverses t r a v e r s e s to t o adjust a d j u s t for for surface s u r f a c e and basement topography in i n establishing e s t a b l i s h i n g the t h e depths d e p t h s to t o basement basement and and 18.3 tthe h e water table. t a b l e . Electrode E l e c t r o d e a-spacings a - s p a c i n g s within w i t h i n the t h e range of 4.6 4 . 6 -- 18.3 meters were determined to t o provide p r o v i d e investigation i n v e s t i g a t i o n depths d e p t h s above and and below below the the water table t a b l e along a l o n g the t h e length l e n g t h of of the t h e traverses. t r a v e r s e s . Trial T r i a l surveys s u r v e y s were were conducted near n e a r Dells D e l l s of of Eau Claire C l a i r e Park Park (Marathon (Marathon Co.), C o . ) , WI W I and and at a t Junction Junction City WI. C i t y (Portage ( P o r t a g e Co.), C o . ) , WI. The Dells D e l l s of Eau Claire C l a i r e traverse t r a v e r s e crossed c r o s s e d the t h e contact c o n t a c t between between the t h e Wolf Wolf River R i v e r Granite G r a n i t e and and aa "shear I1shear zone" zone" in i n felsic f e l s i c volcanics. v o l c a n i c s . Exposures of of the the volcanics v o l c a n i c s in i n the t h e Eau Claire C l a i r e River display d i s p l a y an an intense i n t e n s e fracture f r a c t u r e system. system. The The decreased within aapparent p p a r e n t resistivity resistivity d e c r e a s e d below the t h e water table table w i t h i n the t h e volcanics volcanics but b u t not n o t the t h e granite. granite. at The JJunction u n c t i o n City C i t y traverse t r a v e r s e was was at a t aa water water well w e l l site. s i t e . Basement rock rock at this t h i s location l o c a t i o n is i s early e a r l y Proterozoic P r o t e r o z o i c argillite. a r g i l l i t e . An apparent a p p a r e n t resistivity resistivity decrease 9 meters wide) wide) north d e c r e a s e was noted in i n a narrow zone (6 (6 - 9 n o r t h of of the the welisite w e l l s i t e and and on strike s t r i k e with w i t h the t h e local l o c a l basement basement structure. structure. It I t is i s ccurrently u r r e n t l y planned to t o further f u r t h e r test t e s t this t h i s technique t e c h n i q u e during d u r i n g the the Spring, with S p r i n g , 1989 in i n cconjunction onjunction w i t h a Wisconsin Geological and Natural N a t u r a l History History Survey drilling d r i l l i n g program at a t Junction J u n c t i o n City, C i t y , WI. WI. - 3 �ZIRCONS ZIRCONS OF OF THE THE ST ST CLOUD CLOUD RED RED AND REFORMATORY REFORMATORY GREY GREY GRANITES GRANITES J. Belden, Belden, G. G. Anderson, Anderson, and and I. I. Watkins Watkins J. St St Cloud Cloud State State University University St. St. Cloud, Cloud, Mn Mn 56301 56301 Samples Samples of of both both the the Reformatory Reformatory Grey Grey granite granite and and the the St St Cloud Cloud Red Red granites granites of of central central Minnesota Minnesota were were crushed crushed and and sieved. sieved. Using Using methylene methylene iodide, iodide, zircons zircons and and other other heavy heavy minerals minerals were were separated. separated. No No zircons zircons were were found found in in the the material material larger larger than than the the 100 100 ( 149 149 microns) microns) mesh mesh sieve. sieve. Euhedral Euhedral zircons zircons that that passed passed through through the the 100 100 mesh mesh sieve sieve were were picked picked out out of of the the heavies, heavies, mounted on on aa slide slide for for microprobe microprobe analysis analysis with with the the long long axis axis of of the the crystal crystal parallel parallel to to the the surface surface of of the the slide, slide, then then ground ground to to about about one one half half their their thickness. thickness. Micro Micro photographs photographs of of individual individual zircons zircons were were taken taken using using unpolarized unpolarized and and polarized polarized light light as as well well as as with with crossed polars. crossed polars. ( Observations Observations requiring requiring little little or or no no interpretation interpretationare: are: 1. 1. zircon zircon fragments fragments are are inside inside the the euhedral euhedral crystals crystals 2. 2. non—zirconium non-zirconium bearing bearing inclusions inclusions are are inside inside the the euhedral euhedral crystals crystals 3. 3. concentric concentric banding banding is is visible visible in in all all illuminations illuminations in in zircons zircons from from both both granites granites but but is is far far more more consistent consistent in in those those from from the the St St Cloud Cloud Red Red granite granite 4. 4.microprobe microprobe data data shows shows varying varying concentrations concentrations of of zirconium zirconium in in the the crystals crystals but but no no pattern pattern has has yet yet emerged emerged 5. 5. zircons zircons from from both both granites granites are are fractured fractured but but those those from from the the Refomatory Refomatory Grey Grey show show greater greater fracture fracture development development and and subsequent subsequent mineral mineral growth growth along along the the fractures fracturesthan thanthe theSt. St. Cloud Cloud Red Red 6. 6. microprobe microprobe data data of of uranium uranium concentrations concentrations is is unclear unclear at at this this time time but but work work is is continuing. continuing. Observations Observations requiring requiring appreciable appreciable interpretation interpretation with with some some possible possible interpretations interpretationsare: are: 1. apparent apparent overgrowths overgrowths (Sahama, (Sahama,1981) 1981) on on euhedral euhedral crystals crystals 1. occurred occurred so so the the crystal crystal is is no no longer longer euhedral euhedral or orthe thecrystal crystal has has fractured fractured in in aa strange strange way way 2. 2. the the fractures fractures in in the the euhedral euhedral crystals crystals usually usually do donot not follow follow cleavage cleavage planes planes but but always always appear appear dark dark in inany any light. light. The The dark dark color color may may be be due due to to zircon zircon crystallized crystallized at at aa lower lower (Caruba et et al., al., 1985) 1985) or or may may be be due due to to light light not not temperature (Caruba temperature getting getting through through because because of of the the critical critical angle angle of of illumina— illumination tion on on the the fracture. fracture. This This dilemma dilemma will will be be resolved. resolved. 3. 3. concentric concentric banding banding shows shows different different indices indices of of refraction refraction which which may may be be due due to to different different compositions compositions or or different different latlattice (Exarhos,1984). 1984). tice constants constants(Exarhos, 4 �REFERENCES REFERENCES Caruba,P... R., et et al, al, 1985. 1985, An An experimental experimental study study of of hydroxyl hydroxyl Caruba, groups and and water water in in synthetic synthetic and and natural natural zircons: zircons: aa groups model of the metamict state: American Mineralogist, v. model of the metamict state: American Mineralogist, v. 70, D. 1224-1231 70, p. 1224—1231 Exarhos, G.J., G.J., 1984, 1984. Induced Induced swelling swelling in in radiation radiation damaged damaged Exarhos, ZrSi04, Nuclear Instruments and Methods in Physics Re ZrSiO4, Nuclear Instruments and Methods in Physics Re search, Section B, v. 229, p. 538-41 search, Section B. v. 229, p. 538—41 Sahama, T.G., T.G., 1981. 1981, Growth Growth structure structure in in Ceylon Ceylon zircon, zircon,Bul Bul Sahama, v. 104, p. 89-94 letin de Mineralogie, letin de Mineralogie, v. 104, p. 89—94 5 �P E T R O G E N E S I S AND A M D GEOCHEMISTRY G E O C H E M I S T R Y OF O F RHYOLITES R H Y C L I T E S FROM F R O M THE THE PETROGENESIS C H E N G W A T A N A V O L C A N I C G R O U P , M I D C O N T I N E N T R I F T S Y STEM CI-JENGWATANA VOLCANIC GROUP, MID-CONTINENT RIFT SYSTEM D a n i e l R. R . Block B l o c k and and Mark M a r k E. E. Cavaleri, C a v a l e r i , Macalester M a c a l e s t e r College, College, Daniel S a i n t P a u l , M i n n e s o t a , D e p a r t m e n t of G e o l o gy Saint Paul, Minnesota, Department of Geology R h y o l i t e s form form aa significant s i g n i f i c a n t volume v o l u m e but but low l o w (<1%) ( < I ? ) percentage percentage Rhyolites o f t h e M i d c o n t i n e n t R i f t S y s t e m (MRS). D u e p e r h a p s to their their of the Midcontinent Rift System (MRS). Due perhaps to l i m i t e d e x p o s u r e , the r h y o l i t e s of the M R S h a v e not been limited exposure, rhyolites of the the MRS have not been e x t e n s i v e l y studied. s t u d i e d . This T h i s study s t u d y is is based based on o n chemical c h e m i c a l analyses a n a l y s e s of of extensively s a m p l e s taken t a k e n from from two t w o deep d e e p drill d r i l l cores, c o r e s , V66—1 V 6 6 - 1 and and V66—2, V 6 6 - 2 , from from samples V e r m i l l i o n , Minnesota, M i n n e s o t a , about a b o u t forty f o r t y miles m i l e s south s o u t h of of the the Twin Twin Vermillion, Cities. Cities. T h e purpose p u r p o s e of of studying s t u d y i n g these these cores c o r e s is i s two t w o fold. f o l d . First, First, The t h e s e cores c o r e s represent r e p r e s e n t the t h e southernmost s o u t h e r n m o s t sampling s a m p l i n g of of the t h e MRS. M R S , and and these a l s o one o n e of of the t h e few f e w samples s a m p l e s of of Chengwatana C h e n g w a t a n a rhyolites. r h y o l i t e s . The The also g e o c h e m i c a l data d a t a obtained o b t a i n e d during d u r i n g this t h i s study study t h u s forms f o r n s aa geochemical thus s i g n i f i c a n t addition a d d i t i o n to to the t h e data d a t a available a v a i l a b l e on o n the t h e MRS. M R S . Secondly, Secondly, significant r h y o l i t e s from f r o m the t h e MRS M R S has h a s not n o t been been extensively e x t e n s i v e l y studied. s t u d i e d . Within Within rhyolites the last ten years, n u m b e r of of world w o r l d rhyolite-basalt rhyolite-basalt the last ten years, number aa a s s o c i a t i o n s have h a v e been been examined. examined. Data c o l l e c t e d on' o n the the associations Data collected C h e n g w a t a n a rhyolites r h y o l i t e s will w i l l be be compared c o m p a r e d and and contrasted c o n t r a s t e d this this Chengwatana p u b l i s h e d data. data. published C o r e V66-2 V 6 6 - 2 is i s composed c o m p o s e d entirely e n t i r e l y of of rhyolite. r h y o l i t e . Core C o r e V66-1, V 6 6 - 1 , in in Core c o n t r a s t , contains c o n t a i n s only o n l y aa twenty t w e n t y foot foot section s e c t i o n of o f rhyolite r h y o l i t e in in aa contrast, m u c h larger l a r g e r amount a m o u n t of of basalt. b a s a l t . The T h e chemical c h e m i c a l fingerprints f i n g e r p r i n t s of of these these much c o r e s also a l s o differ. differ. R h y o l i t e s from f r o m V66—2 V 6 6 - 2 are a r e high h i g h in i n silica, silica, cores Rhyolites v a r y i n g from f r o m 73 73 to to 81%. 81%. Rhyolites R h y o l i t e s from f r o m V66—1 V66-1 contain c o n t a i n only o n l y about about varying 68% 5102. S i 0 2 . This T h i s suggests s u g g e s t s that t h a t these t h e s e rhyolites r h y o l i t e s of o f V66—1 V 6 6 - 1 could c o u l d have have 68% b e e n c o n t a m i n a t e d by t h e s u r r o u n d i n g .basalts. R h y o l i t e s from been contaminated by the surrounding basalts. Rhyolites from b o t h V 6 6 2 and V66-1 a r e p e r a l u m i n o u s . A 1 2 0 3 c o n c e n t r a t i o n s vary both V66—2 and V66—1 are peraluminous. Al203 concentrations vary f r o m 10 10 to to 14%, 1 4 % , while w h i l e Ca C a varies v a r i e s from from .05 . 0 5 to to 1.90% 1.90% and and Na2O N a 2 0 from from from 0 8 to 2.91%. .08 to 2.91%. Based on o n the t h e orthoclase-albite-quartz o r t h o c l a s e - a l b i t e - q u a r t z phase p h a s e equilibria, e q u i l i b r i a , the the Based r h y o l i t e s o f V 6 6 2 a r e e s t i m a t e d to h a v e f o r m e d in at rhyolites of V66-2 are estimated to have formed at in t e m p e r a t u r e s l e s s t h a n 8 0 0 d e g r e e s c e l s i u s . R h y o l i t e s f r o m V66-1 temperatures less than 800 degrees celsius. Rhyolites from V66-1 h a v e much m u c h higher h i g h e r albite a l b i t e concentrations c o n c e n t r a t i o n s due d u e to to probable p r o b a b l e basaltic basaltic have c o n t a m i n a t i o n . I t i s p o s s i b l e , h o w e v e r t h a t t h i s a l s points contamination. It is possible, however that this alsoo points t o w a r d s a h i g h e r t e m p e r a t u r e of f o r m a t i o n . towards a higher temperature of formation. T r a c e element e l e m e n t analyses a n a l y s e s show s h o w that that the the two t w o cores c o r e s probably p r o b a b l y have have Trace s l i g h t l y d i f f e r e n t p e t r o g e n e t i c h i s t o r i e s . V66-1 h a s m u c h higher slightly different petrogenetic histories. V66—1 has much higher c o n c e n t r a t i o n s of of strontium, s t r o n t i u m , phosphorus, p h o s p h o r u s , and and titanium t i t a n i u m than t h a n V66-2. V66-2. concentrations U n l i k e t h e l o w s i l i c a l e v e l s , these d i f f e r e n c e s c a n n o t be easily Unlike the low silica levels, these differences cannot be easily e x p l a i n e d by s i m p l e a s s i m i l a t i o n of b a s a l t i c m a t e r i a l . explained by simple assimilation of basaltic material. Based on the geochemistry, petrography, and field field Based on the geochemistry, petrography, and r e l a t i o n s h i p s , these t h e s e rhyolites r h y o l i t e s seem s e e m to to be be similar s i m i l a r in i n origin o r i g i n to to relationships, t h o s e studied s t u d i e d elsewhere e l s e w h e r e in i n the t h e MRS M R S and and in i n other o t h e r continental c o n t i n e n t a l rift rift those systems. T h e rhyolite—basalt r h y o l i t e - b a s a l t association a s s o c i a t i o n present p r e s e n t here h e r e and and in in systems. The s i m i l a r units u n i t s is i s commonly c o m m o n l y associated a s s o c i a t e d with w i t h regions r e g i o n s of of thick thick similar e x t e n d i n g crust. crust. Based on o n these t h e s e observations, o b s e r v a t i o n s , the t h e information information extending Based c o l l e c t e d in i n this this study s t u d y can c a n be be combined c o m b i n e d to to propose p r o p o s e aa model m o d e l for for collected t h e origins o r i g i n s of of these t h e s e rhyolites. r h y o l i t e s . The T h e formation f o r m a t i o n of o f the t h e rhyolites rhyolites the b e g i n s by by partial p a r t i a l melting m e l t i n g in i n the t h e upper u p p e r mantle. mantle. T h e magma m a g m a ponds ponds begins The 6 �at at or near n e a r the t h e crust/mantle c r u s t l m a n t l e interface, i n t e r f a c e , where w h e r e it it fractionate f r a c t i o n a t e until until its i t s density d e n s i t y is i s sufficiently s u f f i c i e n t l y low l o w to to allow a l l o w it i t to to rise r i s e to to the the surface. Rhyolites surface. R h y o l i t e s are a r e produced p r o d u c e d by by mafic m a f i c magmas m a g m a s travelling travelling through t h r o u g h narrow n a r r o w crustal c r u s t a l fractures f r a c t u r e s which w h i c h occur o c c u r either e i t h e r along along the the margins m a r g i n s of of the t h e rift r i f t system s y s t e m or o r in in immature i m m a t u r e zones z o n e s of of where w h e r e small small fractures f r a c t u r e s have h a v e not n o t yet y e t aggregated a g g r e g a t e d into i n t o wide w i d e conduits. conduits. Within Within these t h e s e fracture f r a c t u r e zones, z o n e s , the t h e mafic m a f i c magma m a g m a fractionates f r a c t i o n a t e s and and the the remaining r e m a i n i n g material m a t e r i a l becomes b e c o m e s contaminated c o n t a m i n a t e d with w i t h sialic s i a l i c crust crust as a s it it rises r i s e s to t o the t h e surface. surface. 7 �PRELIMINARY SURVEY OF THE METASEDIMENTS PRELIMINARY PALEOMAGNETIC PALEOMAGNETIC SURVEY METASEDIMENTS THE METAVOLCANICS OF OF THE THE NIAGARA NIAGARA FAULT FAULT SYSTEM SYSTEM IN IN FLORENCE FLORENCE COUNTY COUNTY WISCONSIN WISCONSIN AND Theresa M. Bodus Theresa Bodus and William F. Kean, University of Wisconsin Milwaukee, Department Department of of Geosciences, Geosciences, Milwaukee Milwaukee Wisconsin Wisconsin 53201 53201 is Florence County County in in northeastern northeastern Wisconsin Wisconsin is a region region of of a complex geology geology associated associated with the Niagara complex Niagara fault. fault. The rocks rocks Florence County are which flank the the Niagara Niagara Fault Fault system in in Florence are metaconglomerates, metagreywackes, and metavolcanics metaconqlomerates, metavolcanics to to the the north north and gneisses gneisses to to the the south. south. Isotopic Isotopic Nd ages ages of of these rocks rocks give give ages of 1.80—1.88 1.80-1.88 b.y. b.y. (Barovich (Barovich et et al., al., 1989) 1989) Paleomagnetic studies Paleomaqnetic studies were initiated initiated to aid in determining the relationships location of the relationships of of emplacement emplacement and and relative relative location the units on either side side of of the the fault fault system. system. Seven hand samples samples and and using were stepwise A.F. twenty oriented oriented cores cores were analyzed using stepwise demagnetization and thermal demagnetization thermal demagnetization demagnetization to to determine determine magnetic magnetic directions. The characteristics magnetic directions. characteristics and and magnetic The gneiss samples samples exhibited low to 10"-7 10—7 cqs, cgs, and corresponding l0-6 to low intensity, intensity, 10^-6 low magnetic magnetic susceptibilities susceptibilities of of 2.0-20.0 2.0—20.0 xx 10^-6 10-6 cgs. cgs. The rocks rocks had stronger stronger intensities intensities (i.e. (i.e. 10"-5) 10-5) to the the north of of the fault had and correspondingly strong susceptibilities 10—6. susceptibilities 70.0-310.0 70.0-310.0 xx 10^-6. The A. The A. F. demagnetization demagnetization studies indicate predominately single single removal of component magnetization after the the removal of a soft overprint. overprint. Preliminary that all the rocks are reversely indicate that Preliminary results results indicate reversely polarized and magnetic polarized and magnetic direction direction consistent with Irving's Irving's A.P.W.P. for A.P.W.P. for ages ages of of 1.81 to to 1.84 b.y. b.y. for rocks north of the the Niagara Fault. Fault. REFERENCES REFERENCES Barovich, K.M., K.M., P.3. P.J. Patchett, Patchett, Z.E. Z.E. Peterman, Peterman, and and P.K. P.K. Sims, Nd Nd isotopes isotopes and and the origin of 1.9—1.7 1.9-1.7 Ga Penokean Penokean continental continental crust crust of the Lake Lake Superior Superior region: region: G.S.A. G.S.A. Bulletin, v. 101, n. 3. Bulletin, v. 101, n. 3. p.333—338. p.333-338. 8 �PRELIMINARY PRELIMINARY MAGNETIC MAGNETIC SURVEY SURVEY OF OF THE THE NIAGARA NIAGARA FAULT FAULT SYSTEM SYSTEM IN IN FLORENCE, AND MARINETTE MARINETTE COUNTIES, COUNTIES, WISCONSIN WISCONSIN FLORENCE, FOREST, FOREST, AND Theresa M. Bodus Bodus and a n d Keith K e i t h A. A. Sverdrup, S v e r d r u p , University U n i v e r s i t y of o f Wisconsin Wisconsin T h e r e s a M. Milwaukee, Milwaukee, Department D e p a r t m e n t of o f Geosciences, G e o s c i e n c e s , Milwaukee Milwaukee The The Niagara N i a g a r a Fault F a u l t indicated i n d i c a t e d on on the t h e Wisconsin W i s c o n s i n State S t a t e Bedrock Bedrock Map Map extends e x t e n d s from f r o m northwestern n o r t h w e s t e r n Wisconsin W i s c o n s i n across a c r o s s the t h e state s t a t e to to northeastern n o r t h e a s t e r n Wisconsin. Wisconsin. This study concentrates on the the This study concentrates on northeastern n o r t h e a s t e r n portion p o r t i o n of o f the t h e fault f a u l t in i n Florence, F l o r e n c e , Forest, F o r e s t , and and Marinette M a r i n e t t e counties, c o u n t i e s , Wisconsin. Wisconsin. T o t a l field f i e l d magnetic m a g n e t i c data d a t a was was Total obtained 0.1 o b t a i n e d at at 0 . 1 mile mile s p a c i n g using using p r o t o n procession procession spacing aa proton magnetometer profiles m a g n e t o m e t e r in i n two two N-S N-S p r o f i l e s across a c r o s s the t h e Niagara N i a g a r a Fault F a u l t in in Florence 1). T h e s e profiles p r o f i l e s were were positioned p o s i t i o n e d to to F l o r e n c e county c o u n t y (Fig. ( F i g . 1). These c r o s s the t h e Niagara N i a g a r a fault f a u l t and a n d related r e l a t e d faults f a u l t s as a s they t h e y are a r e plotted p l o t t e d on on cross the ( 1 9 8 4 ) . Expected E x p e c t e d locations locations t h e Northeastern N o r t h e a s t e r n Bedrock Bedrock Geology G e o l o g y Map Map (1984). of by the t h e profiles p r o f i l e s are a r e indicated i n d i c a t e d in i n the t h e figure figure o f the t h e faults f a u l t s crossed c r o s s e d by by The b y arrows. arrows. The data d a t a is i s characterized c h a r a c t e r i z e d by b y relatively r e l a t i v e l y low l o w level, level, constant m i l e s south s o u t h of o f the t h e fault f a u l t and and c o n s t a n t values v a l u e s for f o r roughly r o u g h l y twelve t w e l v e miles several s e v e r a l high h i g h amplitude a m p l i t u d e anomalies a n o m a l i e s to t o the t h e north n o r t h suggesting s u g g e s t i n g aa fundamental f u n d a m e n t a l change c h a n g e in i n the t h e geology g e o l o g y between b e t w e e n these t h e s e two two areas. areas. Measurements M e a s u r e m e n t s of of susceptibility s u s c e p t i b i l i t y have h a v e been b e e n made made on o n seventeen seventeen samples s a m p l e s from f r o m five f i v e sites s i t e s in i n the t h e study s t u d y area a r e a to t o assist a s s i s t In i n modeling. modeling. The The values v a l u e s range r a n g e from f r o m 4.0—308.0 4 . 0 - 3 0 8 . 0 xx 10-6 1 0 - 6 cgs. c g s . Preliminary P r e l i m i n a r y modeling modeling of o f the t h e data d a t a has h a s begun, begun, and a n d results r e s u l t s of of the t h e modeling m o d e l i n g will w i l l be be presented. presented. 9 �_____ MAGNETIC PROFILE PROFILE MAGNETIC t af i lb:Hvynu e b:Hvynu a~ file ignetic dataHIGH HIGH isi s608000.0. 608000.0. gnetic data LOU i s 58020.7. ignetic data gnetic data LOW is 58020.7. il lscale l scaledeflection deflectionis i3000.0 s 3000.0gaisas. gammas. Tine Tue 0:16:50 1:27:20 13:16:41 [4:51:29 [5:39:29 Sta Sta Hag Nag _____ __________ ____— 57800. 0 57800.0 60800.0 158350.0 S 4058587.9 Ew '—i 4 FAULT N k 100 58564.8 - 6 NIAGARA FAULT NIAGARA FAULT 4 4- FAULT FAULT 4— 160 58590.8 - - FAULT FAULT L I 195 58440.6 Figure 1. 1. Magnetic survey proflle Figure Magnetic survey profile Florence county. Florence county. 10 along along Highway N Highway N and U in and U in �SIGNIFICANCE OF CONGLOMERATES, CONGLOMERATES, ARGILLITES, SIGNIFICANCE ARGILLITES, AND AND DIRTY SANDSTONES ITES DIRTY SANDSTONES IN IN THE THE BARABOO BARABOO AND WATERLOO WATERLOO QUARTZ QUARTZITES OF WISCONSIN OF SOUTHEASTERN SOUTHEASTERN WISCONSIN Bruce Brown Bruce A. Brown Wisconsin Geological and Natural History Survey 3817 Mineral Point Road Road Madison, Wisconsin 53705 Madison, Wisconsin 53705 studies of Recent studies of suggest that Wisconsin suggest that conglomerate, and that conglomerate, quartzites of to other quartzites of the the Baraboo Baraboo and and Waterloo Waterloo quartzites quartzites of of southeastern southeastern both contxiin abundant abundant beds of of poorly poorly sorted sorted pebble pebble both contain both are anomalously anomalously rich in clay clay matrix matrix when when compared compared the the "Baraboo "Baraboo interval." interval." A of the the Baraboo Baraboo quartzite quartzite by Henry Henry (1975) (1975) identified identified aa lower lower unit, unit, A study of to 200 mm thick, thick, composed 60 to 60 composed of of predominantly lenticular lenticular pebbly pebbly beds beds up up to to 0.6 0.6 mm thick. Milky quartz quartz pebbles pebbles dominate, dominate, with with lesser lesser amounts amounts of of chert, chert, hematitic hematitic thick. chert, siltstone, single single grain grain and polycrystatline polycrystalline clear clear quartz, quartz, and and chert, siltstone, quartzite. quartzite. No clearly clearly identifiable identifiable rhyolite rhyolite pebbles pebbles were were reported reported by by Henry, Henry, silicious pebbles although he suggested that some fine—grained fine-grained silicious pebbles and and scattered scattered exnbayed quartz grains grains might might be volcanic embayed quartz volcanic materials. materials. Pebble Pebble beds beds become become less less abundant upwards, upwards, and and sandy sandy beds beds contain contain up up to to 10 10 to to20% 20 clay matrix abundant (pyrophyllite and kaolinite). (pyrophyllite The Waterloo Quartzite The Waterloo Quartzite shows shows aa similar similar fining—upward fining-upward tendency, t.endency,with with pebble conglomerates conglomerates and matrix rich (sericite) lenticular pebble (sericite) sandstone sandstone common common in in the lower m) lower part of of the the section. section. Pebble Pebble conglomerates conglomeratesare arethicker thicker(up (uptoto2 2in) and more abundant at Waterloo, Waterloo, but pebble pebble lithologies lithologies are are similar. similar. The lithologic lithologic sequence sequence at Waterloo and Baraboo Baraboo are are nearly nearly identical, identical, and and may be directly directly correlatable. correlatable. Roth fine fine upwards from from pebble pebble conglomerates conglomerates to to sandstone. sandstone. Drilling records suggest suggest aa slate slate unit unit overlying overlying Waterloo Waterloo to to the the Drilling records east, correspond to to the the Seely Seely slate slate at at Baraboo. Baraboo. Ferruginous, Ferruginous, tast, which may correspond silicious silicious slate slate drilled drilled in in aa well at Watertown Watertown may he be equivalent equivalent to to Freedom Freedom Formation. well in Monona, Monona, on the east side of Madison, Madison, encountered Formation. A well encountered pebble pebble to the lower part of the section section at Baraboo Baraboo and and Waterloo. conglomerate similar t-o This rock contains types, including including possible possible volcanic volcanic contains more varied pebble types, material. material. Primary Primary sedimentary sedimentary structures structures in in the the Baraboo Baraboo and and Waterloo Waterloo Quartzites Quartzites suggest distal alluvial alluvial to fluvial depositional depositional environment environment (Henry, (Henry, to braided fluvial 1975). 1975). Consistent Consistent southward southward paleocurrents paleocurrents reported reported by by Dott Dott and and Daiziel Dalziel (1972) (1972) indicate indicate fluvial fluvial transport transport to to the the south. south. Pebble Pebble conglomerate conglomerate lenses lenses are are suggestive suggestive of of bars bars or or possibly possibly sheetfiow sheetflow deposits. deposits. Thin argillite argillite beds beds may overbank deposits. deposits. represent overbank scarcity of of rhyolite rhyolite pebbles pebbles is The scarcity is puzzling puzzling if if the the source source terrane terrane for for the the quartzites was the the 1760 1760 ma. granite granite rhyolite rhyolite terrane terrane to to the the north. north. AA possible possible quartzites explanation is is that the the rhyolite rhyolite was was eroded eroded under under severe severe weathering weathering conditions, conditions, explanation contributing contributing only only the the quartz quartz and and the the kaolinite kaolinite clays clays now now seen seen in in the the matrix. matrix. rhyolite debris may have degraded during Alternatively, rhyolite during diagenesis diagenesis to to form form the the 11 Doc. BAB0463 Doc. BAB0463 �ubiquitous matrix. ubiquit.ous matrix. Abundant metamorphic quartz and the the hematitic hematitic cherts cherts suggest that other other sediment sediment sources sources contributed contributed as as well. well. The Quartzite suggest The Barron Quartzite (Rozacky, 1987) and the Sioux quartzite (Ojakangas (Ojakangas and Weber, 1984) apparently (Rozacky, Weher, 1984) contain significantly significantly less less pebble conglomerate conglomerate and less less matrix, matrix, probably probably 'erranes and and transport transporth:istory. history. reflecting very different different source source terranes reflecting very Samples Samples from from deep deep wells wells and and unpublished geophysical geophysical data data suggest suggest that that the the quartzites of Baraboo and Waterloo are continuous over an extensive extensive area area of of southeastern Wisconsin. southeastern Wisconsin. References References Dott, Dott, R.H., Jr. and Daiziel, Dalziel, I.W.D., I.W.D., 1972, 1972, Age and correlation correlation of of the the Precambrian Baraboo Geology, vol. of Wisconsin: Wisconsin: Journal Journalof' of Geology, vol. 80, 80, Precambrian Baraboo Quartzite Quartzite of p. 552—568. 552-568. 1975, Sedimentology Sedimentology and Stratigraphy of the Henry, D.M., 1975, the Baraboo Baraboo Quartzite Quartzite of of South—Central Wisconsin: South-Central Wisconsin: M.S. M.S. Thesis, Thesis, University University of of Wisconsin—Madison, Wisconsin-Madison, 90 p. 90 p. Rozacky, Sedimentation of The Petrology and Sedimentation of the the Lower Lower Proterozoic Proterozoic Rozacky, W.V., 1987, 1987, The Barron Quartzite, Quartzite, Northwestern Northwestern Wisconsin: Wisconsin: M.S. Thesis, Thesis, University University of of Minnesota—Duluth, 94 94p. p. Minnesota-Duluth, Ojakangas, Ojakangas, R.W. and and Weber, Weber, R.E., 1984, 1984, Petrography Petrography and and Paleo:urrents Paleocurrents of of the the Lower Proterozoic Proterozoic Sioux Sioux Quartzite, Quartzite, Minnesota Minnesota and and South South Dakota, Dakota,in in D.L. D.L. Southwick, of the the Sioux Sioux Southwick, ed., Shorter Shorter contributions contributions to to the the geology geology of Geological Survey, Survey, Report of Quartzite, Minnesota Geological of Investigations Investigations 32, 32, 1—15. p. 1-15. p. 12 Doc. BAB0463 Doc. BAB0463 �GLACIAL DRIFT DRIFT GEOCHEMISTRY GEOCHEMISTRY FOR FOR STRATEGIC STRATEGIC MINERALS, MINERALS, LAKE LAKE COUNTY, COUNTY, MINNESOTA MINNESOTA DNA DNR Project Project #262 #262 Funded by Minnesota Minnesota Future Future Resources Resources Commission Commission R.L. R.L. Buchheit, K.L. K.L. Malmquist, Malmquist, and J.R. J.R. Niebuhr Niebuhr Minnesota Department of Natural Natural Resources Resources Division of of Minerals, MN 55746 Minerals, Ribbing, Hibbing, MN 55746 ABSTRACT ABSTRACT This T h i s mineral m i n e r a l diversification d i v e r s i f i c a t i o n InvestIgation i n v e s t i g a t i o n is i s funded funded by by the t h e Minnesota Minnesota Legislature L e g i s l a t u r e for f o r the t h e July J u l y 1, 1 , 1987 1987 through t h r o u g h June June 30, 30, 1989 1989 biennium. biennium. It I t is is aa p i l o t study s t u d y of o f regional r e g i o n a l geochemical geochemical survey s u r v e y methods methods for f o r Identification I d e n t i f i c a t i o n of of pilot non—ferrous, n o n - f e r r o u s , strategic s t r a t e g i c minerals m i n e r a l s in i n vegetation, v e g e t a t i o n , soils s o i l s and and surface, s u r f a c e , and and g l a c i a l deposits. d e p o s i t s . Analytical A n a l y t i c a l results r e s u l t s can c a n indicate i n d i c a t e the t h e presence p r e s e n c e of o f metallic metallic glacial mineral m i n e r a l deposits d e p o s i t s in i n bedrock b e d r o c k or o r outline o u t l i n e geochemically g e o c h e m i c a l l y anomalous locations locations suitable f o l l o w u p studies s t u d i e s or o r mineral m i n e r a l exploration. exploration. s u i t a b l e for f o r detailed d e t a i l e d followup The project p r o - j e c t area a r e a includes i n c l u d e s T.59—61N., T.59-61N., R.7—IIW., R.7-llW., in i n Lake Lake County, County, excluding e x c l u d i n g lands l a n d s Lying l y i n g within w i t h i n the t h e RWCA. BWCA. This T h i s 400 square s q u a r e mile m i l e area a r e a is is underlain u n d e r l a i n by by the t h e Duluth Dulutli Complex Complex and and North North Shore S h o r e Volcanics V o l c a n i c s which which may may host host potentially p o t e n t i a l l y economic economic quantities q u a n t i t i e s of of platinum, p l a t i n u m , PCE's, PGE's, chrome, cobalt, cobalt, titanium, is minimal with w i t h surface surface t i t a n i u m , base b a s e metals, m e t a l s , gold g o l d and and silver. s i l v e r . Outcrop O u t c r o p is cover c o v e r being b e i n g varying v a r y i n g thicknesses t h i c k n e s s e s of o f glacial g l a c i a l deposits d e p o s i t s of o f the t h e Rainy Rainy and and Superior S u p e r i o r lobes. lobes. Approximately A p p r o x i m a t e l y 1200 1200 locations, l o c a t i o n s , statistically s t a t i s t i c a l l y distributed d i s t r i b u t e d according a c c o r d i n g to to existing e x i s t i n g road r o a d access, a c c e s s , are a r e being b e i n g sampled sampled during d u r i n g the t h e 1988 1988 field f i e l d season. season. Samples 1/4-mile Intervals i n t e r v a l s with w i t h overburden o v e r b u r d e n samples samples Samples are a r e normally n o r m a l l y obtained o b t a i n e d at a t 1/4—mile being d e p t h of o f 55 feet. feet. b e i n g obtained o b t a i n e d from from 4—inch 4-inch diameter d i a m e t e r holes h o l e s augered a u g e r e d to t o aa depth Sampled media Include i n c l u d e glacial g l a c i a l overburden, o v e r b u r d e n , humus, humus, AA and and BB soil s o i l horizons horizons and of available a v a i l a b l e species s p e c i e s Including i n c l u d i n g alder, a l d e r , balsam balsam fir, f i r , Jack j a c k pine, pine, and vegetation v e g e t a t i o n of and w h i t e spruce. s p r u c e . The heavy mineral m i n e r a l concentrate c o n c e n t r a t e and —2 -2 micron micron and black b l a c k and and white (clay) ( c l a y ) fraction f r a c t i o n are a r e assayed a s s a y e d from from the t h e glacial g l a c i a l overburden o v e r b u r d e n samples. samples. Ni, Ni, Samples an art!being b e i n g analyzed a n a l y z e d for f o r Pt, P t , Pd, Pd, Cr, Cr. Au, Au, Ag, Ag, Co, Co, 1, Y, T102, TiO,, Cu, Cu, Pb, Zn, Zn, RI, Rl, Sb, S b , Se, S e , Te, Te, As, A s , MgO, MgO, Fe203. Fe203. Results R e s u l t s of o f this t h i s investigation i n v e s t i g a t i o n are a r e available a v a i l a b l e to t o the t h e public p u b l i c on open o p e n file file with w i t h the t h e Minnesota M i n n e s o t a Department Department of o f Natural N a t u r a l Resources, R e s o u r c e s , Division D i v i s i o n of o f Minerals, Minerals, summary report r e p o r t will w i l l be b e Issued i s s u e d by by DNR—Minerals DNR-Minerals in i n Hibbing, H i b b i n g , Minnesota. Minnesota. AA summary after a f t e r July J u l y 1, 1 , 1989. 1989. 13 �Precambrian Precambrian TTerranes e r r a n e s beneath beneath Northern N o r t h e r n Lake Lake Michigan Michigan D e f i n e d by by Seismic Seismic and and Gravity G r a v i t y Analysis Analysis Defined William W i l l i a m F. F. Cannon, Cannon, Klaus K l a u s J. J. Schulz, Schulz, U.S. U.S. Geological G e o l o g i c a Survey l SurveyReston, Reston, VA, VA, 22092; William 22092; W i l l i a m J. J. Hinze, Hinze, Purdue Purdue University, U n i v e r s i t y , West West Lafayette, L a f a y e t t e , IN, IN,47907; 47907; and and Alan G. Green, Green, Geological G e o l o g i c a l Survey Survey ofo fCanada, Canada, Ottawa, Ottawa, Ontario, O n t a r i o ,K1A K I A0Y3 OY3 A l a n G. A seismic s e i s m i c reflection r e f l e c t i o n profile p r o f i l along e alona g line a 1 i nabout e about 290 l o n gfrom f r o mnear near A 290 kmkmlong the Mackinac t h e Straits S t r a i t sofof Mackinactot onear n e aManitowoc, r Manitowoc, Wisconsin, Wisconsin, was was ccollected o l l e c t e d during d u r i n g the the 1986 experimenti in 1986 GLIMPCE GLIMPCE s eseismic i s m i c experiment n nnorthern o r t h e r n and and western western Lake Lake Michigan. Michigan. Data Data were ont the were recorded r e c o r d e d ffor o r 20 20 seconds seconds t oto pprovide r o v i d e iinformation n f o r m a t i o n on h e ffull u l l thickness thickness of the crust and the uppermost mantle. o f t h e c r u s t and t h e uppermost mantle. The The line l i n ecrosses c r o s s e sseveral s e v e r a lPrecambrian Precambrian terranes t e r r a n e s that t h a tare a r eexposed exposed and and well well studied about 100 km to the west in northern Michigan and Wisconsin. s t u d i e d about 100 km t o t h e west i n n o r t h e r n M i c h i g a n and Wisconsin. These These terranes be pprojected t e r r a n e s can c a n be r o j e c t e d oonto n t o t hthe e sseismic e i s m i c l iline n e ((Figure F i g u r e 11) ) wwith i t h tthe h e aid a i d of of regional r e g i o n a l gravity g r a v i t and y andmagnetic magneticmaps. maps. A A gravity g r a v i t ymodel model along a1 ong the t h e seismic seismic profile interpretation. p r o f i l efurther f u r t h e constrains r c o n s t r a i n sthe t h egeologic g e o l o g i c interpretation. At A t the t h e north n o r t h end end of o f the t h e line, l i n e , the t h ewestern w e s t e r n half h a l f of of the t h eMidcontinent M i d c o n t i n e n t Rift Rift basin b a s i n is i sshown shown by by strong s t r o n g continuous c o n t i n u o u s rreflectors e f l e c t o r s from from basalt b a s a l t flows. flows. Reflectors Ref1 e c t o r s can GaGaini basement can be be traced t r a c e d to t oabout about20 20km km depth. depth. The The rift r i f formed t formedata 1.1 t 1.1 n basement rocks Very high h i g h densities d e n s i t i e s inferred inferred b e l i e v e dtot obebemostly m o s t l yArchean Archeangneisses. gneisses. Very r o c k s believed for f o rthe t h elower 1owercrust c r u s suggest t suggest abundant abundant rrift—related i f t - r e 1 a t e d mafic m a f i c intrusive i n t r u s i v e rocks. rocks. The gneissesappear appearonon The Archean Archean gneisses t h the e s eseismic i s m i c r erecord c o r d asasr i richly c h l y rreflective eflective material by aa mu1 multitude m a t e r i a1 dominated domi n a t e d by t i t u d e oof f short, s h o r t , subhorizontal s u b h o r i z o n t a l reflections. r e f 1 e c t ions. AA dense andsstrongly much dense and t r o n g l y rreflective e f l e c t i v e lower l o w e r crustal c r u s t a llayer, l a y e ras , as much as as 20 20 km km tthick, hick, isi sprobably p r o b a b l y granulitic g r a n u l i t i cgneiss. gneiss. The The Moho, Moho, ggenerally e n e r a l l y llocated o c a t e d aatt the t h e rather rather sharp froms tstrongly sharp change change from r o n g l y r reflective e f l e c t i v e lower l o w e r crust c r u s t to t o acoustically a c o u s t i c a l l ytransparent transparent mantle, mantle, dips d i p s gently g e n t l ynorthward n o r t h w a r d toward t o w a r d the t h e Midcontinent M i d c o n t i n e n t RRift, i f t , probably p r o b a b l y as as aa result reaches a depth about 5555kmkmbeneath g , and reaches a d e p tof h of about beneath the the r e s u l tofo flexural f f l e x u r loading, a l l o a d i nand rrIi fft.t . F a r t h e r south, south, the t h e Niagara N i a g a r a fault f a u l t can can be be projected p r o j e c t e d onto o n t o tthe h e profile p r o f i l efrom from Farther the wherei tit is t h e faultss f a u l t ' sexposure exposure ini nnorthern n o r t h e r nMichigan M i c h i g a n and and Wisconsin, Wisconsin, where i s aa steeply s t hsuture e s u t u rbetween e betweenthe t h eArchean Archean s t e e p l y dipping d i p p i n gfault f a u lzone t zonethat t h arepresents t r e p r e s e n tthe craton c r a t o n on on the t h e north n o r t hand and an an Early E a r l y Proterozoic P r o t e r o z o i c volcanic v o l c a n i c arc, a r c ,the t h eWisconsin Wisconsin magmatic No reflections r e f l e c t i o n s can can be be directly d i r e c t l yascribed a s c r i b e d to t othe t h eNiagara Niagara magmatic terrane. t e r r a n e . No fault, location r e f l e c t i v echaracter character f a u l t ,but b uits t i tgeneral s general l o c a t i ois n marked i s markedbybya achange change in i n reflective of of the t h e crust. c r u s t . The The arc a r c terrane t e r r a n e has has abundant abundant ssubhorizontal u b h o r i z o n t a l reflections reflections throughout t h r o u g h o u t the t h e crust, c r u s t , with w i t hthe t h eexception e x c e p t i o nofo fa afew fewnearly n e a r l ytransparent t r a n s p a r e n tareas areas that t h a t we we interpret i n t e r p r e t as as granitic g r a n i t i c intrusive i n t r u s i v erocks. rocks. Gravity G r a v i t y analysis a n a l y s i s indicates indicates that p r o b a b l ya acombination combination t h a tthe t h eterrane t e r r a n eis idominated s dominatedby bylow l o wdensity d e n s i t yrocks, rocks,probably of An intensely intensely o f caic—alkaline c a l c - a l k a l i n e volcanics v o l c a n i c s and and related r e l a t e d granitoid g r a n i t o i drocks. rocks. An reflective r e f l e c t i v elayer l a y eabout r about6 6km km thick t h i c kata the t t h base e baseofo the f t h earc a r terrane c t e r r a n eappears appears to wei ninterpret TheMoho Moho t ohave have unusually u n u s u a l l y hhigh i g h ddensity, e n s i t y , and and we t e r p r e t iitt as as granulite. g r a n u l i t e . The isi sananessentially 40 40 kmkm deep deepbeneath beneath the t h e arc a r c terrane. terrane. e s s e n t i a l l flat y f l surface a t s u r f a about c e about The The southern s o u t h e r n t third h i r d of o f the t h e line l i n econtains c o n t a i n s an an intensely i n t e n s e l y reflective r e f l e c t i v elower lower crustal c r u s t a llayer l a y eabove r above aalargely l a r g e l ytransparent t r a n s p a r e n tmantle. mantle. The The reflective r e f l e c t i v e crust c r u s t isi s tentatively gneisses t e n t a t i v e l yidentified i d e n t i f i as e d Archean as Archean gneissesaccreted a c c r e t e dtot the o t hsouthern e s o u t h e r nmargin margin of o fthe t h earc a r terrane c t e r r a nduring e d u r i nthe g t hPenokean e Penokeanorogeny orogeny about about 1,850 1,850 mil m i llion l i o nyears years ago. ago. Approximately A p p r o x i m a t e l y t hthe e l olower w e r h half a l f oof f tthe h e ccrust r u s t is i s especially e s p e c i a l l y reflective reflective and and has has high h i g h density. d e n s i t y . As As with w i t h the t h e Archean Archean ccrust r u s t tto o the t h e north, n o r t h , we we interpret interpret this t h i sas aslower l o w e r crustal c r u s t a l granulitic g r a n u l i t i cgneiss. gneiss. The The Moho Moho ddips i p s gently g e n t l ynorthward northward beneath beneath this t h i s terrane t e r r a n eand and appears appears to t o have have an an abrupt a b r u p t ooffset f f s e t near near the t h e contact contact with T h i sunusual unusual Moho Moho offset o f f s e tmay may be bea a w i t hthe t h eWisconsin WisconsinMagmatic Ma m a t i c terrane. t e r r a n e . This vestige v e s t i g eofofdeeply d e e p l ysubducted sub u c t e d crust. crust. 2 14 �01 IS I0• U •50- N UQAL 01 - — - --- — - - - — --Z are equal for velocity of 6 km/s. -Archan —- Ns,th.In A,ch.an T.u.n. baIfloIb ) --- akaIajcaana,.jo.d;.:- — ( Garhc ' ——— I — p00 T.rrans — $outh.,n A,ch.an —0 -15 10 0 I' 0 II rl000 $ NT SHOT Agch- Q_—- - - --- -- ---T -—— WIc.nIn M.gm.tlc T.rr.n. 0 cz u u c m u Em-.? a s aJ a m c aJ a a u > A n c L . a aJ m w c.- m u m aJ a = a h0 c UIN c a 0%- & 2 3 w c .F -02 x u a- aJ m > c a u V - L C E - m a +- w u I v c c w a a 02 z -In - u L m A 0 *- "P .? k.7 0 m c . - & E m 3 L Figure 1. Schematic interpretation of line drawing of GLIMPCE line H in northern Lake Michigan and inferred subsurface terranes interpreted from seismic and gravity analysis. Dashed thrust faults are schematic and consistent with tectonic models for on—land geology west of the line. MRS = Midcontinent rift system. M = Moho. Shot spacing is 62.5 m. Horizontal and vertical scales — 0 I.00 ,- L a J 7 . lk ? u L aJ O K u L . . a?.- m c m m aJ u a u o a �Paleomagnetic Paleomagnetic Studies Studies of of Wausau Wausau Syenite Syenite Complex Complex and and Wissota Wissota Dam Dam Mafic Mafic Dike Dike Lung Lung S. S. Chan Chan and and Paul Paul E. E . Myers Myers Department Department of of Geology, Geology, University University of of Wisconsin-Eau Wisconsin-EauClaire Claire Eau Eau Claire, Claire, WI WI 54701 54701 Remanent Remanent magnetism magnetism of of the the Wausau Wausau syenite syenite complex complex in in Marathon Marathon County, Councy, Wisconsin, Wisconsin, shows shows aa westerly westerly declination declination and and yields yields aa virtual virtual geomagnetic geomagnetic pole pole similar similar to to the the 1.1 1.1 Ga Ga paleomagnetic paleomagnetic pole pole of of the the North North American American craton craton [Zich [Zich et et al., al., 1986] 19861. In In addition, addition, the the paleomagnetic paleomagnetic data data reveal reveal multiple multiple magnetic magnetic components. components. The The magnetization magnetization history of of the the Wausau Wausau syenite syenite can can be be worked worked out out by by comparing comparing the the magnetic magnetic results results with with paleomagnetic paleornagne tic directions directions from from mafic mafic dike dike swarms swarms in in the the Southern Southern Superior Superior Province Province and and aa mafic mafic dike dike at at Wissota Wissota Dam Dam in in Chippewa ChippewaFalls, Falls,Wisconsin. Wisconsin. . The The Wausau Wausau syenite syenite complex complex of of Central Central Wisconsin Wisconsin represents representsa apost-Penokean, post-Penokean, anorogenic anorogenic intrusion intrusion which which is is probably probably coeval coeval with with the the Wolf Wolf River River granite granite [LaBerge [LaBerge and and Myers, Myers, 1984). 19841. The The granite granite and and syenite syenite were were intruded intruded by by aa swarm swarm of of east-northeast east-northeast striking striking mafic mafic dikes. dikes. Rubidium-strontium Rubidium-strontium measurements measurements of of two CaGa [Van Schrnus two samples samples from from Wausau Wausauyielded yieldeda aminimum minimumage ageofof1.52 1.52 [Van Schmusetetal., al., 1975]. 19751. Since Since the the Proterozoic Proterozoic polar polar wander wander curve curve for for North North America America Craton Craton contains contains aa gap gap between between 1.60 1.GO Ga Ga and <lnd1.45 1.45Ga, Ga, aa paleomagnetic paleoinagnetic study study of of the the Wausau Wausau syenite syenite may may help help to to fill fill the the gap gap in in the the polar polar wander wander path. path. 00 The The Wausau Wausau syenite syenite was was sampled sampled at at four four locations locations and and demagnetized demagnetized by by both both alternating alternating field field and and thermal thermal techniques. techniques. Kirschvink's Kirschvink's [1980) [I9801 procedure procedure for for vecroral vectoral analysis analysis of of paleomagnetic paleomagnetic data data was was used used to to extract extract linear linear segments segments from from the the results results of of measurements. measurements. AA linear 1inear segment segment is is defined defined here here as as aa set setof ofthree three or or more more consecutive consecutive points points in in aa demagnetization demagnetization curve curve that that show show less less than than 10° lo0 angular angular deviation deviation about about their their mean meandirection. direction. Each Each linear linear segment segment is is considered considered as as aa magnetic magnetic component. component. In In Fig. Fig. 1,1 , the the magnetic magnetic components components of of all all samples samples are are plotted plotted and and contoured contoured on on an an equal-area equal-areaprojection. projection. 270 180 180 Fig. Fig. 1 Contoured Contoured distribution distribution of of magnetic magnetic components components in in Wausau Wausau syenitesamples samplesatat1 1per per1%1%area. area. syenite 1 We We define define aa magnetic magnetic component component cluster cluster as as aa direction direction that that contains contains three three or or more more components components per per 1% 1% of of stereonet stereonet area. area. Magnetic Magnetic components components from from the the Wausau Wausau syenite syenitecomplex complexform formthree threemagnetic magnetic component componentclusters clusters(Fig. (Fig.1), I), the the most most prominent grominent of of which which (A) ( A ) shows showsaadirection directionof ofD—266°, D-266', 1—14° 1-14' and and aa vgp vgp at at lat—2 lat-2 , long—l72°W. 1 0 n ~ - 1 7 2 ~ ~A.A second second cluster cluster (B) (B) has hasa adirection directionofofD—347°, D-347O, 1—57° 1-57' and This magnetic component component cluster clusterprobably probably and aa vgp vgp at atlat—77°, lat-77O,long—147°E. 1 0 n ~ - = 1 4 7 ~This ~ . magnetic represents represents aa present-field present-fieldoverprint overprint because because of of the thehigh highvgp vgplatitude. latitude. AA third third magnetic magnetic component component cluster cluster (C) (C) shows shows aa direction directionD—62°, D-62'. 1-83' and and 1—83° gives gives aa vgp vgpatatlat—50° lat-50' and andlong—71°W. long-71°w This This vgp vgp lies lies on oncourse course with with the the , 16 �the middle Proterozoic Proterozoic polar America extension of the polar wander wander path path of the North America and probably probably represents represents the primary component acquired acquired at at the the time time of of Craton and intrusion. intrusion. The The magnetic magnetic component component A was likely acquired acquired during during the rhe was likely Keweenawan Keweenawan magmatic magmatic event. event. Ilmenite in the syenite is probably an an oxidation oxidation of of aa titanomagnetite. titanomagnetite. Previous paleomagnetic in the the paleomagnetic studies studies of of mafic mafic dikes in Southern Superior Superior Province Province have have also also yielded yielded virtual virtual geomagnetic geomagnetic poles poles that that Southern lie within the the polar polar wander wander path path (Logan (Logan Loop) Loop) for North North America America during during Keweenawan times times 1.2-1.0 1.2-1.0Ga Ga [Green [Green et et al. al., 1987]. 19871. Keweenawan , The 50 50 mm mafic mafic dike dike below below Wissota Wissota Dam in in Chippewa Chippewa Falls Falls represents represents aa shallow shallow intrusion intrusion into into foliated foliated trondjemite trondjemite of of late-middle late-middleProteroProterozoic Although zoic age. age. Although the the dike dike is is symmetrically symmetrically zoned zoned with with regard regard to to composition and grain size, composition and grain size, numerous inclusions inclusions of of very very coarse coarse plagioclase plagioclase (An55) ( ~ n ~and ~ )norite norite are are confined to to aa 2-rn 2-m zone along along the the north north wall. wall. The The 34-rn 34-m core of the the dike dike consists consists of of ilmenite-bearing ilmenite-bearing clinopyroxene-olivine clinopyroxene-olivine gabbro. gabbro. Grain Grain size size diminishes diminishes outward outward to to aa highly highly altered aphanicic clinopyroxene altered aphanitic clinopyroxene basalt. From basalt. From the the center outward outward the dike dike is is symmetrically symmetrically altered, altered, first first to to epidote epidote replacements replacements of of plagioclase, plagioclase, then then to to chloritechloriteepidote epidote replacements replacements of of pyroxene pyroxene accompanied by conversion of accompanied by conversion of olivine olivine to to talc talc and and serpentine. serpentine. Biotite, Biotite, possibly possibly as as aa replacement replacement of of chlorite, chlorite, appears appears about about 66 meters meters from The from each each contact. contact. The ironirontitanium titanium mineral mineral along along the the dike dike margin margin is is aa titanornagnetite titanomagnetite highly highly altered altered to to hematite. hematite. 0 90 1 80 Fig. 2 2 Nrm directions directions in in Wissota Dam Dam Fig. mafic dike dike and and alpha-95 alpha-95 confidence confidence circles circles (triangles (triangles : sites sites 11 and and 2, 2, circles: circles: site site 3, 3 , squares squares : site site 4). [A). : : core samples samples were were collected collected at four four distances distances from from the the northern northern Oriented core dike dike margin: margin: 10 10 cm, cm, lm, lm, 7m, 7m, and and 25m. 25m. The The samples samples were were demagnetized demagnetized with with alternating alternating field field technique technique and and linear segments segments were determined determined by vectoral vectoral analysis. analysis. As shown shown in in Fig. Fig. 2, 2 , the the remanent remanent magnetism directions of of the the center We center sites sites differ differ significantly significantly from from that that of of the the marginal marginal sites. sites. We interpret interpret such such different different directions directions as as aa result result of different different magnetic magnetic mineralogy. mineralogy. The The differentiation differentiation of of the dike rock may signify signify difference difference in in crystallization temperature, temperature, with with inagnetite magnetite formed along the the dike dike crystallization formed earlier along margin, margin, and and the the ilmenite ilmenite of of the the core core crystallized crystallized later later at at lower lower temperature. The temperature. The nrm nrm of of the the finer-grained finer-grained marginal marginal rocks, rocks, therefore, therefore, may may represent represent an an early early acquisition acquisition at at the the time time of of intrusion. intrusion. Considering the the remanent remanent magnetism of the marginal zone zone of the the dike dike an an early early Considering acquisitionl the the two two marginal marginal sites sites yield yield aa vgp vgp at at lat—-2.2°, lat--2.2O, long—163.87°E. acquisition, long-163.87O~. As As shown shown in in Fig. Fig. 3, 3 the vgp falls falls near the the polar polar wander wander path path at at 1.0 1 .O Ga. Ga. AA comparison of of the the vgp vgp coordinates coordinates with previous results obtained from from dike dike 17 �swarms in in the the Southern Southern Superior Superior Province Province suggests suggests aa relatively relatively younger younger swarms intrusion age age of of the the dike dike at at Wissota Wissota Dam. Dam. intrusion Our preliminary preliminary inferences inferences from from the the Our paleomagnetic studies studies of of the the Wausau Wausau paleomagnetic syenite and and the the mafic mafic dike dike at at syenite Wissota Dam may be summarized as Wissota Dam may be summarized as follows : first , the three magnetic follows: first, the three magnetic components present present in in the the Wausau Wausau components syenite represent (1) a primary syenite represent (1) a primary component acquired acquired at at the the time time of of component intrusion, (2) a present field intrusion, present (2) a field overprint, and and (3) aa remagremagoverprint, (3) netization during during the the Keweenawan Keweenawan netization magmatic event. Secondly, the magmatic event. Secondly, the remanent magnetism directions in remanent magnetism directions in the mafic dike near Wissota Dam the mafic dike near Wissota Dam reflect different magnetic reflect different magnetic mineralogy of the dike rocks. mineralogy of the dike rocks. Thirdly, the mafic dike could have Thirdly, the mafic dike could have been emplaced later than he mafic been emplaced later than the mafic dike swarms swarms in in dike Superior Province. Superior Province. the the 0 Nh I _--_--J Fig. 33 Comparison Comparison of of vgps vgps of of Wausau Wausau Fig. syenite (S) (S) and and Wissota Wissota Dam Dam mafic mafic syenite dike (D) with Southern Superior dike (D) with Southern Superior paleomagnetic data data summarized summarized by by paleomagnetic Green et al. [1987]. Green et al. [1987). Southern Southern References cited cited References Green, J.C., J . C. , T.J. T.J . Bornhorst, Bornhors t , et e t al., a1 . , Keweenawan Keweenawan dikes dikes of of the the Lake Lake Superior Superior Green, region: evidence of evolution of the middle Proterozoic midcontinent rift region: evidence of evolution of the middle Proterozoic midcontinent rift of North America, in H . C . Halls and W.F. Fahrig (eds): Mafic Dyke Swarms, of North America, in H.C. Halls and W.F. Fahrig (eds): Mafic Dyke Swarms, 289-316, Geol. Geol. Asso. Asso. Can. Can. Spec. Spec. Paper Paper 34, 34, 1987. 1987. 289-316, Kirschvink, J.L., J.L., The The least-squares least-squares line line and and plane plane and and the the analysis analysis of of Kirschvink, paleomagnetic data, Geophys. Jour. R. Astr. SOC., 62, 699-718, 1980. paleomagnetic data, Geophys. Jour. R. Astr. Soc., 62, 699-718, 1980. LaBerge, G.L., G.L., and and P.E. P.E. Myers, Myers, Two Two early early Proterozoic Proterozoic successions successions in in LaBerge, central Wisconsin and their tectonic significance, Geol. SOC. Amer. central Wisconsin and their tectonic significance, Geol. Soc. Amer. Bull., 95, 95, 246-253, 246-253,1984. 1984. Bull. , Van Schmus, Schmus, W.R., W.R., L.G. L.G. Medaris, Medaris, and and P.O. P.O. Banks, Banks, Geology Geology and and age age of of the the Van Wolf River River Batholjth, Batholith, Wisconsin, Wisconsin, Geol. Geol. Soc. SOC. Amer. Amer. Bull., Bull., 86, 86, 907-914, 907-914, Wolf 1975. 1975. Zich, C., C., L.S. L.S. Chan, Chan, and and P.E. P.E. Myers, Myers, Preliminary Preliminary paleomagnetic paleomagnetic results results Zich, from the the Wausau Wausau syenite syenite complex, complex, Central Central Wisconsin, Wisconsin, EOS EOS Trans., Trans., 67, 67, from 266, 1986. 1986. 266, 18 �NEW NEM BOUGUER BOUGUER GRAVITY GRAVITY ANOMALY ANOMALY MAP MAP OF OF MINNESOTA MINNESOTA Val W. W. Chandler Chandler and a ~ Bryan d Bryac D. D. Schaap, S c h a a p I Minnesota Geological G e o l o g i c a l Survey, Survey, 2642 MN 2642 University U n i v e r s i t y Avenue, Avenue, St. S t . Paul, P a u l I MN 55114—1057 551 14-1057 The Minnesota i s preparing p r e p a r i n g aa new new Bouguer Bouguer gravity gravity Minnesota Geological G e o l o g i c a l Survey Survey is anomaly 1 : SOO,OOO) , marking marking the t h e completion c o m p l e t i o n of o f aa anomaly map map of o f Minnesota Minnesota (scale ( s c a l e 1:500,000), state—wide s t a t e - w i d e gravity g r a v i t y surveying s u r v e y i n q program program that t h a t began began over o v e r 20 20 years y e a r s ago a g o with w i t h the the goal to acquire a c q u i r e data d a t a at a t aa spacing s p a c i n g of of 1.6 1.6 to t o 3.2 3.2 km. km. This T h i s program program was was iniinig o a l to tiated t i a t e d by by P.K. P.K. Sims, Sims, former former director d i r e c t a r of o f the t h e MGS, MGS, and and the t h e first f i r s t surveying surveying was conducted between 1965-1969 under supervision of R.J. w a s conducted between 1965-1 969 u n d e r s u p e r v i s i o n o f R. J. Ikola. Ikola I n the the In following f o l l o w i n g years y e a r s surveying s u r v e y i n g continued c o n t i n u e d under under supervision s u p e r v i s i o n of o f G.E. G. B. Morey, Morey, G.A. G. A. Durfee, D u r f e e , L.D. L.D. McGinnis, McGinnis, C.P. C.P. Ervin, E r v i n , R.J. R. J. Horton, Horton, and and V.W. V.W. Chandler. C h a n d l e r . The The data were published as a series of 1:250,000—scale sheets d a t a were p u b l i s h e d a s a series of 1 : 2 5 0 1 0 0 0 - s c a l e s h e e t s between between 1968 1968 and and 11987. 987. A A few few oolder l d e r data d a t a sets s e t swere were incorporated i n c o r p o r a t e d that t h a twere were determined d e t e r m i n e d to to be be suitably s u i t a b l y accurate. a c c u r a t e . Over Over tthe h e llast a s t several s e v e r a l years y e a r s additional a d d i t i o n a lcoverage c o v e r a g e has has been b e e n acquired a c q u i r e d within w i t h i n several s e v e r a l of of the t h e published p u b l i s h e d sheets, s h e e t s , and and the t h e gravity g r a v i t y datadatabase, b a s e , which which had had numerous numerous eerrors r r o r s and and ommissions, ommissionsI hhas a s bbeen e e n ccarefully a r e f u l l y edited edited and 860 ggravity and corrected. c o r r e c t e d . The m e ffinal i n a l version v e r s i o n contains c o n t a i n s 55, 55,860 r a v i t y sstations, tationsI e q u a t i n g to to an an average a v e r a q e station s t a t i o n spacing s p a c i n g of of about a b o u t 2.4 2.4 km km state s t a t e wide. wide. The The equating edited e d i t e d data d a t a were were reduced reduced using u s i n g aa density d e n s i t y of o f 2.67 2.67 grams grams per p e r cubic c u b i ccentimeter centimeter and gravity 1967 1 . and the t h e 1967 1967 g r a v i t y formula f o r m u l a (International ( I n t e r n a t i o n a lAssociation A s s o c i a t i o nof o fGeodesy, Geodesy I 1967). . The news state mapi sis ccontoured The new t a t e map o n t o u r e d a at t aa 11-milligal - m i l l i g a l interval i n t e r v a l and and is i sbased based on on gridded gridded data m i ~ i m u mcurvature. c u r v a t u r e . This This d a t a generated g e n e r a t e d at a t aa 1.5-km 1.5-km interval i n t e r v a l using u s i n g minimum map map will w i l l be be aa major major improvement improvement over o v e r the the previously p r e v i o u s l y published p u b l i s h e d state s t a t e map map (Craddock and others, o t h e r s , 1970), 19701, which was primarily p r i m a r i l y based based on on stations s t a t i o n s spaced spaced (Craddock 10 1 0 - m i l l i g a l contour c o n t o u r interval. i n t e r v a l . The The gridded g r i d d e d data d a t a can can 1 0 km km apart a p a r t and and used used aa lO—milligal also a l s o be be used used in l n aa wide wide variety v a r i e t y of of computer computer enhancement enhancement options, o p t i o n s , including including second second vertical v e r t i c a l derivative. derivative. The The high h i g h resolution r e s o l u t i o n of o f the t h e new new state s t a t e map map presents p r e s e n t s aa greatly g r e a t l y improved improved perspective p e r s p e c t i v e on Archean Archean and and Proterozoic P r o t e r o z o i c structures. s t r u c t u r e s . In I n the t h eArchean Archean greenstone-granite g r e e n s t o n e - g r a n i t e terrane t e r r a n eof o fnorthern n o r t h e r nMinnesota, M i n n e s o t a I northeast—striking n o r t h e a s t - s t r i k i n g gravity gravity highs m i l l i g a l s I delineate d e l i n e a t e the the h i g h s and and lows, lows, which which differ d i f f e r in i n amplitude a m p l i t u d e by by 30—60 30-60 milligals, metavolcanic Second vertical v e r t i c a l derivative derivative m e t a v o l c a n i c and and granitic g r a n i t i c belts, b e l t s , respectively. respectively Second enhancement i s extremely e x t r e m e l y useful u s e f u l for f o r picking p i c k i n g contacts, c o n t a c t s I which which enhancement of o f these t h e s e data d a h is are a r e commonly commonly traced t r a c e d by by the t h e zero z e r o contour, c o n t o u r , and and for f o r recognizing r e c o g n i z i n g subunits subunits within w i t h i n the t h e granitic g r a n i t i cand andmetavolcanic m e t a v o l c a n i c belts. b e l t s . In I n the t h e Archean Archean gneiss g n e i s s terrane terrane of gravity o f southwestern s o u t h w e s t e r n Minnesota, Minnesoh, g r a v i t y highs h i g h s and and lows lows delineate d e l i n e a t e mafic m a f i c and and felsic twotwonorthwest—striking to f e l s i cunits, u n i t srespectively, , r e s p e c t i v e l yand , and n o r t h w e s t - s t r i k i n g lineaments l i n e a m e n t s appear a p p e a r to r e f l e c t major f a u l t z o n e s t h a t d i v i d e t h e t e r r a n e i n t o t h r e e d i s t i n c t blocks. b l o c k s . Over Over the t h e Early E a r l y Proterozoic P r o t e r o z o i c Penokean Penokean f ofold-and-thrust l d - a n d - t h r u s t bbelt e l t iin n easteastcentral c e n t r a l Minnesota, Minnesota, an a n arcuate a r c u a t e belt b e l tof o fgravity g r a v i t yanomalies a n o m a l i e s extends e x t e n d s through through southwestern s o u t h w e s t e r n Carlton C a r l t o n County, County, central c e n t r a l Crow Crow Wing Wing County, County, and and into i n t o northnorthcentral c e n t r a l Stearns S t e a r n s County; County; iit t is i s believed b e l i e v e d to t o trace tracethe t h eSerpent S e r p e n t Lake Lake structural structural discontinuity d i s c o n t i n u i t yof o fSouthwick Southwick and and others o t h e r s (1988). ( 1 988 1 S o u t h e a s t of o f this t h i smajor major Southeast structural s t r u c t u r a lfront, f r o n t ,a asomewhat somewhat iirregular r r e g u l a r distribution d i s t r i b u t i o n of o f gravity g r a v i t yhighs h i g h s and and lows magmatic terrane t e r r a n ecomposed composed of o f Penokean Penokean iintrusions n t r u s i o n s of of lows characterizes c h a r a c t e r i z e sa amagmatic varying v a r y i n g compositions composi t i o n s and and gneissic g n e i s s i c rocks r o c k s •. In I n the t h e Middle Middle Proterozoic Proterozoic M i d c o n t i n e n t rrift i f t system, s y s t e m , the t h e gravity g r a v i t ydata d a mdelineate d e l i n e a t ethe t hDouglas e Douglasand andPine Pine Midcontinent faults thenorthwestern n o r t h w e s t e r n margin margin oof f the t h e St. S t . Croix C r o i x horst h o r s tand anddefine define f a u l t salong a l o n gthe several Complex. ts s e v e r a lunits u n i t swithin w i t h i the n t hDuluth e Duluth Complex. Thus Thus tthe h e new new sstate t a t e map map and and iits . reflect major fault zones that divide the terrane into three distinct . 19 �digital d i g i t a l data d a t a base b a s e should s h o u l d be b e extremely e x t r e m e l y useful u s e f u l for f o r geologic g e o l o g i c studies s t u d i e s and and mineral m i n e r a l exploration e x p l o r a t i o n for f o r many many years y e a r s into into the t h e future. future. The The gravity g r a v i t y surveying s u r v e y i n g program program has h a s been b e e n funded funded by by the +he Minnesota Minnesota Iron Iron Range Range Resources R e s o u r c e s and and Rehabilitation R e h a b i l i t a t i o n Board, Board, the t h e Minnesota M i n n e s o t a Department D e p a r t m e n t of of Natural the Minnesota Future F u t u r e Resources R e s o u r c e s Commission Commission (formerly ( f o r m e r l y the N a t u r a l Resources, R e s o u r c e s , the t h e Minnesota Legislative L e g i s l a t i v e Commission Commission on on Minnesota Minnesota Resources), R e s o u r c e s ) , and and the t h e U.S. U.S. Geological Geological Survey. being Minnesota b e i n gfunded fundedby bythe the Minnesota S u r v e y . Publication P u b l i c a t i o n of o f the t h estate s t a t map e mapisi s Future F u t u r eResources R e s o u r c e sCommission. Commission. References R e f e r e n c e s Cited: Cited : Craddock, C r a d d o c k , C., C., Mooney, Mooney, H.M., H.M. ,and and Kolehmainen Kolehmainen V., V., 1970, 1970, gravity g r a v i t y map map of o f Minnesota Minnesota and and northwestern n o r t h w e s t e r n Wisconsin: Wisconsin: S i m p l e Bouguer Bouguer Simple M i n n e s o t a Geological Geological Minnesota Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Map Map M—10, M-10, scale s c a l e 1:1,000,000. 1: 1 , 0 0 0 , 0 0 0 . International I n t e r n a t i o n a l Association A s s o c i a t i o n of o f Geodessy, G e o d e s s y , 1967, 1967, Geodetic G e o d e t i c reference r e f e r e n c esystem, system, 1967: 1 967: International I n t e r n a t i o n a l Association A s s o c i a t i o n of o f Geodesy Geodesy Special S p e c i a l Publication P u b l i c a t i o n 3, 3 , 115 1 1 5 p. p. Southwick, P.L., 1988, S o u t h w i c k , D.L., D.L., Morey, Morey, G.B., G.B., and and McSwiggeri, McSwiggen, P.L., 1 9 8 8 , Geologic G e o l o g i c map map (scale ( s c a l e 1:250,000) 1 : 2 5 0 , 0 0 0 ) of of the t h e Penokean Penokean orogen, o r o g e n , central c e n t r a l Minnesota, M i n n e s o t a , and and accomaccompanying 37, p a n y i n g text: t e x t : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Report R e p o r t of o f Investigations I n v e s t i g a t i o n s37, 25 2 5 p. p. 20 �MAPS OF THE THE LAKE HURON REGION MAGNETIC AND GRAVITY ANOMALY MAPS S. Dwiht J. Hinze2, Hinze2, Pierre Pierre Keating1, Keating 1, DwiahtDads1, ~ods', William William J. and James James G. G. Smith3 smith3 1Geological Survey '~eolo~ical Survey of of Canada, Canada, 1 1 Observatory Observatory Cr., Cr., Ottawa, Ottawa, Ont. Ont. Canada K1AOY3 KlAOY3 2Dept. 2 ~ e p t . of Geological Sciences, Sciences, Purdue Purdue Univ., Univ. , West West Lafayette, Lafayette, IN 47907 47907 3Nobil '~obil Oil Oil Corp., Corp., 4045 4045 N.W. N. W. 64th 64th St., St., Suite Suite 200, 200, Oklahoma Oklahoma City, City, OK 73116 73116 A 1:1 1:l million million scale scale aerornagnetic aeromagnetic compilation of Lake Lake Huron Huron and surrounding areas areas integrates integrates new new surveys surveys over over Lake Lake Huron, Huron, Georgian Georgian Bay, Bay, and and land land areas areas east east of of the the lake lake with with older older aeromagnetic coverage coverage in in Michigan Michigan and and Ontario. Ontario. Existing gravity gravity data data were were compiled compiled at at the the same same scale. scale. A variety variety of derived maps maps have have been been prepared prepared from from these these data data sets sets to to emphasize emphasize particular particular attributes attributes of of the the anomaly anomaly fields fields and and facilitate facilitate the the geologic geologic interpretation interpretation of of the the potential potential field field data. data. In concert with other geophysical geophysical data data and and geologic geologic information from the Lake Lake Huron Huron environs, environs, these these maps map8 are are useful useful in delineating basement structural/petrologic .structural/petrologic provinces provinces of of the lake. lake. Noteworthy Noteworthy is i6 the the magnetic magnetic high high of of the the Grenville Grenville Front Front the tectonic tectonic zone zone that that aids aids in in refining refiningthe theposition positionofofthe the(3renville Grenville Front beneath beneath the the Michigan Michigan Basin. Basin. 21 �THE BARABOOINTERVAL INTERVAL --ENCORE: THE PROTEROZOIC PROTEROZOIC BARABOO ENCORE: COMPOSITION DATA EllAL ET AL COMPOSITION DATA Jeffrey K. Greenbera (Dept. of Geoloav. Wheaton Colleqe. Wheaton IL. 60187) CR. Van surely be to witness C.R. Van Hise Hise would would surely be pleased pleased to witne~ts the the sustained sustained Intrigue intrigue concerning the the Baraboo quartzite and metasedimentary concerning Baraboo quartzite and other other possibly possiblycorrelative correlative metasedlmentary limited by by re\atively relatively few units in Inthe thesouthern southernLake Lake Superior Superior region. region. Although Although limited few to employ everytype typeofof analysis analysis in deciphering scattered outcrops, outcrops, we continue continue to employ every deciphering the the It history ofofthe the'Baraboo 'Baraboointerval.TM Interval.' Ithas hasrecently recentlybeen beensuggested suggested (LaBerge (LaBerge and and Klasner 1988) 1988) that that two quartzitic rocks two different differentsequences sequences of ofBaraboo—type Baraboo-type quartzitic rocks can be be Klasner distinguished (old idea revisited) and that the older sequence represents some type (old idea revisited) and that the older sequence represents s m e type 1850 and thrust thrust southward of clastic clastlcwedge wedgeeroded erodedfrom franArchean Archean basement basement and southward during during Ca. ca. 1850 interpretations depend Ma. arc-continent coll collision Ma. arc-continent ision inincentral centralWisconsin. Wisconsin. These These interpretations depend on on stratigraphic and and structural relationships. relations hips^ indirect stratigraphic Until sufficient age thethe metasedimentary sufficient agedata databecome become available, available*the theorigin originofof metasedlmentary and chemical rocks rocks is is best best indicated indicated by by their theirmodal modal and chemical composition. composition. Compositional Compositional criteria criteria are are nnoww primary factors factors in in the the determination of manatic magmatic origins, origins, The interpretation interpretation of ascertaining both both source source material and and tectonic tectonicenvironment. environment. The of relatively compositional data for for metasedimentary canposltional metasedlmentary rocks can likewise likewi3e be a relatively unambiguousdeterminant determinantof of provenance provenanceand anddepositional depositional environment. environment. unambiguous Tectonic-sedimentation interpretations interpretations of Tectonic-sedimentation of the theBaraboo Baraboo interval interval(see (seeGreenberg Greenberg reassessedthrough throughthe the lntegratlon integration of and Brown 1984) were Brown 1904) were reassessed of chemical chemical analyses analyses from frm over outcrop areas areaswith with other other available data. over twenty twenty outcrop data. The three three major major depositional The deposltlonal (1984) include: clastic hypotheses hypotheses from from Greenberg Greenberg and and Brown B r w n (1984) Include: AA) ) a a near-continuous near-continuous clastlc shelf transgression; transgression: B) B) multiple multlplesequences sequences separated separated by by major major unconformities, unconformltIe~,and and C) epicratoriic environment, basin and fault-bound basins. C) complex complex epicratonic envlronment. basin and range-type range-type fault-bound basins. The The last of ofthese thesewas was previously prevlwsly preferred, preferred,with withthe theconcurrence concurrence ofofSouthwick Southwick and and others others (1986) concerningthe theorigin origin of the interval Sioux in Minnesota. (1906) concerning the Baraboo Baraboo interval Sioux quartzite quartzite In Hinne3ota. Modal/chemicalcharacteristics characteristicsindicate Indicate that that the Baraboo interval rocks rocks are are of Modal/chemica~ Baraboo interval constitution of variable variable provenance. provenance. The typical typical modal constitution of the coarser coarser lithologies lithologles The bespeaks of of variable to mature bespeaks mature weathering weathering and and erosion erosion and and predominantly predminantly felsic felslc igneous Major and and trace trace element contents indicate Igneous or or reworked reworked sedimentary sedimentary sources. sources. Major element contents geparate exposures exposures bear theirown own restricted source areas. For that separate bear evidence evidenceof of their source areas. example, K20, Nb,Nb, andand Zr versus Si% Si02 plots display little of example, X20,HgO, MgO, Zr versus plots display little or or no no clustering clustering of samples, regardless of of grain samples* regardless grain size sllicacontent. content. Rare Rare earth earth abundances abundance3 of ofmany many size or silica arenltic and pelitic peliticsamples samples closely mirror the REE patterns arenitic and the REE patterns of nearby felsic plutons and and extrusives extrusivesofof both Penokeanand andpost-Penokean post-Penokean 1760 1760 Ma. Ha. age. age. Archean plutons both Penokean Archean or mafic are generally absent. mafic terrane terranecomponents components are absent. Eroded ErodedArchean Archeanrocks rocksofofcentral central or northern Wisconsin are are an an unlikely source of the Baraboo Barabm interval interval source for most of sediments. In all sediments. In all instances Instance3 the of data data on on tectonic tectonicdiscriminant discriminantdiagrams diagrams the plots of (such as Tb2 (such Ti02- Fe203+MgO - Fe203+Mg0 and and K20/Na20 i a, 1903; -Th-Co, Tay 1 or K20/Na20-- Fe203+H@, Fe203+MgO,Bhat Bhatia, 1983;Hf Hf-Th-Co, Taylor and McLennan, HcLennan, 1985; 1905; SiO2/Al20 SiO$A120 - -K2O/Na20, K20/Na20* Roser Roser and and Korech, Korsch, 1907) conform3 wl th 1987) conforms with cratonic, passive passive margin, margin, or r ftenvironments. environments. There or rift is no There 1s no Indication lndicatlon of of orogenic orogenic associations(wbduction, (subduction,collision, collision, etc.). etc.). associations ? 22 �Ps As a test of hypotheses, the the composition composition of of Baraboo Baraboo interval interval exposures exposures further further (1984). The (above) of Greenberg supports supports model model CC (above) Greenberg and and Brown Brown (1984). The possibility possiblllty of of multiple multiple sequences (model (model B) sequences B) in ln combination with model model C is is also also compatible compatible with with the the data. data. However, most compelling imp1 ication of of Baraboo interval Interval study study continues continues to to be be Hwever* the most compel l ing implication that the sedimentary mamatic association association represents the the product product of of anorogenic anorogenic that sedimentary -- manatic Such case with many other Proterozoic processes. Such is is also the the case Proterozoic associations associations processes. (Athabasca - Thelon, melon, Gowler, (Athabasca Gowler* Jotnian, Jotnian, Roratma, Roraima,Haninamat). Hamamat). The The most reasonable reasonable age age for most Baraboo interval Similar though for most interval deposition depositlon remains near near 1760 1760 Ma. Ma. though less less evident episodes of of sedlmentation sedimentation could could also also be associated evident episodes associated with earlier earlier or or later later post-orogenicmagnatism manatin in in Wisconsin. Wisconsin. The Jotnian Jotnlan ciastics clastlcs of of Scandanavia Scandanavla were were post-orogenlc in multiple multiple generations separated In deposited in in time by pulses pulses of of felsic felsic to to bimodal bimodal anorogenic magnatim magnatism (Lundqvist Without extensive and accurate (Lundqvist 1979). 1979). Wlthout accurate isotopic Isotopic age exposures might appear all been contemporaneous. data, the Jotnian exposure3 appear to have all contemporaneous. - Tectonin Tectonlsn responsible responsible for for deformation deformation of of the the Baraboo Baraboo interval Interval outcrops outcrops is 1s not Some southward Some southward thrusting is is aa reasonable reasonable interpretation, interpretation, but but it would would likely influences, not It likely have been in in response to to anorogenic anorogenlc (tensional?) (tensional?) influences, not easily comprehended. comprehended. . orogenic. orogen 1c References References Bhatia, M.R., 1983, Plate tectonics Bhatla, M.R.? tectonics and geochemical composition composition of of sandstones: v. 91, 91* p. p. 611-627. 611-627. sandstones: Journal of Geology, Geology* v. Greenberg, J.K. J.K. and and Brown, Brown, B.A., B.A, 1984. Cratonic sedlmentation sedimentation during the 1984. Cratonlc Proterozoic: anorogenic connection In Proterozoic: an anorogenlc In Wisconsin Wlsconsln and and the the upper upper midwest: midwe&: Journal of Geology, Geology, v.92, v.92, p. p. 159-171. 159-171. LaBerge, G.L. G.L. and Klasner, Kiasner, J.S.. J.S., 1988, 1988, The Baraboo Quartzite: a new look lo& at an old problem: (abs.) 34th Institute problem: (abs.1 Institute on Lake Superior superior Geology, Geologyp Marquette, Marquette? MI, M I * p. p. 62-64. 62-64. Lundqvist, 19?9* The The Precambrian Precambrian of of Sweden: Sweden: Lundqvlst, T., 1979, Sveriges Geolgiska Sverlges Geolglska Undersokning, Undersokning* 87p. 87p. Roser, R.J., 1987, Roser* B.P. B.P. and Korsch, R.J., 198?* Determination of tectonic tectonic setting setting of of sandstone—mudstone suites using Si02 sandstone-mudstone suites S102 content and K20/Na20 K20/Na20 ratio: ratio: Journal of of Geology, v.95. Geology* v.95. 1986* Fluvial origin of the lower lower S o u t h ~ l c kD.L.* ~ Morey, G.B. Southwick, D.L., G.B. and Mossier* Mossier, J.H.* J.H., 1986, Proterozoic Quartzite* southwestern southwestern MN: MN: Geological Society of America Proterozoic Sioux SIOUX Quartzite, Bulletin, Bulletin* v.97, v.97* p. 1432-1441. 1432-1441. Taylor, S.R. S.R. and McLennan, S.M., S.M., 1985, 1985* The The Continental Crust: Crust: Evolution: Evolution: Oxford, Oxford, Blackwell, Blackwell, 312 312 p. p. 23 Its Composition and �Structure Structure of the Midcontinent Rift Rift System in Eastern Lake Superior: Preliminary heliminary Results Results from from 8-sec 8-sec Reflection Reflection Seismic Seismic Data Data and and Gravity Gravity and and Magnetic Magnetic Anomalies Anomalies Hinze and andD.N. D.N. Ravat Ravat(Dept. (Dept.of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences,Purdue PurdueUniversity, University, WJJ Hinze W West 47907;317-494-5982) 3 17-494-5982) West Lafayette, Lafayette, IN 47907; McGimis(Engineering (Engineering Geosciences, Geoscience~~ Argonne National National Lab, Lab, 9700 9700 South South Cass Cass L DD McGinnis Argonne Avenue, Avenue*Argonne, Argonne*IL IL 60439; 60439;312-972-8722) 312-972-8722) W WFF Cannon Cannon (USGS, (USGS, Mail Mail Stop Stop 954, 954, Reston, VA 22092; 22092;703-648-6345) 703-648-6345) B B Milkereit Mikereit (Geol. (Geol. Survey Surveyof of Canada, Canada,11Observatory ObservatoryCrescent, Crescent*Ottawa, Ottawa,Ontario, Ontario,Canada Canada K1A KIA 0Y3; OY3: 613-995-5490) 613-995-5490) JJ L L Sexton Sexton (Dept. of Geology, ~ e o l o &Southern * Southern Illinois Illinois University, Carbondale, IL IL 62901; 62901;618618453-3351) 453-335 - - - - - 1) H H FF Wang Wang (Dept. $ePt. of of Geology Geologyand and Geophysics, Geophysics,Univ. Univ. of of Wisconsin, Wisconsin,Madison, Madison*WI WI 53706; 53706; 608-262-5932) 608-262-5932) Seismic Seismic reflection, reflection, gravity, gravity, and and magnetic magnetic anomaly anomaly data data confirm confirm GLIMPCE GLIMPCE interpretations interpretations of the the structural structural style style of of the theMidcontinent MidcontinentRift RiftSystem Systeminineastern easternLake Lake Superior. Superior. InIncontrast contrasttotointerpretations interpretationsmade madeprior priortotoseismic seismicreflection reflectionstudies, studies,eastern eastern Lake Superior Superior is shown shown to to be beunderlain underlain by by a arelatively relativelysymmetric symmetric folded folded graben graben Lake consisting of a thick consisting of thick (>15 (>I5 km) km) btsal b m l layer layerof of mafic mafic volcanic volcanicrocks rocksoverlain overlain by by clastic clastic km sedimentary rocks sedimentary rocks reaching reachingthicknesses thicknessesofofthe theorder orderofof7.5 7.5km. km. A A seismic seismic line line=20 20 km from from the the southern southern shoreline shorelineof of the the lake lakeshows showsthat thatthe thegraben grabencontinues continuesfrom fromthe thecenter center of of the the lake lake into intothe theeastern easternNorthern NorthernPeninsula Peninsulaof ofMichigan Michiganwith withonly onlyminor minorattenuation. attenuation. The The western western margin margin of the the graben graben occurs occurs in the the vicinity of of Grand Grand Island. No Noevidence evidenceof of volcanic volcanic rocks are seen west west of the the graben graben near the southern southern shoreline. shoreline. AA broad broad arch arch with with a relief relief of 3=3km kmoccurs occursoff offDeer DeerPark, Park,MI MI atat =47°N, 47ON, 85°45'W. 85'45'W. The Theaxis axisof of the the graben graben is is interpreted interpretedto to lie lietotothe thewest westofofthe thearch archininthe thevicinity vicinityofofAu AuSable SablePoint, Point*MI. MI. Thick (= km) Keweenawan east of of Keweenawan sedimentary sedimentary rocks rocks overlying volcanic rocks occur east Thick ( 77 1cm) the thearch archassociated associatedwith withaagravity gravityminimum minimumatatthe theend endof ofthe theseismic seismicline. line. Seismic Seismic reflection reflection data dataare areobtained obtainedunder underlicense licensefrom fromGrant GrantNorpac Norpacand andstudies studiesare are supported supportedin in part part by by the theU.S. U.S. Dept. Dept.ofofEnergy, Energy*Office OfficeofofEnergy EnergyResearch Researchunder undercontract contract W-31-109-Eng-38. W-3 1-109-Eng-38. 24 �Preliminary Preliminaw constraints constraintson on the the P-T P-T evolution evolution of of the the Penokean Penokeanorogeny oroaenxeast-central east-centralMinnesota. Minnesota. D.K. D.K. HoIm Holm and and J. Selverstone, Selverstone, Dept. of Earth Earth and and Planetary PlanetarySciences, Sciences,Harvard HarvardUniversity, Universrty,Cambridge, Cambridge,MA, MA, 02 138. 02138. New petrologic Newand andimproved improved petrologictechniques techniques have haveincreased increasedour our understanding understanding of of regional regionalmetamorphism metamorphism during constraints to be made models. Detailed during collision collisionand and allow allow important constraints made on plate tectonic models. Detailed petrologic petrologic studies successful in terrane to studies of of orogenic orogenicbelts beltshave have been successful in using using the metamorphic signature of a terrane to evaluate evaluate the the tectonic tectonic development developmentof of aa region regionand and to to quantify quantifythe thepressure-temperature pressure-temperatureevolution evolutionduring duringorogeny. orogeny. Such Such a study study is is here here applied to rocks rocks which have have been been multiply multiply deformed and metamorphosed metamorphosed during during the Penokean Penokean orogeny. This Thistechnique technique is is particularly paflicularlyuseful usefulinineast-central east-centralMinnesota Minnesotawhere whereconventional conventional geologic very geologic mapping mappingIs is highly highly limited limited by v e v poor poor exposure. exposure. The The Penokean Penokeanorogeny orogeny was was aa major major early early Proterozoic Proterozoic(1875-1825 (18751825Ma) Ma)tectonic tectonicevent eventin inthe theGreat GreatLakes Lakes region. region. Holm Holmand andothers others(1988) (1988)have have proposed proposed aa plate-tectonic plate-tectonicmodel modelfor for the the Panokean Penokean orogeny orogeny based based on of metamorphism metamorphism and and structural structural geology. geology. Their model incorporates incorporates on strain strain analysis, conditions of continental continentalrifting rifting followed followed by by footwall footwall deformation deformation associated associatedwith with oblique oblique continental continental convergence convergence (A-type of the the footwall footwall onto the hangingwall during uplift associated associated with (A-type subduction) subduction) and imbrication of continued continued convergence. Early EarlyProterozoic Proterozoicsupracrustal supracrustalrocks rocks(Denham (Denhamand and Thomson ThomsonFormations) Formations)have have been been multiply multiply deformed deformed and and highly metamorphosed metamorphosed during during the the Penokean Penokean orogeny, with metamorphic metamorphic grade grade increasing increasing from from north north to south. Petrographic Petrographicanalysis analysisof ofthese theserocks rocksindicates indicatesprogressive progressive metamorphism metamorphismduring during an an early early phase of deformation deformationthat thatproduced producedsynkinematic synkinematic (rotated) (rotated)garnet garnet porphyroblasts schistosity. The porphyroblastsand and aa wall-developed welldeveloped schistosity. Thethermal thermalpeak peakof of metamorphism, metamorphism, however, however, occurred occurred after aa later indicated by staurolite later phase phase of of deformation, as indicated staurolite porphyroblasts porphyroblastsoverprinting overprinting both both the the primary primav schistosity schistosQ and and aa younger younger crenulation crewlation cleavage. cleavage. We We have have collected collectedsamples samples across across an an approximately approximately15 15km kmNE-SW NE-SWtransect transect in in garnet garnetand andstaurolite staurolitegrade grade rocks Thomon Formation. Formation. Temperature Temperatureand andpressure pressureestimates estimates of of final final equilibration equilibrationwere were obtained obtained rocks of of the the Thomson using using the the thermobarometric thermobarometrictechniques techniques (on (onrim rimanalyses) analyses)of ofFerry Ferryand andSpear Spear(1978) (1978)and andGhent Ghentand andStout Stout (1981) modified by Hodges and and Crowley Crowley (1%). (1985). The northern most samples of of garnet garnet grade rocks (1981) as modified (Moose temperatures of 440-500° C. Farther (Moose Lake Farther south south in in garnet garnet grade grade rocks rocks h k e area) area) give final equilibration temperatures 440-500ÂC. final final equilibration equilibrationtemperatures temperatures of 470-520° 470-520 C and and a a pressure pressure of around around 6 kb are obtained. Staurolite Staurolitegrade grade Thomson Thomon Formation Formationsamples samples (just (just north north of the Denham DenhamFormation) Formation)give give final equilibration equilibrationtemperatures temperaturesof of 520-590° C and and aa pressure pressureof of around around77 kb. kb. 52G590ÂC Staurolite staurolite+garnet+plagioclase+ Staurolitegrade grade Thomson T h o m n Formation Formation contains contains the the assemblage awmblage staurolite+garnet+plagioclase+ chlorite+muscovite+biotite+quartz. chlorite+muscovite+biotite+quartz.Garnet Garnetshows showsaasystematic systematiccompositional compositionalzoning zoningof of increasing increasing spessartine spessartine and and grossular g r o w l a r content content and decreasing decreasingalmandine almandinecontent contentfrom from rim rimto to core. core. Inclusion-rich surrounded by haloes haloes of inclusion-free two stages of Inclusion-rich(quartz) (quartz) garnet cores surrounded inclusion-free garnet suggest two 25 �contact with garnet growth. Microprobe Microprobeanalyses analyses of piagioctase plagioclase in in contact with garnet indicates indicates two coexisting coexisting plagioclase compositions An attempt attempt was made to plagioclase compositions (albite, (albite,XAnO-O.O5 X ~ ~ = 0 - 0 . 0and 5 oligoclase, XAn"O.23-O.28). X~~'O.23-0.28). An model changes in P and T T using using the the Gibbs Gibbs method method on ongarnet garnet rim rim and and core core analyses. analyses. Assuming oligoclase with garnet garnet and using using almandine and and grossular grossular as as monitors, Gibbs as the plagioclase plagioclase phase in equilibrium with method modelling on two different garnets suggests no change in temperature temperature and an increase in pressure of 1.5-2.0 kb during during garnet garnet growth. growth. This result is 1S2.0 kb is consistent with the model of Holm Holm and others In which which early early formed formed structures structures and and progressive progressive metamorphism metamorphism are considered considered related footwall (1988) in relatedto to footwall deformation southward-directed subduction. subduction. AAsimilar deformation during during southwarddirected similarisothermal isothermalcompression compressionpath pathwas wasobtained obtained by Crawford Crawford and Mark Spear and and Selverstone Selverstone (1983) (1983) on on samples samplesfrom fromthe the lower lower plate plate of a thrust thrust Mark (1982) and Spear modelling predicts predicts a large large change in anorthite anorthite nappe. Our Our results results are are problematic problematic however as the modelling composition (+0.30) composition (+0.30) that is not not observed observed in our samples. Two stage (Xalm,spess) in in the inclusion-rich inclusion-richand and inclusion-free inclusion-free stage modelling modellingusing using compositional compositionalchanges changes(Xaim,spess) staurolite as a phase only for the areas of garnet and and including including staurolite the second stage stage of garnet garnet growth growth again againgives gives no temperature change and only a slight decrease in pressure during garnet growth (60 (60 bars). This Thisresult, result, if real, suggests rapid rapid growth of garnet and high rates of strain. Rapid Rapidgrowth growthrates ratesreported reportedininthe theliterature literature range range from from 0.6-1.5 0.6-1.5 mm/Ma mmIMa (Christensen (Christensen and others, others. 1988; 1988; Staude Staude and and Selverstone, Selverstone, 1988). 1988). Using Usingthese these growth growth rates, rates, the the amount amount of rotation rotationrecorded recordedby by the the garnet garnetduring duringits itsgrowth growthImplies impliesaaminimum minimumshear shear strain strain rate rate of 37.1O14 3-7.10-14Is1s(not (notconsidering consideringbulk bulk strain strainin inthe the matrix). matrix). Assuming Assumingaaslower sloweraverage averagegrowth growthrate rate 0.1 m mm/Ma minimumshear shearstrain strainrate rateofof1.4.1~14 1.4.10- Is. of 0.1 M a gives aa minimum are preliminary preliminary and much further work is We emphasize that the results presented here are Is needed needed to to quantify pressures, pressures, temperatures, strain rates, etc. associated associated with with the the deformational deformationalhistory historyof ofthis thisarea. area. these results indicate indicate that, that, with with further further work, work, such such constraints constraints can can be be obtained obtained and and will will greatly greatly However, these understanding of crustal deformation deformation as well as improve enhance our understanding improve our knowledge knowledge of plate-tectonic plate-tectonic processes processes back back into into the the Precambrian Precambrianera. era. F research has been supported supported by by a Sigma XI grant-in-aid of research research to to Daniel K. K. Holm Hoim and and by by NSF This research Sigma Xi NSF EAR8648145 to to Jane Jane Selverstone. Selverstone. grant EAR86-58145 RaferercBS Christensen, J.N., J.L., DePaolo, D.J., J.N., Rosenfeld, Rosenfeld, J.L.. D.J., 1988, 1988, Eos, 69, p. 508. Crawford, M.L, M.L. and and Mark, Mark, LE., LE., 1982, 1982, Canadian CanadianMineralogist, Mineralogist,20, 20,p.p.333-347. 333-347. J.M., and Spear, Spear, F.S., F.S., 1978, 1978, American American Mineralogist, 64, p. p. 966-985. Ferry, J.M., Mineralogist, 64, Ghent, E., and and Stout, Stout, M., M.. 1981, 1981, Contributions Contributionsto toMineralogy Mineralogyand andPetrology, Petrology,76, 76, p. p. 92-97. 92-97. Hodges, K.V., and Crowley, Crowley, P.D. K.V., and P.D. 1985, American American Mineralogist, Mineralogist, 70, 70, p. p. 702-709. 702-709. Holm, D.K., 1988, Geological Geological Society of America Bulletin, 100, p. p. 1811-1818. 1811-1818. D.K., HoIst, Hoist. T.B., T.B.. and Ellis, M., M., 1988, F.S., and and Selverstone, Selverstone,J., J., 1983, 1983, Contributions to Mineralogy 83, p.p.348-357. 348-357. Spear, F.S., Mineralogy and Petrology, Petrology, 83, Staude, J-M., J-M., and and Selverstone, Selverstone,J.,J.,1988, 1988,Geological GeologicalSociety Societyof ofAmerica America Ab. Ab. w. w. Prog., Prog., 20, 20, p. Staude. p. A332. A332. 26 �THE PENOKEAN PENOKEAN OROGENY OROGENY IN IN MINNESOTA MINNESOTA AND UPPER UPPER MICHIGAN: MICHIGAN: THE A COMPARISON COMPARISON OF OF THE THESTRUCTURAL STRUCTURAL GEOLOGY GEOLOGY OF OF THE THEMICHIGAMME MICHIGAMME AND THOMSON FORMATIONS FORMATIONS Timothy B. B. Hoist Hoist Department Department of of Geology, Geology, University University of Minnesota Duluth Duluth Duluth, Minnesota 55812 Minnesota 55812 An An examination examination of mesoscopic mesoscopic structures structures and and microstructures microstructures and and aa preliminary strain analysis Formation along along aa transect from preliminary strain analysis in in the theMichigamme Michigamme Formation from Covington to Iron Michigan,reveal revealaa striking striking similarity to the Covington to Iron Mountain, Mountain, Michigan, similarity to the structural structural geology geology of of the the Thomson Thomson Formation Formation in in east-central east-centralMinnesota. Minnesota. In In Minnesota there are are two different structural structural terranes, terranes, as as there are Minnesota there two distinctly distinctly different are along this transect transect in inMichigan. Michigan. along In the northern northern terrane terrane in inMinnesota, Minnesota, the dominant structural features features are aa single set of of open open to to close, close, upright, upright, sub-horizontal, sub-horizontal, east-west east-west trending trending folds, folds, with with a single, foliationthat thatisis axial axial'planar planar to to the single, well-developed well-developed foliation the folds. folds. Where fold fold axial surfaces are are not not dipping vertically, the the vergence vergence isis to to the north, axial surfaces dipping vertically, north, with with axial axial axes are sub-horizontal surfaces dipping dipping steeply south. south. Fold Fold axes sub-horizontal except except where where folds folds die out 60° The The foliation is aa out rapidly rapidly along along strike, strike,where where axes axes may may plunge plunge up up to to600. continuous slaty cleavage cleavage in fine-grained fine-grained units and aa disjunctive disjunctive spaced spaced cleavage cleavage the coarse-grained coarse-grainedgraywacke graywacke beds. beds. At At several several places kink bands bands deform deform this this in the foliation, indicating aa small foliation, indicating small amount amount of of late late sub-vertical sub-vertical shortening. shortening. Deformed Deformed concretions, mud mud chips, and a thin thin conglomerate conglomerate unit allow allow the determination determination of of finite strain strain in in the the northern northern terrane. terrane. finite Strain shapes plot plot in Strain ellipsoid ellipsoid shapes in the the flattening field ratios averaging field (0<k<1) X:Y:Z ratios averaging approximately approximately 7:4:1. 7:4:1. Z Z is is (O<k<l)with X:Y:Z The horizontal and and oriented north-south. north-south. The east-west, east-west, vertical foliation approximates the XY plane of the strain XY plane strainellipsoid. ellipsoid. In Michigan, in the Michigan, in the area area from from Covington Covington south south to tothe theBaraga BaragaCounty-Iron County-Iron County line (a (a distance of about County line distance of about 15 15 km) km) structures structures similar similar to to the the northern northern terrane in in Minnesota Minnesota are found. found. AAsingle single foliation foliation is is found, found, again again aa continuous continuous slaty cleavage in the fine-grained units and a disjunctive in the cleavage in fine-grained units disjunctive space space cleavage cleavage in coarse-grained graywackebeds. beds. The attitude coarse-grained graywacke attitude of of the thecleavage cleavagechanges changessomewhat somewhat from north to south from north south along along the the transect, transect, and and is isaxial axial planar planar to, to,and andshows shows normal normal bedding-cleavage vergence relationships relationships (between (between slate slate and greywacke bedding-cleavage vergence greywacke beds) beds) to to folds are are upright upright in in the southern some folds that that exist. some mesoscopic mesoscopic folds exist. These These folds southern part part of of the transect, transect, but but axial axial surfaces surfaces dip dip as as gently gently as as 40 40to to50° 50Âsouth southatatCovington, Covington, Where showing showing northward northward vergence. vergence. Where fold fold axes axes can can be be found, found, they are are sub-horizontal, and bedding-cleavage bedding-cleavage intersections along along the transect transect are sub-horizontal, kink bands bands also also exist exist here, here, and sub-horizontal. Late-stage Late-stage kink and are are also also gently gently sub-horizontal. concretionsand andmud mudchips chipsexist existinin these these rocks, Deformed concretions rocks, and and aa dipping. Deformed preliminary analysis reveals revealsflattening flatteningstrains strainssimilar similartoto those those in the preliminary analysis the northern northern terrane in in Minnesota. Minnesota. 27 �In the southern In southern terrane terrane in inMinnesota, Minnesota, two two main main periods periods of of folding folding have been identified. Early phase (Fj Early phase (F,) folds folds are are isodlinal isoclinal and and recumbent, recumbent, with with east-west east-west F folds as much folds as much as a meter meter or or so so in inamplitude amplitude and and trending fold fold axes. axes. Minor Minor F, wavelength have been been observed, observed, but but nappe-scale nappe-scale structures structures of of this phase wavelength have phase have have been been interpreted interpreted based based on onseveral severallines linesofofreasoning reasoningincluding includingbedding-cleavage bedding-cleavage vergence relationships relationships and facing directions of folds. An vergence of F3 F, folds. An early early foliation, foliation, axial axial planar ttoo these folds, is found found throughout throughout the the southern southern terrane. terrane. As planar folds, is As the the folds folds are are isoclinal and and hinge hinge regions regions of of folds folds are are rare, this isoclinal this foliation foliation is is nearly nearly always always sub-parallel to to bedding. bedding. A found in in the southern sub-parallel A second second phase phase of of folding folding (F2) (FJ isis found southern terrane in Minnesota. style, attitude, attitude, and geometry to terrane Minnesota. These These folds folds are of similar similar style, geometry to the only found in in the the northern terrane. spaced crenulation crenulation cleavage cleavage is the only folds folds found terrane. AAspaced widespreadin in the the southern southern terrane, terrane, in an attitude widespread attitude which which is axial axial planar to to the the F2 F, folds. folds. A A strong strong lineation lineation exists, parallel parallel to the the intersection intersection of of the the two two foliations. foliations. Strain analyses in the southern terrane in Minnesota from deformed conglomerate clasts and and mud mud chips chips indicate indicate that that very conglomerate clasts very large large flattening flattening strains strains accompanied the development of the early accompanied the development of early folds folds and and foliation. foliation. In the the Thomson Thomson Formation Formation in Minnesota, Minnesota, metamorphic metamorphic grade increases progressively progressively from from north to south. The structural geology The geology of of rocks exposed exposed in Michigan Michigan aatt Horse Horse Race Race Rapids Rapids just south just south of of Crystal Crystal Falls, Falls, and at a t Steele Steele Farm Farm and and along along the Sturgeon Sturgeon River River just is quite quite similar similar to the structural north of Iron Mountain, Mountain, is structural geology geology of rocks in the the southern terrane and distinctly distinctly different different from fromthe the rocks rocks of southern terrane in Minnesota, Minnesota, and of the northen terrane in the area northen terrane in Michigan, Michigan, in area just just south southofofCovington. Covington. In In this this The early southern terrane in southern in Michigan Michigan two phases phases of of folding folding are also also found. found. The early phase phase is again again isoclinal isoclinal and and recumbent, recumbent, and and there thereisisa awell-developed well-developed foliation foliation axial planar to to the the folds. foldhinges hinges are arequite quiterare rareso sothis thisfoliation foliation isisusually usually axial planar folds. FF,fold F2 folds open, upright, and found to be sub-parallel sub-parallel to bedding. Fa folds are open, crenulation cleavage cleavageisis found found in in some some places, A spaced spaced crenulation places, in an an sub-horizontal. A is found that isis attitude which which is axial axial planar planar to to the theF'2 Fafolds. folds. A A lineation lineation is found that parallel parallel tto o the intersection intersection of of the the two two foliations, foliations, and and the the metamorphic metamorphic grade grade of of No the rocks rocks in the the southern southern terrane terrane is is higher higher than than in in the the northern northern terrane. terrane. N o strain analysis analysis has been been done in the the southern southern terrane terraneininMichigan. Michigan. The region region of the the boundary between the the northern northern and and southern is not of boundary between southern terrane in Michigan Michigan is as well as is the the northern well exposed exposed as the boundary boundary region region between between the northern and and southern southern It is in that the terranes in in Minnesota. Minnesota. It in this this region region in in Minnesota Minnesota that the best best evidence evidence for nappe-scale structure is found. Based on the similarities for nappe-scale structure found. Based on similarities in structural structural geology in both both northern northern and and southern southern terranes terranes in in the rocks geology in rocks in in Minnesota Minnesota and and Michigan, is suggested that the early in the southern Michigan, itit is suggested that early phase phase of of deformation deformation in southern terrane in Michigan did involve involveaa great great deal deal of of strain, and the terrane Michigan did the development development of of large-scale features features probably probably including including fold fold and and thrust thrust nappes. large-scale nappes. 28 �The Mining and and Geologic History H i s t o r y of of the t h e Silver S i l v e r Islet I s l e t Mine, Mine, and and aa Conceptual Conceptual Ore Genesis Model for Ore f o r the t h e Deposit. Deposit. By Robert Robert J. J. Horton Horton Silver miles s llocated o c a t e d 20 m i l e s east e a s t of of Thunder Bay, Bay, about 3/4 3/4 of of aa mile mile S i l v e r Islet I s l e t iis s i l v e r vein v e i n discovered d i s c o v e r e d on on the the ooff f f the t h e Sibley S i b l e y Peninsula Peninsula in i n Lake Lake Superior. S u p e r i o r . A silver island million i s l a n d produced produced an eestimated stimated 3 m i l l i o n ounces of of silver s i l v e r during d u r i n g a 16 16 year year period p e r i o d from from 1868 1868 to t o 1884. 1884. The island, i s l a n d , roughly 10 10 feet f e e t high high and and 80 80 feet f e e t in in i s located l o c a t e d aatt tthe h e intersection i n t e r s e c t i o n of of a steeply s t e e p l y dipping d i p p i n g gabbroic g a b b r o i c dike, dike, ddiameter, i a m e t e r , is h o s t e d in i n flat f l a t lying l y i n g sediments, sediments, and a fault f a u l t zone zone that t h a t strikes s t r i k e s perpendicular p e r p e n d i c u l a r to to hosted the t h e dike. dike. The silver s i l v e r ore o r e occurs o c c u r s only o n l y in i n the t h e portion p o r t i o n of of the t h e vein v e i n confined confined within ore w i t h i n the t h e dike; d i k e ; the the o r e abruptly a b r u p t l y stops s t o p s where the t h e vein v e i n intersects i n t e r s e c t s the the sediments. Following i s aa b r i e f summary of of the t h e mining and and geologic g e o l o g i c history history Following is brief and a ore o r e genesis g e n e s i s model model for f o r the t h e Silver S i l v e r Islet I s l e t deposit. deposit. MINING M I N I N G HISTORY prospector Joseph Woods patented IIn n 1845, 1845, p r o s p e c t o r Joseph p a t e n t e d 6400 6400 acres a c r e s along a l o n g the t h e Sibley Sibley Peninsula which he sold to the Montreal Mining Company the following P e n i n s u l a which he s o l d t o t h e Montreal t h e f o l l o w i n g year. year. In The "Woods "Woods Patent" Patent" lay l a y idle i d l e for f o r over o v e r 20 20 years. years. I n 1868, 1868, in i n an attempt a t t e m p t to to mining aactivity Ontario, iincrease n c r e a s e mining c t i v i t y iin n O n t a r i o , the t h e Crown levied l e v i e d a two two cent c e n t per per acre a c r e tax tax on mining This iinspired mining lands. lands. This n s p i r e d the t h e Montreal Mining Company Company to t o evaluate e v a l u a t e their their holdings, On July J u l y 10, 10, 1868, 1868, while w h i l e conducting conducting aa h o l d i n g s , including i n c l u d i n g the t h e Woods Patent. Patent. sshoreline h o r e l i n e survey, survey, an eexploration x p l o r a t i o n party p a r t y lead l e a d by by Thomas Thomas MacFarlane landed landed on on what is and d discovered i s now Silver S i l v e r Islet I s l e t and i s c o v e r e d the t h e silver s i l v e r bearing b e a r i n g vein. vein. Five days what The ore later, l a t e r , 1,336 1,336 pounds pounds of of ore o r e was was shipped shipped to t o Montreal. Montreal. o r e assayed assayed at a t 2,087 2,087 Montreal Mining Company ounces of silver s i l v e r per per ton. ton. The Montreal Company worked Silver S i l v e r Islet Islet until u n t i l mid 1870, 1870, producing producing 27,124 27,124 pounds of of ore o r e assayed assayed at a t $25,043.06. $25,043.06. In August of August of 1870 1870 the t h e company sold s o l d all a l l its i t s north n o r t h shore s h o r e holdings h o l d i n g s for f o r $225,000. $225,000. The major obstacle o b s t a c l e facing f a c i n g the t h e newly formed formed Silver S i l v e r Islet I s l e t Mining Mining Company Company The entire was flooding f l o o d i n g and and storm storm damage. damage. e n t i r e mine was was below below lake l a k e level l e v e l and and increasingly i n c r e a s i n g l y larger l a r g e r pumps were required r e q u i r e d when new new leaks l e a k s were were encountered encountered as a s the the workings expanded. expanded. The mine was also a l s o vulnerable v u l n e r a b l e to t o violent v i o l e n t southerly s o u t h e r l y storms storms In which generated g e n e r a t e d waves large l a r g e enough to t o wash completely completely over over the t h e island. island. I n an an attempt mine from storm damage, a t t e m p t to t o protect p r o t e c t the t h e mine damage, aa cofferdam cofferdam was was constructed constructed In around the t h e shaft s h a f t and a wooden breakwall b r e a k w a l l around around the t h e island. island. I n December, 1874, 1874, a violent 350 feet f e e t of of the t h e islands' i s l a n d s ' protective protective v i o l e n t southeasterly s o u t h e a s t e r l y storm swept away 350 breakwall, b r e a k w a l l , composed composed of of 20,000 20,000 feet f e e t of of timber, t i m b e r , 7.5 7.5 tons t o n s of of bolts, b o l t s , and and 5,000 5,000 of rock; and d destroyed of the ttons o n s of rock; and e s t r o y e d some of t h e mines above ground structures. s t r u c t u r e s . An expanded breakwall breakwall was rebuilt, r e b u i l t , to t o act a c t as a s aa buffer b u f f e r against a g a i n s t the t h e waves, waves, that that mine operated iincreased n c r e a s e d the t h e size s i z e of of the t h e original o r i g i n a l island i s l a n d 30 30 fold. fold. The mine operated continuously c o n t i n u o u s l y from from 1870 1870 to t o 1884 1884 except e x c e p t for f o r periods p e r i o d s devoted devoted to t o exploration exploration drilling shipment of of coal c o a l failed f a i l e d to t o arrive arrive d r i l l i n g and and repair r e p a i r of of storm storm damage. damage. A shipment 1884, when during d u r i n g the t h e fall f a l l of of 1883, 1883, causing c a u s i n g the t h e mine to t o flood f l o o d on on January J a n u a r y 20, 20, 1884, Att this A t h i s point p o i n t the t h e mine had reached reached aa tthe h e pumps stopped for f o r lack l a c k of of fuel. fuel. depth and produced an ttotal otal d e p t h of of 1,230 1,230 ffeet, e e t , and a n estimated e s t i m a t e d 3,044,000 3,044,000 ounces ounces of of silver s i l v e r worth $3,500,000. $3,500,000. 29 �GEOLOGIC GEOLOGIC SETTING SETTING The The geology geology of of the t h e region r e g i o n consists c o n s i s t s of of an an Archean Archean basement basement unconformably unconforraably overlain i s part p a r t of of the t h e Wawa— Wawao v e r l a i n by by Proterozoic P r o t e r o z o i c sediments. s e d i m e n t s . The The Archean Archean basement basement is Shebandowan Shebandowan subprovince, s u b p r o v i n c e , composed composed of of mafic m a f i c and and felsic f e l s i c volcanogenic v o l c a n o g e n i c rocks, rocks, minor minor sedimentary s e d i m e n t a r y units, u n i t s , and and felsic f e l s i c and and mafic m a f i c plutonic p l u t o n i c rocks; r o c k s ; with w i t h aa greenschist g r e e n s c h i s t metamorphic metamorphic grade. g r a d e . Jinconformably Unconformably ooverlying v e r l y i n g this t h i s intensly i n t e n s l y deformed deformed greenstone g r e e n s t o n e belt b e l t are a r e the t h e relatively r e l a t i v e l y flat—lying f l a t - l y i n g Proterozoic P r o t e r o z o i c sediments s e d i m e n t s of of the the Gunflint G u n f l i n t and and Rove Rove Formations. Formations. The The Cunflint G u n f l i n t Formation Formation consists c o n s i s t s of of an an iron—rich iron-rich assemblage assemblage of of stratified s t r a t i f i e d sediments. s e d i m e n t s . The The Rove Rove Formation F o r m a t i o n is i s an a n extensive extensive sedimentary s e d i m e n t a r y deposit d e p o s i t composed composed of of black b l a c k pyritic p y r i t i c shale, s h a l e , argillite, a r g i l l i t e , and and graywacke. i s disconformably disconformably graywacke. The The Rove Rove Formation, F o r m a t i o n , up up to t o 1200 1200 feet f e e t thick, t h i c k , is overlain o v e r l a i n by by the t h e Sibley S i b l e y Group Group redbed redbed sedimentary s e d i m e n t a r y sequence. sequence. These These rocks rocks have have been been intruded i n t r u d e d by by diabase d i a b a s e and and gabbro gabbro dikes. dikes. In I n the t h e vicinity v i c i n i t y of of southeasterly s o u t h e a s t e r l y dip. d i p . The The trending t r e n d i n g dike d i k e swarm. swarm. AA the t h e dikes d i k e s and and sediments sediments Silver S i l v e r Islet, I s l e t , the t h e Rove Rove formation f o r m a t i o n has h a s aa shallow shallow sediments s e d i m e n t s are a r e intruded i n t r u d e d by by aa steeply s t e e p l y dipping, d i p p i n g , northeast northeast series s e r i e s of of parallel, p a r a l l e l . faults, f a u l t s , striking s t r i k i n g northwesterly, n o r t h w e s t e r l y , cut cut and and show show 300 300 feet f e e t of of vertical v e r t i c a l displacement. displacement. The N. 500 50' E., E., dips d i p s 75 75 degrees d e g r e e s to t o the the The Silver S i l v e r Islet I s l e t dike d i k e strikes s t r i k e s N. southeast, s o u t h e a s t , and and is is 350 350 feet f e e t wide wide at a t the t h e surface, s u r f a c e , thinning t h i n n i n g to t o 250 250 feet f e e t at a t aa depth d e p t h of of 560 560 feet. f e e t . The The gabbro gabbro dike d i k e has h a s aa metamorphosed metamorphosed contact c o n t a c t with w i t h the t h e host host sediments, is impregnated impregnated with w i t h graphite graphite s e d i m e n t s , has h a s assimilated a s s i m i l a t e d blocks b l o c k s of of shale, s h a l e , and and is and and pyrite. p y r i t e . The The dike d i k e has h a s aa considerable c o n s i d e r a b l e length, l e n g t h , extending e x t e n d i n g at a t least l e a s t 1600 1600 feet feet to t o the t h e northeast n o r t h e a s t and and 1200 1200 feet f e e t southwest s o u t h w e s t of of the t h e island. i s l a n d . Along Along strike, s t r i k e , the the dike d i k e is i s thought thought to t o outcrop o u t c r o p on on other o t h e r islands i s l a n d s over o v e r aa distance d i s t a n c eofof 6060miles. m i l e s . The The Silver S i l v e r Islet I s l e t vein v e i n varies v a r i e s in i n width w i d t h from from aa few few inches i n c h e s to t o 50 50 feet, f e e t , strikes s t r i k e s N. N. 350 35' W. W. and and dips d i p s 85 8 5 degrees d e g r e e s to t o the t h e southeast. s o u t h e a s t . The The vein v e i n has h a s aa strike s t r i k e length l e n g t h of of at at least is composed composed of of calcite, c a l c i t e , harite, barite, l e a s t 1800 1800 feet. f e e t . In I n the t h e sediments, s e d i m e n t s , the t h e vein v e i n is fluorite, f l u o r i t e , and and quartz; q u a r t z ; however, however, within w i t h i n the t h e confines c o n f i n e s of of the t h e dike d i k ethe t h e veins' veins' composition c o m p o s i t i o n is is aa fine f i n e grained, g r a i n e d , homogeneous homogeneous pink p i n k dolomite d o l o m i t ewith w i t h minor minorquartz. quartz. The i s generally g e n e r a l l y thicker t h i c k e r in i n the t h e dike d i k e than t h a n in i n the t h e sediments. sediments. The vein v e i n is The The vein v e i n contains c o n t a i n s both b o t h primary primary and and secondary s e c o n d a r y ore, o r e , which which always always occur o c c u r in in the t h e presence p r e s e n c e of of graphite. g r a p h i t e . About About 90 90 percent p e r c e n t of of the t h e ore o r e is i s primary, p r i m a r y , and and found found throughout is throughout the t h e mine n i n e in i n varying v a r y i n g degrees d e g r e e s of of richness. r i c h n e s s . The The primary primary ore o r e is composed composed of of silver, s i l v e r , argenite, a r g e n i t e , niccolite, n i c c o l i t e , galena, g a l e n a , sphalerite, s p h a l e r i t e , marcasite, marcasite, cobaltite, c o b a l t i t e , smaltite, s m a l t i t e , domeykite, d o m e y k i t e , chalcopyrite, c h a l c o p y r i t e , and and tetrahedrite t e t r a h e d r i t e in i n aa pink pink dolomite d o l o m i t e gangue. gangue. These These ore o r e minerals m i n e r a l s occur o c c u r as a s disseminated d i s s e m i n a t e d grains, g r a i n s , intergrown intergrown aggragrte a g g r a g r t eclusters, c l u s t e r s , and anddendritic d e n d r i t i cforms, forms, and and range r a n g eini n size s i z e from from microscopic microscopic to t o 33 mm mm. The The secondary s e c o n d a r y ore o r e occurs o c c u r s in i n groups g r o u p s of of pockets p o c k e t s irregularly irregularly distributed d i s t r i b u t e d throughout t h r o u g h o u t the t h e vein v e i n system. system. Deposited D e p o s i t e d as a s replacement r e p l a c e m e n t bodies, bodies, cavity v u g s , linings, l i n i n g s , and and veins, v e i n s , these t h e s e secondary s e c o n d a r y ores o r e s occur o c c u r at a t the the c a v i t y fillings, f i l l i n g s , vugs, surface is always always ini nclose close s u r f a c e to t o aa depth d e p t h of of 560 560feet. f e e t . The The secondary s e c o n d a r y ore o r e is proximity p r o x i m i t y to t o primary p r i m a r y ore. o r e . Secondary Secondary ore o r e minerals m i n e r a l s include i n c l u d e quartz, q u a r t z , calcite, calcite, barite, marcasite, b a r i t e , m a r c a s i t e , erhthrite, e r h t h r i t e , and and annabergite. a n n a b e r g i t e . Natie N a t i esilver s i l v e roccurs o c c u r sasa swires, wires, leaves, l e a v e s , and and nuggets, n u g g e t s , commonly commonly in i n clusters c l u s t e r s up up to t o 33 cm cm During the t h e operation operation During of of the t h e mine, mine, two two massive m a s s i v e secondary s e c o n d a r y deposits d e p o s i t s of of native n a t i v e silver s i l v e r were were discovered. winze d i s c o v e r e d . The The first f i r s t "Bonanza" "Bonanza" contained c o n t a i n e d721,632 721,632ounces ouncesofofsilver. s i l v e r . AA winze through t h r o u g h the t h e second second bonanza bonanza showed showed native n a t i v e silver s i l v e r on on four f o u r walls w a l l s for f o r aa length l e n g t h of of 60 60 feet. f e e t . The The following f o l l o w i n g scenario s c e n a r i o is i s aa conceptual c o n c e p t u a l model model for f o r the t h e Silver S i l v e r Islet Islet deposit. deposit 3. 3. . . 30 �ORE GENESIS GENESIS MODEL MODEL ORE The Archean Archean basement basement is i s aa source s o u r c e of of metamorphosed, metamorphosed, metal—rich, metal-rich, The v o l c a n e o g e n i c rocks. r o c k s . During During the t h e Archean—Proterozoic A r c h e a n - P r o t e r o z o i c unconformity u n c o n f o r m i t y (the (the volcaneogenic Eparchean Eparchean interval) i n t e r v a l ) the t h e Archean Archean rocks r o c k s were were exposed exposed to t o an a n extremely e x t r e m e l y long l o n g period period o f intense i n t e n s e physical p h y s i c a l erosion e r o s i o n and and unique unique chemical c h e m i c a l and and climatic c l i m a t i c environments, environments, of which produced produced aa deeply d e e p l y weathered weathered surface. s u r f a c e . This T h i s regional r e g i o n a l weathering w e a t h e r i n g profile profile which contained a variety of elements, derived from metal—rich Archean r o c k s , that that c o n t a i n e d a v a r i e t y o f e l e m e n t s , d e r i v e d from m e t a l - r i c h Archean rocks, were sorted, s o r t e d , fractionated, f r a c t i o n a t e d , and and concentrated c o n c e n t r a t e d by by laterization l a t e r i z a t i o n and and supergene supergene were p r o c e s s e s . With With the t h e onset o n s e t of of Proterozoic P r o t e r o z o i c sedimentation, s e d i m e n t a t i o n , the t h e weathering weathering processes. p r o f i l e was was buried b u r i e d and and preserved p r e s e r v e d in i n aa developing d e v e l o p i n gbasin. b a s i n . The The depth d e p t h of of burial burial profile If a sufficient geothermal gradient was i n c r e a s e d a s t h e b a s i n evolved. I f a s u f f i c i e n t g e o t h e r m a l g r a d i e n t was increased as the basin evolved. e s t a b l i s h e d , deep d e e p circulating c i r c u l a t i n g basinal b a s i n a l brines b r i n e s may may have have further f u r t h e r concentrate concentrate established, elements o r redistributed r e d i s t r i b u t e d them them to t o other other e l e m e n t s within w i t h i n the t h e buried b u r i e d lateritic l a t e r i t i c zone, zone, or h o r i z o n s . horizons. The intrusion i n t r u s i o n of of the t h e gabbro gabbro dikes d i k e s assisted a s s i s t e d in i n the t h e ore o r e genesis g e n e s i s in i n several several The The The dikes d i k e s contributed c o n t r i b u t e d to t o aa higher h i g h e r heat h e a t flow f l o w and and provided p r o v i d e d aa possible possible s o u r c e for f o r additional a d d i t i o n a l metals m e t a l s and and fluids. f l u i d s . The The dikes d i k e s also a l s o partitioned p a r t i t i o n e d the the source sedimentary s e d i m e n t a r y pile p i l e and and the t h e underlying u n d e r l y i n g basement basement rocks r o c k s into i n t o restricted r e s t r i c t e d circulating circulating c e l l s . Most Most importantly, i m p o r t a n t l y , after a f t e r solidification s o l i d i f i c a t i o n and and subsequent s u b s e q u e n t faulting, f a u l t i n g , the the cells. dike d i k e provided p r o v i d e d aa conduit c o n d u i t and and host h o s t rock rock for f o r ascending a s c e n d i n g ore—bearing o r e - b e a r i n g fluids. fluids. Hydrothermal Hydrothermal fluids f l u i d s obtained o b t a i n e d metals m e t a l s from from the t h e lateritic l a t e r i t i c horizon h o r i z o n located l o c a t e d within within the t h e restricted r e s t r i c t e d circulating c i r c u l a t i n g cells c e l l s adjacent a d j a c e n t to t o the t h e Silver S i l v e rIslet I s l e tdike. d i k e . Heat Heat was was provided p r o v i d e d by by the t h e geothermal g e o t h e r m a l gradient, g r a d i e n t , supplimented s u p p l i m e n t e d by by the t h e Keweenawan Keweenawan rifting rifting and associated a s s o c i a t e d intrusive i n t r u s i v e events. e v e n t s . The The fault, f a u l t , produced produced during d u r i n g later l a t e r stages s t a g e s of of and t h e rifting r i f t i n g event, e v e n t , provided p r o v i d e d a aconduit. c o n d u i t . Primary the P r i m a r y ore o r e was was deposited d e p o s i t e d over o v e r aa relatively The r e l a t i v e l y short s h o r t period p e r i o d of of time, t i m e , in i n aa graphite g r a p h i t e rich r i c h portion p o r t i o n of of the t h e dike. d i k e . The primary p r i m a r y ore o r e was was precipitated p r e c i p i t a t e d by by reductions r e d u c t i o n s in i n temperature, t e m p e r a t u r e , pressure, p r e s s u r e , and and r e d u c i n g conditions c o n d i t i o n s confined c o n f i n e d within w i t h i n the t h e dike. d i k e . Secondary S e c o n d a r y ore o r e deposits d e p o s i t s formed formed reducing o v e r aa relatively r e l a t i v e l y long l o n g period p e r i o d of of time, t i m e , possibly p o s s i b l y as a sepitherrnal e p i t h e r m a l or o r mesothermal mesothermal over systems i t as a s cavity cavity systems leached l e a c h e d silver s i l v e r out o u t of of the t h e primary primary deposit d e p o s i t and and redeposited r e d e p o s i t e d it ways. ways. fillings. fillings. 31 �GEOPHYSICAL INVESTIGATIONS, INVESTIGATIONS, INTERNATIONAL INTERNATIONAL FALLS FALLS AND ROSEAU QUADRANGLES, QUADRANGLES, MINNESOTA—ONTARIO MINNESOTA-ONTARIO By BY Horton, and Bruce D. Robert JJ. . Horton, Do Smith Smith Regional aeromagnetic gravity data have aeromagnetic and gravity have been been compiled compiled for for the the International Falls and and Roseau two degree quadrangles by the U.S. U.S. Geological Survey (USGS) in cooperation with the Minnesota Geological Survey (MGS) (MGS) and the Geological Survey Survey of Canada Canada (CGS). (CGS). This compilation was done as part of the Conterminous United States Mineral Assessment Program (CUSMAP) (CUSMAP) for for the the two two quadrangles located along the the U.S.—Canadian U.S.-Canadian border. border. Bedrock Bedrock in in the the area area is is largely buried by largely by Quaternary Quaternary glacial glacial deposits. deposits. Therefore, Therefore, maps maps of of the the bedrock bedrock based primarily on interpretation interpretation of regional geology are based regional aeromagnetic and mapping sparse gravity data supplemented by napping sparse outcrops and lithologic lithologic logging logging of of a limited limited number number of of drill drill holes. holes. Maps of gravity gravity and and magnetic magnetic anomalies anomalies are are presented here along with various maps illustrating computer computer processed processed enhanced maps produced produced to aid geologic interpretation interpretation of the the study study area. area. Data compilation compilation for preparation of aeromagnetic aeromagnetic maps includes includes existing existing data from supplements new data collected The from MCS MGS and CGS which supplements collected by the the USGS. USGS. The new airborne survey 114 mile at at an an elevation elevation survey was flown with a line line spacing spacing of of 1/4 of 300 300 feet feet with with aa high—precision high-precision proton proton sensor. sensor. A variety of navigation navigation systems including radar transponder, LORAN, and photo—recovery photo-recovery were used in in project in order to overcome problems in flight the USCS USGS project flight line location location over over largely featureless largely featureless terrain. terrain. The new new USGS USGS data data were were processed processed along along with with the the map other aeromagnetic data to produce an IGRF—corrected IGRF-corrected total magnetic field field map of quadrangles. quadrangles. Complete Bouguer anomaly gravity maps were also also prepared as as part part of of the the CUSMAP study using new data collected for the project combined with U.S. U.S. Department Department of Defense Defense gravity gravity data data base. base. The new new data were collected collected in in cooperation cooperation with the Minnesota Department of Natural Resources—Division Resources-Division of of on—going gravity Minerals and in cooperation with on-going gravity surveys surveys being done done by by the the MGS. Detailed profiles were made made by the USGS USGS to better define important important The geologic features features interpreted from preliminary preliminary gravity anomaly anomaly maps. maps. The total data set was then processed to produce terrain—corrected terrain-corrected Bouguer Bouguer anomaly anomaly maps maps of of the the two two quadrangles. quadrangles. The compiled aeromagnetic data was processed to to compensate compensate for for inclination and declination of induced magnetic fields fields which offset offset boundaries boundaries of causative causative sources sources from from magnetic magnetic highs. highs. The reduction—to—the—pole reduction-to-the-pole program program magnetic highs highs associated associated with with dipolar magnetic lows to be more shifts the magnetic coincident coincident with with the the source. source. Judicial use of this this enhanced map with with the the original geological interpretation original magnetic map facilitates geological interpretation of the the geophysical geophysical data. Gravity Gravity and magnetic data was further further processed processed to to produce produce color color shaded shaded (CSR), horizontal horizontal derivative, derivative, and and edge edge enhanced enhanced maps. maps. The CSR CSR and and relief (CSR), horizontal horizontal derivative maps emphasize subtle subtle linear linear features features and and level level changes changes in anomaly anomaly intensity. intensity. For example, example, the CRS CRS map of the the reduced reduced aeromagnetic aeromagnetic data data dramatically dramatically emphasizes linear anomalies anomalies due due to to northwest northwest striking striking diabase dikes. dikes. Edge enhanced reduced magnetic and gravity maps emphasize emphasize possible boundaries between geologic units with contrasting contrasting densities densities and/or and/or susceptibilities. susceptibilities. 32 �Interpretation Interpretation of detailed profiles of ground gravity and magnetic surveys through computer modeling of possible bedrock contacts suggests suggests size, size, shape, attitude, shape, attitude, and and physical physical properties properties of of causative causative bodies. bodies. Geophysical Geophysical interpretation interpretation of these maps can be integrated integrated with interpretation interpretation of of geological geological data data to to yield yield an an effective effective mineral mineral resource resource assessment assessment of of the the study study area. area. For CUSMAP studies studies described here, here, regional regional and and site site specific specific electrical electrical geophysical methods geophysical methods were were used. used. Application of electrical electrical geophysical geophysical methods methods is well known known in in the the glacial covered terrain terrain of the the Canadian Canadian Shield Shield and and is is routinely routinely used used by by mineral mineral exploration exploration companies companies in in Minnesota. Minnesota. Current Current implementation implementation of these airborne airborne and ground electrical electrical methods are are too too costly costly to apply over complete 10 lo xx 20 '2 quadrangle. quadrangle. The purpose of this presentation over aa complete presentation is to demonstrate demonstrate some some cost—effective cost-effective applications applications of new new airborne airborne and and selected ground electrical electrical methods in in regional regional mineral mineral resource resource assessment assessment Digital terrain data was processed to enhance trends trends to to aid aid in in programs. interpretation interpretation of of other other geophysical geophysical and and geologic geologic data. data. Interpretation of airborne EM anomalies anomalies and trends which might be be due due to to Interpretation conductive till is facilitated by comparison with trends conductive trends shown shown in in a colored colored shaded shaded relief relief map map of of topography. topography. This map is is also also useful in in showing showing trends trends of of both the East—west trends in the the exposed exposed bedrock bedrock and and glacial glacial deposits. deposits. East-west the central part of the International International Falls Falls Quadrangle Quadrangle result result from from glacial glacial erosion erosion deposition of thick lacustrine sediments and deposition sediments by the the ancient Lake Lake Agassiz. Ground electrical surveys surveys were made in in selected selected parts of the the study study area area supplement interpretation to supplement interpretation of bedrock features features and to to estimate estimate the the thickness thickness of glacial glacial till. till. Frequency and time domain sounding methods were used to to of Measurements of signals estimate till estimate till thickness. thickness. Measurements signals from from natural natural electrical electrical fields (such (such as as generated from from thunderstorms) thunderstorms) using using Audio—magnetotellurics Audio-magnetotellurics (ANT) and and telluric profiling methods added further constraints on overburden (AMT) overburden thickness thickness and and bedrock bedrock conductors. conductors. 33 �Hypabyssal rocks of the North Shore of of Lake Lake Superior: Superior: evidence evidence for for polybaric fractionation fractionation in in the the Midcontinent Midcontinent Rift Rift Eric A. Jerde, Institute Instituteof of Geophysics Geophysicsand and Planetaiy Planetary Physics, Physics, UCLA, UCLA,Los Los Angeles, Angeles, CA CA 90024 90024 The hypabyssal rocks of the North Shore of Lake Superior are found as diabase sills and dikes, and are present present both singly and in groups groups aall ll along the shore shore from from Duluth Duluth to the Canadian Border. Other Otherclusters clusters of of dikes dikes are also present around Lake Superior (1). The The most noteworthy noteworthy swarms swarms on on the the North Shore Shore occur occur near the Border, Border, and and as as aa major major map map unit unit in in the the region of Beaver Bay (e.g. 2). 2). These Theserocks rocksgenerally generallyhave haveolivine olivinetholeiitic tholeiiticcompositions, compositions, although exist. The rocks of the although other, more evolved compositions exist. Themajority majority of of the thehypabyssal hypabyssal rocks North North Shore Shore post-date postdate the the extensive extensive magmatism magmatism responsible responsible for for the the lavas, lavas,and andthus thusprovide providethe the opportunity opportunity to to study study magmatic magmaticproducts productsproduced producedlate latein inthe theevolution evolutionof ofthe theMidcontinent MidcontinentRift. Rift. Even though these dikes dikes and and sills sills appear appear very very similar similar to to one oneanother anotherininmajor majorelement element chemistry (most are aie high-Al), a striking chemistry (most striking range of compositions compositions is apparent apparent in the the trace trace elements. the range from —10 rare-earthelements elements(REE), (REE), thelight lightREE REE range from -10 toto—100 -100 times elements. Among Amongthe therare-earth chondrites, and and the theheavy heavyREE REErange rangefrom from—3 -3 to to —20 -20 times chondrites chondrites (Fig. (Fig.1). 1). Positive Positive europium europium anomalies anomalies are are present in in the most primitive rocks and and are are absent absent to to slightly slightly negative negative in the the more more evolved. Such Suchabundance abundance variations variations of an an order order of of magnitude magnitude suggest suggest that aa significant rocks. sigruf~cantamount amount of fractionation fractionation was was involved involved in in the 1önnation formation of of these these rocks. p I. g Figure 1. Diagram of chondrite-normalized REE data showing variation among the diabases of the North Shore of Lake Superior. a'I p LA Ca M Sm Eu Th Yb Lu Analysis Analysis is is ongoing, ongoing,but but there there appear appear to to be be no nomajor majorregional regionalpatterns patternsininthe thechemical chemical variations variationsalong along the North Shore. Of Ofthe the"evolved" "evolved"material, material, the the greatest greatestamount amount isisfound foundnear near Duluth, in places all all along along the shore. Since Sincethe thehypabyssal hypabyssalrocks rocksof ofthe theNorth North Duluth, but but is is present in Shore final stage stage of of the the rifting rifting process, process, the the apparent apparentrandom random distribution distribution of of Shore represent the fmal compositions compositionsalong along the the shore shoreisis consistent consistent with with aa well well developed developedplumbing plumbingsystem systemallowing allowing magmas magmasto to be be tapped tappedfrom fromcommon commonchambers chambersand and emplaced emplacedat atwidely widelyspaced spacedlocations. locations. Fractionation Fractionationat at multiple multiplelevels levelsin incontinental continentalcrustal crustalregimes regimesisisbecoming becomingmore moreand andmore more recognized recognized as as an an important importantprocess process in in the the generation generationof of magmas magmasseen seeninincontinental continentalsettings settings 34 �(e.g. 3-5). 3-5). In In these these models, models, aamagnesian magnesian melt melt isis produced produced from fromthe themantle, mantle,and andisiscollected collected (underplated) at the base of the crust. Such Suchaa magma magmawould wouldcrystallize crystallizeolivme, olivine,then then olivine olivine and and plagioclase, and eventually become saturated in clinopyroxene as well. Such Suchan anevolution evolution plagioclase, this same samehigh-Al high41 magma magma would produce a high-A1 high-Al magma as discussed discussed by by Klewin Kiewin (5). (5). IfIf this were then emplaced at a higher level level in in the the crust, crust, clinopyroxene clinopyroxene would would not not be be aa stable stable phase phase due to the shrinkage 6,7),and andonly only olivine olivine shrinkage of the the pyroxene pyroxene field field with with lowering lowering pressure pressure (e.g. (e.g. 6,7), and plagioclase would crystallize until until the magma magma was was once once again again saturated saturatedwith with respect respect to to clinopyroxene. clinopyroxene. The Thesuite suiteofofdiabases diabasesfrom fromLake LakeSuperior Superiorprovides providesexcellent excellentevidence evidencefor forjust just such such aa polybaric polybaric fractionation. fractionation. Since Since the primary difference difference between between the the two two fractionation fractionation schemes schemes is is the the presence presence or or crystallizing phase, diagrams such as MgO vs CaO CaO(Fig. (Fig. 2) 2) absence of clinopyroxene as a crystallizing absence work work quite quite well well in in displaying displayingthe the difference differencesince sinceone one quantity quantity(in (inthis thiscase caseMgO) MgO)isisnot not solely solely dependent and the other dependent on clinopyroxene clinopyroxene crystallization, crystallization, and other (CaO) (CaO) isisdependent dependent on on clinopyroxene. clinopyroxene.For Forfractionation fractionationinvolving involvingolivine olivineand andplagioclase, plagioclase,the theconcentration concentrationof ofMgO MgO would expected to to drop drop due due to toincorporation incorporationin in olivine, olivine,but butCaO CaOwould wouldremain re&ainrelatively relatively would be expected unchanged. Whenclinopyroxene clinopyroxenebegins beginsciystallization crystallizationCaO CaOwill willdrop, drop,leading leadingto to aa cross-trend cross-trend unchanged. When on on the the diagram diagram(Fig. (Fig. 2b). 2b). 12 11 I0 . i C 8 7 6 5 3 4 5 6 7 8 9 10 U 12 3 4 5 6 7 8 9 10 11 12 MgO(%) MgO(%) M g 0 (%) M g 0 (%) Figure 2. MgO vs CaO variation Figure 2. MgO vs CaO variationdiagrams diagramsfor forthe thehypabyssal hypabyssalrocks rocksofofthe theNorth NorthShore Shorefrom fromthis this study. " bshows showssuggested suggestedfractionation fractionationpaths. paths. study. Diagram Diagram"b" In Inthe thediagrams diagramsof ofFig. Fig.2,2,most mostsamples samplesare areon onthe theroughly roughlyconstant constantCaO CaOpath, path,indicating indicating that that olivine olivine and and plagioclase plagioclase fractionation fraitionation was a dominant dominant mode. However, However,some somecross-trends cross-trends are These are areconsistent consistent with withaahigh-Al high-A1magma magma("A") ("A")fractionating fractionatingolivine, olivine, arepresent. present. These plagioclase, "B"at some level in the crust. Continued Continuedevolution evolution plagioclase,and and clinopyroxene clinopyroxeneto to produce produce "B" could couldproduce producethe the even evenmore moreevolved evolvedmaterial materialfound foundin inthe the chilled chilledmargins marginsof of the the Lester LesterRiver River and "E").IfIfthe themagma magmaof ofcomposition composition"A" "A"were wereemplaced emplacedat at aa andEndion Endion Sills Sills of of Duluth Duluth (point (point "E"). higher higherlevel, level,the thepyroxene pyroxenestability stabilityfield fieldwould wouldbe besuppressed, suppressed,and andfractionation fractionationofofolivine olivineand and 35 �plagioclase would further down down in MgO, MgO, to to where where clinopyroxene clinopyroxene would plagioclase would take take itit further would be be a phase, i.e. at point "C". would then then lead lead to to a progression of crystallizing phase, "C". Crystallization would compositions toward toward that that of of 'ID. "D". The compositions The presence presence of of still still other other compositions compositions out to very very low low MgO values with CaO CaO —10% -10% isissuggestive crust. suggestiveof of fractionation fractionation at at still still higher higher levels levels in the crust. Three levels of fractionation has been suggested suggested for the lavas lavas of of the the North North Shore ShoreVolcanic Volcanic Group (NSVG) (5). In Inaddition, addition, there there are are several several samples samplesthat that contain contain very high amounts amounts of Whileno nogenuine genuinepicrites picrites have have been been described described for for the North Shore, these samples samples are MgO. While is possible possible that that more magnesian than the parents postulated for much of the rift rift magmatism. magmatism. ItIt is these samples samples represent material brought up from the very base of the crust when the rift was the most developed, and represent material that was evolving toward the high-A1 high-Al "parent" from Thesehigh-MgO high-MgOrocks rocks are are somewhat somewhatsimilar similarto to other, more primitive (picritic?) some other, (picritic?) magma. magma. These the high-MgO material material found found near the the base of the the extrusives exttusiveson on Mamainse Mamainse Point, Point, Ontario Ontario(8). (8). surprising to note that samples samples near near points points "B" "B" & & With regard to trace elements, it is not surprising 'D" variation diagrams, also have have the the "D" showing evidence evidence of of the most fractionation on the variation REE abundances abundances (50-100 (50-100 times times chondrites). chondrites). Even highest REE Even the samples that represent represent crystallization crystallization in the the absence absence of pyroxene pyroxene show show aa general general trend trend from from lower lower REE REE abundance abundance to to higher as the composition goes from high MgO to lower (i.e. (i.e. right right to to left left in in Fig. Fig. 2). 2). Another Another point concerns called a "pareit", "parent",namely namely at at point "A". " A . These Theseare arevery very concernsthe thesamples samplesthat that may be called similar in major element chemistry to the primitive olivine olivine tholeiites tholeiites of the NSVG (9), ( 9 , one one of which was used as a parent in modelling presented by Klewin However, the the incompatible incompatible KIewin (5). However, two or more in the primitive diabases relative to the trace elements are enriched by a factor of ~o of the the NSVG. NSVG. This primitive olivine tholeiites of Thismay may perhaps perhaps be be due due to to replenishment replenishment of of the the fractionating subcrustal subcrustal chambers, chambers, akin akin to to the process fractionating process described described by by O'Hara O'Hara (10), (lo), and consistent with the younger hypabyssal rocks tapping a later magma than the NSVG lavas. References (1) Green, al. (1988) (1988) in Mafic Maficdyke dykeswarms, swarms,Geological Geological Association Association of Canada Canada Green,J.C. J.C. et ct al. Special 289-302. Special Paper Paper 34, 34,289-302. (2) Miller, tripguidebook guidebookfor forselected selectedareas areasin inprecambrian precambriangeology geology of of Miller,J.D. J.D. (1987) (1987)in in Field Fieldtrip northeastern Minnesota, Minnesota Minnesota Geological Geological Survey SurveyGuidebook GuidebookSeries Series#17,43-70. #17,43-70. J. Petrol., (3) Cox, Cox, K.G. K G . (1980) (1980) 3. Petrol., 21, 21, 629-650. 629-650. (4) Weiblen, Weiblen,P.W. P.W. and and Miller, Miller, J.D. (1987) (1987) in Workshop Workshopon on the the growth growth of of continental continental crust, crust, 88-02, 162-164. LPI Technical Report 88-02,162164. (5) Kiewin, J. Geology, Klewin, K.W. K.W. (1989) (1989) J. Geology, 97, 97, 65-76. 65-76. al. (1979) (1979) Contrib. Contrib, Mineral. Mineral. Petrol., Petrol., 70, 70,111-126. 111-126. (6) Walker Walkeret et al. (7) Stolper, Stolper,E. E. (1980) (1980)Contrib. Contrib. Mineral. Mineral. Petrol., Petrol., 74, 74,13-27. 13-27. (8) Berg, Berg,J.H. J.H. and and Kiewin, Klewin, K.W. K.W.(1988) (1988)Geology, Geology, 16, 16,1003-1006. 1003-1006. (9) 3l2p. (9) Brannon, Brannon,J.C. J.C. (1984) (1984) Ph.D. Ph.D.Dissertation, Dissertation,Washington Washington University, St. Louis, 312p. (10) O'Hara, M.J. (1977) Nature, 266, 266, 503-507. 503-507. 36 �STRATIGRAPHIC AND STRUCTURAL EVOLUTION OF THE THE NORTHERN ITASCA METAVOLCANIC METAVOLCANIC STRATIGRAPHIC BELT, BELT, NORTH-CENTRAL NORTH-CENTRAL MINNESOTA MINNESOTA Mark i r s a , Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University U n i v e r s i t y Avenue, Avenue, St. St. Mark A.A. JJirsa, Paul, MN 55114—1057 P a u l , MN 551 14-1057 Geologic i s providing p r o v i d i n g new new insight insight G e o l o g i c mapping in i n northeastern n o r t h e a s t e r n Itasca I t a s c a County is of the Archean, largely the Archean, l a r g e l y supracrustal s u p r a c r u s t a l complex known as a s the the iinto n t o the makeup of northern n o r t h e r n Itasca I t a s c a metavolcanic m e t a v o l c a n i c belt b e l t (NIMB). (NIMB). The NNIMB I M B is i s the w e s t e r n equivalent equivalent western of o f the the Wawa Wawa Subprovince Subprovince of of the t h e Superior S u p e r i o r Province. Province. IIt t iis s bounded on on the the east, east, west, w e s t , and and south s o u t h by by granitic g r a n i t i c rocks. rocks. the north, n o r t h , splays s p l a y s of the t h e Vermilion Vermilion To the the NIMB NIMB from m metasedimentary of the v Vermilion ffault a u l t zone separate s e p a r a t e the e t a s e d i m e n t a r y rocks r o c k s of ermilion Granitic i s generally g e n e r a l l y less less G r a n i t i c Complex Complex (Quetico ( Q u e t i c o equivalent). e q u i v a l e n t ) . Although exposure e x p o s u r e is percent, drilling, tthan han 5 p e r c e n t , ccores o r e s from eexploration x p l o r a t i o n and scientific scientific d r i l l i n g , together t o g e t h e r with with new aeromagnetic a e r o m a q n e t i c data (Bracken (Bracken and Godson, 1988), 19881, fill f i l l data d a t a gaps g a p s between between E-M data d a t a by by the the U.S. U.S. ooutcrop u t c r o p areas. a r e a s . Detailed D e t a i l e d modeling of o f magnetic m a g n e t i c and and E-M Geological G e o l o g i c a l Survey is i s providing p r o v i d i n g valuable v a l u a b l e information i n f o r m a t i o n to to aid a i d geologic g e o l o g i c interpreinterpreEffie—Coon Lake Lake aarea ttation a t i o n in i n the Effie-Coon r e a (western ( w e s t e r n third t h i r d of of map area) a r e a ) where exposure exposure is with i s minimal. A ccooperative o o p e r a t i v e sstudy tudy w i t h the Minnesota Natural N a t u r a l Resources Resources Research R e s e a r c h Institute I n s t i t u t e is i s underway to to define d e f i n e geochemical geochemical characteristics c h a r a c t e r i s t i c s of of the the A data NIMB. N IMB. d a t a base b a s e of of several s e v e r a l hundred hundred analyses a n a l y s e s is i s on file. file. Although the the stratigraphy s t r a t i g r a p h y is i s complicated c o m p l i c a t e d by by folding f o l d i n g and and ffaulting, a u l t i n g , rock rock units to the u n i t s are a r e generally g e n e r a l l y younger younger to t h e north n o r t h within w i t h i n the t h e mapped aarea. r e a . The supracrustal n aapparent p p a r e n t sstratigraphic t r a t i g r a p h i c oorder rder s u p r a c r u s t a l uunits n i t s (Fig. ( F i g . 11)) iin occur ((oldest—youngest) o l d e s t - y o u n g e s t ) and are a r e as follows: f o l l o w s : Units U n i t s 1, 1 , 2, 2, and 3 o c c u r on on two two limbs limbs of o f aa large l a r g e fold f o l d surrounding s u r r o u n d i n g the t h e Wasson Wasson Lake Lake pluton. pluton. The stratigraphic stratigraphic sequence s e q u e n c e differs d i f f e r s somewhat somewhat between between these these two two limbs. limbs. On the the southeast s o u t h e a s t limb, limb, unit broadly and iirregularly s b r o a d l y and r r e g u l a r l y ttransitional r a n s i t i o n a l upward upward from tholeiitic tholeiitic u n i t 11 iis a l c - a l k a l i c vvolcanic o l c a n i c and volcaniclastic v o l c a n i c l a s t i c rocks r o c k s and vvolcanic o l c a n i c rocks r o c k s to ccalc-alkalic Mafic, discontinuous d i s c o n t i n u o u s iron-formation. iron-formation. M a f i c , tholeiitic t h o l e i i t i c volcanics v o l c a n i c s interdigitate interdigitate with Unit limb. U n i t 2 conformably overlies o v e r l i e s unit unit w i t h iron—rich i r o n - r i c h strata s t r a t a on on the t h e north n o r t h limb. of aa monotonous monotonous ssequence massive 1 and consists c o n s i s t s of e q u e n c e of of pillowed p i l l o w e d and m a s s i v e metabasalt metabasalt This sills. T h i s sequence s e q u e n c e contains c o n t a i n s evidence e v i d e n c e of of upward— upwardfflows l o w s and hypabyssal h y p a b y s s a l sills. Unit (Jirsa, 1988). 1988). U n i t 3 contains c o n t a i n s dacitic d a c i t i c to t o andesitic andesitic sshoaling h o a l i n g deposition d e p o s i t i o n (Jirsa, It I t is locally l o c a l l y interbedded i n t e r b e d d e d with w i t h units units 1 vvolcanic o l c a n i c and derived d e r i v e d clastic c l a s t i c rocks. rocks. Unit of aa second m major and 2. 2. U n i t 4 is i s the bbase a s e of a j o r volcanic v o l c a n i c cycle c y c l e and consists c o n s i s t s of of high—iron h i g h - i r o n tholeiitic t h o l e i i t i c metabasalt m e t a b a s a l t flows f l o w s and and sills s i l l s that t h a t are a r e locally l o c a l l y magnetic. magnetic. Unit mafic and and uultramafic U n i t 5 contains c o n t a i n s mafic l t r a m a f i c sills, s i l l s , collectively c o l l e c t i v e l y known as a s the t h e Deer Lake Complex, Complex, that t h a t intrude i n t r u d e bboth o t h aa small s m a l l area a r e a of of compositionally c o m p o s i t i o n a l l y similar similar flows f l o w s and the predominantly predominantly ddacitic a c i t i c volcanic v o l c a n i c and clastic c l a s t i c rocks r o c k s of of unit u n i t 6. 6. The The contact c o n t a c t between between units u n i t s 44 and and 66 extends e x t e n d s more more than t h a n 50 50 kin, km, bbut u t iits t s nature nature iis s enigmatic. e n i g m a t i c . Unit U n i t 7 is i s aa ppoorly o o r l y eexposed, x p o s e d , south-topping, s o u t h - t o p p i n g , metabasalt metabasalt ssequence. equence. The inferred plutonic d i v i d e d into i n t o four f o u r main main i n f e r r e d tectonic t e c t o n i c and p l u t o n i c history h i s t o r y can can be divided eelements l e m e n t s listed l i s t e d chronologically c h r o n o l o g i c a l l y below: below: D1 predominantly 11.. Dl deformation d e f o r m a t i o n involved involved p r e d o m i n a n t l y north—south n o r t h - s o u t h compression c o m p r e s s i o n with w i t h local local perturbations i s adjacent adjacent p e r t u r b a t i o n s related r e l a t e d to t o diapiric d i a p i r i c rise r i s e of o f plutons. p l u t o n s . One such s u c h area a r e a is to was the Wasson Lake pluton p l u t o n which w a s emplaced into i n t o border b o r d e r rocks r o c k s causing causing t o the folding the second s e c o n d deformation. deformation. f o l d i n g and and migmatization m i g m a t i z a t i o n prior p r i o r to t o the The same style 2. i s a northwest-oriented n o r t h w e s t - o r i e n t e d transpressional t r a n s p r e s s i o n a l deformation. deformation. style 2. D2 is of t h e east e a s t in i n the Vermilion V e r m i l i o n District D i s t r i c t (Hudleston ( H u d l e s t o n and and o f deformation d e f o r m a t i o n 60 km to the D2 was was a rregional e g i o n a l transpressional t r a n s p r e s s i o n a l event, e v e n t , affecting affecting oothers, t h e r s , 1988) iimplies m p l i e s tthat h a t D2 a large l a r g e area a r e a of of the the Archean Archean crust. crust. 1 1 37 �Northeast-trending, N o r t h e a s t - t r e n d i n g , dominantly d o m i n a n t l y sinistral s i n i s t r a l faulting f a u l t i n g and and syn— syn- to t o postposttectonic t e c t o n i c emplacement of of variably v a r i a b l y magnetic, magnetic, syenitic s y e n i t i c to t o monzonitic m o n z o n i t i c intrusions intrusions (Bello Lake, Coon Lake and Linden ( B e l l o Lake, Linden plutons). plutons). 4. 4. Ubiquitous, Ubiquitous, northwest—trending, n o r t h w e s t - t r e n d i n g , mostly m o s t l y dextral d e x t r a l faulting. f a u l t i n g . Many Many of of these these faults f a u l t s appear appear to t o be splays s p l a y s or o r to t o be be otherwise o t h e r w i s e related r e l a t e d to t o the the Vermilion Vermilion fault these faults f a u l t s are a r e more more north— northf a u l t zone. zone. The The latest l a t e s t and and most most brittle b r i t t l e of of these northwest-trending n o r t h w e s t - t r e n d i n g and and many many are a r e now now occupied occupied by by Proterozoic P r o t e r o z o i c diabasic d i a b a s i c dikes. dikes. Some a n a l y t i c a l support s u p p o r t was was provided p r o v i d e d by by the the Minnesota Minnesota Some field f i e l d and and analytical Department the Department of of Natural N a t u r a l Resources. Resources. Scientific S c i e n t i f i c drilling d r i l l i n g was was supported s u p p o r t e d by by the Minnesota Minnesota Legislature L e g i s l a t u r e under u n d e r the the Minerals M i n e r a l s Diversification D i v e r s i f i c a t i o n Program. Program. Geophysical Geophysical data d a t a were were provided p r o v i d e d in i n part p a r t by by the the CUSMAP CUSMAP program program of of the t h e U.S. U.S. Geological G e o l o g i c a l Survey. Survey. 3. 3. References: References: Bracken, 1988, R.H., 1988, Aeromagnetic Aeromagnetic map map of of the the northwestern northwestern Bracken, R.E., R.E., and Godson, Godson, R.H., part p a r t of of the t h e Hibbing Hibbing 1° l o xx 2° 2' quadrangle, q u a d r a n g l e , Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report R e p o r t 88—8, 88-8, scale s c a l e 1:62,500. 1:62,500. Hudleston, Hudleston, P.J., P.J., Schultz-Ela, S c h u l t z - E l a , D., D., and and Southwick, Southwick, D.L., D.L., 1988 1988 Transpression T r a n s p r e s s i o n in in an a n Archean Archean greenstone g r e e n s t o n e belt, b e l t , northern n o r t h e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of of Earth p. 1060—1068. 1060-1068. E a r t h Sciences, S c i e n c e s , v. v. 25, 25, p. Jirsa, 1988, G Geologic J i r s a , M.A.,, M.A., 1988, e o l o g i c map of of the t h e Sherry S h e r r y Lake Lake quadrangle, q u a d r a n g l e , Itasca I t a s c a County, County, Minnesota: ~ i n n e s o t a : Minnesota Minnesota Geological G e o l o g i c a l Survey Survey Miscellaneous M i s c e l l a n e o u s Map Map M—64, M-64, scale scale 1:24,000. 1 :24,000. , Figure F i g u r e 1.1. Schematic Schematic pre— pre- or o r early e a r l y faulting f a u l t i n g reconstruction r e c o n s t r u c t i o n of of the the northern northern Itasca I t a s c a metavolcanic m e t a v o l c a n i c belt. b e l t . Supracrustal S u p r a c r u s t a l units u n i t s 1—7 1-7 are a r e described d e s c r i b e d in i n text. text. Small Small arrows arrows indicate i n d i c a t e direction d i r e c t i o n of of stratigraphic s t r a t i g r a p h i c topping. t o p p i n g . Black Black units u n i t s are are iron-formation—bearing. Vertically V e r t i c a l l y ruled r u l e d units u n i t s are iron-formation-bearing. are ultramafic u l t r a m a f i c and and mafic mafic T o n a l i t i c to t o granitic granitic sills s i l l s of of the the Deer D e e r Lake Lake Complex Complex or o r associated a s s o c i a t e d with with it. it. Tonalitic intrusions to be be early e a r l y (pre-D2) (pre-D2) are a r e the the Wasson Wasson Lake Lake pluton p l u t o n (W), (W), i n t r u s i o n s inferred i n f e r r e d to Effie Late, E f f i e pluton p l u t o n (E), ( E l , and and G. G. L a t e , potassic p o t a s s i c or o r alkalic a l k a l i c intrusions i n t r u s i o n s are a r e the the Bello Bello Lake Lake (B), ( B ) , Coon Coon Lake Lake (C), ( C ) , Linden Linden (L), ( L ) , and and Side s i d e Lake Lake (S) ( S ) plutons. p l u t o n s . Little L i t t l e is is known known of of the t h e other o t h e r intrusions i n t r u s i o n s labelled l a b e l l e d g. g. 38 �Tectonic Activity Jacobsville Sandstone Jacobsville Sandstone and Tectonic Kalliokoski J. Kalliokoski Professor Professor Emeritus Emeritus Michigan Technological Technological University University Houghton, 49931 Houghton, MI MI 49931 Between Keweenaw Bay and Ironwood Ironwood the Jacobsville Jacobsville Sandstone Sandstone (Jss) (Jss) occupies occupies aa portion of a rift flank flank basin along the south south side side of of the the Midcontinent Midcontinent Rift Rift and provides a record for late-tectonic late—tectonic activity System (MRS) and activity along the the MRS (Kalliokoski, 1989). 1989). The sandstone rests on the Powder Powder Mills Group of lavas lavas (Kalliokoski, (PMG; (PMG; about 20,000 20,000' thick). thick). The lavas show a weathered surface surface at three three localities. A thick localities. thick lava lava plateau probably existed existed south south and and east east (Hubbard, (Hubbard, 1975), above the reversely reversely polarized PMG 1975), above PMG dikes dikes (Cannon, (Cannon, 1986). 1986). East of Lake Lake Gogebic the PMG dips 1O—150N 10-15O~under the Jacobsville (Fritts, (Fritts, 1969), l969), with with 5,000 of original 5,000' original thickness thickness remaining remaining at the the outcrop. outcrop. West of Lake Gogebic Gogebic these sequences dip 60—90°N unconformable under 60-90O~and lie unconformable under the the Jss Jss (Hubbard, (Hubbard, 1975). Here the the PMG PMG and and its its basement basement underwent underwent aa rotation rotation to to the the north, north, 1975). accompanied and followed followed by by erosion. erosion. A cryptic fault fault through through Lake Lake Gogebic Gogebic (Klasner and and Jones, 1979) may may have accommodated this rotation rotation and defined margin of a tectonic the east margin tectonic highland. highland. About 15,000 15,000' of PMG PMG had been been eroded by Jacobsville Jacobsville time. time. Only a few hundred feet feet of stratigraphic stratigraphic section section can can be be constructed constructed from from the the gently dipping Jss along Keweenaw Keweenaw Bay, Bay, but more complete complete sections sections are are in in TT—6 available drill cores cores and logs logs (Fig. (Fig. 1). 1). TT-6 (2845) (2845') bottoms bottoms in in coarse, coarse, quartz—rich conglomerate. quartz-rich conglomerate. The core is of pebbly and very coarse—grained coarse-grained AE—1 sandstone, with 1% conglomerate (pebbles (pebbles up sandstone, 1% shale shale and and 97. 9% conglomerate up to to 4t)• 4"). AE-1 (2298) (2298') bottoms bottoms in in saprolite—covered saprolite-covered basalt. basalt. The core core lithologies lithologies are much RL—1 (3620') (3620) bottoms finer grained than than in in TT—6. TT-6. RL-1 bottoms in in sandstone. sandstone. In In his his M.S. M.S. thesis Bowers (1989) divides the core into four units with with boundaries boundaries near 400, 1700 400, 1700 and 2500 2500 feet. feet. The uppermost unit resembles resembles the the classic classic red red Jss Jss but the others others do do not. not. These lower units show thin beds of white sandstone, sandstone, red siltstone, and minor grit, with the three units differing red siltstone, differing in in texture texture and and relative lithologic RL—1 shows a fining lithologic abundances. abundances. RL-1 fining upward sequence sequence expressed by by the upward increase in shale and siltstone Taken expressed siltstone (Fig. (Fig. 1). 1). Taken together, together, the three logs show show a fining from west to east. The sections sections satisfy an alluvial alluvial fan fan model model (Kalliokoski, (Kalliokoski, 1982). 1982). The westward westward coarsening suggests that the area southwest southwest of of Lake Lake Gogebic Gogebic became elevated in early Jacobsville time, and that tectonic tectonic forces forces maintained a northeast draining basin during the deposition deposition of of more more than than 3,000 feet of sediment. sediment. There is other evidence as well for for possible possible tectonic activity during Jacobsville Jacobsville deposition: deposition: 11. . A flexural flexural model for for aa subsiding subsiding MRS basin, basin, such such as as that that suggested suggested by by Peterman and erosion to to the and Sims (1988) requires for the Jss, uplift and erosion south of a hinge and subsidence subsidence to to the the north. north. This would explain explain the the Goodman Bulge (Peterman preservation of paleosols paleosols under under the the Jss. Jss. The Goodman (Peterman and have undergone undergone coeval coeval uplift. uplift. Sims, 1988) might have 39 �2. some clasts 2 . In I n the t h e Bete B e t e Crise G r i s e Bay Bay aarea r e a some c l a s t s in i n the t h e Jss Jss are a r e remarkably r e m a r k a b l y similar similar to t o lithologies l i t h o l o g i e s in i n the t h e PLy, PLV, suggesting s u g g e s t i n g that t h a t there t h e r e had had been been sufficient s u f f i c i e n t uplift uplift along a l o n g the t h e Keweenaw Keweenaw reverse r e v e r s e fault f a u l t to t o remove remove the t h e Oronto O r o n t o cover c o v e r and and expose e x p o s e the the PLV PLV (Brojanigo, ( B r o j a n i g o , 1984). 1984). The The position p o s i t i o n of of the t h e paleosol p a l e o s o l localities l o c a l i t i e s suggests s u g g e s t s that t h a t the t h e hinge h i n g e line l i n e between between areas a r e a s of of deposition d e p o s i t i o n and and erosion e r o s i o n must have h a v e been b e e n many many miles m i l e s south s o u t h of o f the the current c u r r e n t southern s o u t h e r n limit l i m i t of of the t h e Jss. Jss. The The flexure f l e x u r e could c o u l d have h a v e arisen a r i s e n from from southerly s o u t h e r l y thrusting t h r u s t i n g along a l o n g the t h e Keweenaw Keweenaw fault f a u l t or o r from from the t h e cooling c o o l i n g of o f the t h e MRS MRS crust. crust. References Re f e r en ce s Bowers, Bowers, Mark, Mark, 1989, 1989, Vertical V e r t i c a l petrologic p e t r o l o g i c changes c h a n g e s of o f Jacobsville J a c o b s v i l l e Sandstone Sandstone at a t Rice R i c e Lake Lake Hole Hole Number Number 1:1: Unpublished U n p u b l i s h e d M.S. M.S. thesis, t h e s i s , Michigan Michigan Technological T e c h n o l o g i c a l University. University. - Kalliokoski, J . , 1988, 1988, Jacobsville J a c o b s v i l l e Sandstone S a n d s t o n e — an a n up—date: up-date: K a l l i o k o s k i , J., Basin B a s i n Geological G e o l o g i c a l Society S o c i e t y Field F i e l d Guide, G u i d e , in i n press. press. Michigan Michigan Peterman, P e t e r m a n , Z., Z . , and and Sims, S i n s , P.K., P.K., 1988, 1988, The The Goodman Goodman Swell: S w e l l : aa lithospheric lithospheric flexure f l e x u r e caused c a u s e d by b y crustal c r u s t a l loading l o a d i n g along a l o n g the t h e Midcontinent M i d c o n t i n e n t Rift R i f t System: System: Tectonics, T e c t o n i c s , v. v . 7, 7 , p. p. 1077—1090. 1077-1090. Others, O t h e r s , from from the t h e author author. — PM-' LP 9 Amas.. 40 lp 20m' �CriHt CD H 0 OCJ)-1• . O'U) t)C) IOQ Logs of holes in the Jacobsville Sandstone. TT-6 ( S W ~Sec. 33, T48N, R43W); AE-1 (Wi Cor. S e c . 36, T48N, R40W); RL-1 (Sec. 14, T55N, R32W) U. 0 CD .0- 0 C) S'-" CD C)- z CD 0• C U1rt tJi — 0 H '- U) I t1 &) '.• CD 0 0 cJ cJJ 0 0 0 0 0 r'-) I I I I 0 pb 9- cg iL/VC -a m a) 0) 0 .0- (•) • CD U) cn' I rr H CD 0'. , ZC) U) CD 03 . H Figure 1 C -n — RL-1 % shale 100 �Gravity Wawa G r a v i t y survey survey of o f aaportion p o r t i o of n othe f t hQuetico e Q u e t i and c o and Wawasubprovinces subprovinces near near Thunder Bay, Bay, O Ontario. Thunder ntario. M. Departmentofof Geology, M. M. M. Kehlenbeck, Kehlenbeck, Department Geology, Lakehead Lakehead UUniversity, n i v e r s i t y , Thunder Thunder Bay, Bay, P. Cheadle, Geology,UUniversity Ontario O n t a r i o and and S. S. P. Cheadle, Department Department o of f Geology, n i v e r s i t y ooff Calgary, Calgary, Calgary, Calgary, Alberta. A1 b e r t a . with IIn n this t h i s study, study, 350 350 new new gravity g r a v i t y stations s t a t i o n sare a r ecombined combined w i t h 50 50 previously previously surveyedsstations mapo fofa apportion surveyed t a t i o n s iinn aa detailed d e t a i l e dBouguer Bouguer anomaly anomaly map o r t i o n ooff the the Quetico Wawasubprovinces subprovincesn onorth andwest westoof ThunderBay, Bay, OOntario. Q u e t i c o and and Wawa r t h and f Thunder ntario. In I n general, general, high h i g h gravity g r a v i t yvalues values characterize c h a r a c t e r i z e the t h esouthern s o u t h e r n and and southwestern southwestern ppart a r t of o f the t h earea areawhere where metavolcanic metavolcanic rocks r o c k s of o fthe t h eWawa Wawa Muchofof tthe h e Quetico Q u e t i c o subprovince subprovince forms forms aa broad broad subprovince dominate. dominate. Much gravitational g r a v i t a t i o n a l low l o w reflecting r e f l e c t i n gextensive e x t e n s i v eexposures exposures ooff gneisses, gneisses, schists, s c h i s t s , and and gravity migmatites. Conversely, Conversely, wwell e l l defined defined g r a v i t y lows lows are a r e associated a s s o c i a t e d with with several several ggranitic r a n i t i c intrusive i n t r u s i v ebodies. bodies. Modelso of subsurfacec oconfiguration Models f subsurface n f i g u r a t i o n oof f tthe h e ddensity e n s i t y contrasts contrasts representative major showa at rtrough-like r e p r e s e n t a t i v e oof f m a j o r rrock o c k uunits n i t s show o u g h - l i k e sstructure t r u c t u r e ffor o r the the metavolcanic T h i s ttrough-like r o u g h - l i k e structure s t r u c t u r e is is metavolcanic rocks r o c k s of o fthe t h eWawa Wawa subprovince. subprovince. This flanked by aa domical domicalf efeature f l a n k e d by a t u r e i in n tthe h e ggranitoid r a n i t o i d rocks r o c k s to t o the t h e south. south. North North ooff the t h e metavolcanic m e t a v o l c a n i c rocks, rocks, a asuccession succession ofo low-grade f low-gradegreywackes greywackes with and and sslates l a t e s occupy occupy aa bbasinal a s i n a l sstructure. t r u c t u r e . This T h i s sstructure t r u c t u r e together together w i t h tthat h a t of of the andggranitoids form tthe t h e metavolcanic metavolcanic rrocks o c k s and r a n i t o i d s form h e subsurface s u b s u r f a c e cconfiguration o n f i g u r a t i o n of of the subprovincei nint this t h e Wawa Wawa subprovince h i s area. area. The gneisses, gneisses, sschists, of the The c h i s t s , and and migmatites m i g m a t i t e s of t h e Quetico Q u e t i c osubprovince subprovince form f o r m aa thick which uunderlies t h i c k southward southward dipping d i p p i n gwedge—shaped wedge-shaped s t structure r u c t u r e which n d e r l i e s the the This iss s wedge-shaped wedge-shaped s tstructure ructure i sstructures t r u c t u r e s ofo fthe t h eWawa Wawa subprovince. subprovi nce. Thi by aa model modelu unit uunderlain n d e r l a i n by n i t ooff greater g r e a t e r density d e n s i t y representative r e p r e s e n t a t i v e of o f mafic mafic gneisses and and aamphibolites. The denser denser substratum substratum iiss modeled with gneisses m p h i b o l i t e s . The modeled w ith dislocations Lakef afaults. d i s l o c a t i o n s corresponding c o r r e s p o n d i n g to t othe t h eQuetico Q u e t i c oand and Hawkeye Hawkeye Lake ults. The The ccross r o s s sectional s e c t i o n a l and andthree t h r e edimensional dimensionalmodels modelssuggest suggesta acombined combined processo of and1alateral t e r a l aaccretion c c r e t i o n ffor o r the t h e crustal crustal process f vvertical e r t i c a l tectonism t e c t o n i sm and eevolution v o l u t i o n ooff this t h i s part p a r tofo the f t h eSuperior S u p e r i o rProvince. Province. 42 �Deformation of of the the Lyon Lyon Lake Lake Massive Massive Suiphide Sulphide Deposit, Deposit, Deformation Wabigoon Subprovince, Subprovince, northwestern northwestern Ontari&-, Ontario1, Canada. Canada. Wabigoon E.R. Koopman2, Koopman2, B. B. Dubé3, Dubk3, J.M. J.M. Franklin2, Franklin2, K.H. K.H. Poulsen2, Poulsen2, and and E.R. M.R. Patterson4. Patterson4. M.R. The Lyon Lyon Lake Lake deposit deposit is is aa typical typical Zn-Cu-Pb-Ag Zn-Cu-Pb-Ag The volcanogenic massive massive suiphide sulphide deposit deposit located located in in the the volcanogenic Sturgeon Lake Lake area area of of the the Wabigoon Wabigoon volcano-sedimentary volcano-sedimentary Sturgeon Subprovince of of the the Archean Archean Superior Superior Province Province of of the the Canadian Canadian Subprovince Shield. The stratiform stratiform deposit deposit is is hosted hosted by by aa quartz quartz Shield. The crystal rich rich fragmental fragmental rhyolite rhyolite and and its its hanging hanging wall wall is is the the crystal basal maf mafic member of of the the overlying overlying volcanic volcanic cycle. cycle. The The basal ic member footwall to to the the ore ore horizon horizon consists consists of of an an upper upper rhyolitic rhyolitic footwall unit composed composed of of interbedded interbedded ash ash and and lapilli lapilli tuff, tuff, unit immediately underlain by aa lower lower rhyolitic rhyolitic unit unit of of coarsely coarsely immediately underlain by fragmental rock. rock. Underlying Underlying the the rhyolite, rhyolite, aa fining fining upward upward fragmental sequence of of sedimentary sedimentary rocks rocks comprised comprised of of greywacke, greywacke, sequence quartzose siltstone, siltstone, graphitic graphitic shale, shale, massive massive po-py po-py bands, bands, quartzose and capped capped by by an an extensive extensive iron-carbonate iron-carbonate and/or and/or iron iron oxide oxide and Banded Iron Iron Formation(BIF). Formation(BIF1. The occurrence occurrence of of aa BIF BIF Banded The underlying the the massive massive suiphide sulphide horizon horizon indicates indicates that that low low underlying temperature hydrothermal hydrothermal venting venting occurred occurred prior prior to to suiphide sulphide temperature deposition. Massive Massive suiphides sulphides form form several several stacked stacked or or en en deposition. echelon lenses, lenses, and and comprise comprise discontinuous discontinuous and and contorted contorted echelon bands of of coarse coarse grained grained sphalerite sphalerite and and pyrite. pyrite. All bands All stratigraphic units, units, as as well well as as dykes, dykes, and and ore ore are are stratigraphic folded(Fig. 1). 1). The The dominant dominant structural structural feature feature controlling controlling folded(Fig. ore distribution distribution is is aa major major open open fold fold characterized characterized by by aa ore east-southeast(Fig. 1). hinge line line trending trending east-southeast(Fig. 1). Hinge Hinge lines lines of of hinge mesoscopic folds, folds, foliation, foliation, and and striations striations measured measured on on mesoscopic bedding, foliation, foliation, and and fault fault planes planes are are all all subparallel subparallel to to bedding, the hinge hinge line line of of the the major major fold fold and and indicate indicate aa direction direction of of the stretching parallel parallel to to the the fold fold axis. axis. Observed Observed faults faults have have stretching limited control control on on ore ore distribution, distribution, because because there there is is no no limited significant stratigraphic stratigraphic or or ore ore displacement displacement related related to to significant them. However, However, faulting faulting is is consistent consistent with with the the style style of of them. folding. The The contact contact between between the the hanging hanging wall wall mafic mafic unit unit folding. footwall rhyolite rhyolite is is characterized characterized by by aa high high strain strain and footwall and zone, possibly possibly aa fault. fault. Mineral Mineral lineations lineations and and striations striations zone, on foliation foliation planes planes are are subparallel subparallel to to the the mesoscopic mesoscopic folds, folds, on and suggest suggest that that this this high high strain strain zone zone may may be be related related to to and folding. structural contour contour map map of of the the hanging hanging wallwallfolding. AA structural footwall contact indicates that the dip dip of of this this contact contact is is footwall contact indicates that the shallowing in in an an eastward eastward direction direction reflecting reflecting the the plunge plunge shallowing effect of of the the major major open openfold. fold. The The deformation deformation at at Lyon Lyon Lake Lake effect has resulted resulted in in the the re-orientation re-orientation of of portions portions of of orebodies orebodies has into attitudes attitudes that that are are much much shallower shallower than than the the steep steep into regional dip. dip. Structural analysis analysis has has assisted assisted in in the the regional Structural increased effectiveness effectiveness of of devoloping devoloping and mining mining these these increased and flatter orebodies. orebodies. flatter ' 2 ' Contribution to tothe theCanada-Ontario Canada-Ontario MineralDevelopment DevelopmentAgreement Agreement 1985-1990. 1985-1990. Contribution MineraJ. Geological Survey Survey of ofCanada. Canada. Geological Sciences de de la la terre, terre, Université Universitg du du Québec Quebec a Chicoutimi. Chicoutimi. Sciences Noranda Mines, Lyon Lake Ignace, Ontario. Ontario. Noranda Mines, Lyon Lake Division, Division, Ignace, 43 �COMPOSITE SECTION 525'LEVEL - 1800'LEVEL ELEVATION IN FEET tunIc, 0400 COMPOSITE SECTION 525 LEVEL - 1800 LEVEL SECTION 12.200E - SECTION t2,200E 600 LEVEL , 000 , SURFACE MOLE SL-23"4 \ . ,/ . 227 .' / SURFACE HOLE SL 2 3 - 1 4 - 3 2 . •00, '-so, so- is 4330 LEVEL t52 LOT NO £t00I,IiI**ll 0W. 1300 LEVEL L — -- J IIotNIA,! 10011 I,, lIl0•PAP3ltlL 0*ClT,c 110*1 .3,0. 0000 LOOIACI \' 1*10410 LlIllOiOOlC 011*1*01 '"A • 190 .00 Flour* 1. CO~po8itec r o u sKlion (12.200E) ol trià Sub Creek Zone. Inset: liometnc projection ol tho deposit the piunne of the mapi llexure North indicates Mm* Isometric Nonh whicn IS 40. ol east Flgur. 1. snowinq Composite cross section (12.200E) 01 th. Subarrow Creek Zone. Inset: projicilon hi ol projection 01 arrow Section 12.200E). true norm (Note is a fleour.. deposil snowing the Section plunge oft3.500E the mayor North indIcates Mini North which is 40 east of true north. (Note: Section t3,500E is S projection of Section t2.200E). ~ u b k ,B., Koopman, E.R., Franklin, J.M., Poulsen, K.H., and Dubé, B., Koopman, ER., Franklin, J.M., Poulsen, K.H., and Patterson, M.R. Patterson, M.R. 1989: Preliminary study of the stratigraphic and structural 1989: Preliminary study of massive the stratigraphic and structural controls of the Lyon Lake sulphide deposit, Wabigoon controls of the Lyon Lake massive suiphide deposit, Wabigoon Subprovince, northwestern Ontario; in Current Research, Part Subprovince, northwestern Ontario; in Current Research, Part C, Geological Survey of Canada, Paper 89-1C, p. 275-284. C, Geological Survey of Canada, Paper 89-iC, p. 275-284. Franklin, J.M., Gibb, W., Poulsen, K.H., and Severin, P. Franklin, J.M., Gibb, W., Poulsen, K.H., and Severin, 1977: Archean metallogeny and stratigraphy of theP. South 1977: Archean metallogeny and stratigraphy of the South Sturgeon Lake area; Mattabi field trip: 23rd annual meeting Sturgeon Lake area; field trip: 23rd75p. annual meeting of the Institute of Mattabi Lake Superior Geology, of the Institute of Lake Superior Geology, 75p. Harvey, J.D. and Hinzer, J.B. Harvey, J.D. andofHinzer, J.B.Lake ore deposits, Noranda Mines 1981: Geology the Lyon 1981: Geology of the Lyon LakeOntario; ore deposits, Noranda Mines Limited, Sturgeon Lake area, Canadian Institute of Limited, Sturgeon Lake area, Ontario; Canadian Institute of Mining and Metallurgy Bulletin, v. 74, no. 833, p.77-84. Mining and Metallurgy Bulletin, v. 74, no. 833, p.77-84. 44q, �POTENTIAL-FIELD ANOMALY ANOMALY NAPS HAPS OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION REGION POTEMTIAL-FIELD Robert Robert P. P. Kucks1, ~ucks', Val Val Chandler2, Chandler 2, S. S. Dwight Dwight Dods3, Dods3, C. C.Patrick Patrick Ervin4, Ervin 4, Peter Hood3, Hood 3, Ken Ken McConnell3, McConnell 3, and and Dennis Dennis Teskey3 Teskey 3 Geological Survey, Survey,Box Box25046, 25046,MS MS 964, 964,Denver, Denver,CO CO80225 80225 Geological 2Ninnesota ~ i n n e s o t aGeological Geological Survey, Survey, 2642 2642 University University Ave., Ave., St. St. Paul, Paul, MN MN 55114 55114 3Geological 3 ~ e o l o g i c a lSurvey Survey of of Canada, Canada, 1 1 Observatory Observatory Cr., Cr., Ottawa, Ottawa, Ont. Ont. 1U. -'-U. S. S. Canada Canada KIAOY3 KlAOY3 4Dept. of ^ept. of Geology, Geology, Northern Northern Illinois Illinois Univ., Univ., DeKalb, DeKalb, IL IL 60115 60115 New New color color magnetic magnetic and and gravity gravity anomaly anomaly maps maps compiled compiled for for GLIMPCE of the GLIMPCE contribute contribute to to the the understanding understanding of the tectonic tectonic development development of of the the Lake Lake Superior Superior region. region. Although Although the the magnetic magnetic data data were were obtained obtained from from aeromagnetic aeromaqnetic surveys surveys of of variable variable specifications, specifications, a consistent consistent data data set set was was prepared prepared by by adjustment adjustment relative relative to to a a common common reference reference field field and and by by analytical analytical continuation continuation of o f all ail data data to to aa datum datum 305 305 mm above above surface. surface. The The availability availability of the the digital digital data data sets sets allows allows application application of of aa variety variety of o f filtering filtering techniques. techniques. Analysis Analysis by by filtering filtering involves involves conversion conversion of o f the the data data into into a a form form that that enhances enhances particular particular anomaly anomaly characteristics, characteristics, such such as a s wavelength wavelength or or trend. trend. Resulting Resulting filtered filtered maps maps include include (1) (1) first first vertical vertical derivative derivative to to sharpen sharpen anomalies anomalies of of shallow shallow origin origin and and small small areal areal extent, extent, (2) (2) horizontal horizontal gradient gradient to to delimit delimit lithologic lithologic or or structural structural boundaries, boundaries, and and (3) ( 3 ) color color shaded shaded relief relief to to enhance enhance particular particular anomaly anomaly trends. trends. The The filtered filtered anomaly anomaly maps maps permit permit aa refined refined interpretation interpretation of of the the geology geology of of the the Lake Lake Superior Superior region. region. 45 �Basalt Basalt geochemistry geochemistry as an an indication indication of tectonic tectonic environment environment part of the Hemlo-Heron Bay Greenstone for the the central central part of the Hemlo-Heron Bay Greenstone Belt, Belt, Ontario. Ontario. Minneapolis, MN MN 55406 Roger Roger J. Kuhns, Kuhns, BHP-Utah BHP-Utah International, International, Minneapolis, 55406 The The Hemlo-Heron Hemlo-Heron Bay Bay greenstone greenstone belt belt is is part part of of the theeast-trending, east-trending, Schreiber-White River River section section of of the Wawa Wawa Subprovince Subprovince within within the the The Hemlo area is located Superior Province of Ontario (Muir, 1986). in Superior Province Ontario (Muir, 1986). The Hemlo area is located in the central central part part of of the the belt belt(Lat. (Lat.48°41.6'N, 48¡41.6'N Long. Long. 85°57.3'W). 85'57.3'W). HernIa Hemlo U-Pb U-Pb dates dates yield yield a 2,772 2,772 ma ma age age for for metavolcanics metavolcanics and and 2,718 2,718 to to 2,684 2,684 ma maages ages for granitoids granitoids intruding intruding the the supracrustal supracrustal rocks rocks (Corfu (Corfu and and Muir, Muir,1986). 1986). Lithologic Lithologic sequences sequences in in the the Hemlo Hemlo area area consist consist of thin thin flows flows and and tuffs tuffs to to thick thick piles piles of of pillowed pillowed and andmassive massivebasaltic basalticmetavolcanics, metavolcanics, and and rhyolitic metavolcanics (Kuhns, 1988). to aa lesser degree intermediate to lesser degree intermediate to metavolcanics (Kuhns, 1988). These These metavolcanics metavolcanics are are intertayered interlayered with with thick thick sequences sequences of of metametaargillite argillite and and metagreywacke metagreywacke which which represent represent turbiditic turbiditic accumulations. accumulations. An Al versus versusFe' Fe'(Fe' (Fe'==FFeTol/FeTol+MgO) An Al e ~ ~ t ~ l / F e ~ ~ t ~variation lvariation + M g O diagram )diagram for for Archean mafic rocks Archean mafic rocks (Naldrett (Naldrett and and Goodwin, Goodwin, 1977) 1977) applied applied to to the the HernIa Hemlo area area mafic mafic rocks rocks indicate indicate aa dominance dominance of of basalt, basalt, and andlesser lessermagnesiummagnesiumMajor Major element element data data (not (notshown) shown) affinity. indicate these basaltic rocks are of tholeiitic indicate these basaltic rocks are of tholeiitic affinity. and and ferrobasalt ferrobasalt compositions compositions (Fig. (Fig. 1A). 1A). Numerous petroNumerous trace trace element element variation diagrams diagrams illustrating illustrating petrogenetic genetic trends trends and and tectonic tectonic environments environments have have been been constructed constructed from from modern and Phanerozoic basaltic suites (i.e. Pearce and Cann, 1973; BVSP, modern Phanerozoic basaltic suites (i.e. Pearce and Cann, 1973; BVSP, 1981). 1981). The The application application of these these diagrams diagrams to to Archean Archean rocks rocks is arguable, arguable, but but their their purpose purpose is is two-fold: two-fold: (1) (1) the the identification identification of petrogenetic petrogenetic sequences, and (2) the identification of possible tectonic environments. sequences, and the identification of possible tectonic environments. The bridge the the MORB MORB and and IAT fields on Hemlo metabasalts metabasalts bridge on Ti Ti versus versus The Hemlo Cr and and Ti/Cr Ti/Cr versus versus Ni Ni diagrams diagrams (Figs. (Figs. 18, 16, C). C). The The data also also exhibit exhibit aa gross trend from from high high Ni Ni and Cr) to to high gross trend and low low Ti/Cr TiICr (high (high Cr) high Ti Ti and and low low Ni Ni and and Cr concentrations, concentrations, indicative indicative of fractionation trends trends from magnesianmagnesianbasalts basalts --> --> basalts basalts --> ferro-basalts. ferro-basalts. This This apparent apparent fractionation fractionation trend trend agrees with the agrees with the distribution distribution of data data on on Figure Figure 1A. 1A. Volcanic Volcanic cycles cycles have have A plot of Nb versus not been resolved due to folding complications. been resolved due to folding complications. plot of Nb versus Zr Zr shows shows a positive positive correlation correlation also also suggesting suggesting aa fractionation fractionation trend trend in in the the basalts (Fig. The D). The data data plot plot within within the the "Type "Type I"I" basalt basalt field fieldofofmodern modern (Fig. 11D). MORB's basalts erupt erupt along along topographically topographically normal normal MORB's (BVSP, (BVSP, 1981). 1981). Type Type I basalts segments of mid-ocean segments of mid-ocean ridge ridge complexes, complexes, although although similar similar signatures signatures can can also also be be obtained obtained from from island island arc arctholeiitic tholeiitic basalts. basalts. Rare for the 2) indicate indicate at at Rare earth earth element element patterns patterns for the metabasalts metabasalts (Fig. (Fig. 2) least two principal principal groups groups of basalts basalts (Fe-types (Fe-types and a n d Mg-rich Mg-rich to to normalnormalleast two types), which support the trace element data above. Ferrobasalts yield ) , which support the trace element data above. Ferrobasalts yield types I 46 �flat and are are typified by ow flat REE REE patterns patterns and typified by low SmN/YbN S ~ N I Y and ~and N CeN/SmN CeN/SrnN ratios, ratios, and and high E, F). characteristics high SmN S r n ~and YbN Y ~ concentrations Nconcentrations (Figs. (Figs. 11 E, F). These characteristics are (BVSP, are similar similar to to ferrobasalts ferrobasalts from from the the Blake Blake River Rivergroup, group,Ontario Ontario(BVSP, Flat REE patterns and total REE abundances of the ferrobasalts 1981). 1981). Flat REE patterns and total REE abundances of the ferrobasalts are are compatible with some ocean compatible with some island island arc arc basalts, basalts, and and Phanerozoic Phanerozoic Type Type I ocean floor basalts. are not present basalts. Since Type Type IIII basalts basalts are present (Fig. (Fig. 1D) I D ) island island arc arc affinities are favored affinities are favored for the the Hemlo Hemlo area area basalts. basalts. The second second basalt basalt group group exhibits LREE enrichment, and has higher SmN/YbN and CeN/SmN ratios exhibits LREE enrichment, has higher S ~ N I Y ~and N C e ~ l s m Nratios and and SmN S m N concentrations, concentrations, and and lower lower YbN Y ~ concentrations Nconcentrations than than the the ferrobasalts ferrobasalts E, F). The second second group group also also yields yields slightly slightly higher higherMg Mgconcentrations, concentrations, (Fig. 11 E, (Fig. but the the REE REE patterns patterns are are typical typical ofofAl-basalts Al-basalts ininother otherArchean Archeansequences sequences (e.g. Blake River River Group). Group). The LREE LREE enrichment enrichment is similar to to some some IAT's. IAT's. In summary, there are summary, there are two two principal principal groups groups of basalts basalts in in the theHemlo Hemlo area. The first group is comprised of ferro-basalts, which exhibit flat area. The group is comprised of ferro-basalts, which exhibit flat REE REE patterns, low Sm/Yb patterns, low Sm/Yb and and Ce/Sm Ce/Srn ratios, ratios, and and are are similar similar totoPhanerozoic Phanerozoic island island arc arc tholeiitic tholeiitic basalts. basalts. These These rocks rocks are are not notLREE LREEdepleted, depleted,therefore therefore they do not not specifically specifically match match Type Type I mid-ocean ridge ridge basalts. basalts. The second they second less well well defined, defined, but but isis comprised comprised of of Mg-rich Mg-rich to tonormal normalbasalts, basalts, group isis less which which are are LREE LREE enriched, enriched, have have high high Sm/Yb SmIYb and and Ce/Sm CeISm ratios, ratios, and and are are terranes and and may similar Al-basalts in in other other Archean Archean terranes may have have IAT IAT affiniaffinisimilar to to Al-basalts type of island Some type island arc arc setting setting is therefore therefore favored favored for at at least least the the ties. ties. Some central central portion portion of of the the Hemlo-Heron Hemlo-Heron Bay Bay greeristone greenstone belt. belt. This conclusion conclusion is is in in part part supported supported by the the presence presence of of intermediate intermediate to to felsic felsic pyroclastics pyroclastics and and turbidite turbidite basins, basins, although although more more regional regional studies studies need need to to be becompleted. completed. I I References References Basaltic Basaltic Volcanism Volcanism Study Study Project, Project, 1981, 1981, Basaltic Basaltic Volcanism Volcanism on the the Terrestrial Terrestrial Planets: Planets: Pergamon Press, Inc., Inc., N.Y., Pergamon Press, N.Y., p. p. 5-29. 5-29. F., and and Muir, Muir, T.L., T.L., 1986, 1986,Preliminary Preliminary U-Pb U-Pb ages ages from fromthe theHemlo Hemloarea, area,northwestern northwestern Corfu, F., Corfu, Ontario [abs]: Geol. Assoc. Assoc. Canada Canada and and Mi Min. Assoc. Canada, 1986, 1986, Progr. Progr. with with Abstr., Abstr., p.p.59. 59. Kuhns, Kuhns, R.J., R.J., 1988, 1988, The The Golden Golden Giant Giant Deposit, Deposit. Hemlo, Hemlo, Ontario: Ontario: Geologic and and geochemical geochemical relationships relationships between between mineralization, mineralization, alteration, alteration, metamorphism, metamorphism, magmatism magmatism and and tectonism: tectonism: Univ. Univ. Minnesota, Minnesota, Minneapolis, MN, Unpub. Unpub. Ph.D. Ph.D. Thesis, 458 p. p. Muir, Muir, T.L., T.L., 1986, 1986, Geology Geology of the the Hemlo Hemlo area, area, District District of of Thunder Thunder Bay: Bay: Ontario Ontario Geological Geological Survey, Survey, Report Report 217, 217, 65p. 65p. Naldrett, 1977, Volcanic Volcanic rocks rocks of the the Blake BlakeRiver RiverGroup, Group, Abitibi Abitibi Naldrett, A.J., A.J., and and Goodwin, Goodwin, A.M., A.M., 1977, greenstone belt, Ontario, Ontario, and and their Jour. Earth Sci., greenstone belt, their sulfur sulfur content: content: Canadian Canadian Jour. Sci., v. 14, 14, p. p. 539539550. 550. Pearce, J.A., and Cann, Pearce, J.A., Cann, J.R., J.R., 1973, 1973, Tectonic Tectonic setting setting of of basic basic volcanic volcanic rocks rocksdetermined determined using using Sci. Letters, v. 19, trace element element analyses: analyses: Earth Planetary Planetary Sci. Letters, v. 19, p. p. 290-300. 290-300. 47 . �____________________________ 6 24 105 1 (mid-ocean Ridge B a s a l t ) 20 lo4 16 5 .c E i= I-. 8 4 0 1 03 io Fe- bamlt3 0 (Island A r c T h o l e i i t e ) (Is1nd Arc , Tholeilte) . ,....., . . . ,,..., . 102 io2 , Io" 100 20 20 18 18' 1 o1 102 , , ,, 103 lo4 cr Cr D < 16 io2 14 12 12 I- U - z lO 8 101 6 4, 2 100 0 100 0 Hi ppm 4'- 100 Zr 3F I 200 300 FO ferrobasilt GROUP 2 3 MB z z E 0, z 2 0, 2 -S U GROUP 1 U GROUPI = ferrobisIt [BA = b a s a l t I'I'I''' FB FB IBA = basalt 0 I 2 3 4 5 MB GROUP I I- l.a 0 1 '"" leA = basalt Mq—bsaIt LMB 0 GROUP 1 z GROUP 2 6 7 1MB = Mq—basIt 0 8 20 30 40 SmH /YbN 50 Mg 60 70 80 90 100 Mg Figure 1.1. Major, Major, trace, t r a c e , and and rare rare earth element variation diaFigure earth element variation diagrams f o r Hem10 area rnetabasal t s (see t e x t f o r discussion). grams for Hemlo area metabasalts (see text for discussion). • Fe—b3a1t3 a Mq—/normel bee1t3 C C U U C Le Ce Pr Nd Figure2.2 . Figure Sm Eu Gd Dy Ho Er Yb Lu Rare earth element patterns f o r Hem10 Rare earth element patterns for Hemlo area rnetabasal t s (see t e x t f o r discussion). area metabasalts (see text for discussion). 48 48 �TECTONIC TECTONIC IMPLICATIONS IMPLICATIONSOF OF THE THESTRUCTURE STRUCTUREAND AND STRATIGRAPHY STRATIGRAPHY OF OF QUARTZITES QUARTZITES IN IN CENTRAL CENTRAL AND AND SOUTHERN SOUTHERN WISCONSIN. WISCONSIN. Gene L. L, LaBerge, LaBerae, Geology Geology Department, Department, University Universityof of Wisconsin-Oshkosh, Wisconsin-Oshkosh, Oshkosh, Oshkosh, Wisconsin, Wisconsin, and and U.S. U.S. Geological Geological Survey, Survey, and John John S. S. Klasner, Klasner, Geology Geology Macomb, Illinois Illinois and and U.S. U.S. Geological Geological Department, Western Illinois University, Macomb, Survey. Survey. ' Structural and stratigraphic relationships of quartzite quartzite in central central and and southern Wisconsin provide constraints on the nature of the 1,850 1,850 Ma Penokean orogen and the 1,790 The Eau EauPleine Pleine 1?790Ma Central plains Orogen. The fault zone in central Wisconsin represents the boundary between rocks of in of the the Wisconsin Wisconsin magmatic terrane on the north north and and aa complex complex of of Archean Archean and and Proterozoic Proterozoic rocks rocks to the south, south, and and appears appears to to be beaasuture suturezone zone(LaBerge, (LaBerge? Schulz and Myers, Myers?1984, LaBerge, 1986). Isolated Isolated exposures exposures of of Early Early occur near, and south of the Eau fault zone and Proterozoic quartzite occur Eau Pleine fault areas. Dott farther south in the Baraboo and Waterloo areas. Dott (1983) (1983) suggested suggested that that the quartzite quartzite and associated slate, dolomite and iron formation in the Baraboo Baraboo Syncline represents a sequence of sedimentary rocks that developed on aa continental margin. margin. We concur and passive continental and suggest suggest that the sedimentary rocks rocks formed formed on on the the passive passive margin margin of an an Archean Archean craton, craton, remnants remnants of of which which are are Wisconsin. LaBerge exposed in central Wisconsin. LaBerge and andKlasner Klasner (1986, (1986, 1988, 1988, in prep) prep) have have of these these quartzites to to interpreted structural and stratigraphic relationships of fold/thrust system suggest a major south-verging fold/thrust system that pre-dates pre-dates the 1,760 1,760 Ma igneous event in southern Wisconsin, and appears, instead, to be related related to aa collisional event during during the the 1,850 1,850 Ma Ma Penokean PenokeanOrogeny. Orogeny. This interpretation suggests that an Archean continental block with on its margin? margin, was accreted as associated Early Proterozoic platform sediments on an exotic terrane against the southern margin of the Wisconsin magmatic terrane. The Theplatform platformsedimentary sedimentary sequence sequence was thrust southward onto the the accreted Archean block, suggesting suggesting that Archean Archean basement basement extended southward southward from from the the Eau Eau Pleine Pleine fault fault zone at at least least to to the the Baraboo Barabooarea. area. Nd/Sm Nd/Sm isotopic isotopicevidence evidence from from the the 1,450 1,450 Ma Ma pluton pluton near near the the WisconsinWisconsinthat Archean crust did not contribute to that Illinois border indicates that that magma magma (Nelson and DePaolo, 1985). This suggests that Archean Archean crust was not present DePaolo, 1985). area. Therefore, in that area. Therefore, Archean crust evidently evidently does not extend as far south as the Illinois border. The Thenorthern northernmargin marginof of the theCentral Central Plains Plains orogen orogen is is projected through 1986), however, however, the the projected through southern southern Wisconsin Wisconsin (Sims, (Sims, Peterman, Peterman, 1986), nature of the boundary boundary between between the Central Plains orogen and the Penokean orogen is is unclear. unclear. If the boundary was the result of northward northward subduction subduction (Doff, 1983), an Andean margin on the Penokean would have developed. (Dott, 19831, on the Penokean would have developed. Southward subduction near a continental continental margin should produce produce major major northnorthNeither is is evident evident in southern Wisconsin. North-verging verging structures. Neither Wisconsin. North-verging features. The structures are localized, localizedl brittle (shallow) (shallow) features. The nature nature of of PenokeanPenokeanCentral Plains juncture juncture in in this this area area is is speculative. speculative. However, However, the lack of of evidence evidence suggest that that rocks of the for an Andean margin or northward vergence may suggest Central Plains orogen were emplaced by by strike-slIp strike-slip movement in this region. region. 49 �REFERENCES REFERENCES CITED CITED Doff, Dott, R. H., H., Jr., 1983, 1983, "The ''The Proterozoic red quartzite enigma in the north-central north-central United States--resolved by by a plate ccollision?" Society ~ l l i s i o n ?Geological Geological ~~ Society of of 129-141. America Memoir 160 (Medaris, L. F., Ed.) pp 129-141. LaBerge, G. L., L., 1986, 1986, "The Proterozoic Geology of the the Lake Lake Superior Superior Region," Region," LaBerge, G. L., and and Mode, Mode, W. W. N., N,, Guidebook, Guidebook, 50th 50thTn-State Tri-StateGeological Geological Field Conference, Vol. 1, 1, papers. papers. G. L., L., and Kiasner, LaBerge, G. Klasner, J. S., 1986, 1986, "Evidence for a major major south-directed south-directed Early Proterozoic Proterozoic thrust thrust sheet in south central Wisconsin, "Abstract, American Annual Meeting, San San Antonio, Antonio, TX. TX. Geological Society of American LaBerge, G. L., L., and Klasner, Ktasner, J. J. S., S., 1988, 1988,"The "TheBaraboo BarabooQuartzite: Quartzite: A new look at LaBerge, G. an old problem." problem." Abstract, Abstract,34th 34th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Marquette, Marquette, Ml, MI,pp. pp.62-64. 62-64. LaBerge, G. G. L., Klasner, J. S. and Myers, E., in in review, review, "New "Newobservations observations on on Myers, P. P. E., the age and structure of Proterozoic Quartzites in Wisconsin," U.S. and structure of Proterozoic Quartzites in Wisconsin," U.S. Geological Survey Bulletin. Bulletin. G. L., L., Schulz, K. J., and Myers, Myers, P. P. E., E., 1984, 1984, "Early "Early Proterozoic Proterozoic Plate Plate LaBerge, G. Tectonics: Evidence Geological Evidencefrom fromnorth-central north-centralWisconsin," W i ~ c o n s i nAbstract, Abstract, ,~~ Geological Society of America, America, Annual Annual Meeting, Meeting, Rena, Reno, NV. NV. continental crust crust Nelson, 6. B. K., K., and DePaolo, D. J., J., 1985, "Rapid production production of continental 1.7 to 1.9 b. y ago: Nd I .7 to 1.9 b. Ndisotopic isotopic evidence evidence from the the basement basement of the North American Mid-continent," Geological Society Society of of America Bulletin, v. v. 9GI 96, pp 746-754. 746-754. Sims, P. P. K., K., Peterman, Z. Z. E., E., 1986, 1986, "Early "Early Proterozoic Proterozoic Central Central Plains Plains Orogen: Orogen: A Sims, A 14, major buried structure in in the north north central central United United States," States," Geology G e o l o ~ v. vv. 14, pp 488-491. 488-491. pp 50 �Possible Late-Stage Thrust Thrust Faulting Faulting in in aaKeweenawan-Age Keweenawan-Age Accommodation Zone Beneath Lake Superior Lake Superior L D McGinnis* (Engineering Geosciences, Argonne National McGinnis* (Engineering National Laboratory, Argonne, Argonne,IL IL60439; 60439;312-972-8722) 312-972-8722) H F Wang Wang (Dept. of of Geology Geology & & Geophysics, Geophysics, U. U. of of Wisconsin, Wisconsin, Madison, WI W I 53706; 608-262-5932) 608-262-5932) J LL Sexton Sexton (Dept. (Dept. of of Geology, Geology, Southern Southern Illinois Illinois U., U., Carbondale, Carbondale, IL 62901; 62901; 618-453—7374) 618-453-7374) JJ Nyquist Nyquist (Health (Health Physics, Physics, Oak Oak Ridge Ridge National National Laboratory, Laboratory, Oak Oak Ridge, TN T N 37830; 37830; 615-574-4646) 615-574-4646) M G Mudrey Mudrey (Geological (Geological & MG & Natural History History Survey, Survey,Madison, Madison,WI Wl 53705; 608-263-5495) 608-263-5495) GB Morey (Minnesota (Minnesota Geol. Survey, St. Paul, B Morey Paul, MN M N 551144; 551144; 612612627-4780) 627-4780) B Milkereit (Geological (Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario B Milkereit Ontario K1A 0E8; 613-995-5490) KIA OE8; W Hinze (Dept. (Dept. of of Earth & W J3 Hinze & Atmos. Sciences, Purdue Purdue U., U., West West Lafayette, IN47907; 47907;317-494-5982) 317-494-5982) Lafayette,IN A Green (Geological Survey of of Canada, Ottawa, Ottawa, Ontario OntarioK1A KIA 0E8; OE8; 613-995-5490) C PP Ervin Ervin (Dept. of Geology, Geology, Northern Northern Illinois Illinois U, U., DeKaib, DeKalb,IL IL 60115; 60115; 815—753-1942) 815-753-1942) A B Dickas (Dept. of Geosciences, Geosciences, U. U. of of Wisconsin, Wisconsin, Superior, Superior, WI 54880; 54880;715—394—8311) 715-394-8311) W Reston, VA W FF Cannon (USGS, Reston, VA 22092; 22092; 703-959-6345) 703-959-6345) A A research team team coordinated coordinated by by Argonne Argonne National National Laboratory Laboratory (ANL), underaa grant grant from from the Department (ANL), under Department of of Energy's Energy's Office Office of Basic has entered entered into Basic Energy Energy Sciences Sciences (DOE/OBES), (DOE/OBES), has into an an agreement agreement with with Grant Grant Norpac, Norpac, Inc. Inc. (GNI) (GNI) to license license deep deep seismic reflection, gravity, gravity, and data in seismic reflection, and magnetic magnetic data in the the Great Great Lakes. Data were were licensed licensed to toassist assistDOE/OBES DOEIOBES in the evaluaevalua- tion of the the hydrocarbon hydrocarbon potential potential of of basins basins of Proterozoic Proterozoic age age in North North America. America. The initial initial acquisition acquisition includes includes 1,042 1,042 line line kilometers kilometers of eight eight second second data datainin Lake LakeSuperior. Superior. Data were were collected 1 2 0 groups groups of of collected using using aa tuned tuned array array of of airguns airguns and and 120 25 meter intervals along a receivers receivers spaced spaced at a t 25 meter intervals along a 3.0 3.0 km km streamer. The The60 60fold folddata datahave havebeen beenprocessed processed and and migrated migrated by GNI. Gravity and magnetic magnetic data data were were also also recorded recorded along along by GNI. most of the profiles. profiles. 52 �to strike strike of of the Profiles are oriented oriented parallel parallel and and perpendicular perpendicular to Mideontinent Rift, tying tying together Midcontinent Rift, together profiles profiles collected collected by by the the GLIMPCEconsortium consortium in in 1986. GLIMPCE 1986. A A 342.8 342.8 km k m profile profile (LS-08) (LS-08) from Duluth to 22 2 2 km krn east of of Isle Isle Royale Royale parallels parallels the axis axis of the the Duluth to rift. An An accommodation accommodation zone of the the profile, profile, zoneinin the the center center of associated with a gravity associated with gravity low, low, separates separates axially axially adjacent adjacent basins, basins, and is is composed composed of aa massive massive block block of of Archean Archean Gneiss. Gneiss. Modest thrusting thrusting and and ramping ramping up up to to the west Modest west isissuggested suggested on on the east flank Thrusting must must have occurred the flank of of the the block. block. Thrusting occurred after volcanism Bayfield and and after volcanism but but before before deposition deposition of of the the Bayfield Oronto Sandstones which Oronto Sandstones which unconformably unconformablycover cover the the truncated crest of of the theblock block and andthe theeroded erodedsuberops subcrops of ofvolcanic volcanic flows. flows. If If thrusting thrusting has has occurred occurred in in this this environment, environment, the the proximity proximity of the Grenville Grenville convergence convergence in space and time might might be be aa cause. cause. post-rift thrust thrust or or reverse reverse faulting faulting occurred occurred parallel parallel to to If post-rift strike, as well as across the strike of the rift as already strike, well across the strike of the rift as already reported, with reported, with thrusts t k u s t s generated generated by by stress stress fields fields emanating emanating then the from aa converging from converging plate plate margin, margin, then the rift may may have have become a secondary become secondary tectonic feature, feature,quenched quenched by by the prevailprevailThe unusually great vertical ing tectonics tectonics of of the the Grenville. Grenville. The unusually great ing extent of extent of the the rift riftbasin basinand anditsitsbillion-year billion-year preservation preservation is is probably a consequence consequence of of its its lateral immobilization immobilization aat t aa probably rather early early stage stage of of its itsdevelopment. development. *Work supported by by the the U.S. Department of Energy, Office of *Work supported U.S. Department 1-1 09-Eng-38. Energy Research, Research, under underContract ContractW-3 W-31-109-Eng-38. 53 �CHARACTERIZATION CHARACTERIZATION OF O F GRAPHITE GRAPHITE OCCURRENCES OCCURRENCES IN I N THE THE SOUTHERN SOUTHERN AND AND WESTERN WESTERN PENOKEAN OROGEN PENOKEAN OROGEN McSwiggen, McSwiggen, Peter P e t e r L., L . , Minnesota Minnesota Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University University Avenue, Avenue, St. S t . Paul, P a u l , Minnesota Minnesota 55114—1057 551 14-1 057 E l e c t r o m a g n e t i c (E-M) (E-M) surveys, s u r v e y s , geologic g e o l o g i c mapping mapping and and bedrock b e d r o c k drilling drilling Electromagnetic have h a v e shown shown that t h a t the t h e rocks r o c k s of of the t h e southern s o u t h e r n and and western w e s t e r n Penokean Penokean orogen o r o g e n concontain t a i n an a n abundance abundance of o f highly h i g h l y graphitic g r a p h i t i c metasedimentary m e t a s e d i m e n t a r y units u n i t s (McSwiggen, (McSwiggen, 1987; 1987; Southwick Southwick and and others, o t h e r s , 1988). 1 9 8 8 ) . Many Many of o f these t h e s e units u n i t s have have been b e e n drilled drilled t h e m , but but b e c a u s e of of the t h e very v e r y pronounced pronounced E—M E-M anomalies a n o m a l i e s associated a s s o c i a t e d with w i t h them, because very the rocks, r o c k s , particularly p a r t i c u l a r l y with with v e r y little l i t t l e detailed d e t a i l e d work work has h a s been been done done on on the regard r e g a r d to t o the t h e graphite. g r a p h i t e . The The purpose p u r p o s e of o f this this investigation i n v e s t i g a t i o n is is to t o characcharact e r i z e the t h e concentrations c o n c e n t r a t i o n s and and abundance of o f the the graphite, g r a p h i t e , nature n a t u r e and and conconterize the origin o r i g i n of o f the t h e graphite, g r a p h i t e , and and the the c e n t r a t i o n s of o f secondary s e c o n d a r y minerals, m i n e r a l s , the centrations formation f o r m a t i o n of of the the graphite—bearing g r a p h i t e - b e a r i n g units. units. The i t s crystallinity, c r y s t a l l i n i t y , the t h e amount amount of o f precious precious The amounts amounts of of graphite g r a p h i t e and and its a n d base b a s e metals, m e t a l s , and and the t h e sediment s e d i m e n t source s o u r c e of o f the t h e host h o s t rocks r o c k s are a r e all all and exceedingly e x c e e d i n g l y variable. v a r i a b l e . The The graphitic g r a p h i t i c units u n i t s range r a n g e from from less l e s s than t h a n 1 percent percent carbon c a r b o n to t o more more than t h a n 40 40 percent. p e r c e n t . The The crystallinity c r y s t a l l i n i t y of of the the graphite g r a p h i t e reflects reflects the the Emily Emily district d i s t r i c t the the t h e metamorphic metamorphic grade g r a d e of of the t h e locality. l o c a l i t y . North N o r t h of of the carbon c a r b o n occurs o c c u r s as a s amorphous amorphous material m a t e r i a l lacking l a c k i n g any a n y crystallization c r y s t a l l i z a t i o n structure. structure. In Moose Lake—Glen Lake-Glen Township Township structural s t r u c t u r a l panel p a n e l of of I n contrast, c o n t r a s t , samples samples from from the t h e Moose to highly h i g h l y crystalline crystalline S o u t h w i c k and and others o t h e r s (1988) ( 1 9 8 8 ) contain c o n t a i n moderately m o d e r a t e l y th Southwick graphite. graphite. The s l a t e to to The host h o s t rocks r o c k s of of the t h e graphite g r a p h i t e range r a n g e in i n composition c o m p o s i t i o n from from slate chert. the least l e a s t amount amount of of clastic clastic c h e r t . The The richest r i c h e s t carbon c a r b o n samples s a m p l e s contain c o n t a i n the sediments; the primary p r i m a r y nonnons e d i m e n t s ; this t h i s suggests s u g g e s t s that t h a t chemical c h e m i c a l sedimentation s e d i m e n t a t i o n was was the organic these samples. samples. o r g a n i c source s o u r c e of of sediment s e d i m e n t in i n these The The carbon-rich c a r b o n - r i c h samples samples also a l s o typically t y p i c a l l y contain c o n t a i n anomalous anomalous values v a l u e s of o f base base metals m e t a l s (Cu (Cu as a s much much as a s 2900 2900 ppm) ppm) and a n d precious p r e c i o u s metals m e t a l s (Au (Au as a s much much as a s 350 350 ppb ppb and ppm). Preliminary p r e l i m i n a r y results r e s u l t s show show that t h a t only o n l y half h a l f the the gold gold a n d Ag Ag as a s much much as a s 66 ppm). in i n the the sample sample is i s separated s e p a r a t e d with w i t h the t h e sulfide s u l f i d e fraction. f r a c t i o n . This T h i s suggests s u g g e s t s that that half h a l f the the gold g o l d may may be be adsorbed a d s o r b e d to t o the t h e graphite. g r a p h i t e . This T h i s relationship r e l a t i o n s h i p seems seems to to hold the rock. rock. h o l d regardless r e g a r d l e s s of of the t h e total t o t a l gold g o l d or o r sulfur s u l f u r content c o n t e n t of of the 1 References: References : McSwiggen, McSwiggen, P.L., P.L., 1987, 1987, Geology Geology and and Geophysics G e o p h y s i c s of o f the t h e Denham-Mahtowa Denham-Mahtowa area, area, east—central e a s t - c e n t r a l Minnesota: Minnesota: Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Miscellaneous M i s c e l l a n e o u s Map Map Series, 1 :48,000. S e r i e s , M—63, M-63, scale s c a l e 1:48,000. Southwick, S o u t h w i c k , D.L., D.L., Morey, Morey, G.B. G.B. and and McSwiggen, McSwiggen, P.L., P.L., 1988, 1988, Geologic G e o l o g i c map map (scale the Penokean Penokean orogen, o r o g e n , central c e n t r a l and and eastern e a s t e r nMinnesota, Minnesota, ( s c a l e 1:250,000) 1 : 2 5 0 , 0 0 0 ) of o f the and a n d accompanying accompanying text: t e x t : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y Report R e p o r t of of Investigations I n v e s t i g a t i o n s 37, 3 7 , 25 25 p. p. Funding Funding Source: S o u r c e : Minnesota Minnesota Geological G e o l o g i c a l Survey S u r v e y and and Mineral Mineral Diversification D i v e r s i f i c a t i o n Program. Program. 54 �GLACIAL GEOLOGY GEOLOGY OF OF NORTHERN NORTHERN MINNESOTA: MINNESOTA: MINERAL EXPLORATION APPLICATIONS APPLICPTIONS Meyer, N., Minnesota M i n n e s o t a Geological G e o l o g i c a l Survey, S u r v e y , 2642 2642 University U n i v e r s i t y Ave., Ave., St. St. Meyer, Gary N., Paul, P a u l , MN 55114 55114 Glacial major G l a c i a l ice i c e from two m a j o r accumulation a c c u m u l a t i o n centers c e n t e r s advanced repeatedly r e p e a t e d l y across across northern the Pleistocene. P l e i s t o c e n e . The Labradorean L a b r a d o r e a n center center n o r t h e r n Minnesota Minnesota throughout t h r o u g h o u t the northeast, o r t h e a s t , and the t h e Keewatin ccenter e n t e r ice from the the ccontributed o n t r i b u t e d iice c e from the n northwest. the g geologic of movements is more more northwest. IIn n ggeneral e n e r a l the e o l o g i c rrecord ecord o f these iice c e movements complete, and ttherefore drift more complex, complex, south west r i f t stratigraphy s t r a t i g r a p h y more s o u t h and w est c o m p l e t e , and h e r e f o r e the d of o f the t h e major bedrock outcrop o u t c r o p area a r e a of o f northeastern n o r t h e a s t e r n Minnesota. Minnesota. The mostly m o s t l y thin t h i n mantle m a n t l e of o f glacial g l a c i a l sediment s e d i m e n t across a c r o s s northern n o r t h e r n St. S t . Louis, Louis, Lake, and Cook Cook C Counties was laid Wisconsinan) l a s t (late (late W i s c o n s i n a n ) ice ice Lake, o u n t i e s was l a i d down by the last Labradorean It a b r a d o r e a n Rainy R a i n y lobe. lobe. I t consists c o n s i s t s primarily p r i m a r i l y of o f locally locally aadvance d v a n c e of o f the L derived, the east e a s t Proterozoic, p r o t e r o z o i c , bedrock. bedrock. The d e r i v e d , disintegrated d i s i n t e g r a t e d Archean, and and to t o the North outcrop of however, was overridden by N o r t h Shore Shore o u t c r o p aarea rea o f the three t h r e e counties, c o u n t i e s , however, o v e r r i d d e n by Labradorean out Superior basin, Superior uperior b a s i n , the S u p e r i o r lobe, l o b e , which L a b r a d o r e a n iice c e moving o u t of o f the S down ddistinctive from ddisintegrated llaid a i d down i s t i n c t i v e rreddish e d d i s h ssediment e d i m e n t dderived e r i v e d from isintegrated Keweenawan bedrock. bedrock. Late Rainy L a t e Wisconsinan R a i n y lobe l o b e drift d r i f t also a l s o overlies o v e r l i e s bedrock b e d r o c k across across northeastern County, northern the Woods Woods County, County, n o r t h e a s t e r n IItasca t a s c a County, n o r t h e r n and and eastern e a s t e r n Lake Lake of o f the but o f Koochiching Koochiching County County (Martin ( M a r t i n and and others, others, and all all b u t the t h e ssouthwestern o u t h w e s t e r n part of 1988; M Martin and oothers, i s buried b u r i e d there t h e r e by by drift d r i f t of o f the the 1988; a r t i n and t h e r s , in i n progress), p r o g r e s s ) , but b u t is Sediment Keewatin Koochiching lobe. lobe. S e d i m e n t deposited d e p o s i t e d by by the the Koochiching Koochiching lobe, lobe, of northern Minnesota w west of Louis i s tthe h e ssurficial u r f i c i a l ddrift rift o f n o r t h e r n Minnesota est o f St. St. L ouis which is County, County, is i s characteristically c h a r a c t e r i s t i c a l l y finer f i n e rin i ntexture t e x t u r ethan t h a nthat t h a tofo fthe theRainy Rainy lobe, lobe, Cretaceous and Ppaleozoic bbeing e i n g dderived e r i v e d cchiefly h i e f l y from from C r e t a c e o u s sshale h a l e and a l e o z o i c ccarbonate a r b o n a t e ffar a r tto o the drift, t h e west w e s t and and northwest. northwest. Koochiching lobe lobe d r i f t , therefore, t h e r e f o r e , is i s aa poor poor sampling mediumf ofor s a m p l i n g medium r ggeochemical e o c h e m i c a l eexploration. xploration. bedrock The remainder r e m a i n d e r of o f the the b e d r o c k ssurface u r f a c e oof f northern n o r t h e r n Minnesota Minnesota iis s overlain overlain byy aa complex complex ppile of interbedded b i l e of i n t e r b e d d e d glacial g l a c i a l sediment s e d i m e n t of of both b o t h Labradorean L a b r a d o r e a n and and Consequently, Keewatin provenance. provenance. C o n s e q u e n t l y , only o n l y the t h e lower l o w e r drift d r i f t of o f both b o t h ssources ources includes The position i n c l u d e s significant s i g n i f i c a n t amounts amounts of o f detritus d e t r i t u s from from local l o c a l bedrock. bedrock. position of derived d i s t a n c e of of transport t r a n s p o r t are a r e determined d e t e r m i n e d pri— prio f locally locally d e r i v e d cclasts l a s t s and the distance manly m a r i l y by by local l o c a l bedrock b e d r o c k topography t o p o g r a p h y and and basal b a s a l ice i c e velocity. velocity. IIn n general, general, toward ttopographic and ssubglacial u b g l a c i a l ttransport r a n s p o r t ccarries a r r i e s eentrained n t r a i n e d ddebris e b r i s toward o p o g r a p h i c lows, lows, and transport distances through lows are longer than across intervening highs t r a n s p o r t d i s t a n c e s t h r o u g h lows a r e l o n g e r t h a n a c r o s s i n t e r v e n i n g h i g h s Evidently had a l o b e had a relatively r e l a t i v e l y high high ((Clark, C l a r k , 1987). 1987). E v i d e n t l y the Koochiching lobe and ttransported whereas tthe ssliding l i d i n g vvelocity e l o c i t y and r a n s p o r t e d bbasal a s a l ddebris e b r i s llong o n g ddistances, i s t a n c e s , whereas he Rainy lobe l o b e had had a a relatively r e l a t i v e l y low low sliding s l i d i n g velocity v e l o c i t y and a n d transported t r a n s p o r t e d newly newly debris only eentrained ntrained d ebris o n l y short s h o r t distances. distances. be ddetermined e t e r m i n e d iin n bbedrock e d r o c k ooutcrop u t c r o p aareas r e a s from from IIce—flow c e - f l o w ddirections i r e c t i o n s ccan a n be Elsewhere glacial g l a c i a l striation s t r i a t i o n measurements. measurements. E l s e w h e r e drumlins d r u m l i n s and a n d end e n d moraines m o r a i n e s are are qeomorphic good ice—flow i c e - f l o w indicators. indicators. IIn n aareas r e a s where basal b a s a l drift d r i f t predates p r e d a t e s geomorphic ffeatures, e a t u r e s , cclast l a s t lithologic l i t h o l o g i c provenance p r o v e n a n c e implies i m p l i e s general g e n e r a l ice ice flow f l o w direction. direction. Partial s t u d y was provided p r o v i d e d by the Department D e p a r t m e n t of of P a r t i a l support s u p p o r t for f o r this study Natural the Mineral M i n e r a l Diversification Diversification N a t u r a l Resources R e s o u r c e s Mineral M i n e r a l Division D i v i s i o n through t h r o u g h the Fund, Fund, and by the t h e Minnesota Future F u t u r e Resources R e s o u r c e s Commission. Commission. References R e f e r e n c e s Cited Cited Clark, till composition: composition: C l a r k , P.C., P.U., 1987, subglacial S u b g l a c i a l sediment s e d i m e n t dispersal d i s p e r s a l and a n d till Geology, v. JJournal o u r n a l of o f Geology, v. 95, 9 5 , no. no. 4, 4 , p. p. 527—541. 527-541. Martin, T.L., C Chandler, and G.N., LLawler, a w l e r , T.L., h a n d l e r , V.W., V.W., a n d Malmquist, Malmquist, M a r t i n , D.P., D.P., Meyer, Meyer, G.N.,, K.L., 1988, Regional K.L., 1988, R e g i o n a l survey s u r v e y of o f buried b u r i e d glacial g l a c i a l drift d r i f t geochemistry g e o c h e m i s t r y over over Minnesota Archean terrane t e r r a n e in i n northern n o r t h e r n Minnesota: Minnesota: M i n n e s o t a Department D e p a r t m e n t of o f Natural Natural Resources, Division Part R esources, D i v i s i o n of o f Minerals M i n e r a l s Report R e p o r t 252, 252, P a r t I, I , 74 7 4 p., p., Part P a r t II, 11, 386 p. P 55 �GEOLOGY NORTHEASTERN MINNESOTA GEOLOGY OF OF THE THEBEAVER BEAVER BAY COMPLEX, COMPLEX, NORTHEASTERN MINNESOTA James James D. D. Miller, Miller. Jr., Jr.. Minnesota Minnesota Geological Geological Survey, Survey. 2642 University Ave., Ave.. St. St. Paul, Paul, Minnesota Minnesota 55108. 55108. The Beaver Beaver Bay Bay Complex Complex (Grout (Groutand and Schwartz, Schwartz, 1939; 1939; Gehman, Gehman, 1957) 1957)isisaasupersuite supersuiteof ofhypabyssal hypabyssal The to plutonic plutonic gabbroic gabbroic to to granitic granitic intrusions intrusionswhich which were were emplaced in the the upper upper portion portion of of the theKeweenawan Keweenawan to North North Shore Shore Volcanic Volcanic Group Group (NSVG; (NSVG; Green, Green, 1972) 1972) during during the thedevelopment developmentof ofthe theMidcontinent Midcontinentrift rift system. The Thecomplex complexisisbest bestexposed exposedalong alongthe theLake LakeSuperior Superiorcoast coastnear nearthe thetowns townsofofBeaver BeaverBay, Bay,Silver Silver system. lakeshore,the theBeaver BeaverBay Baycomplex Complexextends extendsapproximately approximately30 30km km Bay and and Finland, Finland, Minnesota. Minnesota. From Fromthe thelakeshore, Bay to the the north-northeast north-northeast where it becomes becomes covered by Although ititisisstratigraphically stratigraphicallyand and to by thick thick glacial till. till. Although petrologically distinct from most rocks rocks that that comprise comprise the the deeper deeper intrusions intrusions of of the theDuluth DuluthComplex, Complex, petrologically aeromagneticand and gravity gravityanomalies anomaliesover overthe thecovered covered area areaindicate indicateaahigh highratio ratioofofintrusions intrusionstotovolcanic volcanichost host aeromagnetic rocks rocks and and thereby thereby suggests suggeststhat thatthe the Beaver Beaver Bay Bay Complex Complex is is gradational gradationalinto into the the Duluth DuluthComplex. Complex. Geologic mapping mapping at at aa 1:24,000 1:24,000scale scaleencompassing encompassing about about four four 7.5'quadrangles 7S'quadrangles(Silver (SilverBay Bay w/ w/ Split Split Geologic Rock Point Point NE, NE, IlIgen Illgen City, City, Finland Finland and and Doyle Doyle Lake) Lake) was was initiated initiated 44 years yearsago agoby bythe theMinnesota Minnesota Rock Geological Surveys COGEOMAP program. program. We Geological Survey in conjunction with the U.S. U.S. Geological Geological Survey's We report report here here on on the the major majorresult resultof ofthis thisongoing ongoingproject, project,which which has haselucidated elucidatedmuch muchofofthe thevolcanic, volcanic,intrusive intrusiveand and structural structuralhistory historyof of this thispart partof ofthe theKeweenawan Keweenawansection. section. The The volcanic volcanic rocks rocks that thathost hostthe theBeaver Beaver Bay BayComplex Complex are aredominantly dominantlyflows flowsofoftholeiitic tholciiticbasalt basalttoto basaltic basaltic andesite, andesite, but but also also include include arkosic arkosic interfiow interflow units and several thick (100 (5100m) m)rhyolite rhyoliteflows flows(Miller (Miller lakewarddip dipof ofmost mostNSVG NSVGunits unitsisis and others, others,in in press; press; Miller, Miller, 1988; 1988;Green, Green, 1972). 1972). The Thetypical typicalshallow shallowlakeward and disrupted disrupted in in this this area area due due to to block block faulting faultingduring and after intrusion of the Beaver Beaver Bay Bay Complex. Steep Steep fault NEtotoNNE, NNE,parallel paralleltotothe theaxis axisofofthe therift, rift,and andless lesscommonly commonlyWNW. WNW. fault(and (anddike) dike)trends trendsare aredominantly dominantlyNE All All NE-trending NE-trending faults faultsdeveloped developedcoeval coeval with with intrusion intrusion of of diabase diabase (now (nowdikes) dikes)display displaydowndrop downdropof ofthe the lakeside lakesideblock block consistent consistentwith withthe therift riftbasin basindecping deepingtotothe theSE. SE. five major major events. events. Each Each Current mapping mapping indicates indicates that that the the Beaver Beaver Bay Complex was emplaced in five Current event eventproduced produced aaunique uniquesuite suiteof ofrock rocktypes typesthat thatreflect reflectdifferent differentparent parentmagmas magmasand andmodes modesofofemplacement. emplacement. In In order order of of decreasing decreasingage, age,these theseintrusive intrusivesuites suitesare arethe theLax LaxLake Lakegabbro, gabbro,the theFinland Finlandgranite, granite,the theSonju Sonju Lake Lakelayered layeredintrusion, intrusion,the theBeaver BeaverRiver River diabase, diabase, and and the the Silver Silver Bay Bay intrusions. intrusions.The TheBeaver BeaverBay BayComplex Complex also alsoincludes includesseveral severalminor minordiabase diabaseintrusions intrusionswhose whose genetic genetic relationship relationshipwith with the themajor majorsuites suitesisisunclear. unclear. Subophitic Subophiticolivine olivine gabbro, gabbro,oxide-rich oxide-rich gabbro, gabbro, granophyric granophyric gabbro, gabbro, and mafic mafic granodiorite granodioriteof the the Lax Lax Lake Lakegabbro gabbro(Fig. (Fig.1)1)are arethe theoldest oldestintrusive intrusiverocks rocks in in the the area. area. The Theshape shapeofofthe theintrusion intrusionisisdifficult difficult to to discern discern because because the the rocks rocks lack lackinternal internalstructure structureand and have have been been cut cutby by younger youngerintrusions intrusions(Beaver (BeaverRiver River diabase diabaseand and Finland Finlandgranite) granite)and and faults. faults.The Thegranophyric granophyriccharacter characterand andextensive extensivehydrothermal hydrothermalalteration alterationof of most mostLax Lax Lake Lakegabbro gabbrorocks rocksprobably probably isisthe the result result of of their their early early emplacement emplacementinto intowater-rich water-rich volcanics. volcanics. In of the Lax Lake gabbro suite is the Finland In sharp sharp intrusive intrusive contact contact with the north north margin margin of Finland granite granite(Fig. (Fig.1), 1).a ahomogeneous homogeneousmass massofofpink pinktotoorange, orange,granophyric, granophyric,leucocratic, leucocratic,pyroxene pyroxenegranite. granite. Although Althoughthe thegranite granitecontains containsabundant abundantmiarolitic miaroliticcavities cavitiesindicative indicativeof ofaavapor vaporphase, phase,the thepredominance predominanceofof Fe-rich Fe-rich pyroxene pyroxeneover overhornblcnde hornblendesuggests suggeststhat that the the parent parent magma magma was was water-poor. water-poor. Bordering Borderingthe the Finland Finlandgranite graniteon on the thenorth north and and (as (asimplied implied by by aeromagnetics) aeromagnetics)west west isisaadifferentiated differentiated layered termed the theSonju Sonju Lake intrusion layered sequence sequence of mafic cumulates termed intrusion(Fig. (Fig.1;1;Stevenson, Stevenson,1974). 1974). This This intrusionisisthe the most mostcompletely completelydifferentiated differentiatedbody body known known in in the the Keweenawan Keweenawansection section(Weiblen, (Weiblen,1982). 1982).ItIt intrusion grades gradesfrom fromaabasal basalpicrite/dunite picriteldunitetotoananupper upperapatitic apatiticferrodiorite. ferrodiorite. In Inthe thenorthern northernpart partofofthe thearea, area,the the roughly (15-25') to the the south. south. The Thelaminated laminatedupper upperferrodiorite ferrodioriteisis roughly 1000-rn-thick 1000-m-thick sequence sequence dips dips gently gently (15-25°) overlain overlainby byaamassive massivegranophyric granophyricquartz quartzmonzodiorite monzodioriteto togranodiorite granodioritewith withprismatic prismaticpyroxene pyroxeneand andolivine. olivine. This Thismonzo/granodiorite monzolgranodioritegrades grades into intothe the Finland Finland granite granite suggesting suggesting that that ititrepresents representsmelting meltingand andpartial partial assimilation assimilation of of the thegranite granitewhich whichformed formedthe theroof roofofofthe theintrusion. intrusion. The Theeast eastend endofofthe theSonju SonjuLake Lake intrusion intrusion isisabruptly abruptlytruncated truncatedby by aahigh-angle high-anglefault faultwhich which juxtaposes juxtaposes the the layered layeredsequence sequenceand andBeaver BeaverRiver River diabase. diabase.Field Fieldrelationships relationshipsbetween betweenSonju SonjuLake Lakerocks rocksand andBeaver BeaverRiver Riverdiabase diabaseare areunclear unclearand andallow allowthe the possibility possibilitythat thatthe theunits unitsare arecoeval coevalororthat thatthe thediabase diabaseisisyounger. younger. Dikes Dikesand and sills sillsof ofophitic ophiticolivine olivinediabase, diabase, termed termed Beaver River Riverdiabase, diabase,are arethethemost mostpervasive pervasive intrusions intrusions in in the theBeaver BeaverBay BayComplex Complex(Fig. (Fig.1). 1). Steep Steepdikes dikes feed feedthick thick ((< 100 subhorizontal sheets 100 m)m) subhorizontal sheets which whichform formprominent prominentflat-topped flat-toppedhills. hills. The Thediabase diabaseintrusions intrusionsare areunique uniqueininthat thatthey theycontain containabundant abundant inclusions of of anorthosite anorthositeand and less lessabundant abundantgranite, granite, some some as as much much as as100 100rnmacross, across,which whichtend tendtotobebe inclusions concentrated concentrated in in the thelower lowerparts partsofofsheets. sheets.Typically, Typically,the theanorthosites anorthositesare aremassive, massive,coarse-grained, coarse-grained,and and consist consistalmost almostentirely entirelyofoftabular tabularcalcic calcicplagioclase plagioclase(An (An54-80; 54-80;Morrison Morrisonand andothers, others,1983) 1983)with withminor minor olivine, olivine,hypersthene, hypersthene,augite, augite, and and Fe-oxide. Fe-oxide. Some Someinclusions inclusionsare aretectonized tectonizedand anda afew fewdisplay displaymodal modal 56 �layering. The Thegranite graniteinclusions, inclusions, being medium-grained and micrographic and containing Fe-pyroxene and of Finland Finland granite. miarolitic cavities, are probably xenoliths of The Silver Bay intrusions, intrusions,the theyoungest youngest intrusive intrusive unit unit in in the the area, area, occur occur as as many many concentrically concentrically bodies and as irregularly irregularly shaped shapedmasses masseswithin withinor or adjacent adjacentto to Beaver BeaverRiver Riverdiabase diabase(Fig. (Fig. 1). 1). This zoned bodies spatial relationship suggests that the Silver Bay magmas were emplaced through the same same conduits conduits as the the Beaver River diabase. Moreover, Moreover, the the abundance abundance of of Beaver Beaver River River diabase diabaseinclusions, inclusions,which which are are especially especially centered south south of of Silver Silver Bay, Bay, and and the lack tack of of any chill at the margins of the Silver common in the intrusion centered Bay intrusions intrusions indicate that the ferrodioritic magmas were intruded soon after the diabase diabase had crystallized. crystallized. Zoned Silver Bay intrusions grade abruptly abruptly from from a margin of coarse-grained, van-textured Zoned intrusions grade vari-textured granophyric olivine ferrodiorite ferrodiorite to an interior of medium-grained, laminated, laminated, locally locally layered layered olivine olivine ferrogabbro/diorite. ferrogabbroldiorite. Several irregularly shaped intrusions are composed of mediummedium- to to coarse-grained, coarse-grained,granophyric granophyric olivine olivine dionte, similar diorite, similar to ferrodionte ferrodiorite in the margins of the zoned intrusions. These Thesebodies bodies may may represent represent deeper deeper parts of intrusions which fed into zoned masses above. Some Someintrusions intrusionsalso alsocontain containsignificant significantamounts amounts of mafic granodiorite granodiorite to quartz monzodiorite which have resulted from local melting melting of felsic felsic volcanics volcanics and and immiscibility of the ferrogabbro deeper Finland granite, or perhaps from liquid immiscibility ferrogabbro magmas. Petrogenetic models models of of the relationships between between the various intrusive bodies which compose the Beaver Bay Complex and between these rocks rocks and and the underlying Duluth Complex must await more detailed Field relationships and a minor investigations of their their geochemistry. geochemistry, Field relationships and minor amount amount of geochemical geochemical data, however, permit some preliminary preliminary conclusions. conclusions. The The parental parental magma magma to to the the Lax Lake gabbro was probably moderately evolved basalt which which was driven to more felsic compositions compositions by assimilation of nearby waterbearing volcanics. The Thewholly wholly granitic granitic composition composition and extensive extensive volume of the Finland granite strongly anatectic origin. origin. Further suggests a crustal anatcctic Further geochemical geochemicalstudies studies should should test test whether whether this this shallow shallow intrusion intrusion could have fed any of the rhyolitc rhyolite flows flows in in the the area. area. Although of Although the the lithologies lithologies and modes of occurrence of River, and and Silver Silver Bay Bay intrusions are distinct, it is possible that these rocks the Sonju Lake, Beaver Beaver River, rocks are are comagmatic. Preliminary Preliminary geochemical geochemical data data and the the close closespatial spatialand and temporal temporal association associationof of Beaver Beaver River River rocks of of the the younger younger Silver Silver Bay Bay intrusions suggest that that the the parent parent magmas of of the diabase and ferrodioritic rocks latter may have been derived from from further fractionation of Beaver River magma in deeper chambers. The The Lake intrusion intrusion may may have have been beenone one such such chamber. chamber. Though the field relationships arc are obscure, the the Sonju Lakc diabasic troctolite troctolite in the basal zone of the Sonju Lake intrusion suggests occurrence of anorthosite-bearing diabasic the possibility possibility that the Sonju Lake body resulted from intrusion of of Beaver Beaver River River magma magma into intoaa chamber chamberof of sufficiently large size that crystal fractionation fractionation could occur. occur. It also follows that the Silver Silver Bay Bay magmas magmas upper ferrodioritic ferrodioritic differentiate differentiate of of the the Sonju Sonju Lake Lake body. body. More could have been tapped from the upper More geochemical geochemical data are are currently currently being acquired to evaluate evaluate this this model. Gehman, H.M., H.M., Jr., 1957, 1957, The petrology of the the Beaver Beaver Bay Bay Complex, Complex, Lake Lake County, County,Minnesota: Minnesota: Ph.D. Ph.D. Dissertation, University of Minnesota, 92 p. Dissertation, Green, J.C., J.C., 1972, Group, in Sims, 1972, North North Shore Volcanic Volcanic Group, Sims, P.K. P.K. and and Morey, Morey, G.B., G.B., eds., eds.. Geology Geology of volume: Minnesota Geological Geological Survey, Minnesota: A centennial volume: Survey, p. 294-332. G.M., 1939, 1939, The The geology geology of of anorthosites of of the Minnesota of Lake Grout, F.F., F.F., and Schwartz, G.M., Minnesota coast of Superior: Minnesota Geological Survey Bulletin 28, 119 Superior 119 p. Miller, J.D., J.D., Jr., 1988, 1988, Geologic Geologic map of the the Silver Silver Bay Bay and andSplit SplitRock RockPoint PointNE NEquadrangles, quadrangles,Lake Lake Minnesota: Minnesota Minnesota Geological Survey County, Minnesota: Survey Miscellaneous Miscellaneous Map Map M-65. Miller, J.D., Jr., Green, J.C., J.C., and Boerboom, TJ., TJ., in in press, press.Geologic Geologicmap mapof ofthe theIllgen IllgenCity Cityquadrangle, quadrangle. Geological Survey Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Miscellaneous Map, Map, M-66. M-66. D.A., Ashwal, Ashwal, L.D., L.D., Phinney, Phinney, W.C., W.C., Shih, C-Y., C-Y., and Wooden, J.L., 1983, Morrison, D.A., 1983, Pre-Keweenawan Pre-Keweenawan anorthosite inclusions inclusions in in the Keweenawan anorthosite Keweenawan Beaver Bay Bay and and Duluth Duluth Complexes, Complexes, northeastern northeastern Minnesota: Geological Society of of America America Bulletin, v. 94, p. 206. Stevenson, R.J., RJ., 1974, Stevenson, 1974, A A mafic mafic layered layered intrusion intrusion of of Keweenawan Keweenawan age near Finland, Finland, Lake Lake County, County, Minnesota. 160 p. Minnesota. M.S. M.S. thesis, University of Minnesota, Minneapolis, Minneapolis, 160 P.W., 1982, Keweenawanintrusive intrusiveigneous igneousrocks. rocks.ininWold, Wold,RRiJ & Hinze, W.J., W.J., eds,. eds, Geology Weiblen, P.W., 1982, Keweenawan Geology and tectonics tectonics of the Lake Superior Basin: Basin: Geological Society of America Memoir 156, 156, p. 57-82. 57 �91° 5 ç 4 * 4 * '4. .:. 4 4*4*4* * * 4*44444444 4 47°25 •.. • * * • 4 * • 4 4 . * 4 4 ++*+•**+****+,* .44 4 •**+* • t_. _* * * *%• *.s,. • •.•**,****,t.• 4 * .4•. I ,,•,•.•,••+t•• •t • • • —C. 4... + III ''I II 4, •I•1 7 47°2O C) iver Bay x Silver 8y intrusions 5ever River dlbse E prismotic grcnodiorite (J upper g8bbro 0 C L w > C aver Bay \, lower troctolite Flnlnd granite Sonju Leke in t ru Si On Lx Lake gbbro aD 47° 15- Mlscelløneous gobbroic Intrusions North Shore Volcanic Group A 4 2__ 00 I 4 2 Miles 2MiIes 22Kilometers Kilometers FIGURE1.1.Generalized Generalizedgeology geologyofofthe theBeaver BeaverBay Bay FIGURE Complex, Complex,northeastern northeasternMinnesota. Minnesota. IÑÑIà 58 58 �THE PALEOMAGNETIC PALEOMAGNETIC RECORD RECORD OF OF LATE LATE GLACIAL GLACIAL AND AND POST POST GLACIAL GLACIAL THE SEDIMENTS OF LAKE SUPERIOR SEDIMENTS OF LAKE SUPERIOR John S. S. Mothersill Mothersill and and James James Fraser, Fraser, Royal Royal Roads Roads Military Military John vos IBO College, Victoria, British Columbia, College, Victoria, British Columbia, VOS 130 The Late Late Quaternary Quaternary sedimentary sedimentary sequence sequence consists consists The 9900 years ago of glacial till which was deposited about of glacial till which was deposited about 9900 years ago during the last glacial advance into the Lake Superior during the last glacial advance into the Lake Superior Basin. In In the the Canadian Canadian portion portion of of Lake Lake Superior Superior the the till till Basin. deposits are unconformably overlain by a thin sequence of deposits are unconformably overlain by a thin sequence of bedded sands and silts which are conformably overlain by bedded sands and silts which are conformably overlain by thick sequence sequence of of varved varved sediments sediments which which in in turn turn are are aa thick overlain by postglacial silty clays. Paleodeclination overlain by postglacial silty clays. Paleodeclination logs can can be be used used to to correlate correlate and and and paleoinclination paleoinclination logs and indirectly date cores of this sedimentary sequence that indirectly date cores of this sedimentary sequence that have been taken from the major basins of the Canadian have been taken from the major basins of the Canadian portion of of Lake Lake Superior. Superior. In In addition addition the the paleomagnetic paleomagnetic portion data obtained from six cores has been stacked to form form data obtained from six cores has been stacked to 'type' paleodeclination and paleoinclination logs for Lake Lake 'type' paleodeclination and paleoinclination logs for Superior. These 'type' logs can be correlated with the Superior. These 'type' logs can be correlated with the t y p e ' logs logs obtained obtained for for both both Lakes Lakes Huron Huron and andErie. Erie. 'type' it is is concluded concluded that that rhythmic rhythmic sedimentation sedimentation ceased ceased It 9200 years BP in the southeastern lake proper prior to prior to 9200 years BP in the southeastern lake proper and at at about about 8700 8700 years years BP BP in in the the southeastern southeastern bay bay areas. areas. and 8200 However rhythmic sedimentation continued until about However rhythmic sedimentation continued until about 8200 years BP in the northern part of Lake Superior and until years BP in the northern part of Lake Superior and until about 8000 8000 years years EP BP in in the the Nipigon Nipigon Bay Bay area. area. about 59 �FUNDAMENTALUNIT UNIT DIFFERENTIATION OF THE FUNDAMENTAL THE MIDDLE MIDDLE PROTENOZOIC PROTEROZOIC MIDCONTINENT MIDCONTINENT RRIFT I F T SYSTEM, SYSTEM,NORTH NORTH AMERICA M.G. Mudrey, 3817 Mudrey, .Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 Mineral Point Road, Madison, 53705, and Madison, WT WI 53705, A.B. Dickas, Superior, WI WI 54880 54880 A.B. Dickas, University of Wisconsin-Superior, Wisconsin—Superior, Superior, ABSTRACT Analysis of Analysis of geophysical geophysical data data within within the the Lake Lake Superior Superior basin basin of of the t.he Middle Proterozoic Midcontinent Midcontinent Rift Rift system system in in central central North North America America sugsug series of of opposed, opposed, sub-regional sub—regional half-grabens, half—grabens, displaying gests a series displaying igneous igneous sedimentary inf ill packages packages separated separated by accommodation accommodation structures. and sedimentary infill structures. We interpret first—order rift interpret. five first-order rift segments segments (zones) (zones) identified identified by by major major interruption of of gravity gravity and and magnetic magnetic patterns, seismic seismic expression, expression, and interruption terrane composition separated by four four first—order first-order accommodation accommodation strucstructures. Clockwise tures. Clockwise from from the the southwestern southwestern end end of of the the rift, rift, these these segments segments rowa, Superior, Superior, Mackinaw, Mackinaw, and are named named the the Kansas, Kansas, Iowa, and Maumee Maumee zones zones (fig. (fig. Second—order rift segments segments (fundamental 1fl.) . Second-order (fundamental rift rift units) units) are are separated separated Superior zone zone four by second-order accommodation structures. structures. Within Within t.he the Superior four second—order accommodation such such segments are now recognized recognized and and named named the the Chisago, Chisago, Brule, Brule, Ontonagon, and Manitou units Ontonagon, units (fig. (fig. 2). 2). This This model for for the the Midcontinent Midcontinent Rift Rift isisbased basedononthe themod'ern modern East East tn plan plan view the fundamental African Rift Rift (Rosendahl, (Rosendahl,1987). 1987). In fundamental unit unit in in the Gregory Rift is is a parallelogram parallelogram with with lengths lengths on on the the order order of of50 50t.o to 190 km), km), and and widths widths from from20 20to to40 40kmkm(maximum (maximum7070kin). km). 70 km (maximum (maximum 190 cross— to 44 with with an an average average of of 3. 3. In crossLength to width ratios ratios vary vary from from 22 to triangular, defining defining aa half— halfsection the fundamental unit is commonly triangular, Because of graben. graben. of this this haif—graben half-graben geometry, geometry, the the width width of of any any one one rift rift function of halfunit is a function of its its degree degree of of uplift uplift.and and erosion. erosion. When When the thehalf-developed, it graben is initially developed, it is is bordered on its its deep deep side side by by aa curvilinear, normal, normal, listric major curvilinear, listric fault fault system, system, and and on on the the shallow shallow side side by a monocline, or series of normal, normal, small small displacement displacement step step faults. faults. The fundamental unit is bound on its complex structures structures striking striking its ends ends by complex obliquely to the rift axis, axis, and include include interbasinal interbasinal highs, highs, ridges, ridges, and and regions Igneous and sedimentation regions of of uplifted uplifted basement. basement. Igneous sedimentation wedges wedges of of alteralternating isopach patterns distinguish distinguish juxtaposed These iso— juxtaposed rift rift units. These isopach patterns differ by being symmetric symmetric parallel, parallel, but alternating alternating asymasymmetric metric perpendicular, perpendicular, to to the the trend trend of of the the rift rift axis. axis. The least mature of the Midcontinent Rift the Midcontinent Rift System System zones zones appears appears to to be Maumee zone be the the Maumee and and Mackinaw Mackinaw zones zones (table (table 1). 1). The Maumee zone displays displays aa symmetrical, unfaulted, unfaulted, extensional basin associated associated with with a symmetrical, a simple simple gravgravsignature (Brown ity signature (Brown and and others, others, 1982). 1982). The The Mackinaw Mackinaw zone zone is is similar, similar, boundaries of of this this zone zone are are associated associated with differing only in that that t.he the boundaries normal faults, faults, none none of which which can be traced to the listric normal the Moho disconsemi—mature Kansas Kansas zone tinuity (Behrendt (Behrendt and and others, others, 1988). 1988). The semi-mature zone conconsists asymmetric basin plunging sists of an asymmetric plunging to to the the west west and and bounded bounded by by normal normal 1988; Serpa Serpa and and others, others, 1984). 1984). The Iowa Iowa faults (Berendsen (Berendsen and others, others, 1988; zone is identified primarily primarily by zone by strong strong gravity—pattern gravity-pattern changes. changes. An east— eastwest seismic seismic line line in in central central Iowa Iowa is is inconclusive inconclusiveregarding regardingbasin basinsynune— symmetry; and appears as a central horst associated associated and bounded bounded by by reactireacti(Chandler faults, one one of which which can be traced to a depth depth of of 20 20 km km (Chandler vated faults, and others, 1989). The The horst horst may be be aa consequence consequence of of two two opposed opposed funda— fundaothers, 1989). 60 �suggest compression, compression, and may reflect mental units. units. These faults suggest. reflect a Mackinaw, and Kansas greater maturity maturity than than the the Mauinee, Maumee, Mackinaw, Kansas zones. zones. The is the the most mature mature in in the the Midcontinent Midcontinent Rift Rift The Superior Superior zone zone is System (McSwiggen (McSwiggen and and others, 1987), and is recognized by disrupted gravity trends, km, a central central horst bounded bounded by by gravity trends, crustal crustal separation separationofof5050kin, reverse faults, faults, and and gabbroic gabbroic intrusions. intrusions. If the fundamental fundamental rift unit unit reverse concept concept: is a necessary necessary constituent constituent of of modern modern and and ancient ancient rift rift evolution, evolution, then such fundamental units should be recognizable recognizable in the Lake Lake Superior Superior basin. Four Four such such units units can can be identified, identified, average average 150 150 km kin in in length length by basin. 60 60 km in in width, width, for for aa length/width length/width ratio ratio of of 2.5. 2.5. Structural Structural sub—division sub-division of of the the Superior Superior zone zone may may apply apply elsewhere elsewhere along the trend, trend, however the increased increased depth depth of of burial burl-a1of of the the rock units units both directions directions away from the Lake Superior area and the limited disdis— in both such detailed tribution of geophysical data along the rift do not permit such second—order second-order differentiation. differentiation. References Cited References Behrendt, Behrendt, J.C., J.C., Green, Green, A.G., A . G . , Cannon, Cannon, W.F., W.F., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, M.W., M.W., Milkereit, B., C., 1988, 1988, Crustal Crustal Milkereit, B., Agena, Arfena, W.F., and Spencer, Spencer, C., structure GLIMPCE structure of of the the Midcontinent Midcontinent Rift Rift System: System: Results Results from from GLIMPCE deep deep seismic seismic reflectin reflectin profiles: profiles: Geology, Geology,v. v. 16, 16, P. p. 81—85. 81-85. Berendsen, P., Berendsen, P., Borcherding, Borcherding, R.M., R.M., Doveton, Doveton, J., J., Gerhard, Gerhard,L., L.,Newell, Newell, K.D., 1988, Texaco #1, K.D., Steeples, Steeples,B., D., and andWatney, Watney,W.L.,, W.L., 1988, Texaco Poersch Poersch *1, Washington Washington Dounty, Dounty, Kansas: Kansas: Preliminary Preliminary geologic geologic report report of of the the pre—Phanerozoic pre-Phanerozoic rocks: rocks: Kansas Kansas Geological Geological Survey Survey Open—file Open-file Report Report 88—22, 116 p. 88-22, 116 p. Brown, L., Oliver, Oliver, J., J., Kaufman, Kaufman, S., S., and and Steiner, Steiner, D., D., 1982, Brown, L., Jensen, Jensen, L., 1982, Rift structrures structrures heneqath beneqath the the Michigan Michigan Basin Basin and and COCORP COCORP profiling: profiling: Geology, V. Geology, V. 10, 10, p. 645—649. 645-649. Chandler, Chandler, V.W., McSwiggen, McSwiggen, P.L., P.L., Morey, Morey, G.B., G.B., Hinze, Hinze, W.F., W.F., and and AnderAnderson, R.R., son, R.R., 1989, 1989, Interpretation Interpretation of of seismic seismic reflection, reflection, gravity, gravity, and and magnetic magnetic data data across across Middle Middle Proterozoic Proterozoic Midcontinent Midcontinent Rift Rift System, System, Northwestern Northwestern Wisconsin, Wisconsin, eastern eastern Minnesota, Minnesota,and and central centralIowa: Iowa: 73, p. American Association of of Petroleum Petroleum Geologists Geologists Bulletin, Bulletin, v. 73, 261—275. 261-275. P.L., Morey, Morey, G.B., G.B., and and Chandler, Chandler, V.W., V.W., 1987, 1987, New New model model of of McSwiggen, P.L., McSwiggen, the Midcontinent Mjdcontjnent Rift the Rift in in eastern eastern Minnesota Minnesota and and western western Wisconsin: Wisconsin: Tectonics, v. 6, p. p. 677—685. 677-685. Tectonics, v. 6, Rosendahl, B.R., B.R., 1987, 1987, Architecture Architecture of of continental continental rifts rifts with with special special Rosendahi, reference to to East Africa: Annual Review Review Earth Earth and and Planetary Planetary reference Science, v. Science, v. 15, 445-503. 15, p. 445—503. L., Setzer, Setzer, P., R., Farmer, Fanner, H., Brown, Brown, L., L., Oliver, Oliver, J., J., Kaufman, Kaufman, S., S., Serpa, L., Serpa, and and Sharp, Sharp, J., J., 1984, 1984, Structrure the southern southern Keweenawan Keweenawan Rift Rift Structrure of of the COCORP surveys surveys across across the the midcontinent midcontinent geophysical geophysical anomaly anomaly in in from COCORP from northeastern Kansas: Kansas: Tectonics, Tectonics, v. v. 3, 367-384. northeastern 3, p. p. 367—384. 61 �terminology of of the the Midcontinent Table 1. 1. Zone and unit differentiation terminology Rift System and associated associated geologic geologic features. features. MAUMEE MAUImE Zone : •• (Thiel Fault) 1st Order Order Accommodation Structure Accommod; In Structure rn (Thiel Fau Sag baala basin on COCORP COCORP seismic stlamlc lines llnu McClure #I4Sparks S p r h well well stratigraphy. atnUgnphy McClun #14 p 1st Order 1st Order Accommodation Accommodntion Structure structure Gravity 'dogleg', Montcalm Montalm Co., Ca.,Michigan Mlchl~n Seismic Corp. aetsmtc Flrat atlamk lInterpretation n~lallaa First Sclamlc 1VEACKINAVV MACKINAW Zone ! 1st Order Order 1st Accommodation Structure Structure SUPERIOR SUPENOR Zone 1st Order 1St Order Accommodation Structure IOWA IOWA Zone 1st Order 1st Accommodation Accommodatlon Structure structure GLIMPCE line F extension uniting McClure #1 Beaver Island test Amoco St. Amour #1.29 test and seismology Coalescing oC MRS structure ~ l w c l or n MRS ~ atrwtum previously identifled l l ~ i e Fault l DIWIOVSJY Identifled Thiol Fault bye*k on GUMPCE lIne 0 Major change I. MRS strike Interrupted gravity and magnetic patterns ' / UI' yn7) F*ult Uflit Unit It structure Ideatuued IOWA central IdeaUfled wabal horse hmt m etun Presenceof .( extension teultiag a m a h and eonipewssioa ~ ~ l fanlthg o a Pmenm Amoeo # I Xacbeld t u f and at~WJppby Amoco SI Riacheld teat atratigraphy well control Regional amtd ReciomI Order 2nd Order -. ACC0StL Structure Strueton Broken grsvity and magnetic trends Granite tsrrane, southeastern Nebraska Local well control Soulh.Central Magnetic Uneament lines Extension fh1Umg uniting on Mendon a COCORP COCORP siesinic alamnk lhu AInflWtek central Aaymmatrk c a a graben l m l ~ ~ and mtlgmpby, stretigysphy Texaco #1 Tuna #I Noel Nod Poerach Potneb teat and ONTONA3NTONAGON SON Unit BRULE BRULE CEISAGO XmAo - S isopsc polarity on GUMPtE liii. A Altered Gravity Trend N Isopacb GUMPCE C Duluth Complex Intrusion Remanent Magnetic Reversals N Outcrop Thickening Terminated Gravity Trend Transverse flsssmeai Ridge .rcliena Phelt trend Vertical Outcrop 0ipe filmiest Organic Patruloglea isopech Bear Creek Cores S Isopech Petty.Rsy Seismic S alaomer Fenit Field Evidence Coastrictad Gravity Trend : w isopech Petty-Ray Seismic Unit — IKANSAS WSAS Zone Zone. 2nd Order Ordk Accorn. AcuJln. Structure stmctnm Order 2nd Onlw .. Accom. A Structure sbnctllm STRUCTURAL STRUCI'URAL DETAIL DETAIL Interrupted grsvfty InItm~pted p d Q aud and magnetic mgnetk patterns ptWnIS icutheast Minnesota Grauitk Gnnltk intrusions, l n t r u d o q soathast Mlanemta System Bell* P h l m (bawfom?) Fault System Beji. B O ~ I O I and * V,1t1 p v l Qcontrol, mbd,Blabley B h b l q Co., Mien. - MANITOU I5ANmou Unit, Unit . r 1st Order Accommodation Structure Accommodation Stmcture (BeUe Plaine Fault) mow (Belle Plaine Iao J- DECREASING RIFT MATURITY N — Gravity Hi$b Gravity Low uctom . Accommodadon m . i t c c & h Figure 1. Location of of accomodation accomodation Figure 1. principal structures and andnames names of principal structures om I. • rift rift zones zones. Figure 2. 2. Details of Figure of the the Superior Superior showing the Zone shwing the location, names and polarity of fundamental fundamental rift rift 62 units. units. �STRUCTURE OF THE ST'RUCTURE OF W MIDCONTINENT MIDCONTINENT RIFT RIFTSYSTEM SYSTEM FROM 8—SECREFLECTION REFLECTION SEISMIC SEISMIC DATA FROM 8-SEC DATA IN I NWESTERN WESTERN LAKE LAKE SUPERIOR SIJF'ERIOR M.G. Mudrey, Mudrey, JJr., Geological M.G. r . , Wisconsin G e o l o g i c a l and Natural N a t u r a l History H i s t o r y Survey, Survey, 3817 3817 Mineral M i n e r a l Point P o i n t Road, Road, Madison, WI W I 53705, 53705, L.D. McGinnis, McGinnis, E Engineering Geosciences, L.D. ngineering G e o s c i e n c e s , Argonne Argonne National N a t i o n a l Laboratory, Iaboratory, Argonne, Argonne, IL IL 60439, 60439, C. C. Patrick P a t r i c k Ervin, E r v i n , Department of o f Geology, Geology, Northern Northern Illinois I l l i n o i s University, University, DeKaib, IL DeKalb, IL 60115 Nyquist, Health and S Safety Research Division, JJ.E. .E. N yquist, H e a l t h and afety R esearch D i v i s i o n , Oak Ridge National National Laboratory, P.O. Box 2008, L a b o r a t o r y , P.O. 2008, Oak Oak Ridge, Ridge, TN TN 37830 37830 A.B. Dickas, Dickas, D Division A.B. i v i s i o n of o f Sciences S c i e n c e s and and Mathematics, Mathematics, Ijniversity I J n i v e r s i t y oof f Wisconsin—Superior, S Superior, WII 54880 Wisconsin-Superior, uperior, W G.E. Morey, Morey, Minnesota Minnesota G Geological G.B. e o l o g i c a l Survey, S u r v e y , St. S t . Paul, P a u l , MN 55114 A.G. Green, G Geological Survey Canada, Building A.G. Green, eological S u r v e y of o f Canada, B u i l d i n g 7 Observatory Observatory Crescent, K l A 0Y3 OY3 C r e s c e n t , Ottawa, Ottawa, Ontario O n t a r i o K1A J.L J . L Sexton, S e x t o n , Department of o f Geology, Geology, Southern S o u t h e r n Illinois I l l i n o i s University, IJniversity, Carbondale, IL Carbondale, I L 62901 62901 ABSTRACT Structural major S t r u c t u r a l sstyle t y l e and m a j o r features f e a t u r e s of of the t h e Midcontinent M i d c o n t i n e n t Rift R i f t SysSyswestern Lake S Superior ttem e m (MRS) in in w e s t e r n Lake u p e r i o r interpreted i n t e r p r e t e d from sparse s p a r s e seismic s e ~ s m i cdata data have been been cconfirmed by GLIMPCE have o n f i r m e d tby ~ yrecently r e c e n t l y made available a v a i l a b l e proprietary proprietary 60—fold, 8-sec 8—sec CDP CDP seismic rreflection 60-fold, e f l e c t i o n data d a t a and gravity g r a v i t y and magnetic magnetic anomaly data d a t a (see ( s e e McGinnis and a n d others, o t h e r s , this t h i s volume). volume). Two new reflection west r e f l e c t i o n pprofiles r o f i l e s eeast a s t aand nd w e s t of o f GLIMPCE line l i n e C disclose d i s c l o s e aa deep deep asymmetrical ccentral however, the asymmetrical e n t r a l ggraben; r a b e n ; however, t h e new lines l i n e s ddefine e f i n e a southward thickening volcanic t h i c k e n i n g ssedimentary— edimentary- v o l c a n i c wedge in i n contrast c o n t r a s t to t o line l i n e C, C, complexities iin between m major ssuggesting u g g e s t i n g complexities n sstructural t r u c t u r a l bblocks l o c k s between a j o r MRS rift rift a relief r o a d aarch r c h nnear e a r 447° 7 O 20' 20' N., N . , 90° 900 W with with a r e l i e fofo fmany many zones. A bbroad kkilometers i l o m e t e r s on the t h e long, l o n g , nnortheast o r t h e a s t trending t r e n d i n g reflection r e f l e c t i o n line l i n e in i n the t h e west west Lake SSuperior is ooverlain with sslight arm oof f Lake u p e r i o r is v e r l a i n wit.11 l i g h t aangular n g u l a r unconformity u n c o n f o r m i t y by Middle Proterozoic s t r a t a , suggesting s u g g e s t i n g that t h a t the t h e western w e s t e r n arm arn P r o t e r o z o i c ssedimentary e d i m e n t a r y strata, Superior oof f Lake S u p e r i o r may infact i n f a c t include i n c l u d e at a t least l e a s t two two rift r i f t subzones. s u b z o n e s . AA broad ssyncline Bayfield Peninsula broad y n c l i n e nnortheast o r t h e a s t oof f B ayfield P e n i n s u l a is bounded on the t h e south south by a fault. f a u l t . Whether this t h i s is a continuation c o n t i n u a t i o n of o f the t h e Douglas Isie-Royale Isle-Royale Fault F a u l t System System is is not n o t clear. clear. This work w was T h i s work a s ssupported u p p o r t e d by the t h e U.S. U.S. Department of o f Energy, Office Office ooff Energy Research, R e s e a r c h , under u n d e r Contract C o n t r a c t W—31—l09—ENG--38. W-31-109-ENG-38. 63 �METAMORPHISM AND POLYGENESIS POLYGENESISOF ORE DEPOSITS: ANEXAMPLE EXAMPLE METAMORPHISM DEPOSITS: AN FROM FROM THE MADEM MADEM LAKKOS LAKKOS PB-ZN-AG-AU PB-ZN-AG-AUDEPOSIT, DEPOSIT, GREECE GREECE Mark L. Nebel L. Nebel Dept. of Geology, 80401 Geology, Colorado Colorado School School of Mines, Mines, Golden, Golden, CO CO 80401 Economic Economic geologists geologists frequently frequently encounter encounter difficulties difficulties in in applying applying simple, single-event single-event genetic models to complex complex ore ore deposits. deposits. This This simple, genetic models has invariably invariably led led to opposing opposing camps camps of of geologic geologic thought thought which which stubbornly argue that that specific stubbornly argue specific ore deposits, deposits, and even even entire entire classes classes of ore ore deposits, deposits, are are either either 'syngenetic' 'syngenetic' or or 'epigenetic', 'epigenetic', etc., etc., and and that that these formed by by a single these deposits deposits formed single process process during during aa single single geologic geologic event. event. This This type type of of thinking thinking ignores ignores the the fact fact that that ore ore deposits, deposits, like like all other other rocks, rocks, have have long longand andcomplex complex histories. histories. They are are subject subject to to regional and local metamorphic regional and local metamorphic and/or andlor deformational deformational events, events, magmatic intrusion, and magmatic intrusion, and the the effects effects of of interaction interaction with with circulating circulating fluids fluids of of extremely extremely variable variable chemistry. chemistry. These processes processes can can These profoundly change the the morphology and composition of any profoundly change morphology and composition of any rock rock type, type, including including those those containing containing economic economic minerals. minerals. The The recognition recognition of of multiple or events multiple processes processes or events leading leading to the the formation formation ofofeconomic economic mineral deposits, i.e. i.e. the concept can lead concept of 'polygenesis', 'polygenesi~'~ can lead to to aamuch much mineral deposits, better better understanding understanding of not not only only complex complex and andpoorly-understood poorly-understood ore ore deposits, but also those that 'appear' to be simple. deposits, also those that 'appear' to be simple. The The problems problems and and seeming seeming contradictions contradictions encountered encountered in applying applying single-event single-event genetic genetic models models can often often be be avoided. avoided. The The Madem Madem Lakkos Lakkos deposit deposit in in northern northern Greece Greece serves serves as as an an excellent Madem Lakkos Lakkos excellent example example of aa polygenetic polygenetic ore ore deposit. deposit. The The Madem ores ores are are hosted hosted in in marble marble of ofthe theMesozoic(?) Mesozoic(?) Kerdylia Kerdylia Formation, Formation, aa high-grade high-grade metamorphic metamorphic complex complex composed composed of of migmatitic migmatitic biotite biotite gneiss gneiss interlayered interlayered with with marble, marble, hornblende hornblende gneiss, gneiss, and andamphibolite. amphibolite. The Kerdylia Formation is The Kerdylia Formation is intruded intruded by variety of of synsyn- and and postpostby a variety tectonic felsic intrusions intrusions of of Tertiary Tertiary age. age. LongLongtectonic intermediate intermediate to to felsic believed believed to have have formed formed as as an anepigenetic epigenetic replacement replacement body body related related to to Tertiary Tertiary magmatism, magmatism, recent recent research research has has recognized recognized the thepresence presence of Madem Lakkos Lakkos of three three different different and and distinct distinct ore ore types types inin the the Madem deposit deposit that that require require aa much much longer longer and and more more complex complex genetic genetic history. history. Based Madem Based on on ore ore mineralogy, mineralogy, textures, textures, and and geochemistry, geochemistry, the theMadem Lakkos ores can be be characterized characterized as either either 1) 1) Massive Massive Sulfide Sulfide Ore, Ore, 2) 2) Lakkos Replacement Ore, or 3) Skarn Ore types. Replacement Ore, 3) Skarn Ore types. Massive Massive pyrite-sphaleritepyrite-sphaleritegalena galena ore ore exhibits exhibits abundant abundant and and well-developed well-developed metamorphic metamorphic textures textures that that indicate indicate the the ore ore has has been been metamorphosed metamorphosed to at at least least 600°C 6OO0C (amphibolite (amphibolite grade), grade), together together with with its its marble marble and and gneiss gneiss host host rocks. These textures include rocks. These textures include foliated/lineated foliatedtlineated galena galena and and 64 �I sphalerite, slip and deformation twinning in galena and sphalerite, and granoblastic annealing/recrystallization features in galena, sphalerite, and pyrite with the development of 1200 triple-point junctions. In spite of its metamorphism, the ore preserves a generally stratiform nature, a stratigraphic association with other chemical sediments, primary compositional layering, and metal zonation that are consistent with formation as a carbonate-hosted, syndepositional massive sulfide deposit. Replacement ore consists of complex veins and manto-type impregnations in altered marble composed of pyrite, sphalerite, galena, tennantite, chalcopyrite, arsenopyrite, seligmannite, boulangerite, and minor amounts of a wide variety of additional sulfosalt minerals in a quartz-sericite-manganiferous carbonate gangue. Replacement ore cross-cuts and has reacted with the massive sulfide ore, and does not exhibit evidence of metamorphism. Euhedral zoned crystals with mineral and fluid inclusions, open space fillings, and complex textural relationships are characteristic of this ore type, and suggest replacement of marble by reaction with hydrothermal solutions. Replacement ore is enriched in As, Cu, Bi, Sb, Mn, Sn, and Te with respect to the massive sulfide ore, and was deposited from near-neutral pH solutions at temperatures ranging from 200 to 400°C. Preliminary lead isotope data indicate that massive sulfide and replacement ores have a common homogeneous lead source. Skarn ore contains pyrite, chalcopyrite, minor amounts of other sulfide and sulfosalt minerals, and scheelite in a calc-silicate gangue assemblage of garnet, diopside, calcite, quartz, epidote, and minor chlorite and magnetite. Textures similar to those found in the replacement-type ore and an absence of metamorphic features are characteristic of the skarn ore. Fluid inclusions indicate a magmatic source and high temperature, low pressure deposition for the skarn ore. Skarn ores do not exhibit a clear spatial relationship to foliated aplitic igneous rocks in the mine, and appear to represent a distal skarn, related to co-regional intrusions but formed by hydrothermal replacement of marble at some distance from the source magma. A multi-stage genetic model is proposed for the Madem Lakkos Synsedimentary massive sulfide ore was deposited as a stratiform body within a sequence of Mesozoic(?) shallow water platform carbonate, clastic/volcaniclastic, and evaporitic sediments. This ore and its host rocks were metamorphosed to upper amphibolite grade during Tertiary age regional metamorphism. Post-tectonic intrusion of the Stratoni granodiorite into the deposit. 65 �metamorphosed Kerdylia Kerdylia Formation Formation generated generated heat heat and magmatic metamorphosed magmatic skarn mineralization fluids that produced produced skarn mineralization and and aa continuing convective system that that mixed meteoric waters, convective hydrothermal hydrothermal system mixed with with meteoric waters, extensively altered altered the the marble, and formed ores in extensively marble, and formed the replacement replacement ores in part by part by reaction reaction with with and and remobilization remobilization of the the massive massive sulfide sulfide ore ore and in part and part by by addition addition of ofconstituents. constituents. The Madem deposit exhibits exhibits aa distinctive variety of of ore Madem Lakkos Lakkos deposit distinctive variety ore The types whose features cannot cannot be be explained by aa single types whose combined combined features explained by single The genetic process. genetic process. The mineralization mineralization cannot cannot be characterized characterized as as simply 'syngenetic' or 'epigenetic'. It must considered It must be be considered 'polygenetic', formed by by aa series 'polygenetic', formed series ofofgeologic geologicevents eventssuperimposed superimposed over is likely over an an extended extended period period of of time. time. ItIt is likely that that other other complex, complex, enigmatic, enigmatic, and geologically geologically controversial controversial ore deposits deposits have have formed formed in similarly similarly complex in complex ways. ways. 66 �PETROGENETIC EVOLUTION EVOLUTION OF OF THE THE PROTEROZOIC PROTEROZOIC WAUSAIJ WAUSAU IGNEOUS IGNEOUS COMPLEX, COMPLEX, WISCONSIN WISCONSIN PETROGENETIC T. PATTON, M.K. SOD, B. BIDDULPH, Department of Earth Sciences M.K. SOOD, B. BIDDULPU, Department of Earth Sciences T. PATTON, Northeastern I l l i n o i s University, Chicago, IL I L 60625 60625 Northeastern Illinois University, Chicago, The The 1,520 1,520 m.y. m.y. old old Wausau Wausau Igneous igneous complex complex is is located located in i n Marathon Marathon county, county, north north central Wiscon$in. Wisconln. It les west of the Wolf River batholith and covers an It \ies west of the Wolf River batholith and covers an area area of of roughly roughly 300 300 km km (112 (112 ml m i ). 1. Ilt is is composed composed of of two two plutons, plutons, which which are are somewhat somewhat elongated elongated to t o the the northeast. northeast. The The Stettin S t e t t i n pluton, pluton, which which lies l i e s to t o the the northeast northeast of of the the larger Wausau Wausau pluton, pluton, is is elliptical e l l i p t i c a l and and contains contains aa core core of of nepheline nepheline and and pyroxene pyroxene larger syenite by syenitic syenltic rings. rings. The The subcircular subcircular Wausau Wausau pluton pluton extends extends from from syenite surrounded surrounded by north north of of Wausau, Wausau, southward southward to t o west west of of Mosinee, Mosinee, and and is separated separated into i n t o northern northern and and southern by the the Rib RibRiver Riverlineatnent. lineament. The The northern northern segment segment consists consists of of southern segments segments by Wausau granite, which forms Wausau syenites syenites that t h a t grade grade into i n t o quartz quartz syenite syenite and and the t h e Ninernile Ninemile granite, forms the the largest largest unit u n i t of of the the complex. complex. The Stettin pluton is a petrographically petrographically zoned intrusion characterized by S t e t t i n pluton tabular syenite iin zone, amphibole syenite iin and n the wall zone, n the intermediate zone, zone, and pyroxene zone, which show considerable pyroxene and and nepheline nepheline syenites iin n the core zone, considerable textural textural variations. variations. Perthitic alkali a l k a l i feldspar (50—90%), (50-9011, nepheline nepheline (7—25%), (7-25%), bluish—green bluish-green it sodic (5—114%),aegerine-augite aegerine—augite pyroxene pyroxene (14—10%), constitute the sodic amphibo].es amphiboles (5-14g), (4-1011, constitute the major major minerals minerals in i n the the Stettin S t e t t i n rocks. rocks. Zircon, Zircon, apatite, a p a t i t e , fluorite, f l u o r i t e , calcite, c a l c i t e , magnetite, magnetite, fayalite, f a y a l i t e , biotite, biotite, and and quartz quartz occur occur as a s minor minor minerals. minerals. The also shows shows petrographical petrographical zoning with The Wausau Wausau p].uton pluton also w i t h aa wall wall zone zone of of pyroxene—amphibole with pyroxene-amphibole Wausau syenite w i t h mechanically mixed xenoliths of quartzite quartzite and and Xenoliths and and maf mafic Ic schlieren schlieren s c h i s t in i n aa discontinuous discontinuous but but circular circular configuration. configuration. Xenoliths schist and and clots c l o t s are are more more frequent frequent in i n the t h e intermediate intermediate quartz quartz syenite syenite zone. zone. Sodic Sodic plagioclase perthite (60-8011 (60—80%) and quartz (5—12%) plagioclase and and rnicrocline microcline perthite (5-121) constitute constitute the the major aegerine, ffayalite, magnetite, and carbonate form major minerals minerals and and barkevi.kite, barkevikite, aegerine, a y a l i t e , magnetite, form largely of porphyritic, porphyritic, The Ninemile granite consists largely the the minor minor minerals. minerals. The medium—coarse medium-coarse grained, amphibole—biotite amphibole-biotite granite and a core core of biotite—muscovite biotite-muscovite granite (62-651). granite which which possesses possesses miarolitic miarolitic cavitites. cavitites. Perthitic P e r t h i t i c alkali a l k a l i feldspar feldspar (62—65%), plagioclase (5—7%), (5-7%), and and quartz quartz (21—29%) (21-291) form form the the principal minerals minerals with with minor minor plagioclase is an an important important accessory. accessory. Fluorite Is amounts amounts of of sodic sodic amphiboles amphiboles and and biotite. biotite. Fluorite Electron of the principal phases indicate that Electron microprobe studies of t h a t the the Wausau Igneous of anorogenic, Igneous complex complex has has mineral chemistry chemistry characteristic characteristic of anorogenic, alkalic a l k a l i c (felsic) (f e l s i c ) intrusions, intrusions, as a s sunnarized summarized in i n Table Table 1. 1. Chemically, Chemically, the Wausau rocks show overall alkalic to t o subalkalic affinities affinities (Table (Table 2.) 2.) Syenitization Stettin, Syenitizatlon of of volcanics volcanlcs aatt S t e t t i n , miarolitic cavities c a v i t i e s in i n the the Ninemile Ninemile a s well well granite, granite, the the medium medium to t o coarse coarse grained texture texture of of the the rocks rocks of of the the complex, complex, as as of ffluorite volatile—bearing minerals, a s the the appreciable appreciable amounts amounts of l u o r i t e and other volatile-bearing minerals, suggest suggest the presence of of an active magmatic ffluid l u i d phase during the crystallization and emplacement history history of of the the complex. complex. The The Al A 1 content content of of the the amphiboles amphiboles and and the the emplacement relatively sharp contact relations w with wall rock rock aare i t h the wall r e aalso l s o indicative of of epizonal. emplacement, aat depths of of approximately approximately 10—15 km. t depths 10-15 km. epizonal emplacement, The igneous complex was most likely The magma magma tthat h a t formed the.Wausau igneous l i k e l y generated generated in i n aa crusta]. extension—thermal doming doming environment environment through through ppartial melting of of tthe crustal extension-thermal a r t i a l melting h e Penokean ic crust. crust. The The initial i n i t i a l stages stages may may have have involved involved dehydration dehydrationmelting meltingofofthe themaf mafic portions imparting tthe undersaturated characteristics represented at h e ssilica i l i c a undersaturated a t Stettin. Stettin. The The pervasive pervasive thermal thermal doming doming may have caused progressive progressive "softening" "softening" of of the the upper, upper, less thus changing changing tthe h e magma composition tto o silica s i l i c a oversaturation, oversaturation, as as l e s s mafic, mafic, crust; crust; thus T h i s process process may may have have been been aided aided by by the the represented represented by by the the Ninemile Ninemile granite. granite. This The apparent apparent petrographic petrographic and and chemical chemical limited limited assimilation assimilation of of xenocrystic xenocrystic quartz. quartz. The differences observed observed in i n the the Wausau rocks aare r e reflections reflections of the progressive progressive change change differences of the 67 �i n the the source source rock rock and and the the degree degree of of partial p a r t i a l melting, melting, arid and less l e s s the the result result of of in magmatic differentiation. differentiation. magmatia The Wausau Wausau igneous igneous complex complex represents represents aa magmatic magmatic event, event, related related to to The of the the early early Proterozoic, Proterozoic, with with no no apparent apparent the incomplete incomplete continental continentalrifting r i f t i n gof' the l i n k to t o the the Wolf Wolf River River batholith. batholith: petrogenetic link petrogenetic Table 1.1. Table Mineral chemistry chemistry of of the the Wausau Wausau Igneous Igneous Complex. Complex. Mineral ....................................................................... Mineral Mineral Amphiboles Axnphiboles Fe/Fe+Mg Fe/Fe+Mg Compositional Phases Phases Compositional (Figure 1A) 1A) (Figure Stettin Stettin Wausau Wausau Ninemile Ninemile 0.59-0.98 0.59—0.98 0.76-1 .OO 0.76—1.00 0.91-0.99 0.91—0.99 Ferroedenitic to t o ferro— ferroFerroedenitic hastingsitic hornblende, hornblende, hastingsitic some riebeckite, riebeckite, arfved— arfvedsome sonite, arid and ferrorichterite sonite, ferrorichterite Biotites Biotites (Figure 1B) 1B) (Figure Stettin Stettin Wausau Wausau N i nemile Ninemile 0.93-0.97 0.93—0.97 0.70-0.97 0.70—0.97 0.90-0.99 0.90—0.99 Annitic biotite biotite Annitic Pyroxenes Pyroxenes Stettin Stettin Wausau Wausau 0.68-0.89 0.68—0.89 0.69-1 .OO 0.69—1.00 Aegerine (acmite)—augite (acmitel-augite Aegerine Plagioclase Plagioclase Feldspars Feldspars Stettin Stettin Wausau Wausau — Ninemile Ninemile Alkali Alkali Stettin Stettin Wausau Wausau Ninemile Ninemile Feldspars Feldspars (x-ray data) data) (x—ray -- ---Table 2. 2. Table - Albite-oligoclase Albite—oligoclase An0—An21 An0-An21 An0—An12 12 Or.—Or Microcline perthites perthites Microcline 0r39—0r611 0r52—0r63 --- -------------- Chemistry of of the the Wausau Wausau Igneous Igneous Complex Complex rocks. rocks. Chemistry wt. %1 Wt. Stettin Stettth Wausau Wausau Ninemile Ninemile Si02 Si02 Na20+K20 Na20+K20 511.10—66.10 67.50—76.93 C l , FF Cl, 100—1650 0.01—0.35 62.86—66.39 11.20—12.59 16.51—18.21 88—346 0.01—0.22 Chemistry: Chemistry: Alkalic-peralkalic Alkalic—peralkalic Metaluminous Metaluxn.thous Nepheline Nepheline Normative Normative Quartz Quartz Normative Normative 10.20—13.80 A1203 A].203 Zr (ppm) ( P P Zr . ~ 13.211—21.02 68 9.116—11.01 12.52—15.55 140-1500 0.06—0.111 Peraluminous— Metaluminous Quartz Quartz Normative Normative �PARAGASITE PARAGASITE HASTINSSITE HAST!NSTE ANNITE SIOEROPHYLLITE ANNITE SIDE ROPHY LI ITt WOLF R I V E BATHOLITH R BATHOLITH •8 WOLF RIVER 0 N I N E M I L E GRANITE o NINEMILE A WAUSAU COMPLEX COMPLEX WAUSAU 0 S T E T TCOMPLEX I N COMPLEX 0 STETTIN O) + If, a) Ua) U- • • ••s UOLF RIVER BATHOLITH • WOLF RIVER BATHOLITI4 N I N E R I L E GRANITE NINEMILE i o0 - A (A) 00 0.5 0.5 EDENITE VAUSAUCOMPLEX COMPLEX AUS&U S T E T I N COMPLEX 00 STETTIN COMPLEX Fe/Fe+Mg F'e/Fe+Mg 1 FERROEDENITE FERROEDEIflTE 1 pnLI.OGOplTE PHLOGOPITE (B) 1.5 1.5 R L ATOMS RTOMS AL F i g u r e 1. 1. (A) (A) Compositions Compositions ofofamphiboles amphibolesfrom fromthe t hWausau e Wausau Complex Complex in i n terms t e r m s of of Figure A 1 (VI). (B) Compositions o f b i o t i t e s from t h e Fe/Fe+Mg and Fe/Fe+Mg and Al (VI). (B) Compositions of biotites from the Wausau Complex i nint eterms r m s oof f total t o t a lAlAand 1 and Fe/Fe+Mg. Wausau Complex Fe/Fe+Mg. REFERENCES CITED CITED REFERENCES Sood, M.K., P.E. Meyers, Meyers, and e r l i n , 1980. 1980. Petrology, P e t r o l o g y , geochemistry geochemistry Sood, M.K., P.E. and L.A. L.A. BBerlin, and c o n t a c t r e l a t i o n s of t h e Wausau and S t e t t i n s y e n i t e plutons, and contact relations of the Wau5au and Stettin syenite plutons, c e n t r a l Wisconsin, 2 6 t h Ann. I n s t . Lake S u p e r i o r Geol., F i e l d Trip Trip 3, central Wisconsin, 26th Ann. Inst. Lake Superior Geol., Field 3, Univ. o f Wisconsin, Eau C l a i r e , 59 p. Univ. of Wisconsin, Eau Claire, 59 p. 69 2 EASTONITE EASTONITE �___________________________ PETROGRAPHIC AND MICROPROBE STIJDY STUDY OF OF ISOLATED ISOLATED IRON-FORMATION IRON-FORMATIONLENS LENS PETROGRAPHIC MICHIGAN: A SEARCH FOR HIGH-GRADE, HIGH-GRADE, PRE-PENOKEAN PRE-PENOKEAN NEAR REPUBLIC, MICHIGAN: METAMORPHISM METAMORPHISM J.W. Peterson, T. Chacko, S.M. Kuehner, Kuehner, Department Department of of the Geophysical Geophysical Sciences, Sciences, University University of of Chicago, 312-702-8137 IL60637, 60637,3 12-702-8137 Chicago, Chicago, Chicago, IL Though virtually virtually all all the iron-formation in the Republic Quadrangle Quadrangle of Marquette Marquette County, County, Though Michigan, is of Precambrian X age (Van Schmus and Woolsey, 1975), some isolated lenses of W age age Bell Bell Creek Creek Gneiss Gneiss(Cannon (Cannon iron-formation occur occur within the the mafic units of the Precambrian Precambrian W iron-formation 1973). One Oneof ofthese theselenses lensesoutcrops outcropsapproximately approximately one one mile mile southwest southwestof ofthe the and Simmons, 1973). village of Republic, Michigan, in the the southeast southeast comer corner of of section section 12, 12,T.46N., T.46N.,R.30W. R.30W. Samples from from this outcrop outcrop were were examined examined using using petrographic petrographic and and electron electron microprobe microprobe techniques techniquestoto determine whether whether the the mineralogy mineralogy reveals evidence for an earlier, earlier, higher grade of metamorphism metamorphism determine than that that experienced experienced by by the theNegaunee NegauneeIron Iron Formation Formation—1.9 -1.9 b.y. and Woolsey, Woolsey, than b.y. ago (Van Schmus Schmus and figure and and includes includes zones of the the following following The unit unit isis banded banded on on the the scale scale illustrated illustrated in the figure 1975). The assemblages: ferro-tschermakitichornblende hornblende÷+quartz quartz++ magnetite, magnetite, Fe-rich Fe-rich assemblages: ferro-hornblende ferro-hornblende++ ferro-tschermakitic cummingtonite anthophyllite++ quartz quartz ++ magnetite, magnetite, garnet garnet ++ Fe-rich Fe-rich cummingtonite curnrningtonite±k cumrningtonite±kanthophyllite anthophyllite anthophyllite++ quartz quartz ++ magnetite magnetite ++ ferro-tschermakitic ferro-tschennakitic hornblende, hornblende, Fe-rich Fe-rich cummingtonite cummingtonite ±k anthophyllite anthophyllite++ biotite biotite ++ quartz quartz ++ magnetite magnetite ±k ferro-tschermakitic hornblende, garnet garnet ++ Fe-rich Fe-rich cummingtonite anthophyllite++ quartz quartz++ magnetite, magnetite, Fe-rich Fe-rich cummingtonite cummingtonite±kanthophyllite anthophyllite++ cummingtonite±kanthophyllite biotite biotite ++quartz quartz ++ magnetite, magnetite, and and garnet garnet ++ Fe-rich Fe-rich cummingtonite cumrningtonite±k anthophyllite anthophyllite ++ biotite biotite ++ quartz. quartz. A present and and associated with with the the magnetite. magnetite. Garnet A complex complex mixture mixture of Fe-S phases is also present Garnet and and as those those of of the the highest highest grade grade of of the the Negaunee NegauneeIron Iron amphibole compositions compositions are are virtually virtually the same as amphibole Formation (Haase, (Haase,1982) 1982)and andbiotite-garnet biotite-garnetpairs pairs yield yieldpaleotemperatures paleotemperaturesofof—535°C, -535OC, compared compared to to Formation —550°C forNegaunee NegauneeIron IronFormation Formationrocks rocksininthe thesame samevicinity vicinity(Haase, (Haase,1982). 1982). Though the -550° for higher-grade higher-grade mineral, mineral, orthopyroxene, orthopyroxene, has been reported in in some some of of these these isolated isolated lenses lenses(Cannon (Cannon and 1973),our our preliminary preliminary results suggest that there is no mineralogical mineralogical evidence evidencein in this this and Simmons, Simmons, 1973), locality for for an earlier earlier metamorphism more intense than that experienced by the Negaunee Iron locality Formation. Formation. 11 I II E ferro-hornblende lerro-hornblende +terro-tschermakitic +ferro-tschermakitlc hornbtende hornblende +quartz .magnette Fe-cummingtonile janthophyltite +guartz +rnagnetit. U L garnet +F..Cummingtonite tanthophyflite +quartz +magneute +ferro.tschermakllic hotnbiande Fe-cumminglonite tanthophyilite +biotite .quartz +magnetite jprrp-tschermpicitic hprnblei'Ce garnet +Fe-cummingtonite tanthophyllite +guarlz +magnetite Fe-cummingtonsta ianthooiiyilite +biotit. ..guartz +magnetite garnet +Fe-cumrningtonite tanthop9yIIite +biotite +quartz References ReferencesCited Cited Cannon, Cannon, W.F. W.F. and and Simmons, Simmons,G.C., G f . .1973, 1973,Geology of part pan of of the the Southern SouthernComplex, Complcx,Marquette MarquetteDistrict, District,Michigan: Michigan: Journal Journalof ofResearch, Research,U.S. U.S.Geological Geological Survey, Survey, v. v. 1, 1,n. n.2,2,165-172. 165-172. Haase, Haase, C.S., C.S.,1982, 1982,Metamorphic Mctamorphicpetrology petrology of the the Negaunee Negaunee Iron Iron Formation, Formation,Marquette MarquetteDistrict, District,northern northernMichigan: Michigan: mineralogy, equilibria: Economic 60-81.1. mineralogy,metamorphic metamorphic reactions, reactions, and phase equilibria: EconomicGeology, Geology,v. v. 77, 77.60-8 Van Van Schmus, Schmus,W.R. W.R. and and Woolsey, Woolsey, L.L., L.L., 1975, 1975, Rb-Sr Rb-Sr geochronology geochronology of of the the Republic Republic area, area,Marquette MarquctteCounty, County, Michigan: 1723-1733. Michigan:Canadian CanadianJournal JournalofofEarth EarthSciences, Scicnccs,v.v.12, 12,1723-1733. 70 �ONE, POSSIBLY POSSIBLY TWO, TWO, IMPACT IMPACT CRATERS CRATERS UNDER UNDER DePERE, DePERE, WISCONSIN, WISCONSIN, DISCOVERED DISCOVERED VIA VIA WATER WATER WELL WELL ONE, LOGS AND AND DRILL DRILL CUTTINGS CUTTINGS LOGS William F. F. Read, Read, Dept. Dept. of Geology, Geology, Lawrence Lawrence Univ., Univ., Appleton, Appleton, Wis., Wis., 54912 54912 William - Water—well Water-well drillers drillers in in Wisconsin Wisconsin are are required required to to send send descriptions descriptions of of rock rock units units penetrated penetrated by by their their drills drills to to the the Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey. Survey. If If the the well is is to be a "high—capacity" "high-capacity" producer, producer, they they are are required required also also to to send send in in drill drill chips chips collected collected at at 5—foot 5-foot intervals. intervals. From From the the chips chips Survey Survey personnel personnel prepare prepare detailed logs loqs of of the the drill drill holes. holes. These These records, records, which which have have been been accumulating accumulating since since detailed about about 1900, 1900, are are an an extremely extremely valuable valuable source source of of information information on on subsurface subsurface geology. geology. My My interest interest in in impact impact craters craters began began years years ago ago when when II started started work work on on the the Glover Glover Bluff . Bluff structure structure(1) (1). This is is now now "officially" "officially" accepted accepted as as being being of of impact impact origin origin This ( 2 .) . The The Rock Rock Elm Elm structure structure may may also also be be (probably (probably is, is, in in my my opinion) opinion) of of impact impact origin origin (2) ( 3 ) (4). (4). Both Both structures structures appear appear to to be be of of Lower Lower to to Middle Middle Ordovician Ordovician age. age. (3) There There are are plenty plenty of of Lower Lower and and Middle Middle Ordovician Ordovician sedimentary sedimentary rocks rocks in in eastern eastern Wisconsin. Several Several quarries quarries near near Lawrence Lawrence University University were were begun begun in in upper upper Middle Middle Wisconsin. Ordovician Ordovician dolomites dolomites of the the Sinnipee Sinnipee Group Group (5) (5) and and got got down down into into Lower Lower Ordovician Ordovician Prairie Prairie du du Chien Chien dolomite dolomite as as development development progressed. progressed. Lower Lower Middle Middle Ordovician Ordovician strata, strata, mainly mainly the the St. St. Peter Peter sandstone, sandstone, are are commonly commonly thin thin in in this this area area and and may may be be missing missing altogether. In In two two of of these these quarries quarries the the St. St. Peter Peter appears appears only only as as lenses lenses aa few few altogether. meters meters thick. thick. Near Near the the bottoms bottoms of of some some lenses lenses there there are are potato—size potato-size objects objects which which superficially superficially look very much like like chert chert nodules nodules but are quite quite different different in in details details of ( 6 ) . In In external form form and and internal internal composition. composition. II interpret interpret them them as as impact impact bombs bombs (6). external northern Illinois Illinois II found found similar similar objects objects associated associated with with small small spherules spherules that that bear bear aa northern close close resemblance resemblance to to silicified silicified ooids. ooids. But But these these too too are are different different internally internally from from ordinary ordinary ooids. ooids. Some Some appear appear to to have have crystallized crystallized from from glass glass in in aa manner manner similar similar to to that that of of lunar lunar glass spherules spherules and the the "microtektites" "microtektites" found found in in modern modern sea—floor sea-floor sediments. sediments. II interpret interpret them them as as impact impact spherules spherules(7). ( 7 ) . The The Illinois Illinois spherules spherules have have so so far far been been found found only in loose loose chunks chunks of of rock rock but but there there is is good good reason reason to to believe believe that that these these chunks chunks came from near near the the base of the the St. Peter sandstone. sandstone. came from base of St. Peter Since Since these these initial initial discoveries discoveries II have have found found similar similar impact impact bombs(?) bombs(?) and/or and/or impact impact spherules(?) spherules!?) of about about the the same same age age at at aa number number of of other other locations locations in in Wisconsin Wisconsin and and in in Arkansas, Arkansas, Pennsylvania, Pennsylvania, and and Newfoundland. Newfoundland. These These widespread widespread impact impact ejecta(?) ejects(?), plus plus the the known known Lower to Middle Ordovician Ordovician craters craters or or crater crater substructures, substructures, suggest suggest that that Planet Planet Earth may have been hit hit by by an an unusually unusually large large number number df of asteroids asteroids or or comets during during this this time time interval. interval. comets It It occurred to me that the actual abundance abundance of craters craters of of Lower Lower to to Middle Middle Ordovician age might be much greater greater than than the the number number of of known known craters craters now now regarded regarded as as Ordovician age And that that it it might might pay pay to to look look for for buried buried ones ones via via being of of this this age age would would indicate. indicate. And being buried crater crater formed formed near near the the close close logs of, of, and and drill cuttings cuttings from, from, water water wells. wells. AA buried logs of of Lower Lower Ordovician Ordovician time time should should be be filled filled with with an an unusual unusual thickness thickness of of Middle Middle Ordovician Ordovician sediment——in s e d i m e n t ~ i nWisconsin, Wisconsin, St. St. Peter Peter sandstone. sandstone. Conversely, Conversely, the the Lower Lower Ordovician , having Ordovician (Prairie (Prairiedu du Chien Chiendolomite dolomiteininWisconsin) Wisconsin), having been been excavated excavated during durinq crater crater formation, formation, should should be be thin thin or or absent. absent. Unfortunately, Unfortunately, this this criterion criterion alone alone is is an insufficient insufficient guide for buried-crater since the the Prairie Prairie du du Chien, Chien, during durinq aa an buried—crater hunters since brief interval emergence, suffered interval of emergence, suffered considerable considerable erosion erosion by surface surface and subsurface and subsurface water, Chien is is likely likely to to be be found found water, so so that that thick thick St. St. Peter Peter overlying overlying thin thin Prairie Prairie du du Chien impact craters almost almost anywhere. anywhere. An An additional additional criterion criterion must must be be applied: applied: impact craters are are excavations excavations of limited, limited, normally circular, circular, extent; extent; excavations excavations produced produced by by erosion erosion So the the buried—crater buried-crater hunter hunter are likely likely to to be be more more extensive extensive and and irregular irregular in in shape. shape. So are must must look look for for thick thick St. Peter Peter over over thin thin Prairie Prairie du du Chien Chien in in an an area area which which is is at at least least limited limited even if its its shape shape cannot cannot be be determined determined from from the the information informationsupplied suppliedby by well well Even this this criterion criterion leaves leaves open open the the possibility possibility that that the the filled filled "hole" "hole" loqs. Even logs. indicated by a definitely definitely limited limited area area of of thick thick St. St. Peter Peter over over thin thinPrairie Prairiedu du Chien Chien indicated This is is always always an an alternative alternative unless unless the the bottom bottom of of the the simply be be aa sinkhole. sinkhole. This may simply thick thick St. St. Peter Peter goes goes well well below below the the lowest lowest level level reached reached by by holes holeslikely likelyto tohave havebeen been i.e., down into into Cambrian Cambrian sandstone sandstone or the the Precambrian Precambrian generated by by solution: solution: i.e., generated basement. basement. Proof that a buried hole of any kind was produced by impact impact would have to come Impact cratering cratering of of any any magnitude magnitude is is from from rock rock samples samples provided provided by by drill drill cuttings. cuttings. Impact Evidence of of accompanied by aa good good deal deal of of melting melting and and shocking shocking of of the the target targetrocks. rocks. Evidence accompanied one one or or both of these activities activities would have have to to be found found in in drill drill cuttings cuttings before before of anyone would believe that that a buried hole, hole, regardless regardless of extent extent or or depth depth of anyone penetration, penetration, might actually actually be be an an impact impact crater. crater. 71 �Fortunately, Fortunately, Mai and and Dott Dott (8) (8) have have recently recently published published maps maps showing showing (a) (a) variations in the thickness thickness of the the St. St. Peter Peter in in eastern eastern and and southern southern Wisconsin, Wisconsin, and and (b) (b) the the stratigraphic stratigraphic age age of of the the rock rock which which directly directly underlies underlies it. it. The The maps maps are are based on a study of nearly 900 900 "high "high capacity" capacity" wells wells logged logged by by the the State State Survey Survey from from drill drill cuttings. cuttings. From these these maps anyone anyone can can easily pick likely likely locations locations for for buried buried impact impact craters craters using using the the criteria criteria outlined outlined above. above. For For starters, starters, I picked picked the the DePere DePere area, area, one of a number number of areas areas where where the the maps maps show show that that the the St. St. Peter Peter is is unusually unusually thick thick in in a limited limited area and and that that its its bottom bottom cuts cuts well down down into into the the Cambrian. Cambrian. Also Also there there is is good "control" "control" in in that that the the area area contains contains quite quite aa few few high high capacity capacity wells. wells. It It was aa lucky lucky choice. choice. Thin Thin sections sections were prepared prepared from from drill drill chips chips provided provided by by the the State State Survey and, and, sure sure enough, enough, impact impact melt melt (glass, (glass, unaltered unaltered or or partly partly crystallized) crystallized) was found found in in aa number number of of chips chips that that came came from from near near the the bottom bottom of of the the St. mm in in St. Peter. Peter. Some Some features features noted noted in in these these small small samples samples (averaging (averaging about about 55 mm diameter) diameter) are: are: 1. 1. The The melt glass glass is is commonly commonly red, red, often often quite quite aa dark dark red. red. This This is is aa helpful helpful feature feature to to go go by by in in selecting selecting chips chips for for sectioning. sectioning. 2. 2. Individual quartz sand grains, grains, grain qrain fragments, fragments, and bits bits of of sandstone sandstone are are commonly lamellae were were found found in in the the quartz quartz but but commonly present. present. No convincing convincing shock shock lamellae occasional occasional grains grains and and grain grain fragments fragments have have been been converted converted to to diaplectic diaplectic glass. glass. In fragments fragments of sandstone sandstone individual grains may have have been been tightly tightly squeezed together together and some some melting may have occurred occurred at at grain qrain contacts. contacts. 3. In some cases the melt has crystallized completely completely to to aa mixture mixture of of large large 3. In anhedral anhedral crystals crystals of of carbonate carbonate mixed mixed with with aggregates aggregates of of smaller smaller anhedral anhedral quartz quartz crystals. crystals. Drill chips chips consisting of this this kind kind of of material material are are white. white. 4. section, abundant abundant euhedral rhombs rhombs of carbonate carbonate are are present present in in aa 4. In one section, matrix of of red red glass. glass. They They appear appear to to be be miniature miniature phenocrysts. phenocrysts. are 5. granular aggregates aggregates of green, green, or rarely rarely colorless, colorless, epidote epidoteare 5. Rounded granular fairly fairly common common in in red red melt melt glass glass containing containing quartz quartz sand sand grains. grains. In two, rather than than just just one, one, crater crater may may be be that two, In regard to the possibility that present and 66 in Figure 1 almost certainly wells 4, 4, 55 and certainly went went through through the the under DePere: DePere: wells present under bottom bottom of of aa single single crater. crater. The maximum possible size size of this this crater crater is is limited limited to to the the northwest, northwest, northeast, northeast, and and southeast southeast by Survey—logged Survey-logged wells wells Nos. Nos. 7, 7, 3, 3, 22 and and 8. 8. To To the the southwest southwest its its maximum size size is is limited limited by aa cluster cluster of of wells wells for for which which only only drillers drillers' logs logs are are available. available. In In the the middle of this this cluster cluster is is another another Survey—logged Survey-logged well, well, No. 12, 12, where thick thick St. Peter Peter sandstone sandstone rests rests directly directly on on Cambrian Cambrian as as in in wells wells 4, and 6. 6. This This well definitely definitely passes passes through through aa crater crater since since cuttings cuttings from from it it 4, 55 and contain contain an an abundance abundance of of melt. melt. There There may may be be aa separate separate crater crater here. here. If If well 4 , 55 and and 66 the the well 12 12 is Is in In the the same same crater crater as as wells wells 4, driller's driller's log log for well No. 19 19 must must be be regarded regarded as as inaccurate. inaccurate. Or Or at at least least misleading: misleading: the the "lime "lime rock" rock" the the driller driller reported reported under under only only 99 meters meters of of sandstone sandstone could could be be aa slide slide block. block. References: References: (1) (1) Read, Read, W. W. F., F., 1984: 1984: The The circular circular structure structure at at Glover Glover Bluff: Bluff: what what Grieve, R. and and where where it it is is (abs.). (abs.). Meteoritics, Meteoritics,V. v. 22, 22, p. p. 487. 487. (2) ( 2 ) Grieve, R. A. A . F., F., 1987: 1987: Terrestrial Terrestrial impact impact structures. structures. Episodes, Episodes, v. v. 10, 10, p. p. 86. 86. (3) (3) Cordua, Cordua, W. W. S., S., 1985: 1985: Rock Rock Elm Elm structure, structure, Pierce Pierce County, County, Wisconsin: Wisconsin: aa possible possible cryptoexplosion cryptoexplosion structure. structure. Geology, v . 13, 13, p. p. 372—374. 372-374. (4) (4) Read, Read, W. F.,; F.,; Cordua, Cordua, W. W. S., S., 1985: 1985: Comment Comment and and Geology, v. Reply Reply on on Rock Rock Elm Elm structure, structure, Pierce Pierce County, County, Wisconsin: Wisconsin: aa possible possible cryptoexplosion cryptoexplosion Ostrom, M. structure. (5) Ostrom, M. E., E . , 1967: 1967: Paleozoic Paleozoic structure. Geology, Geology, v. v. 13, 13, p. p. 891—892. 891-892. (5) stratigraphic stratigraphic nomenclature nomenclature for for Wisconsin. Wisconsin. Wis. Wis. Geol. Geol. and and Nat. Nat. Mist. Hist. Survey, Survey, Inf. Inf. Circ. 8. 8. (6) (6) Read, Read, W. W. F., F., 1985: 1985: Impact Impact bombs in in Middle Middle Ordovician Ordovician marine marine sediments sediments Circ. of southeastern southeastern Wisconsin. Wisconsin. Abstracts Abstracts of Papers Papers for for 16th 16th Lunar Lunar and and Planetary Planetary Science Science Conference, F., 1986: 1986: Possible Possible impact impact spherules spherules from from near near Conference, p. p. 687—688. 687-688. (7) (7) Read, Read, W. W. F., the the base base of of the the Middle Middle Ordovician Ordovician in in northern northern Illinois. Illinois. Meteoritics, Meteoritics, V. v. 21, 21, p. 251— 251262. 262. (8) (8) Mai, Mai, H., H., and and Dott, Dott, R. R. H., H., Jr., Jr., 1985: 1985: AA subsurface subsurface study study of of the the St. St. Peter Peter sandstone Hist.Survey, Survey,Inf. Inf. sandstone in in southern southern and and eastern eastern Wisconsin. Wisconsin. Wis. Wis. Geol. Geol. and and Nat. Nat. Hist. Circ. Circ. 47. 47. 72 �___________ A S H WA B E NO N 0 / / . 33 / ao / • 0 042 AL I. 0 U E Z •0 0 I. .2 ) 38 F 4.. .-... 47 .2. .-.. ,. 32 -' 65 // , 8 0 27 PE RC 57 I mu. .- I km Wells Fiq. Wells in in TT 23 23 N, N, RR 20 20 E which which pass pass through throuqh the the St. St. Peter Peter sandstone. sandstone. North North 1. Fig. 1. boundaries of the and east boundaries the township are hypothetical hypothetical since since this this area area is is occupied occupied by by old French French land land grants. grants. Empty circles: circles: wells for for which which only only drillers' drillers' logs loqs are are Blacked—in circles: Circles available. Blacked-in circles: wells logged loqqed by by the the State State Survey. Survey. Circles available. surrounded surrounded by by squares: squares: wells in which impact impact melt melt has has been been found. found. Upper figure figure Lower figure: adjacent adjacent to to well: well: well number number (arbitrary). (arbitrary). Lower figure: thickness thickness of of St. St. Peter Peter in in Large circle: maximum possible diameter of crater meters. Larqe circle: maximum crater penetrated penetrated by by wells wells 4, 4 # 55,# meters. lo for for well well 19 19 is is reliable. reliable. 66 if driller's lou I i. gO.fld ,,,,I.CS (IIItSn.d) t.uub.c. sI.,mp. ,n...h f.IIe,, I.IlOt I— 2. ?bove: Above: Cross Cross section section from well 1 to well 22 with with data data from from intervening intervening wells wells Fiq. 2. Fig. projected 5 , 6, b 1 44 projected onto onto it. it. Vertical exaggeration exaweration xlO. ~ 1 0 . Dash Dash marks marks adjacent adjacent to to wells wells 5, indicate levels levels at which which impact impact melt has has been been found. found. Presence fallout Presence of fallout hypothetical: drill chips chips from wells 1,7,2 1,7,2 have not not yet yet been been examined. examined. Below: Below: same hypothetical: same cross cross section section with with no no vertical vertical exaqgeration. exaqqeration. 73 �PRELIMINARYGEOMAGNETIC GEOMAGNETICMODEL MODEL OF OF THE TI-E ST. ST- CROIX CROIX HORST HORST PRELIMINARY IN POLK PO= COUNTY, COUNTYf WISCONSIN WISCONSIN IN FEICH, Laura, Laura, KEAN, KEAN, William William and and SVERDRUP, SVERDRUP, Keith Keith REICH, Department of Geosciences Department of Geosciences University of of Wisconsin Wisconsin University Milwaukeef Wisconsin 53211 Milwaukee, Wisconsin 532].]. Total field field Land Land magnetic magnetic data data was was collected collected in in Polk Polk Total Countyf northwestern Wisconsin, during June and July, l98gf County, northwestern Wisconsin, during June and July, 1989, in order to model the eastern portion of the St. Croix Horst in order to model the eastern portion of the St. Croix Horst and related volcanicsThe St. Croix Horst, a mayor and related volcanics. The St. Croix Horst, a major structural feature of the the Midcontinent Midcontinent Rift Rift System, System, outcrops outcrops feature of structural in Polk Polk County County and and trends trends northeast northeast to to Bayfield Bayfield County, Countyf in Wisconsin. Wisconsin. The study study consisted consisted of of four four survey s u n e y lines lines totalling totalling 60 60 The (Fig. 1). 1). Three Three lines lines traversed traversed west west to to east, east, miles (Fig. miles approximately normal normal to to the the horst. horst. The The fourth fourth line line approximately traversed south south to to north, north, subparal].el subparallel to to the the horst horst axis. axis. traversed Data was was collected collected at at 0.1 0.1 mile mile intervals. intemals. In In general, general, field field Data a p ~for ~for values are are consistent consistent with with available available aeromagnetic aeromagnetic m values maps the area. area- AA magnetic magnetic relief relief of of 3066 3066 gammas gammas was was found found in in the the the 61576 gammas gammas near near the the horst horst area with with aa maximum maximum value value of of 61576 area axis and and aa minimum minimum value value of of 58510 58510 gammas gammas in in the the southeast southeast axis shows the the data data contoured contoured part of of the the study study area. area. Figure Figure 22 shows part with aa contour contour interval interval of of 500 500 gammas. gammas. Magnetic Magnetic with susceptibilitiesf sampled sampled from from outcrops, outcropsf range range from from 0.009 0-009 to to susceptibilities, of 0.004 0.004 cgs. cgs. Values Values for for 0.0003 cgs cgs with with an an average average value value of 0.0003 total magnetic magnetic field field intensity, intensityf declination declination and and inclination inclination total and 73.5 73.5 , used for for modeling modeling are are 58640 58640 gammas, gammas, 33 EE and used respectively. respectively. Preliminary modeling modeling of of the the magnetic magnetic field field data data yields yields Preliminary two models: models: 1) 1) aa rootless rootless system system where where volcanics volcanics are are 55 miles miles two mile thick thick susceptibilities are are high high and and 2) 2) aa 77 mile thick and and susceptibilities thick volcanic sequence sequence with with low low susceptibilities susceptibilities underlain underlain by by aa volcanic deep central central ultramafic ultramafic root root extending extending to to 12 12 miles. miles- Both Both deep half-graben structures structures on on the the eastern eastern flank flank of of models have have half-graben models the horst. horst the SELECTED REFERENCES FOR FURTHER READING Chandler, V., V., 1983, 1983f Correlation Correlation of of Chandler, magnetic anomalies anomalies in in magnetic east-central Minnesota and northwestern Wisconsin: east-central Minnesota and northwestern Wisconsin: on magnitude magnitude and and direction direction of of Keweenawan Keweenawan constraints on Constraints rifting: Geology, v. 11, p. 174-176. rifting: Geology, v. 11, p. 174—176. G - and and Chandler, Chandler, V., V., 1987, 1987f New New Mcswiggenf G., G., Morey, Morey, G. McSwiggen, model of the Midcontinent Rift in eastern Minnesota model of the Midcontinent Rift in eastern Minnesota and western western Wisconsin: Wisconsin: Tectonics, Tectonics, v. v. 6, 6, no. no. 6, Gf and p. 677-685. p. 677—685. Wold, R. R e and and Hinze, Hinzef W., W., 1982, 1982, Geology Geology and and tectonics tectonics of of the the Wold, Lake Superior region: Memoir Geological Society of Lake Superior region: Memoir Geological Society of 280 p. p. America, 156, 15Gf 280 America, 74 �STUDY AREA AREA POLK C O U N T Y t i - LINE2 St. Crolx Fall8 gs LINE 1 9 2 3 0' 9 2 16 SSCALE C A L E 1:250,000 1:250,000 10 MILES 0 I 0 A' A * F'ig. 1. . 5 10 SURVEY LINE LINE BASE STATION STATION Location of study study arez are Location map of and survey survey lines. lines. 75 I 15 KILOMETERS �MAGNETIC ANOMALY ANOMALY MAP MAP MAGNETIC SCALE SCALE 0o 10 MILES MILES 10 5 0 0 IF 0 I6 5 .1_i 10 I 10 16 KILOMETERS I 15 KILOMETERS .'...I a 58500 59000 59600 60000 80500+ GAMMAS POLK COUNTY COIUNTY POLK Fig. 2. 2. Fig. Magnetic anomaly anomaly map map for for Magnetic the study area. the study area. 76 �COMPARISON OF OF TWO TWO ARCHEAN ARCE?EXN ULTRAMAFIC AA COMPARISON ULTR.AMAFICPYROCLASTIC PYROCLASTIC ROCK ROCK UNITS! UNITS, NoRTmsONTARIO NORTHWESTERN ONTARIO Stephen J. J. Stephen D u l u t hl Duluth, S c h a e f e r ! Department Department of o f Geology, Geologyl University U n i v e r s i t y of o f MinnesotaMinnesotaSchaefer, D u l u t h l MN 55812 Duluth, MM 55812 h apart a p a r t on on Two ultramafic u l t r a m a f i c pyroclastic p y r o c l a s t i c rock r o c k units u n i t s occur o c c u r 100 100 km Two o p p o s i t e s i d e s o f t h e Q u e t i c o f a u l t a l o n g t h e s o u t h e r n margin of t h opposite sides of the Quetico fault along the southern margin of thee Wabigoon Subprovince S u b p r o v i n c e of o f the t h e Superior S u p e r i o r Province. Province. D e t a i l e d mapping, mapping! Wabigoon Detailed p e t r o g r a p h y l and and chemical c h e m i c a l analysis analysis h a v e shown shown that t h a t these t h e s e units u n i t s may may petrography, have b e correlated, c o r r e l a t e d ! as a s has h a s been been suggested s u g g e s t e d by by Howard Howard Poulsen P o u l s e n (pers. ( p e r s . comm., corn. be 1 9 8 8 ) . The The two two units u n i t s are: are: 1988). 1) 1) The Dismal Dismal Ashrock Ashrock which which is i s located l o c a t e d 44 km km north n o r t h of o f Atikokan Atikokan and and The i s p a r t o f t h e S t e e p Rock Group (Wilkes a n d N i s b e t ! 1 9 8 8 ) . T his is part of the Steep Rock Group (Wilkes and Nisbet, 1988). This u n i t is 100 t o 400 m t h i c k and 1 0 km i n l e n g t h w i t h e x c e l l e nt unit is 100 to 400 m thick and 10 km in length with excellent e x p o s u r e i n t h e f o r m e r S t e e p Rock i r o n mine. exposure in the former Steep Rock iron mine. 2) 2) The Grassy G r a s s y Portage P o r t a g e Bay BayUltraxnafic U l t r a m a f i c Pyroclastic P y r o c l a s t i c Rock Rock Unit U n i t (GUP) (GUP) The which occurs o c c u r s 100 100 km k m to t o the t h e west, w e s t l along a l o n g the t h e eastern e a s t e r n side s i d e of o f the the which R i c e Bay Bay dome, dome! in i n an an arcuate a r c u a t e fold f o l d interference i n t e r f e r e n c e pattern p a t t e r n 10 10 km km Rice l o n g . It I t has h a s aa maximum maximumthickness t h i c k n e s sofo f800 800in. m. long. Both units u n i t s are a r e delineated d e l i n e a t e d into i n t o sub-units s u b - u n i t s based b a s e d on on physical physical Both i s d i v i d e d into into v o l c a n o l o g i c a l p a r a m e t e r s . The Dismal Ashrock volcanological parameters. The Dismal Ashrock is divided l a p i l l i tuff, t u f f ! volcanic v o l c a n i c breccia b r e c c i a and and pillowed p i l l o w e d flow. flow. The GUP is lapilli The GUP is d i v i d e d i n t o l a p i l l i t u f f and v o l c a n i c b r e c c i a . The l a p i l li divided into lapilli tuff and volcanic breccia. The lapilli f r a g m e n t s a t e a c h l o c a l e r a n g e from s c o r i a c e o u s t o n o n v e s i c u l a r and fragments at each locale range from scoriaceous to non-vesicular and a r e magnetic. magnetic. Two unusual u n u s u a l fragment fragment types types were w e r e recognized r e c o g n i z e d at a t each each are Two 1. composite c o m p o s i t e lapilli l a p i l l i (lapilli-sized ( l a p i l l i - s i z e d fragments f r a g m e n t s consisting consisting l o c a t i o n : 1. location: of multiple m u l t i p l e lapilli l a p i l l i fragments f r a g m e n t s in in a a rind r i n d of o f quenched quenched lava) l a v a ) and and 2. of 2. c o r e d lapilli l a p i l l i (lapilli ( l a p i l l i ffragments r a g m e n t s wwith i t h aa llithic i t h i c ccore o r e and and a a rim r i m of of cored quenched lava) l a v a ) . Spinifex S p i n i f e x and and skeletal s k e l e t a l crystals c r y s t a l s in i n these t h e s e rims r i m s at a t the the quenched S t e e p Rock Rock locality l o c a l i t y document document their t h e i r magmatic magmatic origin o r i g i n as a s opposed opposed to to Steep f o m a t i o n b y a s h a c c r e t i o n . A c c i d e n t a l f r a g m e n t s of c a r b o n a t e and formation by ash accretion. Accidental fragments of carbonate and t o n a l i t e are a r e found found within w i t h i n the t h e Dismal Dismal Ashrock Ashrock and and one one accidental accidental tonalite c a r b o n a t e f r a g m e n t i s found i n t h e GUP. carbonate fragment is found in the GUP. The chemical c h e m i c a l composition c o m p o s i t i o n of of these t h e s e two two units u n i t s shows shows aa good good The c o r r e l a t i o n . Rock samples from t h e l a p i l l i t u f f s and j u v e nile correlation. Rock samples from the lapilli tuffs and juvenile f r a g m e n t s cut c u t from from rock r o c k samples samples are a r e ultramafic; u l t r a m a f i c ; their t h e i r Si02 S i 0 2content content fragments r a n g e s from from 40-46 40-46 wt.% w t . % and and their t h e i r MgO MgO content c o n t e n t ranges r a n g e s from from 16-25 16-25 wt.% wt. % ranges c a l c u l a t e d on on aa volatile v o l a t i l e free f r e e basis. b a s i s . These These samples s a m p l e s plot p l o t within w i t h i n the the calculated k o m a t i i t e field f i e l d on aa Jensen J e n s e n AFM A F M diagram. diagram. However! t h e y a r e much komatiite However, they are much h i g h e r in i n total t o t a l Fe Fe and and Ti02 Ti02 than t h a n those t h o s e on on aa normal normal komatiite k o m a t i i t e trend. trend. higher These d a t a i n d i c a t e t h a t t h e Dismal Ashrock and t h e GUP are are These data indicate that the Dismal Ashrock and the CUP c o r r e l a t i v e . S h e a r zones a t t h e t o p o f t h e Dismal a s h r o c k and on correlative. Shear zones at the top of the Dismal ashrock and on b o t h s i d e s o f t h e G U P i n d i c a t e t h a t a n e a r l y p e r i o d o f d e f o r m a t i o n both sides of the GUP indicate that an early period of deformation, l w i t h some some thrusting, t h r u s t i n g ! may may have have occurred o c c u r r e d before b e f o r e late l a t e movement movement on on the the with Quetico fault. fault. T h i s would would have have resulted r e s u l t e d in i n the t h e splitting s p l i t t i n g of o f an an Quetico This original u l t r a m a f i c ppyroclastic y r o c l a s t i c uunit n i t iinto n t o tthe he u p p e r CUP GUP and and lower lower original ultramafic upper Dismal Ashrock. Ashrock. Dismal Reference Reference . Wilkes! M. M. Wilkes, E. and Nisbet, N i s b e t l E. E . G., G.! E., and Rock Group! n o r t h w e s t O n t a r i o: Rock Group, northwest Ontario: Archean S t r o m a t o l i t e s : Canadian Archean Stromatolites: Canadian p . 370—391. 370-391. p. 77 77 1987, Stratigraphy S t r a t i g r a p h y of o f the t h e Steep Steep 1987, a m a j o r Archean unconformity and a major Archean unconformity and J o u r n a l of E a r t h S c i e n c e s ! v . 2 s1 Journal of Earth Sciences, v.25, �METAMORPHICZONATION ZONATIONIN IN THE ?lETAMORPHIC THE NORTH NORTH SHORE S H O E VOLCANIC GROUP, GROUPtMINNESOTA MINNESOTA ** * Susanne Th. Th. Schmidt and John John C. Green Susanne Schaidt and Green * ** *Mineralogisch_PetrographischesInstitut, Institut, INF *Nineralogisch-Petrographisches INF 236, 236,D6900 D6900 Heidelberg, Heidelberg,West West CaQZ2Qry C ~uiany **Departuient of of Geology, University ofofMinnesota, MN **Department Geologyt University Minnesota,Duluth, Duluth, MI455812 55812 In the (NSVG) aa the southern limb limb of the the North Shore Shore Volcanic VolcanicGroup Group (NSVG) zonation of alteration alteration minerals flows zonation of minerals in in the the basaltic basaltic lava lava f l o w between between Duluth Duluth minerals iinf n f iilll lformer former vesicles ve~icles and Tofte is is observed (Fig. 1). 1). Alteration observed (Fig. Alteration minerals and Tofte alceratiuu ai1tL&@i and fractures and aJ.so repLace replace carry early ormeO fO~~eCI alceraclux~ U ~ I C L U ulLd a~ d ~ icsu3 LSA~COUS and fractures and aLs0 minerals. main features features of as follows: canbebesummarized sumnarlzed as followa: The main of this thiszoning zoningcan minerals, The from a lower 1) Metamorphic facies ranging to Metamorphic facies ranging from lower actinolite—epidote—chiorite actinollte-epidote-chlorite to thomsonite—scolecite--smectite facie8 fades are observed. The an upper upper thomsonite-scolecite-smectite observed* The are an ,--$ ----~4 ~ - 4 *FA A 4 a t + n c ~ v lehad i from top to bottom: bottom: assoclcticnz ra d±tinguishe4 from rilineral top to Cuilwi L U L A U W ~ ~IILALC, a aavLAwb*u...,*-..-..e---.. thomsonite-.scolecite—smectite, heulandite—stilbite—smectite, thom~onite-scolecite-smectite, heulandite-stllbite-smectite, laumontite—prehnite—chlorite—(pumpellyite), laumontite—chiorite, laumontite-chlorite, lauontite-prehnite-chlorite-(pumpellyite) , epidote—actinolite—chiorite. epidote—chlorite—(pumpellyite), epidote-actinolite-chlorite. epidote-chlorite-(pmpellyite), * i . --a? m-m -.- This facies facies succession is consistent with aa trend to This succession is consietent with tohigher highertemperature temperature burial mineral dcpth. asse!ublapb w.LLIi WLL I i li i I I L A eaaing b urid d cpth Eilner&l assen1bidgt 2) clear trend trend is the area area of of the village village 2) The The clear is disturbed disturbed by by aa recurrence recurrence in in the the Little Marais. South of Little Marais of of Little Marais. South of Little Marais the heulandite—stilbite—smectite zone, the upper of the heulandite-stilbite-smectlte zone, typical typical of of the upper parts parts of the occurs apparently sequence, sequence, occurs apparently stratigraphically stratigraphically below below flows flows of of the the laumontite—chiorite zone. zone. B1u.k tectonics can B l u ~ ktectoni~s can explain explain this t h i 3 rocurrence. rccurrence. laumontite-chlorite flows is Albitization of basaltic flows alteration feature. Albitization of the the basaltic isaamain main alteration feature,The The within the the stratigraphic stratigraphic position position within the albitization front is is dependent dependent on on the albitization front the uppermost uppermost part NSVG. Ca-rich Ca—rich plagioclase of KSVG, of the part of of the the sequence eequence is is not not JlPh 2rtpr hhiir-ial tops. w Qltcrcd, vc in th f£1o.r in the l o w topsi t h gr-apnr i ~ r i a l depth d e ~ t halbitization albitizatlon eltcrcdt even flows of In some becomes increasingly pervasive. pervasive. In some flows of the laumontite—chiorite laumontlte-chlorite becomes increasingly completealbitization albitization is is observed. and higher metamorphic facies complete metamorphic facies observed. Further, Further, and flow 18 is dependent onthe the permeability permeability of of the albitizattori front the the albitization front in in each each flow dependent on the flow tops bottomsofofstratigraphically stratigraphically lower flows rock-. the flow tops and and bottoms flows rock-,Whereas Whereas the almost complece compiete alteration, he Iiu.iJ.v U ~ ~ V C C ~ U W L ~ A ~ C L - I O I - S remain remain show alceraLlon, the show almost flow interiors interiors are only altered altered in in aa few, unaltered. unaltered. Massive ~bssiveflow are only few, mainly mainly thin thin the sequence, stratigraphically lowermost flows lowermost part part of of the sequence, i.e., i,eepin in flows in in the stratigraphically laumontite—chiorite up flows up to to flows displaying displaying metamorphic metamorphic grade grade from from lauuontite-chlorite facies. epidote—actinolite—chiorite epidote-actinolite-chlorite facies. Eluw ici.r c!aracterlzea D the zonation zonation cnaracteruea oirerent m3.neLdl addition to In addition to the ~y dirrerenc rnuvstti In assemblages, a compositional the new formed albite replacing a~senblages~ a compositional zonation of of the new formed albite replacing is Ca-rich plagioclase isobserved observed within withinthe the NSVG but also also within single single NSVG Ca—rich plagioclase clear flows. The albite displays a clear flows. The composition composition of of the the new new formed albite displays a metamorphic zonation. zonation. In In neral, generalpiti tcan can be safd t - h ~ t . in upper part metamorphic saii th,t in the upper part of albite shows the sequence sequence albite shows compositions compositlons far faraway away from that of of ideal ideal albite. from that albite. the sequence, i.e., in In lower parts parts of of the sequence, i,e., in flows with higher higher metamorphic metamorphic In lower between 95 95 and and 100 100 % mol Ab Ab approaching approaching facies, albitecomposition composition lies liesbetween fades, albite Z mci that of Composition that of ideal idealalbite. albite. Compositionof ofthe thenew new formed formadalbite albite also displays displays aa 78 �zonation Albite in in flow flow tops tops and and bottoms bottoms of of flows flows zonation within within the the flow flow itself. itself. Albite of cloaer to to stoichiometric stoichiometric composition composition of all all metamorphic metamorphic facies facies lies lies always always cloaer tnan tnan aJ.Dlte albite nInmore moreinner, Inner,i.ess Less intensively lnE@nSlVely alterea alcerea parts p a n s of he respeccive respecclve o the flow. f low. The The metamorphic metamorphic zonation zonation is is furthermore furthermore recognized recognized in in the the composition composition of mflc of the the new new formed formed phyllosilicate phyllosilicate*infilling infillingamygdules amygdulea and and replacing replacing mafic minerahi, minerals, the the stable stable isotopic Isotopic ratios ratios of of alteration alteration minerals, minerals, and and the the nomogentzation 199). flulo inclusions lncluslons (SCHMIDT, (SGHPIIDT, 1989). nomogenlzanon temperatures temperatures or rluia SCHMIDT, SCHMIDT,S.Th. S.Th. (1989) (1989) Alteration Alteration under under conditions conditions of of burial burial metamorphism metamorphiam in in the the North Jorth Shore Shore Volcanic Volcanic Group, Group, Minnesota Mlnnesota — Mineralogical Mineralo~ical and and geochemical in geochemicalzonation. zonation, Heidelberger Hsidelberger Geowissenschaftliche ~eowissen.schaftlicheAbhandlungen, ~bhandiun~en, In press press. - Q 00 ='7 SCH 1000 1000 m LM JC SR :000 3 0 0 m CD TlI 000 3000 Ill KR 4000 400 m 50uu 5000 m 6000 m FR a quadrangle LW 7000 7000 0 dU00 m Fig. Fig, 11Metamorphic Metamorphic zonation zonation within within the the North North Shore Shore Volcanic Volcanic Group. Group. Sampling Sampling positions the flowa flow8 are are indicated indicated in inthe the small small sketch sketch to tothe the positionswithin within the Thiç T h i s fiQure f i m r e is is based based on on 280 280 thin thin sections. sections. 25 258Debve—Scherrer Debve-Scherrer and and 40 40diffractogram diffractogramanalyses analyses and and microprobe microprobe analysis. analysis. The Theletters letters to tothe the left e.g., D: D: Duluth, Duluth, T:T: leftside side indicate indicate the the topographic topographic quddrangle, quadrangle, e.g., Tofte. Tofte. Exact Exact location locationof of flows flowsare aregiven givenininSCHMIDT SCHMIDT(1989). (1989). right.. right. 79 �- licationsofofIgneous IgneousRock Rock Geochemistry Geochemistry in in the thePenokean Penokean Orogen Orogen for Implications for Imp Metallogeny and Tectonic Tectonic Setting: Metallogeny and AA Synthesis of of Recent Recent Data Data Reston,VA, VA,22092 22092 and and P.K. P.K. Sims, Sims, Schulz,U.S. U.S. Geological GeologicalSurvey, Survey,Reston, K.J. Schulz, U.S. Geological U.S. Geological Survey, Survey,Denver, Denver,CO, CO, 80225 80225 Recentgeochemical geochemicalstudies studiesofof igneous igneousrocks rocksinin the the Early Recent Proterozoic Penokean orogenofof the the Lake Superior Penokean orogen Lake Superi or region provide provide important constraints on the tectonic tectonic evolution evolutionofofthe theorogen orogen and and help help important constraints on to establish establish aa basis basis for forpredictive predictivemetallogeny. metallogeny. The The epicratonic epicratonic Marquette which is isnorth zone in in Marquette Range RangeSupergroup, Supergroup, which northofofthe the Niagara Niagarafault fault zone upper Michigan,includes includesa abimodal bimodal tholeiltic basalt basalt and andlesser lesser rhyolite rhyolite upper Michigan, tholeiitic suitehaving having chemical chemical characteristics characteristics(major (majorand and trace traceelements elements volcanic suite including typical of within-plate, magma REEts) typical within-plate,rift-related rift-related magma types. types. The including REE's) compositional characteristics of the compositional characteristics the volcanic volcanic rocks rocks and and results from from recent studies of of the the sedimentary sedimentary rocks continental recent rocks support supportaarifted rifted continental margin history history for thethe Penokean margin forthe thenorthern northernportion portionof of Penokeanorogen. orogen. The major iron thethe Marquette Range major ironformations formationsofof Marquette RangeSupergroup Supergroup probably probably were were deposited duringthe theperiod periodofof rifting rifting before deposited during before actual actual crustal crustal separation, separation, although some iron formations formations also may havebeen beendeposited depositedduring duringlater later although some iron may have evolution of evolution of aa fore-deep fore-deep basin. basin. The Wisconsinmagmatic magmatic terranesoccur occursouth southofofthe theNiagara Niagarafault fault The Wisconsin terranes northern terrane, terrane,consists consists of zone. The northern terrane, the thePembine-Wausau Pembine-Wausau terrane, of zone. The widespread island-arc tholeiitic tholeiitic and sequences widespread island-arc andcaic-alkaline calc-alkaline sequences that thatrange range from to 1880 Maininage ageand andananareally areallymore morerestricted restricted calc-alkaline caic-alkaline from 1860 1860 to 1880 Ma suitethat thatformed formedbetween betweenabout about1835 1835and and1845 1845Ma. Ma. Ophiolitic ultramafic suite ultramafic and basaltic rocks, and basaltic rocks, which which include serpentinite, serpentinite,layered layered totomassive massive gabbro, are found found along along the Niagara fault gabbro, sheeted sheeteddikes, dikes, and andboninite, boninite, are the Niagara fault zone and show showthat that the the fault fault zone zone and zone marks marks the the suture suture between between the Superior Superior craton and terrane. Collision along craton and the thePembine-Wausau Pembine-Wausau terrane. along the the suture suture probably occurred period ofofsouthward southward subduction subduction at about about probably occurred following aa period 1860 Ma. Ma. A terrane, the Marshfield terrane, terrane,contains containsremnants remnants of of A southern southern terrane, the Marshfield mafic to felsic range mafic felsicvolcanic volcanicand andplutonic plutonicrocks rocksthat that rangefrom fromabout about1860 1860 to to 1890 1890 Ma Ma in inage ageand and an anArchean Archean gneiss gneissbasement. basement. This terrane This probably was thethe Pembine-Wausau was accreted accreted to tothe thesouthern southernmargin marginof of Pembine-Wausau following aa period terrane at at about about 1840 1840 Ma Ma following period of ofnorthward northward subduction. subduction. The Eau PI Pleine ei ne shear shear zone zone in in southern southern Marathon Marathon County, County, Wisconsin, Wi sconsi n, The Eau appears to to mark appears mark the suture suture zone zone between between the terranes. terranes. Base-metalmassive massivesulfide sulfide deposits deposits are present Base-metal present in inthe thePembinePembineWausau terraneand andappear appear restrictedtoto aa bimodal, bimodal, calc-alkaline caic-alkaline Wausau terrane to to bebe restricted volcanic suite that volcanic that isiscompositionafly compositional1y distinct distinctfrom from other other volcanic volcanic Thesecompositiona11y compositionallydistinctive distinctive highhighunits within within the the terrane. terrane. These Al20.sulfide-hosting A1 20 - and and light-REE-enriched, 1 ight-REE-enriched, massive massive su1 fide-hosting volcanic volcanic rocks rocks distinctivecomposition composition maytave fi'aveformed formed a within-arcrift. rift. Their distinctive may in in a within-arc enhances theuse useofof lithogeochemistry lithogeochemistry for for massive sulfide exploration enhances the massive sulfide within the within theWisconsin Wisconsin magmatic magmatic terranes. 80 �Late to (about1835 1835Ma) Ma)and andyounger youngeranorogenic anorogenic (1760 (1760 topostorogenic postorogenic(about granitic of rhyol rhyolite graniticintrusions intrusionsand and lesser lesseramounts amounts of i te Ma and 1470-1500 Ma and 1470-1500Ma) Ma) are locally orogen,particularly particularly in locallyabundant abundant within within the thePenokean Penokean orogen, in the the southern Pembine-Wausau terrane and southern portion portion ofofthe the Pembine-Wausau terrane and throughout the Marshfield terrane. rocksrange rangefrom from alkalic terrane. These These rocks ca1calc-alkaline c-a1ka1 i ne totoa1 ka1 ic in in character. mineralization is character. Minor molybdenum molybdenum mineralization isassociated associatedwith withsome some intrusions, have intrusions,and andother otherintrusions intrusions haveanomalous anomalous Sn, Sn,Ta, Ta,Nb, Nb,U, U, and and Th. Th. In particular, Maa1alkali-feldspar in particular,a arecently recentlydiscovered discovered 1733 1733 Ma ka1 i -feldspar granite in the northern thethe Southern Complex northern portion portionofof Southern Complexsouth southofofHumboldt, Humboldt, Michigan, is compositionally similar to rare-metal-rich Michigan, is compositional1y similar rare-metal-rich granites granites of of Nigeria and Sn-W potentialforfor and the the Arabian Arabian Shield Shield and and suggests suggests aa potential Sn-W(Ta-Nb) (Ta-Nb) mineralization mineralizationininupper upperMichigan. Michigan. 81 �THE THE MINERAL HINERAL LAKE LAKE PLUTON: PLUTON: TWO INTRUSIONS INTRUSIONS RATHER RATHER THAN THAN A LAYERED LAYERED COMPLEX? COMPLEX? KARL K A R L E. E. SEIFERT D e p a r t m e n t of o f Geological G e c ~ l c ~ g i c aand al n d Atmospheric A t m o s p h e r i c Sciences, Sciences, Department IA 50011 State t a t e University, U n i v e r s i t y , Ames, A m e s , IA 50011 IIowa owa S I NTRODUCT I ON INTRODUCTION Mellen, The T h e Mineral M i n e r a l Lake L a k e pluton p l u t o n is i s lc'cated l c ~ c a t e d nnear ear M e l l e n , Wisconsin, W i s c o n s i n v on #on the t h e Mellen ss':uuthern ~ : ~ u t h e r nmargin m a r g i n':tf o f Keweenawan kceweendwan eexpcts'.tres x p o s u r e s a s as p apart r t o foft hthe e Me1 l e n CComplex cmplex The (Aldrich, < A 1 d r i c h v 1929; 1 3 2 3 ; Leighton, L e i g h t o n , 1954). 13541. T h e Mineral M i n e r a l Lake L a k e and a n d smaller s m a l l e r Rearing Rearing Pond plutcin, n t r u s i v e ssheets h e e t s of o f aanorthuDsitic n ~ ~ r t h ~ z ~cs igabbrc' gtaib. b r o p l ~ . ~ t t : ~ np,plus l u s aadditi':nal d d i t i n n a l iintrusive Complex aand n d granite, g r a n i t e , form f o r m the t h e western w e s t e r n part p a r t of o f the t h e Mel M e l len len C o m p l e x and a n d are are sseparated e p a r a t e d from f r o m the t h e eastern e a s t e r n part p a r t cf ctf the t h e cu:mplex c~:~mplex bby y the t h e 1.0 1.0 - 11.2 . 2 Ga Ga The Mellen M e l l e n granite. granite. T h e Mineral M i n e r a l Lake L a k e pluton p l u t c ~ nhas h a s been b e e n described d e s c r i b e d as as aa ste9ply mafic s t e e p l y nnorthward ~ : ~ r t h w a r dddipping i p p i n g 44.5 . 5 kkm—thick m-thick m a f i c l1ayerd a y e r e d complex c ~ = ~ m p l intruded eixn t r u d e d as a s a 5ingle s i n g l e magma with w i t h an a n anorthositic a n o r t h o s i t i c gabbrci g a b b r o bbulk u l k composition cc~mpc~sition (Olmsted, From ( O l m s t e d , 1969). 19631. F r c ~ m the t h e base b a s e up u p the t h e plut'Dn p l u t o n cu:'nsists c c t n s i s t s oof f rroughly o u g h l y 1% 1% ultramafic u l t r a m a f i c rocks, r c ~ c k s , 10% 1 9 % anorthositic a n c ~ r t h c ~ s i c'livine t iocl i v i n e gabbrc;, g a b b r ~ l ,73% 73X gabbr':ic gabbrc~ic ancirthosite ferrt:idicsrite a n c t r t h c t s i t e and a n d ancirthosite, a n c ~ r t h c ~ s i tand ea,n d16% 16% f e r r o d i o r i t e (mcunzcqabbrc' < m c ~ n z ~ : ~ g a b bgrgrading cr ~ ading upward quart: mon:odiorite) 1369:). The The o n z o d i c t r i t e l and a n d granite g r a n i t e (Olmsted, ( O l m s t e d , 1969). u p w a r d to to q uartz m pluton also been p l u t o n has has a l s t ~b e e n interpreted i n t e r p r e t e d as a s forming f o r m i n g from f r o m several s e v e r a l magmas magmas (Ktmatar, 11972) 3 7 2 1 bbased a s e d oon n the t h e occasional C I C c a s i c i n a l occurrence CIC c u r r e n c e of n f poorly pcmr l y developed developed (Komatar, thin t h i n rhythmic r h y t h m i c layering l a y e r i n g in i n the t h e anorthcsitic a n o r t h c ~ ~ i gabbrci t igca b b r o intrusion. intrusion. IItt is is h e r e interpreted i n t e r p r e t e d to t o consist c c ~ n s i s of t13f two t w o separate s e p a r a t e intrusions; i n t r u s i o n s ; aa lc'wer lower here aanc'rthc'sitic n c ~ r t h c ~ s i t igcagabbrci b b r a i n tintrusion r u s i ~ z t na nand d a nanu upper p p e r ggranitic r a n i t i c iintrusion. ntrusion. Major d e t e r m i n e d on o n samples s a m p l e s collected collected M a j o r and a n d trace t r a c e elements e l e m e n t s were determined ffrom r m bctth n t r u s i c ~ n sin i n the t h e Mineral M i n e r a l Lake L a k e pluton. pl uton. B a s a l inclusions i n c 1 u s i o n s and and both iintrusions Basal adjacent a l s u sampled s a m p l e d to t o determine d e t e r m i n e their t h e i r compositions cc~mpc~sitic~ns a d . j a c e n t oolder l d e r rrocks a c k s were also a s sciurces s c ~ u r c e socf f ppossible ~ ~ s s i b lcontamination. c eo n t a m i n a t i c ~ n . Three T h r e e plagiciclase p l a g i c ~ c l a s esseparates e p a r a t e s and and as one orthopyro"ene one o r t h c ~ p y r o x e n esseparate e p a r a t e were analyzed a n a l y z e d from f r ~ mthe t h e coarsely c o a r s e l y crystalline crystalline anorthc'sitic Major oxides a b b r c ~intrusion. intrusion. Ma.jor o x i d e s were determined d e t e r m i n e d largely largely a n o r t h o s i t i c ggabbro by X X-ray by - r a y ffluorescence l u o r e s c e n c e (XRF) (XRF1 and a n d trace t r a c e elements e l e m e n t s were were determined d e t e r m i n e d by by instrumental Some trace trace i n s t r u m e n t a l nneutron e u t r o n activation a c t i v a t i o n analysis a n a l y s i s (INAA) CINAAI and a n d XRF. XRF. Some element e l e m e n t and a n d isotope i s c ~ t o p edata d a t a have h a v e been b e e n reported r e p o r t e d previously p r e v i o u s l y (Seifert ( S e i f e r t et et al., a l . , l1985). ?85>. The Anorthositic Gabbro Intrusion Intrusion The T h e anorthc'sitic a n o r t h c ~ s i t i c ggabbrc' a b b r o i nintrusion t r u s i o n cconsists o n s i s t s oof f ttwo w o zones z o n e s with with a a The thin margin t h i n basal b a s a l chilled chilled m a r g i n adjacent a d j a c e n t to t o older o l d e r underlying u n d e r l y i n g country c o u n t r y rocks. rocks. The T h e basal b a s a l chill c h i l l zzone o n e ggrades r a d e s upward u p w a r d into i n t o the t h e aanorthositic n o r t h o s i t i c olivine nlivine g a b b r o zone z o n e which w h i c h in i n turn t u r n grades g r a d e s upward u p w a r d into i n t o the t h e gabbroic g a b b r o i c ancirthosite anorthosite gabbro zone. zc~ne. T he g a b b r o i c aanorthosite n o r t h o s i t e zone z o n e volumetically v ~ ~ l w n e t i cl ayl dominates d o m i n a t e s the the The gabbroic intrusion Lake pluton. p l u t o n . The T h e thin t h i n chill c h i l l zone z o n e and and i n t r u s i o n and a n d the t h e entire e n t i r e Mineral M i n e r a l Lake the t h e upper u p p e r part p a r t oof f the t h e thick t h i c k gabbroic g a b b r o i c anorthosite a n o r t h o s i t e zone z o n e contain c o n t a i n basalt basalt inclusions. Three inclusions. T h r e e plagioclase p l a g i o c l a s e separates s e p a r a t e s and a n d one o n e orthopyroxene orthopyroxene sseparate e p a r a t e were aanalyzed n a l y z e d from f r o m this t h i s coarsely c o a r s e l y crystalline c r y s t a l l i n e intrusion. intrusion. 82 �The Granitic Intrusion Intrusion The qranitic T he g r a n i t i c intrusion i n t r u s i o n consists c o n s i s t s cf o f a llower o w e r rnc'nzodic'rite m o n z o d i o r i t e zzone o n e aand nd The upper with a gradati':na1 g r a d a t i o n a l contact. contact. T h e lower lower zone, z o n e , iin n aann u p p e r ggranite r a n i t e zone zone w ith a ccintact the uunderlying c o n t a c t wwith i t h the n d e r l y i n g aanc'rthcsitic n o r t h o s i t i c gabbri:i g a b b r o i nintrusion, t r u s i o n , is is best best described as a a mon:oqabbr':' m o n z o g a b b r o ggrading r a d i n g uupward p w a r d i into n t o quartz q u a r t z mc'nzodicrite. monzodiorite. d e s c r i b e d as The s t h the e o voverall e r a l l c characteristics h a r a c t e r i s t i c s oof f granite, g r a n i t e , although althctuqh T h e uupper p p e r z zone o n e h ahas This probably tthe h e texture t e x t u r e bbecomes e c o m e s ggranciphyric r a n o p h y r i c l locally. ocally. T h i s intrusion i n t r u s i o n is probably llater a t e r than t h a n the t h e anorthositic a n o r t h o s i t i c gabbr':' g a b b r o intrusion i n t r u s i o nand a n d isi snearly n e a r l cc'nformable y conformable The with margin w i t h the t h e upper upper m a r g i n o fcf t that h a t iintrusion. ntrusion. T h e uupper p p e r ggranite r a n i t e zone zone varies v a r i e s from f r o m ccarse c o a r s e ggrained r a i n e d ggranular r a n u l a r tto o granophyric g r a n o p h y r i c iin n texture t e x t u r e and a n d is is ccharacterized h a r a c t e r i z e d by by the t h e dominance d o m i n a n c e of o f K—spar K - s p a r aand n d qquart: u a r t z cuver o v e r pplagioclase. laqioclase. mc'nzc'diorite The T h e granite g r a n i t e and a n d the t h e K-spar-rich K - s p a r - r i c h upper u p p e r part p a r t of o f the the quartz quartz m onzodiorite "red layer are r e both b o t h red r e d and a n d together t o g e t h e r they t h e y constitute c o n s t i t u t e the t h e " r e d rock" r o c k " portion portion layer a cf t h e Mineral M i n e r a l Lake L a k e pluton. pinton. o f the t h e granitic g r a n i t i c intrusion i n t r u s i o n and the SUMMARY The T h e ggranitic r a n i t i c iintrusion n t r u s i o n is probably p r o b a b l y later l a t e r than t h a n the t h e n':rthcsitic anorthositic gabbrc q a b b r o iintrusion n t r u s i o n and a n d was emplaced e m p l a c e d between b e t w e e nthe t h anorth':'sitic e a n o r t h o s i t i cgabbr':u q a b b r o and and overlying The w o iintrusions ntrusions o v e r l y i n g rocks. rocks. T h e genetic g e n e t i c relationship r e l a t i o n s h i p between b e t w e e n the t h e ttwi:' Whereas was iiss not n o tknown. known. W h e r e a s t hthe e a ancirthcisitic n o r t h o s i t i c gabbri: gabbro w a s iintruded n t r u d e d as as a a crystal c r y s t a l mush aand n d shows s h o w s little l i t t l e eevidence v i d e n c e for f o r differentiation, d i f f e r e n t i a t i o n , the the magma eexhibits ggranitic r a n i t i c magma x h i b i t s the t h e chemical c h e m i c a l and a n d mineralogical m i n e r a l o g i c a l trends t r e n d s expected expected of of d i f f e r e n t i a t i o n . The w o iintrusions n t r u s i o n s ooff aan':rthositic n o r t h o s i t i cgabbro g a b b r ~and la n d T h e ppresence r e s e n c e of ttwo g r a n i t i c ccompositions o m p o s i t i o n s in i n the t h e Mineral M i n e r a lLake L a k plutcin e p l u t o nalsu:' a l s o eexplains x p l a i n s the the granitic gabbrci aadditional d d i t i o n a l sheets s h e e t s oof f anorthositic anorthositic g a b b r o a and n d ggranite r a n i t e tto o tthe h e nnorthwest orthwest cf o f the t h e pluton. pluton. differentiation. REFE RENCES REFERENCES Aldrich, Aldrich, H. H. R. R . ,, 1929, 1 9 2 9 , The T h e geology g e o l o g y of o f the t h e Gogebic G o g e b i c iiron r o n range r a n g e of of Wisconsin: Wisconsin Natural Wisconsin: W i s c o n s i n GGeological eological N a t u r a l History H i s t o r y Survey Survey v. 71, v. 71, 2 7 9 pp. 279 pp. Bulletin, B ulletin, Komatar, F. D., 1972, Komatar, F. D., 1372, Geology G e o l o g y of o f the t h eAnimikian A n i m i k i a nmetasedimentary m e t a s e d i m e n t a r y rocks, rocks, Mellen L a k e gabbro g a b b r o west w e s t of o f Mellen, M e l l e n , Wisconsin Wisconsin M e l l e n granite, g r a n i t e , and a n d Mineral M i n e r a l Lake (M.S. (M.S. tthesis): h e s i s ) : University U n i v e r s i t y ofo fWisconsin, W i s c o n s i n , 75pp. 75pp. Leighton, Leighton, gabbrcu-granophyre W., 194, M. W M. ., 1 9 5 4 , Petrogenesis P e t r o g e n e s i s of of a g a b b r o - g r a n o p h y r e ccomplex o m p l e x in in northern America Bulletin, v. n o r t h e r n Wisconsin: W i s c o n s i n : Geological G e o l o g i c a l Society S o c i e t y of of A merica B u l l e t i n , v. 65, p. 01-442. 6, p. 4401-442. Olmsted, F., O l m s t e d , J. F . , 1969, 1969, Petrology P e t r o l o g y of o f the t h e Mineral M i n e r a l Lake L a k e intrusion, intrusion, 3. northwestern n o r t h w e s t e r n Wisconsin: W i s c o n s i n : in i n Y. Y . W. W. IIsachsen s a c h s e n (editor), ( e d i t o r ) , Origin O r i g i n of of Anorthosite A n o r t h o s i t e aand n d Related R e l a t e d Rocks, R o c k s , New York Y o r k State S t a t e Museum Museum and a n d Science Science Service Memoir 18, 1 8 , p. p. 1149-161. 49-161. S e r v i c e Memoir Seifert, E . , Peterman, P e t e r m a n , Z. n d Windcum, Windom, K. K. E., E . , 198, 1 9 8 5 , Mineral M i n e r a l Lake Lake S e i f e r t , K. K. E., Z. E. E. a and layered NW W Wisconsin: i s c o n s i n : Geological G e o l o g i c a l Society S o c i e t y of o f America America l a y e r e d intrusion, i n t r u s i o n , NW Abstracts v. 17, 17, p. 712" A b s t r a c t s with w i t h Programs, P r o g r a m s , v. p. 712. 83 �MANGANESE POTENTIAL P O T E N T I A L OF O F THE THE CRETACEOUS CRETACEOUS ROCKS ROCKS FLANKING F L A N K I N G THE THE MANGANESE S I O U X RIDGE, R I D G E , MINNESOTA MINNESOTA AND SOUTH DAKOTA DAKOTA SIOUX Dale R. R . Setterholm, Setterholm, Minnesota Minnesota Geological Geological Survey,2642 Survey,2642 Dale S t . Paul, MN 55114, and Richard H. U n i v e r s i t y Avenue, University Avenue, St. Paul, MN 55114, and Richard H. Hamrnond, South Dakota Geological Survey, Science Center, Hammond, South Dakota Geological Survey, Science Center, S D 57069 57069 U n i v e r s i t y of of South South Dakota, Dakota, Vermillion, Vermillion, SD University Cretaceous strata s t r a t a in i n southwestern southwestern Minnesota Minnesota and and eastern eastern Cretaceous South Dakota Dakota have have lithologic, l i t h o l o g i c , geochemical, geochemical, and and depositional depositional South a t t r i b u t e s similar s i m i l a r to t o those t h o s e that t h a t host h o s t economic economic deposits d e p o s i t s of of attributes manganese at a t several s e v e r a l localities l o c a l i t i e s around a r o u n d the t h e world. world. manganese I n v e s t i g a t i o n s are a r e under under way way to t o determine determine if i f the t h e conditions conditions Investigations d e s c r i b e d in i n several s e v e r a l depositional d e p o s i t i o n a l models models (Cannon (Cannon and and Force, Force, described 1 9 8 3 ; Frakes F r a k e s and and Bolton, Bolton, 1984; 1 9 8 4 ; Force Force and and Cannon, Cannon, 1988 1 9 8 8 ), ), 1983; which have have been been proposed proposed to t o explain e x p l a i n these t h e s e ores, o r e s , existed e x i s t e d in in which Minnesota and and South South Dakota, Dakota, and and if i f so, so, whether whether any any anomalous anomalous Minnesota manganese concentrations c o n c e n t r a t i o n s are a r e present. present. manganese The models models propose propose that t h a t aa dilute d i l u t e ore-forming ore-forming solution solution The i n anoxic p o r t i o n s of s t r a t i f i e d s e a s where iron can develop can develop in anoxic portions of stratified seas where iron i s removed a s p y r i t e , and where manganese c o n c e n t r a t e s to is removed as pyrite, and where manganese concentrates to i n normal s e a w a t e r . When v a l u e s up t o 500 times t h o s e common values up to 500 times those common in normal seawater. When i s transported t r a n s p o r t e d to t o an an oxygenated oxygenated t h i s manganese-rich manganese-rich solution s o l u t i o n is this environment, such a s a l o n g t h e margins of a d e positional environment, such as along the margins of a depositional b a s i n , t h e d i s s o l v e d manganese p r e c i p i t a t e s e i t h e r as a s an an basin, the dissolved manganese precipitates either oxide o r carbonate mineral s p e c i e s . P h y s i c a l p r o c e s s e s near oxide or carbonate mineral species. Physical processes near s h o r e may may concentrate c o n c e n t r a t e the t h e manganese-rich manganese-rich material m a t e r i a l to t o yet yet shore h i g h e r g r a d e s . higher grades. In southwestern southwestern Minnesota and in i n adjoining a d j o i n i n g parts p a r t s of of In Minnesota and South Dakota, Upper Cretaceous s t r a t a were d e p o s i t e d a l o n South Dakota, Upper Cretaceous strata were deposited alongg t h e eastern e a s t e r n edge edge of of the t h e Western Western Interior I n t e r i o r Seaway Seaway on on aa gently gently the s l o p i n g s u r f a c e f l a n k e d by t h e Sioux Ridge, a q u a rtzite sloping surface flanked by the Sioux Ridge, a quartzite highland which a t times formed e i t h e r a peninsula o r a group highland which at times formed either a peninsula or a group of i s l a n d s . Rocks of t h e Dakota Formation, Graneros S hale, of islands. Rocks of the Dakota Formation, Graneros Shale, C a r l i l e S h a l e , Niobrara Formation, and Greenhorn Limestone, Greenhorn Limestone, Carlile Shale, Niobrara Formation, and P i e r r e Shale d e f i n e a s h e l f f a c i e s t h a t p a s s e s i n t o nearshore Pierre Shale define a shelf fades that passes into nearshore f a c i e s , such such as a s the t h e Split S p l i t Rock Rock Creek Creek Formation Formation along a l o n g the the facies, S i o u x Ridge p a l e o c o a s t , a n d a r e g i o n a l l y c o n s i s t e nt Sioux Ridge paleocoast, and a regionally consistent llithostratigraphic i t h o s t r a t i g r a p h i c succession s u c c e s s i o n of shallow marine and c o a s t al of shallow marine and coastal c l a s t i c , t h sediments i n Minnesota. Although d e c i d e d l y more sediments in Minnesota. Although decidedly more clastic, thee Minnesota rocks rocks correlate c o r r e l a t e well w e l l with with parts p a r t s of of the t h e established established Minnesota Upper Cretaceous s h e l f sequence i n South Dakota. Upper Cretaceous shelf sequence in South Dakota. Two key key components components of of the t h e manganese manganese depositional d e p o s i t i o n a l models models Two i n t h e s t u d y a r e a . High-manganese/low-iron have been observed have been observed in the study area. High-manganese/low—iron a n o m a l i e s , although a l t h o u g h subeconomic, subeconomic, have have been been observed o b s e r v e d at at anomalies, s e v e r a l places p l a c e s in i n rocks r o c k s deposited d e p o s i t e d on on an an open open shelf shelf several envoronment. These These anomalies anomalies demonstrate demonstrate that t h a t ore—producing ore-producing envoronment. i n t h e seaway, seaway, s o l u t i o n s may have been p e r i o d i c a l l y p r e s e n t solutions may have been periodically present in the and t h a t a t t i m e s , t h e y flowed o n t o t h e e a s t e r n shelf. and that at times, they flowed onto the eastern shelf. Secondly, s t r a t a r e f l e c t i n g c y c l i c o x i c a n o x i c c o n d itions Secondly, strata reflecting cyclic oxic-anoxic conditions have been observed i n both t h e n e a r s h o r e f a c i e s and t h e shelf have been observed in both the nearshore facies and the shelf f a c i e s . This T h i s implies i m p l i e s that t h a t anoxic a n o x i c flowpaths flowpaths existed e x i s t e d between between fades. anoxic parts p a r t s of of the t h e basin, b a s i n , where where manganese—rich manganese-rich solutions s o l u t i o n s had had anoxic 84 �formed, and a n d nearshore n e a r s h o r e sites s i t e s where where oxic o x i c conditions c o n d i t i o n s favorable favorable formed, f o r ore o r e formation f o r m a t i o n existed. existed. for T h i s work work was was cofunded c o f u n d e d by b y the t h e Minnesota M i n n e s o t a Geological G e o l o g i c a l Survey, Survey, This tthe h e South S o u t h Dakota D a k o t a Geological G e o l o g i c a l Survey, S u r v e y , and a n d the t h e Midcontinent Midcontinent U.S. S t r a t e g i c and a n d Critical C r i t i c a l Minerals M i n e r a l s Program Program of o f the t h e U.S. Strategic G e o l o g i c a l Survey. Survey. Geological References: References: E . R . , 1983, 1983, Potential P o t e n t i a l for f o r high-grade high-grade Cannon, W.F., W.F., and a n d Force, F o r c e , E.R., Cannon, s h a l l o w - m a r i n e manganese manganese deposits d e p o s i t s in i n North N o r t h America, America, in in shallow—marine Shanks, W.C., W . C . , ed: e d : Cameron Cameron volume volume on on unconventional u n c o n v e n t i o n a l mineral mineral Shanks, d e p o s i t s : American American Institute I n s t i t u t e of o f Mining, Mining, Metallurgical, M e t a l l u r g i c a l , and and deposits: P e t r o l e u m Engineers, E n g i n e e r s , New New York, York, p. p . 175-189. 175-189. Petroleum F r a k e s , L.A., L . A . , and a n d Bolton, B o l t o n , B.R., B . R . , 1984, 1984, Origin O r i g i n of o f manganese manganese Frakes, g i a n t s : sea s e a level l e v e l change change and a n d anoxic—oxic a n o x i c - o x i c history: h i s t o r y : Geology, Geology, giants: v . 1 2 , p. p . 83—86. 83-86. v.12, E . R . , and a n d Cannon, Cannon, W.F., W.F., 1988, 1988, Depositional D e p o s i t i o n a l model model for for F o r c e , E.R., Force, s h a l l o w m a r i n e manganese d e p o s i t s a r o u n d b l a c k s h a l e b a s ins: shallow-marine manganese deposits around black shale basins: Economic Geology, v . 83, p . 93-117. Economic Geology, v.83, p. 93—117. 85 �t'STRATIGRAPHY" AND OF AA PORTION STRATIGRAPHY" AND GENERAL GENERAL GEOLOGY GEOLOGY OF PORTION OF OF THE THE PARTRIDGE RIVER RIVER INTRUSION, PARTRIDGE INTRUSION,DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA. MINNESOTA. MARK SEVERSON MARK JJ.. SEVERSON ResearchInstitute, Institute, Natural Resources Resources Research 3151 Miller Miller Trunk 3151 TrunkHwy., Hwy., Duluth, Duluth,MN MN 55811 55811 Reloggingofofover over75 75drill drill holes holes (—90,000 ft.) located Relogging (-90,000 ft.) along the the located along northern (footwall) (footwall) contact northern contact of of the thePartridge Partridge River River Intrusion Intrusion(T.58-59N., (T.58-59N., R.13-14W.) feet Series R.13-14W.)has hasindicated indicatedthat thatthe thebasal basal3000 3000 feetofofthe theTroctolitic Troctolitic Series Rockscan canbebesubdivided subdividedinto into at at least least seven major igneous units on Rocks seven major igneous units on the the basis basis of Most of of the units of rock rock type. type. Most unitsare arecontinuous continuous over over an an indicated indicatedeleven eleven mile strike-length extending (NE SW) strike-length extending (NEto to SW)from fromthe theDunka DunkaRoad Road Cu-Ni Cu-Ni deposit deposit Creek Cu-Ni Cu-Ni deposit. deposit. Some to the theWyman Wyman Creek appear to to Someofofthese these igneous igneous units units appear represent single single cool cooling units in ultrarepresent ing units in that thatthey theyare are floored flooredby byaabedded bedded ultramafic whereas, other contain abundant internal members mafic member; member; whereas, other units units contain abundant internal members reflecting reflectingcontinuous continuousmagma magma replenishment. replenishment. Contacts between between each the each of of the units from sharp units range range from sharp to gradational, gradational, and and pinch-and-swell pinch-and-swell thickness thickness variations all1 seven units. The There1 relative variationsare arecommon common toto a1 seven units. ative spatial regularity regularity of that the of these these units units suggest suggest that the Partridge Partridge River River Intrusion Intrusion(PRI) (PRI)was was intruded intruded as several exhibit dips as several subhorizontal subhorizontal sheets sheets that now now exhibit dipsofofapproximately approximately20 20 degrees Lake Superior Superior (SE). However,some some theunits unitsa1 also exhibit degrees towards Lake (SE). However, ofofthe so exhibit downcutting re1 ationships and and 1lateral ateral"facies" "facies" changesindicating indicatinga acomplex complex downcutting relationships changes intrusive history. history. From thebase baseup, up,these theseunits unitsare arecharacterized characterizedbyby(Figure (Figure I): 1): Unit II From the sulfide-bearing augitetroctolite troctolite with minor minorpicrite picrite to peridotite sulfide-bearing augite peridotite layers; layers; troctolite and augite augite troctol troctolite abundantpicrite picrite to Unit I1 II -- troctolite Unit ite with with abundant to peridotite layers sulfide-bearing zones; zones;Unit Unit I11 III - mottled mottled layers and/or and/or minor minor sulfide-bearing textured anorthositic troctolite textured anorthosi tic troctol i te exhibiting exhibiting aa highly highly irregular olivine 01 ivine distribution; Unit with base and IV - -augite augitetroctolite troctolite witha apicritic picritic base andgrading grading distribution; Unit IV upwardsinto; into; Unit VV - coarse-grained anorthositictroctolite; troctolite; Unit upwards coarse-grained anorthositic Unit VI VI -augite troctolite troctolite to base; augite to anorthositic anorthositic troctolite troctolitewith withaapicritic picritic base;and and Unit Unit peridotite/picrite base. VII Field VII - augite augite troctolite troctol itewith witha awell-bedded well -bedded peridotite/picrite base. Field mapping suggests thatanan eighthunit unit(VIII) (VIII) and possibly additional units mapping suggests that eighth and possibly units are above Unit Unit consists of of troctolite to are present present above Unit VII. Unit VIII VIII consists troctolite to anorthositic witha awell-bedded we1 1 -bedded peridotite peridoti tebase. base. Anorthositic Anorthosi tic anorthositic troctolite troctol i tewith Series rocks are are present SEportion portion of the Series rocks present in the the extreme extreme SE the study study area. area. Intrusive into pegrnatitic Intrusive intoUnits UnitsI Ithrough throughVII VIIare arelate-stage late-stage pegmatiticoxide-bearing oxide-bearing ultramafic samplesfor for whole ul tramafic bodies. bodies. Geochemical Geochemical samples whole rock, rock, trace trace element, element, base metals, analyses have precious and base metals, and rare earth earth element element analyses have been been precious and eachof of these these units units to: 1.) determine collected from from each determinebackground background elemental elemental values for for each 2.) determine if any determine if any values each of the the major major units unitsand and their theirmembers; members; 2.) vertical and variation isispresent vertical and lateral lateralgeochemical geochemical variation present and and to towhat what extent; extent; and 3.) determine and 3.) determine ififany anylithogeochemical lithogeochemical signature signatureassociated associated with witheach each of the the major major units is ispresent. present. Establishment internal"stratigraphy" "stratigraphy"(within (withinaasea seaofoftroctol troctolitic Establ ishment ofofananinternal itic rocks) of an excellent excellent opportunity to of the thePR! PRI has has provided provided an to study study the thenature nature present both thethe basement of any any structural structuraldiscontinuities discontinuities presentwithin within both basement and and the the rocks. Cross-sections illustrating illustrating the internal overlying intrusive rocks. Cross-sections the internal overlying intrusive "stratigraphy" ininseveral areas that in both thethe Dunka "stratigraphy" severaldrilled drilled areasindicate indicate that in both DunkaRoad Road numerous NE-trending NE-trending normal and Wet1 egs areas, areas, numerous normal faults parallel para1 lel to the the and Wetlegs This supports Midcontinent Rift Rift are ha1 f-grabenmodel model of of Midcontinent are present. present. This supports the haif-graben Weiblen and andMorey Morey(1980) (1980)which whichenvisions envisionsaastep-and-riser step-and-riser geometry Weiblen geometry at the the 86 �Also within the the base of the dueto to extensional extensional tectonics. base of the Duluth Duluth Complex Complex due tectonics. Also faulthas hasbeen beenidentified identified Wetlegs area, a NE-trending NE-trending pre-Keweenawan(?) pre-Keweenawan(?) fault Wetlegs area, is in direct along which which an an inferred window window of Biwabik Biwabik Iron-formation Iron-formation is direct along Three oxide-bearing oxide-bearinglate-stage late-stage ultramafic ultramafic bodies contact with with the thePRI. PRI. Three bodies are are genetically along this thiszone zonewhich which suggests suggests that they they may may be be genetically also located located along related re1 ated to toareas areaswhere where massive massive iiron-formation ron-formation assimilation assimi 1 ation has has occurred. occurred. discontinuities were theWyman Wyman Creek Creek area, area, no no major major structural structural discontinuities were Within the located in either or Troctolitic Troctolitic Series located eitherthe thebasement basement or Series rocks. rocks. However, However, aa downcutting relationship of of Unit VV into into Units III1and is indicated Wyman and II is indicatedatat Wyman downcutting relationship Creek. Creek. During the course courseof of collecting collecting field geochemical During field geochemicalsamples, samples, aa mile mile long 1 ong zone of of modally laminated oxide-bearing gabbro was was located located zone laminated and and cross-bedded oxide-bearing in previously been beencalled called the the Colvin Colvin Creek CreekHornfels. Hornfels. Mineralogical in what what has has previously Mineralogical and field field relations actually be and relationssuggest suggestthat thatthe theColvin ColvinCreek Creekbody body may may actually be an an intrusive unit magmatic unitthat thatexhibits exhibits magmatic density density current current features. features. Field that the the Colvin Creekbody bodyisissimilar similar to the relationships also suggest suggest that Colvin Creek the Powerline Gabbro Gabbrowhich whichisisexposed exposedwithin withinabout aboutone onemile mileto to the the northeast. northeast. Powerline REFERENCES REFERENCES Weiblen, P.W., Morey, G.B., G.B., 1980, the stratigraphy, stratigraphy, P.W., and and Morey, 1980, A A summary summary ofofthe Weiblen, petrology and AmericanJournal Journal of of and structure structureofofthe theDuluth DuluthComplex: Complex: American Science, v. 280, p. 88-133. Science, 280, p. 88-133. Funding: Minerals Funding: Minerals Coordinating CoordinatingCommittee Committee Minerals Diversification Plan Mineral s Diversification Pl an 87 �________________________ P A R T R I D G E RRIVER I V E R IINTRLJIN NTRUSION PARIRIDEE U 11 PIIL(S MILES \'YMN W Y M A N CREEK CREEK I WETLEG WETLEGS DUNKA RUAD ROAD DUNKA VII VII VII Peridotit V /or Vi VI —2 Iv V V Iv IV ,,Iv \ / ii —/ it / — - —— I FOOT\..'ALL FODTWALL FIGURE FIGURE 111 FOOT VALL FODTW ALL III II? -7-I - 7 —7—7—2—?— ?- I FOOTVALL Strike-length correlation n a j o r igneous igneous units within the the Strke-I.eng-th corr'e1aton oof'f major units wthn basal 33000 0 0 0 f Ft. t . oof' f tthe h e Partridge P a r t r i d g e River R i v e r Intrusion, Intrusion, k,osat UNtTi UNITS1 II = = utfIde—beoring Sulflde-bearlng aougte u ~ i t ekroctolite, t r o c t o l i t e , III1 == tr'octo(t2 t r o c t o l l t e w'th wlth picrite picriteLayers l a y e r s etc.. etc., III I11 == 'Mottied 'Mottled' onor-thasitic anorthositic troctollte. I VIV = =a auite u ~ i t etroctolite, anorthositic -tr-octoti-te. troctotrte. VV == anorthositic troctoijte troctolite, VI VI = = northost-ttc anorthositic ttroct. r o c t , to t o augIt augltetrocioti-te t r o c t o k t e , VII V I I == augite auglte iroctoilte, troctollte, sharp sharp con-tc-t contact -— - —gracla-tionat -gradational con-tact contact — 88 No scoe scaleimplied. Inplled. No �PRECAMBRIAN ROCKS, NEW BEDROCK BEDROCK GEOLOGIC GEOLOGIC MAP MAP OF PRECAMBRIAN ROCKS, REGION, WISCONSIN AND NORTHERN SUPERIOR REGION, EASTERN LAKE LAKE SUPERIOR NORTHERN MICHIGAN P. K. Sims, Sims, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225 80225 A new new geologic geologic map map of of Precambrian Precambrian rocks rocks in in Wisconsin Wisconsin and and northern northern Michigan (scale (scale 1:500,000) 1:500,000) has has been been compiled compiled in in cooperation cooperation with with the the Wisconsin Wisconsin Geological and Natural History Geological History Survey Survey from from published published maps maps and and available available unpublished data. unpublished data. The map has has 108 108 lithologic lithologic units. units. eastern Lake Superior The eastern Superior region region consists consists of of 66 major major Precambrian Precambrian domains that record lithotectonic domains record about 2,500 2,500 m.y. of of geologic geologic time. time. From From oldest to youngest, youngest, these these are are (1) (1) Archean Archean gneiss gneiss terrane terrane of of northern northern Michigan Michigan Archean greenstone-granite Wisconsin (2500-3650 and adjacent Wisconsin (2500-3650Ma), Ma), (2) Archean greenstone-graniteterrane terrane Michigan and adjacent Wisconsin (2700-2600 of northern Michigan adjacent Wisconsin (2700-2600 Ma), Ma), (3) a paired margin assemblage assemblage (Marquette continental margin (Marquette Range Supergroup) Supergroup) and and island-arc island-arc complexes (Wisconsin complexes (Wisconsin magmatic terranes), terranes), separated separated by the the Niagara Niagara fault fault zone, zone, of the early Proterozoic Penokean Penokean orogen, orogen, (4) (4) central central Wisconsin Wisconsin anorogenic anorogenic granite-rhyolite (ca. granite-rhyolite (ca. 1760 1760 Ma) terrane, terrane, (5) (5) 1.47 1.47 Ga Ga Wolf Wolf River River rapakivi rapakivi granite-anorthosite batholith, and granite-anorthosite batholith, and (6) (6) igneous igneous and and sedimentary sedimentary rocks rocks of of the the Ca. 1100 ca. 1100 Ma (Keweenawan) (Keweenawan) Midcontinent Midcontinent rift rift system. system. The Archean gneiss The Archean gneiss and and greenstone-granite greenstone-graniteterranes terranes compose compose the the basement basement of Proterozoic passive the boundary boundary of the Early Proterozoic passive continental continental margin margin assemblage; assemblage; the between the two between two basement basement terranes terranes is is the the Great Great Lakes Lakes tectonic tectoniczone, zone,aapresunied presumed paleosuture. paleosuture. magmatic terranes The Wisconsin magmatic terranes consist consist of of at at least least two two island-arc island-arc northern (Pembine-Wausau) The northern (Pembine-Wausau)terrane terrane is is dominantly dominantly composed composed of of calc-alkaline volcanic rocks deposited deposited in tholeiitic and calc-alkaline in the the interval interval 18601860but contains contains a more restricted 1880 Ma, but restricted succession succession of of calc-alkaline calc-alkalinevolcanic volcanic deposited about rocks deposited about 1835-1845 1835-1845 Ma. Ma. Granitoid Granitoid rocks rocks ranging ranging in in age age from from about about 1870 Ma to 1760 1760 Ma intrude intrude the the volcanic volcanic rocks. rocks. This This terrane terrane was was accreted accreted to to the continental continental margin margin about about 1860 1860 Ma. Ma. The southern southern (Marshfield) (Marshfield) terrane terrane contains remnants of mafic to to felsic felsic volcanic rocks rocks about about 1860 1860 Ma Ma that that were were Archean gneissic gneissic basement, deposited on Archean basement, foliated foliated tonalite tonalite to to granite granite bodies bodies about 1890 Ma, and younger ranging in age from about 1890 Ma to to 1870 1870 Ma, younger undated undated granite granite plutons. plutons. Following Following amalgamation amalgamation of of the the two two arc arc terranes terranes at at about about 1840 1840 Ma, Ma, intraplate magmatism magmatism (1835 alkali(1835 Ma) produced anorogenic anorogenic and and rhyolite rhyolite alkalifeldspar granite that feldspar that straddled straddled the the internal internal suture. suture. complexes. complexes. The 1760-Ma-anorogenic 1760-Ma-anorogenicsilicic-alkalic silicic-alkalic rocks rocks of of central central Wisconsin Wisconsin were were emplaced about 100 culmination of of the the Penokean Penokean orogeny. orogeny. Deep Deep 100 m.y. after culmination seated granitoid rocks intruded within the Pembine-Wausau Pembine-Wausauarc arc terrane terrane rocks were intruded within the approximately contemporaneously contemporaneously with the anorogenic magmatism to the the anorogenic magmatism to the south. south. 89 �The Wolf Wolf River River batholith batholith (1470 (1470 Ma) Ma) constitutes constitutes the the third third successive successive The It is is one one of of the the older older episode of of anorogenic anorogenic magmatism magmatism in inthe theregion. region. It episode intrusions of the 1.4 to 1.5 Ga transcontinental anorogenic province of North North intrusions of the 1.4 to 1.5 Ga transcontinental anorogenic province of America. America. The youngest youngest tectono-magmatic tectono-magmatic activity activity in in the the region region resulted resulted in in The tholeiitic volcanism, layered mafic intrusions, and associated red bed tholeiitic volcanism, layered mafic intrusions, and associated red bed sedimentation within within the the Midcontinent Midcontinent rift rift system system about about 1100 1100Ma. Ma. sedimentation 90 �A Geological Investigation inIn Vicinity Vicinity of of the A Geological Investigation the Volcanic-Plutonic Volcanic-Plutonic Contact, Contact, Northern Block Block of of the Marquette Northern Marquette Greenstone Greenstone Belt, Belt, Michigan. Michigan. J.R. J.R. SMALL, SMALL, and T.J. T.J. BORNHORST BORNHORST (Department (DepartmentofofGeological GeologicalEngineering, Engineering, Geology, Geology, and Geophysics, Michigan Michigan Technological Technological University, University, Houghton, Houghton, MI 49931) 49931) 14 km2 of the During 1988, 1988, 14 the northwesternmost northwesternmost portion portion of of the the Marquette Marquette Greenstone Belt, of the the city Greenstone Belt, located located approximately approximstely 20 miles northwest northwest of city of Marquette, were mapped aatt aa scale geology of Marquette, were geologically geologically mapped scale of of1:9000. 1:9000. The geology this area differs from studies to to the the south this from the the previous previous detailed detailed geologic geologic studies south and east in that east that itit includes includes the the contact contact between between the the volcanic volcanic and and the the bounding bounding The average grade of of metamorphism in the the Penny plutonic rocks. rocks. The average grade metamorphism in Penny Lake Lake area area is of the Archean units units within within the the is higher higher than to to the the south. south. The The structure structure of the Archean indicate at at least area is is complex. complex. Foliations Foliations indicate least two two periods periods of of deformation, deformation, and and the of a pyroclastic unit and aa gabbroic the orientation orientation of pyroclastic unit gabbroic sill sill indicate indicate the the continuation of of aa kilometer scale fold fold which continuation kilometer scale which was was first recognized recognized to the the south south by Johnson Mineralization inin the the Penny Penny Lake area area appears appears by Johnson et et al a1(ILSG (ILSG 1987). 1987). Mineralization to be be sporadic. sporadic. The Archean section in in the the Penny Archean volcanic volcanic section Penny Lake Lake area area is is composed composed of the the Volcanicsofof Silver Silver Mine Mine Lakes Lakes and and is is lithologically similar toto areas areas to to the Volcanics lithologically similar the south south and east, east, such such as as Johnson Johnson et et ala1(ILSG (ILSG1987). 1987). The volcanic volcanic rocks rocks are are composed of pillowed basalts with with minor composed of pillowed basalts minor interbedded interbedded iron iron formation formation and and pyroclastic-sedimentary units. The volcanic section is is intruded pyroclastic-sedimentary volcanic section intruded by by Archean Archean gabbro sill-like sill-like bodies and rhyolite gabbro bodies and rhyolite dikes. dikes. d Archean plutonic Penny Lake Lake area area has has been been divided divided The The Archean plutonic section sectioninin the the Penny into into four different different types. types. The oldest oldest two two have have been been subdivided subdivided into into aa gneiss gneiss unit based on a distinct gneissic fabric and a massive unit which correlates unit based a distinct gneissic and a massive unit which correlates with of Rocking with the Granodiorite Granodiorite of Rocking Chair Lakes Lakes of Johnson Johnson et et ala1(ILSG, (ILSG, 1987). 1987). Both the the gneiss gneiss and and massive massive units quartz monzonite monzonite to to granodiorite granodiorite in in Both units are quartz between these these two two units units is is uncertain; in a composition. The age relationship relationship between uncertain; in broad sense, sense, they they may may represent represent a single, single, extended extended plutonic plutonic event. event. The broad contact between these the volcanics volcanics is is gradational, gradational, zenoliths zenoliths of basalt basalt contact between these units units and and the exist near of the intrusions, exist near the the margins margins of intrusions, and and dike like like bodies bodies of the the granitoid granitoid intrude the the basalts. basalts. The The third type type of of granitoid granitoid intrusion intrusion is is granitic granitic in in compositionand and dike dike like like in form. composition form. These dikes are common common in the the These granite granite dikes Penny Lake Area, Area, and and vary vary in in thickness from under Penny Lake thickness from under .5 .5 meter meter to to over over 10 10 meters. They They cut cut both and are cut both the the gneiss gneiss and and the the massive massive granodiorite, granodiorite, and cut by quartz quartz veins. veins. The dikes have have sharp sharp contacts contacts with with the the volcanics volcanics and and are are variably variably deformed. deformed. The The fourth type type of of granitoid granitoid intrusion intrusion are are four, four, stock-like stock-like bodies of of diorite. stocks are are roughly circular in cross bodies diorite. These These stocks roughly circular cross section, section, and have have maximum diameter few hundred hundred meters. a maximum diameter of of a few meters. The volcanics volcanics are highly highly foliated margins of diorite, but the the contact contact between between the the two two units units foliated near near the the margins of the the diorite, is sharp. sharp. Their massive and the Their massive and unfoliated unfoliated textures textures suggest suggestthey they are are late late in the plutonic history. granite dikes dikes nor nor quartz plutonic history. Neither Neither granite quartz veins veins cut the the diorite diorite stocks, stocks, further suggesting suggesting a late late timing. timing. 91 �Metamorphic grade varies varies within within the the volcanic of the Metamorphic grade volcanic section section of the Penny Penny Lake Lake area, depending depending on on distance distance from from the thelarge largequartz quartzmonzonite-granodiorite monzonite-granodiorite intrusives. facies were were determined determined by by textures textures in in the intrusives. The metamorphic metamorphic facies the field field as well Facies changes changes were were well as as by by limited limited thin thinsection sectionobservations. observations. Facies determined by using using the the change change in calcium determined petrologically, petrologically, by calcium content of of plagioclase, the type plagioclase, the type and color color of of amphiboles, amphiboles, and and the the existence existence of of pyroxenes. pyroxenes. In general, general, the the metamorphic metamorphic grade grade increases increases gradually gradually from south to to north, north, except except for aa portion portion of of the thevolcanic volcanic section section along along the the eastern eastern boundary boundary where where the the grade grade increases increases abruptly abruptly from from greenschist greenschist to to amphibolite amphibolite across across aa north-south north-south trending trending fault. fault. Zones Zones of relatively relatively intense intense alteration alteration and andassociated associated anomalous anomalous precious precious metal are restricted metal mineralization mineralization are restricted to to small small areas areas near near faults. faults. Alteration Alteration in in these areas is most these mineralized mineralized areas most often characterized characterized by by quartz, quartz, carbonate, carbonate, and and sericite. sericite. Sulfides, Sulfides, including including pyrite, chalcopyrite, chalcopyrite, and and sphalerite, sphalerite, are arecommonly commonly found found in in the thealtered alteredrocks rocksasassmall, small,disseminated disseminated grains. grains. Specular Specular hematite hematite isis often often found found associated associated with with granite granite dikes dikes located located within within altered altered zones. zones. Twenty-two from throughout Twenty-two samples samples from throughout the area area were were assayed assayed for for gold. gold. Eight Eight samples anomalousvalues valuesofof greater greater than than ten samples contained contained anomalous ten parts parts per per billion, billion, with with aa maximum maximum assay assay value value of of 274 274 ppb. ppb. This project project was was funded funded by by the theMichigan MichiganGeological Geological Survey Survey and and Michigan Michigan Technological Technological University. University. 92 �AIRBORNE GEOPHYSICAL SURVEYS SURVEYSOF OFTHE THE EFFIE-COON AIRBORNE GEOPHYSICAL EFFIE-COON LAKE LAKE COMPLEX, COMPLEX. MINNESOTA MINNESOTA BY BY Bruce D. Smith, Smith, Victor F. Labson, Labson, Robert Robert J. J. Horton Horton by A program program to improve airborne airborne geophysical geophysical data acquisition and Interpretation interpretation has been implemented by Branch of of Geophysics. Geophysics. The The Effie-Coon Effie-CoonLake Lakearea areaisisone oneofoffour four areas areas chosen chosen to to test test new the USGS USGS Branch geophysical methods methodsto to map geologic for burled geophysical geologic features features favorable favorable for buried mineral mineral deposits. deposits. Airborne Airborne geophysical applications are particularly Important important since glacial and Quatemary Quaternary sediments cover 95% of results from from two new the bedrock bedrock In in the the area. area. This This presentation presentation describes describes preliminary preliminary results new airborne airborne EM EM systems systems and from new new total total field field magnetic magnetic data data processing. processing. The Effie-Coon Lake study study area, area, located located in In north-central Minnesota, Minnesota, is is a 2.7 billion The Effie-Coon Lake billion year year (Ga) (Ga) Precambrian terrain consisting consisting of the Effie Precambrian terrain Effie granitic intrusive complex and and the the Coon CoonLake Lakezoned zonedIntrusive intrusive metavolcanics. The zoned Intrusive, intrusive, thought from from limited limited outcrops outcrops surrounded by metasediments metasediments and and metavolcanics. drilling, to be and shallow shallow drilling, be mainly mainly quartz quartz monzonlte monzonite Is is defined defined mostly mostly from fromaeromagnetic aeromagnetic data. data. AANWNWSE trending 2.1 2.1 Ga mafic mafic dike dike system, system, Interpreted interpreted from from aeromagnetic aeromagnetic maps, maps, Intrudes intrudesthe themetamorphic metamorphic sequences and intrusive Intrusive complexes. complexes. Several Severaldifferent differenttypes typesof of mineral mineral deposits deposits could be present sequences and present in in the the area area including base base metals, metals, gold, gold, and andplatinum platinumgroup groupelement element(PGE) (PGE)deposits. deposits.Advanced Advancedairborne airborne geophysical geophysical methods methods are needed needed to to identify identifysubtle subtle geologic geologic features features favorable favorable for for buried buriedmineral mineraldeposits. deposits. tools for regional (EM) systems could be effective tools regional and and detailed three The two new electromagnetic (EM) properties provide dimensional mapping of electrical electrical resistivity. In general general mapping mapping of electrical dimensional mapping resistivity. In electrical properties provide complementary Information to to aeromagnetic and radiometric radlometric surveys. surveys. The The two two EM systems map shallow shallow and deep system, termed VLF for Very deep resistivity resistivity variations. variations. The shallow shallow penetrating penetrating system, Very Low Low Frequency, Frequency, measures EM EM fields fields generated generated by distant stations at about measures distant Naval Naval communication communication stations about 25,000 25.000 Hz. Hz. Unlike Unlike VLF instrumentation, instrumentation,the the components components measured measuredby bythe the USGS USGS system system are are used used to to compute commercial VLF apparent resistivity resistivity maps. maps. The The deeper deeper penetrating system developed developed by by the Branch apparent penetrating system Branch of of Geophysics Geophysics measures the effect effect of of magnetic fields generated 60,180, 180, and and300 300Hz. Hz. measures the generated by power lines at 60, Apparent resistivities resistlvities computed computed from the VLF data average 300 to Apparent to 400 400 ohm-meters ohm-meters with with some some areas as high as 1000 to 2000 2000 ohm-rn ohm-m and as low as 10's 10's of of ohm-meters. ohm-meters. High High resistivitles resistivities are a guide guide to locating locating shallow shallow or or exposed exposed resistive resistive bedrock bedrock which which is is helpful helpful In in geological geological mapping. mapping. Narrow Narrowresistivity resistivity 93 �highs not not associated associated with bedrock bedrock trends trends are are in in part part due due to to glacial glacial features such such as as eskars eskars which contain highs (>a0 ohm-m) which which may mayhelp help gravels. The Effie complex is characterized by high high apparent resistMtles resistivities (>400 gravels. ohm-rn) to the the define defineboundaries boundaries of of the the intrusive intrusive which which are are not not clearly clearly defined defined by bythe thegravity gravityorormagnetic magneticdata. data. to Areas of low low resistivities resistivities can be attributed attributed to either either thick glacial glacial till or or conductive conductiveshallow shallow bedrock bedrock (for (for Areas example example graphite graphiteIninmetasediments). metasediments). The airborne airborne EM EM instrument instrument which which measures measures magnetic magnetic fields power lines lines has has aa The fields generated generated by power depth of of penetration penetration is is approximately approximately ten times that of of the the VLF VLF system system and and has has aadeeper deeperdepth depthofof depth penetration than most commercial commercial systems. systems. Thus the system system is is much muchmore moresensitive sensitivetotovariations variationsInin penetration bedrock resistivity resistivity than the the VLF VLF system. system. The The measurements measurements are enhance mapping mapping of bedrock are processed processed to enhance conductivebedrock bedrockfeatures features which which may may be beburied buried at at depths depths of of hundreds hundredsof of meters. meters. Important Importantconductive conductive conductive bedrock bedrock features features In in the study study area area are are mainly mainly graphitic graphitic units units In in the the metasediments. metasediments. The The distribution distribution of of these units units isisuseful usefulininunderstanding understandingbedrock bedrockstratigraphy stratigraphy and and structure. structure. In Inaddition, addition,some someconductive conductive these anomalies anomalies could couldIndicate indicatemassive massivemetallic metallicmineralization. mineralization. The VLF VLF and and power power line lineEM The EMmethods methodsdo donot notrequire requireananairborne airbornetransmitter, transmitter,which whichgreatly greatly reduces reduces the the complexity, complexity, weight, weight, and and cost costofofthe thesystems. systems.Successful Successfuldevelopment developmentand andapplication applicationof of methods methods described described In this study study Is is aa critical criticalstep stepinindevelopment development of of electrical electricalmethods methods that that can canbe be routinely used used to to complement complement other other airborne airborne geophysical geophysical data data such such as asmagnetic magneticand andradlometric radiometric routinely measurements. measurements. The The airborne airborne survey survey also alsoIncludes includes standard standard total total field field magnetic magneticdata datawhich whichcombined combinedwith witholder older (1984) USGS USGS data effective flight spacing of 1/8 1/8 mile. mile.AAnumber numberofofdifferent differentstandard standard (1984) data yields yields an effective flight line spacing enhancement enhancement methods used on the the magnetic magnetic data data include: include: a)color a)color shaded shaded relief, relief, b)trend b)trendfiltering, filtering, and and c)boundaryestimatIon. estimation. In Inaddition additionaarelatively relativelynew newmethod methodofofenhancement enhancementusing usingaaterracing terracingoperator operator c)boundary has has been been applied applied to to the thedata. data.This Thisoperator operatorproduces producesmaps mapswith withboundaries boundariesshowing showingterrains terrains with with different differentestimated estimatedrelative relativesusceptibilities. susceptibilities. All InterpretatIon Allofofthe thegeological geologicaland andgeophysical geophysicaldata dataare arebeing beingused usedInInananintegrated Integrated interpretationofofthe the bedrockgeology. geology.Digital Digitalterrain, terrain,shown shownas ascolor colorshaded shadedrelief, relief,Isisbeing beingused usedtotoanalyze analyzepossible possiblesurface surface bedrock expressionsof of bedrock bedrockgeology. geology.Final Finalintegrated integratedInterpretation interpretationmakes makesuse useofofaaGeographic GeographicInformation Information expressions System System(GIS). (GIs). 94 �GEOLOGY OF O F THE THEWEST WESTDEAD D E A DHORSE HORSECREEK CREEKDIATREME-HOSTED DIATREME-HOSTED GEOLOGY R A R E METAL METAL OCCURRENCES, OCCURRENCES, SCHREIBER-HEMLO SCHREIBER-HEMLO DISTRICT, DISTRICT, ONTARIO ONTARIO RARE ** Smyk, Smyk, M.C.,Ontario Ontario Ministry Ministry of of Northern Northern Development ~ c w l o p m e nand and t Mines, Mines, Thunder Thunder M.C., DL., Geology, University of Western Ontario, London, Bay, Kingston, Bay, Kingston, D.L., Geology, University of Western Ontario, London, and Taylor, Taylor,R.P., R.P.,Earth EarthSciences, Sciences,Carleton Carleton University, University, Ottawa. Ottawa. and The Dead Dead Horse Horse Creek Creek complex complex consists consists of of five fiveseparate separatediatremes diatremes located located The immediately west west of of the theMiddle MiddleProterozoic ProterozoicCoidwell Coldwell alkaline alkaline complex complex (Sage, (Sage, immediately 1982). The West Dead Horse Subcomplex diatreme occurs in strongly foliated 1982). The West Dead Horse Subcomplex diatreme occurs in strongly foliated andmetavolcanic metavolcanicrocks, rocks,isisapproximately approximately80 80 by by 40 40mm Archean metasedimentary metasedimentary and Archean in size, size, and and contains contains three three main, main, highly highly radioactive, radioactive, mineralized mineralized zones: zones: (1) (1) in (2) eastern eastern extension, extension, and and (3) (3) western western pits. pits. The T h e eastern eastern pits pits and and eastern pits, pits, (2) eastern eastern extension extension are are situated situated in in the the main main diatreme diatreme which which isis composed composed eastern predominantly of monolithic breccia with hematized clasts set in a carbonatepredominantly of monolithic breccia with hematized clasts set in a carbonaterich matrix matrix that thatalso alsocontains containsriebeckite. riebeckite. The Thewestern western pits pits are are situated situated west west of of rich 130° oblique the main diatreme on a narrow, mineralized structure striking a t the main diatreme on a narrow, mineralized structure striking at 130°, oblique hosted in in aa silicified, silicified, to the the host-rock host-rock foliation. foliation. Here Here mineralization mineralization isis hosted to hematized, carbonate-rich carbonate-rich rock. rock. Although Although the the metal metal associations associations and and hematized, Th, U) U) mineralogy of of the the three threezones zones are a r e broadly broadly similar similar (enriched (enriched in in Zr, Zr, REE, REE, Th, mineralogy significant local variations exist, particularly in the nature and distribution of significant local variations exist, particularly in the nature and distribution of the REE-bearing minerals: the western pits are characterized by high values of the REE-bearing minerals: the western pits are characterized by high values of Be (up (up to to 0.62 0.62 wt.96), wt.%), Sc to 250 250 ppm), ppm), Zr Zr (up (up to to11.6 11.6 wt.%), wt.%), REE REE (up (up to to1250 1250 Be Sc (up (up to pprn), T h (up to 0.52 wt.%) and U (up to 0.31 wt.%). In contrast samples from ppm), Th (up to 0.52 wt.%) and U (up to 0.31 wt.%). In contrast samples from the eastern eastern pits pits and and eastern eastern extension extension contain contain lesser, lesser, but but nevertheless nevertheless the significant abundances of Be (up to 240 ppm), Sc (up to 85 ppm), Zr (uptoto2.8 2.8 significant abundances of Be (up to 240 ppm), Sc (up to 85 ppm), Zr (up wt.%). Th Th (up (uptoto0.15 0.15 wt.%), wt.%), and andUU(up (uptoto0.08 0.08wt.%); wt.%);subequal subequal amounts amounts of of REE REE wt.%), 1220 ppm); and are enriched in P205 (up to 2.46 wt.%) and Y (up to 235 (up to (up to 1220 ppm); and are enriched in P205 (up to 2.46 wt.%) and Y (up to 235 ppm). In In addition additiontotozircon zircon(often (oftenhydrated), hydrated),complex complexCa-Zr-bearing Ca-Zr-bearing silicates silicates ppm). and thorite, phenacite occurs in the western pits, and monazite and xenotime and thorite, phenacite occurs in the western pits, and monazite and xenotimc REE are found foundininthe theeastern easternpits pitsand andeastern easternextension. extension.Chondrite-normalized Chondrite-normalized REE are distributions emphasize the variability of the REE-mineralogy (western pits, distributions emphasize the variability of the REE-niincralogy (western pits, 0.09; eastern eastern pits, pits,LREE..enriched, LREE-enriched, La/LeN L 8 / h N—= 9.1 9.1 to to HREE-enriched, La/LuF HREE-enriched, La/Lu — 0.09; - 17.6). None of the themineralized mineralized samples samples have have aamarked markednegative negativeeuropium europium 17.6). None of anomaly. which which suggests suggests that that the themineralizing mineralizingfluid.s fluids were were nxittj,cd. oxidised. anomaly, 95 �MULTIPLE ARCHEAN TERRANESI IN MULTIPLE ARCHEAN TERRANES N SW SW MINNESOTA MINNESOTA -- THE OLD GRAY OLD GRAY GNEISS SHE SHE AIN'T AIN'TWHAT WHAT SHE SHE USED USED ¶10 TO BE BE D.L. SOUTHWICK, Minnesota Geological University D.L. SOUTHWICK, G e o l o g i c a l Survey, S u r v e y , 2642 2642 U n i v e r s i t y Avenue, Avenue, St. BRYAN Department of Geology and 55114, BRYAN SCHAAP, SCHAAP, Department and Geophysics, Geophysics, S t . Paul, P a u lMN , MN55114, University U n i v e r s i t y of of Minnesota, Minnesota, Minneapolis, M i n n e a p o l i s , MN MN 55414, 55414, and and V.W. V.W. CHANDLER, CHANDLER, Minnesota Geological G e o l o g i c a l Survey. Survey. Major aeromagnetic less a e r o m a g n e t i c and and gravity g r a v i t y lineaments l i n e a m e n t s that t h a t trend t r e n d more more or o r less parallel p a r a l l e l to t o the the Great G r e a t Lakes Lakes Tectonic T e c t o n i c Zone Zone (GLTZ) (GLTZ) subdivide s u b d i v i d e the t h e Archean Archean ggneiss n e i s s terrane t e r r a n e of of southwestern s o u t h w e s t e r n Minnesota into i n t o three t h r e e blocks b l o c k s that t h a t have distinctive d i s t i n c t i v e geophysical g e o p h y s i c a l characteristics. c h a r a c t e r i s t i c s . The block—bounding block-bounding lineaments l i n e a m e n t s are are of north-dipping n o r t h - d i p p i n g zones z o n e s of o f planar p l a n a r structures; s t r u c t u r e s ; therefore therefore tthe h e surface s u r f a c e traces of they t h e y are a r e approximately a p p r o x i m a t e l y parallel p a r a l l e l to t o the the GLTZ in i n three t h r e e dimensions, d i m e n s i o n s , not n o t just just iin n map map view. view. The northernmost n o r t h e r n m o s t block block boundary, boundary, about a b o u t 40 40 km south s o u t h of o f the t h e GLTZ, has has It I t separates s e p a r a t e s the t h e Benson Benson bbeen e e n named the t h e Appleton geophysical g e o p h y s i c a l lineament. lineament. b l o c k on the t h e north n o r t h from from the t h e Montevideo Montevideo block b l o c k on on the south s o u t h and, and, on the the block bbasis a s i s of of sparse s p a r s e drilling, d r i l l i n g , appears a p p e a r s to t o be be aa zone zone of of ductile d u c t i l e shear s h e a r and and faulting f a u l t i n g that t h a t has h a s been been invaded invaded locally, l o c a l l y , and and synkinematically, s y n k i n e m a t i c a l l y , by by sheets s h e e t s of of muscovite m u s c o v i t e leucogranite. l e u c o g r a n i t e . As A s judged judged from from geophysical g e o p h y s i c a l anomaly anomaly patterns p a t t e r n s and and drilling d r i l l i n g data, d a t a , the t h e Benson Benson block block consists c o n s i s t s dominantly d o m i n a n t l y of of granitic g r a n i t i c to t o tonali— tonalitic intrusions into gneissic wall rocks. plutons t i c i n t r u s i o n s i n t o g n e i s s i c w a l l r o c k s . The p l u t o n s range r a n g e from strongly strongly synkinematic as whole whole may may be be aa granitoid granitoid s y n k i n e m a t i c to t o post—kinematic, p o s t - k i n e m a t i c , and and the t h e block b l o c k as intrusive i n t r u s i v e complex complex analogous a n a l o g o u s in i n style s t y l e to t o the the Winnipeg Winnipeg River R i v e r belt b e l t in i n the the Superior S u p e r i o r Province P r o v i n c e of of Manitoba Manitoba and and Ontario. O n t a r i o . The Montevideo block, b l o c k , in in contrast, c o n t r a s t , appears a p p e a r s to t o be be primarily p r i m a r i l y gneissic g n e i s s i c rocks r o c k s comparable comparable to t o those those exposed in i n the t h e Minnesota Minnesota River R i v e r Valley V a l l e y between between Montevideo Montevideo and and Granite G r a n i t e Falls. Falls. M a age a g e component component and and granulite—facies g r a n u l i t e - f a c i e s metamorphism metamorphism that t h a t characcharacThe 3,600 3 , 6 0 0 Ma tterize e r i z e the t h e Montevideo Gneiss G n e i s s have thus t h u s far f a r not n o t been been documented documented in i n the the Benson b block. lock. About45 45kmkmf afarther the lineament l i n e a m e n t that t h a tseparates s e p a r a t e sthe t h eMontevideo Montevideo About r t h e r ssouth, o u t h , the block the Morton block ppasses and ccrosses b l o c k from from the Morton block a s s e s tthrough h r o u g h RRenville e n v i l l e and r o s s e s the the River Sacred Minnesota R i v e r in i n a zone of of no outcrop o u t c r o p between Granite G r a n i t e Falls F a l l s and S acred A zone of A of faulting f a u l t i n g in i n this vicinity v i c i n i t y has h a s long l o n g been postulated p o s t u l a t e d on the basis b a s i s of o f earlier e a r l i e r geophysical g e o p h y s i c a l surveys s u r v e y s and and exposed exposed small s m a l l shear s h e a r zones zones just just t h a t the t h e fault f a u l t zone is i s larger larger nnorth o r t h of of the t h e outcrop o u t c r o p gap. gap. Our data d a t a suggest s u g g e s t that and that previously p r e v i o u s l y thought, t h o u g h t , and and imply imply that t h a t the t h e Morton Morton a n d more fundamental f u n d a m e n t a l that Gneiss G n e i s s and Montevideo Montevideo Gneiss G n e i s s could c o u l d well w e l l be be separate s e p a r a t e and and distinct d i s t i n c t elements elements of o f the t h e Middle Middle Archean Archean crust c r u s t that t h a t have have been b e e njuxtaposed j u x t a p o s e dtectoriically. tectonically. Heart. Heart. All A l l three three blocks b l o c k s of of the t h e Archean Archean gneiss g n e i s s terrane t e r r a n e are a r e truncated t r u n c a t e d geophysi— geophysic a l l y on on the the east e a s t by by anomaly anomaly patterns p a t t e r n s characteristic c h a r a c t e r i s t i c of o f Penokean Penokean plutons plutons cally and, to l e s s e r extent, e x t e n t , of o f folded f o l d e d supracrustal s u p r a c r u s t a l rocks. rocks. S i m i l a r but b u t less less and, t o a lesser Similar diagnostic d i a g n o s t i c patterns p a t t e r n s flank f l a n k the t h e Morton Morton block b l o c k on on the the south s o u t h and and west, west, ssuggesting u g g e s t i n g that t h a t the the Archean gneiss g n e i s s terrane t e r r a n e may be be enveloped enveloped by Early Early Proterozoic magmatic belts. belts. sScientific c i e n t i f i c drilling d r i l l i n g to t o test t e s t these t h e s e interpretainterpretaP r o t e r o z o i c magmatic tions i s underway underway and and will w i l l continue. continue. t i o n s is T h i s work work was was funded funded in i n part p a r t by by the the Minnesota Minnesota Future F u t u r e Resources Resources Commission. Commission. This 96 �Petrography and Sedimentation of The Petrography The Middle Middle Proterozoic Proterozoic (Keweenawan) Nonesuch Nonesuch Formation Western Lake Superior (Keweenawan) Formation Western Superior Region Midcontinent Region Midcontinent Rift Zone Thomas Minnesota-Duluth, Duluth, Thomas J. J. Suszek Suszek (Dept. (Dept. of Geology, University of of Minnesota-Duluth, Duluth, Minnesota 55812) 55812) New information New information from from drill drill hole logs, logs, detailed detailed sedimentological sedimentological descriptions descriptions and petrographic petrographic analysis analysis of Middle Middle Keweenawan Keweenawan Nonesuch Nonesuch Formation Formation in in select Bear Creek drill cores from and Douglas Counties Wisconsin, and Bear Creek drill from Bayfield Bayfield and Douglas Counties Wisconsin, and examination of outcrops in Upper Michigan Michigan provide provide in northwest northwest Wisconsin Wisconsin and and Upper evidence for for source source rocks and environment 1). evidence environment of deposition deposition (Fig. (Fig. 1). These data suggest that Lower Lower Keweenawan Keweenawan volcanic units were were the the major major These data suggest volcanic units contributors the Nonesuch Nonesuch Formation Formation in in northwest northwest Wisconsin, Wisconsin, while while contributors ofof detritus detritus to the Middle volcanics were only Sediment from Early Middle Keweenawan Keweenawan volcanics only minor minor contributors. contributors. Sediment Early Proterozoic and Archean Proterozoic and Archean crystalline crystalline rocks, rocks, although although minor, minor, increase increase ininabundance abundance upsection as older source rocks upsection as rocks were were unroofed. unroofed. Sedimentary structures and stratigraphic stratigraphic relationships relationships suggest suggest that that deltaic Sedimentary structures and processes, sheet floods, floods, turbidity processes, sheet turbidity currents currents and suspension suspension settling settling were were the the primary primary mechanismsofof deposition deposition in in aa lake with mechanisms with constant constant and and perhaps perhaps rapid rapid fluctuations fluctuations in water water levels brought on by by changes changes in in tectonism tectonism and/or and/or climate. climate. The gradational contacts of the Nonesuch Formation The gradational contacts of the Nonesuch Formation with with the the underlying underlying Copper Harbor Harbor Conglomerate Conglomerate and overlying overlying Freda Freda Sandstone, Sandstone, along along with with outcrop outcrop Copper and drill facies facies data, data, suggest suggest deposition deposition of of the the Nonesuch Nonesuch on on aaprograding progradingalluvial alluvial complex in the Midcontinent Midcontinent Rift Rift Zone. Zone. fan complex Examinationofof the the genetic facies, combined combined with with Examination genetic relationship relationship of Nonesuch Nonesuch facies, percentages of the different textural textural elements within each each facies type, and and petrographicdata, data, suggest suggest that that deposition deposition was was generally generally from from the the south petrographic south into the rift rift zone. zone. Deposition occurred in aa basin basin that that was waspartially partiallyrestricted, restricted, Deposition appears appears to to have occurred or perhaps or perhaps completely completely isolated from from areas areas containing containing Nonesuch Nonesuch Formation Formation farther farther east Wisconsin and Upper Upper Michigan. Michigan. east in Wisconsin 97 �Bear Creek Drill Holes Figure1.1. General Generallocation locationof ofoutcrop outcropand anddrill drillhole holestudy study areas. Figure areas. 98 �GRAVITY AND MAGNETIC DATA OVER THE GRAVITY AND MAGNETIC DATA OVER THE WAUKESHA FAULT, S.E. WISCONSIN WAUKESHA FAULT, S.E. WISCONSIN by Keith A. Sverdrup Keith A. Sverdrup F. Kean William William F.Geosciences Kean Department of Department of Geosciences University of Wisconsin-Milwaukee University of Wisconsin—Milwaukee Milwaukee, WI 53201 Milwaukee, WI 53201 In the past few years gravity and magnetic data has been In theover pastthe fewWaukesha years gravity andthe magnetic data has been of collected fault in southeastern corner collected over the Waukesha fault in the southeastern corner ofa thestate. state. The fault can be observed where it passes through the The fault can be observed where it passes through a At this point it appears as a vertical fault quarry inWaukesha. Waukesha. quarry At this appears at as between a vertical 30 fault with ain displacement that haspoint been it estimated with a displacement that has been estimated between 30 feet. (~ikulic and Mikulic, 1977) and 100 (Foley at et al., 1953) (Mikulic and Mikulic, 1977) and 100 (Foley 1953) of feet. The displacement at depth is thought to beetonal., the order 1500 The displacement at depth is thought to be on the order of 1500 feet(Thwajtes, (Thwaites,1957). 1957). feet ~nitially,1500 square miles of gravity data were collected on 1500to square miles of gravity were on a Initially, one mile grid investigate the lineardata extent of collected the fault. aThe oneresultant mile gridgravity to investigate the linear extent of the fault. signature is characterized by a zone The resultant gravity signature is characterized by a zone N40E roughly three miles wide of tightly spaced trending trending N4OE roughly threeextends miles wide tightly spaced for of approximately 6 0 miles from contours. This signature contours. This signature extends for approximately miles from the Lake Michigan shoreline near Port Washington to 60 the southwest the Lake Waukesha Michigan and shoreline near Port Washington- Illinois to the southwest through on towards the Wisconsin border. through and onnorthwest towards the Wisconsin ~ r a v i t Waukesha yvalues on the side of the fault are as border. much as Gravity values on the northwest side of the fault are as much as 19 mgals higher than those to the southeast. 19 mgals than those thefault southeast. Ourhigher initial models ofto the based on the gravity data Our initial models of the fault based on the gravity it as a high angle growth fault downthrown to the data viewed viewed it as a high angle growth fault downthrown to the southeast. The displacement was as little as 40 feet in the southeast. The displacement was as to little as 40 thein the ~iagarandolomite near the surface as much asfeet 2000in feet Niagaran dolomite near the surface to as much as 2000 feet ~recambrian basement. In order to model the large gravityin the Precambrian basement. In order model theto large gravity contrast across the fault it wastonecessary include a high contrast across the fault it was necessary to include a high density mafic material at depth. density mafic material The gravity data at wasdepth. later supplemented by roughly 630 The gravity data was latertaken supplemented roughly 630 square miles of magnetic data on a one by mile grid coincident square miles of magnetic data taken on a one mile grid coincident withgravity gravitystations. stations. Magnetic readings varied between with readings There variedis between no clear linear approximately 57,400 andMagnetic 59,000 gammas. approximately 57,400 and 59,000 gammas. There is no clear Instead there are alinear number feature evident in the magnetic data. feature evident in the magnetic data. Instead there are a number of roughly circular magnetic highs as much as 1300 gammas above of circular highs as much as 1300 gammas These above androughly lows as much asmagnetic 300 gammas below background levels. and lows as much as 300 gammas below background levels. These featuresdo do not not show showany any clear clearindication indicationof ofthe the presence of a features presence fault, rather they suggest individual intrusive bodies ofof a fault, rather they suggest individual intrusive bodies of relatively high susceptibility material and have been modelled as relatively susceptibility material and been modelled Withhigh this supporting information we have are modifying our as such. such. With this supporting information we are modifying our gravity model to incorporate a limited vertical fault consistent gravity model to incorporate a limited vertical fault at consistent intrusives depth. with previous views and individual mafic with previous views and individual mafic intrusives Illinois at depth. 99 �References References Foley, F.C., FC., Walton, Walton, W.C., W.C., and and Drescher, Drescher, W.J., W.J., 1953, 1953, Ground water conditions conditions in in the the Milwaukee—Waukesha Milwaukee-Waukesha area, area, Wisconsin: Wisconsin: Wisconsin p. Wisconsin Geological Geological Survey Survey water water supply supply paper paper 1229, 1229, p. 3—23. 3-23. Mikulic, J.L., 1977, Mikulic, D.G., and Mikulic, J.L., 1977, History of geologic geologic work in the the Sjlurjan Silurian and Devonian Devonian of of southeastern southeastern Wisconsin: Wisconsin: annual Tri-State Tn-State field Guidebook for the 41st annual field conference, conference, p. A19-A27. A19-A27. Thwaites, Thwaites, F.T., F.T., 1957, 1957, Buried Precambrian Precambrian of of Wisconsin: Wisconsin Wisconsin Geological and Geological and Natural History History Survey Survey map. map. 100 �STRIKE-SLIP FAULTING FAULTING IN IN ARCHEAN ARCHEAN ROCKS ROCKS IN IN THE THE VIRGINIA VIRGINIA HORN HORN STRIKE-SLIP AREA, N.E. N.E. MINNESOTA: MINNESOTA: IMPLICATIONS IMPLICATIONS FOR FOR THE THE ORIGIN ORIGIN OF OF THE THE AREA, VIRGINIA HORN STRUCTURE VIRGINIA HORN STRUCTURE JAMES JAMES L. L. WELSH WELSH Department Department of of Geology Geology Gustavus Gustavus Adoiphus Adolphus College College St. St. Peter, Peter, MN MN 56082 56082 Field Field mapping mapping in in Archean Archean metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks in in the the Virginia-Eveleth-Gilbert Virginia-Eveleth-Gilbert area area of of northeastern northeastern Minnesota Minnesota has has revealed revealed the the presence presence of of aa significant significant strike— strikeslip slip fault fault system, system, here here called called the the Pike Pike River River System. System. In In this this area area the the fault fault system system is is composed composed of of two two major major northeasterly northeasterly trending trending faults faults connected connected by by aa series series of of more more northerly northerly trending trending en en echelon echelon strands. strands. The The configuration configuration suggests suggests aa strike strike slip slip duplex. duplex. Movement Movement history history along along this this system system appears appears to to have have been been Although offset offset marker marker units units have have not not been been Although identified, map map patterns patterns suggest suggest that that early early and and possibly possibly the the identified, most most significant significant movement movement was was sinistral. sinistral. Kinematic Kinematic indicators, indicators, however, however, indicate indicate that that (latest?) (latest?) movement movement was was dextral. dextral. In In addition addition high high angle angle slickensides slickensides associated associated with with the the duplex duplex strands strands require require aa vertical vertical component componentof ofmovement. movement. complex. complex. The The Pike Pike River River System System trends trends along along the the axis axis of of the the Virginia Virginia Horn Horn (the (the gentle gentle anticline-syncline anticline-syncline structure structure present present in in the the unconformable unconformable superjacent superjacent Proterozoic Proterozoic rocks, rocks, so so prominently 2-shaped map map pattern pattern of of the the prominently outlined outlined by by the the Z-shaped Biwabik Biwabik Iron Iron Formation), Formation), and and most most certainly certainly exerted exerted aa controlling controlling influence influence on on its its formation, formation, although although the the Proterozoic rocks themselves have not been Proterozoic rocks themselves have not been cut cut by by these these faults. faults. It It is is here here suggested suggested that that late late dextral dextral transpressional transpressional movement movement in in the the basement basement rocks, rocks, possibly possibly aa result of the Penokean collision to the south, created result of the Penokean collision to the south, created aa compressional compressional stress stress within within the the reactivated reactivated Pike Pike River River duplex duplex structure, causing localized uplift of the basement structure, causing localized uplift of the basementrocks. rocks. The The Virginia Virginia Horn Horn structure structure is is thus thus interpreted interpreted to to be be aa drape drape structure over the uplifted basement rocks. structure over the uplifted basement rocks. 101 �Mafic and Clastic Clastic Dikes Dikes as as Keweenawan Keweenawan Paleostress Paleostress Indicators in in the the Huron Huron Mountains, Mountains, Michigan Michigan G. Wilson Wilson and andC. C. Craddock G. Department Department of Geology and and Geophysics Geophysics Wisconsin-Madison University of Wisconsin-Madison Madison, 53706 Wl53706 Madison, WI The Huron Mountains Mountains of northwest northwest Marquette Marquette County, Michigan, Michigan, contain the pre-rift basement rocks closest to the northern northern apex apex of of the the Midcontinent MidcontinentRift RiftSystem System (MRS) and thus are aa strategic paleostresses associated associated with with the the strategic place place to to study study paleostresses formation of the rift. rift. This area is is located located astride astride the the Trans-Superior Trans-Superior Tectonic Tectonic Zone Zone (TSTZ) (Fig. 1), I ) , which bisects the arc formed by the two arms of the the rift rift (Klasner (Klasner et et al, al, 1982). This This zone zone lies lies parallel parallel to to the the direction direction along which major crustal separation is inferred to have taken place place across across the the rift. rift. The study area in in the the Huron HuronMountains Mountains was mapped at a scale of 1:6000 1:6000 so that the rocks rocks and structures could be mapped mapped detail. The and plotted in detail. Thebasement basement rocks rocks of of the the Huron Huron Mountains Mountains consist consist mainly mainly of of The Upper Archean Archean granodiorite granodiorite gneiss gneiss and and amphibolite. amphibolite. The Upper Keweenawan Keweenawan (?) (?) Jacobsville Sandstone overlies the Archean Archean rocks rocks nonconformably. nonconformably. Structures in the Huron Mountains Mountains that reveal northern MRS kinematic kinematic patterns patterns include 1) mafic dike swarms and basement rock joints, joints, which record a prepre- to syn-rift extensional cycle, and and 2) 2) aligned extensional cycle, aligned clastic clastic dikes dikes and joint joint sets sets in in the theJacobsville Jacobsville in the the Huron Huron Sandstone that suggest aa post-rift compressional cycle. cycle. Mafic dikes in as much as 60 m wide have subophitic to to diabasic diabasic textures textures and consist of of Mountains as plagioclase plagioclase and clinopyroxene clinopyroxene with subordinate subordinate amounts amounts of of opaque opaqueminerals. minerals. Dominant mafic mafic dike dike trends trends are are N-S and and E-W, E-W, perpendicular perpendicular and and parallel parallel to to the the rift Dominant axis, respectively respectively (Fig. (Fig. 2). 2). Similar trends for mafic dikes in in western western upper upper Michigan Michigan were described by Baxter Perpendicular dike dike trends are Baxter and and Bornhorst Bornhorst (1988). (1988). Perpendicular are unusual in in a rift ordinarily leads leads to to a single unusual rift environment; environment; crustal crustal extension extension ordinarily single set set subparallel to the the rift Thus, the the perpendicular dike pattern subparallel to rift axis. axis. Thus, perpendicular dike pattern is is presently presently somewhat enigmatic. enigmatic. vertical clastic clastic dikes with a consistently Seven vertical consistently NNE trend (Fig. (Fig. 3) 3) have havebeen been found within the the Jacobsville Jacobsville Sandstone Sandstone of of the the Huron Huron Mountains. Mountains. These aligned aligned clastic dikes are are as much clastic dikes much as 20 cm cm in in width, width, more more than 100 100 m m in in length length (they (they disappear beneath beneath Lake Lake Superior), Superior),and andseparated separatedby by as as much disappear much as as 22 km. km. Cathodoluminescence microscopy microscopyand and petrographic petrographic analysis analysis indicates indicates that the Cathodoluminescence the clastic dike dike rock is aa quartz arenite with with well-rounded well-rounded grains, grains, both both texturally texturally and and clastic quartz arenite compositionally more more mature mature than than the the wall compositionally wall rock, rock, the the Jacobsville Jacobsville Sandstone Sandstone -primarily a feldspathic sandstone with conglomerate, conglomerate, siltstone, and and shale shale members. members. Since Since the Jacobsville Jacobsville Sandstone Sandstone rests rests nonconformably nonconformably on on crystalline crystalline basement basement rocks, it is unlikely that that the clastic dikes were were injected injected from from below. below. An An alternative alternative is is rocks, that the dikes that dikes are are of of the the neptunian neptunian model model -- those those that that fill fill fissures fissuresfrom from above. above. Outcrops of Jacobsville are found found as much as 150 Outcrops of Jacobsville Sandstone Sandstone are 150 m m topographically topographically than outcrops that that display the clastic dikes. An higher than Anexplanation explanationmust, must,therefore, therefore, account for a stress account for stress state state that that permits permits the the opening opening of of extension extension fractures fractures at aa minimum depth depth of of 150 m minimum m in inthe theJacobsville Jacobsville bedrock, bedrock, the the inferred inferredminimum minimum 102 �pre-erosional thickness of the Jacobsville Sandstone Sandstone in in the Huron Huron Mountains. Mountains. reflection profiles profiles AA and F suggest the presence of of reverse faults in GLIMPCE reflection that may be an extension of the rift-related rocks offshore from the Huron Mountains that Keweenaw Fault. Keweenaw Fault. The NNE trend of the clastic dikes, dikes, parallei parallei to the TSTZ, TSTZ, places places them in in an an orientation orientation parallel parallel to to the theprobable probabledirection directionofofmaximum maximumcompression compression expected for the apex expected apex of of the the MRS MRS during during its itscompressional compressionalstage stage of of development development (Fig. 1). 1). The trend of the clastic dikes nearly nearly bisects bisects the acute angle between two major joints in the Jacobsville major sets of vertical joints Jacobsville Sandstone. Sandstone. These These joints appear appear to represent a conjugate shear system, and the clastic dikes would thus correspond to the extension position; aa third dikes. Therefore, extension fracture position; third set set of of joints parallels parallels the dikes. Therefore, the the aligned clastic clastic dikes formed parallel parallel to to a aligned dikes may may have have filled extension extension fractures fractures formed compression associated compression associated with the compressional compressional stage stage of of the the MRS. MRS. The compositional compositional and textural maturity of the clastic dike rock in comparison comparison to the Jacobsville wall rock rock suggests that the dikes the Jacobsville Sandstone Sandstone wall suggests that dikes are are composed composed of of sandstone similar to that found in the Munising Munising Formation Formation (Upper Cambrian), a rock unit that overlies unit overlies the the Jacobsville Jacobsville Sandstone Sandstone in slight slight angular angular unconformity unconformity in in outcrops 60 km to the southeast of the study study area. area. If the dike rock is indeed indeed from from the the Munising Formation, then the clastic dikes provide provide a paleostress paleostress indicator, suggest aa timing for some some of of the the compressional compressional event, and and give give reason reason to extend extend the the known known pre-erosional pre-erosional limit of the Munising Munising Formation Formation in in upper upper Michigan. Michigan. 00 50 SO I - 100 100 200 1 I 300 KILOMETERS KILOMETERS of the the TransTransFig. 11 - Location map and orientation of 1982). Superior Tectonic Zone (after Kiasner Klasner et et al, al, 1982). 103 �N N w N=7 - Circi. 43% Clastic Dike Dike Trends Trends Fig. 3 -- Clastic Fig. 2 - Mafic Mafic Dike Dike Trends Trends FIg. Research in the Huron Research Huron Mountains Mountains is partially partially supported supported by by the the Geological Geological Society of of America, and the University Society America, the Michigan Michigan Geological Geological Survey, Survey, and University of of Wisconsin-Madison. Wisconsin-Madison. REFERENCES REFERENCES Baxter, D. A., A., and Bornhorst, T. T. J., J., 1988, 1988, Multiple Multiple discrete discrete mafic intrusions of Archean to Keweenawan Keweenawan age, age, western western upper upper peninsula, peninsula, Michigan: Michigan: Abstract. Inst. on on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan, p. p. 6-8. 6-8. 34th Annual Inst. Klasner, J. S., Cannon, W. F., F., and and Van Schmus, Schmus, W. R., R., 1982, 1982, The The pre-Keweenawan pre-Keweenawan tectonic history history of of southern southern Canadian Canadian Sheild Sheild and and its its influence influence on formation of the Midcontinent Rift, in in Wold, Wold, R. R. J., J., and and Hinze, Hinze, W. W. J., J., eds., eds., Geology andTectonics of the Lake Lake Superior Superior Basin: Basin: Geol. Geol. Soc. Soc. of of America America Memoir Memoir 156, 156, p. p. 27-46. 27-46. 104 � https://digitalcollections.lakeheadu.ca/files/original/9af34eabd15297edf1bc1cc9977276ea.pdf a17260d67672289910f93f628575c1be PDF Text Text ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON PROCEEDINGS VOLUME 35 VOLUME 35 1989 MAY 1989 2.Field FieldTrip TripGuidebook Guidebook Part 2. Trip 1. 1. North Shore Rhyolites, Rhyolites, Minnesota Minnesota Trip 2. Penokean Penokean Structural Structural Terranes Terranes in East-Central East-Central Minnesota Minnesota Trip 3. 3. Mellen Complex, Wisconsin Wisconsin Trip 4. 4. Archean ArcheanGold Gold Occurrences Occurrences and and Their Their Structural Structural Settings Settings 35th 35th Annual Annual Meeting Meeting May 3-6, 1989 1989 held at at Duluth, 55812 Duluth. Minnesota Minnesota 55812 �Organizing Committee, Committee, 35th 35th Annual Annual Meeting, Meeting, ILSG ILSG(1989) (1989) Richard W. Dept. of Geology, University W. Ojakangas, Ojakangas, Dept. University of of Minnesota, Minnesota, Duluth, Duluth,MN MN55812 55812 John C. C. Green, Green, Dept. Dept. of Geology, Geology, University of Minnesota-Duluth, Minnesota-Duluth, Duluth, MN 55812 55812 Timothy B. B. Hoist, Hoist, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812 55812 Program Chair and and Abstract Abstract Editor: Editor: John Program Chair John C. C. Green Green Guidebook Editor: Timothy B. Hoist Hoist Guidebook Editor: Timothy B. Volume 35 35 consists of Parts Parts 11 and Volume and 2: 2: 1: 1: Abstracts Abstracts 2: 2: Field Trip Guidebooks Guidebooks Published and Distributed Distributed by by Institute Institute on on Lake Lake Superior Superior Geology Geology J. Kalliokoski, Kalliokoski, Secretary/Treasurer SecretaryITreasurer Dept. of Geological Geological Engineering, Engineering, Geology Geology and Geophysics Geophysics Michigan Technological University University Houghton, Michigan Michigan 49931 49931 ISSN 1042-9964 1042-9964 �FIELD TRIP TRIP GUIDEBOOK GUIDEBOOK THIRTY-FIFTH ANNUAL MEETING MEETING INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 3-6, 1989 1989 MAY 3-6, DULUTH, MINNESOTA MINNESOTA Trip 1: North Shore 1: North Shore Rhyolites, Rhyolites, Minnesota Minnesota Leader: Leader: J. C. C. Green Green University of Minnesota University of Minnesota Duluth Duluth Duluth, Minnesota Minnesota 55812 55812 Trip 2: 2: Penokean Structural Terranes in East-Central East-Central Minnesota Minnesota Leader: Leader: T. B. B. Hoist Hoist University of of Minnesota Minnesota Duluth Duluth Duluth, Minnesota 55812 Minnesota 55812 Trip 3: 3: MeIlen Mellen Complex, Wisconsin Wisconsin Leaders: Leaders: K. W. W. Klewin, Klewin, Northern NorthernIllinois IllinoisUniversity, University,DeKaIb, DeKalb,Illinois Illinois6011 601 15 K. 5 J. F. F. Olmsted, Olmsted, SUNY, SUNY, Plattsburgh, Pittsburgh, New New York York 12901 12901 K.E. K.E. Seifert, Seifert, Iowa Iowa State State University, University, Ames, Ames, Iowa Iowa50011 5001 1 TrIp Trip 4: 4: Archean Gold Occurrences Occurrences and Their Structural Structural Settings Settings Part Part A A (Virginia (Virginia Horn) Horn) Leaders: Leaders: Welsh, Gustavus Gustavus Adolphus Adolphus College, College, St. St. Peter, Peter, Minnesota Minnesota 56082 56082 J. Welsh, England, Rhude Rhude and and Fryberger, Fryberger, Inc. Inc. Hibbing, Hibbing, Minnesota Minnesota 55746 55746 D. England, D. Groves, Groves, Newmont Newmont Exploration, Exploration, Ltd., Ltd., Duluth, Duluth, Minnesota Minnesota 55811 5581 1 Levy, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 55812 E. Levy, Part B B (Western (Western and and Central Central Vermilion Vermilion District) District) Leaders: Leaders: Hudleston, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, Minnesota Minnesota 55455 55455 P. J. Hudleston, L. Southwick, Southwick, Minnesota Minnesota Geological Geological Survey, Survey, Saint Saint Paul, Paul, Minnesota Minnesota 55114 551 14 D. L. R. L. L. Bauer, Bauer, University University of of Missouri, Missouri, Columbia Columbia Missouri Missouri 65211 6521 1 Ulland, American American Shield Shield Corporation, Corporation, Duluth, Duluth, Minnesota Minnesota 55802 55802 W. Ulland, Cover: Cover: Anticline in in the the early early Proterozoic Proterozoic Thomson Thomson Formation Formation at at Thomson Dam, view from the east east bank bank of the the St. St. Louis Louis River, River, Thomson just just south south of of the thehighway highway bridge, bridge, looking looking west. west. Drawing Drawing by by Wendell Wendell Wilson. Wilson. �TABLE TABLE OF OFCONTENTS CONTENTS FIELD FIELD TRIP TRIP11 Large Large rhyolites rhyolites ofofthe theKeweenawan KeweenawanNorth NorthShore ShoreVolcanic VolcanicGroup Group J.C. J.C. Green Green.................................................................................... A1- -A15 A15 Al FIELD FIELD TRIP TRIP 22 Penokean Penokean structural structural terranes terranesinineast-central east-centralMinnesota Minnesota T.B. T.B. Hoist Hoist..................................................................................... 61- B17 B17 Bi - FIELD FIELD TRIP TRIP 33 Rock Rock Types Types and and relationships relationshipsofofthe theMellen MellenIgneous IgneousComplex Complex K.W. K.W. Kiewin, Klewin, J.F. J.F. Olmsted, Olmsted, and andK.E. K.E. Seifert Seifert...........................Cl C15 C1- -C15 FIELD FIELD TRIP TRIP44 Archean rocks rocksofofthe theVirginia Virginia General geology and and structure structure of of Archean General Horn HornArea, Area, Northeastern NortheasternMinnesota Minnesota J.L. J.L. Welsh, Welsh, D.L. D.L. England, England,D.A. D.A. Groves, Groves,and and E. E. Levy Levy.......................................................................................... D l3 D l- -D13 Dl Ii Archean Archean gold gold occurrences occurrences and and their their structural structural settings: settings: western western and and central central Vermilion Vermilion district district D.L. D.L. Southwick, Southwick,P.J. P.J. Hudleston, Hudleston,R.L. R.L. Bauer, Bauer,and and - W. W. Ulland Ulland......................................................................................D14 D l 4- D24 D24 •11 �, FIELD FIELD TRIP TRIP#1 #1 LARGE LARGE RHYOLITES RHYOLITES OF THE THE KEWEENAWAN KEWEENAWAN NORTH NORTH SHORE SHORE VOLCANIC VOLCANIC GROUP GROUP Leader: Leader: John John C. C. Green Green Geology Geology Department, Department, University University of of Minnesota, Minnesota,Duluth Duluth INTRODUCTION INTRODUCTION I ) , one of of the the products products of of the the great great The North North Shore Shore Volcanic Volcanic Group (NSVG, (NSVG, Fig. Fig. 1), The Midcontinent Rift of of North Midcontinent Rift North America America (Wold (Wold and and Hinze, Hinze, 1982; 1982; Green, Green, 1983; 1983; Van Van Schmus Schmus and and Hinze, Hinze, 1985), 1985), contains contains aa wide wide variety variety ofofcompositions compositionsofofplateau plateaulavas lavas(BVSP, (BVSP, 1981; Green, 1982a). These range from the predominant olivine tholeiites through These range from the predominant olivine tholeiites through 1981; Green, 1982a). transitional basalts, basalts, basaltic andesites, andesites, andesites andesites and and ferroandesites ferroandesites to to icelandites icelandites and and transitional rhyolites rhyolites (Fig. (Fig. 2). 2). Felsic Felsic rocks rocks (icelandites (icelandites and and rhyolites) rhyolites) are are unusually unusually abundant abundant compared compared to other other Keweenawan Keweenawan plateaus plateaus (e. (e. g. g. Portage PortageLake LakeVolcanics, Volcanics,Mamainse Mamainse Point Point Volcanics, Volcanics, Osler Osier Group, Group, Michipicoten Michipicoten Island, Island, etc.) etc.) and and younger younger plateau plateauprovinces provinces world-wide; they constitute about about 10% of the world-wide; they the southwest southwest limb limb (the (thesection section from fromDuluth Duluthto to Tofte) 25% of of the thenortheast northeastlimb limb(Lutsen (Lutsento toGrand GrandPortage), Portage),as asmeasured measuredby by Tofte) and and about about 25% stratigraphic 2). stratigraphic thickness along the lakeshore lakeshore (Tables (Tables 11 && 2). Airfall Airfall ash and and pumice pumice make make up up aa very very small small percentage percentage of of these these felsic felsic units, units, but but their rarity their rarity is is probably probably exaggerated exaggerated somewhat somewhat by by their their relative relativesusceptibility susceptibility to to erosion erosion and and thus thus their their lack lackofofexposure. exposure. Small Small lava lava flows flows make make up up aa small small portion portion of ofthe thefelsic felsic rocks, rocks, but but the the great great bulk bulk consist consist of of thick thick units, units, several several of of which which can canbe betraced tracedfor forlong long distances. distances. ItIt is is well well understood understood that that magma magmaviscosity viscosity depends depends principally principally on ontemperature temperature and and composition; felsic magmas composition; felsic magmas are predictably predictably many many orders orders of of magnitude magnitude more moreviscous viscous than than basaltic basaltic magmas magmas at at equivalent equivalent stages stages of of crystallization. crystallization. The The most mostcommon common perception for rhyolites perception and expectation expectation for rhyolites is that they they will will erupt erupt as as either eitherdomes domes or orthick, thick, short flows, or as short (high (high aspect-ratio) aspect-ratio) flows, as ash ash or or pumice pumice falls falls or orpyroclastic pyroclasticflows, flows,ininwhich which the the viscous viscous fluid fluid has has been been blown blown apart apart by by its its rapidly rapidly vesiculating vesiculating and andexpanding expanding volatiles. volatiles. Submarine Submarine and and thinner thinner subaerial subaerial ignimbrites ignimbrites are are typically typicallyunwelded, unwelded,whereas whereas thicker thicker subaerial subaerial units have a central central welded welded zone zone (e. (e. g. g. Ross Ross and andSmith, Smith,1961; 1961;Fisher Fisher and 1984; Cas Cas and andWright, Wright,1987). 1987). and Schmincke, Schmincke, 1984; Table Table 33 (from (fromHenry Henryand andothers, others,1988) 1988)summarizes summarizesthe thecharacteristics characteristics typical typical of of pyroclastic pyroclastic flows flows as as contrasted contrasted with with lava lava flows flows and and remobilized remobilized ash ash flows flows (rheoignimbrites). (rheoignimbrites). A-i �Fig.1.1. Generalized Generalized geologic geologic map map of of western western Lake LakeSuperior Superior area, area, showing showing the the North North Fig. Shore Volcanic Volcanic Group Group (NSVG) (NSVG) and and field field trip tripstops. stops. Shore FF A " M Fig.2.2. Alkalies-Iron-Silica Alkalies-Iron-Silica diagram the NSVG NSVG showing showing fields fields ofof rhyolites rhyolites(RHY), (RHY), Fig. diagram for for the icelandites (ICE), andesites (AND), ferroandesites (FA), transitional basalts icelandites (ICE), andesites (AND), ferroandesites (FA), transitional basalts (TB), olivine olivine tholeiites tholeiites(OT), (OT),and andaugite-porphyritic augite-porphyritictransitional transitional basalts basalts(PTB). (PTB). (TB), A-2 A-2 �Table Generalized volcanic Table 1. Generalized volcanic stratigraphy stratigraphy of the southwest southwest limb limb (Duluth Tofte), of the (Duluth to to Tofte), NSVG. From Green, Green, 1979. 1979. # Approx. Approx. (m) tthickness h i c k n e s s (as) Top 1200 >90 >170 >90 >200 1000 315 550 1500 1350 1100 785 3370 70 88720 720 Lithostratigraphic L i t h o s t r a t i q r a p h i c unit unit Lithic L i t h i c character character Middle Keweenawan Keweenawan amygdaloidal Schroeder basalts basalts a a y q d a l o i d a l ophitic o p h i t i c olivine o l i v i n e tholeiites tholeiitem Manitou trachybasalt red—brown granular Manitou t r a c h y b a s a l t flow red-brown q r a n u l a r trachybasalt t r a c h y b a s a l t to to basalt basalt of the (more of t h e Schroeder basalta) basalts) Balmore Bay llava. mostly Belmore avas m o s t l y quartz q u a r t z tholeiita., t h o l e i i t e m , other o t h e r basalts basalt8 Palisade pink, P a l i s a d e rhyolite r h y o l i t e flow flow ggray r a y to to p i n k , porphyritic p o r p h y r i t i c rhyolite rhyolite Baptism River lava. mixed lavas. lavas l a v a s , mostly mostly basalta, b a s a l t s , one f e l s i t e Beaver Bay Bay iintrusive Beaver n t r u s i v ecomplex complex Gooseberry River River bbasalta mixed one ffelsite asalts mixed bbasalta, a s a l t s , one elsite Gooseberry L a f a y e t t e Bluff. B l u f f , Silver S i l v e r Creek Creek C l i f f intrusions intrusions Lafayette Cliff TwoHarbors Harbor,f i fina—grained 'm.laphyre.,"some someq uquartz Two n e - g r a i n e d b a sbasalt. a l t s "melaphyres," a r t z t htholeiite. oleiites Larsasonto pophtic Larsmont h i t i c basaits basalts amyqdaloidal o p h i t i c o l i v i n e t h o l e i i t s Stony S t o n y Point-Knife Ia I s lland a n d diabas. d i a b a s e intrusion intrusion mixed basalta, Sucker River basalt. basalts b a m a l t s , mostly mostly ophitic ophitic mixedbbasalts and aandesites, somef efelaite. Lakewood basalt. basalts mixed a s a l t s and n d e s i t e s , some laitem Lester River diabase Lester R iver d iabase sill Lakeside Lakeaide lavas lavas mixed basalts, b a s a l t s , andasites, andemitem, falaites felmites Endion Endion diabas. diabame m i l l Leif Ericgon Loif Ericson Park Park lavaa lava* mixed bbasalta. a s a l t s , andesites andesites Duluth Complex Complex Lower Keweenawan Keweenawan Ely's basalt. E l y ' s Peak Peak bamalts p o r p h y r i t i c , d i a b a s i c , and o p h i t i c b a a a l t s Total Total Base one felsite asygdaloidal ophitic olivine thol.iita sill gill porphyritic, diabasic. and ophitic basalt. quartz q u a r t z sandstone sandstone Nopeming Sandstone Sandstone Nopeminq Anqular unconformit '5iddle Precambrian slate and graywack. Thomson Formation Table 2. Generalized Generalized volcanic Table 2. volcanic stratigraphy stratigraphy of the northeast northeast limb limb (Lutsen (Lutsen to Grand to Grand Portage), NSVG. NSVG. From Portage), From Green, Green, 1979. 1979. Approx. thickness Approx. thickness (m) (m) llthostratl9raphic L i t h o s t r a t i g r a p h i c unit unit Lithic L i t h k character character Middle MiddleKeweenawan Keweenawan Top TOP Lutsen basal basalts Lutsen ts Olivine O l i v i n e basalts, basalts, oolivine l i v i n e tholelites tholeiites 50 Terrace Point Point basalt b a s a l t flow flow Thomsonite-bearingophi ophitic basalt Thomsontte-bearing tic b asalt 95 GoodHarbor Harbor b8ay Good y aandasites ndtsites Brown, pporphyritic o r 0 h y r i t i C andesite, andesite. trachyandesite trachyandesite 310 310 110 110 Breakwatertrachybasalt trachybasaltflow flowo or Breakwater r ssill ill Brown. coliannar, granular granular trachybasalt Brown, col&ar. 155 155 GrandMarais Maraisf efelsites Grand lsites Pink, red, Pink, red, gray gray pporphyritic o r p h y r i t i c rrhyolite h y o l i t e and and ffelsite elsite 185 185 550 Croftville C r o f t v i l l ebasalts basaltsand andandesites andesites Devil Track Track ffelsites Oevil e l s i tes RedCCliff Red l i f f basalts basalts Kimball Creek Creekf efelsites Kimball lsites Marr Marr Island lavas lavas 310 310 Naniboujox Naniboujou basalts basal t s Granular-diabasic basalts Granular-diabdsic basalts Brule Brule River River rrhyolites h y o l 1tes Pink tto gray pporphyritic Pink o gray o r p h y r i t i c rrhyolite hyolite 310 310 120-275 120-275 400 400 1070 1070 Various fine-grained fine-grained basalts and Various and bbasaltic a s a l t i c andesites andesites Aphyric and andpporphyritic Aphyric o r p h y r i t i c rrhyolite h y o l i t e flows flows Amygdaloida.oophitic olivine Afliygda1oida1, phitic o l i v i n e basalts basalts Pink tto tan, porphyritic Pink o tan, p o r p h y r i t i c felsites, f e l s i t e s , icelandites icelandites Mixed tholelitic Mixed t h o l e i i t i c basalt, basalt, andesites, andesltes, felsites felsites Hovland diabase diabase complex complex Lower Lower Keweenawan Keweenawan 1225((est.) 1225 est.) Mixed porphyritic basalt, basalt, trachybasalt, andesite. rrhyolite trachybasalt, andesne, hyolite Mixed porphyritic Hoviand H0vldnd lavas lavas Reservation River diabase Reservation diabase complex complex (Middle (MiddleKeweenawan) Keueenawan) 610 610 80 80 1380 1380 722UTotal Total flows 772'6 Base RedRock Rockr hrhyolite flow Red y o l i t e flow Red,pporphyritic Red, o r p h y r i t i c rrhyolite hyolite DerondaBay Bayandesite andesite flow flow Deronda Gray-brown, Gray-brown, aphyric andesite andesl t e Grand Portage basal basalts Grand Portage ts Mixed Mixed t tholeiltic h o l e i i t i c basalts; basalts; porphyritic p o r p h y r i t i cbasalts b a s a l t s locally l o c a l l yata base t base Disconformity Cross-bedded quartz sandstone Puckwunge Formation Disconformity Middle Precambrian Shal. and graywacke Rove Formation A- 3 �TABLE 3. CHARACTERISTICS CHARACTERISTICS COMMONLY USED USED TO TO DISCRIMINATE DISCRIMINATE RHYOLITE LAVAS FROM FROM IGNIMBRITES IGNIMBRITES (FROM HENRY ET AL., 1988) 1988) Common in conventional conventional ignimbrites ignimbrites rhyolite Common in Common in rhyolite rheoignimbrites rheoignimbrites lavas lavas and in in Fiamme Fiamme Flow banding banding Ramp structures Eutaxitic texture texture structures Elongated vesicles fragments vesicles Abundant lithic fragments Autobreccias Nonwelded tops, tops, bottoms, sides Autobreccias Vitrophyres at or near tops Gradual thinning thinning at at edges of units Vitrophyres at tops units Lengths generally Wide areal extent of individual c20 km.* km.* generally much <20 individual units units High aspect ratio* Low aspect ratio ratio Glass shards in thin thin section section Broken pheno's, different sizes Gas elutriation pipes pipes *Unlike lava flows, may have have dimensions similar to to those rheoignimbrites may dimensions similar those of of *Unlike rhyolite rhyolite lava flows, rheoignirnbrites other ignimbrites ignimbrites Recently, many many rhyolites rhyolites have Recently, have been been described described which which show show anomalous anomalous behavior behavior These may according according to these these models. models. These may cover cover wide wide areas areas with with low low aspect aspect ratios, ratios, indicating high mobility, mobility, yet yet do do not show some some of of the the common common features features of of ash-flow ash-flow tuffs. tuffs. For some, appears to to have have been a factor For some, high alkali content content (peralkalinity) (peralkalinity) appears factor ininlowering lowering the viscosity viscosity (e. g. Price Price and and others, others, 1986). 1986). For For others, others, aa high high eruptive eruptive temperature temperature and and high rate rate of of effusion effusion appear appear to to have have been been important important contributors; contributors; an increase increase of 100 100 degrees degrees C. will lower lower the the viscosity viscosity about about an an order order ofofmagnitude magnitude (Ekren (Ekren and andothers, others, 1984; relatively low low SiO2 SiO, content content seems seems to be be 1984; Bonnichsen Bonnichsen and Kauffman, Kauffman, 1987). 1987). A relatively A survey of widespread lavas and lava-like units common to many many high-mobility high-mobilityflows. flows. survey of widespread lavas and lava-like units in southwest Idaho and trans-Pecos Texas (Bonnichsen (Bonnichsen and Kauffman, Kauffman, 1987 1987 and and Henry Henry and others, SiO2contents contentsininthe the range range 68 68 to 74%, others, 1988) 1988) shows shows volatile-free volatile-free SiO, 74%, whereas whereas rheoignimbritesinin the the same same areas areas have values of of 72 72 to 77%. rheoignimbrites have S1O2 Si02 values 77%. Many ash ash flows, flows, froth particles, reconsolidate during during and and after made of hot, hot, relatively relatively low-viscosity low-viscosity froth particles, reconsolidate after made of emplacementtoto form form aa devolatilized, "reconstitutedlava" lava"that that can can flow flow en emplacement devolatilized, "reconstituted en masse masse (a (a This flowage, and any subsequent crystallization or devitrification, can rheoignimbrite). rheoignimbrite). flowage, and any subsequent crystallization or devitrification, can Thus the distinction the end result obliterate primary pyroclastic obliterate pyroclastic textures. textures. Thus distinction between between the result of of can become effusive eruption an explosive eruption eruption and and an an effusive eruption can become greatly greatly diminished. diminished. Bonnichsen and Kauffman Kauffman (1987) (1987) and and Bonnichsen and others Bonnichsen and Bonnichsen and others (1988) (1988) have have suggested suggested by which which they they may be recognized, some criteria by recognized, but they and others, notably notably Henry Henry is still still low-aspect-ratio units whose whose origin origin is (1988), have described described widespread, widespread, low-aspect-ratio et al. al. (1988), unclear. unclear. The felsic units units in the the NSVG NSVG show show evidence evidence of of aa wide wide variety variety ofoferuptive eruptive and and The felsic emplacement styles, including large, emplacement large, problematical, problematical,low-aspect-ratio low-aspect-ratioflows. flows. This field trip units throughout throughout the the NSVG section will examine examine several several units section and the physical physical evidence evidence for It is designed their mode mode of of emplacement. emplacement. It designed as aa long long one-day one-day trip, trip, starting starting at atDuluth Duluth Descriptions of of field trip and nearly reaching reaching Grand Portage Portage before before returning returning to to Duluth. Duluth. Descriptions stops of the North stops in other other lithologies lithologies of North Shore Shore (mainly (mainly the the plateau plateau basalts) basalts) can can be be found found in Green, Green, 1979 1979 and 1987, 1987, and and aa discussion discussion of of the the physical physical volcanology volcanology of of the the NSVG NSVG appears geologic map map is also :250,000) geologic also available available (Green, (Green, appears in Green, Green, 1989. 1989. A A regional regional (1 (1:250,000) 1 982b). 1982b). Chemical analyses analyses of of these these felsite felsite units units are are presented in in Table Table 4. 4. A-4 �able Table 4.Chemical 4.Chemical analyses analyses of of felsic felsic volcanic volcanic units units at field field trip trip . stops, recalculated recalculated volatile-free volatile-free A Si02 Si0, Ti02 TiO, A1203 Fe203 -203 FeO FeO MnO Mno MgO MgO CaO CaO Na20 Na20 1(20 K20 P205 p.0. Zr02 ZrO, B C E D F G H J I 75.11 75.41 68.30 75.46 74.85 73.08 69.92 63.81 62.07 72.54 .28 .22 .70 .24 .40 .40 .53 1.11 .99 .25 12.45 11.99 12.76 11.10 11.62 11.76 12.52 12.24 15.09 12.02 1.58 .84 1.61 1.66 8.34 2.79 2.51 .92 3.13 4.09 1.25 3.04 5.79 2.95 3.33 .74 1.63 2.06 6.00 3.64 .03 .06 .32 .01 .07 .30 .09 .27 5.59 2.13 5.92 1.95 2.69 5.68 .02 .03 .01 .06 .08 .12 3.28 .05 .30 .51 .04 .60 .88 .04 .54 .51 .10 .51 .51 1.96 5.72 2.22 5.09 3.54 5.50 .04 .06 .04 — .08 .12 .18 .88 .05 .21 .71 3.43 5.37 1.43 2.26 4.12 4.23 3.67 3.77 4.04 3.86 4.15 .09 .28 .52 .05 — — — A. Stop Creek rhyolite rhyolite (ave. (ave. of of two two analyses). analyses). Stop 1: 1: Tischer Creek B. Stop 2: 42nd Ave E. ignixnbrite (D-87). Stop 2: 42nd Ave E. ignimbrite (D-87). C. Stop Stop 2: 2: icelandite icelandite flow flow beneath beneath BB (0-91). (D-91). D. Stop Palisade rhyolite rhyolite (F-201). (F-201). Stop 3: 3: Palisade E. Stop Stop 5: 5: Silver Silver Beaver Beaver felsite felsite (F-278). (F-278). F. Stop Stop 6: 6: Devil Devil Track Track rhyolite rhyolite (ave. (ave. of of three). three). G. Stop 7: Kimball Creek rhyolite (ave. of Stop 7: Kimball Creek rhyolite (ave. of five). five). H. Stop Stop 8: Rangeline icelandite icelandite (MI-2). (MI-2). 8: Rangeline I. Stop Deronda Bay Bay andesite/icelandite andesite/icelandite (MC-3b). (MC-3b). Stop 9: 9: Deronda J. Stop Rock rhyolite rhyolite (MC-7). (MC-7). Stop 9: 9: Red Rock FIELD FIELD TRIP TRIP STOPS STOPS STOP STOP 1.1. Tischer Tischer Creek Creek at atSuperior SuperiorStreet, Street,Duluth. Duluth. Here the stream stream has has eroded eroded aagorge gorge through through the the small-jointed small-jointed Tischer Tischer Creek Creek Here rhyolite, rhyolite, which is is approximately approximately 300 300 m mthick. thick. This This unit unitcontains containsmany manythin, thin, discontinuous color color bands bands or or laminae laminaethat thatresemble resemblewell-flattened well-flattenedfiamme, fiamme, discontinuous and moderately moderately abundant, abundant, small small xenoliths; xenoliths; both both suggest suggest an anignimbrite ignimbriterather rather and than than aa lava. lava. ItIt also also shows shows occasional occasional open, open, quartz-lined quartz-lined ororquartz-filled quartz-filled tension tension fractures fractures that that must must have have formed formed after after welding. welding. Devitrification Devitrification has has destroyed whatever microscopic microscopic shard or pumice pumice textures were were once once present. present. destroyed The Iaminae laminae (fiamme?) (fiamme?) are generally parallel base of the the unit, unit, but but The are generally paralleltoto the the base locally locally show show folding, folding, indicating indicating flow flow after after deposition deposition and and welding. welding. This This flow flow isis thus probably probablya a"High-temperatureTM "High-temperaturew type according to to Bonnichsen Bonnichsen et et al. al. thus type according (1988). (1988). The The base base of of this thisunit unitisisintruded intruded(and (andprobably probably melted) melted) by by the thethick thick Endion Endion diabase diabase sill. sill. A-5 �STOP STOP 2. 2. Lake Superior Superior shore at at foot foot of of 42nd 42nd Avenue Avenue East, East,Duluth. Duluth. At At this this locality locality isisthe thecontact contact between between two two felsite felsite units, units, an anicelandite icelandite overlain overlain by aa rhyolite the trail reaches rhyolite (Fig. (Fig. 3). 3). Where Where the reaches the shore shore there there are are abundant abundant exposures of the the lower exposures of lower part of aa thick thick (about (about 60 60 m) m) rhyolitic rhyolitic ignimbrite, ignimbrite, full full of small small (1-4 (1-4 cm) cm) slabs slabs and and chips chips ofofwhat whatwere wereprobably probablypumice, pumice, in in aa fine-grained, fine-grained, devitrified devitrified matrix matrix now devoid devoid of of recognizable recognizable shards. shards. Alteration Alteration at to contemporaneous contemporaneous at different different stages, stages, probably probably including including that due due to degassing degassing and later later burial burial metamorphism, metamorphisml has has created created distinct distinct color colorcontrasts contrasts between the the fragments fragments and andmatrix. matrix. Several xenoliths xenoliths are present, present, including including a few blobs blobs (bombs) (bombs) of of chilled chilled mafic mafic lava. lava. The The pumice pumice fragments fragments are not not obviously flattened parallel paralleltoto the the base base of obviously flattened of the the flow, flowl even even though though this this is aa fairly thick that it was thick unit. unit. This indicates indicates that was probably probably erupted erupted at at aarelatively relatively low low temperature et aI.3 al.'s Type Type L) and did temperature (Bonnichsen (Bonnichsen et did not not weld weld ororeven evencompact compact very very much much except except at at the the very very base. base. A very very similar similar texture texture is found found at at the the base base of of the the large, large,Tertiary Tertiary caldera-filling caldera-filling Gomez Gomez Tuff Tuff ofoftrans-Pecos trans-Pecos Texas Texas (Price (Price et et al., ah, 1986). 1986). the impassable impassable cliff cliff up the shore shore to to the the northeast northeast this this rock rock isisdirectly directly In the overlain by another rhyolite with a distinctly different structure. overlain by another rhyolite with a distinctly different structure. Above Above aa narrow narrow transition transition zone zone of of aafew fewcentimeters, centimeters, itit contains contains thin, thin,discontinuous discontinuous color color bands bands and and lamellae, lamellae, rather rather like the the Tischer Tischer Creek Creek unit, unit, but with with aa strong strong lineation lineation of of small small wrinkles wrinkles and and open open fold fold axes. axes. These features features suggest ash flow, resulting suggest aa high-temperature high-temperature ash resulting in in thorough thorough welding welding and and bulk bulk flow, flowl after after emplacement, emplacement, in the direction direction of of the the lineations lineations -- aarheoignimbrite rheoignimbrite of of Bonnichsen Bonnichsen et et aL's aL1sType Type H. H. In the the other other direction direction (SW) (SW) along beach, the basal 22 or or 33 meters meters of of In along the the beach, the basal the the main main unwelded unwelded ash ash flow flow isis not not exposed, ex~osed,but but several several loose loose blocks blocks of of laminated laminated rock, rock, found found only only inin this this vicinity, vkinity,. appear appear to to be be the the strongly strongly compacted compacted and welded welded basal basal portion portion of of this this unit. unit. - roiiLCI...z— J • t- —— uQ(óec pt-topt(i (D-87) - :.. , 4to.' \tcCA(&r .çe& top ociâ, %eøtD (D-qI) Fig. Fig. 3.3. Diagrammatic columnarsection sectionatat field field trip trip Stop Stop 2, 2, lakeshore Diagrammatic columnar lakeshore at foot foot of of 42nd 42nd Ave Ave East, East, Duluth. Duluth. A-6 �Just beyond It beyond this zone is is the the top top of of aa130-rn 130-mthick thickporphyritic porphyritic icelandite. icelandite. It to frothy and the the top meter is highly highly vesicular vesicular to frothy but not pumiceous, pumiceous, and meter or or two two are are penetrated arkosic sandstone sandstone dikes dikes that filled filled in open open cracks cracks in the the flow flow penetrated by by arkosic top before top before eruption eruption of of the the overlying overlying ignimbrite. ignimbrite. The The vesicles vesicles (now (now largely largely calcite are stretched to varying calcite amygdules) amygdules) are stretched to varying degrees, degrees, and large large flowage flowage folds folds are evident. This vesicularity dies out to the southwest as the rock becomes evident. This vesicularity dies out southwest as the rock becomes massive and massive and granular. granular. There is is little brecciation. These textures textures and and brecciation. These structures indicate indicate that this unit unit was was a large large and and fairly fairly hot hot and and rapidly rapidly emplaced lava flow. None of these units None of units can can be be traced traced inland inland for for more more than than aafew fewkilometers kilometers because of glacial ic intrusions. because glacial drift drift cover cover and and intersection intersection by bylarge largemat mafic intrusions. For more details Duluth units units see see Motamedi, Motamedi, 1984. 1984. details on on these these Duluth STOP 3. 3. Palisade Palisade Head, Headl Lake Lake County County (Figs (Figs 4,5). 4?5). This scenic This scenic promontory promontory is made made of of a 90+ 90+ m mthick thickmassive, massive, porphyritic The same rhyolite. The rhyolite. same unit unit forms forms the the prominent prominent Shovel Shovel Point Point to to the the northeast northeast (stratigraphically lower flows (stratigraphically lower flows are are exposed exposed in in the Baptism Baptism River River basin basin in in between), and itit can between)> and can be be traced traced from from East East Beaver Beaver Bay Bay (to (to the the southwest) southwest) at at See also least least 23 km km along along strike strike to to the the northeast. northeast. See also Miller, Miller, 1987 1987 and and 1988 1988 a!.?1987 1987 for for detailed detailed local local geology. geology. and Miller et al., Throughout most of of its Throughout most its extent extent the the Palisade Palisade rhyolite rhyolite closely closely resembles resembles this this exposure with no exposure at Palisade Palisade Head: massive, massive, with no evidence evidence of of pyroclastic pyroclastic texture, texture, Under the only only rare rare xenoliths, xenoliths, and and with with only rare rare broken broken phenocrysts. phenocrysts. Under the microscope after microscope it shows fine-grained, fine-grained, poikilitic quartz pseudomorphic after tridymite, implying implying crystallization crystallizationwell well above above 870 870 degrees degrees CC.. At At the base, basel the the tridymitel only exposure the southwest end of exposure (in (in the southwest end of this this hill) hill) shows shows flow flow laminations, laminations, locally much folded scale, in meters. locally much folded on a small small scale, in the the lowest 11 to 3 meters. At the Elsewhere, larger larger folds folds in laminations Elsewhere, laminations occur occur farther above above the the base. base. At the vesicular (amygdaloidal) the only is vesicular top, the only exposure exposure is (amygdaloidal) but but not not pumiceous pumiceous or or These characteristics suggestan an origin origin as as aa large, brecciated. These characteristics suggest large, unusually unusually mobile, hot However, one one outcrop outcrop in in the interior mobile, hot lava lava flow. flow. However, interior shows shows small, small, discontinuous bands or or streaks streaks that that suggest suggest relict relict fiamme, fiamme? and another another (next (next discontinuous bands stop) contains abundant discontinuous streaks suggesting strongly flattened stop) contains abundant discontinuous streaks suggesting strongly flattened fiamme. fiamme. The Theunit unitmay maybe beaahigh-temperature high-temperaturerhebignimbrite. rheoignimbrite. - - - - - - - - - - - - - - - - py or o r .,reccto.. breccia +op + o ~ U M ~ &WtrLttOI'%S fLdQc rir1esVL (F.wf) qntL o.ttc iior.$ bsLt ou.' Fig. 4. 4. Diagrammatic columnar columnar section sectionofof Palisade Palisade rhyolite, rhyolite,field fieldtrip trip Stops Stops 33 and 4. Diagrammatic A-7 �Fig. Fig. 5.5. View View to to the the southwest southwest of of Palisade Palisade Head Head from from the the top top of of Shovel Shovel Point Point(both (both made Lower cliffs cliffs in in middle middle distance distance at at made of of columnar-jointed columnar-jointed Palisade Palisaderhyolite). rhyolite). Lower right right (at (at Baptism Baptism River River mouth) mouth) are are made made of of the the Silver Silver Beaver Beaver felsite felsite (Stop (Stop5), 5), stratigraphically stratigraphically beneath beneath the thePalisade Palisaderhyolite. rhyolite. STOP STOP 4. 4. Road Road cuts cuts ininPalisade Palisaderhyolite, rhyolite,Minn. Minn.Highway Highway1,1,Illgen lllgenCity. City. Here part part of of the the upper upperportion portion of of this thisunit unitisisexposed, exposed,showing showing inincontrast contrasttoto Here typical typical outcrops, outcrops, aa breccia breccia made made of of diversely diversely oriented oriented blocks. blocks. Each Each block block isis itself flow-laminated. itself flow-laminated. The The laminations laminations appear appear discontinuous discontinuous and and may may be be strongly strongly flattened flattened fiamme. fiamme. Clearly Clearly the the breccia breccia was was formed formed after after cooling cooling across the the ductile-brittle ductile-brittle transition, transition, during during late-stage late-stage movement movement of of the theflow. flow. across STOP STOP5.5. Silver-Beaver 6). Silver-Beaver felsite felsite at at the the Baptism BaptismRiver River(Fig. (Fig.6). (Park (Park at at Rest RestArea AreaatatTettegouche TettegoucheState StatePark Parkheadquarters). headquarters). ,— ) — dbjO.f 51 ,bvded, -gcca. .4 —— - oaded (ç. 27 ) ç.•-' -— = -- ? t6ed {- breccu, Fig. Fig.6.6. Diagrammatic Diagrammatic section section of of Silver SilverBeaver Beaverfelsite, felsite,Stops Stops5a 5aand and5b, 5b,Baptism Baptism River. River A-8 A-8 �A. A. Walk Walk across across Baptism Baptism River River on foot foot bridge, bridge?then left left through through woods woods on on an an unofficial unofficial trail to to aahigh highoutcrop outcrop overlooking overlooking the the river rivermouth mouthatatthe thelakeshore. lakeshore. Here Here is is fairly fairly typical, typicall banded, banded, fine-grained, fine-grained, weakly weakly porphyritic porphyritic to to aphyric aphyric felsite, felsite?dipping dipping steeply steeply to the the east east toward toward the the lake. lake. Across Across the river river the the unit unit is along the the top top of the shore is aatuff-breccia tuff-breccia at atwater water level. level. Follow Follow along shore cliff cliff to to the the south south to to the the first firstbeach-cove. beach-cove. Here Here the basal basal portion portion is is exposed, exposed, overlying overlying aa pale, zone that may pale?chalky-clayey chalky-clayey zone may be be either either altered altered airfall airfall ash ash or or fault fault gouge. gouge. The to 5 m The basal basal 33 to m isis an an irregularly irregularly fractured, fractured? unwelded unwelded tuff-breccia tuff-breccia or or lapilli-tuff lapilli-tuff containing containing fragments fragments of of various various once-glassy once-glassy felsite felsite textural textural types types which which include include pumice, pumice?spherulites, spherulitesl perlitic perlitic cracks, cracks?etc., etc.?considerably considerably altered altered to to kaolinite This kaolinite and and quartz. quartz. This zone zone isis overlain overlain by by what what appears appears to to be be agglutinate, containing faint faint blobby blobby areas areas (Fig. (Fig. 7) 7) and and grading grading up up into into more more agglutinate? containing typical, typicall weakly weakly flow-banded, flow-banded?uniform, uniform?finely finely crystalline crystalline felsite. felsite. Across very discordant, steeply steeplySE-dipping SE-dipping Across the the beach beach to to the thewest westisisa a very discordant? contact contact where where aa laminated laminated basaltic basaltic andesite andesite overlies overlies the the rubbly, rubbly,sand-matrix sand-matrix top top of of another another flow. flow. AA fault fault separates separates these these rocks rocks from from the the felsite. felsite. Return Return to to highway. highway. Fig. Deformed agglutinate agglutinate (?) (?) blobs blobs inin lower lower part part of of the the Silver Silver Beaver Beaver felsite, felsite? Fig.7.7. Deformed lakeshore southwest southwest of of Williams Williams Creek, Creek?Silver Silver Bay Bayarea. area. lakeshore B. After After crossing crossing back back to to the the north north side side of of the theriver, river?go go west west across across the the B. highway and and up up the the trail trail (via (viastairs) stairs) along along the the top top ofof the thebank banktoto aa long longflight flight highway of of wooden wooden steps steps leading leading down down to to the the river riveragain. again. The The outcrops outcrops here here are are near near the the stratigraphic stratigraphic middle middle of of the the Silver Silver Beaver Beaver felsite. felsite. Faulting Faulting has has dropped itit down down relative relative to to its itsexposures exposures at at the the river rivermouth, mouth, but but itit still still dips dips dropped east. east. The The uniform, uniform?typically typically planar planarlamination lamination isis characteristic, characteristic?as as isis the the fine-grained thin section section fine-grained (rather (rather than thandense-aphanitic), dense-aphanitic), aphyric aphyric texture. texture. InIn thin quartz quartz pseudomorphs pseudomorphs after after tridymite tridymite are are abundant, abundant?and andsmall small (1-3 (1-3 mm) mm) spherulites are not uncommon. spherulites are not uncommon. A-9 �, Go downstream the water downstream (if the water level level is is low low enough), enough)?working working toward toward the the top top of the of the unit. unit. A few few meters meters from from the the top top the the flow flow starts starts totoacquire acquire small, small, irregular vesicles, then then becomes becomes broken broken up up in a flow-top irregular vesiclesl flow-top breccia breccia with with lineated lineated vesicles and and ashy This is overlain vesicles ashy gray gray material material between between the the blocks. blocks. This overlain by aa laminated, red tuff tuff only only aa few laminated, red few cm thick, thick, which which lenses lenses in and out. out. These These felsic felsic rocks by aa thin, large rocks are are then then overlain by thinl amygdaloidal basalt basalt flow with with large plagioclase phenocrystsconcentrated concentratedatatthe the base; base; its its top top is intruded by by aa plagioclase phenocrysts is intruded thin black diabase diabase sill. sill. The to have have begun The Silver Silver Beaver Beaver felsite felsite is is interpreted interpreted to begun with with eruption eruption of of glassy ash ash and pumice glassy pumice at aa moderate moderate or or slow slow rate, ratel producing producing an an unwelded unwelded base, base, but then then changed changed to to agglutinate agglutinate as as hotter hotter or or less lessvolatile-rich volatile-richmaterial material became available. available. The The bulk bulk of of the the unit unit was wasproduced produced as aseither eitheragglutinate agglutinate and flowed as aa unit after or a hot hot ash flow that coalesced and (Type V) V) settling/accumulation - perhaps perhaps aa Very High High Temperature (Type settling1accumulation It subsequently in subsequently crystallized rheoignimbrite of Bonnichsen It crystallized in rheoignimbrite of Bonnichsen et et al., al., 1988. 1988. place to tridymite tridymite and and feldspar. feldspar. Climb back up to the trail and and walk walk out out to to the the highway. highway. As the the trip trip progresses progresses up up the the shore shore we we pass passupwards upwards stratigraphically stratigraphically to the exposed the exposed top in in the the Tofte-Lutsen Tofte-Lutsen area area in in southwestern southwestern Cook Cook County. County. An unknown thickness of of lavas lavas was was erupted on top of unknown thickness erupted on of this this sequence sequence and and now now underlies the lake underlies the lake or was was eroded eroded off off before before the the Portage Portage Lake Lake Volcanics Volcanics or or Upper Keweenawan Keweenawansandstones sandstoneswere werelaid laiddown downon on top top of of the Upper the NSVG NSVG here. here. Beyond Lutsen Lutsen we we start descending Here the strata Beyond descending in the the "northeast "northeast limb". limb". Here strata lakeshorel and and dip dipsouth-southeast south-southeast to to south south strike more more easterly easterly than than the the lakeshore, strike (Fig. 8). 8). Grand Marais sits largely largely on on another another large, largel small-jointed small-jointed rhyolite rhyolite complex complex Grand Marais which has been been more more easily easily eroded eroded (to form the the harbor) harbor) than than the the overlying overlying which has "Breakwater trachybasalt". trachybasalt". This thick transitional transitional basalt basalt unit unit that that makes makes This is aa thick the "island" and breakwater breakwater and a cuesta cuesta to to the the west. west. Fig. 8. 8. Generalized geologic geologic map map of of the northeastern northeastern tip of Minnesota showing Generalized Minnesota showing the major major units units of of the the NSVG. NSVG. (from (from Green, Green, continuity along continuity along strike strike of of some some of of the 1979). 1979). A- 10 A-10 �STOP 6. 6. Devil Devil Track Track rhyolite, rhyolite, Highway Highway 61 61 opposite opposite Five Rock east east of of Grand Grand Five Mile Mile Rock Marais. Marais. - This exposure, exposure, at at an an abandoned abandoned wave-cut wave-cut cliff cliff of of the the 5000-year 5000-year old old Nipissing Nipissing stage stage of of Lake Lake Superior, Superior, is is fairly fairly typical typical of of this thislarge largerhyolite. rhyolite. This unit unit can can be be traced for for about about 40 km km to to the the west, west, and and isisabout about 250 250 m m thick. thick. Neither its its traced top or or base baseisisexposed, exposed,and andallalloutcrops outcropsshow showthis thisweakly weaklyflow-laminated, flow-laminated, fine-grained, fine-grained, aphyric to very very weakly weakly porphyritic porphyritic character, character, rather similar to the the Silver Beaver Beaver felsite. felsite. Thin sections sections here here also also show show quartz quartz paramorphs paramorphs after after primary tridymite. tridymite. Tom Tom Fitz Fitz (1988) (1988) has has found found that that the the grain grain size size ofofthese these tridymite toward the the center tridymite plates plates increases increases toward center of of the the unit, unit, implying implying that that itit crystallized as a simple crystallized as simple cooling cooling unit unit (Fig. (Fig. 9). 9). No No significant significant breccia breccia facies facies has been been found. found. The The wide wide extent, extent, lack lack of of breccia breccia or or other other viscous viscous flow flow features features other than than rare rare lineations, lineations, aphyric aphyric texture, texture, and and crystallinity crystallinity suggest suggest that that this this was was aavery veryhot hotpyroclastic pyroclasticflow flowthat thatcompletely completelyconsolidated, consolidated, after after emplacement, to pool ofofdevolatilized devolatilized rhyolite rhyolite magma magma that that crystallized crystallized inin emplacement, to a pool place. place. Assuming that its overall shape was was aa segment of aa sphere Assuming that overall original original shape segment of sphere (it (it appears to pinch appears to pinch out out at at the the western western end end but but is is thick thick through through much much of of the the rest), rest), and and that that its its center center was was at at the the present present lakeshore lakeshore (half (half now now underlies underlies the the lake), lake), itit would would have have had hadan anoriginal originalvolume volumeofofabout about600 600km3. km3. STOP STOP 7. 7. Kimball Creek Felsite, Felsite, Lake Lake Superior Superior shore north north of of Red Red Cliff. Cliff. Here we are are near near the the top top ofofanother anothervery very large large(366 (366mmthick) thick)rhyolite. rhyolite. The The point point at at Red Red Cliff Cliff to to the the south south isisheld heldup upbybya asequence sequenceofofoverlying overlyingolivine olivine tholeiite tholeiite basalts. basalts. This This rhyolite rhyolite isisweakly weakly plagioclase-phyric, plagioclase-phyric, but but otherwise otherwise the the bulk bulk of of this this flow flowisisfine-grained, fine-grained,crystalline, crystalline, and and massive, massive, rather rather like like the theDevil Devil Track Track rhyolite. rhyolite. This This unit unit also also shows shows aa network network of of tridymite tridymite paramorphs paramorphs in inthe the groundmass (Fig. 10), groundmass (Fig. lo), whose whose length length is greatest greatest near near the center center of of the the flow flow (Fig. as a simple (Fig. 9), 9), again again indicating indicating primary primary crystallization crystallization as simple cooling cooling unit. unit. Here (and elsewhere) near the top, however, Here (and elsewhere) near the top, however, itit isis aphanitic aphanitic and and contains contains discontinuous color bands bands and discontinuous color and lamellae lamellae that that are are probably probably flattened flattened and and deformed deformed pumice pumice fiamme. fiamme. These structures structures are are preserved preserved here near the the top top because because of of the the rapid rapid cooling cooling after after welding, welding, preventing preventing the the primary primary crystallization which obliterated crystallization which obliterated them them in in the theinterior. interior. Unfortunately Unfortunately the top top several several meters meters are not not exposed, exposed, as as isis typical typical ofof these theselarge largerhyolites. rhyolites. One One possible possible inference inference is that that the the top topmay maycontain containeasily easilyweathered weatheredand anderoded, eroded, unwelded unwelded pumice pumice and and ash. ash. The base base isis not not exposed exposed either, either, but but aa few few meters meters above, above, the the unit unitshows showsflow-folding flow-folding ofofthin, thin,discontinuous discontinuous streaks streaks and and lamellae lamellae (fiamme?) (fiamme?) (Fitz, (Fitz,1988). 1988). This This unit unit isis thought thought to to have have the the same same origin origin as as the the Devil DevilTrack Trackrhyolite: rhyolite:aahigh-temperature high-temperaturerheoignimbrite. rheoignimbrite. For more more details details on on these these two twolarge largerheoignimbrites rheoignimbrites see see Fitz Fitz(1988). (1988). For STOP STOP 8.8. Rangeline Rangeline icelandite, icelandite,11 1/2 112 mi. mi. EE of ofKadunce KadunceCreek Creek (River). (River). These These road road cuts cuts show show fairly fairly typical typical textures textures and and structures structures of of aa large large (40 (40 m) m) icelandite icelandite lava lava flow. flow. Toward Toward the eastern end end is is the the massive massive lower lower part, part, the eastern to fine-grained and porphyritic; aphanitic to fine-grained and porphyritic; round round amygdules amygdules gradually gradually increase increase aphanitic toward the west. toward the west. Neither Neither top nor nor base base are are exposed, exposed, but but another another icelandite icelandite aa few few miles miles to to the the northeast northeast shows shows strongly strongly stretched stretched amygdules amygdules inin an an aphanitic upper upper crust. crust. Phenocrysts Phenocrysts are areofofplagioclase, plagioclase,ferroaugite, ferroaugite,Fe-olivine, Fe-olivine, aphanitic and and magnetite. magnetite. A-il �£9 0.1 00 I- 100 100 200 300 200 300 V.,tiCal V u t k l dislanc. (inane* abov. above baa. b a r of unit (m). Sotto. Bottom L..gth 01 quwtz Cty$ta*. VS. 350 350 Top SI:.tlgv.plvc P0S.I0fl I' th• Kanbal COsdit rflyodt•. Anhedral quartz q u a r t z masses m a s s e s gradational g r a d a t i o n a l to t ogroups groups Anhedral fused plates plates in inoptical o p t i c a lcontinuity. continuity. oo ffused . 41 0.15 • 4o• 0.0! L.nqth io 30 Sotto. oo Vtic dI.t.nc. aba.. baa. 0* *t (ml 0* tZ ay.t. vS. sbaIlg.pNc posltlo.v hI (hs 0svI T,.ck otipalt.. \ \\%\ i C r o u p s of of plates plates in in optical optical continuity, continuity, Groups some w i t h slight sliqht ra1iatin ra4iatinqnattern. yttern. s o m e with FIG. F I G . 99 F I G . 10 10 FIG. Fig. 9.9. Variation Variation in in lengths lengths of of tridymite tridymite paramorphs paramorphs with height height in the the Devil Devil Track Track and and Kimball Kimball Creek Creek rhyolites rhyolites(from (fromFitz, Fitz,1988). 1988). Fig. 10. Tabular Tabular habits habits of of quartz quartz paramorphs paramorphs after after tridymite tridymite in in the thegoundmass goundmass of ofthe the Fig. 10. Fig. Kimball KimballCreek Creek felsite felsite(from (fromFitz, Fitz,1988). 1988). �STOP STOP 9. 9. Red Red Rock Rock Point Point rhyolite rhyolite atatDeronda DerondaBay, Bay,Grand GrandPortage PortageIndian IndianReservation Reservation (Fig. (Fig. 11). 11). - At At this this locality locality aathick thick(80 (80m) m)andesiteficelandite andesitehcelandite flow flow (MC-3b, (MC-3b, Table Table 3) 3) is is overlain by a large large (>140 (>I40 m) m)rhyolite rhyolite unit unit (MC-7b), (MC-7b), but but the the actual actualcontact contact isis overlain somewhere somewhere under the the beach. beach. The The beach beach shingle shingle contains contains pieces pieces of of both, both, including vesicular vesicular andesite andesite with with pseudomorphs pseudomorphs of of cristobalite cristobalite balls balls in in the the including stretched stretched vesicles. vesicles. The The top top of• o fthe the rhyolite rhyolite is is cut cut out outbybythe theReservation Reservation River diabase diabase intrusion, intrusion, which also ako cuts cuts itit off off to to the the west west so sothat thatitsitslateral lateral River extent is unknown as well. extent is unknown as well. Reseruho, Rwer D3ig VeS3tVe , erptc. (MC 7) çto. tcctsi as (Mc- ) Fig. 11. 11. Diagrammatic Diagrammaticsection section of of the theRed RedRock Rockrhyolite rhyolite at at Stop Stop9,9,Deronda DerondaBay. Bay. Fig. On On the the way way toward toward the the main main cliff cliff outcrop outcrop on on the the south south side side of ofthe thebay, bay, there there are areinstructive instructivelow, low,wet wetoutcrops outcropsand andshallow shallowunderwater underwater"exposures", "exposures", accessible accessible under under favorable favorable lake lake conditions, conditions, of of the the following following gently gently south-dipping sequence, from bottom south-dipping sequence, from bottom toto top: top: a)a) porphyritic porphyritic andesite andesite or or icelandite, icelandite, probably probably part part of of the theMC-3 MC-3complex, complex,overlain overlain -- and andprobably probablybaked baked by by -- b) b)aathin thinbasaltic basalticsill; sill;this thisisisoverlain overlainby, by,and andhas hasbaked bakedsomewhat, somewhat, c) c) aa thin layer layer of of pumice-Iapilli pumice-lapilli tuft; tuff; this this is is overlain overlain by by d) d) aagrayish grayishash ashbed bed2-4 2-4 thin cm cm thick; thick; then then e)e) aa rhyolitic rhyolitic flow-breccia flow-breccia (mostly (mostly underwater) underwater) made made ofof variously-oriented variously-oriented blocks blocks containing containing stretched stretched vesicles. vesicles. Unfortunately Unfortunately boulders boulders cover cover the interval, interval, only only aa few few meters meters thick, thick, between between this this and and the the cliff cliff outcrop outcropahead. ahead. This This isis all all made madeofofred-orange, red-orange,porphyritic porphyriticrhyolite rhyolitethat that does does not not easily easily give give up up clues clues as astoto its its mode modeofofemplacement. emplacement. In Insome some areas areas near near the the base base ititappears appears totobe bea abreccia breccia(simply (simplymore moreofofthe thebasal basal autobreccia autobreccia of aalarge largelava lavaflow?). flow?). In Inothers, others, faint faintsuggestions suggestionsofofpumice pumice chips chips and and spherulites spherulites suggest suggest that that perhaps perhaps this this isis the the basal basalunwelded unwelded pumice pumice zone zone of aa big bigash ashflow, flow, overlain overlain inin the the cliff cliff by by the the devitrified, devitrified, laminated, laminated, welded weldedzone. zone. Because Because of of the the clear clearunderlying underlying breccia brecciaand andthe the lack prefer the the former former model, model, although althoughthis thisflow flowdoes does lack ofofobvious obviousfiamme, fiamme, I I prefer contain containsome somebroken brokenphenocrysts. phenocrysts. The The pumice-lapilli pumice-lapilli tuft tuff and andash ashtuft tuffbeds beds were wereair-falls air-fallswhich whichimmediately immediatelypreceded precededthe therhyolite rhyoliteeruption. eruption. Return Return to to Duluth Duluthvia viaGrand GrandMarais. Marais. A-. 13 �_____ REFERENCES REFERENCES Bonnichsen,Bill Bill and and Kauffman, Kauffman, D. D. F., F., 1987, Bonnichsen, 1987, Physical Physical features features of rhyolite rhyolite lava flows flows in in the Snake River province, southwestern southwesternldaho: Idaho:&i Fink, Fink, J. J. H., H.* the River Plain Plain volcanic volcanic province, editor, The emplacement of silicic editor, emplacement of silicic domes domes and and lava lava flows: flows: Geological Geological Society Society of America Special Special Paper Paper 212, 212* p. p. 119-145. 119-145. Bonnichsen, Bill, Bill, Leeman, Leeman, W. W. P., P., Jenks, Bonnichsen, Jenks, M. D., D., and and Honjo, Honjo, Norio, Norio*1988, 1988,Geologic Geologic field field trip guide guide to to the the central centraland andwestern western Snake SnakeRiver RiverPlain, Plain,Idaho, ldaho,emphasizing emphasizing the silicic rocks: rocks: in in Link, Link, P. P. K. K. and and Hackett, Hackett, W. W. R., R., editors, editors, Guidebook Guidebook to the the geology centrgand and southern southern Idaho: ldaho: Idaho ldaho Geological Geological Survey Survey Bulletin Bulletin 27, 27, geology of central 247-281. p. 247-281. BVSP (Basaltic (Basaltic Volcanism Volcanism Study Study Project), BVSP Project), 1981, 1981, Basaltic Volcanism Volcanism on the the Terrestrial Terrestrial Planets, Pergamon Press, New York, 1286 1286 p. p. Cas, R. R. A. A. F. Cas, F. and and Wright, Wright, J. J. V., V., 1987, 1987,Volcanic VolcanicSuccessions, Successions, Modern Modern and and Ancient: Ancient: Allen Allen and Unwin, Unwin, London, London, 528 528 p. p. Ekren, E. B., Ekren, E. B., Mcintyre, Mclntyre, D. D. H., H., and andBennett, Bennett,E. E.H., H.,1984, 1984,High-temperature, High-temperature,large-volume, large-volume, southwestern Idaho: lava-like ash-flow U. S. lava-like ash-flow tufts tuffs without calderas calderas in in southwestern ldaho: U. S. Geological Survey Professional Professional Paper 1272, 76 p. p. Fisher, R. V. 1984, Pyroclastic V. and andSchmincke, Schmincke, H.-U., H.-U., 1984, Pyroclastic Rocks, Rocks, Springer-Verlag, Springer-Verlag, New New Fisher, R. York, 472 p. York, p. Fitz, T. J., 1988, 1988, Large Large felsic felsic flows flows ininthe theKeweenawan Keweenawan North North Shore Shore Volcanic Volcanic Group Group in in thesis, University University of Cook County, Cook County, Minnesota: Minnesota: unpub. unpub. M. M. S. thesis, of Minnesota, Minnesota, Duluth, 180 180 p. p. Green, Green, J. J. C., C., 1979, 1979, Field Field trip tripguidebook guidebook for forthe theKeweenawan Keweenawan(Upper (UpperPrecambrian) Precambrian) Geological Survey North North Shore Shore Volcanic Volcanic Group, Group, Minnesota: Minnesota: Minnesota Minnesota Geological Survey Guidebook Series, Series, No. 11, 11, 22 22 p. p. 1982a, Geology Geology of of Keweenawan Keweenawanextrusive extrusiverocks, rocks, , Wold, , 1982a, Wold, R. R. J. J. and and Hinze, Hinze, W. W. editors, Geology J., editors, Geology and Tectonice Tectonice of the the Lake LakeSuperior Superior Basin: Basin:Geological Geological America Memoir Memoir 156, 156, p. p. 47-56. 47-56. Society of America 1982b, 1982b, Two Harbors Harbors Sheet, Sheet, Geologic Geologic Map Map of of Minnesota: Minnesota:Minnesota Minnesota Geological Geological Survey. Survey. 1983, Geologic Geologic and and geochemical evidence for for the the nature 1983, geochemical evidence nature and and development development of of the middle middle Proterozoic Proterozoic(Keweenawan) (Keweenawan) Midcontinent Midcontinent Rift Rift of of North North America: America: 94* p. p. 413-437. 413-437. Tectonophysics, v. 94, 1987, Plateau basalts of of the North Shore Shore Volcanic Volcanic Group: Group:& jj , 1987, Plateau basalts the Keweenawan Keweenawan North Biggs, D. Field Guide 3, Geological Biggs, D. L., editor, editor, Centennial Centennial Field Guide Vol. Vol. 3, Geological Society Society of of America, p. 59-62. 59-62. , 1989, Physical Physical volcanology volcanology of of mid-Proterozoic mid-Proterozoic plateau plateau lavas: lavas: the the Keweenawan Keweenawan North Shore America North Shore Volcanic Volcanic Group, Group, Minnesota: Geological Geological Society Society of America Bulletin, v. 101, 101, in in press. press. Bulletin, Self, Stephen, C. D., Price, J. G., G., Rubin, Rubin, J. J. N., N., Parker, Parker, D. D. F., F., Wolff, Wolff* J. J. A., Self, Stephen, Henry, Price, J. Henry, C. lavalike silicic Richard, and Widespread, lavalike silicic Franklin, and Barker* D. S., 1988, Widespread, Franklin, Richard, Barker, D. volcanic rocks of p. 509-512. 509-512. of Trans-Pecos Trans-Pecos Texas: Geology, Geology, v. 16, 16, p. Miller, J. J. D., D., Jr., Jr., 1987, 1987,Geology Geology of of the theKeweenawan Keweenawan (Upper (Upper Precambrian) Precambrian) Beaver Beaver Bay Bay Miller* Complex Complex in the vicinity vicinity of of the the Silver Silver Bay, Bay, Minnesota, Minnesota, hi Balaban, Balaban, N., N., editor, editor, in Precambrian Precambrian geology areas in Field Trip selected areas Field Trip Guidebook for selected geology of Minn. Geol. Survey Guidebook Series No. 17. northeastern Minnesota: Minnesota: Minn. 17. Geologic map map of of the , 1988, 1988, Geologic the Silver Silver Bay Bay and and Split Split Rock RockPoint PointNE NEquadrangles, quadrangles, Lake County, Minnesota: Minnesota: Minn. Minn. Geological Geological Survey Survey Miscellaneous Miscellaneous Map Series Series M-65. M-65. 9- A-14 �Miller, 1987, Road D., Jr., Weiblen, P. W. C., 1987! ~ i l l e rJ. ~ Da1 Weiblen? P. W. and and Green, Green* J. C.? Road log log and and stop stop descriptions for the the Beaver Beaver Bay Bay Complexl Complex, i Balaban, N.?editor, editor* Field Field Trip Trip Balabanl N., descriptions for northeastern in Precambrian Precambrian geology Guidebook for geology of northeastern Guidebook for selected selected areas areas in Minn. Geol. Geol. Survey Survey Guidebook Series No. 17. Minnesota: Minnesota: Minn. 17. Motamedi, Shoaullah, 1984, The Keweenawan lavas in the City of Duluth: Motamedil Shoaullahl 1984?The Keweenawan lavas in the City Duluth: unpub. unpub. M. M. S. S. thesis, thesis* Univ. Univ. of of Minnesota-Duluth, Minnesota-Duluth*140 p. p. Price, J. J. G., G., Henry, C. D., Pricel Henry, C. D.l Parker, Parker* D. D. F., FSl and and Barker, Barker* D. D. S., S.?1986, 1986?Igneous Igneous geology geology of Trans-Pecos Texas: Texas: Field Field trip trip guide Trans-Pecos guide and and research research articles: articles: Guidebook Guidebook 23, 23* Geology, Austin* Austin, 360 p. Bureau of Economic Geologyl Ross, C. C. S. and L.?1961, 19611Ash-flow Ash-flow tufts: tuffs: their their origin, origin*geologic geologic relations relations and and Rossl and Smith, Smith, R. R. L., identification: U. S. Geological p. Geological Survey Professional Professional Paper 366, 366! 81 81 p. Van Schmus, W. A. Van Schmus? W. R. and and Hinze, Hinze, W. W. J., J.l The TheMidcontinent MidcontinentRift RiftSystem: System:Annual AnnualReviews Reviews of Earth v. 13, 13, p. p. 345-383. 345-383. Earth and and Planetary Planetary Science, Science?v. editors, Geology Geology and and Tectonics of the Wold, R. J. and Hinze, Hinze, W. W. J., J., 1982, 1982* editors, Tectonics of the Lake Lake Woldl R. J. and Superior Basin: Geological Society of of America Memoir 156, p. Superior Geological Society 15e1280 280 p. A- 15 �- PENOKEAN STRUCTURAL TERRANES TERRANES IN EAST-CENTRAL MINNESOTA A one-day one-day field trip trip associated associated with the the Thirty-Fifth Annual Meeting of the the Institute on Lake Lake Superior Superior Geology Geology May 3-6, 3-6*1989 1989 By Timothy B. Hoist Holst Department of Geology Geology University of Minnesota Minnesota Duluth Duluth Duluth, Minnesota Duluth1 Minnesota 55812 introduction Introduction I 1 I The orogeny, which which occurred near the the close of The Penokean Penokean orogenyl occurred near of early earlyProterozoic Proterozoic time time (1875-1825 Ma., Van Schmus, (1 875-1825 Ma.* Schmus* 1976, 1976, 1980, 1980, 1981) 1981) involved involved deformation deformation and andmetamorphism metamorphism in Minnesota, Minnesota, Wisconsin, Wisconsin, upper upper Michigan* Michigan, and and the of rocks rocks in the Superior, Superiorl Southern, Southern, and and 1980; Cannon, Grenville provinces Grenville provinces in Canada Canada (HoIst, (Holstl 1982; 1982; Maass Maass and and others, others* 1980; Cannon, 1973; 1973; Brocoum the Penokean Minnesota was Brocoum and Dalziel, Dalziel* 1974). 1974). Until Until recently, recently* the Penokean orogeny orogeny in in Minnesota was usually interpreted as intracratonic (Morey and and Sims, usually interpreted as intracratonic (Morey Sims, 1976; 1976; Sims, Sims* 1976; 1976; Sims Sims and andothers, others, 1980) emphasis on the the role roleofofbasement basementrock rockinvolving involvingverticai "verticalremobilIzation" remobilization" 1980) with with an emphasis in this in (Morey, (Morey, 1979). 1979). Of fundamental fundamental importance importance in this interpretation interpretation is is the boundary, boundary* in west-central Minnesota, Minnesota, between between an an ancient part 3550 west-central ancient (in (in part 3550 Ma.) Ma.) gneissic gneissic terrane terrane and and aa younger (Ca. younger (ca. 2700 2700 Ma.) Ma.) granite-greenstone granite-greenstone terrane terrane (Fig. (Fig. 1). I). Morey Morey and Sims Sims (1976) (1976) suggested that this this boundary boundary is part of suggested that of aa major major Precambrian Precambrian crustal feature more more than than 1200 1200 km long long which which they they called called the the Great Great Lakes Lakes tectonic tectonic zone zone (Sims (Sims and andothers, others*1980). 1980). They They noted noted that that rocks rocks which which overlie overlie the thegranite-greenstone granite-greenstone terrane terrane (Animikie (Animikie Group) Group) are are less less deformed and and metamorphosed than those those which which overlie overlie the the Great Great Lakes Lakes tectonic tectonic zone zone and deformed metamorphosed than Because of of this gneissic terrane. terrane. Because this these these authors authors suggested suggested that that this this early earlyPrecambrian Precambrian . limited intracontinental tectonic movement intracontinental tectonic boundav acted locus for limited movement and and rising rising boundary acted as as aa locus geothermal gradients (Morey, (Morey, 1979). 1979). Recent investigations in Recent structural structural investigations in the early Proterozoic Proterozoic Thomson Thomson Formation Formation in in east-central Minnesota (Hoist* (Hoist, 1982, 1982, 1984c) 1984c) reveal reveal evidence evidence for multiple multiple deformation deformation and and east-central Minnesota document the existence One document existence of of northward-directed northward-directed nappes nappes during the the Penokean Penokeanorogeny. orogeny. One of the would be gravity the possible possible models models of of nappe nappe emplacement emplacement in Minnesota Minnesota would gravity gliding gliding off off aa rising diapir diapir following the suggestions of Morey (1979) and and Sims rising following the suggestions of Morey (1979) Sims and and others others (1980) (1980) for for intracratonic deformation. deformation. However, However* the high high strains strains associated associated with with nappe nappeemplacement emplacement (Hoist, 1985a) 1985a) do do not not support support this this idea idea (see (see the the values values of of strain strain above above aa rising (Holstl rising diapir diapir in Dixon, 1975). 1975). Such strains strains are more more consistent consistent with aa plate plate tectonic tectonic model model(Hoist, (Holst,1985a, 1985a1 1985b). of nappes has also recently been reported reported further further to to the east 1985b). The presence presence of recently been east in in the the al., 1988) 1988) and Penokean orogenic orogenic belt belt (Sims 1987; Klasner, Penokean (Sims and and others, others, 1987; Klasner* at at al.l and Penokean Penokean volcanic rocks have have been been shown shown to to be volcanic rocks be of of island island arc arc affinity affinity (Schulz (Schulz and and others, others, 1984) 1984) resulting in plate tectonic syntheses for several several areas of of the the Penokean Penokean orogenic orogenic belt. belt. The growing body of of structural structural and and petrologic petrologic evidence evidence from from Wisconsin Wisconsin (LaBerge (LaBergeand and 1978) is is others, 1984; 1984; Sims others* Sims and and others, others, 1985) 1985) and and upper upper Michigan Michigan (Cambray, (Cambray, 1977, 1977# 1978) consistent with the Minnesota for for aa convergent consistent with the structural structural evidence evidence in in east-central east-central Minnesota convergent plate plate Recent models of of the 984a, 1984b). 1 984b). boundary model boundary model (HoIst, (Holstl 11984a, Recent models the Penokean Penokean orogeny orogeny in in Minnesota involve aa convergent convergent plate plate margin margin with with subduction subductionofof aa passive or the Minnesota involve passive margin, margin* or close of of aa back-arc back-arc basin basin (Hoim, (Holm,HoIst, Holst, and and Ellis, Ellis, 1988; 1988;Southwick, Southwick, Morey, Morey*and andMcSwiggen, McSwiggen, 1988). 1988). B-i �•VP Middi. Prot&ozoc k" IQneous and k!IJI ssdlm.ntsry rocks I'I Early Prot.rozolc ntrusivs rocks r.a 1 Early Protsrozoc v1 i supracruatals 1 with Iron formation F::::::1 Archean Qranste— greenstoA. terran '1 Arch•an gn.is&c lOOkm Figure Figure 1:1: Generalized geologic map map of of the Generalized geologic the Precambrian Precambrian geology geology of of Minnesota Minnesota (after (after Sims Sims and and others, others, 1980; 1980; Morey Morey and andothers, others, 1982). 1982). GLTZ GLTZ is is the the Great GreatLakes Lakes Tectonic TectonicZone. Zone. Geologic Geoloaic Setting Settinq The can be divided The Precambrian Precambrian rocks of of east-central east-central Minnesota Minnesota can divided into into four four distinct distinct terranes 1) terranes (Fig. (Fig. 1): 1): 1) Archean Archean rocks; rocks; 2) 2) early early Proterozoic Proterozoic stratified stratified rocks; rocks; 3) 3) early early Proterozoic 4) middle middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) sedimentary sedimentary and and Proterozoic plutonic plutonic rocks; rocks; and and 4) volcanic volcanic rocks rocks (Morey, (Morey, 1978). 1978). A A stratigraphic stratigraphic column column for foreast-central east-central Minnesota Minnesota and and detailed descriptions descriptions of different rock rock types types have have been been presented presented by byMorey Morey(1978, (1978, detailed of the different 1979), 1979), although although recent work suggests suggests a rethinking rethinking of some some of of the thecorrelations correlations(Morey (Moreyand and Southwick, Southwick, 1984; 1984; Southwick Southwick and and Morey, Morey, 1988; 1988; Southwick, Southwick, Morey Morey and and McSwiggen, McSwiggen, 1988). 1988). The The Archean Archean terrane terrane consists consists of of aa northern northern granite-greenstone granite-greenstone belt belt terrane terrane (ca. (ca. 2700 2700 Ma.), Ma.), aa southern southern highly highlydeformed deformedgneissic gneissic terrane terrane (in (in part part >3550 >3550 Ma.), Ma.), and and aacentral central sheared, schistose schistose segment the Great Great Lakes Lakes tectonic tectonic zone zone sheared, segment (Morey, (Morey, 1978) 1978) also also known known as the (Sims (Sims and and others, others, 1980). 1980). Along Along this this zone, zone, granitic granitic plutons plutons (2600 (2600 Ma., Ma,, Sims Sims and and others, others, 1980) 1980) acted as aaweld weldbetween betweenthe thenorthern northernand andsouthern southernsegments segmentsforming forming aarelatively relatively stable Archean(Morey, (Morey, 1978). 1978). stable craton craton by by the the end endofofthe theArchean Sedimentation into a large Sedimentation into large basin basin on on this this craton, craton, the the Animikie Animikie basin, basin, began began at at about about 2100 Ma. (Van Schmus, 1976). 2100 Ma. (Van Schmus, 1976). Depositional Depositional patterns reflect reflect contrasting contrastingtectonic tectonicconditions conditions in in the the northern northernand andsouthern southernsegments segments of of the the Animikie Animikie basin. basin. AA relatively relativelythin thinsuccession succession (2-3 (2-3 km) km) ofofpredominantly predominantly sedimentary sedimentary rocks rocks (labeled (labeled the the Animikie Animikie Group, Group, Keighin Keighin and and others, others, 1972) 1972) was deposited deposited north north of the the northern northern front front of of the the Great GreatLakes Lakestectonic tectonic zone, zone, whereas whereas aa much muchthicker thicker and andmore moreheterogeneous heterogeneous succession succession (>6 (>6km) km)ofofsedimentary sedimentaryand and B-2 �vhcanic rocks (Animikie (Animikie and Mule Mille Lacs Groups, Groups, Morey, Morey, 1978) 1978) was was deposited deposited south this volcanic south of this front front (Morey, (Morey, 1983; 1983; Morey Morey and andSouthwick, Southwick, 1984). 1984). Apparently, Apparently, subsidence subsidence was was relatively relatively greater in the the southern southern part part of ofthe thebasin, basin,particularly particularly over over the the Great Great Lakes Lakestectonic tectonic zone zone greater and and the the gneissic gneissic terrane. terrane. Ojakangas Ojakangas (1983) extent of of the the Animikie Animikie basin basin (1983) has inferred the extent on on the the basis basisofofsedimentological sedimentologicaland andtithological lithologicalsimilarities similarities ininMinnesota, Minnesota, Wisconsin, Wisconsin, and and Michigan. Michigan. Because Because rocks rocks of of the the Midcontinent Midcontinent Rift Rift system system (middle (middle Proterozoic Proterozoic igneous igneous and and sedimentary sedimentary rocks, rocks, Fig. Fig. 1)1) separate separate the the Animikie Animikie basin basin into into two two physically physically isolated isolated segments, the strata strata in in the thenorthwestern northwestern segment segment are are assigned assigned to to the theAnimikie Animikieand andMule Mille segments, Lacs Groups Groups whereas whereas those those ininthe thesoutheastern southeastern segment segment are are assigned assigned to to the theMarquette Marquette Lacs Range Range Supergroup. Supergroup. Correlations Correlations have made among among the the Lower LowerProterozoic Proterozoicbedded bedded have been made rocks rocks in in Minnesota, Minnesota,Michigan Michiganand andWisconsin Wisconsin(Morey, (Morey,1983). 1983). All stops stops on on this thisfield fieldtrip triphave havebeen beenmapped mappedhistorically historically as as part part ofofthe theThomson Thomson All Formation. The Thesouthern southernexposures exposureshave haverecently recentlybeen beenassigned assignedto toother, other,as asyet yetunnamed unnamed Formation. units of of early earlyProterozoic Proterozoic metasediments metasediments and metavolcanics, metavolcanics, which older than than the the units which are are older Thomson Formation Formation (Southwick (Southwick and and Morey, Morey, 1988; 1988;Southwick, Southwick,Morey Moreyand andMcSwiggen, McSwiggen,1988). 1988). Thomson Descriptive Descriptive Structural Structural Geology Geoloqy Exposures of of early earlyProterozoic Proterozoic metasediments metasediments and and metavoicanics metavolcanics historically historically called called Exposures greywacke, the Thomson Thomson Formation Formation consist consist of of aathick thicksequence sequenceofofinterbedded interbeddedslate, slate,slaty slatygreywacke, the metagreywacke metagreywacke with with some someintercalated intercalatedvolcanics. volcanics. The The southern southern two-thirds two-thirds of of this thisregion, region, here here designated designated the the southern southern structural structural terrane, terrane, has has aapervasive, pervasive,nearly nearlybedding-parallel bedding-parallel foliation foliation(S1). (SJ. ItIt ranges ranges from from aa slaty slaty cleavage cleavage in in the the north northto to aaschistosity schistosity in in the the south south near near the the Denham DenhamFormation Formation(Hoist, (Holst,1982). 1982). Strain Strain analysis analysis (Hoist, (Holst, 11985a) established 985a) has firmly established the the tectonic tectonic nature natureofofthis thisbedding.paraIlel bedding-parallelfoliation. foliation. Also Also present present in inthe thesouthern southernstructural structural terrane terrane are are isoclinal isoclinal recumbent recumbent folds folds in scales scales ranging ranging from from cms cms to to kms kms(nappes), (nappes), with with east-west east-west fold fold axes axes(F1). (F,). Both Both the the northern northern and and southern southern structural structural terranes terranes have have been been folded folded into into gentle gentle to toopen openupright uprightfolds. folds. Fold Fold axial axial surfaces surfaces strike strike east-west east-west and and fold fold axes axes have In the the southern southernstructural structural terrane terrane have horizontal horizontal to to gentle gentle plunges plunges either either east east or orwest. west. In these well-developed these upright upright folds folds(F2) (F2)refold refoldthe theearlier earlierisoclinal isoclinalrecumbent recumbentfolds folds(F1). (F,). AAwell-developed cleavage, cleavage, vertical or or dipping dipping steeply steeply to to the the south south (axial-planar (axial-planar to the the upright upright folds) folds) is is present present in in both boththe thenorthern northernand andsouthern southernstructural structuralterranes. terranes. In In the the northern northernstructural structural terrane terrane this this cleavage In the the cleavage is is aawell welldeveloped developedcontinuous continuous slaty slatycleavage cleavage ininthe thefiner-grained finer-grainedunits. units. In units units with with graded graded bedding, bedding, and and ininthe theunits unitswith withinterlaminated interlaminatedfine fine and andcoarse coarselayers, layers,the the continuous continuous cleavage cleavage grades grades into into aadisjunctive disjunctivespaced spacedcleavage cleavage(terminology (terminology ofofPowell, Powell, 1979). The spacing spacing of ofthe thecleavage cleavagedomains domainsranges rangesfrom fromcontinuous continuous up uptoto 11 cm cm ininsome some 1979). The of Cleavage domains domains of the themost mostcoarse-grained coarse-grained units, units, but but itit isis rarely rarely over over aa few fewmm. mm. Cleavage constitute constitute from 25% 25Y0 of of the the rock rock (in (inthe the thick thick graywacke graywacke units) units) to to 100% 10O0/~(in (in the the slates slates with with aa continuous continuous cleavage). cleavage). Domain Domain shapes shapes range range from from rough rough to to smooth smooth (smooth (smoothshapes shapes predominate) Within the the microlithons, microlithons, a weak weak fabric, fabric, at at predominate) with with some someanastomosing anastomosingshapes. shapes. Within least, least, isisdeveloped developed everywhere, everywhere,and andcommonly commonlythe thefabric fabricisisstrong strongtotocomplete complete(terminology (terminology of In the the southern southern structural structural terrane terrane the the steep steep foliation foliation isis aawell-developed well-developed of Powell, Powell,1979). 1979). In crenulation crenulation cleavage cleavage (S2). (SJ. This This S2 S2 cleavage cleavage can can be be discrete discrete but but isis most most commonly commonly transitional transitional to to zonal, zonal, or orentirely entirelyzonai zonal(Gray, (Gray,1977; 1977;Powell, Powell,1979). 1979). Spacing Spacing of ofthe thecleavage cleavage domains domains isisvariable. variable. For For the the most mostpart partthe thespaced spacedcrenulation crenulationcleavage cleavagestrikes strikeseast-west east-west and and dips dips steeply steeplyto tothe thesouth southororisisvertical, vertical,and andaxial-planar axial-planartotothe theF2F2folds. folds. Around Around some some microfolds, may fan, microfolds, however, however, the the spaced spaced crenulation crenulation cleavage cleavage may fan, or or be be atataaconstant constantangle angle (up (up to to 40°) 40') totothe theaxial axialplane planeon onone onelimb, limb,and andaxial axialplanar planaron onthe theother otherlimb. limb. The The intersection S1and and S2 S2defines defines aa well welldeveloped developedlineation lineationininthe therock, rock,trending trendingeast-west east-west intersection of of S1 with withsubhorizontal subhorizontalplunges. plunges. Detailed Detailed mapping mapping has has allowed allowed aa boundary boundaryto to be bedrawn drawnbetween between the single main Penokean deformation single main Penokean deformation inin the the north north(the (thenorthern northernstructural structural the area areaofofa a terrane), twotwo Penokean-aged deformations terrane), and and the thearea areaofof Penokean-aged deformations inin the the south south (the (thesouthern southern structural structural terrane). terrane). This This boundary boundary was was interpreted interpreted by Holst (1984c) (1984~)as aa nappe nappe front front by Hoist because because of of the theabrupt abruptnature natureofofthe thechange changeacross acrossthis thisterrane terraneboundary, boundary,and andbecause becausethe the refraction refraction pattern pattern in in the the early earlyfoliation foliation just just south southofofthis thisboundary boundarysuggests suggeststhat thataanappe nappe B-3 �/ front must be be located located in in the the immediate immediate vicinity vicinity to to the the north. north. Underlying the what has hashistorically historically been been called called the theThomson Thomson Underlying the southern southern part part of what Formation is the Formation the early early Proterozoic Proterozoic Denham Denham Formation. Formation. This This has now now been been broken broken into into upper and lower lower members members by by Southwick, Southwick, Morey Morey and and McSwiggen, McSwiggen. (1988). (1988). The rocks rocks of of this this formation have been multiply multiply deformed deformed and metamorphosed inin aa fashion fashion similar similar to the the formation have been and metamorphosed overlying rocks rocks (Holm, (Hoim, 1986a, 1986a, 1986b) 1986b) and and are are here considered part of the overlying considered part the same same nappe nappe terrane. The Denham Denham Formation Formation is is aasequence sequenceofofprimarily primarilyquartz-rich quartz-richmetasedimentary metasedimentary rocks (metaarkose, quartzite, mica schist, and rocks (metaarkose, quartzite, and garnet-staurolite garnet-staurolite schist) schist) with minor minor amounts amounts of marble of marble and and volcanic volcanic rocks. rocks. It has has been been postulated postulated to be be stratigraphically stratigraphically equivalent equivalent to the Chocolay Group of the the Marquette Marquette Range Range Supergroup Supergroup in Michigan Michigan (Larue, (Larue, 1981; 1981; Morey, Morey, 1983). A nearly 1983). Bedding strikes east-west east-west and and dips dipsdominantly dominantlysteeply. steeply. A nearly bedding-parallel bedding-parallel foliation is present present everywhere everywhere in in the the Denham DenhamFormation. Formation. The foliation foliation is refracted refracted at at aa higher higher angle angle to bedding bedding in in the the more morecompetent competent arkosic arkosic and and quartzitic quartzitic units. units. The foliation foliation and bedding and bedding have been been folded folded with with the thedevelopment, development, locally, locally, of of aacrenulation crenulation cleavage. cleavage. Orientations folds vary vary from from horizontal horizontal to vertical and and strike strike Orientationsofof axial axial surfaces surfaces to to these these folds to vertical east-west. east-west. The The Denham Denham Formation Formation also also contains contains aavery verywell-developed, well-developed, nearly horizontal, horizontal, east-west east-west mineral and and crenulation crenulation lineation. lineation. Chocolate-tablet veins Chocolate-tabletboudinage boudinageof of quartz veins bedding throughout throughout the the area. area. occurs parallel to bedding The basement to to this terrane is Archean (2700 (2700 Ma.) Ma.) McGrath McGrath Gneiss Gneiss which which The basement this terrane is the the Archean contains a poorly contains poorly to to well-developed well-developed foliation foliation and a number number of cross-cutting cross-cutting shear zones. zones. ItIt is aa coarse-grained, coarse-grained, pinkish-gray, pinkish-gray, biotite biotite gneiss gneiss containing containing megacrysts megacrysts of of microcline. microcline. Some Some of the megacrysts megacrysts are are rounded, rounded, giving giving the the appearance appearance of augen, augen, but many many are are euhedral euhedraland and oriented to the foliation oriented obliquely obliquely to foliation while still still others others have have aa sigmoidal sigmoidal shape shape and and are arealigned aligned the foliation. foliation. Sense in the Sense of of shear shear from from the thesigmoidal sigmoidalporphyroclasts porphyroclasts (after (after Simpson Simpson and and Schmid, 1983) 1983) indicate indicate that that the the foliation foliation developed developed in aa dominantly dominantly dextral dextral shear shear regime. regime. Schmid, in dip from The foliation foliation is commonly commonly well well developed, developed, strikes strikes east-west, east-west, and varies varies in from to vertical. vertical. A nearly nearly horizontal horizontal east-west east-west mineral mineral lineation horizontal to lineation ranging ranging from from crude to locally well well developed developed is is also present. present. The McGrath McGrath Gneiss Gneiss is locally folded folded and and is is locally is locally strike generally cross-cut shear zones cross-cut by nearly nearly vertical, vertical, commonly commonly anastomosing anastomosing shear zones that that strike generally east-west. east-west. In the the northern northern structural structural terrane terrane there are are some some late-stage late-stage features features including including kink kink bands which deform deform the the steep steep cleavage cleavage ininthe theThomson ThomsonFormation. Formation. The orientation of of bands The orientation these but poles poles to to over these kink kink bands bands is is quite quite variable, variable, but over 100 100 kink kink bands bands define define aa single single The gentle dip of the gentle dip the kink maximum on an maximum an equal-area equal-area projection projection (Clark, (Clark, 1985). 1985). The kink bands bands indicates a sub-vertical finite finite compression during their their formation, formation, estimated estimated to to be about 5% 5% indicates compression during by Clark Clark (1985). (1985). Conditions Of Deformation Deformation Petrographic analysis analysis indicates indicates that that the the basement Petrographic basement and cover rocks rocks have have undergone undergone similar conditions conditions of of deformation deformation related related to to the thePenokean Penokeanorogeny. orogeny. In In all rocks rocks analyzed, analyzed, the predominant appear to to be normal predominant deformational deforrnational processes appear normal crystal-plastic crystal-plastic type, type, involving involving In both and cover dynamic recovery recovery and andrecrystallization. recrystallization. In both basement basement and cover rocks, rocks, quartz quartz has has lattice has produced undulatory undergone ductile deformation. Bending of the crystal undergone ductile deformation. Bending of the crystal lattice has produced undulatory Recovery and and recrystallization are indicated extinction and, locally, locally, deformation deformation bands. bands. Recovery indicated by by the development of of subgrains and strain strain free free new grains grains in and along the margins of quartz subgrains and quartz have occurred aggregates. aggregates. Both brittle brittle and and ductile ductile deformation deformation processes processes have occurred in the the feldspar feldspar deformation is is indicated in the coarser feldspar grains. Brittle deformation feldspar by fractures along which new new grains have Simultaneous ductile ductile deformation deformationofof the the finer finer grained grained feldspars is have recrystallized. recrystallized. Simultaneous indicated by undulatory recovery, and and recrystallization commonlyresulting resultinginin aa undulatory extinction, extinction, recovery, recrystallization commonly indicated granoblastic polygonal strain free free in both polygonal texture. texture. Mica grains grains are relatively relatively strain both basement basement and and cover rocks, rocks, probably probably because because ofofrecrystallization. recrystallization. The The textures textures described described here here indicate indicate dominantly dominantly ductile deformation deformation under moderate moderate to high high temperature temperature and and moderate moderate pressure pressure conditions. conditions. B-4 �Metamorphism Metamorohism Metamorphism the early Metamorphism ofof the early Proterozoic Proterozoic sedimentary sedimentary rocks in in this region region increases increases from from north to south south (Keighin (Keighin and and others, others, 1972). 1972). At the type type locality locality near near Thomson Thomson in the the northern terrane, the the Thomson northern terrane, Thomson Formation Formation is is metamorphosed metamorphosed to lower lower greenschist greenschist fades facies Within (chlorite the Thomson (chlorite zone). zone). Within the Thomson Formation Formation there there is is a progressive progressive increase in increase in metamorphic grade lower amphibolite amphibolite facies (garnet zone) the south south(Morey, (Morey,1979). 1979). metamorphic grade to to lower facies (garnet zone) in the Farther south, south, the the Denham has been been metamorphosed to the the staurolite zone of Farther Denham Formation Formation has metamorphosed to staurolite zone the fades (indicated the amphibolite amphibolite facies (indicated by the the presence presence of of aacoarse-grained coarse-grainedschist schist containing containing quartz÷muscovite+biotite÷garnet÷staurolite). Morey (1983) (1983) has has mapped quartz+muscovite+biotite+garnet+staurolite). Morey mapped the the biotite, biotite, garnet, garnet, and staurolite for early staurolite isograds isograds for early Proterozoic Proterozoic stratifed stratifed rocks rocks in in Minnesota, Minnesota, illustrating illustrating this this progressive the similarity similarity of of the the progressiveincrease increaseinin metamorphic metamorphicgrade gradefrom fromnorth northtoto south south and the trend of metamorphic 7). metamorphic isograds and structural features features (see Morey, 1983, 1983, fig. fig. 7). Petrographic analysis reveals reveals further further information about the timing Petrographic analysis information about timing of of metamorphism metamorphism metamorphismduring duringthe the early early phase phase of deformation and deformation. deformation. Progressive Progressive metamorphism deformation in the the Denham Formationreached reachedthe the garnet garnet zone zone of of the the amphibolite facies as as indicated by the Denham Formation amphibolite facies indicated by presence of syntectonic presence syntectonic garnet garnet porphyroblasts. porphyroblasts. The The peak peak ofofmetamorphism, metamorphism,however, however, occurred during during or or after after the later deformation occurred deformation as indicated indicated by staurolite staurolite overgrowing overgrowing both the schistosity and the crenulation crenulation cleavage. cleavage. Microprobe analysis of garnet Microprobe analysis of garnet shows shows only only slight slight compositional compositional variation variation and and no no 1 986a). Rocks systematic zonation (HoIm, (Holm, 1986a). Rocks of the the southern southern structural structural terrane terrane have have recently recently been studied been studied by Holm Holm and andSelverstone Selverstone (1989). (1989). Using thermobarometric thermobarometric techniques techniques they they final equilibration increasing southward. find temperature and and pressure estimates of final find temperature pressure estimates equilibration increasing southward. Staurolite grade samples samples from from just just north Staurolite grade north of of the theDenham DenhamFormation Formationyield yieldfinal finalequilibration equilibration temperatures of 520-590° 520-590°Cand and aa pressure pressure of of about about 77 kb (depth of about 25 temperatures of 25 km). km). Petrologic and Geochemical Constraints Petroloqic Constraints Penokean aae age volcanic volcanic rocks rocks further furtherto to the the east east have Penokean have been shown shown to to be be of of Island island Horan, Hansen, and arc affinity Schulz affinity (Schulz, ( ~ c h u l z1983; 1983; , Schulz and and others, others, 1984). 1984). Horan, and Spencer Spencer (1987) (1987) suggest that that the the early intrusive rocks rocks in in central were formed at aa suggest early Proterozoic Proterozoic intrusive central Minnesota Minnesota were formed at convergent plate margin, margin, based on isotopic They suggest that convergent plate isotopic and and trace trace element element analysis. analysis. They may have have been been part part of an a gabbro gabbro near Mora, Mora, Minnesota Minnesota may an early early Proterozoic Proterozoic ocean ocean crust, crust, and thus part of Recent geochemical geochemical and isotopic and thus may may represent represent part of aa suture suture zone. zone. Recent isotopic work work reported by by Southwick, Morey, and McSwiggen reported Southwick, Morey, McSwiggen (1988) (1988) shows shows that island island arc arc constituents constituents are not aa major are major portion portion of of the the rocks rocks that that now now make make up upthe thetold-and-thrust fold-and-thrust belt belt of of the the that most of the Penokean Penokean Orogen Orogen in Minnesota. Minnesota. They They also also report report that most of the basaltic basaltic rocks rocks of the the region have a continental (within plate) affinity, indicating indicating that continental crust played played aa role role in determining their their composition. composition. Tectonic Modelling Modellinq HoIm, Hoist HoIst and and Ellis Ellis (1988), using the constraints constraints of structural structural geology, geology, finite finite strain strain Holm. determinations, deformation deformationconditions conditions indicated indicated by by microstructures microstructures and and textures, determinations, textures, and the the results estimates, developed developed a tectonic model results of thermobarometry thermobarometry estimates, model consisting consisting of of southward southward directed oblique subduction along along the Great directed oblique subduction Great Lakes Lakes tectonic tectonic zone. zone. According According to this this model model intense deformation deformation occurred occurred in in the tootwall footwall of the the major major thrust, thrust, which which marked markedthe theboundary boundary (continental) subduction. downgoing and and overriding during A-type between downgoing overriding plates during A-type (continental) subduction. between Sedimentary rocks deposited deposited on on the footwall Sedimentary rocks footwall during during loading loading caused caused by bythrusting thrustingeventually eventually became incorporated into the the deformation deformation zone. zone. Early formed structures structures related related to to footwall footwall deformation are a dominantly deformation are dominantly well-developed foliation foliation in the the gneiss gneiss and andisoclinal, isoclinal,recumbent recumbent Progressive folds folds with with aabedding-sub-parallel bedding-sub-parallelfoliation foliation in the the southern southern structural structural terrane. terrane. Progressive metamorphism during subduction reached reached the the garnet metamorphism during subduction garnet zone zone of the amphibolite amphibolite facies. Various deformation inversions inversions show show that that this early phase Various deformation phase of of deformation deformation involved involved extreme extreme and large flattening (with ZZ vertical) vertical) and large amounts amounts of finite extensional extensional stain in in both both the the flattening (with north-south and east-west east-west directions. directions. B- 5 �, Footwall accretion onto onto the the hanging hanging wall wall Footwafl deformation deformation was was followed by imbrication and accretion during associated with with continued continued compression compression and and isostatic isostatic rebound. rebound. Later during uplift associated Later formed formed structures associated associated with with imbrication imbrication and and deformation deformation within within the the hanging wall consist structures hanging wall consist of of folding development of McGrath Gneiss and open to folding of of the the foliation and development of shear shear zones zones in the McGrath close, upright to overturned overturned folds folds in cover rocks rocks of of both both the thesouthern southern and andnorthern northern close, upright in the the cover structural terranes. The peak peak metamorphic metamorphic event event (represented (represented by staurolite) staurolite) occurred occurred after after the temperatures of the later deformation at at temperatures of around around 520-590° 520-590°Cand and aa pressure pressureofof 77 kb (depth of of about 25 km). about km). Increasing Increasing temperature temperature associated associated with decreasing decreasing pressure pressure (uplift) (uplift) is is explained relaxation caused caused by by crustal crustal thickening thickening and anderosion. erosion. explained by conductive relaxation Southwick, McSwiggen (1988), that several several types types of of plate plate Southwick, Morey, Morey, and and McSwiggen (1988), while while noting noting that margin collisional model for for the the margin collisional models models are are possible, possible, favor favor a collapsing back-arc basin as a model They argue Penokean Penokean orogeny. orogeny. They argue that the lithostratigraphic lithostratigraphic associations the early early associations of the Proterozoic Proterozoic supracrustal rocks rocks in in Minnesota, Minnesota, and geochemical characteristics characteristics of the the and the geochemical volcanic more compatible compatible with back-arc setting setting than than than than with with an anarc-trench arc-trench volcanic rocks rocks are are more with a back-arc environment. environment. GUIDE TO FIELD FIELD TRIP STOPS STOPS The location of the field field trip trip stops stops is is shown shown on on Figure Figure 2. 2. The field trip begins begins at at the the Radisson Duluth Radisson Duluth Hotel Hotel at Superior Superior Street Street and and 5th 5th Avenue Avenue West West inindowntown downtown Duluth, Duluth, Minnesota. Head southwest southwest on Superior Superior Street Street and in in two two blocks blocksjoin join Interstate InterstateHighway Highway 35 going After 14.6 14.6 miles miles on on 1-35, 1-35, take take exit exit 242, 242, turning turning south south (left) (left) on on Canton Carlton going south. south. After County In 2.9 County 1. 1. In 2.9 miles, miles, the the road road crosses crosses aa spillway, spillway, turns turns west, west, and and after after 0.6 0.6 miles, miles, Turn right (north) 210, which which then then turns reaches aa 1 reaches T junction. junction. Turn (north) on Minnesota Minnesota Highway Highway 210, turns left (west) in less (west) less than than 0.1 0.1 mile. mile. In 0.2 miles, miles, Minnesota Minnesota Highway Highway 210 crosses crosses the St. St. Louis Louis River. Pull Pull off off and park just the bridge, River. just before before reaching reaching the bridge, or cross it and and park park in in the the parking parking area on the south side of of the the road. road. STOP STOP 11 THOMSON DAM DAM This is the type This type locality locality of of the theThomson Thomson Formation, Formation, which which here here consists consists of slates slates and and metagraywackes. A metagraywackes. A variety variety of of sedimentary sedimentary structures structures may may be be seen, seen, including including ripple ripple marks, marks, load casts, casts, convolute bedding, bedding, cross cross bedding, bedding, graded graded bedding, bedding, and andsole solemarks. marks. Folds with wavelengths from from cm cm to km They are upright wavelengths km are are present present (Figure (Figure 3). 3). They upright to to steeply steeply inclined inclined to to the south south and have subhorizontal fold axes axes that that trend trend east-west. east-west. Where the subhorizontal fold Where folds folds die die out out along along Two such steeply trend, axes axes may may plunge plunge east east or west trend, west as as much much as as 60°. 60'. Two steeply plunging plunging folds folds may be be seen the foliation may seen in this this area. area. A single single axial-planar axial-planar foliation foliation is is present; present; the foliation ranges ranges from a continuous from continuous slaty cleavage cleavage in in the the fine-grained fine-grained units units to to aadisjunctive disjunctivespaced spacedcleavage cleavage in the the more Abundant carbonate in more coarse coarse graywacke graywacke beds. beds. Abundant carbonate concretions concretions and and weathered weathered concretion voids voids can can be seen flattened concretion flattened in the plane plane of of the the cleavage. cleavage. Strain determinations determinations in this region mud chips, chips, and a thin region using using deformed deformed concretions, concretions, mud thin conglomerate conglomerate bed to the the north of of the reservoir reservoir reveal strain strain ratios ratios of about about X:Y:Z X:Y:Z == 7:4:1, 7:4:1, with with XXvertical, vertical,ZZhorizontal horizontal and north-south north-south (perpendicular (perpendicular to foliation) foliation) and YY horizontal horizontaland andeast-west. east-west. Quartz veins, veins, from a few mm to more than a meter in width are present. Some exhibit ptygmatic folding. from mm to more than a meter in width are present. Some exhibit ptygmatic folding. Basalt dikes of of presumed ageare are also also present, present, as as are Basalt dikes presumed Keweenawan Keweenawan age are kink kink bands bands and and several sets sets of joints. several joints. The The kink kink bands bands dip gently gently and and display display aa single single maximum maximum on on an an 0' to the equal-area projection about 2 equal-area projectionwith withan an average averagestrike strikeofof about about N70E N7OEand andaa dip dip of of about 20° Many of the south. Many the kink kinkbands bandsintersect, intersect, but but the theangle angleofofintersection intersectionvaries variesrandomly randomly between 0 and exists within the kink and 30°. 30'. No cross-cutting pattern exists kink bands bands (Clark, (Clark, 1985). 1985). B-6 �I 4645' Middle Prolerozotc 4Tdd. Protorozoic Igneous Rocks Igneous Rock. Middle Prolerozofc Mddl. Proterozotc Sediments q/s o r Loka 5.dim.nt. Thornson Formotion Thomson Northam Formation Tçrran North.rn T.rran. Thomson Formgton Southern Tsrron Unnomid UnTt of Metassd.t,Iitovolcoriic, Unnomed Politic Schist Unnamed Pelitic Schst Denham formation Denhom Formation Upper Member Upper Member Denham Formollon Denham Formation Lower Member Member Lower McGrath Gn.Tss Figure 2:2: Figure Geologic map map of of the the area area of of the the field field trip trip (after (after Southwick, Southwick, Morey, Morey, and and Geologic McSwiggen, 1988). showing locations of field trip stops. McSwiggen, 1988), showing locations of field trip stops. A Figure 3: 3: Anticline Anticline at at Thomson Thomson Dam, Dam, view view from from the the east east bank bank of of the the St. St.Louis LouisRiver, River, just just Figure south of the highway bridge, looking west. Drawing by by Wendell Wendell Wilson. Wilson. south of the highway bridge, looking west. Drawing B- 7 �Proceed west west on on Minnesota Highway Highway 210 210 for for about about 0.8 mile Driving Directions: Directions: Proceed mile to to the the town town of Canton. Turn right right (north) (north) at at the the stop Carlton. Turn stop sign on on to to Old Old Highway Highway 61. 61. Proceed for one one either the convenience convenience store on the the right rightside side block and park in either store parking parking lot, lot, or or the the large lot on of the road. road. Walk Walknorth north to to first first road roadcut cut outcrop outcrop on on west west side side of of road. road. STOP STOP 2 CARLTON CARLTON ROAD ROAD CUT CUT lnterbedded slates slates and and graywackes graywackes of of the Thomson Formation here dip to Interbedded to the the south. south. is present. is present, flattened in the A subvertical subvertical cleavage cleavage is present. A deformed deformed load load cast cast is flattened in cleavage plane. Numerousdeformed deformedconcretions concretionswith withquite quiteaarange range in in size size are are present plane. Numerous present in The north-south vertical vertical joint joint face face is XZ both slate and and graywacke graywacke beds. beds. The is the the approximate approximate XZ plane of the strain strain ellipsoid ellipsoid in the the northern northern structural structural terrane of the the Thomson Thomson Formation. Formation. Driving Directions: south one block and turn Directions: Reurn south turn right right (west) (west) on on Minnesota Minnesota Highway Highway 210. 210. Proceed about 3 miles Proceed about miles to to the theoverpass overpassintersection intersectionwith with Interstate Interstate Highway Highway 35. 35. Proceed Proceed under the freeway freeway and turn turn left left on onentrance entranceramp ramptoto1-35 1-35South. South. Proceed for approximately approximately 26 miles miles and and take take exit exit 209, 209,Sturgeon Sturgeon Lake. Lake. Turn Turn right right and proceed proceed into into the the town town of of 26 Sturgeon Lake to to the the ITjunction. Sturgeon Lake junction. Turn Turn left on on Highway Highway 61 and and proceed proceed to the the first first right right turn, the abandoned abandoned railroad railroadtrack trackand and then then turns turns left left to to the center turn, which which crosses crosses the center of of town. town. turn right with a bar and a bank In one block turn right (at the intersection with bank on on the the corners) corners) and and follow follow The road winds winds past an old school County 46 out of Pine County of Sturgeon Sturgeon Lake. Lake. The school and and heads heads west west for about a mile, sharply to to the mile, then then bends bends sharply the right and heads north north for a half half mile, mile, and and then then 3.2 miles bends sharply left left and and runs bends sharply runs due due west west for for aa number number of of miles. miles. About About 3.2 miles out out of of Sturgeon Lake (or (or 1.7 1.7 miles west of of the second Sturgeon Lake miles west second sharp sharp bend in the the road) road) there there is is aabridge bridge Park and and proceed to to road cuts on the west side of over the Kettle Kettle River. River. Park of the the river. river. STOP STOP 3 KETTLE KETTLERIVER RIVER ROAD ROAD CUT CUT This bridge was constructed constructed inin the the mid mid 1980s (the old bridge is This bridge was is in aa farmer's farmer's field field just to the the northeast) northeast) and and aa new new road roadcut cutexposes exposesmetasedimentary metasedimentary rocks rocks on on both both the the north north sides of the the road. road. The rocks rocks here here have have been been mapped mapped historically historically as as Thomson Thomson and south sides Formation, but are are part part of the Formation, but the "unnamed "unnamed pelitic pelitic schist" schist" unit unit (Pps) (Pps) of of Southwick, Southwick, Morey Morey and and They are are part of McSwiggen McSwiggen (1988). (1988). They of the the southern southern structural structural terrane terrane of the the rocks rocks deformed deformed during the Penokean orogeny in in east-central Minnesota, and and are are part part of the Penokean orogeny east-central Minnesota, the Moose Moose Lake Lake -Glen Township panal of Southwick, Glen Township structural structural panal Southwick, Morey Morey and and McSwiggen McSwiggen (1988). (1988). The rocks rocks The early here are of here of garnet garnet metamorphic metamorphic grade, grade, and and two two foliations foliations are are observable. observable. The early foliation is subparallel subparallel to bedding, bedding, and and the the later latercrenulation crenulation cleavage cleavage isissubvertical subvertical and and Recent trends east-west. east-west. AA lineation trends lineation exists, exists, parallel parallel to to the the intersection intersection of of the the two twofoliations. foliations. Recent thermobarometricwork work on on samples samples from from this outcrop thermobarometric outcrop (HoIm (Holm and and Selverstone, Selverstone, 1989) 1989) yielded yielded temperature estimates estimates of of 470-520° 470-520°C and and a pressure of around around 66 kb. kb. final equilibration temperature Continue west west on on Pine County County 46 46 for about 2.8 miles. miles. Turn left (south) (south) about 2.8 Driving Directions: Directions: Continue Turn left (east) on another this road south another dirt dirt road. road. Follow this south for 1.5 1.5 miles. miles. Turn on a dirt dirt road. road. Follow mile, the "mainTM roadturns turnstoto the the right right (south), After 1 mile, "main" dirtdirtroad (south), but continue continue straight straight ahead ahead In .3 or .4 .4 mile mile there there isis aarailroad railroadcrossing. crossing. Park near, but but (east) on the the "two-track" "two-track" lane. lane. In not on the the railroad railroad tracks, tracks, and and walk walk along along the the tracks tracks to to the thenortheast. northeast. There There is aa long long railroad cut about .3 .3 mile mile northeast northeast of of the theroad/railroad road/railroadintersection. intersection. 1 8-8 �/ STOP 4 DENHAM DENHAMCEMETERY CEMETERY RAILROAD RAILROAD CUT Rocks exposed another similar the southwest southwest Rocks exposed along along this this cut and another similar cut cut one-half one-halt mile to the have historically historically been called called the the southernmost southernmost exposures exposures of Thomson Thomson Formation. Formation. As the As at the these rocks rocks have have recently recently been been designated designated part of an an unnamed unnamed peletic peletic schist schist unit unit last stop these (Pps), part of the the Moose Moose Lake Lake --Glen GlenTownship Township structural structural panal panal by by Southwick, Southwick, Morey, Morey, and and (Pps), McSwiggen (1988). (1988). A McSwiggen A number number of of F2 F2folds folds are are exposed exposed in this cut. cut. Fold axial surfaces surfaces are are vertical and axes are are subhorizontal. subhorizontal. The S, and east-west. east-west. Fold axes Sl foliation foliation which is is subparallel subparallel to S2 crenulation cleavage (axial-planar to most easily easily seen seen bedding and the S2 cleavage (axial-planar to the the F2 folds) folds) are most in the the more more fine-grained fine-grained schistose schistose units. units. Some Some of of the the metagraywacke metagrayacke units units are are nearly nearly quartzites quartzites here. here. Again Again there is is aaeast-west east-westsubhorizontai subhorizontal lineation. lineation. There There are are quite quite aa number of of early early quartz quartz veins veins which which exhibit exhibit boudinage. boudinage. The rocks number rocks here here are are staurolite staurolite grade grade and garnets Holst and and garnets are are visible visible in in many many samples. samples. Based Based on petrographic petrographic study, Holm, Hoist study, Hoim, Ellis (1988) that the the garnets with the the early early foliation during a Ellis (1988) suggested suggested that garnets were were synkinematic synkinematic with foliation during thermal peak peak of of metamorphism metamorphism occurred occurred after after progressive metamorphic metamorphic event, event, and and that the thermal the later phase of of deformation, deformation, as as indicated indicatedby by staurolite staurolite porphyroblasts porphyroblasts which which overprint overprint both both foliations. the Thermobarometric analysis the S1 S, and and S2 S2 foliations. analysis of samples samples from from this exposure exposure the assemblage assemblagestaurolite÷garnet÷plagioclase÷chlorite+ staurolite+garnet+plagioclase+chlorite+ muscovite+biotite+quartz muscovite+biotite+quartz containing the have yielded temperaturesofof 520-590° 520-590°Cand andpressures pressuresofof about about 7 kb have yielded final final equilibration equilibration temperatures kb (Holm and Selverstone, Selverstone, 1989). 1989). Driving Directions: Return over over the the same Directions: Return same route route to the the town town of of Sturgeon Sturgeon Lake. Lake. After crossing the abandoned left (northeast) crossing abandoned railroad railroad grade grade in in the middle of town turn turn left on the middle of town (northeast) on Highway 61. Follow Highway Highway 61 61 northeast for about 5.2 61. Follow 5.2 miles. miles. Turn left left at at the the intersection intersection and follow Highway one-half mile mile turn turn left left (west) at the stop Highway 61 into into Moose Moose Lake. Lake. In about about one-half stop light one-quarter mile mile up up the the hill to the light in the the center center of town town and and follow follow Highway Highway 27 about about one-quarter the railroad crossing. Park in in the the lot at the on the crossing. Park the old old train train station station on the west side of of the the road, road, and and the south along the the tracks the south side side of of the the railroad railroadtracks. tracks. Walk Walk along tracks to to the the northeast northeast to to some some railroad cut cut exposures. exposures. STOP 5 MOOSE MOOSELAKE LAKE RAILROAD RAILROAD CUT CUT These of metasedimentary rocksare arealso also part part of of the These exposures exposures of metasedimentary rocks the unnamed unnamed pelitic pelitic schist unit (Pps) of the schist the Moose Moose Lake Lake -- Glen GlenTownship Township structural structural panal of of Southwick, Southwick, Morey, Morey, and McSwiggen McSwiggen (1988), and have have historically historically been been mapped mapped as as Thomson Thomson Formation. Formation. In the the last and itit may last decade decade this this cut has has become become distinctly distinctly more more overgrown, overgrown, and may be be necessary necessary to to displace some features here. see some structural features displace some vegetation vegetation to to see some of the the structural here. The Sl S1 bedding-parallel foliationisis well well developed developed in in the the rocks rocks along along this this cut. bedding-parallel foliation cut. Early quartz quartz veins veins show boudinage features documenting documenting finite finite entensional entensionalstrain strainwithin withinthe the plane plane of of the early boudinage features S1 foliation. These These features features can can be seen S, foliation. seen on on outcrop outcrop faces faces in in several several orientations orientations showing showing that that the extension extension within within the plane plane of of this this foliation foliation occurred occurred in in all directions. directions. A mineral mineral lineation defined defined by by muscovite muscovite streaks streaks can can be be seen seen on on the the north north side side of of the tracks tracks at at one one of of folds of of various the first exposures exposures as you walk walk in in along along the the tracks. tracks. Several Several F2 folds various scales scales are are present. At least least one one of of these these folds folds has has an an axial axial plane plane which which dips dips about about 60° 60' to to the the south, south, and the S2 cleavage is is axial planar to the S2 crenulation crenulation cleavage the fold. fold. In some some exposures exposures along along this this cut there are are two two sets sets of ofcrenulation crenulationcleavages, cleavages, both both of of which which are are vertical. vertical. A (presumed) (presumed) Keweenawan basalt basalt dike, dike, vertical and trending approximately N8OEisis exposed exposed in in this cut. approximately N8OE Driving Directions: Continue west west on Highway for 4.0 4.0 miles. miles. Turn right (north) Directions: Continue Highway 27 for (north) off off the the road permission at at the house, road into the the farm farm driveway driveway and and park. park. After After asking asking permission house, walk walk north north from the house, just east house, just east of a line line of of trees trees along along the the edge edge of the the farmer's farmer's field field to to the the banks banks of Glaisby Glaisby Brook. Brook. B-9 �STOP 66(ALTERNATE (ALTERNATE STOP) STOP) GLAISBY GLAISBYBROOK BROOK STOP Rocks of of these theseexposures exposuresalong along Glaisby Glaisby Brook Brookhave havealso alsobeen been mapped historically Rocks mapped historically as Thomson Formation. They are are part part of of aaunnamed unnamed unit unit of of metasedimentary metasedimentary and and as Thomson Formation. They metavolcanic rocks rocks (Pgvi) (Pgvi) ofofSouthwick, Southwick,Morey, Morey,and andMcSwiggen McSwiggen(1988), (1988), but are still part of metavolcanic but are still part of their Moose MooseLake Lake -- Glen GlenTownship Townshipstructural structuralpanal. panal. Although Although the the exposure exposure isisovergrown overgrown their andlichen-covered, lichen-covered, itit isis possible possible to to see seean anisoclinal isoclinalrecumbent recumbentfold fold inin this outcrop, with and this outcrop, with several minor minor folds folds ofofnormal normalvergence vergencerelationship relationship (Figure (Figure4). 4). This This isisthe thelargest largestexample example several of an anF, Fl fold foldfound foundtotodate dateininthis thisregion. region. of Sketch of of F, Fl fold foldatatthe theGlaisby GlaisbyBrook Brookoutcrop outcropabout about 44miles miles west west ofofMoose Moose Figure 4:4: Sketch Figure Lake. Lake. DrivingDirections: Directions: Return Return to to the the town town ofofMoose MooseLake Lakefollowing following Highway Highway 27 27back back to the Driving to the east for for just just over over 44miles. miles. Turn Turn left left(northeast) (northeast) at at the the stop stoplight, light,and andfollow followHighway Highway61 61 to east to the northeast northeast (you (you need need to to turn turn left leftoff offthe the"maine "mainnroad road that that goes goes totothe thefreeway). freeway). Follow Follow the Highway 61 61 to to the thenortheast northeast passing passing through through the the town town of of Barnum Barnum inin just just over over 44miles. miles. Highway Continue for another 6 miles on Highway 61 to the village of Mahtowa. Turn left Continue for another 6 miles on Highway 61 to the village of Mahtowa. Turn left (northwest) on Carlton County 4 at Mahtowa. The road turns north after 0.6 miles, and (northwest) on Canton County 4 at Mahtowa. The road turns north after 0.6 miles, and then west west after afteranother another0.9 0.9miles. miles. Just Just after after the the turn turn to to the thewest, west, turn turnright right(north) (north)onto onto then Carlton County 7 toward Park Lake. Follow Carlton County 7 for 1.7 miles and Park. Carlton County 7 toward Park Lake. Follow Canton County 7 for 1.7 miles and Park. Proceed west west and and slightly slightly south south into into the the woods woods toto aa series seriesofoflinear lineareast-west east-westoutcrop outcrop Proceed ridges. ridges. 8-10 �, STOP 7 PARK PARKLAKE LAKE Rocks Rocks at this this locality locality are are part partofofthe theThomson ThomsonFormation, Formationl and and contain contain two two distinct distinct foliations. foliations. This This region region has has been beenmapped mappedas asPvt2 Pv&by bySouthwick, Southwick,Morey, Morey, and andMcswiggen Mcswiggen (1988): Thomson Formation Formation with with two twofoliations. foliations. The The dominant dominant foliation foliation here is aa cleavage cleavage (1988): Thomson that is is parallel parallel to tobedding bedding(S1). (Sl). The The bedding bedding (S0) (So)and and cleavage cleavage(S1) (St) have have been folded into (FJ that that trend trend east-west. east-west. A crenulation crenulation into open, open, upright uprightsubhorizontal subhorizontal folds folds (F2) cleavage cleavage (S2) (S2) is axial axial planar planar to to these these folds. folds. In In this this area area the thecrenulation crenulation cleavage cleavage (S2) (SJ is is present present in most most outcrops outcrops except except for for some some of of the thegraywacke graywacke units. units. The bedding-parallel bedding-parallel foliation for aa very foliation (S1) (S,) is present everywhere everywhere except except for very few fewcoarse coarsegraywacke graywackebeds. beds. At At the the extreme extreme southwest southwest part part of of this this exposure exposure south south of of Park Park Lake, Lakel small small scale scale isoclinal, isoclinal, recumbent folds (F1) recumbent folds (Fl) are present, present, to to which which the thebeddingbedding-parallel parallelfoliation foliation isis axial planar planar (Figure S,foliation foliation is is at at high high angles angles to to bedding bedding only only in in the the (rare) (rare)hinges hinges of of these these (Figure 5). 5). The S, F, Someofofthe theF1Flfolds foldshave havebeen beenrefolded refoldedby byF2 F2folds folds resulting resulting in in aa Ramsay Ramsay type type 33 F, folds. folds. Some interference interference pattern. pattern. N S 1lcm Figure shown by the silt Sketch of of aa small small fold fold at at stop stop 7, 7, Park ParkLake. Lake. Bedding Bedding (S0) (So) shown silt bed bed Figure 5: 5: Sketch is is folded folded into intoan anisoclinal isoclinalrecumbent recumbentfold fold(F1) (Fl) with withaxial axialplanar planarslaty slatycleavage cleavage(S1) (Sl)parallel parallel with with bedding bedding on the the limbs limbs of ofthe thefold. fold. Bedding Bedding and the S, S1foliation foliation are are folded folded by by later later upright of type interference patterns patterns (Ramsay, (Ramsay, 1967) 1967) and and upright folds (F2) (F2) with the the development development of type 33 interference aa vertical verticalcrenulation crenulationcleavage cleavage(S2). (SJ. Driving Driving Directions: Directions: Return Return south south by the the same same route route (Carlton (Carlton County County 7 and 4) to to the the village village of of Mahtowa. Mahtowa. Turn Turn left left(northeast) (northeast) on on Highway Highway61. 61. Proceed Proceed northeast northeast on Highway Highway 61, 61, passing passing through through the village village of of Atkinson, Atkinsonl and and proceed proceed under under the the freeway freeway bridge bridge 8.1 8.1 miles miles past At the the intersection intersection which which is is 1.05 1.05 miles rniles past pastthe thefreeway freeway bridge, bridge, turn turnright right past Mahtowa. Mahtowa. At (south) (south) and and proceed proceed 0.7 0.7 miles miles south south on on Gillogly Gillogly Road Road to to an an outcrop outcrop on on the the left left(east) (east)side side of of the the road, roadl at at the the top topof of aahill. hill. B-il �STOP 8 GILLOGLY GILLOGLY ROAD ROAD At earlier for two At earlier stops stops on this field field trip trip we we have have seen seen evidence evidence for two periods periods of of folding folding and foliation development in the southern structural terrane, and and one one main period of folding development in structural terranel folding and foliation in (1984) argued argued that that the the early early period of folding in the the northern northern terrane. terrane. Hoist Holst (1984) folding in in the southern The evidence southern terrane terrane also also involved involved the the emplacement emplacement of of nappes. nappes. The evidence he cited for for northward-directed nappes southern terrane terrane included included lithologic lithologic differences differencesbetween between northward-directed nappes in in the southern the (also see the two two terranes terranes (also see Morey Morey and andSouthwick, Southwick, 1984, and Southwick, Southwick, Morey Morey and and 1984, and Mcswiggen, 1988), 1988), and and the pervasive nature of the S1 foliation in the area Mcswiggen, Sl foliation area of of its itsoccurrence. occurrence. Facing area of of the the southern southern Facing directions directions of of F2 folds folds (Figure (Figure 6) 6) also also indicate indicate that that aa very very large area terrane The refraction pattern of of the the St terrane is on the upper upper limb of an an F, F, fold. fold. The refraction pattern Sl foliation foliation pattern pattern in the region region of of this this outcrop outcrop also also suggests suggests the the existence existence ot of northward-directed northward-directednappes nappes in in the the southern terrane, as as explained explained below. below. Several graded beds beds in the Thomson can be be seen at this Several graded Thomson Formation Formation can this locality localitystriking striking east-west and dipping to the the north. north. In the finer finer grained grained tops tops of of these these beds, beds,aacleavage cleavage(S1) (St) can be be observed. observed. ItIt is very very gently gently folded, folded, with with horizontal horizontal axes axes trending trending east-west. east-west. Iflithe the cleavage is traced toward the bottom of a bed, toward the bedl itit isis seen seen to to change change its its orientation orientation markedly, markedlyl and it becomes dipping moderately moderatelytoto the the south south in in the bottom and becomes a spaced spaced cleavage, cleavage, dipping bottom part part of of A crenulation cleavage (SJ, (S2),vertical verticalororvery verysteeply steeplydipping dippingtoto the the south, south, can can be the bed. bed. A crenulation cleavage seen in the upper of the beds. Mud seen upper portion of Mudchips chipsthat that are are flattened flattened in in the the early early S, Slfoliation foliation are present. present. A line line drawing drawing of of these these relationships relationships is is shown shown in in Figure Figure 7.7. To interpret interpret the the pattern of this outcrop, of S0 after the early pattern outcrop, itit is useful useful to to determine determine the the orientation orientation of So and S1 Sl after early phase of deformation, phase deformation, but prior prior to to the thelater laterphase phaseofofdeformation, deformation, which whichproduced producedF2 F2folds, folds, crenulation cleavagel cleavage, and and (very importantly for our puposes the S2 crenulation importantly for puposes here) deformed deformed the the early early S1 cleavage, cleavage, changing changing the geometry This can be S, geometry of of bedding/cleavage beddinglcleavage vergence vergence patterns. patterns. This be done, least to to aafairly fairly good goodapproximation approximation because both the done, at at least becausewe we have have strain strain data data for for both southern and and northern 1985a). Results Results of strain strain southern northern structural structural terranes terranes in the the region region (Hoist, (Holst, 1985a). determinations in in the the southern give the resulted from determinations southern terrane terrane give the finite finite strain strain which resulted from the the strain of the first superposition second deformation superposition of the the strain of the the second deformation upon upon the strain present in the northern deformation. As the only only deformational deformational structures structures present northern terrane are are those those of the the second second deformation, deformation, the the strain strain measured measured there there represents represents the the strain strain associated associated with with strain measured the second By removing that strain removing that strain from from the the finite finite strain measured in the the second deformation. deformation. By south, with the first south, we can can approximate approximate the strain strain associated associated with first deformation deformation in the the southern southern This is illustrated terrane terrane (Hoist, (Holst, 1985a; 1985a; Hoim, Holm, HoIst, Holst, and and Ellis, Ellis, 1988). 1988). This illustrated in Figure Figure 8. 8. By By outcrop we we can reconstruct the removing removing the the second second deformation deformation strain strain from from this this outcrop can reconstruct bedding(S0) /cteavage(S1)geometry geometryprior prior to to the is bedding(So) /cleavage(S,) the second second deformation. deformation. The technique technique is illustrated in Figure to alternating coarse 9. The graded graded sequence sequence is generalized generalized to coarse and fine fine Figure 9. layers, (in the the finest finest and coarsest parts of layers, with the attitude attitude of bedding bedding and and the the S1 Sl cleavage cleavage (in the beds) as Removal of of the the strain associated associated with the the as seen seen now now in in outcrop outcrop (Figure (Figure 9A). 9A). Removal geometrical relationships second deformation allows aa reconstruction deformation allows reconstruction of the the geometrical relationships of these these features features prior prior to to the thesecond seconddeformation deformation (Figure (Figure 9B). 98). The resulting resulting bedding/cleavage beddinglcleavage vergence pattern (cleavage (cleavage refraction refraction pattern) pattern) isis that that to to be expected vergence pattern expected on the the upper upper limb limb and and near the hinge hinge of of aalarge-scale large-scaleisoclinal, isoclinal, recumbent recumbent fold fold (Figure (Figure 10). 10). In the entire entire region region of the the the the southern southern terrane terrane to the the south, south, the the S1 S, cleavage cleavage is seen seen to to be besubparallel subparallel to the the bedding. Significantly that is not true here, and in the outcrop 1 km to the north, along the north, along an an bedding. Significantly that is not true here, and in the outcrop abandoned railroad near near Highway 61, the cleavage/bedding vergencepattern pattern isis the the same abandoned railroad Highway 61, cleavagebedding vergence same as seen this outcrop, there are no seen in in this outcrop, although although there no graded graded beds beds there. there. Further, Further, these two two outcrops are very outcrops are very close close to to the theboundary boundarybetween between the thenorthern northernand andsouthern southernstructural structural terranes. B-12 �Figure6:6: Illustration Illustrationofof facing facing direction directionofofF2 F2folds folds(after (afterBorradaile, Borradaile,1976). 1976). Dashed line is Figure Dashed line is axial plane ofof F1F, fold. fold. Foliation Foliation shown showndiagrammatically diagrammatically isis S2 S2 axial axialplanar planar crenulation axial plane crenulation cleavage. Small Smallarrows arrows indicate indicate stratigraphic stratigraphic tops, topsl large largearrows arrowsindicate indicatefacing facingdirections directions of cleavage. of F2folds. folds. F2 "so Si I Line drawing drawing ofofgeometrical geometricalrelations relationsofofbedding beddin; (S0), (So), early foliation (SJ1 and Figure 7:7: Line Figure early foliation (S1), and crenulation (SJ at Gillogly Road outcrop (Stop 8). Hammer handle isis40 40cm cleavage cmlong. long. crenulation cleavage (S2) at Gillogly Road outcrop (Stop 8). Hammer handle B-13 �N X:Y:Z t5 1:02 Northern A r m NorIh. Aria pj 'II Second Oatormallon Strain S.cond Dito,maion Str.àn Soulharn A r c SOuIh.rn Aria Total Strain (both d~fOrm~llOnal Tolal Strain (both diformailons) NZl0 YZ:t2:1: N X:YZ:4.2t0.3 Lxi 23.1t I, t Modal K Modal I Iod.i H Inlurad Strain of FIfl DaforiMllon Inh.r.d Strain 01 FIrst Oslorinatlon Figure8:8: Representative block diagrams of the state of finite strain in the northern and Figure Representative block diagrams ofinferred the state of finite strain in the northern southern structural terranes, terranes, and andthe thestrain straininferred to have been associated with theand first southern structural to have been associated with the first deformation. deformation. Figure 9:9: Bedding Bedding and and cleavage cleavage atatthe theGillogly GilloglyRoad Road outcrop (Stop 8) (generalized to Figure outcrop 8) (generalized alternating coarse and fine layers instead of graded beds) showing(Stop the present geometry to (A) alternating coarse and fine layers instead of graded beds) showing the present geometry (A) and geometry after removal of the strain associated with the second phase of seformation and geometry after removal of the strain associated with the second phase of seformation (6). (B). Figure 10: 10: Figure Position on onearly earlylarge-scale large-scale isoclinal recumbent fold (nappe) of cleavage Position isoclinal recumbent fold (nappe) of cleavage refraction pattern shown in Figure 9B. refraction pattern shown in Figure 9B. 8-14 �________ _______ Driving Directions: Directions: Return Highway 61 and and turn turn right right Return north north on on Gillogly Gillogly Road Road 0.7 0.7 miles miles to Highway (northeast) on Highway Highway 61. 61. Proceed for for 11 mile to aa road road cut cut with with outcrops outcrops on both both side side of of the road. STOP STOP 9 HIGHWAY HIGHWAY 61 61 ROAD ROAD CUT CUT The structural features features seen the Thomson Thomson Formation Formation are are those those seen in these exposures of the seen at the the type type locality, locality, Thomson Thomson Dam Dam (Stop (Stop 1). 1). Several upright, subhorizontal subhorizontal folds trend east-west. to the south. east-west. An An axial axial planar planar cleavage cleavage is is present, present, vertical or very steeply steeply dipping dipping to Abundant mud chips chips are are flattened flattenedinin the the plane plane of of the the cleavage. cleavage. AA faint Abundant mud faint vertical vertical lineation lineation Is is also present. present. The mud mud chips chips have have been been used used for for finite finite strain strain estimates. estimates. Some examples examples of cleavage cleavage refraction refraction are are present, present, and and they theyshow shownormal normalbedding/cleavage beddinglcleavage vergence vergence of relationships relationships to the upright upright folds. folds. No evidence has locality for the the early early No evidence has been been found found at this locality foliation foliation and recumbent recumbent folding folding seen seen in the the southern southern structural structural terrane. terrane. At point the the At this point terranes seems to be be rather rather sharp. sharp. boundary between the two structural terranes Proceed northeast northeast along along Highway Highway 61 61 for 1 .9 miles miles to to an Driving Directions: Directions: Proceed for 1.9 an intersection intersection with Minnesota Minnesota Highway Highway 210. 210. Turn Turn left (west) on Highway Highway 210 210 and and proceed proceed for for 0.1 0.1 miles miles and and turn turn right right on on the theentrance entrance ramp ramp totothe thefreeway, freeway,1-35 1-35North. North. Return Return to Duluth on on to Duluth Interstate Interstate 35. 35. REFERENCES REFERENCES CITED CITED , I I I I I I Borradaile, G.,J., 1976, facing" (Shakleton's (Shakleton's rule) rule) and and the Paleozoic Borradaile, G.,J., 1976, "Structural "Structural facing" Paleozoic rocks rocks of of the the Malaguide Complex Complex near near Velez Velez Rubio, Rubio, SE Spain: Spain: Koninklijk Nederlandse Akademie Akademie ser. B, v. v. 79, 79, p. p. 330-336 330-336 van Wetenschappen, Wetenschappen, ser. Brocoum, Brocoum, S. J., J., and and Dalziel, Dalziel, 1.I. W. D., D., 1974, 1974, The Sudbury Sudbury Basin, Basin, the the southern southern province, province, the Grenville Front, and and the the Penokean Penokean orogeny: orogeny: Geological Society of America America Bulletin, Bulletin, v. 85, V. 85, p. p. 1571-1580. 1571-1580. Cambray, F. F. W., Michigan: Michigan Basin Cambray, W., 1977, 1977, Field Field guide guide to to the the Marquette Marquette district, district, Michigan: Basin Geological Society Annual Meeting, Meeting, 62 p. p. as aa model , 1978, 1978, Plate Plate Tectonics Tectonics as model for the environment environment of deposition deposition and and deformation of the Early Proterozoic of northern northern Michigan: deformation of the Early Proterozoic (Precambrian (Precambrian X) X) of Michigan: Abstracts with Programs, v. 10, Geological Society of America America Abstracts 10, p. p. 376. 376. Cannon, W. W. F., Young, G. G. M., Cannon, F., 1973, 1973, The The Penokean Penokean orogeny orogeny in in northern northern Michigan, Michigan, Young, M., ed., Association of of Canada Huronian stratigraphy and and sedimentation: sedimentation: Geological Association Canada Special Special Paper, v. 12, 12, p. p. 211-249. 21 1-249. Clark, R.G., Clark, R.G., 1985, 1985, The The structural structural geology geology of the the Thomson Thomson Formation; Formation; Cloquet Cloquet and and Esko Esko quadrangles, east-central Minnesota: Minnesota: unpublished MS thesis, University quadrangles, east-central University of Minnesota Minnesota Duluth, Duluth, Minnesota Minnesota 114 p. diapiric Dixon, strain and progressive progressive deformation deformation in in models models of diapiric Dixon, J. M., 1975, 1975, Finite Finite strain Tectonophysics, v. v. 28, p. 89-124. structures: Tectonophysics, 89-124. Gray, D.R., of crenulation cleavages: cleavages: Journal Journal of of Geology, v. Gray, D.R., 1977, 1977, Morphologic Morphologic classification classification of p. 229-235. 229-235. 85, p. HoIm, D. 0. K., of the Holm, K., 1986a, 1986a, AAstructural structuralinvestigation investigation and and tectonic tectonic interpretation interpretation of the Penokean Penokean orogeny: University of Minnesota Minnesota Duluth, Duluth, 114 114 orogeny: east-central Minnesota, Minnesota, [M.S. [M.S. Thesis]: Thesis]: University a., p. P. , 1986b, 1986b, An account account of of multiphase multiphase deformation deformation during during the the Penokean Penokean orogeny: orogeny: evidence overlying Early Early evidence from from analysis analysis of the the Archean Archean McGrath McGrath Gneiss Gneiss and and overlying in east-central Proterozoic metasedimentary Minnesota: Institute Proterozoic rnetasedimentary rocks rocks in east-central Minnesota: Institute on Lake Lake Superior Geology Geology Abstracts, Abstracts, v. v. 32, 32, p. p. 32-33. 32-33. B-15 �________ _______ ________ Holstl T.B.* Ellis* M., M., 1988, 1988*Oblique Oblique subduction, subduction, footwall footwall deformation, deformation, and HoIm, D.K, D.K, Hoist, T.B., and Ellis, imbrication: imbrication: A model for the Penokean Penokean orogeny orogeny in in east-central A model east-central Minnesota: Minnesota: Geological Society of Bulletinl v. v. 100, 1001P. p. 1811-1818. 1811-1818. of America Bulletin, Holm, D.K., O.K., and and Selverstonel Selverstone,J.* J., 1989# 1989, Preliminary Preliminary constraints constraintson onthe the P-T P-T evolution evolution of of the Penokean orogeny: orogeny: east-central Minnesota: Minnesota: Institute lnstitute on Lake Superior Superior Geology Geology on Lake Abstracts Proceedings, v. Abstracts and Proceedings, v. 35 (this volume). B.*1982, 1982, Evidence Evidence for for multiple multiple deformation deformation during during the Penokean Penokean orogeny orogeny in in the the Hoist, T. T. B., Middle Precambrian Precambrian Thomson Thomson Formation, Formation*Minnesota: Minnesota: Canadian Earth Middle Canadian Journal Journal of Earth Sciencesl v. 19, p. p. 2043-2047. 2043-2047. Sciences, v. 19, 1984a, Penokean tectonics: constraints from the structural geology in 1984al in east-central east-central Minnesota: Institute on on Lake Lake Superior Superior Geology Geology Abstracts* Abstracts, v.v. 30, 30, p. 19. Minnesota: lnstitute 19. 1984b, Proterozoic Penokean orogeny as aa convergent convergent plate plateboundary: boundary: 1984b, The The Early Proterozoic gI p. p. 75. 75. Geological Association Association of of Canada Program with with Abstracts, Abstracts, v. v. 9, , 1 9984c, 8 4 ~Evidence ~ for development during the the early early Proterozoic ProterozoicPenokean Penokean Evidence for nappe nappe development orogeny, Minnesota: Geology, orogenyl Minnesota: Geology, v. 12, 12*p. p. 135-138. 135-138. 1985a, of a large for origin 1985a, Implications Implications of large flattening flattening strain strain for origin of of aabedding-parallel bedding-parallel foliation in the Early foliation in Proterozoic Thomson Thomson Formation, Formation* Minnesota: Journal of Early Proterozoic Minnesota: Journal Structural Geology, Geology, v. 7, 7*p. p. 375-383. 375-383, 1985b, Strain Strain within within early 1985bl early Proterozoic Proterozoic nappes nappes in the the Penokean Penokean orogenic orogenic belt, belt, Minnesota: Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, v. v. 17, 17*p. p. 293. 293. Minnesota: Horan, G.N., and Spencer, Horan, M.F., M.F., Hanson, Hanson, G.N., Spencer, K.J., K.J., 1987, 1987, Pb Pb and and Nd Nd isotope isotope and andtrace traceelement element constraints on the the origin constraints on origin of basic basic rocks rocks ininan anearly earlyProterozoic Proterozoicigneous igneous complex, complex, Minnesota: Precambrian Minnesota: Precambrian Research, v. 37, p. p. 323-342. 323-342. Keighin, C. W., W., Morey, G. B., S. S., Minnesota@i Sims, ELl and Goldich, Goldich* S. S., 1972, 1972, East-central East-central Minnesota Sims, P. P. Keighin, C. Morey* G. K., and Morey, G. B., of Minnesota: K., Morey, G. B., eds., Geology Geology of Minnesota: AA centennial centennial volume: volume: Minnesota Minnesota Geological Survey, p. p. 240-255. 240-255. Kiasner, Klasner* J.S., J.S., Ojakangas, Ojakangas* R.W., R.W.* Schulz, Schulz, K.J., K.J., and and LaBerge, LaBerge, G.L., G.L., 1988, 1988, Evidence Evidence for for development Proterozoic overthrust-nappe development ofof an early early Proterozoic overthrust-nappe system system in in the Penokean Penokean Orogen Institute on on Lake Orogen of of northern northern Michigan: Michigan: Institute Lake Superior Superior Geology Geology Abstracts Abstracts and and Proceedings, v. v. 34* 34, p. 56-57. Proceedingsl 56-57. Schulz, K. J., and E., 1984, The plate LaBerge, LaBerge, G. G. L., SchuIzl K. J., and Myers, Myers, P. P. E.* 1984, The plate tectonic tectonic history history of of on Lake v. 30, north-central Wisconsin: Wisconsin: Institute lnstitute on Lake Superior Superior Geology Geology Abstracts, Abstracts, v. 30, p. p. 25-27. 25-27. K., 1981, Larue, D. D. K.# 1981, The The Chocolay Chocolay Group, Groupl Lake Lake Superior Superior region, region,USA: USA:sedimentologic sedimentologic evidence for deposition evidence deposition in in basinal basinal and platform platform settings settings on on an anearly earlyProterozoic Proterozoic craton: craton: Geological Geological Society Society of of America America Bulletin Bulletin Part Part I,I, v. 92, p.p.417-435. 417-435. v. 92, Maass, R. A. S., S.* Medaris, Medaris, L. G., G., Jr., Jr., and and Van VanSchmus, Schmus, W. W. R., R.*1980, 1980,Penokean Penokeandeformation deformation in in Maass* central Wisconsin, Wisconsinl fr Morey, Morey, G. B., B.* and and Hanson, Hanson, G. G. N., N.#Selected Selected studies studies of of Archean Archean gneisses and lower lower Proterozoic Proterozoic rocks, rocks, southern southern Canadian Canadian Shield: Shield: Geological Geological Society Society of America Special Paper 182, of 182. p. 147-157. 147-157. Morey, and Middle nomenclature for Morey, G.B., 1978* Lower and Middle Precambrian Precambrian stratigraphic stratigraphic nomenclature 1978, Lower Survey Report Report of of investigations east-central east-central Minnesota: Minnesota: Minnesota Geological Survey Investigations 21, 52 P a p. 1979, Field trip guidebook , 1979* guidebook for the Precambrain Precambrain geology geology of east-central east-central Minnesota: Minnesota: Geological Surveyl Survey, Guidebook Guidebook Series Series No. No. 12* 12, 28 p. Minnesota Geological , 1983, 1983, Lower Proterozoic stratified rocks and the the Penokean Penokean orogeny orogeny in in east-central east-central Minnesota: Minnesota: Geological Geological Society Society of of America America Memoir Memoir 160, 160, p. p. 97-112. 97-112. Morey, G. G. B., K., 1976, 1976*Boundary Boundary between between two two Precambrian Precambrian W terranes terranes in in Morey, B.* and and Sims, Sims* P. P. K., Minnesota and its Geological Society Society of of America its geologic geologic significance: significance: Geological America Bulletin, Bulletin, v. 87, p. 141-152. 87# 141-152. Morey, G. B., Morey, G. BSl Sims, Sims, P. K., K., Cannon, Cannon* W. W, F., F., Mudrey, Mudrey, M. G., G,, Jr., Jr., and and Southwick, Southwickl 0. 0.L., L., 1982, 1982* Geologic map map of the Geologic the Lake LakeSuperior Superior Region, Region*Minnesota, Minnesota, Wisconsin, Wisconsin, and and Northern Northern Michigan: Minnesota Minnesota Geological Geological Survey Survey State State Map Map Series Series S-13. S-13. B-16 �________ ________• Morey, G. Moreyl G. B., Ba1 and Southwick, Southwick, D. D. K., 1984, 1984, Early Proterozoic geology geology of of east-central east-central Early Proterozoic Minnesota -- a review Institute on on Lake Superior Geology review and and reappraisal: reappraisal: lnstitute Geology Abstracts, Abstractsl v. 30, V. 301p. p. 35-36. 35-36. Ojakangasl R. 19831 Tidal deposits in the Early Early Proterozoic Proterozoic basin Lake Superior Superior Ojakangas, R. Ws1 W., 1983, Tidal deposits basin in the Lake region -- The region Palms and andPokegama PokegamaFormations: Formations: evidence for for subtidal-shelf The Palms evidence subtidal-sheif deposition of Superior-type deposition Superior-type banded banded iron iron formations: formations: Geological Geological Society Society of of America America Memoir 160, p. 49-66. 49-66. Powell, C. C. McA., Powelll McA.* 1979, 197g1A A morphological morphological classification classification of rock cleavage: cleavage: Tectonophysics, v. v. p. 21-34. 21-34. 58, P. Ramsayl G., 1967, 1967#Folding Foldina and Fracturing Fracturina of Rocks: Rocks: McGraw York, 568 p. Ramsay, J. J. G., McGraw Hill, Hill, New York, Schulz, Schulz, K.J., K.JsI 1983, 1983* Geochemistry Geochemistry of the the volcanic volcanic rocks rocks of of northeastern northeastern Wisconsin: Wisconsin: Institute lnstitute v. 29, on Lake Lake Superior Superior Geology Abstracts and Proceedings, Proceedingsl v. 2g1p.39. Schulz, LaBergel G. L., Sims, Simsl P. P. K., Ks1Peterman, Petermanl Z. E., and and Klasner, Klasnerl J. J. S., Ss1 1984*The The Schulz, K. K. Js1 J., LaBerge, G. L., Z. E., 1984, volcanic-plutonic terrane terrane of northern volcanic-plutonic northern Wisconsin: Wisconsin: implications implications for early early Proterozoic Proterozoic tectonism, Lake Superior Geological Association Association of of Canada Program tectonism, Superior region: region: Geological Program with with Abstracts, v. 9, Abstractsl v. g1p. 103. 103. Simpson, M., 1983, 1983* An evaluation evaluation of criteria to deduce the sense sense of of Simpson, C., C., and and Schmid, Schmid, S. S. M., of criteria to deduce movement in sheared Geological Society Society America Bulletin, v. 94# 94, p. movement in sheared rocks: rocks: Geological America Bulletinl p. 1281-1288. 1281 -1288. Sims, P. Simsl P. Ke1 Precambrian tectonics mineral deposits, deposits, Lake Lake Superior Superior region: region: K., 1976, 1976, Precambrian tectonics and and mineral Geology, v. v. 71, Economic Geology, 71 p. p. 1092-1118. 1092-1118. Sims, K., Card, 0., Morey, 1980, The Simsl P. P. K., Card, K. K. Dm1 Morey, G. G.B., B., and andPeterman, Peterman, Z. Z. E., 1980, The Great Great Lakes Lakes in central majorcrustal crustalstructure structure in central North North America: America: Geological tectonic zone zone - AA major tectonic Geological Society of of America Bulletin, Bulletin, Pt. Pt. 1, v. 91, Society 91, p. p. 690-698. 690-698. Sims, 1985, K., Peterman, Petermanl Z. E., Eland and Schulz, Schulzl K. K. J., Ja1 19851The TheDunbar DunbarGneiss-granitoid Gneiss-granitoid dome: dome: Sims, P. K., Proterozoic tectonic northern Wisconsin: Implications tectonic evolution evolution of northern Implications for early Proterozoic Geological Society Society of of America Bulletin, v. 96, p. 1101-1112. Geological Bulletin, v. 1101-1112. E., Klasner, Sims, W. F., 1987, Sims, P. P. K., Ks1Peterman, PetermansZ. Z. Es1 Klasnerl J. J. S., S., Cannon, Cannon, W. F., and and Schulz, Schulz, K. K. J., 1987, Nappe development upper Michigan Michigan segment early Nappe development and and thrust thrust faulting faulting in in the the upper segment of of the early Geological Society Proterozoic Penokean Penokean orogen: orogen: Geological Society of America America Abstracts Abstracts with Proterozoic Programs, v. 19, Programs, v. l g l p. 246. 246. Southwick, Southwickl D.L., D.Ls1and Morey, Morey, G.B., G.B., 1988, 1988, Tectonic Tectonic imbrication imbrication and and foredeep foredeep development development inin the Penokean Institute on Lake Penokean Orogen, Orogen, east-central east-central Minnesota: Minnesota: lnstitute Lake Superior Superior Geology, Geologyl v. 34, V. 34#p. p. 106-107. 106-107. Southwick, D.L., D.L., Morey, Morey, G. B., Southwickl B., and and McSwiggen, McSwiggen, P.L., P.L11988, 1988, Geologic Geologic map map (scale (scale1:250,000) 1:250,000) of of the the Penokean Penokean Orogen, Orogen, central central and and eastern eastern Minnesota, Minnesota, and and accompanying accompanying text: text: Minnesota Geological Geological Surveyl Survey, Report Report of Investigations 37, Saint Paul, Minnesota Investigations 37, Paul, Minnesota, Minnesotal 25 25 P p. Van Schmus, W. R., history of of the Great Van Schmusl W. R.# 1976, 1976, Early Early and and Middle Middle Proterozoic Proterozoic history Great Lakes Lakes area, area, Transactionsofof the the Royal Royal Society Society of London, North America: America: Philosophical Philosophical Transactions London* v. v. 280, 2801 p. 605-628. 605-628. 19801 Chronology Chronology of igneous rocks rocks associated associated with the Penokean 1980, of igneous with the Penokean orogeny orogeny in in Wisconsin: Wisconsin: Geological Geological Society Society of of America America Special Special Paper Paper 182, 18Z1p. p. 159-168. 159-168. , 1981, 1981 Possible interpretations interpretations of of the the Penokean Penokean orogeny: orogeny: International Proterozoic Proterozoic Wisconsinl Madison, Madison, Abstracts Abstracts Volume, p. p. 44. 44. Symposium, University of Wisconsin, B-17 �-- AND RELATIONSHIPS RELATIONSHIPS OF THE THE MELLEN MELLEN IGNEOUS IGNEOUS COMPLEX COMPLEX ROCK TYPES AND A One One Day DayField FieldTrip Triptotothe theKeweenawan Keweenawanofofthe theMellen, Mellen,Wisconsin WisconsinArea Area A Trip Leaders Leaders Kenneth Kenneth W. W. Klewin; Klewin; Northern Northern Illinois Illinois University; University; Dekalb, Dekalb, IL IL James F. F. Olmsted; Olmsted; SUNY; SUNY; Plattsburgh, Plattsburgh, NY NY Karl E. E. Seifert; Seifert; Iowa Iowa State State University; University; Ames, Ames, IA IA Introduction Introduction purpose of of this this trip tripisistotoprovide providean anopportunity opportunitytotoexamine examinethe therock-types, rock-types,igneous igneous The purpose features features and and relationships relationships of ofthe theMellen MellenComplex. Complex. We will will examine examine exposures exposures that that provide provide opportunities to compare compare this this with with other other layered layered intrusions intrusions and and make make judgements judgements on on conditions conditions opportunities and processes processes of formation. formation. Critical exposures are often inaccessible inaccessible for brief visits but but there there are many that we think think you you will will find find interesting interesting and provide for lively lively discussion. discussion. AA few few important but less accessible accessible are included if time time and and locations we we consider important are noted and will be included conditions permit. permit, Geology of the the Mellen Mellen Area Area General General The Mellen Mellen Complex Complex includes includes several several layered layered basic basic and andrelated relatedintrusions intrusions emplaced emplaced near near The the the base base of of the the Keweenawan Keweenawan volcanic volcanic pile. pile. So So far far as ashas hasbeen beendetermined determined the the volcanics volcanics in inthe the Mellen area are are Lower Lower Keweenawan Keweenawan nearly nearly conformably conformably overlying the older Proterozoic Proterozoic units of of Mellen the the Gogebic Gogebic Iron Iron Range. Range. The The lower lower contact contact of the the complex complex is is slightly slightly discordant discordant cutting to to lower lower stratigraphic levels westward, westward, beveling bevelingacross acrossthe theentire entireProterozoic ProterozoictotoArchean Archeangneisses. gneisses. All All of of the the Proterozoic Proterozoic units units have have been been tilted tilted toward toward the the northwest northwest into into the the Lake LakeSuperior Superior syncline syncline resulting in in northeast northeast strikes strikes and and steep steep northwest northwest dips. dips. Faulting Faulting has has accompanied accompanied this this tilting tilting but itit isis difficult difficulttotodemonstrate demonstrate ininthe thefield. field. Paleomagnetic 966) show show normal normal polarity polarity for the intrusive et.a1.(1966) intrusive rocks rocks Paleornagnetic studies of of Books, Books, et.aL(1 of of the the Complex Complex indicating indicating Middle Middle Keweenawan Keweenawan age age for for acquisition acquisition of of its itsmagnetism. magnetism. Green(1982) Green(l982) places the the Mellen Mellen Gabbro Gabbro equivalent equivalent to to the the Duluth Duluth Complex Complex but but itit could could be beslightly slightly older. older. Halls Halls and and Pesonen(1982) Pesonen(l982) indicate indicate rocks rocks of the the Duluth DuluthComplex Complex are are found foundinincontact contactwith with volcanics volcanics of normal normal polarity polarity while while the the Mellen Mellenappears appears to tointrude intrudeonly onlyreversed reversedvolcanics. volcanics. We We only only know know that that the the intrusives intrusives acquired acquired their their its its magnetic magnetic polarity polarity during during the normal normal period and and they they do do not not cut cutUpper UpperKeweenawan Keweenawansedimentary sedimentary units. units. Intrusive Intrusive Units Units The The Mellen MellenComplex Complex includes includestwo two layered layeredgabbroic gabbroic intrusions intrusions the the Potato Potato River RiverIntrusion lntrusion (PRI) (PRI) (Klewin (Klewin 1987 1987 & & in inreview) review) on on the theeast eastand andthe theMineral MineralLake LakeIntrusion Intrusion(MLI) (MLI)(Olmsted, (Olmsted, 1969; Seifert, in prep.) to the 1969; Seifert, the west. west. These Theseare areseparated separatedby bythe theMellen MellenGranite Granite(MG) (MG)which which intruded intruded the the gabbro. gabbro. Contacts Contacts between between intrusives intrusives of the the Complex Complex are are sharp, sharp, often often with with well well developed developed breccias but chilling chilling isis only only observed observed where where pre-intrusive pre-intrusive rocks rocks are are involved. involved. Several Several smaller smaller intrusives intrusives include include the the Rearing RearingPond Pond(RP) (RP)intrusion intrusion (Olmsted, (Olmsted, 1979) 1979) and and aa number number of of smaller smaller gabbro gabbro and and granophyre granophyre sills sills at at the thewest westend endofofthe thecomplex complex(Leighton, (Leighton,1954) 1954) The The two two larger largerintrusions intrusions have havethe thesize sizeand andcharacter character ofoflayered layeredintrusions intrusions throughout throughout the the world. world. The ThePRI PRIisisabout about3.5 3.5km. km.wide wideand andextends extends along along strike strike for over 30 km. The TheMLI MLIisis about about 5 km. km. thick thick and and about about1515km kmalong alongstrike strikebut butmay mayhave havebeen beenfaulted faultedoff offon onthe thewest westend end indicating greater. The indicating it's true length length was was somewhat somewhat greater. The RP RP is is aa small small intrusion intrusion of ofelliptical elliptical plan plan with km.. ItIt appears appears intruded intruded into the the upper upper part part of of the the MLI MLI but but with dimensions dimensions about 22 by by 44 km.. mapping mapping does not not indicate indicate timing. timing. AAsmaller smallermore moresill-like sill-likeunit unitofofsimilar similarpetrographic petrographiccharacter character (the (the Picritic Picritic Zone, Zone, Figure Figure 1)has 1)hasintruded intruded near near the the base base of of the thePRI. PRI. Northwest Northwest of of the the MLI MLI are are several that intrude intrude Lower LowerKeweenawan Keweenawanvolcanics volcanics or or other other several large large gabbro gabbro and andgranophyre granophyresills sills that c-i �intwsions but to intrusions to the the west west are are also alsoemplaced emplacedinto intoolder olderProterozoic Proterozoic units(Leighton units(Leight0n 1954). 1954). Leighton Leighton (1954) argued on the basis basis of of differences differences between between dip dip of of igneous igneouslamination laminationand andmodal modal Pesonen (1982) (1982) note that the the layering that tilting took place place during during intrusion. intrusion. Halls & Pesonen pole positions positions of of the Complex lie on paleomagnetic pole on the the APW APW curve curve without without structural structuralcorrection correction This permits tilting prior prior to to or during indicating tilting prior to acquisition acquisition of polarity. polarity. This permits tilting during intrusion intrusion but but is not not conclusive. conclusive. Petrology Petrology PRI Mellen Complex Complex may be classified into three The PRI The Mellen three distinct distinct types types of of intrusives. intrusives. The and MLI are from olivine olivine rich to anorthositic are coarse coarse grained grained feldspathic feldspathic gabbros that range from anorthositic and olivine olivine are are largely largely cumulus cumulus while while pyroxenes more compositions (Tables 1 & 2). 2). Plagioclase and layering is is rare but lamination as postcumulus postcumulus oikocrysts. oikocrysts. Rhythmic layering lamination is is well well commonly occur as developed roughly parallel to the regional regional structure structure (Leighton, (Leighton, 1954; 1954; Olmsted, 1969; 1969; Klewin, Klewin, 1987). The PicriticZone Zoneofofthe thePRI PRIare aremore moremafic maficpicritic picritic intrusions intrusions that that 1987). The RP RP and andthe thePicritic represent pulses represent pulses of of unique unique magma. magma. The TheRP RPininparticular particularisissomewhat somewhat more more primitive primitive than than the the others having much higher Mg#'s and more more calcic calcic plagioclase plagioclase in addition to higher higher mafic mafic mineral mineral third intrusive intrusive type is is the the Mellen Mellen Granite. Granite. content. The third Cryptic zoning is observed in the larger that some some in situ. larger intrusions intrusions indicating that fractionation occurred occurred (Olmsted,1969; (Olmsted,1969;1979; 1979;Klewin,1984). Klewin,1984).These These (PRI (PRI & & MLI) are zoned from from fractionation gabbro compositions compositions through throughferrodiorites ferrodioritestotogranitic graniticrocks. rocks. There is gabbroic or anorthositic gabbro is some evidence that excessive amounts of granophyre from addition of crustal granophyre resulted from crustal minimum minimum melt material (Seifert, in in prep). prep). granophyre often often forms forms the uppermost Two distinct granites granites occur occur at at Mellen. Mellen. Brick red granophyre uppermost It is also found intrusive the layered layered intrusions intrusions (Olmsted, (Olmsted, 1969, 1969, Klewin Klewin 1987). 1987). It intrusive into into units of the (Leighton,l954). Granophyres Granophyres gabbros or metavolcanics in the western part of the the complex complex (Leighton,1954). display spectacular simplectite simplectite textures textures in which quartz quark occurs intergrown with alkali feldspar feldspar in in micrographic, radiating radiating fringe fringe and and vermicular vermicular patterns patterns (Leighton, (Leighton,1954). 1954). Where these granitic units are thickened the above granular with with only minor above textures textures give way to to hypidiomorphic hypidiomorphic granular minor the western western part part of the area intergrowth features. This is well displayed at a granite boss in the area called St.Peters StPeters Dome Dome (sic.) (sic.) In contrast contrast with with the the granophyre granophyre is is the the Mellen Mellen Granite. Granite. This This medium medium to coarse coarse porphyritic porphyritic both the the PRI on the granite is one one of of the the younger younger intrusives intrusives of of the the complex.. complex.. It has intruded both the east and and MLI to the west. east west. On Onthe thesouth southitithas hasintruded intrudedboth bothKeweenawan Keweenawan volcanics volcanics and siltstones of of the the underlying Tyler formation. formation. The nature siltstones underlying Tyler nature of the the upper upper contact contact is not not well well known known as exposure is poor. poor. At this time only only preliminary preliminary analytical analytical work has has been been accomplished accomplished on on this intrusive so its its chemical chemical nature nature poorly poorly known known Descriptions of of the Intrusions Intrusions Potato River Intrusion Intrusion General General (Fig. 1) and will be the The PRI PRI forms the eastern eastern half of the the MeIlen Mellen Complex Complex (Fig. the subject subject of of general, the the PRI is poorly the first part of the the the trip. In general, poorly exposed, exposed, being mostly covered by unconsolidated Pleistocene Pleistocene sediment sediment and and heavy heavy forest forest and and many many of of the exposures exposures are are deeply deeply Relief in the area is weathered. Relief is generally generally less less than than 150m 150m with with the the highest highest hills hills underlain underlain by by lower Keweenawari volcanics. The resistant lower Keweenawan volcanics. The best best exposures exposures of intrusive intrusive rocks are are scattered scattered glacially scoured scoured outcrops outcrops and and along along drainages. drainages. The overall length length of of the PRI is 33 glacially 33 km.. km.. It is is divided approximately approximately in in half half by by a fault along the Tyler Forks River River into into a narrow and a much divided much wider segment. segment. The wider The width width of of the the intrusion intrusion ranges ranges from from about 1 km. to 4.5 km. km. averaging averaging 3.6 east of the Tyler Tyler Forks Forks River River where where the trip trip is is focused. focused. Basal and roof contacts of the PRI PRI are are roughly roughly concordant concordant with the enclosing enclosing volcanics volcanics While the PRI is largely by volcanics volcanics it cuts into the the regional regional structure. structure. While largely enclosed enclosed by and with the xenoliths of of metabasite have been underlying Proterozoic units near its western western end. end. Rare xenoliths been found near the base base of of the the intrusion. intrusion. C- 2 �Pm == PProterozojc roterozoic Pm m e t a s e d i m e n t a r y rocks rocks metasedimentary Keweenawan Ks == Keweenawan s e d i m e n t a r y rocks rocks sedimentary Kv == Keweenawan Keweenawan Ky volcanic rocks Ar = Archean rocks Ks Ar Upper Zone POTATO RIVER R I V E R INTRUSION INTRUSION POTATO Main Zone I\ / \ / / — '5, 5'.' 'S 5' Picritic Zone ,_ 'S f / 'S '5 S 5' MINERAL LAKE INTRUSION 5'- 15 REARING POND INTRUSION Ar MELLEN GRANITE GRANITE MELLEN Figure F i g u r e 11 - . -- . -. . - ..- �Exposures of plagioclase-rich plagioclase-rich rocks commonly exhibit lamination lamination of of the the plagioclase plagioclaselaths. laths. Tabet and Mangham Mangham (1978) (1978) reported an an average average orientation orientation of of N64oE, N64oE, 84oNW. 84oNW. Occurrences abet and Occurrences of rhythmic layering layering with with average orientation N57oE, N57oE, 64oNW 64oNW are restricted to the Picritic Picritic Zone Zone near near the middle of the PRI. Contacts the middle of Contactsbetween betweengabbroic gabbroicrocks rocksare aretypically typicallygradational. gradational. The PRI has been been divided divided into into several several zones zones based based on on lithology lithology (Fig.1; (Fig.l; Kiewin, Klewin, in in review). review). Lowermost Lowermost is is aa poorly poorly exposed exposed Border Border Zone of highly highly altered altered olivine olivine gabbro cut by rare contemporaneous contemporaneous or or later later dikes. dikes. Where Where exposed, exposed, the the Border Border Zone Zone isisirregular irregular ininthickness, thickness, ranging up to to 2 m. Most ranging up Mostofofthe theintrusion intrusionisisassigned assignedto tothe theMain MainZone Zoneofofmedium mediumgrained grained rocks rocks ranging from from olivine gabbro (at leucogabbro and andquartz quartzgabbro gabbrototoferrogabbro ferrogabbro (at the the base base ),),leucogabbro (toward the the top). top). The Present locally locally at the top The average average thickness thickness of the main main zone is 3300 3300 m. m. Present of the intrusion intrusion is an Upper Upper Zone Zone of of intrusive intrusive granite and granophyre. granophyre. On Onthe thebasis basisof oftrace trace element geochemistry (Klewin, (Klewin, in review) the granophyric element geochemistry granophyric rocks appear genetically genetically related to the Zone rocks but coarser grained Main Zone grained granitic granitic dikes dikes and and irregularly irregularly shaped shaped granitic granitic intrusions intrusions dikes?) near near the the top top of of the intrusion west west of of the Tyler Forks (large dikes?) Forks River are not. The Thethickness thickness Finally, midway midway into into the the Main Zone Zone is the of the Upper Upper Zone ranges ranges from from zero zero locally locally to to 120 120m. m. Finally, distinctive intrusive Picritic Picritic Zone Zone consisting consisting of of picrite picrite and and troctolite. troctolite. The The thickness thickness of of the the Picritic Picritic distinctive intrusive Zone is is estimated estimated to to be be 175 to 200 m. The Zone TheMain MainZone Zoneisisfurther furtherdivided divided into into Main Main Zones Zones I,I, IIII Zone I occurs below the Picritic Zone, is 850 m and Ill. Ill. Main Zone Picritic Zone, m thick thick and and consists consists of olivine olivine gabbro and and olivine olivine leucogabbro. leucogabbro. Main gabbro Main Zone Zone Il, 11, above above the the Picritic Picritic Zone, Zone, is is 1650 1650 m m thick thick and and consists of of olivine gabbro, olivine leucogabbro, gabbro and quartz-bearing leucogabbro. leucogabbro. The consists leucogabbro, gabbro The arrival of of cumulus cumulus augite occurs near the top of Main arrival Main Zone Zone II. II. The boundary boundary between between Main Main Zones IIIl & Ill Fe-Ti oxides. oxides. Main Ill is marked by the arrival arrival of cumulus Fe-Ti Main Zone Zone Ill 111consists consists of of quartz quartz Zones gabbro, quartz quartz leucogabbro leucogabbroand and ferrogabbro. ferrogabbro. Average Average thickness thickness isis 800 800 m. m. The The arrival arrival of of gabbro, cumulus apatite apatite occurs occurs in Main Zone Ill. cumulus Ill. Petrography and and Mineral Petrography Mineral Chemistry Potato River River Intrusion Intrusion is is composed composed of olivine olivine gabbro gabbro and and olivine olivine bearing bearing Most of the Potato leucogabbro. leucogabbro. Primary mineralogy is plagioclase, plagioclase, olivine, clinopyroxene, clinopyroxene, orthopyroxene, orthopyroxene, Fe-Ti Fe-Ti oxides and apatite. apatite. Major cumulus minerals minerals are plagioclase plagioclase and and olivine. olivine. Plagioclase typically typically forms normally zoned lath-shaped lath-shaped to to blocky blocky grains. grains. Olivine is subhedral to anhedral anhedral and unzoned. Clinopyroxene unzoned. Clinopyroxene is is anhedral anhedral and and forms forms oikocrysts oikocrysts where it is is intercumulus intercumulus and is is often often moderately zoned. zoned. Orthopyroxene Ilmenite moderately Orthopyroxene is less less common common and occurs as as inverted inverted pigeonite. pigeonite. llmenite titanomagnetite occur occur as as small oikocrysts or interstitial patches or as and titanomagnetite as skeletal skeletal cumulus cumulus grains grains in the ferrogabbros. ferrogabbros. Apatite typically occurs as tiny included included grains but is is larger larger and and cumulus cumulus in in of quartz the ferrogabbros. ferrogabbros. Quartz gabbro is is marked marked by by intercumulus intercumulus micrographic micrographic intergrowths intergrowths of and alkali feldspar. feldspar. Late stage gabbro also also contains contains Ca-amphibole, Ca-amphibole, and and rarely rarely fayatitic fayalitic olivine olivine and pigeonite. pigeonite. the Picritic Zone, plagioclase composition ranges from from An71 Excepting the An71 to An36; olivine Fo63 to Fo31 Fo31 and augite Wo44En44Fs12 Wo44En44Fsl2 to Wo43En32Fs25. Fo63 to Wo43En32Fs25. Even Even in in the thegranophyric granophyric rocks rocks the the augite never never becomes ferroaugite ferroaugite attesting to to the modest degree of iron augite iron enrichment enrichment in in the the intrusion. intrusion. Main Zone rocks are are mostly mostly orthoortho- and and mesocumulates, mesocumulates, with with aa notable notable lack lackof ofadcumulus adcumulus growth of plagioclase or olivine. troctolites, however however are are found in the Picritic olivine. Adcumulate Adcumulate troctolites, Picritic Zone. The granophyric rocks exhibit spectacular spectacular radiating sheaves of intergrown intergrown quartz and alkali alkali feldspar. Modal feldspar. Modal layering layering is is rare rare but butoccurs occurs ininthe the Picritic PicriticZone Zone and andplanar planarlamination lamination of of plagioclase is common in the gabbros. plagioclase gabbros. The Theuniversal universaloccurrence occurrence of of the the latter latterand and almost almost total total lack of the former throughout the complex is an an interesting interesting point point that that bears bears on on processes processes and and conditions during during emplacement. emplacement. Contacts conditions Contacts between between different different gabbroic gabbroic rocks rocks are are gradational gradational supporting the the single magma supporting magma pulse pulse hypothesis hypothesis (excepting (excepting the the Picritic PicriticZone). Zone). with both As judged by textural textural and and structural structural relations relations the parent magma magma was saturated with olivine and and plagioclase. plagioclase. Subsequent olivine Subsequent arrivals arrivals as cumulus minerals were: augite augite (after (after 72% 72% solidified), Fe-Ti Fe-Ti oxides oxides (after (after 750h 75% solidified) solidified) and and apatite apatite (after (after 78% 78% solidified). solidified). The solidified), The cumulus cumulus minerals seem to to come come in gradually this may be more apparent than than real due due to the very minerals seem gradually but this poor exposure. exposure. C-4 �References References on the the Potato Potato River RiverIntrusion Intrusion Klewin, K.W., K.W., 1987, 1987, The The petrology petrology and andgeochemistry geochemistry of of the thePotato PotatoRiver RiverIntrusion, Intrusion,northern northern Kiewin, Wisconsin. Unpublished Ph.D. Ph.D. thesis, thesis, Northern Northern Illinois Illinois University, University, DeKaIb, DeKalb, IL, IL, 357 357 p.p. Wisconsin. Klewin, Klewin, K.W., K.W., in review, review, The The petrology petrology of of the the Proterozoic Proterozoic Potato Potato River Riverlayered layeredintrusion, intrusion, northern northern Wisconsin. Wisconsin. Jour. Jour. of of Petrology. Petrology. Mangham, J.R., J.R., 1975, 1975, The The structure structure and andpetrology petrology of ofthe theeastern easternMellen Mellenintrusive intrusivecomplex, complex,Iron Iron Mangham, County, County, Wisconsin. Wisconsin. M.S. M.S. thesis, thesis, University University of of Wisconsin, Wisconsin, Madison, Madison, 134 134 p. p. Tabet, Tabet, D.E., D.E., 1974, 1974, Structure Structure and and petrology petrology of of the the Mellen Mellen igneous igneous intrusive intrusive complex complex near near Mellen, Mellen, Wisconsin. Wisconsin. M.S. M.S. thesis, thesis, University University of of Wisconsin, Wisconsin, Madison, Madison, 81 81 p. p. Tabet, Tabet, D.E. D.E. and and Mangham, Mangham, J.R., J.R., 1978, 1978, The The geology geology of of the theeastern easternMellen Mellenintrusive intrusivecomplex, complex, Wisconsin. -19. Wisconsin. Geoscience Geoscience Wisconsin, Wisconsin,v.v.3,3,.p.1 .p.1-19. Mineral Mineral Lake LakeIntrusion Intrusion General General As noted noted above above the the Mellen Mellen Complex Complex is is divided divided near near its its midpoint midpoint by by the theMellen Mellengranite. granite. As West West of of the the MG MGare arethe theMineral MineralLake Lakeand andRearing RearingPond Pondintrusions intrusions(Olmsted, (Olmsted,1969, 1969,1979) 1979)along along with with several several smaller smaller sills sills that that make make up upthe thewestern westernpart partofofthe thecomplex.(Leighton complex.(Leighton1954). 1954). Exposure here is probably probably somewhat somewhat better than the east. east. Many Manysimilarities similaritiesand and Exposure than that found to the several important important differences between the the complex. complex. Some Someofof several differences may may be found between the two two halves of the these these will will be be considered considered here. here. Like PRI the theMineral MineralLake LakeIntrusion Intrusionisishyperfeldspathic hyperfeldspathicwith withcumulus cumulusplagioctase plagioclase and and Like the the PRI divine. olivine. AAubiquitous ubiquitousfeature featureisisthe thealignment alignmentofofplagioclase plagioclaselaths lathswhile whilemodal modalororrhythmic rhythmic layering layering is is uncommon. uncommon. The Thelower lowerthird thirdofofthe theMLI MLIhas hasbeen beentermed termedanorthositic anorthositicolivine olivinegabbro gabbro and and represents represents that portion in which which both both olivine olivine and and plagioclase plagioclase are are cumulus. cumulus. Above Aboveabout about 1500 m m above above the the base base olivine olivine becomes becomes less lesscommon common and andthe therock rockgrades gradestotogabbroic gabbroic 1500 anorthosite. anorthosite. This This unit, unit,over over 2000 2000mmthick thickisiscomposed composedof ofover over80% 80%plagioclase plagioclase with with minor minor pyroxene pyroxene and and Fe-Ti Fe-Tioxides. oxides. In In many many exposures exposures the the rock rock isistrue trueanorthosite anorthositeand andthe thelamination lamination almost almost perfect. perfect. In In glacially glacially polished polishedexposures exposureswhere where clinopyroxene clinopyroxene oikocrysts oikocrysts are areabundant abundantthe the rock rock has has aadecided decidedspotted spottedappearance. appearance. Near the the top top of ofthe theintrusion intrusionthe thefeldspathic feldspathic rocks rocks give give way waytotoferrodiorite ferrodioritewhich whichininturn turn Near grades grades upward upward through through granodioritic granodioritic to to granitic granitic or orgranophyric granophyricunits. units. In Inthe thewestern westernpart partofofthe the one complex are are found found several several areas areas of ofabundant abundant granophyre granophyre to to the thepoint pointappearing appearingexcessive excessiveififone complex accepts the the hypothesis hypothesis that that their their origin origin isisentirely entirelythrough throughfractionation fractionation of ofaagabbroic gabbroicparent. parent. accepts These These granophyres granophyres are are often often intrusive intrusive into intoenclosing enclosinggabbros gabbrosoften oftenforming formingspectacular spectacularbreccias. breccias. ItIt isisunfortunate unfortunate that that none none of ofthese these isiseasily easilyaccessible accessible for for your yourinspection. inspection. Recent Recentisotope isotopeand and trace trace element element studies studies on on the the MLI MLIsuggest suggestthat thatthis thisevolved evolvedfelsic felsicsection sectionincludes includesaacrustal crustal component and was was emplaced emplaced and and differentiated differentiated as as aa separate separate conformable conformable intrusion intrusion at at the the top top component of 985; Seifert, of the theanorthositic anorthositicunit unit(Seifert (Seifertet.al.,1 et.a1.,1985; Seifert,ininpreparation). preparation). The The upper upper contact contact of ofthe theMLI MLIisiswith withthe theoverlying overlyingRearing RearingPond Pondintrusion intrusionas aswell wellasas what what are are presumed presumed to to be beLower LowerKeweenawan Keweenawanvolcanics, volcanics, now now strongly strongly recrystallized recrystallized by by contact contact metamorphism. metamorphism. Because Because of ofpoor poorexposure exposureitithas hasnot notbeen beenpossible possibletotoobserve observecontact contactrelations relations between between the MLI MLI and and the the RP RPintrusion intrusion so sorelative relativeage age isisinindoubt. doubt. ItIt isis suspected suspected that that like likethe the case Picritic Zone Zone of of the the PRI PRIthe thecloseness closeness of of timing timing prevented prevented any any chilling. chilling. The Thebasal basal case of of the the Picritic contacts of of the the MLI MLIwith withunderlying underlyingvolcanics volcanics and andhornfels hornfelsare areequally equallypoorly poorlyexposed exposedand andwhat what contacts isisexposed exposedisisoften oftencomplicated. complicated. Considerable Considerable reduction reduction of grain grain size size isisobserved observedatatthe thebase base but but composition composition of of these these rocks rocks disallow disallow their theiruse useas asparent parentmagma. magma. Petrography Petrographyand and Mineral MineralChemistry Chemistry Modal Modal analyses analyses of of representative representative rocks rocks are are found found ininTable Table1.1. At At first firstnote notethe therocks rocks labeled "Chill "Chill Zone" Zone" appear appear ordinary ordinarycandidates candidatesbut butchemistry chemistryindicates indicatesthey theyare aresomewhat somewhat labeled evolved. Likewise their their mineral mineral compositions compositions are are evolved evolved in in comparison comparison to to the therocks rocks evolved. Likewise Overlying the the basal basal rocks rocks isis an andivine olivinerich richzone(MG-4) zone(MG-4)that thatisisprobably probablynot not immediately immediately above. above. Overlying C-5 �__________ cottinuous continuous although although better better exposure exposure might might refute refute this. this. This mafic mafic rich zone zone grades grades upward upward over over 1000 -1500 m with with olivine olivine decreasing decreasing and and plagioclase plagioclaseincreasing. increasing. In this portion portion of of the the intrusion intrusion plagioclase lamination is not not well well developed. developed. Pyroxene and Fe-Ti oxides are are both both intercumulus intercumulus the base a very coarse "pegmatitic" "pegmatitic' unit is this level. level. At about about 1500 m above the throughout this encountered that that appears appears to to be roughly parallel with the base. encountered base. It is is in in this this region region only only where where modal layering layering has has been been observed. observed. While it is this horizon horizon isiscontinuous continuous itithas has modal is not not known known ifif this been mapped over aa distance distanceof of about aboutthree threekm.. km.. This mapped over This is is about about the the level level where where olivine olivine becomes rare rare and and the the rocks above above are are rich in plagioclase becomes plagioclase and are laminated. laminated. Olivine, now Fe-rich reappears as a cumulus phase phase in in the the ferrodiorite ferrodioritewhere where plagioclase, plagioclase, pyroxene, oxides oxides and and apatite apatite are are cumulus. cumulus. The pyroxene, The very very Fe-,Ti-,P-rich Fe-,Ti-,P-rich nature nature of of this this requires requires that that fractionation played played aa substantial substantial role role in their development although in addition fractionation addition contamination contamination by crustal material cannot be ruled ruled out. out. Upwards, intercumulus granophyre becomes becomes important important replace olivine olivine and and pyroxene pyroxene as common phases and modal apatite while amphiboles replace apatite decreases. At decreases. At one onelevel levellarge largeeuhedral euhedral zircons zircons are areabundant. abundant. the basal basal chill zone, zone, plagioclase averages about An60, An60, ranging to rims Excepting the rims of of An20 An20 normal zoning zoning about about An10 AnlO is is common common but but less so in the in the the most most felsic felsic units. units. Moderate Moderate normal the more feldspathic feldspathic adcumulates adcumulates Plagioclase Plagioclase in the basal basal Chill Chill Zone Zone is is more morestrongly strongly zoned zoned but but value of of An42. An42. This This corresponds corresponds with with the the whole whole rock rock chemistry. chemistry. Olivine ranges ranges has an average average value from Fo65 near the base to Fo25 in the ferrodiorites. ferrodiorites. The TheChill ChillZone Zoneolivines olivineshave haveintermediate intermediate Clinopyroxene values values are are Wo42En39Fsl9 Wo42En39Fsl9 to to Wo35En25Fs4O Wo35En25Fs40 in the the ferrodiorite ferrodiorite values. Clinopyroxene demonstrating somewhat somewhat more Fe-enrichment than in the the FRI. PRI. Rearing Pond Pond Intrusion Intrusion The Rearing Rearing Pond Intrusion is unique unique in in several several respects, respects, although although itit somewhat somewhat PRI. It is emplaced emplaced at the top of the the MLI MLI and and with with the the resembles the the Picritic Zone Zone of of the PRI. exception of of its extreme western end end where where it intrudes metavolcanics exception extreme western metavolcanics itit is enclosed entirely by other intrusive intrusive rocks. rocks. Like the Picritic Zone it is is composed composed of of olivine olivine rich rich rocks rocksand andexhibits exhibits some modal modal layering. layering. Textures and mineralogy were studied by Olmsted, Olmsted, 1979, 1979, but but much muchwork work remains to to understand its chemistry. chemistry. Based understand its Based on mineralogy mineralogy it too is is differentiated differentiated but not not to to the the degree of of the MLI. Olmsted degree Olmsted1979, 1979, proposed proposed an an elongated elongated funnel funnel shape for the the intrusion intrusion and and on on suggested that that it has experienced the tilting typical of the the basis of orientation orientation of layering suggested the region. region. Near its outer outer perimeter perimeter is is found found aa peridotite peridotitelayer layercomposed composed largely largely ofofcumulus cumulusolivine olivine clinopyroxeneand andplagioclase. plagioclase. The uppermost rocks are gabbro and quartz with intercumulus clinopyroxene gabbro lying above a large large central central troctolitic troctolitic unit. unit. Abundant Abundant olivine in the RP RP averages averages about about Fo80 Fo80 and andisisrather ratherstrongly stronglyserpentinized. serpentinized. The very high high Mg#'s Mg#'s of the the rock rock analyses analyses are are in inline linewith withthis thisprimative primativecomposition. composition. Plagioclase composition compositionranges rangesfrom fromAn85 An85 in in lowermost lowermost rocks rocks to to An50 An50 in the Plagioclase the gabbro. gabbro. Pyroxenes are equally primative with compositions CPX En49Wo46Fs5 En49Wo46Fs5 and OPX OPX ranging rangingfrom from En80 in the troctolite troctolite and peridotite to En68 En68 in in gabbro. gabbro. we will make one stop that While extensive study intrusion we that While time time will not permit extensive study of this intrusion will provide provide an an opportunity opportunity to examine examine two two of of the thethree threemajor majorrocktypes. rocktypes. to the Mineral Lake References to Lake and and Rearing Rearing Pond PondIntrusions. Intrusions. Leighton, M.W., M.W., 1954, Petrogenesis of of a gabbro-granophyre Leighton, gabbro-granophyre complex in in northern, northern, Wisconsin. Wisconsin. BulI.GeoLSoc.America, v.65, p.401-442. Bull.Geol.Soc.America, v.65, Olmsted, J.F., J.F., 1969, 1969, Petrology of the Mineral Mineral Lake Lake Intrusion, Intrusion, northwestern northwestern Wisconsin. Wisconsin. in in Y.W.lsachsen, Origin of Anorthosite and Related Y.W.Isachsen, Related Rocks, Rocks, p.149-162, p.149-162, N.Y.State N.Y.State Mus. Mus. and and Sd. Sci. Serv. Sew. Memoir. Memoir. 1979, Crystallization Crystallization history history and textures of the 1979, the Rearing RearingPond Pondgabbro, gabbro,northwestern northwestern Wisconsin. Am.Mineral., Am.Mineral., v.64, v.64, p844-855. p844-855. Seifert, K.E., Windom,K.E., 1985, Mineral Seifert, K.E., Peterman,Z.E. Peterman,Z.E, and Windom,K.E., Mineral Lake Lake layered layered intrusion, intrusion, NWWisconsin. Geol. Soc. Soc. America Abs. with Prog.,17, NWWisconsin. Geol. Prog.,17, p.712. p.712. of the Mineral , in prep., prep., Geochemistry Geochemistry of Mineral Lake Lake pluton, pluton, NW NW Wisconsin. Wisconsin. C-6 �Field Field Trip TripStop StopDescriptions Descriptions Potato Potato River RiverIntrusion Intrusion All All of of the the stops stopsare are on on county county forest forest land, land, the the roads roads are arequite quite good good there there should shouldbe beno no difficulty difficulty with access. access. Watch Watch for forticks ticks ininthe thespring, spring,logging loggingtrucks trucksininthe thesummer, summer,deer deerhunters hunters in in the the fall fall and and snowmobiles snowmobiles in the winter. winter. The The locations locations are are shown shown in in Fig. Fig. 22 which which shows shows aa portion Theintrusion intrusionessentially essentiallyparallels parallelsWI WlHwy.77 Hwy.77 portion of of the the Saxon Saxon 7.5' 7.5' quadrangle quadrangle map. map. The between between Mellen Mellen and Hurley. Hurley. The The trip tripbegins beginsat atthe theintersection intersectionof of highways highways 77 77 and and122 122inin Upson, Upson, WI. Wl. STOP Hwy. 122 122north northofofUpson. Upson. Picritic PicriticZone Zonerocks. rocks. along Hwy. STOP11 along Proceed Proceed north north from Upson Upson on Hwy. Hwy. 122 122 over over the the range range of of hills hillsthat thatmarks marksthe the Keweenawan, Powdermill Powdermill Group When the the road roadstraightens straightens to to aanortherly northerlyheading heading(-4.5 (-4.5 Keweenawan, Group lavas. lavas. When mi. Upson)look look for foraagravel gravelroad roadto tothe theright right(E). mi. NNof of Upson) (E). Turn Turn onto onto the the gravel gravelroad roadand andpark parkafter after about South of of the the road roadisisaasmall smalloutcrop outcropofofmassive massivetroctolite troctolite(Tables (Tables1&2) 1&2)ofofthe the about 50 50m. m. South Picritic Picritic Zone. Zone. On Onthe thesouth southside sideofofthe theoutcrop outcropthe thebasal basalcontact contact of of the the Picritic PicriticZone Zone with with altered Zone can be seen. altered pegmatitic pegmatitic gabbro gabbro of the Main Zone seen. The Thetroctolite troctoliteisismassive massiveand andhas has adcumulate adcumulatetexture. texture. Plagioclase Plagioclase grains in in this this rock rockare areequant equantininshape shapeopposed opposedtotolath-shaped lath-shaped as Olivine isis anhedral anhedraland andappears appearstotohave haveundergone undergoneconsiderable considerable as ininthe theother othertroctolites. troctolites. Olivine Withcareful carefulstudy study you you can can observe observe small small grains grains of of Cr-rich Cr-rich spinel spinel in in the the adcumulus adcumulus growth. With troctolite troctolite (>7 (>7 wt.% wt.% Cr203; Cr203; whole whole rock rock Cr Cr up uptoto500 500ppm). ppm).InInterms termsofoftexture texture(massive, (massive, Fo67), and and Cr-spinel; Cr-spinel; this this outcrop outcrop isis adcumulate), mineral mineral composition composition (the most primitive, An70, Fo67), adcumulate), unique unique ininthe thePotato PotatoRiver RiverIntrusion. Intrusion. ItIt may may represent represent an an addition additionof of mafic maficmagma magmaunrelated unrelatedtoto the PicriticZone. Zone. the rest restofofthe thePicritic Return to to Hwy.122 Hwy.122 and proceed N about 200 m m to to aa second second gravel gravel road, road, this this time time to to the the Return left left(W), (W), and anddrive driveabout about200 200mmWWand andpark. park. Directly Directly south south isisanother anotheroutcrop outcropofofPicritic PicriticZone Zone rock. Here again again the the base base of of the the Picritic PicriticZone Zonewith withunderlying underlyingMain MainZone Zonepegmatitic pegmatiticrock rockcan can rock. Here be ThePicritic PicriticZone Zonerock rockininthis thisexposure exposureisisananolivine olivinerich richpicrite picritecontaining containing up up to to 50 50 be seen. seen. The modal modal % %olivine. olivine. The Thetexture textureisismassive massivetotolayered layeredwith withfaint faintrhythmic rhythmiclayering layeringvisible visibleininplaces. places. Large Largeoikocrysts oikocrystsof ofclinopyroxene clinopyroxeneenclose enclose olivine olivineand andplagioclase. plagioclase. Cr-spinel Cr-spinelisislacking lackingand and whole whole rock rock Cr Cr content content is is in in the the range range of of 150-200 150-200 ppm. ppm. Nickel Nickelcontent contentisisalso alsolow lowfor forsuch such olivine olivine rich richrocks rocks in inthe the range range of of 700-750 700-750 ppm. ppm. Inasmuch Inasmuchas asthe theAn Anand andFo Focontents contentsare arenot not high highrelative relativeto to the therest restofofthe theintrusion, intrusion,this thisoutcrop outcropmay mayrepresent representaazone zoneofofaccumulation accumulationofof mafic maficminerals. minerals. STOP Alongthe thePotato PotatoRiver. River. Top TopofofMain MainZone ZoneII.II. STOP 22 Along Continue west west on on the the gravel gravel road road about about three three miles miles where where the the road road ends ends at at aa Continue turn-around. turn-around. Just Just to to the the west west isis the the Potato Potato River River and and aa small small waterfall. waterfall. The Therock rockhere hereisis quartz-bearing quartz-bearingleucogabbro leucogabbro (Tables (Tables 11&&2). 2). In Inaasmall smalloutcrop outcropjust justup upfrom fromthe theriver riverthe the distinctive distinctivereddish reddishcolor colorofofweathered weatheredinterstitial interstitialAlk-Feldspar Alk-Feldsparcan canbebeseen. seen. This Thisrock rockisis composed composedofofplagioclase, plagioclase,clinopyroxene, clinopyroxene, Fe-Ti Fe-Tioxides oxidesand andinterstitial interstitialpatches patchesofofmicrographically micrographically intergrown intergrown quartz quartz and and alkali-feldspar. alkali-feldspar. The Thefeldspar feldsparcontains containssome some iron ironwhich whichproduces producesthe thered red color colorwhen whenaltered. altered. The Theoutcrop outcropininthe theriver riverprovides providesan anexcellent excellentexample exampleofoflamination laminationofof plagioclase plagioclasegrains. grains. The Theoutcrop outcropisiscut cutbybyaphanitic aphaniticbasaltic basalticdikes. dikes. Further Furthernorth northalong alongthe theriver river the theintrusive intrusivenature natureofofthe theUpper UpperZone Zonerocks rockscan canbe beseen. seen. STOP Alonggravel gravelroad roadwest west of of Upson. Upson. Main MainZone ZoneI.I. STOP 33 Along Retrace Retracethe the route routeto toUpson Upsonvia viaHwy Hwy122. 122.Turn Turnright right(W) (W)on onHwy.77, Hwy.77,proceed proceedabout about3 3 miles milesand andturn turnright right(N) (N)on ona agravel gravelroad, road,proceed proceed— 2,5 2,5 miles milesand andpark parkalong alongroad. road. Several Several low Theyare areolivine olivinegabbros gabbros(Tables (Tables11&& lowoutcrops outcropsalong alongthe theroad roadare aretypical typicalofofMain MainZone ZoneI. 1. They - C-7 �C) Figure 2 �Table 11 Modes Modes Table SAMPLE SAMPLE ROCKTY PE ROCKTYPE P LAG. PLAG. MINERAL LAKE MINERAL LAKE INTRUSION INTRUSION Chill 6'6-5-65" -5-65" Chi11Zone Zone Ave.M656-8 Ave.MG56-8 Chill ChillZone Zone MO-4 MG- 4 Olivine Gabbro OlivineGabbro MO-6 MG-6 Gabbro Gabbro MG—9 MG-9 Gab. Anorthosite Gab.Anorthosite ""11-9" 1 1-9" Gab. Gab.Anorthosite Anorthosite "3-10" "310" Gab.Anorthosi te Gab.Anorthosite "25-42" 42" Ferrodior ite "25Ferrodiorite MG-16 Q. Monzodio r ite MG16 Q.Mon2odiorlte MO-i? MG17 Q.Monzodiori te Q.Monzodiorite MG- 18 MG18 Granophyre Granophyre MO-19 MG19 Granophyre GranopI'i're 51.2 55.5 55.5 20.0 20.0 40.0 40.0 80.0 80.0 79.5 79.5 78.0 78.0 61.5 61.5 40.0 40.0 30.0 30.0 OL CPX 20.2 3.6 2.5 40.0 *325 9.3 2.9 14.3 OPX 10.8 *38.0 *59.0 *18.0 *127 OXIDE OXIDE 5.4 5.0 HLBD. HLBD. BlOT. BIOT. AP AP 3.8 4.5 4.0 TR TR K-SPAR K-SPAR QZ QZ OTHER OTHER 1.0 1.0 1.0 2.0 5.1 *11.9 TR *8.0 1.4 1.7 1.7 0.7 6.2 2.0 9.2 0.4 1,3 1.8 30.0 5.0 10.0 13.0 3.0 30.0 49.0 20.0 48.0 30.0 #68.0 2.0 10.0 5.0 5.0 TR 1.0 4.0 0.4 3.0 TR TR 2.9 12.0 2.0 (-1 I * POTATO POTATO RIVER RIVER INTRUSION INTRUSION 84-40D Troctollte Troctolite 83-28C Picrlte Picrite 84-43B Q. Leucogabbro Leucogabbro 84-71A Granophyre Granophyre 84.49A OlivlneOabbro Olivine Oabbro 84-516 LayeredTroctoli Layered Troctoli 84-53D OlivineGabbro Olivine Gabbro 84-54C Quartz Gabbro QuartzGabbro 76.0 76.0 25.0 25.0 66.0 66.0 65.0 65.0 65.0 65.0 52.0 52.0 64.0 64,0 50.0 50.0 20.0 55.0 3.0 15.0 1.0 2.0 3.0 3.0 2.0 5.0 2.0 1.0 1.0 25.0 5.0 15.0 45.0 18.0 15.0 1.0 15.0 TR 3.0 5.0 40.0 REARING POND INTRUSION INTRUSION W-39 W- 163 W-163 W—74 W-74 W-6 W-164 01 Oabbro Oabbro Troctolite Troctollte Peridotite Peridotite Gabbro Gabbro Gabbro Gabbro 54.6 52.8 52.8 24.3 24.3 55.6 55.6 52.7 52.7 13.8 25.6 39.7 72.4 0.5 5.1 0.2 13.2 25.5 5.4 2.2 2.2 15.7 7.6 *Iflcludes undistinguished CPX && OPX OPX undistinguished *IncludesCPX # Largely Largelyaltered alteredgranophyric granophyric material material Page 1 0.6 0.6 0.6 1.1 0.3 4.3 14.6 0.1 TR 1.0 3.2 0.4 TR �Table 22 Analyses Analyses Table Mineral Mineral Lake Lake Intrusion Intrusion MO 55,56 MO - 4 MG - 9 116 MO55,56 MG-4 MG-9 MG-1425-42 MG-16MG-17MG-18 MG-19 - 14 25-42 MO - 16 MG - 17MG - 18 MG - 19 58 Ave. 58 Ave. S102 47.70 48.30 43.56 56.40 60.00 Si02 47.70 44.30 50.40 74.40 75.60 1102 2.57 1.86 1.23 0.87 3.31 1.75 Ti02 2.57 1.67 0.26 0.16 A1203 15.40 9.66 24.10 22.60 13.61 15.20 14.20 A1203 1 5.40 12.80 12.40 Oxides Oxides 14.60 0.21 6.62 8.76 2.75 0.38 0.44 FeUt Feot MnO Mno MgO Mgo CeO CaO Na20 Na20 K20 K20 P205 P 205 LOl LO I ? C TOTAL TOTAL ND 20.70 0.28 14.30 6.05 1.98 0.42 0.20 ND 5.65 0.08 2.06 10.90 4.30 0.76 0.39 ND 8.42 0.10 5.42 20.60 12.50 0.31 0.18 9.46 0.13 2.31 1.91 10.40 3.86 0.10 3.66 9.35 2.62 0.42 5.33 3.39 0.33 1.67 0.54 5.27 4.15 2.28 0.60 ND ND 2.11 ND ND 2.29 0.04 0.18 0.62 3.90 5.47 0.04 Mellen Rearing Rearing Pond Pond Mellen Granite Granite Meann=4 RP Mag Mag 87-1 1 p Mean n=4 RP 69.26 0.45 13.88 4.00 0.07 0.40 1.92 0.04 0.08 0.38 4.07 5.35 0.03 ND ND 1.45 44.47 1.18 18.86 37.22 0.32 4.30 7.84 16.41 0.11 0.27 29.19 2.85 0.13 0.09 10.90 10.13 3.47 1.89 5.61 0.05 0.36 0.12 1.04 ND ND 0.01 99.43 99.75 99.87 100.40 99.11 99.71 99.67 100.00 100.03 99.68 95.86 90.79 45 55 39 53 24 25 26 13 7 15 71 76 0.96 2.36 0.44 3.34 3.54 2.48 16.74 0.85 0.92 2.34 4.49 30.69 44,21 3.08 0.00 6.12 0.00 6.70 0.78 3.67 3.35 6.34 2.50 22.30 24.28 0.00 0.00 9.79 1.18 1.31 0.07 0.30 0.27 0.02 1.53 0.09 0.37 0.50 32.44 29.84 2.84 0.00 29.48 0.00 3.63 0.00 0.11 2.02 3.33 12.47 28.70 20.04 0.00 7.62 2.48 21.46 0.00 1.32 2.91 2.34 0.67 0.58 Mg# C/PW Norms Ap Mt Ii 4.91 Ity 2.25 23.35 28.65 0.00 0.00 10.05 16.50 01 10.40 Or Ab An NE a Di 16.22 0.00 0.00 10.27 8.40 38.14 1.99 1.65 0.59 28.80 43.90 2.05 0.00 4.41 0.00 15.90 13.29 13.83 3.18 13.49 35.17 13.41 0.00 10.45 7.56 13.17 0.00 0.31 32.06 32.20 1.13 0.00 30.04 0.52 2.55 0.00 0.65 0.87 33.56 29.73 5.80 0.00 21.32 11055 ,56,58AVE, ChiliZone, OL Gabbro, STOP 14,MG—9. STOP7;7;MGMG14,MG-9,(3ab.Anorthosite, Gab.Anorthosite,STOPS STOPS99&&10 10 M655,56,58AVE, ChillZone,MO-4, MO-4,Ol.Gabbro, 25—42 MG 7, Q. Monzogbbro, STOP 25-42 Ferrodlorlte, Ferrodiorlte, MO— 16, 16,1 17,Q. Monzogabbro, STOP11 11 - - MO— MO 18, 18, 19,Oranophyre, 19, Oranophyre,STOPD STOP D RPMAG, Troctollte; 87— STOP 2 RPMAO, Troctolite; 87- 1liP1PPeridotite, Peridotite, STOP1 12 Page Page1 1 1.00 6.20 0.00 2.21 16.65 43.65 0.00 0.00 6.34 2.18 24.58 1.21 11.96 0.00 0.00 2.82 9.48 70.06 �Toble Table 2 Analyses Analyses PotatoRRiver Potato i v e r Intrusion PRI Bulk Compositions P R I Estimated Bulk Compositions 84-40D 83-28C 84-40D 83-28C 84-43B 84-43B84-71A 84-71A84—49A 84-49A 84-S1B 84-51 B 84-53D 84-53D 84-54C 84-54C , <-) I S102 si 02 1102 Ti02 A1203 Fe203 Fe203 FeO FeO MnO Mno MgO Mgo CeO CaO Na20 Na20 K20 K20 P205 P205 LOt LOI TOTAL TOTAL 46.06 40.91 51.10 0.41 0.99 6.06 3.76 23.32 0.33 19.67 4.80 0.86 0.16 0.06 1.63 19.62 1.94 20.20 2.27 7.92 0.12 9.16 10.26 2.29 0.23 0.01 ND 5.72 0.12 3.58 11.73 3.07 13.76 5.23 5.28 0.16 1.07 0.51 3.20 3.90 3.18 0.17 0.11 ND ND 61.98 0.77 ND 47.98 1.12 19.59 1.78 8.12 0.12 6.57 11.17 2.61 0.44 0.12 44.35 0.23 14.36 2.56 14.56 0.21 14.70 6.75 2.05 0.20 0.02 ND ND 48.56 1.62 19.48 2.89 7.88 0.13 5.40 9.49 2.92 0.54 0.17 49.31 3.49 15.65 3.36 9.28 0.17 4.22 10.47 2.74 0.61 0.29 ND ND MZ M Z IIIII I PZ MZ M Z IIII 48.64 0.97 47.46 0.75 50.88 50.74 1.25 18.70 1.58 17.91 1.90 10.31 20.62 2.03 6.36 0.12 3.01 14.87 MZ MZ I I 9.10 0.13 7.86 2.66 0.32 0.07 0.15 9.50 9.23 2.50 0.38 0.03 ND ND 10.13 4.51 10.77 3.06 0.47 0.13 ND 4.98 9.78 0.21 3.11 9.01 2.86 1.16 0.76 99.59 100.16 100.12 100.20 100.92 99.19 98.64 99.62 99.99 99.08 66 61 50 18 59 65 52 42 61 62 54 0.0 3.3 0.8 0.1 0.4 2.8 0.3 2.5 0.3 - 0.1 2.6 3.1 2.1 0.9 7.2 3.0 26.0 38.3 0.0 2.4 2.6 1.2 1.8 1.9 1.4 1.4 1.5 19.1 33.6 22.1 17.4 10.8 14.1 40.4 0.0 0.0 29.4 0.0 0.0 0.7 4.9 6.6 3.6 23.2 28.6 0.0 3.7 0.2 2.3 1.9 3.7 0.4 0.4 4.2 0.1 6.4 0.3 2.9 2.4 2.8 25.9 41.1 0.0 0.6 9.4 14.8 0.0 62.27 1.71 12.89 4.31 5.68 0.19 2.01 3.73 3.55 3.65 0.44 ND ND 98.93 UZ 100.49 100.43 d Mg# Mg* 31 31 C/PW Norms Ap Mt Ii Or Ab An NE Q Dl Fly 01 19.4 44.2 0.0 0.0 5.4 3.7 20.8 12.1 0.0 0.0 0.0 4.0 11.6 3.2 12.2 15.4 7.8 14.1 5.4 4.1 49.9 0.0 0.0 12.5 40.5 9.1 3.1 3.2 24.7 38.5 0.0 0.0 6.2 15.8 3.2 22.5 38.1 17.6 10.6 0.0 0.0 9.5 9.8 0.0 14.0 2.8 2.3 21.2 36.5 0.0 0.0 7.4 7.1 21.5 1.8 1.0 7.2 5.7 6.9 24.2 24.3 0.0 7.0 6.3 3.3 21.6 30.0 8.5 0.0 12.8 10.6 5.9 6.5 0.0 0.0 84—40D Massive MassiveTroctolite, Troctolite, 83-28C Picrite, STOP 84-400 STOP 11;; 83—43B, 83-43B, Q.Leucogabbro, Q.Leucogabbro, 84—7 8 4 - 7 1A, lA, Orenophyre, Oranophyre,STOP STOP 2 84—49A, O1.Oabbro, STOP 3; 84-51 B, Layered Troctolite, STOP 4; 84-53D, O1.Gabbro, STOP 5; 84-54C, 84-49A, Ol.Gabbro, STOP 3; 84-5 16, Layered Troctolite, STOP 4; 84-53D, Ol.Oabbro, STOP 5; 84-54C,Q.Gabbro, Q.Gabbro,STOP STOP 66 EstimatedBulk BulkCompositions: Compositions:MZ MZI,I,Main Zone1;I;PZ, Picritic Zone; MZ 11, II,Main II; Estimated Main Zone PZ, Picritic Zone; MZ MainZone Zone 11; MZ 1 1 ,Main Ma1nZone Zone ill; III;UZ, UZ,Upper UpperZone Zone MZ 1lit, Page 2 17.5 �2) composed of cumulus cumulus plagioclase plagioclase (An64-62) (An64-62) and and olivine olivine (Fo62-57) (Fo62-57)along alongwith withintercumulus intercumulus clinopyroxene and Fe-Ti clinopyroxene Fe-Ti oxides. oxides. Rhythmiclayering layeringininthe thePicritic PicriticZone. Zone. Along gravel gravel road road west west of of Upson. Upson. Rhythmic SSTOP T O P 44 Along Continue about about one mile N along Continue along the the gravel gravel road road to to an anovergrown overgrown logging logging road road to to the the There is active logging in the area and roads spring spring up from from year year to year. year. To Todistinguish distinguish correct one road to to the the right right directly directly opposite opposite this this one one as as there there are are in in the correct one there there should not be a road other places. places. Park on the overgrown 00 m). overgrown road and walk W up up aaslight slighthill hilltotothe thetop top(50-1 (50-100 m). At the top of of the hill turn right (N) into 100-200 m, m, Here Here is is aa low lowoutcrop outcrop of of layered layered into the woods woods 100-200 troctolite of Picritic Zone. Zone. The troctolite of the the upper upper part of the Picritic Thedistinctive distinctivefeature featureof of this thisrock rockisisrhythmic rhythmic rich layers layers alternate alternate on the the scale scale modal layering. Plagioclase (An67.5) (An67.5) rich and olivine (Fo63.5) rich of centimeters. grains are laminated in centimeters. Lath-shaped plagioclase grains in the the leucocratic leucocraticlayers. layers. Here the plagioclase magnesian respectively than in in the the adjacent adjacent Main Main plagioclase and and olivine olivine are more calcic and magnesian Zone rocks but less so so than than in inthe themassive massivetroctotites. troctolites. This part of the the Picritic Picritic Zone Zone is is the the only only of the intrusion that exhibits rhythmic layering. layering. What part of exhibits rhythmic What do you you make make of of that? that? left. left. STOP 55 Along Main Zone Zone IIII rocks. rocks. Upson. Main STOP Along gravel gravel road W of Upson. Continue along along gravel gravel road road about about 1.5 1.5miles. miles. As the road Continue road turns turns left left to to round round aa hill hill stop stop when you you are are heading heading W W and and park. park. The when The hill hill isisunderlain underlain by by olivine olivine gabbro gabbro of of the the Main Main Zone Zone III1 (Tables 1 & 2). 2). This is is cut cut by by aatypical typicalKeweenawan Keweenawan high high Ti-P Ti-P dike. dike. This is about about the the highest highest occurrence of of olivine gabbro in the occurrence the intrusion. intrusion. Plagioclase here strongly laminated, laminated, its its here is not strongly composition is olivine composition composition is about about Fo55. Fo55. composition is about An60 and olivine STOP Zone lii STOP 66 Along Along gravel gravel road road rest rest of of Upson. Upson. Main Main Zone Ill rocks. rocks. Continue Continue on the gravel gravel road road for for about about 11 mile until there is another another hilt hill just just to the the left. left. If you reach reach a small lake on the the right right you you have have gone gone too too far. far. This hill hill is is composed composed of of quartz quartz diabase dike. bearing gabbro bearing gabbroofof the the Main Main Zone Zone Ill Ill (Tables (Tables 11 && 2) 2) also also cut cut by by a diabase dike. The The rock rock here here is composed composed of of cumulus plagioclase, clinopyroxene clinopyroxene and and Fe-Ti oxides with interstitial quartz and alkali feldspar. feldspar. This is the the lower lower part part of of the the Main MainZone Zone Ill; Ill;after afterthe theappearance appearanceofofcumulus cumulus oxides, oxides, but before cumulus cumulus apatite. apatite. Return to to Hwy.77, Hwy.77, turn turn right (W) (W) toward toward Mellen Mellen which which is is about about 13 miles. miles. On Return Onreaching reaching Mellen proceed proceed N N on Hwy.13 through Mellen through town town about about 11 mile. mile. Turn right Hwy 169 169 to to Gurney Gurney right on Hwy following the Falls State State Park Park where we will will eat eat lunch. lunch. following the signs signs to Copper Falls STOP A walk the the short short distance distance along along the the trails trails to to and andjust just beyond beyond You are encouraged to walk Brownstone Falls Falls where where the the contact between the volcanics (reversed polarity) and the upper Brownstone upper Keweenawan may be seen. Continuing along along the the path beyond the Brownstone seen. Continuing Brownstone Falls Falls you are are proceeding up up section section through through the Copper Harbor Conglomerate, proceeding Conglomerate, the Nonsuch Formation and into the the lower lower part part of of the the Freda Sandstone. Sandstone. As into As you you will will see see the the units units are are vertical vertical here here with with strike uppermost volcanics at the Brownstone Brownstone Falls are rhyolite rhyolite flows overlying strike about about N60E. N6OE. The uppermost basalt. One here is is a fault. basalt. One of of us usat atleast least(JFO) (JFO)thinks thinks the the MidMid-Upper Upper Keweenawan Keweenawan contact contact here fault. What's yours? yours? Mellen Granite Granite Brief optional stops along the road in in both both cases cases to to observe observe the the porphyritic porphyritic granite. C-I 2 �___p33/ / ' ,- t4 • ;:•: i•4 'Ja_? •. -N --. :::: I .; -= - _, - _.•j. I i JQ -ttT ':i' • •'t -- S — - • . 6 — • LaM j — I ON - 5 - %O $437 rL• - --- I • . — - ••- ---- •.. • - • 7 - ——— - --- - -, •- -•••, •• •-•— • —••-—•••••.- -i. S -:—---.:;.,' .— - - • . A14 — • • , - ——-- -. — -. — . '3O - -. T -•—--• 4-_-- ,- Figure 33 Figure • — •.— .- - — — --. —-—-' C-13 :- p—I - - N iL- .4 —. —-- T' , ;'J'=!> - E-. r--- ° •... •.. _/_4j . Liks •4•••• •J•' .• - - -— — - - -, '- t2 iJ--:—_ 1 —- - 1136 L - -' ' $114 - 15 - f-'j . - AS $133 - — "— •— ,coaj 20 -:1 \S — -- -:-- I - • E 7 I - -'-—-- I ENG I • .•. ; —;--'-- -: i- — t< Z --. - -' -- 1 -: -.--- -- -R — - - - / OQ -/ /--:.. —=-— OTJ JT •• .— - :.. :- . - - —. I - p::- Ii - . - -: — - T. - _- — -, ', - • I.. N\ 1 -L _ :, • .1\_j'\ \ —.4 Nort -,: •. ---'-,----- •.-• 1z2!a .Grw.ipll P.--. -. - - •- •' .-x- 23. - c '7' 402_ I 2 I •••(' A . ) 42 776 .r i _: i1 • 1 r1" I °:— -•t 7 I/ / 8tPjsch i• I.. - (I -• -: M -- 29 - �Brecciaalong alongthe theW W side side of of Hwy Hwy 13 about 1 mile N of STOP B B Intrusive Intrusive Breccia of Mellen. Mellen. \ of gabbro enclosed in coarse Blocks of coarse grained grained granite. granite. Note how itit is is possible possibleto to mentally mentally many of of the the gabbro gabbro fragments fragments back back together. together. Also the granite. granite. 'fit many Also note lack of chilling of the Proceed N on Hwy Hwy 13 13 about about 11 mile and turn left onto County County Hwy C. Continue W W about about 3 miles where road turns right (N), continue N 1/2 112 mile. mile. Turn left on gravel road road proceed proceed W about 1/2 112 mile to top top of of rise. rise. STOP C C Massive Mellen Granite cut by by dikes. dikes. outcrops of of granite granite on on both both sides sides of of road. This is Stop at top of hill where where you see outcrops road. This private land so please respect respect the the owners owners fence. fence. Walk Walk south south of of the the road roadto toexamine examinetextures textures and dike occurrences. occurrences. Continue along road, road,first firstW W one one mile mile then then SS one one mile mile to to a T in the Continue along the road. road. Turn Turn right right (W) (W) proceed W W 112 1/2 mile mile to to a 4-corners. proceed 4-corners. Turn Turn left left(S) (S)(This (Thisbecomes becomesNational NationalForest Forest Road Road188 188 .).) continuing for for about about22 miles milesto to aa gravel gravel road road left left to to English English Lake. Lake. Please continuing Please be be respectful respectful here as into the the English English Lake Lake road, road, the natives natives are are sometimes sometimes unfriendly. unfriendly. Turn left (roughly (roughly S) into about 114 1/4 mile mile to to an unimproved but but passable passable road to the right. proceeding about right. Look for a sign sign stating the the name E. Ceres. Proceed carefully carefufly about about 114 1/4 mile looking for for a fork stating fork to to the the right. right. There is an inconspicuous 2-wire power power line line overhead overhead that that follows follows this this fork of the There inconspicuous 2-wire the road. road. ItIf you you to the the top of the arrive at a cottage on the lake arrive lake you have have gone too too far. far. Return to the hill. hill. Park Park in in the the fork far enough enough so others can pass to the the cottage. cottage. STOP 7. 7. Basal contact of the the Mineral Mineral Lake Lake intrusion. intrusion. Walk along under the power power line (200 m) to the under the the third third power power pole pole that that isis planted planted in inthe the outcrop. The for many many drill core holes in in the the outcrop. The hilt hill drops drops rapidly rapidly here into a small small valley. Look for rock. here is fine grained gabbro rock. Most of the rock exposed here gabbro but the rock on the the SE SE corner corner of of the outcrop is for this contact and look is hornfels. hornfels. Look for look for for inclusions inclusions of of hornfels hornfels within within the the fine fine grained gabbro. gabbro. The The texture texture of of the the gabbro gabbro here here at at the thecontact contact isisintergranular intergranular with with very very (Ol.-Fo40, Cpx. elongate Cpx. Wo40 Wo40 (An42-45). (6-5-65 && MG 55 etc. etc. Tables 1 & 2). 2). (01.-Fo40, elongate plagioclase plagioclase (An42-45). Fs26) Note Note that that back along along the the power line away from the En34 Fs26) the contact contact the the rock rock gradually gradually becomes more coarse and and the the texture texture subophitic. subophitic. Proceeding southwesterly through the the woods woods across a small valley valley to the top of the the next next hill hill where where there there are are aanumber number of ofoutcrops outcropsofofbasal basal olivine rich rich gabbro gabbro (MG-4). (MG-4). Return via the power power line. line. STOP 88 Layered Zone. Olivine Gabbro and "Pegmatitic" and Layered Zone. Return to to FR FR 188. FR187. 188. Turn Turn left, left, W, W, proceed proceed about about 2.5 2.5 miles miles to to intersection intersection with with FR187. Turn right, continue westerly about about 112 1/2 mile mile to to a driveway driveway left left into the home of Harold continue westerly Harold Smith, Smith, proceed about 1/2 Park near near the the house house and and seek seek permission. permission. Walk Walk down to 112 mile mile to to the the house. house. Park the beach and and left left to to the south south end end of of the beach and into the trees to the first the first outcrop. outcrop. This is is 600 m above the base Return to to the car and an olivine gabbro about 600 base of of the the intrusion. intrusion. Return and back back along the the road about about 318 3/8 mile mile to to the the base base of of a steep rise in the road. along road. Small outcrop on W W side side of the road gabbro. This unit miles road of of very very coarse coarse "pegmatitic" "pegmatitic" gabbro. unit has has been been mapped mapped over two miles along the north side of Mineral Mineral Lake Lake and beyond beyond and and represents represents an an important important horizon horizon in in the the intrusion. intrusion. If the water water in the lake is very low low we may may cross cross the the river river where where itit exits exits the the lake lake to to that occurs just just above the pegmatite. examine modal layering that pegmatite. Olivine continues as a minor minor above this this level but but is no longer abundant. phase above abundant. The The rock rockisisexceptionally exceptionally feldspathic feldspathic above. above. c-i 4 �\ Briefly: Spotted Anorthositic Gabbro STOP 9 Briefly: Gabbro Return to to FR 187, (Just 187, turn left (W) about 1/2 112 mile to aa large large outcrop outcrop on on the the right. right. (Just this exposure look for for low low blasted outcrops outcrops on on either either side of the road before this exposure look road which which are are good good Poikilitic Anorthositic Anorthositic Gabbro Gabbro (MG-14, (MG-i 4, 11-9). 11-9). An places to collect collect this this rocktype.) rocktype.) Poikilitic An excellent excellent 01. Fo65, Fo65, Opx Opx En66, En66,Cpx CpxWo42,En39,Fs19. Wo42,En39,Fs19. example showing a common texture. texture. Plag. Plag. An60, 01. 10 Briefly Briefly Laminated Gabbroic Anorthosite Anorthosite STOP 10 Continue Won on FR187 FR187 about about 1.5 1.5 miles miles then then north north at at "Pine "Pine Stump Stump Corner" Corner" and and then then Continue W the Lake "3" Campgrounds, Campgrounds,turn turn right right NE NE on on FR FR 189 go go 5/8 about one mile mile past the 518 mile stop at at what was was once once a small gravel gravel pit pit on on the the left left side side of of the road, now quite overgrown. Large what quite overgrown. Large polished outcrop outcrop of of anorthositic anorthositic rock rock in in back back wall wall of the pit (MG-9 Cpx (MG-9 ).). Plag. An60, Cpx Wo37,En29,Fs34. STOP STOP 1ii1 Ferrodiorite, Monzogabbro etc. (Transition (TransitionZone) Zone) Continue along along FR FR 189 189 Cross Continue Cross Brunsweiler Brunsweiler River at 2 miles, miles, continue continue about 3/4 314 mile mile beyond the the river to where turns to to an E E direction. direction. Walk straight straight S into into the the woods woods about about where the road turns 150 m where an an irregular irregular EW EW ridge ridge exposes exposes black black rust rust stained stained Ferrodiorite Ferrodiorite(25-42; (25-42; Plag. Plag, An45, An45, 01. Fo24, Opx. Opx. En37, Cpx.Wo38 En24 Fs38 Fs38 )) note cumulate and 0 1. Fo24, Cpx.Wo38 En24 and laminated laminated texture and and Retrace your your path path back back crossing crossing the the road to the north conspicuously finer grain grain size. size. Retrace north side side working your way north along the west side of the the hill. hill. Several outcrops here show gradually gradually (MG-16, 17). 17). increasing reddish felsic content content (MG-16, STOP 12 Rearing STOP RearingPond PondIntrusion Intrusion go back back over over the the Brunsweiler River past past aa gravel gravel pit pit on right and turn Turn around and go Brunsweiler River right on woods beyond. Continue woods road a few meters beyond. Continue northerly northerly about about 1/2 112 mile, mile, turn turn left left continue continue another 11 1/ 2 mile mile or less, less, then then left left again, again, and left left again again in in about about 1/4 114 mile. mile. (If you encounter encounter a another After the last OOm to a brook bridge over a brook brook go go back.) back.) After last turn turn proceed proceedcautiously cautiouslyabout about1 100m brook where the the road ends. where ends. An Anoutcrop outcrop on on your your left leftisisperidotite peridotite(W-74, (W-74,similar similar to to 87-i 87-111P)of the lower lower part of the Rearing intrusion. Walk along what remains the road (a path by now) Rearing Pond Pond intrusion. remains of the now) cross the jumping rocks, rocks, and and pick pick up up the the remains remainsofof the the road road on on the the other other side. side. AA few the brook jumping few meters meters beyond the the brook brook search search to to the the right right of of the the path for the the remains remains of aa picnic picnic grounds grounds (a (a couple couple large cliff cliff like like outcrops outcrops beyond. beyond. We of fire places is all all that's that's left) left) and several several large We will will work work our our way way around to the left and and circle the hill studying the rocks and their textures and features as we proceed remains of aa State State trout trout hatchery hatchery that that was was proceed (RPMag, (RPMag, 87-liT 87-1I Tand andW-163) W-163) . This is the remains abandoned at the beginning of of WWII. WWll. Good abandoned at GoodArchaeology Archaeology here. here. . STOP D D Granophyre Time Time Permitting Permitting Return to to FR 189, turn right and return to FR 187. 187. Proceed Proceed N on FR FR 187, 187, 1.5 1.5 miles milesto to the inflection inflection point pointofofan an"S" "S"turn turn(Large (LargeOutcrop Outcropononright) right)park park leftWWside sideofofroad. road. A few few the ononleft this point proceed on a meters SW into the woods is an an outcrop outcrop ot of aa granitic granitic rock. rock. From this of 290 about 300 meters, eventually up up a fairly tiring hill. heading of meters, eventually hill. Good exposures of Granophyre here. here. (MG-18, 19) 19) STOP E E Alternate Granophyre exposure. exposure. Morgan Alternate Granophyre Morgan Falls. Falls. From the the intersection intersectionofof FR FR 187 187 && 198 198 go go N 1/2 1/2 mile, mile, turn turn left left on on FR FR 193 193following following the the From Park in in the the lot provided and and walk walk the trail to the signs to Morgan Morgan Falls. Falls. Park the falls. falls. This is a spectacular foot high waterfall waterfall over over the the brick brick red granophyre. granophyre. Contact spectacular 100 foot Contact of of granophyre granophyre and and gabbro can can be seen west gabbro west of the falls along the upper part of the the ridge. ridge. C-15 �GENERAL GENERAL GEOLOGY GEOLOGY AND AND STRUCTURE STRUCTURE OF OF ARCHEAN ARCHEAM ROCKS ROCKS OF OF THE THE VIRGINIA VIRGINIA HORN AREA, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA HORN AREA, J.L. Welsh, Welsh, D.L. D.L. England, England, D.A. D.A. Groves, Groves, E. E. Levy Levy J.L. IIntroduction nt roduct ion The "Virginia "Virginia Horn" Horn" refers refers to to the the prominent prominent Z-shaped 2-shaped outcrop outcrop The pattern pattern of of Animikie Animikie Group Group rocks rocks present present in in the the Virginia-Eveleth Virginia-Eveleth area I ) , and and reflects reflects the the broad broad area of of the the Mesabi Mesabi Range Range (Fig. (Fig. 1), northeasterly trending trending anticline anticline and and syncline syncline into into which which these these northeasterly rocks have been folded. rocks have been folded. These These Proterozoic Proterozoic rocks rocks unconformably unconformably overlie Archean Archean basement basement rocks, rocks, which which are are exposed exposed north north of of the the overlie Mesabi Mesabi Range Range along along the the Laurentian Laurentian Divide. Divide. Supracrustal Supracrustal metavolcanic metavolcanic and and rnetasedimentary metasedimentary rocks and assorted assorted small small intrusive intrusive bodies bodies of of the the basement basement complex complex occur occur along along aa narrow narrow strip strip which which extends extends from from Mountain Mountain Iron Iron on on the the west west to to the the Aurora Aurora vicinity vicinity on on the the east, east, and and which which are are bordered bordered by by the the Giants Giants Range Range Complex Complex on on the the north. north. These These rocks rocks are are particularly particularly well well exposed exposed in in the the anticlinal anticlinal axis axis of of the the Virginia Virginia Horn, Horn, and and have have been been the the recent recent focus focus of of gold gold exploration. exploration. Previous Previous Work Work Until Until recently, recently, Archean Archean rocks rocks in in the the Virginia Virginia Horn Horn area area have have received received little little attention, attention, and and little little has has been been published published on on these these rocks. rocks. Brief Brief descriptions descriptions of of Archean Archean rocks rocks in in the the area area were were first provided by Leith (1903) as a result of his investigations first provided by Leith (1903) as a result of his investigations into into the the geology geology of of the theMesabi MesabiDistrict. District. J.W. J.W. Gruner Gruner also also investigated investigated the the Archean Archean rocks rocks during during his his studies studies of of the the Mesabi Mesabi District, District, and and reported reported an an occurrence occurrence of of visible visible gold gold in in aa felsic felsic porphyry porphyry body body (Grout, (Grout,1937) 1937). Sutton Sutton (1963) (1963) developed developed aa more more detailed detailed geological geological map map of of the the area, area, based based largely largely on on Gruner's Grunerls work, work, and and provided provided petrographic petrographic descriptions descriptions for for some some metasedimentary metasedimentary rocks rocks and and the thefelsic felsicporphyry porphyrybodies. bodies. . The The metavolcanic metavolcanic and and metasedimentary metasedimentary rocks rocks in in the the Virginia Virginia Horn Horn area area have have in in the the past past been been correlated correlated with with the the Ely Ely Greenstone Greenstone and and the the Knife Knife Lake Lake Series, Series, respectively, respectively, of of the the Vermilion District (e.g. Grout et al., 1951). Vermilion District ( e . g . Grout et al., 1951). As As these these rocks rocks are are physically physically separated separated from from the the Vermilion Vermilion District District by by the the Giants Giants Range Range Complex Complex and and were were correlated correlated only only because because of of lithologic lithologic similarity, similarity, designations designations of of Ely Ely Greenstone Greenstone and and Knife Knife Lake Lake Series Series for for rocks rocks in in the the Virginia Virginia Horn Horn should should no no longer longerbe beused. used. D- 1 �Regional map map of h e ffield i e l dtrip t r i area p a r eshowing a showingthe thegeologic g e o l o g i framework c framework and and the the F i g u r e 1.1. Regional Figure of tthe is a major unconformity s e p a r a t i n g g e n t l y d i p p ing The d o t t e d c o n t a c t major roads. roads. The major dotted contact is a major unconformity separating gently dipping P r o t e r o z o i c strata s t r a t a of of the t h e Animikie Animikie Group Group (on (onthe t h e south) s o u t h ) from from deformed deformed Archean Archean Proterozoic rocks. The Animikie Animikie Group, Group, consisting c o n s i s t i n g of of the t h e Pokegama Pokegama Quartzite Q u a r t z i t e and and Biwabik Biwabik rocks. The Iron-Formation ( open c i r c l e s 1 and t h e V i r g i n i a Formation ( d i a g o n a l r u l e ) is is Iron—Formation (open circles) and the Virginia Formation (diagonal rule), invaded by gabbroic rocks of Keweenawan age (1000 Ma) i n t h e s o u t h e a s t c o r n e r of invaded by gabbroic rocks of Keweenawan age (1000 Ma) in the southeast corner of t h e map map area. area. The The field f i e l d trip t r i p stops s t o p s are a r e all a l l within w i t h i n Archean Archean terrane. terrane. the , D- 2 �Lithologic U n i t s Lithologic Units Supracrustal metavolcanic and metasedimentary rocks comprise Supracrustal metavolcanic and area. metasedirnentary rocks the bulk of Archean rocks of the Also included incomprise this the bulk of Archean rocks of the area. Also included in this sequence are a number of small felsic intrusive bodies, the most sequence are a number of small felsic intrusive bodies, the most important of these being a dacite(?) porphyry body, which is the important of these being a dacite(?) porphyry body, which is the target of current mineral exploration. target of current mineral exploration. Metavolcanic rocks of the region occur in two separate Metavolcanic of the region occur in two separate areas, the north rocks and northwest, and the southeast (Fig. 2); and areas, the north and northwest, and the southeast (Fig. 2); and are separated by a central band of metasedimentary rocks. are separated by a central band of metasedimentary rocks. Significant portions of the contacts between the major Significant portions the contacts between and the probably major metasedimentary and of metavolcanic sequences, all metasedimentary and metavolcanic sequences, and probably all contacts between these sequences, are faults. The northern contacts between these sequences, are faults. metavolcanic sequence is also in fault contact The withnorthern the Giants metavolcanic sequence is also in fault contact with Giants north of Range Complex between the Pike River and Highway 5 3 the Range Complex between the Pike River and Highway 53 north of Virginia. Virginia. Metavolcanic Rocks 1etavo1canjc Rocks Metavolcanic rocks consist primarily of grayish green to consist primarily of grayish green to to medium-grained, massive to locally pillowed dark Metavolcanjc green, fine-rocks dark green, fine- to medium-grained, massive to locally pillowed or brecciated flows. While chemical analyses of these rocks have or brecciated flows. While chemical analyses of these rocks have yet to be obtained, the rocks appear to be predominantly of yet to be obtained, the rocks appear to be predominantly of intermediate composition. Dacitic(?) fragmental rocks are intermediate composition. Dacitic(?) fragmental rocks are interlayered with the flows in the southernmost part of the area interlayered with the flows in the southernmost part of the area and northofofBiwabik. Biwabik. Coarser grained, probably intrusive and north Coarserrocks grained, intrusive metadioritic or metagabbroic also probably occur within this metadioritic or metagabbroic rocks also occur within this sequence, as do finer grained mafic dikes. sequence, as do finer grained mafic dikes. Foliation in the metavolcanic rocks is generally not well Foliation in the metavolcanic rocks is generally not well assemblages of chloritedeveloped. Typical greenschist facies developed. Typical greenschist facies assemblages of chlorite— albite+actinolite+epidote are present. Secondary minerals albite+actinolite+epidote are present. Secondary minerals include calcite? and sericite. include calcite' and sericite. Metasedimentarv Rocks Metasedjmentary Rocks Metasedimentary rocks of the area are subdivided into three Metasedimentary of the unit areaof are subdivided three fault-bounded units:rocks a northern moderately to into highly fault-bounded units: a northern unit of moderately to highly altered, relatively quartzose metagraywackes, a central altered, relatively quartzose metagraywackes, a central conglomeratic unit, and a southern unit of metagraywackes. conglomeratic unit, and a southern unit of metagraywackes. Southern metaqrawackes. This unit comprises the bulk of Southern metagraywackes. This unit comprises the bulk of the metasedimentary rocks of the region. Numerous outcrops occur the metasedimentary rocks of the region. Numerous outcrops occur 1 3 5 . These rocks consist predominantly of south of Hwy. south of Hwy. 135. These rocks consist predominantly of Quartz in these rocks interbedded graywackes and slates. interbedded graywackes and slates. these rocks normalized to exclude . When in averages 5 - 1 0 % rarely exceeding 1 5 %Quartz averages 5-10%, rarely exceeding 15%. When normalized to exclude with matrix, all rocks contain greater than 5 0 % lithic fragments, matrix, all rocks contain greater than 50% lithic fragments, with D- 3 �felsic to felsic-intermediate clasts predominating. Intermediate felsic to felsic-intermediate clasts predominating. Intermediate to mafic clasts, though not abundant, are normally present. to mafic clasts, though not abundant, are normally present. Detrital hornblende occurs in graywackes at one locality. Minor Detrital hornblende in graywackes at oneto locality. amounts of sericiteoccurs are ubiquitous. Moderate abundant Minor amounts of sericite are ubiquitous. Moderate to abundant sericite and carbonate are locally present, especially in more sericite and carbonate are locally present, especially in more highly strainedzones. zones. highly strained These sandstones are turbidites, with Bouma A, AB, ABC, and These sandstones are turbidites, with Bouma AB, ABC, and are rare,A,though some Coarse clasts E divisions discernable. E divisions discernable. Coarse clasts are rare, though some pebbly units do occur. pebbly units do occur. Altered metaqravwackes. Outcrops of this unit are not as Altered metacTraywackes. of this unit are consist not as of These rocks abundant as the graywackes to Outcrops the south. abundant as the graywackes to the south. These rocks consist of moderately to highly altered, felsic volcanic-rich metagraywacke. moderately to highly altered, felsic volcanic-rich metagraywacke. In contrast to the southern metagraywackes, these rocks contain In contrast to the southern metagraywackes, these rocks contain 10-25% quartz and generally do not contain clasts of intermediate 10-25% quartz and generally do not contain clasts of intermediate to mafic composition. composition. Secondary sericite and carbonate are to mafic Secondary 60% of the are rock. abundant, in some places comprisesericite as much and as carbonate abundant, in some places comprise as much as 60% of the rock. It is likely that this alteration is related to the quartz It is likely that this alteration is related to the quartz feldspar porphyry bodies that have intruded this sequence. feldspar porphyry bodies that have intruded this sequence. Beds tend to be thick, with a fair development of grading. tend to be thick, with a fair development (after Walker, WhereBeds discernable, Bouma A, AB, and ABC divisions of grading. Where discernable, Bouma A, AB, and ABC divisions (after Walker, 1984) predominate. 1984) predominate. This unit is typically a dark green, ConqlomeraticUnit. Unit. Conglomeratic This unit It is is typically a dark green, heterogeneous, conglomerate. a composite unit, comprised heterogeneous, conglomerate. it is a composite unit, comprisedThe of various subunits based on differences in clast lithology. of various subunits based on differences in clast lithology. The subunits are typically heterolithic, though one distinctive subunits are typically heterolithic, though one distinctive monolithic unit and units of pyroclastic affinity occur within monolithic unit and units of pyroclastic affinity occur within along strike, thissequence. sequence. The subunits are difficult to trace this The subunits are difficult to trace along strike, and at at least least two two of ofthese thesesubunits subunits are in fault contact with each and are in fault contact with each other. other. Clasts are normally rounded and of volcanic origin, but Clasts are normally rounded types, and of generally volcanic origin, butto consist of various compositional of felsic consist of various compositional, types, generally of felsic to intermediate affinity. Particularly interesting are clasts of intermediate affinity. Particularly interesting are are clasts These hornblende clasts not of euhedral brown hornblende. hornblende. euhedral brown These hornblende clasts are not rounded and suggest a crystal tuff origin. One distinctive rounded and suggest a crystal tuff origin. One distinctive subunit is monolithic, with angular to subangular andesitic subunit is monolithic, with angular to subangular andesitic It too clasts, and was probably deposited as a debris flow. clasts, and was probably deposited as a debris flow. It too With the exception of the contains clasts of brown hornblende. contains clasts of brown hornblende. With the exception of the monolithic unit, the conglomerates are typically clast-supported. monolithic unit, the conglomerates are typically clast-'supported. The matrix matrix of of the the conglomerates conglomeratesis isgenerally generally chloritic; quartz is The chloritic; quartz is rare in in the thematrix. matrix. rare 0-4 �Origin Oriqin of of the the Metasedimentary Metasedimentary Rocks Rocks The conglomerates conglomerates are are interpreted interpreted to to be be upper upper fan fan channel channel The deposits, deposits, deposted deposted by by mass mass flow flow mechanisms. mechanisms. The The graywackes graywackes are are interpreted interpreted to to be proximal proximal to to mid-fan mid-fan deposits, deposits, deposited deposited by by turbidity turbidity currents. currents. The The two two graywacke graywacke units units are are also also compositionally different, and and neither compositions compositions are are compositionally compatible with with those those of of the the conglomeratic conglomeratic unit. unit. Nor Nor are are they they compatible compositionally compatible compatible with with the the adjacent adjacent metavolcanic metavolcanic units. units. compositionally These relationships relationships support support the the notion that all all three three sedimentary sedimentary These units units are are in in fault fault juxtaposition, juxtaposition, being being parts parts of of different different submarine submarine fans. fans. The The fans fans were were located located on on the the flanks flanks of of volcanic volcanic edifices, edifices, for for all all the the detritus detritus is is volcanogenic. volcanogenic. Felsic Intrusjveg AA series series of of quartz-feldspar quartz-feldspar (probably (probably dacite) dacite) porphyry porphyry bodies the altered altered metagraywackes metagraywackes along along aa narrow narrow belt belt bodies intrude intrude the trending trending approximately N8OE, N80E, and and also also appear appear to to intrude intrude the the southernmost southernmost exposures exposures of of metavolcanic metavolcanic rocks rocks along along the the contact contact with with the the altered altered graywackes. graywackes. These These bodies bodies are are recognizable recognizable for for the the most part by by their their conspicuous conspicuous ovoidal ovoidal quartz quartz phenocrysts. phenocrysts. Although Although not not present present in in all all rocks, rocks, these these phenocrysts phenocrysts typically typically vary vary in in amount amount from from 2-5% 2-5% and and range range in in size size from from .5. 5 cm cmto to22cm. cm. Plagioclase 20-30% of of the the rock, rock, range range in in Plagioclase phenocrysts phenocrysts comprise comprise 20-30% size size from from 22 mm to to 1.5 1.5 cm, cm, and and are are nearly nearly pure pure albite albite in in composition composition (Sutton, (Sutton,1963) 1963). The The phenocrysts phenocrysts are are set set in in an an aphanitic, aphanitic, white white to to greenish-gray greenish-gray matrix matrix of of quartz quartzand andfeldspar. feldspar. Secondary Secondary sericite sericite and and carbonate carbonate (siderite (siderite or or ankerite) ankerite) are are abundant, giving the rock its white to greenish color. abundant, giving the rock its white to greenish color. Finely Finely disseminated disseminated sulfides sulfides are are associated associated with with quartz-carbonate quartz-carbonate veins veins and and vary vary greatly greatly in in amount amount from from one one location location to toanother. another. Common Common sulfides sulfides are are pyrite pyrite and and arsenopyrite, arsenopyrite, with with rare rare sphalerite sphalerite and and chalcophyrite. chalcophyrite. . At At least least one one non-porphyritic non-porphyritic phase phase (it (it is is microporphyritic microporphyritic in in thin thin section) section) cuts cuts the the main main porphyry porphyry body. body. Numerous, Numerous, generally generally aphanitic, aphanitic, felsic felsic dikes dikes also also cut cut the the southern southern group group of of graywackes. A few of these intrusives contain quartz graywackes. A few of these intrusives contain quartz phenocrysts, phenocrysts, but but most most do do not. not. In In thin thin section section these these dikes dikes Contain contain 30—50% 30-50% plagioclase plagioclase microphenocrysts microphenocrysts in in aa fine fine felsic felsic matrix. matrix. Structure Structure Upon Upon first first examination, examination, these these rocks rocks appear appear to to be be relatively relatively undeformed; beds typically strike N60-70E. undeformed; beds typically strike -N60-70E. However, However, it it has has been been determined determined that that these these rocks rocks have have been been subjected subjected to to at at least least three three D- 5 �periods of of folding, folding, and have been cut cut by a significant significant northeasterly northeasterly trending trending fault/shear fault/shear system system (Welsh, (Welsh,1988) 1988). Folding Foldinq F1 have not not been been recognized in the field, F, folds have field, but but are are identified identified by by reversals reversals in in structural structural facing. facing. F2 F, folds are are tight tight to to isoclinal, isoclinal, trend northeasterly, and and are are steeply steeply plunging. plunging. While aa few are visible in outcrop, most are F, folds are are identified identified few F2 by reversals reversals in in stratigraphic stratigraphic facing. facing. Cleavage Cleavage (S2) (S,) trends are trends are consistently axial planes planes of of the the F2 F, folds. folds. Minor Minor consistently parallel parallel to to the the axial folds with gentle south-plunging axes have been recognized recognized in in three F3. three localities, localities, and and are are tentatively tentatively designated designatedasasF3. Faulting Faultinq These These rocks rocks have been cut by aa complex complex northeast northeast trending trending fault/shear system system which roughly coincides coincides with with the the axis axis of of the the fault/shear Virginia In 2). In the the northern northern part part of of the the area area most most Virginia Horn Horn (Fig. (Fig. 2) . displacement displacement appears appears to to have have been been taken taken up up along along the the Pike Pike River River Fault (Welsh, (Welsh,1988) 1988). Outcroppings Outcroppings adjacent adjacent to to the the fault fault exhibit exhibit Fault the the effects effects of of considerable considerable ductile ductile shear. shear. In the southern southern part part of of the the area, area, aa number number of of subparallel, subparallel, probably probably en en echelon, echelon, fault fault strands strands Cut cut throughmetasedimentary through,metasedimentary rocks rocks and and appear appear to to link link with with the the Pike Pike River River Fault. Fault. The The contact contact between between the the metasedimentary metasedimentary rocks rocks to to the the southeast is rocks and and rnetavolcanic metavolcanic rocks is also also aa fault. fault. Here Here north-topping north-topping metavolcanic metavolcanic rocks rocks are are juxtaposed juxtaposed against against south—topping south-topping metasedimentary metasedimentary rocks. rocks. These These en en echelon echelon faults faults are are interpreted interpreted as as being part of a strike-slip strike-slip duplex duplex (after (after Woodhouse, 1986). Woodhouse, 1986). . Strain Strain in in these rocks rocks is is concentrated concentrated into into narrow narrow zones zones of of ductile ductile shear shear associated associated with with these these faults. faults. Clasts Clasts along along the the margins margins of of the the conglomerate conglomerate are are distinctly distinctly flattened flattened in in the the plane plane of of foliation. foliation. Clasts Clasts internal internal to to the the body body are are generally generally not not as as flattened, flattened, but appear appear to be elongated elongated in in the the vertical vertical direction. direction. Movement Movement along along this this system system was was probably probably complex. complex. Although Although offset offset market market units units have have not not been been identified, identified, map map patterns patterns suggest N40suggest sinistral sinistral drag, drag, as as beds beds are are typically typically rotated rotated to to aa N4050E 50E strike strike in in the the vicinity vicinity of of the the Pike Pike River River Fault. Fault. En En echelon echelon quartz—filled quartz-filled tension tension fractures fractures in in the the dacite dacite porphyry porphyry also also support support aa sinistral sinistral sense sense of of shear. shear. Other Other kinematic kinematic indicators, indicators, however, however, such such as as minor minor Z-folds, 2-folds, and and asymmetric asymmetric pressure pressure shadows shadows on sense of ofshear shearwas was on porphyroclasts porphyroclasts suggest suggest that that the the (latest?) (latest?) sense dextral. dextral. In In addition, addition, high angle angle slickensides slickensides are are associated associated with with the the en en echelon echelon strands strands of of the the duplex duplex and and indicate indicate vertical vertical movement movement at at some some time time in in the the structural structural history history of of the the area. area. D-6 �p — 4 p £ 4 4. 4 S 4 4 4P, 4 4 4 4 4. 4. 4 4 ' +' 4 4 4. 4. 4 4 4 4. + + 4 4 4 4 4 + 4 4 .s 4 4 4 4 4. 4 4 + 4 4 4 4 4 4 9 4 4. 4 4 4 4 4 9 4 4 4 9 4 4. + 4 4 4 4 4 4 4 4 4 4. 4 4 4 4 4 + + + + + + 4 4 4 + + 4 9 4 4 4. 9 4 4 4 4 4 4 4 ' + 4 4 4. + 4. 4 4. 4 + + 4. •\• $$ 4 4 + + 4 4 4 4 + .4 4 9 4. 4 4 + + 4. + + 4. 9 4 4 + + + 4 4 4 4 4 4 $ + 44 4 9 4 4 4 4 4(4 r—r—,—,— 4 4 4 4 4 4 4/4'•\ c..4 44 444 44 44 # ' 4 4. 4 + 4 4 ,/ + 4 4 — 4 4. + 4 ''— • 4 — a)1!d / // / S 1Y3 J '' B I W B I N lm fWllCN. WITH UNX RL YING P W X W F C RHAIM Ul I W )It8,I6 PCI PILWO4 34fl AL,J VY3Cd jYj IA IOIO3 LYP i -— LYIc .'OW t I 1V4 ~ r m u l l v I Ijwi jV1 WVd5013J-ZjbyrC S3I$&MdtO QWV IVtNI jIIW 3AvCv LVIV I,,jtO3 E±1 ltvHy'oO1vjw I 1'-EI I Figure 2. ein6,j EEIJ v&vjp, LTJ IfJ KTAVCLCANlC5 N4l & r A - I N I R U S I W S S3IPiVtAYjyI N S3AISrg1NI-VJV Generalized geologic mapjoofoq the VirginiaWOH Hornearn area showing pezileieueo oi6ojoe6 dew elu!6.nfl 6ulMoqs the Pike.ieAi RiverIfled FaultwesA System. eqi 8J -a L �Economic Geology Geology Economic The dacite dacite porphyry porphyry body body is is aa current current target target for for gold gold The exploration in the area. Gold was first reported in this unit by by exploration in the area. Gold was first reported in this unit Gruner in 1924 (GroutI l937lI and is associated with the quartzGruner in 1924 (Grout, 1937), and is associated with the quartzcarbonate veins veins and and shear shear zones zones within within the the body. body. carbonate Sericite-carbonate alteration alteration has has also also been been identified identified with with Sericite—carbonate the faultlshear zones of Pike River System (WelshI 1988). the fault/shear zones of Pike River System (Welsh, 1988) Although silicification silicification and and sulfidation suliidation along along the the shear shear zones zones Although appears minimal where rocks are exposedI these zones merit appears minimal where rocks are exposed, these zones merit further investigation. investigation. further References Grout, F. I?. F., E d I1937, 1937, Petrographic Petrographic study study of of gold gold prospects prospects of of Grout, Minnesota: Econ. Ge01.~ vol. 32# pp. 56-68. Minnesota: Econ. Geol., vol. 32, pp. 56-68. Grout I F.F., E'. I?. I Gruner, Gruner, J.W., J.W. I Schwartz, Schwartz, G.M., G.M. I and and Thiel, ThielI G.A., G.A. I 1951, 1951 I Grout, Precambrian stratigraphy of Minnesota: Geol. Soc. Am. Bul1.I Precambrian stratigraphy of Minnesota: Geol. Soc. Am. Bull., v. 62, 6ZI pp. pp. 1017—78 1017-78 v. LeithI C. K. I 1903# The Mesabi iron-bearing iron-bearing district district of of Leith, C. K., 1903, The Minnesota: U.S.Geol. U.S.Geo1. Surv. Surv. Monograph, MonographI vol. vol. 43. 43. Minnesota: SuttonI T. T. C., C., 1963, 1963# Geology Geology of of the the Virginia Virginia Horn Horn area: area: M.S. M.S. Sutton, thesisI University of Minnesota, Minneapolis. thesis, University of Minnesota, Minneapolis. WalkerI R.G., R.GeI1984, 19841 Turbidites Turbidites and and associated associated coarse coarse clastic clastic Walker, deposits: in Facies ModelsI R.G. Walker e d a I Geoscience deposits: in Facies Models, R.G. Walker ed., Geoscience Canada Reprint Reprint Series Series 1, l I pp. pp. 171-188. 171-188. Canada WelshI J. J. L., L. 1988, 1988/ Preliminary Preliminary Structural Structural Analysis Analysis of of Archean Archean Welsh, rocks in in the Virginia Horn area, northeastern Minnesota rocks the Virginia Horn area, northeastern Minnesota (abs): 34th 34th Ann. Inst .on Lake Lake Superior Superior Geology, GeologyI v. v. 34, 3dI (abs): Ann. Inst.on part 1, l I pp. pp. 119—120. 119-120. part WoodhouseI N. H e I1986, 198GI Strike-slip Strike-slip duplexes: duplexes: Journal Journal of of Woodhouse, N. H., Structural GeologyI V. EI no. pp. 725-735. Structural Geology, V. 8, no. 7, pp. 725—735. 0-8 �6-0 AAO-1 PJ qse sewer woj pedpy eeie WOH e!U!6J!A Lfl o Aöoioe6 ueeqoiv eq 6UIMOqS devj S)130?J 3INVD1OAVI3VI [A4 3)DYMAVV13p [—Y 3IVJ3V4O1ONO3v13r [-.iY 3NDYMAVIOVj3r4 O3èl3flY [v C AèAHdJOd dSJ—Zb AAA 6468* / AAAAAAA / AAAAAAAA1 / A A A A A A A A A A A A A A A A A A A A A 8 AAAAAAAAAAAAe' AA6AAAAAAAAAA/f AAAAAAAAAAAAA,' /,/ AAAAAAAAAAAAAA, AAAAAAAAAAAAAA/ / AAAAAAAAAAAAAAA,' AAAAAAAAAAAAAAA, / / AAAAAAAAAAAAAAAA/ AAAAAAAAAAAAAAA,/ ,.' I AAAAAAAAAAAAAAA,/ ,1 AAAAAAAAAAAAAAA'/ , 'AAAAAAAAAAAAAAA,/' / / / / AAAAAAAAAAAAAAA//,/ I AAAAAAAAAAAAA& /, / / AAAAAAA4AA / . / / I I A A A A A A A A A_. A A A A A A AAAAA? ', AAAAA, / AAAAF, . ' AAAA_# ri AAAb - / /, / — / D—JY O9i' ,' A A A A £ -p"j ,AAAAAAAAAAAAb A A A A A A A A A A A A AA / - ,48A A A A A A / .iA A AAA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AAAAA AA A A A ..dAAAAAAAAAAAAAA8AAAAAAAA, — -/ A A A A A A A A A A A A A A A A A A A A A A A A .'AAAAAAAAAAAAAAAAAA AAAAAAAAA / •C ejn6i �Road Log Log Road From Duluth, Duluthf travel travel north north along along U.S. U.S. 53 53 to to Eveleth. Eveleth. Pass Pass From 53 through Eveleth, Eveleth, and and turn turn right right at at the the intersection intersection of of U.S. U.S. 53 through and Minn. 135! and proceed toward Gilbert for 1.5 miles, turning and Minn. 135, and proceed toward Gilbert for 1.5 miles, turning left at at dirt dirt road road (with (withgate) gate). Stop Stop at at gate. gate. left . STOP 1. 1. Entrance Entrance to to Viking Viking Explosive Explosive property. property. STOP At this this locality locality At the contact between the southern graywacke-slates and the the contact between the southern graywacke-slates and the conglomeratic unit unit can can be be observed. observed. Rhythmically Rhythmically bedded bedded conglomeratic turbiditic graywackes graywackes are are exposed exposed on on the the east east side side of of the the access access turbiditic road. Though tops are difficult to discern here, tops are north. road. Though tops are difficult to discern here, tops are north. Careful examination of the outcrop reveals that the sediment Careful examination of the outcrop reveals that the sediment layers are are disrupted disrupted along along faults faults at at low low angles angles to to bedding. bedding. layers Small scale isoclinal folds are also present. Small scale isoclinal folds are also present. sericitized graywackes graywackes also also Rhyhmically bedded, beddedf more more highly highly sericitized Rhyhmically occur on the west side of the access road north of the gate, but occur on the west side of the access road north of the gate, but A prominent 'Zf kink fold is also displayed with tops reversed. with tops reversed. A prominent 'Z' kink fold is also displayed in these these metasediment,s. metasediments. in Outcrops on on the the west west side side of of the the access access road road occupying occupying the the Outcrops higher ground, and exposed along the highway are in the higher ground, and exposed along the highway are in the conglomeratic unit. unit. Here Here the the conglomerate conglomerate is is heterolithic, heterolithic, coriglomeratic consisting of various felsic volcanic clasts in chloritic consisting of various felsic volcanic clasts in aa chloritic matrix. Evidence of grading occurs in outcrops on the south south side side matrix. Evidence of grading occurs in outcrops on the of the the highway, highway, and and indicate indicate south south tops. tops. of The contact contact between between the the graywackes graywackes and and the the conglomerate conglomerate is is aa The phyllonite, and and is is exposed exposed along along the the west west edge edge of of the the access access phyllonite, road. Clasts Clasts in in the the conglomerate conglomerate along along the the contact contact are are flattened flattened road. # Z f folds in the the as a result of the strain. Minor asymmetrical as a result of the strain. Minor asymmetrical 'Z' folds in phyllonite can can be be sernen seen in Z-style phyllonite in thin thin sectionf section, as as are are small small Z—style secondary cleavage, cleavage, probably probably the the result result of of pressure pressure kinks. AA secondary kinks. solution is is also also developed developed in in the the phyllonite. phyllonite. solution The phyllonite phyllonite is is interpreted interpreted to to represent represent aa strand strand of of the the The Pike River River shear shear zone, zonef and and appears appears to to run run along along much much (and (and perhaps perhaps Pike along the the length) length) of of the the contact contact between between the the graywackes graywackes and and the the along conglomerate.The contact between the conglomerate and the altered conglornerate.The contact between the conglomerate and the altered graywackes is is also also highly highly strained strained and and altered, alteredf and and probably probably graywackes " 2 " structures structures associated associated represents another another shear shear zone. zone. The The "Z" represents with these shear zones indicate dextral shear. with these shear zones indicate dextral shear. 0-10 �Proceed back back along along Hwy. Hwy. 135 135 toward toward Virginia Virginia for for about about 1/4 114 mile mile Proceed and turn turn right right secondary secondary road. road. Follow Follow this this road road for for and approximately one mile, and turn right on dirt road to landfill. landfill. approximately one mile, and turn right on dirt road to DM&IR Railroad Tracks and park. Walk east for Proceed to Proceed to DM&IR Railroad Tracks and park. Walk east for approximately 1/4 114 mile, mile, until until first first outcrops outcrops are are reached. reached. approximately STOP 2. 2. STOP At this this locality locality two two feldspar feldspar porphyry porphyry "dikes", "dikes", At generally lacking lacking quartz quartz phenocrysts, phenocrysts, are are interfingered interfingered with with generally and porphyry porphyry are are extensively extensively graywackes. Both Both the the metasediments metasediments and graywackes. altered with with sericite sericite and and iron iron carbonate. carbonate. The The porphyry porphyry contains contains altered abundant quartz-iron carbonate veins and abundant disseminated abundant quartz-iron carbonate veins and abundant disseminated J.W. Gruner Gruner reported reported visible visible gold gold at at this this locality locality (see (see pyrite. J.W. pyrite. 1937). Groutf Grout, 1937) Continue eastward eastward along along the the railroad railroad tracks tracks for for approximately approximately 1/3 113 Continue mile to the next set of outcroppings. mile to the next set of outcroppings. STOP 3. 3. STOP ~etagraywackks ofthe thealtered altered graywacke graywacke unit. unit. Metagraywacks of These graywacke-slates graywacke-slates are are more more thickly thickly bedded bedded than than the the These rhythmically bedded bedded turbidites turbidites of of Stop Stop 1. 1. The The rocks rocks are are rhythmically deformedf and show good bedding-cleavage relationships. The high high deformed, and show good bedding-cleavage relationships. The angle between bedding and cleavage suggests that these outcrops angle between bedding and cleavage suggests that these outcrops occur in in the the nose nose of of aa fold, fold, and and top top relationships relationships from from other other occur graywacke outcrops in the area support this interpretation. graywacke outcrops in the area support this interpretation. Cleavages are are gently gently folded, folded, possibly possibly the the result result of of intrusion intrusion of of Cleavages the dacite dacite porphyry. porphyry. The The contact contact with with the the porphyry porphyry occurs occurs the of the south exposure, and is approximately 50 feet south approximately 50 feet south of the south exposure, and is relatively sharp. relatively sharp. From these these outcrops outcrops walk walk south south to to the the outcrops outcrops near near the the abandoned abandoned From buildings which are in sight. buildings which are in sight. STOP 4. 4. STOP Rhude and and Fryberger Fryberger prospect. prospect. Rhude Numerous outcrops outcrops of of quartz-feldspar quartz-feldspar porphyry porphyry have have been been stripped stripped Numerous at this location. In general the QFP consists of quartz at this location. In general the QFP consists of quartz phenocrysts (.5-2 (-5-2cm/2-5%) cm/2-5%) and and plagioclase plagioclase phenocrysts phenocrysts (2 ( 2 mm—1.5 mm-1.5 phenocrysts cm/25-30%) set set in in aa greenish greenish aphanitic aphanitic groundmass groundmassof ofquartz, quartz, cm/25-30%) feldspar, and sericite. Fine-grained disseminated pyrite and feldspar, and sericite. Fine-grained disseminated pyrite and arsenopyrite occur occur in in variable variable amounts amounts throughout throughout the thearea, areaf arsenopyrite particularly in association with quartz-carbonate veins. particularly in association with quartz-carbonate veins. D-11 �phase of of the the intrusion intrusion is is present present at at The non-porphyritic phase this this location. location. It can be seen cross-cutting the the main porphyritic body on an east-southeasterly east-southeasterly trend. trend. Located Located under under the the power power line line to the west is is aa rotated, rotated, rafted rafted sedimentary sedimentary inclusion inclusion within within QFP. QFP. (As (As you take note note of of the the you survey the outcrops take quartz-carbonate veins, and and how how fracturing fracturing attitudes of the quartz-carbonate affects affects these these veins, veins, and and their their relationship relationship to to foliation. foliation. From From these outcrops outcrops proceed proceed east east along along the the railroad railroad tracks tracks for for approximately 1/3 mile mile (about (about 100 100 yards yards before before the the large large railroad railroad approximately 1/3 cut), cut), to to the the outcrop outcrop on on the the south south side side of of the the tracks. tracks, STOP STOP 5. 5. Newmont Newmont Prospect Prospect This historical occurrence occurrence first first received received attention attention at at the the turn turn This of of the the century. century. C. C. K. Leith's Leithts (1903) (1903) exemplary exemplary study study of of the the geology geology of the Mesabi Range Range described described the the older older volcanic volcanic and and sedimentary rocks rocks of of the the Virginia Virginia Horn Horn area. area. He He noted noted the the presence presence of of "porphyritic "porphyritic granite" granite" with with secondary secondary sericite, sericite, chlorite at this this locality. locality. In In 1924, 1924, Dr. Dr. John John Gruner Gruner chlorite and and quartz quartz at led led a field party through through the the Virginia Horn Horn area area and and collected collected several gold-bearing gold-bearing samples samples from from "rhyolite "rhyolite porphyry". porphyry". Petrographic Petrographic descriptions descriptions of of these these samples samples were were published published by by F. F. F. F. Grout (1937), (1937), and and he he noted noted grains grains of of gold gold in in several several samples. samples. On On the the south south side side of of the the railroad railroad grade grade approximately approximately 1/4 1/4 mile mile east east of of the the old old Hercules Hercules powder powder plant, plant, outcrops outcrops of ofquartz, quartz, feldspar feldspar porphyry flank flank aa stream stream channel channel within within aa narrow narrow topographic topographic low. low. AA flat, flat, glaciated glaciated outcrop outcrop on on the the east east side side of of the stream exhibits several quartz and quartz—carbonate vein sets the stream exhibits several quartz and quartz-carbonate vein sets within within variably sericitized sericitized and and silicified silicified QFP. QFP. At At this this location, location, aa prominent, prominent, steeply-dipping steeply-dipping vein vein set set strikes strikes approximately approximately N—S. N-S. Adjacent Adjacent walirock wallrock contains contains very very fine-grained, fine-grained, disseminated disseminated pyrite pyrite and and arsenopyrite arsenopyrite within within aa gray-green gray-green aphanitic groundmass. The N-S veins occupy en aphanitic groundmass. The N-S veins occupy en echelon echelon tension tension fractures fractures which which flank flank narrow narrow shear shear zones zones striking striking N4OE. N40E. The The attitude attitude of of the the tension tension veins veins to to the the shear shear planes planes indicates indicates aa left-lateral QFP left-lateral sense sense of of shear. shear. Other Other vein vein sets sets within within the the QFP include include 1) 1) foliation-parallel foliation-parallel quartz-carbonate quartz-carbonate veins veins within within shears, shears, and 2) 2) subhorizontal subhorizontal quartz-carbonate quartz-carbonate veins veins occupying occupying conjugate conjugate fractures. fractures. Gold Gold mineralization mineralization is is associated associated with with several several vein vein sets. sets. D-12 �Continue east to large railroad cut. Continue east to large railroad cut. STOP 6. Conglomeratatic unit. STOP 6. Conglomeratatic unit. The most extensive exposures of the coarse volcaniclastic most exposures ofthe theunit coarse Here canvolcaniclastic be divided into unitThe occur atextensive this locality. unit occur at this locality. Here by the cana be divided into monolithic unit two subunits which are separated a unit fault, two subunits which are separated by a fault, a monolithic and a heterolithic unit. The northwestern 250 feet of the unit and a heteroljthjc unit. by The northwestern 250 feet of the railroad cut is marked a remarkably monolithic, generally railroad cut is marked by a remarkably monolithic, generally The clasts are quite irregular in matrix supported conglomerate. matrix supported conglomerate. The clasts are quite irregular both size and shape, are angular to subrounded, and unsorted. in both size and are angular to subrounded, and matrix unsorted. Clasts are ofshape, porphyritc hornblende andesite. The is Clasts are of porphyritc Thisisunit is The matrix chloritic, and contains hornblende hornblende andesite. crystal clasts. chioritic, and hornblende clasts. This unit is interpreted tocontains have been depositedcrystal by debris flow, probably interpreted to have been deposited by debris flow, probably subaqueous lahars. subaqueous lahars. In the southeastern half of the cut, the rocks are marked by In the southeastern of the cut, the rocks arethe marked by distinct morphologic andhalf lithologic differences from north. distinct morphologic and lithologic from the north. The remainder of the conglomeratic differences unit is generally like these The remainder the conglomeratic is generally likeare these rocks at the of southeast~part of theunit railroad cut. They rocks at the southeastipart the supported, railroad cut. and often have normal They are generally heterolithic and of clast generally heterolithic and clast often very have little normal The matrix and contains and inverse to normal grading. supported, and inverse normal contains grading. euhedral The matrix contains very clasts? little quartz, buttolocally brown hornblende quartz, but locally contains euhedral clasts? These conglomerates are thought to bebrown upperhornblende fan channel deposits. These conglomerates are thought to be upper fan channel deposits. Upon returning to vehicles drive to Gilbert. Upon returning to vehicles drive to Gilbert. right and proceed uphill toward school. right and proceed uphill toward school. From town, turn From town, turn STOP 6. (optional) Outcops behind Gilbert High School athletic STOP 6. (optional) field. field. Outcops behind Gilbert High School athletic These outcrops contain the best exposures of pillowed These outcrops the best of pillowed Theexposures pillows strike roughly eastmetavolcanic rocks contain in the area. metavolcanic rocks in the area. The of pillows strike with roughly west (note the northeasterly trend the contact the eastwest (note the northeasterly trend of the contact with the metasedimentary rocks to the west), and top north. (The metasedimentary to the and top north. metasedimentaryrocks sequence to west), the west generally tops (The southeast metasedimentary sequence to the west tops are southeast at generally this locality truncated along the contact). The pillows along the contact) The pillows at this locality are truncated by massive volcanics along a N25E trend. Whether this contact by massive volcanics alongcontact a N25E or trend. represents an intrusive shear Whether has not this been contact determined. represents an intrusive contact or shear has not been determined. However, foliation along this contact, minor quartz veining, and However, along this contact, quartz veining, apparentfoliation drag of the pillows into the minor contact suggest right and apparent drag of the pillows into the lateral shear. Confusing the matter contact are the suggest presenceright of pillows lateral shear. Confusing the matter are the presence of pillows on the far northwest corner of the outcrop area. . on the far northwest corner of the outcrop area. 0-13 �FIELD TRIP 4, 4, PART PART BB AND THEIR THEIR STRUCTURAL STRUCTURAL SETTINGS: WESTERN AND CENTRAL ARCHEAN ARCHEAN GOLD GOLD OCCURRENCES OCCURRENCES AND VERMILION DISTRICT VERMILION DISTRICT Hudleston, R.L. R.L. Bauer, Bauer, W. W. Ulland Ulland Leaders: P.J. Hudleston, Leaders: D.L. D.L. Southwick, Southwick, P.J. INTRODUCTION INTRODUCTION Several S e v e r a l rrecent ecent p u b l i c a t i o n s have i g h l i g h t e d the t h e important i m p o r t a n t role r o l e played played publications have h highlighted by the llater a t e r sstages t a g e s of transpressional b y ductile d u c t i l e shear s h e a r zones zones and and faults f a u l t s in i n the of transpressional the western Vermilion district d i s t r i c t of of northeastern n o r t h e a s t e r n Minnesota Minnesota ttectonism e c t o n i s m in i n the (Sims, 1976; Bauer, Bauer, 1985; Hudleston and o others, (Sims, 1976; 1985; Hudleston t h e r s , 1987, 1987, 1988). 1988). These papers papers also a l s o provide p r o v i d e useful u s e f u l summaries summaries of of the t h e regional r e g i o n a l structural s t r u c t u r a l geology, geology, and and we we f o r background and and further f u r t h e r references r e f e r e n c e s on on rrefer e f e r interested i n t e r e s t e d readers r e a d e r s to them for tthe h e deformational d e f o r m a t i o n a l history h i s t o r y of of the t h e area. area. Various lines t h a t the the deformation deformation responsible r e s p o n s i b l e for for l i n e s of of evidence evidence indicate i n d i c a t e that the second second to to tthe h e regional r e g i o n a l ENE cleavage c l e a v a g e in i n the t h e Vermilion district d i s t r i c t was was the affect a f f e c t the the area, a r e a , or o r D2. D2. The regional r e g i o n a l cleavage c l e a v a g e therefore t h e r e f o r e is i s labelled l a b e l l e d S2 S2 and and it is i s rrelated e l a t e d are a r e F2 F2 sstructures. tructures. tthe h e folds f o l d s to t o which it Finite F i n i t e strain s t r a i n studies studies ( H u d l e s t o n , 1976; Schultz—Ela, Schultz-Ela, 1988) and sense—of—shear sense-of-shear observations o b s e r v a t i o n s imply imply (Hudleston, that t h a t D2 was aa transpression t r a n s p r e s s i o n that t h a t involved i n v o l v e d regional r e g i o n a l north-south north-south flattening, flattening, ssteeply t e e p l y to t o moderately pluiging pludging extension, e x t e n s i o n , and and dextral d e x t r a l shear. s h e a r . The most important to form form in i n the later l a t e r stages s t a g e s of of D2 Dz were were zones zones of of i m p o r t a n t structures s t r u c t u r e s to iintense n t e n s e ductile d u c t i l e or o r brittle—ductile b r i t t l e - d u c t i l e shear s h e a r such s u c h as a s the t h e Mud Mud Creek Creek shear s h e a r zone zone and the the shear s h e a r zones zones near near Shagawa Shaqawa Lake. Lake. More brittle b r i t t l e dextral d e x t r a l faults, f a u l t s , such and iits may be be s still manif a u l t and t s ssubsidary u b s i d a r y bbreaks, r e a k s , may t i l l llater a t e r maniaass the Vermilion fault festations f e s t a t i o n s of of the t h e same same transpressional t r a n s p r e s s i o n a l regime. regime. Structural S t r u c t u r a l studies s t u d i e s in i n gold-mining gold-mining districts d i s t r i c t s in i n the t h e Superior S u p e r i o r Province P r o v i n c e of of Canada Canada have have demonstrated demonstrated that t h a t shear s h e a r zones zones were were instrumental i n s t r u m e n t a l and and perhaps perhaps the localization l o c a l i z a t i o n of of gold ores o r e s (Colvine ( C o l v i n e and and others, o t h e r s , 1988, 1988, and and ccritical r i t i c a l in i n the rreferences e f e r e n c e s therein). t h e r e i n ) . The cclear l e a r sspatial p a t i a l association a s s o c i a t i o n between between shear s h e a r zones zones and and of g greenstone—belt tthe h e most important i m p o r t a n t classes c l a s s e s of r e e n s t o n e - b e l t vein v e i n deposits d e p o s i t s of of gold g o l d has has prompted much much interest i n t e r e s t in i n shear s h e a r zones as a s exploration e x p l o r a t i o n targets. t a r g e t s . For this this rreason e a s o n eexploration x p l o r a t i o n geologists g e o l o g i s t s have have been been working in i n the the shear s h e a r zones zones of of the the and tthey have found found sshear phenomena Vermilion district d i s t r i c t for f o r several s e v e r a l yyears, e a r s , and h e y have h e a r phenomena and even some some major shear s h e a r zones zones that that were were not n o t recognized recognized in i n published published mapping by by geological g e o l o g i c a l surveys. surveys. I Because of the widespread widespread academic and and applied a p p l i e d interest i n t e r e s t in i n shear—zone shear-zone of the phenomena, outstanding phenomena, we w e here h e r e describe d e s c r i b e five five o u t s t a n d i n g and easily e a s i l y accessible a c c e s s i b l e sshear hear zone outcrops o u t c r o p s in i n the t h e Vermilion district d i s t r i c t where the t h e features f e a t u r e s of of the t h e rocks rocks can can b e readily r e a d i l y observed observed and and debated. debated. be ROAD LOG LOG AND AND STOP STOP DESCRIPTIONS DESCRIPTIONS ROAD I ~ I The llog beginsaatt tthe The o g begins h e iintersection n t e r s e c t i o n of of St. S t . Louis Louis County route r o u t e 408 408 (Mud (Mud Creek Road) Road) and and sstate Creek t a t e highway highway 1-169 1-169 aapproximately p p r o x i m a t e l y 11.5 11.5 miles m i l e s eeast a s t of Soudan Soudan (Fig. ( F i g . 1 and 2 ). 2). 1 0.0 0.0 Intersection Intersection of Proceed north n o r t h on on of county route r o u t e 408 408 and highway 1—169. 1-169. and hilly h i l l y and and carries c a r r i e s aa 408 and drive d r i v e cautiously; c a u t i o u s l y ; road is crooked and surprising s u r p r i s i n g volume volume of of traffic. traffic. D-14 D-14 �3.7 a r k vehicles v e h i c l e s on accessible accessible h i g h ground and disembark; disembark; walk walk 3.7 Mud Mud Creek; Creek; ppark high to t o outcrops. outcrops. s t o p 1. 1. s h e a r zone; zone; outcrops o u t c r o p s near n e a r the the crossing c r o s s i n g of of Mud ~ u d Stop The Mud Creek shear Creek Road over o v e r Mud Mud Creek: Creek: SE1/4SE1/4 SE1/4SE1/4 ssec. e c . 5, 5, T. T. 62 62 N., N., R. R. 14 14 W. W. S e v e r a l small s m a l l outcrops o u t c r o p s in i n the t h e valley v a l l e y of of Mud Mud Creek Creek illustrate i l l u s t r a t e various various Several ssmall-scale m a l l - s c a l e structures s t r u c t u r e s characteristic c h a r a c t e r i s t i c of of rocks r o c k s that that have have undergone undergone intense intense D2. sshear h e a r strain, s t r a i n , all a l l attributed a t t r i b u t e d to t o D2. The best b e s t exposures are a r e in i n scrub s c r u b just j u s t north n o r t h of of the the creek c r e e k and and within within of the the road road on on the t h e east e a s t side. s i d e . The best aabout b o u t 100 100 m of b e s t example example of of local l o c a l S2' S21 and F2 Fy developed in i n aa lens l e n s of of otherwise o t h e r w i s e uniform S2 S2 is i s here h e r e (see ( s e e Fig. Fig. 3). 3). IIn n g e n e r a l S2 iis s subparallel s u b p a r a l l e l to t o the t h e margins of of the Mud Creek Creek shear s h e a r zone zone (N. (N. general 700 Locally, 70 E.). E.). L o c a l l y , it i t has has been been perturbed p e r t u r b e d and rotated r o t a t e d clockwise c l o c k w i s e about a b o u t 40°, 40° tto o form folds folds w i t h a secondary crenulation c r e n u l a t i o n cleavage c l e a v a g e (S21) ( S 2 @ developed )developed with the axial a x i a l plane. plane. Both cleavages c l e a v a g e s can c a n be traced t r a c e d from from within w i t h i n the the p a r a l l e l to t o the parallel perturbed S2, iin p e r t u r b e d zone outward to t o merge iinto n t o aa ssingle i n g l e pplanar l a n a r ffabric, a b r i c , S2, n tthe he surrounding be s u r r o u n d i n g rock. rock. Good examples of of en echelon tension t e n s i o n veins v e i n s can can also a l s o be found in i n nearby outcrops. outcrops. bend iin i s aa t h e outside o u t s i d e of of the t h e first f i r s t bend n tthe h e road north n o r t h of of the t h e creek c r e e k is On the rroadcut o a d c u t in i n a pinkish p i n k i s h quartz q u a r t z sericite s e r i c i t e schist, s c h i s t , a rock rock produced produced by by intense intense Nice shear shear. s h e a r . Nice s h e a r bands (or ( o r C' C ' planes; p l a n e s ; see s e e Fig. Fig. 4) 4 ) are a r e developed developed in i n this this s rendered friable f r i a b l e by the t h e closely c l o s e l y spaced spaced and and intersecting i n t e r s e c t i n g SS rrock, o c k , which iis and C' C 1 planes. planes. number of A number of features f e a t u r e s of of these t h e s e outcrops o u t c r o p s provide p r o v i d e indicators i n d i c a t o r s of of sense s e n s e of of C' sshear, h e a r , and these t h e s e are a r e consistently c o n s i s t e n t l y dextral. d e x t r a l . They include i n c l u d e shear s h e a r bands bands (or ( o r C' planes); development of of 82' Sf where p l a n e s ) ; local l o c a l development where S2 S5 has h a s been been perturbed p e r t u r b e d and and rotated rotated clockwise; assoc l o c k w i s e ; and formation f o r m a t i o n of of Z folds f o l d s in i n 8S2 3 ffoliation o l i a t i o n (most (most commonly in i n assowith well cciation iation w i t h SSf) $ ) and and in i n quartz q u a r t z veins. veins. Although w e l l developed in i n highly highly Mud Creek, ssimilar be found found through through ssheared h e a r e d rocks rocks such aas s aatt M ud Creek, i m i l a r ffeatures e a t u r e s ccan a n be much of the t h e Vermilion district, d i s t r i c t , increasing i n c r e a s i n g iin n the iintensity n t e n s i t y of of development development f a u l t is i s approached. approached. aass the Vermilion fault The Mud north f l a n k e d on the n o r t h by pillowed p i l l o w e d greenstone greenstone Mud Creek shear s h e a r zone is flanked member of of the E Ely s moderately deformed deformed except e x c e p t in in h a t iis ((upper u p p e r member l y Greenstone) tthat narrow shear zones, and on the south by assorted felsic tuff, tuff-breccia, s h e a r z o n e s , and on t h e s o u t h assorted f e l s i c t u f f , tuff-breccia, block b l o c k breccia, b r e c c i a , and the the reworked reworked sedimentary eequivalents q u i v a l e n t s of of these these of the Vermilion Formation). ((tuffaceous t u f f a c e o u s member of t h e Lake Vermilion Formation). Sims and Southwick (1980, 1985) iinterpreted highly material (1980, n t e r p r e t e d the the h i g h l y schistose schistose m a t e r i a l within w i t h i n the t h e shear shear zone to t o have been derived d e r i v e d chiefly c h i e f l y from from fine—grained f i n e - g r a i n e d felsic f e l s i c to t o intermediate intermediate It the Lake Vermilion sequence. sequence. I t iis s now recognized recognized that that ttuff u f f belonging belonging to t o the sshear h e a r zones of of this this magnitude commonly commonly contain c o n t a i n the the sheared s h e a r e d equivalent e q u i v a l e n t of of many different more o orr less common "fault "fault d i f f e r e n t rock types, t y p e s , all a l l reduced reduced tto o aa more rock" composed chiefly rock" c h i e f l y of of quartz, q u a r t z , sericite, s e r i c i t e , and and chlorite. chlorite. The phyllonitic phyllonitic Mud zone aare the ""fault rocks" aalong f a u l t rocks" long rrocks o c k s of of the the M ud Creek shear s h e a r zone r e ssimilar i m i l a r tto o the 1983, tthe h e Rainy Lake—Seine Lake-Seine River R i v e r fault f a u l t zone zone in i n southern s o u t h e r n Ontario O n t a r i o (Poulsen, ( P o u l s e n , 1983, and tto 1986) and o tthose h o s e aassociated s s o c i a t e d with many other o t h e r strike—slip s t r i k e - s l i p fault f a u l t zones zones the Mud Creek x t e n t of of the eelsewhere l s e w h e r e in i n the Superior S u p e r i o r Province. Province. The westward eextent sshear h e a r zone beneath Lake Vermilion Vermilion has not n o t been been established. established. D-15 �3.7 3.7 R e t u r n tto o vehicles; v e h i c l e s ; continue c o n t i n u e northwest n o r t h w e s t on Mud Creek C r e e k road road Return u s t y outcrop o u t c r o p of of q u a r t z vein v e i n and eenclosing n c l o s i n g quartz—sericite— quartz-sericite5.0 5.0 LOW, Low, rrusty quartz c h l o r i t e schist s c h i s t at a t edge e d g e of of road road on on east e a s t (right) ( r i g h t ) side. side. P a r k vehicles v e h i c l e s on on chlorite Park s h o u l d e r where room room permits; p e r m i t s ; walk to t o roadside r o a d s i d e outcrop. outcrop. shoulder 2A. Several S e v e r a l outcrops o u t c r o p s of of sheared, s h e a r e d , locally l o c a l l y altered a l t e r e d and a n d veined v e i n e d meta— metaSTOP 2A. basalt b a s a l t near n e a r Mud Creek C r e e k Road Road at a t the the southern s o u t h e r n boundary of of Superior Superior ., R. R. 14 1 4 W. W. N a t i o n a l Forest: F o r e s t : SE SE 1/4 1/4 SE SE 1/4 1/4 sec. National sec. 31, 31, T. T. 63 63 N N., Many of of the the small—scale s m a l l - s c a l e manifestations m a n i f e s t a t i o n s of of intense i n t e n s e dexra]. d e x r a l shear s h e a r that that were seen s e e n at a t the the previous p r e v i o u s stop s t o p are a r e seen s e e n to t o somewhat somewhat better b e t t e r advantage a d v a n t a g e in in is located located tthese h e s e exposures. e x p o s u r e s . The most interesting i n t e r e s t i n g and informative i n f o r m a t i v e outcrop o u t c r o p is aabout b o u t 500 500 ft. f t . into i n t o the the woods woods east e a s t of of the the road r o a d (follow ( f o l l o w well w e l l beaten b e a t e n path), path), quartz-sericite-chlorite schist s c h i s t displays d i s p l a y s excellent e x c e l l e n t C' C1 where phyllonitic p h y l l o n i t i c quartz—sericite—chlorite shear and S2' s h e a r bands bands and y ' crenulations. c r e n u l a t i o n s . Brown q u a r t z c a r b o n a t e a l t e r a t i o n Brown quartz—carbonate alteration zones, z o n e s , disseminated d i s s e m i n a t e d pyrite, p y r i t e , and and narrow, narrow, tectonized t e c t o n i z e d quartz q u a r t z veins v e i n s indicate indicate hydrothermal this shear s h e a r zone segment. segment. Grab samples samples of of fformer ormer h y d r o t h e r m a l activity a c t i v i t y in i n this the the occurrence o c c u r r e n c e has has t h e altered a l t e r e d rock r o c k reportedly r e p o r t e d l y yield y i e l d high h i g h gold g o l d assays, a s s a y s , but b u t the nnot o t been explored e x p l o r e d further f u r t h e r because b e c a u s e of of proximity p r o x i m i t y to t o protected p r o t e c t e d lands l a n d s of of the the Boundary Waters Canoe Canoe Area. Area. w e s t on on Mud Mud Creek C r e e k road road R e t u r n to t o vehicles; v e h i c l e s ; Continue C o n t i n u e north n o r t h and west Return following m i l e aa fault f a u l t 'scarp' ' s c a r p ' (ridge ( r i d g e of o f higher h i g h e r grade g r a d e rocks rocks f o l l o w i n g for f o r about a b o u t a mile N. of o f the the Vermilion V e r m i l i o n fault f a u l t and the the road) r o a d ) westward. westward. iimmediately m m e d i a t e l y N. 5.0 5.0 - 6.2 Park - ffairly of rroad with a i r l y sstraight t r a i g h t stretch s t r e t c h of oad w i t h ridge r i d g e immediately i m m e d i a t e l y to to 6.2 the t h e north. north. The ooutcrop is about STOP 2B. The u t c r o p is a b o u t 500 500 fft. t . from the road r o a d on the the logged logged STOP 2B. the road: road: NW 1/4 1/4 SE 3 N., R. 14 14 W. W. rridge i d g e rrunning u n n i n gWSW WSW from the SE 1/4 1/4 sec. sec. 36, 36, T. T. 663 N., R. The Rice R i c e Creek gold g o l d prospect p r o s p e c t is i s located l o c a t e d in i n a zone zone of o f highly h i g h l y deformed deformed and the Vermilion Vermilion deformation d e f o r m a t i o n zone. zone. The VDZ VDZ is is a n d altered a l t e r e d rock r o c k here h e r e called c a l l e d the bounded on on the the north n o r t h by by the the Vermilion V e r m i l i o n fault f a u l t and and on on the thesouth s o u t hby bythe theMud Mud creek f e a t u r e s widespread carbonate c a r b o n a t e and a n d aericite sericite c r e e k sshear h e a r zone. zone. The VDZ features alteration a l t e r a t i o n as a s well w e l l as a s several s e v e r a l gold g o l d showings. showings. Gold is i s usually u s u a l l y associated associated with mica and and tourmaline. tourmaline. w i t h ankerite a n k e r i t e and a n d pyrite p y r i t e and and occasionally o c c a s i o n a l l y with w i t h green g r e e n mica R i c e Creek showing showing is is located l o c a t e d approximately a p p r o x i m a t e l y 1,000 1 , 0 0 0 feet f e e t south s o u t h of of the the The Rice Vermilion V e r m i l i o n fault f a u l t at a t the the south s o u t h contact c o n t a c t of of aa chert c h e r t iron i r o n formation. f o r m a t i o n . Rocks with with were eelevated l e v a t e d gold g o l d values v a l u e s together t o g e t h e r with w i t h sericite-green s e r i c i t e - g r e e n mica—carbonate m i c a - c a r b o n a t e rocks r o c k s were found on a small s m a l l dump dump created c r e a t e d by by early e a r l y explorers e x p l o r e r s for f o r iron i r o n ore. o r e . The outcrop outcrop ssource o u r c e of of this this material m a t e r i a l can c a n also a l s o be be seen. seen. Gold up to 2 ppm is i s associated a s s o c i a t e d with w i t h pyrite p y r i t e and ankerite a n k e r i t e in i n aa dark d a r k brecbrecThis is in i n contact c o n t a c t with w i t h sheared s h e a r e d sericite s e r i c i t e carbonate carbonate cciated i a t e d chert. chert. T h i s chert c h e r t is Subsequent has g o l d values v a l u e s exist e x i s t at a t the the rrocks. ocks. S u b s e q u e n t ddrilling rilling h a s found that t h a t similar gold nnorth o r t h contact c o n t a c t of of the the iron i r o n formation f o r m a t i o n and and in i n shears s h e a r s in i n the the iron i r o n formation f o r m a t i o n as as well between the the w e l l as a s in i n shears s h e a r s in i n a chiorite—sericite—carbonate chlorite-sericite-carbonate sschist c h i s t lying l y i n g between north n o r t h contact c o n t a c t of of the the iron i r o n formation f o r m a t i o n and and the the Vermilion v e r m i l i o n fault. fault. 6.2 Return to vehicles; drive 6.2 Return to v e h i c l e s ; turn t u r n around and d r i v e south s o u t h on Mud Creek Creek Road Road back b a c k to t o highway highway 1-169. 1-169. D-16 �12.4 unction with 1—169; 1-169; turn t u r n left l e f t (east) ( e a s t ) toward toward Ely. Ely. 12.4 Junction 21.0 County route r o u t e 88 88 enters e n t e r s highway highway from from 21.0 abandoned railroad grade, and turn right r a i l r o a d grade, turn r i g h t from vehicles to abandoned abandoned v e h i c l e s and and walk east e a s t to l e f t (north). ( n o r t h ) . Turn left, l e f t , cross cross left onto dirt track. Disembark o n t o d i r t t r a c k . Disembark quarry. quarry. zone; qquarry and nnatural exposures iin the 3. Longstorff Longstorff Bay shear s h e a r zone; u a r r y and a t u r a l exposures n the STOP 3. SEI/4 sec. SE1/4 s e c . 36, 36, T. T. 63 6 3 N., N., R. R. 13 1 3 W., W., west west of of Ely. Ely. Major shear s h e a r zones form aa b i f u r c a t i n g , wishbone-shaped r a c e tthat hat bifurcating, wishbone-shaped ttrace 5 ) . These zones zones rroughly o u g h l y corresponds c o r r e s p o n d s to t o the t h e outline o u t l i n e of of Shagawa Shagawa Lake Lake (Fig. (Fig. 5). are are collectively c o l l e c t i v e l y referred r e f e r r e d to t o here h e r e as a s the the Shagawa Shagawa Lake Lake shear s h e a r zones. zones. The this shear s h e a r zone system aare r e iinformally n f o r m a l l y rreferred e f e r r e d tto o by tthree h r e e arms of of this by the the rrespective e s p e c t i v e bays bays of of Shagawa Shagawa Lake that that they t h e y transect: t r a n s e c t : The Olson Bay shear shear zone and the the L o n q s t o r f f Bay shear s h e a r zone in i n western Longstorff western Shagawa Shagawa Lake Lake and and the the Spaulding S p a u l d i n g Bay Bay shear s h e a r zone zone in i n eastern e a s t e r n Shagawa Shagawa Lake. Lake. The Olson Bay and and Spaulding of the Shagawa Lake Lake ffault, which S p a u l d i n g Bay shear s h e a r zones follow f o l l o w the trace t r a c e of t h e Shagawa a u l t , which iis s inferred i n f e r r e d to t o be be aa tectonically t e c t o n i c a l l y long—lived l o n g - l i v e d structural s t r u c t u r a l feature. feature. T h i s This family such aas Mud f a m i l y of of shear s h e a r zones is i s eequivalent q u i v a l e n t to t o the t h e D2 sstructures, t r u c t u r e s , such s tthe h e Mud Creek Creek and and Tower—Soudan Tower-Soudan shear s h e a r zones zones of of the t h e western western Vermilion Vermilion district. district. of tthe b e s t exposed exposed of h e tthree, h r e e , deforms The Longstorff L o n g s t o r f f Bay Bay shear s h e a r zone, zone, the best felsic tuff, agglomerate, and graywacke of the Knife Lake Group and aa f e l s i c t u f f , agglomerate, of t h e Knife Lake Group and lamprophyre sill along the contact between the Knife Lake Group and the the s i l l along contact t h e Knife Lake Group and Newton Lake Lake Formation Formation (this ( t h i s stop). s t o p ) . Lens—shaped Lens-shaped islands i s l a n d s of of unsheared, unsheared, mildly The zone m i l d l y deformed deformed lamprophyre lamprophyre occur o c c u r locally l o c a l l y within w i t h i n the t h e shear s h e a r zone. zone. terminates to the the west west against a g a i n s t the the Wolf Wolf Lake Lake fault. fault. t e r m i n a t e s to of the w a s found across a c r o s s any of the Shagawa Lake Although no continuous outcrop o u t c r o p was Longstorff Bay Bay zone zone may be be aas s zzones, o n e s , indirect i n d i r e c t evidence suggests s u g g e s t s that the Longstorff wide as 600 m and and the t h e Spaulding Spaulding Bay zone zone (next ( n e x t stop) s t o p ) may be as wide as a s 1.2 1.2 a s 600 The absence of km. o r r e l a t e d aacross c r o s s the of physical p h y s i c a l markers that t h a t could be ccorrelated exposureofof the the zones, zones, hhas zzones, o n e s , together t o g e t h e r with w i t h the the incomplete incomplete exposure a s inhibited inhibited estimates theamount amount of of shear s h e a r displacement. displacement. e s t i m a t e s of of the . Locality L o c a l i t y 3a: 3a: Sheared Sheared lamprophyre lamprophyre in in quarry q u a r r y pit. pit. Intense s t r o n g mylonite foliation f o l i a t i o n aalong l o n g the I n t e n s e shearing s h e a r i n g has produced a strong ssouthern o u t h e r n margin of of the t h e lamprophyre lamprophyre sill s i l l exposed exposed in i n this t h i s quarry. q u a r r y . Former pyroxene and and hornblende hornblende megacrysts, meqacrysts, now now dark-green dark-green spots s p o t s of of actinolite actinolite ± + occur of this chlorite, o c c u r iin n the t h e less lessdeformed deformed lamprophyre lamprophyre t otot the h e nnorth o r t h of this expoeKpchlorite, The sspots highly to ssure, u r e . The p o t s aare re h i g h l y fflattened l a t t e n e d in i n the t h e foliation f o l i a t i o n and have aa weak weak to shapeiis of the the hhigh moderate llinear i n e a r aspect. a s p e c t . Their T h e i r shape s aa typical t y p i c a l product p r o d u c t of i g h fflatlattening Small—scale t e n i n g sstrains t r a i n s displayed d i s p l a y e d within w i t h i n the the Shagawa Shagawa Lake Lake shear s h e a r zones. zones. Small-scale outcrop sshear h e a r bands and actinolite a c t i n o l i t e foliation f o l i a t i o n fish f i s h from this o u t c r o p aarea r e a iindicate ndicate a dextral observed o only d e x t r a l sense s e n s e of shear; s h e a r ; however, however, these t h e s e features f e a t u r e s were observed n l y iin n ccut ut outcrop. Small hand samples and are a r e not n o t readily r e a d i l y distinguished d i s t i n g u i s h e d in i n outcrop. (centimeter ( c e n t i m e t e r scale) s c a l e ) symmetric crenulations c r e n u l a t i o n s and and chevron chevron folds f o l d s deform deform the the foliation believed thelater later stages f o l i a t i o n locally l o c a l l y and and aare re b e l i e v e d tto o have have formed formed dduring u r i n g the stages off shearing. bandsi ninterpreted be younger younger ffeatures e a t u r e s uunrelated n r e l a t e d to to o s h e a r i n g . Kink Kink bands t e r p r e t e d tto o be the of tthe t h e development development of h e shear s h e a r zones zones are a r e well w e l l developed developed llocally. ocally. Locality L o c a l i t y 3b: Sheared ttuff Sheared u f f of of the t h eKnife K n i f eLake LakeGroup. Group. D-17 �n a r r o w dirt d i r t road r o a d southeast s o u t h e a s t of o f the the quarry q u a r r y and and the the abandoned abandoned railroad railroad A narrow ggrade r a d e leads l e a d s to t o art a n abandoned section s e c t i o n of o f highway. highway. A small ooutcrop u t c r o p oof f h ighly highly the ssheared h e a r e d Knife K n i f e Lake tuff t u f f that t h a t contains c o n t a i n s numerous numerous kink k i n k bands bands crops c r o p s along a l o n g the n o r t h side s i d e of o f the the abandoned abandoned highway t o to the s t ofofthe i r t road r o a d intersecintersecnorth highway thee aeast theddirt tion. tion. 21.0 21 .O 25.1 25.1 Return retrace route R e t u r n t to o vvehicles; e h i c l e s ; retrace r o u t e to t o 11 and e n t to o lleft eft and 169 169and andt hthen ((east) e a s t )back back through t h r o u g h Ely. Ely. Minnesota rroute u r n s south s o u t h toward toward Illgen I l l g e n CIty; C i t y ; ccontinue o n t i n u e east e a s t on on Minnesota o u t e 11 tturns highway 169 toward Winton. Winton. 26.1 26.1 County route r o u t e 88 8 8 (signs ( s i g n s for f o r Echo Trail) T r a i l ) enters e n t e r s from from left l e f t (north); (north); turn t u r n left l e f t onto o n t o route r o u t e 88. 88. 28.1 28.1 Prominent p r o m i n e n t roadcuts r o a d c u t s on either e i t h e r side s i d e of of road; r o a d ; park p a r k on on shoulder s h o u l d e r and and disembark. disembark. STOP 4. STOP 4. Spaulding S p a u l d i n q Bay shear s h e a r zone exposed exposed in i n cuts c u t s along a l o n g County County route route 888, 8 , NW1/4 NW1/4 sec. sec. 23, 23, T. T. 63 6 3 N., N., R. R. 12 1 2 W. W. S p a u l d i n q Bay Bay shear s h e a r zone zone occurs o c c u r s primarily p r i m a r i l y in i n the the Knife K n i f e Lake Lake Group, Group, The Spaulding it affects a f f e c t s adjacent a d j a c e n t variolitic v a r i o l i t i c pillow p i l l o w basalts b a s a l t s of of the the Newton Newton Lake Lake aalthough l t h o u g h it Formation the north n o r t h and andunits u n i t sofofthe theEly E l yGreertstorie G r e e n s t o n e to t o the t h e south. s o u t h . This This F o r m a t i o n to t o the shear Lake, farther s h e a r zone zone presumably extends e x t e n d s toward toward Fall F a l l Lake, f a r t h e r tto o tthe h e eeast, a s t , bbut ut has tthis his h a s not n o t been verified v e r i f i e d by publicly p u b l i c l y available a v a i l a b l e mapping. mapping. Locality L o c a l i t y 4a: 4a: Sheared tuff the Knife K n i f e Lake Lake Group. Group. t u f f of of the Highly the Knife K n i f e Lake Lake Group Group near n e a r its i t s conconH i g h l y sheared s h e a r e d tuffaceous t u f f a c e o u s rocks r o c k s of o f the with the Newton Lake Formation Formation are are exposed exposed here. h e r e . The rocks r o c k s contain contain ttact act w i t h the llocal o c a l concentrations c o n c e n t r a t i o n s of of sulfide s u l f i d e mineralization m i n e r a l i z a t i o n and and abundant abundant kink k i n k bands. bands. - Locality L o c a l i t y 4b: 4b: Sheared S h e a r e d Newton Lake Lake basalt. basalt. Variolitic V a r i o l i t i c pillow p i l l o w basalt b a s a l t and and more massive m a s s i v e flows f l o w s of of the the Newton Newton Lake Lake Formation c u t by by discontinuous d i s c o n t i n u o u s shear s h e a r zones z o n e s at a t this this outcrop. o u t c r o p . Strain Strain F o r m a t i o n are cut analyses a n a l y s e s using u s i n g varioles v a r i o l a s from from this this unit u n i t indicate i n d i c a t e high h i g h flattening f l a t t e n i n g strains strains (k=0.06 and 0.10) 0.10) w with plunging (k=0.06 ith X p l u n g i n g moderately m o d e r a t e l y to to the the southwest. s o u t h w e s t . Weak shear shear bands of the the vverthe order o r d e r of o f 5 cm cm are a r e visible v i s i b l e on some of erb a n d s with w i t h spacings s p a c i n g s on on the ttical i c a l outcrop o u t c r o p faces f a c e s at a t aa high h i g h angle a n g l e to t o the the shear s h e a r zones. zones. This Return i s the the end end of of Field F i e l d Trip T r i p 4. 4. R e t u r n to t o vehicles, v e h i c l e s , turn t u r n around, a r o u n d , and T h i s is retrace route r o u t e to t o Ely. Ely. REFERENCES REFERENCES Bauer, R.L., and younger younger uupright R0L.t 1985, 1985, Correlation C o r r e l a t i o n oof f eearly a r l y recumbent recumbent and pright Bauer, folding f o l d i n g across a c r o s s the the boundary boundary between between an a n Archean Archean gneiss g n e i s s belt b e l t and and greenstone g r e e n s t o n e terrane, t e r r a n e , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Geology, v. v. 1 3, p. p. 13, 6 57-660. 57—660. Colvine, Heather, K.B., Marmont, Marmont, S., S., SSmith, P.M., and and C o l v i n e , A.C., A.C., Fyon, Fyon, JJ.A., .A., H e a t h e r , K.B., m i t h , P.M., Ontario Troop, D.G., 1988, Troop, D.G., 1988, Archean Archean lode l o d e gold g o l d deposits d e p o s i t s in i n Ontario: Ontario: O ntario Geological Paper 136 p. p. G e o l o g i c a l Survey S u r v e y Misecl].aneous Miscellaneous P a p e r 139, 139, 136 D- 18 �Green, K.H., 1982, Geologic Green, J.C., J.C., arid and SSchulz, c h u l z , K.H., G e o l o g i c map map of o f the the Ely E l y quadrangle, quadrangle, St. S t . Louis Louis and and Lake Lake Counties, C o u n t i e s , Minnesota: Minnesota: Minnesota Minnesota Geological G e o l o g i c a l Survey Survey Miscellaneous scale 1:24,000. 1:24,000. M i s c e l l a n e o u s Map Map Series S e r i e s M—50, M-50, scale the H u d l e s t o n , P.J., P.J., 1976, Early E a r l y deformational d e f o r m a t i o n a l history h i s t o r y of o f Archean Archean rocks r o c k s in i n the Hudleston, 1976, Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of of Earth Earth Sciences, S c i e n c e s , v. v. 13, 1 3 , P. p. 579—592. 579-592. D.D., and H u d l e s t o n , P.J., P.J., Bauer, Bauer, R.L., R.L., Southwick, Southwick, D.L., D.L., Schultz—Ej.a, S c h u l t z - E l a , D.D., Hudleston, and Bidwell, the boundary boundary between between Archean Archean B i d w e l l , M.E., M.E., 1987, 1987, Structural S t r u c t u r a l geology g e o l o g y of o f the t e r r a n e s of of low—grade low-grade and and high-grade high-grade rocks, r o c k s , northern n o r t h e r n Minnesota, Minnesota, in in terranes Balaban, Balaban, N.H., N.H., ed., ed., Field F i e l d trip t r i p guidebook guidebook for f o r selected s e l e c t e d areas a r e a s in in Precambrian geology g e o l o g y of of northeastern n o r t h e a s t e r n Minnesota: Minnesota: Minnesota Precambrian Minnesota Geological Geological Survey S u r v e y Guidebook Guidebook Series S e r i e s no. no. 17, 1 7 , p. p. 1-42. 1-42. - Hudleston, and H u d l e s t o n , P.J., P.J., Schultz-Ela, S c h u l t z - E l a , D.D., D.D., and Southwick, Southwick, D.L., D.L., 1988, 1988, Transpreession ~ r a n s p r e e s s i o nin i n an a n Archean Archean greenstone g r e e n s t o n e belt, b e l t , northern n o r t h e r n Minnesota: Minnesota: Canadian Canadian Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , v. v. 25, 25, p. p. 1060—1068. 1060-1068. J., 1987, 1987, Kinematics K i n e m a t i c s of of compressional c o m p r e s s i o n a l and a n d extensional e x t e n s i o n a l ductile ductile M a l a v i e i l l e , J., Malavieille, shearing deformation in a metamorphic core complex of the northern s h e a r i n g d e f o r m a t i o n i n a metamorphic c o r e complex of the n o r t h e r n Basin v. 9, 9 , p. p. 541-554. 541-554. B a s i n and and Range: Range: Journal J o u r n a l of of Structural S t r u c t u r a l Geology, Geology, v. Poulsen, 1983, P o u l s e n , K.H., K.H., 1983, Structural S t r u c t u r a l setting s e t t i n g of of vein—type v e i n - t y p e gold g o l d mineralization m i n e r a l i z a t i o n in in the area: Implication I m p l i c a t i o n for f o r the the Wabigoon Wabigoon t h e Mine Mine Centre—Fort C e n t r e - F o r t Frances F r a n c e s area: Subprovince, S u b p r o v i n c e , in i n Colvine, C o l v i n e , A.C., A.C., ed., ed., The The geology g e o l o g y of of gold g o l d in i n Ontario: Ontario: Ontario p. 174—180. 174-1 80. O n t a r i o Geological ~ e o l o g i c aSurvey lS u r v e y Miscellaneous M i s c e l l a n e o u s Paper P a p e r 110, 1 1 0 , p. 1986, An example example of o f an a n Archean Archean subprovince subprovince 1986, Rainy Rainy Lake Lake Wrench Wrench Zone: Zone: An boundary in i n northwestern n o r t h w e s t e r n Ontario O n t a r i o (extended [ e x t e n d e d abs.], a b s . ] , in i n deWit, d e w i t , M.J., M.J., and and boundary Ashwal, the tectonic t e c t o n i c evolution e v o l u t i o n of of greenstone greenstone Ashwal, L.D., L.D., eds., e d s . , Workshop Workshop on on the belts: b e l t s : LPI LPI Technical T e c h n i c a l Report R e p o r t 86-10; 86-10; Houston, Houston, Lunar Lunar and and Planetary Planetary Institute, p. 177—179. 177-1 79. I n s t i t u t e , p. Schultz-Ela, D.D., 1988, 1988, Application A p p l i c a t i o n of o f aa three—dimensional t h r e e - d i m e n s i o n a l finite—element finite-element S c h u l t z - E l a , D.D., method method to t o strain s t r a i n field f i e l d analyses: a n a l y s e s : Journal J o u r n a l of o f Structural S t r u c t u r a lGeology, Geology, v. v. 10, 10, / 263—272. 263-272. Sims, the Sims, P.K., P.K., 1976, 1976, Early E a r l y Precambrian P r e c a m b r i a n tectonic—igneous t e c t o n i c - i g n e o u s evolution e v o l u t i o n in i n the Vermilion V e r m i l i o n district, d i s t r i c t , northeastern n o r t h e a s t e r n Minnesota: Minnesota: Geological G e o l o g i c a l Society S o c i e t y of of America ~ m e r i c aBulletin, B u l l e t i n , v. v. 87, 8 7 , p. p. 379—389. 379-389. Sims, Sims, P.K., P.K., and and Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1978, 1978, Geologic G e o l o g i c map mapof o f the theShagawa ShagawaLake Lake quadrangle, q u a d r a n g l e , St. S t . Louis L o u i s County, County, Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey Survey Geologic scale 1:24,000. 1:24,000. G e o l o g i c Quadrangle Quadrangle Map Map GQ—1423, GQ-1423, scale Sims, Sims, P.K., P.K., and and Southwick, S o u t h w i c k , D.L., D.L., 1980, 1980, Geologic G e o l o g i c map map of o f the the Soudan Soudan quadrangle, q u a d r a n g l e , St. S t . Louis L o u i s County, County, Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey Survey Geologic scale 1:24,000. 1:24,000. G e o l o g i c Quadrangle Quadrangle Map Map GQ—1540, GQ-1540, scale 1985, 1985, Geologic G e o l o g i c map map of o f Archean Archean rocks, r o c k s , western w e s t e r n Vermilion V e r m i l i o n district, district, northern n o r t h e r n Minnesota: Minnesota: U.S. U.S. Geological G e o l o g i c a l Survey S u r v e y Miscellaneous Miscellaneous Investigations I n v e s t i g a t i o n s Series S e r i e s Map Map 1—1527, 1-1527, scale scale 1:48,000. 1:48,000. D-19 �Regional map map of of the t h e field f i e l d trip t r i p area a r e a showing showing the t h e geologic g e o l o g i c framework framework and and the the F i g u r e 1.1. Regional Figure The d o t t e d c o n t a c t is a major unconformity s e p a r a t i n g g e n t l y d i p p ing major roads. major roads. The dotted contact is a major unconformity separating gently dipping P r o t e r o z o i c strata s t r a t a of o f the t h e Animikie Animikie Group Group (on ( o n the t h e south) s o u t h ) from from deformed deformed Archean Archean Proterozoic rocks. The Animikie Group, c o n s i s t i n g o f t h e Pokegama Q u a r t z i t e and Biwabik rocks. The Animikie Group, consisting of the Pokegama Quartzite and Biwabik iron- orm mat ion (open (open circles) c i r c l e s ) and and the t h e Virginia V i r g i n i a Formation Formation (diagonal ( d i a g o n a l rule), r u l e ) , is is Iron—Formation invaded by gabbroic r o c k s o f Keweenawan a g e ( 1 0 0 0 Ma) i n t h e s o u t h e a s t c o r n e r of invaded by gabbroic rocks of Keweenawan age (1000 Ma) in the southeast corner of t h e map map area. a r e a . The The field f i e l d trip t r i p stops s t o p s are a r e all a l l within w i t h i n Archean Archean terrane. terrane. the D-20 �920 30 92° 15 92°OO I. GRA N ITI cC vc.....' V V Figure 2. 2. Geologic Geologic sketch map of the field trip area Figure sketch of the field trip area showing approximate stopmap locations. Modified from showing approximate stop locations. Modified from ( 1 9 8 2 ) and Sims and Southwick Green and Schulz Green and Schulz (1982) and Sims and Southwjck ( 1 9 8 5 ) . Map explanation is on the facing page. (1985). Map explanation is on the facing page. D-21 94 �EXPLANATION FOR FIGURE FIGURE 22 Pdc Duluth Complex; Complex; v various [y] a r i o u s ggabbroic a b b r o i c rocks rocks Middle Proterozoic Proterozoic 1100 Ma) Ma) ( c a . 1100 (ca. INTRUSIVE CONTACT CONTACT 1 Pv 1 VVirginia i r g i n i a Formation; Formation; turbidite turbidite ) : Ppb] Pokegama Quartzite Q u a r t z i t e (tidal ( t i d a l deposits) deposits 1 overlain o v e r l a i n by by Biwabik Biwabik Iron—Formation Iron-Formation - MAJOR UNCONFORMITY UNCONFORMITY ElGiants E vgo ] Early E a r l y Proterozoic Proterozoic 2000 Ma) Ma) ( c a . 2000 (ca - G i a n t s Range batholith; b a t h o l i t h ; granitoid g r a n i t o i d rocks rocks x Vermilion Granitic V ermilion G r a n i t i c Complex, Complex, granitoid g r a n i t o i d rocks, rocks, pparagneiss, a r a g n e i s s , migmatite migmatite INTRUSIVE CONTACT INTRUSIW OR FAULT CONTACT Newton Lake Formation; Formation; tholeiitic t h o l e i i t i c and komatiitic k o m a t i i t i c metabasalt; m e t a b a s a l t ; numerous numerous sills sills FJ K n i f e Lake Group; s e d i m e n t a r y r o c k s o f mixed v o l c a n i c provenance Knife Lake Group; sedimentary rocks of mixed volcanic provenance K iyl V j Eu J I Lake Vermilion Formation; vvolcanic—derived Lake V e r m i l i o n Formation; olcanic-derived sedimentary s e d i m e n t a r y rocks, r o c k s , mainly of of dacitic dacitic pprovenance rovenance Greenstone, upper member; member; cchiefly Ely E ly G r e e n s t o n e , upper hiefly ttholeiitic h o l e i i t i c metabasalt metabasalt Ely E l y Greenstone, G r e e n s t o n e , Soudan Soudan Iron—formation Iron-formation jJEsJ lilil Member; ccherty Member; h e r t y iron—formation i r o n - f o r m a t i o n iinterbedded nterbedded w i t h felsic f e l s i c to t o mafic m a f i c volcanic v o l c a n i c rocks rocks with El Ely Greenstone, member; cchiefly hiefly E ly G r e e n s t o n e , lower lower member; caic—alkaline c a l c - a l k a l i n e metabasalt metabasalt [TI M e t a b a s a l t(unnamed); (unnamed 1 ; probably p r o b a b l y Ely E ~ Y m1 Metabasalt equivalent equivalent ml kti amphibo— Tonalite T o n a l i t e ggneiss, n e i s s , pparagneiss, a r a g n e i s s , amphibollite; i t e ; stratigraphic s t r a t i g r a p h i c pposition o s i t i o n uuncertain ncertain D-22 Late L a t e Archean Ma) ((ca. c a . 2700 Ma) �P Crenulat~on Crenulation Cleavage S2. S2. Cleavage A \ (a) - SingleCleavage Cleavage Single S2 S0 s2=' so Schematic illustration i l l u s t r a t i o n of of the t h e developnent d e v e l o p n e n t of o f F2' F2' folds f o l d s and and S2' S2' Schematic cleavage during a simple deformation that also produced the foliation c l e a v a g e d u r i n g a s i m p l e deformation t h a t a l s o produced t h e f o l i a t i o n CS2) ( s 2 ) being b e i n g folded. folded. Figure F i g u r e 3. 3. C' C t surfaces s u r f a c e s or or shear s h e a rbands. bands. These These develop d e v e l o p in i n rock rock that t h a t has h a s preprev i o u s l y acquired a c q u i r e d aa strong s t r o n g planar p l a n a r foliation f o l i a t i o n due due to t o very v e r y high h i g h shear shear viously strain. C' surfaces s u r f a c e s are a r e new new ssurfaces u r f a c e s of s l i p that t h a tcross c r o s sthe t h emain main s t r a i n . The The C' of slip Figure F i g u r e 4. 4. i s in i nthe t h esame same sense s e n s e as a s the the f o l i a t i o nata moderate t moderate angles; a n g l e s ; slip s l i pon onthem them is foliation overall o v e r a l l sense s e n s e of of shear s h e a r in i nthe t h eshear s h e a rzone. zone. Modified Modified from from Malavieille Malavieille (1987). (1987). D- 23 �N) . modified from Sims and Mudrey (1978) and Green and Schulz (1982). Generalized geologic map of the Shagawa Lake Figure 5. 3-h Geology area showing locations of stops 9 1° 46' � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1989 Description An account of the resource Institute on Lake Superior Geology. Duluth, Minnesota. May 3-6, 1989. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1989 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/e2f7c9cbcfb728f1e2e916113451605b.pdf 56f92e003fa0fe43bd37cefa8c703ef2 PDF Text Text INSTITUTE GEOLOGY NSTITUTE ON ON LAKE LAK SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS 36th 36th Annual Annual Meeting Meeting May 1990 May 9-12, 9-12,1990 held held at at Thunder Thunder Bay, Bay, Ontario Ontario H. L. JAMES VOLUME VOLUME 36 VOLUME May 1990 1990 Part Abstracts Part 1. 1. Abstracts �U Organizing OrganizingCommittee, Committee, 36th 36thAnnual AnnualMeeting, Meeting,ILSG ILSG(1990) (1990) I The The Organizing Organizing Committee Committee comprises comprises the the following members members of of the the Department Department of of Geology Geology Lakehead Lakehead University University Thunder 5E1 Thunder Bay, Bay, Ontario Ontario P7B P7B5E1 General Chairman: Manfred General Chairman: ManfredM. M. Kehlenbeck Kehlenbeck Program Editor: Philip W. Fralick Fralick Program Chair and Abstract Editor: PhilipW. Field Field Trip Guidebook Guidebook Editor: Graham GrahamJ. J. Borradaile Borradaile Volume Volume 36 consists consists of of Part Part 1: 1: Abstracts Abstracts Part 2: Part 2: Field Field Trip Trip Guidebook Guidebook Reference Reference to material material in in Proceedings Proceedings Volume should follow follow the the example example below: below: Brown, Bruce Significance of of Conglomerates in the Baraboo quartzite of A., 1989, 1989, Significance Bruce A., southeastern southeastern Wisconsin Wisconsin [abst.J; [abst.]; Institute Institute on Lake Lake Superior Superior Geology Geology Proceedings, 35th v. 35, 35, 35th Annual Meeting, Meeting, Duluth, Duluth, MN, MN, 1989; 1989; Houghton, Houghton, MI, MI, v. part 1, p. 11-12. partl,p.11-12. Published Published and Distributed Distributed by by Institute Institute on on Lake Lake Superior Superior Geology Geology J. Kalliokoski, Kalliokoski, Secretary/Treasurer Secretary/Treasurer Dept. of Geological Geological Engineering, Engineering, Geology and and Geophysics Geophysics Michigan Michigan Technological Technological University University Houghton, Michigan Michigan 49931 49931 ISSN ISSN 1042-9964 1042-9964 1 1 �U Dedication The pioneer pioneer research by by Harold Harold L. James formed formed the widely foundation which widely accepted foundation which geologists. His contributions and ideas stimulated the work work of many geologists. ideas have have become become so so intricately intricately inteiwoven in many many of the interwoven in the later laterstudies studies that thattheir theirsignificance significance and and individuality individuality are are often often obscured. obscured. Born a Canadian 1912,Hal Halgraduated graduatedfrom from the theState StateCollege CollegeofofWashington Washingtonin in Canadianinin1912, During World War 1II1 he mapped asbestos, talc talc and and zinc World War mapped chromite, chromite, manganese, manganese, asbestos, zinc in in 1938. During 1938. Montana Montana for for the theUS. U.S.Geological GeologicalSurvey, Survey,and andafter afterreceiving receiving his his PhD PhDfrom from Princeton PrincetonUniversity University 1945 continued continued with with the the US. U.S.Geological GeologicalSurvey Survey with withbrief brief interruptions interruptionsatatNorthwestern Northwestern in 1945 Universityand and the the University UniversityofofMinnesota, Minnesota. After After the the War his research research interests interests focused focused on on the University in the Lake Superior mated iron-formations in Superior region. region. His His appointment appointment as asChief ChiefGeologist Geologistcu/in culminated hhis i s 50-year long career with the Survey. Survey. He He isis now now retired retired and andlives livesin inBellingham, Bellingham,Washington. Waslzin~qton. Ajier retirement retirement from from the the Survey, he served served as as chairman of the oil the IGUS IGUS Subcommission Subcoi?~~?~i.s.sio/z 011 Ajter Survey, he Precambrian Stratigraphy. Stratigraphy. The concepts and time time lines linesassociated associated with withWXYZ WXYZ Precambrian terminology which which he heput put forward forward for for consideration consideration are are still still actively activelyused usedto todefine definePrecumbriun Precambrian terminology time and and stratigraphy. stratigraphy. I-us principal work work for for many years years involved .s f l I (11, His principal involved meticulous mapping and and microscopic microscopicstwlv of iron deposits in Michigan. Michigan. His pulled from from the rock conclusions that today provide provide His keen keen eye eye pulled provocative geological evolution of this this region. region. His recognition recognition of of differences differences provocative insight insight into the geological in tile of iron-formations due to original sedimentation as the mineralogy of as opposed opposed to todifference difference in in response response to later metamorphism metamorp1zism led led to to the therecognition recognition of of different different depositional basins basins for the the various ore types and regional regional metamorphic metamorphiczoning zoning patterns. patterns. The Thefacies fadesoriginally originallydefined definedJromil fro/I 1 iron-ft)rmnation studiesnow noware aremajor major tools tools in unravelling iron-formation studies unravelling Early Early Proterozoic Proterozoic terrane. terrane. The The recognition of of regional regionalzonal zonal metamorphic metamorphic patterns patterns led led to to concepts concepts of of older olderArchean Archean remobilized basement and and stable stableProterozoic Proterozoiccratons cratonsthat thatcharacterize characterizeworking workingmodels modelsfor for early early Proterozoic Proterozoic continental continental margins. margins. as President President ui in He was was extremely extremely active in the the Society Society of Economic Economic Geologists, Geologists,serving serving as 1970. 1970. He was was awarded awarded the the Penrose Penrose Medal Medal from from the the Society Society in 1976 1976 in in recognition recognition of o f his hi.\ coin prehensivestudy studyofofPrecambrian Precambrian rock rock of of the the Lake Lake Superior region and for establishing comprehensive establi.shi/~gthe tho origin and histomy iron deposits associated with origin history ofof iron with them. them. great pleasure pleasure that the It is with great the Institute Institute on on Lake LakeSuperior SuperiorGeology Geology recognizes recognizes Harold volume to him. L. James' life-time life-time contribution contribution by by dedicating this volume M. G. G. Mudrey, Mudrey, Jr. Jr. �I I I 36th 36th ANNUAL ANNUAL INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Proceedings and Abstracts Abstracts Thunder Thunder Bay, Bay, Ontario Ontario May 10 10 and and 11, 11,1990 1990 Organized by by M. M M.Kehienbeck, Kehlenbeck,Lake/zead Lakehead University, University,Thunder ThunderBay Bay G. G. J. Borradaile, Borradaile, Lakehead Lakehead University, University,Thunder Thunder Bay Bay P. W W Fralick, Fralick,Lake/tead LakeheadUniversity, University,Thunder Thunder Bay Bay VoLuMl 36. PART 1 PART 2 PROGRAM AND ABsTRAcTs FIELD TRIP GuIDEBooK �I I I TABLE OF CONTENTS CONTENTS Institutes on on Lake Lake Superior Superior Geology Geology to to 1990 1990 . . . . . . . . . . . . . . . . . . i Constitution of the Institute on Constitution of on Lake Lake Superior Superior Geology Geology . . . . . . . . . . . ii11 By-Laws of the Institute on By-Laws of on Lake Lake Superior SuperiorGeology Geology . . . . . . . . . . . . . 111 iii Goldich Medal Guidelines Guidelines ................................ .. ... iv iv Student Travel Travel Award Award . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vv Board of Directors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Local Local Committee Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi vi Student Paper Award Award Committee Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . vi vi ............................... vi vi Goldich Medal Medal Recipient Recipient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii vi i Banquet Speaker Speaker .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii vii ..................................... vii vi i Goldich Goldich Medal Medal Committee Committee . Acknowledgements Acknowledgements . . . . . ... Report of of the the Chairs Chairs of of the the 35th 35th Annual Annual Institute Institute . . . . . . . . . . . . . . . viii VIII Calendar of of Events Events Poster Papers Papers Abstracts Abstracts ..................................... . . . xx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii xvii ............................................ xix xix �U 1 INSTITUTES INSTITUTES ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 DATE 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 PLACE PLACE Minneapolis, MN MN Houghton, MI MI East Lansing, Lansing, MI MI Duluth, MN MN Minneapolis, MN MN Madison, Madison, WI WI Port Arthur, Arthur, Ont. Ont. (Thunder (Thunder Bay) Bay) Houghton, Houghton, MI MI Duluth, Duluth, MN MN Ishpeming, Ishpeming, MI MI St. Paul, Paul, MN MN Sault Ste. Ste. Marie, Marie, WI WI East East Lansing, Lansing, MI MI Superior, WI WI Oshkosh, WI WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN 1-loughton, Houghton, MI MI Madison, Madison, WI WI Sault Sault Ste. Ste. Marie, Marie, Ont. Ont. Marquette, Marquette, MI MI St. St. Paul, Paul, MN MN Thunder Thunder Bay, Bay, Ont. Ont. Milwaukee, Milwaukee, WI WI Duluth, Duluth, MN MN Eau Eau Claire, Claire, WI WI East East Lansing, Lansing, Ml MI International Falls, International Falls, MN MN Houghton, Houghton, MI MI Wausau, Wausau, WI WI Kenora, Kenora, Ont. Ont. Wisconsin Wisconsin Rapids, Rapids, WI WI Wawa, Wawa, Ont. Ont. Marquette, Marquette, MI MI Duluth, Duluth, MN MN Thunder Thunder Bay, Bay, Ont. Ont. �___________ CONSTITUTION CONSTITUTfON OF INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY Article I Name shall be be the the "Institute 'Institute on Lake Superior Superior Geology". Geology. The name of the organization shall Article II I1 Objectives Obiectives The objectives objectives of this organization organization are: are: A. To Toprovide providea ameans meanswhereby wherebygeologists geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas and scientific data. B. To Topromote promotebetter betterunderstanding understandingofofthe thegeology geologyof of the theLake LakeSuperior Superior region. region. C. To Toplan planand andconduct conductgeological gcologiealfield field trips. trips. Article III I11 Status Status No part of of the the income income of of the organization organization shall shall inure inure to to the the benefit benefit of of any any member member or or individual. individual. In the the event event of of dissolution dissolution the assets assets of of the the organization organization shall shall be be distributed distributed to to (some tax free organization). organization). (To avoid Federal and State State income income taxes, taxes, the organization organization should he be not not only only 'scientific" "scientific" or "educational', "educational", but also also 'non-profit".) "non-profit".) Minn. Stat. Anno. Anno. 290.01, 290.01, subd. 4 Minn. Stat. Stat. Anno. Anno.290.05(9) 290.05(9) Internal Rcvcnue Revenue Code s. 1954 lnternd s. 501(c)(3) SOl(c)(3) Article IV Membership members hi^ of the organization shall consist consistofofthe the board board of of directors. directors. Any The membership membership of organization shall Any geologist geologist interested shall be permitted to attend attend and and participate participate in in and and vote vote at at the theannual annualmeetings. meetings. Article V Meetings Meetings during the the month month of of April. April. The The organization shall meet once a year, preferably during The place place and and exact date of each meeting by the board of directors. meeting will be desginated dcsginated by directors. VI Article VI Directors The board of of directors directors shall shall consist consist of the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and the last last three three past Chairman; but ifif the board board should should at at any any time time consist consist of of fewer than five five persons, by reaon of unwillingness or or inability of of any any of of the the above persons to serve serve as as directors, directors,the thevacancies vacancieson on the board may may be filled filled by the annual meeting so as to bring the membership of the board up up to five five members. Article VII Arficlc Vll Ofliccrs Officcrs The officers of this organization shall be be a Chairman and Secretary-Treasurer. Secretary-Treasurer. A. The TheChairman Chairmanshall shallbe beelected electedeach eachyear yearby bythe theboard boardofofdirectors, directors,who whoshall shallgive give due due of any group group that may be promoting the next consideration to the wishes of next annual annual meeting. meeting. His term of of office as Chairman will terminate at the the close close of of the the annual annual meeting meetingover overwhich which successor shall shallhave havebeen beenappointed. appointed. He will he presides presides or when when his his successor will then serve for a period of three years as a member member of of the the board board of of directors. directors. Secretary-Treasurer shall shallbe be elected elected atat the the annual annual meeting. meeting. His term B. The Secretary-Treasurer term of of office office shall be two two years years or or until until his his successor successor shall have been appointed. Article VIII Amendments This constitution may be be amended constitution may amended by by a majority majority vote of of those those persons persons who who are arepersonally personally present at, participating in, and voting at any annual meeting of the organization. organization. *. 11 11 �U BY-LAWS BY-LAWS I. Dutiesofofthe theOfficers Officersand andDirectors Directors Duties A. ItItshall shallbe bethe theduty dutyofofthe theAnnual AnnualChairman Chairmanto: to: A. 1.1. 2.2. 3.3. Preside atatthe theannual annualmeeting. meeting. Preside Appoint all committees Appoint all committeesneeded neededfor forthe theorganization organizationofofthe thearmual annualmeeting. meeting. Assume Assume complete completeresponsibility responsibility for for the theorganization organizationand andfinancing financingofofthe the annualmeeting meetingover overwhich whichhe hepresides. presides. annual B. ItItshall shallbe bethe theduty dutyofofthe theSecretary-Treasurer Secretary-Treasurerto: to: B. 1.1. 2.2. 3.3. Keep Keepaccurate accurateattendance attendancerecords recordsofofall allannual annualmeetings. meetings. Keep accurate records of all meetings of, and correspondence Keep accurate records of all meetings of, and correspondencebetween, between, theboard boardofofdirectors. directors. the Hold Hold all allfunds fundsthat thatmay mayaccrue accrueas asprofits profitsfrom fromannual annualmeetings meetingsor orfield field trips trips and and to tomake make these these funds funds available available for the organization organization and operation operation of future futuremeetings meetingsas asrequired. required. of C. ItItshall shallbe bethe theduty dutyof ofthe theboard boardofofdirectors directorstotoplan planlocations locationsofofannual annualmeetings meetings C. and and to toadvise adviseon onthe theorganization organizationand andfinancing financingof ofall allmeetings. meetings. 11. II. Duties and andExpenses Exvenses Duties 1.1. 2.2. 111. III. Thereshall shallbe beno noregular regularmembership membershipdues. dues. There Registration Registration fees fees for for the the annual annual meetings meetings shall shall be determined determined by by the the Chairman Chairman in consultation consultation with with the the board boardofofdirectors. directors. ItIt isisstrongly strongly recommended recommended that that in these these be be kept keptatataaminimum minimumtotoencourage encourageattendance attendanceof ofgraduate graduatestudents. students. Rules of ofOrder Order Rules The Therules rulescontained contained in inRobert's Robert's Rules RulesofofOrder Ordershall shallgovern governthis thisorganization organizationininall all cases to to which which they they are areapplicable. applicable. cases IV. 1V. Amendments Amendments These may be be amended These by-laws by-laws may amended by by a majority majority vote vote of of those those persons persons who who are are personally personally present present at, participating participating in, and voting voting at any any annual annual meeting meeting of of the the organization; organization;provided providedthat thatsuch suchmodifications modificationsshall shallnot not conflict conflict with the the constitution constitution as presently presently adopted adopted or orsubsequently subsequentlyamended. amended. as Ill �U AwardGuidelines Guidelines Award SAMGOLDICH GOLDICHMEDAL MEDAL SAM Preamble Preamble The TheInstitute Instituteon onLake h k eSuperior SuperiorGeology Geologywas wasborn bornon onororaround around1955, 1955,asasdocumented documentedbyby the thefact factthat thatthe the27th 27thannual annualmeeting meetingwill will be beheld heldinin1981. 1981.The TheInstitutes Institutesare areexemplary exemplary inin their theircontinuing continuing objectives objectives of of dealing dealing with with those those aspects aspects of of geology geology that are are related related geographically geographicallytotoLake LakeSuperior; Superior;ofofencouraging encouragingthe thediscussion discussionofofsubjects subjectsand andsponsoring sponsori~~g field field trips tripswhich whichwill will bring bringtogether togethergeologists geologistsfrom fromacademia, academia,government governmentsurveys, surveys,and and industry; industry;and andof ofmaintaining maintainingan anexceedingly exceedinglyinformal informalbut buthighly highlyeffective effectivemode modeof of operation. operation. During Duringthe thecourse courseofofits itsexistence existencethe themembership membershipof ofthe theInstitute Institute(that (thatis,is,those thosegeologists geologists who who indicate indicate an aninterest interestininthe theobjectives objectivesofofthe theI.L.S.G. I.L.S.G. by byattending) attending)has hasbecome becomeaware aware of their colleagues have made particularly of the thefact factthat thatcertain certainof of their colleagues have made particularlynoteworthy noteworthyand and meritorious geology meritoriouscontributions contributionstotothe theimprovement improvementofofunderstanding understandingofof"Lake "LakeSuperior" Superior1' geology andits itsmineral mineraldeposits. deposits. and The The exemplary exemplary award award was was made made by by I.L.S.G. I.L.S.G. to Sam Sam Goldich Goldich in in 1979 1979 for for his hismany many contributions 50years. years. contributions to tothe thegeology geology of of the theregion regionextending extendingover overabout about50 Award Guidelines Guidelines Award 1) 1) The Themedal medalshall shallbebeawarded awardedannually annuallyby bythe theI.L.S.G. I.L.S.G.Board BoardofofDirectors Directorstotoa ageologist geologist whose whosename nameisisassociated associatedwith with aa substantial substantial sustained sustainedinterest interestin, in,or oraamajor majorcontribution contribution to,the thegeology geologyof ofthe theLake LakeSuperior Superiorregion. region. to, 2) 2)The TheBoard BoardofofDirectors, Directors,I.L.S.G. I.L.S.G.shall shall appoint appoint the the Nominating Nominating Committee. The Theinitial initial appointment appointment will will be of of three three members, members, one one to to serve serve for for three three years, years, one one for for two, two, and and onefor forone oneyear, year,the themember memberwith withthe thebriefest briefest incumbency incumbency to be chairman. chairman. After Afterthe the one first year the Board of Directors shall appoint at each spring meeting one new member first year the Board of Directors shall appoint at each spring meeting one new member who will will serve serve for for three threeyears. years. In Inthe thethrid thridyear yearthis thismember membershall shallbe bethe thechairman. chairman. who The TheCommittee Committeemembership membership should should reflect reflect the themain mainfields fieldsofofinterest interestand andgeographic geographic distribution ofofI.L.S.G. I.L.S.G.membership. membership. distribution 3) By By November November 1,1, the the Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall shall make make its its 3) recommendation recommendation to to the the Chairman Chairmanof of the theBoard BoardofofDirectors Directorswho whowill will then then inform inform the the Board of of the thenominee. nominee. Board 4) 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nomineeofofthe theCommittee, Committee,will willinform inform the the medalist medalist immediately, immediately, and will will have have one onemedal medalengraved engravedappropriately appropriately for for presentation presentation at atthe thenext nextmeeting meetingof of the theInstitute. Institute. 5) ItIt isis recommended recommended that that the theInstitute Instituteset setaside asideannually annuallyfrom fromwhatever whateversources, sources,such such 5) funds funds as as will will be required required to tosupport supportthe thecontinuing continuingcosts costsof of this thisaward. award. April 1981 April4,4,1981 J.J.Kalliokoski, Kalliokoski,Chairman Chairman Bill Bill Cannon Cannon Fred Fred Kehlenbeck Kehlenbeck Glenn Glenn Morey Morey Greg GregMursky Mursky iv �U I I STUDENT STUDENT TRAVEL TRAVEL AWARD AWARD 98OBoard BoardofofDirectors Directorsestaldished establishedthe the1.L.S.G. I.L.S.G.Student Student1'r:ivcI TravelAward Award l to ' Flic I l c II080 o Ssiipjurl ~II)I)OI Institutes. The Lund student at the annual Institutes. s t ~ ~ d cparticipation ~it The awards awards will will be made from fro111a special I.LIIKI up for this purpose. up purpose. This This award award is is intended intended to to help help defray defray some some of of the the direct direct travel travel costs costs to the Institute Institute and and includes includes aa waiver waiver of of registration registration fees, fees, but but excludes excludes expenses expenses for lodging,and andfield fieldtrip tripregistration. registration. The number of awards and value are determined meals, lodging, detern~ined by the the annual Chairman in consultation with the Secretary-Treasurer by Secretary-Treasurer and and will will be announced announced at the annual annual banquet. banquet. set set The following general criteria criteria will will be be considered by the annual The following general considered by annual Chairman, Chairman, who who isis responsible for the selection: responsible selection: active resident resident (undergraduate (undergraduate or or graduate) graduate) student 1) The Theapplicants applicants must must have active status at the the time time of of the the Institute, Institute, certified certified by by the department department head. head. 2) Students Students who who are the the senior senior author on either an oral or or poster poster paper will will be given favored consideration. consideration. 3) It is is desirable desirable for for two two or or more more students students totojointly jointly request requesttravel travelassistance. assistance. priority will will be be given given to to those those in in the Institute 4) IIn n general, general, priority Institute region region who who are arc farthest Farthest away. away. 55)) Each travel award request shall be made in in writing, to the annual Chairman, Chairman, with an explanation of need, possible author status or or other other significant significant details. details. Successful Meeting. Successfulapplicants applicantswill willreceive receivetheir theirawards awardsatatthe the time time of of registration registration for the Meeting. V �I BOARD BOARD OF OFDIRECTORS DIRECTORS 1990 M. M. M. M. Kehienbeck Kehlenbeck 1990 Department P7B5E1 5E1 Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Bay, Ontario P7B 1989 1989 R. R.W. W.Ojakangas Ojakangas (with (with J. C. Green Green and and T. T. B. B. Hoist) Holst) Department Departmentof ofGeology, Geology,University University of Minnesota, Duluth, Duluth, Duluth, Minnesota Minnesota 55812 558 12 1988 J.S. J.S. Kiasner Klasner (with (with J. J. D. D. Hughes Hughes and andK. K.J.J.Schulz) Schulz) 1988 Department DepartmentofofGeology, Geology,Western WesternIllinois IllinoisUniversity, University,Macomb, Macomb,Illinois Illinois61455 61455 R. P. P. Sage Sage (with (with E. E. D. D.Frey) Frey) 1987 R. 1987 Ontario OntarioGeological Geological Survey, Survey, Ministry Ministry of of Northern Northern Development Developmentand andMines, Mines, 77 77 Grenville Grenville Street, Toronto, Ontario M7A M7A1W4 lW4 Secretary-Treasurer Secretary-Treasurer Kalliokoski J.J. Kalliokoski Department Department of of Geology Geologyand andGeological GeologicalEngineering, Engineering,Michigan MichiganTechnological Technological University, University, Houghton, Houghton, Michigan Michigan49931 4993 1 LOCAL LOCAL COMMI11EE COMMIlTEE M. M. M. Kehienbeck Kehlenbeck M. General General Chairman Chairman P. W. W. Fralick Fralick P. Program and Abstract Abstract Editor Editor G. J. J. Borradaile Borradaile G. Trip Guidebook Guidebook Editor Editor Field Trip STUDENT COMMITFEE 1990 STUDENT PAPER AWARD AWARD COMMI'ITEE 1990 J. S. S. Kiasner, Klasner, Chairman Chairman J. Western Illinois Illinois University, University, Macomb, Macomb, Illinois Illinois W. Kangas Kangas W. Cleveland Cleveland Cliffs Cliffs Iron Co., Co., Ishpeming, Ishpeming, MI MI Southwick D. Southwick Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, MN MN GOLDICH MEDAL MEDAL COMMITFEE COMMI'ITEE 1989-90 1989-90 J. J. Brummer, Brummer, Chairman Brummer BrummerConsulting, Consulting, Toronto, Toronto, Ontario Ontario G. Mudrey, Mudrey, Jr. Jr. M. G. Wisconsin Geologic and Natural Natural History HistorySurvey, Survey,Madison, Madison,WI WI W. Cambray Cambray F. W. Dept. of of Geological Geological Sciences, Sciences, Michigan Michigan State StateUniversity, University, East Lansing, Lansing, MI MI vi �GOLDICHMEDAL MEDALRECIPIENT RECIPIENT1990 1990 GOLDICH Dr. Dr. Ken Ken D. D. Card, Card,Lithosphere Lithosphere and and Canadian CanadianShield ShieldDivision, Division, Geological GeologicalSurvey Survey of of Canada, Canada, 588 Booth Booth Street, Street, Ottawa, Ottawa, Ontario Ontario K1A KIA0E4. OE4. 588 Medal Medal awarded awarded by by M. M. M. M.Kehienheck, Kehlenbeck, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario. Ontario. BANQUET SPEAKER SPEAKER BANOUET At At press presstime timewe weare areunable unabletotoconfirm confirmour ourbanquet banquetspeaker speakerdue duetotocircumstances circumstancesbeyond beyond ourcontrol. control. our ACKNOWLEDGMENTS ACKNOWLEDGMENTS We We three three(M. (M.M. M.Kehienbeck, Kehlenbeck,G. G.J.J.Borradaile, Borradaile,and andP.P.W. W.Fralick) Fralick)gratefully gratefullyrecognize recognizethe the unselfish unselfish contributions contributionsof oftime timeand andenergy, energy,by bymany manyindividuals, individuals, without without which which this this meeting meeting could not not have have taken taken place. place. could We We especially especially thank our our Department Department Secretary, Secretary, Sandra Sandra Millar, Millar, for for her hersecretarial secretarialskills skills and and efficiency efficiency in compiling compiling the mailing mailing lists, brochures, Institute Institute volumes, volumes, and and attending attendingtoto many other othertasks. tasks. many The ' h e drafting drafting of of illustrations illustrations for for the theGuidebook, Guidebook,as aswell well as asassistance assistanceduring during the thetechnical technical sessions provided by by Sam Sam Spivak Spivakand and Reino Reino Viitala. Viitala. Two of our our sessions and field trips, trips, was ably provided Two of graduate graduate students, students, Barbara BarbaraSeemayer Seemayer and andDave DaveNicol, Nicol, handled handled the themailing mailingofofbrochures, brochures, helped helped on on the the field field trips trips and and did did many many other other jobs. jobs. The Theassistance assistanceofofBob BobCornell Cornelland andJim Jim Podd Podd of of Lakehead Lakehead University, University, David David Thomson Thomson (Airlane (Airlane Hotel) Hotel) and andnumerous numerouscompany company personnel isis appreciated. appreciated. personnel 'rhanks for for aa job job well well done done also also go go to: to: Thanks Joe -- Joe Brummer, Cambray (Goldich Brummer, Mike Mudrey Mudrey and Bill Cambray (Goldich Medal Medal Committee) Committee) -- Steve Kissin, Kissin, Maurice Maurice Lavigne Lavigneand andJohn John Scott Scott (Field Richard Sutcliffe, Sutcliffe, Steve (Field Trip Trip leaders) leaders) Richard -- and Bill Bill Kangas Kangas (Student John Kiasner, Klasner, Dave Southwick Southwick and (Student Paper PaperAward Award Committee) Committee) John -- To all all those those brave brave souls souls who who conduct conduct the the technical technical sessions sessions and keep keep the theprogram program To time. on time. Special moments Special thanks to Joe Joe Kalliokoski Kalliokoski for his his support support and and sage sage advice advice during during critical critical moments in the the planning planningprocess. process. in Since Since no list list of of this this type type isis ever ever complete, complete, we we thank thankeveryone everyoneelse elsewho whocontributed. contributed. vii vii �35th 35th ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Duluth, Minnesota Minnesota 1989 1989 Duluth, The The 35th 35th annual annual meeting meeting of of the the Institute Instituteon onLake LakeSuperior SuperiorGeology Geologywas was held held from from May May 3-6, 1989, 1989, in Duluth, Minnesota. The Themeeting meetingwas was hosted hosted by by the theUniversity University of of Minnesota, Minnesota, 3-6, as General Chairman, John C. Green Duluth. Richard Richard W. W. Ojakangas Ojakangas served served as Chairman, John Green served served as as Duluth. Program and Abstract Editor, and and Timothy B. Hoist Holst served served as Field Field Trip Trip Program Chairman Chairman and Abstract Editor, Timothy B. Chairman and and Guidebook Guidebook Editor. Editor. Several Several other UMD UMD faculty faculty members members and and graduate graduate Chairman and the the banquet were held students assisted assisted ininvarious variousways. ways. Technical Technical sessions sessions and held at at the the students Radisson & 5. 5. A A total total of of 202 202 persons registered for for Radisson Hotel on on Thursday Thursday and Friday, May May 44 & the the meeting. meeting. Thirty Thirtypapers papers were were presented presented orally orally and and 24 24 were presented as posters. Two Two field field trips trips were were held held on onWednesday Wednesday May May 33 and and two two were were held held on onSaturday SaturdayMay May 6.6. Paper follows: "Midcontinent Papersessions sessions were were organized organized into into four four one-half one-half day day sessions, sessions, as follows: Rift'; Rift";'Mostly "MostlyEconomic Economicand andQuaternary," Quaternary,''"Mostly "MostlyProterozoic" Proterozoic"and and"Mostly "MostlyArchean". Archean". A A total total of of 124 124 persons registered for for field trips. Field Field trip trip1,1,led ledby by John JohnC. C.Green, Green,was was ledby byTimothy TimothyB. B. Minnesota (30 (30 persons). persons). Field Fieldtrip trip2,2,led to the the North North Shore Shore Rhyolites Rhyolites jf Minnesota to (24 persons). persons). East-Central Minnesota Minnesota(24 Holst was was a visit to Penokean Structural Terranes .f East-Central Holst Field Field trip trip 3, 3, led led by by Karl Karl Seifert, Seifert, James James Olmstead, Olmstead, and and Ken Ken Kiewin Klewin was to the the Mellon Mellon Com~lex.Wisconsin Wisconsin (23 (23 persons). persons). Field Field trip trip 4, 4, entitled entitled Archean Archean Gold GoldOccurrences Occurrences & Complex. their their Structural Structural Settings. Settings. Minnesota, Minnesota, had hadeight eightleaders, leaders,asasfollows: follows: J. J. Welsh, Welsh, D. D.England, England, D. D. Groves, Groves, E. E. Levy, k v y , P. P. Hudleston, Hudleston, D. D. Southwick, Southwick, R. Bauer, Bauer, W. W. Ulland Ulland (47 (47persons). persons). A A total total of of 159 159 people attended attended the the annual annual ILSG ILSG banquet. banquet. Mike MikeMudrey, Mudrey,Jr. Jr.presented presented the KalliokoskiofofMichigan MichiganTechnological Technological University University for for his his many many the Goldich Goldich Medal MedaltotoJ.J.Kalliokoski contributions contributions to to teaching teaching and and research research on onthe theLake LakeSuperior Superiorregion, region,asaswell wellasasfor forhis hislong long The banquet speaker was Frederick J. "Sam" Sawkins of the J. "Samo' Sawkins of the service to the Institute. The banquet speaker was Frederick service to the Institute. University of Minnesota, Twin Cities, who spoke on "Ore genesis models for University Minnesota, Twin Cities, who on "Ore genesis models for volcanoplutonic arc Hisagnostic agnosticviews views arc system: system: An Anagnostic agnosticview viewof ofthe theconventional conventionalwisdom." wisdom." His stimulated stimulated discussions discussions for the remainder remainder of of the themeeting. meeting. In T U G assisted assisted seven seven In continued continued support support of of student student participation participation in in the the meeting, meeting, the the ILSG Six UMD UMD students students with with small small transportation transportation stipends stipends and and waiver waiver of of registration registration fees. fees. Six students students were were given given waivers waivers of registration registration and banquet banquet fees fees for for their theirvalued valuedassistance assistance before Anaward awardofof$150 $150was was presented presented to to Torn Tom before and and during during the the meeting meeting and and field field trips. trips. An Suszek of Minnesota, Minnesota, Duluth, Duluth, for for the best best oral student presentation, Suszek of the University University of presentation, and and $150 award award was was presented presented to to Daniel Daniel Hoim Holm of of Harvard Harvard University University for the the best best poster poster aa $150 paper. John John Kiasner, Klasner, Ray Ray Anderson, Anderson, and and Keith Keith Laskowski Laskowski served served on on the the Best BestStudent Student paper. Paper Committee. Committee. Paper An ILSG ILSG Board Board of of Directors Directors Luncheon Luncheon Meeting Meetingwas was held held on onMay May4.4. It An It was was attended attended J. Greenburg, Greenburg, T. T. Hoist, Holst,J.J.Hughes, Hughes,J.J.Kalliokosi, Kalliokosi,M. M.Kehienbeck, Kehlenbeck, by B. Brown, J. C. Green, by Green, J. J.J. Kiasner, Klasner, R. R.Ojakangas, Ojakangas, R. R.Sage, Sage,S. S.Sawkins, Sawkins, and and K. K. Schulz. Schulz. The Thefollowing followingitems itemswere were discussed: discussed: ... viii Vlll �U from the ILSG (1)$500 $500 from ILSG Treasury Treasury in in the U.S. U.S. and and $500 $500 from from the the ILSG ILSG treasury treasury inin (1) Canada will will be made made available available for for travel travel support support for for students students presenting presenting papers. papers. (2) (2) John Hughes Hughes read read aa letter letterfrom fromBurt BurtBoyum Boyum regarding regarding the the making making of of aa video video on on the the Mining History of of the Marauette Marquette Range. Mining Historv Range. (This (Thiswas wasthe thetitle titleof of aafield fieldtrip tripatatthe the34th 34thILSG ILSG at Marquette Marquette in in1988). 1988). ILSG ILSGwill will support support the the idea ideaand andurges urgesthat thatacknowledgment acknowledgmentof of Burt Burt Boyum and Bob Reed be be included included in in the thevideo. video. Boyum (3) R. (3) Voted to to ask ask Bill Bill Cambray to serve on the Goldich Goldich Medal Medal Committee, Committee, replacing replacing R. W. Ojakangas whose term has has expired. expired. (4) was received. received. The balance in the General (4) The Treasurer's report report by by J. J. Kalliokoski Kalliokoski was General account as as of of April April 30, 30, 1989 1989 was $5,593.03. $5,593.03. The The Goldich Goldich Medal Medal Fund Fundcontained contained$352.15. $352.15. M. Kehlenbeck, Kehienbeck, Treasurer of the Canadian Canadian account, account, reported reported aabalance balanceofof$10,299.90 $10,299.90 as as of of April 30, 30,1989. 1989. April We We wish wish to thank thank all all those those who who helped helped totomake makethis thisa asuccessful successfulILSG ILSG meeting, meeting, including all the speakers, the poster-presenters, including all poster-presenters, the field field trip trip leaders, leaders, the thesession sessionchairs, chairs, the the Student Student Paper Paper Judges, Judges,the the Goldich GoldichMedal MedalCommittee, Committee,the theBanquet BanquetSpeaker, Speaker,Mary MaryNash Nash (UMD who handled (UMD Geology Geology Department Department Executive Executive Secretary) Secretary) who handled the the finances, finances, Joan Joan Hendershot Hendershot (UMD (UMD Geology Geology Department Department Senior SeniorSecretary) Secretary) who who did did nmuch m u c h ofofnecessary necessary arrangements, numerousstudent student assistants, assistants,the the guiding guidingBoard Board ofof Directors, and J.J. arrangements, numerous Directors, and Kalliokoski, Kalliokoski, the Secretary-Treasurer Secretary-Treasurer of of ILSG. ILSG. Finally, Finally, the advice advice and and sympathy sympathy of the the organizers of previous meetings has been been most most helpful. helpful. Respectfully Respectfully submitted, submitted, R. W. W. Ojakangas Ojakangas J. C. C. Green Green T. B. Hoist x �CALENDAR OF OFEVENTS EVENTSAND ANDPROGRAM PROGRAM CALENDAR WEDNESDAY. WEDNESDAY. MAY9 MAY 9 Field Field Trips Trips 1, 1, 2, 2, and and 44 Field Field trips trips depart at 88 am. am.from porn the therear rearparking parking lot lot of of the the Airlane Airlane Motor Motor HoteL Hotel. Lunch Lunchisisprovided. provided. TRTPNO. TRIP NO. I I** Sutcliffe (leader) (leader) -- Mafic Mafic intrusions, intrusions, PGE PGE Sutcliffe mineralization and granitoid rocks of the Lac des Tiles mineralization and granitoid rocks of the Lac des Illes area. area. R. R. VANS VANS TRIP NO. NO.2* 2* TRIP G. G. Borradaile Borradaile (leader) (leader) -- Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean ArcheanSubprovinces. Subprovinces. VANS VANS FOR FOR PEOPLE PEOPLEWHO WHO ARE ARE GOING GOING ON ON A A POST-MEETING POST-MEETING TRIP TRIP T N P NO. NO. 4* #* TRIP M. Lavigne Lmigne and and J.J. Scott Scott (leaders) (leaders) -- Base Base metal metal mineralization mineralization in in the the Shebandowan Shebandowan Greenstone GreenstoneBelt. Belt. BUS BUS FOR ARE ALSO GOING ON TRIP I1 FOR PEOPLE PEOPLEWHO WHO ARE All All trips trips terminate terminate at at the theAirlane Airlane Motor Motor Hotel. Hotel. 4 p.m. p.m. -- 88 p.m. p.m. and Check-in Check-in for for Pre-registrants Pre-registrants Registration and p.m. -- 10 10 p.m. p.m. 7 p.m. Welcome Welcome Get-together and Poster Poster Displays Displays Cash Bar Bar * These These field trips trips have have been been duplicated duplicated (i.e. (i.e. pre-meeting pre-meeting and andpost-meeting). post-meeting). * x �THURSDAY. THURSDAY.MAY MAY1010 TECHNICALPROGRAM PROGRAM TECHNICAL I MORNING MORNING SESSION SESSION CHAIRS: CHAIRS: Vat ValW. W.Chandler Chandlerand andDonald DonaldM. M.Davidson. Davidson, Jr. Jr. 7.55 7.55 1.1. WELCOME WELCOME 8:OO Jablinski, Jablinski,J.D.* J.D.* 8:00 Holst,T.B. T.B. Hoist, Cuthill,J.J. Cuthill, Oliver,D.C. D.C. Oliver, Pankka, Pankka,H.S.* H.S.* Bornhorst,T.J. T.J. Bornhorst, 2.2. 8:20 8:20 3.3. $140 Hayes, Hayes,M.J.* M.J.* 8:40 Structural Structuralanalysis analysisof of Archean Archeanmetasedimentary metasedimentaryrocks rocksinin Jardine, the vicinity vicinity of of the the Mineral Mineral Hill HillGold Goldmine, mine,Jardine, the Montana. Montana. Finnish FinnishProterozoic Proterozoicgold goldoccurrences occurrencesand andimplications implicationsfor for the theLake LakeSuperior SuperiorRegion. Region. Geology Geology of of Wright Wright County County using using well well log logdata. data. Nelson,C.L. C.L. Nelson, 4.4. 900 9:00 Venzke, E.A.* Venzke,E.A.* The The geology geology of of the the Greenwood Greenwood Lake Lake area area l)uluth Ihli~th Complex, Complex, Lake Lake County, County, Northwestern NorthwesternMinnesota. Minnesota. 5.5. The The role roleofofvolatiles volatiles in in the theformation formationofofthe thePlatinum Platinum Group Group Element Elementdeposits depositsin inthe theMiddle MiddleProterozoic Proterozoicand and the theTriassic TriassicNoril'sk-Talnakh Noril'sk-Talnakh Intrusions. Intrusions. 9120 9:20 Weiblen, Weiblen,P.P. Sabelin,T.T. Sabelin, Saini-Eidukat,B.B. Saini-Eidukat, Iwasaki,I.I. Iwasaki, 9:4O 9:40 COFFEE COFFEEBREAK BREAKand andPOSTER POSTERSESSION SESSION CHAIRS: CHAIRS: Ted Ted J.J. Bornhorst Bornhorst and andJohn JohnGreen Green 6.6. 1O:OO 10:00 10120 7.7 . 10:20 * Student Student * Ojakangas, Ojakangas,R.W. R.W. Marmo, J.S. Marmo, J.S. Heiskanen,K.!. K.I. Heiskanen, Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits: deposits: A A North North America-Baltic America-Baltic Connection? Connection? Wilkin, Wilkin, R.T.* R.T.* Mavrogenes, Mavrogenes, J.A.* J.A. * Bornhorst, T.J. T.J. Bornhorst, Archean Archean granitoids granitoids of of northern northern Marquette MarquetteCounty, Co~~nty, Michigan. Michigan. xi �U 8. 8. 10:40 10:40 Juneau, PJ. P.J. petrology of iron silicate-rich silicate-rich bodies in the the Origin and petrology Biwabik iron formation, Minnesota. Minnesota. 9. 9. 11:00 1 1:OO Jerde, Jerde, E.A.* E.A.* Reverse zonation the Lester Lester River River Sill, Sill, Duluth, Dulitth, Reverse zonation in in the Minnesota, and evidence evidence for for polybaric polybaric fractionation. fractionation. 10. 10. 11:20 11120 Aubut, A. A. Geology of the Shebandowan Shebandowan Mine. Mine. 11:40 11~40 LUNCH LUNCH BREAK BREAK Tour Lab., Tour of ofRock Rock Mechanics MecLab.,Lalcehead L,akehead University U~ersity Sign-up Sign-up at atRegictration R w a t z o n Desk 1:00 1100 POSTER SESSION SESSION WITH AUTHORS PRESENT AFFERNOON AFTERNOON SESSION SESSION CHAIRS: Ed Frey Frey and and Tim Tim Hoist Holst CHAIRS: Ed 11. 11. 1:30 1130 Kean, Kean, W.F. W.F. Schneiker, Schneiker, R. R. Paleomagnetism of of Baraboo Baraboointerval intervalrocks rocksininWisconsin. Wisconsin. Paleomagnetism 12. 12. 1:50 150 Chandler, Chandler, V.W. V.W. Morey, G.B. Morey, G.B. The The paleomagnetism paleornagnetism of the the early earlyProterozoic Proterozoic Sioux Sioux 13. 1-3. 2:10 2110 Bodus, Bodus, T.M.* T.M.* Kean, Kean, W.F. W.F. Magnetic Magnetic survey of the Niagara Niagara fault fault system system in in northeastern northeastern Wisconsin Wisconsin and and northwestern northwestern Upper Upper Peninsula Peninsula Michigan. Michigan. 2:30 2130 Lagowski, Lagowski,J•* J.* Geology Geology and economic economic potential potential of of northern northernMichigan Michigan graphite. graphite. 14. 14. Johnson, Johnson, A. A. Gere, Gere,M. M. 15. 15. * quartzite. quartzite. 2:50 250 Cannon, Cannon, W.F. W.F. Peterman, Peterman, Z.E. Z.E. Sims, Sims, P.K. P.K. 3:10 3:lO COFFEE COFFEE BREAK BREAK and andPOSTER POSTERSESSION SESSION * Student Student Structural and and isotopic isotopic evidence evidence for for middle middle Proterozoic Proterozoic Structural thrust thrust faulting fmlting of of Archean Archean and and early earlyProterozoic Proterozoicrocks rocks near near the theGogebic GogebicRange, Range,Michigan Michigan and andWisconsin. Wisconsin. xii xii �U I CHAIRS: CHAIRS: Peter Hudleston Hudleston and John Kiasner Klasner Read, Read, W.F.* W.F.* New evidence evidence that that Limestone Limestone Mt., Mt., Michigan Michigan isis part part of New of a large impact impact structure. structure. 17. 17. 350 3:50 Saini-Eidukat, Saini-Eidukat, B.* B.* Review of of analytical analytical methods methods for for the the determination of Review platinum group elements. 18. 4:10 18. 4:lO Victory, D.* D.* Watkins, I.I. The 7'he mineral relief relief of of surfaces surfaces produced produced by by sanding sandingwith with disaggregation, and percussion, thermal disaggregation, quartz percussion, weathering. weathering. 16. 16. 3:30 3130 Tour of Rock Mechanies Mechania Lab., M.Lakehead , Lakehead University Univenity Sign-up at Registration Registrution Desk Dak 6:30 630 CASH BAR 7:30 7:30 BANQUET BANQUET % Presentation of the Goldich Goldich Medal to K.D. K.D. Card, Geological Survey of of Canada, by by M. M. M. M. Kehienbeck. Kehlenbeck. % Dedication of I.L.S.G. volume 36 36 to H. L. I.L.S.G. volume L, James, James, by by M. M. G. G.Mudrey, Mudrey,Jr. Jr. % will do everything Speaker: The Organizing S~eaker: Organizing Committee Committee will everything possible possible to to provide suitable suitable entertainment. entertainment. We We are arepresently presently unable unable to to confirm confirm our our speaker. speaker. Student xiii �U Ii FRIDAY, MAY MAY 11 TECHNICAL PROGRAM MORNING SESSION CHAIRS: Gene G. Mudrev. Mudrey. Jr. Jr. CHAIRS: Gene LaBerge LaBerge and Michael Michael G. 19. 19. 8:00 8:OO Matty, D.J. Stahl, S.D. S.D. Heft, A. A. Huysken, K. K. Petrologic Penoke :in Petrologic and and geochemical geochemical evolution evolution of of the Penokean Peavy Pond Complex, Iron Iron County, County,Michigan. Michigan. 20. 20. 8:20 8:20 Miller, J.D. Schaap, B.D. Chandler, V.W. V.W. The Sonju Lake Intrusion Intrusion and and associated associated Keweenawan Keweenawan rocks: rocks: Geochemical Geochemical and geophysical geophysical evidence evidence of petrogenetic relationships. relationships. 2 1.1. 8:40 8140 Green, J. minerals and and the the P-T trajectory of Tridymite, other Si02minerals Keweenawan lavas, Minnesota. Minnesota. 22. 22. 9:00 9:00 Paces, J.B. Taylor, L.A. L.A. Petrography, mineral chemistry, chemistry, and geothermobarometry ofof mafic mafic granulite geothermobarometry granulite and and eclogite eclogi te nodules from upper Michigan Michigan Kimberlites. Kimberlites. 23. 23. 9:20 920 Koehler, S.R.* S.R.* Geological setting Bush Lake IAIX Geological setting and geochemistry of of the Bush granite in relation to rare-element pegmatites, Florence County, Wisconsin. Wisconsin. 9:40 940 COFFEE BREAK and POSTER POSTER SESSION SESSION CHAIRS: CHAIRS: Zell Zell Peterman Peterman and and Howard Howard Poulsen Poulsen 24. 10:00 10:OO Kalliokoski, J. J. Michigan: A Geology of of Presque Presque Isle Point, Marquette, Michigan: second look. look. 25. 10:20 25. 10120 Jirsa, M.A. M.A. Southwick, D.L. Boerboom, T.J. T.J. f a 1 1ti ng in The significance of of regional-scale left-lateral faulting development of the Vermillion Greenstone Belt development of Belt in in Minnesota. Minnesota. 10:40 26. 26. 10140 ** Student Nachatilo, S.A.* S.A.* Bauer, R.L. R.L. deformat ion Constraints on Archean versus Proterozoic deformation in Archean Archean rocks rocks of of the the Negaunee Negaunee Area, Area, Upper in Michigan. Michigan. xiv �I 27. 11:OO 1 i :00 27. Borradaile, G. G. Particulate flow and the deformation of rock: Field and and experimental results. 28. 11:20 11:20 28. Gregg, W.J. Transposition structures Transposition structuresin in deformed deformed rock, rock, with examples from the Appalachians Appalachians and upper upper Michigan. Michigan. 11:40 LIJNC1I BREAK Tour of Lab., Lakehead of Rock Mechanics Lab., L.ukehead University U~erdy Sign-up Sign-up at at Regictration Registration Desk SESSION WITH AUTHORS PRESENT 1:00 POSTER SESSION 1100 AFTERNOON SESSION SESSION CHAIRS: William Cannon Cannon and and David David Southwick Southwick CHAIRS: William 29. 1:30 1130 Mudrey, M.G. M.G. Dickas, Dickas, A.B. A.B. McGinnis, L.D. Cannon, W.F. W.F. Tectonic ramifications ramifications of of GNIIArgonne GNI/Argonne kdke Lake Superior Tectonic S~lperior Seismic data. data. 30. 30. 11:50 50 Roscoe, S.M. Roscoe,S.M. The reappearance of of the the Huronian Huronian ininWyoming. Wyoming. 331.1. 2:10 2:lO Davis, D.W. problem reconsidered: The Seine-Coutchiching Seine-Coutchiching problem reconsidered: U-Ph U-1% geochronological data concerning the source source and and timing ti~iii~ig Archean sedimentation of Archean sedimentation in in the western western Superior S~iperior Province. Province. Sims, P.K. P.K. The Great Great Lakes Lakes Tectonic Zone -- a major north-verging north-verging late Archean Archean collision collision zone. zone. 32. 2:30 32. 2130 2:50 250 PRESENTATION OF STUDENT PAPER AWARDS PRESENTATION AWARDS 3:00 3100 COFFEE BREAK BREAK 3:30 3130 Watkins, I.I. Shurr, G.W. G.W. Anderson, G.G. G.G. Faults associated with with the Penokean accretion accretion of of allochthonous Minnesota. allochthonous terranes terranes in central Minnesota. 34.3:50 34. 3 5 0 LaBerge, G. G. Kiasner, J. Klasner, Was the Penokean orogeny a hi-polar Was bi-polar event? event? 35. 35. Turek, A. A. Sage, R.P. van Schmus, W.R. of the Michipicoten Advances in geochronology of Michipicoten greenstone belt. 33. 33. 4:10 4110 TAKE-DOWN PPOSTER TAm-DOWN O S E R PAPERS xv �U SATURDAY, MAY 12 12 Field Trips 1, 2, 2, 33 and 4 Field All jield field trips trips depart depart at 8 a.m. All am. from from tile rear parking the parking lot of of the the Afriane Airlane Motor Hotel. Lunch provided. Lunchisisprovided. TRIP T R I PNO. N O .1* l* Sutcliffe (leader) -- Mafic Sutcliffe Mafic intrusions, intrusions, PGE mineralization and llles mineralization and granitoid granitoid rocks rocks of of the Lac des Illes area. area. R. VANS FOR PEOPLE PEOPLE WHO HAVE HAVE GONE ON TRIP NO. 44 TRIP T R I P NO. NO, 2* 2* of the Shebandowan G. Borradaile Borradaile (leader) -- Geology of Shebandowan and Quetico Archean Archean Subprovinces. Subprovinces. VANS TRIP NO. 33 Kissin (leader) -- Granitoid related mineral S. Kissin mineral deposits in the western Lake Superior Superior region. region. BUS B US TRIP T R I P NO. NO. 4* 4* M. (leaders) -- Base metal M. Lavigne Lavigne and and J. Scott Scott (leaders) mineralization Shebandowan Greenstone Belt. mineralization in the Shebandowan BUS FOR PEOPLE PEOPLE WHO ARE ARE NOT GOING ON TRIP 11 terminate at at the theAfriane Airlane Motor MotorHoteL Hotel. All trips terminate ** have been duplicated, (i.e. Indicates trips which which have (i.e. pre-meeting and and post-meeting). post-meeting). xvi mi �U POSTER PAPERS Authors are requested Authors requested to be be present present at at their theirposters postersduring during the thescheduled scheduled times times from 1:00 to 1:30 on Thursday Thursday and and Friday, Friday, and and at other times 1:OO to 1130 on times when when convenient. convenient. from I. Bauer, R.L. and Tabor, J.R. 1. Syntectonic, intermediate-pressure intermediate-pressure regional regional metamorphism metamorphism along along the northern Syntectonic, northern margin of the Quetico Quetico Belt in in northeastern Minnesota: Minnesota: Contrasts margin of Contrasts with with adjacent adjacent boundary areas. 2. Bennett, G., Born, P. and Hatfield, 2. Hatfield, K. K. dolostone unit unit near near Sault Ste. Marie, Ontario A recently discovered discovered dolostone DahI, D.A. and Cartwright, 3. Dahl, 3. Cartwright, D.F. Carbonate in till till units units of of Lake Lake of of the theWoods Woods County, County, Minnesota. Minnesota. 4. Davidson, D.M., Jr. Magnetic susceptibility anisotropy anisotropy and and strain, Thomson formation (Proterozoic), (Proterozoic), Minnesota. Minnesota. 5. 5. Feeney, J.* J." and Kean, Feeney, Kean, W.F. W.F. Paleomagnetism of Keweenawan age basalts of the Chengwatana volcanic group in the St. St. Croix Croix Falls Falls and and Fredrick-Miltown Fredrick-Miltownarea areaof ofPolk PolkCounty, County,Wisconsin. Wisconsin. 6. 6. Geerts, S.D.* S.D.* Geology and mineralization mineralization in in the Dunka Road copper-nickel copper-nickel mineral deposit, deposit, Geology and St. Louis County, County, Minnesota. Minnesota. 7. Jiran, Jiran, J. J. 7. State of Minnesota Minnesota drill drill core core library. library. 8. 8. Johnson, R.C.* R.C.* Structure of the northern Marq~~ette Structure of northern block block of the the Ishpeming Ishpeming Greenstone Belt, Marquette County, Michigan. Michigan. 9. 9. Mancuso, J., J., Stephen, J•* J.* and Kangas, Kangas, W. W. Stratigraphy of the the Negaunee Stratigraphy of Negaunee Iron Iron Formation, Formation, eastern eastern Marquette Marquette Range, Range, Michigan. Michigan. 10. Milkereit, B. et al. 10. al. Crustal structure of northeastern Lake h k e Superior Superior from from GLIMPCE GLIMPCE reflection reflection and and refraction data. ** Student xvii �U 11. Mohn, P.A.* 11. P.A.* and Gregg, Gregg, W.J. W.J. Mesoscopic evidence for B, B1 deformation deformation in lower Proterozoic supracrustal supracrustal rocks rocks near Rockford, Rockford. South Dakota. 12. Morton, R.L., Hudak, G.J., Walker, 12. Walker, J.S. J.S. and Franklin, J.M. volcanology and and hydrothermal hydrothermal alteration alteration associated The physical volcanology associatedwith with the themassive massive sulphide deposits of the South Sturgeon Lake area, northwestern Ontario. sulphide deposits of Ontario. 13. Mudrey, M.G., Dickas, A.B., McGinnis, L.D. L.D. and Cannon, W.F. 13. A.B., McGinnis, W.F. ramifications of of GNIIArgonne GNI/Argonne Lake Tectonic ramifications Lake Superior Superior seismic seismic data. data. 14. O'Brien, M. M. Exploration and mining activity in northwestern northwestern Ontario. Exploration activity in 15. Palmquist, Palmquist, J.C. Archean Mineral Archean and Penokean Penokean strains strains in the the Northern Northern Complex, Complex, Marquette Marquette Mineral District, District, Michigan. Michigan. 16. Saja, D.* and Gregg, Gregg, W.J. W.J. Structural studies in the Huron Huron Bay Bay parautochthon, parautochthon, Upper Upper Michigan. Michigan. 17. Severson, Severson, M.J.* and Hauk, Hauk, S.A. S.A. Geochemistry of of unmineralized unmineralized rocks rocks in in the the Partridge Partridge River Intrusion, Duluth Dulnth Geochemistry Complex. Complex. 18. Shurr, Shurr, G., G., Watkins, Watkins, I., I., Victory, Victory, D.* D.* and and Tozer, Tozer, M.* M.* Geological significance significanceofoflinear linear features features visible visible on on Landsat in westwestGeological Landsat images images in central Minnesota. Minnesota. 19. Smith, Smith, M. M. Bioturbation in the Jacobsville sandstone, sandstone, Lake Lake Linden Linden location - what are the Bioturbation the implications? implications? 20. Thompson, Thompson, M.E., M.E., Ervin, Ervin, C.P., C.P., Mudrey, Mudrey, M.G. M.G. and andBrown, Brown, B.A. B.A. Tectonic ramifications ramifications of of GNIIArgonne GNI/Argonne Lake Superior Tectonic Superior seismic seismic data. data. Informal Informal displays displays by: by: a. Jirsa, M.A., Boerboom, T. and Southwick, a. Southwick, D. B. Ontario h. b. Zayachivsky, Zayachivsky, B. OntarioGeological GeologicalSurvey. Survey. ** Student xviii xviii �U 1 I ABSTRACTS ABSTRACTS xix �U Geology Geoloqv of the the Shebandowan Shebandowan Mine Mine Alan Aubut, Aubut, Inco Inco Exploration Exploration and and Technical Technical Services, Services, Inc., Inc., Thunder Bay, Thunder Bay, Ontario ontario P7C P7C 4Yl 4Y1 owned by Shebandowan Shebandowan Mine, Mine, owned by Inco Limited Limited and and operated operated MacIsaac MacIsaac Explorations, Explorations, is is the the only producing Nickel Copper mine It is northwestern Ontario. Ontario. It is located located 75 km km west—northwest west-northwest Thunder Thunder Bay. Bay. The The by by in of of The geology geology of of the mine mine property property consists consists of mafic of Keewatin Keewatin mafic volcanics and ultramafics ultramafics unconformably unconformably overlain by by Timiskaming Timiskaming type volcanics volcanics and and sediments. sediments. All are intruded intruded by granitic granitic rocks rocks type of the Shebandowan Shebandowan Lake The Crayfish Crayfish Creek Lake Stock. Stock. The Creek Fault Fault is is a major transcurrent fault that crosses the property, just south of the the Shebandowan mine. Shebandowan mine. The suiphide sulphide mineralization at Shebandowan Shebandowan consists consists primarily primarily of of stringer, breccia hosted by sheared stringer, breccia and massive massive sulphides sulphides hosted sheared and and The faulted peridotite. sulphides are faulted peridotite. The main sulphides are pyrrhotite, pyrrhotite, chalcopyrite and and pentlandite. pentlandite. The suiphides sulphides show evidence evidence of of remobilization due remobilization due to to dynamic dynamic metamorphism. metamorphism. Other provide evidence evidence that they Other ultramafics ultramafics in in the immediate immediate area provide komatiite flows are komatiite flows rather rather than than sills sills as as previously previously believed. believed. The The Shebandowan nickel-copper deposit has many physical physical similarities similarities to the the Redross Redross deposit deposit in in Australia, Australia, aa dynamically dynamically metamorphosed metamorphosed nickel-copper sulphide is nickel-copper sulphide deposit deposit hosted hosted by by aa komatiite komatiite flow. flow. It It is postulated that that the the Shebandowan Shebandowan Ni-Cu Ni-Cu mine mine is is also also the the product product of of komatiite hosted sulphide a deformed and remobilized komatiite sulphide deposit. deposit. �I SYNTECTONIC, INTERMEDIATE-PRESSURE REGIONAL METAMORPHISM ALONG THE NORTHERN MARGIN OF THE QUETICO BELT IN NORTHEASTERN MINNESOTA: CONTRASTS WITH ADJACENT BOUNDARY AREAS * I Robert L. Bauer, Department of Geological Sciences, University of Missouri, Columbia, Missouri, 65211 John R. Tabor, Department of Geology, University of Tennessee, Knoxville, Tennessee, 37996 Metamorphism in the schist and migmatite along the northern margin of the Quetico belt is typically post to late tectonic and shows high lateral thermal gradients adjacent to high-level plutons of the region (Percival, Pine and Mackasey (1978), for instance, described a 4 km transition 1989). from the chlorite zone progressively through the biotite, garnet, andalusite, garnet-sillimanite, garnet-cordierite-sillimanite, and migmatite zones in the country rocks north of the Sturgeon Lake batholith (assemblages 1-15 in Fig. Similar low-pressure zonal sequences and high geothermal gradients over 1). distances of less than 6 km have been reported from several localities in the central Quetico belt (Pine and Mackasey, 1978; Sawyer, 1983) and from the area east of Lake Nipigon (Percival, 1983; Pine and Mackasey, 1978). In contrast to these studies, our work along the northern margin of the belt, southeast of International Falls and west of the Sturgeon Lake batholith (SLB), indicates that the schist and migmatite of this area have undergone syntectonic, intermediate-pressure metamorphism that apparently predates the lower pressure, posttectonic metamorphism along the belt margin to the east. The metamorphism in our study area displays a Barrovian zonal series, ranging from the kyanite-staurolite zone to the cordienite - K-feldspar zone (Table 1; The thermal event peaked during the second of assemblages I-VI in Fig. 1). three periods of folding that deform the schist and migmatite of the area Fibrolite tufts from the sillimanite-staurolite zone through (Bauer, 1988). the sillimanite - K-feldspar zone are aligned parallel to an S2 foliation and Cordierite are folded by F3 folds and an S3 crenulation foliation. porphyroblasts locally contain F2-folded inclusion trails of sillimanite and are elongated parallel to a strong L3 lineation that was accentuated by the nearly coaxial nature of the F2 and F3 regional fold systems. Randomly oriented blocky crystals of retrograde muscovite locally replace K-feldspar and sillimanite and may contain inclusion trails of F3The retrograde muscovite and the common partial folded sillimanite. replacement of garnet by biotite + sillimanite suggest a decompression cooling path for the rocks during and following F3 folding. Although porphyroblast growth in the areas of steep thermal gradient north of the SLB is typically post D1 and D2, Kehlenbeck (1976) found evidence for a polymetamorphic history with both syntectonic and posttectonic porphyroblast growth in the rocks north of the SLB north of Thunder Bay. He suggested that either contact or low-pressure regional metamorphism was overprinted on pre-existing regionally metamorphosed rocks in this area. We believe that the syntectonic metamorphism we see in the schist west of the Sturgeon Lake batholith may be correlated with the syntectonic event described by Kehlenbeck (1976). 2 �U REFERENCES REFERENCES CITED CITED B a u c r , R.L. K . L . , 1988, 1988, Bauer, Multiple M u l t i p l e folding f o l d i n g and a n d regional r e g i o n a l fo'd f o l d patterns p a t t e r n s in i n the t h e northern northern Vermilion V e r m i l i o n Granitic G r a n i t i c Complex, Complex, N.E. N.E. Minnesota: M i n n e s o t a : Institute I n s t i t u t e on on Lake Lake Superior Superior Geology, G e o l o g y , Proceedings P r o c e e d i n g s and and Abstracts, A b s t r a c t s , V. V. 34, 3 4 , p.3. p.3. K e h l e n b e c k , M.M. M.M., 1 9 8 6 , Nature N a t u r e of o f the t h e Quetico Q u e t i c o - Wabigoon Wabigoon boundary boundary in i n the t h e de de Kehlenbeck, , 1986, Canadian Journal Courcey-Smiley Lakes area, northwestern Ontario. C o u r c e y - S m i l e y Lakes a r e a , n o r t h w e s t e r n O n t a r i o . Canadian J o u r n a l of of Earth E a r t h Sciences, S c i e n c e s , v. v . 13, 1 3 , p. p . 737-748. 737-748. Pine, P i r i e , J.A. J . A . and a n dMackasey, Mackasey, W.O., W . O . , 1978, 1 9 7 8 , Preliminary P r e l i m i n a r y examination e x a m i n a t i o n of o f regional regional metamorphism in i n parts p a r t s of o f the t h e Quetico Q u e t i c o metasedimentary m e t a s e d i m e n t a r y belt, b e l t , Superior Superior Province, P r o v i n c e , Ontario. O n t a r i o . In J~J Metamorphism Metamorphism in i n the t h e Canadian Canadian shield. s h i e l d . (edited ( e d i t e d by) by) J.A. J . A . Fraser F r a s e r and a n d W.W. W . W . Heywood, Heywood, Geological G e o l o g i c a l Survey S u r v e y of o f Canada, Canada, Paper, P a p e r , 78-10, 78-10, p . 37-48. 37-48. p. Percival, P e r c i v a l , J.A. J.A, . , 1983, 1 9 8 3 , Preliminary P r e l i m i n a r y results r e s u l t s of o f geological g e o l o g i c a l synthesis s y n t h e s i s in i n the the western w e s t e r n Superior S u p e r i o r Province. P r o v i n c e . In Current C u r r e n t Research, R e s e a r c h , part p a r t A. A. Geological Geological Survey S u r v e y of o f Canada, Canada, Paper, P a p e r , 83-la, 8 3 - l a , p. p . 125-131. 125-131. Percival, P e r c i v a l , J.A., J . A . , 1989, 1 9 8 9 , AA regional r e g i o n a l perspective p e r s p e c t i v e of o f the t h e Quetico Q u e t i c o metasedimentary metasedimentary belt, b e l t , Superior S u p e r i o r Province, P r o v i n c e , Canada. Canada. Canadian C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Sciences, S c i e n c e s , v. v. 2 6 , p. p . 677-693. 677-693. 26, Sawyer, , 1983, Sawyer, E.W. E.W., 1 9 8 3 , The structural s t r u c t u r a l history h i s t o r y of o f aa part p a r t of o f the t h e Archean Quetico Quetico metasedimentary m e t a s e d i m e n t a r y belt, b e l t , Superior S u p e r i o r Province, P r o v i n c e , Canada. Canada. Precambrian P r e c a m b r i a n Research, Research, v. 22, p. 445-473. , - Co C) L. C,) (I) C) 0 Temperature (° (O C) cl Fig. 1 Petrogenetic Petrogeneticgrid grid showing showingthe thestability stabilityfields fieldsofof mineral mineral assemblages assemblagesin in pelitic, pel~tic, migmatitic.and and granitic granitic rocks rocks migmatitic. medium and and high high grades grades (from (from Percival, Perctval, 1989). 1989). The Thesmall smallnumbers numberscorrespond correspondtotomineral mineralassembalges assembalgesinin the the at medium in the the vicinity vicini!yof of the the Sturgeon Sturgeon Lake Lake batholith. batholith. The Thelarge largenumbers numbersindicate indicatebathozones bathozones2,2,3, and metamorphic zones zones in metamorphic 3, and of Charmichael, Charmichael,(1978). (1978). The TheRoman Romannumerals numeralsindicate indicatethe themetamorphic metamorphiczones zonesininour ourstudy studyarea areawest westofof the the 4 of batholith. Sturgeon Lake batholith. Fig. 1 3 I �U I Table Table 1. 1. Metamorphic Metamorphic zones, associated associated mineral mineral assemblages assemblages and and reactions reactions Zone Zone Mineral Assemblage Mineral Assemblage Zone Reaction Reaction Zone ky-st.gt-mu-bi-pl-qz-il ky-st-gt-mu-bi-PI-qz-il I ky=sill ky = sill sill-st-gt-mu-bi-pl-qz-il sill-st-gt-mu-bi-PI-qz-il Il st+mu+qz st + mu + qz =sill-s-gt÷bi+H20 = sill + gt + bi + H 2 0 Ill sill-mu-gt-bi-pl-qz-il sill-mu-gt-bi-PI-qz-il IV ksp-mu-sill-gt-bi-pl-qz-il ksp-mu-sill-gt-bi-PI-qz-il mu + qz qz == sill sill + + ksp ksp + H H20 mu + + p1 PI+ 20 ksp-sill-gt-bi-pl-qz-il ksp-sill-gt-bi-PI-qz-il V sill + bi + qz = ccd gtl + ksp + H H20 +qz d+g 20 cd-ksp-gt-sill-bi-pl-qz-il cd-ksp-gt-sill-bi-PI-qz-il VI Mineral Mineral Abbreviations Abbreviations bi bi cd cd gt gt - biotite biotite cordierite cordierite -- garnet garnet - il ksp ksp ky ky ilmenite -- ilmenite - k-feldspar k-feldspar - -- kyanite kyanite mu muscovite mu - muscovite 4 pl -qz -sill sill -St st -p1 plagioclase plagioclase quartz quartz sillimanite sillimanite staurolite staurolite I �U I A RECENTLY DISCOVERED D I SCOVERED DOLOSTONE UNIT UNIT MARIE, ONTARIO. NEAR SAULT SAULT STE. STE. MARIEl ONTARIO. Bennett, B e n n e t t I Ministry M i n i s t r y of o f Northern N o r t h e r n Development Development and and Mines Mines Sault Ontario; S a u l t Ste. S t e . Marie, Mariel O n t a r i o ; P. Born, Bornl Ministry M i n i s t r y of of Northern Northern Lake Superior Development and and Mines, Mines) Toronto; K. K. Hatfield, H a t f i e l d ) Lake Superior Marie, Michigan State S t a t e University, U n i v e r s i t y l Sault S a u l t Ste. S t e . Marie) G. G. unrecognized Born Born ((1987) 1987) rreported eported a previously previously u nrecognized occurrence o c c u r r e n c e of of dolostone d o l o s t o n e in i n Fenwick Fenwick Township, Township) approximately approximately Marie, Ontario. 27 2 7 km km northwest n o r t h w e s t of of Sault S a u l t Ste. S t e . Marie) Ontario. exposed, but The The area a r e a is i s not n o t well w e l l exposed) b u t detailed d e t a i l e d mapping mapping indicates i n d i c a t e s that t h a t the t h e dolostone d o l o s t o n e and and associated a s s o c i a t e d rocks r o c k s probably probably east-west form aan n e a s t - w e s t trending t r e n d i n g fault f a u l t block, b l o c k ) bounded on the t h e south south t h e Lorrain L o r r a i n Formation of of the t h e Huronian Supergroup Supergroup and by by the of the The total Archean rocks r o c k s on the t h e north. north. t o t a l thickness t h i c k n e s s of the exposed dolostone d o l o s t o n e unit u n i t is i s at a t least l e a s t 30 30 meters. m e t e r s . The lowermost one third t h i r d of of the t h e dolostone d o l o s t o n e sequence sequence consists c o n s i s t s mainly of of very very pink dolostone ffine-grained, i n e - g r a i n e d l ppale ale p i n k to t o reddish r e d d i s h pink pink d o l o s t o n e and and Individual dolostone iintercalated n t e r c a l a t e d grey g r e y to t o pink p i n k metachert. metachert. Individual d olostone beds a r e from a few m i l l i m e t e r s t o a t l e a s t a m e t e r t h i c k . beds have have a similar The metachert m e t a c h e r t beds s i m i l a r thickness t h i c k n e s s range r a n g e but b u t form form lless e s s than t h a n 25 25 percent p e r c e n t of of the t h e visible v i s i b l e section. section. beds are from a few millimeters to at least a meter thick. Pale dolostone P a l e grey, g r e y ) clastic clastic d o l o s t o n e iis s most most abundant abundant type t y p e in in This tthe h e upper u p p e r part p a r t of of the t h e carbonate c a r b o n a t e unit. unit. T h i s ccalcarenite alcarenite consists of consists o f variable v a r i a b l e proportions p r o p o r t i o n s of of angular a n g u l a r to t o subrounded subrounded ssand-sized a n d - s i z e d clasts c l a s t s of of fine-grained f i n e - g r a i n e d dolostone d o l o s t o n e and and subrounded subrounded tto o well-rounded w e l l - r o u n d e d quartz q u a r t z grains. g r a i n s . Well Well developed d e v e l o p e d ooliths o o l i t h s aare re llocally o c a l l y present. p r e s e n t . The clastic c l a s t i c dolostone d o l o s t o n e generally g e n e r a l l y forms forms thick thick beds separated by tthin beds s e p a r a t e d by h i n beds beds of of fine f i n e grained g r a i n e d dolostone d o l o s t o n e or or Coarse, a cchert. hert. C o a r s e l pink p i n k coloured coloured b a r i t e l o c a l l y occurs as few few llensoid e n s o i d masses masses up t o 50 50 cm cm across. across. up to barite locally occurs as No were observed No cclearly l e a r l y identifiable i d e n t i f i a b l e stromatolites s t r o m a t o l i t e s were o b s e r v e d in in the dolostone wavey, the d o l o s t o n e of Fenwick Fenwick Township Towns h i p but b u t irregular, i r r e g u l a r ) wavey) laminae mats, are l a m i n a e of brownish c h e r t ) ssuggestive u g g e s t i v e of of algal a l g a l mats) are locally l o c a l l y present. present. of brownish chert, The clastic dolostone is directly overlain by deep red The c l a s t i c d o l o s t o n e i s d i r e c t l y o v e r l a i n by d e e p r e d and red r e d to t o pink p i n k laminated l a m i n a t e d siltstone. s i l t s t o n e . The contact contact between is a b r u p t and and b e t w e e n the t h e red r e d beds beds a n d the t h e dolostone d o l o s t o n e is and abrupt concordant. concordant. The d o l o s t o n e unit u n i t directly d i r e c t l y overlies o v e r l i e s highly highly The dolostone ffractured r a c t u r e d and sheared, s h e a r e d ) locally l o c a l l y laminated, laminatedl g r e e n and maroon maroon green ssiltstone i l t s t o n e and and argillite. a r g i l l i t e . AA few few beds beds of of recrystallized r e c r y s t a l l i z e d chert, chertl at a t least l e a s t 20 20 cm thick thick and one one dolostone d o l o s t o n e bed bed of o f similar similar and sandstone, sandstone) �U I t h i c k n e s s ) was was observed o b s e r v e d within w i t h i n the t h e siltstone. siltstone. thickness, The The presence p r e s e n c e of of red r e d beds beds above above and and below below the t h e dolostone dolostone u n i t ) and a n d the t h e degree d e g r e e of o f metamorphism metamorphism and a n d deformation deformation unit, indicates i n d i c a t e s that t h a t the t h e dolostone d o l o s t o n e is i s post—Quirke p o s t - Q u i r k e Lake Lake Group Group ( H u r o n i a n ) and and pre-Keewenawan. pre-Keewenawan. (Huronian) The only o n l y known known dolostone d o l o s t o n e in i n the t h e general g e n e r a l area a r e a within within the t h e above above constraints c o n s t r a i n t s is i s found found in i n the t h e Gordon Gordon Lake Lake Formation Formation of o f the t h e Huronian Huronian Supergroup(Hofmann Supergroup(Hofmann et e t al. a l . 1983). 1983). A A variety variety of o f sedimentary s e d i m e n t a r y features f e a t u r e s indicate i n d i c a t e the t h e Gordon Gordon Lake Lake Formation Formation was deposited d e p o s i t e d in i n aa shallow, s h a l l o w I active a c t i v e water w a t e r environment environment such s u c h as as nodules aa tital t i t a l flat(Wood, f l a t ( W o o d , 1973, 1973) p. p . 991). 1 ) . The recognition r e c o g n i t i o n of of nodules of o f gypsum gypsum and a n d anhydrite a n h y d r i t e in i n the t h e Gordon Gordon Lake Lake Formation Formation indicates i n d i c a t e s local l o c a l evaporitic e v a p o r i t i c conditions c o n d i t i o n s (Wood, (Wood) 1973, 1973/ p. p. 85). 85). the The The presence p r e s e n c e of o f ooliths o o l i t h s and a n d sulphate s u l p h a t e (barite) ( b a r i t e ) in in the similar indicates a Fenwick Township dolostone d o l o s t o n e of of Fenwick Township i n d i c a t e s a similar depositional environment tto proposed for d e p o s i t i o n a l environment o tthat h a t proposed f o r the t h e Gordon Gordon Lake Lake Formation. Formation. T h e r e has h a s been b e e n aa long l o n g standing s t a n d i n g debate d e b a t e as a s to to There of stratigraphic s t r a t i g r a p h i c equivalence e q u i v a l e n c e of of the t h e Huronian Huronian rocks rocks o f Ontario Ontario and a n d the t h e Middle M i d d l e Precambrian P r e c a m b r i a n rocks r o c k s of o f the t h e Lake Lake Superior Superior r e g i o n . The The lithological l i t h o l o g i c a l and and stratigraphic s t r a t i g r a p h i c similarities s i m i l a r i t i e s of of region. the t h e Chocolay Chocolay Group Group (and ( a n d equivalent e q u i v a l e n t groups groups further f u r t h e r west) w e s t ) and and have the t h e Cobalt C o b a l t Group Group of of the t h e Huronian Huronian of of Ontario Ontario have been been Young pointed p o i n t e d out o u t by by Church Church and and Young Young (1970), (1970)) ( 1983) 1983) and and Cannon (1975). ( 1 9 7 5 ) . However, However) this t h i s time-stratigraphic t i m e - s t r a t i g r a p h i c correlation correlation Cannon has not n o t been been widely w i d e l y accepted a c c e p t e d (e.g. ( e . g. Morey Morey 1973, 1973# P. p. 242-244, 242-244) and Card Card 1978, 1978) p. p. 24) 2 4 ) since s i n c e radiometric r a d i o m e t r i c dating d a t i n g of o f rocks, rocks) considered c o n s i d e r e d to t o underlie u n d e r l i e the t h e Chocolay Chocolay group, group) provide p r o v i d e evidence evidence that t h a t the t h e Chocolay C h o c o l a y Group Group is i s younger y o u n g e r than t h a n the t h e Huronian Huronian Supergroup Supergroup of of Ontario. Ontario. ( The dolostone d o l o s t o n e of o f Fenwick F e n w i c k Township T o w n s h i p very v e r y closely closely The and stratigraphically lithologically r e s e m b l e s ) both both l i t h o l o g i c a l l y s t r a t i g r a p h i c a l l y the the resembles, Kona Dolomite Dolomite and and equivalent e q u i v a l e n t units u n i t s of of the t h e Marquette M a r q u e t t e Range Range Supergroup. Supergroup. REFERENCES REFERENCES CITED CITED Born) P. P. Born, 1987: of 1987: Geology o f the t h e Havilland-Goulais H a v i l l a n d - G o u l a i s Bay Area, Areal District D i s t r i c t of of 11 Algoma; Ontario O n t a r i o Geological G e o l o g i c a l Survey, Survey) O.F.R. 0. F. R. 5602, 5602/ ll4p., 114p. 11 Algoma; 12 photos, and 3 maps in back pocket. 7 tables, figures, figures) t a b l e s ) 1 2 photosI 3 maps i n back p o c k e t . W. F. F. Cannon) W. Cannon, 1975: 1975: Basal B a s a l Conglomerates Conglomerates Marquette Marquette and a n d Weathere.d Weathere.d Zones Zones in i n the the Range Supergroup, Supergroupl Northern N o r t h e r n Peninsula P e n i n s u l a of of 6 �U Michigan Michigan AgeI -- Age, uranium potential, potential, uranium indications i n d i c a t i o n s of of atmospheric a t m o s p h e r i c oxygen, oxygen) and and Z1-Z17, Z1-Z171 in i n Genesis Genesis of of Uranium— Uranium- and and Quartz-Pebble Gold-Bearing Precambrian Precambrian Q u a r t z - P e b b l e Conglomerates, Conglomeratesl Gold-Bearing Paper BB) G e o l o g i c a l Survey Survey Professional Professional P a p e r 1161 1161 -- AA -- BB, Geological States e d i t e d by by Frank Frank C. C. Armstrong, Armstrong) United United S t a t e s Government Government edited P r i n t i n g Office, O f f i c e l Washington. Washington. Printing p. p. K. D. D. Card) K. Card, 1978: Geology Geology of of the t h e Sudbury-Manitoulin Sudbury-Manitoulin Area, Areal Districts D i s t r i c t s of of 1978: Sudbury and and Manitoulin; M a n i t o u l i n ; Ontario O n t a r i o Geological G e o l o g i c a l Survey Survey Report Report Sudbury 166) 238p. Accompanied Accompanied by by Map Map 2360, 2360) scale s c a l e 11 inch i n c h to t o 22 238p. 166, (1: 126,720), miles ( 1 : 126) 7 2 0 ) ) and and 44 charts. charts. miles Church) W. W. R., R. and Young, Young) G. G. M. M. and Church, 1970: D i s c u s s i o n of t h e p r o g r e s s report r e p o r t of of the the 1970: Committee on Huronian Provi n c i a1 Committee on Huronian sstratigraphy: tratigraphy: Provincial Sciences, J o u r n a l of E a r t h S c i e n c e s I v. v. 7, 7 ) p. p. 912-918. 912-918. Discussion of the progress Journal of Earth FederalFederal- Canadian Canadian and H. J. P e a r s o n ) D. D. A. B., B. and Wilson, Wilson) B. B. H. H. H. J., Pearson, 1 9 8 0 : S t r o m a t o l i t e s a n d f e n e s t r a l f a bric i n early and 1980: Huronian Proterozoic H u r o n i a n Supergroup, S u p e r g r o u p I Ontario: O n t a r i o : Canadian Canadian 1 7 ) p. p. 1351-1357. 1351-1357. J o u r n a l of of Earth Earth S c i e n c e s ) v. v. 17, Sciences, Journal Hofmann) Hofmann, Stromatolites Proterozoic fenestral fabric in early Morey) G. G. B. B. Morey, 1973: 1973: Stratigraphic S t r a t i g r a p h i c framework framework of of middle middle Precambrian P r e c a m b r i a n rocks r o c k s in in Huronian ed., G. M., M. ed. Huronian stratigraphy s t r a t i g r a p h y and and Minnesota) in i n Young, Young, G. Minnesota, Huronian G. M. M. , ed., ed. Huronian s e d i m e n t a t i o n ) Minnesota, Minnesota) in i n Young, Young) G. sedimentation, s t r a t i g r a p h y and and sedimentation, s e d i m e n t a t i o n ) G e o l o g i c a l A s s ~ c i a t i o n of stratigraphy Canada S p e c i a l Paper Paper 12, 12) p. p. 211-249. 21 1-249. Canada Special Geological Association of Woodl J. J. Wood, 1973: 1973: Stratigraphy S t r a t i g r a p h y and and depositional d e p o s i t i o n a l environments e n v i r o n m e n t s of o f upper upper Huronian Huronian rocks r o c k s of of the t h e Rawhide Rawhide Lake-Flack Lake-Flack Lake Lake area, a r e a ) Ontario, Ontario) and strati Huronian G , M., M. ed. I Huronian s t r a t i ggraphy raphy and in Young) ed., G. in Young, sedimentation: G e o logi o g ical c a l Association A s s o c i a t i o n of o f Canada Canada Special Special Geol sedimentation: p a p e r 12, 12) p. p. 73-95. 73-95. paper Young) G. G. M. M. Young, 1983: Tectono—sedimentary T e c t o n o - s e d i m e n t a r y history h i s t o r y of of early e a r l y Proterozoic P r o t e r o z o i c rocks rocks 1983: 15-32; the northern Great Lakes region, G r e a t L a k e s r e g i o n , p. p. 1 5 - 3 2 ; in in o f t h e n o r t h e r n of Society Geological S o c i e t y of of America America Memoir Memoir 160, 160, Edited E d i t e d by by L.G. L. G. Geological Medaris) Jr. Jr. Medaris, 7 �Magnetic Survey Survey of of the the Niagara Niagara Fault Fault System System Magnetic in Northeastern Wisconsin and Northwestern in Northeastern Wisconsin and Northwestern Upper Peninsula Peninsula Michigan Michigan Upper T. M. M. Bodus Bodus and and W, W. F. F. Kean Kean T. University of Wisconsin Milwaukee University of Wisconsin Milwaukee The Niagara Niagara fault fault system system has has been been identified identified based based on on The magnetic data. One of the first ground magnetic surveys of the the magnetic data. One of the first ground magnetic surveys of Niagara fault system was conducted on a four square mile area Niagara fault system was conducted on a four square mile area 1958-59 using using vertical vertical near Keyes Keyes Lake Lake by by Weir Weir and and Solberg Solberg in in 1958-59 near intensity magnetometers. Since that time, several aeromagnetic intensity magnetometers. Since that time, several aeroinagnetic surveys have have been been flown flown across across the the area area in in an an attempt attempt to to further further surveys define the the extent extent and and trend trend of of the thesystem. system. This This ground ground magnetic magnetic define paleomagneticstudy studyof of study was was undertaken undertaken in in combination combination with with aa paleomagnetic study the area in order to fully detail the trend of the system and to the area in order to fully detail the trend of the system and to unravel the the tectonic tectonic history history of of the thearea. area. unravel Two hundred thirty seven miles of field field magnetic magnetic data data were were Two hundred thirty seven miles of collected using two EG&G proton procession magnetometers. One collected using two EG&G proton procession magnetometers. One magnetometer was used as a continually recording base station. magnetometer was used as a continually recording base station. The second second magnetometer magnetometer was was used used to to collect collect readings readingsat at .1 .1 mile mile The spacings. The The survey survey area area was was confined confined to to Florence, Florence, Marinette, Marinette, spacings. Dickinson, and and Nenominee Menominee counties counties Wisconsin Wisconsin and and Michigan Michigan (Fig. (Fig. Dickinson, The data was modeled on a computer. The model parameters of 1). The data was modeled on a computer. 1). The model parameters of susceptibility, remnant component intensity, and direction were susceptibility, remnant component intensity, and direction were determined from from laboratory laboratory and and paleomagnetic paleomagnetic analysis analysisof of samples samples determined obtained in the field along survey lines. In areas where obtained in the field along survey lines. In areas where outcrops were were not not available available along along survey survey lines, lines, similar similar units units outcrops from other other outcrops outcrops within within the the study studyarea areawere wereused. used. Model Model from parameters of of length length of of lithologic lithologic or or lithodemic lithodemicunit, unit,depth depthof of parameters unit, and strike half-length were obtained from maps. Because unit, and strike half-length were obtained from maps. Because the maps maps are are based based on on outcrops, outcrops, and and outcrops outcrops are are sparse, sparse,the the the length, depth and strike half-length of the units were adjusted length, depth and strike half-length of the units were adjusted as needed. needed. as indicate that that the the Niagara Niagara Fault Fault The ground ground magnetic magnetic results results indicate The does not trend the way it is represented on the Wisconsin does not trend the way it is represented on the Wisconsin 1984). The The data data points points Northeast sheet sheet map map (Greenberg (Greenbergand and Brown, Brown, 1984). Northeast were upward upward continued continued to to 500 500 feet feet and and the the individual individualanomalies anomalies were produced by by the the faults faults merged merged with with the the regional regional magnetics magnetics and and produced The peaks of these highs did not produced small elliptical highs. produced small elliptical highs. The peaks of these highs did not necessarily coincide with the location of the anomalies produced necessarily coincide with the location of the anomalies produced by the the faults. faults. The The new new trend trend of of the the faults faults are are based based on on the the by individual fault faultanomalies. anomalies. Modeling Modeling results results produced produced only only aa few few individual tectonic settings settings for for the the area. area. tectonic 8 �U I I Figure magnetic F i g u r e 1. 1. M a p iindicating n d i c a t i n g ffield i e l d m a g n e t i c survey s u r v e y lines. l i n e s . Map Brown, Modified t l o i i i f i e i i from f r o m Greenberg G r e e n b e r g aand nd B r o w n , 1984; 1 9 8 4 ; and a n d Champion Champion linLernational n ~ e r n a ~ i o n aCorporation, C lo r p o r a t i o n , 1986. 1986. �U PARTICULATEFLOW FLOWAND AND THE THEDEFORMATION DEFORMATIONOF OFROCK: ROCK:FIELD FIELD PARTICULATE ANDEXPERIMENTAL EXPERIMENTALRESULTS AND G.J.J.Borradaile Borradaile G. Geology GeologyDepartment, Department,Lakehead LakeheadUniversity University ThunderBay, Bay,Ontario Ontario Canada CanadaP7B P7B5E1 5E1 Thunder Field Fieldevidence evidencefrom fromlow-grade low-grademetasedimentary metasedimentaryrocks rocksand andfrom fromtectonically tectonically deformed deformedsediments sedimentsoften oftenshows showsaadiscrepancy discrepancybetween betweenstrains strainsdetermined determinedon onlarge large and andsmall smallscales. scales. Large Largescale scalestrains strains(hand-specimen (hand-specimentotomany manykilometres) kilometres)are areoften often higher higherthan thanthe thestrains strainsofofsmall smallsedimentary sedimentarystructures structuresororindividual individualclastic clasticgrains. grains. When grain-scale strain is removed mathematically from a large structure, it When grain-scale strain is removed mathematically from a large structure, itisis imperfectly imperfectly"de-strained' "de-strained"because becauseconsiderable considerablelarge largescale scaledistortion distortionmay mayremain. remain. ItItisispostulated postulatedthat thatmuch muchof ofthis thismissing missingstrain strainisistaken takenup upby byinterparticle interparticle motion motionwhich whichremains remainselusive elusive to to petrographic petrographicexamination. examination. Thus Thusclastic clasticgrains grainsonly only record recordpart partofofthe thestrain strainhistory historywhile whilemuch muchstrain strainisistaken takenup upby byintergranular intergranular displacements. displacements.This Thisinvolves involvesdisplacements displacementson onmultigranular multigranularboundaries boundariesand, and,being being flow. more moreencompassing encompassingthan thangrain-boundary grain-boundarysliding, sliding,ititisistermed termed'particulate "particulate flow". Recent Recenthigh highpressure pressureexperimental experimental work work has hasconfirmed confirmedthat thatparticulate particulateflow flowisis enhanced enhancedby byhigh highpre-fluid pre-fluidpressures. pressures. These Thesesupport supportsome someofofthe theload loadso sothat thatthe the intergranular intergranularcontact contactstresses stressesare arereduced reduced("effective ("effectivestresses") stresses")and andslippage slippagewithin withinthe the rock mass is eased. These experiments also confirm that grain deformation is rock mass is eased. These experiments also confirm that grain deformation is reduced reducedby bythis thisprocess process(e.g. (e.g.twinning twinninginincalcite calciteisisless lesssevere) severe) and andfluid fluidpressure pressure oscillates oscillatesas as groups groupsofofgrains grainsslide slidepast pastone oneanother anotherproducing producingephemeral ephemeralvolume volume changes changes within within the the specimen. specimen. AAfurther furtherconsequence consequenceof ofthe theexperiments experimentsisis that that the the bulk bulk strain strainexceeds exceedsthe the grain-scale grain-scale strain strain as as the the field field evidence evidence shows. This Thiseffect effectisis greater at at high highpore porefluid fluidpressures. pressures. greater REFERENCES REFERENCES Borradaile, G.J., G.J., 1981. 1981. Particulate Particulateflow flow and andthe the formation formationof of rock rockcleavage. cleavage. Borradaile, Tectonophysics,72: 72:305-321. 305-321. Tectonophysics, Borradaile, McArthur, J., J., 1990. 1990. Experimental Experimentalcalcite calciteaggregates aggregatesininaasynthetic synthetic Borradaile, G.J. G.J. and and McArthur, weaker matrix matrix by by coaxial coaxial and and non-coaxial non-coaxialdeformation. deformation. J.J.Structural StructuralGeology, Geology,InIn weaker Press. Press. 10 �U STRUCTURAL AND ISOTOPIC ISOTOPIC EVIDENCE STRUCTURAL AND EVIDENCE FOR FOR MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC THRUST THRUST FAULTING FAULTING OF ARCHEAN ARCHEAN AND EARLY PROTEROZOIC PROTEROZOIC ROCKS OF AND EARLY ROCKS NEAR NEARTHE THE GOGEBIC GOGEBIC RANGE, RANGE, MICHIGAN AND AND WISCONSIN WISCONSIN William W i l l i a m F.F.Cannon, Cannon, US US Geological G e o l o g i c a l Survey, Survey, Reston, Reston, VA VA Zell Geological CO Z e l l E. E. Peterman, Peterman, US US G e o l o g i c a l Survey, Survey, Denver, Denver,CO Paul Paul K. K. Sims, Sims, US US Geological G e o l o g i c a l Survey, S u r v e y , Denver, Denver,CO CO Faults F a u l t s with w i t h substantial s u b s t a n t i a l reverse r e v e r s edisplacement d i s p l a c e m e n t in i n the t h eMidcontinent Midcontinent R i f t ,such suchasasthe t hKeweenaw e Keweenaw and and Lake Lake Owen Owen FFaults a u l t s ((Figure F i g u r e 1), I ) , have havebeen been Rift, well w e l l documented. documented. They They ooffset f f s e tmost mostunits u n i t of s othe f t Keweenawan h e KeweenawanSupergroup Supergroup but b u t appear a p p e a r tto o be be truncated t r u n c a t e d by by the t h e youngest y o u n g e s t uunits n i t s in i n places, p l a c e s , thereby thereby d a t i n g the t h e fault f a u l tmotion m o t i o n approximately a p p r o x i m a t e l y iin n the t h e interval i n t e r v a l1.1-1.0 dating 1 . 1 - 1 . 0Ga, Ga. An An additional a d d i t i o n a l fault f a u l t or o r set s e t of o ffaults, f a u l t s herein , h e r e i ncalled c a l l e dthe t h eMarenisco M a r e n i s c o Fault, F a u l t , is is a previously p r e v i o u s l yunrecognized u n r e c o g n i z e dcompanion companiontot the o t hKeweenaw e Keweenawand andLake LakeOwens Owens Faults and EEarly Proterozoic F a u l t s and and offsets o f f s e t s Archean Archean and arly P r o t e r o z o i c rrocks o c k s across a c r o s s aa bbelt e l t as as much as 30 30 km kmwwide much as i d e ssouth o u t h ooff the t h e Keweenaw Keweenaw FFault a u l t nnear e a r the t h e Gogebic Gogebic Iron Iron Range. The The eexistence x i s t e n c e of o f Keweenawan Keweenawan o or r yyounger o u n g e r d deformation e f o r m a t i o n i in n some some ooff the the Archean and a r l y PProterozoic r o t e r o z o i c r orocks c k s i in n tthis h i s belt b e l tisi well s w e documented. l l documented. Archean andEEarly Keweenawan and E aEarly r l y PProterozoic r o t e r o z o i c rocks r o c k s along a l o n g the t h eGogebic GogebicRange Range form f o r m an an Keweenawan and u n c o n f o r m a b l e b ubut t s t structurally r u c t u r a l l y cconcordant o n c o r d a n t u nunit i t t hthat a t i is s ttilted i l t e dnorthward northward unconformable along with along w i t h at a t least l e a s some t some of o fthe t h eArchean Archean basement, basement, but b u t the t h e kinematics k i n e m a t i c s and and regional remained r e g i o n a l extent e x t e n t of o f this t h i stilting t i l t i have n g have r e m a i n e dobscure. obscure. We haveused usedt hthe andEEarly We have e oorientation r i e n t a t i o n ofo Keweenawan f Keweenawan and a r l y Proterozoic Proterozoic diabase d i a b a s e ddikes i k e s as as structural s t r u c t u r a lmarkers m a r k e r s to t oaddress a d d r e s s these t h e s e questions. q u e s t i o n s . The The analysis a n a l y s i s isi sbased basedon on the t h eassumption a s s u m p t i o n that t h a tthe t h edikes d i k e were s wereemplaced emplaced nearly nearly vertically v e r t i c a l l yand andthat t h a tthe t h eEarly E a r l Proterozoic y P r o t e r o z o i cdikes d i k e swere were not n o tappreciably appreciably deformed e 1 a t i o n s support s u p p o r t both both d e f o r m e d prior p r i o rtot Keweenawan o Keweenawan time. t i m e . Regional R e g i o n a l rrelations assumptions. u t c r o p s , mostly m o s t l y Archean Archean rocks, rocks, a s s u m p t i o n s . We We have c a t e d aabout b o u t 45 havel olocated 45 ooutcrops, where weccould measure where we o u l d measure o r orientations i e n t a t i o n s o of f ddiabase i a b a s e d dikes i k e s ((see s e e f figure i g u r e 1). 1). Most componento fofddip Most ddikes i k e s have have a a southward s o u t h w a r d component i p iindicating n d i c a t i n gnorthward northward tectonic t e c t o n i c rotation r o t a t i o since n s i n cemplacement. e emplacement. In I n some some ooff the t h e southernmost southernmost outcrops o u t c r o p s tthe h e dikes d i k e s remain r e m a i n nnearly e a r l y vertical v e r t i c a l and and thereby t h e r e b y provide p r o v i d e aa southern southern limit l i m i ttot othe t h erotated r o t a t e darea. a r e a . In I n Michigan, M i c h i g a n , the t h e dikes d i k e sform f o r man anorthogonal orthogonal system andi itt is i spossible p o s s i b l etot odetermine d e t e r m i n e aaunique u n i q u e direction d i r e c t i o nand andamount amount of of s y s t e m and rotation r o t a t i o n that t h a t transposed t r a n s p o s e d bboth o t h ssets e t s ffrom r o m vvertical e r t i c a l to t o their t h e i rpresent present orientation. Figure amountandand shows t hthe e amount d i rdirection e c t i o n o of f r rotation o t a t i o n for for orientation. F i g u r e 1 shows four Ther rotation f o u r areas a r e a s where where tthey h e y aare r e bbest e s t cconstrained. o n s t r a i n e d . The o t a t i o n is i s not n o t uniform uniform and 25 ttoo 60 u g g e s t i n g e ieither t h e r mmultiple u l t i p l e fault f a u l t blocks blocks and vvaries a r i e s from f r o m 25 60 degrees d e g r e e s ssuggesting or o r broad b r o a d folding. folding. 1 Rb-Sr agesoof Rb-Sr ages f bbiotite i o t i t efrom f r o mArchean Archean and and Early E a r l y Proterozoic P r o t e r o z o i c rocks rocks (see 1) help h e l p to t oresolve r e s o l v ethe t h emechanism mechanism ooff deformation d e f o r m a t i o n and and indicate indicate ( s e e Figure F i g u r e 1) that accompanied b y by u puplift l i f t oof f tthe h e ttilted i l t e d blocks. blocks. t h a t northward n o r t h w a r d ttilting i 1 t i n gwas was accompanied Biotite B i o t i t eages ages within w i t h i n the t h e area a r e a containing c o n t a i n i n g rotated r o t a t e d dikes d i k e s are a r e close c l o s e to t o the the ages whereas ages ooff Keweenewan Keweenewan e vevents, e n t s , whereas o l older d e r b biotite i o t i t e ages ages occur o c c u r where where the the dikes maintain dikes m a i n t a i n t their h e i r vertical v e r t i c a l orientation. o r i e n t a t i o n . The The bblocking l o c k i n g temperature t e m p e r a t u r e for for the between 250and and300 300degrees d e g r e e s C, C, t h e Rb-Sr Rb-Sr biotite b i o t i t esystem s y s t e misi thought s t h o u g hto t tbe o be between250 varying v a r y i n g sslightly l i g h t l y as as aa function f u n c t i o n of o f cooling c o o l i n g rate. r a t e . When When r orocks c k s aare r e uuplifted plifted and from f r o m depths d e p t h s where where the t h eambient a m b i e n ttemperature t e m p e r a t u r eexceeds exceeds250-300 250-300degrees d e g r e e sand cooled c o o l e d rrapidly, a p i d l y , the t h e biotite b i o t i t eages ages aproximate a p r o x i m a t e t hthe e t itime m e oof f uuplift. plift. 11 We We �U interpret the the biotite biotiteages ages(1.0-1.1 (1.0-1.1 Ga) Ga) in inthe thezone zone of of rotation rotationas as interpret recording such such uplift upliftand andcooling coolingduring duringlate late Keweenawan thrust thrust recording Keweenawan Older biotite biotiteages ages outside outside of of this thiszone zone record record an an earlier earlier faulting. faulting. Older cool ing event event probably probably associated 1 ization following foll owingthe the cooling associatedwith withstabi stabilization Penokean Penokean orogeny. orogeny. Figure ourinterpretation interpretation of of the structural Figure 2 shows shows our structural and and isotopic isotopic at the the onset onset of faulting data. Figure data. Figure 2a 2a portrays portrays the geometry geometry at faultingand and during Sandstone. relationships during deposition deposition ofofthe theJacobsville Jacobsville Sandstone. Fanning Fanning relationships within sequence of of Keweenawan withinthe thethick thick sequence Keweenawan basalts, basalts,and andunconformable unconformable relationships indicate that that rotation rotation toward therift rift relationships of the the Jascobsville Jascobsville indicate toward the of Oronto of15-30 15-30degrees degrees occurred occurred during volcanism volcanism and and deposition of ofthe theOronto Group. Weinterpret interpret this this as Group. We as flexing flexing ininresponse response to to crustal crustalthinning thinningand and emplacement theload loadof of volcanic volcanic and sedimentaryrocks. rocks.At At this this time emplacement ofofthe and sedimentary time the for biotite biotite was Rb-Sr blocking blocking temperature temperature for was aa nearly nearly the isotherm isotherm of of the the Rb-Sr listric horizontal horizontal surface. surface.Figure Figure2b. 2b.shows showsthe thepresent presentgeometry. geometry. The The listric nature of 30 degrees degreesof of additional ofthe theMarensico Marensico Fault Faulthas has caused caused about about 30 northward rotation of Early Proterozoic northward rotation ofArchean Archean and and Early Proterozoic rocks as as well as as the the Keweenawan sequence. Southward thrustingononthe theorder order of of 10 Keweenawan sequence. Southward thrusting 10 km km is is sufficient thethe present sufficienttotoaccount accountfor for presentgeometry. geometry. North of ofthe theMarenisco Marenisco Fault and Fault the theblocking blockingisotherm isotherm has has been been rotated, rotated, uplifted, up1 ifted, andexposed exposedby by erosion. of Figure 2b biotite biotite ages record the the uplift uplift erosion. Within Within area area aa of Figure 2b ages record event. In In areas areas bb and and c,c,rocks rocksnow now atatthe thesurface surfaceremained remainedabove above the the event. blocking andbiotite biotite ages agesstill still reflect blocking isotherm isotherm and reflectolder olderevents. events. In summary, isotopicand andstructural structuraldata dataindicate indicate that that thrust summary, isotopic thrust faults faults related related to toreverse reverse faults faultswithin withinthe theMidcontinent Midcontinent Rift Rift extend extend for for tens outsideofof the therift. rift. Part tens of kilometers kilometers outside Part of ofthe theMarenisco Marenisco Fault Faulthas has been mapped previously,but butwas wasinterpreted interpreted to to be be of of Archean Archean or Early Early been mapped previously, Proterozoic Proterozoic age. age. Structural Structural analysis analysisofofolder olderrocks rockselsewhere elsewhere near near the the Midcontinent Rift should accountfor for the the possi possibility Midcontinent Rift should account bil i ty of ofMiddle Middle Proterozic on Archean Archeanor or Early Proterozoic Proterozic deformation deformation superimposed superimposed on Proterozoic structures. structures. References References Prinz, 1981, Geologic map thethe Gogebic Range-Watersmeet Prinz,William WilliamC.,C., 1981, Geologic mapof of Gogebic Range-Watersmeet area, area,Gogebic Gogebic and and Ontonagon Ontonagon Counties, Michigan: Michigan: U.S. U.S. Geological Geological Survey Miscellaneous Investigations Investigations Map Survey Miscellaneous Map 1-1365, 1-1365, scale scale 1:125,000. 1:125,000. Z. E., E., Zartman, Zartman,R. R. E., E . , and and Sims, Sims, P. P. K., 1980, 1980, Tonalitic Tonalitic Peterman, Z. gneisses northern Michigan, gneisses of early earlyArchean Archean age age from from northern Michigan, in inSelected Selected studies studies ofofArchean Archean and and Lower Lower Proterozoic Proterozoic gneisses, gneisses,G.B. G.B.Morey Morey and and G. N. N. Hanson Hanson (eds.): (eds.): Geological Geological Society Society of ofAmerica America Special Special Paper Paper G. 182, p. p. 125-134. 125-134. Peterman, Z. Z. E.E. and and Sims, P. P. K., K.,1988, 1988,The TheGoodman Goodman swell: swell: a a lithospheric lithospheric flexure by crustal crustal loading Rift flexure caused caused by loading along along the Midcontinent Midcontinent Rift 7, System, Tectonics, v. p. 1077-1090. 1077-1090. System, Tectonics, v. 7, p. Sims, P. K., K., (in (in press), press), Geologic Geologicmap map of ofPrecambrian Precambrian rocks rocks ininWisconsin Wisconsin Sims, P. and and northern Michigan: Michigan: U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Investigations Map, Map, scale scale 1: 1:500,000. 500,000. 12 �U ye O EXPLANATION i-S—-S-S—I Osonto Gsos.p 000gIoOl.S.Sasnal.. nasd.IOn* t/t.n.Sta,an basalt 110*. MaSqss•It• Ranga 000.Sgsossp L/J A c m a n and P r o r r o i o i cCS crystaltin. A rtCflOafl and Early Early POt.,yao,c ySISOIn. recta* Soc/s — Lht*st tao/I; dash.d .IS.S. ConC.al.d by Jacob.,slla Sandston. — -.2? Fa•II Slid, and dsp of •ad.m.nta,y and nolcanIc 50cc. a!' SlId, and dsp of dike AeW \\ Sttdt Of OnfIlnal 41k. 000a9a dO.cl,an and amo.ani Of (01.5.00 Of 4*.. __a. *1(3 Loc.I.oo and Rb-S. ago of biohi. aa,npl. :•.: ...•.. . .f / . : • , 1 -1L 1 • c ?1 MW—*s•'--,APb I\" t13 — Q85 T ,/ / * y //5/0/' i— " // /// 7/ -/ / / //7' _—— / 0 S — / 2_... — -—aye 5- 9t30 — I /', S I — —— i — I —. — -S -i_/ KIEOMETERS S - —— 1 — ) / S —— *1594 — S — - Mi C — — — — - — I / / / - I_ — -S / —— 55 I Figure 1. mapofof ppart Figure 1. Geologic Geologic map a r t of of northern northernMichigan Michigan and and Wisconsin Wisconsin Geology iiss modified showing newly newly defined defined Keweenawan showing Keweenawan t h thrust r u s t f faults. a u l t s . Geology modified from compilations compilations by by Prinz Prinz (1981) andSims Sims( i(in from (1981) and n ppress). r e s s ) . Biotite B i o t i t eages ages include i ncl ude some some previously reported reported ages ages (Peterman (Peterman and and others, o t h e r s , 1980; 1980; Petermanand andoothers, Peterman t h e r s , 1988). 1988). Figure 2. 2 . Schematic e p r e s e n t a t i o n ofofdevelopment developmentofof Keweenawan Schematic rrepresentation Keweenawan sstructures t r u c t u r e s near near the t h e Gogebic Gogebic Iron Range. PPatterns a t t e r n s aas s in Figure 1. 1. Iron Range. in Figure A.-Structure of Midcontinent MidcontinentRRift andpprior A . - S t r u c t u r e aafter f t e r opening opening of i f t and r i o r to t o onset o n s e t of thrust t h r u s t faulting. faulting. B.-Present t r u c t u r e aafter f t e r southward southward tthrusting h r u s t i n g and and rrotation o t a t i o n of of upper upper B. -Presentsstructure p l a t e above above l ilistric s t r i c thrust t h r u s t surface. surface. plate 13 \ - — \_) = — — N I 'S * ''° ' I — S S ._ —S - ° ___ I -S s - • 0 / —— — - I, �U THE PALEOMAGNETISM PALEOMAGNETISM OF EARLY PROTEROZOIC SIOUX SIOUX OF THE EARLY SOUTHWESTERN MINNESOTA MINNESOTA QUARTZITE, SOUTHWESTERN Val W., and G.B. Morey, Minnesota Geological Geological Survey, Survey, 2642 2642 University University CHANDLER, Va! Avenue, St. Paul, MN 55114-1057 55 114-1057 Paleomagnetic studies were conducted on the Early Proterozoic Sioux Quartzite of southwestern Minnesota, a sequence of hematite- and silica-cemented quartz arenites that were deposited by fluvial processes in several elongate depobasins bounded by northwesttrending faults. AAtotal totalof of 158 158samples samplesof of quartz quartz arenitic areniticmaterial material were were collected collected from from 17 17 sites scattered across four four basins (Cottonwood (Cottonwood County County ,, New Ulm, North Pipestone, and South Pipestone). As judged from alternating-field (AF) and thermal demagnetization studies, the magnetization is dominantly single-component, and as judged from high coercivities and blocking temperatures, the magnetic carrier is hematite. A definitive definitive fold fold test test is is difficult difficult to hematite. A perform, perform, because cross cross beds beds obscure obscure gently gently dipping dipping master master bedding bedding features. features. Nonetheless, most of the magnetization seems seems to have occurred before before aa period period of of regionalregionalformed the the basins. Measured scale tilting that formed Measuredpaleomagnetic paleomagneticdirections directions at at both both site site and and basin levels show good clustering, and the average directions directions obtained obtained from from each each of of the four basins are not significantly different different at at the the 95% 95% confidence confidencelevel. level. After the effects of regional tilting tilting were were removed, the the paleomagnetic paleomagnetic directions from the four four basins yield a 10lOW.and and16°N. 16ON.(k=65, (k=65,a95—11°). a95=l lo). combined paleopole paleopole located locatedatat101°W. After AF demagnetization, clasts from a basal conglomerate in the New Ulm basin show a paleomagnetic bias in the direction of that observed in the overlying quartzite, implying post-depositional magnetization. Furthermore, Furthermore, hematite, the primary magnetic carrier in the Sioux, occurs as a diagenetic mineral with a long paragenetic history 1986; Vander Horck, 1984) 1984) and, in the case of the North Pipestone (Southwick and others, 1986; basin, also as veinlets that formed during a strain event (Morey, 1984) that may have been related to regional tilting. On the Early Proterozoic Proterozoic apparent apparent polar polar wander wander curve curve of of Irving Irving (1979) (1979) the theSioux Sioux paleopole paleopole lies lies along along the the 1700-1650 1700-1650m.y. m.y. segment, segment, which which corresponds corresponds in in part part with with the the time time orogen of of Sims and and Peterman Peterman (1986) (1986)of of 1800-1630 1800-1630m.y. m.y. The Sioux of the Central Plains orogen km north of rocks clearly clearly involved involved with the outcrops are located only some 200-300 krn Central Plains orogen (Fig. 1), I), and Southwick and others (1986) (1986) have tentatively suggested that the northwest-trending faults that bound the individual Sioux basins were Conversely,the theSioux SiouxQuartzite Quartzitecould could have have been been deposited depositedatatsome some related to the orogen. Conversely, time well before the orogen and subsequently modified by tectonic processes associated associated with the orogen. In In the the first first situation situation the the paleomagnetic pole position would reflect diagenetic processes that may have closely followed sedimentation, whereas in the second, it would reflect a period of secondary overprinting that would have involved wholesale wholesale recrystallization of hematite. There There isis no no obvious obvious evidence evidence that the hematite in the Sioux, except for that in veinlets, has been been recrystallized. recrystallized. We therefore suggest that it is more related to diagenetic diagenetic processes. processes. likely that the magnetization we observe is primarily related Although considerable uncertainties still exist, our results are consistent with the conclusions of Morey and Van Schmus Schmus (1980), who suggested that the so-called so-called "Bamboo "Baraboo interval quartzites at the Lake Superior region" were deposited during the interval 176017601630 m.y. References References Cited Irving, E., 1979, 1979, Paleopoles and paleolatitudes of North America and speculations speculations about about displaced terrains: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 16, 16,p. p. 669-694. 669-694. Morey, G.B., 1984, 1984, Sedimentology Sedimentology of the Sioux Quartzite in the Fulda basin, Pipestone County, southwestern Minnesota, in Southwick, D.L., ed., Shorter Shorter contributions contributions to to 14 �_________I I thegeology geologyof ofthe theSioux SiouxQuartzite Quartzite(early (earlyProterozoic), Proterozoic),southwestern southwesternMinnesota: Minnesota: the MinnesotaGeological GeologicalSurvey SurveyReport Reportof of Investigations Investigations32, 32,P.p.59-74. 59-74. Minnesota W.R., 1988, 1988,Correlation Correlationof of Precambrian Precambrianrocks rocks of of the the Morey,G.B., G.B., and andVan VanSchmus, Schmus,W.R., Morey, Lake Superior region, United States: U.S. Geological Survey Professional Paper Lake Superior region, United States: U.S. Geological Survey Professional Paper 1241-F.31 31 1241-F, p.D. Sims. P.K., and Peterman,Z.E., Z.E., 1986, 1986,Early EarlyProterozoic ProterozoicCentral CentralPlains Plainsorogen: orogen: AAmajor major Sims, P.K., and Peterman, buried structure structurein in the the north-central north-centralUnited United States: States: Geology, Geology,v.v.14, 14,p.p.488-491. 488-491. buried D.L., Morey, Morey, G.B., G.B., and andMossier, Mossier,J.FI., J.H., 1986, 1986, Fluvial Fluvial origin origin of of the the lower lower Southwick, D.L., Southwick, Proterozoic Sioux Quartzite, southwestern Minnesota: Geological Society of America Proterozoic Sioux Quartzite, southwestern Minnesota: Geological Society of America 97,p.p.1432-1441. 1432-1441. Bulletin,v.v.97, Bulletin, Vander Horck, M.P., 1984, Diagenesis in in the the Sioux Sioux Quartzite: Quartzite: Unpub. Unpub. M.S. M.S. thesis: thesis: Vander Horck, M.P., 1984, Diagenesis University of Minnesota, Minneapolis, 101 p. University of Minnesota, Minneapolis, 101 p. 7 00 100 Mi 00 Mi. %---+-+ 00 100Km. Km. 100 Figure1.1.Generalized Generalizedgeologic geologicmap mapofofthe thecentral centralplains plainsregion region Figure (fromSouthwick Southwickand andothers, others,1986). 1986). (from 15 I I �CARBONATE IN IN TILL TILL UNITS UNITS OF OF LAKE LAKE OF OF THE THE WOODS WOODS COUNTY, COUNTY,MINNESOTA MINNESOTA CARBONATE D.A. Dahi Dahl and and D.F. D.F. Cartwright Cartwright D.A. Minnesota Department Department of of Natural Natural Resources Resources Minnesota MN 55746 55746 Division of of Minerals, Minerals, Hibbing, Hibbing, MN Division ABSTRACT ABSTRACT Within Lake Lake of the theWoods Woods County, and matrix matrix Within County, carbonate carbonate content content and solubility are are being being used, used, among among other other quantitative quantitative methods, methods, to to solubility characterize the the glacial glacial drift drift that that overlies overlies Archean Archean bedrock. bedrock. characterize Bedrock in in this this northwestern northwestern Minnesota Minnesota county county is is distributed distributed Bedrock as aa belt belt of of Archean Archean supracrustal supracrustal rocks rocks bounded bounded on on the the north north and and as east by by granitic granitic intrusives intrusives and and bounded bounded on on the the south south by by faulted faulted east contactwith with gneisses gneissesof ofthe theQuetico Queticoineta—sedimentary meta-sedimentary subprovince. subprovince. contact The supracrustal supracrustal sequence sequence is is masked masked by by sedimentary sedimentary cover cover The 300feet. feet. (overburden) which which ranges ranges in in thickness thickness from from 60 60to to 300 (overburden) As part part of of aa project project to to encourage encourage exploration exploration in in areas areas of of As deeper (asis is the the case case in in Lake Lake of of the the Woods Woodscounty), county), deeper glacial glacial drift drift (as MnDNR is is conducting conducting an an overburden overburden drilling drilling project project to to characterize characterize MnDNR the the regolith regolith (glacial (glacialdrift drift and and saprolite) saprolite) of of the the area area in in terms terms of of its feasibility feasibility for for use use as as an an exploration explorationmedium. medium. its Three packages packages of of glacial glacial drift drift have have been been recognized recognized beneath beneath Three the surficial surficial Koochiching Koochiching lobe lobe sediments sediments during during descriptive descriptive logging logging the of core core taken taken from from twenty twenty rotasonic rotasonic drill drill holes holes drilled drilled in in twenty twenty of townshipsduring duringthe thefall fallof of 1989. 1989. Matrix Matrix solubility solubility and and carbonate carbonate townships pebble content content of of till till units units within within the the drift drift packages packages are are being being pebble used along along with with textural textural analysis analysis and and trace trace metal metal measurements measurementsto to used develop aa framework framework by by which which the the sub-Koochiching sub-Koochiching drift drift may may be be develop quickly and and accurately accurately differentiated differentiated during during exploration explorationdrilling. drilling. quickly One hundred hundred and and forty forty samples samples of of the the -63um -63um (silt-clay) (silt-clay) One component of of sub—Koochiching sub-Koochiching tills were were leached leached in in 4N 4N HC1 HC1 to to component dissolve any any carbonate carbonate in in the the samples. samples. Weights Weights of of insoluble insoluble dissolve residue were were measured measured and and Ca, Ca, Mg, Mg, and and Fe Fe in in the the soluble soluble portion portion residue Matrix analyzed by by atomic atomic absorption absorption spectroscopy. spectroscopy. Matrix were analyzed were into three fall percent and solubilities range from 3 to 54 percent and fall into three 54 3 to solubilities range from These sub-populations compare well to distinct sub-populations. These sub-populations compare well to distinct sub—populations. subdivisions recognized recognized qualitatively qualitatively during during descriptive descriptive logging. logging. subdivisions Pebble counts counts of of the the coarse coarse (5-15mm) (5-15mm) component component of of the the till till samples samples Pebble also reflect reflect these these distinctions. distinctions. also Characteristic recognition recognition of of the the range, range, median, median, and and Characteristic variability of of the the carbonate carbonatecontent content and and matrix matrix solubility solubilityof ofthe the variability for framework a sub-Koochiching drift packages will provide a framework for provide packages will sub-Koochiching drift recognizing till till units units and and for for resolving resolving intra-till intra-till compositional compositional recognizing variations such such as as contamination contamination by by underlying underlying drift drift units units and and variations incorporation of of siderite/carbonate siderite/carbonate from from underlying underlying saprolite. saprolite. incorporation 16 �U MAGNETIC SUSCEPTIBILITY MAGNETIC SUSCEPTIBILITY ANISOTROPY ANISOTROPY AND STRAIN, STRAIN, THOMSON THOMSON FORMATION FORMATION (PROTEROZOIC), (PROTEROZOIC), MINNESOTA Donald M. M. Davidson, Donald Davidson, Jr. Jr. Department Department of of Geology Geology Northern Northern Illinois Illinois University University DeKalb, IL DeKalb, IL 60115 60115 Four have been Four samples samples of of the the Proterozoic Proterozoic Thomson Thomson Formation Formation have been analyzed analyzed using using a a Sapphire Sapphire Instrument Instrument Model SI-2 SI-2 magnetic susceptibility susceptibility bridge. bridge. Oriented Oriented bulk samples samples were collected collected from from aa fold fold exposed exposed north north of of Carlton, Carlton, Minnesota, well within Minnesota, within the the "northern "northern area" area" interpreted interpreted by Holst Holst (1984) (1984) to to have undergone undergone but but one one phase phase of of Penokian Penokian deformation. deformation. The The purpose purpose of of the the study study was to to evaluate evaluate the the suitability suitability of of susceptibility susceptibility anisotropy anisotropy as as aa measure of of deformation deformation magnitude and and orientation orientation using using these these samples. samples. Natural Strain Natural Strain Data: Data: Hoist (1985) Holst (1985) has presented strain strain data for for the area area based based on on measurements of measurements of deformed deformed concretions concretions and and mudchips. mudchips. Similar Similar data data collected collected by me only only for for "whole"concretions "whole"concretionsare are also also presented. presented. Holst (ID-100) Hoist (nlO0) 1 1 2 2 3 3 1.55 1.39 1.62 Average Average 1.52 4.70 1.52 4.70 Davidson Davidson STA STA 1/4 1/4 STA 22 STA STA 33 STA STA 55 STA STA 88 STA Average Average n n (34) (34) (15) (15) (30) (30) (10) (10) (14) (14) b a Y Y Z Z 3.92 5.84 4.35 X 4.77 4.77 4.70 4.70 4.91 4.91 6.27 6.27 4.20 4.20 2.38 2.38 2.30 2.30 2.83 2.83 3.19 3.19 2.36 2.36 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 4.97 4.97 2.61 2.61 1.00 1.91 1.00 1.91 2.61 2.61 a a 2.00 2.00 2.04 2.04 1.74 1.74 1.97 1.97 1.78 1.78 b b 2.38 2.38 2.30 2.30 2.83 2.83 3.19 3.19 2.36 2.36 l2 23 k K 0.44 0.33 0.48 1.37 1.76 1.47 0.19 0.08 0.19 0.32 0.19 0.33 .42 42 1.53 0.15 0.28 E1-2 =l-=2 .69 .69 .71 .71 .55 .55 .68 .68 .57 .57 2-3 k K .87 .86 .73 .80 .40 .44 .57 .80 .86 .53 .58 .75 .64 .64 .95 .59 .71 .83 1.04 1.16 n=number n=number of of measurements measurements area, the X is vertical and Z is N-S N-S and horizontal; horizontal; hence In this area, concretions concretions are are flattened flattened within within aa well-developed well-developed vertical vertical cleavage. cleavage. 17 �__________ U Magnetic Susceptibility Magnetic Susceptibility Anistropy: Anistropy: Right cylinders cylinders were were cut cut from from the the oriented oriented samples samples and Right and 24 24 orientation orientation measurements were measurements were made made on on each. each. Results to date date are: are: Results to MAX MAX EV(X105) E V(X~O-~) INT INT MIN SD SD (X1-°5) (XI0- 5) EV (MIN) (MIN) R95 DEC R95 DEC INC INC CORE CORE ORIENTATION ORIENTATION DEC DEC INC INC Graywacke 1 Graywacke 1 Slate Slate 1.67 1.67 3.80 3.80 1.62 1.62 3.69 3.69 1.5 1.5 3.40 3.40 1.3 1.3 2.5 2.5 2.6 2.6 6.4 6.4 351 351 351 351 3 3 1 1 303 303 303 303 79 79 18 18 Graywacke 3 Graywacke 3 Slate Slate 3.66 3.66 2.62 2.62 3.43 3.43 2.59 2.59 3.03 3.03 2.49 2.49 3.54 3.54 2.61 2.61 2.7 2.7 4.0 4.0 350 350 291 291 5 5 7 7 18 18 26 26 18 18 19 19 Interpretation Interpretation My natural natural strain strain data, data, although although similar similar to the the values derived derived by Hoist Holst (1985), consistently consistently show strain values, values, hence hence show higher X/Y and lower Y/Z strain (1985), my limited number of larger k k values. values. I attribute the differences to my larger measurements measurements and and to to concretion concretion behavior relative relative to measurements measurements from from 2d 2d sections and sections and deformed deformed mud mud chips. chips. The magnetic anisotophy data are inconsistent, inconsistent, although although the the orientations orientations of of EV EV are are quite quite close close to to similar similar values values for for natural natural strains. strains. believed to contribute contribute to (e.g. near horizontal cores) are believed Sampling problems (e.g. variations. Comparisons the variations. Comparisons of of strain strain and susceptibility susceptibility magnitude magnitude appear appear premature given limited data as as well as the fact fact that that these these rocks rocks are are given the the limited weakly strained strained and may have udergone udergone pressure solution solution effects effects (Borradaile, (Borradaile, 1988). References References Borradaile, G.J., G.J., 1988, petrofabrics and strain: Borradaile, 1988, Magnetic susceptibility, susceptibility, petrofabrics strain: Tectonophysics, 156, Tectonophysics, 156, 1-20. 1-20. Hoist, T.B. , 1984, Holst, T.B., 1984, Evidence for nappe development during the Early Geology 12, Proterozoic Penokian Proterozoic Penokian Orogeny, Orogeny, Minnesota: Minnesota: Geology 12, 135-138. 135-138. 1985, Implications , 1985, Implications of a large large flattening flattening strain strain for for the the origin bedding-parallel foliation Thomson of a bedding-parallel foliation in in the Early Proterozoic Proterozoic Thomson Formation, Minnesota: Formation, Minnesota: Jour. Jour. Structural Structural Geoi. Geol. 7, 7, 375-383. 375-383. 18 �U T H E SEINE-COUTCHICHING PROBLEM RECONSIDERED: U-PB U-PB THE CONCERNING TTHE SOURCE AND AND TIMING TIMING O OF GEOCHRONOLOGICAL DATA CONCERNING H E SOURCE F ARCHEAN SEDIMENTATION IN T THE H E WESTERN SUPERIOR SUPERIOR PROVINCE PROVINCE D.W. DAVIS, DAVIS, Jack Satterly Geochronology Geochronology Laboratory, Royal Ontario Ontario Museum, D.W. Museum, 100 100 Queen's Park, Toronto, Ontario, Ontario, M5S M5S 2C6 Clastic sediments in the Superior Superior Province Province mostly mostly fall fall into into two two categories: categories: an an alluvial alluvial fan-fluvial facies faciesassociation associationof ofsandstone sandstone and and conglomerate conglomerate and a resedimented facies fan-fluvial facies association of of marine marine turbidite (Ojakangas 1985). Rocks Rocks of of the the resedimented facies association association form form the the major major proportion proportion of Archean sediments and make up most of the association supracrustal component of of entire entire subprovinces subprovinces such as the English River, Quetico and Alluvial sediments sediments are relatively relatively minor minor in in volume volume and and are generally exposed along Pontiac. Alluvial within greenstone belts or at the faults either within the boundaries boundaries between between subprovinces. subprovinces. The relationship between these sediment sediment types has been a focus focus for debate in in Archean geology for over a century, beginning with the work of A.C. Lawson (1887, century, beginning (1887, 1913) sediments (Seine (Seine Group) Group) are much in the Rainy Lake area. Lawson Lawson argued that alluvial sediments younger than turhidites turbidites in the area area (Coutchiching (Coutchiching Group). Others Others have have since since argued that that they represent a transition from continental to marine depositional environments. Field they transition from continental marine depositional relationships between these facies facies associations associations are are generally generally complex. complex. Transitional sedimentary facies are rare rare and and ininsome somecases casesturbiditic turbiditic sediments sedimentsoverlie overliealluvial alluvial which is is the the opposite of of what what would would be he expected expected from from a sediments, a relationship which prograding alluvial alluvial fan. It is now possible possible to measure concordant, precise ages on single detrital zircon grains and these studies studies afford afford new new insight into the relationship between sedimentary sedimentary facies facies and their role in in the the tectonic tectonic development development of of the the Superior SuperiorProvince. Province. The Theclassic classic SeineSeineCoutchiching problem problem has been resolved Coutchiching resolved in the Rainy Lake area. Detrital Detrital zircons zircons in in the the Coutchiching of 3059-2704 Ma Coutchiching sediments sediments have have an age range of Ma (Davis (Davis et et al. 1989, errors errors are generally ±Â 2-3 Group was was deformed deformed and and metamorphosed as part 2-3 Ma). The Coutchiching Coutchiching Group of Rice Bay, Bay, and intruded by post-tectonic plutons of a dome structure at Rice plutons such such as as the the Bear  2 Ma. Detrital zircon grains Pass stock at 2693 ± grains in in the the Seine Seine Group Group have a uniform age of of 2693 late in in the the geologic geologic history of the 2693 Ma. Ma. Therefore, Therefore, both sedimentary groups are quite late area but but the the Seine Seine Group Grouppost-dates post-datesdeposition depositionof of the theCoutchiching Coutchiching Group Group and and may may have have derived from from erosion erosionof ofan anactive activevolcanic volcanicedifice edifice overlying overlying the the rising rising Rice Rice Bay Bay dome. dome. been derived The voluminous voluminous Quetico Quetico turbidites turbidites to to the the south have have a detrital zircon age range of 3009-2698 Ma, 3009-2698 Ma,and and were were intruded intruded by by the the late late tectonic tectonic Blalock Blalock Pluton Pluton at at 2688 2688  ± 44 Ma (Davis et al. submitted). Deposition of of the Seine Group may, therefore, have been penecontemporaneous with with parts parts of of the theQuetico Queticosediments. sediments. This This isis supported supportedby byfield field penecontemporaneous evidence in the Geraldton area where Devaney and Williams (1989) have demonstrated in area where Devaney Williams (1989) have demonstrated a transition alluvial and Quetico transition between alluvial and marine marine sediments sediments at at the northern boundary of the Quetico Subprovince. Detrital zircons zircons in both the the Quetico Queticoand andCoutchiching Coutchiching sediments sediments have have aa distinctive distinctive Detrital 19 �pattern in in which which many many of age pattern of the grains grains cluster cluster near near the young young end end of of the the age range, and are similar in age to late-tectonic plutons in the adjacent adjacent Wabigoon Wabigoon Subprovince. Subprovince. The The other grains grains are are generally generally older than than arc-type arc-type volcanism volcanism in adjacent greenstone greenstone belts, belts, but but similar in age to rocks found within metaplutonic terrains in in the the Wabigoon Wabigoon Subprovince Subprovince Winnipeg River Suhprovince. Subprovince. There is also petrographic evidence that that significant significant and the Winnipeg amounts of of felsic felsic volcanic of the the turbidites. turbidites. These These amounts volcanic material material contributed to the provenance of data indicate indicate that thatQuetico-type Quetico-type sediments sedimentsmay may have have been been deposited depositedlargely largelyfrom from erosion erosionof of data active volcanos and older sialic sialic crust during a late orogenic orogenic event. event. The relationship relationship between between sedimentation sedimentation and anddeformation deformationisisclearly clearly evident evident in in the the Manitou Lake area, area, at atthe thesouthern southernmargin marginof of the theKakagi Savant Lake Lake volcanic volcanic Kakagi Lake Lake -- Savant belt. Alluvial sediments are overlain by by marine marine turbidites turhidites (Manitou Lake Group, Group, Teal Teal and and Walker 1977), which are, in turn, structurally overlain by volcanic rocks (Boyer Lake 1977), are, in turn, structurally overlain by Lake Group). Group). Detrital Detritalzircons zirconsininthe theturbiditic turbiditicsediments sedimentsshow showan anage agerange range3039-2706 3039-2706Ma. Ma. Sediments near the base base are areintercalated intercalatedwith with rhyolites rhyolites with an age of <2699 ~ 2 6 9 ±9 33 Ma. The The overlying Boyer Boyer Lake Lake group has an older age age of of 2722 2722 ±Â 5 Ma and was therefore structurally emplaced over over the the sediments, sediments,possibly possibly by thrusting. The entire entire sequence sequencewas was rotated rotated into into aa vertical vertical position position and and intruded intrudedby by the thepost-tectonic post-tectonic Taylor Taylor Lake Lakestock stockatat2696 2696 ± 22 Ma. Therefore, Therefore, sedimentation, sedimentation, probable probable thrusting, thrusting, regional regional folding folding and and late late magmatism occurred within a time span of, at most, 3 ±Â 44 Ma and were likely likely part of of aa single tectonic event. Also, the presence of of out-of-sequence out-of-sequence relationships relationships within within the the supracrustal pile pile suggests suggests that the turhidites turbidites may may have have been structurally structurally superposed superposed on on the the lower alluvial alluvial sediments. sediments. Almost Almost identical identical relationships are found found within the supracrustal sequence sequence in in the the Sioux Lookout Lookout area, on the northern northern boundary boundary of of the Kakagi Kakagi Lake - Savant Savant Lake Lake volcanic volcanic belt (Davis (Davis et al. al. 1988). 1988). This This sequence sequence isis structurally structurally overlain by the Warclub Group, Group, aa belt of turbidites which extends westward westward along along part part of of the boundary between the Subprovinces. The of turbidite turbidite Wabigoon and Winnipeg River Subprovinces. The detrital zircon zircon age pattern of in the Dryden area area indicates indicates that that much much of of the the sediment sediment was was probably derived from the Winnipeg Winnipeg River Subprovince. Subprovince. Deposition Deposition is is dated dated at at about about2714 2714-- 2706 2706 Ma based on on the the age age of of an an intercalated intercalated rhyolite rhyolite and and age age constraints constraints from elastic clastic material and emplacement of Dryberry batholith. batholith. This This time time span span correlates correlates with with deformation, deformation, late late plutonism plutonism and and of the the Dryberry gold mineralization at at the the northern northernboundary boundaryofofthe theWabigoon WabigoonSubprovince, Subprovince,asaswell wellasaswith with metamorphism metamorphism in in the theWinnipeg WinnipegRiver RiverSubprovince, Subprovince, and andtectonic tectonicactivity activity between between the thetwo two subprovinces (Davis (Davis and and Smith, Smith, submitted). submitted). clastic sediments onset of of collisional collisional In summary, deposition of elastic sediments appears appears to mark the onset orogeny. Time constraints on this process from north to south across across the the western western Superior Superior orogeny. Province are are the thefollowing: following: 2714-2706 2714-2706 Ma in the northern northern Wabigoon WabigoonSubprovince, Subprovince,26992699Province 2696 2696 Ma in the the central centralWabigoon, Wabigoon,2698-2688 2698-2688 Ma in in the the Quetico QueticoSubprovince, Subprovince,and and268926892684 Ma in the Shebandowan Shebandowan Subprovince Subprovince (Corfu (Corfu and and Stott Stott1986). 1986).This This process process was was 2684 apparently diachronous diachronous across across the Superior Superior Province Province and may have apparently have been due to progressive progressive southward accretion accretion of of arc arc and and micro-continental micro-continental fragments. fragments. 20 �U-Pb ages ages for for late late magmatism magmatism and and regional regional deformation deformation Corfu, F., and Stott, G.M. 1986. U-Pb in the Shebandowan Belt, Belt, Superior Superior Province, Province, Canada. Canada. Can. Can. Jour. Jour. Earth EarthSci., Sci.,v.v. 23, 23, p. p. 1075-1082. 1075-1082. Davis, D.W., D.W., Pezzutto, Pezzutto, F., F., and and Ojakangas, Ojakangas, R.W. R.W.The The age age and and provenance provenance of of Davis, metasedimentary rocks rocks in the Quetico Quetico Subprovince, Subprovince,Ontario, Ontario, from fromsingle singlezircon zircon analyses: implications implications for forArchean Archean sedimentation sedimentation and and tectonics tectonics in in the the Superior analyses: Province, submitted to Earth Planet. Province. Planet. Sci. Sci. Lett. Davis, D.W., D.W., Poulsen, K.H., New insights insights into into Archean Archean crustal K.H., and Kamo, Kamo, S.L. 1989. New in the the Rainy Rainy Lake Lake area, Superior Province, development from geochronology geochronology in Canada. Jour. Canada. Jour. Geol., Geol.,v.v. 97, 97,p. p. 379-398. 379-398. Davis, D.W., D.W., and Smith, P.M. P.M. Archean Archean gold mineralization in the Wabigoon Subprovince, a in the the Lake of the product of crustal accretion: evidence from U-Pb geochronology in Woods area, Superior Superior Province, Canada. submitted to Jour. Jour. Geol. Geol. Davis, D.W., D.W., Sutcliffe, R.H., R.H., and Trowell, N.F. N.F. 1988. Geochronological Geochronological constraints on the of a late Archean greenstone belt, Wabigoon tectonic evolution of Wabigoon Subprovince, northwest Ontario, Canada. Precamb. Res., v. 39, p. 171-191. Ontario, Canada. Precamb. Res., v. 39, p. 171-191. Devaney, J.R., and Williams, H.R. 1989. Evolution Evolution of of an an Archean subprovince boundary: a sedimentological and structural study of part of of the the Wabigoon Wabigoon -- Quetico Quetico boundary in northern Ontario. Can. Jour. Earth Sci., v. 26, p. 1013-1026. Ontario. Can. Jour. Earth Sci., v. 26, p. 1013-1026. Lawson, A.C. AC. 1887, 1887, Geology of the Rainy Lake region, with remarks on on the the classification classification of of the crystalline crystalline rocks west of Lake Lake Superior. Superior.Am. Am.Jour. Jour.Sci., Sci.,v.v.33, 33,p. p. 473-480. 473-480. Lawson, A.C. A.C. 1913, The The Archean geology of of Rainy Lake re-studied. Can. Can. Geol. Geol.Survey Survey Mem. 111 p. Mem. 40, 40,111 p. Ojakangas, R.W. 1985. Review Review of of Archean Archean clastic clastic sedimentation, sedimentation, Canadian Shield: major felsic volcanic contributions to to turbidite turbidite and andalluvial alluvialfan-fluvial fan-fluvialfacies faciesassociations. associations.in in Ayres, L.D. et al., eds., Evolution of Archean supracrustal sequences, sequences, Geol. Geol.Assoc. Assoc. Canada Canada Spec. Spec.Paper Paper28, 28,p.p.23-47. 23-47. of the the Archean Archean Teal, P.R., and Walker, R.G. 1977. 1977. Stratigraphy and sedimentology of Manitou Group, Group, northwestern northwestern Ontario. Ontario. Geol. Geol. Survey Survey Canada, Paper 77-lA, 77-1A,p. p. 181181184. 184. 21 �U PALEOMAGNETISM OF OF KEWEENAWAN KEWEENAWAN AGE AGE BASALTS BASALTS OF OF THE THE CHENGWATANA CHENGWATANA PALEOMAGNETISM VOLCANIC GROUP GROUP IN IN THE THE ST. ST. CROIX CROIX FALLS FALLS AND AND FREDRICK-MILTOWN FREDRICK-MILTOWN VOLCANIC AREA OF OF POLK POLK COUNTY, COUNTY, WISCONSIN WISCONSIN AREA John Feeney Feeney John and and William William F. F. Kean Kean Departmentof ofGeoscierices Geosciences Department University of of Wisconsin-Milwaukee Wisconsin-Milwaukee University Milwaukee, Wisconsin Wisconsin 53201 53201 Milwaukee, Extensive Extensive paleomagnetic paleomagnetic studies studies have have been been made made in in the the Precambrian Precambrian Keweenawan Keweenawan rocks rocks near near the the shores shores of of Lake Lake Superior. Superior. Over Over 60 60 individual individual paleomagnetic paleomagnetic poles poles have have been been obtained from from these these rocks rocks (Halls (Hallsand and Pesonen, Pesonen,1982). 1982). obtained Exposures Exposures of of Keweenawan Keweenawan age age basalts basalts in in Polk Polk County County (northwestern (northwestern Wisconsin) Wisconsin) give give an an opportunity opportunity to to study study Lake Lake Superior Keweenawan Keweenawan rocks rocks in Superior in their their southernmost southernmost exposure. exposure. 130 130 oriented oriented cores cores from from 18 18 sites sites in in the the St.Croix St.Croix Falls Falls and Fredrick-Miltownarea area of of Polk Polk County, County, Wisconsin Wisconsin were were and Fredrick-Miltown collected and and measured measured for for magnetic magnetic characteristics. characteristics. A.F. A.F. collected demagnetization demagnetization and and remanence remanence acquisition acquisition studies studies indicate indicate that that the the remnant remnant magnetization magnetization is is carried carried by magnetite magnetite and and in some some exposures, exposures,hematite. hematite. Most Most samples samples showed showed aa single single in component component of of magnetization magnetization with with Fisher Fisher average average magnetic magnetic directions directions split split into into two two groups; groups; aa normally normally magnetized, magnetized, or or north 1). north seeking seeking direction direction and and aa "reverse" "reverse" direction direction (Table (Table1). The The normal normal group group gave gave aa magnetic magnetic direction direction and and pole pole position position close to to the the mean mean values values for for the the middle middle Keweenawan Keweenawan Portage Portage close Lake Lake Volcanic Volcanic Group Group given given in in Halls Halls and and Pesonen, Pesonen, 1982, 1982, when when corrected corrected for for geologic geologic dip dip using using lava lava flow flow tops. tops. The The reverse reverse group group showed showed aa large large (60 (60degrees degrees in in declination) declination) asymmetry, asymmetry, possibly possibly caused caused by by magnetic magnetic overprinting overprinting from from adjacent normal normal magnetized magnetized basalt basalt flows. flows. adjacent Susceptibility Susceptibility measurements measurements showed showed aa great great deal deal of of variation variation on on aa within within site site and and aa between between site sitebasis. basis. Mean Mean susceptibility susceptibility from from all all sites sites was was 2892 2892 xx i06 1 0 ^ c.g.s. c.g.s. units, units, and standard standard deviation deviation was was 2686 2686 xx 10-6 l o 6 c.g.s. c.g.s. units. units. The The and i06 c.g.s. units low value value for for aa site site was was 31 31 xx l o 6 c . g . 5 . units and and the the high high low l o 6 c.g.s. c . g . s . units. units. was 9592 9592 xx i06 was 22 �U I TABLE TABLE 11 PALEOMAGNETIC PARAMETERS FOR KEWEENAWAN AGE BASALTS OF POLK PALEOMAGNETIC PARAMETERS WISCONSIN* COUNTY. COUNTY, WISCONSIN* ........................................................... DIRECTION DIRECTION INC. DEC. INC. DEC . K A95 A95 LAT.. LAT V.G.P. V.G.P. LONG. LONG. POL POL 47 .2 288.lk 175.0 17.7 66.4 114.8 -61.0 15.2 29.7 N 85.1 S 183.0 E 316.0 E N R ** 34.9 288.6 1332 2.5 26.5 N 181.2 E N parameter; A95 radius of Symbols; K precision parameter; A95 -- radius of Symbols: K -- precision virtual geographic confidence; confidence; V.G.P. V.G.P. -- virtual geographic pole pole position; position; POL POL magnetization; RR -normal, north seeking polarity; polarity; NN -- normal, seeking magnetization; reverse, reverse, south south seeking seeking magnetization. magnetization. * * Corrected Corrected for geologic dip based on on a flow-top flow-top average average 45.427N, measurement of measurement of NN 23W, 23W, 21W. 21W. Mean Mean site site latitude latitude == 45.427N, longitude = 92.611W. longitude = 92.611W. mean value. **Portage **portage Lake Lake- Volcanic Group Group mean value. REFERENCE REFERENCE Halls, Halls, H.C., H.C., and and Pesonen, Pesonen, L.J., L.J., 1982, 1982, Paleomagnetism Paleomagnetism of Keweenawan Keweenawan rocks: rocks: Geological Geological Society Society of America America Memoir Memoir 156, 173-200. 156, pp. pp. 173-200. 23 �U I GEOLOGY GEOLOGY AND MINERALIZATION IN THE DUNKA ROAD COPPER-NICKEL MINERAL MINERAL DEPOSIT DEPOSIT COPPER-NICKEL COUNTY, MINNESOTA MINNESOTA ST. LOUIS COUNTY, Stephen Geerts Stephen D. Geerts Resources Research Research Institute, Institute, Natural Resources University of of Minnesota, Minnesota, Duluth Duluth The The Dunka Dunka Road Cu-Ni Cu-Ni deposit located within within the deposit is is located the Partridge River Partridge River Intrusion Intrusion (T. (T. 60 60 W., P. R. 13 W.) is part part W.) which is of the Duluth b.y. of the Duluth Complex, Complex, and is approximately is approximately 1.1 1.1 b.y. (Keweenawan) (Keweenawan) in in age age (Figure (Figure 1). 1). Relogging of 46 46 drill drill holes holes at at the Road Cu-Ni Cu-Ni deposit four major major the Dunka Dunka Road deposit identified identified four lithologic units and several internal internal ultramafic ultramafic subunits subunits that lithologic can be be correlated correlated over over two two miles. miles. ultramafic subunits subunits The ultramafic (layers of picrite to peridotite), peridotite), exhibit exhibit relative relative uniform uniform thicknesses and are are present thicknesses and present at the the same same relative relative position position within the within the major major lithologic lithologic units. units. The The major lithologic lithologic units units are the same same as as delineated delineated by by Severson Severson and and Hauck Hauck (1990), (1990), and and upward from upward from the the basal basal contact contact are: are: Unit Unit I, I, a fine— fine- to to coarse— coarsetroctolite (450 grained sulfide-bearing sulfide-bearing troctolite troctolite to pyroxene troctolite (450 ft. thick) with associated ultramafic layers 1(a), I(a), 1(b), I(b), and and Unit I(c); Unit II, 11, a mediummedium- to to coarse-grained coarse-grained troctolite troctolite to to 1(c); pyroxene troctolite troctolite (200 (200 ft. ft. thick) with aa basal basal ultramafic ultramafic Unit 111, III, aa fine-grained, layer 11(a); I1 (a); Unit fine-grained, mottled textured mottled textured troctolitic anorthosite to to anorthositic anorthositic troctolite troctolite (150 (150 ft. ft. thick) with one one minor minor ultramafic ultramafic layer layer 111(a); III(a); and and Unit Unit IV, IV, aa coarse—grained troctolite/pyroxene troctolite to anorthositic coarse-grained troctolite with associated associated ultramafic ultramafic layers layers IV(a) IV(a) and and IV(b) IV(b) (Figure 2). (Figure 2) . Most sulfide sulfide mineralization mineralization occurs occurs within within Unit Unit I. I. Within Within the sulfide Unit I sulfide mineralization mineralization is both both widespread widespread but but Unit I variable 5 % ) , continuity and and variable in in modal modal percentage percentage (rare to 5%), thickness (few thickness (few inches inches to to tens tens of of feet). feet). Sulfide Sulfide mineralization mineralization is generally related with proximity to: to: hornfels hornfels inclusions, inclusions, basal contact with the footwall footwall Virginia Formation, and some of the the internal internal ultramafic ultramafic layers layers within within Unit Unit I. I. Primary Primary sulfide mineralization mineralization includes includes pyrrhotite, pyrrhotite, chalcopyrite chalcopyrite and and pentlandite. pentlandite. Minor amounts amounts of of cubanite, cubanite, bornite, bornite, talnakhite talnakhite been identified and niackinawite/valleriite mackinawite/valleriite have have also also been identified in and in preliminary petrographic observations. preliminary petrographic observations. Precious metal metal Precious mineralization (Pd+Pt+Au) subtle fracturing fracturing mineralization (Pd+Pt+Au) is is associated associated with subtle and alteration alteration of of the the host host rocks. rocks. The alteration alteration assemblage assemblage is chlorite, chlorite, bleached bleached plagioclase, plagioclase, serpentine and and uralite. uralite. Secondary Secondary sulfide sulfide mineralization mineralization occurring occurring as as trace trace amounts amounts of bornite, bornite, is is present present in in these these fractured fractured and and altered altered zones. zones. values range range from from 100 to >2400 Pd+Pt values >2400 ppb over over 10 10 foot foot intervals. intervals. These intervals intervals can can occur occur independently independently as as 10 10 to to as zones, or part of a larger correlatable correlatable 50 foot zones, or as part of a larger foot 50 investigated occurrence/horizon. Two Two mineralized mineralized subareas subareas were investigated 24 �U within the 1) an area which the Dunka Dunka Road Road deposit deposit and and are: are: 1) which is is perforal to aa highly perforal highly anomalous anomalous Pd Pd occurrence occurrence (reported by Morton and 1987; 1989) 1989) herein termed the and Hauck, Hauckl 1987; the usouthwest llsouthwest area", and 2) the the Itnortheast "northeast areatt area" which which contains contains several several drill drill area1l1 holes that that have have near—surface 1% Cu. There are holes near-surface intercepts intercepts of of >> 1% Cu. There are four somewhat large mineralized occurrences occurrences within within the the study study area that area that carry carry >300 >300 ppb ppb combined combined total total Pt+Pd+Au. Pt+Pd+Au. These These mineralized stratigraphically controlled mineralized zones zones appear appear to to be stratigraphically controlled by by Unit I. Three of the ultramafic subunits I. the four ultramafic subunits within within Unit Three of four correlatable zones are found within within the southwest area, correlatable areal and range from range from 40 40 to to 130 130 feet feet thick. thick. High Pd values within these these zones thick with values values of of 800 800 to to 1650 1650 zones range range from from 10 10 to to 20 20 feet feet thick ppb Pd. Pd. In the northeast northeast area, areal the fourth fourth mineralized mineralized zone zone ppb appears continuously I. This This zone zone ranges ranges from from continuously throughout throughout Unit Unit I. appears 120 120 to to 300 300 feet feet thick. thick. High Pd values within this zone zone range range from 10 to 40 40 feet feet thick thick with with values values of of 800 800 to to 1500 1500 ppb ppb Pd. Pd. 30 foot intersections > l ppm ppm Pd+Pt+Au Pd+Pt+Au occur occur Many 5 to intersections of Many 5 to 30 of >1 throughout throughout the the mineral mineral deposit. deposit. References: References: Morton, P., P S Iand and Hauck, Hauckl S. S. A., A - 1987, 19871 PGE, PGEl Au and Ag contents contents of of Mortonl Cu—Ni sulfides found at the base of Cu-Ni of the the Duluth Duluth Complex, Complexl Minnesota: northeastern Minnesota: Natural Resources Research northeastern Natural Resources Research Institute, Institute, Technical Technical Report Report NRRI/GMIN-TR-87-04, NRRI/GMIN-TR-87-041 85 85 pp. pp. Norton, P., and Hauck, F. Hauckl S. S. A., A. 1989, 198g1 Precious metals in in the the Mortonl copper-nickel deposits copper-nickel deposits of of the the Duluth Duluth Complex: Complex: Minn. Minn. Geol. Geol. Survey, pp. 47-48. 47-48. Survey, Inf. Inf. Circ. Circ. 30, 30, pp. Severson, Hauck, SS. A., 1990 1990, Geologyl Geology, geochemistryl geochemistry, J. and Hauckl . A. Severson! M. J., and stratigraphy stratigraphy of of a portion portion of of the the Partridge Partridge River River Intrusion, northeastern Minnesota: Natural Intrusionl Minnesota: Natural Resources Resources Research Institute, Report, NRRIIGMIN-TR-89-lll NRRI/GMIN-TR-89-ll, Research Institutel Technical Technical Reportl Duluth, Minnesota, Duluthl Minnesotal 240 240 pp. pp. CENEFAHZED GIHEOUS LEGEND LEGEND STGATIGPAPHC QLUMN PP II ppHr R TRIAGE RIVER Cl—NI_DRpoCp_____ SVUb> DM10) DUNKA ROAD — OP VIrtEDD — EL ID [Co •YIIAN CREEK - CECTION 17 — 17 L[VIUCAR — 1K LONCUODE - - - 1 LTNT !V Ur-i!T IS UNIT H GO [DIE> 1RVTI_DEAOjO 1PS1S_ CC lION AS K1UD P 11)01 1110) SN 21? UNI I SE VA> INIA FORMATION LUIVvAR!F U ID KM 25 IRON—FOFLL>TIOH I �U TRIDYMITE, OTHER S102 MINERALS AND AND THE PIT TRIDYMITEl S102 MINERALS P / l TRAJECTORY TRAJECTORY OF KEWEENAWAN KEWEENAWAN LAVAS, iAVASl MINNESOTA MINNESOTA Duluth, MN C.Green, Green!Geology GeologyDepartment, Department! University University of of Minnesota, Minnesota! Duluth, Quhth, Duluth, MN John C. 55812 5Ml2 have Four beta and Four Si02 SiQ2 minerals minerals (cristobalite, (cristobalite, tridymite, tridymite, beta and alpha alpha quartz) quartz) have at the North crystallized at one crystallized at one stage stage or or another another in in rhyolites rhyolites of North Shore Shore Volcanic Volcanic Group. Group. Whereas cristobalite is known known only only from from occasional, occasional, hemispherical hemispherical quartz quartz paramorphs paramorphs inin vesicles (metastable, pneumatolytic), and and perhaps perhaps in in spherulitesl spherulites, tridymite tridymite was was the silica (metastable! pneumatolytic), silica is indicated mineral mineral stable stable during during flow flow and andcrystallization crystallization of most most rhyolites. rhyolites. This This is indicated particularly by the the near particularly by near ubiquity ubiquity of of flow flow structure structure formed formed by by quartz quartz paramorphs paramorphs after after (Many of the lavas had previously started to crystallize beta quartz platy tridymite. tridymite. (Many of lavas had previously started to crystallize beta quartz now present now present as phenocrysts phenocrysts -- at higher higher P P in in deeper deeper chambers chambers within within the the crust.) crust.) Aphyric Aphyric rhyolites ponded and also crystallized tridymite (+ feldspar) at the surface, rhyolites ponded and crystallized tridymite (+ feldspar) surfacel without without flow flow structure. 870 degrees degrees C, Cllate-crystallizing late-crystallizingdomains domains crystallized crystallized betabetastructure. On cooling past past 870 573 degrees, the beta quartz (+ tsp) fsp) to to the thesolidus. solidus. Below Below 573 degrees, the beta quartz quartz inverted inverted to to alpha alpha quartz in probably deposited deposited in and some some hydrothermal/pneumatolytic hydrothermal1pneumatolytic quartz quartz was was probably quartz, and re-warming depth and and re-warming burial to Upon openings. Upon later later burial to several several kilometers' kilometers' depth (hydrothermallburial "metamorphism"),the the metastable metastabletridymite tridymite plates plates inverted inverted to alpha (hydrothermalhurial "metarnorphi~rn'~), alpha porphyritic rhyolites, rhyolites,this this nucleated nucleatedon on the the quartz quartz phenocrysts to give give aa In porphyritic quartz. quartz. In phenocrysts to remarkable poiki litic ("snowflake") poikilitic (!'snowflake1') texture. texture. The widespread crystallizationofof tridymite tridymite is is unusual, though noted in The widespread primary primary crystallization unusual, though in around the the world, certain rhyolites rhyolites around world, and and implies implies anomalously anomalously high high temperatures temperatures of of certain eruption. eruption. T°C 0 400 ROO 1200 1200 2 B Kb High Quartz Low Quartz A 26 1600 1600 I I �Transpostion Transpostion structures structures in in deformed deformed rock, rock, with with examples examples from from the the Appalachians Appalachians and and Upper Upper Michigan Michigan William Mi 1 1 iam (Dept. J. Gregg Weqq (Dept. of of Geological Geological Engineering, Engineering, J. Michigan PI1 49931) 49931) Michigan Technological University, University, Houghton, Houghton, MI The term 'transposition' 'transposition9 has h a s come c o m e into into wide wide usage usage in in published descriptions descriptions of of deformed rocks. Unfortunately there t h e r e has h a s been little little consistency consistency in in its i t s application, and and the t h e term has h a s been inappropriately inappropriately applied applied to t o aa wide wide variety variety of structures, structures9 including including slaty slaty cleavage cleavage (Burger (Burger 1982), 1982), crenulation 1961) and schistosity crenulation cleavage cleavage (Rickard tRickard 19611 (Whitten 1966), in in situations where these (Whitten 1966) t h e s e foliations foliations either either render a pre—existing pre-existing foliation f 01 iation obscure, obscurev or when they form domain boundaries boundaries between between rotated rotated segments segments of of an an earlier earlier foliation. foliation. This T h i s broad broad usage usage of of the t h e term to t o indicate indicate any any sort of realignment realignment of o+ aa layering layering has h a s resulted resulted in in much confusion, confusion, and many many rocks r o c k s that that are a r e truly truly transposed transposed have have remained This T h i s confusion confusion remained unrecognized unrecognized as a 5such suchto t othis t h i sday.. day. stems s t e m s largely 1 argel y from from aa mistranslation mi stranslation of of Sanders Sanders (1911) (191 1) work by Knopf in which which illustrations i 1 lustrations of of transposition Knopf (1931) (1931 1 in with crenulation were were perhaps perhaps inadvertently inadvertent1 y switched with crenul ation . cleavage. c 1eavage As 6s Sander pointed out, out, transposition transposition (Umfaltung) (Umfaltung) is is aa mechanical mechanical process that that produces lenticular lenticular elements elements from aa previous previous layering. layering. The T h e elements elements are a r e produced produced by by isoclinal isoclinal folding of of competent layers, followed by boudinage of layers, of the the layers alonq the t h e fold axial axial surface surface in in aa direction direction normal normal layers along to t o the t h e fold axes. axes. A new new foliation foliation need need not not be b e present present in in the t h e transposed transposed layer layer itself itsel+ and and as a s Sander Sander stated stated "the "the only original are original S S layers layers are a r e still still present, present, but but are only misoriented misoriented by by small small particulate particulate displacements". displacements11- Sander Sander never never used used the t h e misnomer misnomer "Umfaltungsclivage" "Um+altungscl ivage" as a s quoted quoted by others others (Knopf (Knopf 1931, 1 9 3 1 9 p. p. 16), and was w a s careful careful to t o point point out out that "cases "cases of true t r u e cleavage cleavage can can be be defined defined when when aa new new S S cuts c u t s an an older older one" one" whereas whereas in in transposition transposition the t h e early early S S surface "is but not not however however cut by a new "is indeed indeed transposed transposed but new . S.'. Sns Studies Studies of of transposed transposed layering layering from from the t h e Northern Northern Appalachians and Upper Michigan Michigan show s h o w that that transposition transposition usually usual1 y develops develops only on1 y in in rocks r o c k s that that have have aa mechanical mechanical anisotropy in Although in the t h e internal internal layering. Although an a n entire entire rock rock unit unit is is sometimes sometimes described described as a s transposed, transposed, it it is is actually only the t h e compentent compentent layers layers within within the t h e unit unit that that show around the s h o w this t h i s type t y p e of of deformation. deformation- The T h e matrix the competent b e characterized characterized by a high high cornpeten< layers layers may may instead instead be strain as. schistosity schistosi t y or o r pinstripe pinstripe layering. layeringstrain foliation foliation such s u c h as Transposed Transposed layering layering usually usually is is recognized recognized by the the presence presence of features f e a t u r e s such such as a s rootless rootless isoclinal isoclinal fold fold hooks hooks and lensoid lensoid remnants remnants of af fold -Fald limbs limbs (Williams (Williams 1967). These These structures structures may may represent represent the t h e dismembered portions portions of of bedding, bedding, although although thick thick secondary secondary layers layers may also also be be transposed. transposi t i on of transposed. The T h e transposition af quartz quartz veins vei n s in in pelitic pel i ti c rocks r o c k s is is extremely common, common, resulting resulting in in white white quartz quartz lenses lenses and and in in quartz—rich quartz-rich rod rod structures structures that that parallel parallel the t h e axes a x e s of of 27 �U DEVELOPMENT OF TRANSPOSED LAYERING tectonic 'pebbles" a I lensoid remnants of fold limbs (in matrix) isolated fold hooks augen (In gneiss) rods (from veins) GREGG- 1990 1 "Whorl" structures "Whorl" s t r u c t u r e s in i n transposed t r a n s p o s e d "Springfield " S p r i n g f i e l d Conglomerate" C~nglomerate~~ from C Central Vermont. Specimen, e n t r a l Vermont. Specimen, from from type t y p e locality, l o c a l i t y , is i s aa cchloritized, h l o r i t i z e d , sulfide—rich s u l f i d e - r i c h mafic mafie rock. rock. Some types 'button' of es a+ 'button' earlier iisoclinal soclinal ffolds.. aldsearlier observed in phyllites l l ite5 may a1 SO structure 1972) may also s t r u c t u r e (Roper (Roper 1972) obser\f represent interfolial segments.. Archean rocks represent inter-+01 ia1 transposed trans m k s * IIn n Rrchean rocks transposition @ for -For the t h e development development t r a n s p o s i t i o n is i s frequently + r e q u e n t l y responsible of augen example iin of auqen structure. s t r u c t u r e 3 ff aor r exa n tthe h e Watersmeet gneisses Green in i n Upper Michigan and in i n numerous nu us examples examples from +ram the the Green Mountains h e &dircmdacksMountains and and tthe Adirondacks the the 28 - �U When flattening Uhen + l a t t e n i n g strains s t r a i n s are a r e extremely extremely high, high, isoclinal isoclinal hooks may may be be ddifficult observe, and tthe f+o old l d hooks i f f i c u l t tto o observe, h e rock rock may may off a pseudo—conglomerate (Ramsay take t a k e on the t h e appearance o a pseudo-conglomerate (Ramsay 1956). AA number o off cases e exist transposed in 1955). x i s t where transposed rocks rocks in high zones been significant have rregionally egionally significant h i g h strain strain zones have been misidentified m i s i d e n t i f i e d as as sedimentary sedimentary units, units, ffor or example tthe he Conglomerate and Paleozoic Hill Springfield Paleozoic Dry Hill Conglomerate and Springfield Dry Conclomerate units u n i t s in i n south—central s o u t h - c e n t r a l Vermont. Vermont. severely transposed rrocks may IIn n s e v e r e l y transpos@d ocks iisolated s o l a t e d fold f o l d hooks hooks may form whorl—structures off in w h o r l - s t r u c t u r e s that t h a t show evidence o rrotations otations i n These structures foliation. indicate tthe h e plane p l a n e of of foliationThese structures i n d i c a t e high high seems vorticity seems tto o be be llittle i t t l e v o r t i c i t y in i n transposed transposed zones zones which structures evidenced in i n less l e s s transposed transposed fabrics.. f a b r i c s . The whorl structures delamination eventually severe and internal d elamination and internal eventually s uf f e r suffer disruption d i s r u p t i o n as as strain s t r a i n progresses. progresses- REFERENCES R EFERENCES Solution Burger, R. and bedding Burger, R. H. S o l u t i o n cleavage cleavage and bedding H.,, 1982, Borradaile, transposition": 6. and J. , t r a n s p o 5 i t i o n " : in i nBayly, Bayly, B. B-M.M.,, Borradaile, G. J., and Atlas of Deformational and C. McA., eds., Powell, C. McA., eds., f3tlas of Deformational and Metamorphic p. 330—331. 330-331. Metamcrphic Rock Fabrics, F a b r i c s , Springer S p r i n q e r Verlag, Verlag, p. Retrogressive Knopf,, E. metamorphism Knopf B. , 1931, R etrogressive metamorphism B., phyllonitization: p h y l l o n i t i z a t i o n : Amer. fimer. jour. JOUP.Sci., Sci., v.21, v.21, p. p. 1—27. 1-27. and and Ramsay, 3. Ramsay, J. 6, G, 1956, 1956, The The supposed 5upposed Moinan Moinan basal basal conglomerate conglomerate at a t Glen S t r a t h f a r r a r , Inverness—shire: Inverness-shire: Geol. Mag. ,, v. Glen Strathfarrar, Geol Mag. v. 93, p. 32-40p. 32—40. . Rickard, M. M. 3.., J., 1961, 19~51, A note n o t e on on cleavages cleavages rock: Geol. v.98, p. rock: Mag., p - 324—332. 324-332. Geol. Mag.., v.98, iin n c renulated crenulated Roper, P. P. 3., J. , 1972, 1972, Structural S t r u c t u r a l significance s i g n i f i c a n c e of o f "button" " b u t t o n " and and Roper, " f i s h scale" scale'' texture t e x t u r e in i n phyllonitic p h y l l o n i t i c schist s c h i s t of of t h e Brevard Brevard "fish the Soc. Amer. Amer. B ull. , Zone, South Carolina: Carolina: Geol. f h o l Soc. Zone, Northwestern Northwestern South Bull., v. p. 853—860. 853-860. v. 83, 83, p. . %,. 1911, Uber Zusammenhange Zusammenhanqe zwischen Teilbewegung Sander, B,. Sander, 1911, Gefuge in i n Gesteinen: Gesteinen: Tscher.. Tscher- flIn. P e t r . Mitt., Mitt., v. 38, und Gefuge Mm. Petr. v. p. 281-317. p. 281—317. E. H. H. T., Structural Whitten, E. Whitten, T., 1966, Structural Rocks, Chicago, Rand McNally, 663 p. p. Chicago, Rand McNally, 663 Rocks, Geology W i l l i a m s , P. P. F - , 1967, tructural h a l y s i s of of Williams, F.,, 1967, SStructural Analysis Broken Hill area of New South Wales: H i l l area of South Wales: Jour. New Broken Jour. A u s t r a l i a , v. v. 14, p. p. 317-332.. 317-332. Australia, 29 o off Folded Folded tthe he L ittle Little Geol. Soc. �U GEOLOGY OF WRIGHT GEOIiOGY WRIGHT COUNTY COUNTY USING LOG DATA DATA USING WELL WEll LOG by Mark J. Hayes and Dr. Charles L. Nelson Department University Department of of Earth Sciences, Sciences, St. Cloud State State University Wright County County well well logs logs were were used to to map bedrock types, types, bedrock elevaelevations, tions, possible possible faults, faults, including including aa previously previouslyuninapped unmapped major major fault fault trending trending southwest-northeast through Wright Wright County County and and a a possible possible explanation for the southwest-northeast positioning of of the the Mississippi Mississippi River River Channel. Channel. Glacial sediments sediments were also also mapped using well logs to give a more precise placement of the St. Croix mapped, Moraine, and a repositioning of the mapped path of the Grantsburg Grantshurg Sublobe Subiobe of Moraine, the the Des Dcs Moines Moines ice ice sheet. sheet. well logs were were used out Three thousand Minnesota Department of Health well of 5000 available available for for Wright Wright County. County. The remaining remaining 2000 2000 logs logs of a total total of of 5000 reasons including incomplete or inaccurate locawere rejected for various reasons localocation (Towntion tion and and strata strata files. files. Each log log had the the following following format: format: location ship—Range—Section),, strata, bedrock ship-~an~e-~ection) strata, and and strata strata thickness. thickness. Sediments Sediments and bedrock types were cataloged into standardized formations, e.g. sandy—clay formations, e.g. sandy-clay and clay— clayStandardization was necessary beboth classified sand were both classified as as clay—sand. clay-sand. Standardization Strata color was also cause percent composition composition of of strata strata was was rarely rarely given. given. Strata color was also light—green, green, green, and and dark dark green green were were standardized so that, for example, light-green, all all classed classed as as green. green. own- It should be noted that well well drillers are not geologists; geologists; however, however, they do know gravel, etc., know the differences between sand and shale, shale, clay and gravel, etc., and differences differences in in color. color. Township—range locations locations were were transformed into rectilinear rectilinear coordinates Township-range coordinates three—dimensional characterisZ-attribute. For numerical data with three-dimensional characteriswith aa Z—attribute. "SURFER" (Golden olden Graphics Graphics tics map file wasgenerated generated using program a map file was using thethe program "SURFER'T tics a file was The file was then thenconverted converted into intoa aGeographic Geographic Information Information Software, Inc.).) . The Software, Inc. System attribute file compatible with "EPPL—I" "EPPL-7"(a(aGIS GISprogram program developed developed by by System attribute file compatible with Management Information the Land Management Information Center, Center, Minnesota Minnesota State State Planning Planning Agency). ~~enc~). the Non—numerical attribute data was mapped using a Thiessen Polygon Polygon Method Non-numerical attribute Department, St. Cloud developed developed by by Dr. Dr. Charles L. Nelson, Earth Sciences Department, State State University. University. Bedrock maps show from just east of the city of Cokato show a curved trend from to to southwest southwest of of Monticello. Monticello. Along this fault are several several series series of of lakes lakes and other Disother topographic topographic features features which which seem seem to to indicate indicate bedrock bedrock control. control. Displacement along along the the fault fault is is unknown. unknown. Bedrock Bedrock elevations elevations are are highest highest in in north—northwestern margin the north-northwestern margin of of the the county. county. An irregular irregular bedrock bedrock ridge ridge extends to to the the east—southeast. east-southeast. The The ridge ridge is is breeched breeched by by several several swales. swales. On the southern southern margin of of the the ridge ridge are are several several semi—enclosed semi-enclosed depressions. depressions. A wide wide low—relief low-relief buried buried valley valley trends trends south south from from the the center center of of the the county. county. level Wright County is covered by At an an elevation of 900 900 feet feet above sea level sediments with with an isolated sandstone deposit near near the MissisMissisunconsolidated sediments 850 feet feet isolated isolated pockets of of sippi sippi River River near near the the village village of of Otsego. Otsego. At 850 30 �U sandstone sandstone and red red granites granites occur occur along along the the river. river. Patches Patches of of shale shale cover cover unconsolidated sediments both unconsolidated sediments and and sandstone sandstone in in aa northwest northwest to to southeastern southeastern trend. unconsolidated sediments trend. Beneath unconsolidated sediments in in the the northwestern northwestern corner corner at at 800 800 feet feet an an area area of of about about 10 10 square square miles miles of of sandstone sandstone exists. exists. A nearly nearly equal equal area area of of sandstone sandstone also also exists exists on on the the far far eastern eastern side side of of the the county. county. AA larger 7 5 0 foot foot larger region region of of shales shales occur occur in in the the center center of of the the county. county. At the the 150 elevation 800 foot foot level level shales. shales. Cretaceous Cretaceous shales shales elevation sandstone sandstone underlies underlies the the 800 covers covers the the southwestern southwestern quarter. quarter. An An arcuate arcuate band band of of sandstones sandstones cuts cuts through through the T O O feet feet above above sea sea level level grey grey granite granite the eastern eastern part part of of the the county. county. At At 100 appears appears in in the the west west central central part part of of the the county. county. Along Along the the river river red red granites granites are are interspersed interspersed with with sandstones sandstones and and shales. shales. Shales Shales covcr cover the the central central secsection tion with with sandstones sandstones and and unconsolidated unconsolidated sediments sediments occurring occurring in in the the southeast. southeast. A five five mile mile wide wide band of of sandstone sandstone surrounding surrounding red granites granites parallels the river river at at 650 650 feet. feet. The The southeast southeast quarter quarter is is also also sandstone. sandstone. Shales Shales and and unconsolidated unconsolidated sediments sediments separate separate the the two two sandstone sandstone bodies. bodies. Granites Granites occupy occupy the the western western one—third one-third of of the the county. county. There north— There are are four four bedrock valleys, valleys, trending south—southwest south-southwest to northnortheast northeast near near the the cities cities of of Annandale, Annandale, Clearwater, Clearwater, Silver Silver Creek, Creek, and Monticello. cello. The The Mississippi Mississippi River appears appears to to be constrained constrained at at present by a series series of small small buried red red granite granite bedrock bedrock highs highs on on the the south south side side of of the the river. river. The The river river was possibly possibly kept kept to to the north north of of the bedrock highs by Grantsburg Sublobe meltwater and sediments, sediments, flowing flowing through through the aforemenaforemenGrantsburg Sublobe tioned glacial tioned valleys. valleys. The The Clearwater channel channel is is apparent apparent even in in the glacial sediments sediments at at the the surface. surface. It It is is the the widest widest of of the the bedrock bedrock channels channels with with aa maximum maximum width width of of one one and and aa half half miles. miles. Several Several narrower narrower and and shorter shorter but but deeper deeper channels channels extend extend northward northward to to the the Mississippi Mississippi River, River, past past the the towns towns of of Maple Maple Lake, Lake, Silver Silver Creek Creek and and Hasty. Hasty. Several Several long long surface surface channels channels eroded into into glacial glacial sediments sediments trend northward ward through through morainic morainic hills. hills. Some Some of of these these channels channels are are superimposed superimposed above above buried buried bedrock bedrock channels. channels. One One channel channel may may be be aa glacial glacial tunnel tunnel valley. valley. The The slope slope of of the the floor floor is is not consistent, consistent, a drainage drainage divide divide exists exists midway along along the the valley, valley, there there are are also also several several enclosed enclosed depressions. depressions. Water Water flowing flowing through through aa glacial glacial tunnel tunnel is is capable capable of of undulating undulating up up and and down down slopes. slopes. The surface surface of of the the northern northern half half of of Wright County County is is St. St. Croix The ~ r o i xend end moThe hills hills are are composed composed of of thick thick deposits deposits of of very very red red clay. clay. They They The trend trend from from the the northwest northwest to to the the southeast. southeast. Deposition Deposition thickness thickness can can exceed exceed 200 200 feet. feet. The The end moraine moraine is is located located on on the the southern southern flank flank of of the the bedrock high. preexisting glahigh. The The central central part of of the the county county consists consists of of reworked reworked preexisting cial cial sediments sediments and and Des Des Moines Moines Lobe Lobe tills. tills. An An eight eight mile mile long long esker esker meanders meanders across across Des Des Moines Moines ground ground moraine moraine in in the the east—central east-central part part of of the the county county from from Pelican Pelican Lake Lake southward southward to to the the Crow Crow River River valley. valley. Des Des Moines Moines tills tills cover cover the the southern southern portion portion of of the the county. county. There There is is little little or or no no correlation correlation between between the the deposition deposition of of Des Des Moines Moines tills tills and and bedrock bedrock topography. topography. There There is is some some correlation correlation between between Des Des Moines Moines outwash outwash and and bedrock bedrock topography. topography. raine. raine. From high high resolution resolution mapping of of bedrock bedrock elevations elevations and and detailed detailed analysis analysis From of Moraine, the path of the Grantsburg of glacial glacial sediments sediments of of the St. Croix End Moraine, Sublobe Sublobe of of the Des Des Moines ice sheet sheet is farther farther to the east than mapped by earlier earlier investigators. investigators. 31 �STRUCTURAL ANALYSIS ANALYSIS OF ARCHEAN ARC TASEDIMENTARY STRUCTURAL METASEDIMENTARY ROCKS IN VICINITY OF THE MINERAL HILL GOLD ROCKS IN THE VICINITY GOLD MINE, MINE, MONTANA JARDINE, MONTANA Joseph D. D. Jabiinski Jablinski and and Timothy Timothy B. B. Hoist Hoist Joseph Department of Geology, University University of of Minnesota, Minnesota, Duluth Duluth Department of Geology, Duluth, Minnesota Minnesota 55812 55812 John John Cuthill American American Copper Copper and and Nickel Nickel Company, Company, Inc. Inc. 4860 Robb Robb St., St., Wheat Wheat Ridge, Ridge, Colorado Colorado 80033 80033 David David C. C. Oliver Oliver Mineral Mineral Hill Mine Mine P. 0. 0.Box Box 92 92 Gardiner, Montana Montana 59030 59030 Jardine Jardine is is located located along along the the western western margin margin of the the Beartooth Beartooth Mountains Mountains in in Placer Placer gold gold was was discovered discovered in in the the Jardine Jardine region in in southwestern southwestern Montana. Montana. 1866, and by Precambrian lode gold 1880Ts, Precambrian iron iron formation-hosted formation-hosted lode gold was was 1866, and by the the mid mid1880's, being the Jardine being mined mined on on Mineral Mineral Hill. Hill. In In 1984, 1984, the Jardine Joint Joint Venture Venture was was formed formed between between American American Copper Copper and and Nickel Nickel Company Company (ACNC) (ACNC) and and Homestake Homestake Mining Mining Company, Company, with with ACNC ACNC acting acting as as the operating operating partner. partner. Renewed surface surface and and Renewed underground exploration by by ACNC underground exploration ACNC has shown shown Mineral Mineral Hill Hill to have have a probable probable ore reserve reserve of 1.0 1.0 million million tons tons at aa grade grade of of 0.3 0.3 ounces ounces of of gold gold per perton. ton. The The bedrock geology geology of the the Jardine Jardine area area consists consists predominantly of Archean Archean metasedimentary metasedimentary rocks rocks which which were were intruded intruded by by granitic granitic stocks stocks and and minor minor mafic mafic dikes dikes and and sills. sills. Greywacke Greywacke and and mudstone mudstone sequences, sequences, which which were were deposited deposited by by turbidity turbidity currents, currents, have have been been regionally regionally metamorphosed metamorphosed to to quartz-biotite schist schist and and biotite schist, schist, respectively. respectively. The original original thickness thickness of of the the sedimentary sedimentary pile pile is is unknown, unknown, and and a diamond diamond drill drill hole hole on on Mineral Mineral Hill, Hill, which to aa depth which was was drilled drilled to depth of of over over 2000 2000 ft., ft., failed failed to intercept intercept the the basement basement to to these The thickness these sediments. sediments. thickness of of the the sedimentary sedimentary pile pile has has probably probably been been exaggerated exaggerated by by tectonic tectonic thickening thickening during during isoclinal, isoclinal, recumbent folding. The The monotonous nature of monotonous nature of this this thick thick pile of metasedimentary metasedimentary rocks rocks is is interrupted interrupted by by aa silicate silicate facies facies iron iron formation formation which which acts acts as the the only onlystratigraphic stratigraphic marker marker horizon ItIt is horizon in in the Jardine Jardine region. region. is this this iron iron formation formation and and proximal proximal schists schists which which host host the the gold gold mineralization. Calculations Calculations from from microprobe microprobe analyses analyses of coexisting coexisting biotite biotite and and staurolite staurolite in in an an aluminum aluminum silicate-rich silicate-rich sample, sample, show show that that peak peak metamorphism metamorphism occurred occurred at 2.9 kb at a pressure pressure and and temperature temperature of of approximately approximately 2.9 kb and and 560° 560' C,C,respectively. respectively. Evidence Evidence for for three three generations generations of of Precambrian folding folding has has been been recognized recognized in in the the Archean Archean metasedimentary metasedimentary rocks rocks of the the Jardine Jardine region. region. During (Fi), isoclinal, isoclinal, recumbent recumbent folds folds were were formed. formed. During the the earliest earliest fold fold phase phase (F1), A A foliation foliation plane, plane, S1. Si, defined defined by by the the growth growth and and preferred preferred orientation orientation of of was created micaceous minerals, during the F1 fold event and is observable micaceous minerals, was created during the Fl fold event and is observable throughout throughout all all rock rock types types in in the the region. region. The The orientation orientation of this this schistosity schistosity isis along texturallyalong or o r nearly nearly parallel to to the the original original compositionallycompositionally- and and texturallydefined defined bedding bedding planes. planes. Si S l surfaces surfaces were were subsequently subsequently crenulated during during the the second and F3 F3 fold fold axial axial surfaces surfaces are are upright upright second (F2) (F2) and and third third (F3) (F3)fold foldevents. events. F2 and and and at at a high high angle angle to to F1 F I fold fold axial axial surfaces surfaces and and to to each each other. other. 32 8 2 and and S3 S3 S2 �U cleavages of of S1. foliations are axial planar planar crenulation crenulation cleavages S l . This zonal zonal crenulation crenulation axial planar by the cleavage (Marshak cleavage (Marshak and and Mitra, Mitra, 1988) 1988) is defined defined by the axial planar alignment alignment of of microfold hinges (symmetric (symmetric zonal crenulation cleavage) and/or domains of reoriented reoriented micas micas (asymmetric (asymmetric zonal zonal crenulation crenulation cleavage) cleavage) and and is is not the result of micaceous of recrystallization of micaceous minerals in the microfold hinges. Linear structures found predominantly structures are are found predominantly in biotite schist because of its rheology and and the the nature nature of ofthe thedeformations. deformations. L2 L2 and and L3 L3 lineations are are the intersection S1i foliation of of S2 S2 and and S3 8 3 axial planar planar crenulation crenulation cleavage surfaces surfaces in the S surface. surface. F2 F2 fold fold axes axes were were the the only only minor minor fold fold lineations lineations which which were were directly directly measurable from from outcrop. The The dominant dominant fold interference pattern created by fold superposition is is a The interference of F2 1, dome Ramsay (1962), Type Ramsay Type 1, dome and and basin basin pattern. pattern. The interference of F2 and and F3 F3 history diagram The structural (see folds are responsible for this pattern. structural diagram folding (Figure below) involves early isoclinal, isoclinal, recumbent recumbent F1 F l folding (Figure IA), lA), with with later refolding by F2 refolding by F2 folds, folds, with with F2 F2 axial axial surfaces surfaces at at aa high high angle angle to to F1 F l axial surfaces surfaces to F1 (Figure F3 fold (Figure IB). 1B). F3 fold axial axial surfaces surfaces are are at at high high angles angles to F l and and F2 F2 fold fold axial axial folds. surfaces IC) and refold both sets of earlier folds. surfaces (Figure 1C) A firm understanding of this fold form is understanding is important for future future regional exploration, the highest since since it has has been been shown shown that that the highest grade grade of of gold gold mineralization mineralization occurs occurs in the the domes of the folded iron formation (John Cuthill, personal communication, 1989). communication, 1989). F, S S A C B FIGURE 1 References References and Mitra, Marshak, S., and Mitra, G., 1988, 1988, Basic Basic methods methods of of structural structural geology: Jersey, Prentice-Hall, Inc., 445 Jersey, Prentice-Hall, Inc., 445 p. p. New Ramsay, J. J. G., 1962, Interference patterns patterns produced produced by by the superposition of 1962, Interference folds of similar folds similar type: type: Journal 1. Journal of Geology, Geology, v. 70, 70,P.P.466-48 466-481. 33 �REVERSE ZONATION ZONATION IN LESTER RIVER RIVER SILL, SILL,DULUTH, DULUTH, REVERSE IN THE LESTER MINNESOTA, AND AND EVIDENCE EVIDENCE FOR FOR POLYBARIC POLYBARIC FRACTIONATION FRACTIONATION Eric Eric A. A. Jerde Jerde Department of Earth and Space Sciences, University of Department of California, California, Los Los Angeles, Angeles, CA CA 90024 The Lester Lester River River Sill Sill intrudes, intrudes, and and is is roughly roughly concordant concordant with, with, the the extrusive extrusive flows flows that that constitute the the North North Shore Shore Volcanic VolcanicGroup Group(NSVG) (NSVG)ofofKeweenawan KeweenawanAge Age(1(l.lGa). .lGa). The sill sill is one of three large sills sills found found in in the the city city of of Duluth, Duluth, Minnesota, Minnesota, the the others others being being the the Endion Endion and and Northland Northland sills, first studied by (1). Since Sincethen, then,the the425 425m mthick thickEndion EndionSill Sillhas hasbeen been the themost most intensely studied 3, 4), and the smaller (5). studied (2, (2,3,4), smaller Northland Northland Sill Sill has has also also been been investigated investigated (5). The most extensive extensive outcrop outcrop of of the the Lester Lester River River Sill Sill occurs occurs in in Duluth, Duluth, along along the the shore shore of of Lake Lake Superior, Superior, beginning beginning just north north of of the the Lester Lester River River and and continuing continuing approximately approximately1.8 1.8 km km in in KitchiKitchiGammi Garnrni Park. ItItcan canbe befollowed followedinland inlandalong alongaastrike strikeof of approximately approximately N18°E N18OE as as aa well defined ridge ridge extending extendingover over25 25km. km.The Thesill silldips dips—20° -20' to tothe thesoutheast, southeast,indicating indicatingaathickness thicknessofof—280 -280 m. m. Outcrop Outcrop along along the shore shore is is excellent, excellent, and and nearly nearly continuous, continuous, providing aa good good cross-section. cross-section. Chemical Chemical analysis analysis of of 36 36 samples samples from from the the sill sillwas wasundertaken undertakenutilizing utilizinginstrumental instrumentalneutron neutron activation analysis (INAA) and electron microprobe analysis of fused glass beads, yielding data for activation analysis (INAA) and electron microprobe analysis of fused glass beads, yielding datafor 34 34 elements. elements. This Thisparticular particularsill sillexhibits exhibitsaa"reverse" "reverse"zonation, zonation,with withthe themost mostprimitive primitivediabase diabase(i.e. (i.e. diabase mg [molar [molarMgO/(MgO+FeO)] MgO/(MgO+FeO)] and and the the lowest lowest abundance abundance of incompatible diabase with with the the highest highest mg elements and S SiO2) occurring in the central regions. The lower half (140 O2) (140 m m stratigraphically) stratigraphically) isis medium-grained, medium-grained, intergranular intergranular diabase. The The upper upper portion portion of of the the sill sill is is more more varied. Most Mostof ofititisis an ophitic diabase, with individual pyroxene pyroxene grains grains up up to to 1 cm cm across. across. Near Near the the top top of of the the sill, sill, stringers of red material become more abundant until, at the topmost part, the rock is a granophyre. stringers material become more abundant until, at the topmost part, the rock is a granophyre. In In general, general, crystallization crystallization from from the the margins margins in in large large sills sills results results in in the the most most evolved evolvedmaterial material being located in the medial portion. portion. An In An example example is is the Palisades Sill of New Jersey (e.g. 6). In the Palisades Sill, the silica content ranges from about 52% at the margins to 60% in the most silica content ranges from about 52% at the margins to 60% in the most evolved rocks, and the incompatible trace elements elements show show great great enrichment enrichment (Fig (Fig la). la). Although Although the the thickness thickness of the the Lester Lester River River Sill Sill is is less less than than that that of of the the Palisades PalisadesSill, Sill,itit isislarge largeenough enoughto toexpect expect extensive fractionation in a slowly cooling environment. The chemical trends across the sill extensive fractionation The chemical trends across the sill (Fig. (Fig. ib) lb) are are opposite opposite in in sense sense to those those trends observed observed in in the the "normal" "normal" Palisades Palisades Sill, with with the themost most 300 I.... 400 a. 250 . 300 a a 200 200 150 5 100 Lester River Palisades k • I) Sm Sm (ppm) 5° (pnn) .ll• 3 6 9 12 5 0 5 10 IS 20 25 Figure Figure 1. Samarium Samariumvariations variations across across the Palisades and and Lester River Sills. Sills, 34 30 35 40 I �U River Sill. Although primitive material in the medial portions of the Lester River Although this this facies facies represents represents the primitive primitive part part of of the the Lester Lester River River Sill, Sill, itit is is considerably considerablymore moreevolved evolved(mg (mg~O.45) 0 . 4 5 than ) the primitive olivine tholeiites tholeiltes of of the theNSVG NSVG(mg (mg20.65; O.65; [7]), [7]), or or even even the the majority majority of diabases diabases from from the the the North North Shore Shore(mg (mg~O.55). rest of the 0.55). "reverse" zoning profile seen in the Lester River Sill makes it unique among The among the the hypabyssal hypabyssal The rocks of the North North Shore. Indeed, sills in in general. general. In Antarctica, the Indeed, such profiles are rare among sills Lake Vanda Sill Sill and and Emmanuel Sheet show show similar similar trends trends (8), although these are not as Lake Vanda Emmanuel Sheet although these as Sill. In In the the Antarctic Antarctic bodies, few of the elemental concentrations pronounced as in the Lester River Sill. vary by as much as a factor of 2 across across the sifis sills (even in the incompatible incompatible elements), elements), whereas whereas in the Lester River Sill the variations 3. variations are are up to factors factors of 3. A likely process that could have produced the pattern seen seen in the Lester Lester River River Sill Sill is is some some form form of multiple intrusion. Multiple intrusion is the preferred model for the emplacement of the 425 m 4). thick Endion Sifi Sill to the south south of the the Lester Lester River River Sill Sill (3, (3,4). The Lester River Sill Sill is located between an an andesite andesite and andaa rhyolite rhyoliteof of the the NSVG. NSVG. The Lester River located between melting point of the rhyolite, temperatures of the intruding material would have been well above the melting and it is apparent from the presence of stringers and blebs of felsic material the upper portions portions of of stringers felsic material in the the sill, that extensive assimilation assimilation of of the therhyolite rhyolitetook tookplace placethere. there. In In the the profile profile of of Fig. Fig. lb, ib, this assimilation is reflected in the chemical chemical trend at the top, which describes a mixing line between the primitive diabase and the rhyolitic host rock. In the inland areas of the Lester River Sill, Sill, where rhyolite was not in contact with the diabase, diabase, there is no "red "red rock" zone, and no discernible discernible mixing mixing features. features. It is presumed that the most primitive diabase diabase of the sill was intruded first, first, since it is this material that contains the blebs and stringers of felsic rock indicating assimilation. contains stringers indicating assimilation. Further intrusion intrusion of more evolved evolved magmas magmas below below those those already alreadypresent present could couldproduce producethe theprofile profileobserved. observed. Mass-balance calculations Mass-balance calculations were undertaken in an attempt to model the generation generation of the primitive diabase in the Lester River Sill. A parent of mean primitive olivine tholeiite diabase A parent of mean primitive olivine tholeiitecomposition composition from from the the NSVG (7) was chosen for mass-balance calculations. From From this this parental parental composition, composition, successive successive increments of of fractionating assemblages were were subtracted subtracted (each (each increment increment consisted consisted of 11 wt% increments fractionating assemblages ± cpx, which form the majority of 01 + + plag k of early early solids solids solids). These These assemblages assemblages consisted of ol produced during during the crystallization crystallization of of basaltic basaltic magmas. magmas. Mineral produced Mineral compositions compositions are are calculated calculated separately separately for for each each increment. increment. In order to successfully successfully obtain compositions compositions similar similar to the more primitive primitive diabase diabase in in the the Lester Lester River Sill, the modelling indicated that the first stage of the fractionation must consist of the 33ol + phase (3A) assemblage + plag plag ++ cpx, cpx, followed followed by a stage stage of of ol 01++ plag, and a third stage stage with with 33 phase (34)) assemblage 01 phases again (Fig. 2). The implication implication of the calculations calculations is is that that at at least least two two (and (and possibly possibly more) more) separate magma chambers at differing crustal levels are required to produce the first Lester River Sill magma from the primitive olivine tholeiite. This Thisresults resultsfrom fromthe thestrong strongeffect effectof of pressure pressureon on the clinopyroxene stability field for basaltic basaltic liquids, liquids, which which shrinks shrinks with with decreasing decreasing pressure. pressure. Therefore, a magma which crystallizes crystallizes ol ++ plag ++ cpx cpx at depth and then rises to a higher, lower could be expected expected to to crystallize crystallize only only ol 01++ plag for a time at the new pressure position in the crust could location At some later time, cpx would location due to this shrinkage shrinkage of the the cpx cpx stability stability field. field. At would then then reappear as a crystallizing crystallizing phase. Magma Magmarising rising to to aa still still higher higher level level would would again again result in only ol 01 + plag crystallizing. Polybaric Polybaricfractionation fractionationsuch such as as this this has has been been used used to explain explain trends trends observed observed + in continental 9), and and has has also also been been proposed proposed for for the the origin origin of of the the compositions compositions continental flood basalts (e.g. (e.g. 9), 35 �U seen in in some someof of the theLake LakeSuperior Superiorvolcanics volcanics(10). (10). seen Additional evidence evidence for for polybaric polybaric fractionation fractionation can can be befound foundusing usingaapseudo-liquidus pseudo-liquidusphase phase Additional thisdiagram, diagram,the theprimitive primitiveolivine olivinetholeiites tholeiitesof ofthe theNSVG NSVG plot plotininaaregion region diagram (Fig. (Fig. 3). 3). InInthis diagram consistent consistent with with aamagma magmathat thatisismultiply multiplysaturated saturatedatatan anelevated elevatedpressure pressure(—10 (-10 kb). The Themost most evolved material material of of the the Lester Lester River River Sifi Sill is is seen seen to to be be consistent consistent with with multiple multiple saturation saturation at at aa evolved is intermediate, suggesting pressure considerably lower (i.e. -1 am). The primitive part of the sill pressure considerably lower (i.e. —1 atm). primitive the sill is intermediate, suggesting region between between the the two two (roughly (roughly 33kb?). kb?). aa region 22 21 21 ^ n 0'4 4 20 20 I I Silica L - o 34 0 A 18' 18 16 16 - 0( 0-0 22 l 3 3 '• lI 44 " • " ' • l 55 66 ' - t I' l. ' I . • I 7 7 8 8 9 9 • Medial Lester River Sill -A 34 3* ' 15 15 + MedIal Lester River SiR o Lester LesterR. R.center center Oe1 - o0Primitive PrimitiveOlivine OlivineThokitie Tholeiiic + Basal Lmtez River Basal 1mstcr RiverSIR Sill A Parent Parent A 1919 17 17 J Calculations Calculations 0o 1 PI'lagiuclase Ia gi oc I ase 100 Clinopyroxene in 0 pv () xcii e MgO M e 0 (%) (%) Figure Figure3.3. Pseudo-liqwdus Pseudo-liquidusphase phasediagram diagramfor forthe the Lester Lester R. R. Sill Sill and andpsimitive primitive ol. 01. tholeiites. tholeiites. Figure2. 2. Mass-balance Mass-balanceresults results for forthe the Lester Lester River River Figure Sill.Each Eachstage stageisis—25% -25% crystallization. crystallization. Sill. Intuitively, Intuitively, itit is not hard to imagine several magma chambers forming at different different levels levels in in aa rifting rifting environment environment where where fracturing fracturing is pervasive. Evidence Evidenceexists existsfor foraahigh high level levelchamber chamberbelow below the the Krafla Krafla volcanic volcanic center center in in Iceland, Iceland,deduced deduced from from studies studiesof of caldera caldera inflation inflation rates rates (11, (11,12). 12).This This chamber chamber is is presumed presumed to to be be an an upper upper crustal crustal chamber chamber filled filled from from another another one below, below, leading to to inflation and uplift of of the the caldera caldera floor. floor. After After aa period period of of time, time, the the magma magma isis injected injected into into the the surrounding surrounding area, forming numerous dikes. This Thisprocess processisisanalogous analogousto to that that suggested suggestedabove above for for the additionalevidence evidencethat that lateral lateral transport transport of of magma magma the formation formation of of the the Lester Lester River River Sifi. Sill. There Thereisisadditional along km) occurs occurs in in Iceland Iceland (13). IfIf aasimilar along the the rift rift over over moderately moderatelylarge largedistances distances(—70 (-70 km) similarprocess process occurred Midcontinent Rift, Rift, itit may may begin begin to to explain explain the the striking strikingsimilarity similarityof of compositions compositions occurred in the Midcontinent observed observed among among the the other other hypabyssal hypabyssalrocks rocksfound foundall allalong alongthe thenorth northshore shoreofofLake LakeSuperior. Superior. References References Sandberg, A.E. A.E. (1940) (1940) Geol. Soc. Soc. America America Bull Bull.,., 551,1,1135-1172. (1) Schwartz, G.M. and Sandberg, 1135-1172. (1) W.G. (1960) (1960) J. (2) Ernst, W.G. J.Petrol., Petrol., 1, 1, 286-303. 286-303. (2) (3) Oestrike, Oestrike, R.W., Jr., Jr., (1983) (1983) Unpub. Unpub. M.S. M.S. thesis, thesis,Univ. Univ. of of illinois, Illinois, Urbana-Champain, Urbana-Champain,lztlp. 141p. (3) (4) Gardner, Gardner, J.E. J.E. (1987) (1987) Unpub. Unpub.M.A. M.A.thesis, thesis,Washington Washington University, University, St. Louis, 359 359 p. p. (4) 7, 325-326. (5) Seifert, Seifert, K.E. K.E. (1985) (1985) Geol, Geol.Soc. Soc.America America Abstracts Abstracts with with Prog., Prog., 117, 325-326. (5) D.N. (1987) (1987) J. Petrol., Petrol., 28, 28,835-865. 835-865. (6) Shirley, D.N. (6) (7) Brannon, Brannon, J.C. J.C. (1984) (1984) Unpub. Unpub.Ph.D. Ph.D.dissertation, dissertation,Washington Washington University, University, St. Louis, 312 3 12 p. p. (7) Acta, 30, (8) Gunn, Gum, B.M. (1966) Geochim. Geochim. Cosmochim. Cosmochim. Acta, 3 0,88 881-920. 1-920. (8) (9) Cox, K.G. (1980) J. J.Petrol., Petrol., 221,1,629-650. 629-650. (9) K.W.(1989) (1989) JJ.. Geol., Geol., 97, (10) Kiewin, Klewin, K.W. 97,65-76. 65-76. (10) Bjomsson, A., A., and and Sigurdsson, Sigurdsson,S. S.(1980) (1980) J. J. Geophysics, (1 1) Johnsen, G.V., G.V, Bjomsson, Geophysics, 47, 4 7,132-140. 132-140. (11) (12) Sigurdsson, Sigurdsson, H. H. (1987) (1987)in in Mafic Maficdyke dykeswarms: swarms: Geol. Geol. Assoc. Assoc. Canada Canada Spec. Spec. Paper Paper 34, 34,55-64. 55-64. (12) H., and and Sparks, Sparks,R.S.J. R.S.J.(1978) (1978) Nature, Nature, 274, (13) Sigurdsson, Sigurdsson, H., 274, 126-130. 126-130. (13) 36 - ---- �U OF SSTATE TATE O F MINNESOTA MINNESOTA DRILL CORE LIBRARY LIBRARY Jacqueline Jiran Jacqueline Minnesota Department Department of of Natural Resources Minnesota Resources Division of Minerals Minerals ABSTRACT The of Minnesota Drill Core Core Library Library is is located located in in the city of Hibbing, T h e State of Minnesota Drill Hibbing, aa 90 90 8:00am a m to to 4:30 4:30 pm daily; Minerals minute drive northwest of Duluth. Duluth. The T h elibrary libraryhours hoursare a r e8:00 Division staff are Division a r e available available during during this thistime timeto todiscuss discuss Division Division projects projects or or subjects subjects related related to Minnesota's Minnesota's mineral mineral potential. Geologists to examine examine aand/or to Geologists are a r e welcome welcome to n d / o r sample sample drill drill core; reservations arc a r c encouraged. encouraged. Drill core corc and cuttings resulting resulting from from iron, iron, base base and and precious precious metal metal exploration exploration in in Minnesota currently stored stored in in two two buildings. buildings. In In anticipation of Minnesota aare r e currently of further f u r t h e r drill drillcore corc acquisitions, aa third building acquisitions, building with with aa capacity capacity of of 630,000 630,000 feet was was constructed. With With the the additional storage, the Drill Core Core Library capacity capacity has has been been expanded expanded to to over over 22 million million feet. Currently, the total total amount amount of of drill drillcore corcand andcuttings cuttingsavailable availableexceeds exceeds 1.5 1.5 million feet, and additional drill drill holes holes are a r e added added monthly. monthly. Also Also as as aa result result of of the the new new expansion, expansion, the the library library 166 linear linear feet. examination table table space space has has increased increased from from 55 55 to 166 feet. Minnesota counties, counties, including including all all of of the Drill Core is available from f r o m 57 57 of the 87 Minnesota counties iinn the Canadian Canadian Shield Shield Terrane of of northern northern Minnesota. Minnesota. These These cores cores arc a r c collected collected through the state's exploratory boring to submit submit their drill through boring law, law, which requires companies companies to core the state aatt the the termination termination of of their state or private private lease. core tto o the lease. An index for f o r the the Drill Drill Core Core Library is available in both printed and and computerized computerized formats and a n d is is sorted by geographic location, as aare r e the corresponding paper files. Other related information available available at a t the the Division Division of of Minerals Minerals office includes: includes: lithologic logs logs ffor lithologic o r many of the the drill drillholes, holes, geochemical geochemical analyses and assays, assays, geophysical studies, and a n d an a n excellent excellent thin thin section section and and polished polished thin thinsection section collection collection (microscopes (microscopes can be be reserved reserved if needed). needed). For ffurther For u r t h e r information information or o rreservations, reservations, contact: contact: Mineral Resources Geologist DNR D N R -- Minerals Division P.O. Box 567 567 Hibbing, MN MN 55746 55746 Phone: (218) (21 8) 262-6767 262-6767 37 �U THESIGNIFICANCE SIGNIFICANCEOF OFREGIONALSCALE REGIONAL-SCALELEFT-LATERAL LEFT-LATERALFAULTING FAULTINGIN INDEVELOPMENT DEVELOPMENTOF OF THE THEVERMILION VERMILIONGREENSTONE GREENSTONEBELT BELTIN INMINNESOTA MINNESOTA THE Boerboom Mark A. A. Jirsa, Jirsa, D.L. D.L.Southwick, Southwick, and andTerrence Terrence J.J.Boerboom Mark Minnesota Minnesota Geological Geological Survey Survey 2642 2642 University University Avenue Avenue St. St. Paul, Paul, MN MN 55114-1057 55114-1057 Northeast-trending longitudinal faults faults were were recognized Northeast-trending longitudinal recognized by the earliest earliest mappers mappers in in the the Vermilion Vermilion greenstone greenstone belt (VGB), (VGB), but until until recently recently their their role role in in the thetectonic tectonic evolution evolution of the the belt belt was was unclear. unclear. Even Evenininthe thebest-exposed best-exposedareas areas of ofnortheastern northeastern Minnesota, Minnesota, longitudinal longitudinal faults faults are are rarely rarely exposed exposed and and their their presence presence was wasinferred inferredmainly mainly from from linear linear topographic topographic depressions depressions across across which which stratigraphic stratigraphic correlations correlations are are tenuous tenuous or 1970s, detailed detailed study study ininthe the or metamorphic metamorphic grades grades are areincompatible. incompatible. In In the the early early 1970s, central central Vermilion Vermilion district district showed showed that that early left-lateral left-lateral faults faults were offset offset by by The right-lateral right-lateral event event appeared appeared northwestnorthwest- to to west-trending west-trending right-lateral right-lateralstructures. structures. The to be the more significant of the two; it accorded well with major right-lateral to be the more significant of the two; it accorded well with major right-lateralfaulting faulting elsewhere elsewhere in in the the Superior Superior Province Province and and was was consistent consistent with with the the overall overall regime regime of ofdextral dextral transpression transpression that that dominated dominated the the tectonic tectonic development development of of the theregion. region. Observations Observations and and inferences inferences from from recent recent mapping mapping in in the the western western and andcentral centralVGB VGB are are the the basis basis for for revised revised thinking thinking about about the the scale, scale, separation separation sense, sense, and and timing timing of of longitudinal faulting. faulting. Many Many of the the early early strike-parallel strike-parallel faults faults are are regional-scale regional-scale longitudinal sinistral sinistral structures structures that that were were fragmented fragmented by by later, later, mostly mostly right-lateral right-lateral fault fault zones zones oriented oriented oblique oblique to their their strike. strike. We Weinfer infersinistral sinistraldisplacement displacement sense sense on on major major longitudinal longitudinal faults from from the the map map geometry geometry of of secondary secondary faults faults and and shear shear zones, zones, which which splay strikesplay from from the the main main structures structures and and offset offset marker marker units. units. Patterns Patterns of of sinistral sinistral strikeslip slip duplexes duplexes and and imbricate imbricate fault fault splays splays both bothindicate indicate dominantly dominantly extensional extensional kinematics. kinematics. Because Because marker marker units units are are rare rare and and displacements displacements on on trunk trunk faults faults may may have havebeen beenvery very great, great, we we also also have have used used the the regional regional distribution distribution of of five five generalized generalized rock rock packages packages to to demonstrate demonstrate offsets. This Thismega-stratigraphic mega-stratigraphic approach approach has has led led us us to to recognize recognize aa fundamental within the the VGB (labelled LLSD on Fig. 1) 1) that that divides divides aa fundamental stratotectonic stratotectonic break within northern one. Although northern terrane from from a southern southern one. Although the the significance significance of of this this break break remains remains to to be be determined, determined, it clearly clearly is is an an early early feature feature that that has has been been disrupted disrupted by by sinistral sinistral fault fault displacements. Left-lateral Left-lateral faulting faulting occurred occurred after after peak peakmetamorphism metamorphismbecause because displacements. metamorphic metamorphic isograds isograds are are displaced displaced at at fault faultboundaries. boundaries. Post-kinematic, alkalic plutons plutons that spatially associated associated with with some some longitudinal longitudinal faults faults are are locally locally inferred inferred to to have have that are are spacially been been emplaced emplaced in in extensional extensional rhombochasms rhombochasms within within sinistral sinistral strike-slip strike-slip duplexes. duplexes. Although unproven, unproven, itit is is probable probable that that some some of of the the sinistral sinistral faults occupy parts of of the the Although earlier earlier structures, structures, including including the the medial medial stratotectonic stratotectonic break break within within the the VGB VGB supracrustal supracrustal sequence. sequence. The fault systems The presence presence of of kinematically kinematically complex longitudinal fault systems in the VGB VGB is is consistent consistent with with recent recent interpretations interpretations of greenstone greenstone belts belts as as the the remnants remnants of of accreted accreted arc-trench systems. systems. Phanerozoic Phanerozoic accretion of arc-trench arc-trench systems systems produces produces linear linear arc-trench blocks blocks of of diverse diverse rock rock suites suites that thatare areseparated separatedand andinternally internallysegmented segmentedby bythrust thrustand and wrench faults. faults. Having recognized some aspects of this deformational deformational style style in inthe the VGB, VGB,we we wrench now can speculate speculate about the broader broader paleotectonic paleotectonic and stratigraphic stratigraphic evolution evolution of the belt destraining" major by "destraining" major fault fault displacements. displacements. by 38 �I Support for mapping and geophysical data were provided by Mineral Diversification Program Program of the the Minnesota Minnesota Legislature Legislature administered administered (1) ( 1) by the Minerals Minerals Coordinating Coordinating Committee. Committee. Legislative Commission on Minnesota Resources (2) (2) CUSMAP CUSMAP Program Program of the U.S. U.S. Geological GeologicalSurvey Survey (3) (3) RLUTONIC P L U T O N I C ROCKS ROCKS late and postkinematic, ulkalic [,-+-,*late - and post - kinematic, alkalic plutons plutons <, a 1, , " * * ,, VERMILION O" ,!a s'e~~,~~j 3, a * ">,,)%,, *w !, ' Vermilion Granitic Vermilion Granitic Complex Complex Eg Giants Giants Range Range batholith batholith -LLSD F. U LTS FAULTS LLSD BRF BRF LLF LLF BL F BLF HF HF VF VF 4 Stratigrophic top direction Leech Lake structural Leech Lake structural disconformity disconformity Bear Bear River River fault fault Lost Lost Lake Lake fault fault Burntside Burntside Lake Lake fault fault Haley Holey fault Vermilion Vermilion fault fault 10 KM — b. SUPRACRUSTAL ROCKS undifferentiated ocks and and sills sills LIII mafic to ultromafic volcanic rocks northern ferrane southern te rrone terrone F7j IJ]JJJII I felsic felsic volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks and and iron — format ion iron - formation mofic to felsic felsic volcanic and iron-formation rnafic to volcanic rocks rocks and iron f for motion / eke structural structural disconformity diconIorm,ty Leecih Lake -Leech graywacke ttuff groywacke, u f f and and slate slate volcanic and volcanic and clastic clastic rocks rocks and and iron iron-formation -formation geologic map map (a) of part of the Figure 1. 1. Simplified Simplified geologic the Vermilion Vermilion greenstone greenstone belt; and and reconstruction (b) (b) to before reconstruction before major major strike-slip strike-slipdisplacement. displacement. 39 I I �U Structure of the northern northern block of of the the Ishpeming Ishpeming greenstone greenstone belt, belt, Structure Marquette County, County, Michigan Michigan I R.C. Johnson, Johnson, Department Department of of Geological Geological Engineering, Engineering, Geology, and Geophysics, R.C. Michigan Michigan Technological Technological University, University,Houghton, Houghton,Michigan, Michigan,49931 4993 1 The The northern northern block block of the Ishpeming Ishperning greenstone greenstone belt is dominated by tholeiitic tholeiitic pillowed basalt sedimentary rocks basalt flows flows with minor minor massive flows and subordinate subordinate pyroclastic and sedimentary 2 covers 150 150km2 krn in in north-central north-central Marquette County, Michigan. There There are are at at least least two two and covers major Archean deformational events: (1) deforrnational events: (1) recumbent recumbent folding folding about east-west axes (Di) (Dl) and and (2) east-west axes (1)2). (2) upright folding folding about east-west (D2). These deformational events resulted in folds with amplitudes amplitudesand and wavelengths wavelengths measured in kilometers kilometers and a Z-shaped Z-shaped pattern of the the distribution distributionof of stratigraphic stratigraphic units. units. Gneissic Gneissicgranitoids granitoidsthat thatbound boundthe theblock blockwere wereintruded intruded during D1 basalt to to amphibolite amphibolite grade. grade. Granodiorite Dl and metamorphosed the surrounding basalt Granodiorite stocks stocks and and quartz quartz and and quartz-feldspar quartz-feldspar porphyritic porphyritic rhyolite rhyolite dikes intrude the basalt in in and and adjacent adjacent to shear shear zones. These Thesefelsic felsicintrusions intrusionsare areinterpreted interpretedas aspart part of of the thesame samemagmatic magmatic event event and and both both were wereprobably probablyemplaced emplacedduring duringD2. D2. T. 501 Explanation Explanation Iron-formation — Trajectory of S1 foliatron 1. 49 I Synform Synforrn showing showing trac, tractof of axial axial plane of plunge plure ofofaxis plane and direction of axis -- Antiform Antdorm showing showingtrace trace of of axial axialplane plane and anddirection directionof of plunge plunpof ofaxis axis —— Fault FauB T. 48 I Figure 1. 1. Sketch Sketch map map showing showingS1 Si foliation foliation trajectory, trajectory, F1 Fl and F2 folds, outcrop pattern Figure of the RCL-the iron-formation iron-formation unit, unit, and major fault in the eastern end of the northern block. RCL -Rocking Chair Chair Lakes. Lakes. -Rocking The youngest youngest folds folds (F2) (F2) control the overall Z-shaped Z-shaped pattern of stratigraphic stratigraphicunits. units. Since are rare, rare, F2 F2 folds are best defined by the folding folding Since sedimentary sedimentaryand and volcaniclastic volcaniclastic rocks rocks are of Si thesoutheast southeastthere thereare aretwo twosmaller smallerfolds folds that that may be be controlled controlled by by the the Sl (fig. (fig. 1). 1).InInthe bounding bounding gneissic granitoids. At Atthe thenorthwest northwestend endof ofthe thebelt, belt, L1 Ll lineations lineationsplunge plunge 40 �I moderately to the southeast and Sl Si is is deformed deformed by by an upright, tight to isoclinal southeastverging to to the the southwest. Further plunging F2 synform verging Further to the east, along the same fold, fold, L1 Ll plunges shallowly to the east and Sl forms an upright, open, shallow easterly plunging F2 synform; while whilebedding bedding (So) (So) forms forms an an open open synformal synforrnal anticline anticline plunging shallowly shallowly to the plunge direction direction indicated in in fig. fig. 1 is is for for folded folded SS1 foliation). This west (note that the fold plunge 1 foliation). contradictoiy fold geometry is produced by folding So S0 and and Si Si surfaces which are apparent contradictory the plunge plunge of of folded folded bedding bedding is is less less than not parallel. L1 Ll in this area is nearly flat lying; the 100 to the the west, west, and and the the plunge plunge of of folded Sl S1 is is less less than than 100 100totothe theeast. east. The contrary 10Âto plunge of fold surfaces may be exacerbated by scissors scissors motion along shear zones. The oldest folds (Fi) can be observed observed folds (F1) northeast and southeast of Rocking Chair I), where the outcrop pattern Lakes (fig. 1), of a pyroclastic pyroclastic unit and gabbro gabbro sills sills define F1 Fl folds. The The southern southern F1 Fl fold is a synformal anticline and the northern synfonnal northern F1 Fl fold is an antiformal syncline. Both Both folds folds are tight to isoclinal, upright, upright, and plunge plunge southeast. in moderately to the southeast. In the the vicinity of the fold hinges, bedding is Si, Si normal to Si, Slisisaxial axialplanar, planar,and andL1 Ll plunges moderately moderately to to the the southeast. southeast. Further to to the the east, east, L1 LI and and F1 Fl folds folds plunge plunge shallowly to the east. east. a) The development of folds in the northern block is shown 2. shown schematically schematically in in figure figure2. recumbent, tight During D1, Dl, large-scale recumbent, developed (fig. to isoclinal F1 Fl folds were developed (fig. 2a). Subsequently, Subsequently,during duringD2, D 2 F1 FI folds folds were refolded forming forming isoclinal isoclinal to to open, open, upright F2 folds (fig. 2b) accompanied 2c). This by shearing shearing(fig. (fig. 2c). c) Figure 2. Figure 2. Schematic cross-section of the northern block showing showing fold fold development and relationships of bedding bedding and and Si foliation, foliation. a) a) Early Early Dl, b) open open recumbent folding folding during during D1, east-west axes D2, folding about east-west axes during during D2, and c) late-stage shearing associated associated with 1)2. E>2. Bar and ball symbol symbol indicate indicate local local stratigraphic stratigraphic tops. deformational sequence maintained the deforrnational So-Si angular relationship relationship relative So-S observed (i.e. S1 S 1 typically dips more 4' I I �U steeplytotothe thenorth norththan thanSo), So),which whichisisconsistent consistentwith withthe theexposed exposedlower lowerlimb limbofofthe theF1Fl steeply recumbent recumbentfold fold(fig. (fig.2c). 2c).AAsimilar similarsequence sequenceofofdeformational deformationalevents eventsisisalso alsoobserved observedinin northernMinnesota Minnesota(Bauer, (Bauer,1985; 1985;Huddleston Huddlestonetetal., al.,1988). 1988). northern This Thisproject projectwas waspartially partiallyfunded fundedby byaagrant grantfrom fromthe theMichigan MichiganGeological GeologicalSurvey Surveyand and the Geological theCOGEOMAP COGEOMAPprogram programofofthe theU.S. U.S. GeologicalSurvey. Survey. References References Bauer, Bauer,Robert RobertL., L.,1985, 1985,Correlation Correlationofofearly earlyrecumbent recumbentand andyounger youngerupright uprightfolding foldingacross across the Archeangneiss gneissbelt beltand andgreenstone greenstoneterrane, terrane,northeastern northeastern theboundary boundarybetween betweenan anArchean Minnesota: Geology, Geology,v.v.13, 13,p.p.657-660. 657-660. Minnesota: P.J.,Schultz-Ela, Schultz-Ela,D., D.,and andSouthwick, Southwick,D.L., D.L.,1988, 1988,Transpression Transpressionininanan Huddleston,P.J., Huddleston, Archean EarthSci. Sci.25, 25,p.p.1060-1068. 1060-1068. Archean greenstone greenstonebelt, belt, northern, northern,Minnesota: Minnesota: Can. Can.J.J.Earth 42 �U ORIGIN ORIGIN AND PETROLOGY OF OF IRON SILICATE-RICH SILICATE-RICH BODIES BODIES IN IN THE THE BIWABIK IRON FORMATION, MINNESOTA MINNESOTA Peter Peter J. Juneau, Juneau, Franklin Franklin Company/E. CompanyIE. I.I. Du Du Pont Pont de de Nemours Ncmours and and Co., Inc., Inc., Wilmington, Wilmington, DE DE Two of taconite taconite containing containing large large amounts amounts Two distinct distinct 'bodiest 'bodies' of of of iron iron silicates silicates and and minor minor amounts amounts of of magnetite magnetite occur occur near near Keewatin, Minnesota. Minnesota. Data Data obtained obtained during during thin-section thin-section and and X-ray X-ray studies lead to the studies lead the conclusion conclusion that that the the bodies bodies are are remnants remnants of of "original" iron formation which did not develop magnetite during original" iron formation which did not develop magnetite during lithification and metamorphism. metamorphism. The bodies occur occurinin the the upper upper 20 20 to to 70 feet The silicate silicate bodies feet (6 (6 to to 21 21 m) m) of of the theLower LowerCherty Cherty member member of of the theBiwabik Biwabik Iron IronFormation. Formation. The The north north body body is 2200 2200 feet feet (671 (671 m) m) long, long, 480 480 feet feet (146 (146 m) m) wide, The south south body body is is located located 800 800 wide, and and 40 feet feet (12.2 (12.2 m) m) thick. thick. The to 1000 feet (244 to 305 m) south of the north body and has 1000 feet (244 305 m) south of the north body and has aa minimum length of of 2300 2300 feet m), is is 1050 1050 feet feet (320 (320 m) m) wide, wide, minimum length feet (701 (701 m), and and 40 feet feet (12.2 (12.2 m) m) thick. thick. Both Both bodies bodies are located located in the the same same stratrigraphic stratrigraphic horizon. horizon. Taconite the silicate Taconite comprising comprising the silicate bodies bodies is grouped grouped into into three -- silicate silicate taconite, taconite, transitional transitional silicate silicate three (3) (3) phases phases -taconite, -- based based on on the the amounts amounts of of taconite, and and silicate-rich silicate-rich taconite taconite -iron silicates silicates and and magnetite magnetite present. present. Silicate Silicate taconite taconite is is highest in iron 40 to 50 highest in iron silicates silicates (generally (generally 40 50 percent, percent, may may be be up up to 90 90 percent) percent) and and lowest lowest in in magnetite magnetite (2 (2 to to 44percent) percent) while while silicate-rich taconite isis highest in magnetite (15 to 20 silicate-rich taconite highest in magnetite (15 20 percent) percent) and and lowest lowest in in iron iron silicates silicates (15 (15 to to 20 20percent). percent). Silicate-rich taconite taconite and and transitional transitional silicate silicate taconite taconite can can be beeconomically economically processed processed but silicate silicate taconite taconite cannot. cannot. The The boundary boundary between between the the silicate silicate bodies bodies and and surrounding surrounding magnetite taconiteisis gradational gradationaland andoccurs occursininaa 66 to 10 magnetite taconite 10 foot foot (1.8 to between the transitional to 3.0 3.0 m) m) zone. zone. The boundary boundary between the transitional zone zone and surrounding surrounding magnetite magnetite taconite taconite is placed placed where where the the first first distinct distinct greenish greenish tinge tinge is is seen seen in in the the magnetite magnetite taconite; taconite; the the exact exact location location of of the the boundary boundary between between the the transitional transitional zone zone and and the silicate silicate taconite taconite isisuncertain. uncertain. 43 �U change in in texture texture and and mineralogy mineralogy is is seen seen ininthe the AA change transition from from silicate silicatetaconite taconitetotomagnetite magnetitetaconite. taconite. In In silicate silicate transition taconite, taconite, the the iron iron silicate silicategranules granules are areusually usuallyunaltered unaltered totopartially partially altered altered and and consist consistdominantly dominantly ofofminnesotaite minnesotaite (primary?), (primary?), with with lesser amounts amounts ofofgreenalite greenalite(primary) (primary)and/or and/orcolorless colorlessminnesotaite minnesotaite lesser small amounts of magnetite occur along granule needles (secondary); small amounts of magnetite occur along granule needles (secondary); In the thetransitional transitional zone, zone,silicate silicategranules granules are aremore morealtered altered outlines. In outlines. of as as distance distance from from the thesilicate silicatebody bodyincreases increases and andthe theamount amount of original iron iron silicates silicatesand andsecondary secondaryminnesotaite minnesotaite needles needles decreases decreases original In magnetite magnetite taconite, taconite, while the theamount amountofofmagnetite magnetiteincreases. increases. In while granules granules consist consist dominantly dominantly of chert chert with with minor minor amounts amounts of of iron iron silicates silicates (minnesotaite, (minnesotaite, stilpnomelane, stilpnomelane, and and possible possible chlorite) chlorite) and and Grains and aggregates of magnetite occur along carbonates. Grains and aggregates of magnetite occur along carbonates. Magnetite and and minnesotaite minnesotaite needles needles are are thought thought granule outlines. outlines. Magnetite granule Because little magnetite to develop developduring duringlow lowgrade grademetamorphism. metamorphism. Because little magnetite to isis found found within within the the silicate silicate bodies, bodies, the the silicate silicate bodies bodies are are considered considered remnant remnant areas areas of of iron ironformation formation which which resisted resisted alteration into into magnetite magnetite taconite. taconite. alteration Carbonaceous Carbonaceous material, material, permeability, permeability, heat heat flow, flow, and and change change in in bulk bulk chemistry chemistry may may have have acted acted as asfactors factorsinindetermining determining development of the development of the silicate silicate bodies bodies within within the the iron ironformation. formation. Of these, a change in magnesium content is thought Of these, a change in magnesium content thought to to be be the the A higher higher magnesium magnesium content content stabilizes stabilizes iron iron dominant factor. factor. A dominant silicates silicates relative relative to to magnetite magnetite and and minnesotaite minnesotaite relative relative toto As a result, magnesium-rich areas in aasilicate-rich As a result, magnesium-rich areas in silicate-rich greenalite. greenalite. iron iron formation formation would would be be better better able able totowithstand withstand higher higher temperatures temperatures before before altering altering to to magnetite magnetite taconite taconite than than would would an area area with with a alesser lessercontent contentofofmagnesium. magnesium. The The source source of of the the an magnesium may either magnesium may either have have been been primary, primary, possibly possibly aa more more magnesium-rich sediment, or secondary, magnesium-rich sediment, secondary, with with enrichment enrichment during during diagenesis or or low-grade low-grade metamorphism. metamorphism. diagenesis 44 �U Geology of Preeque Isle Point, Marquette, Michigan a Second Look J. J. Kailiokoski, Kalliokoski, Professor Professor Emeritus Emeritus MTU, MTU, Houghton, Houghton, Michigan. Michigan. series of AA longer longer series of events events is is recorder recorder by by outcrops outcrops along along the the lie contact. Archean Jacobsville contact than than previously previously reported reported Archean —- Jacobevi p-obable lower lower Proterozoic Proterozoic c,Kaili~kuekl, 1975; Lewan 1975). A probable 1975; unconformity extends extends across across aabasement baseiaeiit of of'Arohean Ar~heaiiserpent serpeiitiii.l.te, unconformity mite, ,cçrnit.e, diabaee The serpentinite is aand iid diabaee. The serperitinite is covered by a a chloritic chloritic j^ranitt?, paleosol the granite paleosml and arid the graniteby by an analuminous aluminous one. one. The The next next event event was was ,u ar t quartz—carbonate alteration, as white veins 1—20mm thick along -I .-arbonate alteration, as white veins l - 2 0 m thick along aridasas f ine-,~rali'ied the shear shear polygons polygons in in serpentinite. serpentiiiite, the and fine—grained iii serpentmnit.e serpentiiiite and (:fig.2>. 2). :).iupreeiiatloriein and qranodiorit.e granodiorite (fig. Textu1-.all-jand and compositionally co~ipaeitional ly the altered rocks r o c k %rCse4ble Feew~bie the altered Texturally !. -calmer "Palmer neiss", ananenigmatic, Gneissit, enigmatic alteration alterationproduct product described described by by fromthe thegegaunee Negaunee iron—forti Gair Gair and Simmons Simmons (1969) (1969) from iron-foi-~t $014 footwall. footwall. At the the point point the the early early alterations alterations in in serpentinite serpentinite are are cut cut by by locally locally abundant, abundant, predominantly vertical, slightly branching branching veins veins of of red, red, fmne—grained, fine-grained, banded, banded, colloforin colloform quartz (jasper), with no fluid fluid Inclusions inclusions or or walirock wallrock alteration alteration (fig. (fig. 3), 3 ) . This This. triple paragenesis is is known known from from Archean Archean basement basement rocks rocks below below an an iron--formation iron--formationalso at and and near near Huron Huron River River (Kalliokoski (Kalliokoski and and Lynatt, Lynott, 1986), 1986). Klliokoki, -7 5-1 triple Its and stratigraphicstratigraphic proximity proximity to toiron—formation iron-formation Its geographic geographic and that the the quartz—carbonate quartz-carbonate alteration is is a wide—spread wide-spread subaqueous subaqueous accompaniment accompaniment iron—formation iron-formation deposition deposition which, which, in in this this instance, instance, affected affected basement basement rocks rocks exposed exposed along along the the footwall footwall unconformity unconf ormity (Kailiokoski (Kalliokoski and and Lynott, Lynott, 1986>. 1 9 8 6 ) . I would would like to suggest further further that that the the jasper jasper veins veins represent represent hydrothermal hydrothermal feeders feeders which which transported iron iron into into the the overlying overlying early early Proterozoic Proterozoic sea. sea. suggests suggests I events were uplift, uplift, erosion of the presumed Lower The succeeding events Proterozoic cover, cover, and the development of a 10—50 10-50 cm cm blanket of of Proterozolc regolith re,%olith 3eiuviumi which overlay an an. active active soil soil layer layer on on the the eluvium:' which Archean Archean basement basement (fig. "fig. 4). 4 ) . The The eluviun eluvium is is an an unsorted, unsorted, matrix—supported matrix-supported breccia. breccia. It It consists consists of of angular, angular, elongate elongate clasts to 10 derived from the red, red, white, 10 x x 25 25 cm) cm) derived from the white, and and grey grey clasts (up (up to veinlets veinlets in in the the serpentinite, serpentinite, in in a fine fine grained grained matrix. matrix. There There are are also also clasts clasts of of quartz—carbonate quartz-carbonatealtered alteredserpentini'te. serpentinite. Locally the the clasts clasts are are imbricated, imbricated, indicative indicative of of down-slope down-slope solifluctiori. solif luction. During During deposition deposition of of the the Jacobsville Jacobsville Sandstone Sandstone the the eluvial eluvial A s proof of this, this, on the west and blanket was unconsolidated. As of the the point point are are 2-60 2-60 cm cm xx 2-50 2-50 mm beds beds of of breccia breccia sides of north sides 15 interl inger with, that t ~ a tunderl underlie, ~ntei-linger w i t h , and/or and or obi o b liqusly i q u e l ~truncate truncate sandstone is identical identical in in composition composition to to the the sandstone beds. beds. This This breccia breccia is eluvium (1-10 mm), nun), most most fragile fragile vein vein segments segments eluvium but but the the thinnest thinnest (1—10 • 45 I �were broken during during transportation. transportation. The The breccia breccia beds beds formed formed from from mudflows mudflows off the serpentinite serpentinite palco—bill, paleo-hill, coeval coeval with with Jacobaville sedimentation 5 a, a, c). c). Jacobsville sedimentation (fig. (fig. 5 I The thin Jacobsville section section CO-4 (O— m) of in) consists ~~ii~is of t ssheets s h e e t s of ~i sandstone, sandstone, silty silty shale, shale, minor fine—grained fine-grained conglomerate, conslomerate, and and breccia exposed exposed in in small small scarps scarps and and broad, broad, flat flat outcrops outcrops(fig. (fig. 6 5 , Trough Troughbeds, beds,foresets, foresets,current current lineations lineations and and rare rare shale shale O. rip—ups rip-ups are predominant features. features. Current Current directions directions indicate indicat.e that the and that that that. the sandstones sandstones transgressed transgressed across across the the basement, basement, and the serpentinite serpentinite formed formed a a topographic topographic high high similar similar to to what what we we see to—day, to-day. The The sandstone sandstonecontains, contains abundant abundant feldspar feldspar and and quartz, quart;, cee ~ i & t i TitOi , k~ and and pebble pebble beds beds contain contain clasts clastsof offeldspar, feldspar,p ~ pointin gr,ÈtiKi 1~ provenance, -pFcivenance. Some Some of of the the quart.z quarts pebble= highly ginitic. pebbles &ow show a highly polished surface, surface, suggestive suggestive of of wind wind action action at at the the source. source, After Jacobeville Jac-okevllle deposition deposition the eluvial blanket and and breccia breccia silica. The weathered zone zone along along the the top top beds were cemented by silica. compacted and the vertical jasper jasper veins veins of the basement became compacted 7 ) . To—day To-day this this zone zone crossing it it were were vertically vertically shortened shortened (fig. (fig. 7). crossing le well into Into its. Its third and erosion. erosion. is third cycle cycle of of weathering weathering and References available fro author :•:• 46 n �U } Figure 6. 6 . Geologic Geologic Figure Map of Of pr--e q u e Isle, iup Preeque Iele a, s , aerpentinite; serpentinite; q-c, quartz—carb. quartz-carb. q—c, alteration; alterat ion; G, G , granite granite; Gw, Gw, weathered granite: granite; weathered D, D , diabase; diabase; Ja, JE, J ac-ubsvi1 ie sandstone: sar~detor~e ; •Jcobsville 1 , 2 , 3 , 4 , location location of of 1,2,2,4, rose rose diagrams. diagrams. rose diagrams: diagrams: On rose n, n , no. no. of cross—bed cross-bed N I / 1. / 2 readings; readings; dashes, trend trend of of dashes, current current lineations; lineations; arrows,trend trough arrows, trend of trough axes, top top viewS view. axes, $ 47 I �U Paleomagnetism of of Baraboo Baraboo Interval Interval Rocks Rocks in in Wisconsin Wisconsin Paleomagnetism William F. F. Kean KeanDepartment Departmentof ofGeosciences GeosciencesUniversity Universityof of William Wisconsin-Milwaukee,P.O. P.O. Box Box 413 413 Milwaukee, Milwaukee, WI WI 53201 53201and and Robert Robert Wisconsin-Milwaukee, Schneiker,Hydrosearch, Hydrosearch,Milwaukee Milwaukee Schneiker, — The Proterozioc ProteroziocBaraboo Baraboo interval intervalis isaa sequence sequenceof ofquartz—rich quartz-rich The metasedimentary metasedimentary rocks rocks of of the the upper upper midwest midwest which which include includethe the Baraboo, Barron. Barren. McCaslin McCaslin and and Waterloo Waterloo quartzites quartzitesof ofWisconsin, Wisconsin, Baraboo, along with with the the Sioux Sioux Quartzites Quartzitesof of Minnesota, Minnesota,South SouthDakota Dakotaand and along Iowa. These These quartzites quartzitesare are associated associatedby by the thesimilarity similarityof of Iowa. their their appearance, appearance,although although there there is is no no firm firm evidence evidenceof oftheir their being time timesynchronous. synchronous. In In Wisconsin, Wisconsin, there there are are also also associated associated being igneous igneous rocks rocks which which include include granites, granites, rhyolites rhyolites and and diorites. diorites. We We have have continued continued paleomagnetic paleomagnetic studies studiesof of this thissequence sequencein in Wisconsin to to better better define define the the time time relationships relationshipsbetween betweenthe the Wisconsin metasediments and and the the igneous igneousrocks. rocks. We We have have recently recently inetasediments concentrated concentrated on on the the outcrops outcrops at at Hamilton Hamilton Mounds Mounds and and Baxter Baxter Hollow. Hollow. Hamilton Mounds Mounds is is an an inlier inlier of of Baraboo Baraboo type type quartzite quartzite Hamilton with aa distinct distinct intruded m.y. with intruded by by aa granite granite dated dated at at 1760 1760 m.y. The granite granite provided provided alteration alteration zone zone adjacent adjacentto tothe thegranite. granite. The no no useful useful paleomagnetic paleomagnetic date date because because the the remanent remanent magnetism magnetism is is too soft. soft. Alternating Alternating field field (A.F.) (A.F.) demagnetization demagnetization removed removed the the too remanence remanence by by 100 100 millitesla millitesla and and the the magnetic magnetic directions directions were were The magnetic magnetic characteristics characteristicsof of the the altered altered very scattered. scattered. The very zone zone indicate indicate the the magnetism magnetism is is due due to tofine finegrain grainmagnetite, magnetite, probably probably resulting resulting from from the the reduction reduction of of hematite hematite in in the the A.F. and and thermal thermal quartzites at at the the time time of of intrusion. intrusion. A.F. quartzites demagnetization demagnetization studies studies show show only only one one component component of of The magnetism magnetism in in the the quartzite quartzite at at Hamilton Hamilton Mound Mound magnetization. The magnetization. is typical typical of of the the Baraboo Baraboo type type quartzites quartzitesin inWisconsin. Wisconsin. The The is remanence remanence is is carried carried by by hematite, hematite, and and appears appears to to be be diagenetic diagenetic in origin. origin. in At Baxter Baxter Hollow Hollow aa granite granite is is exposed exposed below below the thequartzite. quartzite. AA At sheared sheared or or mixed mixed zone zone below below the the quartzite quartzite appears appears to to be be part part of of the granite granite with with assimilated assimilatedquartzite. quartzite. The The contact contact between between the quartzite zone is is not not exposed exposedbut butquartz quartzite is quartz ite and and sheared sheared zone ite is located within within two two meters meters of of the the sheared shearedzone. zone. The The granite granite has has located not been been dated dated but but it it has has been been interpreted interpreted as as being being both both younger younger not and older older than than the the quartzite. quartzite. The The quartzite quartzite and and granite granite at at and Baxter Hollow were previously analyzed by Mercer (1984) Baxter Hollow were previously analyzed by Mercer (1984)and and Kean Kean Mercer (1986). (1986). The The granite granite is is typically typically soft soft magnetically magnetically and and && Mercer of little little use use for for paleomagnetic paleomagnetic studies. studies. The The quartzites quartzites of of this this of area area provide provide good good data, data, with with the the remanence remanence carried carried by by hematite. hematite. In this this report report we we present present data data from from the thesheared shearedzone. zone. The The In sheared or or mixed mixed zone zone is is magnetically magnetically more more complex complex than than the the sheared counterpart counterpart at at Hamilton Hamilton Mounds, Mounds, but but there there is is aa primary primary remanent remanent component carried carried by by magnetite. magnetite. component The The magnetic magnetic directions directions and and pole pole positions positions for for these these sites sites are provided provided in in table table I. I. are 48 I'll �I Table Table II Formation oma at ion No. of ot Mean Mean Samples Samples Hamilton Hamilton Mounds Mounds 10 10 Mean Mean KaDDa Kappa A l ~ h a95 95 Alpha V.G.P. V.G.P. 43.9 332.5 332.5 6.8 19.9 19.9 61 N 150 150 EE 61 77 53.9 174.0 174.0 10.9 19.2 19.2 11 SS 84 84 WW 11 Baxter 10 10 Baxter Hollow Hollow Sheared Sheared Zone Zone 86.3 303.5 303.5 9.3 9.3 16.7 16.7 48 N 98 98 WW 48 Baraboo Baraboo 59.1 199.3 199.3 19.9 15.4 15.4 14 SS 89 89 WW 14 Dec Dec Quartz ite Quartzite Hamilton Hamilton Mound Mound Mixed Mixed Zone Zone 30 30 Quartz ite Quartzite Conclusions Conclusions When When the the pole pole positions positions obtained obtained in in this this and and other other studies studies are are compared compared to to Irvings Irvings (1976) (1976) polarwander polarwander pater pater for for the the time time range 1650-2200in.y. m.y. We We make make the the following following conclusions: conclusions: range 1650-2200 1. 1. The The Baraboo Baraboo Quartzite Quartzite pole pole (structure (structure corrected) corrected) is is very very similar similar to to the the Hamilton Hamilton Mound Mound mixed mixed zone zone and and is is placed placed at 1800 m.y. m.y. based based on on the the location location on on the the at approximately approximately 1800 polar polar wander wander path. path. This This suggests suggests that that the the Baraboo Baraboo Quartzite Quartzite is is at at least least 1760 1760 years years old old and and probably probably older. older. 2. 2. The Baxter Baxter Hollow Hollow sheared sheared zone zone pole pole position position would would place place The its 1650 m.y. m.y. if if one one accepts accepts its its position position on on the the its age age at at 1650 polar polar wander wander path. path. If If the the pole pole position position is is corrected corrected with with the the same same structure structure corrections corrections used used on on the the quartzite quartzite at at this this site, site, it it comes comes near near the the structure structure corrected corrected quartzite quartzite pole. pole. Either Either result result would would imply imply that that the the intrusive intrusive activity activity is is younger younger than than the the quartzite, quartzite, and and possibly possibly as as young young as as 1650 1650 in.y., may., but could could be be as as old old as as 1760 1760 m.y. m.y. 3. 3. The results results from from Hamilton Hamilton Mounds Mounds also also imply imply that that the the The folding 1760 folding of of the the quartzite quartzite at at this this site site is is at at least least 1760 m.y. m.y. old. old. 49 �I I References Irving, E., Irvingf E m f 1978, 1978# Paleopoles Paleopoles and and paleolatitudes paleolatitudes of of North North Aiuerica America and speculations speculations about displaced displaced terrains; terrains; Can. Can. I. I. Earth Earth Sci. Sci. Vol. V O ~ .16, 16# Pp.669—694 Pp.669-694 j Keanf W.F. W.F. and and D. D. Mercer, Mercerf1986, 1986#Paleornagnetisin Paleomagnetism of Kean, of the the Baraboo south Central Central Wisconsin Wisconsin Geosciences Geosciences Wisconsin, Wisconsinl Vol. Vol. Quartzite of south 46-53 10, Pp. 46—53 Mercer, D., Mercerf D e f 1984, 1984# Paleomagnetism Paleomagnetism of of the the Baraboo Baraboo Quartzite: Quartzite: University of Wisconsin—Milwaukee, Wisconsin-Milwaukeef M.S. M.S. thesis, thesisf P. P. 294 294 I I I I I I I I I I I I 50 i �U I GEOLOGICAL GEOLOGICAL SETflNG SElTING AND AND GEOCHEMISTRY GEOCHEMISTRY OF THE THE BUSH BUSH LAKE LAKEGRANITE GRANITE IN IN MENT PEGMATITES, PEGMATITES, FLORENCE FLORENCE COUNTY, COUNTY, RELATION TO RARE-ELEMENT WISCONSIN KOEHLER, Steven R., Dept. of Plant Plantand andEarth EarthScience, Science,University UniversityofofWisconsin Wisconsin- River uwer Falls, tails, River wver Falls, taus, WI Nl54022. 54022. Rare-element Rare-element pegmatites in Florence Florence County, County, Wisconsin Wisconsin have have intruded intruded low lowtotomoderate moderate pressure, fades rocks of metasedimentarylmetavolcanic facies of the theQuinnesec Quinnesec pressure, Abukuma-type Abukuma-type metasedimentary/metavolcanic Formation. Numerous Numerous lines lines of of evidence evidence indicate indicate the the early early Proterozoic Proterozoic age age Bush Bush Lake Lake Formation. Granite Granite is is the thesource sourcefor forthese thesepegmatites. pegmatites. Field Field mapping mapping reveals reveals aa distinct distinct pegmatite pegmatite aureole aureole in in the the Quinnesec QuinnesecFormation Formationnorthwest/north/northeast northwest/north/northeast of of the the Bush BushLake LakeGranite. Granite. Greenberg et a!., a/., (1983) (1983) interpret interpret the the southern southern Penokean Penokean volcanic volcanic belt as as aa complex complex Greenberg et arc environment. environment. Late Late tectonic tectonic intrusion intrusion of the the Bush Bush Lake Lake Granite Granite as as aasecond-order second-order arc diapir diapir occurred occurred after afterpeak peakregional regionalmetamorphism metamorphism(Sims (Simseteta!., a/.,1985). 1985). According According to to Cerny et a!., a/., (1988), (1988), the the tectonic tectonic environment environment and and timing timing of ofgranitic graniticintrusion intrusioncompare compare Cerny et favorably favorably with with documented documented fertile fertilegranite/pegmatite granitelpegmatiteassociations. associations. Compositionally the Bush Compositionally the Bush Lake Lake Granite Granite isis aaperaluminous, peraluminous, megacrystic, megacrystic, biotite biotite Upward gradations from biotite granite into pegmatitic granite. Upward gradations from biotite granite into pegmatitic leucogranite leucogranite and and granite. potassic potassic pegmatite pegmatite are common. common. Pegmatitic Pegmatiticfacies facieswithin withinthe thegranite granitecontain containaccessory accessory Mn-rich garnet, garnet, tourmaline, tourmaline, beryl, beryl, and andmuscovite. muscovite. Bulk Bulk compositions compositions are are silicic, silicic, NaNaMn-rich rich rich (2.84-3.61 (2.84-3.61 wt. wt. % % Na20), NazO), but butare arepoor poorininFe, Fe,Mg, Mg,and andCa Ca(0.29-1.27 (0.29-1.27 wt. wt. % %CaO). CaO). Cs (4.7-13.6 (4.7-13.6 ppm), ppm), Ga Ga (7-51 (7-51 ppm), ppm), and and YY Li Li (17-89 (17-89 ppm), ppm), Rb Rb (235-403 (235-403 ppm), ppm), Cs (7-49 (7-49 ppm) ppm) are are enriched, enriched, while while Ba Ba (34-95 (34-95 ppm) ppm) and and Sr Sr (21-89 (21-89 ppm) ppm)are aredepleted depleted relative to to barren barren granites. granites. High High fractionation fractionation is suggested suggested by by low low Rb/Sr RblSr(17.5-1.9), (17.5-1.9), relative Ba/Rb BalRb (2.9-0.17), (2.9-0.17), Mg/Li MglLi (50.5-4.5), (50.5-4.5), and and K/(Cs Kl(Cs xx 100) 100) (100-17) (100-17) ratios. ratios. Bush Bush Lake Lake Granite Granite K/Rb K/Rb ratios ratios are are low low (172-91), (172-91), but but decrease decrease outward outward to 7.79 7.79 in in albitized, albitized, Li-rich Li-rich pegmatites pegmatites (Koehler, (Koehler, 1989). 1989). REFERENCES REFERENCESC1ED CITED Cerny, Cerny, P. P. and and Meintzer, Meintzer, R.E., R.E., 1988, 1988,Fertile Fertilegranites granites ininthe theArchean Archean and andProterozoic Proterozoic fields of of rare-element rare-elementpegmatites: pegmatites:crustal crustalenvironment, environment, geochemistry, geochemistry,and and petrogenetic relationships, relationships, in in Taylor, Taylor,R.P. R.P.and andStrong, Strong, D.F., D.F., eds., eds., Recent Recent advances advances in in the the geology geology of of granite-related granite-relatedmineral mineraldeposits, deposits,The TheCanadian Canadian Institute Institute of Mining Mining and and Metallurgy, Metallurgy, sp. pub. pub. 39, 39, p. p. 170-206. 170-206. Greenberg, Greenberg, J.K. J.K. and and Brown, Brown, B.A., B.A., 1983, 1983, Lower Lower Proterozoic Proterozoic volcanic rocks rocks and and their their in Medaris, Medaris, L.G., L.G., Jr., Jr., ed., ed., Early Early setting in in the the southern southern Lake Lake Superior Superior district, district, in setting Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region, region, Geol. Geol. Soc. SOC.Am. Am. Memoir Memoir160, 160,p.p. 67-84. 67-84. learing province province in inFlorence FlorenceCounty, County, Wisconsin Wisconsin Koehler, Koehler, S.R., S.R., 1989, 1989, A possible Ta-bearing [abs.]: with Programs v. 21, #4, p. )grams ,, v. p. 39. 39. [abs.]: GSA Abstract / Sims, P.K., P.K., Peterman, Peterman, Z.E., Z.E., and and Schulz, Schulz, K.J., K.J., 1985, 1985,The TheDunbar DunbarGneiss-granitoid Gneiss-granitoid dome: dome: Implications Implications for early early Proterozoic Proterozoic tectonic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: Geol. Soc. v. 96, 96, p.p.1101-1112. 1101-1112. SOC.Am Am Bull., Bull., v. 51 I �U If WAS THE WAS THE PENOKEAN PENOKEAN OROGENY A BI-POLAR EVENT? Gene L. LaBerge, LaBercfeI Geology Geology Department, DepartmentI University of Wisconsin Wisconsin University of Geological Survey, SurveyI and and OshkoshI OshkoshI WI WI 54901, 54901, and and U. S. Geological Oshkosh, Oshkosh, John SS. Klasner, KlasnerI Geology Geology Department, Department, Western Illinois University, UniversityI John Western Illinois Macomb, IL IL 61455, 614551 and and U. S. S. Geological Geological Survey. Survey. Macomb, Thnvn is i c ! now nnw widespread ~.7iAnen~nsA 3 ~ ~ n n m n n th t = t the +hn Penokean D ~ - - l r n % - orogeny There agreement that Y was the tk result of plate tectonic activity. Most authors suggestt was that cevolution of the orogen in Michigan and Minnesota began with th a rift rifting phase accompanied by formation of basins and troughs along the passive margin of the Archean Superior craton, and wass accompankeu or rocks rOCKS of or the Marquette Range Range accompanied ~y by ueposirion deposition of Supergroup in Michigan and equivalent equivalent Animikie Group rocks in in Supergroup in Group rocks Minnesota Minnesota (Schulz (Schulz and and others, othersI in in press). press). However, HoweverI Hoffman Hoffman (1987) (1987) Southwick and others and Southwick others (1988) (1988) have recently recently suggested suggested that that the the iron-bearing sequences formed in foreland basins basins during accretion. Ironaccretion. Nd isotope isotope studies studies on the Biwabik and Negaunee Negaunee Iron— formations 52 Ma formations suggest deposition of these rocks about 2100 2 ± 52 (Gerlach othersI 1988) 1988). Rifting was followed followed by southward southward (Gerlach and others, subduction of oceanic oceanic crust crust to to form form the arc-related volcanic volcanic and and subduction the arc—related plutonic rocks rocks of of the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. These These were were subsequently subsequently accreted to to the the continental continental margin on on the the north north 1989; LaBerge LaBerge and and between 1900 1900 and 1830 1830 Ma (Sims (Sims and othersl others, 1989; othersI 1984; Larue Larue and and Sloss, SlossI 1980; 1980; Cambray, CanbrayI 1978). 1978). Accretion others, 1984; Accretion rocks to to the the continental continental margin of of the the Superior Superior of the magmatic rocks craton about 11860 Ma (Sims (Sims and others, others! 1989) 1989) resulted resulted in in craton about 1,860 (Attoh and and Klasner, KlasnerI thrusting of rocks rocks onto onto the the craton craton (Attoh northward thrusting 1989; others! 1988a, 1988at 1988b; 1988b; Hoist, HolstI 1982, 1982! 1984). 1984). 1989; Klasner Kiasner and others, ----A- RecentlyI LaBerge LaBerge and and others others (in (in press), press)! LaBerge LaBerge and and Kiasner Klasner Recently, (1989, 1988, 1988, 1986) and and LaBerge LaBerge (1986) proposed proposed that that a a similar (1989! sequence of events occurred in sequer in central central and southern southern Wisconsin Wisconsin during the Penokean L orogeny. durin? orogeny. Widely scattered scattered areas areas of of quartz lly (at (at Baraboo) slate, slate, dolomite dolomite and and ironironquartzite, and locally formationI formation, are interpreted to be remnants of a once-extensive once—extensive passive passive margin margin succession. succession. Archean rocks rocks of of unknown unknown extent extent are are locally exposed in in central central Wisconsin and are are believed to to be be the the locally basement on which these sedimentary rocks accumulated. Stri 2lding and and Structures in the quartz ites indicate south-directed folding thrusting of the sedimentary rocks (LaBerge and others, in thr~ in press; press; Cam1 lean rocks. rocks. Cambray, 1987; LaBerge and Kiasner, 1986) onto the Archean This interpretation This interpretatlon is is supported supported by geophysical geophyslcal evidence evidence presented by Cannon Cannon and and others others (1989). (1989). We suggest suggest that that the the 1,750 11750 meter thick thick sedimentary sedimentary succession succession combined combined with with the the widespread widespread meter evidence evidence for for south-verging south-verging folding folding and thrusting thrusting argues argues for for collision collision of of a a substantial substantial mass of of rocks rocks — perhaps perhaps of micro continent size size - with with the the Proterozoic Proterozoic island island arc arc complex, complexI which which continent is now the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. Sims Sims and and others others (1989) (1989) conclude that that this conclude this collision collision occurred occurred about about 1,840 11840Ma. Ma. - - In Wisconsin In the magmatic terrane terrane of north-central Wisconsin (specifically Marathon County) structures (specifically Marathon County) structures are are upright upright - subsubvertical to (LaBerge and MyersI 19841 1987) and have to vertical -- (LaBerge Myers, 1984, - 52 1 �no no consistent consistent sense sense of of structural structural vergence. vergence. The The magmatic magmatic terrane terrane in in the the Dunbar Dunbar area area of of northeast northeast Wisconsin Wisconsin has has aa strong strong northerly northerly sense 1985). Attoh Attoh and and Klasner Klasner sense of of vergence vergence (Sims (Simsand and others, others,1985). (1989) have suggested (1989) have suggested that that the the magmatic magmatic rocks rocks in in the the Dunbar Dunbar area area are are para—allochthonous, para-allochthonousf having having been been thrust thrust northward northward onto onto the the buried continental continental margin. margin. Dismembered Dismembered ophiolite ophiolite (Schulz, (Schulzf1987) 1987) buried in in nort1east northeast Wisconsin Wisconsin likely likely represents represents aa remnant remnant of of oceanic oceanic crust that that was was thrust thrust onto onto the the continental continental margin. margin. crust Taken Taken together, together, from from southern southern Wisconsin Wisconsin to to northern northern Michigan Michigan (Fig. 1), the the Penokean Penokean orogen orogen consists consists of: of: aa deformed deformed remnant remnant of of (Fig. Archean Archean basement basement overlain overlain by by Early Early Proterozoic Proterozoic platform platform sediments sediments deformed deformed by by south—verging south-verging structures; structures; aa region region of of accreted accreted island island arc arc volcanic volcanic rocks rocks with with upright upright structures; structures; aa region region of of island island arc and plutonic plutonic rocks rocks with with north—verging arc inagmatic magmatic and north-verging structures; structures; and and an an Early Early Proterozoic Proterozoic continental continental margin margin with with platform platform sediments sediments and and prominent prominent north—verging north-verging structures. structures. The platform sediments sediments and and rifted rifted continental continental margins margins The platform Formation of of an an ocean ocean basin basin is is the rifting rifting phase. phase. Formation represent the represent documented documented by ophiolite. The The island—arc island-arc volcanic volc:anic by the the presence presence of of ophiolite. rocks plutonic rocks rocks represent represent the the closing closing phase phase of of the the rocks and and plutonic closure resulted resulted in in accretion accretion of of magmatic magmatic rocks rocksI to ocean. Final F'inalclosure to ocean. ---2--l--- & L a v.... .n1-:--,.A \,; ",*.+,, the margins along the continental contirieri~a~ NMLLJLIIZ. ~ L U I N the L I I ~Eau uxu Pleine ~ A C A U C and ~ A I U Niagara LvAawaLa sutures = ~~dres respectively. Prominent promihent southsout.h(Fig. 1) 1) in in the the south south and and north nc&th respectively. (Fig. verging the continental continental margin margin in in central centra11 verging structures structures formed formed on or1 the Wisconsin structures on on the the continental continental margin. mar-gin. Wisconsin and and north—verging north-verging structures --- of -a2 .Ip--We Penokean We contend contend that that interpretations interpretatiu~ls UL the LIE reIluAeaI1 orogeny U L U L J ~ I I ~ as a = north— 11drthdirected directed only only do do not not accurately accurately represent represent the the event—-the event--the evidence evidence indicates that that it it was was bi-polar. bi-polar. . indicates ---L--i LL- ..- -- I-,-...- North Niagara Niagara South South Fault Fault E a u Pleine Pleine Eau Fault Fault SOU t h - v e r g i ng South—verging North—vrr(M ~ o r t h - v c r r1~ i f ~ q Upri ght struc turcs structures structures struc turcs structures structures x X v ARCI1EAN ------- X x A ARCHEAN x South-central S o u t h - c e n t r a l Wisconsin Wisconsin x x , - % - F a i X Northern N o r t h e r n Michigan Mich~gdn WI W i sscons c o n s in in magma m a g ~ n a tic t i c terra t e r r anes ncs Figure F i g u r e 1. 1. Sketch S k e t c h sshowing h o w i n g mmajor a j o r f features e a t u r e s in i n aa north-south f t h Penokean e P e n o k e a n orogen. orogen. n o r t h - s o u t h transect t r a n s e c tofo the 53 I 1 �I References Cited K, and Klasner, J. S., 1989, Tectonic Attoh, K., Tectonic implications implicationsofofmetamorphism metamorphismand andgravity gravityfield fieldininthe thePenokean Penokeanomgen orogenofofnorthern northern Michigan: Tectonics, Tectonics,v.v.8,8,p.p.911-933. 911-933. . 78, Plate Early Proterozoic Protedc Cambray, F. F. W., W., 19' 1978, Plate tectonics tectonicsas asaa model model for for the environment environment of of deposition deposition and deformation deformation of Early (Precambrian)ofofnorthern northernMichigan. Michigan.Geol. Qj. Soc. Amer., Abstracts with programs, No. 10, (Precambrian) 10, P. p. 376. 376. Cambray, F. W., explained as as aa result result of of superimposition superimposition of of simple simpleshear shear on on aa W., 1987, 1987, The The Baraboo b r a b o oSyncline: Syncline: the shape and refoldmg refolding explained pre-existing fold:Abstract, Abstract, Q. Soc. of Amer., Abstracts with programs, programs, p. p. 192. 192. preexisting fold: Geol. ç. Cannon, W. W. F., Schulz, K. J., J., Hinze, Hinze, W. W.J., J., and and Green, Green, A. A. G., G., 1989, Precambrianterranes terranes beneath beneath northern Lake Michigan defined defined by by Schulz, K 1989, Precambrian seismic and gravity analysis; analysis; Institute Institute on Lake Superior Geology, v. 35, Part 1, 1, Abstracts, p. 14, 14, 15, 15, Duluth, MN. MN. Geology, v. Gerlach, and Carlson, Carlson, R R. W., W., I1988, Ndisotopes isotopesin in Proterozoic Proterozoic iron-formatmns: iron-formations: Evidence S , Nd Evidence for for mixed-age mixed-age Gcrlach, D. C., C., Shirey, Shirey, S. 13., B., and provenance and depositional Geophvs. Union Trans., EOS, v. 69. depositional variability variabili% Abstract, Abstract, Am. Geovhvs. !21 Hoffman, P. F., 1987, 1987, hEarly r l y Proterozoic Foredeeps, Foredeep, Foredeep magmatism, magmatism, and Superior-type Superior-typ iron-formations iron-formations of of the theCanadian CanadianShield, Shield, Pp. in Proterozoic lithospheric evolution, edited by A. Kroner, Kroner, American American Geophysical Geophysical Union, Geodynamics Series, No. No. 17, pp. 85-98. Hoist, Evidence for for multiple multiple deformation deformation during during the the Penokean Penokean orogeny orogeny in in the the Middle Precambrian Precambrian Thomson Thomson Formation, Formation, B., 1982, 1982, Evidence Holst, T. B., Minnesota: Canadian Journaloff &rth Sciences: Minnesota: Canadian Journal Sciences: v. 19, 19, p. p. 2043-2047. 2043-2047. 1984,Evidence Holst, T. B., 1984, Hoist, Evidence for for nappe nappe development development during during the the Early Early Proterozoic Proterozoic Penokean Penokean omgeny, orogeny, Minnesota: Minnesota: Geology, v. 12, p. p. Geolon, v. 135-138. 135-138. Kiasner, J. J. S., S., Ojakangas, R R W., W., Schulz, Schulz, K. K. J., and LaBerge, LaBerge, G. G. L., L.,1988, 1988, Widespread evidence for Early b r l y Proterozoic Proterozoic overthrusting overthrusting in in Klasner, the Penokean Penokeanorogen orogenofofnorthern northern Michigan, Abstract, Michigan, Abstract, Geol.Geol. Assoc.. of Canada Caflada and Mi Min. Assoc. of Can., Programs Programs with with abstracts, v. v. 13, 13, p. p. A67. A67. a., Iàasiler, J. S., Sims, P. K, K., Gregg, W. W. J., J., and Gallup, C., l1988b, structural traverse traverse across acrossaa part part of the Penokean S b , AAstructural Penokean orogen, orogen, hasner, Schulz, K. K J., (ed.) v. v. 2, 2, Field Field Trip TripGuidebooks Guidebooks34th 34th illustrating Early Proterozoic overthrusting werthmsting in in northern northern Michigan; Michigan; in Schulz, Annual Institute on Lake Superior Geology, Geology, Marquette, Marquette, Michigan, Michigan,p. p. C1-C36. Cl-C36. 0. L., Lal3erge, G. G. L L., The Protemoic Proterozoic geology of the Lake LaBerge, ., 1986, 1986, The Lake Superior Superiorregion: region: in & LaBerge, G. L., Attig, Attig, J. J. W., W., and and Mode, Mode, W. W. N., N., Field Conference, Conference,Wausau, Wausau, Wisconsin, Wisconsin, p. 1-29. 1-29. Guidebook, Tri-State Geological Geological Field G. L., and Klasner, Evidencefor foraa major major south-directed south-directedEarly EarlyProtemoic Proterozoicthmst thrust sheet sheet in south central Wasner, J. S., S., 1986, 1986, Evidence LaBerge, G. Wisconsin: Abstract, Soc.of ofAmer., Annual AnnualMeeting, Meeting,San SanAntonio, Antonio,Texas. Texas. Wisconsin: Abstract, Geol. Geol.Soc. m., LaBerge, G. 0. L., J. S., S., 1988, 1988,The ThebBaraboo Quartzite: aa new new look lookatatan an old old problem: problem: Abstract, 34th Annual Annual Institute Institute on on L., and Klasner, J. r a b o o Quartzite: Abstract, 34th LaBerge, Lake Superior Superior Geology, Geoloa, Marquette, Marquette,Michigan, Michigan,p.p. 62-64. 62-64. - LaBerge, G. L., and Klasner, J. S., 1989, Tectonicimplications implicationsofofthe thestmcture structureand andstratigraphy stratigraphyofofquartzites quartzites in in central central and and southern LaDerge, 1989, Tectonic Wisconsin: Wisconsin: Abstract, Abstract, 35th 35th Annual Annual Institute Institute on on Lake Superior Geology, Duluth, Minnesota, Minnesota, p. p. 49-50. 49-50. w, LaBerge, G. L., L., Klasner, Kiasner, J. J. S., S., and and Myers, Myers, P. P. E., E., in press, New New observations observationson on the the age and structure of Proterozoic Protemoic quartzites quartzites in in Lakrge, in Sims, Sims, P. P. K, K., and and (ed.), (ed.), contributions contributionsto to the the Precambrian Precambrian gxology geologyofofthe theLake LakeSuperior Superiorregion: region: U. S. Geol. Wisconsin: Wisconsin: & Sur. Sur. Bull. Bull. 1904-B. 1904-B. %, pp. 246-253. M6-253. LaBerge and Myers, Myers, 1984, 1984, Two Early &rly Proterozoic Proterozoic successions successions in central Wisconsin, Wisconsin, GSA Bulletin, Bulletin, v. 95, LaBerge, Schulz, Schulz, and and Myers, Myers, 1984, 1984,The The plate plate tectonic tectonic history history of of central Wisconsin, Wisconsin,Abstract, Abstract, 30th 30th Annual Annual Institute Institute on Lake Superior Sumxior Geology, Wausau, WI Geolo!zy3 Wl Schulz, K. K. J., J., and and Sims, P. P. K, K., and Morey, 0. G.B., B.,ininpress, press,Tectonic Tectonicsynthesis, synthesis, Penokean Penokeanorogen, orogen,and andassociated associatedepicratonic epicratonicrocks: rock Geol. Soc. Soc. of America America DNAG DNAG volume, volume, C-2, C-2, Precambrian, Precambrian,conterminous conterminousU.S. US. -- - Schulz, 1987,An Anearly earlyProterozoic Proterozoicophiolite ophioliteininthe thePenokean Penokeanorogen: orogen: Abstract, Geol. h o c . of Schulz, 1987, p. 87. 87. m. abstracts with programs, programs, v. v. 12, 12, Sims, P. P. K., W. R, R., Schulz, K K. J., J., and and Peterman, Z. Tectonostratigraphic evolution of the Early K, Van Schmus, W. 2 E., E., 1989, 1989, Tectonostratigraphic &rly Protemzoic Proterozoic Wisconsin magmatic magmaticterranes terranesofofthe the Penokean Penokeanorogen: orogen: Canadian Canadian Journal Journal of of Earth Sciences, Wisconsin Sciences, Sims, Peterman, Peterman, and Schulz, I1988, The Dunbar Dunbar gneiss-granitoid dome; dome; implications implicationsfor for &rly Early Proterozoic Proterozoic tectonic tectonic evolution evolution of of Sims, S , The northeastern Wisconsin:Geol. Qj. Soc. of A s r , Bulletin, northeastern Wisconsin: Bulletin, v. %, %, p. p.1101-1112. 1101-1112. the Penokean Pcnokean orogen, orogen, central and Southwick, D. D. L L, Southwick, .,Morey, Morey,G. G.B., B., and andMcSwiggen, McSwiggen, P., P., 1988, 1988, Geological map (scale: 1:250,000) l:ZO,O@l) ofofthe eastern Minnesota, Minnesota, and and accompanying accompanying text, Minn. Geol. Survey, Suwey, Report of Investigations Inwtigations RI-37. RI-37. 54 �U GEOLOGY AND ECONOMIC POTENTIAL OF NORTHERN MICHIGAN GRAPHITE Jason J. J. Lagowski', ~ a g o w s k iAllan Allan ~ ~ M. M. Johnson2, ~ o h n s o nMilton Milton ~~ ere^ Jason Gere3 1 2 Departmnt Mineral Econanics, Ecmanics, Michigan MichiganTechnoLogicaL Technological Department of of MineraL University, Houghton, 4W31 University, Houghton, MI MI49931 Director, Director,MineraL MineralTechnoLogy/BiotechnoLogy Technology/BiotechnologyResearch Research Group Grcup Department of Mining TechnoLogicaL Department of Mining Engineering, Engineering,Michigan Michigan Technological University, University,Houghton, Houghton,MI MI49931 49931 Region II (Upper Region Peninsula) GeoLogist, GeologisttMichigan MichiganGeoLogicaL Geological (Upper PeninsuLa) Survey Division, Division, Department Survey Department of of NaturaL Natural Resources, Rescurces, Marquette, Marquettet MI MI 49855 49855 1ecent Recent cooperative cooperative research research by Michigan Technological Technological University (MTU) Survey (MGS) University (MTU) and and the the Michigan. ~ichigan~Geological e o l o ~ i c aSurvey l (MGS) was was undertaken to to determine determine the the quantity, quantityl quality quality and and distribution distribution of of the the carbon—rich carbon-rich graphitic graphitic slate slate resource resource present present in in northern northern Michigan. The ultimate ultimate goal goal of of this this research research was was to to provide provide Michigan. The mineralogical, chemical mineralogicall chemical and geophysical geophysical data data that that will will aid aid in in commercial development development of identifying uses that will lead to commercial of this this vast and, andl as—yet, as-yetl untapped untapped resource. resource. The graphite graphite is is present present in in the the early early Proterozoic Proterozoic Lower Lower Slate Slate Michigamme Formation Member of the Michigame Formation in in the the Baraga Baraga Group Group sediments. sediments. investigations (Hwang (Hwanga. . ., 1986) suggest that Earlier investigations 1986) suggest that 33 graphite—bearing slate, billion tons of graphite-bearing slatel grading grading 20—25% 20-25% carbon, carbonl exist at mineable depths depths in in a 30-mile 30-mile long long belt in in Baraga Baraga and and Marquette Compositionally, the Marquette counties counties (Fig. (Fig. 1). 1). Compositionallyl the slate slate consists consists predominately of of fine fine silica silica (43-53%), (43-53%I1 carbon carbon (2-47%), (2-47%)# iron iron oxide oxide (10—14%) and and alumina alumina (7-11%). (7—11%). The The slate slate contains contains relatively low (10-14%) concentrations of the alkaline alkaline earth concentrations earth metal oxides oxides CaO CaO (0.4-0.7%) (0.4-0.7%) and MgO (1—3%). (1-3%). Similarly, Similarlyl concentrations concentrations of of the the alkali alkali metal metal oxides oxides K20 K20 (2—3%) (2-3%) and particularly particularly Na20 Na20 (<0.12%) (<0.12%) were were quite quite low. low. This This composition composition is is consistent consistent with with deposition deposition under under reducing reducing anaerobic anaerobic conditions conditions with with minor minor or or no no clastic clastic input. input. , 1986) This and and earlier earlier studies studies (Hwang (Hwang&. . aJe1 1986)(Kramer (Kramer g&. et. al., or 1987) have determined that the graphite is is of the the "amorphous" llamorphousll or cryptocrystalline cryptocrystalline variety. variety. Typical Typical grain grain size, sizel as as determined determined by by electron electron microscope, microscopel ranged ranged from from 11 to to 33 microns. microns. Carbon analyses analyses 90 samples samples collected collected from from drill drill core core at at the the MGS MGS core core repository repository of 90 Marquette, MIl MI, yielded in Marquettel yielded aa range range of of 22 to to 47% 47% carbon. carbon. There There appeared appeared to to be be no no correlation correlation between between graphite graphite (carbon) (carbon) concentration concentration and and metamorphic metamorphic grade. grade. In drill cores cores with high high sample densityl density, there appeared to be a cyclical cyclical increasing sample increasing and and decreasing decreasing of of carbon carbon content content with with depth. depth. This suggest aa This could suggest cyclical cyclical depositional depositional pattern. Thus, Thusl graphite graphite content content might might be be function of stratigraphic stratigraphic positionl position, though more research research is is required to support support this this interpretation. interpretation. 55 �I: I 1 The reducing conditions underthewhich the slate carbon-rich slate was The reducing conditions under which carbon-rich was depositedf makes makes it it an an ideal ideal utrapti fftraplf for of trace trace and and deposited, for a a variety variety of rare rare earth earth elements. elements. Trace element analysis for 54 54 elements elements Trace element analysis for showed the presence of aa very very large large number number of of rare rare earth, earthf presence of alkaline, base metal and the the precious precious metalsl gold and and silver. silver. alkaline, metals, gold Vanadium'is abundant of of the the trace trace elements elements with with aa range range Vanadium is the most abundant of 1300-2000 1300-2000 ppm. ppm. Vanadium content content is is positively positively correlated correlated to to of carbon content. Althoughf there is is a fairly fairly wide wide divergence divergence in in carbon content. Although, there the absolute trace elements, elementsf the the absolute concentration concentration of the the various various trace ratios between trace elements are uniform for for composite composite ratios trace elements are amazingly amazingly uniform samples taken over aa 30-mile 30-mile zone zone (Fig. (Fig. 1) (Lagowski and and Johnson, Johnsonf samples taken over 1) (Lagowski 1989). Based on this observation, a similar similar chemical chemical environment environment 1989). this observation, of deposition deposition is is inferred. inferred. Alsof overprinting has has not not Also, metamorphic metamorphic overprinting these geochemical altered these geochemical relationships. relationships. I The The geology geology of of the the graphitic graphitic Lower Lower Slate Slate Member Member is is structurally events related related structurally complex due to multiple deiormational deformational events to the the 1850 1850 Ma Penokean Penokean Orogeny (Kiasner, (Klasnerl 1978) 1978) and and later later 1100 1100 Ma Ma to Keweenawan rifting. Keweenawan rifting. Extensive glacial glacial overburden overburden makes makes conventional outcrop conventional outcrop mapping mapping virtually virtually impossible. impossible. Fortunatelyf Fortunately, the the graphitic graphitic strata strata are are highly conductive conductive and and can can be be detected detected by by electrical geophysical electrical geophysical methods. methods. In order to determine determine which which geophysical technique technique or or combination combination of of techniques techniques would would provide provide geophysical the most accurate accurate data data for for future future exploration, explorationl aa multi—component multi-component the geophysical was conducted geophysical survey survey was conducted over over an an area area of of known known geology. geology. The results results of of this this investigation investigation indicate indicate that that the the best best The methods are horizontal loop electromagnetics electromagnetics and electrical methods and very in low frequency electromagnetics electromagnetics using the EM16Rf EM16R, used in combination. combination. The The use use of of geophysics geophysics in in conjunction conjunction with with drilling drilling suitable means means of of defining defining graphite-rich graphite-rich strata. strata. is the only suitable Utilization studies Michigan Tech Utilization studies conducted at at Michigan Tech show show several several promising uses for Upper Upper Michigan Michigangraphite graphite (Johnson (Johnson&. . aJ.f1989). promising al.,l989). One potential "as Ifas is" isffuse for for this this material is is as as aa high high quality quality shale substitute substitute in in the the manufacture The shale manufacture of portland cement. The abundant graphite-rich graphite—rich rock abundant rock may also also be considered considered as as an an unrecognized and and untapped untapped fuel fuel resource. resource. Compared Compared on on an an equal equal volume volume basis basis with with coal, coalf rock rock grading grading 30% 30% graphite graphite is is estimated estimated to to be roughly equivalent the heating value of of low low grade grade (60% (60% equivalent to the carbon) coal. coal. If the graphite material can be beneficiated from from carbon) the 15 15 to 25% carbon range to 80+%, this this material also be be an an carbon range material would also ideal metallurgical metallurgical reductant for the Pelletech Process of making self-fluxing self-fluxing iron iron ore ore pellets. pellets. I ri 56 �Figure1.1. Geologic Geologic map map of of western western Upper Upper Peninsula, Michigan Figure Peninsula, Michigan showing graphite-rich slate and geochemical sample showing graphite—rich slate and geochemical sample locations. locations. REFERERENCES CITED CITED REFERERENCES Huang, J.Y.,Carlsm,D.H., Johnson,A.M., a d VarAktine,J. (I%), l4wang,J.Y.,Car(s,D.H.,Johnson,A.p4, and VanLstine,J. (1986), @lPreliminary Investigatim Graphite Reswrces in Michigana@, 'Pretiminary Investigatia, ofof Graphite Resources in Mithigan", 115th Armat Mtg.,ME A I M , New Orleans, LA LA Preprint. Preprint. 115th Arr*aL Mtg.,SME AIME, lieu Orteans, Johnson, A.M., D.H., and and Cho, Cho, P.(1989),"Utitizatlixi P.(1989),Wti lizatimofof Johnson, A.M., Carlsm, CarLs, D.H., U p p - Michigan Michigan Graphite Graphite Resources', Resourcesa@, Geological Survey Survey Divisim, Upper GeoLogicaL Division, -89, O p n File Report, Michigan DNR Michigan OUR Open FiLe Report. •89, Klasner, J.S. (19Th),"Penokean (19?8),"Penokean Deformation D e f o m t ionand &-d Associated Ktasner,J.S. Associated Metamrphism in the Western Marquette Racge, NorthernMichigan", Michigan1@, Metansrphism in the Western Marquette Range, Northern V.89, pages 711-Z2. Geological Society Scciety of of America & m i c a BuLletin, Eulletin, V.89, GeoLogical pages 711-722. Krmr,R.S.,HuangJ.Y., a d Jthrm,A.M.(1987),'A Jchnsm,A.M.(1987),"A MineraLogicaL Mineralogicaland ad. Kraner,R.S.,Hwangj.Y., and Chemical Study Study of ofthe theGraphitic GraphiticLower LowerState SlateNeither, M-r, MichigChnicaL Michigarn Formation, Marquette Marcpette and a d Baraga Earaga Cou,ties, Comties, Nichigan",Geotogicat Michiganl@,Geological Formation, @en File R e p r t -87. Survey Division, Michigan DNR Survey Division, Michigan OUR cen FiLe Report -87. Lagouski,J. And A d Johnson,A.M.(1989),"Geotogic Johnson,A.M.(1989),@@Ge010gic Investigatim of Lagowski,J. Investigation of Graphite-Rich Strata in the M i c h i g m F o m t i m 0 a r a g a a Graphite-Rich Strata in the Michigatine Formation--Baraga andd Marqmtte Cou,ties, Comties, Michigan',Geotogica( Michiganoa,Ceo1ogicalSurvey Survey Division, Divisim,Michigan Michigan Marquette x r ~file Report -89. DNR Q OUR Open FiLe Report -89. 57 �STRATIGRAPHY OF OF THE THE NEGAUNEE NEGAUNEE IRON IRON FORMATION, FORMATION, STRATIGRAPHY EASTERN RANGE, MICHIGAN MICHIGAN EASTERN MARQUETTE MARQUETTE RANGE, JOE MANCIJSO, MANCUSO, JEFF STEPHEN STEPHEN BOWLING GREEN STATE STATE UNIV., UNIV., BOWLING BOWLINGGREEN, GREEN,OHIO OHIO43403 43403 BOWLING GREEN BILL KANGAS KANGAS ISHPEMING, MICHIGAN MICHIGAN 49849 CLEVELAND CLiFFS CLIFFS IRON IRON CO., ISHPEMING, CLEVELAND Introduction Introduction The stratigraphic stratigraphic subdivisions subdivisions of the Negaunee iron formation in the Empire Mine area (Secs. I9 19&&20) 20)differ differsubstantially substantiallyfrom fromthe theiron ironformation formationininthe theCD CDI Pit I Pitarea area(Sec. (Sec.18I) and and to to the the north in Sec. 5, 5, 6, 7 & 8. The TheEmpire EmpireMine Minearea, area, which which comprises mmprises over over 3000' 3000' of of continuous continuousiron iron formation above above the Siamo Siamo Formation, Formation, is is informally informally subdivided subdividedinto into 55 units units based basedon onmineralogy, mineralogy, texture, and and metallurgy. metallurgy. The TheEmpire EmpirePit Pitisisconfined confinedtotothe thesilicate, siiicate,carbonate, carbonate,and andcIastic clasticUnits units interval(1000' (1000'toto2100') 2100')above abovethe theSam0 Siamocontact. contact. The iron formation which occupy occupy an an 1100' 1100' interval formation in inthe the thick between between the the Siamo Siamo Formation Formation and the CD II Pit area area and and to the north north is is less less than than 1600' 1600' thick Summit Mountain is subdivided into 77 informal informal units. units. The Mountainsill. sill. It is The CD CD II Pit Pit is is located located in in the coarse coarse magnetite magnetite unit unit (unit (unit III) Ill) which which occupies occupies aa300' 300' interval intervalfrom from780' 780'to to1080' 1080' above above the Siamo Siamo Formation. Formation. 0 0 0 A 1 Iron formation with clastic interbeds 0 0 0 0 CD 0 Upper unditterentiated undifferentiated iron iron formation formalion 1 Summit Moujitain Sii b Ull JtiQ..HQEiZfl fIIt!.LIQIIc Magnetite-chert-carbonate Magnetite-cl\ert-carhnate iron formation C Cf 0 Magnetite Maqnetite iron iron formation forniation with with coarse silicates silicates ::-:-:-:-: Tracy Sill IC., rn n Carbonate Horizon . 121 Lj Magnetite iron formation with ligtii bands light green bands ( wavy beds with granules granules)) y Dir.grey grybIack, boddod1II. Dk black, thin 1Ii1nbedded F \ Magnetite-carbonate-silicate. Magnetite.carbonate-s~licatechert iron iron formation formation 5'e \ \ \ 1L \ \ Silicate Horizon ' t, \ \ 1 bl b o m CD . r ,? Interbedded coarse ctastic clastic sediment & iron iron tormation formation t4onmi5neiiie carb chort-silicaig IF. Coarse magnetite iron formation ll Lower undifferentiated iron formation 1I Magnetite-chert-silicate. Magnetite-chert~silicatecarbonate iron iron formation formation Magnetite-chertxarbonate Magnetite-chert-carbonate iron tormation formation chip)) ((poker poker chip Interbedded slate slate &8 Interbedded iron iron formation formation 3 w Siamo Slam0 Formation Format~ori 1 Siamo Formation Siarrio Formation CD II PIT PIT AREA CD A m < EMPIRE MINE EMPIRE MINE AREA AREA > > 3000' 3000' 58 I I I I I I 1600' 1600- I I I I I �U Coarse Coarse Clastic Clastic Interbeds Interbeds The Empire mine section includes a 400' zone of iron formation and interbedded interbedded coarse coarse clastic sediments (greywackes (greywackes or arkoses) arkoses) immediately immediately above above the the Siamo Siamo Formation Formationand andaa250250300' zone zone of of coarse coarse clastic clastic sediments sediments and and iron iron formation formation in in the the clastic clastic horizon horizon which which occupies occupies the the 300 interval from approximately to2000' 2000'above abovethe theSiamo Siamo Formation. Formation. The iron formation approximately 1700' 1700' to formation in in the the CD II Pit ara and and north north contains contains no no coarse coarse clastic clastic sediments. sediments. Riebeckite Zone Zone of iron formation containing blue riebeckite is In the Empire Mine a distinct marker zone of feetofofthe thecarbonate carbonateunit. unit. No riebeckite was seen in the CD II Pit area. area. found in the upper 150 150 feet Diabase Diabase Sills Sills thick) and In the CD CD I1 Pit area the Tracy Sill (250' (250'thick) and the Summit Summit Mountain MountainSill Sill (500' (500' thick) thick) ironformation. formation. No metadiabase sills sills intrude intrude the the 3000' 3000' of of iron intrude into the lower 1600' 1600' ofofiron formation in the Empire Empire Mine Mine area. area. Structure and and Oxidation Oxidation The Empire E. and dips 30-45 NW. ItIt is is offset offset by by aa Empire Mine sequence strikes NS to N . 40 E. number displacement. Very Very little oxidation oxidation is associated with number of WNW faults with less than 100' 100' ofofdisplacement. pit area area strikes strikes NS NSand anddips dips30-35 30-35 W. W. ItIt is is cut by EW EW and the faults. The The iron iron formation formation in the CD I pit apparent. North NW faults with less less than than aa few few hundred hundredfeet feet displacement. displacement. Very little oxidation is apparent. North of the CD I1 Pit in W. and dips 20-50 SW. in sections 5, 6, 7, and 8 the iron formation strikes N. 35-40 W. Numerous Numerous major major EW EW and and NW NW faults faults with with displacements displacementsof of over over1000' 1000' transect the iron iron formation. formation. The iron formation is completely completely oxidized oxidized to hematite hematite and and limonite limonite and, and, in in places, places, leached leached of of silica. silica. Correlation Correlation Similarities between the Empire Empire and CD CD II sections sections are few but but include include the the following: following: very similar similar in in mineralogy, mineralogy, texture, texture, and and metallurgy The carbonate unit in the Empire Mine is very I. to the coarse magnetite thickness and magnetite unit (Unit Ill) Ill) of the CD I1 Pit area; however, they differ in thickness position above the Siamo Siamo Formation. Formation. with magnetite rich granules occur in Zones up to 50' thick of wavy-bedded iron formation with 2. 2. above the the coarse coarse magnetite magnetite unit in unit VI approximately approximatelyIOU' 100' above in the the CD CD II Pit area. Stratigraphically Stratigraphicallythis this corresponds closely to the position position of of the the clastic clastic horizon horizon which which occurs occurs just just above above the the carbonate carbonate unit at the Empire Empire Mine. Mine. Several thin lenses lenses (less (less than 2") composed composed of sand sand sized sized quartz quartz grains grains and and 3. 3. stilpnomelane stilpnomelane occur occur in in the the upper upper undifferentiated undifferentiatedunit unit at at the the Empire EmpireMine Mineand andin inunit unitVI VIininthe theCD CDI I Pit area. area. Conclusions Conclusions south, The Empire Empire mine section section and and the CD IIPit Pit section section appear appear to meet meet abruptly abruptly at at 14600' 14600' south, between 18 and and between DDH DDH holes holes 47 47 and and50 50approximately approximately1200' 1200' north north of of the the boundary boundarybetween betweensecs. sees.18 19. 19. The contact cannot be considered considered aa simple simple fault because because the the relationship relationshipis is not not marked markedby by thickness. Contact Contact displacement or oxidation but by an abrupt change in stratigraphy and thickness. relationships relationships indicate indicate either either a complex fault with great displacement such as the Palmer fault, or an Archean fault zone which was active during deposition of the iron formation and reactivated during the Penokean Penokean Orogeny. Orogeny. 59 �I Petrologic and Evolution ofthe Petrologic and GeochemicalEvolution of the Penokean Penokean Peavy Pond Pond Complex Michigan County,M3chigan Peavy Complex,Iron h n County, David J. Stephen D. D. Stahl, Stahl, Adam Heft, and Kristin Huysken J. Matty, Stephen Department of of Geology, Geology, Central Central Michigan MichiganUniversity, University,Mt. Mt.Pleasant, Pleasant, MI MI 48859 The Peavy Peavy Pond Pond Complex Complex (PPC) is a metamorphosed, composite composite pluton of of Penokean Penokean age age intrudescomplexly complexly deformed, deformed, biotite biotite to to (1.85 Ga, Van Van Schmus, personal communication) that intrudes sillimanite grade grade pelitic pelitic to to quartzose quartzoseshales shalesand andgraywackes graywackesofofthe theProterozoic ProterozoicMichigamme Michigamme lavas of of the theProterozoic Proterozoic Hemlock Hemlock Formation Formation (HF). (HF). Formation (MF) and basic pyroclastics and lavas Rocks of the the PPC are characterized Rocks of characterized by by the thelithologic lithologicsuccession succession gabbro-diorite-tonalitegabbro-diorite-tonalitegranodiorite-granite. Gabbro granodiorite-granite. Gabbro and diorite diorite are are most most abundant abundant and andare arecommonly commonly associated with HF wallrocks wallrocks in the southern southern portion portion of of the the complex. complex. The The more more silicic silicic tonalites, tonalites, granodiorites granodiorites and and granites are granites are restricted restrictedto tooutcroppings outcroppings principally principally in the the northwestern northwestern portion portion of of the the complex complex in close proximity proximity to rocks rocks of of the the MF; these rocks often contain xenoliths xenoliths of of MF and and develop develop locally locally into migmatites. The PPC and surrounding surroundingarea areawere weremapped mapped in inexcellent excellentdetail detailby by Bayley Bayley (1959) (1959) and Dutton (1968). Bayley fractional Bayley interpreted interpreted the themafic maficrocks rocks of of the the PPC PPC to to be products of of fractional of aa parental basaltic magma crystallization of magma and and considered considered the more silicic phases of of the complex parental magma. magma. complex to to have have been been derived derived from from variable variable assimilation assimilation of of the the MF MF by by this this parental Bayley's of Bayley's interpretations interpretations were based largely largely on on field field and and petrographic petrographic data; data; due due to to the lack of uninterrupted outcrops, uninterrupted outcrops,however, however, other otherexplanations explanationsfor forthe thedevelopment developmentof ofthe thecomplex complex must mustbe be considered. These of each each phase phase of of the the PPC PPC as as a separate considered. These include include development development of separate magma, magma, variable variable mixing melting of of walirocks, wallrocks, or some combination combination of processes mixing of of magmas, magmas, partial melting of any any of of these these processes with the the fractionation-assimilation fractionation-assimilation process process originally originally suggested suggested by by Bayley. Bayley. tectonic significance significance in intrudesrocks rocks considered considered to The PPC has potential tectonic in that that it intrudes represent aa passive passive margin margin sequence sequence (Larue, (Larue, 1983; 1983; Ueng et al., 1988), 1988), a rifted passive margin assemblage (Cambray, 1978), 19781, a forearc or backarc basin (Van (Van Schmus, Schmus, 1976), 1976), or aa foredeep foredeep (Hoffman, 1988; 1988;Barovich Barovichetetal., al.,1989). 1989). Recent Recent studies studies of of the the HF HF volcanics volcanicsand and the the associated associated (Hoffman, Kiernan Sills (KS; which lie about 44 km Sills (KS; km to to the thenorth northofofthe thePPC) PPC)indicate indicateMORB-like MORB-likegeochemical geochemical characteristics of While these data suggest of these rocks; While suggest aa MOR-like MOR-like rift-related origin origin for these these interpreted to for the the HF and KS (Ueng et al., units, they also also could be interpreted to reflect reflect a back-arc origin for 1988;Wee, Wee,1989). 1989). Data Data derived from from analyses of of the the nearby Badwater (Greenstone) 1988; (Greenstone) Formation indicates an origin origin closely closely related to that thatof of the the HF HFand andthe theKS KÂfor forthese theselavas lavas(Cudzillo, (Cudzillo,1978; 1978;Wee, Wee, 1989). 1989). The goals of our our study were to determine the the processes by which the PPC evolved and to gain insights into insights into the the tectonic tectonic evolution evolution of of this area area through through geochemical geochemical studies studiesof of the the PPC. PPC. . . . . Variations within Major PPC. m i o r Element Vanwithm the PPC the major major oxides oxidesvs. vs.XFeO/(ZFeO+MgO) FeO/(FeO+Mg0) for Plots the for our our PPC PPC data data relative to that that of of the MF, the HF, the the KS, KS, the the Badwater Badwater Fm. Fm.and andthe theNorthern NorthernWisconsin WisconsinArc ArcComplex Complex clearly clearly distinguish distinguish mafic phases phases of of the the PPC PPC from fromother otherunits units largely largelyon onthe thebasis basisofofthe thehigher higherMgO MgOand andlower lowerXFeO FeO ma% concentrations of of the the PPC PPC rocks. rocks. With With increasing increasing differentiation, the mafic PPC phases show show relatively strong depletions depletions in in FeO, FeO, MnO, MnO, and and MgO MgO and corresponding corresponding enrichments enrichments in in A1203, A1203, Na20, K20, K20, and and to to some some extent in Ti02. These Thesetrends trendssuggest suggestfractionation fractionation of of ferromagnesian ferromagnesian plagioclase. Attempts to apply apply Pearce Pearce Element Element Ratio Ratio Diagrams Diagrams to to test test mineral phases instead of plagioclase. this hypothesis failed as there there are areno no truly trulyconserved conserved major major or or trace trace elements elements in in the thePPC PPCrocks; rocks; this is is true truefor for silicic silicic phases phases of of the the PPC PPC as as well. well. The Themore moresilicic silicicphases phases of of the the complex complex tend to to converge towards the compositions of of the the MF rocks rocks indicating indicating possible possible interaction interaction of the MF in the converge towards the evolution of the the PPC as suggested by Bayley (1958). (1958). Generally higher concentrations of evolution of of 1(20, K20, Si02, Si02, and to some extent Na20 Na20 in be interpreted interpreted as in the the silicic silicic PPC phases relative to to the the MF MF could be as resulting from assimilation processes. processes. The The elevated elevated concentrations concentrations of of these these elements, elements, however, however, 60 I �U melting processes processes involving involving minimum melts of of quartz, quartz, could also be explained by partial melting potassium feldspar and and sodic sodic plagioclase plagioclase in the the MF MF rocks. rocks. . . . . PPC Trace Element Elmmt Variations V m d m n s within the PPC Mafic rocks rocks of of the the PPC PPC are are distinguishable from other mafic rocks of of the the region on the Mafic basis of trace element abundances as well as by major major element element concentrations. concentrations. For For example, example, concentrations of Sc and Co are generally lower and concentrations of Ni, Ni, Ta, Ba and Sr STare are generally higher in the the PPC PPC rocks rocks than than in in the theHF, HF,KS KS metagabbros, metagabbros, or or Badwater Badwater Fm. Fm. trends are are clearly clearly visible visible for the transition metal metal elements elements Sc, Sc, Cr, Crl Co, Co, and Ni in Fractionation trends mafic PPC PPC rocks, rocks, suggesting suggesting removal removal of ofphases phases that that preferentially incorporate these elements, mafic elements, perhaps chromite, chromite, olivine, olivine, pyroxene, pyroxene, or some some combination combination thereof. some field field evidence evidence in thereof. There is some the form 80% Hb) for pyroxene fractionation (ca. 80% form of of cumulate-like cumulate-like hornblende-rich hornblende-rich rocks rocks (ca. pyroxene); this trace (metamorphic hornblende hornblende after pyroxene); this is is the the favored favored starting starting point for future future trace element modelling. would increase increase the the relative modelling. Fractionation Fractionation of of oxides, oxides, olivine olivine or pyroxene pyroxene would concentrations of Ba and Rb in more more differentiated differentiated rocks rocks of of the the complex, complex, consistent with observed observed trends. The Theincrease increaseof of Sr Srconcentration concentration with with increasing increasing differentiation supports the assumption of fractionation, since since this this process process would wouldresult result in in aa systematic decrease in Sr of little plagioclase plagioclase fractionation, with increasing fractionation. Limited Limited plagioclase plagioclase fractionation is also supported by REE data data which which are characterized characterized by by relatively relatively flat, flat,LREE-enriched, LREE-enriched, profiles profiles and development development of of only small positive positive and negative negative Eu Eu anomalies. anomalies. Trace element concentrations concentrations of of PPC PPC silicic silicic rocks rocks also also converge converge towards the thecompositions compositions of MF MF rocks, rocks, supporting supporting the the hypothesis of of MF MFinvolvement involvementininthe the evolution evolutionofofthese theserocks. rocks. This This is of discussed further furtherbelow. below. 3Snidergrams mdermm To test the that silicic rocks are are related by assimilation or the validity validity of the hypothesis that silicic PPC rocks partial melting partial meltingof of MF MF rocks, rocks, we we constructed constructed spidergrams spidergrams(modified (modified from from Thompson, Thompson, 1981) 1981) normalized average MF. MF. normalized to average Among other things* things, the spidergrams indicate that rocks of the the H HF Among other F are depleted in LILE MF. The and enriched in HFSE relative to MF. The PPC PPC diorites and gabbros appear similar in most are the higher concentrations of Sr and the lower respects to the HF H F rocks; rocks; major exceptions exceptions are of Th, Th, P, P, Y, Y, and and Yb Ybininthe the PPC PPC rocks. rocks. The lower Tb concentrations concentrations in in particular lower Th concentrations of are noteworthy in that that these thesevalues valuesmay mayreflect reflectdifferences differences in the the relative relative source source regions regions andlor andor paths of ascent paths of the PPC and the the HF. HF. The PPC tonalites, granodiorites and granites granites cluster cluster around around the the average average MF MF composition. There is only a small composition. small overall variation from from unity (and thus from from average average MF) MF) for gabbroic parental parental 1)large-scale large-scale contamination contamination of gabbroic the PPC tonalites. This Thiscould couldresult resultfrom from1) maginas MF or or 2) 2) almost almost complete complete melting melting of of MF MF to to form form magmas by assimilation assimilation of of extensive extensive amounts amountsof of MF the tonalites; the observed major majorelement elementdata. data. The the latter latterhypothesis hypothesis is is broadly broadly consistent with observed elevated concentrations of of the the LILE LILE and and LREE, LREE, as as well wellas asZr Zrand andHf, Hf,ininthe the PPC PPC granites granites and elevated granodiorites relative to average MF MF suggest suggest that that partial melting processes processes rather rather than assimilation processes processes were were dominantly dominantly responsible responsible for the the production production of of these these rocks; rocks; this thisisis consistent with interpretations interpretationsregarding regardingthe themajor majorelement elementcompositions compositionsof of these theserocks. rocks. D .~ s c.r . . Tectonic Discrimination Tectonic We have so far applied We applied only only a few few of the many available available methods methods of of geochemical geochemical discrimination discrimination diagrams to the PPC PPC rocks to learn more about the tectonic tectonic setting setting of of their origin. origin. AFM diagrams diagrams indicate indicate aa distinct calc-alkaline trend for for all all rocks rocks of ofthe the PPC. PPC. When plotted AFM calc-alkaline trend plotted alone, however, however, the the mafic mafic PPC PPC rocks rockscan canbe beinterpreted interpreted to reflect indistinctly either a calccalcalkaline (arc-derived) trend trend or a tholeiitic trend. Inasmuch tholeiitic (MORB-like) (MORB-like) trend. Inasmuch as the the MF MF rocks rocks are are characterized characterized by a distinct distinct caic-alkaline calc-alkaline trend, trend*reflecting reflecting their their derivation derivation from from the theWisconsin Wisconsin arc to the south to the the north and east Archean calc-alkaline plutonics to east (see (see Barovich Barovich et south and andfrom from the the Archeari al., it is conceivable conceivablethat that the calc-alkaline calc-alkaline trend trend of of the the entire PPC suite largely reflects the a]., 1989), 1989), it apparent genetic apparent genetic association of ofthe themore more silicic silicic phases phases of of the the PPC PPC with with the thecalc-alkaline calc-alkaline MF. MF. 61 �I Plots Plots of of Ca0miO2 CaO/Ti02 vs. vs. Ti02 Ti02 and of A1203mi02 A1203/Ti02vs. vs.Ti02 Ti02 (Sun (Sun and and Nesbitt, Nesbitt, 1978) suggest relatively undepleted mantle source that which the derivation of the PPC from aa relatively source similar to that which MORB. The more silicic silicic rocks rocks of ofthe the PPC PPCtrend trend into into the depleted mantle/arc produces MORB. mantlelarc field in the the A1203mi02 of the the CaOPFiO2 CaOmiO2 vs. A12O31TiO2vs.vs.Ti02 Ti02plot, plot,yet yetfall fallbeyond beyondthe the depleted depleted mantlelarc mantle/arc field of vs. Ti02 Ti02 plot. In plot. In both both cases, cases, however, however, there there is is aa strong strongrelationship relationshipbetween between silicic silicic PPC rocks and those of that once the MF that once again again suggests suggests aa genetic genetic nexus. nexus. A MORB-like MORB-like afinity affinity of ofthe the mafic mafic PPC PPC rocks rocks is is also indicated by Zr/Y vs. Zr plots (Pearce Z r N vs. Tb/Yb plots, plots, however however some some PPC PPC gabbros gabbros could could be be interpreted interpreted and Norry, 1979) 1979) as as well well as as Ta/Yb TaNb vs. ThRb be arc-related on the basis of vs. Zr Zr diagram. diagram. In to be of the ZrIY ZrN vs. In both diagrams, diagrams, silicic silicic phases of of the PPC plot with with rocks rocks of of the the MF. MI?. There exists exists at a t this thistime timeno no unambiguous unambiguous explanation explanation for for the the tectonic tectonic setting setting of of the the PPC. PPC. While iitt seems clear that While thatthe theoriginal originalgabbroic gabbroicmagma magma was wasMORB-like, MORB-like, and probably probably originated originated rift or a back-arc back-arc setting, we we are are unable to distinguish between between these in either a MOR-like MOR-like rift that suggests environments aatt this this time. time. To Tocomplicate complicate matters matters further, further,there thereisissome some evidence evidence that suggests that certain arc. We certain PPC PPC gabbros gabbros may may have originated within a volcanic volcanic arc. We cannot cannot unilaterally unilaterally the northern Wisconsin arc to the PPC, but reject these data data due due to to the the relatively relatively close close proximity of the we believe believe that that the we the arc-like arc-like characteristics characteristicsof of these thesegabbros gabbros could could be explained explained by by assimilation assimilation of of MF. The calc.-alkaline arc-like character character of of the more silicic phases of PPC could also reflect MF. calc-alkaline arc-like reflect an an origin within a volcanic arc environment, however, however, there there appears to be substantial substantialgeochemical, geochemical, origin petrologic, and and petrographic petrographic evidence evidence to to support support the the hypothesis that that these petrologic, these rocks rocks were were derived derived largely from or through assimilation largely from assimilation of of the the calc-alkaline calc-alkaline MF. MF. References Barovich, K.M.,Patchett, Patchett, P.J., Peterman, Z.E., Nd isotopes isotopes and and the origin of Barovich, K.M., Z.E., and Sims, P.K., P.K, 1989, Nd of the 1.9-1.7 1.9-1.7 Ga Penokean continental continental crust crust of of the the Lake Lake Superior Superiorregion: region: Geological Geological Society Society of of 333-338. America Bulletin, Bulletin, v. v. 101, 101,p. p. 333-338. Bayley, R., R., 1959, Geology Geologyofofthe the Lake Lake Mary Mary quadrangle, quadrangle, Iron County, Michigan: U.S. U S .Geological Geological Survey Suwey Bulletin, Bulletin, v. v. 1077, 1077,112 112 p. Cambray, F.W., F.W., 1978, Plate tectonics as aa model model for the environment environment of of deposition and and deformation of of the Early Early Proterozoic Proterozoic (Precambrian (Precambrian X) X) of northern Michigan: Michigan: Geological Geological deformation Society of of America America Abstracts Abstracts with Programs, Programs,v. v. 10, 10,no. no. 7, 7,p. p. 376. 376. Cudzillo, T.F., 1978, Geochemistry of Early Proterozoic Cudzillo, T.F., Geochemistry of Proterozoic igneous rocks, northeastern northeasternWisconsin Wisconsin and upper KS, University Universityof of Kansas, Kansas, 202 202 p. p. upper Michigan: Michigan: Ph.D. Ph.D.thesis, thesis,Lawrence, Lawrence, KS, Dutton, C., of the the Florence Florence area, Wisconsin and Michigan: C., 1968, 1968, Geology Geology of Michigan: U.S. U.S.Geological Geological Survey Survey Professional Paper 54 p. Paper 633, 633,54 p. Hoffman, P.F., P.F., 1988, 1988,Animikie AnimikieGroup: Group: A A Penokean Penokeanforedeep?: foredeep?: Annual Annual Institute Institute of Hoffman, of Lake Superior Geology Proceedings and Abstracts, 40-41. Geology Proceedings Abstracts, v. v. 34, 34, pt. pt. 1,1,p. p. 40-41. Larue, D.K, of the the Lake Superior region: region: Tectonostratigraphic D.K, 1983, 1983, Early Early Proterozoic Proterozoic tectonics of Tectonostratigraphic terranes zone: terranesnear nearthe thepurported purportedsuture suture zone:Geological GeologicalSociety SocietyofofAmerica AmericaMemoir Memoir 160, 160, p. p. 33-47. 33-47. Pearce, JJ.A., Petrogenetic implications implications of ofTi, Ti,Sr, Sr, YYand and Nb Nb variations variations in Pearce, . A , and Norry, M.J., 1979, 1979, Petrogenetic volcanic rocks: Contributions volcanic rocks: Contributionsto toMineralogy Mineralogy and andPetrology, Petrology, v. v. 69, 69, p. p. 33-47. 33-47. regularities and Sun, S.S., S.S., and and Nesbitt, Nesbitt, R.W., R.W., 1978, 1978, Geochemical Geochemical regularities and genetic genetic significance significance of of ophiolitic basalts: Geology, Geology,v. v. 6, 6, p. p. 689-693. 689-693. Ueng, W.C., W.C., Fox, Fox, T.P., T.P., Larue, D.K., J.T., 1988, D.K., and Wilband, J.T., 1988, Geochemistry Geochemistry and petrogenesis of of volcanicrocks rocksand andthe theKiernan Kiernan Sills, Sills, southern southern Lake Lake the Early Proterozoic Proterozoic Hemlock Hemlock volcanic region: Canadian Superior region: CanadianJournal JournalofofEarth EarthScience, Science,v.v.25, 25,p. p. 528-546. 528-546. Van Schmus, W.R., Early and Middle Proterozoic Proterozoichistory history of ofthe the Great Great Lake area, area, North W.R., 1976, Early North America: Philosophical Philosophical Transactions TransactionsofofRoyal RoyalSociety Societyof of London, London, Series SeriesA, A, v. v. 280, 280, p. p. 605605628. 628. Wee, S.M., S.M., 1989, 1989, Geochemical Geochemicalinvestigation investigationofofEarly Early Proterozoic Proterozoicigneous igneousrock rockinin northern northern Wee, Michigan and and the northeast U.S.A.: Ph.D. Ph.D. thesis, East MI, Michigan northeast portion portion of of Wisconsin, Wisconsin, U.S.A.: East Lansing, Lansing, Ml, Michigan State State University, Michigan University, 185 185p. p. 62 �I Crustul structure of northeastern Lake Superior from GLIMPCE reflection and refraction data I Milkereit1, P. Morel-à-l'Huissier1, Morel-5-l'Hiiissierl, A.G. I - c c I ~M.D. ~M.D. , Thomas1 B. Milkeroit1, A.G. G Green', Thomas1 A. Tr&u2, M.W. M.W. Lee3 L G C ~and a n d W.F. W.F. Agena3 ~ g e n a ~ A. Tehii2, 1 Geological Geological SSurvey of CCanada, Ottawa, ~ w v e yof anada, O t t a w a , Canada, C a n a d a , K1A K I A 0Y3 OY3 2O Oregon State regon S t a t e University, U i ~ i v e r s i t yCorvallis, ,Corvallis, Oregon O y c g o n 97331 97331 U.S. U.S. Geological Survey, Denver, D c n v e r , Colorado C o l o r a d o 80225 80225 rrlle deep 'l'lle deep structure of of the the Midcontinent hIidcontincnt Rift Rift beneath beneath Lake Lake Superior Superior was was imaged imaged in in detail during during tile tlie GLIMPCE GLIMI'CE reflection reflection survey survey of of tile tlie Great Great Lakes. Lakes. Reflection Reflection profiles profiles across across the rift revealed graben [Behrendt et al., 1988; Cannon et et al., tlie revealed a deep deep asymmetric asymnxtric central central graben [Belirendt et 1988; Cannon al,, 1989; Green Green et al., 1989] whose existence existence and and magnitude magnitude was was not not documented documented before. before. The The 19891 wllose geometry of of tlie the central graben changes along the the axis axis of of the the Midconti~ient~ Midcontinent Rift geometry changes significantly significantly along System and sedimentary rocks, in in places places greater greater than 30 30 km km System and aa sequence sequence of volcanic volcanic and sedimentary rocks, thick, fills fills the graben. graben. Here Herewe wepresent presentadditional additionalGLIMPCE GLIAIPCEseismic seisnlic reflection reflection sections, sections, refraction and stacking velocity velocity analyses, and potential field field data data from from outside tile the main main rift rift basin basin beneath northeastern nortlieastern Lake Lake Superior. Superior. Figure 1. F i g u r e 1. GLIMPCE reflection reflection profiles profiles(A, (A,B, B,FF and and G) C) and GLIMPCE and OBS OBS recording recording site s h e on on shaded relief relief magnetic anomaly anomaly map. map. 0 63 km nHEf 50 -F= �These data data will will shed shed some some light light on on (a) (a)pre-Keweenawan pre-Keweenawan structures structures (aulacogens (aulacogens ?), ?), (b) (b) Keweenawan rocks (based on seismic seismic velocities), areal correlations among Keweenawan velocities), (c) thickness and areal extent of prepre- and post-rift sediments, sediments, and (d) the the correlation correlation between between potential field potential field data data and seismic seismic structures. st,ructures. and one one of of the the ocean ocean Location of of GLIMPCE GLIAIPCE reflection reflection profiles The Location profiles(A, (A,B, B, FF and and G) and bottom seismometers anomaly map map in Figure seismometers (UBS) (OBS) are shown on a shaded relief relief magnetic anomaly 1. At the intersection A and and G we 1. At intersection of profiles profiles A we have obtained obtained a high high quality quality image image of of the upper crust that has some 3-D control. Figure 2 shows a shallow, fault-bounded graben fault,-bounded graben upper that 11% some 3-II control. Figure 2 shows a sl~allow~ preserved beneath [Osler structure preserved beneath early earlyKeweenawan Keweenawan sediments sediments and and volcanics volca~~ics [Osler volcanics volcanics in in structure the interpretation image supports supports a tectonic model of 19891. This This seismic seismic image model of interpretation by by Cannon Cannon et etal., al.?1989]. lower Proterozoic Proterozoic intracratonic intracratonic rifting prior to units and lower to the the advent advent of of Keweenawan Keweenawan volcanic 11nits I suggests rocks (i.e. (i.e. the pre-Ihweenawan rocks suggests that pre-Keweenawan tile Sibley Sibley Group) Group) were were deposited deposited in in aashallow, sl~allow, probably fault-bounded intracratonic probably intracratonic basin. basin. The reflective, reflective? layered layered Lower Lower Keweenawan Keweenawan sequence, found found on on all all profiles profilesinin northeastern northeastern Lake LakeSuperior, Superior,can canbe be used used as as a marker sequence, marker horizon to define volcanic activity activity outside outside the the main horizon define the lateral extent extent of of early early Keweenawan Keweenawan volcanic rift basin. Figure Figure 2. 2. Migrated reflection profiles along lines lines A A and G showing subsurface structure structure I beneath northeastern northeasteru Lake Lake Superior Superior with with (from (from the thetop) top)non-reflective non-reflective post-rift post-rift sediments, sediments, volcanicunit, unit, and an interpreted image Keweenawan volcanic image of of aa Lower Lower Proterozoic reflective Early Keweenawan fault-bounded fault-bounded rift rift (aulacogen). (aulacogen).Generalized Generalizedvelocity-depth velocity-depthprofile profilewas wasdetermined determinedfrom fromOBS OBS recording along line A. wide angle recording I S I • .• •.•:—. I ----0• I Post-rTff I �I wide-angle wavefields wavefleldsrecorded recorded by by OBS OBS [GLIMPCE The T h e wide-angle [GLIMPCE seismic seismic refraction working working group, 1989] seismic recording recordingsystem system have have been been used used to 19891 and the the 120-channel 120-channel reflection reflection seismic to define velocity structure. structure The hasprovided provided useful useful information information define the shallow shallow velocity Thevelocity velocity model model has for structural structural intcrpretations interpretationsofofcomplex complexreflection reflectionsections. sections.Volcanics Volcanicsand andsediments sedimentsofofKeKeweenawan age outcrop outcrop extensively extensivelyinin the the southern southern and and western Lake Superior Superior region. region. On western Lake On weellawan age contrast, iio region. Earlier northeastern Lake Lake Superior Superior region. no post-rift post-rift sediments sediments outcrop outcrop in the northeastern studies that Lake studies [halls [Halls and and West, West, 1971] 19711 presented presented evidence evidence that Lake Superior Superior is underlain underlain by by as as much thick post-rift post-rift sediments. sediments. The TheGLIMPCE GLIMPCE experiment experiment confirms confirms their interintermuch as 3 km thick pretation velocities appropriate appropriate for upper pretation and andsuggests suggests an aneven even wider wider areal areal extension extension of of low low velocities Keweenawan (Bayfield-Jacobsvifleequivalent) equivalent)sandstones sandstonesthan than previously previously thought; thought; it also Keweenawan (Bayfield-Jacobsville also indicates an apparent (glacial drift) drift) in northeastern apparent lack lack of of thick thick unconsolidated unconsolidated sediments sediments (glacial Lake Superior. Findings Lake Superior. Findings of of the the seismic seismic studies studies such such as (a) (a) the the lateral lateralextension extension of of Early Early Keweenawan volcanics, volcanics,(b) (b) the the lateral lateral extension extension of of low low velocity velocitypost-rift post-rift sediments, sediments, and and (c) Kewccnawan along the basin bounding faults and accommodation the position of late late intrusive intrusive complexes complexes along accommodation zones can can be be correlated correlated with with major major t,rends trends and breaks in the gravity and magnetic anomaly zones anomaly patterns. \ References References W.F. Behrendt, J.C., J.C., A.G. A.G. Green, Green, W.F. W.F. Cannon, Cannon,D.R. D.R. Hutchinson, IIutchinson, M.W. M.W. Lee, Lee, B. Milkereit, Milkereit, W.F. Crustal structure structureof of the the Mid-continent Mid-continent Rift Rift system system -- Results from 1988. GLIMPCE deep deep seismic seismic reflection reflection profiles, profiles, Geology, 16, 16, 81 81 -- 85, 85, 1988. Agena, and C. C. Spencer. Spencer. Cannon,W.F., A.G. Green, D.R. ilutchinson, IIutchinson, M.W. M.W. Lee, Lee, B. Milkereit, Milkereit, J.C. Behrendt, Behrendt, II.C. 1I.C. Halls, J.C. Green, Sutcliffe and C. Spencer, Spencer, The The North North AmerAmerGreen, A.B. A.B. Dickas, Dickas, G.B. G.B. Morey, Morey, R. Sutcliffe ican Midcontinent Rift Rift beneath beneathLake LakeSuperior Superiorfrom fromGLIMPCE GLIMPCEseismic seismicreflection reflection profiling, profiling, 8, 305 305 - 332, 332, 1989. 1989. Tectonics, 8, Green, A.G., Milkereit,D.R. DR. liutchinson, Green, A.G., W.F. Cannon, Cannon, 13. B. Milkereit, Hutchinson, A. Davidson, Davidson, J.C. Behrendt, Behrendt, C. Spencer, M.W. Lee, P. Morel-à-l'hluissier and W.F. W.F. Agena, Agena, A A "GLIMPCE" "GLIMPCE" of of the deep Morel-a-1'IIuissier and crust beneath the in: Properties Properties and andProcesses Processes of of the the Earth's Earth's Lower Lower Crust, Crust, crust the Great Great Lakes, Lakes, in: R.F Mereu, Mereu, S. S. Mueller, Mucller, D.M. D.M. Fountain Fountain (Eds.), (Eds.),Geophysical Geophysical Monograph Monograpli Series, Series, 51, 51, 65 65 -- 80, 1989. 1989. GLIMPCE GLIMPCE Seismic Seismic Refraction Refraction Working Working Group, Group,GLIMPCE GLIMPCEseismic seismicexperiments experiments— - long-offset recordings, EOS, 70, 853, 1989. 1989. recordings, 70, 841 841 - 853, Halls, II.C., iI.C., and survey in Lake Lake Superior, Superior, Canadian Journal Journal and G.F. G.F.\Vest, West, A A seismic seismic refraction refraction survey 1971. of Earth Sciences, of Sciences, 8, 610 610 - 630, 630, 1971. 65 �I THE SONJU SONJU LAKE INTRUSION INTRUSION AND ASSOCIATED KEWEENAWAN ROCKS: GEOCHEMICAL AND GEOPHYSICAL GEOPHYSICAL EVIDENCE EVIDENCEOF OFPETROGENETIC PETROGENETICRELATIONSHIPS RELATIONSHIPS GEOCHEMICAL AND Schaap, and Val W. Chandler MILLER, James D., Jr., Brian D. Schaap, Minnesota Geological Geological Survey, Survey,2642 2642 University UniversityAve., Ave., St. St. Paul, Paul,Minn. Minn.55108 55108 Minnesota The The Sonju Sonju Lake Lake intrusion intrusion (SLI) (SLI) is is aa layered layered sequence sequence of mafic mafic cumulates cumulatesthat that is is one one of of the the most most known in in the the Keweenawan Keweenawan section section(Weiblen, (Weiblen, 1982). 1982). It is part of of completely differentiated bodies known the Beaver intrusive supersuite of gabbroic to granitic granitic rocks which were Beaver Bay Complex Complex -- aa multiple intrusive emplaced into emplaced into volcanic volcanic rocks rocks of the the North Shore Shore Volcanic Volcanic Group Group near near Silver SilverBay Bay and and Finland Finland in in northeastern Minnesota (Fig. 1). Preliminary Preliminarygeochemical geochemical data data and and somewhat somewhat equivocal equivocalintrusive intrusive relationships between ferrogabbroic rocks led Miller relationships between the SLI SLI and spatially associated diabasic and ferrogabbroic (1989) (1989) to suggest suggest that all of these intrusive units may be comagmatic and roughly coeval. Also, Also, chemical data be interpreted interpreted to to indicate indicatethat that the the extensive extensivemass massof of granitic graniticto to chemical data of Rogge Rogge (1989) (1989) can can be granodioritic rocks that overlie differentiates of the layered sequence. overlie the SLI SLI are are siliceous siliceous differentiates sequence. However, further mapping However, the results of geochemical and geophysical modelling, together with further and petrographic studies, studies, indicate indicate that the SLI is genetically and temporally distinct from these other units of the Beaver Bay Complex. Complex. The laminated and locally layered, mafic cumulates of the SLI, first described in detail by (15°-25°) Stevenson (1974), occur as a gently (15' -25O) southward-dipping sequence which has a assuming negligible negligible faulting faulting (Figs. (Figs. 1 & & 2). 2). The stratigraphic thickness of about 1100 meters, assuming footwall of the intrusion is composed of a complex mixture of gabbro, granophyre, granophyre, and volcanic hornfels. The homfels. Theuppermost uppermostlaminated laminatedferrodioritic ferrodioritic cumulates cumulates are are overlain by a massive massive granophyric olivine ferrodiorite olivine ferrodiorite that irregularly irregularly grades grades into into a prismatic mafic granodiorite granodiorite over over aa stratigraphic stratigraphic thickness of about 100 100 meters. Farther Farther south south (200-400 (200-400m m upsection?), upsection?), this prismatic prismatic granodiorite granodiorite grades into a leucocratic granophyric granite. The The granodiorite granodiorite and and granite granite are are collectively collectively termed 1). The The eastern eastern margin margin of the SLI SLI is abruptly abruptly truncated by a NNEthe Finland granite (Fig. 1). trending fault that juxtaposes the SLI and olivine gabbroic rocks rocks of of the the Beaver Beaver River River diabase. diabase. The The aeromagnetic aeromagnetic signature signature of the SLI, SLI, which can be traced to the west beneath a cover cover of glacial till, indicates that the intrusion curves to the south, rimming the underside of the Finland granite (Fig. 1). The TheSLI SLIhas hasaahalf-saucer half-saucershape shapewith with aa strike strikelength length of of at at least least 20 20 kilometers. kilometers. The medium-grained ophitic ophitic olivine olivine diabase diabase The Beaver Beaver River River diabase diabase is typically a fine- to medium-grained the Beaver Beaver Bay Bay Complex Complex (Fig. (Fig.1). occurring in dikes and sills throughout the 1). Emplaced into the Beaver River diabase ferrogabbroic rocks Beaver diabase in scattered scattered locations locations are the typically zoned bodies of ferrogabbroic the termed the Silver Bay intrusions. Geochemical Geochemical modelling by Shank (1990) suggested that the Silver Silver Bay intrusions intrusions represent a more fractionated derivative of the original Beaver River diabase magma. Intrusive Intrusiverelationships relationshipsand andaacompositional compositionalhaitus haitusbetween between these theserock rockunits unitsimply, imply, fractionation must have occurred in in aa deeper deeper magma magma chamber. chamber. These however, that this fractionation These conclusions and the general compositional conclusions compositional similarities similarities of the Silver Silver Bay intrusions intrusions and and the the upper upper cumulates of the SLI cumulates SLI led Miller Miller (1989) (1989) to speculate speculate that the SLI represented such such aa chamber, chamber, and if so, that the Beaver River diabase possibly was parental to the layered cumulates of the SLI. Additional mapping mapping along along the eastern margin of the SLI now indicates that the truncation of the intrusion is due largely to the emplacement of a large dike dike of of Beaver River diabase (Fig. 1). Two Two in the the diabase. diabase. Although large inclusions of the SLI have been found in Although aa postmagmatic postmagmatic fault fault also also relative to the steep fault fault that that accomaccomexists between the SLI and the diabase, it is small scale relative km.. modated the diabase. The Thelatter latter had had east east side-down side-downdisplacement of perhaps as much as 1.5 km Further evidence evidence against against the Beaver River diabase or a similar magma composition having been of an estimated estimated parent parent magma for the parental to the SLI is given by the distinct composition of intrusion. AAweighted weightedsum sumof of over over 20 20 whole whole rock analyses analyses through a stratigraphic stratigraphic section of the SLI SLI (Fig. 2) defines defines aa bulk composition composition that that is is overall overall more more evolved evolved than than average averageBeaver BeaverRiver River diabase (Table (Table 1). 1). The Theplausibility plausibility of of this this estimated estimated parent parent composition, composition,which is is very similar similar to that calculated calculated by Stevenson Stevenson (1974), (1974), is is verified verified in two two ways. The most primitive primitive olivine thebase baseof ofthe theintrusion intrusion is is exactly exactly that which should 1) The olivine (Fo79.5) (F079.5) atatthe should initially crystallize from the estimated parent parent magma. magma. Based K ~ ( ~ e of -of ~0.3 0.3 g) Based on an an olivine-liquid olivine-liquid (FeMg) 66 �I (Roeder (Roeder & & Emslie, Emslie, 1970), 1970), the the calculated calculated mg# mg# (Mg/Mgi-Fe) (Mg/Mg+Fe) of of 53.9-55.3 53.9-55.3 should should produce produce cumulus cumulus olivine Fo79.6-8o.5. olivinewith withaacomposition compositionofof Fo79.6-80.5. 2) The crystallization sequence observed in the SLI (Fig. 2), namely 0011 - 01+P1 01+P1-- Oli-P1+Cpx 01+Pl+Cpx -01÷Pl+Cpxi-Feox, Ol+Pl+Cpx+Feox, is identical to that predicted when the estimated parent composition is applied to a low low pressure fractional crystallization model (Neilsen, 1988). In contrast, plagioclase is apparently the first phase to crystallize from a Beaver River diabase composition when its average composition is is applied to the same model. A A liquid liquid line line of descent calculated for the SLI (by (by summing all rocks above a particular particular level) level) also fits that predicted by fractional crystallization crystallization modelling of the the estimated estimated parent parent magma, magma, ifif aa system system open open to to some someperiodic periodic recharge recharge isisassumed. assumed. The The composition composition of of the the granodioritic granodioritic to to granitic rocks which overlie the layered cumulates correspond siliceous differentiate differentiate of of the theSLI SLI correspond very very well well to to that that which which would would be be expected expected for for aa siliceous (Rogge, 1989). 7%(by (byweight) weight) of of olivine olivine Fe-granodiorite, Fe-granodiorite, which which directly directly overlies overlies the 1989). About About 7% layered cumulates, is included in the estimated SLI parent composition (Table 1). However, However,the the amount amount of additional additional granodioritic granodioriticto to granitic granitic material material that that may be be included included in in the the bulk bulk composition composition is is constrained to less than 5% of the total. More More than this will drop the mg# of the bulk composition F079 olivine at the base of the intrusion. composition to to less less than than what what could couldhave havecrystallized crystallized the theFo79 Based Based on on the the relative relative map map areas, areas,the the volume volume of of felsic felsicmaterial materialappears appearsto tobe bemuch muchtoo toogreat greatrelative relative to to the the amount amount of of mafic mafic material materialto tohave have been been derived derivedfrom fromSLI SLIdifferentiation. differentiation. To To test test whether whether this this apparent apparent disproportion disproportion of felsic felsic to to mafic material is is evident evident in the the third dimension, dimension, gravity gravity and and aeromagnetic aeromagnetic data data were were modelled modelled along along aa traverse traverse over overthe the SLI SLIand and Finland Finland granite (Line A, Fig. 1). lIthe km thick thick beneath beneath the the Finland If theSLI SLIisisassumed assumedtotobe beatatleast least11km granite, the magnetic and and gravity gravity models models constrain constrain the the granite granite and and granodioritic granodioriticmaterial material to to extend extend to a depth of at least 1.5 krn at its thickest point, adjacent to the fault/diabase along its SE SE margin 1.5 km (Fig. 1). AAbest bestfit fitof ofthe thegravity gravityand andmagnetic magnetic data data for for such such aa volume volume of of felsic felsic material material is is produced produced with with relative relative proportions proportions of of mafic mafic to to felsic felsic material of about 1:1 1:1 and thereby indicates that the granitic rocks rocks are are not not upper upper differentiates differentiates of of the the SLI. SLI. In conclusion, conclusion, the the SLI SLIisis temporally temporally and and genetically genetically distinct distinct from from other otherbodies bodiescurrently currentlyknown known to comprise the Beaver Bay Complex. ItIt was emplaced beneath beneath a cap cap of the granitic to was emplaced granodioritic rocks of the Finland granite. (Because are compositionally compositionally similar similar (Because these these felsic felsic rocks rocks are to what a siliceous siliceous differentiate differentiate of the SLI SLI would would be, be, the the amount amount of assimilation assimilation is is difficult difficult to to estimate. Perhaps body Perhapsisotopic isotopicdata datamay may reveal reveal the the extent extent of of assimilation.) assimilation.) The Thedifferentiated differentiatedbody which provides the the genetic genetic link link between between the the evolved evolved Silver Silver Bay Bay intrusions intrusions and and the the Beaver Beaver River River diabase diabase isis not not the the older olderSLI SLIand andremains remains unknown. unknown. - ACKNOWLEDGEMENT: ACKNOWLEDGEMENT:Quadrangle-scale Quadrangle-scalegeologic geologicmapping mappingininnortheastern northeasternMinnesota Minnesotahas hasbeen been conducted conducted by by the the Minnesota Minnesota Geological Geological Survey Survey over over the past 5 years with support support from from the the U.S. Geological Geological Survey's Survey's COGEOMAP COGEOMAPprogram. program. Miller, Miller,J.D., J.D., Jr., Jr., 1988, 1988,Geologic Geologicmap map of of the the Silver SilverBay Bay and and Split SplitRock Rock Point Point NE NE quadrangles, quadrangles,Lake Lake County, County,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousMap Map M-65. M-65. Miller, Inst.on onLake Lake Miller, J.D., J.D., Jr., Jr., 1989, 1989,Geology Geology of of the theBeaver Beaver Bay Bay Complex, Complex,northeastern northeasternMinnesota. Minnesota. Inst. Superior SuperiorGeology, Geology,35th, 35th,Duluth, Duluth,Minnesota, Minnesota,p.p.56-58. 56-58. Neilsen, R.L., 1988, 1988,TRACE.FOR: TRACEFOR: A A program for for the calculation calculation of combined major and trace element liquid liquid lines linesof of descent descentfor fornatural naturalmagniatic magmaticsystems: systems: Computers Computers& &Geosciences, Geosciences,v.v.14, 14,p.p.15-35. 15-35. Roeder, Olivine-liquid equilibria: Contributions Contributions to Mineralogy and Roeder, P.L. and and Emslie, Emslie, R.F., 1970, 1970,Olivine-liquid Petrology, Petrology, v. v. 29, 29, p. p. 275-289. 275-289. Rogge, Rogge, M.K., M.K., 1989, 1989,Geochemistry Geochemistryof of the the Sonju Sonju Lake Lake layered layered maflc mafic intrusion: intrusion: Unpub. Unpub. M.S. thesis, Iowa Iowa State State University, University, 92 92 p. p. Shank, Shank,S.G., S.G., 1990, 1990,The Thepetrology petrologyof ofthe theBeaver BeaverBay BayComplex Complexnear nearSilver SilverBay, Bay,northeastern northeasternMinnesota: Minnesota: Unpub. Unpub. M.S. M.S. thesis, thesis,University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,130 130p.p. Stevenson, Stevenson,R.J., R.J., 1974, 1974,A Amafic maficlayered layered intrusion intrusion of of Keweenawan Keweenawanage age near near Finland, Finland, Lake Lake County, County, Minnesota MinnesotaUnpub. Unpub. M.S. M.S. thesis, thesis,University Universityof of Minnesota, Minnesota,Minneapolis, Minneapolis,160 160p.p. Weiblen, inWold, Wold,R.J., R.J., and andHinze, Hinze,W.J., W.J.,eds., eds., Weiblen, P.W., P.W., 1982, 1982,Keweenawan Keweenawan intrusive intrusive igneous igneousrocks, rocks, in Geology Geology and and tectonics tectonicsof of the theLake LakeSuperior SuperiorBasin: Basin: Geol. Geol.Soc. Soc.America AmericaMemoir Memoir156, 156,p.p.57-82. 57-82. 67 �0 .i C) I CD'< SD 3 =3rD _.l CD ° S a D (fl • • q- I0 ;QC)—u)CD 3 CDCD a I Z E COMPLEX BAY BEAVER II CD 0 CD CDCD . D — I o '< OCD.1 CD —. — CD1 o-t—. 0 r1 snInwno Cumulus MineraIqy A6oIeieuM ivaov SNOIIVIUVA MODAL VARIATIONS us ueiej SLI Parent flNOS 3NV1 NOISfl}LLNI 'COFAp - .- .- .- .CFOP PCFO me.- ee;ooioe OUIA!IO TABLE of SL1 aiavJ. 1. •i Compositions i-is suorlisoduloD jo parent magma pu average t?WW and 9g.IAg iOA9 River 1A!I diabase Beaver PCFo CD - O!6fl Si02 ZO!S Ti02 QJj A1203 EOlV FeOt oe C*14 hhQ 81P 47.8 2.06 9O 14.8 8t'I. $C1. 13.4 610 0.19 06L 7.90 56 9.5 2.61 0.55 550 0.30 OCO P066 99.04 cc:a ON L9 NZO CeY4 o K20 SOd P205 TOTAL 1VIOI (Oei9)#6W css (oe6)#w 6C5 E BQ E1 C8P 48.3 II.39 6C• 1.91 16.1 13.2 LIO 0 .f7 1.18 8.11 501. 10.5 2.27 CC0 0.33 0.14 SPO0L 100.45 C1 l.O t9S 6PS PC0 U-eJ S9PIXO S PC0 CD OiU086! Li eedv s!sesose4 J3 01. 00 65 1.91. 1.9 IN Cli 591. 061 81. 6 S LL A JZ 9L1. £01. iH 6 90 E 4 :rne UOSUOf85 'L6I 0860U 6861 3 epJap qndun) (wp S!qj .L APIMS E 0 a 0 0 w 0 0 * 0 N 0 Cumulative Mode aAtenwn3 apo jo the Sonju uoisnziui showing F I G W 2. oiqdi2nn Stratigraphic profile aunou jijoid of nfuo Lake intrusion 2U!MoqS LBPOW SfllflWflO mineralogy, SEAjOIUI modal variations, 'SUOIWUA cumulus 'i(20J!19U1W and compositon UOUSOdWO3 intervals jo the qi intrusion uoisn.nui (Table summed to the bulk pwuins o determine 9uiuuop qi nq composition uowsodwo3 of ojqfl 1,'j OjO4At rock poi analyses averaged o represent SLI iiuoij Parent). Number ris .ioqwnj of Jo whole Oul0A to uosaidai JO LJ3 EA.I1U! is Si noted. pou the composition each interval 9I UOTUSOdLUOO of su 89 191. 1. fl 80 Ui. 51. El P•I. eo 0C WS n3 qj• 91. C$'I OOZ 1.8 C 9• 1.0 50 LI. I.1. I9 IC CI 1.1. 10 p.O c.0 qA ni L E I I — CD — — �I MESOSCOPIC MESOSCOPIC EVIDENCE EVIDENCE FOR FOR B1 Bl DEFORMATION DEFORMATION IN IN LOWER LOWER PROTEROZOIC PROTEROZOIC SUPRACRUSTAL ROCKS NEAR NEAR ROCHFORD, ROCHFORD, SOUTH SOUTH DAKOTA. DAKOTA. SUPRACRUSTAL ROCKS Patrick Patrick Mohn Mohn and and William William J. J. Gregg, Greggl Department Department of of Geological Geological Engineering, Engineeringl Geology, GeologyI and and Geophysics, GeophysicsI Michigan Michigan Technological Technological University, Universityl Houghton, Houghton, MI MI 49931 49931 Introduction Introduction The located in in the the Precambrian Precambrian is located The Rochford Rochford mining mining district district is core 25 miles (40 (40 core of of the the Black Black Hills Hills Uplift, U~lift.approximately a ~ ~ r o x i m a t e l25 v miles kin) west of Rapid City, South Dakota (Figure 1A). Highly deformed lower Proterozoic rocks underlie most of the area and include slate, phyllite, and schist intercalated with metavolcanics, metagabbro, metachert, and various facies of meta—iron formation (Dewitt and others, 1986). Previous work in the area includes several recent )I.S. theses and an extensive mapping effort by the U.S.G.S. in the late 1960's, which culminated with the publication of the first comprehensive geologic map of the district by Richard Bayley in 1972. Structural interpretations thus far have been based primarily on a preferred stratigraphic sequence which was originally proposed by Bayley (1972), based on correlations with a key unit in the Lead district to the north (Ellison Formation at Lead correlated with the Moonshine Gulch Quartzite at Rochford) and also on two available age dates of intercalated volcaniclastic units within the two areas. The present study involved detailed structural/lithologic mapping of an area about 2 miles southwest of the town of Rochford, located in Pennington County, South Dakota. Our objective was to delineate the nature of major structural features within the map area. To accomplish this task, the cornerstone of our field technique involved using fold overprinting relationships to classify and map mesoscopic fabric elements. In addition, detailed lithologic mapping was carried out utilizing a distinctive biotite—garnet phyllite unit as a structural marker horizon. Descriptive structural geoloc!v Style is defined defined by by the the macroscopic macroscopic outcrop outcrop pattern pattern Style group group B. Bl is of of the the biotite-garnet biotite-garnet phyllite phyllite unit unit and and by by mesoscopic mesoscopicB1 Bl folds folds observed observed at at three three key key localities localities within within the the field field area. B l folds folds observed observed in in outcrop outcrop and and also also on on the the area. B1 macroscopic macroscopic scale scale are are tight tight to to isoclinal. isoclinal. Structural Structural analysis analysis of of B1 B l folds folds on on aa mesoscopic mesoscopic scale scaleis isimpossible, impossiblel since since very very few few first first generation generation fabric fabric elements elements were were preserved presemed in in the thefield fieldarea. area. However, Howeverl based based on on the the predominant predominant southeasterly southeasterly plunge plunge of of L2 L2 bedding-cleavage bedding-cleavage intersection intersection lineations, lineationsl the the first first system system of of folds foldsmay may have have trended trended east-west, east-west, with with steeply steeply south-dipping south-dipping axial axial surfaces. surfaces. 69 1 �___ I I Style group group B2 B2 folds foldsrefold refoldolder olderB.1 Bl structures or bedding bedding Style structures or ( S o ) and and are are observable observable on on both both the the macroscopic macroscopic and and (S0) mesoscopic scales. B2 folds are open to tight, with mesoscopic scales. B2 folds are open to tight, with aa pervasive axial plane foliation (S2) (S2) defined defined by by parallel parallel pervasive axial plane foliation preferred-orientation of mica particles. S2 foliation The preferred-orientation of mica particles. The S2 foliation strikes northwest and dips steeply to the northeast and is strikes northwest and dips steeply to the northeast and is the dominant structural fabric throughout the Rochford the dominant structural fabric throughout the Rochford Both B2 B2 fold fold axes axes and and L2 L2 cleavage-bedding cleavage-bedding district. Both district. intersection lineations plunge to the southeast. intersection lineations plunge to the southeast. Third generation generation (B3) (B3)structures structures are are present present throughout throughout the the Third field area and consist of moderately to strongly developed field area and consist of moderately to strongly developed S2cleavage cleavagesurfaces. surfaces. Elements Elements associated associated crenulationson on S2 crenulations with style group B3 are the S3 crenulation cleavage and the the with style group B3 are the S3 crenulation cleavage and S3 planes strike to the L3 crenulation lineation. L3 crenulation lineation. S3 planes strike to the L3 wrinkle wrinkle northeast and and dip dip to to the the south, south, whereas whereas the the L3 northeast \'4K \\ \ IWEX MAP INDEX MAP SOUTH DAKOTA BLACK n u s SOUTh DAKOTA BLACK HILLS I PHANEROZOIC ROCKS LAINCI COUNTY ROGNPORO STUDY AREA RAPID CITY • PRECAMBRIAN CORE KEYSTONE :: PINUSNSTON COUNTY CUSTIN COUNTY CUSTER o I m I P. MOHN 3190 1A Figure 1 Figure 1. lB 1 Index map map of of the the South South Dakota Dakota Black BlackHills HillsCiA), (lA), Index and a sketch of fold overprinting relationships and a sketch of fold overprinting relationships (IB)as as observed observed on on the the back back of of aa mine mine adit adit C1B) located in the southern part of the field area. located in the southern part of the field area. Heavy stippled pattern shows a Bl isoclinally Heavy stippled pattern shows a B isoclinally by B2, B2,with with the the folded chert chert bed bed refolded refolded by folded The I11 interference pattern. resulting type resulting type III interference pattern. The sketch is a pen and ink tracing of a sketch is a pen and ink tracing of a photograph. photograph. 70 I �I lineation lineation plunges to to the the southeast, southeast, roughly parallel to to L2 L2 lineations. lineations. With the the exception exception of local local reversals reversals of of the the plunge direction direction of of L21B3 LZtB3deformation deformation had little little effect effect on on plunge the the orientation orientation of of major major structures structures within within the the map map area. area. Conclusions Conclusions The The results results of of our our detailed detailed work work show, showt at least least within within the the confines confines of of the the map area, area, that that there there is is aa reversal reversal of of the the stratigraphic stratigraphic rock rock sequence sequence proposed proposed by Bayley Bayley (1972) (1972) for for the the area area on on the the western western edge edge of of the the Rochford Rochford anticlinorium, anticlinorium, where where the the present present study study was was undertaken. undertaken. Secondly, Secondlyt distinctive distinctive first first generation generation (B1) (Bl)folds folds were were observed observed both both on scalet which which on the the mesoscopic mesoscopic scale scale and and on on the the macroscopic scale, is defined by the outcrop pattern of the biotite-garnet phyllite I11 interference interference patterns patterns phyllite marker marker horizon. horizon. Type Type III were were produced produced as as aa result result of of overprinting overprinting by aa later later fold fold generation generation (B2) (B2) which which was was non—coaxial non-coaxial to to the the first— firstgeneration generation B1 Bl folds folds (Figure (Figure lB). 1B). AA third third phase of of folding folding is well—developed is evident evident based on the the presence of a locally locally well-developed crenulation crenulation cleavage cleavage (S3). (S3). This This crenulation crenulation cleavage cleavage overprints B2 mesostructures mesostructures in in the the study study area. area. overprints B2 To To the the best best of of our our knowledge, knowledge, the the delineation delineation of of first first generation generation (B1) (Bl)structures structures and and the the distinctive distinctive structural structural overprinting in the the map area area are are the the overprinting relationships relationships observed observed in first in the the Rochford Rochford district. district. first such such examples examples documented documented in The The structural structural relationships relationships we we propose propose for for the the map map area area are are in in general general agreement agreement with with those those proposed proposed by Redden Redden and and French French (1989) (1989) for for the the central central Black Black Hills Hills near near Mystic, Mystict thereby thereby indicating indicating that that similar similar techniques techniques of of structural/lithologic structural/lithologic mapping mapping may be be successfully successfully applied applied to to other other areas areas in in the the Precambrian Precambrian terrane terrane of of the the Black Black Hills. Hills. References References Bayley, Bayleyt R.W., R.Wat 1972 1972 AA preliminary preliminary report report on on the the geology geology and and gold gold deposits deposits of of the the Rochford Rochford district, district, Black Black Hills, Hills, South South Dakota: Dakota: U.S.G.S. U.S.G.S. Bull. Bull. 1332-A. 1332-A. E., J.A. J.A. Redden, Reddent A.B. A.B. Wilson Wilson and and David David Buscher, Buscher, 1986 1986 Dewitt, E., Dewitt, Mineral resource resource potential potential and and geology geology of of the the Black Black Hills Hills Mineral National National Forest, Forest, South South Dakota Dakota and and Wyoming: Wyoming: U.S.G.S. U.S.G.S. Bull. Bull. 1580. 1580. Redden, Redden, J.A. J.A. and and G.M. G.M. French, French, 1989 1989 Geologic Geologic setting setting and and potential exploration exploration guides guides for for gold gold deposits, depositst Black Black potential Hills, Hills, South South Dakota: Dakota: in in United United States States Gold Gold Terranes. Terranes, Part Part U.S.G.S. I, U.S.G.S. Bull. 1857-B; D.R. Shawet R.P. Ashley, and Bull. 1857-B; D.R. Shawe, R.P. Ashley, and L.M.H. L.M.H. Carter, Carter, eds. eds. , 71 �I THE PHYSICAL PHYSICAL VOLCANOLOGY VOLCANOLOGY AND AND HYDROTHERMAL HYDROTHERMAL ALTERATION ALTERATION THE ASSOCIATED WITH WITH THE THE MASSIVE MASSIVE SULPHIDE SULPHIDE DEPOSITS DEPOSITS OF OF THE THE ASSOCIATED SOUTH STURGEON STURGEON LAKE LAKE AREA, AREAf NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO SOUTH R. L. L. Morton1, or ton' G. G. J. J. Hudak1, ~udak' J. J. S. S. Walker1, wa1kerTfand and J. J. M. M. Franklin2 ~ranklin' R. The south south Sturgeon Sturgeon Lake Lake area area of of northwestern northwestern Ontario Ontario is is The underlain underlain by by aa well well preserved preserved Archean Archean submarine submarine caldera caldera which which is is approximately30 30Km Kmin instrike strikelength. length. Within Within the the caldera caldera five fiveash ash approximately flow flow tuff tuff units units have have been been recognized, recognizedfand and these these range range from from 100 100 to to more than than 1200 1200meters meters in instratigraphic stratigraphicthickness. thickness. The The ash ash flow flow more units units vary vary from from massive massive and and pumice-rich pumice-rich to tobedded. bedded. Commonly, Commonlyf quartz crystal-Ipumice—rich pumice-rich basal basal units units are are overlain overlain and and separated separated quartz crystal—, by well well bedded bedded ash ashunits. units. The The five five known known massive massive sulphide sulphide deposits deposits by (Mattabi, (MattabifF-Group, F-Groupl Sturgeon Sturgeon Lake, Lakel Lyon Lyon Lake, Lakel and and Creek Creek Zone) Zone) occur occur within within the the caldera caldera and and are are hosted hosted by by the the ash ash flow flow tuff tuff deposits. deposits. Associated Associated with with the the ash ash flow flow tuffs tuffs are are coarse coarse heterolithic heterolithic breccias breccias which which contain contain clasts clasts that that are are composed composed dominantly dominantly of of precaldera lithologies. lithologies. The The breccias breccias underlie, underliel and and locally, locallyf are are precaldera The breccias breccias vary vary from from 100 100 interlayeredwith, withfthe theash ashflow flowtuffs. tuffs. The interlayered to more more than than 750 750 meters meters in in thickness. thickness. Clasts Clasts in in the the breccia breccia vary vary to from from lapilli-sized lapilli-sizedto tolarge largeblocks blocksat at least least 100 100 meters meters in in diameter. diameter. The The five five ash ash flow flow units units indicate indicate five five separate separate periods periods of of explosive, silicic volcanism volcanism accompanied accompanied by by caldera caldera collapse; collapse; the the explosivelsilicic breccias breccias represent representmesobreccia mesobreccia deposits deposits formed formed from from material material which which slumped slumped into into the the caldera caldera during during and and after after each each caldera caldera collapse collapse episode occurred. occurred. episode Ore Ore forming forming hydrothermal hydrothermal activity activity was was associated associatedwith with at at least least four of of these these eruptive eruptiveepisodes. episodes. Early, Earlyf regional regional carbonatization carbonatization four of of the the rocks rocks is is cross-cut cross-cut by by alteration alteration assemblages assemblages containing: containing: a) a) iron carbonate carbonate ±2 iron iron chlorite; chlorite; b) b) chloritoid chloritoid ±& iron iron carbonate carbonate iron and/or iron iron chlorite; chlorite; c) c) aluminum aluminum silicates silicates (pyrophyllite, (pyrophyllitef and/or andalusite and/or and/or kyanite) kyanite) ++ chloritoid; chloritoid; and and d) d) aluminum aluminum andalusite, silicates. Aluminum Aluminum silicate silicate alteration alteration zones zones are are dominantly dominantly silicates. confined confined to to the the synvolcanic synvolcanic faults faults that that acted acted as as conduits conduits for for the the metallifer~us~ ore-forming hydrothermal hydrothermal fluids. fluids. These These zones zones lead lead metalliferous, ore-forming up massive suiphide turn, surrounded surrounded up to to the the massive sulphide deposits, depositsl which which are, aref in in turn1 by zones of of aluminum aluminum silicatel silicate, aluminum aluminum silicate semiconformable zones silicate ++ by seiniconforinable chloritoidf and and chloritoid chloritoid alteration. alteration. chioritoid, I Department, University University Economic Volcanology Volcanology Research Research Lab, Labf Geology Geology Departmentf Economic Duluthf Duluthf MN 55812 of Minnesota Duluth, MN 55812 Duluth, of Minnesota - * 2 Geological Geological Survey Survey of of Canada, Canadaf Minerals Minerals Resources Resources Division, Division, 601 601 Booth St., St., Ottawa, Ottawaf Ontario Ontario K1A-0E8 KIA-OE8 Booth I I 1 72 I �U GNI/ARGONNE LAKE LAKE SUPERIOR SUPERIOR SEISMIC SEISMIC DATA DATA TECTONIC RAMIFICATIONS OF GNI/ARGONNE M.G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey,3817 3817 Mineral Mineral M.G. Point Road, Road, Madison, Madison, WI 53705 Point 53705 A.B. Dickas, Dickas, Division Division of of Sciences Sciences and and Mathematics, Mathematics, University University of of WisconsinWisconsinA.B. Superior, Superior, Superior, Superior, WI 54880 54880 L.D. Reclamation Engineering Engineering and and Geosciences, Geosciences, Argonne Argonne National National L.D. McGinnis, McGinnis, Reclamation Laboratory, Argonne, Argonne, IL Laboratory, IL 60439 60439 U.S. Geological Geological Survey, Survey, W.F. Cannon, Cannon, Eastern Eastern Mineral Mineral Resources Resources M.S. M.S. 954, 954,U.S. W.F. National National Center, Center, Reston, Reston, VA VA 22092 22092 ABSTRACT Geologic analysis of of Grant-Norpac Grant-NorpacInc. Inc. (GNI)/Argonne (GNI)/Argonne reflection reflection seismic seismic Geologic analysis lines in in western Lake Superior Superior requires requires revision revision of of Middle Middle Proterozoic Proterozoic KeweenaKeweenalines western Lake wan wan stratigraphy, stratigraphy, tectonics tectonics and and basin basin evolution. evolution. The The seismic seismic diagrams diagrams were were prepreviously presented presented as as aa poster poster session session at at the the Duluth Duluth 1989 1989 ILSG ILSG Annual Annual meeting. meeting. viously The Isle Isle Royale Royale Fault Fault is is not not continuous continuous with with the the Douglas Douglas Fault. Fault. No No ververtical or high-angle reverse fault fault with displacement displacement more more than than 0.2 0.2 seconds seconds of of high-angle reverse two-way travel two-way travel time, time, roughly roughly equivalent equivalentto to500 500in, m, is is seen seen to to cross cross Grant-NorGrant-Norpac/Argonne Line-08. Line-08. If If there there is is aa fault, fault, it it does does not not express express itself itself as as highhighangle, angle, but but it it could could be be aa thrust thrust fault, fault, and and as as such such is is not not evident evident in in the the seismic data. seismic data. The The Bayfield Bayfield Group Group rests rests with with strong, strong, regional regional angular angular unconformity unconformity on on the the Oronto Oronto Group, Group, which which has has lost lost up up to to one-half one-halfits its thickness thickness as as aa result result of of eroerosion prior to sion to deposition deposition of of the the Bayfield Bayfield Group. Group. Western Lake Western Lake Superior Superior consists consists of of two two distinct distinct basins basins separated separated by by an an ArArchean-cored ridge western volcanic/sedimenvolcanic/sedimenchean-cored ridge (the (the locus locus of of GLIMPCE GLIMPCE Line-C). Line-c). The western herein named the tary basin is is herein the Claude Claude Jean Jean Allouez Allouez Basin Basin (informally (informally referred referred to as the Allouez Basin); the the eastern eastern basin, basin, the the Jacques Jacques Marquette Marquette Basin Basin (infor(inforBasin); and the intervening ridge, ridge, the mally referred referred to to as the Marquette Basin); Walter White Walter White Ridge Ridge (informally (informally referred referred to to as as the the White White Ridge). Ridge). Each Each basin basin conconsists of multiple volcanic successions successions overlain overlain by aa transgressive transgressive Oronto Oronto sesebasins, and quence which filled filled the the two two basins, and ultimately ultimately covered covered the the White White Ridge., Ridge., Seismic The The Oronto Oronto in in turn turn is is unconformably unconformably overlain overlain by by the the Bayfield Bayfield Group. Group. Seismic cross lines cross lines define define stratigraphic stratigraphic relations. relations. Seismic Seismic form form lines lines in in the the Portage Portage Lake Volcanic Group Group suggests suggests abundant abundant intra-formation intra-formation sedimentary sedimentary units, units, and and supports continuity supports continuity of of the the Greenstone Greenstone Flow Flow from from Isle Isle Royale Royale to to the the Keweenaw Keweenaw Peninsula. Peninsula. It may be possible to define the the lateral lateral extent extent of of the the Oak Oak Bluff Bluff Formation (formerly Formation (formerly the the unnamed unnamed formation formation of of Johnson Johnson and and White, White, 1969). 1969). These relationships These relationships strongly strongly support support aa fundamental, fundamental, rift-unit rift-unitframework framework of of The isolated basins separated isolated basins separated by by syndepositional syndepositional accommodation accommodation structures. structures. The Walter White Ridge Ridge is is the the first first direct direct evidence evidence of of accommodation accommodation structures structures being associated associated with with the the Midcontinent Midcontinent Rift Rift System. System. This work work was Department of of Energy, Energy, Office Office of of Energy Energy supported by by the the 'U.S. U.S. Department This was supported Research, under Research, under Contract Contract W-3l-109-ENG-38. W-31-109-ENG-38. 73 �I Ii ^ I Reference cited: cited: Reference I Johnson,R..F., R.F., and W.S., 1969, 1969, Preliminary Preliminary report on the bedrock geology Johnson, and White, White, W.S., report on the bedrock geology and copper deposits of the Matchwood quadrangle, Ontonagon County, and copper deposits of the Matchwood quadrangle, Ontonagon County, Michigan: U.S. Geological Survey open-file report, 31 p. Michigan: U.S. Geological Survey open-file report, 31 p. ^I 100 0 t_____1 kilometers kilometers Locationof of seismic seismic profiles profiles and and Isle Isle Royale Royale and and Douglas Douglas Faults Faults Location u C) M rIm-. I 2 SW SW Allouez Basin Basin Allouez ;3 0 Walter Walter White White I Ridge Ridge 0 Lfl -1- z z 0 00 I I Marquette Basin Basin Marquette B 0 A A A 00 50 50 IÑÑÑà Archean? B-Bayfield,0—Oronto 0-Oronto B—Bayfield, V,A Keweenawan VolcanicRock Rock V,AKeweenawan Volcanic 7' 1' kilometers kilometers GNA-08(prepared (preparedby by A. A. Dickas Dickasand and M. M. Mudrey, Mudrey,1989) 1989) Interpretationof of CNA-08 Interpretation 74 NE I I I I I I I I I I I I I I I �Constraints on Archean Archean versus versus Proterozoic Proterozoic deformation deformation in in Constraints Archean Archean Rocks of the the Negaunee Negaunee area, area, Upper Upper Michigan Michigan Scott A. Scott A. Nachatilo Nachatilo and and Robert Robert 1.L.Bauer, Bauer,Department Department of of Geological Sciences, Geological Sciences, University University of Missouri, Missouri, Columbia, Columbia, Missouri Missouri 65211 6521 1 The Negaunee Negaunee area area of Michigan's Michigan's upper upper Peninsula Peninsula contains contains deformed Archean Archean greenstones and and metasedimentsof of the the Northern metasediments Northern Complex Complex as well well as asProterozoic Proterozoic metasediments metasediments along along the the northern margin margin of of the Marquette northern Marquette syncline and the southeastern southeastern end of the the Dead Dead River RiverBasin. Basin. Although the Proterozoic Although the Proterozoic rocks rocks of the the area area were were obviously obviously deformed deformed during during the the Penokean Penokean Orogeny, the effects Orogeny, the effects of this this event event on on the theadjacent adjacent Archean Archean rocks rocks are are unclear. unclear. The regional regional foliation foliation trends in in both both the the Archean Archean and andProterozoic Proterozoic rocks rocks are aresubparallel subparallel (vertical, (vertical, striking striking Ca. N.700 70° W.), W.), and the principle ca. N. principle axes axes of of finite finite strain strain measured measured ininprevious previous studies studies (Carter, (Carter, 1989 and Westjohn, Westjohn, 1978) are also nearly parallel in the the Archean Archean and and Proterozoic Proterozoic rocks. rocks. We have analyzed deformation fabrics and finite strains (Rf/phi technique) from analyzed deformation fabrics and finite strains technique) from Archean Archean rocks of of the Kitchi rocks Kitchi Schist Schist and and the the Mona Mona Schist Schist in in an an effort effort totoevaluate: evaluate:(1) (1)the thedeformation deformation sequence in the Archean sequence in Archean rocks, rocks, and and (2) (2) the the degree degree totowhich whichProterozoic Proterozoic deformation deformation has has effected the Archean rocks. As As aalocal localstandard standardof ofcomparison, comparison,we we have haveanalyzed analyzedthe the geometry geometryof of Proterozoic folding folding in the Goodrich Proterozoic Goodrich Quarztite Quarztite and lower lower units units of of the theMichigamme Michigamme Formation Formation along the southeastern margin margin of of the the Dead River River Basin. Basin. Our Our analysis analysis indicates indicates that Proterozoic Proterozoic deformation did not effect effect Archean Archean rocks rocks in in aaductile ductilefashion. fashion. The oldest Archean generated an an L to LS Archean deformation generated LS fabric fabric with with aasteeply steeplyplunging plunginglinear linear axis in the Kitchi Kitchi Schist Schist south of the Dead Dead River Basin. The The planar planar aspect aspect of of the the fabric fabricdefines defines aa locally well well developed vertical foliation foliation striking striking N. N. 700 70° W. locally developed vertical W. that that is is prominent prominent in the the clastic clastic units of both units both the the Kitchi Kitchi Schist Schist and andespecially especially the the Mona Mona Schist Schist throughout throughout the the region region (Figure (Figure 1A). Finite IA). Finite strains strains that we believe believe were were generated generated primarily primarily as a result result of of this thisdeformation deformation were in the of the Kitchi were measured measured in the agglomerates agglomerates of Kitchi Schist Schist and and show show slightly slightly prolate prolate strain strain principle ellipsoids ellipsoids with with the the maximum maximum (X), (X), intermediate intermediate (Y), (Y), and and minimum minimum (Z) (2) principle axes axes vertical, E-W, 2A and vertical, E-W, and N-S, N-S, respectively respectively (Figure (Figure 2A and 3). 3). Strain Strain analyses analyses from from the the Kitchi Kitchi Schist and the adjacent and the the dominant dominant N. N. 70° adjacent Mona Schist (Carter, 1989), and 700 W. W. foliation foliation are are consistent N- to to NNE-directed NNE-directed shortening shortening during during this this event. event. Sparse Sparse folds folds with with E-W E-W consistent with with Ntrending trending axial planes planes occur occur in the the Nealy Nealy Creek Creek (NC) (NC) and and sheared sheared rhyolite rhyolite tuff tuff (srt) (srt) members members of the Mona Mona Schist Schist north north of of the the Dead Dead River River Basin Basin where where the the dominant dominant foliation foliation orientation orientation is These folds that plunge roughly E-W. roughly E-W. These folds have have variable variable hinge-line hinge-line orientations orientations that plunge shallowly shallowly to moderately east east and west. Stretching lineations moderately west. Stretching lineations in these these same same rocks rocks show show aa similar similar distribution, also plunging plunging to to both both the the east east and west. west. We distribution, also Webelieve believethat that these theselineations lineations and and the the sparse folds folds may have have been been reoriented reoriented during a second second period of deformation deformation that is is variably variably partitioned into the NC and srt members members of the the Mona Mona Schist. Schist. The second produced aa set of conjugate cleavages that that are locally second deformation produced conjugate crenulation cleavages developed in the highly foliated NC and sri srt members members of the Mona Mona Schist. Schist. Although some of of the crenulations occur in an area mapped as a broad zone of shear, they also occur several crenulations occur in an area mapped as broad zone of shear, they also occur several Crenulations kilometers outside parts of of the the NC NC member member that that are are not not sheared. sheared. Crenulations kilometers outside of of this zone in parts with axial planes planes that that strike strike NNW-SSE NNW-SSE have "S" asymmetry asymmetry while those with axial axial planes planes that that strike roughly E-W E-W have have "Z" "2" asymmetry asymmetry (Figure (Figure 18). 16). The concomitant concomitant generation generation of these these strike roughly orientations requires that that the the greatest greatest principle principle stress stress be be at a low orientations requires low angle angle to to the the earlier earlierfoliation foliation planes and coincident coincident with the the bisector bisector of of the theangle anglebetween betweenthe theconjugate conjugatecleavage cleavageplanes planes consistent with with this (Cosgrove, 1976); 1976); only only aa NW-directed (Cosgrove, NW-directed compression compression is is consistent this geometry. geometry. Strain analyses analyses of of crenulated samples from from the the srt srt member Strain crenulated samples member are also consistent consistent with NW-SE NW-SE 75 �I: I I directed shortening. shortening. In directed In these these samples, samples, the the XV XY principle principle plane plane of of the the finite finitestrain strainellipsoid ellipsoid isis steeply steeply dipping, dipping, NE-striking, NE-striking, and and normal normal to the the direction direction ofofshortening shortening estimated estimated from from crenulation crenulation axial axial planes planes (Figure (Figure 2B). 2B). We Webelieve believethis thissecond seconddeformation deformation isisalso alsoofofArchean Archean age, age, because becauseNW-directed NW-directedcompression compression is is not not observed observed in inthe theProterozoic Proterozoicrocks rocksof ofthe theregion. region. For For instance, instance, regional regional folding folding of of the theProterozoic Proterozoic Goodrich Goodrich Quartzite Quartzite and and the the lower lowerpart partofof This fold orientation the Michigamme Formation is about a N. 700 W. axial plane (Figure 1C). the Michigamme Formation is about a N. 700 W. axial plane (Figure 1C). This fold orientation and the the associated associated axial axial plane planefoliation foliation requires requires aaNN-totoNE-directed NE-directedcompression. compression. Similarly, Similarly, and strain strain analyses analyses from from reduction reduction spots spots ininthe theProterozoic ProterozoicKona KonaFormation Formationwithin within the theMarquette Marquette syncline compression. These 1978) show show no no evidence evidence of NW-directed NW-directed compression. These data data yield yield an an syncline (Westjohn, (Westjohn, 1978) E-W E-W striking striking XV XY principle principle plane plane of of finite finite strain strain (Figure (Figure 2B) 2B)indicative indicative of ofNN-totoNE-directed NE-directed (1978) reports reports sparse sparse late-stage late-stage kink kink bands bands ininthe theProterozoic Proterozoic shortening. Although Although Klasner Klasner (1978) shortening. Michigamme with near W., he he Michigamme Formation Formation with near vertical vertical kink kink planes planes striking striking N. N.200 200E. E.and and N. N. 50° 500 W., attributes blockuplift upliftof ofthe theArchean ~ r c h e abasement. nbasement. attributes these these to to late-stage late-stageblock Kitchi Schlst Schist Kitchi Crenulatlon Crenulation Cleavage Cleavage Fabrics Fabrics N N Compression • :: 8 B. I I I I Proterozoic Fold Fold Geometry Geometry Figure 1. 1. Archean Archean and and Proterozoic Proterozoic fabric fabric data. A. Poles Poles to to foliation foliation data. A. (crosses) (crosses) and and lineation lineation orientations orientations (triangles). 8.Poles Poles to tocrenulation crenulation (triangles). B. S" asymmetry cleavages; (circles), cleavages; "S" asymmetry (circles), Z" *Z"asymmetry asymmetry(triangles). (triangles). Hinges Hinges of of crenulation crenulation cleavage cleavage (crosses). (crosses). C. C. Proterozoic Proterozoic fold fold geometry; geometry; poles poles to to N N bedding bedding (circles), (circles), poles poles to to axial axial (crosses), foliation planar planar foliation (crosses), (Small line intersection intersection l i n eat a t ion ion (small triangles), and and best-fit best-fit Pi-axis Pi-axis orientation orientation from from poles poles to to bedding bedding (large (large triangle). triangle). 11 76 �InInsummary, Proterozoic summary,although althoughthe theregional regionaltrend trendofofthe thedominant dominantArchean Archeanand and Proterozoicfoliations foliations isissubparallel, subparallel, the theorientation orientationofofsecond seconddeformation deformationconjugate conjugatecrenulation crenulationcleavages cleavagesininthe the Archean Archean rocks rocks isisincompatible incompatible with withthe thedeformation deformation features features recognized recognized in inthe theadjacent adjacent Proterozoic second deformation Proterozoicrocks. rocks. These Thesedata datatherefore thereforesuggest suggestthat thatthe thefirst firstand and second deformationfeatures features we weobserve observeininthe theArchean Archeanrocks rocksof ofthis thisarea areawere werenot notimposed imposedby byProterozoic Proterozoicdeformation. deformation. Carter, Carter, P.J. P.J.Jr., Jr.,1989, 1989,Finite Finitestrain strainestimates estimatesfor forArchean ArcheanMona MonaSchist Schistpillows pillowsand andEnchantment EnchantmentLake Lake Formation Unpublished M.S. Formationmetawackes metawackesininthe theeastern easternupper upperpeninsula peninsulaofofMichigan: Michigan: Unpublished MS.Thesis, Thesis, MichiganState StateUniversity, University,East East Lansing Lansing Ml., MI., 97 97p.p. Michigan Cosgrove Cosgrove,J. ,J.W., W., 1976, 1976,The Theformation formationofofcrenulation crenulationcleavage: cleavage:Jour. Jour.Geol. Geol.Soc. Soc.Lond., Lond.,vol. vol.132, 132.p.p. 155-1 78. 155-1 78. Klasner, Klasner,1978, 1978,Penokean Penokeandeformation deformationand andassociated associatedmetamorphism metamorphismininthe thewestern westernMarquette Marquette Range, northern northernMichigan: Michigan: Geol. Geol. Soc. Soc. Amer. Amer. Bull., Bull.,vol. vol.89, 89,p.p.711-722. 711-722. Range, Westjohn, D.B., 1978, 1978,Finite Finitestrain strainininthe thePrecambrian PrecambrianKona KonaFormation, Formation,Marquette MarquetteCounty, County,Michigan: Michigan: Westjohn, D.B., UnpublishedM.S. M.S. thesis, thesis, Michigan MichiganState StateUniv., Univ.,East EastLansing LansingMl., MI.,72 72p.p. Unpublished Principle Principle Axes Axes of of Finite FiniteStrain, Strain, Principle ofFinite FiniteStrain, Strain, Principle Axes Axes of Archean (Crenulated) and Archean (Crenulated) and Kitchiand andMona MonaSchist Schist Kitchi Proterozoic ProterozoicRocks Rocks N N FIgure Figure 22(above). (above). Principle Principle axes axes of of finite finite strain, A. strain, Archean Archean and andProterozoic Proterozoicrocks. rocks. A. X,Y, X,Y, and and ZZaxes axesfrom fromthe theKitchi KitchiSchist Schistare are open open circles, circles, open opensquares, squares, and andtriangles triangles (this X, Y, Y, and and ZZaxes axesfrom fromthe the (thisstudy). study). X, Mona Mona Schist Schist are areshaded shadedcircles, circles,shaded shaded squares, squares, and andcrosses crosses(Carter, (Carter,1989). 1989). B. B.X,X, Y, axesfrom fromthe thecrenulated crenulatedArchean Archean Y, and andZZaxes Mona Mona Schist Schist (srt (srtmember) member)are areopen opencircles, circles, open open squares, squares, and andtriangles triangles(this (thisstudy). study). X,X, Y, Y, and and ZZaxes axesfrom fromthe theProterozoic ProterozoicKona Kona Formation Formation are are shaded shaded circles, circles, shaded shaded squares, squares, and and crosses crosses(Westjohn, (Westjohn, 1978). 1978). Figure Figure 3 3 (left). (left). Log Log Flinn Flinn plot plot of of finite finite strains strains from from the the Kitchi KitchiSchist Schist(triangles) (triangles) (this (this study), study), Mona Mona Schist Schist (crosses) (crosses) (Carter, (Carter, 1989), 1989), srt srt member member of of Mona MonaSchist Schist (circles) (circles) (this (this study), study), and and the theProterozoic Proterozoic Kona Kona Formation Formation(squares)(Westjohn, (squares)(Westjohn,1978). 1978). Log Flinn Flinn plot plot of ofFinite FiniteStrains Strains Log / 0.5, 0.5 0.4 8 +0 0.3 3.. x 0 -J 0.0 0.1 Log(Y/Z) 77 �I MINING ACTIVITY IN IN EXPLORATION AND MINING NORTHWESTERN ONTARIO ONTARIO NORTHWESTERN ............................................................ 0' BRIEN, BRI EN, M. , RESOURCE RESOURCE GEOLOGIST, ONTARI 0 MINISTRY OF OF GEOLOGIST, ONTARIO NORTHERN NORTHERN DEVELOPMENT DEVELOPMENT AND MINES, MINES, THUNDER THUNDER BAY BAY S., S. m i n e r a l sector s e c t o r in i n Ontario O n t a r i o provided 25,962 d i r e c t jobs The mineral provided 25,962 direct jobs and produced produced materials m a t e r i a l s with w i t h a total t o t a l Canadian dollar d o l l a r value v a l u e of of $6,853,756,000 in i n 1988. 1988. This poster p o s t e r displays d i s p l a y s the t h e producing producing mines mines and and advanced advanced mineral mineral exploration e x p l o r a t i o n projects p r o j e c t s in i n the t h e Northwestern Region of the the Province Currently producing gold gold Province of of Ontario. Ontario. C u r r e n t l y there t h e r e are a r e 88 producing mines, 44 base b a s e metal metalmines1 mines, 6 6 stone s t o n e quarries., q u a r r i e s , and and 55 seasonal seasonal amethyst amethyst mines mines iin n tthe h e region r e g i o n employing employing 2152, 2152, 1133, 1133, 26 26 and 36 36 people There p e o p l e respectively. respectively. There are a r e also a l s o 22 22 projects p r o j e c t s in i nadvanced advanced exploration. exploration. In I n 1989, 1989, the t h e region r e g i o n produced produced approximately: approximately: 50,843 kg 50,843 kg (kilograms) ( k i l o g r a m s ) of gold; gold; 125,310 kg kg of silver; silver; 125,310 30,514,973 30, 514, 973 kg of copper; copper; 6,667,808 6, 667,808 kg kg of of nickel; n i c k e l ; 3,794,754 3,794, 754 kg kg of lead; for a a total t o t a l Canadian Canadian l e a d ; and and 112,799,350 112,799,350 kg kg of of zinc z i n c -- for dollar 225, 284, 402.RRepresentative d o l l a r value v a l u e of of $1, $1,225,284,402. e p r e s e n t a t i v e oore r e samples of of Northwestern Northwestern Ontario O n t a r i o are a r e also a l s o on on display. display. A A statistical s t a t i s t i c a l summary summary booklet b o o k l e t that t h a t tabulates t a b u l a t e s regional r e g i o n a l data data such s u c h as a s reserves, r e s e r v e s , grades, grades, location, l o c a t i o n , ownership ownership and and development development i s available a v a i l a b l e free f r e e of of charge c h a r g e in i n both b o t h English E n g l i s h and and French. French. is I I I I I I 78 I �I LOWER PROTEROZOIC PROTEROZOIC GLACIOGENIC GLACIOGENIC DEPOSITS: DEPOSITS: A NORTH BALTICCONNECTION? CONNECTION? NORTH AMERICA AMERICA -- BALTIC Richard W. Ojakangas, Ojakangas, Department Department of Geology, Geology, University University of of Minnesota-Duluth, Minnesota-Duluth, Duluth, Duluth, MN MN 55812, 55812, Jukka Jukka S. S. Marmo, Marmo, Geological Geological Survey Survey of of Finland, Finland, SF-02150 SF-02150 Espoo Espoo 15, 15, Geology, USSR Institute of Geology, FINLAND, I. Heiskanen, Heiskanen, Institute FINLAND, Kim Kim I. USSR Academy Academy of of Sciences, Sciences, Petrozavodsk, USSR. USSR. ABSTRACT Lower glaciogenic deposits deposits of of approximately the same age(?) Lower Proterozoic Proterozoic glaciogenic approximately the age(?) occur occur Baltic (Fennoscandian) in North North America America and and on the at several several localities localities in the Baltic (Fennoscandian) Shield Shield in in Finland Finland and in the the USSR USSR just just east east ofofFinland. Finland. The main main evidence evidence for aa glacial glacial history history is the association association of of fine-grained fine-grained laminated laminated units units containing containing oversized oversized lonestones lonestones (some (some clearly "dropstones"), "dropstones"), with diamictite diamictite (matrix-supported (matrix-supported conglomerate). conglomerate). associationhas has long long been This "diamictite-dropstone This "diamictite-dropstone laminite" laminite" association been known known in in the Huronian Supergroup Supergroup of of Ontario, Ontario, especially especially in the Gowganda Huronian Gowganda Formation Formation (e.g., (e.g., Young, Young, 1981), the slightly slightly older older Ramsey Ramsey Lake Lake and and Bruce BruceFormations. Formations. In the Upper Upper 1981), but but also in the Peninsula of of Michigan, laminite association associationisis present present in three Peninsula Michigan, the diamictite-dropstone diamictite-dropstone laminite units - the the Reany Reany Creek Creek (Puffett, (Puffett, 1969) 1969) and and Enchantment Enchantment lake lake (Gair, (Gair, 1981) 1981) Formations Formations of Range area area and and in in the theFern FernCreek CreekFormation Formation (Pettijohn, (Pettijohn, 1943) 1943) of of of the the Marquette Marquette Range southern Dickinson Dickinson County, to the the south south(Ojakangas, (Ojakangas,1984). 1984). All three Michigan Michigan southern County, 80 km to occurrences are the basal units occurrences are the basal units of the the Lower Lower Proterozoic Proterozoic rock rock column column at those those Similar deposits deposits are are known in southern west of Hudson localities. localities. Similar southern Wyoming, Wyoming, west Hudson Bay, Bay, and and in central central Quebec, Quebec, and and an an Early Early Proterozoic Proterozoic glaciation glaciation covering covering about about 55 million million km2 km2was was suggested by Young Young (1970). (1970). Such deposits deposits were recently discovered discovered in eastern Finland in the the Sariolian Sariolian Group Group the Karelian Karelian Supergroup Supergroup (Marmo (Marmo and andOjakangas, Ojakangas,1984). 1984). The Urkkavaara Urkkavaara Formation, Formation, of the which we have have interpreted interpreted as as glaciomarine, glaciomarine, is subdivided subdivided into into four four informal informal members members as as argillite member, a graded sandstone member, an upper siltstonefollows: a lower lower argillite member, a graded sandstone member, an upper siltstoneThe argillite member, and and aa diamictite diamictite member. argillite member, member. The lower lower three three members members contain contain dropstones, and the upper siltstone-argillite grades upward into the dropstones, and the upper siltstone-argillite grades upward into the diamictite diamictite fades. facies. Subsequently, Marmo (1986) (1986) described described three three additional members that that overlie the Subsequently, Marmo additional members the initial initial sequence as follows: sandstone member, sequence follows: an an upper graded graded sandstone member, aa parallel-bedded parallel-bedded conglomerate member member and and aa massive conglomerate massive conglomerate conglomerate member. member. He interpreted interpreted these these three members to be be comprised comprised of of glaciofluvial glaciofluvial sediments. sediments. The Urkavaara Urkavaara Formation, Formation, three members about 300 300 m thick, is capped about capped by by aa 100 100 m m thick thick meta-regolith meta-regolith that appears appears to have have been been Close Proterozoic weathering. largely intensive Early largely conglomeratic conglomeratic rock rock prior prior to to intensive Early Proterozoic weathering. Close inspection of the same inspection of same stratigraphic stratigraphic horizon horizon in the Sariolian Sariolian Group Group has has resulted resulted in in the the five other in eastern recognition of glaciogenic glaciogenic characteristics characteristics in in five other areas areas in eastern and and central central recognition Finland; some of these localities localities are are separated separated by by 350 350 km. km. Negrutsa and Negrutsa (1981a,b) described 15 diamictite localities localities in Negrutsa Negrutsa (1981a,b) in the described 15 Sariolian Group and its its equivalents, equivalents, many many with with associated associated lonestones, lonestones, in in Karelia, Karelia, USSR; USSR; they proposed they proposed sedimentary-tectonic sedimentary-tectonic and and volcanotectonic volcanotectonic origins. origins. We We visited visited seven seven localities m 1988, and diamictite units are are associated localities m diamictite and lonestone lonestone units associated in the rock rock column column At one locality, at each. each. At locality, aa thick thick sequence sequence of of diamictite diamictite is is overlain overlain by by thinly thinly laminated laminated metasiltstone with dropstones dropstones that that clearly clearly penetrate and deform the laminae metasiltstone with penetrate and laminae (Ojakangas (Ojakangas et al, 1989). 1989). 79 �The presence The presence of glaciogenic glaciogenic lithologies lithologies in widely widely spaced spaced areas areas of of sedimentary sedimentary rocks on the Baltic Baltic Shield Shield allows allows for for correlation, correlation, as as aa glaciation glaciation isisan anuncommon uncommon"mega"megaevent" related to climatic of these these deposits deposits are are indeed indeed climatic change change (Ojakangas, (Ojakangas, 1988). 1988). If all of of of the the same same age, age, the the area area on on the the Baltic Baltic Shield Shield that was affected affected by by this this Early that was Early Proterozoicglaciation glaciationhad hadaa minimum minimumsize sizeofof about about 500 500 km km by 250 Proterozoic 250 km. km. If the other other diamictite (tilloid) occurrences describedby by Negrutsa Negrutsa and and Negrutsa on the diamictite (tilloid) occurrences described Negrutsa on the Kola Kola Peninsula in northwesternmost northwesternmost USSR been unable unable to to Peninsula USSR are are included, included, although although we we have been study those localities to attempt attempt to the area study those localities to verify verify glacial glacial characteristics, characteristics, the area directly directly affected by the the Early glaciationmay maybe be on on the the order affected by Early Proterozoic Proterozoic glaciation order of 200,000 200,000 km, km , suggestive of aa continental-scale continental-scale glaciation. glaciation. The rock rock Units units in which which these these glaciogenic glaciogenic rocks occur in in Finland Finland and and East Eastkarelia karelia are by lava flows are underlain underlain by flows dated dated at about about 2450 2450 m.y. m.y. and are are intruded intruded by by dikes dikes and and The Huronian Supergroup has 2450 2450 m.y. sills dated at about about 2180 2180 to 2160 2160 m.y. m.y. The Supergroup has m.y. lavas lavas at its its base base and and isis intruded intruded by by Nipissing Nipissing dikes dikes and and sills dated dated at about about 2180 2180 to to 2150 2150 m.y. m.y . I is A contemporaneous or penecontemporaneous glaciationseems seemslikely, likely, and and it is A contemporaneous or penecontemporaneous glaciation Baltic Shields possible American and possible that the the North North American and Baltic Shields were in in close close proximity proximity approximately approximately 2300-2200 m.y. ago ago (Ojakangas, (Ojakangas,1988). 1988). 80 I I I I I I I I I I I �________ _________ ________ _______ I References Cited Cited in the Koli-Kaltimo Koli-Kaltimo area, North Karelia, Marmo, J.S., stratigraphy in Marmo, J.S., 1986, 1986, Sariolian Sariolian stratigraphy North Karelia, Eastern Finland, Finland, in V.A. V.A. Sokolov Sokolov and K.l. K.I. Heiskanen, Heiskanen, eds., eds., Early Early Proterozoic Proterozoic of of in Baltic Shield: the Baltic Shield: Proceedings Proceedings of the the Finnish-Soviet Finnish-Soviet Symposium Symposium held held in Petrozavodsk 19-27 August 1985, 1985, p. p. 149-190. 149-190. Marmo, J.S., Marmo, J.S., and and Ojakangas, Ojakangas, R.W., R.W., 1984, 1984, Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits, deposits, eastern Finland: Finland: Geol. Soc. Soc. America America Bull., Bull., v. v. 95, 95, p. p. 1055-1062. 1055-1062. Negrutsa, T.F., T.F., and Negrutsa, V.Z. V.Z. 1981a, Early Proterozoic Lammos tilloids of the Kola Negrutsa, Lammos tilloids Kola M.J. and Harland, Peninsula, U.S.S.R., Hambrey, M.J. Harland, W.B.eds., W.B.eds., Earth's Earth's PrePreU.S.S.R., in Hambrey, Pleistocene glacial glacial record: record: Cambridge 678-680. Pleistocene Cambridge Univ. Univ. Press, Press, p. 678-680. 1981b, Early Early Proterozoic Proterozoic Sarioli Sariolitilloids tilloids in in the the eastern , 1981b, eastern part of the the Hambrey M.J., M.J., and and Harland, W.B., eds., eds., Earth's PreBaltic ~ a l t i cShield, U.S.S.R., U.S.S.R., in Hambrey Harland, W.B., PrePleistocene glacial record, p. p. 683-686. 683-686. Ojakangas, R.W., 1984, Basal Ojakangas, R.W., 1984, Basal Lower Lower Proterozoic Proterozoic glaciogenic glaciogenic formations, formations, Marquette Marquette Range Supergroup, Range Supergroup, Upper Upper Peninsula, Peninsula, Michigan Michigan (Abs.): (Abs.): 30th 30th Institute Institute on lake lake Superior Geology Proceedings, Proceedings, Wausau, WI., WL, p. p. 43. 43. an uncommon as a key , 1988, 1988, Glaciation: Glaciation: an uncommon "mega-event" "mega-event" as key totointracontinental intracontinental and intercontinental correlation of of early Proterozoic basin fill, North intercontinental correlation North American American and and Baltic cratons, cratons, in fr K.L. Baltic K.L. Kleinspehn Kleinspehn and C. Paola, Paola, eds., eds., New New Perspectives Perspectives in Basin Basin Analysis: Analysis: Springer-Verlag, p. 431-444. 431-444. 1989, Lower Marmo, J.S. and Heiskanen, K.l., 1989, , Marmo, Heiskanen, K.I., Lower Proterozoic Proterozoic glaciogenic glaciogenic deposits: deposits: Finland Finland and U.S.S.R., U.S.S.R., Baltic Baltic Craton Craton (Abs.): (Abs.): 28th 28th International International Geologic Geologic Congress Abstracts, Washington, Washington, D.C., D.C., p. 2-542. 2-542. 1943, Basal of Menominee Pettijohn, F.J., 1943, Pettijohn, Basal Huronian Huronian Conglomerates Conglomerates of Menominee and and Calument Calument districts, Michigan: Jour. Jour. Geology, v. 51, 51, p. p. 387-397. 387-397. W.P., 1969, Puffett, W.P., 1969, The Reany Reany Creek Creek Formation, Formation, Marquette Marquette County, County, Michigan: Michigan: Bull Bull U.S. U.S. Geol. Surv. Surv. 1274-F, 1274-F, p. p. F1-F25. F1-F25. Young, Young, G.M., G.M., 1970, 1970, An An extensive extensive early Proterozoic Proterozoic glaciation glaciation in in North North America? America? Palaeogeogr., Palaeoclimat., Palaeoclimat., Palaeoecol., Palaeoecol., v.v. 7, p. 85-101. 85-101. Palaeogeogr., Ontario, Canada: 1981, The , 1981, The early early Proterozoic Proterozoic Gowganda Gowganda Formation, Formation, Ontario, Canada: 6 Hambray, M.J. M.J. and and Harland, Harland, W.B. W.B. (eds.), (eds.), Earth's Earth'sPre-Pleistocene Pre-Pleistocene Glacial Glacial Record. Record. Cambridge Univ. Press, Press, p. p. 807-812. 807-812. 81 ^. �U Mafic Granulite Granulite and Eclogite Nodules Nodules Petrography, Mineral Chemistry, and Geotherinobarometry Geothermobarometryof Mafic from Upper Michigan Kimberlites. James PACES* & Lawrence A. TAYLOR, Department Departmentof ofGeological GeologicalSciences, Sciences,University University of of James B. PACES* Tennessee, Tennessee, Knoxville, Knoxville, TN 37996-1410. 37996-1410. *pfltly at: Branch Branch of Isotope IsotopeGeology, Geology,U.S. U.S. Geological GeologicalSurvey, Survey,MS MS963, 963, *Presentlyat: Denver Federal FederalCenter, Center,Denver, Denver,CO CO80225. 80225. Accidental Accidental xenoliths xenoliths and and xenocrysts xenocrysts contained contained within diatremes within diatremes from the theMichigan Michigan Kimberlite Kirnberlite Province (Cannon (Cannon and Mudry, Province Mudry, 1981; 1981; Jarvis Jarvis and and 1988)represent represent one of the few means of Kalliokoski, 1988) sampling the deep Phanerozoic crust and upper sampling the Phanerozoic crust upper mantle mantle beneath beneath the the southern southernSuperior SuperiorProvince. Province. These materials are vital vital both both for forinvestigating investigating the composition and chemical composition and chemical history history of of the the deep deep lithosphere, and and for testing lithosphere, testing lithospheric lithospheric structural structural geophysical data models derived derived from geophysical data (i.e., GLIMPSE studies). studies). Diatremes Diatremes were were emplaced emplaced during during the Jurassic Jurassic (Jarvis (Jarvisand andKalliokoski, Kalliokoski,1988) 1988) into a geologically complex complex region region along along the the southern southern Superior Province in Upper boundary of the Superior boundary Michigan (Fig. 1). 1). Although Michigan (Fig. Although the the lithosphere lithosphere in in this this during the area formed formed and/or and/or stabilized stabilized during the late late Archean, it was Archean, was likely likely modified modified during during subsequent subsequent tectono-magmatic processes associated associated with with Lower Lower Penokean orogenesis Proterozoic Proterozoic Penokean orogenesis and and Middle This Proterozoic Midcontinent Rifting. This paper Proterozoic presents initial results of aa nodule nodule study study whose whose long range goal is to to better betterunderstand understandthe thepetrological petrological continental and geochemical geochemical structure structure of the continental and lithosphere and its lithosphere its modification through time. Data reported reported here herewere were obtained obtainedfrom from discrete discrete Ellen E MhicontinentRift(1.1 Ga) 7) Penokean passive (Z") Penokean passivemargin margin(1.8-1.9 (1.8-1.9Ga) (S) Penokean maginatic <SS> Penokean magmaticarc are(1.8-1.9 (1.8-1.9Ga) Ga) 0> Archean Archean (2.7.3.2 (2.7-3.2Ga) Ga) Fig. 1: General General Geological Geological Map. ' \? granulite and eclogite eclogite nodules nodules collected collected by William William Jarvis of Jarvis of Jack Jack Murphy, Murphy, Trustee, Trustee, from from trenches trenches excavated in the the Lake Lake Ellen and Site 69 pipes (Fig. excavated in (Fig. 1). Nodules Nodules range range in in size size from 2 to 8 cm in diameter and weigh 20 and and 400 400 g. g. Paleozoic Paleozoic and weigh between between 20 and low-grade low-grade metamorphic metamorphic clasts clasts were were carbonate and largely excluded. excluded. Although the present nodule largely nodule suite suite nodules) and and does does not represent an is limited (—50 (-50 nodules) an unbiased sampling unbiased sampling of of the the lithospheric lithospheric column, column, lithologies described lithologies described here form form a substantial substantial proportion of of the the"deep" "deep"xenolith xenolith population. population. The The Site 69 pipe contains aa variety variety of of mafic mafic amphibolites amphibolites and granulites, granulites, but but no no discrete discrete upper upper mantle mantle and/or ultramafic pipe ultramafic nodules. nodules. In contrast, the Lake Ellen pipe includes includes a variety variety of of eclogites, eclogites, pyroxenites, pyroxenites, garnet garnet peridotites, spinel peridotites, and mantle mantle xenocrysts xenocrysts (McGee (McGee and Hearn, Hearn, 1983) 1983) in addition addition to less less abundant mafic abundant mafic granulites. granulites. Attempts Attempts to to better are under underinvestigation. investigation. quantify xenolith populations are The current results results focus on lower lower crustal crustal granulite granulite eclogite nodules from the the two two pipes. pipes. and eclogite GRANULITES: Granulites nearly GRANULITES: Gramilitesfrom fromboth both pipes pipes nearly all have have mafic mafic compositions compositionscontaining containingplagioclase plagioclase (18-37 vol.%) and (18-37 vol.%) and dlinopyroxene clinopyroxene (19-40%) ( 1 9 4 % ) along along amphibole (0-11% (0-11% in gtgtwith garnet (16-42%)  with garnet (16-42%) ± amphibole rocks, up up to to 37% 37% in in gt-free gt-free rocks). rocks). Minor (1bearing rocks, 2%) ilmenite ilmenite (occasionally (occasionally rutile) is ubiquitous, ubiquitous, while may be be present, but only quartz and orthopyroxene orthopyroxene may only gt ++qtz qtz in minor amounts. AAsingle singlenodule noduleofofplg+ pig+@ with minor cpx represents + cpx represents the the most-"felsic" with minor rut rut+ most-"felsic" granulite observed. observed. Granulites exhibit exhibit nonfoliated, nonfoliated, (0.5-1.5 mm mm diam.), equigranular (0.5-1.5 dim.), granoblastic equigranutar granoblastic textures. Although textures. Although no no obvious obvious fabrics fabrics are are observed observed nodules, some thin sections in individual individual nodules, sections show show nonnonhomogeneous distributions homogeneous distributions of of phases. phases. Mineral compositions within within single single nodules vary only within small limits that local small limits suggesting suggesting that local equilibrium equilibrium was was acheived. Plagioclase in gtgtacheived. Plagioclase isis most most sodic sodic (An25-40) (An25o) in bearing assemblages assemblages and and most mostcatcic calcic(An5o..s5) (Anso-5s) in gtgtfree assemblages assemblages (Fig. 2). 2). Clinopyroxenes Clinopyroxenes contain low Cr203 0 - 2 0 3 (<0.04 (<0.04 wt.%), wt.%), substantial substantial A1203 A1203 and and low wt.%, and and 1-2 1-2 wt.%, wt.%, resp.) Na20 (3-5wt.%, Na20 (3-5 resp.) and and Mg#'s Mg#'s ((Mg/Mg+Fe2) M ~ / M ~ + of Fof~0.71-0.80. 0.71-0.80. - ~ ~ ) Ilmenite Ilmenitecontains contains 1-2 1-2 wt.% gt-bearing rocks 0.2-0.7 wt.% in in wt.% MgO in gt-bearing rocks and 02-0.7 82 I I I I I I I I I I I I I �I A// (1-10%) + rutile rutile (1-2%) (1-2%) with with accessory accessory Clfeldspar (1-10%) Hearn and apatite, silica, silica, and Fe Fe suffide. sulfide. Heam and McGee McGee (1983) (1983) also report kyanitekyanite- and andcorundum-bearing corundum-bearing similar major-phase eclogites with eclogites with similar major-phase compositions. compositions. Edogites exhibit Eclogites exhibit granoblastic-polygonal granoblastic-polygonal textures textures (05-3 thin (0.5-3 mm diam.) diam.) with no obvious obvious fabrics on a thin section scale. section Only minor intragranular intragranular compositional variations variations are present. compositional present. Omphacitic (Fig. 2) 2) have high A1203 Al203 (14.8 wt.%) clinopyroxenes (Fig. and Na20 (7.7 (7.7 wt%), wt%), low low Cr203 Cr203 (<0.07 wt%), and (Fig 2) 2) Mg#'s between between0.72-0.74. 0.72-0.74. Orange garnets (Fig Mg# == 0.39are high in is-on iron (FeOt = = 20.5 wt%, wt%, Mg# - 2 0 3 (<0.05 0.42) 0.42) and, and, like pyroxene, pyroxene, low lowin in 0Cr203 (<0.05 wt%). K-feldspar is is unequally unequally distributed within single thin K-feldspar sections and contains contains high high 1(20 K2O (—16.3 (-16.3 wt%), low low Na20 (<0.5 Na20 ( ~ 0 . wt%), 5wt%), and andappreciable appreciable BaO BaO (0.3-1.1 (0.3-1.1 of wt%). The Thepresence presenceof of small, small, rounded rounded inclusions inclusions of K-feldsparinin pyroxene and garnet K-feldspar pyroxene and garnet with with similar similar compositions indicates indicatesthat that K-feldspar K-feldspar isis a primary compositions phase. Reddish-brown rutile rutile is relatively pure with phase. Reddish-brown only small small amounts amountsof ofFeO, FeO,Al203, Al203,and andZr02 Zr02 (< (<13, 1.5, 0.5, and 0.4 wt.%, in 0.5, wt.%, resp.). resp.). Degree of alteration alteration in eclogites varies widely. reacts most eclogites varies widely. Clinopyroxene Clinopyroxene reacts readily; first around around grain grain boundaries boundaries and then along readily, first internal net-like fabric. internal fractures producing producing a net-like fabric. Omphacitic pyroxenes pyroxenes in in highly highly altered nodules are are completely replaced replaced by milky, augite-rich aggregates. aggregates. Large books of biotite biotite may also also be developed. developed. Ab Plagioclase / An Pyroxenes & Pyroxenes Garnets Circles = Granulites = Fkbgites Mg Fig. 2: Plagioclase, Garnet Chemistry. Plagioclase, Pyroxene and Garnet Chemistry. Orange, almandine-rich alinandine-rich garnet gt-free garnet gt-free rocks. contains 23-27wt.% wt.%FeOt, FeO, 6-9 contains 23-27 6-9 wt.% MgO, MgO, and and 6-7 6-7 wt.% CaO (Fig. wt.% (Fig. 2). 2). Garnets in some some nodules nodules are are qtz. with both both cpx graphically intergrown cpx and and qtz. graphically intergrown with alteration affect affect Varying Varying degrees degrees of of retrograde retrograde alteration garnets beginning beginning with fibrous, fibrous, green-black green-black rims rims progressing to a distinct pseudomorphic replacement by fme, gtfine, plg-sp-chl pig-sp-chi aggregates. aggregates. Amphiboles Amphiboles in gtbearing granulites granulites exhibit a similar similar mottling mottling of of finefmegrained opaques, opaques, and may may represent represent recrystallization recrystallization of keliphytic aggregates. aggregates. Many Many granulites granulitesalso also show show a network serpentine/chlorite alteration alteration along along network of of serpentine/chlorite grain boundaries adjacent to fresh cpx and pig. pig. This This network may extend into grains grains along along cracks where where it sometimes terminates in in patchy patchybrown, brown, mesostasismesostasislike material. material. These These features features are interpreted interpreted as as devitrified and altered decompression decompression melts formed formed during nodule transport transport and and emplacement. emplacement. WHOLE ROCKCOMPOSITIONS: COMPOSmONS:Granulite Granulite whole WHOLE ROCK whole reconstructed from mineral rock compositions compositions reconstructed chemistry chemistry and modal modal proportions yield close approximations to moderately-evolved,high-Al203 high-A1203 to moderately-evolved, 1). (Table 1). basaltic liquids liquids (Table Typical normative normative (Anso-po), 5-15% 5-15% 01, 01, mineralogy includes includes 50-60% 50-60% P1 PI (An5070), 20-35% Di Di++Hy. Hy. The The single single "felsic" 'felsic' nodule yields an 20-35% andesitic composition and contains contains 13% 13%normative normative Qz and and 3% 3%normative normative corundum. corundum. Eclogites yield yield high-Al, basaltic, whole rock compositions similar to to with the exception the mafic mafic granulites granulites with exception of higher higher alkalies. and and Ti02. Ti02. As a result, result, the the two twoanalyzed analyzed eclogites are Ne normative (6-8% Ne) with otherwise comparable PI, 01 01 and Di. comparable normative Fl, ECLOGLTES: Eclogites constitute the largest ECLOGITES: Eclogites constitute largest mantle xenoliths percentage percentage (85%) of upper mantle xenoliths previously reported from the Lake previously reported Lake Ellen Ellen kiinberlite kimberlite The three (McGee and Hearn, 1983). (McGee Hearn, 1983). three sanidine sanidine eclogites included included in in the present present suite suite are aretexturally texturally compositionally similar to to those described and compositionally earlier. Mineral Mineralassemblages assemblagesconsists consistsof of omphacitic omphacitic clinopyroxene(49-58%) (49-58%)++ garnet garnet (26-38%) (26-38%) t+ KKclinopyroxene TABLE 1: 1:Average Average Reconstructed ReconstructedWhole Whole Rock Rock Compositions Compositions for Granulites and Eclogites N Si02 Si02 Ti02 Mafic Granulites Granulites 6 49.18 Mafk Intermed. Gran. 11 55.98 Interned. Gran. Eclogite Eclogite 2 49.49 1.16 1.16 0.88 0.88 1.74 A1203 FeO FeO MnO MnO MgO CaO CaO Na20 K20 16.01 16.01 18.74 18.74 17.28 17.28 12.26 12.26 11.09 11.09 9.48 0.25 0.24 0.15 6.45 3.93 3.93 6.20 10.70 10.70 6.00 9.86 0.24 0.20 1.00 1.00 83 3.12 2.86 4.43 Total Cr203 Cr203 Total 0.02 0.01 0.01 0.04 99.39 99.93 99.93 99.64 99.64 I �I U Ii F Reconstructed Whole Rock A M Fig. 3: 3: AFM Fig. AFh4 Diagram Diagram For For Reconstructed ReconstructedWhole Whole Rocks. Rocks. Preliminary P-T GEOTHERMOBAROMETRY: GEOTHERMOBAROM~Y: Prelimiiary P-T Qtz± t ~ Opx OPX k estimates from unzoned Gt-Cpx-Plg± Gt-Cpx-Plgk Q estimates assemblages in granulites yield temperature temperature ranging ranging from 712-760° 712-760°Cand andpressures pressures from from 9-12 9-12 kb. kb. Results obtained using several different thermobarometers using several diierent thermobarometers show reasonable agreement ( 210°C 10° and ±T1.5 1.5 kb). kb). agreement (± These These results results are are comparable comparable to to P-T P-Tconditions conditions (Bohlen. observed in regional granulite granulite terrains terrains (Bohlen, observed in regional although pressures pressures for for nodules nodules are are higher higher than than 1987) although similar most uplifted uplifted granulite terrains terrains at similar most Estimated pressures correspond temperatures. Estimated corfespond to depths km. Depths Depths to to seismic-Moho seismic-Moho depths of of 30-42 30-42 km. reflectors in in this area have have been measured measured at at 36-42 36-42 km (Behrendt, (Behrendt, in press). Establishing EstablishingP-T P-T conditions conditions for more difficult due the the lack lack of of a for eclogites eclogites isis more difficult due assemblages. reliable geobarometer for gt-cpx assemblages. reliable Eclogite gt-cpx gt-cpx temperatures temperatures range between 980Eclogite between 9801070°C forpressures pressuresofof 15-40 15-40kb. kb. The presence of 1070° for in this thistemperature temperature range requires kyanite-eclogites in requires a of 14 kb kb (McGee (McGee and Hearn, 1983). minimum of 1983). CpxCpxopx composite xenocrysts xenocrysts (McGee (McGee and Hearn, Hearn, 1983) 1983) yield yield P-T estimates estimates of of 840-920°C 840-920° and 12-17 12-17 kb. kb. Although the opx Although the opx pressures pressures are are questionable questionable for for these xenocrysts, the combined combined data data preserve these xenocrysts, the preserve a consistent geotherm geotherm (Fig. (Fig. 4) intermediate consistent intermediate between between rift lconditions conditions (Berg (Berget etal., al., 1989) 1989)and andcold1 cold, shield hot, d (Pollack and Chapman, conditions (Pollack Chapman,1977). 1977). underplating and hjection underplating magmas injection of basaltic basaltic magmas 1987 Griffi (Bohlen, 1987; Griffm and and O'Reilly, O'Reilly, 1987). Eclogites s i m i l a r compositions compositions may may represent represent basaltic basaltic with with similar magmas emplaced below below the the sei..mic-Moho. seismic-Moho. At least thrie ma$ tectono-magmatic tectono-magmatic episodes episodes at —2.7, -2.7, three major —1.85and and -1.10 —1.10Ga Ga could could be responsible -1.85 responsible for for emplacement of nodule protoliths. Seismic seismic reflectors reflectors the Lake Superior region are interpreted throughout the interpreted to have origins associated with Midcontinent Rifting Rifting (Behrendt d., in press). However, nearby (Behrendt et a!., However, nearby tholeiitic volcanics associated with Penokean Penokean passive passive margin assemblages, assemblages, as as well as as Archean Archean metavolcanics,indicate indicate older older potential metavolcanics, potential magmatic magmatic sources. Further sources: Furthergeochemcial, geochemcial,geochronological, geochronological, and isotopic studies studies which which may may help help constrain protolith isotopic petrogenesis are currently in progress. References: Tectonophys 1172, (inpress); press); Berg Referma%: Behrendl 61. Bebrcndt et ef aL, d.,(1990) (1990)Tedonophys 72, (UI Berg et u d. (1989) EPSL 93,98-10% 93, 98-108; Bohlcn Bohlen (1987) .J M Gaol..95,6174g 95, 617-632; Cannon Cannon & (19S9) (1987)3 & Mudiy Mudry(1980) (1980) USGS C CIre 842; (1987) Mantle irc 8 42 GriMn Griffin&&O'Reilly 0 ' (1987)In, lqP.R. P.H.Nixon, N m n ,nil, ed, Mum&Xenollth.t, X e m b h , J3.. Wiley & Sons. (1988) Sous,413.430; 4 1 M W JJarvi m &&Ilalliokoeki KaU~okvsh (198S)Inst InstSLSuper SuperGaol C d34, 34,46-48; W Wflq McGee M cGe & & Ream Heam (1988) (19X3)USGS USCS Open-fin O p i U eRep Rep83-156. 83-156,22p; Z p ; MacGregor MacGmpr (1974) (1574)Am Am MIneral 59.110-11% 59,110-119; Poilack Chapman (1977) Tectoflophys 38,279-296 38,219.296 Mineral P O W& Chapman (1977)Tdonophys T (°C) 500 1000 1500 0 10 -- 20 ,—. 30 40 New Data 50 Initial results indicate CONCLUSIONS: Initid indicate that mafic igneous derived from igneous granulites were were derived from ma& granulites which equilibrated within within the lower protoliths which lower crust crust Noo at depths depths as great grmt as the theseismic-Moho. seismic-Moho. N granulites with metasediinentary metasedimentary affinities affinities have yet yet recognized. These data are are consistent consistent with with been recognized. models of of aa mafic mafk lower lower crust crust derived derived through through models •= MaScot MaficQtGranulite Granulite O 0 Sanidine S ~ e E CEclogite lo$te \.. 1. 3. i. k McGee McGee & & Hearn, Heam,1983 1983 60 A A CPX-OPX Xncryts OX-OPX COInp. &mp. Xncqats 0PXXenocg.at OPXXenocryt A 70 Fig. 4: Calculated CalculatedP-T P-Tconditions conditionsfor forMichigan Michigannodules. nodules. 84 F I I I I �I ARCHEAN AND AND PENOKEAN PENOKEANSTRAINS STRAINS IN IN THE THE NORTHERN NORTHERN COMPLEX, COMPLEX, ARCHEAN MARQUETTE MINERAL DISTRICT, DISTRICT, MICHIGAN MICHIGAN MARQUETTE MINERAL John C. Palmquist, Palmquist, Department Department of of Geology, Geologyl University, Appleton, Appleton, WI Lawrence Universityl Wl 54912 54912 The complexity Archean rocks rocks in the The complexity of dynamothermal dynamothermal metamorphism metamorphism ofof Archean the Marquette by the Marquette District, District, Michigan Michigan was was recognized recognized by the earliest earliest workers workers ; Van Hi?- and n n A I ni+h 4 0 1 4 \ A w n h n n n -fi+n-nw-h:n (Williams, (Williams, 1891 1891; Van Hise Leith, 1911). Two Archean metamorphic events were documented events were documente( by Gair and Thaden (1968) but the problems; associated associated with with sorting out these Archean events from the Penokean1 Modern techniques of quantitative strain1 overprint overprint remain remain with with us. Recent work analysis give promise of these problems. analysis give promise of 01 solving ~ u l ~ ~some aulllw l l y pi wwlvll vvul A chnwinn thn ~lnce cimilaritv of n f strain ctrain ellipsoid nllincnid axes ayoc orientations, nriontatinnc and aqd showing the close similarity in the the Marquette in the rocks to to those magnitudes the Archean Archean rocks those of of rocks rocks in Marquet magnitudes in Supergroup (Carter, 1989, 1989, p. p. 69) that either Supergroup (Carterl 69) suggested suggested that either the the Archean Archean rocks roc1 were undeformed prior to to the were undeformed prior the Penokean, Penokean, and and thus thus record record only only Penokean Penoke: ctrgin nr that thn rnnztcttrnd ctrainc in +he A r ~ h n a n r n ~ k c ara indnc in the Archean are indeed strain, ~ , m ~or l i that lL,luL , the measured , l l u u ~ ~ strains su~ , . , w ~ m w ~rocks m ~ mmmuwzd Archean but the rocks Archean but rocks behaved behaved in in aa brittle brittlefashion fashion during during the thePenokean Penokean argue for for aa third interpretation, namely namely that that this paper paper II argue third interpretation, deformation. In this the Archean the Archean rock rock fabrics fabrics record record both both Archean Archean and and Penokean Penokean strains, strains, in aa complex sequence sequence of events. events. T n . 8 ~ # w.mw..m,vy .,,w wewww w,,.m.,ua,., w. Lllu w..-.,, w,.,y.a..," a .,... w.,.a.......w..w, svwm.w e L m w m t m e . u q w Strain in variolitic pillow pillow lavas lavas of the Mona Mona Schist Schi Strain measurements in horizontal indicate north-south north-south horizont between and Negaunee between Marquette and Negaunee indicate shortening of 27-36% vertical extension extension of 40-60%, 40-6O0Io, and and near near plane plar shortening of 27-36% and and vertical strain (Carter, strain (Carter, 1989). 1989). These These data are are consistent consistent with with those thosedocumented document( n 4 the +hn K ~ n mC n v r n - t i n n - n A quartzites m ~ ~ - v t v i t n en f thn h A n e n ~ r r 4 ~ n r 4A i i h for slates a m w a of ul ulc Kona nulta Formation 1 u ~ ~ and alw ~ q~u a ta u l L ~ e a of ul ~ the uu w Mesnard l~ v l u a~ l l a t u and allu Ajibik + -,ki Formations of the Formations of the Marquette Marquette Supergroup Supergroup (Westjohn, (Westjohn, 1978; 1978; 1986; 1986; 1987). 1987). New strain strain measurements pressurefringes fringesinin aa chlorite chlorite schist schist from New measurements ofof pressure from the lnwer memhnr nf tho Mona Mnna Schict show chnw a a minimum m i n i m ~ ~vertical vnrtical m e ~ t e n s i n nof of lower member of the extension ... Schist .........,-... -...-..-.-.. The pressure fibers grown 1100%. The 100%. pressure fringes fringes are quartz-chlorite quartz-chlorite fibers grown on the the ends en( s These data suggest of hematite porphyroblasts. porphyroblasts. These suggest the the interpretation interpretatk~n c)f rigid hematite that Archean rocks rocks of of varying varying strengths strengths have have responded responded differently, differently, and a1l d t hat Archean pillow lavas thus yield heterogeneous heterogeneous strain strain indicators. indicators. The The variolitic variolitic pillow Iavi3s t hus yield < n w e-lm+nm w..w, ..,w,,.-w, w. .,.w w,*- -w...w. w,,w.. - --.....-a -..:--..:I.. A..-L--..,L----n &LA &-:--fie primarily Archean strains fringes, developed ~IIIII~IIIY NGIIG~II W ~ I I whereas W I ~ I I G I G ~ ~the LIIG pressure ~ I G ~ ~ U IIIIIYG~, I G U G V W U ~ G ~ in more of Archean strain as as well as in more ductile ductile rocks, rocks, record record larger larger amounts amounts of Archean strain as deformation in the an additional additional increment increment of of Penokean Penokean strain. strain. Penokean Penokean deformation the Archean basement is is concentrated in high Archean basement concentrated in high strain strain shear shear zones zones and and within within the more the more ductile ductile lithologies. lithologies. )---..A ~GGUIU record -&-A:-- - - - n n m . - n 85 An.n-l--, �I The division The division of the the Mona Mona Schist Schist into into an an upper upper (Lighthouse (Lighthouse Point) Point) and and lower lower member by Gair member by Gair and and Thaden, Thadenl 1968) 1968) was was based, based, in in part, part, on the the division division between the the banded greenstonesofof the the upper between banded greenstones upper part part and and the the massive massive greenstones of the greenstones of the lower lower part. part. They They recognized, recognizedl however, howeverl the higher higher metamorphic grade grade of of the metamorphic the layered layered amphibolitic amphibolitic schist schist characteristic characteristic of the Lighthouse suggest that that the boundary boundary separating separating the the Lighthouse Point Point member. member. II suggest members of the Mona members of Mona Schist Schist is is tectonic tectonic rather rather than than stratigraphic. stratigraphic. In In addition to to the abrupt grade, the the strain addition abrupt change change in in metamorphic metamorphic grade, strain fabrics fabrics are are different across different across the the boundary. boundary. Mylonitic Mylonitic fabrics fabrics in the the meta-rhyodacites meta-rhyodacites with the Archean strains strains interlayered with the Lighthouse Lighthouse Point Point Member Member suggest suggest Archean interlayered whereas S-C structures flinty quarz whereas S-C structures in associated associated laminated laminated flinty quarz sericite sericite rock rock indicate movementconsistent consistentinin sense sense and and position indicate up-to-the-north up-to-the-north movement position with with a Penokean Penokean zone zone of of displacement displacement to account account for for the thehigher highermetamorphic metamorphic grade in the Lighthouse Point member (upthrown) and lower grade grade the Lighthouse Point member (upthrown) and lower grade in in the the Lower (downthrown) member. member. These same rocks also show interpreteted as as the asymmetrically developedkink kink bands bands which asymmetrically developed which are are interpreteted the Archean basement of the axial Archean basement manifestation manifestation of axial shortening shortening and andcross-folding cross-folding developed in in the Animikie developed Animikie rocks rocks of of the theMarquette Marquettesynclinorium. synclinorium. The The Archean Archean rocks rocks north north of of the theMarquette Marquette synclinorium, synclinorium, the the "northern "northern complex" appear to to show complex" appear show three three strain strain regimes. regimes. To To the the north, northl in in the Compeau Creek Creek gneiss* gneiss, ductile ductile shear Compeau shear zones zones provide provide evidence evidence of of Archean Archean A dextral of diabase reactivation of diabase dikes. dikes. A dextral transpression transpression regime regime seems seems The central sector, mainly the Lighthouse this zone. well-developed well-developed in in zone. The central sector, mainly the Lighthouse has a complex mylonitic fabric fabric locally locally complex strain strain pattern pattern with mylonitic Point Member, Member, has in the amphibolitic layers and in its felsic layers and vertically vertically stretched stretched boudins boudins in amphibolitic in its Some geologists geologists have have speculated speculatedthat that the the lenticular schist. Some lenticular layers layers in this If that is is correct, correctl the unit are are actually actually extremely extremely flattened flattened pillows. Lighthouse Point member is much more flattened as well as of Lighthouse Point member is much more flattened as well of higher higher metamorphic grade grade than than the lower The strain strain fabric fabric of the the lower lower metamorphic lower member. member. The essentially ranging from dominated by vertical member is member is dominated vertical extension ranging from variolitic pillow pillow lavas lavas to to a minimum undeformed to to 60% undeformed 60% in in variolitic minimum of of 100% 100% in in Future work work will will be directed chlorite directed at at further further chlorite schists schists and slaty slaty units. units. Future northern complex partitioning within the documenting documenting the the strain strain partitioning the northern complex and and the Archean attempting to establish establish the relationships relationships between between the Archean and and Penokean deformations. deformations. REFERENCES REFERENCES CITED CITED Carter, Carter, P. J., JWlJr., Jr., 1989, 198g1Finite Finite strain strain estimations estimations for for Archean Archean Mona Mona Schist Schist pillows and early early Proterozoic Proterozoic Enchantment Enchantment Lake Lake Formation Formation Metawackes in the eastern upper peninsula of Michigan: Metawackes in eastern upper peninsula of Michigan: Michigan Michigan State Univ. unpub.M. unpub.M. S. thesis, thesis, 97 97 p. p. 86 �Gair, J. E. and Thaden, Thaden, ft R.E., E.,1968, 1968,The TheGeology Geologyof ofthe theMarquette Marquetteand andSands Sands Quadrangles, Marquette County, County, Michigan: Michigan: U.S. U.S. Geol. Geol. Survey Prof. Quadrangles, Prof. Paper 397, 77 p. p. Van Hise C. R. K., 1911, 1911, The The Geology Geology of of the the Lake Lake Superior Superior R. and and Leith, Leith, C. C. K., Region: U.S. Geol. Survey Mon. Mon. 52, 52, 641 641 p. p. Williams, G. G. H., 1891, Williams, 1891, The The greenstone greenstone schist areas of the the Menominee Menominee and Marquette regions of of Michigan: U.S. Geol. Geol. Survey Survey Bull. Bull. 62, 62, 238 p. Marquette regions Michigan: U.S. p. 87 �U FINNISH PROTEROZOIC PROTEROZOIC GOLD GOLD FINNISH AND IMPLICATIONS FOR THE LAKE AND IMPLICATIONS FOR THE LAKE OCCURRENCES OCCURRENCES SUPERIOR REGION REGION SUPERIOR Heikki S. S. Pankka Pankka and and Theodore Theodore 1. 3. Bornhorst, Bornhorst, Department Departmentof of Heikki Geological Engineering, Geology, and Geophysics, Michigan Geological Engineering, Geology, and Geophysics, Michigan ~echnologicalUniversity, University, Houghton, Houghton, MI MI 49931 49931 (Pankka (Pankkaalso also Technological with the the Geological Geological Survey Survey of of Finland) Finland) with The Proterozoic Proterozoic geology geology of of Finland Finland is is similar similar to to that that of of The the Lake Superior region and is consistent with Proterozoic the Lake Superior region and is consistent with Proterozoic plate reconstructions reconstructions which which suggest suggest that that Finland Finland and and Greenland Greenland plate were connected connected with with North North America. America. Thus, Thus, it it is is appropriate appropriate to to were use the the geologic geologic setting setting of of Proterozoic ~roterozoicgold gold occurrences occurrences in in use In the the ProProFinland as as analogs analogs for for the the Lake Lake Superior Superiorregion. region. In Finland terozoic of Finland there are a significant number (34) of terozoic of Finland there are a significant number (34) of gold occurrrences occurrrences of of economic economic interest, interest, in in the the Lapland Lapland greengreengold in the Lapland granulite terrane of north Finstone belt and stone belt and in the Lapland granulite terrane of north Finland, and in the Svecokarelian complex of south Finland. land, and in the Svecokarelian complex of south Finland. These three three areas areas have have been been interpreted interpreted as as subparallel subparallel rift rift These intracontinental zones. The The Lapland Lapland greenstone greenstone belt belt was was intracontinental zones. whereas the the other other two two developed developed oceanic oceaniccrust. crust. whereas The Lapland Lapland granulite granulite terrane terrane is is composed composed of of graywackes graywackes The granulitization around 2.1 to 2.0 Ga. This This which underwent which underwent granulitization around 2.1 to 2.0 Ga. Archean baseterrane was overthrusted to the southwest onto terrane was overthrusted to the southwest onto Archean basePlacer gold has been ment and the Lapland greenstone belt. ment and the Lapland greenstone belt. Placer gold has been recovered in in small small amounts amounts from from this this terrane terrane since since the the late late recovered 1800's. This This gold gold was was derived derived from from retrogressive retrogressive shear shear zones. zones. 1800's. The Lapland Lapland greenstone greenstone belt belt of of early early Proterozoic Proterozoic age age (2.5 (2.5 The to 2.0 Ga) consists of bimodal volcanics overlain by quartzto 2.0 Ga) consists of bimodal volcanics overlain by quartzin the the lower lower part part and and of of komatiitic komatiitic to to thothorich sediments sediments in rich leiitic volcanics with related volcaniclastics in the upper leiitic volcanics with related volcaniclastics in the upper part. Mafic Mafic intrusions intrusions are are common common at at 2.4 2.4 and and 2.2 2.2 Ga. Ga. These These part. rocks were were deformed deformed at at about about 1.9 1.9 Ga Ga in in aa style style that that resembled resembled rocks clastic foreland fold fold thrust thrust belts. belts. Synorogenic Synorogenic granitoids, granitoids, clastic foreland sediments, and and felsic felsic volcanics volcanics were were followed followed by by postorogenic postorogenic sediments, granites. Gold Gold mineralization mineralization occurs occurs in in quartz—carbonate quartz-carbonate granites. ultramafic and mafic rocks, in in quartzquartzveins hosted by altered veins hosted by altered ultramafic and mafic rocks, carbonate veins associated with felsic dikes and related gracarbonate veins associated with felsic dikes and related gra— and in disseminated sulfides or breccia pipes hosted nitoids, nitoids, and in disseminated sulf ides or breccia pipes hosted albitized quartzites. quartzites. Faults, Faults, shear shear zones, zones, or or folds folds play play aa by albitized by Gold is is epigenetic epigenetic role in in localization localization of of all all occurrences. occurrences. Gold role and emplaced emplaced after after the the peak and peak of of regional regional greenschist greenschist facies fades metamorphism and and deformation. deformation. metamorphism The Svecokarelian Svecokarelian complex complex ranges ranges in in age age from from about about 2.2 2.2 to to The It consists of a thick succession of metamorphosed 1.75 Ga. 1.75 Ga. It consists of a thick succession of metamorphosed platform to to deep-water deep-water turbidites. turbidites. Mafic Mafic igneous igneous rocks rocks are are aa platform small component component of of the the complex. complex. These These rocks rocks were were deformed deformed small between about about 2.0 2.0 to to 1.75 1.75 Ga Ga during during the the Svecokarelian Svecokarelian orogeny. orogeny. between I 88 i �About About three three quarters quarters of of the the complex complex consists consists of of syntectonic syntectonic tonalite tonalite to to granodiorite granodiorite and and associated associated intermediate intermediate to to felsic felsic volcanics. AA major major portion portion of of the the complex complex represents represents juvenile juvenile volcanics. crust. Gold Gold is is hosted hosted by by tonalite tonalite to to quartz quartz diorite diorite stocks stocks crust. and intermediate intermediate volcanics/intrusives. volcanics/intrusives. AA few few occurrences occurrences are are and in supracrustal supracrustal rocks. rocks. Metamorphic Metamorphic grade grade of of the the host host rocks rocks is is in Gold tends tends to to be be associated associated with with either either amphibolite amphibolite facies. facies. Gold Alteration is is characcharaclithological lithological contacts contacts or or shear shear zones. zones. Alteration terized terized by by quartz-sericite-biotite quartz-sericite-biotite and and K-feldspar K-feldspar and and lacks lacks carbonates. Gold Gold was was likely likely emplaced emplaced during during the the late late stages stages carbonates. of of the the orogeny orogeny and and may may be be linked linked with with magmatic magmatic processes. processes. Geologic Geologic environments environments exist exist in in the the Lake Lake Superior Superior region region that that are are very very similar similar to to gold gold bearing bearing ones ones in in Finland. Finland. Thus, Thus, it it is is reasonable reasonable to to suspect suspect that that numerous numerous significant significant gold gold occurrences occurrences exist exist in in early early Proterozoic Proterozoic rocks rocks of of the the Lake Lake SupeSuperior rior region. region. 89 �p I NEW NEW EVIDENCE THAT LIMESTONE MT., MT., MICH MICHIGAN, SRUCT1JRE IGAN, IS PART OF A LARGE IMPACT STRU CTURE M F. Geology Dept., Dept., Lawrence Lawrence Univ., Univ., Appleton, Appleton, WI WI 54912 William F . Read, Geology Rising abruptly to aa height Of Rising of about 100 m m above the low ground which which immediately immediately surrounds it, Limestone it was was Limestone Mt. Mt. is, topographically, topographically, aa rather rather impressive feature. When When it discovered that the "mountain" "mountain" COnSiStS limestone (or (or dolostone), discovered consists mainly of limestone dolostone), whereas all but one the other other high hills in the area are sandstone, sandstone, quarrymen geologists were immediately immediately of the quarrymen and geologists attracted to to it. it. The other projecting mass of limestone limestone in in the area is is Sherman Sherman Hill Hill (see (see attracted Fig. 1), much smaller and lower than "the mountain." Fig. l), smaller lower than " the mountain. " Geologists soon soon found out that the the (unmetamorphosed) and, Geologists (unmetamorphosed) limestone limestone is is full full of of fossils, fossilsi, and, from these, that the age of the the rock rock is is Ordovician. Ordovician. In the "mountain," "mountain," the layers layers are arei not horizontal but warped down in a pronou pronounced displaced by numerous need syncline syncline and displaced numerous small small faults. f etults. e,. ----,-A -----o- ~ - -e The same same is is true true to to aa lesser lesser degree degree of of Sherman J L L ~ L N U X U Hill. "ALL. - 1 . ~ - 1 . & led LCU to w ~ u n i ~ ~ a e r especulation specunation This considerable involves, not only the two two hills, also a good regarding the cause of the deformation, deformation, which involves, hills, but also of deal of the neighboring where this this is is visible. visible. Fig. neighboring sandstone sandstone (Jacobsville) (Jacobsville where Fig. 1 shows shows most of the known known exposures exposures of of Jacobsville Jacobsville which which are are relevant relevant to to this this paper. paper. These exposures low exposures are low and inconspicuous. inconspicuous. Obviously, Obviously, the the limestone limestone is is much more more resistant resistant to to erosion. erosion. Most structural studies have been aimed primarily at "the "the mountain." mountain." In relatively recent relatively recent years, qeophysics geophysics has has played played a a part part in these studies and some geophysicists geophysicists have covered a good territory beyond Limestone Limestone Mt. Mt. and and its its immediate immediate vicinity. vicinity. For example, Campbell, deal of territory CampbelL. in preparing a 1952 prfparinq 1952 M.S. M.S. thesis thesis on on the the "Silver "Silver Mountain Mountain area" area" (1) (1) did ground did a good deal of ground magnetic gravity work work as as far north as (Silver Mt. Mt. is a a prolecting projecting knob magnetic arid and gravity as Limestone Limestone Mt. Mt. (Silver knob of basalt tens tens of of miles miles to to the thesouthwest.) southwst. The The U.S. U.S. Geological Geological Survey Survey published published in in 1965 1965 aa set set of of (quadrangle by quadrangle) quadrangle) aeromagnetic aeromagnetic maps The (quadrangle by maps covering covering the the area area around around Limestone Limestone Mt. Mt. The contours shown magnetic contours shown in in Fig. I 1 were traced traced from from these these maps, maps. complete bibliography Hoehl's Hoehl's massive massive M.S. M.S. thesis thesis (2) ( 2 ) provides a virtually complete bibliography of the the relevant relevant contribution which he missed, literature literature up to to 1981. 1981. The only contribution missed, an important important one one from from my point of view, is the first large tectonic map of the U.S., published in 1944 by the National view, is large U.S., in 1944 the disturbances in otherwise otherwise flat-lying Research Council. Council. Walter Bucher, who regarded many local disturbances flat-lying of "cryptovolcanic" "cryptovolcanic" activity, activity, was on the committee coHmittee that put this sedimentary rock as evidence of map together, and presumably responsible for getting getting Limestone Mt. Mt. on it as an example of this map goodly number of geologists have subsequently reinterpreted these kind of activity. activity. A qoodly these structures as due to structures to the the sudden sudden collision collision of of aa flying flying oversize oversize meteorite, meteorite,planetesimal,. planetesimal, or or result in comet comet with with the the earth's earth's surface. surface. Any such collision is bound to result in an awesome awesome explosion explosion which excavates a crater very much larger than the projectile itself and causes deformation crater larger the pro] ectile itself aiid causes deformation well beyond the Some geologists g<sologists still the boundaries of the the crater crater and below below its its bottom. Some still adhere adhere to to nward effects r fm a i n long after the the idea that this kind of deformation,of deformation,of which which the dow downward remain 2 to crater crater itself itself has has been been eroded eroded away, away, is is due due to to vulcanism. vulcanism. Others, u t i i e ~ s ,unwilling unwilling to take take sides, sides, refer to the structures in question as the result of some unidentified kind of 'cryptoexplosion." "cryptoexplosion." Except for the circle, which I have drawn in rather arbitrarily arbitrarily on the the assumption assumption that that the the by exposures on Limestone Limestone Mt., Mt., Sherman Hill, and sandstone sandstone to the disturbance recorded by southeast southeast is is in in fact fact the the result result of of impact, impact, Fig. Fig. 1 is is mostly mostly factual. factual. I have been been convinced convinced of of this for quite some time but heretofore heretofore have been been uncertain as to where the center of the the structure was likely to be and, consequently as to size of the circle. structure likely to be and, consequently as to size of the circle. was quided guided mainly by by the M-shaped M—shaped series In a first try at locating locating the the center, center, I was series of exposures exposures (Fig. (Fig. 1) between Limestone Limestone Mt. Mt. and and the the village village of of Pelkie. Pelkie. These These are are the the surface surface expression of a slightly more resistant layer in the Jacobsville which here is folded into a pair of north—plunging north-plunging anticlines. anticlines. A number number of people who who have studied studied large, large, well—exposed well-exposed have noticed noticed similar similar anticlines anticlines plunging plunging away away from from what what is generally generally referred referred impact structures have a "central "central uplift." uplift." Central uplifts uplifts are characteristic characteristic of impact structures structures which have a to as a If the direction of plunge were always directly away from the diameter of more more than than 2—3 2-3 km. km. direction of were always directly uplift, Limestone Mt. Mt. structure structure should be somewhere somewhere on a broad line uplift, then the center of the Limestone a somewhat Result: extending southward southward in in the the direction direction of of the the axes axes of of these these two two folds. folds. Result: somewhat have drawn on Fig. smaller smaller circle circle than than the the one one I have Fig. 1, assuming that that the the distances distances from from Limestone Limestone Mt. structure are, for some reason or other, other, about the Mt. and Sherman Sherman Hill to the center of the structure Unfortunately, the plunge is now always directly directly away from a central uplift, as anyone same. unfortunately, same. This can see who examines Plate 3 of Professional Professional Paper 599-H 599—H issued in 1972 by the USGS. USGS. This paper describes a "cryptoexplosion" "cryptoexplosion" structure structure in southwest southwest Texas named after the peak which Sierra Madera. crowns crowns its its central central uplift: uplift: Sierra Madera. seems to me a rhe magnetic high near The near the the center center of of Fig. Flq. 1 now seems a such much more more reliable reliable indicator indicator of of the actual location location of the (assumed) (assumed) uplift which lies at the center of the (assumed) (assumed) impart impact structure named after Limestone Limestone Mt. Mt. One One thing thing all the the magnetics people agree agree on is that that there there is a slightly curving string of of magnetic magnetic highs highs beginning beginning several several tens tens of of miles miles to to the the southwest and petering out rather rather abruptly abruptly aa short short distance distance north north of of Limestone Limestone Mt. Mt. These highs highs are are generally attributed to a a buried buried ridge ridge of of basalt basalt which which makes makes its its last surface surface appearance appearance on on the way to to Limestone Limestone Mt. Mt. in in the the aforementioned aforementioned Silver Silver Mt. Mt. Keweenawan basalt similar similar to, to, and and which forms the the backbone backbone of of the the Keweenaw Keweenaw Peninsula Peninsula is thought presumably an extension of, that which to underlie most sost of the area where where Jacobsville Jacobsville sandstone is now now present present directly directly below below whatever whatever happens, the unconsolidated unconsolidated material material may may lie lie on on top top of of it. it. As it happens, the strong strong magnetic magnetic high high which which II have chosen as indicating indicatinq the the location location of of the the (assumed) (assumed)central central uplift uplift in in the the Limestone LimestoneMt. Mt. structure structure is is several several km km southeast southeast of of the the main main string string of of magnetic maqnetic highs. (3) highs. Meshref Meshref and and Hinze Hinze (3) have explained explained this this as as due due to to aa horizontally—small horizontally-small block, block, bounded bounded on on all all sides sidesby by faults, faults, having been inexplicably inexplicably pushed pushed closer closer to to the the surface surface at at this this particular particular location. location. Many things happen as, and and soon after, after, the,initial theinitial crater Many crater is is excavated. excavated. They They are are so so complex, and and so so variable--dependin variable——depending on on aa number number of of factors~that factors——that to to describe describe them them numerous, so complex, 2) all in an abstract or depict their their effects effects accurately accurately in in aa diagrammatic diagrammatic cross—section cross-section(Fig. (Fig. 2) more or or impossible. The rise of a central uplift in a crater of the size suggested here is more is impossible. less inevitable, inevitable. Considerable Considerable downsliding downslidinq of of larqe larqe and and small small slices slices of of the the original oriqinal steep steep less " - 7 , ".k.- >---L-- . -A,.--- I 90 1 �I crater walls my cross-section cross—section II have Limestone Mt. walls is is also also more more or or less less inevitable. inevitable. In my have shown shown~imestone Mt. as having dropped down below its original level riding single huge slide block. block. ridinq on top of a sinqle Another possibility is that may have dropped down into a rift ("ring grab4n") that developed that. it may ("rinq qrab6n") i.nthe the rock rock surrounding surrounding the in the original original crater as an its its walls, walls, momentarily compressed compressed by the force force of the the explosion, explosion, bounced bounced back back toward, toward, and and even even beyond, beyond, their their original oriqinallocation. location. This might miqht better explain the fact that, in some places on the east. east side of "the mountain," rock layers are bent sharply upward as if draqqed dragged into that position by by downward movement relative to a either case case the diameter diameter of of the proposed disturbed (hidden) little farther farther east. east. In either (hidden) fault a little outer limits remains the area indicated indicated by by the the circle circle on on Fig. Fig. 1 remains the same. same. Its Its outer limits are are Set set by by apparently apparently undisturbed exposures of Jacobsville along the west branch of the the Otter River to the north and below below the the dam dam responsible responsible for for Prickett Prickett Lake Lake to to the the south. south. So much for for theory. theory. Now what about about evidence evidence to to support support it, it, as as promised promised by by the the title title to to situ," and this paper? paper? The evidence evidence is is divisible divisible into into two two categories: categories: (1) and (2) (2) this (1( "in situ," transported. transported. The "in situ" evidence is derived mainly from the isolated exposure of Jacobsville about Examination of Jacobsville about 2.5 2.5 km km due due west west of of the the peak peak of of the the magnetic magnetic high. high. Examination of aa thin thin section of rock here reveals that most of the original pore space between sand grains has been filled in with small angular fragments in what what is now glass, or partly crystallized crystallized glass-glass—— evidently aa fluid fluid mush mush when when squeezed squeezed into into place. place. Also Also the the original original sand sand grains, grains, in in some some cases cases together, implying implying a temporary, temporary, somewhat more or less crushed, have been squashed together, somewhat plastic condition. These two factors combined are probably responsible responsible for the fact that, among local condition. well drillers, the sandstone near the magnetic high has a reputation reputation for "tightness," well "tightness," meaning that it is is reluctant reluctant to to yield yield an an adequate adequate supply supply of of groundwater. groundwater. It may be mentioned mentioned also also that that the bedding visible visible in in this this small small exposure exposure dips dips about about 200 20' west. west. This This is is as as observed observed in in small small blocks pried out from between intersecting joints. We may be dealing here with cross—bedding, from between intersecting joints. be dealing here with cross-bedding, a very common feature feature in in the the Jacobsville. Jacobsville. If it is "true" "true" (overall?) (overall?) bedding, bedding, the the dip dip is is at least consistent Consistent with with the the idea idea of of aa central central uplift uplift to to the the east, east, which which must must have have been been least accompanied by some some outward outward tilting tilting of of adjoining adjoining sediments. sediments. The transported evidence evidence is found in thin mud flows flows apparently apparently derived derived from from retreating much thicker layers of outwash sand. These assumed glacial ice and intercalated between much sand. These assumed cobbles, are to be seen in two mudflows, heavily laden with slightly rounded pebbles and cobbles, sandpits a short distance east of the village of Alston, as shown in Fig. sandpits short distance east of the village of Alston, as shown in Fig. 1. 1. Although the the drumlin—like low hills direction of the last ice advance was from the northeast, indicated by drumlin-like in this area, suggesting that the cobbles and pebbles in the mudflows should have come from well to the north of the area of "tight" surrounding the (proposed) some place well "tight" sand surrounding (proposed) central sandstone show exactly the same uplift, thin sections of a few of the harder ones composed of sandstone the.same sort of metamorphism exhibited by thin sections sections cut cut from the the isolated exposure exposure of bedrock close close to the (assumed) (assumed) central central uplift. iiplift. REFERENCES REFERENCES ---,-.-. ( 1 ) Campbell, -- -..Area, (1) Campbell, R. N. E., E., 1952, 1952, Area, Houghton County, Michigan," unpublished M.S. thesis, Michigan Technological County, Michigan," M.S. thesis, Technological University. (2) Hoehl, . J., Hoehl, EE. J., 1981, 1981, "Geophysical "Geophysical Investigation Investigation of of the the Limestone Limestone Mountain Mountain Area Area of of Baraqa Baraga and and Houghton Counties, Counties, Michigan," M.S. Michigan," unpublished M .S. thesis, thesis, Michigan Technological Technological University. Meshref, W. N. MM., and W. W. J. J. Hinze, Hjnze, I""" 1970, -."Geologic Interpretation of Aeromagnetic Data in in ((3) 3 ) Meshref, . , and keromaqnetic Data Western Upper Peninsula !port of Investigation Investigation 12. 12. Peninsula of Michig; Michigan," Michigan Geological Survey, Report 'Connhv*?lr^a1 T n v o c t i rrati on n f tthe h o ?i lvor M o n ritain --.-_"Geophysical Investigation of Silver Mountain ' 91 �I I AEROMAGNETICS of the LIMESTONE MT. STRUCTURE Contour Interval—SO gammas Large circle—suggested outer limit of elide biocki from Crater wails K—bedrock esposure W . Read 1989 I I I I I I I 1 Fig. 1 1 CtU zz 00 +-I- U', m2 / POST-CRATFRING SLIDE SLOCIS, ETC. = SURFACE SURFACE BEFORE B E F O R E IMPACT IMPACT - I GLACIAL DEPOSITS 1 I Fig. Fig. t 2 Oiagrammatic Diagrammatic cross-section cross-section along along aa line line passing passing through through Limestone Limestone Mt. Mt. and and the the peak peak of of the the magnetic magnetic high hiyh shown shown in in Fiq. rig. 1. 2 92 1 I I I �THE T H E REAPPEARANCE REAPPEARANCE OF OF THE T H EHURONIAN HURONIAN IN IN WYOMING WYOMING Stuart Stuart M. M. Roscoe Roscoe Geological of Canada, 601 Booth St., Ottawa, Canada KJA Geological Survey Survey of Booth St., K I A 0E8 OE8 Positive Positive matches matches of of all all stratigraphic stratigraphic units units through through the thePhantom Phantom Lake strata, Deep Lake Group and lower part of the Libby Group Lake strata, Deep Lake Group and lower part of the Libby Group inin Wyoming Wyoming with with every every unit unit in in the the western western part part of of the the Huronian Huronian Supergroup in Ontario Supergroup in Ontario show show that that the the two twosuccessions successions were were originally originally contiguous. contiguous. Recognition Recognition of this this establishes establishes an animportant importantcontinental continental sundering sundering and and subsequent subsequent reconstruction, reconstruction, and and improves improves insights insights into into environments of deposition of Paleoaphebian environments of deposition of Paleoaphebian (earliest (earliest Proterozoic) Proterozoic) strata strata in in the the southern southern part part of of the theCanadian Canadian Shield Shield and andWyoming Wyoming structural structural province. province. The The Wyoming Wyoming Province, Province, like like the the Minnesota Minnesota River River Valley Valleyterrane, terrane, was was welded welded onto onto the the southern southern margin margin of of the the present present Superior Superior Province Province at at 2.7 2.7 Ga. Ga. Huronian Huronian strata strata were were deposited deposited 2.5-2.4 2.5-2.4 Ga in in an an ensialic repository developed astride ensialic repository developed astride the the boundary boundary between between the the two two future future structural structural provinces. provinces. Deposition Deposition was was controlled controlled by by synsyn - depositional depositional faulting faulting and and warping warping accompanying accompanying uplifts uplifts in in regions regions to to the east, north, and west as well as by superimposed effects of glacial the east, north, and west as well as by superimposed effects of glacial loading loading and and unloading unloading and and sea sealevel levelchanges. changes. Some Some enigmatic enigmatic granite granite bodies were intruded at 2.4 Ga. bodies were intruded at 2.4 Ga. Following Following intrusion intrusion of of Nipissing Nipissing gabbro gabbro sheets sheets atat 2.2 2.2 Ga, Ga, the the continent was fragmented. continent was fragmented. The The Wyoming Wyoming Province Province fragment fragment was was split split off off along along the the Manitoulin-Niagara Manitoulin-Niagara structural structural zone zone and and rotated rotated about about 135° 135' as asindicated indicated by byforesets foresetsand andother otherdirectional directionalfeatures features inin preserved preserved remnants remnants of of the the southeasterly southeasterly part part of of the the Huronian Huronian Supergroup Supergroup inin the the Medicine Medicine Bow Bow and and Sierra Sierra Madre MadreMountains Mountains inin southern Wyoming. southern Wyoming. The The Boxelder Boxelder Creek Creek Formation Formation in in the the Black Black Hills Hills of of South South Dakota Dakota isisanother anotherremnant remnant ofofrafted raftedHuronian Huronian rocks. rocks. Younger Younger Aphebian Aphebian strata strata were were deposited deposited on on margins margins of of the the Archean cratonic cratonic fragments, fragments, first on shelves shelves during during their their post post 2.2 2.2 Ga Ga Archean first on separation separation and and later laterininforedeeps.formed foredeeps.formed during duringocean oceanclosures. closures. They They include the the iron ironformation-bearing formation-bearing Marquette Marquette Range Range Supergroup, Supergroup, the the include fault-bounded upper part part of fault-bounded upper of the the Libby Libby Creek Creek Group, Group, rocks rocks inin the the Hartville Hartville uplift, uplift, and and the theEstes Estesand andRoberts RobertsDraw DrawFormations Formations inin the the Black Black Hills. Hills. Huronian Huronian rocks rocks were were folded foldedand andmetamorphosed metamorphosed along along with with these these younger younger strata strata during during 1.9-1.8 1.9-1.8 Ga Gacollisions collisions with with island island arc arc terranes terranes toto the the south, south, resulting resulting inin the the preservation preservation of of remnants remnants of of both both sets sets ofofstrata strataofofdisparate disparateage ageand andcharacter character on on the thenorth northsides sides of the theNiagara-Manitoulin Niagara-Manitoulin zone zone and and the theCheyenne Cheyennetectonic tectonic zone. zone. of 93 �I Review of of Analytical Analytical Methods Methods for the the Determination Determination of of Review Platinum Platinum Group GroupElements Elements Bernhardt BernhardtSaini-Eidukat Saini-Eidukat Dept. DepLof ofGeology Geologyand andGeophysics, Geophysics,University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 PGE's (platinum (platinum group group elements: elements: Pt, Pt, Pd, Pd, Rh, Rh, Ru, Ru,Ir, Ir,Os) 0 s )present presentanalytic analyticdifficulties difficulties PGE's due due to to low low natural natural background background levels levels in rocks (Pt and Pd: 10 10 ppb; Ru: 0.1 ppb). The in insolubiity solubilityofofthe thepure puremetals metalsinincommon commonacids acidsand andthe theease easewith withwhich whichRu Ruand andOs 0 soxidize oxidizetoto volatile volatilespecies speciespresent present additional additionaldifficulties difficultieswhich, which, when when ignored, ignored, lead lead to to low low recoveries recoveries of of Os 0 sand andRu Ru(Van (VanLoon, Loon,1984). 1984).Steps Stepswhich whichmust must be beconsidered consideredininany anyPGE PGEanalysis analysis include: include: 1) 1)sample sampledecomposition, decomposition, 2) 2) separation separation of of the the POE's PGE's from from the the products productsof ofthe the sample sample decomposition, decomposition,and and 3) 3) quantitative quantitative determination of concentration. concentration. The The following following survey survey of of analytical analyticaltechniques techniques is is presented presented to to provide provide aa guide guide to to the the current current literature. literature. Sample Sample decomposition decomposition techniques techniques The The major major elements elements in in PGE-bearing PGE-bearing rocks can be readily readily brought brought into into solution solution with with conventional conventionalacid acidtechniques techniquessuch suchasasHF-aqua HF-aquaregia regiadissolution. dissolution.However, However, little littledata data exists exists on on the the solubility solubilityof of major majorplatinum platinum group groupminerals minerals such suchas assulfides sulfidesand andarsenides. arsenides. Reported Reported analyses analyses for Pt Pt and and Pd Pd on onstandard standardreference reference materials materials using using acid aciddigestion digestion usually usually are are low low (Hall (Hall and and Bonham-Carter, Bonham-Carter, 1988), 1988), and and Os 0 s and and Ru Ru are aregenerally generallylost lostas as volatile Chlorination can canbe beused used volatile tetroxides tetroxides unless distillation procedures are employed. Chlorination to to decompose decomposesamples samplesby by passing passingdry drychlorine chlorineover overaamixture mixtureof of the thesample samplewith withNaC1 NaCl and and activated activatedCC (Westland, (Westland,1981; 1981;Dolezal Dolezalet etal., al., 1966). 1966).The Thevolatilized volatilizedmetals metalsare areabsorbed absorbedinin HC1, resulting in soluble can also be HC1, resulting soluble PGE-chlorides. PGE-chlorides. Decomposition Decomposition can be achieved achieved with with oxidizing oxidizing fusions fusionsusing usingNa Naand andKKcarbonate carbonateor orhydroxide, hydroxide, Na202, Na202, borax borax or orboric boric oxide, oxide, Li Li tetraborate tetraborateor or metaborate, metaborate, K K pyrosulfite, pyrosulfite,or or the the alkaline alkalinefluorides fluorides(Johnson (Johnsonand and Maxwell, Maxwell, 1981). 1981).Such Such fusions fusions may may suffer sufferfrom fromslow slow attack attack on onPGE's PGE's (Westland, (Westland,1981), 1981), and and may may also alsoresult resultin inloss lossof ofOs 0 sand andRu. Ru. The reducing fusion fusion (classical (classical lead lead fire fireassay) assay)serves servestwo twofunctions: functions: The reducing decomposition decomposition and and POE PGE separation. separation. The The fusion fusion produces produces aa two two phase, phase, Pb°-slag PbO-slagsystem system in in which which the the PGE's PGE's are are distributed distributedinto into the the Pb°. PbO.Upon Upon oxidation oxidation (cupellation) (cupellation) to remove remove the the Pb, Ir, and Ru occurs. occurs. Pb, the the POE's PGE's are are left left in in aapurified purified metallic metallic state, state, although although loss of Os, Os, Jr. Any number of determination methods can be used on the bead. Detailed accounts Any number of determination methods can be used on the bead. Detailed accountsof of the thePb Pb assay assay method method are given given in in Beamish Beamish and and Van Loon (1977) and Haffty et al. (1977). (1977). To To overcome of the Pb fire assay, similar to matte overcome the limitations limitations of assay, a collection collection method method similar matte smelting wasdeveloped developed (the (the nickel nickel sulfide sulfide fire fireassay; assay;Robert Robertetetal., al.,1971; 1971;1972). 1972). smeltingwas The The sample sample is is decomposed decomposed and and the the POE's PGE's are are distributed distributed into the the sulfide sulfide phase. phase. This This method has proven proven equal equal to to or or better better than collection using Pb. Among the advantages advantages of aa NiS NiS collector collectorare: are: •lower •smaller *smallercharge chargeto to sample sampleratio ratio *lowerfusion fusion temperature temperature •collection *collectionof of all allPGE's PGE's with with no nopretreatment pretreatmentfor forhigh highSS samples samples as as in in the the lead lead method, method, and and •no *nochange change in in charge charge composition composition required for for different samples, samples, except for chromite chrornite ores. The The PGE's PGE's are are separated separatedfrom fromthe theNiS NiSusing usingHC1 HC1 and are are determined determined by by neutron neutron activation activation analysis analysis (NAA) (NAA) (all (all POE's), PGE's), or or are are dissolved dissolved in in aqua aqua regia regia and anddetermined determinedby byemission, emission, absorption absorption or or mass mass spectrometry spectrometry(Pt, (Pt, Pd, Pd, Rh). Rh). Recent Recent advances advancesin in this this method method include includethe the reduction reduction of of collector collectormass mass to to as as little little as as 0.5 0.5 gram gram without affecting affecting element element recovery (Asif (Asif and and Parry, Parry, 1989). 1989). 94 * �I Separation Separation techniques In the Pb fire fire assay assay ,,Ag Ag is is separated separated from from Au, Pt and and Pd by by nitric acid. acid. In In the theNiS NiS fire fire assay, assay, the the PGEs PGE'sare areseparated separatedfrom fromthe thenickel nickelsulfide sulfideby bydissolution dissolutionof ofthe thebutton buttonininHC1; HC1; the the PGE PGE sulfides sulfides are are filtered filtered and and their theirconcentration concentration determined. determined. Any Any POE's PGE's lost lost due duetoto dissolution into HC1 HC1can canbe berecovered recoveredby bycoprecipitation coprecipitation with Te (Shazali et al., al, 1987). 1987). Os 0 s and and Ru Ru can can be beseparated separatedfrom fromcomplex complex solutions solutions and and from from each each other other using using distillation. distillation.The Thetetroxides tetroxidesare arecollected collectedin in reducing reducing or or alkaline alkalinesolutions, solutions, or or in hydrogen hydrogen peroxide (Beamish Loon, 1977; 1977; Walker, Walker, 1988). 1988). Koster Koster & & Schmuckler Schmuckler (1967) (1967) (Bearnish and Van Loon, synthesized synthesized chelating chelating ion ion exchange exchangeresins resinswhich whichstrongly stronglybind bind PGE's PGE's and and Au Au but but not not base base metals. metals. This This method method involves involves acid acid dissolution dissolution of the the sample, sample, binding binding of of aaPOEPGEhydroxy-chloride hydroxy-chloridecomplex complex to to the the resin, and elution (Warshawsky et al., 1980). A variety of determination methods can can be applied. Nadkarni determination methods Nadkarni and Morrison Momson (1974) used an an ion ion exchange exchange resin resin to to separate separatePOE's PGE's from from samples samples already already activated activated with with neutrons; neutrons; the the resin resin with adsorbed Potential loss of adsorbed PGE's was was counted counted to determine determine PGE concentrations. Potential PGE's during dissolution and incomplete elution of PGE's from the resin may may hamper hamper POE extraction methods PGE analysis using resins. Liquid—liquid Liquid-liquid extraction methods are are undergoing intensive research for for both both analytical analytical and and extracfive extractivepurposes purposes (Warshawsky, (Warshawsky, 1983), 1983),but but routine routine laboratory arenot notyet yetcommon. common. laboratorymethods methods for forPOE PGE determination determinationare Determination Determination techniques techniques The The variety variety of of analytical analyticaltechniques techniquesavailable availableto to determine determinePGE's PGE's has hasincreased increasedsince since Crocket Crocket and and Cabri's Cabri's (1981) (1981) review review of of POE PGE analytical analyticalmethods. methods. Graphite Graphite furnace furnace atomic atomic absorption absorption spectrometry spectrometry (GF-AAS), (GF-AAS),inductively inductivelycoupled coupledplasma plasma emission emissionspectrometry spectrometry (ICP-ES), (ICP-ES),and anddirect directcurrent currentplasma plasma emission emission spectrometry spectrometry (DCP-ES) (DCP-ES) are arecurrently currently widely used for for the the determination determination of Pt, Pt, Pd, Pd, and and Rh, Rh, usually usually on on samples samplesfrom from which which PGE's PGE's have have been been separated separated and and concentrated. concentrated. The The trend trend in in determinative determinative techniques techniques isis toward ( N A A) A ) and and inductively inductively coupled coupled plasma-mass plasma-mass toward neutron neutron activation activation analysis analysis (NA spectrometry spectrometry (ICP-MS). (ICP-MS).AAcomparison comparisonof of current currenttechniques techniques can can be be found found in in Hall Hall and and Bonharn-Carter Bonham-Carter(1988). (1988). NAA NAA is is widely widely used used for fordetermination determination of of all allsix sixPGE's PGE'satatlow lowconcentrations concentrations (Hoffman, (Hoffman, et al., al., 1978; 1978;Shazali Shazalietetal., al.,1987). 1987).Decomposition Decomposition and and separation separationsteps stepsare are usually usually employed employedto to increase increasesensitivity sensitivity and and reduce reduce interferences; interferences; these these include includethe the Pb Pb and and NiS NiS fire fire assay assay techniques, techniques, ion ion exchange exchange resins resins and and distillations. distillations.The The sample sample is is bombarded bombarded with with neutrons, neutrons, and and the the intensities intensities and and wavelengths wavelengths of any radioactive daughter daughter elements elements produced producedare aremeasured. measured. Quantitative Quantitativedetermination determinationis is made made by by comparison comparisonwith with standards. standards. Recent in this method of Rh Recent advances advances in method include include the direct direct determination determination of Rh with with no no preconcentration preconcentration using using 38 38MeV MeV alpha alphaparticles particles(Volfinger, (Volfinger,1989). 1989). A A review review of of the the technique technique of of ICP-MS ICP-MScan canbe befound foundininFlouk Houkand andThomson Thomson(1988), (1988), and and its its application application to to PGE PGE determination determination is is described in Date et al. al. (1987) (1987) and and Gregoire Gregoire (1988). (1988). The The decomposed decomposedsample sampleisisintroduced introduced as asaa fluid fluid usually usually via via aa nebulizer nebulizerto toaaplasma plasma are conducted conducted to to aa quadrupole quadrupolemass mass in which which atomization atomizationand andionization ionization occur. occur. The The ions ions are in analyser. analyser. The The technique technique affords affords excellent excellent sensitivity, sensitivity, linear linear dynamic dynamic range range and andmultimultielement capability. capability. Determination Determination of of Pt, Pt, Pd, Pd, and and Rh Rh using using fire fireassay assay preconcentration preconcentrationisis element already aa standard standardtechnique. technique. As As usual, usual,precautions precautionsin in the thedecomposition decompositionstep stepmust mustbe be already 0 s and and Ru. Ru. Techniques Techniques such such as as isotope isotope dilution dilution have have been been taken when when analyzing analyzing for for Os taken developedfor for determination determinationofofPtPtand andOs 0 son onthe theICP-MS ICP-MS(Date (Dateetetal., al.,1987). 1987). developed 95 �I REFERENCES Asif, M and Parry, J.,1989, 1989, Elimination Elimination of of reagent blank problems in the fire-assay pre-concentration Parry, S SJ., pre-concentration of of the platinum group elements and gold with a nickel sulfide bead bead of of less than than one gram mass. mass, Analyst, v.114, V. 114,pp. pp. 1057-1059. 1057-1059. Beamish, F. E. and Van Loon, J.J.C., Bearnish, C., 1977, 1977,Analysis Analysis of ofNoble Noble Metals, Metals,Academic Academic Press, Press, N.Y. N.Y. Crocket, J.H. J.H. and Cabri, LJ., U., 1981, elements, in in Cabri, Cabri, L.J., U., 1981,Analytical Analyticalmethods methods for for the the platinum-group platinum-group elements, ed., Platinum-Group Elements: Geology, Recovery, Can. Can. Inst. Mining Elements: Mineralogy, Mineralogy, Geology, Mining Metall. Metall. Spec. Spec. Pub. 23, pp. 71-82. 71-82. A.R., Davis, A.E. Y.Y., 1987, The potential potential of fire assay and inductively Date, A.R., A.E. and Cheung, Y.Y., inductively coupled plasma source mass spectromeiry spectrometry for the determination determination of platinum group elements in geological geological materials, 112, pp. 1217-1222. 1217-1222. materials, Analyst, v. 112, Dolezal, J., J., Povondra, P., and Dolezal, and Sulcek, Sulcek, Z., Z., 1966, 1966,Decomposition Decomposition Techniques Techniques in in Inorganic Inorganic Analysis, Analysis, American Elsevier Publ. Co., Inc., Inc., N.Y., N.Y., 224 pp. Gregoire, D.C., D.C., 1988, Gregoire, 1988, Determination Determination of platinum, platinum, palladium, palladium, ruthenium, ruthenium, and iridium in in geological geological materials materials by inductively inductivelycoupled coupled plasma plasma mass mass spectrometry spectrometry with with sample sampleintroduction introductionby by electrothermal electrothermal vaporization, J. Anal. Atom. Atom. Spectrom., Spectrom., v. 3, 3, pp. pp. 309-314. 309-314. Haffty, J., Riley, L. B., and Goss, W. D., 1977, 1977, A A manual on fire fire assaying assaying and determination determination of the noble noble metals in geological 1445, 58 58 pp. pp. geological materials, materials, U.S.G.S. U.S.G.S. Bull. Bull. 1445, G.F., 1988, Review of of methods methods to determine gold, platinum 1988, Review platinum and Hall, G.E.M. G.E.M. and Bonham-Carter, Bonham-Carter, G.F., palladium in production production oriented oriented geochemical geochemical laboratories, laboratories,with with application applicationof of aa statistical statisticalprocedure procedureto to bias, J. Geochem. Geochcm. Explor., Explor., v. v. 30, 30, pp. pp. 255-286. 255-286. test for bias, Hoffman, E.L., E.L., Hancock, Hancock, R., R., Naldrett, Naldrett, A.J., A.J., Van Van Loon, Loon,J.C., J.C., Hancock, Hancock,R.G.V. R.G.V.and and Manson, A., Hoffman, A.. 1978, 1978, The determination determination of all the platinum group elements and gold in rocks and ores by neutron activation preconcentration by sample size, size. Anal. Anal. analysis after preconcentration by a nickel sulfide fire assay technique on large sample Chim. Acta, v. 102, 102, pp. pp. 157-176. 157-176. R.S. and Thomson, J.T., J.T., 1988, spectrometry, Mass Spectrom. Rev., Rev., v. 7, Houk, R.S. 1988, Inductively coupled mass spectrometry. 425-461. pp. 425-461. Johnson, W.M. and Maxwell, J.A., 1981, Rock and Mineral Analysis, 2nd John Wiley Wiley and and Sons, Sons, 489 489 Johnson, 2nd ed., ed., John pp., pp., N.Y. N.Y. K0ster.G. Schmuckler, 1967, 1967, Separation Separation of Koster,G. and and G. 0. Schmuckler, of noble noble metals metals from from base base metals metals by by means means of of a new chelating resin, Anal. Chim. Acta, v. 38, 38, pp. 179-184. 179-184. Nadkarni, R.A G.H., 1974, Determination R.A and Morrison, G.H., Determinationof of the the noble noble metals metals in in geological geological materials materials by by neutron activation analysis, Anal. Anal. Chem., Chem., v. v. 46, 46, pp. pp. 232-236. 232-236. Robert, Robert. R. V. V. D., D., van van Wyck, Wyck, E., E., Palmer, Palmer, R., R., 1971, 1971,Concentration Concentration of of the the noble noble metals metals by by aafire-assay fire-assay technique technique using nickel sulfide sulfide as as the the collector, collector, N.I.M. N.I.M. Report Report 1371, 1371, 14 14 pp. pp. 1972,The The development development of of aafire-assay fire-assay Robert, R. V. D., D., van van Wyck, Wyck, E., E., Palmer, Palmer, R., R., and and Steele, Steele,T.W., T.W., 1972, Robdrt, procedure using nickel sulphide as the collector for the noble metals, Journal of the the South South African African Chemical Inst., v. 179-189. v. 25, pp. 179-189. I., Van't Dack, L., and Gijbels, Shazali, I., Gijbels, R., 1987, 1987, Determination Determination of precious metals in ores ores and and rocks rocks by by i e assay and thermal neutron activationigamma-spectrometry activation/gamma-spectrometry after preconcentration by nickel sulphide ffire coprecipitation with tellurium, Anal. Chim. Acta, v. 196, 196, pp. 49-58. J.C., 1984, Accurate Accurate determination of the noble metals I. Sample decomposition decomposition and methods of Van Loon, J.C., separation, Trends Trends in Anal. Chem., v. 3, pp. pp. 272-275. 272-275. v. 3, Volfinger, Volfinger, M., 1989, 1989, Determination Determination of of rhodium rhodium in in geomaterials geomaterialsby by high-energy high-energyalpha-particle alpha-particleactivation, activation,J.J. Radioan. Nucl. Chem., Articles, v. 131, 131, pp. 19-35. 19-35. Walker, RJ., R.J., 1988, 1988,Low-blank Low-blank chemical chemical separation separation of rhenium rhenium and osmium osmium from gram quantities of Walker, from gram of 60, pp. measurement by resonance ionization mass spectrometry, Anal. silicate rock for measurement Anal. Chem., v. 60, 1231-1234. 1231-1234. Warshawsky, A., A., Fieberg, Fieberg, M.M.B., Mihalik, P., P., Murphy, Murphy, T.G. T.G. and Y.B. M.M.B., Mihalik, Y.B. Ras, 1980, 1980, The separation separation of Platinum group metals (PGM) (PGM) in chloride media by isothiourium isothiourium metals, metals, Separation Separation and and Purification Purification Methods, v. 9, pp. 209-265. 209-265. Warshawsky, Warshawsky, A., 1983, 1983, Integrated Integrated ion ion exchange exchange and and liquid-liquid liquid-liquid extraction extraction process process for for the the separation separation of of platinum group metals (POM), (PGM), Separation and and Purification Purification Methods, Methods, v. v. 11,95-130. 11,95-130. Westland, A.D., A.D., 1981, Inorganic platinum-groupelements, elements,in IaCabri, Cabri,L.J., U., ed., Inorganic chemistry of the platinum-group ed., PlatinumPlatinumGroup Elements: Mineralogy, Geology, Recovery, Recovery, Can. Can. Inst. Inst. Mining Mining Metall. Metall. Spec. Spec. Pub. Pub. 23, 23, pp. pp. 5-18. 96 1 �I Structural Structuralstudies studies in inthe the Huron Huron Bay Bay Parautochthon, Parautochthon, Upper Upper Michigan. Michigan. SAJA, (Dept. SAJA, D.B., D.B., and and Gregg, Gregg, W.J. W.J. (Dept. of of Geological Geological Engineering, Engineering, Michigan Michigan Tech. Univ., Houghton, Houghton, Mi. Mi. 49931) 49931) The The Huron Huron Bay Parautochthon, Parautochthon, located located between between the the Huron Huron Mountains Mountains and and Keweenaw Keweenaw Bay Bay in in Baraga Baraga County, County, Upper Upper Michigan, Michigan, is is aa belt bound by the belt of of strained strained Proterozoic Proterozoiciuetasediinents metasediments bound the Jacobsville Jacobsville sandstone sandstone to to the the north north and Archean Archean Gneisses Gneisses to to the the east east and and south south (fig. (fig. 1). 1). This This belt of of deformed deformed metasediments metasediments belongs belongs to to the the Upper Upper Slate Slate Member Member of of the the Michigamme Michigamme Formation. Formation. It consists consists of a thin thin sequence sequence of shelf sediments sediments overlain overlain by aa thick thick sequence sequence of of slates slates and and discontinuous discontinuous psainmitic psanunitic units. Early work in the region region by Klasner (1978) (1978) showed at least least four four generations tectonic lineations generations of foliation foliation and three tectonic lineations exist exist as as aa result result of of the the 1.9 1.9 Ga Ga Penokean Penokean orogeny. orogeny. Recent Recent studies studies by Dyke Dyke (1988), Sikkila (1987), (1987), and Van Roosendaal (1985) (1985) in in the the area area basin have have documented documenteda athrust/fold thrust/fold formerly formerly known known as as the the Baraga Baraga basin belt belt characterized characterized by multiple multiple generations generations of of iinbricate imbricate thrusting associated with northward northward verging verging folds. folds. A prominent prominent change change in in the the structural structural style style and amount of finite strain strain was shown shown by Gregg (1989) to mark the existence of an east-west trending Gr6 nding thrust fault near the village of L'Anse. This large scale th] :ale Figure 1: Generalized geologic map of the Huron Bay Parautochthon. A — Huron River, B - Slate River, C - Silver Falls Anticline, D — Keweenaw Bay, E Falls River, F Mountain Syncline. Little 97 I �I I 1 cm I so I-i 1 cm I I I I I 2: rauics Faults viewed normal Figure L: figure nonnax to 10 the \.ne plane p~-aneof o r cleavage. cxeavage. discontinuity, discontinuity, known known as as the Falls River Thrust, separates separates the the Baraga Belt into into two two previously unrecognized unrecognized structural structural domains, domains, the Huron Bay Parautochthon Parautochthon to the north, and the autochthonous autochthonous the Falls River Slice Slice to to the the south south (fig. (fig. 1). 1). the upper Throughout the Huron Bay Parautochthon, rocks of the slate member display only one one structural structural style style group. group. Generally Generally by Bl B1 folds with with Sl S1 cleavage, this style group is characterized by B1 overprinted by small overprinted small post-kinematic low low angle angle thrust thrust faults. faults. Bl folds display shallow axial plunges to to northwest northwest and and southeast, southeast, and axial planes that that dip to to the the southwest southwest from from 45 45 to to 60 60 degrees. degrees. Fold profiles vary from open to gentle folds with amplitudes amplitudes of less than 2 meters in the north-central north—central and northeast parts of 1), to high amplitude the parautochthon (areas (areas AA and B on fig. fig. 11, S1 tight folds folds along the the south south west west section section (area (area CC of of fig. fig. 1). 1). Sl slaty cleavage continuous mica films cleavage is is defined defined by by anastoinosing, anastornosing, continuous films with bedding-parallel of neomineralized white mica , with fine neomineralized white bedding—parallel fine detrital layer silicates and opaque minerals in the intervening intervening quartzo-feldspathic quartzo-feldspathic microlithons. microlithons. Large chorite-white mica aggregates with (001) (001) traces parallel to bedding occur aggregates occur commonly it a within the microlithons microlithons and and have have strain strain shadows shadows parallel parallel to to SS, feature which which distinguishes Sl S1 from other foliations foliations present in I , 98 i �the allochthonous the allochthonous Falls Falls River River Slice. Slice. The The length length of of the the strain strain shadows shadows increases increases from from east east to west in in the the parautochthon, parautochthon, and and Thrust, with from north to south across the Falls River Thrust, increasing strain. parautochthon increasing strain. In the eastern end of the parautochthon numerous structural domains occur, numerous structural domains occur, marked by small small changes changes in in the the the dip of fold trend of L1 Ll and in in the fold axial axial surfaces surfaces and and slaty slaty cleavage. Thrust faults faults striking striking N58'W dipping 18° 18" to to the the cleavage. N58°W and dipping south the domains domains and drag bedding bedding into south define the into a a near near vertical vertical attitude. Although Although no no second second generation generation fabric fabric elements elements are are attitude. ^ = - l + - are =l^kely post post B1 Bl present in in the area, the the area, the faults most likely structures. structures. Widespread evidence evidence of normal faulting has has been been observed observed in in the parautochthonous both the parautochthonous and and autochthonous autochthonous terrains. terrains. This This evidence in scale from outcrop size evidence of extension, extension, ranges ran' discontinuities to small surfaces a few square discontinuities small slickensided s centimeters centimeters in in area area (fig. (fig. 2). Smaller fault surfaces are curviplanar curviplanar to to nearly nearly cylindrical ~yli..-~.^~in shape. Stereo net analysis ui.ulysis of the the surfaces surfaces shows shows that that the the slickenlines slickenlines are are typically typically parallel to to the the cylindrical cylindrical axis axis which itself itself lies lies in in the the plane plane of Sl cleavage. cleavage. A coating coating of of goethite, goethite, which is is layered layered over over the the of S1 slaty cleavage surfaces, enhances slickensides frequently slickensides and frequently delineates motion as delineates the the plane plane of of motion as it it oscillates oscillates between between the the cylindrical cylindrical fault fault surfaces, surfaces, bedding bedding planes, planes, and and cleavage. cleavage. Further movement along the Further evidence evidence of of movement the preexisting preexisting planes planes of of cleavage is is the the normal normal offset offset along along cleavage cleavage of of aa reduction reduction spot spot cleavage viewed parallel to the the bedding-cleavage bedding-cleavage intersection intersection lineation. lineation. parallel to observed with with Finally, foIds observed Finally, the the existence existence of sigmoidal sigmoidal drag drag folds offset rock deformation. deformation. offset laminar laminar bedding is is evidence evidence of hard rock mn-+ "--- -^.- REFERENCES Dyke, G.A., 1988, Dyke, G.A., 1988, Structure Structure and stratigraphy stratigraphy on on the the Silver Silver River River area, area, Baraga Baraga County, County, Michigan, Michigan, (unpub. (unpub. M.S. M.S. thesis), thesis), Michigan Technological Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 87 87 p. p. W.J., 1989, Gregg, W.J., 1989, Effects Effects of large large scale scale overthrusting overthrusting on on fold fold geometry geometry and and finite finite strain strain in in the the Baraga Baraga thrust/fold belt, belt, Upper Michigan: Geol. of Upper of Michigan Michigan Symposium Symposium I. I. Michigan Michigan Department of Natural Resources, Resources, Lansing, Lansing, Michigan, Michigan, p. 14. Department 14. Klasner, J.S., 1978, Penokean Penokean deformation and associated associated Klasner, J.S., 1978, deformation and metamorphism in in the the Western Western Marquette Marquette Range, Range, northern northern Michigan, Geol. Soc. Amer. Bull., v. 89, 89, p. 711—722. 711-722. Michigan, Sikkila, K.M., 1987, Sikkila, K.M., 1987, A structural structural analysis analysis of of Proterozoic Proterozoic metasediments, northern metasediments, northern Falls Falls River, River, Baraga Baraga County, County, Michigan, (unpub. Michigan, (unpub. M.S. M.S. thesis), thesis), Michigan Michigan Technological Technological University, Houghton, Michigan, Michigan, 103 103 p. p. University, Houghton, Van Roosendaal, Roosendaal, D.J., D.J., 1985, 1985, An An analysis analysis of of rock rock structures structures and and Van of the the Huron Huron strain in cleaved politic pelitic rocks, East Branch of River, River, Baraga Baraga county, county, Michigan, Michigan, (unpub. (unpub. M.S. M.S. thesis), thesis), Michigan Technological University, University, Houghton, Houghton, Michigan, Michigan, 82 82 p. p. Michigan Technological 99 I I �U GEOCHEMISTRY GEOCHEMISTRY OF OF UNMINERALIZED UNMINERALIZED ROCKS ROCKS IN IN THE THE PARTRIDGE RIVER RIVER INTRUSION, INTRUSION, DULUTH DULUTH COMPLEX COMPLEX PARTRIDGE Severson and and Steven Steven A. Hauck Hauck Mark J. Severson Mark Natural Natural Resources Resources Research Research Institute, Institute, University of of Minnesota, Minnesota, Duluth Duluth University The Partridge Partridge River River intrusion intrusion(PRI) (PRI) of of the the Duluth Duluth Complex, Complex, The northeastern Minnesota, contains aa wide wide variety variety of of troctolitic, troctolitic, northeastern gabbroic, and and ultramafic ultramafic rock rock types. types. on correlations correlations in in Based on (83 holes) holes) and and reconnaissance reconnaissance mapping, mapping, the the PRI PRI has has been been drill core core (83 drill subdivided subdivided (Figure (Figure 1) 1) into: into: Partridge River River Troctolite Troctolite Series Series Gabbro Complex (PRGC), (PRGC), and and Oxide-bearing Oxide-bearing (PRTS), Partridge River Gabbro Ultratnafic Intrusions (OUI). Ultramafic Intrusions (OUI). The The PRTS PRTS consists consists of of at at least least eight eight igneous units that that are are correlated correlated in in drill drill holes holes over over an an major igneous indicated indicated eleven eleven mile mile strike strike length length extending extending (NE (NE to to SW) SW) from from the the Dunka Cu-Ni deposit deposit to to the the Wyman Wyman Creek Creek Cu-Ni Cu-Ni deposit deposit Dunka Road Road Cu-Ni (Severson, 1988; 1988; Severson Severson and and Hauck, Hauck, 1990). 1990). These These eight eight units units are are (Severson, characterized by by various various troctolitic troctolitic rocks rocks and and are characterized are diagrammatically diagrammatically portrayed Most portrayed in Figure Figure 2. 2. Most of of the the upper upper units units (Ill-VIlI) (III-VIII) represent represent single single cooling cooling units units in in that that they they are are floored floored by by aa bedded bedded ultramafic member (picrite (picrite to dunite); dunite) ; whereas, other units near the exhibit an overall overall heterogeneous heterogeneous nature the footwall footwall (I (I and and II) 11) exhibit nature and and contain abundant abundant internal internal members members reflecting reflecting continuous continuous magma magma replenishment. lateral ftfaciesff "fades" replenishment. Some Some of the the units also exhibit lateral changes changes along along strike strike and and downcutting downcutting relationships relationships indicating indicating aa complex complex intrusive intrusive history. history. The The PRGC PRGC is is situated situated at at the the southeastern southeastern portion portion of of the the investigated investigated area area and consists consists of oxide—bearing oxide-bearing gabbroic gabbroic and and troctolitic troctolitic rocks; rocks; both both locally locally exhibit exhibit excellent excellent modal modal bedding. bedding. Portions Portions of of the the PRGC PRGC were were originally originally interpreted interpreted as as aa hornfelsed hornfelsed basalt basalt (Colvin (Colvin Creek Creek "Gabbro", MGabbroN,and and parts parts of of the the Powerline PowerlineGabbro). Gabbro). However, reconnaissance reconnaissance mapping mapping revealed revealed the the presence presence of of several several However, unusual unusual sedimentary—like sedimentary-like structures that are not not indicative indicative of of typical typical North North Shore Shore Volcanic Volcanic basalts, basalts, and and an an origin origin via via magmatic magmatic density density currents currents is is suggested. suggested. The are later later pegmatitic pegmatitic intrusions intrusions consisting consisting of The OTJIs OUIs are of dunite, dunite, peridotite, peridotite, clinopyroxenite, clinopyroxenite,and and lesser lesser picrite picrite and and melagabbro; melagabbro; all all are massive oxide (>lo%) and and contain contain semi—massive semi-massive to to massive oxide are oxide—bearing oxide-bearing (>10%) horizons. horizons. These These bodies bodies are are intrusive intrusive into into the the PRTS PRTS and and include include the the Longnose, Longnose, Longear, Longear, Section Section 17, 17, Wyman Wyman Creek, Creek, and and Skibo Fe—Ti Fe-Ti prospects. prospects. The portions of all units The unmineralized unmineralized portions units were were sampled sampled (155 (155 in order order to to establish establish background background geochemical geochemical levels levels and and samples) in lithogeochemical signatures units of of lithogeochexnical signatures for for each each of of the the various various rock rock units Whole the the PRI. PRI. Whole rock, rock, rare-earth rare-earth elements, elements, trace trace metals, metals, and and precious precious metal metal analyses analyses were were conducted. conducted. Background Background Pd, Pd, Pt, Pt, and and Au Au values in in the the major major rock rock groups groups average average 10 10 ppb, ppb, 20 20 ppb, ppb, and and 55 ppb ppb values respectively. respectively. However, However, slightly slightly elevated elevated background background values values are are associated I1 (15 (15 ppb, ppb, 24 24 ppb, ppb, and and 99 ppb ppb respectively), respectively), associated with with Unit Unit II and and the the OUI OUI rock rock group group (15 (15 ppb, ppb, 24 24 ppb, ppb, and and 17 17 ppb ppb respectively). respectively). In ides), five (<I%suif sulfides), five In the the course course of of sampling sampling unmineralized unmineralized rock rock(<1% anomalous anomalous samples samples (>200 (>200 ppb ppb combined combined Pd Pd and and Pt) Pt) were were revealed revealed with with maximum of of 910 910 ppb. ppb. The The OUI OUI units units are are the the most most geochemically geochemically aa maximum I 100 1 �unique unique in in that that they they have have elevated elevated background backgroundvalues valuesfor forTi02, Ti02,V, V, Cr, Cr, relative to to the the other other Pb, Te, Te, Au, and and W relative Pb, igneous igneous rocks rocks of of the the Partridge Partridge River River intrusion. intrusion. Geochemical data (whole (whole rock, REE) support the the breakdown of Co, Co, Cu, Cu, Cd, Cd, C, C, Be, Be, Sc, Sc, the various various rock rock units units identified identified within within the the Partridge Partridge River River intrusion. Several intrusion. Several X—Y X-Y plots plots and and spider spider diagrams diagrams have have been been constructed constructed and and show show aa definite definite clustering clustering of of specific specificrock rockunits, units, and major igneous and within within each each of of the the major igneous rock rock units units some some specific specific rock rock types types also also show show clustering clustering (the (the MG-Number MG-Number plot plot depicted depicted in in Figure Figure 3 is one example). example). For is one For instance, instance, Units Units II and and II I1 exhibit exhibit aa markedly markedly different geochemical signature when compared to to the the other other PRTS PRTS units. One interpretation units. interpretation of of this this difference difference is that that magma magma contamination contamination due due to to assimilation assimilation of of footwall footwall material material was was important in The lower in their their genesis. genesis. lower half of of Unit Unit I, I, which which contains the the most most hornfels hornfels inclusions, inclusions, demonstrates demonstrates aa markedly markedly different geochemical geochemical signature signature when compared compared to to the the other other PRTS PRTS units. units. The The basal basal ultramafic ultramafic horizons horizons within within the the PRTS PRTS all all cluster cluster together together and and represent represent the the most most primitive primitive rock rock type type sampled. sampled. All All rock rock units units of of the the PRGC PRGC exhibit exhibit aa different different geochemical geochemical signature, signature, which, in in turn, turn, is is similar similar to to the the geochemical geochemical signature signature for for the the lower half half of of Unit Unit I. I. The The OUT OUT units units exhibit exhibit aa markedly markedly different different lower geochemical geochemical signature signature when when compared compared to to the the PRTS PRTS ultramafic ultramafic horizons horizons and and to to all all the the other other PRI PRI units. units. Severson, Severson, M.J., M. J., 1988, 1988, Geology and and structure structure of of aa portion portion of of the the Partridge Partridge River River intrusion: intrusion: aa progress progress report: report: Technical Technical Report 78 p. p. Report NRRI/GMIN-TR-88-08, NRRI/GMIN-TR-88-08, Duluth, Duluth, Minnesota, Minnesota, 78 Severson, Severson, N.J., M.J., and and Hauck, Hauck, S.A., S.A., 1990, 1990, Geology, Geology, geochemistry, geochemistry, and and stratigraphy of aa portion portion of of the the Partridge Partridge River River Intrusion: Intrusion: Technical Technical Report Report NRRI/GMIN-TR-89-ll, NRRI/GMIN-TR-89-11, Duluth, Duluth, Minnesota, Minnesota, 236p. 236p. LEGEND PRTS - OUTLINES AREA OF PARTRIDGE RIVER TROCTDLITE SERIES PRGC - PARTRIDGE RIVER GABERO COMPLEX Cu-Ni Deposits MINNAMAX DUNKA ROAD WETLEGS WYMAN CREEK - MMAX - DR - WL - WC Fe-Ti De~ouits (Om SECTION 17 LONGCAR --LONGNOSE SECTION 22 SKIED - - - 17 LE LN 22 SK I FIUURE FIGURE 11: GENERAL GENERAL GEOLOGIC GEOLOGICMAP MAP OF Of THE THE PARTRIDGE PARTRIDGE RIVER RIVERINTRUSION INTRUSION 101 �U I I * I PARTRIDGE RIVER INTRUSION INTRUSION PARTRIDGE r UMMJf VYMAN CREEK I 1 WETLEGS I DUNKA ROAD /' SEC. SEC, 17 17 LEINc3EAR LONGEAR LDt'4GNUSE LDNGMDSI \ V / rv Iv - = FQCT'./ALL FOOTWALL FOOTWALL trIke—lenth within tthe Strlke-length correlotion correlation of' of r'iajor naJor igneous IQneous unI-ts unlts within he bQO1 3000 fft. t . of o f the t h e PortrIcge Partridge River River Intruion, Intrusion, basal 3OO II C:SuIfIdt-hearing —no'e out* troctoirte, ii I1= =tractotte wrth augitt irOct~litQ, troctotitn withpcrI-te picrite ICyer'C layers aic. etc. FIGuRE FIGURE 2: £ L*4IT. UNITS' - - - ou9rte troctoirt VV encethosttic q r t e troctolrte, &not-thosltic troctoirte, Vi V I =s anorthoitic anorthosrtic -tract t r o d .tot o aygitetrocto&ite, t r o c t d l t e , VII VII==augi-te ougfte troctoirte. troctolite. trortoltte, ougrte — — —Qracdetlonni contact sharp contact - ~flnadatlonat contact scale mlled. bNogcaie 1n5)!IeS. III Mottid' Cnorthoe-tle toirte, IV Ill —'Mottlrd' inorthosrtrc 'tro troctolrte, IV — 1har contact - PR1RIflGE PARTRIDGE RIVER RIVER INTRUrnw INTRUSION , 26 26 - PM1ftt) Can TPCCTBITIC nas anra nia u.n a 24 1 re7l man incas m—vnE PRIS PRROGITTR-,iCOtc W JUTS C 22 PRIR1I1E RtiR* R'jIRC cnwain • PawR*u,C sAnnea 20 .Rc • cmvi.. nRa, 'mum' • MIWTHOflTTC S*IBTi. ti.rTeurS Or mc mum cOWLtR C., en IL1Rst JwtRLr.,tI VOX ULTKAHW I E 3"f.r.lVl-I IC.,, <WI> 18 KMTH 3È M O - C A i a C Ii- # <WVW -or. Gftm Utt. 16 C PRTS ISt ICuiffARl HLm..tLC WOSC MUWAW H O W C L SaOa <a> 14 12 - UNIT II "*I4 UNIT I Cu -J PICRITC- 10 r.25 B- 6' flu', 4. 2 0B I I I I I I I I 0.2 0,s 0.4 0.4 0.6 0.6 MG MG NUME:R NUMBER rigre Figure3. 3~ MG Nui*er v,vs.A12G3 MG Number A1203 0.8 I I I I I I 102 i �I The -A major north-verging north-verging The Great Great Lakes Lakes tectonic tectoniczonezone--A Late Late Archean Archean collision collision zone zone P.K. P.K. Sims, Sims, U.S. U.S. Geological Geological Survey, Survey, Denver, Denver, CO CO 80225 80225 The The Great Great Lakes Lakes tectonic tectonic zone zone (GLTZ) (GLTZ) is is an an Archean Archean crustal crustal boundary boundary of of subcontiriental length that that separates separates aa Late Late Archean Archean greenstone-granite greenstone-granite terrane subcontinental length terrane (Wawa subprovince subprovince of the Superior province, Canadian Shield) on the north north from Superior province, from It Archean gneiss gneiss terrane terrane on on the the south. south. It is is generally generally Early to to Late Late Archean an Early interpreted interpreted as as aa paleosuture paleosuture that that resulted resulted from from continent-continent continent-continentcollision. collision. The The tectonic tectonic zone zone is is covered covered at at most most places places in in the the Lake Lake Superior Superior region region by by Proterozoic rocks rocks or or Pleistocene Pleistocene glacial glacial deposits, deposits, and and its its position position and and Proterozoic characteristics previously have been determined mainly by geophysical geophysical data. data. been determined mainly by Geologic Geologic mapping mapping in in the the Marquette, Marquette,Michigan Michigan area area (Sims, (Sims,in in press) press) provides provides direct direct observations observations of of the the structure structure for for the the first first time. time. In the the Marquette Marquette area, area, the the GLTZ GLTZ is is aa 2.4-km-wide 2.4-km-wide zone zone of mylonite mylonite In (orthomylonite) that has has been superposed (orthomylonite) that superposed on on predominantly predominantly massive granitoid granitoid rocks Archean greenstone-granite rocks of of the the Archean greenstone-graniteterrane terrane and and on on previously previously deformed deformed rocks rocks of of the the gneiss gneiss terrane. terrane. Foliation Foliation in in the the mylonite mylonite strikes strikes about about N. N. 60° 60' W. and and dips dips steeply steeply southwest, southwest, subparallel subparallel to to the the boundary boundary between between the the two two terranes. terranes . AA pronounced pronounced stretching stretching lineation lineation and and tight tight fold fold hinges hinges plunge plunge about about 45° 45' S. S. 45' E. E. The The attitude attitude of of the the stretching stretching lineation lineation (line (line of of tectonic tectonic transport) transport) 45° together together with with asymmetric asymmetric structures structuresindicative indicativeof of sense sense of of movement movement indicate indicatethat that collision Marquette area resulted in dextral-thrust dextral-thrust shear collision in in the the Marquette area was oblique and resulted along the the boundary, boundary, northwestward northwestward vergence, vergence, and and probable probable overriding overriding of of the the This greenstone-granite greenstone-granite terrane terrane by the the gneiss gneiss terrane. terrane. This implies implies southward southward subduction of of the the greenstone-granite greenstone-graniteterrane. terrane. Transmittal Transmittal of of the the dextral dextral shear shear subduction stress to to the north iiiay stress across across aa large largearea areaof ofthe theSuperior Superiorprovince provincecrust crust the north may have have been responsible responsible for for the the nearly nearly east-west east-west foliation, foliation, upright upright folds, folds, and and northwestnorthwest- to to east-west-trending east-west-trendingdextral dextral faults faults and and shear shear zones zones at at least least as as far far north Quetico fault north as as the the Quetico fault (Qf, (Qf, fig. fig. 1), I), in in southern southern Ontario, Ontario,aa distance distance of of about about 250 250 km. km. As aa whole, whole, the the GLTZ GLTZ is is characterized characterized by by systematic systematic angular angular bends bends that that alternately west-northwestward, as alternately trend trendwest-northwestward, as in in the the Marquette Marquette area, area, and and northeastward northeastward (fig. 1). 1). This This zigzag zigzag pattern pattern probably reflects reflects original original irregularities irregularities in in the the (fig. continental continental margin margin (Superior (Superior province). province). Late Archean Archean convergence convergence along along this this margin variable trajectory margin resulted resulted in in aa variable trajectory of of stress stress northward northward into into the the greenstonegreenstonegranite granite crust crust and and probably probably in in along-strike along-strikediachroneity diachroneityof of orogeny. orogeny. The The major major deformation deformation was caused caused by by oblique oblique compression compression at at promontories, promontories, which which acted acted as as buttresses buttresses against against which which compressive compressive stress stress was was directed directed into into the the crust. crust. In In addition addition to to the the dominant dominant foliation foliation and and upright upright folds, folds, major major brittle-ductile brittle-ductileto to brittle brittle strike-slip strike-slip faults, faults, such such as as the the Vermilion Vermilion fault fault system system (Vf, (Vf, fig. fig. 1) 1) in in northern northern Minnesota Minnesota and and the the Quetico Quetico and and Rainy Rainy Lake-Seine Lake-Seine River River faults faults (RL-SRf, (RL-SRf, resulted from from a more brittle continuum of the fig. 1) 1) in southern southern Ontario, resulted the fig. transpressive transpressive shear shear caused caused by by collision collision along along the the GLTZ. GLTZ. Precise Precise isotopic isotopic ages ages (Davis (Davis and and others, others, 1989) 1989) suggest suggest that that the the collision collision occurred occurred at at about about 2,690 2,690Ma. Ma. References References D.W., Poulsen Poulsen K.H., K.H., and and Kamo, Kamo, S.L., S.L., 1989, 1989, New insights insights into into Archean Archean Davis, D.W., Davis, crustal development development from from geochronology geochronology in in the the Rainy Rainy Lake Lake area, area, Superior Superior Province, Canada: Canada: Journal Journal of of Geology, Geology, v. v. 97, 97, p. p. 379-398. 379-398. Province, Sims, Sims, P.K., P.K., in in press, press, Great Great Lakes Lakes tectonic tectonic zone zone in in Marquette Marquette area, area, Michigan-Michigan-Implications Implications for for Archean Archean tectonics tectonics in in north-central north-centralUnited United States: States: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-E. 1904-E. 103 �______ ______ I I 9/ 88° I I 1 I I I I I U Geologic map map of of Precambrian Precambrian rocks, rocks, north-central north-central United United States States Geologic EXPLANATION EXPINAT ION I MIDDLE PROTEROZOIC PROTEROZOIC MIDDLE ',-'Â¥'Â¥ Rocks of of Midcontinent Midcontinent rift rift system system Rocks EARLY PROTEROZOIC PROTEROZOIC EARLY 1-1 [_J '1.L-L I Wisconsin magmatic magmatic terranes terranes (1,860-1,889 (1,860-1,889Ma) Ma) Wisconsin I ARCHEAN ARCH EAN Greenstone-granite terrane terrane (2,680-2,750 (2,680-2,750Ma) Ma) Creenstone-granite Gneiss terrane (2,600-3,600 Ma) Gneiss terrane (2,600-3,600 Ma) Direction oof tectonic tectonic transport transport Direction I I 104 1 I �I Geologic Geologic Significance Significance of of Linear Linear Features Features West-central Minnesota Visible on Landsat Images in West-central George W. Shurr, Ivan Ivan Watkins, Denise Victory, and Mary Tozer Department Department of of Earth Earth Sciences Sciences St. Cloud State State University University St. Cloud, Cloud, MN 56301-4498 56301-4498 The geologic significance of linear features visible on Landsat images can Observations of can be assessed assessed by integration integration with with several several data data sets. sets. Observations of linlinwest-central Minnesota are compared ear features features on four Landsat images in west-central with with aeromagnetic aeromagnetic maps and the the resulting resulting data data set set is is then then compared compared with: 1-published 1-published interpretations interpretations of of faults faults in in Precambrian Precambrian crystalline crystallinerocks, rocks, 2-concentration 2-concentration of of radon radon in in groundwater, groundwater, and and 3-water 3-water well well records. records. It It apappears that linear Landsat, in places correspond linear features features visible on Landsat, correspond with Precambrian crystalline rocks and and that these basement faults fault zones in Precambrian have influenced influenced fluid fluid movement movement and and Mesozoic Mesozoic weathering weathering patterns. patterns. Images Images employed in this study are standard EROS produces at scales scales of and 1:250,000 (paper) and were were provided provided by a 1:1,000,000 (film positives) and grant from Linear features from the the Minnesota Minnesota Geological Geological Survey. Survey. Linear features were mapped on on the multispectral scanner images in bands 2 and 4, compiled on an uncorrected mosaic, and compared 1). Individual Individual linear linear mosaic, compared with with aeromagnetic aeromagnetic maps maps (Fig. (Fig. 1). both bands are virtually virtually all parallel to linear aerofeatures observed on both magnetic magnetic anomalies. anomalies. These linear features are believed to be most signifisignificant and form the basis for the interpretation interpretation of lineament lineament zones zones which are corridors of linear-feature linear-feature concentration concentration separating separating large large areas with differdifferent linear-feature linear-feature orientation. orientation. Lineament zones zones correspond with Precambrian Precambrian convergent margins and with fault zones zones trending oblique to the margins However, it is the geologic (Shurr and Watkins, Watkins, in (Shurr in press). press). However, geologic significance significance of individual individual linear linear features features which which is is assessed assessed in in this this current current study. study. Precambrian crystalline Specific linear features and faults in Precambrian crystalline rocks rocks are shown shown in in Figure Figure 2. 2. In addition to linear linear features features shown shown in in Figure Figure 1, 1, some original data set (viz., bands 2 4) are some linear features from the original 2 or 4) included in in Figure Figure 22 where where they they parallel parallel aa fault. fault. Published Published faults faults or or fault fault zones 1-the Serpent Serpent zones which are are marked marked by by Landsat Landsat linear linear features features include: include: 1-the discontinuities (1-A Lake and Malma structural structural discontinuities (1-A and 1-B, 1-By respectively) (South(southwick and and others, others, 1988); 1988); 2-the 2-the Great Great Lakes Lakes Tectonic Tectonic Zone Zone (Sims (Sims and and others, others, 1980); 3-the 3-the Appleton Appleton geophysical 1980); geophysical lineament lineament (Southwick (~outhwickand and others, others, 1989); 1989); 4-a basement fault near Renville (4-A) others, 1989) and a 4-a (4-A)(Southwick (southwick and others, fault bounding bounding aa Precambrian Precambrian depositional depositional basin basin (4-B) (4-B) (Southwick (Southwick and and Mossler, Mossler, 1984); 5-two paired, parallel faults bounding Precambrian Precambrian basins (5-A 1984); 5-two (5-A and 5-B) (Southwick (Southwick and Mossler, 1984); 1984); and 6-faults 6-faults bounding the Nimrod outlier outlier 6-B, respectively) (Southwick and Long Prairie basin (6-A (6-A and 6-By (Southwick and others, others, 1988). These major fault zones zones correspond with lineament lineament zones zones and indiindi1988). vidual faults within the faults within the zones zones are are marked by specific specific linear linear features. features. or In southwest Minnesota, Minnesota, contour maps maps summarizing radon concentrations concentrations Landsat linear linear features. features. in groundwater show patterns patterns corresponding corresponding with with Landsat groundwater show (J, Fig. 2), 21, an an area area of of high high radon radon activity activity in in groundwater groundwater Jeffers (J, Near Jeffers (Southwick Precambrian (Southwick and Lively, 1984) lies along a fault zone mapped in Precambrian quartzite (Southwick (~outhwickand Mossler, 1984); the radon anomaly and fault zone zone Mossler, 1984); 105 �I Ii I are marked are marked by by aa Landsat Landsat linear linear feature. feature. Near Clarkfield (C, ( c , Fig. Fig. 2), 2), concontours tours of radon radon concentration concentration in in groundwater groundwater (Lively (Lively and and Southwick, Southwick,1981) 1981) generally parallel the northeast trend of a basement fault zone zone which has expression expression on on Landsat. Landsat. Near Benson, Benson, (B, (B, Fig. 2), 21, radon radon concentrations concentrations paralAppleton geophysical which has has clear clear definition definition on lel the Appleton geophysical lineainent lineament which on Landsat. Landsat. In In addition, addition, individual individual radon radon anomalies anomalies in in groundwater groundwater overlie overlie linear linear aeroaeromagnetic magnetic anomalies. anomalies. Radon anomalies anomalies in in soil soil gas gas data data have have recently recently been been rerelated to faults in crystalline crystalline rocks in the southeastern southeastern United States (Gates (Gates and Gunderson, 1989); 1989); these data may provide an analogy for the Minnesota groundwater groundwater anomalies. anomalies. In In any case, case, there there is is aa strong strong suggestion suggestion that that fluids fluids move along along faults faults in in bedrock bedrock which which are are marked marked by by Landsat Landsat linear linear features. features. In central Minnesota, geologic central Minnesota, geologic interpretations interpretations of of water water well well logs logs proprovide another another data data base base which which can can be be integrated integrated with with Landsat Landsat observations. observations. Near St. Cloud (Sc, (SC, Fig. Fig. 1) 1) individual individual linear linear features features mapped mapped at at 1:250,000, 1:250,000, generally parallel contours contours summarizing summarizing the elevation of the crystalline crystalline Linear features bedrock surface surface in in eastern eastern Stearns Stearns county. County. Linear features trending trending northnorthwest and east-west outline bedrock highs and follow the trend of bedrock east-west follow lows. Correlation of Cretaceous stratigraphic units shows that the bedrock lows. The lows have thick weathering weathering residuum residuum and and probably probably are are fault fault traces. traces. The individual linear linear features features are are all all components components of of aa northeast-trending northeast-trending linealineament zone zone which corresponds corresponds with an important fault fault zone zone in in central central Minnesota (Watkins (Watkins and and others, others, 1990). 1990). REFERENCES REFERENCES Gates, Gates, A.E., A.E., and Gunderson, Gunderson, L.C.S., L.C.S., 1989, 1989, Role of ductile ductile shearing shearing in in concenconcenGeology, v. 17, tration of radon radon in in the the Brookneal Brookneal zone, zone, Virginia: Virginia: Geology, 17, p. 391-394. p. 391-394. Lively, Lively, R.S., R.S., and Southwick, Southwick, D.L., D.L., 1981, 1981, Radon Radon activity activity in in groundwaters groundwaters of of Minnesota Geological Geological Survey seven test seven test areas areas in in Minnesota: Minnesota: Minnesota Survey Report of of Investigations 25, 25, 60 60 p. p. Investigations Shurr, G.W., G.W., and Watkins, Watkins, I., in press, Basement blocks, tectonics, tectonics, and fluid Shurr, It Proceedings, through the movement --seeping" through the sedimentary sedimentary cover: cover: Proceedings, --- "seeping" movement Seventh thematic conference Seventh conference on on remote remote sensing sensing for for exploration exploration geology. geology. Sims, P.K., P.K., Card, K.D., K.D., Morey, G.B., G.B., and Peterman, Peterman, Z.E., Z.E., 1980, 1980, The Great Sims, Lakes Lakes tectonic tectonic zone zone -- aa major major crustal crustal structure structure in in central centralNorth NorthAxnerAmerGeological Society ica: ica: Geological Society of of America America Bulletin, Bulletin, Part Part I, I, v. v. 91, 91, p. p. 690-698. 690-698. Southwick, D.L., and Southwick, and Lively, Lively, R.S., R.S., 1984, 1984,Hydrogeochetnical Hydrogeochemical anomalies anomalies associassociated with the basal contact of the Sioux Quartzite along the north margin of in Southwick, Southwick, D.L., D.L., ed., Shorter Shorter of the the Cottonwood County basin, basin, 2 contributions contributions to to the the geology geology of of the the Sioux Sioux Quartzite Quartzite (Early (~arlyProterozoic) Proterozoic) southwestern southwestern Minnesota: Minnesota: Minnesota Geological Geological Survey Survey Report of of InvestiInvestigations gations 32, 32, p. p. 45-58. 45-58. Southwick, D.L., Morey, G.B., G.B., and McSwiggen, McSwiggen, P.L., 1988, Southwick, D.L., 1988, Geological map of the Penokean Penokean Orogen, Orogen, central and eastern Minnesota Minnesota and accompanying Minnesota Geological text: text: Minnesota Geological Survey Survey Report Report of of Investigations Investigations 37, 37, 25 25 p. p. Southwick, D.L., and Mossier, Mossier, J.H., J.H., 1984, Southwick, D.L., 1984, The Sioux Quartzite and subjacent subjacent regolith regolith in in the the Cottonwood Cottonwood County County basin, basin, Minnesota, Minnesota, in in Southwick, Southwick, D.L., D.L., ed., Shorter Shorter contributions to the geology of the Sioux Quartzite (Early (Early Proterozoic) Proterozoic) southwestern southwestern Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Report Report of Investigations Investigations 32, 32, p. p. 17-44. 17-44. 106 �Southwick, D.L., Schaapy Schaap, B B., Chandler, V.WSy V.W., l98gy 1989, Multiple Multiple Archean Southwicky D.L.y e yand Chandlery terranes in Minnesota -- the the old gray gneiss gneiss she she ain't ain't what what in southwest southwest Minnesota she she used used to to be: be: Institute on Lake Superior Superior Geology Geology Proceedings, Proceedings, v. v. 96. 35y 35, p. 96. Watkins, I., Shurr, G.W.y C.W., and Anderson, G.G., 199OY 1990, Faults associated with Watkinsy I.> Shurry the Penokean Penokean accretion accretion of of allocthanous allocthanous terranes terranes in in central central Minnesota: Minnesota: Institute Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedingsy v. v. 36. 36. FIGURES FIGURES Precambrian faults faults /Precambrian Bands 2 & 4; Uneament Zone Boundary wIthgwphyskal geophysical expmsslon expression ,Eands Bands 22&&44with Bands 2 &4 ,Bands 22 or 4 ,Bands , ' 2 Figure 2 Figure Figure Figure 11 Linear features Linear features visible visible on on Landsat Landsat and 4 images in bands 2 & 4 and are are parallel to to aeromagnetic aeromagnetic patterns patterns west-central Minnesota (Shurr in west-central (Shurr and Watkins, Watkinsy in in press). press). Correspondence Correspondence of of specific specific Landsat Landsat linear features features with published published structural features structural features in in the the PrecamPrecamwest-central Minnesota brian of west-central (Shurr Watkins, in in press). press). (Shurr and Watkinsy Letters refer Letters refer to to localities localities disdiscussed cussed in in the the text. text. 107 �I BIOTURBATION IN I N THE JACOBSVILLE SANDSTONE, LINDEN LOCATION LOCATION — SANDSTONE, LAKE LINDEN WHAT W HAT ARE THE IMPLICATIONS? IMPLICATIONS? Marian M. M. Smith, Smith, Department of o f Geological Engineering, Engineering, Geology and and Geophysics, Geophysics, Marian Michigan Technological Technological University, U n i v e r s i t y , Houghton, Houghton, M MII 49931 49931 B i o t u r b a t i o n may have been overlooked in i n tthe h e JJacobsville a c o b s v i l l e sandstone and Bioturbation t h e world world due due to t o the t h e size s i z e of o f the t h e traces. traces. The The indeed many sandstone around the ichnofauna reported in observed oonly microscopic ichnofauna i n tthis h i s research can be observed n l y aatt tthe h e microscopic injected llevel. e v e l . Petrographic examination o h i n sections made from sandstone injected off tthin with porosity permeability differing w i t h blue dyed epoxy revealed patterns p a t t e r n s in in p o r o s i t y and p ermeability d iffering within somewhat w i t h i n aa few few centimeters. centimeters. Closer examination revealed various patches in i n the t h e thin t h i n section s e c t i o n where where aa pattern p a t t e r n of o f several several grains grains (approximately) (approximately) mm across would be interrupted 1 mtn i n t e r r u p t e d by by aa zone zone of o f mixed mixed grains grains varying varying in i n diameter diameter from mm to mm. t o 11 mm. These mixed grains do n o t appear tto o be from n a t u r a l grain graiq from . I1 mm not natural s t a i n (possibly (possibly hematite). hematite). IIn n some some s e t t l i n g and they are are often o f t e n coated coated with w i t h aa stain settling t h i n sections actual actual paths can be traced ffor o r approximately 1.5 1.5 c m before it it thin cm becomes becomes diffuse. d i f f u s e . In I n other instances instances the t h e areas of o f mixed mixed small small and and large l a r g e grains grains (with ( w i t h dark coatings) coatings) may cover an an area area approximately approximately 1I cm2. cm2. The thin t h i section ~ sectjon these ttracings an angle angle such such tthat arcuate patches patches ((less seems tto o aalso l s o ccut u t these r a c i n g s aatt an h a t arcuate less than 1mm measurements, speculations could 3mm across) across) appear. appear. From these initial i n i t l a 1 measurements, be made tthat approximately I mm h a t an annelid type burrower tthat h a t was approximately mm wide was was resembling glauconite is i s also a l s o found in i n these responsible. A greenish mineral resembling thin with in t h i n sections along w i t h an apparent sedimentary rock fragments (1 ( 1 mm in length) tthat closely length) hat c l o s e l y resembles resembles recent recent annelid annelid fecal f e c a l pellets. pellets. observations can be substantiated substantiated many many o off tthe IIff these initial i n i t i a l observations h e ttheories heories off the of tthe off Michigan w will i l l be o t h e paleogeography paleogeography and ttectonics e c t o n i c s OF h e Upper Peninsula o open for f o r reinterpretation. r e i n t e r p r e t a t i o n . The sands most often o f t e n interpreted i n t e r p r e t e d as as fluvial, fluvial, coming off o f f of o f alluvial a l l u v i a l fans fans would would change. change. IIff these are indeed indeed ichnofauna ichnofauna and and tthe h e greenish mineral is i s glauconite, glauconite, these sands wwill i l l have tto o be interpreted i n t e r o r e t e d as marine or o r at a t least l e a s t nearshore nearshore continental continental shelf. s h e l f . Cross bedded bedded units m i t s would would iindicate n d i c a t e tthe h e latter l a t t e r to t o be be more more likely. likely. o f the t h e ichnofauna ichnofauna raises r a i s e s many questions as to to The postulated presence of tthe h e age o m o n l y referred off these sediments which are most ccommonly r e f e r r e d tto o as pre put orr has tthe Cambrian. Does tthis his p u t tthis h i s unit u n i t into i n t o tthe h e Cambrian o h e Edicara fauna off tthe i n the t h e Proterozoic Proterozoic been been found? found? o h e "Lost Age" Age" in 1 108 �U I I TECTONIC RAMIFICATIONS LAKE SUPERIOR SEISMIC DATA TECTONIC W I F I C A T I O N S OF OF ONI/AB.GONNE GNI/ARGONNE LAXE DATA Michael E. 0eoiogy, Northern Illinois Michael E, Thompson, Thompson, flepartment Depertment of Geology, Il~inols University, De Univer~icy, De Kaib, Kalb, IL I L 60115 60115 C. P Patrick C. a t r h k Ervth, Ervin, Department Department of of Geology, Geology, Northern Northern Illinois Illinoia University, Unlveraity, De Kalb, IL, IL 60115 Dc Kaib, 60115 M.(. Mudrey, Wisconsin C M.G. Mudrey, Jr.., J r - , Wisconsin e o l o g h a l and and Natural. Nakural Himtory 3817 Geological Uistory Survey, 3817 Polnt Road, Road, MadLson, Madison, WI 53705 53705 Mineral Point B.A. Brown1 Brown, Wisconsin W i a c o n s h Geological and and Natural Natural History History survey, Sumey, 3817 3817 Mineral Point Road, Madison, JI 53705 Mlneral WI 53705 ABSTRACT ABSTRACT gravity anomaly anomaly maps have have been been prepared prepared for for the the Detailed bouguer gravity Superior and Northwest Superhr Northwest Wisconsin Wisconsin map map areas. areas. Data collected collected in in previous years were augmented augmented with with additional additional data &ta collected collected during during 1989. 1989. Strong gravity gradients gradient8 define the posittan position of major major Keweenawan Keweenawan !the deep deep gravity gravity low low over over the the Bayfield Bayfield Peninsula Penineula abuts abuts aa faults. The faults. Btrong po~itfve strong positive gravity feature to the southwest 1n in Bayfield Bayfield County County and and define aa major m a j o r Keweenawan Keweenawan cross croaa fault fault or or adjustment adjustment feature. feature. may define moderate gravity The moderate gravity low low in i n southern southern Iron Iron County County corresponds corresponds to to the Archean Arehean Puritan Puritan batholith batholith and and helps helps to t o define define relations relations to to Proterozoic Proterozoic metavolcanic and and metasedimantary metasedimentary rock rock to to the the south. south. !Shie mpported by the U . S , Geological Sumey, This work wag was supported U.S. Survey, COGEOMAP COCEOMAP progam. progkam. 109 �_______________________ I n ggeochronology e o c h r o n o l o g y of o f the t h e Michipicoten M i c h i p i c o t e n greenstone g r e e n s t o n e belt. belt. Advances iin II A . Turek, T u r e k , Department D e p a r t m e n t of o f Geology, G e o l o g y , University U n i v e r s i t y of o f Windsor, W i n d s o r , Windsor, Windsor, A. Ontario. O ntario. N9B 3P4 3P4 R.P. Sage, S a g e I Ontario O n t a r i o Geological G e o l o g i c a l Survey, S u r v e y I 918-77 918-77 Grenville G r e n v i l l e Street, Street, R.P. Toronto, T o r o n t o , Ont. Ont. lB3 M5S 1B3 W.R. W . R . Van Schmus, Schmus, Department D e p a r t m e n t of o f Geology, G e o l o g y , University U n i v e r s i t y of o f Kansas, Kansas, Lawrence, KS 66045 Lawrence, KS 66045 New N e w U—Pb U-Pb zircon z i r c o n ages a g e s for f o r the t h e Wawa area a r e a enlarge e n l a r g e the t h e existing e x i s t i n g data d a t a base b a s e of of i s now well well aages g e s for f o r this t h i s belt. belt. e x i s t e n c e of o f four f o u r volcanic v o l c a n i c cycles c y c l e s is The existence documented. a s s o c i a t i o n of o f volcanism v o l c a n i s m and a n d plutoriism p l u t o n i s m continues c o n t i n u e s to t o be be The association There cconfirmed. onfirmed. T h e r e is i s no difference, d i f f e r e n c e , in i n terms t e r m s of o f ages, a g e s , between b e t w e e n the t h e internal internal and a n d external e x t e r n a l plutons. plutons. The internal internal b e i n g those t h o s e that t h a t are a r e within w i t h i n the the being while the ssupracrustal u p r a c r u s t a l rrocks ocks w h i l e eexternal x t e r n a l aare r e tthose h o s e ssurrounding u r r o u n d i n g aand n d embaying the greenstone g r e e n s t o n e belt. belt. Michipicoten belt was formed by The M ichipicoten b e l t was formed b y several s e v e r a l volcanic v o l c a n i c cycles c y c l e s and a n d plutonic plutonic over of be divided i m e I that t h a t ccan an b e d i v i d e d into i n t o six s i x events events eevents vents o v e r aa pprotracted r o t r a c t e d pperiod eriod o f ttime, The oldest as shown in i n the t h e tabulation t a b u l a t i o n below. below. o l d e s t event e v e n t is i s dated d a t e d by a granite, g r a n i t e , aa porphyry, next of volcanism p o r p h y r y I and a n d aa volcanic v o l c a n i c at a t ca. c a . 2888 2888 Ma. Ma. The n e x t cycle cycle o f v o l c a n i s m and and associated Alden volcanic has a s s o c i a t e d plutonism p l u t o n i s m was was at a t ca. c a . 2743 2 7 4 3 Ma. Ma. The A lden v o l c a n i c tuff tuff h a s been been Ma dated Ma, tthe 2747 ± 1 5 Ma, h e JJubille u b i l l e ffelsic e l s i c vvolcanic o l c a n i c aatt 2747 ? 11 11 M a and a n d the the d a t e d aatt 2746 f± 15 The Goodreau volcanic JJubille u b i l l e porphyry p o r p h y r y at a t 2742 2742 ±? 6 Ma. v o l c a n i c center c e n t e r yields y i e l d s an a n age age Ma. aand belongs of nd b e l o n g s either e i t h e r here h e r e or o r in i n Event E v e n t III I11 at a t ca. c a . 2717 2717 Ma. Ma. o f 2729 ±? 3 Ma. Event has well by vvolcanic plutonic E v e n t IIV V h a s bbeen een w e l l ddefined e f i n e d by o l c a n i c aand nd p l u t o n i c rrocks o c k s aatt ca. c a . 2696 Na. Ma. The age a t 2701 2 7 0 1 ± 8 Ma Ma can c a n be b e assigned a s s i g n e d to to a g e obtained o b t a i n e d for f o r the t h e McCormic Lake tuff t u f f at 13 Ma New tthis h i s event. N e w ages a g e s that t h a t fit f i t into i n t o Event E v e n t VV are: a r e : 2686 2686 ± 1 3 M a for f o r the the event. Dubreuilville at D u b r e u i l v i l l e external e x t e r n a l granite, g r a n i t e , the t h e internal i n t e r n a l granite g r a n i t e at a t Dickenson D i c k e n s o n Lake Lake, at The youngest Ma. aand 2673 ±? 88 Ma. n d the t h e Lund Lake granitic g r a n i t i c stock s t o c k at a t 2663 2663 ±5 6 Ma. Ma. youngest event Ma pertain e v e n t aatt 2615 M i s thought t h o u g h t to to p e r t a i n to t o a tectonic t e c t o n i c event e v e n t in i n the t h e region. region. a is * * The new ages a g e s reported r e p o r t e d here h e r e conform c o n f o r m to t o the t h e established e s t a b l i s h e d pattern p a t t e r n of o f ages a g e s in in Also, they are in good agreement with ages for other nearby the t h e area. area. Also, t h e y are i n agreement w i t h a g e s f o r o t h e r nearby with of which greenstone g r e e n s t o n e bbelts, i t h tthe xception o t h e 2888 Ma Ma event h i c h has n o t been elts, w h e eexception f the event w h a s not been It appears that the Michipicoten belt evolved in identified in them. i d e n t i f i e d i n them. It a p p e a r s t h a t t h e Michipicoten b e l t evolved i n Moreover, ca. Ma. Moreover, it i t seems that t h a t volcanism, v o l c a n i s m , much of of the t h e associated associated c a . 220 220 Ma. sedimentation, s e d i m e n t a t i o n , aand l u t o n i s m I is i s essentially e s s e n t i a l l y synchronous, s y n c h r o n o u s , or o r coeval c o e v a l in i n the the n d pplutonism, Obviously g r e e n s t o n e belt, b e l t I rather r a t h e r than t h a n sequential. sequential. O bviously a eevolution v o l u t i o n of o f a greenstone It ccogenetic o g e n e t i c relation r e l a t i o n between b e t w e e n volcanics v o l c a n i c s and a n d plutonics p l u t o n i c s is i s likely. likely. I t is i s also also granitoid cclear l e a r tthat xternal g r a n i t o i d terraines o f batholithic d i m e n s i o n s formed h a t tthe h e eexternal t e r r a i n e s of b a t h o l i t h i c dimensions formed by m multiple by u l t i p l e intrusions i n t r u s i o n s over o v e r ca. c a . 220 220 Ma. Ma. 110 I �I Z i r c o n Ages Agcs ffor o r the ilic Michipicoten M i c h i p i c o t c n greenstone g r c e n s t o n e belt belt Zircon (Wawa, (Wawa, Gamitagama, Gamitagama, Michibishu). Michibishu). I EVENT EVENT (Ma) (Ma) 2615 VI Ca. V 2668 Ca. EXTERNAL EXTERNAL INTERNAL INTERNAL PLUTONS PLUTONS PLUTONS PLUTONS VOLCAJICS VOLCA!$ICS 2615 2662 2662 2671 2663 2673 2668 2675 2668 2686 2673 2677 2685 IV Iv 2702 2693 ca. ca. 2696 2696 2696 2694 2698 2696 2691 2698 2701 2698 - I11 ca ca III 2717 2717 II II Ca. ca. 2721 2721 2722 2722 2713 2713 2747 2747 2737 2737 2729 2729 2742 2742 2744 2744 2745 2 74 5 2746 2746 2743 2743 2747 2747 ca. I Ca. 2888 2889 2881 2888 Note: Note: - Ages A g e s in i n above a b o v e tabulation t a b u l a t i o n are a r e as a s reported r e p o r t e d here h e r e plus p l u s as a s reported r e p o r t e d and and Compiled c o m p i l e d by: by: Turek T u r e k A., A . , Keller K e l l e r R., R . , Van Van Schmus Schmus W.R., W.R., (1990). ( 1 9 9 0 ) . The T h e age a g e of o f volcanism volcanism and Mishibishu a n d plutonisrn p l u t o n i s m iin n tthe he M i s h i b i s h u ggreenstone r e e n s t o n e belt b e l t near n e a r Wawa, Wawa, Canadian ( i n press). press). Ontario. C a n a d i a n Journal J o u r n a l of o f Earth E a r t h Sciences S c i e n c e s 27, 2 7 , 5 (in Ontario. 111 �I THEGEOLOGYOFTHEGREENWOODLAKEAREA THE GEOLOGY OF THE GREENWOOD LAKE AREA DULUTH COMPLEX, LAKECOUNTY, COUNTY, NORTHEASTERN NORTHEASTERN MINNESOTA MINNESOTA DULUTH COMPLEX, LAKE Edward Edward A. A. Venzke Venzke Department of of Geology, Geology,University University of of Minnesota MinnesotaDuluth Duluth Department Duluth, Duluth, Minnesota Minnesota 55812 558 12 The The dominant dominant feature featurein in the theGreenwood Greenwood Lake Lake area area isis the the Greenwood GreenwoodLake Lake (or (or"Snake") "Snake") Anomaly. Anomaly. This Thispositive positivemagnetic magneticanomaly anomalywithin within the the troctolitic troctolitic series series of of the the southern southernDuluth Duluth Complex was was previously previously described described by by Vadis Vadis and and others others (1981). (1981).Geologic Geologicmapping mappingatat1:24,00() 1:24,000 Complex scale scale during during the the summer summer of 1989 1989 of four four 7.5' 7.5' quadrangles quadrangles (Greenwood (Greenwood Lake Lake West, West,Greenwood Greenwood Lake Lake East, East, Mt. Mt. Weber, Weber, and andWhyte) Whyte)located locatedpreviously previouslyknown known outcrops outcrops (Bonnichsen, (Bonnichsen, 1971) 1971)as as well and geochemical geochemical analyses. analyses. The well as as new new outcrops, outcrops, all all which which were were sampled sampled for petrography and The area area mapped mapped encompasses encompasses rocks rocks of the the anorthositic anorthositic and and troctolitic series, series, granophyric granophyric granite, granite,and and basalts and sediments of the North Shore Volcanic Group. A geologic map has been constructed basalts and sediments Group. A geologic map has been constructed (Figure (Figure 1) 1) based based on onoutcrop outcropmapping mappingand andaeromagnetic aeromagneticquadrangle quadrangle maps. maps. Aeromagnetic Aeromagneticmaps maps were were used used to to delineate delineate units units using using magnetic magnetic trends trends in in areas areaswith withpoor poortotononexistent nonexistentoutcrop outcrop coverage. coverage. The Theinfluence influenceof ofbedrock bedrockon ontopography topography was was also also taken taken into intoaccount. account. The The oldest oldestrocks rocksare arethe theanorthosites, anorthosites,gabbroic gabbroicanorthosites, anorthosites,and andtroctolitic troctoliticanorthosites anorthosites of Toimidrumlin drumlinfield fieldhas has of the the anorthositic anorthositic series. series. One OneNE-SW NE-SWtrending trendinghill hillon on the theedge edgeof ofthe theToimi extensive anorthositic gabbro. gabbro. A extensive outcrops of gabbroic anorthosite and anorthositic A few few isolated isolatedoutcrops outcropsof of troctolitic troctolitic anorthosite anorthositewith with aa distinctive distinctivespotted spotted appearance appearance caused caused by by poikilitic poikilitic olivines olivinesare arealso also present. present. These Theseisolated isolatedoutcrops outcropsmay maybe belarge largexenoliths xenolithsfrom fromaaprevious previousanorthositic anorthositicintrusion intrusion at at depth. depth. Another Anothersmaller smalleranorthositic anorthositicbody body contains contains1.5 1.5 -- 22 cm cm clots clots of of magnetite. magnetite. Intrusive with the the troctolitic troctolitic series. series. Numerous Intrusive into into the anorthosites anorthosites are rocks associated with Numerous outcrops of labradorite-augite-olivine cumulate ferrogabbro (> 10% oxides) were found alongthe the outcrops of labradorite-augite-olivinecumulate ferrogabbro (> 10% oxides) were foundalong shores shores of of Greenwood Greenwood Lake Lake and and along along NE-SW trending ridges to the northwest. The Theferrogabbros ferrogabbros are are all all magnetic magnetic totovarying varyingdegrees, degrees,and andgenerally generallyhave haveweak weaktotostrong strongigneous igneouslamination lamination Petrographic evidence indicates that magnetite was an early phase (foliation). Petrographic evidence indicates that magnetite was an early phase in the the (foliation). crytallization euhedralgrains grainsofoftitaniferous titaniferousmagnetite magnetite are arecommon common as as crystallizationsequence. sequence.Subhedral Subhedraltotoeuhedral inclusions inclusions in olivine, olivine, augite, augite, and andoccasionally occasionally ininplagioclase. plagioclase. Olivine Olivine is is often often seen seenrimming rimming magnetite. The The early early appearance appearance of of oxides oxides indicates indicates that that the the magma magma was was slightly slightlyenriched enriched in in magnetite. oxygen. oxygen. None None of of the the outcrops outcrops identified identified are are believed believed to represent the lithology of the Greenwood Lake Lake Anomaly Anomaly itself, which which can be be seen seen on ontopographic topographic maps maps to to be becompletely completelycovered covered by by swampy terrain Lake. The terrain and Greenwood Greenwood Lake. The only only direct direct evidence evidence of of the the rocks rockscomposing composingthe the anomaly are from two drill holes holes that that intersect intersect the the anomaly. anomaly. DDH S-1 S-i (Vadis (Vadis and and others, others, 1981) 1981) only penetrated 30 30 feet feet into intobedrock bedrock and andintersected intersectedfoliated foliatedoxide oxideand andolivine-bearing olivine-bearinggabbros, gabbros, only a thin thin band band of of oxide oxide augite augite troctolite, troctolite, and two layers layers (6.5' and and 3.3' thick) thick) of of feldspathic feldspathic oxide oxide peridotite. DDH DDHMN MN27015 27015(USX (USXCorporation) Corporation)at at the the south south end end of of Greenwood Greenwood Lake Lake intersected intersected 56' 56' of offoliated, foliated,moderately moderatelymagnetic magnetic anorthositic anorthositic ferrogabbro, ferrogabbro, a 4' 4' band bandofofstrongly stronglymagnetic magnetic oxide troctolite, 405' of offoliated foliatedanorthositic anorthositicferrogabbro ferrogabbro before before grading grading into into troctolite, and then then another another 405' 90' 90' of offerrogabbro ferrogabbrowith withvariable variablefoliation, foliation,finally finallyending endingininoxide-bearing oxide-bearinganorthositic anorthositicgabbros. gabbros. In general, general, the the anomaly anomaly appears appears to to be be composed composed of of layers layers of of aavariety varietyof ofolivine olivineand andoxide-rich oxide-rich troctolitic troctolitic cumulates. cumulates. The Therelationship relationshipbetween between the the exposed exposed foliated foliated ferrogabbro ferrogabbroand and the the adjacent adjacent 112 H 1 �I rocks of the the Greenwood Greenwood Lake Anomaly is not clear. The Theferrogabbros ferrogabbros are are probably probably part of of the the same intrusive body body as the the more more mafic, mafic, magnetic, magnetic, and and strongly strongly foliated foliated troctolitic troctolitic rocks that compose compose anomaly. anomaly. Two large large bodies bodies of of granophyric granophyric granite granite are are intrusive intrusive to to both both anorthositic anorthositic and and troctolitic troctolitic rocks rocks along along the eastern margin of the Greenwood Greenwood Lake Anomaly. In Incontrast contrasttotothe thegabbros, gabbros,the the granophyre granophyre is relatively resistant and forms large hills and ridges, the the best-known best-known example of which which is Mt. Weber. Weber. Felsic Felsicveins veinswere were observed observed in in gabbros gabbros on Greenwood Greenwood Lake, and a large granophyre dike cuts the magnetic basalt to the east. The Thegranophyre granophyre isis bordered bordered to to the theeast eastby by granophyre magnetic magnetic basalts and at at least leastone onesmall smallbasin basincontaining containingaamagnetic, magnetic,bedded, bedded,quartz-bearing quartz-bearing volcanic sandstone. The Thebasalts basaltsadjacent adjacenttotothe thegranophyre granophyreare areall allmassive, massive,but butbasalts basaltsfurther further volcanic south are amygdaloidal arnygdaloidal at at some some locations. locations. south and and away away from from the the felsic felsicintrusions intrusions are Preliminary geochemical geochemical interpretations interpretations and determination determination of oxide oxidecompositions compositionshas has Preliminary begun. begun. The Theresults resultsof ofthis thiswork workwill willalso alsobe bepresented, presented,with with an an evaluation evaluation of of potential potential Platinum Platinum Group Group Element Element mineralization. mineralization. This This project project has has been been funded funded by by the the Minnesota Minnesota Mineral Mineral Diversification Fund, and by the the Mineral Mineral Resources Resources Research Research Center. Center. References References Cited Cited Bonnichsen, B., 1971, Bonnichsen, B., 1971, Outcrop Outcrop map of of southern southern part part ofofDuluth DuluthComplex Complexand andassociated associated Keweenawan rocks, St. Louis Keweenawan rocks, Louis and and Lake Lake Counties, Counties, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Miscellaneous Miscellaneous Map Map Series SeriesM-11, M-1 1,scale scale1:125,000. 1:125,000. Vadis, Vadis, M. M. K., K., Gladen, Gladen, L. L. W., W.,and andMeineke, Meineke,D.D.G., G.,1981, 1981,Geological, Geological,geophysical geophysical and and geochemical surveys of of Lake, Lake, St. Louis and geochemical surveys and Cook Cook counties, counties, Minnesota Minnesota for the the 1980 1980 drilling project: drilling project: Hibbing, Hibbing, Minnesota, Minnesota, Minnesota Minnesota Department Department of Natural Natural Resources, Resources, Division Division of of Minerals, Minerals,Report Report201, 201,13 13p.p. 113 �—I II ______ r) N N or'0—40 + + ::: :: : + + Grenvoc,d Lcke fJODODfl0( DO00ODoo 00 000 0 000 00 jon o 000000000 DO 00 0 00 0 00 00001 0030000000000W 000000000 DODD 0 DODD EDDDOO0LOOOD0OD 0000001 DO 0000 I 000000' 000000 000000 0-0-0- D-0 * HiHH Il\0oDDDoooooo HI ,P?0O00EOD0DODD0OO 111111 N 1+ * + * 4 4- * * 4- + * 4- * -t * * * fl Whyte 0 00 0 00000 L0 0 0000 0 00 0 00 0 0 0 0 0 000 0 00 0000 0 00 000000poooooo 0000000000000000 * 4- 4 * * + + * * * * * * * 4 *1*, * * * * 4 * -f * * * * * * * * 4-**-*+ * **+ • *4 * * * *_* + * * + * — * * *** * * * -* — * - - * * - 0 DOD 4- NjJriI+,'DODCDDQ 0000000000 0000000 000000 000000 000000 0000000 000_00 0300000 *DOG0D0O000DOOOO0OO =—'DIQO00 00 0 4- * * * *4-4-*+* 4- +*•+*** + LO 0 0 0 0 0 0 0 0 0 0 0 0 0 0 [ 0 0 0 C 0 0 0 0 0 00 0 0 0 00 000000000000000000000000 0 U0 0-0 Oil 30-D jDOODOODCODOG 4- 0 0 0-D-0- 0 0 0 0 000 0000 000i0000 0000 '000000000000000 0000 000000000 D DDO00o0o00JC00ooDoOOD0 L0000000000DOD 00000000000000 100 OO00ODODODD00O00O0ODODO00DOO P E00D 0000000000000000_000000000000 0 GP00000000000U000000000000 0000000000 0000000000000 DDDDooDoo IflOD000UD0DJD0DD Jill II IOOD0ODOOOOCOOOI ii iH Hi fl In iii 0DDDOO0COOD00DQ foo4fl( IJkDDO0DDO0OOODOpD iii Hill iji jI Jj\DOODOODDO0DD0D0 ih0DDODO0O00ooooo ii l1h0oDDooooooocoo OCODODDOO0OD lii ii III DODD [130000000000000] O0DO*DOOI 00000000A ODD0o11TTTll C0D0D H111 OOOoI onDoflt Dog liii liii 1S+M +D1 PooMf4a4i C (1J N +4 4- —to >- 0 0- o2, •444 -0 -&i 0 -t - 0 0 0 i 4-, C 4, 40 '4 2 -0 5 . 2 0 Q (4 2 (4- *2 2 (4 - (_:4 4, 2° oE 0 0(4 01 0= mll 1D :1 4- Ii C. 4-- —'S— I-. — _i i I — — — — — — — — — — — — — — — — CO N '0 04 �I I THE MINERAL RELIEF OF SURFACES PRODUCED BY SANDING SANDING WITH QUmTZ QUARTZ THE MINERAL SURFACES PRODUCED PERCUSSION, THERMAL PERCUSSION, THERMAL DISAGGREGATION, DISAGGREGATIONy AND AND WEATHERING WEATHERING by Denise Denise Victory Victory and and Ivan Ivan Watkins Watkins We We have have hypothesized hypothesized that that the the processes which archaeological archaeological stonestonemasons used when working stone stone left surfaces surfaces that could be used to idenprocess used by those Because the minerals in tify the process those stonemasons. stonemasons. Because in a a rock properties such hardness, coefficient rock have different different properties such as cleavage, cleavagey hardness, coefficient thermal expansivity, expansivity, coefficient coefficient of thermal conductivity, absorption absorption of thermal coefficients for coefficients for radiant radiant energy energy (color), (color), and and reactivity reactivity with with water water conconoxygen and taining oxygen and hydrogen hydrogen ion ion we we were were able able to to devise devise several several observaobservational tests that could be be used used to to classify the the stonemasons method method of of tional surface production. hypothesis on a sample Reformatory tested our hypothesis sample of Reformatory surface production. We tested Grey Grey granite granite supplied supplied to to us us by by Cold Cold Spring Spring Granite Granite Company. Company. We produced surfaces by the methods that archaeologists have have suggested for Peruvian Peruvian surfaces 1 the relative relative mineral relief we we observed for each stone works. stone works. In In Table Table 1 surface with the surface is is tabulated tabulated with the process process used used to to produce produce the the surface. surface. The that, if archaeologist The logical logical conclusions from from the table are that, if an archaeologist relief of a surface, archaeolwere educated educated to to look look for for the the mineral relief surface, that archaeolwould be able to determine the process process the ancient stonemasons stonemasons used used ogist would which are to produce the the artifacts artifacts which are found found today. today. There There are are no no processes processes distinguished from all of the we used on on the the grey grey granite granite that that can can not be distinguished from all other processes. other processes. Of course course it it is possible to hypothesize two or more proHowever, if cesses being used by the the stonemasons stonemasons to to produce produce the the surface. surface. However, if hammering or quartz are combined, result is or wedging and sanding sanding with quartz combined, the result same as just with quartz. the same just sanding sanding with quartz. 115 �— L I — .1 I ———————————————— Table Table 11 RELIEF SURFACE SURFACE MINERAL MINEFKG RELIEF PROCESS PROCESS quartz quartz quartz quartz mica mica mica mica vs vs vs vs vs vs vs vs vs vs biotite biotite HAIvIMERING HAMMERING OR hornblende hornblende feldspar feldspar hornblende feldspar feldspar feldspar feldspar vs vs hornblende hornblende There was was no no pattern. p a t t e r n . Any Any mineral mineral could could stand stand above above any any other. o t h e r . The The There cleavage surfaces s u r f a c e s of of all a l l minerals minerals in i n the t h e rock rock were were observed. observed. cleavage WEDGING WEDGING quartz above biotite biotite quartz quartz above hornblende hornblende quartz above feldspar feldspar hornblende above above mica feldspar feldspar above above biotite biotite NO PATTERN PATTERN OBSERVED OBSERVED DISAGREGATION GATION biotite biotite above above quartz hornblende hornblende above above quartz quartz feldspar feldspar above above quartz quartz NO PATTERN PATmN OBSERVED OBSERVED biotite biotite above above feldspar feldspar hornblende above above feldspar feldspar WEATHERING WEATHERING OR ACID SOLUTION SOLUTION quartz above above biotite biotite quartz quartz above above hornblende hornblende quartz quartz above above feldspar feldspar hornblende hornblende above above biotite biotite feldspar feldspar above above biotite biotite feldspar feldspar above above hornblende SANDING SANDING WITH WITH QUARTZ QUARTZ THEmNL THERMAL AWAY!!! THE BIOTITE BIOTITE HAS BEEN BEEN WEATHERED WEATHEREJI AWAY !!! THE �I FAULTS ASSOCIATED WITH FAULTS WITH THE THE PENOKEAN PENOKEAN ACCRETION OF ALLOCTHANOUS ALLOCTHANOUS TERRANES TERRANES IN IN CENTRAL CENTRAL MINNESOTA by by Watkins, George W. Shurr, Ivan Watkinsy Shurry and Carry Garry G. G. Anderson Anderson Department of Department of Earth Earth Sciences Sciences St. Cloud State State University University Cloud, MN 56301-4498 St. Cloud, 56301-4498 The theory of continental allocthanous terranes continental growth by docking of allocthanous has now now been been accepted accepted by by most most geologists. geologists. Plate Plate tectonic tectonic interpretations interpretations for the Penokean Penokean orogen orogen in in the the Lake Lake Superior Superior region region have have slowly slowly been been emergemerging in the literature (Laruey 1983; 1983; LaBerge LaBerge and and Myers, Myers, literature over over the the past past decade decade (Larue, 1984; Minnesota recent 1984; Barovich Barovich and and others, othersy 1988). 1988). In In central Minnesota recent reinterpretareinterpretaSouth( ~ o l s t1984; 1984; ~ Southtions have recognized the the orogen orogen as as aa convergent convergent margin margin (Holst, convergence is wick and and others, othersy 1988; 1988; Holm Holm and and Selverstone, Selverstone, 1990). 1990). Since convergence is rarely perpendicular to to the the continental continental margin, marginy accretion accretion occurs occurs in in aa transtransmargin is reflected in the faults pressive regime and the geometry of the margin are produced. produced. The The northeast northeast trend, trend, parallel parallel to to the the continental continental margin, margin, that are will be primarily low low angle angle faults faults with dominant dominant dip-slip dip-slip and some some strikestrikeslip displacement. margin, i.e. northwesty northwest, should slip displacement. Faults Faults perpendicular to to margin, should be primarily subvertical subvertical with dominant strike-slip strike-slip and some some dip-slip dip-slip displacement. The relative placement. relative importance importance of each fault trend is is determined by the angle angle of of transpression. transpression. The predicted fault fault geometries have been documented in recent mapping in the area of Mille Mille Lacs Lake and have have also been been observed on several data bases bases farther farther south south in in the the St. St. Cloud Cloud area. area. Linear Linear features features visible visible on on satsat1:1,000,000 correspond with with faults mapped mapped by by ellite images at a scale of l:lyOOOyOOO Mule Lacs other investigators (Shurr and and Watkins, Watkinsy in in press). press). Near Mille Lacs northnorthinvestigators (Shurr east-trending structural discontinuities dip southeast and northwest-trendnorthwest-trendeast-trending structural discontinuities ing faults faults are near vertical vertical (Southwick (southwick and and others, othersy 1988). 1988). In In the the St. St. Cloud Cloud area, satellite linear features mark mark the contact between between Archean Archean gneisses areay Proterozoic granitic and Lower Proterozoic granitic rocks. rocks. This contact and other faults faults have expression on magnetic magnetic data 1:250,000 and and 1:24,000. 1:24y000. clear expression data at at scales scales of of 1:250,000 The fractures fractures and faults associated with accreted terranes terranes have magnetic netic lineations lineations produced produced by by water water flux. flux. The water provided oxygen oxygen from from atmosphere and ion the atmosphere ion transport transport to to convert convert the the primary primary magnetic magnetic mineral, mineral, inagnetite, into into hematite hematite which which is magnetite, is nonmagnetic. nonmagnetic. Magnetic anomaly anomaly maps then then necessarily necessarily have have aa lineation lineation parallel parallel to to the the faulting. faulting. Magnetic Magnetic lineation lineation between the Proterozoic granitic rocks is obvious obvious on the Archean gneisses and Proterozoic aeromagnetic aeromagnetic maps at 1:250,000 1:25Oy0O0 and corresponds corresponds to linear features features visible on aeromagnetic maps on satellite satellite images. images. Lenticular patterns on 1:24,000 aeromagnetic are interpreted as possible strike-slip strike-slip faults and can be investigated in in outcrop. outcrop. Outcrop observations observations along the northeast trend near St. Cloud show show south-dipping south-dipping shear surfaces with with fabric that indicates the south block block fault has has aa strike-slip strike-slip component. component. The The gneisses gneisses of of is upthrown and the fault the northern block are in in places places blocky, blocky, broken broken and and coarse-grained, coarse-grained,but but corresponding change change of magnetite to range to mylonite texture with the corresponding hematite in the the recrystallized recrystallized regions. regions. The presence of of northwest northwest faults faults hematite in is confirmed by observations observations in in outcrops, outcropsy cores, coresy and and thin thin sections, sectionsybut but 117 �I interpretation interpretation of of the the complex complex patterns patterns awaits awaits Ii the the completion completion of of detailed detailed mapping mapping which which is is currently currently underway. underway. Thin sections sections made made from from red red granite granite samples samples collected collected near near faults faultsshow: show: Thin faulted k-spar k-spar porphroblasts, porphroblasts, some some with with tails; tails; mica mica fish; fish;no no magnetite, magnetite,but but faulted abundant microabundant hematite; hematite; and and chlorite chlorite and and biotite biotite partly partly filling fillingubiquitous ubiquitousmicrofractures. fractures. The The reasonably reasonably euhedral euhedral zircons zircons present, present, are are all all fractured fractured with with aa very very dark dark zircon zircon overgrowth overgrowth in in the the fractures fractures indicating indicating low-temperature low-temperature shearing (Belden and and others, others, 1989). 1989). shearing and and metamorphism metamorphism (Belden In summary, summary, observations observations spanning spanning aa scale scale range range from from regional regionalsatellite satellite In images images to to thin thin sections, sectionsy verify verify the the existence existence of of faults faults predicted predicted from from the the accretion accretion model. model. Faults Faults trending trending northeast northeast and and northwest northwest have have been been documentdocumented The structural structural grain grain produced produced during during Penokean Penokean accretion accretion ed at at all all scales. scales. The left left zones zones of of weakness weakness for for subsequent subsequent reactivation. reactivation. During During the the Midcontinent Midcontinent rifting rifting event, event, faults faults were were reactivated reactivated and and some some filled filled with with basalt. basalt. The The recognition recognition of of ubiquitous ubiquitous faulting faulting in in central central Minnesota Minnesota should should preclude preclude any any serious serious consideration consideration of of the the area area for for disposal disposal of of radioactive radioactiveor orhazardous hazardous wastes wastes. REFERENCES REFERENCES Barovich, Peteman, Z.E., Z.E., and and Sims, SimsyP.K., P.K., 1989, 1989,Nd Nd isoisoBarovich, K.M., K.M., Patchett, Patchett, P.J., P.J., Peteman, topes and and the the origin origin of of 1.9-1.7 1.9-1.7 Ga Ga Penokean Penokean continental continental crust crustof ofthe theLake Lake topes Superior Superior region: region: Geological Geological Society Society of of America America Bulletin, Bulletinyv. v. 101, 10ly p. p. 333333- — 338. 338. Belden, Belden, J., J., Anderson, Anderson, G., G., and and Watkins, Watkins, I., I., 1989, 1989$ Zircons Zircons of of the the St. St. Cloud Cloud Red Red and and Reformatory Reformatory Gray Gray granites: granites: Institute Institute on on Lake Lake Superior Superior Geology Geology ProProceedings, ceedings$v. v. 35, 35Âp. p. 4-5. 4-5. Hoim, Holm, D.K., D.K., and and Selverstone, SelverstoneyJ., J., 1990, 1990, Rapid Rapid growth growth and and strain strain rates rates inferred inferred from from synkinematic synkinematic garnets, garnetsyPenokean Penokean orogeny, orogenyyMinnesota: Minnesota: Geology, Geology, v. v. 18, 18 p. 166-169. 166-169. p. Holst, Holsty T.B., T.B., 1984, 1984, Evidence Evidence for for nappe nappe development development during during the the Early Early Proterozoic Proterozoic Penokean Penokean orogeny, orogeny,Minnesota: Minnesota: Geology, Geology, v. v. 12, 12,p. p. 135-138. 135-138. LaBerge, LaBergeyG.L., G.L., and and Myers, Myers, P.E., P.E.$ 1984, 1984,Two Two Early Early Proterozoic Proterozoic successions successions in in central central Wisconsin Wisconsin and and their their tectonic tectonicsignificance: significance: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 95, 95$p. p. 246-253. 246-253. - Larue, Larue$ D.K., D.K., 1983, 1983, Early Early Proterozoic Proterozoic tectonics tectonics of of the the Lake Lake Superior Superior region region tectonostratigraphic tectonostratigraphic terranes terranes near near the the purported purported collision collisionzone, zone,in 9 Medaris, Medaris, L.C., L.G., Jr., Jr., ed., ed., Early Early Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region: region: Geological Geological Society Societyof of America America Memoir Memoir160, 160,p. p. 33-47. 33-47. I Southwick, D.L., Morey, Morey, C.B., C.R., and and McSwiggen, McSwiggen,P.L., P.L., 1988, 1988,Geological Geologicalmap mapof ofthe the SouthwickyD.L., I'enokean orogen, central Penokean orogrn, ccrit r a l and and eastern eastern Minnesota, Minncsot a, and ~ n accompanying ditccompanyinp,text: rcxt: Minnesota Minnesota Ceological Geological Survey Survey Report Report of of Investigations Investigations 37, 37, 25 25 p. p. Shurr, C.W., and Watkins, I., in press, Basement blocks, tectonics, and fluid movement —— ''seeping'' through the ned i mt ut a ry cover: I' I'OC(Pd I I1M , SCVeO t iheunat Ic conference on remote senu ng for exploration geology. — 118 ii I �I The Element deposits 3Jkz Role Roleof of Volatiles V o l a bin inthe theFormation Formationof ofthe thePlatinum PlatinumGroup GOUD E l e m u sitsininthe thg Middle and M~ddleProterozoic ProterozoicDuluth Duluth Complex Com~lex andthe the Triassic TriassicNoril'sk-Talnakh Nor11 sk-TalnakhIntrusions Intrusion3 I PAUL W.WEIBLEN WEIBLEN(Minnesota (MinnesotaGeological GeologicalSurvey, Survey,Saint SaintPaul, Paul,MN MN55114) 551 14) PAULW. TATIANA SABELIN SABELIN(Mineral (MineralResources ResourcesResearch ResearchCenter, Center,UM, UM,Mpls.,MN Mpls.,MN (55455) (55455) TATIANA BERNHARDTSAINI-EJDUKAT SAINI-EIDUKAT(Dept. (Dept.Geology Geologyand and Geophysics, Geophysics,UM, UM, Mpls., Mpls., MN MN BERNHARDT 55455) 55455) IWAO WAOIWASAKI WASAKI(Mineral (MineralResources Resources Research Research Center, Center, UM, Mpls., MN MN55455) 55455) Over Overthe thepast pastdecade, decade,studies studiesof ofPt-group Pt-groupelement element (PGE) (PGE)deposits depositshave have focused focusedon ontwo two contrasting contrastingfacets facetsof oftheir theirprobable probableorigin origin(Macdonald, (Macdonald,1988). 1988). Much Muchevidence evidencedocuments documents their theiroccurrence occurrencein inmafic maficcumulates cumulatesand andrelates relatestheir theircharacteristics characteristicsto tothe the idiosyncracies idiosyncraciesof of melt-crystal melt-crystalequilibria equilibriaand andphysical physicalprocesses processes of of melt-crystal melt-crystal segregation segregationduring duringformation formation of of mafic maficcumulates cumulates (Campbell (Campbell and and others, others, 1983). 1983). At Atthe thesame sametime timeevidence evidencehas hasbeen been found foundfor forsynsyn-and andpost-magmatic post-magmatic transport transport and and deposition deposition from from aa fluid fluid phase phase which which could could have haveevolved evolvedin in closed closed or or have have been been introduced in open magmatic magmaticsystems systems(Ballhaus (Ballhausand and Stumpfl, Stumpfl,1986; 1986;Boudreau, Boudreau,1988). 1988). The Theevidence evidencedescribed describedbelow belowfor forthe therole roleof ofvolatiles volatilesin in the the origin originof of the the occurrences occurrencesof of PGE's PGE'sininthe theMiddle MiddleProterozoic ProterozoicDuluth Duluth Complex Complex in the the Lake Lake Superior Superior region and andthe the Triassic TriassicNoril'sk-Talnakh Noril'sk-Talnakhintrusions intrusionsininthe theSiberian Siberianplatform platformmay may be be related relatedto tosimilarities similarities inintheir theirtectonic tectonicregimes regimesand andgeologic geologicsettings settings(Weiblen (Weiblenand andMorey, Morey,1980; 198kUrvantseva, Urvantseva, 1971). Both are arerelated relatedtotoextensional extensionaltectonic tectonicregimes regimesinincontinental continentalcrust. crust. Both Both 1971). Both intrusions intrusionsare areassociated associatedwith withrift-related rift-relatedfaults: faults:the theNorilsk-Talnakh Norilsk-Talnakhintrusions intrusionssitsitastride astrideaa N-NE N-NEtrending trendingfault faultzone zoneand andthe theDuluth DuluthComplex Complexisisbounded boundedby byfaults faultswhich whichparallel parallelthe the rift riftboundary. boundary.Drilling Drillingand andgeophysical geophysicaldata dataindicate indicatethat thatthe thefaulting faultingininboth bothintrusions intrusions defines definesaahalf-graben half-grabengeometry geometry probably probably related related to to down-to-basin down-to-basin normal normal faulting faulting in in aa continental continental rift. rift. There Thereisisevidence evidencethat thatthe thefaulting faultingoccurred occurredprior priorto, to,during, during,and andafter after intrusion. intrusion. The Thebasement basementrocks rocksofofthe theNoril'sk-Talnakh Noril'sk-Talnakhintrusions intrusionsare areDevonian Devoniancoal coalbearing bearing shales areLower LowerProterozoic Proterozoic shalesand andlimestones limestonesand andthe thecountry countryrocks rocksfor forthe theDuluth DuluthComplex Complexare meta-argillites meta-argillitesand andiron ironformation. formation. Both Bothbasement basementsequences sequencescontain containabundant abundanthydrous hydrous mineral mineralassemblages assemblagesand andlesser lesseramounts amountscarbonaceous carbonaceousmaterial materialand andiron ironsulfides. sulfides. Given Giventhe thenature natureof of the the host host rocks rocks and andthe thedynamic dynamictectonic tectonic regimes regimes ititisisperhaps perhapsnot not surprising surprisingthat thatboth bothintrusions intrbsionsprovide provideevidence evidenceofofdevolatilization devolatilizationofofcountry counrryrocks rocksand and mixing volatiles with intrusive mixingof of country country rocks rocks and country rock volatiles intrusivemagmas. magmas. Evidence Evidencefor for these thesephenomena phenomenafrom. fromfrom fromthe theCu-Ni Cu-Nideposits depositsininboth bothintrusions intrusionsisisshown shownschematically schematically ininFig. Fig.1.1.Similar Similartextural texturalrelationships relationshipsare arecommon commonin in the the field fieldand anddrill drillcore coredata dataononCuCuNi Nideposits depositsininthe theDuluth DuluthComplex Complex(Foose (Fooseand and Weiblen, 1986). 1986). The Thestable stableisotope isotopestudies studies ofofRipley Ripleyand andhis hisstudents studentsover overthe theyears yearsprovide providethe thegreatest greatestin-depth in-depthelucidation elucidationofofthe the roles rolesof ofcountry countryrock rockvolatiles volatilesininthe theformation formationof ofthe theCu-Ni Cu-Nideposits depositsininthe theDuluth Duluth Complex Complex(Ripley, (Ripley,1986). 1986). Evidence Evidencefor forvolatile volatiletransport transportofofPGE's PGE'shas hasnow nowbeen beenfound foundininthe theDuluth DuluthComplex Complexby by Sabelin Sabelin(Sabelin (Sabelin and and others, others, 1989): 1989): Pt-Fe Pt-Fealloy alloyand andPt-Pd Pt-Pdsulfides sulfidesare are found found ininveins veins cuttingolivine olivineand andchrome-spinel chrome-spinelin in aamafic mafic cumulate cumulate in in the the Duluth Duluth Complex. Complex. Perhaps Perhaps cutting more morestriking strikingisisthe thediscovery discoveryby bySabelin Sabelinof ofPd Pdsulfide sulfidereplacing replacing chalcopyrite. chalcopyrite. Similar Similar relationshipshave havebeen beenalluded alludedtotoininthe theTalnakh Talnakhdeposits depositsby byGenkin Genkinand andEvstigneeva Evstigneeva relationships %)by byDahlberg Dahlberg(pers. (pers. (1986).The Thediscovery discoveryofofaahydrous hydrousiron ironchloride chloridephase phase(14 (14wt. wt.%) (1986). comm.)ininaahighly highlyserpentinized serpentinizedsection sectionofoftroctolite troctoliteinindrill drillcore corelends lendscredence credencetotothe the comm.) concept that thatthese thesereplacement replacement textures textures might might be be products productsofoftransport transportofofPGE's PGE'sasas concept chloride chloridecomplexes. complexes. There Thereisisa apaucity paucityofofexperimental experimentaldata data ononvolatile volatiletransport transportofof 119 �U PGE's. PGE's. However,the the results resultsof of an an experiment experimenton on the the roasting roasting of of Cu-Ni Cu-Ni ores ores in in aa mixture mixture However, of of salt salt and and coke coke fragments fragments (Iwasaki (Iwasaki and and others, others, 1971) 1971)indicated indicated that that segregation segregation of of the the metals could be beachieved achievedwith with salt salt and and coke cokebut but not notwith withcoke cokeor orother otherreductants reductantsalone. alone. metals These These results results suggest suggest that that CI Cl isisrequired required asasaatransporting transportingagent. agent. Perhaps Perhaps similar similar requirements requirementsmust mustbe bemet metfor forPGE's PGE's to tobe be concentrated concentratedin in natural natural ores. ores. PAMIMLY C1YSTAWM $ASALIIC MW © 0 u4€ vI OJIWILUS.I 0' e A B Fig. Fig.1.1. Field Field relations relationsof ofhornfels homfelsinclusions inclusionsand andsulfide sulfidemineralization mineralizationininthe the Duluth Duluth A) Schematic Schematicrepresentation representation of of aapelitic pelitic Noril'sk-Talnakh intrusions. Complex and and the the Noril'sk-Talnakh Complex intrusions. A) homfelsinclusion inclusionininmineralized mineralizedgabbro gabbroininthe thefootwall footwallofofthe theDuluth DuluthComplex. Complex.Modified Modified homfels from fromChurchill Churchill(1978, (1978*p. p. 95). 95). B) B) Inclusion Inclusionininaagabbroic gabbroicNoril'sk Noril'sk intrusion. intrusion.Sulfides Sulfides (4) (4) ingabbroic gabbroicpegmatoid pegmatoid(3) (3)mantling mantlingaaxenolith xenolithof of labradorite labradoriteporphyry porphyry (2) (2)in ingabbro gabbro(1). (1). in From From Urvantseva Urvantseva(1971, (1971, P. p. 239). 239). Both Both occurrences occurrences of of sulfide sulfide can can be beinterpreted interpretedtoto representmigration migrationof ofsulfur sulfurfrom fromthe theinclusions inclusionsand andmetals metalsfrom fromthe theenclosing enclosinggabbroic gabbroic represent magma magmaas asshown shownininA. A. I References References Ballhaus, Ballhaus, C.G. C.G. and andStumpfl, Stumpfl*E.F., E.F.*1986, 1986,Sulfide Sulfideand andplatinum platinum mineralization mineralization in in the the Merensky Reef: Reek Evidence Evidence from fiom hydrous hydrous silicates silicates and and fluid fluidinclusions. inclusions.Contrib. Conmb. Merensky Mineralogy Mineralogy Petrology Petrology 94: 94:193-204. 193-204. Boudreau, Boudreau,A.E., A.E., 1988, 1988,Investigations Investigationsof ofthe theStiliwater StillwaterComplex. Complex. IV. IV.The Therole roleof ofvolatiles volatiles ininthe petrogenesis of the J-M Reef, Minneapolis Adit section. Canadian Minerologist the petrogenesis of the J-M Reef*Minneapolis Adit section. Canadian Mineralogist 26: 26: 193-208. 193-208. Campbell, Campbell, I.H., I.H.*Naldrett, Naldrett*AJ. A.J.and andBarnes, Barnes,S.-J., S.-J., 1983, 1983,AAmodel modelfor forthe theorigin originofofthe thePtPtrich theBushveld Bushveldand andStillwater StillwaterComplexes. Complexes.Journal JournalPetrology Petrology24: 24: richsulfide sulfidehorizons horizons- -the 133-165. 133-165. I Churchill, Churchill,K.C., K.C., 1978, 1978*AAgeochemical geochemicaland andpetrological pemlogical investigation investigationof of the theCu-Ni Cu-Nisulfide sulfide genesis MSthesis, thesis,University Universityof ofMinnesota: Minnesota:101 101p.p. Complex*Minnesota. MiinesomMS genesisininthe theDuluth DuluthComplex, Foose, Foose?M. M.and andWeiblen, Weiblen,P.W., P.W.*1986, 1986,The Thephysical physicaland andpetrologic petrologicsetting settingand andtextural texturaland and compositional compositionalcharacteristics characteristicsofofsulfides sulfidesfrom fromthe theSouth SouthKawishiwi KawishiwiIntrusion, Intrusion,Duluth Di~li~th Complex, Naldrett, in Friedrich, Fricdrich. G.li., G l I . , Genkin, Genkin, Ai), All., Naldrett,A.J., A.J.,Ridge, Ridge, Complex, Minnesota, Minnesota, USA. USA. in J.D., J.D., Sillitoe, Sillitoe?R.H., R.H., and andVokes, Vokes,F.M., F.M.,eds., eds.,Geology Geologyand andmetallogeny metallogenyofofcopper copper deposits, for deposits,Soc. SOC. forGeology GeologyApplied AppliedtotoMineral MineralDeposits, Deposits*Special SpecialPublication PublicationNo. No.4,4, Berlin, Berlin*Springer-Verlag: Springer-Verlag:8-24. 8-24. I 120 �Referencescontinued continued ... References Genkin, T.l., 1986, Associations of platinum-group minerals of the Ge&, A.D. A.D. and and Evstigneeva, Evstipeeva, T.l., Noril'sk 1:1203-1212. Noril'sk copper-nickel copper-nickelsulfide sulfideores, ores, Economic EconomicGeology Geology881: 1203-1212. Goryainov, I.N., 1971, The The genesis of the deposit, in in The The petrology petrology and and Goryainov, I.N., genesis of the Talnakh Talnakh deposit, economic economic geology geology of of the the Talnakh Talnakh and and Noril'sk Noril'sk differentiated differentiatedintrusions, intrusions,Urvantseva, Urvantseva, N.N. N.N. (ed.)182-312. (ed.) 182-312. Iwasaki, I., Takahashi, Takahashi, Y., Y., and and Kahata, Kahata,H., 1971, 1971, Segregation Segregation process for for copper copper and and nickel ores, in Progress Progressin in Extractive Extractive Metallurgy, Metallurgy, 1, 1, Gordon and Breach, NY. Macdonald, Macdonald, S.J., S.J., 1988, 1988, The The platinum group element deposits: classification classification and genesis. genesis. Geoscience GeoscienceCanada Canada14: 14:155-166. 1%- 166. Sabein, Sabelin, T., T., Weiblen, Weiblen, P.W., P.W., and and Saini-Eidukat, Saini-Eidukat, B., B., 1989, 1989, Similarities Similarities in textures textures and associations of platinum group minerals in the the Duluth Duluth Complex, Complex, MN h4N and andthe the mineral associations Noril'sl-Talnakh Geol. Soc. Amer. Amer. Abstr. with with Prog. Prog. 21: 21: Noril'sl-Talnakh intrusions, USSR USSR [abstr.1. [abstr.]. Geol. A262. Urvantseva, N.N. (ed.), (ed.), 1971, 1971, The The petrology petrology and and economic economic geology geology of of the theTalnakh Talnakhand and Urvantseva, N.N. Noril'sk differentiated differentiated intrusions, kLeningrad,3l2. n i n j p d , 3 12. Weiblen, P.W. and G.B., 1980, 1980, A summary summary of the stratigraphy, stratigraphy, petrology and and Morey, Morey, G.B., structure structureof of the the Duluth Duluth Complex. Complex. American American Journal Journal Sci. Sci. 280-A: 280-A: 88-133. 88-133. 121 �U Archean Granitoids Granitoids Of Of Northern Northern Marquette Marquette County, County, Michigan. Michigan. Archean Richard T. T. Wilkin, Wilkinf John John A. A. Mavrogenes, Mavr~genes~ Richard and Theodore Theodore J. J. Bornhorst Bornhorst and Department of of Geological Geological Engineering, Engineeringf Geology, Geologyf and and Department ~eophysics~ Michigan Technological Universityf Houghtonf Geophysics, Michigan Technological University, Houghton, MI 49931 49931 MI Granitoid rocks rocks of of Archean Archean age age crop crop out out in in aa large large Granitoid The Archean Archean rocks rocks The have been been subdivided subdivided into into the the northern northern (granite-greenstone) (granite-greenstone) have and the the southern southern (granite—gneiss) (granite-gneiss)complexes. complexes. These These and complexes are divided by a major crustal structure: the complexes are divided by a major crustal structure: the (Simsf 1980). The granitoid rocks Great Lakes tectonic zone Great Lakes tectonic zone (Sims, 1980). The granitoid rocks of the the northern northern portion portion of of the the southern southern complex complex have have been been of described by by Hoffman Hoffman (1987). (1987). The The granitoid granitoid rocks rocks of of the the described northern complex, complexf which which have have not not been been previously previously described, described, northern are the the focus focus of of this this on—going on-going study. study. are portion of of Marquette Marquette County, County, Michigan. Michigan. portion I In the the northern northern complex, complex, the the contact contact between between the the In granitoids and the Marquette greenstone belt is gradational granitoids and the Marquette greenstone belt is gradational and foliations foliations in in the the volcanics volcanics parallel parallel those those in in the the and The presence presence of of abundant abundant amphibolite amphibolite xenoliths xenoliths granitoids. The granitoids. in the the granitoids granitoids near near the the contact contact and and compositionally compositionally in in the the volcanics volcanics suggest suggest that that the the similar granitoid granitoid dikes dikes in similar granitoids intrude intrude the the volcanics. volcanics. The The emplacement emplacement of of these these granitoids belt bounding plutonic rocks is considered to be belt bounding plutonic rocks is considered to be contemporaneous with with recumbent recumbent folding folding of of the the volcanic volcanic rocks rocks contemporaneous (Johnson and Bornhorst, in press). The granitoids range (Johnson and Bornhorst, in press). The granitoids range tonalite based based from tonalite tonalite to to granite granite and and are are dominantly dominantly tonalite from on the the IUGS IUGS classification classification (Streckeisen, (Streckeisenf1973), 1973)# and and on on the the on Debon and and Le Le Fort Fort (1982). (1982). chemical classification classification scheme scheme of of Debon chemical Tonalites tend tend to to be be foliated foliated whereas whereas granites granites are are generally generally Tonalites Although most most of of these these granitoids granitoids were were emplaced emplaced massive. Although massive. during recumbent recumbent folding, foldingf it it is is possible, possiblef as as discussed discussed below below during that some may be younger. that some may be younger. Stocks and and related related rhyolite rhyolite dikes dikes were were emplaced emplaced within within Stocks the greenstone greenstone belt belt during during aa second second deformational deformational event event the Bornhorstf in in press). press). Modally, Modallyf these these stocks stocks (Johnson and and Bornhorst, (Johnson from diorite diorite to to granite granite and and most most are are granodiorite granodiorite or or range from range monzodiorite. One One pluton pluton described described by by Puffett Puffett(1974) (1974) quartz monzodiorite. quartz includes aa porphyritic porphyritic syenite. syenite. Age Age relationships relationships between between includes individual stocks are often equivocal because of spatial individual stocks are often equivocal because of spatial separation. separation. both the the belt belt bounding bounding and and In the the northern northern complex, complex, both In intra-belt granitoids granitoids generally generally fall fall along along calc-alkalic calc-alkalic intra—belt trends; however, howeverf aa tonalite—trondhjemite tonalite-trondhjemite trend trend is is also also trends; observed in the belt bounding granitoids (Debon and LeFort, Fort, observed in the belt bounding granitoids (Debon and Le 2? I �1982;Barker Barkerand andArth, Arthf1976). 1976). on On the thebasis basis of ofthe themajor major 1982; element tectonic tectonic discrimination discrimination method method of of Maniar Maniar and and Piccoli Piccoli element (1989) the the belt belt bounding bounding granitoids granitoids on (1989) on the the north northand and northeast sides sides of of the the volcanics volcanics and and the the intra—belt intra-belt northeast granitoids represent represent an an island island or or continental continental arc arc granitoids environment. This This is isconsistent consistentwith with the the trace traceelement element environment. discriminationmethod method of of Pearce Pearceet.al. et.al. (1984). (1984). Although Although discrimination these plutonic plutonic rocks rocks were were emplaced emplaced during during major major Archean Archean these deformation probably probably related related to to collision/suturing collision/suturingalong along the the deformation Great Lakes Lakes tectonic tectonic zone, zoneftheir their geochemical geochemical character characteris is Great similarto toan anarc arcenvironment. environment. Thus, ThusIthe the environment environment of of similar emplacementmay may be be transitional transitionalfrom fromarc arcto tocollision. collision. emplacement Granitoids Granitoids which which bound bound the the southwest southwest side sideof of the the greenstone greenstone belt belt in in the the northern northern complex complex classify classify as as collisional collisionalgranites, granitesfon onthe thebasis basisof ofmajor majorelements. elements. This This In the southern In the southern is not not confirmed confirmedby by the thetrace traceelements. elements. is complex, complexfthe the Bell Bell Creek Creek Granite Granite of of Hoffman Hoffman (1987) (1987)has has both both major major and and trace trace element element composition composition most most similar similarto to Perhaps these these granitoids granitoids are are younger younger collisionalgranites. granites. Perhaps collisional than aboveI and and were were emplaced emplaced during during the the than those those discussed discussed above, mature mature phase phase of of suturing suturing along along the the Great Great Lakes Lakes tectonic tectonic This hypothesis hypothesis could could be be tested tested by by radiometric radiometricage age zone. This zone. determinations. Although Although this this is is merely merely aa progress progressreport, reportf determinations. it it is is clear clear that that these these Archean Archean granitoids granitoids are are aa critical critical component component to to understanding understandingthe theArchean Archeanin inMichigan. Michigan. References References Barkerf F. F. and and Arth, ArthI J.G., J.G.f 1976, 1976# Generation Generation of of trondjehmitic trondjehmitic Barker, -tonalitic -tonalitic liquids liquids and and Archean Archean bimodal bimodal trondjehmitictrondjehmiticbasalt suites: suites: Geology, GeologyIv.4, v.4# p. p. 596—616. 596-616. basalt Debon! F, Ff and and Le Le Fort, Fortf P., P e f1982, 1982f AA chemical-mineralogical chemical-mineralogical Debon, classification classification of of common common plutonic plutonic rocks rocks and and assocassocTrans. R. Soc. Edinb., Earth Sciences, 73, R. SOC. Edinb.! Earth SciencesI 73#p. p. iations: Trans. iations: 135-49. 135—49. Hoffman, Hoffmanf M.A., M.Aef1987, 1987# The The geology geology of of the the southern southern complex: complex: geology, geologyf geochemistry, geochemistryIand and mineral mineral chemistry chemistry of of selectselected ed uranium—and uranium-and thorium—rich thorium-rich granites: granites: Ph.D. Ph.D. DisserDissertation, tationf Michigan Michigan Technological Technological University, Universityf Houghton, Houghton! 382 p. p. 382 Johnsonf R.J. R.J. and and Bornhorst, Bornhorst, T.J., T.J.! Archean Archean geology geology of of the the Johnson, northern beltI MarMarnorthern block block of of the the Ishpeming Ishpeming greenstone greenstone belt, quettef County, Countyf MI: MI: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin quette, 1904fin in press. press. 1904, 123 �1 Maniar, discrimManiar, P.D. P.D. and Piccoli, P.M., P.M., 1989, Tectonic discrimination of granitoids: granitoids: Geological Society of America Bulletin, Bulletin, v. 101, 101, P. p. 635—43. 635-43. J.A., Harris, N.B.W, N.B.W, and Tindle, A.G., A.G., 1984, Pearce, J.A., 1984, Trace Trace element element discrimination diagrams diagrams for for the the tectonic tectonic interpretation of granitic rocks: Journal Journal of of Petrology, Petrology, v. 25, 25, P. p. 956—83. 956-83. I W.P., 1974, Geology of the Negaunee Quadrangle,MarQuadrangle,MarPuffett, W.P., quette County, Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey ProfProfessional Paper p. essional Paper 788, 788, 51 51 p. P.K., 1980, Boundary between Archean greenstone greenstone and Sims, P.K., gneiss terranes terranes in northern Wisconsin and Michigan: Geologic Society of America Special Paper Paper 182, 182, p. 113113124. 124. A.L., 1973, Plutonic rocks: rocks: classification classification and Streckheisen, A.L., and nomenclature recommended by the IUGS IUGS Subdivision Subdivision on on the the nomenclature Systematics Systematics of Igneous Igneous Rocks: Geotimes, v. v. 18, 18, p. 26— 2630. 30. 124 I I I I I I I I I I I I �PURCHASE OF OFPROCEEDINGS PROCEEDINGSAND ANDABSTRACTS ABSTRACTS AND AND FIELD FIELD GUIDEBOOK GUIDEBOOK PURCHASE Copies of of the the Proceedings Proceedings and and Abstracts, Abstracts, Part Part 1, 1, and and the the Field Field Guidebook, Guidebook, Part Part 2, 2, for for the the Copies 36th Annual Annual Institute Institute on on Lake LakeSuperior SuperiorGeology Geology may may be be purchased purchased during duringthe themeeting. meeting. 36th Proceedings and and Abstracts, Abstracts, Volume Volume 36, 36, Part Part 11 Proceedings Field Guidebook, Guidebook, Volume Volume 36, 36, Part Part 22 Field . . . . . . . . . .$5.00 $5.00 Canadian Canadian . . . . . . . . . . . . . . . . . $5.00 $5.00 Canadian Canadian Payable to to Institute Instituteon onLake LakeSuperior SuperiorGeology Geology Payable ****************************************************************************** Issues of of Proceedings Proceedings and Abstracts, Abstracts, Part 1, 1, and Field Field Guidebook, Guidebook, Part Part2, 2, from from this this and and the the Issues three previous previous meetings, meetings, may may be ordered ordered from: from: three JoeKalliokoski KalZbkosJd,SecretaiySecretary-Treasurer Joe Treasurer Department of Geology and GeologicalEngineering Engineering Department of Geology and Geological Universily Michigan Technological Michigan Technological University Houghton, Michigan 49931 49931 Houghton, 906-482-6107 The cost cost for for each eachpart partordered orderedisis$6.00 $6.00U.S. U.S. The Orders will will be be filled filled while while supplies supplieslast. last. Orders ****************************************************************************** All volumes volumes back to to 1955 1955 are are available available for for photocopying photocopying at the the prevailing prevailing rate, rate, All from the theMichigan MichiganTechnological TechnologicalUniversity UniversityLibraty, Library, from through Mr. M. S. Spence, Archivist. through Mr. M. S. Spence, Archivist. Phone 906-487-2505 � https://digitalcollections.lakeheadu.ca/files/original/0777f53be72394c03c31a48988da325f.pdf fc82e698b41221481038bd2022b4b742 PDF Text Text INSTITUTE GEOLOGY INSTITUTE ON ON LAKE LAKE SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS . e 36th 36th Annual Annual Meeting Meeting May 1990 May 9-12, 9-12,1990 held at held at Thunder ThunderBay, Bay, Ontario Ontario H.L. JAMES JAMES VOLUME VOLUME VOLUME VOLUME36 36 May 1990 1990 May Part Part2. 2. Field Field Trip Trip Guidebook Guidebook �Organizing Committee, 36th Organizing 36th Annual Annual Meeting, Meeting, ILSG ILSG(1990) (1990) Committee comprises comprises the the following following members of the The Organizing Committee Department of Geology Geology Lakehead University Thunder Bay, Bay, Ontario P7B P7B5E1 5E1 General Chairman: Chairman: Manfred Manfred M. M. Kehienbeck Kehlenbeck Chair and and Abstract Abstract Editor: Editor: Philip PhilipW. W. Fralick Fralick Program Chair Editor: Graham Graham J. Borradaile Boiradaile Field Trip Guidebook Editor: & Volume 36 consists of Part 1: m: Abstracts Abstracts mPart 2 2:: Field F W Trip Guidebook Guktnwk to material in Proceedings Volume should should follow the Reference to the example example below: below: A., 1989, 1989, Significance Significance of of Conglomerates Conglomerates in in the the Baraboo quartzite quartzite of Brown, Bruce A., southeastern Wisconsin Wisconsin [abst.]; Institute on Lake Lake Superior Superior Geology Geology [abst.I; Institute Proceedings, 35th Annual Meeting, Duluth, MN, 1989; Houghton, Ml, 35, 1989; Houghton, MI, v. 35, part part 1, 1, p. p. 11-12. 11-12. Published Published and Distributed Distributed by by Institute on Lake Superior Geology Geology J. Kalliokoski, Secretary/Treasurer Dept. of Geological Geological Engineering, Geology and and Geophysics Geophysics Michigan Technological Technological University Michigan University 49931 Houghton, Michigan Michigan 49931 ISSN 1042-9964 1042-9964 �TABLE OF CONTENTS TABLE OF CONTENTS Introduction duction . ........... ... 1 M. M. J. J. Lavigne, Lavigne, Jr. Jr. FIELD TRIP 1 Mafic PGE mineralization Mafic intrusions, intrusions, PGE mineralization and and granitoid granitoid rocks of the Lac des Illes area. rocks of the Lac des Illes area. R. R. H. H.Sutcliffe Sutcliffe ....................... 11 FIELD TRIP FIELD TRIP22 Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean Archean Subprovinces. Subprovinces. U. J. Borradaile . . . 43 . FIELD FIELD TRIP TRIP33 Granitoid-related Granitoid-related mineral mineral deposits deposits in inthe thewestern western Lake Superior region. Lake Superior region. 52 S. A. Kissin FIELD FIELD TRIP TRIP44 Base Base Metal Metal Mineralization Mineralizationin inthe theShebandowan Shebandowan Greenstone GreenstoneBelt. Belt. M. Lavigne Jr., A. J. Aubut & & J. J. F. F.Scott Scott M. J. Lavigne 11 67 �GEOLOGY W THE LAKEIIEAD REGION GEOLOGY OF THE IIAREFIFD REGION by Maurice J - Lavigne Jr. Manriee J. Lavigne Jr. Ontario Ministry of Northern Development and Mines Ontario Ministry of Northern Development and Mines & Thunder Bay Thunder Bay S 1 �c.O —H 'CIt, ((lCD l-' (f) Ft (fl<t H- (1) (DO CD 0.0 flu) P1 H 0.0 C 'It!) N) CD Ni cto) It (DC) —0 r1 O(D H0 l.a. Oct CD Lithatectonic ~ul.$provinces of the Superior Province ( a f t e r Card and C i e a i e l s k i , 1986) 11 H I-I. 'a C II Figure 18 �INTRODUCTION The Lakehead LakeheadRegion Regionisisan anarea area bound houndtoto the the east east by The by LakeSuperior, Superior,to to the the south the international Lake south by by the internationalborder, border, includes includes Lake Nipigon, and extends to the west as far as the town of town of Atikokan. Atikokan. This region region is is underlain underlain by precambrian precambrian rocks of the Canadian Canadian Shield, Shield, in in particular, particular, Archean Archean rocks rocks the Superior Superior Province and Proterozoic Proterozoic rocks the Province and rocks of of the theSouthern Southern Province (Fig (Fig 1). Three subprovinces subprovinces of of the the Superior Province 1). Three Superior Province are are represented; Quetico, and Province represented;Wabigoon, Wabigoon, Quetico, and the the Abitibi—Wawa. The The Southern SouthernProvince Provinceisis subdivided subdivided into into the Abitibi-Wawa. the Nipigon Nipigon Plate Plate and the the Port Port Arthur Homocline, Homocline, the the northern northern fringe fringe of the the Aninikie Aninikie basin basin (enclosed (enclosed nap) nap). Stockwell (1964,1970) (1964,1970) and and Card Card and and Ciesielski Ciesielski (1986) (1986) subdivided the Superior Superior Province Province on the basis of structure structure and lithology. and lithology. In In this thisregion, region,the thesubprovinces subprovinces are are supracrustal-intrusive complexes, the predominance of either either s~ipracrustal-intrusivecomplexes, the predoninance of volcanic or sedimentary rock volcanic rock being a key distinguishing distinguishing characteristic. The Ahitibi—Wawa characteristic. Abitibi-Wawa and the Wabigoon Wabigoon b Suhprovinces are arcuate assemblages Subprovinces assemblages of volcanic rock dominated dominated belts, belts, "greenstone 'greenstone belts', belts", and tonalitic tonalitic to to granodioritic, granodioritic, massive massive to to gneissic gneissic intrusions. intrusions. The Quetico Quetico Subprovince is a linear linear metasedimentary terrane terrane cored by Subprovince granitic intrusions granitic intrusions and and migmatites. migmatites. The subprovince subprovince boundaries are boundaries are broad schist schist zones zones and/or and/or distinct distinct faults, faults, the Seine Seine River—Quetico River-Quetico fault fault couple, couple, which which separate separate the the Quetico from from the the Wabigoon, Wabigoon, being being good examples examples of of both both of of these types these types of of strain. strain. Nipigon Plate Arthur Homocline The Sipigon Plate and the Port nithur Homocline consist consist of flat lying lying sedimentary sedimentary rock rock uncomformibly unconformibly over'ying overlying the the Superior Province. Superior Province. These also include diabase sills sills and dykes, late dykes, late nafic oafic intrusions intrusions and and v,lcanic vzlcanic rocks. rocks 3 :' �ARCHEAN STRATICRAPHY High precision U—Pb zircon geochronology, carried out ,. ,- . at the has resulted resulted in&.draraatic in a dramatic the Royal Royal Ontario Ontario &tuseun, Museura, has <<.r. . of the change in in the the rate rate. of of increased increased understanding understanding,/of the . * archean. archean. Absolute dates dates corbined combined with with structural structural interpretations of well documented lithological distribution distribution interpretations has has resolved resolved the the stratigraphy stratigraphy within within some some greenstone greenstone belts. belts. It has also helped resolve resolve the the relationships relationships between plutonism, volcanism, plutonism, volcanisn, sedimentation, sedimentation, metamorphism, metanorphisra, deformation and deformation and mineralization. mineralization. Many stratigraphic stratigraphic relationships within subprovinces, relationships subprovinces, and in between subprovinces have subprovinces have also also been been resolved. resolved. In the Lakehead Region some some fundamental fundamental distinctions, distinctions, and an2 similarities, similarities can now be he drawn in between the Wabigoon and the Abitibi-Wawa Abitibi-Wawa tonalite-greenstone terranes and and their their relationship the tonalite-greenstone terranes relationship to to-the intervening- paragneiss of interveninq of the theQuetico. Quetico. -paracmeiss Atilcakan, In Atikokan, the the Marrnion Lake Batholith,aatonalite tonalite In larmion Lake Batholith, complex, omplex, has been dated at 3004 3004 ma (Davis (Davis et et al, al, 1988). 1988). This his hatholith batholith is is uncomformibly uncomformibly overlain overlain by the the Steeprock Steeprock Group This roup sedimentary sedinentary rocks rocks and subsequent subsequent volcanic rocks. rocks. This unconformity ncoraformity is is well exposed exposed on on the the east east wall of of the the Roberts Roberts v. pit. Stone et al.(in press) describe the unconformity and the overlying Wagita Formation e overlying Formation as follows; follows; "The "The uncomformity uncoraformity at t the the base of of the the Wagita Formation Formation is is marked by aa transition ransition from from unaltered tonalite tonalite to sericitized sericitized tonalite tonalite and nd a a sericite—carbonate-quartz sericite-carbonate-quartz 'grit', 'grit', which which becomes becomes well well bedded formation added and and clast clast bearing bearing up up section". section". The The ccagita Wagita formation is overlain by the stroriatolitic Mosher Carbonate Formation and altered altered iron iron formation formation (Jolliffe (Jolliffe Ore Zone Zone Formation). This his sedimentary sedimentary sequence sequence is is overlain overlain in in ascending ascending order order by; by; ultranafic pyroclastics, mafic pillow lavas and intermediate to felsic flows, o felsic flows, tuffs tuffs and and breccias. bre overlain by clastic sediments. This sequence is then Felsic tuffs in the Lumby Lake Creenstone Belt,on the 4 - , �I north Lake Batholith, Batholith, have have been been dated dated at orth side side of of the the .Marmjcin Marnion Lake at 950 ma na aria and 2999 aa (Davis Jackson, 1988). 1988). These are 2950 2999 rma (Davis and Jackson, These are considered onsidered to to be be the the stratigraphic stratigraphic equivalents equivalents to the the felsic felsic volcanics older, carbonate olcanics in in the the Steeprock Steeprock nine nine area. area. This older, carbonate sediment bearing, volcariic—sedirnerit:a rysequence sequence has has been diment bearing, volcanic-sedimentary been recognized in many manygreenstone greenstonebelts beltsininthe the northern northern parts parts of cognized in of the he superior superiorprovince province (Thurstori (Thurston and and Chivers, Chivers, 1990). 1990). These These sequences, equences, as well as quartz arenites—iron arenites-iron formation— fornationultrarnafic lava lava sequences sequences recognized recognized in in other other belts, belts, have ultramafic shallow water shallow water sedimentary sedimentary features. features. This is is the the basis basis for for the recognition sequences which the recognition of of early early archeari archean platfot-nal platfornal sequences developed at at about 3000 developed 3000 ma (Wood (Wood et et al, al, 1986). 1986). 1 These These shallow shallow water water guartz—arenite quartz-arenite and and carbonate carbonate I bearing sequences ('2.85 earinq sequences (>2.85 Ga) are generally overlain overlain by mafic—ultramafic afic-ultramafic volcanic volcanic sequences sequences (2.740 (2.740 to 2.700 2.700 Ga) Ga) and and mafic afic to to felsic felsic volcanic cycles cycles (2.775 (2.775 to 2.700 Ga) and comprise what comprise hat is is stratigraphically stratigraphically referred referred to to as as "Keewatin". Keewatin rocks volumetrically dominate Keewatin". rocks volumetrically doninate all all greenstone reenstone belts belts in in the the Superior Superior province. province. The younger younger of of these hese Keewatin Keewatin volcanic sequences sequences are not recognized in the Atikokan area. Atikokan area. They are however, the only recognizable recognizable volcanic sequence sequence older than than 2.700 Ga in the Shebandowan shebandowan greenstone belt of greenstone of the the Abitibi—Nawa Abitibi-Kawa subprovince. subprovince. Thurston Thurston (1986) (1986) interprets interprets two mafic to to felsic felsic volcanic volcanic cycles. cycles. Corfu and Stott Stott (1986) (1986) have generated a date of 2.733 Ga for felsic volcanics volcanics in in the the Middle Middle Shebandowan Shebandowan Lake Lake area. area. Stratigraphic relationships Stratigraphic relationships in this belt have been masked by intense intense deformation. deformation. A common connon thread thread for i.ur both both the the Abitibi-Wawa Abitibi-Wawa and and the the Vabigoon is Wabigoon is that that they they both both contain contain younger younger "Temiskaming""Temiskaming"type greenstone belts in the y p e sequences, sequences, found in many greenstone Canadian Shield. Canadian shield. These volumetrically volunetrically insignificant insignificant sequences sequences consist consist of of alluvial—fluvial alluvial-fluvial sedimentary sedimentary rock, rock, mainly conglomerate and arkose with or without alkalic and shoshinitic volcanic rock (Shegelski, 1980). In the S �Atikokan—?line Centre area, a distinctive conglomerate unit, referred to as as the the Seine Seine Conglomerate, Conglonerate, is is found found along along the the Quetico—Wabigoon uetico-Mabigoon subprovince subprovince boundary. boundary. The The contact contact relationship elationship with with adjoining adjoining Quetico Quetico sediments sediments and and Wahigocn Kabigoon volcanics olcanics is is unclear unclear because because of of poor poor exposure exposure and and shearing. shearing. Poulsen (1984), deduced that the Seine Conglomerates were younger ion ounger on on the the basis basis of of preserved preserved evidence evidenceof of defornat defornati history. istory. This This is is supported supported by by U-Pb C-Pb dates dates of of 2685 2 6 8 5 ma na for for aa clast last in in the the conglomerate conglomerate and and an an age age range range of of 2700 2 7 0 0 tO tG 2795 2795 ma a for for detrital detrital zircons zircons in in the the Quetico Quetico Metasedinents Mstasediments (Danis (Daris ett al, 1990). al, 1 9 9 0 ) . In In the the northern northern Shehandowan Shebandowan greenstone greenstone belt, belt, interdigitated conglomerates "Teniskaming' alkaline volcanics, and sandstones are dated at 2689 ma and the underlying at 2733 ma na (Corfu (Corfu and and Stott, Stott, nderlying "ICeewatin" "Keewatin" volcanic-s volcanics at 1986). 9 8 6 ) . The The contact contact relationship relationship is is obscured obscured by by well well developed eveloped foliation foliation leading leading to to speculation speculation that that the the "Temiskaning" 'Teniskaning" rocks rocks developed developed in in aa fault fault bounded bounded through. through. AA second econd belt belt of of Teniskaming Teniskaroing rocks rocks aa few few miles miles to to the the south south has stratigraphic relationship relationship with as aa clearly clearly discomfort-uable disconforniable stratigraphic with underlying nderlying "Keewatin" "Keewatin" volcanic volcanic rocks. rocks. In In summary, suranary, the the stratigraphy stratigraphy within within the the volcanic— volcanictonalite nalite terrane terrane consist consist of of 33 b.y. b.y. old old tonalite tonalite basement, basement, overlain 'erlain by by aa 33 b.y. b.y. old platfornal platfornal sequence, sequence, 2.74 2 . 7 4 b.y. b.y. subsubalkalic 2.68 b.y. b.y. old old calc—alkalic calc-alkalic volcanics volcanics Ikalic volcanics volcanics and and 2.68 and nd sedimentary sedimentary rocks. rocks. Recent Recent age age dates dates on on detrital detrital zircons zircons from on Quetico Quetico greywacke greywacke range range from from 2700 2700 al, 1990) strongly suggesting a coeval sub—alkalic volcanics. The suggestion to to 2795 2 7 9 5 ma ma (Davis (Daviset et relationship with the by Williams (1987), that at the the Quetico Quetico represents represents an an accretionary accretionary prism prism is is well well accepted. A host to the 3 b.y. tonalite intrusive has yet to bee recognized. recognized. The The last last major major geological geological event event in in the the tonalite— tonalitegreenstone nstone terrane. terrane is represented represented by by the the voluminous voluminous tonalites analites which which intruded intruded from from 2690 2690 to to 2677 2 6 7 7 Ma Ma (Colvine, (Colvine, et et C) �al 1988). granitic Quetico al 1 9 8 8 ) ; TThe. he g r a n i t i c rocks r o o k s in i n tthe he Q u e t i c o intruded i n t r u d e d from from 2670 tO Both of 2670 t 0 2650 Ma Ma (Percival, ( P e r c i v a l , 1989). 1 9 8 9 ) . Both o f these these have widespread ssubprovinces ubprovinces h ave w i d e s p r e a d mmafic a f i c i intrusions n t r u s i o n s which w h i c h aare r e not not well constrained well c o n s t r a i n e d geochronoloyically. CJe0~hr~~n0l9gi~ally. The iisoclinally The s o c l i n a l l y folded, f o l d e d , steeply s t e e p l ydipping d i p p i n g archean a r c h e a n rocks roc off tthe overlain by tthe o h e Superior S u p e r i o r Province, P r o v i n c e , aare re o v e r l a i n by h e shallow shallow off tthe dipping Southern d i p p i n g protei-ozoic p r o t e r o z o i c rocks rocks o he S o u t h e r n Province. Province. The Port Arthur Gunflint Port A r t h u r Honocline i l o m o c l i n e consist c o n s i s t of o f the the G u n f l i n t Formation Formation ((taconite, t a c c n i t e , aalgal l g a l cchert, h e r t , limestone, l i m e s t o n e , and a n d tuffaceous t u f f a c e o u s shale) s h a l e ) and an tthe h e overlying o v e r l y i n g Rove Rove Formation F o r m a t i o n (shale, ( s h a l e , greywacke). greywacke). The age a g e of of poorly but tthese h e s e rocks r o c k s is is p o o r l y constrained constrained b u t is i s cconsidered o n s i d e r e d to t o be be Nipigon older o l d e r than t h a n 1850 1 8 5 0 Ma. Ma. (Morey, ( ? I o r e y , 1983). 1 9 8 3 ) . The X i p i g o n Plate Plate consist c o n s i s t ci o f the t h e Pass P a s s Lake Formation F o r m a t i o n (quartz ( q u a r t z aarenite), r a n i t e ) , the the Passport dolestone, R o s s p o r t Fornation F o r n a t i o n ( " rredbeds" e d b e d s " —- d o l e s t o n e , ssandstone, andstone, ( chart, i l l Formation F o r m a t i o n (nudstone) (mudstone). c h e r t , mudstone) m u d s t o n e ) aand n d tthe h e Kana Kama HFill These T h e s e tthree h r e e formations f o r n a t i o n s comprise c o m p r i s e the t h eSibley S i b l e yGroup G r o u pwhich which uncomfornibly unconiforraibly ooven v e r l iies e s archean a r c h e a n rocks r o c k s and a n d the t h eRove Rove Formation. Formation. These T h e s e sedimentary s e d i m e n t a r y rocks r o c k s are a r eoverlain o v e r l a i nbybythe t hKeweenawan e Keweenawan They hhave volcanic O s i e rGroup. Group. They a v e aalso l s o been been v o l c a n i c rocks r o c k s of o f the t h eOsler intruded by eearly i n t r u d e d by a r l y Keweenawan diabase, d i a b a s e , the t h e dominant d o n i n a ~ lithology tl i t h o l o g y in the Nipigon Plate, and late Reweenawan gabbroic stocks and dykes. METALLOGENY METALLOGEN The Lakehead Region to a wide variety of types i s hhost ost t ~ a k e h e a dR e g i o n is of mineral o f m i n e r a l deposits. deposits. The greenstone—tonalite g r e e n s t o n e - t o n a l i t e terrane terrane volcanogenic with ccontain ontain v o l c a n o g e n i c Cu-Zn Cu-Zn deposits d e p o s i t s aassociated ssociated w i t h felsic felsic volcanic v o l c a n i c rocks, r o c k s , konatiite k o r n a t i i t e (intrusive (intrusive 7 ? extrusive e x t r u s i v e 7) ? ) hosted hosted Ni—Cu deposits, hosted Ni-Cu d e p o s i t s , nafic r n a f i c intrusive intrusive h o s t e d platinum p l a t i n u m metal m e t a l group group deposits, iron deposits, and lode gold deposits. 7 The :' �Quetico Quetico subprovince subprovince contains contains subeconomic sufceconomic rare rare element element deposits group and deposits in in pegmatites pegmatitea and and platinum platinum metal metal group and Cu-Ni Cu-Xi deposits in naf Ic intrusive*. intrusives. Proterozoic. Proterozoic rocks deposits in nafic rocks contain contain numerousveins veins in in sedimentary rocks with with varied varied amounts amounts of af numerous sedimentary rocks silver, zinc, lead, harite and fluorite in; native copper silver, zinc, lead, barite and fluorite in; native copper deposits deposits in in nafic maficvulcanic volcanicrocks; rocks;and andplatinum platinum metal neta groupCu—Ni deposits in CU-xi deposits in mafic i i a f i c intrusives. intrusives. S �REFERENCES REFERENCES Card, rd, lCD. K.D. and and Ciesielski, Ciesielski, A. A. 1986: 86: Subdivisions of of the Province of Subdivisions the Superior Superior Province of the the Canadian Shield. Canadian Shield, Geoscience Geoscience Canada, Canada, 13:5—13. 13:5-13 Colvine, olvine, A.C., A.C., Fyon, Fyon, J.A., J.A., Heather, Heather, N.E., K.B., Marmont, Marnont, S., a., Smith, ith, P.M. P.M. and and Troop, Troop,D.G. D.G. 1988: 988: Archean Archean Ontario Ontario lode lode gold gold deposits deposits in in Ontario. Ontario. Geological Survey, Misc. Geological Survey, Misc. Pap., Pap., 139, 139, 136p 136p Corfu, F. Corfu, F. and and Stott, Stott, G.M. G.H. 1986: U-Pb ages 1986: C-Pb ages for for late late magnatisn magnatisn and and regional regional deformation in Belt, Superior deforiaation in the the Shebandowan Shebandowan Belt, Superior Province, Canada. Canada. Can. Earth Scie., Scie., 23:1075— Province, Can. 3. J. Earth 23:10751082. 1082. Davis, D.W. Davis, D.K. and and Jackson, Jackson, M.C. M.C. Geochronology 1988: 1988: Geochronology of of the the Lumby Lumby Lake Lake Greenstone Greenstone belt: belt: 3 Ga complex within the Wabigoon a a 3 Ga complex within the Wabigoon subprovince, subprovince, northwest northwest Ontario. Ontario. Geol. Geol. Soc. Soc. Am. Am. Bull., Bull., 100(6) :818—824. 100(6):818-824. Davis, D.W., Davis, D.W., Poulsen, Poulsen, N.H. K.H. and and Kamo, Kano, S.L. S.L. New insights 1989: 1989: Kew insights into into Archean Archean crustal crustal development development geochronology in from geochronology in the the Rainy Rainy Lake Lake area, area, Journal of Superior Superior Province, Province, Canada. Canada. Journal of Geology, Geology, 98. 98. Hyde, Hyde, R.S. R.S. Sedimentary facies 1980: 1980: Sedinentary facies in in the Archean Temiskaming Teraiskaning Group, and their Group, their tectonic implications, implications, Abitibi Abitibi greenstone belt, northeastern Ontario, Ontario, Canada. greenstone Precambrian Precanbrian Res., Res., 12:141—160. 12:141-160. Percival, J.A. Percival, J.A. and and Williams, Williams, H.R. H.R. 1989: 1989; The late late Archean Quetico Quetico accretionary accretionary complex, complex, Superior Province, Geology 17:23-25. Province, Canada. Geology 17:23-25. Paulsen, N.H. Poulsen, K.H. Archean tectonics 1984b: 1984b: tectonics and and mineralization mineralization at at Rainy Rainy Lake, Ph.D. Thesis, Thesis, Queens Queens Lake, northwestern northwestern Ontario. Ontario. Ph.D. University, Kingston, University, Kingston, Ont., Ont., 342pp.(unpublished). 342pp.(unpublished). Shegeiski, P.3. Shegelski, R.J. Archean cratonization, 1980: 1980: cratonization, emergence and red bed development, development, Lake Lake Shebandowan Shebandowan area, area, Canada. Precambrian Research, volume 12, Precambrian Research, 12, p.331—347. p.331-347. 9 �S t o c k w e l l , C.H. C.H Stockwell, 1 9 6 4 : F o u r t h report r e p o r t on o n structural s t r u c t u r a l provinces, provinces, orogenies 1964: Fourth nd t i m e - c l a s s i f i c a t i o n o f r o c k s o f t h eorogenies Canadian and of rocks of the Canadian r e ctime-classification ambrian S h i e l d . I n Age d e t e r m i n a t i o n s and Precambrian Shield. 11.determinations G e o l o g i c a l S u rand vey o f e o l o g i c a l s t u d i e s , pIn a r tAge geological Survey of n a d a , P a studies, p e r 6 4 - 1 7 ,part p p . 4II. 4 - 5 4Geological . Canada, Paper 64—17, pp.44—54. 1970: Geology of t h e Canadian S h i e l d , i n t r o d u c t i o n . I n Geology of the Canadian Shield, introduction. In Geology and economic minerals of Canada, part A. Edited by R.J.W. Douglas, Geological Survey of Canada, Economic Geology Report 1, pp.44-54. W i l l i a m s , H.R. H.R. ccillians, 1987c: Structural studies in the Wabigoon and Wood, Wood, 1986: 1986: Quetico subprovinces. Ontario Geological Survey, Open File Report 5668. J., Thurston, P.C., C o r f u , F . a n d D a v i s , D.W. J.,AThurston, P.C., Corfu, r b oand n c i e n t q u a r t z i t e s a n d c aF. n a t eDavis, s i n n D.W. orthw Ancient guartzites and carbonates O n t a r i o ~ e v i d e n c ef o r e a r l y ( A r c hin e a nnorthwestern ) stabi Ontario—-evidence for early (Archean) stability? Geol. Assoc. Can./Mineral Assoc. Can., Progr. with Abstr., 11, p.146. 10 �J9ELD TRIP 1 I I I I I I I I I I �MAFIC INTRUSIONS, MAFIC INTRUSIONS,PLATINUM-GROUP-ELEMENTS PLATINUM-GROUP-ELEMENTS MINERALIZATION MINERALIZATION AND AND DES ILES AREA GRANITOID ROCKS IN THE GRAMITOID THE LAC LAC DES Introductory Introductory Discussion Discussion and Field Field Guide Guide 36th Annual Institute Institute on Lake Lake Superior Superior Geology Geology Thunder Bay, Ontario ' Ontario by R.H. R.H. Sutcliffe Sutcliffe Ontario Geological Survey Survey 77 Grenville Street Street Toronto, Toronto, Ontario Ontario M7A lW4 1W4 11 �INTRODUCTION INTRODUCTION The The Lac Lac des des ties Iles region region provides provides an an opportunity opportunity to to examine a wide range of Late Archean plutonic examine a wide range of Late Archean plutonic rock rock types. types. This This field field trip trip will will emphasize: emphasize: the the role role of of mafic mafic magmatism magmatism in the evolution of this Late Archean plutonic in the evolution of this Late Archean plutonic terrane; terrane; the the relationship and granitoid granitoid plutonism; plutonism; relationshipbetween betweenmafic maficxnag-inas magmas and and and aspects aspects of of platinum—group—elements platinum-group-elements mineralization. mineralization. The The field field trip trip is is based based on on surveys surveys done done in in the the Lac Lac des des lies Iles area area by by the the Ontario Ontario Geological Geological Survey Survey in in 1985 1985 and and 1986. 1986. This This work work included included detailed detailed mapping mapping of of the the Lac Lac des des lies Iles Complex Complex (Sutcliffe (Sutcliffe and and Sweeny, Sweeny, 1986) 1986) and and Tib Tib Gabbro Gabbro (Smith (Smith and and Sutcliffe, Sutcliffe, 1987), 1987), regional regional mapping mapping of of the the granitoid granitoid rocks rocks (Sutcliffe (Sutcliffe and and Smith, Smith, 1988), 1988). and and aa gravity gravity survey survey of the the area area (Gupta (Gupta and and Sutcliffe, Sutcliffe, in in press). press). The The discussion discussio presented presented here here makes makes considerable considerable use use of of excerpts excerpts from from Sutcliffe (1989) and Sutcliffe et al (1989) Sutcliffe (1989) and Sutcliffe (1989) to to which which the the reader reader is is referred referred for for further further details details on on aspects aspects of of the the geochemistry geochemistry of of the the plutonic plutonic rocks. rocks. Previous Previous mapping mapping in in the the area area is is primarily primarily the the reconnaissance reconnaissance mapping mapping and and compilation compilation of al (1974). of Sage Sage et U (1974). OVERVIEW OVERVIEW Mafic racks in the Lac des lies Mafic to to ultramafic ultramafic intrusive in area trending linear zone of area form form part part of of an an east—northeast east-n Late Late Archean Archean mafic mafic piutons plutons which extends over 200 km from Atikokan Atikokan to to Lake Lake Nipigon. Nipigon. This zone parallels the boundary between Subprcvinces (Stockweli et between the the Wabigoon Wabigoon and and Quetico Qu j 1972). 1972). The The rocks rocks examined examined on on this this field field trip trip are are all a11 within within the the Wabigoon WabigoonSubprovince. Subprovince. In In the the immediate immediate region region of of the the field field trip, trip, the the mafic mafic to to ultramafic ultramafic plutons plutons are are intruded intruded into into gneissic gneissic tonalite tonalite host host rocks rocks and and are are distributed distributed in in aa circular circular pattern, pattern, the the diameter diameter of of which which is is approximately approximately 30 30 km tan (Figure (Figure1). 1). These These plutons plutons are are composed composed of of serpentinite, serpentinite, wehrlite, wehrlite, minor minor lherzolite, lherzolite, clinopyroxenite clinopyroxenite and and websterite websterite to to magnesian magnesian gabbronorite gabbronorite and and ferrogabbro ferrogabbro(Sutcliffe (Sutcliffeand and Smith Smith1988). 1988). The The Lac Lac des des Iles Iles Complex Complex (LDIC) (LDIC)is is the the largest largest of of the the mafic ma to to ultramafic ultramafic plutons plutons and and displays displays the the most most complete complete spectrum spectrum of of lithologies. lithologies. The The Tib Tib Gabbro Gabbro is is the the second second largest largest intrusion intrusion and and consists consists of of predominantly predominantly gabbronorite. gabbronorite. The The marginal marginal zones zones of of larger larger intrusions intrusions and an some some of of the the smaller smaller intrusions intrusions consist consist of of hornblendite, hornblendite, and and hornblende hornblende gabbro qabbro to todiorite. diorite. Most Most of of the the mafic mafic to to ultramafic ultramafic intrusions intrusions have have well well preserved preserved igneous igneous mineralogy mineralogy and and are are not not significantly significantlydeformed. deformed. The The form form and and tectonic tectonic setting Ic intrusions, setting of of the themafic-ultramaf mafic-ultramafic intrusions, particularly particularly the LIflC, LDIC, is is similar similar to to mafic mafic intrusions intrusions associated associated with with orogenic orogenic terrains terrains such such as as the the Mesozoic Mesozoic Alaskan Alaskan complexes complexes (Taylor (Taylor1967, 1967, Findlay Findlay 1969). 1969). Preliminary Preliminary U/Pb U/Pb zircon zircon data data indicate indicate that that the the qabbroic gabbroic rocks rocks of of the the Lac Lac des des Iles IlesComplex Comp and and the the Tib Tib Gabbro Gabbro are are 2.69 2.69 Ga Ga (D.W. (D.W. Davis, Davis, Royal Royal Ontario Ontario Museum, Sm/Nd age age of Museum, unpublished unpublished data), data), however, however, an an older older Sm/Nd of 2,738+/—27 2,738+/-27 Ma Ma is is reported reported for for the the ultramafic ultramafic rocks rocksof ofthe the LOIC LDIC by by Brugmann Brugmann and and Naldrett Naldrett(1987). (1987). 12 �A major zone of platinum-group-elements (PGE) (PGE) and Cu—Ni Cu-Ni sulphide occurs in sulphide mineralization, known as the Roby Zone, occurs gabbroic gabbroic rocks rocks of of the the LDIC. LDIC. The property is being developed by Madelaine Mines Limited and this this may become the the first first primary producer of platinum group elements elements (PGE) (PGE) in Canada mineralization in (Northern Miner Miner Press (Northern Press 1988). 1988). The PGE mineralization in the the Roby Zone Zone of the the LDIC is is associated with suiphides sulphides and altered silicates altered silicates in in gabbroic gabbroic rocks. rocks. This mineralization characteristics suggesting the control of both exhibits characteristics magmatic mixing processes (Naldrett (Naldrett and Campbell Campbell 1979; 1979; Todd et al 1982; Sharpe 1985) and volatile dominated processes (Talkington and Watkinson 1 (Talkington Watkinson 1984; 1984; Boudreau Boudreau et al 1986; 1986;Stumpf Stumpfl and Ballhaus Ballhaus 1986). 1986). PGE mineralization also also occurs occurs in in ultramafic rocks of the LDIC and in other intrusions intrusions in the PGE's were area and these occurrences occurrences indicate that PGE's concentrated at several stages in the fractionation concentrated fractionation of the mafic magmas. Two granitoid plutons consisting of hornblende tonalite and biotite biotite tonalite The tonalite intrude intrude older older gneissic gneissic tonalite. tonalite. The gneissic tonalite is dated at approximately 2.77 Ga and the tonalite 2.77 younger hornblende hornblende tonalite U/Pb zircon tonalite at 2.73 2.73 Ga by the U/Pb zircon method (D.W. (D.W. Davis, Davis, unpublished unpublished data). data). The younger younger granitoid plutons contain net—veined mafic dikes contain numerous net-veined the coexistence of mafic mafic and and other textures indicating the felsic magmas. felsic magmas. Although the association association of mafic magmas with late late Archean granitoids granitoids has not been commonly commonly recognized, there are other examples of associated Late Archean mafic and felsic magmatism in the Wabigoon Subprovince Subprovince (e.g. (e.g. Morrison Morrison et al 1986). 1986). Based on field field relationships, relationships, Sutcliffe Sutcliffe (1989) (1989) considered that hornblende tonalite mafic—ultramafic intrusions tonalite and the the mafic-ultramafic intrusions were contemporaneous. The contemporaneous. The geochronology geochronology does does not not support support this this conclusion conclusion and the the mixing textures therefore are probably than that that associated which an an older older phase phase of of mafic mafic inagmatism magmatism than which generated generated the the major major mafic—ultramafic mafic-ultramafic plutons. plutons. Further studies will test studies test this this hypothesis. hypothesis. piutonic rocks In this guide, plutonic rocks are are named using using the the classification of classification of Streckeisen Streckeisen (1976). (1976). a a LAC DES ILES IAC ILES COMPLEX Geo 1 oqy Geoloav Mapping by Pye (1968) (1968) indicated indicated that that the the Lac Lac des des Iles lies Complex (LDIC) Complex (LDIC) has has an an area area of of approximately approximately 30 30 km2. km2. The LDIC (Figure (Figure 2) consists of a predominantly ultramafic sequence centred on Lac des lies and predominantly gabbroic sequences south of the lake (Pye, Watkinson and seauences fPve. 1968; 1968: Watkinson Dunning, description given here is largely based ~ u i n i n ~1979). 1979). , The description on mapping by Sutciiffe Sutcliffe and Sweeny (1986) (1986) and the work of Sutcliffe et al (1989). Sutcliffe (1989). Details of the mineral assemblages assemblages textures for and textures for rock rock types types are are summarized summarized in in Table Table 1. 1. A gravity study study by Gupta Gupta and and Sutcliffe Sutcliffe (in (in press) press) indicates that the LDIC LOIC is is associated with aa 30 30 mgal mgal gravity gravity . - . 13 - �high high and and is is modelled modelled as as aa funnel funnel shaped shaped body body part part of of which which extends to aa depth depth of of 4.5 4.5 km. tan. extends to The The ultramafic ultramafic sequence sequence is is composed composed of of two two coalescing coalescing centers which are defined by the different distributions centers which are defined by the different distributions of of ultramafic ultramafic lithologies lithologies and and by by the the attitudes attitudes of of igneous igneous layering layering (Figure (Figure2). 2). Hornblendite Hornblendite to t o pyroxene pyroxene hornblendite hornblendite and hornblende gabbro occur along the western and hornblende gabbro occur along the western margin margin of of the the LDIC LDIC and, and, with with increasing increasing modal modal pyroxene, pyroxene, grade grade into into pyroxenite. pyroxenite. The The hornblende-rich hornblende-rich lithologies lithologies are are invaded invaded and and brecciated brecciated by by veins veins of of hornblende hornblende diorite diorite to t o quartz quartz diorite. diorite. The The northern northern ultramafic ultramafic center center is is nearly nearly circular circular in in plan with a diameter of approximately 4 km (Figure plan with a diameter of approximately 4 tan (Figure 2) 2) and and consists consists of of several several cycles cycles of of serpentinite serpentinite and and wehrlite, wehrlite, olivine livine clinopyroxenite clinopyroxenite and and clinopyroxenite, clinopyroxenite, and and websterite websterit too gabbronorite. gabbronorite. Lindhardt Lindhardt and and Sues Bues (1987) (1987) have have shown shown that tha these hese cycles cycles are are typically typically 100 100 to t o 500 500 mm thick thick in in plan plan and and individual individual layers layers can can be be traced traced along along strike strike for for up up to t o 1.5 1.5 km. Olivine cumulates are most abundant around the southern tan. olivine cumulates are most abundant around the southern and and eastern eastern perimeter perimeter of of the the center center and and the the rocks rocks become become more pyroxene—rich towards the nothwest. The more pyroxene-rich towards the nothwest. The absence absence of of distinct distinct marker marker horizons horizons and and extent extent of of outcrop outcrop exposure exposure places places significant significant limitations limitations on on the the interpretation interpretation of of the lateral lateral continuity continuity and and thickness thickness of of the the cycles. cycles. Modal Modal layering layering due due to t o variation variation in in proportions proportions of of plagiociase plagioclase and and pyroxenes, pyroxenes, olivine olivine and and clinopyroxene, clinopyroxene, and a orthopyroxene orthopyroxene and and clinopyroxene clinopyroxene is is observed. observed. Generally Generally the the modal modal layers layers are are 11 to t o 20 20 cm cm thick thick and and are are continuous continuous for for meters. meters. Minor Minor disseminated disseminated euhedral euhedral grains grains of of chromite chromite are are enclosed enclosed in in cumulus cumulus olivine olivine and and clinopyroxene clinopyroxene and and are are locally locally concentrated concentrated in in layers layers up up to t o 11 cm cm wide wide in in the the northern northern center. center. Igneous Igneous lamination lamination defined defined by by planar planar alignment alignment of of pyroxenes pyroxenes or or plagioclase plagioclase is is also also observed observed at at several everal localities. localities. Layer Layer attitudes attitudes indicate indicate that that the the northern orthern center center has has an an upright upright funnel—shaped funnel-shaped form. form. Minor Min discordant serpentinite dikes, which iscordant serpentinite dikes, which contain contain angular angular fragments fragments of of pyroxenite pyroxenite intrude intrude the the northern northern ultramafic ultramafic center. The The southern southern ultramafic ultramafic center center is is elliptical elliptical in in plan plan with with an an irregularly irregularly shaped shaped wehrlite wehrlite core core centered centered on on Southeast Southeast Angle Angle Bay Bay of of Lac Lac des des lies. lies. The The wehrlite wehrlite core core is is surrounded surrounded by by websterite websterite which which in in some some areas areas contains contains inclusions inclusions of of wehrlite. wehrlite. Along Along the the eastern eastern margin margin of of the the center center the the websterite websterite grades grades into into gabbronorite. gabbronorite. The The southern southern center center is is predominantly predominantly composed composed of of massive massive rocks rocks and and lacks lacks well well defined defined igneous igneous layering. layering. The The ultramafic ultramafic rocks rocks are are partially partially separated separated from from the the gabbroic abbroic rocks rocks south south of of Lac Lac des des Iles lies by by aa septum septum of of tonalite. onalite. Watkinson Watkinson and and Dunning Dunning (1979) (1979)considered considered that thatthe ultramafics ltramafics were were emplaced emplaced later later than than the the gabbroic gabbroic rocks rocks based ased on on the the presence presence of of gabbroic gabbroic inclusions inclusions in inthe the uitramafics. ultramafics. The The only only clearly clearly defined defined gabbroic gabbroic inclusions inclus observed and observed during during the the current current study study are are troctoiitic t and not readily readily related related to t othe thegabbroic gabbroicsuite. suite. 14 �A 50 m wide, composite dike consisting of olivine A gabbronorite, gabbronorite, olivine websterite to lherzoiite lherzolite with hornblende diorite margins outcrops on the south—west south-west shore of Lac des This des lies lies and and along along the the west west side side of of the the gabbro. gabbro. This dike is olivine—rich olivine-rich (picritic) (picritic) and is potentially a feeder for the southern ultramafic center Gabbroic rocks occur largely in the southern part of the LDIC host to to the the Pd, Pd, Pt the LDIC (Figure (Figure 2) 2) and and are are host Pt mineralization of Based largely on detailed detailed mineralization of the the Roby Roby Zone. Zone. Based studies studies of drill core in in the immediate immediate vicinity of the the Roby Zone, Watkinson and Dunning (1979) (1979) indicated that the the gabbro could ould be divided into into two two major units known as the the Eastern Gabbro abbro (EG) (EG) and and Western Western Gabbro Gabbro (WG). (WG). As defined by Watkinson and Dunning (1979), the atkinson (1979), the WG consists consists of interlayered nterlayered gabbroic, noritic, pyroxenitic, and anorthositic northositic rocks rocks and the the EG consists consists of oxide—rich oxide-rich gabbroic abbroic and and noritic noritic rocks. rocks. This distinction is significant because ecause the the Roby Zone Zone is is interpreted interpreted to to occur along along the the contact ontact of of the the two two units. units. Macdonald (1985), (1985), Sutcliffe and Sweeny weeny (1986), (1986), and Sweeny and Edgar (1987) (1987) suggested suggested that the the relationships relationships between the the units units are complex complex and and that that many of the the layers layers identified identified in in drill core core by Watkinson Watkinson and and Dunning (1979) (1979) are are separate separate intrusive intrusive phases. phases. The gabbroic part of the LDIC consists of a leuco— leucogabbro to anorthositic anorthositic gabbro unit and a unit of predominantly the vicinity vicinity of the Roby predominantly gabbronorite. gabbronorite. In the Zone, these units correspond correspond with the EG and WG respectively, respectively, although although in detail there is not a simple geographic subdivision geographic subdivision (Figure (Figure 3). 3). As defined by Sutcliffe et al (1989), (1989), both the EG and WG contain cumulus plagioclase, oclase, however, however, the the WG contains contains cumulus cumulus orthopyroxene orthopyroxene or alteration This teration products pseudomorphing orthopyroxene. This represents a different different definition of the units than than that of Watkinson Watkinson and and Dunning Dunning (1979), (1979), however, however, because because there there is is an an important geographic geographic connotation connotation to to the the terms tens EG and WG in the Roby Zone, Zone, these these names names have have been been retained. retained. The EG displays igneous igneous lamination lamination and weakly developed wispy modal pervasively altered obscuring the primary layering and is pervasively igneous assemblages. WG typically consists of igneous assemblages. The WG gabbronorite Locally, in gabbronorite to norite and is fresh to altered. Locally, the the vicinity of the the "D 'ID Zone", the the WG contains contains cumulus cumulus olivine. olivine. Within the the WG near the EG/WG EG/WG contact, pegmatitic gabbro, gabbro breccia, gabbronorite, gabbronorite, and clinopyroxenite clinopyroxenite form an arc—shaped arc-shaped zone zone of of variable variable width width (Figure (Figure 3). 3). In this this part of the the WG, pegmatitic gabbro phases occur occur primarily primarily as as inclusions, inclusions, pegmatoidal pegmatoidal segregations segregations and and discordant discordant pegmatite pegmatite dikes. dikes. Pegmatitic phases are rare in the the EG. EG. The WG truncates truncates the igneous lamination and weakly developed developed modal layering layering of of the the EG, EG, indicating indicating that that the the WG WG is younger younger than than the the EG. EG. An intrusion medium—grained hornblende hornblende gabbro gabbro to to intrusion of medium-grained leucogabbro with minor coarse—grained coarse-grained hornblende melagabbro occurs age of the hornblende occurs south south of of the the EG EG and and WG. WG. The aae 15 �gabbro gabbro relative relative to to other other units units of of the the LDIC LDIC has has not not been been determined. determined. Late dikes of microdiorite—gabbro microdiorite-gabbro intrude intrude the the gabbroic gabbroic rocks rocks and locally result result in in intrusion intrusion breccia consisting consisting of of angular angular gabbroic gabbroic and less less common common tonalitic tonalitic fragments fragments in in aa fine—grained fine-grained igneous igneous matrix. matrix. Late Late leucocratic leucocratic tonalitic tonalitic dikes dikes and and veins veins also also cross cross cut cut the the gabbroic gabbroic rocks. rocks. Petrological Petrological and and geochemical geochemical studies studies by by Sutcliffe Sutcliffe et al (1989) indicate that that distinct distinct magma sequences sequences can can be be (1989) indicate recognized on a basis of crystallization crystallization order, differences differences in in cumulus cumulus minerals, minerals, intrusive intrusive relations relations and and geochemical geochemical differences. These sequences are 1) hornblende differences. These sequences are 1) hornblende gabbro, gabbro, 2)gabbro 3) ultramafic. ultramafic. Where Where there there is is 2)gabbro and and gabbronorite gabbronorite and and 3) evidence evidence of intrusive intrusive relations relations the most primitive primitive sequences sequences are are emplaced emplaced late late and and toward toward the the north north end end of of the the complex. complex. In In the the absence absence of of rocks rocks representative representative of of liquids, liquids, parental parental magma magma compositions compositions can can only only be be constrained constrained by by the the compositions compositions of of cumulus cumulus phases. phases. Mineral Mineral chemistry chemistry and and crystallization sequences crystallization sequences indicate indicate that that the the parental parental magmas of of the the gabbroic gabbroic and and ultramafic sequences sequences had tholeiitic tholeiiti basalt basalt parental parental magmas magmas with with high high alumina alumina and and picritic picritic affinities affinities respectively. resvectivelv. - .. . - .>*:..; - . . . . . + . . . . Mineralization Mineralization . . 5. . .. ;teg*'.:;. :p , Exploration Exvloration by bv Texasgulf Texasaulf Canada Limited and Boston Bay Bav Mines 1976 outlined Mines Limited ~imitedin in 1975 1975 and and1976 outlined 20.4 20.4 million million tonnes tonne; of 0.2% Cu ++ Ni Ni of mineralization grading grading 66 ppm Pd and Pt and 0.2% in long Roby Roby Zone Zone along along the the EG/WG EG/WG contact contact in the the 600 600 m long (Northern (Northern Miner Miner Press Press 1976). 1976). Pt/(Pt+Pd) Pt/(Pt+Pd) is is in in the the range range of of 0.1 0.1 (Watkinson (Watkinson and and Dunning Dunning 1979) 1979) to to 0.2 0.2 (Sutcliffe (Sutcliffeet al 1989). 1989). Drill Drill core core sections sections show show that that the the highest highest grade grade mineralization WG immediately immediately adjacent adjacent to to the the mineralization occurs occurs in in the the WG contact with the EQ (Figure 4). contact with the EG (Figure 4). PGE PGE mineralization mineralization in in the the gabbroic gabbroic rocks rocks is is associated associated with with 1) 1) finely finely disseminated disseminated sulphide sulphide mineralization mineralization (1 (1to to 22 modal sulphide) in in altered altered pyroxenite pyroxenite sheets sheets along along the the modal %% sulphide) WG/EG WG/EG contact contact 2) 2) disseminated, disseminated, bleb-like bleb-like and and net-textured net-textured sulphide sulphide mineralization mineralization in in gabbronorite gabbronorite (1 (1 to to 44 modal modal %% sulphide) sulphide) and and 3) 3) coarse coarse interstitial interstitial sulphide sulphide in in pegmatitic peg-matitic gabbro. gabbro. In In addition addition to to mineral mineral assemblages assemblages noted noted in in Table Table 1, rare euhedral apatite is observed in mineralized 1, rare euhedral apatite is observed in mineralized gabbros gabbros in in the the Roby Roby Zone. Zone. AA detailed detailed study study of of drill drill core core from from the the Roby Roby Zone Zonee (Dunning Watkinson and Dunning -(Dunning 1979; 1979; Watkinson Dunning 1979; 1979; Cabri Cabri and and Laflamme Laflamme 1979) 1979) showed showed that that vysotskite vysotskite and and braggite braggite are are the the most most abundant abundant platinum platinum group group minerals minerals (PGM) (PGM) along along with with minor minor isomertieite, isomertieite, merenskyite, merenskyite, kotulskite, kotulskite, sperrylite sperrylite and and moncheite. moncheite. In In addition, addition, electrum electrum and and Pt—Fe Pt-Fe alloys alloys have have been been identified identified by by Sweeny Sweeny (1989). (1989). The The PGE PGE mineralization mineralization is is associated associated with with chalcopyrite, chalcopyrite, pyrrhotite, pyrrhotite, pentlandite pentlandite and and pyrite pyrite interpreted interpreted by by Watkinson Watkinson and and Dunning Dunning (1979) (1979) as as being being slightly slightly metamorphosed metamorphosed equivalents equivalents of of primary primary exsolution exsolution from from monosulphide nionosulphide solid solid solution. solution. Millerite Millerite and and violarite violarite - a 16 �are present in secondary assemblages assemblages (Watkinson (Watkinson and Dunning 1979). PGM in the Roby Zone Zone are most commonly found with postcumulus postcumulus hydrosilicates hydrosilicates near silicate—suiphide silicate-sulphide interfaces interfaces (Talkington and Watkinson 1984). (Talkington Watkinson 1984). In this association, association, the the PGM occur occur both within the the hydrosilicates hydrosilicates and at the the sulphide—silicate interface. sulphide-silicate interface. pGE's also occur in the ultramafic rocks with with sparsely PGE's disseminated disseminated to to net-textured chalcopyrite, pyrrhotite, and pentlandite pentlandite (ci (<1 modal modal %% sulphide). sulphide). This This type type of of mineralization mineralization is is most commonly commonly associated associated with websterite websterite and gabbronoritic gabbronoritic phases of the northern and southern southern ultramafic ultramafic centers. centers. Field and geochemical relations indicate that the EG and WG cumulates cumulates crystallized from a common magma and were subsequently subsequently emplaced as crystal mushes with the more fractionated fractionated and and hydrous hydrous EG EG emplaced emplaced first. first. Lower Lower concentrations concentrations of PGE, Au and S in the EG relative relative to WG suggests the magma prior to suggests that that suiphides sulphides were removed from the to the the crystallization crystallization of the EG cumulates cumulates or that the the parental magma was not saturated saturated in in sulphides sulphides at the time time of cumulate cumulate formation. have localized localized some some sulphide sulphide formation. Magma mixing may have mineralization mineralization along along the the EG/WG EG/WG interface. interface. However, However, because because the the phases phases are are interpreted interpreted to to have have been been emplaced emplaced as as mushes, mushes, there there was probably limited limited opportunity for for sulphides sulphides to to interact interact with with magma. magma. This would suggest suggest aa low low R—factor R-factor and and that this this process may not be the explanation explanation for the high grade grade mineralization. mineralization. Fe—rich Fe-rich pyroxene pyroxene cumulate cumulate sheets sheets intruded intruded into into the the EG EG and WG are are another another possible possible source source of of PGE PGE in in the the Roby Roby Zone. Zone. The close close spatial association of the sheets sheets and mineralization mineralization suggest suggest that that the the pyroxene pyroxene cumulates cumulates are are aa likely source of PGE. As previously noted, the altered likely source of PGE. As previously noted, the altered pyroxene pyroxene cumulate cumulate sheet sheet at at the the EG/WG EG/WG contact contact contains contains particularly particularly high-grade high-grade mineralization. mineralization. Limited Limited sampling sampling of of this this group of rocks rocks suggests suggests that, that, in general, they have higher higher PGE PGE contents contents than than other other samples samples of the ultramafic ultramafic suite. suite. Mixing of magmas which formed the pyroxene cumulates cumulates and the the gabbro gabbro cumulates cumulates may have played a role in causing causing sulphide sulphide saturation saturation in in the the pyroxene pyroxene cumulates. cumulates. The The association association of of PGM PGM with secondary secondary sulphides sulphides and and altered altered silicates silicates lead lead Watkinson and Talkington Talkington (1984) (1984) to to suggest suggest that that fluid fluid processes were active active in in mobilization mobilization and concentration concentration of of PGE PGE in in the the Roby Roby Zone. Zone. The The role role of of fluids fluids in PGE mineralized zones PGE mineralized zones in in the the Bushveld Bushveld and and Stillwater Stillwater Complexes Complexes is is indicated indicated by by the the occurrence occurrence of of pegmatoids, pegmatoids, volatile-rich phases and hortonolite replacement phases and hortonolite replacement pipes pipes (Todd (Todd et al 1982; 1982; Stumpfl Stumpfl and and Balihaus Ballhaus 1986; 1986; Schiffries Schiffries 1982; 1982; Stumpf and Rucklidge Rucklidge 1982). Stumpfl1 and 1982). Fluid-bearing Fluid-bearing phases phases and and fluid fluid inclusions in in both both complexes complexes suggest suggest fluids fluids that that may may be be rich rich inclusions in Cl (Boudreau (Boudreau et al 1986; 1986; Stumpfl Stumpfl and and Balihaus Ballhaus 1986). 1986). Several Several features features of of the the Roby Roby Zone Zone indicate indicate the the importance importance of of aa volatile volatile rich rich magma. magma. These These include: include: the the association association of of PGM PGM with postcumulus postcumulus hydrosilicates hydrosilicates near near 17 �silicate—sulphide silicate-sulphide interfaces; interfaces; the the association association of of PGM PGM with with pegmatitic pegmatitic phases phases and and the the mineralized breccia breccia zones zones cored cored by peginatitic gabbro which which appear appear to to have have been fluid channelpegmatitic gabbro channelways; ways; and and the the highly highly fractionated fractionated Pd/Ir. Pd/Ir. Cl-rich Cl-rich apatite apatite in in mineralized mineralized gabbro gabbro suggest suggest that that the the fluids fluids associated associated with the the mineralizing mineralizing process process were were Cl—rich. Cl-rich. Brugmann Brugmann et al a1 (1989) (1989) have have recently recently proposed proposed aa modification of this hypothesis and suggested modification of this hypothesis and suggested that that the the volatile volatile content content of of the the residual residual magma triggered triggered partial re— remelting melting of of the the gabbro gabbro cumulates cumulates in in a process referred referred to to as as "constitutional "constitutional zone zone refining". refiningn. Occurrences Occurrences of of PGE-bearing PGE-bearing sulphides sulphides in in the the ultramafic ultramafic sequence sequence are are hosted hosted mainly mainly by by websterite websterite at at the the top top of of cyclic cyclic units units and and by by peridotites peridotites at the the base of of overlying overlying units. units. These These occurrences occurrences have have not not been been studied studied in in detail detail but but may represent represent stratifonu stratiform mineralization mineralization related related to to the the interaction interaction of of fractionated fractionated magma magma with with aa new new magma magma pulse pulse in in the the ultramafic ultramafic chamber chamber (Sutcliffe (Sutcliffe and and Sweeny Sweeny 1986; 1986; Brugmann Brugmann and and Naldrett Naldrett 1987). 1987). The The presence presence of of this this mineralization, mineralization, however, however, emphasizes emphasizes that that ?GE's PGE1swere were concentrated concentrated at at several several stages stages in in the the fractionation fractionation of of the the LDIC LDIC magmas. magmas. TIB TIB GABBRO GABBRO Geology Geoloav The The Tib Tib Gabbro Gabbro (Figure (Figure5) 5) is a layered layered intrusion intrusion with with an an area area of of approximately approximately 25 25 km2 located located approximately approximately 15 15 km northwest of the Lac des Iles Complex. The intrusion was northwest of the Lac des Iles Complex. The intrusion was mapped mapped by by Kaye Kaye (1966) (1966) and and Smith Smith and and Sutcliffe Sutcliffe (1987). (1987). The The information summarized here is largely from Smith (in information summarized here is largely from Smith (in press). press). Petrological Petrological and and geochemical geochemical studies studies are are in in progress progress and and most most of of this this summary summary is is based based in in field field observations. observations. The The gabbro gabbro is is emplaced emplaced into into an an older older suite suite of of foliated foliated to to gneissic gneissic biotite biotite tonalite tonalite which outcrops outcrops around around the the eastern, eastern, northern northern and and aouthern aouthern margins margins of of the the intrusion. intrusion. AA younger suite of megacrystic granodiorite and younger suite of megacrystic granodiorite and granite granite intrudes intrudes the the Tib Tib Gabbro Gabbro and and older older gneissic gneissic tonalites. tonalites. The The Tib Tib Gabbro Gabbro is is characterized characterized by by well well preserved preserved primary primary igneous igneous mineralogy mineralogy and and moderately moderately well well developed developed layering. layering. Layer Layer attitudes attitudes indicate indicate that that the the intrusion intrusion is is funnel funnel shaped shaped and and has has been been tilted tilted to to the the northeast. northeast. The The southwest southwest part part of of the the gabbro gabbro therefore therefore represents represents the the base base of survey by Gupta of the the exposed exposed section. section. AA gravity gravity survey Gupta and and Sutcliffe Sutcliffe (in (in press) press) supports supports this this interpretation interpretation and and models models the the 16 16 mgal mgal gravity gravity high high associated associated with with the the intrusion intrusion as as aa tilted tilted basin-shaped basin-shaped body. body. The The intrusion intrusion is is divided divided into into four four zones zones by by Smith Smith and and Sutcliffe Sutcliffe (1987) (1987) which which from from the the southwest southwest to to northeast northeast are are the the Border, Border, Lower, Lower, Middle Middle and and Upper Upper Zones. Zones. The The 50 50 to to 150 150 mm thick thick Border Border Zone Zone is is defined defined on on aa basis basis of of the the abundance abundance of of coarse coarse grained grained to to pegmatoidal pegmatoidal gabbro gabbro which which occurs occurs around around the the northwestern, northwestern, western western and and southern southern margins margins of of the the intrusion. intrusion. The The Lower Lower and and Middle Middle zones zones probably probably represent represent distinct distinct magma magma pulses pulses which which crystallized crystallized from from the the base base upwards. upwards. These These 18 18 �I I I I I I I zones record the crystallization of evolving cumulus assemblages which results in a mappable igneous stratigraphy assemblages stratigraphy with pyroxene pyroxene rich rich cumulates cumulates near the the base and plagioclase— plagioclaseand magnetite-rich magnetite—rich cumulates cumulates near near the the top. top. The Upper Upper Zone Zone consists of consists of amphibole-rich amphibole-rich gabbro gabbro and and is is not not well well layered. layered. wide Lower Lower Zone Zone consists consists of of aa sequence sequence of The 1.5 1.5 kin km wide layered gabbronorite gabbronorite with layers orthopyroxenite and layers of orthopyroxenite melagabbronorite melagabbronorite (pyroxene (pyroxene cumulate) cumulate) near near the the base. base. Above the orthopyroxenite orthopyroxenite the lithologies lithologies become more leucocratic leucocratic anorthosite appears and anorthosite appears as as distinct distinct layers. layers. The The top top of of the the by magnetite-rich magnetite-rich gabbronorite with zone is marked by leucocratic layers. leucocratic layers. The 1.6 1.6 km wide Middle Zone Zone is is predominantly gabbronorite, however, leucocratic predominantly leucocratic units are more abundant Conformable pegmatite abundant than than in in the the Lower Lower Zone. Zone. Conformable pegmatite layers and discordant dikes are common in the upper part of magnetite— the zone. the zone. The top top of the zone is again marked by - magnetite. rich gabbronorite. gabbronorite; The Upper Upper Zone Zone is is characterized characterized by by hornblende—rich, hornblende-rich, massive to to weakly weakly layered layered gabbronorite qabbronorite with with cumulus cumulus apatite. apatite. The layers form a concentric pattern with a shallow shallow inward dip. dip. Leucocratic quartz—bearing quartz-bearing granulite granulite forms forms aa discontinuous septa between the Upper and Middle Zones Zones and the unit is interpreted to be metamorphosed tonalite tonalite but may alternatively be a alternatively a final final product product of of fractionation. fractionation. Layering in the Tib Gabbro is comparable to that developed in developed in the the Mulcahy Mulcahy Gabbro Gabbro (Morrison (Morrison et al 1986). 1986). Planar lamination of feldspars and pyroxene is found throughout the throughout the intrusion. intrusion. Modal layering layering defined by changing compositions compositions of cumulus minerals is best developed the upper upper part part of the the Lower Lower Zone and and occurs occurs in both both in the cyclic and intermittent intermittent layer layer sequences. sequences. Distinctive modal layers include: othopyroxenite othopyroxenite (orthopyroxene (orthopyroxene cumulate) cumulate); websterite (clinopyroxene orthopyroxene cumulate) websterite (clinopyroxene — orthopyroxene cumulate); magnetite—rich anorthosite (plagioclase (plagioclase cumulate) and magnetite-rich cumulate. The modal modal layers are usually tens of centimetres cumulate. in width width and persist for for tens tens of metres metres along along strike. strike. - - e 3 . p Mineralization Mineralization The The Tib Tib Gabbro Gabbro is is the the second second largest of the the mafic des lies Iles area area and and is an an exploratiion intrusions in the lac des target for Intermittent target for PGE PGE and and Cu—Ni Cu-Ni mineralization. mineralization. Intermittent exploration exploration on the intrusion since 1966 has outlined a Cu—Ni sulphide number of areas areas of disseminated Cu-Ni sulphide mineralization in the gabbro, some mineralization some of which contain associated PGE. associated PGE. To To date, the the most significant significant mineralization that has been reported is at the Kuhner Occurrence in the the Border Zone Zone along the south south margin of the intrusion. At this intrusion. this location, location, net textured textured sulphide sulphide mineralization is gabbronorite and mineralization is present in coarse coarse grained gabbronori assay values up to 190 ppb Pt, 390 ppb Pd, 120 ppb Au, 1140 ppm Ni Mi and 710 710 ppm Cu Cu are are reported reported by by Smith Smith (in (in press) press) 19 �GRANITOIDS GRANITOIDS AND AND RELATED RELATED ROCKS ROCKS Tonalite Tonalite Gneissic Gneissic to to strongly strongly foliated biotite tonalite tonalite gneiss gneiss is is the the oldest intrusive intrusive phase ~ h a S ein in the the Lac des lies lies area area and and is is the the host rock rock into into which most of the the younger younger plutons are are emplaced. emplaced. Discordant Discordant intrusive intrusive relations relations between between the the mafic— maficultramafic ultramafic intrusions intrusions and tonalitic tonalitic gneiss gneiss are are locally locally developed developed on on the the margins margins of of intrusions intrusions such such as as the the Tib Tib Gabbro, Gabbro, where where gabbro gabbro apophyses apophyses cross-cut the the fabric fabric of of the the gneiss gneiss and and tonalitic tonalitic gneiss gneiss enclaves enclaves occur occur in in the the gabbro. gabbro. Two Two late late granitoid granitoid plutons plutons occupy occupy the the center center of of the the circular circular structure structure defined defined by by the the mafic mafic intrusions. intrusions. These These plutons plutons also also discordantly discordantly intrude intrude the the tonalitic tonalitic gneiss gneiss and contain contain tonalitic tonalitic gneiss gneiss enclaves. enclaves. The The plutons plutons include include aa hornblende—bearing hornblende-bearing tonalite tonalite with an area of 150 150 km2 and aa younger, younger, foliated foliated to to massive massive biotite biotite tonalite tonalite to to microcline microcline zuegacrystic granodiorite pluton pluton which locally megacrystic granodiorite locally contains contains enclaves enclaves of of the the hornblende-bearing hornblende-bearing tonalite. tonalite. The The hornblende hornblende tonalite tonalite is is intruded intruded by by numerous numerous mafic to to intermediate intermediate dikes dikes and and exhibits exhibits textures textures indicating indicating the the coexistence coexistence of of mafic mafic and and felsic felsic rnagmas magmas (Sutcliffe (Sutcliffe1989). 1989). These These textures textures are are the the focus focus of of the the field field trip trip stops stops in in the the granitoid granitoid rocks. rocks. The The association association of of early early tonalitic tonalitic gneisses gneisses and and later later massive terranes of of the the massive plutons plutons is is common common in in granitoid granitoid terranes western western Superior Superior Province Province (Schwerdtner (Schwerdtner et et al. al. 1979). 1979). Modal Modal analyses analyses of of representative representative tonalites tonalites and and other other samples samples are are shown shown in in figure figure 6. 6. The The tonalite tonalite has has aa medium— mediumto to coarse—grained, coarse-grained, hypidiomorphic hypidiomorphic texture texture and is is massive massive to to weakly weakly foliated. foliated. The The presence presence of of coarse coarse (1 (1 to to 22 cm), cm), blocky blocky to to prismatic prismatic hornblende hornblende is is aa conspicuous conspicuous feature feature of of the the pluton. pluton. The The major major mineral mineral phases phases are: are: 22 to to 44 mm mm subhedral, subhedral, tabular plagioclase of composition tabular plagioclase of composition An28—34 An28-34 (40—58%); (40-58%); anhedral, ; 0.5 anhedral, weakly weakly strained strainedquartz quartz(29—38%) (29-38%); 0.5 to to 22 mm brown—green brown-green pleochroic pleochroic biotite biotite (7—16%) (7-16%) and and subhedral subhedral to to prismatic, prismatic, 22 mm mm to to 22 cm, cm, green green pleochroic pleochroic hornblende hornblende (1(115%). 15%). Accessory Accessory phases phases are are sphene, sphene, apatite apatite and and zircon. zircon. Plagioclase Plagioclase locally locally displays displays weak weak to to moderate moderate oscillatory oscillatory zoning zoning and and minor minor alteration alteration to to sericite sericite and and epidote. epidote. Although Although hornblende hornblende is is locally locally subordinate subordinate to to biotite, biotite, this this lithological litholoqical unit unit is is referred referred to to as as hornblende hornblende tonalite tonalite throughout throughout the the paper paper to to distinguish distinguish it it from from the the younger younger biotite biotite tonalite tonalite in in which which hornblende hornblende is is absent. absent. Mela-tonalite containing containing up up to to 60% 60% hornblende hornblende occurs occurs as as Mela-tonalite irregular irregular patches patches and and intrusive intrusive dike-like dike-like bodies bodies up up to to several several meters meters in in extent extent which which grade grade into into normal normal tonalite. tonalite. Mela-tonaiite Mela-tonalite is is the the major major constituent constituent in in 22 to to 3% 3% of of outcrops outcrops in in the the hornblende hornblende tonalite tonalite pluton. pluton. Hornblende Hornblende in in mela—tonalite mela-tonalite is is typically typically coarse, coarse, occurring occurring as as grains grains up up to to 22 cm cm of of euhedral, euhedral, prismatic prismatic to to skeletal skeletal habit. habit. Textural Textural gradations between between skeletal skeletal hornblende hornblende and and coarse coarse blocky blocky gradations hornblende hornblende are are present. present. The The mela—tonalites mela-tonalites have have complex complex a 20 �internal characterized iharacterized by comb—layering comb-layering and and iternal structures struc colloform colloform structures structures of of mafic mafic material material in in felsic felsic host. host. Skeletal hornblende is best developed in mela-tonalite mela-tonalite adjacent to adjacent to mafic-felsic mafic-felsic interfaces. interfaces. Euhedral skeletal skeletal hornblende grains also occur as wispy schlieren in hornblende tonalite tonalite and in hornblendite units of mafic intrusions. intrusions. The skeletal skeletal grains have hollow hollow cores cores plagioclase. These containing biotite or biotite + + plagioclase. These between amphibole and assemblages probably reflect reaction between trapped liquid. trapped liquid. Large rounded hornblende hornblende aggregates aggregates as as large large as as 22 cm cm in in proto—orbicular texture according diameter locally display a proto-orbicular to the classification of Leveson (1966). (1966). These are present tonalite adjacent to mela-tonalite and mafic dikes. The in tonalite The pale—green pleochroic composite grains have central areas of pale-green hornblende intergrown intergrown with quartz and feldspar producing a sieve texture. sieve texture. Their rims are composed composed of of dark—green dark-green pleochroic grains grains of interlocking interlocking prismatic prismatic hornblende. hornblende. A breccia pipe, approximately 300 m in diameter, is emplaced into the western end of the hornblende-bearing hornblende—bearing tonalite pluton. tonalite pluton. The pipe consists consists of of sub—angular sub-angular hornblende—tonalite fragments hornblende-tonalite fragments and minor hornblendite fragments set in a matrix of fine—grained, fine-grained, comminuted comminuted and and silicified silicified tonalite. tonalite. Tonalite fragments fragments within the the breccia breccia are of the same composition composition and texture as the host rock but contain 2 to 3 cm thick silicified, sericitized and epidotized epidotized rinds. rinds. Mafic dikes dikes and hybrid hvbrid textures textures A wide range of textures indicative indicative of contemporaneous mafic and felsic felsic magmatism is developed associated with the emplacement emplacement of mafic to intermediate dikes in hornblende tonalite. tonalite. The dikes range from parallel-sided intrusions, intrusions, 11 to 2 m wide, with sharp contacts which cross cut foliation foliation disaggregated linear inclusion swarms in in the tonalite, to disaggregated which the the mafic mafic magma magma appears appears to to have have lost lost internal internal contiguity. contiguity. These structures structures are are similar similar to to textures textures indicative of contemporaneous indicative contemporaneous mafic—felsic mafic-felsic magmatism magmatism and and mixing reported reported by Blake Blake (1981), (1981), Marshall Marshall and and Sparks Sparks (1984), (1984). Furman and Spera (1985) (1985) and Hyndman and and Foster Foster (1988). (1988). Mafic dikes are are observed in in approximately 15% 15% of the the outcrops of the the hornblende hornblende tonalite tonalite pluton. The dikes are generally fine—grained, fine-grained, lack chilled margins and are typically back-veined by tonalite which typically back-veined forms wispy nets separating separating rounded rounded centimeter— centimeter- to to decimeter-sized mafic mafic globules. globules. This texture is described as net-veining by Marshall and and Sparks Sparks (1984). (1984). With increased veining the net-textured dikes grade into disaggregated disaggregated dikes dikes in in which which the the mafic mafic to to intermediate intermediate rock forms rounded and elongate elongate bodies bodies which which resemble resemble pillows In pillows of extrusive extrusive rocks rocks in in the the host host tonalite. tonalite. In contrast to other descriptions of similar structures in Tertiary Tertiary intrusives intrusives (Vogel (Vogel 1982; 1982; Brown Brown and and Becker Becker 1986; 1986; 21 �Marshall and Marshall and sparks Sparks 1984), 1984), chilled chilled rinds rinds on on "pillows" npillowsm at at Lac Lac des Iles are generally absent. des Iles are generally absent. Mineralogically the moderately fresh Mineralogically the dikes dikes consist consist of of moderately fresh 0.5 mm laths of plagioclase (andesine An4o_46) and 1 mm 0.5 mm laths of plagioclase (andesine An40-46) and 1 mm grains of prismatic hornblende to pale green fibrous grains of prismatic hornblende to pale green fibrous amphibole, and amphibole, and minor minor biotite, biotite, quartz, quartz, apatite apatite and and opaques. opaques. The mafic to intermediate intermediate dikes locally locally display discontinuous hornblende-rich hornblende—rich reaction reaction rims rims adjacent adjacent to to host host discontinuous In addition, addition, mela-tonalite mela-tonalite to tonalite. tonalite. In to hornblendite hornblendite phases phases are generally are generally associated associated with with zones zones of of dike dike emplacement. emplacement. Magma Mixinq Mixing Maama Field evidence maamas has has evidence suggests suaaests that that mixing mixina between between magmas - --taken place. Geochemical data does not readily constrain the taken place. ~eochemiciidata does not readily constrain the mixing process process due due to of fractionation mixing to complications complications of fractionation of of mafic end mafic end members members and and the the presence presence of of multiple multiple components. components. The most most likely magma chamber the The likely magma chamber configuration configuration during during the emplacment of the late tectonic plutons plutons is that that of a zoned chamber with mafic magma magma underplating underplating felsic magma magma (Figure (Figure This schematic configuration has been supported by 7). This schematic configuration has been supported by 7). gravity studies studies (Gupta (Gupta and and Sutcliffe Sutcliffe in in press). press). An important aspect of the interaction interaction between the mafic and mafic and tonalitic tonalitic magmas magmas at at Lac Lac des des Iles lies is is the the development of hornblende—rich cumulus phases. The skeletal skeletal development hornblende-rich cumulus phases. The texture of these phases suggests they may have formed in a texture may supercooled magma during mixing. supercooled magma during mixing. Field relations and geochemical considerations suggest that the open system magmatic processes at Lac des Iles resulted in a continuum of disequilibrium textures, ranging tonalite magmas to from hybrid tonalite to late late net—veined net-veined mafic mafic and and intermediate dikes. These textures intermediate textures reflect reflect emplacement emplacement and and mixing of basic magma with varying degrees of fractionation fractionation into felsic felsic magma throughout throughout a large large interval interval of of the the cooling cooling history of the felsic magma. Furman and Spera (1985) felsic magma. (1985) have mixing associated with with injection suggested that features of mixing pluton represent a continuum of mafic magma into a Sierran pluton of mixing states states which can can largely largely be be related related to to host host When the host magma has low crystallinity crystallinity. crystallinity. (<30%) convective convective velocities velocities are high and mixing features (<30%) features occur on a a scale scale of of centimeters centimeters or or less. less. At approximately 30—70% 30-70% host crystallinity, crystallinity, mesoscopic mesoscopic schlieren, schlieren, mafic mafic inclusions inclusions and inclusion inclusion swarms swarms are are preserved. preserved. At higher higher crystallinity, outcrop scale scale textures textures such such as as dike dike swarms swarms crystallinity, outcrop and large large inclusion inclusion swarms swarms are are evident. evident. These stages stages correspond correspond to to the the observed observed textures textures at at Lac Lac des des Iles. Iles. Net— Netveined dikes and other conspicuous conspicuous mixing features features at Lac des Iles Iles probably formed at the latest stages of mixing when the efficiency of mixing is reduced but outcrop evidence for the the coexistence coexistence of of two two magmas magmas is is enhanced. enhanced. Breecia Breecia zones zones within the the tonalite tonalite containing fragments of tonalite and mafic mafic rocks rocks with thick thick alteration selvedges selvedges provide evidence explosive degassing of explosive degassing of of the the chamber. chamber. In an evaluation of the situation situation of of aa zoned zoned mafic— maficfelsic chamber, Rice (1985) has shown that mixing (1985) has shown that mixing of of aa 22 �convecting, convecting, density density stratified stratified column column is is possible possible given given large dimensions and a reasonable thermal large dimensions and a reasonable thermal gradient. gradient. An important important aspect aspect of of aa zoned zoned chamber chamber is is the the probability probability of of roll roll over over and and explosive explosive degassing degassing if if the the magmas magmas contain contain volatiles volatiles (Rice (Rice 1985). 1985). Evidence Evidence for for degassing, mixing and and violent emplacement violent emplacement of of mixed mixed chambers chambers has has also also been been documented documented by by Marshall Marshall and and Sparks Sparks (1984). (1984). Density instability of mafic magmas at the instability of magmas the base of of a chamber chamber may be established established by by vesiculation vesiculation of of mafic mafic magma magma and and can can lead lead to to rapid rapid transfer transfer of of mafic mafic magma magma across across aa formerly formerly stable stable mafic/felsic mafic/felsic magma magma interface interface (Eichelberger (Eichelberger 1980; 1980; Rice Rice 1985). 1985). Several Several of of the the associations associations reported reported in in this this study study are are common common to to other other granitoid granitoid terranes terranes in in the the Superior Superior Province Province and and suggest suggest the the model model presented presented here here may may have have wide wide applicability to late granitoids, particularly applicability to late granitoids, particularly those those containing Xenoliths ranging ranging in in composition composition containing hornblende. hornblende. Xenoliths from from hornblendite hornblendite to to microdiorite microdiorite are are aa particularly particularly widespread widespread feature feature in in late late Archean Archean plutons plutons (eg. (eg. Davis Davis and and Edwards, Edwards, 1985). 1985). These These inclusions inclusions have have conventionally conventionally been been interpreted interpreted as as pre—existing pre-existing mafic mafic rocks. rocks. However, However, as as this this and other studies (eg. Didier and other studies (eg. Didier 1987) 1987) have have suggested suggested the the inclusions inclusions may may be be chilled chilled mantle—derived mantle-derived magma. magma. Other Other features features of of contemporaneous contemporaneous mafic mafic and and felsic felsic magmatism magmatism reported reported elsewhere elsewhere include include the the presence presence of of net—veined net-veined dike dike rocks rocks in tonalitic to to granodioritic granodioritic plutons plutons (Davis (Davis and and in tonalitic Edwards Edwards 1985). 1985). Recent Recent precise precise U-Pb U-Pb zircon zircon geochronology geochronology also Archean also indicates indicates aa close close temporal temporal association association of of late late Archean gabbro plutons with granitoid rocks in other parts gabbro plutons with granitoid rocks in other parts of of the the Wabigoon Wabigoon Subprovince Subprovince (Morrison (Morrisonet et al. al. 1985). 1985). These These features features suggest suggest that that mantle—derived mantle-derived mafic mafic magmas magmas are are an an important important aspect asnect of of late late Archean Archean granitoid m-anitoid magmatism. magmatism. 23 �FIELD FIELD TRIP TRIP GUIDE GUIDE The The field field trip trip is is designed aesigned to to be be completed completed in in one One day, aay, including including travel travel from from and and return return to to Thunder Thunder Bay. Bay. The The trip trip includes stops on on includes 11 stop stop on on gneissic gneissic tonalite tonalite host host rock, rock, 33 stops the the Tib Tib Gabbro, Gabbro, 44 stops stops to to examine examine the the granitoids, granitoids, and and one one stop stop at at the the PGE PGE and and Cu-Ni Cu-Ni mineralization mineralization at at the the Roby Roby Zone Zone of of Madelaine Mines Limited. Madelaine Mines Limited. Due to to logging logging and mineral exploration exploration activity activity in in the the field trip area, the road conditions are continually field trip area, the road conditions are continually changing. changing. If If you you are are doing doing this this trip trip on on your your own own you you will will need logging roads roads in in the the area. area. need an an up—to—date up-to-date map map of of logging Proceed Proceed west west from from Thunder Thunder Bay Bay along along highway highway 11/17. 11/17. At At Shabaqua, turn north on highway 17 towards Dryden. Shabaqua, turn north on highway 17 towards Dryden. Turn north on the (also signposted signposted to to the Dog River Road (also Great Lakes Pulp and Paper company Camp 234) Great Lakes Pulp Paper Company 234) which is is approximately approximately 10 10 km km west west of of the the townsite townsite of of Raith Raith and and 11 km west of the the Central Time Time Zone/Eastern Time Time Zone Zone marker. marker. Begin Begin recording recording mileage mileage at at the the start start of of the the Dog River as loaded loaded trucks trucks are are River Road. Road. Drive carefully as using Proceed north on on the the Dog Dog River River Road Road using this this road! road! Proceed for at which which point point there there is a major junction junction for 21 21 1cm, km, at with with aa branch branch road road from from the the east. east. The The first first outcrop outcrop is is the the large large exposure on the southeast side side of branch road approximately approximately 50 50 metres metres from from the the junction. junction. - Stop st00 11 - Gneissic Gneissic tonalite tonalite This This outcrop outcro~has not been studied studied in detail but is is included as a stop to illustrate as stop to illustrate the the host host lithology lithology into into which and granitoid granitoid intrusions intrusions are which the the mafic—ultratnafic mafic-ultramafic and are emplaced. is typical of other other areas areas of gneissic gneissic tonalite tonalite emplaced. As is in northwestern northwestern Ontario, Ontario, the the outcrop outcrop is is complex complex and and several several granitoid granitoid phases phases are are present. present. continue north on the Dog River Road, pass through through camp Continue 234, at 40 km (distance from highway 17) turn 40 (distance from highway 17) turn northeast northeast (right) (right) at the the major major fork. fork. Proceed Proceed northeast northeast for for 6.2 6.2 km and then then turn turn east east along along branch branch road road to to Tib Tib Lake. Lake. Proceed east along road to Tib Lake for 2.7 2.7 km at which point there there is is aa small small track track that that leads leads to to the the north. north. Stop Stop 22 is is on the the west side side of the track track approximately 100 metres metres north north of of the the Tib Tib lake lake Road. Road. - Stop Tib Gabbro Gabbro Border Border Zone Zone Stov 22 — Tib The Border Zone Zone of the the Tib Gabbro Gabbro is is defined based on the the abundant abundant pegmatitic gabbro gabbro that occurs occurs around the the base of the the intrusion. intrusion. This well-exposed outcrop outcrop displays displays the the typical typical textural textural variation variation in in this this zone. zone. Proceeding Proceeding upward from the lowermost exposed part of the the outcrop outcrop textures textures range from coarse—grained coarse-grained and pegmatitic gabbro to medium grained gabbro and gabbronorite with conformable pegmatitic layers. layers. 24 �, Return to to Tib Tib Lake Lake Road Road and and proceed proceed Return 1.2 km. Stop 3 is on the north side 1.2 tan. Stop 3 is on the north side in the bush approximately 10 metres in the bush approximately 10 metres east for another east for another of the road and is of the road and is from the road. from the road. Stop 3 Tib Gabbro Gabbro lavering 1averjg stov 3 — - Tib Layered gabbronorite gabbronorite in in the the upper upper part part of of the the Lower Lower Layered Zone of Zone of the the Tib Tib Gabbro. Gabbro. Well developed intermittent intermittent layering locally locally shows shows modal modal grading grading with with pyroxene-rich pyroxene-rich layering bases and plagioclase—rich tops. tJralitic alteration (green bases and plagioclase-rich tops. Uralitic alteration coloured) occurs along fractures which locally cross cut the fractures primary layering. primary layering. Return Return to to Tib Tib lake lake Road Road and and proceed proceed east east for for another another 0.3 0.3 km. km. Stop 4 is on the south side of the Tib Lake Road, approximately 20 20 metres from from the the road, and is is on the east side of a culvert. the east side of a culvert. - Stop Tib Gabbro Lower Zone Stov 4 4 - Tib Zone This outcrop displays wispy layered gabbronorite near wispy layers consist of the top top of the the Lower Lower Zone. Zone. The wispy plagioclase or pyroxene rich bands in gabbronorite. Thin Thin pyroxenite dikelets of various orientations orientations cut the layering layering and contain contain inclusions inclusions of of host host gabbronorite. gabbronorite. The dikelets are interpretted to be injections injections of cumulate material. AA small hornblende—feldspar Green hornblende-feldspar dikelet dikelet is is also also present. present. Green uralitic alteration alteration of pyroxenes is associated with fractures and is fractures is a late late feature. feature. Return to the Tib lake Road and continue east for for another 3.2 3.2 km, km, past the outlet from Tib Lake, to to a road which runs Turn runs down down the the east east side side of of Tib Tib Lake. Lake. Turn south along this road and proceed for 11 km to to the the junction with another another major logging road which is is referred Take this referred to to here here as as the the "Lac "Lac des des Iles Iles Road". Roadw. Take road to the southwest southwest (in (in the direction of the Dog River Road) for for 6.5 6.5 km, until the junction with the the Take the the Roenicke road Roenicke Lake Lake Road is is reached. reached. Take north for for 1.8 1.8 km and turn west along an unnamed bush road. Proceed along this road, taking the left fork road. after 2.1 km and reaching the outcrop for for stop stop 55 after 5.0 km. 5.0 km. Note: Note: The bush road into this stop is becoming overgrown overgrown and will probably be difficult to to recognize recognize if you are following following this this after after the the spring spring of of 1990. 1990. - Stop Stov 55 - Tonalite Tonalite breccia This distinctive distinctive breccia zone with dimensions of approximately approximately 100 100 by 300 metres cross—cuts cross-cuts the the hornblende hornblende tonalite tonalite east east of of the the Dog Dog River. River. The breccia consists of subrounded subrounded fragments fragments of tonalite with 2 to 33 cm thick thick sericite—epidote-silicif led alteration alteration rinds. The matrix sericite-epidote-silicified consists of altered, fine grained and locally comminuted comminuted tonalite. Rounded irregular mafic clots up to 0.5 0.5 metres long are locally pr<="=on+ present interstitial to +he the tonalite interstitipi <-A 25 . �fragments. Several quartz—feldspar porphyry dikes intrude the breccia. The The breccia breccia is is interpreted interpreted to to be be the the product product of of an an explosive degassing of a magma chamber. explosive degassing of a magma chamber. The The process process is is thought thought to to provide provide further further evidence evidence for for underplating underplating of of granitic granitic magma magma by by mafic mafic magma. magma. Explosive Explosive devolatilization devolatilization is an an expected expected consequence consequence of of the the cooling cooling of of such such aa system system if the the mafic mafic magma magma contains contains volatiles volatiles (Rice (Rice1985). 1985). Return Return to to Roenicke Roenicke Road Road and and then then proceed proceed south south to to the the "Lac "Lac des des Iles lies Road". Roadw. Turn Turn southwest southwest along along the the "Lac "Lac des des Iles Iles Road" RoadM (toward (toward Dog Dog River River Road) Road) and and proceed proceed for for 6.5 6. km km to to the the Garden Garden Road. Road. Turn Turn east east on on the the Garden Garden Road Road and proceed for 1.8 km. Stop 6 is an outcrop and proceed for 1.8 km. Stop 6 ro on the south south side side of of the the road. road. - Stop Stop 66 — Net-veined Net-veined dikes dikes Mafic Mafic dikes dikes are are abundant abundant in in this this area area of of the the tonalite tonalite and and range range from from intrusions intrusions with with sharp sharp contacts contacts to to dikes dikes which which are are extensively extensively veined veined by by tonalite, tonalite, such such as as the the dike dike in in this this outcrop. outcrop. The The back back veining veining texture texture is is known known as as net—veined net-veined since since the the tonalite tonalite forms forms aa wispy wispy net net which which surrounds surrounds rounded rounded centimetre— centimetre- to to decimetre—sized decimetre-sized mafic mafic globules. globules. The The structure indicative of of emplacement emplacement of of the the mafic mafic magma magma structure is is indicative prior consolidationof of the the felsic felsichost. host. prior to to the the consolidation Proceed Proceed for for another another 2.2 2.2 km km east east on on the the Garden Garden Road. Road. Stop 7 is a group of outcrops on either on either side side of of the the road. Stop 7 — Mixing textures In In this this series series of of outcrops, outcrops, mixing mixing of of mafic mafic and and tonalitic tonaliticmaginas magmas has resulted resulted in in aa variety variety of of igneous igneous textures. textures. Net-veined Net-veined and and disaggregated disaggregated mafic mafic dike dike material material is is present present in in the the lower lower part part of of the the outcrop. outcrop. The The disaggregated disaggregated mafic mafic material material could could be be readily readily confused confused with with rounded mafic inclusions. Adjacent to the net rounded mafic inclusions. Adjacent to the net veined veined dike, dike, the the foliation foliation of of the the tonalite tonalite is is destroyed destroyed by by remobilization remobilization of of the the felsic felsicmaterial. material. At At the the top top of of the the outcrop, outcrop, the the hornblende—rich hornblende-rich mela-tonalite mela-tonalite is is interpreted interpreted to to be be aa hybrid hybrid composition composition resulting resulting from from more more complete complete interaction interaction of of the the mafic mafic and and felsic felsicmagmas. magmas. Abundant Abundant skeletal skeletal textures textures in in this this rock rock may may result result from from supercooling supercooling due due to to magma magma mixing. mixing. Turn Turn around around and and proceed proceed west west for for0.7 0.7 km. km. Stop Stop 88 is is an an outcrop on the north side of the road. outcrop on the north side of the road. - - Stop Stop B8 - Hornblendite Hornblendite Hornblendite occurs as outcrop scale pods within the tonalite and are gradational with the mela—tonalite. The hornblendite and mela—tonalite have complex internal structures such as comb—layering and colloform structures. Comb—layering is defined by the alignment of coarse acicular to skeletal hornblende which is oriented perpendicular to 26 �layering. These rocks rocks have have geochemical geochemical characteristics characteristics ering. These which ch suggest suggest that that they they are are cumulates cumulates derived derived from from the the mafic mat dike suite. hornblendites also resemble a suite of suite. The hornblendites rocks which are described in some ks known as as "appinites" I1appinitess1 some Phanerozoic shoshonitic plutonic nerozoic shoshonitic plutonic suites. suites. Return to the "Lac des Ties Road" and turn back to th the Iles Roadn northeast towards Lac des lies. Proceed for 11 km to 11 t northeast towards Lac des Iles. the road the right which provides provides access access to to the the the road on on the right which Nadelaine towards Madelaine Mines Mines property. property. Turn east (right) (right) towards the Madelaine Mines Property, taking a left fork afte after 3.2 At the 3.2 km and another another left left fork fork after after 6.1 6.1 km. km. At Nadelaine Madelaine Mines Mines Property Property there there is is a gate gate and we will be b met by staff from the company. met by staff from the company. Stop 9 — PGE mineralization and geology in the vicinity of the Roby Zone — Madelaine Mines Limited Note: te: Due Due to to the the ongoing ongoing exploration exploration and and development development work work on o thee Roby Zone, which includes extensive stripping and Roby Zone, which includes extensive stripping and blasting, asting, it it is is not not possible possible to to plan plan the the precise precise features features that at can can be examined at this this location prior to arrival at the the site. site. Naps Maps of of the the geology geology of of the the gabbroic gabbroic units units in in the the vicinity of the Roby Zone (Figure 8) show the complex vicinity of the Roby Zone (Figure 8) show the complex relations relations between between intrusive intrusive units. units. Figure Figure 3 shows shows that that the the Roby Roby Zone Zone occurs occurs along along the the contact contact between between uniform EC EG and and the the more more complex complex WG. WG. Sheets and minor discordant dikes of pyroxene The pyroxene cumulate cumulate intrude intrude the the EG EG and and the the EG/WG EG/WG contact. contact. Th sheets websterite in sheets and dikes dikes which are gabbronorite gabbronorite to websterite composition, contain clinopyroxene contain cumulus cumulus orthopyroxene orthopyroxene + + clinopyroxene and intercumulus plagioclase and vary from altered nd intercumulus from altered to to fresh, fresh, even ven where where hosted hosted by by altered altered EG. EG. The highly uralitized pyroxenite oxenite is is termed termed amphibolite amphibolite in in drill drill logs. logs. The altered altered pyroxenite oxenite sheet sheet is is approximately approximately 55 to to 10 10 m m thick thick and and intrudes gabbronorite of rudes the EG but appears appears to grade into gabbronorite the WG and and is is approximately approximately conformable conformable with the the EG/WG contact. Figure Figure 88 is is aa detailed detailed outcrop outcrop map map from from the the "C—Zone". "C-ZO~~~~. This his zone zone is is within within the the WG WG at at the the southern southern end end of of the the Roby Roby Zonee and and illustrates illustrates the the complexity complexity of of the the WG WG unit. unit. The The outcrop crop is is predominantly fresh fresh to to moderately altered altered gabbronorite ronorite of of the the WG WG with with several several units units of of altered altered leucogabbro leucogabbro which form form inclusions inclusions and layers layers within within the the gabbronorite. surfaces gabbronorite. Some of the inclusions inclusions have cuspate surfaces and gradational gradational contacts contacts suggesting suggesting that they were not solid solid at at the the time time of of incorporation. incorporation. Also present within the the gabbronorite abbronorite are are inclusions inclusions of of pegmatitic pegmatitic gabbro, gabbro, altered altered pyroxenite, yroxenite, and and fine—grained, fine-grained, recrystallized, recrystallized, clinopyroxene clinopyroxene amphibolite. The gabbronorite gabbronorite and and leucogabbro leucogabbro are are amphibolite. The discordantly discordantly intruded intruded and and disrupted disrupted by by mineralized mineralized gabbro gabbro pegmatite to 44 mm wide wide mineralized mineralized intrusion intrusion egmatite dikes dikes and and aa 11 to breccia. reccia. The The breccia breccia is is defined defined by an an abundance abundance of of gabbroic gabbroic 27 �inclusions and contains a core of gabbro pegmatite. (Note: Unfortunately this outcrop is now partially destroyed by blasting.) Textures in the WG, such as those shown in Figure 8, suggest that some type of incomplete mixing or contamination of the WG by the EG took place. The presence of rounded inclusions, particularly of EG in WG and complex interfingering of the two gabbro types on a decimeter scale suggests that the EG was not completely solidified when the WG was intruded. Contacts between the two gabbro phases are commonly cuspate, net—veined and disaggregated. These textures are similar to those described in mixing zones between mafic and felsic magmas by Marshall and Sparks (1984) and would be reflected in the chemistry of the rocks only by more detailed sampling than that done in this study. The limited development of modal layering, the presence of cumulate textured dikes of WG intruding EG and the abundance of inclusion—rich outcrops suggests that the cumulates did not form in—situ but were emplaced as crystal mushes. This situation situation contrasts contrasts with with layered layered intrusions intrusions that that crystallized cumulate— crystallized by upward and inward growth of a cumulate liquid Irvineet al 1983). 1983). id interface interface (eg. (eg.Irvine End of trip. Return route to Thunder Bay will be by the recently opened access route to Lac des Iles from highway highway 527. 527. This is is a shorter shorter trip trip than than returning returning via the the Dog Dog River River road. road. Acknowledqments I would like to thank J.M. Sweeny and A.R. Smith for capable assistance mapping the Lac des lies area. J.P. Sheridan is thanked for access to map and sample the Lac des Iles property of Madelaine Mines Limited. D.W. Davis is thanked for permission to use unpublished lished geochonological geochonologic results. K. Gil drafted the figures. s. Published Published with with permission of the Director, Ontario Geological Survey. 28 �REFERENCES REFERENCES Blake, Blake, D.H. D.H. 1981. 1981. Intrusive Intrusive felsic-mafic felsic-mafic net—veined net-veined complexes complexes in in north north Queensland. Queensland. BMR Journal Journal of of Australian and Geophysics, Geophysics, v. v. 6, 6, pp. 95-99. 95-99. Australian Geology Geology and Boudreau, Boudreau, A.E., A.E., Mathez, Mathez, E.A., E.A., and and McCallum, McCallum, 1.5. I.S. 1986. 1986. Halogen Halogen geochemistry geochemistry of of the the Stillwater Stillwater and and Bushveld Bushveld Complexes: Evidence for the transport of Complexes: Evidence for the transport of the the Platinum— Platinum group group elements elements by by Cl-rich Cl-rich fluids. fluids. Journal Journal of of Petrology, Petro v.27, v.27, pp. pp. 967—986. 967-986. Brown, Brown, P.E. P.E. and and Becker, Becker, S.M. S.M. 1986. 1986. 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Stockwell, Stockwell, C.H., C.H., McGlynn, McGlynn, J.C., J.C., Emslie, Emslie, R.F., R.F., Sanford, Sanford, B.V., B.V., Norris, A.W., A.W., Donaldson, J.A., J.A., Fahrig, W.F., W.F., and Morris, Geology ofV the Currie, K.L. Currie. K.L. 1972. 1972. G ~O~OU the Canadian Canadian Shield, Shield. in in Douglas, R.J.W. R.J.w. (editor), (editor), Geology and and Economic Economic Minerals Minerals of Canada. Geological Survey of Canada, Economic Geology Report Geology Report No. No. 1, 1, 838 838 p. p. Streckeisen, A. 1976. 1976. To To each each plutonic plutonic rock rock its its proper proper name. name. Streckeisen, A. Earth-science Earth-Science Reviews, Reviews, v. 12, 12, pp. pp. 1-33. 1-33. Stumpf 1, E.F., E.F., and and Ballhaus, Balihaus, C.G. e.G. 1986. 1986. Stratiform Stratiform platinum platinum Stumpfl, deposits : New data and concepts. Fortschritte der deposits Mineralogie, v. 64, Mineralogie, 64, pp. pp. 205—214. 205-214. E.F., and Rucklidge, J.C. J.C. 1982. 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The The geochemistry, geochemistry, origin origin and and economic economic potential potential of of platinum platinum group group element element bearing bearing rocks rocks of of the the Lac Lac des des lies lies Complex, Complex, northwestern northwestern Ontario. In Geoscience Research Grant Ontario. U Geoscience Research Grant Program, Program, Summary Summary of of Research, Research, 1986-1987. 1986-1987. Ontario Ontario Geological Geological Survey Survey Miscellaneous Miscellaneous Paper Paper 136, 136, pp. pp. 140—152. 140-152. Sweeny, J.M. 1989. The geochemistry Sweeny, J.M. 1989. The geochemistry and and origin origin of of the the Roby Roby Zone, Zone, Lac Lac des des Iles lies Complex. Complex. MSc MSc thesis, thesis, The The University University of of Western Western Ontario, Ontario, London, London, Ontario. Ontario. Talkington, Talkington, R.W., R.W., and and Watkinson, Watkinson, D.H. D.H. 1984. 1984. Trends Trends in in the the Distribution Distribution of of the the Precious Precious Metals Metals in in the the Lac Lac des des Iles lies Complex, Complex, Northwestern Northwestern Ontario. Ontario. Canadian Canadian Mineralogist, Mineralogist, v. v. 22, 22, pp. pp. 125—136. 125-136. Taylor, H.P. Taylor, H.P. 1967. 1967. The The zoned zoned ultramafic ultramafic intrusions intrusions of of southeastern Alaska. Ultramafic and southeastern Alaska. In Ultramafic and related related rocks, rocks, edited edited by by P.J. P.J. Wyllie, Wyllie, 3. J. Wiley Wiley and andSons, Sons, pp. pp. 97—121. 97-121. Todd, Todd, S.G., S.G., Keith, Keith, D.W., D.W., Schissel, Schissel, D.J., D.J., LeRoy, LeRoy, L.L., L.L., Mann, Mann, E.L., E.L., and and Irvine, Irvine, T.N. T.N. 1982. 1982. The The J-M J-M platinum-palladium platinum-palladium reef reef of of the the Stillwater Stillwater complex, complex, Montana Montana : Igneous Igneous Stratigraphy and Petrology. Stratigraphy and Petrology. Economic Economic Geology, Geology, v. v. 77, 77, pp. 1454—1480. pp. 1454-1480. Vogel, Vogel, T.A. T.A. 1982. 1982. Magma Magma mixing mixing in in the the acidic—basic acidic-basic complex complex of of Ardnamurchan: Ardnamurchan: Implications Implications on on the the evolution evolution of of shallow shallow magma magma chambers. chambers. Contributions Contributions to to Mineralogy Mineralogy and and Petrology, Petrology, V. V. 79, 79, pp. pp. 411—423. 411-423. Watkinson, D.H., and Dunning, Watkinson, D.H., and Dunning, G. G. 1979. 1979. Geology Geology and and PlatinumPlatinumgroup Mineralization, Lac des lies Complex, group Mineralization, Lac des Iles Complex, Northwestern Northwestern Ontario. Ontario. Canadian Canadian Mineralogist, Mineralogist, v. v. 17, 17, pp.453—462. pp.453-462. : 32 �List of of Fiaures Figures List Generalized geology of the Lac des lies area. Simplified from mapping by by the the Ontario Ontario Geological Geological Simplified from mapping survey (Sutcliffe and Smith 1988). Location of field Survey (Sutcliffe and Smith 1988). Location of trip stops are shown. trip stops are shown. Figure 2. Geology of the Lac des lies Complex based on mapping by Sutcliffe and Sweeny (1986) with modifications from Lindhardt and Rues (1987). Location of field trip stop is shown. Figure 3. Geological map of the LDIC in the vicinity of the Roby Zone. Location of map is shown on Figure 2. Mineralized zones A to F from Pye (1968). Figure 4. Section through the Roby Zone showing lithologies and total total PGE PGE values values plotted plotted against against length length of of drill drill and hole. Based on diamond drill core logs of Texasgulf hole. Based on diamond drill core logs of Texasgulf Canada Limited. Figure 5. Geological map of the Tib Gabbro. From Smith and Sutcliffe (1987). Location of field trip stops are Figure 1. shown. Figure chemically analyzed samples re 6. 6. Modal analyses of chemically variation in quartz-plagioclase-alkali quartz—plagioclase—alkali feldspar feldspar showing variation and quartz—feldspar—mafic quartz-feldspar-mafic minerals. Figure Schematic cross-section cross—section of of the the crust crust in in the the Lac Lac ure 7. 7. Schematic des Iles area showing possible configuration of zoned lies possible chamber. magma chamber. Figure outcrop map showing details of mineralized mineralized ure 8. 8. Outcrop Located breccia zone zone and pegmatitic gabbro. Located approximately 200 meters meters southeast southeast of of the the Roby Roby Zone in approximately the "C—zone" Phase contacts contacts at at "Aw "A" and and "C-zone" (see (see figure figure 3). 3). Phase "B" are interpreted to be primary igneous 'B" igneous layers. layers. Leucogabbro inclusion at "C" An *tC"has cuspate cuspate surfaces. surfaces. An intrusion breccia zone cross—cuts cross-cuts igneous igneous layering. layering. dikes occur occur in the the core core of of the the Pegmatitic gabbro dikes breccia and also disrupt the layering as at location "D". A channel sample at "E" indicates that the highest values of PGE are associated with the pegmatitic phases. 33 �90°oo' 89030* 49° 15 :TAMNLAxE:s INTRUsIoN: WITH MAGMA MIXING + t + + + + —:--:—..- +••.k•Iomete -. 4+ 49°OO' PROTEROZOIC ! hornblende diorite Early Granitoid Rocks diabase AR CH E A N Late Granitoids k'+T4 biotite tonalite :—_—:—g I— hornblende tonalite Late Mafic to IJltramafic Rocks I mafic maficto tointermediate intermediatedikes dikes ultramaf Ic t gabbro to gabbronorite gabbronorite gabbro to 1 hornblende gabbro, hornblendite T1 tonalltic gneiss Supracrustal Rocks [II 11111 matic metavolcanics t::c:i metasediments -• —— fault fault - PGE PGE occurrence occurrence — contact contact breccia Zone Figure Figure 1. 1. 34 �1 -r Li —L, \j LAG DES ILES alTAao\ "N) strike & dip of layering fault geological contact hornblende gabbro gabbronor its hybrid zone leuco gabbro Gabbroic Rocks Figure 2. hornblendite, hornblende pyroxenite, hornblende diorite clinopyroxenite, welirlite, serpentinite websterite, gabbronorite Ultraroaf Ic & Related Rocks granitoids(unsubdivided) ARCHEAN diabase PROTEROZOIC LI 490 15 ______ ______ ______ —— a �______ I Western Gabbro— Pegmatitic gabbro, gabbro breccia,norite, I -] Pegmatitic gabbro, gabbro breccia, norite, r—- gabbro, gabbronorjte, gabbronorite, clinopyroxene clinopyroxene * + + + + I + + [c:%:::J + ++ ++ + + + + + + I + + U + 4 + 4 t + + + + + + + + + ÷ + "J1 Eastern Gabbro— + + + ++ ++ + + + ÷+ ÷+ 4+ + + + + + t + 4- 4 1 a, L't sj + + t 4 ++ ++ + ++ ++ 4+ ++ + ++ ++ ++ ++ ++ ++ + + + ++ ++ + + ++ +++ ++ + ++ ÷+ ÷+ + + + ++ ++ ++ ++ ++ ++ ++ + + + + + + + + + + + + + + + ROSY + Western Gabbro — Gabbronorite, pyroxenite, gabbro, anorthosite + ZONE Uralitized leuco—gabbro Diabase 0 Approximate location of mineralized - C-, FZONE to surface surface projected to Geological r-ontact rontact road + ÷ + + + ft< 1 + ' ".1 t ... - 0-ZONE + ++ + + + ÷ + + + + + t t 4 4. 4. ÷ + + + + ++ + $ 4 4- + + + + + ++ + + + ++ ++ ++ + + + + + ++ + + + + + + + —'--- Igneous layering (strike and dip) + 4+ + + ÷ + + + ++ Foliation (strike and dip) + 4 4 + 4- + ++ 4 + + ÷ r <'A + + ÷ 200 metres Figure 3. zone �- w E 103 + 75 106 - Section 515 s. 0 20 40 60 80 metres metres 55 0 0 10 10 15 15 20 20 ppm PGE ppm PGE -t .... Eastern Gabbro 0 Gabbro 0Western Gabbro 75 drill 75 drill hole hole number number Altered Altered Pyroxenite + + elevation elevation reference reference Figure 44.. Figure 37 �- ..... _. r.. 70 60 - -. - - - - - -. -• -0 - - V. - ;. - -. - - :1: - • - -s-uii. ::,!. 'I • —I . . • : - : - .. . - : - . . — - - - -. - - . ,l__ - - : 0 - •. . 0.5 'I - . . . . . . . . • . . • . . • • . . . . —a' — - . .•..•......... • F, :: :::MIDDLEZaNE.:::::.::. road LOWER ZONE" .--o :: •: r + + + + -c—r+ + + + + + + + + + P'KUHNER OCCURRENCE + + + .+ + + + + + + + + + + + + + + + + + + + +-+ foliated togneissic gneissic biotite bbttte foliatedto diabase diabase - tonalite — / lithological lithalogical contact contact A RC HE A N ARCHEAN +4 granodiorite grand!a~ite(megacrystic) tmegacrystk> granodiorite, granaciiarite~Hb Hb tonalite tanakite (foliated) (foliated) . . : - #- hornblende+quartz±biotite h&enW auar%-#2bbtite gabbro gabbm magnetite-rich magnetiterichgabbronorite gabbronorite pegmatitic pegmatiticgabbro gabbro quartz quartzgranulite granulite I: - :±j gabbro gabbronorite, m i t e ,norite norite - r' TIB TIB GABBRO GABBRO I-,,.: * * * a tj + mafic metavolcanics PROTEROZOIC PROTEROZOIC 1+ + + I' . • + 1.0 . • . . :87. . . - • -K . -. - --4 - • • - 0 -, * fault fault layering layering (strike (strikeand anddip) dip) foliation foliation (strike (strike and anddip) dip) ultramafic ultremaficcumulates cumulates zone zone contact contact trench trench site site A suiphide sulphide mineralization mineralizationwith with >>SOppb SOppbPOE P6E 00 sulphide subhide mineralization mineralizationwith with >>500ppb SOOppbPOE PGK 38 Figure Figure 5. 5. �QTZ QTZ • HORNBLENDITE HORNBLENDITE + • HORNBLENDE TONALITE HORNBLENDE TONALITE • MAFIC MAFIC TO TO o 0 O o MELA-TONALITE MELA-TONALITE o QUARTZ a QUARTZ FELDSPAR FELDSPAR INTERMEDIATE DIKES DIKES PORPHYRY PORPHYRY • S 0 0 0 055 FELD BIOTITE TONALITE TONALITE 1 S MAFICS Figure 6. Figure 6. PLAG �.1:- C Figure 7. �\ \ ,1 it / / / / channel sample I' Li Itrench / EG — Ieucogabbro WG — gabbronorite gabbroic inclusions pegmatitic gabbro dikes gabbroic intrusion breccia fault 6 0 m Figure 8. 41 �+ opt op pi opt, pi p2 • Rb • net - ap I I - - :- - - phi -phionopite; bto-baotite: act—acttnol its artthr'phyiniate, I nesocurrolate bio, qtz pI. cps. Rb, act, qtz, myt act p1, opt, Rb. p1, opt, Rb, bro pl. qtz, bio p1, Rb, phi cpx. opt, hb. p1, net qtz—quartz. snozoisite • to Rvpxda,onorphtc coarse qrained , lsoqranoiar subophitio .________ - . I F othocunulate, mesocss,su late to hvpidiomorphic nesocuisuiate to orthocunu late mesocunta.Iate 1cm — 6cm 2—4 1w, 2cm, 2—4 cm 2—4 run :—4 mm 2—4 tel ire, — i—S rIS 1—1 nfl 1—3 nfl 1-4 rwt 1-4 no •t'lt-ain liar' hb—hornblende; pi—piaqiociase; ngt—oaynetate: ap—apatite; epidote, olsnozossite chlorite uralite. chlorite sericate epidote. ci anozois Ste add inosite. uraiite, tale anthophviiite, ci inozoisite epidote,ohiorite. as abeve ci epndote. chlorite, to riesi-unhi late - ninorc'art,orcate, - talc flinor ph] opt to ol tosc-rp-rrqt, 'lestut,- adcun:rlate hb Alteration opt to act, nsnor —— cpx, ops. hb, rpn, =.- Tnlercunu 'us Minerals Abbreviations: oi—olivine; ohr—chromite; ops—clinopyroxene; opx—orthops'rosene: —— Rb, - hb pi *cpt+hb*mqt ' ops'opx p1 * pi. p - opt p2 oi Rb, Rb Hornt Tende Gabhro I or's pl •cps*opx . - - opt opt, eRr •oiscps'npt - Pegnst:T ic Gabbro and Gabbronorite Gabbro Maenetite—rioh - Leuccqahbro, Anortr,os+tio Gabbro Gabbronorite Norite —- Hornbiendite, Pyrosene Hornbiendite UI Gabbronorste dike iherrolite , 01 Isc-lsterste- dike — -Rebstei-t.-,Gabbr000ritecps clrnnovroxenite OlCllnorvroierra te, ol ol. ol -cbs serpt-ntrr'ite, wenrirte Cunu us nincrals — 'etronraphy ol Litholoures fron the rae Des Ties Connie,. Rock Tsre Table L Sunnirv of ____ chr, - Or's ci - * + • p1. - ops - + Rb, p1 - - • hb. opt, i pl Rb ap net and qabbro rgt gabbronorite pl • cpx cpy similar to p1 - * pi qtz Rb hb, opt * hb opt pi. pi pl oi cpx - chr. ops 'CPA. opx'cps. pI ol Rio rrcr[se:tuer,v-t. opt cops. pi opt. opi 0] CiceraliIza: �2 FIELD TRIP 2 �1.1.5.0. FIELD TRIP Geology of the Shebandowan & Quetico Archean subprovinces 0. Borradaile Geology Department Lakehead University Thunder Bay, Ontario P7B 5E1 Canada Proterozoic Rocks Proterozoic Rocks 1. 1. KakabekaFFalls. Recessedpost-glacial post—glacialgorge gorgei ninProterozoic Proterozoic shale. shale. Kakabeka a l l s . Recessed Soft sediment deformation in Proterozoic shales — car park exposure. S o f t sediment deformation i n Proterozoic shales - c a r park exposure. 2. 2. Basal con conglomerate of Proterozoic sequence. Basal (Kakabeka Formation). (Kakabeka (Care on Highway!) Archean Rocks Rocks SStructural t r u c t u r a l facing. facing. 33.. Pillow gradedt utuffs. P i l l o w lavas lavas and and graded ffs. (Fig. (Fig. la, l a , bc). be). 4. Fourway School. Younger Younger "Timiskaming-1 "Timiskaming—like" Fourway iken' sequence sequence ooff Archean. Archean. (Fig. 3). 3). ooff downward—structural downward-structural ffacing a c i n g sediments. sediments. (Fig. 5. 12. 11. 6. ' }. Flap Flap i IIntertidal n t e r t i d a lsequence. sequence'. Finnmark exposure. "Timiskaming—like" sediments. Finnmark exposure. "Timiskaming-like" (General structural Fig. 22). ). (General s t r u c t u r a l sstyle t y l e ooff area, area, see see Fig. Quetico gneisses, gneisses, Raith. "phase" deformation. deformation. "phase" D1f afabric. D, bric. Migmatites,d idiktyonitic structure, mmultiMigmatites, k t y o n i t i c structure, ulti. + -4 beltt gneisses. Quetico be1 gneissesi ., ., Shebandowan Mine Mine Road. Shebandowan Road. ! ;y. "." Q,-T" -,. ,. ",- . . ,> Pi c.^".\-~-! , ,. ~. .?'.>: <, .... - , .: ,? .~d t .: < + . ..> . "Timiskaming—like" "Timiskaminci-1 ike" sequence seouence ...,., .. (a) Fragmental Fragmentalr ered igneousrock rock (!?) (U) d igneous (b) conglomerate. Fabrics Fabricsand ands tstrain region (see (see Fig. Fig. 5,6,7);" 5,6,7). r a i n i in n region (c) sslate late - , . Archean rocks rocks ",& Older Keewatin—type Keewati n - t v ~ eArchean (d) ppillow i l l o w lava lava (e) iiron r o n formation formation "A ^-$ -..I -'/; >: , ? z . a ' ', ,?+; ,' ..* .-. 3 4 .E 5 " ,,,: Strain Fig. 1,2)? S t r a i n (see (see Fig. 1,2)? :'.I ,.:4 Â¥ . . .- ~ ;. , ~ . .> 6 :c .;,= Younging? SStructural Younging? tructural 1. SwampCreek CreekP Pillow lavas. Swamp i l l o w lavas. faci ng? facing? 8. Tuffs T u f f s and and ppillow i l l o w lavas. lavas. 9. Increasing metamorphic group) towards Increasing metamorphic grade grade in i nmetasediments metasediments (Kashabowie (Kashabowie group) towards beltt boundary. be1 boundary. 10. ((Structural S t r u c t u r a l facing facing and and folds? folds? Gneissose rocks of the Quetico Belt. 43 seeFig. Fig. 88). ). see �ARCHEAN LITHOLOGIES "TIMISKAMING" METASEDIMENTS 0 IH:.•:1 GREENSTONES I>/-cI GRANITOIDS 1x-'I PARAGNEISS IEI GREYWACKES 7., r..— LAC — - LiIlr- "BELT" LAKE RAITH 7.— '' QUETICO "BELT 9 ---,- ,,C()':/ LA TIMISKAMING METASEDIMENTS c. 2690 my j 0 I0 20 KM MT. McKAY FORMPIt0H L. - �o long ', EIIIII' "cij.p-centre lIne the model the model notural pillow nolurol pillow An idealised lava pillow An idealised natural natural lava pillow before before straining straining and and the the geometric used in in this this paper. paper. geometric model model of of iti t which whichisis used C)T k a- / /__ Fig. F i g . la la up structural tacint U. I (a) Undeformed Undeformed bed with idealised idealised pillow. pillow. The The cusp-t-ntre cusp-to-centre (a) bed with line of of the the pillow pillow gives gives the theyoungingdirection. younging direction,(b) (h) Deformed Deformed bed bedwith with line idealised pillow. pillow. The The cusp-to-ccntre cusp-to-centre line line of of the the pillow pillow now the idealised now tracks tracks the 'stratigraphic thickness' thickness'direction, direction, 1t'. to the -stratigraphic ' . This This may may approximate approximate to the direction, The simple , younging direction direction is is no nolonger longer istructural n i d i i m l facing facine direction. The simole vounoinf ~~~.~~~ -~~~ ~~~~~r perpendicular to of the case, but.bv but, by eroendicular to the the long lonoaxis axisof the pillow nillow in the thegeneral ~eneralcase. definition, it remains perpendicular to bedding. ~ 000 cusp in peor - like pear-like terminations bmhtims crescent - stuoped crescent-shaped pillow pillow Fig. 1b b Fig. tndeformed irdeformed piltow pillow deformot, .. ..[/f,4,//1,~-~4.5/ .....deformation ............... Schematic sequence sequenceofof proeressivcly progressivelydcformed deformed pillows pillows inSchematic ferred from from held Whenthe the linite finite str;nin strain cellipse fen-cd field observations, observations. When l t i n ~ ratio ;ratio reachesaboul4.5 about 4.5the thepillows pillowstk-vclnp develop p~iir.likc pear-like tcrniinations terminations reaches of heterogeneousstrain. strain, and subsequently the ends ends of of aitss a ~ result iresult of :nod suhscqucntly pillow become so pointed pointed thiit that iitt is difficult diftieuls to identify identify the cusp the pillow 45 �sy Sketch of' of aa deformed deformed pillow pillow showing the the selvage sel'age thickthickFIG. PtO. I.1. Sketch ,,S. nesses in the nesses the principal principaldirections direcuons of of strain: wain S . 5..S.S-.The The ratios ratun of d these thicknesses give the ratio ratio of the principal principal strains if the thickness that the be noted noted that of the selvage was originally originally constant. ItIt should should be the not normally in the same are not principal selvage principal selvagethicknesses thicknesses arc ->ame ratio ratioas as the the dimensions: one exception is the unlikcly unlikely event that deformed pilIow's ~illow'silin~'n~iuns: oneexccplion is the cvcm that the original, undelbrmcd Ac original. undefonned pillow pillowwas wasspherical. spherical -. Fig. ic Fig. 1c 46 �N N (B) (A) S moxifflum maxImum Susc.ptibilitin :  Suç~~tibilitià £ inteonediot. A mfrmdiif plunge// inmfctton inlerseclion llmation X: meon fold plunge Irneetion X: i i ~ f l ntold Fl g. /, bed I/ orientation b'Zientation I m. minimun mtftimum 2 Lower-hemisphere equai-azea stereonets showing the mean mean reonets showing n intersection cleavage orientation (great circle) and mean intersectionlineation lineationfor for the eastern eastern Finmark Finmark area (A) the Shebandowan mine area and (B) the (east of Fourway School) (see Fig. I). The principal principalmagnetic magneticsuscepsusceptibility orientations for the slates are also shown. cleavage cleavage ' downward downward structural ,k: ,. . strucfural facing facing Interpretatlo Interpretatic Planof of an an outcrop outcmp surface surfaceon onthe thesouth southside sideofofHig Hig Plan II —17. 17,about about100 100mm west west of of Finmark 11 Finmark Road. Road. Where the the glacial polish Where polish has has been been weathered weathered away away vertical cleavage is pronounced; pronounced; elsewhere the thesedimentary sedimentarydetai deta vertical preserved. Ripple Ripple marks, graded graded bedding, and sand sand intrusions preserved. thatthe thewestward-closing westward-closingfold foldhas hasolder olderrocks rocksininits itscore: core:iti acase t e that anticline. However, However, the east: it it is aa synfonn. synform. '' anticline. the fold foldplunges plunges to to the east: this ht-generation fuss-generation fold fold isis aa downward-facing downward-facingfold fold that that pml pm this inverted flap developedwhen whenfolding folding affected affectedaa locally locally inverted flap of of sedim sedim developed The geometrical shown inin the the sketch sketch atat bo bo The geometrical interpretation interpretation isis shown Younging directions directions are are indicated by by "Y." Y." Younging Fly. 3 47 �F. Stylized regional fold geometry for the Shebandowan gmup deduced from cleavage—bedding and intenection lineation relationships. The fold plunge variation is infened to be quite large, although the principal magnetic susceptibilities of the slates ("max." and "mt.") show relatively little change in orientation within the axialplanar cleavage. Because the susceptibility is due to the grain fabric of the rock, we Suggest that the variation in fold plunge occurred during the development of the folds rather than later. Fig. 6 Geological map of northern part of Shebandowan Lake greenstone structure (SLGS) with horizontal line segment (QT) use for strain estimate of overall shortening. Strain stations (see Table 2 are numbered. lJ clastic meta— [7J sedimentary rocks Fig. fl volcanic rocks (mainly basic) Granitoid rocks Simplified regional geology after Pye and Fenwick (1965) with subprovinces (SW = Shebandowan—Wawa. Q = Quetico. W Wabigoon) after Goodwin (1977). Infonnation on boxed areas is presented in Figs. 2 and 3. 48 �— #9 + + +' + + — — — — —— — RELATIVE STRENGTH OF MINERAL LINEATION A FOLIATION LoR $ — — • — + 4f + + — + +— — + + + — 4 ¼_4. / '-7 + + MINE + + + 4 2 PLUNGING STRAIN FIELDS 5 O + I + I + I I O + + 8OLJNDARY 8ETWEEN OPPOSITELY— —-30 MINERAL LINEATIONS LOCAL FAULTS • SHEBANDOWAN + + + ++ + ,PEEWATAI LAKE +•_.—_ + 55— :÷ +'r+ +' __\LDERCHING . GULL PLUTON'. lt_J___'.J + GNEJSSTERRAIN+_+++1&4++++ •+ + + + + + ii TONALITIC/GRANODIORITIC 0 —— NORTHERN LIGHT — SYN/POST TECTONIC PLUTONS LEG END • + _+ ,- 1"— 7-4" —4• ftJRCHELL LAKE +/ + + ++ ++ +j — ; —;—- 1 — p Fig. 6 7 MI 10KM 25 �-- ... . ... . 0 ~ttf-wa ww) toed (c) (d) F i y. 8 I The The structural structuralfacing facingof of folds. folds. (a) (a)AAgeneral general illustration illustrationof ofthe theconcept conceptof ofstructural structuralfacing facingofoffolds. folds.The Thestructural structu facing remains consistently oriented directions are variable. An outcrop sketch ofofa a small fold racing direction directionremainsconsistently orientedwhile whiteyounging youngingdirectionsare variable.(b) (b)Anoutcropsketch smallF2 F fol which is axial axial planar. (c) (c) Lower Lower hemisphere which demonstrates demonstratesthat thatthe theS2 Si cleavage is hemispherestereographic stereographicrepresentation representationof ofbedding beddi and cleavage and their mutual intersection. ( A schematic profile view of bedding and cleavage. F2 folds face downward since younger youngerbeds beds are are encountered encountereddownward downwardalong alongthe theS2 S;cleavage. c 50 �References References Borradaile, G.J. "Structural facing" G.J. 1976. 1976. "Structural facing" (Shackleton's (Shackleton's rule) r u l e ) and and the the Paleozoic rocks Vdez Rablo, Rabio, SE SE Spain. Spain. rocks of o fthe theMalaguide MalaguideComplex Complex near near Velez Proc. Kon. Proc. Kon. Nederl. Nederl. Akad. Akad. van vanWetens., Wetens., 8 B79, 79,330—336. 330-336. Tectonically deformed as an an iindicator Tectonically deformed ppillow i l l o w llava a v a as n d i c a t o r of of way up up and way and bedding. 469—479. J. Struct. Struct.Geol., Geol.,4, 4, 469-479. Borradaile, Rorradaile, G.J. G.J. 1982. 1982. Borradaile, G.J. G.J. and andSchwerdtner, Schwerdtner, W.M. W.M. 1984. 1984. Horizontal shortening shortening of o fupward upward facing greenstone facing greenstone structures in i nthe thesouthern southernSuperior SuperiorProvince, Province,Canadian Canadian Shield. Can. EarthSci., Sci.,21,21,611—615. 611-615. Can. J. Earth The Shebandowan Group:"Timi Timiskaming G. J. and andBrocon, Brocon, H.G. H.G. 1987. 1987. The Shebandowan Group: skamingBorradaile, G.J. like" 1i k e "Archean Archean rocks rocks in i nNorthwestern Northwestern Ontario. Ontario. Can. J. J. Earth 185-188. Can. Earth Sci., Sci.,24,24,185—188. agesf ofor and regional regional Corfu, F. F. and and Stott, S t o t t , G.M. G.M. 1986. 1986. U—Pb U-Pb ages r llate a t e magmatism magmatism and Corfu, deformation in i nthe theShebandowan Shebandowan bbelt, e l t , Superior Superior Province, Province,Canada. Canada. Can. J1. Jl. Earth 1075—1082. Can. EarthSci., Sci.,23:23: 1075-1082. Application ooff [-S Schwerdtner, W.M., W.M., Bennett, Bennett, P.J. P.J. and and Janes, Janes, T.W. T.W. 1977. 1977. Application L-S Schwerdtner, fabric f a b r i c scheme scheme tto o structural s t r u c t u r a lmapping mapping and and paleostrain analysis. analysis. Can. J. Earth 1021—1032. Can. J. EarthSci., Sci.,14,14, 1021-1032. Strain Schwerdtner, W.M.,SStott, andSSutcliffe, Schwerdtner, W.M., t o t t , G.M. G.M. and u t c l i f f e , R.H. R.H. 1983. 1983. S t r a i n patterns patterns of crescentic crescentic granitoid g r a n i t o i d plutons piutons ini nthe theArchean Archean greenstone greenstone t terrain e r r a i n of of Ontario. J. Struct. 419—430. Struct.Geol., Geol.,5, 5, 419-430. Stott, G.M. and andSchwerdtner, Schwerdtner, W.M. W.M. 1981. 1981. AA sstructural t r u c t u r a l analysis analysis of o f the the central central S t o t t ,G.M. part Shebandowan belt. inetavolcanic-metasedimentary be1 t. p a r t ofo the f the Shebandowan metavolcanic—metasedimentary Ontario Geological Geological Survey, Survey, Open Open FFile i l e Rep. Rep. ## 5349 5349 44 44 p. p. 1 I Gold mineralization Shebandowan Gold m i n e r a l i z a t i o nini the n the Shebandowan beltt and and its i t srelation re1a t i o ntot oregional regionaldeformation deformation patterns. patterns. be1 Ont. Ont. Geol. Geol. Survey, Survey, Misc. Misc.Paper Paper110, 110,181—193. 181-193. Stott, S t o t t , G.M. G.M. and and Schnieders, Schnieders, B.R. B.R. 1983. 1983. 51 �fiELD �Granitoid-related Granitoid-related mineral mineral deposits deposits of of the the western western Lake Lake Superior Superior region. region. Stephen Kissin Stephen A. Kissin Lakehead Lakehead University University Thunder Thunder Bay, Bay, Ontario Ontario P7B P7B5E1 5E1 Canada Canada 52 �Introduction Introduction The locations of surface exposures of granitoid rocks rocks of of the the western western Lake Lake Superior region are illustrated in Figure 1. The Archean granitoids are found in a a Superior region are illustrated in Figure 1. The Archean granitoids are found in western area in the vicinity of Thunder Thunder Bay, which which is separated by Proterozoic Proterozoic from various various plutons lying south of sediments and diabase sills of the Nipigon Plate from Lake Nipigon. The western group is associatd with the Lake Nipigon. The western group is associate) with theShebandowan-Wawa Shebandowan-Wawa greenstone subprovince and and its its boundary boundary with with Quetico Quetico Subprovince Subprovince to to the the north. north. The greenstone subprovince The (6), easterly group of granitoids, with the exception of the Black Black Sturgeon Sturgeon Lake Lake granite granite (6), lies within the Quetico Subprovince. The plutons in Figure 1 are numbered for lies within the Quetico Subprovince. The plutons in Figure 1 are numbered for purposes of identification the following following discussion. discussion. The identification in the The names names of the bodies, bodies, with with aa exceptions, are are those those employed employedby by McCrankad. McCrank.t at. (1981) (1981) in in their compendium. few exceptions, . The Glacier Lake pluton pluton (3) (3)is is aa batholith-sized batholith-sized body consisting consisting of two-mica two-mica leucogranite in the the north north grading grading into into biotite biotite granite graniteto tothe thesouth. south. The rocks rocks show minor penetrative deformation within a kilometer of of their northern contact and and are bounded by aa weakly defined contact aureole in the intruded metasedimentary intruded metasedimentary rocks, rocks, suggesting late tectonic emplacement. emplacement. The rocks are The rocks are moderately moderately to to strongly strongly peraluminous, and although bearing no aluminous minerals other than micas, have the geochemical characteristics (A/(CNK).. 1.1, normative 1.l, normativecorundum, corundum, characteristics of S-type granitoids (A/(CNK)L^. high &O and high initial 87SR/°6Sr). Textural and geochemical patterns suggest <180and high initial "SR/^Sr). geochemical patterns suggest that that has been beentilted tiltedtotothe thenorth northsince since emplacement (Zayachivsky., .eta.,1989). 1989). the pluton has emplacement (Zayachivsky The MNW stock (1), characteristics, appears appears to to be a (I), with with essentially essentially identical characteristics, satellite of of the the Glacier Glacier Lake Lake Pluton. Pluton. The llgour satellite llgour Lake Lake Group Group of of Zayachivsky Zayachivsky (1985) (1985) and and Kissin and Zayachivsky (1985), equivalent to to the Kilgour Lake-Steen Lake metagabbro (1981), is isaa zoned of McCrank McCrankaA. (1981), zoned granitoid granitoid intrusive intrusive with a core of monzogabbro monzogabbro grading outward outward to tonalites tonaliies and and granodiorites. granodiorites. . Also present in the Georgia Lake area are numerous tabular tabular intrusions of leucotonalite to granodiorite of thickness ranging from aa few meters leucotonaliie (trondhjemite) to meters to to aa few tons of meters meters and strike lengths of up up to several several kilometres. The Thepetrogenic petrogenic affinities of these these are are unclear unclear as as is isthe thetiming timingof oftheir theiremplacement. emplacement. In fact, fact, contacts affinities of among the Glacier Lake pluton, the Kilgour Lake group and and the the tabular intrusions intrusions have have not been been observed observed in in the the field. field. exposed to to the south of the Georgia The Glacier Lake pluton is well exposed Georgia Lake Lake area, but but its its eastern eastern margin margin is is unmapped unmappedat at present. present. It is exposed exposed in in the the west west along along Highway 11, 11, but but to the west, between Highway 11 and the Nipigon Nipigon River system, is a region soillwav between betweenthe the Lake Lake reaion of thick thick Pleistocene Pleistocenesediments, sediments, deposited deoositedin in aa spiliway Nipigon basins. Metasedimentary ~ i b i ~ and o n Lake Superior basins. ~etkedimentaryrocks are intruded intruded by granitoids granitoids of variable size and form: form; however, of outcroo outcrop makes Door availability of makes interpretation interoretation of however. poor to thewest, the west, a well-defined intrusion, the the overall geologic geologic picture picture difficult. difficult ' Farther to Church Lake is seen to intrude intrude Archean metasediments metasediments and and Lake quartz quartz monzonite monzonite (4), is "migmatites". "migmatites". The The petrography petrography of of these these rocks rocks is is similar similar to that of of the the Glacier Glacier Lake Lake pluton (Coates, 1972), and it is possible that they are parts of the same batholithicbatholithicsized sized body. body. The Pine Portage intrusion (5) is exposed in a window in Proterozoic Proterozoic rocks rocks at at 53 �Figure 1. * BAY THUNDER: Boy Thunder • Sh,Iabeer Sturgeon L Lake Superior \fiion + Geology of the western Lake Superior region indicating the locations of major granitoid plutons. Numerical codes are discussed in the text. Lake boundaries Province + Subprovince rocks C numbered Dog ) undivided ) Shebandowan Subprovince 25 km N A ear Subprovince (meta sediments + paragneisses LI Quetico Gp. + Nipigon Plate undivided) Southern Province ( Animikie I �composed of two-mica leucogranites the source source of of the the Nipigon NipigonRiver. River. It is composed leucoaranites cut by bv tabular leucotonatites, similar to those in the Georgia Lake area. The leucotonatites,similar The granitoids granitoidsare are closely associated with lithium-bearing pegmatite dikes, cutting metasedimentary closelv lithium-bearina cuttina metasedimentarv rocks rocks - .oeamatite - in rare-element to the east. Geochemical fractionation trends theeast. Geochemical fractionation trends in rare-element and and simple simple pegmatites pegmatites suggest that they are derived by fractionation fractionation of a leucogranite parent. The Black Sturgeon Lake granite (6) is exposed in a window of Archean rocks rocks east of Black Black Sturgeon SturgeonLake. Lake. It is associated with greenstone-like lithologies and may lie in the Wabigoon Wabigoon Subprovince. Subprovince. lies the the Hilma HilmaLake Lakegranite granite(7). (7). The body consists West of the Nipigon Plate lies (Tihor, 1973), 1973), although although textural textural compositional compositional white to pink pink two-mica two-mica leucogranite leucogranite (Tihor, variations of the rock are found, including pegmatitic granite granite and and pegmatite. pegmatite. The The relationship to the Penassen Penassen Lakes stock of Scott Scott (1985), (1985), equivalent to the the Wailer Waller Lake Lake granite of of M McCrank.a!. c C r a n k M(1981), . (1981),isisunclear unclearowing owing to to aa lack lack of of mapping. mapping. The The two two bodies are shown as contiguous by McCrank.eta!., McCrankad., although although the the different different names names were applied to to the separate bodies suggested suggested in in Figure Figure 1. 1. This differentiation of the two supported by bodies is supported by the the rather rather different different petrography petrography of the the Penassen Penassen Lakes Lakes stock, which isismostly mostlycoarse-grained coarse-grainedporphyritic porphyriticgranite granite to to quartz quartz monzonite monzonite with with local local hornblende syenite and syenite phases. syenite and syenite phases. The Mackenzie MacKenzie granite granite (9), (9), equivalent to the Waylan Lake granite of McCrank a aL (1981), has a complex outcrop metavoicanics and at. (1981), has a complex outcrop pattern intruding Archean metavolcanics Group (Gunflint metasediments, lying unconformably below Animike Group (Gunflint and and Rove Rove Formations) sediments and intruded intruded by by Keweenawan Keweenawan diabase diabase sills and and dikes. dikes. According biotite granite. granite. The (1979), it is a medium-to-coarse-grained biotite According to Rogers Rogers (1979), Mackenzie granite is MacKenzie is possibly possibly equivalent equivalent to to the the Kivikoski Kivikoski granite granite (10), (lo), equivalent equivalent to to the the Mcintyre granite of McCrank .. (1981), of the the Mclntyre McCrankad. (1981),as asgranite graniteisisknown knownto tounderlie underliemuch much of city of Thunder Bay as basement to to the the Animike Animike Group. Group. The Gorham granite of McCrank.Qta!. (1981) is included on Figure 1 as part of the McKenzie McCrankad. McKenzie granite (M.M. kehienbeck, pers. Kehlenbeck, pers. comm., comm., 1990). 1990). The Trout Lake granite (11), (1I), Barnum Barnum Lake Lake quartz quartz monzonite monzonite (12) (12) and andWhiteliiy Whitelily similar plutons plutons of of circular to to elliptical outcrop outcrop pattern Lake granite (13) are three similar pattern aligned west to east near the Shebandowan-Quetico Subprovince Subprovince boundary. boundary. The aliened The rocks are characteristically hornblende and biotite-bearing, porphyritic quartz rocks out monzonites. Kehlenbeck Kehlenbeck(1977) f1977) pointed ~ointed outtheir their late latesyntectonic svntectonicemplacement, em~lacement.as as aureoles in indicated by well defined defined contact &nta&aureoles in the the intruded intrudedArchean Archean metasedimentary metasedimentary and metavolcanic metavolcanic rocks. rocks. Mineral Deposits Pegmatites Peamatites The most most spectacular spectacular granitoid-related aranitoid-relatedmineral mineral deposits deoosits of of the the area area are arerarerarepegmatites Georgia element ~ e ~ m a t i t einsthe ~ e o r ~Lake i a area and a small smail but similar pegmatite pegmatite field in in Portage area (Pve. (Pye,. 1965). 1965). These the Pine Portaae These have have been been studied more more recently recently by bv , Zayachivsky (1985) Archibald (1987), and and these these and and other results are reported reported by (7985) and ~rchibald Kissin & Zayachivsky Zayachivsky (1985), (1985), Kissin Kissinetal. d.(1986) (1986) and and Kissin Kissin and Archibald (1988). The The . .. 55 �rare-element pegmatites pegmatitesof ofthe theGeorgia GeorgiaLake Lakearea areaare areshown shownininFigure Figure2.2. The The pegmatites may be subdivided into three groups, a northern group whose members pegmatites may be subdivided into three groups, a northern group whose members show little difference in relative fractionation fractionation of of trace trace element element and and central central and and southern southern group degrees of of fractionation fractionation from from east east to to west. west. group whose whose members members show show increasing increasing degrees Barren pegmatites pegmatites lie lieto to the the east east of of the the central centraland and southern southerngroup group but but are are not not shown in Figure Figure 2. in 2. Most of of the the pegmatites are unzoned unzoned and and contain contain phenocrystic phenocrystic spodumene; spodumene; Most pegmatites are however, the more highly fractionated pegmatites of the central and southern group however, the more highly fractionated pegmatites of the central and southern group show weak to well developed developed zoning and and may may contain, as as well as as spodumene, spodumene, tantalite-columbite group minerals, beryl, cassiterite or staringite and various Li Li tantalite-columbite group minerals, beryl, cassiterite or staringite and various phosphate minerals. minerals. The MNW pegmatite contains spodumene-quartz-intergrowth The MNW (SOUl) (SQUI) and is a potential potential source of of ceramic ceramic grade grade spodumene. spodumene. An entirely separate separate group group of pegmatites occurs within the Quetico Subprovince Subprovince (1978) described described uraniferous, uraniferous, white white albiteto the west of of the the Nipigon NipigonPlate. Plate. Franklin (1978) muscovite-biotite-quartz peamatites pegmatites containing containing 60-100 60-100ppm ppm U. U. The pegmatites have have muscovite-biotite-quartz .peamatites been found to contain uraninite, and all such pegmatites containing accessory apatite contain uianinite, and containing apatite' found to be uraniferous. These trending have been found These pegmatites oeamatites occur occur in in an an east-west east-west trendina. within the the Quetico Quetico Subprovince. Subprovince. sTheir origin is is obscure, obscure, as as they they appear appearto to be be zone within heir origin unrelated to to anatectic mobilizate mobilizate pods pods in in high-grade high-grade metamorphic metamorphic rocks rocks nor nor to to pink syenitic peamatites pegmatites apparently apparently co-magmatic co-magmaticwith withgranitic graniticintrusions intrusionsininthe thearea. area. The The svenitic Hilma Likegranite, Lake granite, however,was however, was mentioned mentioned as as having having an ananomalous anomalous uranium uranium content content thma with respect to other rocks of the area (Franklin, (Franklin, 1978). 1978). - Molybdenum A sub-economic sub-economic molydenite occurrence occurrence is is located located at at Anderson Anderson Lake, Lake, at at the the western margin of the Hilma Lake ggranite. Molydenite occurs as coarse aggregrates in quartz veins and within pink pink pegmatitic pegmat granite. It is unclear as to whether the mineralization process processwas was pegmatit pegmatitic or hydrothermal. The quartz veins lack however, hydrothermal alteration characteristic of veincharacteristics of pegmatites; howeve deposits is also lacking. The average grade of the or porphyry-style porphyry-style molybdenite deposi occurrence is reportedly 2.85% Mo; however, the apparent small size of the reserves is reportedly responsible for a lack lack of of exploitation. exploitation. Non-magmatic deposits, hosted in gra granite Non-magmatic Uranium Superior region region were were summarized summarized by by Uranium occurrences in the western Lake Superior (1978). Those related to granitoid rocks include uraniferous pegmatites in in the the Franklin (1978). Quetico Subprovince and vein-type occurrences occurrences in in granitic granitic basement basement or or cutting cuffing Sibley Group sediments. The The vein-type vein-type occurrences occurrences are not not of direct direct hydrothermal hydrothermal derivation from granitic granitic magmas, but but may may be be related related to uraniferous uraniferous pegmatites pegmatites and and uranium-rich uranium-rich granites as protore. protore. (1) in in The uraniferous uraniferous pegmatites are prominent prominent in in the Greenwich Greenwich Lake Lake area area (U (U(1) 4), and and exploratory exploratory work work has indicated indicated that thatthey they occur occur about about 40 40 km km to to the west west Figure 4), 56 �:/;: m::. NAMA CREEK )••• 7. :NoRTH NAMA CREEK1 SOUTI 5 Postogoni 2 ¶I. . • :• . . • \\\. •• : fr':. NEWK IRK : :'?s .;'9gjz1SALO. : :..Xy SOUTHWESTr fI + • • • a • . . .t.÷_,.Spl + 1÷ + +11- +iI+ e- +1 + de Fault Fault _.___— Contact Contact km I 1,1111111 I10 km 0 0 I Figure F i g u r e 2. 2. 1÷ + + LEGEND LEGEND Metasedin,ent Metasediment I ++I Granifoid Gran~toid 1 1+ + Rare element element pegmatite oeamatite - Nipigon Nipigon diabase diabase I 1 !ANS0NL•.j.j_r+ + t O ~ P ~ 8 8 9 ~ 1 The GeorgiaLake LakePegmatite Pegniatite The Georgia F i eField l d i l lillustrating u s t r a t i n g tthe h e granitoid granitoid rocks rocks and and rare-element rare-element pegmatites. pegmatites. Named pegmatite bodies Named pegmatite bodies were were studied by by Zayachivsky Zayachivsky (1985). (1985). 57 �along Highway Highway 527. As within aa .&aq Asdescribed describedpreviously, previously,these thesepegmatites pegmatitesare arecontained containedwithin relatively narrow narrow east-west east-west trending trending zone. zone. The small pods and :relatively small size of the pegmatite pegmatitepods and lenses and their low low uranium uranium content content preclude preclude the possibility of economic economic deposits. deposits. lenses :mN The vein-type occurrences occurrences (Figure 4) at at Greenwich Greenwich Lake Late (U(1)) and and Innes fines Lake take (U(2)) have been been described described by by Franklin (1S78) (1978) and and Yule Yule (1978). (1979). Both [U(2y> Both occurrences occurrencesare are sub-economic but were the source of considerable excitement in the late %%Â¥& 1970's. Both sub-economicbutwarethesourceofconsiderableexcitement;hthe occurrences are are localized localized in in brecciated occurrences brecdatedshear shear zones zones cutting cuttingall all Archean Arehean lithologies. ÈaiGitoes Lake occurrence occurs in in well defined veins with with quartz and and pyrtte pyrite The Greenwich ;Lake gangue and minor pitchblende yielding grab sample grades of 0.5 to 2.0% U. and minor pitchblende yielding grab sample grades of 0.5 to Hydrothermal ateralion alteration of wall rock is distinct, Hydrothermal is d isfinct,and and the the vein veto contains containsaltered Sibley Group fragments indicating its Proterozoic Proterozoic age. age. The Innes Innes Lake occurrence has no recognisable uranium minerals, although the shear zone recognisable uranium although the shear zoneis is much enriched in apatite, which is thought to to be the carrier of uranium. Hydrothermal be (he carrier uranium. Hydrothermalalteration alterationincluding .jndutfi chloritization, sericitizatton sericitizationand and hetnattization hematitizationisisdistinctive distinctiveabout aboutthe the.&ear shearzones. zones. 'The chloritization, The shear zone zone yielded yieldedvalues valuesas ashigh highas as633 633ppm ppmU308. U.4. (1978) also also described described minor minor uranium occurrences (up (up to 540 Franklin (1978) 540 ppm ppm U) U)in in the Enterprise Mine, one of aa group group of of vein-type vein-type deposits deposits known knownas asthe thelead-zinc-barite tead-zinc-bante veins. These veins. These are arediscussed discussedmore morefully fully in inthe thenext next section; section;however, however, both bothFranklin Franklin (1978) and and Yule Yule (1979) (1979) believed believed that that the the Greenwich Greenwich Lake Lake and and Innes lnnes Lake occurrences occurrences (1978) were formed by by the the same same process processthat that formed formedthe thesulfide-rich sulfide-richlead-zinc-barite lead-zinc-bariteveins. veins. Briefly, the the hypothesis favored is circulation of basinal brines through uranium-enriched circulation basinal brines through uranium-enriched and anomalous anomalous granitic granitic rocks. rocks. The source rocks, the uraniferous pegmatites and The brines brines circulated through faults marginal to the Sibley Group depositional basin and rose and and cooled in response to hydraulic gradients. cooled in response to hydraulic gradients. Lead-zinc-barite The lead-zinc-barite veins veins (Figure (Figure3) 3)are are near nearthe the margins margins of of the the present present outcrop outcrop of the Sibley Group or its inferred former former outcrop. outcrop. The Theveins veins were were studied studied in in detail detail by by who found them to Franklin & Mitchell (1977), who to contain contain galena, galena, sphalerite sphalerite and andbarite, barite, with minor chalcopyrite and marcasite in in quartz quartz and and calcite calcite gangue. gangue. The The veins occur occur in three settings: (A) (A) fractures fractures within within the the Sibley Sibley Group, (B) (B) fractures fracturesat at the theSibleySibleybasement unconformity and (C) fractures fractures within granitic basement. Franklin Franklin&&Mitchell Mitchell believed that the deposits formed by mixing of bacterially reduced H25 with metal-rich deposits formed by mixing of bacterially reduced H2Swith metal-rich derived by occurred in brines derived by leaching leaching of of the theSibley Sibley basinal basinalfill. fill. Deposition occurred in structural structural traps at or near near the the basin basin margin. The Thebasinal basinalcharacter character of of the the brines brineswas was confirmed confirmed in recent recent fluid inclusion studies by Haynes (1988). inclusion studies by Haynes (1988). The differentiation of structural settings by Franklin & Mitchell suggests that type (C) may 1C) mav be a portion oortion of of aa continuum continuumof of deposits depositsextending extendinato to the theuraniferous uraniferous occurrences at Greenwich Lake and lnnes~ake. Innes Lake. The The lead-zinc-barite lead-zinc-bariteveins represent occurrences whereas the the uranium occurrences are a sulfide-rich but uranium-poor end-member, whereas sulfide-poor but uranium-rich. The Thedifferential differential factor seems seems to to have have been been the the relative relative amount of interaction amount interaction with with basinal basinal fill (base metal metal source) or or granitic granitic basement basement (uranium source). 58 �PROTEROZOIC PROTEROZOIC ARCHEAN ARCHEAN Diabase k1 Diabase II...... Sibley SibleyGroup Group I I Anirnikie AnimikieGroup Group L1 A Pb-Zn—Barite Pb-Zn-Barite Granitic Granitic Rocks Rocks Metasedimenfary Metasedirnentary Gneissic Gneissic Rocks Rocks Metavolcanic Metavo'canic Rocks Rocks •ÂAmethyst Amethyst deposit deposit deposit deposit Figure Dorionarea areaillustrating illustrating the Figure 3. 3. The The Dorion the locations locations of of major major amethyst amethyst deposits deposits and and lead-zinclead-zincbarite star is barite veins. veins. The The star is the the location location of ofthe theThunder ThunderBay Bay Amethyst Amethyst Mine. Mine. 59 �Amethyst The The largest largest deposits deposits of of amethyst amethystin in North NorthAmerica America are are located locatedin inthe theThunder Thunder Bay Bay area area (Figure (Figure 3). Amethyst Amethyst isisthe theprovincial provincialgemstone gemstone of of Ontario Ontario and andisisaa significant the region. Nearly Nearlyall allthe the important important significant generator of economic activity in the deposits occur in a 10 km-long, east-west trending near the margin deposits occur in a 10 km-long, east-west trending near the marginofofthe theSibley Sibley Group outcrop and with Hilma Lake granite as the basement. A few other Group outcrop and with Hilma Lake A few otherscattered scattered occurrences occurrences are are spatially spatially related related to the the Sibley Sibley Group Group outcrop outcrop and andare areinvariably invariablyhosted hosted in in granite. granite. The The amethyst amethyst deposits deposits consist consist mostly mostlyof of quartz quartzincluding includingmuch muchofofthe thevariety variety amethyst with minor calcite, barite and sulfides such as pyrite, chalcopyrite and with minor calcite, barite and sulfides such as pyrite, chalcopyriteand bornite. The Thesimilar similargeologic geologicselling settingofofthese thesedeposits depositstotothat thatofofthe thelead-zinc-barite lead-zinc-barite veins suggests that they are cogenetic. cogenetic. Fluid Fluidinclusion inclusionstudies studies by by McArthur McArthur(1988), (1988), reported Kissin(1988), (I=),indicate indicate that that most most amethyst amethyst formed formednear nearthe the reportedin in McArthur McArthur &81Kissin surface at temperatures ranging ranging from from 60 60 to to 90 90 C. C. The deposits appear to be lowdeposits be lowtemperature temperature derivatives derivatives of lead-zinc-barite lead-zinc-bariteveins, poor poor in in sulfides sulfides and andricher richerininquartz. quartz. A crucial crucial factor factor appears appears to to have have been beenpassage passageof of the the quartz-depositing quartz-depositingsolutions solutions through granite. A through aa uranium uranium enriched host rock, e.g. e.g. the Hilma Lake granite. A source source of of silica silica (from (from sericitization sericitization of feldspar) and radioactivity are probable requirements for the the formation formation of amethyst. The Theformation formation of of the the electronic electronic colour colour center in in quartz quartz producing the blue of amethyst has been attributed to the coupled electronic producing the blue of amethyst has been coupled electronic transition: Fe3(substitutional)-+ Fe'(substitutional) + e Fe3(interstitial) + e-Fe2(interstitial) The Fe4*(substitutional) (substitutional) ++ Fe2 Fez*(interstitial) (interstitial) defect defect (Cohen (Cohen&&Hassan, Hassan, The associated associated Fe4 1974) is evidently unstable at high temperatures, as older generations as older generations ofof amethyst amethyst high were observed bebleached bleachedby byinflux influx of of holler hotterfluids. fluids. observed to to be REFERENCES REFERENCES Archibald, Archibald, D.L. D.L 1987: Granitoids Granitoiasand anaPegmatites Pegmatitesof of the thePine PinePortage PortageArea, Area, Northwestern NonnwesiernOntario; Ontario; Unpublished B.Sc. Thesis, Lakehead Unviersity, Thunder Bay, 89 p. Unpublished Lakehead 89 p. Coates, Coates, M.E. M.E. 1972: Geology Geology of of the the Black Black Sturgeon Sturgeon River River area, District District of Thunder Bay; Ontario Ontario Department of Mines Mines and and Northern NorthernAffiars, Affiars, Geological Geological Report Report 98, 98, 41 41 p. p. Cohen, A.J., A.J., and andHassan, Hassan,F. F. 1974: Ferrous Ferrous and and Ferric Ferric Ions Ionsin inSynthetic Synthetic a-Quartz a-Quartz and and Natural Natural Amethyst; American American Mineralogist, Volume Mineralogist, Volume 59, 59, p. p. 719-728. 719-728. 60 �Franklin, J.M. Franklin, J.M. 1978: Uranium in the the Nipigon Nipigon Area, Area, Thunder Thunder Bay Bay District, District, Ontario; Ontario; 1978: Uranium Mineralization Mineralization in Current Research, Part A, Geological Survey of Canada Paper 78-lA, p. 275275Current Research, Part A, Geological Survey of Canada Paper 78-1A, p. 282. 282. Franklin, J.M., J.M., and and Mitchell, Franklin, Mitchell, R.H. R.H. 1977: Lead-zinc-barite Veins of of the the Dorion Dorion Area, Area, Thunder Thunder Bay Bay District, District, Ontario; Ontario; 1977: Lead-zinc-barite Veins Canadian Journal of Earth Sciences, Volume 14, p. 1963-1979. Canadian Journal of Earth Sciences, Volume 14, p. 1963-1979. Haynes, F.M. Haynes, F.M. 1988: Fluid-inclusion in Archean Archean Basement, Basement, Thunder Thunder Bay Bay Fluid-inclusion Evidence of Basinal Brines in Pb-Zn-Ba District, District, Ontario, Ontario, Canada; Canada; Canadian Canadian Journal Journal of of Earth Pb-Zn-Ba Earth Sciences, Sciences, Volume 25, Volume 25, p. p. 1884-1894. 1884-1894. Kissin, S.A., S.A.,and andArchibald, Archibald, D.L. DL. Kissin, 1988: Genesis of Pegmatites in the Quetico Gneiss Belt of of Northwestern Ontario 1988: Pegmatites and Associated Granitoids of the Pine Portage Area; Area; Grant Grant 225, 225, p. p. 44Pegmatites and Associated Granitoids of the Pine Portage 13 Geoscience Research 13jn Geoscience Research Grant Program, Program, Summary Summary of of Research Research1987-1988, 1987-1988, edited by V.G. V.G. Milne, Ontario Ontario Geological Geological Survey, Miscellaneous Miscellaneous Paper 140, 251 p. P- Kissin, S.A.. S.A., and and Zayachivsky, Kissin. Zavachivskv. B. 6. 1985: Genesis Northwestern Ontario 1985: ~enesisof Pegmatites ~ k ~ m a t i t in e sthe Quetico Gneiss Belt of Northwestern Pegmatitesand andAssociated AssociatedGranitoids Granitoidsof ofthe the Georgia Georgia Lake Lake Rare-Element Pegmatites Pegmatite Field; Grant 225, p. 186-199 in Geoscience Research Grant Program, Pegmatite Field; Grant 225, p. Jn Geoscience Research Grant Program, Summary of Research 1984-1985, edited by V.G. Milne, Ontario Geological Research 1984-1985, edited by - V.G. Survey, Miscellaneous 246 p. ~iscellaneousPaper 127, 127,246 Kissin, S.A, S.A., Zayachivsky, Zayachivsky, B B., and Branscornbe, Branscombe, L.A. Kissin, ., and LA. of Northwestern Northwestern Ontario 1986: Genesis of Pegmatites in the Quetico Gneiss Belt of 'Barren' Pegmatites, Granitoids, "Barren" Pegmatites, and and Metasediments, Metasediments, with Additional Data on Rare-Element Pegmatites, Pegmatites,from from the the Georgia Georgia Lake Lake Pegmatite Pegmatite Field; Field; Grant Grant 225, 225, p. p. in Geoscience Research Grant Grant Program, Program, Summary of Research 198565-78 jn edited by by V.G. V.G. Milne, Ontario Geological Survey, Survey, Miscellaneous Paper 1986, edited 130, 235 p. 130,235 McArthur, J1 J. McAfthur, 1988: Fluid Fluid Inclusion Inclusion and and Stable Isotopic Isotopic Studies on Amethyst, Thunder Bay Amethyst Mine, Thunder Thunder Bay District, Ontario; Unpublished Unpublished B.Sc. Mine, B.Sc. Thesis, Lakehead Lakehead University, Thunder Bay, 108 108 p. McArthur, J., McArthur, J., and andKissin, Kissin, S.A. S.A. 1988: Stable Isotope, to the the 1988: Isotope, Fluid Fluid Inclusion, and Mineralogical Studies Relating to of Amethyst, Amethyst, Thunder Thunder Bay Bay Amethyst Amethyst Mine, Mine, Ontario, Ontario, Canada; Canada; p. p. A40 A40in hi Genesis of of America, America, October October 31-November 31-November 3, 3, Denver, Denver, Abstracts Abstracts with with Geological Society of Programs, Volume 20, 423 p. J.D., G.F. D.,Misuira, J .D., and and Brown, Brown, P.A. P.A. McCrank, G.F.D., 1981: Plutonic Rocks in Ontario; Geological 80-23, 171 p. p. 1981: Plutonic Rocks in Geological Survey of Canada, Paper 80-23, 61 �Pye, Pye, E.G E.G 1965: 1965: Georgia Georgia Lake Lake Area; Area; Ontario Ontario Department Department of of Mines, Mines, Geological Geological Report Report 31, 31,113 113 p. p. Scott Scoff, J. J. 1985: MacGregor Township, District District of of Thunder ThunderBay; Bay;p.p.67-70jn 67-70 j Summary MacGregor Township, Summary of of Field Field Work and Other Activities 1985, Ontario Geological Survey, edited by J. Wood, Wood, Work and Other Activities 1985,Ontario Geological Survey, edited by J. O.L. O.L. White, White, RB. R.B. Barlow, Barlow,and andA.C. A.C. Colvine, Colvine, Ontario OntarioGeological GeologicalSurvey, Survey, Miscellaneous Paper 351 p. 126,351 p. Miscellaneous Paper 126, Yule, GM. Yul e, G.R. 1979: 1979: Investigations Investigations of of the the Good Good Morning Morning Lake Lake Radioactive Radioactive Fault Fault Breccia: Breccia: Innes Innes Lake Lake Area, Dorion Township, Northwestern Ontario; Unpublished B.Sc. Thesis, Area, Dorion Township, Northwestern Ontario; Unpublished B.Sc. Thesis, Lakehead University, Thunder Bay, 93 p. p. Lakehead University, Thunder Bay, 93 Zayachivsky, B. B. Zavachivskv. 1985: Granitoids 1985: ~ r a n i o i d and sand Rare-Element Rare-Element Pegmatites Pegmatites of the Georgia Georgia Lake Lake Area, Area, Northwestern Ontario; Unpublished M.Sc. Thesis, Lakehead University, Northwestern Ontario:- Unoublished M.Sc. Thesis. Lakehead Universitv. Thunder Thunder . Bay, 234 p. Bay, 234 p. - Zayac/iivsky, 8.. 8., Kissin, and Branscombe, Kissin. S.A., S.A. and Branscornbe. L.A. LA. Zavachivskv. 1989: The Granitoid 1989: ~ h Georgia e ~ e &Lake Lake ~ i aPegmatite pegmatite Field, Field, Northwestern ~orthwesternOntario, Ontario, Part Part II. 11. Granitoid Rocks and their Relationship to Rare-Element Rare-Element Peamatites: Pegmatites;o. p.A20 A20in jj Geological Relationshio to Geoloaical Association of Canada and Mineralogical Association of Canada, May 15-17, Association of Canada and~ineralogical~ssociationof Canada, May15-17, Montreal, Joint Annual Meeting, Program with Abstracts, Volume Volume 14, 14, 135 135p. p. 62 �- Quetico Subprovince ( meto sediments paragneisses ) + Shebondowon Subprovince ( undivided ) Plutonic rocks Province 0 Figure 4. Figure 4. + Subprovince boundories stop locations Geology Superior region region showing numbered Geology oof f the t h e western western Lake Lake Superior showing numbered f i efield l d t rtrip i p stops. U ( 2 ) indicate i n d i c a t ethe t h elocations l o c a t i o nof s othe f t hGreenwich e GreenwichLake Lakeand and Innes Lake Lake U ( 1 )and and U(2) U(l) �*. FIELD TRIP LOG This field trip will attempt to illustrate as many of the features as as possible possible in in one one day. Unfortunately, some of the most interesting ones are the most inaccessible. inaccessible. The The trip route is illustrated in Figure 4, together with a simplified geological map. Stop 1: Southeast Southeast margin margin of of the the Mackenzie MacKenzi granite (Lakeshore Drive near Silver Harbour Drive near Silver Harbour Road). Road). In this location location the intrusive intrusive contact of the the Mackenzie MacKenziegranite granite with with Archean Archean can be seen. seen. The metavolcanic can The metavolcanics metavokxnics are are amphibolitic amphiboliiic near near the contact reflecting their contact metamorphism metamorphism to hornblende hornblende hornfels hornfels facies, fades, according according to Rogers (1979). South of Lakeshore Drive the granite is in fault contact to Rogers (1979). South of Lakeshore Drive the granite is in fault contact with with the Proterozoic Formation. A outcrop occurs Proterozoic Gunflint Formation. A small small Gunflint outcrop occurs on on the the north west of of the the granite granite co contact. The granite is jointed north side of Lakeshore Drive, west quartz-calcite vein is and in places places the joints have been been mineralized. AAsmall s amounts of base metal visible here, but other veins contain pyrite and small a sulfides. Small Smallveins veins of of amethyst amethyst also also occur occur ininthe thearea. are A short distance to the west and south toward Silver Harbour are a series of silver mines, which operated in the late 19th Century. From north to south these are the 3A, Beck or Silver Harbour and Algoma Mines. The shafts have been capped or sealed and most dump material has been removed in recent years. Little can be seen of these. These deposits were formed in Keweenawan times (Franklin 1986) and are unrelated to granitic rocks of the area. Stop 2: Main phase, Mackenzie granite (Highway 11-17 near Mackenzie River bridge). The massive and leucocratic character of the granite can be be seen seen here. (1979), the the color color index index is is always always5 s 5, making a making the granite g According to Rogers (1979), leucogranite. The The only only primary primarymafic mafic mineral mineral is is biotite biotite and and the the only only accessories accessories noted noted are traces of sphene and apatite. No Nomineral mineraloccurrences occurrencesare areassociated associated with this pluton pluton apart apart from from some some small small but but commercial commercial amethyst-bearing amethyst-bearingveins veins east of the the Mackenzie MacKenzieRiver. River. 64 �Stop S t o 3: ~ 3: Anderson occurrence (East Loon Road Anderson Lake Lake Molybdenum Molybdenum occurrence (East Loon Road from Highway 11-17. Continue 1.8 km to north Highway Continue 1.8 km to north side side of of Loon Loon Lake. Turn Turnright rightimmediately immediately past past bridge bridge over over small small stream. stream. Continue Continue about about 200 m m to Hydro Hydro transmission lines and clearing. clearing. Park Parkand and continue continue north north on on road road by by foot for about about 3 3 km km to to Anderson AndersonLake.) Lake.) The molybdenite occurrence described described in the introductory text was diamond drilled to the chaotic scene drilled and and blasted blasted at surface in the 1960's, giving rise to here. Good Goodspecimens specimensofofcoarse-grained coarse-grainedmolybdenite molybdeniteand andpegmatitic pegmatiticgranite granite host host rock rock may may be becollected. collected. Stop S t o 4: ~ 4: Thunder Bay Bay Amethyst Mine (back-track on on East East Loon Loon Road to junction with road road to to Thunder Thunder Bay Bay Amethyst Amethyst Mine. Mine. Turn right right and and continue continue for approximately 10 km to the Mine.) Mine.) Note: This m: Thisisisaacommercial commercialoperation operationentered entered by by - permission owner. There permission of the owner. There is to be be no no hammering hammerina nor collecting kollecting in in the the pit. pit. Collecting may be done done in in the the designated dump area, but material collected here is not to designated dump be broken by hammering. be broken by hammering. The The amethyst-bearing amethyst-bearing vein system occupies an an east-west east-west striking, near near vertical fault fault zone. The Thefault fault isisparallel parallel to to the the trend trend of occurrence occurrence of of other other amethyst amethyst deposits deposits in in the area area (Figure (Figure 3) and may form a major margin margin to the the Sibley Group depositional basin. The fault is offset by steps of a few meters by a Group The fault is series of northerly faults. The northerly striking en-echelon faults. The easterly easterly and and westerly limits of the the fault fault have have not notbeen beendetermined. determined. The The amethyst amethyst reaches reaches its its most most spectacular spectacular development development in in large large vugs vugs where where crustiform cm long long and and 10 10to to 15 15 crustiform aggregates aggregates contain contain crystals of quartz 30 to 40 cm cm cm in in diameter. diameter. The Thecrystals crystalsdisplay display growth growth zoning, zoning, which which is is consistent consistent throughout throughout the the deposit. deposit. The Theveins veinscontain containlittle little apart apart from from quartz, quartz, although although minute sulfide crystals occur in some growth zones. The Thealtered alteredgranite granite countryrock countryrock contains contains occasional occasionalaccumulations accumulations of pyrite, chalcopyrite, chalcopyrite, bornite bornite and other minor sulfides. The vein system is surrounded by a well-defined, and other minor sulfides. The vein system is surrounded by a well-defined, sericitized, sericitized, hydrothermal hydrothermalalteration alterationzone. zone. The The vuggy vuggy character character of of the the vein vein indicates indicates that it must have formed near the surface. surface. However, However,even evenmore moreconvincing convincingis is the the presence presence of breccia breccia fragments in in the the vein vein consisting consisting of of Sibley Sibley Group lithologies. The The Sibley Sibley Group Group has has been been entirely entirely removed removed from the area by erosion, but its its former presence presence is obvious. On On aa granite granite knob knob north northof of the the vein, vein, aa chloritized chloritized and and hematitic hematitic surface possibly may may represent representaaPrecambrian Precambrianpaleoregolith. paleoregolith. 65 �Stop 5: High-grade central portion of the Quetico Subprovince (Highway 11, east side of Lake Helen). In this this area, area, well well developed developed miamatites migmatites are indicative indicative of of the the highest In hiihest metamorphic grades attained in the Quetico Subprovince. Metamorphic metamorphic grades attained the QueticoSubprovince. ~e-morphicgrades grades decline rapidly rapidly to to the the north, decline north, and and much muchof of the the metasedimentary metasedimentary terrane terrane in inthe the Georgia Lakearea Lake area is is lower lower amphibolite amphibolite to to upper upper greenschist greenschist faci. fades. Georgia Stop 6: McVittie cutting the the Postagoni McViie Pegmatite Pegmatite cutting Postagoni Lake Lake sill silt (turn (turn off off Highway 11 at George Creek and continue from Highway 11 at George Creek and continue from approximately km to to well-defined clear cut cut on approximately 88 krn well-defined clear on west west side side of of road Lake. Park west on on foot foot for for road at at Postagoni Postagoni Lake. Park and and proceed proceedwest 1/2 km 112 kmto to north northside sideof of Dive Dive Lake Laketo to McVittie McViie pegmatite.) pegmatite.) The McVittie is a a north 10m mwide, wide, The McVittie Pegmatite Pegmatite is north striking striking vertical vertical dike dike approximately approximately10 which cuts the east-west striking tonalites of the Postagoni Lake sill. The which cuts the east-west striking tonalites of the Postagoni Lake sill. The pegmatite is is typical typical of of the the north pegmatite north group group pegmatites pegmatiies of of the the Georgia GeorgiaLake Lakearea areain i that that itit is is unzoned unzonedand and contains containsno norare-element-bearing rare-element-bearingminerals minerals other other than than spodumene. The spodumene. Thespodumene spodumeneisistypical typicalphenocrystic phenocrysticspodumene spodumenacontaining containing several percent iron and forming euhedral, prismatic crystals up to several percent iron forming euhedral, prismatic crystals up to 10 10cm cmlong. long. The spodumene appears greenish owing to its iron content and partial The spodumene appears greenish owing to its iron content and partial decomposition to decomposition to chlorite chloriteand andsericite. sericite. REFERENCES REFERENCES Franklin, JJ.M., .M., Kissin, LA., S.A., Smyk, Smyk, M.C., M.C., and andScott, Scott, S.D. S.D. 1986: Silver Deposits Associated with the Proterozoic Rocks of the Thunder Bay District, Ontario; Canadian Journal of Earth Earth Sciences, Volume 23, p. p. 1576-1591. 1576-1591. Rogers, J.A. 1979: The Southeastern Margin of the Mackenzie Granite, Northwestern Ontario; Unpublished B.Sc. Thesis, Lakehead University, Thunder Bay, 68 p. 66 �FIELD TRIP 4 �METAL MINERALIZATION MINERALIZATION BASE METAL IN TTHE HE SHEBANDOWAN GREENSTONE BELT Introductory Discussion and Field Guide 36th Annual. Institute on Lake Superior Geology Thunder Bay, Ontario by Maurice J.Lavigne Jr. Jr. Development and and Mines Mines Ontario Ministry of Northern Development Thunder Bay, Ontario Aubut A.J.Aubut. A. J . Technical Services Services Inc. Inc. Inco Exploration and Technical Thunder Bay, Ontario John Scott Scott rio Ministry Ministry of of Northern Northern Development Development and and Mines Mines Ontario Thunder Bay, Ontario 67 �INTRODUCTION Mineral deposits deposits of of the the Shebandowan Shebandowan greenstone greenstone belt belt bring bring about an an extra extra degree of controversy controversywith withrespect respectto to their their about degree of origins as the origins as the result result of the destruction of prerequisite prerequisite diagnostic textures textures and diagnostic and relationships relationships by by intense intense deformation. This is deformation. is especially true true for for deposits deposits which which as synvolcanic LD2date deformation, ::-idate deformation, such such as synvolcanic mineralization. mineralization. Althoughunintended, unintended, thisfield fieldtrip triphighlights highlightsthe the trial trial Although this nd tribulations toto "pigeon hole" highly and tribulationsofoftrying trying "pigeon hole" highlydeformed deforced mineralization. Three styles r!ineralization. styles of of base base metal metal mineralization mineralization will will be examined during the the cdurse course of this this trip, trip, and and all all are are proposed candidates candidates for for synvolcanic synvolcanic origins. origins. Allan Aubut will be presenting arguments arguments which which favour favour that that the the Shebandowan nickel-copper nickel-copper mine mine is is komatiite konatiite flow flow hosted, hosted, te., Kambalda ie., Kambalda type. type. The other authors authors will bring forth forth arguments that the North Coldstrean Coldstream Mine is is the the stringer stringer zone of a I<uroko type, volcanogenic, volcanogenic, pclymetallic polymetallic sulphide sulphide Kuroko type, zcne deposit and that the Vanguard prospect is is the the exhallative exhallative component component of of such such aa deposit. deposit. 68 �KILOMETERS 5 HWY 11 ó I 5 I 10 15 I 20 u.s.L CANADA r 25 30 SUPERIOR 0 HWY 527 �STOP 1; SHEBANDOWAN MINE INTRODUCTION The The Shebandowan Shebandowan Mine Mine is is aa nickel-copper nickel-copper deposit deposit owned owned by by Inca Inco Limited Linited and is is presently presently being being operated operated by by MacIsaac MacIsaac Explorations. Explorations. It It is is located located in in northwestern northwestern Ontario, Ontario, 75 75 kilometres of Thunder Bay. The mine kilorne*'.reswest—northwest west-northwest of Thunder Bay. nine is is situated south—western of of Lower Shebandowan situatedononthe the south-westernshore shore Lower Shebandowan '~ .~. Lake (Fig. 1). 1). It It has has been in production since since 1972 1972 at a an in semi-continuous sani-contin~iousproduction an average average production production rate rate of of about about 2000 2000 tons tons per per day. day. Presently Presently reserves reserves of of broken broken and and developed developed material material stand stand at at approximately million tons grading approximately .2 2 nillion grading 2.10 2.10 per per cent cent nickel nickel and 0.95 per per cent c-snt copper. copper. Accessory Accessory platinum platinum group group metals metals and 0.95 and and gold gold are are also also recovered. recovered. Concentrate Concentrate produced produced is is shipped shipped by by truck truck to to Sudbury, Sudbury, Ontario, Ontario, for for smelting smelting and and refining. refining. The The Shebandowan Shebandcwan Mine line has has had had aa iony long history history with with nickel— nickelcopper s p p e r suiphide sulphide mineralization '"uneralizaticn being being first first discovered discovered in in 1913 1913 at at what what is is now now Discovery Discovery Point, Point, on on Lake Lake Shebandowan Shebandowan (just (just east east of of stop stop2, 2 , Fig Fig 1). 1). The The International International Nickel Sickel Company of Canada, Canada, now now Inco Inco Limited, L i r u t a d , optioned optioned the the property property Ccmpany of in in 1936. 1936. The The property property was was purchased purchased for for $250,000 $250,000 in in 1937 1937 (Daily (Daily Times Tines Journal, Journal, 1937). 1937). moo Incoexplored exploredthe theproperty property off off and 28 years. years. Between Between 1965 1965 and and 1968 1968 and on on for for the the next next 28 exploration exploration was was intensified intensified with faiththe the collaring collaring of of an an exploration 1966. AA production production decision decision was was exploration shaft shaft in in 1966. announced in 1968 and the first shipment of ooncentrate was was r.tade in 1972. 70 �iç t9i 'Ca C,' Mafic Volcanics Felsic Volcanics Ultramafics Tim iskaning Sediments Timiskaming Volconics Felsic Intrusives I PC KM 2 — General Geology Shebandowan Mine Area General Geology of ASTOCL SHEBANDO WAN LAKE 4 �REGIONAL GEOLOGY The ?ha area area in in the the vicinity vicinity of of the the Shebandowan Shebandowan Mine Mine (Fig. (Fig. 2) 2) is is underlain tholeiitic volcanics volcanics unconforraably unconfornably underlain by by ricewatin Keewatin tholeiitic overlain by Timiskaning Tiniskaming type type sediments sediments and and calc-alkaline cab-alkaline volcanics. volcanics, This This unconformity unconformity is truncation of of is indicated indicated by by aa truncation Keewatin axialsurface surfacetrends, trends,the the dissimilarity dissir.ilarity in Iiriewatin axial in chemistry chemistry (tholeiitic (tholeiitic versus calc—alkaline) calc-alkaline) and and the the presence presence of jasper jasper from from Reewatin Keewatin banded iron iron formation, formation, as as clasts clasts within conglomerates 'ifchin Tiniskaminy Tiniskanin~-) conglomerates (Borradaile (Borradaile and Brown, Brown 1087; Sheyelski, Shegelski, 1930) 1930). 1937; -. MINE MIXE GEOLOGY GEOLOGY the thethe Shebandowan the vicinity vicinityofof ShebandowanMine Mine the thegeology geology cart can be be divided divided into intotwo two domains domains separated separated by by the theCrayfish CrayfishCreek Creek Fault, Fault, a regional reyional dextral dextral transcurrent transcurrent fault. fault. To To the the south south In In of the thz fault fault the the rocks rocks are are predominantly predominantly tholeiitic tholeiitic basalts, basalts, andesites andesites and some some felsic felsic pyroclastios pyroclastics (Figs. (Figs. 22 and and 3). 3). Intercalated Intercalated with these these are are several several peridotite peridotite bodies bodies :. believed to to be komatiite komatiite flows flows (Morton, (lorton, 1982). 1982). These These ultranafics ultranafics are are now now either either serpentinite serpentinite or or talc—carbonate talc-carbonate schist. overlain, in close proximity schist. All All are are uriconfornably unconforiaably overlain, 1n close proximity to to the the fault, fault, by by Timiskaming Timiskaning volcanic volcanic breccia. breccia. .,. -' , To To the the north north of of the the fault fault aa thin thin wedge wedge of of intercalated intercalated nafic mafic volcani.cs and and ultranafics ultramafics is is present present between between the the fault fault and and volcanics 'jranitic granitic rocks Lake Stock. Stock. Within Within this rocks of of the theShebandowan Shebandowan Lake this wedge appear to to be be two distinct volcanic wedge are are what what appear twc distinct volcanic cycles cycles characterized characterized by by intercalated nafic mafic flows flows and and ultramafics. ultramafics. intercalated The northern northern cycle cycle includes includes the the ultramafic ultramafic unit unit that that hosts hosts The the the Shebandowan Shebandowan nickel nickel copper copper deposit deposit while while the the southern southern cycle ultramafic unit unit that cycle includes includes an an ultranafic that hosts hosts chronite chronite mineralization mineralization (Figs. (Figs. 3 3 and and 4). 4 ) . The The relationship relationshipbetween betwe the nafic mafic-vobcanics volconics and and the the ultramafics ultranafics is isunclear unclear due due to to widespread deformation with the theCrayfish Crayf widespread deformation associated associated with Creek Fault deformation nation zone. zone. -, 'b �xx xxx x xxxxxx xx xxx x xx xxx xx -- x x x x x x x —4 F'elsic Intrusives . Timiskaming Timiskaming l!1 8;::- n'#.8;: 1-:sl, Volcanics Volcanics Ultramafics 1000 Level Plan .,.".. .... ". ."."". Volcanics ....., Mafic Votcanics Metres Figure Figure 3: 3: Mine Shebandowan Mine 1000' Level Plan —- Shebandowan 1000' �N ;IN INN' Felsic I x NI IN IN'. Intrusives 4N N N 'C iN> 1N x :::::::t:;:sN N LC1 Timiskaming N I'Tr11 Volcanics 1NNNNNN YZZt NN N N N Ultramafics :;;;:::1NN)CNN Mafic "jN 'C :ij 9 lcanics L,C N NN N N (N N N N NN N NN N JN I Ni-Cu I Suiphides N N N IN NNx 7W N 1N1 • Chromite Mineralization "''r'"L f"jN I 1"" (N N .'JN JN N 2 Ci N 'C IN N N NN N FN N JNL N :::;:;;;;:i NN "IN N 4."jN N N IN' 1' N 0 I' N N Nx I'CI /NJ 1I N r Nj -'iixN N N 48::':;:;ix jf N 'C • N N x N 'C N ':JxL:;;;:::1 hS"''*'# ..tNNNC' M""' J /NJ ::1N C j Nf r 50 Metres £NNNNN, 2NNTS%N * 25 r fy NN £;:;;I N :::IN a N :::::.J 'Ci 'C I N N jN .'—;;;;:;::'J N tt IN 25000 E Section hebandowan Figure 4: 25000E Section Shebandowan Mine 74 Mine �STRECTUPAL STRUCTURALGEOLOGY GEOLOG The The main main structural structural feature feature of of the the Shebandowan Shebandowan Mine Mine is is the the Crayfish Crayfish Creek Creek Fault. Fault. This This major major dextral dextral transcurrent transcurrent fault fault dips dips steeply steeply to to the the south. south. Though Though aa distinct distinct fault fault breccia breccia a wide zone zone zone up to to several several metres metres thick thick is is present present a wide zone of of deformation deformation characterized characterized by by extensive extensive shearing shearing is is present. present. To th fault To the the south south of the fault much much of of the the deformation deformation is is hosted hosted by by the the Timiskaning Timiskaning volcanic volcanic breccia breccia resulting resulting in in aa highly highly possessing foliated f a t e d quartz quartz sericite sericiteschist schist possessingremnant remnant breccia breccia ,. , fragments ~. ~ , . fragments and and relict relict hornblende-phyric hornblende-phyric texture. texture. ~ ",*.::<,: . . ... ., . North North of of the the fault fault shearing shearing is is' not not as as pervasive, pervasive, likely likely due due to to the the more more incompetent incompetent nature nature of of the the ultramafic—mafic ultramafic-mafic contacts contacts and and the the ultramafics ultranafics themselves. themselves. This This resulted resulted in in deformation deformation being being focused focused into into numerous numerous narrow narrow shear shear zones, zones, commonly commonly concentrated concentrated along along contacts contacts with with dextral dextral transposition transposition of of slices. slices. This This tectonic tectonic reworking reworking has has had had aa major major effect effect on on the the nickel—copper nickel-copper mineralization mineralization Producing producing significant significant sulphide sulphide movement. The The sulphide sulphide zones zones show show .. numerous nunerouy signs signs of this this remobilization remobilization such such as: as: disseminated disseminated zones zones occurring occurring above, above, below below and and in in blocks blocks within withinmassive riassivn suTphide zones; as between semi— sulphide zones; as sharp sharpcontacts contacts betweenmassive massiveorcr semimassive riassive ore ore and and disseminated disseminated sulphide sulphide bearing bearing ultranafic; ultranafic; the presence of pentiandite banding within the massive sulphides. sulphides. ~- and and the presence of pentlandite banding within the massive ~ .~, .!: .".~ Another Another factor factor that has has greatly greatly added added to to the the complexity complexity of of deposit is the presence of numerous apophyses of the the the deposit is the presence of numerous apophyses of the Shebandowan Shebandowan Lake Lake Stock. Stock. These These frequently frequently follow follow along along contacts, contacts, shears shears and sulphide sulphide zones zones as as well as as crcss—cuttiny cross-cutting these these features. features. This This has made interpretation interpretation of of stratigraphy stratigraphy in in the the mine environment environment very v e r y difficult difficult as as well as as producing producing dilution dilution problems problems in in the the ore. ore. 75 �MINERALI ZATIOX 'Â¥1iSERALIZATIO A) A) Sickel-Copper Xickel-Copper The Mine hosts threemain main typesofofore: ore: stringer stringer The Shebandowan Shebandowan Mine hosts three types suiphides, breccia sulphides, brecciasulphides sulphidesand andmassive nassive suiphides. sulphides.Though Though disseminated suiphides are are present economic disseminated sulphides present they they are arenot notofof economic rnortance q ~ortance. The st'ilnger suiphides are confined to nineralized Th? Â¥itcinge sulphides are confined to caineralized shear shear zcnes. Sulphides Suiphides present include chalcopyrite, zones. chalcopyrite, pyrite and ninor ninor pyrrhotite pyrrhotite and and pentlandite. pentlandi'te. Breccia suiphides sulphides consist consist of of fragments fragments of of ultramafic, ultramafic, volcanic volcanic and and granite g,raniteset set in in aa matrix matrix of of pyrrhotite, pyrrhotite, chalcopyrite and pentlandite. Frequently Frequently chalcopyrite chalcopyrite coats coats many of of the the inclusions inclusions within within the the breccia breccia suiphide. sulphide. Chalcopyrite is also commonly concentrated along the the margins margins of ,sf the tha breccia breccia zones. zones. Massive Massive sulphide sulphide is is composed composed of of pyrrhotite, pyrrhotite, chalcopyritze chalcopyrite and and entIandite. pentlandite. The The latter latter is is usually usually present present as as discontinuous discontinuous layers that are generally generally parallel parallel to to the the ore ore zone zone contacts. contacts. These These layers layers also also wrap wrap around around large large inclusions. inclusions.:.. .:. . ' s..,. The average copper to copper-nickel ratio ratio is is 0.36 0.36 with it it being being higher, higher, or or more copper copper rich, rich, in in the the western western portions portions of the nine mine and lower, lower, or more nickel rich, rich, in in the the eastern eastern portions portions of of the the mine. This This variation variation in in copper-nickel copper-nickel ratio ratio corresponds to to the higher proportion of the the more chalcopyrite rich breccia sulphide sulphide in in the the western part of of the the ore ore body. bodv. 76 �B) Chromite Chromite Uneconomic chromite mineralization is is also present in in the the Shebandowan Mine Mihe environment. This chromite is is hosted by ultramafics within the second volcanic cycle, close close to to the the Crayfish Creek Fault. Chromite is present as finely finely disseminated grains in all the ultramafics disseninated ultraraafics in in the the area area (Morton, (Morton, 1982). 1922). The second nafic volcanic—ultramafic volcanic-ultramafic cycle cycle hosts chronitite chromitite ' . (chronite rock) as massive to strongly (chronite strongly contorted contorted bands bands . . millimetres to varying from from a few millilietres to several several metres metres in in thickness. On either side of this nain main zone thickness. zone chromite is is found as brecciated chromitite chromitite and and chromitiferous chromitiferous peridotite. Chrornitite mineralization has has been been traced . .,, peridotite. chromitite mineralization discontinuously along strike for a distance of about 33 kilonetres. kilometres. Chromium trioxide trioxj.de assays have been reported as high as as 44 44 per cent but are typically much lower. lower. Minor platinum platinum group group metals cietals are associated with the the chromite. chrrmite. The The chrome—iron chrome-iron ratio varies from from 1.2 To 1.8 1.8 although although it it rarely rarely exceeds exceeds 1.6. 1.6. GENESIS OF THE NICKEL-COPPER ORE SICKEL-C The ore body has been subjected subjected to to intense intense structural structural deformation which has resulted in the remobilization defor~ation remobilization of nickel—copper nickel-copper sulphides. Primary textures have been obscured obscured if not erased. Regardless, Regardless, away from the Crayfish Creek Fault Deformation Zone there is evidence that many if if not all of of these these ultramafics ultramafics are are komatiites. komatiites. konatiite a komatiite is defined simply sinply as being an an ultranafic ultranafic volcanic rock with 18 18";or or greater greater MgO >I90(Arndt (Arndtand and Brooks, Brooks, 1980). These high magnesian raagnesian flows flows have have aa number number of of physical physical . 77 �characteristics characteristics which can can he be used used to to identify identify then. then. AA conclusive conclusive feature feature of komatiite komatiite flows flows is is the the presence presence of of aa relatively relatively thin thin layer layer with with spinifex spinifex texture. texture. According According to to Arndt Arndt et et ai. a:. (1979) (1979) most ultramafic flows flows are are not not spinifex spinifex textured textured but but massive massive with with polyhedral polyhedral jointing. jointing. These These Polyhedra polyhedra are are coarse coarse in in the the centre centre of of the the flow flow and and become become finer finer as as the the contacts contacts are are approached. approached. It It is is this this polyhedral polyhedral jointing that is common commcn in many of the ultramafic ultranafic bodies bodies at at S1banJowan. Sh.=banJowii. Another Another common common feature feature at at Shebandowan Shebandowan is is the the presence presence of of chemical c5umical sediments, sediments, as as both both handed banded cherty cherty iron iron formation formation and and chert, immediately c'l':~rt, innediately overlying overlying the the ultramafics ultramafics (Morton, (Morton, 1982). 1982). This This feature feature implies inplies that that when when the the sediments sediments were were deposited deposited the the ultramafics ultranafic,~must have have been been present present as as flows flows on on the the ocean ocean floor. floor. The The Shebandowan Shebandowan Mine Mine ore ore body body shows shows aa lot lot of of physical physical similarities similarities with the the komatiite konatiite hosted hosted Redross Redross deposit, deposit, in in the Kambaida region region of of Australia. The The Bedross Redross deposit deposit is is the Eanbalda located located 58 33 kilometres kilometres south qouth of of Falgoorlie. Kalgoorlie. It It has has been been affected affected by by regional regional dynamic dynamic metamorphism metanorphism with with faulting faulting and and shearing, shearing, primarily primarily along along the the footwall fcctwali contact contact between between the the sulphide sulphide bearing bearing komatiite komatiite flow flow and and nafic mafic volcanics volcanics (Barrett (Barrett et et al, al, 1977). 1977). The The sulphides sulphides have have undergone undergone major major remobilization remobilization along along the the footwall footwall contact contact and and shear shear zones. zones. AA major major ore ore type type consists consists of of brecciated brecciated wall wall rocks rocks cemented cenented by by sulphides. sulphides. Contacts Contacts between between massive nassive or or semi—massive semi-massive ore ore and and disseminated disseminated ore ore are are commonly conxcnly very very sharp sharp with with none none of of the the intervening intervening matrix matrix ore ore associated associated with with other other Ranbalda Kambalda deposits deposits (ibid.). (ibid.). The The ore ore zones zones at at Redross Redross possess possess structures structures and and textures textures remobilization of of both both disseminated disserainatad and and more more produced by by renobili:ation produced massive nassive mineralization mineralization (ibid.). (ibid.). 78 �Shehandowan Mine .\L the the Shebandowan At Mine the the same sane chaeacteristics characteristics exist exist an affinity affinity of of sulphide mineralization for including an including sulphide mineralization for one one side of of the It is therefore suggested side the ultramafic ultraraafic body. body. It is therefore suggested that that the h e Shebandowan nickel-copper deposit is is the product of of dynamic netamorphisn metamorphism of a sulphide bearing komatiite konatiite flaw flow with with remobilization remobilization and and subsequent subsequent redeposition redeposition of of the the sulphides in sulphides in low low strain strain areas. areas. FIELD TRIP FIELD TRIP STOPS STOPS 5 1; Shebandowan Mine Headframe, Headframe, Fig. Fig. 5 STOP 1; At this stop stop we will examine strongly strongly deformed Timiskaming Timiskaming cab—alkaline volcani& calc-alkaline volcanic breccia breccia as as well well as as the the ultranafic ultranafic unit hosting the Shebandowan Shebandowan nickel—copper nickel-copper deposit. deposit. The Main structural feature at the Shebandowan Mine is is the the Creek Fault. South of the fault Tiniskanirg Tiniskaning Crayfish Creak volcanics have been strongly deformed deforned and are now now quartz— quartzsericite 5ericite schist with possessing relic textures. North of of the the deornation has fault fault deformation has not not been been as as focused into narrow narrow shear shear zones separating lenses of serpentinized peridotite. This This deformation has resulted in the remobilization remobilization of the the Ni-Cu Xi-Cu sulphides and subsequent deposition in in lower lower strain strain areas areas within the the host host ultranafic. ultramafic. STOP 1A. STOP 1A. This outcrop outcrop consists of strongly strongly deformed deforned hornblende hornblende phyric phyric Tiniskaming type volcanic breccia. Note the the highly highly foliated foliated Fault, nature reflecting its proximity to the Crayfish Creek Fault, approximately 100 100 metres to the the north. Though Though strongly stronaly foliated note the many similarities with the undeformed Tiniskaming long the Tiniskaming volcanic volcanic breccias breccias seen seen to to the the east east ealong the road leading to Shehandowan road leading tothe the Shebandowan Mine. Mine. 79 �Co C Mat Ic Volcanics Felsic Volcanics Iiitrarnafics Figure 5: Timiskaming Volcanics Felsic Intrusives Ta Metres tOO Stop 200 Shebandowon Mine Ore mat ics hosting Shebondowiru jC Lake Stock intruding Ultra- Ia) Apophyses of Shebandowon Production Shaft Stop 1 - Shebandowan Mine 0 Lake She bando wan �STOP 13. STOP IB. This consists of This outcrop, outcrop, beside beside the the #2 ? 2 Shaft Shaft headfrarne, headframe, consists of serpentinized peridctite peridotite with numerous narrow zones zones of talc— talc- carbonate schist that form torn an anastomosing anastonosing network. network. It It is is this unit that is host to the nickel-copper sulphides. sulphides. Note Note on or. the north side of the outcrop a feldspar feldspar porphyry dyke, dyke, of the LakeStock, Stock, cutting cubuing across across anapcphysis an apophysis of theShebandowan Shebandowan Lake the 2eridotite. the peridotite. STOP Fig. 66 2, Fig. STOP 2, w-nw,,fofStop Stop11is is aa narrow unit of Approximate1y 3 km w-nw Approximately narrow unit of serpentinized serpentinized peridotite hosting Ni-Cu Xi-Cu suiphides sulphides hosted hosted by by banded mafic volcanics. These rock rock units units are are exposed exposed in in aa small trench on the side of a hill, hill, approximately 75 75 metres met.res north of the Crayfish Creek Fault. Points Points of interest interest at at this outcrop are: the banding within the t-he nafEc mafic volcanics, volcanics, ultramafic and the breccia sulphides. The the thin wedge of ultranafic latter consist cf of numerous nafic to ultranafic volcanic fragments cemented by pyrrhotite, chaicopyrite chalcopyrite and pentlandite. This suiphide pentlandit?. sulphide zone zone averages 1.88% 1.88% Ni Xi and and 1.61% 1.61% Cu. Note Mote the porphyry dyke, an apophysis apophysis of the the Shebandowan Shebandowan Lake Stock, Stock, intruding intruding the the sulphides. sulphides. STOP STOP 3, 3, Fig. Fig. 77 4.5 Km tv—sw of the the Shebandowan Shebandowan mine mine headfrane headfrane is a typical w-sw of exposure of of ultranafic ultranafic rock, rock, common common in in the the area, area, exposure interdigitated with felsic volcanic fragmentals, fragnentals, nafic volcanics and With the and and and intruded intruded by by aa felsic felsic dyke. dyke. Kith the exception of of portions portions of of the the ultrarnafic ultramafic rock and the dyke, dyke, exception the entire outcrop is is strongly strongly foliated foliated to to schistose. schistose. Well developed developed mineral aggregate lineations lineations and and clast clast elongations elongations are are vertical. vertical. Stratigraphic tops are to the south, south, as �N-) o 1.88% Ni 5 Figure 6: Metres 2.5 1.61 %Cu Stop 2 — Trench IflOOE Stop 2 Maf Ic Volcanics Shebandowan Mine '-C, Ultramafics Breccia Suiphides Felsic Intrusives Trench 15200E — Shebandowan Mine c x lxxx x Fx �Figure 7: Stop 3 - meters (approximate) Otto Lake Rd. xtize -. - 1 tuft, agrnerate Strongly sheared PYROCLASTIC Lap [.:.YC:1Oc1ASTC itzaN PORPHYRY '7J1 QUARTZ-FELDSPAR to potysutwed UJRAMAFC �interpreted i a t e r ~ r e t from dfron the t h e occurrence o c c u r r e n c 3 oof f black black chert c h e r t fragments f r a g n e n t s in in the metresoof t!>e lower l o w e r few few metres f t the h e Efelsic e l s i c fragmental f r a ~ n e n t a laatt site s i t eA?A on on Fig. 7. These clast are interpreted to have been derived from an underlying chert bed, exposed at site on Fig. 7. The margins of the ultrarnafics are schistose, and more often than not, covered. The relationship with the enclosing felsic volcanic rocks is therefore unclear. The ondeformed ::ndeformed interior i n t e r i o r of o f the t h e ultranafic u l t r a m f i c is is fine f i n e grain, g r a i n , and am3 has has polyhedral p:-;iybedral jointing. j o i n t i n 5 . .It I t can c a n be b e argued a r g u e d that that these t h e s e two two textural t e x t u r a l observations o i i s e r v a t i o n s support s u p p o r t an a n extrusive e x t r u s i v e origin o r i g i n for f o r this this unit, u a i t , although a l t h o u g h they t h e y could could common c m m o n juxtapcsit4on j u x t a p c s i t ; a n with with be b e considered c o n s i d e r e d equivocal, e q u i v o c a l . the The chemical a l s o lends l e n d s some some c h e m i c a l sediments s e d i n e n t s also support s u p p o r t to t o an a n extrusive e x t r u s i v e origin. o r i g i n . Definitive D e f i n ~ t i v eflow f l o w features feature8 such a s spinnifex s p i n n i f e h and a n d flow f l o w top t o p breccia breccia have h a v e not n o t been been 5uch as observed o b s e r v e d in i n th th,eultranafic u l t r a m a f i c rocks r ~ c k in si n this t h i 3 area. a r e a . The The positive positive identification i d e n t i f i c a t i o n of flow rocks r o c k s in in the t h e area area would would o f ultramafic u l t r a m a f i c flow support % u p p o r t the t h e contention c o n t e n t ~ o nthat t h a t the t h e Shehandowan Shebandcwan Mine X i n e is i s aa Rambalda I < x ~ b a l d atype t y p e nickel n i c k e l deposit d e p o s i t since s i n c e the t h e host h o s t rock r u c k at at the t h e nine nine has textures destoyed by shearing. 2s had h a d its i t s primary pr STOP 4; .'orth Ccldstream Mine, Burchell Lake INTRODUCTION 2liTRODECTIOX Copper C o p p e r mineralization m i n e r a l i z a t i o n was was discovered d i s c o v e r e d on on the t h e north n o r t h side s i d e of of Burchell B u r c h e l l Lake Lake in i n 1872. 1 8 7 2 . Copper C o p p e r was was produced p r o d u c e d in i n 1903, 1 9 0 3 , 1906, 1906, 1916—17, t o t a l of o f 102 1 0 2 000 000 000 000 1916-17, 1957—58 1957-58 and a n d 1960—67 1960-67 for f a r aa total pounds. pcunds. Most Most of o f this t h i s production p r o d u c t i c m occurred a c c u r r e d fran f r o m 1960 1 9 6 0 to t o 1967 1967 when %"he>the t h : e mine n i n e was w a s operated o p e r a t e d by by Noranda Xoranda at a t aa capacity c a p a c i t y of o f 1000 I000 tons w a s producing p r o d u c i n g 14 14 000 000 000 000 pounds 'aunds of o f copper capper t a n s per p e r day d a y and a n d was annually. m i l 1 produced p r o d u c e d concentrate c m c e n t r a t e containing c o n t a i n i n g 26¾ 26% a n n u a l l y . The The mill copper, c o p p e r , 2.65 2 - 6 5 o.p.t. c - p - t . silver silver and a n d 0.09 0 . 0 9 o.p.t. c.$.t.. gold. g o l d * The The ore ope contained c a n t a i n e d 2¾ ?%,copper, c o p p e r , 0.012 0.012 o.p.t 0 . p . t gold g o l d and 0.22 0 . 2 2 o.p,t. ~~.p.t, silver. silver. The closed as the result of depleted The mined n reserves. 84 �REGIONAL GEOLOGY The ?he North Xorth Coldstream Coldstream Mine Nine is is located located in in the the western western portion portion of :>f the t . 1 ~Shebandowan Shebandowan greenstone greenstone belt. belt. Stratigraphic Stratigraphic and and structural structural trends trends are are northeasterly. northeasterly. Outcrops Outcrops have have well well developed developed foliation fgliation and and are are often often schistose. sc!~istose. According According to to Stott Stott and and Schwerdtner, Scl-.werdtner. 1981, 1981, deformation deforxation in in this this area area was as dominated dcminated by by sinistral sinistral shear. shear. The The nine nine is is on on the the souanwestern linh s~>uci~western i i ~ of b of an an anticline anticline with witn an an axial axial plane plane striking striI<ing northeast northeast (Fig. (Fig. 2) 8 ) . The ?ha? anticline 2nticl ine is is cored c<>redwith with felsic felsic volcanics volcanics which which are are overlain overlain by by nafic nafic volcanics. volcanics. At .At aa regional regional scale, sca.le,the the mine mine is is at at-this this contact, contact, with wit-hfeisic felsic volcanics volcanics as as stratigraphic stratigraphic footwall footwall and and mafic mafic volcanics volcanics as as hangingwall. hangingwall. Along Along its its entire entire length, length, this this mafic—felsic mafic-felsic volcanic olcanic contact contact is is aa 11 km km wide wide schist schistzone. zone. At At the the ninesite, inesite, this this contact contact was was intruded intruded by by aa gabbroic gabbroic stock stock which hich is is the the immediate immediate footwali £ootwal to to the the nine. nine. Foliation Foliation orientation minesite shows shows aa departure departure from from the the rientation at at the the minesite regional regional orientation, orientation, in in that that it it consist consist of of an an enclave enclave of of east ast trending trending foliation, foliation, with with dextral dextral kinematic kinenatic indicators. indicators. Wether ether or :>r not not this this foliation faliation orientation orientati~nis is independent independent of of elsic plutons, plutons, both both to to the the north north and and south south of of the the nine mine is is feisic as Of yet undetermined. MINE GEOLOGY Copper C ~ p p e mineralization rmineralizationat atthe theNorth SorthColdstream Coldstream>line >line consist consist of lenses with with aa high high density density network network of of chalcopyrite chalcopyrite and and >f lenses pyrite yrite veinlets veinlets (stringers). (stringers). Some Sone massive massive and and disseminated disseminated ineralization also also exist. exist. As As seen seen on on the the 500 5 0 0 foot footlevel level mineralization plan (Fig. (Fig.9), 9), cross-section cross-section geometry geometry of of these these lenses lenses is is plan ariable, with with maximum maximum horizontal horizontal dimensions dimensions of of 200 200 by by 200 200 variable, feet. eet. The The greatest greatest dimension dimension of of these these ore ore lenses lenses (plunge) ($lunge) is is oriented oriented at at 50 50 degrees degrees to to the theeast. east. Giblin, Giblin, (1964) (1964) reported reported three three types types of I>Âcoarse caarse grain graic veins veins which which crosscut crosscut the the orebodies. crebodies. The The most nost common conmon type type of cf vein vein consist r2onsist of of 85 �Figure 8: Geology Western Shebandowan Volcanic Belt 86 �quartz, carbonate, pyrite and chalcopyrite. Carbonate veinlets constitute the second commonest type. Relatively rare are veins rare a re v e i n s cconsisting o n s i s t i n g of o f quartz, q u a r t z , carbonate, c a r b o n a t e , barite, barite, purple fluorite, dark brown sphalerite and chalcopyrite. The by 400 h e ore o r e is i s hosted h o s t e d by by a a massive m a s s i v e siliceous s i l i c e o u s lenses, l e n s e s , 1000 1 0 0 Q by 400 feet, e e t , cconsisting c n s i s t i n g aalmost l m o s k entirely e n t i r e l y of s f aphanitic a p h a n i t i c quartz q u a r t z and and historically i s t o r i c a l l y has h a s been b e e n referred r e f e r r e d to t o as as chert, c h e r t , with w i t h or o r without igithout Locally, ;anetc .' -. ccnnctatcns. ,-.,*---tations. L o c a l l y , fabric f a b r i c is i s discernable Fiiscerz65l2 .&.. nega.scopically, n q ~ s c o p i ~ s l l yaand n, d ggenerally e n e r a l l y in i n these t h e s e ccases a s e s tthe h e siliceous siliceous .~.,8..." rock The r o c k is i s white. white. The most m o s t common common colour, c o l o u r , and a n d always alwa>rs in i n close close association A subtle a s s o c i a t i o ~with w i t h the t h e ore, o r e , is i s brownish b r o w n i s h mauve. mauve. A subtle variant ~ y a r i a n tto t o this t h i s last l a s t colour c o l o u r is i s buff, b u f f , and a n d appears a p p e a r s to t o be be restricted r e s t r i c t e d to t o the t h e south s o u t h central c e n t r a l portion p o r t i o n of o f the t h e mineralized mineralized complex, c o m p l e x , in i n close c l o s e proximity p r o x i m i t y to a non—siliceous buff alteration o f mafic m a f i c rock. rock. a l t e r a t i o n of The The dominant d o m i n a n t lithology l i t h o l o g y surrounding s u r r o u n d i n g the t h e siliceous s i l i c e o u s rock r o c k is i s aa chlorite c h l o r i t e schist, s c h i s t , then t h e n sericitic s e r i c i t i c schist. s c h i s t . The northern n o r t h e r n band band of r;E chlocitic c h l o r i t i c schist s c h i s t separates s e p a r a t e s the t h e ore o r e complex complex from f r o m aa yabbroic a b b r o i c stock. s t o c k . At , A t the t h e eastern e a s t e r n end end of g f the t h e complex c o n p l e s aa lens l e n s of of sericitic s e r i c i t i c schist s c h i s t separates s e p a r a t e s this t h i s chlorite c h l c r i t e schist s c h i s t from f r o m the t h * ore ore ccmplex. c c m ~ : l e s . At . A t the t h e western w e s t e r n end, e n d , the t h e chlorite c h l o r i t e schist s c h i s t contains contains abundant All a b u n d a n t bluish b l u i s h quartz q u a r t z segrecjations s e g r e g a t i o n s and a n d magnetite. magnetite. A ll contacts the complexa nand c o n t a c t s between between t h e oore r e complex d t h the e s esericitic r i c i t i c sschist chist are a r e sharp, s h a r p , and a n d the t h e smaller siliceous s i l i c e o u s pods p o d s are a r e boudin b o u d i n like l i k e in in that The t h a t the t h e sericitic s e r i c i t i c foliation f o l i a t i o n wraps w r a p s around a r o u n d them. them. The southern s o u t h e r n contact c o n t a c t has h a s been b e e n described d e s c r i b e d by by Scott, S c o t t , (1963) ( 1 9 5 3 ) as as sharp, s h a r p , although a l t h o u g h as a s described d e s c r i b e d above, a b o v e , there t h e r e appears a p p e a r s to t o be b e aa transition t r a n s i t i o n locally l o c a l l y from f r o m buff b u f f siliceous s i l i c e o u s to t o buff b u f f alteration, alteration, in i n less less strained s t r a i n e d rock. r o c k . The sharp s h a r p contacts c o n t a c t s are a r e most n o s t likely likely the t h e products p r o d u c t s of o f shear s h e a r juxtaposition j u x t a p o s i t i o n and a n d the t h e destruction d e s t r u c t i o n of of gradational g r a d a t i o n d l contacts. c o n t a c t s . The gradational g r a d a t i o n a l contact c o n t a c t between b e t t s e e n the the gabhro s a b b r o stock s t o c k and a n d tthe h e cchlorite h l o r i t e schist s c h i s t indicate i n d i c a t eaagabhroic gabbroic protolith protolith at a t this t h i s location l o c z t i g n for f c r the t h e schist. schist. G i b l i n (1964), (1964), Giblin noticed n c t i c e d an a n increasing i n c r e a s i n g amount amount of o f bluish b l u i s h quartz q u a r t z in i n this this 87 �Figure 9: Geology 500' Level North Coldstream Mine �chlorite siliceous rock. rook. This nay may be chlorite schist schisttcwards towards the the siliceous This be interpreted the gabbro. cjabhro. interpreted as as increasing increasing silicification of the protolith for for the chlorite schist schist at margin protolith the chlorite at the the southern margin The of the ore nay be mafic volcanic, although a gabbroic gabbro the ore complex may protolitn. is also also possible. possible. protolit3 is The protolith rotolith for for the the sericitic sencitic schist schist nay nay be felsic felsic volcanic preserved, questionable, volcanic as as indicated indicated by by poorly poorly preserved, questionable, frajrientai As intense intense alteration alteration is frdyciental texture. texture. As is probable, probable, the the protolith protolith to to the t.he sericite sericiteschist schistcould could also also be be nafic nafic volcanic volcanic or or intrusive. intrusive. GENESIS GENESIS OF THE NORTH COLOSTREAM COLDSTREAM MINE Several fundanntal fundamental questions questions must must be be answered answered in in order order to to contemplate theNorth NorthCol'Jstrearn Coldstream Mine. Mine. What contemplate the the origin originofofthe is the siliceous host? host? -chert —chert or or silicification; silicification What is is the or felsic the host host rock? rock? —mafic -mafir: or felsicvolcanic volcanic—or -or gabbro gabbro: The nasive of the the siliceous nassive nature nature of siliceous zone, zone, the the lack lack of of sedimentary features, and andother other sedinentary sedimentarylitholcgies, lithologies, its its sedimentary features, absence onstrike, strike, and contacts all all support absence on and the the gradational gradational contacts support silicification. Silicification Silicification of this this intensity intensity is is only only known ld deposits (of known to to occur occur in inhydrothermal hydrothermal jo gold (of all all ages) ages), silicification. and and in in the theKeiko Keikozone zoneof ofsome someHuroko Kuroko type t.ype volcanoyenic volcan::?yenic massive massive sulphide salphide deposits. deposits. The former can be negated negated as as aa gold content content at at the the North Coldstream Coldstream of of 450 450 ppb ppb is is much much too too low, Siliôification in low, and is is typical typical of of the the latter. latter. Silicification in gold gold systems systems tends tends to to be be "late", "late", ie ie post post tectonic, tectonic, is is of of the the highest ore ore grades grades and and is is superimposed superimposed on on fabrics. fabrics. Silicification Silicification at at this this site site predates predates deformation deformation as as evidenced evidenced by by siliceous siliceous boudins boudins and and inherited inherited fabric. fabric. A volcanogenic volcanogenic origin origiri is is also also supported supported by by the t.he "stringer" "stringer" style style of of the the ore, ore, the the piped piped shaped shaped host host silicification silicification and and to t some some extent, extent, the the sequence sequence of of alteration. alteration. It therefore therefore appears appears that thatthe theNorth NorthColdstream Coldstrean Mine is is the the stringer stringer zone zone of cf avoloanocjenic a volcanogenic massLve xassive sulphide sulphide deposit. deposit. 89 �At one location iocation there there isisevidence It one evidence that thatthe thegabbro gabbromay nay be be a hust lust rock. rock. If Ifone one considers considers the theapparent apparent increasing increasing sLiciEicatLon or the gabbro gahhro to indicate its its presence presence durin'j durin 1 . LC ificat ion of Lh. nneralizng event, 5.:Âmineralizing event,then thenthe thenineralizing mineralizingevent eventmust nust be be However,the thelack lackofof fabric fabric within rost volcanic. post volcanic. However, within the the yabbro at the end of the gabbro the east east end the mineralized complex complex indicates indicates gabbro is that the t'r't.-i is.post tectonic, tectonic, and therefore therefore post that . -...,, ,.Â¥ Thioy under the .c;:!raIrac12n. L :.. ~ : n . T ~ k i . ~this this -j under consideration, consiaaraticn, the chtoritic chloritic schist along the margin of o the gabbro gabbro may be releted to emplacement and and the blue quartz generated during related feldspar destruction and chioritization. Ghloritization. . .1- complex appears This mineralized ccoplex mafic rwfic volcanic volcanic contact. contact. This is regional scale, reyional scale, but difficult difficult to to to be located located at at aa felsic— felsiccertainly true true at at a a demonstrate decionstrate at at mine mine scale. scale. FIELD TRIP STOPS FTELD STOPS STOP 4ct; STOP 4a; This is an an outcrop of altered hornblende This hornblende gabbro gabbro on on the the Despite northern margin of the the mineralized mineralized complex. complex. Despite epidote-chiorite alteration and multiple shear epidote-chlorite shear sets, sets, igneous igneous textures and mineralogy are textures are preserved. preserved. This gabbroic gabbroic stock stock composition and texture has variable conposition texture and this this location location we find f i ~ da a medium nediun grain, grain, equigranular eguigranulargabhro gabbroand anda aperdmatitic pegmatitic hornblende is fibrous phase. In thin section the hornblende fibrous and secondary. secondary. I I I STOP STOP 4b; 4b; Group of outcrop's outcrops on on south south side side of of road, road, only only 25 2 feet Group feet from from stop 4.3. 4a. These outcrop% outcrops have have rare, rare, ghost ghost like, like, relic relic igneous igneous textures textures which indicate indicate that that the the protolith protolith is is gabbro. gabbro. The The yabbro chloritized at the -.^t-,-hhas been sheared and increasingly increasingly chloritized the 90 I I �Thechlorite chlorite is expense of epidote. expense of epidote. The 1.5 pervasive pervasive and and also also Blue quartz seyregations and occurs occurs as as segregation. se3regation. Blue quartz se::;recjations and Leucoxene and nagnetite are irregularly raagnetite are irregularly distributed. distributed. Leucoxene and grains, nagnetite as sub—millimetre magnetite a r e dispersed dispersed as sub-millinetre grains, nagnetite nagnet-it.eare also also Some cm occurs ra in in length. length. Some occurs as as acicular acicular crystals crystals up up to to 35 e layers layers in in the the chlorite chlorite schist schist are are in in fact, fact, fibrous fibrous thethe magnetite—leucoxene hornblende, hornblende, which which are are later laterthan than maqnetite-leucoxene more random alteration, and alteration, and have hava a a ncre random orientation orientation than than . . . chlorite, post l o r i t e , indicating iric-iic~itir'.q post tectonic tectonic growth. grcwth. The distribution distribution of The of quartz quartz as as irregular irregular blebs, hlebs, and and the the volume volume of of this this quartz quartz could could be be produced produced in in situ situ during during shearing and chlorite chlorite alterati-on, alteration, as as opposed opposed to shearing and to . .> : silicification silicification from from an an external external source. source. chlorite schist schist zone zone are are Those quartz rich rich portion of the the ch1orit.e . termed "quartz "quartz complex" complex" in in mine mine terminology. terminology. , ~ J , - , . :',, ' STOP STOP 4c; 4c; This white siliceous zone zone is is the transition transition from from the the quartz quartz It complex to the more massive brownish mauve rock. It nauve host rock. consist of of strained strainedquartz quartzand and101Osericxte consist "; sericiteand and leuooxene. leucoxene. STOP 4d: 4d; STOP It's This brownish mauve siliceous rock This rock is is the the ore ore host. host. it's white siliceous unit is that only dissimilarities with the white mosaic of fine, it unstrained, and as such is an even grain riosaic fine, equant quartz equant. quartz crystals. crystals. STOP STOP 4e; 4e; A ft third variety of the silicification is is buff coloured and with the brownish mauve only aa subtle subtle difference exist iiith snatially related to aa buff buff variety is spatially variety. This This variety variety. relate3 to alteration zone along the south central portion of the mineralized nip,eralized complex. complex. This buff alteration is the . -. ' . �sericit of aa felsic a r i c i t Lzatlcn i z a t i c n sf f e l s i crock r o c k bearing b e a r i n g quarts q u a r t s eyes, eyes, L5sLhiV i s s i b l y f flsic a l s i c volcanic. v o l c a n i c . Thec The c odour l o u r oof f tthe h e ssilicification ilicification na . ,.iv reflect r c i f l e c the t t h composition e c o n p o s i t i c n of o f the the protolith. protolith. STOP TOP 4f; 4f; This h i s is i s an a outcrop of The h e rock r o c k is i s massive, cassive, the buff alteration described in 4e. fine f i n e grain, g r a i n , and a n d textureless. featureless. STOP 4g; An An ooutcrop u t c r o p oof f oore r e iin n ssharp h a r p ccontact o n t a c t wwith i t h aa ssericite e r i c i t e schist. Â¥ichi'-it At A t the t h e top t o p of o f the theoutcrop, o u t c r o p , fragmental f r a g m e n t a l textures t e x t u r e sof o fequivocal equivocal origins rigins and a n d aa siliceous s i l i c e o u s boudin b o u d i n wrapped w r a p p e d in i n sericitic s e r i c i t i c schist. schist. STOP 4h . This buff outcrop is included in the sericite schist unit its because b e c a u s e of o f i t s felsic f e l s i c appearance, a p p e a r a n c e , although a l t h o u g h it it. ray m a y contain contain more A t this t h i s location l o c a t i o n aa fragmental fragmental n o r e chlorite c h l o r i t e than t h a n s e r i c i t e . At sericite. helm terpreted texture. texture mar equivocal STOP as volcanic, hut is ccnsidered an 4i; large ridge at the east issgabbro. g a b b r o . The The lack la.ck oof f fabric f a b r i c indicates i n d i c a t e s that t h a t ititwas wasnot not This e n d of o f the t h emineralized m i n e r a l i z e dcomplex comp h i s l a r g e r i d g e a t t h e e a s t end affected f f e c t a dby by the t h edeformation d e f o r m a t i o n that t h a tproduced p r o d u c e d the t h eadjacent adjacen schist n u s t therefore t h e r e f o r ebe b eyounger y o u n g e r and a n d crosscut c r o s s c u t the t h e ore s c h i s tand a n dmust complex. It cannot therefore be the host rock. 92 ~ �Vanguard Prospec INTRODCCTTON The Vanguard Prospect is situated south of the junction between Highway 802X and Highway 11 at Kashabowie, Ontario (Fig. 8 ) . A private bush road trends south of this intersection and accesses the showine; area. The prospect is situaced on Mining Locations K 5 6 and 271. The property is private land and permission frcra the owners is required to visit the prospect. The property is currently under option to Minnova Inc. GEOLOGY The prospect area is underlain by sheared volcanic r the Shebandowan Greenstone Belt. Anorthositic gabbro suite rocks intrude the volcanic sequence. The mineralized zone strikes 0 6 0 degrees and dips steeply to the south. The zone has been traced intermittently along strike for 1 3 1 0 m ( 4 3 0 0 ft.). The prospect consists of two mineralized sections about 7 0 0 m apart and have been designated the West and East stop we will be examining the east zone. The Vanguard East Occurrence forms part of a large outcrop knoll on the east side of the bush road approximately 8 0 0 metres south of Highway 11. The occurrence is very well . exposed by stripping and trenching. At the Vanguard East location, a massive sulphide lens containing sphalerite, chalcopyrite, pyrite and pyrrhotite is hosted by a variolitic to massive mafic volcanics; bedded silicic tuff caps a portion of the mineralized zone and has been interpreted by Minnova to be "exhalite". Alteration associated with the deposit includes silicification and iron ��The rocks are chloritized. With reference to Fig. 10, the sulphide ninsralization is ZJ, this zone yielded 2 . 4 7 % Cu, 6 . 9 2 % 40.6 grams per ton Ag, and 1.39 grams per ton Au across an apparent width of 4 ~eters. The sulphide ore is finely banded and in the sample -xanined, consisted of approximately 25'6 sphaierite, 7 0 % pyrite, and the balance silica, rock fragments, and other gangue minerals. Chalcopyrite also occurs in the suphide The two other major rock units exposed near the main trench ara a silicified variolitic mafic volcanic and a chocolate brown (weathered surface) carbonate-rich rock. An alteration zone consisting of massive to bedded silica/carbonate with disseminated iron sulphides is situated west of the south end of the main t.rench. The contact area between this zone and the varioliti:: nafic volcanic to the west is marked by quartz (veins?). Sheared but otherwise hell preserved volcanic features such i s varioles can be examined throughout the large flat stri-pped area north of the sulphide lines. Most of the faulting trends approximately 270 degrees with apparent dextral offsets. The intense deformation of the rocks of the showing area is perhaps explained by the proximity of the Crayfish Creek Fault. This fault presumably underlies the low ground to the' east of the stripped area. �. . .. Reef a r a n c e s .:rndt, X. Â¥WiO and Brooks, C. K c r a a t i i t e a ; G e o l o g y , Vol.8, - " '\r-,'Jt, V., 1979: p p 135-156. - " - A F r a n c i s , D. a n d H y n e s , A . J . The F i e l d C h a r a c t e r i s t i c s a n d P e t r o l o g y o f A r c h e a n and p r o t e r o z o i c K o m a t i i t e s ; Can. yol17, B a c r e t t , P.M., Mineralogist, " , ;?p : 4 7 - 1 6 3 . B i n n s , H.A., G r o v e s , 9.1.. Marston, R.J. and McQueen, K.G. 1977: S t r u c t u r a l H i s t o r y and Metamorphic M o d i f i c a t i o n of Archean Volcanic-type Nickel D e p o s i t s , Y i l g a r n B l o c k , W e s t e r n A u s t r a l i a ; Economic G e o l o g y , ~ 0 1 . 7 2 , pp 1195-1223. ~ o r r a d a i l e ,G. 19B7: a n d Brown, H. The Shebandowan G r o u p : " T i r a i s k a m i n g - L i k e " Archean Rocks i n S o r t h w e s t a r n O n t a r i o ; CJES, V o l . 2 4 , pp 185-188. The D a i l y T i m e s J o u r n a l 1937: I n t . X i c k e l Buys Shebandowan O r e ; p u b l i s h e d i n Fort William, Ontario. G i b l i n , P.E. 1964; B u r c h e l l L a k e Area; O n t a r i o D e p a r t m e n t o f M i n e s , G e o l o g i c a l R e p o r t 1 9 , 39p. N o r t o n , P. 1982: Archean V o l c a n i c S t r a t i g r a p h y , P e t r o l o g y a n d CLcraistry of Mafic and L ' l t r a m a f i c Rocks, Chromite a n d t h e Shebandowan Xi-Cu Mine. Shebandowan, N o r t h n e s t e r n O n t a r i o ; U n p u b l i s h e d PhO T h e s i s , Carlton L'niversity. �.. Pye, E . G . and Fenwick, 3 . G . 1964: Atikokan-Lakehead Sheet, Geological Compilation S e r i e s ; O n t . D e p t . o f M i n e s , >!ap 2 0 6 5 , S c a l e 1:253,440. S c o t t , S.3. 1963: R e p o r t on t h e N o r t h C o l d s t r e a m Mine L t d . i dz~::kl LS:::~ : S h e g e l s k i , R.2. 1980: A r c h e a n C r a t o n i z a t i c r n , Emergence a n d Red Bed Dfivelopraent, L a k e Shebandowan A r e a , C a n a d a ; Precambrian Research, Vol.12, pp 331-347. S t o t t , G.M. 1981: A S t r u c t u r a l A n a l y s i s of t h e C e n t r a l P a r t o f t h e Shebandowan Metavolcanic-Metasedimentary Belt.; Ontario 44p.l G e o l o g i c a l S u r v e y , Open F i l e R e p o r t 3349, �PURCHASE OF PROCEEDINGS AND ABSTRACTS AND FIELD GUIDEBOOK Copies of the Proceedings and Abstracts, Part 1, and the Field Guidebook, Part 2, for the 36th Annual Institute on Lake Superior Geology may be purchased during the meeting. . . . . . . . . . . $5.00 Canadian . . . . . . . . . . . . . . . . . $5.00 Canadian Proceedings and Abstracts, Volume 36, Part 1 Field Guidebook, Volume 36, Part 2 Payable to Institute on Lake Superior Geology Issues of Proceedings and Abstracts, Part 1, and Field Guidebook, Part 2, from this and the three previous meetings, may be ordered from: Joe KaSEokoski, .Secretary-Treasurer Department of Geology and Geological Engineering Michigan Technological University Houghtan, Michigan 49931 The cost for each part ordered is $6.00 U.S. Orders will be filled while supplies last. .............................................................................. All volumes back to 1955 are available for photocopying at the prevailing rate, from the Michigan Technological University Library, through Mr. M. S. Spence, Archivist. Phone 906-487-2505 .............................................................................. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1990 Description An account of the resource Institute on Lake Superior Geology. Thunder Bay, Ontario. May 9-12, 1990. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1990 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/1596d2e3228c258cd2151bf57792baf5.pdf adc222c122cfc2f81dda355b3c92682c PDF Text Text a THIRTY-SEVENTH THIRTY-SEVENTH ANNUAL ANNUAL INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY oenp4iáoh/e — - PROCEEDINGS: PROCEEDINGS: PART PART 11 - ABSTRACTS MAY 1-4, MAY 1-4, 1991 1991 EAU CLAIRE, CLAIRE,WISCONSIN �U Committee, 37th Annual Meeting Organization committee, Meeting ILSG, ILSG, 1991 1991 Chairman: Paul General C hPaul E. E Myers Mvers PHONE: 715-836-3713 PHONE; 715-836-3713 Editor: Luff! S. Chan Geology Department Department Geology Li University of Wisconsin Eau Claire, Claire. WI 547024004 S4702.4004 I VOLUME 37 PROCEEDINGS VOLUMEJiZ PROCEEDINGS U (Includes Meeting Program) Program) ABSTRACTS (Includes PART I: ABSTRACTS 2: FIELD TRIPS PART 2: Referenceto to material material in this follow the example Refereace this volume volume should follow example below. below. Morey, Glen Glen B., and Southwick, Southwick, David David L., L,, 1991, Manganese mineralization mineralization in early Many, 1991, Mangame early Proterozoic iron-formation of the Emily District, Cayuna Range, east-central Pm€erowi r o i i - f i ' o n of Emily District, Cquna Range, east-central Minnesota, (abst.j; Institute 37th Annual Minnesota, [tabst.]; Instituteon enLake LukeSuperior SuperiorGeology Geology Proceedings, 37th Meeting, Eau Claire, part 1, p. 75-76. Meeting, EM Ctairv,WI, WI, 1991; v.v. 37, part 75-76. Published and Distributed Published Distributed by: by: I I I U Institute on Institute on Lake Lake Superior SuperiorGeology Geology M.G. Mudrey, Jr., Jr., Secretary/Treasurer M.G. Secretary/Treasurer Geologicaland and Natural Natural History Survey Wisconsin Geological Survey 3817 Mineral Mineral Point Road 3817 WI 53705 53705 Madison, WI Li Li PURCHASE OF PROCEEDINGS PURC&iSE PROCEEDIh'GS VOLUMES Copies Copies of of the the 37th 37th ILSG ILSG Proceedings Proceedings(Part (Part I,I, Abstracts Abstractsand and Part Part II, H, Field Field Trips) Trips) may may be be purchased purchased during during $5.00 (US) each. each. the meeting for $5.00 Payable to the institute Instituteon onLake LakeSuperior SuperiorGeology Geology Issues of Proceedings and 1,and Field Guidebook, Guidebook, Part and Abstracts, Abstracts, Part Part 1, Part 2. 2. from from this this and previous meetings may be ordered from: I I I G. Mndrey, Mudrey, Jr. Michael G. Address, See above PHONE: PHONE: 608-263-1705 608-263-1705 The cost of $6.00 U.S. US. Orders Orders will will be filled tilled while supplies of each part isis$6.00 supplies last, last. All All volumes volumes back back to to 1955 1955 are are rom the available for for photocopying photocopyingaatt the the prevailing prevailingrate rate f from the Michigan Michigan Technological TechnologicalUniversity UniversityLibrary Librarythrough through Mr. M.S. MS. Spence, Spence, Archivist. Archivist. Phone Phone906-487-2505. 906487-250s. I 1 L �a 37th Annual Institute on Lake SuperiorGeology Proceed iii gs Ray Wachs Civic center Eati Claire1 VisconSin May 1-4, 1991 Orqaizized kv Mvcrs. I.Jniversitv of \Visconsin-1 ZIU Claire i ..s. i ;fliLNitV of Wise' )nsin—Lau Claire Volume 37 Part 1 Abstracts �TABLE OF OF CONTENTS CONTENTS Institutes on on Lake Lake Superior Superior Geology Geology to to1991 1991 L L L Constitution Constitution of the the Institute Institute on on Lake Lake Superior Superior Geology Geology ii ii By-Laws By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology iii iii Goldich Medal Medal Guidelines Guidelines iv Student Travel Travel Award Award \v Board of of Directors Directors vi vi L Local Local Committee Committee vi vi rL Student Paper Paper Award Committee Committee vi [ Goldich Goldich Medal Recipient Recipient vii Banquet Speaker Speaker viii L Acknowledgements viii Goldich Medal Medal Committee Committee l vi V. Report of the the 36th 36th Annual Annual Institute Institute Report of the Chairs Chairs of ix L Calendar of Events Events xi [ Programs Programs Poster Papers Papers Xiii xiii I XV I L L L L L L Abstracts Abstracts 1 �INSTITUTES ON INSTITUTES ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY INSTITUTE INSTITUTENUMBER NUMBER 11 2 3 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 DATE PLACE 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Minneapolis, Minneapolis, MN MN Houghton, MI Houghton, MI East East Lansing, Lansing, MI MI Duluth, Duluth, MN Minneapolis, MN Minneapolis, MN Madison, WI Madison, WI Port Arthur, Arthur, Ont. Port Ont. (Thunder (Thunder Bay) Bay) Houghton, Houghton, MI MI Duluth, MN Duluth, Ishpeining, Ishpeming, MI MI St. St. Paul, Paul, MN MN Sault Sault Ste. Ste. Marie, Marie, MI MI East East Lansing, Lansing, MI MI Superior, Superior, WI WI Oshkosh, Oshkosh, WI WI Thunder Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN Houghton, Houghton, MI MI Madison, Madison, WI WI Sault Sault Ste. Ste. Marie, Marie, Ont. Ont. .,: Marquette, Marquette, MI MI :c, St. St. Paul, Paul, MN MN Thunder Thunder Bay, Bay, Ont. Ont. ., . ~ , Milwaukee, Milwaukee, WI WI Duluth, Duluth, MN MN Eau Eau Claire, Claire, WI WI :. .,,i East East Lansing, Lansing, MI MI .,International International Falls, Falls, MN MN Houghton, Houghton,MI MI Wausau, Wausau, WI WI Kenora, Kenora,Ont. Ont. Wisconsin Wisconsin Rapids, Rapids',WI WI Wawa, Wawa,Ont. Ont. Marquette, Marquette, MI MI Duluth, Duluth, MN MN Thunder Thunder Bay, Bay,Ont. Ont. Eau Eau Claire, Claire, WI WI 1 �CONSTITUTION SUPERIOR GEOLOGY OFINSTITUTE INSTITUTEON O NLAKE LAKE SUPERIOR GEOLOGY CONSTITUTIONOF ArticleI I Article Name kb!!s The Thename nameofofthe theorganization organizationshall shallbe bethe the'Institute "Instituteon onLake LakeSuperior SuperiorGeology. Geology". Article ArticlcIII1 Objectives The T h eobjectives objectivesofofthis thisorganization organizationare: are: region exchange A.A.ToTo provide providea ameans meanswhereby wherebygeologists geologistsininthe theGreat GreatLakes Lakes regionmay may exchangeideas ideasand and scientific scientificdata. data. B.B.ToTo promote better understanding ofofthe geology promote better understanding the geologyofofthe theLake LakeSuperior Superiorregion. region. C.C.ToTo plan and conduct geological plan and conduct geologicalfield fieldtrips. trips. Article ArticleIII I11 aaus Status No Nopart partofofthe theincome incomeofofthe theorganization organizationshall shallinure inuretot othe thebenefit benefitofofany anymember memberororindividual. individual. tnInthe theevent eventofofdissolution dissolutionthe theassets assetsof ofthe theorganization organizationshall shallbe b edistributed distributedtoto (some (sometax taxfree freeorganization). organization). (To (Toavoid avoidFederal Federaland andState Stateincome incometaxes, taxes, the the organization organization should should be be not not only only scientiflc "scientific" oro reducational, "educational",but butalso alsonon-profit".) "non-profit".) Minn. 290.01, Minn.Stat. Stat.Anno. Anno. 290.01.subd. subd.4 4 Minn. 290.05(9) Minn.Stat. Stat.Anno. Anno. 290.05(9) 1954 501(c)(3) 1954Internal IntcrnalRevenue RevenueCode C d cs.s.50I(c)(3) Article ArticleIV IV Membership Membership The Themembership membershipof ofthe theorganization organization shall shall consist consist of of the the board board of of directorsdirectors. Any Anygeologist geologist interested interestedshall shallbe b epermitted permittedtotoattend attendand andparticipate participateininand andvote voteatatthe theannual annualmeetings. meetin&% ArticleVV Article Meetings The year, preferably preferably during during the the month month of of April. April. The T h eorganization organizationshall shallmeet meet once once aa year, T h eplace placeand and exact exactdate dateofofeach eachmeeting meetingwill willbe bedesginated desginatcdby bythe theboard boardofofdirectors. directors. ArticlcVI VI Article Directors The and T h eboard boardofofdirectors directorsshall shallconsist consistofofthe theChairman, Chairman,Secretary-Treasurer, Sccreta~y-Treasurer, andthe the last last three three past pastChairman; Chairman;but butififthe theboard boardshould shouldatatany anytime timeconsist consistofoffewer fewerthan thanfive fivepersons, persons, by byrcaon rcaon vacancies ofofunwillingness unwillingnessororinability inabilityofofany anyofofthe theabove abovepersons personstotoserve serveas asdirectors, directors,the the vacancieson on the theboard boardmay maybe b efilled filledbybythe theannual annualmeeting meetingso soas asto t obring bringthe themembership membershipof ofthe theboard boardup up tot ofive fivemembers. members. ArticleVII VII Article Officers ixGQxs The and T h eofficers officersofofthis thisorganization organizationshall shallbeb ea aChairman Chairman andSecretary-Treasurer. Secretary-Treasurer. A. A.The T hChairman e Chairmanshall shallbeb eelected electedeach eachyear year by bythe theboard board ofofdirectors, directors, who who shall shallgive givedue due consideration considerationtotothe thewishes wishes of of any any group group that that may may be b e promoting promotingthe thenext nextannual annualmeeting. meeting. His Histerm termofofoffice officeasasChairman Chairmanwilt willterminate terminateatathe t theclose closeofofthe theannual annualmeeting meetingover overwhich which he shall have been appointed. appointed. He hepresides presides or orwhen when his hissuccessor successor shall have been H ewill willthen thenserve serve for foraa period threeyears yearsas asaa member member of of the theboard boardofofdirectors. directors. periodofofthree B. T hSecretary-Treasurer e Secretary-Treasurershall shallbe beelected elected at a t the the annual annual meeting. meeting. His Histerm termofofoffice office shall shall B.The be betwo twoyears yearsoro runtil untilhis hissuccessor successorshall shallhave havebeen beenappointed. appointed. Article VIII VIII Article Amendments Afwdnwm This Thisconstitution constitutionmay maybe b eamended amended by by aamajority majorityvote voteofofthose thosepersons personswho whoare arepersonally personally present present at, at, participating participatingin, in,and andvoting votingat atany anyannual annualmeeting meetingof ofthe theorganization. organization. II �BY-LAWS Duties of of the .Duties the Officers Officers and and Directors Directors A. .4 It It shall shall be be the the duty duty of of the the Annual Annual Chairman Chairman to; to: 1.. 1 2. 2 3. 3. Preside Preside at at the the annual annual meeting. meeting. Appoint all committees needed for for the the organization organization of Appoint all committees needed of the the annual annual meeting. meeting. Assume complete complete responsibility responsibilityfor for the the organization organization and and financing financing of of the the Assume annual meeting annual meeting over over which which he he presides. presides. It It shall shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurer to: to: B. B. 1. 1. 2. 2. 3. 3. Keep Keep accurate accurate attendance attendance records records of of alt all annual annual meetings. meetings. Keep accurate records of all meetings of, Keep accurate records of all meetings of, and and correspondence correspondence between, between, the the board board of of directors. directors. Hold Hold all all funds funds that that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field field trips and and to to make make these these funds funds available available for for the the organization organization and and operation operation trips of future as required. of future meetings meetings as required. C. of the the board board of of directors directors to annual meetings C. It I t shall :shall be be the the duty duty of to plan plan locations locations of of annual meetings and to and to advise advise on on the theorganization organizationand andfinancing financingof of all allmeetings. meetings. II. Duties and and Expenses F.mensas 1. 1. 2. ill. There shall shall be be no . There no regular regular membership membership dues. dues. , Registration fees for the Registration fees for the annual annual meetings meetings shall shall be be determined determined by by the the Chairman Chairman is strongly recommended that in consultation in consultation with with the the board board of of directors, directors. it It is strongly recommended that these be encourage attendance attendanceof of graduate graduatestudents. students. these be kept kept at at aa minimum minimum to to encourage Rules of Order The rules The rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern this this organization organization in in all all cases cases to to which which they they are are applicable. applicable. IV. Amendments . . . . , ~ ::~.. . . These by-laws maybe be amended amended by by aa majority vote of of those who are are These by-laws may majority vote those persons persons who personally present present at, at, participating participatingin, in,and and voting voting aatt any any annual annual meeting meeting of of the personally the with the the constitution constitution organization; provided that such modifications shall not conflict with as presently adopted or as or subsequently subsequently amended, amended. Ill iii �Award Guidelines Guidelines Award SAM GOLDICH GOLDICH MEDAL SAM MEDAL Preamble The Institute Geology was born born on or or around around1955, 1955, as as documented documented by by The Institute on o n Lake Lake Superior Geology the fact that the meeting will will be be held held in 1981. 1981. The TheInstitutes Institutes are are exemplary exemplary the 27th 27th annual annual meeting in their theircontinuing continuingobjectives objectives of of dealing dealing with with those those aspects aspects of of geology geology that that are are related related geographically to to Lake Lake Superior; Superior;of ofencouraging encouragingthe thediscussion discussion of ofsubjects subjects and and sponsoring sponsoring field trips tripswhich whichwill willbring bringtogether togethergeologists geologistsfrom fromacademia, academia, government government surveys, surveys, and and industry; and of maintaining an exceedingly exceedinglyinformal informal but but highly highly effective effective mode mode of of operation. operation. During the the membership membership of of the the Institute Institute (that geologists During the course course of of its its existence existence the (that is, is, those those geologists an interest interest in in the the objectives objectives of of the the I.LS.G. I.L.S.G.by byattending) attending)has hasbecome become aware aware who indicate an of the colleagues of the fact factthat thatcertain certainofoftheir their colleagueshave have made made particularly particularly noteworthy noteworthy and and meritorious meritoriouscontributions contributionsto tothe theimprovement improvementof ofunderstanding understanding of of"Lake "LakeSuperior" Superior"geology geology and its mineral and mineral deposits. deposits. The exemplary award was wasmade madeby byI.L.S.G. I.L.S.G.toto Sam Sam Goldich Goldich in in 1979 for his 1979 for his many many exemplary award contributions to 50 years. years. contributions to the the geology geology of the the region region extending extending over over about about 50 . Award Guidelines Award G .u ~ d a 1) The T h emedal medalshall shallbe beawarded awarded annually annually by the LL.S.G. I.L.S.G. Board of of Directors Directors to to aa geologist geologist whose name is associated associatedwith withaasubstantial substantialsustained sustainedinterest interestin, in,or oraamajor majorcontribution contribution to, the geology geology of the the Lake Lake Superior Superior region. region. appoint the the Nominating Nominating Committee. Committee. The initial 2) The TheBoard Board of ofDirectors, Directors, LL.S.G. I.L.S.G. shall appoint appointment will will be one for two, and appointment be of of three three members, members, one to serve serve for for three three years, years, one and one for one year, year, the the member memberwith with the the briefest briefest incumbency incumbencytotobe bechairman. chairman.After After the the one first year the the Board Board of of Directors Directorsshall shallappoint appointat a teach each spring springmeeting meeting one one new new member who will will serve serve for forthree threeyears. years. In the the thrid thrid year year this this member member shall shall be be the the chairman. chairman. The Committee should reflect reflect the main fields Committee membership membership should fields of of interest interest and and geographic geographic distribution of of I.LS.G. I.L.S.G. membership. membership. 3) By 1, the Goldich make its its Goldich Medal 3) By November November 1, Medal Nominating Nominating Committee Committee shall make recommendationto to the the Chairman of the Board of, Directors Directors who will then inform the recommendation card of who will then inform the .z.:,: , ..~ . , ~ . ~ , . Board of the the nominee. nominee. 4) The nominee of of the the Committee, Committee,will will inform inform 4) TheBoard Board of ofDirectors Directors normally normally will willaccept accept the nominee the medalist and will will have the medalist immediately, immediately, and have one one medal medal engraved engraved appropriately appropriately for presentation of the Institute. presentation aatt the next meeting meeting of 5) It It is 5) is recommended recommended that that the the Institute Instituteset set aside aside annually annually from fromwhatever whatever sources, sources, such such funds as as will will be be required required to to support support the the continuing continuingcosts costs of of this this award. award. April 4, April 4, 1981 1981 J. Kalliokoski, Chairman J. Chairman Bill Cannon Cannon Fred Kehlenbeck Glenn Morey Glenn Greg Mursky iv �STUDENT TRAVEL TRAVEL AWARD STUDENT AWARD l'hc I080 1986 Board Board of 4)1Directors Directorsestablished establishedthe theI.L.S.G. 1.LS.G. Student Student Travel Travel Award I'hc Award totosLIl)I)orL siipport sttideiit participation s~iidcnt participationat atthe the annual annual Institutes. Institutes. The Theawards awardswill willbe bemade made from fromaa special special fund fund intended to to help defray some some of of the the direct direct travel set up up for set for this this purpose. purpose. This award is intended travel costs to to the Institute costs Institute and and includes includes aa waiver waiver of ofregistration registrationfees, fees,but butexcludes excludesexpenses expenses for for meals, lodging, lodging, and and field field trip trip registration. The meals, Thenumber numberof ofawards awardsand and value are determined by the annual Chairman in in consultation consultation with with the the Secretary-Treasurer Secretary-Treasurerand and will willbe be announced announced at the annual annual banquet. banquet. The following The following general general criteria criteria will will be be considered considered by by the the annual annual Chairman, Chairman, who who is is responsible for the responsible the selection: selection: 1)) The graduate) student student 1 Theapplicants applicantsmust must have have active resident (undergraduate or graduate) status at at the time of the status the Institute, Institute, certified certified by by the the department department head. head. 2) 2) Students Studentswho who are are the the senior senior author author on on either either an an oral oral or or poster poster paper paper will will be be given favored favored consideration. consideration. It is 3) It 3) is desirable desirable for for two twoor ormore morestudents students to tojointly jointlyrequest requesttravel travelassistance. assistance. 4) In priority will will be 4) In general, general, priority be given given to to those those in in the the Institute Institute region region who who are arc farthest away. away. 5) Each made in in writing, writing, to 5) Eachtravel travelaward awardrequest request shall shall be be made to the the annual annual Chairman, Chairman, with an or other significant significant details. with an explanation explanationof of need, need, possible author status or details. Successfulapplicants applicantswill willreceive receivetheir theirawards awardsatatthe thetime timeof of registration registrationfor for the the Meeting. Successful V �BOARD BOARDOF OFDIRECTORS DIRECTORS 1991 P. P.E. E.Myers Myers(with (withL.L.S.S.Chan) Chan) 1991 Department Departmentof ofGeology, Geology,University Universityof ofWisconsin, Wisconsin,Eau Eau Claire. Claire,Wisconsin Wisconsin 54701 54701 1990 1990 H. M.H. M.Kehlenbeck Kehlenbeck Department Departmentof ofGeology, Geology,Lakehead LakeheadUniversity, University,Thunder Thunder Bay, Bay,Ontario Ontario P7B P7B 5El 5E1 1989 1989 R.W. W.Ojakangas Ojakangas(with (withJ.J.C.C . Green Greenand andT.T.B.B.Holst) Hoist) Department 55812 Universityof ofMinnesota, Minnesota,Duluth, Duluth,Minnesota Minnesota 55812 Departmentof ofGeology, Geology,University ft. 1988 J. D. D.Hughes Hughesand andK. K.J. J.Schulz) Schulz) 1988 J.J. S. S.Klasner Klasner(with (withJ. Department Departmentof ofGeology, Geology,Western WesternIllinois IllinoisUniversity, University,Macomb, Macomb,lilnois Illnois 61455 61455 Secretary-Treasurer Secretary-Treasurer M. M.G. G.Mudrey, Mudrey,Jr. Jr. Wisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey, Survey,3817 3817Mineral Mineral Point Point Road, Road,Madison, Madison,WI WI 53705 53705 LOCAL LOCALCOMMITTEE COMMITTEE P. E. E.Myers Myers General GeneralChairman Chairman L. S. S.Chan Chan Program Program and and Abstract Abstract Editor Editor and and Field Field Trip Trip Guidebook Guidebook Editor Editor P. L. ft. P. Willis Registration RegistrationCoordinator Coordinator STUDENT STUDENT PAPER PAPERAWARD AWARD CoMMITTEE COMMITTEE 1991 1991 J.' S. S. Klasner, Klasner, Chairman Chairman Western Western Illinois IllinoisUniversity, University,Macomb, Macomb,Illinois Illinois GOLDICH MEDAL COMMITTEE COMMITTEE1990-91 1990-91 GOLDICH MEDAL M. M. C. G.Mudrey, Mudrey,Jr. Jr. Wisconsin Wisconsin Geologic Geologic and and Natural Natural History HistorySurvey, Survey, Madison, Madison,WI WI F. W. W. Cambray Cambray F. Dept. Dept. of of Geological GeologicalSciences, Sciences,Michigan MichiganState State University, University,East East Lansing, Lansing,MI MI H. H. H. Halls Halls H. Dept. Dept. of of Geology, Geology,Erindall Erindall College, College,Mississauga, Mississauga, Ont. Ont. LSL L5L 1CO 1CO j j '1 vi U j �Biographical Biographical Sketch Sketch of WILLIAM J. HINZE HINZE WILLIAM J. 1991 1991 Goldich Goldich Medal Medal Recipient Recipient William WilliamJ.J. Hinze Iiinzebegan beganhis hisearth-science earth-sciencecareer careeratatthe theUniversity Universityof ofWisconsin, Wisconsin,where wherein in1951 1951 he he received received aa bachelor bachelor of science science in geology. gwlogy. From From1954 1954to to1955 1955he he served served in inthe the U.S. US. Anny Army Corps of Engineers at their Research and Development Laboratory, after which he returned to the Corps of Engineers at their Research and Development Laboratory, University of Wisconsin, receiving his doctorate in geology and physics in 1957. From 1956 University of Wisconsin, receiving doctorate gwlogy From 1956to to 1958 & Laughlin Steel Steel Company. In In1958 1958he hejoined joined 1958 he he worked worked as as aa staff staff geophysicist geophysicist for for Jones Jones & the thefaculty facultyof of the the department departmentof of geology gwlogy at atMichigan Michigan State State University. University, where where he he held appointments appointments of full professor. professor. InIn1972 1972he hetook tookhis hispresent presentpost postas asprofessor pmfessorof ofgeophysics gwphysics in inthe the of assistant assistant to to full Department of Earth and Atmospheric Sciences Sciences atat Purdue PurdueUniversity. University. In In 1985 he he served served as as aa visiting visiting professor professorat atthe the University Universityof of Lausanne Lausannein inSwitzerland. Switzerland. In Hinzehas hasmade mademany manysignificant significantand andlasting lastingcontributions contributionsto to In the the course course of ofhis hiscareer careerHinze potential-field potential-field geophysics. In Inaddition additionto to numerous numerous abstracts abstracts and and technical technical reports, he avenges averages several truly remarkable severalformal formalpapers papers per per year, year. either eitheras as chief chief author author or or as as co-author—a w-authorremarkable record rewrd if his fonnidable duties are considered. formidable professional professional duties considered. For For instance, instance, from from 1975 1975 to 1982 1982 he he was was chairman chairman of of the the U.S. US. National National Magnetic Magnetic Anomaly Anomaly Map Map Committee, Committee, and and from from 1985 1985to 1989 1989he cowchaired Magnetic Anomaly Regional chairedthe the North North American AmericanMagnetic Anomaly Map Map Committee. Committee. He Heedited editedThe TheUtility Utilityof ofRegional Gravity and which was was published published by by the the Society Society of ofExploration Exploration and Magnetic Magnetic Anomaly Anomaly Maps, Maps, which Geophysicists Geophysicists in in 1985. 1985. From From1986 1986to to1988 1988he heco-chaired w-chaired the theU.S. US. National National Science Science Foundation's joint U.S./Indian Lineaments: Their U.S./hdian workshop workshop "Regional "Regional Geophysical Lineaments: Their Tectonic and Economic Significance" Significance"and and co-edited co-editedthe the workshop workshopvolume, volume,which whichwas waspublished publishedby by the theGeological GeologicalSociety Society of of India M i a in in 1989. 1989. Since Since1985 1985he hehas hasdealt dealtwith withproblems problemsconcerning concerning the distribution distribution and archiving of task, has has served in of geophysical gwphysical data data for for the the worldwide worldwide scientific scientificcommunity community and, related to this task, various various posts posts with with the the U.S. U.S. Geodynamics Geodynamics Committee, Committee, the International International Lithospheric Commission, and has and the the National National Academy Academy of of Science/National Sciendational Research Research Council. Council. From From1988 1988to tothe thepresent presenthe hehas served served as as aa consultant consultantto to and and member memberof of the the Advisory Advisory Committee Committee on on Nuclear Nuclear Waste Waste of of the the Nuclear Nuclear Regulatory Regulatory Commission. He Hehas hasserved servedfrom from1986 1986both both as as aa member member and and vice-chainnan vice-chairman of of the the board of directors directors of of Deep Deep Observation Observation and and Sampling Sampling of the the Earth's Earth's Continental Continental Crust, Crust, Inc. Inc. (DOSECC), and as aa co-chairman (DOSECC), and co-chairman of of the the Potential Potential Fields Fields Committee Committee of the the Great Great Lakes Lakes International Program on Crustal Evolution Evolution (GLIMPCE). (GLIMPCE). He He has has been been aa member member of of the theU.S. US. Geodynamics Geodynamics Committee Committee of the National Academy of Science/National ScienceJNational Research Council since 1989. 1989. During Hinze has has been at at the forefront of geophysical gwphysical research During his long long and and successful successful career career Hinze in in the the Lake Lake Superior Superiorregion region and and the the surrounding surrounding Midcontinent. His Hisdoctoral doctoralresearch, research,aagravity gravity investigation investigationof of the the Baraboo Bamboo Syncline Syncline region, region, which which was was published published in in the the Journal Journalof ofGeology Geologyin in 1959, gravity studies studies of of its its time. time. His 1959, was one of the most innovative gravity His 1960 1960 Economic Economic Geology paper paper on on the the gravity gravity method method in in iron-ore iron-oreexploration, exploration, which which was was largely largely based based on on his his experiences experiences with Jones & Laughlin Steel Company, became a classic work among explorationists; Jones & Laughlin Steel Company, became a classic work among explorationists; aa slightly slightly revised version reappeared Exploration Geophysicists' volumes on mining reappeared in in 1966 1966in in the Society Society of Exploration geophysics. Duringthe the1960s 1960sHinze Hinzewas wasthe theprincipal principalinvestigator investigatorof of several severalmajor major aeromagnetic aeromagnetic gwphysics. During and gravity the Upper Upper Peninsula Peninsula of of Michigan, Michigan,and and the the Michigan Michigan gravity studies studies of of the the western western Great Great Lakes, Lakes,the Basin. The Theaeromagnetic aeromagneticstudies studiesover overLake LakeSuperior Superiorcomplemented complemented the seismic seismic investigations of vii �the and in in 1966 the results results were were published published with with the the Lake Lake Superior Superior Experiment, Experiment, and 1966 the the seismic seismicstudies studies in in the frequently cited The Earth Beneath the Continents (American Geophysical Union Geophysical the frequently cited The Earth Beneath the Continents (American Geophysical Union Geophysical Monograph 10). In1982 1982R.J. R.J.Wold Woldand andhe heco-edited co-editedGeology Geologyand andTectonics Tectonicsof ofthe theLake Lake Superior Superior Monograph 10). In Basin today the Basin (Geological (GeologicalSociety Societyof of America America Memoir Memoir 156). 156). which which remains remains today the definitive definitive reference reference on Lake on Lake Superior Superior geology geology and and geophysics. geophysics. In Inrecognition recognitionof of his hiscontributions contributionsto toMidcontinent Midcontinent geology, he geology, he was was awarded awardedan an honorary honorary membership membership in in the the Michigan Michigan Basin Basin Geological Geological Society Society in in 1986. 1986. Today Hinzemaintains maintainshis his high high profile profilein in geophysical geophysical studies studies of of the theLake LakeSuperior Superiorregion. region. Today Hinze Since the mid-1970s he has been a leading investigator of Mideontinent seismicity Since the mid-1970s he has been a leading investigator of Midcontinent seismicityand andits itsprobable probable relationship relationshipto to basement basement structure. structure. Through Throughhis hisinvolvement involvementwith with DOSECC DOSECCand andother otheragencies, agencies,he be has been a leading pioponnent of deep scientific drilling in the Lake Superior region. has been a leading pmponnent of deep scientific drilling in the Lake Superior region. He He and and his his students students are are presently presentlyconducting conductingcombined combined studies studiesof of seismic-reflection, seismic-reflection, gravity, gravity, and and magnetic magnetic data data to to investigate investigate crusthi crustal structure structure beneath beneath Lake Lake Superior. Superior, aa task task that that epitomizes epitomizesthe thestrong strong generalist characterizeshis his career. career. generalist approach approachthat that characterizes Perhaps Perhaps Bill Bill Hinze's Hinze's greatest greatest legacy legacy is is his his students. students. Through Throughorganizational organizationalskills skillsthat thatare are unsurpassed he has has inspired unsurpassed and and an an enthusiasm enthusiasm for for his his work work that that is is contagious, contagious, he inspired many many to to learn learn and and achieve they were were capable. capable. The achieve far far beyond beyond what what they they thought thought they The careers careers of of many many successful successful geophysicists worldwide proudly bear his imprint. geophysicists worldwide proudly bear his imprint. His is is truly truly aa career carter that His thathas has made made aa difference. difference. VAL W. W. CHANDLER CHA1'DLS VAL Minnesota Geological Minnesota Geological Survey Survey ~ >' Ban quet Speaker Speaker Banquet Paul IC. Sims,US. U.S. Geological Geological Survey, Survey,Denver. Denver,Colorado, Colorado,will willbe bethe the speaker speaker at the K. Sims, the Annual AnnualILSG ILSG Banquet in Ray Wachs Banquet Wachs Civic Center (Rm (Rm A) A) at at8:30 8:30pm pm on onThursday, Thursday,May May 2, 2, 1991. 1991. His topic topic will be 'Archean and Overview.' He "Archean and Early Early Proterozoic Proterozoic Geology Geology of the Lake Superior Superior Region Region -- An An Overview." He will will be Morey of of the the Minnesota Minnesota Geological GeologicalSurvey. Survey. introduced by Glen Morcy - Acknowledgements Acknowledgements We greatly appreciate the enthusiastic enthusiastic and vital vital assistance assistance of the the many many UW-Eau UW-Eau Claire Clairegeology geology student drivers, volunteered student drivers, registration helpers, helpers, projectionists, projectionists,and gofers. We also thank those who volunteercd to serve serve as as session session chairs, speakers, and authors; their dedication to to the the philosophy philosophy of ofthe theILSG ILSG isis conspicuous. conspicuous. viii viii �36th 36th ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Thunder underBay, Bay, Ontario Ontario 1990 1990 The 36th annual meetinggof Geology of the theInstitute Instituteon onLake LakeSuperior Sup Geol was held from Bay, Ontario. Ontario. The from May May 9 9 through May 12 12 in Thunder Bay, The meeting meeting was was hosted by Lakehead Bay. Manfred Lakehead University, University, Thunder Bay. Manfred M. M. Kehlenbeck Kehlenbeck served as General Chairman, Chairman, Graham Graham Borradaile Borradaile edited edited the the Field FieldTrip TripGuidebook, Guidebook,and andPhilip Philip W. W. Fralick Fralick assisted assisted with the the program programorganization. organization. .. ..;. ~.. ... . , . , ' ,:-7--. <,.* <<A . ,:. . ,. The and banquet banquet were were held held at at 'the the Airlane Motor Hotel on The technical technical sessions and on Thursday, May 11. A A total total of of 191 191geologists geologists registered for the the Thursday, May 10 and Friday, May meeting. meeting. Thirty-five Thirty-five oral oral and and twenty twenty poster papers papers were were presented presented on on aa wide wide variety variety of of subjects subjects pertinent to to the thegeology geology of of the the Lake LakeSuperior SuperiorRegion. Region. Three Three of of the the four four field field trips trips were were held held as as both both prepre- and and postpost- meeting meeting trips trips on on May respectively. The The fourth field trip trip was was held held on on May May 1 12. 9 and May 12 12 respectively. 2. Richard May 9 Sutcliffe of the the Ontario led 2 trips to the des Dies mes area Sutcliffe of Ontario Geological Geological Survey Survey led the L.ac Lac des area to to exposures of of mafic intrusions, intrusions, PGE PGE mineralization mineralization and and granitoid granitoid rocks. rocks. Graham Graham Borradaile Borradaile of of Lakehead field trips trips to to examine examinethe thegeology geology of of the the Lakehead University University led led 22field Shebandowan Shebandowan and Quetico Quetico subprovinces. subprovinces. Two Two trips led by Maurice Lavigue and John Scott Scott of the Ministry Ministry of Northern Development Development and Mines offered insigbt insight on base metal mineralization in the belt. The the Shebandowan Shebandowan greenstone belt. Thefinal finalfield fieldtrip tripwas wasled ledby bySteve Steve Kissin Kissin of Lakehead University University and focused on granitoid-related mineral deposits in the western Superior totalofof187 187geologists geologists registered registered for for the the seven seven field field Superior region. AAtotal excursions. excursions. To To transport transport the the entire entiregroup groupto torelatively relatively isolated areas required a total of 10 vans and 3 large buses. buses. In 10 vans Inaddition additionto tothe thetrip tripleaders, leaders,the thefollowing following members members of the Geology Department acted acted as asvan van drivers: drivers: P. Fralick, Frali M. Kehlenbeck, S. Kissin, D. Nicol, R. Viitala. Viitala. i... Nicol, S. S. Spivak, Spivak, B. Seemayer and it. : A total of on May 10. Manfred of 140 140 people attended the annual annual banquet b Kehienbeck Kehlenbeck presented presented the the 1990 1990Goldich Goldich Medal Medal to to Ken KenCard Cardof ofthe theGeological GeologicalSurvey Survey of of Canada for his many significant contributions to the geological understanding of Canada for his many significant contributions to the geological understanding of the the rocks in the Great Great Lakes Lakes Region. Region. J.J. J.J.Brummer, Brummer,M.G. M.G. Mudrey Mudrey and and F.W. F.W. Cambray Cambray served on the the Goldich Goldich Medal Medal Committee. Committee. Dedication Dedicationof of the the1990 1990I.LS.G. I.L.S.G. publication publication to to H.L. H.L. James James in in recognition recognition of of his his life-time life-time achievements achievements as a geologist in the Lake Lake Superior area area was was presented presented by by Mike Mudrey. Mudrey. After After numerous numerousunsatisfactory unsatisfactory replies to inquiring we were were delighted delighted to to have Herr inquiring participants during the day-long day-long program, we Doktor Doktor Professor Professor Wolfgang Wolfgang Gottlieb Gottlieb von von Schlunimerklutz Schlummerklutz (a.k.a. (a.k.a. Richard Ojakangas), Ojakangas), Direktor Institut filer fuer Welt Welt Probleme entertain all assembled Direktor of of the the Wissenschaftliche Wissenschaftliche Institut with with his presentation of recent research on the origin origin of Panzerenkotklotzen. His His meticulous research research and and marvellous marvellous illustrations illustrations made made aalasting lastingimpression. impression. Recognition of the importance importance of student student participation in the the meetings meetings of the the Institute led to the continued financial support of 16 student contributors in 1 1990. 16 in 990. Funds Institute to the continued financial for this waiver of of registration fees were drawn equally from the this assistance assistance which includes waiver two treasuries of the Institute. AAtotal totalofof$2,060.00 $2,060.00was spent in 1990. Four Four awards awards were ix �presented for the best oral oral and and poster poster papers papers by students for a total of $600.00. The recipients of the 1990 Best Student Paper Paper Awards Awardswere: were: Stephen D. Geerts, Natural 1990 Best Resources Research of Research Institute, Institute, Duluth, Duluth, MN.; MN.;Joseph Joseph D. D. Jablinski, Jablinski, University of Minnesota, Falls; and David R. Koehler, Koehler,University University of of Wisconsin, Wisconsin, River Falls, Minnesota, Duluth; Duluth; Steven Steven R. B. Saja, Michigan Technological Technological University, University,Houghton. Houghton J. J. Kiasner, Klasner, W. W. Kangas and D. Southwick served served on the Best Student Student Paper Paper Committee. Committee. The I.LS.G. 4.. The ~a~ 4 Themeeting meeting was was attended by J. I.L.S.G. Board Board of of Directors Directors met on on May Kalliokoski, M. Kehienbeck, J. Klasner, Lung Chan, M. Lavigne, P. Myers, M. Mudrey, Kehlenbeck, R. Ojakangas, Ojakangas, R. R. Sage, Sage,and andM. M.Smyk. Smyk. The The following following items items were were discussed: discussed: (1) (2) (3) (4) (5) (6) - The 1991 meeting meeting will be at at Eau Eau Claire, Claire, WI WI - Paul Myers as General The site site for for the the 1991 Chairman. Chairman. Voted to to accept accept Henry Henry Halls Halls on on the the Goldich Goldich Medal Medal Committee Committee to replace replace J.J. Brummer Bmmmer whose term term has has expired. expired. To continue papers. Funds continue the practice practice of of travel travel support for students presenting papers. Funds to be drawn drawn equally equally from the ILSG treasuries in the United States States and and Canada. Canada. The treasurer's report wasreceived. received. The balance balance in in the General report by by J. J. Kalliokoski Kalliokoski was account as as of of March March 27, 27,1990 1990 was $8,463.75. The Goldich Medal Fund contained $911.76. Fourteen Medals Medals are are in in care care of of G.B. G.B. Morey. Morey. Since Sincethe the 1990 1990meeting meeting was held in Thunder changing. Consequently, Thunder Bay Bay the the account account was was actively actively changing. Consequently, no meaningful statement could be made. M. M.Kehlenbeck, Kehlenbeck,however, however, assured the the Board that that all allexpenses expenses would would be met met and and that that no nodeficits deficitswould would be be incurred. incurred. Offers to host future future meetings meetings of the Institute Institute were received received from the Ministry Ministry of Northern Development Development and and Mines Mines (Marathon, (Marathon,Ontario), Ontario),Michigan Michigan Technological Technological University, and the the Minnesota MinnesotaGeological GeologicalSurvey. Survey. Alter After many many years years of of service, service, Joe Joe Kalliokoski Kalliokoski tendered tendered his his resignation resignation as asSecretarySecretaryTreasurer of the Institute. Joe has not only been carrying out the duties Institute. Joe has not only been carrying out the duties of of this this office, but has been of the Institute been very very active in many aspects of the functioning of Institute and has a sustained sustained record of contributions. contributions. His His sage sage advise has been a great help and comfort chairmen in in the the past. past. Voted comfort to many general chairmen Voted to to ask ask Mike Mike Mudrey to assume the the office office of of Secretary-Treasurer. Secretary-Treasurer. I wish wish to thank all those who dedicated their time and and expertise expertise to to make make the the 1990 1990 meeting meeting aa success. success. Respectfully submitted, submitted, M.M. Kehlenbeck M.M. x �CALENDAR OF EVENTS CALENDAR TUESDAY, APRIL APRIL 30 TUESDAY, Civic - Civic 3:00-5:00 p.m. p.m. 300-500 Early Registration Registrationfor forField FieldTrips Trips#1 #1 and and #2 #2 Participants Participants Early Center Inn Inn (CCI) Center (CCI) Lobby Lobby FIELD TRIP TRIP #1 #1 FIELD P.K. Sims, Sims, and and J.S. J.S. Kiasner Mountain shear Klasner (Leaders) (Leaders) "The "The Mountain shear zone zone - aa P.K. post-Penokean discrete ductile deformation zone" deformation 5:00p.m. for A Antigo (Park Inn) Inn) 5 0 0 p.m. Two Two vans veins depart for ntis (Park p.m., Park Park Inn, Pre-Field 8:30 p.m., Pre-Field Trip TripConference CoIfference - WEDNESDAY, MAY 11 FIELD TRIP TRIP #1 #1 FIELD 8:00 a.m. for the 8:00 a.m. Vans Vansdepart depart from from Park ParkInn, Inn,Antigo, Antis, for the mountain mountain area. area. Vans Vans by about about9:00 9:00p.m. p.m. return to CCI by FIELD TRIP TRIP #2 #2 FIELD L.S. Chan, L.S. Chan, P.E. P.E. Myers, Myers, and and R.L. R.L. Hay, Hay, (Leaders): (Leaders): "Features "Features and and contact in western significance of of the significance thePrecambrian-Cambrian Precambrian-Cambrian contact Wisconsin" Wisconsin" Pre-trip Seminar 8:00 a.m. Pre-mp Seminar CCI, CCI, Farwell Farwell Rm. Rm. a.m. Vans from CCI 8:20 a.m. Vans depart from CCI Lobby Lobby 2:00-5:00 p.m. 4:00-8:00 p.m. 8:00-11:00 p.m. Staff, CCI CCI Gibson Room Pre-Conference Planning Planning Session -- Staff, Pre-Conference Registration and Registration and check-in check-in for for pre-registrants, pre-registrants,Civic Civic Center Center Inn Inn Lobby Lobby Informal Get.together and Cash Informal Get-together and Cash Bar Bar Music by: by: Bill BillJordan Jordan Jazz Jazz Quintet Music THURSDAY, MAY 2 7:15 a.m - Civic Center Center Inn Inn (CCI) Lobby, Civic Registration - Lobby, (CCI) TECHNICAL SESSION TECHNICAL SESSION All Technical Technical Sessions Sessions are are in Room Center (RWCC); Poster Poster Sessions All Room C, Ray Wachs Civic Center in Rooms D B and of oral oral papers in RWCC RWCC Rooms and E. E. Schedules Schedules of papers are are shown shown on on pages pages xiii xiii and and xiv. xiv. a.m. Contributors should have posters up by 9:00 9:00 a.m. 8:00 a.m. 8:00 Introduction and Paul Myers, and Lorry Larry Introduction andWelcome: Welcome: Paul Myers,Conference Conference Chairman, and Claire Eau Claire Schnack, Chancellor, Schnewk, Chancellor, University University of Wisconsin - Eau 8:20-10:00 a.m. 8:20-10:OO Morning Session Chairs: R.W. Ojakangas Morning Session#1. #I. Chairs: R.W. Ojakangasand andA.B. A.B. Dkkas Dickas 10:00 1 0:OO a.m. a.m. 10:20-11:50 a.m. a,m. 10:20-11:50 - COFFEE BREAK COFFEE BREAK Morning Session G.L. Morning Session#2. #2.Chairs: Chairs: G.L.LaBerge LaBergeand andK. If.Schultz Schultz xi �NOON-2:00 p.m. BOARD Farwell BOARD LUNCHEON LUNCHEONAN]) ANDANNUAL ANNUALMEETING: MEETING: FanvellRoom, Room,CCI CCI 12:30-1:30 p.m. POSTER #1 - Authors POSTER SESSION SESSION #1 Authors present present (Poster (Posterpapers, papers,p.p. xv) xv) 1:40-3:00 p.m. Afternoon Chairs: V.W. AfternoonSession Session#1.#1. Chairs: V.WChandler .Chandlerand andG.B. G.B.Morey Morq - - COFFEE COFFEE BREAK BREAK -- Remove Remove Poster Papers Papers 3:00 p.m. 3:20-4:50 p.m. Afternoon MM. Kehienbeck AfternoonSession Session#2. #2.Chairs: Chairs: MM. &hienbeck and andC.C.Craddock Craddock 6:00-7:30 p.m. CASH CASH BAR: BAR: RWCC RWCC ROOM ROOMAA 7:30-10:00 p.m. ANNUAL ILSG ILSG BANQUET BANQUET -- RWCC RWCC Rooms A and B B -- Presentation to WJ. WJ.Hinze, Hinze,Purdue PurdueUniversity University Presentation of of the the Goldich Goldich Medal Medal to by V.W. Chandler V.W. Chandler Speaker: K. Sims, Sims,"Archean "Archean and and Early Early Proterozoic ProterozoicGeology Geology of the Speaker: Paul Paul K. introduced by Lake Superior An Overview"; introduced by G.B. G.B. Morey. Morey. SuperiorRegion Region -- An -- FRIDAY, 1991 FRIDAY, MAY MAY 3, 3,1991 8:00 p.m. Registration 8:00 a.m.-3:30 a.m.-330 p.m. Registrationand andSale SaleofofExtra ExtraProceedings ProceedingsVolumes Volumes 8:20 a.m. Morning Chairs: M.M. G. GMudrey, and MorningSession Session#1. #l. Chairs: . Mudrey,Jr.Jr. and7'.T.A.A.DeMatties DeMatties COFFEE COFFEEBREAK BREAK 10:00 a.m. 10:20-11:30 a.m. Morning G.W. Adams Chairs: G.W. A d a mand andBA. BA.Brown Brown MorningSession Session#2. #2.Chairs: 12:30-1:30 p.m. POSTER SESSION SESSION #2 -- Authors Authors present (poster (poster papers, papers, p. p. xvi) xvi) 1:40-2:40 p.m. Afternoon Chairs: W.S. #l. Chairs: W.S.Cordua Corduaand and M. M. Jirsa AfternoonSession Session#1. 2:40 p.m. Student Student Award Award Presentation, John Klasner Klasner -- - COFFEE Remove Poster Papers Papers COFFEEBREAK BREAK -- Remove 3:00 p.m. 3:20-4:30 p.m. Afternoon J. J. Kaliokoski AfternoonSession Session#2. #2.Chairs: Chairs: SalioImskiand a dJ. .C. C.Green Green 7:00-8:30 p.m. Pre-Trip Pre-Trip #3 #3Seminar, Seminar,CCI, CCI,Farwell Farwell Room, Room, M.G. M.G. Mudrey, Jr. and and B.A. B.A. Brown Brown SATURDAY, MAY 4, 1991 4,1991 FIELD TRIP #3 (Leaders), "Proterozoic Mudrey, Mudrey, Jr., and and B.A. BA. Brown Brown (Leaders), "Proterozoic volcanogenic massive sulfide deposits of northwestern northwestern Wisconsin' Wisconsin" 8:00 a.m. Bus departs from from front front entrance of of CCI M.G. xli xii �PROGRAM -- DAY 1, THURSDAY, THURSDAY, MAY 2, 1991 2,1991 L Atil hors Ii Inc 8:20 AM L 8:40 AM AM 8:40 L 9:00 AIvI 9:00 AM I 1 9:40 AM 10:20 AM 10:40 AM 11:00 AM AM 11:00 1 1 Read, William William F. F. Anderson, 1 Anderson, Raymond It. R 1 I 11:20 AM L Morey, G.B. G.B. and D.L Morev. D.L. Southwick Bachman, R.L. 11:40 AM 11:50 AM L 1:40 PM 1 The Relationship of of Topography Topography and and Gravity over over the the Lake Superior The Superior Swell:Evidence Evidencefor foraa Keweenaw Keweenaw Hot Hot SDOI Spot Swell: Aeromagnetic Surveying SurveyingProgram ProgramininMinnesota: Minnesota:Past Pastand and Future Future 1 Acromagnetic Physical Volcanology of the Footwall Rocks at the Winston Lake Massive Sulfide Deposit Geology & & Petrography Petrography of of the the Amnicon Amnicon Pluton, Pluton, Douglas Douglas County, County. Geology I COFFEE BREAK Wisconsin isc cons in 1 COFFEE BREAK Product of 1 The Neda Iron Iron Formation Formation -- AA Product of Vulcanism? Vulcanism? 1 1 1 The Amoco MG. The M.G.Eischeid Eischcid Oil Oil Test: Test: 4200 4200 Meters Meters of of Clastic Clashc Rocks of Midcontinent Rift Rift System Midcontinent System Manganese Mineralization MineralizationininEarlv EarlyProterozoic ProterozoicIron-Formation Iron-Formation of of the the Mansanese Emily District, Cuyuna Range, East-Central Minnesota The Homestake Mine: An Early Proterozoic Iron-Formation Hosted Gold Deposit CONCLUDING REMARKS BY SESSION CHAIRS END OF MORNING SESSION Laberge, Gene L. Early Proterozoic Rocks in the Monico, Wisconsin Area: Implications Magmatic Terrane Terranc on the Wisconsin Wisconsin Magmatic Isoclinal Slump Slump Folds Folds in in the the Lower Pokegama Ouartzite: Isoclinal Quartzite: Evidence Evidence for Seismicity Seismicityand and Slope Slope Instability InstabilityDuring During Deposition Deposition of of the for Animikie Group Group Animikie Continuous Strike-Slip Strike-SlipFault-En Fault-En Echelon Echelon Fracture Fracture Arrays in in Deformed Archean Rocks: for Fault Propagation Deformed Rocks: Implications for Mechanics 2:00 2 0 0 PM Hemming, S., S., G.N. GN. Hanson, Hemming, S.M. McLennan, and W.D. S.M. Sharp Sharp 2:20 2 2 0 PM Craddock, John John P. and 'Craddock, Andrew Moshoian Moshoian 2:40 PM 240 J Jerde, e r d e , Eric A A Evolution in in the Midcontinent Rift: Evidence Magmatic Evolution Evidence from from HypabyssalRocks Rocksof of the the North North Shore of Lake Superior Hypabyssal Superior COFFEE BREAK Cambray, F. William and Kazuya Fujita Cambray, F. Camhray, F. William William and Glenn Scott Scott Collision Induced Induced Ripoffs, Ripoffs, Ancient Ancient and and Modern: Modern: The The Midcontinent Collision Midcontinent Rift System and the the Red Red Sea-Gulf of Aden Rift System and Sea-Gulf of Aden Compared Compared A Late Keweenawan Thrust ? Marquette Keweenawan Thrust Marquette County, County,Michigan Michigan 'Manson, M.L. "Manson, M.L and H.C. Halls Halls Canibray, F. William Cambray, William and Joseph J. 1.Maneuso Mancuso 4:40 PM 4:40 The Geology and Geophysics of Major Post-Keweenawan Post-Keweenawan Faults in the Eastern Lake Superior Region the Detachment Faulting Faulting and and the Origin of the Asymmetric Detachment Asymmetric Depositional Pattern of of the Marquette Pattern Marquetie Trough CONCLUDING REMARKS REMARKS BY BY SESSION CHAIRS CONCLUDING 4:50 4 5 0 AM AM END O OFF AFTERNOON SESSION END SESSION L L The Wisconsin Gravity Minimum: Source & Implications POSTER SESSION 12 30 PM__J L 11 tie j Perspectives Osterberg, Steven A. and Ian R. Morrison Dickas, AJbert B. B. and and M.G. MG. Dickas, Albert Mudrey, Mudrev. Jr ..Jr. 9:20 AM 10:00 AM AM 10:00 Allen, David J. and William J. Hinze AJlen, David David J., 1., William 1 L. "Allen, Hinze, Hinze. and William William F. F. Cannon Chandler, Val W. 3:00 3 0 0 PM PM 3:20 3 2 0 PM 3:40 3 4 0 PM PM 4:00 4 0 0 PM 4:20 PM 4:20 XIII xiii �1991 PROGRAM -- DAY R DAY 2, FRIDAY, MAY MAY 3, 3,1991 I — Authors 'runt- Title — A.M.: A.M.: SYMPOSIUM ON O N MINERAL RESOURCES POTENTIAL OF O F NORTHERN NORTHERN WiSCONSIN WISCONSIN 8:20 8:20 Mv! AM 1 8:40 840 AM AM TA. and I DeMatties, DeMatties, T.A. and W.F. W.F. 1 DeMatties, TA. and MG. DeMatties, T.A M.G. Mudrw. Mudrey, Jr. 1 Hanson, Hanson., Jay Jav.C. C. 9:20 920 AM AM 1 9:40 940AIM AM I Bend, A Lower Proterozoic, Copper- and Gold-Enriched 1 Ground Geophysical Leading to the Bend Geophysical Bend Copper-Gold Coppcr.Gold - to .. . . Surveys Leading Discovery The The Lynne Lynne Massive Massive Sulfide Sulfide Deposit, Deposit, Oneida OneidaCounty, County,Wisconsin Wisconsin 1 Volcanogenic Volcanogenic Massive-Sulfide ~Deposit e b i int Taylor Taylor County, County,Wisconsin Wisconsin Rowell Rowell 9:00 900 AM AM Kennedy, Lawrence P., Teresa A. Harding, A Hardina. John A A.Schaff, Schaff, and Anne ~ n n M. e kZielinski Zielinski . Counts'. of the Flambeau Deposit, 1 Geology and Mineralogy Mineralogy of Deposit, Oneida Oneida County. 1 Thresher, Thresher, Jr., Jr.. J.J. Wisconsin .. I 10:00 10:00AM AM 10:20 AM la20 1 1 1 Mudrey, Jr., Jr., M.G. M.G. and and B.A. BA. Mudrey, Brown 10:40 la40 AM Brown, Bruce, A. A 11:00AM 11:00 AM I. Evans, Thomas J. 1 COFFEE BREAK BREAK Platinum Group Group Element Element Potential Potential of of Keweenawan Keweenawan Intrusive Intrusive Rock Rock in Wisconsin Wisconsin Nonmetallic Mineral Resources Resources and and Minor Metals Potential of Nonmetallic Mineral of Northern Wisconsin Wisconsin Regulating Metallic Mineral Development Development in in Wisconsin Wisconsin CONCLUDING REMARKS REMARKS BY BY SESSION SESSION CHAIRS CHAIRS 11:20 11:20 AM 11:TOAM 11:30 .... .AM .- . Geological Setting of of the Early Proterozoic BaseBase- and and Precious Precious Metal-Rich Metal-Rich Metavolcanic Meiavolcanic Belt Belt of of Wisconsin Wisconsin I END O MORNING SESSION -~ - OF - -F MORNING -~ - SESSION ~ POSTER SESSION SESSION 1230 1230PM PM Klasner. John S. and P.K. P.K. Sims Sims Klasner, 1:40 1:40PM Backthrusting in the Felch-Calunict I Thick-Skinned Thick-skinned back thrust in^ in Fclch-Calumcl Troughs Trouch* Region, Ki;Wn, - with the Southern Alps Northern Michigan Michigan -- A comparison with Alps 2:00 2:00 PM PM 2:20 2:20 PM PM A Preliminary Preliminary Study of Rejuvenated Movement Movement Along Along aa Precambrian Fault, Fault. St. St.Croix CroixCounty, Counlv. Wisconsin Wisconsin Middleton, Michael D. D. J.D., Jr., J.B. Paces, 1 Miller, J.D., Paces, J I Geochronology of of the the Duluth Complex: A Progress Report Geochronolo&y Complex: A and RE. R.E. Zartman Zartman STUDENT AWARD PRESENTATION 2:40 240 PM PM 1 300PM PM 3:00 3:20 PM 320 pM 3:40 340 PM 4:00 4:00 PM I Seifert, Karl E., Zell F. E. Peterman, and Scott ScoU E. Thieben Thieben I COFFEE BREAK The Nature Nature and and Source Source of of Midcontinent Midcontinent Rift Igneous Rocks Windom, Kenneth E., E, W.R. Windom, Kenneth W.R. Van Schmus, Schmus, Karl E. Seifert, Seifert, E.T. Wallin, Wallin. and R.R. Anderson Archean and Proterozoic Proterozoic Tectono-Magmatic Tectono-Magmatic Activity Activity Along the in Northwestern Northwestern Iowa, Iowa, Southern Margin of the Superior Superior Province Province in USA Chan, Lung Lung S. S. Paleomagnetism of of Central Dike Swarm: Palmmagnetism Central Wisconsin Wisconsin Dike Swarm: Constraints Constraints on on Thermomechanical Model of Midcontinent Rift CONCLUDING REMARKS BY SESSION CHAIRS 4:20 PM 4:30 PM J j J Li END OF AFTERNOON SESSION Li Student Contribution 'Student Contribution xiv -J J �POSTER SESSION DAY 1, THURSDAY, MAY MAY 2,1991, 2, 1991, DAY 12:30 PM PM -- 1:30 1:30 PM, PM, ROOMS ROOMS D D& &E E,,RW CWIC 12:30 CIVIC CENTER CENTER Brehm, Daniel J., C. Patrick Ervin, M.G. Brown, & & M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, M. L. Czechanski Czechanski M.L. Wisconsin: 1990 COGEOMAP Program Program Wisconsin: 1990 COGEOMAP Brown, B.A. and R.S. Maass Preliminary Bedrock Geology Map of Eau Claire County, Extension of Gravity Filed Coverage in East-Central Wisconsin *Dahl, Linda Linda J.J. and and Susan E. E. Brink *Dahl, I PreliminaryDrill Drill Core Core Study Studyof ofTwo TwoHoles HolesDrilled Drilledon on the the Preliminary Cuyuna Iron Iron Range Range and and Emily Emily Manganiferous Manganiferous Iron Iron Formation Formation Cuyuna District of of Minnesota Minnesota District *Mariano, J.J. and W.J. 'Mariano, W.J. Hinze Geophysical Investigations Investigationsofofthe the Midcontinent Midcontinent Rift in Geophysical Eastern Lake Superior Using Variable Magnetization Magnetization Eastern 1 Modeling 11 Modeling Nicholson, S.W., SW., K.J. Ki. Schulz, Nicholson, Schulz, W.F. W.F. Cannon, and and L.G. Cannon, L.G. Woodruff Woodruff Keweenawan The Porcupine Porcupine Mountains The Mountains Area, Area, Michigan Michigan - aa Keweenawan Central Volcano? Central Volcano? Reichhoff, J.A., J.A., S.A. S.A. Hauck, Hauck, and and D.L. DL. Reichhoff, Southwick Lithogeochemistry and and Geological Geological Mapping Mapping in in the the Vermilion Lilhogwchemistry Vermilion Minnesota, as as an an Aid Aid to Mineral Greenstone Bely, Bely, Minnesota, Exploration Exploration Severson, Mark 3. J. and Steven Steven A. A. Hauck Correlation of of Igneous Igneous Units Units at at the the Minnamax Deposit. NE NE Correlation Minnamax Deposit, Minnesota Teskey, D. Three-Dimensional Modelling Modelling of of the the Magnetic Anomaly Anomaly Three-Dimensional Lake Superior Central Lake Turnock, AC., A.C., D.C. D.C. Kamineni, Kamineni, and R. McGregor McGregor Chemistry and and Metamorphism Metamorphism of of an Archean Pillow Chemistry Pillow Basalt Welsh, James James L. L. and and Jayne Reichhoff Welsh, 1I 1 Geochemistry of of Archean Archean Rocks Rocks form form the the Virginia Virginia Horn area: Geochemistry Preliminary Interpretations Interpretations Preliminary Witthuhn, Kathleen 'Witthuhn, Stress Analysis Analysis of of the the Midcontinent Midcontinent Rift in Michigan Stress Michigan and Minnesota Zanko, L., Zanko, L., A. A. Gokee, Gokee, B. B. Dewey, Dewey, S. S. Hauck, and J. Pastor Geostatistical and and GIS GIS Evaluation of Biochemical Geostatistical Biochemical and Ecological Data Data From From Three Three Mineralized Mineralized Sites Sites (Au (Au & & Cu-NiCu-NiEcological PGE), Northeastern PGEt. Northeastern Minnesota: Minnesota: Implications Irn~licationsfor for Mineral Mineral in ~Exploration x ~ l & a t i oin n a Boreal Forest Student Contribution *Student xv I �POSTER POSTER SESSION SESSION DAY 2, 2, FRIDAY, MAY 33,, 1991 DAY PM-1:30 PM, PM, RROOMS D& &E E,,RW CIVIC RW C M C CENTER CENTER 112:30 2 3 0 PM-1:30 OOMS D Campbell, Frederick Frederick K. Campbell, The Feasibility of of Recovering Recovering Metals Metals From From aa Hazardous Waste Site; A A Brief Case Study Waste Geerts, Stephen D. Geeris, D. Horizons Geology of of Platinum Platinum Group Element-Enriched Element-Enriched Horizons Geology Prospect, St. St. Louis within the Dunka Copper-Nickel Prospect, within the Dunka Road Road Copper-Nickel Louis County, Minnesota Green, John C., Ed. Ed. Venzke, Venzke, Green, John C., and Tom Lawler and Lawler Drift Pebble Pebble Lithology Lithology of of the the Tomahawk Tomahawk Road Road Area, Area, Lake Lake Drift County, Minnesota, Minnesota, Used Used to to Help Help Infer Infer Local Bedrock County, Local Bedrock Heine, John John J., Tom A. Heine, A. Toth, Steven A. A. Hauck, and Steven George W. Shurr George Shurr Geology of of the the Meridian Meridian Aggregates AggregatesQuarry Quany and and the Gwlogy Surrounding Area, Area, St. St. Cloud, A Study of the Surrounding Cloud, Minnesota: Minnesota: A Study of the Bedrock Influences Influences on on the the Pre-Late Pre-Late Creiaceous Cretaceous Weathering Weathering Bedrock Profile Hinz, Peter Peter Hinz, Industrial Minerals Minerals of of Northwestern Northwestern Ontario Ontario Industrial Hinz, Pete1 Peter Hinz, Exploration and and Mining Activityin in Northwestern Northwestern Ontario Ontario Exploration Mining Activity TMJohnson, JamesS., S.,Denise Denise A. 'Johnson, James Stavish, Mary Mary K. Tozer, and Slavish, Surface Expression Expression of of Major Major Bedrock Bedrock Structural Structural Features Surface George W. Schurr Morrison, Ian R. R. Pick Lake Pick Lake Zinc-Copper-Silver Zinc-Copper-Silver Deposit Deposit Thompson, M.D., Thompson, M.D., L.D. L.D. McGinnis, M.G. MG. Mudrey, McGinnis, Mudrey, Jr., Jr., and CA'. C.P. Ervin Midcontinent Rift Rift Structure Structure Interpreted Interpreted From From the the Midcontinent GNtJArgonne Seismic Seismic Data Data Set Set GNIIArgonne Toth, Toth. Thomas Thomas A., A.. John John 3. I. Heine, & Steven A. A.1-lauck Hauck Regional Stratigraphic Stratigraphic Model Model of of Late Late Cretaceous Sediments Regional Sediments and their their Relationship with the Underlying and Underlying Pre-Late Cretaceous Weathering Weathering Profile Profile along along the the Minnesota Minnesota River River Cretaceous Valley, Minnesota Minnesota Valley, Woodzick, Thomas Thomas L., Gary Woodzick, P. Murdock, and Douglas E. Pride A Study Study of of Thematic Thematic Mapper Mapper Lineaments A Lineaments in Northwest Nevada J U 1 J U *Student Contribution Contribution "'Student J xvi U J �L L C [ L L [ ABSTRACTS ABSTRACTS xvii �Wisconsin Gravity Gravity Minimum: Source and Im~lications Implications The Wisconsin Source and '' and William William J. Hinze, D David David J. J. Allen and Department of Earth and Atmospheric Sciences, University, West Lafayette, Indiana Purdue University, The 1) attains its its most most negative The Wisconsin Wisconsin Gravity Gravity Minimum Minimum (Fig. (Fig. 1) negative values values of 1.5 Ga Ga Wolf Wolf River River Batholith, Batholith, but but extends extends approximately -95 approximately -95 milliGals milliGals over the outcrop of the 1.5 discordantly across the the Archean 1.9-1.8 Ga Penokean discordantly across Archean Marshfield Marshfield Terrane, Terrane. the 1.9-1.8 Penokean PembinePembineWausau Wausau Terrane, Terrane, and the the 1.76 1.76Ga Gaanorogenic anorogenic rhyolite-epizonal rhyolite-epizonal granite granite terrane terrane of of southern southern Wisconsin. The edges that the edges of of the the minimum minimum are arecharacterized characterized by by sharp sharp gradients gradients indicating indicating that source trend of of the anomaly source of the the anomaly anomaly lies lies atat shallow shallow depths. depths. The north-northeast north-northeast trend anomaly is discordant with the east-west discordant with east-west Penokean Penokean structural structural grain grain in in Wisconsin, Wisconsin, suggesting suggesting that that the the source of the source of the anomaly anomaly may may be be younger younger than than 1.8 Ga. Ga. Thus, Thus, we we propose propose that that the the entire entire Wisconsin Gravity Minimum Minimum is produced produced by by the Wolf River Batholith. Wisconsin Gravity Batholith. Although Although the the batholith batholith outcrops only in in northeast northeast Wisconsin, Wisconsin, the anomaly anomaly suggests suggests that itit lies lies buried buried beneath beneath aa thin thin outcrops cover cover of older older Precambrian Precambrian roof roof rocks rocks and and early earlyPaleozoic Paleozoic sedimentary sedimentary rocks rocks throughout throughout a substantial portion of Wisconsin. Wisconsin. Forward modeling modeling of gravity Forward gravity data along along several several profiles profiles across across the the Wisconsin Wisconsin Gravity Gravity Minimum South and and west of the Minimum supports supports the buried buried Wolf Wolf River RiverBatholith Batholith hypothesis. hypothesis. South west of the its its outcrop, the Wolf River River Batholith Batholith may may be be buried buried beneath beneath approximately approximately 44 km outcrop, the Wolf km of older older Precambrian rock, and and the batholith 10 and 15 15 km km (Allen, (Allen, 1990). 1990). Precambrian rock, batholith extends extends to depths between between 10 Figure Figure 22 is is an an interpreted geologic cross-section based on a gravity model along along a based on gravity model northwest-southeast northwest-southeast profile (Fig. (Fig. 1). 1). In northern northern Wisconsin, Wisconsin, the the negative negative gravity gravity anomaly anomaly is produced produced by by the the density density contrast contrast between between the the granitic granitic rocks rocks of of the theWolf WolfRiver RiverBatholith Batholith and the the 1.76 the denser denser Penokean Penokean and and Archean Archean rocks. rocks. In southern southern Wisconsin, Wisconsin, however, however, the 1.76 Ga anorogenic rhyolites-epizonalgranites granites and and Baraboo Baraboo quartzites quartzites have have densities densities similar similar to to that iinorogenic rhyolites-epizonal of the Wolf River Batholith; thus, the source of the gravity anomaly in southern Wisconsin the Wolf River Batholith; thus, the source of the gravity anomaly in southern Wisconsin is the density between the the Wolf Wolf River and the the denser, pre-l.76 Ga rocks the density contrast contrast between River Batholith Batholith and denser, pre-1.76 rocks which underlie the anorogenic granites, rhyolites, and quartzites. The lower crustal structure underlie the anorogenic granites, rhyolites, and quartzites. crustal structure shown shown in Figure Figure 2 was was obtained obtained by by projecting projecting aa crustal crustal model model based based on on aacombined combined seismic seismic reflection-gravity interpretationalong alongGLIMPCE GLIMPCEline lineHH in in Lake reflection-gravity interpretation Lake Michigan Michigan (Cannon (Cannon et et al., 1991) As shown in Figure 1991) west along along geophysical-anomaly geophysical-anomaly strike strike into intoWisconsin. Wisconsin. As shown in Figure 2, the the lower crustal structure does does not not significantly contribute contribute to to the the Wisconsin Wisconsin Gravity Gravity Minimum. Minimum. The emplacement of the emplacement of the Wolf Wolf River River Batholith Batholith may may have have been been controlled controlled by by prepreexisting the Eau existing structures. structures. For example, example, the Eau Pleine Pleine Shear Shear Zone, Zone, a 1.8 1.8 Ga Ga suture suture between between the the Pembine-Wausau Terraneand and the the Marshfield Terrane, has Pembine-Wausau Terrane Marshfield Terrane, has been been identified identified beneath beneath Lake Lake Michigan and projects the most negative portion of Michigan (Cannon (Cannon et et al., al., 1991) 1991) and projects through through the most negative portion of the the Wisconsin Gravity Minimum Minimum where where the Wolf River Batholith Wisconsin Gravity Batholith is thickest thickest (Fig. (Fig. 2). 2). The shear zone may have have acted acted as as aaconduit conduit along alongwhich which magma magma was was preferentially preferentially transported transported at 1.5 1.5 Ga. outcrops north northof of the the shear shear zone, zone, but but is is buried Ga. Also, Also, the Wolf Wolf River River Batholith Batholith outcrops buried to the the south. The northern portion of the batholith may have been uplifted relative to the southern south. northern of the batholith may have been uplifted relative to the southern portion portion at aa later later time timeduring duringshear shear zone zonereactivation. reactivation. Alternatively, the batholith batholith originally originally may have been emplaced to shallower levels in the Pembine-Wausau Terrane than have been emplaced to shallower levels in the Pembine-Wausau Terrane than in in the the Marshfield Marshfield Terrane. Terrane. The southeast southeast margin margin of of the theWisconsin Wisconsin Gravity Gravity Minimum Minimum closely closely approximates approximates a I �prominent magnetic magnetic boundary boundary which which separates separates aa positive positive anomaly anomaly to to the northwest prominent northwest from aa negative anomaly to the magnetic boundary, boundary, herein herein called called the the negative anomaly the southeast southeast (Fig. (Fig. 2). This magnetic Winnebago magnetic anomaly, anomaly, continues continues northeast northeast beyond beyond the the Wisconsin Wisconsin Gravity Gravity Minimum, Minimum, of the edge suggesting that it is not suggesting not the the magnetic magnetic signature signature of edge of of the the batholith, batholith, but but instead instead reflects reflects a pre-1.5 pre-1.5 Ga Ga structure structure which which controlled controlled the location location of the the southeast southeast margin margin of of the the Wolf River Batholith. Batholith. with the Wisconsin The general general correlation correlation of the the Wisconsin Wisconsin Gravity Minimum Minimum with Wisconsin Arch Since the Wolf River Batholith is suggests a possible genetic relationship. possible genetic relationship. Since Wolf River Batholith less dense dense than than the surrounding surrounding rocks, rocks, it may may have have been been intermittently intermittently uplifted uplifted over over the the past past 1.5 1.5 Ga in in response to buoyancy forces. buoyancy 60 -.4 50 40 30 20 -j 10 0 —10 —20 j —30 —40 —50 J —60 —70 —80 —90 J —100 F-I 0 0 - - 50 50 100 100 150 150 200 200 J 250 250 I Scale 1 : Kilometers Kilometers Figure 1: Figure 1: Bouguer gravity anomaly anomaly map map of of the Wisconsin Bouguer gravity Wisconsin area area based based on on four four kilometer kilometer gridded data. The Theline lineindicates indicatesthe theprofile profileshown shown in Figure 2. j J 2 U �_______ ____________________________ __________________ 0NW SE 2 0 ..... . . . -0 o m -. . .... _J . . . .......: :: :: a ; C . o0 .: .: 3 : ;. i—. .;-.. .:.. >- ..... ..... . . ....-.. . ............ - .: ... .-. ...... .. .. .. ...:.. '. . ..:. . -0 LI) Mi -. '0 .... .... ....... ..... .. .. . . . . . . . •. -0 --. .. 0 a — In_ - . -.- .-- -. cn o OR ...... -----------------— ........ Lrrzcr t r r c Or c ~oLOWZA r L O WCAUST ~~ m u s t MaGNETIC M A G N E T I C£NOSAL.Y ANOMALY I I SO 50 00 100 100 PRENTICE 200 250 200 250 DISTANCE DISTANCE (KM) (KM) WAUSAU WAUPACA — +I . J' I I 150 ISO •_• -. 'vj7 gfJ • A / PEMBINE-WAtJSAU TERRA. / 400 350 350 £1CRANITC 3açnQrsn\+ \ ' 300 300 SILW7U*LE _ANOROCtN1C FELSIC ROCKS..r - , ' — — -10 L__'__J I ' N FAULT MARS1ELDTERRANE , / / ICLEINE / / / / / " \ 1SHEARZONE N SUPERIOR,,I,...,I •I / /N N N/N / / / / / \ , / CRATON ..I..("S. ' ' ' / , ' , — -40 ', / / •1 N LAG ABA J -, I — 20 I N N N N S. .. I N N , .1 N S. N N — — N 'N N N N S. N •M... N N . • ' • • . - N \ — — • • S. — • • \ — • UPPER M&E . - 50 Fiaure 2: 2: Bouguer Bouguer gravity gravity and and total total intensity intensity magnetic magnetic anomaly anomaly profiles profiles and and related related geologic geologic Figure showing major major crustal crustal units units and and terranes. terranes. The dashed dashed line line indicates indicatesthe thegravitational gravitational model showing effect 20 km. See SeeFigure Figure1 1for forthe thelocation locationof ofthe theprofile. profile. effect of of density density variations variations beneath beneath 20km. REFERENCES REFERENCES CITED CITED implications, unpub. unpub. M. M. S. S. Allen, D. D. J., J., 1990, 1990,The TheWisconsin Wisconsin gravity gravity minimum: minimum: source source and and implications. Thesis, Thesis, Purdue PurdueUniv., Univ., W. W. Lafayette, Lafayette, IN, IN, 183 183p. p. Cannon, W. F., Lee, Lee, M. M. W., W., Hinze, Hinze. W. W.J., J., Schulz, Schulz, K. J., J., and and Green, Green, A. A. C., G., 1991, 1991.Deep Deep crustal crustal structure of of the the Precambrian Precambrian basement basement beneath beneath northern northern Lake LakeMichigan, Michigan,midcontinent midcontinent North 207-2 10. 19,207-210. North America: America:Geology Geology19, —as �The Relationship of Topography and Gravity over the Lake Superior Swell: Evidence for a Keweenaw Hot Spot? David J. Allen, William J. J. Hinze, Hinze, Department Department of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences, Purdue University, IN, and andWilliam WilliamF.F.Cannon, Cannon,USGS, USGS,Reston, Reston,VA VA Purdue University, West West Lafayette, Lafayette, IN, The The Lake Lake Superior Superior Swell Swell (Dutch, (Dutch, 1981) 1981) is is a a broad broad topographic topographic dome dome surrounding the Lake Superior Basin, the location of the most intense 1.1 Ga Lake Superior Basin, location of the most intense 1.1Ga Keweenawan rifting rifting activity. activity. Centered Keweenawan Centered on on Lake Lake Superior is a radial drainage drainage pattern pattern of of approximately approximately 1000 1000 km km diameter. diameter. Within Within this this area, area, streams streams flow flow radially radially outward outward from from the the relatively relatively small small inward-directed inward-directed drainage drainage system system of of the the Lake Lake Superior Basin (Figure 1). In addition, recent analysis of the regional gravity Basin (Figure 1). regional gravity and and topographic data indicates indicates that that aabroad broadnegative negativegravity gravityanomaly anomalyisisalso alsocentered centeredon on Lake Superior and is related to isostatic compensation of the Lake Superior Swell. is related to isostatic compensation of the Lake Superior Swell. The regional negative anomaly is defined by determining average gravity as a function of radial distance 1). As function distance from from aa central central point point in inLake LakeSuperior Superior (Figure (Figure 1). shown shown in in Figure Figure 2, 2, the theaverage averagegravity gravitydecreases, decreases, in inan anapproximately approximately linear linear manner, from a radial km, the the gravity gravity manner, from radial distance distance of of 650 650 km to to 300 300 km. Within Within300 300 km, anomalies produced by anomalies by the the Midcontinent Midcontinent Rift Rift obscure obscure the the regional regional anomaly, anomaly, while while km, the the average gravity is influenced by remote features unrelated to the beyond 650 km, the Lake Superior Swell. of topographic data indicates Lake Swell. Analysis Analysis of topographic data indicates that the the average average topography varies in an an inverse inverse manner manner to tothe thegravity gravity(Figure (Figure2). 2). Furthermore, the between average gravity relationship between gravity and and average average topography topography (Figure (Figure3) 3) suggests suggests that the that the Lake Lake Superior Superior Swell Swell is is in in approximate approximate isostatic isostatic equilibrium equilibrium (for aa fully fully -112 mGals/km). compensated topographic mCals/km). topographic load load of of density density2.67 2.67 g/cm3, slope slope == -112 Recently, has been been proposed that Recently, itit has that aa mantle mantle plume plume (the (theKeweenaw Keweenaw hot spot) spot) is related to to the the origin origin of of the the 1.1 1.1Ga Ga rifting rifting and and igneous igneous event event which which led led to to the thelarge large volume of basalts and the the short shorttime timespan spanof oftheir theireruption eruption(Hutchinson (Hutchinsonetetal., al.,1990; 1990; Nicholson and and Shirey, Shirey,1990). 1990). We propose that the the drainage drainage pattern, pattern, the the topographic topographic dome, and the negative gravity anomaly may still reflect the short-lived the negative gravity anomaly may still reflect the short-livedKeweenaw Keweenaw hot spot. spot. The persistence of the topographic related to a The persistence of topographic dome must be be isostatically isostatically related fundamental change change imprinted imprinted on on the lithosphere fundamental lithosphere by the the mantle mantle plume. plume. For a u s t which has has example, the Lake Superior Swell may be supported isostatically isostatically by a crust Beneath the Lake been thickened by the been the addition additionof ofKeweenawan Keweenawan basaltic basaltic rocks. rocks. Lake for example, example, the the crust crust thickens thickens by by as much as 15 km. km. The Superior Basin, Basin, for The negative negative gravity anomaly, anomaly, however, however, extends extends well well beyond beyond the theLake LakeSuperior SuperiorBasin, Basin, suggesting suggesting that the the crust crust may may have have been been thickened thickened (to (to aa lesser lesser degree) degree) over a much much broader broader area, well beyond beyond the outcrop of the the rift rift rocks. rocks. The Theobserved observed gravity gravity anomaly anomaly may may (of approximate approximate magnitude magnitude 11 be accounted for by a gradual gradual thickening thickening of of the the crust a u s t (of km) from from 650 650 km to to 300 300 km km radial radialdistance distance(Allen, (Allen,1990). 1990). The source of of the gravity anomaly, alternatively, may be a density contrast in contrast'in the mantle related to basalts. The to the the extraction extraction of of the the Keweenawan basalts. The depleted depleted upper upper mantle rocks are expected to be less dense (by at most 0.10 g/cm3) than undepleted 0.10 g/cm3) undepleted rocks due to the rocks due the removal removal of of the dense dense phase phase garnet garnet and/or an an increase increase in the the ratio (Boyd (Boyd and andMcCallister, McCallister, 1976; 1976; Oxburgh and Parmentier, Parmentier, 1977). 1977). The The MgO/FeO ratio 4 I - �negative negative gravity gravityanomaly anomalymay maybe beaccounted accountedfor forby by an an upper upper mantle mantlewhich whichbecomes becomes increasingly increasingly depleted depleted toward toward the the center center of of the theLake Lake Superior Superior Swell. Swell. Again, this this suggests suggests that that the theupper uppermantle mantlewas wasdisturbed disturbed over over aa region region much much broader broader than than the the outcrop outcropof of the therift riftrocks. rocks. 100 75 40 75 40 Figure ofofcentral North America 1:Map Mapofofpart part central North Americashowing showingmajor majordrainage drainagesystems. systems. Figure1: Arrows of stream streamflow. flow. Shaded Shadedareas areasare arecovered coveredby byPhanerozoic Phanerozoic Arrows denote denotedirection directionof platform platform sedimentary sedimentaryrocks; rocks;unshaded unshaded areas areasare areexposed exposedPrecambrian Precambrian rocks rocks of of the the Canadian ofthe theMidcontinent Midcontinent CanadianShield. Shield. Heavy Heavydashed dashedline lineshows showsapproximate approximateaxis axisof Rift Rift (MCR). (MCR). Short Shortdashed dashedline lineisisoutline outlineofofpresent presentLake LakeSuperior Superiordrainage drainagebasin. basin. Circle 1000km km diameter. diameter. Cross Crossin inLake LakeSuperior Superiorindicates indicatesposition position of ofcentral central Circleisis1000 point pointused usedininthe theradial radialaveraging averaginganalysis. analysis. 5 �-4 0 AVERAGE AVERAGE GRAVITY GRAVITY AND ANDAVERAGE AVERAGETOPOGRAPHY TOPOGRAPHY VERSUS VERSUS RADIAL RADIALDISTANCE DISTANCE CENTRAL POINT AT AT 47.97 47.97 N. p4, 888.39W CENTRAL POINT 8.39 W I • AVERAGE AVfRAGf GRAVITY GRAVITY VERSUS VERSUSAVERAGE AVERAGETOPOGRAPHY TOPOGRAPHY FOR FOR RADIAL DISTANCES DISTANCES FROM FROM 300 3 0 0KM KMTO TO 650 6 5 0KM KU SLOPE SLOPE= —114 -114 MGALS/KM. UCALS/KU. YIWT Y 1 N k —9 - 9 MOALS. MGALS. R= R = —0,963 -0.963 0 I I I )C 0 x —I 0 I •o C/) I LI I I -J 0 Ix I Lii >-I C. I I 'C > Cr 0 'C Cr . C S I x 0 In S •I • S S 00 00 - I- j >- > 'C', Cr 4 o' . J IS •GRI ITt '<CLEVATION 100 0 • I 'C C 0>o p1 - j Ui xx IC1 I IC 1 Cr I 200 I I -1- 300 400 500 600 700 0 800 RADIAL DISTANCE (NM) 0 00' 0 250 250 360 300 3 TOPOGRAPHY TOPOGRAPHY (M) (M) Figure Figure 3: 3: Average Averagegravity gravityvs. vs.average average topography topographyfor forradial radialdistance distancebetween between 300 300 km km and and650 650km. km. j j REFERENCES REFERENCESCITED CITED Allen, Allen, D. D. J., J., 1990, 1990, The Wisconsin Wisconsin gravity minimum: minimum: source source and andimplications, implications, unpub. M. S. S . Thesis, Thesis, Purdue PurdueUniv., Univ.,W. W.Lafayette, Lafayette,IN, IN,183 183p.p. unpub. M. Boyd, R., and and McCallister, McCallister, R. R. H., H., 1976, 1976, Densities Densities of of fertile fertile and andsterile sterile garnet garnet Boyd, F. F. R., J Figure Figure 2: 2: Average Averagegravity gravity and andaverage average topography topography vs. vs. radial radialdistance distancefrom from the the central central point point indicated indicatedininFigure Figure1.1. peridotites: 509-512. peridotites:Geophys. Geophys.Res. Res.Lett. Lett.3,3,509-512. I., 1981, 1981, Isostasy, Isostasy, epeirogeny, epeirogeny, and the the highland highland rim rimofofLake LakeSuperior: Superior: Z.2. Dutch, S. S. L, Dutch, Geomorph. N. F., Suppl.-Bd. 40, 27-41. Geomorph. N. F., Supp1.-Bd. 40,2741. R., White, White, R. R. S., S., Cannon, Cannon, W. W. F., F., and andSchulz, Schulz,K. K. J., J., 1990, 1990,Keweenaw Keweenaw Hutchinson, D. D.R., Hutchinson, hot hot spot: spot: geophysical geophysical evidence evidence for for aa 1.1 1.1 Ga Ga mantle mantle plume plumebeneath beneath the the RiftSystem: System:J.J.Geophys. Geophys.Res. Res.95(7), 95(7),10869-10884. 10869-10884. MidcontinentRift Midcontinent W., and andShirey, Shirey,S.S.B., B., 1990, 1990, Midcontinent Midcontinent Rift Rift volcanism volcanism in in the theLake Lake Nicholson, S. S. W., Nicholson, Superior region: region: Sr, Sr, Nd, Nd, and andPb Pbisotopic isotopicevidence evidencefor for aa mantle mantleplume plumeorigin: origin: Superior J.J. Geophys. Geophys.Res. Res.95(7), 95(7),10851-10868. 10851-10868. Oxburgh,E. E.R., R., and andParmentier, Parmentier,E.E.M., M., 1977, 1977,Compositional Compositional and anddensity densitystratification stratification Oxburgh, in oceanic lithosphere causes and andconsequences: consequences:J.J.Geol. Geol.Soc. Soc.London London133, 133, in oceanic lithosphere - causes 343-355. 343-355. - 6 J j Li �THE THEAMOCO AMOCO M.G. M.G. EISCHEID EISCHEID OIL OILTEST: TEST: 4200 1200METERS METERS OF OFCLASTIC CLASTIC ROCKS ROCKS OF OFMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM SYSTEM , :, Raymond Raymond R. Anderson Anderson . i. Iowa Iowa Department Denartmentof of Natural Natural Resources Resources ' , . ~:..'- ,.::. .. . . . .. ... . ,., . Geological GeologicalSurvey Survey Bureau Bureau . .~. . . - . iowa IowaCity, City,Iowa Iowa52242 52242 - ,> , The rheM.G. M.G. Eischeid Eischeid#1 #1deep deeppetroleum petroleumtest testwell wellwas wasdrilled drilledby bvAmoco AmocoProduction Production Company A riland andOctober, October,1987, 1987,near nearthe thetown townof of Flalbur Halbu?(Carroll (CarrollCounty) County)in in Company between between fipril west-central west-centralIowa. Iowa. Theewell wellreached reachedaatotal totaldepth depthofof5355 5355mm(17,851 (17,851feet) feet)including including235 235 feet feetof of glacial dacial drift, drift. 130 130feet feetof of Cretaceous CretaceousDakota DakotaFormation, Formation.2392 2392 feet feet of of Paleozoic Paleozoic strata including Pennsylvanian through Cambrian units dominated by carbonates, 813 Â¥ feet of an unidentified sandstone unit ("Unit H"), and 14,085 feet of "Red Clastics" assigned to the Keweenawan Supergroup, before reaching t.d. 151 feet into a mafic dike in the crystalline basement. The well was primarily drilled by rock bit, with duplicate samples sets presently reposited at the geological surveys of Iowa and Nebraska. In addition to the cuttings, five short cores were taken (see Fig. 1 for intervals intervals cored) cored) totaling about 66 feet. Splits are reposited at the Iowa Geological Survey Bureau. A series of preliminary investigations of Eischeid rock samples and geophysical logs were conducted shortly after the release of the materials. These investigations included stratigraphic and petrographic studies, analysis of source rock potential, porosity studies, clay mineralogy analysis, fluid inclusion studies, integrated isotopic and fluid inclusion analysis of vein-filling minerals, and the determination of an age for the basal basal dike. dike. The results of these studies were published by the Iowa Geological Survey Bureau Bureau (Anderson, (Anderson,1990a). 1990a). Of Of particular particular interest interestin inthe theEischeid Eischeidwell wellwere werethe the14,000 14,000feet feetof ofKeweenawan Keweenawan "Red clasticsections sectionsin in the theMidcontinent MidcontinentRift Riftsystem system "Red Clastic" Clastic" strata, one one of of the thethickest thickestclastic (MRS) (MRS) strata strata ever ever examined. examined. The Thesix sixformations formationsinitially initially described described and and assigned assigned to the the Keweenawan b Witzke Witzke (1990) (1990) constitute constitute two groups groups temporarily temporarily named named the the Keweenawan Supergroup Supergrou by "Upper" C asticSequences" Sequences" (Figure (Figure 1). 1). "Upper"and and "Lower "Lower Red Re Clastic 8f. Unit Unit H H "Unit H" H" displays displa s a coarser average grain size and is less well-cemented than the rocks of underlying "Upper Red Clastic is more arkosic than the quartz Clastic Sequence", Se uence", and is uartz arenites arenites of of the theoverlying overlyingMt. Mt. Simon SimonFm. Fm. The Theunit unitwas wasdiscussed discussedby byMcKay McKay(1990) (1990)who who described described itit as asbeing beingdominated dominatedby bytwo twoprimary primarylithologies, lithologies, aa fine fine to tovery very coarse coarse arkosic arkosic sandstone siltstone. McKay sandstone and and aa micaceous, micaceous, shaley shaley to sandy sand&sil~tone. McKay reported trace trace amounts amounts of of rnicrobrecciated fragments observed observed in in all all units of microbrecciated lithic lithicfragments fragmentsin in "Unit "Unit H",,similar to fragments the the "Red "Red Clastic Clastic Sequences", Se uences", and interpreted the the fragments fragments as the products products of of structural structural movements along fault zones that pervasively cut the the MRS sequence. Grains movements d o n fault pervasively cut Grains with with similar similar lithologic fabrics are not observed in the Mt. Simon interval of the well and have not been been reported reported in insimilar similar age age rocks rocks in in the the region. region. Consequently Consequently these rocks are thought to to be be of of Proterozoic Proterozoicage ageand andthe themay may be be associated associated with the the "Upper "Upper Red Red Clastic Clastic Sequence". Sequence". "Upper "Upper Red Clastic ClasticSequence" Sequence* The units totalling is composed of three three informal informalunits totalling The "Upper "Up e r Red RedClastic ClasticSequence" Sequence".is 6895 6895 feet, and an?occupies occupies the the same same stratigraphic strati aphic position position as the the Bayfield Bayfield Group Group of of f Wisconsin which it is correlated. Both Bot groups groups are aredominated dominatedby by fluvial fluvial deposition, deposition, Wisconsin with which but display dis la different compositional compositional characteristics. characteristics. The The Bayfield Bayfield is more mature mature than than the and others others (1990 (1990) reported reported that the the underlying un er yin Oronto Oronto Group, Group, whereas whereas Ludvigson and wer Red Clastic Clastic "Upper Red Red Clastic Elastic Sequence" Sequence" is is less less mature mature than than its itsunderlying underlying "Lower Sequence". Sequence". An Anupward upwardincrease increasein inthe thevolcanic volcanicrock rock fragment fragment component componentof of "Upper "UpperRed Red s^ 4.0 7 7 �-J J Clastic Clastic Sequence" Se uence" sandstones sandstones may record the unroofing of basalts on the the nearby nearby central central horst horst (Anderson, (An erson, 1990b). 1990b). 5 "Lower "LowerRed Red Clastic ClasticSequence" Sequence"' ...-.vfi., The The "Lower "Lower Red Red Clastic ClasticSequence" Sequeii&enis is also dsb composed cbfflbosed of three three informal informalunits unitsand and totals 7190 feet of strata. thebasal basalclastic clasticsequence sequence in in the theEischeid Eischeidwell well and and bears bears strata. ItItisisthe many similarities to the Oronto Group with which whichititisiscorrelated. correlated. The similarities to Group of of Wisconsin Wisconsin with primary difference between between the two groups groups are the basal basal units: units: the the Copper Copper Harbor Harbor Conglomerate (Oronto (Oronto Gp) Gp)being beingdominated dominatedby by very very coarse coarse volcanic volcanic clasts, clasts, "Unit B' Bn ("Lower by quartz ("Lower Red Clastic Clastic Sequence") Sequence") )) being being dominated dominated by uartz sand grains. grains. These These differences differences can can be be explained explained by the relative positions of the Oronto ronto Gp Gp and and the theEischeid Eischeid well well in in the the MRS. MRS. The TheOronto OrontoGroup Groupisisdescribed describedfrom fromexposures exposureson onthe thecentral centralhorst. horst. Early in rift rift history histo the the horst horst area areawas was aa graben, graben, and and the theconglomerate conglomerate clasts class were were apparently apparent! eroded eroded from romvolcanic volcanic rocks rocks that capped capped the the footwalls footwallsof of the thegraben-bounding graben-bounding faults. The T eEischeid Eischeidwell well was was drilled drilled off off the the central central horst, horst, and and penetrated penetrated the thefluvial fluvial system s stem that drained the the rift-bounding nft-bounding Proterozoic terrane. These Thesefluvial fluvialsystems systems had their e i r headwaters headwatersin inthe thegranites ranitesand andgneisses gneisses that that dominate dominatethe thebasement basementof ofthe theregion, region, and t%equartz quartzsands sandsthat thatdominate dominate"Unit "UnitB". B". and were were the thesource sourceof ofthe The Themiddle middleunit unitininthe the"Lower "LowerRed RedClastic ClasticSequence", Sequence", Unit UnitC, C,isisalmost almost1500 1500feet feet thick thick and and displays displaysclose close lithologic lithologicand and sedimentological sedimentologicalsimilarity similarityto to the theNonesuch NonesuchShale Shale of the the Oronto OrontoGroup. Group.Both Bothare arecharacterized characterizedby bygray graytotoblack blacksiltstone siltstoneand andshales. shales. (1990) identified a number number of of sedimentary sedimentary structures structures that that they they Ludvigson and others (1990) interpreted interpretedasasevidence evidenceofofdeposition depositionininaalake lakeor orsimilar similarstanding standingbody body of of water. water. Calcite Calcite cements C".than than in in other other"Red "RedCla.stic" Clastic" strata strata in in cements and and vein vein fills fills are are more more abundant abundantin in "Unit "Unit C', the high angle angle tectonic tectonic dips dipsranging rangin from the Eischeid Eischeidwell, well, and and cored cored intervals intervals display display high from 65° 65O to to vertical vertical and and slightly sli htly overturned. overturned. Ludvigson Ludvigson and and Spry Spry (1990) (1990) described described calcite calcite veinlets and ault surfaces surfaceswith with rough rough facets facets indicating indicating reverse reverse faulting faulting during during the the and slickensided slickensided fault later, of later, compression compression phase phase of of rift rift development. development. The Thepresence presenceofofsuch suchaathick thicksequence sequenceof lake lake sediments sediments outside outside of of the the former formercentral centralgraben graben suggests suggests that the the lakes lakes that that formed formed in in the the MRS MRSwere werelarge, large,extending extendingwell well beyond beyond the thelimits limits of of the thegraben-bounding graben-boundingfaults. faults. Seismic as much as 15 miles Seismic interpretations interpretations suggest suggest they they may may have extended ext es beyond beyond the the graben graben(Anderson, (Anderson,1990c). 1990~). a ^ 7 J J J ! -4 Figure Figure1: 1 : Correlation Correlationof of Eischeid EischeidRed RedClastics Clasti with with the theKeweenawan Keweenawan Supergroup Supergroup mean mean 1 1 1 framewoñ framework ,-Eischeid ,Eischeid - composhion composition ?? QF17L4 Q,F,,L, — 1 Unit UnitHH g. Q ~ F , , L , unit Keweenawan Supergroup J Q76F17L7 Unit G G Chequarnegon SS 0 QJnL9 Q&LB Unit UnitFF QeviI Island SS 6 % Q5SL13 QAGL,~ UnitE Unit E OrientaSs 0m Q75F1L UnitD FredaFm QF24L3 Unit C Nonesuch Fm a. (1) a. a C) Cl) o 0 8 -J QVFI2L1 Unit B ci. a. 0 —I C 0 Copper Harbor Fm 0 �Eischeid Petroleum Potential Potential Eischeid Petroleum Although of liquid liquid petroleum petroleum were Although no no shows shows of were encountered encounteredduring duringthe thedrilling drillingof of the the Eischeid well, trace trace amounts of methane Eischeid well, amounts of methane and and ethane ethane were were detected, detected, and and rare rare a intergi-anular black residues residues (suggestive of oil oil movement) inter anular black su estive of movement) were were observed observedin inthe the"Lower "Lower Red Red Clastic astic Sequence". Sequence". The Thedark ar shales shalesand andsiltstones siltstonesin inthe thelower lowersequence se uencewere wereshown shown by Palacas and and others others (1990) to once once have been organic-rich potential by Palacas (1990) to have been organic-rich p t e n t i a petroleum troleum source source !i S8 rocks, but are rocks, but are presently presently overmature. overmature. Methane Methane clathrates clathrates were were identified icfcntified in in fluid fluid inclusions in calcite and Spry who suggested suggested that that petroleum petroleum inclusions in calcite veins veins by by Ludvigson Ludvigson and S ry (1990) 1990) who was mobile mobile durin during the the compression compression phase phase of of MRS was istory. On On the the basis basis of of comparisons corn arisons S history. between between fluid fluid inclusions inc usions ans ans isotope isotope data data from from vein-filling vein-filling calcites calcites in in the the rift-flanking rift-flanking basins oil test) basins (Eischeid (Eischeid oil test) and and faults faults bounding boundin central central horsts horsts (Ludvigson (Ludvigson and and Anderson, Anderson, 1986), Ludvigson and and Sp Spry (1990) (1990)su suggested that such such fluid fluidwould wouldbe be transported transported towards towards 1986 ,Ludvigson ested that the may still still be be trapped the flanks anks of of the the rift. rift. TThis h i s petroleum petro eum may trapped on on the the flanks flanks of of the the Midcontinent MidcontinentRift Rift System. System. ^ .. &h as A The The M.G. M.G. Eischeid Eischeid #1 #1 well well offers offers aa great eat potential potentialto toincrease increaseour ourunderstandin understandin of the the development developmentof of the theMidcontinent MidcontinentRift Ri tSystem Systemand andthe theclastic clasticstrata strataassociated associated wit wit f F, it. it. Also, Also, the the rocks rocks encountered encountered in in the the well well demonstrated demonstrated that that large largevolumes volumes of of petroleum petroleum was was probably probably generated general from organic-rich units and may still be trapped ed within within the the structure. structure. References Anderson, The Amoco M.G. Eischeid Eischeid #1 #1 deep Anderson, R.R., R.R., 1990a, 1990a. The Amoco M.G. deeppetroleum petroleum test, test, Carroll CarrollCounty, County, Iowa. Iowa. Iowa Iowa Department 185 p.p. Departmentof ofNatural NaturalResources. Resources,Geological GeologicalSurvey SurveyBureau, Bureau,Special SpecialReport ReportSeries SeriesNo.2, No. 2,185 Ludvigson Ludvigson G.A. G.A. and and Anderson, Anderson. R.R., R.R., 1986, 1986,The The Douglas DouglasFault Fault atatAmnicon AmniconFalls FallsState StatePark, Park,Wisconsin: Wisconsin: Brittle Keweenawan Rocks. in Keweenawan Rocks. Proceedings Proceedings of of the the 32nd 32nd Annual Annual Meeting, Meeting, institute Institute Brittle cataclastic cataclastic textures textures in of of Lake SuperiorGeology, Wisconsin Geological Geological and NaturalHistory HistorySurvey, 50-51. Lake Superior Geology,Wisconsin and Natural Survey,pp.SO-Si. * the following references are * all all of of the following references are in in Anderson, Anderson,1990a 1990a** ** ** ** Anderson, R.R., 1990b, Review of current current studies studies of of Proterozoic eview of Proterozoic rocks rocks in in the the Amoco Amoco M.G. M.G. Eischeid #1 petroleum petroleumtest well. Carroll County, Iowa. Iowa. p.p.175-184. 175-184. testwell, Can-oilCounty, Anderson, data over Anderson, R.R., R.R., 1990c, 1990~.Interpretation Interpretation of of geophysical geophysical data over the the Midcontinent Midcontinent Rift Rift System System in in the the area area of of the #\petroleum petroleumtest, test,Carroll CarrollCounty, County,Iowa. Iowa.p.p.27-38. 27-38. the M.G. M.G. Eischeid E i i c i d *1 Ludvigson, G.L., (3.L., McKay, McKay, R.M., R.M., and and Andersoo, Anderson, R.R, R.R., 1990, 1990,Petrology Petrologyof of Keweenawan Keweenawan sedimentary sedimentaryrocks rocks in in the the M.G. M.G. Eiscbeid Eischeid #1 #1drillhole. drillhole.p.p.77-112. 77-112. Ludvigson, G.L., G.L., and Spry, P.G., Tectonic and paleahydrologic paleobydrologic significance carbonate veinlets P.G., 1990, 1990,Tectonic significance of carbonate veinlets in the Keweenawan sedimentary rocks Eischeid #l #1 drillhole. rocks of the Amoco MX3. M.G. Eischeid drillhole. p.p.153-168. 153168. Kewcenawan sedimentary McKay Regional aspects aspectsof of the the Mt. Mt. Simon Simon Formation Formation and and the the placement McKay R.M., R.M., 1990, 1990, Regional placement of of the the Mt. MI. SimonSimon pre-Mt. pre-Mt. Simon Simon sedimentary sedimentarycontact contact in in the the Amoco Amoco M.G. Eischeid Eischeid #1 #Idrillhole. drillhole.p. p.59-66. 59-66. , Palacas, J.W, Daws, M.J.,and and Anderson, Anderson, R.R., Rit, 1990, Palacas. J.G., J.G., Sebmoker, Schmoker, J.W., Daws. T.A., T.A., Pawlewicz, Pawlewicz, MJ., 1990,Petroleum Petroleum source-rock #1 well, well, source-rock assessment assessment of Middle Proterozoic (Keweenawan) (Kcweenawan) sedimentary sedimentary rocks, Eiscbeid #1 Carroll CarrollCounty, County,Iowa. Iowa.P.P.119-134. 119-134. Witzke, BJ., 1990, 1990, General General stratigraphy stratigraphy of of the the Phanerozoic Phanerowic and and Keweenawan Kcweenawan sequences sequences in in the the area area of of the the WWte, BJ., M.G. Eischeid #1drillhole, drillhole,Carroll CarrollCounty, County,Iowa. Iowa.P. P.39-58. 39-58. Eischeid#1 99 I �THE THEHOMESTAKE HOMESTAKEMINE MINE AN AN EARLY EARLY PROTEROZOIC PROTEROZOICIRON-FORMATION IRON-FORMATIONHOSTED HOSTEDGOLD GOLDDEPOSIT DEPOSIT R.L. R.L.Bachman Bachman District DistrictGeologist Geologist Homestake HomestakeMining MiningCompany Company Lead, Lead,South SouthDakota Dakota mine in the the northern northern Black Black Hills Hills of of South South Dakota, Dakota, USA USA isis the thelargest largest ironironformation-hosted hasprOduced produced 1,126 1,126tonnes tonnes (36.2 (36.2million million oz.) oz.)ofofgold goldfrom from formation-hosted gold gold deposit deposit known, known, and andhas The deposit was In 1990 the mine produced 12 tonnes of gold. million tonnes of ore milled. In 1990 the mine produced 12 tonnes of gold. The deposit was 130 130 million tomes of ore milled. discovered in 1876, 1876,and and the themine minehas hasoperated operated continuously continuously to to the the present present day. Gold Goldore oreisiscurrently currently discovered in mined 2,438meters. meters.Gold Goldisisthe theprincipal principalcommodity commodityproduced producedalong alongwith withaaminor minorsilver silver mined for fordepths depthsto to2,438 by-product. 5:l;base basemetal metalcontent contentisisnegligible. negligible. by-product. The Thegold/silver goldlsilverratio ratioaverages averages5:1; J j The The Homestake Homestake The Thedeposit deposit lies lies within within the theEarly EarlyProterozoic Proterozoiccore coreof ofthe theBlack BlackHills Hillsuplift, uplift,which whichrepresents represents the the southern rocks.Tectonism Tectonismand andthermal thermalactivity activityassociated associatedwith with southern most most exposure exposureof of Trans-Hudson Trans-Hudson orogen orogenrocks. the the Trans-Hudson Trans-Hudson event event occurred occurred as as aaresult resultofofthe thecollision collisionofofWyoming Wyomingand andSuperior SuperiorCratons Cratons contemporaneous contemporaneouswith with the the Penokean Penokean orogen. orogen. Proterozoic Proterozoicgold goldmetallization metallizationisisinterpreted interpretedtotobe beaa result result of of an an evolved, evolved,long longlived livedtecto-thermal tecto-thermalprocess processthat thatrelied reliedon onplate platescale scaleshear shearzones zonesasasfluid fluidconduits conduits asfluid fluidmobilizers. mobilizers. and zones zones of of high high geothermal geothermalgradient gradientas and Gold Gold ore orebodies bodiesatatHomestake Homestakeare arehosted hostedalmost almostexclusively exclusivelyby by the theEarly Early Proterozoic ProterozoicHomestake Homestake Formation, (15toto35% 35%total totalFe) Fe)consisting consistingofofsiderite sideritephyllite phylliteand/or and/orgrunerite gruneriteschist. schist. Formation,an aniron-formation iron-formation(15 The Theunderlying underlying Poorman Poorman Formation Formationisiscomposed composedof ofan anupper uppersequence sequenceofofsericite sericiteto.biotite-dominant to-biotite-dominant carbonate-quartz carbonate-quartz and graphitic graphiticphyllites phyllitesand andaalower lowervoluminous voluminoussequence sequenceofofhornblende-plagioclase hornblende-plagioclase schist schist of of tholeiitic tholeiitic affinity. affinity.The Theoverlying overlyingEllison EllisonFormation Formationconsists consistsofofsericite-quartz sericite-quartzphyllite phyllite@elitic (pelitic and and tuffaceous tuffaceous strata) strata) interbedded interbeddedwith with quartzite. quartzite. Strata Stratathat thatcontain containthe theHomestake Homestakedeposit depositwere werecomplexly complexlydeformed deformedby byaaseries seriesisoclinal isoclinaland andsheath sheath fold fold events events that that are are synchronous synchronous with with extensive extensive ductile ductile and and ductile-brittle ductile-brittle shearing. Mine Minearea area rocks rocks have metamorphism; metamorphic intensity arnphibolitefacies facies metamorphism; intensity have been been subjected subjected to upper greenschist-lower greenschist-lower amphibolite 1.72Ga GaS-type S-typegranite granitenortheast northeast of ofthe themine minepost-dated post-dated increases to to the thenortheast. northeast. Intrusion Intrusion of aa 1.72 increases with late regional metamorphism, metamorphism, and and appears appears contemporaneous contemporaneous with late stage stagesemi-brittle semi-brittledeformation deformation regional (Bachman (Bachman et al., al., 1990). 1990). Individual Individual ore bodies bodies are arecontained contained within within plunging plunging synclinal synclinal fold fold structures structures ofofFlomestake Homestake Formation Formation known known as as ledges. ledges. Ten Tenofofthese thesestructures structureshave haveproduced producedgold goldfrom fromrelatively relativelyundeformed, undeformed, elongate elongate tabular zones of quartz, quartz, siderite, siderite,chlorite, chlorite, pyrrhotite, pyrrhotite,arsenopyrite, arsenopyrite,minor minor pyrite, pyrite, and and native native gold. gold. Ore Ore mineralization mineralization is is developed developed within within and and adjacent adjacentto todilated dilatedsegments segmentsof oflate-stage late-stageductileductilebrittle aL, 1990). folds and brittle shears (Caddey et al., 1990). These Theseshears shearsand andassociated associated ore ore bodies cross-cut earlier folds overprint metamorphic metamorphic fabric. fabric. overprint 10 J J j �I I I I I I I I I At At least least two two stages stagesof of mineral mineral alteration alterationare are observed, observed, one oneof of which which issynmetamorphic is synmetarnorphic and andappears appears to to predate predate gold goldmineralization, mineralization,and anda asecond secondsynchronous synchronouswith withgold goldmineralization. mineralization. The Thepre-gold pre-gold mineral alteration stage is represented by extensive potassium and carbonate mineral alteration stage is represented by extensive potassium and carbonate metasomatism. metasomatism. Ore-stage Ore-stage hydrothermal hydrothermal alteration alterationappears appearsretrogressive retrogressiveproducing producingextensive extensivechlorite chlorite and and siderite sideritereplacement replacement of of the Homestake Formation in and adjacent to the ore bodies. the Homestake Formation in and adjacent to the ore bodies. Timing Timingof ofgold goldmineralization mineralizationatatHomestalce, Homestake, even even though though not not dated dated directly, directly, isis regarded regarded as asearly early Proterozoic. Proterozoic. Dating Datingofofzircon zirconfrom fromtuffaceous tuffaceoussediments sedimentswithin withinthe theEllison EllisonFormation Formation gave gave an an age ageof of 1.97 1.97 Ga Ga(Redden (Reddenetetal., al.,1990) 1990)and andprovide provideananapproximate approximateage agefor forHomestaice HomestakeFormation Formationdeposition. deposition. The The approximate approximate age ageof ofregional regionalmetamorphism metamorphism and and major majorregional regionalductile ductiledeformation deformationisis1.84 1.84 Ga Ga (Zartman (Zartmanand andStem, Stem,1967). 1967).The TheCrook CrookMountain MountainGranite Graniteand andassociated associateddeformation deformationat at1.72 1.72Ga Gaappears appears to topost-date post-dategold goldmineralization. mineralization. ItItisisinterpreted interpretedthat thatgold goldwas wasintroduced introducedafter afterpeak peakmetamorphism metamorphism (1.84 Ga) and prior to granite emplacement (1.72 Ga) by epigenetic processes. (1.84 Ga) and prior to granite emplacement (1.72 Ga) by epigenetic processes. I 1 REFERENCES REFERENCES Bachman, Crook Bachman, R.L., R.L., Campbell, Campbell, T.l., T.J.,and andSneyd, Sneyd,D.S., D.S.,1991, 1991, CrookMountain Mountaingranite graniteand andits itsrelation relation toto Early EarlyProterozoic Proterozoicgold goldmineralization mineralizationatatthe theHomestalce Homestake mine, mine, northern northern Black Black Hills, Hills, SD: SD: Geol GwlSoc. Soc. America, America, Abstracts Abstracts with with Programs, Programs, v. v. 22, 22, no. no. 6,6,p.2. p.2. Caddey, S.W., Bachman, R.L., Campbell, T.J., The Homestalce Caddey, S.W., Bachman, R.L., Campbell, T.J., Reid, Reid,R.R., R.R.,Otto, Otto,R.P., R.P.,1990, 1990, The Homestakegold gold mine, an Early Proterozoic iron-formation hosted gold deposit, Lawrence County, mine, an Early Proterozoic iron-formation hosted gold deposit, Lawrence County,South SouthDakota: Dakota: U.S. U.S.Geol GeolSurvey SurveyBull. Bull. 1857-3 1857-1(in (inpress). press). Redden, DeWitt, 1990, U-Th-Pb geochronology Redden, J.A., J.A., Peterman, Petennan,Z.E., Z.E.,Zartman, Zartman,R.E., R.E.,and and DeWitt,E.,E. , 1990, U-Th-Pb geochronologyand and preliminary preliminaryinterpretation interpretationofofPrecambrian Precambriantectonic tectonicevents eventsin inthe theBlack BlackHills, Hills,South SouthDakota: Dakota:(3eol. Gwl. Assoc. Assoc.Canada CanadaSpec. Spec.Paper Paperononthe theTrans-Hudson Trans-HudsonOrogen Orogen(in (inpress). press). Zartman, R.E., and Stem, T.W., 1967, Isotopic age and geologic relationships Little Elic Zartman, R.E., and Stem, T.W., 1967, Isotopic age and gwlogic relationshipsofofthe the Little Elk Granite, northern Black Hills, South Dakota; U.S. Geol. Survey Prof. Paper 575-D, Granite, northern Black Hills, South Dakota; U.S. Geol. Survey Prof. Paper 575-D, p.p.D157D157Dl 63. Ill �EXTENSION OF GRAVITY FILED COVERAGE IN EAST-CENTRAL WISCONSIN: 1990 COGEOMAP PROGRAM Daniel Daniel J. J. Brehm, Brehm, C. C. Patrick Patrick Ervin, Ervin, Dept. Dept:of of Geology, Geology, Northern Northern Illinois University, University, DeKalb, DeKalb, IL IL 60115 60115 M.G. M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, Brown, M.L. M.L. Czechanski, Czechanski, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Mineral Mineral Point Point Rd. Rd., Madison, Madison, WI WI 53705 53705 Illinois J • During During the the summer summer of of 1990, 1990, approximately approximately 4800 4800 additional additional measurements of of the the earth's earth's gravity gravity field field were were made made in in an an area area measurements 44 && 45 45 degrees degrees latitude latitude and and by 88 88 & 90 degrees degrees bounded by by 44 bounded & 90 longitude. longitude. Most Most stations stations are are located located at at surveyed surveyed elevation elevation points points posted posted on on USGS USGS topographic topographic sheets sheets and and are are spaced spaced one one mile mile apart, apart, except except where where access access was was limited. limited. Northern Northern Illinois Illinois University's Lacoste-Romberg LaCoste-Romberggravity gravity meter meter G409 G409 was wasused. used. Data .University's Data are are tied tied to to the the State State of of Wisconsin Wisconsin Primary Primary Gravity Gravity Base Base Station Station Network (Ervin, (Ervin, 1983), 1983), which which is is in in turn turn tied tied to to the the International International Network Gravity Gravity Standardization StandardizationNetworlc-1971 Network-1971 (DMAAC, (DMAAC,1974). 1974). Normally Normally accepted accepted field field and and processing processing procedures procedures were were used. used. These These data data have have been been combined combined with with earlier earlier data data to to produce produce aa much much more more detailed tailed Bouguer Bouguer gravity gravity anomaly anomaly map. map. The The northwest northwest section section of of the the area area is is underlain underlain by by primarily primarily Proterozoic Proterozoic and and Late Late Archean Archean rocks, rocks,comprised comprisedof ofqüartzite, quartzite, granite, granite, rhyolite, rhyolite, granodiorite, granodiorite,gneiss, gneiss, metavolcanics, metavolcanics, and and metasediments. metasediments. This This variability variability is is reflected reflected in in the the complex complex character character of of the the Bouguer Bouguer gravity gravity anomalies. anomalies. The The north-central north-central part part of of the the region region contains contains the the southern southe part which is is part of of the the Middle Middle Proterozoic Proterozoic Wolf Wolf River River Batholith, Batholith, which composed with composed primarily primarily of of granitic granitic and and syenitic syenitic rocks, rocks, with inclusions inclusions of of quartz quartz monzonite, monzonite,anorthosite, anorthosite,and and gabbro. gabbro. The The greater greater homogeneity homogeneity of of the the Wolf Wolf River River Batholith Batholith produces produces aa smoother smoother Bouguer Bouguer gravity gravity field field than than exists exists in in the the northwest northwest section. section. The The southern southern and and eastern eastern areas areas of of the the map map largely largely overly overly Paleozoic Paleozoic sedimentary sedimentary rocks, rocks, possibly possibly underlain underlain at at depth depth by by an an extension extension of of the the Wolf Wolf River River Batholith Batholith (Allen, (Allen, 1990), 1990). resulting resulting in in aa Bouguer Bouguer gravity gravity field field dominated dominated by by longer longer wavelength wavelength anomalies anomalies than than in in the the rest rest of of the the survey surveyregion. region. REFERENCES REFERENCES Allen, Allen, D.J. D.J.,1990, 1990, The The Wisconsin Wisconsin Gravity Gravity Minimum: Source Source and and Implications, Implications,unpub. unpub. Ms MS thesis, thesis, Purdue Purdue Univ., Univ.,West West Lafayette, Lafayette, IN., IN., 183 183p. p. , Ervin, C.P.,1983, 1983,Wisconsin Wisconsin Gravity Gravity Base Base Station StationNetwork, Network,Wis. Wis Ervin, C.P., Geol. Geol. && Nat. Mat. Hist. Hist. Sun. S u m .Misc. Misc.Pap. Pap. 83-1, 83-1,43 43 p. p. - North North -j DMAAC, DMAAC, 1974, 1974, World World Relative Relative Gravity Gravity Reference Reference Network Network - America, DMAAC Ref. Ref. Pub. Pub. No. No. 25, 25,1974 1974Supplement. Supplement. America, DMAAC 12 J �I I I I i Nonmetallic Mineral Mineral Resources Minor Metals Metals Potential Potential Nonmetallic Resources and and Minor of Northern of Northern Wisconsin Wisconsin , .: .. Bruce nice A. A. Brown Brown Wisconsin Geological and Natural :nL and Natural History HistorySurvey Survey . . The Precambrian Precambrian terranes northern Wisconsin Wisconsin contain The terranes of of northern contain significant significant nonmetallic nmetallic mineral mineral resources resources and and have have the the potential potential for for other other metal metal deposits deposits in addition addition to to volcanic—hosted volcanic-hosted massive massive sulfides. sulfides. The The region region has has aa long long history stone and a variety of story as a producer of building and ornamental ornamental stone crushed stone crushed stone products. products. Other Other products products include include weathered weathered or or "rotten" "rotten" granite granite and clay clay from from weathered weathered crystalline crystalline rocks rocks and and glacial glacial deposits. deposits. Northern Northern Wisconsin contains contains potentially potentially economic Wisconsin economic occurrences occurrences of of industrial industrial minerals minerals (talc, graphite, graphite, marble,-kyanite, marble, kyanite, nepheline (talc, nepheline syenite, syenite, silica silica sand, sand. and and others) others) rare metals (molybdenum, Significant and rare (molybdenum, beryllium, beryllium, lithium, lithium, and and others). others). Significant deposits of deposits of iron iron are are also also present present but but are are not not currently currently economical economical to to produce. produce. In recent years, years, dimension dimension stone st-oneproduction production has has maintained maintained aa low low but but steady level steady level of of activity; activity; the the. crushed crushed stone stone industry industry has has grown grown significantly. significantly. This growth in response growing demand for ha? been been in response to a growing for high high quality quality railroad This growth has ballast and changing changing construction construction specifications specifications that that reQuire require higher higher quality aggregates aggregates for for base base course course and and asphalt asphalt paving paving mixtures. mixtures. Specialized Specialized metavolcanic rock operations produce crushed crushed metavolcanic rock for for roofing roofing granules granules and aggregates for 'aggregates for terrazzo terrazzo stone stoneand and synthetic syntheticgranite graniteproduction. production. metal potential Although base base and Although and precious precious metal potential has has attracted attracted much much attention attention recently, the recently, the nonmetallic nonmetallic minerals minerals have have long longbeen been and and will continue continue to to be be aa major economic economic resource . Important Important factors major resource of of northern northernWisconsin Wisconsin. factors are are aa good good transportation network and transportat ion network and Wisconsin's favorable favorable location location in in respect respect. to markets in The future future development in the markets theupper upperMidwest. Midwest. The development of of regulatory regulatoryframework framework on t:he the state for ure on stateand and local localLevel level will willhave have*important important implications inipl-i.cations forfut future deve 1 opmen t of hi s industry-. development of tthis industry. �j J J Preliminary Preliminary Bedrock Bedrock Geologic Geologic Map Map of of Eat, Eau Claire County, Claire County. Wisconsin Wisconsin J B.A. Brown Brown & B.A. & U.S. R.S. Maass Maass Wisconsin Geological and Wisconsin Geological and Natural Natural History HistorySurvey Survey Eau Claire Claire Cotwty is underlain Eau County is underlain by by rocks rocks ranging ranging froni from Early Early Proterozoic Proterozoic and and Archean Archean (?) ( ? ) to to Late Late Cambrian Cambrian age. age. Precambrian Precambrian rock rock is is exposed exposed in in scattered cattered outcrops outcrops along along the the Eau Eau Claire Claire River River and and tributaries tributaries in in northeastern northeastern Eau au Claire Claire County. County. The The Precambrian Precambrian consists consists of of aa suite suite of of amphibolites amphibolites and and granitic gneisses what is probably a a younger younger granitic gneisses of of possible possible Archean Archean age, age, and and what is probably sequence of inetavolcanic and metasedimentary metasedimentaryrocks rocksand andgranitic graniticintrusions intrusions of of equence of metavolcanic and probable Penokean Penokean (1850 maficdikes dikescut cut older older units probable (1850 Ma) Ma) age. age. Underformed Underfonned mafic unit.sand and may he as Kewanawan. asyoung youngasas Kewanawan. may be The Precambrian i.s i.s overlain overlain by Cambrianclastic clastic and The Precambrian by Upper Upper Cambrian and carbonate carbonate rocks Mound, and Trempealeau The Upper rocks of ofthe theElk Elk Mound,Tunnel TunnelCity, City, and TrempealeauGroups. Groups. The Upper Cambrian contains two sedimentary cycles. The lower lower cycle Cambrian contains two fining—upward fining-upward sedimentary cycles. The cycle consists of Mount that grades into the consists ofthe thebasal basal Mount Simon Simon sandstone sandstone that grades upward upward into the glauconitic sandy dolomite dolomite of of the the St. Lawrence Lawrence glauconitic Tunnel Tunnel City City Group Group and sandy Format ion. ion. Format Eau Claire County has no no historical historical record Eau Claire County has recordof ofmineral mineralproduction productionfrom from the Precambrian. Residual clay with thethe Cambrian/Precambrian the Precambrian. Residual clay is isassociated associated with Cambrian/Precambrian unconformity, and Wonewoc ion 1s is aa potential ica sand. andthe the WonewocFormat Formation potential source source of of sil silica sand. mconfotmi~y, The only Paleozoic Faleozoic unit unit potentially the St.St. Lawrence The only potentially suit-able suitable for foraggregate aggregateisi.s the Lawrence dolomite, whichis is present. present only on ridge ridge tops area nf in the thesouthwestern southwestern area of the the dolomite, which only on tops in county. Pleistocene county. Pleistocene alluvial alluvial deposits deposits along along the the Chippewa Chippewa and Eau Eau Claire Claire fers Principal aqui Rivers eriols. Principal Rivers are are the the primary primary source sourceof ofconstruction constructionmat materials. aqui'fers arc are the alluvial alluvial deposits deposits and and the the Mount Mount Simon Simon sandstone. sandstone. J J j 14 �I I fl 1 , Collision Induced Collision Induced Ripoffs, Ripoffs, Ancient and and Modern: Modern: The Mideontinent Rift System System and and the Red Sea—Gulf Midcontinent Rift Sea-Gulf of of Aden Aden compared. compared. - ' F. William Cambray F. William Cambray and and Kazuya Kazuya Fujita, Fujita, Dept. F p t . of of Geol. Geol. Sci., Sci., Michigan State State University, East MI 48824—1115; Michigan University, East Lansing MI 48824-1115; 517—355—4626) 517-355-4626) Slab pull is considered to major force force in in determining determining slab is considered to be a major the rate Irregular or the rate and and directions directions of of plate plate motion. motion. oblique convergence oblique convergence will will result result in in closure closure of of an an ocean ocean at at some some localities localities prior prior to to others. others. Once a portion portion of of the the subducting plate has subducting has sutured, sutured, the the plate plate will will slow slow down down or or stop. Adjacent, stop. Adjacent, unclosed unclosed sections sections of oceanic oceanic crust, crust, however, will however, will continue continue subduct subduct under under the the influence influence of of slab slab pull( fig.1.l). This may may result result in in tensional tensional stresses pull( fig.l.l). This stresses in in a portion portion the a the subducting subducting plate. plate. Since fractures fractures are are more likely t to likely o develop in in the the weaker, continental continental part of of the the subducting subducting plate, plate, aa fragment fragment of of the the plate plate may may be be detached detached along an intracontinental Opening along intracontinental rift rift system system (fig.1.2). (fig.1.2). of this of this rift rift system system would would be be limited limited to to a a small small ocean ocean basin continuing subduction close the the remaining remaining basin since since continuing subduction will close portion of Closure of portion of the the original original ocean ocean basin. basin. Closure of the the original ocean original ocean basin, could could then then result result in in compression compression in in ig.1.3). This sequence the rift rift system system (f(fig.1.3). sequence explains explains the the synchronous association extension and compression, compression, near synchronous association of of extension and the the subsequent subsequent deformation and deformation of of the the rift rift fill, fill, as as found found in many once once extensional extensional regions. regions. The Red Sea Sea is is a a modern example example of of this this process. process. Closure Tethys occurred occurred first the Mediterranean Mediterranean and of the Tethys first in the and left left a portion a portion of of the the African African plate, plate, with with attached attached oceanic oceanic crust, region. still subducting the Zagros crust, still subducting under under the Zagros region. Continuing slab slab pull pull in Continuing in this this region, region, combined combined with with the the restraint to induced the the detachment of the restraint to the the west, west, induced detachment of the Arabian Peninsula Peninsula along along the the Red Red Sea Sea and and Gulf Gulf of Arabian of Aden Aden Mid Continent Rift (fig.2). Extension in the Proterozoic Mid system of North America was coincident with the the Grenville Grenville The rift compressional event event to to the the south compressional south and and east. east. The rift experienced only limited limited opening opening which we suggest suggest was was due due to slab—pull slab-pull along an unclosed segment in the collision zone of the belt (fig.3). Grenville Orogenic zone of the Grenville (fig.3). Subsequently, the the entire entire collision collision zone zone closed closed and and the Subsequently, rift was pushed back into place giving rise to a complex complex pattern of of folds folds and and flower flower structures structures (fig.4). (fig.4). 15 �TURKEY GREECE BITLIS ARABIAN NORTH 1 /"ass? ' Early Miocene Fig. 2 Fig. 2 3. COMPLETE CLOS -I Fio 1 J Fig. 3 Fig. 3 j J 4 —4 Fig.4 4 Fig. 16 Cambray and F u j i t a (1991) Cambray and Fujita (1991) �DETACHMENT DETACHMENT FAULTING FAULTING AND AND THE THE ORIGIN ORIGIN OF OF THE THE ASYMMETRIC ASYMMETRIC DEPOSITIONAL DEPOSITIONAL PATTERN PATTERN OF OF THE THE MARQUETTE MARQUETTE TROUGH.F.wjlljam TROUGH.P.William Cambray, Dept Dept of of Cambray, Geological Sciences, Sciences, Michigan Michigan State State University, University, East East Lansing Lansing MI MI Geological 48824., Joseph Joseph J.Mancuso, J-Mancuso, Dept. Dept. of of Geology, Geology, Bowling Bowling Green Green State State 48824., University, Bowling Bowling Green, Green, OH OH 43403., 43403., and and Went Went Slitor, Slitor, C.C.I., c.c.I., University, 504, 504, Spruce Spruce Street, Street, Ishpeming, Ishpeming, MI MI 49849. 49849. L L L L L L The Marquette Marquette Trough Trough is is one one of of several several fault fault bound bound basins basins The set into into the the Archean Archean crust crust of of northern northern Michigan Michigan which which contain contain set tower Lower Proterozoic Proterozoic metasedimentary metaseditnentary rocks. rocks. The The pattern pattern is is interpreted interpreted as as deposition deposition in in rift rift basins basins associated associated with with the the development development of of aa passive passive margin margin prior prior to to the thePenokean PenokeanOrogeny. Orogeny. The by collision collision of of an an island island arc arc to to the the The orogeny orogeny was was triggered triggered by south. south. Deposition Deposition in in the the trough trough began began with with the the Siamo Siamo Formation Formation which consists consists of of alternating alternating layers layers of of pelite pelite and and arenite, arenite, the the which latter latter having having turbidite turbidite characteristics. characteristics. This was was followed followed by by aa thick thick sequence sequence of of banded banded iron iron formation, formation, the the Negaunee Negaunee BIF. BIF. The The iron iron formation formation is is interbedded interbedded with with clastic clastic lenses lenses which which thicken thicken and and become become more more frequent frequent towards towards the the southern southern margin margin suggesting suggesting provenance provenance from from this this direction, direction, sole sole marks marks indicating indicating aa turbidite turbidite origin origin have have been been found found at at the the base base of of these these layers. layers. The The clastic clastic lenses are are somewhat somewhat irregular irregular in in distribution distribution and and disappear disappear lenses rather rather abruptly abruptly to to the the north. north. Changes Changes in in the the pattern pattern of of clastics elastics is is often often associated associated with with faults. faults. This This pattern pattern is is similar similar to to asymmetric asymmetric fault fault basins basins which which have have been been describe describe in in relation relation to to major crustal crustal detachment detachment faults faults in in the the Cenozoic Cenozoic of of the the Western Western US US major (fig.l). (fig.1) The The overall overall stratigraphic stratigraphic pattern pattern suggests suggests that that such such aa detachment detachment may may be be present. present. On On the the south south side side the the stratigraphy stratiara~hvis is truncated truncated adjacent adjacent to to the the margin margin which which is is consistent consistent with with continual displacement during sedimentation whereas the continual displacement during sedimentation whereas the . succession succession is is more more continuous continuous across across the the margin margin of of the the trough trough (fig.l). The Palmer Gneiss is a candidate for the main detachment L L L (fig.1). The Palmer Gneiss is a candidate for the main detachment fault fault on on the the south south side, side. outcrops Outcrops of of the the gneiss gneiss close close to to the the contact contact with with the the Proterozoic Proterozoic rocks rocks are are broken broken and and contain contain chlorite, chlorite, this this lithology lithology passes passes into into aa banded banded gneiss gneiss to to the the south south near near the the Tilden Tilden Mine. Mine. The The banding banding consist consist of of normal normal gneissic gneissic texture texture interspersed interspersed with with mylonite. mylonite. This This association association is is similar similar to to the the description description of of detachment detachment surfaces surfaces in in the the western western US. US. The The chlorite chlorite rich rich material material represents represents the the high high level level breccia breccia which which formed formed in in the the brittle brittle zone zone and and the the banded banded mylonite mylonite is is the the deeper deeper ductile ductile portion portion of of the the detachment detachment fault. fault. The The two two were were brought brought together together by by aa large large normal normal displacement. displacement. The The Penokean Penokean orogeny Orogeny complicated complicated the the picture, picture, reactivating reactivating some some of of the the normal normal faults faults as as reverse reverse faults faults but but the the basic basic pattern pattern is isstill stillrecognizable recognizable (fig. (fig.2) 2). - 17 �MZXNNlsb 10 3HZ 11nn0uw4 Irnouz ñt%V1Wt3) put •Osnotnj4 (1661 N ______ ______ 8I MCqUHEXLIE M?HIDI UITH CLAStICS flNflflN CHOCOLflY CROUP $31LW13 A'IO3oN3 JflOIfD 2R3UU N I I I �A LATE LATE KEWEENAWAN KEWEENAWAN THRUST THRUST ?? MARQUETTE COUNTY, MICHIGAN. MICHIGAN. '.William Cambray Dept Dept of of Geological Geological Sciences, Sciences, Michigan State State F.Wulliam Cambray University, East Lansing Lansing Michigan 48824 48824 and Glenn Glenn Scott, Scott, Callahan Callahan University, East Mining Mining Co. Co. Marquette, Marquette, Michigan. Michigan. Records from a drill drill hole on on the the southern southern margin margin of of the the Records from ( Hole 1(30, ( Hole M30, sec. Quadrangle. sec. 17 17 T47N T47N R25W, R2SW, Sands Sands Quadrangle. Core Core made made available available by by CCI CCI Ishpeming.) describe a 'Cambrian 'Cambrian a clastic dike' occurring occurring at depth of of 360 360 feet. feet. The overlying overlying clastic dike' at a depth is deformed material is deformed and metamorphosed Proterozoic Kona and Kona Proterozoic Formation. 'dike' has is an an Formation. Re-examination Re—examination of of the the 'dike' has shown shown that that it is sorted unmetamorphosed quartz arenite arenite containing containing immature, poorly sorted fragments of the the Icona Kona Formation. similar to to fragments of Formation. The The lithology lithology is very similar the outcrops of the local local outcrops of Jacobsville Jacobsville Sandstone. Sandstone. Although Although the the Jacobsville has been described as Cambrian in the past it it is is now now widely believed believed to t o be be late late Keweenawan Keweenawan in in age. age. AA re—examination re-examination of of widely core reveals reveals that that the the sandstone sandstone bedding is is vertical and and the the the core fragments of of Kona Kona Formation Formation included included in in the the sandstone sandstone are are aligned aligned fragments parallel parallel to t o this this vertical vertical bedding. bedding. All All the exposures exposures in the the immediate region region are are Lower Lower Proterozoic Proterozoic rocks, rocks, mostly Kona Kona Formation. Formation. We We interpret interpret the pattern pattern observed observed in in the drill drill hole hole to to late Keweenawan Keweenawan thrust placing the Kona Formation Formation over over indicate a late the the Jacobsville Jacobsville (fig.2). (fig.2). During During the the Keweenawan Keweenawan widespread widespread rifting rifting produced clastic clastic filled filled basins basins throughout throughout the the Lake Lake Superior Superior region. Towards Towards the the end end of of the the period period the the Jacobsville Jacobsville Sandstone, Sandstone, and the the equivalent equivalent Bayfield Bayfield Group Group formed formed a widespread widespread blanket blanket over much much of of the the region. region. This This was was followed followed by by aa compressional compressional event rise to event which gave gave rise to thrust thrust faulting faulting on on the the Keweenaw Keweenaw Peninsula Peninsula and and several several reverse reverse faults faults in in the the Nidcontinent Midcontinent Rift Rift section of of Wisconsin Wisconsin and and Minnesota. Minnesota. Until now there there has has been been no no record event east east of the record of of this this late late compressional compressional event the Keweenaw Keweenaw Peninsula. Peninsula. The The sequence sequence of of events events proposed proposed is is as as follows. follows. 1) 1) Extensional tectonics tectonics associated associated with the opening opening of of the the Midcontinent Midcontinent Rift Rift System System produced produced aa rift basin basin above above the the Marquette Marouette Trough Trouqh which which filled filled with with sediment sediment derived derived from from the the surrounding Archean Basement the Proterozoic surounding k chean Basement and the ~roterozoic and netasediments metasediments (fig. (Ciq. 1) 1). The sediments sediments contain contain unweathered unweathered microcline microcline and and fragments fragments of mylonite mylonite from from the the gneisses. gneisses. Pelite Pelite lenses lenses mark mark the the bedding bedding surface surface and and compaction compaction structures structures are are clearly clearly visible. visible. Fragments Fragments of of the the Kona Kona Formation up up to to 55 centimeters centimeters long long by 2 2 centimeter centimeter wide wide are are aligned parallel parallel to to the the bedding. bedding. The The poor poor sorting sorting suggests suggests that that this this locality locality was was close close to to the the fault fault scarp. scarp. 2) The conpressional produced in a thrust close to compressional event produced to the the original and transported original rift rift margin margin and transported the the adjacent adjacent Kona Kona Formation over over the the Jacobsville Jacobsville basin, tilting the the sandstone sandstone to to its its present present vertical vertical position position in in the the process process (fig (fig2). 2). Marquette Trough Trough This pattern pattern of of deformation deformation in in the the late late Keweenawan Keweenawan is is not not surprising considering considering the the structures structures seen to the the west. If If it it is is more widespread widespread it it adds adds another another factor factor to t o be be considered considered when when attempting to t o unravel unravel the the structure structure of the the older older Proterozoic Proterozoic in in the the Great Great Lakes Lakes region. region. 19 �__ C N) LL. E' 1 Kona FM. coarse lenses . Jaoob!vllI! Sst. 1 rIg. 2 rig. I [J L._ CoMpresilenJi Pkn. BItting Pkr. L 1 Caribray and Scott 1991 LATE REWEEIIAWAN THRUSTING, MARQUETTE MICHIGAN __ __ _ CT r I __ L L �Hazardous The The Feasibility Feasibilityof ofRecovering RecoveringMetals MetalsFran Froma a HazardousWaste Waste Site Site Case AA (Brief) (Brief) CaseStudy Study Frederick -11 FrederickK.K.Campbell Minnesota Minnesota Pollution PollutionControl ControlAgency Agency 520 520Lafayette LafayetteRoad Road 55155 55155 St. St.Paul, Paul,Minnesota Minnesota The National Lead (NL))/Taracorp/Golden fTaracorp/C3olden Site (Site)isislocated located in in St. Site (Site) St.Louis Loui Park, Hennepin Park, HennepinCounty, County,Minnesota. Minnesota. The The Site Siteis isapproximately approximately 10 10 acres acres in insize size and ofofa asecondary secondarylead leadsmelter. smelter. The and is isthe theformer formersite site The Site Site is isincluded included in inthe the U.S. (NPL) U.S. Environmental EnvironmentalProtection ProtectionAgency's Agency's (EPA'S) (EPA's) National NationalPriorities PrioritiesList List(NPL) 5) and and is isalso alsopresent presenton onthe theMinnesota Minnesota Pollution PollutionControl ControlAgency's Agency's(MPCA' (MPCA'S) (PLP). Permanent (PLP). The The secondary secondarysmelter smelterwas was operated operatedbybyNL NL PermanentList Listof ofPriorities Priorities and lead,lead lead oxide oxide andTaracorp Taracorpbetween between 1940 1940 and and 1981, 1981,and andwas was used used to to reprocess reprocess lead, and trambatteries batteries and and scrap scrap into into various variouslead leadalloys. alloys. The The main main and lead leadsulfate sulfatefran solid by the the smelter smelterwas was slag slagfran from the the blast blast furnace furnacewhich whichwas was solidwaste wasteproduced produced by deposited deposited on—site on-sitebetween between 1940 1940arid and 1962. 1962. The the presence presence of ofthe thelead-bearing lead-bearingslag slag in constitutes aa potential potential threat threatto tothe thelocal localsurficial surficialand and in the thesub-surface subsurface constitutes bedrock and is isthe themain main reason reasonfor forthe the inclusion inclusion of of the theSite Siteon onthe the bedrock aquifers, aquifers,and NPL NPL and and the thePLP. PLP. The The slag, slag,which which is is aa major major component componentof of the thefill fillmaterials materialson onthe theSite, Site,is is heterogeneous ..etercqeneousin innature. nature. Limited Limited analytical analytical data indicate that the slag contains part per to 45,900 45,900 part per million million (4.5 (4.5percent) percent)lead. lead. Visual Visual inspection inspectxonof of contains up up to data indicate that the slag slag inin sane samples, while other sarriples slagsamples samples indicates indicatesaahigh highiron ironcontent content some samples, while other sanples cubic yards yardsof of fill fill have 16,000 cubic have a a high high lead lead(galena) (galena)content. content. Approximately Approximately 16,000 materials arepresent presenton onthe the Site, Site,and and it it is isestimated estimated that that25 25toto90 90percent percent of of materials are the he fill fillisisslag. slag. redy for for the the Site Site is isan an asphalt asphalt "cap, "cap",installed installed in in 1988 1988 which which The current current remedy The was andthereby therebyprevent prevent was designed designed to toprevent preventinfiltration infiltrationof ofprecipitation precipitationand leaching The EPA EPA is is currently currentlyengaged engaged in in aa five-year five-year leaching of of lead lead fran fromthe theslag. slag. The review required by by the theSuperfund Suprfundprogram program (Cctnprehensive (Cmprehensive reviedof of the theSite, Site,which which is isrequired Environmental Compensation,and and Liability Liability Act Act (CERCIA)). (CERCLA)). This This review review Environmental Response, Response, Canpensation, and represented process process will willconsider consider the the status statusof ofthe theSite Site andthe therisks risks representedby bythe the hazardous materials (slag) (slag) that that retain hazardous materials remainon on the theSite. Site. In In this thiscontext, context,other otherrnre more permanent renedies remedies such such as as encapsulation, encapsulation,fixation fixationor orexcavation excavationand and ranoval ?33nOvalmay may permanent permanent EPA An alternative alternative permanent raredy remedy which which bythe the EPAand and the the MPCA. MPCA. An be considered consideredby be P.s) merits As)from from the the (Cd, therecovery recovery of of lead leadand andother othermetals metals(Cd, merits consideration considerationis isthe andeconomic economic barriers barriersmust mustbe beoverccne overcane in in order order to to Technical,regulatory regulatoryand slag. slag. Technical, recovery of of lead lead fran from the the slag slag aa feasible feasiblealternative. alternative. make the the recovery make Technical barriers to tothe the recovery recovery of of lead lead fran from the the slag slagrevolve revolve around around the the Technical barriers heterogeneous natureofofthe theslag slag and andthe thevariable variable iron, iron, lead and silica silicacontent content iieterogeneousnature lead and Environmental Technology of theslag. slag. The The U.S. U.S. Bureau Bureau of ofMines, Mines,through throughits its Environmental Technology of the has investigated investigated the the possibility Research Program, Program, has possibilityof ofrecovering recoveringlead leadfrom frommill mill Research such as as an tailings Missouri. tailingsinin Missouri. Approaches Ap~roachessuch an air airsparged spar- hydrocyclone wra=ycloneshow s h promise andmay may also also permit permit recovery recovery of of lead leadfrom from slag. slag. Another Another technique, technique, promiseand by the theEPA EPA in inits its utilizingaa flame flame reactor reactor process, process, has has been been evaluated evaluated by utilizing Superfund Superfund Innovate InnovateTechnology Technology Evaluation Evaluation (SITh) (SITE)Program. Program. 21 �J I Regulatory barriers to Regulatory barriers tothe therecovery recovery of of lead lead fran from the the slag slag are are related related to tothe the involvanent TheResource Resource Conservation Conservationand and involvement of of tvo twomajor major statutory statutoryauthorities. authorities. The Recovery Act (m) (ICRA)and and CEIWmay may both regulate this type rredial activity activity Recovery Act CERCIA both regulate this type of of remedial of of hazardous waste and andcleanup cleanupstandards standardsare arecauplex complex Definitions hazardous waste at atthe theSite. Site. Definitions issues context and inin order to to make inthis this context andmust mast be be clarified clarified order makerecovery recovery of oflead lead issues in frau permanent remedy. fromthe theslag slaga afeasible feasible permanent raedy. 1Econcniic barriers to to the the recovery of lead lead from fran the Econdc barriers recovery of the slag slag at at the the Site Siteare are similar those that axe faced during thethe cievelopnent ofofan shilartoto those that axe faced during -1-nt anore oredeposit. deposit. The The costs of the costsfor forexcavation, excavation,rancval removaland and transportation transprtatim of the slag slag to toaasmelter melter will will prob&1y given the volume, andand heterogeneous besubstantial substantial given the volume,distribution distribution heterogeneousnature nature probablybe The metallurgical metallurgicalproblans problems in inseparating separating the thelead lead fran fromthe the of thematerial. material. The ofthe incentive for thistype typeof of slag be significant. significant. The The econanic economic incentive forconç'leting completing this slagmay may be permanent raTedial action action is is the developnent permanent remedial theprospect prospect of ofindustr±al/camercial industrial/commercial development of ofthe the Site. Site. I 1- J J J Li Li LI Li J 22 �PALEOMAGNETISM OF CENTRAL WISCONSIN DIKE DIKE SWARM: SWARM: CONSTRAINTS ON THERMOMECHANICAL MODEL MODEL OF MIDCONTINENT RIFT Lung S. C/ian Lung Chan Department of Department of Geology Geology Eau Claire University of Wisconsin - Eau Five mafic mafic dikes dikes in incentral central Wisconsin Wisconsinwere weresampled sampledfor forpaleomagnetic paleomagneticdeterminations. determinations. The The palwpoles paleopoles Five obtained reveals obtained reveals more more than than one one dike dikeintrusion intrusion episode. episode. The Thepreliminary preliminary paleomagnetic palwmagnetic results results can can be divided into two groups. The mafic dikes dikes in in Marathon Marathon City, City, Big BigFalls FallsPark, Park,and and Little Little Falls Falls Park Park Eau Claire County yield yield aa cluster cluster of of palmpoles paleopoles that that lie lie near near the the 11.1 Ga paleomagnetic paleomagnetic pole pole of of the the .1 Ga in Eau North American craton. The paleopoles North American craton. palwpoles of the the dikes dikes in in Lake Lake Wissota Wissota and and Jim Jim Falls Falls in in Chippewa Chippewa County are about 1.0 Ga. Ga. The Thelack lackof ofintermediate intermediatepoles polesimplies impliesepisodic episodicdike dikeintrusions. intrusions. Similarly, Similarly, about 1.0 and volcanic volcanicunits unitsin inthe the Lake Lake Superior Superior area area also show show an an episodic episodic nature. nature. Keweenawan dike swarms and The determination determination of the to our The the intrusion intrusion ages ages is is conducive to our understanding understanding of the the thermomechanical thennomechanical state of is located located about about 200 200 km km from from the the rift rift axis. The axis. The state of the the midcontjnent midcontinent rift. rift. The The dike dike swarm swarm is recurrence of dike at such recurrence dike intrusion intrusion activities activities at such aa far fardistance distance from from the therift riftaxis axisimplies impliesoscillation oscillation between strong strong tensile stress during the intrusive stress between intrusive stages and weak tensile or compressional compressional stress during the inter-intrusive likely resulted resulted from from fluctuation fluctuation in in magmatic magmatic inter-intrusive stages. Such variation in stress likely along the rift axis. activity along axis. 23 �AEROMAGNETIC SURVEYING PROGRAM IN MINNESOTA: PAST AND FUTURE PERSPECTIVES PERSPECTIVES CHANDLER, VAL VAL W., W., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul.MN MN 55114 55114 The high-resolution aemmagnetic Minnesota Geological The high-resolution aemmagnetic surveying surveying program pmgram of the Minnesota Geological Survey Survey(MGS), (MGS),,\ which began in 1979 1979with support support from from the Legislative Legislative Commission Commission on on Minnesota Minnesota Resources (LCMR). (LCMR), will be completed completed in in 1991. 1991. InInaddition additiontotothe theLCMR-sponsored LCMR-sponsoreddata, data,data datahave havebeen beencontributed contributedby bythe theU.S. U.S. Geological Geological Survey Survey and and the the Geological GeologicalSurvey Survey of Canada Canada for for north-central Minnesota and by USX Corporation Corporation for for southwestern Minnesota When Whencomplete, complete,the thestatewide statewideaemmagnetic aemmagneticdata database basewill will be be the the only one one of its its kind kind in in North America America to to encompass encompass aa relatively relatively large large area area with with such such detail. detail. All Allsurveying surveyingto to date has maintained nearly the same specifications, the key ones being close flight-line spacing (400—500 date has maintained nearly the same specifications,the key ones being close flight-line spacing (400-500 meters). In the present present survey meters) and low low terrain terrain clearance clearance(150—200 (150-200 meters). survey over over southeastern southeasternMinnesota, Minnesota, some spacing, owing to burial-related some data data can can be be flown flownatat10(X)-meter 1000-meter spacing, burial-related smoothing smoothingof of anomalies anomaliesfrom from Paleozoic strata. Paleozoic I The The data, data, which which have have already alreadyserved served aa broad bmad spectrum spectiurnof of economic economicand andscientific scientificinterests, interests,are are available available as as 1:24,000-scale 1:24,000-scale contour contour maps, amps.1:250,000-scale 1:250,000-scalecontour contour and and color colormaps, maps, and and as as digital digital tapes of flight-line and gridded data. flight-line gridded data. test drilling drillinghas hasled ledto toseveral severalmajor majorrevisions revisionsof ofthe the Use of the aeromagnetic aeromagneticdata data in in conjunction conjunctionwith with test Precambrian Precambrian geology geology of of Minnesota, Minnesota, most most of of which which lies lies concealed concealed beneath beneath aa thick thick mantle mantle of Pleistocene Pleistocene glacial materials. Inverse andPoisson Poisson analysis analysis of gravity and Inversemodeling modelingof ofaeroinagnetic aeromagneticanomalies anomaliesand magnetic data have assisted significantly in a recent reinterpretation of the Early magnetic data have assisted significantly in a recent reinterpretation of the EarlyProterozoic ProterozoicPenokean Penokean I orogen in east-central Minnesota. Aemmagnetic the omgen Aemmagneticdata data have have been been consistently consistently used in interpreting the , partially exposed Archean greenstone-granite greenstone-granite tenane terrane of of north-central north-central Minnesota. Minnesota. Derivative-enhanced Derivative-enhanced aeromagnetic and gravity data part of of interpret the geology geology of the poorly poorly exposed central part aeromagnetic data have have been used to interpret Protcrozoic Duluth Complex of northeastern Minnesota. In Innorthern northernand and central central Minnesota, Minnesota, the Middle Proterozoic aeromagnetic data are being used to investigate a major major dike dike swarm swann of Early Protemzoic Pmterozoic age. The aeromagnetic The Minnesota Geological Geological Survey plans further interpretive wo& in the Archean greenstone-granite Survey farther work in the Archean greenstone-granite terrane of northwestern and the the Middle Middle Proterozoic Archean gneiss gneissterrane terrene of of southwestern southwesternMinnesota, Minnesota,and northwestern Minnesota, Minnesota,the the Archean Duluth Complex. Complex. I, Looking aeromagnetic surveying remain. remain. In Looking to the future, future, several several major tasks tasks related to aeromagnetic In a recent workshop hosted workshop hosted by the theMOS MGS and and sponsored sponsored by by the the L.CMR, LCMR, several recommendations were made for future geophysical geophysical woit workininthe thestate. state.Among Amongthe therecommendations recommendationspertinent pertinenttotoaeromagnetic aemmagneticsurveying surveying were (1)10 (1) to accelerate accelerateprocessing processingand andinterpretation interpretationof ofaeromagnetic aeromagneticdata dataininconjunction conjunctionwith withtest testdrilling drillingand and geologic (2) to to make make the the digital digital aeromagnetic aeromagnetic data data available available in in more more diverse diverse media than presently geologic mapping; mapping; (2) available, available, with with emphasis emphasison on PC-based PC-basedtechnology; technology;and and(3) (3)to toexpand expandthe theMGS MGSphysical-property physical-propertydata database base on Minnesota's Minnesota's bedrock and glacial sediments. The TheMGS MGS plans plans to to pursue pursue these these recommendations recommendations aggressively. I aggressively. itgion, much In the broader perspective of the Midcontinent region, much remains remains to to be be done. In Inmost mostareas areasthe the ' aeromagnetic coverage aemmagnetic coverage is is simply simplyinadequate, inadequate,especially especiallywith with regard regardto toflight-line flight-linespacing spacingversus versusdepth depthto to basement. The Thetremendous tremendoussuccess successofofthe theaemmagnetic aemmagneticsurveying surveyingprogram pmgramininMinnesota Minnesotapresents presentsaastrong strong incentive the Midcontinent Midcontinentregion regionto topursue pursuesimilar similarprograms. programs. incentive for for other other state state or or federal federal agencies agencies woiking workingin inthe 24 j I —j �CONTINUOUS STRIKE-SLIP CONTINUOUS STRIKE-SLIP FAULT-EN FAULT-EN ECHELON ECHELON FRACTURE FRACTURE ARRAYS IN DEFORMED DEFORMED ARCHEAN ARCHEAN ROCXS: ROCKS: IMPLICATIONS IMPLICATIONS FOR FOR FAULT FAULT PROPAGATION PROPAGATION b CHAN IC $ MECHANICS I John Craddock and John P. P. craddock and Andrew Andrew Moshoian, Moshoian, Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN 55105 55105 Abstract AbsmaGL A A regional regional strike—slip strike-slip and and en en echelon echelon fracture fracture array array (orientation: dimensions in 90) is observed in three dimensions in (orientation: N—B, N-S, 90) Archean Archean rocks rocks in in northern northern Minnesota, Minnesota, northern northern Michigan, Michigan, and and western western Wisconsin. Wisconsin. Distinct Distinct fault fault planes planes (Mode (Mode I) I) change change along strike strike into into single single or or conjugate conjugate en echelon echelon fracture fracture arrays arrays (Mode (Mode II) 11) resulting resulting in in an an undulating undulating fault fault trace trace with with an an average average amplitude amplitudeof of—5 -5cm cmand andwavelength wavelengthofof—1-1in. m. Both Both dextral dextral and and sinistral sinistral displacements displacements are are found found in in the the same same outcrop, outcrop, and and fault fault displacements displacements change change along along strike. strike. Brittle Brittle en en echelon echelon shear shear sense sense indicators indicators generally generally compliment compliment the the observed observed fault fault displacement, displacement, but but not not always. always. Mode and II I1 fractures fractures cut cut and and cross—cut cross-cut each each other other and and Mode II and are are thus thus contemporaneous contemporaneous features, features, indicating indicating that that the the Mode Mode I extensional fractures I extensional fractures became became strike—slip strike-slip faults faults where where initially macimum principal principal compressive compressive stress stress (0-1) (Cl) was initially the the maximum was parallel parallel to to the the strike-slip strike-slip fault. fault. Mode Mode II I1 en en echelon echelon sets sets can can be be used used as as shear shear sense sense indicators indicators for for the the strike—slip strike-slip faults faults however, however, displacements displacements along along individual individual Mode II I1 fracture fracture planes planes are are opposite opposite that that of of the the strike—slip strike-slipfault. fault. The The undulating undulating fault fault planes planes resulted resulted from from the the interaction interaction between between propagating propagating Mode Mode II fractures fractures and and Mode Mode II I1 en en echelon echelon shear shear fracture fracture pods, pods, both both of of which which are are three three dimensionally dimensionally continuous continuous and and locally locally out—of—phase. out-of-phase. Timing Timing constraints constraints on on these these fault fault systems, systems, which which are are regionally regionally distributed distributed in in Archean post-2.6 Archean rocks rocks of of the the Great Great Lakes Lakes region, region, indicate indicate aa post—2.6 13? and pre-1.1 pre-1.l BY BY age BY and age for for this this deformation. deformation. 25 �PRELIMINARY DRILL DRILL CORE CORE STUDY STUDY OF OF TWO TWO HOLES HOLES DRILLED DRILLED ON ON THE THE CUYUNA CUYUNA IRON IRON RANGE AND EMILY EMILY MANGANIFEROUS MANGANIFEROUS IRON IRON FORMATION FORMATION DISTRICT DISTRICT OF OF MINNESOTA MINNESOTA J. DAHL DAHL and and SUSAN SUSAN E. E. BRINK, BRINK, Twin Twin Cities Cities Research Research Center, Center, U.S. U.S. Bureau Bureau of of LINDA J. Mines, 5629 Minnehaha Avenue Avenue South, South, Minneapolis, Minneapolis, MN 55417 Mines, 5629 Minnehaha MN 55417 Two diamond diamond drill drilled core holes holes were were recently recently completed completed in in manganiferous manganiferous iron iron Two ed core Central Minnesota--one on the Cuyuna formations in in Central Cuyuna Range Range and and one in in the the Emily Emily The purposes purposes for drilling were were first drill core core for for geologic geologic District. District. The for drilling first to t o obtain obtain drill characterization and to conduct conduct characterization and whole whole core core leaching leaching experiments, experiments, and and subsequently subsequentlyto geophysical logging hydrologic flow testing. This geophysical logging and and hydrologic flow testing. This drilling drilling program program was was costcostBureau of Mines shared by shared by the the U.S. U.S. Bureau Mines and and the the University University of of Minnesota-Mineral Minnesota-Mineral Resources Research Research Center Center under under a Resources a Bureau Bureau Cooperative Cooperative Agreement Agreement and and is is part part of of the Bureau's situ mining the Bureau's ongoing ongoing research research on on in in situ mining of o f critical critical and and strategic strategic minerals. gathered from these two holes will minerals. The information information gathered will be used used in in the the mining techniques techniques can evaluation of o f whether whether or or not not in in situ mining can be be utilized to to recover manganese from from the the manganiferous manganiferous iron iron formations formations in in Central Central Minnesota. Minnesota. the use In In situ situ mining mining involves involves the use of of fluids fluids to t o remotely remotely solubilize solubilize and and mobilize target metals in ore deposit mobilize target metals in an an ore deposit and and transport transport them them to to the the surface surface via via recovery wells where recovery wells where the the fluids fluids can can be be directly directly processed processed for for metal metal recovery. recovery. The success success of of an an in in situ situ mining operation operation depends depends to t o aa large large degree degree on on whether whether the target ore minerals can be selectively dissolved and and whether the dissolved transported to target metal can can be be transported to the the production production wells wells via via fluid fluid flow flow channels. channels. physical the inherent The degree degree of of sulccess success is by the The is governed governed by inherent chemical chemical and and physical characteristics of the ore body characteristics of body such such as as the the types types of o f ore ore minerals, minerals, types types and and kinetics of ore abundance abundance of reactive reactive gangue gangue minerals, minerals, kinetics ore and and gangue gangue mineral mineral dissolution, ore dissolution, ore zone zone permeability, permeability, proximity proximity of of ore ore minerals minerals to to the the fluid fluid path, path, and groundwater groundwater flow flpw characteristics characteristics in in both both saturated saturated and and unsaturated unsaturated deposits. deposits. the relationships At the microscale, microscale, the relationships between between the the ore ore and and gangue gangue minerals, minerals, Low target particularly particularly texture and composition, composition, are are very very important. important. Low target metal metal solution cannot cannot contact if the leach recoveries will will occur occur if leach solution contact the target target ore ore example, minerals regardless regardless of of how how well well the the leach leach chemistry chemistry is is optimized. optimized. For example, target ore minerals may be encapsulated by by unreactive unreactive gangue gangue or or short short circuiting circuiting and as joints may occur of leach fluid fluid may occur due due to structural controls controls such such as joints and clay swelling Also, may be microfractures. microfractures. Also, fluid fluid pathways pathways may be plugged plugged by by clay swelling or or accumulation of of mobilized particles. particles. This type type of of information information obtained obtained through through a petrographic petrographic study study of of preleach preleach and and postleach postleach ore ore samples samples provides provides valuable valuable guidance in in predicting in in situ situ mining metal metal recoveries recoveries and and the the feasibility feasibility of of in situ situ mining for aa prospective in prospective ore ore body. body. Bureau research research is is providing providing new new insights insights into into predicting predicting in in situ situ mining mining Potential problems and metal recoveries. metal recoveries. Potential and constraints constraints are are being being identified identified and and research, modeled before before field field leach leach mining tests are initiated. As part of this research, conducting a geologic geologic characterization characterization study the Bureau is conducting study of of the the drill core core from from stratigraphy, gangue the Cuyuna Range Range and and Emily Emily District District which which includes: includes: stratigraphy, gangue and and ore mineralogy, mineralogy, textural textural relationships, re1 ationships, assays, assays, detailed detailed whole whole rock rock chemical chemical analyses of selected selected samples, samples, permeability and porosity, porosity, fracture analysis, analysis, and and characterization magnetic susceptibility. susceptibility. AA combination of laboratory geologic characterization techniques are are being being used techniques used on whole core core samples samples to t o determine determine ore/gangue ore/gangue and and These techniques structural structural relationships relationships of of preleach preleach and and postleach postleach material. material. These techniques scanning electron include petrographic petrographic analysis analysis of of polished include polished thin thin sections, sections, scanning electron microscope imaging, electron microscope electron microprobe analyses, analyses, and and X-ray X-ray diffraction. diffraction. 26 �Hole Hole G-1 G-1 from from the the Cuyuna Cuyuna Range Range was was drilled drilled on on the the National National Steel Steel Corporation's Corporation's former former Gloria Gloria underground underground mine site site near near Ironton, Ironton, MN, located in in the the northwest northwest 1/4 1/4 of of the the southeast southeast 1/4 1/4 of of the the southeast southeast 1/4 1/4 of of Section Section 28, 28, Township Township 47N, 47N, Range Range 29W, 29W, Crow Crow Wing Wing County. County. This This hole hole was was drilled drilled to t o aa depth depth (along (along the the incline) incline) of 1200 1200 ft ft at at an an inclination inclination of of 55 55 degrees degrees to to the the northnorthnorthwest. northwest. Hole Hole E-1 E-1 was was drilled drilled on on public public land land near near Emily, Emily, MN, MN, and and located located in in the the southeast southeast 1/4 1/4 of of the the southwest southwest 1/4 1/4 of o f the the northwest northwest 1/4 1/4 of of Section Section 21, 21, Township Township 138N, 138N, Range Range 26W, 26W, Crow Crow Wing Wing County. County. This This hole hole was was vertically vertically drilled drilled to t o aa depth depth of of 787 787 ft. ft. The The following following descriptions descriptions of the stratigraphy stratigraphy from each each hole hole are are based based Detailed solely upon upon hand hand sample sample observations. observations. Detailed petrographic petrographic analyses analyses are are solely currently currently ongoing. ongoing. HOLE HOLE G-1 G-I Depth, ft (along (along the the incline) incline) Deoth, ft Glacial 85 Glacial surficial surficial material material 00 -85 - 202 202 Rabbit Rabbit lake Lake Formation Formation -- Dark Dark to to medium-dark medium-dark gray gray carbonaceous carbonaceous argillite, 1-2% marcasite marcasite and and pyrite, pyrite, argillite, locally locally mineralized mineralized with with << 1-2% contains which are are variably variably contains minor minor 0.2-mm to 15-cm thick clastic beds which hematitic. hematitic. - 1167 1167 Trommald Trommald Iron Iron Formation Formation 85 85 - 202 202 - - 438 438 Thick-bedded Thick-bedded facies facies -- Massive Massive and and mottled appearing appearing beds beds (2-5 up to to 1.5 1.5 m) m) of of intermixed intermixed goethite, goethite, limonite, and (2-5 cm and up hematite with (< 11 mm mm with locally occurring thin-bedded thin-bedded clastics clastics (< thick) Manganese mineralimineralithick) and and massive to thin-bedded thin-bedded chert. chert. Manganese zation zation begins begins at at 243 243 ft. ft. 438 q38 -- 659 659 Mixed thick- and and thin-bedded facies facies -- Massive Massive to to mottled mottled to to thin-bedded thin-bedded iron iron formation formation consisting consisting of of interbedded interbedded goethite, goethite, limonite, limonite, hematite, hematite, and and manganese manganese oxides oxides with with minor minor locallylocallyoccurring occurring argillized argillized clastics clastics and and oolitic oolitic chert. chert. 659 1167 659 -- 1167 Thin-bedded Thin-bedded facies facies - Oxidized Oxidized interval interval (659-922 (659-922 ft) ft) consists consists cm thick) of alternating alternating thin beds (0.2-5 (0.2-5 mm and and up up to to 11 cm thick) of of hematitic/goethitic iron formation, argillizedclastics,chert, hematitic/goethiticironformation,argillizedclastics,chert, and and magnetite. magnetite. The transition transition from from oxidized oxidized to to reduced reduced iron iron formation 922-943 ft. formation occurs occurs from from922-943 ft. Reduced iron iron formation formation (943(9431167 consists of of very very fine-grained, fine-grained, thinly-bedded thinly-bedded (0.5mm 1167 ft) consists (0.5 mm 22 cm cm thick) alternating dark to t o light light gray gray to to dark dark greenish greenish cm) 3.5 cm) gray gray bands. bands. The The unit unit contains contains minor minor thin thin (0.5 (0.5 mm mm -- 3.5 chert chert and and clastic clastic interbeds. interbeds. Magnetite Magnetite beds beds are are partially partially oxidized ft. oxidized to to hematite hematite above above 913 913 ft. 202 202 - - - - 1167 1200 Mahnomen Mahnomen Formation Formation - Medium to to light light gray, gray, massive massive to to weakly weakly bedded, bedded, 1167 -- 1200 sericite-quartz sericite-quartz semischist with are are 0.25-1 0.25-1 mm mm in in diameter. diameter. 1% 7%dark dark mafic mafic porphyroblasts porphyroblasts that that Hole G-1 G-1 was was drilled drilled along along cross cross section section A-A" A-A" on on Plate Plate 33 described described in in "Geology Cuyuna North Range, Minnesota" G e o l o g y and Ore Deposits of the Cuyuna Minnesota" by by Robert Robert Gordon Gordon Schmidt, U.S. U.S. Geological Geological Survey Survey Professional Professional Paper Paper 407, 407, 1963, 1963, 96 9 6 pp. pp. Schmidt Schmidt suggested that Trommald Iron that the contact between the Trommald Iron Formation Formation and and the the underlying 27 �Mahnomen Mahnomen Formation Formationwas was folded. folded. Using Using this this interpretation, interpretation,hole hole 6-1 G-l should should have have contacted contactedthe theMahnomen MahnomenFormation Formationat atapproximately approximately760 760ftftdepth depthalong alongaa65-degree 65-degree incline. incline. Hole Hole 6-1 G-l located located the the contact contact between between these these two two formations formations at at 1167 1167 ft ft which which is is approximately approximately 400 400 ft ft lower lower than than proposed proposed by by Schmidt, Schmidt,thereby thereby proving proving that that the the proposed proposedfold foldisisnot notpresent. present. Also, Also, the the oxidized oxidized zone zonein in the the upper upper part part of 800 ft ft below below bedrock bedrock surface) surface) of the the Trommald Trommald Formation Formation extends extends deeper deeper (about (about 800 than than previously nreviouslv described described by bv Schmidt. Schmidt. HOLE E-1 Deoth. ft ft Depth, -- 169 00 169 Glacial Glacial surficial surficial material material 169 169 - - 321 321 Ferruginous Ferruainous graywacke aravwacke -- Light Light to to medium-gray, medium-gray,well-bedded well-bedded(1-5 (1-5mm) mm) clastics elastics consist consistof of fine finesiltsilt-to to medium medium sand-sized sand-sizedgrains grainsofofquartz, quartz, argillized araill ized feldspar, feldsoar. and and disseminated disseminatedhematite hematiteininaa clay-rich clay-richmatrix. matrix. Irregular, irregular, mottled-appearing mottled-appearingiron iron oxide oxide staining staining loosely loosely follows follows bedding bedding and and fractures fracturesin in 1I mm mm to to 55 cm cm bands. bands. Argillization Argillization varies varies from from slight slight at at the the top top of of the the bedrock bedrock (221-305 (221-305ft) ft) to to extreme extreme at at the the bottom bottom of of the the unit unit (310-321 (310-321ft). ft). 321 - 437 437 - 437 Cherty Chertv iron iron formation formation -- Consists Consists of ot massive massive white white chert chert with wiin disdisseminated seminated clots clots (1-5 (1-5 mm diameter) diameter) of of hematite hematite and and goethite goethite interinterbedded bedded with with predominantly predominantly massive massive to to thinly thinly bedded bedded hematitic hematitic iron iron formation. formation. Towards Towards the the top top of of the the unit, unit, the the chert chert is is thinly thinly and and irregularly irregularly bedded bedded (321-328 (321-328ft). ft). Thin, Thin, argillized argillized clastic clastic beds beds (1-10 ft (1-10 mm) are are interbedded interbedded with with iron iron formation formation from from 337-350 337-350ft. - 734 734 Manganiferous Manaaniferous iron iron formation formation -- From From 437-584 437-584 ft, ft, the the unit unit consists consists of of hematitic, hematitic, manganiferous, manganiferous, thin-bedded thin-beddedto to massive massive iron iron formation formationwith with minor minor oolitic oolitic to to massive massive chert chert interbeds. interbeds. Manganese Manganese oxides oxides occur occur in in zones zones intermixed intermixed with with hematite hematite and and as as beds beds and and irregular irregular lenses lenses (1 (1 mm mm -- 33 cm cm thick). thick). From From 584-734 584-734 ft. ft, the the unit unit consists consists of of thin thin to to thickly 10 cm) cm) interbedded interbedded hematitic hematitic and and goethitic goethitic iron iron thickly (1 (1 mm mm -- 10 formation, formation, chert, chert, and and manganese manganese oxide-rich oxide-richbeds beds with with intervals intervalswhere where iron iron formation, formation, chert, chert, or or manganese manganese oxides oxides predominate. predominate. 734 734 J - 761 761 Manganiferous Manqaniferous chert chert - Oolitic Oolitic granule-rich granule-richchert. chert. Sooty Sooty manganese manganese - - oxides and the the matrix matrix as as irregular irregular vuggy vuggy oxides locally locally replace replace oolites oolites and patches. patches. AA medium medium grey, grey, massive massive chert chert bed bed (80 (80cm cm thick) thick) occurs occurs at at 765 ft. ft. 765 761 761 22 - ,, - Argillized, Argillized, finely finely bedded bedded (1 (1 mm mm -cm) of cml, slate slate consists consists of mediummedium- to to fine-grained fine-drained clastics elastics with with - - ~disseminated magnetite octahedra. disseminated hematite hematite pseudomorphs pseudomorphs after aftermagnetite octahedra Localized Localized iron-oxide iron-oxidestaining staining generally generally follows followsbedding. bedding. - 763 763 Argillized Araillized thin-bedded thin-bedded slate slate - - 767 767 Manganiferous Manaaniferous chert chert -- Same Same as as 734-761 734-761 ft. ft. 763 763 - 767 767 - - 787 787 - Argillized Araillized thin-bedded thin-bedded slate slate - Same Same as as 761-763 761-763 ft. ft. The The stratigraphy stratigraphy of hole hole E-1 E-1 identified identified that that the the dip dip of of the the sedimentary sedimentary The information information from from this this hole hole was was layers layers in in this this area area flatten flatten to to the the north. north. The added added to to the the geologic geologic database database of of holes holes previously previously drilled drilled (approximately (approximate1y 40 40 years stratigraphy of of the the Emily Emily district. district. years ago) ago) to to further further define define the the stratigraphy 28 j ~~ j �GEOLOGIC SETTING OF THE THE EARLY PROTEROZOIC PROTEROZOIC BASE- AND PRECIOUS-METAL-RICH PRECIOUS-METAL-RICH METAVOLCANIC BELT OF WISCONSIN I . 3 Theodore A. A. DeMatties, Ernest K. K. Lehmann & & Associates, Inc., Inc., 430 430 First Avenue North, 55401 North, Minneapolis, Minneapolis, Minnesota Minnesota 55401 I M.G. M.G. Mudrey, Jr., Jr., Wisconsin Geological Geological and Natural History Survey, 3812 Mineral Point Road, Road, Madison, Wisconsin 53705 Wisconsin 53705 .. , Since the the late late 1960s, 1960s, measured measured and and inferred inferred resources resources of ofF . .. . Since massive—sulfide over 100 million short tons of volcanogenic volcanogenic massive-sulfide' The mineralization mineralization have have been been discovered discovered in in northern northern Wisconsin. Wisconsin. -%he largest deposit, deposit, near Crandon, was identified by Exxon Minerals and contains approximately 75 75 million short short tons of ore ore averaging averaging most recent discovery 5% zinc, 1.1% 1.1% copper, copper, and and 0.4% 0.4% lead. lead. The most was made by Noranda Exploration Inc. at Lynne, Exploration Inc. at Lynne, in in Oneida Oneida County. County. One of o f their discovery holes holes contained contained a a 128—foot 128-foot intercept intercept Significant copper, and 2.95% grading 22.7% 22.7% zinc, zinc, 0.64% 0.64% copper, 2.95% lead. lead. Significant precious metal values are are associated associated with with many of o f the the known known deposits. deposits. "... . t d I The deposits occur within the the Early Proterozoic Proterozoic Penokean Penokean belt (1850—1900 fold belt (1850-1900 Ma) which has been divided by Greenberg Greenberg and and Brown (1983) (1983) into into two two major terranes: terranes: the the northern northern terrane terrane supported by a supra—crustal supra-crustal sequence sequence deposited on the the Archean ~rchean basement (Sims' (Sims' Continental Continental Margin Margin assemblage; assemblage; Sims Sims and and others, others 1989) and and a southern terrane composed of volcanogenic rock and 1989) and This southern terrane, Early Proterozoic granite intrusives. granite intrusives. This southern terrane, the the Terrane (also (also known known as as the the Wisconsin Wisconsin Penokean Penokean Wisconsin Maginatic Magmatic Terrane by a an volcanic belt) , is is characterized volcanic belt), characterized by n island—arc island-arc basin basin assemblage containing abundant calc—alkaline metavolcanic units calc-alkaline units Sims and associated lesser amounts of metasedimentary rock. rock. Sims and and others (1989) (1989) have further further divided the the Wisconsin Magnetic Magnetic Terrane Terrane into two volcanic volcanic arc arc terranes on on the the basis basis oof lithology and and f lithology structure; they include the northern Pembine—Wausau terrane structure; they include the northern Pembine-Wausau terrane and and 1 29 a �J the the Marshfield Marshfield terrane terrane to to the the south. south. The The three three terranes terranes are are believed believed to to be be separated separated from from one one another another by by major major paleosuture paleosuture zones zones (Niagara Fault, Eau Eau Pleine PleineShear ShearZone) Zone). (Niagara Fault, 1 1 The The Pembine—Wausau Pembine-Wausau arc arc sequence sequence is is the the focus focus of of base— base- and and precious—metal precious-metal exploration exploration activity activity that that has has resulted resulted in in the the discovery discovery of of aa number number of of massive—sulfide massive-sulfide deposits deposits and and occuroccurrences. rences. The The dominant dominant volcanic volcanic complex complex in in this this terrane, terrane, based based on on regional regional gravity gravity and and magnetic magnetic data, data, has has been been referred referred to to 1 informally informally as as the the "Ladysmith—Rhinelander "Ladysmith-Rhinelandergreenstone greenstone belt". belt". At At 1 its its western western end, end, the the complex complex can can be be further further subdivided subdivided into into three three major major regional regional units, units, based based on on geophysics geophysicsand and known known lithology. lithology. They They include include aa central central volcanic—arc volcanic-arc sequence sequence that that defines defines the the structural structural core core of of the the complex, complex, aa marginal marginal back—arc back-arc basin basin sequence, sequence, and and aa number number of of major major felsic felsic centers centers (DeMatties, (DeMatties, 1989). 1989). These These units units may may correlate correlate with with LaBerge LaBerge and and Myers' Myers' (1984) (1984) amphibole—greenschist amphibole-greenschist succession succession in in the the Wausau Wausau and and Eau Eau Claire Clail areas. areas. Within geologi( Within this this geologic geologic framework, framework, three three distinct distinct geologic environments (1) environments appear appear to to host host massive—sulfide massive-sulfide mineralization: mineralization: (1) syngenetic syngenetic strata—bound strata-bound and and stratiform stratiform sulfide sulfide mineralization mineralization J J within, within, along along the the flanks flanks of, of, or or near near the the stratigraphic stratigraphic top top of of the the felsic felsic centers; centers; syngenetic syngenetic strata—bound strata-bound and and stratiform stratiform massive—sulfide massive-sulfide mineralization mineralization associated associated with with cherty cherty magnetic magnetic 1 iron-formation iron-formation and and located located in in the the main main volcanic volcanic arc arc sequence; sequence; and and epigenetic epigenetic stringer—sulfide stringer-sulfide mineralization mineralization and and syngenetic syngenetic 1 strata—bound strata-bound and and stratiform stratiform massive—sulfide massive-sulfide mineralization mineralization - * associated associated with with mafic mafic piles piles within within the the back—arc back-arc basin basin sequence. sequence. Based Based on on our our present present knowledge knowledge of of the the region, region, the the three three defined defined host host environments environments and and their their association association with with meta-argillite meta-argillite formations formations appear appear to to be be major major regional regional features features controlling controlling the the localization localization of of metal—bearing metal-bearing massive—sulfide massive-sulfide mineralization mineralization in in I 30 j j �.. ~ . . . the the western part of thee complex. complex. Other Other host host environments environments will will undoubtedly undoubtedly be be identified identified as as exploration exploration continues continues in in the the complex. Â¥ complex. References: References: DeMatties, A., 1989, 1989, AA proposed proposed geologic geologic framework framework for for DeMatties, Theodore Theodore A., massive massive sulfide sulfide deposits deposits in in the the Wisconsin Wisconsin Penokean Penokean volcanic volcanic belt: belt: Economic v. 84, 84, p. p. 946—952. 946-952. Economic Geology, Geology, v. , 1960, 1960, The The Ritchie Ritchie Creek Creek Main Main Zone: Zone: AA Lower Lower Proterozoic Proterozoic copper—gold copper-gold volcanogenic volcanogenic massive massive sulfide sulfide deposit deposit in in northern northern Wisconsin: Wisconsin: Economic Economic Geology Geology v. v. 85, 85, p. p. 1908—1916. 1908-1916. Sins, Sims, P.R., P.K., Van Van Schmus, Schmus, W.R., W.R., Schulz, Schulz, R.J., K.J., and and Peterman, Peterman, Z.E., Z.E., 1989, 1989, Tectono—stratigraphic Tectono-stratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terranes terranes of of the thePenokean Penokean Orogen: Orogen: Canadian Canadian Journal v. 26, Journal Earth Earth Science, Science, v. 26, p. p. 2145—2158. 2145-2158. Mudrey, Mudrey, M.G., M.G., Jr., Jr., Evans, Evans, T.J., T.J., Babcock, Babcock, R.C., R.C., Cummings, Cummings, M.L., M.L., Jr., Jr., Eisenbrey, Eisenbrey, E.H., E.H., and and LaBerge, LaBerge, G.L., G.L., 1991, 1991, Case Case history history of of metallic metallic mineral mineral exploration exploration in in Wisconsin Wisconsin 1955—1990: 1955-1990: AIME, AIME, Case Case' Histories Histories of of Mineral Mineral Discoveries, Discoveries, v. v. 3, 3, p. p. 117—132. 117-132. I LaBerge, LaBerge, C.L., G.L., and and Myers, Myers, P.E., P.E., 1984, 1984, Two Two Early Early Proterozoic Proterozoic successions successions in in central central Wisconsin Wisconsin and and their their tectonic tectonic significance: significance: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 95, 95, p. p. 246-253. 246-253. 31 �I ONTARIO ONTARIO :.. à Ironwood / I I I I ,. . Iron District Phillips .- THORNAPPLE Ladysmilh FLAMBEAU \LVI4N? Rhinelander / 5'1 I RITCHIE _*._______ BENDI '_# — Eau Claire -, . Somo Area of regional geologic map I . Thunder Bay —. tMe c/ford Ladysmith District PELJCAN RIVER (j Chicago ' IZ'CRANDON WOLF— — RIVER Wausau s S Crandon District Â¥ Population center center Population Major massive-sulfide massive-sulfide Major deposit or or occurrence occurrence deposit Wisconsin massive-sulfide districts districts (1 Wisconsin , massive-sulfide I Green Bay• 50 mites miles 50 I___________1 ' , ,.. ,.- . . . .~ .. , . ' ~ .- . 50km 50km ' '-I Index Map Map of of Wisconsin WisconsinMineral MineralDistricts Districts ~ U U U Li Li U J -J 32 �° LrLrsJ metadiolite and metasyenite I ments, and cherty iron tormation I PPEWA CLEAR CREEK metavolcanic flows and subvolcanic intrusives PROSPECT Regional geologic map Pmv I Pms — graphitic, sulfide-bearing meta-argitlites \ Pmvl — dominantly intermediate to matic . Pvs — dominantly tutlaceous metasediments; includes metagraywacke, reworked metatufis, and associated chemical metasediments Back-Arc Basin Sequence Metagabbro, altered ultramatic intrusives, syenodiorile S.. AY E R .\'#" metavolcanic tlows and interbedded metatufts and tultaceous metasediments Piv — dominantly intermediate to matic ± \ Pmv — mafic 10 ultramafic volcanicintrusive complex; includes metavolcanic flows, interitow tufts and sedi- Main Volcanic Arc Sequence Lower Proterozoic Metavolcanic and Related flocks CH £55 2 .2 Metagranite, quartz metadiorite, Lower Proterozoic (?) intrusive Rock Units Pb:Hj Lower Proterozoic Barron Ouartzite :.J units locally covering basement metavolcanic units not shown Undifferentiated Cambrian sandstone lormations; thin (.c SOft) sandstone Sedimentary Rock Units —— , — Contact, based on airborne magnetic data __________ Q • 0 I 0 POSct \\ L N / -J ziV — / \\ C (2'.i' Pb 4 9 LYNNE PROSPECT 5km I Sniies Reverse and normal magnetized mafic dikes (Keweenawan age) Deposit with defined reserves \\\\\ \\\' A Shear zone —— Projected or interred fauft — Nv — dominantly telsic melavolcanic tutls/lapilli metatults (lilhicicrystal), cherly metalults, and associated chemical metasediments (metachert) Feisic Center(s) END PROJECT,'Ce, Au) - ____ ______ __ ___ Eflflflrrflflflrcrrnrr-rrr—', �J BEND, BEND, A A LOWER LOWER PROTEROZOIC, PROTEROZOIC, COPPERCOPPER-AND ANDGOLD-ENRICHED GOLD-ENRICHED ,. VOLCANOGENIC VOLCANOGENIC MASSIVE-SULFIDE MASSIVE-SULFIDE DEPOSIT DEPOSIT IN IN TAYLOR COUNTY, WISCONSIN TAYLOR COUNTY. WISCONSIN Theodore F. Rowell, A. DeMatties DeMatties and andWilliam William F. Rowell. Ernest ErnestK. K .Lehmann Lehrnann&& Theodore A. Associates, 430 Associates, Inc., Inc. , 430First FirstAvenue AvenueNorth, North,Minneapolis, Minneapolis,Minnesota Minnesota 55401 55401 Exploration and 1991 by the Exploration work work conducted conducted between between 1976 1976 and 1991 by the Jump Jump River River Venture (Wisconsin Mineral Resources Incorporated and Chevron USA Joint Joint Venture (Wisconsin Mineral Resources Incorporated and Chevron USA Inc.) economic Inc.)has hasidentified identifieda potentially a potentially economiccopper—gold copper-gold deposit deposit within within the the Chequamegon Chequarnegon National National Forest Forest in in Taylor TaylorCounty. County,Wisconsin. Wisconsin. Geophysical Geophysical follow-up and evaluation by diamond drilling (over 30,000 feet follow-up and evaluation by diamond drilling (over 30,000 feet in in 25 2 5 holes) holes) of of the aa single-line AEM (INPUT) anomaly identified in 1977-78 resulted in (INPUT) anomaly identified in 1977-78 resulted in the single-line AEM discovery volcanogenic discovery of ofthe theBend Bend volcanogenicmassive—sulfide rnassive-sulfide deposit. deposit. Geologically the project project area area lies part of Geologically the lies within within the the west—central west-central part of the the Ladysmith—Rhinelander VolcanicComplex, Complex,aa member memberofof the the Lower Ladysrnith-Rhinelander Volcanic Lower Proterozoic Proterozoic Penokeari Penokean volcanic volcanic belt belt of of northern northernWisconsin. Wisconsin. The The copper—gold copper-gold mineralization mineralizatk (up to 2000 feet). occurs an upright, occurs within within an upright, steeply steeply dipping, dipping, thick thick (up to 2000 f e e t ) , and and relatively undistrubed felsic sequence dominated by rhyolite—rhyodacite relatively undistrubed felsic sequence dominated by rhyolite-rhyodacite flows, flow flow breccias, and flow breccias, and fine fine to to coarse coarse pyroclastic pyroclastic tuffs t u f f sand andsubordinate subordinatesedimensedimensection iis A t depth, depth,this thisflow—pyroclastic flow-pyroclastic section s intercalated Intercalated with with or or tary tary rocks. rocks. At which intruded intruded by by aathick thick(nearly (nearly1000 1000 feet) feet)series seriesofofsilicic silicicrhyolite rhyoliteflows flows which The felsic succession or center The felsic succession or center has has may may be be part p a r t of of aa larger largerdomal domal structure. structure. developed developed along along the the flanks flanks of ofaalarger largervolcanic volcaniccomplex. complex. J I U LI Ore Ore reserves reserves are a r e hosted hosted by by an an altered altered quartz quartz crystal crystal rhyolite rhyolite tuff tuff (quartz—sericite schist) and (quartz-sericite schist) andhave havebeen beendi'C'ided divided into intoa acopper—rich copper-rich hanging-wall hanging-wall horizon and aa gold-rich (HW1 and =old-richfootwall footwall(FW) (FW) zone. zone. horizon (HW) Two to semimassive semimassive igreazer (greater than (50-YU%) to tnan TWOstacked stacked stratiform stratiformmassive massive(50—90%) 30%) sulfidelenses lenses(the (theupper upper lens lens and and the the middle lens) at at or middle lens) o r near near the the 30%) sulfide stratigraphic tuff constitute thethe hanging—wall stratigraphic top top of of the t h equartz quartzcrystal crystal tuff constitute hanging-wall over 40 feet true thickness to over 40 feet t r u e thickness and and These lenses lenses range rangefrom from55 to horizon. horizon. These 34 J J j �containmostly mostlyfinefine-totovery very fine-grained, fine-grained, granular, granular. pyrite pyrite with contain with varying varying amountsofofinterstitial interstitial chalcopyrite ± tetrahedrite tetrahedrite 2± bornite bornite ±  gold gold amounts chalcopyrite 2 tellurides. Gangue include quartz, and sericite. sericite. tellurides. Gangue minerals minerals include quartz, carbonate carbonate (calcite) (calcite),• and Petrographic analysis analysisindicates indicatesthat thatthe the majority majorityof of the the pyrite pyrite grains Petrographic grains contain contain very fine inclusions of of chalcopyrite and bornite. bornite. Individual Individual very fine to tosubmicroscopic submicroscopic inclusions chalcopyrite and beds within within the and unaltered unaltered quartzquartzbeds the lens lens may may be be fragment-bearing fragment-bearing (altered (altered and crystal tuff vague to to well—developed crystal t u f ffragments) fragments)and andexhibit exhibit vague well-developed bedding/laminabeddingllaminations. tions. Sedimentaryfeatures features such such aas observed in in Sedimentary s graded graded bedding bedding have have been been observed drill core, origin. drill core, suggesting suggesting a a syngenetic syngenetic origin. Both lenses lenses extend extend to Both to subcrop subcrop, and are are overlain overlain by by about 120 feet feet of of glacial glacial moraine. moraine. and about 120 Near the the subcrop Near subcrop there is evidence of oxidation and supergene enrichment. Supergene there i s evidence of oxidation and supergene enrichment. Supergene minerals minerals include and bornite. bornite. include chalcocite chalcocite and Each lens iis serniconformable, Each lens s partially partially underlain underlain stratigraphically stratigraphicallyby bya a semiconformable, poorly developed stockwork—stringerororstringer stringer like like zone consisting of of fine poorly developed stockwork-stringer zone consisting fine cross-cutting chalcopyrite chalcopyriteanastomasing anastomasing cross-cutting chalcopyrite veinlets veinlets and/or andlor pyrite pyrite± 2chalcopyrite veinlets-veins andlor and/or fine fine pyrite veinlets-veins pyrite matrix matrix supporting supporting altered altered (silicified) (silicified)medium medium to coarse—sized, subrounded—subangular quartz crystal tuff fragments. to coarse-sized, subrounded-subangular quartz crystal tuff fragments. Locally wispy wispy chalcopyrite chalcopyrite stringers Locally s t r i n g e r s may may overprint overprintbedded bedded massive massive sulfides. sulfides. The stockwork by weak weak to to strong The stockwork stringer s t r i n g e rmineralization mineralization may may be be accompanied accompanied by strong No silicification and silicification and generally generally weak, weak, wispy wispy chlorite chlorite alteration. alteration. N o well—developed well-developed Locally these zones may carry carry alteration pipe to date. alteration pipe has has been been recognized recognized to date. Locally these zones may ore—grade gold gold values ore-grade values.- Both lenses enveloped by by aa pyritic 30% Both lenses aare r e enveloped pyritic stockwork stockwork sulfide sulfidehalo halo(up (uptoto 30% sulfides) which extends throughout the stratigraphic upper portions of the sulfides) which extends throughout the stratigraphic upper portions of the The stockwork crystal tuff The stockwork crystal tuff unit unitand andalong alongstrike strikean anundetermined undetermined distance. distance. halo consists consists of of ppyrite halo y r i t e disseminations, disseminations, bands, bands, laminations, laminations, discontinuous discontinuous cross—cutting and parallel (to foliation and bedding) veinlets cross-cutting and parallel (to foliation and bedding) veinlets and and is isassociated associate" Stockwork—stringer mineralization mineralization with widespread pervasive sericitization. with widespread pervasive sericitization. Stockwork-stringer developedstratigraphically stratigraphically below below both both lenses lenses grades grades both both vertically vertically and developed and laterally into laterally into the the halo. halo. The footwall The footwall gold gold zone zone is i s comprised comprised of of at at least leasttwo twostratiform stratiformore—grade ore-grade (plus 0.1 0.1 oz/ton) ranging from from less less than than 10 10 feet feet to to over (plus ozlton) gold gold assay assay subzones subzones ranging over 35 �designated as as the 20 feet true 20 feet true thickness. thickness. One One designated the "tuck Yuck under" undern subzone subzone is is stratigraphically belowthe the upper upper lens and stratigraphically below and hosted hosted by by stockwork stockwork sulfides. sulfides. A second occurs within, within, above above and and along second occurs along strike strike of of aa thin thinlower lower massive massive sulfide sulfide lens (or 600—foot (or group groupofoflenses) lenses)below belowthe the 600-foot elevation. elevation. Both Both assay assay subzones subzones Primary Cu, Cu, As, appear appear to to have have continuity continuity along along strike strike and and down down dip. dip. Primary A s , Bi, Bi, and Sb Sb dispersion dispersion patterns developed developed in the the stockwork stockwork halo halo indicate a geochemical continuitybetween betweenthe the lower lower sulfide sulfide lens lens and geochemical continuity and the the lower lower gold gold zone zone drilling is is needed and at depth. and suggest suggest that that it it may may widen widen at depth. Additional Additional drilling needed to to gold tellurides tellurides present present include fully delineate delineate these gold gold subzones, subzones. Hypogene Hypogene gold include calaverite calaverite (AuTe), (AuTe) , petzite petzite (Ag3AuTe2), (Ag3AuTe2), and and krennerite krennerite (AuAgTe4). (AuAgTe4). J J Widespread goldvalues valuesgreater greater than than 0.01 0 . 0 1 oz/ton ozlton have have been been found found Widespread gold Higher values throughout throughout the the stockwork stockwork sulfide sulfide halo. halo. Higher values can can form form poorly poorly developed strataform assay assay subzones subzones of of limited limited down downdip dipor or lateral lateral extent. extent. developed strataform The and geochemical geochemicaldata dataobtained obtainedthus thusfar far indicate indicate that that the The geologic geologic and the deposit exhibits zoningpatterns, patterns, Bend Bend deposit exhibits characteristic characteristichypogene hypogenecopper—gold copper-gold zoning i.e. by several several i.e. development development of of copper-rich copper-rich massive-sulfide massive-sulfide lenses lenses accompanied accompanied by The isopach isopach data data indicate indicate that that the parallel gold subzones. prominent parallel subzones. The the locus locus of of the the sulfide sulfide systems systems was was both both within within and andalong alongaapaleotopographic paleotopographic high high The massive— developed by aa thickening thickeningofof the the quartz quartz crystal developed by crystal tuff tuff unit. unit. The massivesulfide tends to to be be more fragment-bearing and and disrupted disrupted near sulfide mineralization mineralization tends more fragment-bearing near the margins, where generally well—developed the top top of of the thepile pilethan thantoward towarditsits margins, where generally well-developed The sulfide is believed to be sulfide system system is believed to be laminations and beds beds are are evident. laminations and evident. The be the plunging This may may be the result resultof ofpaleotopographic paleotopographic plunging in two two directions. directions. This control on sulfide control sulfide deposition. deposition. J J The of tetrahedrite of the The presence presence of tetrahedrite explains explains the the unusual unusual geochemistry geochemistry of the mineralization whichincludes includes anomalous anomalousconcentrations concentrationsofofarsenic, arsenic, bismuth, mineralization which bismuth, of tellurium high owing Concentrations of tellurium are are also also anomalously anomalously high owing to to and antimony. antimony. Concentrations the the tellurides tellurides present. present. A reserve base A geologic geologic reserve base estimate estimate as asof ofMarch March 1,1,1991, 1991,ofofdrill—indicated drill-indicated 2.77% and -inferred short tons tons of and -inferred reserves reserves includes includes approximately approximately 2.2 2.2 million million short of 2.77% oz/ton gold, copper, 0.05 copper, 0.05 ozlton gold, and and 0.43 0.43 oz/ton ozlton silver silver in in the the stratigraphically stratigraphically J j 36 �I I I upper upper hanging-wall hanging-wall copper-rich copper-rich horizon horizon and and an an additional additional 1.5 1.5 million million short short tons of 0.14 oz/ton tons of 0.14 ozlton gold, gold, 0.26% 0.26% copper, copper, and and 0.11 0.11 az/ton ozlton silver silver in inthe thefootwall footwa gold gold subzones. subzones. Exploration Exploration for for additional additional reserves reservesisi scontinuing continuingdown—plunge down-plunge and and along strikee of unit; at of the the productive productive mineralized mineralized unit; at least least five five high-priority high-priority hysical-geologic targets f a r , two geophysical-geologic targets have have been been identified identified thus thus far, two of of which which have hav been partially drill tested. �j j J ONTARIO Marquelle Iron Area of regional geoiogic map , Somo / • 'S IHORNAPPLE Ladysmfth FLAMBEAU -A 1 Chicago 5ti S (RITCHIE 1CREEK' BENDS '.1 Med!ord . Eat, C/afro J • Crystal Fafl's District Phillips — River Wausau Crandon District S  I' i Population Population center center 7yMajor massive-sutfide Major massive-sulfide I deposit deposit or or occurrence occurrence I (j(-,Wisconsin Wisconsin massive-sulfide massive-sulfidedistricts districts - Ladysmith District &j - 50 50 miles miles ' 50km 50km -A j . ' ! Index IndexMap Mapof ofWisconsin WisconsinMineral MineralDistricts Districts j j J J -I j J j j j J �e -doffllnmnlyintermafale @ mafc ,4( - CH -:-: I Pvs PROSPECT (LLSCHOOLHOUSE '-' '#t .. '\ Feisic Center(s) Felslc Cenler(s) ' i;II''—,., • Regional geologic map Pmvj>.. .—' .— R ' 4., .4 / 0 o ••_2' Pnwf 'fl ' I - -J 2 — (Zn,Pb,Cu,Au) 0 J a PROSPECT I SPIRIT "ini" / i' ø'fl Pvszv W\ RIVE' E C PAA9)/ LYNNE PROSPECT 5km Smiles (Keweenawan age) netized mac dikes Reverse and normal mag- Deposit with with delinetlfflserves defined reserves Deposit PR0SPECT.\\4 • Prospecti P THUNDER A 0 .7,c-y-- .—. j PROJECT(cu,Aa) ..... .-, I •'#J\ \pmv - -, cherly netatutfs, chew metalulls,and and assoassociated chemical chemical nietasedidated mewedments (metactiert) (metachen) ments Pfv — dominantly felsic metavolcanic tuffs/tapilli metatuffs (lithiclcrystat), maatufls (rihiislal), "' //_7 I cD , '?': ;"'—_.-' (','.'—\)--_ p FM -<,f4 Pry , J\\\\',1/X'-\__' c.')-7-Vc, '/\ V\'A Pmv Pms—graphitic. graphitic,sullide-bearing sulfide'ang meta-argillites Pms mela-amilites -dominantly int6fmediate to msftc kanic flows and.subvokanicinlwsives - Pvs — dominantly tuffaceous metasediments: includes metagraywacke. reworked metatuffs, and associated chemical rnetasediments t,'I\\\' (',','''' ',IJK PbLC Pvs PPEWA /<i ::Css: \J-\-.cy --: I AWYER it\'f S /5-g' "'a' .., ......... ....,....... ..... .. . CLEAR CREEK tufts and and mffaceous tuffaceous metasediments tuffs malasediments niotsvolcsnicflows and intertwddcdmela- I N ments, and cherty iron menls. anddÈit ironformation formation canic flows, interflowlullsand inteiflow tufts and sedic@.Bows. sedi. intrusive complex; includes metavol- 'p\N Pmv — mafic toto uftramafrc Pmv mnk ultramaticvolcanicvolcanic- intiusive complex: includesmetavo!- Main Volcanic Arc Sequence Metagabbro, altered ultramafic intnjsives, syenodiorite Back-Arc Basin Back-Arc Basin Sequence Sequenn .4.4 . Lower Proterozoic Metavolcanic and Related Rocks metadiorite and rnetasyenite Metagranite, quartz metadiorite, Lower Proterozoic (7) IntrusIve Rock Units Shear zone — — Projected or inferred fauft . ,... units locally covering basement metavoicanic units not shown magnetic data Contact, based on airborne Lower Proterozoic Barron Ouartzite Undifferentiated Cambhan sandstone formations; thin (<50 It) sandstone —— ri r ci r— ci r- r r— r r— ci r- rT r— r Sedimentary Rock Units —— g L 2' 2 2 C r r—i �L__ a 0 LL. I - I L_. -1000 0 1400 €LE ASL L. 016 WSW < " LL_ I 1990-1991 drillholes 1986-1989 drillhales L_ L L.. 0 = WeakJy mineralized 90-4 LL LWEI SEA ENE 7.4, 5.6 5.2 90-4 0.10 0.10 5.7' [LL I FW FW NW HW HW FW FW NW FW FW FW FW FW EW FW HW NW FW HW FW MARCH MARCH1991 1991 I Longitudinal Longitudinal Projection Projection of of Mineralization, Mineralization,Bend Bend Project Project - Taylor Taylor County, County, Wisconsin Wisconsin L 1.12 0.02 0.02 0.38 0.01 0.03 0.06 0.01 0.05 0.02 0.22 0.02 0.29 0.089 0.089 (cut) (cut) 0.35 0.35 0.190 0.190 (uncut) (umut) 0.139 0.10 0.139 0.10 0.085 0.055 0.041 0.038 0.058 0.052 0.067 0.041 0.093 0.072 0.476 0.058 0.023 0.024 0.119 0.35 0.09 0.13 0.068 0.091 0.61 1.51 Ag Ag ozfton oznon 0.076 ozlton oznon Au Au FW FW . Footwail Footwallzone zone 1.87 1.87 1.28 0.20 0.04 2.46 61.4' 5.1' 16.5' 11.9' 69.5' 0.01 5.2' 6.1' 0.02 0.11 0.13 (71') 0.10 0.09 0.08 0.08 2.22 3.88 0.10 2.66 5.98 0.90 % % Cu Cu 29.9' HW HW- Hanging Hangingwail wall zone zone 91-8 91-7 90-6 - 21.8' 90-3 90-5 14.7' 12.3' 90-2 21.1' 40.7' (14.1') (26.6) True True Thickness Thlcknese 90-1 DDH# DOH# Assay AssayData Data �S. ID COOS Albert B. Dickas, Professor of Geology/Extension, University o f Wisconsin-Superior, Superlor, Wlsconsln 54880 M. G. Mudrey, 3r.< Wisconsin Geological and Natural History Survey, Madlson Wisconsin, 53705 N ZWWt H ID lID' p.00 DIN ft i (DH H C rfi-'1D Di ftH • '< (0 (DID Dii- rtC N a'< a N ft o H ID OOW o om a DiW nj'a rtID'< (:1 Nt OlD Di ON'l CDI P0 ftC 01 DiiID tOW ID'—Oft (tHctfrt,P1 ft Di l-.m CD fti-r 1 mDiC OIft (A rtctH m— N HWIDN H, i-i,ftC awo Di p.m o 1 OH (D0W0 H tQQ,i- (DID <: Hi-ft X rt (D (A p.pa.fl) The Amnicon intrusion is chemical1 structurally, and petrographically similar t o $he otikr ma or K=weenawan intrusive suite? assoc4ated with the Mldcontinen? &ift ln t h e western Lake Su erlor reglon, t h e Duluth Igneous Sulte t o the north and the ~ e y l e nIntruslye Suite t o the east (Table 1), and probabl represents a mxnor, high-level differentiated gabbroic bozy. t • tt(fl ID F--tOPN'Q I IDrtIDCN H (AID(AH0ft IDOOCO ijDirtCOCH, r14<CO10013'<001 OH XHrtUM W1NtNHC HCD'<WHHItH"ft' DItOrtID WU<N IDHHHt'ftID IDQaH"HIDHID DH"l-C H'<H"H"IDPftD p-C) ctW HOIC I OflO'O0 NQi OCt Qi' ( '0 oDIrtID O HHIOD) OH (D'< 00 a frtt<rtO WC (D0 (DH P•ID IDIDNHO<C ctaHH"ftaftDiftON C IDDiftCtftC'N CHND10H"OCOQ)< DIN '.ONN H.IDNrbYP< —' WDlWDitNNftON I-c. IDOWft N (DD)tHDiUIftIDDi rt0 Nt H QADIDWO CnaftmIDft<D' ID (AfflH,H,HWIDIDft00)00" :HOOH"0NNt0Di 0 N H"0HDiOPIDO 1Y ID NOHH OO(DWDiftHNItDi IDOftlDCO ft1 ft IDOID0'<O IDH-ct<(DtO OW frfI ID DftrtHH"Di HNIACIO ti-QIDHOIDQ4IHDIH" CN0ffl 01 IDtrnrCooJDHDO (DX HID 0' 0DiNIftC DiO-NrH"H"0NC '<CDt QlI t1 rrp'rt0flQi —'cta FCC 0Di0Q' IDftWLOIH ftrF flhrtOf 0 r1<H"C (DIDNXD 0 N'i mi-'-o (DID CC O0IDHOCOHfflID ui—.DiDi IDP.0J-COtOtO WO Ja aft p-DiNlft NiQthb tOImO)_h ftI ft Di CD • N t D)IDOWNO WNt'<C 1ft HO'NftftDl'<N ftQ WOO • (I) N itO 0) N '< <N Oft p0) M 0 10 H- (0 ft 'H O0 tOC ID N ID 0" * OH 0 ft 'OH, OCO 010 C1N (0 COft01 0 HOCID ftD)rt 0) HQHCDO ftmnIHmwC 0) pi N odaoO aCO id tQtft UH.ftftclH ft WH-OH 00 CO N HID N 0>0 rUfl ftHID 0 HO o\° COt D)tDI mtDrt tID tH<I-rtD <ftW—OW O HQlF-'ft jp DIDN rQ10rhQHCHft OO '<HaIDfrtlCtIDt0'< F-4J0 D cC,-'.DlOft(DdCOH" IDWftID (DCOOO Oo\0WAH (OHHCO ftIDW >fta-tt<ftWDOH"i- X(DC H"OftHnHDit dO' ID 0 bH" 0' N HifitO 0 0 (DO -ma otCCHrtO ct0OCO NftO tftN ftCftctCDtON ODiH"WDiNO ft OWOFH,OH"NH 0HNH ft O i-CA tQ o\°O (DO Di 100 OH"H '<ftQ• OftID NWH" COCOIDO CO NHWCO IDIDIDO it l0It(AOIDDiH"IDft ma '<H"WIDO) WOO HX OIOID t 0) CO ID 10 ttOP 0< CA 0) d - 0 ft CO N , O 01 tV DIH"D' dOft HNDIP-P-ffl COlt - CO ft d-'i11 aIDwH, ft i-CaoH" OH" ptflU)ØH"DIW ft aCNJOCAH"d HQi d 0N fflftWH-dQi01O HDIU1O 0)0 0 OftD) ID PHOOdM <Na '<H"rt IJIDID CDI Oft (0 O tttUft LQIDO)OPIDH i-W(D'< WWHID-0< NftO C dNO< IDuCd0DiQi0 H" Qi (ANt OO ONIDCO (DdIUNitNZ CIDH"ID N011CCO H-H-ftH,Qj ftaart-4ID> O'1Di aftWO adOltftft (DO OIDH"CQJO ID CIDP&OCACO CO ctdoH"rt- QIDQi H IDCOCO O SN a.p.ft ID'< 0 DI P-P• 01< H, COtD :10 00 OH (AID C P•0 N -O I 010< 'C N 0 ft CO H" H Di C N ft Dl z 0 'C ft H- (51 N ID C H. :1 C - 0 CU) P. 03:1 aft QiODID :1 0) P1 H"< H IN 0' 0 H. tO H 0 P'OWC-'Oft 0)0 pCDDid0iDi cHOP' aaNN iC hl,W0 (DftDIOmS<ft itNiDifi t OH-H oDi H0 C IDftftl 1.51:1 OD'H"ID<' H"Q)H ti HoaID (AID CCC (A—4HH" —10 1101 tb'IDOCOi OlD CO wd 10 ft0 - • The s ~ a l l ,sill-like Amnicon kntruskon located,southeast of S u erlor &Douglas Count ) , Wlsconsln, identifled by D+ckas avd otEers (i9 9 and ~ e n g e y (1970), has noy been mapped 1n detcll The Amnlcon biuton exceeds 6 square km. ln outcrop area and 1s named for exposures alon the bank of the Amnicon River in sec. ?t is poorly exposed in sec 31 and 3'2, 32, T. 48 N., R. 12 W. T. 48 N., R. 12 w., and sec. 5 and 6 T. 47 N - , R. i2 w. ( ~ i g u r e 1). N? contact? were observed, and the qutcrop ext9nt c o ~ n c ~ d e s roxlmatel wlth the map ed magnetlc signature (Dlckas and. Field relagions lndlcate lntruslve contact wlth :&?ers, 1969y surrounding ckengwatana basalt and interbedded volcaniclastic units is well constrained t o the north, and moderately The southern margin appears t o constra+ned t o the east and west. be a chllled contact. (U ft HOODS H CO cOD N C cit H OiOCW OW rtt' ID rP)rtH Ii Z em uDaHtOP1 wOdCrtt'- -MDIftC 0J 0 ID 00 '-,,O CD Hi-HID NPN 0 p)WH.CCHDIH NIDNO F-t PrFID tIDIDH(Q0DiNC CdftCCO<frDi <0 00 (DID D'COftN(DN A C$DiH"ct ft HtCCO H H" WNciDNftftIDftH<ID P1 HID ftN ON ftWONO OOHa>NNCA 0'ODH"ft OWt-0rtO t HIDN0CCOIDID DiCO dCOH"d 1< ON CCAXZ it H-ftID 00 ourtC(ACDiCD tDiH-0HQiH" ci-aai-"Wt p•lo'fl m P- 00) -ZCO HZO0cl'< ID0ID0'H,DI WP-d -OZ CIDWHDi0N '<Oft ii (DC 0 a AOH.NH C H"bl NH" 'CNCOft Di-ftDi IDHO) tO a0'NW (DWFtIDH 1 HN DiD) P• HCOt o0-.NffltftDift0 H p-HDi0 NOH H za• ft:i mtdO IDl-'1WD fttlrr'lOft ftwui 0I'tQ HHWHNIDX 0CC DIN HIDCdtoftO 0WN OW a)Dio0tmD' WrtIDHDiH,w0N (A çtI In ::rO alt 000 H-IDN(tID ID aIDtO O'(D d Z0 i Cs—' OW ft. DiH"COIDCO ct(AHNCN OOCI-N rtW Fl (DO P• H< tO C'00(0 0) a H tDHft H" tOftH•¼oHOftO HIDLqOi-CD'<H0tWH' 10Dl C'Q 0 0 CAftHn<Di tOOtN H-l• (ON O ft ID00Q0 'jIQID p. OH 0CMCH 0 ID (D OftHIDOID 00 O 0k- OHICOOOIC (DF-'Hi- •HO H0 Di H —fti-COftQi O C)ID CftNJWC tQH C4 ND) H0W fti-'ct CwCO0-'rhODiN 0. i-CO CrtWHI N P-CA OC'<ID OH 0 tomWft (0 HftoamCftID 10- (D'<N NOD'H 0C' Dim < ft.Q'iift n0DiHtn0HIDft NftIDHNftSCP0P ftDiC'< QiC 0 H(DDIP DiIDmCH-C HIDawH" H N ftrt rtftDiNW0DCOON (Am IDMCO ftDJID O ID'<CD(D,Qft '<(Od N •t5 NIDDiW0Wft0 - CCPP N IDZOID OC ft am ftIDNftHftN o iIDIDftHID ft (DIlDiOt N i-ID -• 0 OH"COO • Dio'o)ab(DPCD)XIDO H.orMtOIDOH"aCOH"Nrt -"DIDNIDID dON OiCi artifi ftHi HOC> wWOtID CH, OtmN mH-Nomm0ft rtWN OQi O(DtOd l--d1QQi 0.Dft ftWCO(D i—ID H DIDlftDiOH" DitODlOO1 D)iNftDi amDioIDDirnC HH,CDi C OW IDIDfti ,-'-O (Od xftDidIDDaCODi '-CD NO ND)FiDift NH"IDi14<O (1 rtHrfN CA d NCO 0) QiOHW CO (A FC a—< iID CHOP-H" IDIBO I 0Ci ID' awC(DNDiID00 -CO H"0 '—'0 WDi'OIUIDft DiooaOCOftrittO 0> DaftCOrtONO iDWO i-'IDP•ftID N H rt(DrtO H- ON -t -.- 0 ctIDCO HH,tt mct O DiffltftonmWaOWJO HH 0 d - IC Z H C 0 n [A C) C 0 C 0 Z - C t1 t Z 0 Zn 0 Z (AZ HH 0 (DPI CS "1 0 'C Z 0 0 H P1 •d C Z :ri F< 0 t' 0 rrnrrrrnrr-flrcrnr-r-r SEOLOGY AND PETROGRAPHY OF THE AMNICON PLUTON, DOUGLAS COUNTY, WISCONSIN �Ni • •%%_,•_ I ENTA SANDSTONE I I Falls1 N OR1ENTA I mile SANDSTONE -Illgl,'.ay 2 cIIENGWAANA VOLCANICS ' - -jitE::: -1 PLUTON 4, fc CIIENGWATANA - Areal Areal distribution distribution of of the the Amnicon Amnicon Pluton Pluton and and its its relation or relation to to regional, regional, Middle Middle Proterozoic Proterozoic (Keweenawan) (Keweenawan) geology geology of the Nidcontinent Midcontinent Rift Rift System System within within Douglas Douglas County, County, Wisconsin. Wisconsin. the Figure 1. 1. Figure 0 61K SE 5000 Feet +80 NW tall Bayf.eliI Norito J .Amnicon Norm .80 48N-ISW E_48N-12W Ilicloway 5)— I .t —— HIgt.ny2andSS GIo.cioolCuaar* gS N - I S. 1W1 — p BAYFIELD.OR0NTOU') CLASTICS R.tl0..OII Dii, 3-to SE 42 -j j j Li 2 Stc t'vr 4S0-t( neLine diagram diagram interpretation interpretation of of the the upper upper two two and ar one2. Line Figure 2. Figure as as half half seconds seconds of of reflection reflection seismology, seismology, magnetics, magnetics, and and gravity grak in. collected 2-53 and and 53, 53, Douglas Douglas County, County, Wisconsin. Wisc collected along along highways highways 2—53 Display Display presented here here courtesy courtesy of of Halliburton Halliburton Geophysical Geophysical Services, Inc., Inc., Texas. Texas. Services, -j j J -j �O1C F1(D tZ na_ pj n-tm <o PflJP) HQJCD ¼00DN p. DN It'D t', C - DQa HD 0) tO) E-'WD IF-'tQ 0) Q 0 • CD D' 0 D CD tO P• (0 O' c t-. CDI-'D N N D (0 rt- P• 0 N CD it NJ1t't 0300 CD 01 0 CD N CD ct DO OH, U'-O 100 OH CDO 0(0 a -'D' .- O1S 0— D CD C (0 rt Hi 0 0 - 'C it it N f----'- DDO 10DN 0010 D10P- I-'-f-- H(O }-IDO DCDCD NO' itOD 'IDO' 0 Z-'< - 0100 Df--H P-CN rtNrl- 0)rt(0 NH CD WND 10(DH zj—J CO-a (tH C U - - • t <P '<H- OCD ftC-" HDO) 0)0 I-'- tQb' H--t OON 100 0)0 ODE'- D f-00 '-C -tOfl OHO CIOCO 0 D F-'o C-ct NIflO rto,Z NJ :— J 0-kb Z0 N1 •-0• Yrt- - (0 - In 1<0 uDw O0)rt HHCD OtOD CDCtO 000) CD OH HCDOJ NHD CDtOO tDP- CO)tO OINCD O'N CD0) ZCHi O'iOO 010 -tOt rtDF-'- WORD' D10 HD (tH D0 rtCrt 0100) HCOH CD CD ifiDi '-0 rtrh 0 0)ht,0) H NO-C it 01'< :t:QCW- HH •-OW DCD f-tOrt (0 D 00- 0001 WN F-'-O, 10 m D U Table 1. Chemical anal ses of the two etrographic phases within the Amnicon Flvton, witg comparison of the Amnicon trqctolice phase with slmllar phases from the Mellen and Duluth lntruslves. D 1!) D D' (OCt <CDk p-ftC YIP- CHW NO0 ctrtffl P-OD DOD' Nt Yrt ctO HOD CDP- COt OF-"O) DN N D'O 0) (OCt DD(0 CDctO HhtO H Z ct moC D CDO0 N rtk-rt N OtO 01 00 N,OW (1) fflrtH 0) D)H-O) 't NDH (BOO) HçtQ 10 DO ito DH PH" CDT'(D f-i H '— b'CDa_ DCDD D DCDD 'U 'C 0<0 OP-fl Ifi DittO) ' CD N-< 0—]'- D'03 HO 01kb C. CD C\ A IlitIl 111111 I_I H D 0 P• (0 DC D'NJN flout 0 'U 0 0) '0 1 HH .N 0 • tbHHU1-3O3HHH01 H HHA —]IOONJHO1000IH-] '0 U) '— - — NJ —' it C H C C - C-' — CD H H CD ND GO 000-U)H0001NJ0H N H OHHNJOWHU3-J H-I WINJU1ANJUNJO1aW'-) HC-'D (00 0) D' H HU (DD rtD P.tS 0 H U 0 N H -' —s CD 0, —]HouNJooaHow D '0 < I-'- H01rt UlOtO03HO '—3 MQD(OHH-I-'- 0)WAG\NJkbHNJtOU0)A 0000 0 H 01 H CD' (FHOONJ0000NJOO 01 ONflJ 0 OONJNJ NDit tOIOONJO0)000DI-"0 rt-O' it wpNJcokbHHo1A--J Of-tO ZC'C '0(00 'UN CD N 1< 'U 0 D 0' '.0 N frtü-'H, DD O—'O t-'-CDP- P+'-P Hi OO 0 10 CD (0 'C H WCW 0)0010 D 0' 0 C it Hr'Q rhO DND ONJOJDOJ —]DHD Ow tOHrtDit (OHCD W NDNHN CD0)CDP) WCDtt tON 0)OCDDCD (t—HN H D CDt H1tP CDNOI'lO NOW0)(0 OClfltflLO NJ 'tot—"d U --- I fflN 010 I-'-W • DC -GD rHO tOO o'CD'.Q Qiçtk H OdD ND< 0 10 P-WI-'- 003 10—] 'CC P-kb (OtON H -- X- ZOrt HD 00 fl)Q.i. -'•QD CD H CD••C 0) 0 N C q t< 'ci- o- OdD -mm CD ,--'cr to 0)0 t000) -0 0 H 0—C N •D- '--'f--NJ (0 ct (OH O'D NJ (0 N 01 %% kbtrt ot-NZ U) D p•- NH 0D P-0) 0) '<010 F--i— - NJr CD CD , 0- H - D- CD- <H • m Uff)O— (Z: (A tllDtCD 0)'--'bit CD ic WDD C U f-cict References: Dickas, A. B. et al., 1969 Relationships of regional magnetics to the bedrock geolo y of the South Range Quadrangle, Douglas CoUnCY Wlsconsln: ~gstracts,15th Inst. Lake Super lor Geology, p . 12-i4. N •—CDqaa_ rp ro'x rtH • HDD N- H-OH . '<c OOD '—'--'CD NOH Omit mztr 'ci WCD Green, J. C., 1972 North Shore volcanic Group, in Sims,.P. K. Ieds), Geology of Minnesota: A centennial and More G. B. M. ~cliwartzvolume), Minnesota Geological survey, p. volume 294-332Klewin, K. W. 1987< The petrology and zeochemistry,o the Keweenawan potato Rlver Intryion, nort ern W+scqnsIn; un ubllshed Ph. D. dissertation, Northern Illlno~sUn~versity, 357 p . Mengel, J. T., 1970 Geology of the western Lake Superior region, privately printed, $6 p. Tabet, D. E., and Mangham, J. R., 1978, The geology of the eastern,Mellen Intrusive Complex, Wisconsin: Geosclence Wisconsin, v. 3, p. 1-19. Weiblen, P. W., 1982, Keweenawan intrusive igneous rocks in R J. Wold and W. J. Hinze (eds): Geology and tectonics of &he Lake Superlor Basln, Geol. SOC. America Memolr 156, p. 57-82. C. CD OOP- rrrrrrrrr----r Amnicon Mellen (1) Duluth (2) Oxide ( 8 ) Troctol~te Granophyre (3) sio2 : . .-.,.,, 50.4 69-8-71. 47.7 Ti02. $ . 1.8 0.3- 0. 1.3 A1203 18.3 11-7-12. 18.4 FeO 9.9 4.3- 5. 10.6 MnO 0.2 0-1- 0.1 0.1 0.2 5.1 0.3- 0.8 6.1 5.3 9.9 2.0- 1.7 9.9 11 2 3.2 Na20 3.2- 3.5 2.9 2.4 K20 0.6 4.1- 4.1 0.6 0.5 P205 0.4 0.1-<O. 1 0.2 0.2 LO1 0.8 1.9- 0.9 Totals 100.6 97.8-100.7 99-8 97.8 n Potato River Intrusion (1) Possible Earent ma ma ~ o m p o s ~ t i oof Eastern ellem 1n?rusLve SuLte) (Klewln 1987, p. 152) (2) bossible parent ma ma composition of ~ o r t hShore Volcanic Group (Green, 19727 '(3) Percentage range of two analyses of granophyre phase - - �REGULATING REGULATING METALLIC HETALLIC MINERAL HINEPAL DEVELOPMENT DEVELOPHENT IN IN WISCONSIN WISCONSIN I Thomas Thomas J. Evans, Evans, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey 1 I Despite Despite the the significant significant potential potential for for metallic metallic mineral mineral deposits deposits in in the the Ladysmith/Rhinelander Ladysmith/Rhinelander volcanic volcanic complex complex of of northern northern Wisconsin, Wisconsin, only only one one mining mining project project has has received received permits permits for foractual actualmineral mineral development. development. In In part, part, the the regulatory regulatory framework framework for for metallic metallic mining mining has has been been responsible responsible for for the the slow slow pace pace of of mine mine development. development. The The statutes statutes and and administrative administrative rules rules governing governing metallic metallic mineral mineral development development in in Wisconsin Wisconsin form form aa comprehensive, comprehensive,broad-based broad-based regulatory regulatory framework. framework. In In addition addition to to extensive extensive environmental environmental regulations regulations focusing focusing on on groundwater, groundwater, surface surface water, water, air, air, water-supply water-supplywells, wells, and and wastewater wastewater discharge discharge activities, activities, Wisconsin Wisconsin has has adopted adopted aa net net proceeds proceeds tax tax on on the the occupation occupation of of metalliferous metalliferous mineral mineral mining. mining. " The The regulations regulations affecting affecting metallic metallic mining mining in in Wisconsin Wisconsin include include aa thorough thorough assessment assessment of of environmental environmental impacts impacts and, and, together together with with the the extensive extensive permitting permitting requirements, requirements,result result in in aa lengthy lengthy process process from from mineral mineral discovery discovery to to eventual eventual mine mine start-up. start-up. However, However, the the process process does does provide provide aa mechanism mechanism that that will will lead lead to to positive positive decisions decisions on on the the necessary necessary permits, permits, as as long long as as the the environmental environmental standards standards can can be be addressed. addressed. I I I; The The net net proceeds proceeds tax tax provides provides aa reasonable reasonable tax tax basis basis for for mineral mineral development. This tax, often misunderstood or mischaracterized development. This tax, often misunderstood or mischaracterized by by the the mining mining industry in the early years after its adéption in 1977, was modified industry in the early years after its adoption in 1977, was modified in in 1981 1981 to to clarify clarify and and expand expand certain certain allowable allowable deductions deductions and and to to reduce reduce the the overall overall tax tax rate rate so so that that it it was was more more closely closely tied tied to to the the profitability profitability of of mining mining ventures. ventures. Although Although the the tax tax is is an an added added burden burdenor or "cost "costof of doing doing business" business"in in Wisconsin, Wisconsin, it it does does not not have have aa significant significantimpact impacton on the the overall overallpotential potential for for mining mining in in Wisconsin. Wisconsin. The The modified modified net net proceeds proceeds tax, tax,aa "workable" "workable"mine-permitting mine-permittingprocess, process,and and recent recent decisions decisions that that favor favor mineral mineral leasing leasingcreate create aa positive positive climate climatefor for mining; mining; however, however, the the small small but but vociferous vociferousanti-mining anti-miningactivity activity and and recent recent 1 legislation legislation that that would would severely severely limit limit mining mining in in the the state state do do much much to to obscure obscure that that positive positive climate. climate. It It is is important important to to remember remember the the "upside" "upside"when when you you are are 1 up up to to your your ears ears in in the the "downside". "downsiden. I 44 �GEOLOGY OF HORIZONS OF PLATINUM PLATINUM GROUP GROUP ELEMENT ELEMENT -- ENRICHED ENRICHED HORIZ WITHIN WITHIN THE DUNKA DUNKA ROAD ROAD COPPER-NICKEL PROSPECT PROSPECT ST. LOUIS ST. LOUIS COUNTY, COUNTY, MINNESOTA MINNESOTA Stephen 0. Geerts Geerts Stephen D. Natural a t u r a l Resources Resources Research Research Institute, Institute, University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth The Dunka Dunka Road Road Cu-Ni Cu-Ni prospect p r o s p e c t is i s located l o c a t e d within w i t h i n what is i s informally informally known W.), which is W., R. R. 13 W.), i s part part known as as the t h e Partridge P a r t r i d g e River R i v e r intrusion i n t r u s i o n (T. (T. 60 60 W., of of the t h e Duluth D u l u t h Complex, Complex, 1.1 1.1 b.y. b.y. (Keweenawan) (Keweenawan) in i n age age (Figure ( F i g u r e 1). 1 ) . Seven Seven major lithologic 1 i t h o l o g i c units, u n i t s , along a l o n g with w i t h several s e v e r a l internal i n t e r n a l ultramafic u l t r a m a f i c subunits, s u b u n i t s , have have been been identified i d e n t i f i e d and and are a r e correlatable c o r r e l a t a b l e over o v e r the t h e deposit. d e p o s i t . The ultramafic u l t r a m a f i c subunits subunits (layers of p picrite uniform tthicknesses are ( l a y e r s of i c r i t e tto o ddunite), u n i t e ) , eexhibit x h i b i t rrelative e l a t i v e uniform h i c k n e s s e s and a re present p r e s e n t at a t the t h e same same relative r e l a t i v e position p o s i t i o n within w i t h i n the t h e major m a j o r lithologic l i t h o l o g i c units. units. The The major m a j o r lithologic l i t h o l o g i c units u n i t s are a r e the t h e same as ddelineated e l i n e a t e d by Severson and Hauck (1990), Unit I, a finefine(1990), and upward upward from from the t h e basal basal contact c o n t a c t are a r e (Figure ( F i g u r e 2): 2): U n i t I, to anorthositic pyroxene t o coarse-grained sulfide-bearing a t r o c t o l i t e ttoo pyroxene c o a r s e - g r a i n e d sulfide-bearing n o r t h o s i t i c troctolite troctolite with and ft. tthick) hick) w i t h aassociated s s o c i a t e d uultramafic l t r a m a f i c llayers a y e r s 1(a), I ( a ) , 1(b), 1 (b), and t r o c t o l i t e (450 (450 ft. 1(c); Unit medium- to pyroxene I(c); U n i t II, 11, aa mediumt o coarse-grained c o a r s e - g r a i n e d ttroctolite r o c t o l i t e ttoo pyroxene troctolite Unit ft. thick) t h i c k ) with w i t h aa basal ultramafic u l t r a m a f i c layer l a y e r 11(a); II(a); U n i t III, 111, t r o c t o l i t e (200 (200 ft. aa fine-grained, m o t t l e d textured t e x t u r e d troctolitic a n o r t h o s i t e to anorthositic f i n e - g r a i n e d , mottled t r o c t o l i t i c anorthosite t o anorthositic troctolite Unit anorthositic f t . thick); thick); U n i t IV, I V , aa coarse-grained coarse-grained a northositic t r o c t o l i t e (200 (200 ft. troctolite coarse-grained t r o c t o l i t e to t o pyroxene pyroxene troctolite t r o c t o l i t e (400 (400 ft. ft. thick); t h i c k ) ; Unit U n i t V, V, a c oarse-grained anorthositic coarse-grained ft. thick); a n o r t h o s i t i c troctolite t r o c t o l i t e (300 (300 ft. t h i c k ) ; Unit U n i t VI, V I , aa finef i n e - tto o c oarse-grained troctolitic f t . thick) t h i c k ) with w i t h basal ultramafic ultramafic t r o c t o l i t i c anorthosite a n o r t h o s i t e to t o troctolite t r o c t o l i t e (400 (400 ft. layer V I I , aa coarse-grained c o a r s e - g r a i n e d troctolitic t r o c t o l i t i c anorthosite a n o r t h o s i t e to to l a y e r VI(a); V I ( a ) ; and Unit U n i t VII, anorthositic ft. t thick) basal uultramafic h i c k ) wwith i t h basal l t r a m a f i c layer l a y e r VII(a). VII(a). a n o r t h o s i t i c troctolite t r o c t o l i t e(400.4(400+ ft. Most I. The The sulfide sulfide Most sulfide s u l f i d e mineralization m i n e r a l i z a t i o n occurs occurs within w i t h i n Unit U n i t I. mineralization m i n e r a l i z a t i o n is i s both b o t h interstitial i n t e r s t i t i a l and and widespread, widespread, but b u t variable v a r i a b l e in i n modal percentage percentage (rare ( r a r e to t o 5%), 5%), continuity, c o n t i n u i t y , and thickness t h i c k n e s s (few (few inches i n c h e s to t o tens t e n s of of feet). Sulfide feet). S u l f i d e mineralization m i n e r a l i z a t i o n is i s generally g e n e r a l l y related r e l a t e d with w i t h proximity p r o x i m i t y to: to: hornfels Virginia i n c l u s i o n s , basal basal contact c o n t a c t with w i t h the t h e ffootwall ootwall V i r g i n i a Formation, and and h o r n f e l s inclusions, some of I. Primary P r i m a r y sulfide sulfide o f the t h e internal i n t e r n a l ultramafic u l t r a m a f i c layers l a y e r s within w i t h i n Unit U n i t I. mineralization pyrrhotite, and cubani cubanit. te. m i n e r a l i z a t i o n includes chalcopyrite, p e n t l a n d i t e and i n c l u d e s chalcopyrite, y r r h o t i t e , ppentlandite Minor M i n o r amounts amounts of o f bornite, b o r n i t e , native n a t i v e copper, copper, talnakhite t a l n a k h i t e and and mackinawite m a c k i n a w i t e or or valleriite v a l l e r i i t e have have also a l s o been been identified i d e n t i f i e d in i n preliminary p r e l i m i n a r y petrographic petrographic observations. Pt+Pd values observations. v a l u e s range ranae from f r o m 100 100 to t o >2400 >2400 ppb ~ o over bo v e r 10 10 foot foot intervals, i n t e r v a l s , and and these t h e s e occur o c c u r as as iisolated s o l a t e d values v a l u e s or o r along a l o n g stratigraphic stratigraphic horizons h o r i z o n s in i n the t h e upper upper 3/4 3/4 of of Unit U n i t I. I. Several Several Cu/PGE-enriched Cu/PGE-enriched horizons h o r i z o n s have have been been identified, i d e n t i f i e d , and and occur laterally The most l a t e r a l l y throughout t h r o u g h o u t the t h e prospect. prospect. most continuous c o n t i n u o u s horizon, h o r i z o n , (RED (RED Horizon) H o r i z o n ) is i s found found directly d i r e c t l y beneath beneath ultramafic u l t r a m a f i c layer l a y e r 11(a), I I ( a ) , within w i t h i n the the uppermost uppermost portion p o r t i o n of of Unit U n i t I. I. This T h i s horizon h o r i z o n ranges ranges from from 10 10 to t o 30 30 feet f e e t thick thick and Two other and contains c o n t a i n s average average values v a l u e s of o f 0.65% 0.65% Cu Cu and and 1200 1200 ppb ppb Pt+Pd. Pt+Pd. other horizons, h o r i z o n s , (ORANGE (ORANGE Horizon H o r i z o n and and YELLOW YELLOW Horizon) H o r i z o n ) occur o c c u r roughly r o u g h l y at a t 100 100 and and 200 200 feet f e e t beneath beneath Red Red Horizon, Horizon, respectively. r e s p e c t i v e l y . These These are a r e less l e s s continuous c o n t i n u o u s horizons horizons that t h a t range range from from 10 10 to t o 50 50 feet f e e t thick t h i c k and and contain c o n t a i n average average values v a l u e s of o f 0.70% 0.70% Cu Cu and Only Pt+Pd. Only one one PGE-enriched PGE-enriched horizon h o r i z o n has has been been identified identified and 1000 1000 ppb ppb Pt+Pd. outside Unit Horizon), I. It I t occurs in in U n i t VVII (MAGENTA H o r i z o n ) , directly d i r e c t l y beneath beneath o u t s i d e of o f Unit U n i t I. ultramafic i t has has been been identified i d e n t i f i e d in i n only o n l y six s i x drill drill u l t r a m a f i c layer l a y e r VII(a). V I I ( a ) . Although A l t h o u g h it holes i t ranges ranges from f r o m 10 10 to t o 30 30 feet f e e t thick t h i c k and and contains c o n t a i n s average average h o l e s to t o date, date. it values values of o f 0.90% 0.90% Cu Cu and and 1875 1875 ppb ppb Pt+Pd. Pt+Pd. 45 �j. The Cu/PGE-enriched The predominant predominant hhost o s t rock r o c k for f o these r these Cu/PGE-enriched horizons horizons iiss coarse-grained which may may eexhibit coarse-grained a anorthositic n o r t h o s i t i c t troctolite, r o c t o l i t e , which xhibit some ubtle some ssubtle minor a1 alteration. The a1 alteration t e r a t i o n . The t e r a t i o nassemblage assemblage ffracturing r a c t u r i n g accompanied accompanied wwith i t h minor within serpentine, uuralite w i t h i n these these mineralized m i n e r a l i z e d zones zones i is s serpentine, r a l i t eand and saussurite. saussurite. TThis his type of throughoutt the type o f alteration a l t e r a t i o assemblage n assemblage has has also a l s o been been observed observed throughout h e eentire ntire prospect, but with Although the prospect, b u t is i s not n o talways always associated associated w i t h mineralization. m i n e r a l i z a t i o n . Although the majority m a j o r i t y of o f sulfide s u l f i d emineralization m i n e r a l i z a t i o nisi sbelieved b e l i e v e dtot obebeprimary, primary, mineralized mineralized zonest that f r a c t u r e d / a l t e r e dzones zonescan cancontain c o n t a i nsecondary secondary zones h a t are a r e intersected i n t e r s e c t e dby by fractured/altered sulfides Themmajority s u l f i d e s and and textures, t e x t u r e s , suggesting suggesting local l o c a lenrichment. enrichment. The a j o r i t y ooff the the sulfide (5 mm) and and commonly rimmed (5 mm) commonly rimmedby bysecondary secondary s u l f i d eitself i t s eisl f coarse-grained i s coarse-grained red-brown red-brown bbiotite. i o t i t e . IIlmenite l m e n i t e occurs occurs in i n two two habits h a b i t s within w i t h i nthese these zones, zones, as euhedral host rock, rock, and and as as ""bleb-like" euhedral tto o subhedral subhedral llaths a t h s throughout throughout t the h e host bleb-like" black shiny ddroplets within This second b l a c k shiny roplets w i t h i n the t h e sulfides. s u l f i d e s . This second i ilmenite l m e n i t e habit h a b i t has has only o n l y been been i identified d e n t i f i e d in i nsulfide s u l f i d ezones zones that t h a tare areenriched enriched in i nPd Pd and/or and/or Pt. Pt. References: Morton, P., A., 1987, PGE, Au and and Ag Ag contents contents of o f Cu-Ni Cu-Ni P., and and Hauck, Hauck, S. A., base o off tthe Duluth Complex, nnortheastern ssulfides u l f i d e s found at a t the t h e base h e Duluth ortheastern Minnesota: Natural ResearchI nInstitute, N a t u r a l Resources Resources Research s t i t u t e , Technical Technical Report Report NRRI/GMIN-TR-87-04, 85 pp. NRRI/GMIN-TR-67-04, 85 Morton, 1989, Precious Precious metals metals i in Morton, P., P., and and Hauck, Hauck, S. S. A., A., 1989, n the t h e copper-nickel copper-nickel Minn. Geol. ddeposits e p o s i t s of o f the t h eDuluth D u l u t hComplex: Complex: Minn. Geol. Survey, Survey, IInf. n f . Circ. C i r c . 30, 30. pp. 47-48. 47-48. pp. Severson, M. M. J., J., and S. A., 1990, Geology, geochemistry, and and and Hauck, S. A., stratigraphy of a portion of Partridge River s t r a t i g-r a p. h -y o f a p o r t i o n o f the the P artridge R i v e r IIntrusion, ntrusion, northeastern Natural n o r t h e a s t e r n Minnesota: ~innesota: N a t u r a l Resources RResearch e s e a r c h ~Institute, nstitute; Technical Report, NRRI/GMIN-TR-89-11, Duluth, Minnesota, Report, NRRI/GMIN-TR-89-11, Duluth, Minnesota, 240 240 pp. pp. _1 j = tMIT VII -J UNIT VI IMIT V CENERAUZED IGNEOUS GENERALIZED IGNEOUS $TRATCRAPHIC COLUMN STRATIGRAPHIC COLUMN UNIT IV UNIT fil I_____I UNIT UNIT I — —K — 111 UNIT I Insow ..,.— r_AL_.r 'H * qRNIA FOlIaTiON BIWASIC ON-FOlMAT1ON IIGC II WOAL C flc PRNIIGL PlYtI INTmITD a a,cn. zn oa s,.n—c a,... 1' j -A 46 �DRIFT PEBBLE LITUOLOGY DRIFT LITHOLOGY OF OF THE THETOMAHAWK TOMAHAWK ROAD ROAD AREA, AREA, LAKE COUNTY, MINNESOTA, MINNESOTA. USED TO HELP HELP INFER INFER LOCAL LOCAL BEDROCK BEDROCK John John C. C. Green, Green,Univ. Univ. of ofMinnesota, Minnesota,Duluth; Duluth;Ed. Ed.Venzke Venzke&&Tom TomLawler, Lawler,D.N.R. D.N.R. 1-libbing Hibbii Abstract In In 1989 1989 a multi-media, regional, geochemical geochemical orientation and andreconnaissance rewmaissance survey surveywas was completed completed for for a portion portion of of Lake Lake County, County, Minnesota. The Theresults resultsofofthis thissurvey surveysuggest suggestthat that three threeanomalous anomalouslocalities localities exist exist across also concluded that that the thegeochemical geochemicalsurvey survey reflects bedrock lithologies, lithologies, despite across the the project project area, area. It was also variable gladal glacial overburden overburden thickness thickness of of several several deposit deposit types types and and aacomplex wmplex depositional depositional history, history, (Buchheit (Buchheit et et al,, p. 1). 1). These These results were related to scale, "Geologic 'Geologic al., 1989, p. to the the geology geology as mapped by by Green on on the the 1:250,000 1:250,000 scale, Map of Harbors Sheet', of Minnesota, Minnesota, Two Harbors Sheet",(1982) (1982) but but the thecomplex complex pattern pattern of of geochemical geochemical results results made obvious obvious the need need for for aa more moredetailed detailedgeologic geologicmap mapto toassess assessthis thisrelationship. relationship. Traditional Traditional geologic geologic maps are are aa reflection reflectionof ofthe thequantity quantityand andquality qualityof ofavailable availablegeologic geologic information, information, which did not not provide computer which did provide the the needed needed detail. detail. Improved Improvedquality qualityof ofgeophysical geophysical surveys surveys and and sophisticated sophisticated computer enhancement techniques now provide provide the the means means to generate inferred geologic geologic maps. maps. For techniques now For accuracy accuracy and detail detail these maps provided in in Minnesota Minnesota by by an maps require require high high resolution resolution aeromagnetic aeromagnetic and and regional regional gravity gravity surveys, surveys, provided aeromagnetic survey survey funded funded by by the Legislative Commission on on Minnesota Minnesota Resources Resources (LCMR) (LCMR) and aa gravity Legislative Commission gravity survey by the the Minnesota Minnesota Geologic GeologicSurvey Survey(MGS). (MGS). Geologic interpretations interpretations made from remote measurements survey by measurements of properties are nseudo-Qeoloic mans. mans. of physical physical properties are known known as as pseudo-eeolo-ic As the practicality practicalityof ofthese these maps, maps,the theDepartment Department of ofNatural NaturalResources Resources (DNR) (DNR) contracted contracted A s a pilot test of the with private consultants to to interpret interpret geophysical geophysicaldata dataand andmake makemaps mapsinintwo twoareas. areas. One of the areas selected private consultants selected was was a four four township township block in the McDougal Lakes Lakes Area of of Lake Lake County, County, in the interior interior of of the the Duluth DuluthComplex, Complex, aa Proterozoic intrusivecomplex. complex. This This area was mapped by Robert Robert J. Ferderer, Proterozoiclayered layered maCic mafic intrusive Ferderer, Eagan, Eagan, Minnesota. Minnesota. Ferderer's Ferderer's pseudo-geologic pseudo-geologic map is much much more more detailed detailed than than its itspredecessor predecessor The TheTwo TwoHarbors Harborsgeologic geologicmap. map. Lithologic Lithologic units and structural features features are areconfirmed confirmed by by verification verification procedures procedures wherever wherever tested. In addition addition to to lithologic lithologic units and structural features features this this map map has hasthree threedimensional dimensional aspects aspects shown shown by depth to to magnetic magnetic source forward modeling modeling profiles. profiles. A portion of this map in the pebble count area is shown on source calculations and forward Plate Plate 3. 3. In feet deep, and there are In this this area area glacial glacial cover cover is is 00 to to 65 65 feet are some some outcrops, outcrops, but prior prior to to this this program program there drill holes, holes, with with there were were only only three three drill drillholes. holes. To T overify verifythe thepseudo-geologic pseudo-geologicmap mapititwas wastested testedwith: with: 1) Six drill lithologic loggingusing usingassays assaysand andthin thinsection sectionstudies; studies; 2) 2) Geophysical Geophysicalmeasurements measurementson onthe thecore; core; 3) 3) Ground lithologic logging geophysical traverses over overselected selected features: features;and and 4) till and and outcroo outcrop studies studies that that relate 4 ) Pebble Pebble counts wunts of glacial olacial till geophysical traverses lithologic observations to to geophysical geophysicalparameters. parameters. The h h & g k observations The pebble pebble count, count, thin thin section, outcrop studies, and drill core logging were done by, logging were by, or under the the direction direction of, of,John John C. C.Green Green(University (Universityof of Minnesota Minnesota - Duluth). The glacial drift Theu -nebble sed 1 countine technique used by byGreen Greenand andVenake Venzke(1990) ( 1 W )was was to to determine determineififglacial drih pebble pebble composition drift-covered areas. areas. A can be used to determine the the lithology litholoey of ofthe the underlying underlying bedrock in drift-covered A strip strip of of composition can sections sections was chosen along the the Tomahawk Tomahawk Road Roadwhere, &here,with withadditional addLtioLa1outcrop outcropmapping mappingand anddrill drillhole holelogging, log&& an an improved improved geologic geologic map could be made made to t oevaluate evaluatethe theresults resultsof ofthe thepebble pebblecounts wuntsand andthe thepseudo-geologic pseudo-geologic map. Although hole coverage. coverage. Bedrock Although some some contacts contacts are are poorly poorly constrained constrained due to gaps in outcrop and drill hole units gabbro and and troctolite troctolite of of the Bald Bald Eagle Eagle Intrusion, Intrusion, and and one one or two troctolite units of anorthosite, olivine olivine gabbro troctolite units were m a p ~ e dBased .Basedon oncounts countsofofthe the50 50largest largestpebbles nebblesinineach eachsample, sample.four fourlithologic litholodcdrift driftunits unitswere weremapped: maoned: were mapped. 1) 1) Troctolitic; ~roct&tic; 2) Transition Transition Zone; 3) 3) Anorthositic; ~northositic;and and 4) 4) Mixed Mixed Volcanic ~ o l & n i c(Plate 5). 5). In type, In general, the the most most abundant abundant pebble pebble type type in in these these samples samples corresponds corresponds to to the the underlying underlying bedrock rvoc. suggesting that this technique can be useful for"remotely for 'remotely sensing' types in in coveredareas. covered areas. However, suggesting that technique can sensing" bedrock bedrock types owe&; in the drift is dominated byby llthologies (Archean, the eastern eastern 1/4 1/4ofofthe thearea areathe the drift is dominated lithologies (Archean,Animikie, Animikie,Keweenawan Keweenawanlavas, lavas, granophyre) 10's of km) kin) from from the the E E,,ENE, ENE, or ESE. This granophyrc) that that have have been been transported for for long long distances (several 10' s of This must have been carried bedrock). Elsewhere clearly not not basal basal till till (directly (directly overlying bedrock). Elsewhere carried by by the Superior SuperiorLobe Lobeand andisisclearly in the 1 the study study area, area. ice transport transoort has has produced oroduced some some gradations madations or or transition transition zones zones in the drift pebble nebble assemblages, assemblaees. compared bedrock contacts. here) was wasprimarily compared to t othe thebedrock contacts.-,Also, since sinceglacial glacialtransport transportin inthe theRainy RainyLobe Lobe(dominant (dominanthere) roughly bedrock contact contact fanorthosite (anorthositeyvstroctolite), rouehly ~-a r a l l eto l the main bedrock troctoliteVthe thepebble nebbleassemblage assemblaeeat atany anvsample sarnole site site - . parallel may the technique will be may have have come come largely largely from from aa few fewkm km up-ice. ~ ~ - i c eThus . thetechnique'wiU be most most successful successful when the drift driftisis - .. 47 47 �1 relatively thin thin and to exclude the existence existenceof ofan anupper upper drift drift sheet that is is relatively and its its stratigraphy stratigraphy is is known known well well enough enough to exclude the sheet that not in in contact contact with with local localbedrock, bedrock,and and where where rock rock boundaries boundaries are arc at at large large angles angles to to ice ice transport transport direction, direction, not (Green and and Venzke Venzke 1990). 1990). Comparing results with with Fcrdcrcr's Fcrdcrer's map there is aa corrclativc correlative relationship relationship between between the the west west Comparing geochemical results contact area of of his his lb2 sb2unit unit and and high high geochemical geochemicalassays. assays.Th This unitisi5similar similarininareal arealextent extentto to the the dg dg unit unit on on is unit contact area thc Harbors Sheet. Sheet. Anomalous correlate with Ferderer's the Two Two Harbors Anomalous geochemical geochemical values values also correlate Fcrderer's fault faultzones. zones. Buchheit, R.L., R.L., Malmquist, "GlacialDrift Drift Geochemistry for Strategic Minerals; K.L. and and Niebuhr, Nicbuhr, J.R., J.R., 1989, 1989, "Glacial Geochemistry for Strategic Minerals; Buchhcit, Malmquist, K.L. Duluth Complex, Lake County, Minnesota",Minnesota MinnesotaDcpt. Dept.ofof Natural Natural Resources, Divisionof of Resources, Division Duluth Complex, Lake County, Minnesota", Minerals, Report 262. Minerals, 262. Green J.C. J.C. and and Vcnzke, Venzke, EA., ES., 1990, Lithology of of the Road Area, Area, Lake Green 1990, "DriFt "Drift Pebble Pebble Lithology the Tomahawk Tomahawk Road Lake County, County, Minnesota: Can Can itit be be Used Used to to Infer infer Local Dept. of Division Minnesota: Local Bedrock?", Bedrock?". Minnesota Minnesota Dent. of Natural Natural Resources, Resources, Division of Minerals, Minerals, part of of Report Report 290. 290. -I j J J * 00 ::::: a - J 'a. a... .-..t... ot 1" I. Plot. 3. "op of Outcrop. one Dclii Hal.. a,,d 'hair R.lolion.hlp I, ha A..o'aootI.c l'.l.rp..Iol,or. •dap *t (1*09) I C*O •t (AV.,fl. - 'no —-—"-.0-I. —.•ofral,_fl•!t'o — oo •'.I— .4 a.—. ' —. OOq S.. a_a.,, — V.. S.'! (aDI—a. .4 V.. w Ca.!" S.'—— •—'.°. •a" a' I.. a'.., V.' SO! .,, J J ,'w—......, •.•..,..a' •t. 593 t.. .v..l•, -I H j 1" Plate S. Wop of Sompl.. She—in2 the.. £saign.'a.n? IC Glacial Drill Unit.. CO So tao..... ISIC 48 1s9 �I I I I I I I I I I I I I I I - I I GROUND GROUND GEOPHYSICAL GEOPHYSICAL SURVEYS SURVEYS LEADING LEADING TO TO THE THE BEND COPPER-GOLD DISCOVERY BEND COPPER-GOLD DISCOVERY Jay Associates, Inc., Inc., Jay C. C. Hanson, Hanson,Ernest ErnestKK*. Lehmann Lehmann & & Associates, North, Minneapolis, Minnesota 55401 North, Minneapolis, Minnesota 55401 SUMMARY SUMMARY ' ' . . . . ,..,.,< 430 430 First First Avenue Avenue ,. . ... .~,.. ,~ The The initial initial ground ground geophysical geophysical surveys surveyswere were intended intendedto tofollow follow up up aa1977 1977 INPUT airborne electromagnetic (AEM) anomaly located in the Chequamegon INPUT airborne electromagnetic (AEM) anomaly located in the Chequamegon National Forest in • Wisconsin. National Forest in Taylor TaylorCounty County, Wisconsin. The The anomaly anomaly was was delineated delineated on on only only one one flight flight line. line. The The ground ground geophysics geophysics consisted consistedof ofhorizontal-loop horizontal-loop frequency electrornagnetics (HLEM) and total-field magnetics frequency electromagnetics (HLEM) and total-field magnetics profiling. profiling. Five Five north—south surveylines, lines, spaced spaced 400 400 feet feet apart, apart, were north-south survey were placed placed over over the the anomaly. on two of the anomaly. A A strong strong nonrnagnetic nonmagnetic conductor conductor was was encountered encountered on two of the central central lines, lines, suggesting suggesting the t h eoccurrence occurrenceof of aasteeply steeplydipping dippingmassive massive sulfide sulfide lens with short strike length. Subsequent drilling, which began with two lens with short strike length. Subsequent drilling, which began with two cored holes drilled on each of the surveylines, lines, verified verified tthe cored holes drilled on each of theanomalous anomalous HLEM HLEM survey he conductive source conductive source as as being being due duetotomassive massivechalcopyrite chalcopyritemineralization. mineralization. Assays The Assays of of core core samples samples indicated indicated the thepresence presenceofofore—grade ore-grade gold gold as a swell. well. The importance of ground geophysical follow-up over single-line or poorly defined importance of ground geophysical follow-up over single-line or poorly defined AEM anomaliescannot cannot be be overestimated. AEM anomalies overestimated. INTRODUCTION INTRODUCTION North—central Wisconsinhas has been been aa focal North-central Wisconsin focal point point for formassive—sulfide massive-sulfide exploration exploration since Copper initiated initiated aa large in the since Kennecott Kennecott Copper large exploration exploration program program in the late late led to 1950s. 1950s. They They were were originally originally led to the t h e area area because because of of favorable favorable outcrops outcrops (primarily (primarily in in Rusk Rusk County), County),new newvolcanogenic volcanogenicmodels, models,and andimproved improvedAEM AEM surveys in in particular particular were for the systems. The AEM AEM surveys systems. The were responsible responsible for the initial initial discoveries Flambeaudeposit depositand. and, to to aa major extent, the discoveries of of the the economic economic Flambeau major extent, the Further subeconomic Thornapple deposit, deposit, both subeconomic Thornapple both located located near near Ladysmith. Ladysmith. Further to to the the east, AEM exploration programs by the Central Wisconsin Joint Venture (Getty east, AEM exploration programs by the Central Wisconsin Joint Venture (Getty Minerals and Ernest • Noranda, Minerals and Ernest K. K .Lehmann Lehmann&&Associates) Associates). Noranda, and and Exxon Exxon led led to to the mid— the discoveries discoveries at a t Ritchie Ritchie Creek, Creek. Pelican Pelican River, River,and andCrandon Crandonininthe the mid- to to More recently, an exploration program funded by the Jump River late—1970s. late-1970s. More recently, an exploration program funded by the Jump River Joint Venture Resources), although Joint Venture (Chevron (ChevronUSA USA and andWisconsin Wisconsin Mineral Mineral Resources), although flown much earlier earlier by by the joint venture led to flown much the Getty-Lehmann Getty-Lehmann joint venture (CWJV), (CWJV), led to the the 49 �geophysical discovery of geophysical discovery of the the Bend Bend massive massive sulfide sulfide in in1986. 1986. In In 1990, 1990, Noranda Noranda announced its discovery Lynne deposit, discovery of of the thezinc—rich zinc-rich Lynne deposit, also also originally originally announced its delineated AEM. This delineated with withAEM. This paper paper will will discuss discuss the the sequence sequence of of geophysical geophysical events events that thatultimately ultimately led ledtotothe theBend Bendcopper—gold copper-gold discovery. discovery. DISCUSSION DISCUSSION The Forest in The Bend Bend deposit deposit is i s located located in in the theChequamegon Chequamegon National National Forest in Taylor Taylor County, 1 2 miles miles northwest northwest of of Medford. Medford. The airborne County, about about 12 airborneanomaly anomaly may may have at least have been been recognized recognized at least as as early earlyas as1974 1974when when National National Lead Lead Industries Industries conducted an AEM (INPUT)survey survey over over the the area. However, However, no no ground AEM (INPUT) conducted an follow-up was done, done, probably probably because because of of the the poor follow-up was poor quality quality of of the theanomaly. anomaly. At about the survey over the same same time, time, Kerr-McGee AEM survey over Kerr-McGee Corporation Corporation also flew flew an AEM the area area but, b u t , again, again,did didnot notperform performground groundgeophysics. geophysics. Later, in AMAX and in 1977, 1977,adjacent adjacent surveys surveyswere wereflown flownsimultaneously simultaneously by byAMAX AMAXobtained obtained CWJV. surveys detected CWJV. Both Both surveys detected the the Bend Bend massive massive sulfide. sulfide. AMAX prospecting permitsinin the the area area but, prospecting permits but, because because of of difficulties difficulties in in securing securing aa land land position, pursue exploration position, did did not not 'pursue exploration efforts efforts and and left left the the area area in in1978. 1978. The Getty—Lehmann jointventure venturedissolved dissolved in in 1983 when Getty ceased Getty-Lehmann joint 1983 when ceased mineral mineral Chevron Resources, Resources, which whichalso alsohad hadan aninterest interest in in the the exploration operations. operations. Chevron joint partner and joint venture, venture, became became the the major major partner and continued continued the the exploration exploration work work I t s ground ground geophysical geophysical program program began began through (JRJV). Its through a new new joint joint venture (JRJV). with andground groundmagnetics magneticssurveys surveys in in February, with HLEM HLEM and February, 1986, 1986. Five geophysicallines, lines, each each approximately approximately 5000 5000feet feet long, long, were were Five north—south north-south geophysical magnetics were were run run with positioned Ground magnetics with aa GeoGeoAEM anomaly. anomaly. Ground positioned over the the AiM No o metries at 50m e t r i c ~proton proton precession precession magnetometer magnetometer at 50- and and 100-foot 100-foot intervals. intervals. N residual could be be discerned discerned in in the residual anomaly anomaly could the vicinity vicinity of of the theAEM AEM response. response. MaxMin II HLEM HL.EM profilingwas wasalso alsoundertaken. undertaken. profiling MaxMin I1 A constant A constant600—foot 600-foot separation was was maintained maintainedbetween betweenthe the transmitter transmitter coil coil and and receiver separation receiver coil, coil, In-phase and and quadquadresulting in in aa penetration penetration depth depth of of about about 300-400 300-400 feet. feet. In-phase - rature components ofthe the vertical vertical secondary secondary field field were were recorded recorded for for three three rature components of The 444 444 Hertz Hertz data data are are shown shown in in profile profile frequencies atat100—foot intervals. The 100-foot intervals. A strong strong bedrock form in Figure 1. bedrock conductor conductor (up (up to to 93 93 mhos) mhos) was was defined defined form in 1. A The first first and 8W 8Wand andformed formedthe thebasis basis for for the the initial drilling. 4W and drilling. The on lines 4W on 50 -J �% PrIn..rp 10J .5J oJ 5J I0 SOUTH SOUTH FIGURE FIGURE11 2OOi. In— Phase In-Phase 0 200fl. ————. Out-of- Phase -.-. . HLEM HLEM Coil CoilSeparation Seporotlon • 600 600Feet Feet - --- NORTH NORTH LOO L4W L8W LI2W L 14W r— r- r r n r r— r— r— r BEND MAXMIN PROFILES PROFILES -444 444HZ HZ BEND MAXMIN r r r. r r ri r �two two holes, holes, drilled drilled in inOctober October1986, 1986,were werecollared collaredon onlines lines4W 4 W and and8W 8W and and intersected intersected aa thick thick massive-sulfide massive-sulfide conductor, conductor, now now known known as the the Bend Bend deposit. deposit. To copperTo date, date, 25 25 cored coredholes holes have havedelineated delineated 3.7 3.7 million million tons tons of of coppergold gold mineralization mineralization in two two zones. zones. Depending Depending on permit permit requirements, requirements, mining mining operations operations could could begin begin as as early early as a s1995. 1995. J j In In order order to toinvestigate investigatethe thepossibility possibilityofofthe theoccurrence occurrenceofofdeep deepmineralization mineralization along EM-37survey survey was was performed. Large— Largealong strike, strike,a large—loop a large-looptime—domain time-domain EM-37 loop systemsare are often often used used for exploring deep ore deposits. loop electromagnetic electromagnetic systems exploring deep deposits. At survey lines lines were were added, added, east east and and west of the At Bend, Bend, several several additional additional survey west of the original five-line with thethe EM—37 five-line grid, grid,and andsurveyed surveyed with EM-37 system. system. The The data data indicate both east east and indicate deep deep conductors conductors both and west west of of the the Bend Bend deposit, deposit, very very nearly nearly on strike strikewith with the theknown knownmineralization. mineralization. At At this this time time drilling drilling has has not not confirmed the results resultsofofthe the EM-37 survey. confirmed EM—37 survey. was detected detected by by aa single ItIt is is important important to to note note that thatthe theBend BendAEM AEM anomaly anomaly was single line spacing spacing used used during during the flight flight line line during during the the 1977 1977 survey. survey. The The nominal nominal line the high—amplitude survey was Considering that thatthe the high-amplitudeHLEM HLEM 114 mile mile (1320 (1320 feet). feet). Considering was 1/4 anomaly hasaashort short strike strike length length at at the feet), itit is anomaly has the subcrop subcrop (400+ (400+ feet), is fortunate fortunate If the the flight flight line line had had been been displaced displaced that the the deposit deposit was was detected detected at all. all. If slightly slightly to to the the east east or o rwest, west,the theresponse responsewould wouldhave havebeen been greatly greatlydiminishdiminishcomplicate ed, reducing reducing its its attractiveness attractiveness as asan anexploration exploration target. target. To complicate matters, conductors are are located locatedtoto the the north, north, northmatters, several several other other formational formational conductors northof these One of these was was drilled drilled shortly shortly after after the the initial initial east, and and southwest. southwest. One Several discovery of Bend and found to discovery of Bend and to be be conductive conductive graphitic graphitic argillite. argillite. Several holes, too responses along along strike strike with too shallow shallow to to test testthe theweak weakEM—37 EM-37 responses with the Bend conductor, were Bend conductor, were drilled drilled and and found found to to contain contain little little or or no no sulfide sulfide the geologic section containing containingthe the host host felsic felsic tuff tuff However, the geologic section mineralization. However, unit persists. Geophysical worki sis continuing continuingalong alongthe the Bend Bend volcanic volcanictrend trend in in aan n attempt attempt to to Geophysical work drilling southwest of Bend Bend has has shown that the locate locate sister sister orebodies. orebodies. Recent Recent drilling southwest of shown that the felsic tuff host host rock rock does feet at at least. felsic tuff does strike strike for for several several thousand thousand feet least. Ground Small geophysical worktotothe the northeast northeast suggests suggests similar similartrends trends in in that that area. geophysical work area. Small volcanogenic massive-sulfidedeposits depositssuch suchaas Bend usually usually occur occur in in clusters volcanogenic massive-sulfide s Bend clusters and undoubtedly result result in and continued continued exploration exploration will will undoubtedly in additional additional discoveries. discoveries. 52 j �CONCLUSION CONCLUSION Innorth-central north-central Wisconsin, Wisconsin, it is likely likely that that most massive-sulfide deposits will In it is most massive—sulfide deposits will be small, small, averaging averaging only only aa few fewmillion milliontons tons and will be geophysically expressbe and will be geophysically expressedas asshort—strike—length short-strike-length anomalies. anomalies. This may be a result of (1) primary ed This may be a result of (1) primary sulfide deposition, deposition, (2) ( 2 )structural structural complications. ( 3 ) conductive overburden, sulfide complications, (3) conductive overburden, ( 4 ) depth depth of ofburial, burial,and/or a n d l o r(5) ( 5flight—line ) flight-line orientation and location. There(4) orientation and location. ThereAEM surveys surveys should should be be flown flown with with 118-mile (660 feet) spacing. All fore.most most AEM fore, l/8-mile (660 feet) spacing. All single-line anomalies anomalies and subtle anomalies anomalies should should be be investigated with approsingle—line and subtle investigated with appro— priateground groundtechniques, techniques, ifi fpossible. possible. pilate El ,,-Over theyears yearsseveral severalAEM AEMexploration exploration programs were undertaken in o r Over the programs were undertaken in or For various reasons the Bend For various reasons the Bend AEM anomaly anomaly was not investigated. not recognized for i t s importance, not well AEM was not investigated, not recognized for its importance, not well defined or, o r , perhaps, perhaps, not not detected detected at at all. all. Whatever the reason, the discovery defined Whatever the reason, the discovery illustrates the need for persistence and thoroughness in in exploration, exploration, even if illustrates the need for persistence and thoroughness even if an area area has has been been looked looked at at before. before. Weak or poorly defined AEM anomalies or an Weak or poorly defined AEM anomalies or anomalies without direct magnetic magnetic support support should should always always be be considered considered for for anomalies without direct f u r t h e revaluation evaluation ififgeologic geologicconditions conditions warrant. warrant. further -^around the Bend Bend area area by bydifferent different companies. around the companies. 53 �GEOLOGY OF THE MERIDIAN AGGREGATES QUARRY AND AN0 THE SURROUNDING AREA, ST. ST CLOUD, MINNESOTA: MINNESOTA: A STUDY OF THE BEDROCK INFLUENCES ON THE PRE-LATE PRE-LATE CRETACEOUS WEATHERING CRETACEOUS WEATHERING PROFILE. PROFILE. John A. Hauck John J. Heine, Heine, Tom A. A. lath, Toth, and Steven A. Natural Natural Resources Resources Research Research Institute Institute of Minnesota-Duluth Duluth, MN 55811 Minnesota-Duluth Duluth, 55811 University George W. W. Shurr Shurr . . rtment of of Earth Department Earth Sciences Science St. Cloud State St. Cloud, Mn. State University University Mn. 56301 56301 The The Meridian Meridian Aggregates Aggregates Quarry Quarry in in St. St. Cloud, Cloud, Minnesota Minnesota contains contains aa complex complex group group of of metamorphic metamorphic and and igneous igneous rocks. rocks. Residual clays clays overlie overlie the the bedrock bedrock in in some some areas areas of of the the quarry. quarry. The The focus focus of of the the study study is is to t o relate relate the the composition composition and and physical physical characteristics characteristics of of the the parent rocks to the overlying residual clay 1:1200, in in clay deposits. deposits. The quarry has has been mapped at at aa scale scale of of 1:1200, order order to to give give sufficient sufficient control control of of the the geology geology and and structural structural characteristics. This information has been characteristics. information has been linked linked with with information information from from regional studies studies to t o better better understand understand the controls controls on clay distribution in in the the St. St. Cloud Cloud area. area. Because Because the the composition composition of of the the parent parent rock rock is is a critical factor factor in in the the composition composition of of the the clays clays that form during weathering, detailed mapping of of the rock Five major rock types rock types types in in the the quarry quarry was was critical. critical. Five major types have have been been mapped: 1) 1) aa dark metamorphic metamorphic rock rock type, type, 2) 2) gray gray reformatory reformatory granite, granite, 3) 3) St. St. Cloud Granite, 4) mafic mafic dikes, dikes, and and 5) 5) a porphyritic porphyritic rhyolite rhyolite dike. dike. The The Granite, 4) dominate rock rock type type in in the the quarry quarry is is the the dark dark gray gray metamorphic. metamorphic. All All of of the the rock i n the the western quarry wall wall where residual clays clays have have rock types types can can be be found found in developed developed on on them. them. The The most most important important physical physical characteristic characteristic related related to t o the the formation formation of of the the residual residual clays clays is is the the presence presence of of faults faults throughout throughout the the quarry. quarry. Many of of the the residual residual clay clay occurrences occurrences in in the the St. St. Cloud Cloud area area are are found found in in linear linear bedrock bedrock lows. lows. Work Work in in the the Meridian Meridian Aggregates Aggregates Quarry Quarry shows shows that that the the residual residual clays clays are are found found in in bedrock bedrock lows lows along along fault fault traces. traces. This This conclusion conclusion is is based based on bedrock bedrock and and drill drill hole hole information information from from the the quarry. quarry. In the quarry quarry area, area, glacial glacial deposits deposits rest rest directly directly on on bedrock bedrock or or the the residuum. residuum. Any Any overlying overlying residual other areas residual clays that may have developed developed in in other areas of the quarry, would would have been removed prior to or during glaciation, leaving pockets of of residuum residuum in bedrock bedrock lows. out1 ined lows. Three Three major major structural structural features features in in the the quarry were were outlined by mapping: 1) an an east-west east-west trending trending fault fault zone zone on on the the north north wall wall of the the mapping: 1) quarry; 2) a central, central, northeast northeast trending trending fault fault zone; zone; and 3) 3) a western, western, quarry; 2) northwest northwest trending trending fault fault zone. zone. The The deepest clay clay formation formation in in the the quarry quarry is is associated the the northwest northwest fault fault zone. zone. Drill Drill hole hole information, information, provided provided by by Meridian Aggregates Aggregates outlines the extension extension of this zone outside the the active active quarry quarry area. area. In addition, addition, the the drill drill hole hole information information locates locates the the deepest deepest clay clay development development near near where where the the northwest northwest fault fault zone zone an an the the east-west east-west fault fault zone zone are are thought thought to t o intersect. intersect. Other northwestern trending, residual residual clay clay filled filled bedrock bedrock lows, lows, have have been been identified identified to to the the northeast northeast and and southwest, southwest, which which correspond correspond with with linear linear features features visible visible on on high high altitude altitude photos. photos. 54 j J j j �The residual sidual clay clay deposits deposits ininthe theMeridian Meridian Aggregates Aggregates Quarry Quarry vary vary in in grade rade both both vertically vertically and and horizontally. horizontally. The residual residual clays clays vary vary from from The kaolinite-rich aolinite-rich to t o chiorite-illite-rich chlorite-illite-rich horizontally. horizontally. This This variation variation in in clay clay grade rade appears appears to to be be controlled controlled by by the the distribution distribution of o f the the bedrock bedrock composition. omposition. The The kaolinite-rich kaolinite-rich residual residual clays clays are are located located above above the the St. St. Cloud loud Granite Granite and and the theporphyritic porphyriticrhyolite rhyolitedike. dike. The The amount amount of of chlorite chlorite and and illite llite increases increases in in the the dark dark metamorphic metamorphic rocks rocks and and the the gray gray reformatory reformatory granite, ranite. and and is is dominate dominateininthe theresidual residual material material above abovethe themafic mafic dikes. dikes. The The depth epth of of weathering weathering also alsovaries varieshorizontally, horizontally, and and is is controlled controlled by by the the northwest orthwest trending trendingfault faultzone. zone. The The residual residual clays d a y s are are deepest deepest in in the the center center off the the fault fault zone, zone, and and thin thin to to the thenorth north and and south, south, away away form form the the fault fault zone. zone. The +hornblende he vertical vertical variation variationisisincrease increasequartz quartzfeldspar, feldspar,and andbiotite, biotite, ±hornblende with with depth depth in in residuum residuum above above the the granitic granitic and and metamorphic metamorphic rocks. rocks. The The increase increase in in these these minerals minerals is is consistent consistent with with decreasing decreasing chemical chemical weathering weathering effects effects with with depth. depth. 55 �Isoclinal IsoclinalSlump-folds Slump-foldsininthe theLower LowerPokegarna Pokegama Ouartzite: Quartzite: Evidence Evidence for for Seismicity Seismicilyand andSlope Slope Instability InstabilityDuring DuringDeposition Depositionof ofthe theAnimikie AnimikieGroup Group Hemming, Hemming. S.; S.; Hanson, Hanson,G.N.: G.N.; McLennan, McLennan.S.M.; S.M.; Sharp. Sharp,W.D., W.D., State StateUniversity Universityof ofNew NewYork Yorkat atStony Ston Brook, Brook. Stony Stony Brook, Brook, NY NY 11794 11794 The basement of of the the Superior The Early EarlyProterozoic ProterozoicPokegama PokegamaQuartzlte Quartziteoverlies overlies Archean basement Superior Province Provincein in the Minnesota. Its constrained by is constrained by geologic geologic the northwestern northwesternpart partof ofthe theAnimikie Animikie Basin, Basin, Minnesota. Its age age is relationships [I ,2,3] and and Pb Pbisotope isotopedata data on on detrital detrital and cross-cutting cross-cutting quartz quartz [4] [4] as asbetween between2.17 2.17 relationships[1,2,3] and 1.95 Ga. The depositional environment of the very fine grained, lower Pokegama and 1.95 Ga. The depositional environment of the very fine grained, lower PokegamaOuartzite Quartzitehas ha been on the the nature nature of of crossbedding crossbedding in in the the sandy sandy middle middle Pokegama Pokegama beeninterpreted Interpretedas as tidal tidal flat, flat. based on Quartzite to the the better better exposed exposed Palms Formation in Quartzite and and suggested suggestedcorrelation correlationand and similarity similarity to Palms Formation in Wisconsin Wisconsin[51. [5]. The Thesoft softsediment sedimentdeformation deformationwe we recognize recognizein in the the lower lower Pokegama, Pokegama. mostly mostly tight tight to t isociinal isoclinalfolds foldsand and refolded refoldedfolds, folds, may may provide provideimportant importantinformation informationconcerning concerningtectonic tectonicactivity activityinil the theAnimikie AnimikieBasin Basinduring duringthis thistime timeinterval. interval Abundant olds can can be be found found In inthe the only onlywell-exposed well-exposedoutcrop outcrop in in the the lower lower Abundant evidence evidence for for slump-f slump-folds north of of Eveleth, Eveieth, MN. MN. The Pokegama PokegamaQuartzite Quartzite(Figs. (Figs.1-6). 1-6). ItIt is is located located immediately immediately north The outcrop outcropis is approximately approximately500 500ftftlong longand and5-8 5-8ftft high. high. ItIt is is characterized characterized by by interbedded interbeddedsiltstones siltstonesand andargillites argillites with thick). Folding with numerous numerousthin, thin, fine fine sandstone sandstone layers layers (up to several inches thick). Foldingisisgenerally generallyvery very tight tight to toisoclinal, Isoclinal,and andrecumbent recumbent(Fig. (Fig.7), 7).and and these these characteristics characteristics are suggested suggested by by Farrel Farrel and Eaton Eaton [6] [6] to toindicate: indicate: 1) 1) long longdistant distanttransport transportof ofthe theslumps slumpsand and 2) 2) a a southeasterly southeasterlypaleoslope, paleoslope,consistent consistentwith withprevious previousinterpretations interpretationsof ofshoreline shorelineposition position15.7][5,7]. Figures from field field photographs, photographs, of of some someof ofthe thefold foldnoses. noses. These Figures1-6 1-6 are line drawings, from These folds folds addition to correspond correspondto totype type33refolded refoldedfolds, folds,defined definedby byRamsay Ramsay[8,6,9]. [8,6,9]. In In addition to the the numerous numerous isoclinal isoclinalfold fold noses, noses,shear shearsurfaces surfacesand and at at least least one one sheath fold indicate indicate substantial substantialhorizontal horizontal displacement displacement[6.10]. [6,10]. The The Pokegama PokegamaQuartzite, Quartzite,as aswell well as as the the Biwabik BIwabik and and Gunflint Gunflint Iron-formations, Iron-formations,are arehere hereinterpreted interpreted to tohave havebeen beendeposited depositedin inaa tectonically tectonicallyactive active basin. basin. This Thisinterpretation interpretationisisbased basedon: on: 1) evidence for for soft-sediment deformation in in the the lower lower Pokegama Pokegama Quartzite Quartzite (this (this study); study): 1) evidence soft-sediment deformation 2) deformation, observed observed in the Biwabik Iron-formation: 2) evidence evidence for soft-sediment deformation, in the Wwabik iron-formation; 3) 3) presence presenceof of early early brecciation brecciatton[11] [ l l ] and andisoclinal isoclinalfolds foldsin inthe the Gunflint Gunflint Iron-formation Iron-formationin inOntario: Ontario; 4) great just below below the the contact contact with with the the Biwabik, in the easterr eastern great variation variation in in facies of the Pokegama just Mesabi comm., 1990): Mesabi district district (Ron (Ron Graver, Graver, per. comm.. 1990); and and 5) and Wwabik Biwabik Iron-formation Iron-formation across a of the the Pokegama Quartzite and 5) sudden sudden change change in in thickness thickness of presumed presumedfault fault in inthe theeastern easternMesabi Mesabidistrict district[12). [12]. Strike-slip Strike-slip faulting faulting in in the the region region north northof of the the Animikie Animikie Basin Basin at about 1.95 1.95 Ga has been been documented documents by of pseudotachylite pseudotachylitein inthe the Rainy RainyLake-Sein Lake-SeinRiver River fault fau by Peterman Petermanand and Day Day [13] [I31using usingRb-Sr Rb-Sr dating dating of system. They associated with with one of the Early Theyinterpret interpretthe thefaulting faultingto tobe be aa result result of stresses associated Early Proterozoic, the Penokean. Penokean,as asdescribed described by by Hoffman Hoffman [14]. [14]. The Proterozoic, circum-Superior circum-Superiororogens, orwens. including including the The shales and turbidites turbidites of the Virginia and Thompson Formations, which form the upper part of the of Thompson Formations, which form the Animikie deposited in foreland basin associated associated with the Animlkie Group, Group, are are interpreted Interpretedto l o have have been been deposited In a foreland Penokean Orogen [1]. Penokean Oroaen 111. Understanding Understandinathe thetectonic tectonicsetting seninaof of the the Animikie Animikie Basin Basin prior prior to to turbidite turbidite deposition depositionclearly clearlyhas has important importantimplications implicationsfor for understanding understandingthe the Early Early Proterozoic Proterozoichistory historyin inthe the Great Lakes Region. The location of the Animikie Basin across the Great Lakes tectonic zone 1151, Great Lakes Region. The location of the Animikie Basin across the Great Lakes tectonic zone 1151, and between the the Superior Superior Province Province and and the the and the location location of of Penokean Penokeanmagmatism magmatism generally between - - 56 .. - J - .J j �MinnesotaRiver River Valley Province Province makes makes the sedimentary rocks rocks within withinthe the Aninilkle AnImIMebasin bask)important Important Minnesota the sedimentary for ofofthe forevaluating evaluatingthe thenature natureand andlocation location thepre-Penolce,an pra-Penokeancontinental continentalmargin. margin. An Anoblique oblique extenstonalsetting, setting,either eitherdrtven drivenby byor orassociated associatedwith, wfth,strike strikesup slipfaulting faultingIsIssuggested suggestedas as aa woiidng working extensional model modelfor forearly eaW Animikie Anhlkle Group Group deposition. deposition. Such Suchaasetting settingcould couldbe beassociated associatedwfth withthe thepassive passive margin ofaaback backarc arcbasin basin(such (suchas asseen seenbetween betweenJapan Japanand andChina, China,and and consistent consistentwith withthe the marginside sideof Interpretationof of Van Van Schmus Schmus [161 (161 and The time time Interval Interval for fortectonic tectonicactMty activity interpretation and Southwick Southwlck et ata/. at (11). [1)). The during duringdeposition depositionofdthe thePokegama PokegamaOuartzite Quartzitemay maybe beconstrained constrainedbetween between2.17 2.17 and and1.95 1.35 Ga. Ga. The The 1.95 Pb-Pb age Is is from from quartz gash gash veins veins in Inthe the upper upper Pokagama Pokegama Quartzite. Quartzite. Additional Additional age Ga Pb-Pb age 1.95 Ga constraintsfor for pseudotach,lltes pseudotachylitesand andquartz quartzveins veinsin Inthe thebasement basement and and sedimentary sedimentary rocks rocks of of the the constraints region, region. in Inconjunction conjunctionwith withan anunderstanding understandingof of their their kinematic kinematic significance, significance, may may lead lead ltoo important Important further onthe theearly earlyevolution evolutionofofthe theAnimikie AnimikleBasin. Basin ' furtherconstraints constraintson References: MN Geol. 37; [2) References: (1) (11Southwlck, Southwick, D.L D Letat, eta/..1988. 1988, MN Geol.Sur., Sur.,Report Re&; ofofInvestigations lnve Southwlck, Day. Southwick.0.L, D.L.and and Day,W.C.. W.C.. 1983, 1983.Can. Can.Jour. Jour.Earth EarthSci..v.20.p.622; Scl.,v.20,p.622; (31 [3] Hanson, G.N., and Malhotra, Geot. Soc. Soc. America Bull.. Bull., v.82.p.1107v.82.p.1107: 141 [4) Hemming Hemming et R., 1971, 1971. Ged. et al, at.,1990, 1990.EOS, EOS. Malhotra. R., v.71 .p.654;151 (51Ojakangas, Ojakangas.R.W..1983. R.W..1983. Geol. Geol. Soc. Soc. America America Mom. Mem. 160. 160. p.49; p.49; [6] (61Farrel, Farrel,S.G., S.G., and and v71p.654; Eaton, [7) Morey, Eaton.5,1987, S..1987.Geoi. Ged.Soc. Soc.Spec. Spec.Pub, Pub.no no29; 28; [71 Morey,G.B.,1972, GA.1972,MN MNGeol. Geol.Sur. Sur.Centennial CentennialVol; Vol: [SI Folding and 181Ramsay, Ramsay. J.G.,1967, J.G..1967. Folding and Fracturing Fracturingof of Rocks. Rocks. McGraw-Hill, McGraw-Hill.New NewYork; York;[9) (91Rarnsay, Ramsay,J.G., J.G.. and andHuber, Huber,M.i., M.I.. 1987, 1987.The The Techniques Techniques of of Modem ModemStructural StructuralGeology, Geology.v.2, v.2.Folds Foldsand andFractures. Fractures, Academic J.R.L, 1982, AcademicPress; Press;110) [lo) Allen, Alien. J.R.L. 1982. Sedimentary Sedimentary Structures, Structures. Their Their Character Characterand andPhysical Physical Basis, Franklin, J.M. Basis, 0ev. Dev. in in Sod Sed. 306, 306. Elsevier; Elsevier; till (11) Franklin, J.M.eta!, era/,1972, 1972.IGC IGCField FieldExcursion Excursion034; C34;[12) [I21 Gundersen, and Gundersen.J.N., J.N.. and andSchwartz, Schwartz,G.M.,1952, G.M.,1%2. MN MNGod. Geol.Sur. Sur.Bull. Bull.43; 43;(Peterman, [Peterman.Z.E. Z.E. andDay, Day,W, W., 1989. Geology. Geology. v.17,p.1089; v.17.p.1089; [14) (14)Hoffman, Hoffman.P.F., P.F.. 1988, 1888.Ann. Ann. Rev. Rev.Earth Earthand andPlan. Plan.Sd, Scl.v.16,p. v.16.p.543; 543; [15) Sims, Van ims.P,K P.Ketetai.. al..1980, 1980,Geol. Ged.Soc. Soc.America AmericaBull., Bull..v.91,p.690; v.91.p.690; [16) [I61 VanSchrnus, Schmus,1976, 1976.Phd. PM. Trans. .R. R.Soc. Soc.Lond..v280,p.605. Lond..v280.p.605. - —E:c — 'a. C - - - -a a Fig. of converging converging fold Fig.11Relatively Relatively large large area of fold features. features. HeartHeartshaped asas shapedsand sandbody bodyand andelongate elongaterefolded refoldedfold foldare areInterpreted Interpreted type type33refolded refoldedfolds foldsofofRamsey Ramsay[81. (81. Note Notethe thefanning fanningcleavage cleavageinin the theargiilfte, argillite. between betweenthe the refolded refolded folds. folds. Hammer Hammerfor forscale. scale. 57 �Fig. 3 Fold Fold nose nose with with several sandy sandy layers layers that that are are thickened thickened in Fi9.3 pair of of fold fold noses. noses. Hinge one (labeled) clearly visible visible on on Fig. 2 AA pair the and thinned thinnedto toboudinaged boudinagedon onthe thelimbs. limbs. The The box box possible to tell if the nose on the right the nose noseto to the theleft. left. It is not possible right the hinge and the approximate location location of Fig. left of drawing. Non..... Fig. 4. N< drawn on this figure is the is refolded. Note Notescale scale bar bar at lower left scale bar at lower left of drawing. — Fig. 44 Detail Detail of of Fig. Fig.3.3. Note thinning to separation limbs separation of the limbs and thickening thickening in the hinge of the sandier layer. in — J - ——a— C— — ----t=_ -. — — --—s— —,-— — — = —4 a -2CM - Recumbentisoclinal isoclinalfold. fold. Lower limb is thinned thinned and Fig. 66 Recumbent quite disrupted. disrupted. Note bedding is quite Notescale scale bar bar at lower lower left left of drawing. drawing. 58 j Fig. 55 An An early earlytight tight fold fold refolded refolded by by a a later later tight tight recumbant recumbant ffold. Fig. Note scale scale bar bar at at lower lowerof ofdrawing. drawing: Note Fig. Stereoplot of of fold fold hinges in in the the Lower LowerPokqama. Pokegama. The ~ i g7, Stereoplot plane representing the approximate attitude of bedding at th6 the @ane the approximate attiiude of bedding outcrop is also plotted (1]. outcrop is plotted [I]. �Magmatic Evolution in in the Magmatic Evolution the Midcontinent Midcontinent Rift: Rift: Evidence Evidence from from Hypabyssal Rocks Rocks of of the the North North Shore Shore of of Lake superior Lake Superior Hypabyssal Eric A. Jerde Jerde Department Angeles, CA 90024 Earth arid and Space Sciences, Sciences, University of California, Los Angeles, 90024 Department of Earth The hypabyssal dikes dikes and sills sills of northeastern northeastern Minnesota associated with the 1.1 1.1 Ga Midcontinent Rift are aa suite suite of rocks rocks distinct distinct from from the the flows flows of the the North North Shore ShoreVolcanic Volcanic Midcontinent Rift are provide valuable are far far less less significant significant volumetrically, volurnetrically, they provide valuable Group, and although although the the dikes dikes are information about processes operating operating during during rifting. In general, general, the diabase diabase is is ophitic, ophitic, with with pyroxenes pyroxenes 1-3 1-3 cm cm across across containing containing varying varying plagioclase and olivine chadacrysts. Exsolution are amounts of enclosed plagioclase Exsolution features featuresin in pyroxene pyroxene are common, but do not dominate the grain population. In In aa few samples, samples, coarse coarse symplectites symplectites are are present, with blebby oxides within the pyroxene. Some Someof of these these symplectites symplectitesdisplay display exsolution lamellac Thisisisevidence evidencethat that the the oxides oxides and and pyroxene pyroxeneformed formed lamellae in the pyroxene. This comagmatically, and not not simply simply as an alteration of a pre-existing phase phase such as olivine comagrnatically, and olivine since since exsolution features are unlikely to form in alteration products. exsolution features are unlikely to form in alteration products. Plagioclase as laths laths and and fragments fragments formed during rapid cooling, cooling, Plagioclase is is present mainly mainly as although a small number of phenocrysts phenociysts are usually seen. These are not large These are not large (usually (usually <2 mm), and many display display prominent pits pits and and dusty regions, interpreted as resorption features resulting resulting from from rapid decompression. decompression. Such Suchan anorigin originhas hasbeen been suggested suggestedfor forsimilar similarfeatures featuresin in plagioclase the Rio Rio Grande Granderift rift (Lipman, (Lipman,1969), 1969),and and the the southern southernRocky RockyMountains Mountains plagioclase from from the (Doe et al., aL, 1969). Plagioclase compositions compositions range rangefrom fromlaths lathsand andchill chillfragments fragmentsofofAns<,.;, An5n, to phenocryst cores coresup upto toAnon. An. The Thephenoczysts phenocrystsoften oftenhave have rims rimsof of the the "chill" composition, and a few are are complexly complexly zoned. zoned. Olivine up to to 33mm, rnm,and andoccasional occasional Olivine occurrs occwrs as as fine fine disseminated disseminated grains, grains, glomerociysts glomerocrystsup up to to 1 1cm. cm. It is generally generally unzoned, unzoned,with withcompositions compositionsmainly mainlybetween betweenFom Fo and " oikocrysts up Fop. Oxides PoTT). Oxidesmake makeup upaafew fewpercent percentof ofall allsamples, samples, most most being <1 mm across. Both Both ilmenite ilmenite and spinel phases are present, and most grains display some oxyexsolution features. thermometiy (Table 1) performed performed on on plagioclase plagioclase and and pyroxene pyroxene gave gave crystallization Mineral thermometry of 1000 1000-- 1150°C. 1150°COxides Oxidesyielded yieldedtemperatures temperaturesbetween between 850°C 850eCand 1000°C, 1000°C temperatures of and oxygen fugacities QEM buffer, buffer, which are consistent fugacities approximately one one log unit below the QFM with results from the Portage Lake klcanics Volcanics (Paces, (Paces, 1988). Oxide Oxide phases phases re-equilibrate re-equilibrate rapidly with aa cooling cooling liquid, liquid, and thus the temperatures obtained for the oxides are probably best interpreted as as near-solidus temperatures. The Theoxygen oxygenfugacities fugacitiesindicated indicatedare areconsistent consistent (1990) for the evolution of the Sonju Lake intnision, intrusion, also with the modelling by Miller et al. (1990) which QFM. which produced produced the the best best results resultswhen when using using oxygen oxygenfugacities fugacitiesone onelog logunit unitbelow belowQEM. The The chilled chilled margins were were analyzed analyzed by INAA INAA and microprobe microprobe fused bead techniques techniques for chemistry. Modelling bulk chemistry. Modellingof offractionation fractionationwas was done done using the CHAOS program (a more 59 �gdms core qthna core gene core C) Cl a 2 + 4 3 + 4 5 + . + 6 7 . 0 + 8 13 9 10 11 I3RD fract. (I atm) 12 Silver Ray intrusions 47th Avenue Sill Lester River Sill BRD C LL L. L... —15.0 860 plagiociase —13.0 961 I Cl Là C Là S 2 • -o 6 7 8 9 l0 II 12 0 000 I' 0° oa° 0 a C 0 4 5 6 sj a • 8 MgO (%) 7 9 10 1,111 L1 0 .0 0 Iii 1! 12 BRD.5..2-.5 BRD.5-o..5 I3RD 0-0-0 Thisstudy Otlierdikes 13 - - 3 4 5 6 8 tVlgO (%) 7 9 10 II 12 Dingnim showing I-aim models and hypabyssal rocks. ('Other dikes" from Green et al., 1987) 3 0 00 'I' 1,1,1,1 0 • L_ [ hypahyssal rocks. L L L_ Fig. 3. Diagram showing possible frnciionnlion pnlhs for nil 1. 0 __ Fig. S 6 MgO (%) Eli Cl a 1150 ± 50 Fig. 2. Dingtnm showing hypabyssal material matching I-atm model. (Silver Ray intnisions from Shank. 1990; 1. Miller, pers. Comm.; 47th Avenue SiU from K. Seifert, pert Comm. 5 6 7 S 9 10 11 12 —14.8 10 —12.3 9 11 1o2 12 7 853 990 1- Oxide 1000 (1150 9 5kb) 1050 ± 50 1100 ± 50 "gdm&' — groundmaea 1138 1126 1066 1192 1245 1236 1064 1015 1009 1065 a3oTtJ 1194 1156 1211 1192 dfl Pyrox.n. geoth.riaom.ter results. Piagiociaee Mineral Temperatures in °C. P—S CL—i HP—i BR—i P.R—i SB—i tsijtj& Tale i. LJ L LL. r 0 __ L �recent version of TRACEFOR TRACE.FOR described described by Nielsen, 1988a,b). 1988a,b). One Oneatmosphere atmospheremodelling modelling (Fig. 1) 1) shows shows that the the majority majority of of the thehypabyssal hypabyssalrocks rocksformed formedatatmoderate moderatepressures pressureswhere where the onset of pyroxene crystallization pyroxene stability stability at atdepth. depth. This crystallization is earlier due to greater pyroxene earlier earlier ciysta]iization crystallization results results in in the the earlier earlier depletion depletion of Ca, Ca, leading to the offset of the data from the model trend. trend. A Anumber numberof ofhypabyssal hypabyssalrocks rocksshow showevidence evidenceof fractionation fractionation at near surface surface levels levels (Fig. 2), 2), falling falling on on the the model model trend. trend. It is possible through polybaric fractionation It is possible through polybaric fractionationto torelate relateall allof of the the varied varied hypabyssal hypabyssal rocks rocksto to aa single primary parent, the high-Al "primitive olivine tholeiites," which are a common single primary parent, the high-A1 "primitive divine tholeiites," which are a common composition compositionamong among the the volcanic volcanic rocks rocks associated associated with with the Midcontinent Rift. In In such suchaa scenario, sw&ho, aa primitive primitiveolivine olivinetholeiite tholeiitemagma magmacrystallizes crystallizesol+plag+pyx ol+plag+pyxatatdepth depth(—10 (-10 kb?), kb?), driving the composition to lower Ca and Mg (BRD in Fig. 3). Continued fractionation driving composition to lower (BRD Continued fractionation at depth depth could could lead lead to to compositions compositionssimilar similarto tothe theSonju byMiller Milleretetal. al. SonjuLake Lakeparent parentproposed proposedby (1990). (1990). IfIfaathe themagma magmaofofBRD BRDcomposition compositionisisinjected injectedtotoananintermediate intermediatedepth depth(—3-5 (-3-5 kb?), kb?), the the crystallizing crystallizing assemblage assemblagewould would lose lose pyroxene pyroxenedue due to to shrinkage shrinkage of the pyroxene stability field, field, and and the the ol+plag ol+plagcrystallization crystallizationwould wouldcarry canythe theliquids liquidsto tolower lowerMg Mg(point (pointBBin inFig. Fig.3), 3), where againcrystallize, crystallize,and andthe the liquid liquid compositions compositions then then migrate migrate down down in in where pyroxene pyroxene would would again Ca, along the trend trend seen seen by by many many of the the hypabyssal hypabyssal rocks rocks (toward (toward C in Fig. 3). IfIfsome some liquids surface regions, regions, pyroxene pyroxene liquids of BRD BRD composition compositionwere were actually actually injected injectedto to near near surface crystallization crystallization could could be be delayed delayedeven evenfurther, further,and andthe theliquids liquidswould would follow followthe thetrend trend shown shownin in the modelling for 1-atm 1-atm pressure (toward D in Fig. 3). Sills Sills such such as as the Lester River and 47th 47th Avenue are in this group, as are the Silver Silver Bay intrusions. In Inreality, reality, there there can can of of course coursebe be many cross cross trends, but the the overall overall picture picture of multi-level multi-level fractionation fractionation is apparent. The The resorption resorption features featuresseen seenin in the the plagioclase; plagioclase;evidence evidencefor forevolution evolutionat at various variouslevels levelsin in the crust, are consistent process. The Thechemical chemical consistent with the chemistry, which suggests the same process. similarity alsoevidence evidencefor for lateral communication among among similarity among among samples samplesof of the the entire entiresuite suiteisis also chambers chambers for for great great distances distances along along the the rift. rift. These Thesetwo twoprocesses processeshave havebeen beeninferred inferredfor forthe the Mid-Atlantic rift in Iceland, which indicates that some modem rift processes were occurring Mid-Atlantic in Iceland, which indicates that some modem rift processes were occurringatat 1.1 Ga. Ga. References: References: Doe, Doe, B.R., Lipman, Lipman, P.W., P.W., Hedge, Hedge, C.E., C.E., and and Kurasawa, Kurasawa,II. H.(1969). (1969).Contributions Contributionsto to Mineralogy and Petrology, 2 1, 142-156. 142-156. Green, J.C., J.C., Bornhorst, Bornhorst, Ti., T.J., Chandler, Chandler,V.W., V.W., Mudrey, Mudrey, M.G.J., M.G.J., Meyers, Meyers, P.E., P.E., Pesonen, Pesonen, L.J. and Wilband, J.T. (1987) In: Mafic dyke swarms (Halls, R.B. and and Wilband, J.T. (1987) In: Mafic dyke swarms (Halls, R.B. andFahrig, Fahrig,W.F., W.F., ed.), 289-302. cd.).Geological GeologicalAssociation Associationof of Canada CanadaSpecial SpecialPaper Paper34, 34,289-302. Lipman, America Bulletin,80, 80, 1343-1354. Lipman, P.W. P.W.(1969). (1969). Geological GeologicalSociety Society of ofArnericaBulletin, 1343-1354. Miller, J.D., Jr., Schaap, B.D. and Chandler, V.W. (1990). 36th Miller, J.D., Jr., Schaap, B.D. and Chandler, V.W. (1990). 36thAnnual AnnualInstitute Instituteon onLake Lake Superior Geology, 66-68. Superior 66-68. Nielsen, R.L. (l988a) Acta, 552, (1988a)Geochimica GeochimicaaetCosmochimica CosmochimicaAda, 2, 27-38. Nielsen, R.L. (1988b) Computers and Geosciences, 14, 15-35. (1988b) Computers Geosciences, 1 4, 15-35. Paces, University, Houghton, Houghton, 413p. 4l3p. Paces, J.B. (1988) (1988) Ph.D. Ph.D. dissertation, dissertation,Michigan MichiganTechnological Technological University, Shank, S.G. (1990) M.S. thesis, University of Minnesota, Minneapolis, l3Op. thesis. University Minnesota, Minneapolis, 130p. 61 �SURFACE EXPRESSION EXPRESSION OF SURFACE OF MAJOR MAJOR BEDROCK BEDROCK STRUCTURAL FEATURES FEATURES JamesS.S. Johnson, Johnson,Denise DeniseA.A. Slavish, Stavish, Mary James Mary K. K. Tozer, Tozer, and and George George W. W. Shurr Shurr Departmentofof Earth Earth Sciences, Sciences, St. St. Cloud State University, University, St. Department Cloud State St.Cloud, Cloud,MN MN 56301 56301 Continental lithosphere lithosphere in in Minnesota subdividedinto intoaaseries seriesoof strucContinental Minnesota isissubdivided f structural blocks plate tural blocksbounded bounded by by fault faultzones zonesthat thatare arecomponents components of o f Precambrian Precambrian plate margins. Major Major fault fault zones basement zones in in the thecrystalline crystalline basement have have expression expression in in landfonns For example, example, in in western landforms and and surface surface sediments. sediments. For western Minnesota, Minnesota, the the Great Great Lakes TectonicZone Zoneisislocated locatedatat the the southern southernlimit limit of Lakes Tectonic of the theLake Lake Agassiz Agassiz plain; plain; and in in southwestern Minnesota, faults faults bounding the Fulda Pipestone structural structural and southwestern Minnesota, bounding the Fulda and and Pipestone basins (Southwick (Southwick and and Mossler, Mossier, 1984) 1984) correspond correspond with the theend end moraine moraine complex complex on on basins Equivalence of of basement structure the southwestern southwestern margin margin of of the theDes Des Moines Moines lobe. lobe. Equivalence basement structure and surface surface features featureswill will be in three Agassiz beach beach and be described described in three other other areas: areas: 1) Agassiz area in Minnesota, 2) 2) Swanville Swanville spillway spillway area area in in central centralMinnesota, Minnesota, area in northwestern northwestern Minnesota, and 3) north north of and 3) of Lake Lake Mille Mille Lacs. Lacs. complexatat the the margins margins ooff the In northwestern northwestern Minnesota, Minnesota, the beach beach complex the Lake Lake Northwest— Agassiz plain forms to the Agassiz plain forms aa broad broad arc arc opening opening to the south south and and east. east. NorthwestArchean trending faults faultsininthethe Archeanbasement basement generally generally converge converge toward toward the curve curve of of the arc parallel the Near Greenbush, MN, Greenbush, MN, the arc and and parallel the sides sides of of the thearc arc ofofbeach beach ridges. ridges. Near sharp variations variations in in the sharp the elevation elevation of ofthe thebeach-ridge beach-ridge crest, crest, mark mark the the position position of gradients associated with the the Vermillion In of large largeareomagnetic areomagnetic gradients associated with Vermillion Fault FaultZone. Zone. In central hasaa broad broadarc arc to to the central Minnesota, Minnesota, the the St. St. Croix Croixend endmoraine moraine complex complex has the west between the Serpent Serpent Lake Lakeand andMalmo Malmo structural discontinuities discontinuities mapped west between the structural mapped by by and McSwiggen (1988). On Onthe theinside inside of of the the arc Southwick, Morey, Morey,and McSwiggen (1988). arc of of the the end end moraine, several several eskers eskerstrend trend perpendicular perpendicularto to and andterminate terminateatat the the position position moraine, of the discontinuity. North North of of Lake Mille Lacs of the Malmo Malmo discontinuity. Lake Mille Lacs patterns patterns of o f lowland lowland peat peat and uplandtill till are geometry and upland are similar similartotothe the geometry of ofProterozoic Proterozoic thrust thrustduplexes. duplexes. Eskersin in this this vicinity generally located along steep Eskers vicinityare are generally located alongareas areasofof steepareomagnetic areomagnetic gradient and and trend trend parallel parallel to gradient to the thecontours. contours. Correspondenceo fofmajor majorstructural structural features Precambrian Correspondence featuresininthethe Precambrianbasement basement with geomorphic features and and surface surface sediments sedimentshelps helpsto to explain explain why linear geomorphic features why linear features on Landsat Landsat images images appear appear to to mark basementstructures. structures. Beach features mapped mapped on mark basement ridges, morainic and some someeskers eskers visible as linear morainic margins, margins, and areare allallvisible as Landsat Landsat linear features; eskers trending perpendicular perpendiculartotostructural structural features features are are not not easily easily eskers trending mapped obviouslinear linear features. features. Paleotectonic and mapped asasobvious and recent recentearth earthmovements movements along along the lithosphere 1 ithosphere block block boundaries boundaries influenced influenced patterns of o ferosion erosionand and deposition. As As aa consequence, consequence,patterns patternsofoferosion erosionand anddeposition deposition visible visible as as linear features imagesshow show fidelitywith with structures structures in in the linear features on on Landsat Landsat images fidelity the PrePrecambrian cambri an basement. basement. REFERENCES REFERENCES CITED CITED Southwick, D.L., D.L., and Mossler, J.H., Southwick, and Mossier, J.H., 1984, 1984, The The Sioux Sioux Quartzite and and subjacent subjacent regolith ininthe Basin, Minnesota, Minnesota, in in Southwick, D.L., regolith theCottonwood Cottonwood County County Basin, Southwick, D.L., ed., Shorter contributions to the geology of the Sioux Quartzite (Early ed., Shorter contributions to the geology of the Sioux Quartzite (Early Minnesota Geological Geological Survey Proterozoic), Southwestern Southwestern Minnesota: Minnesota: Minnesota Survey Report Report of Investigations Investigations 32, 32, p. p. 17—44. 17-44. Southwick, D.L., D.L., Morey, P.L., 1988, mapof of the Southwick, Morey, G.B., G.B., and and McSwiggen, McSwiggen, P.L., 1988, Geologic Geologic map Penokean Orogen, central and eastern Minnesota, and accompanying text: Penokean Orogen, central and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of Investigations 37, 25 p. Minnesota Geological Survey Report of Investigations 25 p. 62 J I �MASSIVE SULFIDE DEPOSIT, ONEIDA ONEIDA COUNTY, COUNTY, WISCONSIN WISCONSIN THE LYNNE MASSIVE SULFIDE DEPOSIT, Lawrence P. Lawrence P. Kennedy, Kennedy, Teresa Teresa A. A. Harding, Harding, John John N. N. Schaff, Schaff, & Anne N. M. Zielinski, Zielinski, Noranda Noranda Exploration, Ex~loration.Inc., Inc.. Rhinelander, Wisconsin The Lynne Lynne deposit ic-hosted, ZnThe deposit is is aa volcanicvolcanic-to tovolcanicl•ast volcaniclastic-hosted, Zn- Pb-Cu—Ag orebody located Proterozoic magmatic magmatic terrane terrane Pb-Cu-Ag orebody located in in the the early Proterozoic of northern Wisconsin. based on on the .of northern Wisconsin. A preliminary preliminary ore reserve, based first 39 holes in in an an open-pit open-pit mine design, is calculated at at 6.1 6.1 *Â¥firs million illion tons tons grading grading 7.14% 7.14% Zn, Zn, 0.34% 0.34% Cu, Cu, 1.89% 1.89% Pb, Pb, 3.09 opt opt Ag, Ag, and and hosted by by a gently-dipping 0.013 .013 opt opt Au. Au. The mineralization is hosted gently-dipping sequence of fragmental rhyolites, chiefly lapilli crystal tuffs, tuffs, sequence of fragmental rhyolites, chiefly lapilli to crystal and less abundant dacite to andesite flows, volcaniclastic and less abundant dacite to andesite flows, sandstones and relationships in the rhyolitic sandstones and siltstones. siltstones. Facies relationships rhyolitic pyroclastic rocks to the north (down-dip) yroclastic rocks to the north (down-dip) suggests proximity to aa volcanic constructional feature. tonalite intrudes and olcanic constructional feature. A footwall tonalite partly encloses encloses the lowermost part of the deposit, number of the lowermost part of deposit, and a number of subvertical, east— to southeast-trending faults disrupt subvertical, eastsoutheast-trending disrupt the downdip extension extension of mineralization. Many of of these these faults faults are are occupied occupied dip of mineralization. by feldspar-phyric, rhyolitic to basaltic dikes. b y feldspar-phyric, rhyolitic to basaltic dikes. The bulk of of the the Zn-Pb-Cu-Ag Zn-Pb-Cu-Ag mineralization mineralization occurs within aa sequence of chemical sedimentary rocks which thicken and coalesce coalesce ence chemical sedimentary in the central central part of the deposit. Lenses, lobes and stratiform of the deposit. stratiform bodies odies of massive to to semi-massive semi-massive sulfide sulfide are interbedded interbedded with laminated to disrupted carbonate conformable talc units, chert, onformable units, chert, laminated to carbonate rocks, and narrow narrow beds beds of of volcaniclastic volcaniclastic and and sedimentary sedimentary rocks. rocks. talcose rocks underlie of laminated, underlie and partly enclose lenses of laminated, The talcoserocks pyrrhotite—rich chert sphalerite-rich massive masEive sulfide, sulfide, and and also also pyrrhotite-rich chert and sphalerite-rich The talcose talcose host disseminated disseminated sphalerite, host sphalerite, pyrrhotite, pyrrhotite, and and galena. galena. The unit is overlain by thick beds beds of massive sulfide and lenticular lenticular masses of of carbonate and chert masses chert containing containing disseminated to bedded bedded aggregate thickness the sulfide-rich sulfide-rich sedimentary sedimentary sulfides. The aggregate sulfides. thickness of the rocks exceeds 325 feet the center center of the deposit; deposit; its its lenticular feet in in the lenticular rocks exceeds have formed formed as as a a nature and symmetry suggests suggests that that it it may have nature and symmetry with an undetermined hydrothermal mound, mound, with undetermined amount amount of replacement replacement mineralization. mineralization. Sphalerite is mineral, followed Sphalerite is the the most abundant abundant sulfide sulfide mineral, followed in in abundance pyrite, and chalcopyrite. chalcopyrite. galena, pyrite, abundance by pyrrhotite, pyrrhotite, galena, native silver, silver, Tetrahedrite (var. freibergite) polybasite, native freibergite) or or polybasite, Tetrahedrite (var. pyrargyrite, electrum, and native also economically economically are also pyrargyrite, electrum, native gold are important minerals. minerals. The sulfide sulfide distribution distribution and metal metal zonation zonation is important is similar to the zoning similar zoning documented documented in in other other volcanogenic volcanogenic massive sulfide deposits. deposits. Chalcopyrite Chalcopyrite and pyrrhotite pyrrhotite are are most most abundant abundant in sulfide talcose unit, whereas silver silver minerals and galena are the lowermost talcose unit, whereas are concentrated concentrated in in diopside-rich diopside-rich cherts cherts and and cherty beds in in the the upper upper Calc-silicate minerals, minerals, including part of of the the deposit. deposit. Calc-silicate including diopside, diopside, ferrosalite, garnet, garnet, tremolite, widespread; most ferrosalite, tremolite, and epidote, epidote, are widespread; of these minerals formed as a result of decarbonation reactions reactions during the emplacement emplacement of footwall tonalite, perhaps during tonalite, or perhaps during of the footwall the late stages stages of of hydrothermal hydrothermal activity. activity. 63 �- j THICK-SKINNED BACKTHRUSTING IN THE BACKTHRUSTING IN FELCH-CALUMET FELCH-CALUMET TROUGHS TROUGHSREGION, REGION,NORTHERN NORTHERNMICHIGAN-MICHIGAN-A A COMPARISON COMPARISON WITH WITH THE T H ESOUTHERN SOUTHERNALPS ALPS J JOHN S. S. KLASNER, KLASNER, Department Department of ofGeology, Geology, Western Western Illinois Illinois University, University, and and U.S. U.S. Geological 61455and andP. P.K. K. SIMS, SIMS, U.S. U.S. Geological Geological Survey, Survey, MS MS 905, 90q GeologicalSurvey, Survey, Macomb, Macomb,Illinois Illinois61455 Box Federal Center, Box 25046, Federal Center,Denver, Denver,Colorado Colorado80225-0046 80225-0046 j The The Felch Felch and and Calumet Calumet troughs troughs region region is is on on the the south south edge edge of of the the Superior Superior craton. craton. Rocks 1850 Rocks of of the the Wisconsin Wisconsin magmatic magmatic terranes terraneswere were accreted accreted to tothe thecraton cratonapproximately approximately1850 Ma deformation and and metamorphism metamorphism Ma along along the the north-verging north-verging Niagara Niagara fault, fault, causing causing complex deformation of of Archean Archean basement basement and and Early EarlyProterozoic Proterozoic strata strata on onthe theforeland. foreland. In In the the study study area, area, deformation deformationisischaracterized characterizedby bythick-skinned, thick-skinned,south-verging south-vergingbackthrusting backthrusting and and backfolding backfolding opposite on the the continental continental foreland. foreland. That opposite the the overall overall sense sense of of north-verging north-verging deformation deformation on That near-recumbent near-recumbent minor minor folds foldswith withaccompanying accompanying axial-planar axial-planar subhorizontal subhorizontal foliation foliation are are evident evident in in both both Archean Archeanand andEarly EarlyProterozoic Proterozoicrocks rockssuggests suggeststhe the presence presence of ofcrystallinecrystallin'-cored cored nappes, nappes, such such as as that that of of the theCarney CarneyLake Lakeblock. block. Deep Deeptectonic tectoniclevels levelsare areexposed exposedin inthe theFelch Felchand andCalumet Calumettroughs troughsregion, region, indicating indicating major major involvement involvement of Archean Archean rocks rocks in the deformation. Both Bothinvolvement involvement of basement basement and and the existence existence of of backthrusts backthrusts are arecommon common in in younger younger orogens, orogens, such as in the southern southern Alps. Alps. Comparing 1850Ma Ma Penokean Penokean orogen orogen in in northern northern Michigan Michigan with with a section section Comparing aa section section of of the the1850 in common features. features. Proceeding in the the 30 30 Ma southern Alpine Alpine orogen orogen reveals reveals several common Proceeding inward from by the from the the continental continental margin, margin, both both orogens orogens have have 1) 1)accreted accreted oceanic oceanic crust crust as as shown shown by the presence presence of of ophiolite; ophiolite; 2) 2)aazone zoneofofthick-skinned, thick-skinned,complex complex deformation deformation with with associated associated backthrusting and backfolding; 3) aa master backthrusting and backfolding; 3) master thrust thrust along along which which strata strata were were tectonically tectonically transported 4) inboard inboard of of the the basement basement arch, arch, deformation that transported over over a basement arch; arch; and and 4) is of basement basement rocks. rocks. The is mainly mainly thin skinned, skinned, but also also involves involves some thrusting thrusting of TheAlpine Alpine orogen multiply deformed deformed nappes, whereas whereas deep deep erosion of the the Penokean orogen consists consists of multiply Penokean orogen orogen the minor minor recumbent recumbent folds folds and and aa makes recognition recognition of of nappes nappesdifficult. difficult. Nevertheless, Nevertheless, the subhorizontal subhorizontal foliation foliation in in the the Felch Felch and and Calumet Calumet troughs troughs area area are are structures structures similar similar to to those those in a'=" in the the Alps, Alps, and and their theirpresence presencestrongly stronglysuggests suggests that that nappes, nappes, now now mostly mostly eroded, eroded, may may also exist exist in the the Penokean Penokean orogen orogenof ofnorthern northernMichigan. Michigan. J j j J j j K:\PKS\ABS\NorMich (3-22-91) -j 64 -J �EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS IN IN THE THE MONICO, MONICO, WISCONSIN WISCONSIN AREA: AREA: IMPLICATIONS IMPLICATIONS ON THE WISCONSIN MAGMATIC MAGMATIC TERRANE TERRANE L. GENE L . LABERGE, Geology Dept., Dept., UW—Oshkosh, UW-Oshkosh, Oshkosh, WI 54901 54901 The Wisconsin magmatic terrane terrane is is a a major east—trending east-trending belt belt of Early Proterozoic volcanic and plutonic plutonic rocks rocks in in the the Lake Lake Superior Superior region. region. The The Monico area area is is a a "window" "window" into into the the Early Early Proterozoic rocks through the the Pleistocene Pleistocene deposits that that blanket blanket most of northern Wisconsin, and, therefore, therefore, may afford afford an an opportunity to determine the the relationships relationships between major units units within the the volcanic volcanic belt. belt. This paper presents preliminary data from a project funded by a Faculty Development Grant from from UWOshkosh, with support from from the the Wisconsin Wisconsin Geological Geological Survey, Survey, and and the U.S. U.S. Geological Geological Survey. Survey. Similar to other parts parts of of the the Wisconsin Wisconsin magmatic magmatic terrane, terrane, at at least two distinctly different sequences sequences of rocks rocks are are present present in in Monico area. the Monico area. One sequence, sequence, exposed exposed mainly north north of of Highway Highway 8, consists mainly of amphibolite—facies amphibolite-facies gneissic gneissic rocks rocks with with little preservation of lithology :ittle of primary features. features. The dominant lithology a foliated granitoid gneiss with abundant mafic blocks. is a Numerous segmented segmented mafic mafic dikes dikes are are also also present. present. The other 8, other sequence, sequence, exposed exposed mainly mainly south south of of Highway Highway 8, consists of several mafic to felsic felsic successions successions of of greenschist— greenschistfacies volcanic rocks with subordinate volcanogenic sedimentary f a d e s volcanic sedimentary rocks. rocks. The repetitions repetitions in in successions successions may may be be due due to to aa combination of tight folding folding and and faulting. faulting. Several large large metadiabase dikes and and the the "Jennings "Jennings granite" granite" intrude intrude the the volcanic volcanic successions. Although pillow basalts, debris flows, successions. flows, and flow— flowbanded rhyolite and and felsic breccias are dominant in in the the Monico Monica banded area, drill cores to the the east east and and west west of of the the area area of of outcrop outcrop This suggests contain higher proportions of of sedimentary sedimentary rocks. rocks. This Suggests Monica area that rocks in the Monico area may may represent represent aa volcanic volcanic center center (a (a By contrast, the volcanic island?) island?) within the the magmatic magmatic terrane. terrane. By areas with abundant sedimentary sedimentary rocks rocks may may represent represent intra—arc intra-arc or or back—arc back-arc basins basins between between volcanic volcanic centers. centers. The two major sequences of rocks in the map area are presumably in fault contact, and it is is probable that the gneissic rocks represent uplifted, deeper deeper levels levels of of volcanogenic volcanogenic rocks rocks that were formed during earlier stages stages of of subduction subduction within within aa mature By contrast, contrast, the mature island island arc. arc: By the greenschist—facies greenschist-facies rocks rocks may may The represent later products of the the general general subduction subduction event. event. The fault separating the two rock sequences sequences may be the the result result of of deformation during docking of of the the magmatic magmatic terrane terrane with with rocks rocks of of the Superior Superior Craton Craton to to the the north. north. Thus, the rocks exposed in in the the Wisconsin inagmatic terrane may may represent represent various various tectonic tectonic slices magmatic terrane mature island arc and associated of a mature associated intra—arc intra-arc and and back—arc back-arc basins. basins. 65 �L - Sketch of hypothetical east-west (longitudinal) section along the LJ L L L L of volcanic centers along the island arc. Wisconsin magmatic terrane showing various stages of development L LL LL �The T h e Geology and a n d Geophysics Geophysics of major majorpost-Keweenawan post-Keweenawan faults in faults in the the eastern eastern Lake Lake Superior Superior region region Manson, M.L. M.L. and H.C. Manson, a n d Halls, Halls, H.C. Department of of Geology, University of Department Geology, University of Toronto, Toronto, Erindale Erindale campus, campus, 3359 Mississauga MississaugaRd., Rd., Mississauga, Mississauga,Ontario Ontario L5L L5L 1C6 1C6 The eastern outline eastern Lake Superior Superior shoreline shoreline has has aa characteristic saw-tooth outline primarily occupied are primarily occupied by by Middle MiddleKeweenawan Keweenawan volcanics in which which promontories promontories are of the of the l.lGa l.lGaMidcontinent MidcontinentRift RiftofofNorth NorthAmerica America(MCR), (MCR),and andembayments embayments by by This pattern generatedby bymajor major ENE ENE Upper Keweenawan clastics. elastics. This pattern appears appears to be generated to to WSW WSW faults, faults, some some of of which which are arerelated related totoArchean Archean structures structures within within the the southern Superior Province. Province. At Mamainse southern Superior Mamainse Point, Point, more more than than 5km of of volcanics volcanics are are bound against sandstones sandstonestotothe thesouth south by by aa fault that in new Ontario bound against that appears, appears, in Ontario Geological Survey aeromagnetic data, to extend inland along the southern Survey aeromagnetic data, to extend inland along the southern margin greenstone belt. belt. The The Montreal Montreal River fault, of the the adjacent adjacent greenstone fault, possibly possibly related related to to the the Kapuskasing structure, defines defines the the northern Kapuskasing structure, northern margin margin of ofthese these greenstones greenstones and and extends into into rift rift straw extends strata underlying underlying eastern eastern Lake Lake Superior Superior in in GSC-GLIMPCE GSC-GLIMPCE aeromagneticdata. data.At At Havilland Havilland Bay. aeromagnetic Bay, aa 500m 500m thick thicksuccession succession of Jacobsville Jacobsville sandstonehas hasbeen beenupturned upturnedand and folded folded against against aa little-recognised little-recognised fault fault exposed sandstone exposed directly alongside directly alongside Highway Highway 17. 17.Further Furthereast-west east-west faults faultshave have been been observed observed bounding Keweenawan bounding Keweenawan strata strata in the the Goulais Goulais Bay Bay area area and and at at Grindstone Grindstone Point. Point. Whilst the exact nature of these faults is unclear, significant the exact nature of these faults is unclear, significant vertical vertical displacements across acrossthe theMamainse MamainsePoint Point and and Havilland Havilland Bay Bay faults is suggested displacements suggested potential field data from detailed gravity profiles profiles collected collected during during 1990. 1990. Regional Regional potential indicate the lateral extent of of many many of ofthe thefaults faultsand andsuggest suggest broad structural units normal to the rift rift axis. axis. This Thiscontrasts contrasts with withpost-Keweenawan post-Keweenawan faults in in the the western western lake region which which are parallel to to the lake region are generally generally parallel the axis of the the rift. rift. The Thechange change in in structural structural style from west west to east east is highlighted in in the the centre centre of the lake, where aa series of of arcuate arcuatefault fault segments segmentsappear appeartotolink link the the Isle Isle Royale Royale and and Michipicoten Michipicoten series 1991). Sampling Island faults via via Superior Shoal (Teskey et at, Superior Shoal (Teskey et al., 1991). Sampling with with aa submersible has has revealed revealed aa complex complex structure for Keweenawan volcanics exposed for Keweenawan volcanics exposed at the possibly involving involving drag (Manson and and at the Shoal, Shoal, possibly drag folding folding and and block block rotations rotations (Manson Halls, 1991). 1991). Constraintson on the the sense senseand andtiming timing of of the faults will will have Constraints the eastern eastern faults have relevance to models models describing describing the the closure closureof of the the MCR, MCR, possibly requiring a relevance to possibly requiring Grenville influence, quantifying Grenville influence, and and offer offer aamethod methodfor for quantifyingpost-Keweenawan post-Keweenawan deformation within deformation within the the southern southern Superior Superior Province. Province. Manson, M.L., and Manson, and Halls, H.C., H.C., 1991, 1991, An An investigation investigation of ofSuperior Superior Shoal, Shoal, central central press, CJ.E.S. Lake Superior, with a manned submersible, in with a manned submersible, in press, C.J.E.S. Teskey, D.J., D.J., Thomas, Thomas, M.D., M.D., Gibb, R.A., Teskey, R.A., Dods, Dods, S.D., S.D., Kucks, Kucks, R.P., R.P., Chandler, Chandler, K., Phillips, V.W., Fadaie, Fadaie, K., Phillips, J.D., J.D., 1991, 1991, High High resolution resolution aeromagnetic aeromagnetic survey EOS, V.72, V.72, No.8 of Lake Superior, Superior, EOS, 67 �-j OF THE MWCONTINENT GEOPHYSICAL GEOPHYSICAL INVESTIGATIONS INVESTIGATIONS OF MIDCONTINENT RIFT IN INEASTERN EASTERN LAKE LAKE SUPERIOR SUPERIOR USING USING VARIABLE VARIABLE MAGNETIZATION MODELING MARIANO, J. AND HINZE, W.J. (Dept. MARIANO, J. (Dept. of of Earth Earth and andAtmospheric Atmospheric Sciences,Purdue Sciences.Purdue Univ., Univ., West West Lafayette, Lafayette, IN. IN. 47907 47907 Magnetic Magnetic anomalies anomalies over eastern Lake Superior are very useful in tracing tracing the the subsurface subsurface extent extent and and geometry geometry of of the the Keweenawan Keweenawan volcanic volcanic rocks rocks of of the the Midcontinent Midcontinent Rift. Rift. In In 1987, 1987, aa high high J J resolution surveywas wasflown flownover overLake Lake Superior Superiorasas'part part of of the resolution aeromagnetic aeromagnetic survey the Great Great Lakes Lakes Multidisciplinary Multidisciplinary Program on Crustal Crustal Evolution. Evolution. In In order order to to take take full full advantage advantage of of these these new new data, data, improved improved quantitative quantitative magnetic magnetic modeling modeling techniques techniques have been developed and and applied applied to to the the volcanic volcanic rocks. rocks. The TheKeweenawan Keweenawan basalts basalts have have retained retained aa strong strong remanent remanent magnetization magnetization derived derived when when they they cooled cooled through through the the Curie Curie point point isotherm isotherm of ofmagnetite. magnetite. Post-depostional Post-depostional structural structural deformation of these rocks rocks has has rotated rotated the the remanent remanent magnetization magnetization vector vector resulting resulting in in aa spatially spatially varying varying direction direction and and intensity intensity of of magnetization magnetization, when when vectorially vectorially added added to to the the vector. An induced induced magnetization magnetization vector. An algorithm algorithm to toaccomodate accomodate these these variations variations in in magnetization magnetization has and tested has been been formulated formulated and tested and and has has been been applied applied to to the the volcanic volcanic rocks rocks of of eastern eastern Lake Lake J Superior. Superior. The which is is based The magnetic magnetic modeling modeling procedure, procedure, which based on on the the equivalent equivalent point point source source concept, concept, is is termed termed the the equivalent equivalent point point dipole &pole (EPD) (EPD) method, method, and and calculates calculates the the magnetic magnetic response response of aa given given volume volume of of anomalous anomalous magnetization magnetization by summing the magnetic fields fields due due to to a series of point point dipoles dipoles of of specified specified spacing spacing contained containedwithin withinthe thevolume. volume. This This approach allows allows the to vary the direction direction and magnitude magnitude of magnetization magnetization to vary freely freely over an an anomalous anomalous unit. unit. The The accuracy and speed of this calculation are directly dependent on the point dipole spacing. accuracy speed of this calculation are directly dependent on the point dipole spacing. The The optimum calculation time, time, but but still results optimum spacing spacing minimizes minimizes calculation results in in acceptable acceptable calculation calculation error. error. Given Given the the simplicity simplicity of the the dipole dipole calculation calculation and and the the speed speed of of modern modern computing computingfacilities, facilities,this this is is fortunately fortunately not not aa problem. problem. In Ingeneral, general,aadipole dipole spacing spacingequal equal to to one one tenth tenth the thedistance distancebetween between the plane and and the the point point dipoles dipoles yields yieldserrors errorsless lessthan thanone onepercent. percent. Figure 11 shows the observation observation plane shows comparisons of the comparisons of the EPD EPD calculation calculation with with the the conventional conventional method method of ofanomaly anomalycalculation calculation (Tal\vani (Talwani and and Heirtzler,1964). Heirtzler.1964). The to profiles The EPD EPD method method has has been been applied applied on on aa two two dimensional dimensional basis basis to profiles that that have have been been studied with the gravity and seismic reflection methods in eastern Lake Superior. These studied with the gravity and seismic reflection methods in eastern Lake Superior. These profiles profiles include recentlyreleased releasedseismic seismicreflection reflectionsections sections with of TWYI' TWTT as as well well as as include recently with upup toto88ss of previously availableGLIMPCE GLIMPCEdata datawith withupuptoto 16 ss of previously available of T\V1T. TWTT. On On these these sections, sections, the the Keweenawan basalts are are clearly clearly imaged imaged as as aa series Keweenawan basalts series of of strong, strong, laterally laterally continuous continuous reflections reflections with with dips generally generally ranging from -30 -30 to to ±30 +30degrees. degrees. Extensive Extensive paleomagnetic paleomagnetic studies studies in in the the Lake region indicate indicate that that the both aa normal Lake Superior Superior region the basalts basalts possess possess both normal and and reversed reversed remanent remanenl Assuming magnetization to the the induced induced component. component. Assuming original original magnetization component component in in addittion addittion to horizontality of the the basalt basalt flows, flows, the the apparent apparent dips dips derived derived from from the the seismic seismic reflection reflection sections sections are vector back back to to the the horizontal in the are used used to to rotate rotate the the remanent remanent magnetization magnetization vector horizontal in the plane plane of of the the profile. The rotated remanent vector is then added to an induced magnetization vector, resulting The rotated remanent vector is then added to an induced magnetization vector, resulting in in aa spatially spatially varying varying direction and and magnitude magnitude of of total total magnetization. magnetization. Modeling results indicate that the Modeling results indicate that the consideration consideration of of variable variable magnetization magnetization will will provide provide basalts. much much greater greater confidence confidence in in the the structural structural interpretations of of the theKeweenawan Keweenawan basalts. Preliminary models in in eastern Lake Superior suggest that a large volume volume of of reversely reversely polarized polarized rocks is is necessary to account account for the observed aeromagnetic anomalies. 68 J J �(a) s 020 .0 4!o 50 DISTANCE (1(M) N 0 iS 50 50 50 50 10 a 2C S = —S S C 10 o 20 50 40 50 DISTANCE (1(M) 70 (b) s z 50 '00 N — 0° ¶0 20 I'S 10 0 — 50 40 50 DISTANCE (1(M) 60 70 60 90 '00 5'O *o 100 100 0• - " 0 20 t'o.'oiot'o7'0 40 DISTANCE (1(M) 70 .o I Figure Figure 1.1. (a) (a) The The magnetic anomaly due to combined induced and remanent magnetization calculated calculated by by the the EPD EPD method method (dashed) (dashed) and andthe theTalwani Talwani and and Heirtzler Heirtzler method method (solid). (solid).Note Notethat that these these are are essentially essentially coincident coincident over over the the entire entire length length of of the the profile. profile. The Thetotal totalmagnetization magnetization vector vector in in the the plane plane of ofthe theprofile profileisisshown shownfor forevery everyfifth fifthdipole. dipole. (b) (b) The Themagnetic magneticanomaly anomalydue due to to combined combined induced induced and and remanent remanentmagnetization magnetization with with aagradational gradational rotation rotation of of the the remanent remaneni vector vector using using the the EPD EPD method method (dashed) (dashed) and andwith withhomogeneous homogeneous magnetization magnetization using using the the Talwani Talwani and A single singlehorizontal horizontalplane plane of of total total magnetization magnetization vectors vectors isisshown shown. and Heirtzler Heirtzler method method (solid). (solid). A The The induced induced and and remanent remanent magnetization magnetization vectors vectors and and the the disturbance disturbance of the the remanent remanent vector vector are are and the compatible compatible with with conditions conditions in in the the Lake Lake Superior Superior region region and the volcanic volcanic rocks rocks of of the the Midcontinent Rift. Rift. Mideontinent Reference Reference . , . Talwani, Talwani, M. M. and and Heinzler, Heirtzler. J;, 1..1964, 1964,Computation Computation of of magnetic magnetic anomalies anomalies caused caused by by twotwoMineral Industries, dimensional structures of arbitrary shape. IN: Computers in the dimensional structures of arbitrary shape. IN: Computers Mineral Industries, 1. 1. Stanford Stanford Univ. Publ. Publ. Geol. Sci., Sci.. 90): 9(1): 464-480 69 69 �A MOVEMENT ALONG A PRELIMINARY PRELIMINARYSTUDY STUDY OF OF REJUVENATED REJUVENATED MOVEMENT ALONG A FAULT,ST. St CROIX A PRECAMBRIAN PRECAMBRIAN FAULT, CROIXCOUNTY, COUNTY, WISCONSIN WISCONSIN Michael MichaelI). D.Middleton, Middleton,Department DepartmentofofPlant Plantand andEarth EarthScience, Science, University University of of Wisconsin-River Wisconsin-River Falls, Falls, River RiverFalls, Falls,WI WI54022 54022 The The eastern eastern margin margin of of the the Midcontinent Midcontinent Rift Rift system is marked by by the the Hastings-Lake Hastings-Lake Owen fault in western western Wisconsin. Wisconsin. Precambrian Precambrian displacement displacementalong along this this high high angle anglefault faulthas hasbeen beenestimated estimatedatatapproximately approximately3,000 3,000m. m.(Craddock, (Craddock,1972) 1972) based upon upon geophysical geophysical evidence. A A number number of of workers workers have have suggested suggested that that the the Hastings-Lake Owen fault was reactivated in the of the late late Cambrian, Cambrian, causing causing thinning thinning of the the Cambrian Cambrian section and an an unconformity unconforrnity between the the Cambrian Cambrian and and Ordovician Ordovician sequences sequences in in Minnesota Minnesota (Morey (Moreyand andRensink, Rensink,1969; 1969;Cavaleri, Cavaleri, et. et. al., al., 1987). 1987).Evidence Evidence from aa number number of of exposures exposuresin inSt. St.Croix Croix County, County, Wisconsin Wisconsin supports supportsthese theseviews, views, and further further refines refines the the timing timing and andamount amountof ofpost-Precambrian post-Precambrian movement movement along along the the fault. fault. The The surface surfaceexpression expression of of the the Hastings-Lake Hastings-Lake Owen Owen fault faultin inSt. St.Croix Croix County Countyisis aa series series of low escarpments with a northeast northeast trend trend formed formed by by differential differential erosion erosion of of the softer Cambrian sandstones to the west which have been displaced upward upward against more resistant Ordoviaan Ordovician dolomites to to the the east. east. A A quarry quarry along along this this trend trend cut cut into into dolomites dolomites of of the the Lower Lower Ordovician Ordoviaan Prairie Prairie du du Chien Chien Group Groupshows showsevidence evidence of this displacement. In In sharp sharpcontrast contrastto tothe therelatively relatively flat-lying flat-lying bedrock units in this this region, the sttata strata in the the quarry quarry dip dipapproximately approximately 20° 20' to the east. These These strata strata dip downthrown side, side, and and these these dips dips were were most most probably probably dip away away from the fault on its downthrown caused by drag. The Thedisplacement displacementof of the the Cambrian Cambrian sandstones sandstonesagainst against Lower Lower Ordovician Ordovician dolomites and the drag drag folding folding within within the the dolomites dolomites both both demonstrate demonstrate post-Early Ordovician Ordovician movement movement along along the the fault. fault. In In addition, addition, features features within within the the dolomite itself provide evidence for movement of the the fault fault in in the theEarly EarlyOrdovician Ordovician during deposition of the sediments. The The beds beds in in the thequarry quarrythicken thicken away awayfrom from the the fault, with lower strata showing higher higher dips than those above. above. Sharply Sharply truncated stromatolite stromatolite beds, thick thick dolomitic dolomitic conglomerates, conglomerates, erosional relief relief along contacts, contacts, and and mudcracks mudaacks all attest to to periodic erosion and and exposure exposure of of the the sea sea floor floor during during deposition of the Prairie du Chien Group at this site, perhaps due due to to recurrent recurrent small small movements along the fault. fault. 70 �The The amount amountof of Post-Precambrian Post-Precambrian displacement displacementalong along the the Hastings-Lake Hastings-Lake Owen Owen fault fault in in this thisregion region can canbe bedetermined determinedat atexposures exposuresin in the thevicinity vicinity of of Hudson, Hudson, Wisconsin. Wisconsin. Cambrian Cambriansandstones sandstoneshave havebeen beendisplaced displacedupward upwardapproximately approximately85-100 85-100 m. the Cottage Grove fault which m. against against Ordovician Ordoviaan strata strata along along the the fault. fault. Along Along the Cottage Grove fault which parallels parallels the the Hastings-Lake Hastings-Lake Owen fault to to the the northwest, northwest, displacement displacement is is even even greater, greater, approximately approximately115-125 115-125 m. The Theevidence evidencegathered gatheredin inSt. St.Croix Croix County County demonstrates demonstrates later later recurrent recurrentmovements movements and andgreater greaterPost-Precambrian Post-Precambrian displacement displacement than than has has previously previously been been reported reported for for the the Precambrian Precambrian faults in in this this region. region. References ReferencesCited Cited Cavaleri, The Geology Geology of of the Cavaleri, M., M., Mossier, Mossier, J.H. J.H. and andWebers, Webers,G.F., G.F., 1987, 1987, The the St. St. Croix Croix River River Valley, in Balaban, N.H., Ed., Field Trip Trip Guidebook Guidebookfor for the the Upper Upper Mississippi Mississippi Valley, in Balaban, N.H., Ed., Field Valley, MinnesotaGeological Geological Survey, Survey, Valley, Minnesota, Minnesota, Iowa Iowa and and Wisconsin. Wisconsin.Minnesota Guidebook GuidebookSeries Series#15, #15,p. p.23-43. 23-43. Craddock, and Southeastern Southeastern Craddock, C., C., 1972. 1972. Keweenawan Keweenawan Geology Geology of East-central and Minnesota, Eds, Geology Geology of of Minnesota: Minnesota: AA P.K. and and Morey, Morey, G.B., G.B., Eds, Minnesota, in in Sims, Sims, P.K. Centennial MinnesotaGeological GeologicalSurvey, Survey,p.p.416-424. 416-424. Centennial Volume. Volume.Minnesota Morey, and Rensink, 1969. Rejuvenated Rejuvenated Precambrian Precambrian faults faults as as aa cause Morey, C.B. G.B. and Rensink, D.C., D.G., 1969. cause of of Paleozoic structures in Minnesota. Annals of the the Institute Institute of Paleozoic structures in southeastern southeastern Minnesota. Annals of of Lake Lake Superior Superior Geology. Geology. 15th, 15th,Wisconsin Wisconsin State State University, University, Dept. Dept. Ceol., Geol., Oshkosh, Oshkosh,WI, WI,May May8-9. 8-9. 71 �GEOCHRONOLOGY GEOCHRONOLOGYOF OFTHE THEDULUTH DULUTHCOMPLEX: COMPLEX:AAPROGRESS PROGRESSREPORT REPORT MILLER, MILLER, .ID., J.D., JR., JR., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave., St. St. Paul, Paul, MN MN 55114 55114and and LB. J.B.Paces Pacesand andR.E. R.E. Zartman, Zarunan,U.S. U.S. Geological GeologicalSurvey, Survey.Box Box25046, 25046,MS MS963, 963,Denver DenverFederal Federal Center, Center, Denver, Denver, CO CO80225 80225 Recent Recenthigh-precision high-precisiondating datingofofvolcanic volcanicrocks rocksassociated associatedwith withthe theMidcontinent MidcontinentRift Rifthave havecontributed contributed much muchtoward towardunderstanding understandingthe thetiming, timing,duration, duration,and andtectonomagmatic tectonomagmaticevolution evolution of the the Li-Ga 1.1-Garifting riftingevent. event. However, However, similar similargeochronological geochmnologicalcontrol control for for associated associated plutonic plutonic rocks rocks is not yet yet available. available. The Theprimary primary objective innortheastnonheastobjectiveof ofthe thepresent presentstudy studyisistotodate dateindividual individualgabbroic gabbroicintrusions intrusionswithin withinthe theDuluth DuluthComplex Complexin ern em Minnesota Minnesotausing using high-precision high-precision U-Pb U-Pb techniques techniques (1) (1) to to determine determine the the temporal temporal range of of intrusive intrusive activity activity within within several severalwell-studied well-studiedareas areasof of the thecomplex, complex,as aswell wellas asbetween betweenthese theseintrusions intrusions and and the the overlying overlying volcanic volcanic rocks, rocks,and and(2) (2)tototest testmodels, models,which whichhave havepreviously previouslybeen beenbased basedonongeologic geologicmapping mappingand andgeophysical geophysicalinterpreinterpretation, tation,for forthe theemplacement emplacementofofthe theDuluth DuluthComplex. Complex. The Duluth Complex is large, The Duluth Complex is large,composite compositemafic maficintrusive intrusivesupersuite, supersuite,which whichwas wasemplaced emplacedatatshallow shallow depths (<7 km) beneath a comagmatic edifice of plateau basalt during the development depths (<7 km) beneath a comagmatic edifice of plateau basalt during the development of of the the Midcontinent Midcontinent Rift Rift (Fig. (Fig.I). 1).Multiple Multipleintrusions intrusionswere werealso alsoemplaced emplacedhigher higherinto intothe thevolcanic volcanicpile, pile,with withthe themost mostvoluminous voluminousof of these thesebeing beingthe theBeaver BeaverBay BayComplex. Complex.The TheDuluth DuluthComplex Complexisiscomposed composedofofseveral severallithologieally lithologicallydistinctive distinctive rock Morey,1980). 1980).The Theoldest oldestintrusive intrusive rockseries, series,previously previouslyinterpreted interpretedto tobe betemporally temporallydistinct distinct(Weiblen (Weiblen&&Morey, rocks rocksare areaalayered layeredsuite suiteof ofgabbroic gabbmiccumulates cumulatesin in the thenorthern northern area, area, termed termed Nathan's layered layered series series (Fig. I). 1). Their Theirevolved evolvedcompositions compositionsand and reversed reversed magnetic magneticpolarity polarity suggest suggestthat that these these rocks rocks may may be be similar similar in in age ageto to the the nearby nearby Logan Logan sills sills(1109 (1 109±Â22 Ma; Ma, Davis Davis & & Sutcliffe, Sutcliffe,1985). 1985). These Thesegabbros gabbrosare areintruded intrudedby by aastructurally structurally complicated complicatedsuite suiteof of dominantly dominantlyplagioclase plagioclasecumulates, cumulates,termed termedthe theanorthositic anorthositic series series (Fig. (Fig. I), 1).which whichoccur occur throughout plagioclasecrystal crystalmushes mushes(Miller (Miller & &Weiblen, Weiblen, throughoutthe thecomplex complex and andare arethought thoughttotohave haveintruded intrudedasasplagioclase 1990). 1990). Anorthositic Anorthositicseries seriesrocks rocksare areintruded intrudedthroughout throughoutthe thecomplex complexby bylayered layeredintrusions inbusionsofofiroctolitic troctolitictoto gabbroic gabbroiccumulates, cumulates,collectively collectively termed termed the thetroctolitic troctoliticseries. series.The Theapparent apparenttruncation truncationofofaeromagnetic aeromagneticpatterns patterns related relatedtotoSE.dipping SE-dippinglayering layeringininintrusions intrusionsalong alongthe theunexposed unexposedwestern westernmargin marginof ofthe theDuluth DuluthComplex Complex(Fig. (Fig. 1) 1)led led Miller Milleret etal. al.(1990) (1990)totospeculate speculatethat thattroctolitic troctoliticseries seriesintrusions intrusionsyoung youngtotothe thesouth southasasaaresult resultofofsuccessuccessive siveintrusive intrusiveoverplating. overplating. AAfelsic felsicseries seriesalso alsocomprises comprisesaasignificant significantportion portionof ofthe theDuluth DuluthComplex Complex (Fig. (Fig.I)1) but geochronologicstudy. study. butwas wasnot notincluded includedininthis thisgeochronologic Differentiated Differentiatedsamples samplesfrom fromseven sevenmafic maficintrusive intrusivebodies bodieswere werechosen chosen that, that,based basedon on geologic geologicand andgeogeophysical physical evidence, evidence,span span the the temporal temporal and and spatial spatial(areal (arealand andstratigraphic) stratigraphic)limits limitsof of intrusive intrusiveactivity activity in in the the Duluth Duluth Complex (Table (Table 1; 1; Fig. 1). 1). Between Between30 30and and40kg 40 kgofofrock rockwas wasprocessed processedfor foreach eachsample sampleyielding yieldingclear clear zircon (± baddeleyite) grains lacking obvious cores or rims. Air-abrasion and hand-picking yielded crack-and and zircon ( baddeleyite) grains lacking obvious cores or rims. Air-abrasion and hand-picking yieldedcrackinclusion-free inclusion-free grains, grains,which which were were analyzed analyzed individually individually or or as as2-5 2-5grain grainaggregates aggregates weighing weighing 30 30 to to 150 150jig. ug. UU contents 200 to to 1000 1000ppm, ppm, and most most fractions fractions are are less less than 1.5% 1.5% discordant. Preliminary Preliminary ages agesfor for contents range range from from 200 five five of of these these samples samples are are reported in Table 1. 1. The Thetwo twoanorthositie anorthositicsamples samples(FCI, (FC1,AS3) AS3)plus plusone onetroctolitic troctolitic series level. Fractions series ferrogabbro ferrogabbro (Dl) (Dl) yield yieldidentical identical ages agesat at the the95% 95%confidence confidencelevel. Fractionsfrom fromall allthree threerocks rocksreregressed gressed together together result result in in an an age age of of 1099.1 1099.1±Â0.6 0.6 Ma Ma with with aa lower lower intercept intercept age of-I of -1±Â40 40Ma Ma(MSWD (MSWD== 1.3), 1.3). The aswell wellas asthe thehypabyssal hypabyssalferrodiorite ferrodiorite from from the the Beaver Beaver Bay Bay ComThe troetolitic troctolitic series series olivine olivine gabbro gabbm (P02), (PG2).as plex plex (SBG2), (SBG2). yield yield younger younger ages ages of of1096.1 1096.1±Â0.8 0.8and and1095S 1095.9±Â0.5 0.5Ma, Ma,respectively, respectively,which whichare areclearly clearlyresolved resolved from from the older older ferrogabbro ferrogabbm and anorthosite dates. Although Although additional additional analyses are required before final age determinations determinations are are made, made, the thefollowing followinghave havebeen beenestablished: established: - Although Although the the onset onset of of igneous igneous activity activity as as represented by Nathan's layered layered series has not yet been deter— mined, mined, the the bulk bulk of of the the Duluth Duluth Complex Complex and and associated associated hypabyssal hypabyssal intrusions intrusions were emplaced between 1099 Thisfurther furthersupports supportsprevious previousobservations observationsthat thatvolumetrically volmetricallymost mostKeweenawan Keweenawan 1099 and 1096 1096 Ma. This igneous Ma (Davis (Davis & & Sutcliffe, Sutcliffe,1985; 1985;Davis Davis& & igneous activity activity occurred occurred over over aa time time span span between between 1099 1099and and 1094 1094Ma Paces, Paces, 1990; 1990; Van Van Schmus Schmus et a!., a]., 1990). Since Sinceparts pansof ofthe theDuluth Duluth Complex Complex are are older older than than the the normalnormalpolarity rocksmay may represent represent aa means means of of sampling sampling polarity lavas lavas exposed exposed along along rift rift margins, margins, these these intrusive intrusiverocks magmas that are are more more deeply deeplyburied buried within within the the central central rift rift graben. graben. magmas associated associated with lavas lavas that — The The relative relativeages ages of of intrusive intrusiverocks rocks based based on ontheir theirmagnetic magneticpolarity polaritymust must be be viewed viewed with with considerable considerable caution. caution. Although Althoughall allof ofthe theanalyzed analyzedrocks rockspossess possessnormal normalmagnetic magnetic polarity, polarity, three three of the the intrusive intrusive bodies bodies have have emplacement emplacement ages ages of 1099 1099Ma, Ma, older older than than the the major majorR-N R-N magnetic magnetic reversal reversal placed placed at at about about I09L6 1097.6±Â3.7 3.7 Ma Ma (Fig. (Fig. 1;1;Davis Davis & & Sutcliffe, Sutcliffe, 1985). 1985). This Thisdisparity disparityisislikely likely related related to to the the slow slow cooling cooling of of - • 72 �1I 90 CANADA r___aiScRIPTloN or MAP UNITS Middle ProlerpzO,c (Keoae enasyan Superoroupi Sedsmentary Rocks (Baylield & Oronto Groups) • shale and Ieldspalhic ID quartz Ose sandslone nlrusive Rocacs l,ncludes Duluth COmoleal R - granod.oriI.c IC graniI.c bc I5 domnaruly subvolcanc malic rocks dominanbly Irootolilic rocks !-dom, nanlly gabbro.c rocks Xc -dorn.nanlty anorlh ostIbc rocks • need lroclob,t,c so goat crc rocks abundant Volcan.c Rocks North Shore Volcan,c Gtou:SoleyI,c basall beat caIn some anoes!te shyol,be. and nt ertlom seo,men lacy C;. Early P.ocarn,n!r lAnjrnrk.p O'puol arolillIe and greyvacke Rove S V!n.r.a nrc ran lornlat!crr re 0° cl p a;-.. &ctlarn lyerm,ll,cn dIstrict ntaas.ae to OnelSs.c. yr anItIc 504; IIC 1 ;kS locally micat,tsc metacoboan,; and metased.me-:a -' 'sty banded ron bornOatcI] sno.r.n SYMBOLS -— .;.WISCONSIN .• . —. Aopron,malo geolog.c corrtaCI. dariec .srre,r ,nberred Irom geopnysscal data Large-scale laull 20 40 20 30 4CM. —u ing samples samples collected collected for for U-Pb isotope analyses. Figure 1. 1. Generalized geology of northeastern Minnesota show showing Complex and and related related intrusions zircons from from Duluth 0 uluth Complex Table 1. 1. Preliminary Preliminary U-Pb U-Pb ages for zircons Sample Sample Rock Series Series T-R-Sec. T-R-Sec. Rock Type Upper Intercept Age (Ma) (Ma) i2a ±2a Age error error No. of of No. analyses analyses Lower Intercept Intercept Lower Age (Ma) (Ma) i±2a Age 2a error error Dll D PG2 A53 AS3 FCI FC1 NLS5 LLG2 LLG2 Troctolitic Troctolitic Anorthositic Anorthositic Anorthositic Nathan's L.S. L.S. Beaver Bay Complex Complex Beaver Bay Complex Complex 49-15-1 59-12-8 49-14-6 61-8-10 64-2-2 56-7-6 fen-ogabbro ferrogabbm olivine gabbro olivine gabbroic anorthosite gabbmic gabbroic anorthosite anorthosite gabbroic olivine gabbro gabbro olivine fenogabbro ferrogabbro 1099.0  ± 0.8 1099.0 1096.1 i ± 0.8 0.8 1096.1 1098.9* 1098.9. 1099.2  ± 1.7 1099.2 in progress in progress 3 3 3 3 1 4 --22 ± i 441 1 O** 56-7-29 ferrodiorite ferrodiorite 1095.9  ± 0.5 0.5 1095.9 44 ±7 5 SBG2 SBG2 0" O* .2rnpb,206pbage agefrom from single single analysis analysis *2CTPb/2çÈ **Regression forced forced through through 0 0 Ma lower intercept due due to clustering clustering of of data data near near concordia concordia 73 �these these plutonic plutonic rocks racksbetween betweenzircon zirconcrystallization crystallizationtemperatures temperatures(—900°C) (-90O0C) and the the Curie Curie point point of of the theFe-Ti Fe-Ti oxides oxides (c590°-350°C). (c59O0-350T). — - The The similar similar ages ages of anorthositic anonhositicseries seriesrocks rocks(AS3 (AS3 & &PC!) FC1)taken takenfrom fromwidely widely separate separateareas areasof of the the complex occurredas asaarestricted restrictedtemporal temporalevent eventthroughout throughout complex suggest suggestthat that the the emplacement emplacementof ofthese theserocks rocksoccurred the Duluth Complex around 1099 1099 Ma. This Thisisisconsistent consistentwith withtheir theirunique uniquepetrogenesis petrogenesis(Miller (Miller & & Weiblen, Weiblen, 1990). 1990). — - The The essentially essentially identical identical 1099-Ma 1099-Ma age age of of anorthositic anorthositicand and troctolitic troctolitic rocks at Duluth (AS3 & Dl), Dl), while while not contradicting contradicting field relations relations indicating that the the anorthositic rocks are older, does lead to the speculation that the thought. At the petrogenesis of these these two two series series may may be be more more closely closely linked linked than previously thought Atthe the very least, least, itit implies implies that that the the types typesof of parent parentmagmas magmas that that gave gave rise rise to to these these two two rock rock series series were were either either very very closely closely related related or or were weregenerated generatedby bymechanisms mechanismsthat thatwere werevery very nearly nearly synchronous. synchronous. - Speculation Speculation (Miller et al., 1990) 1990)that that the the troctolitic troctolitic series seriesintrusions intrusions along the western margin young to — the south is strongly strongly contradicted contradicted by by the the distinctly distinctly younger younger age age of the the troctolitic series sample from the northwest (Kawishiwi) part of the complex (PG2; 1096 compared to to the sample at at Duluth Duluth (Dl; 1099 1096 Ma) compared 1099 Ma). Given & Hauck, Hauck, 1990), 1990).itit Giventhe thecomplexity complexityof ofintrusive intrusiverelationships relationshipsininthe theKawishiwi Kawishiwi area area(Severson (Severson & seems seems likely that that troctolitic troctolitic series seriesrocks rocksof ofvarious variousages agesmay mayexist existininthis thisregion. region. - The The similarity similarity of of 1096-Ma 1096-Maages ages between between the theKawishiwi-area Kawishiwi-area olivine olivinegabbro gabbm (PG2) (PG2)and and the the ferrogabbro ferrogabbro — (SBG2) representing the youngest intrusive unit of the hypabyssal Beaver Bay Complex (Miller, (SBG2) representing the youngest intrusive unit of the hypabyssal Beaver Bay Complex (Miller,1988) 1988) implies implies that magmas magmas were were simultaneously simultaneously emplaced emplacedat at several severalstratigraphic stratigraphiclevels levels within within the thevolcanic volcanicpile, pile, at least late in the the intrusive intrusive history. Dating Datingof ofthe theLax LaxLake Lakegabbro, gabbro,which which mapping shows to be among the earliest earliest intrusions intrusionsin in the the Beaver BeaverBay BayComplex Complex(Miller, (Miller,1988), 1988).will willdetermine determinewhether whetherintrusive intrusiveactivity activity in this hypabyssal hypabyssal environment environment began began as asearly earlyas asititdid didininthe thedeeper deeperDuluth DuluthComplex. Complex. In summary, high-precision dates generated by this this study study place very important constraints on the timing and emplacement emplacement mechanisms mechanisms for for the the Duluth Duluth Complex Complexand andrelated related intrusions, intrusions. as aswell well as asproviding providingadditional additional data bearing on the broader evolution evolution of of the the Midcontinent Midcontinent Rift. Rift. These Thesepreliminary preliminary results resultsgive givecause causetotorethink rethink previously proposed concepts concepts hypothesized hypothesized from from field, field,geochemical, geochemical,and and geophysical geophysical data, data, and and offer offerincentives incentives for for further furtherintegration integration of of these thesedata datatoward towardbetter betterunderstanding understandingofofrift riftprocesses. processes. REFERENCES REFERENCES CITED CITED Davis, D. W., & & Paces, Paces, 1. J. B., B.. 1990, 1990,Time Time resolution resolution of of geologic geologicevents eventson on the theKeweenawan KeweenawanPeninsula Peninsulaand and implications EarthPlan. Plan. Sci. Sci.Letters, Letters,v.v.97, 97,p.p.54-64. 54-64. implications for for development development of the the Midcontinent Midcontinent Rift system: Earth R.H., 1985, Nipigon plate plate and andnorthern northemLake Lake Superior: Superior: Geol. Davis, Davis, D.W., D.W., & Sutcliffe, R.H., 1985, U-Pb ages from the Nipigon Soc. Am. Bull., v. v.96, Am. Bull., 96,p. p. 1572-1579. 1572-1579. Miller, J.D., J.D., Jr., 1988, 1988, Geologic Geologic map of the the Silver SilverBay Bay and and Split Split Rock Rock Point NE quadrangles, quadrangles. Lake County, Minnesota: Minn. Minn. Geol. Geol.Surv. Surv.Misc. Misc.Map MapM-65, M-65,scale scale1:24,000. 1:24,000. Miller, J.D., Cambray,F.W., F.W., 1990, 1990,Style Styleof ofemplacement emplacementof ofthe theDuluth Duluth J.D., Jr, Jr, Chandler, Chandler, V.W., V.W., Southwick, Southwick,D.L., D.L., &&Cambray, Complex: Am. Abstr. Abstr. with with Programs, Programs, v. v. 22, 22, p. A369. A369. Complex: Geol. Geol. Soc. Soc. Am. Miller, J.D., J.D., Jr., & & Weiblen, P.W., P.W., 1990, 1990,Anorthositic Anorthositic rocks of of the the Duluth Complex: examples examplesof ofrocks rocksformed formed from plagioclase crystal mush: mush: J.J. Petrol., Peml., v. v. 31, 31,p.p. 295-339. 295-339. Palmer, H.C., & Davis, Davis, D.W., D.W., 1987, 1987,Paleomagnetism Palmmagnetismand andU-Pb U-Pb geochronology geochronology of of volcanic volcanic rocks rocksfrom from H.C., & Michipicoten Island, Lake Superior, Canada: precise calibration of the Keweenawan polar precise calibration of the Keweenawan polar wander wander track: track: Precambrian Res., Res., v. v.37, 37, p. p. 151-171. 151-171. Severson, & Hauck, Hauck, S.A., S.A., 1990, 1990,Geology, Geology,geochemistry, geochemistry,and and siratigraphy stratigraphy of of aaportion portionof ofthe thePartridge Partridge Severson, M.J., M.J., & River intrusion: Duluth, Duluth,Univ. Univ.ofofMinn., Minn.,Nat. Nat.Resources ResourcesResearch ResearchInst. Inst. Tech. Tech. Report ReportNRRJ/GMIN-TR-89NRRVGMlN-TR-8911,236 11,236p. p. Van Schmus, W.R., W.R., Martin, M.W., M.W., Sprowl, D.R.. D.R., Geissman, J., J., & Berendsen, Berendsen, P., P., 1990. 1990, Age, Age, Nd Nd and Pb isotopic composition, and magnetic of the the 1100 1100Ma Ma Midcontinent MidcontinentRift: Rift: magnetic polarity polarity for for subsurface subsurfacesamples samplesof Geol. Geol. Soc. Soc. Am. Am. Abstr. Abstr. with with Programs, Programs, v. v. 22, 22, p. p. A174. A174. P.W. and and Morey, Morey, G.B., 0.8., 1980, Weiblen, P.W. 1980,AAsummary summary of of the the stratigraphy, stratigraphy, petrology, and structure of the Duluth Complex: Am Am J.J. Sci., Sci., v. v. 220-A, 280-A, p. p. 88-133. 88-133. 74 �MANGANESE MINERALIZATION IIN EARLY PROTEROZOIC PROTEROZOIC IRON-FORMATION MANGANESE MINERALIZATION N EARLY IRON-FORMATION OF OF THE THE EMILY EMILYDISTRICT, DISTRICT,CUYUNA CUYUNARANGE, RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA MOREY, D.L. L.Southwick, Southwick,Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University Avenue, St. Paul, MOREY, G.E., G.B., and and 0. Minnesota Minnesota 55114 55 114 Early EailyProterozoic Pmtemwicstrata strata of of the the Emily Emily district district at at the far far northern end of the Cuyuna Iron Range Range define define the (Southwick and others, 1988). As [hesouthwestern southwestern closure closure of the Animikie Aniiikie basin in east-central Minnesota (Southwick A such, Anitnikie Gmup Group of the such, the the rocks rocks of of the the Emily Emily district are correlative with strata of the well known Animikie Mesabi Mesabi range. range. However, However.unlike unlikethe themonodlinal monoclinalnature natureof ofthe theMesabi Mesabirange, range,strata stratain inthe theEmily Emilydistrict districtare are thrown thrown into inw aa series series of of broad, broad, open, open. eastward-plunging folds with near-vertical axial planes. Geometric Geometric relationships relationships imply imply that that the the basal basal contact contact of of the the Animikie ~ ~ m i kGroup Groupoverlies i e overlies an an unconformity unconfo&ty cut cutonto ontoolder older folded rocksof of the the North North range ranee (Chandler (Chandler and Malek, Malek. 1991). 1991). That Thatunconformity unconformitvmarks marksthe theboundary boundary folded rocks between between twice-deformed twice-deformedrocks rocks of of the the Penokean Penokean fold-and-thrust fold-and-thrustbelt belt and and the the once-deformed onc&efonned rocks rocksof of the the Animilde Animikiebasin basinOn On the the Mesabi Mesabi range, range, the the Animikie Animikie Group Gmup consists consists of a lower lower quartz arenitic arenitic sequence sequence (Pokegama (Pokegama Quartzite). Quartzite), an an intermediate intermediateiron-rich iron-rich sequence sequence(Biwabik (BiwabikIron IronFormation), Formation),and andan anupper upperblack-shale— black-shalegraywacke graywacke sequence sequence (Virginia (Virginia Formation). In Inthe the Emily Emily district, district,however, however. the the stratigraphic stratigraphic position position of of the the Biwabik Biwabik is is occupied occupied by by several several lenticular lenticular units units of iron-formation iron-formation intercalated within both PokegarnaPokegama- and Virginia-like Virginia-likematerials. materials. The area—can be dividei divided The main main iron-formation iron-formationof the Emily district—termed districtÑterme Unit A of the Ruth Lake areaÑca into epiclastic lithotope into seven seven lithotopes lithotopes (Fig. 1). 1). They Theyare are(1) (1)an anepiclastic lithotopeof of quartz-rich quartz-rich siltstone siltstone and and shale; shale; (2) (2) aa mixed lithotope;(3) (3) an an oolitic oolitic and and pisolitic pisolitic lithotope; lithotope; (4) (4) a ihick-bedded thick-bedded lithotope mixed epiclastic—jaspery-chert epiclastic-jaspery-chertlithowpe; lithotope of o cherry (5) aa mixed mixed thickthick- and and thin-bedded thin-beddedlithotope lithowpecharacterized characterizedby bythick thick cherty or or granular granular iron-formation; iron-fonnation; (5) intervals intervalsof of slaty slaty or or nongranular nongranular iron-formation; iron-formation; (6) (6) aa thin-bedded thin-bedded lithotope lithowpe consisting consisting of of laminae laminae to w very very thin lithotope. In nongranulai iron-formation; and (7) a ferruginous chert lithowpe. thin beds beds of of nongranular In general. general,lithotopes lithotopes 1, I. 2, 2. and the oxide (hematite) and have textural textural attributes attributes indicative of lhe (hematite) facies facies of of ironironand 33 contain contain primary ~rimarvhematite and formation. contrast. lithotope and has has textural attributes formation. In Incontra& lithowpe 66 contains contains appreciable appreciable carbonates or silicates and indicative carbonate facies of iron-formation. iron-formation. Lithotopes Lithotopes44 and and 55are areinterlayered interlayeredand andcontain contain indicative of the carbonate mixtures silicates, and thus were deposited in generally similar similar mixtures of of oxides oxides (hematite-magnetite) (hematite-magnetite)and silicates, sedimentological affected by by currents currentsand and at atdepths depthsintermediate intermediatebetween betweenoxides oxide: sedimenwlogicalregimes regimes in in waters watersvariably variablyaffected and of lithotope lithotope 77 isis uncertain. uncertain. It Irisis aa thin-bedded and carbonate carbonate facies. The Thesedimentological sediienwlogical significance of thin-bedded laminated laminated unit deposited in a deeper water regime as evidenced by a stratigraphic position transitional between between thin-bedded thin-bedded iron-formation iron-formation and overlying overlying p r i m w hematite. hematite. - - black shale; yet it contains primary Sedimentological Sedimentologicalparameters parameters imply imply that that Unit Unit A A was was deposited deposited during duringtwo twotransgressive-regressive uan&ressive-regressive cycles water 10 to the the north north and and east. east. Well-rounded Well-rounded grains grains cycles in in aa basin basin with with a strandline strandline to w the west and deeper wakr of lithotopes 1-5. imply that of the sedimentation of terrigenous temeenous quartz, auartz. which which persist nersist throughout ihroughout liihownes 1-5. much sedimentation occurred &curred relatively relativelyclose closeto w the the strandline. strandline. Although Although Unit unit A A in in the the Emily Emily district district has has many many mineralogical, mineralogical. textural, textural. and and chemical chemicalattributes attributes indicative of indicative of "ordinary" "ordinary" iron-formation, iron-formation. it locally locallv contains remains manganese manganese oxides oxides in in amounts amounts 10 10to to 100 100times times greater of 0.6 to Formation (Morey and greater than than the the norm normof w 0.8 percent in the Biwabik Biwabik Iron ~ronkormation and Morey, Money,1990). 1990). Manganese Manganese oxides oxides occur occur principally principally in in lithotopes 1-5 1-5 as disseminated grains, grains, as thin ihin pods or or lenses, lenses, and and as a layers layers as as thick thick as as 1.5 1.5 meters meters that typically typically contain wntain about about 10 10percent Mn; some some contain wntain as as much much as as20-30 20-30 percent percent Mn. Manganese Manganeseoxides oxidesare areparticularly particularly abundant abundant near Ruth Lake where two laterally persistent zones to the the 10-50 percent range. Both w 18 18 meters thick have manganese tenors enriched to Both zones zone zones about about 15 15 to more stratigraphic positions positions occupied occupied by by the the oolitic-pisolitic oolitic-pisoliticlithotope. lithotope. They Contain contain or less less coincide coincide with stratieraphic more or various psiomelane and and quanz. quartz. Goethite Goethite and and various proportions proponions of psilomelane and cryptomelane. cryptomelane, as well as hematite and manganite may be locally locallv abundant abundant-where wherethey theyoccur, occur. they they are are secondary secondary phases phases that that formed formed during during aa maneanite mav be " period period of of intense intense chemical chemical weathering weathering that modified modified these rocks rocks in in Late Late Jurassic ~ u k s ior or c Early Early Cretaceous Cretaceoustime. time. 75 75 �The origin. They Themanganese manganese oxides oxides are are most most likely epigenetic eqigenetic in origin. They are are confined to the porous and permeable permeablepails pansof ofUnit UnitA; A,rocks rockswith withthe thegreatest greatestprimary primary porosity—such porosity~suchas as quartz q u m arenitic areniticrocks rocksin inthe the epiclastic lithotope and the oolitic-pisolitic lithotope-.-.-have the most manganese. Morey and others (1991) others (1991) epiclastic lithotope and the oolitic-pisolitic lithotopeÑhav the most manganese. have have suggested suggested that that the themanganese manganesewas was deposited deposited by by aa refluxing refluxing process process involving involving reducing reducingsolutions solutionsthat that leached North range. range. The the Nonh Themanganese manganese was was subsequently subsequently precipitated precipitated leached manganese manganese from older older rocks mcks of the where depositional basin just where the the reducing reducing solutions solutionscame came into into contact contact with oxidizing oxidizing conditions in the depositional below themanganese manganesemust musthave havebeen beenprecipitated precipitatedearly earlyin inthe the below the the sediment-water sediment-water interface. interface. Much Muchof ofthe diagenetic porn spaces normally normally filled with silica the iron-formation, iron-formation, because because texturally it occupies pore diagenetichistory history of of the cement. cement. Mesozoic redistributionof ofmanganese. manganese. The The abundance of of Mesozoic weathering weathering of the rocks mcks caused some redistribution manganese theRuth RuthLake Lakearea areain inthe theEmily Emilydistrict districtaa potential potential target target for for in-situ in-situ mining mining techniques techniques manganesemakes makesthe currently and the theMineral MineralResources ResourcesResearch ResearchCenter Centerofofthe the currentlybeing beingdeveloped developedby by the theU.S. U.S. Bureau Bureauof ofMines Minesand University University of of Minnesota. Minnesota. l'his Diversification Thisproject projectwas wassupported supportedin in part pan by by the the basic basic research component of the Minerals Diversification Program, theMinerals Minerals Cooniinating CoordinatingCommittee Committeefor for the theMinnesota Minnesota State State Legislature. Legislature. Program, administered administeredby by the REFERENCES REFERENCES CITED CITED Chandler, Chandler, V.W., V.W.,and and Malek, Malek, K.C., 1991, 1991,Moving-window Poisson analysis of gravity and magnetic data from the Penokean orogen, east-central p.p.123—132. 123-132. from the Penokean omgen, east-centralMinnesota: Minnesota:Geophysics, Geophysics,v.v.56,56, Morey, Morey, G.B., G.B., and and Morey, Morey, P.R., 1990, 1990, Major Major and minor minorelement elementchemistry chemistryof of the the Biwabik BiwabikIron IronFormation Formation and and associated associatedrocks, rocks,Minnesota, Minnesota,ininAIME, AIME,Minnesota MinnesotaSection, Section,163rd 163rdAnnual AnnualMeeting, Meeting,and andMining Mining Symposium, Symposium,51st, 5lst. 1990. 1990, Proceedings: Proceedings: University University of Minnesota, Minnesota, Duluth, Duluth, Continuing Continuing Education Education and and Extension, p.p.259—287. Extension,Center Centerfor forProfessional ProfessionalDevelopment, Development, 259-287. Morey, Morey, G.B., G.B., Southwick, Southwick, D.L., and and Schonler, Schottler, S.P., S.P., 1991, 1991,Manganiferous zones in the Early Early Proterozoic Proterozoic iron-formation Range, east-central east-centralMinnesota: Minnesota: Minnesota iron-formation in in the Emily district of the Cuyuna Iron Range, Geological 42 p.p. Geological Survey SurveyReport Reportof of Investigations Investigations39, 39.42 Southwick, Southwick, D.L., D.L., Morey, Morey. G.B., G.B., and and McSwiggen, McSwiggen, P.L. 1988, 1988,Geologic Geologic map (scale 1:250,000) 1:250,000) of of the the Penokean text: Minnesota Penokean orogen, omgen, central central and eastern Minnesota, and accompanying text: Minnesota Geological GeologicalSurvey Survey Report 25 p.. Invesligations37, 37.25 p.,11p1. pi. Reportof of Investigations w E Back ramp platform litholopes Ramp hMrashett basin wave ag.Iated Solo.. fa,.weaiher wave base Low energy e,alor. 050 ,a1wy flyer ood ,.se 00a1s Figure Figure 1. 1. Schematic Schematicprofile profile of of lithotopes lithotopes in the Emily district. No No vertical vertical or or horizontal scale scale intended. intended. Environmental Phanerozoic limestone-shale sequences. Environmental nomenclature nomenclature is is typical of that used in Phanemzoic sequences. 76 �PICK LAKE ZINC—COPPER—SILVER ZINC-COPPER-SILVER DEPOSIT DEPOSIT IAN R P.. MORRISON, MINNOVA MINNOVA INC. INC. The Pick Lake massive sulphide The sulphide deposit is is situated situated 20 20 kin east of of Thunder Thunder Bay, Ontario Ion east north of Schreiber, Schreiber, 145 145 kin and km from Minnova's Ninnova's Winston Winston Lake Lake mine. mine. nd 1.5 1.5 1cm The deposit occurs 1000 meters stratigraphically below The of the Winston Lake Lake deposit deposit at the the the base of of a sequence sequence of calc—alkalic volcanics and sediments. calc-alkalic sediments. First indications of the deposit came in 1984 when Minnova drill tested a weakly the within a zone mineralized horizon horizon zone of strong hydrothermal alteration. Drill hole hole WL-9 WL—9 intersected 0 0.3 meters of massiv massive alteration. .3 meters clastic of altered pyrrhotite within a thick sequence a thick sequence clasti weakly sediments and intentiediate sediments intermediate to to felsic ash which was weak1 mineralized with zinc. zinc. Subsequent drilling down dip led to t the discovery of thin but high high grade grade massive massive suiphides. sulphides. Exploration Exploration drilling has continued to systematically test the Pick Lake deposit at depth and has defined a steeply plunging sheet with a strike length of 400 meters, dip length of less than 22 1400 meters but an average of 1400 average thickness thickness less than meters. In 1990, drill hole WL—67 meters. WL-67 intersected 13.4 13.4 meters of of massive sulphides grading 2.6% 2.6% Cu, 26.0% 26.0% Zn and 106 106 g/t Ag at at a a vertical depth of 1050 1050 meters. meters. Drilling to to date at Pick Pick Lake totals 27,000 36 holes. holes. 27,000 meters meters over over 36 — — - — — — - - Core and poster poster display: display: regional geological map of N. regional N. W. W. Ontario geological map of the Winston Lake property geological the 1:2000 section (Pick 1:2000 composite section (Pick Lake Lake stratigraphy) stratigraph 1:2000 1:2000 longitudinal section section (Pick (Pick Lake Lake deposit) deposit) surface surface geology map of the the Anderson showing showing (Pick (Pick Lake) Lake) core representative of the fringe mineralization mineralization core core representative of thin massive suiphides core sulphides massive massive sulphide intersection intersection WL—67 WL-67 sample sample suite of Pick Pick Lake Lake stratigraphy stratigraphy 77 �PLATINUM GROUP PLATINUM GROUP ELEMENT ELEMENT POTENTIAL POTENTIAL OF OF KEWEENAWAN INTRUSIVE INTRUSIVE ROCK IN WISCONSIN KEWEENAWAN H.G. Jr., Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 M.G. Itudrey. Hudrey, Jr., Mineral Point Mineral Point Road, Road, Madison, Madison, Wisconsin Wisconsin 53705, 53705, and and Bruce Bruce A. A. Brown, Brown, Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Mineral Point Mineral Point Road, Road, Madison, Madison. Wisconsin Wisconsin 53705 53705 ABSTRACT ABSTRACT > Whole Intrusion, Sawyer Whole rock rock analyses analyses of of platinum platinum in in the the Round Round Lake Lake Intrusion, County, County, Wisconsin Wisconsin discloses discloses platinum platinum enrichment enrichment with with increasing increasing iron iron and and titanium accompanied titanium accompanied by by decreasing decreasing paladium. paladium. Anomalous chromium and and vavanadium nadium also also correlate correlate with with iron iron and and titanium. titanium. The Round Lake Intrusion Intrusion is is known known only from boreholes and geophysgeophysical data. It is at least 88 km long long and 22 2 2 km wide and is inferred to to exextend to a depth of of 1400 1400 mm (Roder, (Roder, 19773; 19773; Stuhr, Stuhr, 1976). 1976). Diabasic olivine olivine gabbro and troctolite occur at at the the margin of an an oxide-rich core of of the the trough-shaped intrusion. Dominant trough-shaped Dominant minerals are olivine, plagioclase and and titanomagnetite in titanomagnetite in various various proportions. proportions. In the core of of the the intrusion, intrusion, olivine olivine and and plagioclase plagioclase crystallized crystallized early early and and iron-titanium iron-titanium oxides oxides cryscrystallized tallized late. late. The core of of the the intrusion intrusion consists of a magnetitite unit unit of 12 to to 26 26 percent clusters clusters of of oxide oxide and and silicates, silicates, 9-15 9-15 percent percent olivine, 2-10 2-10 percent percent plagioclase, plagioclase, 54 54 to to 72 72 percent percent titanomagnetite titanomagnetite and and less than An50;; titanomagnetite titanomagnetite less than 3 3 percent percent ilmenite. ilmenite. Plagioclase is An averages Usp50 contains 1.3 1.3 percent percent VV on. 0. 50~ommercial Commercial poaverages Mt Mt U s p and contains potential of the Re vanadium-rich ecause ilmenite-ulvospinel vanadium-rich core core is is limited limited because ilmenite-ulvospinel intergrowths are are narrow, narrow, and and ultra-fine ultra-fine grinding grinding would would be required for for beneficiation. However, However, added beneficiation. added values from from platinum group elements may alter alter the the economics. economics. Pt ppb RL-Ol-O316 RL-01-0316 RL-05-O557 RL-05-0557 RL-Ol-0324 RL-01-0324 RL-09-1190 RL-09-1190 RL-09-1179 RL-09-1179 RL- 01-0184 RL-01-0184 RL-05-0320 RL-05-0320 RL-02-0078 RL-02-0078 RL-10-0386 RL-10-0386 ' diabase <5 ,.. ,, , <. . C5 diabase dibase 7 dibase ~ 7 * .,. - . diabase 8 diabase 8 magnetite/troctolite 11 11 lower magnetite/troctolite lower rnagnetite/troctolite lower magnetite/troctolite 30 30 Magnetite/troctolite 75 Magnetite/troctolite 75 magnetitite 106 magnetitite 106 magnetitite 116 116 magnetitite magnetitite 120 magnetitite 120 ,- PcI Co Cr V ppb ppm ppm ppm 38 103 41 35 28 29 54 105 155 142 189 35 94 50 408 478 391 609 1050 na na na >2000 1 3 3 4 1 5 170 349 790 541 2420 2530 2820 Stuhr, Stuhr, S.W., S.W., 1976, 1976, Geology of of the the Round Round Lake Lake Intrusion, Intrusion, Sawyer Sawyer County, County, Wisconsin: unpublished unpublished M.S. M.S. thesis, thesis, University University of of Wisconsin-Madison, Wisconsin-Madison, 148 148 p. P. 7Q 78 IntruRoder, D.L., 1973, 1973, The petrology petrology and and chemistry chemistry of of the the Round Round Lake Lake Intrusion, sion. Northwest Wisconsin: unpublished unpublished H.S M.S. thesis, University of of Wisconsin-Madison, Wisconsin-Madison, 115 115 p. p. U j �The The Porcupine P orcupine Mountains M ountains Michigan aarea, rea, M ichigan vvolcano? olcano? -- aa Keweenawan K eweenawan I central central ." byY b S.W. Nicholson.K.J. K.). Schulz. Schulz, W.F. W.F. Cannon. and L.G. L.G. Woodruff S.W. Nicholson. Cannon, and Woodruff U.S. VA. 22092 Survey, National Center -- MS MS 954, 954, Reston, Reston, VA. 22092 U S . Geological Geological Survey, National Center Although to the system is mostly mostly basaltic Although magmatism magmatism related related to the Midcontinent Midcontinent rift rift system basaltic composition, intermediate and about 10 of the the composition, intermediate and felsic felsic rocks rocks comprise comprise about 1 0 ttoo 15% 15% of volcanic region. Locally, and felsic volcanic section section iinn the the Lake Lake Superior Superior region. Locally, intermediate intermediate and felsic rocks dominate the Porcupine area of rocks dominate the the volcanic volcanic suite, suite. as as they they do d o in in the Porcupine Mountains Mountains area of northern Michigan. Michigan. The Porcupine Mountains Mountains area area iiss aanomalous northern T h e Porcupine n o m a l o u s in the the Midcontinent rift rift system system not not only of felsic Midcontinent only because because of of its its abundance abundance of felsic rocks rocks but but also also because of of the coincidence of of two low and -- aa gravity gravity low because the coincidence two geophysical geophysical anomalies anomalies and aa magnetic low -- superimposed broader magnetic In addition, 1). magnetic low -superimposed on on a broader magnetic high high (Fig. (Fig. 1). addition, the abundant abundant rhyolite rhyolite and rocks form partial ring ring ooff topographic the and intermediate intermediate rocks form aa partial topographic highlands making making up the structurally complex complex and felsic and apparently apparently folded highlands t h e structurally folded felsic volcanic pile. For clarity, clarity, the the entire entire area area underlain by the the elliptical elliptical broad broad volcanic pile. For underlain by magnetic high the corresponding corresponding topographic topographic highlands) highlands) will will be called the the magnetic high (and (and the be called Porcupine Mountains Within this vvolcanic Porcupine M o u n t a i n s volcanic v o l c a n i c center. center. Within this o l c a n i c ccenter, e n t e r , the the Mountains themselves themselves make make up highlands, Porcupine PPorcupine o r c u p i n e Mountains up tthe h e northern northern highlands. Porcupine Peak forms forms the the western western highlands, and the the hills hills around around the firetower Bergland firctowcr Peak highlands, and the Bergland the southeastern southeastern highlands make up highlands (Fig. Earlier workers that this this make up the (Fig. 1). 1). Earlier workers suggested suggested that area is is aa remanent remanent of of an Icelandic-style central central volcanic (White, 1972; 1972; area an Icelandic-style volcanic complex complex (White. Green, Kopydlowski, 1983), but evidence supporting this suggestion has has 1983). but evidence supporting this suggestion Green, 1977; 1977; Kopydlowski. been largely To mapping, geochemical, this hypothesis, hypothesis, mapping. geochemical, been largely undocumented. undocumented. T o evaluate evaluate this isotopic, and and geophysical geophysical studies studies were were recently recently undertaken Porcupine isotopic, undertaken in tthe h e Porcupine Mountains area. area. Mountains Preliminary results of of mapping studies indicate indicate many Preliminary results mapping and and geophysical geophysical studies many similarities between Icelandic Icelandic central central volcanoes the inferred inferred Porcupinc Porcupine volcanoes and the similarities between Mountains center. For Porcupine Mountains Mountains volcanic volcanic center. For instance, instance, the the Porcupine Mountains center center formed formed at the rift zone 40km kmwide, wide,comparable comparable in in size size at the edge edge of of an an active active rift zone and and is is about about 30 30 to to 40 to Icelandic Icelandic central central volcanoes. volcanoes. Earlier that an accumulation accumulation to Earlier workers workers recognized recognized that felsic and intermediate of rocks, called the the 'unnamed" lensof felsic intermediate rocks, "unnamed" formation, formation, formed formed a lensshaped body body underlain underlain by the the northwest-dipping Lake shaped northwest-dipping basalts basalts of of the t h e Portage Portage Lake Volcanics (Fig. 1). The "unnamed' formation formation iiss being formally formally named named the Volcanics (Fig. 1). T h e "unnamed" the Porcupine Volcanics review). This formation Porcupine Volcanics (Cannon (Cannon and and Nicholson, Nicholson, in review). This formation is is more more than thins away than 2 2 km km thick thick at its its thickest thickest but but thins away from from the the Porcupine Porcupine Mountains Mountains area. area. The T h e thickness t h i c k n e s s ooff the t h e overlying o v e r l y i n g Copper C o p p e r Harbor H a r b o r Conglomerate C o n g l o m e r a t e decreases decreases substantially over the Porcupine Porcupine Volcanics. substantially o v e r the Volcanics. Recent mapping mapping hhas the southern southern highlands highlands Recent a s shown shown that that much much rhyolite rhyolite in the occurs as flows of intermediate occurs a s subvolcanic subvolcanic bbodies o d i e s that that intrude intrude flows intermediate composition. composition. These rhyolites porphyritic, containing both quartz quartz and feldspar These rhyolites are a r e commonly commonly porphyritic, containing both feldspar phenocrysts. Near the Porcupine Volcanics southern highlands, highlands. hcnocrysts. Near the top top of o f the the Porcupine Volcanics in the the southern ann extrusive small feldspar feldspar phenocrysts. In extrusive rhyolite rhyolite body contains contains mostly mostly small phenocrysts. In contrast, rhyolite bodies bodies in the northern highlands highlands are extrusive flows. ntrast, most most rhyolite the northern a r e extrusive flows. However, typically massive massive aphyric aphyrie flows flows oor owever. these these rhyolites rhyolites are a r e typically r they they may may contain contain only Understanding the u a r t z phenocrysts. phenocrysts. Understanding t h e cchemical hemical nly ssparse p a r s e feldspar f e l d s p a r ±Â qquartz relationships among rhyolite bodies in the Porcupine Porcupine Volcanics awaits the relationships among the t h e rhyolite Volcanics awaits the results of of detailed geochemical studies. results detailed geochemical studies. Gravity modeling modeling across across the center requires Gravity the Porcupine Porcupine Mountains Mountains volcanic volcanic center requires the the presence stock to felsic stock presence ooff a felsic t o account for the low low gravity anomaly beneath the the 79 �Portage Lake Volcanics Magnetic high (ft j_. Strike and dip /0 Gravity (in mgals) II Magnetic low GEOPHYSICAL ANOMALIES 1Vpl1I a km 10 sedimentary rocks x -la w n n 3 C V Z-C: C 0) m Â¥*- 4-1 *<-xu .P- w'n Â¥*->0) sm 0Q C m E c 0 0 I-<->-= w m 0 .- .- - \ Â¥I-' - 0 3 C.£m Â¥*- 0 a%- 0 s %-Â¥I0 0-7 C> > W -c Â¥*- .- s- c-0 C -3 C. 0 u I . part of the upper location of Porcupine Mountains volcanic center in the northwestern Volcanics coincide with an peninsula of Michigan. -a C m w .- cr s - 0 % wQ- 0 Â¥IC w w-c: u Â¥*- I à .- - L_ L I m L. L W C (L- c±i L_ C 0 Lt 0 I Â¥! L... .- CL The topographic highlands of the Porcupine low and gravity low anomalies coincide and elliptical magnetically high anomaly. Smaller magnetic are superimposed on the middle of the magnetic high. FIG. 1: Map showing -S.-' 5 1 Keweenawan Lillill Porcupine Voicanics [Vs EXPLANATION GEOLOGIC UNITS ____ m LC[ 0 _ w =, (0 �A felsic volcanic also is is consistent volcanic center center (Kiasner (Kiasner and and Jones. Jones. 1989). 1989). A felsic stock stock also consistent with with inference of the The the coincident coincident low low magnetic magnetic anomaly anomaly (King, (King, 1987). T h e geophysical geophysical inference of the aa felsic felsic stock stock lying lying beneath beneath the the volcanic volcanic center center supports supports the the comparison comparison with with the Icelandic model of of aa central Icelandic model central volcano volcano overlying overlying aa shallow shallow magma magma chamber. chamber. interpretation in Numerous Numerous faults faults and and apparent apparent folding folding complicate complicate structural structural interpretation in highlands (in the Porcupine For this area. For example, example. in in the northern northern highlands (in the Porcupine Mountains Mountains Statee Wilderness Wilderness Area). Area). a a change change in in the the dip dip of of volcanic volcanic units units from from south south ttoo north north However, detailed detailed mapping led Hubbard (1975) 5 ) to to propose propose an an anticline. anticline. However. mapping indicates indicates that some individual ual stratigraphic stratigraphic units units cannot cannot be be traced traced across across the the proposed proposed fold. fold. different An n alternative alternative model model for for the the structure structure of of the the northern northern highlands highlands is i s that that different flow-dome (1-3 km rhyolite bodies may may represent represent individual individual small small (1-3 km wide) wide) flow-dome complexes, still intact, exes. some some with with carapace carapace breccias breccias still intact, and and possibly possibly localized localized along along aa Similar major caldera-bounding een c a l d e r a - b o u n d i n g fault. fault. S i m i l a r flow-dome f l o w - d o m e ccomplexes o m p l e x e s hhave a v e bbeen (Macdonald eett al.. in Iceland Iceland (Macdonald documented ented in in the the Torfajokull Torfajokull volcanic complex complex in al.. coincident the coincident area of 1990). Thus, Thus, we we suggest suggest that the elliptical area of highlands highlands and and the shape of of the volcanic shield, shield, although the original original shape geophysical sical anomalies anomalies reflect the the volcanic although it has been been somewhat somewhat modified modified by by post-rift post-rift compressional compressional deformation. deformation. share many The T h e Porcupine Porcupine Mountains Mountains volcanic volcanic center center appears appears ttoo share many similarities similarities off the with ith Icelandic-style Icelandic-style central volcanoes, but but aa more more complete complete understanding understanding o the structures along area e a will will require require careful careful interpretation interpretation of of structures a l o n g nearby nearby seismic seismic structural units of stratigraphic reflection flection profiles, profiles, detailed detailed correlation correlation of stratigraphic u n i t s and and structural isotopic aand of chemical, analysis nalysis within within the t h e center, center. and and careful careful analysis analysis of c h e m i c a l , isotopic nd volcanological data. ., : 7 data. References R eferences of stratigraphic stratigraphic Revisions in review, and and Nicholson, Nicholson, S.W., S.W.. in review, Revisions of northern Michigan. Michigan. Supergroup of of northern Keweenawan Supergroup nomenclature nomenclature within tthe h e Keweenawan U.S. Geological U.S. Geological Survey, Survey, Bulletin Bulletin 1970-A. 1970-A. region. Keweenawan plateau Green, 1977, Keweenawan plateau volcanism volcanism in in the the Lake Lake Superior Superior region. reen. J.C., 1977. p. 407-422. Geological Association Association of of Canada, Geological Canada. Special Special Paper Paper 16, 16, p. 407-422. Carp River Geology Hubbard, 1975, ubbard, 11.A., H.A., 1975, Geology of of Porcupine Porcupine Mountains Mountains in in Carp River and and White White v. 3. 3, U.S. Geological Pine quadrangles, Pine quadrangles, Michigan. Michigan. U.S. Geological Survey, Survey, Journal Journal of o f Research, Research, v. p. 519-528. quadrangle. River 1° Iron River Aeromagnetic map map of King, King, E.R., E.R., 1987, 1987. Aeromagnetic of the the Iron 10 xx 2° 20 q uadrangle. Miscellaneous Survey, Geological Wisconsin. U.S. G Michigan and Michigan and Wisconsin. eological S urvey, M iscellaneous Inverstigations Inverstigalions Series, Series, 1-1360-F. I-1360-F, 1:250,000. anomaly map map and Bouger gravity Klasner, J.S., 1989, J.S., and Klasner. and Jones, Jones. W.J., 1989, Bouger gravity anomaly and geologic geologic and Wisconsin. Wisconsin. Michigan and quadrangle, Michigan interpretation of of the Iron River the Iron River 10 10 xx 20 quadrangle, J-1360-E. Series. Miscellaneous G e o l o g i c a l Survey, Survey, M i s c e l l a n e o u s Ilnverstigations nverstigations S e r i e s . I-1360-E. U.S. Geological Cannon, Cannon, W.F., W.F.. 1:250,000. . 1:250,000. The Kopydlowski, opydlowski. P.J., 1983. Oak Bluff Bluff Volcanics. central P.J.. 1983, The Oak Volcanics. aa Middle Middle Keweenawan Keweenawan central thesis, unpublished M.S. M.S. thesis. region. Michigan. Mountains region, volcano; Porcupine Mountains Michigan. unpublished Michigan Michigan Technological Technological University. Houghton. Houghton. 88 8 8 pp. 1990. Macdonald, R., McGarvie, McGarvie, D.W., D.W.. Pinkerton, Pinkerton, H., H., Smith, Smith. R.L., R.L., and and Palacz, Palacz. Z.A., Z.A.. 1990. Macdonald, R., I. Petrogenetic evolution of o f tthe h e Torfajokull Torfajokull volcanic v o l c a n i c ccomplex. o m p l e x , IIceland c e l a n d I. 31, p. Journal of of Petrology. Relationship between the Relationship between the magma magma types. types. Journal Petrology, v. v. 31, p. 429-459. 429459. Quarterly eastern Iceland. volcano, eastern Walker, The alker, G.P.L., G.P.L.. 1963, 1963. The Breiddalur Breiddalur central central volcano. Iceland. Quarterly 119. p. p. 29-63. Journal Journal of the the Geological Geological Society Society of of London. London, v. v. 119, 29-63. White, hite. W.S., W.S.. 1972, 1972, The T h e base base of ofthe theUpper UpperKeweenawan, Keweenawan, Michigan Michigan and and Wisconsin. Wisconsin. U.S U S .Geological .Geological Survey Survey Bulletin Bulletin 1354-F, 1354-F. 23 2 3 pp. pp. 81 �PHYSICAL PHYSICALVOLCANOLOGY VOLCANOLOGY OF OF THE THEFOOTWALL FOOTWALL ROCKS AT ROCKS AT THE WINSTON LAKE LAKE MASSIVE SULFIDE DEPOSIT Steven A. A. Osterberg Osterberg Steven Geology Dept., Dept., Economic Economic Volcanological Volcanological Research Lab. Lab. 55812 University of of Minnesota—Duluth, Minnesota-Duluth, Duluth, MN 55812 Ian R. R. Morrison, Morrison, P7C lE7 Minnova, Inc., Thunder Thunder Bay, Bay, Ontario Ontario P7C 1E7 Footwall Footwall racks rocks at at the the Winston Winston Lake Lake massive massive sulfide sulfide deposit deposit consist of amphibolite grade, sequence consist of an amphibolite grade, hydrothermal].y—altered hydrothermally-altered sequence north—south trending of north-south trending volcanic volcanic and and volcaniclastic. volcaniclastic rocks. Geological mapping, drill drill core, core, and and petrographic petrographic studies studies allow allow dedeanalysis of of the stratitailed subdivision and volcanological volcanological analysis graphy. graphy. Thick (100—325m), to felsic felsic (100-325m), massive massive to to poorly—bedded poorly-bedded tuafic mafic to Thick volcaniclastic rocks rocks form form the the base base of the stratigraphy and are are bounded to the the west west by by granitic granitic intrusive intrusive rocks. rocks. Intercalated and suggest suggest the felsic pyroclastic rocks form marker horizons horizons and deposits thicken thicken southward. southward. The clastic rocks by l00—850m rocks are are overlain overlain to the east by 100-850m of interlayered felsic and maf Ic lava flows which, in general, interlayered felsic and mafic lava flows which, general, thicken southward. constitute 80% of the southward. Felsic flows, which constitute the succession, are quartz—feldspar—phyric, and rarely succession, quartz-feldspar-phyric, massive, massive, and rarely flow—banded and flow-banded and brecciated. brecciated. Mafic lava flows vary from massive to well-pillowed, and and aphyric aphyric to to feldspar-phyric. feldspar-phyric. Local mafic mafic and felsic dikes dikes are present near are present near the the south end of the sequence and are are thought thought to to represent represent feeders feeders to to the the lava lava flows. flows. is 75-200m thick Immediately above the lava flows a 75-200m Immediately above the lava flows is a thick sequence of pyroclastic Pumice-bearsequence pyroclastic and and volcaniclastic volcaniclastic rocks. rocks. Pumice—bearing to the north ing felsic felsic pyroclastic pyroclastic rocks predominate predominate to north with with The pyroclastic pumice size and content increasing northward. size and content increasing northward. rocks interfinger rocks interfinger to to the the south south with mafic-felsic volcaniclastic rocks. The volcaniclastic rocks. volcaniclastic rocks are locally locally transected transected by aa laterally limited (100—125n), but thick (150m), laterally (100-125m), (150m), succession of The maf mafic rocks are aphyric mafic lava flows, sills, and dikes. aphyric maf ic lava flows, sills, and ic rocks are thought to fill an axial trough, and to represent a feeder comfill an axial trough, and plex to to lavas lavas higher higher in in the the section. section. The flows vary from from maspeperites and sive to pillowed; peperites and cm—scale cm-scale sheet sheet flows are locally locally well-developed. The Winston Lake Lake Horizon Horizon caps caps the the footwall footwall sequence sequence and and mafic—felsic consists of 3—4 3-4 interlayered interlayered mafic lava lava flows and mafic-felsic volcaniclastic rocks rocks and and cherty cherty tuffs. tuffs. The lavas lavas are are aphyric, aphyric, laterally extensive southward. Vo].laterally extensive (>2km), (>2km), and and thicken thicken (2-BOrn) (2-80m) southward. Volcaniclastic rocks thickness and are caniclastic rocks and and tuffs tuffs vary vary from from l-20m 1-2Om in thickness are massive, to well-laminated. well—laminated. massive to The stratigraphy stratigraphy at Winston Winston Lake Lake developed developed with with cyclic cyclic accumulation of volcaniclastic accumulation volcaniclastic and volcanic volcanic rocks; lava flows flows In contrast, contrast, rift—related southward were derived from from aa rift-related southward source. In felsic pyroclastic pyroclastic rocks felsic rocks appear appear to to have have been derived from from an an unrelated northward northward source. source. The lack lack of hydrovolcanic or vesivesicular deposits volcanism prevailed suggests deep water cular deposits suggests water volcanism prevailed at at Winston Winston Lake. Lake. 82 �-- THE THE NEDA NEDA IRON IRON FORMATION FORMATTON—— AA PRODUCT PRODUCT OF OFVOLCANISM? VULCANISM? William Alexander St., Appleton, WI W i l l F. F. Read, Read, 1905 1905 14. N. Alexander WI 54911 54911 The Neda iron formation crops out along the east, south, and southwest flanks of the It lies at the top of the upper Ordovician Maguoketa shale and is Wisconsin Arch (Fig. 1). It reaches a maximum The formation is discontinuous. overlain by Silurian Mayville dolomite. thickness of about 12 meters. Downdip. sway from the arch, its extent is not well known. The Neda is characterized by an abundance of oblate spheroidal structures not more than These have generally been described as ooids, implying that they about 2 mm in diameter. originated by wave and current action on the aea floor. Near the village of Neda in eastern Wisconsin. the type locality, the formation was Two types of ore were fonnerly mined in small open cuts and shallow underground workings. in "soft recognized: &&gnized: "soft ore.' ore," in in which which the the "ooids" "ooids" are are weakly weakly cemented cemented together, together, and a "hard ore, Ore xt is is generally generally not not which which they they are are well well cemented. cemented. Hard ~ard ore Occurs occurs as as aa capping capping on on the the soft soft ore. ore. It more more than than aa meter meter thick. thick. My formation are based mainly on petrographic My ideas i d concerning i n c o m i n g the the origin origin of of the the Neda Neda formation Lakeside examination of 0 0 aa few r e thin h " sections i o n of Of hard hard ore ore from from the thetype locality. localit". Lakeside 70 7 0 was was used to 5y attach the rock to the slide. This cement, unlike epoxies, does not gelatinize in acids. soaking the section for several days in strong (6N) nitric acid I got rid of most of the hematite Removal of these ingredients did and linonite which makes an untreated section largely opaque. It appears that the iron oxide minerals are finely disseminated not leave holes in the section. through the host materi•ala in which they occur. Fig. Fig. 11 outcrop Outcrop of of Ordovician—Silurian ordovician-silurian boundary boundary in in parts parts of of Minmesota, HinnÇÈot Iowa, on down—dip aide Iowa, Illinois, Illinois, and and Wisconsin. wimconsin. Dots ~ o t sare o n the &--dip side of the the line. line. Areas Nçd formation formation is is exposed exposed are are stippled. stippled. The Ordovician—Silurian Ordovician-Silurian Ar-as where wh-r- Neda boundary Devonien; boundary is is overlain overlain in in places plat-s by by post—Siluriem post-Silurian sedisenta: sediments: 0 D — m vonian; C — carboniferous. Carbonirxrous. Geology, Geology, except except Weds ~ e d aareas, areas. from from U.S. U.S. Geological Geological Survey, Survey, Geologic Map Map of of the the United United States, States, 1/250,000, 1~250,000,1932. 1932. Geologic - - 0' 0-, �work has been done On thin sections of the Heda so far as I an aware, very little have contented oxides have been removed. Most workers formation from which most of the iron A rather detailed study of polished surfaces or acetateinpeels. themselves with the examination Neda was published 1934 by Hawley and Beavan (1). of the mineralogy of the Neda formation at mixture material obtained from a mining company —— presumably athem They worked mainly withThin crushed lisonite by soaking in a fragments were clearedexamined of hematite and of hard and of softnitric ore. and hydrochloric by transmitted light under a acid, then combination a mineral by petrographic methods was petrographic microscope. If the identification of checked it by powder X—ray diffraction. uncertain, and the mineral seemed important, they "ooids" alone are so varied and complex that it is not In the hard ore from Neda, the am convinced, however, that they were not formed easy to draw conclusions about their origin. I ooids in the usual sense of the term. It seems to by sedimentary processes and are therefore not volcanic origin. A volcanic me more likely that they are miniature accretionary lapilli of abundant transported origin is suggested by Hawley and Beavan's observation that 'the most They also obser-ved that the lava." fragments in the ore are rough, angular grains of scoriaceous I found to brown volcanic glass. cleared of iron oxides, im a "dirty, green lava, when of in ooids." They are not what I take to be volcanic glass mainly as nuclei fragments really glass Or some amorphous or open to question whether they are acoriaceous and it is crystalline material which may have been derived from glass. submicroscopically Hawley and meavan reject the idea that Where did this glass come from and how old is it? active when the Neda formation was deposited. They came from nearby volcanoes which were it from which the glassy fragments Were prefer a precambrian source to the "west or northwest" objection to a nearby, contemporary source I is transported by streams or marine currents. Their is recognized in this part of North America." that "as yet no igneous activity of such age The youngest their proposed alternative, think there is a much sore serious objection toaxis of the Wisconsin Arch) and northwest (the Precambrian volcanics to the west (along with only a very small percentage of whatever glsaa may present take Superior region) are Keweenawan. volcanics is likely to have escaped originally have been present in the Keweenawan Even if we assume that there was more devitrification as early as OrdovicisnSilurian time. fragments of it remain then than there is now, how could transported fleas in the geweenawan velsasics in the source area, alteration was actively apparently unaltered in the rieds formation while,formation, glassy fragments should be abundant progressing? one may also ask why, in the Neda more abundsnt in the source while fragments of crystalline lava, which certainly would have been Igneous activity of Pa,leozoic or later age may not have been recognized in area, are miasinq. in Hawley and meavan's day but now we have the the area where the Neds formation was deposited take Ellen kimberlite to remind us that there has, in fact, been post—Keweenawan volcanic Whether it extended down into the area where the Made was activity south of Lake Superior. deposited remains to be seen. Most of the •'ooids" in my thin sections show a thick costing of slightly anisotropic say be material surrounding any nucleus that may be visible. This, together with the nucleus, In "ooids" which lack a visible nucleus, the core consists regarded as the "core" of the "ooid." There is evidence Most of it is pale green or brown. entirely of the nearly isotropic material. Both varieties show imperfect green. that the brown variety was formed by oxidation of thevisible —— otherwise around what may be taken concentric lamination around the nucleus, if one is Light passing The laminae are most clearly ylsible XN. roughly as the center of the core. long dimensions of the laminae (and also, of course, at through them is polarized parallel to the guess in otherwise stra,n is that this is a result of My right angles to the long dimensions) . look as if they may betheparticles inclusions which isotropic material. There are abundant small long parallel to of volcanic ash, also platy or lath—shaped crystals which are elongatadin alternate shells around dimensions of the laminae. The material which forms cores also occurs the cores, material as was The same question may be asked concerning this slightly anisotropic core is it glass or some amorphous or sumicroscopically asked about certain nuclei in the "ooids': of which many shell fragments identified the material crystalline material? Hawley and seavan According to Ross and Kerr (2) , halloysite is a they observed consisted as halloysite. If the green or brown core submicroscopically crystalline clay mineral related to kaolinite. been weathered. The material which I observed is halloysite, it has presumably material I suggest that the material forming cores in weathered may very well have been volcanic glass. but composed of the same material, the "ooids" I observed, and shells separated from the cores lava onto nuclei which, in some cases, tiny droplets of liquid were formed by the accretion ofThe of droplets. I think, spread out over the rounded surface Thus are visible; in others, not. the previously accreted material which had had time to harden or become extremely viscous. imperfect lamellae were formed. Alternating with the shells of green or brown core material are shells composed of It is generally completely isotropic but may material which is transparent and colorless. The refractive showing low birefrimgence. contain very small, nearly equidimenaional crystalsthan the mean refractive index of core index I found to be close to 1.54. a little lower Scattered reflected present in it. commonlyclear material look tomato—red XN. material, opaque patches of iron oxide minerals are light from these patches makes a good deal of the adjoining in transparent, colorless shells as Hawley and Beavan identified the material which they found about 1.54They too found that it has a refractive index of colorless opal. transparent shells seems to have The mode of deposition, or emplacement, of the large Some of these shells were originally composed Of relatively been rather extraordinary. projecting from the - Euhedral outlines of these crystals may be seen In one case which I observed a shell of of thews inner and/or outer surfaces of shells composed euhedral crystal of the same material is present in crystals, mow paeudomorphs. this core type pinches out and a single, isolated. the shell was growing material a short distance beyond its tip. I see this as evidence that the direction of growth toward the isolated crystal, which is in line with it. What controlled lameliae in adjacent core is uncertain. Transparent, colorless sheila roughly perallel theof the core and of the "ooid' as This means that they also parallel the outer tension surfaces material, developed in core material of Possibly more or less evenly spaced zones of a whole. 84 �If these zones of tension were been entirely Composed. expected that they whic4 the "oojd" sees originally to have due to shrinksge as a result of etier cooling or dehydration it is to be would parallel the outer surface of the "ooid." crystals and show no pseudOmorphs of antecedent Many of the colorless, transparent shellscrystalline some ehells of this from the This other. were preeusably amorphous or sumnicroscopically each with of many very thin shells in contact start. type are clearly composites madeup a crack, which opened, was filled, and then reopened several may be the result of deposition in tines. idea, L. embraced by other workers, that the oblateness of the The I am doubtful about theis due to sediments. compreçsion under the load of overlying masses of "ooids" in the Neda formation structures a few cm in diameter which appear to be depositioflal surface, picking up soft ore contains cylindrical which rolled down an inclined flattened tangentially. material, mud—like in consistency, "Ooida" in these structures are If so. the additional material as they progressed. deposited. place before overlying sediments were indicating that the flattening took while the "ooids" were still soft and most likely cause of the flattening would be rapid rotation known as airborne. spheroidal bodies 1-10 mm in diameter surrounded by Kimberlites and kimberlitic ejects contain nucleus—Usually a sineral grain——is "pelletal lspilli." In these, some kind of a The latter often exhibits a poorly defined very fine—grained. optically unresolvable, material. lath—shaped sinerals with their long dimensions concentric structure and contains platy or parallel to the surface of the is present; otherwise This does parallel to the concentric layering, if thisthese bodies as quenched lava droplets. clement (3) originally explained lapillus. i attribute the concentric structure in concentric structure, however. suggested that accretion may also not eccouflt for their later to accretion, clement (4) lapilli it is not clear core material of Neda "ooids' of kisberliteS. concentric etructure in pelletsi of Neda ooids and also be responsible for the to account for the oblatenesssomehow initieted after whether the rapid rotation postulated numerous pellets1 lepilli was in progress during accretion or was accretion had ended, of pelletsl lapllli I do not features of Neda "ooids" with those produced the weda formation was In comparing certain volcanic activity which, in my opinion, mean to imply that the This is not an impossibility. the same as, or similar to, that which produces kimberlites. however. Many "ooids" in the Neda hard ore show evidence of deformation after the rlgld clear This caused solidified. shells had been emplaced but before core material had completely the fragments. accompanied by flowage of clear layers and displacement of by a later fragmentation of the of landing; (2) impact causes of deformation are (1) shock"ooids" material, Possible(3) and matrix; (4) compression viscous flow of the accumulated core volume of an 'ooid" core after landing; arrival Where deformation decreased the under the load of overlying sediments, was squeezed out into the surrounding matrix, ieces of pre—existing material have observed fragments of fossils, sand grains. Wd support the concept of a Many workers "ooids" serving, as nuclei in Neda ooids - — these occurrences sppear to volcanic crater near - L L. - a sedimentary origin, rather than a volcanic one. I suggest, however, that that normal marine intervals of quiescence, by sea water and AccretionarY lapilli will sea level may be filled, during be deposited in it. sediments containing the remains of organisms may of these Fragments when en eruption occurs. crater well as outside of, the fall inside, as be blown aloft by a subsequent L. lapilli, the sediments, and hard parts of organisms all may eruption. does not see likely, to me, that the Neda formation was deposited under water. as I propose, an aquatic land -- land which, to allow for occasional coaling. I think that deposition took place on It If temperature 'ooids" and the matrix was due to high the fluidity of core environment material in of deposition is ruled out because it would have caused rapid far above sea level. the crster of the source volcano, was not flooding I of sections. It surrounding "ooida" in my thin have looked et a good deal of the matrix by which may be bits of volcanic glass replaced contains many angular fragments, mostly opaque, fragments they saw were Hawley and Beavan saw a lot of these, too. However, the They are iron oxides. kinds. many of so by high temperature in scoriaceous; the ones I saw are not. There are other inclusions material, kept imbedded in what appears to have been fluid or plastic (?) replacement seems to have occurred, After hardening, a good deal of deuteric main purpose here is my opinion. description and interpretation of the matrix, My shall not attempt furthervolcanic origin, and I think it is sufficiently promoted by to promote the theory of consideration of the ooids" alone. Rr nmxN cr5 (1) (2) (3) (4) Ore of and A. P. Besvan. 1934. "Mineralogy and Genesis of the Mayville Iron American Mineralogist. vol. 19. p. 493—514. Wisconsin. "Halloyaite arid Allophane." U, s. Geological Survey, Ross. c. S., and P. F. Ierr. 1934. Profeapional Paper la5—G. p. 135—148, "Icisberlites fros the Mao Pipe, L.esOtho." Lesotho Kimberlites. Clement. C. R. • 1973. p. 110—121. Study of Some Major Icilaberlite Pipes in the Clement, c, IL, 1982. "A conparative Geological Ph.D. thesis. univ. of cspe Town. Northern cape and orange Free State." Hawley. .7. E., 85 �LITHOGEOCHEMISTRYAND ANDGEOLOGICAL GEOLOGICALMAPPING MAPPINGININ THE THE VERMILION VERMILION GREENSTONE BELT, LITHOGEOCHEMISTRY GREENSTONE BELT, MINNESOTA, AS AS AN MINNESOTA, AN AID AIDTO TOMINERAL MINERALEXPLORATION EXPLORATION Reichhoff, J.A., J.A., Hauck, Hauck, S.A. S.A. Reichhoff, Natural Resources ResearchInstitute Institute Natural Resources Research University ofofMinnesota-Duluth University Minnesota-Duluth Duluth, MN MN 55811 55811 Duluth, Southwick, D.L. Southwick, D.L. Minnesota Geological Survey Minnesota Survey 2642 University University Avenue 2642 Avenue St. Paul, Paul,MN MN 55114 55114 The Vermilion Vermilion greenstone greenstonebelt belt in northern tectonic The northern Minnesota Minnesota is aa complex complex tectonic assemblageofoflate late Archean volcanic and andsedimentary sedimentaryrocks rocksthat thatconsists consists of the assemblage Archean volcanic the where oreore has classic Vermilion Vermilion district, district, whereiron iron hasbeen beenmined mined for for more more than than a century, and its subsurface theglacial glacial cover. Several cycles and its subsurface extensions extensions to the the west west beneath beneath the cover. Several other than than iron iron have occurredinin the the belt of mineral mineral exploration exploration for forcommodities commodities other have occurred over the years, generally the most most intensive intensive of over generally without withoutsuccess; success; perhaps perhaps the of these these has has been in in the recognition that the the last lastdecade, decade, following the thegeneral general recognition the Vermilion Vermilion greenstonebelt belt isistectonically a part of the productive Shebandowan-Wawagreenstone tectonically a part of very the very productive Shebandowan-WawaAbitibi subprovince To assist assist industry with the Abitibi subprovinceofo fthe t h eSuperior Superiorprovince provinceofofCanada. Canada. To the difficult task of of conducting this poorly exposed difficult task conductingexploration explorationinin this poorly exposedregion regionofofMinnesota, Minnesota, the State has regional mapping mappingprojects projectsaimed aimedatatproviding providing the the geological, geological, has conducted conducted regional frameworkrequired requiredfor for mineral mineral potential geophysical, and and geochemical geochemical framework potentialassessment assessment and and The lithogeochemistry lithogeochemistry and andmapping mappingproject projectdescribed described here here is is strategic planning. planning. The within the Vermilion Vermilion designed to provide regional data on rock compositions compositions within greenstone be1 belt. greenstone t. Recent geological geological mapping, Recent mapping, supported supported by by detailed detailedaeromagnetic aeromagnetic mapping mapping and and shallow drilling in poorly exposed areas, has led to the recognition at least shallow drilling in poorly exposed areas, has led to the recognition ofof at three volcanic-sedimentary cycles in the belt. These Theseare: are: (1) volcanic-sedimentary cycles the Vermilion Vermilion greenstone greenstone belt. dominantly calc-alkaline calc-alkaline sequence aa dominantly sequence that that includes includesrocks rockssouth southofo fthe theMud MudCreek Creek and and Wolf Lake Lakefaults faults in the Vermilion district and the Bear BearRiver Riverfault fault in Vermilion district and southeast southeast oof f the dominantlytholeiitic tholeiitic sequence that includes northeast Itasca (2) aa dominantly sequence that includes rocks rocks northeast Itasca County; County; (2) a mixed volcanic sequence north and northwest of these faults; and (3) north and northwest of these faults; and (3) a mixed volcanic sequence (calc(calcalkaline and tholeiitic) ofofunknown stratotectonicaffinity affinity (in the and tholeiitic) unknown stratotectonic the "Virginia "Virginia horn") horn") that lies south of sequence (1) and is separated from it by intrusive granitic rocks lies south of sequence (1) and is separated from it by intrusive granitic rocks of the batholith. the Giants Giants Range Range batholith. Approximately 280 rock rock samples havebeen beencollected collectedfrom fromthese thesethree three volcanic Approximately 280 samples have sequences and analyzed for major elements, minor elements, and trace elements sequences and analyzed for major elements, minor elements, and elements (70 (70 Thesedata dataform formanan analyticallyconsistent consistentset set that that characterizes elements total). These elements total). analytically comparisons, facilitates comparisons, and facilitates the lithogeochemistry of the volcanic volcanicsequences sequences and Thedata data also also provide provide the correlations and correlations and petrochemical petrochemical interpretations of o fthem. them. The statistical background metal statistical background on on the the distribution distributionof of metalbackground background concentrations, concentrations, and and pathfinder elemental associations in in the pathfinder elemental associations the rocks rocks that isisnecessary necessary for formeaningful meaningful interpretation ofofthe have interpretation themore morethan than6,200 6,200 partial partialrock rockanalyses analysesthat that haveaccumulated accumulatec over the past andexploration explorationactivities activities in the the Vermilion Vermilior over past century century from from academic academic and greenstone be1 belt. greenstone t. Productsoof the lithogeochemistry lithogeochemistryproject projectwill will be: be: (1) (1) aa generalized generalized regional Products f the the central part shows geologic map map oof f the part ofofthe theVermilion Vermiliongreenstone greenstone belt beltthat that showssample sample locations for 70-elementrock rockanalyses; analyses;(2) (2)a acomputer computer file(electronic) (electronic) locations forthe the280 280 new new 70-element file file (electronic) (electronic) of data; (3) (3) aa computer of the the new new analytical analytical data; computer file of the the archival archival provides report that describes methodologies and analytical data; and (4) (4) a report that describes methodologies and provide: interpretations. 86 . U j J �THE NATURE NATURE AND SOURCE SOURCE OF MIDCONTINENT RIFT IGNEOUS ROCKS IGNEOUS ROCKS !1(ailT. Seçfrt1, ZeOT!E. fPetennan2 ant Scott tE. 'Thieben3 (Departmentof of ~geological a' A i4tmospfieric Sciences, lown LowaState State University, 'University,S^mes, Thnes Ifi IA ' 'Department e o l o tV w ~ f k T Sciences, V 2 500111 5001 fBrancfi S. geolbgica4TSurvey, yesleral Center, (Denver, Co 'Branch of Isotope Isotope,geology, (geology,V. 11.5. QeohgicdSurvey, '(Denver D e n w fahraf~enter, 'Denver, CO 80225 8022.5 (Department of geologicalsciences, 'University of Texps, J.ustin, 'IX 78712 Trace element and Nd-Sr isotopic data Midcontinent Nd-Sr isotopic data indicate indicate that the Keweenawan Midcontinent igneous rocks rocks originated originated from from both both mantle and crustal crustal sources sources with with mafic maficrocks rocks being being Rift igneous from the the mantle and and more more felsic felsic rocks rocks being being derived derived from fromthe the crust. crust. The Mineral derived from the occurrence of interlayed interlayed mafic mafic and and Lake intrusions near Mellen, Wisconsin, illustrate the intrusions with with mixed The bimodal felsic intrusions mixed mantle mantle and and crustal crustal origins. origins. The bimodal source source of igneous rocks explains the bimodal bimodal compositional distribution distribution of these Midcontinent Rift igneous and other other flood flood basalt province province rocks. rocks. and 1984; Dosso, Nd-Sr isotopic data for Midcontinent Midcontinent Rift Rift igneous rocks (Brannon, 1984; 1984; Paces and and Ben, Bell, 1989) 1989) plot in three largely separate fields on an Nd-Sr(T) 1984; Nd-Sr(T) diagram diagram with T ==1100 The three fields 1100Ma, Ma,suggesting suggestinglimited with limitedmixing mixingand andcontamination. contamination. The fields represent aa mafic mafic rock rock mantle field field surrounding surrounding Nd-Sr Nd-Sr values values of of zero, zero, and and lower lower and and represent fields for for more felsic felsic rocks. rocks. The mafic rocks rocks plot plot in the the field field upper crustal fields The Mineral Mineral Lake mafic by other Midcontinent rocks indicating an an origin origin from from slightly slightly depleted depleted defined by Midcontinent Rift mafic rocks or near chondritic mantle. mantle. The The Mineral Mineral Lake Lake felsic felsic rocks fall close to the crustal crustal fields felsic rocks. rocks. Some defined by other Midcontinent Midcontinent Rift felsic Some mixing mixing is indicated indicated by by the narrow narrow connecting the mafic isthmus connecting mafic mantle mantle field with with the the more more felsic felsic lower lower crustal crustal field. field. Spider diagrams Spider diagrams of of trace trace element element data data for for the the Mineral Mineral Lake Lake mafic mafic rocks rocks relative relative to to field for flood basalts at., 1984) 1984) indicates that the mafic mafic the calculated field basalts (Thompson (Thompson et al., rocks, and perhaps other Keweenawan mafic mafic rocks, rocks, are are contaminated. contaminated. Consequently, the Mineral Lake mafic rocks are derived derived from slightly depleted depleted mantle mantle contaminated contaminatedwith with material. Similar crustal material. Similar plots plots for for the the Mineral MineralLake Lake felsic rocks rocks indicates indicates they are are similar similar to felsic rocks mixed mantle mantle and and crustal crustal origin origin on on the the basis basis of of isotopic isotopicevidence evidence rocks with aa mixed (Thompson et et al., The felsic felsic melts melts were were probably generated by by heat 1984). The probably generated heat from from (Thompson al., 1984). upwelling mantle mantle melts melts of of the the type type which produced upwelling produced the the mafic mafic intrusion intrusion and and followed followed channels opened by by earlier earlier fast moving moving mafic mafic magmas. magmas. REFERENCES Brannon, J. J. C. C. (1 (1984) flows of the Keweenawan North 984) Geochemistry of successive lava flows Shore Volcanic Group. Ph.D. dissertation, Washington Group. Ph.D. dissertation, Washington University, University, St. Louis. 87 �Dosso, L. (1984) (1984) The nature of of the the Precambrian Precambrian subcontinental subcontinental mantle. mantle. Isotopic Isotopic study study (strontium, (strontium, lead, neodymium) neodymium) of of the the Keweenawan Keweenawan volcanism of the north north shore shore of of Lake Lake Superior. Ph.D. Ph.D. dissertation, dissertation, University University of of Minnesota, Minnesota, Minneapolis. Minneapolis. Paces, J. B. Paces, J. B. and and Bell, Bell, K. K.(1989) (1989)Non-depleted Non-depletedsub-continental sub-continental mantle beneath the Superior Superior Province Province of the Canadian Canadian Shield: Shield: Nd-Sr Nd-Sr isotopic isotopic and and trace traceelement element evidence Rift basalts. basalts. Geoch. Geoch. Cosmoch. Cosmoch.Acta, Acta, 53, 53, 2023-2035. 2023-2035. evidence from from Midcontinent MidcontinentRift Thompson, R. A., Hendry, G. 0. LL.and R. N., N., Morrison, M. A,, andParry, Parry,S. S. J. J.(1984) (1984)An Anassessment assessment of and mantle in magma genesis: an elemental approach. approach. of the the relative relative roles of crust and Phil. Trans. Trans. Roy. Soc. London LondonA, A, 310, 310, 549-590. 549-590. J J j Ij -A -A -A 88 -j �CORRELATION OF CORRELATION OF IGNEOUS IGNEOUS UNITS AT THE MINNAMAX MINNAMAX DEPOSIT, NE MINNESOTA DEPOSIT, NE Mark J. J. Severson Severson A. Hauck Steven A. Natural Inst. N a t u r a l Resources Resources Research Research Inst. University U n i v e r s i t y of o f Minnesota, Minnesota, Duluth Duluth The Minnamax Minnamax Cu-Ni situated within The Cu-Ni Deposit D e p o s i t (Babbitt ( B a b b i t t Deposit) D e p o s i t ) is is s ituated w i t h i n what has been informally been i n f o r m a l l y rreferred e f e r r e d tto o as as the t h e Partridge P a r t r i d g e River R i v e r intrusion i n t r u s i o n of o f the t h e Duluth Duluth Within are Complex (1.1 (1.1 Ga), Ga), northeastern n o r t h e a s t e r n Minnesota Minnesota (Figure ( F i g u r e 1). 1). W i t h i n tthe h e ddeposit eposit a re a wide vvariety types, and and hhornfelsed u l t r a m a f i c , and and ffootwall o o t w a l l rrock o c k types, o r n f e l sed a r i e t y of o f ttroctolitic, r o c t o l it i c , ultramafic, Many sspecific iinclusions n c l u s i o n s (both igneous(?)). p e c i f i c rrock t y p e s are ( b o t h sedimentary and and igneous(fl). Many o c k types are holes and can can grossly be ccategorized ccorrelative o r r e l a t i v e between between drill drill h o l e s and g r o s s l y be a t e g o r i z e d iinto n t o seven subhorizontal s u b h o r i z o n t a l troctolitic t r o c t o l i t i c units, u n i t s , three t h r e e types types of o f hornfelsed h o r n f e l s e d inclusions, i n c l u s i o n s , and and aa late late Also are units within ccross-cutting r o s s - c u t t i n g pegmatitic p e g m a t i t i c phase. phase. A l s o present present a r e ccorrelative orrelative u nits w i t h i n the the by detailed These correlative ffootwall o o t w a l l rrocks. ocks. These c o r r e l a t i v e rock r o c k units u n i t s were were iidentified d e n t i f i e d by detailed off 61 d drill holes are pportrayed on n nine rossrrelogging elogging o rill h o l e s (117,605' (117,605' of o f core) c o r e ) and are o r t r a y e d on i n e ccrosssections s e c t i o n s through t h r o u g h various v a r i o u s portions p o r t i o n s of o f the t h e deposit. deposit. off tthe att tthe Dunka Road Road Cu-Ni Cu-Ni DDeposit Most o h e rrock o c k uunits n i t s ddefined efined a h e Dunka e p o s i t ((located l o c a t e d tto o by Severson (1990) a are tthe h e immediate immediate SW of o f Minnamax) Minnamax) by Severson and and Hauck Hauck (1990) r e present p r e s e n t aatt Minnamax. However, However, the overall somewhat more more ccomplicated p i c t u r e at omplicated the o v e r a l l picture a t Minnamax is i s somewhat 1) ppinch-out and i n c h - o u t and tthan h a n Dunka Road Road due due to t o rock r o c k type t y p e changes changes that t h a t are a r e manifest m a n i f e s t by: by: 1) reappearance of specific marker-bed units, off reappearance of s p e c i f i c marker-bed u n i t s , 2) 2 ) ddown-strike o w n - s t r i k e ggradational r a d a t i o n a l changes o extent of some extremely horizons, uultramafic ltramafic h o r i z o n s , 33)) e x t r e m e l y limited l i m i t e d aareal real e x t e n t of some uultramafic ltramafic horizons, 4) g gradational r a d a t i o n a l changes changes in i n the t h e troctolitic t r o c t o l i t i c rock r o c k types t y p e s between between any any h o r i z o n s , and 4) some areas areas a pparticular marker hhorizon may ""disappear" two d drill two holes. r i l l holes. IIn n some a r t i c u l a r marker o r i z o n may d i s a p p e a r " and marker h horizon, may ""disappear" be rreplaced e p l a c e d by aanother n o t h e r marker o r i z o n , which in i n tturn, u r n , may d i s a p p e a r " llaterally. aterally. of tthese difficulties, of seven horizontal IIn n sspite p i t e of h e s e llocal ocal d i f f i c u l t i e s , aa gross g r o s s stratigraphy s t r a t i g r a p h y of horizontal are off (from bottom 2) a r e present p r e s e n t at a t Minnamax and cconsist onsist o (from b o t t o m tto o igneous uunits n i t s (Figure ( F i g u r e 2) augite heterogeneous, ssulfide-bearing Unit ulfide-bearing a u g i t e ttroctolite r o c t o l i t e and ttroctolite roctolite ttop): op): U n i t II - heterogeneous, with homogeneous ttroctolites with w i t h abundant sedimentary inclusions; i n c l u s i o n s ; Unit U n i t II I 1 -- homogeneous roctolites w ith a mottled present basal p picrite horizon SW Minnamax); Minnamax); Unit U n i t III 111 -- m ottled basal icrite h o r i z o n (II ( I 1 iis s p r e s e n t only o n l y in i n SW with augite anorthositic a n o r t h o s i t i c ttroctolite r o c t o l i t e tto o a u g i t e ttroctolite roctolite w i t h ccharacteristic h a r a c t e r i s t i c oolivine livine I oikocrysts o i k o c r y s t s (III (111 is i s present p r e s e n t mainly m a i n l y in i n SW S W Minnamax Minnamax and and is i s enveloped enveloped by by Unit Unit I tto o of NE); Unit mixed ttroctolite I V - mixed r o c t o l i t e and augite a u g i t e ttroctolite r o c t o l i t e (at ( a t tthe h e base or o r top t o p of tthe h e NE); U n i t IV Unit different U n i t IV I V in i n two d i f f e r e n t areas) areas) with w i t h aa basal basal ultramafic u l t r a m a f i c horizon h o r i z o n ("± ( "  ppicrite"); icrite"); anorthositic with Unit homogeneous a U n i t VV -- homogeneous n o r t h o s i t i c troctolite t r o c t o l i t e (gradational ( g r a d a t i o n a l contact contact w i t h Unit U n i t IV); IV); with basal ultramafic Units V I I -- homogeneous ttroctolites roctolites w i t h basal u l t r a m a f i c horizons horizons and U n i t s VVII and VII (more abundant abundant and tthicker (more h i c k e r ultramafic u l t r a m a f i c horizons h o r i z o n s in i n the t h e Bathtub B a t h t u b cross-section). cross-section). Specific horizons drill hole 2): : S p e c i f i c marker h o r i z o n s utilized u t i l i z e d in in d rill h o l e ccorrelations o r r e l a t i o n s iinclude n c l u d e ((Figure F i g u r e 2) "pocket p picrite", Unit and Unit U n i t III, 111, "± " picrite", p i c r i t e " , "pocket i c r i t e " , ttop o p ooff U n i t IIV V ((augite a u g i t e ttroctolite), r o c t o l i t e ) , and The ttroctolitic are commonly c cut tthe h e base of o f Units U n i t s VI V I and and VII. VII. The r o c t o l i t i c rrock o c k uunits nits a r e commonly u t by granophyric veins, bodies, and and p pegmatitic pyroxenite tthin hin g ranophyric v e i n s , hybrid h y b r i d hornblendite h o r n b l e n d i t e bodies, egmatitic p yroxenite Chlorine-rich drops which which c coat bodies (OUI (OUI -oxide - o x i d e ultramafic u l t r a m a f i c intrusions). intrusions). C h l o r i n e - r i c h drops o a t the the ccore o r e surface s u r f a c e are a r e common in i n the t h e OUI OUI and and ultramafic u l t r a m a f i c horizons. horizons. Several e enigmatic Units att I I a n i g m a t i c hornfelsed h o r n f e l s e d inclusions i n c l u s i o n s are a r e present p r e s e n t in in U n i t s VVII and VVII I) ggranular gabbro These are r a n u l a r gabbro a r e grouped grouped in i n two two categories c a t e g o r i e s which which include: i n c l u d e : 1) Minnamax. These tto o olivine o l i v i n e gabbro gabbro which which contain c o n t a i n crude crude ovoid-shaped ovoid-shaped plagioclase-filled p l a g i o c l a s e - f i l l e d zones zones granular oxide-rich olivine gabbro which which also and 2) g ranular o xide-rich o l i v i n e gabbro a l s o contains contains ((vesicles?), v e s i c l e s ? ) , and The llater plagioclase-filled hercynite). p l a g i o c l a s e - f i l l e d ovoids o v o i d s and and modally m o d a l l y bedded bedded magnetite (± ( h e r c y n i t e ) . The ater inclusion megascopically i n c l u s i o n ttype ype m e g a s c o p i c a l l y resembles resembles the t h e material m a t e r i a l present p r e s e n t within w i t h i n the t h e Colvin Colvin While these these two two iinclusion Creek ""Hornfels" area ((Smiles Creek H o r n f e l s " area 5 m i l e s SW SW of o f Minnamax). Minnamax). While n c l u s i o n ttypes ypes are exact nnature remains unknown. unknown. a r e rreadily e a d i l y ccorrelative o r r e l a t i v e between between drill d r i l l holes, holes, ttheir h e i r exact a t u r e remains - - 89 �j Interestingly, modally magnetiteisisalso alsopresent presentinin picritic picritic horizons modally bedded bedded magnetite horizons which occur occurat at the the same stratigraphic levels as which same stratigraphic as the the second second inclusion type. type. Anotherenigmatic enigmaticrock rocktype typeisis present present within within the the lower of the Another lower 50-100' 50-100' of the Virginia Formation This rock with the rocks. This Formation footwall rocks. rock is is generally generally concordant concordant with overall bedding trend, exhibits bedding trend, exhibits aa gradational(?) gradational(?) contact contact with with the thesurrounding surrounding sedimentaryrocks, rocks,and andgenerally generallyexhibits exhibits aa granoblastic sedimentary granoblastic texture; texture;the themassive massive sulfide ore sulfide ore is is restricted restrictedtotothe therock rocktypes typesabove above this this horizon. horizon. Preliminary petrography and andgeochemistry geochemistryindicate indicatethat that this petrography thishorizon horizoncontains containshornblende hornblende and and olivine (serpentinized), Cl contents (up (up to 1300 ppm) andand highhigh MGMGNumbers olivine (serpentinized),high high C1 contents to 1300 ppm) Numbers (10-20) whichare aresimilar similar to values (10-20) which values within within ultramafic ultramafic horizons, horizons, and and high high Cr Cr ppm)which whichare are much muchhigher higherthan than anything anything sampled within the contents (800-2300 (800-2300 ppm) sampled within overlying troctolitic troctolitic rocks. dateinfer infer that overlying rocks. These These date that this thishorizon horizonmay may represent represent either (chilled material?) or aa either aa metamorphosed early Keweenawan sill sill (chilled metamorphosed mafic flow within VirginiaFormation Formation- ---further further study on this this study on metamorphosed mafic flow within thethe Virginia horizon is is pending. pending. Severson, M.J., S.A., 1990, J., and and Hauck, Hauck, S.A., 1990, Geology, Geology, geochemistry, geochemistry, and and stratigraphy stratigraphy Severson, M. of a portion of the Partridge River intrusion, northeastern of a portion of the Partridge River intrusion, northeasternMinnesota: Minnesota: Natural Resources ResearchInstitute, Institute, Technical NRRI/GMIN-TR-89-11, Resources Research TechnicalReport, Report, NRRWGMIN-TR-89-11, Duluth, Minnesota, 240 p. p. Minnesota, 240 j j 11 <? LEGEND Â¥ -È PRTS- OUTLINES AREA OF PARTRIDGE RIVER TROCTOLITE SERIES PRGC - PARTRIDGE RIVER GABBRO COMPLEX Cu-Nl Dewails MINNAMAX DUNKA ROAD VETLEGS VYMAN CREEK - - MMAX - DR -- WL VC W t S tOU1) SECTION 17 17 LONGEAR LE LONGNOSE LN 22 SECTION ZS SKU0 SK -- J j j U j J CEOLIC MAP THE PARTRIDGE rIGURE GENERAL GEOLOGIC MAPorOF THE PARTRIDGERIVER RIVERft4TRUSIDN INTRUSION FIGURE 1I- GENERAL J 90 �'C 'e I II IV - / - - FOOTWALL / / v . I FOOTWALL I1 Ill .I V v ----- -- - - - DUNKA ROAD 15 MILES MILES k LOCAL BOY / TIGER BOY MINNAMAX/BABBIT SOUTHERN EDGE r rirt I ntrL45lon, uttranaf u ~ t r n n oc t i emtrusien, * - n,.nrpn-ti,n,I rr'n+n rt H 'rnl n MnI:r,4 Mn rrk 1 Qq [3 El Ni El R t L I Z El U I GENERALIZED! Strike—Length correLationoof najor Igneous Strike-length correlation f major Igneous units units within within the t h e basaL basal 3000 3000 fFt. t . of o f the t h e Partridge Partridge River River intrusion. intrusion. / -1- r- r ITt PARTRIDGE P A R T R I D G E RIVER R I V E R INTRUSIEN INTRUSION r- n aug!te troctolite, -troctolite, IiI1 = troctolite Sulflde-beorlng au@@ t r o c t o l l t ewth wlthp;crl-te plcrlteLoyers layers etc., etc. II = SutFide—becring northostic Ill Ill == 'Mottled' 'Mottled' onorthositic anorthosltlc troctotite, troctollte, IV I V==uugrte auQltetroctoUte, trOctoUte, VV = onorthosltlc oide VII == nnorthositic troctofltp, onorthositic troctoUte t r o c t o l l t e to t oou9ite a u v t etroctoUte, troctollte, OW DUI = oxide troctolrte, VI V I 8& VII UNITS' UNITSv FIGURE IGURE 2: 2: FOOTWALL -- ^ LONGNOSE) LONGEAR SECTION V1) 'v i r— WYMAN CREEK - Ià I in r r COOfl w+ -0" odd bdd nodal hdd �- THREE-DIMENSIONAL THREE-DIMENSIONALMODELLING MODELLINGOF OFTHE THEMAGNETIC MAGNETICANOMALY ANOMALY CENTRAL LAKE SUPERIOR CENTRAL SUPERIOR D. D. TeskeyY ABSTRACT ABSTRACT Two Two and and one-half one-half dimensional dimensional modelling modelling of the the central central portion portion of of Lake Lake Superior Superior has has been been carried carried out out using using the thehigh high resolution resolution aeromagnetic aeromagneticdata datacollected collectedby by the theGSC's GSC's Oueenair Queenairaircraft aircraftinin1987 1987 for for the theGreat GreatLakes LakesInternational InternationalMultidisciplinary MultidisciplinaryProgram Program on on Crustal CrustalEvolution Evolution(GLLMPCE). (GLIMPCE). Individual 2.5dimensional dimensional models modelsfor forprofiles profilesspaced spacedapproximately approximately10 10km km apart apartcan canbe becombined combined Individual2.5 using dimensional models. models. These Thesemodels modelsindicate indicate up up to to40 40km km of of using trigonal trigonal surfaces surfaces to to produce produce 33dimensional volcanic with the lower members volcanic flows, flows, with members having having reversed reversed magnetization, magnetization,similar similar to to the thelower lowerOsler Osier group. seismic group. These Thesemodels modelstend tendtotoagree agreewith withthe theinterpretation interpretationofofthethe seismicprofiles profilesshot shotinin1986 1986asas part part of ofthe theGLIMPCE GLIMPCEprogram. program. j J J j J 92 �MIDCONTINENT RIFT RIFT STRUCTURE MIDCONTINENT STRUCTURE INTERPRETED INTERPRETED FROM FROM THE GNI/ARCONNE GNI/ARGONNE SEISMIC SEISMIC DATA DATA SET SET M.D. L.D. McGinnis McGinnis M.D. Thompson Thompson && L.D. Argonne Argonne National National Laboratory Laboratory Argonne, IL 60439 60439 Argonne, IL M.G. M.G. Mudrey, Mudrey, Jr. Jr. Wis. Nat. Hist. Surv.. Sun., 3817 3817 Mineral Mineral Point Point Rd. Rd. Wis. Geol. Geol. & Mat. Madison, Madison, WI WI 53706 53706 C.?. C.P. Ervin Ervin Dept. Dept. of of Geology, Geology, Northern Northern Illinois Illinois Univ. Univ. DeKalb, 60115 DeKalb, IL IL 60115 Midcontinent rift rift structure structure is is interpreted interpreted from 2500 km of of Midcontinent orthogonally-oriented orthogonally-orientedseismic seismic profiles profiles located located in in Lake Superior Superior to to have have evolved evolved in in the the following following sequence: sequence: A) Localized Localized volcanic-filled al., 1990) and volcanic-filled basins basins first first developed developed (Hinze (Hinze et al., and later later coalesced coalesced to to form form the the main main axial axial rift riftbasin. basin. Volcanic Volcanic flows suggesting flows extruded extruded at at this this time time are are constant constant in in thickness, thickness, suggesting that that the the major major component component of of rift rift subsidence subsidence began began after after development development of of the the primary primary axial axialbasin. basin. B) The main main rift rift stage stage involved involved crustal crustal extension, extension, subsidence, subsidence,and and rapid rapid lava lava extrusion. extrusion. Lava Lava flows flows interpreted interpreted as as Portage Portage Lake Lake and and Osler Osier equivalents equivalents exhibit a pronounced fanning geometry towards exhibit a pronounced fanning geometry towards the the rift's rift's axis, axis, indicating extrusion into a rapidly subsiding basin. indicating extrusion into a rapidly subsiding basin. C) Volcanic Volcanic cessation cessation is is marked marked by by aa region-wide region-wide mixed mixed sediment-volcanic sediment-volcanic facies sequence from fades that that separates separates a lower, lower, dominantly dominantly volcanic sequence from an an upper upper sedimentary sedimentary series. series. D) D) Post-volcanic Post-volcanicsedimentary sedimentary basins basins developed, developed,reaching reachingthicknesses thicknessesofof7 71cm, km, or or more. more. E) Sediment Sediment basin ional event basin development development was was interrupted interruptedby byaacompress compressional event that that reactivated reactivated the the normal normal boundary boundary faults, faults, producing producing high-angle high-angle reverse reverse and and thrust thrust faults. faults. Faulting Faulting and and folding folding involved involved all all of of the the volcanics volcanics and and the the older older Oronto Oronto group group sediments. sediments. F) A F) A regional youngest regional unconformity unconformity developed developed and and is is overlain overlain by the youngest Keweenaw-age Keweenaw-agesediments. sediments. The clearly The geometry geometry and and location location of of several several major faults is clearly detailed detailed by by the the seismic seismic data data set. set. A southeast southeast extension extension of of the the Keweenaw Keweenaw Fault Fault from from the the Keweenaw Keweenaw Peninsula Peninsula is is strongly strongly corroborated. The Douglas Douglas Fault Fault must must parallel parallel the the southern southern corroborated. The shoreline, Keweenaw shoreline, juxtaposing juxtaposing its its southern southern dip dip against against the the Keweenaw Fault's Fault's northward northward dip, dip, and and probably probably dies dies out out near near the the Porcupine Porcupine Mountains. Mountains. Ebinger Ebinger (1989) (1989) described described a similar similar fault geometry in in the the Western Western Rift Rift System System of of East East Africa. Africa. AA shear shear fault fault or or accommodation accommodation zone zone is is imaged imaged on on the the northeast northeast side side of of White White Ridge, Ridge, which which acts acts to to separate separate aa dominantly dominantly thrust thrust fault fault regime regime to to the northeast from the high-angle reverse faults observed the northeast from the high-angle reverse faults observed on on White White Ridge. Ridge. Synthesis Synthesis of of the the structural structural features features imaged imaged by the the seismic seismic profiles profiles suggests suggests that that crustal crustal shortening shortening was was directed directed NW-SE NW-SE in in western western Lake Lake Superior Superior and and NE-SW NE-SWin in the the eastern easternlake. lake. AA net net N-S N-S 93 �-J component component of of crustal crustal shortening, shortening,as as argued argued by by Cambray Cambray (1988), (1988). could could explain explain the the fault fault and and fold fold geometries geometries observed throughout throughout the The Keweenaw Keweenaw Volcanics Volcanics behaved behaved as as aa single single "thrust" "thrust" the lake. lake. The sheet between sheet in in the the western western lake, lake, overriding overriding aa basal basal decollement decollement between Animikie Animikie and and pre-Portage pre-PortageLake Lake Volcanic Volcanic units. units. Tilted, Tilted, folded, folded, and and uplifted uplifted volcanic volcanic units units imaged imaged in in the the eastern eastern lake lake also also support support this this "thrust" "thrust" sheet sheet interpretation. interpretation. J REFERENCES REFERENCES CITED CITED Cambray, Caubray, F.W., F.W., 1988, 1988, AA Tectonic Tectonic Model Model for for the the Mid-continent Mid-continent Rift Rift System: Abstract Volume, 34th Institute on Lake System: Abstract Volume, 34th Institute on Lake Superior Superior Geology, Geology, Marquette, Marquette, MI, MI, p. p. 17. 17. Ebinger, Ebinger, C.J., C.J., 1989, 1989, Geometric Geometric and and Kinematic Kinematic Development Development of of Border Border Faults Faults and and Accommodation Accommodation Zones, Zones. Kivu-Rusizi Kivu-RusiziRift, Rift, Africa, Africa, TECTONICS, TECTONICS, v.8, v.8, no.1, no.1, pp. pp. 117-134. 117-134. J Hinze, , L.W. Hinze,W.J. W.J., L.W. Braile, Braile, and and V.W. V.W. Chandler, Chandler, 1990, 1990, AA Geophysical Geophysical U Profile Profile of of the the Southern Southern Margin Margin of of the the Midcontinent Midcontinent Rift Rift System System in in Western Western Lake Lake Superior, Superior, TECTONICS, TECTONICS, v.9, v.9, no.2, no.2, pp. pp. 303-310. 303-310. J j -3 j U j 1 U U U 94 J �REGIONAL REGIONAL STRATIGRAPHIC MODEL MODEL OF OF LATE LATECRETACEOUS CRETACEOUS SEDIMENTS SEDIMENTS AND AND THEIR THEIR RELATIONSHIP WITH WITH THE THEUNDERLYING UNDERLYINGPRE-LATE PRE-LATECRETACEOUS CRETACEOUS WEATHERING WEATHERING PROFILE PROFILE ALONG THE THE MINNESOTA RIVER VALLEY, ALONG MINNESOTA RIVER VALLEY, MINNESOTA. MINNESOTA. ThomasA.A.Toth, Toth, John Heine, and Thomas John J. Home, and Steven Steven A. A. Hauck Hauck ResearchInstitute Institute Natural Resources Resources Research University ofo fMinnesota-Duluth University Minnesota-Duluth Duluth, Duluth, MN 55811 MN 55811 The presence of pre-Late The presence of pre-Late Cretaceous Cretaceous residual residual kaolin kaolin deposits, deposits, and kaolinitic kaol ini tic Cretaceous Cretaceous non-marine non-marine and marine sediments sediments in in southwestern Minnesota Minnesota is is well welldocumented. documented. Current Falls, Current work work in in the thearea areafrom fromRedwood Redwood Falls, Mn. is being the detailed detailed regional Mn. to Fairfax, Fairfax,Mn. Mn. is being conducted conducted to understand understand the regional stratigraphic relationships pre-Late Cretaceous relationshipsofofthethe pre-Late Cretaceousresiduum residuum and and Late Late Cretaceous sedimentsthat that are are found found on on both both sides Cretaceous sediments sides of of the theMinnesota Minnesota River River valley. val 1 ey. in grade, grade, both both vertically The residual residual deposits deposits vary vary greatly greatly in vertically and and horizontally, from from kaolinite-rich kaolinite-rich to parent rocks to grus. grus. The The parent rocks for these these residual of factors residual deposits deposits consists consists of ofgranites granitesand andgneisses. gneisses. AA number number of influence the grade gradeof of this this residual These factors factors can influence the residual material. material. These can be be grouped grouped into into three threegroups: groups: 1)1)composition composition of ofthe theparent parent rock, rock,2)2)chemical chemical weathering weathering effects, effects, and and 3) 3) physical influences. influences. Presently, Presently, some some of these residual residual of these deposits are portland cement, and are used used in inthe theproduction productionofof portland cement, andmay maysoon soonbe be used used as filler ininlivestock as filler livestockfeed. feed. Overlying the pre-Late residual deposits Overlying pre-Late Cretaceous Cretaceous residual deposits is is aasequence sequence of kaolinites, siltstones, kaol inites, composed of kaolmnitic kaol initic sandstones, sandstones, siltstones, mudstones andlignite. lignite. These These sediments sedimentsare arediscontinuous, discontinuous, commonly commonly filling mudstones and filling topographic low areas areasin in the residual Secondarykaolinites kaolinites are topographic low residual deposits. deposits. Secondary are white to to light pisolitic. Near Near The The top of white lightbrown brown in in color, color,and and commonly commonly pisolitic. ofsome some sections kaolinites, aa pisolite sections of secondary secondary kaolinites, pisolitebench bench ofofiron-cemented iron-cemented material material is River valley, the kaolinites appear is present. present. In the the Minnesota Minnesota River thesecondary secondary kaolinites appear Late Cretaceous and overbank to occur occur in in Late Cretaceous stream stream channel channel and overbank deposits. deposits. The secondary kaolinitic material is presently presently being secondary kaolinitic material is being mined mined for use in the manufacture face-brick. manufacture ofof face-brick. secondary Late Cretaceous sedimentsoverlie overlie residual deposits, and Cretaceous sediments residual and and secondary secondary deposits, and are lignites, sandstones sandstones and shales, lignites, are composed composed oof f non-marine non-marine and and marine marine shales, and siltstones. Some the shale shale units ininthis Some o fofthe thissequence sequence are are considered considered to to be be ball significant. The ball clays, ball clays, clays,and and are are the themost most economically economically significant. The ball clays, which which are kaolinite in contain organic organic material, which are dominantly dominantly kaolinite in composition composition contain impart thethe sediments. impart aa light light gray gray totoblack blackcolor colortoto sediments.This Thispackage package of of Late Late Cretaceous sediments is is wide-spread Currently, Cretaceous sediments wide-spread ininsouthwestern southwestern Minnesota. Minnesota. Currently, the ball manufacture ball clays claysare areused used ininface-brick face-brick manufactureininMinnesota. Minnesota. Pleistocene glaciation and eroded erodedparts partsor or all all glaciationhas hassubsequently subsequently scoured scoured and of the sequence,resulting resultinginindeposition depositionof of aa thick thick blanket the Late Late Cretaceous Cretaceous sequence, blanket of till andandoutwash deposits cover cover till outwash material material ofo fvarying varyingthickness. thickness. Glacial deposits much the study study area, area, leaving the best for study along the the walls much ofof the best exposures exposures for study along of Rivervalley valley and andtributaries. tributaries. of the the Minnesota Minnesota River 95 �Initial observations concerning the stratigraphic model Initial Minnesota River valley andFairfax Fairfax include: Minnesota River valleybetween between North North Redwood Redwood and .; : , .>..*>., .:, .,.. , . I . 1 I I I I for the the The grade gradeof of the the primary 1. The primary kaolinite kaolinite isisdependent dependent upon upon the type type parent material. parent Thedegree degreeofofweathering weatheringofofthe thebedrock bedrock primarykaolinite kaolinite is The totoa aprimary This inconsistency inconsistencyisiseither eitherthe theresult resultoof differential inconsistent. This f differential removalbybyglacial glacial activity activity ororreflects thethe Late Cretaceous removal reflects Late Cretaceoustopography topography of the area. the area. 2. 3. The Thesecondary secondarykaol kaolinite is discontinuous andvariable variable in thickness 3. inite is discontinuous and thickness across the study area. across the area. 4. grain size 4. There is aa change change inin grain size and and texture texture ofofthe thesecondary secondary kaolinite from kaolinite from east east to to west. west. 5. Evidenceofoffluvial fluvial deposition includesthe thequartz, quartz, kaol kaolinitic5. Evidence deposition includes initicsupportedconglomerate conglomeratefound found thebase baseofofthe the secondary secondarykaolinite. kaolinite. supported atatthe Elevations of the Elevations the pisolite pisolitebench benchare areconsistent consistentalong alongCrow Crow Creek Creek andcan canbebeused used a time lineififthe thethick thick pisolitic pisolitic bench and as as a time line bench isisindeed indeed the result of laterization event. the ofthe thesame same laterization event. 6. 6. Cretaceous non-marine and marine marine shales rarely 7. The Late Cretaceous non-marine and shales are rarely preserved. Sedimentary structures and stratigraphic marker marker are are lacking. 8. 8. 1 I provide a fossils that would provide fossils 9. Organic Organic remains remainsare arefound foundininthe theform formofof carbonized carbonizedimprints imprints in in the 9. whichform formthe thelignitic lignitic material. Theseimprints imprints are are the shale, which material. These the Tree branches branches and and trunks trunks formed remainsofof leafs leafs and thin twigs. Tree remains and thin formed the nucleus for siliceous concretions with the woody material material since nucleus removed. removed. Theseobservations observationsare arebeing beingincorporated incorporatedinto into aa stratigraphic These stratigraphicmodel model for the the Minnesota River valley valley area. for theLate LateCretaceous Cretaceous sequence sequence inin the Minnesota River area. I I j I J J j J J 96 -J �I I I I I I I I I I I I CHEMISTRY CHEMISTRY AND AND METAMORPHISM METAMORPHISM OF OF AN AN ARCHEAN ARCHEAN PILLOW PILLOW BASALT BASALT Turriock A.C.(2), D.C. Turriock A. C. ( 2 ) , Karnineni Kamineni D. C. (l),MoGregor (1),McGregor H. R . (1) (I) (1) ( 1 ) AECL AECL Research, Research, Whiteshell Whiteshell Laboratory, Laboratory. Pinawa, Pinawa, Manitoba, Manitoba, ROE ROE lLO, 1L0, Canada. Canada. (2) ( 2 ) Geological Geological Sciences, S c i e n c e s , University U n i v e r s i t y of of Manitoba, Manitoba, Winnipeg, Winnipeg, R3T R3T 2N2, 2N2, Canada. Canada. Abstract Abstract In I n southeastern s o u t h e a s t e r n Manitoba, Manitoba, on on the t h e western western edge edge of of the t h e Superior Superior River greenstone Bird Province is aa r o v i n c e of of Archean Archean age, age, the t h e Bird River g r e e n s t o n e belt b e l t is Pillow basalts are rocks. of supracrustal small mall sub—province sub-province of s u p r a c r u s t a l rocks. P i l l o w b a s a l t s are aa lower stratigraphic ower s t r a t i g r a p h i c formation, formation, approx. approx. 22 km km thick, t h i c k , in i n aa sequence sequence olastic and volcanics felsic mafic and bimodal of of bimodal mafic and f e l s i c v o l c a n i c s and c l a s t i c metametasedimentary edimentary rooks. rocks. Two Two samples samples of of basalt b a s a l t have have been been analysed analysed (both ( b o t h core c o r e and and rim), rim), The dyke. cross—cutting plus a basalt, sheared plus The l u s aa sheared b a s a l t , p l u s a c r o s s - c u t t i n g dyke. basalt, are sheared the and compositions of the pillow cores, ompositions of t h e p i l l o w c o r e s , and t h e s h e a r e d b a s a l t , are Archean to other similar irnilar to other Archean tholeiites t h o l e i i t e s of of diverse d i v e r s e volcanic volcanic They arid to modern pillow tholeiites. formations, ormations, and t o modem p i l l o w t h o l e i i t e s . They have have flat f l a t EEl REE They are enriched in Nb-Zr-V they plot as E—MORB. patterns, and They are enriched a t t e r n s , and i n Nb-Zr-Y t h e y p l o t as E-MORB. in n C02 CO2 and and Sr S r compared compared to t o rims. rims. The rims of the pillows The r i m s of t h e p i l l o w s are a r e darker d a r k e r (abundance (abundance of of hornblende) hornblende) They are porphyroblasts. corranon garnet and contain and c o n t a i n common g a r n e t p o r p h y r o b l a s t s . They are enriched e n r i c h e d in in They also have Ca, Mn compared to cores. Fe+3, Fe, Mg, e+3, Fe, Mg, C a , Mn compared t o c o r e s . They a l s o have flat f l a t REE REE patterns, i n Nb-Zr-V Nb-Zr-Y and and Ti-Zr-V Ti-Zr-Y they t h e y plot p l o t outside o u t s i d e the t h e field field a t t e r n s , but b u t in of igneous rooks due to enrichment in Y. f igneous rocks due t o enrichment i n Y. The cross—cutting c r o s s - c u t t i n g dyke dyke is is an an andesite a n d e s i t e which which has h a s not n o t been been subject u b j e c t to t o the t h e alteration a l t e r a t i o n seen seenira i n the t h e rims r i m s of of the t h e pillow p i l l o w basalt. basalt. is distinct d i s t i n c t from from that t h a t of of the t h e pillow p i l l o w basalt, b a s a l t , as as magma is Its I t s primary primary magma shown shown by by enrichment enrichment in i n light l i g h t REE, REE, decreasing d e c r e a s i n g from from La La to t o Dy. DY. The The formations formations are a r e steeply s t e e p l y dipping, d i p p i n g , and and show show post-folding post-folding The shear s h e a r zones. zones. The alteration a l t e r a t i o n of of pillow p i l l o w rims r i m sisi sprercietarnorphic, premetamorphic, arid sheared basalt nd ddid i d nnot o t aaffect f f e c t tthe h e sheared b a s a l t or o r the t h e late l a t e dyke. dyke. During During cummington ite have overgrown ende and 1 sm, hornbl rnetamorph ~et.amorphisrri, hornblende arid cummingtonite have overgrown tthe h e 52 52 interpreted is This foliation 01 i a t i o n (main (main folding f o l d i n g event). event). This i s i n t e r p r e t e d as as indicating bathcii i t h i e probably from from tthe h e adjacent ad ~ a c t i n tbathoiit.hc i n d i c a t i n g that t h a t heat h e a t flow, flow, probably intrusion, i n t r u s i o n , continued continued after a f t e rdeformation. deformatio 97 I �Geochemistry Archean Rocks from the the Virginia Virginia Horn Horn area: area: Geochemistryof ofArehean Interpretations Preliminary Interpretations James JamesL. L.Welsh Welsh Department of Department ofGeology Geology Gustavus Gustavus Adoiphus Adolphus College College St. Peter, St. Peter, MN 56082 56082 Jayne Reichhoff Jape Reichhoff Natural Resource Resource Research Institute Institute University of Minnesota, Duluth Duluth Archean supracrustal rocks Archean supracrustal rocks exposed exposed in the the anticlinal anticlinal core core of of the the Virginia Virginia Horn Horn structure of the Mesabi Iron Range of northeastern Minnesota comprise a structure of the Mesabi Iron Range of northeastern Minnesota comprise a sequence of of folded foldedmetavolcanic metavolcanicand andmetasedimentary metasedimentary units, units, some some and and perhaps which are are tectonically tectonically stacked, stacked, and and into into which which are are intruded intruded a series all of of which series of small felsicporphyry porphyrybodies. bodies. A A major major through-going through-goingstructure, structure, the Pike gold-bearing felsic River faultlshear fault/shear system cuts this sequence. River sequence. Chemical Chemical analyses analyses for for major major and minor elements have been obtained for a suite of 66 samples representing suite of representing all all principal lithologies. lithologies. Metavolcanic rocks rocks of of the the area are Metavolcanic areprincipally principallyflows, flows,some some pillowed, pillowed, with with subordinate intercalated fragmental units. Major Majorelement elementanalyses analysesof of these these rocks rocks show them them to to range range in composition compositionfrom frombasalt basalt to to dacite, dacite, with with basalt basalt and andesite predominating. The major and minor element data suggest that that these predominating. these rocks rocks are are grouped into two two distinct distinct geochemical geochemical suites. suites. The The basaltic basaltic rocks rocks show show tholeiitic affinities and have flat lIFE REE patterns; patterns;the theandesitic andesiticand anddacitic daciticrocks rockshave havecaiccalcalkaline affinities and are REF. Rocks Rocks in in the the are somewhat somewhat enriched in the light REE. Gilbert and McKinley McKinleyareas areas appear appear to be tholeiitic, while those those in in the Biwabik Biwabik area are are calc-alkaline. The The nature natureof of the thefield Held expression expression of the transition between between these two suites is not yet clear, though though the the Pike River Fault may play a role. The felsic porphyries porphyries plot plot in in aa very very tight tight cluster around 70% Si02 and Na20 70% Si02 and 8% 8%Na20 +1(20. These rocks would appear to be more silicic than other dacite porphyries + K20. These rocks would appear to be more silicic dacite from the Vermilion District. These Vermilion District. These rocks rocks have have undergone undergonesericite-carbonate sericite-carbonate silicification. With alteration and the high 5i02 Si02values values might might suggest suggest secondary secondary silicification. of occasional occasional quartz quartz veins, however, there appears appears to be be little little the exception of however, there petrographic evidence for for secondary silicification. silicification. Likewise, the the consistent consistent 5102 S102 values of of the the various various samples samples would wouldseem seemtotorule ruleout out silica silicaintroduction. introduction. Perhaps the higher Si02 Si02 values, as as occur occur in these intrusives, might might be aa clue clue as as to to why why these bodies are auriferous, while similar-appearing similar-appearing dacitic dacitic bodies bodies with lower lower 5i02 Si02 contents contents elsewhere elsewhere in the the Vermilion District are are not. not. Greywackes range range from 55-70% 55-70%Si02, Si02, the the majority plotting as as "dacites", "dacitesn, suggesting possible derivation from the the calc-alkaline calc-alkaline portions portionsof of the thevolcanic volcanicpile. pile. The composition compositionofofthese these greywackes greywackes is is consistent consistent with greywackes throughout the Vermilion Vermilion District. 98 �ARCHEAN AND PROTEROZOIC PROTEROZOIC TECTONO-MAGMATIC TECTONO-MAGMATIC ACTIVITY ALONG THE ThE SOUTHERN SOUTHERN MARGIN OF THE THE SUPERIOR PROVINCE IN NORTHWESTERN IOWA, PROVINCE IN NORTHWESTERN IOWA, USA USA Kenneth B. E. Windom', W. W. R. R.Van VanSchmus2, Schmus2,Karl Karl B. E.SeiferO, Seifert', B. E. T. T. Wallin2, Wallin2,and R. R. R. R.Anderson3 Anderson3 Iowa State State University, University, Ames, IA ..24 'Department of of GeolQgical Geological and Atmospheric Sciences, Iowa IA 50010 50010 . 2Department 'Department of Geology, University of of Kansas, Kansas, Lawrence, Lawrence, KS KS 66046 66046 3Geological Survey Bureau, Bureau, Iowa Iowa Department Department of of Natural Natural Resources, Resources, Iowa Iowa City, City, IA 52242 'Geological Survey 52242 A A Precambrian Precambrian igneous igneous complex complex of layered layered ultramafic and mafic rocks occurs occurs within within the the basement of northwestern meters of of Phanerozoic Phanerowicsediments. sediments. northwestern Iowa Iowa beneath beneath approximately approximately 300 meters This layered layered series series has has been been named named the the Otter OtterCreek Creek complex. complex. It is is marked marked by by aa circular circular magnetic anomaly,one one of of several several that that lie lie north north and and west west of of an an inferred inferred suture that that has been magnetic anomaly, postulated Superior Province Province and and an an Early Proterozoic postulated as the boundary between between the Archean Archean Superior Proterozoic terrane. terrane. The layered layered series series is is tilted tilted steeply steeply to the the northwest; northwest; rocks rocks representing representing the upper upper portion of the by erosion or tectonic the original original magma magma chamber chamber have have been removed removed by tectonic processes. processes. A A block of banded iron formation, formation, itself itself intruded intruded by by lamprophyre lamprophyre dikes, dikes, isis contained contained within within the the layered sequence. fonnation/lamprophyre block has has undergone high-temperature igh-temperature sequence. The iron iron formation/lamprophyre metamorphism followed by a retrograde retrograde event. event. The banded iron formation formation was deposited deposited in a supracrustal supracrustal environment, then intruded incorporated into into a mafic magma by the the lamprophyre. lamprophyre. This assemblage assemblage was apparently apparently incorporated magma that that subsequently crystallized crystallized to to form form the the layered layered complex. complex. Radiometric dating of of the layered rocks subsequently and the lamprophyre, Ga and an NdISm isotopes, isotopes, yields yields an isochron of approximately 2.9 Ga lamprophyre, using using Nd/Sm of zero to slightly negative values. The lamprophyre and layered complex fall value eNd value zero to slightly negative The lamprophyre and layered complex fall on on the the same isochron and thus appear to be be essentially essentiallycoeval. coeval. Archean lamprophyre has been reported reported from the Superior Superior Province as having having been formed formed during during the closing stages of the the various various in both subprovinces. subprovinces. Trace element abundances abundances in both the lamprophyre lamprophyre and layered complex complex are are consistent with derivation from a primitive to partially depleted mantle and thus support the consistent with derivation from a primitive to partially depleted mantle and thus support the isotopic isotopic evidence. evidence. The alteration, similar to that seen The entire entire layered complex complex has undergone low-temperature alteration, We interpret the the high-temperature high-temperature rocks from fromArchean Archeangreenstone greenstone belts. belts. We in other other mafic mafic rocks metamorphism experiencedby by the the iron formation and lamprophyre to have occurred during metamorphism experienced formation and lamprophyre to during incorporation of these lithologies as incorporation into the mafic magma magma and the retrograde retrograde metamorphism metamorphism of resulting from the the same same event event that that produced prograde paragenesis of low-temperature minerals in the layered complex. complex. Although Althoughmost mostprimary primary phases phases were were replaced replaced with with secondary secondary phases phases istribution such as serpentine, chlorite, chlorite, uralitic uralitic amphibole, epidote, epidote, and albite, major cchemical redistribution does not appear to to have have affected affected these these rocks A younger Archean quartz monzodiorite gneiss gneiss occurs occurs near near the the layered layered complex, complex, but the known. The originally crystallized crystallized contact relations are not known. Themagma magma from which the monzodiorite originally 99 �formed formedatatapproximately approximately 2523 2523 Ma Ma(Van (Van Schmus Schmus et et al., al.,1987). 1987). AAmantle mantleseparation separationage ageofof2.9 2.9 Ga Gahas hasbeen beendetermined determinedfor forthis thisrock, rock,indicating indicatingthat thatititcould couldhave haveformed formedby bypartial partialmelting melting of of material materialderived derivedfrom fromthe thesame samemantle mantlerocks rocksthat thatproduced producedthe theOtter OtterCreek Creeklayered layeredcomplex. complex. Tectonic Tectonicuplift uplifttilted tiltedthe thelayered layeredigneous igneousbody bodyand andthe thequartz quartzmonzodiorite monzodioriteand andexposed exposedthem them erosion. totoerosion. Felsic F d s i cvolcanism volcanismoccurred occurredata tapproximately approximately1775 1775Ma Ma(Wallin (Wallinand andVan VanSchmus, Schmus.1988) 1988) and volcanics andcovered coveredthe theexposed exposedrocks. rocks. These These volcanicsyield yielda adepleted depletedmantle mantleseparation separationage ageof of2.7 2.7 Ga. area rsimilar in in age and stratigraphic position rhyolites Ga.They They e similar age and stratigraphic positiontoto rhyolitesfound foundinincentral centralWisconsin Wisconsin (Smith, (Smith, 1978; 1978;Van VanSchmus, Schmus, 1978), 1978),but buthave havebeen beenmore morestrongly stronglyaltered alteredthan thanthe theWisconsin Wisconsin rhyolites, rhyolites,being beingdepleted depletedininLILE LILEwhich whichresulted resultedinina acomposition compositionequivalent equivalent totokeratophyre. keratophyre. These PenokeanOrogeny Orogeny Thesevolcanics volcanicsmay mayhave haveformed formedininthe thewaning waningstages stagesof ofthe the1850-1900 1850-1900Ma MaPenokean oro rthey theymay maybe berelated relatedtotothe theproposed proposed1750 1750Ma MaCentral CentralPlains PlainsOrogeny Orogeny(Bickford (Bickford et etal., al.,1986) 1986) Analysis Analysis of ofthe thecombined combineddata dataindicates indicatesthe thepresence presenceofofprimitive primitivetotoslightly slightlydepleted depleted mantle mantlematerial materialto tothe thesouthern southern margin marginof ofthe theSuperior SuperiorCraton Craton at at approximately approximately 2.9 Ga. Ga. Varying Varying degrees degreesof ofpartial partialmelting meltingofofthis thismantle mantleproduced producedlamprophyric lamprophyricdikes dikesand andcontemporaneous contemporaneous mafic maficmagma magmabodies, bodies,including includingone onewhich whichcrystallized crystallizedtotoform formthe theOtter OtterCreek Creeklayered layeredcomplex. complex. The entire complex subsequently underwent low-temperature alteration, resulting The entire complex subsequently underwent low-temperature alteration, resultingmainly mainlyininthe the formation formationof ofhydrous hydrousminerals. minerals. Subsequent Subsequenttectono-magmatic tectono-magmaticactivity activityinvolving involvingpartial partialmelting melting ofofrocks rocksderived derivedfrom fromthe the2.9 2.9Ga Gamantle mantlesource sourceoccurred occurredininthis thisregion regionatatapproximately approximately2.5 2.5Ga Ga and and1.75 1.75Ga Garesulting resultingininaaquartz quartzmonzodiorite monzodioritepiutonic plutonicrock rockand andfelsic felsicvolcanics, volcanics, respectively. respectively. REFERENCES REFERENCES Bickford, Zeitz, history M.E., E., Van VanSchmus, Schmus, W. W.It, R.,and and Zeitz,1986. 1986.Proterozoic Proterozoic historyofofthe themidcontinent midcontinent =&ford, M. region region of of North North America. America. Geology, Geology,14:492-496. 14:492-496. Field Precambrian rhyolites rhyolitesand andgranites granitesininsouth-central south-centralWisconsin: Wisconsin: Field Smith, E. E. I.I. 1978. 1978. Precambrian Smith, relations relationsand andgeochemistry. geochemistry. Geological Geological Society Society of of America America bulletin, bulletin, 89:875-890. 89:875-890. Van southern Van Schmus, Schmus, W. W. R. R.1978. 1978.Geochronology Geochronologyofofthe the southernWisconsin Wisconsinrhyolites rhyolitesand and granites. granites. Geosciences Geosciences Wisconsin, Wisconsin, 2:19-24. 2: 19-24. Early and andmiddle middleProterozoic Proterozoic Van W. R., Bickford, Bickford, M. M. E., E., and and Zeitz, Zeitz, I.I. 1987. 1987. Early Van Schmus, Schmus, W. provinces InternationalLithosphere Lithosphere Program. Program. Edited Editedby by provincesin inthe the central central United United States. States. InInInternational A. A. Kröner. Kroner.American AmericanGeophysical GeophysicalUnion UnionGeodynamics GeodynamicsSeries, Series,17:43-68. 17:43-68. , . theArcheanArcheanGeochronological studies studies of of the Wallin, E. E. T., T.,and andVan VanSchmus, Schmus, W. W. R. R.1988. 1988. Geochronological Wallin, Geological Society of America Proterozoic transition, north-central United States. , , ..Proterozoic transition, north-central Un Programs, "Abstracts ~ b s t r a c twith with s Programs, 20:131. 20: 131. Li j — J J 100 -4 �I STRUCTURAL STRUCTURAL ANALYSIS ANALYSIS OF OFTHE THEMIDCONTINENT MIDCONTINENT RIFT RIFT BASED BASED ON ON SLICKENSIDE ANALYSIS SLICKENSIDE ANALYSIS Kathleen Kathleen Witthuhn, Witthuhn, University University of of Minnesota Minnesota I I I I I. I I I I I I ABSTRACT ABSTRACT ,a& Midcdri*l"e"* Rift Rif Midcontinent ,.,.,. . . ,,^i . The is a 1.11 billion billion year year feature feature which which has hasbeen been defined primarily by geophysical studies. Many studies have exned primarily by geophysical studies. Many studies have examined amined the the rift rift from from aapetrologic petrologic view view but butfew fewhave haveexamined examined the the structural structural geology geology in in any anydetail. detail. This This study study examines examines the thestructural structural .: aspects aspects of of the the rift, rift, elucidates elucidates the the directions directions of of opening opening and andclosing, closing, and and constrains constrains the the timing timing of ofthe thesystem, system,by byutilizing utilizingpaleostress paleostress stratigraphy. Preliminary field work in Minnesota, stratigraphy. Preliminary field work in Minnesota, Canada, Canada, and and the the Upper Penninsula of Michigan has yielded data on fault and joint Upper Penninsula of Michigan has yielded data on fault and joint populations, populations from from which which stress stresstensors tensorswere werecalculated. calculated. ClassifiClassification of faults and cation of faults and establishment establishment of of the the sense sense of of movement movement was was accomplished slickensides,recrystallization recrystallization on on the the fault fault accomplished by by analyzing analyzing slickensides, plane, plane, and and Reidel Reidelfractures fracturesas asprimary primarymovement movementindicators. indicators. Faults Faults with with opposite opposite sense sense ofofmovement movement(dextral (dextral vs. vs. sinistral, sinistral, normal normal vs. vs. reverse) reverse) have have similar similar attitudes attitudes indicating indicating aa 1800 180Âreversal reversal of of stress stress direction. direction. This This study study proposes proposes the the direction direction of of opening opening and and closing closing of of the the rift rift was was constrained constrained by by the thegeometry geometry of of the thefault faultsystems systems and andby by simUar directions of of the similar directions the far far field fieldstresses. stre .. 101 �j A A STUDY OF THEMATIC THEMATICMAPPER MAPPERLINEAMENTS LINEAMENTSIN INNORTHWEST NORTHWESTNEVADA NEVADA Woodzick, Thomas L., Orbital Orbital Technologies Technologies Corporation, Corporation, Madison, Madison, WI WI Murdock, OH Murdock, Gary P., P., Battelle Memorial Memorial Institute, Institute, Columbus, Columbus, OH Pride, Douglas E., The The Ohio OhioState StateUniversity, University, Columbus, OH Analysts were able to identify Analysts of the the 1970's 1970's were identify major linear patterns (>250km long) long) such such as the as the Midas Trench and Rye Rye Patch lineaments lineaments in the area between Reno and Winnemucca J J J on single-band Landsat-1 Landsat-] images and relate them them to to the the geomorphology geomorphology and structure structure of of the the Basin Basin and and Range Range province. province. Multiband Thematic Mapper (TM) data data with with an animproved improved (30m) resolution provide provide an an opportunity opportunity to to re-examine the area area in terms terms of of the the spatial spatial (30m) resolution re-examine the distribution numerous shorter distribution of its numerous shorterlinear linearfeatures, features.68,000 68,000lineament lineamentsegments segmentswere wereinitially initially interpreted scale interpreted (primarily (primarily from fromthe thedeeply deeplyincised incisedand andshadowed shadowedranges) ranges)onona 1:100,000 a 1:100,000 scale — band-234 Subsequentreprocessing reprocessingof of the thedata datawith with an anintensity-hue-saturation intensity-hue-saturation band-234 TM image. Subsequent (IHS) transformation transformation and and edge-enhancement edge-enhancement enabled enabledanother another36,000 36,000 lineament lineament segments segments to be interpreted basins. Digitization interpreted from fromthe thetopographically topographically subdued subdued intervening intervening basins. Digitization of the x-y coordinates of of the lineament endpoints x-y coordinates endpointswas was accomplished accomplished at aa digitizing digitizing tablet, using using aa puck puck with with a head-tail head-tail audio audio prompt prompt and andaadomain-clearing domain-clearing technique technique to to accommodate accommodate lineament clusters. lineament clusters. Once digitized, TM lineament lineament set became became amenable amenable to to visualization, visualization, Once digitized, the TM manipulation, and analysis as well with other otherspatially spatially manipulation, and well as as coregistration coregistration and and integration integration with addressable aeromagnetics,known knownmining miningactivity, activity, and and Digital DigitalElevation Elevation addressable data datasets setssuch suchasasaeromagnetics, Model with a geographic information informationsystem system(GIs). (GIS). The The via processing processing with Model (DEM) (DEM) datadata --- via results of such treatments treatments with the PANACEA GIshave have been been the thefocus focus of of presentations presentationsby by PANACEA 015 Murdock, Pride, Woodzick Woodzick and and others others at meetings in in both both Canada Canada and the United States. States. Selected examples from this body of of work work (e.g., (e.g., lineament lineament intersection intersection enhancement enhancement and and comparison willbe bediscussed discussedwith with respect respectto totheir theirsignificance significance comparison of TM/DEM TM/DEM lineament lineamentsets) sets)will for mineral and in light by the the next next mineral exploration exploration and light of of the theadvanced advanced capabilities capabilities offered by generation of of orbital orbital monitoring monitoringsystems systems such such as as RADARSAT RADARSATand and Eos. Eos. 102 j �GEOSTATISTICAL GEOSTATISTICAL AND AND 615 G I S EVALUATION EVALUATION OF OF BIOGEOCHEMICAL BIOGEOCHEMICAL AND AND ECOLOGICAL ECOLOGICAL DATA DATA FROM FROM Cu-Ni-PGE), NORTHEASTERN NORTHEASTERN MINNESOTA: MINNESOTA: THREE MINERALIZED MINERALIZED SITES SITES (Au (Au && Cu-Ni-PGE), THREE IMPLICATIONS IMPLICATIONS FOR FOR MINERAL MINERAL EXPLORATION EXPLORATION IN IN AA BOREAL BOREAL FOREST FOREST L. L. Zanko, A. A. Gokee, Gokee, B. B. Dewey, Dewey, S. S. Hauck, Hauck, and J. J. Pastor Natural Natural Resources Resources Research Research Institute Institute University University of of Minnesota, Minnesota, Duluth Duluth Duluth, Minnesota Duluth, Minnesota 55811 55811 Detailed biogeochemical biogeochemical and and ecological ecological studies studies of vegetation vegetation were were conducted conducted in in the the boreal boreal forest forest of of northeastern northeastern Minnesota. Minnesota. These These studies studies were were implemented implemented over over three three mineralized mineralized sites: sites: 1) 1) Raspberry Archean Rasoberrv Prospect: Prosoect: Archean (2.7 (2.7 Ga) Ga) gold gold mineralization mineralization in in the the Shagawa Shear Shear Zone Zone (SSZ), (SSZ), Vermilion Vermilion greenstone belt, belt, 5 miles west of of Ely, Ely, Minnesota; Minnesota; 2) 2) Spruce Spruce Road Road (SR): (SRI: 3) 3) South South Filson Filson Creek Creek (SFC): fSFC1: the the Duluth Duluth Complex. Complex. basal basal Cu-Ni Cu-Ni mineralization mineralization of of the the Duluth Duluth Complex; Complex; "cloud Cu-Ni-PGE mineralization mineralization of "cloud zone" zone" Cu-Ni-PGE of The The two two Keweenawan Keweenawan age age (1.1 (1.1 Ga) Ga) Duluth Duluth Complex Complex sites sites are are 15 15 miles southeast southeast of of Ely. Ely. The The SR SR site site consists consists of of low low grade grade Cu-Ni Cu-Ni sulfide sulfide mineralization mineralization at at the basal SEC site has discreet, of the the Duluth Complex, Complex, whereas the SFC basal contact of fracture-controlled fracture-controlled secondary secondary Cu-Ni-PGM Cu-Ni-PGM "cloud "cloud zone" zone" mineralization. mineralization. Glacial Glacial overburden overburden thickness thickness at at the the three three sites sites varies varies from from 0-40 0 - 4 0 ft. ft. Over 1300 vegetation vegetation samples samples were were collected collected from from 17 17 plant plant species species Over 1300 Sampling took took place over over two two weeks weeks in in late late August August and and early early September September of of both both years. years. Tissue samples samples (1100) (1100) submitted for INAA and and DCP DCP analysis analysis included included leaves, leaves, twigs, twigs, for multi-element multi-element INAA needles, and and outer outer bark. bark. Analysis of 500 500 vegetation vegetation samples samples from from the Raspberry Raspberry site in in 1989 1989 during during 1989 1989 and and iggo 1990 at at the the three three sites. sites. shows Abies balsamea tremuloides (quaking shows Abies balsamea (balsam (balsam fir) fir) twigs, twigs, Pop'ilus Popu7us tremuloides (quaking aspen) aspen) leaves, leaves, Corylus Cory7us cornuta cornuta (beaked (beaked hazel) hazel) leaves leaves and and twigs, twigs, Acer Acer spicatum spicatum (mountain maple) maple) twigs, and macrophyllus (large-leaved aster) leaves and Aster macrophy7lus leaves contain anomalous anomalous gold gold values. values. Many Many of the gold anomalies anomalies in in vegetation vegetation overlie aa zone zone of of sericite-iron sericite-iron carbonate carbonate alteration alteration associated associated with the the SSZ. A. balsamea balsamea twigs twigs recollected recollected in in 1990 1990 verify verify the the gold gold anomaly. anomaly. SSZ. At the two Cu-Ni sites, A. balsamea (twigs), 600 tissue samples from A. (twigs), sites, 600 Picea ana (black twigs and bark), bark), Pinus banksiana (jack (jack pine pine Picea marl mariana (black spruce spruce -- twigs calyculata bark), bark), Ledunigroenlandicum Ledum groenlandicum (labrador (labrador tea tea -- twigs), twi'gs), Chan,aedaphne Chamaedaphne ca7ycu7ata (leatherleaf twigs), Alnus Ainus crispa crispa (green (green alder alder -- twigs twigs and leaves), Alnus Alnus (leatherleaf - twigs), rugosa (speckled (speckled alder alder -- twigs twigs and and leaves), leaves), and A. A. macrophyllQs macrophy77us (leaves) (leaves) were were analyzed analyzed for for base base and and precious precious metals. metals. Anomalous Anomalous levels levels of of Ni, Ni, Co, Co, Au, Au, P.. mariarza balsamea (twigs), and A. and Pd Pd were were found found in in A. (twigs), P mariana (twigs), L. L. groenlandicum A. inacraphyllus macrophyllus (leaves). (leaves). These These anomalies anomalies appear appear groenlandicum (twigs), (twigs), and andA. to t o correspond correspond closely closely to to the the bedrock bedrock mineralization. mineralization. Bacillus cereus cereus spore spore counts counts and and other measures of microbial activity activity in soils were used as bioindicators bioindicators of of natural metal enrichments. enrichments. S. 6. cereus cereus counts, total mineralization, and total carbon carbon and and nitrogen, nitrogen mineralization, and pH analyses analyses were done on the ft. intervals across acrossthe A horizon horizon of of soils soils collected at 200 ft. each 6. cereus cereus counts counts ranged ranged from from 1,000 1,000 to t o 576,000 576,000 spores/gm spores/gm soil, soil, each site. site. B. - - 103 �..%. matching spatial ofsoil soilmetal metal anomalies. Initial results indieate matching spatial variation variation of anomalies. resultsore indicate that 8. cereus counts can be an effective indicator Initial of concealed bodies that B. cereus counts can be an effective indicator of concealed ore bodies in northern Minnesota. The effectiveness effectiveness of other soil soil properties as in northern Minnesota. The of other properties as biogeochemical prospecting tools is being evaluated. biogeochemical prospecting tools is being evaluated. Ecological characterization characterization consisted consisted of of identification and Ecological identification and quantification of tree, shrub, and herbal species present within 550 tree and herb plots and 1100 shrub plots. Geostatistical interpretation of the tree, shrub, and herb data will be used to map the various plant communities U at each site as well as the spatial distribution of metals. A geographical information system (GIS) will be used to determine what spatial relationships exist between the geochemical, geological, ecological, and geographical data. The ecological, nutrient uptake, geostatistical, and GIS studies are being used to better characterize and identify variables that affect metal uptake and concentration by boreal forest vegetation over metallic mineralization. j J J J j U Li 104 J J � https://digitalcollections.lakeheadu.ca/files/original/01407a8326f54b05f39f8f88362f45fc.pdf 31ba8d1a4cc4815ebcb8fbf8d66c44bf PDF Text Text r IT I THIRTY-SEVENTH THIRTY-SEVENTHANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY I I I I I I I I I I I I, TI t: r1 PART22 --FIELD FIELDTRIPS TRIPS PROCEEDINGS: PROCEEDINGS: PART MAY MAY1-4, 1-4,1991 1991 EAU EAUCLAIRE, CLAIRE,WISCONSIN WISCONSIN �Organization Committee, Committee, 37th Annual Annual Meeting Meeting ILSG, ILSG, 1991 1991 General Chairman: Chairman: Paul E. General E. Myers Myers PHONE: 715-836-3713 715-836-3713 Editor: Lung L u w S. Chan Geology Department Geology Department University of Wisconsin Wisconsin Eau Claire, WI 54702-4004 54702-4004 PROCEEDINGS VOLUME PROCEEDINGS VOLUME 37 37 PART I: ABSTRACTS ABSTRACTS(Includes (Includes Meeting Meeting Program) Program) PART 2: 2: FIELD TRIPS TRIPS Reference to to material material in Reference inthis thisvolume volumeshould shouldfollow follow the thee.rample examplebelow. below. Morey, Glen Glen B., B., and South wick,David David L., L., 1991, 1991, Manganese Manganese mineralization mineralization in in early Moray, Southwick, Proterozoic iron-formation of the Emily District, Cayuna Range, east-central Proterozoic iron-formation of the Emily Cayuna Range, east-central Minnesota, [abst.]; [abst.]; Institute on Proceedings, 37th 37th Annual Annual on Lake Lake Superior Superior Geology Geology Proceedings, Meeting, Eau Claire, WI, 1991; v. 37, pan 1, p. 75-76. Meeting, Eau WI, v. 37, part I, 75-76. Published and Distributed Distributed by: by: Institute on Lake Superior Institute on Lake SuperiorGeology Geology M.G. Mudrey, Mudrey, Jr., Jr., Secretary/Treasurer M.G. Secretary/Treasurer Wisconsin Geological Geological and and Natural History History Survey Survey Mineral Point Road 3817 Mineral Madison, WI 53705 53705 ***********see** PURCHASE OF PROCEEDINGS PROCEEDINGS VOLUMES VOLUMES Abstracts and and Part II, Trips) may (luring Proceedings (Part I,I, Abstracts Copies of the 37th ILSG Proceedings 11, Field Field Trips) may be be purchased purchased diiriiig the the meeting for for $5.04) $5.00 (US) each. Payable 1'ayal)le to the Institute Institute on onLake LakeSuperior SuperiorGeology Geology Proceedings and and Abstracts, Abstracts, Part Part 1,1, and Field Guidebook, Part 2, Issues of Proceedings 2, from from this this and andprevious previousiiieetiiu,s meetings may be ordered from: from: may he Michael G. Mudrey, .Ir. Jr. See above above PHONE: Address, See PHONE: 608-263-1705 608-263-1705 l'he cost of Orders will he filled while supplies last. All (955 a are The of each each part is $6.00 $6.00 U.S. U S . Orders will be All volumes volumes hack buck to 1955 rt available photocopyingat atthe theprevailing prevailingrate ratefrom fromthe theMichigan MichiganTechnological TechnologicalUniversity UniversityLibrary library through wailiible for photocopying lhriiuflh MS.Spence, Spence,Archivist. Archivist.Phone Phone906.487-2505. 906-487-2505. Mr. MS. �37th Annual Institute on Lake SuperiorGeology Procee:d.ings L . . Ray Wachs Civic Center L Eñu Claire, Wisconsin May 1-4,. 1991 Organized by P.U. Myers, University of Wisconsin-Eau Clairc LS. Chan, Ulniversity of Wi.sconsin-Eau Claire Volume 37 Part 2 Field Trips �TABLE OF OF CONTENTS CONTENTS Calender of Events Events Field Trip 11 - "The Mountain Shear Zone 'The Zone - aa Post Post Penokean Penokean Discrete Ductile Ductile Deformation DeformationZone" Zone" iii iii Field Trip 2 and Significance of the "Features and the PrecambrjanPrecambrianCambrian Contact in in Western Western Wisconsin" Wisconsin" 33 Field Trip 33 "Proterozoic Volcanogenic Volcanogenic Massive Sulfide Proterozoic Sulfide Deposits of Northwestern Northwestern Wisconsin" Wisconsin" 57 �CALENDAR OF EVENTS EVENTS TUESDAY, APRIL APRIL 30 30 - 3:00-5:00 p.m. p.m. 3:OO-500 Early Registration Registrationfor forField FieldTrips Trips#1 #1 and and #2 #2 Participants Civic Early Participants - Civic Center Inn (CCI) Lobby Lobby FIELD TRIP # #1 FIELD 1 P.K. P.K. Sims, and J.S. J.S. Kiasner Klasner (Leaders) (Leaders) "The "The Mountain Mountain shear shearzone zone -- aa post-Penokean discrete discrete ductile ductile deformation deformationzone" zone" 5:00 p.m. Two for Antigo Antigo (Park Inn) 500 p.m. Two vans depart for Inn) 8:30 p.m., p.m., Park Inn, Pre-Field Trip Conference Inn, Pre-Field Trip Conference WEDNESDAY, MAY 11 TRIP #1 #1 FIELD 'I'iUP 8:00 a.m. a.m. Vans Vansdepart departfrom from Park Park Inn, Inn,etntigo, Antigo, for for the mountain mountain area. area. Vans Vans return to CCI by about 9:00 p.m. return to CCZ by about 9:00 p.m. FIELD TRIP #2 L.S. Chan, L.S. Chan, P.E. P.E. Myers, Myers, and R.L. R.L. Hay, Hay, (Leaders): (Leaders): "Features "Features and and contact in western significance significance of the Precambrian-Cambrian Precambrian-Cambrian contact in Wisconsin" Wisconsin" 8:00 a.m. a.m. Pre-trip Pre-trip Seminar 8:00 Seminar CCI, CCZ, Farwell Farwell Rm. Rm. 8:20 a.m. Vans depart from CCI Lobby Vans depart CCZ Lobby 2:00-5:00 p.m. Pre-Conference Planning Session Pre-Conference Planning Session - Staff, Room Staff, CCI Gibson Room 4:00-8:00 p.m. Registration and and check-in check-in for pre-registrants, pre-registrants,Civic Civic Center Center Inn Inn Lobby Lobby 8:00-11:00 p.m. - Informal Get-together Get-together and Cash Cash Bar Bar by: Bill Bill Jordan Jordan Jazz Quintet Music by: THURSDAY, THURSDAY. MAY MAY 22 7:15 a.m - Registration Lobby, Civic Civic Center Center Inn (CCI) (CCI) Registration - Lobby, TECHNICAL SESSION SESSION All Technical Sessions are in Room All Room C, C, Ray Ray Wachs Wachs Civic Civic Center Center (RWCC); (RWCC); Poster Poster Sessions Sessions in RWCC Rooms D and E. Schedules of oral papers are shown on pages xiii and xiv. in RWCC Rooms D and Schedules of oral shown pages xiv. Contributors Contributors should should have have posters postersup upby by 9:00 9:00 a.m. a.m. 8:00 a.m. Introduction and Paul Myers, Paul Myers,Conference ConferenceChairman, Chairman, and Larry Larry Introduction andWelcome: Welcome: - Schnack, Schnack, Chancellor, Chancellor,University Universityof of Wisconsin wsconsin - Eau Claire 8:20-10:00 8:20-10:OO a.m. 10:00 a.m. a.m. 10:OO 10:20-11:50 10:20-11:50 a.m. Morning Chairs: R.W. MorningSession Session#1. #l. Chairs: R.W.Ojakangas Ojakangasand andA.B. A.B. Dickas Dickas COFFEE COFFEE BREAK BREAK Morning G.L. Chairs: G.L.LaBerge LaBergeand andK.K.Schultz Schultz MorningSession Session#2; #2;Chairs: �11 L -- L NOON-2:00 p.m. BOARD BOARD LUNCHEON LUNCHEONAND ANDANNUAL ANNUALMEETING: MEETING:Farwell FarwellRoom, Room. CCI CCI 12:30-1:30 p.m. POSTER SESSION SESSION #1 - Authors Authors present (Poster (Posterpapers, papers,p.p.xv) xvl 1:40-3:00 p.m. Afternoon Chairs: V.W. AfternoonSession Session#1. #l. Chairs: V.W.Chandler Chandlerand and(jB. G.B.Morey Morey - -- COFFEE BREAK BREAK -- Remove Remove Poster Papers Papers 3:00 p.m. U 3:20-4:50 p.m. Afternoon M.M. AfternoonSession Session#2. #2.Chairs: Chairs: M.M.Kehienbeck Kehlenheckand andC.C.Craddock Craddock 6:00-7:30 p.m. CASH BAR: RWCC ROOM ROOMAA 7:30-10:00 p.m. ANNUAL ANNUAL ILSG ILSG BANQUET BANQUET-- RWCC RWCC Rooms A and and BB - U Presentation Presentation of of the the Goldich Goldich Medal Medal to to W.J. WJ. Hinze, Hinze, Purdue Purdue University University Chandler by by V.W. V.W. Chandler [ Speaker: K. Sims, Sims,"Archean "Archeanand andEarly EarlyProterozoic ProterozoicGeology Geologyof of the the Speaker: Paul PaulK. introduced by G.B. Lake Lake Superior Superior Region Region -- An An Overview"; Overview"; introduced G.B. Morey. - [ IL FRIDAY, MAY 3, 3,1991 1991 p.m. 8:00 8:00 a.m.-3:30 a.m.-330 p.m. Registration Registrationand andSale Saleof ofExtra ExtraProceedings ProceedingsVolumes Volumes 8:20 a.m. Morning Chairs: M.M. G. G. Mudrey, A.A.DeMatties #l. Chairs: Mudrey,Jr.Jr.and andT.T. DeMatties MorningSession Session#1. COFFEE COFFEE BREAK BREAK 10:00 a.m. L L [ 10:20-11:30 a.m. Morning G.W. MorningSession Session#2. #2.Chairs: Chairs: G.W.Adams Adamsand andBA. BA.Brown Brown 12:30-1:30 p.m. POSTER SESSION #2 -- Authors Authors present (poster (poster papers, papers, p. p. xvi) xvi) 1:40-2:40 p.m. Afternoon Session W.S. #l.Chairs: Afternoon Session#1. Chairs: W.S.Cordua Corduaand and M. M. Jirsa 2:40 p.m. Student Award Award Presentation, John Klasner Klasner - -- COFFEE COFFEE BREAK BREAK -- Remove Remove Poster Papers 3:00 p.m. 3:20.4:30 p.m. Afternoon J. J. Kaliokoski Afternoon Session Session#2. #2.Chairs: Chairs: Kaliokoskiand andJ.J.C. C.Green Green 7:00-8:30 p.m. Pre-Trip Pre-Trip #3 Seminar, Seminar,CCI, CCI,Farwell Farwell Room, Room, M.G. M.G. Mudrey, Jr. and WA. B.A. Brown Brown L SATURDAY, MAY 4, 1991 1991 SATURDAY, FIELD TRIP #3 Mudrey, Mudrey, Jr., and and B.A. Brown Brown (Leaders), (Leaders), "Proterozoic "Proterozoic volcanogenic massive sulfide deposits of northwestern northwesternWisconsin Wisconsin" from front front entrance of CCI 8:00 a.m. Bus departv departs from M.G. ii II �WEDNESDAY, MAY 1, 1991 FIELD TRIP #1 and J.S. J.S. KJasner Klasner (Leaders) (Leaders) P.K. Sims, and - "The "The Mountain shear shear zone zone - a post-Penokean post-Penokean discrete ductile ductile deformation deformationzone" zone" discrete HI iii �MOUNTAIN SHEAR ZONE, ZONE, OCONTO OCONTOCOUNTY, COUNTY, WISCONSIN-WISCONSIN-A POST-PENOKEAN DISCRETE DUCTILE DEFORMATION DEFORMATION ZONE ZONE P. K. Sims, Sirns, U.S. U.S. Geological Geological Survey Survey Denver Box 25046, MS MS 905, 905, Denver Federal Center Denver, CO 80225 80225 Klasner, Department Department of of Geology Geology John S. Kiasner, Western Illinois University and U.S. Geological U.S. Geological Survey Survey Macomb, IL 61455 61455 Warren C. Day, U.S. U.S. Geological Geological Survey Survey Box 25046, 25046, MS MS 905, 905, Denver Denver Federal Federal Center Center Denver, CO 80225 Denver. 80225 E. Peterman, Peterman, U.S. U.S. Geological GeologicalSurvey Survey Zell E. Box 25046, MS 963, Denver Federal Box 25046, MS 963, Denver Federal Center Center Denver, CO 80225 80225 of Institute on Field trip, 37th Annual Meeting of Lake Superior Superior Geology, Geology, Eau Eau Claire, Claire,Wisconsin Wisconsin May 1, 1, 1991 1991 iv �CONTENTS CONTENTS Page Page Introduction . . . . . . . . . . Penokean orogen . . . . . . . . . . . penokean Rock units units, Mountain area . . . Rock Outside O u t s i d e of o f sshear h e a r zzone one . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waupee Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waupeevolcanics Mafic lava flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mafic Felsic volcanic volcanic rocks and and minor minor interbedded interhedded mafic volcanic rocks Felsic Granodiorite Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shear zone . . . . . . . . . . . . . . . . . . \Vaupee Waupee Vblcanics Volcanics . . . . . . . Amphibole schist schist . . . . . . . . . . . . . . . . . . Quartz diorite schist schist . . . . . . . . . . . . . . . Interlayered biotite biotite and and amphibole amphihole schist schist . . . Biotite schist . . . . . . . . . . . . . . . . . . . . Biotite-amphihole schist Biotite-amphibole schist . . . . . . . . Amphibole schist schist . . . . . . . . . . . . . Magnetite-rich sch ist . . . schist Granite gneiss . . . . . . . . . . . . . Baldwin Baldwin Conglomerate . . . . . . . Hines Quartz Diorite Diorite . . . . . Regional structure . . . . . . . . . . . . . . . . . Shear zone . . . . . . . . . . . . . . . . . . Mesoscopic structure structure . . . . . . Mesoscopic Microscopic structure . . . . . Kinematic analysis . . . . . . . . Geoharometry Geobarometry and geothermometry . . . Conclusions Conclusions . . . . . . . . . . . . . . . . . . Regional significance significance . . . . . . . . . . . Acknowledgments . . . . . . References cited . . . . . . . Field stops and road log Field log . . . . 1 I . L L L L V 2 2 2 3 . 3 4 4 4 5 D 6 6 7 7 7 9 9 l0 10 10 11 11 12 12 13 14 14 16 �INTRODUCTION INTRODUCTION by Sims Simsand and M.G. M.G. Mudrey, Mudrey,Jr. Jr. revealed revealed the the existence existence of of aa Reconnaissance mapping in 1980 by belt of remarkably well exposed mylonitic rocks near Mountain in Oconto County, Wisconsin. belt of remarkably well exposed mylonitic rocks near Mountain in Oconto County, Wisconsin. Subsequently, the mylonitic mylonitic rocks rockswere were systematically systematicallymapped mappedtotodetermine determine their their relation relation to Subsequently, the to the the regional deformation (Sims, 1989), and Kiasner made detailed structural studies of critical outcrops regional deformation (Sims, 1989). and Klasner made detailed structural studies of critical outcrops to to determine determine the the sequence sequenceof of deformational defonnational events events and and the the sense sense and and direction direction of of movement movement within within the the shear shear zone zone (Sims (Sims and and others, others, 1990). 1990). The Mountain shear shear zone zone is is aa discrete discrete ductile ductile deformation deformation zone zoneas as much much as as 1.5 1.5 km wide that post-dates Early Early Proterozoic Proterozoic regional regional deformation deformationof of the the Penokean Penokean orogeny. orogeny. A post-dates A body body of of quartz quartz diorite, formally named named the the Hines Hines Quartz Quartz Diorite, Diorite, that that was was intruded intruded into into the the shear diorite, formally shear zone zone at at about about the close of the shearing event has a U-Pb zircon concordia intercept age of 1,812.7± 3.6 Ma (Sims the shearing event has a U-Pb zircon concordia intercept age of 1,812.723.6 Ma (Sims and others, 1990), which places placesaafirm firmminimum minimumage ageon onthe thetime time of ofshearing. shearing. The Mountain shear 1990), which zone and other E. shear zones in N.55°-60° 55'-60 E. in the the Wisconsin Wisconsin magmatic terranes terranes record record aasignificant significant zone otherN. episode of ductile deformation that that probably probably resulted resultedfrom fromaa collision collision of unknown rocks to the south of the area after of after the the Penokean Penokeanorogeny. orogeny. PENOKEAN OROGEN Ma Penokean Penokean orogen orogen developed developed as as an embayment in the southern The 1,990-1,835 1,990-1,835 Ma southern margin margin of the Archean Superior craton. Rocks of the orogen are exposed in Wisconsin, northern Michigan, Superior Rocks of the orogen are exposed in Wisconsin, northern Michigan, and Minnesota Minnesota (Cannon, (Cannon,1973; 1973;Morey, Morey,1973; 1973; Sims Sims and and Peterman, Peterman,1983). 1983). The orogen orogen consists consists of of two twodistinct distinctlithologic lithologic domains domains (fig. (fig. I): northern deformed deformed 1): a northern continental margin assemblage overlying an Archean basement; and a southern assemblage of island southern continental an Archean basement; arcs, the Wisconsin magmatic terranes (Sims and others, 1989). The northern rocks include Wisconsin magmatic terranes (Sims and others, 1989). northern include the Marquette (Cannon and and Gair, Marquette Range Range Supergroup Supergroup in Michigan Michigan and Wisconsin Wisconsin (Cannon Gair, 1970), which Mille Lacs Lacs Groups Groups in in Minnesota Minnesota (Morey, (Morey, 1983), 1983), and and comprise comprise aa correlates with the Animikie and Mille south-facing continental-margin assemblage. They consist of a lower rifted passive-margin sequence They consist rifted passive-margin sequence overstepped northward by a synorogenic foredeep sequence (Barovich and others, 1989; Southwick northward by a synorogenic foredeep sequence (Barovich and others, 1989; Southwick and others, 1988). 1988). Early EarlyProterozoic Proterozoicregional regional deformation deformation involved involved northward-directed thrusting and related folding folding of the supracrustal supracrustal rocks rocks and and produced produced metamorphism metamorphism and basement gneiss gneiss domes caused by crustal thickening (Sims and Peterman, 1983; HoIm and others, 1988; Attoh thickening Peterman, 1983; Holm others, 1988; Attoh and and Klasner, 1989). Klasner, 1989). The Thesouthern southernmagmatic magmatic terranes terranesconsist consistofofEarly EarlyProterozoic Proterozoiccalc-alkaline calc-alkaline and and tholeiitic volcanic and caic-alkaline calc-alkaline plutonic rocks rocks (Sims (Sims and and others, others,1989). 1989). The Niagara Niagara fault zone zone separates separates the thesouth-facing south-facing continental continental margin margin assemblage assemblage and the the oceanic arc terranes in Wisconsin and Michigan (fig. 1). It is a broadly arcuate, terranes in Wisconsin and Michigan (fig. 1). is arcuate, convex-northward convex-northward of ductile shears as system of as much as as 10 10 km wide that contains contains flattened flattened steeply steeplydipping dippingrocks rockshaving having dominantly down-dip down-dip stretch stretch lineations lineations (Larue and Ueng, Ueng, 1985; 1985; Sedlock Sedlock and and Larue, Larue,1985). 1985). It dominantly contains a dismembered ophiolite and has has been been interpreted interpreted as asaapaleosuture paleosuturezone zone(Schulz, (Schuiz,1987) 1987) between the two terranes, which were juxtaposed at about 1,860 Ma (Sims and others, 1985). two terranes, which were at about 1,860 Ma (Sims and others, 1985). rocks and and related related intrusive rockssouth south of of the the Niagara Niagara fault fault are are part part of of the The oceanic arc rocks intrusive rocks Pemhine-Wausau terrane of the Pembine-Wausau terrane the Wisconsin Wisconsin magmatic magmatic terranes (Sims (Sims and and others, others,1989). 1989). The The to 1,889 1,889Ma. Ma. The The granitoid rocks are mainly granodiorite granodiorite and tonalite; metavolcanic rocks are 1,860 to tonalite; post-tectonic. Sims they range in age from from 1,760 1,760 to 1,870 1,870 Ma, with with the younger group being post-tectonic. Simsand and others (1989) have proposed that that the the Penokean Penokeanorogeny orogenyterminated terminatedbetween between1,835 1,835Ma Maand and1,840 1,840 �Ma, when when the the Marshfield Marshfield terrane (see was sutured sutured to the Pembine-Wausau Pembine-Wausau terrane along the (see fig. 1) was Eau Pleine shear zone. shear zone. ROCK UNITS, AREA UNITS, MOUNTAIN MOUNTAIN AREA The Mountain shear zone zone is in in the the eastern eastern part part of of the the Pembine-Wausau Pembine-Wausauterrane. terrane. The major rock units exposed within within and and adjacent adjacent to the Mountain shear zone are metavolcanic Mountain shear zone are metavolcanic rocks rocks and and sedimentary rocks, assigned to to the the Waupee Volcanics, granodiorite granodiorite and minor related volcanogenic sedimentary mylonitized equivalent equivalent in the the shear zone--granite gneiss (unit Xgn, fig. fig. 2)--and 2)--and the the Hines Hines Quartz its mylonitized Diorite. The sheared metavolcanic rocks (units Xwi and Xwa, fig. 2) and the granite The sheared metavolcanic rocks (units Xwi and Xwa, fig. 2) granite gneiss gneiss are overlain along the northern margin of the shear zone by a metaconglomerate, named the overlain along the shear zone the Baldwin Baldwin Conglomerate. These These rocks rocks are are Early Early Proterozoic Proterozoic in age. They They are are intruded intruded by by and and occur occur as a roof pendant in in anorogenic anorogenic rocks rocks of of the theMiddle MiddleProterozoic Proterozoic(—1.47 (- 1.47 Ga) Ga) Wolf Wolf River River batholith. batholith. The stratigraphic stratigraphic nomenclature nomenclature used used in in this this report report was was adopted adoptedearlier earlier(Sims, (Sims,1989), 19891,and and isis based largely on previously proposed proposed geologic names. names. Mancuso Mancuso (1957) (1957) assigned the the name name Waupee Waupee to the the metavolcanic metavolcanic rocks exposed exposed in in this this and and adjacent adjacent areas areas to the east Volcanics to east because because of of typical typical exposures near Waupee Creek, and this formal designation is retained herein. exposures near and this formal designation is retained herein. Lahr (1972) (1972) renamed this unit the the Waupee Waupee Formation, Formation, but but the the earlier earlier nomenclature nomenclature appropriately appropriately emphasizes emphasizes affinity of of the the rocks. rocks. Mancuso Baldwin Conglomerate the volcanic affinity Mancuso (1957) (1957) also proposed the the name name Baldwin for the Baldwin Creek, Creek, which whichisisaccepted accepted herein. herein. Lahr the metaconglomerate metaconglomerateexposed exposed in in the thevicinity vicinity of Baldwin (1972) assigned assigned the the undeformed quartz diorite exposed in section 12, T. 31 N., R. 16 E., east of the 16 the quartz diorite exposed in section 12, T. 31 N., village of Mountain (see Sims, 1989), to the Hines Quartz Diorite because of its exposures village of Mountain Sims, 1989), to the Hines exposures near Hines Creek. Mancuso (1957) (1957) had had included Creek. Previously, Previously, Mancuso included these rocks rocks in in his his "Macauley "Macauley Granite.t Granite." Although Lahr (1972) correctly correctly renamed renamed the granitoid rocks "Macauley Gneiss,' neither of these Although "Macauley Gneiss," terms are are used used herein herein because becausethey theyeach eachinclude includesubstantial substantialamounts amountsof of metavolcanic metavolcanic rocks rocks as as well well as granitoid rocks. rocks. within the the Mountain shear zone differ profoundly profoundly in in structure structure and to some Because the rocks within extent in mineralogy mineralogy and degree of metamorphism from those outside of it, it, the the rocks rocks within within and outside of the shear zone are described separately below. Slightly to moderately deformed shear zone are described separately below. Slightly to moderately deformed rocks rocks (D1) of of the the Waupee Waupee Volcanics and and the intrusive granodiorite granodiorite were converted (D,) converted to to mylonitic mylonitic schists and gneisses within within the the shear shear zone (D2). gneisses (D,). The The undeformed undeformed Hines Hines Quartz QuartzDiorite Dioritewas wasemplaced emplaced within within the shear zone at or or near near the theend endofofthe theductile ductiledeformation. deformation. Outside or of Shear Zone Zone Waupee Volcanics Volcanics Within the map map area area (fig. (fig. 2), 2), the theWaupee WaupeeVolcanics Volcanics is is divided divided into into four four mappable mappable units. units. Outside of the the shear shearzone, zone, ititconsists consists of of aaunit unitofofmafic maficlava lava flows flows (unit (unit Xwm, Xwm, fig. 2) and a unit unit of of rocks (unit (unit Xwf). Xwf). Sheared correlative predominantly felsic volcanic rocks correlative rocks within the shear shear zone zone are: are: (1) amphibole schists (unit (unit Xwa) and (2) (2) interlayered interlayered quartz-biotite quartz-biotite and and amphibole amphibole schist schist (unit (unit Xwi), respectively. A A body body of quartz quartz diorite dioriteschist schist(unit (unitXwq), Xwq),presumably presumably aasubvolcanic subvolcanic intrusion, intrusion, Xwi), respectively. occurs within the shear zone. Chemical Chemicalcompositions compositionsof of two two representative representative rocks rocksare arelisted listedinintal)IC table 1. 1. 2 �Mafic lava Mafic lava flows flows This rock unit southeast of of the shear unit (Xwm, (Xwm, fig. 2) is is dominantly dominantly exposed exposed southeast shear zone, zone, and is is of dark-gray, dark-gray, fine-grained fine-grained porphyriticlava porphyritic lava flows flowsthat thatare arehighly highlyaltered. altered. The rocks composed mainly of are generally generally massive and unfoliated to to weakly weakly foliated but locally locally have a distinct distinct compositional compositional layering visible on weathered surfaces. Possible relicts of pillow rinds can seenatatplaces. places. The The layering visible on weathered surfaces. Possible relicts of pillow rinds can bebeseen lavas are metamorphosed to togreenschist greenschist facies. facies. lavas In the occur as stubby the least least altered alteredrocks, rocks,plagioclase plagioclase megacrysts megacrysts occur stubby laths with broad albite albite twinning and as aggregates of randomly oriented stubby laths. The twinning and aggregates of randomly oriented stubby laths. The plagioclase plagioclase is altered altered variably variably sericite, and and calcite. calcite. The to epidote/clinozoisite, epidote/clinozoisite, sericite, Themafic mafic minerals minerals are are completely completely altered to to palepaleand skeletal opaque green actinolite and, and, locally, locally, to sphene, sphene, which which shows incipient crystallization, and oxides. Quartz as anhedral, anhedral, strained, sutured grains. oxides. Quartz generally generally is absent, but in two sections occurs as Biotite is dark brown. brown. Felsic volcanic volcanic rocks rocks and minor minor interbedded interbedded mafic mafic volcanic volcanic rocks This rock rock unit unit (Xwf (Xwf,fig. fig.2) 2)isismainly mainlyexposed exposedin in sections sections44 and and5, 5, T. T. 31 31 N., R. 17 17F. E.(see (seeSims, Sims, 1989). felsic tuff, intercalated metasedimentary 1989). It consists of massive to layered metamorphosed felsic rocks, and and generally generally thin thin interbedded interbedded layers layers of of mafic mafic tuff. tuff. The rocks rocks, rocks have a penetrative cleavage cleavage (Si) and, at (S,) at least least locally, locally, are arefolded folded(F1). (F,). The felsic granular rock rock of felsic tuff tuff isis aalight-gray, light-gray, fine.grained, fine-grained, inequigranular, inequigranular, xenomorphic xenomorphic granular composition. ItIt isiscut general dacitic composition. cut by by widespread widespread narrow narrow shears shears but but lacks lacks mylonitic mylonitic textures. Plagioclase occurs occurs mainly mainlyas as anhedral anhedral grains grains generally generallyless lessthan than 0.3 0.3 mm mm in in diameter, but Plagioclase locally forms forms phenocrysts phenocrystsas as much much as as 1.5 mm in diameter. locally 1.5 mm diameter. It is is poorly poorly twinned. twinned. Some Somegrains grains contain abundant rounded quartz inclusions. inclusions. Quartz Quartz grains grains are are anhedral, anhedral, clear, and approximately grains. Stubby brown brown to pale-red biotite is preferentially orientated the same size as the plagioclase grains. orientated in the (Si) foliation and is intergrown with about equal amounts of muscovite. The biotite (S,) is intergrown equal amounts of muscovite. The biotiteisislocally locally altered to chlorite. sphene, opaque opaque oxides, allanite, and zircon are altered chlorite. Sparse, Sparse, poorly crystallized crystallized sphene, oxides, allanite, are accessory minerals. minerals. The The sedimentary sedimentary rocks rocks are are mediummedium-to todark-gray, dark-gray,fine-grained, fine-grained, thinly thinly layered, foliated rocks rocks composed of plagioclase, quartz, and biotite and, locally, either garnet or cummingtonite. Good composed of plagioclase, quartz, and biotite and, locally, either garnet or cummingtonite. Good N., R. R. 17 E., F., on on the ridges just just north of Bear exposures can be seen in the center center of of section section 5, 5, T. 31 N., Paw road, west of Waupee Creek Creek (stop (stop5,5,fig. fig. 8). 8). Granodiorite fig. 2) 2) that that have an average composition of granodiorite granodiorite Porphyritic granitoid rocks (unit Xg, fig. (table 2; 2; fig. fig. 3) 3) intrude the metavolcanic rocks on the southeast side of the Mountain metavolcanic rocks on the southeast side of the Mountain shear zone. T. 31 N., N., R. R. 17 E., E., but but extend into sec. 5 (see Sims, They are are most most extensively extensively exposed in section 7, T. 1989). The 1989). The granodiorite granodiorite intrudes intrudesthe thesurrounding surroundingmetavolcanic metavolcanicrocks rocks lit-par-lit, lit-par-lit, to form migmatite, migmatite, and contains of them them (mainly amphibolite) that that are and contains moderate to abundant abundant elliptical elliptical inclusions inclusions of (mainly amphibolite) F. The oriented N. consistently oriented N. 1Oo3O 10'-30' E. Thegranodiorite granodioriteextends extendsnorthward northward into into the the shear shearzone, zone, where where The chemical itit has has been been deformed deformed into into aagneiss, gneiss, termed termed granite granite gneiss gneiss (unit (unit Xgn, Xgn, fig. fig. 2). chemical 2). odiorite (number composition of of one sample of granodiorite composition (number 35-85) 35-85) is is given given in in table table 1.1. 3 �The characterized by The granodiorite granodiorite isisaa pinkish-gray, pinkish-gray, generally generally massive, medium-grained rock characterized by light-gray or pinkish-gray pinkish-gray subhedral microdine light-gray microche porphyrocrysts porphyrocrysts (—1 (-1 cm crn long) and and pink pink plagioclase plagioclase phenocrysts as 1.5 1.5 cm cm long) long) in in aa finer finergrained, grained,essentially essentiallyequigranular equigranulargroundmass groundmass of of phenocrysts (as much as feldspar, quartz, feldspar, quartz, hornblende, hornblende, and biotite. biotite. The mafic mafic minerals minerals typically typically form clusters clusters between between feldspar grains. Adjacent Adjacent to to the the southeast southeast margin margin of of the the shear shear zone zone (fig. (fig. 2), 2), the the rock rock feldspar and quartz grains. is partly deformed into into protomylonite, protomylonite, but itit lacks lacks a penetrative penetrative structure. structure. Plagioclase (oligoclase) occurs as blocky blockyto tolath-shaped, lath-shaped, subhedral subhedral crystals crystals that that have have CarlsbadCarlsbadPlagioclase (oligodase) albite and, less commonly, peridline twins. twins. A weak but distinct commonly, pericline distinct concentric concentric normal zoning zoning can be distinguished in a few sections. sections. Myrmekite Myrmekite commonly commonly occurs adjacent to microcline. Phenocrysts Phenocrysts IPcore-mantle core-mantle aggregates aggregates and and type type TIP IIP structures; Hanmer, Hanmer, locally structure (type (type IP locally have have aa mortar structure 1982) that comprise intragranular, intragranular, fine-grained fine-grained recrystallized recrystallizedplagiodase. plagioclase. Adjacent Adjacent to to the shear 1982) that plagioclase contains abundant abundant tiny tiny rounded rounded inclusions inclusions of of quartz. quartz. zone, the plagioclase Quartz generally occurs as sutured grains grains that that are aresomewhat somewhatcrackled crackled and andshow showundulose undulose extinction. extinction. Most Most quartz quartzisisinterstitial interstitialbut butsome someforms formsanastomosing anastomosing aggregates aggregates as as much much as as 55 mm long. long. Microcline commonly commonlyoccurs occursas as phenocrysts phenocrysts that that have undulose Microcline undulose extinction extinction and and contain contain inclusions of of mynnekitic myrmekitic plagioclase plagioclaseand and quartz. quartz. At At places, places, elliptical elliptical quartz grains grains and and aggregates aggregates of grains are clustered near near grain grain margins. margins. Type TypeTM IM mantle mantle aggregates aggregates and and type type TIM IIM structures (Hanmer, (Hanmer, 1982) 1982) are are present present locally. locally. Judged Judgedfrom fromits itsmorphology, morphology, microcline behaved more brittlely plagioclase to In aa thin thin section, section, from from the the center center than associated plagioclase to the the strain strain related related to the shearing. In of section 77 (fig. 8), for example, plagioclase has been partly reduced to fine-grained intragranular (fig. plagioclase fine-grained intragranular and mantle mantle aggregates, aggregates, whereas whereas nearby nearby microcline microcline is only strained and crackled. Not Notuncommonly, uncommonly, shears shears transect transect microcline microclinemegacrysts. megacrysts. The dark-green to tobluish-green, bluish-green,poikilitic poikilitichornblende hornblendecommonly commonly0.5 0.5 The principal principal mafic mafic mineral mineral isis dark-green to to 1 mm in diameter. diameter. It is is partly partly intergrown intergrown with biotite of of approximately approximately the same same grain grain size, size, probably is is aa primary primary mineral, mineral, but but also also isis partly partlyaltered altered to to biotite. biotite. The which probably The secondary secondary biotite biotite and and associated reaction products-magnetite, products--magnetite, sphene, and epidote--tend to to form ill-defined pseudomorphs after after hornblende. pseudomorphs hornblende. The Thesecondary secondary biotite biotite isis much much finer finer grained grained than than the theoriginal original biotite. The Theaccessory accessoryminerals minerals are aremainly mainly zircon, zircon, apatite, and and altered altered allanite. allanite. Shear Shear Zone Zone Waupee Waupee Volcanics Volcanics Amphibole schist schist Xwa (inside (inside shear zone) superficially (outside Mafic rocks in unit Xwa superficially resemble those in unit Xwm (outside shear zone) shear zone) in in being beingdark-gray dark-grayporphyritic porphyriticlavas, lavas,but but they theyare arevariably variablymylonitized mylonitized and andfoliated, foliated,less less slightly higher metamorphic grade (lower amphibolite facies). An exception exception isis altered, and and have have aa slightly facies). An the mafic rocks in the extreme northeastern northeasternpart partofofthe theshear shearzone, zone,west westofofNelligan NelliganLake Lake(see (seeSims, Sims, The chemical 1989), highly altered and and bleached bleached and anddefinitely definitelygreenschist greenschist facies. facies. chemical 1989), which which are are highly is listed listed in in table table 1.1. composition of a representative representative sample sampleof of amphibole-facies amphibole-facies lava lava is 4 �Plagioclase sparse anhedral Plagioclase occurs as sparse anhedralporphyroclasts porphyroclastsas asmuch much as as 55 mm in diameter, but mainly has been recrystallized to finer finer grained grained aggregates. aggregates. Core-mantle aggregates has recrystallized to aggregates (Hanmer, 1982) are common. common. Quartz Quartz grains grains are are sparse. sparse. The amphibole is either a green green or or aa bluish-green bluish-green hornblende; the latter latter appears to replace the ihe former. former. The Thehornblende hornblendecommonly commonlycontains containsoriented orientedblebs blebs of of magnetite. Olive-green Olive-greento tobrown brown biotite and and associated associated sphene spheneisislocally locally associated with the hornblende and and appears appears to to be be mainly mainly an alteration Skeletal opaque opaque oxides occur in aa few alteration product product of it. it. Skeletal oxides occur few sections. sections. Zircon Zircon is a sparse sparse accessory accessory mineral. Quartz Quartz diorite diorite schist schist Quartz diorite diorite schist schist isis aadark-gray, dark-gray, speckled, speckled, medium-grained medium-grained metamorphosed rock that that intrudes the amphibole schist in section 33, T. 32 N., R. 17., and presumably is a subvolcanic body. intrudes the amphibole schist in section 33, T. 32 N., R. 17., and presumably is a subvolcanic body. It It has has aaconspicuous conspicuousfoliation foliation and andlineation lineationexpressed expressedby byaligned alignedhornblende hornblendeaggregates. aggregates. This structure structure isis modified modified by by local local mylonitic mylonitic structures, structures, characterized by by grain-size grain-sue reduction through through recrystallization. (table 3), 3), the rock recrystallization. Narrow Narrow mylonitic mylonitic shears are arecommon. common. Compositionally Compositionally (table rock overlaps overlaps that of of the the Hines Hines Quartz QuartzDiorite Dioritebut butititdiffers differsfrom from ititininmegascopic megascopic appearance appearance and and by by being deformed. deformed. Plagioelase (An-) occurs occurs as as concentrically concentrically zoned, zoned, elongate elongate subhedral subhedral crystals crystals having having Plagioclase (An15.) combined Carlsbad-albite Carlsbad-albite twins twins and and pericline pericline twins. twins. It is is partly partly recrystallized recrystallized to IP IP core-mantle core-mantle aggregates (Hanmer, (Hanmer, 1982) 1982) and fine-grained intragranular aggregates (mortar structure). In Inshears, shears, aggregates recrystallized recrystallized plagioclase plagioclase is is intergrown intergrown with with recrystallized recrystallized hornblende. hornblende. Hornblende Hornblende isis altered altered to tovarying varying degrees. The Theleast leastaltered, altered,possibly possibly original original hornblende, is medium strongly poikilitic and medium to to dark dark green. green. ItItisisintergrown intergrownwith with aa bluish-green bluish-green hornblende hornblende that that isisstrongly is probably an alteration product of the green hornblende. Locally, Locally, either of the hornblendes have a partial partial rim rim of of aa secondary secondary fibrous fibrous pale-green pale-green actinolitic actinolitic hornblende or actinolite. Recrystallized Recrystallized hornblende grained and and dark green. green. Much hornblende in in mylonitic mylonitic shears is fine grained Much of of the the original(?) original(?) hornblende hornblende is is replaced replaced by by pseudomorphs pseudomorphsof offine-grained fine-grainedsecondary secondarygrayish-olive grayish-olive to to brown brown biotite. biotite. Quartz Quartz grains grains are areinterstitial interstitialand andparagenetically paragenetically late. late. The Thegrains grainshave haveundulose unduloseextinction extinction and indiameter diameter that that retain retain the approximate outline and are are recrystallized recrystallized to sutured sutured grains —0.5-0.8mm -0.5-0.8 mm in of rnrn in in of the the original original 3-4-mm-diameter 3-4-mm-diameter grains. The Theaccessory accessoryminerals minerals are arezircon, zircon, as asmuch much as as 0.15 0.15 mm diameter, diameter, apatite, apatite, and and altered alteredallanite. allanite. The 2) isis interpreted interpreted as asaacoeval, coeval,subvolcanic subvolcanic intrusive intrusive The quartz quartz diorite dioriteschist schist(unit (unitXwq, Xwq, fig. fig. 2) rock associated with the metamorphosed porphyritic lava flows (units Xwm and Xwa). rock associated with the metamorphosed porphyritic lava flows (units Xwm Xwa). Interlayered biotite biotite and and amphibole amphibole schist schist Interlayered Interlayered biotite biotite and andamphibole amphiboleschist schist(fig. (fig. 4; 4; table table 4) is is the the most most abundant abundant rock rock unit unit in in the the Mountain Mountainshear shearzone zone(unit (unitXwi, Xwi,fig. fig.2). 2).The Therocks rocksare aredark-gray dark-graytotopinkish-gray, pinkish-gray,generally generallyfine fine grained grained schists, schists, which which can be be designated designated primarily primarily as asbiotite, biotite,biotite-amphihole, biotite-amphibole, and andamphibole amphibole schist. schist. More Morerestricted restrictedrock rocktypes typesinclude includecummingtonite-bearing cummingtonite-bearingschist, schist,gedrite-bearing gedrite-bearingschist, schist,and and magnetite-rich schist; none none of these magnetite-rich schist; these units units were were mapped mapped separately separately(Sims, (Sims, 1989), 1989), and and only only the the magnetite-rich are representative of of the the major major magnetite-rich schist schist is is discussed discussed following. following. The modes in in table table 44 are rock rock types; types; the the cummingtonite-, curnmingtonite-,gedrite-, gedrite-, and and magnetite-rich magnetite-rich schists schists are are generally generally too too fine fine grained grained 5 �for accurate accurate modal modal analysis. analysis. The metamorphic grade of of the the rocks rocks isismainly mainly lower lower amphibolite amphibolite facies. The rocks are grossly equivalent to the interbedded felsic and mafic volcanic rock The rocks are grossly equivalent to the interbedded felsic and mafic volcanic rock unit unit (Xwf) (Xwf) outside the shear zone, and represent strongly deformed variants of the volcanic rocks within the shear zone, and represent strongly deformed of the volcanic within shear zone. The Theschists schists are areintruded intruded by by granite granite gneiss gneiss and, adjacent to the the main main body body of granite gneiss, by dikes of pink leucogranite gneiss that are part of the granite gneiss body. gneiss, by dikes of pink leucogranite gneiss that are part of the granite gneiss body. Biotite schist Biotite schist is the the dominant dominant rock rock type type in in the theinterlayered interlayered schist schist unit unit (Xwi). (Xwi). It consists consists Biotite schist principally of plagioclase and quartz and contains variable amounts of K-feldspar and biotite; itit is principally of plagioclase and quartz is gradational into biotite-amphibole gradational biotite-amphibole schist schist and and cummingtonite-, cummingtonite-, gedrite-, and and magnetite-bearing magnetite-bearing schists. schists. Plagioclase, the most most abundant occurs as as anhedral 4), occurs anhedral to to subhedral subhedral Plagioclase, the abundant mineral mineral (table (table 4), porphyroclasts as much as 2 mm in diameter, and as smaller, recrystallized grains (oligoclase) porphyroclasts mrn in diameter, and as smaller, recrystallized grains (oligoclase) as as mantle aggregates and intragranular aggregates aggregates (Hanmer, 1982). 1982). Combined Combined Carlsbad-twinning Carlsbad-twinning in porphyroclasts is is partly partly obliterated obliterated by bystrain. strain. Locally, Locally,the theporphyroclasts porphyroclastsare areantiperthite. antiperthite. The the porphyroclasts recrystallized, is intragranular plagioclase untwinned or weakly twinned. generally weakly twinned. The recrystallized, intragranular plagioclase generally is untwinned porphyroclasts commonly contain small rounded blebs of quartz; the recrystallized porphyroclasts commonly recrystallized grains lack quartz are generally weaklytoto moderately moderatelyaltered altered to to sericite, sericite, and and (or) blebs. The porphyroclasts porphyroclasts are generally weakly (or) epidote/clinozoisite and and calcite. calcite. Quartz commonly of sutured grains, reciystallized as lensoid lensoid aggregates aggregates of grains, which which in part part commonly is recrystallized express a foliation; grains are generally larger than the express foliation; the recrystallized recrystallized grains generally somewhat somewhat larger the associated associated plagioclase. Many recrystallized plagioclase. Many quartz quartz aggregates aggregates contain contain inclusions inclusions of of recrystallized recrystallized plagioclase plagioclase and biotite, of the quartz occurred biotite, indicating indicating that recrystallization recrystallization of occurred after grain grain size-reduction size-reduction of plagioclase and biotite. Biotite is various shades of olive brown, and for the most part occurs occurs in in shears shearsin in association association with recrystallized plagioclase, plagioclase, K-feldspar, K-feldspar,and and minor minor quartz. quartz. This with This biotite biotitecommonly commonly isis obliquely obliquely oriented to the strike of the shears. In relatively unsheared rocks, the biotite retains its oriented strike of the shears. relatively unsheared rocks, its original original with sphene. grain size and orientation; orientation; commonly, commonly, this biotite biotite isis associated associated closely closely with is sparse sparse or absent in most K-feldspar is most of of the the biotite biotite schist. schist. It occurs as interstitial twinned twinned microcline grains, grains, rare rare microcine porphyroclasts, and as recrystallized, very fine grained material microcline porphyroclasts, as recrystallized, very fine grained in shears and core-mantle core-mantle aggregates. aggregates. Accessory Accessory minerals minerals are are zircon, zircon, apatite, apatite, opaque opaqueoxides, oxides, and and allanite (altered). Riotite-amyhil,ole schist Biotite-amohibole This rock type differs mainly from biotite schist schist in containing containing aa few few percent percent of ofamphibole. amphibole. The amphiboles are mainly mainly hornblende or related related actinolitic actinolitic hornblende hornblende or or actinolite, actinolite, but but include include colorless clinoamphiboles, mainly cummingtonite(?). The hornblende is a green or bluish-green colorless clinoamphiboles, mainly cummingtonite(?). green or bluish-green variety, which which locally locally isis variably variably altered altered to actinolitic hornblende hornblende or actinolite. actinolite. It is commonly commonly intergrown with with biotite, biotite, and occurs as both original intergrown original crystals crystals and as as recrystallized recrystallized hornblende hornblende with with K-feldspar and and quartz quartz in shears. The associated biotite, plagioclase, plagioclase, and locally, K-feldspar Theclinoamphibole clinoamphiboleisis relatively widespread widespread as a minor component of of the the rocks. rocks. ItItisistypically typically colorless, acicular or bladed, angle of of tos-15'. 10 0l50. Tentatively, and has a high relief and an extinction extinction angle Tentatively, the the mineral mineral is is identified identified as cummingtonite. cummingtonite. 6 �Amphibole schist schist Amohibole Amphibole schist is interlayered. with the the biotite biotite and as Amphibole schist is interlayered with and biotite-amphibole biotite-amphibole schists, schists, mainly mainly as subordinate discrete compositional layers a meter or more thick. Contacts with the biotite-bearing subordinate discrete compositional layers a meter or more thick. Contacts with the biotite-bearing schists are are sharp. schists sharp. The Theschist schistisisdark darkgray, gray,fine finetotomedium mediumgrained, grained,generally generallyequigranular, equigranular, and and strongly foliated. It ranges from massive and homogeneous to a thinly layered strongly foliated. It ranges from massive and homogeneous to a thinly layered rock. rock. It It is is dominantly of of lower dominantly lower amphibolite amphibolite facies facies metamorphic metamorphic grade. grade. The rocks The rocks are are mainly mainly composed composed of of amphibole amphibole and and plagioclase plagioclase (table (table 4) 4) but but locally locally contain contain as as much as 10 percent quartz and (or) magnetite and sparse biotite. Epidote and chlorite are the the much as 10 percent quartz and (or) magnetite and sparse biotite. Epidote and chlorite are principal alteration minerals. The principal Theamphibole amphibolevaries varieswidely widely from green hornblende hornblende to tobluish-green bluish-green hornblende, or actinolitic hornblende, to pale-green actinolite, reflecting a decrease in metamorphic grade from lower amphibolite to actinolite ca. 0.1-0.3 0.1-0.3 actinolite facies. facies. Plagioclase Plagioclaseisis partly partly recrystallized recrystallized to to ca. mm-diameter grains, which are finer grained than the associated amphibole. Quartz mm-diameter grains, which are finer grained than the associated amphibole. Quartz is an an interstitial mineral. Magnetite Magnetiteisisdisseminated disseminatedthrough throughthe therocks rocksasassmall smallsubhedral subhedralcrystals. crystals. Magnetite-rich schist Magnetite-rich schist 20 modal modal percent percent of magnetite is exposed on Magnetite-bearing schist containing as much as 20 of the broad hill in the SEI/4 the southwest southwest side of SE1/4 of of section section 6, 6, T. T. 31 31 N., N., R. 17 17 E. and on the the lower lower immediately to to the the west west (fig. (fig.8). 8).The The magnetite magnetite units units trend trend northeastward but their and smaller hills immediately their lateral extent and length have not been delineated. The magnetic rocks are interlayered lateral extent length not been delineated. magnetic rocks interlayered with with biotite-amphibole schist and and amphibole amphibole schist. schist. principal lithotypes lithotypes contain contain uncommon uncommonamounts amountsof ofmagnetite: magnetite: (1) Two principal (I) actinolite-magnetite actinolite-magnetite schist and and (2) cummingtonitecummingtonite- or or grunerite(?)-magnetite grunerite(?)-magnetite schist. schist. Although both of these rock types are compositionaUy compositionally layered, the magnetite is disseminated disseminated through them, them, apparently indiscriminantly, indicating indicating that that the the magnetite is a metamorphic mineral formed by the breakdown indiscrirninantly, of iron-rich of iron-rich silicate silicate minerals minerals that that were were redistributed redistributed during during the theductile-brittle ductile-brittle deformation deformation accompanying the the shearing. shearing. Possibly the protolith protolith had had aa higher higher iron iron content content than than most most of of the the other other accompanying Possibly the volcanic rocks rocks in the interlayered schist unit. schist unit. Granite Granite gneiss gneiss Granitic Granitic gneiss ranging in composition from tonalite to granodiorite granodiorite(table (table5; 5;fig. fig. 3) is a major fig. 2). 2). It crops out in the western part of section constituent of the Mountain shear shear zone zone (unit (unit Xgn, Xgn, fig. 5S and the eastern eastern part part of of section section 6, 6,T. T. 31 31 N., N.,R. R.17 17 E. E. (fig. (fig. 8), within an area area of of about about 11km2, km2, and forms spectacular, spectacular, nearly nearly continuous continuous exposures exposureson onseveral severalhills hillsininthis thisarea. area. The gneiss gneiss contains local rafts of amphibolite. from other felsic rocks in the shear amphibolite. It is distinguished distinguished from shear zone zone mainly mainly in in being coarser grained and and lighter lighter in in color. color. The gneiss isis megascopically medium-grained rock characterized megascopically a light-gray, light-gray, generally medium-grained characterized by by narrow, discontinuous, commonly intersecting intersecting dark-gray dark-gray mafic-rich mafic-rich zones zones and by coarse, lensoid narrow, discontinuous, commonly lensoid zones are seen to quartz aggregates. aggregates. In thin thin section, section, the dark-gray dark-gray zones to be be ductile ductile shear shear zones zones (S-C (S-C structures; Lister and and Snoke, Snoke, 1984) 1984) composed composed mainly mainly of fine-grained (commonly (commonly less than 0.2 0.2 mm in diameter) biotite, biotite, rare rarehornblende, hornblende, plagioclase, plagioclase, and and microcline microcline that that have have formed formedby bygrain-size grain-size protomylonite, but but in part part they are reduction of the original minerals. Overall, Overall, the rocks rocks are are mainly protomylonite, orthomylonite, orthomylonite, as defined by by Wise and others others (1984). (1984). 7 �Plagioclase (oligoclase) is It occurs is typically typically bimodal. bimodal. It occurs as as (1) (1) sub-rectangular sub-rectangular to to lath-like lath-like porphyroclasts 1-5 with somewhat somewhat finer finer grained, grained, anhedral, anhedral, nearly nearly equigranular equigranular porphyroclasts 1-5mm mm across associated with (—0.5-1mm mmdiameter) diameter) and (2) as plagioclase (-0.5-1 as fine-grained, fine-grained, recrystallized, recrystallized, intragranular intragranularplagioclase plagiodase less than than 0.2 0.2 mm mm in indiameter. diameter. Both the commonly less the porphyroclasts porphyrodasts and the the associated associated intragranular intragranular plagioclase are periclinelaws, laws, are twinned twinned according according to to the thecombined combinedCarlsbad-albite Carlsbad-albitelaws, laws,and andlocally, locally,pericline and at places have a small amount of patch antiperthite; in a few sections, quartz blebs at have small of antiperthite; in a few sections, quartz blebs are arevisible. visible. are present in Rarely, K-feldspar blebs are in the the plagioclase. The Therecrystallized recrystallizedplagioclase plagioclaseoccurs occurs as astype type IP IP mantle aggregates aggregates (Hanmer, (Hanmer,1982), 1982),intragranular intragranularplagioclase plagioclasethat that at atplaces places completely completely obliterates obliterates the original grains, and and as fine-grained fme-grained material material in in narrow narrow shear shear zones zones that that transects all the original It is minerals except except biotite. The recrystallized plagioclase generally is untwinned. The recrystallized plagioclase generally is untwinned. It is typically typically less less altered by by weathering than the the original original grains. grains. Quartz is recrystallized of coalesced, coalesced, sutured sutured and and strained grains that are recrystallized into aggregates aggregates of are Quartz distinctly coarser grained than the associated recrystallized plagioclase, distinctly coarser grained the associated recrystallized plagioclase, microcline, microcline, and biotite. biotite. Typically,the the aggregates aggregatesare are lensoid, lensoid,as as much much as as 44 or 55 mm mm in in length, length, and andconsist consist of of several several Typically, individualgrains grains0.3 0.3toto 11mm mminindiameter. diameter. Some quartz is crackled crackled by by late late brittle brittle fractures. fractures. The individual The aggregates locally locally contain contain considerable considerable plagioclase plagioclaseand and are are transected by late aggregates late shears shearsfilled filled with with recrystallized biotite, biotite, plagioclase, plagioclase,and andmicrocline. microcline. The The quartz quartz lenses lenses impart impart a foliation to the rock, recrystallized which is conspicuous conspicuous on on weathered weathered surfaces surfaces because because the the quartz stands out in relief. which sparse. ItIt occurs Microcline generally is sparse. occursmainly mainly as as interstitial interstitialgrains grains between between plagioclase plagioclase and and quartz and as recrystallized fine-grained (—0.2-0.3 mm in diameter) material intergrown with and as recrystallized fine-grained (-0.2-0.3 mm in material intergrown with plagioclase and biotite in in narrow narrow shears. shears. Biotite is is grayish olive to greenish greenish brown brown and and occurs occursentirely entirelyas asclots dotsof ofvery very fine fine(0.1-0.2 (0.1-0.2 mm) mm) Biotite grain size that are nearly confined to narrow shears--the Cand S-surfaces of Berthé and others are nearly confined to narrow shears-the C- and S-surfaces Berth6 and others (1979) and and Lister and intergrown with withrecrystallized recrystallized (1979) and Snoke Snoke (1984). (1984). The biotite biotite generally generally isisintergrown plagioclase and microcline, and commonly is oriented obliquely to the the S-surfaces S-surfaces (foliation), (foliation), thus thus indicating a unidirectional movement movement along along the theS-surfaces S-surfaces(Simpson, (Simpson, 1986). 1986). With Withfew fewexceptions, exceptions, the biotite is is closely closely associated with epidote, sphene, and magnetite, magnetite, suggesting suggesting that itit probably probably isis secondary after after hornblende. hornblende. Sparse secondary Sparsegarnet garnet isisassociated associated with with biotite biotite in in one one section. section. Amphibole is is uncommon uncommonin in the the granite granite gneiss. gneiss. Where present, it is a dark-green Amphibole dark-green or darkdarkIn two sections, it is in late shears bluish-green hornblende that is intergrown with biotite. is intergrown sections, it shears and and bluish-green hornblende by prograde metamorphism. metamorphism. Possible Possible pseudomorphs pseudomorphs of an appears to have have formed from from biotite biotite by original hornblende consist of epidote, biotite, biotite, sphene, sphene, magnetite, magnetite, quartz quartzand, and,locally, locally, hornblende. hornblende. minerals include zircon, zircon, apatite, apatite, and allanite (altered). Accessory minerals The chemical composition of 3 samples of granite gneiss is given in table 1. 1. is the the granodiorite granodiorite (fig. (fig.2). 2). The granodiorite borders the The protolith of the granitic gneiss is southeast margin of the shear shear zone, zone, strikes strikes into into it, it, and was incorporated into into the the shear shearzone, zone, where where it was deformed and metamorphosed under under conditions conditions of of the the lower lower amphibolite amphibolite facies facies during the the ductile shearing. shearing. The Thedeformation deformationwas wasaccompanied accompanied by by pronounced pronounced mineralogic mineralogic changes changes in the the amounts amounts of modal quartz and amphibole. amphibole. Comparison Comparison of of modal modal analyses analyses of of the the granitic granitic gneiss gneiss 5) and and the granodiorite (table 2) indicate indicate that the the gneiss gneiss contains about 15 15 percent more more (table 5) quartz than the the protolith and and has has much much less amphibole. The The apparent apparent decrease decrease in in K-feldspar K-feldspar in in the gneiss, as as indicated indicated by by modal data, probably results from original variations variations in in the amount of of KKgneiss, feldspar in the granodiorite, granodiorite, and and thus thus almost almost certainly certainly isis aa sampling sampling problem. 8 �The The increase increase in in modal modal quartz quartz in in the thegneiss gneiss (fig. (fig. 3) over over the the protolith protolith appears appears to to be be related related to to metamorphic metamorphicreactions reactionsaccompanying accompanyingthe the deformation. deformation. Specifically, Specifically,the the increase increasein in quartz quartzfrom from an an average average of of about about 21 21 percent percent in in the thegranodiorite granodiorite to to an anaverage average of of more more than than 36 36percent percent in inthe the gneiss is attributed to the separation of silica from plagioclase during recrystallization. Relatively gneiss is attributed to the separation of silica from plagioclase during recrystallization. Relatively undeformed undeformed plagioclase plagioclase in in the the granodiorite granodiorite appears appearshomogeneous homogeneous in in thin thin section, section, whereas whereas in in the the partly partly deformed deformedrocks, rocks, plagioclase plagiodase contains contains abundant abundant tiny tiny inclusions inclusions of of quartz. quartz. Within Within the theshear shear zone zoneitself, itself, the theplagioclase plagioclase appears appears to to lack lack tiny tiny quartz quartz blebs, blebs, but instead instead contains contains larger, larger, generally generally rounded inclusions of quartz or coalesced groups of inclusions sufficiently large to be rounded inclusions of quartz or coalesced groups of inclusions sufficiently large be counted counted modally. Quantitative estimates of the amount of quartz clearly associated with modally. Quantitative estimates the amount of quartz clearly associated withparticular particular plagioclase plagioclase grains have not been been determined, determined, but but we we suggest suggest that that the the aggregate aggregate amount amountofofsilica silica derived of the plagioclase plagioclase isis on on the the order order of 10 percent, to account recrystallization of derived from from recrystaffization account for the increase increase of of modal modalquartz quartzininthe thegranite granitegneiss. gneiss.Chemical Chemicalanalyses analyses (table (table 1) 1)also alsoshow showhigher higher 5i02 SiO, values in the shear zone. The processes involved in the release of silica from plagioclase during values in the shear zone. The processes involved in the release of silica from plagioclase during progressive progressive deformation deformation are are presumed presumed totobe, be.first, first,exsolution exsolutionof ofsilica silica as as aasubsolidus subsolidus reaction reaction during duringinitial initialrecrystallization recrystallizationof ofplagioclase plagioclaseand, and, second, second, the the migration migration and andcoalescence coalescence of of individual individual quartz quartzblebs blebsinto intolarger largergrains grainsduring duringductile ductile deformation deformation of of the therock. rock. Inasmuch Inasmuchasasthe thequartz auartzwas was relatively more mobile than the associated plagioclase (and microcline) in the stress field, relatively more mobilethan the associated plagioclase (and microcline) the stress field, itit differentially differentially flowed flowed into into lensoid lensoid masses masses oriented orientedperpendicular perpendiculartotothe themajor majoraxis axisofofstress. stress. Baldwin Baldwin Conglomerate Conglomerate The Baldwin Conglomerate Conglomerate (unit (unit Xb, Xb,fig. fig. 2) 2) isis aa lens-shaped lens-shaped metaconglomerate metaconglomerate unit unit about about TheBaldwin 2.3 2.3 km km long long and andaamaximum maximumof of150 150m m wide wide that thatisisexposed exposedlocally locally along the northwest northwest margin margin of of the theshear shearzone. zone. ItItunconformably unconformablyoverlies overlies metavolcanic metavolcanic rocks and granite granite gneiss gneiss within within the the shear shear zone HagerRhyolite Rhyolite(Lahr, (Lahr,1972). 1972). zoneand andisistruncated truncated and andintruded intrudedon onthe thenorth northby bythe theHager The Themetaconglomerate metaconglomerate has has relict relict sedimentary sedimentary layering layering and possible possible scour scour features features and and contains gneiss, and and quartzite. quartzite. All containssubrounded subroundedtotosubangular All but but the the subangularclasts clastsof of metavolcanic metavolcanic rocks, gneiss, quartzite quartziteare areofoflocal localderivation; derivation;the thequartzite quartziteclasts clastsprobably probablywere werederived derived from from the the more moredistal distal quartzite quartzite bodies bodies exposed exposed at at McCaslin McCaslin Mountain Mountain and and Thunder Thunder Mountain, Mountain, 20 20 km km and and1010 km, km, respectively, respectively,north northofofthe theMountain Mountainshear shearzone zone(Sims, (Sims,1990; 1990;Sims Simsand andPeterman, Peterman, 1988). 1988). Clasts Clastsof of the theHines HinesQuartz QuartzDiorite Diorite(unit (unitXh, Xh,fig. fig.2)2)have havenot notbeen beenreported reportedininthe themetaconglomerate metaconglomerate (Lahr, (Lahr, 1972). medium-grained 1972). The Thematrix matrixisisa gray, a gray,finefine-toto medium-grainedrock rockcontaining containingquartz, quartz,feldspar, feldspar,biotite, biotite, muscovite, and hornblende. A weak foliation exists that is approximately parallel to the bedding. muscovite, and hornblende. A weak foliation exists that is approximately parallel to the bedding. Hines HinesQuartz QuartzDiorite Diorite The fig. TheHines HinesQuartz QuartzDiorite Diorite(unit (unitXh, Xh, fig.2)2)occurs occursmainly mainlyasasa alenticular lenticularintrusive intrusivebody bodyabout about 33km long and 0.4-0.5 km wide in the southwestern part of the Mountain shear km long and 0.4-0.5 km wide in the southwestern part of the Mountain shearzone. zone. Except Exceptfor for exposures exposureson onhills hillsininthe theSWI/4 31N., N., R.R.1616E.E.(see (seeSims, Sims,1989), 1989),outcrops outcropsare aresmall small SW1/4section section12, 12,T.T.31 and intrudes adjacent anddispersed. dispersed.The Thequartz quartzdiorite diorite intrudes adjacentmetavolcanic metavolcanicrocks rocksand andcontains containslocal, local,small small inclusions of them. It is intruded to the southwest by the Belongia Granite inclusions of them. It is intruded to the southwest by the Belongia Granite(unit (unitYwb, Ywb,fig. fig.2) 2)of ofthe the Wolf 1972).which whichisisnot notdiscussed discussedininthis thisreport. report. WolfRiver Riverbatholith batholith(Lahr, (Lahr,1972), The virtuallyundeformed, undeformed,indicating indicatingthat thatititwas wasintruded intrudedinto intoand andalong alongthe the Thequartz quartzdiorite dioriteisisvirtually shear meter-thickdike dikeininthe theSE1/4NWI/4 SE1/4NW1/4section section7,7,T.T.31 31N., N.,R.R. shearzone zoneas asthe theshearing shearingwaned. waned. AAmeter-thick 17 17E. E.(fig. (fig. 8)is 8) isintruded intrudedalong along the the 2S,foliation. foliation. ItIthas hasa aU-Pb U-Pbzircon zirconage ageofof1,812.7±3.6 1,812.723.6Ma Ma(Sims (Sims and andothers, others,1990). 1990). 9 �The The rock rock isisdark darkgray, gray,locally locally slightly slightly mottled, mottled, massive, massive, and and medium medium grained. grained. Primary Primary subophitic textures are by plagioclase plagioclase laths, laths, but but the theprimary primarymafic maficmineral--apparently mineral-apparently subophitic textures are retained retained by clinopyroxene--is so highly highlyaltered altered to to aa pale-green pale-green amphibole amphibole (actinolitic (actinolitic hornblende), hornblende), actinolite, actinolite, clinopyroxene--is so biotite, and opaque oxides and locally chlorite that its primary texture is largely obliterated. biotite, and opaque oxides and locally chlorite that its primary texture is largely obliterated. Although little little deformed, Although deformed, the the quartz quartzdiorite dioriteisiscut cutby bylocal localmylonitic mylonltic shears. shears. Plagioclase(Ann4), (An), thethe major mineral (table Plagioclase major mineral (table3),3),isisweakly weaklyaltered, altered, has has aa moderate moderate concentric concentric zoning, is tabular tabular to lath-shaped, and is twinned according to to the the combined Carlsbad-albite and the pericline laws. mm long. long. Quartz laws. Crystals Crystalsare aretypically typically2-4 2-4 mm Quartz isis interstitial, interstitial, somewhat somewhat strained, and and highly variable variable modally (table 3). 3). The as an an alteration alteration mineral The biotite biotite associated associated with with clinopyroxene clinopyroxene as mineral is dark dark reddish reddish brown. brown. Elsewhere in the rock, the biotite is dark yellowish brown, and is always associated with opaque Elsewhere rock, the biotite is dark yellowish brown, and is always oxides. Cummingtonite Cummingtoniteisis aa local local alteration alteration product product of of actinolitic actinolitichornblende, hornblende, occurring occurring as as colorless colorless needles Apatite, zircon, zircon, and and allanite needles extending extending outward outward from from the theactinolitic actinolitichornblende. hornblende. Apatite, allanite are common accessory accessory minerals. REGIONAL STRUCTURE REGIONAL STRUCTURE The rocks rocks southeast southeast of the the shear shear zone zone have have aasingle singlepenetrative penetrative structure structure (cleavage (cleavage or or schistosity, S) that is interpreted as the regional foliation. It is generally subparallel to layering and schistosity, S,) that is interpreted as the regional foliation. It is generally subparallel to layering pillow structures (Se) but locally is is crosscutting. crosscutting. The structure (So) but structure is is expressed expressed by by sub-planar sub-planar fractures, fractures, biotite sheets, sheets, and flattened clasts. s1 occurs both in the aligned biotite S, occurs the metamorphic metamorphic and and granitoid granitoid rocks. rocks. Flattened mafic volcanicinclusions inclusionsininthe thegranodiorite granodioriteare areoriented orientedparallel paralleltotoS,.S1.S,1 is Flattened mafic volcanic is oriented northward and dips steeply; within within the the map area, the strike ranges from about N. N. 150 15 W. W. to N. N. 25 ' E. (fig. 5). SHEAR ZONE The Mountain Mountain shear zone zone sharply sharply truncates truncates and and isis distinctly distinctly younger younger than the the regional regional foliation () and foliation (S,) and resulted resulted from a ductile ductile shear shear deformation deformation (D2) (D,) that was superimposed superimposed on the regional D2 structures structures are modified regional foliation foliation (fig. (fig. 2; table table 6). 6). D, modified locally locally by two two younger younger ductile ductile deformation which do do not not appreciably appreciabty affect the distribution of the DJ, which the rocks, rocks, and and deformation events events (D3 (D3 and D4), still younger younger kink kink bands formed by brittle deformation (Sims and others, 1990; Fk, table 6). (Sims others, 1990; F,,, Mesoscopic Structure Structure Mesoscopic 55, E. E. and and isis ito 1 to2.5 2.5km kmwide. wide.S2 S, foliation foliationwithin within the the shear shear The shear zone strikes about N. 55 average strike strike of of N. N.55" 55' E. dip. Northwest-oriented E. and a moderately moderately steep southeast dip. Northwest-oriented zone has an average of the shear S-surfaces within within the the shear zone are local local relicts of S,,/S,. The southeastern margin margin of zone--the abrupt. Jt zone-the transition transition between between mylonitic mylonitic and and non-mylonitic non-mylonitic rocks--is abrupt. It is is composed of narrow zones of mylonitic mylonitic rocks rocks that that clearly clearlytruncate truncateS, S structures (as can be seen at stop 2). The Thetransition transition zone is 100 wide. The 100 m or less wide. The boundary boundary is is aa zone zone of of deformation deformation and and differential differential displacement displacement of the without apparent separation. the walls walls accomplished by ductile flow, flow, without separation. The shear zone is truncated on on the the north north and andnortheast northeastends endsby by the theyounger youngerHagen Hagen Rhyolite, Rhyolite, and on 1.47 Ga Wolf Wolf River River batholith, batholith, on the the southwest southwest end end by by granitic granitic rocks rocks (unit (unit Ywb, Ywb, fig. fig. 2) of the 1.47 which had had little or or no tectonic effect on the rocks in the shear zone. Accordingly, which Accordingly, neither the the full full width nor the termination width termination of of the the shear shearzone zoneisisknown. known. 10 �The The dominant dominant structures structures in the the shear shear zone zone are arerelated related totoD2 D, and andconsist consist mainly mainly of of an an SSsurface (S2) (S,) resulting from tectonic tectonic layering and and aa mylonitic mylonitic foliation; foliation; aa stretching stretchinglineation lineation(L2), (L,), expressed by elongate elongate clasts, clasts, rodding, rodding,and andbiotite biotitestreaks, streaks;and andrare rare folds folds of of S, 2 surfaces expressed by surfaces (L2). (L,).The The resulting structure is an L-S tectonite (Ramsay, 1980). The younger ductile structures (D3, D4) that structure is an L-S tectonite (Ramsay, 1980). The younger ductile structures (D3,D,) that are modi' the are superposed superposed on on the the older older structures structures (table (table 6) 6) do do not not appreciably appreciably modify thegeometry geometry of of the the rocks. rocks. In S consists In the the granitoid granitoidrocks, rocks, which which were were relatively relatively isotropic initially, initially, S, consists dominantly of thin anastomosing, commonly commonly sigmoidal sigmoidalbiotite-rich biotite-richzones zonesand and oriented, oriented, flattened flattened aggregates of quartz (S-C (S-C structure); structure); aa related related lineation lineation isis given given by by streaked streaked biotite biotite aggregates aggregates and and quartz quartz rods, rods, composed of of fine-grained fine-grained recrystallized recrystallized aggregates of quartz. In Instrongly stronglyanisotropic anisotropicrocks, rocks,such suchas as bedded tuff, locallyexpressed expressed by by brecciated brecciated and and boudinaged, boudinaged, hard hard (siliceous) (siliceous) layers layers that that have have tuff, 2S,isislocally been has been been tectonically deformed deformed into been tightly tightlyfolded foldedso sothat thatSO/S1 S,,/Sl has into parallelism parallelismwith withS2. S? Elsewhere, Elsewhere, segments of S0/S1 surfaces have not been completely transposed. In layered felsic-mafic In layered felsic-maficrocks rocks(unit (unit segments of So/Slsurfaces have not been Xwa, fig. 2) 2) in the Xwa, fig. the northeastern northeastern part part of ofthe theshear shearzone, zone,the thefelsic felsiclayers layerscommonly commonly have have aa conspicuous 2 foliation biotite that that obliterates S, conspicuous S, foliation expressed expressed by by recrystallized recrystallized biotite S,, whereas whereas the themafic mafic layers 2 foliation layers have have only only a weak S, foliation generally generally expressed expressed by aligned hornblende or chlorite. In Inthese these rocks, rocks, SSocommonly commonlyisis not not appreciably appreciably reoriented reoriented or ortransposed. transposed.The Thefelsic-mafic felsic-maficlayer layercontacts contactsmay may show a slightly zig-zag, sawtooth sawtooth (chevron (chevron fold) fold) pattern pattern similar slightly zigzag, similar to to that thatformed formedby byaaslip slipcleavage. cleavage. F2 are not common, but have F, folds are have been been observed observed at ataafew few localities, localities, especially especially in interlayered interlayered felsic-malic volcanic rocks. The folds generally plunge gently to moderately northeast or felsic-mafic rocks. The folds northeast orsouthwest. southwest. Microscopic Microscopic Structure Structure The The mylonitic mylonitic rocks in the the shear shear zone zoneare arecharacterized characterizedby byrecrystallization recrystallization as asindicated indicated by by conspicuous grain-size reduction. Biotite and quartz are entirely, or nearly entirely, recrystallized, conspicuous reduction. Biotite and quartz are entirely, or nearly entirely, recrystallized, whereas and microcline, whichwere were harder harder than than the whereas plagioclase plagioclase and microcline, which the matrix, matrix, were were only onlypartly partly recrystallized. (1984), the the rocks rocks are aremainly mainly recrystallized. According According to the the classification classification of Wise and others others (1984), protomylonite protomylonite or ororthomylonite. orthomylonite. Biotite Biotite occurs occurs in in irregular, irregular,anastomosing anastomosing trains, trains,commonly commonly associated with recrystallized plagioclase and, locally, microcline. Both the biotite associated with and, locally, microcline. Both the biotite and feldspar are are very mm diameter). Quartz very fine fine grained grained (—0.2 (-0.2 mm Quartzisisrecrystallized recrystallizedinto intooriented orientedlenses lensesororrods, rods,which which are are coarse-grained coarse-grained aggregates aggregates of of individual individual sutured grains <0.5 <0.5 mm mm in in diameter; diameter; commonly, commonly, itit contains inclusions of plagioclase and biotite and, locally, sphene and amphibole. Plagioclase contains inclusions plagioclase biotite and, locally, sphene and amphibole. Plagioclase commonly mm in in diameter diameter and and commonlyisis only only partly recrystallized, recrystallized, itit occurs occurs as as porphyroclasts porphyroclasts as asmuch much as as55 mm commonly has mantles 1982)ofoffine-grained fine-grained(—0.1-0.2 (-0.1-0.2 mm) mm) IPstructures; structures;Hanmer, Hanmer,1982) commonly has mantles (type (type IP plagioclase. plagioclase. Also, Also,fine-grained fine-grainedrecrystallized recrystallizedplagioclase plagioclaseoccurs occurs as as veinlets (shears) (shears) that thattraverse traversethe the rocks. rocks. Kinematic KinematicAnalysis Analysis The The sense sense of of movement movement during during the theF2 F, shear shear deformation deformation has has been been determined determinedfrom fromS-C S-C fabrics fabrics (Berthe (Berth6and andothers, others,1979; 1979;Lister Listerand andSnoke, Snoke,1984) 1984)ininthe themylonitic myloniticgranite granitegneiss gneiss(unit (unitXgn, Xgn, fig. fig. 2), orientation orientation of of stretch stretchfabrics fabrics (long (long axes axes of of strain strain ellipsoids), ellipsoids), and and other otherfield field data datasuch suchasas described described by by Simpson Simpson (1986). (1986). S-C S-Cmylonite mylonitefabrics fabrics(fig. (fig. 6) 6) in in granite granitegneiss gneissfrom from several severallocalities localities show show that the the southeast southeastblock block of of the the Mountain Mountain shear shear zone zoneisisupthrown upthrown relative relative to to the thenorthwest northwest block. block. Stretch Stretchfabrics, fabrics,as asindicated indicated by by the theorientation orientation of ofthe thelong long(X) (X)axes axesof ofstrain strainellipses, ellipses,also also suggest (La,)plunge plungesteeply steeplysouth south suggest the the same same sense sense of of movement. movement. Stereoplots Stereoplotsshow showthat thatstretch stretchaxes axes(Lb) to to east. east.This Thissteeply steeplyplunging plungingstretch stretchfabric fabricisispossibly possibly caused caused by by aa simple simple shear shearcouple couplehaving having aa 11 �dip than the dip shallower dip dip of of the the stretch stretchaxis, axis,as as shown shown on on figure figure 7. 7. Stereoplots at some some localities localities indicate stretch fabric, fabric, whereas whereas aa stereoplot stereoplot at one locality indicates indicates a steep indicate a steep steep easterly easterly Lzb La, stretch Thisdifference difference in in orientation orientationofofstretch stretchfabrics fabricssuggests suggestsaa varying varying sense sense southerly stretch fabric. fabric. This movement of of the shear couple along the length of of the shear zone. of movement Field data suggest suggest that the the sense sense of of movement movement in in the the horizontal horizontal plane plane was was generally dextral (right lateral). At Atthe themap mapscale scale(fig. (fig.2), 2), Si S, foliation foliation appears appearsto to have have been been rotated rotatedclockwise clockwisetoward toward parallelism with granodiorite with the shear zone, which is consistent consistent with with dextral dextral movement. movement. Also, the granodiorite body (unit Xg, dextrally in in the the shear zone as granitic displaced dextrally granitic gneiss (unit Xgn). Xgn). In body (unit Xg, fig. fig. 2) is displaced is supported supported also alsoby by measured measuredaxes axes addition, S-C fabrics suggest dextral movement. Such Such movement movement is of extension extension (L2b) as well as by computed ellipsoid axes; these axes plunge toward the east-southeast (La,) as well as by computed ellipsoid axes; these axes plunge toward the east-southeast that the upthrust southeast block block had had a dextral component component of of quadrant of stereoplots, indicating indicating that movement in the horizontal plane, as as shown shown on on figure figure77 (Sims (Simsand andothers, others, 1990). 1990). On the other movement in horizontal plane, hand, the different horizontal horizontal shear sense from place the variation in in orientation orientationof ofL2b hnsuggests aa different place to to place along the shear zone. GEOBAROMETRY GEOBAROMETRY AND GEOTI-IERMOMETRY GEOTHERMOMETRY The regional regional D1 Dl deformation deformation textures textures and and associated associated M1 M, metamorphic metamorphic minerals minerals were were overprinted in the shear zone by shear-induced D2 fabrics and M2 metamorphic mineral assemblages overprinted in the shear zone by shear-induced D2 metamorphic mineral Hornblendegeobarometry geobarometryof of granitoid granitoid rocks rocks and and metabasalt metabasalt indicates indicates (Day and others, in press). Hornblende M, pressure pressure of of about about 4.5±1 4.5  1Kbar Kbarwas waselevated elevatedduring duringM2 M, to to approximately approximately 6.0±1 6.01 1 that the the regional regional M1 Kbar both within and adjacent to the shear shear zone. Garnet-biotite Garnet-biotitegeothermometry geothermometryindicates indicatesthat thatM1 MI ranged from 5850 585 * to 615 °C, "C,but but that that M2 M2 equilibrium temperatures may may have increased to as as much much as 654 654 C. Inasmuch Inasmuch as as garnet garnet is is rare rare both both outside outside and and inside inside the shear zone, the estimated peak Two-feldspar geothermometry indicates that inside inside M2 thermal thermal conditions conditions are are only approximate. approximate. Two-feldspar the shear shear zone zonethe thefeldspars feldsparsunderwent underwentcontinuous continuoussubsolidus subsolidusreequilibration reequilibration from from peak peakNI2 M, conditions (574 (574 'C C atat6.0 temperatures (280 (280 * 0C at 6.0 6.0Kbar). Kbar). These data Cat conditions 6.0Kbar) Kbar)down down to to very very low low temperatures indicate that both both pressure pressureand andtemperature temperatureincreased increasedduring duringshear-induced shear-inducedM2 M2recrystallization recrystallization within the Mountain shear within shear zone. zone. CONCLUSIONS within the the Mountain shear zone are Rocks within are L-S L-S tectonites tectonites that that fit fit with with the the classic classic definition of aa shear The shear is shearzone zone(Ramsay, (Ramsay,1980). 1980). The is aa local local (discrete) (discrete) linear linear zone zone of of high high ductile ductile deformation. Neither Neither the thewidth width nor nor the thelength length are areknown, known, but we presume that the shear zone had parallel sides prior to to emplacement emplacement of of the theWolf Wolf River River batholith. batholith. In this area, area, the the batholith batholith was was ernplaced passively. passively. emplaced Ramsay classifiedshear shearzones zonesaccording accordingtototheir theirdisplacement displacementfields. fields. The The Mountain Rarnsay (1980) classified shear zone appears to fit best Ramsay's (1980) type (iii) classification; that is, it is a heterogeneous heterogeneous appears to fit best Ramsay's (1980) type (iii) classification; heterogeneous volume volume change. change. Ramsay and Graham (1970) noted simple shear with accompanying heterogeneous that most most deformation from from natural natural orogenic orogenic processes lead to states states of heterogeneous strain, and Ramsay (1980, (1980,p.p. 89) 89) noted noted that "the of practically all shear shear zones zones is is that of Ramsay "the basic basic component component of practically all of heterogeneous simple shear shear .. . . made made up of aa number number of of elements elementsshowing showing homogeneous homogeneous simple simple shear.' The shear." TheMountain Mountainshear shearzone zonehas hasthe thefollowing following features that fit these criteria. . . 12 �(1) Deformation Deformation within within the the shear shearzone zonewas was not not uniform; uniform; domains domainsof ofrelatively relatively low low strain, pre-F2 features features are high strain, strain, where where the country rocks have where pre-F, are preserved, as as well as domains of high been mylonitized, are present. been mylonitized, are present. (2) The nature, nature, magnitude, magnitude, and and orientation orientation of of displacement displacement varies both across and along the shear by the the variation in (a) the shear zone, zone, as as suggested suggested by variation in (a) shape shape of of the the strain strain ellipsoids ellipsoids at at different different localities, (b) percentage percentage of flattening and stretching among the outcrops where strain analyses of flattening and stretching among the outcrops where strain analyseswere were carried out (Sims and others, 1990), pattern along the shear zone; the orientation 1990), and (c) movement pattern orientation out (Sims of the maximum principal shortening direction apparently rotated from nearly nearly west in the northern northern part of the exposed shear zone to north-northwest at at its its southwestern southwestern exposed segment, as indicated by the orientation (La,). orientationofofdeformed deformedclasts clasts(L2b). (3) L-S tectonites of the shear shear zone zone appear appear to tohave haveformed formedprimarily primarily by by plane plane strain, strain, as as indicated by the Flinn Flinn K K values values (Flinn, (Flinn, 1962) 1962) at attwo two localities, localities, which are are very very close close to to 1,1,the thevalue value for plane strain strain (Sims (Sims and others, others, 1990). 1990). Rocks Rocksatatanother anotherlocality, locality,however, however, have have aa K K value value of of 2.4, 2.4, indicating that they lie in the field of apparent constriction. the field of apparent constriction. (4) The The magnitude of both flattening and stretching increases from the southeast margin of the shear zone toward toward the interior. interior. (5) Finally, Roy (1977) (1977) has pointed out that that mylonites mylonites within shear shear zones zones develop develop in in stages stages and that that this this development developmentisisaccompanied accompanied by by chemical chemical mobility. Chemical Chemical mobility mobility is suggested in the Mountain shear shear zone zone by by an apparent apparent substantial substantialgain gain in modal quartz quartz and and some some increase increase in in Si02 SiO, (table 1) of the granodiorite gneiss (unit Xgn) within it, as compared to undeformed granodiorite 1) the granodiorite gneiss within compared undeformed (unit Xg), but this this apparent apparent gain gain has hasnot notbeen beenconfirmed confirmedby by quantitative quantitativechemical chemical studies. studies. REGIONAL SIGNIFICANCE SIGNIFICANCE Prior to the the study study of of the the Mountain Mountain shear shearzone zone(Sims (Sims and and others, others, 1990), 1990), major major northeastnortheasttrending shears shears in in the the Wisconsin Wisconsin magmatic terranes terranes were were known known to have formed subsequent subsequent to to the the main regional regional deformation in the Penokean Penokean orogen orogen (Sims (Sims and Peterman, Peterman, 1983, 1983, p. 8), but data data on on the precise timing were lacking. lacking. The The fortunate fortunate existence existence of of a datable datable intrusive intrusive rock (Hines (Hines Quartz Quartz Diorite, 1,812.7±3.6 1.812.723.6 Ma) within within the the Mountain Mountain shear shearzone, zone,which whichwas was emplaced emplaced during duringthe thewaning waning stages of the ductile deformation deformation and and thus thusestablishes establishes aa firm firm younger limit for the the shearing, provides a benchmark basis. Thus, it can be presumed now that the benchmark for the time of shearing on a regional basis. steep Jump River and Athens shear zones (fig. 1) as (Sims 5O0-60' E. trend (Sims River and Athens shear zones (fig. 1) as well well as others of of N. N. 50°-60 Ma. A and others, 1989) 1989) have comparable ages of about 1,815 1,815 Ma. A deformed deformed intrusive intrusive rock rock within within the the Athens shear zone, age of Athens zone, which which has aa crystallization crystallization age of 1,832±9 1,83229 Ma (Sims (Sims and others, others, 1989), 1989), is is consistent with with this this interpretation interpretation that that the shearing 1,840Ma. Ma. The consistent shearing post-dates post-dates 1,840 The recognition recognition of aa 35m.y. my. after after the themain maincontinent-arc continent-arccollisional collisionalevent event(—1,860 (- 1,860 major ductile ductile deformation deformationevent event25 25toto35 Ma; Sims and others, 1985) along the Niagara fault zone indicates the complexity and tong duration 1985) along the fault zone indicates the complexity and long duration of tectonic events in the the Penokean Penokean orogen orogen and and the theneed needtotoidentify identifyspecific specificevents, events, perhaps perhaps by by names to them, such as has been done in the Wopmay orogen in the Northwest Territories Territories assigning names Bowring, 1984). 1984). ItIt seems seemsimprobable improbable that thatthe the—1,815 (Hoffman and and Bowring, 1,815 Ma ductile deformation deformation could could be aa late late tectonic tectonic episode episode related related to tothe thecollision collision that thatsutured suturedthe theWisconsin Wisconsin magmatic magmatic (arc) (arc) terranes to the the continental continental margin margin at at about about 1,860 1,860 Ma. Ma. Instead, Instead,we wesuggest suggestthat thatthe the—1,815 -1,815 Ma Ma ductile deformation resulted from a continent-continent ductile deformation probably probably resulted continent-continent or continent-arc continent-arc collision collision far removed from northern Wisconsin, probably to to the the south south or or southeast. southeast. AA possible removed Wisconsin, probably possible candidate candidate was was accretion of the Central Central Plains Plains orogen (Sims and Peterman, 1986) 1986) to the North American continent. - 13 �ACKNOWLEDGMENTS ACKNOWLEDGMENTS K.J. G.L. LaBerge, LaBerge, and and Bruce Bruce Brasaede Brasaemle assisted assisted in the geologic mapping mapping of of the K.J. Schulz, Schuk, G.L. Mountain area 1985-86. areainin1985-86. REFERENCES REFERENCES CITED CITED Attoh, Kodjopo, Kodjopo, and and Kiasner, Klasner, J.S., J.S., 1989, 1989, Tectonic Tectonic implications implications of metamorphism metamorphism and andgravity gravityfield field in the 11-933. the Penokean Penokean orogen orogenofofnorthern northernMichigan: Michigan:Tectonics, Tectonics,v.v.8,8,p.p.9 911-933. Barovich, K.M., KM., Patchett, Nd isotopes and the origin of Patchett, P.J., P.J., Peterman, Peterman,Z.E., Z.E., and andSims, Sims, P,K., P.K., 1989, 1989, Nd 1.9-1.7 Ga Ga Penokean Penokean continental continental crust crust of of the Lake Superior region: region: Geological Geological Society Society of America 101,p.p.333-338. 333-338. America Bulletin, Bulletin,v.v.101, Orthogneiss, mylonite Berthe, Berthe, D., D., Choukroune, Choukroune, P., P., and and Jegouzo, Jegouzo, P., P., 1979, 1979, Orthogneiss, mylonite and noncoaxial noncoaxial deformation in granites--the example of the South American shear zone: Journal deformation granites--the example of South American shear zone: Journal of of Structural Geology, v. 1, p. 3 1-42. Structural Geology, v. 1, p. 31-42. Cannon, W.F., 1973, The Penokean orogeny in northern Michigan, jj Young, 1973, The Michigan, in Young, GM., G.M., ed., ed., Huronian Huronian stratigraphy and sedimentation: Geological 12, p. p. GeologicalAssociation Association of of Canada Canada Special Special Paper Paper no. no. 12, 25 1-27 1. 251-271. A revision Cannon, Cannon, W.F., and Gair, Gair, J.E., J.E., 1970, 1970, A revision of of stratigraphic stratigraphic nomenclature nomenclature for for middle middle Precambrian rocks 81, p. rocks in in northern northernMichigan: Michigan: Geological GeologicalSociety Societyof ofAmerica America Bulletin, Bulletin, v. v. 81, 2843-2846. 2843-2846. Day, W.C., P.K.,and and Peterman, Peterman, Z.E., Z.E., in press, Temperature-pressure Temperature-pressure estimates W.C., Sims, P.K., estimatesofofdynamically dynamically recrystallized rocks in the Early Proterozoic Mountain shear zone, northeastern recrystallized Mountain shear zone, northeasternWisconsin: Wisconsin: U.S. Geological 1904-H, p. p. —.. Geological Survey Survey Bulletin Bulletin 1904-H, deformation: Geological Flinn, Flinn, D., 1962, 1962, On folding during three-dimensional three-dimensionaldeformation: GeologicalSociety Societyof of London London Quarterly Quarterly Journal, Journal,v.v.118, 118,p.p.385-433. 385-433. Hanmer, Hanmer, Simon, Simon, 1982, 1982, Microstructure Microstructure and and geochemistry geochemistry of of plagioclase plagioclase and microcline microcline in in naturally naturally deformed granite: Journal of Structural Geology, v. 4, p. 197-2 13. deformed granite: Journal of Structural Geology, v. 4, p. 197-213. Hoffman, P.F., Short-lived 1.9 1.9 Ga Ga continental continental margin and its P.F., and and Bowring, Bowring, S.A., S.A., 1984, 1984, Short-lived its destruction, destruction, Wopmay orogen, northeast Canada: 12,p.p.68-72. 68-72. Canada: Geology, Geology,v.v.12, Holm, D.K., D.K., Hoist, Hoist, T.B., T.B., and and Ellis, Ellis,M., M.,1988, 1988,Oblique Obliquesubduction, subduction,footwall footwalldeformation, deformation, and and Hoim, imbrication--a imbrication-a model for the Penokean orogeny in east-central Minnesota: Geological GeologicalSociety Society of America 100,p.p.1811-1818. 1811-1818. AmericaBulletin, Bulletin,v.v.100, Lahr, M.M., of a greenstone M.M., 1972, 1972, Precambrian geology geology of greenstone belt belt in in Oconto OcontoCounty, County,Wisconsin Wisconsin and and geochemistry of the the Waupee Waupee metavolcanics: metavolcanics: Madison, Madison,University UniversityofofWisconsin, Wisconsin, M.S. M.S. thesis, thesis, 62 p. Larue, D.K., 1985, Florence-Niagara Florence-Niagara terrane--an terrane-an Early Early Proterozoic Proterozoic accretionary accretionary D.K., and and Ueng, Ueng, W.L., W.L., 1985, complex, Lake 96,p.p.1179-1187. 1179-1187. Lake Superior Superior region, region,U.S.A.: U.S.A.: Geological GeologicalSociety SocietyofofAmerica, America,v.v.96, Lister, mylonites: Journal Journal of Lister, G.S., G.S., and and Snoke, Snoke, A.W., A.W., 1984, 1984, S-C mylonites: of Structural Structural Geology, Geology, v.6, v. 6,p.617-638. p. 617-638. Mancuso, JJ., J.J., 1957, 1957, Geology Geology and mineralization mineralization of the the Mountain Mountain area, area,Wisconsin: Wisconsin: Madison, Madison; Mancuso, University of 32 p. p. of Wisconsin, Wisconsin, M.S. M.S. thesis, thesis, 32 Morey, Stratigraphic framework framework of of Middle Middle Precambrian Precambrian rocks in Minnesota, in G.M. 1973, Stratigraphic G.M. Morey, G.B., G.B., 1973, Young, ed., ed., Huronian Huronian stratigraphy stratigraphy and andsedimentation: sedimentation: Geological Association of Canada, Special 12,p.p.211-249. 21 1-249. Special Paper Paper12, Animikie basin, Lake Superior Superior region, region, U.S.A., U.S.A., in in Trendall, Trendall, A.F., A.F., and and Morris, Morris, R.C., R.C., 1983, Animikie basin, Lake 1983, ______ 13-68. Iron-formation--facts and problems: Elsevier ElsevierScience SciencePublishers, Publishers, Amsterdam, Amsterdam, p.p. 13-68. Iron-formation--facts Ramsay, J.G., 1980, 1980, Shear zone geometry--a review: review: Journal JournalofofStructural StructuralGeology, Geology,v.v.2,2,p.p.83-99. 83-99. Ramsay, J.G., J.G., and Graham, R.H., Strain variations variations in in shear shear belts: belts: Canadian R.H., 1970, 1970, Strain Canadian Journal Journal of of Earth Earth Sciences, 7,p. p. 786-813. 786-813. Sciences, v. v. 7, 14 - �Roy, S., S., 1977, 1977,Mylonite Mylonitemicrostructures microstructures and and their theft bearing bearing on development developmentof of mylonites--an mylonites-an example example from deformed deformed trondhjemites trondhjemites of of the the Bergen Bergenarc arcregion, region, SW SW Norway: Norway: Geological GeologicalMagazine, Magazine, v. 114, 114, p. 445-458. 445-458. 1987, AnEarly EarlyProterozoic Proterozoic ophiolite ophiolite in in the the Penokean Penokean Orogen: Geological K.J., Schulz, Schuiz, 1987, An GeologicalAssociation Association of Canada Program and Abstracts, v. 12, p. 87. Canada Program and Abstracts, v. 12, p. 87. Sedlock, R.L., R.L., and and Larue, D.K., Fold axes axes oblique oblique to to the regional plunge and D.K., 1985, Fold and Proterozoic Proterozoic Sedlock, terrane accretion terrane accretion in in the the southern southern Lake Lake Superior Superiorregion: region: Precambrian PrecambrianResearch, Research,v.v.30, 30,p. p. 249249262. Journal of Simpson, Carol, Carol, 1986, Determination of movement Simpson, 1986, Determination movement sense in in mylonites: mylonites: Journal of Geological Geological Education, v. Education, v. 34, 34, p. p. 246-261. 246-261. P.K., 1989, 1989, Geologic Geologic map map of of Proterozoic rocks near Mountain, Sims, P.K., Mountain,Oconto OcontoCounty, County,Wisconsin: Wisconsin: U.S. 1:24,000. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries SeriesMap Map1-1903, 1-1903,scale scale1:24,000. 10 1990, Geologic Geologicmap map of of Precambrian rocks of of Iron 1990, Precambrian rocks Iron Mountain Mountain and andEscanaba Escanaba 1%'' quadrangles, northeastern Wisconsin and northwestern Michigan: U.S. Geological Survey quadrangles, Wisconsin northwestern Michigan: US. Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries SeriesMap Map1-2056, 1-2056,scale scale1:250,000. 1:250,000. Sims, P.K., P.K., Klasner, Klasner, J.S., J.S., and and Peterman, Sims, Peterman, Z.E., Z.E., 1990, 1990, The Mountain Mountain shear shear zone, zone, northeastern northeastern Wisconsin, U.S.A.--A discrete ductile deformation zone within the Early Proterozoic Wisconsin, USA.--A discrete ductile deformation zone within Early Proterozoic Penokean 1904-4p. p. A1-A15. A1-A15. Penokean orogen: orogen: U.S. U.S.Geological GeologicalSurvey SurveyBulletin Bulletin1904-A, Sims, P.K., P.K., and and Peterman, Peterman, Z.E., 1983, Evolution of of Penokean Penokean foldbelt, foldbelt, Lake Lake Superior Superior region, region, and Sims, 1983, Evolution its tectonic of the Great Medaris, L.G., L.G., Jr., ed., ed., Early Proterozoic Proterozoic geology geology of Great tectonic environment, in Medaris, Lakes region: Geological Society of America Memoir 160, p. 3-14. Geological Society of America Memoir 160, p. 3-14. 1986,Early EarlyProterozoic Proterozoic Central Central Plains orogen-A orogen--A major major buried buried structure structure in the north-central north-central United States: Geology, Geology,v.v.14, 14,p.p.488-491. 488-491. 1988,The The Mountain Mountain shear shear zone--Relevance zone--Relevancetotoage age of of quartzite quartzite at McCaslin 1988, McCaslin and Thunder northeastern Wisconsin: Thirty-fourth meeting, Institute Institute on Lake Lake Superior Superior Mountains, northeastern Thirty-fourth annual meeting. Geology, Marquette, Michigan, p. 97-99. Marquette, Michigan, p. 97-99. .K.,Peterman, and Schulz, Schuiz, K.J., K.J., 1985, Dunbar gneiss-granitoid gneiss-granitoid dome--Implications dome--Implicationsfor for Sims, P P.K., Peterman, Z.E., and Geological Society Society of America Proterozoic tectonic Proterozoic tectonic evolution evolution of of northern northern Wisconsin: Wisconsin: Geological America 96, p. p. 1101-1112. 1101-1112. Bulletin, v. 96, Sims, P.K., Van Schmus, Schmus, W.R., W.R., Schulz, Schuiz, K.J., K.J., and Peterman, Peterman, Z.E., Z.E., 1989, 1989,Tectonostratigraphic Tectonostratigraphic Sims, P.K., evolution of the EarLy Proterozoic Wisconsin Wisconsinmagmatic magmaticterranes terranes of of the Penokean orogen: Early Proterozoic orogen: Canadian Journal Canadian Journal of ofEarth EarthSciences, Sciences,v.v.26, 26,p.p.2145-2158. 2145-2158. D.L., Morey, G.B., and Southwick, D.L., and McSwiggen, McSwiggen, P.L., P.L., 1988, 1988, Geologic map (scale (scale 1:250,000) 1:250,000) of the the Minnesota Penokean orogen, central and eastern Minnesota, and accompanying text: Penokean orogen, and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of 25 p. 37,25 of Investigations Investigations 37, Wise, D.U., D.U., and others, 1984, Fault-related rocks: Suggestions Wise, 1984, Fault-related Suggestionsfor for terminology: terminology: Geology, Geology,v.v. 12, 12,p. p. 39 1-394. 391-394. - �HELD STOPS FIELD STOPSAND AND ROAD ROAD LOG LOG FIELD STOPS ARE SHOWN ON FIGURE 88 STOP 11 Riverview road, 0.7 0.7 mi mleast east of of County County Highway Highway(Co. (Co.hy.) hy.)W. W. Park Park in in open space at Riverview road, junction. Walk road junction. Walk east east 0.1 0.1 mi mi through through woods to prominent knob. knob. Massive to pillowed pillowed porphyritic porphyriticbasalt. basalt. Pillows Pillows are are about 11ft thick and 2 ft long; they they Massive trend N. 500 50' W., W., dip steep, and top to southwest. southwest. Outcrops Outcropsare aretypical typical of of Xwm Xwm unit (Sims, 1989); 1989); they they are are outside the shear shear zone. zone. of Waupee Volcanics (Sims, Drive west west on on Riverview road to to Co. Co. hy. hy. W; W; turn left (southwest) Drive Riverview road (southwest) on hy. hy. W and and mi; turn left left (east) on Bear Paw road and proceed for 1.1 1.3 mi; 1.1 mi; mi; park on proceed for 1.3 north side of road. STOP STOP 22 This outcrop area extends extends westward westward for about 0.2 0.2 ml. mi. It contains contains dominantly dominantly felsic felsic volcanic rocks rocks (Xwf, (Xwf, fig. fig.2;2;Sims, Sims,1989) 1989)that thatare are intruded intruded on the west volcanic west by by porphyritic (Xg, fig. fig.2). 2). The outcrops are outside the shear zone. granodiorite (Xg, unit; a crude The most easterly easterly outcrops outcrops are are aalayered layered biotite-garnet biotite-garnet s.chist schist of Xwf Xwf unit; crude layering is is expressed expressedby bygarnet-rich garnet.richzones. zones.Numerous Numerousflattened flattenedclasts clastsare arepresent. present. S, 1 layering foliation is subparallel subparallel to to layering layering (So); (Se);ititisisoriented oriented N. N. 28' 280 E., E., 78' 780 NW. NW. (fig. (fig. 9). 9). A A foliation ft-wide zone zone of of folding foldingdeforms deformsS,.5r Axial planes planes to to these folds trend trend N. 70' 700 E. and 3 ft-wide 820 SE. This correspondsto to S2 s2inside insidethe theshear shearzone. zone. The dip 82' Thisorientation orientation roughly roughly corresponds folded zone is interpreted to folded zone to be be aasmall smalldomain domain of ofF2 F2deformation deformation that that developed developed outside the shear shear zone. zone. Westward, narrow dikes dikes of of granodiorite-tonalite granodiorite-tonaliteand andpink pink aplite aplite of of Xg Xg unit unit cut cut the Westward, narrow schist. The The westernmost westernmost outcrops outcrops are aredominantly dominantly porphyritic porphyritic granitoid granitoid rocks rocks (Xg unit, fig. 2) 2) that that contain inclusions of of amphibolite amphibolite and and biotite biotite schist. schist. The granitoid rocks are fig. are nearly massive. massive. Return to Bear Paw road. road. Proceed of 0.4 0.4 mi. mi. Walk Proceed west west for a distance of Walk north about Return 0.05 mi ml to outcrop outcrop of of aa pink pink granite granite gneiss. gneiss. STOP 3 cut by by pink pinkaplitic apliticgranite; granite; these these rocks rocks are are within within the The granite granite gneiss gneiss (Xgn, fig. fig. 2) is cut Mountain zone. The Mountain shear zone. Thegranite granite gneiss gneiss has has aa prominent prominent 2S2foliation foliationexpressed expressed by by 86 SE aligned E., 86' SE(fig. (fig. 10). 10). The Thesoutheastern southeastern aligned biotite sheets that is is oriented oriented N. N. 530 53- E., margin of of the shear zone lies margin lies in the northeast-trending northeast-trending valley valley to the east of Stop Stop 3. Return to Bear Paw Paw road. Proceed Proceedwest weston onthis thisroad roadtotojunction junction with with County County Highway Highway W. road. Park W. Turn Turn right right (northeast) (northeast) on onHighway Highway W and proceed to Riverview Riverview road. Park on on Riverviewroad road and and walk walk southwest southwest on on Highway HighwayW Wfor for aa distance distance of of 0.35 0.35 mi. mi. Walk Riverview Walk southeastward onto mylonitic granite granite gneiss. gneiss. onto outcrops outcropsof ofmylonitic STOP STOP 44 These outcrops These outcrops of of granite granite gneiss gneiss (mylonite) (mylonite) (Xgn, (Xgn, fig. fig. 2) 2) have havewell-defined well-defined S-C S-C structures (Berthé 1984). C is a foliation oriented (Berth6 and others, others, 1979; 1979; Lister and Snoke 1984). subparallelto to the the southeastern southeastern boundary boundaryofofthe theshear shearzone. zone. The relation subparallel relation of S (an oblique foliation) to C indicates that the southeast block of the shear zone is upthrown 16 �relative to to the block. The relative the northwest northwest block. The sense sense of of movement movement in in the the horizontal horizontal plane plane was was generally, but not everywhere, dextral. The stretching lineation (X finite strain generally, but not everywhere, dextral. The stretching lineation (X finite strain axis), axis), as indicated deformed clasts, clasts, plunges plungessteeply steeplysouth southto to east; east; itit is is subparallel subparallel to to the the as indicated by by deformed intersection of intersection of SS and and C. C. Return to Riverview road. road. Proceed Return Proceed southwestward southwestward on on County County Highway Highway W to junction with Bear Paw road, and continue southwest on Highway W for a distance distance of of 1.3 1.3 mi. and continue southwest on Highway W Park in low area, near house house on on northwest northwest side side of of road, road, and and walk walk southwestward southwestward on Highway W Wfor for 0.1 0.1mi. mi. Proceed northwestward to outcrops in the County Highway the woods. woods. STOP STOP 55 These outcrops outcrops are within the shear These shear zone zone and and are aredominantly dominantly felsic felsic biotite biotite schist schist of of (fig. 2). 2). The foliation that that has been folded into a S, foliation unit Xwi Xwi (fig. The schist schist has a prominent prominent S2 (fig. 11). 11). The series of east-southeast plunging plunging folds (F3) (F,) (fig. The axes axes of of these these folds foldshave, have, in in turn, been folded by younger north-trending folds (F4). The axes and axial planes turn, folded younger north-trending folds (F4). axial associated with F4 cannot cannot be be measured on these these outcrops. outcrops. these outcrops, outcrops,the theS2 2 foliation is expressed by by brecciated and boudinaged siliceous siliceous In these layers that are generally parallel to At surfaces places, however, S/S are generally S,. places, however, So/S, surfaces (siliceous layers) are are not transposed parallel parallel to to s2 The occurrence layers) not completely completely transposed S,. The occurrence of isolated isolated domains in which the older SO/S1 foliation is preserved is characteristic of the mylonite domains older S,,/S, foliation is preserved is characteristic of (shear) zone as as aa whole. whole. Return to parking area. Proceed nil to road Proceedwest weston onHighway Highway W for a distance distance of of 1.4 1.4 mi junction junction on left. Proceed Proceed on onthis thisroad roadinto intothe thevillage village of of Mountain Mountain and and to to Wisconsin Wisconsin Highway 32-64. 32-64. Turn left (southeast) on and proceed southward for Highway on Highway Highway 32-64 32-64 and a distance of 0.9 0.9 mi to to low low outcrop outcrop on on north north side sideofofhighway highway in in borrow borrow pit. pit. STOP STOP 66 This outcrop is the Hines Quartz Diorite (unit This (unit Xh, Xh, fig. fig. 2) (named by by Lahr, 1972), 1972), a late-to post-tectonic rock intruded intruded into the Mountain late-to post-tectonic rock Mountain shear shear zone. zone. (It has not not been been noted outside the shear zone). The TheHines HinesQuartz QuartzDiorite Dioritehas hasaaU-Pb U-Pbzircon zirconconcordia concordia intercept age age of of 1,812.7±3.6 1,812.723.6 Ma (Sims (Sims and othets, others, 1990). 1990). km wide wide that that The Hines Quartz Quartz Diorite Dioriteisisaalensoid lensoid body body about about 33 km km long long and and 0.4-0.5 0.4-0.5 km S, foliation; itit is is virtually undeformed, undeformed, although although locally locally was intruded subparallel subparallel to to the theS2 cut by by mylonitic mylonitic shears, shears, and and therefore therefore it establishes a minimum age for the Mountain Mountain shear zone. zone. The Thequartz quartzdiorite dioriteisisdark darkgray, gray,slightly slightlymottled, mottled, massive, massive, and and medium medium grained. Primary plagioclase (Ans4) (An35) laths, grained. Primary subophitic subophitic textures are retained by plagioclase laths, but the the altered to amphibole, primary mafic mineral--probably mineral-probably clinopyroxene--is clinopyroxene--is highly highly altered amphibole, hiotite, biotite, and locally chlorite. chlorite. The The amphibole amphibole is is mainly mainly actinolitic hornblende and actinolite, hut but includes cummingtonite. Noie: AAfacies Note: faciesof ofthe theanorogenic anorogenicBelongia Belongia Granite Granite(unit (unitYwb, Ywb, fig. fig. 2) 2) of of the the 1.47 1.47 Ga Ga Wolf River batholith is exposed on the low knob on the southwest side of Highway Wolf is the low knob on the southwest side of Highway 32 32 This intrusive intrusive rock rock truncates truncates the southwest margin of of the Mountain and 64. 64. This southwest margin Mountain shear shear 4 zone. I This concludes the field trip, but, an additional but, an additional stop stopisisdescribed described below below because because of of its its significancetotothe thegeology geoto' of significance of aa broader broader region. region. To Toreach reach Stop Stop 7, 7, return to to Mountain, Mountain, 17 �then proceed W; turn right (east) and proceed to to County County Highway Highway W; and proceed proceed on onHighway Highway W for a distance of 2 mi. Outcrop Outcropon onleft left(north) (north)side sideofofHighway HighwayW Wisisstop stop7.7. STOP 7 The Baldwin Conglomerate (unit Xb, fig. fig. 2) 2)is is exposed on the south-facing slope of the hill. hill. The Baldwin Conglomerate is a lensoid unit about about 2.3 2.3 km km long long and aa maximum maximum of of 150 150 (sec. 6, 6, T. T. 31 31 N., N., R. R. 17 17 E.) E.) along along the the northwest northwest margin m wide that is exposed locally (sec. of the Mountain shear within the shear zone and shear zone. ItItoverlies overliesmetavolcanic metavolcanic rocks within is truncated and intruded (by dikes) on the north by the Hager and intruded (by dikes) on the north by the HagerRhyolite Rhyolite(Ywh, (Ywh, fig. fig. 2) of the Wolf of Wolf River batholith batholith (Lahr, 1972). 1972). The Theconglomerate conglomerate has has relict relict sedimentary sedimentary layering and possible scour features and contains contains subrounded subrounded to to subangular subangularclasts clasts of of metavolcanic rocks, rocks, granite granite gneiss, gneiss, and and quartzite quartzite (as (as much much as as 25 25 cm cm in in diameter). diameter). All All but the quartzite from the shear zone of the but quartzite clasts clasts are are derived derived locally locally from zone itself. itself. Clasts of Hines Quartz Diorite have not been reported in the conglomerate (Lahr, (Lahr, 1972). 1972). The matrix of the conglomerate is is a gray, gray, fine- to medium-grained rock rock containing containing quartz, quartz, feldspar, biotite, muscovite, feldspar, muscovite, and hornblende of a proximal source. E., 78' 780 NW. It is interpreted The The conglomerate conglomerate has has a foliation foliation that that is is oriented oriented N. N. 66 66ÂE., 2 foliation as S, foliationinasmuch inasmuchas asititisisparallel paralleltotoS2 S, in in the the mylonitic mylonitic rocks of the shear shear zone. zone. The source of the quartzite was the quartzite now exposed quartzite clasts clasts almost almost certainly was exposed at McCaslin and Thunder Mountains, less than 20 km to the north north (Sims (Sims and and Peterman, Peterman, Sims, 1990). 1990). Thus, Thus, inasmuch inasmuch as as the Baldwin Baldwin Conglomerate Conglomerate was deformed deformed during 1988; Sims, during the ductile deformation along the Mountain shear zone, and prior to to emplacement emplacement of of the Hines Quartz Diorite, the quartzite clasts and their parent rocks are older than clasts and than 1,812 Ma, Ma, the the age age of of the Hines Quartz Diorite. 1,812 Diorite. 18 �'C I: ij I IT L I) El [ IT: Table 1--Chemical analyses of selected rocks in Mountain area, Wisconsin : ii r >n 18.90 17.70 2.69 7.30 99.87 0.04 0.03 1.48 4.77 7.35 3.29 2.28 0.73 0.25 0.16 49.00 51.80 9 Nb w o m m 1.32 w 0.086 00 M Peacbck 99.85 100.09 0.056 2.43 0.129 0.46 0.161 0.18 363 440 658 511 541 0.270 0.36 2.735 0.05 0 '0- 00 M O O u 0.248 0.37 402 4 97 7 6 2 8 42 93 115 165 18 27 8 48 195 54 22 22 148 12 35 2 47 175 70 431 22 168 17 299 99.69 3,62 2.34 0.18 0.05 0.04 0.45 0.03 0.09 2.21 0.55 73.20 13.00 0.83 3.10 130-85A 14 -I o'? Q O M 0.041 2.95 377 1 27 9 346 1.33 0.167 711 7 91 15 208 35 99.77 7.52 2.68 2.97 0.65 0.23 0.05 0.40 0.02 0.01 1.64 2.89 17.40 0.21 63.10 50.10 19.00 0.90 10.80 4.57 9.68 2.64 0.64 0.70 0.17 0.19 0.99 0.02 0.05 153-85 150-85 100.45 ("I 396 99.49 0.41 2.39 6.48 0.02 0.05 0.02 0.29 0.06 0.02 0.22 12.40 0.61 1.52 75.60 129-85A - f \ o m IM- - K/Rb Rb/Sr Zr Y 48 555 21 92 99.59 100.77 0.23 0.09 0.04 0.68 0.01 0.04 2.22 3.60 2.50 0.19 0.05 0.05 0.58 0.04 0.15 0.50 72.70 13.20 0.89 3.18 39-85 (weight percent) Minor elements (parts per million) by X-ray fluorescence 0.02 0.01 0.19 1.28 0.01 1.15 0.29 0.05 0.02 0.66 0.10 0.16 5.52 2.79 1.33 1.09 3.40 1.47 2.19 3.44 10.90 69.30 14.20 0.98 3.14 35-85 1.00 72.40 14.50 0.31 2.19 27-85 1.69 2.00 9.54 3.54 23-85B 20-85 W i n - M m ^- in M m Rb Sr Sum CO2 H20+ H20- MnO P205 MgO CaO Na20 K20 Ti02 FeO Fe203 203 Si02 Sample No. M alor oxides [Major oxide analyses by A. Bartel, E. Brandt, S. Roof, J. Taggart, and K. Stewart. FeO, 1120, and CO2 by F. Brandt and S. Roof. Minor element analyses by K. Barovich, K. Futa, and Z. Petermani 1] I1 4 u in cs*i. o* r �C N) cliii :riiii r' 20-85 23-85B 27-85 35-85 39-85 129-85A 130-85A 150-85 153-85 i - ci riiuii i r r:r: ii n flT Amphibolite (unit Xwa), SW1/4 SW1/4 sec. Amphibolite sec. 33, 33, T. 32 N., R. R. 17 17 E. E. Porphyritic mafic mafic metavolcanic metavolcanicrock rock(unit (unit Xwm), Xwm),NE1/4 NE1/4 NW1/4 NWI/4 sec. 4, T. 31 N., R. 17 Porphyritic N., R. 17 E. Feisic metavolcanic rock (unit SW1/4 NW1/4, NWI/4, sec. Felsic (unit Xwf), Xwf), SW1/4 sec. 4, 4, 1. T. 31 31 N., N., R. R. 17 17 E. E. N., R. 17 F. Porphyritic granodiorite granodiorire (unit Xg), Xg), NE1/4 NE1/4 SW1/4, sec. Porphyritic sec. 5, T. T. 31 N., E. Granitic gneiss (unit Xgn), NE1/4 SW1/4, SW1/4, sec. sec. 5, 5, T. T. 31 N., R. 17 17 E. Granitic gneiss (unit Xgn), Xgn), SW1/4 NW1/4, NW1/4, sec. sec. 5, 5,T. T.31 31 N., N., R. R.17 17E. E. Granitic gneiss (unit Xgn), NW1/4 NW1/4 NW1/4, sec. 5, T. 31 N., R. 17 sec. 5, T. 17 F. E. Hines Quartz Diorite Diorite (unit (unit Xh), Xh), NW1/4 NW1/4 NW1/4, NW1/4, sec. sec. 13, 13,T. T. 31 31 N., N., R. R.16 16 F. E. Intermediate metatuff metatuff (unit (unit Xwi), Xwi), SEI/4 SE1/4 SW1/4, SW1/4, sec. sec. 1,1,T. T.31 31 N., N., R. R. 16 16 E. E. Table Table 1 (continued) fl F �I Table 2.-Approximate 2.--Approximate modes modes of of granodiorite granodiorite Table Constituent 101 101 60B 60B 35 35 112 112 Plagioclase Plagioclase 42.8 49.5 40.7 Quartz 18.2 15 15 K-feldspar 24.6 17,5 Biotite 8.8 Hornblende 1.8 Alteration minerals minerals 3.3 3.3 Accessory minerals 0.5 I I 101 101 60B 60B 35 35 112 112 165 165 34A 34A 34B 34B 10 10 7.5 Tr. 0.5 0.5 165 165 34A 34A 34B Average 44.8 51.8' 51.8 55.2 55.2 23.3 47.5 47.5 37.6 14.6 14.6 18.2 18.2 21.6 21.6 35.2 35.2 21 21 15.4 20.6 11 40 16 5.4 10.6 9 7 1.4 7.5 9.8 9.8 99 0 6 00 7.3 7.3 0.1 0.8 Tr. 2.1 Tr Tr.. 5.7 Tr. 0.2 Sample localities Sample localities NE1/4 N.,R. 17 17 E. NE1/4 SW1/4 sec. 7, T. 31 N., SE1/4 SWI/4 SW1/4 sec. sec. 5, 5, T. T. 31 31 N., N., R. 17 17 E. NE1/4 SWI/4 NE1/4 SW1/4 sec. sec. 5, 5, T. T. 31 31 N., N., R. R. 17 17 B. E. NW1/4 SEI/4 NW1/4 SE1/4 sec. sec.7, 7, T. T. 31 31 N., N., R. R. 17 17 E. SE1/4 NE1/4 NE1/4 sec. sec.7,7, T. T. 31 31 N., N., R. R. 17 17E. E. NE1/4 SW1/4 SW1/4sec. sec.5, 5,T. T.31 31N., N., R. R. 17 17B. E. Same as 34A. Pink Pink leucogranite leucogranite that that cuts cuts granodiorite. granodiorite. 21 1.5 1.5 Tr. Tr. Â¥) j) 0.1 ) 0.1 22 �Table 3.--Approximate 3.--Approximate modes of Quartz Diorite Diorite Table of Hines Quartz and and quartz quartz diorite diorite of of the theamphibole amphiboleschist schist unit unit Hines Quartz Quartz Diorite Diorite Quartz diorite diorite Quartz Constituent Constituent 147 147 150 150 134 134 172 172 Plagioclase 47.7 54.2 65.6 48.8 Quartz Quartz 32.6 2 9.7 22.6 0 0 0 12.4 0.9 5.6 12.2 Amphibole Amphibole 6.3 141.7 18.4 15.8 Alteration Alterationminerals minerals 0.1 0.1 Tr. Tr. Accessory Accessory minerals minerals 0.9 0.9 K-feldspar Biotjte Biotite 1.2 1.2 'Includes Includesrelicts relictsofofclinopyroxene. clinopyroxene. Sample Samplelocalities localities 147 147 150 150 134 134 172 172 Roadcut, NEI/4 NE1/4 NW1/4 NW1/4 sec. sec. 14, 14, T.31 ~ . 3N., N., 1 R. R. 16 16E. E. Roadcut, Outcrop, NWI/4 NW1/4NW1/4 NW1/4sec. sec.13, 13,T. T.31 31N., N., R. R. 16 16E. E. Outcrop, Outcrop,SE1/4 SE1/4NW1/4 NW1/4sec. sec.33, 33,T. T.32 32N., N., R. R.17 17E. E. Outcrop, Outcrop, NE1/4 NE1/4 SEI/4 SE1/4sec. sec.33, 33,T. T.32 32N., N., R. R.17 17E. E. Outcrop, 22 Tr. Tr. 0.7 0.7 0 0.4 0.2 �N) 0 0.8 0 00 Tr.r T Tr. Tr. Tr. Tr. Amphibole Amphibole Muscovite Muscovite Epidote/clinozoisite Epidote/clinozoisite Sphene Sphene Chlorite Chlorite Calcite Magnetite Magnetite 141-1 88 79 76 199 64 12 13 2 0.5 0.5 TI. Ir. 0.2 0.2 0.2 0.2 Tr. Tr. 0.5 0.5 Tr. Tr. 00 4 4 0.6 0.6 47.8 47.8 46.2 46.2 12 12 64 64 0.2 0.2 Tr. Ir. Tr. Tr. 00 00 0.2 0.2 0.3 0.3 00 1.8 1.8 8.3 8.3 38.7 38.7 50.5 50.5 Plagioclase has abundant tiny tiny quartz quartz droplets. Plagioclase droplets. 0.2 0.2 /jt4'!.i/,i.. T. 31 31 N., N., R. R. 17 NE1/4 sec. sec. 5, 17 E. E. 5, T. NW1/4 NE1/4 sec. 5, 31 N., R. R. 17 17 E. NW1/4 NE1/4 NE1/4 sec. 5, T. 31 NW1/4 sec. 6, 31 N., Ft. R. 17 17 E. E. SW1/4 NE1/4 NE1/4 sec. 6, T. 31 31 N., 16 E. sec. 1, R. 16 SE1/4 SW1/4 SW1/4 sec. 1, T. 31 N., R. E. sec. 7, T. T. 31 31 N., R. 17 17 E. NE1/4 NW1/4 NW1/4sec. 17 E. sec. 7, 7, T. 31 N., R. 17 NW1/4 NW1/4 NW1/4 sec. sec. 7, N., R. R. 17 17 E. E. SW1/4 SW1/4 SWl/4 sec. 7, T. 31 N., 0 17 cmT. N I 11?J .JLI'. 31 N., ''.1! R. 17 E. NE1/4 NE1/4 scc. 5, Included with biotite in mode. ' Included mode. I Accessory Accessory minerals minerals Calcite .8 4.9 4.9 Biotite Biotite 22 41.2 41.2 Quartz K-feldspar K-feldspar 50.8 50.8 Plagioclase Plagioclase 13 13 0.4 0.4 Ir. Tr. 0.1 0.1 0 0 0 0 44.2 44.2 0.1 0.1 2.4 2.4 00 0.6 0.6 3.5 3.5 47.7 47.7 199 199 of 01 Ir. TI. 1 1 Tr. Tr. 00 Tr. Tr. 0.5 Tr. Tr. 0 0 5.8 5.8 2.1 2.1 37.3 37.3 53.3 53.3 It. Tr. It. Tr. 00 0I 11 Tr. Tr. 00 2.5 2.5 8.5 8.5 10 10 37 37 41 41 3 3.5 3.5 00 Tr. Tr, 22 00 13 13 00 41.5 41.5 '42 '42 It. 6 Tr. 0 1 Tr. 5 28 0 29 31 0.2 0.2 It. Tr. Ti. TI. Tr. Tr. 0.3 0.3 Tr. Tr. 0 0 Tr. Tr. 11.5 11.5 00 37.5 37.5 50.5 50.5 -- 0.5 Tr. TI. It. Tr. Tr. Tr. 1 1 Tr. Tr. 00 00 37 37 00 21.5 40 40 It. Tr. It. Tr. It. TI. Tr. Tr. 1 1 It. Tr. Tr. Tr. 00 15 15 10 10 22.5 22.5 51.5 51.5 173 173 91 91 It. Tr. (0 (0 It. TI. 0.2 0.2 0.3 0.3 It. Tr. 22 0 68.5 0 0 1 25 Tr.. Tr Tr. Tr. 164 164 991l 18 18 167 167 168 168 170 170 173 173 r— N., RI sec. 7, Rl 17 17 E. NE1/4 NE1/4 NE1/4 sec. 7, T. 31 N., sec. 7, R. 17 E. E. NE1/4 NEI/4 NE1/4sec. 7, T. 31 N., Ft. SW1/4 NW1/4 W 1 / 4 sec. sec. 27, 27, T. 32 32 N., Ft. R. 17 E. sec. 33, R. 17 17,E. E. NE1/4 SEI/4 SE1/4sec. 33, T. 32 N., R. 31 N., R. 16 E. SE1/4 SE1/4 sec. 12, T. N., 16 E. 12, SEI/4 SEI/4 sec. T. 32 32 N., N., Ft. SW1/4 SW1/4sec. sec. 33, R. 17 E. 33, T. SWI/4 SW1/4 T. N., R. 17 sec. 7, T. 31 N., 17 E. E. NW1/4 SW1/4 NWI/4 SWI/4 sec. 7, Tr. Tr. 22 Ir. Tr. It. Tr. It. Tr. 22 00 64 64 0 00 Tr, TI. 32 32 schist Amphibole schist 18 164 18 164 3 I Tr. Tr. Tr. T 37 3 31.5 31 27.5 L_J Amphibole is clinoamphibole, probably probably cummingtonite. cummingtonite. Amphibole is aa clinoamphibole, Ti. Tr. 00 Tr. Tr. Sample localities Sample localities It. Tr. Ir. Tr. 00 0 0 0 0.8 0 7.2 21.7 23.6 46.7 170 170 interlayered Diotite biotite and amphibole schist interiaycreu schist Ii_] biotite-amphibole schist Biotite and biotite-aniphibole 76 79 88 141-1 167 168 76 79 88 141-1 167 168 Table i aoie 4--Approximate 4.--~pproximaiemodes moucs ' t1 r: Ei L ii r' ti 11 t_J 111_I �39.0 10.6 6.0 6.0 00 0.2 0.2 . Quartz Quartz Microcline Microcline Biotite Biotite Hornb!ende Hornblende Alteration minerals minerals a>. Accessory minerals 129-85B 129-85B 130-85A 130-85A 130-85B 130-85B 39 39 46 46 50 50 44.2 Plagioclase Plagioclase 0.7 0.3 u.5 0n 8.4 8.4 0 41.2 49.4 46 46 t_.. 1.0 1.O 1.3 0.5 0 8.4 8.4 1.5 40.4 48.2 50 50 tj tj r: F I 0.7 0.7 0.1 0fi 12.0 12.0 1.0 32.2 54.0 85B 85B 129129- . 1.O 1.0 0.5 0.5 00 6.5 6.5 8.0 37.0 47.0 85B 85B 130130- 55 55 Tr. Tr. 1.2 1.2 129-85A 129-85A 18-1 18-1 44 44 40A 40A 45B 45B 0.5 0.5 2.0 2.0 Tr. Tr. 0.7 0.7 00 5.4 19.0 30.5 44.4 45B fl1 Tr. Tr. 0.3 0.3 0 6.5 6.5 8.7 36.1 48.4 44 44 Tr.. Tr 0.9 U 0 , 10.77 10 0 30.7 57.7 18-1 18-1 fl 0.4 0.4 1.0 1.1) 0 1.1 11 30.9 37.1 29.5 85A 129129- 0.4 0.6 0.2 8.2 5.9 35.9 48.8 Average Average NEI/4 NE1/4 SE1/4 SE1/4sec. sec.6,6,T. T.31N., 31N, R. R. 17E. 17E. NWI/4 NEI/4 sec. 5, T. 31N., R. 17E. NW1/4 NE1/4 sec. 5, T. 31N.. R.17E. SE 1/4 NW1/4 NW1/4 sec. T. 31N., 31N., R. 17E. 17E. SE1/4 sec. 5, 5, T. NWI/4 R. 17E. 17E. NW1/4 NEI/4 NE1/4sec. sec.5,5,T. T.31N., 31N, R. R. 17E. 17E. NW1/4 SWI/4 SW1/4 sec. sec.33, 33,T., T., 32N., 32N, R. NW1/4 Same Same as as 129-85B, 129-85B, Leucogranite Leucogranite gneiss. gneiss. 0.7 0.7 .o 1.0 1 15.0 15.0 1.3 34.4 46.1 40A 40A 3.4 3.4 9.4 38.3 46.7 55 55 Sample Sample localities localities 0.4 0.4 u. I 0.1 0n 8.2 8.2 5.0 35.3 51.0 13013085A 85A Table 5.--Approximate 5.--Approximate modes of granite granite gneiss gneiss LJ i; R. 17E. SW1/4 sec. 5, T. T. 31N., 31N., R. 17E. NW1/4 SW1/4 sec. 5, T. R. 17E. T. 31N., R. 17E. SW1/4 NE1/4 31N., SWI/4 NEI/4 5, T. T. 31N., 31N, R. R. 17E. 17E. NW1/4 sec. 5, SE1/4 NW1/4 17E. SW1/4 T. 31W., 31N, R. 17E. SW1/4 NW1/4 NWI/4 sec. 5, T. sec. 5, T. R. 17E. R. 17E. SW1/4 NW1/4 T. 31N, 31W., SWI/4 NWI/4 Same as 130-85A. Same as 130-85A. Tr. Tr 39 39 ;i 11i:t j Constituent .._j �N) U, ( F1 F4 F3 F2 F 2 F1 Deposition Event EJ rr L_il I Uj [fl r r r' r c L3 Fold axes axes Kink bands L1 S L4b Lineations Shears Shears L4a Fold axes axes Foliation S3 Foliation L2b '2a Fold axes Long axes of strained clasts clasts Stretched S2 S Regional foliation Regional ~Flattened l a t t e n e dclasts clasts Foliation Foliation S Symbol Bedding, pillow structures pillow structures intrusive contacts contacts Structural element Variously oriented kink bands Variously oriented and fold axes associated with kink bands Fabric is poorly developed Appears to fold fold F3 F3 Seen as fold fold axes on S, surface Geometric element. element. Not Geometric Not generally observed Stretched clasts that lie in lie in S2 plane 2 plane Tectonic layering, mylonitic foliation in granitic gneiss foliation (unit Xgn) Folds of of S,2 Folds Best observed observed south of shear shear but present in isolated zone, but isolated within shear zone outcrops within Primarily is layering between Primarily felsic and and mafic rocks felsic Explanation r Late-state brittle deformation. Not systematically studied. Number of events not not known. known. Shears are parallel to to cross cross faults faults . Rarely observed. observed. Yielded Rarely Yielded a northnorthwest-trending northwest-trending fabric Late folding folding that that created aa westwestnorthwest-trending fabric northwest-trending Foliation associated with with simple simple shear due to relative relative upthrow upthrow 4,formed by from southeast. L2a fold of S1 and S. fold of S, and Sw '2b bbcaused caused by simple simple shear associated by associated with with upthrow Flattened clasts suggest regional regional compression Original depositional and intrusive Original feature Nature of event 6--Sequence of events, structural elements, elements, and and nature of events in the Mountain Table 6.--Sequence Mountain shear shear zone zone [C ti L I (J �91° 88° 89° 9Qs /'T NSIN 460 J 1 I. . .. ... HI 1 50 KILOMETERS 50 KILOMETERS 00 EXPLANATION EXPLANATION • Middle Proterozotc Proterozoic lKeweenacsanl IKeweenawanI mafic mafic igneous igneom rocks of Midconttneni and sedimentary sedimentary rocks Midcontinent rift nf!system w-~~113001,200 Mal 11.000-1200 Mil ,* ,. .-..*\ :- • - -- Contact Contac, High angle angle fault High WISCONSIN MAGMATIC MAGMArlc TERRANES WISCONSIN TERHANES Meiauolcatiic and granilnid Meiavolcanic granttoid rocks rocks in in Pernbine'Wausau Pembme-Wausau rterrane e 11.760-1.880 Ma1 1.7601.880 Ma) Metavolcanic and qranttoid rocks in t m Marshiteld Marshheid terrane 8mane Metavoicanic qmnitmd rocks 1.835 1.8W 1,890 Ma) 11.835 Mal 0 LI CONTINENTAL-MARGIN CONTINENTAL MARGIN ASSEMBLAGE ASSEMBLAGE Marquette Range Range Supergroup Superyroup (1.820 1.820-2.100 Ma) and and Marquene 2.100 Mat gneiss.granite, granite, and and greenstone greenstone (2.600-3.550 )2,600.3,550 Ma1 Ma) gneiss. Sedimetuary rocks of Paleozoic Sedimentary Paleozoi~age age Anorngentc rocks 11.4701.510 1,4701510 Ma) A r o y e n i c igneous rocks Mai ________ 7 Gnetss 2.800 Ma) Gneiss in Marshfield Marshheld errane wrrane f12.800 Mat Thrust fault Thrus . o_r _,, ,, Shear zone y \^ y a Shear zone A Athens EE Eau Pleme Pleine Eau J.i Jump River Jump RIWF MM Mountain Mountain Michigan. the Lake Superior region, region, northern northern Wisconsin and Michigan. Figure 1. Generalized Generalizedgeologic geologic map map of of the the eastern part of the location of the Note the location the Mountain Mountain shear shear zone. zone. 26 �L L EXPLANATION MIDDLE PROTEROZOIC PROTEROZOIC (1600.900 (1600900 Ma) MIDDLE Belongia Granite oof Btlongia Granite f Wolf River River baiholith batholith Ywu N1480 1-1480 Ma) Ma1 __________ L V wh [ [ U.' z 0 5..' Lx. C U.' x L ______ Hager Rhyolite Rhyolite EARLY PROTEROZOIC PROTEROZOIC Xh Hines Quartz Dtorite Quartz Diorite Xb Baldwin Conglomerate Baldwin Conglomerate Granite gneits—Defortned gneiss-Deformed and and metamorphosed granodiorite metamorphosed granodlorite Blotite schist Biotite schist and and amphibole amphibole schist schist Interlayered Interlayered *n. Xwi _________ Xwq Quartz dionte Quartz diorite schist schist X Wa Amphibole schist schist with with thin layers Amphibole layersooff felsic schist lelsic schist ___________ d 9 Granodiorlie—Equivalent to to unit Xgn Xgn shear zone zone kin n ghem WAUPEE VOLCANICS VOLCANICS WAUPEE _______ Xwni Dominantly felsic volcanic rocks rocks Dominantly felsic volcanic Mafic lava lava flows (lows Mafic - Trace ooff S, foliation foliation Trace 4 Trace of of S9 foliation foliation Trace Southeastem boundary ol of shear  Southeastern shear zone zone Figure 2. Geologic Geologicmap mapof o fthe theMountain Mountainshear shearzone zoneand andvicinity, vicinity. Oconto OcontoCounty. County, Wisconsin Wisconsin 27 �QUARTZ QUARTZ A EXPLANATION S A a. Granite gneiss; gneiss; ®, Average Average Granite Granodiorite; Granodiorite; A, Average Field of of granodiorite granodiorite Field Field of of granite granite gneiss Field b a A 8 K-FELDSPAR PLAGIOCLASE Figure FigUre3. 3. Quartz-K-feldspar-plagioclase Quarlz-K-feldspar-plagioclase diagram diagram showing showing modal modal composition composition of of samples samples from from the the granitic granitic gneiss gneiss and and granodiorite granodioriteUnits units a 1' A K-FELDSPAR C 8 PLAGIOCLASE Figure 4. Quartz-K-feldspar-plagioclasediagram diagram showing modal composition of samples samples from interlayered interiayered biotite biotite 4. Quartz-K-feldspar-plagioclase and amphibole amphibole schist schisl unit and 28 �Figure 5. Contoured, Contoured,equal-area e ual areaprojection projectionof of 68 68 poles poles to to foliation foliationoutside outside of shear shear zone. zone. Contours Contours are 1. 3.5.and and FigureS. are 1.3.5, percent.The t h egreat greatcircle circle(N. (N.8°8"E., E.,90C) 90') isisthe thecalculated calculatedmean meanof of Si jfoliation foliation 77percent, NW / C clast r I€ I II4l ii It iiiI1IiII 'In II''''' I''''' e g 1 o i i 2 Figure ol01granitic 9neiss 6 Photograph Phoiograpn granitic gneissslab slabshowing showingS-C S Cfabric fabricviewed viewedparallel raileltotothe theshear shearzone zonefrom fromthe menortheast. northeast Figure6. The adjacent totothe showndiagrammatically daqrammatica~adlacent thephotograph. photograph The Thelong longaxis axis Thedirection directionofofrelative relativemovement movementisisshown ofofthe stretched clast lies within the S plane me siretched clast lies within the S olane 29 �Shear zone Shear zone Figure7.7.Block Blockdiagram diagramshowing showingrelationship relationshipofofstrained strainedclasts clasts(strain (strainellipsoids) ellipsoids) to simple shear envelope. Note Figure to simple shear shear zone envelope. Note that the stretch (long) axis of the clasts (LZh) dip more steeply than the that the strelch (long) axis of the clasts (L2b) dip more steeply than the shear zone 30 �E"D — r I I! I-'- -.\'.- - N'. ' v14 I o' ! IFL?F'I,i / —— •:- ::M(lulliI - / r' ' F\ - - j -- - I H - ,',> —. ) '1 5 - ,. I I I In ci::' Aj - I / -' - - :' C, I - - <_1H • • _:. -' I ' I -' L I LFORESTI ,:' -, - 2-" 2, — F T (I - I F - C / —- ) 32 I - 8• .. - IIop:, I? ) ', — r'' i i: 9( ' :------, KT — 31 I V'-' ;\ I •.q.L•: :s::.I. IwLo9901?1 i5.-/IecJ IF • I / R. 17E. r.. (} L _"' —.- ft 16E, I: Y-"N I:C 5 1 NATIoNAJ4I '[I - I - 2/F?? __________________ r FIgure 8, Map of part ol Mountain 71/2-minute quadrangle showing tied stops F I 17 N _____ c: tI • - H j - 0 -'• ______ I,0 2 1>'".•J's. '9010 - :I1 r: "0, [] "04 —1230' SLUnchstop(afterstopa) 1 -5 - --5- I -I I I 1 H )Jl'ot/Irlr -. --— t �NW Figure Figure9. 9. Contoured Contouredequal-area equal-areaprojection projectionof of 33 33 poles poles to to 1Stfoliation. foliation.Contours Contoursare are1,1,16, 16,20 20percent. percent.The Thegreat greatcircle circle isisthe Sifoliation foliation thecalculated calculatedmean meanof ofSi N N N 53° E, 86° SE Figure 43 poles poles to to S2 2 foliation. Figure 10. 10. Contoured Contouredequal-area equal-areaprojection of 43 foliation.Contours Contours are 1, 1, 1020,3040 "120, 30 40percent. percent.The Thegreat great circle 2 foliation foliation circleis is Ihe the calculated calculated mean of 89 N Figure Contoured equal-area projection ofof 5050 poles totoS2 foliation. Poles S2 loliationContours Contodrsare are2,6, 2. 6. and1212percent; percent;50 50points pointstoto Figureii.11. Contoured equal area Prolcction and (1-3)(contours (mntoursare are2,2.10, 10.20, 20.30, 30, and40 40percent). percent)A,A.girdle giroledefined defined tolaed longaxes axesofofdeformed oeformedclasts ciasts(L3) long and bybyfolded tol~ation (F3 toldsl. maximum mncenuabon lineanons represcntod dot 2S2 foliation (F3 folds); 9.Bmaximum concentration ofoflineations represented bybydot 32 �WEDNESDAY, MAY MAY 1, 1,1991 WEDNESDAY, 1991 FIELD FIELD TRIP #2 L.S. L.S. Chan, Chan,P.E. P.E. Myers, Myers, and andR.L. R.L.Hay Hay (Leaders) (Leaders) "Features "Featuresand andsignificance significanceof of the the Precambrian-Cambrian Precambrian-Cambriancontact contactininwestern westernWisconsin" Wisconsin" 33 �Field Field Trip #2 Precambrian-Cambrian Precambrian-CambrianBoundary BoundaryininWest-Central West-CentralWisconsin Wisconsin Lung. Lung. S. S. Chan, Chan,Paul Paul E. E.Myers, Myers, and andRichard Richard L. L. Hay Hay INTRODUCTION INTRODUCTION Geologists the stratigraphic stratigraphic record. record. Recent Recent Geologists have have realized realized long long ago ago the the predominance predominance of of gaps in the developments in event stratigraphy and the introduction of the idea of 'catastrophic uniformitarianism' developments in event stratigraphy and the introduction of the idea of 'catastrophic uniformitarianism' to togeology geologyhave have called called for for increasing increasing effort efforton onthe thestudy studyof ofgeologic geologicgaps gaps and and boundaries boundaries[Ager, [Ager, 1981]. 19811. The The Precambrian-Cambrian Precambrian-Cambrian boundary boundary is aa very very big topic. topic. It represents represents aa time time when when dolomite dolomite accumulation accumulation and and stromatolite stromatolite formation formation decreased, decreased; when when red red biogenic biogenic limestone limestone and and phosphorite phosphorite deposits increased, and when living organisms abruptly became skeletalized deposits increased, and when living organisms abruptly became skeletalized [Rozanov, [Rozanov, 1984]. 19841.Most Most studies studies of of the thePrecambrian-Cambrian Precambrian-Cambrian (PC-C) (P6-6)boundary boundary are areconcerned concernedwith withits itsstratigraphic stratigraphic aspects, aspects, as as exemplified exemplified by the objectives of the Working Working Group Group on on the thePC-C PC-6Boundary Boundary (JUGS) (IUGS)[Crowe [Croweand and Brasier, Brasier, 1989]. 19891. Consequently, the major controversies about the PC-C PC-6 boundary are focused upon uponits its biostratigraphic biostratigraphic definition definition and and geochronometry. geochronometry. In In the the mid-continent, mid-continent, the thePC-C PC-Âboundary boundary is is generally represented represented by by aagap gapalmost almost 500 500 my. my. long. long. In Inmost most areas, areas, the the 0.9-1.1 0.9-1.1 Ga Ga Keweenawan Keweenawan Event Event that that affected affected most most of of the theMid-continent Mid-continentrepresents representsthe thelast lastgeological geologicalrecord recordininthe thePrecambrian. Precambrian.AAfew few intracratonic intracratonicbasins basins formed formed near near Lake Lake Superior Superior while while most most of the the mid-continent mid-continent remained remained emergent emergent above above the thesea-level sea-levelduring duringthis thisvast vast interval interval of of time. time. The Theabsence absenceof of continuous continuousstratigraphic stratigraphicsections sections across the PC-C boundary has perhaps limited the potential usefulness of the area for studying across the PC- boundary has perhaps limited the potential usefulness of the area for studying the the major major events events and and phenomena phenomena atatthe theboundary. boundary.The Thenon-stratigraphic non-stratigraphic aspects aspects of of the thePC-C PC-? contact, contact, however, however, still still present present many many geological geological problems that may be important for the the understanding understanding of of the the geological geological processes processes and andhistory history of ofthe theboundary. boundary. One Oneofofthe theproblems problemsisisthe theage ageand andmanner mannerof ofthe thepeneplanation peneplanation process. process. The ThePC-C PC-âunconformity unconformity in in west-central west-central Wisconsin Wisconsin is represented by a gentle gentle surface surface with with regional regional dip less less than than 1°. lo.The The smooth smooth morphology morphology of of the thePC-C PC-6contact contactpresumably presumablyresulted resulted from fromprolonged prolongedweathering weatheringand and peneplanation. peneplanation.The Thegeology geologyofofthe thesurface, surface,however, however,isishighly highlyvariable. variable.Precambrian Precambriancrystalline crystallinerocks rocks below below the theunconformity unconformity are are weathered weathered totoaathick thicksaprolite saproliteininsome some areas, areas, but but may may be beunweathered unweathered or orpartially partially weathered weathered in in others. others. The Theformation formation and and condition condition of of the thePrecambrian Precambriansurface, surface, the theage age of ofthe thesaprolitization, saprolitization,the thespatial spatialvariations variationsininthe thedegree degreeofofweathering weatheringof ofthe thePrecambrian Precambrianbasement, basement, and andpossible possiblepre-transgression pre-transgression uplift uplift of of the themid-continent, mid-continent, are areamong among the theproblems problemsawaiting awaitingfurther further examination. examination. The Thealteration alterationprofile profiledeveloped developed on onPrecambrian Precambrian rocks rocks by by weathering weathering prior prior to to the theMt. Mt.Simon Simon Sandstone potassic diagenesis diagenesis over a wide wide area area of of the themid-continent mid-continent [Duffin, [Duffin, Sandstonehas hasbeen beenmodified modifiedby by potassic 1989]. 19891.The Theauthigenic authigenicpotassic potassicminerals mineralsare areK-feldspar K-feldsparand andillite-rich illite-richmixed-layer mixed-layerillite-smectite illite-smectite(ItS). (11s). The TheK-feldspar K-feldsparoccurs occursprincipally principally as asaareplacement replacementofofprimary primaryigneous igneousfeldspar, feldspar,and andthe theI/S 11smay may be be chiefly chieflyaareaction reactionproduct productofofkaolinite kaolinitewith withpotassic potassicfluids. fluids. Potassic Potassic alteration alteration of ofgranite graniteisisexhibited exhibited atatStop StopI 1(Chippewa (ChippewaFalls) Falls)and andStops Stops3 3and and4 4(Neillsville). (Neillsville).Authigenic AuthigenicK-feldspar K-feldsparisisalso alsowidespread widespread ininthe theMt. Mt.Simon SimonSandstone, Sandstone,and andauthigenic authigenicK-feldspar K-feldsparfrom fromthe theIllinois IllinoisBasin Basinhas hasgiven givenaaK-Ar K-Ardate date of of394±6 39426Ma Ma[Duffin [Duffinetetal., al.,1989]. 19891.Dates Datesofof390-400 390-400Ma Ma have have been been obtained obtained from fromthe theauthigenic authigenic K-feldspar 19881,suggesting suggesting aawidespread widespread K-feldspar of of Ordovician Ordovician tuffs tuffs of ofMinnesota Minnesotaand andIowa Iowa[Hay [HayetetaL, al.,1988], K-feldspar K-feldspar episode episode in in the theearly earlyDevonian. Devonian. Basinal Basinal brines brines have have been been postulated postulatedfor forthe theK-feldspar K-feldspar episode, and oxygen-isotopic data suggest that the K-feldspar formed at elevated episode, and oxygen-isotopic suggest the K-feldspar formed at elevated temperatures. temperatures. Illitization Illitizationepisodes episodesatat350-375 350-375Ma Ma(late (lateDevonian-early Devonian-earlyMississippian) Mississippian)and and250-275 250-275Ma Ma (Permian) (Permian) have havebeen beendocumented documentedbybyK-Ar K-Ardating datingofofI/S 11sininOrdovician Ordoviciantuffs tuffsand andthe theMt. Mt.Simon SimonSandstone Sandstone[Hay [Hay al.,1988; 1988,Duffin Duffinetetal.,al.,19891. 19891. etetal., 34 34 �The important implications for for the the lead-zinc lead-zincmineralization mineralizationin inthe theUpper Upper The K-feldspar event event may have important Valley.Lead Lead isotope isotope data for some Upper Mississippi Mississippi Valley. some Upper Mississippi Valley ores reveal Pb-leaching Pb-leaching event event early Devonian Devonian time [Doe al., 1983]. 19831. The similar age of the potassic diagenesis suggests at possibly early [Doe et et al., link between between the hydrothermal a possible possible link hydrothermal event and the the Pb-Zn Pb-Zn mineralization. mineralization. Duffin Duffin et et al. al. [1989] [I9891 suggested that the fluids in the basal sandstone aquifers could have interacted with the Precambrian the fluids basal Precambrian basement and the paleosols. paleosols. The The nature of the Precambrian-Cambrian granitic basement Precambrian-Cambrian surface, thickness and distribution of of the the paleosols, and the the fracture pattern pattern of the distribution paleosols, and the PG-C PG-6 surface surface could could have have played played an important role in guiding the fluid flow and in the ore mineralization. guiding ore mineralization. Late Proterozoic Proterozoic to to Late LateCambrian Cambrian also also represents represents aatime time of of substantial substantial latitudinal latitudinal migration migration and and climatic changesofof the the paleocontinent. Paleomagneticevidence evidenceshows showsthat thatthe thecenter center of of the climatic changes paleocontinent. Paleomagnetic paleocontinent must must be located at high latitudes latitudes during during the the Late Proterozoic and at equator paleocontinent equator during during the Late Cambrian [e.g. Irving, 1979; Van der Voo, 1981J. Late Keweenawan age glacial deposits Late Cambrian [e.g. living, 1979; der Voo, 19811. Late Keweenawan age glacial deposits in in Lake Superior area are also evidence of continental are also evidence of continental glaciation glaciation during the late Proterozoic Proterozoic [Murray, [Murray, was relatively relativelyquiet quiet in in this this part part of the 19551. Despite the large large horizontal horizontal motions, motions, tectonic tectonic activity activity was 1955]. paleocontinent and and was was represented representedmainly mainly by by formations formations of gentle arches arches and and highlands. highlands. Why Why was was there such a long manage long interval of apparent apparent lack lack of tectonogenesis? tectonogenesis? How did paleozoic formations manage to maintain an almost perfect horizontality? What was was the the geometry geometry of of the the epeirogenic epeirogenic blocks? blocks? How did the drastic climatic changes changes and continental glaciation affect the morphological did morphological development of the Precambrian and the paleosols? paleosols? We We may may have to resolve resolve to to geophysical geophysical means to to answer answer Precambrian surface surface ancj some of these questions. However, field observations can can undoubtedly undoubtedly provide provide important important constraints and tests on on geophysical geophysical models and and hypotheses. hypotheses. We have outlined above several questions related to the the Precambrian-Cambrian Precambrian-Cambrian unconformity unconformity in the mid-continent. The traditional traditional focus focusof of the the Institute mid-continent. The Institute on Lake Lake Superior Superior Geology Geology has has been been geology and and ore ore mineralization. mineralization. ItIt isisour our hope hope that this field trip to the PC-C Precambrian geology PG- boundary outcrops in western Wisconsin and encourage research outcrops Wisconsin could could promote promote discussion discussion and research on on Paleozoic Paleozoic geology of of the Lake Superior geology Superior region. region. PRECAMBRIAN TERRANES TERRANES Numerous papers papers on the Precambrian of the the Lake Superior region have been published Numerous Precambrian geology of published in recent years. The correlation of the Precambrian rock sequences in in the Lake Superior area is years. The is best summarized in three U.S.G.S. Denison et al. U.S.G.S. professional papers by Morey and Van Schmus Schmus [1988], Denison summarized [1984], and and Harrison and Peterman Peterman [1984]. [1984]. The The most most comprehensive descriptions descriptions of of the thePrecambrian Precambrian outcrops in west-central Wisconsin Wisconsin are are given given in in two two field field trip trip guidebooks guidebooks by by Myers Myers et e tat. al.[1980] [I9801and and Maass and Sims Sims et al. [1989] Maass and Van v a n Schmus Schmus [1980]. [1980]. LaBerge and Myers Myers [1984], [1984], and [I9891 presented two two different syntheses on the the Precambrian Precambrian magmatic magmatic terranes terranes in in west-central west-central Wisconsin. Wisconsin. - identifed two LaBerge and and Myers Myers [19841 [I9841 identified two major major Based on structure structure and and metamorphic metamorphic facies, facies, LaBerge Proterozoic metamorphic sequences in in west-central west-central Wisconsin: Wisconsin: a younger younger greenschist greenschist facies facies caiccalcalkaline sequence showing northeasterly trending fold-axes alkaline fold-axes and an older amphibolite-facies amphibolite-facies quartzfeldspathic gneiss and and amphibolites. amphibolites. The The spatial extents of the feldspathic gneiss the two two Proterozoic Proterozoicsuccessions successionsroughly roughly coincide with with the the tectonostratigraphic terranes postulated et at. The latter model, al. [1989]. [1989]. The model, coincide tectonostratigraphic terranes postulated by Sims Sims et however, contends contends that the two early Proterozoic Proterozoic terranes are separate separate entities. The The Eau Eau Pleine Pleine Shear Shear Zone between between Ladysmith Ladysmith and Mosinee that separates separates the the Marshfield Marshfield tectonostratigraphic terrane terrane inin the south from Terrane in in the north from the the Pembine-Wausau Pembine-Wausau Terrane north probably probably represents the paleosuture paleosuture between the two Terrane supposedly contains maGc matic to two terranes terranes [Sims [Sims et et a!., al., 1989]. 19891. The Marshfield Terrane supposedly contains [elsie volcanicsequences sequencesthat that formed formedon on an an Archean Archean basement. basement. All All the the field field stops stops on on this this trip are felsic volcanic located in the the Marshuield Marshfield Terrane. 35 �South South of of the thetown townNeillsville Neillsville near near the theBlack BlackRfrer, River,Precambrian Precambrianbedrock bedrock consists consists primarily primarily of Archean 19741. Archean gneissic gneissic rocks and early early Proterozoic metamorphic metamorphic and and plutonic plutonic rocks rocks [Myers [Myers et et al., al., 1974]. At At Lake LakeArbutus Arbutusnear nearHatfield, Hatfield,the thesub-Cambrian sub-Cambrianconsists consistsof of high high grade grade metamorphic metamorphic rocks rocks or or gneiss gneiss and and migmatite migmatite (Stop (Stop 5). 5). The The principal principal rock rock types types are are an an interlayered interlayered sequence sequence of of quartzo-feldspathic quartzo-feldspathic gneiss Schmiis, 1980]. 19801. Uranium-lead dating dating on on two two gneiss gneiss gneiss and and amphibolite amphibolite complex complex [Maass maass and and Van Van Schmus, specimens specimens has has yielded yielded ages agesof of 2.5 2 5 and and 2.8 2.8 Ga Ga [Sims [Sims et et al., al., 1989]. 19891. No Archean rocks are known north north of In the theChippewa ChippewaValley Valley area, area,layered layered amphibolite amphibolite and and feldspathic feldspathic gneiss gneiss form the the core core ofNeillsville. Neillsville. In of Recent zircon dating of the the eastward eastward plunging plunging Penokean Penokeanorogen orogen[Myers [Myerset et al., al., 19801. 19801. Recent dating has has yielded yielded an an age of 1835±10 m.y. [Sims et aL, 1989]. age of 1835±1m.y. [Sims et al., 19891. In In both both Archean Archean and andProterozoic Proterozoicrocks, rocks,cataclasis cataclasis played played a major major role in in the the metamorphism metamorphism and and deformation deformation throughout throughoutthe theregion. region.At Atleast leasttwo twogenerations generationsofoffold folddeformation deformationand andshearing shearing can can be observed in the Archean feldspathic gneiss exposed below Lake Arbutus Dam be observed in the Archean feldspathic gneiss exposed below Lake Arbutus Dam [Maass [Maass and and Van Van Schmus, 19801. In In the theChippewa Chippewaamphibolite amphibolitecomplex, complex,cataclasis cataclasis is is manifested manifested by by development development of of Schmus, 1980]. interlensing interlensingfoliation, foliation,transposition transpositionofoforiginally originallydiscordant discordant structures structuressuch suchas asdikes dikes and and xenoliths, xenoliths,and and transposition The amphibolite terrane transposition of offold foldfragments fragments into intotectonic tectonicxenoliths xenoliths [Myers [Myers et et al., al., 19801. 19801. The isis flanked provinces that that are less deformed and metamorphosed. the flanked by by volcanic-sedimentary provinces the nature nature of of the thecontact contactbetween betweenthe theamphibolite amphiboliteterrane terraneand andthe thevolcanic-sedimentary volcanic-sedimentaryterrane terraneisisuncertain. uncertain. Both Both the theArchean Archeanand andProterozoic Proterozoicterranes terraneswere weresynkinematically synkinematicallyintruded intrudedby bytonalitic tonaliticand andgabbro gabbro plutons plutons between between1880 1880and and1820 1820m.y. my. [Sims [Simset etal., al., 1989]. 19891.In In many many locations, locations, such such as as Lake LakeWissota, Wissota, Little Little Falls, Falls, and and Neillsville, Neillsville, rocks that belong belong to to the the amphibolite amphibolite complex complex are present present in ingenerally generally foliated plutons as xenoliths. foliated plutons as xenoliths. Late LatePrecambrian Precambriandikes dikes of of the theKeweenawan Keweenawan age agecut cutall allthe theother otherrocks rockswith withstrong strongdiscordance. discordance. Most Most Keweenawan-age Keweenawan-age dikes dikes have have an an ENE ENEstrike. strike.Prolonged Prolongedpre-intrusion pre-intrusionerosion erosionisisevident evidentsince since the themafic maficdikes dikes often oftencontain containchilled chilledmargins margins indicative indicative of intrusion at shallow depth and high thermal thermal gradient 19801. Two Two sets of dike dike orientation orientation can can be beobserved. observed. gradientacross across the thedike dikemargins margins[Myers [Myerset etal., al., 1980]. Paleomagnetic Paleomagneticresults resultsfrom fromcentral centralWisconsin Wisconsindike dikeswarms swarmsreveal reveal episodic episodic dike dike intrusions intrusions during duringthe the Keweenawan Proceedings]. Keweenawan event event [Chan, [Chan,Part Part11ofofProceedings]. PRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIAN UNCONFORMITY UNCONFORMITY The ThePC-C PC-â boundary boundary isisrepresented representedby byaahighly highlyvariable variable surface surface in in the themid-continent mid-continent area. area. The The morphotectonic characteristics of basement surface in the Midwest were described by Rudman et morphotectonic characteristics of basement surface in the Midwest were described by Rudman etal. al. [1965] surface forms [I9651and and Thwaites Thwaites[1980]. [1980].In west-central Wisconsin, Wisconsin, the the PC-C PC-€surfa forms an an extensive planation planation surface degree.Archean Areheaniron ironformations formationsand andProterozoic Proterozoicquartzites quartzites surfacewith withaaregional regional dip dip of of less less than than I1degree. form formisolated isolatedmonadnocks monadnocks on onthe thepeneplain. peneplain.Some Someofofthese thesemonadnocks monadnockswere wereseveral several hundred hundred feet feet ininelevation. elevation.The Thepeneplain peneplainwas wasmantled mantledbybyaalayer layerofofpaleosols paleosolsasasmuch muchasasseveral severalhundred hundredfeet feetthick thick [Cummings 19801.In Insome someareas, areas,Cambrian Cambrianrocks rocks directly directly rest rest upon upon barren, barren,moderately moderately [Cummingsand andScrivner, Scrivner,1980]. weathered weatheredPrecambrian Precambrianformations. formations. Considering Considering the the low low paleolatitude paleolatitude of of the thecontinent continentduring duringthe theCambrian, Cambrian, deep deepweathering weathering of of the the Precambrian Precambrian surface surfacemust must have haveoccurred occurredbefore beforethe theUpper UpperCambrian Cambriandeposition. deposition.The ThePrecambrian Precambrian basement, basement,however, however,shows showsvariable variable degree degreeof of weathering. weathering. Where WhereCambrian Cambrian formations formations are areinincontact contact with with Precambrian Precambrian plutonic plutonic rocks, rocks, the thePrecambrian Precambrian basement basement isisgenerally generallydeeply deeply saprolitized saprolitized toto kaolinite-rich 1980;Stop Stop1]. 11.In InNeillsville, Neillsville,for for example, example,spheroids spheroidsover over kaolinite-richsoils soils[Cummings [Cummingsand andScrivner, Scrivner,1980; 66mmacross acrossdeveloped developed in in weathered weatheredgranites; granites;Mt. Mt. Simon Simon sandstone sandstone and and conglomerate conglomeratetill fill the thewedges wedges among amongthe thespheroids spheroids[Stops [Stops33&&4]. 41. In Insome someareas areassuch suchas asBig BigFalls Falls in in Eau Eau Claire Claire County Countyor orRock Rock Dam 21,qambrian Cambriansandstones sandstonesrest rest upon upon Proterozoic Proterozoicamphiholite amphiboliteand and Dam ininJackson JacksonCounty CountyIStop [Stop2], metarhyolites that are only partially weathered. In the Jackson County Iron Mine, Upper Cambrian metarhyolites that are only partially weathered. In the Jackson County Iron Mine, Upper Cambrian Mt. deposited Mt.Simon Simonand andEau EauClaire Claireformations formationsare arerepresggted representedby byangular angularbreccia brecciaand andsandstones sandstonesdeposited �on on the theslopes slopesof of the theiron ironformation formationmonadnock monadnock [Stop [Stop7]. 71. The The variable variable degree degree of of weathering weathering of the the PC-C PC-â contact contact has has raised raised questions questions about the the timing timing of the PC-surfacewas was already already a gentle gentle and and smooth smooth the planation planation process. process. ItItisisunquestionable unquestionable that thatthe thePC-surface surface surface with with isolated isolated monadnocks monadnocks by by Late LateCambrian Cambrian time. time. The Thechilled chilledmargins margins of mafic mafic dikes indicate prolonged prolonged erosion erosion even even during during the theProterozoic Proterozoic time. time. The Therelatively relativelyunweathered unweathered Precambrian Precambrian outcrops in some localities, however, suggest relatively immature weathering or intense outcrops in some localities, relatively immature weathering or intense erosion and removal removal of weathered material material during during the the transgression transgression event. event. Budel Budel [1957] [I957 presented aa model model on on the theformation formationofofpeneplains peneplainswhich whichconsists consistsof of two twoconcurrently concurrentlyactive active leveling leveling surfaces: surfaces: an an exposed exposed wash wash surface at the top top of of the the deep deepsaprolite saproliteand andaaburied buried basal basal surface surface of of weathering at the the bottom bottom in contact with unweathered bedrock. The limited weathering in some sub-Cambrian profiles suggests in contact with unweathered bedrock. The limited weathering in some sub-Cambrian profiles suggests aa very very late-stage late-stage development of the peneplain peneplain or or aa rapid rapiddenudation denudationof ofthe thewash washsurface surfaceshprtly shortly before before the the deposition deposition of of the the Mt. Mt. Simon Simon Sandstone. Sandstone. The latter latter theory theory points points to to the thepossibility possibility of Cambrian Cambrian uplift or or eustatic eustatic movement movement before before the theDreisbachian Dreisbachian transgression. transgression. UPPER UPPERCAMBRIAN CAMBRIAN MOUNT MOUNTSIMON SIMONFORMATION FORMATION The The sediment sediment above abovethe theunconformity unconformity consists consists largely largely of Upper Cambrian Cambrian Mt. Mt. Simon Simon formation formation deposited deposited on onthe themid-continent mid-continentregion regionof ofNorth NorthAmerica Americaduring duringthe theDreisbachian Dreisbachian transgression. transgression.The The Mount Mount Simon Simon formation formation isis aafine-coarse-grained, fine-coarse-grained, poorly poorly sorted, sorted, quartz quartz arenite arenite with with aalocal localbasal basal conglomerate. conglomerate. In Inthe theUpper UpperMississippi MississippiValley, Valley, the thethickness thicknessof of the theformation formationvaries variesfrom from180 180toto40 40 meters. meters. Lochman-Balk Lochman-Balk [1971] [I9711 gave aa summary summary on the the Cambrian Cambrian paleogeography paleogeography and andpaleoecology paleoecology of of the theNorth NorthAmerica Americacraton. craton.Previous Previousstudies studiesbybyThwaites Thwaites[1923], [1923],Ostrom Ostrom[1964, [l%4,1966, 1 x 6 , 1967], 19671, Asthana Asthana [1969], [1%9], and and Ostrom Ostrom [19881 [I9881 have outlined outlined the the general generalstratigraphy stratigraphy and andpaleodepositional paleodepositional environment environment of ofthe thelocal localsequences sequencesininwest-central west-centralWisconsin. Wisconsin. - In In the theChippewa Chippewa Valley Valley area, area, the the lower lower part part of of the theMount MountSimon Simonformation formation isis aacoarse-grained. coarse-grained, thick-bedded sandstones. The The relief relief of the thick-bedded quartz sandstone and and conglomeratic conglomeratic sandstones. the deposition deposition was was probably The presence presence of of trace tracefossils fossils probablyvery very shallow; sedimentary channels are less than 11 meter deep. The (rusophycus?), (rusophycus?), and planar planar and and bipolar bipolar cross-bedding cross-bedding suggest suggest aa littoral littoral or orshallow shallowmarine marine tidal tidalflat flat environment environment of deposition deposition for the lower lower part of the the formation. formation. The upper part part of of the theMt. Mt. Simon Simon formation formationcontains containsfeldspathic feldspathicsandstone sandstonewith withsmall-scale small-scaleripple ripplebedding, bedding,brachiopod brachiopodfragments, fragments,and and worm worm trails trails (planolites). (planolites). Iron-oxide Iron-oxide concretions concretions are arecommonly commonly present. Some Some concretions concretions are areas aslarge large as as1.5 1.5 cm cm in in diameter. diameter. The Thegrain grainsize sizedata dataobtained obtainedby byAsthana Asthana[1969] [1%9] indicate indicatean anunimodal unimodalgrain grainsize size in in the thelower lowerpart partofofMt. Mt.Simon, Simon,aabimodal bimodaldistribution distribution in in the the middle middle and and the the upper upper parts. parts. The Thegrain grain size fining upward upward sequence. sequence.The The upper upper part part of the size distribution distribution shows shows a generally generally fining the formation formation represents subtidalshallow shallowmarine marinedeposition. deposition. The Thepresence presenceofof10-20 10-20mm mmdiameter diameteriron-oxide iron-oxide represents aasubtidal concretions concretions and andhorizontal horizontalworm worm trails trails suggest suggest a much much broader transgression transgression toward the top top of of Mt. Mt. Simon Simon Formation. Formation. Presence Presence of of brachiopods brachiopods and and ripple ripple bedding bedding in in the the upper upper part part of of Mt. Mt.Simon Simon Formation Formationisisdiagnostic diagnostic of of aashallow-marine shallow-marine subtidal subtidal deposition, deposition, probably probably above the the wave wave base base atat aa depth depthofof10-15 10-15m. m. The Thepart partofofthe thesection sectioncontaining containingiron-oxide iron-oxideconcretions concretionsmay mayrepresent representa aslightly slightly deeper deeperwater waterthan thanthe thesandstones sandstonescontaining containingbrachiopod brachiopodfragments. fragments. There Thereare areaafew fewquestions questionsconcerning concerning the theorigin origin and and source source of of the thedetrital detritalgrains grainsand andthe the age age of ol' the thediagenesis. diagenesis. Asthana Asthana [1968] [I9681 reported reported aalarge largerange rangeininK-feldspar K-feldspar content contentininthe theformation. formation.Qi Qiand and Chan Chan have have also alsoidentified identified several several lithotypes lithotypes in in the the formation formation [Suppl. [Suppl. notes notes ininthis thisfield field guidej. guide]. The The age age of of the thepotassic potassicdiagenesis diagenesis in in the theMt. Mt.Simon Simonformation formation in in Wisconsin Wisconsin is is still still uncertain. uncertain. Further Further mineralogical and stable isotope mineralogical and isotope studies studies will will be conducive conducive to our understanding understanding of of the the sediment sediment source, source,the thediagenetic diageneticenvironment, environment, and and the theregional regionaltectonics tectonics atatthe thetime timeofofdeposition. deposition. 37 �I Field Field Trip Trip 2: 2: Route Route Map Map and andStop StopDescriptions Descriptions Eagleton I 'limFal Tilde 'I .1 _ ___ STOP iJ4" LYE fl° * :P'J --___ Icona / Fall ) Cre - I 7 IWillard] ___ r RJ'E t2r( — o r usselI r / — eon Falls 121 ________ ef 'L 4STOP4 Faircj,Id TThb ":ii 5 Gran vile orth leld, cr — 32! ork Al rnacente. 'i1 -' - \?iatfl&d 7 Eli. " n I Price ,- indepen / / Eleva L t - — so0 Loyal ugusta jF — ] I N- — ___ H T Grenwood - L Bracke C:.., STOP 2 '- 1 // _- Irni I — 91 Ei1t$çn : iii — 'l - frhcrp LINE _Lfl-iNYL -- - ______ — — —— SEaL, TATE PARK oDwaF I - STOP 5 STOP. H eha a I -5 1./ :I — rcadia — / 20 st r4oAR I — Fork (t0 • Era in N 1L1J P I 38 ALLL_, BLAO+L STATE NORTH �STOP 1: GEOLOGY OF OF IRVINE IRVINEPARK, PARK, CHIPPEWA CHIPPEWA FALLS, FALLS, WISCONSIN Location: NW1/4 NW1/4 SW1/4 Section Section 31 31 T29N T29N R8W, R8W; Chippewa Chippewa Falls Falls 15' Quadrangle Location: Quadrangle Summary of of Features: Features: Mt. Simon Simon basal conglomerate on o n Precambrian saprolitized saprolitized granite Summary is Middle trondhjemite showing Middle Proterozoic Proterozoic biotite trondhjemite showing spheroidal spheroidal and saprolitic saprolitic weathering weathering is unconformably overlain overlain by by feldspathic feldspathicconglomerate conglomerateand andsandstone sandstoneof of the the Mt. Mt. Simon Simon Sandstone Sandstone of of unconformably Late Cambrian age. The The configuration configuration of of the thePrecambrian Precambriansurface surfacewas was mapped mappedby by Thwaites Thwaites [1957]. [1957]. 19871. The Precambrian-Cambrian Precambrian-Cambrianunconformity unconformityatatIrvine I ~ nPark Park e isisdescribed describedinindetail detailby byOstrom Ostrom[1978, [1978,1987]. The Precambrian composedofofaadeeply deeplysaprolitized saprolitizedtrondhjemite. trondhjemite.Myers MyersetetaL al. Precambrian at at Irvine I ~ nPark Park e isiscomposed [1980] reported that the [I9801 reported the trondhjemite trondhjemiteat atIrvine IrvinePark Parkisis probably probably part part of of aa larger larger granitic granitic pluton which occupies Valley between between Eau Eau Claire Claire and and Jim Jim Falls Falls and and that it is is part part of of aa complex complex occupies the Chippewa Chippewa Valley WNW-trending granite-amphibolite complex of Middle Proterozoic age. The trondhjemite WNW-trending granite-amphibolite complex of Middle Proterozoic age. The trondhjemite at at Chippewa [I9801 at 1,840±15 1,840515m.y. m.y. Chippewa Falls was dated by Van Schmus Schmus [1980] Saprolite is aa "soft, 'soft, earthy, clarrich, clay-rich,thoroughly thoroughly decomposed decomposed rock rock formed formed ininplace placeby bychemical chemical [AOl, 1972]. 19721. ItIt is is characteristic of areas areas of prolonged prolonged weathering of igneous and metamorphic rocks" [AGI, tropical Saprolites in in thc the tropical to subtropical weathering weathering on a granitoid granitoid bedrock bedrock surface of low low relief. relief. Saprolites Piedmont of United States attain aa thickness thickness of over over 100 100 rn. m. The saprolite at at this this outcrop outcrop Piedmont Province of contains high high clay clay content. content. The feldspar contains feldspar and quartz grains grains tend to to be bequite quiteequidimensional equidimensional and and possess sharp edges edges and corners. The saprolite altered upward upward until until at the possess sharp saprolite becomes becomes increasingly increasingly altered the N 7 (I I / 39 A �unconformity. unconformity. It It isis composed composed mostly mostly of quartz, quartz, clay clay minerals and chlorite. Was the the saprolite saproliteformed formed before before or orafter afterdeposition depositionofofMt. Mt.Simon SimonSandstone? Sandstone?Evidence Evidencesuggests suggests that that most most of of the theweathering weathering and and saprolitization saprolitization preceded preceded Mt. Mt. Simon Simon Sandstone Sandstone deposition, deposition, although although there thereisis also also evidence of later modification. modification. A A comparison comparison of of the theclay claymineralogy, mineralogy, heavy heavy mineralogy, mineralogy, and clast clast texture texture classification classification in the the saprolite saprolite and andoverlying overlying sandstone sandstone reveals reveals aa strong strong provenance provenance relationship relationship between between the thetwo twounits. units. Cummings indicated that that most most of the clasts Cummings and Scrivner Scrivner [1980] [I9801 indicated clasts over 1.0 1.0 mm mm in in the the saprolite saprolite are are composite whereas the coarser size fraction in the composite grains grains composed composed of quartz and and K-feldspar, K-feldspar, whereas the Mt. Mt. Simon Simon Sandstone Sandstone isis composed composed predominantly predominantly of of quartz quartzgrains. grains. The Theclay clayminerals, minerals,according according to to Cummings [1980], are 80-90% kaolinite and 10-20% 10-20% illite and vermiculite, and maroon maroon Cummings and Scrivner Scrivner [1980], color color of of the thesaprolite saprolite atatthis thislocality locality isisaaresult resultofofmore morerecent recentweathering weatheringofofchlorite. chlorite.Reddish Reddish spheroids spheroids of of altered altered trondhjemite trondhjemite are arefound foundininthe thelower lowerpart partofofthe thesaprolite. saprolite.Plagioclase Plagioclaseand and part part of of the themicrocline microclineare arereplaced replacedby byK-feldspar K-feldsparand andlesser lesserphyllosilicate. phyllosilicate. This This isis an an excellent excellent example example of the theregional regionalpotassic potassicalteration alterationofofPrecambrian Precambrianrocks rocksbelow belowthe theSub-Cambrian Sub-Cambrianunconformity. unconformity. The TheMt. Mt.Simon SimonSandstone Sandstonethickens thickensfrom fromabout about35 35mmatatChippewa ChippewaFalls Fallstotoabout about270 270 m m in in southern southern Wisconsin Wisconsin [Asthana, 1969]. 19691. The Thenorthernmost northernmost exposures exposures of of this this formation formation are are near near Ladysmith Ladysmithand and Conrath, Conrath, Wisconsin, Wisconsin, and and probably probably represent represent the theapproximate approximateoriginal originallimit limit of of Mt. Mt. Simon Simon deposition deposition in in this thisregion. region. Ostrom Ostrom [1964], [1964], in in aadetailed detailedregional regional synthesis synthesis of of the theCambrian Cambrian stratigraphy stratigraphy of of Wisconsin [1964], concluded that the Mt. Simon Sandstone formed in that the Mt. Simon Sandstone formed in aa marine marine littoral littoral and and nearshore nearshore Wisconsin 119641, shelf shelf environment environmentby bya aslowly slowlytransgressing transgressing sea, sea, which which migrated migrated S&NW SE-NW over over aa deeply deeply eroded eroded Precambrian Precambriansurface. surface. ItIthas hasbeen beensuggested suggestedthat thatthe thebasal basalconglomeratic conglomeratic sandstones sandstonesof of the theCambrian Cambrian sequence sequencewere werebest bestinterpreted interpretedasassubtidal subtidalshelf shelforortidal-channel tidal-channeldeposits. deposits. The TheMt. Mt. Simon-Eau Simon-EauClaire Claire sequence sequence was was regarded regarded as asprogradational. progradational. Driese Driese [1979], [1979], based based on on sedimentary sedimentary structures structures and and paleontological evidence, argued that the Mt. Simon Sandstone is "largely progradational, shoalingpaleontological evidence, argued that the Mt. Simon Sandstone is "largely progradational, shoalingand andfining-upward fining-upward tidal tidal sequence." sequence." According According to to Driese Driese [1979] [I9791the the sandstones sandstones atatIrving IrvingPark Parkbelong belong to tothe thelower lowerand andmiddle middleunits unitsofofthe theMt. Mt.Simon SimonSandstone. Sandstone. Asthana 18%feldspar feldspar of of which which 81% 81% isis Asthana [1969] [I9691 showed showed that that the theMt. Mt.Simon SimonSandstone Sandstone averages averages 18% K-feldspar; K-feldspar; the feldspar feldspar content ranges ranges from from 2.85 2.85 to to 40.07% 40.07% and and that that its itsabundance abundance decreases decreases generally generallyupward upward in in the theformation. formation.Authigenic Authigenicorthoclase orthoclaseoccurs occurscommonly commonly as as rhombic rhombicovergrowths overgrowths on ondetrital detritalgrains. grains.AApetrographic petrographicdescription description of ofseveral severalspecimens specimens of of the theMt. Mt.Simon Simonformation formationisis given 11.Cummings Cummingsand andScrivner Scrivner[1980] [I9801compared compared givenin inthe thesupplementary supplementarysection section[Qi [Qiand andChan, Chan,Suppl. Suppl.1]. the themineralogy mineralogyand and texture textureof ofthe theMt. Mt.Simon SimonSandstone SandstoneatatIrvine IrvinePark Parkwith withthe theunderlying underlyingsaprolite, saprolite, and andconcluded concludedthat thatthe thesilt siltand andclay clayfractions fractionsofofboth bothshow showconsiderable considerablesimilarities. similarities.The Thesaprolitized saprolitized trondhjemite trondhjemitecould couldhave havebeen beenaasource sourceofofclasts clastsfor forthe theMt. Mt.Simon SimonSandstone. Sandstone.The Thecoarser coarserfractions fractions of the Mt. Simon Formation are devoid of the composite quartz-feldspar grains characteristic of the Mt. Simon Formation are devoid of the composite quartz-feldspar grains characteristicof ofthe the underlying abundant epidote epidote and and garnet not found underlying saprolite. saprolite. The sandstone sandstone also contains contains abundant found in in the the underlying underlying saprolite. saprolite. These These minerals, minerals, however, however, are abundant abundant in in the theamphibolites amphiholites nearby nearby (e.g. (e.g. Jim Jim Falls) Falls)and andcould couldhave havebeen beenderived derivedfrom fromthem. them. Based Based on onthe thework workofofmany manygeologists, geologists, ititappears appearsthat thatthe thePrecambrian Precambrianbasement basement was was deeply deeply weathered weatheredtotoform forma asaprolite saproliteininLate LatePrecambrian Precambriantime time(between (between900 900and and500 500m.y.). m.y.). The Thesaprolite saprolite was was locally locally preserved preserved during during slow slow transgression transgression of the the Late LateCambrian Cambrian seas seasand anddeposition depositiono1 ofthe the saprolite saproliteresulted resulted inintheir theirincorporation incorporationasasinterstitial interstitial materials materials in in the the Mt. Mt. Simon Simon Sandstone. Sandstone. With With more morerecent recentexposure exposureofofthe thelower lowerPaleozoic Paleozoicformations formationsto toground groundwater watercirculation, circulation, some some alteration alteration ofofchlorite chloritetotoiron ironoxides oxidesoccurred. occurred. 40 �\PVNE r. PARK PAPK C •ictYQ CT, CWPPEWA FALLS FALLS Ct-\tPPEWA C I -g 1^ . C 0 6 —I Cl) 7; .t--.tr. F r e s h , spheroidally spheroidally Fresh, weathered w e a t h e r e d pink p i n k granite granite 1840 1840 Ma Ka "gruss' + Duncan Cr. of Duncan Cr. rcNNFoRMITY Red and green saprolite (paleo— so 1?) Fresh granite I—I SIGNIFICANCE Corners C o r n e r s weather weather SIGNIFICANCE first first If If this t h i s granite granite is is composed composed of 30% quartz, quartz, 70% 75%feldspar, feldspar, which which weathered toclay c l a ywhich wtaich was was washed -bed weathered to away away (sedimentary (sedimentary "winowi.ng"). "winowing"). calcalrelatively relatively culate culate the t h ethiciciess thickness of of granite granite fresh f r e s hrock rock needed needed to to produce produce the t h e approx. appmx. 600' 600' of ofPa.leozoic Paleoznic quartz quartzsandstones sandstonesfound found in in the theregion regionsouthwest southwest of of Eau Eau Claire. Chire. of a C —4 0 v-I C) —I I) horizontal joint SPHEROIDALWEATHERI WEATHERING SPHEROIDAL MG unconformity at Fig. 1. 1. Precambrian-Cambrian Precambrian-Cambrian unconformity at Irvine IrvinePark. Park. Fig. 41 �STOP2:2:PRECAMBRI PRECAMBRIAN-CAMBRIAN CONTACT A T ROCK DAM, HAY C R E E K STOP -CAMBRIAN CONTACT AT ROCK DAM, HAY CREEK Location:Hay H a yCreek, Creek,0.15 0.15mile miledownstream downstream from Rock Dam; SE 114 NW 114 Sec 15 Location: from Rock Dam; SE 1/4 NW 1/4 Sec 15 T26N R4W; Fairchild 15' Quadrangle T26N R4W; Fairchild 15' Quadrangle Summary of of Features: Features: Mt. Mt. Simon basal conglomerate on partly weathered Summary Simon basal conglomerate on partly weathered Precambrian rnetarhyolite Precambrian metarhyolite ConglomeraticMt. Mt.Simon SimonSandstone Sandstoneoverlies overlies unconformably Penokean-age metamorphic rocks. Conglomeratic unconformably Penokean-age rocks. [I9801 contended contendedthat thatthe thePrecambrian Precambrian unit is a metarhyo1ite:a felsicmetamorphic mylonite containing Myersete taL al.[19801 Myers unit is a metarhyolite:a felsic mylonite containing lenticularclusters clustersofofstrained strainedquartz quartzinin a very fine matrix of K-feldspar, quartz and muscovite. In thin lenticular a very fine matrix of K-feldspar, quartz and muscovite. In thin 1.0-2.5 mm long, with a coarse-grained core that grades section, the clusters of strained quartzare are1.0-2.5 section, the clusters of strained quartz mm long, with a coarse-grained core that grades 57%,quartz, 35%. muscovite, outwardinto intoa afine-grained fine-grainedmatrix. matrix.Estimated Estimatedcomposition composition is:K-feldspar K-feldspar outward is: quartz,crops 57%,phyllite muscovite, 35%,out 3%, magnetite 2%, and biotite, 1% [Myers et al., 19801. A muscovite-rich near the 3%, magnetite 2%, and biotite, 1% [Myers et al., 1980]. A muscovite-rich phyllite crops out near theis of Rock Dam. The rock is composed of K-feldspar, quartz, and muscovite. The foliation base base of Rock Dam. The rock is composed of K-feldspar, quartz, and muscovite. The foliation is N87W, 85N. 85N. Complementary Complementary joint joint sets sets atatNI8W, N18W,73E 73Eand and N77E. SS account for the bloc@ N87W, N77E, 8S account for the blocky appearance of the outcrops. appearance of the outcrops. Thebasal basalMt. Mt.Simon Simonisis a conglomeratic layer containing large pebbles of vein quartz and The a conglomeratic containing pebbles veinthequartz and metarhyolite. Some thepebbles pebbles are over alayer foot across. The large contact surfaceofwith underlying inetarhyolite. Some ofofthe are over a foot across. The contact surface with the underlying metarhyolite shows shows aalocal localrelief reliefofofabout about5 5 meters. The Precambrian rocks do not appear to be metarhyolite meters. The Precambrian rocks do not appear to be deeplyweathered weatheredininthis thisparticular particular outcrop. deeply outcrop. 'I ;sI 1/ - - -- L t TtfT, — -z \ i/Il 24 k / / - J104- — I / -_ -,ooer1 lIT 29 -. - - -. 25 -7 t -l\ -- H - 7 ------I -. '-- - - - - - -< -v f;c 42 �STOPS STOPS 33 & & 4: 4: SPHEROIDAL SPHEROIDALWEATHEIW4G WEATHERING IN NEILLSVILLE NEILLSVLLLE GRANITE GRANITE QUARRIES QUARRIES Location: Location: Stop S t o p 33 NW N W1/4 114NW N W1/4 114SEC SEC20 20T24N T 2 4 NR2W; R2W,Neillsville Neillsville 15' 15' Quadrangle Quadrangle Stop SE1/4 114SW S W1/4 114 SEC SEC 10 10 T24N T 2 4 N R2W; R 2 W ; Neillsville Neillsville 15' Quadrangle S t o p 44 SE Summary ThePrecambrian-Cambrian Precambrian-Cambrian boundary boundary displays displays a spectacular spectacular S u m m a r y of Features: The spheroidal weathering features in the Neillsville granite in two quarries spheroidal weathering features in t h e Neillsville in two quarries in in the the Neillsville Neillsville area. area. I The River Valley, Valley, isis aa Penokean Penokean pluton. A The NeilIsville Neillsville granite, located in the Black River A description description of of its petrography petrography and andcomposition composition isisgiven given by by Maass Maass and and Van Van Schmus Schmus[1980]. [1980]. Zircon Zircondating datingyields yields an an age the age age is is about 40 Ma older age 1875±25 1875±2 m.y. m.y. [Sims [Sims eett al., al., 1989]; 19891; the older than than other othersimilar similar Penokean Penokean plutons plutons in in the thearea. area.The Thegranite graniteisiscomposed composedofofsubequal subequalamounts amountsofofquartz, quartz,microcline, microcline, and and plagioclase plagioclase (An (An 26-28); 26-28); and and approximately approximately 2% biotite [Maass [Maass and Van Van Schmus, Schmus, 1980]. 19801. Fresh Fresh rock rock isis gray gray and altered altered rock rock isis pink, pink, both both because because of of pyrite pyrite weathering weatherins to to ferric ferric oxide oxide and and replacement replacement of of igneous feldspar by authigenic K-feldspar. A strong set of lineation trends N4SE and plunging 820 by authigenic K-feldspar. of lineation trends N45E and plunging 82O pervades pervades the granite. granite. The Thegranite granitecontains contains xenoliths xenoliths of mica mica schists schists which which display display at least least three three generations generations of of deformation. deformation. Two Two sets sets of crenulation form an oblique angle of about 30°. 30". A third third set of as the lineation in the granite. The northern of lineation lineation aligns aligns in the same same direction direction as lineation in northern end end of of the the quarry is a mixture of granite and granodiorite which contain similar structures. The nature of the quarry is a mixture of granite and granodiorite which contain similar structures. The of the contact contact between between the thetwo twounits unitsisisunknown. unknown. I r ejuvrue Mounds • . - I - . '5 - /O(j — _________ - J' 'O3 - - .6 - lB h ry 111 s - —= —. -—, 4PneVIeCr- :-- H - STOP4APr --r': -IV_AIL L 24 —- STOP3 19 ',.I1 - H 43 pJ N 2OJ ., '-I - Th\BMw8S -— 1,icliitv 00 —, - / -. — —— 79 I - - -: - - — h.r ihilije / 12 - 'e ' _6. ' £evai. I tI, / - ______________ '._-14 - / ' I._ K 21 H H- 2 �The granite isis exposed exposed in in several several old old quarries quarries atat Stop Stop 4. 4. In the The Neillsville Neillsville granite the largest largest quarry, the the sandstone sandstone on top top of ofthe thePQ-C PC-Âboundary boundary isisabout about10 10meters metersthick thickand andoverlain overlainby byrecent recentglacial glacial outwash. outwash. The spheroidally spheroidally weathered granite granite isis spectacularly spectacularly exposed exposed in this this quarry. The The PC-Q PC-â boundary meter across. across. The The granite granite boundary is is at at about about 1070' 1070'elevation. elevation. The The spheroids spheroids are are sometimes sometimes over 66 meter is over is identical identical to those those found found atatStop Stop3.3.Relatively Relativelyunweathered unweathered corestones corestonesranging ranging from from 11 m to over 66 m m have have been been isolated isolated by by zones zones of of intense intenseweathering weathering where where grus erus formed. formed. The The granite eranite shows shows a foliation foliation that that strikes strikesN45W ~ 4and and 5dips dips 30°SW. ~ 3WSW. A sub-planar s ~ b - ~ l a nfabric fabricin a r in the the grus strikes hN58W 5 8 and and ~ dips dips 16E[Nelson, [Nelson,19801. 19801. 16E In Inboth bothquarries, quarries,the thePrecambrian Precambriansurface surfaceweathers weathersinto intoaaclay-rich clay-richspheroidally spheroidally weathered weathered pinkish pinkish granite. and conglomerate conglomeratecan canbe be found found on on top top of of and and in in the the wedges wedges between between the the granite. Sandstone Sandstone and weathering weatheringspheroids. spheroids.The Thegranite/Mt. granitemt.Simon Simonunconformity unconformityhas hasaafew fewfeet feetofofrelief, relief,which whichfollows followsthe the tops tops of of the thegranite granitespheroidS, spheroids,and andcoarse coarsematerial materialhas hasfilled filled the thewedges wedges between between the thespheroids. spheroids. The The clasts clasts in in the thebasal basal conglomerate conglomerate are areentirely entirelyquartz quartzpebbles. pebbles. AAdacite dacitedike dikecut cutacross acrossthe theNeillsville Neillsville granite granite in in the thenorthern northernend endofofthe thequarry. quarry.The Thedike dikeisiscomposed composedofofquartz, quartz,oligoclase, oligoclase,biotite biotite and and minor recrystallization textures textures are arenearly nearly identical identical to to those those minor microcline. microcline. Microscopic deformation and and recrystallization in The weathering in the the granite graniteand andgranodiorite granodiorite[Maass [Maassand andVan VanSchmus, Schmus,19801. 19801. The weathering sequence sequencefor forminerals minerals in the theNeillsville Neillsville Granite Granitedetermined determinedby byNelson Nelson[1980, [1980,unpubl. unpubl. work] work] suggests suggests that that plagioclase plagioclase in in the the in saprolite saproliteisisweathered weatheredinto intoa aclay. clay.Biotite Biotitemica micaisissimilarly similarlyweathered weatheredby byhydrolysis hydrolysis to tochlorite. chlorite.IlliteIlliterich richI/S US of of diagenetic diagenetic origin origin is the the principal principal clay clay mineral mineral in the saprolite at Stop Stop 3. 3. Here HereK-feldspar K-feldspar replaces in pink pink bodies bodies of of granite granite within replaces primary primary microcline microcline and plagioclase plagioclase in within the saprolite. saprolite. In In the the quarry quarry at at Stop Stop4,4,exfoliation exfoliation sheets sheetsofofthe thespheroids spheroidsconsist consistlargely largely of of authigenic authigenic K-feldspar, K-feldspar, and and primary preprimary igneous igneous textures textures have have been beenlargely largely obliterated obliterated by by diagenetic diagenetic alteration alteration superimposed superimposedon on preMt. Simon weathering. Potassic alteration extends to the quarry floor in fractured area, —10 m below Mt. Simon alteration extends to the quarry floor in fractured area, -10 below the thesub-Cambrian sub-Cambrianunconformity. unconformity. The at the two before the deposition The weathering weathering and and saprolitization saprolitization at two outcrops outcrops occurred occurred before deposition of the the Mount Mount Simon Simon Sandstone. Sandstone. Uplift and erosion occurred after the the plutonic plutonic emplacement. The time of the theuplift upliftisisuncertain. uncertain. The Thepresence presenceofofcorestones corestonesnot notentirely entirelyconverted convertedtotogrus grussuggests suggestseither eitheranan immature immature weathering, weathering, which which implies aa short duration between the exposure exposure of of the thesurface surfaceand andthe the Dreisbachian Dreisbachian transgression, transgression, or denudation denudation of of substantial substantial portion portion of of the thesaprolite saproliteby byerosion, erosion,which which may may suggest suggest a pre-transgression pre-transgression uplift that led led to to rapid rapid erosion erosion of ofthe theweathered weatheredprofile. profile. 44 �w p-Il 1 P CD = CD CD p-f-) CD p ri- a 0- 1 9. CD (I) Fig. 3 Spheroidal weathering features in Neillsville quarry. 1 a -c 0) CD Z CD C — 00) C CD CD C B C a NJ C) U) :31 t r'r:r :r - f' r F Fig. 2 Basal conglomerate of Mount Simon Sandstone in Neillsville quarry. �.1 u-- - 1 7) Neillsville Granite-Sandstone Contact i—i 3 sKt'4ci'-iS •&or. pt.wkjrttpks. fl r r r' r"i — Z r- r steeply steeply west-plunging west-plunging lineation lineation weathered (75°) is spheroidally (75') is spheroidally weathered in 5-10 cm cm in concentric concentric layers layers 5-10 thick. The outermost rinds are thick. The outermost rinds are bleached; bleached; inner inner ones ones are are ironironquartz Cross-bedded stained. stained. Cross-bedded quartz sandstone sandstone of of the the Mt. Mt. Simon SimonFm. Em. deposited in the depression was was deposited in the depression between between the the spheroids. spheroids. (A) (A) and and SW-dipping surface (B) a steep, (B) a steep, SW-dipping surface of of one one spheroid spheroid isisoverlain overlain by by Mt. Simon Sandstone at (C). Mt. Simon Sandstone at (C). The The sandstone sandstone isis overlain overlain by by orange-brown cobble orange-brown cobble till till on on the the south south side side of of the the exposure. exposure. The The directly overlies till till directly overlies weathered weathered granite granite to to the the north. north. P€ Pâ granite granitegneiss gneisswith withstrong, strong, r- �STOP 5: 5: LAKE LAKEARBUTUS ARBUTUS DAM DAM Location: SE Location: SE 1/4 114 SEC SEC 3 T22N R3W, Hatfield 7½" 7%" Quadrangle Summary ooff Features: Weathered Summary Weathered Mt. Mt.Simon Simon Sandstone Sandstoneoverlying overlying Archean Archean gneisses. gneisses. In the on top of the Hatfield Hatfield and andLake LakeArbutus Arbutusarea, area,glacial glacial outwash outwash generally generally overlies overlies directly directly on ol' Precambrian rocks. Archean rocks are well exposed below the Uike Arbutus Dam. The Archean Precambrian rocks. Archean rocks well exposed below the Lake Arbutus Dam. The Archean rocks are interlayered interlayered scquence sequenceof of quartzo-feldspathic quartzo-feldspathicgneiss, gneiss, amphibole amphibole gneiss, and metarhyolite that that formed about 2.8 Thefeldspathic feldspathicgneiss gneissshows showsaagneissic gneissic 2.8 Ga G aago ago[Van [VanSchmus Schmusand andMaass, Maass,1980J. 19801.The microcline [Van [Van banding ranges from 0.1 to 3cm 3 cm thick thick and and contains contains principally principally quartz, plagioclase and microcline Schmus and Maass, 1980]. The rocks underwent at least two generations of fold deformation; the 19801. The generations of fold deformation; thefirst first one produced produced aa foliation foliationwhich which was was refolded refolded about aboutan aneasterly easterlyfold foldaxis axisplunging plunging atatabout about400. 40". were sheared to dikes intrude the gneissic The metavolcanics metavolcanics were to form form aa phyllonite. phyllonite. Several mafic dikes gneissic and a strong foliation, indicative of a probable phyllonites. Some Some of of the dikes phyllonites. dikes show astrong probable synkinematic synkinernatic origin origin. The boundary between the ft. the Mt. Mt. Simon Simon Sandstone and the Archean rocks rocks is present about about 400 400 ft. south of the covered by by talus, talus, but but could could be he located the Dam. Dam. The Theboundary, boundary, however, however, is is presently presently covered located to within within 15 feet. The upper 20 feet of of the the Archean Archean rocks rocks are are partially partially weathered. weathered. A A 6-10' 6-10' section of exposed oonn a talus Mt. Simon Simon is is exposed talus slope slope above above the the Archean Archean metavolcanics. metavolcanics. The sandstone sandstone is is deeply deeply weathered and crumbles easily in hand specimens, hut relict sedimentary structures like lamination and crumbles easily in hand specimens, but relict sedimentary structures like lamination On the lake side of the Lake Lake Arhutus Arbutus Dam, Dam,Mt. Mt.Simon Simon sandstone sandstone and cross bedding are still visible. visible. On is exposed at water level. is exposed level. ii STOP 6: HALLS HALLS CREEK 1/4 SEC 19 Location: NW SE 114 N W 1/4 114 SE 19 T22N R3W Summary ooff Features: Mt. Mt. Simon Simon conglomeritic conglomeritic sandstone over over Precambrian Precambrianmetavolcanics metavolcanics boundary isis exposed exposedalong alongaameander meanderabout about300' 300'from fromHwy H' E. E.The Theboundary boundary isis located located The PC-C PG- boundary at about 2' 2' above above the thewater waterlevel leveland andmay may be be covered covered by by aa thin thin layer layer of of gravel gravel and and talus. talus. The The Mt. Mt. Simon basal layer is a conglomeratic Simon basal conglomeratic sandstone. sandstone. The Precambrian Precambrian is is aa weathered weathered metavolcanics metavolcanics of ol' unknown age age (Proterozoic?). (Proterozoic?). The weathered weathered rocks rocks do do not not appear to contain unknown contain iron iron oxide. oxide. STOP 47 �STOP IN JACKSON JACKSON COUNTY IRON STOP 7: 7: PRECAMBRIAN-CAMBRIAN SURFACE IN IRON MINE MINE ! Location: Location: NE NE 1/4 114SE SE1/4 114SEC SEC15 15T21N T21NR3W; R3W,U.S.G.S. U.S.G.S. 1:50,000 150,000 Jackson County County Map Map I I Summary of o f Features: Features: Precambrian Precambrianiron ironformation formationand andquartz quartzfelldspathic feldspathicgneiss gneiss overlain overlain by Upper Upper Cambrian CambrianEau EauClaire Claireformation formationcontaining containing aa basal basalbreccia brecciakiyer. layer. The Jackson miles east east of of Black Black River River Falls Falls was was an an open pit pit Jackson County County Iron Iron Mine Mine located located about about 66 miles taconite operation active during the early eighties. The ore body is a lens-shaped 915 mx 550 m body operation active during the early eighties. The ore body is a lens-shaped 915 m x 550 m body [Jones, [Jones, 1977, 1977, Unpublished Unpublished work]. work]. The primary primary ore mineral is inagnetite magnetite residing residing in in Archean Archean iron iron formation which is embodied in quartz-feldspàthic schist and and gneiss. gneiss. The The iron formation quartz-feldspathic schist formation is is composed almost entirely entirely of of quartz, quartz, magnetite, magnetite, cummingtonite-grunerite, cummingtonite-grunerite, biotite, biotite, garnet, garnet,calcite, calcite,ferroactinolite, ferroactinolite, Ca-rich hornblende. hornblende, sphene, sphene, apatite, apatite,pyrite, pyrite, and and K-feldspar. K-feldspar. The The iron-formation iron-formationisishighly highly deformed deformed and exhibits prominent compositional bands ranging from a few mm to several meters. exhibits prominent compositional bands ranging from a few mm to several meters. The The compositionaL bands often often formed isoclinal isoclinal folds foldsand andwere weretransposed transposed along along foliation. foliation. The The iron mound compositional bands has 200 ft. St. of ofwater. water. has been been completely completely excavated excavated and the the open open pit pit isis at at present present filled filled with with over over 200 Fragments Fragments of the the iron iron formation formation could could be be found found on the the slopes slopes of the the pit. pit. The T h erocks rockssurrounding surrounding the the iron mound are upper greenschist-amphibolite facies metamorphic rocks. The principal rock types are are upper greenschist-amphibolite facies metamorphic rocks. The principal rock types arc quartz-biotite-plagioclase schist, mica-garnet-staurolite mica-garnet-staurolite schist. quartz-biotite-plagioclase schist, schist, mica-chlorite-andalusite mica-chlorite-andalusite schist, schist, and amphibolite wide are are present. present. amphibolite gneiss. gneiss. Quartz Quartzveins veinsover over11 ftft wide The The contact contactbetwcen betweenthe theArchean Archeanand andPaleozoic Paleozoicformation formation isis an an undulatory undulatorysurface. surface. The TheArchean Archean rocks are generally weathered. The depth of the weathered zone varies from 6 to 50 meters, probably rocks are generally weathered. The depth of the weathered zone varies from 6 to 50 meters, probably controlled controlled by by fracture fracturepatterns patterns[Jones. [Jones,1977]. 19771.The The Paleozoic Paleozoic rock immediately above the the unconformity uncontbrmity is is a framework-support framework-supportbreccia breccia containing containingangular angular to tosubangular subangularfragments fragmentsofofiron ironformation, formation,schists, schists, and and quartz quartz pebbles. pebbles. Fragments Fragments from from the the iron iron formation formation are aretabular tabularininshape shapeand andoccasionally occasionally imbricated. of them them over over 1/2 m in in diameter, diameter, tend to concentrate 112m concentrate in in certain certain imbricated. Quartz fragments, fragments, some of levels. siltstoneand and shale shale can can be be found levels. Upper Cambrian Cambrian glauconitic glauconitic siltstone found above above the thebreccia breccialayer. layer. Mudcracks, Mudcracks, iron concretions, concretions, and and worm worm trails trails are commonly commonly present in in the theargillaceous argillaceous layers. layers. The The rock rock isis lithological lithological similar similar to the the Eau Eau Claire Claire formation formation which which overlies overlies stratigraphically stratigraphically the Mount Mount Simon Simon Sandstone. Sandstone. The during the the late Proterozoic The iron iron formation formation probably probably formed formed a monadnock monadnock during Proterozoic time. time. The The basal basal breccia deposit on on the slopes and base base of the monadnock. breccia layer layer represents represents a slump deposit slopes and monadnock. Since Since the Eau Eau Claire formation is in direct contact with the iron formation, this particular outcrop Claire formation is in direct contact with iron formation, this particular outcrop was was probably probably located located at at aa relatively relatively high high part part of of the theslope. slope. I- Leus L F L T1TI . Rr-4q; • ii! i / ——- — A •: •Pôrrij - STOP 7 - - MIMNG BIar' RAILROAD I Jackson Countyt • Taibgs dp -* N*\ DuPy\ l!BR0cKWAY/ Mine Oun 48 >, •—•' - RERVA11ON �a '0 r FIG. 1 CJa&s, •'qiij n •1 Margin of Ri ,n, Toic Schist ''.1., Iron Formation 50 Hongingwall Schist El and Footwall Schist + + Diobosic Intrusives Granitic Unit METERS nfer,ed Contact — Known Contact + JACKSON COUNTY IRON MINE r' Cflf1 -17 r: r: r: r r Modified from Jackson County Iron Company Mine Mop August 1977 rr �REFERENCES REFERENCES CITED CITED AmericanGeological GeologicalInstitute, Institute,1972, 1972,Glossary Glossaryof of Geology. Geology. American States, States, U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper1241-F., 1241-F.,31 31p.p. Murray, Murray,R.C., R.C., 1955, 1955,Late LateKeweenawan Keweenawanor orEarly EarlyCambrian Cambrian glaciation glaciation in Upper Upper Michigan, Michigan, Bull. Bull. Geol. G a l . Soc. Soc. Amer., Amer., 66, 66,341-344. 341-344. Myers, Myers, P.E., P.E., M.L. 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Cummings, Precambrian-Cambriancontact, contact,Irvine IrvinePark, Park,Chippewa Chippewa Precambrian-Cambrian Arts & & Lettr., Lettr.,68, 68,22-29. 22-29. Falls, Wis. Wis. Acad. Acad. Sci. Sci. Arts Falls, Denison, R.E., R.E., E.G. E.G. Lidiak, Lidiak, M.E. M.E. Bickford, Bickford, and and E.B. E.B. Denison, Kisvarsanyi, Kisvarsanyi, 1984, 1984, Geology Geology and and geochronology geochmnology of of Precambrianrocks rocksin in the the Central CentralInterior InteriorRegion Regionof ofthe the Precambrian United States, States,U.S.G.S., U.S.G.S., Prof. Prof. Paper Paper1241-C, 1241-C,20 20 pp. pp. United Stuckless,and andM.H. M.H. Delevaux, Delevaux,1983, 1983,The The Doe, B.R., B.R., J.S. J.S. Stuckless, Doe, possible bearing of the granite granite of the the UPH UPHDeep DeepDrill Drill possible Holes, northern northern Illinois, Illinois, on onthe theorigin originofofMississippi Mississippi Holes, Valley ore ore deposits, deposits. Jour. Jour.Geophys. Geophys.Res., Res.,88, 88,22-29. 22-29. Valley Driese, S.G., S.G., Paleoenvironments of the Upper Upper Cambrian Cambrian Driese, Mt. Simon Simon Formation Formation of ofwestern westernand andwest-central west-central Mt. Wisconsin, MS thesis, thesis, U. U. Wisconsin-Madison, Wisconsin-Madison,207p. 207p. Wisconsin, Duffin, M.E., M.E., 1989, 1989, Nature and and origin origin of ofauthigenic authigenic Duffin, the K-feldspar inin Precambrian IC-feldspar Precambrian basement basement rocks rocks of the North American AmericanMidcontinent, Midcontinent,Geology, Geology, 17, 17,765-768. North 765-768. Duffin, M.E., M.E., M.C. Lee, Lee, G.deV. G.deV, Klein, Klein, and R.L. Hay, Hay, and ItL. Duffin, sandstones and and 1989, Potassic diagenesis of Cambrian sandstones Hole, Precambrian Granitic basement in UPH-3 Deep Hole, UpperMississippi Mississippi Valley, USA., Jour.Sedi. Sedi. Petrol., Petrol., 59, 59, Upper U.S.A, Jour. 848-861. 848-861. R.L., M.C. M.C. Lee, Lee, D.R. D.R. Kolata, Kolata, J.C. J.C. Matthews, Matthew, and and Hay, R.L., J.P. Morton, Morton, 1988, 1988,Episodic Episodic potassic potassic diagenesis diagenesis of of J.P. Ordoviciantuffs tuffs in in the the Mississippi Mississippi Valley area, area. Geology, Geology, Ordovician 16, 743-747. 743-747. 16, Harrison J.E., J.E., and Z.E. Z.E. Peterman, Peterman, 1984, 1984, Introduction Introduction to to Harrison correlation of of Precambrian Precambrian rock rock sequences, sequences,U.S.G.S. U.S.G.S. correlation 1241-A,7p. Paper 1241-A, Prof. Paper 7p. Irving, E., E., 1979, 1979, Paleopoles and paleolatitudes paleolatitudes of of North North Irving, America and and speculations speculations about about displaced displaced terranes, terranes, America Sci.,16, 16,669-694, 669-694,1979. 1979. Can. J.J. Earth EarthSci., Can. D., 1977, 1977,Geology Geology of of the the Jackson Jackson County County Iron Iron Jones, 0., Jones, Mine, Unpublished Unpublishedreport, report,copy copyavailable available upon upon request. request. Mine, Twoearly earlyProterozoic Proterozoic LaBerge, G.L., P.E. Myers, Myers, Two Lal3erge, G.L., and P.E. successions in central Wisconsin Wisconsin and their tectonic tectonic successions in ccntral and their significance, Bull. ~ u l lGeol. Geol. . Soc. Amer., Amer., 95, 95,246-253. 246-253. significance, Soc. 1971. The of Lochman-Balk, C., C., 1971, The Cambrian of the craton of United States, States,in in 1-lolland, Holland, C.H. of the United C.H. (ed), Cambrian of the New New World, World,Wiley-Interscience, Wiley-Interscience,London, London,79-168. 79-168. R.S. and W.R. W.R. Van Van Schmus, Schmus, 1980, 1980. Precambrian Precambrian Maass, It.S. tectonic history history of the the Black Black River River Valley, Valley, 26th 26th Inst. Inst. tectonic Lake Superior Superior Geology, Geology, Field Eau Claire, Claire, Lake Field Trip Trip 2, Eau Wisconsin. Wisconsin. Schmus. 1988, 1988, Correlation Morey, G.B.. G.B., and W.R. Van Schmus, Correlation of United Precambrian Rocks Rocks of of the the lake lakeSuperior Superiorregion, region, United Precambrian Precambrian Precambrian Geology Geology of the theChippewa ChippewaValley, Valley, 26th 26th Inst. Inst. Lake Lake Superior SuperiorGeology, Geology, Field Field Trip Trip 1,1,Eau Eau Claire, Claire, Wisconsin. Wisconsin. Nelson, P., P., 1980, 1980, Petrography Petrography and weathering weathering of of the the Nelson, Neillsville Granite, Unpublished report available Neillsville Granite, available upon upon request. request. O~trom, 1966, 1966, Cambrian Cambrian stratigraphy stratigraphy in in western Ostrom, Wisconsin, Guidebook Guidebook to to the the Michigan Michigan Basin Basin Wisconsin, Geological Society 1966 Annual Geological Society Annual Field Field Conference: Conference: W.G.N.S. 79p. W.G.N.S. Info. Cir. Cir. 7,7,79p. Ostrom, M.E., M.E., 1978, 1978,Irvine Irvine Park: Park: Precambrian/Paleozoic Precambrian/Paleozoic Ostrom, unconformity unconformity at at Chippewa Chippewa Falls, Falls, Wisconsin: W.G.N.H.S. W.G.N.H.S. Outcrop Outcrop Description ~ e s c r i ~ t iCH29N/08W/31. oCH29N/08W/31. n Ostrom, ME., M.E., 1987, 1987,Precambrian/Paleozoic PrecambrianPaleowic unconformity unconformity Ostrom, at Chippewa Chippewa Falls, Falls, Wisconsin, Wisconsin, W.G.N.H.S. W.G.N.H.S. outcrop outcrop Description TR TR 24N/08W/18. 24Nl08W118. Ostrom, Ostrom. M.E., M.E., 1988, 1988,Cambro-Ordovician Cambro-Ordovician Field Guide to to Western Wisconsin, Field tour by by representatives representatives of of Wisconsin, Field Amoco Ammo Production Production Co. Co. Ostrom, Guildbook,for for CambroCambroOstrom, M.E., M.E., 1970, 1970, Fieldtrip Fieldtrip Guildbook Ordovician Ordovician Geology Geology of Western Western Wisconsin, Wisconsin, W.G.N.S. W.G.N.S. Information Circular 11, 131p. lSlp. Rozanov, A.Y., A.Y., 1984, 1984, The The Precambrian-Cambrian Precambrian-Cambrian Rozanov, boundary in in Siberia, Siberia,Episodes, Episodes,7,7,20-24. 20-24. AJ., C.H. C.H. Summerson, Summerson, and and W.J. WJ. Hinze, Hinze, 1965, 1965, Rudman, A.J., Geology of basement Geology of basement in in Midwestern Midwestern United United States, States, Bull. A.AY.G., A.A.P.G., 49, 49, 894-904. 894-904. Bull. Sims, P.K., Schmus, K.J. KJ. Schulz, Schulz. and Z.E. Sims, P.K., W.R. W.R. Van Schmus, and Z.E. Peterman, 1989, 1989,Tectonostratigraphic Tectonostratigraphicevolution evolutionof of early early Peterman, Proterozoic Wisconsin magmatic Proterozoic Wisconsin magmatic terranes of the the Penokean Orogen, Orogen, Can. Can. J., J., Earth EarthSci., Sci.,26, 26,2145-2158. 2145-2158. Thwiites, P.E., and others, others, 1980, of buried 1980, Map Map of Thwaites, Precambrian Precambrian of Wisconsin, Wisconsin, W.G.N.S. W.G.N.S. Sheet. Van of North Van der der Voo, Voo, It., R., 1981, 1981, Paleomagnetisni Paleornagnetism of North America: America: A A brief briefreview, review, in in McElhinny, McElhinny,M.W. M.W. and and D.A. D.A. Valencio Valencio (eds.), Paleoreconstruction Paleoreconstruction of the the Continents, Continents, Geodynamicser.2,A.G.U.. Washington,D.C., D.C.,167-176. 167-176. Geodynamic ser. 2, A.G.U., Washington, Van Schmus, Schmus, WIt., W.R., Chronology Chronology of igneous igneous rocks rocks associated with the Penokean Penokeanorogeny orogenyininWisconsin, Wisconsin,inin Selected Studies of of Archean Archean gneisses gneisses and Lower Lower Selected Studies Proterozoic Proterozoic rocks rocks of of Southern Southern Canadian CanadianShield, Shield, in Morey, G.B., I lanson (eds.), Morey, and G.N. G.N. Hanson Spec. (cds.), GSA Spec. G.B., and Paper Paper 182, 182,159-168. 159-168. c, 50 �SUPPLEMENT PEThOGRAPHIC CIIARACTERISTICS SUPPLEMENT1: 1: NOTES ON PETROGRAPHIC CHARACTERISTICSOF OF THE THE MOUNT MOUNT SIMON FORMATION, EAU CLAIRE, WISCONSIN SIMON FORMATION, EAU CLAIRE, WISCONSIN Authors: Qi Qi Zhu Z h u (Visiting (Visiting Scholar Scholar from from Chongqing Chongqing Petroleum College, College, China) and and Lung S. Chan (University at Eau Claire) (University of Wisconsin Wisconsin at I I We We have have conducted conducted aa petrographic petrographicstudy studyon onMt. Mt. Simon Simon Sandstone Sandstone samples samples collected collected from from the thetype typ locality of of the formation in Eau Eau Claire. Claire. Nineteen Nineteen specimens specimens were collected at at different different stratigraphic stratigraphi levels levels of the formation. Based on on the the petrographic petrographicobservation, observation,we wehave have identified identified the thefollowing followingtypes type of lithologies lithologies in the the formation. formation. The Theapproximate approximate levels levels of of the thespecimens specimens and andthe themineralogical mineralogica ! abundance abundance are areshown shownininFig. Fig. S1.1. Sl.1. Type I.I. Coarse-Fine Coarse-Fine Conglomeratic Conglomeratic quartz sandstone (MS-I, (MS-1, Plate Plate 1). 1). I The The conglomerate conglomerate consists consists of 20% 20% quartz quartz pebbles pebbles and and 80% 80% quartz quartzcobbles. cobbles. Magnetic Magnetic grains grains are are occasionally present. present. The quartz grains show high high degree of rounding and maturity. maturity. About 10% 10% of of the the grains grains display display dissolved dissolved edges. Individual Individual quartz quartz shows shows wavy wavy extinction indicating a source source from fro metamorphic rocks. About 20% polycrystallineand and quartz-vein quartz-vein fragments. fragments 20% of of the thedetrital detritalgrains grainsare arepolycrystalline All the the quartz quartzgrains grains are areclear clearand andstructureless, structureless,with withfew fewimpurity impurity inclusions. inclusions. Cementing material materia consists mostly of matrix material material with with 80% silt (0.1 -- 0.05 mostly of 0.05 mm) and 20% euhedral euhedral potash potash feldspar feldspa or or irregular irregular feldspar feldspar or or kaolinite. kaolinite. Both Both detrital detrital grains grains and and cementing cementing matrix matrix are are very very well sorted. 1t I The Thepetrographic petrographiccharacteristics characteristicsofofthe thesandstone sandstonesuggest suggestaashoaling shoalingdeposition depositionwith withmultiple multiplecycles cycle of erosion. potas erosion. Original Original or or primary primary cementing cementing materials materials are replaced replaced entirely entirely by by authigenic authigenic potash feldspars. feldspars. The matrix matrix material material suggests suggests a multiple multiple cycle cycle of deposition, deposition, indicating indicating strong wave wave or oi current motion motion and and active active pore pore current current flow flow during during the the deposition. deposition. 1 Type II. 11. e.g. e.g. MS-2. MS-2. Quartz sandstone. sandstone. I , 1 This This type type of of quartz quartz sandstone sandstone contains contains about about 60% 60%medium-fine medium-fine grained grained sand sand and and 40% 40% medium mediu grained grained sand and and minute minute amount amountof of silt silt size size particles. particles. The The sand is is 95% quartz and about about 5% 5%feldspar. feldspar The are The quartz quartz grains grains are areclean cleanand andmonocrystalline; monocrystalline;polycrystalline polycrystalline quartz and impurity impurity inclusions ar absent. The quartz quartz sands sands are are subrounded subrounded to tosubangular subangular and and moderately moderately sorted. sorted. The The fetdspars feldspars are ar mostly minerals that develop around a detrital mostly authigenic minerals detrital core core of of microcline microcline or or plagioclase. plagioclase. Most of o the Some of of the authigenic feldspars feldspars tend tend to form suturethe authigenic authigenic feldspars feldspars show euhedral form. form. Some type intergrowth pattern patterninininterstitial interstitialspaces spacesamong among the the quartz quartz grains. grains. Many feldspars develop aroun type around detrital detrital feldspar feldspar grains. grains. Detrital Detrital feldspars feldspars are arenormally normally not not stained, stained,microcline microcline in in composition composition while whil authigenic twinning isisobserved observedin insome someof of the the detrital feldspar authigenic feldspar are are well well stained. Plagioclase twinning grains. grains. The orientation orientation in in the theauthigenic authigenicfeldspar feldspar often often makes makes aa10-12° 10-12" angle angle with with the the twinning twinnin orientation veins and orientationof of the thedetrital detritalcore. core. Fragmentsof Fragments ofquartz quartzveins and granites granites are are present present in in minute minute amount. The The same Thecementing cementingmaterial materialalso alsocontains containssmall smallquantity quantity of of silica. silica. The same lithological characteristics are ar 7, 8, 8, 11, 11, 12, 13, 14, and these specimens 4,5, present in in MS-3, MS-3, 4, present 5, 7, and 15 (Plate 2). Feldspar composition in these ranges ranges from from 55 to to 15%, 15%,and andnormally normally not notexceeding exceeding10%. 10%. 51 �Type III. IIL Volcaniclastic-like Volcaniclastic-like feldspathic quartz sandstone This This type type of of quartz quartz sandstone sandstonediffers differs from from Types I and II IIin in that thatmorphology morphology and and composition composition of of the the feldspars. feldspars. This This type type of of quartz quartzsandstone sandstonecontains contains40-60% 40-60%feldspar feldsparand andshows showsaa strong strongdissolution dissolution of of the thecrystal crystaledges. edges. InInMS-b MS-10 collected at about 15 15 m m from the the base base of of the theMt. Mt.Simon Simon Formation, Formation, mica to mica grains grains present in in matrix matrix material material seem seem to to show show aa preferred preferredorientation, orientation,which which may be due to strong current flow through the interstitial pore spaces during or after the deposition. We suggest that strong current flow through the interstitial pore spaces during or after the deposition. We suggest that the the presence presence of of aa strong strong interstitial interstitial pore pore current current may may be an an important important factor factor in in the the formation formation of of authigenic authigenicfeldspar. feldspar. MS-9 (Plate (Plate3) 3) MS-9 This contains 50% 50% feldspar feldspar and and 50% 50% quartz quartz. About About 20% This specimen specimen contains 20% of the the quartz quartz grains grains are are subrounded, subrounded,30-40% 30-40%subangular subangularand and40% 40%show showdissolution dissolution edges. edges. The The dissolution dissolution grains grains show bonebonelike, like, curve curve or or sharp sharp shards. shards. Feldspar Feldspar grains grains are are mostly mostly fine fine sand sand size, size, and and in in the theforms formsofofsingle single crystals. euhedral and and form form intergrowths. intergrowths. Many form around crystals. Most of the feldspars feldspars are subhedral to euhedral aa core core grain grain of of dissolved dissolved residue and enlarge around the core. Other Other feldspars feldspars do not not indicate indicate aa core core grain. grain. Cementing Cementing material material are areinconspicuous. inconspicuous. The Thefeldspars feldspars basically basically form the interstitial interstitial materials. materials. MS-b MS-10 The of this this specimen The lithological lithological characteristics characteristics of specimen are similar similar to that that of ofMS-9. MS-9. Feldspar Feldspar grains grains constitute constitute about about 50% 50% of of the thespecimen. specimen.ItItcontains containsabout about10% 10%ofofcoarse-grains coarse-grains pebble-size pebble-size detrital detrital quartz quartz fragments fragments with with good good degree degree of of rounding rounding and and uniform uniform composition, composition, and about about 2% 2% sericite sericite mica mica fragments. fragments. Type Type IV. IV. Feldspathic Feldspathic Quartz Quartz Siltstone Siltstone MS-19 MS-19 This specimen specimen contains contains 80% 80% quartz, quartz, about about15% 15%irregular-shaped irregular-shaped quartz quartzgrains grainsshowing showing strong strong This dissolution dissolution edges edges and and 20% 20% feldspar feldspar with with or or without without aa detrital detrital core. core. Quartz Quartz grains grainsare aresubrounded subroundedtoto subangular subangularand andmoderately moderatelysorted. sorted.Cementing Cementingmaterials materialsare aremostly mostlyiron-rich iron-rich mineral mineral or orsericite sericitemicas micas in in interstitial interstitial pores. pores. MS-18 MS-18 This with 70% 70% quartz and >25% feldspar. feldspar. Sericite Sericite and and This specimen specimen contains contains 80% 80% silt and 15% 15% fine tine silt with ferric ferricmineral mineral are arepresent presentatatabout about2-3%. 2-3%.Quartz Quartzgrains grainsare aremostly mostlysubrounded subroundedtotosubangular subangularand andwell well sorted. The Thefeldspars feldsparsare aremostly mostlysecondary secondarypore porefiller, filler,crystal crystalforms forms are areless lesswell well developed developed as asMS-S MS-8 sorted. or orMS-9 MS-9 and and are aresimilar similar to tokaolinite kaolinite cement. cement. Part Part of ofthe thefeldspars feldsparsare areauthigenic authigenicand andauthigenic authigenic overgrowth. and MS-10. MS-b. overgrowth. Feldspar Feldspar abundance abundance is also lower than in MS-9 and Based on on the thepetrographic petrographicobservations, observations, the theMt. Mt. Simon Simon formation formation in in Eau Eau Claire Claire can can be be divided divided into Based several several zones. zones. The The basal basal layer layer of of the theMt. Mt.Simon Simon Sandstone Sandstone isis represented represented by by aaconglomerate conglomerate and and coarse coarse sandstone sandstone layers. layers. The The dominance dominance of of rounded rounded quartz quartzsand sand indicates indicates high high degree degree of of maturity. maturity. ItItisisalso also evident evident that that the thesandstone sandstoneunderwent underwentmultiple multiplecycles cyclesof of erosion erosion and anddeposition. deposition. The Thedetrital detrital quartz grains and quartz cement show corroded edges that resembles quartz that formed in a volcanic quartz grains and quartz cement show corroded edges that resembles quartz that formed in a volcanic setting. setting. ItItisis questionable questionable whether whetherthe thecementing cementingmaterial materialrepresents representsthe theprimary primaryoriginal originalcementing cementing medium. medium. The Theclay claycontent contentininthe theconglomerate conglomerateisisvery verysmall, small,suggesting suggestingaasecond secondcycle cyclecementation cementation process. process. The TheMt. Mt.Simon SimonFormation Formationcontains containsseveral severalbeds bedsthat thatare areenriched enrichedininfeldspathic feldspathiccomposition. composition.Based Based 52 52 �on on the theform formand andcrystallinity, crystallinity, the potash feldspars feldspars are are authigenic a u t h i g e ~ in c nature. About About 50% 50% of the the quartz quart grains, derived there there though normal transportatio~ transportation grains, on the other other hand, hand, are are terrigenous temgenous detrital detrital grains derived means. means. The Theother otherquartz quartzgrains, grains,however, however,exhibit exhibitdissolved dissolvededges edgesand andform formirregular irregularshards. shards.This Thisform forr of quartz bears similarities to quartz that forms in a volcaniclastic environment. quartz bears similarities to quartz that forms in a volcaniclastic environment. The The authigenic authigenic feldspar feldspar crystals crystals and their their formation formation conditions conditions present present aacomplicated complicated problem. problem Some grains. Others Others do do not contain any core and Some of of the the feldspars feldspars contain contain aa core core of of dissolved dissolved feldspar grains. am are are entirely entirely authigenic authigenic in in origin. origin. Some of the the core core grains grains contain contain obvious obvious twins, others do not. Some Somi of of the thecore coregrains grainsare arepossibly possiblydissolved dissolvedquartz, quartz,with with brainline brainline structures. structures.Some Someauthigenic authigenicfeldspars feldspar simply simply follow the forms of existing existing detrital quartz quartz and andfeldspar feldspar grains grains or orfill-in fill-in cracks cracks and andveins veinsinii existing existinggrains. grains. 1 I Most Most of of the the authigenic authigenic feldspars feldspars are are euhedral euhedral to to subhedral. subhedral. When When the the growth growth condition condition is is confined confine1 by by surrounding surrounding quartz quartz grains, grains, the thefeldspar feldspar may may !form form dog-teeth dog-teeth like like crystal crystal edges. The source of o feldspars, questions. First, the source feldspars, morphology and authigenesis authigenesis have presented some interesting questions. sourci of of the thefeldspar feldspar has has been beenan anenigma. enigma. The Thedepositional depositional medium medium and and water water conditions conditions at at the the time time of o deposition deposition also represent problems problems for for understanding understanding the origin of the Mt. Mt. Simon Simon Formation. Formation. The Thi high high percentage percentage of of feldspar feldspar in in particular particular beds beds of of the theformation formation may may be be indicative indicative of of the thefollowing follow in^ conditions. conditions. (1) (1)The Thetransported transporteddebris debrismay maycontain containsubstantial substantialamount amountofofvolcanic volcanicquartz quartzfragments, fragments as (2) During During the the early early deposition deposition of the the Mt. Mt. Simon Simoi as suggested suggested by the forms forms of the the quartz quartz grains. grains. (2) sandstone, sandstone, there theremight mighthave have been beenvolcanic volcanic eruptions eruptions in in aanearby nearbyarea. area.The Thedeposit depositsurely surelycontains contain quartz quartz grains grains sufficiently sufficiently washed and eroded eroded by by ocean ocean waves. waves. The The primary primary cementing cementing material material may ma' contain volcaniclastic volcaniclastic material being eliminated eliminated during redeposition. The eroded erode! contain material that that were were being during the the redeposition. primary primary cement might be enriched in potassium feldspar and constituted the source of the the authigenic authigenii feldspar feldspar in the the Mt. Mt. Simon Simon Formation. Formation. (3) (3)The Theobserved observed dissolution dissolution of of quartz quartz isisprobably probably related relate! genetically event at the to the theformation formationof ofthe theauthigenic authigenicfeldspars feldsparsand andmay mayimply imply an volcaniclastic event tht -genetically to time time of of the thedeposition. deposition. 53 �Type Type LI. Sandstone Sandstone Conglomeratic Conglomeratic MS-i. MS-1. Sig. 4x1" Sig. 4xiO Type II. 11. Quartz QuartzSandstone Sandstone Type MS-3 MS-3 Sig. lOxlO 10x10 Sig. Type III. 111. Volcaniclastic-like Volcaniclastic-like Type feldspathic sandstone fe]dspathic sandstone MS-9 MS-9 10x10 Ri. lOxiO * 54 �Fig. S1.1 Grain Fig. Sl.1 Grain Composition Composition of of Mt. Mt. Simon Simon Sandstones Sandstones based based on on 500 500 points points I Level Level zo EAU 250 EAu CLAIRE FORMATEON FORMATION - 2: © Ct z (/D 2: C I Specimen Specimen DMQ I DSQ 3.2 3.2 1.2 1.2 MS-i MS-1 44.4 32.2 32.2 MS-2 MS-2 68.6 3.8 3.8 MS-3 MS-3 MS-4 MS-s MS-5 MS-7 MS-7 MS-9 MS-9 64.6 2.2 55.8 65.2 00 DO DM AKF PITY C) 11.2 0.8 0 0 0.8 0.8 0.2 7.4 20.2 5.6 0 - 25 0 1.4 Lit 2.4 0.2 2.8 3.0 0.8 0.8 00 29.4 0.2 2.4 6.8 0.4 2.0 1.6 1.6 2.4 2.4 24.8 1.6 2.0 2.0 1.6 Oh 0.6 65.2 2.8 1.0 1.0 10.2 4.0 0.8 4.0 4.0 2.4 2.4 2.4 2.6 2.2 24.0 26.6 43.6 6.6 0.2 MS-b MS-10 MS-Il MS-11 33.6 8.0 1.8 1.8 11.6 2.2 1.8 1.8 36.6 4.0 - 60.7 6.5 6.5 2.7 0.4 2 2.8 9.0 0.4 3.7 3.7 2.2 22 3.0 69.6 4.5 4.5 0 17.7 MS-12 MS-12 11.4 4.0 0.4 MS-13 MS-13 58.6 &4 6.4 5.8 5.8 23.6 1.2 1.4 1.4 2.0 0.4 1.0 MS-14 MS-14 61.4 8.6 8.6 6.0 13.0 5.0 1.4 1.4 3.0 0.6 1.6 MS-IS MS-15 61.1 &8 8.8 0 72.2 2.5 10.8 10.8 3.7 3.7 2.7 0.3 0.3 0.6 0.6 4.7 MS-16 MS-17 MS-17 MS-Is MS-18 9.1 0 0 -MS-19 P4; DPQ DPQ - - a -- 60.0 3.6 5.6 50.3 6.0 6.0 54.0, 3.3 -- 12.9 0.2 7.4 13 6.4 9.9 0.5 0.5 2.5 6.7 6.7 4.3 0.9 lM 13.6 10.6 4.3 4.3 13.6 0 1.0 7.6 3.6 2.7 - 25.9 0 2.0 DMQ Deirital monocrystalline quartz; DPQ -- Detrital DMQ -- Detrital monocrystalline quartz; Detrital polycrystallinc polycrystalhnc quartz, quartz: Strained quartz; QO -- Quartz overgrowth; DO -- Detrital Detrital orthoclase: SQ -- Strained SQ orthoclasu. DM -- Detrital Detrital microcline; AK K-feldspar; AK .- Authigenic Authigenic K-feldspar; PRY 0 PHY - Phyllosilicate; Phyllosilicate; 0 - Others. Others. 55 �Supplementary SupplementaryNotes Notes 2. 2. Mineralogical Mineralogical data datafor fordiagenetically diagenetically altered altered paleosols paleosols at at Stops Stops 1, 1, 3, 3, & & 44 Analysis Analysis done done by by Richard Richard L. L. Hay Hay Irvine Irvine Park Park / / \ , / / U A — ¼ - s_ L 5c. prc).4.. 1st 1stNejjlsvjlle Neillsville Quarry Quarry(Stop (Stop3)3) A (Altered) Granite , 7 /. Fresh Oligoclase PC / Q 35 24 Mr 14 8 Pc 47 0 Mc 3 5 K.F 0 52 l'h 0 10 B / /1'1 / — ÷K — -p. A • Covcre — Microeline Graniie F. '-KR — 3 (Altered) Q 43 43 Mr 40 C) Pc 12 0 Mc 5 5 KF 0 49 0 3 'C I 2nd 2ndNeillsville Neillsville Quarry Quarry(Stop (Stop4)4) Cc Granite Gnciss (Altered) Q 24 13 Mr 51 31 Pc 18 0 Mc —1 —1 1cF 0 53 Ph 0 2 -G. e "(0 m oQ- Quartz - Quartz Mr Mr- Microcline - Microcline l'cI'c- Plagioclase - Plagioclase Mc -~ k a Mc- Mica KF KT- Authigenic - AuthigenicK-feldspar K-feldspar Ph AuthigenicPhyllosilicate Phyllosilicate 1'h- -Authigenic Saprolite & gruss [i< Granite Granite&tegranite granitegneiss gneiss 56 56 C �1991 SATURDAY, MAY MAY 4, 4, 1991 SATU1mAY, FIELD TRIP #3 #3 M.G. Mudrey, Jr., Jr., and andB.A. B.A. Brown (Leaders) (Leaders) Proterozoic "Proterozoicvolcanogenic volcanogenic massive massive sulfide sulfide deposits of northwestern northwesternWisconsin" Wisconsin" 57 �L [ PROTEROZOIC VOLCANOGENIC PROTEROZOIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE SULFIDE I I [ 1 WISCONSIN DEPOSITS OF NORTHWESTERN WISCONSIN M.G. Jr., and and B.A. LA. Brown M.G. Mudrey, Mudrey, Jr., Brown Wisconsin Geological and Wisconsin Geological and Natural Natural History History Survey, Survey, Madison, Madison, WI WI L INTRODUCTION: INTRODUCTION: [ Field trip trip 3 Field 3 represents represents aa departure departure from from the the usual usual format format followed followed by by previous Institute The emphasis previous Institute field field trips. trips. The emphasis is is on on massive massive sulfide sulfide L mineralization, and particularly particularly on on the the Flambeau, Flambeau, Lynne, Lynne, and and Bend Bend deposits. deposits. mineralization, and The regional geology The regional geology has has been been covered covered in in previous previous Institute Institute field field guides guides [ 4 1984, 1986) and regional geology (1980, 1984, and in in several several papers papers about about the the regional geology (Sims (Sims and an I [ others 1990, Greenberg others 1990, Greenberg and and Brown, Brown, 1983). 1983). Because Because time time is is limited, limited, we we will will 1 depart depart from from tradition tradition and and not not visit visit any any outcrops. outcrops. We will will proceed proceed directly directly to to L where we Hawkins, where Hawkins, we will will examine examine core core from from the the Bend Bend and and Lynne Lynne deposits, deposits, guided by personnel Lehman and E. K. Lehman and Associates Associates and and Noranda. Noranda. personnel from from E. Then we we will Then will to to Ladysmith, where Ladysmith, where we we will will examine examine core core from from the the Flambeau Flambeau Deposit, Deposit, guided guided by L personnel of the Mining Co. personnel of the Flainbeau Flambeau Mining Co. The The following following notes, notes, based largely largely on on papers papers by by DeMatties DeMatties (1989) (1989) and and Mudrey Mudrey and and others others (1991), (1991). are are intended intended to to C provide brief outline provide a brief outline of of the the geology, geology, mineralization, mineralization, and and exploration exploration history, history, and and will will be be supplemented supplemented by by reprints reprints provided provided to to trip trip participants. participants. ii L E GEOLOGIC FRAMEWORK: GEOLOGIC FRAMEWORK: The Penokean Penokean orogen in northern Wisconsin consists of consists two distinct of two distinct The orogen in northern Wisconsin terranes. The northern oxideterranes. The northern terrane terrane contains contains platform platform sediment, sediment,including including oxide- L facies iron iron formation, facies formation, turbidite, turbidite, and and minor minor tholeiitic tholeiitic volcanic volcanic units units deposited on deposited on an an Archean Archean continental continentalmargin. margin. The The northern northern terrane terrane extends extends east east This into Michigan Michigan and and west west across across the the Midcontinent Midcontinent Rift Rift into into Minnesota. Minnesota. This 1 terrane terrane has has historically historically been been aa major major producer producer of of iron iron but but is is not not known known to to 1 contain major contain major massive massive sulfide sulfide deposits. deposits. The southern known only only in in Wisconsin, Wisconsin, represents represents an island island arc The southern terrane, terrane, known 58 \geology\sulfide ,bab �L. volcanic terrane terrane accreted accretedto to the the Superior Superior Craton Cratonduring during the the Penokean Penokean orogeny volcanic orogeny L HA). (1850MA). (1850 [ This terrane, the Penokean Volcanic Belt of Greenberg and Brown This terrane, the Penokean Volcanic Belt of Greenberg and irown i (1983) or or Wisconsin WisconsinMagmatic Magmatic Terrane Terrane of ofSims Sims(1987), (1987). consists consistsof ofcalc-alkaline calc-alkaline (1983) volcanicrock rockand andvolcanogenic volcanogenicsedimentary sedimentaryrock. rock. The Penokean arc terrane, in volcanic The Penokean arc terrane, in contrast to to the the continental continentalmargin margin terrane, contains significant massive contrast terrane, contains significant massive sulfidemineralization. mineralization. To date. seven deposits totalling nearly 100 million sulfide To date, seven deposits totalling nearly 100 million L tons have been discovered, including the 60 million ton Crandon deposit. tons have been discovered, including the 60 million ton Crandon deposit. MASSIVE SULFIDE SULFIDEDEPOSITS DEPOSITS MASSIVE L DeMatties (1989) (1989) recognized recognizedtwo two mineralized mineralized districts in the western DeMatties districts in the western L area of the volcanic belt, the Ladysmith district centered on the Flambeau area of the volcanic belt, the Ladysmith district centered on the Flambeau deposit in in Rusk Rusk County County and andthe the Somo Somo district district to the east in Price, Lincoln. deposit to the east in Price, Lincoln, [ L and Taylor TaylorCounties. Counties. The massive sulfide deposits belong to the Cu-Zn group and The massive sulfide deposits belong to the Cu-Zn group of Franklin Franklinand andothers others(1981) (1981) and andrepresent represent at least three district host of at least three district host environments. environments, L . . The first first environment environmentis isexemplified exemplifiedby by the theFlambeau Flambeau and Ritchie Creek The and Ritchie Creek main zone zonedeposits, deposits,and andconsists consistsof of syngenetic strata-bound and stratiform main syngenetic strata-bound and stratiform mineralization associated with felsic volcanic centers. This association is mineralization associated with felsic volcanic centers. L This association is typical of of many many of ofthe theclassic classic deposits deposits in inthe the Canadian Canadian Superior Province. typical Superior Province. The felsic-hosted felsic-hosteddeposits depositsconsist consistof oftabular tabular to lenticular layers of massivi The to lenticular layers of massive L r to semi-massive semi-massivesulfide, sulfide,enveloped envelopedby by a disseminated sulfide halo with no to a disseminated sulfide halo with no I distinctly recognizable recognizablealteration alterationpipe. pipe. distinctly The mineralization is copper I (chalcopyrite) rich and associated with quartz-sericite + amphibole or 1I The mineralization is copper (chalcopyrite) rich and associated with quarcz-sericite ± amphibole or L I chlorite-carbonatealteration. alteration. chlorite-carbonate Host rock in this environment is commonly felsic crystal tuff (quartz- Host rock in this environment is commonly felsic crystal tuff (quartz- L sericite schist). schist). sericite Cherty tuff and metachert commonly occur interbedded with Cherty tuff and metachert commonly occur interbedded with Disseminated sulfide of the or stratigraphically stratigraphicallyabove abovethe thehost hosttuff. tuff. or Disseminated sulfide of the 1 footwall grade upward into massive sulfide, which is commonly in sharp contact footwall grade upward into massive sulfide, which is commonly in sharp contact L with the the hanging hangingwall wallrock. rock. Primary jointing may be present in these deposits with Primary jointing may be present in these deposits \ I \geology\sulfide bab . 59 �with zinc with zinc enrichment enrichment occurring occurring stratigraphically stratigraphically above above the the copper copper rich rich ore. ore. Precious metals Precious metals may may be be uniformly uniformly distributed distributed through through the the massive massive sulfides sulfides or or occur as occur as assay assay zones zones throughout throughout the the sulfide sulfidehalo. halo. DeMatties DeMatties (1988) (1988) reported reported that gold gold appears appears to to be be locally locally enriched enriched in in the the Ritchie Ritchie Creek Creek ore ore body body near near crosscutting faults crosscutting faults that that have have been been intruded intruded by by mafic-intermediate mafic-intermediate dikes. dikes. L The second second environment The environment described described by DeMatties DeMatties (1989) (1989) is is that that of of syngenetic strata-bound syngenetic strata-boundand and stratiform stratiform massive massive sulfides sulfides associated associated with with cherty cherty L magnetic The Thornapple magnetic iron iron formation formation within within the the main main volcanic volcanic arc arc sequence. sequence. The Thornapple deposit north north of The deposit deposit of Ladysmith Ladysmith is is an an example example of of this this type. type. The deposit consists consists 1 of lenses of lenses of of copper copper and and zinc zinc bearing bearing pyrite-pyrrhotite pyrite-pyrrhotite in in quartz-amphibole quartz-amphibole L The mineralized mineralized schist, which is is interpreted interpreted to to have have been been aa mafic mafic tuff. tuff. The schist, which lenses grade Thornapple lenses grade laterally laterally into into cherty cherty magnetic magnetic iron iron formation. formation. The Thornapple L deposit is not associated associated with a center but is located deposit a felsic felsic center located in in predominantly mafic rocks rocks of of the the volcanic volcanic arc arc sequence. sequence. Zoning Zoning is is also also evident evident within within the the Thornapple deposit, Thornapple deposit, with with sphalerite sphalerite enriched enriched in in the the upper upper ore ore lenses. lenses. Some Some stringer and stringer and disseminated disseminated sulfide sulfide occurs occurs stratigraphically stratigraphically below below the the main main chalcoyrite-bearing chalcoyrite-bearinglens. lens. L Limited information Limited information suggests suggests that that there there are are precious metals precious metals (0.029 (0.029oz/ton oz/ton Au) Au) in in this this deposit depositas as well. well. DeMatties' third DeMatties' third type type comprises comprises epigenetic epigenetic stringer stringer sulfide sulfide mineralization and mineralization and syngenetic syngenetic stata-bound stata-boundand and stratiform stratiform massive massive sulfide sulfide at at or or [ near near the the top top of of mafic mafic volcanic volcanic piles piles within within back back arc arc basin basin sequences. sequences. The The itivela zone zone on on the the Ritchie Ritchie Creek Creek prospect prospect occurs at the contact contact between between Kivela L massive mafic mafic to flows and and overlying overlying cherty cherty tuff tuff and and volcanogenic volcanogenic massive to izntermediate intermediate flows metasedimentary rock. sulfide halo halo is is developed developed in in the the flows flows and and is is metasedimentary rock. A sulfide associated associated with with intense intense quartz-sericite quartz-sericitealtertion. altertion. The halo grades grades into into an an alteration veinlets of of pyrite-pyrrhotite pyrite-pyrrhotite chalcopyrite chalcopyrite ±2 alteration pipe pipe of of stringers stringers and and veinlets quartz quartz in in brecciated brecciated and and altered altered country countryrock. rock. L The environments of mineralizaton DeMatties environments of mineralizaton described described by DeMattiesby (1989) provide (1989) provide The 60 \geology\sulfide .bab �F? the basis for the for aa geological geological model model to to guide guide exploration exploration in in the the western western part part of of the volcanic volcanic belt. the belt. AA similar similar stratigraphic stratigraphic model model has has yet yet to to be developed developed for for eastern part of known deposits the eastern of the the belt, belt, although although known deposits such such as as Crandon, Crandon, 1 1 I Pelican, Pelican, and and sulfides in barren sulfides in Marinette County occur in in similar host rock 1 [ I settings. settings. [ L The lithologic lithologic similarity, similarity, similar similar tectonic tectonic setting, setting, and and presence presence The of of mineralization throughout the the belt belt suggests suggests aa potential potential for for more more mineralization throughout 1 discoveries (Mudrey and and Kalliokoski, Kalliokoski, in in press; press; Mudrey, Mudrey, 1979; 1979; and and Mudrey Mudrey and and discoveries (Mudrey 1 others, 1991. others, 1991. ; I iI I I EXPLORATION AN!) EXPLORATION AND DEVELOPMENT DEVELOPMENT HISTORY HISTORY [ I Thehistory history of The of exploration exploration in the Penokean belt up up to to 1976 1976 is is1 Penokean volcanic volcanic belt suimnarized summarized in detail detailby byMudrey Mudrey and others others (1991). (1991). An was the the in An important important factor factor was existence of aa good existence good database database from from early early surveys surveys of ofthe theWisconsin Wisconsin Geological Geological L and Natural Hisory Survey Survey in which C.E. and in which C.E. Dutton recognized the the presence of Dutton recognized of "greenstone beltn 'greenstone assemblages and and hints of mineralization mineralization similar similar to that that of of 1 belt" assemblages hints of i massive sulfide sulfide bearing bearing Archean Archean terranes terranes of of Canada. Canada. Although exploration exploration of of1 [ the terrane began the in the the 1950s, 1950s. real real progress progress was made only only after after the began in I 1I successful application of of ground ground and and airborne airborne geophysics geophysics allowed allowed conductive conductive successful application L anomalies to anomalies to be identified identified beneath beneath the the thick thick glacial glacial overburden. overburden. The The result result1 has has been been aa series series of of significant significant discoveries, discoveries, from from the the announcement announcement of of the the L Flambeau deposit in in 1968 1968 and and Crandon Crandon in in 1976 1976 down down to to the the Lynne Lynne and and Bend Bend Flambeau deposit I I [ i projects of projects of the the 1990s. 1990s. I With the the permitting permitting of of the the Flambeau Flambeau deposit deposit in in early early 1991 1991 and and with with [ startup scheduled startup scheduled for for the the summer summer of of 1991, 1991, the the Penokean Penokean terrane terrane may may finally finally become become aa producing producing district. district. I 61 \geology\sulfide bab . ii �REFERENCES: REFERENCES: DeMatties, DeMatties, T.A., T.A., 1989 1989 aa proposed proposed geologic geologic framework framework for for massive massive sulfide sulfide deposits in the Wisconsin Penokean Volcanic Belt, Economic deposits in the Wisconsin Penokean Volcanic Belt, Economic Geology, Geology, Vol. Vol. 84, p. 946-952. 84, p. 946-952. Greenberg, Greenberg, J.K., J.K., and and Brown, Brown, B.A., B.A.,1983. 1983. Lower Lower Proterozoic Proterozoic volcanic volcanic rocks rocks and and their setting in the southern Lake Superior district. In Early In Early their setting in the southern Lake Superior district. Proterozoic Medaris, Edited by by L.G. L.G. Medaris, Proterozoic geology geology of of the the Great Great Lakes Lakes region. region. Edited Jr. Geological Society of America, Memoir 160, pp. 67-84. Jr. Geological Society of America, Memoir 160, pp. 67-84. Mudrey, Mudrey, M.G., M.G., 1979. 1979. The The massive massive sulfide sulfide occurrences occurrences in in Wisconsin: Wisconsin: Wisconsin Wisconsin Geol. Nat. History Misc. Paper 79-2, 2Op. Geol. Nat. History Misc. Paper 79-2, 20p. Mudrey, M.G., M.G., Jr., Jr.,Evans, Evans,T.J. T.J. Babcock, Babcock,R.C., R.C., Jr., Jr.,Cummings, Cummings,M.L., M.L., Jr. Jr. Mudrey, Eisenbrey, Eisenbrey, E.H., E.H., and and LaBerge, LaBerge, G.L., G.L., 1991, 1991,31. 31. Case Case history history of of metallic metallic mineral in V.F. V.F. Hollister, Hollister, ed., ed., mineral exploration exploration in in Wisconsin, Wisconsin,1955 1955 to to 1991, 1991,in I Case Case histories histories of of mineral mineral discoveries, discoveries,volume volume 3, 3, porphyry porphyry copper, copper, molybdenum, molybdenum, and and gold gold deposits, deposits,volcanogenic volcanogenic deposits deposits (massive (massive sulfides), sulfides), and and deposits deposits in in layered layeredrock: rock: Society Society of of Mining, Mining, Metallurgy Metallurgy and and Exploration, Exploration, Inc. Inc. (SMNE), (SMME) , 272 272p. p. Mudrey, J., in in press, press, "Metallogeny, "Metallogeny,Lake Lake Superior Superior Mudrey, M.G., M.G., Jr. Jr. and and Kalliokoski, Kalliokoski,J., Region," Precambrian of the U.S., Chap. 2, P.K. P.K, Sims, S h , ed., ed., Decade Decade of of Region," Precambrian of the U.S., Chap. 2, North North American American Geology, Geology, Geological Geological Society Society of of America, America, Boulder, Boulder, CO. CO. Sims, Sims, P.K. P.K., 1987, 1987, Metallogeny Metallogeny of of Archean Archean and and Proterozoic Proterozoic terranes terranes in in the the Great Great Lakes Lakes region: region: U.S. U.S. Geol. Geol. Survey Survey Bull. Bull. 1694, 1694,p. p. 55-74. 55-74. , Schmus,W.R.., W.R., Schulz. and Peterman, Peteman, Z.E., Z.E., 1989, 1989, TectonoTectonoSims, P.K., P.K.,Van Van Schmus, Sims, Schulz, K.J., K.J., and stratigraphic stratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean PenokeanOrogen. Orogen. Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, Vol. V O ~ 26, .26,p. p. 2145-2158. 2145-2158. 62 \geology\sulfide .bab � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1991 Description An account of the resource Institute on Lake Superior Geology. Eau Claire, Wisconsin. May 1-4, 1991. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1991 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/6f4ce8e493668b59ee17a019748a7712.pdf 2891383c5858fd84a92605ce6ea24145 PDF Text Text INSTITUTE UTE ON ON •L A KE SUPERIOR S UPERIOR GEOLOGY G EOLOGY PROCEEDINGS PROCEEDINGS MEETING 338TH8 ANNUAL ANNUAL ~ ~ MEETING MAY 1992 MAY6-9, 6-9,1992 HELD AT AT HURLEY, WISCONSIN HURLEY, WISCONSIN VOLUME 38 PART MAY PROGRAM & ABSTRACTS �ORGANIZING COMMITTEE 38TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY General General Chairman: Chairman: Albert Albert B. B. Dickas, Dickas, University University of of Wisconsin-Superior Wisconsin-Superior Program Program Chairman Chairman and and Proceedings ProceedingsEditor: Editor: Bruce Bruce A. A. Brown, Brown, Wisconsin Wisconsin Geological Geologicaland and Natural Natural History History Survey Survey Volume 38 consists consists of Part Program and and Abstracts Abstracts Part 1: 1:Program Part 2: Field Trip Guidebook Guidebook Published Published and distributed distributed by Institute Institute on on Lake Lake Superior SuperiorGeology Geology M.G. Mudrey, Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland andNatural Natural History HistorySurvey Survey 3817 38 17 Mineral Point Road Road Madison, Madison, Wisconsin Wisconsin 53705-5100 53705-5100 ISSN ISSN 1042-9964 1042-9964 �INSTITUTE ON INSTITUTE - L A K E m SUPERIOR S UPERIOR GEOLOGY G EOLOGY uLAK ER I PROCEEDINGS 38m ANNUAL MEETING MAY 6-9, 1992 HURLEY, WIscoNsIN ORGANIZED BY ALBERT B. DIcKAs, UMvERsnY Oi WISCONSIN-SUPERIOR BRUCE A. BROWN, WISCONSIN GEoi.ooIcAL AND NATURAL HISTORY SURVEY VOLUME 38 MAY 1992 PART 1 PROGRAM & ABSTRACTS �CONTENTS Institutes Instituteson onLake LakeSuperior SuperiorGeology Geologytoto1991 1991 i1 Constitution Constitutionof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology iiii By-Laws By-Lawsof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology iii iii GoldichMedal MedalGuidelines Guidelines Goldich iv v StudentTravel TravelAward Award Student V Boardof ofDirectors Directors Board Vi vi LocalCommittee Committee Local vi vi Student StudentPaper PaperAward AwardCommittee Committee vi vi GoldichMedal MedalCommittee Committee Goldich V1 GoldichMedal MedalRecipient Recipient Goldich VU vii BanquetSpeaker Speaker Banquet Viii Vlll Reportof of the theChair Chairof ofthe the37th 37thAnnual AnnualInstitute Institute Report ix ix Calendarof of Events Events and andProgram Program Calendar xi xi Abstracts Abstracts 1 vi ... 1 �INSTITUTES ON LAKE SUPERIOR GEOLOGY Institute Number Institute Date 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Place Place Minneapolis, MN Minneapolis, Houghton, MI East Lansing, MI Duluth, MN Minneapolis, MN Madison, WI Port Arthur, Ont. (Thunder (Thunder Bay) Houghton, MI Duluth, MN Ishpeming, MI Ishperning, St. Paul, MN MN Sault Ste. Marie, MI East Lansing, MI Superior, WI Oshkosh,WI Oshkosh, WI Thunder Bay, Bay, Ont. Ont. Duluth, MN Duluth, MN Houghton,MI Houghton, MI Madison, WI Sault Ste. Marie, Ont. Ont. Marquette, MI St. Paul, MN Thunder Bay, Ont. Milwaukee, WI Duluth, MN Eau Claire, WI East Lansing, MI International Falls, MN Houghton,MI MI Houghton, Wausau,WI Wausau, WI Kenora, Ont. Wisconsin Rapids, WI Wawa, Ont. Ont. Marquette, MI Duluth, MN ThunderBay,Ont. Thunder Bay, Ont. Eau Claire, WI WI Hurley,WI Hurley, WI �____________ CONSTITUFION OF INSTITUTE INSTI1VIt ON CONSTITUTION OF ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Articlc Art icic I I Name EaEX ArticlcIII1 Article Qbiedivc~ Objectives Theobjectives objediw of ofthis thisorganization organizationare: are: The Thename n a eofofthe theorganization organhationshall shallbe bcthe the"Institute -Instituteon onLake LakeSuperior SuperiorGeology". Gdogf. The A. provide a means whereby A.ToTo provide a means wherebygeologists gdogistsininthe theGreat GreatLakes Lakesregion regionmay mayexchange exchangeideas ideasand and scientific scientificdata. data. B. promote understanding B. ToTo promotebetter bctter understandingofofthe thegeology geologyofofthc thcLake LakeSuperior Superiorregion. region. C. plan conduct C. ToTo planand and condudgeological geologicalfield fieldtrips. trips. ArticleIII I11 Artide Status Sl.iu No Nopart partofofthe theincome incomeof of the the organization organization shall shall inure inure to to the thebenefit benefit of of any any member member or orindividual. individual. In Inthe theevent eventofofdissolution dissolution the the assets assets of of the the organization organization shall shall be be distributed distributed to to (sometax taxfree freeorganization). organization). (some (To (To avoid avoidFederal Fcdcraland andState Stateincome incomctaxes, taxes,the thcorganization organintionshould shouldbebenot notonly only'scientific" 'scientificor or'cducational, "cducationaY,but butalso also"non.profit".) %on-profito.) Minn.Stat. Stat.Anno. Anno.290.01, 290.01, subd. SUM.44 Minn. Minn. Minn.Stat. Stat.Anno. Anno.290.05(9) 290.05(9) 1954 Revenue 1954 Internal ln~crnd RcwnucCode C d cs.s.501(c)(3) 501(c)(3) IV ArticleIV Artidc members hi^ Membership The Themembership membership of of the theorganization organization shall consist of the board board of of directors. directors. Any Anygeologist geologist interested interested shall shall be be permitted pcrmittcd to to attend attend and andparticipate participateininand andvote voteatatthe thcannual annualmeetings. meeting<. ArliclcVV Article Mcetinsq Meetings The Theorganization organizationshall shall meet meet once once a year, preferably prekrably during the month month of April. The Thcplace placeand and exact e n c t date dateof ofeach cachmeeting meetingwill will be desginatcd desginatcd by the thc board board of of directors. directors. Ar~iclcVI VI Article Directors Directors The Theboard boardofofdirectors directorsshall shallconsist consist of the the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and and the the last last three thrcc past pastChairman; Chairman;but butififthe theboard boardshould shouldatatany anytime timeconsist consistof offewer fewerthan thanfive fivepersons, persons, by by rcaon rcaon of of the above persons asdirectors, directors,the thevacancies vacancieson on of unwillingness unwillingnessor or inability inability of any of persons to toserve serveas the so as theboard boardmay maybe befilled filled by by the annual a ~ u ameeting l as to to bring bring the the membership membership of of the the board board up up tofive fivemembers. members. to Arlicle VII 0fficcrs Officcrs Theofficers officersof of this thisorganization organization shall be aa Chairman Chairmanand andSecretary-Treasurer. Secretary-Treasurer. The A. The T%e Chairmanshall shallbebeelected electedeach cachyear yearby bythe theboard boardofofdirectors, dircctors,who whoshall shallgive givedue due A. Chairman considerationto tothe thewishes wishes of of any group that that may may be bepromoting promotingthe thenext nextannual annualmeeting. mecting. consideration asChairman Chairmanwill will terminate terminateatatthe theclose doseofofthe theannual annualmeeting meetingover overwhich which Histerm termofofoffice ofice as His he shall have have been been appointed. appointed. He his successor successor shall Hewill will then then serve serve for for aa he presides presides or or when when his as aa member member of of the the board board of of directors. directors. period of of three three years years as period B. B. The TheSecretary-Treasurer Secretary-Treasurershall shall be be elected elected at at the theannual annualmeeting. meeting. His Histerm termofofoffice oficcshall shall be two two years years or oruntil until his his successor successor shall have have been appointed. appointed. be Article VIII WII Article -Amendmen& Amendments Thisconstitution constitution may may be amended amended by aa majority majority vote vote of ofthose thosepersons personswho whoare arepersonally personally This present at, at,participating participatingin, in, and and voting voting at at any any annual annualmeeting metingof ofthe theorganization. organization. present �BY-LAWS 'BY-JAWS I. Duties of of the the Officers Officers and and Directors Directors Duties A It It shall shall be be the the duty duty of of the the Annual Annual Chairman Chairmanto: to: A. 1. 1. 2. 2. 3. 3. B. B. Preside at the the annual annual meeting. meeting. Appoint committees needed for the organization organization of the annual meeting. Appoint all all committees meeting. Assume for the organization Assume complete responsibility for organization and financing financing of of the the annual meeting meeting over over which which he presides. presides. It shall shall be be the the duty duty of of the theSecretary-Treasurer Secretary-Treasurerto: to: 1.. 1.. 2. 2. 3. 3. Keep Keep accurate accurate attendance attendance records records of of all allannual annualmeetings. meetings. Keep Keep accurate records records of all all meetings meetings of, of, and and correspondence correspondence between, between, the the board board of of directors. directors. Hold all funds funds that may may accrue as as profits profits from from annual annual meetings meetings or or field field trips and to make these funds available for the organization and operation operation of future future meetings meetings as as required. required. C. ItIt shall shall be the the duty of the board of directors to plan plan locations locations of annual meetings meetings C. and to to advise advise on on the theorganization organizationand andfinancing financingof ofall allmeetings. meetings. II. 11. Duties and and Expenses Expenses 1. 1. 2. 2. III. 111. There There shall shall be be no noregular regularmembership membershipdues. dues. Registration Registration fees for the annual meetings shall be determined by by the Chairman in consultation with the board of directors. It is strongly recommended consultation board of directors. is strongly recommended that that these be kept kept at at aaminimum minimum'to to encourage encourage attendance attendanceof of graduate graduatestudents. students. Order Rules of Order in all all The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shallgovern govern this this organization organization in The to which which they they are are applicable. applicable. cases to IV. IV. Amendmenu Amendments These by-laws bylaws may majority vote of those those persons persons who who are are may be be amended amended by by aa majority vote of personally present meeting of personally present at, at, participating participatingin, in,and and voting voting at at any any annual annual meeting of the organization;provided provided that that such such modifications modifications shall shall not not conflict conflict with the the constitution constitution organization; as presently presently adopted adopted or orsubsequently subsequentlyamended. amended. as iii III �Award Guidelines Guidelines SAM SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamlde as documented documented by by The Institute Institute on on Lake LakeSuperior SuperiorGeology Geology was was born born on on or oraround around1955, 1955, as The the fact fact that that the the27th 27th annual amual meeting meeting will be be held in in 1981. 1981. The The Institutes Institutes are are exemplary exemplary the in of dealing with with those aspects of in their their continuing continuing objectives objectives of of geology geology that are are related related geographically to Lake Lake Superior; Superior; of of encouraging encoumging the the discussion discussionof of subjects subjectsand andsponsoring sponsori~~g field will bring bring together togethergeologists geologists from from academia, academia,government governmentsurveys, surveys, and and field trips trips which which will industry; and of maintaining an exceedingly informal but highly effective mode of operation. industry; and of maintaining an operation. During During the the course course of of its its existence existence the membership membe'nhip of the Institute Institute (that (thatis, is,those thosegeologists geologists who who indicate indicate an an interest interest in in the the objectives objectives of the LLS.G. 1.LS.G. by by attending) attending) has has become become aware aware of the the fact factthat thatcertain certainofoftheir theircolleagues colleagueshave havemade madeparticularly particularlynoteworthy noteworthy and and meritorious contributions to the improvement of understanding of "Lake Superior" geology meritorious contributions to the improvement of understanding of Xake Superior" geology and and its itsmineral mineraldeposits. deposits. The exemplary award was was made made by by 1.LS.G. I.LS.G. to to Sam exemplary award Sam Goldich Goldich in in 1979 1979 for for his his many many contributions to 50 years. years. to the the geology geology of the region region extending over about about 50 Guidelines Award Guidelines 1) by the 1.LS.G. ILS.G. Board 1) The Themedal medalshall shallbe beawarded awarded annually annually by BoardofofDirectors Directorstotoaageologist geologist whose name is associated with with aa substantial substantialsustained sustained interest interest in, or a major contribution to, the the geology geology of of the the Lake Like Superior Superiorregion. region. 2) The TheBoard BoardofofDirectors, Directors,I.LS.G. 1.LS.G. shall shall appoint appoint the the Nominating Nominating Committee. The The initial initial appointment appointment will will be of three members, members, one to serve seme for for three threeyears, years, one onefor fortwo, two, and and one After the the one for for one one year, year, the the member member with with the briefest incumbency to be chairman. After first year the Board of Directors shall appoint at each spring meeting one new member spring seme for for three three years. years. In the the thrid thrid year year this this member member shall shall be be the thechairman. chairman. who will serve The Committee Committeemembership membership should reflect the main main fields fields of of interest interestand and geographic geographic of I.LS.G. 1.LS.G. membership. membership. distribution of 3) By By November November 1,1, the Goldich Goldich Medal Medal Nominating Nominating Committee Committee shall shall make make its its recommendation to the the Chairman Chairman of of the the Board Board of of Directors Directorswho whowill will then then inform inform the the of the the nominee. nominee. Board of TheBoard BoardofofDirectors Directorsnormally normallywill will accept accept the the nominee nomineeof ofthe theCommittee, Committee,will will inform inform 4) The the medalist and will medalist immediately, immediately, and will have have one one medal medalengraved engraved appropriately appropriately for for presentation at at the the next next meeting meeting of the the Institute. Institute. 5) It is recommended recommended that the Institute Institute set set aside asideannually annuallyfrom fromwhatever whatever sources, sources, such such 5) as will will be required required to to support support the thecontinuing continuingcosts costs of ofthis thisaward. award. funds as April 4, 1981 1981 April 4, J. J. Kalliokoski, Kdliokoski, Chairman Chairman Bill Cannon Cannon Fred Kehlenbeck Kehlenbeck Glenn Morey Morey Greg Mursky Mursb iv �STUDENT TRAVEL TRAVEL AWARD -STUDENT AWARD the 1.LS.G. LLS.G. Stildcnt Student Travel Award ' l'hc 1 % ~l98ô 1080 Board of [)irectors Directors established established thc Aw:triI to t o s111~1~ot.t participation at fi11~1 sstudent t t ~ d ~participation t~t at the the annual Institutes. The Theawards awards will willbe bemade made from froniaaspecial spcci;d fund purpose. This set up u p for this purpose. This award award is intended to help help defray defray some of the direct direct travel travel costs to the Institute Institute and and includes includes aa waiver waiver of registration registration fees, fees*but but excludes excludes expenses for lodging,and and field fieldtrip tripregistration. registration. The The number number of of awards and value are are determined meals, lodging, by with the the Secretary-Treasurer Secretary-Treasurer and will will be be announced announced by the annual Chairman in consultation with at the annual annual banquet. banquet. The following following general general criteria criteria will will be be considered by the annual considered by amual Chairman, Chairman, who who isis responsible for the the selection: selection: 1) The resident (undergraduate (undergraduate or graduate) student Theapplicants applicantsmust must have active resident status at the the time time of of the the Institute, Institute, certified certified by by the the department department head. head. 2) Students Studentswho who are are the the senior senior author on either an oral oral or or poster poster paper paper will will be given favored consideration. consideration. 3) ItItisisdesirable desirablefor fortwo two or ormore more students studentsto tojointly jointly request request travel travel assistance. assistance. Ingeneral, general, priority priority will will be given given to those in in the the Institute Institute region region who who arc arc 4) In farthest farthest'away. away. 5) Each Eachtravel travelaward awardrequest request shall shall be be made made in in writing, writing*to the annual annual Chairman, Chairman, explanation of need, possible author status status or or other othersignificant significantdetails. details. with an explanation registration for the the Meeting. Meeting. Successful applicants applicants will willreceive receivetheir theirawards awardsatat the the time of registration V �BOARD OF DIRECTORS 1992 AlbertB.B.Dickas Dickas Albert University UniversityofofWisconsin-Superior, Wisconsin-Superior,Superior, Superior,Wisconsin Wisconsin54880 54880 1991 P.E.Myers Myers P.E. Department DepartmentofofGeology, Geology,University UniversityofofWisconsin, Wisconsin,Eau EauClaire, Claire,Wisconsin Wisconsin 54701 54701 M.M.Kehlenbeck Kehlenbeck 1990 M.M. Department DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,Ontario OntarioP7B P7B5E1 5El 1989 R.W.Ojakangas Ojakangas R.W. Department DepartmentofofGeology, Geology,University UniversityofofMinnesota, Minnesota,Duluth, Duluth,Minnesota Minnesota55812 55812 Secretary-Treasurer Secretary-Treasurer M.G.Mudrey, Muclrey,Jr.Jr. M.G. WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey Wisconsin 3817 Mineral Point Road, Madison, Wisconsin 53705 3817 Mineral Point Road, Madison, Wisconsin 53705 LOCAL COMMITTEE LOCAL COMM ~E A.B.Dickas Dickas A.B. General GeneralChairman, Chairman,University UniversityofofWisconsin-Superior, Wisconsin-Superior,Superior, Superior,Wisconsin Wisconsin 54880 54880 B.A. Brown Brown B.A. Proceedings ProceedingsEditor, Editor,Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey 3817Mineral MineralPoint PointRoad, Road,Madison, Madison,Wisconsin Wisconsin53705 53705 3817 STUDENT PAPER AWARD COMMITTEE 1992E STUDENT PAPER AWARD C O ~1992 PenelopeMorton Morton Penelope Chairman, Chairman,Department Departmentof ofGeology, Geology,University UniversityofofMinnesota, Minnesota,Duluth, Duluth,MinneMinnesota 55812 sota 55812 GOLDICH MEDAL COMMITTEE 1991-92 GOLDICH MEDAL C O ~1991-92 E F.W. Cambray Cambray(1992) (1992) F.W. Department Departmentof of Geological GeologicalSciences, Sciences,Michigan Michigan State StateUniversity, University, East East Lansing, Lansing, Michigan Michigan H.H.Halls Halls(1993) (1993) H.H. Department Departmentof of Geology, Geology,Erindall ErindallCollege, College,Mississauga, Mississauga, Ontario OntarioL5L L5L1CO 1CO R.D. Sage Sage(1994) (1994) R.D. Ontario OntarioGeological GeologicalSurvey, Survey,777 777Grenville GrenvilleStreet, Street,Toronto, Toronto,Ontario, Ontario,M7A M7A 1W4 lW4 vi �CiTATION CITATION Cannon, Goldich Goldich Medal Medal recipient, recipient, 1992 1992 W. F. Cannon, W. F. (Bill) Cannon richly richly deserves deserves this this highest highest honor honor of of the the Institute on Lake W. Lake Superior SuperiorGeology Geology because of his many outstanding outstanding contributions to geology and and mineral mineral deposits deposits of of the the Lake Superior Superior region. region. Bill received B.S. B.S. and and Ph.D. degrees from Syracuse Syracuse University and in between between sandwiched sandwiched in in an an M.S. degree degree from from Miami MiamiUniversity. University. He He was wasborn, born,raised, raised,and andstill stillremains remainsan aneasterner easterner at at heart, M.S. flat country of of the the Lake Superior and hence is ideally suited to work in the mostly flat Superior region. Bill joined joined the the U.S. U.S. Geological Geological Survey Surveyinin 1967. 1967. During During his his early early career with the USGS USGS he he was was Bill mainly a geologic mapper, mapper, who who slogged sloggedthrough through the the murky murky swamps swamps of of the the Upper Peninsula Peninsula in in his his L. L. Bean L. Bean rubber-soled rubber-soled shoes, and turned out out an anincredible incredible number number of ofhigh highquality qualitygeologic geologic These maps maps will will remain remain as as a legacy to his innate ability legacy to ability as aa mapper. mapper. In quadrangle maps. maps. These quadrangle addition, he was involved at various various times times with withiron iron and and manganese manganese resource resource studies studies on on a large involved at scale, and he continues today as an expert on worldwide manganese resources. From 1977 continues as an expert on From 1977toto1981, 1981, he coordinated lWOquadrangle, quadrangle, coordinated aa successful successful mineral mineral resource assessment assessment of the the Iron IronRiver River1°x2° Michigan-Wisconsin. Michigan-Wisconsin. days in in the field when he he was was named named Chief Chief of of the Branch of field terminated terminated in 1981, 1981, when These glory glory days of the USGS, Eastern Mineral Mineral Resources Resources and and then then (1984-88) (1984-88) Associate Chief Geologist of USGS, both of of which credit, while while Branch Branch Chief he hired hired several severaltop-flight, top-flight, younger younger which he served served ably. ably. To his credit, geologists, including our colleague colleague Klaus Klaus Schulz. Schulz. Chief Geologist, Geologist, he he conceived conceived and and master master minded a joint U.S.-Canadian While Associate Chief U.S.-Canadian deep deep with Alan Alan Green Green of the Geological of Canada as crustal study (GLIMPCE), in conjunction with Geological Survey of well as personnel personnel from numerous state and universities. universities. This state and and provincial surveys and This project focused focused and potential potential field investigations of of the the deep deep structure of the Midcontinent on seismic and MidcontinentRift Rift System, System, and it has Perhaps this project and has produced produced more more than than 50 50 papers papers and and abstracts. abstracts. Perhaps project with with its many many ramifications is the single most productive scientific scientificachievement achievementcarried carried out out in in the the Lake Superior Superior region in the post-World War II period. ItIt truly truly brought brought Keweenawan studies in the Lake Superior Superior region Bill is author or coauthor coauthor of of more more region out of the doldrums and into the forefront of science. science. Bill than 100 100 reports and and maps, maps, several severalof of which which concern the rift rift system. system. Conversations with him, Bill is a modest, generally quiet quiet guy guy who whonever neverpats patshimself himselfon onthe theback. back. Conversations about geology geology (or (or geophysics) geophysics) or sports sports at at Syracuse, Syracuse, however, however, are are always always lively, and he's whether about a stimulating guy He isisunique uniqueamong amongmy my guy to to be be with with in in the the field field or, or, after after work, work,in in the the local local bar. bar. He he drinks drinks aa manhattan manhattan before beforedinner, dinner,ififyou you know know what what that thatis. is. close acquaintances in that he know what Bill's middle initial (F.) stands for, but to many of his close associates it stands I don't know for aa fine, fine, fine finefellow. fellow. P. K. Sims Sims v" �BANQUET SPEAKER Duff Kerr, Kerr and Associates, Denver, Colorado, Colorado, will be the speaker speaker at at the Annual Annual ILSG ILSG Banquet. He will speak on: Industrial petroleum exploration of the Midcontinent Rift Frontier. tier. VIII �37TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY EAU CLAIRE, WISCONSIN, 1991 Meeting of the Institute on Lake Superior 1991 The 37th Annual Meeting Superior Geology met from from May May 1-4, 1-4,1991 in Eau Claire, Wisconsin-Eau Claire, Wisconsin. Wisconsin. The host for this meeting was the University of Wisconsin-Eau Claire. Paul Paul E. Myers Myers was the General Chairman. Lung Lung S. S. Chan Chan coordinated coordinated publications and field trips. The in two two parts: parts: Part I contains the The Proceedings Proceedings of this conference were published in abstracts, and Part II II contains conference field trips. contains field guides for the three conference Technical Center Inn, Inn, Eau Eau Claire. Claire. A A total total Technical sessions sessions and banquet were held in the Civic Center of 154 154 geologists geologists from from the Lake Lake Superior Superior region region registered, registered, and and 92 92 people people attended attended the the annual annual banquet. The technical sessions included 31 oral papers and 23 poster papers. A symposium The technical sessions included papers and 23 poster papers. symposium on the mineral resources comprised eight resources potential of northern Wisconsin comprised eight papers by geologists geologists from from the mining mining industry industry and and Wisconsin Wisconsin Geological Geological and and Natural History History Survey. Survey. (#1), led led by by Paul Paul K. K. Sims Sims and and John John S. S. Klasner, Kiasner, studied studied "The "The A pre-conference field trip (#I), Mountain shear zone-a zone—a post-Penokean discrete ductile ductile deformation deformation zone." zone." The The guidebook guidebookfor for this field trip was authored authored by P.K. Sims, Sirns, J.S. Kiasner, Klasner, W.C. Day, Day, and and Z.E. Z.E. Peterman. Peterman. A second second pre-conference pre-conferencefield field trip (#2) concentrated concentrated on the "Features "Features and and significance significance of the Precambrian-Cambrian contact in western western Wisconsin." Wisconsin." The trip, including stops The trip, including stops near near Wisconsin,was wasled ledby byLung Lung S. S. Chan Chan and and RichRichEau Claire, Black River River Falls, and Nefflsvffle, Neillsville, Wisconsin, ard L. Hay, with additional additional field field guide guide materials materials by Paul E. Myers. A post-conference post-conference field trip, entitled "Proterozoic volcanogenic massive massive sulfide sulfide deposits deposits of Northwestern Wisconsin," involved involved mainly mainly the the inspection inspection of cores cores from from the the Flambeau, Flambeau, Lynne, and Bend deposits Hawkins, deposits at Ladysmith and H a w h s , Wisconsin. Co-leaders Co-leaders for for this this trip trip were were M.G. Mudrey, Jr., and B.A. Brown, both of the Wisconsin Geological and Natural History History Survey. Survey. three field field trips. trips. Vans for the pre-conference pre-conference field A total of 87 people attended these three Squire, Tony Tony Jones, Jones, Zach Zach Kostalek, Kostalek, driven by undergraduate undergraduate geology geology students students Mike Mike Squire, trips were driven and Michelle Barnes from the University of Wisconsin-Eau Claire. Annual Banquet Banquet on May 2 was attended attended by 92 people. Val Val W. W. Chandler, Chandler,MinneMinneThe Annual sota Geological Survey, presented the 1991 1991 Goldich Medal to William Purdue UniverUniverWilliam J. Hinze, Purdue sity, for for his his many contributions as an educator and in geophysical geophysical studies of the Great Lakes region. The TheGoldich GoldichAward Award Committee Committee included included M.G. Mudrey, Jr., H.H. H.H. Halls, and F.W. F.W. Carnbray. The TheAnnual Annual Banquet Banquetspeaker speakerwas Paul K. Sims. His His topic topic was, was, "Archean "Archean and and Early Early Cambray. Proterozoic Geology of the Lake Superior Region-an Region—an Overview." Overview." Students travel travel awards awards totalling totalling $1080 $1080 were were presented presented to to five five students students giving giving papers: papers: Students Sidney Hemming, Matt Manson, James James Johnson, Johnson,Denise DeniseSlavish, Stavish,and andMary MaryTozer. Tozer. Three Three $150 David J. Allen, Alien, John John Mariano, Mariano, and and awards for best oral and poster papers went to to 3 students: David Michael D. Thompson. John Klasner, Klasner, John Gardener, Gardener, and William Cannon served on Thompson. John on the Best Best Student Paper Award Award Committee. Committee. The I.L.S.G. The meeting meeting was atI.L.S.G. Board of Directors met met in in Eau Eau Claire Claire on on May May 2. 2. The tended by M.G. Mudrey, Jr., M.M. Kehienbeck, Kehlenbeck, P.E. Myers, L.S. L.S. Chan, J. Klasner, Kiasner, R.W. Ojakangas, and A.B. Dickas. Ojakangas, The following items were were discussed: following items 1992meeting meeting will will be at Hurley, Wisconsin, on May 6-9. Co-hosts Co-hosts Thesite sitefor forthe the 1992 (1) The A.B. Dickas of University of of Wisconsin-Superior Wisconsin-Superior and B.A. for this conference are A.B. Brown of Wisconsin Geologicaland and Natural Natural History History Survey. Survey. Wisconsin Geological ix �(2) Treasurer's Report: (2) Wisconsin with with Bruce Brown Brown having a full Michigan account was transferred to Wisconsin power of attorney with M.G. Mudrey, Jr. Jr. $1000 $1000was was placed placed in ready ready checking checking account account and remainder (about $4000) was placed in a CD (Mt. Horeb). The Goldich account account was placed in a three-year CD, the rest in 6-month CDs total about $6800. Mudrey has old field trip guidebooks; proceedings are still at Houghton Tech. old Goldich Goldich medals. medals. Their present value is approximately Glen Morey still has old approximately $200. In In1988 1988there therewere were12 12medals, medals, then then valued valued at at $115 $1 15== $1380. (3) Procedures for limited limited student student travel assistance assistanceawards: awards: A motion was made (M.K.) (M.K.) to develop develop a form form for itemizing itemizing anticipated anticipated costs costs for for travel and lodging with total awards not exceeding $1000 (shared equally by Canadian U.S. treasuries) treasuries) and individual awards of no more than $200. This motion and U.S. motion was not not voted on. Another motion was made (J.K.) (J.K.) to provide assistance assistance to faculty in bringing students to institutes to a maximum maximum of of $50. $50. The motion The motion was amended amended to recommend recommend that that partial or total remission of fees may, at the discretion of the local committee, be used as an incentive for attracting students. The The motion passed. Lung Chan Chan and and I wish to thank those who generously donated donated time and and talents to to make make the 1991 1991 meeting a success. success. Respectfully submitted, submitted, P.E. Myers General Chairman, I.L.S.G., I.L.S.G., 1991 1991 x �CALENDAR OF EVENTS AND PROGRAM Wednesday,May May66 Wednesday, Field Trip Trip11 Early EarlyProterozoic Proterozoicand andArchean Archeanrock rockofofthe theGogebic GogebicRange. Range. Field Leaders: G.L. LaBerge, R.W. Ojakangas, and K. Licht Leaders: G.L. LaBerge, R.W. Ojakangas, and K. Licht Registrationand anddeparture, departure,Holiday HolidayInn Innlobby lobby am Registration 8:00 am 8:00 6:30 pm Return 6:30pm Return Field Trip Trip22 Evolution Evolutionof of the theKeweenawan Keweenawansedimentary sedimentarysequence. sequence. Field Leaders: M.G. Mudrey, Jr., and A.B. Dickas Leaders: M.G. Mudrey, Jr., and A.B. Dickas Registrationand anddeparture, departure,Holiday HolidayInn Innlobby lobby am Registration 8:00 am 8:00 6:30 pm Return 6:30pm Return 4:00-8:00 pm and check-in, check-in, Holiday HolidayInn Innlobby lobby 4:00—8:00 pm Registration Registration and 7:00-11:00 pm (cash bar)/Poster bar)/Poster session, session,Holiday Holiday Inn Inn Conference ConferenceRoom Room 7:00—11:00 pmIcebreaker Icebreaker (cash Thursday,May May77 Thursday, All technical technical sessions sessionsand andposter poster sessions sessionsare areininthe theConference ConferenceRoom Roomatatthe theHurley, Hurley,WisconWisconAll sin,Holiday HolidayInn. Inn. Contributors Contributorsshould shouldhave haveposters postersupupby bynoon, noon,Thursday, Thursday,May May7.7. sin, 7: 15am am 7:15 Registration,Holiday HolidayInn Inn lobby lobby Registration, ArcheanSession: Session:Frank FrankLuther, Luther,session session chair (8:30-9:50 am) am) Archean chair (8:30—9:50 TheodoreJ.J.Bornhorst, Bomhorst,Richard RichardT. T.Wilkin, Wilkin,and andRodney RodneyC. C.Johnson Johnson 8:30 am Theodore Temporalprogression progressionofofArchean Archeangranitoid granitoidrocks, rocks, Temporal Ishpeming greenstone belt and vicinity, Michigan Jshpeming greenstone belt and vicinity, Michigan 8:50 am A.C. Turnock Turnockand andD.C. D.C.Kamineni Karnineni A.C. Thermaland andregional regionalmetamorphism metamorphismin inArchean Archean basalt, basalt, Thermal Bird River Greenstone Belt, Manitoba, Canada Bird River Greenstone Belt, Manitoba, Canada 9:10 am BarbaraE. E.Seemayer Seemayerand andManfred ManfredM. M.Kehlenbeck Kehlenbeck Barbara Variations in metamorphic grade of metapelites along transects transects Variations in metamorphic grade of metapelites along acrossthe theQuetico QueticoSubprovince Subprovince across 9:30 am TerrenceJ.J. Boerboom Boerboomand andMark MarkA. A. Jirsa Jirsa Terrence Geology and andtectonic tectonicsetting setting of of the the Archean GiantsRange Range Batholirh; Batholith; Geology Archean Giants Western Wawa Subprovince, Minnesota Western Wawa Subprovince, Minnesota 9:50 am Coffee break break Coffee xi �Geophysics chair (10:10—11:50 GeophysicsSession: Session:C.C.Patrick PatrickErvin, Ervin,session session chair (10:10-11:50 am) am) 10:10 10: 10 am Daniel DanielJ.J.Brehm, Brehm,C.C.Patrick PatrickErvin, Ervin,and andJeffrey JeffreyK. K. Greenberg Greenberg Gravity Gravitymodel modelofofthe theWolf WolfRiver River Batholith Batholith 10:30 10:30 am Lung LungS.S.Chan, Chan,Zachary ZacharyKostalek, Kostalek,and andRichard RichardL. L. Hay Hay Isotope Isotope and andpaleomagnetic paleomagnetic dating datingof of weathered weatheredgranite granitebelow belowthe the Precambrian-Cambrian Precambrian-Cambriancontact contactininNeillsville, Neillsville,Wisconsin Wisconsin 10:50 10:50 am Stephen StephenA. A.Kissin, Kissin,Graham GrahamJ.J.Borradaile, Borradaile,Joe Joe D. D. Stewart, Stewart,William William A. A.Ross, Ross, andThomasz ThomaszWerner Werner and Magnetic Magnetic and and petrographic petrographic detection detectionof of heat heattreatment treatmentinin Gunflint Chert Gunflint Chert 11:10 am Timothy TimothyB.B.Hoist Hoistand andHaakon HaakonFossen Fossen 11:10 On Onthe theuse useof of paleocurrent paleocurrent indicators indicatorsinindeformed deformedrock rock 11:30 11:30 am am Michelle MichelleL.L.Barnes, Barnes,Georgia GeorgiaL. L.Osborn, Osborn,and andLung LungS. S.Chan Chan An An integrated integratedgravity gravityand andmagnetic magneticsurvey surveyofofthe theRock Rock Elm Elm structure, structure, westernWisconsin Wisconsin western 1l:5O am Lunchbreak break 11:50 am Lunch Institute Instituteon on Lake Lake Superior SuperiorGeology GeologyBoard Boardof of Directors DirectorsLuncheon Luncheon(by (by invitation) invitation) Posterson ondisplay display Posters Proterozoic W.W.Ojakangas, session chair ProterozoicSession SessionI:I:Richard Richard Ojakangas, session chair(2:00—3:20 (2:00-3:20 pm) pm) 2:OO pm pm Gene Gene L. L. LaBerge LaBerge 2:00 The The Early Early Proterozoic ProterozoicEmperor Emperorvolcanic volcaniccomplex: complex:Implications Implicationsfor for the the geology geology of the eastern eastern Gogebic Gogebic District, northern northernMichigan Michigan KathyLicht Lichtand andT.P. T.P. Flood Flood 2:20 pm pm Kathy 2:20 The from the The chemistry chemistry and and petrography petrography of ofmafic maficrocks rocks/rom the Early EarlyProterozoic ProterozoicEmperor Emperorvolcanic volcaniccomplex complexnear nearMarinesco, Marinesco,Michigan Michigan xii xii 2:40 pm pm 2:40 S.R. S.R. Hemming, Hemming, S.M. S.M. McLennan, McLennan,and andG.N. G.N. Hanson Hanson Provenance Provenanceofofthe theAnimikie Animikie Group, Group,NE NE Minnesota, Minnesota, basedon onNd Nd and and Pb Pbisotopes isotopes based 3:OO pm pm 3:00 Mark Mark E. E. Davidson Davidsonand andJohn JohnC. C. Palmquist Palmquist Implications Implicationsof of strain strainand andmagnetic magneticanisotrophy anisotrophystudies studiesfor for the the Penokean PenokeanOrogeny, Orogeny,Upper UpperMichigan Michigan 3:20pm pm 3:20 Coffee break break Coffee �Proterozoic ProterozoicSession SessionII:11:Bruce BruceA.A.Brown, Brown,session sessionchair chair(3:40—4:40 (3:40-4:40 pm) pm) 3:40 pm Richard W. Ojakangas Ojakangas and and Jukka Jukka S. S. Marmo Manno Early sequences of Early Proterozoic Proterozoicleptire leptite & & halleflinta halleflinta (tuff (tuff&& tuffite) tuffite) sequences southern southernFinland Finland reinterpreted reinterpretedas asshear shearzones: zones:Significance Significance to to Lake Superior Superior geology geology 4:00 pm M.G. M.G. Mudrey, Mudrey,Jr., Jr., and andB.A. B.A. Brown Brown Penokean from formational formational contacts Penokean structural structuraltrends trendsdefined defined from contacts and cleavage cleavageanalysis analysisalong alongthe theGogebic GogebicRange, Range,Wisconsin Wisconsin 4:20 pm Xinping XinpingYin Yin and andJames James A. A. Grant Grant Geochemistry Geochemistryof of the metadiabases metadiabases in in the the Republic Mine area, area, northern northernMichigan Michigan 4:40 pm End End of of technical technicalsessions sessionsfor for the the day day Posters Posters on on display display 6:00—7:00 pmMixer, Mixer, cash cash bar bar 6:00-7:00 pm 7:00-10:OOpm Annual Banquet Banquet 7:00-10:OOpm Annual Announcement Announcementof of 39th 39thAnnual Annual Meeting Meetinglocation, location,1993. 1993. Goldich F.Cannon Cannonby byPaul PaulK. K.Sims. Sims. GoldichAward Awardpresentation presentationto toWilliam WilliamF. Banquet Banquetspeaker: speaker:Duff Duff Kerr, Kerr, Kerr Kerrand andAssociates, Associates,Denver, Denver,Colorado; Colorado; IndustrialPetroleum PetroleumExploration Explorationof ofthe theMidcontinent Midcontinent Rift Frontier Industrial Frontier Friday, Friday,May May88 8:00 8:00 am am Registration, Registration,Holiday HolidayInn Innlobby lobby MidcontinentTectonics Tectonicsand andProcesses ProcessesSession SessionI:I:William WilliamJ.J.Hinze, Hinze,session sessionchair chair Midcontinent (8 :30-10:00 am) (8:30-1090 am) 8:30 am William F.Cannon Cannon WilliamF. Process Processrates ratesduring duringMidcontinent Midcontinent rfting: rifting: Clues Cluestotothe theorigin originofofthe theMidcontinent MidcontinentRift RiftSystem System 8:55 am J.D. J.D. Miller, Miller,Jr. Jr. The need for The need aa new new paradigm regarding regardingthe thepetrogenesis petrogenesis of of the theDuluth DuluthComplex Complex 9:20 am Albert AlbertB. B.Dickas Dickas Preliminary Preliminaryreport, report,geology geologyand andgeophysics geophysicsof of the the Terra/Patrick TerraIPatrick#7-22 #7-22 wildcat wildcathydrocarbon hydrocarbontest, test,Midcontinenr MidcontinentRift, Rift,Keystone KeystoneTownship, Township, Bayfield BayfieldCounty, County,Wisconsin Wisconsin xiii XIII �9:40 am am David J. Allen and Val W. Chandler of high-resolution high-resolution aeromagnetic aeromagnetic data for for investigating The utility of investigating the the Midcontinent Rift Rift in east-central east-central Minnesota 10:00 break 10:OO am Coffee break Midcontinent Tectonics II:A.B. A.B.Dickas, Dickas,session session chair chair Midcontinent Tectonicsand andProcesses ProcessesSession SessionII: (10:20—11:20 (10:20-11:20 am) am) 10:20 am am Pieter PieterBerendsen Berendsen Structure and composition composition of Keweenawan rift-related igneous igneous and Structure sedimentary rocks in Kansas 10:40 am am Kathleen 10:40 Kathleen M. M. Witthuhn Witthuhn A structural structural analysis MidcontinentRft analysis of the Midcontinent Rift in inMichigan, Michigan, fault array based on a fault arrayanalysis analysisutilizing utilizing slickensides 11:00 am John 11:OO am John C. C. Green Green Palisade Rhyolite, Minnesota. The Palisade Rhyolite, Lake County, County, Minnesota: rheoignimbrite in A cryptic rheoignimbrite in the North Shore Shore Volcanics Volcanics 11:20am am Lunch break 11:20 Posters on display Economic GeologySession SessionI:I:Lawrence LawrenceKennedy, Kennedy,session sessionchair chair(1:00—2:20 (1:00-2:20 pm) Economic Geology 1:00 pm Anthony J. Deevy Magino, the the making of aa mine 1:20 pm Susan E. Brink compositional study of aa managaniferous iron-formation, Textural and compositional managaniferous iron-formation, Emily District, deposition District, Cuyuna Range, with implications/or implications for original original deposition and in in situ leaching leaching of manganese manganese 1:40 pm G.B. Morey, Peter L. McSwiggen, and Jane M. Cleland G.B. of an an exhalative contribution to the manganese manganese mineralogy of Evidence of the Trommald Formation, Formation, Cuyuna Iron Iron Range, Range, east-central east-central Minnesota 2:00 pm Susan E. Brink petrology and geochemistry of the Spirit volcanogenic The petrology volcanogenic massive massive prospect, north-central north-central Wisconsin sulfide prospect, Wisconsin 2:20 pm break Coffee break Presentation Presentation of student student awards xiv �Economic chair EconomicGeology GeologySession SessionII:3.1Allan : AllanM.M.Johnson, Johnson,session session chair(2:40—3:40 (240-3:40 pm) pm) 2:40 pm Penelope PenelopeMorton Mortonand andStephen StephenD. D.Geerts Geerts High temperature hydrothermal alteration High temperature hydrothermal alterationassociated associated with with PGE PGEenrichment enrichmentofofCu-Ni Cu-Nisulfides, sulfides,Dunka DunkaRoad, Road,Duluth DuluthComplex, Complex, NE NE Minnesota Minnesota 3:00 pm Mark Mark J.J. Severson Severson Sulfide PGE mineralization Sulfide and andPGE mineralizationat at the the basal basal contact contactof ofthe the Minnamax Minnarnax deposit, deposit, Duluth Duluth Complex, Complex, NE Minnesota 3:20 pm Daniel Daniel N. N. Miller, Miller,Jr. Jr. Accessing Accessing the the Anaconda Anaconda Geological GeologicalDocuments DocumentsCollection Collection Minnesota Michigan -- Ontario Ontario Minnesota-Wisconsin -Wisconsin--Michigan 3:40 pm End Endofoftechnical technicalsessions sessions 5:00 pm Field departurefor for Marquette Marquette Field Trip Trip 4 departure Saturday, Saturday,May May99 Field Trip Trip 33 Geology GeologyofofKeweenawan Keweenawanrock rock near nearthe thePorcupine PorcupineMountains, Mountains, Ontonagon Ontonagonand andGogebic Gogebic Counties, Counties,Michigan. Michigan. Leaders: Leaders: W.F. W.F. Cannon, Cannon, S.S. S.S. Nicholson, Nicholson, C. C. Hedgman, Hedgman, L. Woodruff, Woodruff, and and K.J. Schulz Schulz Departurefrom fromHoliday ~ o l i dInn, Inn, a ~ Hurley Hurley 8:00 am Departure 4:30pm Return Return Field Trip Trip 4 Geology Field Marquette area, Geologyofofthe theGreat GreatLakes Lakestectonic tectonic zone zone in the Marquette area, Michigan—A Michigan-A late Archean Archean paleosuture. paleosuture. Leader: Leader: P.K. Sims Sims and and Z.E. Peterman Peterrnan 8:00 am am (Eastern (EasternDaylight Daylight Savings)—Departure SavingsbDeparture from from Ramada Ramada Inn, Inn, Marquette, Marquette,Michigan Michigan 4:30 4:30 pm pm (Eastern (Eastern Daylight Daylight Savings)—End SavingsbEnd of trip trip 6:00 6:00pm (Central (Central Daylight Daylight Savings)—Return SavingsbReturn to to Hurley Hurley xv �POSTER POSTER PRESENTATIONS PRESENTATIONS Archean Archean Frank Frank R. R. Luther Luther Magnetite Magnetite octahedra octahedrain inpillow basalt basalt near nearWawa, Wawa,Ontario Ontario Geophysics Geophysics C. Patrick Patrick Ervin, Ervin, M.G. M.G. Mudrey, Mudrey, Jr., Jr., B.A. B.A. Brown, Brown, and and M.L. M.L. Czechanski Czechanski 1991 program in 1991COGEOMAP COGEOMAP gravity mapping program in west-central west-central Wisconsin: Wisconsin: The Driftless Driftless Area Proterozoic Proterozoic Bradley Bradley Hellickson, Hellickson, Stanley Stanley Radzevicius, Radzevicius, and Garry Garry Anderson Anderson Petrology and structure of a rapakivi body from east-central Petrology and structure of a rapakivi body east-centralMinnesota Minnesota Daniel Daniel Holm, Holm, Timothy Timothy Hoist, Hoist, and and Daniel Daniel Lux Lux Thermochronologic Thermochronologicevidence evidencefor post-Penokean post-Penokeanunroofing unroofing in the the Lake Superior Superior region region in G.B. Morey Morey and and Terrence Terrence J. J. Boerboom Boerboom Rare Rare earth earthelement elementdistribution distribution patterns in in Early Early Proterozoic Proterozoiciron iron formations formations of of the the Penokean Penokean orogen, orogen, east-central east-centralMinnesota Andrew D. Moshoian, Moshoian, Karl Karl R. Wirth, Wirth, and and John John P. Craddock Craddock The Kenora-Kabetogama Kenora-Kabetogama dike trace element dike swarm: swarm: Results of trace element studies Midcontinent Midcontinenttectonics tectonics and and processes processes Albert Albert B. Dickas Dickas and and M.G. M.G. Mudrey, Mudrey, Jr. Jr. Precambrian Precambrianhydrocarbon hydrocarbonpotential potential of of the the western western Great GreatLakes Cheryl A. Hedgman Hedgman Cheryl Petrology and fades of Petrology and provenance of a conglomerate fades of the the Jacobsville Jacobsville Sandstone: Sandstone: Iron Iron to to Bergland, Bergland, Michigan R.J. Horton, Horton, R.J. R.J. Bisdorf, Bisdorf,and andR.P. R.P. Kucks Kucks Airborne geophysical geophysicalsurvey survey of of northwestern northwesternWisconsin Wisconsin Airborne William William F. Kean Kean and and John Feeney Magnetic studies studies of the Dresser-St. Croix Falls area, area,Polk Polk County, County,Wisconsin Wisconsin S.D. McDowell, K.L. Price, J. Huntoon, and T.J. T.J. Bornhorst Thermal modeling and illite/smectite geothermometry Thermal modeling and illitelsmectite geothermometry of of the the Precambrian PrecambrianOronto OrontoGroup, Group,Wisconsin Wisconsinand Michigan Michigan xvi xvi �Economic Economic geology geology P. Hinz and R.T. Lucas of industrial industrial minerals minerals in northwestern Ontario Exploration and mining activities of Stephen A. Kissin, Peter G. Harvey, Elizabeth A. Jennings, Samuel T. Spivak, Spivak, and Eric J. Mosley fluid inclusion, stable stable isotopic and and structural structural studies of the Alteration, fluid Bay District, District, Ontario Ontario Rabbit Mountain Silver Mine, Thunder Bay Peter L. McSwiggen, McSwiggen, G.B. G.B. Morey, and and Jane M. Cleland Cleland Acmite in the Trornrnald Trommald Formation Formation of of the the Cuyuna Iron Iron Range: Range: Revisited Acmite M.G. Mudrey, Jr., and A.B. Dickas Early Proterozoic Proterozoic metal-rich Geologic setting of the Early metal-richvolcanics volcanics of the upper Great Great Lakes region region Richard Patelke Richard Patelke and and Mark Mark Severson Severson Petrology Petrology and and origin originof ofthe thenorthern northernColvin ColvinCreek CreekBody, Body, Duluth Duluth Complex, Complex, NE Minnesota xvii �ABSTRACTS �The High-Resolution Aeromagnetic Aeromagnetic Data Data for for Investigating Investigating The Utility Utility of High-Resolution the Minnesota the Midcontinent MidcontinentRift Rift in in East,.Central East-CentralMinnesota David J. J. Allen Department Department of of Earth Earthand andAtmospheric AtmosphericSciences, Sciences, Purdue University, University, West Lafayette, Indiana 49707 49707 Val W. Chandler Minnesota Geological Survey, St. St. Paul, Paul, Minnesota 55114 55114 Geological Survey, Introduction Introduction Aeromagnetic data data are useful for delineating the structure structure of of the the Midcontinent Midcontinent Rift System (MCR). (MCR). Along Along the western western arm arm of of the theMCR, MCR, magnetic magnetic anomalies anomalies have have been used to and sedimentary to map map buried buried Keweenawan Keweenawan volcanic and sedimentary rocks rocks and and to to identify identify major structures, structures, including including basins basins and and faults faults(e.g., (e.g., Sims Simsand andZietz, Zietz,1967; 1967;King King and and Zietz, 1971). 1971). In In 1991, 1991,the theMinnesota MinnesotaGeological Geological Survey Survey (MGS) (MGS) completed a highhighresolution Minnesota (Chandler, (Chandler, 1991). Nearly all of resolution aeromagnetic aeromagnetic survey of Minnesota of the state state was surveyed with a terrain meters and a flight line separation terrain clearance clearance of of 150-200 150-200 meters of 400-500 meters. database, the only meters. This statewide statewide aeromagnetic aeromagnetic database, only one in North North America encompassingaa large large region region with with high resolution, America encompassing resolution, provides provides a new new opportunity opportunity to examine the the western western arm armof of the theMCR MCR in in detail. detail. A 213 meter meter data grid was generated generated from from the the aeromagnetic aeromagneticsurvey. survey. This data set contains contains detailed detailed information information about the the Precambrian Precambrian basement basementof of Minnesota Minnesota and and provides excellent images images of of the MCR, including the the Duluth Complex provides excellent MCR, including Complex and North North Shore Volcanic Group,aa large large portion portion of of the the St. Croix Horst, Horst, the Belle Plaine Fault, Fault, Volcanic Group, and the extreme extreme northern northern tip tip of of the Iowa Iowa Horst. To To take take full full advantage advantage of of these these data, data, new methods methods of of display display are are presently presently being beingdeveloped, developed, including including stereoscopic stereoscopic data presentation presentation and andimproved improved shaded shadedrelief relief techniques. techniques. Results Preliminary Results is aa magnetic magnetic Figure 11is present study studyfocuses focuses on the St. St. Croix Croix Horst (SCH). Figure The present Wisconsin. The MGS 213 m grid map of east-central Minnesota and adjacent Wisconsin. m data grid data from from an anolder olderUSGS USGS survey survey in in extreme extreme western westernWisconsin Wisconsin was merged with data 1967) and data from from the the DNAG DNAG 2 km magnetic magnetic grid, based on on aa (Sims and Zietz, 1967) (1966), for addition, the the Twin Twin survey by Patenaude (1966), for the the remainder remainder of of Wisconsin. Wisconsin. In addition, metropolitan region was not not included included in in the thehigh-resolution high-resolution aeromagnetic aeromagnetic Cities metropolitan area,the theMGS MGS 213 213 m m grid grid is is based based on on data dataacquired acquired by by the theUSGS USGS in in survey; in this area, As shown shown in Figure 1, 1, The specifications specifications for 1961. The for each each survey survey are are listed listed in in Table Table 1. As new high-resolution high-resolution data data clearly clearly portray portray features featureswhich which are arepoorly poorlyresolved resolved by by the new the older older USGS USGS surveys surveys and and completely completely absent absent in in the the DNAG DNAG 2 km data data grid. grid. the is an aninterpretive interpretivemap mapof ofthe theMCR MCR based based on on the theaeromagnetic aeromagneticdata. data. Figure 22 is underlain by by (essentially (essentiallynon-magnetic) non-magnetic) Keweenawan sedimentary rocks are are Areas underlain characterized by subdued subdued magnetic magnetic patterns, patterns, whereas whereas(magnetic) (magnetic)Keweenawan Keweenawan characterized anomalies, many many of of which which are are volcanic rocks rocks are are often associated with narrow linear anomalies, continuous for over over 50 50 km km along alongstrike. strike. Where continuous for Where the rift rocks rocks crop crop out, they strike strike parallel to is useful useful for for to the the trends trendsofofthe themagnetic magneticanomalies. anomalies. This correlation correlation is mapping packages and and delineating within the SCH. mapping volcanic volcanic packages delineating folds folds within SCH. In addition, addition, abrupt terminations terminations of of the the linear linearanomalies anomaliesare areuseful useful for for identifying identifying faults. faults. abrupt Several northeast-trending northeast-trending anomalies anomalies are areproduced produced by byKeweenawan Keweenawan dikes. dikes. Several o the rift axis (Figs. (Figs. 1-2). Within Within of the These dikes lie west of the MCR MCRand and strike strike parallel parallel tto the SCH, SCH, lineaments lineaments cut cut across across the the magnetic magnetic anomalies anomalies associated associated with with the thevolcanic volcanic the rocks. rocks. The lineaments lineaments do not not truncate truncate or orsignificantly significantly offset offset the themagnetic magnetic 33 �46 45 km km 0 I ——I 10 20 30 40 50 Figure 1: 1: Shaded Shaded relief relief presentation presentationofofmagnetic magnetic Figure datafor foreast-central east-central MN MN and and adjacent adjacentWI. WI. The The data sun illumination illumination isisfrom from the the northwest. northwest. sun 10 20 30 40 50 I— —I 0 Figure Figure2: 2: Interpretive Interpretivemap mapofofthe theMCR MCRbased basedon on aeromagnetic data. aeromagnetic data. Table Aeromagnetic Survey Survey Specifications Specifications (see (see Figure Figure1)1) Table1:1:Aeromagnetic Survey Survey A MGS,1991 1991 A MGS, l? Sims and Zietz,1967 1967 B Sims and Zietz, C USGS, 1961 C USGS, 1961 Patenaude,1966 1966 DD Patenaude, 44 Flight Fliehtline lineseoaration s e ~ a r a t i oand nanddirection direction North-South 500 North-South 200m mabove aboveground ground 500mm 200 East-West 500 (150 m) 500ftfl(150 m)above aboveground ground 11mile mile(1600 (1600m) m) East-West East-West 500 500ftft(150 (150m) m)above aboveground ground 11mile mile(1600 (1600m) m) East-West North-South North-South (900m) m)above abovesea sealevel level 66miles miles(9600 (9600m) m) 3000ftft(900 3000 Elevation Elevation �anomalies, suggesting that that they might be produced by dikes, faults of anomalies, suggesting produced by of minimal minimal displacement, or fracture zones within which which the magnetic character character of of the the volcanic volcanic rocks was altered. altered. The most prominent anomalies are' are associated with reverse faults prominent magnetic magnetic anomalies associated with along the margins of juxtapose volcanic volcanicand and sedimentary sedimentary rocks. rocks. Of of the SCH SCH which juxtapose particular interest interest is is the thePine PineFault. Fault.North Northofofthe thePre-Paleozoic Pre-PaleozoicTwin TwinCities Cities Basin, Basin, this to the east in this fault faultplaces places older older volcanic volcanic rocks to in contact contact with with younger younger sedimentary sedimentary rocks to the west. The rocks to The new new magnetic magnetic data indicate indicate that that the the Pine Pine Fault Faultcontinues continues northeast 46%, to to within within 20 20 km km of of the the Minnesota-Wisconsin Minnesota-Wisconsinborder border(Figs. (Figs.1-2). 1-2). northeastbeyond beyond46°N, Additional Problems Problem5 Thus far, the magnetic data data have have been been used used in in a qualitative the high-resolution high-resolution magnetic qualitative manner t o interpret the the structure structure of of the the SCH. SCH. Continued Continued efforts effortsto to enhance enhance the the manner to display of this this data images of of the the SCH SCH and and better better data set set will will hopefully result in improved images resolution of the structural structuralcomplexities complexities within the the rift's rift'svolcanic volcanic rocks. rocks. Magnetic modeling will will be be aa powerful powerful tool toolfor forquantifying quantifying interpretations interpretations of of the the SCH. AAmajor be to determine the sources sources of the continuous continuous linear major objective objective will will be magnetic with the magnetic anomalies anomalies associated associated with the rift's rift'svolcanic volcanic rocks. rocks. These anomalies anomalies might be produced produced by contrasts contrasts between between volcanic volcanic flows and interfiow interflow sedimentary sedimentary units, differences differences in magnetic magnetic properties properties between between adjacent adjacent packages packages of ofvolcanic volcanic rocks, or magnetic reversals. These hypotheses will be evaluated using magnetic evaluated using magnetic magnetic reversals. modeling in conjunction conjunction with magnetic properties measurements measurements of of volcanic volcanic rocks rocks from the the SCH. SCH. Magnetic modeling will will also be be usefid useful for investigating the the longer longer wavelength wavelength anomalies (not evident in the shaded relief presentation of Figure 1). Analytical anomalies evident shaded relief presentation of Figure 1). Analytical techniques which account account for for structural structural rotation of the remanent techniques which remanent magnetization magnetization vector vector (e.g., (e.g., Mariano Mariano and Hinze, Hinze, 1991), 19911, in in conjunction conjunction with with available available seismic seismic reflection data data and more reliable models models of the deeper deeper and gravity gravitymodeling, modeling, will lead to more structure of the SCH. structure of the SCH. The MGS data set set also provides an opportunity to examine other portions of the MCR. MCR. For For example, example, these data data may may lead lead to to an animproved improved understanding understanding of of the the St. Croix Croix and Iowa Iowa Horsts along the Belle Plaine Fault Fault in in between the St. transition between southeastern southeastern Minnesota. Minnesota. In addition, addition, the data data may may also also assist assist ininimproving improving interpretationsof of the theDuluth DuluthComplex Complex and North Shore Volcanic Volcanic Group. interpretations Group. Finally, the detail provided by the MGS survey suggests suggests that that aa similar MGS survey similar high-resolution high-resolution survey survey of of Wisconsin might of northwestern Wisconsin might be be extremely extremely useful useful for for investigating investigating the the nature of the the transition transition between between the thewestern westernarm armof of the the MCR MCR and the the Lake Lake Superior Superior Basin. REFERENCES REFERENCES Chandler, Chandler, V.W., V.W., 1991, Aeromagnetic Aeromagnetic anomaly of Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey anomaly map of State StateMap MapSeries SeriesS-17, S-17,scale scale1:500,000. 1:500,000. E.Rm7and Zietz, I., 1971, 1971, Aeromagnetic King, E.R., Aeromagnetic study study of ofthe the midcontinent midcontinent gravity gravity high of central United States: Am. Geol.Soc. States:Geol. SOC. Am. Bull., Bull., v. v. 82, 82*p. p. 2187-2208. 2187-2208. Mariano, J., and andHinze, Hinze7W.J., W.J., 1991, 19917Geophysical Geophysical investigations midcontinent rift in eastern eastern Manano, investigations of of the the midcontinent Superior using using variable variablemagnetization magnetization modeling, modeling, [abst.1; Labst.]; Institute Instituteon onLake LakeSuperior SuperiorGeology Geolo~ Lake Superior Annual Meeting, Meeting7Eau Eau Claire, Claire,WI, WI,1991; 1991; v. 37, part 1, p. 68-69. 68-69. Proceedings, 37th Annual part 1, Smith7 Patenaude, R.W., R.W., 1966, 1966, A Patenaude, A regional regional aeromagnetic aeromagnetic survey survey ofofWisconsin7 Wisconsin,ininSteinhart, Steinhart, J.S., J.S., and Smith, T.J., eds., eds., The Theearth earthbeneath beneaththe thecontinents: continents:American AmericanGeophysical GeophysicalUnion UnionGeophysical GeophysicalMonograph Monograph T.J., Series Series10, 10,p. p. 111-126. 111-126. Sims, P.K., P.K, and and Zietz, Zietz, I., I.,1967, 1967,Aeromagnetic Aeromagnetic and and inferred inferredPrecambrian Precambrianpaleogeologic paleogeologic map map of ofeasteastSims, central Minnesota Minnesota and andpart partofofWisconsin: Wisconsin: USGS USGS Geophysical Geophysical Investigations Map GP-563 [with text], central 66 p., scale scale 1:250,000. 1:250,000. 5 �AN ANINTEGRATED INTEGRATEDGRAVITY GRAVITYAND AND MAGNETIC MAGNETICSURVEY SURVEY OF'THE THEROCK ROCKELM ELMSTRUCTURE, STRUCTURE,WESTERN WESTERNWISCONSIN WISCONSIN OF Michelle MichelleL. L. Barnes, Barnes, Georgia Geop'a L. L. Osborn, Osbom, and andLung LungS.S.Chan Chan Department DepamentofofGeology Geologv University University of of Wisconsin-Eau Wucomin-Eau Claire, Claire, WI W 54701 54701 The TheRock RockElm Elm structure, structureylocated locatedininPierce PierceCounty, CountyyWisconsin, Wisconsin,isisan anapproximately approximately four fourmiles milesinindiameter, diameter,sub-circular sub-circularstructure structureof of uncertain uncertainorigin. origin.The Thestructure structurecontains contains Paleozoic Paleozoic strata strata tilted tilted away awayfrom fromaacentral centraldome domewhere wherebrecciated brecciatedrocks rocksare arepresent. present. Several Severalhypotheses hypothesesfor forthe theorigin originof of the the structure structurehave have been been suggested: suggested: 1) 1)meteorite meteoriteimpact impact (Cordua, (Corduay1985), 1985),2)2)volcanic volcanicactivity, activityyand and3)3)tectonic tectonicactivity. activity.Of Ofthe thethree, three,we welooked lookedmost most closely closelyat atthe thefirst firstone oneand andhave haveconducted conductedan anintegrated integratedgravimetric gravimetricand andmagnetic magneticsurvey survey determinethe theplausibility plausibilityofofthis thishypothesis. hypothesis. totodetermine Gravity LaCoste&&Romberg Romberggravity gravitymeter meteratatone one Gravitymeasurements measurementswere weretaken takenusing usinga aLaCoste mile miles.FreeFreemileintervals, intervalsymostly mostlyatatUSGS USGSelevation elevationmarkers, markersyover, over.an anarea area12 12miles d e sxx141 4miles. air airand andBouguer Bouguercorrections correctionswere wereapplied appliedto toall allmeasurements measurementsand andterrain terraincorrections correctionswere were applied was used to applied where where needed. needed. AA proton proton precession precession magnetometer magnetometer was' to measure measure the the ambient magnetic field and the vertical gradient of the field intensity in and around the ambient magnetic field and the vertical gradient of the field intensity in and around the structure. structure.Multiple Multiplemeasurements measurements were were taken taken atatstations stationspositioned positioned about aboutevery everyquarter quarter mile mile along along the thegrid grid pattern patterncreated createdby by the theroads roads in in the thearea. area. We 1 and 2) to We have have compared compared our our gravity gravity and magnetic magnetic results (Figures 1 to those thoseof of the theManson MansonImpact ImpactStructure StructureininIowa, Iowaywhich whichhas hasstrong strongmagnetic magneticanomalies anomaliesassociated associated with withits itsboundary boundary(Hartung (Hartungand andAnderson, Andersony1988). 1988).The TheRock Rock Elm Elm structure structure does doesnot notshow show significant significantmagnetic magnetic anomalies anomalies along along its its boundary boundary nor nor with with its itscentral centraldome. dome.The Thegravity gravity data dataalso alsodo donot notsupport supportthe thehypothesis hypothesisofofan animpact impactorigin. origin.AAnorthwest-southeast northwest-southeast trend trend in inthe thegravity gravityanomaly anomalycoincides coincideswith withthe theRiver RiverFalls Falls anticline anticlineand and the theLake LakeOwen OwenThrust Thst Fault Fault of ofthe theMid-Continent Mid-ContinentRift Rift System. System. We We have have also also computed computed gravity gravity and andmagnetic magnetic anomalies anomaliesof ofhypothetical hypotheticalimpact impactstructures structuresconstructed constructedfrom fromknown h o r ngeological geologicalconstraints. constraints. Thesimulated simulatedmodels modelsdo donot notresemble resemblethe thegeophysical geophysicalresults resultsobserved. observed. The References References CorduayW.S., W.S.y1985, 198SY RockElm Elm structure, structure,Pierce Pierce County, County, Wisconsin: Wisconsin: AApossible possible Cordua, Rock cryptoexplosion structure, structureyGeology, Geologyy13, 13 372-374. cryptoexplosion 372-374. Hartung, J.B., J.B., and andR.R. R.R. Anderson, Anderson, 1988, 1988 A Compilation Compilation of Information and Data Data Hartung, A onthe theManson MansonImpact ImpactStructure, Structure,LPI LPITechnical Technical Report Report Number Number 88-08. 88-08. on 6 �ROCK ROCK ELM, ELM, TOP TOP SENSOR SENSOR Contour Contour Interval, Interval, 500nT 500nT ROCK ELM, ROCK ELM, GRADIENT GRADIENT Contour Interval, Contour Interval, 200nT 200nT 1. Magnetic Magneticanomalies anomaliesof of the the Rock Rock Elm area. The circle represents approximate Figure 1. represents the approximate boundary of the structure. structure. GRAVITY GRAVIW ANOMALY ANOMALY AT AT ROCK ELM ROCK ELM Contour Interval, ContoatInterval, 2Ogu 20gu Figure Gravityanomaly anomalyof of the the Rock Rock Elm Elm area. The circle circle represents represents the the approximate approximate Figure 2. Gravity area. The 7 boundary of the structure. structure. 7 �rift-related Structure Stmctureand and composition composition of of Keweenawan Keweenawan rift-related igneous igneous and and sedimentary seamentaryrocks rocksin inKansas. Kansas. Pieter PieterBerendsen Berendsen Kansas KansasGeological GeologicalSurvey Survey During the last last decade decade a series series of of holes holes were were drilled into the the During Precambrian Precambrian basement. basement. Prominent Prominent among among these these are arethe theNoel NoelPoersch Poersch#1 #I , which which is the deepest deepest drill hole hole to to date in in Kansas Kansas at a t11,300 11,300feet, feet, and andtwo twoOZ OZ drill t o the the Poersch Poersch hole. hole. These These three three drill holes, holes, which which are ininclose closeproximity proximity to wells in Washington County, northeastern northeastern wells were were drilled drilledin in1984-85 1984-85by Texaco in Kansas 1).The TheFinn F i n#1-4 #1-4 and and the theFriederich Friederich #1-8 #l-8 in in Marshall Marshall and and Kansas (Figure (Figure 1). Riley respectively, are Riley counties respectively, are two two other wells with significant sigdicant penetrations penetrations into 1).Studies Studies of of well well cuttings cuttings and andsome some into the the Proterozoic Proterozoic basement (Figure (Figure 1). generated a lot of new data and made core from these and older drill holes core and older drill holes generated a lot of data and made itit possible to better interpret the nature of rift. possible better the nature of rift. Comparative petrographic studies of of representative representative outcrop outcrop samples samples from &om the the Lake Lake Superior Superior region region and and subsurface subsurface samples samples from from Kansas Kansas were were conducted. The mineralogical composition compositionand and the the heavy heavy mineral mineral content of of general stratigraphic correlations core and cuttings allow comparison and cuttings allow comparison and general stratigraphic correlations with with rocks rocks from from the outcrop belt in the Lake Superior Superior area. area. The The amount amount of of quartz, quartz, plagioglase plagioglase and K-feldspar, the amount and and nature natureof of rock rock fragments, fragments, the d ldiscriminating discriminatingfactors. factors. thetourmaline, tourmaline,zircon, zircon,and andepidote epidote content contentare areall Chemical the basalts and Chemical analysis of of the and gabbros gabbros encountered in the the four four drill holes in northeastern Kansas shows them to be alkalic to subalkalic northeastern Kansas shows to be alkalic to subalkalic (Figure 2). Baddeleyite from gabbro in the upper upper portion portion of of the the Poersch Poerschdrill drill (F'igure 2). hole of 1097.5 1097.5 3Ma hole yields a concordant concordant U-Pb age of 3Ma (Van Wan Schmus and and others, others, 1990). This This is essentially essentially the same age as published published data for for the the Lake Lake Superior Superior region, and indicates that thatno noage ageprogression progressiontook took place place along along this this arm of the rift. The lower 3874 feet in the Poersch drill hole penetrated aa arm of the rift. The lower 3874 Poersch predominantly which detrital monazite predominantly arkosic arkosic section section from which monazite and and zircon zircon were were recovered. ages of of these minerals range recovered. U-Pb provenance ages range from &om 1.7-1.8 1.7-1.8 Ga, Ga, 1.4-1.5Ga, From this itit 1.4-1.5Ga, and 1.1-1.2 Ga (Martin, Personal Communication). Communication). From appears appearsthat thatmost mostofofthe thearkosic arkosicsedimentary sedimentaryrocks rockswere werederived derivedproximally proximally from the adjacent rift margins, which consist of 1.7-1.8 Ga mostly granitic adjacent rift margins, which consist of 1.7-1.8 basement and and younger younger (1.45 (1.45 Ga) Ga) granitic granitic plutons. plutons. No No evidence evidence of of early early Proterozoic or Archaen Archaen detrital detrital minerals minerals was found, found,indicating indicatingthat that transport transport of sedimentary materials materials along the axis of the the rift from farther farther up north may may not have been significant. not have been significant. Core of the OZ drill hole has stable stable magnetic magnetic fiom gabbro gabbro of Core taken from remanence from shallow, shallow, reverse reverse to steep, remanence which which demagnetizes demagnetizes from steep, reverse reverse inclination inclination and and appears appears to todate datefrom fiomoriginal originalcooling cooling(Van (Van Schmus Schmus and and others, 1990). rocks that that 1990). This may be correlated with Lower Lower Keweenawan Keweenawan rocks occur below below the the R tto reversal. o N magnetic reversal. In I n the the Poersch Poersch drill drillhole holea apredominantly predominantlyvolcanic volcanic section, section, approximately 4580 foot foot thick thick overlies overlies the the mostly arkosic sedimentary rock section. Based on seismic from a COCORP line four four miles miles north of seismic evidence from COCORP line of the Poersch propose that that aa high-angle, (1991) propose high-angle, Poersch drill drill hole, hole, Woelk Woelk and Hinze Hinze (1991) west-dipping, reverse fault fault is responsible for the transposed order west-dipping, reverse responsible for order of of the the major rock packages. This This fault fault has has an approximate strike of N 40°E, 4 0 0 and and ~ ~ rock packages. dips steeply to shows that that a t o the west. west. Examination Examination of the seismic seismic profile profile shows 8 �steeply east-dipping reverse fault, having aa strike could strikeofofN400E, N~OOE, could also also be be responsible for the transposition. transposition. North-northeastand northwest-ternding faults dominate North-northeast- and northwest-ternding faults dominate the the structures associated with the rift in Kansas. Presently, a pattern pattern of structures of roughly rectangular rectangular structural structuralblocks, blocks,each eachhaving havingaanarrow narrowrange rangeof ofelevations elevationsabove above sea level, gives gives a characteristic characteristic appearance. appearance. Apparent Apparentcompound compound vertical vertical offset on faults faults can be as offset on as much much as as 2000 2000 feet. feet. Within Within the the Paleozoic Paleozoic era repeated reactivation repeated reactivation of earlier tectonic tectonic trends can can be be documented. documented. The The rift-related rocks rocks were subjected to magnitude and and number number of of times to which rift-related faulting in the Proterozoic Proterozoicisisunknown unknown The The last last major major adjustment adjustment on on faults faults occurred during the Pennsylvanian Ouachita orogeny. Preliminary studies in Ouachita Preliminary Kansas indicate of rocks rocksof ofwidely widely indicate that that sedimentary sedimentary and and igneous igneous suites suitesof differing ages may be be juxtaposed juxtaposed in in adjoining structural structural blocks. References: References: Martin, M.W., Department of University of of Kansas. Kansas. (Personal Martin, M.W., Department of Geology, Geology, University (Personal Communication) Communication) Martin, M.W., D.R.,Geissman, Geissman, J., J., and and Van Schmus, Schrnus, W.R., W.R., Martin, M.W., Sprowl, D.R., Berendsen, P., and Berendsen, P., 1990, 1990,Age, Nd and Pb isotopic composition, and magnetic polarity for subsurface samples of the the 1100 Ma Ma midcontinent midcontinent rift: [Abstract] [Abstract]Geological Geological Society Society of America, v. 22, no. 7, p. A174. Woelk, T.S., T.S., and and Hinze, Hinze, W.J., W.J., 1991, 1991, Model Modelofofthe themidcontinent midcontinentrift rift system system in in northeastern Kansas: northeastern Kansas:Geology, Geology,v. v. 19, 19,p. p. 277-280. 277-280. 9 �PRECAMBRIAN FSECAMEEIAN BEDROCK BEDROCK N miles 55 miles 00 t II IlL Ii I - HFZ HFZ Humboldt HumboldtFault FaultZone Zone fault fault , ----- inferred fault --inferred contact 00 ? ,'A ,'A: ! ' * km . 5 km . inferred fault — — — inferred contact Figure ininthe of F i ~1. 1-eBasement Basementstrticture sim~cture thevicinity ~cinity of the theFinn, l?in.n,Poersch Poerschand andFriedFriederich eri& drifl drill holes, holes, north-central n o r h x n t i d Kansas. Kansas. S 6 C z 2 0 40 40 44 44 52 52 48 48 56 56 60 60 SIC2 SIO2 Figure22Alkalies h a l i e svs vsSi02 SiOzdiagram diagramshowing sho&ng Keweenawan Kewemawan lavas and gabbrog. Figure gabbro. 10 �GEOLOGY AND AND TECTONIC SETTING SETTING OF OF THE THE ARCHEAN ARCHEAN GIANTS GIANTS GEOLOGY RANGE BATHOLITH; BATHOLITH;WESTERN WESTERNWAWA WAWASUBPROVINCE, SUBPROVINCE,MINNESOTA MINNESOTA RANGE BOERBOOM,Terrence TerrenceJ., J.,and andMark MarkA. A.Jirsa Jirsa BOERBOOM, MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN MN55114-1057 55114-1057(612-627-4780) (612-6274780) Minnesota TheGiants GiantsRange Rangebatholith batholith(ORB) (GRB)isisaalarge largecomposite compositegranitoid granitoidbody body of of Late LateArchean Archean The agethat that intrudes intrudes supracrustal supracrustal rocks truncated by by the the age rocks of of the the Wawa Wawa subprovince. subprovince. It It isistruncated km to to ProterozoicDuluth DuluthComplex Complexatatits itseast eastend, end, and andextends extendswestward westward for formore more than than 200 200km Proterozoic north-central Minnesota, where it is deeply buried beneath Quaternary sediment. This north-central Minnesota, where it is deeply buried beneath Quaternary sediment. This studyisis based based on on detailed detailedoutcrop outcropmapping, mapping,and andto toaalesser lesserextent extenton ondrill drillcore coreand and study geophysical data in the westernmost exposed part of the batholith and several satellite geophysical data in the westernmost exposed part of the batholith and several satellite metasedimentaryrocks rocks plutons. The TheGRB GRBintrudes intrudescomplexely complexelydeformed deformedmetavolcanic metavolcanicand andmetasedimentary plutons. of the Lake Vermilion Formation. Two main periods of deformation have been identified of the Lake Vermilion Formation. Two main periods of deformation have been identified inthe thesupracrustal supracrustalrocks: rocks: aa Di D levent eventthat thatproduced producedlarge largescale, scale,locally locally recumbent recumbent folds folds but but in onlyaararely rarely preserved preservedcleavage; cleavage;and and aa D2 D2 that that produced produced NE-trending, NE-trending, upright upright folds folds and and only associated, steep axial planar cleavage. Mineral lineations and foliations that parallel F2 associated, steep axial planar cleavage. Mineral lineations and foliations that parallel F2 fold axes indicate that peak metamorphism (M2), which varies from greenschist to fold axes indicate that peak metamorphism (M2), which varies from greenschist to amphibolitefacies, facies, occurred occurred during during D2. D2. Field Fieldrelationships relationshipsshow showthat thatsome someportions portions of of the the amphibolite GRBare areolder olderthan thanD2 D2and andthe theassociated associatedM2 M2 metamorphism, metamorphism,and and others othersare areyounger. younger. ORB Localized structures that were generated after M2 and after plutonism are assigned toD3. D3. Localized structures that were generated after M2 and after plutonism are assigned to The GRB exposed in the study area consists of earlier, preto syn-D2, lineated and The ORB exposed in the study area consists of earlier, pre- to syn-D2, lineated and hornblende-bearinggranodiorite granodioriteand andmonzodiorite, monzodiorite,and andlater, later,muscovitemuscovite-and andbiotitebiotitehornblende-bearing bearing granite which was only slightly affected by D2 deformation. Several smaller, bearing granite which was only slightly affected by D2 deformation. Several smaller, ovoid plutons of petrochemically diverse alkalic a f f ~ t were y emplaced after peak ovoid plutons of petrochemically diverse alkalic affinity were emplaced after peak metamorphisminto intosupracrustal supracrustal rocks rocks adjacent adjacent to The best best exposed exposedexample example of of metamorphism to the the GFG3. ORB. The the earlier suite of rocks is the Britt granodiorite which occurs in and near a large antiform the earlier suite of rocks is the Britt granodiorite which occurs in and near a large antiform inthe thesouth southpart part of of the the map map area. area. The Therock rockisismetaluminous metaluminousand andI-type. I-type.The Theproportions proportionsof of in Rb, Y, Yb, Nb and Ta in the Britt granodiorite imply that it was emplaced in a volcanic arc. Rb, Y, Yb, Nb and Ta in the Britt granodiorite imply that it was emplaced in a volcanic arc. Thistectonic tectonicinference inferencealso alsois is supported supported by by major major element element data dataand anddiscrimination discriminationplots. plots. This The granodiorite is intruded by the Shannon Lake granite, a weakly to moderately foliated, The granodliorite is intruded by the Shannon Lake granite, a weakly to moderately foliated, multiphase,biotite-muscovite biotite-muscovitegranite. granite. Emplacement Emplacementof of the theShannon ShannonLake Lakegranite graniteclearly clearly multiphase, post-dated M2 in the area. However, weak NE-trending fabrics cross the trend of post-dated M2 in the area. However, weak NE-trending fabrics cross the trend of magmaticallyrelated relatedpegmatite pegmatiteand andaplite aplitedikes dikesthat that occur occurboth both in in the the granite graniteand andin in the the magmatically adjacent supracrustal rocks. Thus, some regional deformation occurred after intrusion. adjacent supracrustal rocks. Thus, some regional deformation occurred after intrusion. Geochemicaldiscrimination discriminationdiagrams diagramsfor forthe the Shannon ShannonLake Lake granite graniteplace place itit between between the the Geochemical island-arc and continental-collision classes of granitoids. Some plutons of alkalic rocks island-arc and continental-collision classes of granitoids. Some plutons of alkalic rocks (suchas asthe theIdington Idingtonpluton) pluton)are areintruded intrudedby by Shannon ShannonLake Lakegranite, granite,and andtherefore thereforeare are (such somewhat older than the Shannon Lake. However, the alkalic plutons and the Shannon somewhat older than the Shannon Lake. However, the alkalic plutons and the Shannon D2, and andmay may be be broadly broadlycontemporaneous. contemporaneous. Lakeare areboth bothpost-tectonic post-tectonicwith withrespect respectto toD2, Lake The Britt granodiorite and the Shannon Lake granite were emplaced beforeand andafter afterthe the The Britt granodiorite and the Shannon Lake granite were emplaced before D2 deformation, respectively. D2 is a transpressive deformational event of wide main main D2 deformation, respectively. D2 is a transpressive deformational event of wide begenerally generallycorrelated correlated across acrossthe the southern southern Superior SuperiorProvince. Province. regionalextent extentthat thatcan canbe regional High-precisionU-Pb U-Pbdating datinghas hasbeen beendone doneon onzircons zirconsfrom fromthese thesetwo tworock rockunits, units,and andthe the High-precision (R. Zartman, Zartman, U.S. U.S. preliminaryresults resultsindicate indicatethat that D2 D2ended ended between between 2674 2674 and and 2685 2685 Ma Ma (R. preliminary fullreport reportof of the the geochronologic geochronologicwork work will will GeologicalSurvey, Survey,pers. pers. communication). communication). AAfull Geological bepublished publishedsoon. soon. be Thisproject projectwas wassupported supportedininpart partby bythe theMineral MineralDiversification DiversificationProgram Programadministered administeredby bythe theMinerals Mnerals This CoordinatingCommittee Committeefor forthe theMinnesota MinnesotaState StateLegislature. Legislature. Coordinating 11 �TEMPORAL PROGRESSION OF ARCHEAN GRANITOID ROCKS, ISHPEMING GREENSTONE BELT AND VICINITY, MICHIGAN Theodore J. Borrthorst, Richard T. Wilkin1, and Rodney C. Johnson2 Department of Geological Engineering, Geology, and Geophysics, Michigan Technological University, Houghton, MI 49931 Granitoid rocks can now be integrated into the volcanic rock unit and structural framework of the Ishpeming greenstone belt and the development of the Great Lakes tectonic zone The Ishpeming greenstone belt is composed of more than 13,000 meters of mafic and felsic volcanic rocks erupted during active north-directed subduction about 2700 Ma. These volcanic rocks were intruded by a composite batholith of tonalite and granodiorite, and minor quartz monzonite and Since, the tonalite suite rocks granite (tonalite suite). (GLTZ; Sims, 1991). contain a penetrative foliation associated with recumbent folding (D1), this suite is pre- to early syn-deformation. Both the volcanic section of the greenstone belt and the tonalite suite formed during active north-directed subduction prior to collision along the GLTZ. Continental collision along the GLTZ resulted in progressive deformation of the volcanic-plutonic arc about 2700 Ma. Development of the magmatic arc ended with the onset of largescale north-directed recumbent folding (D1) that was followed by upright folding (D2) and development of shear zones (D3). A trondhjemite to granite suite occurs as intrusive stocks and plugs both interior and exterior to the volcanic section. Intra-belt stocks and rhyolite dikes are aligned subparallel to axes of F1 and F2 folds but cut by shear zones. The trondhjemite to granite suite is syn- to late-upright folding. A hornblendite-diorite-syenite suite occurs as scattered weakly foliated pipe-like to stock-sized bodies. While relative age with respect to the trondhjemite to granite suite is not established in the field, we interpret this suite as with large scale shear zones (D3) that define boundaries of lithostratigraphic blocks within the volcanic section. Both trondhjemite to granite and hornblenditediorite-syenite suites were emplaced during collision along the GLTZ. A late granite suite is found throughout the area and consists of massive rocks cutting foliated rocks. These rocks are the youngest Archean granitoid rocks and are posttectonic with respect to collision along the GLTZ. coeval 12 �In the the Canadian Canadian portion portion of of the the southern southern Superior Superior Province, Province, Sutcliffe (1991) Sutcliffe (1991) has identified identified aa temporal temporal progression progression of of granitoid granitoid rocks. rocks. A foliated foliated tonalite tonalite suite suite is is related related to to arc arc construction subduction. Syntectonic tonalite construction during during subduction. Syntectonic foliated foliatedtonalite was emplaced emplaced during during collision. collision. Granite to to granodiorite, granodiorite, Granite diorite diorite to to syenite syenite and and two-mica two-mica granite granite suites suites are are latelate- to to post-tectonic. Temporal progression post-tectonic. progression of Archean Archean granitoid granitoid rocks rocks in in the the Ishpeming Ishpeming greenstone greenstone belt belt and vicinity vicinity is is comparable comparable to to the the southern southern Superior Superior Province Province as as aa whole. whole. This partially funded Michigan Geological This research research was was partially funded by the the Michigan Geological Survey, Survey, U.S. Geological Geological Survey Survey (COGEOMAP), (COGEOMAP),and and Western Western Mining Mining Corporation Corporation (USA). (USA). REFERENCES REFERENCES CITED CITED Sims, P.K., P.K., 1991, 1991, Great Great Lakes Lakes tectonic tectonic zone zone in in Marquette Marquette area, area, Sims, Michigan Implications for for Archean Archean tectonics tectonics in in Michigan -- Implications Geological Survey Survey north-central United United States: U.S. Geological Bulletin Bulletin 1904-E, 1904-Elp. p. E1-E17. El-E17. Sutcliffe, R.H., R.H., 1991, 1991, Archean Archean plutonic plutonic rocks rocks in in the the southern southern Sutcliffe, Superior Superior Province: Province: Magrnatism Magmatism during arc-construction arc-construction and and arc-accretion: arc-accretion: Minnesota Minnesota Geological Geological Survey Survey Information 34, p. p. 16-22. 16-22. Information Circular Circular 34, 1 1 Present Present address: address: Department Department of of Geosciences, Geosciences, Pennsylvania Pennsylvania State State University, University, University University Park, Park, PA PA 16802 16802 2 Present (USA), Marquette, Present address: address: Western Western Mining Mining Corporation Corporation(USA), Marquette, MI MI 49855 49855 13 �Gravity Model of the Wolf River Batholith Daniel J. Brehm and C. Patrick Ervin, Dept. of Geology, Geology, Northern Northern Dekalb, IL Illinois University, DeKalb, IL 60115 60115 Jeffrey K. K. Greenberg, Wheaton College, College, Wheaton, Wheaton, IL IL 60187 60187 Recently acquired gravity data has more extensively extensively delineated the approximately -30 -30 mGal Bouguer Bouguer gravity gravity anomaly anomaly associated with the Wolf River Batholith, which outcrops outcrops in in northeast northeast Wisconsin. Wisconsin. This anomaly is is superimposed superimposed on on the the Wisconsin Gravity Gravity Minimum, Minimum, aa -60 -60 mGal mGal Bouguer Bouguer gravity gravity anomaly anomaly over the the Wisconsin Wisconsin Arch. Arch. The gravity field shortfield was upward continued to to eliminate eliminate shortwavelength, shallow shallow anomalies that that tend tend to to mask the the field field associated associated with with the the batholith. batholith. A second filter filter was applied applied to to minimize the affect of the Wisconsin Arch in the area minimize the affect &IL,,C .A~SCGGS~Z in the area associated associated with the the Wolf River River Batholith. Batholith. 7 1 - Modeling of the the filtered filtered gravity gravity field field indicates indicates that that the batholith has a variable thickness, averaging between between 1.5 1.5 and and 2 km thick. thick. This model supports the conclusions of Anderson Anderson (1980), who proposed on on the basis of of geochemical data, data, that the batholith was emplaced at relatively relatively shallow shallow depths depths (less (less than 4 km), and that it is fairly thin (less (less than than 55 km km thick). thick). The model also also suggests suggests that that the the batholith batholith does does not not extend extend far far past its its western, western, eastern, eastern, and and northern northern outcrops, outcrops, but but does does extend extend a considerable considerable distance distance in in the the subsurface subsurface beyond beyond its its southern southern boundary. boundary. Although the Wisconsin Gravity Minimum reaches reaches its its most most negative value over the batholith, batholith, the the Wolf River River Batholith Batholith is is not fully coincident with nor the the sole sole cause cause of of the the Wisconsin Wisconsin Minimum. Minimum. REFERENCES REFERENCES Anderson, J.L., J.L., 1980, 1980, Mineral Equilibria and Crystallization ~recambrianWolf River Conditions in in the Late Precambrian River Rapakivi Rapakivi Massif, isc cons in, Amer. Amer. Jr. Jr. Sci., Sci., v. v. 280, 280, p. p. 289—332. 289-332. Massif, Wisconsin, 14 �Textural Textural and and Compositional Compositional Study Study of of aa Manganiferous Manganiferous Iron-Formation, Iron-Formation, Emily Emily District, with Implications Implications for for Original District,Cuyuna Cuyuna Range, Range, with Original Deposition Deposition and and In Situ Situ Leaching of ofManganese Manganese Susan Brink, Geologist Susan E.E. Brink, Geologist U.S. Bureau Bureau of ofMines Mines The U.S. Bureau Bureau of of Mines Mines is is conducting conducting geologic geologic and and geochemical geochemical The U.S. characterization iron-formation of characterization studies studies on on drill drillcore corefrom fromthe themanganiferous manganiferous iron-formation of the Emily Cuyuna to determine whetherin in situ Emily District, District, CuyunaIron IronRange, Range, Minnesota Minnesota to determine whether situ izedtotorecover recoverhigh-grade high-grademanganese manganese solutions leach mining techniques can can be beutil utilized solutions from low-grade low-grademanganese manganese ore. ore. In this units of the manganese-oxide-bearing thisstudy, study,three threelithologic 1 i tho1 ogic units of the manganese-oxide-bearing ironironformation were and consist thinlybedded, bedded, chert-hematite formation wereidentified identified and consist of aa thinly chert-hematite ironironlaminated, fine-grained to thickly thicklybedded, bedded, granular, variably formation; a well laminated, granular, variably sandy, manganese-oxide-hematite-goethite manganese-oxide-hematite-goethiteiron-formation iron-formationthat that contains interbeds interbeds of manganese-oxide-bearing oolitic to and aabasal basal unit unitofof manganese-oxide-bearing oolitic tosandy sandy chert. chert. of chert; chert;and The of well-rounded, The presence presence of well-rounded, terrigenous quartz-sand-grains; quartz-sand-grains; hematitic hematitic and and manganese-oxide granules; a variety containingcombinations combinations manganese-oxide granules;and and a varietyof ofoolite-types oolite-types containing of suggest aa near of quartz, quartz, hematite, hematite, and and manganese-oxide manganese-oxide suggest near shore shore depositional depositional environment for the the granular granular subunits subunits of of the iron-formation. environment for iron-formation. The average assay assay grade <0.1 %% Mn, grade of the the three threeunits unitsis is <0.1 Mn,11.4 11.4%%Mn, Mn,and and 10.1 10.1 % % Mn, Mn, respectively. respectively. The The manganese manganese minerals minerals identified identified in in the the Emily Emily district district are are manganite, mangani te, crypton'ielane, hollandite, cryptomel ane, holl andi te, braunite, brauni te, and and 11 iithiophorite. thiophorite. Microscopic textural re1 ationshipsand and microanalysis microanalysis of the the composition composition Microscopic textural relationships of ore ore and and gangue gangue mineralogy situleach leach of mineralogyare areimportant importanttotothe the success successofof in in situ mining. mining. The The leach leach fluid fluidmust must be be able able to to access, access, selectively solubilize solubilize manganese, andand then transport it itutil izing the natural permeability permeabil ity of of the therock. rock. manganese, then transport utilizing Manganese mineralization is Manganese mineralization is strongest strongest in in the the granular granular facies of the the ironironfades of formation, formation, likely likely because because of of higher higher intergranular intergranular porosity porosity and and higher higher permeability permeability than than in in the the finely finely bedded bedded to to laminated laminated nongranular nongranular strata. strata. rep1replaced aced original chert granul ar Manganese-oxides commonly havehave Manganese-oxides commonly original chertmatrix matrixof of the granular fades. facies. Preliminary Prel imi nary experimental experimental data on on similar simi1 armanganiferous mangani ferous rocks to to date date have shown utions selectively dissolveMn Mn from from rocks rocks ininwhich which have shownthat that aqueous aqueousSO,-so1 SO-solutions selectively dissolve fine-grained and iron-oxidesare areintimately intimately mixed, mixed, as as in the fine-grainedmanganese-oxides manganese-oxides and iron-oxides the Emily rocks. rocks. Porosity/permeability Porosi ty/permeabi 1 i tydata dataononcore coresamples samples from from the theEmily Emilysuggest suggest thatleach leachsolutions solutions should morefavorably favorably access manganese-oxidesfrom fromthe themore more that should more access manganese-oxides granular strata of of the theiron-formation iron-formationthan than from from strata strata of ofwell-laminated, we1 1-1 aminated,very very granular fine-grained iron-formation iron-formation or chert. chert. 15 �The the Spirit The Petrology petrology and and Geochemistry Geochemi stry ofof the SpiritVolcanogenic Vol canogenic Massive Massive Sulfide Sulfide Prospect, Prospect, North-Central North-CentralWisconsin. Wisconsin. Susan Brink, Geologist* Geologist* Susan E.E. Brink, University UniversityofofMinnesota Minnesota The The Spirit Spiritzinc-lead-copper zinc-lead-coppervolcanogenic volcanogenic massive massive sulfide sulfide prospect prospect is is located massivesulfide sulfide district district ofof ananEarly Penokean located within withinthe theSomo Somo massive EarlyProterozoic Proterozoic Penokean volcanic-magmatic volcanic-magmatic terrane terrane in in north-central north-central Wisconsin. Wisconsin. A A petrographic petrographic and and geochemical studyofof the the lithologic was geochemical study lithologicpackage package that thathosts hoststhe thesulfide sulfide wasmade. made. Four majorinterbedded interbeddedrock rockunits unitswere wereidentified identifiedand andinclude includetholeiitic tholeiitic mafic Four major mafic and caic-alkaline felsic felsic volcaniclastic and calc-alkaline volcaniclastic pyroturbidites, pyroturbidites, felsic felsicfragment-rich fragment-rich According to data data from from trace traceelement el ement debris debri s flows, fl ows,and andminor mi normeta-carbonate. meta-carbonate. According discrimination the finely nature of discriminationdiagrams diagrams and and the finelybedded bedded nature of the the rocks, rocks,the thebimodal bimodal submarine volcanicswere wereerupted eruptedinin an an island-arc island-arc tectonic submarine volcanics tectonic setting settingand andwere were deposited distally from deposited subaqueously, subaqueously, distally from the the eruptive eruptivecenter, center,perhaps perhapsininaaback-arc back-arc basin. basin. Regional dynamothermal metamorphism produced isoclinally folded rocks in i socl i nal ly folded in dynamothermal metamorphi sm produced which the is well well foliated foliated(63°) (63') and and lineated. 1ineated. Prograde Prograde metamorphic metamorphic which the rock rock fabric fabric is mineral reachedthe thestaurolite-quartz staurolite-quartz subfacies mineral assemblages assemblages reached subfacies of ofthe thealmandinealmandineyields aa amphibolite metamorphism. amphi bol i te facies faciesof of metamorphism. Garnet-biotite Garnet-biotitegeothermometry geothermometry yields andsphal sphalerite-pyrrhotite-pyrite maximum temperature between 4100 410' and and 500° 500' CC and eri te-pyrrhotite-pyrite maximum temperature between geobaronietry indicates aa metamorphic pressure of of 55 kb. geobarometry indicates metamorphic pressure kb. The mainsul sulfide-bearing mineralized The main fide-bearing mineral ized horizon horizon is ischaracterized characterizedbybyenrichment enrichment of Ti, Ga, Sc and anddepletion depletion in in Si, Si, Na, of Fe, Fe, Cu, Cu, Pb, Pb, Z, Z,Mg, Mg, Mn, Mn, Ti, Ga, and and Sc Na, K, K, Rb, Rb, Sr, Sr,and and stratiform, stratabound sulfide lens (up 9.3m m thick) thick)isisdeveloped developed Ba. The The stratiform, stratabound sulfide (up to to 9.3 Ba. in schist which occurs below belowaachloritized chloritized mafic schist. The in aa muscovite-quartz muscovi te-quartz schist which occurs schist. The felsite occurring above the chloritized mafic schist contains quartz-pyrite felsite occurring above the chloritized mafic schist contains quartz-pyrite laminae (0.5 (0.5 cm cm thick) thick) with with low base base metal metal content. content. These These laminae laminae are are laminae solely on on the the rare earth Based solely earth interpreted as as being being aa hydrothermal hydrothermal exhalite. interpreted exhalite. Based element pattern of samples et al. felsic samplesand andthe themodel model proposed proposed by by Campbell Campbell et a1. element pattern of 33felsic (1984), laminae may 1 aminae maybe be genetically geneticallycapable capable (1984), the felsic fel sicunit unitwith withthe thequartz-pyrite quartz-pyrite of significant massive sulfide deposit. of hosting hosting an an economically economically significant massive sulfide deposit. *presently asaa geologist geologist at the the U.S U.S Bureau Bureau of of Mines, Mines, Twin Twin Cities Cities *Presently employed employed as Research Center, 5629 Minnehaha Minnehaha Ave. Mi nneapol is, Research Center, 5629 Ave. S., S., Minneapolis, MN 55417 55417 MN 16 �PROCESS PROCESS RATES RATES DURING MIDCONTINENT MIDCONTINENT RIFTING: CLUES CLUES TO TO THE THE ORIGIN ORIGIN OF OF THE THE MIDCONTINENT MIDCONTINENT RIFT RIFT SYSTEM SYSTEM William F. Cannon, U.S. U.S. Geological Survey, Survey, Reston, Reston, VA VA 22092 22092 Two developments developments in in recent recent years, the the acquisition acquisition of of deep deep seismic seismic reflection reflection profiles (Cannon (Cannon and others, 1990) 1990) and and the the determination determination of of aa precise geochronologic framework framework (Davis (Davis and Sutcliffe, Sutcliffe, 1985; 1985; Palmer Palmer and and Davis, Davis, 1987; Davis and Paces, 1990), make it possible to study quantitatively quantitatively processes related to to the the Midcontinent rift system system (MRS). (MRS). One step step in in these these studies is to estimate estimate rates rates of of processes. processes. This paper presents the the results results of of calculations which place considerable considerable constraint constraint on process some simple calculations process models models by comparison comparison to rates of younger and modern processes, helps and, by helps clarify clarify the the nature nature and and cause cause of of rifting. rifting. Subsidence Subsidence rate: Because numerous stratigraphic stratigraphic horizons horizons that that can can be be traced traced on on subsidence curves can be drawn. Figure seismic sections are precisely dated, subsidence Figure 1 shows a curve determined for the western Lake Superior region near near the the rift rift axis. Subsidence Subsidence accelerated accelerated for for the the 15 15 m.y. m.y. during which which the the voluminous voluminous basalts were erupted but then abruptly slowed slowed near the the end end of of volcanism volcanism and and continued at a slower slower rate for for at least several several tens tens of million million years years during during postrift sedimentation. sedimentation. The average subsidence subsidence rate rate during during volcanism volcanism was was about 1.3 1.3 mm/yr but may have exceeded 5 mm/yr during the the most rapid rapid subsidence subsidence toward the the close close of of volcanism. volcanism. During sedimentation, subsidence averaged only a few tenths tenths of of aa millimeter millimeter per per year year at at most. most. Macma Macnna generation aeneration rate: rate: For For the the entire entire rift rift II estimate estimate that that roughly roughly 2x106 2 x 1 0 ~km3 km3 of volcanic rocks rocks were were erupted. erupted. A comparable comparable amount of intrusive rock was probably emplaced within km3 within and and at at the the base base of of the the crust, crust, so so about about 4xl06 4x10~ km3 of of basaltic magma magma was3generated was generated in in about about 15 15 m.y. m.y. generation rate rate is is basaltic The magma generation 3 /yr. thus about about 0.25 0.25 km km /yr. thus Average eruption eruption rate rate was was about about 0.13 0.13 km3/yr. km3/yr. The eruption Eruption rate: Average eruption rate rate with time, time, but but that that is difficult difficult to to quantify quantify my have changed significantly with the older older flow sequences sequences which which because of incomplete incomplete preservation of the originally extended well beyond their their present present outcrop outcrop belts. belts. The Portage Portage Lake Volcanics, which probably erupted from a single center center near near the the end end of of Volcanics, volcanism, had an eruption eruption rate rate as as high high as as 0.2 0.2 km3/yr. k~n~/~r. Extension rate: Extension rate: A common common estimate estimate of the present extension across the rift in the Lake Superior region is about about 50 km. km. The The rift rift probably probably closed closed about 30 km during later compression, so so original original extension extension was was probably probably about about 80 80 km. km. Assuming that extension coeval, I calculated the extension extension extension and volcanism were coeval, rate averaged averaged 55 mm/yr. Com~arisonto to younger vounaer processes: processes: One of the most features of the the Comparison most striking features rift is the great volume volume of basalt produced in in aa relatively relatively short short time. time. The average eruption rate of 0.13 0.13 km3/yr is about about half half of of the the peak peak production production rate for Columbia River River basalts, basalts, which which maintained maintained that that rate rate for only only about 0.5 0.5 m.y., m .y., and about one—fourth one-fourth the average eruption rate of the Deccan basalts, probably the most rapidly erupted basalts of the Phanerozoic (Baksi, (Baksi, 1988). the However, the eruption rate for the Portage Lake Volcanics matched that of the Columbia River River basalts basalts and and was was half half that that of of the the Deccan. Deccan. Because basalts were Columbia probably being erupted from other centers synchronously synchronously with the Portage Lake, 17 17 �the the MRS, MRS, toward toward the the end end of of its its volcanic volcanic phase, phase, may may have have matched matched or or exceeded exceeded The eruption eruption rate rate for for the the Portage Portage Lake Lake the eruption eruption rate rate of of the the Deccan. Deccan. The the Volcanics Volcanics was was about about twice twice the the modern modern rate rate of of the the Hawaiian Hawaiian hotepot hotspot (Swanson (Swanson 1972), 1972), the the most vigorously vigorously erupting erupting volcanic volcanic center center of of the the modern modern earth. earth. There for the the volcanism volcanism of of the the MRS, MRS, and and There are are clearly clearly no no modern modern analogs analogs for only only rarely rarely in in earth earth history history have have continental continental flood flood basalts basalts been been erupted erupted at at rates comparable comparable to to the the MRS. MRS. On On the the modern modern earth, earth, the the only tectonic tectonic setting setting rates in in which basaltic magma is is generated generated at at rates rates comparable comparable to to the the MRS MRS is is ridge 2,000 2,000 km km long long (about (about the the length length of of the the MRS) MRS) midocean ridges. ridges. AA ridge midocean spreading spreading at at aa rate rate of of 55 cm/yr cm/yr produces produces about about 0.7 0.7 km3/yr km3/yr of of basaltic basaltic magma, magma, or or about 33 times times the the production production rate rate of of the the MRS. MRS. However, However, the the extension extension rate rate for for about the the MRS MRS is is an an order order of of magnitude magnitude less less than than such such aa ridge. ridge. The The MRS, MRS, therefore, therefore, was to 44 times times more more productive productive of of magma magma per per unit unit of of extension extension than than are are was 33 to modern midocean midocean ridges. ridges. modern These These relationships relationships require require that that the the mantle mantle beneath beneath the the MRS MRS was was much much hotter hotter than than mantle mantle beneath beneath modern modern midocean midocean ridges ridges in in order order for for great great volumes volumes of magma magma to to have have been been generated generated during during extension. extension. They They are are consistent consistent with with of origin origin of of the the MRS MRS magmatism magmatism in in response response to to the the arrival arrival of of the the head head of of aa new new mantle mantle plume plume beneath beneath the the region region at at about about 1.1 1.1 Ga. Ga. The The great great burst burst of of basaltic basaltic volcanism, volcanism, but but the the limited limited time time span span for for it it and and related related extension, extension, represents represents the the time time required required to to dissipate dissipate the the anomalous anomalous amount amount of of thermal thermal energy energy in in the the plume head. head. plume Postvolcanic sedimentation: sedimentation: Figure Figure 11 illustrates illustrates the the marked marked difference difference in in Postvolcanic subsidence subsidence rate rate during during volcanism volcanism from from that that during during later later sedimentation sedimentation and and implies implies that that the the sedimentary sedimentary rocks rocks of of the the Oronto Oronto Group Group and and younger younger sequences sequences were not not deposited deposited in in an an active active rift. rift. The The rate rate of of development development of of the the were sedimentary sedimentary basin basin is is consistent consistent with with the the rate rate of of subsidence subsidence caused caused by by decay decay of of the the rift-generated rift-generated thermal thermal anomaly anomaly in in the the mantle, mantle, augmented augmented by by isostatic isostatic compensation compensation of of loading loading by by the the sedimentary sedimentary fill, fill, and and does does not not require require postvolcanic extension. extension. Although Although thick thick accumulations accumulations of coarse, nearly nearly postvolcanic massive conglomerate, conglomerate, such such as as the the Copper Harbor Conglomerate, are generally massive assumed to to be be evidence evidence for for extensional extensional uplift uplift of of adjacent adjacent highlands, highlands, the the assumed sedimentation rate rate is is not not extreme extreme and and may may not not require require active active tectonism. tectonism. As As sedimentation indicated by ages ages of of underlying underlying Portage Portage Lake Lake Volcanics Volcanics and and interlayered interlayered flows indicated flows the accumulation accumulation rate rate of even even the the coarsest coarsest (Davis and Paces, 1990), the (Davis conglomerates was was about about 11 mm per per 5,000 5,000 yr. yr. The The continued continued supply supply of of coarse coarse conglomerates alluvium alluvium during during more more than than aa kilometer kilometer of of sedimentation sedimentation likewise likewise does does not not require require extension, extension, and and could could have been accomplished by isostatic isostatic renewal of original rift-flank rift-flank uplifts uplifts during during their their erosional erosional destruction. destruction. original References References Cited Cited Baksi, A.K. A.K. 1988, 1988, Estimation Estimation of lava extrusion and magma production rates of Baksi, two flood flood basalt basalt provinces: provinces: Journal Journal of of Geophysical Geophysical Research, Research, v. v. 93, 93, p. p. two 11809-11815. 11809—11815. Cannon, W.F., W.F., in in press, The Midcontinent rift in the Lake superior superior region with Cannon, emphasis emphasis on on its its geodynamic geodynamic evolution: evolution: Tectonophysics. Tectonophysics. Cannon, W.F., W.F., Green, Green, A.J., A.J., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, B. B. Milkereit, Milkereit, B., B., Behrendt, Behrendt, Cannon, J.C., Halls, Halls, H.C., H.C., Green Green J.C., J.C., Dickas, Dickas, A.B., A.B., Morey, Morey, G.B., G.B., Sutcliffe, Sutcliffe,R., R., J.C., 18 �and Spencer, C., C., 1990, 1990, The The North American Midcontinent rift rift beneath beneath Lake Lake Superior Superior from from GLIMPCE GLIMPCE seismic seismic reflection reflection profiling: Tectonics, Tectonics, V. v. 8, 8, p. p. 305—332. 305-332. Davis, D.W., J.B., 1990, 1990, Time Time resolution resolution of of geologic geologic events events on on the the D.W., and and Paces, Paces, J.B., Keweenaw Keweenaw Peninsula Peninsula and and implications implications for for the the development development of of the the Midcontinent rift rift system: system: Earth Earth and and Planetary Planetary Science Science Letters, Letters, v. v. 97, 97, p. p. 54—64. 54-64. Davis, D.W., D.W., and and Sutcliffe, Sutcliffe, R.H., R.H., 1985, 1985, U—Pb U-Pb ages ages from from the the Nipigon Nipigon plate plate and and northern northern Lake Lake Superior: Superior: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 96, 96, p. 1572—1579. 1572-1579. p. Palmer, H.C.,, and Davis, Davis, D.W., D.W., 1987, 1987, Paleomagnetism Paleomagnetism and and U-Pb U—Pb geochronology geochronology of H.C., and of Michipicoten Island——precise of the the Keweenawan Keweenawan polar polar wander Island~precisecalibration of track: Precambrian Precambrian Research, Research, v. v. 37, 37, p. p. 157—171. 157-171. Swanson, D.A., volcano: Science, v. D.A., 1972, 1972, Magma Magma supply supply rate rate at at Ki].auea Kilauea volcano: v. 175, 175, p. p. 169—172 ACE (MA) 1110 0 1090 1100 5 1080 1070 1060 1050 I 10 —' o z20 2 25 RIFlING RIFTING AND MAGMATISM MAGMATISM I I— Al Z i k SUBSIDENCEE AAND ND I SEDIMENTATION 1 Figure Figure 1. 1. Subsidence Subsidence curve curve for for the the axial axial region region of of the the Midcontinent Midcontinent rift rift beneath beneath Lake Lake Superior. Superior. Solid Solid circles circles identify identify stratigraphic stratigraphic horizons horizons for for which precise U-Pb radiometric ages are known (Cannon, in press). which precise U—Pb radiometric ages are known (Cannon, in press). 19 �ISOTOPE AND ISOTOPE AND PALEOMAGNETIC PALEOMAGNETIC DATING OF WEATHERED GRANITE GRANITE BELOW BELOW ThE IN NEILLSVILLE, WISCONSIN THEPRECAMBRIAN-CAMBRIAN PRECAMBRIAN-CAMBRIAN CONTACT IN Lung S. Chan Chan & & Zachary Zachary Kostalek Kostalek Department of Department of Geology Geology Universityofof Wisconsin-Eau Wisconsin-Eau Claire, Claire, Eau Eau Claire, WI University WI 54701 54701 Richard L. L. Hay Hay Department Departmentof of Geology Geology University of Illinois, Illinois, Urbana IL 61801 University of IL 61801 The Precambrian-Cambrian (PC-C) is represented represented by a nonconformity nonconformity (PC-C) contact in central Wisconsin is between the the Upper Upper Cambrian Cambrian Mount Mount Simon Simon Sandstone Sandstone and and the the late lateProterozoic Proterozoiccrystalline crystallinerocks. rocks. In Neillsville, the the section below the contact is a 3 m thick zone of of weathered weathered granites. granites. Petrographic Petrographic of the weathered weathered granite overprinted by diagenetic studies of granite show show that that the the pre-Mt. pre-Mt. Simon Simon paleosol is overprinted reactions with pore fluids from the Mt. Simon Sandstone [Hay and Liu, 1991]. The abundance in fluids Mt. and Liu, 19911. authigenic K-feldspar in in the the paleosol paleosol is is attributable attributable to widespread hydrological hydrological events that that occurred authigenic occurred in the Valley during during the mid- and late Paleozoic. Potassium-argon dating the Upper Upper Mississippi Mississippi Valley dating of of an an ilhitic clayand and authigenic authigenic K-feldspar in in the the altered granite illitic clay granite within within22 meters metersof of the thePC-C PC-Cin inNefflsville Neillsville yielded, respectively, respectively, 38529 385±9 Ma and 411±10 411±1Ma Ma ages. ages. These These ages are are compatible compatible with with previously previously reported ages of potassic diagenesis in the Upper Mississippi Valley [Hay et al., 1988; Lee Lee and ages of potassic diagenesis the Upper Mississippi Valley [Hay et al., values of of the illitic clay and K-feldspar are not in f i 1 8 0 values K-feldspar are in equilibrium, equilibrium, Aronson, 1991]. 19911. Measured Measured 6180 suggesting a probable probable higher higher diagenetic diagenetic temperature of the the K-feldspar K-feldspar than of the the illitization. illitization. have conducted a paleomagnetic study to to determine determine ififthe theweathered weathered granite granite was remagnetized We have during the diagenesis. block samples samples were were collected collected from from three three quarries in diagenesis. Eighteen Eighteen oriented oriented block Neillsville. At At least least four four 1" 1" diameter diameter xx 7/8" 7/8" length length specimens were were prepared prepared from from each each sample. sample. NRM NRM intensity measurements, measurements, thermal demagnetization, demagnetization, and alternating field field demagnetization demagnetization were were conducted at at the theInstitute InstituteofofGeomagnetism Geomagnetismand andRock Rock Magnetism Magnetism at at the theUniversity Universityof of Minnesota. Minnesota. progressively (Help from the UM UM Magnetics Group is gratefully acknowledged.) The samples were progressively 650° at 10°C 10° increments 80 demagnetized at temperatures up to 650°C incrementsand and in in alternating alternating fields up up to 80 milliteslas and 10 10 mT increments. Principal Principal component component analysis analysiswas wasconducted conducted to to delineate linear segments from from the the measurement results. For For samples samplesthat that do do not not yield linear segments, segments measurement results. segments, the magnetization step step before before aa substantial drop in NRM intensity isis used used as the magnetization substantial drop NRM intensity the representative representative direction. Orthogonal Orthogonal vector projections are used to help the component analysis. The acceptability of the results results from from individual individual blocks blocks is based on on the thefollowing followingcriteria: criteria: (1) stability stability of the magnetic magnetic component component upon demagnetization, demagnetization, of the the demagnetization demagnetization method as indicated by the the reduction reduction of NRM intensity NRM intensity (2) efficiency of during the demagnetization, demagnetization, and the same same sample. sample. (3) consistency consistency of magnetic components in specimens prepared from the Thennoremanent curves obtained from thermal demagnetization of the samples samples reveal reveal dominant dominant Thermoremanent 300-350°Cindicating blocking temperatures at about 300-350°C, indicatingilmenite ilmeniteor/and or/and aa titanomaghemite as the principal magnetic magnetic carriers. carriers. About 20% of the specimens do not yield stable NRM principal NRM components components and specimens consistent directions. unstable specimens from from three three blocks blocks do do not show consistent directions. The The large large number number of unstable samples reveals substantial weathering stable weathering effects. The magnetic magnetic components components obtained from the stable samples are present field. field. No No tilt correction correction are not randomly distributed, but but do not cluster about the present surface suggests no major major postpostbeen applied applied to to the the specimens; specimens; the the attitude attitudeof ofthe thePC-C PC-C contact contact surface has been 20 �Proterozoic tectonic rotation rotation of representative directions of the the sites. sites. The representative directions from the acceptable acceptable samples appear to form two general clusters, one with a southwesterly to westerly declination appear to form two general clusters, one with southwesterly declination and and aa second second one with with aa southeasterly southeasterlydeclination. declination. The The first first cluster cluster yields a mean direction direction at at D=263°, D=263', 1=50°, 1=50° and aa virtual 23°; the second cluster yields yields aa mean direction virtual geomagnetic geomagnetic pole at at 1469W, 146¡W23' ; the second cluster direction of D=140°, D=140°1=45°, 1=4S0,and aa pole pole at at125°E, 12S0E,9°. 9'. The two poles are compared to the the paleomagnetic paleomapetic poles poles of stable by Irving Irving [1977]. [1977]. The The first firstcomponent component can can be be interpreted interpreted as stable North North America compiled by as aa late late Proterozoic overprint, as indicated indicated by the the similarity similarity in in paleopole paleopole coordinates. coordinates. A A similar similar magnetic magnetic component in the the1.52 1.52Ga-old Ga-old syenite syenite in Wausau, eastern eastern Wisconsin, [Zich et al., 1986] 19861 component is present present in and in in Keweenawan-age Keweenawan-age mafic mafic dikes in central central Wisconsin Wisconsin [Chan, 1991]. 19911. The The presence presence of ofsimilar similar magnetic components implies aa widespread widespread remagnetization remagnetization event components in in these these rocks rocks plausibly implies event during during the late granite appears appears to be aa magentic component component in the Nefflsville Neillsville granite late Proterozoic. Proterozoic. The The second second magentic Cambrian-age remanent magnetism acquired acquired during Cambrian-ageoverprint, overprint, and and can can be interpreted interpreted as a chemical remanent during the latethe weathering weatheringand andformation formationof of the thepaleosol. paleosol. None None of the components components observed appears appears to to be be latePaleozoic age. Unfortunately, Silurian-Devoniansegment segmentof of the the apparent Unfortunately, the poorly constrained Silurian-Devonian polar wander wander path path ofofstable stableNorth NorthAmerica America renders rendersaaconclusive conclusivecomparison comparison impossible. impossible. Most Most Silurian-Devonian however, show showpaleopoles paleopoles at at high high latitudes latitudes of about 40°. 40° Silurian-Devonianpaleomagnetic results, however, The low latitude therefore, argues against a Devonian latitude of of the the paleopole paleopoleobtained obtainedfrom fromNefflsville, Neillsville, therefore, Devonian remagnetization. remagnetization. References References Chan, 1991, dike swarm: swarm: constraints constraints on thermomechanical 1991, Paleomagnetism Paleomagnetism of Central Central Wisconsin dike thermomechanical model of Midcontinent rift, Inst. Inst. Lake Lake Superior Superior Geology Geology Proc., Proc., 37th Annual Annual Meeting, Meeting, Eau Eau Midcontinent rift, Claire, WI, WI, 1991; 37, Pt. 1, 1, p. 23. Hay, R.L., M. Lee, Lee, D.R. D.R.Kolata, Kolata,J.C. J.C.Matthews, Matthews,and andJ.P. J.P.Morton, Morton, 1988, 1988, Episodic Episodic potassic potassic diagenesis diagenesis R.L., M. of Ordovician Ordovician tuffs tuffs in in the theMississippi MississippiValley area, Geology, 16, 16, 743-747. 743-747. 1991, Kaolinite was a precursor to diagenetic diagenetic K-feldspar K-feldspar of Paleozoic age in in Hay, R.L., R.L., and J. Liu, 1991, Hay, Wisconsin, Prog. and and Abstr. Clay Mineral. Wisconsin, Mineral. Soc. Soc. 28th 28th Ann. Ann. Meeting, Meeting, Houston, Houston, October 5-10, 1991, 1991, p. 70. 70. N. America America and displaced Irving, E., E., 1979, Paleopoles Paleopoles and paleolatitudes of N. Irving, and speculations about displaced terranes, terranes, Can. Can. J.J. Earth EarthSci., Sci., 16, 16,669-694. 669-694. the Lee, M., J.L. Aronson, Lee, M., and J.L. Aronson, 1991, Repetitive Repetitive occurrence occurrence of ofpotassic potassic diagenesis diagenesisin in the the region of the Upper Mississippi Valley (UMV) Mineral District: implications for a persistent paleoUpper Mississippi Valley (UMV) Mineral District: implications for a persistent hydrological setting settingfavorable favorablefor fordiagenesis, diagenesis,Prog. Prog. and andAbstr. Abstr. Clay Clay Mineral. Mineral. Soc. Soc. 28th 28thAnn. Ann. hydrological October 5-10, 1991, 1991, p. 98. 98. Meeting, Houston, October Zich, C., C., L.S. L.S. Chan, and P.E. P.E. Myers, Myers, 1986, 1986, Preliminary Preliminary paleomagnetic the Wausau Wausau Zich, paleomagnetic results results from the syenite complex, complex, central centralWisconsin, Wisconsin, EOS, EOS, Trans., syenite Trans., 67, 266. 21 �Implications of and Magnetic Magnetic Anisotropy Anisotropy Studies Studies for the the Penokean Penokean Implications of Strain and Upper Michigan Michigan Orogeny, Upper Davidson, John John C. C. Palmquist, Palmquist, Lawrence Lawrence University, Appleton WI, WI,54912 54912 Mark E. Davidson, This Thisstudy study applies appliesgeometric geometricstrain strain analysis analysisand and magnetic magnetic anisotropy anisotropy techniques techniquesto to the the Michigamme Michigamme Slate to to constrain constrain the the kinematics kinematics of of the thePenokean Penokean Orogeny. Orogeny. The The Michigamme MichigammeSlate Slate(Baraga (BaragaGroup, Group,Marquette MarquetteSupergroup) Supergroup)of of Upper UpperMichigan Michiganisispresent presentinin the of the the 1.88 Ga Penokean Penokean Orogeny. Orogeny. Our data the allochthon allochthon and parautochthon parautochthon of 1.88 Ga data was was collected collected within the allochthon on a 15 15 mile traverse traversefrom fromCovington, Covington,MI MIto tothe thesouth south along highway M-95. Early Early sedimentary sedimentary rocks of the Marquette Supergroup were were deposited deposited on on aa passive passive continental continental margin. Post Postpassive-margin passive-marginrifting riftingwas wasfollowed followedby by rapid rapidsubsidence subsidenceand andthe the deposition of turbidites turbidites from two two source source areas: areas: aa volcanic volcanic arc to the the south, south, and and aa deposition continental source to the north north (Barovich, (Barovich, 1989). 1989). These These turbidites are contained in the Michigamme Slate of Michigan and the correlative Thomson Thomson Formation Formation of of Minnesota. Minnesota. The The allochthon is characterized by tight upright upright to to overturned overturned folds folds with with steep steepaxial-plane axial-plane cleavage dipping 54° 5 4 to S6°W. S6'W. Iron-carbonate Iron-carbonate concretions concretions are are pancake-shaped, pancake-shaped, and and flattened in the plane of cleavage. The Theparautochthon parautochthon exhibits exhibits significantly significantly less less intense intense folding, extended ellipsoids ellipsoids on on the the cleavage cleavage plane. plane. The folding, and mineral grains form vertically extended The Michigamme of 53%, compared to to a (maximum) value value of of Michigamme Slate Slate exhibits exhibits a mean shortening of 64% for for the the Thomson Thomson Formation Formation (Hoist, (Holst,1985). 1985). Strain data measurements measurements from the 64% Michigamme Michigamme Slate Slate overlap overlap those those for for the the Thomson Thomson Formation Formation for for comparable comparablelocales localesin inthe the orogen (Figure (Figure 1). 1). Our Ourstrain straindata datashows showsthe the pancake pancakeshape shapeof of the the concretions, concretions,which which we we interpret as the result of of an an homogeneous homogeneouspure pureflattening flatteningstrain strain(x(x:: yy::z == 1.0: 1.0 :1.0 1.0 ::0.2). 0.2). In the northern area of the Thomson Formation, Formation, Holst Hoist (1985) (1985) finds finds xx : yy :: z = 1.5: 1.5 : 1.0: 1.0 : 0.2. 0.2. The TheThomson ThomsonFormation's Formation'sstrain strainellipsoid ellipsoidhas hasstrong strongvertical vertical extension extension accompanied accompanied by by flattening. flattening. Preliminary Preliminarymagnetic magnetic anisotropy anisotropy (ams) (am) axial axial orientation orientation values indicate indicate maximum maximum at at N20°W @55°. This N 2 0 T 055'. Thisisisnearly nearlyperpendicular perpendicular to to the the cleavage cleavage plane, and and hence hence the the maximum maximum extension extension found found through through our our strain strain analysis. The Theintermediate intermediateand and minimum minimumams amsdirections directions fall very close to the cleavage plane. plane. The The ams ams strain strain intensity intensity values were were found found to to be very minor when compared to the data from the concretions. concretions. As indicated in Figures 11 and 2, the the ams ams data data is is aa major major underestimation underestimation of the strain strain amount amount found found within the Michigamme Michigamme Slate. The Theams amsdata, data,shown shownmore more clearly clearly in in Figure Figure 2, can be seen to exhibit little indication strain: magnetic anisotropy does not appear appear to to correlate correlate with with conventional conventional strain strain of strain: anisotropy in either the Thomson or or Michigamme Michigamme Formations. Formations. We found good correlation with Davidson's ams values for the the Thomson Thomson Formation, but neither ams study exhibits exhibits correlation correlation with with the the strain strain observed observedthrough through conventional conventionalstrain strainanalysis. analysis. 22 �_____,1985; Davithori/Palmquist ams 0 Hoist strain analysis N L Davidzoxt/Pa1mqiist strain o D.M. Davidson ams Hoist's strain strain area area Davidson/P almLquist strain area 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 c2-c3 Figure Figure1: 1:Logarithmic Logarithmicdeformation deformationplot. plot. N '.4 cz-c3 Figure Figure2: 2: Logarithmic Logarithmicdeformation deformationplot plotshowing showingthe theams amsdata datapoints. points. References: References: Barovich, Barovich,K.M., K.M., et.al., et.al., 1989; 1989;Nd Nd isotopes isotopesand andthe theorigin originof of 1.9-1.7 1.9-1.7Ga GaPenokean Penokean continental continentalcrust crust of the Lake Superior region: Geological GeologicalSociety Society of of America America Bulletin, Bulletin, v. v. 101, 101,p. p. 333-338. 333-338. Borradaile, Borradaile,G.J., G.J., 1988; 1988;Magnetic Magnetic susceptibility, susceptibility, petrofabrics and strain: Tectonophysics, Tectonophysics, 156, 156, p. p. 1-20. 1-20. Davidson, Jr., Davidson,D.M. D~M. Jr., 1990; 1990;Magnetic Magneticsusceptibility susceptibilityanisotropy anisotropyand andstrain, strain,Thomson Thomson Formation Formation(Proterozoic), (Proterozoic),Minnesota: Minnesota: Institute Instituteon onLake LakeSuperior SuperiorGeology Geology Proceedings, Proceedings,Abstracts, Abstracts,v.v.36, 36,p.p.17-18. 17-18. Hoist, Hoist,T. T. B.,1989; B.,1989; The ThePenokean PenokeanOrogeny Orogenyin in Minnesota Minnesotaand and Upper UpperMichigan: Michigan:aa comparison comparisonof of the the structural structuralgeology geologyof ofthe theMichigamme Michigammeand and Thomson Thomson Formations: 35, Formations:Institute Instituteon onLake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,Abstracts, Abstracts,v. v. 35, p. 27-28. 27-28. p. _______, 1985;Implications Implicationsof of aa large large flattening flattening strain strain for for the origin origin of aa bedding-parallel bedding-parallel foliation ThomsonFormation, Formation,Minnesota: Minnesota:Journal Journal of foliation in in the the early Proterozoic Thomson of Structural StructuralGeology, Geology, v. v. 7, 7,p. p. 375-383. 375-383. 23 �MAGINO, THE THE MAKING OF A MINE MAGINO, Anthony Anthony J. J. Deevy Deevy Muscocho Muscocho Explorations Explorations Ltd. Ltd. Box 209 Box 209 Dubreuilville, Ontario 1BO Dubreuilville, Ontario POS POS 1BO ABSTRACT Gold Mine is Wawa, Ontario. The is located located 38 38 miles NE of of Wawa, Ontario. The Magino Gold There was limited limited gold gold production production in in the the late late thirties. thirties. The The present present operation operation was was officially officially opened opened in in October October 1988. 1988. It is a 700 700 ton ton per per decline accessed day decline accessed mine with ore ore coming coming from from several several small small blastblasthole hole and and shrinkage shrinkage stopes. stopes. The host for for the the gold gold is is the the Webb Lake Lake Granodiorite Granodiorite Stock Stock which which was was intruded intruded into into the the Coudreau Goudreau Deformation Deformation Zone. Zone. The The ENE ENE striking striking deformation zone zone overprints deformation overprints the the generaly generaly EW EW striking striking isoclinally isoclinally folded sedimentary rocks rocks which the east-end east-end of of folded volcanic and sedimentary which make up the Michipicoten Greenstone the Michipicoten Greenstone Belt. Belt. The The ore-shoots ore-shoots are are controlled controlled by by dilatancy associated dextral dilatancy associated with the the Goudreau Goudreau Deformation Deformation Zone. Zone. Shearing, bleaching and with the Shearing, and silicificatioon silicificatioon occured occured with the gold gold emplacement. emplacement. The history of of exploration exploration and and present present operation operation are are discussed. discussed. 24 �PRELIMINARY PRELIMINARY REPORT, GEOLOGY AND GEOPHYSICS OF THE TERRA/PATRICK TERRAJPATRICK #7-22 WILDCAT WILDCATHYDROCARBON HYDROCARBON TEST, TEST, MIDCONTINENT MIDCONTINENTRIFT, RIFT,KEYSTONE KEYSTONE TOWNSHIP, TOWNSHIP, BAYFIELD BAYFIELD COUNTY, COUNTY, WISCONSIN WISCONSIN Albert B. B. Dickas, Dickas, Department Department of of Geology, Geology, University University of of Wisconsin-Superior, Wisconsin-Superior,Superior, Superior, Wisconsin, 54880-2898 54880-2898 The Terra/Patrick TerraJPatrick #7-22 borehole, borehole, located located in in the the southwest southwest quarter, quarter, northeast northeastquarter, quarter, Section 22, Township 47 north, Range Range 6 west, is being being drilled drilled as as aajoint joint venture venture between Terra Energy, Energy, Inc. Inc. of of Traverse Traverse City, City, Michigan Michigan and and Patrick Patrick Petroleum Petroleum Company of Jackson, Michigan, Michigan, operating under a farmout arrangement arrangement from Amoco Amoco Production Company (USA). This well-site is situated approximately 5 miles northeast Production Company (USA). This well-site situated approximately 5 miles northeast of the Hazel Hazel Hills Hills site announced announced by byAmoco Amocoininthe theSpring Springofof1985. 1985.This This latter latter borehole borehole was never drilled because of a lack of existing exploration drilling legislation and the never because a lack of existing exploration drilling mid-1980's decline in crude mid-1980's decline crude oil oil value. value. The Terra/Patrick TerraIPatrick borehole was spudded spudded shortly shortly after after midnight, midnight,March March9, 9,1992. 1992. The The state-issued state-issued permit allows allows drilling to to 6000 6000 feet, with restrictions restrictions concerning concerning control controlof of mud chemistry additives, casing standards, and analyses analyses of cuttings. Extensive Extensiveand and involved public hearings were conducted in Bayfield Bayfield County prior to the the issuance issuance of of the drilling drilling permit. permit. This borehole, a central rift horst test, will be the fourth conducted conducted along alongthe the Midcontinent Midcontinent Rift Rift System System since since 1984. 1984. The The first first (Kansas, (Kansas,1984) 1984) drilled aa reversed reversed rift rift sequence sequence caused caused by by faulting. faulting. The Thesecond second(Iowa, (Iowa,1987) 1987) tested tested the the western, western, halt-graben half-graben flank of the the rift. rift. The The third, third, also also aa flank flank test, test, was was initiated initiated in in the the Upper UpperPeninsula Peninsulaof of Michigan All have have failed failed to to find hydrocarbon Michigan in in 1987. 1987. All hydrocarbonreserves. reserves. The Bayfield County (Chequamegon) (Chequamegon) prospect prospect isis seismically seismically identified identifiedas as aa large largefourfourway anticlinal structure caused caused by by drag folding along the hanging wall of the Douglas anticlinal structure Douglas fault fault (Fig. (Fig.I). I). The anticline, with an axis that parallels the strike of the Douglas Douglas fault, fault, extends over aa surface surface area area of of approximately approximately 37,000 37,000 acres (60 (60 square square miles) miles) and andhas has several thousand feet of structural closure. Reservoir Reservoir quality strata are being sought in all three units which comprise comprise the Oronto Oronto Group Group of of volcaniclastic volcaniclastic rocks--oldest rocks--oldestto to youngest, the Copper Copper Harbor, Harbor,Nonesuch, Nonesuch, and andFreda Fredaformations. formations. Depending upon upon the the final final drilling drilling outcome outcome (see (see note note below), below), additional additionalinformation informationwill will Depending be be available available at the time time of of presentation presentationof of this this report. report. At the time time this this abstract abstractwas was prepared prepared(March (March24, 24,1992), 1992), the subject subject borehole borehole was was drilling an injunction action, action, filed filed on behalf of drilling in in excess excess of of 3500 3500 feet. Simultaneously an the Lac Lac Courte Courte Oreilles Oreilles band band of of Chippewa Chippewa Indians, Indians, was in its third day of of testimony testimony in in the Dane Dane County County (Wisconsin) (Wisconsin) Circuit Circuit Court. Court. 25 �FIGURE1.1. FIGURE CHEQUAMEGONPLAY PLAY SCHEMATIC SCHEMATIC CHEQUAMEGON Ereda SS J- ... -. :::1orteae LktVotcaics BasalNonesuch NonesuchSand Sandand andCopper CopperHarbor HarborFm. Fm. RESERVOIR- - Basal RESERVOIR SOURCE- SOURCE NonesuchShale Shale Nonesuch SEAL- SEAL 26 NonesuchShale Shale Nonesuch 26 �PRECAMBRIAN PRECAMBRIAN HYDROCARBON HYDROCARBON POTENTIAL POTENTIAL OF OF THE THE WESTERN WESTERN GREAT GREAT LAKES LAKES Albert B. B. Dickas, Dickas, Department Department of of Geology, Geology, University University of Wisconsin-Superior, Superior WI, 54880, and Wl, 54880. and M. M. G. G. Mudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geologicaland andNatural NaturalHistory HistorySurvey, Survey,Madison, Madison,WI, Wl, 53705. 53705. Hydrocarbon Hydrocarbonshows showshave havebeen beenreported reportedininthe thewestern westernGreat GreatLakes Lakessince since1852. 1852. Occurrences Occurrences include include stained stained core, surface exposures, and indigenous shows shows in in mine mine roof roof strata. strata. All All emanate emanate from from aa single single source, source, the the Nonesuch NonesuchFormation Formation(maximum (maximumage age of Ga) of of the Oronto of 1.074 1.074 Ga) Oronto Group, Group, Keweenawan Keweenawan Supergroup, Supergroup, aa(Midcontinent) (Midcontinent)rift rift derived, derived, middle middle Proterozoic Proterozoic volcaniclastic sequence. Indirect Indirectage-dating age-dating(Rb-Sr) (Rb-Sr) indicates indicateslive live oil oil hosted hostedby bythe theNonesuch NonesuchFormation Formationhas hasa aminimum minimumage ageofof1.047 1.047Ga. Ga. Nonesuch NonesuchFormation Formation distribution distribution along along strike strike is is mapped mappedfor for 300 300km, km,from fromthe theUpper Upper Peninsula WI/Mn border. border. Borehole Peninsula of Michigan to within 30 km of the WIIMn Boreholestratigraphic stratigraphic studies studies suggest suggest lateral lateral deposition deposition into into rift rift flank flank basins. basins. Reflection Reflectioncorrelations correlationsindicate indicate source source rock rockthickness, thickness,measured measuredininoutcrop outcropas asmaximum maximum215 215 meters, meters, to to be betectonically tectonically controlled. controlled. Anticlinal, Anticlinal, drag dragfolding, folding,unconformity, unconformity, and andfault fault trap trap structural structural geometries geometries are are seismically seismically identified. Stratigraphic Stratigraphictrapping trappingmay maybe beassociated associatedwith withvarying varying depositional depositionalenvironments. environments. lntergranular Intergranularporosity porosityexceeds exceeds1313percent, percent,with withfracture fracture porosities porositiescommon. common. Recognizedanticlinal anticlinal closure is of aa scale scale defined defined by by seismic seismic profile profile spacing spacing Recognized approximating km, extending to to two-way-travel two-way-traveldepth depth of of 33 to to 44 seconds. Field approximating 88 to to 10 10 km, Field studies studies suggest suggestprimary primaryreservoirs reservoirs would would be bespatially/time spatiallyltimeassociated associated with with crustalcrustalextension, thermal events. events. Secondary Secondaryhydrocarbon hydrocarboncharges chargesinto intoaxial axial and and flank flank extension, domains domains may may have have been beencontrolled controlledby bysubstitution substitutionof ofcompression compressionfor forextension extension tectonics, causing causingstabilization stabilization of of oil oil and andgas gasaccumulations accumulationsprior priorto toinitiation initiationofof tectonics, Phanerozoic Phanerozoic time. Maturation Maturationanalyses analysesfavor favor gaseous gaseous over over liquid liquidreservoirs. reservoirs. 27 �t 4 m a . 0 Precambrian bedrock @ Phanerozoic bedrock m Boreholes . 1 . 5km Northwestthickening thickening • Northwest synriftcolumn column synrift (seismic) (seismic) i-r fl LI. ' Southeasterlythickening thickening • Southeasterly synriftcolumn column(core (coreand andseismic) seismic) synnft Non-fluorescing NonesuchFm. Fm. Nonesuch • 8 Non-fluorescing organicassemblage assemblage organic Lineargravity gravitytrend trend • d Unea Diffusegravity gravitytrend trend Diffuse Ouluthgabbro gabbrooutcrop outcrop Duluth Northerlythickening thickening , • Northerly synriftcolumn column synnft (outcropand andseismic) seismic) (outcrop fluorescingNonesuch NonesuchFm. Fm. • Fluorescing organicassemblage assemblage organic • ri-r I I l .U...L . a8 . -- \ Boundary Boundarycentral centralriftriftstructure structure Southerlythickening thickening Southerly synriftcolumn column synrift [\T xwn (seismic) (seismic) • down DisturbedOronto OrontoGroup Group Disturbed sequence sequence ' / Location of of hydrocarbon hydrocarbon test test boreholes boreholes Location drilled in Wisconsin through 1992. drilled in Wisconsin through 1992. 1 ~valuatio*criteria criteria Evaluation pertaining to the the pertaining to hydrocarbon (HC) hydrocarbon (HC) potential of of the the potential Lake Superior basin Lake Superior basin segment of the segment of the Midcontinent Rift Rift Midcontinent System. System. Reservoir Reservoir - Reservoir-quality Reservoir-qualitystrata stratawWiin withinCopper CopperHarbor Harbor Conglomerate, Nonesuch and Freda Conglomeratel Nonesuch and FredaFormations Formations - Oronto OrontoGroup Groupintergranular intergranularporosity porosityranges rangesfrom from7-15% 7-15Y0 - - I Passive Passive EvaluationCriteria Criteria Evaluation % '1 / Maturation Maturation Geothermalgradient gradientwithin withinnormal normaltotohigh highrange range - Geothermal Oilseeps seepsparaffinic, paraffinic,low lowininsulfur, sulfur,and and32° 32OAPI API - Oil - Migration Migration PrincipalProterozoic Proterozoicstructure structureininplace placeatattime timeofof - Principal migration primary migration by Earlyextension-phase extension-phasemigration migrationfollowed follow~d bylater later - - Early compression-phasemigration migration compression-phase Crudefound foundintergranular intergranularand andalong alongfractures fractures - Crude - 1 Active Active Each rift rift unit unit in Lake Lake Superior Superior basin. basin. Each Differentiation of Midcontinent rift in for HC potential must be individually evaluated individually evaluated for HC potential. Source Source NonesuchFormation: Formation:—1.074 -1 -074Ga Gaininage age --Nonesuch 1.5%, White Pine Mine, Michigan TOC averages 1 .WO, White Pine Mine, Michigan - TOC averages 1 Accommodation Accommodationstructure structure 1 1 1 , Structure - Two stage tectonic s-tr$tzage tectonichistory historycreated createdmultiple multiplestructure structure combinations combinations - - Structures Structuresinclude includefold, fold,fault, faultland andstratigraphic stratigraphictraps traps Seal seal - shale/ ill isis60/40 - Lake LakeSuperior Superiorregion regionrift riftclastic clasticinfinfill 60140 shale1 sandstone sandstoneratio ratio crystallization - Mineralization Mineralizationseals sealsformed formedby bycalcite calcite crystallization �1991 COGEOMAP COGEOMAP Gravity Gravity Mapping Mapping Program Program in in West-Central West-Central Wisconsin: Wisconsin: 1991 The The Driftless Driftless Area Area C. C. Patrick Patrick Ervin, ErvinI Dept. Dept. of of Geology, GeologyI Northern Northern Illinois Illinois University, Universityf DeKalb, DeKalb! IL IL 60178, 6O17af e-mail: e-mail: T6OCPE1@NIU.BITNET T6OCPEl@NIU.BITNET M.G. M.G. Mudrey, MudreyI Jr, JrI B.A. B.A. Brown, Brownf and and M.L. M.L. Czechanski, Czechanskif Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey, SurveyI 3817 3817 Mineral Mineral Point Point Rd., Rd.! Madison, MadisonI WI WI 53705 53705 During During the the summer summer of of 1991, 19911 nominal nominal one-mile one-mile grid grid gravity gravity coverage 45 degrees degrees coverage was was extended extended to to an an area area bounded bounded by by 44 44 && 45 latitude latitude and and by by 90 90 and and 90.5 90.5 degrees degrees longitude. longitude. Stations Stations are are located 1:24000 located at at surveyed surveyed spot spot elevations elevations posted posted on on USGS USGS 1:24000 topographic topographic sheets. sheets. Northern Northern Illinois Illinois University's University's LaCosteLaCosteRomberg Romberg gravity gravity meter meter G409 G409 was was used. used. Data Data are are tied tied to to the the State State of of Wisconsin Wisconsin Primary Primary Gravity Gravity Base Base Station Station Network Network (Ervin, (Ervin! 1983), 1983)1 which which is i s in in turn turn tied tied to to the the International International Gravity Gravity Standardization Standardization Network-1971 Network-1971 (DMAAC, (DMAAC! 1974). 1974). Older Older data data have have been been merged merged with with these these data data to to yield yield aa much much more more detailed detailed representation representation of of the the Bouguer Bouguer gravity gravity anomaly anomaly field field than than was was previously previously available. available. The The northeast northeast half half of of the the area area is is underlain underlain by by glacial glacial deposits deposits that that are are in in turn turn underlain underlain by by Cambrian Cambrian sedimentary sedimentary rock, rock! primarily primarily sandstone, sandstoneI except except in in the the northeastern northeastern corner, cornerI where where lower rock! primarily primarily granite, granitef underlies underlies lower Proterozoic Proterozoic intrusive intrusive rock, the the till. till. The The southwestern southwestern half half of of the the survey survey area area extends extends into into the the driftless driftless area area and and is is dominated dominated by by the the Cambrian Cambrian sandstone sandstone that that is is covered covered by by the the glacial glacial deposits deposits in in the the northeast, northeastf although although lLower 1Lower Proterozoic Proterozoic and and uupper uUpper Archean Archean rock rock crop crop out out along along several several of of the the river river systems. systems. The The extreme extreme southwest southwest corner corner of of the the area area also also contains contains aa few few remnants remnants of of the the Ordovician OrdovicianPrairie Prairie du du Chien Chien dolomites. dolomites. Much Much of of the the area area is is covered covered by by marsh marsh and and swamp, swampIand and the the surface surface becomes becomes more more dissected dissected as as the the Mississippi Mississippi River River is is approached approached to to the the west. west. In In this this type type of of terrain, terrain, the the road road system system tends tends to to follow follow the the topography topography rather rather than than the the section section lines, linesI so so the the station station distribution distribution deviates deviates significantly significantly from from aa one-mile one-mile grid grid over over much much of of the the area. area. Access Access problems problems were were further further compounded compounded by by the the high high rainfall rainfall during during the the field field season season that that flooded flooded many many roads. roads. We We anticipate anticipate obtaining obtaining supplementary supplementary data data in in these these areas areas in in 1992. 1992. Due Due to to the the dissected dissected topography topography in in the the southwest, southwestI terrain terrain corrections corrections were were applied applied to to the the data. data. The The Bouguer Bouguer gravity gravity minimaf but but ascends ascends in in the the anomaly field field is is dominated dominated by by broad broad minima, anomaly southwest southwest to to values values above above -15 -15 mgals mgals and and in in the the northwest northwest to to over over -20 -20 mgals. mgals. The The field field descends descends below below -80 -80 mgals mgals in in an an east-west east-west trending trending minima minima located located in in the the southwestern southwestern corner corner of of Marathon Marathon County Marshfield. This This minima minima is is flanked flanked on on the the County and and west west of of Marshfield. 29 �north north by by aa fault fault that that separates separates if i f from from aa relatively relatively positive positive anomaly anomaly apparently apparently associated associated with with metamorphosed metamorphosed early early Proterozoic and Proterozoic mafic mafic to to ultramafic ultramafic intrusive intrusive rock rock (Mudrey (~udrey and others, othersf 1982). 1982). AA second second relatively relatively positive positive anomaly anomaly lies lies south south of of the the minima minima in in Wood Wood County. County. The The source source of of this this anomaly anomaly is is not not known. known. REFERENCES REFERENCES Ervin, Ervinf C.P., C.Paf1983, 1983f Wisconsin Wisconsin Gravity Gravity Base Base Station Station Network, Networkf Wis. wise Geol. Geol. and and Nat. Nat. Hist. Hist. Surv. Surv. Misc. Misc. Pap. Pap. 83—1, 83-lf43 43 p. p. DMAAC, North DMAACf 1974, 19741 World World Relative Relative Gravity Gravity Reference Reference Network Network -- North America, Americal DMAAC DMAAC Ref. Ref. Pub. Pub. No. No. 25, 25f 1974 1974 Supplement. Supplement. Mudrey, 1982, biucireyf M.G., bi.GefJr., J r e 1Brown, 8rownf B.A., E.A.~and an6 Greenberg, G r e e n ~ e r gJ.K., ,7.Kef ~ 1982f Bedrock Bedrock Geologic Geologic Map Map of of Wisconsin, Wisconsinf Wis. Wis. Geol. Geol. and and Nat. Nat. Hist. Hist. Surv., Surve1Madison, MadisonfWI. WI. 30 �THE PALISADE RHYOLITE, LAKE COUNTY, COUNTY, MINNESOTA: RHYOLITE, LAKE MINNESOTA: A CRYPTIC CRYPTIC RHEOIGNIMBRITE RHEOIGNIMBRITE IN THE NORTH NORTH SHORE SHORE VOLCANICS VOLCANICS C. Green Green John C. Geology Department, University of Minnesota Duluth Geology Department, The Palisade Palisaderhyolite, rhyolite, > 90 m thick, is one of the most easily easily accessible of the several The large rhyolite rhyolite flows flows in the NSVG. broken up up somewhat somewhat by by faulting, faulting, it large NSVG. Although Although itit has has been been broken can be traced with certainty for 18 km and possibly for 29 km northeast from Beaver can be traced with for 18 k m and possibly for 29 k m northeast from BeaverBay. Bay. In most outcrops it is massive massive and and porphyritic, porphyritic, with with a ffew e w percent percent of 18 quartz, quartz, alkali alkali feldspar, and oxidized and oxidized ferromagnesian ferromagnesian silicate phenocrysts. phenocrysts. Its groundmass groundmass is made made of fine-grained fine-grained feldspar and and flow-aligned flow-aligned tabular tabular quartz quartz paramorphs paramorphsafter afterprimary primarytridymite. tridymite. With alkali feldspar With aa flow flow breccia near near the the top top at lllgen City and folded folded flow-banding flow-banding near the top and bottom, ititlooks looks near the like an unusually and widespread widespread lava lava flow, flow, perhaps unusually large large and perhaps like other highly highly mobile, mobile, high-T high-T silicic lava flows recently silicic recently described described from from various various Tertiary Tertiary and and Mesozoic Mesozoic provinces. provinces. Close petrographic examination examinationofof the the base base and and top, top, however, Close petrographic however, indicates indicates that that the the Palisade rhyolite was was emplaced emplaced as asaahot hotpyroclastic pyroclasticflow flow that that completely welded to Palisade rhyolite t o the the base, base, Bothininthe thelaminated laminatedtop topbreccia brecciazone zoneand and in inthe the and flowed after after welding welding -- aa rheoignimbrite. Both basal meter only, only, thin sections reveal a groundmass groundmass of of welded glass shards. shards. Over basal meter Over aa narrow narrow transition zone of one one or two t w o meters metersabove above the the base base these these shards shards are completely deformed This transition zone until only until only aa fine, fine, planar planar flow flow lamination lamination isis present. present. This zone contains contains strong strong lineations that that show show the the direction direction of of flow after lineations after welding, welding, and and flow-folds, flow-folds, some some isoclinal, isoclinal, are are developed iin the overlying overlying zone. zone. This passes developed n the passes upward into the massive interior that makes makes up the great great bulk bulk of of the flow. the The Palisade Palisade rhyolite rhyolite illustrates illustrates the the necessity necessity of careful petrographic The petrographic as as well well as as field field examination of of the the tops tops and and bases bases of of felsic felsic flows flows in order examination order tto o interpret their origin origin correctly. 31 �Petrology of aa Conglomerate Conglomerate Pacies Facies of of the the Petrology and and Provenance Provenance of Jacobsville Ironwood to to Bergland, Bergland, Michigan Michigan Jacobsville Sandstone: Sandstone: Ironwood Cheryl Cheryl A. A. Hedgman, Hedgmant U.S. U.S. Geological Geological Survey, Surveyt Reston, Restont VA VA 22092 22092 West West of of Lake Lake Gogebic, Gogebict from from Ironwood Ironwood to to Bergland, Berglandt Mich., Michetthe the Late Late Proterozoic Proterozoic (Keweenawan) (Keweenawan) Jacobsville Jacobsville Sandstone Sandstone is is dominated dominated by by conglomerates conglomerates and and coarse coarse lithic lithic arenite arenite in in contrast contrast to to areas areas farther farther east east where where it it is is aa finer finer grained, grainedtsubinature submature to to mature, maturet quartzose, quartzoset feldspathic feldspathic and and lithic lithic arenite arenite with with minor minor shale, shalet siltsiltstone, stonet and and conglomerate conglomerate (Kalliokoski, (Kalliokoskit1982). 1982). This This paper paper presents presents data data indicating indicating aa southern southern source source for for these these western western conglomerates conglomerates and sandstonest which which is is consistent consistent with with aa current current theory theory and coarse coarse sandstones, of of active active thrust thrust faulting faulting south south of of the the Jacobsville Jacobsville along along the the Pelton Pelton Creek Creek fault fault (Cannon (Cannon and and others, otherst 1990; 1990; Sims, Simst 1990). 1990). The The conglomerate conglomerate is is clast-supported clast-supported and and poorly poorly sorted sorted with with aa Clay fills fills most most interstices interstices and and coats coats all all coarse sandy sandy matrix. matrix. Clay coarse grains. The The clasts clasts are are subrounded subrounded to well rounded and range in in grains. ironsize from from 3-15 3-15 cm. cm. Clast Clast lithologies lithologies are are predominantly predominantly ironsize formation ite from from Early Early Proterozoic Proterozoic units formation and and quartz quartzite units and and vein vein quartz quartz from from Archean Archean units. units. Only Only minor amounts amounts of of volcanic volcanic clasts clasts (probably (probably from Keweenawan Keweenawan units) units) are are present. present. Medium to TT1 and TT6 drill to very coarse coarse sandstone sandstone from the TTl cores, corest located located approximately approximately 16 16 km km east east of of Wakefield, Wakefield# were were studied. Two Two general general trends trends can can be seen: 1) 1) a decrease decrease upsection upsection studied. in in mafic and silicic silicic volcanic volcanic clasts clasts believed believed to to be be derived derived from from Keweenawan 2) an increase increase upsection in granitic clasts Keweenawan units units and 2) believed to to be be derived derived from from Archean Archean units. units. Iron—formation Iron-formation clasts clasts believed are rarely rarely seen seen in in the the sand-size fraction fraction making it difficult to to are distinguish distinguish sediment sediment contributed contributed by by Early Early Proterozoic Proterozoic units. units. These These trends trends indicate indicate initial initial erosion erosion through through aa cover cover of of Keweenawan Keweenawan rocks and presumably through Early Proterozoic rocks rocks into the the Archean Archean basement. basement. into Dips Dips within the the western portion of the Jacobsville Sandstone Sandstone range from from 34° 34O NN in range in the the lower lower part part of of the the section section to to 90 g o N in in the the upper upper part, part, excluding excluding areas areas where the the Jacobsville Jacobsville has has been been dragged up up on on the the Keweenaw Keweenaw fault. fault. In In contrast, contrastt most of of the the dragged Jacobsville east east of of Lake Lake Gogebic Gogebic is is relatively relatively flat flat lying. lying. The The Jacobsville fanning fanning nature nature of the the dips west of Lake Gogebic is consistent consistent with with sedimentation sedimentation on on aa fault fault block that that is is rotating rotating to to the the north. north. This This fault fault block rotation was caused by thrust faulting faulting along the fault the Keweenaw fault to the north and the Pelton Creek fault to the the south. south. Uplift and and erosion erosion of Keweenawan, Keweenawant Early Early Protero— Proteroto zoic this fault fault block zoic and Archean units along the southern end of this is the the source source of the conglomerates conglomerates and coarse sandstone in is in the the Jacobsville Sandstone Sandstone west west of of Lake Lake Gogebic. Gogebic. Jacobsville 32 �References References Cited Cited Cannon, Z . E . , and and Sims, Sims, P.K.,l990, P.K.,1990, Structural Structural and and Cannon, W.F., W.F., Peterman, Peterman, Z.E., isotopic isotopic evidence evidence for for Middle Middle Proterozoic Proterozoic thrust thrust faulting faulting of of Archean Archean and and Early Early Proterozoic Proterozoic rocks rocks near near the the Gogebic Gogebic Range, Range, abs. in Institute on Michigan and Wisconsin: Michigan and Wisconsin: abs. in Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedings, V. v. 36, 36, p. p. 11—13. 11-13. Kalliokoski, Kalliokoski, J., J., 1982, 1982, Jacobsville Jacobsville Sandstone: Sandstone: in in R.J. R.J. Wold Wold and and Tectonics of the Lake W.J. W.J. Hinze, Hinze, eds., eds., Geology Geology and and Tectonics of the Lake Superior Superior Basin: Basin: Geological Geological Society Society of of America, America, Memoir Memoir 156, 156, p. 147—155. 147-155. p. Sims, Sims, P.K., P.K., 1990, 1990, Geologic Geologic map of of Precambrian Precambrian rocks, rocks, Marenisco, Marenisco, Thayer, Thayer, and and Watersmeet Watersmeet 15—minute 15-minute quadrangles, quadrangles, Gogebic Gogebic and and Ontonagon Ontonagon Counties, Counties, Michigan, Michigan, and and Vilas Vilas County, County, Wisconsin: Wisconsin: U.S. 1:62,500. U.S. Geological Geological Survey Survey Map Map 1—2093, 1-2093, scale scale 1:62,500. 33 �PETROLOGY OF A A RAPAKIVI BODYFROM FROMEAST-CENTRAL EAST-CENTRALMINNESOTA. MINNESOTA. PETROLOGY AND AND STRUCTURE STRUCTURE OF RAPAKIVIBODY HELLICKSON, Bradly, RADZEVICIUS, Stanley, ANDERSON, Garry,Dept. Dept. of HELLICKSON, Bradly, RADZEVICIUS, Stanley, ANDERSON, Garry, of Earth MNM56301-4498 E a r t h Sciences, Sciences, St. S t . Cloud CloudState S t a t eUniv., Univ.,St.SCloud, t . Cloud, N 56301-4498 AA 10 granitic 10 m. m. wide wide g r a n i t i c dike d i k elocated l o c a t e dini nthe t h eMeridian M e r i d i a nAggregate Aggregate quarryin q u a r r y ' i nWaite Waite Park, has an an east-west east-westsstrike Park, MN, MN, has t r i k e and and ddips i p s to t o the t h e south south at a t aasteep steepangle. angle. This T h i s tabular t a b u l a rbody body isi sbounded bounded on on the t h e north n o r t h and and south south sides sides by by nearly n e a r l y continucontinuous ous parallel p a r a l l e l basaltic b a s a l t i cdikes, dikes, and and isi scrosscut c r o s s c u t by by aa small small basaltic b a s a l t i cdike d i k e with with V a r i a b l e sized s i z e d basaltic b a s a l t i c xenoliths x e n o l i t h s are a r e found found within w i t h i n the t h e dike, dike, N60E sstrike. t r i k e . Variable aaN6OE The north n o r t h contact c o n t a c t of o f the t h e dike dike one of o f which which isi s 1 1ni.m. by by 10 10 m. m. ini ndimension. dimension. The one appears besstructural, with appears t to o be tructural, w i t h calcite-filled c a l c i t e - f i l l e dslickensided s l i c k e n s i d e dsurfaces s u r f a c e s within within t h e basalts b a s a l t snear near the t h e contact c o n t a c tand and mineralized m i n e r a l i z e d shears shears containing c o n t a i n i n g epidote e p i d o t e within within the m. The south south ccontact o n t a c t is i s undulatory u n d u l a t o r y with w i t haawave wave length l e n g t h of o f 55tot o1010m. t h e dike. d i k e . The the The The rapakivi r a p a k i v ibody body displays d i s p l a y saaporphyroblastic p o r p h y r o b l a s t i ctexture t e x t u rcomposed e composedofo fpotassium potassium feldspar by minor minor amounts amountso fofbbiotite f e l d s p a rand and quartz q u a r t zaccompanied accompanied by i o t i t e and and saussuritized saussuritized T e x t u r a l l ythe t h epotassium potassium feldspar f e l d s p a r grains g r a i n s at a tthe t h emargin marginare are p l a g i o c l a s e . Texturally plagioclase. (. 1-.5 cm), cm), do donot n o tdisplay d i s p l a yobvious obviousconcentric c o n c e n t r i claminations, l a m i n a t i o n s , and and are are small (.1-.5 small As the t h e center c e n t e r of.the o f . t h ebody bodyisi approached, s approached, the t h epotassium potassium feldspar feldspar anhedral. As anhedral. grains g r a i n s increase increaseini nsize s i z (.3—2.1 e (.3-2.1 cm), cm),become become subhedral subhedral to t o euhedral euhedral and and display display cores aare obvious concentric c o n c e n t r i c laminations. l a m i n a t i o n s . Often Often times times small small anhedral anhedral cores r e vvisible. isible. obvious An An aphanitic a p h a n i t i c matrix m a t r i xcomprises comprises 45-55 45-55 percent p e r c e n t of o f the t h eRapakivi Rapakivibody. body. The The matrix matrix consists c o n s i s t s of o fvermicular v e r m i c u l a r quartz q u a r t z either e i t h e rimming r rimminglarge l a r g epotassium potassium feldspar f e l d s p a r or or q u a r t z grains g r a i n s or o risi completely s completelynetworked networked with w i t hsmaller s m a l l e rpotassium potassium feldspar feldspar quartz g r a i n s forming forming aa granophyric granophyric texture. t e x t u r e . The The remainder remainder of o f the t h ematrix m a t r i xis icomposed s composed grains mm) sstrained t r a i n e d qquartz u a r t z ggrains, r a i n s , aaltered l t e r e d feldspar f e l d s p a r and and bbiotite. iotite. o f small small (less ( l e s sthan than .2.2mm) of Also present p r e s e n t are a r e accessory accessory mminerals i n e r a l s such asas a l lallanite, a n i t e , zzircon, i r c o n , eepidote, p i d o t e , chlorite chlorite Also such and calcite. c a l c i t e . The The llatter a t t e r three t h r e e are a r e confined c o n f i n e d to t o regions r e g i o n s of o f fracture f r a c t u r e or o rshear. shear. and Shearing is i sextremely extremelycommon common aat t aalll l scales scalesand andappears appears to t ohave haveplayed p l a y e da adominant dominant Shearing r o l eini nthe t h edevelopment development of o f this t h i sbody. body. Metasomatic Metasomatic aactivity c t i v i t y during d u r i n g the t h eshearing shearing role process may may have e a d to t o the t h edevelopment development of o fboth b o t hthe t h eobserved observedmineral m i n e r aassemblage l assemblage process have llead and the t h e Rapakivi Rapakivi ttexture e x t u r e displayed d i s p l a y e d iinn this t h i srock r o c kbody. body. and 34 �Provenance of the Animikie Group, Nd and and Pb isotopes Provenance Group, NE Minnesota, based on Nd S. R. Hemming, Hemming, S. S. M. M. McLennan, McLennan, and and G. G. N. Hanson, ESS, ESS, SUNY SUNY Stony Brook, NY Nd and Pb isotope data (Fig. 1, 1, Fig. 2) on samples from the Animikie Group in the northern margin margin of of the the Animikie Animikiebasin basin from from an an early early Mesabi Range reflect the progression of the northern near-shoreline facies near-shoreline facies with northern northern sources, sources, to a later relatively relatively deep-water facies with with sediments sediments derived from rising mountain ranges to to the the south southassociated associatedwith withthe thePenokean Penokeanorogen. orogen. Based Based on on derived facies analyses, the northern shoreline of the Animikie basin is interpreted to have been near the facies analyses, basin is interpreted to have been near the Pokegarna Quartzite Quartzite and and Biwabik Biwabik present northern northern margin of the basin during deposition of the Pokegarna Iron-formation by argillite argililte with with some some thin, thin, Iron-formation [1,2]. The Theoverlying overlying Virginia Virginia Formation is dominated by very fine [3]. Throughout infrequent,thin, thin,olive olive green greentuff tuff fine graywacke intervals [3]. Throughout the interval are infrequent, horizons. horizons. Lucente Lucenteand andMorey Morey[3] [3]interpret interpretthe thedeposition depositionof of the the Virginia Virginia Formation Formation to to have have been been dominantly dominantlyfrom frompelagic pelagicprocesses processes in in aa relatively relatively deep-water deep-water environment. in central Minnesota was studied studied by The petrogenesis of early Proterozoic mafic rocks in rocks are are arc-related. arc-related. The Pb and Nd isotopic isotopic Horan et al. [4], [4], who concluded that these rocks compositions associated granitic granitic plutonic plutonic compositionsof of these these mafic mafic rocks rocks are are the same as the geographically associated 1850Ma Mafor forthese theserocks rocksisisdominantly dominantly00to to -3, -3, with with depleted depleted mantle mantle model rocks [5]. [5]. The The CNd EN^ atat1850 model the sources for these rocks have evidence of a LREE Therefore ages of 2.1 to 2.4 Ga [4,5]. to 2.4 Ga [4,5]. Therefore rocks have evidence of enriched history LREE enriched enriched component [4,5]. [4,5]. The initial initial enriched history or or were were contaminated contaminated by an old, LREE isotope composition rocks precludes precludesthe the Superior Superior Pb isotope composition of the K-feldspars from the granitic rocks Province as as the thecontaminating contaminatingcomponent component[51. [51 Spencer [5] suggested that these are mantle mantle Province characteristics or that there is a contribution from the early Archean rocks of the Minnesota River characteristics the early Archean rocks of the Minnesota River of central central Minnesota Minnesota Valley terrane. The TheNd Nd isotopic isotopiccompositions compositions are included in the field of magmatic rocks in the general field of magmatic rocks in in Fig. 11 and and the the Pb Pb isotopic isotopic compositions compositions are included in Penokean magmatic rocks in Fig. 2. Van Penokean VanSchmus Schmusand andBickford Bickford[6] [6]and and Greenberg Greenberg and and Brown Brown that the early Proterozoic igneous rocks of the Wisconsin magmatic terrane are also [7] suggested [7] suggested Proterozoic also arc-related. The ThePb Pbisotopic isotopiccomposition compositionof ofearly earlyProterozoic Proterozoicrocks rocks from from Wisconsin Wisconsin [8] [8] are are included in rocks in in Fig. 2, and the the field field Nd isotopic included in the the general general field of Penokean magmatic rocks compositions at 1850Ma Ma [9] [9] are are shown in Fig. 1. compositions at 1850 1. = -10.5 at A silty unit of lower lower Pokegama Quartzite Quartzite from Midway, Minnesota has hasENd EN^ = 1850 Ma GaGa slope in in 2O7PbI2O4Pb 1850 Ma (Fig. (Fig.1)1)and and22whole wholerock rocksamples sampleslieliealong alonga 2.6 a 2.6 slope 2Wb1204Pb vs 206pb/204pbspace, space,consistent consistentwith withthe theinterpretations interpretationsof ofaaSuperior SuperiorProvince Provincesource source based based on 206PbPmPt) petrology [1] and whole wholerock rocksamples samples[lo]. [10]. Both Both Nd Nd (Fig. 1) and Pb [I] and Pb isotopes from quartz and petrology (Fig. 2) isotopes isotopesfrom fromthe theBiwabik BiwabikIron-formation Iron-formationappear appearto torecord recordaamixture mixture of of early early Proterozoic and of Gerlach et al. Proterozoic and Archean sources. This This is is consistent consistent with the Nd isotope data of [11]. [I 11. Two Twocore coresamples samplesfrom fromthe theupper upperslatey slatey member member (location (location22 of of the Mesabi Mesabi Deep Deep Drilling Drilling Project) from -6atat 1850 1850Ma Ma(Fig. (Fig.1). 1). The intermediate Project) from the the Biwabik Biwabik Iron-Formation have ENd EN^ ofof-6 intermediate slate from 1850Ma Maofof-3, in from the the MINTAC MINTAC mine, mine, which which Morey Morey [1] [I] interpreted as a tuff, has ENd EN,^ atat1850 -3, in the range rocks from fromcentral centralMinnesota. Minnesota. Ten Ten sedimentary sedimentary (he range of the the early Proterozoic igneous rocks samples samples from fromthe the Virginia Virginia Formation Formationfrom from location 2 of the Mesabi Deep Drilling Project Project have have Nd 1850Ma Maofof2.8 2.8and and3.2 3.2(Fig. (Fig. 1). 1). All EN^ at at1850 1850Ma Maofof-0.9 -0.9toto+0.3, +0.3,and andtwo twotuffs tuffshave haveENd EN^ atat1850 Virginia a 1.8 GaGa slope in 2O7PbI2O4Pb space(Fig. (Fig.2). 2). The The a 1.8 slope in 207PbPPb vs vs2O6Pb/2O4Pb 206Pb/204Pb space Virginiasamples sampleslielieclose closetoto data preclude substantial contributor contributorto tothe theVirginia VirginiaFormation. Formation. The preclude the the Superior Superior Province as a substantial early Penokean magmatic early Proterozoic Proterozoicsource source indicated indicated by the the data, which is suggested suggested to be the Penokean magmatic terrane to the the south south of of the Animikie Animikie basin, is consistent consistent with the evolution of the Animikie Animikie basin basin as a foredeep foredeepresulting resulting from from Penokean Penokean orogenesis orogenesis [12]. [12]. 35 �References: References:[1] [l]Morey, Morey,G.B., G.B.,1972, 1972,MN MNGeol. Geol.Sur. Sur.Centennial CentennialVol., Vol., p.p.204; 204; [2] [2] Ojakangas, Ojakangas,R.W., R.W., 1983, 1983, Geol. Geol. Soc. Soc. America AmericaMem. Mem. 160, 160, p. 49; 49; [3] [3] Lucente, Lucente, ME., M.E., and andMorey, Morey,G.B., G.B., 1983, 1983,MN MN Geol. Geol. Sur., Sur., Report Report of Investigations Investigations28; 28;[4] [4]Horan, Horan, M.F., M.F., Hanson, Hanson, G.N., G.N., and and Spencer, Spencer, K.J., K.J., 1986, 1986, Precambrian PrecambrianResearch, Research,v.v. 37, 37, p. p. 323; 323;[5] [5]Spencer, Spencer,K.J., K.J., 1987, 1987,unpublished unpublished Ph.D. Ph.D. thesis, thesis. SUNY SUNYStony Stony Brook; [6] [6] Van Van Schmus Schmusand and Bickford, J.K., and Brown, B.A., B.A., Bickford, 1981, 1981,in in Precambrian Precambrian Plate Plate Tectonics, Tectonics, Elsevier, p. 261; [7] Greenberg, J.K., 1983, P.K., and Delevaux, M.H., M.H., 1984, Economic 1983,GSA GSA Mem. Mem. 160, 160,p. 67; 67; [8] [8] Afifi, A., A., Doe, B.R., B.R., Sims, P.K., Geology, Geology,v.v.79, 79,p.p.338; 338;[9] [9]Barovich, Barovich,K.M., K.M., Patcheti, Patchett, P.J., P.J., Peterman, Peterman, Z.E., and Sims, P.K., P.K., 1989, 1989,GSA GSA Bul., E.J., and Mezger, K., Bul., v.v. 101, 101,p.p.333; 333;[10] [lo]Hemming, Hemming,S. S,McLennan, McLennan, S.M., S.M., Hanson, Hanson, G.N., Krogstad, E.J., K., 1990, (abs) EOS, v.71, v. 71,p.p.654; 654;[11] [ l l ]Gerlach, Gerlach, D.C., D.C., Shirey, Shirey, S.B., S.B., and and Carlson, Carlson, R.W., R.W., 1988, 1988, (abs) (abs) EOS EOS vol. vol. 69, P.L., 1988, MN MN Geol. Geol. Sur. Sur. Report Report of 69, p. 1515; 1515;[12] [12]Southwick, Southwick, D.L., Morey, Morey, G.B., G.B., and McSwiggen, P.L., Investigations Cosmochim. Acta, v. 50, p. Investigations37; 37;[13] [13]Shirey, Shirey, S.B., S.B., and and Hanson, Hanson, G.N., 1986, 1986, Geochim. et Cosmochii. 2631; 2631; [14] [14] Stile, Stille,P., P.,and andClauer, Clauer,N., N.,1986, 1986,Geochim. Geochim.etetCosmochim. Cosmochim.Acts, Acta,vol. vol. 50, 50,p.p.1141; 1141;[15] [15] Jacobsen, M.R., 1988, Geophys. Research Research Letters, v. v. 15, p. 393; [16] Gariepy, Jacobsen,S.B., S.B., and andPimentel-K.lose, Pimentel-Klose, M.R., Gariepy, C., and andAllegre, Allegre,C.J., C.J., 1985, 1985,Geochim. Geochim.et etCosmochim. Cosmochim. Acts, Acta, v. 49, p. 2371. 2371. 0.1 0.0 —0.1 —0.2 z —0.3 U) —0.4 WMT —0.5 —0.6 —15 central MN —10 0 —5 Nd 5 10 in the Mesabi Range. Fig. 11 Plot PlotofoffSm/Nd fSm@Jdvs. vs. eNd &N(I at at 1850 1850 Ma for samples of the Animikie Group in Fig. is the deviation of 1Nd/14Nd from fSmNd is Sm/Ndfrom fromCI CIchondrite chondriteand andCNd EN^ is deviation of 143Nd/^Nd fromCI CI fSm/Nd isthe the deviation deviation of Sm/Nd chondrite chondrite in in parts per 10,000. PP == Pokegaxna Pokegama Quartzite, B == Biwabik Biwabi Iron-formation, Iron-formation, and and V == Virginia Virginia Formation. M= Range Supergroup samples [9].additional For additional reference, the M= Marquette Marquette Range Supergroup samples [9]. For reference, the fields forfields late for late .. Archean central Minnesota Minnesota [4,5] and Archean Superior SuperiorProvince Province rocks rocks [13], [13], early Proterozoic plutonic rocks hfrom m central Wisconsin Wisconsin[9], [9],and andGunflint GunflintIron-formation Iron-formationfrom fromOntario Ontario[14,15] [14,15] are areshown. shown. 36 �65.0 14 16 18 20 22 24 26 28 30 32 34 36 38 40 60.0 55.0 CQ 50.0 C 45.0 C'2 40.0 35.0 17.5 17.0 16.5 C / tuffs (1774+/-62 Ma) 16.0 15.5 N C CQ 15.0 14.5 14.0 14 16 18 20 22 24 26 28 30 32 34 36 38 40 206 Pb/ 204 Pb Fig. 22 Pb Pbisotope isotopeconpositions conpositionsof ofsamples samplesfrom fromthe theAnimikie AnimikieGroup Groupin in the the Mesabi Mesabi Range. Range. The Thesame same Fig. symbolsapply applyasasininFig. Hg. 1.1. a)a)Plot Plotofof2O8Pbi2O4Pb 208PbWPb vsvs206PbPmPb. Growth curve is p=8, 4 with tics ticsatat symbols 2O6Pbf2O4Pb. Growth curve is j=8, ,4,,with 100Ma Ma intervals. intervals.b)b)Plot Plotofof2O7Pb/2O4Pb 207PbPMPb vs 206PbPaPb. Growth 8 with 100Ma Ma 100 vs 2O6Pb/2O4Pb. Growthcurve curveisispj=8 with tics tics at at 100 intervals.For Forreference, reference,fields fieldsincluding includingfeldspar feldsparand andwhole wholerocks rocksfor forlate lateArchean Archean latelate-totopostpostintervals. kinematicplutonic plutonicrocks rocksofofthe theSuperior SuperiorProvince[16] Province[16]and andearly earlyProterozoic Proterozoicplutonic plutonicrocks rocksof ofcentral central kinematic Minnesota[4,5], [4,5],and andfeldspar, feldspar,galena, galena,and andwhole wholerocks rocksfrom fromboth bothvolcanic volcanicand andplutonic plutonicrocks rocks Minnesota fromwisconsin(WMT) (WMT)[8] [8]are areshown. shown. fromWisconsin 37 �EXPLORATION EXPLORATION AND MINING MINING ACTIVITIES ACTIVITIES OF OF INDUSTRIAL INDUSTRIALMINERALS MINERALSIN IN NORTHWESTERN NORTHWESTERNONTARIO ONTARIO ....................................... Hinz, Hinz, P. P. and and Lucas, Lucas, R. R. T., T. , MINES MINES AND AND MINERALS M I NERALS DIVISION, D I V I SI ON, ONTARI 0 ONTARIO MINISTRY M I N I STRY OF OF NORTHERN NORTHERN DEVELOPMENT DEVELOPMENT AND AND MINES, MINES, THUNDER THUNDER BAY BAY ....................................... The The "Northwestern Northwestern Ontario O n t a r i o Industrial Industrial Minerals Minerals Program" Program" was was initiated, i n i t i a t e d , in in 1987, as aa province-wide 1987, a s part p a r t of of province-wide strategy s t r a t e g y to t o stimulate s t i m u l a t e development development of of Ontario' Ontario1ss industrial i n d u s t r i a l mineral mineral resources resources and and related r e l a t e d manufacturing manufacturing industries. industries. The Industrial The Industrial Minerals Program Minerals Program provides provides assistance a s s i s t a n c e to t o prospectors p r o s p e c t o r s and and industry i n d u s t r y by by conducting conducting property p r o p e r t y visits, visits, sample preparation, s amp1e preparation, analyses and analyses and discussion d i s c u s s i o n r e l a t i n g t o t h e industrial industrial mineral mineral industry. industry. relating to the There There are a r e over o v e r 50 50 industrial i n d u s t r i a l mineral mineral commodities known commodities known to t o occur occur within within Northwestern Ontario. Northwestern Ontario. Current Current production includes: production includes: two quarries two quarries producing almost producing almost 1,000,000 1,000,000 tons t o n s of of railway r a i l w a y ballast b a l l a s t material; m a t e r i a l ; two two granite granite dimension dimension stone s t o n e quarries quarries producing producing blocks blocks and and slabs s l a b s of of pink pink granite g r a n i t e for for use u s e as a s monument monument and and dimension dimension stone; s t o n e ; aa t h i r d dimension dimension stone s t o n e quarry q u a r r y will w i l l start start third production p r o d u c t i o n in i n April A p r i l 1992 1 9 9 2 and and produce produce rough blocks rough blocks and and slabs s l a b s of of green green granite; one quartz granite; one quartz q u a r r y which which quarry produced produced 17,000 17,000 tons t o n s of of crushed crushedquartz; quartz; and and one one quarry q u a r r y produced produced 8,000 8,000 tons t o n s of of crushed crushed diabase d i a b a s e for f o r use use in i n soil s o i l erosion erosion proj p r o jects. ects. 38 38 This This poster p o s t e r displays d i s p l a y s current c u r r e n tproducers, producers, sites s i t e s of of advanced advanced exploration e x p l o r a t i o n and and high high potential i n Âormation p o t e n t i a l areas. a r e a s . Detailed D e t a i l e d information on i s available a v a i l a b l e from from on all a l l the t h e properties p r o p e r t i e s is the Resident the Resident Geologists' G e o l o g i s t s t Office O f f i c e in in Thunder ThunderBay. Bay. �Exploration and prospecting is Exploration and prospecting is c u r r e n t l y under way t o e v a l u a t e currently under way to evaluate aa f o r their their number of properties number of properties for dimension s t o n e , g a r n e t , amethyst and dimension stone, garnet, amethyst and g r a p h i t e p o t e n t i a l . graphite potential. . . Northwestern Ontario includes the Northwestern Ontario includes the Resident G e o l o g i s t s t D i s t r i c t s of Resident Geologists' Districts of Kenora, Red Lake, Sioux Lookout, Kenora, Red Lake, Sioux Lookout, Thunder Bay, Bay, Beardmore-Geraldton, Beardmore-Geraldton, and Thunder and Schreiber-Hemlo. Schreiber-Hemlo. The The program is is program j o i n t l y funded funded by by the the jointly 1991 Northern O n t a rio 1991 Northern Ontario (NODA), Development Agreement Development Agreement (NODA), aa s u b s i d i a r y agreement t o t h e Economic subsidiary agreement to the Economic and Regional Development Development Agreement and Regional Agreement (ERDA) s i g n e d by t h e Governments of (ERDA) signed by the Governments of Canada and Ontario. Canada and Ontario. CANADA-ONTARIO CANADA-ONTARIO The project p r o j e c t is i s staffed s t a f f e d by by Peter P e t e r Hinz, Hinz, The G e o l o g i s t , and Robert Lucas, A s s i stant Geologist, and Robert Lucas, Assistant G e o l o g i s t . Geologist. 39 �Thermochronoiogic evidencefor for post-Penokean post-Penokeanunroofing unroofingininthe the Lake Superior Thermochronologic evidence Superior region. Daniel Daniel Hoim, Holm,Dept. Dept.of ofEarth Earthand andPlanetary PlanetarySciences, Sciences, Harvard Harvard University, Cambridge, Cambridge, MA MA 02138 02138 Timothy Hoist, Timothy Hoist,Department Departmentof ofGeology, Geology,University Universityof of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 Daniel Lux, Lux,Department Departmentof ofGeology, Geology,University University of of Maine, Maine, Orono, Orono, ME ME 04469 04469 Introduction. Determining Introduction. Determiningthe thetime, time,amount amountand andnature natureof ofunroofing unroofing of of rocks rocksdeeply deeply buried buried during collision is fundamental to an understanding of of the processes of lithospheric deformation. During the past decade, the construction construction of temperature-time temperature-time histories has become an increasingly important technique for assessing unroofing unroofing histories. histories. Because changes in the cooling history (shown as inflection points on temperature-time curves) are likely to be a reflection of tectonic tectonic events, events, these these data are extremely useful for discerning and and dating dating such such events events as as well well as as for for characterizing characterizing their their history of of ancient orogenic roots is thermal significance. Determining Determining the the post-collisional post-collisional cooling history due to thermal thermal overprinting overprintingassociated associatedwith withyounger youngerevents. events. Such Such has has been been the the commonly difficult due case in the the Precambrian Precambrianof ofMichigan Michiganand andWisconsin Wisconsinwhere where'events' 'events'dated datedatat—1630 -1630 Ma, Ma,—1330 -1330 Ma, and —1140 Mahave havemasked masked the the earlier earlier cooling cooling history Ma -1 140 Ma history of of rocks rocksinitially initiallyburied buriedduring duringthe the—1830—1860 -1830-1860 Ma Penokean orogeny. Here, we present 40ArP9Ar cooling ages from rocks metamorphosed during the Here, we present ^Ar/^Ar ages from rocks Penokean orogeny in east-central east-central Minnesota, an area apparently affected to a lesser extent by these later events. Proterozoic Lakes tectonic tectonic zone, an Archean crustal Proterozoic rocks in east-central east-central MN lie athwart the Great Lakes discontinuity along which alternating discontinuity alternating extensional and contractional events have occurred throughout throughout the Early and Middle Proterozoic. Denham Formation cover rocks (predominantly quartzite and Denham Formation (predominantly dolomite interbedded interbedded with with conglomerate and volcanic volcanic rocks) rocks) were dolomite conglomerate and were deposited deposited on on Archean Archean quartzofeldspathic basement basement (the McGrath quartzofeldspathic McGrath Gneiss) Gneiss) in in an anEarly EarlyProterozoic Proterozoic(2100—1900 (2100-1900 Ma) Ma) to amphibolite amphibolite facies during extensional basin. They Theywere were subsequently subsequently deformed and metamorphosed to Ma), having reached burial depths km. the Penokean Penokean orogeny orogeny(1860—1830 (1860-1830 Ma), depths in in excess excessof of21—25 21-25 km. Several rock rock forming forming 'events' 'events' following following the the Summary of of previous previousgeochronology*. geochronology*. Several Lake Superior Superiorregion. region. These include Penokean orogeny have been identified in the Lake include the formation formation of of a plutonic-volcanic Ma, intrusion intrusion of the Wolf River plutonic-volcanicterrane WIatat—1760 -1760 Ma, River terranein insouth-central south-centraland andnorthern northernWI Ma, and and magmatism magmatism associated with the Mid-continent Batholith at at —1469 -1469 Ma, Mid-continent Rift Rift System Systematat—1100 -1 100 Ma. In MN, post-orogenic granites U-Pb ages ages of of 1770 Ma Ma and and U-Pb U-Pb crystallization crystallization ages ages of of granites yield minimum U-Pb 1812±9 Ma. Ma. Initial 181239 Initial conventional conventional K/Ar K/Ar and and Rb/Sr chronologic data from eastern and central central MN MN were recomputed and summarized in Keighin Keighin et et al. al. (1972 (1972 Centennial CentennialVolume; Volume;MN MNGeol. Geol. Surv.). Surv.). K/Ar K/Ar biotite biotite and and muscovite muscoviteages agesfrom frombasement basementand andcover coverrocks rocks group groupinto intoages ageslargely largelyaround around—1730 -1730 Ma (7 ranging from Ma(6 (6ages agesranging ranging from from 1610-1650 1610—1650Ma). Ma). Rb/Sr dates dates ages ranging from1670—1770 1670-1770 Ma) and —1630 -1630 Ma include 1±18 Ma include errorchron errorchronages agesof of1746±86 17463336Ma Maand and174 1741k18 Maand andbiotite biotiteages agesininthe theinterval intervalofof1750—1740 1750-1740 Ma for the McGrath McGrath Gneiss. Gneiss. There have been several several studies studies using using both the Rb/Sr and Ar/Ar systematics systematics in the the regionally regionally equivalent equivalent rocks of MI and WI. The Theoldest oldestages, ages, generally generally preserved in a belt belt just south south of of MidMidcontinent Rift MaRbISr Rb/Srbiotite biotiteages agesand andone oneAr/Ar Ar/Arhornblende hornblendeplateau plateau age age of of Rift rocks, rocks, are are 1692—1750 1692-1750 Ma 1704 Ma. To Tothe thesouth, south,whole-rock whole-rock Rb/Sr Rb/Sr and and Ar/Ar Ar/Ar biotite ages are reset in response to a regionally regionally recognized but cryptic event at about 1630 1630 Ma. Younger Younger events events superimposed superimposed on on this this regional regional 1630 1630 Ma imprint, Rb/Srand andAr/Ar Ar/Arsystematics, systematics,occur occuratat—1330 -1330 Ma Maand and—1140 -1 140Ma. Ma. imprint,recognized recognizedininboth bothRb/Sr Results of Results of of this this study. study.AAcoarse-grained coarse-grainedamphibolite amphibolite schist schist was sampled at the type locality of the Denham Formation. Coarse well-developed foliation foliation at Coarseamphibole amphibole and and finer-grained finer-grained biotite form a well-developed this locality, the amphibole commonly containing large largeinclusions inclusionsofofplagioclase. plagioclase. A biotite separate of 1754k13 1754±13 Ma. Ma. A hornblende separate from from the the same sample gives a (DH-MN-4) gives a plateau age of plateau age of 1756±16 Ma, concordant with the biotite age. These two ages, 1756k16 with the biotite age. These two ages, from from minerals minerals with with highly discordant closure temperatures (—500°C and —300°C), indicate rapid cooling roughly highly discordant closure temperatures (-500° and -300°C) indicate cooling roughly60—100 60-100 Ma after after metamorphism metamorphism during during the the Penokean Penokean orogeny. orogeny. We observe consecutive increments observe that that of of the the first first 10 10 increments increments in the hornblende spectra, four consecutive increments (3—6) give concordant ages of —1615 Ma and have K/Ca ratios an order of magnitude greater than (3-6) give concordant ages of -1615 Ma and have K/Ca ratios an order of magnitude 40 �those of the plateau increments. In In addition, addition, these these same four increments, when subject to regression on the 15±9 Ma with the isotope-correlation isotope-correlation intercept plot, yield a concordant concordant intercept age age of of 16 1615k9 with an an 40ArP6Ar. These combined observations lead lead us us to to interpret interpret the "mini" "mini" plateau age age atmospheric initial ^Ar/^Ar. —1615Ma Maasasdating datingthe theplagioclase plagioclaseinclusions inclusionsininthe thehornblende. hornblende.The The younger younger age age is is consistent of -1615 with plagioclase having thaneither eitherbiotite biotiteororhornblende. homblende. These having a lower lower closure closure temperature (—230°C) (-230°C than Maevent eventrecognized recognizedin inMI MIand and WI WI also also affected data may indicate indicate that that the the regional regional low-grade low-grade —1630 -1630 Ma the rocks of east-central east-central MN, although although perhaps to a lesser extent. yields aa plateau plateau age age of of 1705k19 1705±19 Ma and Muscovite from the McGrath Gneiss (sample DH-MN-6) yields biotite (sample DH-MN-7) yields yields aa plateau plateau age ageof of 1702k12 1702±12Ma. Ma. The The concordant concordant mica mica ages indicate rapid cooling (from (from temperatures temperaturesabove above 350°C 350° to below 300°C) 300°Cof the gneiss at about about 1705 1705Ma. Ma. Discussion. Considering the high closure temperature for Ar diffusion in hornblende Discussion. Considering the high closure temperature for Ar diffusion in hornblende(—500°C) (-500°C and apparent lack of intrusions in this region it seems seems unlikely that the cover rock rock ages ages represent represent therefore interpreted interpreted as asrepresenting representingsimple simplecooling. cooling. Rapid cooling from thermal resetting, and are therefore 500°C to below below 300° 300°C is a strong indication of of tectonically driven uplift. In temperatures above 500° contrast, rocks cooled during isostatic rebound will have relatively slow uplift rates so that that mineral mineral pairs will will give give measurable measurableage agedifferences. differences. It has has long long been been observed observedthat thatcontinental continentalextension extension commonly commonly occurs occurs along alongpreviously previously overthickened crust crust with with a characteristic characteristic time time lag lag between between the the end end of of thrusting thrusting and the peak of overthickened of extension Ma.These Thesegeneralizations generalizationsseem seemtotoindicate indicatethat thatregions regions of of overthickened overthickened crust extension of of —30—100 -30-100 Ma. for post-collisional post-collisionalextension. extension. In the Precambrian Precambrian of of MN, MN, we observe create characteristics favorable for Maafter afterthe thePenokean Penokeancollisional collisional orogen orogen and was coeval coeval with that rapid cooling cooling began began roughly roughly 60—100 60-100 Ma with regional rhyolitic volcanism volcanism and and granite granite emplacement emplacementininMI MIand andWI. WI. Major regional rhyolitic Major cooling cooling occurred occurred dominantly MaRbISr Rb/Sr ages ages cited cited above dominantlyin inthe thetime-span time-span1755—1740 1755-1740 Ma as indicated by the 1740—1750 1740-1750 Ma for this considering the concordant this region. However, However,cooling coolingapparently apparentlycontinued continueduntil until—1700 -1700 Ma considering concordant 1705 1705 Ma basement basementmuscovite muscoviteand andbiotite biotiteages agespresented presentedhere hereasaswell wellasasthethe—1700—1750 -1700-1750 Rb/Sr RbISr biotite biotite and 1704 1704Ma Ma homblende hornblendeplateau plateau ages ages in in northernmost northernmost WI and MI. All of of these these observations observationsare, are, in ingeneral, general,characteristic characteristicof of Phanerozoic Phanerozoicextensional extensionalregimes regimes worldwide. Based Based on on these thesesimilarities, similarities, we we believe these data might best be explained by a major Ma. The The regional regional extent of this extensional episode in in the the Lake LakeSuperior Superiorregion regionatat—1750—1700 -1750-1700 Ma. this episode episode has largely largely been obscured obscured by later later disturbances disturbancesin both Rb/Sr RbISr and Ar/Ar ArIAr systematics systematicsin in much much of MI and WI. The Thelow-grade low-grade—1630 -1630 Ma event well recognized in those areas may have have also also affected affected the rocks of east-central 15±9 Ma east-centralMN MN (although (although to to aalesser lesserextent) extent)as assuggested suggestedby bythe the16 1615k9 Ma preferred preferred plagioclase age Ma clustering of K/Ar mineral ages. plagioclase ageand andthe the—1630 -1630 Ma Structures unroofmg of ancient compressional orogenic roots may be Structures associated associated with extensional unroofing deformational features features (e.g., (e.g., detachment detachment faults). faults). The difficult to recognize due to localization of deforrnational The of extensional structures difficult. paucity of exposure exposure in this region would also make identification of We do suggest suggest that late-stage late-stage anastomosing anastomosing shear shear zones which cross-cut the dominant dominant foliation foliationin in the the McGrath Gneiss Gneiss might might be be attributed attributed to to extension. extension. Also, a single isolated outcrop at the Denham McGrath theregional regionaleast-west east-west orientation orientation perhaps perhaps Formation type locality locality has has upright upright folds folds oriented oriented —90° -90' totothe reflecting rotation during extensional unroofing. unroofing. Detailed Detailed structural analysis of recently drilled core samples may may ultimately ultimately test test our explanation of the the cooling cooling ages ages by by allowing identification of samples explanation of identification of extensional extensionalstructures structures(or (or lack lack thereof) thereof) associated associated with tectonic tectonic unroofing. Conclusion. Cooling Coolingages agesprovide provideone onemethod methodfor fordifferentiating differentiating between between relatively relatively fast, fast, tectonically tectonically driven driven uplift (e.g., (e.g., via via post-collisional post-collisional extensional extensional unroofing) unroofing) and slow, slow, isostatic isostatic unroofing following following cessation cessation of of convergence. convergence. We Wesuggest suggestthat thatrapid rapidcooling coolingand andmagmatism magmatism30—100 30-100 unroofing Ma after unrecognized after burial burial associated associated with the the Penokean collisional orogeny may reflect a previously unrecognized post-tectonic unroofing event in the Lake Lake Superior Superior region, possibly analogous to to that that commonly commonly observed observed in in Phanerozoic Phanerozoicmobile mobilebelts beltsworldwide. worldwide. in this this section. section. We will make them available ** We regret not not having room to cite references in upon request. request. 41 �___________________________________ 1800 AGE AGE 1600 1 1 1800 lo .—I LJ McGrath Gnelss Gneiss (Biotite) McGrath (Blotite) I AGEAGE 16001600 ] DH-MN-7B • • 1400 Formation (Hornblende) Denham Formation DH-MN-4H Tg=1692Ma Tg=1728Ma Tp=1702±l2Ma Tp=1756±l6Ma 1400— 1400 I I %39Ar 0 b" EEl I I I I I I %39Ar 100 10 100 1800 1800 - McGrath Gneiss (Muscovite) McGrath Gneiss (Muscovite) AGE DH-MN-4H DH-MN-4H * 1614.6 ± 0.6 Ma plateau points r-i 'Nenham Formation (Plagloclase?) Denham Formation (Plagioclase?) I 160OU C,, DH-MN-6M Tg=l7OlMa Tp= 1705±19 Ma 1400 0 %39Ar - AGE 1 I & 36/40 100 I Formation (Biotite) (Blotite) Denham Formation 1600DH—MN-4B 0 Tg=1725Ma Tp = 1756 ± 15 Ma 1400 0 %39Ar Tg ==total total gas gas age age Tp == plateau plateauage age Hoim, Lux Holm, Hoist, Holst, and and Lux 42 100 �ON ON THE THE USE USEOF OFPALEOCURRENT PALEOCURRENTINDICATORS INDICATORSIN INDEFORMED DEFORMEDROCK ROCK HoIst, Holst, Timothy B., B., Department Department of Geology, Geology, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, Minnesota Minnesota 55812, 55812, and Fossen, Fossen, Haakon, Haakon, Department Department of Geology Geology and and Geophysics, Geophysics, University Universityof ofMinnesota, Minnesota,Minneapolis, Minneapolis,Minnesota Minnesota55455 55455 A A number numberof of sedimentary sedimentary structures structures have have long long been been used used as as indicators indicators of of current current direction at the time of deposition of the sediments that contain them. When the deposits direction at that contain them. When the deposits are there has has been beenpostpostare flat-lying flat-lyingand andundeformed undeformedthis thisisisaastraightforward straightfotwardprocess. process. IfIf there deposition deformation, including any displacement, rotation, tilting, folding, and finite deposition deformation, including any displacement, rotation, tilting, folding, and finite strain, strain, the the deformation deformation history history must must be be known known in in some some detail detail in inorder orderthat thatthe thebeds bedsmay may be to be valid. valid. This be restored restoredto their their original original position, for any paleocurrent data to This process process can be be far far from fromsimple. simple. can IfIf read read correctly correctly from from undeformed undeformedrocks, rocks, sedimentary sedimentarystructures structureswhich whichare arecurrent current indicators indicatorsyield yieldaa horizontal horizontalvector vector indicating indicatingthe the direction directionof of current current flow. This Thisvector vectormay may be deflected deflected from from its its original original position position by by many manytypes types of of deformational deformationalprocess. process. In In the the be general general case case the the deformation deformation history history may may involve involve several several episodes episodes of of deformation, deformation,each each of of which which may may have haveincluded includedone one or ormore moreofofthe theprocesses processesofofdisplacement, displacement,rotation, rotation, tilting, tilting, folding, folding, and finite strain. To Torestore restorethe the beds bedsto to correct correct onginal original position, position, aa series series of of deformation deformation inversions inversions needs needs to be performed. In Inpractice, practice, the the necessary necessaryinformation information to to perform perform these these inversions inversionsis is almost almost never never completely completely known. known. Finite Finite strain strain analysis analysis in in rocks rocks has has progressed progressed aa great great deal deal in in the the last last few few decades, decades, but suitablefinite finitestrain straindata data but still still many many rocks rocks are are not not amenable amenable to strain analysis. Even Evenifif suitable may may be be recovered, recovered, information information on strain path, path, necessary necessary if the the current current vector vector isisto tobe be restored to correct initial position, has proven to be extremely elusive. Veins and strainrestored to be extremely elusive. and shadow shadow fibers have have provided provided this information information in in some some situations, situations, with with results results showing showing evidence of non-coaxial strain histories sufficiently often so that if strain path information evidence of non-coaxial strain histories sufficiently often so that if strain path information is is lacking, lacking, paleocurrent paleocurrentdata datamay maybe beconsidered consideredsuspect. suspect. finite finite strain strain and and strain strain path path data data are are known, known, removal removal of these these effects effects by by deformation inversion may still leave the bedding bedding in aa position position other other than than original, original, and and effects also be be considered. considered. This is effects of folding, tilting, rotation and displacement must also is also also the starting point for consideration of rocks with with negligible negligible finite finite strain. strain. Ramsay (1961) Ramsay (1961) showed that the effects of strain and folding on sedimentary structures were the effects of strain and folding on sedimentary structures were more more profound profoundthan than had hadgenerally generally been beenappreciated, appreciated, and andoutlined outlinedaa technique techniquefor fordeformation deformation inversion inversion of folding folding once once effects effects of of finite finite strain strain had hadbeen beenremoved. removed. This This technique technique involves of the material involves rotation rotation of material about about an an axis axis perpendicular perpendicular to plunge plunge direction direction of of measurable measurable folds in the area, area, until until the fold fold axes axes are are horizontal, horizontal, and and then then rotation rotationof of the the in question question about strike to to restore restore to to horizontal. horizontal. This This is aarelatively relatively about the the strike bed in straightforward this procedure procedure straightforward technique, but will only result resultininaacorrect correct interpretation interpretationifif this is indeed indeed aa deformation deformationinversion. inversion. In In the general general case, this will will almost almost certainly certainly not not be be is true. true. Paleomagnetic Paleomagnetic studies studies in a number number of areas areas have have shown shown fairly fairly large large rotations, rotations, as as 140 degrees degrees during during displacement displacement deformation. deformation. In many many of these these areas, areas, finite finite much as 140 strain is is minimal, minimal, and the rocks rocks on an an outcrop outcrop scale appear nearly undeformed. undeformed. Early Early episodes of such rotation leave only a magnetic record in the rock, which may episodes of rotation magnetic record the rock, which may be be eliminated or or rendered rendered effectively effectively undecipherable undecipherable by by later later deformation deformation and/or andlor eliminated IfIf 43 �pateomagnetic data data are are not available, one can only assume assume that that no no metamorphism. metamorphism. If paleomagnetic when attempting attempting to to restore restore paleocurrent paleocurrent vectors. vectors. This such rotation has taken place when This often often may not be aa safe safe assumption. assumption. Even in areas without such displacement rotations, and with minimal finite strain, complications complications are certainly certainly possible. possible. In areas of plunging folds with a seemingly simple simple deformation history, history, it has has been been shown, shown, again again from from paleomagnetic paleomagnetic studies, studies, that that the the Using technique outlined in Ramsay technique outlined Ramsay (1961) is not not aa correct correct deformation deformation inversion. inversion. Using progressive demagnetization demagnetization techniques progressive techniques on on rocks rocks from from an an area area where where there there were were several several resetting, McClelland deformation history periods of magnetic resetting, McClelland Brown Brown (1983) (1983) found that the deformation history fold in the the Old Old Red Red Sandstone Sandstone in in Pembrokeshire Pembrokeshire involved involved marked marked changes changes of a particular fold in plunge (both (both steepening and gentling during deformation), deformation), and in plunge plunge direction direction during fold development, development, even even through nearly nearly 180 180 degrees degrees (opposite (opposite plunge plunge directions) directions) such as these during during one one stage. stage. Studies Studies such these show show that that when wheninformation information (from (from paleomagnetic studies) about fold or displacement displacement histories is is not not available, available, paleocurrent paleocurrent paleomagnetic data data should should be be considered consideredsuspect. suspect. In addition addition to errors errors in in orientation orientation of of aasingle singlecurrent current vector vector introduced introduced in in paleocurrent data from unknown or partially partially known deformation histories, problems problems may may sets, which are purely an artifact of the also arise because of apparent patterns in data sets, Depending on the deformation history, not the the original originalpaleocurrent paleocurrent pattern. pattern. Depending the deformation history, and not deformation deformation history and the the geometrical geometrical relationships relationships between between bedding, bedding, true true current current direction, and the various deformation components, deformation processes processes may create an apparent apparent single single cluster cluster of of paleocurrent paleocurrent vectors, vectors, an an apparent apparent bimodal, bimodal, bipolar bipolar distribution, or may even spread spread out to aa large large degree degree an an original original fairly fairly close closeclustering. clustering. As certain As certain of of these these patterns patterns are are generally generally taken taken as as being being indicative indicative of of particular particular environments of deposition, there are obvious obvious dangers involved involved in in placing placing much much faith faith in in studies of paleocurrent paleocurrent patterns deformed rock where information information necessary studies patterns in deformed necessary to perform perform a complete complete deformation deformation inversion inversion is is not not available. available. Many studies have shown that deformation histories of deformed, or or apparently apparently undeformed rock are much more complex than they appear appear to be. be. In general, detailed detailed detailed information information on deformation history in not attainable in in rocks. rocks. In the absence of detailed considered and complete information on deformation history, paleocurrent data must be considered suspect. Orientation Orientationerrors errorsintroduced introducedby by deformation deformation processes processes may may be be substantial, substantial, and and artificial patterns may be introduced introduced to a group group of data. data. REFERENCES REFERENCES McClelland Paleomagnetic studies of fold fold development development and and propagation McClelland Brown, E., 1983, Paleomagnetic McClelland Brown, Brown, E., E., and in the and the Pembrokeshire Pembrokeshire Old Old Red RedSandstone, Sandstone, & McClelland VandenBerg, J., eds., Paleomag Paleomagnetism of Orogenic Orogenic Belts: Belts: Tectonophysics, v. 98, netism of VandenBerg, J., s, 131-149. p. 131-149. Ramsay, J. J. G., G., 1961, 1961, The The effects effects of of folding folding upon upon the theorientation orientation ofofsedimentary sedimentary 84 -- 100. 100. structures: Journal Journal of of Geology, Geology, v. v. 69, 69, p. p. 84 44 �Airborne Survey of of Northwestern Northwestern Wisconsin. Wisconsin. Airborne Geophysical Geophysical Survey by by R.J. R.J. Horton, Hortonf R.J. R.J. Bisdorf, Bisdorf! and and R.P. R.P. Kucks Kucks USGS, USGS! Branch Branch of of Geophysics, Geophysicst MS MS 964, 964! Denver Denver Federal Federal Center. Center. In In 1988, 1988! the United United States States Geological Geological Survey Survey conducted conducted an an airborne geophysical geophysical survey survey over northwestern northwestern Wisconsin Wisconsin as as part part of of the the Great Great Lakes Lakes International International Multidisciplinary Multidisciplinary Program Program on on Crustal Crustal Evolution Evolution (GLIMPCE) (GLIMPCE) program. The The 6000 6000 line-kilometer line-kilometer survey survey covered covered portions portions of of Bayfield, Bayfield! Burnette, Burnettel Douglas, Douglas! and and Washburn Washburn counties. counties. The The survey direction was north-south! north-south, the spacing survey flight flight line line direction the flight flight line line spacing 800 800 meters, metersf and and the the survey survey altitude altitude 91 91 meters meters above above ground ground level. level. Magnetic Magnetic and and very very low low frequency frequency (VLF) (VLF) resistivity resistivity data data were were collected. collected. The The geology geology of of the the survey survey area area consists consists of of Precambrian Precambrian bedrock bedrock overlain overlain by by glacial glacial deposits. deposits. The The oldest oldest bedrock bedrock units units are are Middle Middle Keweenawan, Keweenawan! Chengwatana Chengwatana volcanic volcanic rocks rocks composed composed of of mafic mafic to to intermediate intermediate lavas lavas and and interbedded interbedded sedimentary sedimentary rocks. rocks. The The Upper Upper Keweenawan, Keweenawanf Copper Copper Harbor Harbor Conglomerate Conglomerate overlies overlies the the volcanic volcanic rocks. rocks. The The youngest youngest bedrock bedrock units, units! the the Upper Upper Keweenawan Keweenawan Bayfield Bayfield Group Group sandstones, sandstonesf are are juxtaposed juxtaposed against against the the Chengwatana Chengwatana volcanic volcanic rocks rocks by by the the Douglas Douglas fault. fault. Late Late Wisconsin Wisconsin to to Holocene Holocene glacial glacial deposits deposits consist consist of of alluvium, alluviumt peat, peat! lake lake silt, siltf clay, clay! ice—contact ice-contact and and outwash outwash sand sand and and gravel, gravel! and and clayey clayey to to loamy loamy ground ground moraine moraine and and till. till. These These glacial glacial deposits deposits range from from less less than 11 to to greater greater than than 100 100 feet feet thick. thick. The features on on the the aeromagnetic aeromagnetic map map (Figure (Figure1) 1) The most most obvious obvious features are are related related to to the the Ashland-Lake Ashland-Lake Superior Superior syncline. syncline. The The axis axis of of the the syncline through the center syncline strikes strikesnortheasterly northeasterlythroughthe centerof ofthe thesurvey surveyarea. area. The narrow, narrowf northeasterly—trending northeasterly-trending linear linear anomalies anomalies are are produce produce by by The dipping dipping volcanic volcanic rocks, rocksf upturned upturned along along the the northwest northwest and and southeast southeast limbs limbs of of the the syncline. syncline. The The Copper Copper Harbor Harbor Conglomerate Conglomerate occupies occupies the the center center of of the the syncline syncline where where aa relatively relatively deep deep and and flat-lying, flat-lying! magnetic magnetic basement basement produces produces the the broad—gradient broad-gradient magnetic magnetic anomaly. anomaly. In In the mapf the the Douglas Douglas fault, faultf has has brought brought the the the northern northern portion portion of of the the map, relatively relatively non—magnetic non-magnetic Bayfield BayfieldGroup Group sandstones sandstonesin in contact contact with with the the older, older! southeast—dipping, southeast-dipping! magnetic magnetic volcanic volcanic rocks. rocks. In In the the extreme extreme southern southern portion portion of of the the survey survey area, area! the the low—amplitude low-amplitude magnetic magnetic anomaly magnetic basement anomaly is is thought thought to to be be caused caused by by deep deep magnetic basement below below thick thick sedimentary sedimentary rocks. rocks. Unlike Unlike the the aeromagnetic aeromagnetic map, mapf the the VLF VLF apparent apparent resistivity resistivity map map (Figure 2) reflects reflects aa combination combination of of topographic, topographicf bedrock bedrock and and (Figure 2) surficial surficial geologic geologic features. features. Across Across the the northern northern portion portion of of the the survey survey area area low low resistivities resistivities are produced produced by by conductive conductive lake lake sediments sediments deposited deposited in in the the topographically-low topographically-low region region between between Lake Lake Superior Superior and and the the Douglas Douglas fault. fault. South South of of the the Douglas Douglas fault fault sand, sandf gravel, gravel! and and moraine moraine deposits deposits produce produce the the intermediate intermediate resistivities resistivities that that cover cover the the majority majority of of the thesurvey surveyarea. area. Small conductive conductive Small anomalies anomalies result result from from deposits deposits of of clay clay and and peat peat in in lakes lakes and and shallow shallow depressions. depressions. The The highly highly resistive resistive zones zones are are produced produced by by thick, thickfclay— clayfree free sand sand and and gravel gravel deposited deposited as as outwash outwash or or ice—contact ice-contact deposits. deposits. Subtle Subtle northeast—striking northeast-striking features features observed observed throughout the the survey survey area area reflect reflect the the direction direction and and resultant resultant deposits deposits of of southwesterly southwesterly glacial glacial advances advances and and the the influence influenceof of underlying underlying bedrock bedrockfeatures. features. 45 45 �CD N3 0 + Li, 0 Li, I (V 0 fl2 S CD 0 + CA3 N N rii N cJ, C C cJ, C rn C C C C C C C C N C N CC C CC ffl CN rn rn rn C C C C C C CCCCCCCC.fl C C C C C C C C rn r-4 CC C 0 a, 0 Li, Lighter ~ i m r1. e1. Gray-scale Gray-scale aeromagnetic aeromagneticmap map of of the the northwestern northwesternWisconsin Wisconsin survey surveyarea. area. Lighter Figure represent magnetic field field highs, darker shades of gray shades of gray represent magnetic field highsf darker shades of gray represent magnetic field shades of gray represent magnetic produced by dipping Chengwatafla linear, northeast-trending anomalies are ~ O W S . Narrow, Narrowf linearf northeast-trending anomalies are produced by dipping Chencpatana lows. produced by deep volcanic rocks. rocks. The The broad—gradient broad-gradient anomaly anomaly in in the the center center of of the the map map is is produced by deep volcanic Conglomerate. magnetic basement basement below below the the Copper Copper Harbor Harbor Conglomerate. magnetic �I l.A — t% c_fl — t, — (P1 I + + + + 0 luij 0,, '-1, Figure 2. 2. Gray—scale Gray-scale VLF VLF apparent apparent resistivity resistivitymap map of of the the northwestern northwesternWisconsin Wisconsinsurvey surveyarea. area. Figure Light shades shades of of gray gray represent represent high high resistivity resistivity areas, areas, dark dark shades shades of of gray gray represent represent low low resistivity resistivity areas. areas. Conductive conductive lake lake sediments sediments produce produce the the low low resistivity resistivity terrain terrain across across the northern portion the survey survey area. area. Sand, gravel gravel and moraine moraine deposits deposits produce produce the the northern portion of the Sand, intermediate that cover cover the the majority majority of of the the survey survey area. area. High resistivity resistivity intermediate resistivities resistivities that areas a r e a sare areproduced producedbybythick thickdeposits depositsofofclay—free clay-freesand sandand and gravel. gravel. �Magnetic Magnetic studies studies of of the the Dresser-St. Dresser-St. Croix Croix Falls Falls Area, Area, Polk Polk County, Wisconsin. Wisconsin. County, William F.Kean, Department Department of of William F.Kean, Wisconsin-Milwaukee, Wisconsin-Milwaukee, P.O. P.O. Box Box Geosciences, Geosciences, University University of of 413, Milwaukee, 413, Milwaukee, WI WI 53201 53201 John John Feeney, Feeney, Wisconsin Wisconsin Department Department of of Natural Natural Resources, Resources, 2300 2300 Martin Martin Luther Luther King, King, Jr. Jr. Drive, Drive, Milwaukee, Milwaukee, WI WI 53212 53212 The The ground ground magnetic magnetic study study by by Reich Reich (1989) (1989) and and the the paleomagnetic paleomagnetic study study by Feeney Feeney (1990) (1990) have have been been incorporated incorporated and and compared in the the Dresser—St. Dresser-St. Croix Croix Falls Falls area area compared to to the the bedrock bedrock map in by Cordua Cordua (1989). (1989). Paleomagnetic Paleomagnetic results results from from 11 11 locations locations give give by five five normal normal sites, sites, four four reversed reversed sites sites and and two two mixed mixed sites. sites. The The pole pole positions positions when when corrected corrected for for dip dip give give magnetic magnetic directions directions close close to to either either the the North North Shore Shore volcanics volcanics or or the the Gargantua Gargantua volcanics. The The remanent remanent intensities intensities and and susceptibilities susceptibilities are are volcanics. typically typically large, large, with with ratios ratios of of the the remanent remanent to to induced induced components components ranging ranging from from .4 . 4 to to 1.4. 1.4. This This implies implies that that remanent remanent intensities magnetic surveys intensities will strongly strongly influence influence land land magnetic surveys and and interpretations. The The land land magnetic magnetic surveys surveys by by Reich Reich (1989) (1989) interpretations. showed showed aa significant significant number number of of anomalies anomalies about about 1/4 1/4 to to 1/2 1/2 mile mile wide wide and and 300.0 300.0 gamma gamma to to 500.0 500.0 gamma gamma in in intensity. intensity. Preliminary Preliminary modelling modelling suggests suggests these these features features are are caused caused by by magnetic magnetic characteristics characteristics of of individual individual flows flows rather rather than than by by bedrock bedrock topography topography as as originally originally proposed. proposed. In In addition, addition, the the combined combined rock rock magnetic magnetic and and land land magnetic magnetic studies studies are are reasonably reasonably consistent consistent with (1989) and and could could be be used used to to extend extend the the with the the mapping mapping by by Cordua Cordua (1989) mapping mapping in in areas areas covered covered by by glacial glacial drift. drift. References References Cordua, S., 1989, 1989, A A Summary Summary of of the the Bedrock Bedrock Geology Geology of of the the Cordua, William S., Dresser—St. Dresser-St. Croix Croix Falls Falls area, area, Polk Polk County, County, Wisconsin Wisconsin and and Chisago County, County, Minnesota. Minnesota. 53rd Annual Field Chisago Annual Tri-State Tn-State Field Conference Guide Guide Book, Book, River River Falls, Falls, WI. WI. Conference Feeney, of Keweenawan Keweenawan Age Age Basalts Basalts of Feeney, John, John, 1990, 1990, Paleoinagnetism Paleomagnetism of the the Chengwatana Chengwatana Volcanic Volcanic Group Group in in Polk Polk County, County, Wisconsin. Wisconsin. Unpublished MS MS thesis, thesis, University University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, Unpublished 218 pp. pp. 218 Reich, Laura, Laura, 1989, 1989, Geomagnetic Geomagnetic Model of the the St. Croix Croix Horst Horst in in Reich, Polk County, County, Wisconsin. Wisconsin. Unpublished Unpublished MS MS thesis, thesis, University University Polk of Wisconsin-Milwaukee, 141 pp. pp. of Wisconsin-Milwaukee, 141 48 �MAGmTIC AND OF HEAT HEAT MAGNETIC AN]) PETROGRAPHIC DETECTION OF TREATMENT TREATMENT IN IN GUNFLINT G r n L I N ' TCHERT CrnRT Stephen Graham J. StephenA. A Kissin and Graham J. Borradaile, Borradaile,Department DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University, Thunder Thunder Bay, Bay, ON P7B P7B5E1; 5El;Joe JoeD.D.Stewart, Stewart,Department DepartmentofofAnthropology, Anthropology, Lakehead Mehead University, 5E1; William A. Ross, Ontario Ministry of Culture University, Thunder Bay, ON P7B P7B 5El; William A. Ontario Ministry of Culture and and Communications, 1825East EastArthur ArthurStreet, Street,Thunder ThunderBay, Bay,ON ON P7E 5N7; Communications, 1825 5N7; and and Tomasz Tomasz Werner, Department of of Geology, Geology, Lakehead Lakehead University, University, Thunder Bay, ON 5El. P7B 5E1. In the was the the material material of choice for the the Thunder Thunder Bay, Bay, Ontario Ontario area, area, "taconite" Yaconite" was manufacture of stone implements implements during during the the late late Paleo-Indian Paleo-Indianperiod periodCa. ca. 9000 9000 b.p. (Fox, (Fox, 1975; Dawson, Dawson, 1983). 1983). The "taconite" which occurs as stratabound Yaconite*'is an iron-bearing chert, which nodules and lenses of the local Gunflint lenses in calcareous calcareous and and siliceous siliceous siltstones of Gunflint Formation. Formation. Studies have indicated flaking indicated that heat heat treatment treatmentofofsiliceous siliceousmaterials materialsimproves improvestheir theirflaking characteristics, both in ethnographic characteristics, both ethnographic (Hester, (Hester, 1972; 1972; Mandeville, Mandeville, 1973) 1973) and experimental experimental investigations (Crabtree and and Butler, Butler, 1964, 1964, Mandeville and Flenniken, Flenniken, 1973; 1973; Flenniken Flenniken and and Garrison, the Thunder Bay area Garrison, 1975). 1975). The The possibility possibility that heat treatment treatment was employed in the technology has been suggested Dawson,1983), 1983),and andaamethod method of of detection of technology has suggested (Fox, 1975; 1975; Dawson, such treatment is is important important in in the thecontinuing continuingstudy study of of this this culture. culture. "Taconite" specimens specimens£ro from three three bedrock bedrock outcrops outcrops in in the Thunder Bay Bay area area were were heated at 2½hr. hr.and and allowed allowedtotocool cooltotoroom roomtemperature. temperature. Comparison at 425 425 and and 500°C 5OO0Cfor 2+ Comparison to unheated unheated specimens specimens revealed revealed some some color color differences differences attributable attributable to toheating; heating;however, however,the the mesoscopic and microscopic of the specimens did not permit microscopic heterogeneity of permit mineralogical mineralogical reflectance and microhardness microhardness techniques techniques to to be be usefully usefully employed. employed. Optical Optical microscopy microscopy using transmitted transmitted and andreflected reflectedlight lighton onpolished polishedthin thin sections sectionsrevealed revealeddistinctive distinctivedifferences differences in most specimens. specimens. The The most most pronounced pronounced effect effect of of heating heating was aa loss loss of of organic organic carbon, carbon, resulting and migration &om resulting in bleaching bleaching of most most carbon-rich carbon-rich specimens specimens and migration of carbon carbon from inclusions to grain boundaries boundaries and and cracks. inclusions to cracks. Decarbonation Decarbonation of siderite siderite with with production production of hematite isis also alsosignificant sigmficant in in carbonate-rich carbonate-richspecimens. specimens. hematite Non-destructive measurementofof magnetic magnetic properties properties revealed Non-destructive measurement revealed that that magnetic magnetic susceptibility, saturation isothermal isothermal remanent susceptibility, saturation remanent magnetization magnetization and and magnetic magnetichysteresis hysteresis changed as heating. Because Because the natural natural remanent remanent magnetism magnetism parameters all changed as a result of heating. (NRM) of of the the Gunflint Gunflint cherts cherts is is highly highly variable and unstable, this property is not aa useful useful parameter for heated £ro from unheated unheated material material although although itit has been used in for distinguishing distinguishing heated archeological work work in in Europe. Europe. Also, in the manufacture and Also, mechanical action and shock in M . We We took took ten ten specimens specimens of of the cherts cherts use of implements would wouldperturb perturb and and alter the m NRM. and broke them in two. two. One One part partwas was kept kept as as a2 control control sample sample and the other other half half heated. heated. aswell well as as the thehysteresis hysteresis after heating heatingas In this way, the the susceptibilitywas was measured measured before and after properties. Instead Insteadof ofusing using the the natural naturalmagnetization magnetization of of the the samples, samples, we compared their ability to retain a large large (saturation) (saturation)magnetization magnetization in an an inducting inducting field field of of 950 950 mT mT (9500 (9500 ability oersteds). This ( E M ) increased greatly as a result of of This isothermal isothermal remanent remanent magnetization magnetization (IRM) These parameters parameters alone alone allow allow one one to to distinguish distinguish between heating as did the susceptibility. These and the theunheated, unheated,control controlspecimens. specimens. cherts which which had had been heated and 49 �Hysteresis loops in unheated unheated materials materialsare arefrequently ikequently"wasp-waisted" "wasp-waisted because of the the presence of of two two magnetic magnetic minerals minerals (Jackson (Jackson et et al.. al., 1990). 1990). Heated Heated specimens specimenslose lose"wasp"waspin hysteresis hysteresis behavior are are variable. variable. waistedness", although the the changes changes in waistedness", Petrographic of Gun£lin Gunflint cherts cherts appear to provide a means by Petrographic and magnetic studies of which may be be detected. Magnetic which heat treatment in in the the manufacture manufacture of stone implements may Magnetic methods are are particularly attractive, attractive, as they are non-destructive so long as an artifact under investigation will will fit fit the the constraints constraints imposed imposedby bysample sampleholders holdersand andinstruments. instruments. Moreover, the as normal normalchert chertor orflint flintwith withmuch much the magnetic magnetic methods methods will will be applicable applicableto to samples samples such such as lower iron contents contents than than the thespecimens specimenswe we need. need. REFERENCES REFERENCES Crabtree, D.E. and Notes on onexperiments experimentsin inflint flintknapping: happing: 1. 1. heat B.R., 1964. 1964. Notes and Butler, Butler, B.R., treatment treatment of of silica silica materials: materids: Tebiwa, Tebiwa,v.v. 7,7,p. p.1-6. 1-6. Dawson, K.C.A., K.C.A.,1983. 1983. Cummins CumminsSite: Site: A late Paleo-Indian (Piano) (Plano) site site at at Thunder Thunder Bay, Bay, Ontario: Ontario 39,p.p.3-31. 3-31. OntarioArcheology, Archeology,v.v.39, altered novacuilte and Garrison, Garrison,E.G., E.G.,1975. 1975. Thermally Thermally altered novaculite and stone tool tool Flenniken, J.J. and manufacturing 1. 125-131. manufacturing techniques: Journal J o m a lofofField FieldArcheology, Archeology,v.v.2,2,p.p.125-13 ministry of Natural Natural W.A., 1975. 1975. The Paleo-Indian Paleo-Indian Lakehead M e h e a d Complex: Complex: Ontario ministry Fox, W.A., Resources Historic Historic Sites Sites Branch, Branch, Division of Parks, Research Report Report6,6,p.p.29-53. 29-53. evidence of of thermal thermal alteration of T.R.,1972. 1972. Ethnographic Ethnographic evidence of siliceous siliceous stone: stone: Hester, T.R., Tebiwa, v. v. 15, 15,p. p. 63-65. 63-65. Tebiwa, Jackson, M. Worm, H.-U. and and Banerjee, Banerjee, S.K., S.K, 1990. 1990. Fourier Fourieranalysis analysisofofdigital digitalhysteresis hysteresis data: rock rockmagnetic magneticapplications: applications: Physics Physics of of Earth Earthand andPlanetary PlanetaryInteriors, Interiors,v. v. 65, 65, p. 78-87. 78-87. p. Mandeville, M.D., 1973. 1973. A consideration of the thermal pretreatment consideration of pretreatment of of chert: chert: Plains Plains Mandeville, M.D., Anthropologist, 18,p.p.177-202. 177-202. Anthropologist,v.v. 18, Mandeville, M.D. and and Remiken, Flenniken, J.J., JJ., 1973. 1973. A comparison comparison of the the flaking flaking qualities qualities of Mandeville, M.D. Nehawka chert before and after thermal pretreatment: Plains Anthropologist, Nehawka before pretreatment: Plains Anthropologist, v. 19, 19, p. p. 146-148. 146-148. 50 �ALTERATION, FLUID INCLUSION, STABLE ISOTOPIC ISOTOPIC AND ALTERATION, FLUID STRUCTURAL STUDIES OF OF THE RABBIT MOUNTAIN SILVER MINJ3, MINE, STRUCTURAL STUDIES THUNDER THUNDER BAY BAY DISTRICT, ONTARIO ONTARIO Stephen A. Kissin, Peter G. Harvey, Elizabeth A. Jennings, Samuel T. Spivak Kissin, Peter Spivak and Eric J. Mosley, Department of Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, ON ON P7B Mosley, Department P7B 5E1 5El The The Rabbit RabbitMountain MountainMine Minewas wasthe thefirst firstdiscovered discoveredof of aa number numberof of silver silvermines mines lying lying well inland of of Lake Superior. Total Total production production from from the the mine mine amounted amountedto toapproximately approximately 50,000 oz. oz. in the period during which which the the mine operated sporadically period 1882-1893, 1882-1893, during sporadically (Tanton, (Tanton, 1931). modest, the the discovery discoveiyof of the the Rabbit Rabbit Mountain Mine led 1931). Although Although production was modest, to additional e.g. Silver Silver Mountain, Mountain, Beaver, Beaver, Badger Badger and Porcupine, additionalsignificant sigdicant discoveries, discoveries, e.g. extending silver mining in in the the Thunder Bay District, following following depletion depletion and and closure of the famous Silver Islet Mine. Sporadic Sporadicactivities activities subsequent to the the main main period periodof ofmining mining did did not permitted underground not yield additional additionalproduction; production;however, however, in in 1967-1968, 1967-1968, dewatering permitted underground sampling sampling and and mapping. mapping. The The deposit depositconsists consists of of two two veins, no. 11vein, carrying most of the the ore, ore, and andno. no.22vein, vein, essentially with trace trace quantities of of sulfide sulfide minerals. minerals. Both veins strike at essentially aa barren system with about 230° withdips dipsofofS50 to 70' 70°northwest. northwest. The The no. no. 11 vein vein varies varies£ro from 11 to to 33 m in 230' with O to thickness, and no. 22 vein, outcropping vein, is is about about11m mthick. thick. outcropping about about 100 100northwest northwest of of no. no. 11vein, A few minor veins veins with withthe the same same attitudes attitudes outcrop outcrop between between no. no. 1 1vein veinand andno. no.22vein. vein. The veins veins are in in Rove Rove Formation Formation shales shales in in faults faults that thatoffset offsetcapping cappingLogan Logan diabase diabasesills. sills. Brecciation Brecciation and recementation recementationof of earlier earliervein vein deposits depositsby by later later deposits deposits is is observable observable in in the the field. field. The The ores ores contain contain acanthite acanthite (pseudomorphous (pseudomorphousafter after argentite), argentite),native nativesilver, silver, sphalerite, sphalerite, galena, pyrite wg-filling pyrite and andchalcopyrite. chalcopyrite. Gangue Gangue consists consists of quartz, quartz, including including aavug-fiuing amethystine variety, variety, calcite calciteand andgreen greenand andpurple purplefluorite. fluorite. Barite was reported by Tanton (1931) and earlier was not not encountered encounteredin inthis thisstudy. study. earlier workers, workers, but was of The veins and and their their narrow narrow alteration alteration zones zones (typically (typically 10 cm wide) The wide) cut cut the zone of contact metamorphosed shale, which developed microscopic-sized porphyroblasts of metamorphosed shale, which developed microscopic-sized porphyroblasts of andalusite in in response responseto tointrusion intrusionofofthe thediabase diabasesill, sill,Ca. ca. 13 13 m thick. The Theveins veinspinch pinchdown down andalusite to aafew centimetres width in the diabase and wallrock alteration is negligible. The few centimetres width in the diabase and wallrock alteration is negligible. The alteration zones zones in in the the shales shalesare areoften oftendelineated delineatedby bybleaching bleachingowing owing to to aaloss lossof of carbon, carbon, alteration which which is present in the unaltered shale. The Theonly only mineralogical mineralogical change noted is alteration of illite(1M) illite(1M) to to illite(2M). illite(2M). Studies of trace content content in in uniformly uniformly spaced spaced samples samples taken taken perpendicular to to no. no. 22 vein indicate apparent depletion depletion in in Cu Cu and and possible possible depletion depletion in in As As perpendicular in aa zone zone extending extending 55 ft from the vein. Within Within this this zone zone Zn, Zn,Pb, Pb, Co, Co,Ni Ni and andAg Agexhibit exhibit cases are below below the enrichment, and, although although concentrations apparent enrichment, concentrationsofofHg Hg in in most most cases ft.of of the the detectionlimit limit of of the the atomic atomicabsorption absorptionspectroscopy spectroscopytechnique techniqueemployed, employed,within within22ft. detection vein clear enrichment in Hg is present. vein clear enrichment in Hg is present. Fluid quartz, sphalerite sphalerite and purple purple fluorite fluorite indicate indicate the Fluid inclusions in calcite, quartz, the presence presence of two episodes of of ore deposition separated by a period of cooling, cooling, aa pattern pattern common to all 51 �Early calcite productive silver mines mines of of the inland calcite yielded yielded productive silver inland area area(Jennings, (Jennings, 1986). 1986). Early homogenization temperatures ranging ranging from from 125 6s0C, whereas whereas post-fracture post-fracture calcite calcite homogenization temperatures 125 to 65°C, homogenization temperatures lay lay in in the the90-100°C 90-100° range, sphalerite sphalerite in inthe the80-115°C 80-115°range range and one as compared compared to to 99.7OC 99.7°Cin in another. another. Two 308S° as Two adjacent adjacent one purple purple fluorite fluorite yielded yielded 308.5°C inclusions homogenized to liquid and inclusions in calcite homogenized and vapour vapour at atCa. ca. 100°C, 100°Cindicating boiling at -15.0°C near surface surface depths depths during during position. position. Final melting melting temperatures of of -15.7 -15.7 and and-15.0°C, corresponding to 19.4 19.4 and and 18.8 18.8equiv. equiv. wt.% wt.% NaC1, NaCl, respectively, respectively, were determined. determined. Initial Initial melting temperatures ininother melting otherdeposits depositssuggest suggestNaC1-CaC12 NaCl-CaC12 or or CaC12 CaC12 aqueous aqueous systems systems (Jennings, 1986), -50.6and and -35.6OC -35.6°Cwere wereobtained obtainedfrom fromthe the Rabbit Rabbit Mountain sphalerite 1986), -50.6 specimens. The Theformer formerisisin inagreement agreementwith withthe theeutectic eutecticfor forNaC1-CaC12-H20, NaCl-CaC12-H20,but the latter latter temperature C 0 2on onthe theNaC1NaCltemperatureisisdifficult difficultto to interpret, interpret,but butmay mayreflect reflectthe theeffect effectofofdissolved dissolvedCO2 CaCJ2-H20 system. Daughter Daughter minerals were not observed in fluid inclusions from Rabbit CaC12-H20system. Mountain Mountain specimens. specimens. Sulfur isotopic isotopicanalyses analysesyielded yielded6% 6S == -1.2, -1.2, + 3.5, 3.5, + + 9.3 9.3 and ++ 9.9 9.9 %o %o in in sphalerite and a galena 3S%osphalerite sphaleritegave gave&MS 6% = -9.3%0. wide galena grain grain paired paired with with the the ++3.5%o -9.3%o. The wide variation in &'S 6 ? 3 in in sphalerite sphaleriteisissuggestive suggestive of a lack lack of of isotopic isotopic equilibrium, equilibrium, possibly possibly as a result of precipitation from a solution undergoing undergoingoxidation. oxidation. The The isotopic isotopic temperature temperature from the sphalerite-galena sphalerite-galena pair pair isis -35.6°C, -35.6OC, an unreasonably unreasonably low low figure figure probably probably also also indicating indicating sequential deposition deposition from from aa solution solutionundergoing undergoing oxidation. oxidation. 1. 1. 2. 2. 3. 4. The results results lead lead to tothe thefollowing followingconclusions: conclusions: Ores were deposited Ores deposited at at low low pressure pressure from frommoderately moderately saline salinesolutions, solutions, which which experienced sporadic sporadic boiling. boiling. The lack sulfides and and the mild wallrock lack of of isotopic isotopic equilibrium equilibrium among sulfides mild nature of of walirock alteration suggest suggest relatively rapid deposition. Most Hg, found found in in minerals minerals Most metallic components components of of veins veins as as well well as as Ni, Ni, Co and Hg, (Franidin et al., 1986), seem seem to to have have been been added added to wallrock walirock elsewhere in the district (Franklin solutions. Cu and As, as well as carbon, carbon, alteration zones from the ore-depositing ore-depositing solutions. were depleted in in alteration alteration zones. zones. The process in in which whichthermal thermal highs highswere wereseparated separated The deposition depositionof of ores ores was a pulsatory process by a period period of of cooling cooling and and fracturing. fracturing. REFERENCES Smyk, M.C., M.C.,and and Scott, Scott, S.D., S.D., 1986. 1986. Silver Franklin, J.M., Kissin, S.A., S.A., Smyk, Silver deposits associated associated with Proterozoic rocks Jour. Earth Earth Sci., Sci., rocks of of the the Thunder Thunder Bay Bay District, District,Ontario: Ontario: Can. Jour. v. 23, p. 1576-1591. 1576-1591. Jennings, E.A., E.A., 1986. 1986. A survey Jennings, survey of the the Mainland Mainland and and Island Island Belts, Belts, Thunder Thunder Bay Bay silver silver Fluidinclusions, inclusions, mineralogy, mineralogy, and sulfur isotopes: Unpubi. Unpubl.M.Sc. M.Sc. district, Ontario: Fluid thesis, Lakehead M e h e a d University, University, 159 159 p. p. William and Port Port Arthur, Arthur, and and Thunder ThunderCape Capemap-areas, map-areas, Tanton, T.L., Tanton, T.L., 1931. 1931. Fort William Bay District, Ontario; Ontario; Geol. Geol.Surv. Sum. Can., Can., Mem. Mem. 167, 167,331 331 p. p. Thunder Bay 52 �THE EMPERORVOLCANIC VOLCANICCOMPLEX: COMPLEX: IMPLICATIONS THE EARLY EARLY PROTEROZOIC PROTEROZOIC EMPEROR IMPLICATIONSFOR FOR THE THE GEOLOGY GEOLOGY OF OF THE THE EASTERN EASTERNGOGEBIC GOGEBIC DISTRICT, DISTRICT, NORTHERN NORTHERN MICHIGAN MICHIGAN Gene Geology Dept., Dept., UW Oshkosh, Oshkosh, Gene L. LaBerge, LaBewe, Geology OshkoshI WI, Wl, and and U.S. U.S. Geological GeologicalSurvey Survey The Volcanic Complex constitutes a thick The Emperor Emperor Volcanic thick pile pile of of Early Early Proterozoic Proterozoic volcanic volcanic rocks and and sills sills in in the the sedimentary sedimentary sequence sequence on the eastern Gogebic Except for for aa rocks Gogebic range. range. Except number number of of diabase diabase dikes dikes and and sills, sills, igneous igneous rocks rocks are are scarce scarce on on the the western westernGogebic Gogebicrange. range. However, However, igneous igneous rocks rocks are abundant east of Wakefield, Mich., Mich., where wherethey theyreach reachaa thickness thickness of at at least least 2,000 2,000 m. m. Although Althoughthe thepresence presenceof ofvolcanic volcanic rocks rockson onthe theeastern eastern Gogebic range has been known for over 100 years (Irving and Van Hise, 1892), Gogebic range has been known for over 100 years (Irving and Van Hise, 18921, few few Irving and and Van Hise (1892) (1892) stated stated that thatthe the studies undertaken on on these these rocks. rocks. Irving studies have have been undertaken volcanic with the volcanic rocks rocks are are interbedded with the Ironwood Ironwood Iron lron formation, formation, an aninterpretation interpretation substantiated substantiated by by subsequent subsequent exploration exploration drilling drilling for for iron ironore ore in inthe thearea. area. Mapping (1973)documented Mapping by by Trent Trent (1973) documented the the distribution distribution of ofigneous igneousrocks rocksand andshowed showed some Dann(1978) (1978)showed showedthat thatthe thevolcanic volcanicrocks rocksrange rangeinin some of of the the Iithologies lithologies present. present. Dann composition prehnitecomposition from frombasalt basaltto todacite daciteand andthat thatthey theyhave havebeen beenmetamorphosed rnetamorphosed to t oprehnitepumpellyite pumpellyite or or to t o lower lowergreenschist greenschist facies. facies. Trace Traceelement elementstudies studiesby bySchulz Schulz(Sims (Simsand and others, others, 1990) 1990)indicate indicatethat thatthe thevolcanic volcanicrocks rocksare arebimodal bimodalrift-related rift-related tholeiites tholeiitesand and rhyolite. rhyolite. Geologic mapping mapping in in 1991 1991by byLaBerge LaBergeand and J. J. S. S. Klasner Klasnerindicates indicatesthat thatthe theEmperor Emperor Geologic Volcanic Volcanic Complex Complex consists consists of of aa variety variety of ofsubaqueous subaqueous mafic mafic and and felsic felsic volcanic volcanic rocks rocksand and sills. sills. Mafic Maficrocks rocksinclude includesills, sills, pillowed pillowedand andmassive massive flows--some flows--some with withcolumnar columnarjointing, jointing, and and extensive extensive hyaloclastites hyaloclastites and and pillow pillow breccias. breccias. Felsic Felsicrocks rocksinclude includemassive massivefelsite felsite breccias, lithic tuffs, tuffs, hyaloclastites, hyaloclastites,and andbreccia-hyaloclastite breccia-hyaloclastite debris debris flows. Kokelaar breccias, lithic Kokelaar (1986)states statesthat thathyaloclastites hyaloclastitesform formmainly mainlyininwater waterless lessthan than200 200mmdeep deepand and are aremore more (1986) abundant in inshallower shallower water. water. The Theabundance abundanceofofhyaloclastites hyaloclastites(Figure (Figure1)1)ininthe theEmperor Emperor abundant volcanics, therefore, therefore, suggests suggests extrusion in shallow Shallow water waterdeposition depositionisis volcanics, shallow water. water. Shallow further furtherindicated indicatedby bythin thininterbeds interbedsof ofoolitic ooliticiron ironformation. formation. The Emperor Emperor volcanic Ironwood Iron lron formation formation that that The volcanic rocks form a wedge wedge within the Ironwood (1973)shows showsthat thatthe the thickens eastward eastward from from Wakefield, Wakefield, Mich. Trent's Trent's mapping mapping (1973) thickens formationsare aretruncated truncatedby bymajor majorfaults faults(the (thePresque PresqueIsle lsleFault Faultand andthe theSunday SundayLake LakeFault) Fault) formations between Wakefield and Mareniso, Mich. between Wakefield and Mareniso, Mich. hyalo~lastites~ andinterbedded interbedded Thedistribution distributionofofvolcanic volcanicrocks, rocks,the theabundance abundanceofofhyaloclastites, The and ooliticiron ironformation formationindicate indicatethat thatthe theEmperor EmperorVolcanic VolcanicComplex Complexformed formedininshallow shallow water water oolitic basin subsiding subsiding markedly ttoo the the east east during during iron formation deposition. deposition. Truncation Truncationofof ininaabasin the theformation formationalong alongfaults faultsmay maybe beaa primary primary feature. feature. This Thissuggests suggests deposition depositionininaahalf half graben, perhaps perhaps during during continental continental rifting rifting(Figure (Figure2). 2). Deformation Deformationduring duringthe thePenokean Penokean graben, Orogeny resulted resultedin inthrusting thrusting(Klasner (Klasnerand and others, others, 1991) 1991)tot oproduce producethe thePresque PresqueIsle Isleand and Orogeny Sunday Lake Lake Faults and Rotation of of the the district districtduring during Sunday and the the present present distribution distribution of of rocks. rocks. Rotation Keweenawan Keweenawantilting tiltingproduced producedthe thepresent presentmap mappattern. pattern. 53 �References Cited Cited Dann, Dann, J. C., C., 1978, 1978, Major-element Major-element variation variation within withinthe theEmperor Emperor Igneous Igneous complex complex and and the the Hemlock and Badwater Badwater volcanic volcanic formations: formations: Houghton, Hemlock and Houghton, Michigan, Michigan, M.S. M.S. Thesis, Thesis, Michigan Technological Technological University, University, 199 p. Irving, R. D. and Van Hise, C. Series of of Michigan and Irving, C. R., R., 1892, 1892, The The Penokee Penokee Iron-Bearing Iron-Bearing Series Wisconsin: IXX, 534 p. Wisconsin: U.S. U.S. Geological Geological Survey Survey Monograph Monograph IXX, 534 p. Klasner, J. J. S., S., Ojakangas, Ojakangas, R. R.W., W., Schulz, Schulz, K. K. J., J., and LaBerge, LaBerge, G. G. L., L., 1991, Nature Klasner, Nature and Style of Deformation inthe theForeland Foreland of of the theEarly EarlyProterozoic Proterozoic Penokean Penokean Orogen Orogen Deformation in Northern Michigan: Michigan: U.S.G.S. 1904-K, 22 U.S.G.S. Bulletin 1904-K, 2 2 p. p. Northern Kokelaar, B. P., P., 1986, Magma-water Magma-water interactions interactions in in subaqueous subaqueous and emergent basaltic Kokelaar, B. volcanism: Bulletin vol. 48, 48, p. 275-289. volcanism: Bulletin of Volcanology, Volcanology, vol. Sims, P. P. K., K., Van Van Schmus, Schmus, W. W. R., R., Schulz, Schulz, K. K. J., J., and and Peterman, Peterman, 2. Z. E., E., 1990, 1990, Sims, Tectonostratigraphic evolution of of the the Early Early Proterozoic Proterozoic Wisconsin magmatic magmatic terranes of the Penokean Orogen: Canadian terranes Penokean Orogen: Canadian Journal of Earth Earth Sciences. Sciences. Trent, A., 1973, 1973,Geological GeologicalMap Mapofofthe theMareniso Marenisoand andWakefield WakefieldNE NEquadrangles, quadrangles, Trent, V. A., Gogebic County, Michigan: U.S. U.S. Geological GeologicalSurvey SurveyOpen-File Open-File Report. Report. Gogebic County, Figure 1. Figure 1. 54 Debris flow from from the Emperor Emperor volcanics. volcanics. Larger felsite f e l s i t e clasts clasts hyaloclastite (gray) iin n aa ffine ine h y a l o c l a s t i t e matrix. Paper clip c l i p is i s 33 cm. cm. �w L L L L L U U M - —-L- &././w £ Water W a t e r SSurface urface2 E T TYLER 4 / A 'II RAM SAY 41 A&q4V 44 V / PURITAN 7 // 7 Figure Figure 2a. 2a. Figure Figure 2b. 2b. / -J 7 / 1' I /7 / / BAD RIVER 'I- / 7 I I I Diagram showing showing hypothetical h y p o t h e t i c a l setting s e t t i n g of of the t h e Emperor Emperor Volcanics Volcanics Diagram s i l l s formed formed during during subsidence subsidence of of aa half h a l f graben graben that t h a t deepens deepens and sills and to t o the t h e east. east. S i m p l i f i e d sketch s k e t c h map map showing showing relationships r e l a t i o n s h i p s of of rocks rocks on onthe the Simplified eastern e a s t e r n Gogebic Gogebic range. range. Note Note that t h a t Emperor Emperor volcanics v o l c a n i c sand andsills sills are a r e truncated t r u n c a t e d by by major major faults. faults. 55 �THE CHEMISTRY AND PETROGRAPHY OF MAFIC ROCKS FROM THE EARLY PROTEROZOIC EMPEROR VOLCANIC PROTEROZOIC VOLCANIC COMPLEX COMPLEX NEAR MARINESCO, MARINESCO, MICHIGAN T. P., P., Geology Department, St. St. Norbert Licht, Kathy and Flood, T. College, DePere, WI 54115 54115 The Emperor Volcanic Complex (EVC) (EVC) is an Early Proterozoic Proterozoic sequence of mafic and felsic rocks located in the eastern Gogebic Range. Range. A portion of the EVC crops out near Marinesco, Michigan as massive basalts, pillow basalts, basalts, and and hyaloclastites. hyaloclastites. The The purpose of this this study was to characterize characterize the basalts and hyaloclastites petrographically and chemically in order to make inferences inferences regarding regarding the the formation formation and and alteration alteration of of these these rocks. rocks. The outcrop area of this study is located approximately 10 km north of Marinesco, Michigan and encompasses an area basalts approximately 600m approximately 600m by by 300m. 300m. The outcrop exposes pillow basalts that contain quench quench cracks cracks and and alteration alteration rims. rims. Pillows Pillows range range in in Hyaloclastite, which forms as the result size from 0.lm to 2in. size from O.lm to 2m. the of the interaction interaction of molten rock with seawater or saturated sediments, sediments, varies varies greatly greatly in in texture. texture. Fragments produced through through Some this interaction vary in size interaction vary in size from from aa few fewnun mm to to .5m. .5m. Some fragments contain alteration rims that are similar to pillow rinds. Some pillows included in the hyaloclastite appear rinds. virtually unaltered while others others are highly fractured fractured and and altered. altered. Petrographic Petrographic analysis analysis reveals that the various mafic rocks rocks are characterized by similar mineral assemblages including epidote, plagioclase, and chlorite, with lesser lesser amounts amounts of of Textures are calcite, quartz, and and amphibole. amphibole. Textures are variable. variable. Massive Massive and pillowed basalts are primarily composed composed of subhedral subhedral to to euhedral euhedral mostly mostly fine-grained fine-grained plagioclase, plagioclase, some some euhedral euhedral epidote, epidote, actinolite, and and sporadic sporadic pockets pockets of of quartz. quartz. chlorite, calcite, calcite, actinolite, Rinds on pillows are are comprised comprised mainly of plagioclase, plagioclase, some some chlorite and epidote, epidote, and vein fillings fillings of recrystallized recrystallized quartz. quartz. The hyaloclastite is is composed of angular angular basalt fragments fragments similar similar in texture to the massive basalt in a coarse to fine—grained fine-grained matrix that is is composed composed mainly of epidote, chlorite, chlorite, and and quartz. quartz. Epidote is medium to to coarse—grained coarse-grained and in in many samples samples epidote epidote "flowerettes" are ttflowerettes" are present. present. The chlorite chlorite is is mostly mostly amorphous. amorphous. The quartz is is usually fine-medium fine-medium grained grained and and recrystallized. recrystallized. Some flow structures structures occur occur around the the basalt fragments. fragments. Preliminary chemical chemical data indicates indicates that the the hyaloclastites hyaloclastites are similar ranges SiO, ranges similar in in composition composition to to the the massive massive basalts. basalts. Si02 from 57.2% 57.2% — 63.6%, MgO varies varies from from 2.8% 2.8% - 6.3%, 6.3%, Cr varies from 4oppm. Chemical 5lppm 63ppm and Cu varies from loppm lOppm - 40ppm. 51ppm - 63ppin composition of pillow rinds rinds tend to to be lower lower in in silica silica (54.4%) (54.4%) and higher higher in in Cu Cu (49ppm). (49ppm) - - - . 56 - �suggests The abundance of pillow lavas and hyaloclastites suggests intrusion into into water that extrusion onto the seafloor or shallow intrusion saturated sediments sediments occurred. occurred. The quenching of basaltic lava lava during eruption/intrusion eruption/intrusion resulted in the formation of hyaloclastites. Chemically, the basaltic fragments within the hyaloclastites. hyaloclastites show no greater degree of alteration than the the the exception exception basalts from which the fragments were derived, with the of the alteration alteration rims rims that that surround surround individual individual fragments. fragments. 57 �MAGNETITE MAGNETITE OCTAHEDRA OCTAHEDRA IN IN PILLOW PILLOW BASALT BASALT NEAR NEAR WAWA, WAWAfONTARIO ONTARIO by Frank Frank R. R. Luther, LutherfUW-Whitewater, UW-WhitewaterfWhitewater, Whitewater#WI WI by 53190 53190 Octahedral Octahedral magnetite magnetite crystals crystals in in Archean Archean pillow pillow basalt basalt found found south south of of the the Hwy. Hwy. 101 101 and and Lucy Lucy Pit Pit Road Road intersection intersection near near the the east east end end of of Wawa Wawa Lake Lake have have interested interested numerous numerous geologists geologists since since they they were were noted noted by by Ronald Ronald Sage Sage (Precambrian (Precambrian Geologist, Geologistf Ontario Ontario Geological Geological Survey) Survey) several several years yearsago. ago. Questions Questions related related to to these these crystals crystals include: include: (1) (1) are are they they of of igneous (2) are are the the crystals crystals evidence evidence igneous or or metamorphic metamorphic origin; origin; (2) bearing on on the the origin origin of of the the numerous numerous iron iron formations formations in in the the bearing region; region; and and (3) (3) given given that that pillow pillow basalt basalt is is voluminous voluminous in in the the Michipicoten Michipicoten greenstone greenstone belt, beltf why why are are the the crystals crystals confined confined to to the the rather rather small small area area southeast southeast of of Wawa Wawa Lake? Lake? Field Field studies studies by by the the author author and and Ronald Ronald Sage Sage have have shown shown that that the the magnetite magnetite octahedra octahedra are are confined confined to to an an area area of of about1 1km2 km2. There is is no no recognizable recognizable correlation correlation with with There about . pillow pillow selvages, selvagesf interiors, interiorsf amygdaloidal amygdaloidal zones, zonesf or or stratigraphic stratigraphic horizons; horizons; less less commonly commonly rnagnetite magnetite crystals crystals are are flows. The The magnetite magnetite crystals crystals present in in massive massive basalt basalt flows. present occur occur randomly randomly through through various various pillowed pillowed and and massive massive flows. flows. Petrographically, Petrographicallyf the the magnetite magnetite crystals crystals cut cut across across the the relict relict ophitic/subophitic ophitic/subophitic texture texture of of the the basalt basalt (now (nowalbite, albitef actinolitef epidote, epidotef chlorite, chloritef carbonate carbonate +/-pyrite, +/-pyritef actinolite, hematite). hematite). Preliminary Preliminary reflected reflected light light examination examination suggests suggests that that the the magnetite magnetite is is relatively relatively pure pure and and does does not not show show exsolution/oxidation. exsolution or or exsolution/oxidation. exsolution The above above evidence evidence shows shows the the magnetite magnetite octahedra octahedra to to be be The of metamorphic metamorphic origin; origin; presumably presumably the the crystals crystals were were of generated during during greenschist greenschist facies facies metamorphism metamorphism of of the the generated greenstone belt. belt. Frost Frost (1991) (1991) states states that that metamorphic metamorphic greenstone development of of magnetite magnetite in in metabasites metabasites is is somewhat somewhat unusual, unusualf development especially especially in in iron iron carbonate-rich carbonate-rich environments environments such such as as the the ankerite-siderite rich rich Michipicoten Michipicoten greenstone greenstone belt belt in in the the ankerite-siderite of Wawa. Wawa. One One can can conclude conclude that that the the isolated isolated area area vicinity of vicinity of magnetite magnetite porphyroblasts porphyroblasts was was not not subjected subjected to to the the of complete carbonate carbonate "soaking" "soaking" which which affected affected most most of of the the complete greenstone belt belt in in the the Wawa Wawa district; district; the the lesser lesser degree degree of of greenstone carbonation kept kept the the oxygen oxygen fugacity fugacity low low enough enough to to allow allow carbonation magnetite to to crystallization. crystallization. magnetite Reference: Reference: Frost, B.R., B . R S f1991, 1991f Magnetic Magnetic petrology: petrology: factors factors that that control control Frost, the occurrence occurrence of of magnetite magnetite in in crustal crustal rocks, rocksf in in Oxide Oxide the Minerals: petrologic petrologic and and magnetic magnetic significance, significance, D.H. D.H. Minerals: Lindsley Lindsley ed., e d e fMineralogical Society Society of of America America Reviews Reviews in Mineralogy Mineralogy 2j,5 , p. p. 489-506. 489-506. in 58 �THERMAL MODELING MODELING AND AND ILLITE/SMECTITE ILLITE/SMECTITE GEOTHERNOMETRY GEOTHEMOMETRY THERMAL OF OF THE THE PRECAMBRIAN PRECAMBRIAN ORONTO ORONTO GROUP, GROUPl WISCONSIN WISCONSIN AND AND MICHIGAN MICHIGAN K. L. L. PRICE, PRICEl J. J. HUNTOON, HUNTOONl AND AND T. T. J. J. BORNHORST BORNHORST S. D. D. MCDOWELL, MCDOWELLl K. S. Department Department of of Geological Geological Engineering, Engineeringl Geology, Geologyl and and Geophysics Geophysics Michigan Michigan Technological Technological University University Houghton, Houghtonl MI. MI. 49931 49931 The thermal history history of of Oronto Oronto Group Group sediments sediments in in the the White White The thermal Pine-Iron River syncline area has has been estimated Pine-Iron River syncline area estimated using using aa organic combination combination of illite/smectite (uS) (11s) geothermometry, geotherm~metry~ organic thermal one dimensional thermal maturity maturity indicators, indicatorsl and and one dimensional thermal thermal maturity data constrain modeling. Clay Clay and and organic organic maturity data are are used to constrain modeling. the the thermal thermal modeling, modelingl which which requires requires estimation estimation of of heat heat flow flow (including (including temporal temporal changes changes in in heat heat flow),  £ 1 0 time ~ time ) of of deposition deposition and erosion erosion of of sedimentary sedimentary rocks, rocksl and and lithology-dependent lithology-dependent thermal properties. properties. The The model model outputs outputs the the time-temperature time-temperature thermal history and and time-temperature time-temperature indices indices (TTI) (TTI) for for specified specified history positions I/S positions within within the the rock rock column, columnl and and estimates estimates I/S using Waples (1980, AAPG Bull., v. expandability using Waples (l98Ol AAPG Bullalv. 64, 64#p. p. 619) 619) expandability correlation correlation between between expandability expandabilityand and TTI. TTI. Model Model results results most most closely closely match match data data when when the the sediments sediments are are exposed exposed to to aa thermal thermal pulse pulse starting starting at at 1115 1115 Ma, Mal peaking peaking between between 1105 1105Ma Ma and and 1090 1090Ma, Mal and prodwing aa heating heating cycle cyc1.e of of roughly roughly 35 35 and ending ending by by 1080 1080 Ma, Mal producing Ma duration duration and and maximum maximum temperatures temperatures at at the the level level of of the the Nonesuch 110-125'~. Plausible Plausible total total thickness thickness for for Nonesuch Formation Formationof of110-125°C. the the Freda to 66 Km. Km. Freda Sandstone Sandstone range range from from 44 to Illite/smectite Illite/smectite geothermometry geothermometry (modified (modified from from Pollastro, Pollastrol 1990, 19901 SEPM SEPM Spec. Spec. Pub.) Pub.) has has been been carried carried out out on on clays clays from from the the Nonesuch and Freda drill holes holes in in Wisconsin Wisconsin Freda using using core core from from drill near near the the Michigan Michigan border border (DO-14, (D0-141DO-5), DO-5) from from the the White White PinePineIron and WPB-ll WPB-1, respectivelyl respectively, as Iron River River syncline syncline area area .(WP (WP and as well well as as samples samples from from the the mine mine itself), itself) and and from from aa series series of of drill drill holes holes extending extending northeast northeast to to the the vicinity vicinity of of Trimountain, TrimountainlMI. MI. Expandabilities Nonesuch Formation Formation range in the the Nonesuch range from from a maximum Expandabilities in of 25% 25% smectite smectite (Ri (Rl ordered) in the Iron Iron River Syncline Syncline area area to to values values of of <15% <15% smectite smectite (>R1 (>Rl ordered) ordered) in in Wisconsin Wisconsin and and <5% <5% To smectite (>R1 (>Rl ordered) ordered) at at White White Pine. Pine. To the the northeast northeast smectite expandabilities expandabilities decrease to to trace trace percentages, percentagesl and in in the the vicinity of of Winona Winona pure pure illite illite dominates dominates the the Nonesuch Nonesuch vicinity Formation. maximum Formation. Application Applicationof of I/S I/S geothermometry geothermometry indicates indicates maximum temperatures temperatures in in the the Nonesuch Nonesuch of of approximately approximately 115°C 115'~in in the the Iron Iron River at White Pine, River syncline, synclinel140°C 140'~ in in Wisconsin, Wisconsinl 160°C 160'~ at Pinel and and The most 190'~ near near Winona. Winona. most reliable reliable temperature temperature in the the 190°C smectite smectite to to illite illite sequence sequence is is that of the the change change in in ordering ordering Using from RO RO to to Ri Rl at at 100°C. 100'~. Using just just this this temperature temperature from constraint, above 100°C 100'~ everywhere in in constraintl temperatures temperatures were well above 59 �was reached at distances the Nonesuch Nonesuch Formation, Formationl and 100°C 1OO0c was distances contact of of at at least 300 m at White above the Freda-Nonesuch contact White Pine and 1120 1120 mm at at Winona. Winona. The data indicate indicate aa general general increase temperature northeast northeast toward toward the the Keweenaw Keweenaw Peninsula Peninsula increase in in temperature data also confirms confirms organic organic thermal native native copper copper district. district. The The data thermal maturity results results that indicate indicate maturities were higher higher in in the the relative to the the Iron Iron River River syncline syncline area area and and White Pine Pine area area relative increase increase westward westward into into Wisconsin Wisconsin from from the the area area of of the the syncline. syncline. The I/S I/S results results may also also be be used used to to estimate estimate geothermal geothermal gradients in gradients in the the drill drill holes. holes. In In the Winona area, areal aa gradient gradient of is estimated, estimatedl a value value identical identical to the the average average of SSOC/KXII 55°C/Km is gradient in the modern rift now forming the Salton Trough Salton Trough in in gradients are California. Higher Higher geothermal gradients are suggested suggested in in the the California. White white Pine Pine area, areal which, whichl coupled coupled with with lower lower I/S I/S temperatures temperatures imply decrease in thickness of the the Freda Freda Sandstone Sandstone to imply a decrease in the thickness to the the If true, this supports a Freda depocenter possibly off truel west. west. the Keweenaw Peninsula and in turn suggests suggests deeper erosion erosion of of rocks of the Keweenaw Keweenaw Peninsula Peninsula due to an increase increase in vertical in vertical rocks displacement along along the Keweenaw fault from Wisconsin to the displacement the There a relationship between deeper Keweenaw Peninsula. There may be a relationship between deeper Keweenaw Peninsula. burial burial near the the depocenter depocenter off the the Keweenaw Keweenaw Peninsula Peninsula and and native native copper copper deposits. deposits. The The results results of clay clay expandabilities expandabilities and and geothermometry geothermometry in in While both both expandabilities expandabilities the Wisconsin Wisconsin wells the wells are are anomalous. anomalous. While estimates in Nonesuch Formation Formation are are and temperature estimates and temperature in the the Nonesuch reasonable and with results reasonable and consistent consistent with results further further east, eastl the the change change with depth in the Freda Sandstone expandability with Sandstone there there is is in expandability transition from not. The transition from >80% >80% RO smectite smectite to to <20% <20% Ri Rl smectite smectite not. depth interval interval of of <125 <I25 m, m, a very very abrupt abrupt takes place over a depth versus depth profiles from relative to I/S versus depth profiles from transition transition relative to I/S In addition, both the highly expandable smectite elsewhere. In additionl the expandable smectite elsewhere. and and minor amounts amounts of of kaolinite kaolinite in in the the shallower shallower Freda Freda are are very very SEPM Spec. poorly crystalline. crystalline. Pollastro and Barker Barker (1986, (1986# SEPM Spec. investigated aa well well with a a similar similar expandability expandability Pub. 38) . investigated Pub. 38). profile that had undergone undergone erosion erosion and noted noted that that the the abrupt abrupt transition took place at The transition took at the top top of of overpressuring. overpressuring. The abruptness of the the clay clay transformation, transformationl coupled coupled with with the the poor poor crystallinity of the shallow shallow claysl clays, suggests retrograde retrograde crystallinity of the suggests alteration Freda Sandstone Sandstone after after diagenesis by alteration of of clays clays in the Freda circulating circulating low low temperature temperature waters, watersl perhaps perhaps during during deposition deposition of Bayfield Bayfield Group Group sediments. sediments. The fact fact that that clays clays in the the Nonesuch in the same wells appear to have preserved their Nonesuch same wells appear to have preserved their in turn turn indicates that the Nonesuch diagenetic character character in indicates that Nonesuch Formation here here is is aa permeability permeability barrier. barrier. It is also also quite quite reasonable reasonable to assume assume that that the Nonesuch Nonesuch Formation, Formationl during during diagenesis, depth at which which fluid pressures pressures first first diagenesisl might might mark mark the the depth hydrostatic pressures. exceeded hydrostatic pressures. 60 �ACMITE IN IN TIlE THETROMMALD TROMMALD FORMATION FORMATION OF OF THE THECUYUNA CUYUNA IRON IRON RANGE: RANGE: REVISITED REVISITED MCSWIGGEN, MCSWGGEN?Peter L., G.B. Morey, and Jane M. Cleland, Minnesota Geological Survey, Survey, 2642 2642 55 1 14 University Aveune, St. Paul, Minnesota 55114 In In the the process process of reevaluating possible protoliths protoliths for the the ferromanganese ferromanganese ores ores of the the Cuyuna Cuyuna North NaFesi206, that that was was first first North range, range, we we rediscovered rediscoveredthe theunusual unusual sodic sodicpyroxene pyroxeneacmite, acmite,NaFeSi2O6, described from the Trommald Trom maidFormation Formationby byGrout Grout(1946). (1946). Discovery occurred in a core obtained from the Memtt Merritt Number 2 mine (Sec. 33, T.47N.R29W) T.47N.R29W) where where two kinds of acmite were recognized; recognized; one one aa tea-green tea-green variety that occurs occurs in small small crosscutting veins veins and a second second tan tan to brown variety that occurs as disseminated grains in granules and as core grains in oolitic structures brown variety that occurs as purportedly rimmed by hematite and chert. The two acmite varieties was concentrated in a purportedly rimmed by hematite and The two acmite varieties was concentrated in alayer layer some 7.5 m (25 feet) thick that forms a marker some (25 forms a marker bed bed in in the the Merritt Memtt Number Number 22 and andFerro F m oMines. Mines. Both mines produced appreciable quantities of ferromanganese ferromanganese ore ore averaging averaging 12-14 12-14percent percent Mn. Mn. Therefore Therefore itit seems seems likely likely that that the the origin origin of of the the acmite acmiteisis significant significantto toaa better better understanding understandingof ofthe the origin origin of of the the protoliths protoliths to to the the ferromanganiferous ferromganiferousores. This seveml This investigation investigation focuses focuses on on compositional and and textural relationships of acmite acmite from from several different different settings. settings. Much Muchof ofthe theacmite acmiteoccurs occursas asfme-grained, fme-grained, tan tantotobrown brown material material in inbeds bedsor or lenses, rock. However lenses, with sharp contacts between it and the surrounding rock. However in in some some situations, situations, contacts contacts are are irregular irregular and the acmite is clearly secondary. Acmite Acmite also also occurs occurs as as rounded clasts clasts of either or as as intergrowths intergrowths with rhodonite rhodonite (MnSiO3). (MnSi&). These Theseclasts clasts either coarse coarse crystals, fine fine material, or commonly commonly form formcore coregrains grainsin in oolitic ooliticor or pisolitic-like pisolitic-like structures structureswhere wherethe therim rimmaterial materialisiseither either hematite hematite or or red-colored, cryptocrystalline acmite. However Howeverthese thesegrains grainsmay maynot notbe beof ofordinary ordinary sedimentary origin. Several areactually acmite acmite crystals crystals growing growing into into a Severalgrains grainsshow show that that the the cores cores are center center filled filled with quartz. Other Othercore coregrains grainshave havesecondary secondaryacmite acmitegrowths growths forming formingvariously variously shaped appendages on the rounded clasts. clasts. Acmite Acmite also also occurs occurs as zoned rims around around other kinds of core core grains, grains, including including Mn-oxides, qquartz, m , rhodonite, and rhodochrosite. The Theveined veinedacmite acmite described described by Grout Grout (1946) is is clearly secondary secondary in nature, whereas whereas many of the the other other textural relationships appear to be primary sedimentary structures. Compositionally, Compositionally, the theacmite acmitevaries varies from from approximately 95 mole% mole% NaFeSi2O6; NahSi206; the remainder is made up of other pyroxene approximately 80 80 to to 95 components, containing containing Ca Caand and Mn. Mn. Acmite/aegirine Acmitelaegirine is is a fairly common common mineral mineral series series in in sodium-rich sodium-rich igneous igneous rocks, rocks,but but itit also also occurs in blueschist-facies metamorphic rocks. The TheTrommald Trommald Formation, Formation, however, however?isisaa formation of sedimentary rocks that has been metamorphosed no higher than the upper greenschist facies. Thus ThusGrout Grout (1946) (1946) suggested suggested that that the the acmite acmite formed by a reaction between sodium-rich hypogene hydrothermal solutions and a mixture of chert and hematite. Experimental Experimental work work has has shown that acmite/aegirine can form over a wide range of P-T conditions. The acmitelaegirine can The upper upper stability stability limit limit of acmite 1200°C in in the the pressure pressure acmite as defmed by its its solidus occurs over a temperature range of 780°780°-1200 interval 11 to 10 10 kbars kbm (Bailey, 1969). The Thelower lowerstability stability limit limitfor foracmite acmitehas hasbeen been investigated investigated by by Likhoydov (1981). He Hehas hasshown shownthat thatacmite/aegirine acmitdaegirinecan canform formaccording according to tothe thereaction: reaction: 0.5 Fe203 + 2 Si02 + NaC1 + 0.5 H20 = NaFeSi2O6 + HC1 where the temperature of the reaction is very dependent on the pressure pressure and and on on the the concentration concentration of of NaCl in the solution (Fig. 1). seawater watercontains containsabout about0.5 0.5 molar molarNaC1, NaCl, Likhoydov's 1). Given Giventhat thatsea data suggest that acmite could easily form at temperatures of 200° 200°C or less at very low pressures. Acmite of possible authigenic origin have also been been reported reported from from from from the the Green Green River Formation Formation Utah (Milton and Eugster, 1959), 19591, and from Caithness, Scotland Scotland (Fortey (Fortey and and of Wyoming and Utah Michie, 1978). 1978). 61 �6kb 4kb 0.2 kb 1 kb 2 0.0 hematite hematite ±+ quartz 3000 4.00° 5(JØO Temperature T e m p t u r e (°C) (OC) Figure relative to hematite and quartz 1. Stability Stability of acmite acmite relative quartz Figure 1. (after (after Likhoydov, Likhoydov, 1981). 1981). This project is supported by the U.S. Mines—Selective Mining in Minnesota. U.S. Bureau of Mines-Selective Minnesota. REFERENCES CITED CITED Bailey, D.K., D.K., 1969, The stability stability of of acmite acmite in in the the presence presenceof of H20: H20: American AmericanJournal Journalof of Science, Science, V. 1-16. v. 267-A, p. 1-16. N.J., and Michie, U., U., 1978, Fortey, N.J., 1978, Aegirine of possible authigenic authigenic origin origin in in Middle Middle Devonian Devonian sediments in Caithness, Scotland: Mineralogical magazine,^. 42, p. 439-442. Mineralogical Magazine,v. Grout, F.F., F.F., 1946, 1946, Acmite occurrences on the Cuyuna Range: American AmericanMineralogist, Mineralogist,v. v.31, 31,p. p. 125-130. 125-130. G.G., 1981, 1981, Stability Stability of the aegirine-quartz-hematite aegirine-quartz-hematiteassociation, association,as as shown shownby by Likhoydov, G.G., data: Dokiady experimental data: DokladyAkad. Akad. Nauk. Nauk. SSSR, SSSR,v. v. 242, 242, p. p. 174-176. 174-176. H.P., 1959, Mineral assemblages of the Green River Formation, Formation, in Milton, C. and Eugster, H.P., Abelson P.H. P.H. ed., Researches Researches in in Geochemistry: Geochemistry: New York, John Wiley & Sons, p. 118-150. 118-150. 62 �ABSTRACT Accessing the the Anaconda Geological Geological Documents Documents Collection Collection Wisconsin -- Michigan Minnesota Michigan -- Ontario Ontario Minnesota -- Wisconsin Daniel Daniel N. N. Miller, Miller, Jr.1 Jr.' The International Archive of of Economic Economic Geology Geology is is a unique International Archive unique public repository and research facility available to research facility available to the the mining mining industry and industry and researchers. researchers. The central part of the the archive archive is is the the Anaconda Collection made made available Anaconda Geological Geological Documents Documents Collection available to to the the University University in 1987 1987 by by ARCO ARC0 Coal Coal Company. Company. It consists consists of 1.8 1.8 million documents documents and represents represents more than than 90 90 years years of of corporate corporate records and files files covering covering mineral mineral exploration exploration and mine mine development development records activities throughout throughout much much of of the United States States and 110 110 foreign foreign countries. countries. Others have described this this collection collection as as the the largest largest and most significant significant body of of economic economic geologic geologic data data in in the the world. world. The Anaconda Collection is a wealth of original unpublished geological material material compiled geological compiled by mining geologists, geologists, engineers, engineers, and and specialists specialists who followed followed the the original original policies policies prescribed prescribed by by Reno Reno Sales. Sales Sales establishedthe established the geological geological department H. Sales. department for for Anaconda Anaconda and was their their Chief Chief Geologist Geologist from from 1905 1905 until until he he retired retired in in 1954. 1954. Throughout his a highly Throughout his career, career, he he proved to to be be a highly competent competent administrator, organizer, organizer, and and long-range long-range planner planner who who expected expected the the administrator, staff to employ employ their their highest highest level level of of professional professional competence competence at at His all times. times. His direct, direct, systematic, systematic, analytical, and scientific scientific approach to to exploration played aa major role approach exploration played role in in the the company's company's efforts toward toward data data gathering gathering and record record keeping, keeping, coupled coupled with with peer efforts review files grew grew review of of all all work work performed. performed. As a a result, result, Anaconda's files over over the the years years and and became became the the envy envy of of the the industry. industry. Today, the the Anaconda Geological Geological Documents consists Today, Documents Collection Collection consists codified material on on more than 18,000 geological reports, of codified than 18,000 reports, with 5,500 documents documents and and 6,500 6,500 maps maps on on mining mining prospects prospects alone. alone. over 5,500 There There are are more more than than 10,000 10,000 documents documents with with geologic, geologic, geochemical, geochemical, geophysical, drilling, drilling, assay, assay, and and commodity commodity data data analyses analyses and and many geophysical, thousands of of letters, letters, memoranda memoranda and other other documents: documents: annual annual reports, smelter smelter data, data, surface surface and and underground underground maps maps of of all all kinds, kinds, reports, engineering drawings drawings and mine plans, aerial photographs, remotely remotely engineering sensed imagery, imagery, and and even even thin thin sections sections of of rock rock specimens. specimens. sensed All of of the the material material is is systematically systematically indexed on on aa computer computer and readily readily retrievable retrievable by by country, country, state state or or province, province, data base and name, mining district, commodity, author, author, and and county, county, project/mine project/mine name, district, commodity, date. date. Inventory Inventory searches searches offer access to to the offer initial initial cross-indexed cross-indexed access 1.8 million documents. In of million individual individual documents. In most most instances, instances, print-outs print-outs of inventory inventory searches searches tailored tailored to to specific specific inquiries inquiries can can be developed developed for individual individual users. users. average retrieval retrieval time for for quickly for The average documents is is two two and and one-half one-half minutes. minutes. documents Director, International Archive of Economic Economic Geology Geology Director, International University of Laramie University of Wyoming, Wyoming, Laramie 1 63 �This This collection collection is is maintained maintained and and operated operated entirely entirely as as aa selfselfsupported system through user fees supported system through user fees and and contributions contributions from from the the Neither minerals minerals industry. industry. Neither state state nor nor university university funds funds are are categories of Researchers may may select select any any one one of of the the five five categories of involved. Researchers involved. membership membership in order to to have have direct direct access access to to the the files. files. Each Each membership level level carries carries with with it it certain certain privileges privileges and and membership Separate charges are made for all restrictions. for all reproductions reproductions restrictions. Due ordered. Due to to limitations limitations on work work space, space, access access to to the the ordered. collection is by appointment only, and users should call at collection is by appointment only, and users should call at least least a a week in in advance advance to to reserve reserve research research space. space. The The facilities facilities are are open open to to the the public public from from 88 a.m. a.m. to to 55 p.m., p.m. , Monday Monday through through Friday. Friday. Special arrangements to work work on the weekend can be made made in in some some Members may cases. may also place place orders orders for for reproductions reproductions by by cases. telephone. telephone. Presently, this this archive archive is is handling handling between between 45 45 and and 50 50 Presently, sustaining sustaining client client memberships memberships that that are are primarily primarily corporations, corporations, companies, and and consultants consultants directly directly involved involved in in mineral mineral companies, cases, rapid rapid access exploration. In In most cases, access to to the the information information saves saves exploration. companies companies and and individual individual consultants consultants time time and and money. money. The The other other key key item is is that that there there is is information information available available here here that that is is no no longer longer item available from from any any other other source. source. available example, in in this this part of of the the Great Great Lakes Lakes region region we we have have For example, the the following: following: STATE OR OR PROV. PROV. STATE REPORTS REPORTS Files Documents Files Documents Files Files MAPS MAPS Documents Documents Michigan Michigan 42 42 87 87 66 36 36 Minnesota Minnesota 42 42 77 77 10 10 21 21 Ontario Ontario 88 88 168 168 16 16 29 29 Wisconsin Wisconsin 38 38 68 68 8 8 18 18 For For additional additional information information contact: contact: International International Archive Archive of of Economic Economic Geology Geology American Heritage Heritage Center Center American P.O. P.O. Box Box 3924, 3924, University University Station Station Laramie, Laramie, WY 82071 82071 or call call (307) (307) 766 766 3704 3704 or or 766-6506 766-6506 or 64 �THE NEED NEED FOR FOR AANEW NEWPARADIGM PARADIGM REGARDING REGARDING THE THEPETROGENESIS PETROGENESIS OF THE THE DULUTH DULUTH COMPLEX COMPLEX MILLER, J.D., Ave., St. Paul, MN J.D., Jr., Minnesota Geological Survey, 2642 University Ave., 55114 55114 Recent Recent high-resolution high-resolution U-Pb U-Pb isotopic isotopic age age dates dates of zircons zircons from from Duluth Duluth Complex Complex intrusions rocks intrusions (Paces (Paces and and Miller, Miller, in prep.) indicate indicate that troctolitic and anorthositic anorthositic series series rocks have indistiguishable of about about 1099 (s.4-0.9) (±0.4-0.9)Ma Ma (Table (Table 1). 1). These indistiguishable crystallization ages of unexpected results results compel compel aa significant significantshift shift in in what what has has come come to to be be accepted acceptedas asthe thebasic basic paradigm of the Duluth Complex — that that itit is is predominantly composed composed of two two major major rock rock Complex series series which differ differ in parent magma types, types, emplacement emplacement styles, styles, crystallization crystallization histories, histories, and intrusive ages. With Withhis hiswork work in in the the Duluth Duluth area, area, Taylor Taylor (1964) (1964) was the first first to subdivide subdivide the the Duluth Duluth Complex Complex into into two two distinct distinctrock rock units units on on the the basis basis of of rock rock type, type, intrusive relationships, stratigraphic occurrence, and internal structure. At At Duluth, Duluth, anorthositic anorthositic gabbroic rocks occur occur as a multiple-intrusive, multiple-intrusive, structurally complicated, complicated, laminated (±olivinecumulates, cumulates, which which Taylor Taylor characterized characterizedas as an an laminated suite suite of plagioclase plagioclase (±olivine) igneous igneous breccia. AA4-km-thick, 4-km-thick,well-differentiated, well-differentiated,stratiform stratiform sequence sequence of troctolitic to ferrogabbroic rocks at Duluth and ferrogabbroic cumulates cumulates occurs occurs below the cap of anorthositic anorthositic rocks and has has been been termed termed the the layered layered series. series. Detailed revealed many of the characteristic Detailed mapping mapping elsewhere elsewherein in the complex complex revealed characteristic features features of the two rock suites defined defmed at Duluth. With With the the publication publication of the MGS Centennial Centennial Volume Volume in in 1972, 1972, which included included summaries summaries of this mapping, the terms anorthositic anorthositic series series and troctolitic series acquired a semi-formal status as a chronolithologic and troctolitic series acquired semi-formal status chronolithologic classification. The The genetic genetic implications implications of this this classification classificationwere were first incorporated incorporatedinto into aa petrologic petrologicmodel modelby by Weiblen Weiblen and and Morey Morey (1980) (1980) who postulated that the older anorthositic series was produced from quartz quartz tholeiitic tholeiitic basalt, aa composition composition common common among among early early rift rift lavas, lavas, by flotation flotation of from plagioclase chambers. They plagioclase and sinking sinking of mafic minerals in Duluth Complex chambers. They further further suggested tholeiite parent magma, suggested that that the rocks rocks of the troctolitic troctolitic series series formed from olivine tholeiite aa common emplacedand and common composition compositionamong amongyounger youngerrift rift lavas, lavas, which which had had been been emplaced fractionally fractionally crystallized crystallized in in chambers chambersbetween between the the anorthositic anorthositicseries series cap cap and and its its ultramafic ultramafic base. Most Mostrecently, recently,Miller Millerand andWeiblen Weiblen(1990) (1990)showed showedthat thatboth bothseries seriescould couldhave havebeen been produced produced from fromaa common commonprimary primary magma magma of of high-Al high-A1olivine olivine tholelite tholeiite composition composition and and suggested that the major difference difference between their parent magmas was the amount amount of suggested intratelluric plagioclase plagioclase crystals crystals which they contained contained upon emplacement emplacementinto into the the Duluth Duluth intratelluric Complex. They Theyconcluded concludedthat thatstructurally structurallycomplex complexanorthositic anorthositicrocks rocks were were formed formedfrom from gabbroic gabbroic magmas magmas charged charged with with as as much much as as 60% 60%plagioclase plagioclase creating creatingviscous viscouscrystal crystal mushes, whereas whereasthe the well-differentiated well-differentiatedtroctolitic troctolitic series series rocks rocks fractionally fractionally crystallized crystallized from from mushes, crystal-poor magmas. magmas. Miller Millerand andWeiblen Weiblenhypothesized hypothesizedthat thatcrystal crystalmushes musheswere wereproduced produced crystal-poor early in in the the evolution evolution of of the the Midcontinent Midcontinentrift rift when when magmas magmas tended tended to to pond pond in in lower lower crustal crustal early chambers plagioclase flotation. flotation. As chambers where high pressure would have promoted plagioclase As rifling rifting progressed, crustal crustal magma magma chambers chambers were were thought thought to to have have migrated migrated to to shallower shallowerdepths depths progressed, and and become become more more open open to to recharge recharge and and expulsion, expulsion, thereby thereby producing producing less less evolved evolvedand and less less crystalline magmas. The Theideas ideascommon commonto toboth both these these models, models, that that anorthositic anorthositic series series rocks crystalline were significantly significantly older older than than troctolitic troctolitic series series rocks and and that each each series series was related to to aa were particular stage stagein in the the tectonomagmatic tectonomagmaticevolution evolution of of the the rift, rift, were were not not based based on on definitive definitive particular Rather, they they were were constructs constructs that explained the observable differences evidence. Rather, differences in the internal structure, structure, modal modal mineralogy, mineralogy, cumulus cumulus texture, mode of crystallization, crystallization,and areal areal internal distribution distribution of the two series. ItItnow now appears appearsfrom from the the age age dates dates that the the anorthositic anorthositic and and troctolitic 1086 troctolitic rocks rocks evolved evolvedwithin withinaavery veryshort shorttime timeinterval intervalin inthe the22-million-year 22-million-year(1108(1108-1086 Ma) rift Ma) magmatic magmatichistory historyof ofthe theMidcontinent Midcontinentrift. Field evidence evidencefor for the the relative relative ages ages of of the the two two series series extends extends from from that that which which clearly clearly Field shows the the anorthositic anorthositicseries series to to be be the the older older to to that which would best be be classified classified as as shows 65 �ambiguous. ambiguous. In Inthe thedefinitive definitivecategory categoryare are1) 1)inclusions inclusions of anorthositic anorthositic rock in troctolitic/gabbroic troctoliticlgabbroicrocks rocks and and the the absence absence of the the reverse, reverse, and and 2) 2) sharp sharp intrusive intrusivecontacts, contacts, rarely rarely chilled, chilled,between between troctolitic/gabbroic troctolitic/gabbroic rocks rocks and and anorthositic anorthositic rocks. Not Notdefinitive definitiveare are contacts contacts between between troctolitic troctolitic and and anorthositic anorthositicrocks rocks described described as as obscure, obscure, ambiguous, ambiguous,or or hybrid Beltrame, 1974; Miller, 1986). Still Still hybrid zones zones of mixing (Taylor, (Taylor, 1964; Phinney, 1972; Beltrarne, other other evidence, evidence, such such as as the the presence presence of conformable conformable anorthositic anorthositic layers layers in stratiform stratiform troctolitic intrusions intrusions (Foose (Foose and and Cooper, Cooper, 1978; 1978;Bonnichsen, Bonnichsen, 1972; 1972; Phinney, Phinney, 1969), 1969),the the commonly commonly leucocratic leucocratic composition of many troctolitic troctolitic rocks, and the successive emplacement emplacement of of gradually gradually less less plagioclase-rich plagioclase-rich mushes mushes in in the the creation creationof of some someanorthositic anorthositic series series suites suites (Miller, (Miller, 1986), 1986), suggest suggest that the transition from anorthositic (crystal mush) to troctolitic (magma-dominated) (magma-dominated) magmatism was gradational. Whereas Whereas these these more more ambiguous field relations tended to be overlooked or dismissed as minor ambiguous field relations to overlooked dismissed as minor complications complications to to the the general general picture picture of two-stage two-stage magmatism, magmatism, they are are now seen seen as as being being consistent consistentwith with the the approximate approximatecontemporaneity contemporaneityimplied impliedby by the theage agedata. data. Under Under the the tighter tighter time time constraints constraints imposed imposed by by the the age age dates, dates, several severalnew new or or modified modified models models must must be be developed developed and and tested tested to to explain explain the petrogenesis petrogenesis of the anorthositic anorthositic and and troctolitic troctolitic series. Some Somepossibilities possibilities include: include : -the the two two series series represent represent a rapid progression from emplacement emplacement of plagioclaseplagioclase— enriched enrichedmushes mushesto to magma-dominated magma-dominatedintrusions intrusionsthat thatcould couldreflect reflectthe theevolutionary evolutionary stages stages of a lower lower crustal crustal staging staging chamber chamber from from which which progressively progressivelyless lesscrystal-rich crystal-rich magmas were tapped. Such be caused caused by flushing flushing of the staging Suchan an evolution evolution may may be chamber chamber brought brought on on by by frequent frequentrecharge recharge and andexpulsion. expulsion. —the -the two two series seriesrepresent represent the the products products of different different magma magma processes, processes, perhaps perhaps related related to crystallization shallow emplacement emplacement into crystallizationat at different different crustal crustal depths depths prior to shallow into the the Duluth Complex, which acted concurrently concunently on a common primary primary magma magma type. type. Polybaric Polybaric fractionation fractionation in multi-tiered staging staging chambers has been proposed to explain the compositional compositional range range observed observed in many Keweenawan hypabyssal and volcanic rocks (Klewin, (Klewin, 1989; 1989;Jerde, Jerde, 1991). 1991). -the the two two series series were were produced from from aa common common parent magma magma moderately moderately enriched enriched in in — plagioclase plagioclase crystals crystals by by flotation flotation or or flow concentration of the entrained plagioclase into the roof zone zone of the Duluth Duluth Complex, and subsequent subsequent fractional fractional crystallization crystallization of the the crystal-poor crystal-poor magma below the anorthositic cap. Such Suchaa model model has has been been used used to to explain explain the gabbroic gabbroic and and overlying overlying stratiform stratiform anorthositic anorthositic rocks of the Keweenawan Keweenawan Mineral Mineral Lake Lake intrusion intrusion of of the the Mellen Mellen Complex Complex in in Wisconsin Wisconsin(Olmsted, (Olmsted,1968) 1968)and andthe the plagioclase-rich plagioclase-rich upper upper parts parts of of the the Logan Logan Sills Sills in in northern northern Minnesota Minnesota (Phinney, (Phinney,1968). 1968). Although do not not refute the the possibility possibility that the anorthositic anorthositic Although the the results results of of the the age age dates dates do rocks rocks are are slightly slightly older older than than the the troctolitic/gabbroic troctoliticlgabbroicrocks, rocks, within the the resolution resolution of of the the dating dating (1.5 (1.5 Ma), Ma), the the very very similar similarcrystallization crystallization ages ages for for the two two suites suites strongly strongly suggests suggestsaa common Duluth Complex. Complex. Therefore, the twocommon petrogenesis over a large portion of the Duluth series series classification classification may may be be aa misleading misleading representation representation of the intrusive intrusive history history of the the complex complex and and should should perhaps be abandoned. With With more more high-resolution high-resolution dating dating of Duluth Complex Complex intrusions, intrusions, especially especially among among the the many many discrete discrete layered, layered, troctolitic/ troctolitic/ gabbroic gabbroic intrusions intrusions now now classified classified as as being being part part of the the troctolitic troctolitic series, series, the the two two series series chronolithologic further. Other chronolithologic classification classification may unravel still further. Other age age dates (Table (Table 1) 1) from this study study indicate indicate that that magma-dominated magma-dominated intrusions intrusions producing producing troctolitic/gabbroic troctoliticlgabbroic rocks preceded preceded and and postdated postdated the the 1099 1099 Ma event in other areas of the complex. Also, Also,the the multiple troctoliticl gabbroic and anorthositic rocks and the variety multiple intrusive intrusive nature nature of both troctolitic/ of contact contact relationships relationships observed observed between them imply extended and overlapping periods of both crystal mush and magma-dominated types of magmatism. magmatism. While Whilethe the validity validity of of the the series designations designations awaits geochronologic verification, an even more compelling reason awaits geochronologic verification, an even more compelling reason to to abandon abandon the the chronolithologic chronolithologicclassification classificationat at this this time time is is that that itit will will free free future futurepetrologic petrologic and field studies studies of the bias imposed imposed by its genetic genetic implications. implications. 66 �________ REFERENCES CITED CITED Beltrame, Beltrame, R.J., 1974, 1974,Field Field mapping mapping in in the the Duluth Duluth Complex: Complex: Gabbro Gabbro Lake Lake quadrangle, quadrangle, northern northern Minnesota: Minnesota Geological Geological Survey Open-file Open-file Report, 29 p. Bonnichsen, Bonnichsen, B., 1972, 1972, Southern Southern part of Duluth Complex, Complex, in Sims, Sims, P.K., P.K., and Morey, Morey, G.B., eds., eds., Geology Geology of Minnesota: AACentennial Centennialvolume: volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey,p.p. 361-387. 361-387. Foose, Foose, M.P., and and Cooper, Cooper, R.W., 1978, 1978, Preliminary geologic report on the Harris Lake area, northeastern Minnesota: U.S. 24 p. U.S.Geological GeologicalSurvey SurveyOpen-File Open-FileReport Report 78-385, 78-385,24 p. Jerde, Midcontinent Rift, Jerde, E.A., 1991, 1991,Geochemistry and petrology of hypabyssal rocks associated with the Midcontinent northeastern Ph.D. thesis, University of California, Los Angeles, Angeles, 305 305 p. northeastern Minnesota: Unpublished Unpublished Ph.D. Kiewin, K.W., 1989, Polybaric fractionation in an evolving continental rift: Evidence from the Klewin, 1989, rift: Evidence from the Keweenawan Keweenawan Midcontinent Midcontinent rift: Journal Journalof of Geology, Geology,v. v. 97, 97,p. p. 65-76. 65-76. Miller, J.D., Jr., 1986, 1986, The The geology and petrology of anorthositic rocks in the Duluth Complex, Snowbank Snowbank Lake Lake quadrangle, quadrangle, northeastern northeastern Minnesota: Unpublished Unpublished Ph.D. Ph.D. thesis, thesis,University Universityof of Minnesota, Minnesota, Minneapolis, Minneapolis, 280 280 p. p. Miller, J.D., Jr., and and Weiblen, Weiblen, P.W., P.W., 1990, 1990, Anorthositic rocks of the Duluth Complex: Examples Examplesof ofrocks rocks formed 39. formed from plagioclase plagioclase crystal mush: Journal Journalof ofPetrology, Petrology,v.v.31, 31,p.p.295-3 295-339. Olmsted, J.F., 1968, 1968,Petrology Petrology of of the the Mineral MineralLake Lake intrusion, intrusion, northwestern northwesternWisconsin, Wisconsin, in in Isachsen, Isachsen,Y.W., Y.W., Olmsted, LF., ed., The Science Service The origin origin of anorthosite anorthosite and related rocks: New York State Museum and Science Memoir Memoir 18, 18,p. p. 149-161. 149-161. Paces, J.B. and Miller, J.D., J.D., Jr., in prep., Precise U-Pb ages of Duluth Complex and related mafic intrusions, intrusions, northeastern northeastern Minnesota: Minnesota: Submitted Submitted to Journal Joumal of of Geophysical Geophysical Research Research 4/92. 4/92. Phinney, Phinney, W.C., W.C., 1968, 1968,Anorthosite Anorthositeoccurrences occurrencesin in Keweenawan Keweenawan rocks rocks of of northeastern northeastern Minnesota, Minnesota, in in Isachsen, Isachsen, Y.W., Y.W., ed., The The origin origin of anorthosite anorthosite and and related related rocks: New York York State StateMuseum Museumand and Science Science Service ServiceMemoir Memoir 18, 18,p. p. 135-147. 135-147. 1969, The Minnesota: Minnesota ,1969, The Duluth Complex in the Gabbro Lake quadrangle, Minnesota: Minnesota Geological Geological Survey 20 p. Survey Report Report of Investigations Investigations 9, 9,20 p. ,1972, 1972,Northwestern Northwestern part of Duluth Complex, in in Sims, Sims,P.K., P.K., and and Morey, Morey, G.B., G.B., eds., eds., Geology Geology of Minnesota: AACentennial Centennialvolume: volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey, p. 335-345. Taylor, Minnesota: Minnesota Taylor, R.B., 1964, 1964,Geology Geology of the Duluth gabbro complex near Duluth, Minnesota: Minnesota Geological 63 p. Geological Survey Survey Bulletin Bulletin 44, 44.63 Weiblen, Weiblen, P.W., and and Morey, Morey, G.B., G.B., 1980, 1980, A A summary summary of the the stratigraphy, stratigraphy, petrology, and and structure structure of the the Duluth Complex: American AmericanJournal Journalof of Science, Science,v. v. 280-A, 280-A, p. p. 88-133. 88-133. ------------------------ Table Table1.1.Summary Summaryof ofU-Pb U-Pbage agedates datesof of zircon zircon and and baddeleyite baddeleyite from from Duluth Duluth Complex Complex and and inprep.). prep.). related intrusive intrusiverocks rocks(from (fromPaces Pacesand andMiller, Miller,in related Samule Sample Rock Rock Unit Unit Location Location FC1 FCl Anorthositic Anorthositic Series Series Forest Forest Center Center AS3 AS3 Anorthositic Anorthositic Series Series Duluth Duluth area area 1099.2±0.4 1099.2k0.4 55 P02 PG2 Troctolitic Troctolitic Series Series Powerline Gabbro Gabbro Troctolitic Troctolitic Series Series upper upper layered layered series series Nathan's Lay. Series Series Basal Basalcontact contactUnit unit df Beaver Beaver Bay Bay Complex Complex Sonju Sonju Lake Intrusion Intrusion BeaverBayComplex Beaver Bay Complex Silver Silver Bay Intrusions Intrusions Dunka area Dunka R. area 1098.6±0.5 1098.6*0.5 88 Duluth Duluth area area 10993±0.3 1099.3k0.3 66 Gunflint Gunflint Trail Trail 1106.9k0.4 1106.9±0.4 55 Finland Finland 1096.1±0.5 1096.lkO.5 44 SilverBay Silver Bay 1095.8±1.1 1095.8kl. 1 66 Dl Dl NLS5 NLS5 SLI1 SLIl SBG2 SBG2 207m206?b age ace 207EhL206Pb 1099.0±0.3 1099.0k0.3 Analyses Analvses 55 67 �RARE EARTH ELEMENT ELEMENT DISTRIBUTION DISTRIBUTION PATTERNS IN EARLY EARLY PROTEROZOIC WON-FORMATIONS IRON-FORMATIONS OF THE PENOKEAN PENOKEAN OROGEN, EASTEASTCENTRAL MINNESOTA MINNESOTA Morey, G.B., G.B., and Terrence J. J. Boerboom, Minnesota Minnesota Geological Geological Survey, 2642 2642 University Paul, MN MN 55113 55 113 Avenue, St. Paul, Minnesota consists consists of of two two major components, components, an The Penokean orogen in east-central Minnesota allochthonous fold-and-thrust fold-and-thrust belt on the southeast allochthonous southeast and one or more more tectonic tectonic foredeeps foredeeps on on the the terranes northwest. The The fold-and-thrust fold-and-thrust belt consists consists of several discrete structural panels or krranes that have have small-scale small-scale features consistent with large-scale northwestbounded by cliscontinuities discontinuities that northwestnappes. Correlations panels are are impossible. impossible. The fold-and-thrust belt belt flanks flanks aa verging nappes. Correlations between the panels tectonic foredeep which extended to the Mesabi Mesabi range range in in northern northern Minnesota Minnesota and and the the Gunflint Gunflint range range in Ontario. Ontario. Although structural structural details are complicated, complicated, the orogen orogen also also can can be be divided divided into into an an early early extensional phase when sedimentary rocks, including iron-formation, iron-formation, were deposited deposited on a extensional southward-facing continental margin, and a subsequent subsequent compressional compressional phase when these and metamo~hosed metamorphosed and and when when one one or or more more northwardnorthwardcontinental-margin deposits were folded and migrating foredeep foredeep basins were partly filled fdled with iron-formation, iron-formation,as as well well as as detritus detritus derived derived from from both the north and the south. The The fact fact that that iron-formation iron-formationwas was deposited depositedduring during both both extensional extensional and compressional phases of the Penokean orogeny is is of considerable considerablesedimentological sedimentological significance. significance. persisted in in east-central east-centralMinnesota Minnesota from from approximately approximately 2200 2200 Extensional tectonic conditionspersisted m.y. m.y.. Bodies m.y. to about 1900 m.y.. Bodies of of iron-formation iron-formation deposited deposited during during that that interval interval include include those those in in range, the the Trommald Trommald Formation Formation of of the Cuyuna North range, Glen Township, the Cuyuna South range, Philbrook area. The and the Philbrmk The first frst two units units have sedimentological features indicative of "Algomatype" iron-formation, features indicative indicative of iron-formation,whereas whereas the latter two units have mineralogical features hydrothermal-fumarolic hydrothermal-fumarolicprocesses. m.y. to 1870 m.y. and iron1870 may. Compressional tectonic conditions persisted from about 1900 m.y. during that that time time are are assigned assigned to tothe theAnimikie AmmikieGroup. Group. They include the formations deposited during respectively, and the Biwabik and Gunflint Iron Formations of the Mesabi and Gunflint ranges, respectively, A of of the the Ruth Ruth Lake Lake area areain inthe theEmily Emilydistrict. district. These units units of of iron-formation iron-formation have have so-called unit A of "Iake "Lake Superior-type" iron-formations. sedimentological attributes indicative of of 95 95 REE REE analyses. analyses. In general, Algoma-type iron-formations have We report here the results of moderate REE abundances (La = =0. lx-0.9 xx 1986 0.1~-0.9 1986North North American American shale shale composite--NASC), composite-NASC), and and generally flat to somewhat are generally somewhat depleted depleted in the the heavy heavy elements elements (most (most La/Ybn M b n == 11 - 3). In addition, addition, iron-formation from Glen Township Township has consistently larger negative Ce anomalies anomalies (most CdCe*n Ce/Ce*n iron-formation = 0.65 = 0.65 -- 0.90), whereas iron-formation from the Cuyuna South Range has small negative to (Ce/Ce*n = 0.82 -- 1.04). Both units have positive Eu anomalies (most positive Ce anomalies (CdCe*n EuIEu*n Philbrook iron-formations EuEu*~ = 1.1 -- 1.5). 1.5). The Trommald Trommald and Philbrmk iron-formations have REE concentrations that = 0.1 x-lx are similar to the Algoma-type iron-formations ((La La = x- l x1986 1986NASC). Rocks Rocks associated associated Philbrook iron-formations iron-formations have with the Philbmk have generally generally flat flat REE RIB patterns patterns (most (most La/Ybn LdYbn == 0.7 -- 1.9) and consistent negative Ce anomalies (Ce/Ce*n = = 0.73 - 0.93). In contrast those from the Trommald 1 -3) HREE-depletedpatterns patterns(most (mostWYbn La/Yb = =1 3) and and both both positive and negative Ce Formation have HREE-depleted anomalies (Ce/Ce*n = = 0.58 -- 1-24], 1.24), relative to the 1986 NASC standard. Iron-formations of the wide range rangeof of REE REEabundances. abundances. In the the Biwabik Biwabik Iron lion Formation, slaty Animikie Group display aa wide = 0.5 x 1986 (La == 0.1 0.1 -- 0.5 1986 NASC) than the cherty units (Lan = units contain larger concentrations concentrations (La standard). The 0.09 - 0.1 x 1986 1986 NASC American shale standard). The slaty units are slightly HREE-depleted (most W La/Ybn Ybn = = 1.06 1-06-- 1.71), 1.71), whereas the cherty units have flat to slightly HREE-enriched slopes slopes = 0.75 - 1.18). In general both show very small, both positive and negative Ce Ce anomalies anomalies ( W b n= (La/Ybn (Ce/Ce*n = = 0.8 -- 1.6) and positive Eu anomalies anomalies (most (most EuIEu*n E u E u *= = ~ 1.2 -- 2.0). The Emily (Ce/Ce*n = 0.32 - 0.87) Formation, on the other hand, shows pronounced negative Ce anomalies (CdCe*n 68 �0.4 x - 2.0 x 1986 and higher total total REE REE(most (mostL.a L a = 0.4 1986 NASC, but have similar similar slopes slopes and and positve positve Eu Eu anomalies anomalies to the other foredeep iron-formations. Although small local differences exist, broad similarities in the REiE REE data imply that tectonic setting was not lbther the data imply that not particularly particularly important important in in iron-formation iron-formation sedimentationsedimentation. Rather the various units of iron-formation were deposited from from aa compositionally compositionally homogeneous homogeneous reservoir reservoir that persisted over at least 150 m.y. m.y. of of geologic geologictime. time. However the general lack of pronounced pronounced Ce anomalies and the presence of positive Eu anomalies implies that the reservoir reservoir was not simple "ocean watern, water", but rather had a "hydrothermal" component. "hydrothermalt' The project was supported in part by the U.S. U.S. Bureau of Mines Selective Mining Mining in Minnesota Minnesota Minerals Initiative and the Minnesota Minnesota Department Department of of Natural Natural Resources, Resources, Division Division of of Minerals, Public Geologic Sample Sample Program. 69 �EVIDENCE OF AN EXHALATIVE CONTRIBUTION TO THE EVIDENCE EXHALATWE CONTRIBUTION THE MANGANESE MANGANESE MINERALOGY OF OF THE TROMMALD FORMATION, CUYUNA CUYUNA IRON IRON RANGE, RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA and Jane Jane M. M. Cleland, Minnesota Minnesota Geological Survey, 2642 Morey, G.B. Peter L. McSWIGGEN, and 55114 University Aveune, St. Paul, Minnesota 55 114 The The Trommald Trommald Formation Formation on the the Cuyuna Cuyuna North range range in east-central Minnesota Minnesota was a major major producer producer of iron iron ore for for 80 80 years. Between Betweendiscovery discoveryin in1904 1904and andclosing closingin in 1984, 1984,the therange range shipped more than 106 106 million tons, much of which which was was ferromanganese ferromanganeseore orethat that contained contained5-15 5-15 percent percent manganese. ItItisisthat that manganese manganesecomponent componentthat that sets sets the the Cuyuna Cuyuna range apart from fkom other Early iron-mining districts k l y Proterozoic iron-mining districts in the lake Superior Superior region. interpretations assumed that the ferromanganese ferromanganese ores Until very recently, most geologic interpretations ores were were formed through formed through the oxidation oxidation and and leaching leaching of a "green "green carbonate carbonateslate" slate" protolith protolith located locatedat at or or near near aa granular) and and thin-bedded thin-bedded (slaty, (slaty, non-granular) non-granular) ironirontransition between thick-bedded (cherty, granular) formation. These Thesetwo two lithofacies lithofacies were were thought to represent considerably different sedimentological regimes, the thin-bedded rocks deposited "deeper" water below wave base under mildly regimes, the deposited in "deeper" reducing conditions the thicker bedded rocks reducing conditions the thicker rocks deposited deposited near near or or above above wavebase wavebaseunder under oxidizing oxidizing conditions. In Inthat thatmodel, model, the the distribution distributionof of the the ferromanganese ferromanganeseores ores would would have have been controlled controlled by the configuration of the Trommald depositional basin. the pretectonic paleogeographic configuration paragenesis of the In an effort to better understand the paragenesis the ferromanganese ferromanganeseores, ores, we we reexamined reexamined core h m a hole drilled drilled on the property of the Merritt Number 2 mine in the northwestern part of core from been in storage since the the the North range. The The site site was was one one of four drilled in 1942 1942 and the core has been 1 950s. The The Menitt Merritt core core is is of of particular particular interest because because it intersects the entire Trommald Trommald 1950s. Formation carbonate slate." Formation in the the vicinity of unaltered "green carbonate We focus here on observations fiom from the thick-bedded upper part of the iron-formation. structures are an important component of the cherty rocks. rocks. They They were were thought thought by by Grout Grout Spherical stmctures (1946) jasper and (1946) to to be oolites oolites or or pisolites pisolites consisting consisting of jaspa and chert chert rims rims concentrically concentricallysurrounding surrounding cores acmite. In cores of quartz, feldspar, or acmite. In reality reality these these spheroids spheroids are far more complex than envisioned by Grout. The Thetypical typicalspheroid spheroidcontains containsaa clast clast at at its its center, center, surrounded surrounded by bands of lateral mineral growth. Both variety of of Both the the central central cores cores and and the associated associated rim material consist of aa variety minerals and/or hematite. hematite. Very minerals including acmite, rhodonite, rhodochrosite, Ba-feldspar, andor Very little little free k e quartz has been found; material previously thought to be jasper jasper consists mostly mostly of of rhodonite rhodomte or quartz acmite. acmite. Some spheroids Some spheroids have fairly simple simple mineralogical and textural textural attributes, attributes, but others others are are very very include: clasts complex. Some Someof the the observed complexities include: clasts of Ba-feldspar surrounded by rhodochrosite; rhodonite surrounded surrounded successively by hematite, Ba-feldspar and and ultimately ultimately rhodochrosite; rhodochrosite; rhodochrosite; clasts clasts of rhodonite rhodonite surrounded surrounded by rhodochrosite; rhodochrosite; clasts clasts of of acmite acmitesurrounded surroundedby by red red cherty-looking acmite; clasts of of rhodonite rhodonite surrounded by by red red cherty-looking cherty-looking rhodonite; rhodonite; clasts clasts of of cherty-looking Mn-oxide rhodochrosite surrounded Mn-oxide surrounded surrounded by acmite; acmite; clasts clasts of rhodochrosite surrounded by acmite; clasts of rhodochrosite rhodochrositesurrounded surrounded by hematite, hematite, which in in turn is is surrounded surrounded by rhodochrosite. rhodochrosite. Most of the minerals acmite which was ffirst by Grout ~ sdescribed described t Grout minerals described described above, other than acmite (1946), have not been been reported reported previously previouslyfrom fromthe theTrommald TrommaldFormation. Formation. Of particular interest is is (19461, the Ba-feldspar which also occurs in veins with rhodonite and carbonate, carbonate, and and as as a secondary secondary mineral surrounding grains grains of of stoichiometrically stoichiometricallypure pure K-feldspar. K-feldspar. The composition of the Bamined feldspar in these rocks varies from fiom about about 10 10to to 22 22 mole mole percent percent BaA12Si2O8. BaAl2Si2Og. been reported reported from from only only aa few few llocalities inthe theworld. world. Much of it is associated associated Ba-feldspar has been d i t i e s in deposits andor and/or Pb-Zn with deposits inferred to be of exhalative origin, including manganese deposits deposits. These These include includeBroken Broken Hill, Hill, New South South Wales Wales (Segnit, (Segnit, 1946), 19461,southern southern Grampian Grampian Highlands, Highlands, Scotland (Coats (Coats and others, 1984; Fortey and Beddoe-Stephens, 1982), 1982), central North 70 �Greenland (Jakobsen, 1990), 19901, Sweden (Bostrom and others, 1979; Lundstrom and Wadsten, 1979), Japan (Nakano, 19791, 1979), Wales Wales (Smith and others, 1949), Namibia Namibia (Vermaas, 1953), 19791, Japan 19531, and Greece (Reinecke, 1982). Stratiform Stratiform tourmalinites tourmalinites and barite veins also exist on the North range, hydrothermal component for the origin of these and are additional evidence for a fumarolic hydrothermal deposits. This project is supported by the U.S. U.S. Bureau of Mines-Selective Mines—Selective Mining in Minnesota. Minnesota. REFERENCES CITED CITED Boström, Bostrom, K., K., H. Rydell, and 0. 0.Joensuu, Joensuu,1979, 1979,Lângban—an LAngban-an exhalative sedimentary sedimentary deposit: Ecomonic Ecomonic Geology, Geology, v. 74, 74, p. 1002-1011. 1002-1011. J.S., N.J. NJ. Fortey, Coats, J.S., Fortey, N.J. N.J. Gallagher, and A. Grout, 1984, 1984, Stratiform barium Dalradian of of Scotland: Scotland: Economic enrichment in the Dalradian Economic Geology, Geology, v. 79, p. 1585-1595. 1585-1595. NJ., and Fortey, N.J:, and B. B. Beddoe-Stphens, Beddoe-Stphens, 1982, 1982,Barium Barium silicates silicatesin in stratabound stratabound Ba-Zn Ba-Zn mineralization in the Scottish Dalradian: Mineralogical Mineralogical Magazine, Magazine, v. 46, p. 63-72. p. F.F., 1946, Acmite Acmite occurrences occurrences on on the the Cuyuna Cuyunarange, range,Minesota: Minesota: American Grout, F.F., Mineralogist, Mineralogist, v. 31, 3 1, p. 125-130. 125-130. Jakobsen, U.H., 1990, 1990, A hydrated barium silicate silicate in umetamorphosed umetamorphosed sedimentary sedimentary rocks of central North Greenland. Mineralogical MineralogicalMagazine, Magazine,v. v. 54, 54, p. p. 81-89. 8 1-89. Lundström, Lundstrom, I., and T. Wadsten, 1979, 1979, Barium feldspar feldspar from Lillsjön, Lillsjon, southern southern Sweden: Sweden: 101, p. 229-232. 229-232. Geologiska Foreningens i Stockholm Forhandlingar, Forhandlingar, v. 101, barium microcline, microcine, hyalophane Nakano, S., 1979, Intergrowth of barium hyalophane and and albite albite in the the barium-containing alkali alkali feldspar feldspar from from the the Noda-Tamagawa Noda-Tamagawa mine, mine, Iwate Iwate Prefecture, Prefecture, Japan: Mineralogical Mineralogical Journal, Journal,v. v. 9, 9, p. p. 409-416. 409-416. Reinecke, Cymrite and celsian in manganese-rich metamorphic Reinecke, T., 1982, 1982, Cynxite metamorphicrocks rocks from from Andros Island/Greece: Contributions Contributionsto to Mineralogy Mineralogy and and Petrology, Petrology, v. 79, p. 333-336. 333-336. Segnit, E.R., E.R., 1946, 1946, Barium-feldspar from from Broken Broken Hill, Hill, New New South SouthWales: Wales: Mineralogical Magazine, v. 27, p. 166-174. Mineralogical 166-174. Smith, W.C., W.C., F.A. F.A. Bannister, and M.H. M.H. Hey, Hey, 1949, Cymrite, a new barium mineral from the Benallt manganese mine, mine, Rhiw, Rhiw, Carmvonshire: Carnarvonshire: Mineralogical 1. Magazine, v. 28, 28, p. p. 676-68 676-681. F.H.S., 1953, A new occurrence of of barium-feldspar barium-feldspar at Otjosondu, SouthVermaas, F.H.S., Africa, and an X-ray method for determining determining the composition of West Afica, hyalophan: American AmericanMineralogist, Mineralogist,v. v. 38, 38, p. 845-857. 845-857. 71 �HIGH TEMPERATURE TEMPERATURE HYDROTHERMAL ALTERATION ALTERATION OF Cu-Ni SULFIDES, ASSOCIATED WITH WITH PGE PGE ENRICHMENT ENRICHMENT OF SULFIDES, DUNKA ROAD, ROAD, DULUTH COMPLEX, COMPLEX, NE NE MINNESOTA Penelope Morton Morton and Stephen D. Geerts Penelope Geerts Department of Geology Geology University of Minnesota-Duluth Minnesota-Duluth Duluth, 5581 2 Duluth, MN, 55812 The Dunka Road Cu-Ni deposit deposit occurs occurs at at the base of of the Partridge River Intrusion Road Cu-Ni (PRT)within within the the 1.1 Ga Ga Duluth Duluth Complex. Complex. The The deposit deposit is approximately approximately 55 km by 1.25 km (PRT) km areal extent. extent. Relogging Relogging of of 80 80 drill drill holes holes has has identified identified seven seven major major lithologic lithologic units that in areal can be correlated correlated over over the the whole whole deposit deposit as as well well as as 27 km along along strike within within the thePRT PRT (Geerts, 1991; 1991; Severson (Geerts, Severson and and Hauck, Hauck, 1990). 1990). All All units units (I (I through through VII) VII) are are primarily primarily composed of troctolitic troctolitic anorthosite anorthositeto t opyroxene pyroxenetroctolite troctoliteand andininlesser lesseramounts, amounts, gabbroic gabbroic anorthosite and and olivine olivine gabbro. gabbro. Units Units 11,II, VI VI and VII have basal ultramafic units; and VII basal ultramafic units; other other anorthosite contacts between between units units have have been been interpreted interpreted on the basis basis of of other other mineralogical mineralogical and and textural differences (Figure 1). differences (Figure 1). About 90% 90% of of the the total totalsulfide sulfide mineralization mineralization occurs within Unit Unit I.I. It is interstitial and widespread, widespread,however howeveritit varies variesinin mode modefrom from rare rareup uptto and o 55% % and and it also also varies varies in in continuity and 0 cm tto m. Major and thickness from 110 o 1100 m. Major sulfide minerals minerals include include pyrrhotite, chalcopyrite, minor cubanite. cubanite. These are usually usually primary. primary. Minor amounts chalcopyrite, pentlandite and minor These are of bornite, bornite, native native copper, copper, sphalerite, sphalerite, galena, galena, pyrite, pyrite, talnakhite talnakhite and and mackinawite mackinawite or or valleriite occur throughout unit I and textures indicate that in most cases these minerals valleriite unit I and textures indicate that in most cases these minerals tend to t o replace replace the the primary primarymineral mineralassemblage. assemblage. Three CuIPGE Cu/PGE enriched enrichedhorizons horizonshave havebeen beenidentified identifiedwithin within unit II (Geerts, (Geerts, 1991), 19911, This horizon occurs of which whichhas hasbeen beencalled calledthe theRED RED horizon. horizon. horizon occurs the most most continuous continuous of directly ultramafic layer layer (lla, (Ila, Figure Figure 1) 1) in in the the uppermost portion of of unit directly beneath beneath ultramafic uppermost portion unit I.I. ItIt ranges from 33 tto averageCu Cucontent contentofof 0.57% 0.57% and and Pt Pt+Pd ranges from o 10 10 m m thick and and contains an average Pd recognized in in 887% contents of 991).1. It has been recognized of 986 986ppb ppb(Geerts, (Geerts,11991 7 % of the the holes holes logged. logged. Texturally than the the rest of unit Texturally this zone zone is is more more coarse-grained coarse-grained than unit I and contains more more secondary sulf ides that elsewhere in the section. For example bornite, pyrite, sphalerite, example bornite, sphalerite, secondary sulfides that elsewhere in the section. galena and native copper copper have have only only been recognized recognized in in the the enriched enriched zones, zones, in particular particular galena and the RED RED zone. both below Detailed logging, logging, both below and and above above the RED RED horizon horizon shows shows that the the predominant host rock, rock, anorthositic anorthositic troctolite, troctolite, exhibits predominant host exhibits subtle subtle fracturing fracturing and and alteration. alteration. Plagioclase has been been saussuritized, saussuritized,pyroxene pyroxeneisis now now greenish Plagioclase has greenish uralite uralite and and olivine olivine is abovethe the RED REDisisalso alsoserpentinized. serpentinized.The The majority majority of the ll(a) above the serpentinized. Olivine Olivine in inUnit Unit11(a) sulfide itself is sulfide is coarse-grained coarse-grained (5 mm) mm) and and commonly commonly rimmed by secondary secondary red-brown red-brown biotite. biotite. Plagioclase Plagioclaseboth bothinside insideand and outside outside of of this thiszone zone is is cumulus, cumulus, occurring occurringas asanhedral anhedral tabular tto crystals. The varies from from 2 to tto o subhedral, subhedral, tabular o lath-shaped lath-shaped crystals. The average average grainsize grainsize varies t o 66 mm throughout all the the troctolitic rocks throughout all rocks (Units (Units I-VII), 1-VII), however however within the the red red zone zone the the grainsize increases tto 4-10 1 0 mm. mm. grainsize increases o 4Plagioclase in in 50% 50% of of the samples throughout the section contains Plagioclase samples throughout contains reddish-black reddish-black Within the RED zone, where plagioclase is in contact needle-like inclusions. inclusions. the RED zone, where plagioclase is in contact with finefinegrained secondary sulfides (in particular bornite and remobilized remobilized chalcopyrite), chalcopyrite), the the needles needles are absent from the edges of the plagioclase. plagioclase. Where Where the the needles needles are are absent in a particular plagioclase crystal, crystal, the plagioclase plagioclase plagioclase shows undulatory undulatory extinction. extinction. These plagioclase plagioclase + I 72 �crystals are are interpreted interpreted to t o have have been been recrystallized recrystallized during during sulfide sulfide °remobilization'. "remobilization". crystals Microprobe analysis of plagioclase the zone zone plagioclase from from 18 1 8samples samplesfrom from within within and outside the generally An content varies varies from 60-65% whereas whereas within within the the recrystallized recrystallized show that generally o 75-90%. These compositions compositions of ofplagioclase plagioclase areas the the An An content content has been been increased increasedt to 75-90%. These are consistent alteration by by saline saline solutions solutions at temperatures in excess of 7 0 0 ~ ~ are consistent with with alteration at temperatures in excess of 700°C (Sassani and Shock, Shock, 1990). (Sassani and 1990). REFERENCES REFERENCES Geerts, S.A., 1991. Cu-Ni Geerts, S.A., 1991. Geology, Geology,Stratigraphy, Stratigraphy,and andmineralization mineralizationofofthe theDunka DunkaRoad RoadCu-Ni Northeastern Minnesota. Minnesota. Natural NaturalResources ResourcesResearch Research Institute InstituteTechnical Technical prospect, Northeastern Report, Duluth, Minnesota, NRRIITR-91-14, Duluth, Minnesota, 63 63 pp. pp. Report, NRRI/TR-91-14, Shock, E.L., E.L., 1990. 1990. Supercritical mass-transfer during during aqueous aqueous Sassani, Sassani, D.C., D.C., and and Shock, Supercritical mass-transfer alteration of of mafic mafic intrusive intrusive rocks. rocks. GSA Programwith with Abstracts, Abstracts, V. V. 22, 22, #7, #7, pp alteration GSA Program 213. Severson, M.J., M.J., and and Hauck, Hauck, S.A., S.A., 1990. Geology, Severson, Geology, geochemistry, geochemistry, and stratigraphy of aa portion of the portion the Partridge Partridge River River Intrusion, Intrusion, Northeastern Minnesota. Natural Northeastern Minnesota. Natural Resources Research Institute, Institute, Technical Resources Research Technical Report, Report, NRRI/GMIN-TR-89-1 NRRIlGMIN-TR-89- 1 1, Duluth, Duluth, Minnesota, Minnesota, 240 240 pp. pp. 73 �FIGURE FIGURE 1. 1. GENERALIZED GENERALIZED IGNEOUS IGNEOUS STRATIGRAPHIC STRATIGRAPHIC COLUMN COLUMN fl UNITUNIT VII"11 Anorthcitic Anorthositic Troctolite Troctolite — coarse—grained, basal uitramofic ultromafic layer coar3e-grained, basal layer Vll(a) Vll(a) - VIl(o) MAGENTA Horizon UNIT VI Troctotitic Trocto!itic Anorthosite Anorthosite to to Troctolite Tractolite — basal ultrornafic - fine— fine- to coarse—groined, coarse-gmined. basal uitramafic layer layer Vl(o) Vl(a) UNIT V Anorthositic Anort3ositic Troctolite Troctolite UNIT IV Anorthc'sitic Troctolite to Troctolite/Augite Anorthositic Troctolite Troctolite/Augite Troctolite Troctolite Vl(o) - — coarse—grained coarse-grained - — coarse—grained coarse-grained 11(a) UNIT III Troctolitic Troctolitic Anorthosite Anofthosite to t oAnorthositic Anorthositic Troctolite Troctolite — mottled olivine - fine—grained, fine-grained, mottied olivine texture texture UNIT Troctolite Troctolite to to Augite Augite Troctalite Troctolite — - medium— medium- to t o coarse—grained, coarse-grained, basal basal ultramofic ultramaficlayer layer11(a) ll(a) It 1(b) KO) RED Horizon GRANGE Horizon Horizoc ORANGE 1(a) l(a) UNIT UNIT I I YELLOW YELLOW Horizon Horizon Anorthositic Anorthositic Troctolite Troctdite to toAugite AugiteTroctolite Troctolite — - fine— fine- to to coarse—grained. coarse-grained. sulfide sulfide bearing, bearing, abundant abundant hornfe!s hornfels inclusions inclusions and ond local local ultramafic ultramaficlayers layers (a) [(a) and and1(b) l(b) VIRGINIA FORMATION {-I 74 BIWABIK BIWABIK IRON—FORMATION IRON-FORMATION SCALE (m) �THE THEKENORA KENORA-- KABETOGAMA KABETOGAMADIKE DIKE SWARM: SWRESULTS RESULTSOF O F TRACE TRACE ELEMENT ELEMENT STUDIES STUDIES Andrew AndrewD. D.Moshoian, Moshoian,Karl KarlR. R. Wirth Wirth and andJohn JohnP. P.Craddock Craddock Geology MN,55105 55105 GeologyDepartment, Department,Macalester MacalesterCollege, College,St. St.Paul, Paul,MN, The Kabetogamamafic mafic dikes dikescomprise comprise aa swarm swarmthat thatextends extendsfrom fromthe theMesabi MesabiIron Iron TheKenora Kenora-- Kabetogama Range, Range,Minnesota, Minnesota,northwest northwesttotoKenora, Kenora,Ontario, Ontario,aadistance distanceofofabout about300 300km km(Figure (Figure1). 1).AARb Rb--Sr Sr isochron isochronfor forthe thedikes dikesgives givesan anage ageofof2120±67 2120 k 67Ma Ma(Beck (Beckand and Murthy, Murthy,1982), 1982),suggesting suggestingthat thatdike dike emplacement emplacementmay mayhave haveoccurred occurredcontemporaneously contemporaneouslywith withEarly EarlyProterozoic Proterozoicextension extensionin inthe theAnimikie Animikie Basin in northeast northeast Minnesota KK dikes dikesstrike strike—N-S -N-S in Minnesota Basin of of the theLake LakeSuperior Superiorregion region(e.g., (e.g.,Morey, Morey,1983). 1983).The TheKK and -.E-W in west-central Minnesota and everywhere have vertical dips and cross-cut a variety and -E-W in west-central Minnesota and everywhere dips and cross-cut a varietyof of Archean parallel to Archean granite-greenstone granitegreenstone terranes. The The dikes are undeformed and are everywhere parallel to faultfaultfracture arrays in the country rock that are filled with epidote, quartz and calcite (Craddock and fracture arrays in the country rock that are filled with epidote, quartz and calcite (Craddock and Moshoian, are common commonalong along most of of these brittle brittle features Moshoian, 1991). 1991). Strike-slip Strike-slip offsets are featureswhich whichare areclosely closely spaced meter), regionally regionally distributed distributed and and appear genetically spaced(—1 (-1 meter), genetically related to the the evolution evohtionof of the theKK KK mafic maficdikes dikes(Penokean?). (Penokean?). Trace samples. The Trace element element concentrations concentrationswere determined determined for 12 samples. Theconcentrations concentrationsindicate indicate Southwick and and Day Day (1983) (1983) recognized many of significant geochemical geochemical variation between dikes. Southwick significant recognized that many the thedikes dikeshave been deuterically phases. Most Mostof the havebeen deutericallyaltered altered to secondary hydrous mineral mineral phases. of the incompatible incompatibleelements, elements,with withthe theexception exceptionof ofsome someof ofthe thealkali alkalielements, elements,are arewell well --correlated correlated suggesting suggestingthat thatthe thetrace traceelements elementsremained remainedrelatively relatively immobile immobile during this this alteration alterationepisode. episode. The The dikes dikescan canbe beseparated separatedinto intothree threedistinct distincttypes typeson onthe thebasis basisofoftheir theirRare RareEarth EarthElement Element(REE) (REE) patterns patterns(Figure (Figure2). 2). Group GroupI 1dikes dikeshave havehigh hightotal-REE total-REEconcentrations concentrations relative relative to Cl Cl Chondrite Chondrite(Sun (Sun andMcDonough, McDonough,1989) 1989)(samples (sampleslOa, lOa, lOb, lob, 13). Sample Sample lob, lob, which which is is located located near near Lake Lake Kabetogama, Kabetogama, isis and characterized 50. Rocks Rocks from from this this group groupalso alsohave haveaasignificant significant characterizedby byhigh high(La/Sm)cu= (L.a/Sm)a=1.67 1.67and andYbcn Ybm==50. negativeEu-anomalies, Eu-anomalies, suggesting suggestingthat thatplagioclase plagioclase fractionation has occurred. Group Group22dikes, dikes, negative represented (La/Sm)cn= 2.37, 2.37,but butwith withlow lowYba Yb ==10.76. 10.76. The Theslope slope representedby bysample sample1,1,are areLREE W E enriched with (La/SmIa= of of the theREE REE pattern patternof ofthis thissample sampleisisthe thesteepest steepestof of all all the the samples samplesanalyzed, analyzed, and andcrosses crossesthe thepatterns patterns ofofother 1,1,which MN,also alsoshows showsaapositive positiveEuEuotherdike dikerocks. rocks.Sample Sample whichisislocated locatedjust justwest westofofTower, Tower,MN, anomaly. 3 dikes (samples 4, 4,8,9,15,17,19,26,27) 8, 9, 15, 17, 19, 26, 27) show anomaly.Group Group 3 dikes (samples show nearly nearlyflat flatREE REE patterns, patterns,with with (La/Sm)a ranging ranging from 0.97(sample (sample04) 04)toto1.08 1-08(sample (sample 81, ranging from (sample (La/Sm)cu from 0.97 8), and and Ybm Th ranging from 1212 (sample 4)4)toto3131 (sample (sample8). 8).These Theserocks rockswere weretaken takenfrom fromvarious variouslocations locationsaround aroundnorthern northernMinnesota Minnesota(Figure (Figure1). 1). Figure Figure33isisaaspider-diagram spider-diagramofoftrace traceelement elementconcentrations concentrationsnormalized normalizedtotoNN-MORB -MORBwith with increasing increasingincompatibility incompatibilityfrom fromright right to to left. left. All Allof ofthe therocks rocks of of the the representative representative suite suiteshow show Ta/La progressiveenrichment enrichmentin inthe thehighly highlyincompatible incompatible elements. Most Most samples samples have normalized Ta/La progressive ratios> ratios >I 1except exceptfor forthose thoseininGroup GroupI 1(eg. (eg.sample samplelob). lob).Normalized NormalizedSrSrvalues valuesare arevariable variableasaswell, well,and and arelikely likelydue duetotoplagioclase plagioclasefractionation. fractionation.Group Group33dikes dikesare areenriched enrichedininBa Barelative relativeto tothose thoseof of Group Group are whichhave havehigher higherLa/Sm La/Smratios ratios(Figure (Figure4). 4).On Onmany manytectonic tectonicdiscriminant discriminantdiagrams diagrams(Figure (Figure5), 5),most most I1which dikesplot ploton onthe thefields fieldsofofMORB MORB(Group (Group3) 3)or or volcanic arcs (Group and 3). 3). Sample SampleI1(Group (Group2)2)isis dikes (Group 1 I and highly highlyenriched enrichedininTa Taand andplots plotsininthe thefield fieldofofwithin-plate within-platemagmas. magmas. Thetrace traceelement elementdata dataindicate indicatethat thatthe thedike dikesamples samplescan cannot notbe berelated relatedby bysimple simplecrystal crystal The fractionation. We interpret the data to indicate that the dike magmas fractionation. We interpret the data to indicate that the dike magmaswere werederived derivedfrom fromdifferent different mantle mantlesources, sources,or orthat thatthey theywere werevariably variablycontaminated contaminatedwith withcontinental continentalcrust crustororlithosphere, lithosphere,oror, ,oror both. both. 75 �Figure I Figure FigureCaptions Captions Figure Kabetogamadikes dikesininNorthern NorthernMinnesota h4innesotaand and Southern SouthernCanada. Canada. Figure11Map MapofofKenora Kenora--Kabetogama Locations Locationsof of selected selecteddikes dikesare are shown shown in italics. Modified Modifiedfrom fiom Southwick Southwickand andDay, Day,1983. 1983. Figure Figure22REE FUZEpatterns pattemsofofselected selecteddike dikesamples. samples. Figure Figure33Incompatible Incompatibletrace traceelement elementpatterns pattemsofofselected selecteddike dikesamples. samples. Figure Figure44Ba/La B a avs. vs.La/Sm LdSmdiagram diagramofofallallsamples samplesanalyzed analyzed Figure Th- -Ta Tadiagram diagramof ofall allsamples samplesanalyzed. analyzed. (From (FromWood Woodeteta!., al.,1979) 1979) Figure55H1/3 Hf/3--Th References References Beck, 1982.Rb Rb- -SrSrand andSm Sm- -Nd Ndisotopic isotopicstudies studiesof of Proterozoic Roterozoicmafic mafic dikes dikesinin Beck, W., W., and and Murthy, Murthy, V. R. 1982. northeasternMinnesota Minnesota(abstract). (abstract).Proceedings, Proceedings,28th 28thInstitute hstituteon onLake LakeSuperior SuperiorGeology, Geology,International International northeastern Falls, Falls.MN, MN.p.D.5.5. Craddock, P.'and k dA. A.D. D.Moshoian. Moshoian.1991, 1991,Continuous Continuousstrike strike- -slip slipfault fault- -en enechelon echelonfracture fracturearrays arraysinin craddock;J.J.P. implicationsfor forfault faultpropagation propagation mechanics (abstract). Proceedings, Proceedings,37th 37th deformedArchean Archeanrocks rocks: :implications deformed Institute EauClaire, Claire,WI, WI,p.p.25. 25. Instituteon onLake LakeSuperior SuperiorGeology, Geology,Eau Morey, Lower Proterozoic stratified 1983 Lower Proterozoic stratifiedrocks rocksand andthe thePenokean Penokeanorogeny orogenyinineast east- -central centralMinnesota. Minnesota. Morey,G. G.B.B.1983 Ed. Medaris,Jr.Jr.Geological GeologicalSociety SocietyofofAmerica, America,Memoir Memoir160. 160.p.p.97 97- -112. 112. Ed.L.L.G.G.Medaris, Southwick, Geology and petrology Southwick,D. D.L., L.,and andW. W.C.C.Day. Day.1983. 1983. Geology and petrologyofofProterozoic Proterozoicmafic maficdikes, dikes,north north- -central central Minnesota EarthSciences., Sciences.,20, 20,p.p.622 622- -638. 638. Minnesotaand andwestern westernOntario. Ontario.Canadian CanadianJournal JournalofofEarth Sun, Chemical andand isotopic systematics ofofoceanic Mcbnough.1989. 1989. Chemical isotopic systematics oceanicbasalts: basdts:implications implications Sun,S.S.S., S.,and andW. W.F.F.McDonough. formantle mantlecomposition compositionand and processes. In InMagmatism Magmatismin inthe the ocean ocean basins. Edited Editedby by Saunders, Saunders,A.A.D.D. and and for M. Society M.J.J.Norry. Norry.Geological Geological SocietySpecial SpecialPublication PublicationNo. No.42, 42, p.p.313 313- -345. 345. Wood, Wood,D. D.A., A.,J.J.L.L.Joron, Joron,and andM. M.Treuil. Treuil. 1979. 1979.AArere- -appraisal appraisalofofthe theuse useofoftrace traceelements elementstotoclassify classifyand and discriminatebetween betweenmagma magmaseries serieserupted eruptedinindifferent differenttectonic tectonic settings. settings. Earth Earthand andPlanetary PlanetaryScience Science discriminate Letters. Letters.45, 45,p.p.326 326- -336. 336. 76 76 �L) zC U z z 0 L) z 0 10 20 30 40 50 1 10 100 1000 1 Nd I I t S • S IS SmEu I I I I I I I I Th I 5' I 2 La/Sm 3 1c • Figure 4 - — YbLu Figure 2 I RARE EARTH ELEMENTS -\J — . LaCe I ''''''liii 11111 I 4 z U z0- C z z C Th 0.1 1 10 100 1000 Hf/ 3 Ta Figure 5 INCOMPATIBLE TRACE ELEMENTS CsRbBaTh U TaLa Ce Sr Nd HfSmEuYbLu �PENOKEAN STRUCTURAL TRENDS DEFINED DEFINED FROM FORNATIONAL CONTACTS AND PENOKEAN STRUCFORIVULTIONALI CONTACTS ANJ3 CLEAVAGE ANALYSIS ALONG THE GOGEBIC RANGE, WISCONSIN CLEAVAGE GOGEBIC RANGE, WISCONSIN MIJDREY, Jr., Jr., and and B.A. B.A. BROWN, BROWN, Wisconsin Wisconsin Geological Geological and and Natural Natural History History M.G. MUDREY, Survey, 3817 Survey, 3817 Mineral Point Point Road, Road, Madison, Madison, WI WI 53705 53705 ABSTRACT Structural Tyler Formation Structural reconstruction reconstruction of of the Paleoproterozoic Paleoproterozoic Tyler Formation by by rotating out the dip of Mesoproterozoic Keweenawan Keweenawan bedding orientation rotating of Mesoproterozoic orientation along along the Gogebic Range in northern Wisconsin suggests in northern suggests that that Paleoproterozoic Paleoproterozoic units units (Tyler (Tyler and earlier formations) formations) were were gently gently deformed deformed along along axes axes trending trending 04° 04O toward W. prior prior to deposition toward S. S. 79° 7g0 W. deposition of of Mesoproterozoic Mesoproterozoic quartzite quartzite (basal (basal Keweenawan Bessemer Keweenawan Bessemer Quartzite). Quartzite). This analysis analysis suggests suggests that that the the cleavage cleavage near near Hurley, Wisconsin, Wisconsin, is Hurley, is not a slaty cleavage, cleavage, but is is probably fracture fracture cleavage cleavage related to related to late late Keweenawan Keweenawan tectonism. tectonism. Keweenawan (Mesoproterozoic) Bessemer Quartzite Quartzite rests with The lower lower Keweenawan (Mesoproterozoic) Bessemer rests with slight slight angular angular discordance discordance on on the the Penokean Penokean Tyler Tyler Formation Formation (Paleoproterozoic). (Paleoproterozoic). All All the the units units generally generally dip dip at at 70° 70 to to the the northwest northwest (Montgomery, (Montgomery,1977). 1977). We have have rotated rotated the the bedding bedding of of Tyler Tyler units units immediate immediate below below the the Bessemer Bessemer contact contact back back to to the the pre-Bessemer pre-Bessemer position position using using the the bedding bedding orientation orientation of of the the Bessemer for western end of Gogebic, the Bessemer for rotation. rotation. At the the western of the the Gogebic, the Tyler Tyler dips dips approximately 15° east, the Tyler dips approximately approximately 15O to to the the northwest. northwest. In the east, approximately Analysis of 15° to the the southeast. 15O southeast. Analysis of these these localities localities on on steronets steronets and and computer computer structural rotation rotation programs suggests structural suggests a fold fold axis axis trending trending east-north-east east-north-eastand and plunging Rotation of plunging gently gently to to the the west-south-west. west-south-west. Rotation of the the cleavage cleavage in in the the Tyler Tyler to its presumed pre-Bessemer orientation results results in in a pre-Bessemer dip to to the the pre-Bessemer orientation pre-Bessemer dip south, which which we find understanding of south, find incompatible incompatible with our understanding of Penokean Penokean deformation deformat ion along along the the Gogebic Gogebic Range. Range. On the basis of reconstructed reconstructed thickness thickness of of post-Tyler strata along along the the post-Tyler strata Wisconsin-Michigan state Wisconsin-Michigan state line, line, the the recognition recognition of of well well developed developed slickensides slickensides planes, and minor, minor, centimeter-scale along the cleavage planes, centimeter-scale offset offset of of Freda Freda and and Tyler units units across across those those cleavage cleavage planes, planes, we we suggest suggest that that the the cleavage cleavage is is aa Tyler Keweenawan tectonism, fracture cleavage related to late late Keweenawan tectonism, that that Tyler Tyler and and Keweenawan sedimentary sections sections are are probably probably repeated, repeated, and and that that measured measured Keweenawan sedimentary thicknesses are thicknesses are too too great. great. Hotchkiss (1919) clearly clearly recognized recognized bedding bedding plane plane Hotchkiss (1919) faults near the base of the Ironwood Ironwood Iron-formation Iron-formation on on detailed detailed maps maps of of underground workings underground workings along along the the Gogebic Gogebic Range. Range. The The faults faults are are recognized recognized by by offsets offsets in in diabase diabase dikes dikes that that cut cut the the sedimentary sedimentary strata strata at at aa high high angle. angle. References Cited Hotchkiss, 1919, Geology of the Gogebic Hotchkiss, W.O., W.0., 1919, Gogebic Range Range and and its relation relation to to recent recent 501mining developments: developments: Engineering Engineering and and Mining Mining Journal, Journal, v. v. 108, 108, p. p. 443-452, 443-452,501mining 507, 507, 537-541, 537-541,577-582. 577-582. Montgomery, 1977, Deformation Montgomery, W.W., W.W., 1977, Deformation of the Tyler Tyler slate (Middle Precambrian) Precambrian) in northern northern Wisconsin Wisconsin and western Upper Upper Michigan: Michigan: unpub. unpub. M.S. M.S. thesis, thesis, University University of Wisconsin-Madison, 115 of Wisconsin-Madison, 115 p. p. �GEOLOGIC GEOLOGIC SETTING SETTING OF OF THE THE EARLY EARLY PROTEROZOIC PROTEROZOIC METAL-RICH METAL-RICH VOLCANICS VOLCANICS OF OF THE THE UPPER UPPER GREAT GREAT LAKES LAKES REGION REGION MtJDREY, M.G., Jr., MUDREY, M.G., Jr., Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, 3817 3817 Wisconsin Mineral Mineral Point Point Road, Road, Madison, Madison, WI WI 53705 53705 DICKAS, A.B., DICKAS, A.B., Division Division of of Sciences Sciences and and Mathematics, Mathematics, University University of of Wisconsin-Superior, Wisconsin-Superior,Superior, Superior,WI WI 54880. 54880. ABSTRACT ABSTRACT Since Since the the late late 1960s, 1960s, more than than 100 100 million million short short tons tons of of volcanogenic volcanogenic massive-sulfide massive-sulfide mineralization mineralization have have been been measured measured and and inferred inferred in in northern northern Wisconsin. Significant precious precious metal metal values values are are associated associated with with many many of of the the Wisconsin. Significant known known deposits. deposits. The The deposits deposits occur occur within within the the Early Early Proterozoic Proterozoic Penokean Penokean fold fold belt belt (1,850 (1,850-- 1,900 1,900 Ma), Ma), which which has has been been divided divided into into two two major major terranes: terranes: the the northern northern terrane, terrane, which which consists consists of of aa supra-crustal supra-crustalsequence sequence deposited deposited on on the the Archean Archean basement, basement, and and aa southern southern terrane, terrane, which which is is composed composed of of volcanogenic volcanogenic rock rock and and Early Early Proterozoic Proterozoic granite. granite. This This southern southern terrane, terrane, the the Wisconsin Wisconsin Magmatic Magmatic Terrane Terrane (also (also called called the the Wisconsin Wisconsin Penokean Penokean volcanic volcanic belt), belt), is is characterized characterized by by island-arc island-arcassemblages assemblages containing containing abundant abundant calc-alkaline calc-alkaline metavolcanic units units and and associated associated lesser lesseramounts amountsof ofmetasedinientary metasedimentary rock. rock. metavolcanic Within Within this this geologic geologic framework, framework, three three distinct distinct environments environments appear appear to to host host massive sulfide sulfide mineralization: mineralization: syngenetic syngenetic stratabound stratabound and and stratiform stratiform sulfide sulfide massive mineralization within, within, along along the the flanks flanks of, of, or mineralization near the stratigraphic top of or stratigraphic the the felsic felsic centers; centers; syngenetic syngenetic stratabound stratabound and and stratiform stratiform massive-sulfide massive-sulfide mineralization mineralization associated associated with with cherty cherty magnetic iron-formation iron-formation in in the main volcanic mineralization and volcanic arc arc sequence; sequence; and and epigenetic epigenetic stringer stringer sulfide sulfide mineralization syngenetic massive sulfide mineralization mineralization syngenetic stratabound stratabound and and stratiforin stratiform massive associated piles within within the associated with with niafic mafic piles the back-arc back-arc basin basin sequence. sequence. The The three three defined defined host host environments environments and and their their associated associated meta-argillite meta-argilliteformations formations appear appear to to be be major major regional regional features features controlling controlling the the localization localizationof of metal-bearing massive sulfide mineralization in the west part of the area. metal-bearing massive sulfide mineralization in the west part of the area. Other host host environments environments will will undoubtedly undoubtedly be identified identified as exploration exploration Other continues continues in in the the area. area. 79 �EARLY PROTEROZOIC PROTEROZOIC LEPTITE LEPTITE & HALLEFLINTA HALLEFLINTA(TUFF (TUFF&&TUFFITE) TUFFITE) EARLY SEQUENCES SEQUENCES OF SOUTHERN SOUTHERN FINLAND FINLANDREINTERPRETED REINTERPRETED AS SHEAR SHEAR ZONES: ZONES: SIGNIFICANCE SIGNIFICANCE TO TO LAKE LAKESUPERIOR SUPERIOR GEOLOGY GEOLOGY OJAKANGAS, W., Department of Geology, Geology, University of of Minnesota, Minnesota, Duluth, Duluth, OJAKANGAS, Richard Richard W., Duluth, Duluth, Minnesota Minnesota 55812; 5581 2;MARMO, MARMO,Jukka JukkaS., S.,Geological GeologicalSurvey SurveyofofFinland Finland SF-02150, 15,Finland Finland SF-02150, Espoo Espoo 15, Many Many Early Early Proterozoic Proterozoic volcanogenic volcanogenic sequences sequences in in southern southern Finland Finland and and adjacent adjacent (i.e., epiclastic epiclastic Sweden as bedded tuffs and Sweden have have long been been interpreted interpreted as bedded tuffs and "tuffites" "tuffites" (i.e., While volcanic sediments), and commonly have been called leptites and halleflintas. volcanic sediments), and commonly have been called leptites and halleflintas. While definitions Fennoscandinavia, definitions of of these these unfamiliar unfamiliar terms termsvary, vary,even evenin in Fennoscandinavia, leptites leptites and and halleflintas can can be be described as The halleflintas as fine-grained fine-grained quartzofeldspathic quartzofeldspathic metavolcanic rocks. The halleflintas the finer finer grained grained of of the the ttwo halleflintas are the w o (<0.25mm) à ‡ 0 . 2 5 m r nand andare are commonly commonly thinly thinly bedded bedded (<2.0 restudy of of several such units in in Finland ( ~ 2 .cm). cm). 0 AA restudy several such units Finlandhas hasprovided providedevidence evidence for foraa structural structural origin origin as as tectonic tectoniclayering layering(i.e., (i.e.,shear shearbands) bands) rather rather than thanas asprimary primarybedding. bedding. We We studied studied aa 11 km km wide widevertical verticalshear shear zone zone in in the the Tampere Tampere Schist Schist Belt Belt in in some some detail. Massive plagioclase porphyry was clearly the main protolith; in a zone about detail. Massive plagioclase porphyry was clearly main protolith; in a zone about ten ten meters wide there there is is aa gradual gradual transition transition from from unsheared unsheared plagioclase plagioclase porphyry to t o highly highly sheared and thinly thinly banded rock. Glassy sheared and banded rock. Glassy pseudotachylite, evidently the product product of of intense intense granulation andfusion fusiondue duet to frictional heat, heat, was was found found at at two granulation and o frictional t w o spots. spots. Kinematic Kinematic indicators indicators suggest suggest a a dominant dominant horizontal horizontal movement movement in in this this zone. zone. Color differences differences between between adjacent adjacent thin thin bands bands appear appear to t o reflect reflectcompositional compositionalchanges changesand andmay maybe belargely largely due due to t o metasomatism metasomatism by by sodium-, sodium-, potassium-, potassium-, magnesium-, magnesium-, silica-, silica-, and and calcium-bearing calcium-bearing solutions solutions rather rather than to t o original original compositions compositions of thin beds. beds. Silicification Silicificationappears appearsto t ohave have greenschist grade and amphibolite Subsequent process. been aa widespread widespread process. amphibolite and greenschist grade been metamorphism has produced produced skarns skarns and and other other metamorphic metamorphic rock rock types types in the metamorphism has the thinly thinly sequence. banded sequence. The The above above shear shear zone zone contains contains sulfide sulfide mineralization, mineralization, and and intensive intensive drilling drilling has has attempted that was attempted to t o locate locate sphalerite sphalerite mineralization mineralization that was originally originally spotted spotted in in large large mineralized glacial erratics. Drilling mineralized glacial Drilling has has resulted resulted in intercepts intercepts of of Zn-Pb-Ag Zn-Pb-Ag mineralization. mineralization. Elsewhere in the Tampere Schist Belt, gold gold has has been been discovered in shear shear zones; zones; in one one silicified shear shear zone, zone, 110 ppm ppm Au is is present. present. In (Orijarvi) Leptite Leptite Belt, Belt, three three In another another wide wide shear shear zone zone in in the the Southern Southern Finland Finland (Orijärvi) sulfide bodies mined out. out. Metsämonttu bodies have been mined Metsamonttuwas wasaaZn-Pb Zn-Pb deposit, deposit, Aijala Aijala was wasaaCuCuZn deposit, and deposit. The and Orijärvi Orijarvi was a Zn-Cu deposit. The significance significance of of shearing shearing in in the vicinity vicinity of the overlooked, and and while the ore bodies bodies were were logically logically interpreted the mines mines has has been overlooked, interpreted as as strata-bound Kuroko-type sulfides, we emphasize Kuroko-type volcanogenic volcanogenic sulfides, emphasize the possibilities possibilities of of an an epigenetic-metasomatic origin or a remobilization remobilization of primary volcanogenic volcanogenic sulfide in in this this zone of structurally-prepared structurally-prepared volcanogenic volcanogenic rock. rock. 80 �also visited leptite belts in We also in the Stockholm Stockholm area, area, and and made observations similar above. At are in in close close proximity proximity tto mine that that tto o those cited above. A t one one locality, locality, sheared sheared rocks are o aa mine has been been in in existence existencefor for centuries. centuries. Photographs Photographs in the literature on parts of leptite leptite belts belts that we were were not not yet yet able able to t o visit visit are are highly highly suggestive suggestive of of tectonic tectonic layering. layering. some "tuff "tuff sequences" zones? We Could some sequences" of of the theLake LakeSuperior Superior region region also also be be shear zones? are positive positive that that some some "thinly "thinly bedded sequencesofof mafic mafic and andfelsic felsic tuffs" tuffs" in are bedded sequences in Archean Archean terranes decades past past are, are, in reality, the result terranes that we we have have even even mapped mapped ourselves ourselves in decades result shearing. A reinspection of such "tuff of shearing. "tuff sequences" sequences" may may be be warranted, for for ititcould could make make additional terrane terrane worth worth prospecting for both gold and sulfide additional prospecting for sulfide deposits. 81 �PETROLOGY BODY, PETROLOGY AND AND ORIGIN ORIGIN OF OF THE NORTHERN COLVIN CREEK BODY, DULUTH DULUTH COMPLEX, COMPLEX, NE ME MINNESOTA MINNESOTA RICHARD RICHARD PATELKE PATELKE and andMARK MARK SEVERSON SEVERSON UNIVERSITY and UNIVERSITY OF OF MINNESOTA, MINNESOTA, DULUTH DULUTH and NATURAL RESOURCES RESEARCH RESEARCHINSTITUTE, INSTITUTE, DULUTH NATURAL RESOURCES DULUTH The The Colvin Colvin Creek Creek Body Body (CCB, (CCB, Colvin Colvin Creek Creek Hornfels Hornfels of of Bonnichsen Bonnichsen 1972, 1972, Tyson Tyson occurs within coarse—grained troctolite, anorthositic troctolite, and augite augite troctolite troctolite of of the the Partridge Partridge River River Intrusion Intrusion (PRI) (PRI)of of the the 1100 1100 m.y. m.y. Duluth Duluth Complex, km NN of of Duluth Duluth and and about about 13 13 km km ENE ENE Complex, NE NE Minnesota. Minnesota. It It is is located located about about 90 90 km of exposures of the basal contact of Hoyt Hoyt Lakes. Lakes. This This is is about about 55kin km SE from exposures contact of of the the Duluth Duluth Complex, Complex, the the CCS CCB is is estimated estimated to to be be about about 600—1200 600-1200 meters meters above above the the base base of of the the Complex. Complex. 1975) 1975) occurs within coarse-grained troctolite, anorthositic troctolite, and This his hornfels hornfels body body consists consists of of aa series series of fine—grained fine-grained to to medium—grained medium-grained units units of of basaltic basaltic composition composition and and aa coarser—grained coarser-grained gabbroic gabbroic unit. unit. In In the the finer— finergrained grained rocks rocks textures textures are are granoblastic granoblastic and and fabrics fabrics include include both both lava lava flow flow and and sedimentary sedimentary features. features. In In the the past past the the CCB CCB has has been been interpreted interpreted as as aa large large xenolith More recently recently it it has has been been suggested suggested that that it it is is of of xenolith of of Keweenawan Keweenawan basalt. basalt. More igneous igneous origin origin (Severson (Seversonand and Hauck Hauck1990). 1990). Field Field relations relations within within the the CCB CCB are are consistent consistent with with the the hypothesis hypothesis that that the the hornfels hornfels block block is is aa stratigraphic stratigraphic stack stack of of sediments sediments and and basalts, basalts, contact contact metamorphosed metamorphosed to to pyroxene-hornfels pyroxene-hornfels facies facies by by the the Duluth Duluth Complex. Complex. This This block block has has been been rotated rotated 70—90 70-90degrees degreesso sothat thataa cross—section cross-sectionis isnow nowexposed exposedat atthe thesurface. surface. Dips Dips are are now now to to the the north north and and most most indicators indicators give give aa northward northward topping toppingdirection. direction. Aside Aside from from the the rotation rotation there there is is little little definite definite kinematic evidence evidence of folding folding or or faulting, faulting, although although some some bedding bedding parallel parallel faults faults may may be be present, present, along along with with some some sigmoidal sigmoidal clots clots of of pyroxenes pyroxenes and and oxides. oxides. The The block block strikes strikes approximately approximately N6OE N60E along along aa length length of of 2400 2400 meters meters with with an an apparent apparent stratigraphic stratigraphic thickness thickness of 680 1.6 sq. sq. km. km. The The CCB CCB 680 meters. meters. The The hornfels hornfels block block has has an an areal areal extent extent of of about about 1.6 has has not not been been drilled drilled and and there there is is no no good good estimate estimate of of how how far far it it extends extends below below the the surface. surface. The The actual actual boundaries boundariesof of the the CCB CCB are are defined defined from from outcrop outcrop control control and and from from the the magnetic magnetic signature, signature, the the CCB CCB is is aa magnetic magnetic high high similar similar to to the the nearby nearby Powerline Powerline Gabbro. Gabbro. This This is is probably probably due due to to both both the the magnetite magnetite contained contained in in rocks rocks and and ubiquitous ubiquitous magnetite magnetite and and augite—magnetite augite-magnetite dikes, dikes, veins, veins, and and masses. masses. MAIN MAIN LITHOLOGIC LITHOLOGIC UNITS UNITS The The five five main main units units present present at at Colvin Colvin Creek Creek are are described described below below in in order order from from north north to to south south (youngest (youngestto to oldest). oldest). The The GOG GOG is is aa medium—grained medium-grained to to very very coarse—grained, coarse-grained, oxide oxide rich, rich, gabbro gabbroto to olivine gabbro. gabbro. It It contains contains some some areas areas of of modal modal layering, layering, and and has has anorthosite anorthosite olivine inclusions. Plagioclase inclusions. Plagioclasepercentage percentagevaries varies from from 50 50 to to 80% 80% in in the the unit unit itself itselfand and up 10-25%, up to to 85—90% 85-90% in in the the anorthosite anorthositeinclusions. inclusions. Olivine Olivine content contentranges rangesfrom from10—25%, augite 5—15%, 5-15%, and and oxides oxides 1-10%. 1-10%. This Thisis is clearly clearly an an igneous igneousunit, unit, similar similarto tothe the augite Powerline Gabbro Gabbro to to the the east, east, it Powerline it is is apparently apparently unmetamorphosed, unmetamorphosed, and and assumed assumed to to be younger younger than thanthe thebasaltic basaltic portion portionof ofthe the hornfels. hornfels. The The GOG GOG makes makesup up about about15% 15% be of of the the exposed exposed CCB. CCB. The The "Cross—Bedded "Cross-BeddedBelt' Belt"(XBB) (XBB)rocks rocks are are granoblastic, granoblastic, fine fineto to medium medium fine— finegrained, grained, have have aa dominant dominant mineralogy mineralogy of of plagioclase plagioclase (An (An 65—70), 65-70), aluminous aluminous pyroxene, pyroxene, magnetite, magnetite, ilmenite, ilmenite, with with traces traces to to aa few few percent percent of of olivine, olivine, orthopyroxene, orthopyroxene, cordierite, cordierite, biotite, biotite, and and covellite. covellite. There There are are millimeter millimeter to to centimeter scale, scale, high high angle angle cross-bed cross-bed sets, sets, defined defined by by modal modal layering layering with with centimeter pyroxene and and oxide oxidebases. bases. The pyroxene Thebed—sets bed-sets have have aa 25—40 25-40 centimeter centimeterthickness thicknessbut butare are not not traceable traceablefor for any any great great distance. distance. The The granoblastic granoblastictexture, texture,fine finegrain grainsize, size, cross-bedding, and cross—bedding, and the the stratigraphic stratigraphicthickness thickness of of about about 300 300 meters meters lead lead this this to to be interpreted interpreted as as aa metasedimentary metasedimentary unit. unit. This This unit unit makes makes up up about about 35% 35% of of the the be hornfels body. body. At At 300 300 meters, meters, the the thickness thickness of of the the XBB XBB unit unit is is about about the the same same hornfels stratigraphic thickness thickness as asthe thetotal totalofofKeweenawan Keweenawaninterf interflow sedimentary rock rock stratigraphic low sedimentary 82 �measured measured on on the the Lake Lake Superior Superior Shore. Shore. Ameboidal granoblastic, fine fine to to medium-grained, medium—grained, generally generally Ameboidal Augite Augite (AA), (AA), is is a granoblastic, massive unit. The the other other granoblastic granoblastic The mineralogy is is essentially the same as the units, plagioclase, and ilmenite +1— olivine. plagioclase, augite, augite, magnetite, magnetite, and ilmenite +/olivine. There There are are concentrations more or concentrations of of augite augite and and Fe—Ti Fe-Ti oxides occurring as small stringers more less perpendicular to material defining defining the the less perpendicular to bedding bedding and and rounded rounded clots clots of the same material bedding These bedding or or layering. layering. These parallel parallel layers layers of of augite augite and and Fe-Ti Fe-Ti oxide oxide concentrations are interpreted interpreted to be flow flow tops, tops, indicating indicating flows flows roughly roughly one one meter meters. Flow tops are actually actually only meter or or less Less thick thick up up to to as as much as as ten meters. only seen seen for a few unit has has pyroxenite pyroxenite zones few meters length length in in scattered scattered locations. This unit along veinlets (and (and along its its upper upper contact contact with with the the XBB XBB unit unit and and contains contains numerous numerous veinlets healed mixed with healed joints) joints) of of pyroxene pyroxene intimately intimately mixed with Fe-Ti Fe-Ti oxides. oxides. This This is is interpreted interpreted as as aa subaerial, subaerial, amygduloidal, amygduloidal, metavolcanic metavolcanic unit unit making making up up about about 15% 15% of the the CCB. CCB. Amygduloidal the AA AA and is very Amygduloidal Gabbro Gabbro (AMG), (AMG), is stratigraphically below the similar similar to to the the AA in in its its mineralogy mineralogy and granoblastic granoblastic texture. Here Here the the pyroxene pyroxene and oxide oxide concentrations concentrations are are less less regular, regular, and and there there are are concentrations concentrations of of plagioclase unit. This is also thought plagioclase occurring occurring as as small small clots clots throughout the unit. to be another 15% 15% of of the total be aa subaerial subaerial metavolcanic metavolcanic unit unit constituting constituting another total hornfels. hornfels. Colvin Creek (MCC), (MCC), at the base of the hornfels sequence, sequence, is a Massive Colvin massive massive rock rock of of roughly roughly the the same same mineralogy mineralogy and and composition composition as as the the metavolcanic metavolcanic containing plagioclase, plagioclase, augite, Fe—Ti Fe-Ti oxides, but areas of of units, containing but it also has areas high olivine olivine concentration. concentration. These These are are ophitic ophitic zones zones but but it it is is uncertain uncertain if if these these high original igneous igneous feature feature or or due due to to metamorphism. The MCC contains contains some some are an original small cavities and and has has plagioclase plagioclase clots similar to those in the AMG small cavities ANG unit, but lacks well well defined defined volcanic volcanic features. features. In aa few few locations locations there there are are large large plagioclase phenocrysts, phenocrysts, their their origin origin is is also also unclear. The contact with the AMG plagioclase unit unit above above is is gradational gradational over over about about 1-10 1-10 meters. meters. This This is is thought thought to to most most likely likely be aa thick thick lava lava flow flow or or near near surface surface sill. sill. This unit covers about be about 20% of the exposed exposed area area at at Colvin Colvin Creek. Creek. Whole rock rock geochemistry geochemistry indicates indicates that CCB rocks rocks are are similar similar to to Whole that the CCB Keweenawan igneous igneous rocks rocks and and selected selected interf interflow North Shore Shore Keweenawan low sediments of the North Volcanic Group, Group, but but are are not not strict strict analogues analogues for for any unit in the Keweenawan. Volcanic This work work has has been been supported supported by by the the UMD Graduate This Graduate School, School, UMD-NRRI, and and the the Coleraine Coleraine Minerals Minerals Research Research Laboratory. Laboratory. .................................................................. W., 1972, 1972, Southern Southern Part Of the Duluth Bonnichsen, W., Duluth Complex Complex in Sims, Sims, P.K., P.K., and Morey, G.B., G.B., editors, editors, Geology of Minnesota: Minnesota: A Centennial Centennial Volume: Volume: Minnesota Minnesota Geological Survey Survey pp. pp. 361-387. 361-387. Geological M. J., and and Hauck, Hauck, Steven Steven A., A., 1990, 1990, Geology Geology and and geochemistry geochemistry of of aa portion portion Severson, M.J., Severson, the the Partridge Partridge River River Intrusion: Intrusion: Natural Natural Resources Resources Research Research Institute— InstituteUniversity of of Minnesota, Minnesota, Duluth, Duluth, Technical Technical Report Report NRRI/GMIN-TR-89-ll. NRRI/GMIN-TR-89-11. University of of Tyson, R.M., R.M., 1976, 1976, Hornfelsed Hornfelsed Basalts Basalts in in the the Duluth Duluth Complex: Complex: M.S. M.S. Thesis, Thesis, Cornell Cornell Tyson, University, University, Ithaca, Ithaca, New New York, York, 85 85 pages. pages. 83 �. x )— 1- oog U) U) II 00 00 mo mo 4Q °o o Id -J uNorrEkENuI(o )ROCIOLUIC SIRICS '1 JL • EJ ivo [J DULUTIl COMPLEX 0 flJE1ERS 1000 FT — SWAMP CONTACT AREA OF OUTCROP CLEVtTI0N 7 9M ORIGINAL CAt) ARE) GiOI.OGY DY U J. SF'/EIVSON-•- URRI 1550 T.59N., R.13W. St. Louis County Minnesoto DULUTH COMPLEX NORTHERN COLVIN CREEK BODY 0 POWERLJNE GABBRO? �VARIATIONS VARIATIONS IN IN METAMORPHIC METAMORPHIC GRADE GRADE OF OF METAPELITES METAPELITES ALONG ALONG TRAMSECTS T W S E C T S ACROSS THE THE QUETICO QUETICO SUBPROVINCE SUBPROVINCE THUNDER THUNDER BAY, BAY, ONTARIO ONTARIO BARBARA BARBARA E. and MANFRED MANFRED 14. M. KEHLENBECK E. SEEMAYER SEEMAYER and DEPARTMENT DEPARTMENT OF OF GEOLOGY, GEOLOGY, LAKEHEAD LAKEHEAD UNIVERSITY, UNIVERSITY, THUNDER THUNDER BAY, BAY, ONTARIO ONTARIO The The Archean Archean rocks rocks of of the the western western Superior Superior province province of of the the Canadian Canadian Shield Shield have have been been subdivided subdividedinto into aa series series of of subprovinces. subprovinces. These These subprovinces subprovinces form form east—west east-west trending trending terranes terranes typified typified by by either either metavolcanic metavolcanic successions successions and granitic granitic intrusive intrusive rocks rocks as as represented represented by by the the Wawa Wawa and and Wabigoon Wabigoon subprovinces, subprovinces, or or by by metasedimentary metasedimentary gneisses gneisses and and migluatites migmatites characteristic of the the Quetico Quetico and and English English River River subprovinces. subprovinces. Many Many workers workers have have attempted attempted to to define define the the boundaries boundaries separating these subprovinces separating these subprovinces from from one one another. another. These These attempts attempts commonly commonly focus focus on on aa comparison comparison between between adjacent adjacent subprovinces subprovinceswith with regard lithological character, characterl orientation orientation of of structural structural regard to to lithological elements, elementslmetamorphic metamorphicgrade, gradelgeophysical geophysicalanomalies, anomaliesland and geochemical geochemical parameters. parameters. Although Although such such comparisons comparisons are are valuable valuable in in identifying identifying differences subprovincesl the the actual actual boundary boundary differences between between adjacent adjacent subprovinces, remains remains aa poorly poorly defined defined feature featurein in most most cases. cases. The The objective objective of of the the present present study study was was to to analyze analyze metamorphic metamorphic index index minerals minerals in in metapelites metapelites and and to to compare compare these these results results to to typomorphic analytical work work was was typomorphic mineral mineral assemblages. assemblages. Much Much of of the the analytical confined confined to to garnet garnet because because of of its its widespread widespread occurrence occurrence in in the the metapelites. metapelites. One Hitachi One hundred hundred thirty thirty two two garnets garnets were were analyzed analyzed using using aa Hitachi 570 Results 570 S.E.M. S.E.M. Results show show that that the the garnets garnets cover cover aa range range of of compositions compositions from from almandine almandine (54—92) ( 5 4 - 9 2 ) spessartine spessartine (1—33) (1-33) pyrope pyrope (2(225) 25) grossularite grossularite (0-17) (0-17) suggesting suggesting aa parent parent rock rock composition composition relatively relatively low low in in calcium calcium and and rich rich in in iron iron and and magnesium. magnesium. With With increasing increasing grade grade of of metamorphism metamorphism garnet garnet compositions compositions reflect MgO contents. CaOand andMnO MnO and and increasing increasingFeO FeOand andnMg0 contents. reflectdecreasing decreasingCaO Geobarometry Geobarometry using using the the equilibrium equilibrium assemblage assemblage garnet garnet ++ sillimanite sillimanite ++ plagioclase plagioclase ++ quartz quartz resulted resulted in in pressures pressures of of 55±k 1.5 1.5 Kbar. Kbar. Electron Electron microprobe microprobe analyses analyses of of twenty twenty samples samples containing containing biotite biotite and and garnet garnet showed showed temperature temperature ranges ranges from from 517°C 517OC in in metasedimentary rocks to to a maximum metasedimentary rocks maximum of of 714°C 714'C in in the the migmatite migmatite complex. complex. In In general, generallaa pattern pattern of of steadily steadily increasing increasing temperatures temperatures northward by a rather northward is is interrupted interrupted by rather sharp sharp drop drop north north of of the the highest grade rocks. highest grade rocks. The The widely widely held held view view that that the the metasedimentary metasedimentary terranes terranes of of the the western western Superior Superior province province possess possess aa symmetric symmetric distribution distribution of of metamorphic grades gradesfrom from low—grade low-grade rocks rocks near near the the margins margins to to higher higher metamorphic grade grade rocks rocks near near the the central central parts parts is is not not supported supported by by this this detailed detailed study study of of the the Quetico Quetico subprovince subprovincenorth northof ofThunder ThunderBay. Bay. It lowIt is is common common to to find find high-grade high-grade rocks rocks juxtaposed juxtaposed with with lowgrade grade schists schists near near the thesubprovince subprovincemargin. margin. The The variations variations in in metamorphic metamorphic grade grade are are not not only only profound profound in in transects transects across across the the regional regionalstrike strikeof of the the rocks rocksbut but also also occur occur parallel parallel to to the the strike. strike. The The latter latter variations variations are are particularly particularly well well demonstrated demonstrated near near the the 85 �southern gneisses and southern margin margin where where high high grade grade schists schists and and gneisses and low—grade low-grade slates 10 slates are are exposed exposed in in outcrops outcrops over over a a strike strike distance distance of of about about 10 . km. km The The variations variations in in metamorphic metamorphic grade grade throughout throughout the the Quetico Quetico subprovince subprovince between high—grade high-grade and and low—grade low-grade assemblages assemblages and and analyses, corresponding analysest contradict contradict aa simplistic corresponding mineral mineral simplistic distribution. distribution. An An explanation explanation for for this this pattern pattern of of distribution distribution lies lies to to some some extent in in the the evolution evolution of of the the Quetico Quetico terrane. terrane. Several Several models models invoking mobilist viewpoint viewpoint have have been presented presented in in the the invoking the the mobilist literature. literature. Based on on the the evidence evidence from from this this study, studyt we we conclude conclude that Archean crustal crustal that aa model model of of subduction—driven subduction-driven accretion accretion of of Archean elements elements best best explain explain the the field field and and laboratory laboratory data. data. The The Quetico Quetico terrane terrane represents represents an an accretionary accretionary prism prism composed composed primarily primarily of of detritus detritus shed shed southward southward from from the the Wabigoon Wabigoon island island arc arc and inicrocontinent terranes. The prism and microcontinent terranes. The prism comprises comprises quartzofeldspathic pelitic sediments. sediments. Southward Southward oblique oblique quartzofeldspathic and and pelitic accretion accretion of the the Wawa Wawa terrane terrane signalled signalled the the onset onset of of polyphase polyphase deformation, metamorphism, and regionalmetamorphisml and development developmentof of deformation, low low pressure pressure regional thrusts. thrusts. Northward dipping dipping thrusts thrusts and thrust thrust nappes nappes resulted resulted in in tectonic tectonic stacking stacking of of diverse diverse rock rock types types from from different different levels levels of of the the accretionary accretionary wedge. Continued Continued north—south north-south compression compression led led to to the sheetst and and the the the coaxial coaxial refolding refolding of of earlier earlier folds folds and and thrust thrust sheets, development sub-verticall east—west east-west striking striking development of of aa pervasive pervasive sub—vertical, schistosity. schistosity. Late Late north—south north-south dextral transpression transpression is is seen seen in in structures structures reflecting reflecting more more brittle brittle deformation deformationand and the the intrusion intrusionof of post-kinematic plutons near the post-kinematic plutons the southern southern margin. margin. This late late This intrusive intrusive activity activity produced produced contact contact metamorphic metamorphic effects effects which which overprint overprint the the regional regional metamorphism. metamorphism. At At the the present present level level of of erosion, erosion, the the pattern pattern of of distribution distribution of metamorphic metamorphic grade and and the the orientation orientation of of planar planar and and linear linear structures structures appears to correspond correspond to to the the proposed proposed evolutionary evolutionary model. model. The The boundaries boundaries between between the the Quetico Quetico subprovince subprovince and and adjacent adjacent volcanic terranes in in the area by this study volcanic terranes area covered covered by study are are best best described described as as products products of of aa complex complex fault—fold iault-fold geometry. geometry. In In the the area area studied studied there there appears appears to to be be no no distinct distinct line line of of demarcation demarcation between between subprovinces. subprovinces. 86 �THE BASAL CONTACT SULFIDE AND AN]) PGE MINERALIZATION AT THE OF THE THEMINNAMAX MINNAMAX DEPOSIT, DULUTH DULUTJ3 COMPLEX, NE NE MINNESOTA MINNESOTA OF Mark J. Severson Severson Natural Resources Research Institute Institute University of Minnesota, Minnesota, Duluth Duluth The Minnamax (Babbitt) Cu-Ni deposit, located within the Partridge Partridge River fiver Troctolite Troctoliteof of the Duluth Complex (1.1 Ga), Ga), northeastern northeastem Minnesota Minnesota (Fig (Fig 1), I), contains containsboth both troctolite-hosted troctolite-hosted disseminated disseminated ore and footwall-hosted footwall-hosted massive sulfide ore. This talk talk pertains pertains to to the the massive massive sulfide ore zone, which is restricted to a small portion portion of of the deposit, and is referred to as as the the Local bBoy y area. Detailed Detailedrelogging relogging of of 76 76 underground underground drill holes, along along with pertinent surface holes, has been completed within within the Local Local Boy Boy area area (from (from drifts drifts B, C, and and D). D). Relogging of of drill core indicates a highly undulatory nature nature of of the basal contact of the highly undulatory Duluth Complex with with the footwall footwall Virginia VirginiaFormation. Formation. Intrusive rocks of the the Complex Complex consist of augite troctolite, norite; all all exhibit exhibit gradational gradational contacts contacts with each other other and and all all troctolite, troctolite, troctolite, and and norite; may occur at any stratigraphic position position relative relativeto tothe theundulatory undulatorybasal basalcontact. contact. However, norite is the the most most common common rock rock type type adjacent adjacent to to sedimentary sedimentary homfels homfels inclusions inclusions and at at the the basal basal contact of the the magma. magma. The contact due to contamination contamination of Thespatial spatialconfiguration configuration of of the theintrusive intrusiverocks rocks indicates that the the troctolite, etc. was intruded as multiple pulses along along bedding bedding planes planes of of the indicates that multiple pulses Virginia Formation. Formation. The The Virginia Virginia Formation hosts the majority of the massive sulfide ores which are present within within hornfels homfels inclusions inclusions positioned positioned above the basal contact, and within within the the footwall footwallrocks rocksatat and and below the basal contact. Massive Massivesulfide sulfideore oreisisnot notas ascommon common within within the the intrusive intrusiverocks, rocks, and when present it is generally in close proximity to homfels inclusions. when present it is generally in close proximity to homfels inclusions. Megascopic ore ore textures are extremely varied, but all textures extremely varied, textures are indicative indicative of structural structural preparation preparation in the footwall footwall rocks. Overall, Overall,the themassive massivesulfide sulfideores oresare arespatially spatially distributed distributed in in aa spotty spotty manner manner in in an east-west (EW) direction direction that corresponds corresponds to aa major major EW-trending EW-trending anticline anticline present present within within east-west (EW) the the footwall footwall rocks. rocks. All these these factors factors suggest suggest that that an an immiscible immisciblesulfide sulfide melt melt was was injected injected into into the structurally structurally prepared footwall rocks along the anticlinal axis in aa "vein-like" "vein-like"setting. setting. At At some some later later period, period, the thefootwall-hosted footwall-hosted massive massive sulfide sulfide ore ore zone zone was was re-intruded re-intrudedby bymultiple multiplesills sills of the the troctolitic troctolitic rocks. rocks. The end end result result isis aadisjointed disjointed zone zone ofofmineralized mineralized inclusions inclusions and and mineralized footwall rocks separated by "barren" "barren" intrusive intrusive rocks. Sulfide textures that the sulfides textures indicate indicate that sulfides formed by cooling cooling of of aamonosulfide monosulfidesolid solid solution (MSS) followed followed by by limited limited replacement replacementatat very very low low temperatures. temperatures. Minerals Minerals contained contained within pyrrhotite, chalcopyrite, chalcopyrite, cubanite, cubanite, and and pentlandite. pentlandite. Locally within the sulfide ore are dominantly pyrrhotite, W l y present present are are maucherite, maucherite, sphalerite, sphalerite,bornite, bomite,talnakhite, talnakhite,mackinawite, mackinawite, and and an an unknown unlmown Cu-sulfide Cu-sulfide (ItCptt). ("Cpl'). Also Also present present in minor minor amounts amounts are are native native silver silver (both (both primary primary and andsecondary), secondary), parkerite, chalcocite, chalcocite,covellite, covellite,godlevskite, godlevskite, violarite, violarite,magnetite, magnetite,and andzincian zincianhercynite. hercynite. parkerite, Although no discrete PGE minerals were identified, analytical results results (from 1,050 1,050 drill drill core % Cu) Cu) core samples samples with with an an average averagesample sampleinterval interval of of 55 to to 10 feet long) of the high-grade (> (>11% massive sulfide ore ore confirms confirms the presence of several anomalous PGE Thesespot spotvalues values massive PGE values. These are are mainly mainly confined confined to an an EW-trending EW-trending zone that also roughly corresponds to to the the EW-trending EW-trending anticline (Fig 2). Maximum Maximumvalues valuesobtained obtained in in the the Local Local Boy Boy massive sulfide ores include: Pd Pd anticline = = 11,100 11,100ppb; ppb; Pt == 8,300 8,300ppb; ppb; Au == 10,900 10,900ppb; and Ag == 34 34 ppm. ppm. Underground Undergrounddrill drillhole hole 10198 probably metal-bearing drill hole found to to date datewithin within the the 10198 probably represents the best precious metal-bearing 87 �Complex. Within hole are are ten tenPd Pdvalues values>> 1 ppm, five Au Au values values > 11ppm, Within the the 300 300 foot foot long hole ppm, and three Pt values > 1 ppm. 1 ppm. and three Pt values origin of of the PGE mineralization mineralizationisistwofold. twofold. A primary origin is suggested by the The origin suggested by presence of maucherite presence maucherite grains which which contain contain extremely extremely fine-grained fine-grained myrmekitic native silver silver intergrowths (J)rimary intergrowths (primary silver). silver). Generally, drill holes that contain contain anomalous POE PGE values also also contain this silver-bearing type type of of maucherite. maucherite. Since contain Since maucherite maucherite appears appears to to have have formed formed early early in the paragenetic sequence, this suggests that silver (and PGEs) were scavenged from the sulfide sulfide by maucherite, and thus thus the PGEs PGEs are are related related to to aa primary primary (magmatic) (magmatic) process. process. However, melt by However, a hydrothermal origin for the PGEs is also hydrothermal origin also indicated. indicated. Anomalous Anomalous POE PGEvalues valuesare arecommonly commonly associated with with Cl-drop Cl-drop encrusted encrusted massive massivesulfide sulfidedrill drillcore. core. The spatial distribution of the Cldrop encrusted drill core also coincides with with the the EW-trending EW-trendinganticline anticline(Fig (Fig2). 2). Presence of the Boy area area were invaded by Cl-bearing solutions solutions that Cl-drops indicates that the rocks of the Local Boy may have been capable of transporting and concentrating PGEs. POEs. Therefore, Therefore, both both primary/magmatic prima.ry1magmatic (sulfides injected into a "vein-like" Vein-like" setting) and later secondary/hydrothermal processes processes appear appear to to have have been been factors in controlling POE secondarylhydrothermal PGE distribution in the Local Boy area. However, However,ititisisdifficult difficulttotoseparate separatethe theprimary primaryand andsecondary secondaryprocesses. processes. This is due due to to the the coincidence coincidence of of several several features features within within an an EW-trending EW-trending zone zone which which include: include: 1) anticline in the footwall rocks; 2) overall overall massive massive sulfide sulfide distribution; distribution; 3) 3) spatial spatial distribution distribution of anomalous POE values; spatial distribution distribution of of Cl-drop 4) spatial Cl-drop encrusted encrusted drill core. core. anomalous PGE values; and and 4) Reactivation of structures structures that controlled controlled the initial "vein-like" "vein-like" massive massive sulfide sulfidedistribution distributioncould could have been responsible responsible for for channeling channeling later later hydrothermal hydrothermal solutions. solutions. 88 �1 LEGEND Cu-Ni ~ e ~ o s i t s ' MINNAMAX DUNKA RDAD WETLEGS WYMAN CREEK SERPENTINE DUNKA PIT - - DR WL WC S DP Fe-Ti Deposits (OUO SECTION 17 LDNGEAR LONGNDSE SECTION 22 SKIBD WATER HEN - - 17 LE LN 22 SK WH 1: Figure 1: Locotion deposits within within tthe Figure Location of' o f Cu—Ni Cu-Ni deposits he Par'tridge Complex P a r t r i d g e River River Troctolite T r o c t o l i t e off o f the t h eDuluth Duluth Complex. * >2.0 p p m 1.0 - 2.0 p p m ANOMALOUS PRECIOUS METALS (Pt, Pd, o r A u ) 0.8 — - 1.0 1.0 ppm ppm Figure Figure 2: 2: Distribution anomalous precious precious metal metal values values and and Distribution of of anomalous Cl-drop core in the Local Local Boy Boy area, area, Cl—drop encrusted encrusted drill core in the Minnamax Minnamax deposit deposit 89 �THERMAL AND AND REGIONAL IN ARCHEAN BASALT, BASALT, THERMAL REGIONAL METAMORPHISM IN GREENSTONE BELT, MANITOBA, CANADA BIRD RIVER GREENSTONE Turnock A.C.(1), Turnock A.C.(l), Kamineni Kamineni D.C. D.C. (2), (2), (1) Geological Geological Sciences, Sciences, University University of of Manitoba, Manitoba, Winnipeg, 2N2, Canada. Canada. Winnipeg, MB, MB, R3T R3T 2N2, (2) AECL AECL Research, Research, Whiteshell Whiteshell Laboratory, Laboratory, Pinawa, MB, Pinawa, MB, ROE ROE 1LO, lL0, Canada. Canada. Abstract In southeastern southeastern Manitoba, on the the western edge In edge of the the Superior Superior Province (Archean), the Bird River greenstone belt is subsmall sub— Province (Archean), the Bird River greenstone belt is aa small Pillow basalts a lower lower province of of supracrustal supracrustal rocks. rocks. basalts are are a stratigraphic thick, overlain ic and stratigraphic formation, formation,approx. approx. 22km kmthick, overlainbybymaf mafic and felsic volcanics volcanics and and clastic clasticnieta—sedimentary meta-sedimentary rocks. rocks. Samples Samples from from felsic 3 localities localities are are described described with with chemical chemical and and mineral mineral analyses. analyses. and 2 have compositions similar other Archean # 1 2 have compositions to other Samples 1 Samples # tholeiites; their flat ratios of Nb-Zr-Y and tholeiites; flat REE patterns and ratios and TiTiThe exceptions exceptions are Zr—Y Zr-Y are are comparable comparable (with (with exceptions) exceptions) to to MORB. MORE. The are the Y, the selvedges selvedges of of the the pillows pillows of of Sample Sample #2, #2, which which are are enriched enriched in in Y, Fe+3, Fe, Fe+3, Mg, Ca, Mn compared compared to cores cores and and to to sample sample #1. #l. The The Fe, Mg, chemical anomalies anomalies are ascribed chemical ascribed to to diagenetic diagenetic or or hydrothermal hydrothermal alteration, Sample #3, #3, a cross-cutting cross-cutting dike, dike, alteration, possibly possibly syn-gentic. syn-gentic. Sample is an an meta-andesite. meta—andesite. steeply dipping dipping The formations are are folded, folded, faulted, faulted, and and steeply The formations D2), with with a regional foliation 52. (deformation D2), S2. There There are are postpostDuring metamorphism, metamorphism, hornblende, hornblende, garnet folding shear zones zones (D3). (D3). During garnet folding shear and cuinmingtonite have overgrown overgrown the the main S2 This cummingtonite have S2 foliation. foliation. This indicates that heat flow, flow, probably from the the adjacent adjacent batholithic batholithic intrusion, continued intrusion, continued after after deformation. deformation. This This thermal thermal recrystallrecrystallM3. The samples are in the aureole of a ization is called M3. a late— latetectonic batholith tectonic batholith of of granite granite and and granodiorite, granodiorite, the the Lac Lac du du Bonnet Bonnet (LDB) batholith. batholith. We interpret interpret that this this batholith batholith is is the the heat heat (LDB) source source for for M3 recrystallization. recrystallization. In samples samples #1 and 2 2 the the compositions compositions of of plagioclases plagioclases are are rich rich in In Ca and Al A1 (An 63 -- 91), 91), which is anomalous as compared compared to the compilation of of Spear Spear (1981). (1981). They are comparable comparable to to the the calcic calcic plagioclases the low-pressure low—pressure calcic schists schists (garnet—hornblende plagioclases of of the (garnet-hornblende zone) of of the the Panamint Panamint Mountains Mountains (Labotka (Labotka 1987). 1987). The hornblendes The hornblendes are rich rich in in tschermaks tschermaks molecule, molecule, especially especially #2 #2 selvedges. selvedges. We We interpret compositions as as the interpret these these compositions the result result of of the the enhanced enhanced instability instability of epidote epidote at at low low pressures pressures (andalusite (andalusite type type facies). facies). 1989)is the the An additional additional indicator indicator of low low pressures pressures (Yardley 1989)Is abundance of in samples samples #2 #2 and and 3, 3, this this is is caused by abundance of cunimingtonite cummingtonite in the the preference preference of of amphibole amphibole to to lower lower its its content content of of Al A1 at at low lowP. P. The selvedges of the pillows of sample sample 22 have have porphyroblastic porphyroblastic garnet, plus small small amounts amounts of of biotite. biotite. Temperatures of M3 are are thereby 600°C (range; thereby determined determined as as 565 565 -- 600° (range; additional error may may be be additional error 50 The garnet—hornblende garnet-hornblende geothermometer of Graham Graham && Powell Powell 50 O). The 608OC. (1984) gives 575 575 —- 608°C. The preservation preservation of cores of hornblende hornblende The of inclusions inclusions of biotite in in cores O ) . �indicates indicates that that M2 M2 biotite biotite was was aa reactant reactant that that was was used used up up by by the the M3 M3 recrystallization. recrystallization. metamorphic aureole late—tectonic granite in an an The thermal metamorphic aureole of a late-tectonic Archean greenstone belt may be outlined outlined by mapping the the appearance appearance of the garnet-hornblende garnet-hornblende assemblage assemblage (without (without chlorite, chlorite, as as pointed pointed in out by Labotka 1987) out by Labotka 1987) in the meta-basites. meta-basites. The ability ability of of amphiboles, garnet, plagioclase and epidote epidote to to react react in in the the postposttectonic thermal thermal aureole the late batholiths batholiths are the tectonic aureole indicates indicates that that the source of of advective advective heat. heat. It remains to be determined wether or Ptotal, in not there was a loss loss of of H20, H20, or or conditions conditions of PH2O pH20 << Ptotal, in this environment. environment. 91 �STRUCTURAL ANALYSIS ANALYSISOF OF THE THE MIDCONTINENT MIDCONTINENT RIFT RIFT IN A STRUCTURAL MICHIGAN, BASED ON A A FAULT FAULT ARRAY ARRAY ANALYSIS ANALYSIS UTILIZING SLICKENSIDES SLICKENSIDES Kathleen Kathleen M. M. Witthuhn Witthuhn Department of of Geology Department Geology and and Geophysics Geophysics University of Minnesota University Minnesota Minneapolis, Minneapolis, Minnesota Minnesota The Midcontinent Rift 1.1 billion billion year year old old crustal crustal structure structure which which has has The Midcontinent Rift is is a 1.1 Many studies been defined been defined primarily primarily by by geophysical geophysical studies. studies. Many studies have have examined the rift rift from examined the from a petrologic petrologic view view but but few few have have examined examined the the structural geology geology in in any Initial field work work in in Minnesota, Minnesota, Canada, Canada, structural any detail. detail. Initial and the Upper of Michigan yielded data data on on fault and Upper Peninsula Peninsula of Michigan yielded fault and joint joint populations, from which which scattered populations, from scattered stress stress tensors tensors were were calculated. calculated. Examinationofof nearly nearly 600 600 small small scale scale fault fault structures on both both of of the Examination structures on the synclinal limbs along along a transect synclinal limbs transect northwest northwest across across the the Lake Lake Superior Superior syncline, from from the the Keweenaw Peninsula to to Isle Royale syncline, Keweenaw Peninsula Royale in in Michigan, Michigan, was was more successful successfulinin isolating isolating two two consistent consistent stress stress fields fields for for each each limb limb of the more the syncline, that that would would satisfy satisfy criteria criteriafor for closing closingoff the syncline, theMidcontinent Midcontinent Rift Rift This study System. This study evaluates evaluates existing existing models models by by applying applying geometrical geometrical and and statistical methods methodstoto the the data data to determine determine the the kinematics kinematics of of the closing statistical closing of of the the Midcontinent Midcontinent Rift Rift System. System. The Keweenawan Portage Lake Lake Volcanics Volcanics (PLV) (PLV) form form aa broad The Keweenawan Portage broad anticline, anticline, with an an axis just causing the the lava lava flows flows west west of of with just west west of of Delaware, Delaware, Michigan, Michigan, causing Delaware of the the anticlinal anticlinal axis axis trend trend Delawaretoto trend trend northeast, northeast, while while those those east east of mainly A majority mainly east-west. east-west. A majority of the the small small scale scale fault fault orientation orientation data data collected on the east-west collected on east-west trending trending flows flows of of the the Keweenaw Keweenaw Peninsula Peninsula are are parallel with parallel with this this trend, trend, having having steeply steeplypitching pitchingslickensides, slickensides, indicating indicating dip-slip motion motion on on the the faults. dip-slip faults. However, However, there there are two two smaller smaller fault fault populationstrending trendingslightly slightlyeast eastand and west west of of north, populations north, with with low low angled angled slickenside orientations, suggesting slickenside orientations, suggesting strike slip slip motion. motion. All of the the fault fault All of orientations collected collected from from the the northeast orientations northeast trending trending PLV PLV are parallel parallel with with 92 �this this orientation orientation and and the the low low angled angled pitch pitch of ofthe theslickensides, slickensides, also, also,indicates indicates strike-slip 1). strike-slip motion motion along along these these faults faults (figure (figure 1). Figure Figure 1. 1. Diagram Diagramofofthe themajor majorfault faulttrends trendson onthe theKeweenaw KeweenawPeninsula Peninsula showing showing their their compatibility compatibilitywith with the thecomputed computedcompressive compressivetensor. tensor. y1 Fault data from Fault orientation orientation data from Isle Royale, Royale, on on the the north north limb limb of of the the Lake Lake Superior Superior syncline, syncline, exhibited exhibited two two shallowly shallowly dipping dipping populations, populations, one one trending trending northeast northeast and and the the other othernorthwest, northwest, with withslickenside slickenside lineations lineations suggesting suggesting mainly mainly strike slip slip motion motion along along the the faults. faults. The The quality quality of of fault fault sense sense criteria criteria was was excellent, excellent, with with fault fault slickenline slickenline growths growths allowing allowing for for incontrovertible incontrovertible macroscopic macroscopic determinations determinations of of fault fault motion. motion. Implimentation of a fault Implimentation of fault inversion inversion analysis analysis for for data data from fromthe theKeweenaw Keweenaw Peninsula Peninsula resulted resulted in aa southerly southerly compression, compression, while while that from from Isle Isle Royale Royale National National Park, Park, indicates indicates two two tensors, tensors, one one southerly southerly and and the the other other easteastsoutheasterly southeasterly compression. compression. These These tensors tensors are are compatible compatible with model of of with a model southerly southerly extension extension and and compression, compression, introduced introduced by Cambray Cambray and and Fugita Fugita (ILSG, (ILSG, 1991), 1991), with with the the central central portion portion ofofthe theMidcontinent Midcontinent Rift Riftcontaining containing more more material material to to be becompressed compressed than than the thesouthwestsouthwest- and and southeast southeast trending trending limbs limbs to to the thewest westand andeast, east,respectively. respectively. With With this this in in mind, mind, aa 93 �I southerly southerly compression compression would would lead lead to to an aneast-west east-west extrusion extrusion along alongthe the northern northern limb limb of of the the syncline, syncline, caused caused by by contact contact of of this thislimb limbwith withthe the Contact ofof arcuate arcuate shoreline shoreline ofofMinnesota Minnesotaand andOntario, Ontario,Canada, Canada,combined. combined. Contact this this sort sortwould would modify modify the thelocal localstress stressfield fieldaround around Isle IsleRoyale, Royale, on onthe the northern northern limb, limb, and and create create aamaximum maximum compressive compressive stress stress in in aamore more easterly direction. direction. easterly Theseconclusions conclusions are are confirmed confirmed by by examination examination of of the thetrend trend of of These slickensides, from from both both study study areas, areas, which which describes describes the the motion motion on on each each slickensides, 2). limb asascalculated calculated by by the thefault faultarray arrayanalysis analysisprogram program (figure (figure2). limb Figure2.2. Rose Rosediagram diagram of of the thetrend trendofof slickensides slickensideson on Figure normal normaland andreverse reversefaults faultson onIsle IsleRoyale Royale(a (aand andb) b) and andthe theKeweenaw KeweenawPeninsula, Peninsula,Michigan Michigan(C (cand andd). d). 94 �Geochemistry of the the Metadiabases in the Geochemistry of Metadiabases in the Republic Republic Mine Mine Area, Area, Northern Northern Michigan Michigan Xinping Xinping Yin Yin Department of Geology, Department of Geology, Bryn Bryn Mawr Mawr College, College, Bryn Bryn Mawr, Mawr, PA PA 19010 19010 James James A. A. Grant Grant Department of Geology, Department of Geology, University University of of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812 55812 There There are are three three layers layers of of Precambrian Precambrian metamorphosed metamorphosed and and altered altered diabase within the the Negaunee iron formation diabase interlayered interlayered within Negaunee iron formation and and several several other other small small bodies bodies in in the the Goodrich Goodrich quartzite quartzite and and Precambrian Precambrian granitic granitic gneiss gneiss in in the Mine area, area, which which isis located at the the the Republic Republic Mine located at the core core of of the theRepublic Republic synclinoriumand andinin the the center syncline syncline in in the the Marquette Marquette synclinorium center of of the the regional regional Northern Michigan. All the metamorphic zones in diabases underwent metamorphic zones in Northern Michigan. diabases underwent extensive extensive regional regional pretectonic pretectonic hydrothermal hydrothermal alteration, alteration, metamorphism metamorphism and and deformation, and local local metasomatism, whichresulted resultedinin the deformation, and metasomatism, which the formation formation of of amphibolite, actinonite actinonite schist, schist, cummingtonite cummingtonite or o r grunerite schist, andalusite schist, muscovite schist and chlorite schist from the the center andalusite schist, muscovite schist and chlorite schist from center of of metadiabases metadiabases to to the contact contact between between the the metadiabases metadiabases and and the theNegaunee Negaunee iron and from from the iron formation, formation, and the limb limb to to keel keel of of the theRepublic Republic syncline. syncline. That That all these these rocks rocks are are formed formed from from same same protolith protolith is is suggested suggested by: by: 1). the t h e stratigraphically conformable conformable relationship between the the 1). metadiabases and Negaunee iron iron formation, formation, which which are are identical identical and and metadiabases and the the Negaunee uniform in the uniform in the whole whole area, area, 2). 2). the thegradual gradualtransition transition between between the the diabase diabase and amphibolite amphibolite outside Republic Mine, gradual change change of the the and outside of of the the Republic Mine, 3). 3). the gradual species and and volume volume of of minerals minerals and and the the mineral mineral assemblages assemblages from from the the species center of the the metadiabases metadiabases to to the the contact contact between between the the metadiabases metadiabases and and center the and from from the the limb limb to to the the iron iron formation formation and the keel keel of of the the syncline, syncline, 4). 4). the the relict amphibolite amphibolite bodies bodies in in different different zones, zones, 5). 5). the the existence existence of of relict relict minerals, such relict plagioclase plagioclase inin all the rock rock types, types, and and the the relict relict minerals, such as as the the relict all the andalusite andalusite in in the the muscovite muscovite schist schist and and chlorite-garnet schist, schist, 6). 6 ) . the the extensive relict textures, such the relict relict diabase diabase textures textures ininamphibolite amphibolite extensive relict textures, such as the and the the pseudomorph of amphibolite amphibolite from from pyroxene, pyroxene, 7).the 7).the gradual gradual decrease of Ca, Mg, decrease of Mg, Na, Na, Sr, Sr, V. V, Cr, Cr, Sc, Sc,Fe++, Fe++, Th, Th, and andYYcorresponding corresponding to to the the gradual increase of of Al, Al, Ti, Ti, K, K, P, H20, gradual increase H20, Nb, Nb,Zr, Zr, Rb, Rb, Ni, Ni, Ce, Ce, La, La, Fe+++, Fe+++, Mn, Mn, Si, Si, Co, Co, and and Ba Ba of of rock rock bulk bulkchemical chemical composition composition from from the the center center ofofmetadiabases metadiabases to the and the iron the contact contact between between the the metadiabases metadiabases and iron formation formation and and from from the 8). the gradual gradual decrease decrease of of the limb limb to to the the keel keelofofthe theRepublic Republicsyncline, syncline, 8). anorthite content inin the and the anorthite content the plagioclase plagioclase and the increase increase of of the the Al/Si, Al/Si, Al/Ca, Al/Ca, K/Na K/Na and and Fe/Mg Fe/Mg ratios ratios in in various various amphiboles amphiboles in in these these two twodirections. directions. 95 �The evidence The evidence above above together together with with the the structural structural analysis analysis suggest:1). suggest:!). before the regional hydrothermal alteration the extensive regional the decomposition metamorphism the diabase metamorphism ofof the diabase resulted resulted in in the decomposition of pyroxene pyroxene and in the and plagioclase plagioclase in the diabase diabase and and the the formation formation of of mafic mafictotoperaluminous peraluminous rocks through the leaching and sodium rocks through the leaching of of iron, iron, magnesium, magnesium, calcium calcium and sodium in the the diabases, 2). these diabases, these rocks rocks with with the different different chemical chemical compositions compositions are metamorphosed to amphibolite, actinonite actinonite schist, cummingtonite schist, schist, the second second episode episode of of andalusite and and muscovite muscovite schist, and and finally finally 3). the andalusite hydrothermal alteration resulted in the extensive alteration of these metamorphicrocks rocksand and in in the local metamorphic local metasomatism metasomatism at the the contact contact between between formation. These metadiabases and and Negaunee the metadiabases Negaunee iron iron formation. These conclusions conclusions are further supported by: by: 1). 1). the the zoning zoning of of the the garnet garnet in in chlorite chlorite schist, schist, which which further supported is defined the inner inner garnet garnet core; core; the middle altered altered garnet garnet ring ring with with defined by by the the middle garnet rim muscovite, biotite, quartz quartz and and chlorite; chlorite; and and the the outer garnet rim with with distinct overgrowths distinct overgrowths and and well-developed well-developed faces; faces; all three garnet zones zones are are three garnet then cut by by the thechlorite chloriteveins veinscontaining containing quartz quartz and and epidote, epidote, 2). then cut the existence at least least three three different different generation generation of of plagioclase: plagioclase: the relict existence of of at the relict plagioclase with anorthite content larger than 50, 50, the intergranural recrystallized and ithe plagioclase recrystallized plagioclase plagioclasewith with lower lower anorthite anorthite content, content, and the plagioclase (most albite) as as the inclusions in amphiboles; all of of these these plagioclase plagioclase underwent extensive sericitization, sericitization, 3). 3). the extensive sericitization of gradual decrease decrease of anorthite content center to andalusite, andalusite, 4). 4). the the gradual of anorthite content from from the the center the the edge edge of of the the relict relict plagioclase; plagioclase; and the increase increase of of the the Al/Si, Al/Si, Na/Ca, Na/Ca, and the 5). K/Na and Fe/Mg ratios center to the the edge edge of of the theamphiboles, amphiboles, 5). K/Na and Fe/Mg ratios from from the the center the the three three sample sample subspaces subspaces in the the cumulative cumulative possibility possibility diagram, diagram, in in the multi-peak curves of distribution pattens, and in the histogr ms for all the multi-peak curves of distribution pattens, and in the histogrtms for the elements, least three three geological geological processes, processes, 66). ) . the the Pearce Pearce elements, which which suggest suggest at at least elements which also also suggests suggests three three possible possible geological geological processes processes and and elements ratios ratios which the decomposition of amphiboles and and plagioclase plagioclase as major major mechanism mechanism for for the decomposition of amphiboles 7). the isocon analysis the regionally pretectonic pretectonic hydrothermal hydrothermal alteration, alteration, 7). the regionally the isocon analysis results which which indicate are at at least least three three major major isocons, isocons, which which are are results indicate that that there there are well demonstrated by two chemographic chemographic methods, suggesting at least least well demonstrated by two methods, thus thus suggesting three geologic processes. The detailed calculations to compare the chemical three geologic processes. The detailed calculations to compare the chemical composition and the the least compositionand and variation variationbetween betweenthe the various various rock rock types types and between adjacent rocks, and between altered metadiabase-amphibolite, metadiabase-amphibolite, between and between different the keel keel of of the the syncline syncline using using isocon isocon different sections sectionsfrom fromthe the limb limb to to the analysis method methodrevealed revealedthe thetotal total mass mass loss loss or or gain analysis gain for for whole whole rocks, rocks, and and the absolute and relative relative loss loss or gain for each elements, elements, which which also also absolute and for each supports the conclusions distinct reflections reflections along along supports conclusions discussed discussed above. above. 8). 8). the the distinct all the the element element concentration concentration curves occur not only from the muscovite curves occur not only from the muscovite schist to schist to the chlorite chlorite schist, schist, but also from from the the amphibole amphibole schist schist to the but also andalusite andalusite schist, schist, which which indicates indicatesthe the distinct distinct change change of of the physical physical and and chemical three different different geologic geologic processes. processes. chemical conditions conditions for for the three !' 96 �The degree degree of metamorphism and hydrothermal alteration is partially controlled by the structural structural position of the metadiabases. Comparedtoto the the relatively simple structures structureson on the the limb limb of the Compared relatively simple the syncline, syncline, numerous kinds of faults (especially the large-scaled axial faults which numerous kinds of faults (especially the large-scaled axial faults which cut cut the keel of of the the syncline), syncline), joints joints and and sliding sliding between between layers layers are are well developed in the developed in the keel. keel. These These structures structures are the the channels channels through through which which the the hydrothermal fluid has flown through and they mark the position where hydrothermal fluid has flown through and they mark the position where The the the most intensive intensive alteration of metadiabases happens. The comprehensive comprehensive analysis analysis of of the the above above information information also also suggests suggests that the fluid fluid flow flow direction direction runs runs from from the thecontact contact between between the themetadiabases metadiabases and and the iron formation to the center of the metadiabases and that the second the iron formation the center of the metadiabases and that the second episode episode of of hydrothermal hydrothermal activity activity is is aa result result hydrothermal hydrothermal alteration alteration and and local local metasomatism metasomatism rather rather than than ofofretrograde retrogrademetamorphism. metamorphism. References R eferences Cannon, Cannon, W.F., W.F., 1975, 1975, Bedrock Bedrock geologic geologic map of of the theRepublic Republic Quadrangle, Quadrangle, Marquette USGS, open-file Marquette County, County, Michigan: Michigan: USGS, open-file map, map, Scale Scale 1:24000 1:24000 Cannon, W.F., and Kiasner, Klasner, J.S., J.S., 1972, 1972, Guide Guide to to Penokean Penokean deformation deformation style style Cannon, W.F., and and of the and regional regional metamorphism metamorphism of the western western Marquette Marquette range, range, Michigan, In Field Michigan, In Field Trip Trip Guidebook, Guidebook, 18th 18th Ann. Ann. Inst, Inst, on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Michigan, Michigan, pp B1-B38 B 1-B38 Cleveland Cliff Iron Co. Cleveland Cliff Co. 1988. 1988. Republic Republic Open Open Pit Map, Map, Scale: Scale: 1:1200 1:1200 Frost, Parageneses in in the Frost, B.R., B.R., 1979, 1979, Metamorphism Metamorphism of iron-formation: iron-formation: Parageneses the system Fe-Si-C-O-H, Econ. Geol., Geol., V. P. 775-785 775-785 Fe-Si-C-0-H, Econ. V. 74, 74, P. Hasse, of the Hasse, C.S., C.S., 1982, 1982, Metamorphic Metamorphic petrology petrology of the Negaunee Negaunee Iron Iron Formation, Formation, Marquette Marquette district, district, northern northern Michigan: Michigan: Mineralogy, Mineralogy, metamorphic metamorphic reactions and phase equilibria, Econ. Geol., v. 77, 60-81 reactions and equilibria, Econ. Geol., 77, p. 60-8 1 Grant, J.A., J.A., 1986. 1986. The The isocon isocon diagram-A diagram-A simple simple solution solution ton ton Gresens' Gresens' Grant, equation alteration. Econ. Econ. Geol., Geol., v. 81, equation for metasomatic metasomatic alteration. 8 1, p. 1976-1982 1976-1982 Gresens, Gresens, R.L., R.L., 1967. 1967. Composition-volume Composition-volume relationships relationships of of metasomatism. Chem. Geol.., Geol.., V. V. 2, P. P. 47-55. 47-55. metasomatism. Chem. James, J.L., J.L., 1955. 1955. Zones Zones of of regional regional metamorphism metamorphism in the the Precambrian Precambrian of of James, northern 1465-1488. northern Michigan. Michigan. GSA GSA Bill., Bill., V.66, V.66, No. No. 12, 12, p. 1465-1488. Klasner, J.S., Klasner, J.S., 1978. 1978. Penokean Penokean deformation deformation and associated associated metamorphism metamorphism in in western Marquette Marquette district, district, northern northern Michigan, Michigan, GSA 89, the western GSA Bull., Bull., v. 89, p. 711-722. 71 1-722. p. 97 �the Proceedings of of this this meeting meetingmay maybe beordered ordered from from Issues of the M.G. Mudrey, Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do Wisconsin c/o WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 38 17 Mineral Point Road 3817 53705-5100 Madison, Wisconsin 53705-5 100 Part 1: 1: Program and Abstracts: $7.00 U.S. Trip Guidebook: Guidebook: $7.00 $7.00 U.S. Part 2: Field Trip Orders filled while supplies last. Orders will will be filled last. All volumes back to 1955 are available for photocopying at the prevailing rate, from the Michigan Michigan Technological Technological University University Library, Library, through through Mr. Mr. M.S. M.S. Spence, Spence,Archivist. Archivist. Telephone Telephone (906) (906) 487-2505 487-2505 � https://digitalcollections.lakeheadu.ca/files/original/c5253427f96384daf3ddcc7f4512e8bf.pdf 105a711f529b6cdd5f7bf1c12a27cac1 PDF Text Text 7. �ORGANIZING COMMITTEE 38TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY General General Chairman: Albert B. Dickas, University University of Wisconsin-Superior Wisconsin-Superior Program Chairman and Proceedings Proceedings Editor: Bruce Brace A. Brown, Brown, Wisconsin Geological and Natural History Survey Survey Volume 38 consists of Part 1: 1: Program Program and and Abstracts Abstracts Part 2: Field Trip Guidebook Guidebook Published and distributed distributed by Institute on Lake Superior Superior Geology M.G. Mudrey, Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 3817 38 17 Mineral Point Road Madison, Wisconsin 53705-5100 53705-5100 ISSN 1042-9964 1042-9964 �INSTITUTE INSTITUTE ON ON •LAK E• SUPERIOR SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS 38m ANNUAL MEETING MAY 6-9,1992 HURLEY, WIscoNsJl4 ORGANIZED BY ALBERT B. DIcicAs, UNIvERsn'Y O WISCONSIN-SUPERIOR BRUCE A. BROWN, WISCONSIN GEOLOGICAL ANI) NATURAL HISTORY SURVEY VOLUME 38 PART 2 MAY 1992 FIELD TRIP GUIDEBOOK �CONTENTS CONTENTS Trip Trip1:1:Archean Archeanand andEarly EarlyProterozoic ProterozoicGeology Geologyofofthe theGogebic GogebicDistrict, District, Northern Michigan Michiganand andWisconsin Wisconsin Northern Leaders Leaders GeneL. L. LaBerge, LaBerge,University UniversityofofWisconsin—Oshkosh Wisconsin-Oshkosh Gene Richard W. W. Ojakangas, Ojakangas,University UniversityofofMinnesota—Duluth Minnesota-Duluth Richard J. Licht, Licht, St. St. Norbert Norbert College College Kathy J. Kathy Trip2: 2: Evolution Evolutionof of the theKeweenawan Keweenawan Sedimentary SedimentarySequence Sequence Trip Leaders Leaders Albert B. B.Dickas, Dickas,University UniversityofofWisconsin—Superior Wisconsin-Superior Albert M.G. M.G. Mudrey, Mudrcy,Jr., Jr., Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey Trip Supergroup Rocks near Trip3: 3: Geology Geology of Keweenawan Supergroup near the the Porcupine PorcupineMountains, Mountains, Ontonagonand andGogebic GogebicCounties, Counties,Michigan Michigan Ontonagon Leaders Leaders William WilliamF. F. Cannon, Cannon, Suzanne SuzanneW. W. Nicholson, Nicholson, Cheryl Cheryl A. A. Hedgman, Hedgman, Schulz, Laurel G. G. Woodruff, Woodruff,and andKlaus Klaus J.J. Schulz, Laurel U.S. Geological GeologicalSurvey, Survey,Reston, Reston, Virginia Virginia U.S. Trip4: 4: Geology Geology of the Great Great Lakes Lakes Tectonic Zone in the Marquette Trip Marquette Area, Michigan-A Late Late Archean Archean Paleosuture Paleosuture Michigan—A Leaders Leaders P.K. Sims Simsand andZ.E. Z.E. Peterman, Peterrnan,U.S. U.S.Geological GeologicalSurvey, Survey,Denver, Denver,Colorado Colorado P.K. 41 75 103 �ARC HEAN AND EARLY PROTEROZOIC GEOLOGY OF THE GOGEBIC DISTRICT, NORTHERN MICHIGAN AND WISCONSIN Gene L. LaBerge University Universityof ofWisconsin—Oshkosh Wisconsin-Oshkosh Richard W. Ojakangas Richard University Universityof ofMinnesota—Duluth Minnesota-Duluth WITH A CONTRIBUTION CONTRIBUTION FROM Kathy J. Licht St. Norbert College �This This field field trip trip is is the the outgrowth outgrowth of of numerous numerous student student field field trips trips led led by by the the authors authors over over the the past past quarter quartercentury. century. Most Most of of the the stop stop localities localities have have been been suggested suggested by by geologists geologists who who have have worked in in the the district. district. However, However, some some localities localities are are the the result result worked One of us (LaBerge) spent of our own studies in the area. of our own studies in the area. One of us (LaBerge) spent several 1991, supported supported by by the the several weeks weeks mapping mapping in in the the area area in in July, July, 1991, U.S. U.S. Geological Geological Survey, Survey, and and Ojakangas Ojakangas worked worked in in this this region region intermittently intermittently with with U.S. U.S. Geological Geological support support from from 1978 1978 until until 1990. 1990. 2 �EARLY EARLYPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGYOF OFTHE THEGOGEBIC GOGEBICDISTRICT DISTRICT NORTHERN AND WISCONSIN WISCONSIN NORTHERNMICHIGAN MICHIGANAND INTRODUCTION The Gogebic Gogebic range range extends extendsfrom from Lake Lake Gogebic, Gogebic! Michigan, Michiganl The westward 128 km kmto tonear nearLake LakeNamekagon, NamekagonlWisconsin Wisconsin westward approximately approximately128 The major major structure structure in in the the area area is is aa north-facing north-facing 1). The (Figure1). (Figure and monocline monocline that that exposes exposes Archean Archean rocks rocks to to the the south south and and Middle Middle and -(~eweenawan Supergroup) rocks rocks to to the the north. north. Late Proterozoic Proterozoic (Keweenawan Late Supergroup) 7 SUPERIOR LAKE / — (C ( \000EBIC WAKEFIELD HURLE> LI. EN — - KiARENI3CO t • I. , + I + 4- 4- 0 10 5 4- 4- 4 + -f 4- 4- - -- vJ- . 4+ s LAX - cl SUE E I Ci -4- 20 KM EXPLANATION EXPLANATION MIDDLE PROTEROZOIC PROTEROZOIC MIDDLE - EARLY EARLY PROTEROZOIC PROTEROZOIC Volcanics and and volcanics sediments sediments I I Graywacke—slate Iron—Formation Iron-Formation ARCH EAN 1-4-4- 4! I m y ). vt.I Granitoids Volcanics Volcan ics 1. Generalized Generalized map map of of the the Gogebic Gogebic range, rangel showing showing the the Early Early Figure 1. Figure Proterozoic Proterozoic rocks rocks sandwiched sandwiched between between Archean Archean rocks rocks on on the south south and and Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan Supergroup Supergroup the rocks on on the the north. north. (Adapted (Adapted from from Morey Morey and and others, others, rocks 1982) 1982) 33 �Early Early Proterozoic Proterozoic rocks rocks lie lie discordantly discordantly between between these these major major sequences. sequences. As As aa result result of of the the steep steep northerly northerly dip dip of of the the monocline tiltingl1 the the geological geological monocline (a (a consequence consequence of of Keweenawan Keweenawan tilting), the district is basically a stratigraphic cross-section. map of map of the district is basically a stratigraphic cross-section. The known The general general geology geology of the the Gogebic range has been known since (1892)1Van Van Hise Hise since the the pioneering pioneering work work of of Irving Irving and and Van Van Hise Hise (1892), and and Leith Leith (1911), (1911)1Hotchkiss Hotchkiss (1919), (1919),and and Aldrich Aldrich (1929). (1929). Although Although subsequent the subsequent studies studies have have done done much much to to "refine" I1refineIt the geological geological picture picture -- - and and much much still still remains remains to to be be done done -- - most most of the the early early interpretations interpretations have have withstood withstood the the test test of of time. time. The The broad-scale broad-scale geology geology of the the eastern eastern Gogebic district is is presented on on the Iron Iron River Quadrangle (Cannon, lo x 2° 2 ' Quadrangle (Cannonl1986). 1986) River 1° . STRATIGRAPHY The The Gogebic Gogebic range range contains contains excellent excellent exposures exposures of of rocks rocks that that range range in in age age from from Archean Archean (about (about 2,700 21700Ma) Ma) and and Early Early Proterozoic Proterozoic ProterozoictKeweenawantI (2,300 11900Ma), Ma), to to Middle and Late Protero~oic-~~Keweenawan~~(2#300-- 1,900 (1,200 (11200-- -600 -600 Ma). Ma). Stratigraphic Stratigraphic and and structural structural relationships relationships of of several several of of the the rock rock sequences sequences can can be be observed observed in in outcrops. outcrops. Thus,it 'Thuslitis is possible possible to to demonstrate demonstrate the the relationship relationship of of the the rock rock sequences sequences to to each each other. other. The The general general sequence sequence of of rock rock units units in in the the Gogebic Gogebic district district is is shown shown in in Figure Figure 2, Z1 aa diagrammatic diagrammatic longitudinal longitudinal section section along along the the Gogebic Gogebic range. range. w Keweenawan Keweenawan tr ofl E --- - Prit + + g Puritan * - - Figure Figure 2. 2. Idealized Idealized sketch sketch showing showing generalized generalized stratigraphic stratigraphic section section on on the the eastern eastern Gogebic Gogebic range. range. 4 �ARCHEA&N ROCKS ARCHEAN ROCKS Archean Archean rocks rocks in in the the Gogebic Gogebic range range are are variably variably deformed deformed and and metamorphosed greenstones and granitoid rocks typical metamorphosed greenstones and granitoid rocks typical of of Archean Archean greenstone-granite greenstone-graniteterranes terranes (or (orbelts), belts) and, and, indeed, indeedlare are an an The district district is is extension extension of of the the Wawa Wawa Greenstone Greenstone belt belt of of Canada. Canada. The near near the the southern southern margin margin of of the the Superior Superior Province Province of of the the Canadian Canadian Because this this fied fieldtrip tripis isconcerned concerned primarily primarily with with the the Shield. Because Shield. Early only aa brief brief description description of of the the Archean Archean Early Proterozoic Proterozoic rocks, rockslonly rocks is is presented presented here. here. rocks Archean volcanic volcanic rocks rocks are are exposed exposed in 'in aa belt belt Ramsay Formation. Formation. Archean Ramsay about about 55 km km wide wide and and 16 16 km km long long in in the the eastern eastern Gogebic Gogebic range range (Prinz and and others, othersl 1975). 1975). Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) named named (Prinz volcanic volcanic and and sedimentary sedimentary rocks rocks in in the the Ramsay-Wakefield Ramsay-Wakefieldarea area as as the Ramsay Ramsay Formation. Formation. The The Ramsay Ramsay Formation Formation consists consists mainly mainly of of the pillowed, pillowedl fragmental, fragmentalland and massive massive basaltic basaltic rocks rocks in in the the eastern eastern part part of of the the area; area; however, howeverlfelsic felsic volcanic volcanic rocks rocks and and metametagraywackes graywackes are are dominant dominant to to the the west, westl near near the the Wisconsin Wisconsin border. border. Most Most of of the the rocks rocks have have been been metamorphosed metamorphosed to to greenschist greenschistfacies, faciesI Locallyl with with well-preserved well-preservedpillows pillows and and other other primary primary features. features. Locally, especially especially adjacent adjacent to to the the Puritan Puritan Quartz Quartz Monzonite, Monzonitelthe the rocks rocks have have been been metamorphosed metamorphosed to to amphibolite amphibolite facies, faciesland and few, fewlor or no, nol The Ramsay Ramsay Formation F o m t i o n may may be be the the primary features features are are preserved. preserved. The primary oldest rock rock unit unit in in the the Gogebic Gogebic range range proper, properl however, howeverl older older oldest gneisses 3#560Ma) Ma) are are exposed exposed in in the the Watersmeet Watersmeet area, areal some some gneisses (to (to3,560 30 km km southeast southeast (Sims (Simsand and others, othersl 1984). 1984) 30 . kritan Quartz Ouartz Monzonite. Monzonite. The The volcanic-sedimentary volcanic-sedimentarysequence sequence of of Puritan the Ramsay Ramsay Formation Formation has has been been intruded intruded by by large large granitoid granitoid masses masses the named the the Puritan Puritan batholith batholith (Schmidt (Schmidtand and Hubbard, Hubbardl1972). 1972). The The named Puritan Puritan Quartz Quartz Monzonite Monzonite exposed exposed in in the the central central and and western western Gogebic range range is is aa weakly-deformed weakly-deformedpost-tectonic post-tectonicpluton pluton that that Gogebic ranges ranges in in composition composition from from granite granite to to tonalite tonalite and and has has been been dated dated 2#735±& 16 to 2,735 16 Ma Ma (Sims (Simsand and others, othersl1984). 1984). to Granitoid rocks rocks are are also also extensively extensively exposed exposed in in the the Granitoid Marenisco area area on on the the eastern eastern end end of of the the Gogebic Gogebic range. range. Parts Parts of of Marenisco the granitoid granitoid has has prominent prominent gneissic gneissic banding banding and and associated associated the otherl more more extensive extensive phase, phasel is is aa weakly weakly amphibolite. The The other, amphibolite. deformed medium-grained medium-grainedgranite granitewith withwidely widelyscattered scatteredpeglnatite pegmatite deformed (Frittsl1969; 1969;Trent, Trentl1973) 1973) bodies (Fritts, bodies . The Archean Archean rocks rocks were were eroded eroded and and are are unconformably unconformably overlain overlain The by Early Early Proterozoic Proterozoic rocks rocks of of the the Marquette Marquette Range Range Supergroup. Supergroup. by Because the the Gogebic Gogebic range range is is aa north-dipping north-dipping monocline, monoclineI Early Early Because Proterozoic rocks rocks rest rest on on Archean Archean rocks rocks to to the the south south along along the the Proterozoic entire length length of of the the range. range. entire EARLY PROTEROZOIC PROTEROZOIC ROCKS ROCKS EARLY At the the ends ends of of the the Gogebic Gogebic range range the the Archean Archean rocks rocks are are At unconformably overlain overlain by by rocks rocks of of the the Chocolay Chocolay Group Group of of the the unconformably 5 �Marquette Marquette Range Range Supergroup, SupergrouplSunday Sunday Quartzite Quartzite and and Bad Bad River River the eastern eastern end end and and only only Bad Bad River River Dolomite Dolomiteat at the the Dolomite Dolomite at at the Chocolay Group rocks are absent from the central western westernend. end. Chocolay Group rocks are absent from the central part and evidently evidently were were eroded eroded prior prior to to deposition deposition part of of the the range, rangeland of overlying units. of overlying units. The Sunday Sunday Quartzite Quartzite was was deposited deposited Sunday Ouartzite. Ouartzite. The Sunday unconformably uncon~ormablyon on Archean Archean rocks rocks (mostly (mostlythe the Ramsay Ramsay Formation), Formation) The basal basal no regolith regolith on on the the Archean Archean has has been been observed. observed. The however, howeverl no unit is is aa prominently prominently cross-bedded cross-beddedreddish reddish quartzite. quartzite. unit Conglomerate cm Conglomerate layers layers with with quartz quartz and and granite granite cobbles cobbles to to about about 88 cm Most of of the the are are present present within within the the lower lower part part of of the the formation. formation. Most formation formation is is aa gray gray vitreous vitreous quartzite quartzite in in which which cross-bedding cross-beddingis is common common and and current current ripple ripple marks marks are are well well developed developed in in places. places. According According to to Schmidt Schmidt (1973) (1973)the the Sunday Sunday Quartzite Quartzite is is present present only only on on the the eastern eastern end end of of the the range, rangelwhere where it it has has aa maximum maximum thickness thickness of about about 46 46m. m. One One of of the the type type localities localities of of the the Sunday Sunday of Quartzite Quartzite has has been been described described in in the the center center of of the the district district near near the the Newport Newport Mine Mine (Van (VanHise Hise and and Leith, LeithI1911) 1911) and and the the problem problem of of this locality" has this "lost lllost 10cality~~ has been been discussed discussed by by Schmidt Schmidt (1973) (1973). The Sunday Sunday Quartzite Quartzite grades grades upward upward into into the the Bad River River Dolomite. Dolomite. The Bad Bad River River Dolomite. Dolomite. The The transition transition is is marked marked by by interbedded interbedded Bad dolomite dolomite and and quartzite; quartzite; the the dolomite dolomite beds beds are are thicker thicker and and more more abundant abundant and and quartzite quartzite beds beds are are thinner thinner and and less less abundant abundant upward. upward. dolomite weathers weathers to to aa distinctive distinctive tan/brown tanlbrown color color and and The dolomite The contains contains abundant abundant layers layers and and irregular irregular patches patches of of gray gray to to black black chert. Stromatolitic Stromatolitic layers layers with with mounds mounds that that range range in in size size from from chert. about about 5-50 5-50 cm cm in in diameter diameter become become more more abundant abundant upward upward in in the the dolomite. Stromatolitic Stromatolitic units units tend tend to to be be prominently prominently silicified. silicified. dolomite. Maximum Maximum thickness thickness of of the the dolomite dolomite is is about about 120 120 m, ml but but in in most most areas it it is is considerably considerablyless. less. areas AA period period of of erosion erosion followed followed deposition deposition of of the the quartzite quartzite and and dolomite dolomite of of the the Chocolay Chocolay Group, Groupl removing removing the the Sunday Sunday Quartzite Quartzite and and Bad River River Dolomite Dolomite from from all all but but the the eastern eastern and and western western ends ends of of Bad the Gogebic Gogebic range. range. the Palms Formation Formation is is the the basal basal unit unit of of the the Palms Formation. Formation. The The Palms Palms Menominee Group Group of of the the Marquette Marquette Range Range Supergroup. Supergroup. It It rests rests Menomiaee unconformably on on the the Bad Bad River River Dolomite Dolomite and and Sunday Sunday Quartzite Quartzite on on unconformably rangel and and on on the the Puritan Puritan Quartz Quartz the east east and and west west ends ends of of the the range, the Monzonite and and Ramsay Ramsay Formation Formation in in the the central central part part of of the the range. range. Monzonite Little or or no no regolith regolith is is developed developed on on the the erosion erosion surface. surface. Little The Palms Palms Formation Formation is is about about 146 146 meters meters thick thick and and contains contains aa The basal mud-rich mud-rich unit, unitl aa central central interbedded interbedded mud-silt-sand mud-silt-sandunit, unitl basal and an an upper upper sand-rich sand-richunit unit (Ojakangas, (Ojakangas 1983). 1983) AA thin thin (usually (usually and less than than 33 mm thick) thick) conglomerate conglomerate occurs occurs locally locally at at the the base base of of less (Aldrich! 1929). 1929). The The Palms Palms grades grades abruptly abruptly upward upward the formation formation (Aldrich, the into the the Ironwood Ironwood Iron-formation. Iron-formation. Thin Thin (1-5 (1-5cm) cm) beds beds of of granular granular into iron-formationare are interbedded interbedded with with quartzite quartzite (Ojakangas, (Ojakangasl1983) 1983) iron-formation across aa thickness thickness of of 10 10 m. m. The The abundance abundance and and thickness thickness of of beds beds across of iron-formation iron-formationincreases increases upward with with a a corresponding corresponding decrease decrease of in detrital detrital beds. beds. Recent Recent studies studies by by Ojakangas Ojakangas (1983) (1983) indicate indicate in . 66 �that that the the Palms Palms Formation Fomtion may may have have been been deposited deposited by by tidal tidal currents sea currents in in aa transgressing transgressingsea(Figure (Figure3). 3j . Figure Sedimentational model model showing showing lateral lateral relationships relationships of of Figure 3. 3. Sedimentational the the siliciclastic siliciclastic tidal tidal facies, faciesI the the iron-formation iron-formation facies shelfI and and the the deeper-water deeper-waterturbidite-mud turbidite-mud facies on on the the shelf, facies. Thicknesses Thicknesses of of units units not not drawn drawn to to scale. scale. facies. (From Ojakangas, OjakangasI1983) 1983) . (From Ironwood Iron-Formation. Iron-Formation. The The transition transition from from the the Palms Palms Formation Formation Ironwood into into the the Ironwood Ironwood Iron-Formation Iron-Formationrecords records an an abrupt abrupt change change from from detrital to to chemical chemical sedimentation. sedimentation. Like Like other other iron-formations, iron-formationsI detrital the the Ironwood Ironwood contains contains little little detrital detrital material material even even though though it it is is 150-275mm thick. thick. 150-275 Although iron-formation iron-formationhas has aa simple simple composition composition ---- chert chert Although is extremely extremely varied varied in in appearance. appearance. Both Both and iron iron minerals minerals -- -- it is and the the chert chert and and the the iron iron minerals minerals are are varied varied in incolor. color. Although Although it it is is widely widely cited cited as as indicating indicating the the chemistry chemistry of of the the depositional depositional 1954)1 the the mineralogy mineralogy of of iron-formations iron-formationsis is environment (James, (JamesI1954), environment the product product of of the the depositional, depositionalI diagenetic, diageneticI metamorphic, metamorphicI and and to to the some extent, extentI the the weathering weathering environment environment that that the the rocks rocks have have some undergone. Still Still moderate moderate subsequent subsequent changes changes to to the the primary primary undergone. mineralogy do do not not usually usually reduce reduce our our ability ability to to infer infer primary primary mineralogy mineralogy. mineralogy. it Iron-formationshave have two two basic basic textural textural types. types. One One is is Iron-formations laminated with with layers layers of of chert chert about about 5-10 5-10 nun laminated mm thick alternating alternating with layers layers of of iron iron minerals minerals of of similar similar thickness. thickness. This This with laminated type type of of deposit deposit is. is comonly referred to to as as "slaty" 1lslatyll laminated commonly referred 4). It It has has aa grain grain size size and and bedding bedding iron-formation(Figure (Figure4). iron-formation characteristic of of siltstones siltstones (LaBerge, (LaBergeI1964, 19641 Dimroth, Dimroth! 1968). 1968). The The characteristic l1chertyI1 other textural textural type type of of iron-formation, iron-formationIreferred referred to to as as "cherty" other iron-formationIconsists consists of 1-10 1-10 cm cm thick thick layers layers containing containing fine fine iron-formation, (c2 mm) llgrainsn of chert with variable amounts of iron sand-size sand-size (<2 mm) "grains" chert with variable amounts iron minerals set in a chert matrix. These layers of llgranularll chert minerals set in a chert matrix. These layers of "granular" chert are extremely extremely variable variable in in thickness thickness over over short short distances, distancesI are commonly forming lenses (Figure 5). The cherty lenses are are The cherty lenses commonly forming lenses (Figure 5). 7 �_ Figure Figure 4. 4. Photo Photo of of thin-bedded thin-bedded (laminated) (laminated)iron iron formation formation with with some some thick-bedded thick-bedded(granular) (granular) layers. layers. Mt. Mt. Whittlesey, Whittlesey, nearMellen, near-Mellen,WI. WI. . ,: : * A. ' ;— — ,. ::::: : .,: ..— .vr : • . • '&. .• .. • . .. . ¶ , .- g_:L...' I .Figure Figure 5. 5. Photo Photo of of thick, thick, irregularly irregularly bedded, bedded, granular granular iron-formation. iron-formation. Mt. Mt. Whittlesey, Whittlesey, near nearMellen, Mellen, WI. WI 88 . �separated by 0.5-3 typically separated 0.5-3 cm layers layers of laminated laminated iron iron "Cherty" iron-formations have the grain size minerals. minerals. llChertyll iron-formations size and and bedding characteristics characteristics of of sandstones sandstones (Mengel, (Mengel, 1963; 1963; Dimroth Dimroth and and mineralogy of the minerals is Chauvel, Chauvel, 1973). 1973). The mineralogy the iron iron minerals is almost almost completely completely independent independent of of the the textural textural varieties varieties of of ironironironformation. (llchertyll) ironformation. Most geologists geologists agree agree that that granular granular ("cherty") formation formation represents represents shallow-water shallow-water deposition deposition and and laminated laminated ironironformation formation represents represents somewhat somewhat deeper deeper (quieter) (quieter)water water deposition. deposition. Several Superior region Several iron-formations iron-formations in in the the Lake Superior region have been subdivided into."members" on the basis of their been subdivided into."membersNon the their bedding Hotchkiss (1919) divided (textural) characteristics. characteristics. Hotchkiss (1919) divided the (textural) the Ironwood Ironwood Iron-formation Iron-formationinto into five five members. members. The -60 -60 m thick thick Plymouth Plymouth Member is is an an irregularly irregularly bedded bedded granular granular cherty cherty unit unit with a basal zone containing some detrital quartz quartz and and patches patches of zone containing overlying 46 46 m thick thick Yale Yale Member Member is is stromatolitic stromatolitic jasper. jasper. The overlying mainly an even-bedded (slaty) siderite-chert unit with a basal mainly an even-bedded (slaty) siderite-chert carbonaceous zone and a layer that is probably probably carbonaceous pyritic slate zone The succeeding Norrie Member is a 60 m thick unit m thick unit of of The succeeding Norrie Member is a 60 tuffaceous. tuffaceous. The Pence Member is The Pence Member is irregularly bedded cherty iron-formation. irregularly bedded cherty iron-formation. about 45 m of siderite-chert siderite-chert iron-formation, iron-formation, and the uppermost uppermost Anvil Anvil Member Member is is aa 15-60 15-60mm thick thick mixture mixture of of slaty slaty and and cherty cherty ironironThese members are continuous and uniform throughout formation. formation. These continuous uniform throughout However, they are are difficult difficult to the length of of the the range. range. However, to the 128 128 km length distinguish east of Wakefield, Michigan, where a thick distinguish east of Wakefield, Michigan, where a thick sequence sequence of volcanic rocks, 1973), is is rocks, the the Emperor Emperor Volcanic Complex Complex (Trent, (Trent, 1973), interbedded with interbedded with the the iron-formation. iron-formation. Gogebic range Iron ores. Iron ores. The iron iron ores ores on on the the Gogebic range were produced by chemical removal the chemical removal of of silica silica from from the the iron-formation. iron-formation. Dissolution of the Dissolution the silica silica required required the the removal removal of of nearly nearly 50 50 volume of the percent of the the original original volume the rock rock and and produced produced very very The ore ore consisted consisted mainly of earthy earthy goethite goethite porous orebodies. porous orebodies. The hematite; however, and hematite; however, in in open open spaces spaces produced produced by removal removal of of silica, botryoidal masses of silica, large large botryoidal of crystalline crystalline hematite hematite and and goethite were found, goethite found, as as well as as local local concentrations concentrations of of psilomelane psilomelane (romancheite), (romancheite), manganite, manganite, rhodochrosite, rhodochrosite, calcite, calcite, presence of manganocalcite, manganocalcite, barite, barite, gypsum, gypsum, and and marcasite. marcasite. The presence of iron iron ore ore cobbles cobbles in in Keweenawan Keweenawan rocks rocks in in the the district district suggests suggests that at least least some some of the the ore ore was was formed formed prior prior to to deposition deposition of of rocks of rocks of the the Keweenawan Keweenawan Supergroup. Supergroup. Nearly all all the the mines mines on on the the Gogebic Gogebic range range were were underground underground mines mines (Figures (Figures66 and and 7). 7). Mining Gogebic range on the the Gogebic range began began in in 1884 1884 and and ended ended in in 1967, 1967, when when the the underground mines could no longer open pit could no longer compete compete with the large large open taconite mines taconite mines elsewhere elsewhere in in the the world. world. Ore was taken taken by rail rail to to Ashland, Wisconsin, and Ashland, Wisconsin, and Escanaba, Escanaba, Michigan, from from where it was shipped to shipped to steel steel mills mills in in Indiana Indiana and and Ohio. Ohio. Emperor Volcanic Volcanic Complex. Emperor Complex. The The Emperor Emperor Volcanic Complex Complex constitutes a constitutes a thick thick pile pile of of volcanic volcanic rocks rocks and and sills sills in in the the sedimentary sequence sequence on the eastern Gogebic range where they sedimentary reach a thickness thickness of of at at least least 2,000 2,000 meters. meters. Although Although the the volcanic rocks been known volcanic rocks in in the the eastern eastern Gogebic Gogebic range range have have been known for for 100 1892), few studies have been few studies 100 years (Irving (Irving and Van Hise, 18921, undertaken undertaken on on these these rocks. rocks. Irving Irving and Van Hise (1892) (1892) stated stated 9 �___ GOGEBIC RANGE GOGEBIC RANGE GENERALIZED GEN E R A L I Z E D CROSS CROSS SECTION SECTION . (P. I b ... .0.. °o0 0.•. 0 :. .o;,; 0 ° . fl 0 :. - PLTMQJTII yap - ) --•------• ,O •- £pds,t - - \ \ \, / -- \ ./ . c \ —. \ /\ -<\ -. \/ / \ -, \, _y -':': — \ FORSATION —. — .' a \\ IlOH*Uc)O \ /,/\\ \\,S ,'—_-c' \ \ \ \ //,;/ " \ -: Poll I IOIUI.l l(P. __1__ _____:_.__ .. // 1.' \ 'a. ', •-' / /,'• // /1 '\/ \ Q.j U Y'\' \ç.\ — UUITI I NC, M G WE WK ST '31 // •0 0. ----------Q // 'I /1 \ \ \ \\ \ IAT ION . Figure 6. Schematic diagram showing showing the the occurrence occurrence of of iron iron (From Goldich orebodies on the orebodies the Gogebic Gogebic range. range. (From Goldich and Marsden, 1956) Marsden, 1956) Lake mine in in 1960. 1960. Note the the stockpile stockpile of of iron iron Figure 7. Sunday Lake ore in in the the upper upper left. left. Photo taken from from the the top top of of In Wakefield, Wakefield, Michigan. Michigan. Radio Tower Hill Hill In 10 �that that the the volcanic volcanic rocks rocks are are interbedded interbedded with with the the Ironwood Ironwood IronIronformation, formation, which which has has been been demonstrated demonstrated convincingly convincingly by by subsequent subsequent Mapping by by Trent Trent exploration or iron iron ore ore in exploration drilling drilling ffor in the the area. area. Mapping (1973) documented the distribution of igneous (1973) documented igneous rocks rocks and and showed showed some some of of the the lithologies lithologies present. present. Dann Dann (1978) (1978) showed showed that that the the volcanics dacite, and and that that volcanics range range in in composition composition from from basalt to to dacite, they have have been been metamorphosed metamorphosed only only to to prehnite-pumpellyite, or to to they prehnite-pumpellyite, or He also also elaborated elaborated on on the the possible possible lowest lowest greenschist greenschist facies. facies. He volcanic volcanic setting setting in in which which the the rocks rocks may may have have formed. formed. Trace Trace element studies by Schulz (Sims and others, 1990) element studies Schulz (Sims others, 1990) indicate indicate that that the the volcanic volcanic rocks rocks are are rift-related rift-relatedcontinental continental tholeiites. tholeiites. Reconnaissance Reconnaissance mapping in in 1991 1991 by LaBerge LaBerge and J. S. Klasner Klasner indicates that the Emperor Volcanic Complex indicates that the Emperor Volcanic Complex consists consists of of aa wide wide Both variety variety of of mainly mainly subaqueous subaqueous volcanic volcanic rocks rocks and and sills. sills. Both mafic mafic and and felsic felsic volcanics volcanics were were recognized. recognized. Mafic Mafic rocks rocks include include sills (such as the Wolf Mountain sill of Trent, 1973) sills (such as the Mountain sill Trent, 1973) pillowed pillowed and and massive massive flows, flows, some some with with columnar columnar jointing, jointing, and and extensive extensive Felsic hyaloclastites and pillow breccias (Figure 8). rocks hyaloclastites and pillow breccias (Figure 8). Felsic rocks include include hyaloclastites, hyaloclastites, massive massive felsite felsite breccias, breccias, and and units units comprised comprised of of felsite felsite breccia breccia with with 2-10 2-10 cm cm clasts clasts in in a a finer finer hyaloclastite 9). The The felsite felsite breccia breccia -hyaloclastite matrix matrix (Figure (Figure9). hyaloclastites may may be be debris debris flows flows from from aa subaqueous subaqueous felsic felsic dome. dome. hyaloclastites Although in the the Emperor Emperor Volcanic Volcanic Complex Complex with with Although there there are are zones zones in strong strong foliation, foliation, large large areas areas are are almost almost undeformed. undeformed. Because Because of of the metamorphic grade the low low metamorphic grade and and minimal deformation, deformation, primary primary features are are well-preserved. well-preserved. features The The relationship relationship between between volcanism volcanism and and iron-formation iron-formationhas has long (e.g., Van Van Hise Hise and and Leith, Leith, long been been debated, debated, with with some some advocates advocates (e.g., 1911) volcanic contributions 1911) arguing arguing in in favor favor of volcanic contributions of of iron, iron, and and others others (e.g., (e.g., James, James, 1954) 1954) contending contending that that there there is is no no genetic genetic relationship relationship between between volcanism volcanism and and iron-formation iron-formationdeposition. deposition. The The presence presence of of aa thick thick volcanic volcanic sequence sequence interbedded interbedded with with the the iron-formation iron-formationin in the the eastern eastern Gogebic Gogebic range range shows shows that that there there certainly certainly was was volcanism volcanism contemporaneous contemporaneous with with iron-formation iron-formation deposition deposition in in the the Lake Lake Superior Superior region. region. Therefore, Therefore, the the Gogebic Gogebic range range is is similar similar to to the the Hamersley Hamersley range range in in Western Western Australia Australia and and the the Proterozoic Proterozoic iron-formations iron-formationsin in South South Africa Africa where where numerous numerous volcanic ash layers layers are are interbedded interbedded with with the the iron-formations iron-formations volcanic ash (LaBerge, 1966a, 1966a, 196Gb). 1966b) (LaBerge, . Tyler and and Copps CORDS Formations. Formations. The The Ironwood Ironwood Iron-Formation, Iron-Formation, and Tyler locally the the Emperor Emperor Volcanic Complex, Complex, are overlain locally overlain by a 2,000 2,000 m graywacke-slatesequence. sequence. The The unit unit is is thickest thickest in in the the thick graywacke-slate thick western and and eastern eastern ends ends of the the range, range, and has been completely completely western removed by erosion erosion prior to to deposition deposition of the Keweenawan removed Keweenawan Supergroup in in an an area area near near Wakefield, Wakefield, Michigan. Michigan. Throughout Throughout most most Supergroup the range range the the unit is is called called the the Tyler Formation, however the of the Tyler Formation, however the correlative(?) portion at the eastern end of the range is called correlative(?) portion the eastern range is the Copps Copps Formation. Formation. The The Tyler Tyler Formation Formation is is correlated correlated with with the the the Michigamme Formation to the east, and with the Thomson, Rabbit Michigamme Formation to the east, and with the Thomson, Rabbit Lake, Virginia and and Rove Rove Formations Formations to to the the west and north in in Lake, Minnesota and and Ontario. Ontario. All these these units deposited Minnesota units were probably deposited in the the same same basin. basin. in 11 �Figure 8. Pillow Pillow breccia breccia in in Emperor Emperor Volcanic Volcanic Complex. Complex. Pillows Pillows and in aa hyaloclastite hyaloclastite matrix. matrix. and pillow pillow fragments fragments in Jackknife Jackknife is is on on aa pillow. pillow. Figure 9. 9. Felsic Felsic phase phase of of Emperor Emperor Volcanic Volcanic Complex. Complex. Felsite Felsite Figure clasts clasts in in aa finer finer hyaloclastite hyaloclastite matrix. matrix. Jackknife Jackknife is is 88 . cm. cm 12 �The The relationship relationship of of the the Tyler Tyler Formation Formation to to the the underlying underlying iron-formation is iron-formation is unclear. unclear. According to to Hotchkiss Hotchkiss (1919) (1919) the the basal unit of the the Tyler Tyler Formation Formation is is the the Pabst Pabst Member, Member, aa distinctive distinctive unit unit containing containing mainly mainly jasper jasper and and quartz quartz pebbles. pebbles. 10, from drill hole data (Atwater, Figure 10, (Atwater, 1938) 1938) shows shows the the relationship ironrelationship of the the conglomerate conglomerate to to the the underlying underlying ironHotchkiss (1919) relationships between formation. formation. Hotchkiss (1919) interprets the relationships Atwater the Tyler Tyler and the iron-formation to be unconformable. the iron-formation to be unconformable. Atwater (1938) did not believe* believe' that that aa major major unconformity unconformity separated separated the (1938) did the Schmidt and Hubbard (1972) Ironwood Ironwood and and Tyler. Tyler. Schmidt (1972) interpreted interpreted the the formations sedimentation to have been formations to be gradational and sedimentation continuous Gocrebic. However, However, Trent Trent (1973) (1973) stated stated continuous in in the the central central Gogebic. that that field field relationships relationships indicate indicate an an unconformity unconformity between between the the Schmidt (1980) Ironwood and Tyler Ironwood Tyler on on the the eastern eastern Gogebic. Gogebic. Schmidt (1980) summarizes summarizes the the field field evidence evidence pertaining pertaining to to the the Ironwood-Tyler Ironwood-Tyler contact contact as as well as as the the several several alternative alternative interpretations. interpretations. 1 ATLANTIC MINE NO 3 SHAfl D 0 HOI I 2 PLUMMER SHAF1 51H LEVEL CROSSCUI 3 PENCE NO 2 SHAFT AND 0 0 HOLE 4 MONTREAL NO 4 SHAFT 20TH I EVE1 ' ' 1 5 MONTREAL NO 4 SHAFI BTH LEVEL I I 1 l HOLE 6 OTTAWA 10TH LEVEL SHAFT CROSSCIII 7 GARY 19IH LEVEL NO 16 CROSSCUI 1) U HOLE 8 NORRIE 14TH AND 17TH LEVELS 9 AURORA E SHAFT 13TH LEVEL 10 PABS1 G SHAD I I BONNIL R2E Figure 10. Figure 10. 2 MRFS 0 &-\TJ I 0 H ~ I: ? I ~ N I A I XAI 3 ~IKIMETERS c .. vCRTICAL SCALE 1 >(L;Iu! n:ii Longitudinal section Longitudinal section through through part of of the the Gogebic Gogebic district, showing district, showing one one interpretation interpretation of of "Pabst Member" Membern of of the the relationship between the "Pabst relationship between the Tyler Formation and and the the Anvil and and Pence Pence Members Members of of Tyler Formation the the Ironwood Ironwood Iron-Formation. Iron-Formation. The upper slate is is aa upper slate layer layer of thin-bedded thin-bedded carbonate carbonate iron-formation, iron-formation,at at least least partly partly within within the the Anvil Anvil Member. Member. Compiled from measured in mines and and drill drill holes. holes. measured sections sections in Location sections given in map Ironwood Location of sections map of Ironwood Iron-Formation in in lower lower part part of of diagram. diagram. Modified Iron-Formation (1938,p. p. 163, 163, fig. fig. 2) 2) (From from Atwater from Atwater (1938, (From Schmidt, Schmidt, 1980) 1980) 13 �The The Tyler Tyler Formation Formation consists consists dominantly dominantly of of intercalated intercalated argillite argillite with with lesser lesser amounts amounts of of metasiltstone metasiltstone and and graywacke. graywacke. Graded sequences indicative Graded metagraywacke metagraywacke beds beds containing containingBouxna B o w sequences indicative of deposition by turbidity turbidity currents currents are common, common, but structureless structureless beds beds are are even even more more abundant abundant and and aa grain-flow grain-flow mechanism mechanism may may also also have have been been operative. operative. Sole Sole marks marks and and small-scale small-scale cross-bedding cross-bedding indicate westindicate a a paleocurrent paleocurrent trend trend from from east-southeast east-southeast to to westnorthwest northwest (Alwin, (Alwin,1976). 1976) . The The "average" "averagengraywacke graywacke of of the the Tyler Tyler consists consists of of 28 28 percent percent micaceous micaceous matrix matrix and and 72 72 percent percent framework framework grains grains (Alwin, (Alwin,1976). 1976). Of 73 percent percent are are monomono- and and polycrystalline polycrystalline Of the the framework framework grains, grains, 73 quartz quartz and and chert, chert, 10 10 percent percent are are plagioclase plagioclase (mostly (mostly altered altered plagioclase), plagioclase), and and 17 17 percent percent are are rock rock fragments, fragments, mainly mainly of of granitic granitic to to quartz quartz dioritic dioritic and and volcanic volcanic origin, origin, but but some some grains grains of sedimentary sedimentary and and metamorphic metamorphic origin origin also also are are present. present. Thus, Thus, the the "average" "averagev graywacke graywacke of of the the Tyler Tyler is is compositionally compositionally submature submature quartzose quartzose lithic lithic graywacke graywacke that that is is texturally immature immature as defined by by angular angular framework framework grains grains and and poor poor sorting. sorting. The The paleocurrent paleocurrent directions directions and and the the composition composition of of the the graywacke graywacke suggest suggest that that the the Tyler Tyler Formation Formation was was derived derived from from aa dominantly "graniticvsource source to to the the southeast. southeast. dominantly "granitic" MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC ROCKS ROCKS Following the Penokean orogeny, about about 1,860 Following the Penokean orogeny, 1,860 -- 1,830 1,830 Ma, Ma, the the Gogebic and the the rest Gogebic range range and restof ofthe theLake LakeSuperior Superior region region was was subjected subjected to to erosion erosion for fornearly nearly700 700 million million years. years. Erosion Erosion removed removed an an unknown unknown thickness thickness of of rocks rocks in in the the range, range, but but more more rock rock was example, at at was removed removed from from some some areas areas than than in in others. others. For For example, least preserved in least 2,000 2,000 meters of the the Tyler Tyler Formation Formation is is preserved in the the western western Gogebic, Gogebic, and and aa comparable comparable thickness thickness of of the the Copps Copps Formation Formation is is preserved preserved at at the the eastern eastern end end of of the the range. range. However, However, all Ironall of of the the Tyler, Tyler, and and some some of of the the underlying underlying Ironwood Ironwood IronFormation Formation as as well, well, was was removed removed in in the the eastern eastern Gogebic Gogebic where where the the range range experienced experienced more more folding. folding. The The erosion erosion interval interval presumably presumably ended ended with with the the onset onset of of the the Middle Middle Proterozoic Proterozoic Keweenawan Keweenawan rifting rifting event. event. Bessemer Bessemer Ouartzite. Ouartzite. In Gogebic range In most of of the the Gogebic range the the Bessemer Bessemer Quartzite, Quartzite, the the basal basal unit unit of of the the Keweenawan Keweenawan Supergroup, Supergroup, unconformably unconformably overlies overlies the the Tyler Tyler Formation. Formation. However, However, locally locally on on eastern part of of the the range range the the basal basal Keweenawan Keweenawan rests rests on on the the the eastern Ironwood Iron-Formation Iron-Formation or or the the Emperor Emperor Volcanic Volcanic Complex. Complex. The Ironwood The quartzite is is approximately approximately 100 100 mm thick, thick, has has channel channel cross-bedding cross-bedding quartzite and and is is aa relatively relatively mature mature quartz quartz sandstone sandstone (Ojakangas (Ojakangasand and Matsch, Matsch, 1982). 1982). The The Bessemer Bessemer Quartzite Quartzite evidently evidently originated originated in in a fluvial environment environment in in aa slight slight sag sag that that presaged presaged the the Keweenawan Keweenawan fluvial rifting rifting that that developed developed into into the the Midcontinent Rift System System (Ojakangas (Ojakangas and and Matsch, Matsch, 1982). 1982). 14 �Overlying the the Bessemer Bessemer Quartzite Quartzite is is aa thick thick Powder Mill Mill Group. Grouu. Overlying Powder sequence sequence of of mainly mainly basaltic basaltic lava lava flows flows that that formed formed during during the the Volcanic activity activity main main phase phase of of Keweenawan Keweenawan rifting rifting in in this this area. area. Volcanic (and Ma ago ago and and produced produced approximately 1,200 1,200 Ma (and rifting?) rifting?) began approximately hundreds hundreds of of lava lava flows flows that that have have an an aggregate aggregate thickness thicknessof ofmore more than 3,000 3,000m. m. The The lowermost lowermost basaltic basaltic lava lava flows flows that that overlie overlie the the than Bessemer Bessemer Quartzite Quartzite in in the the Bessemer, Bessemer,Michigan, Michigan,area areaare arepillowed, pillowed, suggesting either aa lake lake or or aa suggesting that that they they were were extruded extruded in in water, water, either fluvial system. fluvial system. Keweenawan Supergroup Supergroup volcanic volcanic rocks rocks are are overlain overlain Oronto Group. Group. Keweenawan Oronto by a thick sequence of mainly red clastic rocks in the Lake by a thick sequence of mainly red clastic rocks in the Lake Various representatives representatives of of this this sequence sequence are are Superior region. region. Various Superior The basal basal unit unit of of the the well exposed exposed north north of of the theGogebic Gogebicrange. range. The well Oronto the Copper Copper Harbor Harbor Conglomerate, Conglomerate, which which is is as as thick thick Oronto Group Group is is the The major lithology is red arkosic sandstone and The major lithology is red arkosic sandstone and as 2,000 2,000m. m. as siltstone with with numerous numerous conglomeratic conglomeratic horizons. horizons. The The Copper Copper siltstone Harbor Harbor Conglomerate Conglomerate probably probably represents represents alluvial alluvial fan fan deposits deposits formed formed near near aa rugged rugged source source area area along along the the south south side side of of Lake Lake Superior. Superior. The The Copper Copper Harbor Harbor Conglomerate Conglomerate is is overlain overlain by by the the Nonesuch Nonesuch Formation, Formation, aa 100 100 meter meter thick thick clastic clastic unit, unit, that that is is dominantly dominantly The Nonesuch Nonesuch was was probably probably gray to to black black carbonaceous carbonaceoussiltstone. siltstone. The gray deposited deposited in in aa lake lake developed developed on on the the subsiding subsiding pile pile of of volcanic volcanic (e.g., Suszek, Suszek,1991). 1991). In In rocks and and Copper Copper Harbor Harbor sediments sediments (e.g., rocks addition addition to to the the world world class class copper copper deposits deposits of of the the White White Pine Pine mine, mine, the the Nonesuch Nonesuch Formation Formation also also contains contains one one of of the the oldest oldest known occurrences occurrences of of petroleum. petroleum. known The Freda Freda Sandstone Sandstone of of the the Oronto Oronto Group Group consists consists of of The clastics, and and conformably conformably overlies overlies approximately 3,000 3,000 mm of of red red clastics, approximately the Nonesuch Nonesuch Formation. Formation. The The Freda Freda strata strata is is believed believed to to consist consist the of fluvial fluvial deposits deposits formed formed during during continued continued subsidence subsidence of of the the of Middle Proterozoic Proterozoic rift. rift. Middle KEWEENAWANTILTING TILTING KEWEENAWAN Following the the onset onset of of deposition deposition of of the the volcanic volcanic and and Following sedimentary rocks rocks along along the the Keweenawan Keweenawan Midcontinent Midcontinent Rift Rift System, System, sedimentary the south south side side of of the the rift, rift, including including the the Gogebic Gogebic district, district, was was the (65-90') to to the the north. north. tilted steeply steeply (659O0) tilted TECTONIC SEFING SETTING TECTONIC Early Proterozoic Proterozoic rocks rocks in in the the Gogebic Gogebic range range unconformably unconformably Early overlie Late Archean greenstone and granite of the Superior overlie Late Archean greenstone and granite the Superior L a m e (1981, 1983) suggested Province of the Canadian Shield. Province of the Canadian Shield. Larue (1981, 1983) suggested that the sedimentary rocks of the Lake Superior region (the that the sedimentary rocks the Lake Superior region (the Marquette Range Range Supergroup) Supergroup) were were deposited deposited in in aa number number of of grabengrabenMarquette like basins basins in in aa platformal platformal environment. environment. Sims Sims and and others others (1990) (1990) like 15 �proposed that that rocks rocks of of the the Marquette Marquette Range Range Supergroup Supergroup formed formed on on aa proposed rifted continental continental margin. margin. Break-up Break-upof of the the Archean Archean craton craton rifted resulted in in the the development development of of oceanic oceanic crust crust off off the the southern southern resulted margin of of the the Superior SuperiorProvince. Province. Therefore, Therefore, the the sedimentary sedimentary margin rocks were were deposited deposited during during aa rifting rifting stage stage that that developed developed into into aa rocks (1988) passive margin. Nd isotope studies by Gerlach and others passive margin. Nd isotope studies by Gerlach and others (1988) indicate that that iron-formations iron-formationsin in the the Lake Lake Superior Superior region region were were indicate deposited about 2,100 Ma. deposited about 2,100 Ma. concept of of aa rif rifted margin in in the the Lake Lake The concept The ted continental continental margin Superior region is probably best exemplified by the eastern Superior region is probably best exemplified by the eastern Gogebic range. range. As As discussed discussed earlier, earlier,the the stratigraphic stratigraphic Gogebic Wakefield, succession increases considerably in thickness east of of Wakefield, succession increases considerably in thickness east Michigan, and igneous rocks (volcanic rocks and sills) become aa Michigan, and igneous rocks (volcanic rocks and sills) become major component of the succession. The increase in thickness of major component of the succession. The increase in thickness of the sedimentary sequence and the influx of volcanic rocks is the sedimentary sequence and the influx of volcanic rocks is suggestive of of aa half half-graben near Wakefield Wakefield suggestive -graben structure structure with with a a hinge hinge near and a boundary fault (or faults) near Lake Gogebic. Emplacement and a boundary fault (or faults) near Lake Gogebic. Emplacement of basaltic basaltic sills sills (e.g., (e.g., the the Wolf Wolf Mountain Mountain sill sill of of Trent, Trent,1973) 1973) of and eruption of continental tholeiites (Sims, and others, 1990) and eruption of continental tholeiites (Sims, and others, 1990) The would be be characteristic characteristicof ofaarif rifted continental margin. margin. The would ted continental presence of the sills and volcanic rocks in the Ironwood Ironpresence of the sills and volcanic rocks in the Ironwood IronFormation as well as dramatic eastward thickening of the ironFormation as well as dramatic eastward thickening of the ironthat major major graben graben formation formation and and volcanism volcanism formation indicates indicates that formation occurred during deposition of the Ironwood Iron-Formation (Figure occurred during deposition of the Ironwood Iron-Formation (Figure 11). 11) Following the the rifting rifting and and passive passive margin margin stages, stages, aa phase phase of of Following convergent tectonics produced a volcanic island arc (the convergent tectonics produced a volcanic island arc (the Wisconsin magmatic magmatic terranes) terranes) that that collided collided with with the the Superior Superior Wisconsin Isotopic ages ages in inrocks rocksof ofthe thernagmatic magmatic terrane terrane range range craton. Isotopic craton. (Sims and others), and docking occurred 1.890 Ma to 1,840 Ma from from 1,890 Ma to 1,840 Ma (Sims and others), and docking occurred 1.860 Ma (Sims and others, 1990). Barovich and others about about 1,860 Ma (Sims and others, 1990). Barovich and others (1989) showed showed that that Nd Nd isotopes isotopes indicate indicate that that much much of of the the (1989) graywackes in the Michigamme Formation were derived from an Early Early graywackes in the Michigainme Formation were derived from an Proterozoic source. source. This This suggests suggests that that the the graywackes graywackes were were Proterozoic deposited in in aa foreland foreland basin basin during during docking docking of of the the island island arc arc on on deposited the margin margin of of the the Superior Superiorcraton. craton. the 16 16 Deformation and and metamorphism metamorphism of of rocks rocks of of the the Marquette Marquette Range Range Deformation Supergroup on the Gogebic range resulted from the collision of Supergroup on the Gogebic range resulted from the collision of the island arc with the margin of the Superior craton. This the island arc with the margin of the Superior craton. This collision fits fits very very well well with with aa foreland foreland basin basin model model as as developed developed collision Hoffman (1987) for the Early Proterozoic rocks that surround by by Hoffman (1987) for the Early Proterozoic rocks that surround Archean Superior Superior Province. Province. This the Archean This model model was was utilized utilized by by the Southwick and Morey (1991) to explain lithologic and structural Southwick and Morey (1991) to explain lithologic and structural relationships in in east-central east-centralMinnesota. Minnesota. AA similar similar foredeep foredeep relationships model, with associated southward subduction and collision of aa model, with associated southward subduction and collision of volcanic arc against the craton to the north was proposed by volcanic arc against the craton to the north was proposed by Ojakangas (in (inpress) press)to toexplain explainthe theorigin originofofthe theMichigainme Michigamme Ojakangas Formation of the Upper Peninsula of Michigan, as well as the the Formation of the Upper Peninsula of Michigan, as well as origin of the Copps and Tyler formations in the vicinity of the the origin of the Copps and Tyler formations in the vicinity of Gogebic range. In this model, the iron-formation was deposited Gogebic range. In this model, the iron-formation was deposited northwardon the the peripheral peripheral bulge bulge on on the the north north side side of of the the northwardon migrating foreland basin, whereas the aforementioned turbidite migrating foreland basin, whereas the aforementioned turbidite �sequences sequences were were deposited deposited in in the the deeper deeper axial axial parts parts of of the the basin. basin. This This would would require require that that the the Ironwood Ironwood Iron-Formation Iron-Formationand and the the overlying overlying Tyler Tyler Formation Formation have have aa gradational gradational and and conformable conformable relationship, relationship, and and that that they they were were deposited, deposited,at at least leastin inpart, part, tholeiitic volcanism volcanism contemporaneously. In In this this model, model, axial axial tholeiitic contemporaneously. (Hoffman, 1988) and hydrothermal activity activity in (Hoffman, 1988) in the the foredeep foredeep would would have provided the iron and silica that were precipitated have provided the iron and silica that were precipitated as as ironironformation formation on on the the shelf, shelf, as as upwelling upwelling brought brought the the solutions solutions to to aa favorable site site of of deposition. deposition. favorable Note Note that that the the foreland foreland basin basin model model provides provides an an alternative alternative interpretation interpretation for for the the Ironwood Ironwood and and the the intertonguing intertonguing Emperor Emperor Volcanic ted continental Volcanic Complex Complexcompared comparedwith withaarif rifted continental margin margin model. model. Obviously Obviously more more work work is is needed needed to to resolve resolve this this problem. problem. Deformation Deformation during during the the Penokean Penokean orogeny orogeny may may have have resulted resulted in in reactivation reactivation of of the the normal normal faults faults in in the the graben graben structures. structures. We We suggest suggest that that the the structure structure in in the the eastern eastern Gogebic Gogebic may may represent represent aa half-graben half-graben that that has has been been subjected subjected to to thrusting thrusting during during the the Penokean orogeny orogeny (Figure (Figure12). 12). Perhaps Perhaps significantly, significantly, erosion erosion Penokean prior prior to to deposition deposition of of the the Keweenawan Keweenawan Supergroup Supergroup cut cut deepest deepest into into the the Early Early Proterozoic Proterozoic sedimentary sedimentary sequence sequence in in the the central central Gogebic, where where the the proposed proposed thrust thrust faults faults are are present. present. Whereas Whereas Gogebic, over 2,000 2,000 mm of of the the Tyler Tyler Formation Formation remain remain on on the the western western Gogebic Gogebic over in Wisconsin, Wisconsin, and and aa similar similar thickness thickness of of Copps Copps Formation Formationis is in present at at the the eastern eastern end end of of the the range, range, erosion erosion removed removed all all of of present the Tyler Tyler and and part part of of the the iron-formation iron-formationeast east of of Wakefield. Wakefield. the Assuming that that erosion erosion cut cut down down to to aa relatively relativelyuniform uniform level, level, Assuming then the the central central Gogebic Gogebic may may have have been been uplifted uplifted at at least then least 2,000 2,000 mm more than than areas areas to to the the east east and and west. west. An An Archean Archean cored cored gneiss gneiss more dome is is present present near near Watersmeet Watersmeet about about 50 dome 50 km km to to the the east. east. That That area may may represent represent an an even even more more pronounced pronounced uplift. uplift. Therefore, area Therefore, rocks on on the the eastern eastern Gogebic Gogebic range range may may record record depositional depositional and and rocks deformationalevents events of of both both the therif rifted and convergent convergent deformational ted margin margin and tectonics during during the the Early Early Proterozoic Proterozoic in in the the Lake Lake Superior Superior tectonics region. region. 17 �w -- -- '---'---'——-— '- - E - tRON WOOD 4 —.-.—'.--— ___A._ Water Surface-7 - - EROR 4u , --- - -::,/_.-- — / M A vA I RAM SAY / / b A y I— 1-i • V V 18 Figure 11. Figure 11. pre-Penokean Diagram showing hypothetical pre-Penokean relationships on the eastern Gogebic relationships on the eastern Gogebic range. range. Figure Figure 12. 12. Simplified geologic map Gogebic Gogebic range. range. (Not (Not to of the eastern eastern part of of the the scale) scale) �STOP STOP DESCRIPTIONS DESCRIPTIONS Field Trip Gogebic Field 19 �Stop stow 1. 1. Tyler Wler Formation. Formation. Location: Location: Roadcuts Roadcuts at at junction junction of of U.S. U.S. Hwy. Hwy. 22 and and Hwy. Hwy. 51 51 north north of of Hurley, HurleyI WI WI Rocks Rocks exposed exposed at at this this locality locality are are representative representative of Tyler Formation, Formationlwhich which is is of the the upper upper part part of of the the Tyler about 21100meters meters thick thick here. here. It It thickens thickens westward westward to to about 2,100 about about 2,900 2#900meters meters in in Wisconsin Wisconsin and and thins thins eastward eastward to to zero Ramsay! where where it it was was entirely entirely removed removed by by zero east east of of Ramsay, erosion erosion prior prior to to deposition deposition of of Keweenawan Keweenawan strata. strata. The The Tyler Tyler is is unconformably unconformably overlain overlain by by the the Bessemer Bessemer Quartzite Quartzite and and aa substantial substantial thickness thickness of of Keweenawan Keweenawan volcanic volcanic rocks. rocks. The relationship of of the the Tyler Tyler to to the the underlying underlying The relationship Ironwood Ironwood Iron-Formation Iron-Formationis is uncertain uncertain because because of of poor poor outcrop. Atwater, outcrop. Most Most geologists geologists (e.g., (e.ge1 Atwater,1938) 1938) consider consider the the two two formations formations to to be be conformable conformable (Schmidt (Schmidt and and Hubbard, Hubbardl 1972); 1972); however, howeverl Aldrich Aldrich (1929) (1929)presents presents evidence evidence for for erosion erosion of of the the iron-formation iron-formationand and aa basal basal conglomerate conglomerate at at the the base base of of the the Tyler. Tyler. The The presence presence of of aa graywacke-slate graywacke-slatesequence sequence overlying overlying the the iron-formation iron-formation is is characteristic characteristic throughout throughout the the Lake Lake Superior Superior region region elsewhere on on the the western western Gogebic Gogebic range, rangeI the the As elsewhere As beds here here strike strikeeast-northeast, east-northeastl dip60°-75° 60'-75' northwest, northwestl beds dip block that that and top top to to the the northwest, northwest! part part of of aa large large block and was tilted tilted northward northward during during Keweenawan Keweenawan rifting rifting to to form form was aa large large north-facing north-facingmonocline. monocline. Schmidt Schmidt and and Hubbard Hubbard (1972) and and Kiasner Klasner and and others others (1991) (1991) pointed pointed out out that that (1972) cleavagelbedding relationships relationships in in these these (and (andother) other) the cleavage/bedding the outcrops outcrops are are unusual unusual and and may may be be of of tectonic tectonic significance. significance. As As shown shown in in the the accompanying accompanying diagrams diagrams 13) the (Figure 13), (Figure the graywacke-slate graywacke-slatewas was dipping dipping gently gently southward prior prior to to Keweenawan Keweenawan time. time. Because Because the the southward cleavage cleavage dips dips less less steeply steewlv than than the the bedding, beddingl rotation rotation of the the rocks rocks southward southward to to their their pre-Keweenawan pre-Keweenawansubsubof horizontal attitude attitude results results in in aa south-dipping south-dipping horizontal cleavage. cleavage. Cannon and and others others (1990) (1990)showed showed that that originally originally Cannon vertical Early Early Proterozoic Proterozoic diabase diabase dikes dikes in in the the Archean Archean vertical terrane to to the the south south of of the the Gogebic Gogebic range range now now have have aa terrane southward explained by by aa northward northward southwarddip. dip. This This dip dip is is explained rotationalong alongthe theeast east-northeast-trending Marenisco rotation -northeast - trending Marenisco faultlaa major major listric listric thermal thermal fault fault with with perhaps perhaps 10 10 km km fault, of of southward southward thrust thrust motion motion on onit. it. This This motion motion explains explains the present present steep steep northward northward dip dip of of the the major major monoclinal monoclinal the structure structure of of the the Gogebic Gogebic range. range. Alwin (1976) (1976)showed showed that that the the Tyler Tylerconsists consists Aiwin dominantly of of intercalcated intercalcated argillite argillite and and slate slate with with dominantly lesser amounts amounts of of siltstone siltstone and and graywacke. graywacke. Graded lesser Graded 20 �NORTH NORTH SOUTH SOUTH I Rocks o f Earlv Proterozo~c METERS 6OO METERS NORTH SOUTH B Figure Figure 13. 13. diagram and cross Generalized block diagram cross section section illustrating structural illustrating structural relationships relationships in in Ironwood, Ironwoodl Mich.-Hurley, Heavy dashed Mich.-Hurley, Wis., Wise1area. area. Heavy dashed line, linel A, Block diagram fault. Al diagram showing showing relationship relationship of of fault. pre-Keweenawan strata Midcontinent pre-Keweenawan strata to to rocks rocks of of Midcontinent foliation in in q Tyler Formation rift. rift. Note that that S1 S' foliation l e r Formation dips dips less less steeply steeply than than bedding. bedding. Modified from from B, Reconstructed Schmidt and Hubbard (1972). Schmidt and Hubbard (1972) Bl ~econstructed post-Penokean, post-Penokeanl pre-Keweenawan pre-Keweenawan position position of of the the Note gently south dipping strata shown strata shown in in A. A. Note gently south dipping S1 Sl foliation. foliation. Modified from from Schmidt Schmidt and Hubbard (From Klasner Klasner and and others, others! 1991) 1991) (1972). (From (1972). . 21 �graywacke sequences indicate indicate graywacke beds beds containing containing Bouina Bouma sequences marks and deposition deposition by turbidity turbidity currents. currents. Sole Sole marks and small-scale paleocurrent trend small-scale cross-beds cross-beds indicate indicate a a paleocurrent trend toward toward the the west-northwest. west-northwest. Framework Framework grains grains in in the the quartz and feldspar graywackes are quartz feldspar and and rock rock fragments fragments granitic, volcanic,and of graniticl volcaniclandmetamorphic metamorphic rocks. rocks. Therefore, Therefore, the the source source area area for for the the Tyler Tyler sediments sediments is is inf erred to to be be an an Archean Archean granitic-metarnorphic inferred granitic-metamorphic The Tyler (cratonic) source area (cratonic) source area to to the the southeast. southeast. The Tyler was was only slightly slightly metamorphosed to to sub-greenschist sub-greenschistfacies facies during during the the Penokean Penokean orogeny, orogenyl and and the the metamorphic metamorphic grade grade here was not changed during the Keweenawan here was not changed during the Keweenawan rifting. rifting. At this this exposure, exposurel note note graded graded graywacke graywacke beds beds topping NW, mud-chips mud-chips in topping NWl in some some beds, bedsl rare rare sole sole marks, marksl some soles, loading on some solesl flame flame structures, structuresl and and smallsmallassemblage of sedimentary scale cross-bedding. scale cross-bedding. The assemblage sedimentary structures structures indicates indicates a turbidity turbidity current current mechanism, mechanisml and and deposition on a submarine likely but but not not deposition submarine fan fan is is likely In the fan of essential. In fan model the "packets" npacketsll of graywacke graywacke essential. beds beds would would be be channel channel deposits deposits whereas whereas the the mudstones mudstones would would be be overbank overbank deposits. deposits. Continue east on Continue on U.S. Hwy 2 2 to to Golf Golf Club Club Road Road just just east east of of Ironwood. Thrn Ironwood. Turn right right (south) (south) on on Golf Club Road and proceed about miles south south to 1.1 miles to large large brick buildings buildings of of the the Newport Newport Mine. Mine. Walk Walk to to the the northeast northeast across across the the small small field field to to old old railroad railroad cuts, cutsl that that are are just just north north of of the the main main building building behind behind the the trees. trees. Caution: Caution: Area Area is is now now part part of of aa gravel gravel washing washing operation. operation. Stop 2. Sto~ 2. Newport mine (Archean/Early Proterozoic Old Nemort (ArcheanIEarlv Proterozoic Unconformity). Unconformitv) . The Palms Palms Formation Formation of the Menominee Group the Group of the Marquette Marquette Range Range Supergroup Supergroup rests rests upon upon the the 2,700 21700m.y. m.y. old Puritan Puritan Quartz Quartz Monzonite Monzonite (Schmidt, (Schmidtl1976). 1976). The The Marquette Range Marquette Range Supergroup Supergroup in in the the Gogebic Gogebic range range was was deposited on on aa moderately moderately flat flat erosion deposited erosion surface surface developed developed on on Archean Archean "granite" I1granitenand and greenstone. greenstone. steeply dipping dipping (to (to the the At this this locality, localityl the the steeply north) unconformable unconformable contact contact between between the the Palms Palms north) Formation is exposed exposed in in the the old old Formation and Archean granitoid granitoid is railroad cut. Small depressions in the the surface, surfacel as as can can railroad cut. depressions in be seen seen here, herel contain contain laminated laminated cherty cherty'material, some material, some granular and and somewhat somewhat resembles resembles ironironwhich is is granular of which formation. The mm in in diameter diameter formation. granules are are 0.5 to to 1.0 mm The granules and consist consist of of mixtures mixtures of of chert, chertI chlorite, chlorite, and and and calcite. There calcite. few phosphatic argillaceous There are also a few phosphatic argillaceous chips just just above above the the contact. contact. Note that that there there is is no no appreciable appreciable evidence evidence of of weathering weathering of of the the granite granite Palms. beneath the Palms. beneath the 22 �Red Red argillaceous argillaceous and and silty siltybeds beds of of the thelower lower member member of of the the Palms PalmsFormation Formationare areexposed exposedhere. here. They They contain contain wavy wavy bedding bedding and and small small mudcracks, mudcracksfand and have have been been interpreted interpreted as as upper upper tidal tidal flat flat deposits depositsof of aa transgressing transgressing sea sea(Ojakangas, (Ojakangas 1983). 19831 . cross it, it, and and continue continue north north approximately approximately Return Return to to U.S. U.S. Hwy. H w y . 2, cross on right, rightlbeyond beyond the the Kangas Kangas farm. farm. mile to 11 mile to rock rock knob knob on S t o3. ~3. Stop Contact Contact between between Bessemer Bessemer Ouartzite Ouartzite and and Powder PowderMill Mill Volcanics Vol canics This This exposure exposure is is approximately approximatelytwo twomiles milesnorth northof of and the the interval interval between between these these two two stops stops Stop Stop 2, and demonstrates demonstrates the the thickness thickness of of the the Early Early Proterozoic Proterozoic The exposure exposure shows shows the the contact contact sequencein inthis thisarea. area. The sequence between between the the basal basal Keweenawan Keweenawan Bessemer Bessemer Quartzite Quartzite and and the the Thus the the overlying overlying basalt basalt of of the thePowder PowderMill MillGroup. Group. Thus exposure exposure illustrates illustrates the the abrupt abrupt change change from from sedimentation sedimentationof of quartzose quartzose sandstone sandstoneto to flood floodbasalt basalt volcanism volcanism during during the the Middle Middle Proterozoic Proterozoic in in this this part part of of the Lake Lake Superior Superiorregion. region. Only Only the the lowermost lowermost basalt basalt the flows softl silty silty flows are are pillowed, pillowedl and and locally, locallyI the the soft, sediment sediment was was squeezed squeezed up up between between rubbly rubbly blocks blocks and and pillows. Some Some units units of of Bessemer-type Bessemer-typequartzite quartzite do do pillows. occur occur higher higher in inthe the flow flowsequence. sequence. These These features features indicate indicate that that volcanism volcanism here here was was initiated initiated in in aa sedimentary basinl overwhelmed overwhelmed sedimentation, sedimentationland and sedimentary basin, resulted resulted in in aa thick thick sequence sequenceof of subaerial subaerialflows. flows. Flows Flows just to to the the north north are aremassive. massive. just S t -o 4. ~4. Stop Ironwood Ironwood Iron-Formation Iron-Formationand and Ironwood-Tyler Ironwood-Tvler relationshi~s. (Modified (Modified from from Schmidt, Schmidtl1972) 1972) relationships. Location: Exposures Exposures on on the the east east and and west west banks banks of of the the Location: Black River River upstream upstream from from Hwy. H w y . 22 on on the the western western Black (NE ', XI SW, SWAl Sec. Sec. 12, 12, outskirts of of Ramsay, RamsaylMichigan. Michigan. (NE outskirts T.47N. R.46W.) R.46W. T.47N., The Ironwood Ironwood Iron-Formation Iron-Formationis is aa major major sedimentary sedimentary The Gogebic range, rangel and and is is the the source source rock rock for for all all of of the the Gogebic Unfortunatelylthe the ironironiron ores ores mined mined in in the the area. area. Unfortunately, iron formation is is very very poorly poorly exposed exposed on on the the eastern eastern formation Gogebic. Excellent Excellent exposures exposures of of the the Ironwood Ironwood IronIronGogebic. Formation are are present present on on Mt. Mt. Whittlesey, Whittleseylsoutheast southeast of of Formation Mellenl Wisconsin, Wisconsinl however, howeverl that that locality locality is is more more than than Mellen, 30 miles miles away, awayl and and will will not not be be visited visited on on this this trip. trip. 30 Schmidt and and Hubbard Hubbard (1972) (1972) described described several several Schmidt exposures along along the the Black Black River River at at this this locality locality that that exposures illustrate different different phases phases of of the the iron-formation iron-formationas as illustrate well as as possible possible stratigraphic stratigraphic relationships relationships between between well qler the Ironwood Ironwood Iron-Formation Iron-Formation and and the the overlying overlying Tyler the Formation. They They describe describe thin-bedded thin-bedded chert-carbonate chert-carbonate Formation. 23 23 �iron-formation Member of iron-formation at the the top top of the the Anvil Member of the the Ironwood Ironwood Iron-Formation Iron-Formation on on the the east east bank bank of of the the river river 600 upstream from bridge on 600 feet feet upstream from the the bridge on the the secondary secondary road road south of south of Hwy. Hwy. 2. 2. Granular Granular jasper jasper is is described from from test pits Sec. 121 12, T.47Na1 T.47N., R.46W. test pits in in the the SE(, SE%# SW1X, SWA1 Sec. R.46W. Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) conclude conclude that that the the rocks rocks are are basically unmetamorphosed basically umetamorphosed examples examples of of the the ironironformation. Time formation. Time limitations limitations will will not not permit permit us us to to visit all of the localities described by Schmidt and the localities Hubbard (1972), and those interested in examining (1972)1 interested unaltered iron-formation unaltered iron-formationshould should consult consult their their 1972 1972 guidebook. guidebook. Schmidt Schmidt and and Hubbard Hubbard (1972) (1972) also also discussed discussed alternative alternative interpretations interpretations of the relationship between Tyler and the Tyler and Ironwood Ironwood Formations. Formations. The The contact contact is is (600 the Black Black River River 180 180 mm (600 exposed on the east bank of the ft.) roadl where where Schmidt Schmidt ft.) upstream from from the the secondary secondary road, and Hubbard (1972) (1972) interpreted interpreted the the contact contact to to be be and Hubbard gradational. gradational. We will examine examine only the exposure on the west bank of the Black River just just south south of Hwy. 22 where where aa lens lens of of carbonate iron-formation carbonate iron-formation and a a sulfide sulfide unit unit is is present present within the within the lower lower part part of of the the Tyler Tyler Formation. Formation. Although .ong the the stream stream exposure poor, there outcrops a1 along there are outcrops exposure is is poorl slatel massive bank consisting consisting of highly carbonaceous carbonaceous slate, sideritic pyrite/marcasite, and sideritic and concretionary(?) concretionary ( ? ) pyrite/marcasite, iron- formation. iron-formation. Stop 5. Radio Tower Radio Tower Hill Hill in in Wakefield. Wakefield. Palms Marmette Range RanqeSupercrroup Su~erqrouq Palms Formation Formation of of Marguette Location: Location: The The purposes of this this stop stop are are to to (1) (1) examine examine an excellent (2) an excellent exposure exposure of of the the Palms Palms Formation Formation and and (2) obtain obtain a a scenic scenic view view of of this this part part of of the the Gogebic Gogebic range, rangel and of the of the the Archean terrane terrane to to the the south, southl and the Keweenawan terrane Keweenawan terrane to to the the north. north. From hill, several From the the top top of the the hilll several abandoned abandoned iron iron mines mines can can be be seen seen in in the the lowland lowland immediately immediately to to the the thi north (refer (refer to to Figure Figure 7); 7); the the ridges ridges in in the north intermediate distance basalt of early early intermediate distance are are underlain underlain by basalt of Keweenawan (Middle Proterozoic) Proterozoic) age. age. The The lowland lowland in in Keweenawan (Middle the far far distance is underlain the late late Keweenawan Keweenawan distance is underlain by the Jacobsville Jacobsville Sandstone. Sandstone. The to the the south south overlooks overlooks Archean Archean terrane terrane The view to consisting of the the Ramsay Ramsay Formation Formation (mafic (mafic and and felsic felsic consisting metavolcanic rocks) rocks) and the the Puritan Puritan Quartz Monzonite metavolcanic and related related rocks rocks (—2,700 (-21700r n.y.1 which which constitute constitute aa m.y.), major batholith batholith more more than than 150 150 km km long. long. major area, the Palms Palms Formation unconformably Formation unconfombly In this areal overlies overlies the Archean Ramsay Formation Formation and is overlain overlain 24 �which conformably by by the the Ironwood IronwoodIron-Formation, Iron-Formation,which conformably underlies underlies the the low low area area north north of of the the hill hill and and also also southwest of of the thehill. hill. Low Low on on the the next next hill hill to to the the southwest Further east, rare rare Sunday Sunday Quartzite Quartziteis ispresent. present. Furthereast, east, east, the Palms Palms unconformably unconformably overlies overlies the the Bad Bad River River the Dolomite,and and has has aa thin thin phosphatic phosphatic conglomerate conglomerateat at its its Dolomite, with The Palms dips steeply northward, in accord base. The Palms dips steeply northward, in accord with base. the regional regional dip dip of of Proterozoic Proterozoic rocks rocks in in the the Gogebic Gogebic the This regional dip resulted mainly from range. This regional dip resulted mainly from range. toward the the northward northward tilting tilting during during Keweenawan Keweenawan time, time, toward axis of of the the (Keweenawan) (Keweenawan)Lake Lake Superior Superior syncline. syncline. The The axis Early deformed Early Proterozoic Proterozoic rocks rocks were were not not appreciably appreciably deformed (Penokean or metamorphosed metamorphosed during during the the tectonic tectonic event event (Penokean or that closed closed Early Early Proterozoic Proterozoic deposition, deposition,but but orogeny) that orogeny) the east-northeast at 20-25° 20-25' a few folds plunging to the east-northeast at a few folds plunging to have been been recognized. recognized. have Exposures Exposures of of the the Palms Palms Formation Formation at at this this locality locality are representative representative of of the the formation formation which which extends extends for for are Representative rock types 80 km to the west-southwest. Representative rock types 80 km to the west-southwest. well-exposed well-exposedat at the the top top of of the the hill hill include include the the upper upper part of of the the middle middle member member which which consists consists of of interbedded interbedded part argillite, argillite,siltstone, siltstone, and and sandstone, sandstone, and and the the transition transition to the the massive massive quartzite quartzite of of the the upper upper quartzite quartzitemember. member. to The middle middle member member is is thin thin bedded, bedded, with with beds beds generally generally The 2-10cm cm thick. thick. In In general, general, beds beds of of buff buff to to pink pink 2-10 siltstone and and white white sandstone siltstone sandstone alternate alternate with with buff, buff, red red or green green beds beds of of more more argillaceous argillaceous material; material;coarsecoarseor grained, grained, dark-red, dark-red,hematitic hematitic sandstone sandstone beds beds are are also also present. Most Most beds beds are are quite quite continuous continuousacross across the the present. outcrop but but "pinch "pinchand and swell" swellnirregularities irregularities impart impart aa outcrop waviness to to the the generally generally uniform uniform bedding. bedding. Lenticular Lenticular waviness beds of of sandstone, sandstone,commonly commonlycross-bedded, cross-bedded, arecommon. common. beds are Flaser bedding bedding is is present present locally locally where where the the mud mud supply supply Flaser was subordinate subordinateto to the thesand sandsupply. supply. Minor Minor cut-and-fill cut-and-fill was and soft-sediment soft-sedimentdeformation deformation structures structuresalso also are are and present. Symmetrical Symmetrical but but irregular irregular ripple ripple marks marks and and present. mud cracks, cracks,although although not not visible visible at at this this locality, locality,are are mud (Ojakangas,1983). 1983). present on on the the next next hill hill to to the the east east (Ojakangas, present Measurement Measurement of of 42 42 cross-beds cross-bedson on this this hill hill shows showsaa strong paleocurrent paleocurrent trend trend to to the the west west with with aa weaker weaker strong trend to to the theeast. east. Nearly Nearly 200 200 measurements measurements in inthe the trend formation as as aa whole whole accentuate accentuatethis thisbimodality. bimodality. formation Correction for for plunge, plunge, if if indeed indeed the the entire entire formation formation Correction has aa plunge plunge as as well well as as aa tilt, tilt, would has would rotate rotate the the major major and minor minor modes modes clockwise, clockwise, thus thus relocating relocatingthe themodes modes to to and the west-northwest west-northwestand and east-southeast, east-southeast,respectively. respectively. the General characteristics characteristics of of the the formation, formation, and and General especially the the bimodal bimodal cross-bedding cross-beddingpattern, pattern, the the especially bedding styles, styles, and and the the overall overall lithologies lithologies are are highly highly bedding suggestive of of deposition deposition in in aa tidal tidal environment. environment. suggestive Recall that that the the lower lower member member interpreted interpretedas asupper uppertidal tidal Recall 25 �flat, was was seen seen at at Stop Stop 2. 2. Here Here on on Radio Radio Tower Tower Hill, Hill, flat, the middle member is interpreted as middle tidal flat, the middle member is interpreted as middle tidal flat, and the cross-bedded quartz sand upper member is and the cross-bedded quartz sand upper member is interpreted as as lower lower tidal tidal flat flat or or subtidal subtidal (Ojakangas, (Ojakangas, interpreted 1983). 1983) Thin sections sections from from this this locality locality show show that that the the Thin sandstone beds beds are are feldspathic feldspathicquartzite. quartzite. Well-rounded Well-rounded sandstone unit quartz quartz grains grains and and feldspar feldspar (mostly (mostlyfresh freshKKunit feldspar) grains grains are are the the dominant dominant framework framework feldspar) constituents, with with chert chert grains grains aa poor poor third. third. Silica Silica constituents, illitic clay clay is is present present in in many many cement is is abundant abundant and and illitic cement samples as as minor minor to to abundant abundant matrix. matrix. Illite Illite is is also also samples the major major constituent constituent of of the the argillaceous argillaceous beds beds with with the chlorite locally locally prominent. prominent. The The coarser-grained, coarser-grained, chlorite hematitic sandstone beds are really thin beds beds of of ironironhematitic sandstone beds are really thin formation, consisting of granules of hematite, chert, formation, consisting of granules of hematite, chert, and iron iron silicates silicates in in addition addition to to the the common common quartz quartz and grains. grains. Deformation of of the the Palms Palms Formation Formation has has not not been been Deformation well studied. Basically, it is part of a large well studied. Basically, it is part of a large monocline in in which which folding folding is is rarely rarely seen seen except except at at monocline this locality. On the west flank of the hill, several this locality. On the west flank of the hill, several open, round-crested round-crestedfolds folds exhibit exhibit aa cleavage cleavage that that is is open, flatter than the bedding. The extent, origin, and age flatter than the bedding. The extent, origin, and age of these folds and their associated cleavage is not of these folds and their associated cleavage is not known, but but the the folds folds may may have have formed formed when when the the beds beds were were known, approximately flat-lying, presumably during the approximately flat-lying, presumably during the Penokean orogeny. orogeny. Alternatively, Alternatively, the the folding folding might might Penokean have been caused by drag along the Sunday Lake fault, aa have been caused by drag along the Sunday Lake fault, northwest-trending fault that passes just west of this northwest-trending fault that passes just west of this hill. hill. Stop 6. 6. Stop Archean Ramsay Ramsav Formation Formation (pillowed (pillowed meenstone) Archean reenstone) Location: Roadcut Roadcut along along U.S. U.S. Hwy. Hwy. Location: limits of Wakefield, about 2.5 mi. limits of Wakefield, about 2.5 mi. of Highways 2 and 28 in Wakefield. of Highways 2 and 28 in Wakefield. at eastern eastern city city 22 at SE of the junction SE of the junction Archean Ramsay Ramsay Formation Formation forms forms part part of of the the The Archean The Archean basement upon which the Early Proterozoic rocks Archean basement upon which the Early Proterozoic rocks Prinz and others (1975) were deposited. According to were deposited. According to Prinz and others (1975) metavolcanic rocks rocks of of Archean Archean age age extend extend eastward eastward for for metavolcanic approximately 15 km along the range in the vicinity of approximately 15 km along the range in the vicinity of Wakefield. They are intruded on the south and west by Wakefield. They are intruded on the south and west by the Puritan Puritan Quartz Quartz Monzonite, Monzonite, and and are are bounded bounded on on the the the east by gneissic rocks of the Puritan Quartz Monzonite. east by gneissic rocks of the Puritan Quartz Monzonite. They reported reported that that the the eastern eastern two-thirds two-thirdsof of the the belt belt They Archean rocks is mainly mafic to intermediate flows of of Archean rocks is mainly mafic to intermediate flows and pyroclastic rocks with sparse felsic volcanic and pyroclastic rocks with sparse felsic volcanic rocks. However, However, intermediate intermediate to to felsic felsic rocks rocks are are rocks. dominant in the western part of the belt. The rocks dominant in the western part of the belt. The rocks generally strike west to northwest (roughly parallel to generally strike west to northwest (roughly parallel to 26 �the the strike strike of of Early Early Proterozoic Proterozoic rocks) rocks) and and dip dip steeply steeply to to the the south. south. Pillows Pillows indicate indicate that that the the lava lava flows flows generally generally face face southward. southward. Prinz Prinz and and others others (1975) (1975)suggested suggested that that the the mafic mafic and felsic volcanics volcanics each each have have aa thickness thickness of of and the the felsic approximately approximately 3,000 3,000meters. meters. Metamorphic Metamorphic grade grade increases from greenschist facies increases from greenschist facies in in the the west west to to amphibolite amphibolite facies facies along along the the eastern eastern margin. margin. Rocks Rocks exposed exposed here here are are typical typical pillowed pillowed mafic mafic volcanic rocks that have been metamorphosed volcanic rocks that have been metamorphosed to to They are are composed composed of of fine-grained fine-grained greenschist fades. They greenschist facies. sodic plagioclase, quartz, epidote-zoisite, sodic plagioclase, quartz, epidote-zoisite,and and chlorite, chlorite, with with some some pale pale amphibole, amphibole, carbonate carbonate and and biotite biotite (Prinz (Prinzand and others, others, 1975). 1975). Pillows Pillows with with tops tops facing facing southward southward are are well-exposed well-exposed on on the the south south side side of of the the highway. highway. Take Take U.S. U.S. Hwy. Hwy. 22 east east of of Wakefield Wakefield city city limits limits about about two two miles miles to to Go to compressor station on pipeline and turn Go to compressor station on pipeline and turn Great Lakes Lakes Road. Road. Great left mile in in is is aa "Y"; "Yn; keep keep left (north) (north)on on gravel gravel road. road. About About 0.3 0- 3 mile Walk west west on on logging logging 1.5 miles miles to to end end of of road. road. Walk left and and go go about about 1.5 left road road ± 2 270 270 paces, paces, then then go go north north through through the the woods woods to to the the high high The outcrop outcrop is is an an escarpment escarpment along along SW SW side side of of hill hill in in the the hill. The hill. R.44W., (Wakefield NE 7%Minute %, Sec. Sec. 18, 18, T47N., R.44W., (Wakefield NE Minute SE (, SE Quadrangle.) Quadrangle.) Stop 7. Archean-Early Archean-Earlv Proterozoic Proterozoic unconformity. unconformitv. The The unconformity unconformity between between the the Archean Archean Ramsay Ramsay greenstone greenstone and and the the Early Early Proterozoic Proterozoic Sunday Sunday Quartzite Quartzite is is exposed exposed along along the the southwest southwest side side of of this this hill. hill. Note Note the the schistosity schistosity in in the the otherwise otherwise massive massive greenstone, greenstone, and and the the very very thin thin basal basal conglomerate. conglomerate. Just Just westward westward from from the the unconformity, unconformity, the the Sunday Sunday Quartzite Quartzite at at first first glance glance appears appears to to be be conglomeratic, conglomeratic, but but it it is is aa thin thin skin skin along along the the face face of of the the outcrop outcrop and and is is probably probably aa fault fault breccia. breccia. This This prominent prominent exposure exposure is is probably probably aa fault fault scarp. scarp. Moving Moving along along the the base base of of the the escarpment, escarpment, note note the the crosscross-bedding (some (some of of it it herringbone herringbone type, type, with with crosscross-bedding beds in in successive successive beds beds oriented oriented at at 180° 180' to to each each beds mudchip conglomerates, conglomerates, other), the the numerous numerous layers layers of of mudchip other), and mud-cracked mud-crackedhorizons. horizons. These These are are included included in in aa and series of stacked stacked tidal tidal channels channels to to about about 22 mm thick, thick, series each each starting starting with with aa mud-cracked mud-crackedhorizon. horizon. These These are are overlain by by aa cross-bedded cross-bedded unit unit that that includes includes overlain herringbone herringbone cross-beds, cross-beds, and and ends ends with with a a parallel-bedded parallel-bedded unit. At this this exposure, exposure, 41 41 cross-beds cross-beds yield a broad yield a unit. trimodal (but (but largely largely bimodal-bipolar) the trimodal bimodal-bipolar) pattern with the major mode mode to to the the northwest northwest and and aa less less prominent prominent mode mode major 27 �to to the the southeast. southeast. All All of of these these features features are are characteristic characteristic of of aa tidal tidal environment environment of of deposition deposition for for the the Sunday Sunday Quartzite. Quartzite. Thus Thus aa sandy sandy tidal tidal environment environment transgressed peneplained Archean Archean craton. craton. transgressed onto onto aa peneplained Continue Continue along along escarpment escarpment and and note note the the nature nature of of the the transition transition from from the the quartzite quartzite into into dolomite. dolomite. This This is is the the Bad Bad River River Dolomite. Dolomite. Note Note also also the the abundance abundance of of white black chert chert within within the the dolomite, dolomiteIand and the the white and and black Hanirnering Please! presence stromatolites. Hammering Please! presence of of stromatolites. Because Because the the vertical vertical facies facies give give the the horizontal horizontal facies facies relationships, relationshipsl it it seems seems that that the the carbonate carbonate was was deposited deposited seaward seaward of of the the terrigenous terrigenous sands sands that that are are now now the the Sunday Sunday Quartzite, Quartzitel and and this this carbonate carbonate environment environment then then transgressed transgressed over over the the quartz quartz sands sands as as the the sea sea transgressed transgressed northward. northward. Stop Stop 8. 8. Mafic Mafic phase. phase, Emperor Emperor Volcanics Volcanics (with (withcontribution contribution by by K. K. Licht) Licht) Location: NE'(, NE NE14• %, Sec. Sec. 24. 24, T.47N., T.47N., R.43W. R.43W. on Location: NE Forest Forest Service Semice Roads Roads 523 523 and and then then 8640 8640 approximately approximately 6.5 6.5 miles miles north north of of Marenisco, MareniscotMichigan. Michigan. Rocks Rocks exposed exposed on on this this hill hill illustrate illustrate several several varieties varieties of of the the mafic mafic phase phase of of the the Emperor Emperor Volcanic Volcanic Complex. Complex. The The Emperor Emperor Formation Formation is is at at least least 2,000 21000 meters thick thick in in this this area area but but thins thins rapidly rapidly to to the the west west meters and 10 miles miles to to the the west west in in the the and is is not not recognized recognized 10 Wakefield Wakefield area. area. The The volcanics volcanics are are truncated truncated on on the the east east by by major major faults. faults. Therefore, Thereforel the the volcanic volcanic rocks rocks form foxm an an eastward-thickening eastward-thickeningwedge wedge interbedded interbedded with with the the Ironwood Iron-Formation Iron-Formationand and the the wedge wedge is is truncated truncated by by Ironwood faults faults as as shown shown by by Trent's Trent's (1973) (1973)mapping. mapping. The Emperor Emperor Volcanic Volcanic Complex Complex consists consists of of aa mafic mafic The and and felsic felsic phase. phase. Dann D a m (1978) (1978)showed showed that that the the rocks rocks range range in in composition composition from from basalt basalt to to dacite. dacite. Mapping Mapping by by LaBerge and and J. J. S. S. Kiasner Klasner in in 1991 1991 indicates indicates that that the the LaBerge mafic phase phase Emperor Emperor volcanics volcanics are are the the products products of of mafic mainly subaqueous subaqueous eruptions, eruptionsland and include include massive massive and and mainly pillowed basalts, basaltsI pillow pillow breccias, breccias! hyaloclastites, hyaloclastitesland and pillowed debris debris flows. flows. Exposures near near the the base base at at the the north north end end of of the the Exposures hill are are pillowed pillowed basalt basalt with with little little or or no no interpillow interpillow hill hyaloclastite. hyaloclastite. Higher Higher on on the the hill hill and and in in the the cliffs cliffs along along the the western western side side of of the the hill, hilllsome some exposures exposures are are mainly hyaloclastite, hyaloclastitelothers others are are hyaloclastite hyaloclastite mainly containing containing pillows pillows and and pillow pillow fragments, fragmentsIand and some some exposures are are mainly mainly pillows pillows(Figure (Figure14). 14). exposures Figure 15 15 is is aa possible possible interpretation interpretationof of the the Figure rocks shallow rocks exposed exposedhere. here. Lava Lava fountaining fountaining in in aa shallow 28 �Pillow breccia with pillow fragments fragments in in a Jackknife is hyaloclastite cm long. long. hyaloclastite matrix. matrix. Jackknife is 88 cm Figure Figure 14. 14. ,. ,.t# - flSJ#%/% fS ..F — 'S1 fl - Water Surface Hyaloclastite formed by 4, shallow-water fountarning. ii 41 fr1-1 I_4 4 I ': 4 * a A. u 14 Ilebri S f (iw. ni p1 OW I,?It(. I I— end hyalocldst.itC. Pillows and pillow breccia i:. formed by flows into —_... • or onto hya1ocaSt1te / Li ) 4 .4 -. Li • •fr,.• 01 1ii Figure Figure 15. 15. ' iii t Sketch showing showing possible environment environment of of formation formation 8. of basalts exposed exposed at at Stop Stop 8. 29 �\ MARENISCO QUADRANGLE QUADRANGLE MICHIGAN—COGEBIC MICHIGAN-GOGEBlC CO. CO. 7.5 MINUTE MINUTE SERIES S E R I E S(TOPOGRAPHIC) (TOPOGRAPHIC) 30 NW4 5' QUADRANGLE N W ( 4 MARENtSOO MARE&!SCO 15' QGADRANGLE �subaqueous subaqueous environment environment may may have have produced produced aa Later eruptions eruptions may may have have resulted resulted hyaloclastitedome. dome. Later hyaloclastite in in emplacement emplacement of of pillow pillow lavas lavas onto onto (or (orinto) into) the the hyaloclastite. Additional Additional hyaloclastite hyaloclastite may may have have hyaloclastite. formed formed on on the the surface surfaceof of the the flow. flow. Pillows Pillows and and pillow pillow fragments fragments cascading cascading off off the the flow flow front front may may have have became became mixed mixed with withhyaloclastite. hyaloclastite. Debris Debris flows flowsof of hyaloclastite hyaloclastite and and pillow pillow breccia breccia may may also also have have been been formed. formed. Rocks Rocks collected collected from from this this stop stop were were analyzed analyzed in in Some textures textures thin-section thin-sectionand and by by chemical chemicalanalysis. analysis. Some and and unique unique findings findings will will be be described described in in the the following following paragraphs. paragraphs. Many Many pillows pillows within within the the hyaloclastite hyaloclastite contain contain reaction reaction rims rims around around the the outer outer margins margins and and along along quench quench cracks. The The thicknesses thicknesses of of these these rims rims vary vary from from aa few few cracks. millimeters millimeters to to aa few fewcentimeters. centimeters. The The reaction reaction rims rims are uniform highly highly altered altered are characterized characterized by by aa fairly fairly uniform basaltic texture with some remnant tabular basaltic texture with some remnant tabularplagioclase. plagioclase. Vein within the the reaction reaction rims rims contain contain Vein fillings, fillings) within chlorjte, recrystallized quartz, and chlorite) recrystallized quartz) andepidote. epidote. . Jasper Jasper occurs occurs sporadically sporadically and and tends tends to to be be "molded" between the pillows and in fractures l1mo1dedl1between the pillows and in fractureswithin within Si02 for for the the jasper jasper may may have have been been pillows. Source Source of of Si02 pillows. gelatinous gelatinous ooze ooze on on the the seafloor seafloor at at the the time time of of eruption. The The source source of of the the Fe Fe was was probably probably the the eruption. extruded basalt. basalt. extruded The The massive massive basalt basalt on on the the north north end end of of the the hill hill has Si02content contentofof62.48's. 62.48%. In In has an an abnormally abnormallyhigh highSi02 thin-section, thin-section)epidote, epidote) recrystallized recrystallized quartz, quartz)chlorite, chlorite) and and calcite calcite are are associated associated with with the thealtered alteredbasalt. basalt. The texture) but but The hyaloclastite hyaloclastite varies varies greatly greatly in in texture, varies little little in in composition. composition. The The included included basalt basalt varies fragments are are highly highly altered. altered. The fragments The hyaloclastite hyaloclastite matrix matrix is composed composed of of plagioclase, plagioclasel calcite, calcite)quartz, quartz)chlorite, chlorite) is amphiboleland and epidote. epidote. amphibole, 9. Stow 9. Stop Felsic phase. ~hase, Em~erorVolcanics Volcanics Felsic Emperor Location: Outcrop OutcropininSESE1A?4NE NE1,?4 Sec. Sec. 20, 20) T47N., T47N.) R.44W R.44W Location: 523 near Presque Presque Isle Isle River River on on Forest Forest Service Service Road Road 523 near approximately 66 miles miles north north of of Marenisco, MareniscoI Michigan. approximately Michigan. This exposure exposure contains contains rocks rocks representative representative of of This some varieties varieties of of the the felsic felsic phase phase of of the the Emperor Emperor some Volcanics. The The dominant dominant lithology lithology at at this this locality locality Volcanics. angular) tan, tan) 22 to to 10 10 cm, cml consists of of relatively relatively angular, consists monolithic clasts clasts of of microcrystalline microcrystalline felsite felsite in in aa monolithic 31 �Whereas the the small small finer hyaloclastite hyaloclastite matrix. matrix. Whereas finer hyaloclastite hyaloclastite fragments fragments typically typically have have aa whitish whitish alteration rind! the the larger larger felsite felsite clasts clasts generally generally alteration rind, lack lack alteration alterationrinds. rinds. Prinz Prinz and and others others (1975) (1975) stated stated that that the the felsite felsite clasts clasts as as well well as as the the matrix matrix have have aa In zones zones of of deformation deformation the the dacitic dacitic composition. composition. In hyaloclastite hyaloclastite matrix matrix tends tends to to be be strongly strongly foliated, foliated! whereas whereas the the felsite felsite clasts clasts tend tend to to show show little little deformation deformation (Figure (Figure16). 16). Some Some clasts clasts contain contain abundant abundant perlitic perlitic cracks, cracks! others others are are more more massive massive felsite. felsite. This This lithology lithology of of the the felsic felsic phase phase of of the the Emperor Emperor extends extends westward westward at at least least 55 km, k m l where where there there are are extensive extensive exposures 14 and and 23 23 north north of of Wolf Wolf Mountain. Mountain. exposures in in Secs. Secs. 14 In In addition addition to to the the variety variety of of rock rock exposed exposed here, here! Sec. Sec. 14 14 north north of of Wolf Wolf Mountain Mountain contains contains extensive extensive brecciated brecciated felsite Although felsite with with scattered scattered quartz quartz phenocrysts. phenocrysts. Although the the rock rock is is extensively extensively brecciated, brecciated, there there appears appears to to have have been been little little or or no no movement movement of of adjacent adjacent blocks blocks with with respect respect to to one one another. another. In In short, short! the the rock rock appears appears to to be be aa felsic felsic dome dome that that has has been been brecciated. brecciated. Surrounding Surrounding the the brecciated brecciated felsite felsite are are numerous numerous exposures exposures with with breccia breccia fragments fragments of of felsite felsite in in aa felsic felsic hyaloclastite matrix matrix (Figure (Figure17). 17). It It is is suggested suggested that that hyaloclastite the felsite felsite breccia breccia may may be be aa felsic felsic dome dome emplaced emplaced into into the felsic felsic hyaloclastite hyaloclastite produced produced by by an an earlier earlier eruption. eruption. Debris Debris flows flows off off the the dome dome may may have have resulted resulted in in more more widespread widespread units units of of the the felsite felsite breccia/hyaloclastite breccia/hyaloclastite as shown shown in in Figure Figure 18. 18. as 32 �Figure Figure 16. 16. Photo Photo of of sawed sawed slab slab of of Emperor Emperor Volcanics Volcanics from from Stop Stop 9. Larger, Larger, angular angular felsite felsite clasts clasts in in aa finer finer 9. grained, is grained, foliated foliated hyaloclastite hyaloclastite matrix. matrix. Slab Slab is 18 18 cm cm long. long. Figure 17. Figure 17. Photomicrograph Photomicrograph of hyaloclastite hyaloclastite from from Note phase of tie Emperor Volcanics. phase of the Emperor Volcanics. Note cracks cracks in in the the oval oval clast clast on on the the right right photo. mm. photo. Bar Bar scale scale is is 22 mm. the the felsic felsic the perlitic the perlitic side side of of 33 �Water Surface C a r a p a c e o f hyaloclastite formed (IuI-~ e aI rIl ~ ier Figure Figure18. 18. fountaininq. Sketch Sketch of of possible possible relationships relationships within within the the felsic felsic Highly fractured fractured phase phase of of the the Emperor EmperorVolcanics. ~olcanics. Highly felsite felsite blocks blocks become become dispersed dispersed in in finer finer grained grained felsic f aa felsic hyaloclastite hyaloclastitein indebris debrisflows flowsofoff subaqueous subaqueous lava lavadome. dome. Stop Stow 10. 10. Archean Archeanmetacrravwacke metaqrawacke Location: 2, about about 10.5 10.5 mi mi SE SE of of Location: Roadcuts Roadcuts on on Highway Highway 2, Marenisco, 'A, X , Sec. Sec. 30, 30, T. T. 46 46 N., N., R. R. 41 41W. W. (Thayer, (Thayer, Marenisco,SWSW MI MI 15' 15' quadrangle). quadrangle) . The metagraywacke metagraywacke in in these these roadcuts roadcutsis is part part of of aa The km wide wide and and 20 20 km km long. long. The The northeast-trendingbelt belt 44 km northeast-trending rocks rocks are are highly highly folded folded on on tight tight north-northeastnorth-northeasttrending km trending axes, axes, and and the the unit unit is is probably probably about about 11km thick. thick. The The graywacke graywacke is is aa fine-grained, fine-grained,thinthin-to to thick-bedded thick-beddedrock rock with with aa pervasive pervasive northeast-trending northeast-trending schistosity(S2) (S,) that that is is Penokean Penokean in in age; age; an an older older schistosity (Si)that that is is Archean Archean in in age age is is nearly nearly schistosity(Si) schistosity parallel parallel to tobedding. bedding. Graded Graded beds beds are are common, common,and andtops tops at at this this outcrop outcrop are areto tothe thesouth. south. Reversals Reversals of of grading grading indicate apart. indicate that that the the fold fold crests crests are are about about200 200mm apart. 34 �The The rocks rocks were were metamorphosed metamorphosed to to amphibolite amphibolitegrade grade during the the Archean Archean and and are are totally totally recrystallized; recrystallized;most most during of of the the garnet garnet was was retrograded retrogradedto to chlorite chlorite++ muscovite muscovite ++ epidote and and opaques opaques during during the the Penokean Penokeanorogeny orogeny(Sims (Sims epidote The nature of the original sediment and others, others,1984). 1984). . The nature of the originalsediment and is is unknown unknown because because of of the the thorough thorough recrystallization, recrystallization, but CIA indices (chemical indices but CIA indices (chemical indicesof of alteration) alteration) calculated calculated for for the the graywackes graywackes indicate indicatean anoriginal original immature detritus that had undergone little immature detritus that had undergone little if if any any weathering in the source area and could have weathering in the source area and could have been been immature immature volcaniclastics. volcaniclastics. The The area area was was mapped mapped by by Cannon Fritts (1969), Trent (1973), and Prinz (1981) . Cannon Fritts (1969), Trent (1973), and Prinz (1981) of (1986b) produced a structural and tectonic map (1986b) produced a structural and tectonic map of the the . region. region. Ma) Stoo11. 11. Watersmeet Watersmeet Gneiss Gneiss(3560 (3560Ma) Stor Location: Roadcuts Roadcuts on on Highway Highway 45, 45, about about 44 mi mi NN of of the the Location: This junction junctionis is on on the the junction and 45. 45. This junction of of Highways Highways 22 and Roadcut location location edge of of the the village village of of Watersmeet. Watersmeet. Roadcut SS edge is SSedge, edge,NENE'A, 1/, Sec. Sec. 4, 4,T. T. 46 46 N., N., R. R. 39 39 W. W. is (Watersmeet, (Watersmeet,MI, MI, 15' 15' quadrangle). quadrangle) . This This exposure exposure is is located located in in the the northern northern part part of of the the Watersmeet Watersmeet dome dome which which has has an an Archean Archean core coreabout about25 25 km km wide wide in inaaNNkm long long in in an an E-W E-Wdirection direction and and about about 88 km direction. The The dome dome is is considered considered to to be be aa mantled mantled SS direction. gneiss dome. dome. Sims Sims (1990) (1990) recognizes recognizes considerable considerable Early Early gneiss Proterozoic Proterozoic rocks rocks in in the the core core infolded infolded with with the the Archean. Deformation Deformation of of the the Archean Archean and and adjacent adjacent Early Early Archean. Proterozoic Proterozoic rocks rocks occurred occurred during during the the Penokean Penokeanorogeny. orogeny. The rocks rocks in in the the core core were were metamorphosed metamorphosed to to the the The amphibolite amphibolite fades, facies,aa15 15km-wide km-widezone zoneof of epidote epidote amphibolite amphibolite facies facies surrounds surrounds the the core, core, and and this this in in turn turn passes outward outward into into greenschist greenschistfacies. facies. (This (This is is the the passes Watersmeet metamorphic metamorphic node node of of James, James,1955). 1955). The The Early Early Watersmeet Proterozoic Proterozoic rocks rocks to to the the north north of of the the dome dome have have been been overturned toward toward the the northwest. northwest. This This area area was was studied studied overturned Peterman and and others others by Sims Sims and and others others(1984) (1984)and andPeterxnan by (1980). (1980) The gray gray gneiss gneiss is is aa tonalitic tonalitic augen augen gneiss gneiss about about The 3560 Ma Ma old old (zircon (zircondata) data) (Sims (Sims and others, 1984); 1984); it it and others, 3560 is aa medium-gray, medium-gray,mediummedium- to to coarse-grained, coarse-grained,biotitebiotiteis rich, irregularly irregularly layered layered rock rock with with plagioclase plagioclase augen. augen. rich, The alternating alternating layers layers are are feldspar-quartz-rich feldspar-quartz-richand and The biotite-rich. AA modal modal analysis analysis showed showed 48% 48% plagioclase, plagioclase, biotite-rich. 30% quartz, quartz, 8% 8% K-feldspar, K-feldspar,and and 13% 13%biotite. biotite. AA possible possible 30% protolith protolith was was dacitic dacitic volcanic volcanic rock rock (Sims (Simsand and others, others, 1984). In In this this exposure, exposure, biotite biotite leucogranite leucogranite veins veins 1984). Ma old old (Rb/Sr (Rb/Srand and U-Pb U-Pbmethods) methods) cut cut the the gneiss. gneiss. 2590 Ma 2590 Secondary whole-rock whole-rock and and mineral mineral isochrons isochrons give give ages ages of of Secondary Ma and and are are thought thought to to approximate approximate the the time time 1750 to to 1800 1800 Ma 1750 span of of the the Penokean Penokean event event in in this this area area (Sims (Sims and and span 35 �others, 1984) others, 1984). Whereas the Archean gneisses of of the the area area may may have have Whereas the Archean gneisses been folded folded three three times, times, the the cross-cutting cross-cutting Late Late Archean Archean leucogranite shows shows only a single leucogranite single foliation, foliation, that that of of the the Penokean Penokean event. event. gneiss is The gneiss is comparable comparable in in age age to to those those of of the the Minnesota Minnesota River River Valley, Valley, about about 3500 3500 Ma Ma old: old: these these are are parts parts of of the the ancient ancient gneiss gneiss terrane terrane that is is separated separated granite-greenstone terrane from the granite-greenstone terrane to to the the north north by by the the GLTZ, the GLTZ, the Great Great Lakes Lakes Tectonic Tectonic Zone Zone of of Sims Sims and and others others (1980). (1980) 36 �References Cited Cited References Aldrich, H. H. 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L., L., 1964, 1964,Development Development of of Magnetite Magnetite in in Iron-Formations LaBerge, Iron-Formations of the Lake Superior Region: Economic Geology, vol. 59, p. of the Lake Superior Region: Economic Geology, vol. 59, p. 1313-1342. 1313-1342. 38 38 LaBerge,G. G. L., L., l966a, l966a. Altered Altered Pyroclastic Pyroclastic Rocks Rocks in in IronLaBerge, IronFormation Hamersley Range, Western Australia: Economic Formation Hamersley Range, Western Australia: Economic Geology, vol. 61, p. 147-161. Geology, vol. 61, p. 147-161. �Pyroclastic Rocks Rocks in in South South African African LaBerge, LaBerge! G. G. L., L.! 1966b, 1966b1 Altered Altered Pyroclastic GeologyI vol. vol. 61, 611p. p. 572-581. 572-581. Iron-Formation: Economic Economic Geology, Iron-Formation: Larue, D. K., K.! 1981, 19811 The The Chocolay Chocolay Group, Group! Lake Lake Superior Superior region, region! Larue! D. U.S.A.: sedimentological sedimentological evidence evidence for for deposition deposition in in basinal basinal and platform settings on an early Proterozoic craton: and platform settings on an early Proterozoic craton: Geological Bulletin! vol. vol. 92, 92! p. p. 417-435. 417-435. Geological Society Society of of America America Bulletin, Larue, Larue! D. D. K., K.! 1983, 1983! Early Early Proterozoic Proterozoic tectonics tectonics of the the Lake Lake Tectonostratigraphic terranes terranes near near the the Superior region: region: Tectonostratigraphic Superior purported zone! in Medaris, Medaris! L. L. G., G e lJr., Jr.! Early Early purported collision collision zone, Geological Proterozoic Proterozoic geology geology of of the the Great Great Lakes Lakes region: region: Geological Society merica Memoir Society of America Memoir 160, 1601p. p. 33-47. 33-47. Mengel, Mengel! J. J. T., T.! Jr., Jr.! 1963, 1963! The The Cherts Cherts of of the the Lake Lake Superior Superior IronIronBearing Bearing formations: formations: Ph.D. Thesis, Thesis! University University of of Wisconsin. Wisconsin. Morey, Morey! G. G. B., B. Sims, Sims P. P. K., K. Cannon, Cannon! W. W. F., F. Mudrey, Mudrey! M. M. G., G. Jr., Jr. and and Southwick, D. L., L.! 1982, 1982! Geological Geological Map of the the Lake Lake Superior Superior Southwickl D. region: Minnesota, Minnesota! Wisconsin, Wisconsinl and and Northern Northern Michigan: Michigan: region: Minnesota Minnesota Geological Geological Survey Survey State State Map Map Series Series S-13. S-13. Ojakangas, Ojakangas! R. W., W.! 1983, 1983! Tidal Tidal deposits deposits in in the the Early Proterozoic Proterozoic basin basin of of the the Lake Lake Superior Superior region region -- the the Palms Palms and and Pokegama Pokegama Formations: Formations: Evidence Evidence for for sub-tidal sub-tidaldeposition deposition of of SuperiorSuperiortype banded iron-formation: iron-formation: jinEarly EarlyProterozoic Proterozoic Geology Geology of of type banded Geological the by L. G. Medaris), Geological the Great Great Lakes Lakes Region Region (edited (editerby G. Medaris) Society Society of of America America Memoir Memoir 160, 1601 p. p. 49-66. 49-66. Ojakangas, Ojakangas! R. W., W.! in in press, press! Sedimentology Sedimentology and and provenance provenance of of the the Early Proterozoic Proterozoic Michigaxnme Michigamme Formationl U.S. Early Formation, Michigan: Michigan: U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-IL 1904-R. Ojakangas, Ojakangas! R. R. W. W. and and Matsch, Matsch! C. C. L., L.! 1982, 1982! Minnesota Minnesota Geology, Geologyl Univ. Univ. of of Minnesota Minnesota Press, Press! Minneapolis, Minneapolisl255 255 p. p. Peterman, Peterman! Z. Z. E., E e lZartman, Zartman! R. R. E., E e land and Sims, Sims! P. P. K., K.! 1980, 19801 Early Early Archean tonalitic gneiss gneiss from from northern northern Michigan! Michigan,U.S.A.! U.S.A., j Morey! G. G. B., B a 1and and Hanson, Hanson! G. G. N., N.! Selected Selected studies studies of of Archean Archean Morey, and lower lower Proterozoic Proterozoic rocks, rocksl southern southern Canadian Canadian Shield: Shield: and Geological Geological Society Society of of America America Special Special Paper Paper 182, 182! p. p. 125-134. 125-134. Prinz! W. W. C., C.! 1981, 19811 Geologic Geologic map map of of the the Gogebic Gogebic Range Range -Prinz, Watersmeet area, area! Gogebic Gogebic and and Ontonogan Ontonogan Counties, Countiesl Michigan: Michigan: Watersmeet Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries Series U.S. Geological Map 1-1365, I-1365! scale scale 1:125,000. 1:1251000. Map Prinz! W. C., C.! Gair, Gairl J. J. E., E.! and andcannon! W. F., F.! 1975, 1975! "Greenstone: I1Greenstone: Prinz, Cannon, W. Field Trip Trip 2", 2If121st 21st Annual Annual Institute Institute on on Lake Lake Superior Superior Field Geologyl Marquette, Marquette! Michigan, Michigan! pp. pp. 41-85. 41-85. Geology, Schmidt! R. G e l1976, 1976! Geology of the Precambrian Precambrian W (Lower (Lower Schmidt, G., Countyl Michigan: Michigan: Precambrian) Rocks Rocks in in Western Western Gogebic Gogebic County, Precambrian) Geological Survey Survey Bulletin Bulletin 1407. 1407. U.S. Geological 39 �Schmidt, Schmidtl R. G., 1980, 19801 The The Marquette Range Supergroup Supergroup in in the the U.S. Gogebic Gogebic Iron Iron District, District, Michigan Michigan and and Wisconsin: Wisconsin: U.S. Geological Geological Survey Survey Bulletin Bulletin 1460, 14601 96 96 p. p. Schmidt, R. G and Hubbardl Hubbard, H. A A., Schmidtl v 11972, 19721 Penokean Penokean orogeny orogeny in in the the central and western Gogebic Gogebic region, Michigan and Wisconsin: regionl Michigan and Wisconsin: Field A, 19th Field Trip Trip Al 19th Annual Annual Institute Institute on on Lake Lake Superior Superior Geology, Houghton, Geologyl Houghtonl MI, MIl p. p. A1-A27. Al-A27. Sims, Simsl P. P. K., K s 11990, 19901 Geologic Geologic map map of of Precambrian Precambrian Rock, Rockl Marenisco, Mareniscol Thayer, and Watersmeet 15 Minute Minute Quadrangles Gogebic and Thayerl Ontonagon Ontonagon Counties, Countiesl Michigan Michigan and and Vilas Vilas County, Countyl Wisconsin: Wisconsin: U.S. Geological U.S. Geological Survey Survey Miscellaneous Miscellaneous Investigation Investigation Map Map 1-2093. 1-2093. Sims, Z. E., E e l1976, 1976# Geology Geology and and Rb-Sr Rb-Sr ages ages of of Simsl P. P. K., K e 1Peterman, Petermanl Z. reactivated reactivated Precambrian Precambrian gneisses gneisses in in the the Marenisco-Watersmeet Marenisco-Watersmeet area, areal Northern Northern Michigan: Michigan: Journal Journal of of Research, Researchl U.S. U.S. Geological Survey, Geological Surveyl vol. vol. 4, pp. pp. 405-414. 405-414. Sims, Z. E., E e lPrinz, Prinzl W. C., C e 1and and Benedict, Benedictl F. F. C., Ce1 Simsl P. K., K a 1Peterman, Petermanl Z. 1984, Geology, Geology, geochemistry and age Archean and 1984# age of Archean and Early Early Proterozoic Proterozoic rocks rocks in in the the Marenisco-Watersmeet Marenisco-Watersmeetarea, areal northern northern U.S. Geological Michigan: Michigan: U.S. Geological Survey Survey Prof. Prof. Paper Paper 1292-A, 1292-Al41 41 p. p. Sims, Simsl P. K., K e 1Van Van Schmus, Schmusl W. R., Schulz, Schulzl K. K. J., J a 1and and Peterman, Peterman#Z. Z. E., Tectonostratigraphic evolution of the Early E e l1990, 19901 Tectonostratigraphic Proterozoic Penokean Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Orogen: Can. Jour. Jour. Earth Earth Sci. Sci. Southwick, D. L. and MoreyI Morey, G. B B., imbrication and a 1 1991, 19911 Tectonic imbrication Southwickl foredeep foredeep development development in in the the Penokean Penokean orogen, orogenl east-central east-central Minnesota-An Minnesota-An interpretation interpretation based on on regional regional geophysics geophysics and and results of U.S. Geological Geological Survey results of test test drilling: drilling: U.S. Survey Bulletin Bulletin 1904-C, 1904-Cl17 17 p. p. Suszekl T. T. J., J a 11991, 1991, Petrography Petrography and and sedimentation sedimentation of of the the Middle Middle Suszek, Proterozoic (Keweenawan) Nonesuch Formation, Formationl Western Lake Proterozoic (Keweenawan) Western Lake Superior region, region, Midcontinent Midcontinent Rift Rift System: System: unpublished unpublished M.S. M.S. Superior thesis, University University of thesisl of Minnesota, Minnesotal Duluth, Duluthl 198 198 p. p. e 1 1973, 19731 Geological Geological Map of of the the Marenisco Marenisco and and Wakefield Wakefield Trentl Trent, V. A A., NE quadrangles, quadranglesl Gogebic Gogebic County, Countyl Michigan: Michigan: U.S. U.S. Geological Geological Survey Open Open File File Report, Reportl scale scale 1:48,000. 1:481000. Survey Van Hisel C.R. C.R. and and Leith, Leithl C. C. K., K a 11911, 19111 Geology Geology of of the the Lake Lake Van Hise, Superior Superior Region: Region: U.S. Geological Survey Survey Monograph Monograph 52. 52. U.S. Geological 40 �KEWEENAWAN SEDIMENTARY ROCK OF THE THE SOUTH SHORE, LAKE SUPERIOR A.B. Dickas Dickas Department Department of of Geology, Geology, Wisconsin-Superior University of Wisconsin-Superior M.G. Mudrey, Mudrey, Jr. Jr. Wisconsin Wisconsin Geological and and Natural Natural History History Survey, Sumey, Madison, Wisconsin �INTRODUCTION The sedimentary sedimentary and igneous igneous rock composing composing the Precambrian Precambrian (Middle (Middle Proterozoic, Roterozoic, Keweenawan) section of the Lake Superior stratigraphic column column have have had had aa long long history history of of study. Almost six decades ago (19331, (1933), the geology of of the the "Lake "Lake Superior Region," Region," constituting Excursion C-4, was presented as Guidebook International Geological Geological Guidebook 27 of the XVI International Congress. The W. 0. 0. Hotchldss The field field guide guide for for this this excursion was prepared by W. Hotchlciss of of the the MichiMichigan College College of Mining Mining and and Technology Technology (now (now Michigan Michigan Technological TechnologicalUniversity) University)and andwas was purchased 25 cents. cents. purchased for for the the sum sum of of 25 In his introduction to that guidebook, guidebook, C. K. kLeith i t h (University (University of Wisconsin) stated: The The Lake Superior Superior region q i o n has been of special special interest to students of pre-Cambrian geology because it presents the largest and most varied pm-Cambrian pre-Cambrian succession succession that geology because has has been been definitely definitely worked worked out. Its Itscontent contentof ofvaluable valuableiron imnand andcopper copperores oreshas has made made possible possible more intensive intensive and detailed studies studies than have been accorded to extensive extensive pre-Cambrian pre-Cambrian areas elsewhere. The Thepre-Cambrian pre-Cambriansuccession successionnow now known known (in the Lake Superior Superior area) area) represents a greater mater thickness of sediments sedimentsand and aa larger larger time time than than all all the the post-Cambrian post-Cambrianof of North North America. America. It is k i t h , in a later section of this guidebook, presented the is interesting interesting to to note how Charles Charles Leith, Keweenawan Keweenawan sequence, sequence, now now known as as the the Midcontinent Midcontinent Rift Rift sequence: sequence: Keweenawan: Keweenawan: Next Next below below (the (the Cambrian) Cambrian)is is the the nonfossiliferous nonfossilifemusKeweenawan Keweenawan series, consisting of an immense mass, possibly 5 miles (8 km) thick, thick, of sandstone, sandstone, series, consisting an immense mass, miles intercalated shales shales and conglomerates, containing in its lower part large quantiwith intercalated ties of of extrusive extrusive lavas lavas and intrusive laccoliths and sills. In In degree degree of of metamorphism metamorphism ties is more more like like the the Cambrian Cambrian than the underlying Humnian It has has characterischaracterisitit is Huronian series. series. It tic reddish, reddish, yellowish, yellowish, and and purplish purplish colors colors and and carries cames various various evidences evidencesthat that itit was was tic essentially aa continental continental deposit deposit under semiarid conditions. Its Its lower lowerpart part isis tilted tiltedin in essentially marked unconformity unconformityto tothe theCambrian, Cambrian,but but its itsupper upperpart part lies liesnearly, nearly,ifif not notquite, quite, maiked in an an independent independent parallel to to the Cambrian. Cambrian. Obviously, Obviously,ititwas wasmainly mainlydeposited depositedin parallel basin before the incursion of the Upper Cambrian sea. Although the Keweenawan is sea. Although Keweenawan in the the sense senseof of preceding preceding the the Upper Upper Cambrian Cambrian transgression, transgression,having having pre-Cambrianin pre-Cambrian structural and and igneous igneousaffiliations affiliationswith with the the pre-Cambrian, pre-Cambrian, and and being being nonfossffiferous, nonfossiliferous, structural may be be Cambrian Cambrianin in the the sense sensethat thatitit was was being being formed formedatatthe thesame sametime timeas asMiddle Middle itit may and Lower Lower Cambrian Cambriansediments sedimentsin in distant distant Cambrian Cambrianseas. seas. and Today as as we we gather gather for for this this 38th 38th Institute Institute on on Lake Lake Superior SuperiorGeology Geologyfieldtrip, fieldtrip,comparisons comparisons Today 1933 form form distinct contrasts. In In1992, 1992,with with aasingular singularexception, exception,the the with conditions in 1933 copper mines mines are are closed closed and and the the massive massive iron iron ore ore fields fields have have fallen fallen under under different different economic economic copper Yet,aanew new era era of of evaluation evaluation and exploration has climates. Yet, has begun. begun. The Lake Superior Keweenawan section section is is widely widely recognized recognized as as one one of of the the fmest fmest extant extant examples examples of of continental continental Keweenawan rifting. The Theadvent adventofofindustrial industrialfield fieldevaluation evaluationof of the the hydrocarbon hydrocarbon potential potential of of these these rift rift rifting. indhctly facilitated facilitatedthe thecollection collectionof ofapproxiapproxistrata, beginning beginning in in 1983, 1983,has has directly directly and and indirectly strata, mately 4200 4200 km km of of seismic seismic reflection reflection data data in in the the Lake Superior Superior district dismct alone, alone, in in addition addition to to mately supportive supportive magnetic magnetic and and gravity gravity surveys. surveys. This new new period period of of exploration exploration within within the the Lake Lake Superior Superior region has altered altered our interpretation interpretation of This its geologic development, especially during Keweenawan time. m y of these updated geologic its geologic development, especially Keweenawan Many of these updated geologic 43 43 �relationships will be examined during the process of this field mp. trip. Our Our principal principal focus will be on the geology and geologic history of the youngest Precambrian rock in the region, the rifting,initiated initiatedcirca circa 1100 1100Ma. Ma. The The Keweenawan. This This rock rock is is a remnant of major continental rifting, resultant Midcontinent Midcontinent Rift System System trends trends from the Lake Superior Superior region to to as far far southwest southwest as as central central Kansas Kansas and and as as far far southeast southeastas as southern southernOhio. Ohio. As of this writing (March 2, 1992) has been been underway underway for for several weeks weeks for for 1992) site preparation has the Terra/Patrick TerraPamck #7-22 wildcat borehole, borehole, a test test of the the hydrocarbon hydrocarbon potential potentialof of the theWisconWisconsin section of the Midcontinent rift of national significance and interest. Located 47N, 22,47N, Locatedin in 22, this well well will will be be operated operated by by Terra Terra 6W, Keystone Township, Bayfield County, Wisconsin, this Energy, Energy, Ltd of Traverse Traverse City, Michigan, in partnership with Patrick Petroleum Company of arrangements with Amoco Ammo Production Production Company Company(USA), (USA), Jackson, Michigan, under farmout arrangements Houston, Texas. The The target target depth depth will be 6,000 feet, permitting a test of the oil or gas large dragdragpotential of the Oronto Oronto Group Group sequence sequence of sedimentary sedimentary rocks. The The structure structureis is aa large with north north closure closure against againstthe theDouglas Douglasreverse reversefault. fault. The The surface surface expression expression of of fold anticline with 60 square square miles. Available Available information information this structure structure extends over an area of approximately 60 on this state state record depth wildcat will be included in the 38th Institute on Lake Superior Geology Proceedings as an abstract abstract (Albert (Albert B. Dickas). The site of the TerraPatrick Terra/Patrick #7-22 borehole is approximately 6 miles miles north-northeast north-northeast of of an Oronto borehole Amoco M Production Oronto Group Group wildcat test W h o l e announced in 1985 by Ammo u c t i o n Company (USA). This bborehole, h o l e , planned for 13, 13,46N,7W, 46N,7W, and targeted for 15,000 feet, was never drilled for economic economic and and legislative legislative reasons. 44 �GEOLOGY GEOLOGYOF OF THE THEMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM SYSTEMALONG ALONG THE THESOUTH SOUTH SHORE MICHIGAN SHORE OF OF LAKE LAKE SUPERIOR, SUPERIOR, WISCONSIN WISCONSIN AND MICHIGAN Reprinted from Dickas, Reprinted with with permission /rom Dickas, Albert B. (editor), (editor),1989, 1989, Lake Superior Superior basin basinsegment segment of the Midcontinent Rift Rjft System: System: Field Field trip trip guidebook guidebook T344.28th T344, 28th International International Geological Geological Congress, Congress. 62 62 pages. Introduction Introduction The The Midcontinent Midcontinent Rift Rift System System has been mapped over an axial length of in excess of 3,300 km. structure are contained krn.Portions Portionsofofthis thisPrecambrian Precambrian(Ca. (ca.1.1 1.1 Ga) extensional structure contained in in the the states states of of Kansas, Kansas, Nebraska, Nebraska, Iowa, Minnesota, Wisconsin, Michigan, and Ohio. This Thisreport report presents presents the geology of this rift system within the geographic region generally defined as northwestthe geology of this rift system within the geographic region generally defined as northwestern em Wisconsin Wisconsin and and the the adjacent adjacent upper upper peninsula peninsula of of Michigan. Michigan. Wisconsin Wisconsin Section Section The The Midcontinent MidcontinentRift Riftsequence sequenceof of Precambrian Precambriansedimentary sedimentarystrata stratain inthe thewestern westernLake Lake Superior Superior region region constitutes constitutes some some of of the the oldest oldest known known and and studied studied such such assemblages assemblagesin in the the United United states. states. These Theseunits unitswere wereinitially initiallydescribed describedby byHunt Hunt(1873), (1873),who whonamed namedthem themthe the Keweenaw Keweenaw Group Group after after the cupriferous cupriferous strata exposed along the Keweenaw Peninsula of Michigan. Thwaites Thwaites(1912) (1912)divided dividedthis this section sectioninto into the the Oronto Oronto (lower) (lower) and Bayfield (upper) (upper) groups (Fig. (Fig. 1). More More recently recently the the U. U. S. S. and and Ontario Ontario Geological Geological surveys surveys have have been been inforinforgroups mally termKeweenawan KeweenawanSupergroup. Supergroup. mally using usingthe theterm The outcrop outcrop belt belt of of the theOronto OrontoGroup Groupisis traced traced from from northwestern northwesternWisconsin Wisconsin east east and and northnorthThe east to to the the tip tip of of Keweenaw Keweenaw Point, Point, Michigan. The TheOronto OrontoGroup Groupcrops crops out out principally principally along along east Ashland syncine syncline(Fig. (Fig.2), 2),which whichisiscentrally centrally located located on the St. Croix horst. The TheAshland Ashland the Ashland the syncline is asymmetrical as the steeper dips are found within the southern limb. The horst is is syncline is asymmetrical steeper limb. The horst bounded by by the the reverse-throw reverse-throwDouglas Douglas and and Isle Isle Royale Royale faults faults to to the the north north and and the the Lake Lake bounded Owen and and Keweenaw faults to the south. While Whileseismic seismicinformation information suggests suggests the the presence presence Owen of Oronto Orontocomponents componentsin inthe theflanking flankingbasins, basins,deep deepdrilling drillinghas has yet yetto toconfirm confirmthis thisconjecture. conjecture. of (FredaSandstone) Sandstone)inin However,on on the thebasis basis of ofaadrag dragfold foldexposure exposureof of Oronto Orontotype typestrata strata(Freda However, Douglas County, County,Wisconsin, Wisconsin,White White(1966) (1966)supported supportedthe the concept conceptof of Oronto Orontostrata stratabeing being Douglas found north north of of the the Douglas Douglas fault. Alternately, Alternately,White White (1966) (1966) supported supported the possibility of found post-Oronto(Bayfield (BayfieldGroup) Group)inliers inliersbeing beingfound foundwithin withinthe thehorst horstposition positionas assuggested suggestedby by post-Oronto heavy heavy mineral mineralanalyses analysesconducted conductedby by Tyler Tyleretetal. al. (1940). (1940). The OrontoGroup Groupisis 40 40percent percent sandstone sandstoneand and 60 60 percent percent shale shale (Thiel, (Thiel, 1956) 1956) and and constitutes constitutes The Oronto aa maximum maximum 6,100 6,100 m m thick thick sequence sequence of reddish conglomerate, conglomerate, sandstone, and mudstone. ItIt shows rela-. shows aa general general upward upwardincrease increasein in maturity, maturity, from frompoorly poorly sorted sortedarkosic arkosicto toquartzose, quartzose,relatively tively well-sorted well-sortedsedimentary sedimentaryrocks. rocks. Much Muchofofthis thisgroup groupwas waslocally locallyderived derivedthrough through erosionof of Middle MiddleKeweenawan Keweenawanbasalts basaltsand andtransported transportedonly onlyaashort shortdistance distancetotoits itsdeposideposierosion tional tionalbasin. basin. 45 �The Thelowest lowestunit unitof of the theOronto OrontoGroup, Group, the the Copper CopperHarbor HarborConglomerate, Conglomerate, conformably conformablyoveroverlies liesbasement basementlavas lavasand andlocally locallyinterfingers interfingerswith with them them (White (White and and Wright, Wright, 1960). 1960). While While exposures exposurescan canregionally regionallyexceed exceed1,800 1,800m min in thickness, thickness,as asmuch muchasas 610 610 m m of of this this column column may may be be basic basic volcanics volcanics (Halls, (Halls, 1966). 1966). Overall Overallthis thisunit unitisisaafining-upward fining-upwardaccumulation accumulationof of brown brown to red,arkosic, arkosic,pebble pebble to to boulder boulder conglomerate, conglomerate,dominantly dominantlycomposed composedof of mafic maficto tofelsic felsic tored, volcanics, volcanics,with with lesser lesseramounts amountsof of rather rather coarse, coarse, cross-bedded, cross-bedded, graywacke graywackesandstone sandstone(Daniels, (Daniels, 1982). Within the sands, stratification is crude, shallow water flow regime structures 1982). Within the sands, stratification is crude, shallow water flow regime structuresare are common limited. Bedding Bedding plane plane dips dips range from from common and and lateral lateral correlations correlations for any distance are limited. ten degrees to overturned. The depositional regime of the conglomerate facies reflects a ten degrees to overturned. The depositional regime of the conglomerate facies a prograding, prograding,alluvial alluvialfan fan complex complex (Daniels, (Daniels,1982), 1982),while the sandstone sandstone units are are more more suggessuggestive tive of of shallow shallow water. water. AAlocalized localized"redder" "redder" arenaceous arenaceousfacies, facies,found found along along the the Keweenaw Keweenaw Peninsula, flood plain or or standing-water standing-waterdeposit deposit by White White and and Wright Wright Peninsula,has has been been classified classifiedas as aa flood (1960). (1960). The Thesame sameenvironment environmentisiselsewhere elsewherelocally locallysupported supportedby bythe thelimited limitedpresence presenceof of algal algal stromatolites stromatolitesin in the thevicinity vicinityof of Copper CopperHarbor, Harbor, Michigan, Michigan,the thelocation locationof ofthe thetype type section sectionof of this thisformation. formation. 11 — F'1a.n1 anit 'I' I. 'I' MuD—CO z -p si o rst M I D - C O NTI T I I'T NENT RIIF' F'T 2 —orst 2 'I' I. A. 'I' I C R. .A. P II Y T I M E S T R A T I G R A F H Y 3 u . r ' e nsu a 3 — tJ. P en xiiixisu. 1la. TIM 4 - L peninsula - —-- i... -- Iowa I Minn I 1 Wisc 11 Freda. Ss 1 NoneSuch Fm r 7 d -Val s , V A i "'I- "  ¥ 7 v ,.,"'I^^ 7 7 A ." V-01 s > < I >"4 i V < " , ^ >tans_> v > < - ' < A< 7 Mich Freda ss .. a! NoneSuch Tnor > St croik chenkwi. d pex1ins.iia. - rt, a g e, > l=>p ^ - 2 4 Lake \ ' A . < > J 7 < L,,7, VOlS', * VO-1 s + Q ffl , , I-. < 4 r v L grap hic terminology terminology and and time time relationships relationships of Upper FIGURE FIGURE 1: 1: Strati Stratigraphic Upper Keweenawan Keweenawan sedimentary sedimentary rocks permission of (1986), reprinted reprinted by by permission of the the rocks along along the the Midcontinent Midcontinent Rft RiftSystem System trend. trend. After Dickas (1986), American Association Association of of Petroleum Petroleum Geologists. Geologists. American 46 �In conformable and interfingering interfingering contact with the Copper Harbor Conglomerate Conglomerate is the the Formation, a hydrocarbon source rock Dickas, 1991) Nonesuch Formation, 1991) and the center center of industrial industrial interest focused on on the the Midcontinent Midcontinentrift riftsince sincethe theearly early1980's. 1980's. These strata are gray to distinguishable from enveloping grain size size ranges ranges black, easily distinguishable enveloping red to brown formations. The grain from medium sand to clay with with shale subordinate to to siltstone siltstone and and sandstone. sandstone. This unit is is the the from at least 140 m m in in northern northern Wisconsin Wisconsin to to a maxithinnest of the Oronto Group, ranging from mum 200 m in adjacent Michigan. Framework Frameworkcomposition composition emphasizes emphasizesmafic mafic rock rock fragfragments, with analysis showing ranges ranges of of 15 to to 30 30percent percent (Hite, (Hite, 1968). 1968). Of economic interest is the cupriferous nature of the basal 10 m of the Nonesuch Formation, especially in the cupriferous 10 White Pine, Michigan area where an estimated 11 million tones of of copper have been found (Cox et al., aL, 1973), predominantly predominantlyin inthe theform formof ofchalcocite chalcociteand andnative nativecopper. copper. The The variety variety of of sedimentary structures found in this formation have locally been employed employed as as supporting supporting environments. The best model appears to be that of evidences for a variety of depositional environments. reducing conditions conditions within a standing standing body of water (Hubbard, 1975), distinguished by frequent variations variations in water depths (Daniels, 1982), influenced by fluvial and deltaic associations (Barghoorn (Barghoom et al., 1965), 1965), and marked by periodic salinity levels exceeding that of Hieshima and and Pratt Pratt (1991) (1991) offer offer evidence evidencesupsupgypsum precipitation. Recently, Recently,however, however, Hieshima porting a marine embayment embayment environment. copper is found in direct lithologic The copper lithologic association association with finely finely disseminated disseminated carbonaceous carbonaceous 0.5% of of the the formation formationby byvolume. volume. Kelly and Nishioka (1985) believe matter which averages 0.5% copper copper precipitation was directly facilitated by the intimate presence of organic material. The organic organic matter, upon chemical extraction, shows remarkable structural features that have been preserved by a bituminization, rather rather than than aa carbonization, carbonization,process. process. This material is found both as matrix masses and as recognizable remains, such as bacteria cells, algal-like units and fungal hyphae, with volume distribution being concentrated in the finest grained Overall,individual individuallaminae laminaeare are alternately alternately rich and poor in organic components. strata. Overall, Moore et al. (1969), after thin-section analysis of the organic rich shale layers, concluded these units arc are characteristic of lake, swamp and tidal flat environments and that the majority of preserved preserved organic organic material material developed developedin in place. place. vugular also of interest because, at the White Pine mine, associated vugular The cupriferous zone is also porosity and fractures often are arc filled filled with small amounts amounts of solid solid and liquid liquid hydrocarbons. hydrocarbons. Analysis by Barghoom Barghoorn et al. (1965) indicates this Nonesuch crude oil contains higher concentrations of alkanes alkanes and and lower lower percentages percentagesof of aromatic aromaticss than an average crude crude oil, and and associated with Paleozoic production production in the the state state of of resembles the paraffinic crude commonly associated Pennsylvania. Further Furtheranalysis analysishas has indicated indicatedthe the oil oil is is indigenous indigenous to to its its host host rock rock (Eglinton (Eglinton et al., aL, 1964), is of organic origin (Moore et et al., al., 1969), and and was was formed formed under under mild mild formational temperature conditions (Barghoom environment is is also also (Barghoorn et et al., a!., 1965). A low thermal environment supported by Brown (197 I), who reported the presence of pink bornite and djurleite in (1971), reported presence of pink bornite and djurleite in the the Formation, minerals minerals which which cannot cannot exist exist above above respective respective ranges ranges of of 75 75 degree degreeCC Nonesuch Formation, and 95 degree C (167 (167 F F and 203 203 F). The Nonesuch crude presently represents one of the oldest known known liquid liquid hydrocarbon, hydrocarbon, being approximately 1,046 million years in age. This was determined for the Nonesuch host by approximately million years in age. using rubidium-strontium ratios. This date date is verified by the work of Ruiz et al. ratios. This a!. (1984), who obtained an age age of of 1,047 +I-35 cutting +1-35million millionyears years by by Rb-Sr Rb-Sr dating dating of of calcite calcite filled veins cutting 47 �acrossthe the cupriferous cupriferous shale shale of of the the Nonesuch Nonesuch Formation in the White As this this across White Pine Pine area. As calcite contains primary liquid oil inclusions, Kelly and Nishioka (1985) refer to this dateas as calcite contains primary liquid oil inclusions, Kelly and Nishioka (1985) refer to this date the time of oil entrapment and thus consider it as a minimum age for White Pine hydrocarthe time of oil entrapment and thus consider it as a minimum age for White Pine hydrocarbon. bon. The upper upper unit unit of of the the Oronto OrontoGroup, Group,the the Freda FredaSandstone, Sandstone,lies liesconformably conformablyover overthe theNoneNoneThe such Formation. The nature of the Freda Sandstone upper contact is not known for nowhere such Formation. The nature of the Freda Sandstone upper contact is not known for nowhere is this this formation formation found found in in exposed exposed (Myers, (Myers, 1971) 1971)or or drilled drilled contact contact with any any unit unit of of the the is Bayfield Group or its Michigan correlative, the Jacobsville Sandstone (Fig. 1). While listed Bayfield Group or its Michigan correlative, Jacobsville Sandstone While listed by Hite Hite (1968) (1968)as asexceeding exceeding3,660 3,660m min inthickness, thickness,only only1,500 1,500 m m is found found on on the the north north coast coast by of the Keweenaw Peninsula (Halls, 1966), near the type section at Freda, Michigan. The of the Keweenaw Peninsula (Halls, 1966), Michigan. The FredaSandstone Sandstoneisiscomposed composedof ofbasal, basal,subordinate subordinateconglomerate conglomeratefming-upward fining-upwardtotosandstone sandstone Freda color,aarepetition repetitionof ofthe theCopper CopperHarbor Harborred redto tobrown brownspectrum spectrumisisobserved, observed, andsiltstone. siltstone. InIncolor, and interrupted by spotty and laminar unoxidized zones (Daniels, 1982). With an analyzed maturity interrupted by spotty and laminar unoxidized zones (Daniels, 1982). With an analyzed maturity indexof of 0.63, 0.63, aafeldspar feldsparrange rangeof of 10 10to to24 24percent percent (Hite, (Hite,1968), 1968),and andthe thegrain grainshape shapebeing being index angular to sub-rounded, these sandstone units arc classed as immature. Daniels (1982) considers angular to sub-rounded, are immature. Daniels (1982) considers theaverage averagesand sandunit unitto tobe be aa fme-grained fine-grained feldspathic feldspathic lithic lithic arenite. arcnite. Sedimentary Sedimentarystructures structures the include cross-bedding, mud-cracks, graded beds, ripple marks, and a wide variation include cross-bedding, mud-cracks, graded beds, ripple marks, and a wide variation inin paleocurrentindicators. indicators. The Theimplied implieddepositional depositionalenvironment environmentranges rangesfrom fromfluvial fluvial(Daniels, (Daniels, paleocurrent 1982) to fluvial plain or tidal flat (Hamblin, 1961). 1982) to fluvial plain or tidal flat (Hamblin, 1961). Along the theeastern easternshore shoreof of Lake Lake Superior, Superior, in in the the Pt. Pt. Mamainse Mamainse region region of of Ontario, Ontario, aa 60 60m m Along section of gray sandstone is found unconformably overlying Keweenawan basalts. Work by section of gray sandstone is found unconformably overlying Keweenawan basalts. Work by Hamblin (1961) (1961)and and Annels Annels (1973) (1973)allows allows correlation correlation of of these these strata, strata, termed termed the the Mica Mica Bay Bay Hamblin sandstone, to the Freda sandstone and suggests a fluvial environment of deposition. sandstone, to the Freda sandstone and suggests a fluvial environment of deposition. Overallthe the Oronto OrontoGroup Groupcan can be be viewed viewed as as aa thick thick sequence sequence of of clastic clastic sedimentary sedimentary rocks rocks Overall that are stratigraphically unified by similar heavy mineral suites, an upward and distal dethat are stratigraphically unified by similar heavy mineral suites, an upward and distal dethree formations formations creasing in in grain grain size, size, and and an an upward upward increase increase in The three creasing in lithologic lithologic maturity. maturity. The of this group were derived from a common source of Keweenawan igneous material (Tyler of this group were derived from a common source of Keweenawan igneous material (Tyler et at., al., 1940). 1940).While Whileeach eachformation formationisisinterpreted interpretedin inlight lightof of slightly slightlydifferent differentdepositional depositional et environments, Elmore and Daniels (1980) view the group environment as a trangressiveenvironments, Elmore and Daniels (1980) view the group environment as a trangressiveregressivealluvial alluvialfan, fan,lacustrine lacustrineand andfluvial fluvialsystem systemthat that filled filledthe the developing developingMidcontinent Midcontinent regressive Rift basin during the final stages, and after cessation, of volcanic activities. Rift basin during the final stages, and after cessation, of volcanic activities. TheBayfield BayfieldGroup, Group,wherever whereverstudied, studied,isisfound foundto tobe be in in distinct distinct contrast contrast to to the the Oronto Oronto The Group. The TheBayfield Bayfieldsequence sequencedisplays displaysaahigher higherdegree degreeof of compositional compositionalmaturity maturityand and Group. structurallythe the bedding bedding is is more more commonly commonly subhorizontal. subhorizontal. In Interms termsof ofheavy heavyminerals mineralsthe the structurally tourmaline-zircon to epidote ratio is reversed in the Bayfield Group as compared to the Freda tourmaline-zircon to epidote ratio is reversed in the Bayfield Group as compared to the Freda and Nonesuch Nonesuch assemblages assemblages (Tyler (Tyler et et a!., al., 1940). 1940). There Thereisis aa question question as as to to the the type type of of contact contact and between these groups. Supporting an unconformable contact is the reported change in between these groups. Supporting an unconformable contact is the reported change in paleomagneticpole poleposition position(Du (DuBois, Bois,1962), 1962),the thechange changeinin accessory accessoryminerals minerals(Tyler (Tylereteta!., al., paleomagnetic 1940) and the immediate change from steep Oronto dips to low Bayfield dips (Morey and 1940) and the immediate change from steep Oronto dips to low Bayfleld dips (Morey and Ojakangas,1982). 1982).InInsupport supportof ofaaconformable conformablecontact, contact,or orone one of of minimal minimal hiatus, hiatus, is is the the lack lack Ojakangas, Orontoage age in in the the basal basal Orienta Orienta sandstone sandstone (Thwaites, (Thwaites, 1912), 1912), and and the the nature nature of of the the of clasts clasts of of Oronto of previously mentioned Freda Sandstone drag fold exposure in Douglas County, Wisconsin previously mentioned Freda Sandstone drag fold exposure in Douglas County, Wisconsin (Tyler et et at., al., 1940). 1940). From Fromaatectonic tectonicpoint pointof of view, view, Morey Morey and and Ojakangas Ojakangas (1982) (1982) state statethe the (Tyler 48 �______ 04 Isle Royale J•) Isle .o3rale1/ TI1iel P'a.u.lt .Superior ayfie 1 d a.sixi 3rx1clir1e - MI Jacosiile a.si ICe-we eu aw P'a.u. it I_i. Qre n P'a.tiit ..slilaxid sfilandSy-ricilne Sync line Basalt a.s a. it L1 Cla.st].os -Iiv-er F'ails $yucline l ] Ga.bbro u RIFT: I F T : NORTHERN N O R T H E R N SECTOR SECT-? OKm5O o Mi 25 OMi 25 FIGURE2:2:Midcontinent Midcontinent Rifi Systemtrend trendand andgeology geologyfrom fiomnorthwestern northwesternMinnesota Minnesotainto intothe the FIGURE Rift System Upper Michigan. Projection UpperPeninsula PeninsulaofofMichigan. ProjectionofofKeweenawan Keweenawangeology geology under underwestern westernLake L d eSuperior Superwr isis shown by hachured hachuredpatterns. patterns.From FromDickas D i c h(1986), (19861,reprinted reprintedby bypermission permissionofofthe theAmerican American shownby Association AssociationofofPetroleum PetroleumGeologists. Geologists. change changefrom fromOronto OrontototoBayfield Bayfield sedimentation sedimentationmarks marksaatransition transition from fkoman an extensional extensionalregime regime onecharacterized characterizedby byvertical verticaltectonic tectonicprocesses, pracessesyi.e., i.eaY theactivation activationof of the theSt. St.Croix Croixhorst horst totoone the by byuplifting upliftingof of4,600 4'600mm(Thiel, (Thiely1956). 1956). The Thetype typesection sectionfor forthis thisgroup p u pisisalong alongthe thesouthwestern southwesternshore shoreof ofLake LakeSuperior Superiorfrom fromthe the Apostle Islands to just east of Superior, Wisconsin. Reported group thicknesses Apostle Islands to just east of SuperioryWisconsin. Reported group thicknessesrange rangefrom fiomaa minimal minimal815 815mmininoutcrop outcrop(Craddock, (Craddocky1972), 1972)'totoaamaximum maximum2,100 2y100mmininthe thesubsurface subsurfaceasas suggested suggestedby byseismic seismicreview review(Mooney (Mmneyetetal., al.' 1970). 1970). Because Becauseofofthe therelative relativeuniformity uniformityinincomposition, composition,the thethree threeBayfield Bayfieldsandstones sandstonescan canbe bededescribedasasaaunit. unit.Thiel Thiel(l956) consideredthe theoverall overallcomposition compositiontotobebe99% 99%sandstone sandstoneand and1% 1% scribed (1956) considered shale. 80% shale.Peirographic PetrographicstudIed studiedbybyMyers Myers(1971) (1971)showed showedthat thatquartz q mconstitutes constitutesapproximately approximately80% ofofframework frameworkgrains. grains.The TheOrienta Orientaand andChequamegon Chequamegonsandstones sandstonesand andsiltstones siltstonesare arecommonly commonly red dinincolor colorand andfeldspathic feldspathicininmineralogy mineralogyand andcontain containlayers layersof of shale shaleand and conglomerate. conglomerate. The The Devil's Devil'sIsland Islandsandstone sandstoneisisbuff bufftotowhite whiteinincolor colorand andso soquartzose quartzoseas astotobe beclassified classifiedasasanan almost almostpure p morthoquartzite. o r t h o q d t e .An Anascending ascendingfluvial-lacustrine-fluvial fluvial-lacustrine-fluvialenvironment environmentofofdeposition depositionisis marks'and andaareturn return to tocross-bedding mss-bedding documentedby byrespectively, respectivelyytrough troughcross-bedding, mss-bedding' ripple ripplemarks, documented theChequarnagon ChequamagonSandstone Sandstone(Morey (Moreyand andOjakangas, Ojakangas,1982). 1982).Myers Myers(1971), (1971)'states statesthe the ininthe 49 �Bayfleld Keweenawan sediments Bayfield Group Group sedimentary sedimentary rocks rocks were derived mainly from older Keweenawan sediments and and probably represent the reworking of of Omnto Oronto Group Group units. units. Ojakangas O j h g a s and Morey (1982), (19821, however, believe the Bayfield were derived from an older granitic terrane. Bayfleld Group clastics we= 2), the basic structure of of Lake Lake Superior Superior is is aa continuation continuation of of West of the Thiel fault (Fig. 21, northwestern Wisconsin Midcontinent Rift Rift geology. geology. The Ashland syncline is projected offshore as as the Lake Superior syncline. Evidence Evidenceisislent lentby by northwest northwest dips dips of of Oronto OrontoGroup Group sedimentary sedimentary rocks along the Keweenaw Peninsula (Daniels, 1982) 1982) and the southeast dips in sedimentary rock of the same age which outcrop on the southwest shore of Isle Royale (Wolff and Huber, 1973). This This major major syncline syncline was was later later disrupted disrupted by reverse reverse faulting, faulting, forming forming the offshore offshore segment of the St. Croix horst (Fig. 2). Both Both the the Bayfield Ba*eld basin basin and andthe the St. Croix horst offshore extension are considered to be floored by Middle Keweenawan floored Middle Keweenawan Croix horst offshore extension are considered clastics clastics of the Oronto Oronto and/or Bayfield groups (Green, 1982). Thus, Thus, the the western western portion portion of of Lake Superior Superior is generally generally portrayed to to be immediately immediately underlain by Keweenawan Keweenawan Supergroup thickness (Ilinze (Hinzeet etal., al., 1982). 1982). Supergroupclastics clastics up to to 10 10km in thickness Michigan Michigan Section Section Keweenawan-age outcrops outcrops form the entirety entirety of the Keweenaw Peninsula jutting into into southsouthKeweenawan-age Thekeel keelof of this this peninsula peninsulais is formed formed of of Portage Portage Lake Lake Superior (Fig. 2). The central Lake Superior which all all Upper Upper Keweenawan Keweenawan sedimentary sedimenmy rocks rocksin inthe thearea arearest rest(Fig. (Fig.1). 1). volcanics, upon which Those outcrops outcropsnorth north and and northwest northwest of of the the Portage Portage Lake Lake Volcanics Volcanics form form the the classic classic Oronto Oronto Those Group. South South and and southeast southeastof of the the Portage Portage Lake Lake volcanic volcanic outcrop outcropbelt belt and andin in contact contactwith withthe the Group. Keweenaw fault fault is is found found aa thick thick sequence sequence of of northerly northerly dipping dipping clastics clastics named named the the Keweenaw Jacobsville JacobsvilleSandstone Sandstoneby by Lane Lane and and Seaman Seaman (1907) (1907) from from outcrops outcropsnear near Jacobsville, Jacobsville,located located near near the the southeast southeast base of the Keweenaw Peninsula. By By geologic geologic position these these outcrops outcrops appear to to be an an easterly easterly extension extension of the River Falls syncline. However, However, because because the the River River appear axtnot notinindirect directcontact contactdue duetotothe the Falls syncline synclineand andthe theJacobsvile Jacobsvillesandstone sandstoneoutcrops outcropsare Falls exposureof intervening interveningArchean Archeangranitoid granitoidrocks, rocks,this this area area of of Jacobsville Jacobsvillesandstone sandstonedeposition depositionisis exposure herein herein referred referred to to as as the the Jacobsville Jacobsvillebasin basin (Fig. (Fig. 2). 2). basin the the Jacobsville Jacobsvillesandstone sandstone has has aa maximum maximum thickness thickness of of 867 867m m by by drill drill hole hole In this basin measurement measurement (Kalliokoski, (Kalliokoski, 1982), 19821,but but on on the the Keweenaw Keweenaw Peninsula Peninsulaproper proper its its maximum maximum determined by geophysics to be approximately 3,000 m. The formation formationis is thickness has been determined m. The p~dominatelyquartzose quartzoseand andisis composed composedof of conglomerates, conglomerates, sandstones, sandstones, siltstones, siltstones,and and predominately shales, generally found found in repetitive upward-fining sequences. The The conglomerates conglomeratesare are generally generally basal, basal, up up to to 100 100m m in in thickness thickness and and contain contain clasts clasts composed composed of of iron iron formation, formation,vein vein quartz, volcanics, volcanics, and metamorphic rocks. The Thesandstones sandstonesare arefine fine to to coarse coarsegrained, grained, light light quartz, reddish reddish to to purple purpleto tomottled mottledcream-white cream-whitein in color colorand andcontain containstructures structuresranging rangingfrom fromcrosscrossbedding to oscillation oscillation and and current current ripple-marking. Shales Shalesand andmudstones mudstones appear appearto to be be in in the the The overall overall minority in terms of thickness and are found interbedded with laminated sands. The section section varies varies from from sub-arkose sub-arkose to to aa quartz quartz arenite, arenite, with with plagioclase plagioclasefound found more more commonly commonlyin in the the younger younger layers layers(Kalliokoski, (Kalliokoski,1982). 1982). The The Jacobsville Jacobsvillesandstone sandstonewas was derived derived from from highlands highlands situated situated to to the the southwest southwestand and southsoutheast fluvial, east of the the depositional depositional basin. The Thedetermined determinedenvironments environmentsof of deposition deposition include includefluvial, 50 �lacustrine, and alluvial fans. Because Because the the Jacobsville sandstone is nowhere found in direct dkct contact with either either the the Oronto Oronto or or Bayfield Bayfield Group Group formations, formations, its its exact exactrelationship relationshipwithin withinthe the Keweenawan Supergroup Supergroup is in some doubt. As As itit overlies overliesPortage Portage Lake Lake volcanics volcanics and and underlies the Late Cambrian Cambrian Munising Munising sandstone sandstone there seems seems little doubt doubt regarding regarding its its Keweenawan age. Considering Consideringthat thatTyler Tyleret et al. al. (1940) (1940)noted noted aa strong strong similarity similaritybetween between the the Jacobsvile JacobsvilleSandstone Sandstoneand andthe the Orienta Orientasandstone sandstone heavy heavy mineral suites and that Kalliokoski Kalliokoski (1982) (1982) related the Jacobsville Jacobsville Sandstone Sandstone to to the the Fond Fond du Lac Lac Formation Formation of Minnesota Minnesota on on the the basis of sediment, sediment, mineral, mineral, and and clay clay matrix comparison, comparison, most most workers workers today today consider consider the the Jacobsville Sandstone Sandstone to be a Michigan Michigan equivalent equivalent to the Bayfield Group Group of neighboring neighboring Wisconsin Wisconsin (Fig. (Fig. 1). 1). References References Annells, R. N., 1973, 1973,Proterozoic Proterozoic flood flood basalts basalts of eastern eastern Lake Lake Superior; Superior the the Keweenawan Keweenawan volcanic rocks rocks of the the Mamainse Mamainse Point Point area, area, Ontario: Ontario: Geological Geological Survey Survey of of Canada CanadaPaper Paper 72-10, 511p. 72- 10,5 Barghmm, E. S., W. G. Meinschein and J. W. Schopf, 1965, Paleobiology of a bcambrian Barghoorn, Precambrian shale: Science, Science, v. 148, 148, p. 461-472. Brown, A. C., C., 1971, 1971,Zoning Zoning in in the the White White Pine Pine copper copper deposit, deposit, Ontonagon Ontonagon County, County,Michigan: Michigan: Economic 543-573. Economic Geology, Geology,v. v. 66, 66, p. p. 543-573. Cox, D. P., R. G. Schmidt, Schmidt, J. D. Vine, H. Kirkemo, Kirkemo, E. B. Tourtelot Tomelot and and M. Fleisher, Fleisher, 1973, 1973, Copper, Copper, in Brobst, D. A. and and W. P. Pratt (eds.), United States mineral resources: U. S. Geological Geological Survey Survey Professional hfessional Paper Paper 820, 820, p. 163-195. 163-195. in Sims, Sims,P. P. K. K. and andG. G. B. B. Morey Morey(eds.): (eds.): Craddock, C., 1972, 1972,Regional Regionalgeologic geologic setting, setting,in Craddock, Geology of Minnesota: Minnesota: A A centennial centennialvolume, volume, Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 281-291. 28 1-291. Geology Daniels, Daniels, P. A., 1982, 1982,Upper Upper Precambrian sedimentary rocks, Oronto Oronto Group, Michiganin Wold, Wold, R. R. J., and and W. J. Hinze Hinze (eds.), Geology and tectonics of the Lake Wisconsin, in Wisconsin, Superior Superiorbasin: basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p. p. 107-133. 107-133. Dickas, A. A. B., B., 1987, 1987,Hydrocarbon Hydrocarbon potential of the Midcontinent Rift System, System, proceedings proceedings of Dickas, MidcontinentRift Rift System System Scientific ScientificDrilling Drilling Workshop, Workshop, Duluth, Duluth, Minn, Sept. 24-25, 24-25, Midcontinent 1987, 1987, p. 22-27. 22-27. DuBois, DuBois, P. M., M., 1962, 1962, Paleomagnetism Paleomagnetism and and correlation of Keweenawan rocks: Geological Survey 75 p. Surveyof of Canada CanadaBulletin, Bulletin,v.v. 71, 7 1,75 p. Eglinton, T. Beisky, Belsky, A. A. L. L. Burlengame Burlengame and and M. M. Calvin, Calvin, 1964, 1964,Hydrocarbons Hydrocarbons Eglinton, G., G., P. P. M. M. Scott, Scott,T. of biological 145, p. 263-264. biological origin origin from from aa one-billion one-billion year old sediment: Science, v. 145, Elmore, Elmore, R. R. D. D. and and P. P. A. A. Daniels, Daniels,Jr., Jr., 1980, 1980,Depositional Depositionalsystem system model model for for Upper Upper Keweenawan v. 61, 61, Keweenawan Oronto Oronto Group Group sediments, sediments,Northern Northern Peninsula, Peninsula,Michigan Michigan (abs): (abs): Eos, Eos, v. p. 1195. p.1195. 51 51 �Green, J. C., 1982, 1982, Geology Geology of the Keweenawan Keweenawan extrusive rocks, in Wold, Wold, R. J. and and W. W. J.J. Hinze Hinze (eds.), (eds.), Geology Geology and and tectonics tectonics of the Lake Superior Superior region: Geological Geological Society Society of of America America Memoir Memoir 156, 156,p. p. 47-55. 47-55. Halls, Halls, H. C., C., 1966, 1966,A A review review of of the the Keweenawan Keweenawan geology geology of of the the Lake LakeSuperior superiorregion, region,ininJ.J. S. Steinhart and T. J. Smith (eds.), The Earth beneath the continents: American Steinhart and Smith (eds.), The beneath the continents: AmericanGeoGeophysical physical Union Union Geophysical GeophysicalMonograph Monograph 10, 10,p. 5-27. 5-27. Hamblin, Hamblin, W. K., K., 1961, 1961,Micro-cross-lamination Micro-cross-lamination in in Upper Upper Keweenawan Keweenawan sediments sedimentsof of northern northern Michigan: v. 31, 3 1,p. p. 390-401. 390-401. Michigan: Journal Journal of of Sedimentary SedimentaryPetrology, Petrology, v. Hieshima, Hieshima, 0. G.B. B.and andL. L.M. M. Pratt, Pratt,1991, 1991,Sulfur/carbon Sulfur/carbonratios ratiosand and extractable extractableorganic organicmatter matter of the the Middle Middle Proterozoic Proterozoic Nonesuch Nonesuch Formation, Formation, North American American Midcontinent MidcontinentRift: Rift: Precambrian Precambrian Research, Research, v. v. 54, 54, p. p. 65-79. 65-79. Hinze, J., R. R. J.J. Wold Wold and and N. N. W. O'Hara, O'Hara, 1982, 1982,Gravity Gravity and and magnetic magneticanomaly anomalystudy study of of Hinze, W. W. J., Lake andW. W. J.J. Hinze Hinze(eds.), (eds.), Geology Geologyand andtectonics tectonicsof ofthe theLake Lake LakeSuperior, Superior,in in Wold, Wold, R. R. J.J. and Superior Superior basin: basin: Geological Geological Society Society of America America Memoir Memoir 156, 156, p. p. 203-22 203-221. 1. Hite, Hite, D. D. M., M., 1968, 1968,Sedimentology Sedimentologyof of the the Upper Upper Keweenawan Keweenawan sequence sequenceof of northern northernWisconWisconsin dissertation, University University of Wisconsin-Madison, Wisconsin-Madison,217 217 p. p. sin and and adjacent adjacent Michigan: Ph. D. dissertation, Hubbard, H. H. A., A., 1975, 1975,Geology Geology of of Porcupine PorcupineMountains Mountains in in Carp CarpRiver Riverand andWhite WhitePine Pine Hubbard, v. 3,3, p. p. 519-528. 519-528. quadrangles, Michigan: Michigan: U. U. S. S. Geological GeologicalSurvey SurveyJournal Joumal of of Research, Research,v. quadrangles, Hunt, T. T. S., S., 1873, 1873,The Thegeognostical geognosticalhistory historyofofmetals: metals:American AmericanInstitute Instituteof ofMining Miningand and Hunt, Engineering EngineeringTransactions, Transactions,v.v.1,I,P.P.33 331-345. 1-345. Kalliokoslci,J., J., 1982, 1982,Jacobsville JacobsvilleSandstone, Sandstone,in inWold, Wold,R. R. J.J.and andW. W. J.J.Hinze Hinze(eds.), (eds.),Geology Geology Kalliokoski, and and tectonics tectonics of of the the Lake Lake Superior Superiorbasin: basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p. p. 147-155. 147-155. K.Nishioka, Nishioka,1985, 1985,Precambrian Recambrimoil oilinclusions inclusionsin inlate lateveins veinsand andthe therole role Kelly, W. W. C., C., and and 0. G.K. Kelly, of of hydrocarbons hydrocarbonson oncopper coppermineralization mineralizationatatWhite WhitePine, Pine,Michigan: Michigan:Geology, Geology,v.v.13, 13,p. p. 334-337. 334-337. Lane, A. C. C. and andA. A. E. E.Seaman, Seaman,1907, 1907,Notes Noteson onthe thegeological geologicalsection sectionofofMichigan, Michigan,part part1,1,the thePrePreLane, A. Ordovician: Ordovician:Journal Journalof ofGeology, Geology,v.v.15, 15,p.p.680-695. 680-695. Mooney, H.M., M.,P.P.R. R.Famham. Famham.S.S.H. H.Johnson, Johnson,G. G.Volz Volzand andC. C.Craddock, Craddock,1970, 1970,Seismic Seismicstudies studies Mooney,H. over the Midcontinent Gravity High in Minnesota and northwestern Wisconsin: Minnesota over the Midcontinent Gravity High in Minnesota and northwestern Wisconsin: Minnesota Geological 1911p. GeologicalSurvey SurveyReport Reportof ofInvestigations Investigations11, 11,19 p. Moore, Moore,L. L.R., R.,J.J.R. R. Moore Mooreand andE. E. Spinner, Spinner,1969, 1969,AA geomicrobiological geomicrobiological study study of of the the Precambrian Precambrian Nonesuch Shale: Proceedings of the Yorkshire Geological Society, v. 37, p. 35 1-394. Nonesuch Shale: Proceedings of the Yorhhire Geological Society, v. 37, p. 351-394. Morey, Morey, G. G. B. B. and andR. R. W. W. Ojakangas, Ojakangas,1982, 1982,Keweenawan Keweenawansedimentary sedimentaryrocks rocks of ofeastern easternMinnesota Minnesotaand and northwestern northwesternWisconsin, Wisconsin,in inR. R. J.J. Wold Woldand andW. W.J.J.Hinze Hime(eds.),Geology (eds.),Geologyand andtectonics tectonicsofofthe theLake Lake Superior Superiorbasin: basin:Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, 156,p.p. 135-146. 135-146. 52 52 �Myers, W. D., 1971, sedimentology and tectonic significance of the the Bayfield Group (Upper Myen, 1971, The sedimentology Keweenawan?), Wisconsin and Minnesota: Ph. D. dissertation, University of Wisconsin-Madison, 269 p. Ojakangas. pm-volcanic quartz sandstones and related Ojakangas, R. W. and G. B. Morey, 1982, 1982, Keweenawan pre-volcanic rocks of the Lake Superior Superior region, region, in Wold, R. J. and W. J. Hinze Hinze (eds.), Geology Geology and and tectonics tectonics of the Lake Superior Superior basin: Geological Geological Society Society of America Memoir 156, 156, p. 85-96. Ruiz, J., L. M. Jones and W. C. Kelly, 1984, 1984, Rubidium-strontium dating of ore deposits hosted by Rn-rich rocks, using calcite and other common Sr-bearing Sr-bearing minerals: Geology, Geology, v. 12, 12, p. 259-262. 259-262. Thiel, E. C., 1956, 1956, Correlation Correlation of gravity anomalies anomalies with the Keweenawan Keweenawan geology of Wisconsin Wisconsin and and Minnesota: Geological Ivhnesota: Geological Society Society of America Bulletin, v. 67, 67, p. 1079-1100. 1079-1100. Thwaites, Thwaites, F. T., 1912, 1912, Sandstones Sandstones of the Wisconsin shore shore of Lake Superior: Superior: Wisconsin Wisconsin Geological Geological Bulletin, 25,117 25, 117p. and Natural History Survey Bulletin, p. Tyler, S. A., R. W. Marsden, F. F. Gmut Grout and G. A. A. Thiel, 1940, Studies of of the the Lake Superior PrePrecambrian cambrian by accesory-mineral accesory-mineralmethods: Geological Geological Society Society of America Bulletin, Bulletin, v. 51, p. 142914291538. 1538. White, W. S S., ., 1966, 1966, Tectonics of the Keweenawan basin, western Lake Superior region: U. S. E-l to E-23. Geological Survey Professional Professional Paper 524-E, p. E-1 White, W. S., and J. C. Wright, 1960, White, 1960, Lithofacies Lithofacies of the Copper Copper Harbor Conglomerate, Conglomerate, northern noxthem Michigan: Michigan: U. S. S. Geological Geological Survey Survey Professional Pmfessional Paper Paper 400-B, W B , p. p. B-5 B-5 to to B-8. B-8. Wolff, R. G. and and N. K K Huber, Huber, 1973, 1973,The The Copper Copper Harbor Harbor Conglomerate Conglomerate (Middle Keweenawan) Keweenawan) on on Isle Royale, Michigan, and its its regional implications: U. S. Geological Geological Survey Survey Professional mfessional Paper Paper 754-B, p. to B-15. B-15. p. B-1 B-i to 53 �____ _____ CENTRAL RWf DEVELOPMENT CENTRAL NORTH NORTH AMERICAN CASE FOR SEGMENTED RIFT DEVELOPMENT Reprinted with with permission permission from Dickas, Dickas, A. B. Reprinted B. and and M. M. G. G. Mudrey, Mudrey,Jr, Jr. 1989, 1989, Abstracts, Abstracts, 28th InternationalGeological GeologicalCongress, Congress,vol. vol.1,1,p. p. 1-396 1-396toto1-397. 1-397. International The The Midcontinent MidcontinentRift Rift System System (MRS) (MRS) is is aa major Middle Proterozoic Proterozoic intracontinental, intracontinental, thermotectonic therrnotectonic structure structure that that has has been been traced by regional regional gravity gravity and and magnetic magnetic data, data, subsursubsurface face drilling, drilling, and and outcrop outcrop control over a length of 3,300 km in the central United States. In In the Lake outcrop is is known, known, this this structure structurewas was Lake Superior Superior region, region, the the only only area area in in which which MRS outcrop infilled by plateau lavas and sedimentary rock comprising Keweenawan Supergroup. Supergroup. infihled comprising the Keweenawan About 1140 rift. After 1140 Ma, basalt was extruded along the rift. After cessation cessation of of volcanic volcanic activity, activity, generally elastic, sedimentary rock rock was was deposited. deposited. Geophysical Geophysical analysis analysis in generally maturing upward, clastic, the 1950's 1950's (Thiel, (Thiel, 1956) 1956)suggested suggestedaa broad broad graben graben with a central horst separating separating wedgeshaped rocks. These shaped thick accumulations accumulations of low-density sedimentary rocks. These sedimentary sedimentary sections sections were identified by negative gravity anomalies. Since Sincethen, then, models models and and geologic geologic maps maps of of the the rift have been consistent in demonstrating an early developed symmetrical extensional have consistent demonstrating developed symmetrical extensional crustal crustal basin filled filled with with extrusive extrusiveand and volcaniclastic volcaniclastic rock, subsequently subsequently modified modified by by latelatephase compressional faulting forming the presently identified central horst (Fig. 2, previous phase compressional faulting forming the presently identified central horst (Fig. 2, previous paper). rN % 14 w IL NE MO KANSAS KS @ Gravity High High Gravity o ioo #11 o OH I io - 1 Gravity Low Low Gravity r///,2 Accommodation AccommodationStructure Structure FIGURE 3: 3: Gravity FIGURE Gravityexpression expressionofofthe theMidcontinent Midcontinent Rift System, R4ft System,showing showingthe thelocation location and and extent offirstofflrstorder rift riftzones. zones. order 54 Recent Recent acquisition acquisition of over over 4200 4200 km of onshore onshore and and offshore offshore reflection reflection seismic seismic data data and and analyanalysis sis of deep deep mineral mineral exploration exploration drill drill holes holes from from northern northern WisconWisconsin sin suggest suggest aa different differentgeometry geometry for the MRS. This geometry, for This geometry,as as proposed here, is similar similar to to strucstructures attributed attributed to to the Gregory Gregory rift rift in East Africa. Bosworth al. Bosworth et et al. (1986) (1986) suggest suggest the the Gregory Gregory rift rift structure structure formed formed through through the the development of deep, crustal, crustal, opposing detachment systems. As these detachments intersect at depth, depth, one one side side locks, locks, resulting resulting in in half-graben development. development. With lateral rift propagation, propagation, aa subresubrelateral gional gionalseries seriesof oftaphrogeosynclines taphrogeosynclines (haif-graben) (half-graben) are formed, formed, with adjacent adjacent grabens grabens displaying displaying igneous igneous and sedimentary sedimentary infill infill packages of opposing geometry. opposing geometry. The initial rift is thus unable unable to extend extend laterally laterally in uniform uniform strucstructural patterns but rather forms a linear linear pattern of individualized, individualized,en en echelon, asymmetric asymmetric basins, each each �history and and geometry geometry and each each separated by a type of cross-structure, cross-structure, with its own infihling infilling history generally referenced as "accommodation" faulting. faulting. On a regional regional basis, the fmal final structural configuration of a rift may also be dependent upon total extension developed at right angles to rift propagation. Schuepbach (1980) suggest Schuepbachand andVail Vail(1980) suggest that with such differential differential rift development, and even though structural extension along rift strike may be synchronous, basin formation and filling fifing could (1984) supcould be diachronous. Quenneil Quennell(1984) ported ported this this evolution evolution by by mapping mapping the the Dead Dead Sea Sea rift as divided divided into three three unique segments, segments,each each operating operating independently in geologic development. Viewed Viewed as as an an entirety, entirety, a rift may thus display first-order, representing coeval stages first-order, regional-size regional-size rift rift segments segments(Dickas, (Dickas,1986), 1986), representing stages of differing differingrift rift maturity. In Inturn, turn,these thesesegments segmentsmight mightbe be divided divided into into subregional-sized, subregional-sized, second-order second-order subbasins separated separatedby by "accommodation" "accommodation" faulting. faulting. Viewed Viewed from from the the perspective perspective of this this geometry, geometry, the the extent extent of the MRS is is here here interpreted interpreted to to be composed (1987). Clockcomposed of of five five first-order first-order rift rift segments, segments, termed termed "zones" by by Rosendahi Rosendahl(1987). Clockwise from are here named Kansas, Kansas, Iowa, from the the southwestern southwestern end end of the the MRS. MRS, these zones are Superior, identified on the basis of major major interrupinterrupSuperior, Mackinaw, Mackinaw, and Maumee (Fig. 3), and are identified tions tions in gravity gravity and and magnetic magnetic patterns, patterns, seismic seismic review, review, terrane terrane compositions, compositions, and and borehole borehole analysis. analysis. function of of overall overall rift rift extension, extension, zones zones may may be be further further divided divided Locally, and and developing developing as as aa function Locally, into into a series series of structurally structurallyindependent independent basins. These These second-order second-order sub-basins, sub-basins, termed termed by Rosendahi Rosendahl(1987), Withinthe theSupeSupe"units" by (1987), are separated by "accommodation" faulting. Within rior rior zone zone of of the the MRS, MRS, four four units units are are now now recognized recognized on on the the basis basis of of seismic seismicinterpretation, interpretation, interrupted geopotential geopotential trends, and core analysis. These These sub-basins sub-basinsare are here here named named the the interrupted These units appear appear to to have have underChisago, Brule, Ontonagon, and Manitou units units (Fig. (Fig. 4). 4). These similar history of structural structural development development during the early phase of MRS evolution. evolution. gone a similar On On the the basis basis of differential differential listric listric movements movements along along axial-oriented, axial-oriented,rift rift fault fault systems, systems,igneous igneous and and sedimentation sedimentationwedges wedges of alternating alternating isopach isopach patterns patterns distinguish distinguish juxtaposed zones. patterns of of these these wedge wedge geometries geometriesdiffer differ by by being being symmetrical symmetricalparallel, parallel, but but alteralterIsopach patterns nating asymmetrical asymmetrical perpendicular, perpendicular, to to the the MRS MRS axis. axis. nating In light light of this suggested suggested model, future future stratigraphic stratigraphic and and seismic seismic correlations correlations can no longer longer be be the framework frameworkof of aa symmetric symmetric rift rift model model existing existing along along the the entirety entiretyof of the the interpreted within the bedependent dependentupon upon consideration considerationof of isolated isolated igneous igneous MRS axis. axis. Instead, Instead,such suchcorrelations correlationsmust mustbe MRS and sedimentary sedimentary packages packages and isopach geometries created in response response to to first- and and second-order second-order and be directed directed to to basebasedegree of tectonic development. development. Exploration Explorationphilosophies, philosophies, whether whether they they be degree metal or hydrocarbon evaluation, must be constrained so as to recognize related regional and metal or hydrocarbon evaluation, must be constrained so as to recognize related regional and subregional subregional alterations alterationsin in structural structuralstyle. style. 55 �Central Structure (St. Croix Horst) SCHEMATIC SECTION FIGURE FIGURE4: 4:Structural Structuralrift riftunits unitscomposing composingthe theSuperior Superiorrift riftzone, zone,Midcontinent MidcontinentRift Rift System, System, as defined by accomodation accomodation structures structures(A.S.) (AS.) and isopach isopachthickening thickening trend, trend, References References 1986, A new look at Gregory's Rift: Rift: the the strucstrucBosworth, W., J. Lambiase, and R. Keisler, 1986, tural style 582-583. style of continental continental rifting: Eos, v. 67, p. 557, 557,582-583. Dickas, A.B., 1986, Seismologic analysis of arrested stage development A.B., 1986, development of the Midcontinent Rift, in M.G. Mudrey, Jr. (ed), Precambrian petroleum potential, Wisconsin and Michigan: Geoscience Wisconsin, Wisconsin Geological and Natural History Survey, v. 11, p. 45-52. Quennell, A.M., 1984, The western Arabia rift-system, in J.F. A.H.F. Robertson Robertson A.M., 1984, J.F. Dixon and A.H.F. Society Special Special (eds.), The geological geological evolution of the eastern Mediterranean: Geological Geological Society Publication 17, Publication 17, p. 775-788. Rosendahl, B.R.,11987, B.R.,11987, Architecture of continental special reference reference to to East EastAfrica: Africa: Rosendahi, continental rifts with special Annual Review Earth Earth and and Planetary Planetary Science ScienceLetters, Letters,v. v. 15, 15, p. 445-503. 1980, Evolution of outer highs on divergent divergent continental continental Schuepbach, M.A. M.A. and P.R. P.R. Vail, 1980, margins, in Continental Continental tectonics: tectonics: National Academy of Science, Science, 197 197 p. p. 56 1956, Correlation of gravity gravity anomalies anomalies with the Keweenawan geology geology of of WisconWisconThiel, E., 1956, sin and Minnesota: Geological Society of America Bulletin, v. 67, p. 1079-1100. 1079-1100. �LAKE FRONTIER LAKE SUPERIOR SUPERIORBASIN BASIN AS AS A HYDROCARBON FRONTIER Mod(fied from aa series of requested articles written by Albert Albert Dickas Dickasfor for the daily print print media Modified from of January, 1992, during site preparations preparations for the the Terra/Patrick TerrdPatrick#7-22, #7-22, of northwest Wisconsin,January, Bayjield County, County,Wisconsin Wisconsin exploratory exploratory wildcat. wildcat. Since Since the initial discovery of crude oil at a depth of 21.2 m beneath the rolling hills of Titusville, Titusville,Pennsylvania Pennsylvania in in 1859, 1859,hundreds hundreds of of thousands thousands of of boreholes boreholeshave havesought soughtthis this natural resource in the United States. Wisconsin Wisconsin has played a small role in this 133 133 year old "hydrocarbon revolution." Between 49 boreholes Between 1865 1865and and 1992, 1992,49 boreholes have sought economic volumes of oil oil or or gas gas in the the Badger state. Not Notone oneof ofthese thesewells wellshowever, however,has hasfound foundanyanything thing other other than than fresh fresh and and salt salt water. water. The The majority majority of of exploration exploration in in Wisconsin Wisconsin has has taken taken place place close close to to the the Lake LakeMichigan Michiganshoreshoreline (Fig. 5). 5). Here line between Milwaukee and Door County (Fig. Here the rocks form the western edge of the Michigan Michigan basin, basin, one one of of the the most most prolific prolific producers producers of of hydrocarbon hydrocarbonin in the theUnited UnitedStates. States. Unfortunately, Unfortunately, this this productivity productivity is is basically confined to the deeper deeper portions portions of the basin, and and not not along alongits its edges. edges. The Theremaining remainingarea areaof ofWisconsin Wisconsinhas haslong longbeen beenconsidered considerednon-producnon-productive because of the great geologic age and physical nature of much of its bedrock. tive because of the great geologic age and physical nature of much of its bedrock. In In the the early early 1980s, 1980s,pessimism pessimism turned turned to to guarded guarded optimism. optimism. Petroleum Petroleumgeologists geologistsbegan begantoto recognize recognize that that rocks rocks deposited deposited during during early early chapters chapters of earth earth history--the so so termed termed PrecamPrecambrian brian Eon--possesses, Eon--possesses, contrary contraryto to conventional conventionalwisdom, wisdom,those thoseseven sevento toeight eightcharacteristics characteristics necessary necessary for for the the development development of of an an oil oil or or gas field. field. Studies Studies suggested suggested these characteristics characteristics were often often contained containedwithin within rift rift structures, structures,formed formed by the the dissection dissection of pre-existent pre-existent conticontias Africa Africa is is presently presently being being torn tom into into portions along along the the African African Rift Rift Zone. Zone. nents, much as has been been known known for for 35 35 years years that that northwestern northwestern Wisconsin Wisconsin occupies occupies aa portion of of the the worldworldItIt has krn from from Kansas Kansas to to Ohio Ohio by way way of Lake Lake class Midcontinent Midcontinent Rift Rift System, System, extending extending3300 3300 km class Superior. With Withthe therecognized recognizedassociation associationof of ancient ancientrift rift rocks rocks with with economic economichydrocarbon hydrocarbon Superior. reserves, that that portion portion of of the theMidcontinent Midcontinentrift rift lying lyingbetween between the the upper upperpeninsula peninsulaof of Michigan Michigan reserves, and Kansas Kansas was was quietly quietly invaded invaded by the United States oil and gas industry. Initial Initialinterests interests and included Mobil, Mobil, Texaco, Texaco, Standard Standard of California, and Amoco, among others. Field Fieldcrews crews included 1980's and andspecial special "frontier "frontier region" region" analysis analysisteams teams of of geologeolobegan operating operating in the early early 1980's began gists, geophysicists, geophysicists, paleontologists, paleontologists, and geochemists were formed. Studies Studiesranged ranged from from gists, hand investigation investigationof of rock rock samples samplesto to sophisticated sophisticated computer computer reviews reviews of of newly newly collected collecteddata data hand pertaining pertainingto tothe theseismic, seismic,magnetic magneticand andgravity gravitycharacter characterof ofthe therift. rift. In 1984 1984Texaco Texacomade madethe thefirst firstmove moveby bydrilling, drilling,ininnortheast northeastKansas, Kansas,their their#1 #1Noel Noel Poersch Poersch In well 3444 m. m. InIncertain certainaspects aspectsthis thiswas wasaaguinea-pig guinea-pigborehole. borehole. well to to aa record record state statedepth depth of of 3444 Because Because the the rift rifthad had never never been been drilled drilledbeyond beyond normal normal water-well water-welldepths depthsof ofseveral severalhundreds hundreds of of feet, feet, industry industry was was probing probing into into the geologic darkness. Expectations Expectationswere were based based upon upon comparison comparisonof of Kansas Kansasdata datato tothe thenear-surface near-surfacegeology geologyof ofDouglas Douglasand andBayfield BayfieldCounties, Counties, Wisconsin, aa region region where rift rocks are exposed at the surface and The Wisconsin, and thus thus easy easy to to study. study. The Texacodrilling drilling plan plan envisioned envisionedseveral several thousands thousands of feet feet of sandstone sandstone and organic organic shale shale Texaco overlyingan an even even thicker thicker sequence sequence of layered layered lava. Under Underideal idealconditions conditionseither eitheroil oil or or gas gas overlying would have formed within the organic shales and subsequently moved upward into the would have formed within the organic shales and subsequently moved upward into the sandstones sandstones until until trapped trapped and andconcentrated concentratedinto into an an economic economic "pool." "pool." 57 �Drilling results were were not not released released until until mid-1988. mid-1988. This Drilling ceased in early 1985 1985 but detailed results three year delay made sense when information became becamepublic. public. The drill sequence sequence appeared reversed when compared to expectations, with lava and related igneous rock overlying overlying thick thick sandstone layers. Shale Shalewas was found found only only in trace trace amounts amounts and that shale present was not not possible. possible. The organic. Without Without organic organic shale shale an oil or gas field is not The Texaco Texaco well was classed as "dry and and abandoned" abandoned" and and exploration exploration geologists geologists began began to to reinterpret reinterpretthe the geologic geologic history of the Midcontinent Midcontinent rift. rift. Amoco Amoco Production Production Company Company was was the the second second major major player player to to enter enter the thesearch searchfor forPrecamPrecambrian-age rift hydrocarbon. Disenchanted Disenchantedby by the the Kansas Kansas results, results, Amoco Amoco geologists geologistschose chose west-central Iowa as their preferred drilling site. In 1987their their#1 #1Eischeid EischeidboreboreIn March March of of 1987 hole was set into operation and seven months later reached 5,441 m. m. reached a state state depth depth record record of of 5,441 This This borehole was shrouded in secrecy, protected by fence and guard. Under Underfavorable favorable weather weather conditions conditions a nearby hill was covered covered with curious curious observers observers and and industry industry scouts scouts and and skimpy reports were issued daily daiiy by the media. media. Even Even after after the the projected projected depth depth was was reached reached Amoco, Amoco, following following the lead established by Texaco in Kansas, maintained secrecy. With With the the release 1990 encouragement was given by the fact a normal release of information information in the spring spring of 1990 sequence of rock colunm column was drilled--shales were found found and they were organic. organic. The The high high risks risks associated associatedwith with the the oil oil and and gas gas business business is is largely largely attributed attributed to to the the fact fact that that while while the the proper proper conditions conditions for for an an economic economicreservoir reservoir are are often often found, found,the the sought soughtafter afterproduct productisisoften often absent. The Iowa venture was high risk in planning and execution and the end result was The Iowa venture was high risk planning and execution and the end result was labeled labeled "dry and and abandoned." The The third third borehole borehole to to test the Midcontinent rift was initiated in late 1987 and completed two months later. The Theoperator operatorwas wasagain again Amoco Amoco Production Production Company, Company, but now the geographic geographic site months finaltotal totaldepth depthwas was near the upper peninsula community community of Munising, Michigan. The Thefmal was near 2210 m. While Whilecomplete completeinformation informationhas has not not yet yet been released, it has been reported that all 2210 formations composing composing the the target Oronto Oronto Group Group were drilled--but not in the the normal three of the formations order order as as known known from fromWisconsin Wisconsingeology. geology. It is is interesting interesting to to note note this this borehole borehole is is located located in in aa region region of of historic, historic, little little known, known, exploraexploraIt In1865 1865the theOntonagon OntonagonPetroleum PetroleumCompany, Company, financed financed by by aa capital capital stock stock tion for crude oil. In $500,000, was was formed formed for for the the purpose purpose of "engaging in in and and carrying carryingon on the thebusibusioffering of $500,000, offering mining~petroleum."By ByDecember Decemberof of that that year yearthe the first first and and only only venture venture of of this this ness of mining---petroleum." company was was underway, underway, fueled fueledby by aa rapid rapid increase increase in in the the price price of of oil oil stock stockand and an an outbreak outbreak company While microfilm microfilm records indicate "two Thefinal finaldrilling drilling depth depth was was 38 m. While of "oil fever." The (of oil) oil) have have been been hoisted hoisted up," up," there there isis no no record record of of the the Ontonagon OntonagonPetroleum PetroleumComCombarrels (of pany pany beyond beyond the the year year of of its its incorporation. incorporation. Since Since 1929 1929 active active underground underground oil oil seeps seeps have have been been reported reported from from the the White White Pine Pine mine minein in Ontonagon County, County, Michigan. Analyses Analysesshows showsthis thiscrude crudeto tobe be very very similar similarchemically chemicallyto to Ontonagon high grade grade oil of Phanerozoic Phanerozoic age produced in the state of Pennsylvania. Radiometric Radiometricageagedating techniques techniques suggest suggestthe the White White Pine Pine product product may may be be the the oldest oldest known known crude crudeoil oilin inthe the dating Whilethese thesevolumes volumesare aremodest, modest,their theirpresence presencekeeps keeps alive alive the the possibility possibility of of "black "black world. While gold" gold" production productionin in northern northern Wisconsin. Wisconsin. 58 �As As of of early early March, March, 1992, 1992,site sitepreparation preparation was was underway underway for for the the fourth fourthtest testof ofthe thehydrocarhydrocarbon potential potential of of this this rift. rift. Located Located in in Bayfield Bayfield County, County, Wisconsin, Wisconsin, this this wildcat wildcat has has been been programmed programmed as as aa 1825 1825m m (6000 (6000ft.) ft.) test test of of the the Oronto Oronto Group Group in its position position overlying overlying the the central St. Croix horst. Available information on this TerraPatrick Terra/Patrick #7-22 borehole will be presented presented in in the the Proceedings Proceedings volume volume of this 38th meeting of the Institute on Lake Superior Superior Geology. Geology. 59 �60 Wisconsin. in degrees 75 and areas, River Isle Presque and Pine White the in grees de- 10 about to area Mountain Porcupine the in overturned from varies tude atti- Structural rn/km. 4 than more at basinward thickens Nonesuch the Park, State Isle Presque of east km 40 about area Pine White the In southwest. the area. to thins generally and thickness, in m 180 about averages Nonesuch The Pine White the in petroliferous is and material organic in rich is rock The dikes. clastic as such features dewatering and bedding graded show many and microscale, in common are alternations grain—size rhythmic Thin, thick. mm 1 than less laminae many with laminated evenly to massive—appearing from ranges bedding The color. in darkest the is rock grained finest The sandstone. medium to shale black to gray medium a is Nonesuch the Generally, quences. se- bed red overlying or underlying the than maturity compositional and tural tex- greater of generally and color in drab more is Nonesuch The Description: 1968 Hite, from (modified 1982) Daniels, and Jr. Daniels, P.A. and Jr. Mudrey, M.G. Authors: 1956). quadrangle, topographic 15—minute (Thomason Michigan County, Gogebic W., 45 R. N., 50 T. 30, and 19 Sec. River, Isle Presque the of Mouth Location: Formation Nonesuch — Park State Isle Presque Title: �Both The The Nonesuch Nonesuch possesses possesses aa great great variety variety of of sedimentary sedimentary features. features. Both Laminated stratifiLaminated stratifihorizontal stratification and cross stratification occur. horizontal stratification and cross stratification occur. irregular, and and ripple ripple stratifistratification lenticular, wavy or irregular, cation is is the the most most conmion; common; lenticular, 60 cm cm in in thickness, thickness, and and the the thicker thicker cation also also occur. occur. Units rarely exceed exceed 60 Units rarely cation beds are are coarser coarsersandstone sandstoneand and conglomerate. conglomerate. Alternating Alternatinglaminae laminae of of fine fine beds common. gray sandstone sandstoneand and black black shaley shaley ailtstone siltstoneless less then then 0.5 0.5 cm can thick thickare are common. gray The cross—stratification cross-stratification is is of of two two types, types, planar planar cross cross stratification stratification and and rib rib The and furrow. furrow. Both Both of of these these types types are are abundant abundant on on the thePresque Presque Isle IsleRiver River in in and Michigan. Shrinkage Shrinkage cracks cracks and and disturbed disturbed bedding bedding occur occur locally locallyand and sometimes sometimes Michigan. abundantly. Sediment Sediment and and current current transport transport data data support support aa dominant dominant flow flow abundantly. in the regime to tothe the west-southwest during during deposition deposition of of the theNonesuch Nonesuch in thePresque Presque regime west—southwest Islearea. area. Isle Discussion: The The sedimentary sedimentary structures indicate that that the the depositional depositional envienvistructures indicate Discussion: ronment ronment of of the the Nonesuch Nonesuch Formation Formation was that of of a standing standing body of of water, with with was at at least least high high perhaps significant significant variation variation in in water waterdepth. depth. Salinity Salinity was perhaps enough to to precipitate precipitate gypsum. gypsum. enough initial - The initial formation formation of of this this water water body body could could have have occurred occurred either either due due The to creating a closed topographic to subsidence subsidence along along the the rift, creating topographic low low that would as local local base level, or perhaps, more likely, the the disruption disruption of of rethen act act as then gionaldrainage drainagepattern pattern sometype type damming. gional bybysome ofof damming. 61 �Title: Parker Parker Creek Creek —- Oronto Oronto Group Group IR 47/O1E/30 47/01E/30 Location: Location: Approximately 300 300 a m upstream to to the the southeast southeast from from the the northwest northwest corner Sec. 30, 30, T. T. 47 47 N., N., H. R. 1 F., E., Iron Iron corner of of section section 30. 30. NWl/4, NW1/4, Sec. County, Wisconsin (Oronto (Oronto Bay Bay 77 1/2—minute 1/2-minute topographic topographic quadrangle, quadrangle, 1980). Author: Author: M.G. Mudrey, Mudrey, Jr. Jr. (modified (modified from from Myers, Myers, 1971 1971 and and Rosenberry, Rosenberry, 1924) 1924) M.G. Description: Description: Approximately Approximately 600 600 am of of continuous continuous exposure exposure from from the the last last Kewee— Keweenawan nawan lava lava flow, flow, through through the the Copper Copper Harbor Harbor and and Nonesuch Nonesuch Formations Formations into into the the lower of the the Freda Freda area area exposed exposed along along Parker Parker Creek Creek (also (also known known as as Davis Davis lower 300 300 in m of Creek). Creek). Because Because the the upper upper reaches reaches of of the the creek creek tend tend to to run run parallel parallel to to the the bedding, bedding, the the Copper Copper Harbor Harbor appears appears to to be be much much thicker thicker than than normal. normal. All E., 85 85degrees degreesNW. NW. There There are are aa All of of the the units units trend trend N. N. 60 60 degrees degrees F., few, very minor minor flexures flexures and and faults faults in in the the wall wall of of the the valley, valley, but but the the sec— secfew, very tion tion appears appears to to be be continuous continuous with with no no repetition repetition by by faulting. faulting. Approximately Approximately 200 200 mm of of Copper Copper Harbor Harbor Formation Formation are are exposed exposed in in the the upper upper reaches reaches of of the the creek. creek. The The unit appears appears to to consist consist of of five five main main conglomeritic conglomeritic zones 60 am in thickness, thickness, interbedded zones about about 30 30 to to 60 interbedded with coarse, coarse, sandy sandy 62 �conglomerate. Both Both lithologies lithologies are are clast—supported clast-supported conglomerate. conglomerate. The The Copper Copper conglomerate. Harbor is is relatively relativelytypical, typical, consisting consistingof of rounded rounded cobbles cobblesof of Keweenawan Keweenawan volvolHarbor canic canic rock rock and and granite graniteand and iron iron formation formationfrom from the the underlying underlyingEarly Early Protero— Proterozoicand and Archean Archeansuccession. succession. zoic About310 310inm of of Nonesuch Nonesuch Formation Formationis isexposed. exposed. The The Nonesuch Nonesuch consists consists of of About The lower lower several dark dark colored colored slate slate units, units, interbedded interbedded with with sandy sandyslate. slate. The several contact contact of of the the Nonesuch Nonesuch and and the the Copper Copper Harbor Harbor is is gradational gradationalin inthat thatthe the nonconglomerate asthe theupper upper nonconglomerateinterbeds interbeds become become finer finer grained grained and and more more abundant abundantas Bedding is is clearly clearly defined defined in in the the contact with with the theNonesuch Nonesuch isisapproached. approached. Bedding contact Nonesuch, Nonesuch, and and local local cross cross bedding bedding and and deformation deformation structures structures can can be be recogrecognized. The The upper upper contact contact of of the the Nonesuch Nonesuch with with the the Freda Freda is is also also gradational gradational nized. in that thatsand sand beds become more commonand and slate slatebeds beds less lessso. so. beds become more common in of the the Freda Freda Formation Formation is is aa thick The lower lower member member of thickbedded, bedded,fine— fine- to to The Local pebble Local pebble is strongly stained with iron. mediwgrained sandstone that is strongly stained with iron. medium—grained sandstone that The middle middle Member Member of of the the Freda Freda is is seen seenonly onlyat at the the zones are are common. common. The zones It is much better exposed in Spoon Creek It is much better exposed in Spoon Creek creek. northernmost outcrop in the creek. northernmost outcrop in the and very fine—grained sandsiltstone This member consists of siltstone and very fine-grained sandto the west. This member consists of to the west. stone with with occasional occasional shale shale and and cross—stratified cross-stratified fine—grained fine-grained sandstone sandstone stone to compared beds. Bedding is more pronounced in the middle member Bedding is more pronounced in the middle member compared to the the lower lower beds. member. The The upper upper member member of of the the Freda Freda is is best best seen seen at at the the mouth mouth of of the the member. The Montreal Montreal River River to tothe theeast, east, particularly particularlyat at Superior SuperiorFalls FallsininMichigan. Michigan. The upper member member consists consists of of thick thick bedding bedding units units of ofmicaceous micaceous siltstone, siltstone, very very upper fine—grained, fine-grained, laminated laminated sandstone sandstone with with abundant abundant scours scours and and and and current current direcdirection tion indicators, indicators, and and slightly slightly conglomeritic, conglomeritic, fine—grained fine-grained sandstone sandstone with with bedbedding poorly poorly developed. developed. The The White White River River location location is is probably probably in in the the upper upper memmemding ber. ber. Discussion: Clearly, Clearly, the the Oronto Oronto Group Group represents represents aa single single depositional depositional epiepiDiscussion: sode, the the individual individual formations formations representing representing various various environments environments within within that that sode, episode. All All of of the the units units appear appear to to be be gradational. gradational. The The Freda Freda appears appears to to episode. thicken from from its its type type locality locality near near Freda, Freda, Michigan, thicken Michigan, to to the the Montreal Montreal River River and west. west. The The Nonesuch, Nonesuch, conversely, conversely, appears appears to to thin thin toward toward the the west west from from and Presque Isle Isle State StatePark. Park. At At Copper Copper Falls Falls State State Park Park the the dominant dominant shale shale unit unit Presque the shale-bearing shale-bearing interval interval is thick; however, however, the appears to to be be less lessthan than2020inm thick; is appears thick. about140 140inm thick. about All along along the the Gogebic Gogebic Range, Range, the the Early Early and and Middle Middle Proterozoic Proterozoicunits units dip dip All northwest at at aa steep steepangle. angle. Reconstruction Reconstruction of of the the thickness thicknessof of the thesection section northwest results in in an an estimate estimate that that is is too too thick, thick, 20 20 km km of of section section from from Hurley Hurley to to results Lake Superior. Superior. In Keweenaw and and In Michigan Michigan this iseasy easyto tounderstand understand as as the the Keweenaw this is Lake associated faults faults clearly clearly repeat repeat parts parts of of the the section; section; however, however, in in Wisconsin Wisconsin associated because of of poor poor exposure, exposure, the the faults faults are are not not readily readilyrecognized. recognized. As As will will be be because seen and and discussed discussed at at White White River, River, there there is is at at least least one one major major anticline anticline seen known in in outcrop outcrop at at Marble Marble Point, Point, and and at at least syncline with with the the least one one major major syncline known Freda. AA more more reasonable reasonable estimate estimate for for the the total total thickness thickness of of the the Oronto Oronto Freda. km. Group would would be be 55 km. Group 63 �NE 25 0 Distance NE25 D i s t a n c e ffrom rom N E 2 5 tto o El/4 E 11425 25 == 1/2 112 mile mile ml conglomerate conglomerate Lo.QI sandy s a n d y conglomerate conglomerate sandstone •:.:1...sandstone sandstone s a n d s t o n e and a n d shale shale -.A. shale slate conglomerate ale glomerate ;hale late on glomerate andy conglomerate ate 0 E '/425 Sketch of o f geology geology in i n Parker Parker Creek Creek from from Rosenberry Rosenberry (1924). (1924). Sketch 64 �70 ::.'.) Silistone ona shole,grOy to block, alter- noting and laminated to 40 very thin bedoccasional •35 medium- to coorse-grained sandstone units 3 to 6" thick o few frne, thin- bedded sand(UNIT 4) 65 ---tones Unit 2 :=2-:- SttsIns. —--=. ded (1/4— I"); Ss, some Os -- lTt.oi alternating and ::_l laminated, with tUN IT 7) 90 alternating, some Unit I. irregular irregular bosal basal contocis, contocfs, generolly generally (UNIT 3) .;)5ac.irflobIW. 61 — sm.— to c.- grain— sole-morks Sandstone, Sandstone, blactc block medium— to coarsemedium- to coorsegroined. groined. some some Ss. blk., vTto c.—groined thin to thick 85 thick—bedded thick-bedded (UNIT ( U N I T 8) 8) bedded (UNIT 6 (UNIT I) 30 Stratigraphic Stratigraphic section section showing showing 100 100 feet of of typical typical Nonesuch Nonesuch Formation Formation (figure (figure 20 of of Rite, Hite, 1968). 1968). 20 Stratigraphic Stratigraphic section section showing showing 100 100 feet feet of of typical typical Lower Lower Freda Freda Formation Formation (figure (figure 30 30 of of Rite, Hite, 1968). 1968). 65 �Stratigraphic section showing Stratigraphic section showing 100 100 feet of typical typical Middle Freda Freda Formation Formation (figure 33 of of Hite, Hite, 1968). 1968). (figure 33 Siltstone, red micoceous and Siltstone, red rnicoceous,lOm- laminated, 1terbedded with irioted with sholes ond cross-bedded siltstones, inter— 21 70 C\ stratified (UNIT 3) I Sandstone, red very fine— to tine groined, 10mm— 65 oted,w,th 40 U. :.—• ... —.....- .: bedding which becomes more abundant upword in the section distorted bedding rn central 60 part of the unit. 6iltstone, red micaceous, irregular lam— motions with micro (ripple) cross—stab (UN IT 4) in upper part. interbedded St red, fine-grained (UNIT 2) _30 -:;.-: micro cross- — Sandstone, red fmne—groined, : 55 Sandstone, same as 95 Unit4,but sandstone, white to green, finegroined cross—bedded (UN I T 8) larger scale Cross—strata. —U.LNLL6)-. 90 Shale and fine silistone, brick red, micaceous, laminated. 85 interbedded coorse—grouned cross—bedded sandstone ocair 6 feet below the top of the unit (UNIT 5) 80 Sandstone red fine-groined, bedding poorly developed shale pebbles common in upper part (UNIT 7) laminated, rib and furrow StruClurC (UNIT I) Stratigraphic section feet ofFreda typical Upper Freda Formation Stratigraphic section showing showing 100 feet of 100 typical Upper Formation (figure 42 of Hite, 1968). (figure 42 of Hite, 1968). 66 �- Oronto Oronto Group Group Title: Title: Copper Copper Falls Falls State State Park Park — AS AS 45/02E/17B 45/02E/17B Location: Northwest of Mellen on Location: Northwest. of Mellen on Highway Highway 169. 169. SE1/4, SE1/4, Sec. Sec. 17, 17, T. T. 45 45 N., N., B. R. 22 E., E., Ashland Ashland County, County, Wisconsin. (Mellen (Mellen and and High High Bridge Bridge 77 1/2—minute 1/2-minute topographic topographic quadrangles, quadrangles, 1967 1967 and and 1984, 1984,respectively). respectively). Author: M.G. Mudrey, Mudrey, Jr. Jr. Author: M.G. Copper Falls Falls is is formed formed where where the the Bad Bad River River cuts cuts through through the the rereDescription: Description: Copper sistant ridge ridge of of Keweenawan Keweenawan lava lavaflows. flows. Downstream, Downstream, 0.6 0.6 km km from from Copper Copper Falls Falls sistant at the north, the the contact between basalt to the south and rhyolite to the north, Tyler Tyler Forks Forks River River joins joins the the Bad Bad River River at at Brownstone Brownstone Falls, Falls, which which occurs occurs at at the the contact contact between between basalt basalt to to the the south south and and rhyolite rhyolite to to the the north. north. The The conconglomerate of of the the Copper Harbor Formation is exposed in the lower glomerate gorge at lower gorge Devils Gate Gate about about 200 200 mm downstream downstream from from Brownstone Brownstone Falls. Falls. The Devils The conglomerate conglomerate is Montreal River is 129 129 m thick; thick; at the the Montreal River the the conglomerate conglomerate is is 515 515 mm thick. thick. NorthNorthwest Nonesuch Formation; west of of the the conglomerate conglomerate is is the the black shale shale of of the the Nonesuch Formation; northnorthwest west of of the the Nonesuch Nonesuch is is the the sandstone sandstone of of the the Freda Freda Formation. Formation. There There is is black black shale distributed distributedthrough through141 141inm of of section, section, but but only only2020inm are are considered considered shale Nonesuch Formation. Formation. Above the the interval interval with black shale, the sediment sediment is is red red Nonesuch shale, the shaley shaky arkose. arkose. 67 �The name Copper Copper Falls comes comes from a a small small copper copper prospmt prospect in a small small raravine working was south of of the the concession concession building. building. The working was begun by vine about 200 m south the Ashland Mining Company CompanyininAugust August1864 1864and andclosed closed in in February 1866. Copthe Ashland Mining 1866. Cop- per in quartzvein veininindiabase diabasewas was prospected. prospected. per in aa quartz reopened at the the turn turn of reopened at of the the century. century. Apparently the property Apparently the property was was Discussion: Discussion: Although faults faults complicate complicate the the local local geology, the the essentially essentially conformable relationship between the Oronto Group Group and Keweenawan conformable Keweenawanflows flows can can be seen. lowerparts parts of seen. The the Oronto Group, Group, the the Copper Harbor and the The lower of the theOronto Nonesuch, Nonesuch, are significantly significantly thinner thinner here here than than at at localities localities to to the the east. east. 68 �Title: Title: South South Fish F i s h Creek Creek Exposures Exposures in i n banks banks of of South South Fish F i s h Creek beneath bridge b r i d g e on on north—south north-south secondary m i l e s south south of of U. U. S. S. Highway Highway 22 on on the t h e east e a s t line l i n e of of the t h e SE-, SE*, secondary road road 1.2 1.2 miles SE, S E ~NE*, , NE*, Sec. Sec. 20, 20, T.47N., T.47N., R.5W., R.5W., Bayfield Bayfield County County (Moquah (Moquah 7.5 7.5 minute minute topographic topographic quadrangle, 1964). 1964). Location: Location: Author: Author: M. E. E. Ostrom Ostrom (modified (modified from from Myers, 1971) 1971) M. Exposures of of steeply—dipping steeply-dipping Freda Freda Sandstone Sandstone exhibit e x h i b i t the t h e lithologic lithologic Description: Exposures and mineralogic character c h a r a c t e r of of the t h e formation. formation. A description d e s c r i p t i o n of of the t h e strata s t r a t a downdownand is: stream from from the t h e bridge b r i d g e is: stream PRECAMBRIAN SYSTEM PRECAMBR IAN SYSTEM Keweenawan Keweenawan Series Series Oronto Group Group Oronto Freda Sandstone Sandstone Formation Formation (11.0 (11.0 feet) feet) 11.0' 11.0' Sandstone, grayish g r a y i s h red r e d to t o reddish r e d d i s h brown, brown, uniformly fine—grained, fine-grained, Sandstone, hard, h a r d , cross—bedded cross-bedded with w i t h parting p a r t i n g lineation. l i n e a t i o n . Much Much leaching. leaching. deformation. Current ripple r i p p l e marks found in in Penecontenporaneous deformation. float. float. 69 �BASE OF EXPOSURE Significance: Significance: Provides Provides evidence evidence of of environmental, environmental, geologic geologic and and structural structural history. Examine Examine lithology lithology and and mineralogy. mineralogy. What What do do they they signify? signify? What What direcdirechistory. tion tion is is the the top top of of the the beds? beds? Measure Measure dip dip and and strike strike of of beds. beds. What do do these these mean mean in in terms terms of of structural structural history? What What is is the the origin origin of of the the red red color? color? References: References: 70 From From what what direction direction did did the the sand sand come? come? Thwaites, Thwaites, 1912; 1912; Myers, Myers, 1971. 1971. �Chequamegon Formation Formation Title: U l e : Washburn Washburn Harbor Harbor --- Chequamegon BA 48104W/33 48/04W/33 Location: Outcrop on northside of J,ocatton~ of Washburn Harbor, Harbor! SW1/4, SW1/4, SEll SEl/ Sec. 33, T48N, R4W, Bayfield County, Wisconsin (Washburn 4 ! 33, T48Nr R4Wr Bayfield Countyf Wisconsin (Washburn 4, 7.5—minute quadrangle, 7.5-minute quadrangle! topographic, topographic! 1975). 1975). thor: M.G. Nudrey, Mudrey, Jr. Jr. (1992) (1992) Author: Description: Description: This low outcrop of Chequamegon sandstone of of the the Chequamegon sandstone Bayfield Group Group consists consists of of thick, thick, massively massively bedded, bedded! fine fine —- to Bayfield to medium-grained! grayish—red, grayish-red! quartzose quartzose sandstone. sandstone. The The grains grains medium-grained, are subangular subangular to to subrounded. subrounded. The bedding surfaces surfaces are are gritty gritty to coarse coarse grained, grained, but but are are thin thin and and discontinuous. discontinuous. Some Some bedding planes display scattered scattered small small quartz quartz pebbles. pebbles. Here! planes display Here, bedding dips gently to the southeast; southeast; however, at Big Rock Wayside Park Park at at the the east east quarter quarter corner corner of of Section Section 24, 24! T48N, T48Nf R5W, crossbedded R5Wf crossbedded sandstone sandstone dips dips 15 15 degress degress to to the the northwest, northwest! suggesting that that small, small! low-amplitude low-amplitude folds folds with with aa suggesting northeasterly northeasterly trend trend may may occur occur in in the the region. region. Discussion: The Chequamegon Qiscussion~ Chequamegon sandstone sandstone is is similar similar to to the the underlying Orienta sandstone, sandstone! which is found in fault contact �with with Keweenawan Keweenawan volcanics volcanics and and Oronto Oronto group group strata. strata. Bayfield Bayfield Group strata strata are are not not known known to to have high high dips, dipsI and and on on this this Group basis have have been been distinguished distinguished from from the the upper upper parts parts of of the the basis underlying underlying Freda Freda sandstone. sandstone. The The Douglas Douglas Fault Fault intervenes intervenes between between this this locality locality and and South South Fish Fish Creek Creek where where the the Oronto Oronto Group A petroleum petroleum Group dips dips south south at at aa high high angle angle to to the the south. south. A test test well well has has been been drilled drilled between between these these two two locations locations immediately immediately adjacent adjacent to to the the Douglas Douglas Fault. Fault. At At the the time time of of this this writing, writingI no no further further information informationwas was available. available. 72 �REFERENCES General geology, in Wisconsin Wisconsin Geological Aldrich, Aldrich, H.R., H.R., 1925, 1925,VI. VI. General geology, & Geological and and History Survey Natural History Survey Township Township Report Report T. T. 45 45 N., N., R. R. 22 W. W. (1924), (19241,p. p. 36—69. 36-69. Daniels, P.A., P.A., Jr., Jr., 1982, 1982, Upper Precambrian Precambrian sedimentary rocks: rocks: Oronto Oronto Group, Group, Daniels, Michigan—Wisconsin, in Wold, Wold, R.J., Michigan-Wisconsiny R.J., and and Hinze, Hinze, W.F., W.F., eds., eds., Geology Geology and and tectonics the Lake Superior basin: tectonics of the Lake Superior basin: Geological Geological Society Society of of America America Memoir 107—133. Memoir 156, 156,p. p. 107-133. Dickas, Comparative Precambrian Precambrian stratigraphy Dickasy A.B., 1986, 1986, Comparative stratigraphy and and structure structure along along the Mid—continent rift: the Mid-continent rift: American Association Association of of Petroleum Petroleum Geologists Geologists Bulletin, v. 70, 70, no, no, 3, 3, p. p. 227. 227. Bulletin, 1982, The sandstone architecture architecture of the Eckert, K.B., 1982, the Lake Lake Superior Superior region: region: Michigan Michigan State State University, University, Lansing, Lansing, unpublished unpublished Ph.D. Ph.D. dissertation, dissertation, 504 p. 504 p. Green, Keweenawan plateau plateau volcanism Green, J.C., 1977, 1977, Keweenawan volcanism in in the the Lake Lake Superior Superior region, region, Bara,dr, W.R.A., W.R.A., ed., Volcanic regimes in Bara&dr, regimes in Canada: Geological Geological Association .16, p p. 407—422. Association of of Canada Canada Special Special Paper Paper.16, . 407422. Hainblin,W.K., W.K., 1965, 1965, Basement Basement control control of of Keweenawan Keweenawan and and Cambrian Cambrian Hamblin, Association of of sedimentation American Association sedimentation in in the the Lake Lake Superior Superior region: region: American Petroleum Geologists Bulletin, 49,p. p. 950—959. 950-959. v.,49, Petroleum Geologists Bulletin, v. Hatch, J.R., and Morey, Morey, G.B., G.B., 1985, 1985, Hydrocarbon Hydrocarbon source source rock rock evaluation evaluation of of Hatchy J.R., Proterozoic Solor Church Church Formation, North American Mid-Continent Mid—Continent Middle Proterozoic Formation, North System, Rice County, County, Minnesota: Minnesota: American Association Association of Petroleum Rift System, Geologists Bulletin, v. 69, 69, no. no. 8, 8, p. p. 1208—1216. 1208-1216. Geologists Bulletin, v. Hite, D.M., 1968, 1968, Sedimentology of the Upper Keweenawan Keweenawan sequence sequence of northern Hite, D.M., University of Wisconsin, Madison, Wisconsin and Wisconsin and adjacent adjacent Michigan: Michigan: University of Wisconsin, Madison, unpublished Ph.D. thesis, p. thesis, 217 217 p. unpublished Hubbard, H. A., lW5, 1975, Keweenawan Keweenawan geology geology of of the the North North Ironwood, Ironwood, Ironwood Ironwood and and Hubbard, H.A., Little Girls Girls Point Point quadrangles, Little quadrangles, Gogebic Gogebic County, County, Michigan: Michigan: U.S. Geological Survey Geological Survey Open Open File File Report Report OF OF 75—152, 75-152, 23 23 p. p. or copper—bearing system, $J in Geology Irving, R.D., 1880, The The Keweenawan Keweenawan or Geology of of Irving, R.D., 1880, copper-bearing system, Wisconsin, p. p185, 205—206. Wisconsin, v. v. III., III., . 185, 205-206. frontier oil oil province: Kerr, S.D., Lee, C.K., C.K., and and Kerr, S.D., 1984, 1984, Midcontinent—a Midcontinent-a frontier province: Oil Oil Journal, August August 13, and Gas Gas Journal, 13,1984, 1984,p.p.144—150. 144-150. Superior regions region, U.S. A., and and its its Morey, G. B., 1978, in the G.B., 1978,Metamorphism Metamorphism in the Lake Lake Superior U.S.A., crustal evolution, evolution, in Fraser, J.A., and edseS relation to crustal Fraser, J.A., and Heywood, Heywood, W.W., W.W., eds., relation Metamorphism Metamorphism in in the the Canadian Canadian Shield: Shield: Geological Geological Survey Survey of of Canada Canada Paper Paper 78-10, p. 283—314. 283-314. 78—10, P. ., , Morey, and 0 Ojakangas, R.W.W., 1982,Keweenawan Keweenawan sedhentary sedimentary rocks rocks of Morey, G. I3B., and jakangas R. , 1982, eastern Minnesota and eastern Minnesota and northwestern northwestern Wisconsin, Wisconsin, in $J Wold, Wold, R.J., R.JeSand and Hinze, Hinzes W.F., W.F., eds., Geology Geology and and tectonics tectonics of of the the Lake Lake Superior Superior Basin: Basin: Geological Geological Society of 135-146. Society of America America Memoir Memoir 156, 156, p. p. 135—146. 73 �Mudrey, Mudrey, M.G., M.G., Jr., Jr., 1979, 1979, Geologic Geologic summary summary of of the theAshland Ashland 2° 20 quadrangle: quadrangle: Wisconsin WOFR Wisconsin Geological Geological and and Natural Natural History History Survey Survey Open—file Open-file Report Report WOFR 79—1, 79-1, 39 39 p. p. Myers, Myers, W.D., W.D., II, 11, 1971, 1971, The The sedimentology sedimentology and and tectonic tectonic significance significance of of the the Bayfield Bayfield Group Group (Upper (Upper Keweenawan?), Keweenawan?), Wisconsin Wisconsin and and Minnesota: Minnesota: University University of of Wisconsin, Wisconsin, Madison, Madison, unpublished unpublished Ph.D. Ph-D.thesis, thesis,269 269p. p. Ostrom, Ostrom, M.E., 1967, 1967, Paleozoic Paleozoic stratigraphic stratigraphicnomenclature nomenclatureof ofWisconsin: Wisconsin: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Information Information Circular Circular 8, 8, chart chart and and text. text. Ostrom, ME., and Ostrom, M.E., andSlaughter, Slaughter,A.E., A.E., 1967, 1967,Correlation Correlation problems problems of of the the Cambrian Cambrian and and OrdOvician Ordovician outcrop outcrop areas areas of of the the Northern Northern Peninsular Peninsular fsicJ [sic] of of Michigan: Michigan: Annual Annual Field Field Excursion, Excursion, Michigan Michigan Basin Basin Geological Geological Society, Society, p. 1—5. 1-5. p. Paull, Paull, R.K., R.K., and and Paull, Paull, R.A., R.A., 1980, 1980, Field Field Guide Guide to to Wisconsin Wisconsin and and Upper Upper Michigan: Kendall/Hunt Publishing Publishing Co., Co., Dubuque, Dubuque,Iowa, Iowa,260 260p. p. Michigan: Kendall/Hunt Rosenberry, Rosenberry, S.C., S.C., 1924, 1924,VI. VI. General General geology, geology,in: &: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Township Township Report Report T. T. 47 47N., N., R. R. 11 E. E. (1924), (1924), p. 17—28. 17-28. p. Thwaites, Thwaites, F.T., F.T., 1912, 1912, Sandstones Sandstones of of the the Wisconsin Wisconsin coast coast of of Lake Lake Superior: Superior: Wisconsin p. Wisconsin Geological Geological and and Natural Natural History History Survey Survey Bulletin Bulletin 25, 25, 117 117 p. Weiblen, Weiblen, P.W., P.W., and and Morey, Morey, G.B., G.B., 1980, 1980, A summary summary of of the the stratigraphy, stratigraphy, petrology and and structure structure of of the the Duluth Duluth Complex: Complex: American petrology American Journal Journal of of Science, Science, v. v. 280—A, 280-A, pt. pt. 1, 1, p. p. 88—133. 88-133. Wold, R.J., R.J., and and Hinze, Hinze, W.F., W.F., eds., eds., 1982, 1982, Geology Geology and and teconics teconics of of the the Lake Lake Wold, Superior Basin: Basin: Geological Geological Society Society of of America America Memoir Memoir 156, 156, 280 280 p. p. Superior 74 �GEOLOGY OF GEOLOGY OF KEWEENAWAN KEWEENAWAN SUPERGROUP ROCKS SUPERGROUP ROCKS NEAR THE NEAR PORCUPINE MOUNTAINS, PORCUPINE MOUNTAINS, GOGEBIC ONTONAGON & & GOGEBIC ONTONAGON COUNTIES, MICHIGAN COUNTIES, MICHIGAN William F. Cannon, Cannon, William Suzanne W. Nicholson, Nicholson, Suzanne Cheryl A. Hedgman, Laurel Laurel G. G.Woodruff, Woodruff, and Klaus J. Schulz U.S..Geological Geological Survey, U.S Survey, Reston, Reston, Virginia �5 5 5 LiL trip stops. 1r:-1 Figure 1. CONTOUR INTERVAL 50 FEET 0 0 10 ii Statute MiIe j Kilometers ________ �WAN SUPERGROUP SUPERGROUPROCKS ROCKSNEAR NEAR THE THE PORCUPINE PORCUPINE MOUNTAINS, MOUNTAINS, GEOLOGY OF KEWEENA WAN ONTONA GONAND AND GOGEBIC GOGEBIC COUNTIES. COUNTIES, MICHIGAN MICHIGAN ONTONAGON William F. Cannon, Suzanne W. W. Nicholson, Nicholson, Cheryl Cheryl A. A. Hedgman, Hedgman, Laurel LaurelG. G.Woodruff, Woodruff, and Cannon, Suzanne J. Schulz Klaus J. Schulz U.S. Geological Survey, Survey, Reston, Reston, VA U.S. INTRODUCTION INTRODUCTION This field trip trip examines examines the the geology geology of of rocks rocksof ofthe theKeweenawan KeweenawanSupergroup Supergroup(1 (1.1 .IGa) Gal and and related intrusive rocks rocks of of the Midcontinent rift rift system system (MRS) (MRS) in the western part of the the northern northern peninsula of of Michigan. The The combination combination of of stops stopsincludes includesall all formations formations of ofthe theKeweenawan Keweenawan Supergroup in in this this region. Examination Supergroup Examination of of all alldescribed described localities localitiesrequires requires more more than than aa single single day day and participants are are encouraged encouragedto to use usethis this guidebook guidebookon ontheir theirown own to to supplement the the localities that will will be be visited visited on on our one-day trip. Because Because of uncertainties uncertainties of weather, weather, road road conditions, conditions, and and remaining snow snow pack pack in in early earlyMay Mayininthis thisregion regionofofvery veryheavy heavysnowfall, snowfall,the thestops stopsthat thatwe we will will visit visit will will not not be be known known until until the the date date of of the the trip. trip. Stops Stopsare arenumbered numberedin in stratigraphic stratigraphic order, order, from from oldest oldest to youngest, youngest, not in the order in which they will will be be visited. GENERAL GENERALGEOLOGY GEOLOGY Supergroup is is aa very very thick thick sequence sequence of of volcanic and sedimentary rocks The Keweenawan Supergroup that was deposited deposited during and shortly shortly after after an an episode of continental continental rifting riftingat atabout about11.1 .IGa, Ga, when when formed within the the MRS formed the Proterozoic Proterozoic craton. The TheKeweenawan KeweenawanSupergroup Supergroup was was deposited deposited in in and and marginal to to rift rift graben graben and in a post-rift post-rift thermal thermal basin basin more or less centered on the axis of the the of the field trip (figs. 11 and former rift. In the area area of and 2), 21, the the Keweenawan Keweenawan stratigraphic section (fig. (fig. 3) 3) Quartzite)that thatis is overlain overlainby by aa great greatthickness thickness of of consists of a thin thin basal basal quartzite (Bessemer (Bessemer Quartzite) subaerial flood flood basalt flows and and felsite felsite flows (Powder subaerial and lesser lesser andesite and (Powder Mill MillGroup Groupand andPortage Portage Lake Volcanics). Volcanics). The progressively thicker thicker toward toward the rift Lake The volcanic section section becomes progressively riftaxis axisand and exceeds 20 20 km and others, others, 11988; 988; Cannon and others, exceeds km in in places places beneath beneath Lake Superior (Behrendt and 1 990). 1990). In the vicinity vicinity of of the thePorcupine Porcupine Mountains, Mountains, the the volcanic volcanic sequence sequence includes, at the the top, top, aa stratovolcano stratovolcano composed mostly of andesite andesite and rhyolite flows flows and and sub-volcanic sub-volcanic felsic felsic intrusions intrusions Volcanics). These (Porcupine Volcanics). These late late intermediate and felsic volcanic rocks rocks are are atypical atypical of of the theMRS MRSas as a whole and are limited to aa few few felsic felsic volcanic volcanic centers. centers. fluvial sedimentary sedimentary rocks rocks and and lesser lesser lacustrine lacustrine Conformably overlying the volcanic rocks rocks are are fluvial sedimentary rocks (Oronto (Oronto Group), which which are are as as much much as as 88 km km thick thickbeneath beneathLake LakeSuperior Superior(Cannon (Cannon and others, others, 11990) 990) and and at at least 5 km thick on shore in the field field trip trip area. area. Post-rift reverse faulting faulting has caused caused block block rotation rotation on a very large scale scale so so that that the Post-rift Keweenawan Supergroup Supergroupsection sectionisissteeply steeplytotovertically verticallydipping. dipping. More than 13 13 km km of of volcanic volcanic rocks and 5 km generally north-facing north-facing section. This km of of sedimentary sedimentary rocks rocks are exposed in a generally This thick section constituted at least half of the crustal enormously thick crustal thickness by by the the close close of of rifting riftingand and thus our field trip trip provides provides aa traverse through the upper half of the Middle Middle Proterozoic Proterozoic crust. The initial initial subsidence of the the MRS MRS is is recorded recorded by deposition deposition of of the theBessemer Bessemer Quartzite Quartzite(stop (stop 1), 1 ), a blanket of relatively relatively pure, fluvial fluvial quartzite quartzite as as much much as 100 100m mthick thick(Ojakangas (Ojakangasand and Morey, Morey, It formed in a broad basin, basin, more more or or less less centered centeredon onthe thesite Siteofofthe thefuture future deep deeprift. rift. The 1982). 1982). It The age of of deposition has an an upper upper bound boundof of about about 1109 1109 Ma, Ma, the age age of of the oldest overlying basalt age flows (Davis (Davis and Sutcliffe, 1985). 1985).Following Followingdeposition depositionofofthe theBessemer, Bessemer,the thearea areabecame became volcanivolcanias 15 km) of basalts and lesser andesites andesites and and rhyolites rhyolites cally active and a great thickness (as much as in only about 1155 m.y. m.y. The accumulated in The earliest earliest basalts basalts constitute constitutethe the Siemens Siemens Creek Creek Formation Formation of 975a) (stops (stops 11 and and 2). 2), which lies the Powder Mill Mill Group (Hubbard, 1 1975a) lies conformably conformably on on the the Bessemer Bessemer Quartzite. Soft flow (seen Quartzite. Softsediment sediment deformation deformation ofofthe theBessemer Bessemer by by the overriding overriding basal basalt flow (seen at flow is stop 1) 1) indicates a very short interval between the units. Locally, Locally, as at Stop stop 1, the basal flow is pillowed, but but all allsucceeding succeedingflows flowsare aresubaerial. subaerial. 77 �00 1 ,00730" 10G130 2 — •••_o___ o —- — 'KtOMETERS UE8 \' �________ EXPLANATION EXPLANATION Intrusive rock. rocks Intrusive O.bbrc or dleb...—grancphyn. ifitrunin. cOrgia000 I, f.rr.d f.I.la .tcob Volcanic and ..dimsntery rock. Jccob.vllla S.nd.ton.— •d end bran, f.ld.p.thln and aantoo.. scndstone. all (atcn.. nunglanut. O r o n l oGroup Group SAUGL— Ornate Fr.do Fcnn.tlc,,— r.d .cndst.n. end nu.,dsl,n. Noc.aoh Shale— gre—bl eat .llt.tone. shela. hoe needol000 Capper Herbs, Cnnqlansn.te— tears. nod—bins ..nglnr.te sad Ccpp.r Harbor Ccnglanr.te basalt ,m,H.r Bergland Grasp Perapie. Vclo.nlo. rhyollt. m..H.r— .phyr a to gaunt. and f.ldoper in abner 1.1 don... fleas end d.brl. floe. pitynlo rhy.lit* Poroopin. Voloeni.. basalt cod end., it. .e.,*.r thin °F ft... of and.. It. and miner tholelillo ba.clt ParIng. 1.1.. Vnl.noloe—nmotly nphltlo IlicleIltI. bdeelt floe.. naHasIt.. nhy.llt. utid intart lee t.ngla,arnt. nil,,, Po.dennsi II I I iii 1! Creep Fc.d.nniIl Creep (endlvld.d)— Thnl.iltic kooelt flea.. .nlncç II end.slt. end rhyc lit. anacin Leear Prat.ronuie cod Arch.., rack. (cndlvldad) Tr.ndofpronlnanl •.ran.gn.liu lin..n.nl. Mountainsarea area showing showing PorcupineMountains Figure Figure 2. 2, Generalized Generalizedgeologic geologicmap mapand andsection section of of the thePorcupine the location of field trip stops. the location of field trip stops. 79 �STOP j# 12a 12 Jocobsville Jocob,ville Sandstone Lj Sandstone Freda Sandstone Nonesuch Shale Copper Harbor Horbor Conglanerate Conglamrote rnmber) (bosoitk rnerther) (bosa; Porcupine Volcanic, Volcanics 1o I Portage Volcanics Portage Lake Volconic, 4 5 Kollander Kal lander Creek Formation 3 - 2 1 0 Sernena Siemens Creek Formation Bess-r Quartzite Bessner Quartzite KM Early Preterozoic Eorly Proterozoic rocks rocks Figure Stratigraphicsection sectionof ofKeweenawan Keweenawan Supergroup Supergroup rocks in the field field trip trip area area Figure 3. Stratigraphic showing the stratigraphic position of stops. Thicknesses are approximate average stratigraphic position of stops. Thicknesses are approximate average thicknesses for for the area. area. Some Some formation formation thicknesses thicknesses vary significantly significantlyacross across the the region. region. 80 �Overlying the Siemens Creek Formation Formationisisaathick thick section section of of more felsic felsic rocks Siemens Creek rocks (stop (stop 3) 3) of rhyodacite, rhyodacite, tra~hyandesite~ trachyandesite, andesite, andesite, and andbasalt. basalt. These rocks constitute constitute the composed of the Kallander Kallander Creek (Hubbardl 1975a). Powder Mill Mill volcanic volcanic rocks rocksare are Creek Formation Formation of of the the Powder Mill Group (Hubbard, 1 975a). The Powder distinguished from overlying overlying basalts basalts of similar similar character character largely on the the basis basis of of their theirreversed reversed to the normal polarity magnetic polarity as opposed to polarity of of younger younger units unitssuch suchas asthe thePortage PortageLake Lake Volcanics. In Michigan, Michiganl the Powder Mill Mill Group crops out in in aa belt belt that that isisseparated separated from from the the Volcanics by by the the Jacobsville Jacobsville Sandstone, Sandstone, which which lies with outcrop belt of the the overlying overlying Portage Portage Lake Volcanics subsurface, however, the Powder Mill Mill rocks. In the subsurfacef Mill and and angular unconformity unconformity on Powder Mill Lake probably probably form form a continuous Portage Lake continuousdepositional depositionalsequence. sequence. Supergroup range rangein incomposition compositionfrom from olivine olivine tholeiite tholeiite to Volcanic rocks of the Keweenawan Supergroup rhyolite. By high-Al olivine olivine tholeiite tholeiite (A1203 (Al2 03==15-19 wt%) followed by rhyolite. By far far the the dominant dominant rock type is high-A1 15-19 wt%) lesser high-Fe high-Fetholeiite tholeiite and and rocks rocks of of intermediate and and felsic felsic composition composition (Green, (Green, 1982; Brannon, lesser Brannon, 1984; Paces, Paces, 1988). 1988). The Theolivine olivinebasalts basaltscommonly commonly are are ophitic in in texture texture and and the the dominant dominant plagioclase. The most are geochemically geochemically similar similar to to phenocryst is plagioclase. most primitive primitive Keweenawan Keweenawan basalts are ridge basalts. basalts. However, primitive midocean ridge However, incompatible incompatible trace elements in most Keweenawan are enriched enriched compared comparedto to depleted depletedor or primitive primitive mantle. mantle. Radiogenic basalts are Radiogenic isotope isotope analyses analyses (Sr. (Sr, Nd, Pb) of of the the main stage stage high41 high-Al olivine olivine tholeiites tholeiites suggest suggest that that aa likely likely source source of of the voluminous and Pb) (Pacesand andBell, Bell,1989; 1989; Nicholson Nicholson and and Shirey, Shirey, 1990). 1990). basalts is a mantle plume (Paces Some of of the the oldest flowsl flows, such Some such as as those in in part part of of the the Siemens Siemens Creek Creek Formation, Formation, have distinctly different distinctly different chemical chemical compositions compositions than the younger basalts. These These basal basal rocks rocks are are transitransitional to weakly characterized by by low low A1203 A1203 content content and clinopyroxene weakly alkaline alkaline olivine basalts characterized phenocrysts. Locally, phenocrysts. Locally, in other parts of the rift, basal basal flows flows are are picritic picritic but but such such flows flows have havenot notbeen been identified in in this this area. area. Flows Lake Volcanics Volcanics north north of the Keweenaw Flows near the base of the exposed Portage Lake Keweenawfault fault were erupted at about 1096 near the the top top of the formation 1096 Ma Ma and those near formation at at about about 1094 1094Ma Ma(Davis (Davis and Paces, Paces, 1990). 1 990). Thus, Lake Volcanics, Volcanics, at at least 8 km in this Thusl the great thickness of Portage Portage Lake this area, areaf was erupted in only aa few few million millionyears. years. The Theestimated estimatederuption eruptionrate ratefor forPortage PortageLake LakeVolcanics Volcanicsinin the present eruption eruption rate the western western Lake Lake Superior region must have approximated the rate of of the the Hawaiian Hawaiian hot spot, spotl the the most mostvigorous vigorous volcanic volcanic center center of of the themodern modernearth earth(Cannon, (Cannonfin in press). press).Because Because synchronous volcanism volcanism occurred occurredalong alongthe theentire entiretrend trendofofthe therift, rift, the the rift rift system system as as a whole was was producing producing basalt at at aa rate rate unrivalled unrivalled by byany any modern modernanalog. analog. area of of the the Porcupine Porcupine Mountains Mountains contains contains aafelsic felsicto to andesitic andesitic volcanic volcanic center center that that The area became active late late in in the the volcanic volcanic history history of of the the regionl region, at at about about 1090 1090 Ma. The became active ThePorcupine Porcupine called the the "unnamed "unnamed formation") formation") (Cannon and and Nicholson, Nicholson, 1992) were erupted erupted Volcanics (previously called from from that that center center and and accumulated accumulated as much as 5 km of of andesite, andesite, rhyolite, rhyolite, and and basalt basalt in inaalarge large shield shield deposited on top of the the Portage Portage Lake Lake Volcanics lava field and centered near the Porcupine Mountains. The Thepresent presentarcuate arcuate shape shape of the the mountains mountains and and the the unusual unusual hook-shaped map pattern reflection of the of the Porcupine Porcupine Volcanics is partly a reflection the original original shape shape of the the volcanic volcanic shield. shield. The Porcupine Volcanics consists of aa sequence of subaerially deposited andesite, andesite, basalt, felsite, and quartz-porphyry quartz-porphyry lava flows, and and minor minor interbedded interbedded volcaniclastic volcaniclastic lithic lithic sandstone, sandstone, siltstone, 1 975b). The abundance siltstonel and and conglomerate (Hubbard, (Hubbardl 1975b). abundance of felsic rocks rocks and the predomipredominance of of andesite over basalt clearly distinguish the Porcupine Volcanics from the nance the underlying underlying Portage Lake LakeVolcanics. Volcanics. Felsite Felsite is is most most common common near nearthe thetop topof of the the formation formation where it it occurs occurs as Portage both flows flows and and domes domes (stops (stops 55 and and 6). 6). The major element chemistry of basalt, basalt, basaltic basaltic andesite, andesite, and and andesite andesite of of the thePorcupine Porcupine Volcanics and the Portage Volcanics are are very very similarl similar, but the Porcupine Portage Lake Volcanics Porcupine Volcanics are are distinctly distinctly enriched in rare earth elements WEE) (REE)and andTh Thcompared comparedtotothe thePortage PortageLake LakeVolcanics. Volcanics. The two two formations differ more profoundly in their rhyolite chemistry. Rhyolite Rhyolitethat that occurs occurs most mostcommonly commonly in the Portage Volcanics is is aphyric aphyric or or may may contain contain sparse sparse quartz quartz phenocrysts. phenocrysts. Rhyolites Rhyolitesof of the the Portage Lake Volcanics Portage Lake Lake Volcanics Volcanics on on Keweenaw Peninsula Peninsulahave havevery verylow low abundance abundance of of incompatible trace elements (such as as REE, REE,Zr, Zr,Y,Y,Hff Hf, and andThIl Th), whereas whereasthe the rhyolite rhyolite body body near near Bergland Bergland (stop (stop 41, 4), one one of of the few few rhyolite rhyolitebodies bodies with withthe thePortage PortageLake LakeVolcanics Volcanics in in the the Porcupine Porcupine Mountains Mountainsarea, area, has has moderate abundances of incompatible incompatible trace trace elements. elements. In contrast, the numerous rhyolite bodies in Volcanics range rangefrom fromrhyolites rhyolitesthat that are areaphyric aphyricto to those those with with abundant quartz andlor and/or the Porcupine Volcanics 81 81 �The thrust faulting faulting and and folding can be indirectly dated in the interval of approximately 1060 1060 and othersl others, 1984; Bornhorst and andothers, others, 1988; 1988; Cannon Cannonand andothers, others, 11990). to 1040 1040 Ma Ma (Ruiz (Ruiz and 990). The The cause of of the regional compression compressionisisnot not known known with certainty cause certainty but but isislikely likelylinked linkedininsome somemanner manner orogeny, which was in progress at that time. with the the Grenville Grenville orogeny, STOPS FIELD TRIP STOPS Stop .--BessemerQuartzite Quartziteand andbasalt basaltat at the the base base of of the the Powder Mill Mill Group Group Stop 11.--Bessemer A low east of of the county road (see (seefig. fig. 4) 4) shows quartzite of the low rock rock knob knob in in aa pasture pasture east upper part part of of the Bessemer Quartziteinincontact contactwith with the the overlying overlying basal basalbasalt basaltflow flow of of the the Powder Powder upper Bessemer Quartzite Mill Group. The 975a). Thebasalt basaltisisthe the lowermost lowermostflow flowofofthe theSiemens SiemensCreek CreekFormation Formation(Hubbard, (Hubbard,11975a). The Siemens Creekisiscomposed composedpredominantly predominantlyofofthin thinflows flows of of basalt and and minor minor andesite. andesite. Average Siemens Creek Average thickness of of flows is about 3 m, but the basal flow flow is about 50 m thick at this locality. Here, Here, the the basal flow flow is nonporphyritic holocrystalline. Unlike basal nonporphyritic and holocrystalline. Unlike some of the basal basal flows along along strike strike to to the the flows do west, these flows do not not contain contain clinopyroxene clinopyroxene phenocrysts. Chemical Chemical analyses analyses (table 1) of the flows are similar to the basal flows the younger younger high-alumina high-alumina main-stage basalts of the Portage Portage Lake Volcanics. The Creekflow flow is is pillowedl pillowed, which which is very very unusual for for basalts of the Volcanics. The basal basal Siemens Siemens Creek Supergroup, nearly all of which Keweenawan Supergroupl which are are subaerial. subaerial. In places, placesl stringers of the the quartzite quartzite been injected injected up up into into rubbly rubbly material material at at the the base baseof of the the flow, flow, indicating have been indicating that that the theBessemer Bessemer was was unconsolidated at the time of eruption. eruption. that dips here here are areabout about65O 65° N. N. Contrast Note that Contrast these these with with steeper steeper to slightly slightly overturned overturned dips at stops 2 and 3, higher in the Powder Mill section. This Thisupdip updipfanning fanningrelationship relationship commonly commonly Hubbard (1 (1975a) to propose that they they were were deposited deposited in in aa shown by the Powder Powder Mill Mill flows flows led ledHubbard basin that was centered centered south (updip) (updip) of the the present present outcrop outcrop belt belt and and the the volcanics volcanics originally originally thickened in that direction. direction. If that interpretation interpretationis is correct, correctDthere there must musthave havebeen been aa rapid rapid change change in in depocenters at the outset outset of of volcanism volcanism because because most most paleocurrent paleocurrent directions directionsin inthe theBessemer Bessemer are are northerly Morey, 1982). (Ojakangas and Morey, 1982). northerly (Ojakangas Stop 2.--Basalt 2.--Basalt flows flowsofofSiemens SiemensCreek CreekFormation Formation Roadcuts along along Powderhorn Road Road(fig. (fig.41, 4), which which follows the the valley valley of of Powder PowderMill MillCreek, Creek, provide a convenient cross section of the Powder Mill Mill Group in its its type type area area as defined by by Hubbard Hubbard 975a). At exposed and and at at stop stop 33 (1975a). At stop stop 22typical typicalbasalt basaltflows flowsofofthe theSiemens SiemensCreek Creek Formation Formation are exposed Creek Formation Formationcan canbe beseen. seen. Steeply Steeply north-dipping north-dipping basalt basalt flows flows of the the Kallander Creek the Siemens Siemens Creek Formationare arewell wellexposed exposedininoutcrops outcropson onthe thehill hillwest westof of the the road road and and in in low low roadcuts. The Creek Formation The meters or less thick. Commonly these these fine-grained flows have have basalt flows flows are thin, thin, typically a few meters thick. Commonly amygdaloidal and and rubbly rubbly flow flow tops, seen locally locally at at the the base base of of some flows. amygdaloidal topsl and and pipe vesicles can be seen show patchy alteration to to chlorite and and have have abundant abundantchlorite chloritein inthe the matrix, matrix. This The basalts show This relarelatively high high degree of metamorphism is typical of basalts basalts of the the Siemens Siemens Creek Formation and is one distinction between distinction betweenthem them and and less less metamorphosed metamorphosed basalt basalt of the the overlying overlyingPortage PortageLake Lake Volcanics. Volcanics. Some flows are porphyritic Some flows porphyritic with withsmall smallplagioclase plagioclase phenocrytsts. Stop 3.--Kallander Creek Creek Formation Formation About 2 km km north north of of stop stop2, 2, aaroad roadimprovement improvementproject projecthas has produced produced freshly freshly blasted blastedoutoutCreekFormation. Formation. Because Becauseall allflows flowsare aredipping dippingnearly nearly90 90° in in this this area, the crops in the Kallander Kallander Creek area, the passes up upthrough through about about 22 km km of of section, section, an impressive impressive pile pile of of basaltl basalt, yet yet this drive between stops passes erupted into into the the deepest deepestparts partsofofthe therift. rift. The is only 10% of the total thickness of basalt erupted The flows flows in in the Kallander Creek Formation Formationare arebasaltic basalticto toandesiticD andesitic,more morerarely rarelyrhyoliticl rhyolitic, and and generally generally aa few few Kallander Creek Creekisismore morefelsic felsicthan thanthe the Siemens SiemensCreek. Creek. At this this stop stop the the meters thick. Overall, Overall, the Kallander Creek flows include chloritized chloritized amygdular basalt, basalt, fine-grained fine-grained basalt basalt with with plagioclase phenocryts exposed flows stone"),non-porphyritic non-porphyriticandesite, andesite,andesite andesitewith with pla~ioclase plagioclasephenocrysts, phenocrysts, and tuff tuff (locally a TMdaisy -daisy stonew), breccias containing containing both both basalt basalt and andandesite andesitefragments. fragments. Although Although rhyolite occurs higher in the breccias formation, none flows are none is is exposed exposed here. The TheKallander Kallander Creek Creek flows are generally generally less metamorphosed than the Siemens Siemens Creek flows. 83 �asv c'RokFor 48N. 47N. Falls ° fPuritSch Figure4. 4. Location setting foi for stops 1, 2, and Figure Location and geologic setting and 3. 3. Geology Geologygeneralized generalized and modified from Hubbard (1975a). 975a). Note scale between between the the two two adjacent Note change change in scale quadrangles. quadrangles. 84 �TABLE 1: 1: CHEMICAL CHEMICALANALYSES ANALYSESFOR FORSOME SOMEVOLCANIC VOLCANICUNITS UNITSININTHE THEKEWEENAWAN KEWEENAWANSUPERGROUP SUPERGROUP TABLE ELEMENT ELEMENT 1 2 N=2 N=4 Si02 Si02 52.02 Ti02 Ti02 1.75 14.32 1.85 9.42 0.17 6.93 8.18 3.57 1.57 0.23 A1203 A1203 Fe203 Fe203 FeO FeO MnO Ph0 MgO MgO Cao CeO Na20 Na20 K20 K20 P205 SUM SUM Cr Cr Ni Ni Nb Nb Rb Rb Sr Sr Zr Y V La La Sm Sm Yb Hf Ta Ta Th Th 3 N=5 77.23 0.12 12.91 0.60 1.19 0.03 0.30 1.43 1.57 4.62 0.01 99.99 100.00 233 2.9 4 N=1 48.66 1.69 16.51 1.83 10.38 0.18 7.37 10.59 2.29 0.32 0.18 100.00 71.79 0.42 12.84 1.74 3.49 0.10 1.18 0.23 0.76 7.38 0.06 99.99 188 204 2.5 50 212 8 7 470 123 18 281 16 19.0 4.9 1.67 3.12 1.04 1.94 112 76.9 12.9 10.00 10.24 3.92 39.48 252 100 23 32 219 53 1130 103 273 27.3 94 20 35 1 11.6 4.0 2.08 2.65 0.58 1.04 <2 10.4 22.2 2.96 35.70 5 6 N=2 N=1 1 47.60 2.26 17.03 2.04 12.30 0.19 7.60 5.11 4.09 1.26 0.53 100.00 168 95.5 17 1.70 16.99 1.65 10.90 0.22 8.16 6.50 2.86 2.53 0.20 100.00 159 188 8.7 61 37.2 7.1 3.55 4.475 0.86 2.63 1 Average analysis of of Siemens Siemens Creek Creek basalts basalts Average analysis analysis of of rhyolite Average rhyolite from quarry quarry near near town town of of Bergland Bergland Average Average analysis of basalts basalts of of the thePortage PortageLake LakeVolcanics Volcanicsnorth northofofcrossroads crossroadsatatMerriweather Merriweathernear nearBergland Bergland Analysis Analysis of rhyolite rhyolite at at quarry quarry near near White White Pine Pinemine mine Average Average analysis of basalts basalts at at Lake Lake of of the theClouds Cloudsoverlook overlookininPorcupine PorcupineMountains MountainsWilderness Wilderness State StatePark Park analysis of basalts 6 Average Average analysis basalts of the the Portage Portage Lake LakeVolcanics Vofcanics on on Keweenaw Keweenaw Peninsula Peninsula 6 7 Average analysis analysis of of basalts basalts from from the thePorcupine PorcupineVolcanics Volcanics 7 Average 33 44 5 5 48.29 490 1 2 2 7 N=8 126 26 11.9 4.0 2.12 2.65 0.59 1.20 50.68 2.47 14.36 2.11 11.94 0.23 5.32 6.46 2.70 2.89 0.86 100.00 64 42 18 62 407 294 56 55.7 11.1 5.11 7.10 1.32 5.94 �Stop4.--Portage 4.--PortageLake LakeVolcanics Volcanics Stop This Thisstop stopillustrates illustratesrhyolite, rhyolite,basalt, basalt,and andinterfiow interflowsandstone sandstoneofofthe thePortage PortageLake LakeVolcanics. Volcanics. Exposures and quarry quarry along alongthe thenorth north side sideof of Michigan MichiganHighway Highway 28 28 (fig. (fig. 5). The The Exposures are in a roadcut and prominent expression prominentsouth-facing south-facingscarp scarpthat thatruns runsparallel paralleltotothe thehighway highwayusually usuallyisisthe thegeomorphic geomorphic expression ofofthe the Portage Lake theKeweenaw Keweenawfault, fault,but buthere herethe thefault faultlies liesmore morethan thana amile miletotothe thesouth, south,and and the Portage Lake Volcanics underlie the lowlands surrounding the north end of Lake Gogebic as well as the highlands Volcanics underlie the lowlands surrounding the north end of Lake Gogebic as well as the highlands northofofthe thescarp. scarp. north The are a thick thick pile of dominantly basaltic, subaerial flows, flows, with ThePortage Portage Lake Lake Volcanics are with lesser lesser rhyolites rhyolites and and interflow interflow sedimentary sedimentary rocks. At Atthis thislocality, locality,however, however,rhyolite rhyoliteisisthe thedominant dominant rock rocktype, type,although althoughgood goodexamples examplesof ofbasalt basaltare are in inthe theroadcut. roadcut.Another Anotherunusual unusualfeature featurehere hereisisthe the local localdevelopment development of of pillows pillowsalong along the the toe toe of of aaflow flowwhere whereititapparently apparentlyentered enteredaabody bodyof ofwater waterinin whichsandstone sandstonewas wasbeing beingdeposited. deposited. which The Thestratigraphy stratigraphy in inthe the quarry quarryarea area consists of an ophitic ophitic basalt basalt flow flow overlain overlain by by aa thin thin interinterflowsandstone sandstonetotosiltstone siltstonewhich whichininturn turnisisoverlain overlainby byan anamygdaloidal amygdaloidalbasalt. basalt.The Theamygdaloidal amygdaloidal flow basalt basaltexhibits exhibitswell welldeveloped developedpipe pipevesicles vesiclesatatroad roadlevel. level. Rhyolite Rhyoliteoverlies overliesthe theamygdaloidal amygdaloidalbasalt basalt and andisiswell wellexposed exposedin inthe the quarry quarry floor floor and and walls walls and and is is overlain overlain by by ophitic ophitic basalt basalt flows flows on onthe the hillside compositionally to to low Ti02 hillsideabove above the quarry. quarry. The Thebasalts basaltshere here are are identical compositionally Ti02basalts basaltson on 1). KeweenawPeninsula Peninsula(table (table1). Keweenaw ItItisisnot notclear clearwhether whetherthe therhyolite rhyoliteisisaasingle singleshallow shallow intrusive intrusivebody bodyor oraaseries series of of flows. flows. ItIt contains containsseveral severallenticular lenticular masses masses of of basalt basalt and and an an unusual unusual greenish sandstone. Are Arethese thesexenoliths xenoliths ininan anintrusion intrusionor ordiscontinuous discontinuousinterbeds? interbeds?Several Severalfeatures featuressuggestive suggestiveof of extrusive extrusiveorigin origincan canbe be Foldsare arepresent presentnear near the the contact contactof of the therhyolite rhyolitewith withthe theunderlying underlyingbasalt. basalt. In Inthe theupper upper noted. noted. Folds part partof ofthe thequarry, quarry, the therhyolite rhyoliteshows showswell-developed well-developed columnar columnar jointing, some some of of which whichisisbent, bent, following followingaaramp rampstructure structureininthe therhyolite. rhyolite.The Thepossibility possibilityofofaaseries seriesofofflows flowsisisenhanced enhancedby bythe the distribution distributionof ofspherulitic spheruliticrhyolite. rhyolite.Spherulites Spherulitesare arecommon commonthroughout throughoutthe thequarry quarrybut butare areconcenconcentrated tratednear nearthe the base base of of the the rhyolite, rhyolite, near near the the contact contactwith withaasedimentary sedimentary lens, lens, and and near near the the top top of of the thequarry. quarry.More Moremassive massiveororstony stonyrhyolite rhyoliteoccurs occursbetween betweenthe thespherulitic spheruliticzones. zones. Alteration Alterationrelated relatedto tocopper coppermineralization mineralizationis is widespread widespread in in the the quarry. quarry. Epidote EpidoteisisdissemidissemiSecondarycopper copperminerals mineralsare are nated anunusual unusualgreenish greenishcolor. color.Secondary natedin inmuch muchof of the therhyolite, rhyolite,giving givingititan abundant on on joint joint surfaces. surfaces. abundant Stop Stop5.-Porcupine 5.-Porcupine Volcanics: Volcanics:Rhyolite RhyoliteatatSummit SummitPeak Peak Summit one of of the highest Summit Peak Peak is the highest highest point point in in Porcupine Porcupine Mountains Park and one highest points points in in the the state. state. The Theobservation observationtower toweratatthe thesummit summitprovides providesaapanoramic panoramic view of of the the field field trip triparea area (fig. highlands are 6).ToTothe thesouth, south,the the highlands areunderlain underlainbybythe thePortage PortageLake LakeVolcanics Volcanicsand andPorcupine Porcupine (fig.6). Volcanics Volcanics along along the the main main monocline monocline of volcanic volcanic rocks rocks of of the the Keweenawan KeweenawanSupergroup. Supergroup. The The lowlands OrontoGroup Groupininthe theeasteastlowlandsimmediately immediatelyto to the thesoutheast southeastare are underlain underlain by by rocks rocks of of the the Oronto plunging plunging Iron IronRiver River syncline. syncline. Looking Lookingeast eastalong alongstrike, strike, the thesmelter smelteratatWhite WhitePine Pinecan canbe beseen seenin inthe the distance. distance. To Tothe thenorth, north,the theinterior interiorofofthe thepark parkextends extendsover overthe therugged ruggedtopography topography in in the the foreforeground ground to to Lake Lake Superior Superior in in the the distance. distance. The Theinterior interiorofofthe thepark parkisismaintained maintainedas asaawilderness wildernessarea area contains the the largest largest stand stand of of virgin virgintimber timberin inthe thestate. state. and access access is is only only by byhiking. hiking. ItItcontains and Most Mostof ofthe thepark parkinterior interiorisisunderlain underlainby byaathick thickunit unitofofrhyolite rhyolitecomposed composedofofaaseries seriesofof flows flowsand anddomes domestypified typifiedby bythe therocks rocksseen seenat atSummit Summitpeak. peak. Good Goodexposures exposuresof ofcoarse coarserhyolite rhyolite breccia the trail leading to to the summit and at at the overlook platform west of breccia are along the of the the summit. summit. Thisbreccia brecciaisisprobably probablythe thecarapace carapaceof of aarhyolite rhyolitedome. dome. This Excellent Excellent exposures exposures of typical typical intermediate intermediateand and felsic felsic units unitsofofthe thePorcupine PorcupineVolcanics Volcanicscan can be seen seen on the north north side side of the the hill hill (549 (549m melevation) elevation)near near the center of Sec. Sec. 31. 31. Take Takethe theBeaver Beaver be Creek Creek Trail about 0.5 mi mi from from the the Summit Summit Peak Peak parking lot. The Theunits unitsdip dipto tothe thesouth southand andinclude, include, in in stratigraphic stratigraphic order, order, sparse sparse outcrops outcrops of of intermediate intermediateto to mafic maficrocks rocksininthe thecreek creekbed, bed,overlain overlainby byaa vesicular vesicular siliceous siliceous andesite, andesite, which is is in in turn turn overlain overlain by by aacoarse coarse rhyolite rhyolite breccia breccia or or debris debris flow. flow. The in size size from from nearly nearly aa meter meterto to less lessthan than 11 cm. cm. The The breccia breccia is is The breccia breccia contains clasts ranging in clast clast supported supported and and some some clasts clasts are are subrounded. Overlying Overlyingthe thebreccia brecciaisisaamedium-grained medium-grainedbasalt basalt flow. flow. Capping Cappingthe thehill, hill,and andoverlying overlyingthe thebasalt, basalt, isisan anaphanitic aphanitic massive massive rhyolite that is is microspherulitic. microspherulitic. 86 �—H-- -j I, /1 —. SCALE1:25 1:25000 OW SCALE I 0 KILOM€TE 1 2 KILOMETERS 1 1000 1000 1 A — - 1 7 1000 + - - A 00 1000 1000 00 - .5.5 2000 .?OM- - METERS METERS 4000 3000 3000----4000 - - 2000 2000 1000 1000 00 1 MILES MILES -5000 5000 - 6000 6000 1000 7004 8000 8000 9000 WOO 10000 10!00 itt: I FEET CONTOUR INTERVAL INTERVAL55METERS METERS CONTOUR Figure 5. Location Locationand andgeologic geologic setting setting of ofstop stop4. 4.Geology Geologygeneralized generalizedfrom fromunpublished unpublished Figure compilation by by Walter Walter White. White. compilation 87 �88 (unpublished). mapping cooperative Survey Geological Corp./Michigan Range Copper from generalized Geology marked. well are all but shown, not are peak Summit on tower and platform observation and improvements, trail and road Recent 5. stop of setting geologic and Location 6. Figure METERS 5 INTERVAL CONTOUR FEET 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 Oa0 0 MILES 2000 1001) METERS 0 1 KILOMETERS 0 51N. R.44W. 1000 .5 1 �Stop Stop 6.--Porcupine Volcanics: Rhyolite Rhyolite quarry quarry near near White White Pine Pine here are are part part of of a small rhyolite body near the top The rocks exposed here top of of the thePorcupine Porcupine Volcanics. The beyond the the hill hill into into which the quarry is Volcanics. The body body probably probably does not extend much beyond is cut cut (fig. 7). The Thequarry quarryprovides providesaacross crosssection sectionthrough throughpart partof ofaasubaerial subaerialagglutinate agglutinatedeposit. deposit. form at vents by spatter of erupting magma and and buildup buildup of of mounds of of hotl hot, Agglutinate deposits form viscous material. material. The mound of erupted material materialeventually eventuallyflows flowsoutward outward under underits its own own weight weight resulting in large large flow flow folds such as seen seen in in this this quarry. quarry. The The near-vent near-vent nature of this deposit deposit is is deduced from the the presence presenceof of lithic lithic fragments fragments within within the the rhyolite, rhyolite, large flow flow folds and deduced from and stratification stratification of rhyolite rhyolite (light (light and dark units). At Atthe theedges edges of of agglutinate agglutinate deposits, deposits, flowage typically has has homogenized the the magma and and such such stratification stratification and and folding foldingare are generally generally not notpreserved. preserved. feldspar phenocrystsl phenocrysts, which which are are typically typically aligned parallel to to the The rhyolite here contains feldspar It is enriched substantially in such incompatible stratification incompatible trace trace elements elements as Zr, Ba, Ba, stratification and and foliation. It Hf, Hfl and and the the light light rare rareearth earth elements elements compared to the the rhyolite rhyolitein inthe thePortage PortageLake Lake Volcanics Volcanics near near Bergland (table 1). 1). These and sources sources for for the the two two Bergland (table These differences suggest different petrogenesis and rhyolites in spite of their physical physical proximity. proximity. Stop 7.--Basalt 7.--Basalt flows within withinthe theCopper CopperHarbor HarborConglomerate Conglomerate(Lake (Lake of the the Clouds Clouds overlook) overlook) Along the road road leading leading to Lake Lake of the the Clouds Clouds overlook overlook are several exposures of conglomerconglomerate of the Copper Conglomerate. To the north Copper Harbor Conglomerate. north is is aa good good view view of of Lake LakeSuperior Superior and and the the lowlowlands underlain underlain by by sedimentary sedimentaryrocks rocksofofthe theOronto OrontoGroup. Group. From From the the overlook overlook parking parking lotl lot, aa short short hike leads to to the overlook and a spectacular view of Lake Lake of the the Clouds Clouds and and the the Porcupine Porcupine MounMountains Wilderness State State Park. Park. The overlook is along the south escarpment of of a high ridge supported by a series of northdipping lava flows flows within the Copper Harbor Conglomerate (fig. 88). ) . The The low low area area south south of of the the ridge, ridgel within the Copper Conglomerate (fig. including Lake Lake of of the the Cloudsl Clouds, is underlain underlain by by sandstone sandstoneand andsiltstone siltstone and andaafew few basalt basalt flows flows which which Conglomerate. The higher regions farther farther south are are constitute the lower lower part part of of the the Copper Copper Harbor Conglomerate. by volcanic volcanic rocksl rocks, mostly rhyolite underlain by rhyolite of the the Porcupine Porcupine Volcanics. Toward surface shows shows a series series of of thin areal a large glaciated surface Toward the the east east end of the the overlook overlook area, basalt flowsl flows, which average a few meters thick. Individual flows can be readily identified by which average few can be identified by chilled chilled vesicular bases, in places containing inclusions of older flows, and by rubbly or vesicular tops. vesicular basesl in places containing inclusions of older flows, and by Abundant epidote alteration and and vesicle vesiclefillings fillingsalso alsoimpart impartaadistinctive distinctivegreenish greenishcast castto toflow flow margins. Hubbard the flows flows in as mostly andesite with with minor (1975b) described the in the Copper Copper Harbor as minor margins. Hubbard (1 basalt, but chemical analyses of two samples from this locality (table 1) indicate that they are basalt basaltl chemical analyses of two samples from this locality (table 1) indicate that similar to an an average basalt from the the Porcupine Porcupine Volcanics. Compared Comparedto toPortage PortageLake LakeVolcanics, Volcanics, these basalts are enriched in incompatible incompatible trace trace elements. Stop 8.--Upper part part of ofCopper CopperHarbor HarborConglomerate Conglomerateat atUnion UnionBay BayCampground Campground Good exposures of reddish sandstone containing containing thin conglomerate conglomerate beds are abundant along Superior at at this this locality locality (see (seefig. fig. 91. 9). The is noted noted for for The Copper Copper Harbor Conglomerate Conglomerate is the shore of Lake Superior volcanogenicconglomerates, conglomerates,which whichform formmost mostof of the the lower lower part part of the section coarse volcanogenic section throughout throughout much of its outcrop finer grained grained sandstones. sandstones. But, outcrop belt belt and which grade up into finer Butl north of the the Porcupine Mountains Mountains there there is is aa different different facies faciesrelationship. relationship. The lower part of the the formation formation isis lava flows; flows; conglomerate is very very subordinate. subordinate. These mostly sandstone, sandstonel siltstone and lava conglomerate is These rocks underlie south of the highway. The the high hills immediately south Thecoarse coarse conglomerate conglomerate facies is less abundant and is higher in the section. The Theexposures exposureshere here at at Union Union Bay Bay are near the base of the upper upper unit unit are probably probably about about 1,000 1,000 m above the the base base of of the the formation. formation. The and are The sandstones sandstones at at Union Union Bay Bay dip dip 10-20° to 10-20 to the the north. north.They Theyare arevolcanogenic volcanogenicand and quartz-poor. quartz-poor. They Theyshow showexcellent excellentexamples examples of of generally indicating indicating aa northeastward northeastwardcurrent currentvectorl vector, and and aa variety variety of of other trough cross bedding, bedding, generally sedimentary features features including including desiccation cracksl cracks, rip-up rip-up clasts, clasts, oscillation and current ripples, ripplesl and sedimentary swash marks. marks. Conglomerate north north of of the Porcupine The exposures of Copper Harbor Conglomerate Porcupine Mountains Mountains are are the the from the the source source highlands highlandsto tothe thesouth southof of any any part part of of the the unit unit on land. land. The farthest removed from The compared to to exposures exposuresfarther farther south south probably relative scarcity of thick units units of of coarse coarse conglomerate conglomerate compared 89 89 �ft 41 W. \/ - 2 /4 I /— ° -- 0 ' -- ( '— —---- _\__ \— Cdn9$,Wc3i:T2 k1 > 1. 50 N. / r: -- i 1 1 OCO 0 - w 2003 , - - 5 - 5 1 1MILE MILE 0 1000 H U H 1 SCALE 1:24000 1:24000 SCALE , w 3000 I 4000 —* — I - 00 5030 FEET 7000 6000 FEET I 1 KILOMETER 1 KILOMETER 4 CONTOUR CONTOURINTERVAL INTERVAL20 20FEET FEET Figure 7. 7.Location Locationand andgeologic geologicsetting settingofofstop stop6.6.Geology Geology generalizedfrom fromJohnson Johnsonand and Figure generalized White (1 969). White (1969). 90 �_______ R. 44 W. 51 N. KILOMETERS KILOMETERS 1 1 [ - - - H - MILES1 1 MILES .5 .5 .5.5 H 0 H 0 W 0 1 2 1I 0 2 3 H— k 1 1 SCALE 1:25000 1:25 000 SCALE 1 1CENTIMETER (2ENllMElE.RON ONTHE T I EMAP MAPREPIIESENTS REPRESENTS250 2%METERS MEIERSON ONTHE THEGROUND GROUND CONTOURINTERVAL INTERVAL 55METERS METERS CONTOUR Figure8.8.Location Location andgeologic geologicsetting settingofofstop stop7.7 Geology . Geologygeneralized generalizedfrom fromHubbard Hubbard Figure and (1 975b). (1 975b). 91 �R. 43 W. 51N. SCALE 1:24 000 — .5 — KILOMETERS 1 2 METERS 1000 2000 0 1000 0 .5 1 MILES 1000 0 1000 2000 3000 5000 4000 6000 7000 8000 9000 10000 FEET CONTOUR INTERVAL 5 METERS Figure9.9.Location Location andgeologic geologicsetting settingof ofstop stop8.8.Geology Geologygeneralized generalizedfrom fromHubbard Hubbard and Figure (1 975b). (1 975b). 92 �reflects the distal nature of these rocks and may may be be aa good good representative representativeof of much much of of the the Copper Copper Harbor beneath Lake Lake Superior. Superior. The unit here here shows shows aa crude coarsening-upward coarsening-upward trend as as opposed proximal parts parts of of the the unit. unit. This to the fining-upward trend typical of the more proximal This relationship relationship is is consistent with with northward northwardprograding progradingalluvial alluvialplain plain deposition. deposition. Several large large boulders boulders are are distributed distributed along the the beach and are are composed composed of conglomerate conglomerate typical of the lower lower part part of of the the formation formationelsewhere. elsewhere. These These conglomerates conglomerates contain contain almost excluexcluKeweenawan Supergroup Supergroupvolcanic volcanicrocks rockstypes typescommon commonininthe theregion. region. An An interestsively clasts of Keweenawan boulders. Although ing question is the source of these boulders. Althoughthe theCopper Copper Harbor Harbor does does contain contain some some conglomerate beds of this aspect aspect nearby, nearby, none none of of the thestreams streamsentering enteringLake LakeSuperior Superiornear nearhere here seem capable capableof of transporting transporting such such large largeboulders. boulders. Most have low low gradients, seem gradients, especially especially near the lakeshore, and and the the streambeds streambedsdo donot notcontain containsuch suchlarge largeboulders. boulders. No outcrops outcrops of coarse conglomlakeshore, erate would be expected nearby to the north north beneath beneath the lake; lake; so so ifif the theboulders bouldersare areglacial glacial erratics, erratics, they must perhaps from from the vicinity of must have have been transported for a long distance, distance, perhaps of Isle Isle Royale. Royale. Stop 9.--Nonesuch Shale Shale at at Bonanza Bonanza Falls Falls The most most complete exposure of the Nonesuch Nonesuch Shale in the region is along the Big Big Iron Iron River River BonanzaFalls, Falls,although althoughaccess accesstotoparts partsofofititisisdifficult difficult and and dangerous dangerousat at times times of of high water near Bonanza (see fig. fig. 10). 10). The TheNonesuch Nonesuchisisexposed exposed nearly nearly continuously in in aa gently gently southeast-dipping southeast-dipping section section Fallsto to the the sharp sharp bend bendin inthe the river river near nearthe the northeast northeast corner corner of of from just upstream upstream of Bonanza Bonanza Falls (1991) section 13. AAdetailed detailedmeasured measuredsection section is is presented presented by Suszek Suszek (1 991 ) and fig. fig. 11 11isisgeneralized generalized from that section. The Theexposed exposed rocks total 226 226 m m of of section, section, which which includes includes nearly nearly all of the Nonesuch, although neither the the upper nor lower contact Nonesuch, contact is is directly directlyexposed. exposed. The Nonesuch Shale Shale is is distinguished distinguished from from other other sedimentary units of the the Keweenawan Keweenawan by the the predominance of of gray, gray, green or or black, black, fine-grained fine-grained sediments. sediments. The Supergroup by TheBig BigIron IronRiver River predominanceof ofsiltstones siltstones and andfine finesandstones sandstonesover overtrue trueshales. shales. Many rocks show section has aa predominance trough cross asymmetrical ripples, ripples, rib rib and and furrow furrow structures, and cross bedding, symmetrical and asymmetrical and parting parting lineations. The shales, which which are most abundant lower in lineations. The finer-grained finer-grained rocks rocks include include well-laminated shales, in the section. The shaleyunits unitscommonly commonlyhave haveball balland and pillow pillowstructures structuresand andcalcareous calcareousconcretions. concretions. Theshaley The Nonesuch displays coarsening-upward at scales ranging from aa few coarsening-upward sequences at few meters meters to to the the entire entire thickness thickness of of the the unit. unit.On Ona asmaller smallerscale, scale,normally normallygraded gradedsequences sequences are are common common in in units from a few centimeters centimeters to aa few few meters meters thick. thick. concentrations of In the lower 10 10m m of of the thesection sectioncopper copper mineralization mineralizationcan can be be seen as concentrations chalcocite, bornite bedding planes. planes. The mineralization is is cogenetic cogenetic with the bornite and malachite along bedding the copper mineralization mineralizationat atthe the White White Pine PineMine Minewhere wherethe thedowndip downdip extension extension of of this unit major copper unit is is mined just just to to the the south south and and east. east. A good good exposure exposure of of the the mineralized mineralized base of the Nonesuch Nonesuch Shale and the top of of the theCopper Copper Harbor Conglomerate Conglomerate is is along alongthe the Little Little Iron Iron River River near nearthe thecenter centerof of the the SW SW 114, 1/4, Sec. 13, 13, but but It is an easy walk requires aa walk walk of about 1 mi south from Highway Highway 107. 107. It walk along along an an unmaintained unmaintained trail on the east bank of the river river for those those who who can can spend spend more time in the area. Remains Remains of of early early mining efforts for there, as as well well as as "ore" "ore" specimens from from old dumps. for native native silver silver can can be seen there, White Pine Mine Mine White The trip will will not not visit visitthe theWhite WhitePine Pine Mine; Mine; but butbecause because of the the importance importance of of this thisorebody, orebody, the following following brief briefsummary summary is is provided. provided. copper and andsilver silverfrom from aa very very large large strataform strataform orebody in the base of White Pine recovers copper Shale and and in in places places from from the upper few meters the Nonesuch Shale meters of of the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. Excellent summaries summariesof of the the geology geology and and origin origin of of the the orebody orebody are are provided provided by by White and Wright (1966), and others others(1 (1968), White (1 (1971), and Brown Brown(1 (1971). mostly of of (1966), Ensign Ensign and 9681, White 971 1, and 971 1. Ore, Ore, composed composed mostly copper, grades about about 1 .1%%Cu Cuand and99glt g/t Ag Ag over a mining height height chalcocite and lesser native copper, 1.1 typically about 5 m. m. Some Somebeds bedswithin withinthat thatinterval intervalconsistently consistentlycontain containgreater greater than than 3% 3%Cu. Cu. Reservesare areabout about200,000,000 200,000,000 tt of extractable ore. ore. Mining Mining of of the the gently gentlydipping dippingorebody orebody is is by by Reserves and pillar pillar method. method. The mine workings underlie about about 35 35 km2 km2 of of the low country room and country south south and and town of east of the town of White WhitePine. Pine. 93 �1 w - 1 7 4 - - i I 00 55 I + 1MILE MILE 00 47 7 I KILOMETER ; KILOMETER - CONTOUR CONTOUR INTERVAL INTERVAL 20 20FEET FEET Figure 10. 10. Location Locationand andgeologic geologicsetting settingof ofstop stop9.9.Geology Geologygeneralized generalizedfrom fromCopper Copper Figure Range Corp./Michigan CorpJMichiganGeological GeologicalSurvey Surveycooperative cooperativemapping mapping(unpublished). (unpublished). Range 94 �STRATIGRAPHIC SECTION SECTION OF NONESUCH NONESUCH SHALE SHALE AT AT BONANZA BONANZA FALLS FALLS STRATICRAPHIC Generalized from from Susiek Suszek (1991) (1991) Sandstone, Sandstone, siltstone, siltstone.rnudstone. mudstone. Fineto Fine— to coarse—grai ned. coarsening-upward coarsening—upward trend. coarse-grained, trend. 200— Reddish-brown increase in in top top 50 rn Reddish—brown units increase m of unit. unit. 8 3 SiItstone, sandstone. muastone. mustone. Fine— Siltstone. sandstone. Fine- to to medi.rn—grained, general general coarsening mediim-grained, ccarsening upward upward trend. trend Sndstcne. Sandstone, shale. shale. Coarse- to to fine— fine- grained. grained. Coarse— Fine— tornediun—grained. Sandstone. shale. Sandstone, shale. Fineto mediim-grained. CContains o n t a i n s some some red—brown red-brown units. units. oc Shale, sandstone. sandstone, mudstone. mudstone. Black B l a c k to to dark dark gray. gray. Lominites. Lcminites. trough trough cross c r o s s bedS, beds. and end undulatory undulatory bedding. Chioritic and henatitic Chloritic hematitic beds and and lenses. Calcareous concretions. lenses. concretions. Sandstone, siltstone. siltstone. mudstone. mudstone. Light to to dcrk dark gray wwith gray i t h some s o m e beds b e d s of of red red hematitic hematitic mudstone mudstone and siltstone. Fine—grained. Contains siltstone. Fine-grained. Contains carbonate lominite iominita units, ball boll and pillow pillow structures, and colcareous concretjons. structures, calcareous concretions. Fissil. shcie, Fissile shale. mmudstone, u d s t o n e , siltstone. siltstone. Block to Black to laninites with w i t h interbeds interbeds dark gray. Carbonate Carbonate lanintes of siltstone siltstone and and sandstone. sandstone. SSiltstone, i l t s t o n e , sandstone, sandstone. shale. shale. Fine—grained. Fine-grained. Dessication Dessication cracks, cracks, ball ball and pillow structures, floating floating clasts. clasts. Figure Measuredstratigraphic stratigraphicsection sectionof ofNonesuch Nonesuch Shale Shale along Big Iron River near Figure 11. Measured Falls, generalized from Suszek 991).1. Bonanza Falls, Suszek (1 (1991 95 �Copper Copper was introduced introduced to to the the Nonesuch Nonesuch Shale Shale mostly mostly during during early early diagenesis, diagenesis, probably probably by by upward upwardcirculating circulatingconnate connate water water which whichdissolved dissolvedcopper copper from from the the underlying underlyingredbeds. redbeds. Chalcocite, Chalcocite, largely of diagenetic diagenetic pyrite. pyrite. AAlater largely of of submicroscopic submicroscopic size, size, formed by the replacement of laterphase phaseofof others (in copper mineralization, documented by Mauk and others (1989) and Mauk and copper mineralization, Mauk (1989) and Mauk and others (inpress), press), introduced introduced native native copper, mostly mostly in in structurally structurallydisturbed disturbed zones. zones. This Thissecond secondstage stagemineralization mineralizationisis probably probably cogenetic with withthe theclassic classicnative nativecopper coppermineralization mineralizationof of the theKeweenawan KeweenawanSupergroup Supergroup basalts. basalts. Stop O.--Nonesuch Shale and Stop110.-Nonesuch and Freda Freda Sandstone Sandstoneat at Presque PresqueIsle IsleRiver River The The upper upper portion portionof ofthe theNonesuch NonesuchShale Shaleand andthe thebase baseof ofthe theFreda FredaSandstone Sandstoneare arewell well exposed exposed in in the the gorge gorge of of the thePresque Presque Isle Isle River River near its mouth mouth and and along the shore shore of of Lake Lake Superior Superior west west of of the theriver river(fig. (fig.12). 12).Continuous Continuousexposures exposuresalong alongthe thepicturesque picturesquegorge gorge of of the theriver riverextend extend from fromjust justupstream upstreamof ofNawadaha NawadahaFalls Falls to to the the lakeshore. lakeshore. Exposures Exposures continue continue in in bluffs bluffsalong alongthe the lakeshore for about about half half aamile milewest westof ofthe theriver rivermouth. mouth. In the the interest of of time, time, we will limit limit our our lakeshore for examination near the the river river mouth mouth and and aa short short distance to to the west along examination to exposures near along the the shore. shore. This This requires requires a round trip trip hike hike of of nearly nearly aa mile, mostly mostly on on well-maintained well-maintained trails trails and and stairways. stairways. The The rocks rocks exposed exposed here here are on the northeast northeast limb limb of of the the Presque Presque Isle Isle syncllne, syncline, aa gentle gentle 10ÂSW. SW.The TheNonesuch NonesuchShale Shalehere hereisis northwest-plungingfold. fold. Dips Dips range range from nearly nearly flat to to about about 100 northwest-plunging very for stop 9 on the Big Iron River Riverabout about30 30 km km to to the the east. east. The very similar similar to that described described for The lower lower part with copper part of of the thesection sectionin inthis thisarea area (not (notexposed) exposed) is is also also strongly strongly mineralized mineralized with copper and and contains contains aa fine-scale with the stratigraphy at the white fine-scale stratigraphy directly correlatable correlatable with White Pine Pine mine, mine, indicating indicating that thatsedimentary sedimentary conditions conditions were were very very uniform uniformover overthe theentire entireregion regionsurrounding surroundingthe the Porcupine Porcupine Mountains Mountainsduring duringNonesuch Nonesuchdeposition. deposition. The The upper upper part partof ofthe theNonesuch Nonesuchexposed exposedhere, here, as asdescribed describedin inmore moredetail detailby bySuszek Suszek (1991), consistsof offining-upward fining-upwardsequences sequencesand andlaminites laminitesinterbedded interbeddedwith withgraded gradedsandstones sandstonesand and (1991 1, consists siltstones. Most Mostrocks rocksare aredark darkgray graywith withaafew fewreddish reddishlenses lensesand and beds. beds. The upward to the through a zone in which The Nonesuch Nonesuch grades upward the Freda Freda Sandstone through which dark dark gray gray laminated siltstone and sandy mudstone mudstone is interbedded laminated and small-scale cross-bedded siltstone interbedded with withmediummediumto to coarse-grained coarse-grained reddish brown sandstone. The The upper upper contact contact of of the theNonesuch Nonesuchisisplaced placedwhere where the the reddish reddishsandstone sandstonebecomes becomes dominant. dominant. .-- Stop FredaSandstone Sandstonealong alongPresque Presque Isle IsleRiver River Stop 11.-11 Freda This This stop, stop, near near the the axis axis of of the thePresque Presque Isle Isle syncline (fig. 12), 121, shows showsreddish reddishcross crossbedded bedded sandstone typical of the lower lower part part of of the the Freda Freda Sandstone. Sandstone. The The gently gently southwest southwest dipping dipping beds beds exposed here are are probably probably 100-200 100-200 m above the the base base of of the the formation and slightly slightly higher higher stratistratigraphically than those seen seen at at stop stop 10. They They are are mostly mostly lithic lithic sandstone sandstone and and are somewhat somewhat micaceous in places. The The Freda Freda marks the return return to to fluvial fluvial redbed redbed deposition deposition following followingthe thelacustrine lacustrine deposition of of the theunderlying underlyingNonesuch NonesuchShale. Shale. deposition The The Freda Freda is a very thick unit unit in in much much of of the therift riftininthe theLake LakeSuperior Superiorregion regionand andisisvolumetvolumetrically the dominant unit unit of of the the post-rift post-riftsedimentary sedimentary fill. fill. Along Along the the Montreal Montreal River, River, about 30 30 km km to to the is even even thicker the west, west, about about 4,000 4,000 mmofofFreda Fredaare are exposed. exposed. Seismic Seismic sections sections indicate that itit is beneath the the Lake. Lake. beneath The generally becomes becomesfiner-grained finer-grainedand andmore moremature matureupward. upward. Excellent The Freda Freda Sandstone generally Excellent exposures of the upper part of the seen near nearthe the mouth mouth of of the Montreal the Freda Freda can be seen Montreal River, in in bluffs bluffs along the the lakeshore. lakeshore. along Stop 12.-12.- Jacobsville JacobsvilleSandstone Sandstone Stop The roadcut along the west side of the road is a fairly typical exposure of the the conglomerate conglomerate found abundantly in the Jacobsville Sandstone Sandstone in in this this region. region. Although Although exposures exposures are rare, rare, west of of Lake Gogebic the Jacobsville appears to be dominated by by conglomerate conglomerateand and coarse coarse sandstone sandstonein in contrast it is to mature quartzose, quartzose, feldspathic, feldspathic, and lithic is a submature to contrast to to areas areas farther east where it arenite with with minor minor shale, shale, siltstone, siltstone, and and conglomerate conglomerate layers (Kalliokoski, 1982). 1982). At strikes east eastand anddips dips9O 9° to to the the north, north, but only about 500 m At this this stop stop the the conglomerate conglomerate strikes to the the north north ititdips dips steeply steeply to the south south (62°) (62O)as as aa result result of drag drag along the Keweenaw The to Keweenaw fault. fault. The 96 96 �17 45W. R. 1 /' 20/ 12 —- Pres ue ..v / -, — $ - 'c — V I' / 1' — — I I — 7 — Presgue Isi State Campgro ere • 'Manido — 1 / 224 — /i/ ,/" \ —. I I -I I 3O(, I - ._ :i 'I _.. 'Z1CS, \fl I '0 / J l'\ '% ( 1 1--\ \ -__ L_._jr _2Li II — - y:.__i . 25 — —— —— — ——— — r MILES 1 MILESI - - - - I * - - - .5 .5 - - .5 .5 I LJ . I ____ J KILOMETERS1 1 KILOMETERS : — /iS awadaht ails 0 / 1 —i. j'I / 29 / 'T50 J 0 0 1 2 1 0 0 —1 1I SCALE 1:25 1:25 000 000 SCALE CENTIMETER ON ON ThE THEMAP MAP REPRESENTS 250 METERS ON THE GROUND 11CENW4ETER REPRESENTS 250 METERS ON ThE GROUND CONTOUR INTERVAL INTERVAL 55 METERS METERS CONTOUR Locationand and geologic geologic setting setting of of stops stops 10 10and and 11. 1 1. Geology Geologygeneralized generalized from from Figure 12. 12. Location Figure Copper Range CorpJMichigan Geological Survey cooperative mapping (unpublished). Copper Range Corp./Michigan Geological Survey cooperative mapping (unpublished). 97 �R. 45 W. 405 21 : ' . r_) 2 Portage Lake V canics - fflN AWAL - KE 12Jacob Gravel Pit - T. 48 N. lie Sandston r 28 (H -- 410 NH ' H H . H) omaston 500 500 H +-- / 0 2000 2000 METERS METERS 1000 1000 00 H H H H 1000 0 1000 ! , 2000 2000 — 1 1 1 ! 4000 4000 ! 6000 6000 FEET FEET SCALE 1:25 1:25 000 000 11 CENTIMETER CENTIMETER ON THE THE MAP MAP REPRESENTS REPRESENTS 250 METERS METERS ON ThE THEGROUND GROUND CONTOUR CONTOUR INTERVAL INTERVAL 5 METERS METERS Figure Figure 13. 13. Location Locationand andgeologic geologic setting setting of of stop stop12. 1 2.Geology Geologygeneralized generalized from from Copper Copper Range CorpJMichigan Geological Survey cooperative mapping (unpublished). Range Corp./Michigan Geological Survey cooperative mapping (unpublished). 98 �is poorly poorly consolidated and and weathers weathers to to a material that superficially conglomerate is superficially resembles resembles glacial till or or outwash, which covers covers most of the roadcut. From From time to time parts parts of this this material material slump till away to of fresh conglomerate to expose expose less less weathered conglomerate, conglomerate, and small exposures of conglomerate are usually exposed in the drainage drainage ditch ditch beside beside the road. road. conglomerate is is clast-supported. clast-supported. Coarse sandy matrix matrix surrounds pebbles. pebbles. Where The conglomerate Coarse sandy Where weathered, it is generally unconsolidated unconsolidatedbut buton onfresher freshersurfaces surfacesisisfairly fairlywell wellcemented. cemented. Clay fills weathered, interstices and and coats coats all all grains, grains. It It is uncertain whether the clay is a product of diagenetic diagenetic most interstices mechanicalinfiltration infiltration resulting resulting from from seepage seepageof of muddy muddy water water through coarse cement or is an early mechanical alluvium. are subrounded subroundedto to well well rounded, rounded, range rangein in size sizefrom from 3-1 3-10 cm, and consist mostly Clasts are 0 cm, mostly of of iron-formation (63-77%) iron-formation (63-77%)and and quartzite quartzite (8-20%) (8-20%) derived derived from from Early Early Proterozoic Proterozoic rocks rocks such such as as those those Range. Small amounts of altered rhyolite (1-5%) (1-5%) are are believed believed to be be now exposed in the Gogebic Range. from Keweenawan Keweenawan Supergroup Supergrouprocks. rocks. Vein Vein quartz quartz (9-1 (9-10%), litholoderived from 0%), chert (1%), (1%I, and other lithologies (1 % % or or less) less) derived derivedfrom from Archean Archean rocks rocks are are minor. minor. Several Several other conglomerate conglomerate outcrops outcropsto to the west have have similar compositions, compositions, but outcrops outcrops less less than 2 km km to to the thesoutheast southeastalong alongJackson Jackson Creek (shown by X on the map) are dominated dominated by by vein vein quartz quartz (73-82%) (73-82%) with Creek (shown with lesser lesser amounts amounts of of (11-13%) and iron-formation iron-formation (9-1 (9-12%). suggest that that most most of of the quartzite (1 1-13%) and 2%). These These clast lithologies suggest area to to the the south had been been stripped stripped of of Keweenawan Keweenawanvolcanics volcanicsby bythe the time time of of Jacobsville source area deposition. Although Althoughthe thesurface surfaceconsisted consistedmostly mostlyofofEarly EarlyProterozoic Proterozoicsedimentary sedimentaryrocks, rocks, the the presence of of large quantities of vein vein quartz quartz pebbles pebbles indicates indicates at at least leastsome some drainages drainageswere wereeroded eroded Archean crystalline crystalline rocks. down into into Archean In a few places appear to to be imbricated imbricated but but otherwise bedding within within places clasts found in in place appear conglomerate units units is is not not apparent. apparent. Clay nearly all all clasts clasts so so that that the the conglomerate Clay and iron coatings cover nearly clasts are are broken brokenopen. open. Many various lithologic types are not apparent unless clasts Many clasts clasts have have aa highly highly like desert desert varnish varnish and and some somehave havedistinctly distinctly striated striated shiny surface or patina that looks looks remarkably like surfaces of of unknown origin. origin. AAfew fewclasts clastshave havebeen beenfound foundthat thathave haveshapes shapes and and surface textures surfaces resembling ventifacts. east of of the the road, road, slightly higher in the section, the In the streambanks east the conglomerate conglomerate is is interinterwith coarse sandstone. sandstone. The are poorly poorly sorted, sorted, discontinuous discontinuous irregular layered with The sandstone sandstone layers are approximately 5-30 5-30 cm thick. The layers approximately Thesandstone sandstoneconsists consists of of subangular subangularto tosubrounded, subrounded, medium medium to coarse coarse sand (.25-2 mm) mm) and and gravel (2-30 (2-30 mm) mm) with with larger larger cobbles cobbles scattered scattered throughout. throughout. In thin thin section the sand is framework framework supported predominantly of of quartz and feldspar with with supported and composed predominantly minor lithic fragments, biotite, and and muscovite. muscovite. Pores Poresare are filled filled with withclay clayand andmany manygrains grainsare are coated coated with with iron iron minerals. minerals. 99 �CITED REFERENCES CITED Behrendt, J.C., Green, Green, A.G., A.G., Cannon, Cannon, W.F., W.F., Hutchinson, Hutchinson, D.R., D.R., Lee, Lee, M., M., Milkereit, B., Behrendt, J.C., B., Agena, W.F., C., 1988, Crustal structure of the Midcontinent Rift System-System-W.F., and Spencer, Spencer, C., Midcontinent Rift GLIMPCEdeep deepseismic seismicreflection reflectionprofiles: profiles:Geology, Geology,v.v.16, 16, p. p. 81 81-85. results from GLIMPCE -85. Bornhorst, T.J., T.J., Paces, J.B., Grant, Grant, N.K., N.K., Obradovich, Obradovich, J.D., J.D., and and Huber, Huber, N.K., N.K., 1988, Age of Bornhorst, Paces, J.B., mineralization, Keweenaw Keweenaw Peninsula, Peninsula, Michigan: Michigan: Economic native copper mineralization, Economic Geology, v. 61 9-625. 83, 83, p. 619-625. Brannon, J.C., 1984, flows of the Brannon, J.C., 1984, Geochemistry Geochemistry of successive lava flows the Keweenawan KeweenawanNorth North Shore Volcanic Volcanic Group: Group: St. Louis, University, Ph.D. Ph.D. dissertation, dissertation, 31 312 Shore Louis, Washington University, 2 p. Brown, A.C., A.C., 1971, 1971,Zoning Zoningininthe theWhite WhitePine PineCopper Copper deposit, deposit, Ontonagon Ontonagon County, Michigan: Michigan: Economic Geology,v. v. 66, 66, p. P. 543-573. Economic Geology, Cannon, W.F., W.F., in press, The Midcontinent Cannon, Midcontinent Rift Rift in in the the Lake Lake Superior Superior region region with withemphasis emphasis on on its geodynamic evolution: Tectonophysics. Tectonophysics. Cannon, W.F., W.F., Green, Green,A.G., A.G., Hutchinson, Hutchinson, D.R.., D.R. Lee, Lee, M., M., Milkereit, B., J.C., Halls, Cannon, B., Behrendt, Behrendt, J.C., Halls, H.C., Green, Green, J.C., J.C., Morey, Morey, G.B., G.B., Sutcliffe, Sutcliffe, R., Spencer, C., C., 1989, The North H.C., R., and Spencer, American Midcontinent MidcontinentRift Rift beneath beneathLake Lake Superior Superior from from GLIMPCE GLIMPCE seismic reflection reflection profiling: Tectonics, v. 8, p. 305-322. profiling: Tectonics, v. Cannon, W.F., W.F., Peterman, Peterman,Z.E., Z.E.,and andSims, Sims,P.K., P.K., 1990, 1990, Structural and isotopic evidence for for Cannon, thrust faulting Archean and and Early Early Proterozoic Proterozoic rocks rocks near near the the Middle Proterozoic thrust faulting of of Archean Gogebic Range, Range, Michigan Michiganand andWisconsin Wisconsin(abs): (abs): 36th 36th Institute Institute on on Lake Lake Superior Superior Geology, Bay, Ontario Ontario Proceedings, Proceedings,Part Part1,1,Abstracts, Abstracts, p. p. 1 11-13. Geology, Thunder Bay, 1-13. Cannon, W.F., W.F., and and Nicholson, Nicholson, S.W., S.W., 1992, Contributions Cannon, Contributions to to the the geology geology and and mineral mineral resources of of the the Midcontinent Midcontinent rift resources rift system, system, A--Revisions A--Revisions of stratigraphic stratigraphicnomenclature nomenclature Supergroupof of northern northern Michigan: Michigan: U.S. within the the Keweenawan Keweenawan Supergroup U.S. Geological Geological Survey Bulletin 1970, p. A1-A8. A1 -A8. Copper Range CorpJMichigan Corp./Michigan Geological Survey Survey cooperative cooperative mapping program, unpublished unpublished on file at Geological Survey Division, Division, Michigan Department maps on Department of Natural Natural Resources, Lansing, Mich. Resources, Mich. Davis, D.W., D.W., and Paces, J.B., 1990, Time Davis, Paces, J.B., Time resolution of geologic geologic events events on on the the Keweenaw Keweenaw Peninsulaand andimplications implicationsfor fordevelopment developmentofofthe theMidcontinent Midcontinentrift rift system: system: Earth Peninsula Earth and Planetary Science ScienceLetters, Letters,v.v. 97, 97, p. 54-64. 54-64. Davis, D.W., D.W., and Sutcliffe, R.H., Davis, R.H., 1985, 1985,U-Pb U-Pbages ages from from the the Nipigon Nipigonplate plate and and northern northernLake Lake Superior: Geological 572-1 579. Geological Society Society of of America America Bulletin, Bulletin, v. v. 96, 96,p.p.1 1572-1 579. Ensign, C.O., C.O., White, White, WS., W.S., Wright, Wright, J.C., J.C., Patrick, Patrick, J.L., J.L., Leone, Leone, R.J., R.J., Hathaway, Hathaway, D.J., D.J., Tramell, Tramell, Ensign, J.W., Fritts, J.W., Fritts, J.J., J.J., and andWright, Wright, T.L., T.L.,1968, 1968,Copper Copperdeposits depositsin inthe theNonesuch Nonesuch Shale, Shale, White Pine, in Ridge, J.D., ed., 933Pine, Michigan, in Ridge, J.D., ed., Ore Ore deposits of the the United United States, States, 119331967; the Volume: American the Graton-Sales Graton-Sales Volume: American Institute Institute of of Mining, Mining, Metallurgical, Metallurgical,and and Engineers,Inc., Inc.,New NewYork, York, p. p. 460-488. 460-488. Petroleum Engineers, Green, J.C., 1982, rocks, in Wold, Wold, R.J., R.J., and and Hinze, Hinze, Green, J.C., 1982, Geology Geology of Keweenawan Keweenawan extrusive rocks, W.J., basin: Geological W.J., eds., eds., Geology Geology and tectonics of the Lake Lake Superior Superior basin: Geological Society of America Memoir 156, p. 47-55. 100 �______ Hinze, W.J., Braile, L.W., and Chandler, Chandler,V.W., V.W., 1990, 1990, A geophysical profile profile of the southern Hinze, W.J., Braile, L.W., v. 9, 9, of the Midcontinent Lake Superior: Superior: Tectonics, v. margin of Midcontinent Rift System in western Lake p. 303-310. 303-310. Hubbard, H.A., H.A., 11975a, 975a, Lower Keweenawan volcanic rocks of Michigan Hubbard, Michigan and and Wisconsin: Wisconsin: U.S. Geological Survey SurveyJournal Journalof of Research, Research,v.v.3,3, p. p. 529-541. 529-541. U.S. Geological 1 975b, Geology Geology of of Porcupine Mountains in Carp River and White Pine 1975b, Pine quadrangles, Michigan: Journal of of Research, Research,v.v.3, 3, p. P. 51 519-528. Michigan: U.S U.S Geological Geological Survey Journal 9-528. Johnson, R.F., White, W.S., R.F., and White, W.S., 1969, 1969,Preliminary Preliminaryreport report on on the the bedrock bedrockgeology geology and and deposits of of the the Matchwood quadrangle, quadrangle, Ontonagon OntonagonCounty, County,Michigan: Michigan: U.S. copper deposits Report, 31 31 p. Geological Survey Open-File Open-File Report, Kalliokoski, J., 1982, in Wold, Wold, R.J., R.J., and Hinze, Hinze, W.J., W.J., eds., Kalliokoski, J., 1982, Jacobsville Jacobsville Sandstone, Sandstone, in eds., Geology basin: Geological and tectonics of the Lake Lake Superior basin: Geological Society of America Memoir Memoir p. 147-1 147-156. 56. 156, p. King, °x2° quadrangle, King, E.R., E.R., 1987, Aeromagnetic Aeromagnetic map of the Iron Iron River River 11Ox2O quadrangle, Michigan Michiganand and l-1360F, Wisconsin: U.S. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Map 1-1 360F, scale scale 1:250,000. 1:250,000. Klasner, J.S., 1989, Klasner, J.S., 1989, Bouguer Bouguer gravity gravity anomaly anomaly map and geologic interpretation of the the Iron Iron °x2° quadrangle, Wisconsin: U.S. River 1 Ox2O quadrangle, Michigan and Wisconsin: U.S. Geological Geological Survey Survey Miscellaneous Investigations Investigations Map Map 1-1 I-i 360E, 360E, scale scale 11:250,000. :250,000. Mauk, J.L., Kelly, Mauk, J.L., Kelly, W.C., W.C., van van der der Pluijm, Pluijm, B.A., B.A., and and Seasor, Seasor, R.W., R.W., in in press, press, Relations Relations between between deformation and sediment-hosted copper mineralization: mineralization: evidence evidence from from the White deformation Pine portion of of the the Midcontinent rift rift system: system: Geology. Pine portion Geology. Mauk, J.L., Seasor, R.W., Kelly, Kelly, W.C., W.C., Andrews, Andrews, R.A., W.S., 1989, Mauk, J.L., Seasor, R.W., R.A., and and Nelson, W.S., 1989, The The White White Pine stratiform stratiform copper deposit, in in Margeson, Margeson, G.B., G.B., ed., ed., Precambrian Precambrian geology geology and and occurrences, Michigan's upper upper peninsula: peninsula: Society metal occurrences, Society of of Economic Economic Geologists Geologists field conference, conference, p. 143-153. 143-153. Nicholson, S.W., S.W., and and Shirey, Shirey, S.B., S.B., 1990, 1990, Midcontinent Nicholson, Midcontinentrift riftvolcanism volcanismin inthe the Lake Lake Superior Superior region--Sr. Nd Nd and and Pb Pbisotopic isotopicevidence evidencefor foraamantle mantleplume plumeorigin: origin: Journal Journal of of region--Sr, Geophysical Research, Research,v.v.95, 95,p. p. 10581 10581-10868. Geophysical -10868. Ojakangas, R.W., R.W., and and Morey, Morey, G.B., G.B., 1982, Keweenawan Ojakangas, Keweenawanpre-volcanic pre-volcanicquartz quartzsandstones sandstonesand and Superior region, region, in in Wold, Wold, R.J., R.J., and Hinze, Hinze, W.J., W.J., eds., related rocks of the Lake Superior eds., and tectonics tectonics of the Lake Superior Superior basin: basin: Geological Geology and Geological Society of America America Memoir 156, p. 85-96. 85-96. Paces, J.B., J.B., 1988, Magmatic characteristics Paces, Magmatic processes, processes, evolution evolution and mantle source characteristics contributing to basalts-Portage Lake Lake basalts, basalts, contributing to the the petrogenesis petrogenesis of Midcontinent Midcontinentrift riftbasalts--Portage Michigan: Houghton, Keweenaw Peninsula, Peninsula, Michigan: Houghton, Michigan Michigan Technological Technological University, University, Ph.D. dissertation, 413 p. Ph.D. p. Paces, J.B., J.B., and and Bell, Bell, K., K., 1989, Non-depleted the Superior Paces, Non-depleted sub-continental mantle beneath the of the Canadian Shield: Nd-Sr isotopic and trace element evidence from from Province of Canadian Shield: Midcontinent rift basalts: Geochimica CosmochimicaActa, Acta,v.v. 53, 53, p. p. 2023-2035. 2023-2035. Geochimica et Cosmochimica 101 �Ruiz, Ruiz, J., Jones, Jones, L.M., L.M., and and Kelly, Kelly, W.C., W.C., 1984, 1984,Rubidium-strontium Rubidium-strontiumdating dating of of ore ore deposits deposits hosted hostedby byRb-rich Rb-richrocks rocksusing usingcalcite calciteand andother othercommon commonSr-bearing Sr-bearingminerals: minerals: Geology, v. 12, 12, p. p. 259-262. 259-262. Geology, Suszek, Suszek, T.J., T.J., 1991, 1991,Petrography Petrographyand andsedimentation sedimentationof ofthe theMiddle MiddleProterozoic Proterozoic (Keweenawan) Formation, western Lake Superior Superior region, region, Midcontinent Midcontinent rift (Keweenawan) Nonesuch Formation, rift system: 98 p.p. system: Duluth, Duluth,University UniversityofofMinnesota-Duluth, Minnesota-Duluth,M.S. M.S.thesis, thesis,1198 White, paleohydrologicmodel modelfor formineralization mineralizationof ofthe theWhite WhitePine Pinecopper copper White, W.S., W.S., 1971, 1971,AApaleohydrologic deposit, Geology, v. v. 66, 66, p. 1-13. deposit, northern northern Michigan: Economic Economic Geology, 1-13. White, 966, Sulfide White, W.S., W.S., and andWright, Wright,J.C., J.C., 1 1966, Sulfidemineral mineralzoning zoningininthe thebasal basalNonesuch NonesuchShale, Shale, northern northern Michigan: Michigan: Economic EconomicGeology, Geology, v. 61, 61, p. p.1171-11 1171-1 190. 90. 102 �GEOLOGY OF ThE GREAT LAKES TECTONIC TECTONICZONE ZONE INTHE IN THE MARQUE TIE AREA, MARQUETTE AREA, MICHIGAN MCHIGANA ARCHEAN ALATE LATE ARCHEAN - PALEOSUTURE PALEOSUTURE P.K. P.K. Sims Sims and and Z.E. Z.E. Peterman Peterrnan U.S .Geological Geological Survey, Survey, Federal Federal Center, Center, U.S. Denver, Denver, Colorado Colorado �the geology geology of tectonic zone in the Guide to the of the the Great Lakes tectonic Marquette area, area, Michigan--A Michigan--A Late Archean paleosuture P.K. and Z.E. Peterman P.K. Sims and SUMMARY length The Great Lakes tectonic zone (GLTZ) is is an Archean crustal boundary of subcontinental length that separates a greenstone-granite terrane (southern part of of Superior Superior province of Canadian Shield) on on the the north north from a partly partly older older gneiss gneissterrane terrane on on the south., south. The TheGLTZ GLTZisisgenerally generally Shield) collision. The tectonic zone is paleosuture resulting resulting from continent-continent collision. interpreted as a paleosuture covered in most of the Lake covered Lake Superior Superior region region by by Proterozoic Proterozoic rocks rocks or orPleistocene Pleistoceneglacial glacialdeposits, deposits, and its position and and characteristics characteristics were were previously previously determined determined mainly mainlyby by geophysical geophysical data. data. Geologic mapping mappingin in the the Marquette, Marquette, Michigan Michigan area area provides provides for for the first time direct Geologic direct observations of of the structure. observations In the the Marquette Marquette area, area,the theGL1'Z GLTZisischaracterized characterized by by aa zone zone of of mylonite mylonite (orthomylonite) (orthomylonite) that that formed at brittle-ductile brittle-ductile transition transition conditions; conditions; this this was superposed on on previously previously deformed deformed rocks rocks of both the Archean Archean greenstone-granite greenstone-graniteterrane terraneand andthe theArchean Archeangneiss gneissterrane. terrane. The W. Foliation in the mylonite strikes about boundaries of the GLTZ GLTZ trend trend about aboutN. N. 600 60' W. N. 70' 70° W. W. and and dips dips steeply steeply southwest. southwest. A pronounced pronounced stretching lineation and tight fold hinges N. about42° 42' S. S. 430 43O E. The attitude attitude of of the the stretching stretching lineation (line (line of of tectonic tectonic transport), transport), plunge about of movement sense, indicate that collision together with asymmetric structures indicative of collision at at this this was oblique. oblique. This resulted in dextral-thrust locality was dextral-thrust shear along along the the boundary, boundary, northwestward northwestward vergence, and and probable probable overriding overriding of ofthe the greenstone-granite greenstone-graniteterrane terrane by by the the gneiss gneiss terrane. terrane. vergence, Transmittal of the dextral shear stress across a large area of of the the greenstone-granite greenstone-granite crust crust (Superior province) to the the north north may may have have formed formed the thenearly nearly east-west east-west foliation, foliation, upright upright folds, folds, and northwestdextralfaults faultsand andshear shearzones zones at at least least as as far north as the northwest- to east-west-trending east-west-trending dextral the Quetico fault, fault, in in southern southern Ontario, Ontario, a distance distance of of about about 250 250 krn. km. These structures in Superior province rocks are superposed on on older older recumbent recumbent folds. folds. angular bends bends that alternately trend As a whole, the GL1'Z GLTZ is characterized by systematic systematic angular trend westwestnorthwestward, as in in the the Marquette Marquette area, and northeastward. northeastward. This northwestward, as This zigzag zigzag pattern probably probably reflects relict irregularities in the continental margin (Superior province) province) composed composed of of greenstone-granite crust. crust. Late Archean convergence convergence along this margin resulted in aa variable variable greenstone-granite LateArchean trajectory of stress into the the greenstone-granite greenstone-granite crust crust and and probably probably in in along-strike along-strike diachroneity diachroneity of of orogeny. The orogeny. The major major deformation deformation resulted resulted from from oblique oblique compression compression at at promontories, promontories, which which which compressive compressivestress stresswas wasdirected directedinto intothe thecrust. crust. In addition to to acted as buttresses against which the dominant strike-slip faults faults also also formed, formed, such such as as the the dominant foliation, foliation, major brittle-ductile brittle-ductile to brittle strike-slip Vermilion fault fault system system in in northern northern Minnesota Minnesota and the Quetico and Rainy Vermilion Rainy Lake-Seine Lake-Seine River River faults in southern Ontario; these resulted from a more brittle continuum of the the transcurrent transcurrent shear caused by collision along the GLTZ. INTRODUCTION km The Great Lakes tectonic zone (GLTZ) is an Archean crustal boundary more than 1,000 1,000 krn long that separates a greenstone-granite terrane (southern part of Superior province) greenstone-granite terrane province) on the north from a gneiss gneiss terrane terrane on on the thesouth south(Sims (Sims and andothers, others,1980; 1980;Sims Sims and and Peterman, Peterman, 1981; 1981; Peterman, 1979). The The GLTZ GLTZisiscovered covered throughout throughout most of of the the Great GreatLakes Lakesregion region by by younger younger 105 �glacial deposits, deposits,but but recently recentlyitithas has been been delineated delineated and studied Proterozoic rocks or Pleistocene Pleistocene glacial in outcrop in an area area south southof of Marquette, Marquette,Michigan Michigan (fig. (fig. 1). 1). The The boundary boundary was was first first recognized recognized in in Minnesota Minnesota (Sims (Sims and andMorey, Morey,1973; 1973; Morey Morey and andSims, Sirns,1976) 1976) from regional geologic relations, relations, which which indicated indicated that that the two adjoining basement terranes terranes had had different geologic histories histories and probably had evolved separately. Regional evolved separately. Regional magnetic magnetic and and gravity gravity data were utilized to determine the the position position of of the the boundary. boundary. Later Later(Sims, (Sims,1980), 1980),the the boundary boundary approximately delineated delineated in the western part of was approximately of Upper UpperMichigan Michigan(Sims, (Sims, 1980; 1980; Sims and others, 1984) 1984) and northwestern Wisconsin (Sims and others, 1985), 1985), east of the the Middle Middle Proterozoic Midcontinent rift system, system, and itit was was inferred by by indirect indirect evidence evidence to to extend extend eastward through the Sudbury the Middle Middle Proterozoic Proterozoic Sudbury structure, where it is truncated by the Grenville tectonic zone (Sims (Sims and others, others, 1980). 1980). Recent geologic geologic mapping in the Sands Sands and and Palmer Palmer7½-minute 7%-minutequadrangles, quadrangles, Michigan Michigan (fig. (fig. 1), I), previously mapped mapped by by Gair Gair and Thaden (1968) (1968) and Gair (1975), (1975), has delineated this Archean outcrop for for the thefirst firsttime time(Sims, (Sims,1991). 1991). It is exposed exposed on the south side side of the the Early Early boundary in outcrop Proterozoic Proterozoic Marquette Marquette synclinorium, synclinorium, and its northwestern projection projection into the the trough trough coincides coincides with a major Early Early Proterozoic Proterozoic fault, fault,the the Richmond Richmondfault. fault. In the Marquette area, area, the the GLTZ GLTZisis wide that is overprinted krn wide overprinted on rocks of both the the greenstone-granite greenstone-granite a mylonite zone about 2 km terrane and Inthis this area, area,the theGL1'Z GLTZisisinterpreted interpreted as asaacontinentcontinentand the the Archean Archean gneiss terrane. In continent collision zone. The resulting in in dextral dextral wrench wrench shear shear on on the the collision zone. The collision collision was oblique, resulting 60ÂW.-trending the N. 60° W.-trending boundary boundary and and northwestward northwestward vergence vergence of of the the gneiss gneiss terrane terrane against the greenstone-granite terrane. The purpose of this field guide is to examine examine the exposed exposed GLTZ GLTZ in the context of of the regional geology, to to discuss discuss genetic geneticrelationships relationshipsbetween betweenconvergence convergencealong alongthe theboundary boundaryand and structural structural geology, features in the Archean rocks to the north, and to present present aa new new interpretation interpretation of of the theevolution evolution of the GLTZ throughout throughout the the Lake Lake Superior Superior region. region. GEOLOGIC GEOLOGIC SETI1NG SETTING in the Sands and Palmer moderately well exposed in The Great Great Lakes Lakes tectonic tectonic zone (GLTZ) (GLTZ) isis moderately 7%-minute quadrangles in Upper Upper Michigan Michigan (fig. (fig. 1). 1). It separates separates the thetwo two distinctive distinctive Archean 7½-minute terranes in the area. area. The Thenorthern northerngreenstone-granite greenstone-granite terrane terraneisiscomposed composed largely largely of Late granitoid rocks, rocks, with with subordinate subordinate approximately approximately coeval metavolcanic and Archean granitoid metasedimentary metasedimentary rocks rocks of of greenstone greenstone affinity. affinity. The layered rocks and most of the granitoid rocks were metamorphosed metamorphosed (mainly to greenschist greenschist facies) facies) and deformed during Late Archean orogeny. The southern southernArchean Archeangneiss gneissterrane terraneisiscomposed composedmainly mainlyof oflayered layered gneiss, gneiss, migmatite, migmatite, orogeny. The and amphibolite--rocks that are are distinct distinct from from those those in in the the greenstone-granite greenstone-granite terrane. terrane. Except amphibolite--rocks that Except post-tectonic, generally for late-tectonic to post-tectonic, generally small(?) small(?)granitoid granitoidbodies, bodies,the therocks rocksofofthe the terrane terrane are metamorphosed, metamorphosed, mainly to to amphibolite amphibolite facies. facies. The rocks exposed within within the two two terranes in Upper Michigan Michigan are are closely closely similar to those in Minnesota (Morey (Morey and and Sims, Sims, 1976; 1976; Sims and 1980), thus others, 1980), thus establishing establishingthe the identity identity of ofthe the GLTZ GL1'Z in in the the Marquette area. are overlain overlain in in the Marquette the Republic The Archean rocks in Michigan are Marquette synclinorium, synclinorium, the trough, River, Clark Clark Creek, Creek, and and Baraga Baraga basins basins by by shelf and foredeep deposits deposits of of trough, and the Dead River, Cannonand andGair, Gair,1970; 1970;Barovich Barovich the Early Proterozoic Proterozoic Marquette Marquette Range RangeSupergroup Supergroup(fig. (fig. 1;1;Cannon and others, 1989). 1989). 106 �Bayley(1897) (1897)introduced introducedthe thenames names"northern northerncomplex" complef for the Archean rocks rocks Van Hise and Bayley north of the Marquette synclinorium and southern complef for the Archean rocks south north synclinorium and "southern complex" for the Archean rocks south of the syndilnorium. synclinorium. relationships in A Late Archean age age for for the the GL1'Z GLTZisis now now established established by regional geologic relationships north-central United United States. States. The Archean rocks in in the the greenstone-granite greenstone-granite terrane terrane in in northern northern north-central Minnesota (Hudleston and others, 1988) and northernmost Michigan (fig. 1; Sims, 1991) are others, 1988) Michigan (fig. 1; Sirns, are mainly by by ductile ductileand and brittle brittle structures structures formed formed in in response to dextral dextral shear, shear, which which characterized mainly accords with with the the deformation deformation pattern pattern observed observed in in exposures exposures of ofthe the GLTZ GLTZ south of Marquette. west-trending steep foliation and upright These structures include a generally generally west-trending upright folds, folds, widespread indicative of dextral shear; the Z-shaped folds, and northwest- to west-trending dextral faults, indicative the (Johnson and Bomhorst, Bornhorst, 1991). structures are superposed on recumbent folds (Johnson 1991). In In contrast, contrast, Early Early Proterozoic Penokean Penokean deformation deformation in in the the Marquette Marquette area had little effect on the Archean Proterozoic basement (Cambray, 1984). Cambray (1984) (1984)proposed proposed that that the Penokean deformation was basement (Cambray, 1984). produced by by horizontal horizontal compression compressionthat thatwas wastransmitted transmittedfrom fromthe thebasement basement to to the folded folded cover cover produced rocks by narrow ductile shears in the basement. Readjustment of rigid basement blocks along rocks by narrow ductile shears in the basement. weaknesses,which whichresulted resultedininsome someshortening shorteningbut but not not folding folding of of the the these shears utilized old weaknesses, basement rocks. proposed a rocks. For Forthe theEarly EarlyProterozoic ProterozoicMarquette Marquettesyndlinorium, synclinorium, Cambray (1984) proposed nearly north-south compressional which initially initially produced produced reverse dip slip axis, which slip on on faults faults compressional axis, bounding the syncline and compressed the Early Proterozoic sedimentary rocks within the bounding and compressed the Early Proterozoic sedimentary within the syncline into into west-trending west-trending folds. folds. Subsequently, resistance resistance to this movement within the the trough trough resulted in sinistral sinistral strike strike slip slip motion and and the thedevelopment development of ofF2 F, folds folds with with northwest-trending northwest-trending axial surfaces and variable variable plunge. plunge. Gair and Thaden (1968) applied the the name "Compeau "Compeau Creek Creek Gneiss" Gneis? to both the (1968) applied the foliated foliated rocks of of the Archean Archean greenstone-granite greenstone-granite terrane terrane (northern complex) granitoid rocks complex) and the the layered layered gneisses and and massive massive intrusions intrusions of of the the gneiss gneiss terrane terrane (southern complex), gneisses complex), and subsequent investigators extended extended this this terminology terminologyto to the the western western parts parts of of the southern investigators southern complex complex (Cannon 1973). To apply this this name name to rocks in in both both Archean terranes, however, and Simmons, Simmons, 1973). however, is inappropriate, because the two two terranes terranes consist consist of of distinctive distinctive rock types of different origins. origins. Accordingly, in in this this guide guide informal informal lithologic lithologicnames namesare are used used to to describe the Accordingly, the crystalline crystalline rocks rocks in in the two terranes. ARCHEAN GREENSTONE-GRANITE TERRANE TERRANE greenstone-granite terrane terrane in the Marquette area The greenstone-granite area (fig. (fig. 1) 1) consists of a several thousandmeter-thick succession succession of metamorphosed metamorphosed subaqueous subaqueousmafic mafictotofelsic felsicflows, flows,pyroclastic pyroclastic rocks, rocks, volcanogenic sedimentary sedimentaryrocks rocksthat that is is intruded intruded by by small smallbodies bodies of of gabbro gabbro and ultramafic and volcanogenic rocks and by large plutons of granitoid rocks (Bornhorst, Johnson and Bornhorst, (Bornhorst, 1988; 1988; Johnson Bomhorst, 1991). 1991). The metamorphosed volcanic rocks rocks have have been been named named the the Ishpeming Ishpeming greenstone greenstone belt belt (Morgan and DeCristoforo, 1980); they represent represent the southwestern extension of of the Wawa 1980); they southwestern extension (Shebandowan) subprovince of of the the Superior province province of of Canada (Card and (Shebandowan) subprovince and Ciesielski, Ciesielski, 1986). 1986). volcanicrocks rocksadjacent adjacenttotoan an ultramafic ultramaficbody bodynorth northofofIshpeming Ishpemingare are host host to to the gold Felsic volcanic deposits of the the Ropes Ropes mine mine(Brozdowski (Brozdowski and and others, others,1986; 1986;Brozdowski, Brozdowski, 1988, 1988, 1989), and the ultramauic body bodyhosts hostsadditional additionalmineral mineralprospects prospects(Bodwell, (Bodwell,1972). 1972). Foliated Foliated tonalite from the ultramafic the 1978) in in the the greenstone-granite greenstone-granite terrane, terrane, has a U-Pb northern complex (Hammond, 1978) U-Pb zircon zircon age age of of 2,703±16 by Zell Zell E. Peterman), and associated rhyolite has aa U-Pb 2,7032 16 Ma (recalculated (recalculated by U-Pb zircon zircon age age byZeil ZellE. E. Peterman). Peterman). These ages are consistent with with more ± 69 Ma (recalculated of 2,780 2,780269 (recalculated by precise U-Pb ages in the Wawa subprovince in adjacent Canada (Corfu and Stott, Wawa subprovince in adjacent Canada Stott, 1986). 1986). 107 �Figure 1. 46°45 Xmsç MICH —- A 0 0 -r 5 5 •F )1f 8P30' 10 1''• Marc1uette IAKU SIJPURIOR 10 MILES 15 KILOMETERS (h' — Geologic map of part of Marquette 1°x2° quadrangle, Michigan. After Sims (1991). Palmer 7½-minute quadrangle is immediately west of Sands quadrangle. Marquette 7½-minute quadrangle is immediately north of Sands quadrangle. 880 00 �________ _________ CORRELATION CORREIATION OF O F MAP MAP UNITS Archean Archean terrane Greenstone-granite terrane Reany Creek Creek Formation Formation .- \ J Proterozotc Middle Unconformity Unconforrnity Granitoid rocks— Dominantly granodiorite lie but Granitoid rocks-bminantly grandiodteand andtonal tonalite Including granite; generally including generalb foliated foliated Mafic Mafic to felsic felsic flows flows and and pyrodastic pyrodasticrocks r o c kand and volcanogenic sedimentary rocks wkanogenic sedimentaq rocks Ultramafic Utramafiirocks rocks > 1-1'a m i i: Penokean orogeny Penokean orogeny deformation deformation and and metamorphism metamor~ism xm1L..... 1 +1 \\\\'' ) \ .\I. ,-!t~yt p W}Mzgy 1 1 Unconformity Unconforrnily Xmn Menominee Group J — Marquette Marquette Range Range Supergroup suwrgrOup Xc j granite and massive granite Contact Contact - J a A 1 . I Late Unconformity I -15 —15 kf5 J DESCRIPTION OF MAP UNITS DE!XRPTION UNnS Middle Mlddle Proterozoic Proierowic . Jacobsvllie Jacobsville Sandstone Sandstone Early Proterozoic Alkali granite 33 ±25 Alkali granite (1.7 (1,733 *25 Ma) Ma) ,, Marquette Range SUPWSTOUP Supergroup , Marquette j Vertical Bearing and lineation— Bearing andplunge plungeofof lineation-May Maybebecombined combinedwith with foliation symbol foliation symbol Direction Direction of stratigraphic tops tops --15 } Ahean y\.;;3,77, dip of foliation Strike and dip foliation Inclined Inclined 4— + I F, Transcurrent fault— Transcurrent fault-Showing Showingrelative relathhorizontal horizontalmovement m-mt A Thrust Thrustfault—Sawteeth fault-Swteeh on upthrown upthrownside side 50 Continent-continent collision ((=2,690 Cmtinentantinent colliskm ~ 2 , 6 9Ma) Ma) 0 South of North of ofGLTZ GLTZ South of GLTZ GLTZ North Gnelss terrane terrane Gneiss Greenstone-granitetterrane emne Greenstone-granite !'zá'_1 + _±I - - ".1 e:w;aJ , 4 1 - wuI Gneiss, migmatite, amphibolite—lncludes Gneiss, migmatite,and and amphibolide-Includes foliated foliated 7High-angie Wih-anglefault—Bar fault-& and andball ballon ondownthrown downthrownside side Chocolay Group I 3 Ago Early h dy Proterozolc Proterozoic I Unconformity unconformity Gneiss terrane terrane Tilden (Hammond, Granite near Tilden (Hammond, 1978) 1978) [\-.\' -"i Baraga Group Group Bearing of minor minor fold Bearins and plunge of fold MyloniteMylonlte— Dominantly Dominantly orthornylonite orthomyionite CRSZ Carp River shear zone CRFSZ Carp River Falls Falls shear zone zone DRSZ DRSZ Dead River River shear Dead shear zone zone GLTZ GLTZ tectonic zone Great Lakes tectonk zone GGT GGT R 217 Greenstone-granite terrane terrane Ropes mhse Ropes mhe J. Michigamme MkhlgammeFormation—Dominantly Fonnatbn-Domlmntlysiaty slatyrocks rocksIn Inlower lowerpart part 88' 89' Ciarksburg C l a h b u r g Volcanica Volcnnlcs Member Member of of Michigamme Mkhigamm Formation Fonnatbn Goodrich Quartzite G o d r i c h Quartzite 41' map Menominee Group, undlvlded, undivided, in trough Menominee Group, i n Republic Republic tmugh 1 Xmn 1 w 1 1 Xch Edge of Siamo Ajibik Quartzite, S i m o Slate and Ajibik Quartzite, undivided undivided L_ eozoicNç Negaunee Iron-formation Negaunee Iron-formatbn cover o o Cisocolay Chocolay Group, undivided undivided 4OKIWMETERS 46' INDEX MAP 4OMLIS �Granitoid Rocks Rocks The Late Archean granitoid granitoid rocks rocks in the the greenstone-granite greenstone-granite terrane terrane (fig. (fig. 1) 1)are aredominantly dominantly pink pink to grayish pink, pink, generally generally medium medium grained, grained, porphyritic, porphyritic,foliated, foliated,and and homogeneous homogeneous tonalite tonalite or granodiorite (Gair P. 18-23). xenoliths and and schlieren of of biotite (Gau and and Thaden, Thaden, 1968, 1968, p. 18-23). They contain xenoliths schist and amphibolite. amphibolite. In foliated granite is also a In the theSands Sandsquadrangle quadrangle(fig. (fig. 1), I), weakly foliated common rock rock type (table 1), I), but its age relation to the the tonalite-granodiorite tonalite-granodiorite was was not determined. determined. The bimodal composition of the granitoid rocks suggests, however, that that the the granite represents suggests, however, represents aa event. discrete magmatic event. The granitoid rocks of of the greenstone-granite greenstone-granite terrane terrane in the Marquette area area exposed exposed on on both both sides of the Marquette altered (table 1). Plagioclase Marquette synclinorium synclinorium are strongly altered Plagioclase (oligoclase) (oligoclase) is saussuritized and albite albite twinning twinning is largely obscured, and biotite is largely changed to to chlorite chlorite and opaque oxides (locallyrutile). rutile). The rocks are highly fractured and and fracture fracture surfaces are are highly fractured oxides (locally coated by chlorite and other propylitic minerals. Along the southern margin of the Marquette propylitic minerals. Along the southem margin of syndilnorium, the granitoid granitoidrocks rocksare are exceptionally exceptionallyrich richininquartz quartz(table (table1). 1). The granitoid rocks synclinorium, the in the Sands Sands quadrangle also are are protomylonites. protomylonites. The Theprotomylonite protomylonite isis characterized characterized by by recrystallization of quartz to shes and and localized localized shear-induced shear-induced recrystallization recrystallization of of to fine fine grain grain sizes plagioclase and potassium potassium feldspar feldspar to fie-grained fine-grained polycrystalline polycrystallineaggregates aggregates(type (type IP, 1P, llP, liP, 1M, lM, and 111M 1M structures of Hanmer, Hanmer,1982). 1982). The relative homogeneity of the foliated granitoid rocks, the occurrence of of sharp-walled sharp-walled the occurrence xenoliths, and and the general absence of a lithologic layering layering that that could represent relict xenoliths, relict sedimentary sedimentary or volcanic layering layering suggest suggestthat thatthe the granitoid granitoid rocks rocksof ofthe the greenstone-granite greenstone-granite terrane terrane are of magmatic origin. origin. Their pervasive foliation foliation is is attributed attributed to to deformation deformation subsequent subsequent to primary magmatic crystallization, as as discussed discussedfollowing. following. Structure The rocks in the greenstone-granite greenstone-granite terrane terrane (northern complex), complex),on onthe the north north side side of of the the GLTZ (fig. 1), I), record early recumbent recumbent folding folding (F1) (FJ of metavolcanic rocks of the Ishpeming Ishpeming greenstone greenstone (fig. Superposeddeformation deformation(D2) (D2)produced produced northwestnorthwest- to to west-trending west-trending upright, upright, upwardupward- and belt. Superposed An downward-facing 1991). An downward-facingfolds folds(F2) (F2)that thatare are Z-shaped Z-shaped in in plan plan view view (Johnson (Johnson and and Bomhorst, Bornhorst, 1991). axial plane The Z-symmetry Z-symmetry of of the theF2 F2folds folds is is consistent consistent with with plane foliation was developed during Fp F2. The their development dextral shear component. component. Associated development in a deformation deformation regime with a dextral Associated by D2. Younger, Younger, northwestnorthwest- to to west-trending west-trending faults, faults, some someof of granitoid rocks also were deformed by which have demonstrable demonstrable dextral dextral movement, movement, transect transect and and offset offset the the folded folded rocks. rocks. Commonly, which have Commonly, these faults faults separate separatedomains domainsof ofvolcanic volcanic rock rock that that have have opposite oppositestratigraphic stratigraphicfacing facingdirections. directions. of fig. fig. 1) 1) is is Foliation and lithologic layering layering in in the the vicinity vicinityofofthe the Ropes Ropes mine mine (R, (R, near center of puzzling with respect to the dominant regional structure. Here, foliation and lithologic layering with respect to Here, foliation and lithologic layering strike strike about aboutN. N.700 70' E. and are are nearly nearly vertical (Brozdowski, (Brozdowski, 1988, 1988,p.p.A-44). A-44). The published area (Negaunee (Negaunee SW SW quadrangle; quadrangle; Clark Clark and and others, others, geologic map map that that includes the Ropes mine area hte 1975) also also shows showsaa steep steep (stretch?) (stretch?) lineation that plunges southeastward in unit Wkf of the Late Archean Kitchi Schist (included in unit unit Wv Wv on on fig. fig. 1). 1). Possibly, the northeast-trending foliation Possibly, the large-scaleD2 D2Z-fold. Z-fold. the Ropes Ropes mine mine area arearepresents representsthe theeast-northeast-trending east-northeast-trendinglimb limbofofaalarge-scale in the 110 �greenstone-granite terrane terrane of of the the Marquette area Table 1. 1. Approximate Approximatemodal modal content content of of granitoid granitoid rocks rock in Archean greenstone-granite ['Fr., pr., trace; blank, absentj absent] Rock Rock Constituent Constituent Sample Sample number 136R l36R lilA 177A 17Th 177B 179A 179A 179B 179B 182A 18% 182B 182B 183A 183A 186A 186A 199 199 200 202 208 208 21LA 21lA 136-1 136-1 203 1 1 22 33 Plagioclase Plagioclase 37 37 35 35 60 60 66 54.5 54.5 48 52.5 52.5 38 54.5 36 36 56.5 60 60 39 39 41 41 273 27.5 33 33 61.2 58.5 58.5 50.6 50.6 Quartz Quartz 30 30 32.5 24 24 21.5 28.5 28.5 45 36 34 24 24 27.5 27.5 37.5 28 28 30 30 27 39 39 23 28 26 26 22.2 373 37.5 Potassium Potassium feldspar feldspar 30 31 31 10 10 5.5 2.5 00 24.5 14.5 14.5 31 31 33 11 30 24 32 32 373 37.5 3.8 12.8 1.4 1.4 Biotite Biotite Ti. Tr. Tr. Ti. Tr. Tr. 10 10 Ti. Tr. Tr. Tr. Ti. Tr. 0.2 Ti. Tr. 11 66 77 Ti. Tr. 66 4 Tr. Chlorite Chlorite 1.3 1.3 33 Epidote Epidote 0.5 Tr. Tr. 63 6.5 7 7 55 Ti. Tr. 10 10 0 Ti. Tr. Ti. Tr. Ti. Tr. Ti. Tr. 3 3 Ti. Tr. Tr. Tr. 88 Ti. Tr. Tr. Tr. 2.5 13 1.5 03 0.5 0.6 00 Ti. Tr. Sphene Sphene Opaque Opaque oxides oxides Tr. Tr. Accessory minerals minerals Tr. Tr. Ti. Tr. 0.2 Muscovite Muscovite Tr. Tr. Ti. Tr. Ti. Tr. Ti. Tr. 0.5 3.6 3.6 Ti. Tr. 0.5 4 Tr. Ti. Tr. 11 Tr. 0.5 Tr. Tr. Tr. Tr. 11 11 Ti. Tr. Tr. Tr. Tr. Ti. Tr. Tr. Tr. 1 1 Tr. Tr. 0.2 0.2 Tr. 'Fr. 23 2.5 23 2.5 Ti. Tr. 1.8 Ti. Tr. 0 0 Ti. Tr. Tr. Tr. Ti. Tr. 1.3 1.3 7 DESCRIPTIONS SAMPLE DESCRIF'TXONS 136R. corner of Pink, fineof biotite biotite schist. Sands W., 675 ft N. of the the SE. SE. corner of f i e - to to medium-grained, medium-grained,slightly slightly porphyritic, porphyritic, altered granite; granite; contains containswispy wispy inclusions of Sandsquadrangle, quadrangle,1,800 1,800 ft W., sec. 3, T. 47 N., R. 25 W. sec.3,T.47N.,R.ZW. lilA. T. 47 Pink, medium-grained, porphyritic, massive, massive,altered altered granite; granite; cut cut by by cldorite-coated chlorite-coatedfractures. fractures. Sands 5., 2 2,150 E. of of the the NW. corner of sec. sec. 16, T. medium-grained, porphyritic, Sands quadrangle, 775 ftft S., ,l50 ftft E. 47 N., N., R. 25W. 25 w. 17Th. Pink, porphyritic, massive, massive,altered altered granite. granite. Sands P i i fine-grained, fie-grained, porphyritic, Sands quadrangle. quadrangle. Same Samelocality localityas as177A. 177A. 179A. 26, Pinkish-gray, medium-grained, medium-grained,porphyritic, porphyritic,altered altered tonalite; tonalite;contains containsoriented oriented layers layersof ofbiotite biotite schist. schist. Palmer quadrangle, S., 2 250 W. of of the the NJ2. NE. corner of sec. 50 ftft W. see 26, quadrangle, 650 ft S., T. 47 N., N.,R. 26 26 W. w. 179B. 182A. foliated, altered altered tonalite. tonalite. Biotite Gray, medium-grained, foliated, Biotite is is fresh. Palmer Palmerquadrangle. quadrangle.Same Samelocality localityasas179A. 179A. W. Pinkish-gray, medium-grained medium-grained altered altered tonalite gneiss. gneiss. Sands quadrangle, 1,350 ft E., 100 ft N. of the SW. Sands quadrangle, 1,350 E., N. SW. coiner corner of of sec. sec. 31, 31, T. 47 N., R. 25 W. �182B. Pinkish-gray altered tonalite gneiss. Sands Piish-gray to medium-gray, medium-gray, altered Sands quadrangle. quadrangle. Same Samelocation locationasas182A. 182.4. 183A. Pinkish-gray, fine- to medium-grained Pinkish-gray, fmemedium-grained granite granite gneiss. gneiss. Sands Sandsquadrangle, quadrangle,675 675ftftN., N.,300 300ftftE.of E.of the theSW. SW.corner wrnerofofsec. sec.31, 31,T.T.47 47N., N.,R.R.2525 W. W. 186A. Pinkish-gray, medium-grained, altered altered grandorite granodiorite gneiss. Palmer Pinkish-gray, medium-grained, Palmerquadrangle, quadrangle,2,500 2,333ftftN., N., 2,200 2,200ftft E. E. of of the theSW. SW.corner wrnerofofsec. sec.36, 36,T. T.47 47N., N.,R.R.2626 W. W. 199. Pinkish-gray, medium-grained medium-grained granite granite gneiss. Sands Sandsquadrangle, quadrangle,1,000 1,000 ftft S., S.,2,000 2,000 ft W. of the the NE. NE. corner mrnerofofsec. sec.16, 16,T. T.46 46N., N., R. R.25 25W. W. 200. Pinkish-gray, fine- to to medium-grained medium-grained altered altered tonalite gneiss. gneiss. Sands N., 2,075 2,075 ftft E. E. of of the SW. SW. corner corner of of sec. sec. 9, T. T. 46 46 N., N.,R. 25 Piish-gray, fmeSands quadrangle, quadrangle, 775 ft N., 25 W. W. 202. Gray, fine-grained chlorite-coated fractures. fractures. Sands E. of of the SW. wrner corner of sec. 5, 5, T. T. 46 46 N., tine-grained biotite tonalite tonalite gneiss cut by chlorite-mated Sandsquadrangle, quadrangle, 850 850 ft N., N., 2,350 2,350 E. N.,R. R. 25 25 W. W. 208. Pink, medium-grained, 2,150 ftftN., N., 2,000 2,WO ftft W. W. of of the theSE. SE.corner wrnerofofsec. sec.8,8,T.T.46 46N., N.,R.R.2525 W. W. medium-grained, leucocratic leucocratic granite granite gneiss. gneiss. Sands Sandsquadrangle, quadrangle,2,150 211A. Pink, medium-grained, altered granite W. of of the SE. corner granite gneiss. Sands Sandsquadrangle, quadrangle,2,550 2,550 ft S., 150 ft W. wrner of of sec. sec. 7, T. 46 N., N.,R. 25 W. W. 136-1. Pink, medium- to coarse-grained, foliated foliated granite granite gneiss. gneiss. Fractures mated coated by chlorite. chlorite. Sands as136R. l36R. Sands quadrangle. Same Samelocation locationas 203. Pink, medium-grained, leucwratic leucocratic granite granite gneiss. gneiss. Sands 2,300 ftft W. W. of of the the SE. SE. wrner corner of sec. 5, T. 46 N., R. 25 W. Sands quadrangle, 200 ft N., N., 2,300 W. 1. Average of 14 samples of of foliated tonalite. Marquette Marquettequadrangle, quadrangle,north northofofthe theMarquette Marquettesyndlinorium syncborium(Gair (Gauand andThaden, Thaden,1968, 1968,table table6,6,no. no.1). 1). 2. Average of five samples of of foliated grandorite. granodiorite. Marquette Marquettequadrangle, quadrangle,north northofofthe theMarquette Marquettesynclinorium synclinorium(Gair (G& and andThaden, Thaden,1968, 1968,table table6,6,no. no.9). 9). 3. Average of 11 11 samples of quartz-rich, foliated tonalite. Sands Sandsquadrangle, quadrangle,south southof of the theMarquette Marquettesynclinorium syncborium (Gair (G& and andThaden, Thaden,1968, 1968, table table 6, 6, no. no. 6). 6). �The The steep, steep,northwestnorthwest- to to west-trending west-trending shear zones and faults in the the greenstone-granite greenstone-graniteterrane, terrane, as exposed in the northern complex, are tens tens of of meters meters to to aa few fewhundred hundred meters meters wide. wide. They are exposed in complex, are highly highly schistose zones characterized by an intense, intense, close-spaced close-spaced foliation, a steep steepstretching(?) stretching(?) ilneation, 1991). The faults are of lineation, and strong retrograde alteration (Johnson and Bornhorst, 1991). of both ductile and brittle-ductile types. Major structures include the Dead River shear zone both ductile types. Major structures include the Dead River shear zone (fig. 1, DRSZ) (Puffett, 1974), whichforms formsthe the northern northern boundary boundaty of of the Dead River 19741, which River basin; basin; the the Carp Carp River River shear shear zone zone (CRSZ), (CRSZ),east-northeast east-northeastof of the theRopes Ropesmine, mine,which which separates separates two two different different blocks of Archean volcanic rocks; rocks; and the Carp River River Falls Falls shear shear zone zone(CRFSZ), (CRFSZ),which whichforms forms the in this area. The the northern northern margin margin of of the the Marquette Marquettesynclinorium synclinorium in TheCarp CarpRiver RiverFalls Fallsshear shear zone is reported becut cutby byrelatively relatively undeformed undeformed mafic mafic dikes of presumed presumed Late Late Archean Archeanage, age, reported to tobe indicating an Archean age for the the shear shearzone zone(Baxter (Baxter and andBornhorst, Bornhorst,1988). 1988). In the the area areanorth northof ofthe thePalmer Palmerfault fault(fig. (fig. 1), I), foliated foliated and fractured Late Late Archean Archean granitoid granitoid rocks form partly fault-bounded domes surrounded by Early Proterozoic rocks of the Marquette rocks of Marquette Range Supergroup. The large Archean granitoid body in the Sugarloaf Mountain area, 88 km km The large Archean granitoid body the Sugarloaf north north of of Marquette, Marquette,isisalso alsoaadome; dome;foliation foliationin inadjacent adjacentmetavolcanic metavolcanic rocks rocks (Puffett, (Puffett,1974) 1974) dips dips gently to moderately moderately away away from the granite granite contact. contact. Late-Tectonic Late-Tectonic Conglomerate Conglomerate (Archean) (Archean) The is the the Reany Reany Creek Creek Formation Formation The youngest Archean unit in the greenstone-granite terrane is (Puffett, 1969; 1974). 1974). On the basis of a reinterpretation reinterpretation of of age age and and structural structuralrelationships, relationships, the the Reany Creek Formation is no longer included included as as part part of of the the C Chocolay Group or the Marquette h w l a y Group or the Range Supergroup Supergroup (Sims, 1991). ItIt isis aa heterogeneous heterogeneousbody body of of conglomerate, conglomerate, arkose, arkose,chloritic chloritic slate, slate, graywacke, graywacke, and and boulder-bearing boulder-bearingslate. slate. It It transects transectsstructures structuresin in the theolder oldervolcanic volcanicrocks, rocks, isis less deformed than than the themetamorphosed metamorphosedvolcanic volcanic rocks, rocks, and is bounded along along its its southern southern margin by the northwest-trending northwest-trending Dead River River shear shear zone zone (fig. (fig. 1). 1). Its age age has been uncertain uncertain (see Puffett, of basin basin fill,and and relationship relationship to to the Puffett, 1974), 19741, but its penetrative penetrative foliation, asymmetry asymmetry of Dead Dead River River shear shearzone zonestrongly strongly suggest suggest that itit developed developed concurrently concurrently with dextral shear along the similartoto"Timiskaming-type" "Timiskaming-typensequences, sequences, such such as as the theSeine Seine the Dead Dead River Rivershear shearzone. zone.ItItis issimilar Group, Group, in northern northern Ontario, Ontario,now now commonly commonly interpreted as forming in Archean analogs to modern modem pull-apart pull-apartbasins basins(Poulsen, (Poulsen,1986). 1986). fa ARCHEAN A R C H W GNEISS GNE3SS TERRANE TERRANE The Archean gneiss gneiss terrane terrane in the Marquette area (fig. 1) constitutes the the greater greater part of the southern complex, complex, as defined defined by by Van Hise Hise and andBayley Bayley (1897). (1897). ItItconsists consistsofofgneiss, gneiss,migmatite, migmatite, southern amphibolite, substantial amounts of and amphibolite, of deformed and undeformed granite pegmatite, and Cannon and and Simmons Simmons (1973) (1973) have have described described the the massive to weakly weakly foliated foliated granite granite plutons. plutons. Cannon as Late Late Archean. Archean. general rock types in much much of of the southern complex. complex. One rock has been dated as sample of of gray gneiss (called Compeau Creek Gneiss by Gair, 1975) 1975) collected in the A sample SEY&W% ofofsection SE¼SWV4 section36, 36,T.T.4747N., N.,R.R.27 27W. W.(Hammond, (Hammond,1978) 1978)has hasaaU-Pb U-Pb zircon zircon age age of of 2,779521 802576 Ma (recalculated (recalculated by Zell E. E. Peterman). Peterman). 2,779 ±21 Ma Ma and and a lower intercept age of 802±76 Gneiss Gneiss and and Associated Granitoid Granitoid Rocks Rocks Compositiondly layered, Compositionally layered, medium-grained medium-grainedgneiss gneissand andmigmatite migmatiteare are the the dominant rock types in the gneiss gneiss terrane in in the the Marquette Marquettearea. area.Layered Layeredfelsic felsicgneisses gneissesranging rangingin in composition composition from from the to granite granite predominate. predominate. Smaller Smalleramounts amountsof of massive massive to to layered layered amphIbolite amphibolite are tonalite to 113 �intercalated intercalated with with the the felsic felsic gneiss, but amphibolite constitutes layers several tens of meters thick thick at be seen seenon onthe thegeologic geologicmap map of of the thePalmer Palmer7½-minute 7%-minutequadrangle quadrangle(Gair, (Gair,1975, 1975, at places, places, as as can can be p1. 1), which whichisisimmediately immediatelywest westofofthe the Sands Sands quadrangle. quadrangle. The pi. I), The felsic felsic gneisses gneisses are are gray gray to to pinkish gray; typically, compositionallayering layeringisisexpressed expressedby bydifferent differentproportions proportions of of the the major typically, compositional silicate minerals, as plagioclase-quartz-biotite-microperthite,(2) (2) microperthitemicroperthiteas for for example, example, (1) (1) plagioclase-quartz-biotite-microperthite, quartz-plagioclase-biotite, and (3) biotite-quartz-plagioclase-microperthite. Textural differences quartz-plagioclase-biotite, and at layering. Pink aplitic granite and granite at places places emphasize the compositional compositional layering. granite pegmatite pegmatite commonly transect the gneiss and and amphibolite amphibolite and and locally locallyform formmigmatite. migmatite. Metasedimentary commonly transect rocks such as iron-formation, form layers in the felsic of the Republic felsic gneisses in the vicinity vicinity of trough (Cannon and Simmons, 1973); they were not observed in the Palmer and Sands and Simmons, they were not observed in the Palmer Marquette area. area. quadrangles, in the Marquette Pinkish-gray to pink, medium-grained, massive massive to weakly weakly foliated, foliated, homogeneous homogeneous granite granite (table (table 2) 2) intrudes intrudes the the gneisses gneisses in several places. places. Hammond Hammond (1978) (1978) delineated delineated aa body body of of massive massive granite granite about 44 km2 km2in areal areal extent extent south south of of Ishpeming Ishpeming (unit (unit Wgt, Wgt, fig. fig. 1), I), which which he he informally informally called the the "Tilden granite." granite." ItIt isisaagray porphyritic, and massive granite grayto topink, pink,medium-grained, medium-grained, locally locally porphyritic, that locally gneiss. ItIt isis cut locally contains oriented xenoliths of mafic gneiss. cut by by pink pink pegInatite pegmatite and andisishighly highly fractured. The Thefractures fractureshave haveslickensided slickensided surfaces and a thin coating of chlorite and other propylitic propylitic alteration minerals. minerals. U-Pb U-Pb isotopic isotopic data data on on aa sample sample of of the thegranite granitenear nearTilden Tilden (Hammond, 1978) 1978) indicate an age age of of 2,585±15 2,5855 15 Ma Ma (R.E. (R.E. Zartman, Zartman,oral oralcommun., commun.,1991). 1991). fig. 1) about about 2 km in diameter occurs about 3 A nearly nearly circular circular body body of alkali granite (unit Xga, fig. A km south of Humboldt (Schulz (Schuiz and others, 1988). The The granite graniteisislight light red red to tobrick brickred, red,generally generally massive, fineto medium-grained, and equigranular to hypidiomorphic granular. The granite massive, fine- to medium-grained, and equigranular to hypidiomorphic granular. granite is is the Arabian Arabian Shield Shield similar compositionally to Sn-W mineralized mineralized alkali feldspar feldspar granites of the (Jackson and Ramsay, Ramsay, 1986) 1986) and the the Nigerian Nigerian younger granite province province (Kinnaird (Kinnaird and and others, others, interpreted as a Thegranite granitehas hasaaRb-Sr Rb-Srwhole-rock whole-rockage ageofof1,733 1,733±525 25 Ma, which which is interpreted 1985). The crystallization crystallization age (Zell E. Peterman, Peterman, written written commun., commun., 1988); 1988); it is aa post-tectonic post-tectonic intrusion. intrusion. Structure Structure the gneiss gneiss terrane terrane (southern (southern complex) complex) form aa northwest-trending northwest-trending antiformal antiformal Archean gneisses in the structure by Paleozoic Paleozoic rocks rocks to to the theeast east(Sims, (Sims,1992). 1992). structure that that closes closes to to the thewest west and andisisoverlapped overlapped by An infolded belt of Early Proterozoic (Marquette Range Supergroup) rocks indents the Archean the Republic Republic trough (fig. 1). In Inthe thearea areawest westofofthe theRepublic Republictrough, trough,Taylor Taylor(1967) (1967) fold nose in the determined two two principal principal phases phases of of deformation: deformation: (1) (1)early, early,probably probablyflat-lying flat-lyingfolds foldswith withaxial axial determined trending northeastward, northeastward, and and(2) (2)younger youngerupright upright folds foldswith with steep steepnorthwest-trending northwest-trendingaxial axial planes trending surfaces. The Theyounger younger folds foldsmainly mainly control the the distribution distribution of of the the rock rock units. units. In the the Marquette Marquettearea, area,early earlygently gently inclined inclined to recumbent recumbent folds that trend trend northwestward northwestward and and plunge gently gently northward northward (fig. (fig.2) 2) are are the the dominant dominant structure in the gneisses. gneisses. These Thesefolds folds deform deform an older older foliation foliation (Si). (S,). Boudinage Boudinageaccompanied accompaniedthe thefolding; folding; the theboudins boudinsplunge plungesubparallel subparallelto to gently inclined inclined fold fold hinges. hinges. A later steep, northwest-oriented foliation, that that is axial planar planar to northwest-oriented foliation, northwest-trending folds, occurs at least locally, but but it does not significantly affect the significantly affect distribution of the rock stop 3. 3. rock units. These Theseyounger younger structures structures will will be examined at stop 114 �Table 2. Approximate Approximate modal modal content content of of granitoid granitoid rocks rocks in the the Archean Archean gneiss gneiss terrane terrane of the Marquette Marquette area area [Tr., trace; blank, absenti absent] Rock Constituent Constituent Sample Sample No. 153A 153A 146-88 146-88 11 226A 226B 226B Plagioclase Plagioclase 34.7 33.5 25 263 393 Quartz 28 23.8 25 38.2 32.7 Potassium feldspar 28 28 34.2 40 40 33.0 25.0 9 8.0 8.0 33 2.2 3 3 Biotite Biotite Chlorite Chlorite Muscovite Muscovite Tr. Tr. Tr. Tr. Tr. Tr. 22 Tr. Tr. Tr. Tr. Tr. Epidote Epidote Tr. Sphene Sphene Opaque Opaque oxides oxides Tr. Tr. Accessory minerals minerals 03 0.5 Tr. 0.3 Tr. DESCRU'TIONS SAMPLE DESCRIPTIONS 153A. Pinkish-gray, medium-grained, medium-grained, foliated foliated granite, granite, SE%NE!4 SE¼NE¼ of section T. 46 46 N., N., Pinkish-gray, section 7, T. R. 26 W. W. Biotite R. Biotiteisisweakly weakly altered. 146-88. "Tilden granite" granite"ofofHammond Hammond(1978). (1978). Quartz Quartz and biotite are recrystallized in Tilden shears; biotite is slightly altered to chlorite. 1. "Tilden granite" granite"of ofHammond Hammond (1978, (1978,p.p.63). 63). Potassium-feldspar Potassium-feldspar is microperthite. Tilden has concentric zoning. zoning. Highly Plagioclase has Highly fractured. fractured. 226A. Light-gray, mediuni-grained,foliated foliatedgranite. granite. Cut Cut by by fractures. fractures. Biotite Light-gray, medium-grained, Biotite isis highly highly N., R. 26 W. altered to chlorite. chlorite. Quarry, Quarry,SE¼SW½ SE%SW?hof of section section 21, T. 46 N., 226B. Pale-reddish-brown, mediuin-grained foliated foliated granite. granite. Cut Pale-reddish-brown, medium-grained Cut by by shears, shears,some somewith with mylonite. Biotite mylonite. Biotite is is highly highly altered to chlorite and calcite. Same Samelocality locality as as 226A. 226A. 115 �GREAT GREATLAKES LAKES TECTONIC TECTONIC ZONE ZONE is characterized characterized in in the the Marquette area The GLITZ GLTZ is area by by a mylonite mylonite zone about 22 km km wide that that has has The been been superposed superposedon onpreviously previously deformed deformed layered rocks and granitoid rocks of the the northern northern Archean Archean greenstone-granite greenstone-granite terrane terraneand andpreviously previously deformed rocks of the southern southern Archean Archean gneiss rocks of of the the two two terranes. terranes. The gneiss terrane. Therefore, Therefore,the themylonite mylonite overprints rocks The great great width width of this this shear shear zone zone and and the thepreponderance preponderanceof of mylonite mylonite distinguish distinguish it from the other, other, much much narrower narrower shear shear zones zones and and faults faults in in the the region. region. The Themylonite myloniteabruptly abruptlygrades gradesnorthward northward into into protomylonite and highly fractured and altered rocks along the northeast wall of the GLTZ protomylonite and highly GLTZ (fig. (fig. 3). 3). Boundaries Boundaries(walls) (walls) of of the theGLTZ GLTZare aresubparallel subparalleland andtrend trendN.N.55°-60° 55O-600 W., W., subparallel subparallel to to the the contact between the Archean greenstone-granite and gneiss terranes (fig. 3). Foliation in contact between the greenstone-granite gneiss terranes (fig. 3). Foliation the the 750 mylonite Thus,the thefoliation foliationstrikes strikes10°100mylonite has has an anaverage averageattitude attitudeofofN.N.7Q0 700W., W., 75O SW SW (fig. (fig. 4). Thus, 15° more westward westwardthan than the the trend trend of of the shear zone walls. walls. The 15O more The angular angular relationship relationshipbetween between the the orientation orientationof of the thefoliation foliationand andshear shearzone zoneboundaries boundariessuggests suggestsdextral dextralwrench wrench shear shearalong alongthe the walls 1986,fig. fig.2b). 2b). A A pronounced rodding (stretching) lineation in the walls (Simpson, 1986, the mylonite mylonite has has an average plunge of 42° and an average bearing of S. 43° E. an average plunge of 42' and an average bearing of S. 43O E. Hinges to the stretching lineation lineation (fig. (fig. 4). 4). The Hinges of tight to open open folds folds plunge subparallel to The folds folds have asymmetricalpatterns. patterns. Z-shaped folds have both symmetrical and asymmetrical folds are are most most common, common, but SSshaped and both both may may occur occur in in the the same outcrop area, as on the shaped folds coexist and the west west shore shore of of Powell covers outcrops outcrops and and prevented prevented determination of Powell Lake (fig. 3). Nearly Nearly pervasive pervasive lichen covers 0 t 0 • 0 + ++ + + ++ 0 + ++ + ++ + ++ Lower Lower hemisphere hemisphere Equal-areaprojection projectionof ofpoles polesto tofoliation, foliation,lineations, lineations, and and fold fold axes axes in gneisses of Figure 2. Equal-area Archean gneiss gneiss terrane. terrane. Archean 116 �fold symmetries symmetriesover overlarge largeparts partsof ofthe the GLTZ. GLTZ. Ridley have demonstrated demonstrated that fold Ridley and Casey (1989) (1989) have folds, with with axes axes subparallel subparallelto to the the maximum maximum extension extension direction direction (X finite strain strain symmetrical folds, axis), are produced by wrench shear, axis), shear, whereas whereas asymmetric asymmetric folds, with axes close to the the extension extension form in in a regime of of combined combinedwrench wrenchand andthrust thrustshear. shear. In wrench shear, because the direction, form fold axis does does not not lie lie initially initiallywithin withinthe theslip slipplane planeofofshear, shear,the the axis axisrotates rotates toward toward the the direction maximum extension extensionwith withthe theaddition addition of ofprogressive progressivestrain. strain. In of shear displacement and maximum combined wrench wrench and thrust shear, at high high strain strain the the fold fold axial axial plane and and both both limbs limbs approach approach parallelism with the the shear plane. plane. Ridley parallelism with Ridley (1986) (1986) has further shown that dextral wrench shear and sinistral wrench shear can result from strain inhomogeneity in in the same shear-parallel shear-parallel extension within a single deformation regime. deformation regime. Mylonite Mylonite The mylonite (1984), mylonite in the the GLTZ GLTZisismainly mainly orthomylonite, orthomylonite, as as defined defined by by Wise Wise and and others others(1984), inasmuch as as surviving survivingmegacrysts megacrystscompose compose10-20 10-20 percent rock. theterminology terminolor of of inasmuch percent of of thethe rock. InInthe Hanmer because the the porphyroclasts have Hanmer (1987), (1987), the the mylonites mylonites are are mainly mainly "heteroclastic" "heteroclastic" because mylonite having havingmore more uniform uniform textural variable size ranges, but include include "homoclastic" "homoclastic" mylonite characteristics. Ultramylonite Ultramyloniteisis absent absent except except on on aa scale scaleof of aa few few centimeters. centimeters. The mylonite typically typicallyhas has aa pronounced pronounced planar planar foliation foliation that that differs markedly markedly from from the the more irregular foliation in in rocks rocks outside outside the the GLTZ. GLTZ. In In this this respect, respect, the the mylonite mylonite fits the pattern of of most mylonite zones in comprising a "straight zone." zone." Quartz recrystallized into Quartz typically typically is recrystallized "ribbon quartz," quartz,"yielding yieldingaapronounced pronouncedrodding rodding (stretch) (stretch) lineation. lineation. The "ribbon Therelatively relatively stiff stiff minerals, minerals, recrystallized to to finer grain sizes, with the plagioclase and potassium feldspar, are generally recrystallized development of core-mantle structures (White, 1976) or type 1P IP and 1M 1M structures structures (Hanmer, (Hanmer, these structures structures form form oriented oriented aggregates aggregatesof ofquartz quartz and and feldspar feldspar that that produce a . 1982); 1982); these prominent stretch stretch lineation. lineation. Accompanying Accompanying biotite biotite is is mainly mainly recrystallized recrystallized in planar or irregular irregular shears. The Thequartz-poor quartz-pooramphibolite amphibolitein in the theGLTZ GLTZhas hasaaconspicuous conspicuous lineation lineation given given by elongate aggregates of of actinolite and and chlorite. chlorite. The in rocks rocks in in the GLTZ are The mafic mafic mineral assemblages in are upper greenschist greenschist facies, fades, indicating retrogressive alteration of amphibolite amphibolite to to actinolite actinoliteschist. schist. Interpretation The Great Lakes Lakes tectonic zone has been interpreted (Gibbs and others, 1984) 1984) as a paleosuture that juxtaposed juxtaposed the the Archean gneiss and greenstoneresulting from continent-continent coffision collision that greenstoneInthe theMarquette Marquettearea, area,the thestretching stretchinglineation, lineation, which which represents the line of granite terranes. In tectonic transport transport (Schackleton (Schackleton and and Ries, Ries,1984), 1984),indicates indicates that that collision collision was oblique, oblique, resulting resulting in in dextral wrench-thrust shear along the N. 60° W.-trendingboundary boundary (paleosuture). (paleosuture). Asymmetric 60ÂW.-trending Asymmetric structures, mainly microscopic, indicate indicate northwestward northwestwardvergence vergence and and probable probable overriding of the structures, Archean greenstone-granite greenstone-granite terrane terrane by by the the Archean Archean gneiss gneiss terrane. collisionwould wouldbe beexpected expectedtotoproduce producedextral dextralshear shearacross acrossaalarge largeregion regionnorth north of of The oblique collision of the area affected by by this dextral dextral transcurrent transcurrent shear is not the GLTZ GLTZ (fig. (fig. 5). 5). The extent of known, however, however,because because dextral dextral shear shear was was the the dominant mechanism of deformation definitely known, deformation throughout most of the Superior Superior province (Card, in press). Structures in the greenstone-granite greenstone-granite rocks of northern Minnesota (Wawa subprovince) are similar to to those those in in northern northern Michigan. Michigan. In northern Minnesota, remarkably similar Minnesota, deformed deformed and and metamorphosed sedimentary rocks of the the Vermilion Vermilion district district(Sims, (Sims,1976; 1976;Sims Sims and and metamorphosed volcanic and sedimentary 117 �_ 1r30. : = —. (n1 - 31 32 . , / \ 1 . / ) - N 6 \'\ 4 fl \ :.' / I SS I ... S ..•... 12 S ' \ $"za' I ,L '-S R.26W.I R.25W. lUtE I - o0 I I p 1 KILOMETER Figure Figure 3. 3. Structure Structuremap mapofofsouthwestern southwesternpart partofofSands Sands7½-minute 7%-minutequadrangle quadrangleshowing showing the the Great GreatLakes Lakestectonic tectoniczone. zone. Modified Modifiedfrom fromSims Sims(1991). (1991). 118 �________ _________ _______ D(PLANATION EXPLANATION Figure 3--Continued 1 Wsg Archean Greenstone-granite terrane tenane Biotite schist and and granitoid rocks [ e l Wggm I[ [wgn Mylonlte—Protollth MylonitÑProtolit dominantly dominantly granttoid granitoid rocks rocks but but includes includes blotite schist sdilst and biotite and amphlbolite amphibolite Gneiss terrane Gneiss, migrnatite, migmatite, and andamphibolite-includes amphibolitdncludeifoliated foliatedand and granite massive massive granite Mylonfte—Oomlnantly mylonitic Mylonite-Dominantly myloniticquartzofeldspathic quarlzofeldspathicgneiss gneiss wgmj [Â¥Wgm Silkified . Silicified rocks rocks :.'I... .. .. . --— — — Boundary between rocks of of greenstone-granite Boundary between rocks greenstone-granite terrane terrane . ------ 25 + - —ts F45 20 and gneiss gneiss terrane terrane within wIthin the Great and Great Lakes tectonic (GLTZ ) zone (GLTZ) Approximate outer limit limit of of orthomylonite orthomylonite in in Great Great Lakes tectonic zone Strike Strike and dip of foliation foliation Inclined Indined Vertical Bearing and and plunge plunge of of minor fold Bearing fold Bearing and andplunge plungeof olineation—May f lineation-Maybebe combinedwith with Bearing combined symbols Ioliatlon foliatton symbols + + + ++ +- 0 •. ++ . . Lower Lower hemisphere hemisphere 4. Equal-area Figure 4. Equal-areaprojection projection of of poles polesto to foliation foliation (crosses), (crosses), stretching stretching lineation (dots), (dots), and and fold hinges (open circles) in mylonite mylonite of of the the Great Lakes Lakes tectonic tectonic zone, zone, Sands Sands and and Palmer 7½-minute 7%-minute quadrangles, Marquette area, area, Michigan. Michigan. 119 �\ '' I 95° Complex continental-margin sequences Plutonic and volcanic rocks Middle Proterozoic Volcanic, sedimentary, and plutonlc rocks of Mldcontinent rift system (i.1,100 Ma) Early Proterozoic Turbid,tes overlying shelf deposits 96° 940 E 930 cover )" ,°. Rocks of gnelss terrane Rocks of greenstone-granite terrane (Sutienor province) ean EXPLANATION (ntad A 91° f No PalOoZOiC(o>,A>dI>c(1, 92° -, s 89° 89° A A Trace of Great Lakes tectonic zone I3LTZ) Thrust fault— Sawteeth on overthrust block — — — Trend of magnetic anomaly A movement I ± Transcurrent fault— Showing relative horizontal High-angle fault 4 owisconsin magmat(c terranes ,__a_rv•r r.a.cntyJ pFAULLII ,' ',a 900 Figure 5. Simplified tectonic map of the Lake Superior region showing Great Lakes tectonic zone and adjacent Archean terranes. After Sims (1991). Terminology of Early Proterozoic rocks modified from Southwick and Morey (1991). I 97° �Southwick, 1985)compose composean an east-trending east-trendingbelt belt between between higher higher grade grade rocks rocks of of the Late Archean Southwick, 1985) Archean Vermilion Granitic and the Giants Granitic Complex Complex (Quetico (Quetico subprovince, subprovince, fig. 5) (Southwick, 1972) and Giants Range batholith to the south. The Themeasured measuredstrain, strain,aacleavage, cleavage,upright upright folds, folds, and a mineral mineral lineation in this belt have been attributed to the the main" "main"phase phaseof ofdeformation deformation(D2) (D,) that thatfollowed followed an early nappe-forming event event (Dl) (D1) (Bauer, (Bauer, 1985). 1985). The nappes show little little evidence of of aa (D,) penetrative fabric (Hudleston, 1976). 1976). Hudleston and others others (1988) (1988) attributed attributed the the (D2) deformation to regional dextral transpression, transpression, as as the the strain pattern requires requires aa northeastnortheastsouthwestcomponent componentofofshortening shorteningininaddition additiontotoshear. shear. They They further further proposed proposed that that major major southwest dextral faults, such such as the Vermilion fault (fig. (fig. 5), 5), are are later, more brittle, expressions of this D2transpressive transpressive deformation resulted from from oblique oblique shear regime. They Theyconcluded concluded that that the theD2 compression between between the two more rigid crustal blocks blocks to to the the north (Quetico (Quetico subprovince) subprovince) and south (Giants Range batholith). A Asimilar similar tectonic tectonic regime regime has been recognized recognized in the the Rainy Rainy Lake area area (fig. (fig. 5; 5; Poulsen Poulsen and andothers, others,1980; 1980;Day Day and andSims, Sims,1984; 1984; Wood, Wood, 1980), 1980), where where early early recumbent folding by upright folding and dextral strike-slip folding was followed by strike-slip faulting. Recent precise isotopic analyses of of zircon, zircon,titanite, titanite, and and rutile rutile from the Rainy Lake area, area, Canada Canada (fig. 5; Davis and others, others, 1989), which lies lies between between the the Quetico Quetico and 1989), which and Wabigoon Wabigoon subprovinces, subprovinces, provided time time constraints constraints on on these these structural events. events. The have provided The major major deformation, deformation, including including nappe emplacement, emplacement, thrusting, and local doming, took place between 2,696 Ma and 2,692 Ma; followed shortly shortlyby bytranscurrent transcurrent faulting faulting and and simultaneous simultaneous deposition deposition of this deformation deformation was followed conglomerate/arenite (Timiskaming-type rocks, as as in in Seine Seine Group), Group), which which occurred occurred in in the the conglomerate/arenite (Tirniskaming-type rocks, 2,692-2,686Ma. Ma. Late (Algoman) granitic plutons were emplaced about 2,686 Ma, interval 2,692-2,686 and although some are older. InInthe theWawa Wawasubprovince, subprovince,west west of of Thunder Thunder Bay Bay (fig. (fig. 5), Corfu and found that that the D1 deformation occurred occurred during duringor or before before the the intrusion intrusion of of the Stott (1986) found Dl deformation Shebandowan Lake Lake pluton pluton at at 2,696± 2,696±2 Ma. Ma. Deformation Shebandowan Deformation D2 D2 in this area occurred between 2,689+3/-2 +3/-2 Ma Ma and and 2,684+ 2,684+6/-3 by Davis and others (1989) for 2,689 61-3 Ma, similar to the age age suggested suggested by D2 in the Rainy Lake wrench fault zone. These ages are compatible D, in Rainy Lake wrench fault zone. compatible with the less precise on rocks in in northern Minnesota and Michigan (Peterman, isotopic ages on (Peterman, 1979), 1979), and it seems seems probable that the the rocks rocks and and structures structuresthroughout throughout the the Wawa Wawa and and Quetico Quetico subprovinces subprovinces are approximately coeval coeval (Percival, (Percival, 1989). 1989). Although Although convergence convergencealong alongthe the GLTZ GLTZ undoubtedly was approximately probably occurred occurred in the approximate diachronous, collision probably approximate interval interval2,692-2,686 2,692-2,686 Ma (Davis and others, 1989), 1989), to yield the transcurrent transcurrentfaults faultsand andTimiskiming-type Timiskiming-typerocks. rocks. Kinematic Analysis Kinematic Analysis attitude of of the the stretching stretchinglineation lineation (line (line of of tectonic tectonic transport) transport) in in the themylonite mylonite exposed exposed south south The attitude of Marquette together micro-structures that that reveal reveal sense of of together with with asymmetric asymmetric meso- and micro-structures movement, indicate that that the theoblique obliquecollision collision resulted resulted in: in: (1) dextral-thrust shear along the the GLTZ, and and (2) (2) northwestward northwestward vergence and probable overriding of the Archean Archean greenstonegreenstonegranite terrane terrane by by the the Archean Archean gneiss gneiss terrane. terrane. Kinematic Kinematicindicators--rotated indicators--rotatedmica micagrains grainswithin within narrow compositional layers, asymmetric porphyroclasts porphyroclastswith withtails tails (o (a type; Simpson, 1986), and and asymmetric microfolds in in mylonitic myloniticlayering-demonstrate layering--demonstratenorthwestward northwestwardvergence. vergence. This information implies southward subduction of (Wawa of the the Archean Archean greenstone-granite greenstone-granite terrane terrane (Wawa subprovince) beneath beneath the Archean gneiss gneiss terrane terrane (fig. (fig. 1). 1). 121 �Evolution The northwest direction of tectonic transport during suturing of the Archean terranes, terranes, as as ascertained from the Marquette area, area, provides provides a means for determining the evolution evolution of the GL1'Z GLTZ and the variable trajectory of stress into the the Superior Superior province province crust. The GL1'Z bends that GLTZ in the Lake Lake Superior Superior region region is is characterized characterized by systematic angular bends alternately (fig.5). 5). Presumably this zigzag zigzag pattern pattern alternately trend northeastward and west-northwestward west-northwestward (fig. reflects relict relict irregularities irregularities in in the the margin margin of of the the Archean Archean greenstone-granite greenstone-graniteterrane terrane (or Superior reflects was aa continental margin before the province) crust, which was the convergence convergence and and coffision collision with the southern Archean gneiss terrane. gneiss terrane. segmentsof ofthe the GLTZ GLTZ have have different different The northeast-trending and west-northwest-trending west-northwest-trending segments structural styles. styles. Deformation Deformation along along the the northwest-trending northwest-trending segments of the GLTZ, GLTZ, as as by data data from the particularly shown by the Marquette Marquettesegment, segment,was wasprincipally principally caused caused by by dextral dextral transpression resulting from oblique oblique collision. coffision. Transmittal Transmittal of of this this transcurrent transcurrent shear into rocks rocks north of of the theGLTZ GLTZyielded yieldedaawidespread, widespread,pervasive pervasivewest-northwestwest-northwest- to towest-striking west-striking foliation, foliation, subparallel upright upright folds, and northwestnorthwest- to west-trending west-trending dextral dextral faults faults and and shear zones in the the Archean greenstone-granite terrane. northwest-trending segment segment of of the the GLTZ in northwestern Wisconsin The similarly-oriented northwest-trending Wisconsin has structural features in common common with withthe the Marquette Marquette segment. segment. Foliation and many structural and upright upright folds folds in low amphibolite-facies amphibolite-facies rocks rocksof of the the Archean Archean greenstone-granite greenstone-granite terrane terrane (unit (unit Wga, Wga, fig. fig. 4, Sims low and others, others, 1985) 1985) strike strike west-northwest and mineral lineations and fold hinges mainly plunge gently southeast. The gently southeast. The boundary boundary between the two terranes is not exposed exposed because of a glacial cover, but but is presumed presumed to lie along along the the south south edge edge of of unit unit Wga. Wga. Numerous northwest-trending cover, faults, some of of which which reactivated reactivatedin in Early EarlyProterozoic Proterozoictime, time,have havebeen been mapped mapped in in the dextral faults, area (Sims (Sims and and others, others,1985; 1985; fig. fig. 1). 1). Coffisionalong alongthe the northeast-trending northeast-trending segments segmentsofofthe the GLTZ, GLTZ, on on the the other hand, produced Collision northeast-trending structures structures of of apparently apparentlymore morerestricted restrictedareal areal extent. extent. In the northeastnortheast-trending northeastthe boundary is covered by Early trending Marenisco segment (fig. 5; Sims and others, 1984), the lithologic layering layering and and foliation foliation in rocks of Proterozoic sedimentary sedimentary and and volcanic volcanic rocks, however, lithologic Archean greenstone-granite greenstone-graniteterrane terrane near near the boundary boundary trend trend northeastward northeastward and are the adjacent Archean 45°-50° SW. These deformed into upright, moderately tight northeast-trending folds that plunge 45' -50' SW. subparallel to to the the covered covered Archean Archean GLTZ GLTZ boundary. boundary. Archean structures are presumably presumably subparallel metamorphism has been overprinted overprinted by by Early Proterozoic Penokean nodal nodal metamorphism metamorphism centered on on the theWatersmeet Watersmeet dome dome(Sims (Simsand andothers, others,1985; 1985;Sims, Sims, 1990); 1990); the presence of of relict relict garnet at aa few rocks of of the the greenstone-granite greenstone-granite terrane terrane near the boundary few places in the Archean rocks suggests that that these rocks were metamorphosed metamorphosed to to at least upper greenschist facies in Archean time. Similarly, Similarly, north-verging north-verging Penokean deformation in the the boundary boundary zone zone overprinted overprinted Archean Archean structures (Sims and others, 1984). plane S, 2 (Penokean) (Sims and 1984). An axial plane (Penokean) penetrative penetrative cleavage, cleavage, striking northeast SE., was was superposed superposed on on the previously previously folded folded rocks. rocks. Apparently northeast and and dipping dipping 45°-70° 45'-70' SE., Apparently the Archean rocks were not refolded, however, as aa result result of of the Penokean deformation. however, as In the northeast-trending segment of of the the GLTZ (fig. (fig. 5), 5), neither neither the terrane terrane boundary northeast-trending Minnesota segment nor adjacent Archean rocks on either side are exposed. These These rocks rocks are are covered covered in in west-central west-central by thick thick Quaternary glacial deposits deposits and and in in central central Minnesota by by Early Proterozoic Minnesota by sedimentary and volcanic rocks rocks of of the the Animikie Animikie basin basin (Southwick (Southwickand andothers, others, 1988). 1988). The GLTZ GLTZ 122 �has been investigated, computer-generated investigated, however, however, by a detailed detailed aeromagnetic aeromagneticsurvey, survey, by computer-generated the second second vertical vertical derivative derivative of of the the gravity gravity field, field, and and by by shallow shallow test drilling drilling (see (see mapping of the Southwick and Southwick and Sims, Sims,in inpress); press);the the boundary boundary has has been been located located rather rather accurately on on the basis of these data. The Thedrilling drillinghas hasshown shown that that the therocks rocks on on the thenorthwest northwestside sideare arevolcanogenic volcanogenic sedimentary and mafic to intermediate rocks,which whichare aremetamorphosed metamorphosed to to upper upper intermediate volcanic volcanic rocks, greenschist facies facies and and intruded by by Archean Archean tonalite (Southwick (Southwickand and Chandler, Chandler, 1983). 1983). These greenschist of the the Archean Archean greenstone-granite greenstone-granite terrane terrane in exposed exposed parts parts of of the Lake rocks are typical of region. A by COCORP COCORP Superior region. A seismic seismic reflection profile in central Minnesota acquired by (Consortium for Continental Reflection Profiling)has hasbeen been interpreted interpreted to indicate that the Reflection Profiling) the GL1'Z north-dipping tectonic tectonic feature feature (Gibbs and others, this area area isisaashallow shallow(—30°) (-30° north-dipping others, 1984). 1984). GLTZ in this In east-central Minnesota, the the GLTZ GLTZ isis covered covered by by Proterozoic Proterozoic rocks of the the Animikie Animikie basin. The structural structural style style in the the Proterozoic Proterozoiccover cover indicates indicates north-verging north-verging tectonism tectonism (Southwick (Southwick and others, others, 1988), 1988), and as in the Marenisco Marenisco segment, the Archean crustal crustal boundary had aa role role in in defining Penokean deformation. deformation. Deformation along both of the northeast-trending of the northeast-trending (Minnesota and Marenisco) segments of GL1'Z resulted mainly from northwest-southeast crustal shortening, probably dominantly by GLTZ resulted mainly from northwest-southeast crustal shortening, probably dominantly by flattening strain. The Thedirection directionofoftectonic tectonictransport transportduring duringconvergence convergencewas was virtually virtually perpendicular to the the juncture of of the the two two terranes terranes at at these theselocalities. localities. The origin of the the zigzag zigzag pattern of the the south south edge edge of of the the Superior Superiorprovince, province, now now marked marked by by the the GL1'Z, is uncertain. uncertain. The is one one of of a sequence GLTZ, The prevailing prevailing thought is that the Wawa subprovince is of stacked island arcs that formed from north north to south above north-dipping formed progressively progressively from subduction zones zones as as the the continental mass mass to to the south of the GLTZ GLTZ (i.e., (i.e., Archean gneiss terrane) terrane) migrated migrated to the the north north (Card, (Card,1990). 1990). With Withthis thisinterpretation, interpretation,possible possible modern modem analogs analogs of the Superior province are the convergent-plate boundaries of the western Pacific, as for Superior province are the convergent-plate of the western Pacific, as for example those of the the Indonesian Indonesian region region (Hamilton, (Hamilton,1979). 1979). The physical of the southern margin of the Superior physical resemblance of Superior province to the the AppalachianAppalachianOuachita Paleozoic orogenic belt (Thomas, 1977), however, suggests a possible alternative Paleozoic orogenic belt (Thomas, 1977), however, alternative margin. In this interpretation, the interpretation for the origin of the Superior margin. the Superior Superior margin margin. Two interpretations have been been made for the origin of the was a rifted continental margin. margin: (1) Paleozoic continental margin: (1)rift riftsegments segmentswere were offset offset by by transform transform faults, faults, as as suggested suggested by by 1983),or or (2) (2) intersections intersections between between active activerift rift arms arms at at triple junctions junctions (Rankin, Thomas (1977, (1977, 1983), with the 1976). Of these these two two suggestions, suggestions, the rift-transform mechanism seems the more more likely, with 5) and and the northwestern northwestern Minnesota and Marenisco Marenisco segments segmentsbeing being the the rifted rifted segments segments(fig. (fig. 5) Wisconsin and and Marquette segments being highly highlymodified modifiedtransform transformfaults. faults. Regardless of the Wisconsin the by which whichthe the zigzag zigzagArchean Archeancontinental continentalmargin marginoriginated, originated,the thesubsequent subsequent trace trace of of mechanism by the orogenic belt was probably probably inherited inherited from from the the shape shape of of the earlier margin. CONCLUDING CONCLUDING REMARKS REMARKS Convergence along the the irregularly shaped shaped margin margin of of the the Archean greenstone-granite greenstone-granite terrane terrane (GLTZ) resulted resulted in in aa variable variable trajectory trajectory of of stress stress into the the continental continentalcrust crust and and probably probably in in diachroneityofoforogeny. orogeny. Structural Structuraldata data from fromthe the Marquette Marquette area, in particular, as along-strike diachroneity well as as elsewhere elsewhere along alongthe the GLTZ, GLTZ, suggest suggestthat thatthe the major major direction direction of of tectonic tectonic transport transport was well northwestward. Accordingly, promontories such as those along the concave parts of the northwestward. Accordingly, promontories the Marquette and and Wisconsin Wisconsin segments of the GLTZ GLTZ (fig. (fig. 5), where the zone bends from a northeast orientation orientation to to aa northwest northwest one, one, must must have have projected projected as as buttresses buttressesagainst against which which 123 �compressive compressive stress was directed into the continental crust. Oblique Obliquecompression compression at atthese thesepoints points produced produced dextral dextral shear across across the region north of of the the suture, suture, probably probably at least least as as far far northward northward as km. This as the the Quetico Quetico fault fault (fig. (fig. 5), a distance distance of about 250 km. This shear shear imposed imposed aa roughly roughly easteastwest, west, steep steep structural structural fabric fabric on the the rocks rocks and, also as a late, more more brittle brittle expression expression of the the shear shear regime regime (Hudleston (Hudleston and andothers, others,1988), 1988),the thenorthwestnorthwest- to towest-trending west-trending dextral dextraltranscurrent transcurrentfaults. faults. Along Along the the Marenisco Mareniscoand andMinnesota Minnesotasegments segmentsof ofthe theGLTZ GLTZ(fig. (fig.5), 5),where whereconvergence convergencewas was more more perpendicular perpendicular to to the theancient ancientcontinental continentalmargin, margin, aanortheast-trending northeast-trendingstructural structuralfabric fabricwas was imposed imposed on on the therocks rocksimmediately immediately cratonward cratonward from from the thesuture. suture. We We suggest suggest that the the main main structural structural fabric fabric (D2) (D2) in rocks of the Archean greenstone-granite greenstone-granite terrane 5)resulted resulted terraneininthe thenorth-central north-centralUnited UnitedStates States(Wawa (Wawaand andQuetico Queticosubprovinces; subprovinces;fig. fig. 5) from along the the GLTZ. GL1'Z. The from the the coffision collision along The predominance of orthomylonite rather than ultramylonite ultramylonite and and the thenearly nearly pervasive pervasive retrogressive retrogressive alteration alteration (greenschist (greenschist facies) fades) in inrocks rocksof of the the greenstone-granite greenstone-granite terrane terranesuggest suggest that that the theexposed exposedcollision collision zone was developed at aa moderately level (at (at brittle-ductile brittle-ductile transition transition conditions). conditions). As discussed in a moderately shallow shallow crustal level previous report (Sims and others, 1980), the Archean structures previous report (Sims and others, 1980), structures in in this this regime regime also also played played aa strong strong role role in in subsequent subsequenttectonism, tectonism, especially especially in the the Early Early Proterozoic Proterozoic north-verging north-verging deformation. deformation. We We further further suggest suggest that the the late-tectonic late-tectonic granite bodies in the Archean gneiss terrane are are possibly related to the collision along the the GLTZ GLTZ and presumed presumed southward southward subduction. subduction. The possibly related collision along available available age data on these these granites granites are are compatible compatible with a presumed 2.69 2.69 Ga age for the coffision. collision. The The "Tilden "Tilden granite" granite" of Hammond (1978) (1978) in Michigan Michigan has a Late LateArchean Archeanage age (2,585±15 both the U-Pb and Rb-Sr Rb-Sr systems systemsare are disturbed. disturbed. In the (2,5852 15 Ma), although although both the Minnesota Minnesota River southwestern Minnesota, Minnesota, aa large large pluton pluton of of late-tectonic late-tectonic granite granite (Sacred (Sacred Heart River valley, in southwestern Granite) and a Rb-Sr age of Granite) has has aaPb-Pb Pb-Pb age ageof of about about2,605 2,605 Ma (Doe (Doe and and Delevaux, Delevaux, 1980) and about andand Delevaux (1980) have shown thatthat 207Pb-204Pb about 2.7 2.7 Ga Ga(Goldich (Goldichand andothers, others,1970). 1970).Doe Doe Delevaux (1980) have shown ^Pb-^Pb values in the Sacred Heart Heart Granite Graniteare arecharacteristic characteristicof of ensialic ensialic environments, environments, as contrasted with the the ensimatic ensirnatic (arc) (arc) granitoid granitoid bodies bodies in the the Superior Superior province (greenstone-granite terrane). with The The ensialic ensialic environment indicates that the Archean gneiss terrane had been cratonized cratonized prior prior to to emplacement of the Sacred Sacred Heart Granite. Granite. Precise emplacement of Precise ages ages are are required required to to test test the thehypothesis hypothesis that that the the Late Late Archean Archean granites granites south south of of the theGLTZ GLTZwere wereindeed indeed formed formedduring duringcontinent-continent continent-continent collision. collision. Cumulative Cumulative data on on the the Archean Archean Superior Superiorprovince province (see (see Hoffman, Hoffman, 1989, 1989, for review) review) indicate consists of of generally east trending belts that itit consists belts of of island island arc arc and related rocks that were assembled progressively from from north to south south (Card, (Card, in in press), press),before beforefmally finallycoffiding colliding with the Archean Ma. 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Sims, P.K., P.K., Peterman, Peterman, Z.E., Z.E., Zartman, R.E., R.E., and and Benedict, Benedict, F.C., F.C., 1985, 1985, Geology and geochronology of granitoid granitoid and and metamorphic rocks rocks of of Late Archean age geochronology of age in in northwestern northwestern Wisconsin: U.S. U.S. Geological GeologicalSurvey Survey Professional ProfessionalPaper Paper1292-C, 1292-C,17 17p. p. Sims, P.K., P.K., and Southwick, D.L., D.L., 1985, 1985, Geologic Geologicmap map of of Archean Archean rocks, western Vermilion Vermilion district, northern northern Minnesota: Minnesota: U.S. U.S.Geological GeologicalSurvey SurveyMiscellaneous Miscellaneous Investigations Investigations Series Series Map 1-1527, 1:48,000. Map 1-1527, scale scale1:48,000. Sims, P.K., and Morey, Morey, G.B., G.B., eds., eds., Southwick, D.L., D.L., 1972, Vermilion granite-migrnatite granite-migmatite massif, massif, in Sims, of Minnesota--A centennial volume: volume: Minnesota Geology of MinnesotaGeological GeologicalSurvey, Survey, p. p. 108-119. 108-119. Southwick, D.L., D.L., and and Chandler, V.W., 1983, Subsurface Subsurfaceinvestigations investigationsofofthe the Great Great Lakes V.W., 1983, tectonic zone, west-central Minnesota: Geological Geological Society Society of America Abstracts Abstracts with Programs, v. Programs, v. 15, 15, p. 692. 692. Southwick, D.L., D.L, and Morey, Tectonic imbrication imbrication and and foredeep foredeep development in the Southwick, Morey, G.B., 1991, Tectonic the Penokean Penokean orogen, east-central east-central Minnesota--An Minnesota-An interpretation based on on regional regional geophysics and and the the results of of test drilling, drilling, j Sims, geophysics Sims, P.K., P.K., and and Carter, Carter,L.M.H., L.M.H., eds., eds., Contributions of Lake Lake Superior Superior region: region: U.S. Contributions to Precambrian geology geology of U.S. Geological Geological Survey Bulletin 1904-C, 1904-C, 17 17 p. D.L., Morey, G.B., G.B., and McSwiggen, P.L., 1988, 1988,Geologic Geologicmap mapof of the the Penokean Penokean McSwiggen, P.L., Southwick, D.L., text: Minnesota Geological orogen, central and eastern Minnesota, and accompanyingtext: Report of p., scale scale1:250,000. 1:250,000. Survey Report of Investigations Investigations37, 37,25 25p., Taylor, W.E.G., W.E.G., 1967, The The geology geologyofofthe the lower lowerPrecambrian Precambrian rocks rocks of of the the Champion-Republic area of Upper Upper Michigan: Michigan: Evanston, Evanston,Illinois, Illinois,Northwestern Northwestern University University Report Report 13, 13,33 33 p. p. Thomas, WA., 1977, of Appalachian-Ouachita salients salients and and recesses recesses from from reentrants 1977, Evolution of and promontories promontories in in the the continental continentalmargin: margin: American AmericanJournal JournalofofScience, Science,v. v. 277, 277, p. 1233-1278. 1233-1278. 1983,Continental Continental margins, margins, orogenic orogenicbelts, belts,and and intracratonic intracratonic structures: structures: Geology, 1983, Geology, v. v. 11, 11, p. 270-272. 270-272. Van Hise, C.R., W.S., 1897, 1897,The TheMarquette Marquetteiron-bearing iron-bearingdistrict district of of Michigan: Michigan: U.S. C.R., and Bayley, Bayley, W.S., Geological Survey Monograph 608 p. Monograph28, 28,608 p. 129 �White, of strain on the White, S.H., S.H., 1976, 1976, The effects of the microstructures, microstructures, fabrics, and deformation deformation mechanisms mechanisms in quartzites: quartzites: Royal RoyalSociety Societyof of London LondonPhilosophical PhilosophicalTransactions, Transactions,ser. ser. A283, p. 69-86. A283, p. 69-86. Wise, Wise, D.U., and and seven sevenothers, others,1984, 1984,Fault-related Fault-relatedrocks--Suggestions rocks-Suggestions for terminology: Geology, Geology, v. 12, 12,p.p.39391-394. v. 1-394. Wood, of the Hewitt Lake area, Wood, John, John, 1980, 1980, Geology of area, District District of of Kenora, Kenora,Patricia Patriciaportion: portion: Ontario OntarioGeological GeologicalSurvey, Survey,Report Report186, 186,122 122p. p. 130 �Field stops and road log Field stops stops shown shown on figure figure 66 Miles 0 0 3.8-6.3 Depart from from Ramada RamadaInn Inninindowntown downtown Marquette Marquetteon onMichigan Michiganhighway highway28 28 (M28) (M28) and proceed proceed west. west. of pillow pillowbasalt basaltalong alongM28. M28. Basalt Basaltcomprises comprisesaamajor majorpart part of of Numerous outcrops of Archean greenstone-granite terrane terrane (Wawa (Wawa subprovince) subprovince) in the the northern northern complex complex of Marquette Marquette district. district. Proterozoic rocks of Marquette Early Proterozoic Marquette syncline syncline lie to the the south southof ofhighway. highway. 7.2 Turn left (south) (south)from from M28 M28 onto ontoM35. M35. 10.8 M35 intersects Marquette County road road 480 480 (Co. (Co. 480). 480). Continue Continue south south on on M35. M35. 11.2 Outcrops Outcrops of Early Proterozoic Proterozoic Negaunee Negaunee Iron-formation. Iron-formation. 14.1 o'clock, Empire Empire iron iron mine mine waste waste rock. rock. Pass through Palmer. High dumps at 12 o'clock, 16.9 Turn right right (west) (west)on onCounty Countyhighway highway 565. 565. 18.1 At road road fork fork turn turnright rightonto ontoCounty Countyhighway highway 476. 476. 19.5 Stop 1. 1. Roadcut Roadcutinin"Tilden Tilden granite" granite" (Hammond, (Hammond, 1978). 1978). The "Tilden granite" granite" is aa pinkish-gray pinkish-gray to to pink, pink, medium-grained, medium-grained,locally locally porphyritic, porphyritic, massive to weakly weakly foliated, foliated, homogeneous homogeneous granite granite that that locally locally contains contains oriented oriented of mafic mafic gneiss. gneiss. It intrudes xenoliths of intrudes gneisses gneisses and in turn turn isis cut cut by by pink pink pegmatite. pegmatite. surfaces and a thin The granite is is highly fractured; the fractures have slickensided surfaces of chlorite chlorite and and other other propylitic propyliticalteration alterationminerals. minerals. The granite has a U-Pb coating of concordia intercept age of 2,585±15 Ma (R.E. Zartman, 2,585Â15 Zartman, oral oralcommun., commun., 1991). 1991). Chemically, the granite has characteristics of post-orogenic, within within plate plate granite on Chemically, the on Bornhorst, written written commun., commun., 1990), 1990), which is consistent consistent discrimination diagrams diagrams (T. Bornhorst, with its its post-tectonic post-tectonic field field relationships. relationships. Continue southwest Continue southwest on on Co. Co. 476. 476. 19.7 Turn around and return to to M35. M35. 22.4 Junction of Co. 476 and M35. M35. Proceed Proceed southeast southeaston onM35. M35. 23 gneiss terrane). terrane). Stop 2. High High roadcut roadcut on on M35 M35 in in Archean Archean gneiss (of Archean gneiss Road shoulder is narrow. Be Becareful. careful. Excellent outcrop outcrop of of layered layered gneiss gneiss(of (ofArchean Archeangneiss gneissterrane) terrane) on on the the northeast Excellent side of road. Amphibolite Amphibolite and and quartzofeldspathic quartzofeldspathic gneiss gneiss are are interlayered, and are by red pegmatite. Pegmatite cut by Pegmatite and and aplite aplite are areboudined boudined and andbrecciated; brecciated; boudins boudins 131 �plunge plunge parallel to to recumbent recumbent fold fold axes. axes. Tight Tightfolds foldswith with axial axial planar planar foliation foliation plunge 25' with a strike strike of of N. N. 50 5 ' W., W., as as does does aa mineral mineral lineation. lineation. plunge about about 25° This This outcrop outcrop is is typical typical of the gneiss of the Archean gneiss terrane, but amphibolite amphibolite is abundant here. Tight is uncommonly uncommonly abundant Tight recumbent recumbent folds folds that thatplunge plunge gently gently northward northward are are the the dominant dominant structures structures in in this this part part of of the thegneiss gneiss terrane. terrane. Return M35. Return to tovehicle vehicle and and continue continue southeast southeaston onM35. 23.7 M35 intersects private road road (Cleveland (ClevelandCliffs Cliffs Iron Iron Company). Company). 24.2 Stop 3. area. Outcrop 3. Low Low outcrop outcrop on on northeast northeast side of road in grassy grassy area. Outcrop has has been been covered covered by by loose sand sand and and isislichen lichen free. free. This outcrop contains contains northwest-trending northwest-trending folds folds with an an axial axial planar planar foliation foliationvisible visible 600 on polished polished surfaces surfaces that that strikes strikesN. N. 65° 65' W., W., and and dips dips 60' NE. NE. This structure structure is is superposed on recumbently folded folded gneiss, gneiss, and and therefore therefore is younger. younger. Thick Thick layers layers of felsic gneiss retain retain a dominant older older foliation foliation that that strikes strikesN. N. 250 25' W. W. The steep foliation and and associated associated folds foldsare are parallel parallel to to the the trend steep northwest-trending northwest-trending foliation of the (of Marquette district). district). Although the antiformal antiformal southern complex complex (of Although minor minor in in this this area, area, upright upright northwest-trending northwest-trending folds are the dominant dominant structures structures in in the theRepublic Republic area, 30 km km to to the thewest. west. area, 30 M35. Continue southeast southeast on on M35. Continue 132 24.3 Turn around around at atCommunity Community Club Club and and proceed proceed northwest northwest on on M35 M35 toward toward Palmer. Palmer. 24.9 M35 intersects private private road road (CCI). (CCI). Continue Continue north north on on M35 M35 to to intersection intersection with with 480. Co. 480. 32.3 Intersection of M35 and Co. 480. Turn Turn right right (east) (east) on onCo. Co.480. 480. 35.6 Turn right (south) on secondary road. road. Roads Roads for for remainder remainder of of field field excursion excursion are are unmarked; accordingly, we have have arbitrarily arbitrarily assigned assigned letter letter designations A through L accordingly, we L (see fig. 3) to specific segmentsas asan anaid aidininlocation. location. The main main road into area specific segments (road A) A) is is aa graded graded sandy sandy dirt road; other other roads roads followed followed on the trip are are not not and may may be be rutted rutted or orsoft, soft,requiring requiringsome somecare careinindriving. driving. graded and 39.6 Road A A crosses crosses Chicago Chicago and and Northwestern Northwestern railway railway near near Gentian. Gentian. 39.7 (B) and andcontinue continuesouthwest southwest on on B. B. road fork fork (B) Take right road 40.6 Junction with east-west east-west road road (C). (C). Proceed Proceed west west on on CC for for0.3 0.3 mi. mi. �40.9 40.9 Stop 4. Rock Rockknob knobnorth northside sideof of road road C. C. Stop This This outcrop outcrop isis typical typical of of the the Archean Archean greenstone-granite greenstone-granite terrane. terrane. ItIt consists consists of of granite granitegneiss gneiss (or (or foliated foliated granite) granite) that thatcontains containslenses lensesof ofbiotitic biotiticand andchioritic chloritic amphibolite. amphibolite. These Theserocks rocksare arecut cutby bygranite granitepegmatite pegmatiteand andaplite, aplite,which whichcrosscut crosscut the the foliation foliation in in the the granitoid granitoid rocks. rocks. Note Notethat thatcrosscutting crosscutting aplite aplite and and pegmatite pegmatite are are not 70ÂW. W.and anddips dips65° 65' Sw. SW. not sheared shearedout. out.Foliation Foliationstrikes strikesN.N.70° Although Although this outcrop lies near the the north north margin margin of of the theGreat GreatLakes Lakestectonic tectoniczone zone and although it has a foliation subparallel to that in the GL1'Z, the outcrop and and although it has a foliation subparallel the GLTZ, the outcrop and those those to tothe thewest-northwest west-northwest are areexcluded excluded from from the theGLTZ GLTZbecause becausethe thecrosscutting crosscutting pegmatite pegmatite and and aplite aplite are are not not sheared sheared out out and and the the rocks rocks are are protomylonite. protomylonite. The The northern northern boundary boundary isis placed placed at at the theabrupt abrupttransition transitionfrom from"straight-banded" "straight-banded" mylonite in the GL1'Z GLTZ to to rocks rocks that that retain retainrecognizable recognizable igneous igneous structures, structures, such such as as here. The Therocks rockstotothe thenorth northofofthe theGLTZ GLTZare areprotomylonite. protomylonite. Return Return totovehicle vehicleand andcontinue continuewest weston onCCfor for0.2 0.2mile. mile. 41.1 41.1 Intersection Intersection of roads C and D. Turn Turnleft left on onDDand andcontinue continuefor for0.4 0.4 mi. mi. 41.5 41.5 Stop 5. Outcrops Outcropsofofmilky milky quartz quartz and andaltered alteredArchean Archeanrocks rocksabout about50 50yards yardswest west of of Stop D. road D. road Milky Milky quartz and and silicified silicified country rock, such as those exposed here, here, characterize characterize the the hifis hills to the west. These Theseoutcrops outcrops comprise comprise the the most most eastern eastern exposed exposed part part of of aa quartz km long. The quartz 1.4 l un long. quartz body body quartz lense, oriented about about east-west, east-west, that is about 1.4 may may occupy a major tension fissure zone related to to dextral dextral wrench wrench shear shear within within the the GLTZ. GLTZ. Turn Turn around around and and proceed proceed north north on onDDtotointersection intersectionwith with C. C. Then Then follow follow C and D to to road road fork fork at atGentian Gentiancrossing. crossing. 42.8 42.8 sharply right from road B B onto onto road road E; E;continue continuesouth southfor for1.2 1.2ml. mi. Turn sharply 44 44 Road Road fork; fork; continue continue south south on on road road F. F. 44.35 44.35 Road fork (G), (G), then turn left at road Road fork; fork; continue south on right fork road fork fork onto onto H Hand and east on on H Hto tolocked lockedgate. gate. continue east 45.0 45.0 and walk walk on private road east east and and northeast northeast to towest west shore shoreof ofPowell Powell Lake Lake Park and (distance 0.3 mi). walk 0.3 mi). Walkisiseasy. easy. Stop Thisisisan anexceptionally exceptionally good good series series of of outcrops outcrops of of mylonite mylonite within the Stop 6. This GLTZ clean. The dominantly granite granite GLTZ because because they they are areperiodically periodically washed washed clean. Therock rockisisdominantly gneiss containing pods pods of of migmatized migmatized amphibolite amphiboliteand and hornblende hornblende schist. schist. The The protolith is is granite and and amphibolite amphibolite of the Archean greenstone-granite terrane. 133 �variable. A Foliation in the the gneiss gneiss strikes strikes about about N. N. 75° 75' W. W. and and dips dips 75° 75' SW., SW., but is variable. conspicuous stretching stretching lineation lineation plunges plunges uniformly uniformly about about550 55' and bears bears S. S. 45° 45' E. Both dextral and sinistral asymmetric folds plunge plunge subparallel subparallel to to the lineation; dextral folds predominate. predominate. Porphyroclasts Porphyroclasts are are common, common, but they they do do not not clearly clearly have internal monodlinic symmetly and and elongate elongate tails, tails, necessary necessary to to determine determine monoclinic symmetry 1986). movement sense sense (Simpson, (Simpson,1986). Return to parked vehicle at locked lockedgate. gate. Proceed Proceed west west on on road road H H to road fork vehicle at (distance 0.25 mi), then then turn right on H to 0.25 mi), to junction of of H H with with JJ (distance (distance0.15 0.15 mi). mi). 45.4 Junction of of roads roads H and J. Turn Junction Turnsharply sharply left left on on JJ and and continue continue for for 0.2 0.2 mi. mi. 45.6 45.6 Road fork. Continue Continueon onright rightfork fork(K) (K)for for0.1 0.1ml. mi. 45.7 45.7 northwest, a distance distance of about about 750 750 ft, to outcrops. outcrops. Park and walk on trail to northwest, Stop 7. Low Low outcrops outcropsof of pink pink mylonitic mylonitic gneiss with lenses of biotite schist. Protolith is considered to be felsic felsic gneiss gneissof ofArchean Archeangneiss gneissterrane. terrane. Foliation N. 750 75' W. and dips dips 65° 65' SW. A quartz quartzrodding rodding lineation lineationplunges plunges50° 50' and and strikes N. strikes SW. .A S. 45' 45°E. E. Note abundant ribbon ribbon quartz. quartz. This outcrop is in the southern part bears S. of the GLTZ. Return to road. Turn Turnaround aroundand andfollow follow roads K and J to road road fork fork with with H. Proceed south on H H to to junction junction (1.5 (1.5 mi). 46.2 Continue south on L. 47.3 Road L intersects power line. Park Parkand andwalk walk750 750ftft southwest southwest to tolow low outcrops outcrops along power line. Stop 8. Outcrops Outcropscomprise comprise pink pink granite granitegneiss gneiss with amphibolite layers and lenses, cut by Foliation strikes strikes N. 40° 40' W., by pink pink granite granite pegmatite. pegmatite. Foliation W., and and dips dips 80' 80°NE. NE. Rocks are not sheared. sheared. Two Twoparallel parallel diabase diabasedikes dikes cut cut the theArchean Archean gneiss. gneiss. These outcrops are are within the Archean gneiss terrane, a distance of about 0.65 0.65 km south of the south boundary boundary of the (3L1'Z. GLTZ. Thus, Thus, we have crossed from the Archean greenstone-granite terrane, through the GLTZ, into the the Archean Archean gneiss gneiss terrane terrane to to the the south south of of the the GLTZ. GLTZ. Suggest returning to Co. Co. 480 via End of field trip. Suggest via dirt roads L, G, F, E, and A. 134 �U) w -J In — U) w I 0— -0 Figure 6. Field Fieldtrip tripstops. stops.Marquette Marquetteand andmost mostofofMichigan Michiganhighway highway 28 are are just north north of of the the Figure map area. area. 135 �Issues of the Proceedings of this meeting may may be ordered ordered from from M.G. Mudrey, Mudrey Jr., M.G. Jr., Secretary-Treasurer Secretary-Treasurer do c/oWisconsin WisconsinGeological Geologicaland and Natural Natural History History Survey Survey 3817 38 17 Mineral Mineral Point Road Road Madison, Madison, Wisconsin Wisconsin 53705-5 53705-5100 100 1: Program and Abstracts: $7.00 U.S. Part 1: Part 2: Field Trip Guidebook: Guidebook: $7.00 U.S. Orders Orders will will be filled while supplies last. last. All volumes back to 1955 1955 are are available available for for photocopying photocopying at at the the prevailing prevailing rate, rate, from from the the Michigan Michigan Technological Technological University University Library, Library, through through Mr. Mr. M.S. M.S. Spence, Spence, Archivist. Archivist. Telephone Telephone (906) (906) 487-2505 487-2505 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1992 Description An account of the resource Institute on Lake Superior Geology. Hurley, Wisconsin. May 6-9, 1992. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1992 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/a357bd85b85ecf4d6d0697f4cc4a3867.pdf f15062cdc56fb94eb534f98788368468 PDF Text Text ��CONTENTS Institutes on Lake Superior Geology to 1993 Constitution of the Institute on Lake Superior Geology 11 By-Laws of the Institute on Lake Superior Geology lV Goldich Medal Guidelines v Student Travel Award Vi Board of Directors V11 Local Committee V11 Student Paper Award Committee V11 Goldich Medal Committee V11 Goldich Medal Recipient V11l Past Goldich Medal Recipients V11l Banquet Speaker V11l Report of the Chair of the 38th Annual Institute lX Calendar of Events and Program Xl Abstracts 1 �INSTITUTES ON LAKE SUPERIOR GEOLOGY Institute Number Date Place 1 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, On tario Houghton, Michigan Duluth, Minnesota Ishpeming, :rvlichigan St. Paul, Minnesota Sault Ste. Mmie, Michigan East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Michigan St. Paul, Minnesota Thunder Bay, Ontario Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 �CONSTITUTION OF INSTITUTE ON LAKE SUPERIOR GEOLOGY Article I Name The name of the organization shall be the "Institute on Lake Superior Geology". Article II Objectives The objectives of this organization are: A. To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. B. To promote better understanding of the geology of the Lake Superior region. C. To plan and conduct geological field trips. Article ill Status No part of the income of the organization shall inure to the benefit of any member or individual. In the event of dissolution the assets of the (some tax free organization). organization shall be distributed to (To avoid Federal and State income taxes, the organization should be not only "scientific" or "educational", but also "non-profit".) N1inn. Stat. Anno. 290.01, subd. 4 N1inn. Stat. Anno. 290.05(9) 1954 Internal Revenue Code s.501(c)(3) Article IV Membership The membership of the organization shall consist of the board of directors. Any geologist interested shall be permitted to attend and participate in and vote at the annual meetings. Article V Meetings The organization shall meet once a year, preferably during the month of April. The place and exact date of each meeting will be designated by the board of directors. Article VI Directors The board of directors shall consist of the Chairman, Secretary-Treasurer, and the last three past Chainnan; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the annual meeting so as to bring the membership of the board up to five members. ., II �Arricle VII Officers The officers of this organization shall be a Chairman and Secretary-Treasurer. A. The Chairman shall be elected each year by the board of directors, who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. His term of office as Chairman will tenninate at the close of the annual meeting over which he presides or . when his successor shall have been appointed. He will then serve for a period of three years as a member of the board of directors. B. The Secretary-Treasurer shall be elected at the annual meeting. His term of office shall be two years or until his successor shall have been appointed. Article VITI Amendments This constitution may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organization. 111 �BY-LAWS I. Duties of the Officers and Directors A. It shall be the duty of the Annual Chairman to: 1. 2. 3. B. It shall be the duty of the Secretary-Treasurer to: 1. 2. 3. C. II. Keep accurate attendance records of all annual meetings. Keep accurate records of all meetings of, and correspondence between, the board of directors. Hold all funds that may accrue as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. It shall be the duty of the board of directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. Duties and Expenses 1. 2. III. Preside at the annual meeting. Appoint all committees needed for the organization of the annual meeting. Assume complete responsibility for the organization and fmancing of the annual meeting over which he presides. There shall be no regular membership dues. Registration fees for the annual meetings shall be detennined by the Chairman in consultation with the board of directors. It is strongly recommended that these be kept at a minimum to encourage attendance of graduate students. Rules of Order The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. IV. Amendments These by-laws may be amended by a majority vote of those persons who are personally present at, participating in, and voting at any annual meeting of the organization; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently amended. IV �Award Guidelines SAM GOLDICH MEDAL Preamble The Institute on Lake Superior Geology was born on or around 1955, as documented by the fact that the 27th annual meeting will be held in 1981. The Institutes are exemplary in their continuing objectives of dealing with those aspects of geology that are related geographically to Lake Superior; of encouraging the discussion of subjects and sponsoring field trips which will bring together geologists from academia, government surveys, and industry; and of maintaining an exceedingly informal but highly effective mode of operation. During the course of its existence the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the LL.S.G. by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the improvement of understanding of "Lake Superior" geology and its mineral deposits. The exemplary award was made by LL.S.G. to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Award Guidelines 1) The medal shall be awarded annually by the LL.S.G. Board of Directors to a geologist whose name is associated with a substantial interest in, or a major contribution to, the geology of the Lake Superior region. 2) The Board of Directors, LL.S.G. shall appoint the Nominating Committee. The initial appointment will be of three members, one to serve for three years, one for two, and one for one year, the member with the briefest incumbency to be chairman. After the first year the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In the third year this member shall be the chairman. The Committee membership should reflect the main fields of interest and geographic distribution of LL.S.G. membership. 3) By November 1, the Goldich Medal Nominating Committee shall make its recommendation to the Chainnan of the Board of Directors who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, will inform the medalist immediately, and will have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. April 4, 1981 1. Kalliokoski, Chairman Bill Cannon Fred Kehlenbeck G.B. Morey Greg Mursky v �STUDENT TRAVEL AWARD The 1986 Board of Directors established the LL.S.G. Student Travel Award to support student participation at the annual Institutes. The awards will be made from a special fund set up for this purpose. This award is intended to help defray some of the direct travel costs to the Institute and includes a waiver ofregistration fees, but excludes expenses for meals, lodging, and field trip registration. The number of awards and value are determined by the annual Chairman in consultation with the Secretary-Treasurer and will be announced at the annual banquet. The following general criteria will be considered by the annual Chairman, who is responsible for the selection: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away. 5) Each travel award request shall be made in writing, to the annual Chairman, with an explanation of need, possible author status or other significant details. Successful applicants will receive their awards at the time of registration for the Meeting. VI ������This page intentionally left blank ����������������������������������������������������������������������������������������� https://digitalcollections.lakeheadu.ca/files/original/857b56a669d6b629e3610cd1383eaa73.pdf a8a6e46a4714c10523dfb417929437a2 PDF Text Text ������������������������������������������������������������������������������������������������������������������������������������������������������������������� Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1993 Description An account of the resource Institute on Lake Superior Geology. Eveleth, Minnesota. May 5-8, 1993. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1993 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/686cdd7814f1ea17de0e13904c023eff.pdf f93685aadb30642819adb0efd3b82089 PDF Text Text S Proceedings Proceedings 40th 40th Annual Meeting May 11 11--14 14,1994 , 1994 Michigan MichiganTechnological Technological University University Houghton, Michigan Michigan Volume 40 Volume 40 Part abstracts Part 1—Program I-Program and ab Editors: horst and McDowell Editors:Theodore TheodoreI.J.Born Bornhorst and S. Douglas McDowell �40TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume 40 40 consists consists of of Volume Part 1: Part 1 : Program Program and and Abstracts Abstracts Self-guided geological geological field field trip trip to to the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan Part 2: Part 2 : Self-guided Part 3: Part 3: Volcanic Volcanicgeology geologyof of eastern eastern Isle Isle Royale, Royale, Michigan Michigan Fart 4: Part 4 : Michigan Michigankimberlites kimberlitesand anddiamond diamond exploration exploration techniques Part 5: Part 5 :Lessons Lessonsfrom frommining miningcase casehistories: histories: West West Menominee Menominee Range, Range, Michigan Michigan below: Reference to material in Volume 40, Part 1 should follow the example below: L.G., Cannon, W.F. W.F. and Back, J.M., J.M., 1994, Chalcocite mineralization in the Woodruff, L.G., Portage Lake volcanics, Keweenaw Peninsula, Peninsula, Michigan Michigan (abst.): (abst.): Institute Institute on on Lake Geology Proceedings, Proceedings,40th 40thAnnual AnnualMeeting, Meeting,Houghton, Houghton,MI MI 49931, 49931, v. v. 40, Superior Geology part 1, p. 77. 1, Published and distributed by Published Institute on Lake Superior Geology M.G. Mudrey, Jr., Jr., Secretary-Treasurer, I.L.S.G. I.L.S.G. M.G. 106 N 3rd Street 106 N Mt. Horeb, Horeb, Wisconsin Wisconsin 53572 ML ISSN 1042-9964 ISSN All volumes volumesare are available for for photocopying photocopying costs from from All Library Archives Archives Michigan Technological University Library Michigan Technological University Universityisisan anequal equalopportunity opportunityeducational educationalinsututiordequal institution/equalopportunity opportunity employer. Michigan �__ -- Institute on Lake Superior Instituteon SuperiorGeology Geology Proceedings Proceedings 40th Annual Meeting Meeting May 1994 May11—14, 11-14,1994 Michigan MichiganTechnological TechnologicalUniversity University Houghton, Michigan Michigan Volume Volume 40 40 Part Part 1—Program 1-Program and andabstracts abstracts Editors:Theodore Theodore3.J. Bornhorst Bornhorstand andS. S.Douglas Douglas McDowell Editors: McDowell Department Departmentof ofGeological GeologicalEngineering, Engineering,Geology, Geology, and andGeophysics Geophysics MichiganTechnological University, Michigan University, Houghton, Houghton, Michigan Michigan 49931-1295 49931-1295 �CONTENTS PART 1 PROGRAM AND AND ABSTRACTS ABSTRACTS PROGRAM ............................. i Constitution of the Institute on Lake Superior Geology .................... ii ... ilL By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology ....................... m Goldich Medal Guidelines Guidelines. ........................................ iv Institutes totes on Lake Superior Geology to 1994 1994 I I I I I I I ! I i I Goldich Medal Committee v Past Goldich Medalists v ..................................... v Banquet Speaker ............................................... vv Banquetspeaker Student Travel Award Award ...........................................vi Student Travel Award Application Form ............................... vi BoaM of Directors ............................................. vii BoardofDirectors Local Committees ............................................. vii LocalCommittees vii Report of the the Chair Chair of of the the 39th 39th Annual Annual Institute Institute ......................... ix 1994 Goldich Medal Recipient Program of of Events Events Abstracts Abstracts V ...............................................xi ......................... .......................... J 1 1 �INSTITUTE SUPERIOR GEOLOGY INSTITUTE ON ON LAKE SUPERIOR GEOLOGY INSTITUTE INSTITUTE NUMBER NUMBER 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 DATE DATE - PLACE CHAIRMAN CHAIRMAN 1955 1955 1956 1956 1957 1957 1958 1958 1959 1959 1960 1960 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 Minneapolis, Minnesota Houghton, Houghton, Michigan Michigan East Michigan East Lansing, Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Port Arthur, Arthur, Ontario Ontario Houghton, Houghton, Michigan Michigan Duluth, Duluth, Minnesota Minnesota Ishpeniing, Ishpeming, Michigan Michigan St. St. Paul, Paul, Minnesota Minnesota Sault Sault Ste. Ste. Marie, Marie,Michigan Michigan East Lansing, East Lansing, Michigan Michigan Superior, Superior, Wisconsin Wisconsin Oshkosh, Oshkosh, Wisconsin Wisconsin Thunder Bay, Bay, Ontario Ontario Duluth, Minnesota Minnesota Houghton, Houghton, Michigan Madison, Madison, Wisconsin Wisconsin Sault Sault Ste. Ste. Marie, Marie, Ontario Ontario Marquette, Marquetta, Michigan Michigan St. Paul, Paul, Minnesota Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Milwaukee, Milwaukee, Wisconsin Wisconsin Duluth, Minnesota Minnesota Eau Eau Claire, Claire, Wisconsin Wisconsin East East Lansing, Lansing, Michigan Michigan International International Falls, Falls, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Wausau, Wausau,Wisconsin Wisconsin Kenora, Ontario Ontario Wisconsin Wisconsin Rapids, Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette,Michigan Michigan Duluth, Minnesota Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Eau Eau Claire, Claire,Wisconsin Wisconsin Hurley, Hurley, Wisconsin Wisconsin Eveleth, Minnesota Minnesota Houghthn, Houghton, Michigan Michigan C.E. Dutton C.E. A.I{. Snelgrove Snelgrove AK B.T. SandeftuSandefur B.T. R.W. Marsden Marsden R.W. E.N. Cameron & E.N. & R.A. R.A. Hoppin E.N. Cameron E.N. E.G. Pye E.G. LK Snelgrove A.K Snelgrove H. Lepp ~ P P H. A.T. Broderick AT. Pit Sims P.K. Sims& & Kit R.K.Hogberg Hogberg R.W. White White R.W. W.J. W.J. Hinze LB. A.B. Dickas Dickas G.L. LaBerge G.L. M.W. Bartley Bartley & E. Mercy M.W. D.M. Davidson D.M. J. Kaliokoski J. Kalliokoski M.E. Ostrom M.E. P.E. Giblin P.E. J.D. Hughes Hughes M. Walton M. M.M. Kehlenbeck Kehienbeck M.M. G. Mursky D.M. Davidson Davidson D.M. P.E. Myers W.C. W.C. Cambray D.L. Southwick D.h Southwick T.J. Bornhorst Bornhorst G.L. LaBerge G.L. LaBerge C.E. Blackburn C.E. J.K. Greenberg J.K. E.D. E.D. Frey & & R.P. Sage Sage J. S. Kiasner J. Klasner J.C. Green J.C. M.M. Kehlenbeck Kehienbeck M.M. P.E. Meyers P.E. LB. AB. Dickas Dickas IlL. D.h Southwick Southwick T.J. T.J. Bornhorst 1 �a- CONSTITUTION OF OF INSTITUTE ON CONSTITUTION LAKE SUPERIOR SUPERIOR GEOLOGY LAKE Article I Name The name of the organization shall be the "Institute on Lake Superior Geology". The name of the organization shall be the "Institute on Lake Superior Geology". Article I1 II Objectives Objectives The objectives objectives of ofthis this organization organization are: are: A. To A Toprovide provideaa means meanswhereby wherebygeologists geologists in the Great Great Lakes Lakes region region may may exchange ideas and scientific data. ideas data. B. To B. Topromote promote better better understanding understandingofofthe thegeology geology of the Lake Superior Superior region. region. C. To plan and conduct geological field trips. C. To plan conduct geological field trips. III Article I11 Status No part of the income income of ofthe the organization organization shall shall insure insure to to the the benefit of any any member member No part or individual. In the event of dissolution the assets of the organization shall be or individual. In the event of assets distributed to tax free organization). (some distributed (some tax organization). (To avoid avoidFederal Federaland and State State income taxes, taxes, the the organization should be not only (To or "educational, "educational, but but also "scientific" or also "non-profit".) "non-profit".) Minn, Stat. Anno, Minn. Anno. 290.01, 290.01, subd. 4 Minn, Stat. Mi. Stat. Anno. Anno. 290.05(9) 290.05(9) Internal Revenue 1954 Internal RevenueCode Codes.501(c)(3) s.501(cX3) W Article IV Membership The membership membership of ofthe the organization organization shall shall consist consistof ofthe theboard boardofofdirectors. directors. Any Any The geologistinterested interestedshall shallbe bepermitted permittedtotoattend attendand andparticipate participatein inand and vote voteaatt the the geologist annual meetings. Article V Meetings organization shall shallmeet meetonce onceaayear, yea; preferably preferably during duringthe the month month of ofApril. April. The The The organization by the the board of directors. directors, place and exact date of each meeting will be designated by Article VI Article Directors board of of directors directorsshall shall consist consistof ofthe theChairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and and the the The board fewerthan than last three past past Chairman; Chairman: but but if the the board should aatt any time consist of fewer by reason reason of unwillingness unwillingness or or inability inability of of &y any of of the the above persons persons to five persons, by as directors, the vacancies on on the the board may may be be filled filledby bythe the annual annual meeting serve as as to bring the membership the board up so as membership of tl+e up to to five members. Article VII Officers officersof ofthis thisorganization organizationshall shallbe beaa Chairman Chairman and and Secretary-Treasurer. The officers A. The A TheChairman Chairmanshall shallbe beelected electedeach eachyear yearby by the theboard board of of directors, who shall due consideration considerationto tothe the wishes wishes of ofany anygroup groupthat that may may be be promoting promotingthe the give due ' as 0Chairman terminate at at the next annual meeting. meeting. His Histerm termof ofoffice office as wwill ill terminate closeof ofthe theannual annual meeting meeting over which whichhe he presides presides or or when when his his successor shall shall close been appointed. appointed. He will then then serve for for aa period periodof ofthree threeyears yearsas as aa have been the board of directors. member of the B. The be elected electedat atthe the annual annualmeeting. meeting. His term term of of B. The Secretary-Treasurer Secretary-Treasurer shall be officeshall shallbe betwo twoyears years or or until until his his successor shall shall have have been appointed. office U �Article VIII Article VIII Amendments Amendments This constitution constitution may may be amended amended by by aa majority majorityvote vote of of those persons persons who who are are personally present at, participating in, and voting at any annual meeting at any annual meeting of of the participating in, and organization. organization. BY-LAWS BY-LAWS I. I. I Duties and Directors Duties of the the Officers Officers and Directors A. It A It shall shall be be the the duty dutyof of the theAnnual Annual Chairman Chairmanto: to: 1.. Preside 1 Preside at at the the annual annualmeeting. meeting. 2. Appoint all committees needed for for the the organization organization of the the annual 2. annualmeeting. meeting. 3. 3 . Assume Assume complete complete responsibility responsibilityfor the organization organization and and financing financingof of the the annual meeting annual meetingover over which which he he presides. presides. . . I B. It shall B. shall be the the duty dutyof of the the Secretary-Treasurer Secretary-Treasurer to: to: I 1.. Keep accurate accurate attendance 1 attendancerecords records of of all annual annual meetings. meetings. 2. Keep accurate accurate records 2. records of all meetings meetings of, of, and correspondence correspondence between, the the I board of directors. of directors. 3. Hold Hold all all funds fluidsthat thatmay mayaccrue accrueas asprofits profitsfrom from annual annualmeetings meetingsor orfield field trips trips of these funds funds available for the organization and operation of and to make these future future meetings as as required. I C. C. I I II. 1 1. Duties and and Expenses Expenses 1.. There shall 1 shall be no regular regular membership membership dues. for the annual meetings by the Chairman 2. Registration fees forthe meel& shall be determined by Chairman in consultation consultationwith with the theboard boardof ofdirectors. directors. It is is strongly strongly recommended that these a t aa minimum minimum to to encourage encourage attendance attendance of of graduate graduate students. students. these be kept at III. 111. Rules of Order Rules The rules contained Order shall govern this this organization in all The contained in Robert's Rules of Order cases to which they are are applicable. applicable. IV. Amendments Amendments These by-laws may may be be amended by by a majority vote of of those those persons persons who who are are These personally present present at, participating participating in, and voting aatt any annual annual meeting of the personally organization; that such rganization; provided that such modifications shall not conflict with the o constitution as constitution as presently presently adopted adopted or or subsequently subsequentlyamended. I I I It It shall shall be be the theduty dutyof ofthe theboard boardof of directors directorsto to plan planlocations locations of of annual annual meetings and to advise advise on the the organization organization and and financing financing of all meetings. meeting's. I I I I iii �Award Award Guidelines Guidelines SAM GOLDICH GOLDICH MEDAL SAM MEDAL Preamble Preamble The Institute Institute on was born born on on or or around around 1955, 1955, as as documented documentedby bythe the fact fact that that The on Lake Lake Superior Superior Geology Geology was the 27th annual meeting was held in 1981. The Institutes are exemplary in their continuing objectives the 27th annual meeting was held in 1981. The Institutes are exemplary in their continuing objectives of dealing with those that are to Lake of dealing with those aspects aspects of of geology geology that are related related geographically geographically to Lake Superior; Superior; of of encouraging the the discussion of subjects subjects and and sponsoring sponsoring field field trips trips which will bring bring together together geologists which will geologists encouraging discussion of from academia, academia, government government surveys, surveys,and and industry; industry; and and of maintaining an an exceedingly informal but but exceedingly informal from of maintaining highly effective operation. highly effective mode mode of of operation. During the the course of its its existence the membership of the the Institute existence the membership of Institute(that (thatis, is,those thosegeologists geologistswho who During course of indicate the LL.S.G. by attending) attending) has has become becomeaware awareof ofthe thefact factthat that indicate an an interest interest in inthe theobjectives objectives of of the I.L.S.G. by certain of of their their colleagues have made made particularly particularly noteworthy noteworthy and and meritorious meritorious contributions contributions to to the the certain colleagues have improvement of of understanding understanding of and its its mineral mineral deposits. deposits. improvement of "Lake "Lake Superior" Superior" geology geology and The exemplary exemplary award to Sam Sam Goldich in 1979 forhis his many many contributions contributions to to the the The award was was made made by by I.L.S.G. I.L.S.G. to Goldich in 1979 for geology of ofthe the region region extending over about 50 50 years. years. geology Award Guidelines Guidelines 1) of Directors Directors to to aa geologist geologist whose The medal shall be awarded awarded annually annually by by the theI.L.S.G. I.L.S.G. Board Board of name is associated with a substantial substantialinterest interestin, in,ororaamajor majorcontribution contributionto, to,the thegeology geology of of the the Lake Superior Superior region. region. 2) The Board The Board of of Directors, Directors, I.L.S.G. I.L.S.G. shall shall appoint appoint the theNominating NominatingCommittee. Committee. The The initial initial appointment will be of three members, one to serve for three years, one for two, and one appointment will members, one serve three years, one for two, and one for for one one year, the to be be chairman. chairman. After the the member member with the briefest incumbency to the first first year year the theBoard Board of Directors Directors shall shall appoint appoint at at each spring who will will serve serve for for three three of spring meeting one new member member who years. In the third year this member shall be the chairman. The Committee membership should In the third year this member shall be the chairman. The Committee membership should reflect the main fields interest and andgeographic geographicdistribution distributionof ofI.L.S.G. I.L.S.G. membership. membership. fields of interest 3) By November November 1, 1, the the Goldich Medal Nominating Nominating Committee Committee shall shall make its its recommendation to Goldich Medal the Chairman of the Board of Directors who will then inform the Board of Chairman of the Board of Directors who will then inform the Board of the thenominee. nominee. 4) The Board Board of of Directors Directors normally will accept the nominee nominee of the Committee, Committee, will inform the medalist immediately, and will have one medal medal engraved appropriately for for presentation presentation at at the the next meeting of the the Institute. 5) It is that die the Institute is recommended recommended that Instituteset setaside asideannually annuallyfrom fromwhatever whatever sources, sources, such such fhnds fundsas as will be be required to support the continuing costs of this award, the continuing costs this award. April 4, 4, 1981 1981 J. Kalliokoski, J. Kalliokoski, Chairman Bill Cannon Cannon Fred Fred Kehlenbeck Kehlenbeck GB. G.B. Morey Morey Greg Mursky iv �GOLDICH GOLDICH MEDAL MEDAL COMMIflEE COMMITTEE 1993-94 1993-94 RJ). R.D. Sage Sage (1994) (1994) Ontario Survey, Sudbury, Sudhury, Ontario Ontario Geological Geological Survey, Ontario Glen Glen Adams (1995) (1995) Crystal Crystal Exploration Exploration Inc., Inc., Crystal CrystalFalls, Falls,Michigan Michigan P.C. P.C. Morton (1996) (1996) Department Geolo', University Department of of Geology, Universityof ofMinnesota Minnesota Duluth, Duluth, Duluth, Duluth,Minnesota Minnesota , GOLDICH GOLDICH MEDALISTS MEDALISTS 1979 Samuel SamuelS.S.Goldich Goldich awarded 1980 not 1980 notawarded 1981 1981 Carl Carl E. E. Dutton, Dutton, Jr. Jr. 1982 1982 Ralph RalphW. W. Marsden Marsden 1983 1983 Burton BartonBoyum Boyum 1984 Richard RichardW. W. Ojakangas Ojakangas 1985 Paul PaulK. K.Sims Sims 1986 G.B. G.B. Morey Morey 1987 1987 Henry Henry H. H. Halls Halls 1988 1988 Walter S. S. White White 1989 Jorma Kalliokoski 1989 Jorma Kalliokoski 1990 Kenneth 1990 Kenneth C. C. Card 1991 William J. 1991 William J. Hinze ffinze 1992 William 1992 William F. F.Cannon 1993 Donald 1993 Donald W. W. Davis 1994 Cedric 1994 Cedric Iverson 1994 o&1icII I4fetatQecipieat Cetiric Celtic.Iverson BANQUET BANQUET SPEAKER Colorado Geoffrey GeoffreyS. S.Plumlee, Plumlee,U.S. U.S.Geological GeologicalSurvey, Survey, Denver, Denver, Colorado in Predicting Predicting The Crucial Crucial (but (but underutilized) underutilized)Role Roleof of the theEconomic EconomicGeologist Geologist in Effectsof of Mineral Mineral Resource Resource and Remediating Remediating the the Environmental Environmental Effects Development. Development. v �P STUDENT TRAVEL AWARD 1986 Board of Directors established the LL.S.G. Student Student Travel Travel Award Award to to support student student The participation at the annual Institutes. The awards will1be be made from aa special fund set up for this madefrom special fund purpose. This award is intended to help defray some of the the direct travel travel costs costs 60 to the the Institute Institute and and includes includes a waiver waiver of of registration registration fees, ftm, but but excludes excludes expenses expenses for meals, lodging, and field Geld trip trip The number by the registration. registration. The number ooff awards and end value value are determined determinsd by (be annual annualChairman Chairman in in .consultation with the Secretary-Treasurer be annoannouncedat at the the annual annual banquet. Secretary-Treasurer and will be banquetThe following general criteria will be considered by the annual Chairman, who is responsible for the selection: 1) 1) The applicants muç must have active mudent resident (tmdeqduate (undergraduate or orgraduate) graduate) staphat student sstatus t W q at at the time of the Institute, certified by the department head. (betimeofthelngtitute,certifiedbythçdepartmenthe& s. d are the 2) 2) Students Studentswho who are thesenior geniorauthor authoron oneither eitheran a oral n dor orposter posterpaper paperwill willbe be given given favored consideration. consideration. 3) 3) It students to It is is desirable desirable for for two or more mort stiidents to jointly j ~ ~ srequest b - t travel r a vassistance. assistance. e l 4) In general, priority will be given to those in the Institute region who are farthest away. 5) Each ~ a ctravel htravelaward a& request &wt shall (ballbe bt made nude in in writing, writing, to the annual annual Chairman, Chairman,with an explanation of need, possible author author status status or other significant details. details. Successful applicants will receive their their awards Successful appl@ntswi&receive awards at atthe thetime tineof ofregistration registrationfor forthe theMeeting. Meeting. ' INS11TUTE ON LAKE SUPERIOR GEOLOGY Student Travel Award Application Please print: Student Name: Date: Address: I certify that the above named person Is an active !ee1t student. Department Head . Typed Department Head Signature Date Educational Status: Are you the Senior Author of an oral or poster paper? Will any other students will be traveling with you? Yes No How many? Statement of Need: (It you need more room, please use the back of the page.) Other Significant Details: Please return to: vi �BOARD OF DIRECTORS 1994 Theodore Theodore J. J. Bornhorst, Bornhorst, Chairman Chairman Michigan Technological University, University, Houghton, Houghton, Michigan Michigan 49931 49931 1993 David David L. Southwick Southwick Minnesota Geological Survey, St. St. Paul, Paul, Minnesota 55114 Geological Survey, 65114 I I 1992 Albert Albert B. B. Dickas Dickas Wisconsin-Superior, Superior, Superior, Wisconsin Wisconsin 54880 University of Wisconsin-Superior, 54880 1991 Paul t.Meyers Paul E Meyers Department University of Wisconsin, Wisconsin,Eau EauClaire, Claire,Wisconsin Wisconsin 54701 54701 Department of of Geology, Geology, University Secretary-Treasurer M.G. Jr. M.G. Mudrey, Jr. Wisconsin Geological Geologicaland andNatural Natural History Survey 3817 Mineral Point Road, Madison, Wisconsin Wisconsin 53705 COMMIFFEES LOCAL COMMITTEES GENERAL CHAIRMAN GENERAL CHAIRMAN Theodore J. J. Bornhorst I Department of Geological Geological Engineering, Geology Geology and Geophysics, Geophysics, Michigan Technological Technological University, Houghton, Michigan Michigan 49931 49931 I EDITORS PROGRAM AND ABSTRACTS EDITORS PROGRAM Theodore J. J. Bornhorst Bornhorst I I Department of Geological Geological Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Michigan 49931 49931 Douglas McDowell S. S. Douglas McDoweU Department of of Geological Geological Engineering, Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological University, Houghton, Michigan 49931 49931 TECHNICAL SESSIONS COMMITTEE TECHNICAL SESSIONS I I I J. Bornhorst Theodore J. Bornhorst Department of of Geological Geological Engineering, Engineering, Geology Geology and Geophysics, Geophysics, Michigan Michigan Technological Technological Michigan 49931 University, Houghton, Michigan 49931 A. Gere, Gere, Jr. Jr. Milton A. GeologiëalSurvey SurveyDivision, Division,Michigan MichiganDepartment DepartmentofofNatural NaturalResources, Resources,Marquette, Marquette, Geological Michigan 49855 vii vii I �LOCAL COMMITTEES COMMITTEES continued continued SBmENr PAPER STUDENT PAPER Co1nsnrrEE COMMITTEE MS M AGere, Gore,Jr. Jr.(Chair) (Chair) Geological Survey Survey Division, Division,Michigan MichiganDepartment Department ofNatural of Natural Resources, Marquette, Marquette, Michigan Michigan 49855 49856 S. Beske-Diehl Beske-DiehI Department of ofGeological Geological Engineering, Engineering,Geology Geology and andGeophysics, Geophysics,Michigan MichiganTechnological Technological 49931 University, Houghton, Michigan 49931 Klasner J.S. Klasner Geology,Western Western Illinois illinois University, University, Macomb, Macomb, Illinois Illinois 61455 Department of Geology, 61455 SESSION CHAIRS SR. Blaske AJLBbuke MWR, Incorporated, Incorporated, Lansing, Lansing, Michigan Michigan 48917 MWR, 48917 1 MS Gere, Jr. M.A. Gem. Jr. Division,Michigan Michigan~Department of Resources, Marquette, Michigan ~Geological & l o ~ i csurvey aSurvey l ~ivision, e p a r t m e nof t ~Natural a t u r a~esources, l ~arquette, ~ichigan 49855 J.D. Pasteris Pasteris Department of Earth Department Earth and andPlanetary PlanetarySciences, Sciences,Washington Washington University, University, St. St. Louis, Louis,Missouri Missouri 63130 J.M. Robertson Robertson Geologicaland andNatural Natural History Wisconsin 53705 Wisconsin Geological History Survey, Survey, Madison, Wisconsin 53705 D.M. Rossell D .M. Bossell Independent Geologist, Marquette, Michigan 49855 Independent Geologist, Marquette, 49856 I G.W. Scott G.W. Scott Company, Ishpeming, Ishpexning, Michigan Michigan 49849 Cliffs Mining Services Company, P..Sundeen Sundeen P Geological Survey Survey Division, Division,MMichigan Department of of Natural Natural Resources, Lansing, Geological ichigan Department Lansing,Michigan Michigan 48909 48909 1 L.G. Woodruff L .G. Woodruff U.S. Geological Survey, St Paul, Minnesota 55112 vii:i �39th Annual Annual Institute Institute on 39th on Lake Lake Superior SuperiorGeology Geology Eveleth, Eveleth, Minnesota Minnesota I in Eveleth, The 39th Annual Institute Instituteon onLake LakeSuperior SuperiorGeology Geology was was held May May 5-8, 1993 in Minnesota, under nearly perfect weather weather conditions. conditions. Co-hosts Co-hosts for the meeting meeting were the the Minnesota Minnesota Geological Survey,the the Minnesota Minnesota Department Department of Natural Natural Resources Division, and and the Geological Survey, Resources -- Minerals Division, Minnesota, GeologicalSociety. Society. David DavidL L.Southwick Southwickwas wasthe theGeneral GeneralChairman, Chairman, Jane Jane Cleland Range Geological Mesabi coordinated the the technical technical sessions sessions as as Program Program Chair, Chair, and and Mark Mark Jirsa Jima organized organized the the four four bus bus and and bag-lunch events as Field Trip Chairman. Proceedings Proceedingsof the 39th Institute Institutewere were published published in in two two Volume Part 11contains contains the the program program and abstract abstract of of papers given in the technical parts: Volume 39, Part bag-lunch May 66 and 7; P Part sessions on May art 22 contains contains the thefield fieldguides guides for for the the field field trips tripsconducted conductedMay May 5, 5, 6, 6, and 8. and8. and the annual The technical sessions and annual banquet banquet were were held held in inthe theHoliday Holiday Inn, Inn,Eveleth, Eveleth,Minnesota. Minnesota. A total total of of 182 182people peopleregistered registeredfor forthe themeeting meetingand and104 104attended attendedthe thebanquet. banquet. The technical A of 31 31 oral oral presentations presentations and 2211 posters. Field program consisted of Field trips trips11through through44(see (seebelow) below) program 77, attracted 60, 51, and 41 participants, respectively, demonstrating once onceagain againthat that the field attracted 77,60,51, respectively, demonstrating trips are are the the major major inducement inducement for for people people to attend attend ILSG. ILSG. A highlight of the annual annual banquet banquetwas wasthe thepresentation presentationofofthe theGoldich GoldichMedal Medalto toDonald DonaldW. W. Davis Davis of the the Royal Ontario Museum, Toronto, Toronto, in recognition of ofhis his outstanding outstanding contributions to to highhighof of Precambrian Precambrian rocks rocksand and events eventsin in the the Lake Lake Superior Superior area. area. The precision radiometric dating of The citation for Don Don was was read read by by Ken Ken Card, Card, who who also alsopresented presentedthe the medal medal on onbehalf behalf of ofthe the Institute. Institute. precision The banquet address banquet addresswas wasgiven givenby byRobert RobertZierenberg Zierenbergof of the theU.S. U.S. Geological Geological Survey, who was aa JOIJLJSSAC Distinguished Lecturer in 1993. His topic was "Implications JOIIUSSAC Distinguished Lecturer in 1993. was "Implications for massive massive sulfide sulfide genesis from ODP leg leg 139 drilling drilling in in Middle Middle Valley, Valley,northern northern Juan Juan de Fuca Ridge". de Fuca Eidge". Becausefield fieldtrips trips are are so so central central to to the the success and and survival survival of ofthe the Institute, Institute, the trips Because trips associated associated the 39th ILSG and their leaders are here specifically acknowledged. with 39th ILSG and their leaders are here specifically acknowledged. with Trip 1, 1993: Geology and taconite taconite mines mines of ofthe the Mesabi Mesabirange. range. Leaders Ronald G. Graber, 1, May 5, 1993: Geology and R.W. Ojakangas, Robert J. J. Waidler, Waidler, and andG.B. G.B. Morey. Morey. R.W. Trip 2, May 6, 1993: DNR DNR Core Library open house and core display. Leaders LeadersG.B. G.B. Morey, Morey, Mark J. Severson, Dennis P. Martin, Dale F. Cartwright, and Gary N. Meyer. J. Severson, Martin, Dale F. Cartwright, and Gary N. Meyer. Trip 3, 8, 1993: 1993: Geology Geology of of Archean Archean greenstone greenstone -- granite granite terrane terrane in in the theCook Cook to to Side Side Lake Lake 3, May May 8, area. Leaders Mark Jirsa, Terry Boerboom, and Peter McSwiggen. Leaders Mark Jirsa, Terry Boerboom, and Peter McSwiggen. Trip .4, 4, May May 8, 8, 1993: 1993: The Duluth Complex Complex at at Duluth. Duluth. Leaders Leaders James James D. D. Miller, Miller, Jr., John John C. C. Green, and Val W. Chandler. p Travel awards totalling totalling $1,120 $1,120 were made to students students Zaira Zaira Arias, Arias, Sidney SidneyHemming, Hemming, Nick Nick Van Wyck, and Hristo Stoynov to facilitate their participation in the Institute. Awards of $150 Travel and Hristo Stoynov to facilitate their participation in the Institute. Awards of $150 each Wyck, were made to Zaira Arias of Queens University and Michael Handke of Lawrence University University for student oral presentation and best student poster, respectively. best student oral presentation and best student poster, respectively. The Board of Directors of of the the Institute Institute on met in Eveleth, Minnesota on on Lake Lake Superior Superior Geology Geology met May 6, 1993. In attendance were M. M. Kehlenbeck, LB. Dickas, D.L. In attendance were M.M. Kehlenbeck, A.B. Dickas, D.L. Southwick, Southwick, T.J. Bornhorst, Bomhorst, M.G. Mudrey, Jr., and J.M. Robertson. Principal actions taken were: J.M. Robertson. Principal actions taken were: M.G. Mudrey, Jr., Michigan Technological TechnologicalUniversity Universitytotohost hostthe the40th 40thAnnual Annual Institute Institute in 1. An An offer offer from Michigan in Houghton, Michigan Michiganin in 1994 1994was wasaccepted acceptedwith withthanks. thanks. T.J. TJ. Bornhorst Bomhorst will will be Chairman. Chairman. Houghton, ix �. , 2. The (Southwick) agreed to explore upper management TheChairman Chairqn.(Southwick) 1.04with withupper managementofofthe theOntario OntarioGeological ~ e o l o ~ i &' Survey the possibility of oftheOGB the 005 hosting ILSG in Marathon, Ontario, or elsewhere in the hosting%i&G in.Mhtho&&tariO$ieelsewhere TO Province, in 1995. correspondence with Wood, OGS 1995.[Subsequent [Subsequentconversations conversationsand &correspondence withJohn John-Wood, OGS Director, Director, lead us to believe that a 1995 meeting in Marathon is likely). us to believe that a 1995 meetingin Marathon is likely). 3. It was decided that a mid-year conference-call meeting of the ILSG Board (in ILSGBoard {inOctober October or or November) could provide useful guidance for the chairman of the next annual meeting, and should meeting, andshould, become normal practice henceforth. The Secretary-Treasurer (Mudrey) was instructed to work with the 1994 chairman (Bornhorst) to arrange such a conference call in the of 1993. thefall faUof 1993. . - : , received 4. 4. The Theannual -ml report itpertofofthe dieTreasurer * ~ u r e r was wasreceived and Â¥aapproved. &OW. The Thecentral centralILSG VLSGaccounts accounts (investments 1993. (invettmentsand çnchecldng Aechingaccount) accotmt) showed showedaanet net-positive balance balanceofof$13,678.43 $13,678.43 as ~sof efMay May 6,6,1998. Details Detail* of of the the accounts account# may may be be obtained obtajnai from from the Secretary-Treasurer Secretary-Treasurerupon upon request. request. POST-MEETING POST-MEETINGNOTE: NOTE: The The on-site on-siteaccount account for for the the 39th 39thILSG ILSGatatEveleth, Eveleth,managed managedby bythe theMinnesota MinnesotaGeological GeologicalSurvey Survey through theProfessional ProfessionalDevelopment Developmentand andConference Confuenc*Services Servif* Office Office of of the the University Uniwr* of of throughthe Minnesota, closed in in September 1993 with with an an operating operating low loss of,$1,99$,27$~r of $1,991.27 forthe themeeting. meeting. The deficit wu was covered covered from fromthe thecentral central ILSG ILSGtreasury. treasury. As General Chairman of the Eveleth Af General Chairman o f Eveleth meeting, meeting. -. II am fill responsibility for am deeply deenlv chagrinned chaerinned by by this this financial financial mismanagement mismanaeementand and accept accent full res~oneibilitv for it, it. II have investigated the the sources and have thoroughly thoroughlyinvestigated the matter, matter,identified identifiedide sour%$of of unanticipated &anti&ated costs, costs,and informed the %tarySecretary-Treasurer of my sure Ted informed the surer and and next nextyear's year's Chainnan Chairmanof my findings. findings. II am amsure Ted Bornhorst from my errors errors and run aa meeting Bornhorst will profit f rom my meeting in in Houghton Houghton that thatfinishes finishesin inthe theblack. black. A* Respectfully submitted, David David L. L. Southwick Southwick General General Chairman, Chairman,39th 39thILSG ILSG x �I I I I I I I I I I I I I I I I I I PROGRAM PROGRAM �I a -— ______ CAT LENDAR OF EVENTS AND PROGRAM Wednesday, May May 11 8:00 aa.m. 8:00 m. I -- 5:00 p.m. p.m. Field Field Trips Trips 1 1 and and 22 5:00 I I U 5:00 p.m. p.m. 500 - Underground geology geologyofofthe theWhite WhitePine Pine and and Caledonia Caledonia Mines, Mines, Underground Ontonagon County, Michigan. Leaders: Staff White Pine Mine, Ontonagon County, Michigan. Leaders: Mine, Whiteman, R.W. Seasor and T.J. Bornhorst. R. R. Whiteman. R.W. Seasor and T.J. Bornhorst. 2. 2. Lessons from from mining mining case casehistories: histories: West Menominee Range, Range, Michigan. Leader: A.M. Johnson Michigan. Leader AM. - Registration - Second 8:00 p.m. Registration Second floor, Floor, Memorial MemorialUnion UnionBuilding Buildingon onthe the campus campus of of 8 :00 p.m. Michigan Technological University. Michigan Technological University. 7:00 p.m. -- 10i00 1000 p.m. p.m. Poster 7 :00 p.m. PosterSession Session and and cash cashbar barin inBallroom Ballroom B, B, Memorial Memorial Union Building (Authors at posters 7:30 p.m. 9:00 p.m.). (Authors a t 7:30 p.m. 9:00 p.m.). - I Thursday, May May 12 12 Thursday, I All technical technical sessions sessionsare are in in Ballroom Ballroom A, A,Memorial Memorial Union UnionBuilding Building All on the campus of Mwhigan Michigan Technological University on 4:30 p.m. 7:15 aa.m. m . -- 4 :30 p.m. I 11.. Registration -. Second Second Floor, Floor, Memorial MemorialUnion Union Building Building on on the the campus campus of of Registration Michigan Technological University. University. Michigan Technical Session JI - Resources Session Session Chairs: Chairs: J.M. Robertson and G.W. Technical G.W. Scott 1 8:10 a.m. 8:10 Opening.- 40th Annual Institute Opening Instituteon on Lake Lake Superior Superior Geology Geology T.J. Bornhorst, Bornhorst, General General Chairman Chairman T.J. I 8:15 aa.m. m. Welcome Address Address - President Curtis Curtis J. J. Tompkins, Tompkins, Michigan Michigan Technological Welcome University I 8:30 8 :30 aa.m. m. T.J. Bornhorst, T J. Forty years of Institutes on on Lake Superior SuperiorGeology Geology 88:50 5 0 aa.m. m. M.J. Lavigne, M.J. Archean rifts rifts and and gold: Examples Archean Examples from the central Shebandowan greenstone belt 99:10 :lO aa.m. m. and Beck, J.W. J.W. Lehmann, E.IC. E.K. and Birch Lake Lake prospect prospect . A A major major PGMprospect PGM prospect in in the the Duluth Complex The Birch Complex 9:30 a.m. F.H., Moray, Morey, G.B., G.B., McSwiggen, McSwiggen,P.h P.L.and and Cleland, Cleland, J.M. J.M. Melcher, F.H., origin oj fmanganese North On the origin, manganeseoxides oxides in in iron-formation iron-formationof the Cuyuna North Range, East-central East-central Minnesota - New New evidence evidencefrom fromthe the U.S. U.S.Bureau Bureau of of Range, Gloria drill drill site Mines Gloria I I • I I I - - - 9:50 am. CoffeeBreak Break Coffee xi' �f T à '* . Coffee Break Break Coffee 9:50 a.m. 9 50 a.m. Han, T.M. T.M. Genesis of ofhematite hematiteand and magnetite magnetite in in Precambrian Precambrian magnetite ironGenesis ironlow metamorphic metamorphicgrade. grade, Lake Lake Superior Superior D District, istrict,USA USA - AA formation of low microscopic observation observation microscopic 10:20 am. a.m. 10243 - 10:40 ajn. Pasteris, J.D., Harris, Pasteria, Harris, T.N., and and Sassani, Sassmi, D.C. D.C. Dual immiscibility of ofdominantly dominantly aqueous aqueousfluids fluids in in rocks rocks of ofthe the Dual southwestern footwall footwall of of the theDuluth Duluth CmnpteC, Complex,NE NEMinnesota Minnesota southwestern 11:00 am. a.m. 11-00 Pufahi, P. and Fralick, Pufahl, Fralick, P. Depositional controls onshallow shallowwater wateriron ironformation formation accumulation, accumulation, Depositional controls on (Jogebic Range, Wisconsin Gogebic Range,Wisconsin 11:20 am. a.m. 1130 Mine; G.C. (IC. Miner, possible metasomatic origin, origin for for the Longwise Longnose oxide-rich oxide-rich ultramafic ultramafic body A A metammatic 11:40 am. a.m. 11:40 Woodruft LG., L.G., Cannon, Cannon, W.F. WY. and and Back, J.M. J.M. Woodruff, Chalcocite mineralization in the Portage Lake Volcanics, Keweenaw Chaicocite mineralisation the Portage Volcanics, Keweenaw Peninsula, Michigan p.m. Optional and B, B, Memorial Memorial Union Union Building Building 12:00 noon noon -- 1:40 p.m. Optional Luncheon, Luncheon, Room Room 105A and 12AO stuff of of life: life: Provisiolung Provisioning the the early early miners" miners Speaker: Larry Lorry Lankton Lankton "The "The stuff - p.m. Board 100,Memorial MemorialUnion Union Building Building 12:00 noon - 1:40 1:40 p.m. Board of of Directors Directors Meeting, Room Boom 100, 1 2:00 noon (by invitation only) (by invitation - - Technical Session I UI - Fluids fluids and and Environment Environment Session SessionChairs ChairsTechnical A.R.Blaske Blaske and and P.C. P.C. Morton A.R. 1:40 p.m. Person, M. Person, oreformation formation within within continental continental Hydrologic mode& models of of sediment sediment - hosted hosted ore Hydmbgic rift basins 2:00 p.m. RB. and Suchoski, TA. White, R.B. Suchoski, T.J. Useof ofrunoffrunoff-and and sedimentantml sediment-control models modelsin in the the design design of of mine mine Use hydrologic controls 2:20 p.m. and Wessels, J.N. Lapakko, K.A. KA.and Release of ofadd acid and and trace metals from quartz-carbonate hosted gold mine Release tailings tailings 2:40 p.m. Loukola-Ruskeeniemi, K. Loukola-Ruskeeniemi, K. geochemistryoof Proterozoicblack blackshales shalesinineastern easternFinland: Finland: Environmental geochemistry f Proterozoic pilot study a pilot 3:00 p.m. Break Coffee Break 3:20 p.m. Eger, P. Wetland treatment treatment of of mine mine drainage drainage - an an alternative alternative to conventional conventional Wetland treatment or voodoo treatment? treatment voodoo treatment? xli �I * 3:40 p.m. 3:40 p.m. S.R Davis, S.R Metallic mineral mineral resources management at at Voyageurs Metallic resources and and ecosystem ecosystem management Voyageurs National Park. Park, Minnesota National Minnesota I 4:00 4:00 p.m. p.m. Johnson, AM. Johnson, AM. solutions for for muting mining related problems Geotechnical solutions I Room 105 A and B, Memorial 44:30 3 0 p.m. - 5:00 5:00 p.m. IGOP ZGCP Organizational OrganizationalMeeting Meeting -- Room Memorial Union Union Building Building I 6:00 6:00 p.m. - - - 7:00 p.m. p.m. Social Seaman Mineral Museum, ROO Social - Seaman Museum, Fifth Fifth Floor, Electrical Electrical Energy Energy Resources Center 6:30 p.m. -- 7;30 p.m. Cash Cashbar, bar,Ballrooms BallroomsAAand andB, B, Memorial Memorial Union Building - I 7:30 p.m. Annual 7:30 p.m. p.m. - 9:30 9:30 p.m. AnnualBanquet, Banquet,Ballroom BallroomA, A, Memorial MemorialUnion Union Building Building Speaker: GeoffreyS.&Plumlee Plumlee "The crucial crucial (but (but undenttilized) underutilized) role of the Speaker: Geoffrey economic geologistsin inpredicting predictingand and remedialing remediating the environmental economic geologists environmental effects mineral resource effectsooff mineral resource development" Friday, May Friday, May 13 13 Technical Session Session HI m --Regional Regional Geology Session Technical SessionChairs: Chairs:J.D. J.D.Pasteris Pasterisand andD.M. D.M.Rossell Rossell 8:30 a.m. S.A. and Fralick, P.W. P.W. Kissin, SA. Granitoid the Elliot ElliotLake Lakearea, area, Ontarin Ontario and and their relationship relationship to Gmnitoid rocks of the U-Th-REE bearing pegmatites U-Th-BEE 8:50 a.m. LaBerge, G.L. G.L. and Klasner, J.S. J.S. Merge, implications of ofEarly Early Proterozoic Proterozoiclithostratigraphy lithostratigraphy on on the the eastern eastern Tectonic implications Gogebicm Range, Northern Michigan e , Northern Michigan I 9:10 a.m. Kiasner, J.S. Klasner, J.S. and andLaBerge, Merge, G.L. G.L. Structural Northern Michigan Structuralevolution evolutionof ofthe theeastern easternGogebic Gogebic Range, Northern Michigan I 9:30 a.m. VanWyck, N., Johnson, Johnson, C. and VanWyck, N., and Gross, Gross,S. S. Archean crust in in the the Wausau-Pembine Wauaau-PembineTerrane; Terrane; continental continental underthrusting, or island island arc arcbasement? basement? underthrusting, I 9:50 a.m. Coffee Break Break I I I I I I 10:20 a.m. Uribe, R.D. Ri). Cambrian Mt. Mt. Simon Sandstone, Petrography and diagenesis diagenesis of the Upper Cambrian SE Minnesota 10:40 a.m. Kissin, and Fralick, Kissin, S.A. SA. and Fralick, P.W. P.W. Early the Anirnike AnimikeGroup, Group, Ontario Ontario and and Michigan, Early Proterozoic Proteromic volcanics volcanic8 ooff the Michigan. and their theirtectonic tectonicsignificance significance 11:00 a.m. Bennett, and Hatfield, KG. G., Born, P. and KG. Bennett, G., The stratigraphic stratigraphic significance dolostoneunit unit near near Sault Ste. significance of aa dolostone Ste. Marie, Marie, Ontario Ontario flu I �11:20 1120 a.m. a.m. VanWyck N., Medaris, Jr., .. Medaris, Jr..L.G. L.G.and andJohnson, Johnson,C.M. C.M. VanWyck N The Wolf River A-type magmatic event Wisconsin:UU/Pb and Sm/Nd Sm/Nd The WolfRiver A-type magmatic event ininWisconsin: / P b and constraints on timing and petrogenesis constraints on timing and petmgenesis 11:40 11:40 a.m. a.m. Smyk, Smyk, M.C. M.C. and and Schnieders, Schnieders,B.R. B.B. A geological geological Marathon: Marathon: The Therocks rocks of of the the North North Shore Shore of of Lake Superior Superior 12:00 12:OO p.m. p.m. -- 1:30 1:30 p.m. Optional OptionalLuncheon, Luncheon,Room Boom105 105AA and andB, B, Memorial MemorialUnion UnionBuilding Building Speaker: Stanley StanleyDyl Dyl "Minerals "Mineralsand and decorative decorative arts arts in inRussia" Russia" - Technical TechnicalSession SessionW IV- Mideontinental Midcontinental Rift Rift System System Session Session Chairs: Chairs: L.G. L.G. Woodruff Woodruff and and P. P. Sundeen Sundeen 1:30 p.m. p.m. Allen, D4., WJ.,Dickas, Dickas,A.B., AB., and and Mudrey, Mudrey, M.G., M.G., Jr. Jr. DJ., Hinze, Hinze,W.J., Geophysical investigations investigations of the Midcontinent rift system: AAnew new model model for for western western Lake Superior Superior and andnorthern northernWisconsin Wisconsin 1:50 150p.m. p.m. Palacas, Palacas, J.G. J.G.and and Burruss, Burruss,B.C. R.C. Preliminary Preliminarysource-rock source-rock and maturity maturity evaluation evaluationof of the the Precambrian Precambrian Nonesuch Formation in in the the Terra TerraPatrick Patrick#7.22 W-22borehole, borehole, Midcontinent rift system, Bayfield County, County,Wisconsin Wisconsin 2:10 2 1 0 p.m. p.m. Waggoner, Waggoner,T.D. T.D. Echo Echo Lake Gabbro, Gabbro,Houghton Houghton County, County, Michigan Michigan 3:00 p.m. p.m. 3:20 3:20 p.m. p.m. Boerboom, Boerboom, TA. TJ. Archean h h e a n crustal crustalxenoliths xenoliths in inaaKeweenawan Keweenawan hypabyssal hypabyssal sill, sill, northeastern northeastern ' Minnesota. Minnesota. White Whitewas was right! right! END END OF OFTECHNICAL TECHNICALSESSIONS SESSIONS Saturday, Saturday,May May14 14 8:00 8:00 a.m. a.m. -- 5:00 5:00 p.m. p.m. Field FieldTrips Trips33and and44 3. 3. Michigan Michigan kimberlites and diamond diamon exploration iloration techniques. Leaders: Leaders: S.M. S.M. Carison Carlson and and W. W. Floodatrand Floodstrand 4. 4. Geology Geology of the Keweenaw Keweenaw Peninsula, Peninsula, Michigan. Michigan. Leader: Bomhorst Leader: T.J. T J .Bornhorst Friday, Friday,May May13 13to toThursday, Thursday,May May19 19 Field Volcanic geology of Eastern Eastern Isle Royale, Michigan. Michigan. Leader: fieldTrip Trip55--Volcanic geology of Leader: W.I. W.I.Rose Rose xiv xiv '"•)•• .nfl,. �Poster Session 7:00 p.m. p.m. Wednesday, Wednesday, May May 11 11 to to 12.-00 12:00 noon noon Friday, Friday, May 7:00 May 13 13 SessionChair: Chair: M MA Jr. Session A Gere, Gere, Jr. Chenier, F. Chenier, P. Inventory of of the the Michigan Michigan Geological Survey Division's Division's Upper Upper Peninsula Peninsula significant Inventory Geological Survey significantwater waterwell well cuttings libtwy at at Escanaba. Escanaba cuttings library Frey, B. BA. Frey, A. Minnesota drill core examination and and assay assay Minnesota core examination Kean, W. Kean, W. Paleomo.gnetiszn ofaa 1500 1500 MA MA mafic mafic dike dike at at Waterloo, Paleornagnetism of Waterloo,Wisconsin Wisconsin Kropf, E.P., E.P., Wirth, Wirth, KR. KR. and Craddock, J.P. J.P. Kropf, New Archmn-hosted Archean-hosted pselidotechylite pseudotachylite occurrences, occurrences, western western Lake Lake Superior Superior region New region Lawler, T. Mineral potential evaluation, central Minnesota, phase II basic data Mineral potential evaluation, central Minnesota, phase basic data Leslie, M M., Wetzel,T., T.,Wirth, Wirth,K.R. Kit. and Craddock, J.P. J.P. .,Wetzel, Petrography and structure of the Keweenaw Chengwatana Petrography and structure of the Zfeweenaw ChengwatanaVolcanics Volcanics near near Dresser, Dresser, Wisconsin Wisconsin Luther, Luther, P.R. P.R. Petrology and whole rock rock W analyses of the the central central portion portion of a large Petrology and y s e s of large Early Early Proterozoic Proterozoic diabase diabase dike, dike, preliminary report Eastern Lake of the Woods, Ontario A Eastern Lake of the Woods, Ontario - Apreliminary report Miller, Jr., J.D., T.J., and Green, J J.C. J.D., Boerboom, Boerboom, T J.,Chandler, V.W. V.W. and .C. Geology of the "Greater" Beaver Bay Complex, Northeastern Minnesota Geology of the "Greater" Beaver Bay Complex.Northeastern Miller, Sr., Miller. S S.A -~ ------, -..r , S.A. Assessment of Spring Spring Creek Creek aquifer aquifer vulnerability vulnerability to pollution using Assessment of using DRASTIC, DRASTIC, water testing; testing, groundwater modeling, and historical records: a project of the MTU groundwater and historical a project of the MTU Regional Groundwater Education Education in inMichigan Michigan(GEM) (GEM Center Center ~ Nelson, S., Lawler, T., T., Lehr, Lehr, J.D., J.D., Theobald, P., P., Ryder, J., Sutley, S. S. and and Tripp, Tripp,R. R. Heavy mineral& minerals from glaciofitwial sediments in Minnesota from glactofluvial in Minnesota S.W., WooWoodruff, LG. L.G. and and Cannon, Cannon, W.F. Nicholson, S.W., W.F. Geochemistryof ofthe theHollander Kallander Creek Creek Volcanics, 1.1 1.1 da Ga Midcontinent Midcontinent rift rift system, Wisconsin and and Geochemistry Michigan Michigan BA. and Petrie, MA. Rogers, BA. MA Hydrogeologicinvestigations investigationsof ofpetroleum petroleumcontamination contaminationin in Karst, lGzrst,central centralUpper UpperPeninsula Peninsula of of Hydrogeoloeic Michigan Schmitz, M.D., M.D., Wirth, Wirth, KR. KR. and Craddock, Craddock, J.P. Origin of the Early Proterozoic Kenora-Kabetogama ma/ic dike swarm Origin, Praterozoic Kemra-Kabetogamamafic swarm W.T. and and Gere, MA, M.A., Jr. Jr. Swenor, W.T. Marquette, Michigan Michigan core and and sample repository Update on the the geological core repository - Marquette, - Update xv �Watkins, LW. Anorthosites: Igneous cumulate or metasomite White, R.B. and Wollensak, M.S. Biodegradation of environmental contaminants utilizing white rot fiengus Minnesota Department of Minnesota Department of Natural NaturalResources, Resources,Minerals MineralsDivision Division A compendium of mineral resource information, Minnesota A compendium of mineral resource information,east-central Minnesota Posters Abstracts Posters Without Without Abstracts Sage, R.P., Lightfoot, Lightfoot, P.C. P.C. and and Doherty, Sage, R.P., Doherty, W. W. Geochemist'y of cyclical bimodal basalt-rhyolite magmatism magmatism of of the the Archean Archean Wawa Belt, Geochemistry of cyclical bimodtd basalt-rhyolite Wawa Greenstone Greenstone B elt, Ontario: aapossible continental-arc setting possible continental-arc setting Sage, liP., Sage, R .P.,Lightfoot, Lightfoot, P.C. PC,and andDoherty, Doherty, W. W. Goechemical characteristics of granitoids from the the Michipicoten Michipicoten Greenstone GreenstoneBelt. Belt, Wawa Wawa Goedwmical characteristics of granitoidsfrom Subprovince, Superior Pmvince: Implications for source regions and tectonic evolution Subprovince, Superior M i n c e : Implications for source regions and tectonic evolution xvi �AR ST1{ACTS ABSTRACTS �GEOPHYSICAL GEOPHYSICAL INVESTIGATIONS OF OF THE THEMIDCONTINENT MIDCONTINENTRIFT RIFTSYSTEM: SYSTEM: A AND NORTHERN NORTHERN WISCONSIN WISCONSIN A NEW NEW MODEL MODELFOR FOR WESTERN WESTERN LAKE SUPERIOR AND ALLEN, J., Purdue Purdue University, West Lafayette, Lafayette, Indiana Indiana 47907 ALLEN, David David J., J., and and HINZE, HINZE,William William J., 47907 DICKAS, University of Wisconsin-Superior Wisconsin-Superior (Extension). Superior, Wisconsin 54880 DICKAS, Albert Albert B., B., University (Extension), Superior, 54880 MUDREY, M.G., Jr., Jr.,Wisconsin WisconsinGeological Geologicaland and Natural Natural History Survey, Madison, Wisconsin Wisconsin 53705 MUDREY, M.G., 53705 Seismic Seismic reflection data data are areof of enormous enormousvalue valuefor forinvestigating investigatingthe the1100 1100Ma Ma Midcontinent MidcontinentRift Rift System. Superior, together together with with proprietary proprietary data System. Recently released released eight-second eight-second proffles profiles from Lake Superior, datafrom from northwestern better understanding understanding of of the the western western Lake Lake Superior Superior and and northwestern Wisconsin, Wisconsin, have resulted in aa better Wisconsin Wisconsin segments segments of the the rift riftsystem. system. Combined Combined interpretation interpretation of of these these seismic profiles with gravity gravity data datareveals revealsseveral severalinteresting interestingstructural structuraland andstratigraphic stratigraphicfeatures, features,including includingtwo twopre-Keweenawan pre-Keweenawan ridges within the therift riftinterior, interior,the thetermination terminationof ofmajor majorreverse reverse faults, faults, aa flanking flanking sedimentary sedimentary basin basin ridges within located east of the St. Croix Horst, and, possibly, an Archean batholith buried beneath the rift. located east of the St. Croix Horst, and, possibly, an Archean batholith buried beneath the rift. Along Along the theLake LakeSuperior Superiorsyncline syndine(Fig. (Fig. 1), I), seismic seismic data data image image up up to to99km kmof of sedimentary sedimentaryrocks rocks(the (the majority majority of of which which are arelikely likelyOronto OrontoGroup Groupstrata) strata)and andup uptoto1818km kmofofvolcanic volcanicflows. flows. Along Alongthe theAshland Ashland syncline the Oronto synclinein in Wisconsin Wisconsin (Fig. (Fig. 1), I), the Oronto Group Groupisisas asthick thick as as44 km, km, and andthe theunderlying underlyingvolcanic volcanicflows flows have however, are separated separated have aa maximum maximumthickness thicknessof of 14 14km. The The Ashland Ashland and and Lake Lake Superior synclines, however, by by aa prominent prominentridge ridgethat thatwas wasfirst firsthypothesized hypothesizedby byWhite White(1966) (1966)on the basis of gravity gravity and and magnetic magnetic data. km) arevery verythin thin(<2 (4 km) and and pinch pinch out outin innorthern northernWisconsin, Wisconsin, data. Along AlongWhite's White'sRidge, Ridge, the thevolcanic volcanic strata strataare placing placing Oronto strata strata directly directlyon ontop topofofthe thepre-rift pre-riftbasement basement(Fig. (Fig.1). 1).Southeast Southeast of of Grand Grand Marais, Marais, Minnesota, the Lake Lake Superior Superior syncline syncline is deflected around around the the southern southernend endof of aasimilar similarridge ridge(Fig. (Fig.1). I). Stratigraphic White's Ridge Ridgeand andthe theGrand GrandMarais Mars Ridge Ridge remained remained topographically topographically Stratigraphic relations indicate that White's positive pinch out out gradually gradually onto the ridges, ridges, positive as as the the adjacent adjacent volcanic volcanic basins basins subsided. subsided. The The volcanic flows pinch with withno no evidence evidencefor forsubstantial substantialnormal normalfaulting. faulting. As the the Douglas Douglas Fault Fault (Fig. (Fig. 1) 1) approaches approaches Lake Lake Superior, it bends east and and follows follows the the southern southern margin margin of of White's White's Ridge. Ridge. Displacement across the fault gradually gradually decreases to the the east east until until the thefault faultisis replaced replaced by by aa fold foldnear nearthe theeastern easternmargin marginofofWhite's White'sRidge. Ridge. The The seismic seismic data also also indicate indicate that that the theIsle Isle Royale km southwest southwest of the the terminations terminations of the -40 km the Isle. Between the the Douglas Douglas Royale Fault Fault gradually graduallyterminates terminates—40 and forces resulted resulted in in folding foldingrather rather than than development development of and Isle Isle Royale Faults, late-stage rift compressional forces major major reverse reverse faulting. faulting. East sedimentary strata strata within withinan an East of the the Hastings HastingsFault Fault(Fig. (Fig. 1), I), seismic data image up to to 66 km of sedimentary asymmetric basin which is syndine. This basin is is is spatially spatiallyassociated associated with with the thePaleozoic Paleozoic River Falls syncline. characterized characterized by aa pronounced pronouncednegative negativegravity gravityanomaly anomalythat thatachieves achieves its its lowest lowest values valuesnear nearEmerald, Emerald, Wisconsin. Gravity modeling indicates indicates that that strata stratawithin within the theEmerald Emerald Basin Basin have a low low density density and andare are probably and Hincldey Hinckley sandstones sandstones probably correlated correlatedwith withthe theBayfield Bayfield Group Group of of Wisconsin and the Fond du Lac and of Minnesota. Interestingly, Interestingly, the northern margin of the the Emerald Emerald Basin Basin corresponds to the northern termination terminationof of the theHastings HastingsFault Faultand andthe thesouthern southerntermination terminationofofthe theLake LakeOwen OwenFault Fault(Fig. (Fig.1). 1).Although Although the the exact exact relation between between the the Hastings Hastingsand andLake Lake Owen Owen Faults Faults is is unclear, unclear, local gravity gravity and and magnetic magnetic characteristics areconsistent consistentwith with—10 -10 km kmof of left-lateral left-lateraloffset offsetalong alongaacross-fault. cross-fault. characteristicsare In In western western Lake Lake Superior, Superior, the rift's rift's igneous igneous and and sedimentary sedimentary rocks rocks cannot fully account for the the observed —30 observedgravity gravitysignature. signature.AAnortheast-striking, northeast-striking, -30 mGal mGal negative negative anomaly anomaly persists persistsafter afterthe theeffect effectof of the rocks is is removed removed from from the the observed observed gravity gravity field. field. The trend, amplitude, and gradients gradients of this the rift rift rocks anomaly anomaly suggest suggest that that itit may may be be produced producedby by aaburied buriedgranite granitebelt belt within withinthe the Archean Archean greenstone-granite greenstone-granite terrane liesbeneath beneaththe therift rift(Allen (Alienetetal., aL,1993). 1993). As shown shown in in Figure Figure 1, 1, the Douglas Douglas and andIsle IsleRoyate Royale terrane that that lies Faults terminate terminate as as they they approach approachthe the proposed proposedgranite granitebelt, belt, both both pre-Keweenawan pre-Keweenawan ridges ridges occur occur above this structure, structure, and andthe theSt. St. Croix M iHorst Horstterminates terminatesatatthe thesouthern southernmargin marginof of this thisfeature. feature.Therefore, Therefore, this this this Archean batholith might have acted as as aa buttress buttressthroughout throughoutthe thehistory historyof of development developmentof of the therift, rift, redirecting redirectingboth both the theearly earlytensional tensionalstresses stressesand andthe thelate latecompressional compressionalstresses. stresses. 1 �w Legend 48N Bayfield Group (Fond 00 0 I, + .4. 47N do Lac, Hi!Id.y. JacoSvdte SaMon.s( Oronto Group (Solo.' Q'*.th Foninj Volcanic Strata (Poflaga —. a, PayS.' Mt Noith aIa G,o.csi igneous intrusions fl.AShwMaftenConlax.s( Pie-Rift Pre-RlftRidge Rid (voSt <2 In, VSkI Archean Granite ArolMinGrMKe Ibtulad bensath r*I jocksi Rmrixlton-hitrode) Seismic SeismicProfile ProfileLocations Locations 46N 45N 0 50 100 150 200 250 km - Figure Figure1: 1:Geologic Geologic map map of of the the western western Lake Lake Superior Superior region based on on interpretation interpretationof of seismic seismicreflection reflection and andgravity gravitydata. data.Insert Insertshows showsthe thelocations locationsof ofthe theseismic seismicprofiles profiles used used in in this thisstudy study(e.g., (e.g., McGinnis McGinnis and Mudrey, Mudrey,1991; 1991;also alsorefer referto toacknowledgments). acknowledgments). Ref erçnces Allen, W.J., Alien,Dj., D.J.,I-line, Hinze, W.JDickas, .Dickas, , A.B., A.B.,and andMudrey, Mudrey,M.G., M.G.,Jr., Jr.,1993, 1993,An Anintegrated integratedseismic seismic reflection/three-dimensional reflection/thiee-dimensional gravity gravityinvestigation investigationofofthe theMidcontinent MidcontinentRift RiftSystem, System,USA: USA: western westernLake LakeSuperior Superiorregion region(abst): (abst):AAPG AAPG Hedberg Hedberg Research 1993. ResearchConference, Conference,Basement Basementand andBasins Basinsof ofEastern EasternNorth NorthAmerica, America,Ann AnnArbor, Arbor,MI, MI,November November10-13, 1043,1993. McGinnis, reflection profiling profiling and and tectonic evolution evolution of McGinnis,L.D., L.D., and andMudrey, Mudrey,M.G., M.G., Jr., Jr., 1991, 1991, Seismic reflection of the the Midcontinent Midcontinent Rift and Natural RiftininLake LakeSuperior: Superior:Wisconsin Wisconsin Geological Geological and Natural History HistorySurvey SurveyMiscellaneous MiscellaneousPaper Paper91-2. 91-2. White, the Keweenawan Keweenawan basin, White,W.S., WS., 1966, 1966,Tectonics Tectonicsof the basii western westernLake LakeSuperior Superiorregiorc region:USGS USGSProfessional ProfessionalPaper Paper524-E. 524E. - Acknowledgments Seismicprofiles profilesininWisconsin Wisconsinwere wereprovided provided to to the the authors authorscourtesy courtesyof ofTexaco Texaco Exploration Explorationand andProduction, Production,Inc. Inc. Seismic of of Denver, Denver, Colorado Coloradoand andAmoco AmocoProduction ProductionCompany Companyof of Houston, Houston,Texas. Texas. �I I I THE STRATIGRAPHIC SIGNIFICANCE SIGNIFICANCE OF OF A T HE STRATIGRAPHIC A MARIE, ONTARIO. S AULT STE. MARIE, ONTARIO. SAULT DOLOSTONE UNIT NEAR D OLOSTONE UNIT NEAR Bennett, G., MNDM, P.,, G. ,Mines Minesand andMinerals MineralsDivision, Division, MNDM, Born, Born, P. Bennett, G., Lake Superior University, Ottawa, K. G., C a r l e t o n University, Ottawa, Hatfield, H a t f i e l d , K. Lake S uperior Carleton State S t a t e University, University, Sault S a u l tSte. Ste.Marie, Marie,Michigan. Michigan. geological mapping iin Fenwick Township Township While undertaking g e o l o g i c a l mapping n Fenwick near Sault Ste. in 1986, Peter of tthe Marie Ontario i n 1986, P e t e r Born of he n e a r S a u l t Ste. While Ontario Geological 30 meter meter tthick Ontario Geological Survey, Survey, identified identified a a 30 hick unit, known dolostone-chert u n i t , llithologically i t h o l o g i c a l l y ddistinct i s t i n c t from known carbonate u units 1987). The The e t al., a l . , 1987). carbonate n i t s in i n Ontario Ontario (Born (Born et dolostone-chert dolostone-chert sequence directly and dolostone-chert d i r e c t l y overlies o v e r l i e s ffractured r a c t u r e d and sheared, green sheared, g r e e n and and maroon maroon siltstone s i l t s t o n e and and is i s overlain o v e r l a i n by by red red maroon laminated laminated siltstone tto o maroon s i l t s t o n e and sandstone. sandstone. The basal b a s a l one of tthe dolostone unit mainly of of iintercalated n i t cconsists o n s i s t s mainly ntercalated tthird h i r d of he d olostone u with minor rrecrystallized chert. Much Much of of tthe upper dolostone with e c r y s t a l l i z e d chert. h e upper portion unit dolostone made made up up llargely s aa cclastic l a s t i c dolostone argely p o r t i o n of of the the u n i t iis of of medium tto o coarse sand-sized sand-sized grains g r a i n s of of dolostone and quartz. O Oolitic quartz. o l i t i c dolostone is i s locally l o c a l l y present. present. Barite B a r i t e occurs as as as few iirregular r r e g u l a r replacement bodies bodies about midway in i n the the dolostone-chert d o l o s t o n e - c h e r t sequence. sequence. dolostone-chert-siltstone The d o l o s t o n e - c h e r t - s i l t s t o n e assemblage forms an 400 meter meter wide wide southeastward southeastward trending, trending, ssteeply approximately 400 teeply dipping, ffault-bounded block between between (Huronian) (Huronian) LLorrain dipping, ault-bounded block orrain metavolcanics tto Formation tto o tthe h e ssouth o u t h and Archean metavolcanics o the the north. A An altered dike north. n a l t e r e d mafic (diabase) (diabase) d i k e iintrudes n t r u d e s tthe he (Bennett et 1989; Bennett dolostone. (Bennett e t al. al. 1989; Bennett et e t al. al. 1993), 19931, The authors dolostone-chert assemblage a u t h o r s conclude tthat h a t tthe h e dolostone-chert represents a carbonate facies of f a c i e s of tthe h e Gordon Lake Formation represents of the Huronian Supergroup for the a) of t h e Supergroup f o r t h e following following reasons: reasons: ((a) The rred or maroon colored rocks are generally below ed o r colored rocks are g e n e r a l l y llacking a c k i n g below Cobalt Group of of tthe tthe h e Cobalt h e Huronian Supergroup (b) ( b ) The metamorphic grade of the assemblage is higher of metamorphic of t h e i s h i g h e r tthan h a n tthat h a t of the Keweenawan rocks on the east shore of Lake Superior. t h e Keweenawan rocks on t h e e a s t , s h o r e of Lake Superior. (c) (c) Jackson et (1992) have have rreported presence of of e t al. al. (1992) e p o r t e d tthe h e presence outheast dolostone iin n tthe h e Gordon Lake Formation about 60 km ssoutheast of Fenwick Fenwick Township. The previous1 previously proposed of Township. ((d) d ) The y proposed depositional of tthe d e p o s i t i o n a l environment of h e Gordon Lake Formation iis s consistant dolostonec o n s i s t a n t with features f e a t u r e s iin n tthe h e Fenwick Township dolostone1973). ssiltstone i l t s t o n e assemblage assemblage (Wood, (Wood, 1973). 3 �The The dolostone d o l o s t o n e of of Fenwick Fenwick Township Township closely c l o s e l y resembles resembles in i n terms terms of lithology and stratigraphic association, the Kona of l i t h o l o g y and s t r a t i g r a p h i c a s s o c i a t i o n , t h e Kona Dolomite Dolomite of of the t h e Marquette Marquette Range Range Supergroup Supergroup of of northern northern Michigan. The dolostone of Fenwick Township Michigan. The dolostone of Fenwick Towns h i p provides provides additional a d d i t i o n a l evidence evidence for f o r the t h e previously p r e v i o u s l y proposed proposed correlation correlation of Cobalt Group of the Huronian Supergroup of Cobalt Group of t h e Huronian Supergroup and and the t h e Chocolay Chocolay Group 1983) Group of of the t h e Marquette Marquette Range Range Supergroup Supergroup (Young, (Young, 1983) REFERENCES CITED REFERENCES CITED Leahy, E. 3., Melisek, 3., Bennett, G., Bennett, G., Leahy, E. J . , Melisek, J., Born, Born, P. P. and and 1989. Sault Ste. Marie Resident K. Hatfield, H a t f i e l d , K. 1989. S a u l t Ste. Marie Resident Geologist's Geologistf s District-1988; i n Report of A c t i v i t i e s 1988, Resident Misc. Paper Paper 142, 142, Resident Geologists, Geologists, Ont. Ont. Geol. Geol. Survey, Survey, Misc. 207-217. pp 207—217. District-1988; in Report of Activities 1988, Bennett, G . , Leahy, Leahy, Walmsley,J. Walmsley,J. Hailstone, Hailstone, M. M. (1993). (1993). Sault Sault Bennett, G., in Marie Resident Geologist' s District-1992; Ste. S t e . Marie Resident Geologisti s District-1992; in Report Report of of Activities A c t i v i t i e s 1992, 1992, Resident Resident Geologists, Geologists, Ont Ont Survey, Misc. Paper 161, Geol. p 207-232. Geol. Survey, Misc. Paper 161, p 207-232. 1987: Geology Geology of of tthe Havilland-Goulais Bay Born, P. 1987: h e Havilland-Goulais Bay Area, Area, Born, P. 0. Geol. Survey, Algoma; Ont. District of F. R. R. 5602, 5602, D i s t r i c t of Algoma; Ont. Geol. Survey, 0. F. 114p. 114p. with w i t h maps. maps. 1992. Jackson, Jackson, S.L. S. L. and and Henderson, Henderson, I. I. 1992. Geology Geology of of the the Area; in Summary of Field Aberdeen Area; i n Summary of F i e l d Work Work and and other o t h e r activities, a c t i v i t i e s , 1992; 1992; Ont. Ont. Geol. Geol. Survey, Survey, Misc. Misc. Paper Paper 160, 160, pp pp 47—52. 47-52. 1973: 1973: Stratigraphy S t r a t i g r a p h y and and depositional d e p o s i t i o n a l environments environments of of Huronian rocks of the Rawhide Lake-Flack upper upper Huronian rocks of t h e Rawhide Lake-Flack Lake Lake M. , ed. area, a r e a , Ontario, Ontario, ini Young, n Young, G. G.M., ed.,, Huronian Huronian Geol. stratigraphy s t r a t i g r a p h yand andsedimentation: sedimentation: Geol. Assoc. Assoc. of of Canada Special Canada S p e c i a l paper paper 12, 12, p. p. 73-95. 73-95. Wood, Wood, J. J. 1983: Tectono-sedimentaryh history of early 1983: Tectono-sedimentary i s t o r y of early the Proterozoic P r o t e r o z o i c rocks rocks of of t h e jorthern n o r t h e r nGreat GreatLakes Lakes region, region, Young, G.M. G. M. G. S. A. p. 15-32; 15-32; in i n G.S.A. p. Memoir Memoir 160, 160, Edited Edited by by L.G. L. G. Medaris, Medaris, Jr. Jr. 4 �I I ARCHEAN ARCHEANCRUSTAL CRUSTALXENOLITHS XENOLITHS IN INAAKEWEENAWAN KEWEENAWANHYPABYSSAL HYPABYSSAL SILL, SILL, NORTHEASTERIsI MINNESOTA. WHITE RIGHT! NORTHEASTEFW MINNESOTA. WHITEWAS WASRIGHT! BOERBOOM, Terrence J.,J., Minnesota University Avenue, Avenue, St. Paul, MN 55114 BOERBOOM, Terrence MinnesotaGeological Geological Survey, 2642 2642 University 55114 I I I I I I I I I I I I I I Recent Recent field field studies studieshave haveidentified identifiedabundant abundantxenoliths xenolithsof of Archean Archean crust crust in in the the earliest of several intrusions along the northeast-trending transition earliest of several intrusions along the northeast-trending transition zone zone between between the theupper upperportion portionofofthe theDuluth DuluthComplex Complexand andthe theBeaver BeaverBay BayComplex Complex in in northeastern (Boerboom and andMiller, Miller, 1994). 1994). This This inclusion-rich, inclusion-rich, highly highly northeasternMinnesota Minnesota(Boerboom contaminated, contaminated, mafic mafic hypabyssal hypabyssal intrusive intrusive unit, unit, informally informally termed termed the theShoepack Shoepack Lake redistributed by Lake inclusion-rich inclusion-rich ferrodiorite ferrodiorite(SLID), (SLID), has been widely redistributed by intrusion intrusion of granophyric granophyricand andanorthositic anorthositiccomponents componentsof ofthe theDuluth DuluthComplex, Complex,and andby bylater laterNENEtrending mafic dikes and sills related to both the Duluth and Beaver Bay Complexes. trending mafic dikes and sills related to both the Duluth and Beaver Bay Complexes. Most Mostoutcrops outcropsof ofSLID SLIDcontain containabundant abundantxenoliths xenolithsof ofKeweenawan Keweenawanfelsic felsic to tomafic mafic volcanic rocks, but at its northern extent nearly all xenoliths volcanic rocks, but at its northern extent nearly all xenoliths are areArchean Archeancrust. crust. Similar Similar but but unrelated unrelatedcontaminated contaminateddiabase diabasecontaining containingabundant abundantKeweenawan Keweenawan inclusions inclusions has has been been mapped mapped to tothe thesouth, south, and andisisinterpreted interpretedas asthe thefirst firstmagma magmapulse pulse of of the theBeaver BeaverRiver River Diabase Diabasedike dikeand andsill sillcomplex complexof of the theBeaver BeaverBay Bay Complex Complex (Miller (Miller and andothers, others,1989). 1989). Although Althoughthe theSLID SLIDisisclearly dearly older older than thanthe theBeaver BeaverRiver River Diabase, Diabase, ititsimilarly similarlyrepresents representsan aninitial initialpulse pulseof of magma magmarelated relatedto toincipient incipientconduit conduit opening. opening.These Theseearly, early,inclusion-rich inclusion-richphases phasesare areinferred inferredtotohave have'cleaned 'cleanedthe thepipes' pipes' and andcleared clearedthe theway wayfor forlater laterinclusion-free inclusion-freedikes dikesand andsills. sills. R7W , —VV—.. SS s 4Anorthositic Rocks R6W R5W •—--.t # . , -& .. & Approximate Approximatelocation location of study area of study area A NORTH SHORE VOLCANIC GROUP —------ , Shoepack ShoepackLake Lakeinclusioninclusionrich ferrodiorite(SLID) (SLID) richferrodiorite Archean Archeanxenoliths xenolithsininthe theSLID SLIDrange rangefrom fromsingle singledisaggregated disaggregatedquartz quartzcrystals crystalstoto outcrops 50mmacross, across,but butmost mostare arebetween between0.3 0.3and and11meter meterininsize. size. outcropsasaslarge largeasas50 Compositions Compositionsinclude includebiotite biotiteschist schistlocally locallycut cutby byfolded foldeddikelets dikeletsof ofgranite granitepegmatite, pegmatite, volcanogenic volcanogenicgraywacke graywackehaving havinggraded gradedbedding, bedding,pink pinkgranite, granite,pegmatite, pegmatite,and andgranitic granitic gneiss, monzodioritewith withlocally locallyabundant abundantlamprophyre lamprophyre gneiss,and andgranodiorite granodioritetotomonzodiorite inclusions—all ofArchean Archeanrocks rockswest westof ofthe theMidcontinent Midcontinentrift rift inclusions-all components compohentstypical typicalof system. Frozen amoeboid stringers of felsic material, trails of granular quartz grains, system. Frozen amoeboid stingers of felsic material, trails of granular quartz grains, and andsmall smallrock rockfragments fragmentsininvarious variousstates statesofofassimilation assimilationcommonly commonlyemanate emanatefrom from 5 �felsic inclusions. inclusions. The ferrodiorite host host rock rock ranges ranges from from dense dense black black to to pinkish pinkish gray gray fdsic variably assimilated assimilated xenoliths. due to variably .. The part of the SLID that contains Archean xenoliths' xenoliths overlies overlies aa northwestnorthwestwho postulated postulated a sub- ' White (1966), (19661,who trending gravity low, first first recognized by White Keweenawan ridge of Archean basement extending northwestward from the shoreline of Lake Superior. Geophysical modeling of this area by others supports White's interpretation of the negative gravity anomaly (Ferderer, 1982; Chandler, 1990; Allen and others, 1993). Geologic evidence other than Archean crustal xenoliths also supports White's interpretation. Multiple northeast-trending intrusive components of the Beaver Bay Complex form thick stacks of sheeted intrusions both northeast and southwest of the gravity low, but over the gravity low are pinched into narrow dike-like bodies (Miller and Chandler, in prep). This configuration suggests a buried control on their shapes. In addition, Jirsa's (1984) study of interflow sedimentary strata in the North Shore Volcanic Group has defined two sub-basins separated by a paleotopographic high that roughly corresponds to "White's basement high," and also to the necked zone of magmatic emplacement of the Beaver Bay Complex. Such a paleotopographic high implies that relative basement uplift occurred before or during deposition of the flow/interfiow sequences. Other areas of shallow crustal basement inferred from geophysical modeling underlie the Bayfield Peninsula in Wisconsin and an area southwest of Isle Royale (White, 1966; Allen and others, 1993). The Archean crustal xenoliths in northeastern Minnesota strongly support interpretations of of a pre- to syn-magmatic, high bl block geophysical interpretations syn-inagma^c, topographically nigh ock ofof older crustal rocks in northeastern Isle Royale and mtheastem Minnesota, Minnesota, and by.inference, inference, near Kovale and . " in h northern northern Wisconsin. isc cons in.' Field mapping mapping was program. wasfunded fundedin inpart partby bythe theUSGS-COGEOMAP USGS-C&BOMA~' .program. ,, REFERENCES CITED Allen, W.J.,Dickas, Dickas, A.B., A.B.,and andMudrey, Mudrey, M.G., M.G., Jr., Jr.,1993, 1993,Aa'lntegrktaf An integrated sdattfc seismic refteeUon/ reflection! ABen, D.J., Hinze, WJ., %. + three-dimensional gravity investigation rift system,system, USA: Western Western Lake three-dimensional gravity investigation of the Midcontinent Midcontinentrift Superior Region [abs.1: Basement Basement and and Basins of ofEastern EasternNo* North America,AAPG America, AAPG Hedberg Research Superior Regionbbs.1: --Research , Arbor, Michigan. : Conference, Ann Arbor, Michigan. Boerboom, T.J., Tj., and Geologicmap map of of the the Silver SilverIsland Island Lake, Lake, Wilson Wilson~ake.ind Lake, and western western andMiller, Miller, J.D., J.D., 1994, 1994, Geologic quadrangles, Cook and and Lake Counties, Counties, Minnesota: Minnesota Survey Toohey Lake quadrangles, Minnesota Geological Geelo&al Survey Miscellaneous (in prep.). MiscellaneousMap MapSeries, SerieÈscale scale 11:24,000 24,000 tin m.). Chandler, V.W., 1990, Geologic interpretation of gravity and magnetic data over the central part of the Duluth Comple; northeastern Minnesota: Economic Geology, v. 85, p. 816-829. Ferderer, R.J., 1982, Gravity and magnetic modelling bf the southern half of the Duluth Complex, northeastern Minnesota: Unpublished M.A. Thesis, Indiana University, Indiana, 99 p. Jirsa, M.A., 1984, Interfiow sedimentary rocks in the Keweenawan North Shore Volcanic Group, northeastern Minnesota: Minnesota Geological Survey Report of Investigations 30, 20 p. Miller, J.D., and Chandler, V.W., in prep, Geology, petrology, and tectonic significance of the Beaver Bay Complex, northeastern Minnesota: GSA Special Paper. Miller, J.D., Green, J.C., and Boerboom, T.J., 1989, Geologic map of the illgen City quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-66, scale 1:24,000. White, W.S., 1966, Tectonics of the Keweenawan basin, western Lake Superior region: U. S. Geological Survey Professional Paper 524-E, 23 p. 6 �I p I FORTY FORTY YEARS YEARS OF OF INSTITUTES INSTITOTES ON OH LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY BORNHORST. Theodore J., Department BORNHORST, Theodore J., Department of of Geological Geological Engineering, Engineering, Geology Geology and and Geophysics, Geophysics, Michigan Michigan Technological Technological University, University, Houghton, ~ o u ~ h t o nMI MI , 49931 49931 The The Institute Institute on on Lake Lake Superior Superior Geology Geology (ILSG) (ILSG) began in in 1955 1955 with annual at locations locations annual meetings meetings held held in in April April or or May May of of each each year, year, at been held held at throughout throuahout the the Lake Lake Superior Suoerior region. region. Meetings Meetings have have been at 18 18 different locations, with 9 locations repeating (repeat interval different locations, with 9 locations repeating (repeat interval with time meeting locations around around 11 11 years). years). More More diversity diversity with time in in meeting locations is Over indicated indicated by by 66 single single locations locations occurring occurring in in the the last last 10 10 years. years. Over the 40 years of ILSG, there have been 30 chairmen; 9 have been the 40 ILSG, have been chairman chairman twice twice (repeat (repeat interval interval around around 11) 11) and and 21, 21, once. once. For For the the 55 from previous previous years years from from 1990 1990 to to 1994, 1994, all all chairmen chairmen have have been repeats repeats from years, years, indicating indicating less less diversity diversity with with time time in in annual chairmen. chairmen. The The ILSG ILSG was was founded founded to to bring bring together together geologists geologists from from academia, academia, government and industry industry to to discuss discuss the the geology of areas government surveys, surveys, and related Goldich Medal Medal related geographically geographically to Lake Superior Superior (see (see the Sam Goldich Award Award Guidelines). Guidelines). The The attendance attendance over over the the 40 40 years years of of ILSG, ILSG, estimated of 6000, clearly indicates indicates that that the the ILSG ILSG has has estimated to to be be in in excess excess of 6000, clearly years 1966 to met met its its objectives. objectives. Data on attendance is known for the years 1969, 1969, and and 1982 1982 to to present, present, and and suggest suggest aa cyclical cyclical pattern. pattern. The provides The number number of of abstracts abstracts published in proceedings volumes provides another measure of of the the success success of of the the ILSG ILSG in in bringing bringing another quantitative quantitative measure total number number of of abstracts abstracts over over the the 40 40 years years together together geologists. geologists. The total meetings, the number of of abstracts abstracts is is approximately approximately 1450. 1450. For For annual annual meetings, the number Overall, the ranges ranges from from 12 12 to to 60, 60, with with aa median median of of 31. 31. Overall, the number number of of abstracts dramatically abstracts gradually increased from 1955 to 1983, and then dramatically increased and has has stayed stayed higher higher than than in in earlier earlier years, years, increased in in 1984 1984 and although although slightly slightly declining declining from from 1985 1985 to to 1994. 1994. The total number of authors authors on on abstracts abstracts over over the the 40 40 years years is is approximately approximately 2450. 2450. For annual meetings, the with a a the number of authors ranges from 14 to 126, with median median of of 49. 49. Both Both the the number number of of abstracts abstracts and and number number of of authors, authors, documents geology of of the documents a significant volume of discussion on the geology Lake Lake Superior Superior area. area. The only available mix of academia, government government available means of analyzing the mix surveys, surveys, and and industry industry is is through through the the abstracts. abstracts. For every abstract, abstract, over the other author author the 40 40 years of ILSG, the senior author and every other was categorized categorized as as affiliated with either academia (includes (includes students) , government students), government surveys, surveys, or industry industry (includes (includes consultants) consultants). patterns are nearly nearly identical, using using The proportion and temporal patterns Published affiliation affiliation of either: senior senior author author only, only, or or all all authors. authors. Published contributions most of of the 40 contributions by academic geologists have dominated most year year history of of the the ILSG, ILSG, with a median of about 65 % of contributions each overall pattern in in the the proportion proportion of of academic academic each year. year. The overall contributions contributions is is one one of of aa gradual gradual increase increase from from around around 40 40 %% in in 1955, 1955, to to 80 80 % in in 1975, 1975, followed followed by aa decrease decrease to to about about 45 45 %% in in 1994. 1994. Government survey over the 40 Government survey contributions contributions have gradually increased over years of ILSG from around 20 % to around 35 %, %, with with a median median of of about about were much much Published 25 %. %. Published contributions contributions by industry geologists were 25 proportion greater in %. The proportion in the the first first 66 years years of of the the ILSG, ILSG, around around 25 25 %. of contributions fell to a lowfell around of near 0, while ofindustry industry contributions to1975 a low around 1975 of near 0, while at same timetime academic contributions peaked, and peaked, has since and has since atthe the same academic contributions 7 �The increased increased to to around around 10 10 %. %. The median median proportion proportion of of industry industry The contributions of ILSG contributions over over the the 40 40 years yearsof ILSGis is66%. %. The ILSG ILSG has has succeeded at bringing together a mix of geologists from succeeded at brin~ingtogether a mix of geologists from academia, academia, government government survey, survey,and and industry. industry. While While published published contributions contributions from from industry industry are are low, low, an an analysis analysis of of attendees, attendees, which which is is not not possible, possible, may may indicate indicate higher higher industry industry geologist geologist participation Rarticipation in in ILSG. ILSG. The The ILSG ILSG has has had had aa focus focus on on Precambrian Pmdombrian geology geology and and mineral mineral resources resources throughout Every abstract abstract was was categorized categorized as as throughout its its 40 40 year year history. history. Every related resources, basic basic geology, geology, geophysics, aeophysics, related to to either either resources, have dominated dominated glacial/environmental, glacial/environmental,or or other. other. Basic Basic geology geology topics topics have ILSG abstracts, with a median contribution of about 60 % over the 40 40 ILSG abstracts, wi-th a median contribution ot about 60 % over the Basic years. Basic geology geology contributions cmItributi0ns gradually gaxidually increased increased from from 1955 1955 to to years. 1972, The proportion proportion of of and have have since since fallen fallen to to around around 45 45 %. %. The 1972, and resource resource related related papers papers was was greatest greatest in in the the first first 55 years years of of the the ILSG, ILSG, at around 50 %, and since then it has remained variable at about 30 %% at around 50 %, and since then it has remained variable at about 30 (overall Geopbyics abstracts abstracts have remained remained (overall median median of ofabout about3030%)%.) . Geophysics consistent Glacial/environmental consistent with with aa median median of of 89%% contribution. contribution. Glacial/environmental topics teoics have have aa median median of at 22 %% contribution. contribution. As As the the 1994 1944 Chairman, Chairman, I I was was directed by the Board of Directors to increase the proportion of directed by the Board of Directors to increase the proportion of with the glacial/environmental glacial/environmentalcontributions. contributions. Solicitations, Solicitations, with the help help of of M. M. A. A. Gere, -re, Jr., Jr., resulted resulted in in aa dramatic dramatic increase increase of of glacial/environmental 20 %% for for 1994 1994 (by (by far far the the 40 40 glacial/environmental abstracts abstracts to to about about 20 year year high). high) . North What What is is the the future future of of the the ILSO? ILSG? The The role role of of geologists gedogists in in North The ILSG America ILSG has has America today today is is much much different different than than it it was was in in 1955. 1955. The changed It is is important important that that the the ILSG IIiSG look look changed over o w its its 40 40 year year history. history. It a lengthy to had& lengthy discussion discussion on on the the The Board Board of of Directors Directors had to its its future. future. The future of the annual annual board board meeting meeting in in 1993, 1993, and and will will continue continue future of ILSG ILSG at at the the in 1994. 1994. Can Can or or should should the the ILSG maintain its focus on the discussion discussion in the ILSG into Precambrian/resource Should the ILSG expand ~Z~an into d all all areas areas Precambrian/resourcegeology? geology? Should The critical question of geology of the Lake Superior region? is, of geology of the Lake Superior region? The critical question is, what of success? success? what changes ehangas must must the the ILSG ILSG undergo undergo to to insure insure 40 40 more more years years of II thank thank Mary Mary L. L. Larson Larson for for the the hours hours of of compilation compilation from from proceedings proceedings volumes volumes in in the the Michigan Michigan Technological Technological University University Library Library Archives. Archives. 8 �I U I INVENTORY DIVISION'S UPPER INVENTORY OF THE MICHIGAN GEOLOGICAL SURVEY DIVISION'S I Frank Frank Chenier, Chenier, District District Geologist; Geologist; Michigan Department Department of Natural I I I I I I I I I I I I I PENINSULA PENINSULA SIGNIFICANT SIGNIFICANT WATER WELL CUTTINGS LIBRARY AT ESCANABA ESCANABA Resources; Resources; Geological Geological Survey Survey Division; Escanaba, Escanaba, Michigan Michigan Drill Drill cuttings cuttings from from approximately approximately 570 570 selected selected water wells wells representing representing the the geology geology of of the the Upper Peninsula Peninsula are are maintained by the the Geological Geological Survey Survey Division of the Michigan Department Department of Natural Natural Resources Resources office office at at Escanaba. Escanaba. The collection collection includes includes rocks rocks of of precambrian precambrian and and paleozoic paleozoic age age and and overburden overburden samples. samples. Environmental Environmental and and groundwater groundwater conditions as well as potential mineral investigation of some some of mineral resources resources can can be assessed by the investigation these these cuttings. cuttings. In In addition, addition, the the office office maintains maintains aa library library of of available available water water well well logs logs for for the the entire entire U.P. U.P. All of of the the above above are are available available for for study study and and review. review. For more information information contact Frank Chenier at (906)786—2351. Frank Chenier at (906)786-2351. �METALLIC MINERAL METALLIC MINERAL RESOURCES RESOURCES AND AND ECOSYSTEM ECOSYSTEM MANAGEMENT MANAGEMENT AT AT VOYAGEURS NATIONAL PARK, MINNESOTA VOYAGEURS NATIONAL PARK, Davis, Steven R., R., U.S. Bureau Bureau of of Mines/IFOC, MinesIIFOC, Denver, Denver, CO CO 80225-0086 80225-0086 Under a Memorandum of Understanding with the the National the Under Memorandum of Understanding with National Park Park Service, Service, the IntermountainField FieldOperations OperationsCenter Centerofofthe the U.S. U.S. Bureau Intermountain Bureau of Mines Mines recently recently completed completed a hardrock mineral mineral study studyon on the the Voyageurs VoyageursNational NationalPark Parkarea areaofofnorth northcentral centralMinnesota. Minnesota.The The hardrock prompted by by proposed proposed changes in in the the State's Metallic Minerals Leasing Rules aimed aimed study was prompted at encouraging mineral mineral exploration exploration and and development. development. The announcement prompted a great deal The prompted by the Park's management might what aa likely likely mineral mineral development development might of uncertainty uncertainty by management staff as to what and what ramifications ramifications itit might might have have on on Park resources and operations. operations. encompass, and USBM study study includes includes aa comprehensive comprehensiveanalysis analysisofofthe the region's region's historical historical mining mining The USBM activities and and apparent apparent mineral mineral potential, potential, as as well as descriptive models models of of known known mines mines in in similar similar geologic tenanes. terranes. The geologic Thefinal finaldocuments, documents, aa Mineral MineralLand Land Assessment Assessment and Executive Summary, include socioeconomic socioeconomicimpact impactanalyses analysesofofaa typical typical mine and an applicable mine development, development, and applicable include managementplan planincorporating incorporatingan anecosystem-sensitive ecosystem-sensitiveapproach. approach. Included Included in in the the environmental management thta package is a series of resource management maps in both hard copy and GIS (digital) form, data in both hard copy and GIs (digital) form, allowing for site specific project and proposal proposal analysis analysis and management. management. This project is an opportunity to impart a better better understanding of what potential metallic mineral resources exist in the area, area, and the likely development and the development scenario scenario that might occur if these resources are identified resources identified and and developed. developed. The report also details details the the environmental environmental concerns concerns related to mineral developments and andcurrent current state-of-the-art state-of-the-artmitigation mitigationtechnologies. technologies. The project project therefore impart impart aa better understanding understanding of of mineral mineral development developmenton onthe thepart partof ofthe the Park Park should therefore Service personnel, and alleviate some of the concerns relative to disruptions of regional Service personnel, and alleviate some of concerns relative disruptions regional ecosystem integrity and balance. Objective Objective and and comprehensive comprehensive studies studiessuch suchas as these, these, tailored tailored ecosystem to the specific issues and management needs of the National Parks involved, should the specific issues and management needs National involved, should prove valuable to to the the P Park primary Bureau Bureau of of Mines Mines goals goals of of ark Service, and at the same time achieve primary valuable continuing resource evaluation and increased mineral awareness. increased mineral awareness. �a Wetland Wetland Treatment Treatment of of Mine Mine Drainage Drainage -an Alternative to Conventional Conventional Treatment or Voodoo Treatment? Paul Eger Minnesota Department of Natural Resources St. Paul, Minnesota I I I I I I I I I I I I Although wetlandshave havebeen been used used to to treat of this Although wetlands treat mine mine drainage drainage the application application of this technology has not always been successful. The type and size of wetland that is needed is technology has not always been successful. wetland that needed a function of the input drainage quality, the effluent requirements and and the the length length of of time time treatment treatment is required. required. of the 90% of both pilot pilot and full scale tests have demonstrated demonstrated that that from from 50 - 90% Results from both influent copper, nickel, cobalt and zinc can be removed from neutral mine drainage in free water influent Acid mine has been been treated in aa pilot surface wetlands. wetlands. Acid mine drainage drainage has treated in pilot system system representing representing a subsurface wetland. wetland. The pH of the drainage has generally been increased from influent values values the drainage generally and 7. Over between 4 and and 55 to effluent values between 6.5 and Over90% 90%of of the the influent influent copper, copper, nickel, cobalt and zinc have been removed. been removed. Although require much much less less maintenance maintenance than thanconventional conventional Although wetland treatment systems will require technology, plans for maintenance and replacement must be included for successful long term term technology, plans maintenance and replacement must be included for successful long treatment. treatment �MINNESOTA MINNESOTA DRILL DRILL CORE CORE EXAMINATION EXAMINATION AND AND ASSAY ASSAY FREY, PREY. Barry Barry A., A., Minnesota Minnesota Department Department of Natural Natural Resources, Resources, Division of Minerals, Minerals, 1525 1525 Third Avenue E., E., Ilibbing, MN 55746 Hibbii, MN 55746 Current work includes includes the new logging of 100 100 drill drill core core samples samples and assaying of 212 new new samples samples of existing DNR Drill Core Library existing DNR Library samples samples for most of which which no no modern modem descriptive descriptive logs logs and little little chemical data Samples are are from Central Minnesota, where rocks associated chemical data are are available. available. Samples Minnesota, where associated with the Penokean Orogen dominate dominate and and there are few Drill cores were were laid out and logged Penokean few outcrops. outcrops. Drill logged in a qualitative manner and then sampled in order to determine alteration, mineralization, and protoliths. qualitative order alteration, mineralization, and protoliths. The The entered into aa digital digital database databasefor for future futureGIS GISapplication. application. The fields and current descriptive logs were entered codes are listed elsewhere elsewhere on the poster. An Anexample example of of the thedatabase databaseprintouts printouts from from the the most most recent recent logging is also also shown. shown. Logging project has has verified verified or or expanded expandedthe theknowledge knowledgeofofthis thisProterozoic Proterozoicterrane. terrane. Three Three this project Logging for for this interesting features observed in this geologic setting are the presence of tourmaline, granitic granitic intrusive intrusive relationships, relationships, and the presence presence of of ultramafic ultramafic rocks. rocks. Grain mounts mounts taken while core core logging logging have have identified vein or stratiform tourmaline from several additional core samples. Amounts of tourmaline are identified vein or stratiform tourmaline from several additional core samples. Amounts of tourmaline are generally small. Where stratiform, the tourmaline is generally found with oxide, chert, silicate, or sulfide Where stratiform, the tourmaline is generally chert, silicate, or sulfide veinlets have been found in They hey have have chemical sediment. Granitic intrusives and veinlets in several severalplaces. places. T intruded phyllitic phyllitic schists, schists, metagabbro, metagabbro, and magnetite magnetite chert chert iron iron formation. formation. Some intruded Some(within (withinphyllitic phylliiic schist) schist) rocks while while others othersare aregood goodintrusives. intrusives. The may be sweated out from surrounding rocks The intrusives intrusives and veins may help to explain the recrystallized nature common with the quartz rich portions may to explain the recrystallized common with the rich portions of of these these iron iron magnetite, or Inplaces, places,this thisgranite graniteisisrelatively relatively fresh fresh with with assimilated magnetite, or itit may may be be extremely extremely formations. In altered with carbonate, when fresh, it appears to be carbonate, epidote, epidote, and and chlorite chlorite to tocreate createepidotites. epidotites. Even when be tectonized, with were with carbonate carbonate having having aaspatial spatialassociation. association. Four drill drill cores cores with with ultramafic ultramaf~c rocks were Chemistry subdivides subdividesthese thesebased basedon onrelative relativeabundances abundancesofofVVversus versusCr, Cr, Ni, Ni, and MgO logged. MgO logged. Chemistry by differences differencesin inmineralogy mineralogy and degree degree of of alteration. alteration. The contents, and logging by The more more magnesic magnesic rocks are more pervasively and destructively altered compared compared to to the vanadium vanadium rich rich rocks. *are areaalso alsounderwent underwentaaperiod(s) period(s)ofofpre-Pleistocene prePleistoceneweathering weathering before before being being The rocks rocks of of the thearea glacially scoured. These effects have been superimposed on the original rock types. Weathering effects These effects have been superimposed rock Weathering effects include limonitic, limonitic, red hematitic, and goethitic goethitic alteration alteration may may be include goethitic alteration, alteration, although some goethitic hydrothermal in in nature. nature. regionally There are are numerous numerous observed observed ore-mineral oremineral occurrences and alteration. Carbonate is regionally abundant within altered volcanics, as an iron formation component, as marble, and as minerals associated abundant within altered volcanics, as an iron formation component, as marble, and as minerals associated with most veins. Some Inassociation associationto to this, this, preliminary preliminary Someveins veinshave have associated associated skarn skarn and mineralogy. In examination of thin sections unexpected local occurrence sections indicated the unexpected occurrenceof ofbright brightblue-violet blue-violetpleochroic pleochroic sodic amphiboles associated with carbonate, epidote, zoisite alteration. Stratiform sulfides occur in numerous DDH's, as asdoes doesgraphitic graphiticargillite-phyllite argillite-phyllitewhich which isis often often These sulfides are typically pyrrhotite or pyrite, but lesser associated with the the stratiform stratiformsulfides sulfides . These sulfides are typically pyrrhotite or lesser chalcopyrite or or sphalerite sphalerite isis sometimes sometimes found. found. Sevn SevenDDH's DDH'salso alsohad hadtrace traceamounts amountsofofbornite. bornite. from the the latest latest logging logging occurred occurredin in K-1, K-i, BM-2, Possible visible sphalerite from BM-2, MLCH-7, MLCH-7, MLCH-5, MLCH-5, Drill core K-i MLCH-11, BM-i, CW-1, MLCH-9, T-665, MLCH-2, and C4 (see analytical results). BM-1, CW-1, MLCH-9, T-665, MLCH-2, and C4 (see analytical results). K-1 had the most most visible sphalerite, sphalerite, with withthe thechemical chemicaldata dataverifying veri'ing the sphalerite. Reddish-orange Reddish-orange siderite is also present and looks looks similar similar to to sphalerite. sphalerite. Analytical results for 212 212 new samples have been received from our contractor, contractor, Bondar-Clegg Bondar-Clegg & & Ltd. of Ottawa, Ontario. Forty package with with Company Ltd. Fortynine ninesamples samples were were analyzed analyzed using a 52 52 element package 163 samples samples analyzed analyzed using using aa 21 21 element elementpackage packageincluding includingAu, Au,Pt, Pt, and andPd. Pd. Some Someof of these these analyses analyses were were from drill from drill core core logged logged during during the the previous previous biennium. biennium. From the standpoint geology, there there are are many many significant significantassay assayresults. results. The standpoint of economic geology, The highest highest . 12 �Zn A 5 foot sample from from DDH DDH K-1 K-i had Zn values values to to date date have have come come from from the recent analyses. A had a Zn assay >>20000 20000ppm. ppm. AAsample samplefrom fromDDH DDHH12 H12had had aaZn Znvalue value of of 683 683 ppm. Beside BesideZn, Zn,these thesesamples samples had had anomalous Ag, Pb, Cu, Au, Pt, Pd, Cd, Mo, F, Sb, Hg; and separately, other elements. anomalous Ag, Pb, Cu, Au, Pt, Pd, Cd, Mo, F, Sb, Hg; and separately, other elements. The new analyses had had several Cu values over 600 600 ppm ppm from from DDH's DDH's H6, K-I, 17. Drill cores from values over K-1,and and B1-l Bl-117. several had anomalous anomalousAs As(to (to234 234ppm), ppm),Cd Cd(to (to134 134ppm), ppm),FF(to (to14.075 14,075 ppm), ppm), and Hg Hg several different areas had (to (to 428 428 ppb). ppb). The Thehighest highest Pb Pbvalues values (to (to762 762ppm) ppm) caine came from from the the unusual unusual association of MgO rich (to (to 24.54%) 24.54%) altered TC-101 and and TC-102. TC-102. These were also also high high in in Cr, Cr, N Ni, altered ultramafics in DDH TC-101 These samples were i,and Hg. The many places within The data data indicates indicates that thathydrothermal hydrothermal processes processes were active in in many within Central Central Minnesota, and and that thatthere theremay may be beaahigh highprobability probabilityfor forundiscovered undiscoveredeconomic economicmineralization. mineralization. 13 �GENESIS OF GENESIS OFHEMATITE HEMATITEAND ANDMAGNETITE MAGNETITE IN INPRECAMBRIAN PRECAMBRIANMACNETITE MAGNETITE IRON-FORMATION IRON-FORMATIONOF OF LOW LOW METAMORPHIC GRADE,LAKE LAKE SUPERIOR DISTRICT, USA USA - AA MICROSCOPIC MICROSCOPIC OBSERVATION GRADE. SUPERIOR DISTRICT, OBSERVATION METAMORPHIC HAN, T. T. M., M., Consulting Applied Mineralogist, Ishpeming, HI MI 49849 49849 HAD, metamorphic grade Precambrian Precambrian magnetite magnetite iron-formations iron-formations of of the Lake Lake The low metamorphic Superior District examined Superior examined in in this this study study were the the Biwabik of the Mesabi Range, the Ironwood Ironwood of of the the Gogebic Gogebic Range, Range, and and the Marquette Range. The the the Negaunee Negaunee of of the the Marquette flange. The banded type and Biwabik and Ironwood Ironwood iron-formations iron-formations consist consist of of both an evenly "banded irregularly wavy The Negaunee Negaunee iron-formation iron-formation is is exclusively exclusively the the an irregularly wavy banded banded type. type. The evenly banded type which which consists dominant subtypes, subtypes, i. e. e. carbonate-chert carbonate-chert evenlybandedtype consists of two dominant magnetite in the wavy wavy banded banded iron-formation and silicate-carbonate-chert. silicate-carbonate-chert. The magnetite hematite, iron coexists with hematite, iron carbonates, carbonates, layered layered iron-silicates iron-silicates and chert. The iron-formation has essentially the same mineral mineral assemblage assemblage but but is is evenly banded iron-formation generally free of hematite. number of of The study was done done by by microscopic examination of a substantial substantial number sections prepared from from these these iron-formations, iron-formations, polished sections from specimens collected from before is employed. employed. The The results before and after after an an induced induced oxidation oxidation procedure procedure is indicated that: that: (a) both the hematite hematite and and the the magnetite magnetite in these these (a) The origin of both indicated iron-formations is more complicated complicated than believed. (b) iron-formations is far farmore than previously previouslybelieved. (b) Some Some of the or developed developed shortly shortly hematite is probably aa product product of primary sedimentation, or deposition; and be a a result result of of authigenic authigenic growth growth generated generated after deposition; and some some of it may be from the the migration migration and and precipitation precipitationofofFe* Fe from from acidic acidic pore pore fluids fluids during during from diagenesis. (c) various hematites functioned functioned as "starting "starting points" points" responsible responsible diagenesis. (c) The varioushematites for the the development development of magnetite present present in the iron-formations. iron-formations. (d) for of most most of of the the magnetite in the (d) proceeds concurrently by replacing replacing the The magnetite development apparently proceeds concurrently by hematite on hematite on one one hand hand and and overgrowing overgrowing into into the the host host of of the the hematite hematite on on the the other. other. (e) More More than one stage (f) AA (e) stage of of overgrowth overgrowth is is evident evident on on some some magnetite. magnetite. (f) progressive change of of magnetite in some of the carbonate-chert progressive morphological change carbonate-chert subtype, i.e. it changes changes from clusters of lath-shaped lath-shaped pseudomorphs pseudomorphs to aggregates from clusters to aggregates subtype, (g) The The newly newly formed of anhedral grains and and finally finally to to coalesced coalesced octahedra. octahedra. (g) magnetite is believed to the solid solid diffusion diffusion of of Fe++ Fe++ magnetite is believed to be a product resulting from the the hematites. hematites. The The Fe* Fe is hematite toward the is generated generated from from the the reaction reaction between hematite metamorphism. and carbonaceous matter in in the iron-formation iron-formation during low grade metamorphism. hematites became became aa minor minor ore ore As a result, both the primary and diagenetic hematites mineral while magnetite became became a major ore ore mineral mineral in in the the Precambrian Precambrian ironironMuch of of the magnetite magnetite I in n the ironformation of the the Lake Lake Superior Superior District. District. Much formation currently furnace feed on on the the Hesabi Nesabi and and Marquette Marquette formation currently processed processed for for blast furnace enriched through process. Much of the the hematite hematite previously previously and and ranges was enriched through such a process. currently mined on the Mesabi, Mesabi, Gogebic Gogebic and and Marquette Marquette ranges ranges is is of of postmetamorphic postmetamorphic currently origin and represents represents an product of of the the magnetite, magnetite, iron iron carbonates carbonates and and origin an oxidation product layered iron-silicates. iron-silicates. These interpretations based on: on: (a) the morphological morphological character character and and the the These interpretations are are based mineral association of the magnetite; and (b) the morphologies, microstructures, mineral association of the magnetite; and morphologies, microstructures, impurities and and microtextural microtextural relationships relationships of of preexisting preexisting hematite hematite Inclusions inclusions in in impurities the existing magnetite. Many of these features are revealed after induced the existing magnetite. Many of these features revealed Induced oxidation. oxidation. 14 �I GEOTECHNICAL GEOTECHNICAL SOLUTIONS SOLUTIONS FOR MINING RELATED RELATED PROBLEMS PROBLEMS • Allan M. Johnson Johnson Department Mining Engineering Engineering Department of of Mining Technological University Michigan University Michigan Houghton, 49931 Houghton, MI 49931 ABSTRACT ABSTRACT Mining practices of the the 19th 19th and early early 20th 20th centuries centuries have have sometimes sometimes resulted in problems problems of current concern. These Theseproblems problemsinclude includeunsightly unsightly or or unsafe unsafe conditions conditions at the the mines mines and, and, in in some someinstances, instances, environmental environmentaldamage damage to varying degrees. Examples types can be found in all of the the older older iron iron ore oreand and Examples of problems of these types copper Michigan. More than 20 20 years years of of studies studies of problems problems on the the West copper mining districts in Michigan. Morethan types: Menominee Iron Iron Range Range in in Iron Iron County Countyhave haveidentified identified problems of the the following following types: Menominee 1) 1) 2) 2) 3) 3) 4) inadequately capped and sealed mine mine shafts shafts and raises; raises; the the threat threat of of surface surfacesubsidence subsidenceabove aboveshallow shallowmine minestopes; slopes; presently unacceptable disposal of mining waste rock; and presently unacceptable disposal mining waste rock; and mineralized mineralized and and acid add mine minedrainage. drainage. 4) These ,Thesestudies studies with with solutions solutions to problems of these these types typeshave have been reported reported in in the theliterature literature in published reports. One of these studies addressed a serious acid drainage problem at and in published One of these studies addressed a serious add drainage the the Dober Dober Mine Mine complex complex in in the theIron IronRiver RiverValley. Valley. and Here (pH2) 2)with withhigh highlevels levelsof ofdissolved dissolvedmetals metals (iron (ironand andaluminum) aluminum) Here acid acid waters waters (pH flowed Neutralizationof ofthe theacid add by by the theriver riverwaters waters caused caused insoluble insoluble flowed into the Iron River. Neutralization Fe boy) to precipitate, precipitate, turning turning the the waters watersyellow yellowbrown. brown. This Fe and and Al A1 hydroxides hydroxides (yellow boy) highly highly visible visible pollution affected the Iron River some seven miles to its confluence with the Brule south. Residents marks its its border border with with Wisconsin to the south. Residents of of both both states states Brule River, River, which which marks were affected. were affected. To studywas wasdone doneto toquantify quantify the the extent extent and and nature nature of of the the Toaddress address this this problem, problem, aastudy acid acid drainage. drainage. ItItwas wasdetermined determined that that aa huge huge teservoir feservoir of of acid acid water water was was present in the the underground was also alsolearned learned that that acid add waters waters flowed flowed from from the the Dober Dober underground mine minecomplex. complex. ItIt was Mine in response to groundwater inflow into the elevated western part of the mine Mine in response to groundwater inflow into the elevated western part of the minecomplex. complex. Calculations showed that that the the acid acid waters, waters, which which flowed flowedatatan anaverage avenge rate of 50 gpm, would Calculations showed would continue to impact the river system for at least 50 continue system for at least 50 years, years, at at which which time time the the mine minewould would have have been been sufficiently sufficiently flushed flushed of of the theacid. add. Bench scale tests tests of of methods methods to to neutralize neutralize the the acid add led led to to aaconceptual conceptualdesign design Bench and and pilot scale whereby mix with and whereby controlled amounts of river water would be diverted into the mine to mix neutralize treated drainage drainage from from the the mine mine was to to be be diverted diverted through through aa series series neutralizethe theacid. add. This This treated 15 �of downstream downstpm ponds adjacent to the the river in in which which settling settling would would remove remove the the metal metal returned to the the river. river. The precipitates. From From there there aa clear clear effluent effluent would be returned Thetest testresults results were promising and an engineering and economic assessment indicated the concept be were promising and an engineering and economic assessment indicated the concepttotobe precipitates. feasible. feasible. The acceptedand and supported supportedby bythe thelocal localcommunities communitiesand andthe theMichigan Michigan The plan plan was was accepted Department of Natural Resources. Ultimately it was funded through Act 307 (Michigan's Natural Ultimately it was funded through Act 307 (Michigan's "Superfund"), Act. The Thesystem systemwas wasbuilt builtand andbecame became "Superfund"), as the first first cleanup under the Act. operational in 1988. It is working as designed, with significant improvement operational in 1988. It is working as designed, with significant improvementto tothe theIron Ironand and Brule Brule River River system. system. References References 1986. 1986. Groundwater GroundwaterContamination ContaminationProblems Problems in in the theIron IronRiver RiverMining Mining District District of o Michigan (with (with David David M. M. Cregger). Cregger). Volume VolumeI,I,International InternationalSymposium Symposiumon onEnvironmental &-&onmental Geotechnology, in Environmental Environmental Geotechnology, Geotechnology, Hsai-Yang ~ s & - ~ Fang, a n ~ed., ed.,Envo EnvoPublishing Publishing Geotechnology, in Co., Co.,Bethlehem, Bethlehem, PA. PA. 1985. ControlAcid Acid Mine MineDrainage: Drainage: AAMichigan MichiganCase CaseHistory. History. 1985. AASynergetic SynergeticApproach ApproachtotoControl International 16-21. Printed PrintedininVolume VolumeII, 11,Mine Mine International Mine Water Assoc., Granada, Spain, Sept. 16-21. Water, ed., Talleres TalkiesGraficos GraficosARTE, ARTE, S.A., S.A., Maracena Maracena(Granada), (Granada),pp. pp. Water, R. R. Fernandez-Rubio, Pemandez-Rubio, ed., 695-708. 695-708. 1983. MineClosings. Closings. Invited Invited paper for for Session: Session: Water Water 1983. Hydrologic HydrologicConsiderations ConsiderationsininMine Resources SME-AIME Meeting, Meeting,Salt Salt Lake LakeCity, City,UT, UT,October October18-21, 18-21, Resources in in the the Western Western States, Slates,SME-AIME 1983. , 1983. Preprint -ria 83-365, 83-365, 55pp. pp.and andMining MiningEngineering, Eneineering,June June1984, 1984,pp. pp.644-648. 644-648. �PALEOMAGNETISM OF A A 1500 MA MA MAFIC MAFIC DIKE DIKE AT WATERLOO WATERLOO WISCONSIN KEAN, William, Department of Geosciences, Geosciences, University of KEAN, Milwaukee, P.O.Box P.O.Box 413 Milwaukee, Wisconsin- Milwaukee, 413 Milwaukee, Wi .53201 Wi. 53201 A recently quarry of of Waterloo Waterloo Quartzite A recently opened opened quarry Quartzite exposes exposes aa 1.5 1.5 meter thick cuts almost thick mafic dike that cuts almost vertically vertically through through dike is assumed assumed to be the the quartzite. The dike the same same age age as as a drill core core from the nearby nearby Portland mafic dike found found in drill Quarry, and dated at at 1450-1500 1450—1500 Ma Ma by by Ar/Ar Ar/Ar dating. The The dike studied for paleomagnetic analysis to aid in determining was paleomagnetic analysis in determining a more more reliable reliable paleopole paleopole position position for for the the 1500 Ma time a 1500 Ma time was frame frame for for central central North North 1\merica. America. the site site and and Twelve 2.54 2.54 cm cm diameter diameter cores cores were were drilled drilled from from the subjected to alternating field demagnetization demagnetization to lOOmT.,and 100mT.,and isothermal remanent remanent magnetism magnetism studies. Magnetite Magnetite saturation isothermal be the dominant dominant magnetic magnetic mineral.The mineral.The appears to be saturation direction of of Dec=308 Dec=308 deg.,Inc=-18.82 deg.,Inc=—18.82 deg. characteristic direction paleomagnetic pole pole of of 146 deg.E,18.66 deg.E,18.66 deg.N yields a paleomagnetic deg.N and an alpha 95 of 11 deg. deg. The The dike dike seems seems to cut across the folds folds in the quartzite so so no no structural structural corrections corrections have been made. of the Wolf Wolf River River Batholith Batholith (Hershberg, 1976), and Studies of (Hershberg, 1976), the Wausau Wausau Syenite Complex (Zich, Chan, and Myers (Zich, Chan, and Myers 1986) 1986) which are both dated at about 1500 1500 Ma indicate indicate posible Ma but show remagnetization at about 1100 Ma show aa component component results presented presented here. here. Also Also the magnetic similar to the results directions from the dike dike are significantly significantly different directions different from from Mercer 1984) those in the surrounding quartzite in surrounding quartzite ( Mercer 1984). ( References: References: E.L., 1976, Paleomagnetism Paleomagnetism of the Hershberg, E.L., the Wolf River M.S. Thesis,U.W.Madison, Thesis,U.W.Madison, 66 Batholith. M.S. 66 p. D.A., 1984, Paleomagnetism Paleomagnetism of the Baraboo Mercer, D.A., Mercer, M.S. Thesis, Thesis, U.W.Milwaukee, U.W.Milwaukee, 294 Quartzite. M.S. 294 p. Myers,P.,1986, Zich,C.,Chan,L.,and Myers, P., 1986, Preliminary Preliminary Zich,C.,Chan,L.,and Paleomagnetic results from the Wausau Syenite Syenite Complex, Central Central Wisconsin. Wisconsin. Eos,vol 67,p.266 17 �PROTEROZOIC VOLCANICS OF OF THE THE ANIMIKE ANIMIKEGROUP, GROUP, ONTARIO ONTARIO AND AND EARLY PROTEROZOIC MICHIGAN, AND THEIR TECFONIC SIGNIFICANCE MICHIGAN, AND TECTONIC SIGNIFICANCE KISSIN, Stephen Stephen A. A. and ERALICK, FRALICK, Philip Philip W., W., Dept. Dept. of of Geology, Geology, Lakehead Lakehead KISSIN, University, Thunder Bay, ON P7B SE1, Canada University, Thunder Bay, ON 5E1, Canada Although volcanic volcanicash ash components componentsare are found found in in the Early Although Early Proterozoic Proterozoic Animike Animike throughout the unitsare arerare. rare. The Gunflint Group throughout the Lake Lake Superior Superior region, volcanic units Gunflint Volcanics of Ontario and the have been been little studied in comparison of the Emporer Emporer Volcanics Volcanics of Michigan have formations, the the Gunflint Gunflint Formation Formationand and the the Ironwood Ironwood Iron Iron Formation, Formation, to associated iron formations, respectively. We report here the initial results of petrographic and geochemical work on on work respectively. here the initial results of petrographic units, together together with with data data on on the lapilli lapiui tuffs tufts of of the the Gunflint Gunifint Formation Formation. these units, The Gunflint Lavas occur conformably within within the the Gunflint Gunflint sedimentary rocks near Mink Mountain, Jean Jean Township, Township, Ontario. Ontario. The outcrop consists of ofthin thin bedded, bedded, The very limited outcrop Pillowedstructures structuresenveloped envelopedinin chert chert were were described by massive, aphanetic aphanetic basalt. Pillowed massive, described by (1960). The distinguished Goodwin (1960). Thebasalts basaltsare arevery veryfine-grained, fine-grained, with with few few microscopically distinguished features apart from plagioclase. Some units contain spherulites of microcrystalline quartz plagioclase. Some units contain spherulites microcrystallie quartz and K-feldspar that may be absorbed and recrystallized felsic lapilli. absorbed and recrystallized Emporer Volcanics The Emporer Volcanics are exposed in the Wakefield and Marenisco Quadrangles, Gogebic County, County, Michigan. Michigan. They have been described described most most recently recently by LaBerge LaBerge (1992), (1992), documented aasuite flows, hyaloclasites, hyaloclasites, and and pillow pillow who documented suiteof of mafic mafic sills, sills, massive and pillowed flows, breccias associated with felsic hyaloclasites, tufts, and breccias. The volcanics have been breccias associated with felsic hyaloclasites, tuffs, and breccias. The volcanics have been to be be interbedded interbedded with iron Irving and Van Hise (1892). known to iron formation formation since since the work of living Whole rock geochemistry reveals revealsthat that in in spite spiteof ofaarange rangein in major major element element chemistry, chemistry, the Gunflint Gunflint Volcanics Volcanics and mafic mafic Emporer Emporer Volcanics Volcanics have have indistinguishable indistinguishable chondritenormalized REE plots. The felsic Emporer Volcanics are somewhat depletedin inREEs, REEs,but but , REE plots. The felsic Volcanics are somewhat depleted relationship to to the the mafic mafic units units (Fig. (Fig. 1). 1). the plot indicates their probable close genetic relationship The classification classificationof ofthe thebasalts basaltsaccording accordingtotothe thetrace traceelement elementcontent contentof ofPearce Pearceand and + MgO MgO <c 20 wt wt Cann (1973) (1973) was was applied applied to samples fulfilling fulfillingthe the criterion criterion of of 12 12 < CaO CaO + Cam %, as well as to the Gunflint Volcanics, which are obviously basaltic but with low CaO %, the Gunflit Volcanics, which obviously basaltic but with low CaO + These affinities MgO. These samples plot in the the fields fields of of alkaline alkaline ocean-floor ocean-floor basalts. basalts. These MgO. suggest that that Gunfliit Gunflint Volcanics and and Mafic Emporer Emporer Volcanics may may have have formed in a backsuggest environment when when the the Penokean Penokean island island arcs, arcs,sutured sutured to to the the craton craton at 1860 ma ma arc spreading environment (Sims& et&aL. 1989),were were still still at at some some distance distance to to the south. (Sims , 1989), tuft beds are thickest and most numerous in the Kaministikwia The Gunflint lapilli tuff Kaministikwia near the apparent depositional edge of of the the unit unit. At tuff River gorge near At this this locality locality the lapilli tuff shalés. The beds are interbedded interbedded with carbonaceous carbonaceous shales. The lapilli lapilli are are mostly calcite-cemented and evidence of of sedimentary sedimentary reworking reworking(Shegelski, (Shegelski,1982). 1982).Although Althoughaagraded graded air-fall air-fallbed bed show evidence is present, the remaining beds may may have have been been accumulated accumulated by bysedimentation sedimentation shed shed from from the the Shield. The xenocrysts up up to to 2-3 2-3 rnm mm lapilli contain sanidine and quartz xenocrysts adjacent Archean Shield. The lapilli The Gunflint Volcanics in diameter, likely likely derived derived from from explosive explosive rhyolitic rhyolitic volcanism. volcanism. The Volcanics clearly are are not not viable viable sources sources for for these these constituents, constituents,and andthe the Emporer Emporer Volcanics are unlikely. unlikely. clearly The most likely source is a distal island arc, now highly metamorphosed in Penokean Penokean likely a distal island arc, now highly metamorphosed orogenic terrane. orogenic 18 �References References Goodwin, A.M., 1960, Gunflint Iron Iron Formation Goodwin, A.M., 1960, Gunflint Formation of the the Whitefish Whitefish Lake Lake area: Ontario Ontario Department of Mines, v. 69, Part 7, Department of Mines, v. 69,Part 7, p. p. 41-63. 41-63. Irving, living, R.D. and and Van Van Hise, Hise,C.R., C.R., 1892, 1892,The The Penokee Penokee iron-bearing iron-bearing series series of of Michigan Michigan and Wisconsin: U.S. Geological Survey Monograph 19, 534 Wisconsin: U.S. Geological Survey Monograph 19,534p. p. LaBerge, LaBerge, G.L, G.L,1992, 1992,The TheEarly EarlyProterozoic ProterozoicEmporer EmporerVolcanic VolcanicComplex: Complex:implications implicationsfor for the geology of the eastern Gogebic District, northern Michigan: Program the geology of the eastern Gogebic District, northern Michigan: Program & & Abstracts, Abstracts, Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology,38th 38th Annual AnnualMeeting, Meeting, p. p. 53-55. 53-55. Pearce, Pearce,J.A. JA.and andCairn, Cam,J.R., J.R., 1973, 1973,Tectonic Tectonicsetting settingof of basic basic volcanic volcanic rocks rocks determined determinedusing using trace traceelement elementanalyses: analyses:Earth Earthand andPlanetary PlanetaryScience ScienceLetters, Letters,v.v.19, 19,p. p. 290-300. 290-300. Shegeiski, R.J., 1982, The The Gunflit Gunflint Formation Formation in in the the Thunder Thunder Bay Bay area, area, j J.M. Shegelski, RJ., J.M.Franklin, Franklin, ed., Proterozoic Geology of the Northern Lake Superior area: Field Trip Trip 4, 4, ed., Proterozoic Geology the Northern Lake Superior area: Geological Association of Canada Mineralogical Geological Association of Canada - Mineralogical Association Association of Canada Canada Joint Joint Annual Meeting, p. 15-31. Annual Meeting, p. 15-31. Sims, W.R., Schulz, Schulz,KJ., KJ., and and Peterman, Z.E., Tectono-stratigraphic Sims,P.K., P.K., Van Schmus, W.R., Z.E., 1989, 1989,Tectono-stratigraphic evolution evolution of of the theEarly EarlyProterozoic ProterozoicWisconsin Wisconsin magmatic terranes of the the Penokean Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, O of Earth ~ Sciences, v. 26, p. p. 2145-2158. 2145-2158. Orogen: Canadian J a I I 100 .-U I— I I I I I I I . It az 0 .— 10 - 1= = . C-) . 00 It —. '—S I I I La Ce Nd SmEu Tb I Yb Lu Fig. Fig.1.1.Chondrite-nornialized Chondrite-normalizedrare rareearth earthelement elementplot plotfor forAnimike AnimikeGroup Groupvolcanics. volcanics.Solid Solid lines dashedlines linesmafic - Emporer lines- Gunflint GunflintVolcanics; Volcanics; short dashed mafic EmporerVolcanics; Volcanics;long longdashed dashedlines linesfelsic felsicEmporer EmporerVolcanics. Volcanics. - - - 19 I �GRANITOID ROCKS OF OF THE EWOT GRANITOID ROCKS ELLIOTLAKE LAKEAREA, AREA,ONTARIO ONTARIOAND ANDTHEIR THEIR RELATIONSHIP RELATIONSHIP TO TO U-Th-REE U-Th-FUSE BEARING BEARING PEGMAITIES PEGMATITES KISSIN, A. arid and FRALICK, FRALICK, Philip PhilipW., W., Dept. Dept.ofofGeology, Geology,Lalcehead Lakehead KISSIN, Stephen StephenA. University, Thunder Bay, Bay, ON ON P7B P7B 5E1, 5E1, Canada Canada Archean Archeangranitoid granitoidrocks rocksintrusive intrusive into into metavolcanic metavolcanic terrane terrane form formthe thefootwall footwall of of the the Huronian Supergroup in the Quirke Syncline of the Elliot Lake Huronian Supergroup the Quirke Syncline the Elliot Lake area, area,Ontario. Ontario. These These granitoids granitoids have never been been studied studied in in detail, detail, attracting attracting little interest interest in in relation relation to to U-ThU-ThREE FUSEdeposits depositsof of the theElliot ElliotLake Lakearea areabecause becauseofoftheir theirlow lowlevels levelsof of radioactivity radioactivity (Robertson, (Robertson, 1981; Charbonneau, 1982). 1981; Charbonneau, 1982). Recent Recentdiscovery discoveryof of U-Th-REE U-Th-REE bearing bearingpegmatites pegmatites(Kissin (Kissinand and Fralick, 1991) in the north footwall of Quirke Syncline indicate that the granitoids merit Fralick, 1991) the north footwall of Quirke Syncline indicate that the granitoids merit investigation investigation as as parental parentalbodies bodiestotothe thepegmatites. pegmatites. The granitoid body at the Huronian The granitoid body at the Huronianfootwall footwall has hasbeen beeninformally informally named named the the Kindioganii Kindiogami River River Batholith Batholith(Breaks, (Breaks,1991). 1991). ItIt consists consists of pink to to brick brick red, red, equigranular equigranular biotite booksand andclots clotsofofbiothe biotite asas biotitegranite. granite.The Thegranite graniteisisuniformly uniformlycoarse-grained, coarse-grained,with withbooks the themain mainmafic maficmineral mineral(CI (CIc<10), 10).with withlessor lessormuscovite muscoviteand andaccessory accessoryhornblende, hornblende,sphene, sphene, and zircon. and zircon Analyses Analyses of of seven seven granite granitesamples samplesand andone oneassociated associatedaplite apliteyield yieldhigh highSi02 SiO2(70-77 (70-77 wt wt%), %), high highA12O3 A1203(12-14 wt %) %)and and low lowMgO, MgO, CaO, CaO,and andT102 TiO, (most (most << 11wt wt %). %). Total Totaliron iron as asFe2O3 Fe,03 is variable variable (1-4 (1-4 wt wt %), %), but but 1120 H20 (generally TheK20 K20isisusually usually (generally<c 11 wt%) is low. The greater thanNa20. Na;0. InIna aShand Shanddiagram diagram(Fig. (Fig.1),I),the thegranites granitesare aresubaluminous subaluminoustotoslightly slightly greaterthan peraluminous, peraluminous, whereas whereas associated associated pegmatites pegmatites are aremetaluminous metaluminous to toperaluminous. peraluminous. Some trace elements, notably Cs, Be, Sc, Ni and Cr are depleted, Some trace elements, notably Cs,Be, Sc,Ni and Cr are depleted,whereas whereasothers, others, notably Nbare areenriched enrichedrelative relativetotomost mostgranitoids. granitoids. Rare Rareearth earth notably Th, U, U, Zr, Zr, Ta, Ta,and andNb , elements elements exhibit exhibit aa roughly roughly linear linear trend trend of ofheavy heavy REE REEdepletion depletionand andslight slighttotonegligible negligible negative negative Eu Euanomalies anomaliesininaachondrite-normalized chondrite-normalizedplot plot(Fig. (Fig.2). 2). Application Maniarand andPiccoli Piccoli(1989) (1989)classifies classifiesthe the Applicationof ofthe thediscrimination discriminationcriteria criteriaofofMan.iar rocks rocksas aspost-orogenic post-orogenicgranitoids. granitoids. Although Althoughininthe theI-,I-,S-, S-,A-, A-,and andMM-classification classificationbased based on on petrographic petrographiccharacteristics characteristics(e.g., (e.g., Pitcher, Pitcher, 1983), 1983), the the rocks rocks have have the the general generalcharacteristics characteristics of al.,1987), 1987).they theydo donot notfulfil fulfilthe themore moredetailed detailed of A-type A-type (anorogethe) (anorogenic)granitoids granitoids(Whelan (Whelanetetal., . . . trace element discrimination criteria. Their parentage appears to be mixed, anorogenic with tion criteria. Their parentage appears to be mixed, anorogenic with trace element discrumna an anorogenic orogenictype typegranitoid. granitoid. The Thepegmatites pegmatitesthemselves themselvesexhibit exhibitaamixed mixedgeochemical geochemicalsignature signatureaccording accordingtotothe the criteria criteriaof ofèerny fiemy(1991a). (1991a). Although Althoughthey theybear bearmany manycharacteristics characteristicsof of rare-earth rare-earthpegmatites pegmatites of relative enrichment in Nb >> Ta, NYFfamily family of of rare-element rare-elementpegmatites pegmatites including including relative Ta, of the theNYF Zr, Zr,U, U,Th, Th,and andF,F,they theylack lackenrichment enrichmentin inY, Y,Sc Sc and and REE. FUSE. These Thesepegmatites pegmatitesseem seemtotofitfit into intothe themixed mixedfamily familyof of rare-element rare-elementpegmatites pegmatitesininwhich which NYF NYFcharacteristics characteristicsare arediluted diluted by by LOT LCTpegmatite pegmatiteattributes. attributes. The The bulk bulk compositions compositions lack lack the thesubaluminous subaluminous toto metaluminous of NYF pegmatites, and the metaluminous composition composition of pegmatites, and the associated associated granitoids granitoids of of this this pegmatite pegmatite group groupbear beara amixed mixedgeochemical geochemicalsignature. signature. Parental Parentalgranitoids granitoidsbear bearmany many characteristics characteristics of of anorogenic anorogenicgranites, granites, as asin inthe thecase caseofofKindiogami KindiogamiRiver RiverBatholith, Batholith,they they appear appeartransitional transitionaltotoother othertypes. types.ëerny fiemy(1991b) (1991b)has hassuggested suggestedthat thatsuch suchmixed mixedpegmatites pegmatites may may arise arisefrom: from: 1) 1)anatectic anatecticgranites granitesderived derived from from partially partially depleted depleted crust; crust; 2) 2) anatexis anatexis of of �both by both depleted depleted and andundepleted undepletedcrust, crust,or or3)3)ananNYF NY.Fmagma magmabecoming becomingcontaminated co assimilation of undepleted material. assimilation of undepteted material. Whatever Whatever the theultimate ultimatesource sourceof ofthe granites of the Kindiogami Batholith, they and their associated pegmatites are distinctive their associatedpegmatites are distinctiveand provide a plausible proximal source for detrital Huronian Supergroup. The pegmatite field detrital U, U,Th, Th, and andREE REEdeposits depositsininthe the associated associatedwith roof and proximal regions may have been largely removed by the effects of erosion. pegmatitic deposits in the Arabian Shield have been found to be both large erosion.Similar S and al., 1985). andof ofhigh highgrade grade(Jackson (Jacksonet£t-aL 1985). . \ References Breaks, F.W., 1991, Project Unit 91-10. Geology of the Rocky Island Lake - Lac aux Sables area, jjj Sunimaiy of field work and other activities: Ontario Geological Survey Miscellaneous Paper 157, p. 40-45. èerny, P., 1991; Rare-element granitic pegxnatites. Part I: Anatomy and internal evolution of pegmatite deposits: Geoscience Canada, v. 18, p. 49-67. ëerny, P., 1991b, Rare-element granitic pegmatites. Part II: Regional to global environments and petrogenesis: Geoscience Canada, v. 18, p. 68-81. Charboneneau, B.W., 1982, Radiometric study of three radioactive granites in the Canadian Shield: Elliot Lake, Ontario, Fort Smith and Fury and Hecla, N.W.T., j1 Uranium in granites: Geological Survey of Canada Paper 81-23, p. 91-99. Jackson, NJ., Drysdall, A.R., and Stoeser, D.G., 1985, Alkali granite-related Nb-Zr-REE-U- Th mineralization in the Arabian Shield, jg High heat production granites, hydrothermal circulation and ore genesis: London, The Institution of Mining and Metallurgy, p. 479-487. Kissin, S.A., and Fralick, P.W., 1991. A possible pegmatitic source for the Elliot Lake paleoplacer deposits: Program with Abstracts, Geological Association of CanadaMineralogical Association of Canada - Society of Economic Geologists, Joint Meeting, v. 16, p. A66. Mainar, P.D., and Piccoli, P.M., 1989, Tectonic discrimination of granitoids: Geological Society of America Bulletin, v. 101, p. 635-643. Pitcher, W.S., 1983, Granite type and tectonic environment, K. Hsu, ed., Mountain building processes: London, Academic Press, p. 1940. Robertson, J.A., 1981, The uranium deposits of Ontario - their distribution and classification: Ontario Geological Survey Miscellaneous Paper 86, 37 p. Whelan, J.B., Currie, K.L, and Chappell, B.W., 1987, A-type granites: geochemical characteristics, discrimination and p&rogenesis: Contributions to Mineralogy and v. 95, p. 407-419. Petrology, I I I I �it 1000 — 5 Ui I- 100 - cc C z0 0 0 0 cc NA 14 IC - 14A 13 II 12 I-——- I La Ce I SmEu Nd I I I Tb Yb Lu River Fig. 1. Chondrite-normalized rare earth element plot for granites of the Kindiogaini River Batholith of the Elliot Lake area. 18 I.- a 0 0c'.j [4 + o [2 c'J a z U) o Cu 08 C 06 06 08 10 + + [4 I6 /(CaO AlgOs CaO + Na20 NapO+ 1<20) KpO ) molar 41203 /( 2.. Shand (crosses) of of the the Elliot Lake area. area. Fig. 2 Fig. Shand diagram diagram for for granites granites (circles) and pegmatites (crosses) ' 22 �I p STRUCTURAL STRUCTURALEVCIUTION EVOLUTIONOF OFTHE "MEEASTERN EASTERNGOGEBIC GOGEBICRANGE RANGE NORTHERN NORTHERNMICHIGAN MICHIGAN John John S. 61455 S. Kiasner, Klasner,Department DepartmentofofGeology, Geology,Western WesternIllinois IllinoisUniversity, University, Macomb, Macomb, ILIL61455 and andU. U. S. S. Geological Geological Survey, Survey, and and Gene GeneL.L.LaBerge, LaBerge,Department DepartmentofofGeology, Geology,University Universityof of Wisconsin, Oshkosh, WI 54901 and U. S. Geological Survey Wisconsin, Oshkosh, Wl54901 and U. S. Geological Survey The range is is an an area area of of outcropping, outcropping,iron-bearing iron-bearingrocks rocks that that extends The eastern eastern Gogebic Gogebk range extends Lithostratigraphic some 100 km from northern Wisconsin to northern Michigan. some 100 km from northern Wisconsin to northern Michigan. Lithostratigraphic relationships relationships (LaBerge (LaBerge and and Klasner, Klasner, this this volume) volume) indicate indicate that that Early EarlyProterozoic Proterozoic(EP) (EP) volcanic volcanic and andsedimentary sedimentary rocks rocks of of the the Menominee Menominee Group Groupwere weredeposited depositedininaadeveloping, developing,fault-bounded fault-bounded trough trough in inthis thisregion, region,much muchlike like the the Marquette Marquette trough trough some some 180 180 km km to to the the east. east. Following Following this this extensional extensionalevent, event, EP EPstrata strataof of the the Copps Cows formation formation were were deposited deposited in inaa compressional compressional foreland foreland basin. basin. All All EP EPstrata stratawere werethen thensubjected subjectedto toatatleast leasttwo twopenetrative, penetrative,thin-skinned, thin-skinned, fault compressional events, and subsequently to a series of thick-skinned compressional events, and subsequently to a series of thick-skinned fault events events that that affected affected Much later, these deformed strata weretilted northward both Archean and EP strata. both Archean and EP strata. Much later, these deformed strata were tilted northwardduring during the the formation formationofofthe theMiddle MiddleProterozoic Proterozoic(MP)Midcontinent (MP)Midcontinent Rift Rift (Cannon (Cannon and and others, others. 1993). 1993). COMPRESSIONAL COMPRESSIONALEVENTS EVENTS underlying Archean D1 During this this initial initial event event most ER EP strata were detached from underlying Archean Dl - During basement, creating northeast-trending folds and north-verging, bedding-parallel shears basement, creating northeast-trending folds and north-verging, bedding-parallel shears in in the the supracrustal supracrustalsequence. sequence. D2 Dl folds folds in the the EP EPstrata stratawere werefurther further Da- - Both Boththe thebedding-parallel beddina-parallelshears shears and and Di deformed into a series of gently northeast-plunging folds that also appear to be detached deformed into a series of gently northeast-plunging folds that also appear to be detachedfrom from Archean inasmuchas as Dl Dj and and D2 D2 structures structures have have not not been been found found in in the the basement Archean basement basement inasmuch basementrocks. rocks. 0 3 - Folds Folds of of aa third third event, event, overprinting overprinting Di Dl and and D2 D 2were wereobserved observed ininaafew few places. places. These These folds folds may maybe berelated relatedto to later laterfaulting faultingassociated associated with with the the Presque Presque Isle Isle set set (see (see below). below). - - - The Copps Copps formation formationwas was deposited depositedin inangular angular unconformity unconformity on on underlying underlying EP EP strata, The (see in the the Cows Coppscontain containclasts clasts that that (see LaBerge and Klasner, Klasner, this volume). volume). Basal Basal conglomerates conglomerates in indicate ChocolayGroups Groups were were the the source. sourceevidence evidence implies implies that, indicate Menominee and Chocolay source. This source prior to to deposition depositionof of the the Copps, Copps, there must have been some uplift upliftofofpre-Copps pre-Coppsstrata, strata, prior Because the Copps strata and the underlying EP strata possibly as a forearc bulge. the underlying EP strata all all possess possess possibly as a forearc bulge. folds and axial planar foliation), we suggest the same same structural structuralpattern pattern(northeast-trending (northeast-trending planar foliation), suggest that the the structural structural evolution evolution of of the the whole whole ER EP stratigraphic stratigraphic sequence is the the result result of of aacontinuum continuum deformation that occurred after deposition of Copps of north-verging deformation that Copps of coaxial, coaxial, thin-skinned, thin-skinned, north-verging that strata. strata. FAULTEVENTS EVENTS FAULT Other of deformation in in the thp eastern eastern Gogebic Gogebiciron iron range range are found in in three Other manifestations manifestations of sets --the Lithe Presque Isle set, the Presque Isle set, and the Sunday Lake set. fault sets -the Little Presque Isle set, the Presque Isle set, and the Sunday Lake set. - Little Little Presque Presque Isle Isle fault set set -- Faults of of this thisnorth-northeast-trending north-northeast-trending set, set, fault especially as extensional extensional growth growth faults, faults, but they especially the the Little LittlePresque Presque Isle Islefault, fault, formed early as in were later later reactivated reactivatedin in Middle Proterozoic (MP) time. This continued movement resulted in truncation juxtapositionofof EP EP strata in the northeast-trending Wolf Mountain anticline anticline truncation and juxtaposition were against Archean occurs in in an en echelon pattern pattern along along the the southwest southwest Archean rocks. The juxtaposition occurs This interpretation is supported by magnetic extension of the Little Presque Isle fault. extension of the Little Presque Isle fault. This interpretation is supported by magneticdata. data. of the the Little LittlePresque PresqueIsle Isleset set cut cut the the unconformable unconformable contact contactbetween betweenMP MPKeweenawan Keweenawan and and Faults of underlying them. Faults underlying EP EP and andArchean Archean strata, also also indicating indicating late late MP MP movement movement on on-them. , �Presque Isle Isle fault faultset set- -The Thesouth-side-up, south-side-up,east-northeast-trending east-northeast-trending Presque Presque Isle Isle Group depositional depositionaltrough. trough. We suggest that, fault marks the southern southern edge of the Menominee Group Isle fault fault was was aa growth like the Little Little Presque Presque Isle fault, the Presque Presque Isle growth fault. fault. Other parallel parallel faults of the the Presque PresqueIsle Isleset set cross cross cut cut and and offset offset the the Little Little Presque Presque Isle Islefault fault near nearthe the core coreof of the the Wolf Mountain anticline, anticline, giving the the Little Presque Presque Isle Isle fault fault its its en echelon pattern in this Wolf region. region. - Sunday Lake fault Sunday Lake fault set set The south-side-up, south-side-up, left-lateral left-lateral Sunday Lake fault fault truncates the parallel faults faultsof of this this set set occur to the north, one at at truncates the Presque Presque Isle Isle fault. Several parallel where conspicuous conspicuous shearing the Copps Mine Mine exploration exploration prospect where shearing and associated associated mineralization is found. found. Formation of .the the Midoontinent Rift resulted resulted in in northward northwardtilting tilting (up (up to 70 degrees) Formation-of Midcontinent Rift degrees) of Archean, EP easterly tending the Archean, trendingaxis. axis. The Thenortheast-trending northeast-trending EPand and MP MP strata strata along an easterly depositional trough troughwas wasalso alsorotated rotatedso sothat that the the map mappattern pattern is a view looking lookingdown downthe the original original - the the Uttle LittlePresque Presque Isle Isle fault forming the northern northern edge of of the the trough trough and and keel of the trough -edge. During the Presque Isle fault forming the southern edge. During MP rotation, faults of the the Little Little offsetting the EP-MP Presque Isle Isle set were were reactivated, reactivated, offsetting EP-MP unconformity. unconformity. REFERENCES CITED CITED Cannon, W. F F., Z. E E., ., and and Sims, Sims, P. P. K., K., 1993, 1993, Crustal-scale thrusting and origin of Cannon, W. ., Peterman, Peterman, 2. cross section of the 35-kilometer-thick cross the Midcontinent Midcontinent rift the Montreal River River monocline monocline -- aa 35-kilometer-thick in northern Michigan: Tectonics, v. 12, p. 728-744. northern Michigan: Tectonics, v. 12, p. 728-744. - LaBerge, G. E., E., and and Kiasner, Klasner, J. J. S., S., 1994, 1994, Lithostratigraphic Lithostratigraptlirelations relations on on the the east eastGogebic GogebiiRange: Range: implications on tectonism in the Penokean Orogen: Orogen: Institute on Lake Lake Superior Superior Geology, Geology, this this volume. 24 �p NEW ARCHEAN-HOSTED ARCHEAN-HOSTED PSEUDOTACHYLITE OCCURRENCES, WESTERN WESTERN NEW PSEUDOTACHYLITE OCCURRENCES, LAKESUPERIOR SUPERIOR REGION REGION LAKE KROPF, Elizabeth P., WIRTH, WIRTH, Karl Karl R. R. and and CRADDOCK, CRADDOCK,John John P., P., Geology Geology KROPF, P., Dept., Macalester Dept., MacalesterCollege, College, St. St. Paul, Paul, MN M N 55105 55105 Pseudotachylite occurrences were were recently discovered discovered in in the the western Lake Superior region hosted in Falls, MN MN (Minnesota River Archeanrocks: rocks: 1) 1) Granite Falls, in aa variety variety of of Archean Valley terrane), 2) Deer Lake complex, MN (Wawa terrane), Valley terrane), Lake complex, MN (Wawa terrane), 3) Rossport, ONT ONT (Wawa terrane). terrane). All All of of these these pseudotachylites pseudotachylitesare areadjacent adjacentand and parallel parallel to to mafic (Wawa dike swarms, swarms, in contrast to the pseudotachylite dated and and described described by by Peterman Peterman pseudotachylite dated and Day (1989) along the the Rainy Rainy Lake Lake fault fault in in the the Wabigoon Wabigoonterrane terrane in in western western (1989) along Ontario. Granite Falls, Falls, MN MN Granite Pseudotachylite has been discovered crosscutting folded folded Archean Archean amphibolite-grade amphibolite-grade host rocks of of the the Minnesota MinnesotaRiver RiverValley Valleyterrane terrane(Himmelberg, (Himmelberg,1968; 1968; Bauer, Bauer, 1980) 1980) near Granite Falls, MN. The pseudotachylite is parallel to the regional foliation Falls, MN. The pseudotachylite is parallel to the regional (N70°E,75 75° N),isis<<2 cm in in width, can be traced m, and and contains (N70°E O N), 2 an traced in in outcrop outcrop for for —50 -50 m, "amygdules" of calcite (diameter: .5 cm; Fig. 1), calcite-quartz mixes, and plagioclase 'amygdules" of (diameter: an; Fig. I), calcite-pahz mixes, and plagioclase inclusions in calcite. Mafic Mafic dikes, which cross-cut cross-cut the Kenora-Kabetogama swarm (—2.2Ga), Ga),are arealso alsoparallel paralleltotothe thepseudotachylite pseudotachyliteare areaanumber numberof of calcite calcite veins. veins. The The (-2.2 outcrop is located 70 70 km km to the south of the boundary between the Wawa (north) terranes. The is and (south) terranes. and Minnesota Minnesota River River Valley Valley (south) The pseudotachylite pseudotachylite is compositionally layered along its margins and preserves some relict flow foliation compositionally layered along its margins and preserves some relict Dextral winged winged swirls defined by inclusions inclusions (Fig. (Fig. 2) 2) and and "amygdules" "amygdules" of calcite. calcite. Dextral porphyroclasts are present and preserve the displacement sense porphyroclasts the opposite opposite kinematic displacement of S-C S-C structures structures in the country calcite is is mechanically mechanically twinned twinned country rock. rock. The amygdule calcite 'of and preserves a horizontal shortening axis (magnitude: -0.74%) that is parallel (magnitude: -0.74%) that is parallel to of the pseudotachylite. Two Two phases phases of of calcite calciteveins veinsare are present, present, one set the strike of preserves twinning strains (shortening magnitude: -2.5%) identical those in in the magnitude: -2.5%) identical totothose calcite amygdules. amygdules. The The second second vein veinset set contains contains aa horizontal, horizontal, veinpseudotachylite calcite pseudotachyliteshortening perpendicular strain (magnitude: -2.4%). Inferred differential shortening strain (magnitude: -2.4%). Inferred differential stresses for the different twinning strains are and 200 MPa (calcite the are 66 66 MPa MPa (pseudotachylite) (pseudotachylite) and 200 MPa veins). Deer Lake MN Deer Lake Complex, Complex, M N This Archean ultramafic complex isis composed of interlayered This Archean ultramafic complex composed of interlayered gabbro, gabbro, peridotite and and pyroxenites pyroxenites (Jirsa, (Jirsa, 1990) 1990) in Itasca county. The Kenora-Kabetogama Kenora-Kabetogama mafic dikes (strike: (strike: N45OW) N45°W)crosscut crosscutthe thecomplex complexand, and,parallel paralleltotothe the dikes, dikes, are a mafic number zones which which are locally thin (1-5 (1-5 mm), mm), regularly-spiced regularly-spaced cataclastic cataclastic zones locally number of of thin mylonitic and contain contain some some pseudotachylite pseudotachylite material. material. Ross port, ONT Rossport, Archean granites granites and granodiorites along Lake Lake Superior Superiorare arecrosscut crosscutby by 22 thin thin Archean pseudotachylites(5 (5mm mm wide) wide) which which were were locally locallyinjected injectedininthe the country country rock. rock. pseudotachylites Maficdikes dikes of of unknown unknown age age are are adjacent adjacent and and parallel parallel to to the the pseudotachylite pseudotachylite veins Mafic (strike: N-S). (strike: 25 �Foliated Granite Falls Falls pseudotachylite pseudotachylite (width=2cm) with with calcite calcite amygdules. amygdules. Figure 1: Foliated Figure 2: 2: Close-up Close-upof of swirled swirledporphyroblast porphyroblastfrom fromFig. Fig.1.1.View Viewisis3.5X2.2 3.5X2.2 mm. REFERENCES REFERENCES Bauer, R.L., area, Minnesota River River R.L., 1980, Multiphase deformation deformation in in the. the,Granite Granite Falls-Montevideo Falls-Montevideo area, Valley: in in G G.B. Moreyand and G.N. G.N. Hanson Hanson (eds.), (eds.), Selected SelectedStudies StudiesofofArchean ArcheanGneisses Gneissesand and Lower Lower Valley: .B. Morey SpecialPaper Paper 182, 182,p.p. 1-17. Proterozoic Rocks, Southern Canadian Shield, C. G. S. A. Special 1-17. Himmelberg, Geology of of Precambrian Precambrian Rocks, Rocks, Granite Granite Falls-Montevideo Falls-Montevideoarea, area, southwestern southwestern Himmelberg, G.R., G.R., 1968, 1968,Geology Minnesota: Minnesota Minnesota Geological Survey Survey Publication SP-5. Minnesota: SP-5. M., 1992, 1992,Bedrock Bedrockgeologic geologicmap mapofofnortheastern northeasternItasca Itascacounty, county,MM: MN:Minnesota MinnesotaGeological Geological Survey Survey Jirsa, M., Map M-86. Map Peterman, Z. E. on Archean Archean faults faults in in the the western E. and andDay, Day,W., W., 1989, 1989,Early Proterozoic activity on Superior provinceevidence from pseudotachylite: Geology, v. 17, p. 1089-1092. Superior province- evidence from pseudotachylite: Geology, v. 17,p. 1089-1092. 26 �N I TECTONIC TECTONIC IMPLICATIONS OF EARLY PROTEROZOIC LITHOSTRATIGRAPHY ON P1 I 4 I I I I I . THE EASTERN EASTERN GOGEBIC GOGEBIC RANGE, NORTHERN NORTHERN MICHIGAN MICHIGAN GENE L. L.aBERGE, Department of Geology, UW Oshkosh, Oshkosh, WI LaBERGE, Department of Geology, U W Oshtosh, WI 54901 54901 and U.S. U.S.Geological Geological Survey Survey and JOHN JOHN S. KLASNER, KLASNER, Department Department of Geology, Geology, Western Illinois illinois University, Macomb, IL IL 61455 and U.S. Geological Geological Survey. Survey. Our recent mapping on the eastern Gogebic range reveals abrupt abrupt changes in stratigraphy stratigraphy and and structure that occur mainly mainly at at the newly discovered discovered Little Little Presque Presque Isle Isle fault east east of Wakefield, Michigan. Michigan. These Thesechanges changeshave have an animportant importanthearing bearing on on interpretations inteipretationson on history and and tectonic tectonic evolution evolutionof of this this part part of the Penokean orogen. depositional history In the the western western part of of the the map map area area (Figure (Figure1), I), the thePalms PalmsFormation Formationand andunderlying underlying Chocolay Group Group form form aa northdipping north-dipping stratigraphic stratigraphicsequence. sequence. These strata are not not exposed exposed Chocolay strata are east of of the Little Presque Isle fault, although immediately east although the the Palms Palms Formation Formation reappears reappears 10 10 Similarity in lithology of the Palms in the two areas suggests that it was km to the east. east. of areas deposited as a continuous continuous stratigraphic stratigraphic unit. Its absence in the 10 10 km Ioninterval interval is is probably probably aa of faulting (Klasner and LaBerge, this volume). consequence consequence The The Ironwood Iron-formation, which overlies the Palms Formation, Formation, shows shows abrupt abrupt changes within within the the map maparea. area. For For nearly nearly 100 100km Ion to to the thewest, west, ititconsists consists of of alternating alternating units iron-formation with with relatively relativelyuniform uniformthickness. thickness. However, east of granular and laminated iron-formation of the Little Little Presque Presque Isle Isle fault the the Ironwood appears to be be much much thicker, and and isiscomposed composed mainly of laminated iron-formation. There is is also also an an abrupt abrupt change change in the the Emperor Emperor Volcanic Volcanic Complex, which is is interbedded with the the iron iron formation, formation,across acrossthe theLittle LittlePresque PresqueIsle Islefault. fault. To the west, the interbedded with Emperor is mainly basalt flows and diabase sills. To the east, the volcanic rocksare aremainly mainly Emperor basalt flows and diabase sills. To the east, the volcanicrocks and felsic hyaloclastites hyaloclastites of of rift-related rift-related tholeiites. tholeiites. The mafic pillow breccias and Thecombined combined thickness of iron-formation and volcanic volcanic rocks changes abruptly across the Little Presque Presque Isle Isle fault. West meters. East Westof ofthe thefault, fault,the thethickness thickness is is about about 250-300 250-300 meters. East of of the thefault, fault, the the is much much greater but cannot be accurately measured thickness is measured because of structural complexities. complexities. We interpret these relationships to indicate that the Little Presque Isle fault was active during deposition of of the iron-formation. iron-formation. The area east east of of the theLittle LittlePresque Presque Isle Islefault fault appears appears during deposition The area to be aa remnant of a graben-like structure bounded by the Little Presque Isle and Presque remnant a graben-lie structure Little Presque Isle and Presque Isle Isle faults. faults. The change from granular to laminated laminated facies of iron-formation iron-formation suggests suggests a change change from shallow-water shallow-water deposition deposition in in the the west west to to deeper water deposition in a developing trough to the east. The rockswithin within the thepostulated postulated graben suggests suggests that Theincrease increaseininvolcanic volcanicrocks bounding faults may have served as channelways for the magmas. These relationships are bounding may have served as channelways for the magmas. interpreted to indicate indicate that rifting rifting occurred occurredduring duringiron-formation iron-formationdeposition. deposition. Older geological geological literature literature refers refers to a number of "ianges" south "ranges" south of of the theGogebic Gogebic Early Proterozoic Proterozoic iron-formation. iron-formation. These district district that contain Early These include the Marenisco, Turtle, Manitowish, Vieux Desert, Desert, and and Conover Conover "ranges" "ranges"of of Alien Allenand andBarrett, Barrett,(1915). (1915). They, and Manitowish, Vieux Dutton and Bradley (1970), and Prinz (1981) showed that these areas areas contain contain iron-formations iron-formations other sedimentary rocks interbedded with volcanic rocks. We suggest that these and sedimentary rocks with volcanic rocks. We suggest "ranges" 'ranges" may represent graben-like environments similar to that on the eastern eastern Gogebic Gogebic range. If so, these various "ranges" may represent a series of grabens formed on these "ranges" may series grabens formed the the rifted rifted range. continental margin that were intensely deformed during continental during later later convergent convergenttectonism. teetonism. I I 27 �In the eastern Gogebic range range the the Coops Copps Formation Formation of of the Baraga Group Group overlies overlies the the iron-formation and and other other rocks rocks with with marked marked unconformity unconformity(Figure (Figure 1). 1). A basal conglomerate A basal conglomerate with cobbles of of iron-formation, iron-formation, volcanic volcanic rocks rocks similar similar to to the the Emperor, Emperor, and Archean granitoids, as well as as complete complete removal of the the Menominee Menominee and Chocolay Group Group rocks rocks demonstrate the the unconformable unconformablerelationships. relationships. We We interpret interpret the the Copps Copps to to represent representaa demonstrate sequence of of turbiites turbidites deposited deposited in in aa foreland basin basin on eroded remnants of rocks rocks deposited deposited rifled passive margin. earlier on a rifted References Cited Allen, R.C., R.C., and of northern northern Alien, and Barrett, Barrett, L.P., L.P.,1915, 1915,Contributions Contributionsto to the the pre-Cambrian pre-Cambrian geology of Michigan and and Wisconsin: Wisconsin: Michigan Michigan Geol. Geol. and and Biol. Biol. Survey SurveyPub. Pub. 18, Geol. Geol. Ser. Ser. 15, Michigan p. 65-129 p. 65-129. Dutton, C.E., R.E., 1970, 1970,Lithologic, Lithologic,geophysical, geophysical, and and mineral mineral commodity commodity Dutton, C.E., and and Bradley, Bradley, R.E., maps of of Precambrian Precambrianrocks rocksininWisconsin. Wisconsin: U.S. U.S. Geol. Geol. Survey Survey Misc. Misc. Geol. Geol. Inv. mv. Map Map maps 1-631. 1-631. Klasner, J.S., J.S., and G.L., Klasner, and LaBerge, L-ge, G.L., 1994, 1994,Structural StructuralEvolution Evolution of of the the Eastern Eastern Gogebic Gogebic Range, Northern Michigan: 40th Institute on Lake Superior Geology, Abstracts and Northern Michigan: 40th Institute Abstracts and Proceedings, this this volume. W.C., 1981, Geologic Prinz, W.C., 1981, Geologic map map of the the Gogébic Gogebic Range-Watersmeet Rangewatersmeet area, Gogebic and Ontonagon Counties, Counties, Michigan, Michigan, Misc. Misc. Inv. mv. Series SeriesMap Map 1-1365 1-1365. Ontonagon Trent, V.A., V.A., 1973, Geological map of the Marenisco and Wakefield 1973, Geological map the Marenisco and Watefield NE quadrangle, Gogebic County, County,Michigan: Michigan: U.S. U.S. Geol. Survey File Report, Open Pile Report, scale 1:48,000. 1:48,000. Gogebic Survey Open LAKE -A- OGEBIC vs C) .ç S -, 55 ¶ V S $5 S si f 5_____ 5 5 Sc 0 () ç Figure 1. Figure 1. KM $ 1•I ,j Sketch nap mapofofthe the geology geology of of the Sketch the eastern easternGogebic Gogebic range range showing showing (Modified the major majorlithologic lithologic units units and and sstructural the t r u c t u r a l features. features. (Modified Trent, 1973, 1973, and and Prinz, Prinz, 1981.) ffrom r o m Trent, 1981.) 28 �U RELEASE HOSTED GOLD RELEASE OF ACID AND TRACE METALS FROM QUARTZ-CARBONATE HOSTED GOLD MINE TAILINGS TAILINGS fl LAPAKKO, K. A. A. and and WESSELS, WESSELS, 1. I. N., N., Division Divisionof of Minerals, Minerals, Department Department of of Natural Natural Resources, Resources,500 500 Lafayette Road, Box 45, St. St. Paul, Paul, Minnesota, Minnesota, 55155-4045. 55155-4045. Exploration for gold Exploration for gold (and (and other other non-ferrous non-ferrous minerals) minerals) is is presently presently occurring occurring in inMinnesota. Minnesota. Prior to mineral resource development, the potential mine wastes must be characterized wastes characterized and the the quantity quantity and and development, potential quality of drainage projected. This will be be used used to identilS' the types of drainage projected. T his infonnation information will identify the of mine mine waste waste management and drainage control required to protect protect the water water resources resourcesof of the thestate. state. Little information information characteristicsof, of, or or drainage quality qualityfrom, from, such such mining mining wastes. wastes. The has been compiled on the characteristics The lack lack of of management such information will inhibit the effectiveness and efficiency of drainage quality prediction and delay inhibit effectiveness efficiency of development of techniques to mitigate of this project was to development mitigate the the problems problems identified. identified. The objective objective of to characterize and determine release of acid and trace metals from tailings which are representative representative of characterize mining potential mining wastes wastes from from Minnesota. Minnesota. Ten tailings samples were from operating operating North North American American gold gold mines. mines. These sampleswere collected from Thesesamples samples of tailings tailings which which might might be generated provide the best best presently presently available available approximation approximation of generated ifif present present provide exploration belt exploration exploration site site in in Minnesota. Minnesota. The explorationled to development of a greenstone belt Thegeologic geologicsettings, settings, hydrothermal quartz-carbonate hosted hosteddeposits, deposits, from from which which the the gold mine tailings were hydrothermal quartz-carbonate were collected collected are are The gold tailings to a majority of those presently under exploration in Minnesota. similar a majority of those presently under exploration in Minnesota. gold tailings were were similar characterized and subjected to dissolution testing testing for 151 weeks to to examine the relationship between the solid-phase characteristics and release of acid and trace metals. fine, with 47% 47% to 97% 97% of each sample occurring occurring in the minus 270 mesh The samples were quite fine, fraction The and 26% 26% to 91 % in the minus 500 mesh fraction. The total sulfur contents, an indicator of acid 91% in the minus 500 mesh fraction. content, an indicator production potential, potential, ranged ranged from from 0.1% 0.1% to 7.63%. production 7.63%. The carbon dioxide dioxide content, indicator of neutralization potential, ranged from 0.61 0.61% % to 21.85%. 21.85%. Most Most of the the sulfur sulfurwas wasassociated associated with with pyrite pyrite and and pyrrhotite, pyrrhotite, with with iron ironsulfide sulfideminerals minerals constituting 0.58% 0.58% to 13.6% constituting 13.6% by by weight weight of of each eachsample. sample. Total calcium carbonate carbonate plus plus magnesium magnesium content varied varied from from 1.4% 1.4% to to 21 21%. %. Siderite Siderite was was present present in in appreciable appreciable amounts (14% (14% carbonate mineral content 31% and in minor minor amounts amounts (0.1 (0.1% and 31 % by weight) in two samples and % to 1.9%) 1.9%) in in seven seven samples. samples. Three samples contained contained ankerite ankerite(Lapakko, (Lapakko, 1992). 1992). The major rock forming minerals minerals were were quartz quartz (16%-44%), (16%-44%), feldspar (1 %-37%), mica (4%-24%), and chlorite (2%-21 %). feldspar %-37%), (4%-24%),and chlorite (2%-21%). wet-dry cycle dissolution test was conducted A wet-dry conducted on the the tailings tailings (Lapakko, (Lapakko, 1994). 1994). The 75-g 75-g reactors in in aacontrolled controlledtemperature temperature and andhumidity humidityroom, room, and rinsed rinsed samples (as received) were placed into reactors mL of of distilled water. The ThepH pHofofdrainage drainagefrom fromone onesample sample(T9) (T9) was was neutral neutral for for 120 120 weekly with 200 ml. after 122 weeks of dissolution, and reached reached 3.45 after 151 weeks. weeks, dropped below 6.0 122 151 weekly Nine samples drainage (generally at at or or above above pH pH 8) throughout throughout the the experiment. samples produced alkaline drainage Based of three of these Based on the composition of these samples and their rates of of iron ironsulfide sulfideand andcalcium calcium plus plus carbonate mineral dissolution (as indicated by the rates of sulfate, calcium, and magnesium magnesium dissolution (as indicated by the rates of sulfate, magnesium drainage), their after six sixto tofourteen fourteenyears. years. Based release in drainage), their drainage drainage could become acidic after Based on on similar similar data data analysis it was concluded that the six remaining samples, terminated after after 57 57 weeks weeks of of dissolution, dissolution,would would to produce alkaline to to neutral neutral drainage. drainage. For For the theestimates estimateson onthese these nine ninesamples, samples,assumptions assumptions continue to were required which lend uncertainty to the predictions. More accurate estimation requires More accurate estimation requiresadditional additional information on the formation of coatings on the surfaces of of sulfide and and carbonate carbonate minerals minerals present present in the waste. mine waste. mine A relationship rates and solid-phase sulfur sulfur wntent content of the samples was relationship between sulfate release rates determined by regression analysis. Samples which were inconsistent with the relationship defined, as well determined regression Samples which were inconsistent relationship as some "typical" as "typical"samples, samples, were were analyzed analyzed for for specific specific surface surface area (BET) and surface surface morphology morphology (SEM). (SEM). release rates rates were apparently apparently due due to to differences differences in in pyrite specific surface area The anomalous sulfate release 29 �resulting from from variations in pyrite There was was no apparent resulting variations in pyrite particle particle size size and and morphology. morphology. There apparent evidence evidence that something something other other than the the pyrite pyrite surface area was controlling the the rates of pyrite oxidation. oxidation. suggesting that (maximum concentrations concentrationsofof 140 140to to 4900 4900 pg/L) jigiL) were were observed observed Elevated arsenic concentrations (maximum T7, T8, and 19, contentsgreater greater than than 1000 1000 ppm. ppm. in drainage from solids T7, T9,which which had had solid-phase solid-phase arsenic contents A fourth sample (T6) had had a solid-phase arsenic arsenic content contentof of 1200 1200ppm, ppm,but butno noarsenic arsenic was was detected detected in in the the laboratory drainage. Elevated antimony concentrations (250 to 2800 jzglL) were observed observed in in drainage drainage laboratory draiinage. Elevated antimony concentrations to pg/L) were from T7, T7, T8, contentsofof20 20ppm, ppm,40 40 ppm, ppm, and and 290 from T8, and and T9, T9,with withsolid-phase solid-phase antimony antimony contents 290 ppm, ppm, in excess excess of of 700 700 pg/L j.tg/Lwwas observedin indrainage drainage respectively. AAmaximum maximum molybdenum molybdenum concentration in as observed from T9, which had aa solid-phase solid-phase molybdenum molybdenumcontent contentofof1100 1100ppm. ppm.Concentrations Concentrationsofofbarium, barium,copper, copper, nickel, and zinc were also occasionally detected in drainage from some samples. The concentrations nickel, occasionally detected in drainage from some samples. The concentrations ofof As, Cd, Cu, Mo, Mo, Ni, Ni, Pb, Pb,Sb, Sb,and andZn Znininthe thelaboratory laboratorywere wereininqualitative qualitative agreement agreement with that in the available, field field concentrations concentrationswere were 1 to 5 times field. In fourteen of twenty-five times those those in in the the field. twenty-five cases available, It was concluded that trace metal concentration in laboratory drainage was better suited as laboratory. laboratory. in laboratory drainage was better suited as an indicator of potential potential elevation in in the field, but not as aa quantitative measure. measure. quartz-carbonate hosted gold gold mines mines produced produced acid acid drainage, drainage, In summary, one one of the tailings from quartz-carbonate yielded the the potential potentialfor foracid aciddrainage drainagein insix sixtotofourteen fourteenyears yearsofofdissolution. dissolution. The The remaining remaining while three yielded six samples tested tested were were predicted predicted to to remain remainneutral. neutral. Trace Trace metal release from the tailings was variable, with arsenic, antimony, and molybdenum molybdenumhaving havingthe thehighest highestconcentrations concentrationsinindrainage. drainage. The The trace trace metal metal release was in qualitative agreement with field concentration concentration data. In: Achieving Achieving 1992, Characterization Characterization and Static Static Testing Testing of Ten Gold Mine Tailings: In: Lapakko, K. A, 1992, Potential Through Through Reclamation: Reclamation: Proceedings of the 1992 American AmericanSociety Societyfor forSurface SurfaceMining Mining Land Use Potential Reclamation Meeting, Meeting,Duluth, Duluth, MN, MN, June June 14-18, and Reclamation 14-18, 1992, p. 370-384. 370-384. Lapakko, K. K. A,, A., 1994, disposalof ofmine minewaste: waste: Laboratory Laboratory investigation: investigation: Presented Presented at at the the , Lapakko, 1994, Subaqueous disposal Land Reclamation Reclamation and and Mine Mine Drainage Drainage Conference Conferenceand andthe theThird Third International International Conference Conference International Land Abatement of of Acidic Acidic Drainage, Drainage, Pittsburgh, Pittsburgh, PA, PA, April 24-29, 24-29, 1994, 9 p. on the Abatement 30 �I I I I I. I I I I I ARCHEAN RIFTS AND SHEBANDOWAN ARCHEAN RIFTS AND GOLD: GOLD: EXAMPLES FROM THE CENTRAL SHEBANDOWAN GREENSTONE -. -- .- -. - BELT - -- LAVIGNE, Maurice J J., LAVIGNE, . , Ministry of of Northern Development and Mines, Suite South, Thunder Bay ON BOOS, 435 435 James James St. S t . South, Mines, S u i t e 8002, P7E 6E3 6E3 Shebandowan The discovery of of 41 4 1 gold occurrences in i n tthe h e central c e n t r a l Shebandowan Greenstone Belt B e l t in i n the t h e last l a s t 10 10 years years has led l e d to t o the t h e realization realization of a new of new gold gold belt. b e l t . The gold mineralization m i n e r a l i z a t i o n iis s sspatially p a t i a l l y (and (and in related i n some cases demonstrably), temporally temporally and and. genetically g e n e t i c a l l y related These assemblages assemblages occur occur as to t o ""Timiskaming" Timiskaming" ttype y p e assemblages. assemblages. These as Thesebbelts long narrowl ilinear belts. km) narrow near b e l t s . These e l t s contain contain long (75 (75 km) greywacke, iron conglomerate, greywacke, i r o n formation, formation, shoshonitic s h o s h o n i t i c pyroclastic pyroclastic and One area, particularly and alkalic a l k a l i c intrusive i n t r u s i v e rocks. rocks. area, p a r t i c u l a r l y rich r i c h in in iron known as a s the t h e Matawin IIron r o n Range and and i r o n formation formation and gold, gold, was known A t the the from tthis, h i s , the t h e term term Matawin Matawin Gold Gold Belt Belt was was dubbed. dubbed. At Stewart Stewart property, property, gold occurs within w i t h i n the t h e intrusive i n t r u s i v e breccia b r e c c i a of of a syenite mineralization s y e n i t e stock. stock. The m i n e r a l i z a t i o n is i s characterized c h a r a c t e r i z e d by by disseminated pyrite p y r i t e and and hematite hematite alteration. a l t e r a t i o n . Gold in i n the the Matawin Matawin Iron I r o n Range area a r e a consists c o n s i s t s of single s i n g l e ladder l a d d e r veins to t o more Att Gold Creek Creek complex vein v e i n arrangements arrangements iin n granodiorite g r a n o d i o r i t edykes. dykes. A South, occurs aas disseminateds usulfides South, tthe h e gold gold occurs s disseminated l f i d e s i in n ffelsic elsic volcanics. The ddelineation e l i n e a t i o n of late l a t e Archean rifts r i f t s serves s e r v e s as a s aa "first f i r s t sstep" t e p Mexploration e x p l o r a t i o n ccriteria. riteria. I 1 I I I 31 �EVALUATION, CENTRAL CENTRAL MINNESOTA. MINNESOTA, PHASE PHASE II BASIC BASIC DATA DATA MINERAL POTENTIAL EVALUATION, Department of of Natural Natural Resources, Resources, Division Divisionof ofMinerals, Minerals, 1525 15253rd 3rd LAWLER, Tom, Minnesota Minnesota Department Ave. E., ilibbing, Ave. Hibbing, Minnesota Minnesota 55746 The Minnesota Department Department of Natural Resources, Minerals Division, has completed a program using using contemporary methods methods to to begin begin to to evaluate evaluate the the mineral mineral potential potentialof ofaa large large part part of of Central Minnesota. Minnesota. contemporary This This project isis oriented orientedtoward toward identifying identifyingnonferrous nonferrous metallic metallic mineralization, mineralization, associated associated alteration or or lithologic units units and and structures permissive permissiveof of such such mineralization. mineralization. The purposes are: are: 1. 1. To To serve land use planning within the D .N.R.; 2. To D.N.R.; To encourage encourage private exploration through better data access, and; 3. To To serve servegovernment governmentagency agency planning of future future programs. Creating an 1. Defining Defining mineral an improved improved regional regional mineral potential potential evaluation evaluation was done done by: 1. units and and structures structures permissiveof permissive ofmineral mineraldeposits. deposits. 2. 2. Defining occurrences, or lithologic lithologicunits Defining basic bedrock lithologic maps, which lithologic locations from existing drill core. core. 3. Creating 1:62,500 1:62,500 scale inferred geologic maps, display supplemented by some display interpreted interpretedmineral mineral potential, potential, using usingavailable availablegeophysical geophysicaland and geologic geologicdata supplemented field work. and; 4. Re-evaluating Re-evaluating existing existing geochemical geochemical surveys using contemporaneous contemporaneous statistical field and; 4. analytical methods. methods. A contract was was completed completedby byDr. Dr. Don Don L. L. Shettel ShettelJr. Jr. and and Dr. Dr. Patrick O'Hara to interpret three three existing ground water water and lake sediment geochemical data sets using state of the art statistical sediment geochemical data sets using state of statistical and geochemical modeling methods. methods. From Fromthese these models models Drs. Drs. Shettel Sheneland and O'Hara O'Haraconstructed constructedanomaly anomaly maps maps for gold, gold, base base metals, metals, iron ironand and uranium. uranium. Contracts were were also completed completedby by Dr. Dr. Allan Spector Spector to to make make an inferred inferred geologic geologic map map of of the twenty township Shephard Area Area at a scale of 1:62,500 and a second twelve township map map extending extending this this area to the northeast. Dr. Dr.Spector's Spector'smaps mapsdisplay displaystructurally structurallydeformed, deformed,folded foldedand and faulted, faulted,greenstones greenstones with associated units and intrusives. An important aspect of of this this contract intrusives. An important aspect contract was was associated metasedimentary metasediientary units construction of of 1:62,500 scale maps displaying displaying several several high high m mineral potential areas as modeled from ineral potential areas as modeled geophysical characteristics characteristicsof ofknown knownmines mineslocated locatedininsimilar similarPrecambrian Precambrianterrains. terrains. These These models models are are primarily based on Dr. Spector's Some of of these these areas areas of of high mineral Spector's experience experience with with such such features. features. Some potential are coincident with anomalous geochemical geochemicalresults resultsdefined definedby byDrs. Drs. Shettel Shettel and and O'Hara. O'Hara. Geophysical measurements of density and magnetic susceptibility were made on selected logged samples for computer modeling of geologic features. features. Detailed Detailedmagnetic magnetic ground ground traverses traverses were were completed completed along roads using an A.T.V. A.T:V. or golf cart for for transportation. transportation. In summary resultsinclude: include: Improved definitionof definition ofgeologic geologicfeatures; features; Lithologic Lithologicunits units results - significant and features features permissive permissive of economic economic ore deposits; deposits; Detailed inferred geologic maps with definition of areas Detailed inferred geologic-maps definitionof Multi element geochemical anomalies with significant pathfinder element having- high mineral potential; Multi element geochemical anomalies with significant pathfinder element anomalies coincident with with favorable inferred geologic anomalies coincident geologic features. features. To test test the the inferred inferred geology, geology, in cooperation with the M.G.S., M.G.S., six and into bedrock bedrock six vertical vertical holes holes were were drilled drilled through glacial overburden and far enough to obtain hard bedrock samples. Hand lens examination of the core confirms inferred geologic fax hard bedrock samples. Hand lens of the core confirms inferred geologic bedrock bedrock maps maps in in most most of of the the drill drillholes holes and andprovides providesencouraging encouragingindications indications of mineral potential. 32 �I I I a • I The The Birch Lake Prospect Prospect -- AA Major PGM Prospect in the Duluth Complex by Ernest K. K. Lehmann Lehmann North Central Mineral Mineral Ventures Inc., Inc., Minneapolis, Minnesota and John W. W. Beck 3M Company, St. Paul, Minnesota 3M ABSTRACT I I I I I I I I I I I I I The (PGM) is The Birch Birch Lake Lake Platinum Group Metals Metals (PGM) Prospect is located within the the Duluth Complex on on the St. Louis/Lake County border border just east east of the the Dunka Taconite Mine of of LTV Steel Steel and about 10 miles south south of of Ely, Ely, Minnesota. Minnesota. The surface of the the area is marked by by aa humocky terrane terrane developed developed on on the surface surface of of the Complex Complex and covered with with aa thin thin ground ground morraine. morraine. The copper-nickel in the The area area was was originally explored for for copper-nickel 1950's 1950's and 60's 60's including drilling by Duval. Duval. These drill holes encountered encountered copper-nickel copper-nickel mineralization mineralization but but were not analyzed for for PGM5. PGMs. Resampling Resampling of of the drill core core in in the early 1980's 1980's by state agencies revealed ore and near ore concentrations of PGMs PGMs in This a program of of in two two holes. holes. This work work coincided with a program PGM exploration being carried out by by the the Beaver Beaver Bay Bay Joint Joint Venture Venture and and its Subsequent drilling 1991 was its partners. partners. drilling in 1988 1988 through through 1991 carried carried out by by the the venture. venture. The PGH Lake occurs within the the PGM prospect at Birch Birch Lake South Kawishiwi intrusive, a part the Complex. Kawishiwi intrusive, a of the Duluth Complex. Mineralization the the Mineralization is is confined to to aa unit near the base of the intrusive intrusive which consists of of aa copper-nickel copper-nickel sulphide sulphide rich rich olivene olivene troctolite is iron oxide troctolite zone zone and and is associated with iron rich troctolites. troctolites. These These units units dip dip at at shallow shallow angles angles to to the the east. east. The area area drilled drilled is is on the the south south flank flank of aa strong oval oval magnetic anomaly mineralized anomaly which is believed to be the the same depth as the mineralized zone; the rocks above above the the minerilized mineralized zone zone typically typically have a low magnetic This magnetic susceptibility. susceptibility. This magnetic magnetic anomaly may indicate indicate increased increased sulphide sulphide and/or and/or iron iron oxide oxide content content at at its its center, center, giving giving aa strong strong suggestion suggestion of of better potential potential for for enconomic mineralization mineralization on on this this as as yet yet untested untested target. target. The The mineralized mineralized zone zone is is characterized characterized by by serpentinization serpentinization and of a and saussuritization saussuritization and and the the occurrence occurrence of a high chlorine chlorine content content which causes a unique rusting of the rocks on exposure to air. air. The The PGM PGM values are are associated associated with copper copper and nickel. �Pt:Pd Ratios ios of o Rat d are are in in the t:he range range of of 1:1 1:l to to 1:2, rather rather than than ratios of 1:3 ratios 1:3 to 1:4 1:4 characteristic characteristic of the the Minnamax, Minnamax, Inco Inco and and Dunka Road copper-nickel deposits which contain only accessory Dunka Road copper-nickel deposits which contain only accessory amounts The mineralogy of amounts of of POMs. PGMs. The mineralogy of the the PGMs PGMs at at Birch Birch Lake Lake is is poorly known known though though complex complex platinum-palladium-bjsmuth-telluride platinum-palladium-bismuth-telluride sulphosalts sulphosalts have have been been identified. identified. The The deposit deposit is is believed believed to to have formed formed in in aa trough trough in in the the base base of the the complex, complex, perhaps perhaps caused by faulting faulting which which permitted chlorine chlorine rich rich solutions solutions to to caused by deposit and deposit and enrich enrich PGMs PGMs in in the the zone zone of of pre-existing pre-existing copper-nickel copper-nickel sulphide sulphide mineralization. mineralization. Considering Considering the the substantial substantial thickness thickness of of the the mineralized mineralized zone zone and and its its possible possible major major areal areal extent, extent, the the potential potential exists exists for a world class PGM deposit mineable by large scale highly for a world class PGM deposit mineable by large scale highly mechanized Initial investigations the mechanized methods. methods. Initial investigations suggest suggest the a bulk possibility of making sulphide concentrate for sale possibility of making a bulk sulphide concentrate for sale to to existing Preliminary existing smelters smelters in in Canada Canada or or Europe. Europe. Preliminary economic economic analysis suggests that that at least hole contains analysis suggests at least one one drill drill hole contains mineralization of economic grade at current prices under mineralization of economic grade at current prices under such such aa scenario. Further drilling of the deposit is planned to test scenario. Further drilling of the deposit is planned to test its its economic potential. economic potential. �I p PETROCRAPHY AND STRUCTURE OF THE KEWEENAW CHENCWATANA NEAR DRESSER, WISCONSIN VOLCANICS LESLIE, Magnus, Wetzel, Todd, Wirth, Karl, R. and Craddock, John P., Geology Dept., Macalester College, St. Paul, MM 55105 Dresser Trap Rock quarry provides a unique look at 6 flows of the Chengwatana volcanic group (Age: —1.1 Ga) which range in thickness from 10 to 70+ meters. The flows are basaltic diabases whose primary mineralogy consists mainly of unzoned plagioclase (An 45-50) and augite with lesser amounts of illmenite and hornblende. The P 1 1 1 . . No modal olivine or olivine alteration products exist in these samples, but previous chemical analysis indicates that the flows are olivine normative (Cavaleri et al., 1987).The Theflows flowsstrike strikeNNNE anddip dip 13-20W. 13-20°W,Flow Flowbottoms bottomstend tendtotobebeaphyric aphyric and and 1987). N E and rapidly coarsen into subophitic or intergranular intergranular textures. textures. The centers of of the flows coarseness in in proportion proportion to the thickness are understandably more coarse, with the coarseness of the flow. Flow centers contained in the quarry exhibit two textures. The most of contained in are intergrowth termed "luster-mottled" common texture is an ophitic ophitic pyroxene-plag. intergrowth 'luster-mottled" due to the spoiled appearance of the rocks on exposed faces. A few flow centers the spotted appearance of the rocks on exposed with 1-2 an cm plagiodase plagioclaselaths laths in in aa mediummediumexhibit a plagioclase-phyric texture often with grained groundmass. Flow Flow tops are are fine grained and all have amygdules filled with fine amygdules chlorite, epidote, epidote, quark quartz and calcite. alteration mineralization, primarily chlorite, Major and trace element analysis (INAA and XRF) is being conducted across across the the Major and XRF) is being conducted stratigraphy from flow stratigraphy from Dresser west to the the Taylor's Falls area to: 1) delineate differentiation trends across the successive successive Chengwatana Chengwatanaflows flowsand, and, 2) 2) characterize characterize of the Keweenawan rift. the Chengwatana sequence in the overall stratigraphy of exposed in in the quarry were erupted episodically, with with the exception The flows exposed of the fifth/sixth fifth/sixth flow of interflow of flow boundary boundary which which exhibits exhibits a remarkable example of sedimentation of the This surface surface sedimentation the flowtop flowtopbreccia breccia type type as as described described by by Jirsa Jirsa (1984). This represents the deposition of fluvial sediments over over the the rough rough brecaated, brecciated, top top of of flow flow five and is composed of of angular angularfragments fragments of of subjacent subjacent flows and fine grained, cross-bedded sand. on the western wall of of cross-bedded sand.The The fluvial fluvial sediments sediments are well exposed on meters before before tapering tapering off off the quarry, where where they they reach reach aa maximum maximum thickness thickness of of 5-8 meters on either side of the central paleochannels. side of the central paleochannels. lava flows in in the quarry have undergone undergone very very low low to to low-grade low-grade The lava metamorphism, as well as hydrous alteration. The flows contain significant as hydrous alteration. The of epidote, chlorite, chlorite, and of the flow tops having become amounts of and actinolite; actinolite; many of epidosite. The plagioclase present in significantly altered samples has has been been The plagiodase in altered samples converted to albite albite indicating indicating metamorphism in the low grade grade albite-actinolitealbite-actinolitechlorite fades. facies. Hydrothermal Hydrothermal alteration has has caused caused the the alteration alteration of of pyroxenes pyroxenes to to uralite, variant of of hornblende; hornblende; and the dominant epidotization uralite, a semi-fibrous variant overprint exhibited in in nearly nearly every every sample. sample. Previous Previous studies studies have have indicated indicated aa depth depth of burial of at krn and andtemperatures temperaturesapproaching approaching440°C 440T(Cordua, (Cordua,1989). 1989). at least least 22 km The outcrop structures in the volcanic flows are straightforward and include the following features: 3 systematic joint sets (N-S. 90°; E-W, 90°; N-S, 45°E), and a conjugate thrust fault pair (N-S. 45°E and N-S, 35°W) which are not crosscut by the 35 �(older) joint surfaces are commonly commonlyfilled filledwith withcalcite calciteand/or and/or quartz (older) joints. All the the joint which has has been been plastically plastically deformed. deformed. Both Both vertical vertical joint sets commonly preserve preserve sub-horizontal striations with dextral stepping directions (and minute offsets). a1 striations with dextral stepping directions minute offsets). The east-dipping thrust thrust faults faults are are quite quite numerous, numerous, whereas only one west-dipping thrust fault has been observed which is preserved as a .5 m width quartz quartz zone. Within this gouge zone we have observed epidote-filled echelon fractures, fractures, striated striated and idote-filled en echelon stepped chlorite-quartz-epidote, S-C structures, and late-stage syntaxial structures, and late-stage syntaxial calcite calcite fillings. All of these kinematic indicators documenthangingwall hangingwallmotion motionas as up up and and tors document to the east; this fault displacement also offsets the other thrust faults (N-S, 45°E) and offsets thrust faults (N-S, 45OE) and is interpreted as being younger. The gouge gezone zone isis composed composed of of quartz+chlorite÷ quartz+chlorite+ epidote+adularia÷calcite÷hematite (+opaques) and represents a green schist ques) and represents schist metamorphic assemblage ("400?C,r4 kb) that is is similar similarto to the themetamorphic metamorphicgrade gradein in. the host volcanic rocks. Calcite and quartz joint and and fault quartz are are abundant abundant as as secondary secondary minerals filling joint surfaces, faces, and and contain contain mechanical mechanical twins twins or or deformation deformation lamellae, which allowed allowed us us to characterize characterize the the state stateof of stresè stressin in these these rocks rocks after after mineralization. Quartz Quartz containing deformation lamellae was observed only associated associatedwith with the the thrust thrust faul fault erved only gouge zone whereas twinning was observed in all phases of calcite. These in all phases of calcite. These deformation lamellae bracket the differential (calcite) tial stress magnitudes as as >10 >10 MPa (calate) and >50 MPa (quartz), respectively. Twinning in calcite allows for a detailed and >50 respectively. calate allows for a detailed strain analysis analysis with the the caveat caveat that that the the age ageof of the the calcite calate is not known. Our results results include include strain analyses of calcite fillings in joints and thrust st faults; calcite amygdules were rare: joint set I (N-S. 900; sub-horizontal shortening II1(E-W, N45OE), joint tening trend: trend: N45°E), joint set 1 90°; shortening trend: N5°E), thrust fault I (N-S. 45°E; shortening trend and plunge: (N-S, 45OE; shortening trend plunge: N90°E, 40°), thrust fault II (N-S, (N-S, 45OE; 45°F; shortening shortening trend trend and and plunge: plunge:N4°E, N4OE,70°F). 70°E) These complex twinning strains are best interpreted reted as representing regional stress and strain field changes over a long time periodd(e.g., (e.g., joint-filling joint-filling deformation, then thrusting), rather than as variations in the stress field within the area of I1square stress square km.. A regional regional interpretation interpretation of of these these thrust thrust faults, faults, in conjunction with the detailed flow of thrust faulting flow stratigraphy, stratigraphy,is is in in progress progress to to characterize characterize the extent of faulting along the Keweenaw-Lake Keweenaw-Lake Owen-Hasting Owen-Hastingfault fault(Middleton, (Middleton,1991; 1991;McGovern McGovernetetal., al.,1993). 1993). REFERENCES REFERENCES Cavaleri, The Geology Geology of the Cavaleri, M., M., Mossier, Mossier, J. J. H. H.and andWebers, Webers, C. G.F., F., 1987, 1987, The the St. Croix Crow River Valley: Minnesota Geological Survey, Guidebook Series #15, p. 2343. Minnesota Geological Survey, Guidebook Series 23-43. Cordua, area, Wisconsin and and Minnesota: Cordua,W., W., 1989, 1989, Bedrock Bedrock geology geology of of the theDresser-St.Croix Dresser-St-CrowFalls area, Minnesota: 53rd Annual Tri-State field Conference Guidebook, River Falls, WI. 53rd Annual Tri-State field Conference Guidebook, River Falls, WI. Jirsa, A., 1984, 1984, Interflow Interfiow sedimentary sedimentary rocks in the Keweenawan North North Shore Volcanic Volcanic Group, Group, Jiisa,M. M.A., northeastern Minnesota: Minnesota Geological Survey Report of Investigations 30. northeastern Minnesota: Minnesota Geological Survey Report Investigations McGovern, M.G., Craddock, J.P.,,Webers, G.F., G.E. 1993, Evidencefor forlatePaleozoic latePaleozoicdisplacement displacement of of the the 1993, Evidence Keweenawan Keweenawanthrust thrustfault faultfrom fromfolded foldedPaleozoic Paleozoicoutliers outliers in in Michigan's Upper Upper Peninsula: Peninsula:39th 39th Annual AnnualProceedings Proceedingsofofthe theLake LakeSuperior SuperiorInstitute, Institute,p.p.56-57. 56-57. Middleton, M.D., 1991, A preliminary study study of of rejuvinated rejuvinated movement movementalong alongaa Precambrian Precambrianfault, fault.St. St. Croix county, WI: 37th Annual Institute LakeSuperior SuperiorGeology, Geology,p.p.70-71. 70-71. Instituteon onLake 3.6 �Environmental geochemistry of Proterozoic black shales in eastern Finland: a pilot study LOUKOLA-RUSKEENIEMI, Kristi, Geological Survey of Finland, FIN-02150 Espoo, Finland The Precambrian geology of Finland is comparable in many aspects to that of the Lake Superior region. In particular, both areas contain black shales and the environmental geochemistry of these may be direcUy compared because of similarities in climate. Thick (20-400 m) formations of 5- and C-rich black schists occur in eastern Finland (black schist = metamorphosed black shale). Median concentrations of both graphitic carbon and sulfur are 6-9%. These black schists are spatially associated with the disrupted remnants of 1.96-1.97 Ga ophiolites, occurring over 250 km of strike length along a probable former rift zone in the Kainuu and Outokumpu areas. The thickest black schist formations occur at Talvivaara, where 300 Mt of black schist with Ni+Cu+Zn > 0.8% are present. The Talvivaara deposit is syngenetic in origin and the main part of the contained metals were precipitated in organicrich mud during deposition. The primary fine-grained spheroidal pyrite (<0.01 mm) contains 0.3-0.4% Ni which has, during recrystallization, been incorporated in pynhotite and pentlandite. The deposit has undergone amphibolite facies metamorphism and tectonic deformation. The deposit included Mn-rich horizons and up to 17% interlayered black calc-silicate rocks. The Ni-Cu-Zn-rich black schist is easily weathered when in contact with surface waters. The background concentrations of the black schist area have been compared with those of different bedrock, namely the Late Archean granite gneiss areas adjacent to the Talvivaara area. The Hg concentrations of pike (a large northern predatory fish) seem to correlate with bedrock geochemical characteristics: Lake Hg in pike (ppm) of black schists Distribution of schists Kolmisoppi Jormasjärvi Alanne 0.96 0.76 0.33 Abundant Hg-rich schists in mica schist Black schist interlayers in No black black schists schists Average in 67 Finnish forest lakes 0.56 (Verta, 1990) Chemical concentrations of stream and lake waters, ground water and stream and lake sediments axe compared. Spring water results of pilot sampling committed in August 1993 (n = number of samples): Black schist area Cu Zn Ni Co Pb Cd Mn Al > > > > > SO4 > pH C n 4.08 97.3 69.90 3.33 0.15 > 0.25 > 183 Granite gneiss area 031 1.08 4.17 0.65 0.20 0.31 - 6.39 0.96 0.41 0.64 <0.02 38.5 244. - 90.4 272. 7.3 1.0 - 1.7 4.8 12 5.2 - 1.7 > 390 - 4 Sampling is continuing this year, but these results already indicate that the natural background values are dependent on bedrock geochemical characteristics in the Talvivaara area. The bedrock at Talvivaara contains anomalous Cu, Zn, Ni, Co and Mn. elevated Cd and Hg, but in most places not elevated Pb concentrations, which can also be seen in the chemical composition of spring waters. 37 �PETROLOGY ANALYSES OF PETROLOGY AND WHOLE ROCK ANALYSES OF THE THE CENTRAL CENTRAL PORTION PORTION OF OF A LARGE LARGE EARLY PROTEROZOIC PROTEROZOIC DIABASE DIABASE DIKE, DIKE, EASTERN EASTERN LAKE LAKE OF OF THE THE WOODS, WOODS, ONTARIO ONTARIO -- AA PRELIMINARY PRELIMINARY REPORT REPORT by Frank Frank R. R. Luther, Luther, Geology Geology Program, Program,tJW-Whitewater, UW-whitewater, Whitewater, whitewater, WI WI 53190 53190 The study, part of the The dike under study, the 2100 2100 m.y. KenoraKenoraKabetogama Kabetogama (Southwick (Southwick and Day, Day, 1983) 1983) dike dike swarm, swarm, extends extends at at least least 60 60 km km from from the the Pipestone-Cameron Pipestone-Cameron Fault Fault on on the the northwest northwest through Whitefish Bay and through the the center of Whitefish and Kakagi Kakagi Lake Lake to to southern southern Godson informally named named the the Whitefish Whitefish BayBay Godson Township; it is informally Kakagi Kakagi Lake Lake (WBKL) (WBKL) dike dike in in this this report. report. The The objective objective of of this this study was to use field observations observations as as well as as mineral and and rock rock chemistry chemistry to to constrain constrain the the intrusive intrusive history history of of the the dike. dike. In Whitefish Bay the WBKL WBKL dike dike is is 70-80 70-80 m wide with well-developed well-developed chill chill borders borders in in contact contact with with the the Archean Archean granitic granitic country country rocks; rocks; no no chill chill borders borders were were observed observed within within the the dike. dike. The The intrusive intrusive contact contact with with the the granite granite is is irregular irregular with with apophyses apophyses of basalt at at the the mesoscopic mesoscopic scale scale while while the the regional strike strike and dip is constant constant at 1400 vertical over over the the area area studied. studied. Igneous Igneous layering layering characterized characterized by by modal modal variation variation in in plagioclase, plagioclase, pyroxene, pyroxene, and and magnetic magnetic opaques opaques is is noticeable noticeable between 10 10 and 30 30 m from from the the dike dike border. The The layering is often often distorted distorted and/or and/or truncated. truncated. The The massive massive central part of the dike dike is is a low—quartz-content low-quartz-content diorite diorite which which contains contains small small well-developed well-developed cross-cutting cross-cutting mafic mafic pegmatites. pegmatites. Microscopically, Microscopically, the the chill chill border border is is characterized characterized by by altered phenocrysts (up (up to to about about 11 mm mm in in diameter) diameter) of of pyroxene, pyroxene, unaltered unaltered to to partly altered altered phenocrysts phenocrysts of of zoned zoned plagioclase plagioclase (an6o-70), smaller opaque (anso-70), and smal-ler opaque minerals minerals in in aa brown-green brown-green cryptocrystalline groundmass cryptocrystalline groundmass of of devitrified devitrified tachylite. tachylite. The The groundmass groundmass contains contains xenocrysts xenocrysts of of quartz quartz and and K-feldspar K-feldspar indicating indicating interaction interaction with with the the country country rocks. rocks. Proceeding Proceeding into into the dike, the the interior interior of the dike, the grain grain size size gradually gradually coarsens coarsens (over (over about about 55 m) m) to to 3-7 3-7 mm. mm. In In the the center center of of the the dike, dike, (1) (1) vapor-phase vapor-phase alteration alteration of of plagioclase plagioclase and and pyroxene pyroxene is is severe, severe, (2) (2) the the plagioclase plagioclase shows shows complex complex oscillatory oscillatory zoning zoning and, and, (3) (3) up up to to 10% 10% quartz quartz is is present present along along with with micrographic micrographic to to symplectic symplectic intergrowths intergrowths of of quartz quartz and and feldspar. feldspar. Whole-rock Whole-rock chemical chemical analyses analyses (by (by XRAL) XRAL) presented presented below below show show the the dike dike margin samples samples to to be be chemically chemically very very similar similar both both to to one one another another and and to to the the N-i N-1 dikes dikes analyses analyses of of earlier earlier workers. workers. Sample from aa plagioclase plagioclase layer layer shows shows predictably predictably higher higher Al, Al, Sample 55 from Ca, from the the dike dike center center Ca, and and Na Na and and lower lower Mg Mg and and Fe. Fe. Sample Sample 66 from shows shows higher Si, Si, Al, and Na and and lower lower Ca, Ca, Mg, Mg, Fe, Fe, and and Ti Ti as as well as a higher LOt indicative of a more felsic composition well as a higher LO1 indicative of a more felsic composition and and of of more more vapor-phase vapor-phase alteration. alteration. 38 �spl Spl no: no: 1 1 49.3 49.3 3102 SI02 AL2 03 12.5 ALaOs 12.5 CAO CAO MOO MGO NA2 0 MA20 1(2 K2 00 9.28 9.28 6.12 6.12 1.72 1.72 0.28 0.28 FE2 03 16.5 FEaOa 0.21 0.21 MNO MNO TI 02 TI02 P205 P205 LO LO1I TOTAL TOTAL 2.15 0.21 0.21 1.80 1.80 100.1 100.1 55 2 2 3 3 44 47.8 47.8 13.0 13.0 10.1 10.1 5.45 5.45 1.88 1.88 0.26 0.26 18.0 18.0 0.24 0.24 2.30 2.30 0.24 0.24 0.75 0.75 48.5 12.7 8.65 5.52 1.96 0.32 18.0 0.25 2.24 0.22 1.70 48.4 12.8 9.66 5.42 2.01 0.37 17.7 0.25 2.22 0.21 1.10 100.1 100.1 100.1 48.8 16.0 9.64 4.30 2.31 0.59 14.9 0.21 1.96 0.20 1.35 100.3 100.2 6 6 54.1 15.4 6.91 1.82 3.24 0.78 13.9 0.20 1.49 0.47 1.95 100.4 77 47.9 12.5 8.26 5.57 2.68 0.84 17.0 0.25 2.16 0.22 1.65 99.11 - from FRL. element data data available from bc ations and Samples Samples - locations and minor element FRL. contact. 1. 1. LW87-1—la, LW87-1-la, diabase 11 cm from west contact. diabase 0. LW87-1-lb, diabase 2. 2. LW87-1-lb, 0.33 mm from wes westt contact. contact. lmm from west contact. 3. LW87-1-lc, LW87-1-lc, diabase 1 contact. diabase 3 3mm from west contact. 4. 4. LW87—1—le, LW87-1-le, diabase contact. as e -rich diabase from 5. 5.LW87—1—2a, LW87-1-2a, plagioci plagioclase-rich from the the layered layered diabase. diabase. ily altered quartz diabase from mid-dike. 6. 6. LW87—4—3, LW87-4-3, deuterica deuterically 7. 7. LW87—4—llc, LW87-4-llc, diabase 3 cm from from east east contact. contact. The The WBKL dike was a major feeder feeder to to early early Proterozoic Proterozoic The distorted and truncated truncated igneous igneous layering layering atory-zoned plagioclase record a complex and the he oscill and oscillatory-zoned complex history history causing of intrusion/extrusion, quiescence, and back-flow causing the crystallized distortion, distortion, re-melting, re-melting, and/or erosion erosion of of the crystallized border of of the the dike. dike. The increase in in quart quartzz in the dike extrusion proceeded. interior shows magmatic evolution as lava lava extrusion proceeded. eted as deuteric Alteration of the dike interior is interpr interpreted because of of (1) (1) stronger stronger alteration in in the the interior, (2) the egmatites, and presence of (3) a lack of of of the the mafic ppegmatites, and (3) hydrothermal alteration alteration cross-cutting the the margin of the the dike. dike. Many of of these these observations observations and conclusions support those of Southwick Southwick and and Day Day (1983). (1983). flood basalts. flood basalts. I I I I I I I REFERENCE Southwick, Southwick, D.L., D.L., and and Day, Day, W.C., W.C., 1983, 1983, Proterozoic Proterozoic mafic dikes, north-central Geology and petrology of of Minnesota and western 622—638. Ontario. Ontario. Can. Can. 3. J. of Earth Sciences Sciences 20, 622-638. a, 39 �ON THE ON THE ORIGIN ORIGIN OF OFMANGANESE MANGANESE OXIDES OXIDES IN IN IRON-FORMATION IRON-FORMATION OF OF THE THE CUYUNA NORTH NORTH RANGE, CUYUNA RANGE, EAST-CENTRAL EAST-CENTRAL MINNESOTAMINNESOTA- NEW NEW EVIDENCE EVIDENCE FROM THE U.S. U.S. BUREAU BUREAU OF MINES GLORIA GLORIA DRILL SITE MELCHER, Frank H H.; G.B.; McSWIOGEN, McSWIGGEN, Peter Peter LU; CLELAND, M., MELCHER, .,MOREY, G.B.; .;C L E L W . Jane M., Geological Survey, 2642University 2642 University Avenue, Avenue, St. Paul, Minnesota Geological Paul, MN 55113 55113 The Tronimald Formation on the Cuyuna North Range is unique in that it contains the highest reported manganese values of any Early Proterozoic iron-formation in the world, and as such is the largest resource of this metal in the United States. Traditionally, the Trommald has been divided into a lower thin-bedded facies containing Fe-Mn-Mg-Ca carbonates, Fe silicates, magnetite and chert, and an upper thick-bedded facies composed of granular chert, hematite, magnetite, manganese hydroxides, and minor silicates and carbonates (Schmidt, 1963). Near the Merritt mine, uncommon Na-, Mn- and Ba-rich silicates indicative of hydrothermal fumarolic processes occur near the contact between thin- and thick-bedded rocks (Morey and others, 1992). To further elucidate the complex history of the manganese oxides and to investigate the possibility of their in ! situ leaching, the U.S. Bureau of Mines drilled a long inclined core at the Gloria mine, approximately 1.5 km to the northeast of the Merritt site (Dahl, 1992). That core was drilled to an inclined depth of 366 m (304.8 m below the surface) and intersected a complete section of Trommald Formation (true thickness of 168 m) as well as short intervals of the overlying Rabbit Lake and underlying Mahnomen Formations. DahI and others (1992) divided the Trommald into an upper oxidized interval separated from a lower unoxidized interval by an oxidation boundary at a depth of 234 m below the surface. The oxidized part was further subdivided into a thin-bedded facies, a mixed thin- and thick-bedded facies, and a thick-bedded facies. In that scheme, the thickbedded and part of the thin-bedded facies were thought to have been oxidized and leached during subsequent ore-forming events. We observe that some of the thin-bedded rocks contain primary hematite and are chemically akin to thick-bedded rocks. The core is presently being investigated at the Minnesota Geological Survey in terms of mineralogy and geochemistry, and some preliminary results are presented here. The Mahnomen Formation consists of sericite-biotite quartzite interlayered with thin layers or lenses of toumialinite. Beds of chlorite-bearing oxide (hematite) iron-formation mark the base of the Trommald Formation. They are overlain by approximately 40 m of thin-bedded strata containing abundant carbonates, silicates and magnetite. Features indicative of syndepositional reworking, possibly under shallow-water conditions, include granule-rich layers, breccias, and pebble-size conglomerate. The silicate-carbonate iron-formation also contains considerable sulfides (pyrite, pyrrhotite, chalcopyrite, arsenopyrite), commonly in irregular, discordant, composite veins—along with quartz, carbonates, and stilpnomelane— in stratiform layers and lenses, or as inclusions in intercalated beds of chert. The sulfides are typically replaced by magnetite, which in turn is martitized. Mafic tuffaceous material, as well as tourmaline-bearing sericite schist, is intercalated with the iron-rich strata. Preliminary data imply that the silicate-carbonate ironformation is poor in Mn (<2 wt.% MnO) which is at variance with similar rocks from the Merritt site. In turn, there are higher contents of Ca, P, and S observed in the thin-bedded facies of the Gloria Gloria mine. mine. A transitional interval of approximately 4 m separates thin-bedded silicate-carbonate ironformation below from thin-bedded oxide iron-formation above. Individual laminae contain chert, primary hematite, stilpnomelane, and limonite. Carbonates are rare, and magnetite where present is martitized. Individual layers of nearly monomineralic chert are interlayered throughout. A highly brecciated interval contains interealations of argillized shale or tuffitic sediments. Manganese-rich layers first appear in thin-bedded oxide iron-formation about 75 in (true thickness) above the Mahnomen Formation. These massive, concordant hematite-goethite-Mn-oxide-bearing intervals as much as 4 in thick are partly enveloped by brecciated oxides, and have maximum MnO (total) 40 �I I values of 12 0.2. The latter is similar to the Mn-Fe ratios in values 12 wt.% and Mn-Fe ratios of about 0.2. unoxidized thin-bedded rocks at the Merritt site. unoxidized Memtt site. Mn values increase markedly about 110 wt.% for for about 110 m above the base, and stay above above 5 wt.% 55 m (true thickness). As such this zone straddles the boundary between thin-bedded (true thickness). As such this zone straddles the boundary between thin-bedded and overlying thick-bedded strata. strata. Mn-oxide-rich Mn-oxide-rich layers layers in in thin-bedded thin-bedded strata have brecciated or "gnarled ore" textures and are conformably interlayered with intervals of decomposed iron"gnarled are conformably with formation containing containing abundant secondary limonite. Mn-oxide-rich layers in thick-bedded strata are are interlayered conformably with thick beds of admixed chert having a relict micronodular texture, interlayered conformably beds admixed micronodular texture, and with secondary limonite. The layers typically occur as brecciated rubble zones that exhibit exhibit numerous discordant textural features. Manganese minerals minerals include include manganite, manganite, cryptomelane, cryptomelane,and and pyrolusite (Dahl, 1992). Whole-rock Whole-rock assays over 1.5-m intervals show that Mn-rich layers in 1.5-m intervals show that Mn-rich layers in thick-bedded strata contain as much as 50 wt.% wt.% MnO, MnO, and and MnFe Mn/Fe in in places places>> 1. 1. The The zones zones also also have have elevated elevated Ca, Ca, Mg (attributed (attributed to secondary secondary carbonates), and P values and are enriched in Ba (as much as Pb, Sr, Ag, and As. as 1.8 %), Pb, The of thick-bedded, thick-bedded, oxide oxide iron-formation iron-formation The uppermost 12 12 m of Trommald Formation consists of where p primary hematite is abundant but where manganese oxides are lacking. Mn-Fe ratios are are r* manganese oxides are lacking. Mn-Fe ratios generally less than 0.01. The overlying Rabbit Lake Formation differs considerably; beds of overlying considerably; beds of sulfide (pyrite) iron-formation are intercalated with thick beds of oxide iron-formation, intercalated with beds of oxide iron-formation, iron-formation carbonaceous carbonaceous shale, and and thin layers layers of tuffaceous tuffaceous material. The The sulfide sulfide iron-formation iron-formation (35.7 (35.7 wt.% wt.% Fe203, (31 ppb), As, Cu, Co, Ni, Pb, Sr, V. V, Mo, and Se Fe203, 26% 5) S) contains elevated values of Au (31 (230 (230 ppm). PP~). Several Trommald Formation in the Gloria drill core are unique, and it seems to Several features features in the Trommald be special importance that no direct correlation correlation can be made with the well-documented drill core be of special mine. Granular fabrics, fabrics, extensive extensivesynsedimentary synsedimentarydeformation deformationtextures, textures, and and of the nearby ~Merritt e m tmine. t Granular extensive sulfide documented for the first time in the thiin-bedded thin-bedded facies of extensive sulfide mineralization mineralization have been documented relationships among the various iron iron and manganese oxides the Trommald Formation. Paragenetic relationships oxidation events events in in the the upper upper part part of of the the are difficult to interpret because of several superimposed oxidation Trommald Formation. Formation. However, However, we we have have found no evidence that the major major elements elements were were redistributed on on aa scale scale larger larger than than tens tens of ofmeters. meters.Therefore Therefore the the manganese manganese oxides, oxides, significantly redistributed along with other other enriched enriched elements, elements, seem seem likely to be synsedimentary precipitates derived from a hydrothennally the hydrothenually influenced influenced source source of uncertain uncertain affinity affinity and redistributed on a small scale to form the present present enriched enriched zones. zones. ' I I I I I REFERENCES CITED REFERENCES CITED Dahi, of Minnesota manganese manganesedeposits depositsfor forininsitu situmining: mining:Skillings' SUllings' Dahl, L., L., 1992, 1992, Characterization of Mining D. 4-9. Minine Review, v. 81, 81. no. 41, 41. p. Dahl, Brink, S.E., R.L., Tuzinski, brink. s.E.. Blake, lake.^.^.. Tuzinski. P.A., P.A.. and and Adamson, Adamson. N.R., N.R.. . 1992, 1992. Dahl. L.J., - . Site - characterization characterization of Minnesota manganese deposits to evaluate the potential for in situ leach mining: Littleton, Colorado, Inc., Annual Colorado, Society for Mining, Metallurgy, and Exploration, . Meeting, Meeting, Phoenix. Phoenix. Morey, G.B., P.L. and Cleland, J.M., 1992, Evidence of of an exhalative contribution G.B., McSwiggen, P.L. to the the manganese manganese mineralogy mineralogy of the the Trommald Trommald Formation, Formation, Cuyuna Cuyuna iron iron range, range, east-central east-central Minnesota: Institute on Lake Minnesota: Institute Lake Superior Superior Geology, Geology, 38th 38th Annual, Annual, Hurley, Hurley,Wisconsin, Wisconsin, Proceedings, 1. 70-71. Proceedings, part part I,1,p.p.70-7 Schmidt, R.G., R.G., 1963, Geology and ore deposits of the the Cuyuna Cuyuna North North range range Minnesota: Minnesota: U.S. U.S. Geological Survey Professional Paper, 407, 96 p. 407.96 Survey Professional - I ' I I I I �GEOLOGY NORTFIEASTERN MINNESOTA MThNESOTA GEOLOGY OF OF THE THE "GREAThR" "GREATER" BEAVER BEAVER BAY BAY COMPLEX, NORTHEASTERN J. J. D. D. Miller, Miller, Jr., Jr., T.J. TJ.Boerboom, Boerboom,V.W. V.W. Chandler, Chandler,Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University UniversityAve., Ave., St. St.Paul, Paul, MN MN 55114, 55114, and and J.C. University of of MinnesotaÑDduth Minnesota—Duluth,Duluth, Duluth,MN MN 55812 55812 J.C. Green, Green. Dept. DepL of of Geology, Geology, University The the USGS's The Minnesota MinnesotaGeological Geological Survey Surveyrecently recently completed completed an 8-year mapping project, supported in part by the COGEOMAP intrusions of the COGEOMAP program, program, whose whosemain main objectives objectiveswere were to to delineate delineate the the multiple multiple subvolcanic intrusions the Middle Middle Proterozoic BC) ofof northeastern northeasternMinnesota Minnesotaand andtotocharacterize characterizeits itstransition transitioninto intothe themore more Proterozoic Beaver Bay Complex (BBQ plutonic (DC). These been accomplished accomplished and and the the the Duluth Complex 0. These objectives have largely been plutonic environment environmentof the results results are are set set forth forthin in the theform formof of three three1:24,000-scale l:24,000-scale geologic geologicmaps maps (Miller, (Miller,1988; 1988; Miller, Miller. Green Green and andBoerboom, Boerboom. 1989; Miller, Green, Green, Boerboom, and Chandler, 1993). 1993), the imminent imminent publication publicationof of two twoothers others (Miller, (Miller, Boerboom, Boerboom, and andMiller, Miller,ininprep.), prep.), and andan anopen-file open-filemap map of of the theLittle LittleMarais Marais quadrangle, quadrangle, also also in in and Jerde, in prep.; Boerboom Boerboomand preparation. These maps,which whichwe wepresent presentininour ourposter posteras asaa mosaic mosaiccompilation, compilation, include include all all or or parts parts of of eleven eleven 7.5' Thesemaps, quadrangles 440-square-mile-area Fig. (Fig. 1). Although has been historically historically called called the quadranglesand and cover cover aa440-square-mile-area Although this this area area covers covers what what has BBC of aemmagnetic aeromagnetic data over BBC (Grout (Grout and and Schartz, Schartz, 1939), 1939). reconnaissance reconnaissancemapping mapping to the east and interpretation of covered needfor foran an expanded expanded definition definition of of the the BBC. BBC. covered areas areasto to the thewest west suggest suggestthe theneed Twelve major intrusive (lithodemic) units were identified within the area of the the BBC, BBC, which which represent represent at at Twelve major intrusive (lithodemic) units were identified the mapped area least central part part of the North North Shore Shore least six six major emplacement emplacementevents events of mafic to less common felsic magmas into the central Volcanic events reflects reflects the the composite compositenature natureof of Volcanic Group. Gmup. This Thisnumerical numericaldisparity disparitybetween between map map units and intrusive events some of correlating units over over such suchan anextensive extensivearea. area. Because Because of of these these correlation correlation the uncertainties uncertainties of some events events and and the problems, it and northern northern pam. parts.The Thesouthern southern BBC BBC contains, contains,in in it is is convenient convenient to to subdivide subdivide the the BBC into southern and order Lax Lake gabbro gabbro and the diorite; the the separate separate but but correlative(?) k l a t i v @ ? ) Blesner Lake diorire: order of successive successive emplacement, emplacement,the LaxLuke the Finland abase sill, and and Finland Radar RadarStation Stationgranophyre; eranonhvre:the thelayered layeredmafic maficSonju SoniuLake Lukeintrusion, intrusion.the the Victor VicforHead di diahme . -. ..dl . - ihp. -theextensive with its -mrthosite anorthosite inclusions inclusions and and composite composite bodies bodies of of the the extensivedikes dikesand andsills silkof ofBeaver BeaverRiver ~ i v ediabase diabase r ferrogabbroic Silver Bay intrusions. intrusions.Although Althoughthe theBeaver BeaverRiver River diabase diabaseand and its its composite composite intrusions intrusionscan can be be traced fermgabbmic throughout north of of about about 47%' 47°30'latitude. latitude. From oldest oldest totoyoungest, throughout the the BBC, a distinct distinct suite suite of intrusions intrusions occurs north youngest, the Lake inclusion-rich inclusion-rich &rife diorite (see (see Bcerboom, Boerboom, this volume), the Cabin thenorthern northern BBC BBC units units are arethe the Shoepack ShoepackLuke Cabin Creek porphyritic ferrogabbro, the porphyritic diorite, dorife,the theUpper UpperManitou ManitouRiver Rivergabbro, gabbro,the theWilson WilsonLake ferrogabbro, theHoughtaling HoughtalingCreek Creektroctolite, rrocfolite, and Beaver River diabase, diabase, together intrusions. The River gabbro and again, again, the theBeaverRiver together with several composite intrusions. The Upper UpperManitou ManiwuRiver gabbro is Lake gabbro/Blesner is probably probably correlative correlativewith with the the Lax LaxLake gabbrolBlesnerLake diorite dorite units units of of the the southern southernBBC, BBC, because becauseall allare are irregular internal smicture, structure, are strongly strongly altered, altered,and andhave haveaasimilar similarrange rangeofofrock rocktypes. types. A A possible possible irregular in form, lack internal comagmatic keelcomagmatic relationship relationshipbetween the the Houghtaling Creek Creek troctolite, troctolile, a 2- to 3-km-wide, northeast-trending, keelshaped Lake intrusion, a well-differentiated, well-differentiated, 1-km-thick, sheet-like shaped intrusion, intrusion, and and the the lower lower section section of of the the Sonju Late body, isissuggested olivine-plagioclasecumulates. cumulates. More texturesand and compositions of their olivine-plagioclase suggestedby bythe thesimilar similartextures discussion discussionof of petrologic petrologic and andtectonomagmatic tectonomagmatic relationships relationshipsof of the the BBC BBC are are given given in in Miller Miller and and Chandler Chandler(in (in review). review). General (heBeaver BeaverBay Bay and andDuluth Dduth complexes complexes are are the the shape, shape,cumulate cumulatecharacter, character,and and Generalcriteria criteriathat that distinguish distinguishthe environment environmentof of emplacement emplacement of individual mafic intrusions. Whereas Whereas DC intrusions are typically thick tabular bodies rocks, BBC intrusions tend be thinner (c2km) (<2km) bodiesof of mostly mostly mafic mafic cumulates cumulatesemplaced emplaced adjacent adjacentto to other other intrusive rocks, sheet-like sheet-likebodies bodies or ordikes dikesof of typically typically non-cumulate non-cumulate mafic mafic rocks that commonly are in contact with volcanic country rock. betweenBBC BBCand andDC DCininthe themap maparea areaisisaa northeast-trending, northeast-trending,55- to to 8-km-wide 8-km-wide transition zone rock. The Theboundary boundarybetween bounded bounded by the the Houghialing HoughfalingCreek Creek troctolite frocfolile totothe thesoutheast southeastand andby by gabbroie gabbmicanorthosites anorthositesof of the the DC DC to to the the northwest. zoneisisaacomplex, complex,heterogeneous heterogeneousmixture mixtureof of DC DCand andBBC BBCrock rock types, types, from fromoldest oldestto to northwest. Within Withinthis thiszone youngest, rock, (2) highly contaminated mafic mafie intrusions youngest, (1) strongly strongly metamorphosed metamorphosed to to partially remelted remelted volcanic rock, of inclusion-rich diorite, diorite, (3) plutons, (4) (4) plagioclase-phyric plagioclase-phyric mafic mafie intrusions, intrusions,and and (3) large granopyhyre plutons, of Shoepack Lake inclusion-rich (5) ferro gabbro - Plagioclase Plagioclase phenocryst (5)mafic mafii dikes dikesand andlayered layeredcumulates cumulatesof ofthe theWilson WilsonLake Lakeferrogabbro phenocryst compositions compositions and textures Creek porphyritic &rite diorite are textures and and the theferrodioritic fermdiorificmatrix matrix composition composition of the CabIn Cabin Creekporphyritic are consistent consistent with its its being aa hypabyssal gabbroic anorthositic anorthositie locks. rocks. If the deeper DC gabbmii If so, this would imply that DC DCand andBBC BBC hypabyssal equivalent equivalent of the magmatism magmatismwere, were, in part, part, contemporaneous. Recently Recentlyacquired acquiredU-Pb U-Pbages ages (Paces (Pacesand Miller, 1993) 1993) bracket DC and BBC Lake BBC magmatism magmatism between between 1099 1099Ma, the the age age of of DC gabbroic anorthosite, and 1096 1096 Ma, the age of the Sonju Lake intrusion intrusion and andaaSilver SilverBay Bay intrusion, intrusion,but butdo donot not reveal reveal whether whether the themagmatism magmatism overlapped. overlapped. ItIt is is apparent apparentfrom from Figure Figure11that thatan anextensive extensiveband bandof of subvolcanic subvolcanicintrusions intrusions occurs occursin in the the North North Shore ShoreVolcanic Volcanic Group toGrand GrandPortage. Portage. Although Althoughthese theseintrusions intrusionsfit fitthe thegeneral generalcriteria criteriadistinguishing distinguishingthem themfrom from Gmupfrom from Duluth Duhithto the band should be considered considered part of the the Duluth DuIuth Complex, Complex, itit will willrequire require more more work work to to determine detennme how much of this tend BEC. between Torte Tofte and and Grand Grand BBC. Miller Millerand andChandler Chandler(in finreview) review)suggest suggestthat (hatthe the intrusive intrusive rocks near the lakeshore between Marais Marais be beincluded includedininthe theBBC BBC(eastern (easternBBC, BBC,Fig. Fig.1). 1).The Themain mainintrusive intrusiveunit unitthere thereisisanorthosite-bearing anorthosite-bearingdiabase diabase which signature directly to toBeaver BeaverRiver Riverdiabase diabasein inthe thenorthern northernBBC. BBC. Another be traced (racedby by its its aeromagnetic aemmagnetic signature which can can be phase porphyry, aaplagioclase-phyric Cabin Creek phaseisisthe theLeveaux Leveauzporphyry, plagioclase-phyricdiorite dioritethat thatisis very similar similar to the Cabin Creek porphyritic diorite diorileof of the the northern northernBBC. BBC. More Moremust mustbe belearned learnedof ofthe thewell-exposed well-exposedbut but incompletely incompletelymapped mapped subvolcanic subvolcanic intrusions too should should be be included included in in the the BBC. BBC. West intrusionsfarther farther northeast northeast of of the the project project area area to determine determine whether they too West -. . 42 �I southwest of of the the study study area, area,thick thick glacial glacial cover makes interpretation and southwest interpretation tenuous. tenuous. However, However, aemmagnetic aeromagnetic data integrated with shallow in a large area area covering integrated shallow drilling drilling and and rare tare outcrop in ig. 1) covering the central central Duluth Duluth Complex Complex (CDC, (CDC, F Fig. 1) suggest BBC-like sheeted intrusions. These suggest the presence of BBC-like Theseintrusions, intrusions, informally informally termed the Cloquet Cloquet Lake Lake layered series, seem to be enclosed merge, in part, part, with the the Houghlalimg Houghtaling Creek troctolite. enclosed in volcanic rock and seem to merge, troctolite. A A preliminary 1:100,000-scale 1: 100,000-scalegeologic geologicmap mapofofriris thisarea areawi will alsobebeshown shownatatthe theposter postersession. session. Very Verylittle littleisis ll also known of of the hypbyssal hypabyssal rocks rocks tentatively tentalively mapped mappedfarther farthersouthwest. southwest. REFERENCES CITED REFERENCES CITED Boerboom, T.B, and and Miller, Miller, J.D.. J.D., Jr.. Jr., in preparation. preparation, Geologic Geologicmap mapof of the theWilson WilsonLake Lakeand andparts partsof of the the Silver Silver Island Island Lake Lake Boerboom, T.B. and Toohey Lake quadrangles: Minnesota Minnesota Geological Survey Misc. Map Series, scale scale 1:24,000. 124,000. F.F. Schwartz, G.M., G.M., 1939, The The geology of of the anorthosites of of the Minnesota Minnesota coast coast of of Lake Superior: Superior: Grout, F .F. and SchwarU, Minnesota Geological Geological Survey Survey Bulletin Bulletin 28, 28, 119 119 p. Miller, J.D., J.D., Jr., the Split Split Rock Rock Point Point NE NE and and Silver Silver Bay Bay quadrangles, Lake County. County, Minnesota: Minnesota; Jr.. 1988, 1988, Geologic map of of the Minnesota Geological Survey M Misc. isc. Map Series, M-68, M-68. scale scale 1:24,000. 1:24,000. Miller, J.D., J.D., Jr., Jr., Green, JC., J.C., and andBoerboom, Boerboom, T.B., T.B.. 1989. 1989,Geologic Geologic map of the the IlIgen City quadrangle, quadrangle. Lake County, Comity, Minnesota: Misc. Minnesota: Minnesota Geological Survey M i . Map Series, Series, M-69, M-69, scale 1:24,000. 1:24,000. Miller, J.D., J.D., Jr.. Jr., Green, V.W., Geologic map map of of the Finland and Doyle Lake Green,J.C., J.C., Boerboom, Boeiboom. T.B., T.B., and Chandler, Chandler, V .W.,1993, Geologic quadrangles, Misc. Map Series. Series, M-73, scale quadrangles. Lake County, County. Minnesota: Minnesota; Minnesota Geological Survey Misc. scale 1:24,000. 1:24.000. Miller, Miller, J.D., J.D., Jr., Jr, Boerboom, Boeiboom. T.W, T.B., and and Jerde, Jerie. E.A., E.A., in in preparation. preparation, Geologic map of the the Cramer CraniCT and and Cabin CabinLake Lakequadrangles: quadrangles: Minnesota Misc. Map Series, scale M i i t a Geological Survey Misc. scale 1:24,000. 1:24,000. Miller, J.D.. J.D., Jr. and and Chandler, Chandler, V.W., V.W., in in review, review. Geology, Geology, petrology petrology and tectonic significance of the the Beaver BeaverBay Bay Complex, Complex. Miller. Minnesota: Geological Society of America Special Paper. Paper. northeastern Minnesota; Paces, J.B. and Miller. Miller, J.D., Paces. J.B. J.D., Jr., Jr.. 1993, 1993. Precise Precise U-Pb ages of Duluth Duluth Complex and related mafic intrusions, intrusions. northeastern Geochronological insiits insights to physical, paleomagnetic, and and lectonomagmatic tectonomagmatic processes Minnesota: Geochronological physical. petrogenetic, petrogenetic. paImmagnetic, processes associated with the the 1.1 1.1Ga Ga Midcontinent Midcontinent rift rift system: system: Journal Journal of of Geophysical Geophysical Research, Research v. 98, 98, p. 13,997-14.013. p. 13,997-14,013. wen I' t I Ik — C p 16 :1K Eastern r 7— BI3C MIDDLE PROTEROZOIC (Keweenawan Supergroup) J: SEDIMENTARY Rocgs S Bayfield and Oronto Gps INTRUSIVEROOCS Subvolcanic maflc rocks md. Beaver Bay Complex Duluth Complex (Z) /• Geologic Map Coverage 50 0 Kilometers Southern BBC M-68 - Silver Bay/Split Rock NE M-69 - fllgenCfty M-72 - Doyle Lake/Finland LM - Little Marais (in prep.) Northern BBC C-CL - Cramer/Cabin Lake (in prep.) S-W-T - Silver Island Lake/Wilson Lake/Toohey Lake (in prep.) CDC - Central Duluth Complex and western BBC? Figure of Figure 1. 1. Generalized Generalizedgeology geology of northeastern northeasternMinnesota showing showing the location of maps covering Complex. Solid covering the Beaver Beaver Bay Complex. Solid outlines outlines show show areas areasof of 124,000 124.000 geologic maps (published (publishedMGS MGS Miscellaneous Miscellaneous Map Series are indicated indicated by by MMnumber). number). Dashed Dashed outline shows the the central central Duluth Duluth Complex Complex study area area for which geologicmap mapis isin inpreparation preparation. which aa 1:100,000 1:100/100 geologic Granitoid rocks Gabbroic cumulates Troctolitic cumulates C....) Anorthositic cumulates Early gabbroic rock 41111m) Logan sills VolcArqlc Rocxs (2) Schroeder Basalts = PLV C) NSVG - Normal polarity €2) NSVG - Reversed polarity LOWER PROTEROZOIC (Animikie Group) Creywacke, shale 41 Iron—formation ARCHEAN Granite-Greenstone terrane =Graniteree ens tone terrane 43 �ASSESSMENT OF SPRING CREEK CREEKAQUIFERVULNER AQUIFER VULNERABILITY TO POLLUTION USINGDRASTIC, DRASTIC. WATER WATER ASSESSMENTOF -LUTION USING TESTING, MODELING, AND AND HISTORICAL TESTING, GROUNDWATER GROUNDWATER MODELING, HISTORICAL RECORDS: RECORDS: AA PROJECT PROJECT OF THE THE MTU MTU REGIONAL GROUNDWATER EDUCATION EDUCATION IN IN MICHIGAN MICHIGAN(GEM) (GEM)CENTER CENTER MILLER, MILLER, Scott Scott A.. A., Sr., Sf., School School of of Forestry Forestry and and Wood Products, Michigan Michigan Technological University, University, Houghton, MI 295 MI 49931-1 49931-1295 The Spring Creek weilfield wellfield supplies supplies approximately one-half of the public drinking water water supply supply for the City of Ironwood and Erwin Township in Michigan and and the City of Hurley, Wisconsin. Wisconsin. The origin of E. E. coil colicontamination wntamination in in two two of ofthe thewells wellswas wasinvestigated investigated by by the theMichigan Michigan Technological University Regional Regional Groundwater Groundwater Education Education in in Michigan Michigan (GEM) (GEM) Center. Center. ARC/ INFO and ERDASgeographicinformation ERDASlgeographic informationsystems systems(GIS) (GIS)aided aideddata dataanalysis analysisand andpresentation. presentation. aquifer vu1nerabilitymap.-implemented vulnerabilitymapçimplemented on ARCIINFO A DRASTIC aquifer ARCIINFO GIS, GIs, was created created to provide provide a regional perspective on relative vulnerability of aquifers to pollutants originating at the ground perspective relative vulnerability of aquifers to pollutants originating at theground surface. The seven seven DRASTIC DRASTIC parameters parameters are are Depth Depth to to water, water, Recharge, Aquifer type, Soil, Soil, surface. Topography (slope), (slope), Impact of the vadose zone, and hydraulic Conductivity. Potential sources vadose zone, and hydraulic Conductivity. Potential sources of pollution were mapped to identify areas of particular particular concern. concern. Surface Surfacewater water testing testing estabestablished the presence of FL coil and fetal streptococci in Spring Creek and septic effluent pollution E. coli and fecal streptococci septic effluent pollution records providprovidin a wetland at the headwaters. Michigan Department of Public Health (MDPH) records ed clear evidence of aa close hydraulic connection between Spring Creek and the upper close hydraulic connection the upper Spring Spring Creek aquifer. Groundwater quality quality declined declined when when mine mine wastewater wastewater entered entered the the creek and Creek and improved when the wastewater was diverted. MODFLOW 2-D modeling demonstrated that was diverted. MODFLOW 2-D modeling demonstrated that aa improved when pumping well well located located close close to to a creek in hydraulic to the aquifer can draw creek hydraulic connection connection to pumping water into the well. water of F. The presence presence of E. coil colt and and fecal fecalstreptococci streptococci in in Spring Spring Creek Creek at at the the wellfield wellfield isis apparently apparently contamination in the upstream wetland. wetland. Fecal wliforms coliforms and streptococci independent of sewage wntamination streptococci 3/4 mile mile downstream of the wetland. wetland. Wildlife and livestock along the were barely detectable 314 for indicator indicator organisms organisms reaching reaching the the wellifeld. wellfield. creek can account for -1 aquifer may may draw draw a significant amount amount of of creek water. Wells screened in the upper unconfined unconfined aquifer Preventing wntamination contamination of of Spring Spring Creek Creek.is therefore a priority. The DRASTIC is The DRASTIC map mapindicates indicates :high risk riskof the wellfield wellfield is at relatively 'high of contamination contamination by vertical vertical movement movement into into the the aquifer aquifer from the ground surface. An active rail line along the creek valley and over the aquifer is rail line over the aquifer is cause cause confined aquifer is is an an option, option, but but this this water water has a higher for concern. Drawing from the deeper ~nfined~aquifer used only when when mixed with softer water from concentration of dissolved solids and is presently used the upper aquifer. Drilling Drilling wells farther away away from from Spring Spring Creek Creek or or into intoaquifers aquifersnot not closely closely connected with with surface water is recommended. Should the MDPH designate the water entering recommended. as surface water, a treatment plant will be needed. needed. The best long-term option the affected wells as is to develop aa welihead protection plan that includes an alternative wellhead that includes alternative water water source. source, 44 �A A POSSIBLE POSSIBLE METASOMATIC METASOMATIC ORIGIN FOR THE THE LONGNOSE LONGNOSE OXIDE-RICH OXIDE-RICH ULTRAMAFIC BODY ULTRAMAFIC BODY MINER, MINER,Owendolyn GwendolynC., C., Department Departmentof of Earth Earth and and Planetary Planetary Sciences, Sciences, Washington Washington University, University, St. Louis, MO 63130 63130 The TheLongnose Longnosebody bodyisisaatitanifemus titanifemusoxide-rich oxide-richultramafic ultramafic body body hosted hosted by by the the Partridge Partridge River intrusion of the troctolite series of the Duluth Complex. The body is located Complex. The is located 83 83 km north of River intrusion of the troctolite series Duluth 30,T. T. 59 59N., N., R. R 13 13W. W.ItItlies liesalong alongthe the trace trace of aa normal normal fault faultthat that cuts cuts two two Duluth in insection section30, other oxide-rich ultramaflc bodies, the Longear and 'Section 17' (Fig. 1). This fault offsets This other oxiderich ultramafic the Longear and 'Section 17' (Fig. sedimentary units, bringing bringing the the Biwabik Biwabik Iron Iron sedimentarystratigraphy, stratigraphy, but not the the Partridge River igneous units, Formation into contact with the Virginia Formation (Severson, 1988). Formation into contact with the Virginia Formation (Severson, 1988). Linscheid funnel, 760 760 m m long, long, up up Linscheid(1991) (1991)described describedthe theLongnose Longnosebody body as as an asymmetrical asymmetrical funnel, to 490 m wide, and with a maximum thickness of 167 m. The body is gradationally zoned inward and of 167 m. The is zoned inwanl to 490 m from oxide dunite, dunite, which hosts discordant discordant from an an oxide oxideclinopyroxenite clinopyroxemte to to an an oxide oxide peridotite peridotite to an oxide massive oxide zones (>80% oxides). In many cases, olivine is completely replaced by serpentineserpentineIn many cases, is completely replaced by massive oxide zones (>80% group minerals. The ilmenite-to-magnetite ratios vary among the distinct units within the group minerals. The ilmenite-to-magnetite ratios vary among distinct units Longnose is the the dominant dominant oxide m mineral. ineral. Longnoseand andwithin withinthe the massive massive oxide oxideunit unit itself, but ilmenite is Most magnetite grains show exsolution lamellae of spinelss and ilmenite. Secondary hydrous Most magnetite grains show cxsolution lamellac. spinelss and ilmenite. hydrous mineral to zones of intense fractures. mineral assemblages assemblagesoccur occur in in all all rock rock types types and and are not limited to There of the theLongnose Longnosebody. body. if Longnose Thereare aremany many questions questions regarding the origin of If the Longnose body is an source of of the the low-Sic, low-Si02,high-Fe-Ti high-Fe-Timelt? melt? If if it is not an intrusion, intrusion, an intrusion, intrusion, what is the source does crystal mush or after does itit represent representigneous igneousmaterial material that that was was reworked while still aa crystal crystallization or solidified material, fluids fluids must must crystallization was was complete? complete? Whether Whetherthere therewas was aa crystal mush or have been present present in in the the reworked areas. What Whatare are the the composition and origin of these fluids? Although concentration of platinum-group Althoughthe theLongnose Longnose body body has has no no known known appreciable appreciable concentration platinum-group elements, Bushveld. Both elements, itit resembles resembles the the platinifemus platinifemus dunite dunite pipes of the Bushveld. Both the thepipes pipes of the the Bushveld cores, which which host host massive massive oxide oxide zones, zones, Bushveld and and the the Longnose Longnose body consist of Fe-rich dunite cores, and and marginal marginal pymxenitic pyroxenitk and and gabbroic gabbmic rocks. rocks. The Thecomposition compositionof of olivine olivine from from the the Bushveld Bushveld pipes pipes ranges from Fow Fo93 to toFFog4; theLongnose, Longnose,it itranges ranges FoototoFofi6 Fo (Linscheid, frfrom om Fogo (Linscheid, 1991). 1991). w ; ininthe Schiffries Driekop pipe in the Bushveld formed by infiltration Schifflies(1982) (1982)suggested suggestedthat the the Driekop metasomatism, of which which is the the formation of a metasomatism, one oneof of the the most most important important characteristics of monomineralic monomineralicrock rock such such as as dunite (Korzhinskii, (Korzhinskii, 1970). The The Longnose Longnose body body has has aa conspicuous conspicuous dunite is in in turn turnsurrounded surrounded by byttoctolitic troctoliticrocks. rocks. In dunite core, core, which which grades grades outward to pyroxenite and is this Longnose body and this context, context, itit seems seemsreasonable reasonable to to suggest suggest aa metasomatic metasomatic model for the Longnose and to to exnlore possible nossible lines of evidence. explore lines evidence. r _____ _Ñ_. _ _ of ._ _ In the with noritic noritic host rocks and produced the Driekop Driekop pipe, pipe, metasomatizing metasomatizing fluids fluids reacted with olivine-rich rocks (Schiffries, (Schif&ies, 1982). Schiffries' Schif&ies'model modelisis that that fluids fluids passed passed through through the the troctolitic troctolitic olivine-rich rocks rocks removing appropriate to produce producedunite. dunite. These components were were rocks removing appropriate components in order to transferred occurrence of such transferred to to secondary minerals. In Inthe theLongnose Longnosebody, body, the occurrence such secondary minerals clinopyroxene indicate indicate the presence of a minerals as as chlorite, chlorite, serpentine, serpentine, amphibole, amphibole, and and Ti-rich clinopyroxene fluid fluid that that transported transportedat atleast least calcium, calcium, iron, iron,titanium, titanium, and and water. if were involved, then how howwere weretheir theireffects effectsconcentrated concentratedin inone one If metasomatizing metasomadzing fluids fluids woe area? fault that that connects connects three three oxide-rich, oxide-rich, area? One Onepossible possibleanswer answerlies liesin in the theexistence existenceof aa normal fault ultramafic Formation, which could could be be aa Onone oneside sideof of this thisfault faultis is the the Biwabik Iron Formation, ultramafic bodies. On wide actinolite actinolite source of of Fc-rich Fe-rich fluids. fluids. Also, has noted notedthe thepresence presenceofof<2 cm wide Also,Linscheid (1991) has Q cm veins in the Longnose body. body. In from area.surrounding surrounding the Longnose In the drill core f rom the Longnose body there the area All of these ffractures could are are numerous numerousmillimeter-scale mdkmem-scale fractures fractmaand andcross-cutting mss-cuttiug features. featunx. A ll ofthese ractu~ could ~ serve as conduits conduitsfor forpercolating percolating fluids. serve as Present on: possible possible correlation of ilmenite-toihnemte-toPresent research research on on the the Longnose Longnose body is focused on: magnetite rock type within the body, electron microprobe microprobe magnetite ratios ratios with with respect respect to rock type and and spatial position within -~ .à ...‘. ~ . 45 �S analyses on exsolved and unexsolved ilmenite and magnetite grains to provide T-f02 esfintnes of the formation and reequilibration conditions in the Longnose body, and electron microprobe analyses of secondary minerals to place temperature and compositional constraints on the possible metasomatizing fluids. Fig. 1. Location of three oxide-rich ultramafic bodies along the trace of a normal fault (after Severson, 1988). Oxide-richultr-c bodies Virginia Formation 0 Duluth Complex N t REFERENCES CIT ED Korzhinskii, D.S., 1970, The theory of metasomatic zoning: London, Oxford Univ. Press, 162 p. Linscheid, E.K., 1991, The petrography of the Longnose peridotite deposit and its relationship to utelithithtomplexflinpubL MS. thesis, UidMinn., Duluth, MN. d SchifiSts, CM, 1982, The peirogenesis of a plañniferous dunite pipe in the nskweA. Cotr\er Infiltration metasomatism by a chloride solution: Ecoa GeoL, v. 77, p. 1439-1453. Severson, 1sf., 1988, Geology and structure of a portion of the Partridge River intrusion: A progress report: Natural Resources Research Institute, Univ. Minn., Duluth, Tech. Rept., NRRI/GMIN-TR-88-08, 78 p. 46 �HEAVY MINERALS FROM GLACIOFLUVIAL GLACIOPLUVIAL SEDIMENTS SEDIMENTS IN MINNESOTA MINNESOTA M i o t a Department Department NELSON, Sherry (prepared abstract), LAWLER, Tom and LEHR, J.D., Minnesota of Natural Resources, Division of Minerals, 1525 3rd Avenue E., Hibbing, of Natural Resources. of Minerals. Avenue E.. Hibbh. Minnesota M i t a , 55746; THEOBALD, Paul, RYDER, Jean, SUTLEY, Stephen andTRIPP, TRIPP, Richard, Richard, U.S. U.S. '55746;THEOBALD,P~U~,RYDBR, Jean, SUTLEY, Stephenand Geological Survey, Survey, Branch Branch of of Geochemistry, M .S. 973, 973, Eox Geochemistry, M.S. Box 25046, Federal Federal Center, Center, Geological 80225-0046 Denver, Colorado Colorado 80225-0046 A study which which analyzed analyzed the theheavy-mineral heavy.-Qiinei'alfraction fraction of ofnortheastern northeasternprovenance provenanceglaciofluvial glaciofluvial sediments sediments was conducted by by the the Minnesota Minnesota D Department of Natural Resources, Division of Minerals, in cooperation cooperation epartment of,NaQ@ Resources,Diykiiof Minerals, in U.S. Colorado. Eighty-eight samples samples were were with the u .S.GGeological eo~ogicalSurvey, SurveyBranch ,Branchofof Geochemistry,&Denver, m ~ r ,Colorado. , collected from from ggravel pits across a broad area of Minnesota, sieved to pass separated (sp r a d pitsacrossa Minnesota,,sieved pass. 0.83mm, 0.83mqseparated (sp gr gr collected —2.85) into three heavy-mineral fractions and then examined geochemically and mineralogically. -2.85) into threeheavy-m+ral fractions amj then .&m@ed geochemically and mineralogidy. .. A summary of the o fsample sample preparation preparation and and analysis, analysis, the the s.ymmy of the sampling samplingstrategy, strategy, the the methods of geological characteristics of of the samples, and the samples,and the geochemical geochemical and mineralogical mineralogical data for for the theheavyheavymineralconcentrate and &the paramagnetic paramagneticand &nonmagnetic nonmagnetic heavy-mineral fractions is ispres.&ntedin Openmineral presented in Open- concentrate file and others, file Report Remit 284 284 (Nelson ( N e wMri often. 1992). 1993. The geochemical and mineralogical data were analyzed by statistical techniques including basic statistics, correlations, histograms, and multivariate factor analysis of the individual data sets and by glacial the data s&. sets. Spatial geochemical and mineralogical data a and glacial lobe within thedata Spatialdata dataplots plots portraying portrayingthe thegeochemical nd .. the statistical results were prepared. prepared.: Fairly strong evidence of :the the local derivation derivation of aa significant significant fraction of of the the heavy heavy minerals, minerals,, particularly fraction, areindietfted are indicated in in the thespatial spatialdataplots. data plots.. Many of the patterns particularly those those iin nthe nonmagnetic fractian, Manyof variation in the geochemical mineralogical data define discrete clusters of samples definediscrete clsamples with with similar similar of variaf~on in&e geochemical and @uip&~&gieal The platinum group, with fire assay gold values, forms an anomaly which is characteristics. characteristics. platinum group,' fire assay gold valyes, an anomaly which is most most enriched along and southwest of the contact of the Duluth Complex. High concentrations consistently ~igh'concentrations . P , of andalusite or sillimanite occurred only in samples straddling the contact of the theintrusive intrusiveDuluth Duluth Complex with the adjoining metasediments. Several results show samples rich in in precious, base base metals, metals, and/or associated multi-element associations clustering along and just to the justto thewest westof of the theMississippi MississippiRiver. River. Three "hot spots" were identified: 1) sample number 23960 is enriched in elements and mbnlsusually minerals usually extremely differentiated granites, 2) sample number 23935 his has extreln6:characteristics extreme characteristics that associated with exf&e$differentiatedgrani~. 2)samplebnumber deposits, and 3) sample number typical would be attributed attributed to base metal metaldeposW,and 3)shple number 23908 23908 has values which exhibit exhibittypical anomalous characteristics for the platinum group assemblage. Many of the discrete clusters defined for @platinum group assemblage. Many of the' discrete clusters definedinin would the results exhibit characteristics expected from bedrock results exhibit characteristics expected bedrock in the thevicinity. vicinity. The results results also also show show strong geochemical and mineralogical evidence mineralization in (tadmineralogical evidence for mineralionin several areas previously f + ~ r * @ s~ not known (mownto to be mineralized.. . . surprisingly A report an interpretation of the results from A reportthat that will will present present.an interpret&g-of the,&ults fromthe thegeochemical gepdwnhl and and mineralogical min@ogicd the statistical data analysis, and the resultant spatial data plots is being prepared pl@,,b being prepared as as aacooperative cooperative data, +$a. analysis,& the resultant effort by a team of scientists the DNR and the This report will be available in July mm of from the DNR@ die USGS. This report w i l l be available 4 July 1994 1994 data, from the DNR, Division of Minerals, Hibbing, Minpesota. from the DNR,~ i v i s i o nof 'M , iee&, Hibbing, M i*. ~ *.. , . . . . . ,. ' ~~ Reference: ~ : , . .. . ,. L., Sutley, S .J., and Tripp, R.B., 1992, Chemical and mineralogical analyses and geological .,. Nelson, S. S.L., Sutley;SJ., characteristics of heavy minerals from glaciofluvial sediments in Minnesota; test and pilot study . .., data: Minnesota Department of Natural Resources Open-file Report 284, lOOp. A cooperative project with the U.S. Department of the Interior, Geological Survey, Denver, Colorado. . . 47 P �Geochemistry of the Geochemistry the Kallander Kallander Creek Creek Volcanics, Volcanics, 1.1 Ga Midcontinent Rift System, Wisconsin and Wisconsin and Michigan Michigan S.W. Nicholson,1 L.G. L.G. Woodruff,2 Woodruff? and and W.F. W.F. Cannon1:1 Cannon1: uSGS, S.W. USGS, National National 2 2280Woodale Woodale Dr., Dr., Mounds Mounds View, Center MS 954, Reston V VA A 22092; 22092; USGS, USGS, 2280 View, Center MN MN 55112 55112 (KCV)isisthe theyounger youngerofoftwo twounits units that that compose the The Kallander Creek Volcanics Volcanics (KCV) Powdermill Group, the earliest volcanic rocks to be erupted from the Powdermill the earliest volcanic erupted from the 1.1 1.1Ga in Wisconsin Wisconsin and and Michigan. Michigan. The system (MRS) (MRS)in The older older volcanic volcanic Midcontinent rift system rocks in the Powdermill Group are the Siemens Creek Volcanics (about 1.5 km the Powdermill Group are the Siemens Creek Volcanics (about 1.5 km dominated by high-alumina flood basalts which were probably thick), dominated probably fissure fissure fed. fed. KCV overlieithe-Siemens+Creek overliethe:SiemensCreek Volcanics Volcanics and are are composed composed of of aa sequence sequence of of The KCV andesite,and The KCV rhyolite'2-4-km-thick.~The KCV has been postulated to to be be the the basalt, andesite, andrhyolite'2-41cm-thick. partly eroded Ma erodedremnant remnantof ofaacentral centralvolcano volcanoerupted eruptedbetween betweenabout about1108 1108and and1102 1102Ma (Cannon and others, 1993). 1993). The outcrop outcrop belt extends more than 100 100 km along strike, but the the true true extent extent of of the the formation formation is unknown because it is overlain by younger rocks at both both ends. ends. The basalts basalts and of the the KCV KCV have average 5i02, S i a , P205, and and FeO FeO and basaltic basaltic andesites andesitesof contents somewhat higher than for the underlying underlying basalts basalts of the the Siemens Siemens Creek Lake Volcanics and Porcupine Porcupine Volcanics and the overlying overlying basalts basalts of the fee Portage Portage Lake Volcanics, whereas whereas MgO MgO and and CaO CaO contents contentsare are somewhat somewhatlower. lower. The most striking Volcanics, striking characteristic of of the KCV KCV is is the the high high average T Ti02 characteristic i e content (about 3.5 wt %) %) compared Portage Lake Volcanics to that that of of the theSiemens SiemensCreek CreekVolcanics Volcanics (about (about1.5-2.5 1.5-2.5 wt %), %), Portage 1.7-2.7 wt wt %), %),and and Porcupine Porcupine Volcanics Volcanics(about (about2.2 2.2wt wt%). %). There There appear appear to be (about 1.7-2.7 5i02 content from basalt through the intermediate no large compositional gaps in Si02 intermediate of the KCV. KCV. Average trace element compositions of and more more felsic felsic volcanic rocks of Kallander Creek basalts and basaltic andesites and basaltic andesites show show significant significant differences differences in Lake, and comparison to average average basalt basalt compositions compositions of the the Siemens Creek, Portage Lake, KCV have lower contents contents of compatible trace trace elements elements Porcupine Volcanics. Volcanics. The The KCV such as Cr and and Ni Ni and andhigher highercontents contentsof of incompatible incompatibletrace traceelements elementssuch suchas asNb, Nb,Y, Y, REE, Hf, and Th than many other basalts, except for a few individual flows in both REE, Hf, and Th than basalk, for a few individual the Porcupine PorcupineVolcanics Volcanics and•the and the basalSiemens basal SiemensCreek CreekVolcanics. Volcanics. In detail, distinctive trace element characteristics make it possible to recognize distinctivetrace-element two suites suites of volcanic rocks within the Kallander Creek Volcanics. Volcanics. Both Both suites suites range from basalt to intermediate rocks ançl rhyolite and are indistinguishable in and rhyolite and are major element composition. The Thelowermost lowermost1.5 1.5 km km of of the theKCV KCV consist consist of of basalt basalt with minor andesite and rhyolite, all of which have steep straight REE patterns andesite and rhyolite, all of which have steep straight REE patterns (basalts and andesites andesites have have (Ce/Yb)= (Ce/YbIn=8.0-10.6; 8.0-10.6; rhyolites rhyolites have have (Ce/Yb)= (Ce/YbIn=11.2-11.4). 11.2-11.4). The upper part of the Kallander Creek contains all three rock types as well, but part of the Kallander Creek contains as REE patterns are much less steep steep and and LLandesites dominate. The Theslopes slopesof of these these REF shaped (basalts and andesites have (Ce/Yb)= 2.9-5.8; rhyolites have (Ce/Yb)= 3.4shaped (basalts (Ce/Yb)n= 2.9-5.8; rhyolites have (Ce/Yb)n= 3.4 7.7). Similar distinctions between the upper and lower suites 7.7). suites can be made made by using using ratios. For of basalts and andesites other trace element ratios. For example, the lower group of 48 �have Y/Nb= 0.8 and Ta/Th= Ta/Th' 0.6, 0.6, whereas whereas the upper group group of basalts and andesites have Y/NbY/Nb= 2.0 2.0 and and Ta/Th= Ta/Th 0.3. 0.3. This work, in conjunction with with previously previously gathered gathered Nd Nd and Pb isotopic data, data, documents fluctuations in magma sources and eruptive style during development development of the MRS in Wisconsin Wisconsinand and Michigan. Michigan. Volcanism Volcanismbegan beganwith with the the eruption eruption of of a MRS in thin discontinuous group of basalts that contain clinopyroxene phenocrysts and are discontinuous group of basalts that contain clinopyroxene generally rich in incompatible Ti02. These These rocks form the incompatible trace elements, including TiO2. basal unit of the Siemens Creek Volcanics and are postulated to unit of the Siemens Volcanics and are postulated be fissure-fed flood basalts derived by small degrees of of partial partial melting meltingwithin withinthe themantle mantleplume plume that that led led to the development of the MRS (Nicholson and Shirey, 1992). Overlying this basal Shirey, 1992). Overlying the development of the MRS unit, most flood basalts, basalts, which which are poorer most of of the the Siemens Siemens Creek Creek Volcanics Volcanics comprise flood in incompatible trace element abundances and and which which were were most probably derived from plume melts probably augmented by the addition of of melts from another source, possibly subcontinental lithosphere (Nicholson and subcontinental lithosphere (Nicholson and Shirey, Shirey, 1992). 1992). The lower lower unit unit of of the the Kallander Kallander Creek Creek Volcanics Volcanics is broadly similar in incompatible trace element contents contents to the basal Siemens SiemensCreek Creekunit unit and, and, thus, thus, may be the result of of an additional additional small small degree degree of partial melting from deep within the plume. However, the major element However, the major element compositions compositions and low compatible compatible trace element content of of the lower KCV suggest that that this this batch batch of of melt melt underwent underwent some KCV suggest fractionation before before eruption. eruption. The upper Kallander Creek unit, with its The upper Kallander its abundance abundance of rocks, is is most most similar similar to to the younger Porcupine of intermediate and and felsic felsic volcanic rocks, Porcupine Volcanics, which is is considered a broad central volcano at the top top of of the the volcanic volcanic Volcanics, which section (Nicholson and others, others, 1991). 1991). By By analogy with the the Porcupine PorcupineVolcanics, Volcanics, the upper upper KCV KCV is most likely derived by mixing of crustal and mantle melts. (Note, the isotopic isotopic analyses needed to to constrain constrain hypotheses hypotheses for for the the origin origin of of the the KCV KCV are are in in preparation). Overlying Overlyingthe theKallander KallanderCreek Creek Volcanics Volcanics are the Portage Lake highalumina alumina fissure-fed flood basalts, most probably derived by shallow melting within the 1990), and and finally finally by by the thePorcupine PorcupineVolcanics. Volcanics. the plume plume(Nicholson (Nicholsonand andShirey, Shiiey,1990), Cannon, R.E., Peterman, Z.E., Z.E., and Davis, Davis, D.W., D.W., Cannon, W.F., W.F., Nicholson, S.W., S.W., Zartman, R.E., 1993, The Kallander Creek Volcanics--A remnant of the Keweenawan central The Kallander Creek Volcanics-A of Keweenawan central volcano centered centerednear nearMellen, Mellen,Wisconsin Wisconsin[abs.]: Labs.]: Institute on Lake Superior Superior Geology, Proceedings, v. 39, Geology, Proceedings, v. 39, p. p. 20-21. 20-21. Nicholson, L.G.,1991, 1991, The The Nicholson, S.W., S.W., Schulz, Schulz, K.J., K.J., Cannon, W.F., W.F., and and Woodruff, Woodruff,L.G., Porcupine Mountains area, Michigan--A Keweenawan central volcano? Porcupine Mountains area, Michigan~AKeweenawan central volcano? [abs.]: [abs.]: Institute 79-81. Instituteon onLake LakeSuperior SuperiorGeology, Geology, Proceedings, Proceedings, v. v. 37, 37, p. 79-81. Nicholson, S.W., 1990,Midcontinent Midcontinentrift riftvolcanism volcanism in in the Lake S.W., and Shirey, S.B., S.B., 1990, Superior Superior region: region: Sr, Nd, and and Pb Pb isotopic isotopic evidence evidence for a mantle mantle plume plume origin: origin: Journal p. 10851-10868. 10851-10868. Journalof of Geophysical GeophysicalResearch, Research,v. v. 95, 95, p. 1992, Nd 1.1Ga Ga Midcontinent Midcontinent ,1992, Nd and andPb Pbisotopic isotopicevolution evolutionof of basalts basalts of of the the1.1 rift: rift: evidence evidence for aa region-wide region-wide model model for for plume-lithosphere-asthenosphere plume-lithosphere-asthenosphere interaction 7 p. p. interaction[abs.]: [abs.]: U.S. U.S. Geological Geological Survey SurveyOpen-File Open-FileReport Report92-525, 92-525,7 49 �Geochemistry of the Kallander Creek Volcanics, 1.1 Ga Midcontinent Rift System, Wisconsin and Michigan S.W. Nicholson,1 L.G. Woodruff,2 and W.F. Cannon1:1 USGS,Nationa National 0x1': USGS, 2 Center MS 954, Reston VA 22092; USGS, 2280 Woodale Dr., Mounds View, ' MN 55112 The Kallander Creek Volcanics (KCV) is the younger of two units that compose the Powdermill Group, the earliest volcanic rocks to be erupted from the 1.1 Ga Midcontinent rift system (MRS) in Wisconsin and Michigan. The older volcanic rocks in the Powdermill Group are the Siemens Creek Volcanics (about 1.5 1cm thick), dominated by high-alumina flood basalts which were probably fissure fed. The KCV overliethe-SiemenszCreelc,Volcanics and are composed of a sequence of basalt, andesite; and: rhyolite:24km thick;. The KCV has been postulated to be the partly eroded remnant of a central volcano erupted between about 1108 and 1102 Ma (Cannon and others, 1993). extends more more than than 100 100 kkm along strike, strike, 1993). The outcrop belt extends m along but the true extent of the formation is unknown because it is overlain by younger rocks at both ends. The basalts and basaltic andesites of the KCV have average Si02, P205, and FeO contents somewhat higher than for the underlying basalts of the Siemens Creek Volcanics and the overlying basalts of the Portage Lake Volcanics and Porcupine Volcanics, whereas MgO and CaO contents are somewhat lower. The most striking characteristic of the KCV is the high average Ti02 content (about 3.5 wt %) compared to that of the Siemens Creek Volcanics (about 1.5-2.5 wt %), Portage Lake Volcanics Porcupine Volcanics (about 2.2 wt wt %). There appear appear to be (about 1.7-2.7 wt wt %), %), and Porcupine %). There no large in S5i02 from basalt basalt through through the intermediate i a content from arge compositional gaps in and more felsic volcanic rocks rocks of of the the KCV. KCV. Average Average trace trace element element compositions compositions oof Kallander in and basaltic andesites show significant differences in ander Creek basalts and comparison to average basalt compositions of the Siemens Creek, Portage Lake, and Porcupine Volcanics. The KCV have lower contents of compatible trace elements such as Cr and Ni and higher contents of incompatible trace elements such as Nb, Y, REE, Hf, and Th than many other basalts, except for a few individual flows in both the Porcupine Volcanics .and the basal Siemens Creek Volcanics. In detail, distinctive trace element characteristics make it possible to recognize two suites of volcanic rocks within the Kallander Creek Volcanics. Both suites range from basalt to intermediate rocks ançl rhyolite and are indistinguishable in major element composition. The lowermost 1.5 km of the KCV consist of basalt with minor andesite and rhyolite, all of which have steep straight REE patterns (basalts and andesites have (CeIYb)8= 8.0-10.6; rhyolites have (CeIYb)n= 11.241.4). The upper part of the Kallander Creek contains all three rock types as well, but andesites dominate. The slopes, of these REF patterns are much less steep and Lshaped (basalts and andesites have (Ce/Yb)= 2.9-5.8; rhyolites have (Ce/Yb)n= 3.4 7.7). Similar distinctions between the upper and lower suites can be made by using other trace element ratios. For example, the lower group of basalts and andesites 50 �whereasthe theupper uppergroup group of of basalts basalts and and andesites andesites have Y/Nb= 0.8 0.8 and Ta/Th=' Ta/Th= 00.6, .6,whereas have Y/Nb= Y/Nb= 2.0 and Ta/Th= 0.3. 2.0 and Ta/Th= 0.3. with previously previously gathered gathered Nd Nd and and Pb isotopic data, This work, in conjunction conjunction with documents fluctuations in in magma magma sources sources and and eruptive eruptive style style during during development of the MRS in Wisconsin Wisconsinand and Michigan. Michigan. Volcanism Volcanismbegan beganwith with the the eruption eruption of of a of MRS in thin discontinuous group of basalts that contain dinopyroxene clinopyroxene phenocrysts phenocrystsand and are are TiC2. These rocks form the generally rich in incompatible trace elements, including Ti02. basal unit of the Siemens Creek Volcanics and are postulated the Siemens Volcanics and are postulated to be fissure-fed flood of partial partial melting meltingwithin withinthe themantle mantleplume plume that that led led basalts derived by small degrees of and Shirey, Shirey, 1992). 1992). Overlying this basal to the development development of of the the MRS MRS (Nicholson and unit, most of the Siemens Creek Volcanics comprise flood basalts,which which are are poorer poorer the Siemens Volcanics comprise flood basalts, element abundances abundances and and which which were were most most probably derived in incompatible trace element from plume melts probably. augmented by the addition of melts from another probably augmented-by,the addition of melts from 1992). source, possibly mssiblv subcontinental subcontinental lithosphere lithosohere (Nicholson (Nicholson and and Shirey, Shirev. 1992). The lower unit of the Kallander Creek Volcanics is broadly similar in he &it the Kallander creek ~ilcanicsis broadly similar in. incompatible trace trace element element contents contentsto to the the basal basalSiemens SiemensCreek Creekunit unitand, and,thus, thus, may may incompatible be the result of an additional small degree of partial melting from deep within the of an additional of melting from deep plume. However, plume. However,the themajor major element element compositions compositions and low compatible compatible trace element content of the lower KCV suggest that this batch of melt underwent some KCV suggest that this batch of melt fractionation before before eruption. eruption. The upper Kallander Creek Creek unit, unit, with with its abundance of intermediate and felsic volcanic rocks, is most similar to the younger rocks, is most similar to the younger Porcupine and felsic Volcanics, which isis considered considered aa broad broad central central volcano volcanoat at the the top top of of the volcanic Volcanics, which section (Nicholson and others, 1991). By analogy with the Porcupine Volcanics, the 1991). By analogy with Volcanics, the of crustal and and mantle melts. (Note, the upper KCV KCV is most likely derived by mixing of of the KCV are in in isotopic analyses needed to constrain hypotheses for the origin of KCV are preparation). Overlying preparation). Overlyingthe theKallander KallanderCreek Creek Volcanics Volcanics are the Portage Lake highbasalts, most most probably probablyderived derived by by shallow shallow melting melting within within alumina fissure-fed flood basalts, the plume 1990), and finally by the Porcupine Porcupine Volcanics. Volcanics. plume (Nicholson (Nicholson and andShirey, Shirey, 1990), Zartman, R.E., Peterman, Peterman, Z.E., Z.E., and and Davis, D.W., D.W., Cannon, W.F., W.F., Nicholson, S.W., S.W., Zartman, 1993, The Kallander Creek Volcanics--A remnantofofthe the Keweenawan Keweenawan central central 1993, Volcanics~Aremnant volcano centered near Mellen, Wisconsin [abs.]: Institute on Lake Superior centered near Mellen, Wisconsin [abs.]: Institute 39,p. Geology, Proceedings, v. 39, p. 20-21. 20-21. Nicholson, S.W., Schulz, K.J., Cannon, W.F., and and Woodruff, L.G., L.G., 1991, The The S.W., K.J., Cannon, W.F., Porcupine Mountains Mountains area, area, Michigan--A Michigan-A Keweenawan central volcano? [abs.]: [abs.]: Institute on Lake Superior Geology, Proàeedings, v. 37, 79-81. Institute on Lake Superior Geology, Proceedings, 37, p. 79-81. Nicholson, S.W., 1990,Midcontinent Midcontinentrift riftvolcanism volcanism in in the Lake S.W., and Shirey, S.B., S.B., 1990, Superior region: Sr, Nd, and Pb isotopic evidence for for a mantle plume plume origin: origin: Journal 95,p. 10851-10868. Journal of of Geophysical GeophysicalResearch, Research, v. 95, p. 10851-10868. 1992, Nd and Pb of basalts basalts of of the the 1.1 Ga Midcontinent Midcontinent ,1992, Pb isotopic isotopic evolution of 1.1 Ga rift: evidence for a region-wide rift: region-wide model for plume-lithosphere-asthenosphere plume-lithosphere-asthenosphere interaction [abs.]: 7 p. 92-525,7 [abs.]: U.S. U.S. Geological Survey Open-File Report 92-525, interaction p. 51 �EXPLORATION AND MINING MINING ACTIVITY EXPLORATI ON AND ACT1 VI TY IN I NNORTHWESTERN NORTHWESTERN ONTARIO ONTARI 0 0' MarkS.,S., Ministry Ministry of 0' BRIEN, BRIEN, Mark of Northern NorthernDevelopment Development and and Mines, Mines, Suite B002, 435 James St. South, Thunder Bay ON P7E 6E3 Suite 435 James St. South, Thunder Bay ON P7E 6E3 The The mineral mineral' sector s e c t o r in i n Ontario Ontario provided provided an an estimated estimated 18,244 18,244 direct jobs and produced products with a total Canadian dollar d i r e c t jobs and produced products with a t o t a l Canadian dollar value billion $5. 1 b i l l i o n in i n 1993. 1993. value of of $5. Four Canada iin were from Four of of the t h e top t o p gold gold producers producers iin n Canada n 1993 were from northwestern Ontario: Williams Mine (492,251 oz), Golden Giant northwestern Ontario: Williams Mine (492,251 o z ) , Golden Giant Mine oz) and and tthe Mine (422,528 (422,528 oz), oz), Campbell Campbell Mine Mine (300,472 (300,472 oz) h e David David Bell Bell Mine (215, 188 oz). Mine (215,188 0 2 ) . This mines and and advanced advanced This poster p o s t e r displays displays the t h e producing producing mines mineral exploration projects in the northwestern portion of the the mineral e x p l o r a t i o n p r o j e c t s i n t h e northwestern p o r t i o n of Province of Ontario. The base map is a collage of the Bedrock Province of Ontario. The base map i s a c o l l a g e of t h e Bedrock Geology Geology Map Map of of Ontario. Ontario. Currently tthere h e r e aare r e 7 producing gold mines, 2 base metal mines, 1 platinum group mines, 2 base metal mines, 1 platinum group metal metal mine, mine, 66 quarries, 2 peat moss producers, 5 amethyst mines and 99 amethyst q u a r r i e s , 2 p e a t moss producers, 5 amethyst mines and amethyst producers in the region employing approximately 2700 people. producers i n t h e region employing approximately 2700 people. Quarry crushed dimension stone, stone, I1 crushed Quarry producers producers consist c o n s i s t of of 22 dimension granite, 1 quartz, 1 diabase and 1 soapstone producer. There quartz, 1 diabase and 1 soapstone producer. granite, are also 5 projects in the advanced exploration stage. a r e a l s o 5 p r o j e c t s i n t h e advanced exploration s t a g e . Representative of Northwestern Ontarioaare on display. display. Representative samples samples of Northwestern Ontario r e on A statistical summary booklet that tabulates regional data A s t a t i s t i c a l summary booklet t h a t t a b u l a t e s r e g i o n a l d ata such as reserves, grades, location, ownership and development is a s reserves, grades, location, is available free of charge. Many other free brochures are also a v a i l a b l e f r e e of charge. o t h e r f r e e brochures a r e a l s o available. available. 52 �PRELIMINARY SOURCE-ROCK EVALUATION OF PRELIMINARY SOURCE-ROCK AND AND MATURITY MATURITY EVALUATION OFTHE THE PRECAMBRIAN PRECAMBRIAN NONESUCH NONESUCHFORMATION FORMATIONIN INTHE THETERRA TERRAPATRICK PATRICK#7-22 #7-22 BOREHOLE, MIDCONTINENT BAYFIELDCOUNTY. COUNTY, WISCONSIN WISCONSIN RIFTSYSTEM, SYSTEM. BAYFIELD BOREHOLE. MIDCONTINENTRIFT' - James G. and and BURRUSS, C., U.S.~Geological PALACAS, James BURRUSS, ~Robert o b e rC., t U.S. e o l o ~ i c aSurvey, l ' s u r vBox e~, Denver, CO 25046, MS971, Denver, CO80225 80225 A wildcat wildcat well, westofofAshland, Ashland, Wisconsin, Wisconsin, was well,Terra TerraPatrick Patrick#7-22, #7-22, about about88ml mi(13 (131cm) km) west recently drilled drilled to Proterozoic Keweenawan Keweenawan to test test the the petroleum petroleum potential potential of Middle Proterozoic rocks in the Midcontinent pyrolysis analysis analysis was was performed performed on MidcontinentRift Rift System. Rock-Eval Rock-Eva1 pyrolysis m) section section of of the the Nonesuch Nonesuch 25 samples, 22 of which were were from from the the 436-foot 436-foot (133 m) Formation. (3m) m)interval. interval. Total organic organic Formation. Each Eachsample samplewas wasaacomposite compositeof of aa 10-foot 10-foot (3 carbon and averaged wt. % % and averagedabout about0.1 0.1 carbon (TOC) (TOO content content ranged rangedfrom fromessentially essentiallyzero zeroto to0.44 0.44 wt. %. The above values, however however should should be be considered consideredminimum. minimum. Although wt. %. Although special special' care was taken to remove drilling mud contaminants contaminants and larger larger sized sized chips chips of reddish reddish brown brown (oxidized) (oxidized)caved caved particles, particles, variable variable amounts amounts of the oxidized, oxidized, caved caved material material remained in dilution effects. This in the the samples, samples, causing causing in in some some cases serious dilution This is is remained illustrated by analysis illustrated analysis of a duplicate sample that was high-graded by meticulously individual dark-gray, fine-grained fine-grained particle. particle. The results results showed an picking out each individual relatively thin increase in 0.44 wt. wt. %. %. It is possible that relatively thin (about (about0.5-2 0.5-2 ft; increase inTOC TOCfrom from0.1 0.1toto0.44 0.2-0.6 m) m) organic-rich organic-rich silty shales that have have TOC of of from from 1.0 to to 2.5 2.5wt. wt. %, %,which which have have 0.2-0.6 been analyzed analyzed by others in nearby mineral exploration coreholes and outcrops, are also and others of oxidized oxidized caved caved materials materials and present but but completely completely masked masked by a combination of thicker, very organic lean, indigenous indigenous rock units. units. We speculate speculate that the average average TOC content may wt. % % but but certainly certainly not not higher higher than than0.5 0.5wt. wt.%. %. content may be be as ashigh highas as0.4 0.4 wt. Of the 25 samples analyzed only 3 gave gave reliable reliableTmax Tmaxvalues. values. These ranged from 436°C to to 441° 441°Cand and averaged averaged 438T, 438°C,maturity maturity values values indicative indicative of of the the early phase phase of 436OC of oil generation for Type II kerogen. This maturity ranking is consistent with maturity I1 ranking maturity generation for values obtained by previous previous workers. workers. values obtained for for comparable comparable Nonesuch rocks by In conclusion, the maturation maturation level favorable for oil level for the Nonesuch is favorable generation but generation but the the source-rock source-rock potential for this particular drillhole sample set, based content, is is rated rated poor poor to to at atbest bestfair. fair. On On the the other other hand, hand, as shown on the solely on TOC content, mud log, ppm by volume, and mud log, the the presence presence of of methane methane gas, gas, averaging averaging about about 1,000 1,000 ppm and throughout most of the Nonesuch lesser volumes of ethane to butane gases occurring throughout Formation indicates Formation indicates some some hydrocarbon hydrocarbon potential. potential. 53 �DUAL IMMISCIBILITY IN ROCKS ROCKS OF OF THE THE DUAL IMMISCIBILITY OF OF DOMINANTLY DOMINANTLY AQUEOUS AQUEOUS FLUIDS FLUIDS IN SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, NE MINNESOTA SOUTHWESTERN FOOTWALL OF THE DULUTH COMPLEX, NE MINNESOTA Jill Dill; HARRIS, N.; SASSANI, David C., C., Dept. Dept. Earth & & Planetary PASTERIS, Jill HARRIS, Teresa N.; Sciences, Washington Washington University, University, Campus CampusBox Box1169, 1169,St. St.Louis, Louis,MO MO 63130-4899 63130-4899 Sciences, Microthermometric and and Raman Raman microprobe microprobe analyses analyses were were made madeon on about about 150 150 fluid fluid inclusions inclusions Microthermometric in 6 rock sections from drillhole FHL-2, which sampled the Fish Lake area of the Duluth in 6 rock sections from drillhole FHL-2, which sampled the Fish Lake area of the Duluth Complex 25 25 k km of Duluth. Duluth. The in quartz quartz and Complex m northwest of The inclusions, inclusions, which were investigated in apatite grains grains in in troctolitic troctolitic to only of of aqueous aqueous fluid fluid (vapor (vapor bubble bubble in in apatite to gabbroic gabbroic rocks, rocks, consist consist only liquids-solidphase), phase),aasingle singlevolatile volatilephase phase(CH<±Nd02) (CH4NgCO2), or both aqueous and volatile liqu&solii phases. This This work work isisfocussed focussedon onthe theaqueous aaueous inclusions, inclusions. which contain 0 to 48 wt. % % total total ohases. dissolved salts with CaCI2/(NaCI + CaCl2) weight ratios ranging up to 0.9. Homogenization dissolved salts with CaClJ(NaC1 + weight ratios ranging up to 0.9. Homogenization temperatures of of the the aaueous aqueous Inclusions inclusions ranae range from 100° to 400° 400°C (see (see fiaures). figures). temoeratures 100Âto vs. total total dissolved dissolved salt salt suggest that The attached attached plots plots of of homogenization homogenization temperature temperature vs. different rocks rocks encountered fluids of different compositions and and that that individual individual rocks rocks interacted interacted with more than one fluid during their history. Most of the rocks that were investigated with more than one fluid during their history. Most of the rocks that were investigated have have mineral assemblaaes assemblages that that indicate their interaction with with aa fluid fluid chase, phase, for for instance, instance, mats mats of of olivine, and and ~ K-feldspar replacing plagioclase; chlorite and amphibole replacing pyroxene and olivine, - f e l d s ~replacing & pkgioclase; of the fluid inclusions quartz and and (earlymany of inclusions lie lie along along secondary trails in (late-crystallizing) quartz and late-crystallizing) apatite. temperature, and and CaCIJ(NaCI CaClS(NaCl + The ranges in in values values of of salinity, salinity, homogenization homogenization temperature, Gaol2) ratio indicate the complexity CaCL) complexity of the the igneous, igneous, magmatic-hydrothermal, magmatic-hydrothermal, and postpostprocesses that that interacted interacted in these rocks; rocks; our group and and others others have have provided provided magmatic processes evidence of of both strong magmatic and sedimentarylmetasedimentary sedimentary/metasedimentarycomponents componentsin inthe the aqueous and and volatile volatile fluids. fluids. Thus, aqueous Thus, the the data dataon on the the accompanying accompanying figures could be interpreted as representing such a diverse array of fluid fluid sources and timings as to defy their tracking. We believe that aa more more reasonable reasonable alternative alternative model is that many of the inclusions inclusions were trapped when when the system was in a field of two coexisting fluids, fluids, i.i.e., a field of fluid e., a field of immiscibility. There in the the general general chemical immiscibility. There are are two two possible possible regions regions of such immiscibility in system H20-(C-0-H-N) H20-(C-O-H-N) gases-salt: gases-salt: brine-brine immiscibility at at high high temperatures temperaturesand andbrinebrinesystem In the the inclusion inclusion parameters parameters (see vapor at lower temperatures temperatures (Bowers (Bowers and and Helgeson, Helgeson, 1983). In figures), the the main main lines of evidence for an the bimodal distribution in figures), an immiscibility immiscibility model are the salinity, lack of correlation correlation between (Tb) and and either either salinity salinity or salinity, between homogenization homogenization temperature (Th) composition, differences differences in Th Tb between pairs of adjacent inclusions (particularly those composition, extremes in salinity), salinity), and pairing of high salinity with with low low gas gas content in mixed representing extremes aqueous-volatile inclusions. alone does does not not account accountfor forall allof of the the above above A model of brine-brine immiscibility alone features, however, however, in in that that salinity salinity and and density density do do not not co-vary; co-vary;in infact, fact,all allbut butaafew few of of the the features, homogenize to to the liquid. liquid. In fri other otherwords, words,there thereisisaalack lackof of evidence evidencefor for aqueous inclusions homogenize the one-step segregation of the system at high temperature into a coexisting saline brine and high saline Further refinement refinement of of an an immiscibility model fluid. Further a lower-density, much less saline aqueous fluid. aqueous inclusions inclusions that that is required to explain the formation formation of coexisting coexisting liquid-dominated aqueous have similar liquid:vapor Iiquid:vapor ratios ratios but widely ranging salinities and CaClJ(NaCI + Ca012) but ranging salinities and CaCLJNaCI + CaCI,) ratios. could have have occurred occurred in in two two stages, stages,initially initiallyby bythe thesegregation segregationofofC-0-H-N 0-0-H-N Immiscibility could from brine brine and subsequently subsequently by by the the segregation segregationof oftwo twobrine-like brine-likefluids. fluids. This model volatiles from requires that the bimodal distributions noted noted in in the the figures figures do not of dual immiscibility requires bimodal salinity distributions not just reflect sampling statistics and that the physical parameters, such as wetting properties, of just physical parameters, such as wetting and physically physically within within the the the immiscible fluids precluded them from interacting chemically and C~CU �¶ I d I n extensive fracture system extensive fracture system in in the the rocks. rocks. Dual immiscibility requires much more stringent stringent geological geological conditions conditionsthan thandoes does oneone chemical reactivity step, brine-brine immiscibility. The The physical physicalproperties properties (e.g., (e.g., fractures) and chemical (e.g., (e.g., susceptibility to hydration) hydration) of the Duluth Duluth rocks, rocks, as as well well as as the the rift riftenvironment environmentof ofthe the Complex, were critical in the development of dual episodes of fluid immiscibility. critical in the development of dual episodes of fluid immiscibility. In In the the first first stage some combination combination of of factors factors moved moved the the bulk bulk composition composition of of the thelatelatestage of immiscibility, immiscibility, some stage, magmatic-hydrothermal magmatic-hydrothermalfluid into into the the field field of of liquid liquid ++ vapor; multiple episodes of physical physical segregation segregation of brine brine and and volatiles volatiles probably probably occurred, occurred, enhanced enhanced by by the the periodic periodicdrops drops in pressure during rifting. This depletion in volatiles moved the aqueous component of the pressureduring rifting. depletion involatiles moved component of the ' original Hp-salt "binary", original bulk fluid toward the Kid-salt "binary",eventually eventuallyinducing inducingthe the second second stage stage of of immiscibility. Two Twocoexisting coexistingbrines brinesdeveloped, developed, with withcontrasting contrastingsalinities salinitiesand anddensities. densities. IfIf these two aqueous aqueous fluids fluids remained remainedphysically physicallysegregated segregated within the fracture system system of of the the host rocks during isobaric cooling (e.g., system evolution at fixed depth) or isothermal host rocks during isobaric cooling (e.g., system evolution at fixed depth) or isothermal increase in in pressure pressure (e.g., (e.g., change change from from hydrostatic hydrostatic to lithostatic lithostatic pressure pressure after after rifting), rifting), then then both Trappingof ofthese thesefluids fluidswould would produce producetwo two populations populations both fluids would increase in density. Trapping of liquid-dominated liquiddominated brines brines with contrasting salinities, like those seen in the figures figures below. below. Severat distinctive petrologic features of drillhole FHL-2 and many other portions Several FHL-2 other portions of of the the Duluth Complex can be explained explained by a mobile, mobile, high-salinity high-salinity brine that interacted interacted with the the melt melt and pegmatoidal and host rock during during subsolidus ccooling: onilig: pegmatoidal zones, zones, the the gradational gradational nature nature of the the contacts between 990), between inferred inferredigneous igneousstratigraphic stratigraphic zones zones (Severson (Seversonand andHauck, Hauck,11990), enrichment in anorthite content in in the rims rims of of plagioclase plagioclase grains, bulk-rock bulk-rock concentrations concentrations of of up to 3200 and Saini-Eidukat, 1991), and iron-rich compositions of 3200 ppm pprn chlorine chlorine (Dahlberg (Dahlberg and Saini-Eiukat 19911. and iron-rich comoositions of .. pyroxenes pyroxenesand andolivines. olivines. . sr — aA 450 N MX sA A a 350 250 atsA A • S a a —I — .gA 200 a 150 100 — %o a — e S • A" S 35c -1 50 t — I8aS 40C1' A a 300 I— lsaniplole4lll — I S S —— SOC 25c a. — 200 — U S__I.. 150 100 50 - 5go Sathty: wt% toS salts 15 - lo — Semplel847l ample 18471 N sanplele474 Sample18474 — San1p1e184751 Sample 18475 a 18476 0 18488 = - Sanple18521 A sample Sampte18476 c.Sample Sample16486 Homogenization vs. total salinity for foi ailS Homogenization temperature vs. aà 6 samples samples investigated investigatedin in this (hisstudy. study. "so 4s 40 as .tio so i5 io SaI.itr wt%tt sa4ts . . Homogenization HomogeTOaton vs. total salinity salinity in intwo two of of the the samples at the the left. left Note sampbs shown at Notethe thebimodal bimodal distribution insalinity. salinity. All All inclusions inclusionsinin distributionin both bothdiagrams diagrams homogenize homogenizeto tothe theliquid (quidphase. phase. I I 55 I �HYDROLOGIC HYDROLOGICMODELS MODELS OF OF SEDIMENT-HOSTED SEDIMENT-flOSTEDORE OREFORMATION FORMATIONW1TIIIN WITHIN CONTINENTAL CONTINENTALRIFT RIFTBASINS BASINS PERSON, PERSON, M., M., Dept DeptGeology Geologyand andGeophysics, Geophysics,The TheUniversity Universityof ofMinnesota, Minnesota,310 310 Pillsbury Pisbury Aye, Ave, SE, SE, Minneapolis, Minneapolis,MN MN 55455 55455 Much Much attention attention has recently recently been been placed placed on on the theinterrelationship interrelationship between between compressional tectonics and the paleohydrology of sedimentary compressional tectonics paleohydrology sedimentary basins (Bethke (Bethke and Marshak, Marshak, 1990; 1990; Oliver, Oliver, 1992; 1992; and and Sverjensky Sverjensky and and Garven, Garven, 1992). 1992). These These studies studieshave have proposed that during orogenic events, uplift of the land surface and tectonic shortening proposed that during orogenic events, uplift of the land surface and tectonic shortening can can induce quantifies of of induceregional regional subsurface subsurface flow flow systems systems capable capable of transporting significant significant quantities heat and fluid mass over hundreds of kilometers. Such transient flow events, which remain heat and fluid mass over hundreds of kilometers. Such transient flow events, which remain active active until until erosional erosional processes processes incise incise the the landscape landscape (Garven (Garven and and Freeze, Freeze,1984a,b) 1984a,b) or or compressional stresses wane (Ge and Garven, 1992), are thought to have formed compressional stresses wane (Ge and Garven, 1992), are thought to have formedeconomic economic metal edges of foreland and intracratonic metalore oredeposits depositsand andpetroleum petroleum accumulations accumulations at at the edges intracratonic sag basins (Garven, 1989 and Garven et al., 1993). To sag basins (Garven, 1989 and Garven et al., 1993). To date, date, however, however, little littleattention attentionhas has been been given giventotounderstanding understanding the the interrelationship interrelationship between between extensional extensionaltectonic tectonic events events and and the the paleohydrology palcohydrology of of continental continental rift systems systems (Person (Person and Garven, 1992, 1992, 1994). 1994). This This study attempts to fill this gap by presenting a series of generic mathematical study attempts to fill this gap by presenting a series of generic mathematicalmodels models of of hydrothermal within actively actively rifting rifting basins. The numerical numerical experiments experiments illustrate illustrate hydrothennalfluid fluidflow flow within the the important important control control of of permeability permeability and water table table configuration configuration in determining determining which driving—force on fluid motion (compaction, density, or topography) will dominate driving-force on fluid motion (compaction, density, dominate during during basin evolution. The idealized models also help to infer the role of groundwater basin evolution. The idealized models also help to infer the role of groundwaterflow flowin in the the formation of sediment—hosted, hydrothermal ore deposits within continental rift basins. formation of sediment-hosted, hydrothermal continental rift basins. The The unique unique stratigraphic stratigraphic relations, relations, heat heat flow flow and and tectonic tectonic conditions conditions associated associated with with continental rifts warrants quantitative analysis. continental rifts warrants quantitative analysis. Assuming rift basin basin subsidence subsidenceand and basal basal heat heat flow flow can can be berepresented representedusing using aa Assumingthat thatrift 'standard' 'standard'geodynamic geodynamicmodel model (Gamer (Garnerand and Turcotte, Turcotte,1986), 1986).two twodistinct distinctgroundwater moundwaterflow flow systems systems evolve evolve within within continental continental rifts rifts during during basin basin evolution. evolution. During ~ k r i the nthe~initial initial (stretching) (stretching)phase phaseof of rifting lifting(Fig. (Fig. la), la),subsidence subsidenceisisaccommodated accommodatedby byfault faultblock blockmotion, motion, and andaatopography-driven topography-drivengroundwater groundwaterflow flowsystem systemdevelops developswithin withinthe thepermeable permeablealluvial alluvial fan fandeposits. deposits.Within Within the theless lesspermeable permeable lacustrine lacustrine facies facies located located in in the the center center of of the the basin, basin, compaction-driven compaction-driven groundwater groundwater flow dominates. dominates. Here, Here, the thecompacting compactinglacustrine lacustrine sediments sedimentsfocus focuspore porefluids fluidslaterally laterally from fromthe the basin basin center center into into the the alluvial alluvial fan fan deposits deposits due due totothe therelatively relativelylarge largepermeability permeabilitycontrast contrastbetween betweenthe thetwo twodepositional depositionalenvironments. environments. Thermal Thermalanomalies anomaliesresulting resulting from from convective convective heat heat transfer transfer are are restricted restricted to to alluvial alluvialfan fan facies faciesnear nearthe thebasin basin framing framingfault. fault. During During the the thermal thermal cooling cooling (flexural) (flexural) stage stage of of basin basin development development(Fig. (Fig. ib), lb),laterally laterallyextensive extensiveon-lap on-lap facies faciesare are deposited, deposited, and and density-driven density-driven groundwater groundwater flow flow dominates dominates in in the thepermeable permeablealluvial alluvial fan fan deposits depositswhile whilecompactioncompactiondriven drivenflow flowcontinues continueswithin withinthe thelacustrine lacustrineand andon—lap on-lap facies. facies. The Thepresence presenceof ofaapermeable permeable aquifer resulted in long-range fluid transport to the aquiferwithin withinthe theon—lap on-lap hfacies i e s resulted the edge ed e of of the the basin. During both stages of basin evolution Darcy flow rates varied from l0 10-1 basin. During both of basin evolution Darcy flow rates varied from 10- to to 10-1 m/y. between the lacustrine and alluvial fan deposits respectively. The observed m/y. between the lacustrine and alluvial fan deposits The observedpresence presence of ofore oremineralization mineralization within within alluvial alluvial fan deposits deposits at the edges of of some some continental continental rift rift systems, RiftBasin Basin of of Angola, Angola, supports supportsthe thefindings findingsof of this thisstudy. study. systems,such suchas asthe theCretaceous CretaceousRift �I REFERENCES REFERENCES Bethke, C.and andS.S.Marshak, Marshak,1990, 1990,Brine Brinemigration migrationacross acrossNorth North Americt America:the theplate platetectonics tectonicsof ofgroundwater groundwater Bethke,C. hydrology, AnnualReviews ReviewsofofEarth Earthand andPlanetary PlanetarySciences, Sciences,v. v. 18, 18,p.p.287—315. 287-3 15. hydrology.Annual Garner, Garner,D.L., DL..and andD.L. 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Garven, Garven,0., G.,Ge, Ge,S.,S.,M.M.Person, Person,and and1).D.Sverjenski, Sverjenski,1993. 1993,The Thegenesis genesisof of stratabound stratabound ore oredeposits depositsin in the the Midcontinent MidcontinentBasins BasinsofofNorth NorthAmerica: America:I.I.The Therole roleofofregional regionalgroundwater gmundwaterflow. flow.American AmericanJournal Journal ofofScience, Juneissue. issue. Science,June Ge, S. and 0. Garven, Hydromechanica] Ge, S. and G. Garven,1992, 1992, Hydromechanicalmodeling modelingofoftectonically tectonicallydriven drivengroundwater groundwaterflow flowwith with application to the Arkoma Foreland basin, Journal of application to the ArkomPoreland basin, Journal ofGeophysical GeophysicalResearch, Research,v.v.97, 97,p.p.9119—9144. 9119-9144. Oliver, Oliver,J.,J.,1992, 1992,The Thespots spotsand andstains stainsofofplate platetectonics: tectonics:Earth EarthScience ScienceReviews, Reviews,v.v. 32, 32,p.p.77—106. 77-106. Person, 1992, Person,M. M.and and0.G.Garven, G-, 1992,Hydrologic Hydrologicconstraints constraintson onpetroleum petroleum generation generationwithin withincontinental continentalrift rift basins: Theory and application theRhine RhineGraben, Graben.American AmericanAssociation Association of of Petroleum Petroleum basins: Theory and applicationtotothe Geologists GeologistsBulletin, Bulletin,v.v.76, 76,p.p.468—488. 468-488. Person, AAsensitivity Person,M. M.and andG.G.Garven, Garven,1994, 1994, sensitivitystudy studyofofthe thedriving drivingforces forceson onfluid fluidflow flowduring duringcontinental continental rift riftbasin basinevolution, evolution.Geological GeologicalSociety SocietyofofAmerica AmericaBulletin, Bulletin,v.v.104, 104,p.p. Sverjensky, Tracing D.A. A.and and0.G.Garven, Garven,1992, 1992, Tracinggreat greatfluid fluidmigrations, migrations.Nature, Nature,v.356, v. 356, 481-482. Sverjensky,I). p.p.481—482. + + B + ++ + Not Not totoscale scale + LEGEND R-3Crystalline CrystallineBasement Basement [;E] Pie—Rift Pre-Rift .. Basal BasalAquifer Aquifer , ., ~. Figure Figure1.1. - - Alluvial Lacustrine AlluvialFan Fanand andLacustrine Deposits (Initial Stage of Rifting) Depos@ (~nitial~tageof ~ifting) Carbonate Aquifer ,. , , . (Thermal/Flexural (Thermal/Fle~.~tate.,of ~ ~ f t -i n o ) State of Rifling) Conceptual Conceptualmodel modelofofgroundwater groundwaterflow flowsystem systemduring duringinitial initialand andflexural flexural stages stagesofofcontinental continentalrift riftevolution. evolution.Arrows Arrowsdepict devictdirection directionofofgroundwater moundwater motion topography—, motiondue duetoto topography-, density—, density-, and and compaction compactiondriven drivenflow flowsystems. systems. Two distinct groundwater flow systems Two distinct groundwater flow systemscan canform formwithin withincontinental continentalrifts riftsdue due totochanges changesinintectonic, tectonic,thermal, thermal,and andhydrologic hydrologicboundary boundaryconditions conditionsduring during basin basinevolution. evolution. 5J �z 0 H oz t11 Plcn -S 09 0 or z nm nI.t c-fl rn 0 0 0 M C) DEPOSITIONAL CONTROLS ON SHALLOW WATER IRON FORMATION ACCUMULATION, GOGEBIC RANGE, WISCONSIN. PUFAHL, Peir and FRALICK, Philip, Dept of Geology, Lakehead University Thunder Bay, ONT P7B 5E1, Canada. 0 liji LZo -I > I I r° I o -< SLATY IRON FORMATION -n t)III C) P1 c ot.z OZrfl SMALL GRAINSTONE LENSES AND WAVY BEDDING ('1 côr GRAINSTONE LENSES a zrn Cflg t - -I ci Well exposed, glacially polished iron formation outcrops near the town of Mellen, Wisconsin. There units form a portion of the western Gogebic iron range which strikes eastwest through the area. Iron formation exposure of this calibre is unusual in the LakeSuperior region and provides an opportunity to investigate physical and chemical sedimentary controls on accumulation of this type of sediment SLUMPS �I • I I I A 40 x 40 40 m m section section of of hon ironformation formationcomposed composed of of trough troughcross-stratified cross-stratified chert grainsxonesand and parallel parallel laminated laminated slaty slaty iron iron formation formation was was mapped mapped in detail (Figure 1). grainstones (Figure 1). The units. The The sequence sequence is is composed composed of three three distinct stratiographic stratiographic units. Thefirst firstcomprises comprises 12 12m m of parallel laminated slaty iron formation with small chert lenses appearing at the bottom laminated slaty formation the bottom of the is a 15 succession of of large trough the section. section The second second is 15 in m thick succession trough cross-stratified cross-stratified grainstone 10-12min. . The The third thirdunit unitlies liesimmediately immediatelyabove above grainstone lenses, lenses, some some extending extending laterally laterally 10-12 the m of ofslaty slatyiron ironformation formation. Paleocurrent Paleocurrent data data the grainstone grainstonesuccession succession and is composed of 88 m is dominantly unidirectional from the north. Slaty iron formation is dominated by parallel laminated laminated beds beds 2-5 2-5mm mm in in thickness. thickness. In regions where slaty iron formation coexists with small grainstone lenses the characteristic In regions where slaty iron formation grainstone characteristic wavybedding. bedding. Ripple Ripple lamination is present present in in the the lowest lowest parallel lamination lamination gives rise to wavy stratigraphic unit. Many beds are both physically and chemically graded. Variations graded. Variations in in the the stratigraphic Many beds are both physically distribution of Al, Mn, beds and and throughout the entire distribution Mn,Fe and Mg are seen seen within individual beds entire span section. Mineralogically span of the section Mineralogically the dominant dominant phases are are hematite, hematite, magnetite magnetite and andchert chert with minor amounts of greenalite, apatite apatite and and manganese manganese oxide. oxide. The trough cross-stratified chert chert grainstone lenses are composed of rounded chert and hematite ranging in in size size from from 0.1 0.1 to 2 mm. Many Many chert chertgrains grains are are coated coated with with hematitegrains grains ranging hematite, suggesting rolling by bottom currents through hon-rich muds. A few of the largest A few hematite, suggesting by bottom currents through iron-rich cores composed composed of of ilmenite. ihuenite. The hematite grains possess possess cores Thematrix matrix isisdominately dominately chert chert & & with traces of stilpnomelane. Lenses range from 2 to 40 cm thick and may extend calcite stilpnomelane. Lenses range from 2 to 40 cm thick and may extend laterally 00.70 15m. a The laterally .70 toto 15 Thesmallest smallestgrainstone grainstonelenses lenses appear at at the the base base of of the the section section calcite within slaty iron formationformation. The largest lenses are found in the succession of trough The largest lenses are found in the succession of troughcrosscrossare common at at the 1-3cm in length, are stratified grainstones. Ripups Ripups of of slaty slaty iron iron formation, formation, 1-3 of the stratified (30cm cm thick, 8-11 8-11m wide) at the top top of of the the succession. succession. base the largest largest lenses lenses (30 by aa coarsening coarseningupwards upwards sequence sequencein inwhich which muddy muddy shelf The section section is characterized characterizedby pass through ripple laminated fine sand into a succession of cross-stratified deposits through ripple laminated fine sand into a succession of cross-stratifieddunes. dunes. deposits of offshore offshorebars. bars. The This sequence is characteristic of The thin thin ripple ripple lamination lamination in in slaty slaty iron iron formation in the lowermost slaty unit may represent sands moved by storm produced the lowermost slaty may represent sands moved by storm produced currents. The alsoindicative indicative of of storm storm currents. Thedominantly dominantlyunidirectional unidirectional paleocurrent paleocurrent pattern pattern isisalso enhanced currents. Slumping is suggested throughout the sequence by the presence of of currents. Slumping is suggested throughout the sequence by extensive convolute bedded slaty iron formation. formation. bar complex the Upper Upper Cretaceous The offshore offshore bar complex composing the Cretaceous Sussex Sussex Sandstone Sandstone in the the The is similar similar to to the chemical sedimentary sedimentaiy succession described Powder River Basin, Wyoming is above. The Thesedimentological sedimentologicalcontrols controlsforming forming the the carbonate carbonatesequence sequencein inWyoming Wyoming should therefore closely sedimentation on present during therefore closely parallel parallel those those governing governing sedimentation on the the shallow shallow shelf present hon formation. deposition of the slaty and cherty iron formation The Theoffshore offshorebar barsequence sequenceininWyoming Wyoming claystonethrough through interbedded interbedded sandstone sandstone and also grades gradationally from silty claystone and claystone to sandstone and contains a sequence of sedimentary structures similar similar to to that that present in also the hon alsodemonstrates demonstratesan anasymmetrical asymmetricaldistribution distribution ironformation. formation. The TheSussex Sussexsandstone sandstonealso facies resulting resulting in aa steeper steeperdepositional depositionalslope slopewhich which endured enduredhigher higherdepositional depositional of fades energies, and underwent periodic slumping probably similar to observed in the energies, and underwent periodic slumping probably similar to that observed the of Proterozoic bar Proterozoic bar succession. succession. �FIYDROGEOLOGICINVESTIGATIONS INVESTIGATIONS OF HYDROGEOLOGIC OF PETROLEUM PETROLEUM CONTAMINATION CONTAMINATION IINNKARST, KARST, CENTRAL CENTRAL UPPER UPPER PENINSULA PENINSULA OF OF MICHIGAN MICHIGAN Beth A. A. Rogers, MalcolmPPirnie Engineers, E. Lansing, Beth Rogers, Malcolm i r n i e En ineers, E. Lansing, MI MI Mark A.A. Petrie, Petrie, Department Mark Department of o f Natural Natura Resources, Resources, Marquette, Marquette, MI MI ? BACKGROUND BACKGROUND Hydrogeologic Hydrogeolo i c iinvest4ations n v e s t i ations have havebeen beenconducted conducted iinn response r e s onse to t o ffuel uel Upper Michigan contaminattono of contamination f rresidential e s i d e n t i a water water supply su p l y wells w e l l s iinn aa small Upper Michigan community(due (due An i initial cannot be be disclosed). disclosed An nitial community t o tol i tlitigation, i g a t i o n , the the location l o c a i o ncannot investigation i n v e s t i g a t i o nidentified i d e n t i f i esome d somepossible possiblesources sourcesand and poorly p o o r l ydefined d e f i n e hydrogeology. hydrogeolo y. A subsequenti ninvestigation thesource sourcei didentification A subsequent v e s t i g a t i o n r erefined f i n e d the e n t i f i c a t i o n and and provided provided bbetter et e r definition of othe d e f i n i t i o nofo fthe thevertical v e r t i c aand l andhorizontal horizontalextent extent f t hcontaminant e contaminantplumes. plumes. 9! ? J. f GEOLOGIC GEOLOGIC SETTING SETTING The ssite basin, near The i t e lies t i e son onthe theNorthwest Northwest edge edge ooff the Michigan Michigan basin, near the contact contact between the Michigan Basin Paleozoic sediments and the Precambrian between the Paleozoic sediments and the Precambrianmetamorphics metamorphics medium ooff the the Canadian Canadian Shield. Shield. AAtt the the surface surfaceare areWisconsinan-aged Wisconsinan-a ed tthin, h i n medium textured gglacial (ground moraine) textured l a c i a l tills t i 1 1s ground moraine)(Farrand (Farrand and and Bell, Be11, 1982). 1982). Underlying ~ n d e r f y i the nthe ~ drift Middle a gray, d r i f tisi the s the MiddleOrdovician O r ovicianTrenton Trenton Group; Grou ; a gray, brown, brown, oorr buff b u f f colored, colored, t i ngray grayshale shalepartings, partings,sometimes sometimes ffine i n e grained, rained, limestone limestone or o r dolomite, dolomite, with w i t h thin with calcite ffossiliferous, o s s i i f e r o u s fractured, fractured, vuggy vuggy w i t h some some c a l c i t e ccrystals r y s t a l s or pyrite in vugs fOstrom anddaughter, Slaughter,1967, 1967,SSinclair, Vanlier, 1963). Underlying the Ostrom and i n c l a i r , 1960 1960 and and Vanlier, Trenton Group (estimated to be at least 250 feet jrenton Group (estimated t o be a t l e a s t 250 f e e t t hthick i c k i in n this area) are the Black River River Limestone, the Prairie Chienformation formationand the Late Cambrian Black Limestone, the P r a i r i edu duChien Munising Sandstone Sandstone(Sinclair, (Sinclair, 1960 andVan1 Vanlier, 1960 and i e r , 1963). 19631. Regional groundwater groundwater flow Munisin is to the Southeast, generally parallel to the dip of the bedrock structure. i s t o t e Southeast, generally p a r a l l e l t o the d i p o f the bedrock structure. A ? R a DISCUSSION DISCUSSION Surficial light brown till: l i gbrown, h t brown, brownororeddish-brown, r reddish-brown, S u r f i c i a l deposits deposits are are gglacial l a c i a l till: fine to medium clayey sand, sandy clay or clayey silt, with t r a c e tot osome some fine fine f i n e t o medium clayey sand, sandy c l a y o r claye s i l t , w i t h trace gravel, ran ranging from33t oto 99 ffeet Gravel tto o coarse coarse gravel i n g from e e t tthick. hic Gravel percentage percentage increases increases with w i t h depth; depth; cobbles cobbfes of o bedrock bedrock are incorporated incorporated just j u s tabove above the the bedrock bedrock surface. surface. I. ? The bedrocki is The bedrock s ffairly a i r l yhomogeneous homogeneous t otoaat t lleast e a s t 60 60 feet f e e t below be1ow ground round level level 1 (bgl), (bgl), the the total t o t a ldepth de t h of o f investigation. investigation. It Itisi sgrayish-brown grayish-brown to t o buff bu f dolomite, dolomite, microcrystalline, m i c r o c r y s t a l l ine, fractured fractured with w i t h some some ddissolution i s s o l u t i o n features, features, containing containing few few to to somevugs vugsand and few some (<2"t hthick) zonesoor bedsooff shaley shaley dolomite dolomite to some few t otosome t h ithin n (<2" i c k ) zones r beds to shale, generally depthoof 20f feet bgl. The shale, generally occurring below below aa depth f 20 e e t bgl The vugs commonly commonly are are are ffilled ffilled i l l e dwith w i t h calcite c a l c i t ecrystals c r y s t a l s or o rpyrite, p y r i t e , fractured, fractured, which which often o f t e n are i l l e d with with reddish-browns silty Pleaser refer reddish-brown i l t y clay. Please e f e r tto o the the core core and and ddrill r i l log l l o for g f oMW-hOD. r MU-1100. . Groundwater flowisis strongly strong1y influenced influenced by by the thesecondary secondary permeability permeabil it y Groundwater flow (fractures). Thede depth the 40 40 monitor monitor wwells fractures). The t h t to o groundwater roundwater i nin the e l l s (Figure (Figure 1) 1)ranges ranges from 0.5 0.5 tto from o 29 29 ffeet e e t bgl, g1, with w i t ha acorrespondin9 corresponding range range in i n ground ground surface elevations of only 18.5 Waterl levels of 18.5 feet. Water e v e l s ffluctuate l u c t u a t ewidely widelywith w i t hseasonal seasonal changes, changes, with w i t h as as 1 muchas as18.25 18.25ffeet much e e t noted from from May May tto o September September i in n one one well, MW-HID. MW-111D. weref rfrustrating IInitial n i t i aattempts l attemptstot ocontour contourthe thegroundwater groundwater eelevation l e v a t i o n data were ustrating (Figs. 2 & It was respondingddifferently & 3). 3). It was apparent apparent tthat h a t several several wells w e l l s were were responding ifferently (Figs. so well hydrographsoof ttoo changing chan i n conditions, conditions, so w e l l hydrographs f eelevation l e v a t i o n versus versus time time were were prepared 4-61. In I n the the hydrographs h drographs iitt is i sobvious obvious that t h a tsome some wells w e l l s do do not not pre arer? (Figs. ?igs. 4-6). reflect concertwwith the m majority r e f e c t changing c!I anging groundwater groundwater e elevations evations i ninconcert i t h the a j o r i t y of o f the the wells. These "anomal "anomalous" wells probablyare arescreened screenedi nin zones zoneshydraul hydraulically we11s These ousn we1 1s probably i c a l ly from the the rrest They were were not iisolated s o l a t e d from e s t of o f the the aquifer. aquifer. They n o t used used iinn subsequent subsequent ?. r 60 �interpretation, in i potentiometric surface i n t e r p r e t a t i o n ,resulting resulting n potentiometric surfacemaps maps (Figs. (Figs. 77&& 8) that t h a t agree agree well with (Figs. 9 & w i t hthe theobserved observed contamination contamination plumes plumes (Figs. & 10). 10). A groundwaterhigh highi is found aatt the Western edge thestudy study area, area, roughly roughly A groundwater s found Western ed e o of f the corresponding bedrockand andtopographic topographichigh, high,wwith groundwaterflowing flowingooff correspondin tto o a bedrock i t groundwater f f the the 1 i high South(Fig. (Fig. 7). This high high iiss not high ttoo the the North, orth, East East and and South 7). This n o t reflected r e f l e c t e ddeeper deeper in the regional regional flow i n the the aquifer, aquifer, where where groundwater groundwater f follows o lows the f l o w to t o the t h eSoutheast Southeast (Fig. 8). Horizontal Horizontal hydraulic hydraulic gradients gradients vary vary around around t this h i s high, high, from from 0.022 0.022 to to 0.028 ft/ft tot othe East ft/ft 0.015 ft/ft ft/fttot the o the Eastand and0.026 0.026 - 0.031 0.031 ft/ft theNorth, North 0.012 0.012 -- 0.015 to the South, wwith nonoseasonal Althought the i t h llittle i t t l etot o seasonal fluctuations. f l u c t u a t i o n s . Although h e vvertical ertical hydraulic gradient contamination the deep ittle contaminationwas was found found in in'the deep wells: gradient isi sdownward, downward, 1little 1 detection of of aa single singlecompound, compound, aatt ttrace r a c e levels, levels, on ononly onlyone onesampling sampling date date each each in i n 22 of o fthe the1212deep deep wells, wells, and and one one of o f those those detections detections was was not n o t repeated repeated iin n aa duplicate duplicatesample. sample. A A total t o t a l ofo 24 f 24slug slugtests t e s t swere wereperformd erformedon on14 14moni2tor moni$or wwells e l l s (8 8 shallow). shallow). Hydrauli cm/s, with c o n d u c t i v i t i e range s rangefrom from1.37x10 1.37~10 to t o 4.25x10 4.25~10' cm/s, w i t an an average average Hydraul conductivities of A A 24-hour 24-hour constant constant rrate a t e pumping ~ u m p i n g ttest e s t yielded y i e l d e dcomparable comparable o f 1x10 1x10" cm/s. cm/s. hydraulic cm/s, wwit hydraulic conductivity conductivity values values ooff 2.35x104 2.35~10' ttoo 1.52x10 1.52~10' cm/s, i t h aa Transmissivity of 1.92 to 12.4 m2/day and Storage Coefficient of 1.O6x10 o T r a n s m i y i v i t y o f 1.92 t o 12.4 m /day and Storage C o e f f i c i e n t o f 1.06~10" tto k is 1.26x103 and the the larger 1.26~10' (the (thesmaller smallernumbers numbers are from from MW-6 MW-6 and l a r g e rfrom fromMW-112D). MW-112D). A markedseasonal seasonalf l ufluctuation plumesi is evident. The The A marked c t u a t i o n iin n the contaminant contaminant plumes s evident. plumes reach aa maximum maximum thespring spring (Fig. 9) 9) when when snow snow mmelt e l t and and heavy heavy rrains ains plumes reach i ninthe flush Later iinn the 10), f l u s h residual residual contaminants contaminants i into n t o the the aquifer. aquifer. Later t h e year year (Fig. (Fig. lo), lesser sizes, tto lesser recharge recharge i is s rreflected e f l e c t e d in i n the the greatly g r e a t l yreduced reduced plume plume sizes, o the the point point where evident. Since knownl eleaking where ddiscrete i s c r e t e sources sources become become evident. Since aalll l known a k i n g ffuel u e l storage storage tanks have beenremoved, removed,these thesecontaminant contaminantsources sources probablyare aree ieither residual have been probably t h e r residual fuel epikarst, f u e l in i n the the drift d r i f or t oin r isediments n sediments filling f i l l i n the g the epi karst,or oLNAPL r LNAPL trapped trapped in in fractures fractures above above the high high water water table. table. CONCLUSIONS CONCLUSIONS Carbonate young regimes Carbonate hydrogeology, hydrogeology, even even in i n young regimes such such as as tthe h e rrecently ecently glaciated influenced byby karst l a c i a t e d Midwest, Midwest, often o f t e n isi sstrongly s t r o n 1y influenced k a r development s t developmentwhich whichmay may I be It isi ssuggested i n rock rock cores. cores. It suggested that, t h a t iiff e so so subtle as as to t o be be unnoticeable unnoticeab e in potentiometric flow maps prove difficult potentiometric f l o w ma s prove d i f f i c u l t tto o interpret, i n t e r p r e t , innovative innovativedata data handling hand\ i n g </ techniques techniques may may be be needed. nee ed. REFERENCES REFERENCES CITED CITED Farrand, W.R. W.R. and and D.L. D.L. Bell, off Northern B e l l , 1982, Map Hap ooff Quaternary Quaternary Geology Geology o Northern Michigan, Departmentoof Natural Resources, Resources,Geological Geological Survey SurveyDivision, Division, Michigan, Michigan Department f Natural Lansing, Lansing, Michigan. Michigan. Ostrom, M.E. andA.E. A.E. Slau Slaughter, Ostrom, M. E. and hter, 1967, 1967, Correlation CorrelationProblems Problems of o f the theCambrian Cambrian and and Ordovician Areas, northern Northern Peninsula Peninsula ooff Nichigan, Michigan, Michigan Basin Society, Society, Ordovician Outcrop Areas, June, June, 1967. 1967. Sinclair, the Groundwater Resourcesoof Delta Sincl a i r , W.C., W .C., 1960, 1960, Reconnaissance Reconnaissance o of f the Groundwater Resources f D elta County, Geological Survey County, Michigan, Michigan, Michigan Michigan Department Department of o f Conservation, Conservation, Geological Survey Division, Division, Lansing, Lansing,Michigan, Michigan,Progress ProgressReport ReportNumber Number 24. 24. Vanlier, Resourcesoof Van1 i e r , K.E., K. E., 1963, 1963, Reconnaissance Reconnaissance oof f the Ground-Water Ground-Water Resources f Alger County, County, Michigan, Michigan, Michigan Michigan Department Department of o f Conservation, Geological Geological Survey Division, Division, Lansing, Lansing, Michigan, Michigan, Water Water Investigation I n v e s t i g a t i o n 1. 1. 61 �ORIGIN MAFIC DIKE ORIGIN OF OFTHE THEEARLY EARLYPROTEROZOIC PROTEROZOICKENORA-KABETOGAMA KENORA-KABETOGAMA MAFIC DIKE SWARM SWARM SCHMITZ, Mark D., WJRTH, Karl R., CRADDOCK, John P., Geology Department, Macalester SCHMTIZ, Mark D., WIRTH, Karl R., CRADDOCK, John P., Geology Department, Macalester College, College, St. Paul, Minnesota Minnesota 55105 St. Paul, 55105 The dike swarm swarm intrudes over over90.00 90,O km2 km2 of of northern Minnesota Minnesota and southern southern The Early Early Proterozoic Proterozoic Kenora-Kabetogama Kenm-Kabetogama dike Ontario. Dikeswere weresampled sampledfrom fromoutcrops outcropsthroughout throughoutthe theexposed exposedeastern easternportion portion of of the the swarm, swarm, from from the the Mesabi Mesabi Ontario. Dikes Iron Range, north to Kenora, Ontario. Samples from dikes buried beneath glacial cover in noithwestern Minnesota Iron Range, north to Kenora, Ontario. Samples born dikes buried beneath glacial cover in northwestern Minnesota were were obtained obtained from from drill drill core. Mne. The Theswarm swannisiscomposed composedof ofthousands thousandsof ofdikes, dikes, ranging ranging from from 1-120 1-120rn m wide, wide, some someof of which can be traced for over 100 km. Pllyric basalt at the quenched margins of the dikes coarsens to diabase and which be traced fot over 100 km. Phyric basalt at the quenched margins of the dikes coarsens to diabase and gabbro gabbro in in the the cores cores of of large large dikes dikes (>20 (a20 m m in in width). width). Rare Rarecomposite compositedikes dikes are are composed composed of of aa similar siniilarmarginal marginal basalt basalt and have medial felsic granodiorite intrusions. Dike margins are porphyritic, with plagioclase, pyroxene, and and have medial felac granodiotite intrusions. Dike margins are porphyritic, with plagioclase, pyroxene, andrare line Fe-Ti pyroxene, magnetite, %Ti oxide oxidephenocrysts phenocrystsin inaagroundmass groundmassof ofplagioclase plagicclasemicrolites, mictolites,pyroxene, magnetite, and and green green hydrous hydroussilicates; silicates; the of the primary primary inintruded magma. Alteration themargins marginsare are believed believed to tobest best represent represent the thecomposition composition of magma. Alteration within within dikes dikes is isvariable, variable, and and isisbelieved believedto tohave havebeen beenlargely largelydeuteric deutericin innature. nature.ItItwas wasnot notaccompanied accompaniedby bysignificant significantchemical chemical compositional compositionalchanges, changes,and andmobilization mobilizationof ofelements elementswas wasrestricted restrictedto toK, K,Rb, Rb, Sr, St,Ba, Ba,Ca, Ca,and andMn. Mn. All basalts following following aa tholeiitic All dikes dikesof of the theKK KKswarm swarmare arecomposed composedof ofFe-rich Fe-richquartz quartz normative normative basalts tholeiitic trend trend on on the AFM diagram. Dike margin rocks have nearly constant silica contents and exhibit a wide range in magnesium the AFM diagram. Dike margin rocks have nearly constant silicacontents and exhibit a wide range in magnesium index rocks. Coherent index (Mg/Mg+Fe), (Mg/Mg+Fe), typical typical of of continental continental tholeiitic tholeiitic rocks. Coherent trends tends of of Mg Mg depletion depletion and and Ti, Ti, PPenrichment enrichment with differentiation are seen on major element bivariate diagrams. Our data set shows a distinct grouping with differentiation are seen on major element bivariate diagrams. Our data set shows a distinct grouping of of samples samples into intohigh highMg-low Mg-lowTi, Ti,and andlow lowMg-high Mg-highTi Tigroups, groups,similar similartotothat thatseen seenby by Southwick Southwickand and Day Day (1983). (1983). Trace Traceelement elementanalyses analysesof ofthe thedikes dikeshave havebeen beenstudied studiedtotobetter betterconstrain constrain the thetrends trendsin inboth bothwithin-dike within-dikeand and inter-dike intet-dike variation. variation. Most Mostgabbro gabbrocore corerocks rockscan canbebesuccessfully successfullymodelled modelled from from their their basaltic basaltic margins margins using using major major element element mixing mixing and andtrace traceelement elementfractionation fractionationmodels. models. In In the thecomposite compositedikes, dikes, the theextremely extremelydifferentiated differentiated granodiorite granodioriteportions portionshave havetrace traceelement elementpatterns patternsexhibiting exhibitingboth both fractionation fractionation and contamination contamination processes. processes. Large Large negative Ta anomalies, and highly enriched incompatible elements including Th, require an upper crustal component Th,requirean crustal negative Ta anomalies, and highly enriched incompatibleelements of of contamination contaminationin inaddition additionto toextreme extremedifferentiation differentiationto toproduce produce the the granodiorites(Figure granodiorites(Figure 1). The Thenegative negativeTi, Ti,P,P, Zr, Sr, and Ba anomalies in the extended trace element patterns of these felsic samples are due to large degrees of Zr, Sr, and Ba anomalies in the extended trace element are due fractionation amphibole, fractionationincluding includingaccessory accessoryphases phasesofofapatite, apatite,zircon,ilmenite, zin-onÂ¥ilffldte amphibok,and and potassic potassicfeldspar. feldspar. Inter-dike variation has been studied using analyses from the margins of dikes. Margin (he dikes. Margin rocks rocksfall fallalong alongtwo two Intet-dike variation has teen studied using analyses distinct distinctarrays arraysin inplots plotsof ofcompatible compatibleelements elements(Ni, (Mi,Cr, Cr,Co) Co)versus versusZr Zr(Figure (Figure 2). 2). These Thesetwo twotrends trendscorrespond correspondtotothe the groupings based on major element chemistry. REE patterns of both groups are essentially parallel over large groupings on major element chemistry. REE patterns of both groups are essentially parallel over large variations variations in HFSE HPSE (Zr= (Zr=48-162 48-162 ppm). ppm). Both Bothgroups groupsofofdikes dikeshave haveflat flatMORE-like MORB-likechondrite.normalized chondrite-normalizedREE REE patterns [e.g. (La/Sm)CN= 0.86-1.07] with absolute abundances of 15 to 6th chondrite. The total absolute REE patterns 1e.g. (La/Sm)cN= 0.86-1.071 abundances of 15 to 60x chondtite. The total absolute RBE abundance abundanceisisclearly clearlycorrelated correlatedwith with the thehigh high and and low-Zr low-Zr groups (Figure (Fiime 3). AA distinctive distinctivedifference differencein in the the slopes slopesof of the HREE is the basis of Figure 4, which divides the high-Zr group into two subgroups; these two subgroups are the HREE is the basis of Figure 4, which divides the high-Zr group into two subgroups; two subgroups are believed believedto torepresent representdifferent differentmagma magmaseries seriesand andpossible possibledifferences differencesin in source. Within Withineach eachsubgroup, subgroup,the theREE REEand and extended extended trace (raceelement element patterns patterns suggest suggest aa fractionation Sactionation series. Eu Euanomalies anomaliesbecome becomeprogressively progressivelylarger larger with with increasing increasing enrichment, enrichment, suggesting suggesting fractionation fsaclionationof of plagioclase, plagioclase. consistent consistent with with major majorelement elementmodelling modellingand and petrographic petrographicevidence. evidence. Patterns Patternswithin withinthe thelow-Zr low-Zrgroup groupdodonot notillustrate illustrateaaclear cleardifferentiation differentiationsequence, sequence,but butshare share similarities similaritieswith withboth bothhigh-Zr high-Zrgroups. groups. Extended Extendedtrace daceelement elementpatterns patternsof ofthe diedike dikemargin marginsamples samplesare are well well correlated correlated with with the the exception exceptionof of the the highly highly incompatible incompatible mobile alkali elements, Cs, Rb. Rb, K, K,and to some some extent Ba. Ba. Low Lowabundances abundancesof ofthe thehighly highly incompatible incompatibleelements elementsare aresimilar similarto toMORE MORBand andindicate indicateaa depleted depletedsource. source. Little Littleevidence evidenceof ofcrustal crustalcontamination contamination isisseen, (0.47.0.85) ratios. Samples seen,as asindicated indicatedby byminor minorTa-anomalies, Ta-anomalies,and andlow low(TlilLa)CN (Th/La)cN (0.47-0.85) Samplesof of KK KKdikes dikesplot plotininthe the N-MORB N-MORB field fieldof ofFigure Figure1,1,with withvery veryfew fewsamples samplespulled pulled along along aa vector vector of of crustal crustal contamination. contamination. This Thisdiagram diagram illustrates illustratesthe thedistinct distinctcomposition compositionofofdikes dikesnear nearTower, Tower,MN, MN.and andthose thosefound foundinindrill drillcore corefrom fromnorthwestern nonhwesternMN. MN. 62 �A dike near Tower, MN with a trend and field characteristics similar to those of the KK swarm is seen to have a very different face element chemistry. It has enriched, OIB-like REE and extended trace element pattterns, and plots within the OrB field of the Hf13-Th-Ta diagram. It also shows a low degree of crustal contamination. The Tower dike represents a melt from a different magma source not observed elsewhere in the KK swarm, and might be related to a different magmatic event (i.e. Keweenawan Rift). While the thousands of NW-trending dikes observed in northwestern MN by aeromagnetics have been previously assumed to be of KK affinity, the six samples of four drill cores analyzed have trace element patterns that are distinct from the rest of the KK swarm (Figure 3). Two of the dikes sampled appear to have reversed polarity aeromagnetic signatures. The three samples from these "reversed" dikes have similar REE and extended flee element patterns: highly enriched in incompatible elements, similar to OIB, with large negative Ta and P anomalies suggesting crustal contamination. The other two dikes have "normal" polarity. Samples from one dike have OIB like patterns highly enriched in incompatibles and show signs of extreme cuistal contamination. A sample from the other "normal" dike is highly. altered,. but has a distinctJlat trace element pattern similar to MORB. These dikes from northwestern MN might berepresentatives of one or more different dike swarms. Conversely, they might be part of the Kenora-Kabetogama swarm, with their different compositions a function of extreme crustal contamination, or the tapping of different mantle sources. Reference: Southwick, D.L., and Day W.C., 1983, Geology and petrology of Proterozoic mafic dikes, northcentral Minnesota and western Ontario: Canadian Journal of Earth Sciences, v. 20, p. 622-638. Figure 1 Hf /3 Figure 2 Th Zr 1000 Towcrdjk, 1k Bewnce *11 o,.t NonF till Ce 4nur drill Cat Graaoditt.. --—,- I a 13 High Zirtonium Basalts Is Low Zireonlun' fla..lt. 1410 1.2 I.' 1 I I LaCe Figure 3 I Nd J..l SmEu REE I Th II Yb Lu 40 Pa Low Ziivonium Basalts 60 80 100 120 Zr 140 160 180 Figure 4 63 �I r THE ROCKS GEOLOGICAL MARATHON: MARATHON: THE ROCKS OF OF THE THENORTH NORTH SHORE SHOREOF OFLAKE LAKE AA GEOLOGICAL I SUPERIOR SUPERIOR SMYK, MarkC.,C., and SCHNIEDERS, BernieR.,R.,Ontario Ontario Geological SMYK, Mark SCHNIEDERS, Bernie Geological Survey, Survey, Ministry MinistryofofNorthern NorthernDevelopment Development and and Mines, Mines, Suite Suite B002, B002, 435 435 James James St. St. South, South, Thunder Thunder Bay, Bay, ON, ON, P7E P7E 6E3 6E3 i s underlain underlain by by aa variety v a r i e t y of of Lake Superior Superior is The north north shore shore of of Lake The Precambrian Precambrian rocks rocks and and hosts hosts numerous numerous economic economicmineral mineraldeposits. deposits. The hosted by by the t h e Town Town of of The 41st 4 1 s t Institute I n s t i t u t e on on Lake Lake Superior Superior Geology, Geology, hosted Marathon exceptionally varied varied Marathon in i n 1995, 1995, will w i l l highlight highlight the t h earea' area1s exceptionally geology. geology. Neoarchean Neoarchean greenstone greenstone belts b e l t s and and granitoid granitoid plutons plutons of of the t h e Wawa Wawa The supracrustal subprovirice underlie most The supracrustal rocks rocks subprovince underlie most of of the the region. region. (2.77 (2.77 to t o 2.70 2.70 Ga) Ga) consist c o n s i s t of of komatiitic komatiitic to t o tholeiitic t h o l e i i t i c basalt, basalt, caic-alkalic c a l c - a l k a l i c basalt b a s a l t to t o rhyolite, rhyolite, clastic c l a s t i c sedimentary sedimentary rocks rocks and and i r o n formation. formation. They They have have been been tectonically t e c t o n i c a l l y juxtaposed, juxtaposed, deformed deformed iron and and intruded intruded by by massive massive to t o gneissic gneissic granite, granite, granodiorite granodiorite and and tonalite. t o n a l i t e . Greenstone Greenstone belt b e l t rocks rocks host host the t h e gold gold. deposits deposits at a t Hemlo Hemlo (Field the (Field Trip Trip 1), I), t h e volcanogenic volcanogenic massive massive sulphide sulphide (VMS) (VMS) deposits deposits at a t Manitouwadge Manitouwadge (Field ( F i e l d Trip Trip 2) 2 ) and and the t h e VMS VMS and and gold gold deposits deposits of of The Wawa Wawa the 3). The t h e Winston Winston Lake Lake and and Schreiber Schreiber area area (Field (FieldTrip Trip3). subprovince subprovince was was amalgamated amalgamated with with the t h e accretionary accretionary prism prism rocks rocks of of the t h e Quetico Quetico subprovince subprovince to t o the t h e north north during during late l a t e Neoarchean Neoarchean plate plate convergence convergence and and crustal c r u s t a l transpression. transpression. Paleoproterozoic Paleoproterozoic sedimentary sedimentary rocks rocks are a r e represented represented by by the the Gunflint Ga) and Rove Gunflint (2. ( 2 . 11 Ga) Rove formations formations of of the t h e Animikie Admikle Group. Group. Mesoproterozoic, Mesoproterozoic, pre—Keweenawan pre-Keweenawan rocks rocks consist consist dominantly dominantly of of red-bed of the t h e Sibley Sibley Group Group(1.34 (1.34 Ga). Ga). red-bed sedimentary sedimentary rocks rocks of The The development development of of the t h e Midcontinent Midcontinent rift r i f t (1.11 (1. 11 to t o 1.09 1.09 Ga) Ga) resulted r e s u l t e d in i n the t h e deposition deposition of of Keweenawan Keweenawan lavas lavas and and sedimentary sedimentary rocks rocks of of the t h e Osler Osler Group, Group, now now exposed exposed on on offshore offshore islands. islands. Associated Associated intrusive i n t r u s i v e rocks rocks include include the t h e Prairie P r a i r i e Lake Lake carbonatite, carbonatite, diatremes, K i l l a l a Lake Lake and and Coldwell Coldwell alkalic a l k a l i c complexes, complexes, diatremes, the t h e Killala (Field 4 ) and and tholeiitic t h o l e i i t i c diabase diabase sills s i l l s and anddikes. dikes. The The (Field Trip Trip 4) Coldwell Coldwell complex, complex, the t h e largest l a r g e s t alkalic a l k a l i c complex complex in i n North North America, America, consists consists of of three t h r e e intrusive i n t r u s i v e centres centres of of gabbroic gabbroic to t o syenitic syenitic magmatism. magmatism. Significant S i g n i f i c a n t deposits deposits of of copper-nickel-PGE, copper-nickel-PGE, rare r a r e metals metals associated with (T, Zr, Z r , Be) Be) and and rare-earth rare-earth elemei±ts demerits aare r e associated with these these (Y, intrusive i n t r u s i v e rocks. rocks. The ( F i e l d Trip Trip 5) 5) are a r e aa crucible c r u c i b l e of of geologic geologic The Slate S l a t e Islands Islands (Field The majority majority of of the t h e islands i s l a n d s are a r e underlain underlain by by Neoarchean Neoarchean activity. a c t i v i t y . The supracrustal supracrustal rocks rocks which which are a r e unconformably unconformably overlain overlain by by Paleoproterozoic Keweenawan Paleoproterozoic Animikie Animikie Group Group sedimentary sedimentary rocks. rocks. Keweenawan Osler Group basalts and diabase comprise the Mesoproterozoic, Osler Group basal ts and diabase comprise t h e Mesoproterozoic, Perhaps the t h e most most unique unique aspect aspect of of Midcontinent Midcontinent rift r i f t assemblage. assemblage. Perhaps the islands' geology is the extensive development of shatter t h e islands1 geology i s t h e extensive development of s h a t t e r cones, cones, which which have have been been alternatively a l t e r n a t i v e l y ascribed ascribed to t o hypervelocity hypervelocity meteorite meteorite impact impact and and endogenic, endogenic, volcanic volcanic activity. activity. I 1 , I I I 64 �UPDATE ON THE GEOLOGICAL GEOLOGICAL CORE CORE MARQUETTE, MICHIGAN MICHIGAN AND SAMPLE SAMPLE REPOSITORY REPOSITORY - MARQUETTE. - I I WWilliam i l l lam 1. T. Swenor, Swenor, Geological Technician Technician Milton A. Gere, Jr., Regional Regional Geologist Geologist Milton A. &re, Jr.. Geological Survey Survey Division, Division, Michigan RegionI I,,Marquette, Geological Michigan DNR, DNR, Region Marquette, MI MI The Michigan Michigan DNR' DNR's GeologicalSurvey SurveyDivision Division (GSD) maintains the Geological The s Geological (GSD) maintains Geological Core Coreand andSample Sample This "Rock Library" collection collection of currently "Rock Library* o fcore coreand and samples samples currently Repository aatt Marquette, Marquette, Michigan. Michigan. This represents36 36oof the83 83counties countIesi ninthe the state: state; however, theMajority majority ooff the materials are from however, the from represents f the the western one-half of the Upper Peninsula. Thus, Precambrian agedrocks rocks are are lmore represented western one-half o f the Upper Peninsula. Thus, Precambrian aged o r e represented than the Paleozoic materials. than Paleozoic aged aged materials. As ooff the end ooff 1993, Repositorycollection collection contains As 1993, the the Geological Geological Core Core and and Sample Sample Repository contains778 778 complete complete feet, filling drill from195 195 holes holes ddrill r i l lhole holecores cores totaling totaling 236,436 236,436 feet, f i l l i n g17,135 17,135 boxes; boxes: d r i l lcuttings cuttingsfrom representing 64,154 64,154feet feet ooff ddrilling contained abbreviated representing rilling containedini 507 n 507boxes; boxes; 386 386holes holes represented represented by abbreviated core from from 131,855 131,855feet feetoof f ddrilling, r i l l i n g ,held heldin i1,907 n 1,907boxes; boxes:174 174boxes boxes of o fmiscellaneous miscellaneous materials core overburdend drilling assay pulps, pulps, etc.) soils, overburden etc.) (chip samples, samples, soils, r i l l i n g materials, materials, outcrop outcropsamples, samples, assay Including 4,498 4,498feet feet ooff represented overburden Thisgives givesaacollection collectiont total including represented overburden d rdrilling. i l l i n g . This o t a l of o f 1,404 1,404 feet (82.75 (82.75miles) miles)oof alll l contained ddrill r i l lholes holesrepresenting representing 436,943 436,943 feet f ddrilling r i l l i n gplus plusother othersamples, samples, a contained in 19,723 boxes of materials. i n 19,723 boxes o f Thecore coreand andsample sample collectioncontinues continues grow better represent The collection t otogrow i ninanan e feffort f o r t t to o better represent the geology geology ooff the state. Materials are submitted to the Repository from a number of sources: 1) As partial are submitted t o the Repository from a number o f sources: 1) As a-apartial requiremento foff ufulfilling various state state requirement l f i l 1ingstate statemetallic metal 1i and c andnon-metallic non-roetall i cmineral mineral leases; leases; 2) 2) From Frcia various sponsoredprojects: projects;3)3) Through Throughcompany company donations of single holes large collections;4)4) sponsored donations o f single holes on on up up t o to large collections; Fromother otherstate state and agencies, such such as as the the US. U.S. Bureau Mines. From and federal government government agencies, Bureau ooff Mines. 146holes holestotaling totaling 34,639 34,639feet feetoof addedt otothe thecollection. collection. IIn n 1993, 1993, 146 f ddrilling r i l l i n gini n3,677 3,677 boxes boxes were were added Muchoof Exploration, Inc. Inc. Much f the core core was was donated donated by by Western Western Mining Corporation Corporation and and Resource Resource Exploration, Besidesthe themany many Shaled drilling, as the Western Syncline, or or Besides d rdrill i l l holes holes of o f Nonesuch Nonesuch Shale r i l l i n g , known known as Western Syncline, PresqueI sIsle deposit, Resource Exploration, Inc. Inc. donated boxesooff outcrop Presque l e deposit. Resource Exploration, donated 125 125 boxes outcrop samples, samples, ssoil oil samples,assay assaypulps, pulps,splits, splits, etc. along results from work iinn the samples, alongwith withhundreds hundreds of o f assay assay results from previous previous work U.P. This aalll l helps useful. U .P. This helps our our collection collectionbe bemore more useful. I I I I I I I SomeCore Core and sample materials on-loan several universities ffor Additionally, SOM and sample materials areare on-loan t o to several universities o r research. research. Additionally, material iiss reviewed on-site or or borrowed short tern term studies studies periodically periodically by material reviewed on-site borrowed f ofor r short by consultants, consultants, exploration and academiaand andindividuals. individuals. and mining mining companies, companies, academia TheRepository Repositoryi sisalso alsothe the storage storagessite DataCollection. Collection. The i t e for f o r the theG.5.D.'s 6.s.D.'~ Metallic MetallicMine MineMap Hap and and Data During 1993, 1993, the the balance balanceooff the inventoried was During inventoriedcollection collection wasmoved moved from fron Lansing Lansing ttoo Marquette. Harquette. Additionally, we several years we obtained obtained a collection collectionofo M.A. f M.A. Hanna's Hanna's Michigan Michigan materials and and several years ago ago we also received receivedaalarge large collection collection ofo fUSX andcross crosssections, sections, etc. etc. These These w e also USX (U.S. (U.S. Steel) Steel) mine nine maps maps and materials assist with andthe themine minesubsidence subsidence potentiali nInspecific specific materials with understanding understanding ooff the geology geology and potential areasoof thestate, state, thus thus they they also also are are an anaid aidt to the public public safety. safety. areas f the o the Thef facility thethe corecore andand cuttings, by appointment ononweekdays The a c i l i t yisi sopen ooenfor forvisitors v i s i t o rto s study t o study cuttings, by a~wintntent weekdays between8:30 8:30a.m a.m. and4:W 4:00p.p.m., Eastern tine. time. Some Somesampling samplingcan canbebearranged arrangedf ofor onaa case-bycase-bybetween . and m., Eastern r on case basis. Copies Copiesoof dataderived derivedfro from thestudy studyo of thecollection collection are are ttoo be be case f data m the f the be submitted submitted tto o be madepart parto of thepublic public record recordf for For information informationor or an an appointment, appointment,c acall made f the o r future use. use. For l l BBill ill SwenorororMMilt Swenor i l t Gere &?re at a t 906-228-6561. 906-228-6561. maintainsa11 all we1 well1 logs and thousandso fofselected selectedwe11 wellcuttings cuttingsf for Additionally, the theGSD GSD maintains and thousands o r ooili l and and gas wells wells In Waterwell wellrecords recordsf ofor the entire entire state are gas i n Lansing. Lansing. Water r the are also also kept kept in i nLansing Lansing by by the GSD. information. Copies Copiesoof Peninsula, Region RegionII,,water BSD. Call 517-334-6907 517-334-6907 f ofor r information. f aall l l Upper Upper Peninsula, water well records and andselected selectedwell wellcuttings cuttings are maintained maintainedby bythe theBGSD theDNR' DNR's office near near records SD at at the s D i sDistrict t r i c t 3 3Office information. Escanaba. Call Frank Frank Chenier Chenier aatt 906-786-2351 906-786-2351 f for o r more more information. 65 �GOLD POSSIBILITIES INI MICHIGAN' SS lATE ARCHEAN HENLCCK GOLD POSSIBILITIES N MICHIGAN' LATE ARCHEAN HEMLOCKFORMATION, FORMATION, AND THE PAINT RIVER GROUP IS STILL A USEFUL STRATIGRAPHIC AND THE PAINT RIVER GROUP IS STILL A USEFUL STRATIGRAPHICTERM. TERM. TROW, Jim,Department DepartmentofofGeological GeologicalSciences, Sciences, Michigan MichiganState State University, TROW, Jim, University, East lansing, Michigan 4882k East lansing, Michigan 48824 Almost everyoneseems seemst oto believe believe that Formation is is Proterozoic. that the theHemlock Hemlock Formation Froterozoic. Almost everyone However, However, aa late late Archean Archean age age for f o r the the Hemlock Hemlock is is suggested suggested by by Francis Francis Pettijohn's Pettijohn's field mapping (1951, USGS OF) of T.42N., R.30W., Dickinson County, f i e l d mapping (1951, USGS OF) of T,42N., R.30W., Dickinson County, by by Dave Dave Paddock's Paddock's gravity gravity survey survey (1982, (1982, MSU MSU MS MS Thesis) Thesis) of of the the Iron Iron River-Crystal River-Crystal Falls Falls Basin by Jim Jim Basin showing showing tthat h a t the the Hemlock Hemlock and and the the Badwater Badwater both both underlie underlie the the Basin, Basin, by mow's 1st Symposium) using U USGS aeromagnetic datat oto-trace trace three Trow's (1989, (1989, NGS MGS 1st symposium) using SGS aerorcagnetic data three magnetic horizons (Mansfield the Hemlock, Hemlock,East EastKKiernan magnetic horizons (Mansfield member member ofofthe i e m SSill, i l l , and and Skunk Creek I-F) from Iron County S and E along strike into the late Archean Skunk Creek I-F) from Iron County S and. E along s t r i k e into the lateArchean Dickinson GroupSix-Mile Six-Nilelake lake and and Solberg Solberg strata strata inInDickinson Dickinson Group Dickinson County, County, and and.by by Warren Beck's and Rama Murthy's (1991, USGS Bl904—I) recent Hemlock Nd Warren Beck's and Kama Murthy's (1991, USGS 31904-1) recent Hemlock Nd errorerrorchron chron with with an an age age of of 2.7 2.7 ±? 0.5 0.5 Ga. Ga. To reconstruct palinspastically To reconstruct palinspastically to t o an an early early Penokean Penokeanpattern, pattern, the theAinasa Amasa Oval and related domes are translated back 5 miles 55W along the Bush Oval and related, domes a r e t r a n s l a t e d back 5 miles SSW along the Bush lake lake Fault, f a u l t , and and rotated rotated back back 60 60 counterclockwise counterclockwise to t o appear appear tot obebealmost ahnostE-W E-w Archean endofofthe the gneissic gneissic core AnasaOval Oval Archean trends trends.• The The now—northern now-northern end coreof ofthe theAmasa appears to andDave Dave Wen-long Ueng Ueng and appears t o have have originated originated near near present present Iron IronRiver. River. lien-long larue v. 7, similar rotation. rotation. Iarue (1988, (1988, Tectonics, Tectonics, v. 7, no. no. 3) 3) envisaged envisaged aa somewhat somewhat similar At the Iron Iron placergold gold.panned panned from from the Iron River River aatt Iron A t the the turn turn of of the thecentury, century,placer River if traced River led lednowhere nowherewhen when traced tracedNW NW upstream. upstream. However, tracedNE MEup—ice up-ice in in However, if the Pleistocene (with SW SWglacial glacialmotion) motion)itit leads the IangJade -lade Pleistocene Lobe Lobe (with leads back back to t o the the northern Hemlock northern half halfofofthe the Hemlockofofthe theAinasa Anasa Oval. Oval. Bill B i l lCannon's Cannon's 10 1 xx 22 Iron Iron River Map 1-1360-A)shows showsairborne airborne EEM anomaliesinin this River Quadrangle Quadrangle(1985, (1985,USGS USGS M ap I-1360-A) M anomalies area thethe Amasa area and and in Inthe thesouthern southernhalf h a lof f of AmasaOval, Oval,which whichWarren Warren Peterson's Peterson's 10x 1 x 22 Iron 1—1360—a) suggests occuri ninthe the area area of *on River RiverQuadrangle Quadrangle(1985, (1985,USGS USGS Nap Map I-1360-C) suggests occur of W and NW NWglacial-motion glacial-motion vectors vectors of W and. of the theGreen GreenBay BayLobe. Lobe. If Sims (1992, USGS I f the theHemlock Hemlock isisArchean, Archean,then thenPaul Paul Sims (1992, USGSMap Map 1-2185) 1-2185) cannot cannot use supposed correlation correlation with use its itssupposed withthe theProterozoic ProterozoicBadwater Badwater Greenstones Greenstones to to justify thethe Paint River Group with thethe Michigamme justifycorrelating correlating Paint River Group with Michigwme Formation, Formation, aallthough the latter plausible forf Marquette County, though the lattercorrelation correlationis is plausible o r Marquette County,where where ClarksClarksburg equalBadwater, Eadwater,and andthe theBBijiki equal the the Riverton i j i k i I-F I-F may may equal Riverton I-F. I-F. HowHowburg may may equal ever, ever, that t h a tcorrelation correlationdoes doesnot notsquare squarewith w i t hobservations observations to tothe thesouth southwhere where an an almost WSW canbeIetraced traced W S W within w i t h i n the the almost complete complete Marquette Marquette Supergroup Supergroup section sectioncan Calumet Calunet Though Trough (and (and its its westward westwaxd extension) extension) from from the the Randville Randville Dolomite Dolomite at a t the the Calumet Calumet Iron Iron Mine, Mine, sec. sec. 8. 8. T.klN., T.&lN., R.28., R.28., Dickinson Dickinson County, County, stratigraphically stratigraphically upward Wisconsin, holes and and exposures exposures of of Paint upward to t o Commonwealth, Commonwealth, Wisconsin, d rdrill i l l holes Faint River River Group sequenceexposes exposesnonoHemlock, Hemlock, Group rocks rocks.• This This conformable conformable sequence asasi lillustrated l u s t r a t e d in In the stratigraphic column. Michigamme the accompanying accompanying strat$graphic column. Here, Here, the thethick thick Michigamme gradedgradedbedded graywackiesunderlie underlie the the Badwater Badwatel'and andthe theeentire bedded graywackies n t i r e Paint Faint River River Group, Group, as as suggested H a lJames James(1958, (1958,USGS USGSP314-C). ~314-c). suggestedby byHal This T h i s north/south north/south stratigraphic stratigraphio dilemma dilemma may nay be be reconciledby reconciled by seimentology: sedimentology: If If Marquette Marguette Supergroup Supergroup sedimentary sedimentary basin basin development development migrated migrated northward, northward., as as the Penokean orogeny soon thereafter rolled northward, then the appropriate the Penokean orogeny soon thereafter r o l l e d northnard., then the appropriate environment Michigamme in Iron Ironand and environment for f o rthe thethick thick Michiganae graded-bedded graded-bedded graywackes graynackes in Dickinson Counties may have occurred in Baraga "time", whereas that environDickinson Counties may have occurred In Baraga "time", whereas that environment maynot nothave haveexisted, existeduuntil late int River "time" nearnear lakelake Nichigamme, ment may n t i l late Faint River "time" Michigamme, in Marquette County. This involves merely fine tuning excellent Survey work. i n l&rguette County. This Involves merely fine tuning excellent Surveywork. The meatand andpotatoes potatoesbottom bottoml iline of this this paper A Along-unrecognized The meat n e of paper is isthis: this: long-unrecognized Archean greenstone bbelt probably contains gold. Archean greenstone e l t (Hemlock) gr em lock) probably gold. Let's L e t ' s go go: thiso 66 �I I I I I I I I I I I I I I I I I I Pre-KeweenawanRocks RocksIninIron Iron and and Dickinson Dickinson Counties, Counties, Michigan, N. Pre-~eweenawan Michigan,by byJim J i mThow, Trow, M . S. 5. U. U. Iron County Dickinson . Dickinson County Iron County - .1 Fortune lakes Slate $1 Fortune Lakes Slate 0 > ft Hiaatha Graywacke Hiverton Iron—Formation Dunn Creek Slate (with Wauseca Pyritic Member) '4 +' 51 —4 I ' Badwater Greens tone Jflebigamme • 0 •-1 Granite, Diorite, Granite, Diorite, Pegnatite fegmatite lie tagabbro Metagabhro Intrusive IntrusivePeavy PeavyPond PondComplex Complex Badwater Gre en tone Formation Nichigamme Formation Vulcan Vulcan Iron-Formation Iron-Formation Felch Formation Felch Formation 63 à Felch Formation Formation Felch (quartz-mica schist, (quartz-mica schist, garnetm e t grunerite schist, quartzite, grunerite schist, quartzite, fe1dsthic quartz-mica feldsmthic quartz-flea schist schist greenschist of his Iameys DickinsonkENXXXXXXfl4.Ealus greenschist of h i s Dicfclnson suIameyls1961 1961FF310 PP33.0 p.p.131— 131Horizon?* 133 ainfaibolite) Group) amitibolite) ~ roup) Horizon?* Raudvifle Dolomite Randville Dolomite BanilvllleDolOBite Banilville Doldte (slate, graywacke, - ft9 (slate, g r a y n a ~ hquartzite, quartrib, 0 Â¥ arkose plus Bayiey' 2 = yivs B ~ Y ~ sY1959 1959 's ° B1077 B1077 p. p. 14—i? magnetic 11-17 -tic se ;; , g Sturgeon Quartzite Quartzite Sturgeon -. u 0 Pem Fern Creek 28 Creek Formation Foniation ° Sturgeon Quartmite Sturgeon Quartnit8 Fern Creek Formation Fern Creek Fomation some arkose) arkose) (including some (including f% lciernan ~ S i lSills l sanda other n d Metagabbros Metagabbros ; I o ~ A 0 c fletagabbro (Aiqfaibolite) (Mjtiboflte) Hetagabla-o 8 — S.d >4' ?2 41.1;, ^M Unnamed Graywa eke ?=? ?? Fence Graynaeke Fence Lake Strata in SE Baxaga Co. IalceStrataInSl3BaxagaCo. 0 Gneissic Granite Gneissic Granite and Banded Gray Gneiss A 4 G4 0--I id -0 .a S An8sa—Fence River Iron—FormagAm6a-Fence River Iron-Fonnations tions s-at -'-4 $4 't 51051 Formation (inciuang Hemlock Formtion (including p1 Mansfield IronBird and Mansfield Bird and IronFormations) & h i Formations) 'd .p o d 4' Quartz-Sericite--Magnetite Z rI cdN Quartz-sericite-Vagaetite ' Schist, Skunk Skunk Creek Creek IronIronO'd-.-I Schist, 0 TI.—I 2 Formation, and andPorphyritic Porjyritic El —143--4 (3 Fen-nation, *> 8 51 Red Felsite 0 Bed Felslte g " g-'-I 2(0 .C $-i >3 Magnetic low low nay My be be East Magnetic East or Porphyritic Porphyritic Ph 014 Branch Arkose Branch Arkose or Red Red Granite Granite - Nargeson IkCgeSOII Creek Gneiss Gneiss of of Aiinsa Oval Asaaa.Oval I, + ^2 .-I ! 4 5 4 IL I Unnamed Graywacke (see Janes, James Unnamed Graywacke (See 1961, PP310, PP31O,p.p. 25.) 25.) 1961, ! Grunerite Zone in Six-Mile 0) Grunerite Zone In Six-Mile 0, lake -1' Amphibolite Six-Nile lake Amphibolite Six-Bile lake Anphilollte 40 C ss Onl a .J -d 5 051 0 % o 2 Solberg Schist (inclmling (including S o l k g Schist Skunk Creek Creek Iron Iron Formation) Skunk Formation) ; I ! * i I East Branch East Branch Arkose Ark- 4, Red Granite Gneiss of R e d Granite Norway lake area Noruaybke- - *Outsidearea area discussed, discussed, Quinnesec Quinnesec Fornation Formation overlies overlies Randvifle Â¥Outsid BanAvllleDolomite Dolomite in Wisconsin (mow), and overlies in Wisconsin in InMenominee Henodnee River R i v e r ESE SSS from tram Pembine Pemblne ( Trow), aod narbles, on W, W, N,N, and and.EEsides sides of marhies. arkosites, arkoeites, quartzites, qusu-kites, and and schists schists on Duntar Duntar gneiss dome dome (Schulz, (Schuiz, 1982, 1982, Inst. Inst. on onL. L.Superior SuperiorGeo1ogy Geology, pp.- 43) 43) 6-7 �PETROGRAPHY OF THE THE UPPER PETROGRAPHY AND DIAGENESIS DIAGENESIS OF UPPERCAMBRIAN CAMBRIAN MT. MT. SIMON SIMON SANDSTONE, SE MINNESOTA. SANDSTONE, SE MINNESOTA. URIBE, URIBE, Ruben Ruben D., D., Department Department of of Geology, Geology, University University of of Minnesota— MinnesotaDuluth, Duluth, MN 55812. Duluth, Duluth, MN 55812. The The Mt. Simon Simon Sandstone Sandstone is is the the lowermost lowermost formation formation of of the the Dresbachian Dresbachian The stage . stage (Upper (UpperCambrian) Cambrian). The unit unit rests rests unconformably unconformably on on aa wide wide variety variety of of Precambrian Precambrian rocks rocks in in southeastern southeastern Minnesota. Minnesota. Its Its average average thickness thickness is is about about 260 260 feet. feet. The The Mt. Mt. Simon Simon Sandstone Sandstone is is dominantly dominantly aa medium—to (Q954F41L05) white medium-to fine—grained fine-grainedquartz quartzsandstone sandstone white to togray, gray, noticeable featureof of(Q95.4F,.iLo.5) the unit unit is is with with sporadic sporadic thin thin shale shalebeds. beds. A A noticeable feature the The presence presence of the of authigenic feldspar. The the abundance abundance of authigenic potassium potassium feldspar. of mineralization of authigenic authigenic feldspar feldspar may be correlated correlated with mineralization of midcontinent midcontinent Mississippi Mississippi Valley—type Valley-type lead—zinc lead-zinc deposits. deposits. Petrography microprobe analysis Petrography and and microprobe analysis were used used to to identify identify the the framework framework and and matrix matrix constituents constituents of of the the Mt. Simon Simon Sandstone Sandstone and and to to determine determine the the diagenetic diagenetic textures, textures, paragenetic paragenetic sequence sequence and and chemical chemical composition total of of 95 95 thin thin sections sections were were composition of of authigenic authigenic minerals. minerals. AA total All studied - All studied and and point point counted counted with with 600 600points pointson oneach each(Table (Table1)1). samples samples were were from from drill drill holes. holes. The The sandstone sandstone has has undergone undergone aa varied varied diagenetic diagenetic history, history, which which includes includes precipitation precipitation and and dissolution dissolution of of authigenic authigenic minerals, minerals, Potassium dissolution dissolution of of unstable unstable detrital detrital grains, grains, and and compaction. compaction. Potassium feldspar feldspar is is the the most most common common authigenic authigenic mineral mineral in in the the Mt. Mt. Simon Simon Sandstone. Sandstone. The The feldspar feldspar is is present present in in almost almost all all the the samples samples as as euhedral euhedral to to subhedral subhedral overgrowths overgrowths on on detrital detrital grains, grains, ranging ranging from from 0.2 0.2 to The overgrowths overgrowths are are not not to 23.5 23.5 volume volume percent percent in in the the thin thin sections. sections. The in in optical optical continuity continuity with with the the detrital detrital cores, cores, and and are are usually usually pure pure orthoclase orthoclase in in composition, composition, as as evidenced evidenced by by electron electron microprobe microprobe detrital quartz contacts and and analysis. Quartz cement cement is is present along detrital analysis. Quartz Authigenic dolomite in dolomite in very very few few cases cases as as distinct distinct overgrowths. overgrowths. Authigenic exhibits two rhombic*exhibits two different different textures: textures: 1) 1) Euhedral, sand—sized sand-sized rhombic— shaped shaped crystals crystals with with considerable considerable zonation zonation showing showing iron—rich iron-rich (red) (red) and and iron—poor iron-poor (clear) (clear) dolomite, dolomite, and and 2) 2) Rhombic Rhombic fine—grained fine-grained subhedral subhedral crystals illitic matrix. matrix. Poikilotopic calcite is found in a crystals replacing replacing illitic few few samples samples partially partially replacing replacing detrital detrital and and authigenic authigenic minerals. minerals. Calcite Calcite is is also also present present as as isolated isolated patches patches filling filling pore pore spaces. spaces. Two texturally Kaolinite Kaolinite cement cement is is present present in in nearly nearly all all samples. samples. Two texturally well—crystallized vermicular vermicular different different types types of of kaolinite kaolinite occur: occur: 1) 1) Well-crystallized aggregates Micron-sized particles particles finely aggregates in in pore spaces spaces and 2) Micron-sized laminated laminated around around detrital detrital grains, grains, displaying displaying aa wavy—looking wavy-looking pattern pattern Other secondary parallel to the stratification. parallel to the stratification. secondary authigenic authigenic minerals minerals found found in in the the unit unit include include hematite, hematite, pyrite pyrite and and leucoxene, leucoxene, present present as as grain grain coatings coatings and and pore pore fillings. fillings. The The total total average average porosity porosity for for all all the the samples samples taken taken from from the the Mt. Mt. Simon Simon Sandstone Sandstone is is 15.5 15.5 percent; part of of it it is is secondary secondary porosity porosity which which is is evidenced evidenced by by dissolution dissolution of of cements cements and and labile labile detrital detrital grains grains throughout throughout the the unit. unit. The The final final objective objective of of this this study study is to describe the paragenetic sequence seauence of of the the authigenic authiaenic minerals. minerals. This part of the the study study is is presently in progress. �I HIA Bi 8Q9 SCH&KANV669 TOTAVE • I I P NUMBER OF SAMPLES 21 18 18 22 COMMON• 593 628 51.2 62.7 66,5 60.51 POLYCRYSTALLINE 2.0 1.6 31 0.6 41 2.30 VEIN(?) ,i 1.9 1.0 2.1 1.17 227 6503 1.4 1.4 1.0 1O . 0.1 0.3 1A2 1.42 0.34 0.34 1.05 1.05 2.81 16 QUARTZ g v MULTICYCLE FELDSPAR H TOTAL QTI 61.4 653 615 ORTHOCLASE ORTHOCLASE 2.2 2.2 1.9 1.9 0.5 0.5 MICROCLINE 1.0 1.0 MICROCLINF. PLAGIOCLASE F'LAGIOCLASE 0.5 0.5 0.3 0 3 3.1 3.1 TOTALFELDSJ'AR 17 54 I SEDIMENTARY MuscoviTE ... ILLI'rIC(')CLAY CEMENT CEMENT 0.4 •' 0.12 0.07 0.6 t22 0.4 0.4 0.3 :. 0.3!.. .: 0.1 0.12 0.1 0.03 1.6 37 14. 1.0 1.55 256 435 4.35 QUARTZ 3.9 1.9 2.7 1.9 2.4 PELDSPAR FELDSPAR 9,7 9.7 5.0 5.0 0.8 0.8 3.2 3.2 3.1 3.1 DOLOMITE 1.3 DOLOMITE 1.3 CALCITE 0.1 CALCITE 0.1 2.9 2.9 4.6 4.6 33.66 0.7 0.7 KAOLINITE KAOUNITE FOSSILS GLAUCONITE PORES : 1.3 1.3 LEUCOXENE 1.4 COLLOPI-IANE .. pyRIm REPLACED 0.4 . .FELDSPAR (F) CLASSIFICATION CLASSIFICATION (Q) FELDSPAR (F) LITHICS (L) UTHICS 0.9 0.9 1.28 1.28 0.1 0.1 0.08 1.78 1.78 0.08 0.4 0.4 1.3 1.3 HEMATITE HEMATITE • 1.59 1.59 0.4 0.4 8.3 8.3 0.5 0.5 PYRITE PYMTE QUARTZ I 18 00 0.6 :. SIDERITE S IDERITE . I .:. :; 0.3 0.6 0.6 . MICA MICA I I . METAMORPHIC TOTALROCKFRAIJ MATRIX ' 0.1 1.0 1.O 2.6 LOS : . BIOTITE I I• 643 ' 0.6 01 PLUTONIC ROCK FRAO. ... : • 4.1 4.1 0.27 . 02 0.2 . 1.4 02 . . 0.34 034 1.09 1.09 0,7 0.59 0.2 007 0.63 0.6 2.6 15:9 182 13.0 14.5 16.0 ISM 943 92.2 77.66 98.1 0.9 0.9 0.3 0.3 1.0 1.0 95.7 3.8 3.8 0.5 0.5 97.0 2.4 2.4 0.6 0.6 95.42 4.12 4.12 0.46 0.46 5.7 5.7 Table!: Petrographic Tablel: Petrographic summary summary for for the the Mt. Simon Simon Sandstone, Sandstone, based based on on 95 thin sections from 5 drill holes in southeastern 95 thin sections southeastern Drill hole locations Minnesota. Minnesota. Drill locations are are listed listed below. below. Northern Natural Northern Natural Gas Gas Hollandale 1-A 1—A (H1A) (=A) Hollandale sec.7,T.103N,R.19W. SE1/4SW1/4 sec.7,T. SE1/4SWI/4 1 0 3 ~ ,19W. ~. Freeborn Countv County Freeborn . - New Jersey New Jersev Zinc Zinc B—i B-1 sec.25,T.104N.,R.9W. NW1J4SW1/4 sec. NW1/4~~1/4 25,T. l04N., R. 9W. Fillmore Countv County Fillmore Pan Ocean Ocean Oil, Pan Oil, Ltd. Ltd. SQ—9 SQ-9 SE1/4SW1/4 sec.l,T.lO4N.,R.32W. SE1/4SW1/4 sec.1,~.104~. ,R.32W. County Martin County Minneqasco KAM-1 RAN—i Minnegasco sWl/45W1/4 sec.4,T.1081,4.,R.22W. SW1/4SW1/4 sec.4,T.108N..R.22W. Waseca County Waseca County Minnegasco SCE-1 SCH—1 Minnegasco NW1/4NE1/4 sec.6,T.lO8N.,R.22W. NW1/4NE1/4 sec.6.T.lOEN..R.22W. Waseca County County Northern Northern Natural Natural Gas Gas Vermillion 66—9 66-9 (V66—9) (v66-9) Vennillion W1/4NW1/4 sec.ll,T.ll4N.,R.lBW. W1/4NW1/4 sec.l1,~~.114N. ,R.lEW. Dakota Dakota county county 6-9 �WAGGONER1 WAGGONER. ECHO ECHO LAKE LAKE GABBRO, GABBRO, HOUGHTON HOUGHTON COUNTY, COUNTY, MICHIGAN MICHIGAN IL, Cliffs Mining Services T. D., Cliffs Mining Services Co., Co.. Ishpeming, Ishpeming, MI MI ff1. 49849 49849 The Jacobsville sandstone The Jacobsville sandstone between between Lake Lake Gogebic Gogebic and and Keweenaw Keweenaw Bay Bay has has long long been been thought thought to to cover cover the the Powder Powder Mill Mill Group Group (extrusive (extrusive volcanics) volcanics) which which form form the the southeastern southeastern flank flank of of Midcontinent Midcontinent Rift Rift Basin. Basin. The The relative relative magnetic magnetic and and gravity gravity highs highs were were interpreted interpreted as as fault fault blocks blocks of of the the Group Group at at shallow shallow burial. burial. Jacobsville Jacobsville thicknesses thicknesses range range from from 00 to to +3600 +3600 feet feet based based on on outcrop outcrop and and drilling information. Further geophysical data suggest thickness in excess of Further geophysical data suggest thickness in excess of drilling information. 9000 9000 feet feet in in some some areas. areas. Based Based on on the the geological geological interpretation interpretation and and seeking seeking knowledge knowledge of of the the copper copper potential potential in in the the lower lower flow flow units, units, an an exploration exploration hole hole was was completed completed in in 1975. was collared collared 990'N. 990'N, 1480'W 1975. The The hole, hole, Echo Echo Lake Lake ff1, #l, was 1480'W of of the the SE SE corner comer of of Section Section 22, 22, T49N, T49N, R37W, R37W, Houghton Houghton Co., Co., Michigan. Michigan. Collar Collar elevation elevation was was +1375' +1375'. The The hole hole encountered encountered 95 95 feet feet of of glacial glacial till till followed followed by by 805 805 feet feet of of JacobsJacobsville At 900 900 feet, feet, the the hole hole entered entered weathered weathered olivine olivine gabbro gabbro for for ville sandstone. sandstone. At 20 20 feet feet and and was was terminated terminated at at 1315 1315 feet feet in in fresh fresh olivine olivine gabbro. gabbro. Minor Minor zones zones of of more more basic basic rock rock approaching approaching aa picrite picrite are are present. present. Shattering Shattering normal normal to to the the vertical vertical hole hole is is evident evident in in both both core core and and thin thin section, section, affecting affecting both both labradorite labradorite and and olivine. olivine. Serpentinization Serpentinization of of the the olivine Specific gravity gravity of of the the gabbro gabbro ranges ranges olivine along along the the fractures fractures is is common. common. Specific from Magnetite occurs occurs as as thin thin (mm) (mm) bands bands normal normal to to core core angle angle from 2.94 2.94 to to 3.11. 3.11. Magnetite in and the the magnetic magnetic iron iron content content at at 10251 1025' measured measured in the the upper upper part part of of the the hole, hole, and 4.3%. 4.3%. The The core core was was devoid devoid of of sulfides sulfides and and the the Pt/Pd Pt/Pd analysis analysis did did not not exceed exceed background. background. Both Both the the magnetic magnetic and and gravity gravity signature signature can can be be reinterpreted reinterpreted as as an an elongate elongate plutonic plutonic body body similar similar in in shape shape to to the the Mellen Mellen Gabbro Gabbro and and possibly possibly with with a It can can also also be be postulated postulated that that at at depth depth near near the the a granophyric granophyric component. component. It lower lower Proterozoic Proterozoic contact, contact, base base metals metals may may occur. occur. 70 �ANORTHOSITES: E., ANORTHOSITES:IGNEOUS IGNEOUSCUMMULATE CUMMULATEOR ORMETASOMITE? METASOMITE?ROGERS, ROGERS, Michael Michael E., WATKINS, Ivan W., W., Department WATKINS, Ivan Department of Earth Sciences, St. St. Cloud Cloud State State University, Universi St. Cloud, MN. St. Cloud, MN. 56301. 56301. Paradigms problems and and interpreting interpreting data within the Paradigms are are guide guide lines lines or rules used for solving problems wi confines of of that paradigm. Paradigms and Paradigms are are an anintegral integral part part of of any any scientific scientific discipline, an geology is no different. The The prevalent paradigm paradigm of of today today is is that that the the anorthosites anorthositesof of the the Duluth Complex along the north shore of Minnesota are igneous cummulates. Why? Well, they, Duluth Complex along the north shore of Minnesota are igneous cununulates. Why? Well, have have an anobvious obviousigneous igneoustexture texture and andbesides, besides, they they are arenot not associated associated with with metamorphic metamorphicrocks rocks like the slates and greenstones near Virginia and Ely Minnesota(Phinney, 1966, like the slates and greenstones near Virginia and Ely Minnesota(Phinney, 1966, p. 142). 142). Plagioclase magma simply floated towards the top Plagioclase crystals from the gabbroic magma top of the the intrusion, intrusion, settled to the bottom, or sometimes both (Phinney, 1966, p. 135). Besides accumulating Besides accumulating as settled to the bottom, or sometimes both (Phinney, 1966, phenocrysts in magmatic chambers, anorthosites are also observed phenocrysts in magmatic chambers,anorthosites are also observed as asinclusions inclusions within within dikes, dikes, sills, and flows. Where present, nearly all of these inclusions are rounded (Phinney, 1966, p. sills, and flows. Where present, nearly all of these inclusions are rounded (Phinney,1966, p. 135). as lenticular lenticularmasses masseswithin withinthe thesurrounding surrounding gabbro. gabbro. Temperature Temperature 135). Anorthosites Anorthosites also also occur as estimates ratios samples and and suggest that estimatesfor for anorthosites anorthosites are are based on 018/016 018/01*' ratios from several samples most anorthosites crystallized under conditions of about 1000° to 1100°C with most anorthosites crystallized under conditions of about 1000" to 1100'C with a water fugacity between between500 500bars baretoto2000 2000bars bars(Isachsen, (Isachsen,1966, 1966,p. p. 439). 439). Study and sampling was done at the large disused Study and sampling was done at the large disusedanorthosite anorthositequarries quarriesatatCarlton CarltonPeak Peak(SE (SB of NE 1/4 of Sec 20, R4W, T59N). At this site anorthosite dominates the quarry but 1/4 1/4 of NE 1/4 of Sec 20, R4W, T59N). At this site anorthosite dominates quarry but is is spotted spottedwith withhundreds hundredsof of gabbroic gabbroic inclusions. inclusions. When Whenviewed viewed from from the the proper proper orientation orientation these these gabbroic spots appear as elongate lenses which are oriented parallel to one another. of gabbroic spots appear which are oriented parallel to one another. Many of these spots can be found with a deep red rim of hematite surrounding them. These samples are surrounding These samples are these spots can extremely dipped in extremely friable friable and needed to be dipped in epoxy epoxy glue in order to cut, polish and thin section. Without this epoxy, the samples simply could not have been thin sectioned. Air bubbles rising Without this from fractures thin section from fracturesin inthe thegabbroic gabbroic spots spots as as well well as as plucking plucking of the entire thin section sample was a common occurrence. Obviously, these samples are highly fractured. The gabbro Obviously, these samples The gabbrospots spots common themselves are the most severely fractured/friable and in many cases themselves erely fractured/friable and in many cases these these spots spots are are parallel parallel to to major fractures within the samples. In In lL'._.1JC addition addition to to this, this, several rounded spots spots had visible 'tails 1) which which are are "tails" to them them (Fig. (Fig. 1) identified structure identified by Carol Carol Simpson as shear structure geometries 250). Another geometries(Simpson, (Simpson,1986, 1986, p. 250). Another feature is the the feature worth worth note note in this this paper paper is apparent apparentgrain grainof of the the rock rock which, which, when when broken, broken runs runssubparallel subparallelto to the the gabbro gabbro spots spots and and not n FIGURE 1: Gabbro spot showing diagnostic along along the shortest shortest path path as as would would be be tail, expected. expected. tail,aatypical typicalshear shearstructure structureshape. shape. IfIf the thelarge largescale scale features features and and hand hand samples sampleswere weresuggestive suggestiveof of shear shearzone zone genesis, genesis, then the thin The first first step step was was to to thin thin section section the the anorthosite anorthosit itself, thin section section evidence evidence is overwhelming. The without withoutthe thegabbro gabbrospots. spots. The Thefirst firststriking strikingthing thingabout aboutthe theanorthosites anorthositesof of this thisarea area is isthat even even they they are are highly fractured. Most Most fracture fracture fills are chlorite, chlorite, yet yet there there are are many more that have haveplagioclase plagioclase as asaafracture fracturefill fill itself. itself. Also Alsocbmmon cbmmonin inthe theanorthosites anorthositesare areplagioclase plagioclase crystals rounded and crystals that that have have both both very very typical typical angular angular crystal crystal faces and very atypical rounded and curved curvedcrystal crystal faces. faces. Both Both of of these these features features can be found within the same crystals. Where Where the the crystal crystalfaces faces are are smoothly smoothly rounded rounded the thecrystal crystal h-' boundary boundaryappears appearsvery veryfuzzy. fuzzy.Upon Uponcloser closer examination, examination,one onecan cansee seeaaseries seriesof of fractures fractures that aresubparallel subparallel to to the the crystal crystal face. face. Also Also that are present presentwithin withinthe theanorthosite anorthositethin thinsections sectionsare are several severalexamples examplesof of shear shear structures. structures. One Onesuch such feature nlaeioclasecrystal, crystal, roundedand and featureisisaaplagioclase , . rounded FIGURE2:2: & l a s e ' ~ o r p h y r o ~ t with exhibiting FIGURE exhibitingtails, as an aninclusion inclusion within within another ano plagioclase tail another plag ta! inside Inside another plogcrystal. clystal. plagioclasecrystal crystal(Fig. (Fig. 2). Moving Movingfrom fromthe - - &,as .. 71 �anorthosite can see see an an interesthe interesting trend. trend. Many anorthositeto tothe thegabbroic eabbroicspot spotinclusions, inclusions, one one can Manvof of the spots in the anorthosite are highly fractured while others are more massive. the spots in the anorthositeare highly fractured while others are &e massive. Beginning with the the more more massive massive samples samples (which (which still needed to be epoxied for for thin thin sectioning) sectioning) one can observe plagioclase and pyroxenes. The pyroxene has been slightly to moderately one can observe plagioclase and The pyroxene has been slightly to moderately altered altered along along it's it's fractures fracturesand and exhibits exhibits aa vermicular vermicular texture at these points. The Themain main alteration minerals are chlorite and hematite. Within many anhedral pyroxenes Within many anhedralpyrbxenesare are perfectly perfectly alteration rounded plagioclase crystals. Within many anhedral plagioclase crystals there are rounded pyroxene crystals which are highly altered to chlorite and hematite. Several more pyroxenes show an almost perfect textbook quality porphyroclast with tails. P1 B v1any of the more circular and rounded pyroxenes have curious fracture patterns which change direction and ior.c circle around the pyroxene crystals(Fig. 3). Moving to the more fractured spots, the pyroxertes appear much more heavily altered. Within many of these heavily FIGURE 3: Circuldr fracture patterns altered pyroxenes are more circular plagioclases. .rounded pyroxenes. surrounding And And within G&in these theseplagiocl plagi ses aiy chlocitr "' ure surrounding rounded pyroxene&. fills (Fig. 4). fills encased encased within withinpig. 4). Moving Moving to tethe the.' '' most highly fractured material within most highly fractured material within the the pro, 3 anorthosites, can hardly anorthosites, one onecan' hardlyrecognize recognizethe the altered altered ro, fl B pyroxenes round pyroxenesanymore. anymore.Many Manystifi stillencase enca~e'lound;:C-L,!.;+& t.f5 plagioclase chlorite and plagiiklase,with withchlorite and hematite hematite present. pres&t.''' l-ie.^c.ia ll .. As other two spot As with with the tHeothertwo spotsamples samplesthere thereare arethe the ". rounded patterns, roundedpyroxenes, pyroxenes,circular circularfracture fracturepatterns, rounded crystal faces, chlorite rounded plag pl&guy&d f-, ddoritefracture fracturefills, &,7jpyroxenes FIGURE pyroxenesaltered alteredentirely entirelyto to chlorite, chlorite, and and more more FIGURE 4:4: Rounded piag wi shear pyroxene. pwxerle. Note Notethe ttiechlorite <shteittefracture ftticfuiiefills. His. shear structure structurepatterns. patterns. The The question questionthat thatneeds needstotobe beasked askednow nowis;is;ififthis thisisiftruly trulyan anigneous igneouscumn-tulate, cummulate,can canthese these things thingsbe be present? present? And Andthe flieanswer answerisisunequivocally unequivocally"No". "No". Phinney Phinneyhad haddifficulty difficultyconstructing constructing aa theory of anorthosite anorthosite in in northeastern northeastern Minnesota. An theorythat thatcould couldexplain explainall all four four occurrences occurrences of An igneous made in in the field field and and in in the lab. lab. The north north igneous model model just does does not agree agree with observations observationsmade shore rocks. As pbbro gabbro was was sheared sheared and and ground ground up shoreanorthosites anorthositesare aremetamorphosed metamorphosed gabbroic gabbroic rocks. up water fluxremoved removed and anddeposited depositedminerals mineralsuntil untilan analmost almost plag plag pure pure composition composition waterflux recrystallized certainly recrystaffizedfrom from it. it. The Thelenses lensesand androunded itoundedinclusions i~lusions certainlyfit fit this (hismodel. modeLMany Many anorthosite oneis is not not looking looking. anorthositebodies bodiesdo donot notexhibit exhibitshear sheargeometries. geometries. However, However,ifif one perpendicular structures. Additionally, perpendiculartotothe thesense 'senseof of shear, shear, one one cannot cannot observe the shear structures. Additionally, preliminary we have have conducted conducted supports supports aa metasomtic metasomatic environment. environment. For For preliminarygeochemical geochemical evidence evidencewe those theirparadigm paradigmand andcannot cannotaccept acceptthe theobservations observationsthemselves, themselves, thosewho whoare arerestricted restrictedby bytheir then be added to the thereare aredozens dozensof of ad ad hoc's hoe's which which can be the cummulate cummulate theory. However, However,the the then there more exceptionsthere thereare are to to aa rule r6teor or theory, theory, the Ideless less and and less less^that that theory theory is is capable capable of of making making moreexceptions predictions. cannot theorvcannot cannotmake makepredictions, oredictions,ititisisuseless. useless. IfIf aaparadigm ~aradlem cannotallow allow oredictinns.IfIfaatheory someone then that someoneto to problem problemsolve &ve accurately, accurately;then that paradigm paradigmisisalso alsouseless. deless.The Thereal realgenesis genesisof of the the north by no nomeans means resolved resolved by this this paper. paper. What Whatcannot cannotbe bedenied, denied, northshore shoreanorthosites anorthositesisisby however, inability of however, isisthe theinability of the the cummulate cummulatemodel model to to hold up upeven even under undercommon commonobservational observational techniques. timefor foranother anotherparadigm. paradigm. techniques. ItItisistime REFERENCES REFERENCES Jsachsen, bachsen,Yngvar, ~ n ~ v W., a r ,1966, 1966, ~ . , Origin Originof of anorthosite anorthotiiteand and related relatedrocks rocks- aa summarization: York Museum and Science ScienceService, Service,Memoir Memoir18, 18,p.435-445. p.435-445. summarization:New New Yo&State State Museum and %&a '.-c ,. a U - Phinney, Phinney,William WilliamC., C., 1966, 1966, Anorthosite Anorthositeoccurrences occurrencesin in Keweenawan Keweenawanrocks rocksof of Northeastern Memoir 18, NortheasternMinnesota: Minnesota:New NewYork YorkState StateMuseum Museumand andScience ScienceService, Service,'Memoir 18,p.135-147. p.135-147. Simpson, Simpson,Carol, Carol,1986, 1986, Determination Determinationof of movement movement sense sensein inmylonites: Journal Journalof of Geologic Education, v.34, 246. GeologicEducation, v.34,p.p.246. Â¥iv 72 �AND SEDIMENT-CONTROL MODELS USE OF RUNOFF- AND IN THE DESIGN OF MINE IN THE DESIGN MINE HYDROLOGIC HYDROLOGIC CONTROLS CONTROLS Richard Richard B. White, P.E. P.E. Principal Hydrologist Hydrologist and and Thomas J. Suchoski Suchoski Senior Hydrotogist Hydrologist EarthFax Engineering, Inc. Midvale, Utah Utah and Bath, Michigan Michigan ABSTRACT ABSTRACT I I  I I I at mine surface facilities facilities is an important aspect Control of of runoff and erosion at Control of environmental protection. Regulations regarding the installation environmental Regulations regarding installation and maintenance maintenance 5 of runoff- and and sediment-control sediment-control facilities at at coal coal mines mines have have been been in in place place over over 115 years since since implementation implementation of of the Surface Mining Control and Reclamation Act Act of years of 1977. Similar Similarlaws lawsgoverning governingenvironmental environmentalcontrols controls at at mineral mineral mines mines are currently considered on being considered on aa Federal Federal level. Several models have been developed developed for for the the design of runoffrunoff- and andsedimentsedimentcontrol facilities at mining and industrial operations. These models range from control facilities at mining and industrial operations. These models range from simple simple analytical and empirical approaches approaches to to detailed detailed computer computer codes. codes. Models'have Modelshavebeen been to estimate rainfall-runoff rainfall-runoff relations, sediment yield, yield, the the erosion potential of developed to streamflow, and the sedimentation characteristics characteristics of of control structures. channelized streamflow, structures. These models will be reviewed, along with examples of their implementation. These models will reviewed, with of implementation. 7.3 �BIODEGRADATION OF BIODEGRADATION OF ENVIRONMENTAL CONTAMINANTS CONTAMINANTS UTILIZING WHITE UTILIZING WHITE ROT ROT FUNGUS FUNGUS Richard B. White, Richard White, P.E. P.E. Hydrologist Principal Hydrologist and and Mark S. Wollensak Wollensak Project Project Geologist Geologist EarthFax Engineering, Inc. Inc. Midvale, Utah Utah and and Bath. Bath, Michigan Michigan ABSTRACT ABSTRACT . White rot rot fungi fungiare areaacommon, common,naturally-occurring naturally-occurringclass class of ofwood-degrading wood-degrading fungi that 980s thatevolved evolvedto todegrade degradelignin. lignin. Extensive Extensiveresearch researchconducted conducted since since early 11980s has shown shown that many utilized by by the the fungi for has many of of the thesame same mechanisms mechanisms utilized for lignin lignin degradation also also promote the degradation the degradation degradation of ofseveral severalcarbon-based carbon-based environmental environmental contaminants include polycyclic aromatic hydrocarbons, contaminants. These These contaminants include polycyclic aromatic hydrocarbons, pesticides, pesticides, herbicides, herbicides, wood preservatives, preservatives, chlorinated chlorinated solvents, solvents, PCBs, PCBs, explosives, explosives, cyanide, dyes, dyes, and others. cyanide, The utilize an extra-cellular, free-radical, non-specific mode of degradation degradation hef fungi utilize anextra-cellular, which allows them to degrade both soluble and insoluble contaminants, whether they which allows them to deorade and insoluble contaminants. whether thev absorbed or orin insolution. solution. The secreted by the fungi fungi include are absorbed The extra-cellular extra-cellular substance substance secreted include several enzymes enzymes (which (which catalyze batalyze the the initial oxidation several oxidation of of contaminant contaminant molecules), molecules), hydrogen ions (to maintain maintain a slightly slightly acidic charge balance hydrogen acidicpH), pH), electrons electrons(to (to maintain maintainaa charge balance and to reduce contaminants through the breaking of chemical bonds), and hydrogen contaminants through the breaking of chemical andhydrogen (a highly highly effective effective oxidizer). peroxide (a oxidizer). In addition, the fungi fungi secrete secrete veratyl veratyl alcohol alcohol (a (a free-radical mediator mediator which which catalyzes reductions) and oxalate (an organic acid which which free-radical is a highly effective reductant). Application of Application of white whiterot rotfungi fungifor forthe theremediation remediationof ofcontaminated contaminatedsoils soilsinvolves involves fungal-inoculated substrates with with the mixing fungal-inoculated the soil. The Thematerials materialsare are moistened during mixing to to provide which is conducive mixing provide an environment environment which conducive to fungal fungal growth. growth. The The soil/substrate soillsubstrate mixture mixture is is then then placed placedin in aa biocell biocell and and aerated to promote promote contaminant contaminant degradation. Case degradation. Case histories historiesof of bench-scale bench-scale tests tests and and field field applications applications are are presented. presented. 74 �MAKING THE MOST OF IT: COMBINING COMBINING FIELD, FIELD,MICROSCOPIC MICROSCOPIC AND AND BIBLIOGRAPIIIC BIBLIOGRAPHIC FINDINGS TO INTERPRET SHOWINGS AROUND LAKE SUPERIOR INTERPRET SHOWINGS LAKE WILSON, Graham C.: C.: Turnstone Geological Geological Services ServicesLtd, Ltd,P.O. P.O. Box Box 130, 130, Station Station "B", "B", Toronto, Toronto, Ontario, Ontario, CANADA CANADA M5T 2T3 and and IsoTrace IsoTrace Laboratory, Laboratory, University University of Toronto, Toronto, 60 60 St. St. George George Street, Toronto, (e-mail:gcw@quartz.geology.utoronto.ca). gcw@quartz.geology.utoronto.ca). Tomnto, Ontario, Ontario, CANADA CANADAM5S M5S1A7 1A7(e-mail: Electronic Electronic Education: Education: A project has manner for research and learning has been been initiated initiated to present present geological geological information in an accessible accessible manner purposes, to produce produce a PCPCmultimedia educational educational software software tailored tailored to a broad audience. The eventual aim is to purposes, using using multimedia compatible product product on on CD-ROM, CD-ROM, with a wide range of data data enclosed within a "shell" structure of menu options, options, help screens and and indices. indices. The Theinformation informationto to be be offered offered in inthis thissystem systemcan canbe bedivided dividedinto intofour fourelements: elements: help screens annotated entries, database, with with = 1. 1. A bibliographic database, ~ 330,000 0 , 0 0 0annotated entries, 2. 2. An image image bank, with hundreds of colour colour photographs and other figures, 3. AAbook and bookononcomputer computerdatabases databasesininEarth Earthand andenvironmental environmentalscience science applications, and 4. AAsetset ofof "tutorials" illustrating "tutorials" illustratingselected selectedthemes, themes,one oneexample examplebeing beingthe thegeology geology of of the theSuperior Superior region. region. • .1 The Lake Superior Tutorial: Tutorial: The Lake Superior region provides excellent examples examples of of many many facets facets of of Archean Archeanand andProterozoic Proterozoicgeology. geology. A A partial partial The Lake Superior region provides excellent listing includes banded banded iron iron formations, formations, metavolcanic metavolcanic rocks, rocks, mafic-ultramafic mafic-ultramafic and and alkaline alkaline intrusions, intrusions, and and deposits deposits listing includes metamorphism, Products of progressive deformation, metamorphism, of copper, silver, silver, gold gold and and platinum platinum group group elements (PGE). Products the emplacement of minor intrusions intrusions and veins, hydrothermal hydrothermal alteration mineralizing events can can all be examined alteration and mineralizing km of of the the shore) shore) have have been beenintegrated integratedinto into in the the field. field. Selected Selected features features of Superior Superior geology ((in in an area within 100 km a sequential "tutorial" presentation. sequential "tutorial" presentation. . tutorial comprises comprises30 30 frames, frames, each each consisting consistingofofan an image image (with (with aa brief brief caption) caption) or or a short The Superior Superior tutorial paragraph of text. The viewer can browse through the screens, which are analogous to a slide show. If further can which analogous to a slide show. If paragraph information is is required, required, a second screen screen can can be revealed revealed with an explanatory explanatory paragraph, paragraph, and and perhaps perhaps aa selection selection of references. The visual approach, combined with a "layered" access to information, is designed to hold appeal references. combined with a access to information, is designed to hold appeal for both casual and specialized viewers, and will hopefully promote worthwhile discussion! discussion! Follow-up Follow-up queries queries can can be addressed to a database which (in old-style terms) functions as a cross-linked card index. Areas referred to in addressed a database (in cross-linked card in the tutorial, proceeding anticlockwise around the lake from Sault Ste. Marie, are as follows: tutorial, proceeding anticlockwise around the lake from Sault Ste. Marie, 1. The Wawa area 1. area 2. The TheHemlo Hemlogold gold camp camp 3. The Coldwell alkaline The Coldwdl alkalinecomplex complex belt 4. Iron formations and gold in the Beardmore-Geraldton belt The North Shore of Superior 5. 5. Islet: native silver 6. Silver Islet: 6. Lac des Iles: 7. 7. Hes: PGE PGE in in mafic-ultramafic mafic-ultramafic rocks Kakabeka Falls 8. 8. Falls 9. The TheDuluth Dulathcomplex complex 10. Keweenaw Keweenaw Copper Copper Country Country and Pet rography: Field Geology and Petrography: The site site selection is dictated more more by the availability of of materials than by by a any systematic aim aimto todefine defmethe the "top "top ten" ten" ny systematic features of the regional geology. geology. In the Lake Superior tutorial, tutorial, deposits of of three three native nativeelements elements(Au, (Au,Ag Agand andCu) Cu) are included, while volcanogenic massive sulphides suiphides are are omitted. omitted. In the wider context context of of the CD-ROM project, project, this is compensated for by by the use of examples examples from other other parts parts of of the world. The initial selection is is divided divided roughly roughly compensated for 2:1 between field items (outcrops, landscape features) and photoniicrographs of rocks and ores. photomicrographs of 2:l 75 �Bibliographic Bibliographic Database: Database: Although it is anticipated Oat that image fileswill will fill fill80-90% 80-90% of of the thecapacity capacityof ofthe theCD-ROM, CD-ROM, the the driving driving force force behind behind MINLIB database database (Wilson,11991), and to to present present it it in the project project is is to tomake makeavailable available the theheavily-annotated heavily-annotated MINLffi 991), and in conjunction with a review of the use of computer databases in the Earth sciences sciences ((coincident, in part, part, with Wilson, c o i n c i i , in 11992a,b). 992a,b). MINLIB is not designed to to compete with with major databases databases such such as as GeoRef, GeoRef, which have broader thematic rhematic and systematic systematic coverage, coverage, nor to to supplant supplantmaterial material compiled compiled by by regional regionalsurveys surveys (including (including mineral mineral deposit deposit inventories assessment files) files) and and other geographically specializedpublications publications(e.g., (e.g., Sheahan, Sheahan, 1 1984). inventories and assessment geographically special'& 984). ItIt is intended to cover a broad range of topics, topics, but but with withclear clearemphasis emphasis on on aspects aspects of of economic economic geology, mineralogy, mineralogy, petrology and keywords <up (up to 30 lines and structural $tructuralgeology. geology. A A relatively relativelyintensive intensive selection selection of ,keywords lines per per record) record) facilitate facilitate recovery of robject subject matter. matter. Within Withinthe the cmrent currentcontents contents(-28,000 (=28,000 records), recovery of articles articles with with diverse combinations of records), there features in the Lake Superior region. Examples there is is significant significantcoverage coverage for for many many geological geological features Examples include the Wawa subprovince (230 references), the Keweenawan<110), Keweenawan (110), the Gunflint iron iron formation00). formation (50), (he the Hemlo gold camp camp (200), (200), subprovince (230 the (80), the Duluth complex complex ( (120), the Lac des des lies Iles complex complex and and the Silver Silver Islet mine mine (20), (20),the the Coldwell ColdweU complex (80). 120), and the associated PGE mineralization (80). (80). la In terms of the the cumulative literature, coverage of these subjects varies from sketchy to substantial. Available m material is weighted towards towards recent recent articles articles (MINUB (MINLIB was was initiated initiated in in 1983, 1983, and aterial isW1ghted only only 18% 18% of of records recordsconcern concernitems items published pubrished prior to to that thatyear). year). While the thrust "hard-rock" geologists thrust of MINLIB MINLIB will will appeal appeal especially to economic and "hard-rock' geologists and mineralogists, several hundred "popular" "popular*articles articles are are included, included, and and ititisishoped hoped that that these, these, in inconjunction conjunctionwith with the the image image bank bank and and several hundred tutorials, will be of high-school students, rockfaounds, rockhounds, and toothers to others interested in extending their of broad broad appeal appeal to tdhigh-school knowledge of of die the natural world. world. The wider for the wider audience audierd-for the tutorial tutorial approach and the supporting imageiy imagery may in every every 40 40 records). records). This includes books on on local local appreciate material in in the "popular" category of of the the database database (o (= 11 in appreciatematerial This includes mining exampleswould wouldbe beBan-, Barr, 1988; 1988; Lefolfi, Lefolii, 1987; 1987;Smith, Smith,11986), certainfield fieldguides guides(e.g., (e.g., Pye, Pye, mining history (recent examples 986). certain 1968) and articles in non-technical publications such as Canadian Geographic and National Geographic. 1968)and publications such as Canadian Geogquhk and National Geographic. References: References: .BARR,E., BARR.E., 1988, 1988, Silver Silver Islet, Islet, Striking Striking iitt Rich Rich in in Lake Lake Superior. Superior. Natural Natural Heritage/Natural HeritagdNatural IHistory, i i i r y , Toronto, 159pp. 159pp. LEPOLII,K., Ltd, Toronto, LEFOULK.. 1987, 1987, Claims: Claims: Adventures Adventures in the Gold Trade. Key Porter Potter Books Ltd. Toronto. 264pp. 264BD. Lake and east to Lake Superior. Ontario Dept. Dept. of Mines PYE,E.G., PYJ3.E.O.. 1968, 1968,Geology Geologyand and Scenery: Scenery: Rainy Rainy Lake Mmes Geol. Guide 1, 118pp. ll8pp. Book 1, of Mi-Continent Mid-ContinentBasement BasementU.S.A. U.S.A. Geol.Soc.America Geol.Soc.America Microform SHEAIIAN,P., 1984, Geological Bibliography of SHEAHAN.P., 15, 56pp. 56pp. Publication 15, SMITH,P., SM1TH.P.. 1986, Harvest from the Rock. Rock. Macmillan of Canada, Toronto, Toronto, 346pp. 346pp. WILSON,G.C., 1991, mineral exploration. exploration. Geol.Assoc.Canada Geol.Assoc.Canada WILS0N.G.C.. 1991,MINLIB: MINUS: aacomputer computerdatabase database emphasizing emphasizing mineralogy and mineral Prog.w.Abs. 16. 16, Toronto, 133. / Mineral.Assoc.Canada Mineral.Assoc.Canada Prog.w.Abs. database management management systems. systems. In 'Mineral Databases'(Smith,D.G.W. (Smith,D.G.W. and and WILSON.G.C., 1992a, Databases Databases and and database WILS0N.G.C.. 1992a. In 'M Mineral Databases' Congress, Kyoto, Kyoto, Japan, Japan, sponsored by by the Ozawa,T., editors), Workshop at the 0zawa.T.. editors). Workshop the 29th 29th International International Geological Congress, Mineralogical Association, l83pp., 31pp. 3lpp. International Mineralogical International Association, 183pp.. WILSON,G.C., Ibid., 38pp. WILS0N.G.C.. 1992b, 1992b.Bibliographic Bibliographic databases. /Aid., 38pp. �CHALCOCITE MiNERALIZATION MINERALIZATION IN IN THE THEPORTAGE PORTAGELAKE LAKEVOLCANICS,, VOLCANICS, PENINSULA, MICHIGAN KEWEENAW PENINSULA, MICHIGAN KEWEENAW Laurel 0. Woodruff1, woodruff1, William William F. F.Cannon2, ~ a n n o nJudith Judith ~ , M. M. Back2 ~ a c k ~ Laurel G. U.S. Geological Survey; 'St. Pad, MN, 2Reston, VA U.S. Geological Survey; 1st Paul, MN, 2~eston,VA Seven chalcocite chalcocite deposits deposits occur occur in in the the Michigan Michigan copper copper district district in in the the western western part part of of the the Seven Peninsula of Michigan, a region better known for native copper mineralization. Upper Peninsula of Michigan, a region better known for native copper mineralization. The The chalcocite deposits, mostly discovered discovered in in the the 1970's. 1970's, ran range in tonnage from 0.1 0.1 to to 4.5 4.5 million Upper e in metric tons, and most have average grades from 2.5% to 3.0% Cu. The chalcocite deposits metric tons, and most have average grades from 2.5% to .O% Cu. The chalcocite depositsare are within the the 1.0 1.0 Ga Ga Portage Portage Lake Lake Volcanics Volcanics near near the the northeast northeast tip tip of of the theKeweenaw KeweenawPeninsula, Peninsula, restricted 13 km, km, stratigraphically stratigraphically below below the the Bohemia Bohemia Conglomerate Conglomerate and and just just restricted to an an area area 22 km km by. by 13 within to above the Keweenaw fault (Figure 1). the Keweenaw fault (Figure 1). On copper.mineralization mineralizationin inthe the Keweenaw Keweenaw Peninsula Peninsula can can be be subdivided On aa regional regional scale. scale copper subdivided into three three types types or ordistricts, each with a characteristic style of mineralization: (1) native copper districts, a style of mineralization: in fissure fissure deposits (2) native native copper in lode deposits in both basalt and and conglomerates, deposits in basalt, (2) and (3) chalcocite in basalt. The chalcocite district is along strike and stratigraphically basalt The chalcocite district is along strike and stratigraphically lower than the native copper native copper lode lode district district and and is is directly directly stratigraphically stratigraphically below the native native copper fissure district (Figure 1). Although these three districts are adjacent to one another, there Although these three districts are adjacent there is little district (Rgure overlap, suggesting that the three styles of mineralization are interrelated and part of regional overlap, suggesting that the three styles of mineralization are interrelated and part of aa regional mineralizing system. system. We We have have attempted attempted to to define define the mineralizing mineralizing process for the chalcocite deposits and to determine determine the genetic genetic connection between chalcocite mineralization and native copper mineralization. mineralization. In all predominant sulfide sulfide is is chalcocite. chalcocite. In all the the chalcocite chalcocite deposits, the predominant In most, most, bornite bomite in in trace amounts is the only other sulfide. One exception is the Mt. Bohemia deposit amounts sulfide. One exception is the M t Bohemia deposit which contains chalcocite pyrite-chalcopyrite-bomitechalcocite in addition addition to to aareplacement replacementsequence sequenceofofpyrite-chalcopyrite-bornitechalcocite, in which Fe-sulfides were replaced by successively more Cu-rich Cu-rich sulfides chalcocite, Fe-sulfides sulfides (Robertson, The chalcocite deposits occur in fragmental tops of basalt flows in much the same 1975). chalcocite same style style 1975). as native copper copper lode deposits. Chalcocite Chalcociteoccurs occursas as an an amygdule amygdulemineral, mineral, as as open-space open-spacefillings fillings disseminated in in altered altered basalt, basalt, and and in in veinlets veinlets cutting cutting basalt. basalt. Related around basalt fragments, disseminated Related alteration minerals include epidote, quartz, hematite, hematite, pumpellyite, pumpellyite, chlorite, albite, albite, K-feldspar, K-feldspar, laumontite, and laumontite, and titanite. titanite. 3345 values 0%o, ranging ranging from from 8% values for chalcocite from six of the the deposits deposits are all less than 0%, Although basalts in the rift are sulfur-poor because of degassing -0.1% to -21%. -0.1%0 -21%0. Although basalts in are sulfur-poor because degassing during during eruption, sulfur and copper copper were were derived derived by by hydrothermal hydrothermal alteration of the underlying underlying volcanic volcanic Individual deposits have a section during burial metamorphism .downdip from the deposits. during burial metamorphism downdip deposits. roughly correlated correlated with with the the tonnage tonnage of of copper copper ore in the deposit: deposit: 6% which isis roughly restricted range of oMS the largest deposit has the highest 345 values (-0. 1% to -4.2%o) and the smallest deposit has the the highest S^S values (-0.1%0 to -4.2%) deposit to -6.6%o). This correlation can be interpreted as indicating that chalcocite l5.6%o can chalcocite was was lowest ((-15.6% -6.6%). This deposited during progressive oxidation of a mineralizing fluid, which probably carried a limited limited amount of sulfur and/or copper copper chloride. chloride. sulfur along along with with abundant abundant copper copper complexed complexed as as bisulfide biisulfide and/or Because of the large isotopic fractionation between sulfide sulfide and and sulfate, sulfate, oxidation oxidation of of sulfide sulfide in in the the M8• sulfide becoming increasingly increasingly isotopically isotopically depleted depleted in ^S. fluid would result in residual aqueous sulfide veinlets in in one deposit, which have the further indicated by late native copper-bearing copper-bearing veinlets This is further most depleted values of any samples from that deposit, indicating.that indicating that most of the the sulfide sade had had been oxidized oxidized before before the the deposition deposition of the the veinlets, but the copper copper remained remained in in solution. solution. with lower sulfur isotope values is consistent consistent with with aa The lower tonnage tonnage of deposits with diminution of the due to the progressive the ability ability of the the fluid fluid to precipitate precipitate copper copper dsulfide slueil progressiveoxidation oxidation diminution The fluid. of the the mineralizing mineralizing fluid. After all sulfur was stripped from the fluids by oxidation, oxidation, abundant abundant $ p I 77 �* dissolved dissolvedcopper copperremained remainedininmsidual residualfluids fluidsand andwas wasavailable availablefor fordeposition depositionasasnative nativecopper. copper. We Webelieve believethat thatchalcocite chalcocitemineralization mineralizationconsumed consumedthe thelimited limitedsupply supplyofofsulfur sulfurininthe theregional regional system systemasasa aprecursor precursortotonative nativecopper copperdeposition. deposition. Negative Negativesulfur sulfurisotope isotopevalues valuesfor forchalcocite chalcociteoccur occurthroughout throughoutthe theKeweenaw Keweenawdistrict, district,asas evidenced -9.4% forfor chalcocite ininveins evidencedby by345 6% values valuesofof-ó.7% -6.7%to to-9.4%0 chalcocite veinscutting cuttingthetheBaltic Balticnative native copper copperlode lode(Livnat, (Uvnat,1983), 1983).and andsecond-stage second-stagechalcocite chalcocitemineralization mineralizationatatthe theWhite WhitePine Pinedeposit deposit (Mauk 1992),showing showingthat thatoxidation oxidationof of sulfide-bearing sulfide-bearingfluids fluids was was widespread. widespread. The The (Maukand andothers, others,1992), zonal theKeweenaw KeweenawPeninsula Peninsulasuggests suggeststhat thatother otherchalcocite chalcocite zonalarrangement arrangementofofdeposit deposittypes typeson onthe deposits depositsmight .might . bebefound foundelsewhere elsewhereininthe theKeweenaw Keweenawvolcanic volcanicsection, section,peripheral peripheraltotonative nativecopper copper mineralization. mineralization. References ReferencesCited Cited Livnat, Livnat,A., A.,1983, 1983,Metamorphism Metamorphismand andcopper coppermineralization mineralizationofofthe thePortage PortageLake LakeLava LavaSeries, Series, northern northernMichigan: Michigan:unpublished unpublishedPh.D. Ph.D,Dissertation, Dissertation,University UniversityofofMichigan, Michigan,Ann AnnArbor, Arbor. 292 p. 292 p. Mauk, Mauk,J.L., J.L,Brown, Brown,A.C., A.C.,Seasor, Seasor,R.W., R.W., and andEldridge, Eldridge,C.S., C.S.,1992, 1992,Geology Geologyand andstable stableisotope isotope and andorganic organicgeochemistry geochemistryofofthe theWhite WhitePine Pinesediment-hosted sediment-hostedstratiform stratiformcopper copperdeposits, deposits,inin Bomhorst, Bornhoist,Ti. T.J.(ad.), (ed.),Keweenawan Keweenawancopper copperdeposits depositsofofwestern westernUpper UpperMichigan: Michiian:Soc. Soc.Econ. Econ. Geol. 13,p.p.63-98. 63-98. Geol.Guidebook, Guidebook,v.v.13, Robertson, Robertson,J.M., J.M., 1975, 1975,Geology Geologyand andmineralogy mineralogyofofsome somecopper coppersulfide sulfidedeposits depositsnear nearMount Mount Bohemia, Econ.Geol., Geol.,v.v.70, 70,p.p.1202-1224. 1202-1224. Bohemia,Keweenaw KeweenawCounty, County,Michigan: Michigan:Econ. l u 10 KILOMETERS o 1: JV Copper tiahor Congbmemte 0 Portage M e Volcanics Generalized geologic geologic map map of ofthe theKeweenaw KeweenawPeninsula, Peninsula,Michigan. Michigan. Region Region of of Figure 1.1. Generalized Figure chalcocite mineralization contains seven small, high-grade chalcocite deposits. chalcocite mineralization contains seven small, high-grade chalcocite deposits. 78 �Archean Archeancrust crustininthe theWausau-Pembine Wausau-Pembiie Terrane; Terrane; Continental Continental underthrusting, underthrusting, or o r island island arc arc basement? basement? Nicholas NicholasVan VanWyck, Wyck,Clark ClarkJohnson, Johnson,and andStuart StuartGross. Gross.Department Departmentof of Geology Geologyand and Geophysics, Geophysics, University of Wisconsin, Madison WI, 53706 University of Wisconsin, Madison WI, 53706 Conventional ConventionalU/Pb UIPband andsingle singlezircon zirconevaporation evaporationdata dataon on zircons zircons from from aa strongly strongly deformed deformed gneiss 20km kmsouth southof ofthe themapped mappedtrace traceof of the theNiagara Niagara Fault Fault (N45.78286°, (N45.78286', W88.68963°), W88.68963"), gneisslocated located20 within the Wausau-Pembine Terrane (Sims et al. 1989), yield a simple concordia plot with an an within the Wausau-Pembhe Terrane (Simset al. 1989). yield a simple concordia plot with zircon evaporations upper 2604Ma, Ma,and andaalower lowerintercept interceptage ageof of 590 590 Ma. Ma. Single Single zircon evaporations upperintercept interceptage ageofof2604 from ages at at 2610 2610 Ma. Ma. Together threeseparate separategrains grainsall allgive five single singleplateau plateau Pb/Pb Pb/Pb ages Together these these data data fromthree indicate a crystallization age of 26 10±7 Ma. indicate a c q k d l i i o n age of ?.61&7 Ma. . 45 45 40 40 0 GrainAT=1620 Grain A T-1720 OrainAT=1720 3535 • GrainBl=1600 5 - 3300 5 2525 C) 3 ? 3'2 20 ^ 1515 10 10 5 5 00 V77)1m1 I 2 5 ( 0 2580 2 5 1 0 2600 2 6 0 0 2620 % 2 0 22640 6 à ‡ 22660 6 6 0 22680 6 1 0 22700 70 (Ma) Pb2°'/Pb2°6 Age pbm/Pb^ Age (Ma) 2560 8 9 tO II 12 The TheNd Ndwhole wholerock rockisotope isotopecomposition composition(TDM= (TDM=2.99 2.99Ga Gaand andE(T)Xa1 &om=-2.5) -2.5) isis typical typical of of true true Archean basement. Feldspar common Pb (6/4=16.08, 7/4=15.76), similarly indicate an old age Archean basement. Feldspar common Pb (6/4=16.08,714=15.76), for this sample. The high 7/4 ratio is in good agreement with the proposed end-member model for this sample. The high 714 ratio is in good agreement with the lower lowercrust crustrequired requiredfor forthe thePenokean Penokeanmixing mixing model model described described by Van Wyck and Johnson Johnson (1993) (1993) and into feldspars. One andrequires requiresremobalization rtkobaliition of of Archean Archean lead l&into One possible interpretation interpretation of the feldspar Pbdata dataisisthat thatthe thestrong stronggneissic meissicfabric fabricand and outcrop outcrop scale scale folding folding are are related relatedto to aa feldsoarPb Penokean high grade metamorphic and fabric forming event, and therefore may be of use therefore use in in ~enokeanhigh grade metamorphicand fabric forming event, deciphering Alternatively, the the relatively relatively simple simple decipheringthe thePenokean Penokean kinematic kinematic history of this area. Alternatively, zircon zirconsystematics systematicsand andlack lackof ofaaPenokean Penokeanlower lowerintercept intercept age age argues argues against against a high high grade grade Penokean metamorphism, and in turn suggests that feldspar lead was not a closed system closed systemduring during ~enoke&metamorphism, and in turn suggests that feldspar lead was the thePenokean. Penokean.Under Underthis thisscenario, scenario,the thestructures structuresrecorded recordedat at this this outcrop outcrop could could be PrePen okean. Penokean. Collectively Collectivelythese thesedata dataargue argue for for the the presence presence of Archean crust within the Wausau-Pembine terrane. Thisisisthe thefirst firstreported reportedpresence presenceofofcrust crustof ofthis thisage ageininwhat whathas hasbeen been previously previously terrane. This thought to be a juvenile package of rocks; this leads to the following possible interpretations: interpretations: thought to be a juvenile package of rocks, this leads to a) a) The TheSuperior Superiorprovince province isis underthrust underthrust at at least least 20 20 km to the south, as has been implied by the gravity gravity data data of of Attoh Attoh and and Klasner Klasner (1989). This Thiscrust crustisisnow nowexposed exposedas asaa basement basement culmination, culmination, and one would predict that structures such as the Dunbar Gneiss Dome, along strike to the east, and one would predict that structures such as the timing and mechanism for the exposure these may be similarly similarly cored by Archean crust. The The timing and mechanism for the exposure of of these 7.9 �I deeper deepercrustal crustallevels levelsare areunknown, unknown,but butanalogies analogieswith withdeep deepcrustal crustalexposures exposuresproduced producedby by extensional extensionaltectonics tectonicsare areappealing. appealing. b) ageisisfrom frombasement basementtotothe theWausau-Pembine Wausau-Pembiieterrane, tenane,which whichhas hasbeen been b) Alternatively, Alternatively,this thisage previously previouslythought thought to toconsist consistof of juvenile juvenile crust crustformed formedininan anisland islandarc arc environment. environment. In In either eithercase, case, the the feldspar feldsparcommon commonPb Pband and 143Nd/1Nd 143~d/1% ratio ratiomeasured measuredininthis thissample sampleoffers offersan an appealing appealingexplanation explanationfor forthe thehigh highPb2071204 Pb207/204signatures signaturesof of galenas galenasand and feldspar feldsparleads leadsreported reported for thisregion, region,as aswell wellasasthe thereported reportedtrend trendofofincreasingly increasinglynegative negativeENd eNdvalues for Penokean Penokean forthis intnisives verses distance from the Superior Province. On account of intrusives verses distance from the Superior Province. On account of the the absence absenceof of reported reportedold old crust crustin in the theWausau-Pembine Wausau-Pembiieterrane, terrane,Barovich Barovichetetal., al.,(1989) (1989) have havesuggested suggestedthat thatmantle mantle contamination eNdPenokean Penokean contaminationby bySuperior SuperiorProvince Provincederived derivedsediments sedimentsexplained explainedthe thelow lowENd intrusives in the northern Waasau-Pembine Wausau-Pembinetenane. terrane. Mother Anotherexplanation explanationisis now now possible; that of of interaction interaction with with pre-existing pre-existingolder oldercrust, oust, rather ratherthan thanaa large largescale scale mantle mantle contamination contamination process. process. References: References: Attoh, K., and and Kiasner, Klasner,J.J. S., S., 1989, 1989,Tectonic Tectonicimplications implicationsof of metamorphism metamorphism and and gravity gravity field fieldin in Attoh, K., the v.8, the Penokean Penokean orogen orogen of of northern northern Michigan: Tectonics, v. 8,p.911-933. p. 911-933. Barovich,Karin E; Sims,Paul Sims,Paul K K (1989): (1989): Nd Nd isotopes Barovich,Karin M; M, Patchett,P PatchekP Jonathan; Jonathan; Peterman,Zell Petennan.ZeU E; isotopes and and the origin of 1.9-1.7 Ga Penokean continental crust of the Lake Superior region. GSAB the origin of 1.9-1.7 Ga Penokean continental crust of the Lake GSAB 101(3), 101(3), 333-338. 333-338. Sims, Sims, P. K., K., Van, Van, S. S.W. W.R., R..Schulz, Schulz,K. K.J.,I..and andPeterman, Petennan,Z.Z.E., E.,1989, 1989,Tectonostratigraphic Tectonostratigraphic evolution of the early Proterozoic Wisconsin magmatic terranes of the evolution of the early Proterozoic Wisconsin magmatic terranes of the Penokean PenokeanOrogen: Orogen:Can CanJ.J. Ear. Ear. Sci. Sci. v. 26, 26, p. p. 2145-2158. 2145-2158. Van Van Wyck, Wyck, N. and and Johnson, Johnson,C. C. M. M. 1993, 1993,Lead Lead isotopes isotopesand and the the Penokean Orogeny: Omgeny: Crustal Crystal growth growth revisited. revisited. GSA GSA Abs Abs v. v. 25, 25, p.A236 p.A236 Zircon data Zircon age age data Zircon Zircon fraction fraction fQQ75gj ((10-75p IOO-75is 1W75p lOO-75ps 100-75p LM2Abd LM2 AM LM2Abd LM2 AM 206/204 206/204 Meas. Meas. 206*1238 206*/238 5398 5398 0.396274 0.396274 5096 5096 0.400454 0.400454 4124 4124 0.398362 0.398362 6476 0.431821 0.431821 6476 4834 4834 0.403347 0.403347 207*1235 207*/235 8.86105 8.86105 8.95252 8.95252 8.89045 8.89045 9.9453 9.9453 9.06484 9.06484 207*/206* 207*/206* * 0.162177 0.162177 0.16214 0.16214 0.161862 0.161862 0.167037 0.167037 0.162997 0.162997 207*/206* 207*/206* 206*/238 206*/238 207*/235 M7*/235 Age Age (Ma) (Ma) Age Age (Ma) (Ma) 2151.86 2151.86 2323.8 2323.8 2478.48 2478.48 2171.13 2171.13 2333.17 2333.17 2478.11 2478.11 2161.49 2K1.49 2326.82 2326.82 2475.21 2475.21 2313.92 2313.92 2429.72 2429.72 2528.17 2528.17 2184.43 2184.43 2344.57 2344.57 2486.99 2486.99 Age Age (Ma) (Ma) 80 �S I N I I I I The TheWolf Wolf River RiverA-type A-type Magniatic MagmaticEvent Eventin inWisconsin: Wisconsin: U/Pb UIPb and andSm/Nd S d N d Constraints Constraintson on Timing Timing and andPetrogenesis Petrogenesis Nicholas L. Gordon Gordon Medaris MedarisJr., and and Clark Clark M. Johnson, Johnson, Department Department of Geology Geology and and Nicholas Van Van Wyck, Wyck,L. Geophysics, Geophysics,University Universityof ofWisconsin, Wisconsin,Madison MadisonWI, WI,53706 53706 A U/Pb U/Pbzircon zircon age ageand and l43Nd/WNd ^~d/~4"^ ratio ratio have have been been determined determined for for syenite syenite from from the the Stettin Stettinintrusive intrusive A complex, complex,and andaaU/Pb UPbzircon zirconage, age,for forPrecambrian Precambrianbasement basement from from aa borehole borehole at at Oshkosh. Oshkosh. The Thedata dataindicate indicate that thatduration durationof of Early EarlyMesoproterozoic MesoproterozoicA-type A-type magmatism magmatismin in Wisconsin Wisconsin may may have have been been on on the the order orderof of 80 80 m.y. my. and and that that various variousproportions proportions of mantle mantle and and crustal crustal components components are are incorporated incorporated in in different different lithologies lithologies of of the the Wolf Wolf River Riverpetrologic petrologicprovince. province. Abundant and inclusion inclusion free free zircons zircons were separated from from aa pyroxene pyroxene syenite syenite Abundant euhedral, euhedral,diamagnetic diamagnetic and collected collectedat at an an abandoned abandonedquarry quarry in in the the south south central central part pan of the Stettin Stettin complex. Fractions Fractions 1,2 1.2 and and 33 were were unabraded mg ((typically unabraded and and the the sample sample size size was was approximately 1 mg typically 20-30 grains). Fractions Fractions44and and66were were identical identical to to 11 through through 33 except exceptthat that they they were were abraded for for over over 24 hours. Fraction Fraction55was wasaasingle singlezircon zircon crystal, 200 lie. gg. Abraded Abradedand andunabraded unabradedzircon zirconfractions fractions crystal, also also abraded, abraded, which weighed approximately 200 together Ma, which is is interpreted interpreted as the crystallization crystallization age age of the the Stettin Stettin together give give concordia concordiaages agesof of 1565+3-5 1565+3-5 Ma, syenite. syenite. , Diamagnetic, replicate analyses analyses were Diamagnetic, euhedral euhedral zircons zircons from fromthe the Oshkosh Oshkosh borehole have been abraded and replicate performed performed over over aa one one year year period. Fractions Fractions1,2 1.2and and33were wereless lessthan than0.5 0.5mg mgsample samplesize sizeand andwere wereabraded abraded for andare aredifficult difficultto tointerpret. interpret. Although for 15 15 hours. All Allfractions, fractions,except except for for 1, 1, do not lie on concordia and Although three three fractions fractions(1,2, (1,2,and and 5) 5) give give consistent consistentPb206IU238 Pb2061U238ages of approximately 1471 Ma, it is more likely that these zircons have experienced lead loss approximately 1475 that these zircons have experienced lead loss from from a slightly older age of approximately 1475 Ma, which is well 15 Ma within error errorof of the thepreviously previouslypublished publishedage agefor forthe theWolf WolfRiver Riverof of1485± 1485±1 Ma (Van Schmus Schmuset et al al well within 1975). An Anadditional additionalcomplication complicationmaybe maybezircon zirconinheritance. inheritance.Fractions Fractions44and and55were wereanalyzed analyzedone oneyear year later later and and are are 11 mg mg sized sized samples. samples. One Onezircon zirconpopulation populationisisdark darkbrown brownin incolor, color,inincomparison comparisontotothe the majority majority of zircon zircon grains, grains, which which were were clear clear to light colored. Fraction Fraction44has hashad hadthe thedarker darkergrains grainsremoved removed shows approximately 10% shows no no indication indicationof of inheritance. inheritance. Fraction Fraction 5, 5. which contained contained approximately 10%dark brown grains, does does show show an an inheritance inheritance component. component. Unfortunately Unfortunatelythe thedata datacan cannot notresolve resolvewhether whetherititisisArchean Archeanor or Penokean Penokean inherited inheritedzircons, zircons,which whichwill willrequire requiredetailed detailedsingle singlezircon zirconanalysis. analysis. 02Th oses Oshkosh borehole &277 0.264 (LOTS 0.2 $1 0273 0.254 0.254 0.271 vaso 0.250 oasa 0246 0È 3.0 3.0 354 3.1 rPbp3sU 3JW 3S6 a70 a74 20TPbrIJ "Wll 81 �Stettin pyroxene syenite are slightly REE concentrations for Stettin slightly lower than those for Wolf River adamellite adamellite and momnite, monzonite, but the chondite-normalii chondite-normalized REE patterns are similar, with LREE eenrichment ~ c h m e nand t 4.90, and == 1.31). &ox& C(T)xal for relatively flat flat HREE HREE(for (for syenite, syenite,(CeiTb)CN (Ce/Tb)a = = 4.90. and (Th/Yb)CN (Tb/Yb)cN for syenite syenite is +2.9, derivation from a mildly depleted subcmstal subcrustal lithospheric lithosphenc source, suggesting derivation source, in contrast contrast to to Wolf River River NdT (Nelson, 1991). 1991), indicating significant granitic rocks, in which epsilon N ~ ranges T from -0.3 to -4.0 (Nelson, amounts of crustal contributions. contributions. Nd model complex and and Wolf Wolf River River also differ for the Stettin complex model ages also batholith, being 1.65 1.65 Ga Ga and 1.9 1.9 to to 2.1 Ga, respectively. respectively. 1000 0 v s -. 3(0 E Avenge VW River Jioo a lm =E u c 0 6 l0 La ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu nepheline syenite, isotopically Geochemical differences between the Stettin complex (syenite and nepheliie depleted) and the Wolf River batholith (predominantly adamellite, isotopically enriched) reflect River batholith (predominantly adamellite, enriched) reflect evolving evolving compositions due to increasing mantle-crust interactions in an A-type igneous cycle. The Wolf magma compositions of the the Stettin complex at River magmatic event was initiated by mantle upwelling (plume?) and generation of 1565 Ma Ma by by partial partial melting melting of of mildly mildly depleted depleted lithosphere. lithosphere. Later mantle-derived melts Later melts were were contaminated contaminated with crustal (quartz syenite and granite) at 1517 1517 Ma (Van Schmus, Schmus, crostal material material to form form the Wausau complex complex (quartz Thermalmaturation, maturation, magma magma ponding, ponding, and crustal crustal anatexis culminated at 1485 1485Ma (Van pers. comm.). Thermal Schmus Schmus et et al., 1975) 1975)in in production production of of the the voluminous voluminousWolf Wolf River Riverbatholith. batholith. Mesoproterozoic A-type magmatism that affected much of North America Amenca was diachronous, The Early Mesoprotemzoic diihronous, beginning in Wisconsin and ending in Labrador and the southwestern Cordillera Cordillera 115 and 135 M.y. later, beginniig 135 M.y. respectively (Anderson, (Anderson, 1983). The Stettin complex, which so far is the oldest dated intrusion in this this The Stettin complex, dated intrusion in contipental-scale magmatic event. igneous suite, is thus the harbinger of a major, continental-scale References References ll, Cullers Anderson JL, CutlersRL RL(1978) (1978)Geochemistry Geochemistryand andevolution evolutionof of the the Wolf Wolf River River Batholith, a late late Precambrian U.S.A: Precamb Res 7,287-324. 7, 287-324. Precambrianrapakivi rapakivi massif in North Wisconsin, U.SA Anderson J JL anorogenic granite granite plutonism plutonismof of North North America. America. Geol Geol Soc Soc Am Mem L (1983) (1983) Proterozoic Proterozoic anomgenic Anderson 161:133-152. Nelson, B. K., growth near near the Archean craton: craton: the isotopic record from K, (1991) (1991) Proterozoic Proterozoic continental growth anorogenic granites Wisconsin: Eos 544. Eos 72, 72,544. anomgenic granites in Wisconsin: Schmus,WR; Medaris,LG; Medaris,LG; BanksJO Banks,PO (1975) Geology and and age age of of the the Wolf Wolf River River batholith, batholith, Wisconsin: Wisconsin: Van Schnnis,WR; GSABuII 86, 907-9 14. GSABdl86,W-914. 82 �A COMPENDIUM OF MINERAL RESOURCE INFORMATION, EAST-CENTRAL MINNESOTA Minnesota Department of Natural Resources, Division of Minerals, 1525 3rd Ave. E., Flibbing, Minnesota 55746 The administration of state-owned lands includes the management of those lands for mineral resources. The Minnesota Department of Natural Resources Minerals Division administers state-owned mineral rights for the benefit of schools, the university, local units of government and the public. As a part of this responsibility, the Minerals Division has maintained mineral resource records and information. This compendium of minerals information for east-central Minnesota is provided by the Minerals Division for all people who work in the field of land management, both within various levels of government and outside government. It is intended to serve as a guide to available information, by providing maps showing the location of known mineral resources and the geographic extent of information sources, and listing a knowledgeable contact person for each theme. Further, it is intended to document the presence of some known subeconomic mineral resources, which may have a higher value in the future, and therefore should be considered in current planning. It does not contain a map of speculative resource locations for all commodities, because that would require a complex evaluation and presentation. This compendium is intended to be a starting point for all who need or want access to mineral resource information in east-central Minnesota. Three mineral commodities are currently being extracted in east-central Minnesota - peat for horticultural applications, aggregate for construction purposes, and dimension stone for buildings or monuments. There have been over 70 years of mining of two other mineral commodities - iron and manganese, from from Crew Crow Wing County and adjacent Moreover, large large quantities quantitiesof of iron iron and manganese, adjacent areas. Moreow, manganese resources are still present here, having been identified by past drilling. vnawsctsw(tillpraittthere,kavtagbeteidentitiediiyoftdrilUng. that mining for for the the W above five axamodities, commodities,as aswell wellas as other other mincralg, minerals, bIt is reasonable reuoaable to aassume i ~ a a e&at e five be propotad proposed in in (be the future future in in this this rtgion. region. The setting tuggeitt suggests that thatother otherplausible plausibleminerals minerals could be The geologic geologic sctt&is could iach^ include iJdustTid industrialmiiMTdi minerals<ç suchu asgnphite, graphite,p garnet oroli^ otherlbiwivet. abrasives,barite. barite,berylberyllium,ghmphse; phosphate; 'could mt or minerals such suchas as gold, gold, tilver, silver, coppar, copper, lead, lead, zinc, zinc, bismuth, bismuth,chromium, chromium,platinum, platinum,nickel, nickel,or or or metallic metallic mineralf rare earth metals. There are known mineral occurrences for almost all of these commodities, but not in ran meld*. There amknown mineral occmreneti for abBOM ill thege commodities, but not in sufficient, known known quantitiesfor forextraction. extraction. As As aa result, these these "other* "other minerals mineralsare are referred referred to to here here as as sufficient, speculativemi+cal mineral(dowcfs, resources,wfaidi whichwould wouldW have be dueovered discoveredininlarger larger qmatity quantityand and quality quality to to specdative e toto be evaluation initiates such suchdevelopment developmentevituation, evaluation,primarily primarily warrant development w ~  ¥ work. w o rThe The k private private sector sector iiritiites spurred by by market market denumd demand inthe in the form formof of favorable favorablecoianodity commodityprices. prices. All All futun futuredevelopment developmentproposals proposals spurred would be be gubject subject to the compendium of law review and and permitting permitting would compendium of law applicable applicable to the environmental environmental review process. The study area (see the first map) covers the part of Minnesota that very nearly corresponds to Minnesota's Department of Natural Resources administrative region III. Our study area differs from DNR Region III boundaries in that we use county boundaries for the border with two minor exceptions. Because most of our minerals databases contain county designations, it was more practical to use entire county boundaries as much as possible. The two exceptions are small areas within Itasca and Anoka counties, which were included to accommodate the entirety of DNR Region III. The minerals information in this compendium is presented primarily in the form of maps, and is organized around seven general themes: State-Owned Lands and Mineral Leasing, Peat, Industrial Minerals, Sand and Gravel, Iron Ore and Manganese, Other Speculative Minerals, and Mineral Exploration Data (see Table 1). A common package is presented for each theme, and contains an explanation, a bibliography or digital database reference, and a set of index maps. No part of the package was intended to stand alone. The explanation defines what is included in the theme, describes it and the maps, and summarizes the information. Each bibliography was created from those references judged most helpful. The maps for 83 �three three themes themes were were created created from fromexisting existingdigital digitaldatabases1 databases, and do not have bibliographies (see Table Table I). 1). A specialist with extensive knowledge of each theme has written the explanation, created the bibliography, A specialist withextensive knowledgeof each written the explanation, created the bibliography, and and designed designed the the theme theme maps. maps. ItIt was was not not practical practical to toillustrate illustrateall all of of the the references references on onall allthe themaps. maps. The The following following maps maps were were created created by by overlaying overlayingmineral mineral resource resourcedata data on onaabase basemap mapassembled assembled from the Information System System (MLMIS) (MLMIS) 100 100database. database. MLMIS is aa gridthe Minnesota Land Land Management Management Information gridcell based database of Minnesota's natural resources, public land survey, and ownership. The database cell based Minnesota's resources, land survey, and ownership. The database was was designed designed for use use with with EPPL7, EPPL7,aaraster-based raster-basedGIS CISpackage packagedeveloped developed by by the theLand LandManagement Management Information Information Center, Center, Minnesota Minnesota Office Office of of Planning. Planning. The captured from The data data for for MLMIS MLMIS were werecaptured frommaps maps ranging ranging in in scale scale from from 1:24,000 1:24,000 to to 1:1,000,000 1:1,000,000 through grid-overlay techniques and digitizing. MLMIS was designed to be used in regional through grid-overlay techniques and digitizing. MLMIS was designed to used in regionaland and statewide planning, planning, not not for site specific work, and isis divided into two databases, divided into two databases, based on on cell cell size: size: MLMIS4O 100 The The cell cell size sizeof ofMLMIS4O MLMIS40 is is 40 40 acres acres and and isis available available as as statewide statewidefiles. files. MLMIS40 and andMLMIS MLMIS100. The size of 100 is approximately 2.5 Thecell cellsize ofMLMIS MLMIS100 2.5 acres acres(the (thelength lengthof of each eachside sideof ofthe thecell cellisis100 100meters) meters) and 100 isis available and is is the the spatially spatiallycorrected correctedversion versionof ofMLMIS4O. MLMIS40. MLMIS MLMIS100 available as as county county files filesand andenables enables the user to better match geographically referenced data from other sources. the user to better match geographically referenced data from other sources. For 100 toto For this thisstudy studyof ofeast-central east-centralMinnesota, Minnesota,staff staffused usedthe thepublic publicland landsurvey surveyfiles filesofofMLMIS MLMIS100 map map their their 'occurrence" "occurrence"data datathat thatwere werestored storedinintabular tabulardatabase databaseformats formatsas astownship, township,range, range,section, section,and and sometimes forty. The references were mapped through digitizing the reference boundaries or by matching sometimes forty. The references were mapped through digitizing the reference boundaries or by matching the 100 files. andsections sectionscovered coveredby bythe thereferences referenceswith withthe theMLMIS MLMIS100 files. the township, township, range, range,.and , . . .. ~ . > .. ~ , . .. .. ~ ', , ~ # . , . ~ . . .. .. , . , , . ,:.,~. . . ~ ~ . . . . ,. , ; . . ~ .. , ., .. 84 � https://digitalcollections.lakeheadu.ca/files/original/39759c212b92a75f106d8045c6c295a3.pdf b89931cafd8d01019fb19c3187acf300 PDF Text Text tL&&Ntat By: By: Theodore TheodoreA J. Bornhorst Bornhorstand andWilliam WilliamI.I.Rose Rose Institute Instituteon onLake LakeSuperior Superior Geology Geology Proceedings Proceedings Volume 40, Part 2 �Proceedings Proceedings Volume 40, Volume 40, Part Part 22 FIRSTPRINTING—MAY PRINTING-MAY 1994 1994 SECOND PRINTING—SEPTEMBER PRINTING-SEPTEMBER 1994 SECOND 1994 FIRST Publisher Publisher Institute Instituteon onLake Lake Superior Superior Geology Geology Distributor Distributor TheodoreJ. J. Bornhorst Bornhorst Theodore do c/oDepartment DepartmentofofGeological GeologicalEngineering, Engineering,Geology, Geology, and andGeophysics Geophysics MichiganTechnological Technological University University Michigan Townsend Drive Drive 1400Townsend 1400 Houghton, Houghton, Michigan Michigan49931-1 49931-1295 295 ISSN 1042-9964 ISSN 1042-9964 Volume 3, 4, and Volume 40 40consists consists of ofParts Pam 1, 1, 2, 2,3,4, and 5. 5. Reference Volume 40, 40, Part Part22should shouldfollow follow the the example below: below: Reference to Volume Bornhorst, 1. J. and and Rose, Rose,W. W.I.,I.,1994, 1994, Self-guided Self-guided geological geologicalfield field trip trip to to the T. J. the Keweenaw Peninsula, Michigan: Institute on Lake Superior Geology Proceedings, Keweenaw Peninsula, Michigan: Institute on Lake Superior Geology Proceedings, 40th 40thAnnual AnnualMeeting, Meeting,Houghton, Houghton,Ml, 40, part part2, 2, 185 185p. p. MI,v.v. 40, �1 PREFACE PREFACE In 1983 1983 we, with the help of Jim Jim Paces, put together together a "Field Guide to the Geology Geology of the the Keweenaw Keweenaw Annual Institute Institute on on Lake Lake Superior Superior Geology Peninsula, Michigan" Michigan" (Bornhorst (Bornhorst and others, 1983) for the 29th Annual Technological University Universityon onMay May11-14, 11-14,1983. 1983. At At that that time, time, we considered that that "It is held at Michigan Technological presumptuous for for us us to put together together a book book which which is based based mainly mainly on on the work of others," presumptuous others," but we did "because hundreds of people come to the Keweenaw Keweenaw each year to look look at at geological geological features features and andmany many 1983guide guide was was aa smashing smashing success and after 10 and 1/2 112 years a total of them ask us for advice." The The 1983 and others. others. At the time we completed the 1983 guide, we expected of 1850 copies were sold to geologists and to revise However,this this did did not not happen happen for for a variety revise and and update update the the guide guidethrough through new new editions. editions. However, variety of reasons, especially the fact that the 1983 reasons, 1983 version was done with a typewriter before word processing on computers became became popular. popular. Due Due to to the the sheer sheermagnitude magnitude of changes changes made to the 1983 1983 guide, guide, including including increasing the the number number of of stops stops from from 24 24 to to 56, 56, this this guide guide is is being published published an all new introduction and increasing Geology. The 40th Annual Annual Institute on Lake Superior Superior Geology. The Institute Institute on on Lake Lake as a new new publication publication for the 40th Geology meeting meeting in in May May 1994 is the deadline deadline forcing forcing completion completion of of this this guide, guide, which which will be Superior Geology published under the Institute on Lake Superior Superior Geology name, as would probably have been appropriate appropriate for the 1983 guide. guide. the 1983 We have 1983 guide. guide. The text, figure figure have designed designed this guide guide to to make make revisions revisions much much easier easier than than the the 1983 captions, etc. are computerized. Maps make revisions revisions easier. easier. We really do expect Maps have have been produced to make and we we get get the the momentum momentumto toadd addnew newstops. stops. We welcome your to revise this guide as mistakes are found and comments comments and and suggestions. suggestions. contributed a mountain 150 years ago, dozens of geologists have contributed Starting with Douglass Houghton almost 150 information on on the the Keweenaw Keweenaw Peninsula. Peninsula. We have faithfully of geological information faithfully tried to transmit transmit the the ideas ideas are doing doing serious serious geological geological within this mountain of information. However, However, this this guide guide is is for for people people who who are field trips. trips. �U ACKNOWLEDGMENTS ACKNOWLEDGMENTS Mary Mary Larson, Larson, an anundergraduate undergraduatestudent studentin inScientific Scientificand andTechnical TechnicalCommunication Communicationwith withaageology geologyminor, minor, played thetext textofofthis thisguide; guide;editing, editing,assembling, assembling,and andwriting writingaafew fewsegments. segments. She She played a key key role roleininthe undertook undertook this project both both as as aawork workstudy studystudent studentand and for foraascientific scientificand andtechnical technicalcommunications communications class. class. Her Hereffort effortisissincerely sincerelyappreciated. appreciated.Jane JaneCookman, Cookman,ananundergraduate undergraduateininGeology, Geology,prepared preparedmany many Laurie, Gail and Ellen of the the maps maps in in the the road road log. log. Finally, the senior senior author author (Bomhorst), thanks Laurie, Ellen for for of tolerating the extra hours at the office officeneeded needed to to complete complete this this guide. guide. to DEDICATION DEDICATION "Self-guided geological field trip to the the Keweenaw Keweenaw Peninsula, Michigan" the late late This "Self-guided Michigan" is dedicated to the mapping in in the theKeweenaw KeweenawPeninsula. Peninsula. Walter S. S. White, White, who who spent spent much much of of his his life lifedoing doinggeologic geologicmapping Walter �Proceedings Proceedings Volume Volume 40, Part Part 22 Institute on Institute on Lake Lake Superior Superior Geology Geology trip to the Self-guided Self-guided geological field trip Keweenaw Peninsula, Peninsula, Michigan Keweenaw Michigan Bornhorst and By: By: Theodore Theodore J. J. Bornhorst and William WilliamI.I.Rose Rose Department Departmentof ofGeological GeologicalEngineering, Engineering,Geology, Geology,and andGeophysics Geophysics Michigan University, Houghton, Houghton, Michigan Michigan 49931-1 295 Michigan Technological University, 49931-1295 for Published for 40th 40th Annual Meeting Meeting Institute on Lake Superior Geology Institute on Lake Geology Houghton, Houghton, Michigan Michigan May 11—14, 1994 May ll-I4,1994 ISSN 1042-9964 1042-9964 ISSN Cover photoÑClif photo—Cliff Mine Minedrca circaearly early 1900s. 1900s. Photo from from Mlii Photo MTUArchives Archivesand andCopper CopperCountry CountryHistorical HistoricalCollections; Collections;Donor DonorTony TonyVranesich. Vranesich. �U' TABLE OF TABLE OF CONTENTS CONTENTS && PREFACE PREFACE i ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ii ii DEDICATION DEDICATION iiii USING THIS THIS GUIDE GUIDE iv iv LIST LIST OF OF STOPS STOPS vi LIST OF OF MAPS MAPS xii xii LIST OF OF FIGURES FIGURES XV LIST LIST OF OFTABLES TABLES INDEX TO TO GEOLOGY GEOLOGY ON ON MAPS MAPS GEOLOGY GEOLOGY OF OF THE THEKEWEENAW KEWEENAWPENINSULA PENINSULA MAIN ROAD LOG LOG AND AND STOP STOPDESCRIPTION DESCRIPTION - xviii xviii xix xix 1 1 33 33 LEG A A - REDRIDGE REDRIDGE 117 117 LEG B -- OWL OWL CREEK CREEK 124 1% LEG C C -- HORSESHOE HORSESHOE HARBOR HARBOR 128 LEG D D -- EASTSIDE EASTSWE OF OF THE THEKEWEENAW KEWEENAWPENINSULA PENINSULA 132 LEG E E-932 - 932CREEK CREEK 144 LEG LEG FF -- FIVE FIVE MILE MILE POINT POINT 149 LEG LEG G G -- COPPER COPPER CITY CITY 155 LEG LEG H H -- MCLAIN MCLAIN STATE STATE PARK PARK 158 LEGI-L'ANSE LEG I - L'ANSE 172 REFERENCES REFERENCES 178 �iv USING 11118 THIS GUIDE GUIDE A NUMBER NUMBER OF STOPS ARE ON PRIVATE PRIVATE LAND. LAND. PLEASE PLEASE RESPECT RESPECT PRIVATE PRIVATE PROPERTY. PROPERTY. PROBLEMS OF ACCESS ARE MINIMAL, BUT THIS CAN QUICKLY CHANGE IF EVERYONE PROBLEMS MINIMAL, BUT THIS CAN QUICKLY CHANGE IF EVERYONE DOES NOT USE DOES USE LOW LOWPROFILE PROFILEOUTDOOR OUTDOOR PRINCIPLES PRINCIPLES AND AND ASK ASK PERMISSION PERMISSION WHEN WHEN POSSIBLE. OLD MINEROCK ROCK PILES PILESARE AREHAZARDOUS, HAZARDOUS, SO SO COMMON COMMON SENSE SENSE MUST MUST BE BE POSSIBLE. OLD MINE APPLIED. APPLIED. for geologists and and geology geologystudents. students. It begins with with an an introductory introductory description description with with This guide is designed for figures and tables. The Theroad roadlog logconsists consistsof ofaamain main log logwith withsequentially sequentiallynumbered numbered stops, stops, maps, maps, figures, figures, and tables (sequence (sequence for for figures figures and and tables tables continues continues from from introductory introductory description) description)followed followedby by separate separate legs. Each leg has separate sequentially numbered stops, maps, figures, and tables (leg numbers has separate sequentially numbered stops, maps, figures, (leg numbers are are by the letter of the leg). preceded by leg). 240 m or I" 2000 ft) scale Ml maps have north to the top. top. Most All Most maps maps are are 1:24,000 1:24,000 (1 cm = 240 1" == 2000 scale (Figure (Figure 1689.6 m or 3/8 I (5280 ft)). Several maps and I are 1:168960 cm = lb). maps in Legs D are 1:168960 (1 = 1689.6 318" = 1 mile (5280 ft)). Dots ib). follow the road traveled for the main main road log, log, and and open open circles circles are are used used for for the the legs. legs. The field trip stops stops are are grouped grouped below below in in topics topics to to assist assist in in design design of of your your field fieldtrip. trip. TOPIC TOPIC Glacial Glacial 2, 3. 7, 16, 29, 33, A2, F2, Hi, H2, H3, H4, H5, H7, H9 Rift-flanking Rift-flanking clastic clastic sedimentary sedimentary rocks rocks 10, 11, 12, 12, D5, El, El,11 I1 Rift-filling dominantly clastic clastic sedimentary rocks Rift-filling dominantly igneous igneous rocks rocks 12, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,28, 28,A1, Al, A3, A3, Cl, Cl, Fl, Fl, H6, H8 1, 4, 6, 8, 14, 15, 16, 18, 19, 20, 21, 30, 31, Bi, Dl, El, F3, Gi Native Copper Copper Deposits Deposits 5. 8, Scenic Scenic 7, 16, 25, D4, D6 9, 13, 15, 16, 17, 18, 28, 30, 32, 34, 81 We encourage you to be imaginative and make make up up your your own own subset subsetof of stops. stops. To visit all the stops stops listed based in this guide would take at least five days. We We have have designed designed several trips with different emphasis based on about 10 10 stops per day. Stops Stopsare arelisted listedininapproximate approximateorder order of of visiting. visiting. One-day trip with emphasis Oneday emphasis glacial glacial features features A2, A2, 7, 33, 33, Hi, HI,H2, H2,113, H3, H4, H4, H5, H5, H7, H7, H9 H9(requires (requires special specialpermission) permission) One-day coverage of of rift rift geology geology in in the theHoughton/Calumet HoughtonlCalumetarea area Oneday trip with broad coverage Al, A3, 4, 5, 6, 6, A1, A3. H8, H8, 10, 10, 12, 12, 13, 13, 15, 15, 16 16 �V One-thy One-day trip tripwith withemphasis emphasison onmineral mineraldeposits deposits 5, 8, 8, 13, 13, 15, 15, 16, 16, 17, 17, 18, 18, 30, 30, El El 4, 5, One-day trip trip with with emphasis emphasison onigneous igneousgeology geology One-day 4, 6, 31, El, El, Gl 6, 15, 15, 16, 16, 18, 19, 20, 31, G1 One-thy One-day trip tripwith withbroad broadcoverage coverageof ofgeology geologyand andscenery scenery 4, 7, 10, 10, 12, 12, 13, 13, 15, 15, 16, 16, 18, 18, 24, 24, 25, 25, 27 27 One-thy One-day trip tripwith withscenic scenicoverview overviewand andgeology geology 7, 16, 22, 24, 24, 25.28, 25, 28,Cl, Cl, D4, 04, D6 06 16, 21, 22, Two-day trip with with broad broad coverage coverage of of geology geology and and scenery scenery 4, 5, 10, 10, 12, 12, 13, 13, 15, 15, 16, 16, 18, 18, 20, 20, 21, 21, 22, 22, 25, 25, 28, 30, 30, Cl, Cl, H8, H8, A3 A3 so many excellent stops we almost don't We are are not not sure surewhich which stops stops There are so don't like to make suggestions. We are the most popular, but our guess is the following: 4, 7, 10, 12, 15, 16, 18, 21, 25, and 27. following: 4, If you use this guide, we would really really like like to to hear hearabout aboutyour yourexperience. experience. What Whatstops stopsdid didyou youlike? like? What like? etc. etc. Piease mail. With your your comments comments and and Please drop a letter letter or or postcard postcard in in the the mail. stops you don't like? suggestions we èan make this guide better. can make this guide better. suggestions �vi LIST LIST OF OF STOPS STOPS The The following following list of stops stops can can be be used to to help help you you design design your your The self—guided self-guided geological geological field field trip trip to to the the Keweenaw Keweenaw Peninsula. Peninsula. The The appropriate maps for location location of of stops stops are are shown shown in in Figure Figure 1A. 1A. The appropriate maps for each stop stop and and trip trip route route are are located located in in Figure Figure lB. IB. We hope hope you you enjoy enjoy seeing seeing the the Keweenaw Keweenaw and and its its geology. geology. STOP STOP APPROPRIATE APPROPRIATE MAP PAGE PAGE STOP DESCRIPTION STOP DESCRIPTION MAIN ROAD ROAD LOG LOG 1 (2) 33 seventh Street, Seventh Street, City City of of Houghton Houghton (Portage Lake Volcanics (Portage Lake Volcanics [PLy]) [PLV]) 2 (2) 34 Boughton Houghton grooves)) grooves 3 (2) 36 Hurontown (glacially caned basalt) (glacially carved basalt) 4 (3) 39 South Range Quarry South Quarry Volcanics Volcanics [PLy]) [PLV]) 5 (3) 42 (native Baltic Mine Shaft No. 33 (native Baltic Mine Shaft copper deposit within Portage Lake Lake Volcanics [PLy]) Volcanics [PLV]) 6 (2) 43 city of Sheldon Avenue, Avenue, City of Houghton Houghton (Portage Lake Volcanics (Portage Lake Volcanics [PLy]) [PLV]) 7 (4) 44 Overlook Keweenaw Waterway Overlook 8 (4) 48 Quincy Mine Adit Mit Quincy Mine Volcanics [PLy]) Volcanics [PLVI) 9 (4) 53 Quincy Quincy Mine Mine Rock Rock Piles Piles (native (native copper deposit within Portage Lake Lake Volcanics [PLy]) [PLV]) Volcanics 10 (6) 56 M-26 M-26 near near Sandstone) Sandstone) 11 (7) 59 Hungarian Falls Hungarian Falls (Keweenaw (KeweenawFault) Fault) 12 (8) 64 Natural Wall Ravine Ravine (Keweenaw Natural (KeweenawFault) Fault) 13 (9) 68 wolverine Mine Shaft No. 22 (native Wolverine (native copper deposit within Portage Portage Lake Lake Volcanics [PLy]) Volcanics [PLV]) 14 (9) 74 Scales Creek creek (Portage Lake Volcanics Volcanics Scales (Portage Lake [PLVI) r PLVI ) water water tower tower Tamarack Tamarack (glacial (glacial (Portage Lake (Portage Lake (Portage Lake (Portage Lake (Jacobsville (Jacobsville �vii LIST OF LIST OF STOPS STOPS (Cont'd.) (Cont'd.) STOP STOP PAGE APPROPRIATE APPROPRIATE PAGE MAP MAP STOP STOP DESCRIPTION DESCRIPTION 15 15 (9) (9) 74 74 Allouez ~llouez(conglomerate (conglomerate in in Portage Portage Lake Volcanics [PLy]) Lake Volcanics [PLV]) 16 16 (9) (9) 75 75 Bumbletown Bumbletown Hill (Allouez (Allouez Gap Gap Fault Fault and and Portage Portage Lake Lake Volcanics) ~olcanics) 17 17 (11) (11) 82 82 Cliff Cliff Nine Mine (native (native copper copper vein vein deposit) deposit) 18 18 (12) (12) 83 83 Phoenix vein phoenix Mine (native (native copper copper vein deposit deposit and and Portage Portage Lake ~ a kvolcanics Volcanics e [PLy]) [PLVI) 19 19 (12) 87 87 Eagle Eagle River River (Portage (PortageLake Lake Volcanics Volcanics [PLy]) [PLVI) 20 20 (12) 89 89 M-26, M-26, Eagle Eagle River River (Portage (Portage Lake Lake volcanics Volcanics [PLy]) [PLVI) 21 21 (12) 89 89 Eagle Eagle River River Falls Falls (contact (contactof of Portage Portage Lake Lake Volcanics Volcanics and and Copper Copper Harbor Harbor Conglomerate) Conglomerate) 22 (14) 90 90 Eagle Eagle Harbor Harbor Lighthouse Lighthouse (Lake (Lake Shore Shore Traps) Traps) 23 (16) 93 93 Silver Silver River River (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) 24 (16) 96 96 Esrey Esrey Park Park (Lake (LakeShore Shore Traps) Traps) 25 (17) 98 98 Brockway Brockway Mountain Mountain Viewpoint Viewpoint 26 (17) 100 100 Hebard (Copper Harbor Harbor Hebard Park park (Copper Conglomerate) Conglomerate) 27 (17) 100 100 Dan's Dan's Point Point (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) 28 (18) 104 104 Fort Fort Wilkins Wilkins State State Park Park (native (native copper copper veins veins within within Copper Copper Harbor Harbor Conglomerate) Conglomerate) 29 (20) 105 105 Mandan Mandan (Mandan (Mandanesker) esker) 30 (21) 105 105 Delaware Delaware Mine Mine (native (nativecopper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics [PLy]) [PLVI) �LIST LIST OF OF STOPS STOPS (Cont'd.) (Cont'd.) STOP STOP APPROPRIATE APPROPRIATE MAP MAP 31 31 (21) 32 32 (10) PAGE PAGE 110 STOP STOP DESCRIPTION DESCRIPTION US-41 near Delaware Delaware (Portage (Portage Lake Lake US-41 Volcanics Volcanics [PLy]) [PLV]) 113 Mohawk Mine (native (native copper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics [PLy]) [PLVI) 33 33 (24) 114 Calumet Calumet (glacial (glacialgrooves) grooves) 34 34 (24) 116 Osceola Osceola Mine (native (native copper copper deposit deposit within within Portage Portage Lake Lake Volcanics Volcanics r [PLy]) PLVI ) LEG LEG A Redridge Al A1 (A2) 117 Houghton Houghton Canal Canal Road Road (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) A2 A2 (A2) 117 Cole's Cole's Creek Creek (glacial (glacial sediments) sediments) A3 A3 (AS) 120 Redridge Cliffs Cliffs (Freda (FredaSandstone) Sandstone) 124 124 Owl Owl Creek Creek [PLy] [PLV] and LEG LEG BB Owl Owl Creek Creek El Bl (B2) (B2) (Portage Lake volcanics (Portage Lake Volcanics Copper Falls Copper Falls Mine) Mine) LEG C Horseshoe Horseshoe Harbor Harbor Cl Cl (C2) (C2) 131 131 Horseshoe Horseshoe Harbor Harbor (Copper (CopperHarborS Harbor Conglomerate) Conglomerate) LEG Peninsula LEG DD Eastside Eastside of of the the 1(eweenaw Keweenaw Peninsula Dl Dl (D2) (D2 132 132 Mount Mount Bohemia Bohemia (diorite (diorite stock stock within within the Portage Lake Volcanics the Portage Lake Volcanics [PLy]) [PLV]) D2 D2 (Dl) (Dl) 136 136 Bete beach from Bete Grise Grise (white (white sand sand beach from Jacobsville Sandstone) Jacobsville Sandstone) D3 D3 (02) (D2) 137 137 Haven Haven Park Park (Portage (Portage Lake Lake Volcanics Volcanics [PLy] near the [PLV] near the Keweenaw Keweenaw Fault) Fault) D4 D4 (Dl) (Dl) 139 139 South South Point point (view (view of of the the tip tip of of the the Keweenaw Keweenaw Peninsula) Peninsula) DS D5 (Dl) (Dl) 139 139 Eastern Eastern Keweenaw Keweenaw Peninsula Peninsula (Jacobsville (Jacobsville Sandstone) Sandstone) �-- ix LIST LIST OF OF STOPS STOPS (Cont'd.) (C0nt8d.) APPROPRIATE APPROPRIATE PAGE PAGE MAP MAP STOP STOP D6 D6 (D3) (D3) STOP STOP DESCRIPTION DESCRIPTION 141 141 Gay Gay (stamp (stamp sands) sands) 144 144 932 932 creek Creek (Keweenaw (KeweenawFault) Fault) LEG LEG EE 932 932 creek Creek El El (E2) (E2) LEG LEG FF Five Five Mile Mile Point Point Fl Fl (Fl) (Fl) 149 149 W.C. W.C. Verde ~ e r d eRoadside ~oadsidePark Park (Copper (Copper Harbor Harbor Conglomerate) Conglomerate) F2 (F3) 149 Allouez Allouez Gap Gap (kettles) (kettles) F3 (F3) 153 North North of of Abmeek Ahmeek (Portage (PortageLake Lake Volcanics [PLy]) Volcanics [PLV]) 155 155 copper Copper City City Rhyolite ~hyolite(Portage (Portage Lake Lake Volcanics [PLy)) Volcanics [PLV]) LEG LEG GG Copper Copper City City Gl Gl (Gi) (GI) LEG LEG HH Mctain McLain State State Park Park Hl HI (Hl) (HI) 158 158 Red Red Jacket ~acket(glacial (glacialsand sand and and H2 (Hl) 158 West West Tamarack Tamarack (glacial (glacialgravEls) gravels) H3 (H2) 161 Cloverland Clwerland Road Road (Washburn (WashburnStage. Stage beach beachridges) ridges) H4 (H4) 161 Lake Lake Annie Annie (glacial (glaciallake lake baymouth baymouth gravel) gravel ) bar) bar ) H5 (H3) 161 Sand Sand Ridges Ridges M-203 M-203 (Nipissing (Nipissingbeach beach ridges) ridges) (H3) 165 McLain McLain State State Park Park (Freda (FredaSandstone) Sandstone) (H5) 165 Till Till along along M—203 M-203 (till) (till) H8 (H6) 168 Hancock Rancock Campground campground(Nonesuch (NonesuchShale) Shale) H9 (136) 168 Superior Superior Sand Sand and and Gravel Gravel (glaciofluvial (glaciofluvialsediments) sediments) 174 174 L'Anse L'Anse Red Red Rocks Rocks (Jacobsville (Jacobsville H6 137 . LEG LEG II L'Anse L'Anse fl I1 (12) (12) Sandstone) Sandstone) �Figure Route and Stop Map I 4> Route Number iF 2P Kilometers 3P A..... Leg Route and Stop Number �15 13 Figure 1B: Index Index of 1:24,000 1:24,000 Scale Scale Maps Maps El F2 F3 H2 H 'Vt I C' AS 'V 3 See Map Ii I Region Covered Covered Region A6 1 LI Q 1p 2Q Kilometers 3 byMap MapNumber Number by Main Route Route and and Main Stop Number Number Stop See Map 12 ......' Leg Route Route and and Leg Stop Number Number Stop �xli LIST OF MAPS LIST MAPS MAP MAP 1 MAP 2 MAP MAP 33 MAP 4 MAP 55 MAP MAP 66 MAP 77 MAP 88 MAP MAP 9 1 34 34 35 35 40 40 45 54 55 60 60 63 67 MP 10 MAP 10 77 77 MAP MAP 11 11 83 83 MAP 12 MAP 12 84 84 MAP 13 MAP 13 91 91 MAP MAP 14 14 92. 92 MAP 15 MAP 15 94 94 MAP 16 MAP 16 95 95 MAP MAP 17 17 99 99 MAP 18 MAP 18 101 101 MAP MAP 19 19 106 106 MAP 20 MAP 20 107 107 MAP 21 MAP 21 108 MAP 22 MAP 22 111 Ill MAP 23 MAP 23 112 112 MAP MAP 24 24 115 115 �Xlii UST LISTOF OFMAPS MAPS (Cont'd.) (Cont'd.) MAP MAP Al A1 118 MAP MAP A2 A2 119 MAP MAP A3 A3 121 MAP MAP A4 A4 122 MAP MAP AS A5 123 MAP MAP 81 Bl 125 MAP MAP 82 B2 126 MAP MAP Cl Cl 129 MAP •C2 C2 130 MAP MAP Dl Dl 133 MAP MAP D2 D2 134 MAP MAP D3 D3 142 MAP MAP El El 145 MAP MAP E2 E2 146 MAP MAP Fl Fl 150 MAP fl MAP F2 151 MAP fl MAP F3 152 MAP MAP Cii Gl 156 MAP MAP HI HI 159 MAP MAP H2 H2 162 MAP MAP 113 H3 163 MAP MAP H4 H4 164 MAP MAP H5 H5 166 �xiv LIST OF MAPS (Cont'd.) MAP 1-16 H6 169 MAP Ii MAP I1 173 MAP MAP 12 12 175 �xv LIST OF OF FIGURES FIGURES &?&FPage Index map of route, route, stops stops and and 1:24,000 1:24,000 scale scale maps. maps. x Figure 2: Figure 2: Location of the Keweenaw Keweenaw Peninsula native copper district 22 Figure 3: Figure Geology of the Lake Lake Superior Superior segment segment of of the the Mideontinent Midcontinent rift rift system. system. 33 progression of major geologic events of the North Temporal progression American rift system. system. 55 Map showing showing the Midcontient rift system system in relation relation to to the the (GFTZ). Grenville front front tectonic tectonic zone zone (GVFZ). 6 6 Figure Figure 6: 6: Geologic map of the the Keweenaw Keweenaw Peninsula. Peninsula. 7 Figure 7: Figure 7: Geologic map and stratigraphic stratigraphic column of the central central Keweenaw Keweenaw Peninsula. Peninsula. 88 Columnar stratigraphic section of the Keweenaw Fault in the the Calumet-Mohawk area. Calumet-Mohawk area. 9 9 Figure Figure 1: 1: Figure 4: Figure Figure 5: 5: Figure 8: Figure 8: Generalized stratigraphic section of the Portage Lake Volcanics from Victoria to Copper Harbor. Harbor. 13 13 Schematic cartoon of the depositional environment of the Copper Copper Harbor Harbor Conglomerate. Conglomerate. 15 15 Figure 11: Figure 11: Faults and minor minor folds folds in in the thecentral centralKeweenaw Keweenaw Peninsula. Peninsula. 17 17 Figure 12: Figure 12: Paragenesis of secondary minerals in flow top top deposits deposits and and veins, veins, and conglomerate conglomerate deposits. deposits. 21 21 Distribution of amygduleamygdule- and vein-filling minerals in the Calumet Calumet cross section of of the PLV. PLy. 22 22 Figure Figure 14: 14: Speculative Speculative ice-marginal positions positions during during the the Wisconsin Wisconsin ice iceretreat. retreat. 28 28 Figure 15: 15: Enlarged view of ice-marginal ice-marginal positions during the Wisconsin Wisconsin ice ice retreat. 29 Figure Figure 16; 16: End moraine moraine of of the the Keweenaw Keweenaw Bay Bay Lobe Lobe glacier. glacier. 30 30 Figure 17: Figure 17: Keweenaw Bay lobe glacier and position of glacial glacial Lake Lake Duluth. Duluth. 30 Figure 18: Figure 18: Physiographic divisions of the the central central Keweenaw Keweenaw Peninsula. Peninsula. 31 31 Figure 9: Figure 9: Figure Figure 10: 10: Figure 13: Figure 13: �xvi xvi LIST LIST OF OF FIGURES FIGURES (Cont'd.) (Cont'd.) Figure Figure 19: 19: High level level drainage drainagethrough through the the Portage PortageGap. Gap. 31 Figure Figure 20: 20: Geologic Geologic profile of the the South South Range Range Quarry. Quarry. 38 Figure 21: 21: Cross section on MAP MAP2. 2. section A-A' on 41 Figure Figure 22: 22: View View from from Portage Portage overlook overlookfacing facing south. south. 46 Figure Figure 23: 23: The The Quincy Quincy Mine Mine location. location. 49 Figure 24: 24; Sketch Sketch map map of of the theQuincy Quincyand andHancock Hancock Mines. Mines. 50 Figure 25: 25: Geologic Geologic cross cross section section for for Maps Maps H6, H6, 4, 4,and and5.5. 51 Figure 26: 26: Contoured Pb and and Sn Sn in in Torch TorchLake. Lake. Contoured concentrations concentrations of Pb 57 Figure 27: 27: Relationships Relationships of of Jacobsville JacohsvilleSandstone. Sandstone. 58 Figure Figure 28: 28: Geologic sketch sketch map map of of the the Hungarian Hungarian Falls Palls area. area. 61 Figure Figure 29: 29: Geologic Geologic sketch sketch map map of of the the Natural Natural Wall Wall Ravine. Ravine. 65 Figure Figure 30: 30: Geologic map map and and cross cross section, section. Wolverine Wolverine Mine, and and vicinity. vicinity. 69 Figure Figure 31: 31: Thickness to Mandan. Mandan. Thickness of the the Kearsarge Kearsarge flow flow (top) (top) from from Isle Isle Royale Royale to 70 Figure Figure 32: 32: Paragenesis Paragenesis of of secondary secondaryminerals mineralsin inthe theKearsarge Kearsargeamygdaloid. amygdaloid. 71 Figure Figure 33: 33: Cross Cross section section of of Kearsarge Kearsargeamygdaloid amygdaloid showing showing the banding banding of of mineral mineral assemblage. assemblage. 72 Figure Figure 34: 34. Thickness Thickness of of the the Kingston Kingston Conglomerate Conglomerate at at the the Kingston Kingston Mine. Mine. 78 Figure Figure 35: 35: Outcrop Outcrop map mapof ofthe theAllouez-Bumbletown Allouez-BumbletownHill Hillarea. area. 79 Figure Figure 36: 36: Physiographic Physiographic and and glacial glacial features features of of the the Allouez Allouez Gap. Gap. 80 Figure Figure 37: 37: Map betweenSeneca Senecaand andthe the Map and andsection sectionof ofthe theGreenstone Greenstoneflow flowbetween Cliff Cliff Mine. Mine. 81 Figure Figure 38: 38: Map Mapand andsection sectionof ofthe theGreenstone Greenstoneflow flownear nearPhoenix. Phoenix. 86 Figure Figure 39: 39: Stratigraphy Stratigraphyof of the thePortage PortageLake LakeVolcanics Volcanicsabove abovethe theGreenstone Greenstone Flow. Flow. 88 Stratigraphic Stratigraphiccolumn column of of the theLake LakeShore ShoreTraps. Traps. 97 Figure Figure 40: 40: �xvii LIST OF OF FIGURES (Cont'd.) (Cont'd.) Measured stratigraphic stratigraphic sections from Horseshoe Harbor and Dan's Point. 103 Figure Dl: Figure Geologic map showing andesitic dikes near Mount Bohemia. 135 Figure Figure D2: D2: Geologic sketch map of part of of the the Keweenaw Keweenaw Fault Fault in in the the vicinity vicinity ofDeerLake. of Deer Lake. 138 Geologic Geologic map showing the location of rhyolites on the eastern eastern tip tip of the the Keweenaw KeweenawPeninsula. Peninsula. 140 Figure El: Figure El: Location of of the the region region of of chalcocite chalcocitemineralization. mineralization. 147 Figure Flgure Hi: HI: Physiographic and glacial glacial features features west of of Calumet. Calumet. 160 Figure 112: H2: Results Results of of gravity gravitymeasurements measurements across across Bear Bear Lake. Lake. 167 Figure H3: H3: Geologic section section through through the the Hancock Hancock "fairground" "fairground"tezrace terrace glacial glacial deposit. deposit. 170 Physiography and glacial glacial features features of the northern northern part part of of Portage Portage Lake. Lake. 171 Geologic Anse redrocks. L'Anse redrocks. Geologic sketch sketch map map and and cross cross section section of of L' 177 Figure 41: 41: Figure D3: D3: Figure 114: H4: Figure Flgure Ii: 11: �xviii LIST LIST OF OF TABLES TABLES Avenge Averageand andrepresentative representativegeochemical geochemical data data for for least least altered altered lavas lavas of the Volcanics. the Portage PortageLake LakeVolcanics. 12 Table Table 2: 2: Stages in the theLake LakeSuperior SuperiorBasin. Basin. Stages of of glacial glacial lakes lakes in 27 Table Table 3: 3: Major-element composition composition of the the Kearsarge Kearsargeflow. flow. 69 Table Table 4: 4: Volume Volume percent percent amygdule amygdule minerals minerals from from mapped mapped assemblages assemblages shown in Figure 33. shown in Figure 33. 72 Table 5: 5: Avenge Averagemajor-element major-elementcomposition compositionof of the theScales ScalesCreek Creekflow. flow. 79 Table 6: 6: Avenge Averagecomposition compositionofofthe theGreenstone GreenstoneFlow. How. 87 Table Table El: El: Chemical Chemical composition composition of of intrusive intrusiveplug plug on on932 932Creek. Creek. 148 Table 01: Gl: Chemical Chemical types types of of rhyolites PLV. rhyolites within within the the PLV. 157 Table Table 1:1: �xix XIX INDEX TO TO GEOLOGY GEOLOGY ON ON MAPS MAPS Map No. Quadrangle Quadrangle Reference Reference 1 MTLJ MTU Campus Map Map White, 1956; Hase, 1973 1973 2 Chassell Chassell White, 1956 1956 3 South Range, Chassell White and Wright, 1956; White, 1956 1956 4 Chassell, Hancock White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a 5 Chassell, Hancock White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a 6 Laurium 956b Cornwall and Wright, Wright, I1956b 7 Laurium Cornwall and Wright, 956b Wright, 11956b 8 Laurium Cornwall and Wright, 1956b 1956b 9 Ahmeek White and others, others, 1953 1953 10 Mohawk Davidson and others, 1955 1955 11 Mohawk Davidson and others, others, 1955 1955 12 Phoenix Phoenix Cornwall, 1954a 1954a 13 Eagle Harbor Cornwall and Wright, 1954 1954 14 Eagle Harbor Cornwall and Wright, 1954 1954 15 Delaware Delaware Cornwall, 954b Cornwall,11954b 16 Delaware Delaware Cornwall, I1954b 954b Cornwall, 17 Lake Medora Cornwall, 954c Cornwall,11954c 18 Lake Medora, Fort Fort Wilkins Wilkins 954c; Cornwall, 1955 Cornwall, I1954; 1955 19 Lake Medora Cornwall, 1954c 1954c 20 Delaware Delaware Cornwall, 1954b 1954b 21 Delaware Cornwall, 1954b 1954b 22 Eagle Harbor Harbor Cornwall and Wright, 1954 1954 �xx 23 Eagle Eagle Harbor Harbor Cornwall Cornwall and Wright, Wright, 1954; 1954;'Cornwall, Cornwall, 1954a 1954a 24 Laurium Laurium Cornwall Cornwall and andWright, Wright,19561, 1956b Al Chassell Chassell White, White, 1956 1956 A2 Chassel1,Hancock Chassell,Hancock White, White, 1956; 1956; Cornwall Cornwall and and Wright, Wright, 1956a 1956a A3 Oskar Oskar Cornwall Cornwall and and Wright, 1956a; 1956a; White White and and Wright, 1956 1956 A4 Oskar White, White, 1968 1968 AS Beacon Hill Hill White, White, 1968 1968 B1 Eagle Harbor Cornwall and Wright, Wright, 1954 1954 B2 Eagle Harbor Harbor Cornwall and Wright, 1954 1954 Cl Fort Wilkins, Lake Medora Medora Wilkins, Lake Cornwall, 1954c; 1954~;Cornwall, Cornwall, 1955 1955 C2 Fort Fort Wilkins Wilkins Cornwall, Cornwall. 1955 1955 Dl Michigan Michigan DNR-Keweenaw DNR-Keweenaw and and Houghton Houghton Counties Counties White, White, 1968 1968 D2 Delaware Delaware Cornwall, 954b Cornwall,11954b D3 Gay Gay White, 1968 1968 El Eagle Harbor Harbor Eagle Cornwall and Wright, 1954 1954 E2 Eagle Harbor, Harbor, Bruneau Bmflea~Creek Creek Eagle Wright and 954b and Cornwall, Cornwall, I1954b Fl Phoenix Phoenix Cornwall, Cornwall, 1954a 1954a F2 Phoenix,Mohawk,Ahmeek Ph0enix.Mohawk.Ahmee.k Cornwall, 1954a 1954a;Davidson Davidson and andothers, others, 1955; White and and others, others, 1953 1953 p3 Ahmeek White and others, others. 1953 1953 01 Ahmeek,Mohawk White and others, others, 1953; 1953; Davidson Davidson and and others, 1955 1955 Hi Laurium Cornwall and and Wright, 1956b; C~rnwall 1956b; Hughes, Hughes, I1963 963 H2 Hancock, Hancock. Muggen Creek Creek Cornwall and Wright, 1956a 1956a �xxi Cornwall and Wright, Cornwall Wright, 1956á; 1956a; Warren, Warren, 1981 1981 H3 Hancock H4 Hancock Hancock H5 Hancock, Oskar Oskar Cornwall and Wright, 1956a 1956a H6 Hancock Hancock Cornwall and Wright, 1956a 1956a Ii I1 Michigan DNR-Houghton County County White, 1968 1968 ¶2 12 Michigan DNR-Baraga County County White, 1968 1968 �Geology 1 GEOLOGY OF TilE THEKEWEENAW KEWEENAW PENINSULA, PENINSULA,MICHIGAN MICHIGAN INTRODUCTION INTRODUCTION The Keweenaw Keweenaw Peninsula Peninsula is located located on the the margin margin of of Lake LakeSuperior. Superior. The geology geology of the the Keweenaw Peninsula consists consists of of two two quite quite distinct distinct episodes. episodes. The bedrock is composed of consolidated between about about 1100 and and 1000 million million years yearsago ago (Ma) (Ma) as as part part of of the Midcontinent rift rocks deposited deposited between Midcontinent rift system of North America. The bedrock is overlain by unconsolidated glacial sediments deposited during system The bedrock is overlain by unconsolidated the past 2 million glaciation of of North North America. America. The million years years as as part part of of Pleistocene Pleistocene continental glaciation The field field trip trip glacial materials. materials. Because the cultural history of the Keweenaw contains stops to view both bedrock and glacial Peninsula is so dominated by the mining of native copper from the bedrock, more emphasis is placed on on the geology of the bedrock. the bedrock. BEDROCK GEOLOGY GEOLOGY This Peninsula was was taken taken from from aa combination combination This description description of the bedrock geology of the Keweenaw Peninsula of Bornhorst (in press). press), Bornhorst Bornhorst (1992), and Bomhorst and others (1983) (1983) without without specific specific citation citation or or quotation. quotation. Midcontlnent Midcontinent Rift Rift System System is on on the the margin of the Lake Superior segment of the Midcontinent rift The Keweenaw Peninsula is from Kansas Kansas to Lake Superior system. The Midcontinent system. %dcontinent rift system system extends northeasterly northeasterly from Superior and and then then southeasterly through lower Michigan (Fig. 2). It was formed at about 1100 Ma by extensional thinning lower Michigan (Fig. 2). crustal block. block. Present day crystal crustal thickness in the Lake Superior region of the rigid Precambrian Superior crustal between 40 and 50 km, km. which is thicker than adjacent areas (Halls, 1982). 1982). is between Beneath Lake Superior the rift is filled with more than 25 km of volcanic volcanic rocks, including including about about 10 km of Portage Portage Lake Volcanics Volcanics (PLy) (PLV) (Fig. (Fig. 2) 2) (Cannon (Cannon and and others, others, 1989; 1989; Hinzc Hinze and others, others, 1990; 1990; Cannon, 1992). The ThePLy, PLV,with withaatotal totalthickness thicknessofofabout about55km kmofofrift-filling rift-fillingvolcanic volcanicrocks, rocks, isisexposed exposed on the Keweenaw Peninsula. Large in response response to to a period period of rifting Large volumes volumes of magma magma were extruded in over an asthenospheric mantle plume (Hutchinson and others, 1990). Rift magmatism extended from 1109 asthenospheric (Hutchiinson and others, 1990). to 1087 1087 (Davis and Paces, 1990; 1990; Paces and Miller, 1993). The ThePLV PLVof ofthe theKeweenaw KeweenawPeninsula Peninsulaerupted erupted during a 2 to 3 million year span of time, time, at about about 1095 1095 Ma Ma (Davis (Davisand andPaces, Paces,1990). 1990). It It is part of a vast association of igneous rocks of similar similar age, including the Duluth Gabbro 3). Gahbro (Fig. 3). the rift-filling volcanic rocks, rocks, A thick succession of rift-filling clastic sedimentary rocks overlie the by volcanism, volcanism, to to one onedominated dominatedby bysedimentation. sedimentation. While and represent a change from a period dominated by magmatic activity continued as thermal anomaly anomaly of the the magmatic activity waned, waned, subsidence subsidenceofofthe the rift rift basin basin continued as the thermal asthenospheric plume decayed (Cannon and Hinze, 1992; Hutchinson Hutchinson and and others, others, 1990). A total thickness total thickness km of ofrift-filling rift-filling clastic clastic sedimentary sedimentary rocks exist beneath to 88 km of up to beneath the the center of Lake Superior, with with a maximum exposed thickness in the western Upper Peninsula of Michigan, of 6 km (Fig. 2) (Cannon, 1992; 1992; Cannon and others, 1989). 1989). These Theseclastic clasticsedimentary sedimentaryrocks rocks are are dominated dominated by by red-colored red-colored conglomerates conglomerates Conglomerate) and red-colored sandstones (Freda Sandstone), with aa thin thin intervening intervening gray (Copper Harbor Conglomerate) to black black shale shale (Nonesuch (Nonesuch Shale). Late Lateininthe thethermal thermalsubsidence subsidence phase phase of of the the rift. rift. Cannon Cannon and andothers others (1989) and Hinze and and others others (1990) (1990) propose propose that that mature mature red-colored red-colored sandstones sandstones (Jacobsville Sandstone) Sandstone) basin. The is poorly poorly constrained, constrained, was deposited across the entire basin. The age age of these rift-filling sedimentary strata is but is likely between about 1085 1085 and and 1060 1060Ma. Ma. �2 Geology Geology A . B B GLIMPCE GLIMPCE Line A Shoreline Slate && Islands, 3000 Superior Shod. shot ~uitou Shore {. en ra'r F—I?.,. - 3 5:.8 10- Lower ~rotnowic? At Yu At Faultblocks or introsivu I 151 EXPLANATION EXPLANATION Yj YjJaoobsville JacobtvillcSandstone Sandstone(Middle (MiddleProterozoic) Proterozoic) Yb Bayfield Group (Middle Yb Bayfield Group (MiddleProterozoic) Proterozoic) Yo Yo Ozonto OrontoGroup Group(Middle (MiddleProterozoic) Prokrowic) Lake (Middle Yp Pflge Portage LakVolcanics cVolcinio, (MiddleProtezozoic) Proterozoic) Yu rocks older older Yu Undivided UndividedMiddle Middle Proterozoic Protauwicrocks than thanPortage PortageLake LakeVolcanics Volcanics Ag GnSss Gneiss(Archean) (Archean) Figure 2: 2: (a) Location Location of the the Keweenaw Keweenaw Peninsula native copper district within the North North American American Midcontinent rift system system((from Bomhorst,ininpress). press). The large black area contains from Bornhorst, contains all major major Midcontinent rift areas contain contain minor minor deposits. deposits. (b) (b)Interpretative Interpretativecross-section cross-sectionacross acrossthe the deposits, the two smaller smaller areas deposits, Cannon and and others others (1989) (1989) from from Superior segment segment of the Midcontinent Midcontinent rift system by Cannon Lake Superior A. seismic-reflection seismic-reflection profile Line A. �Geology A fanas B NMddgan ?JWMto,idn Th— NE MI wow AWg nBe ROpuwk, 1100 Figure3: 3: (a) (a) Geology Geology of of the theLake LakeSuperior Superiorsegment segmentof ofthe theMidcontinent Midcontinentrift riftsystem system (from (from Paces Pacesand and Figure igneous rock Miller, U-Pbdates datesaxe arelisted listed below belowabbreviated abbreviatedmajor major igneous rock units: units: Miller, 1993). 1993).High Highprecision precisionU-Pb BBC, BBC,Beaver BeaverBay Bay Complex; Complex;CCD, CCD, Canton CarltonCounty County dikes; dikes; CC, CC, Coldwell ColdwellComplex; Complex;LS, LS,Logan Logansills; sills; LST, LST, Lake Lake Shore ShoreTraps; Traps; MPF, MPF, Mamainse Mamainse Point Point Formation; Formation; MBD, MBD, Marquette-Baraga Marquette-Baragadikes; dikes;MC, MC, NSVG. North Shore Volcanic Mellen Intrusive Complex; MW, Michipicoten Island Formation; Mellen Intrusive Complex; MIF, Michipicoten Island Formation; NSVG, North Shore Volcanic Group; Group; PIll, PRI, Pigeon PigeonRiver Riverintrusives; intrusives;PLV, PLV,Portage PortageLake LakeVolcanics; Volcanics; PMG, PMG, Powder PowderMill MillGroup; Group; for igneous rock PD, PD, Pukaskwa Pukaskwa dikes; dikes; OVG, OVG, Osler Osier Group. Group. (b) (b)Absolute Absoluteage agecorrelation correlation for igneous rock units units of of the the Midcontinent Midcontinent rift rift system system(from (fromPaces Pacesand andMiller, Miller, 1993). 1993). 3 �4 occiogy The last phase of the Midcontinent Midcontinent rift rift system was characterized by a transformation of original original normal faults faults into into reverse reverse faults faults(Fig. (Fig.22and and4). 4). The Keweenaw graben bounding normal Keweenaw Fault is now a lowlow- to to high-angle reverse fault, but originally was a major graben bounding growth fault (Cannon and others, high-angle reverse was bounding growth fault and 1989). The The Keweenaw Keweenaw Fault Fault has has several several kilometers kilometers of of reverse reverse displacement displacement which caused steepening of already tilted strata (due to syn-depositional downwarpage). downwarpage). Faults, fractures, and broad open folds within developed in in response response to to this compressional event (White, (White, rift-filling strata of the Keweenaw Peninsula developed 1968; Butler and Burbank, km of ofred-colored red-colored shallow shallow dipping dippingsandstone sandstone(Jacobsville (Jacobsville Burbank, 1929). 1929). Over 33 km movement along along the the Keweenaw Keweenaw Fault Fault in in a riftSandstone) was deposited during and after active reverse movement flanking basin (Fig. 2 and 4). Cannon Cannonand and others others(1993) (1993) have have determined that high-angle reverse reverse faulting faulting ± 20 Ma, based on reset Rb-Sr biotite ages within older Precambrian basement rocks occurred about 1060 1060 + near the the Michigan-Wisconsin Michigan-Wisconsin border. border. The timing and probable probable cause of this this compressional compressional event is is continental collision continental collision along along the the Grenville Grenville front front (Fig. (Fig. 5) 5) (Cannon, (Cannon, 1994; 1994;Cannon and Hinze, Hinze, 1992; 1992; Hoffman, Hoffman, 1989). This Thisregional regionalcompression compression phase phase may have started as early as 1080 1080 Ma (Cannon, 1994), 1994), and was likely completed by 1040 1040 Ma, Ma, based on thermal models (Price (Price and McDowell, 1993; 1993; Price Price and and others, others, in in review). review). The rocks of of the the Midcontinent Midcontinent rift rift system system were were subsequently subsequently overlain by Paleozoic Paleozoic sedimentary sedimentary with the Michigan basin. An rocks associated associated with Michigan basin. Anisolated isolatedoutlier outlier of ofOrdovician Ordovician limestone limestone at at Limestone Limestone Mountain Mountain and Sherman Sherman Hill Hill occurs occurs about about 35 35 km krn south of Houghton, and is underlain by rift-flanking rift-flanking basin filling Jacobsville Sandstone. Sandstone. The largely atectonic. atectonic. The The Paleozoic Paleozoic geologic geologic processes were largely ThePaleozoic Paleozoic rocks were removed removed by by erosion erosion from from the the Keweenaw Keweenaw Peninsula. Peninsula. The present present day day landscape landscape of of the theKeweenaw Keweenaw Peninsula Peninsula isisstrongly strongly influenced influencedby byPleistocene Pleistocene glaciation, especially by by features features associated associated with with withdrawal withdrawalofof the the Wisconsin Wisconsin ice ice sheet about 15-8 glaciation, especially 15-8 thousand years years ago. ago. Bedrock Stratigraphy of of the the Keweenaw Keweenaw Peninsula volcanic rocks rocks and clastic The bedrock of the the Keweenaw Keweenaw Peninsula is composed composed of subaerial volcanic sedimentary rocks of the Keweenawan Supergroup(Fig. (Fig.6). 6). The volcanic and sedimentary rocks on the Keweenawan Supergroup northwest side of the Keweenaw moderately toward toward Lake Lake Superior (Fig. (Fig. 7) and Keweenaw Peninsula generally dip moderately include the PLV, PLy, Copper Harbor Conglomerate, Nonesuch Shale and the Freda Sandstone (Fig. 8). The Copper Harbor Nonesuch Shale and the Freda Sandstone (Fig. 8). The Jacobsville Sandstone, which which fills fills a rift-filling rift-filling basin basin on on the southeast side of much of the Jacobsville Sandstone, the Keweenaw Keweenaw Peninsula, Fault. The Peninsula, is in fault contact with the PLV along the Keweenaw Keweenaw Fault. The Jacobsville Jacobsville Sandstone Sandstone is younger than the Freda Sandstone and related to to aa late phase phase of of regional regional compression. compression. The bedrock strata are unconformably capped capped by Pleistocene Pleistocene glacial glacial deposits. deposits. Portage Portage Lake LakeVolcanics Volcanics (PLV) (PLV) The Portage Portage Lake Lake Volcanics are composed of a succession of more than 200 200 individual individual subaerial subaerial tholeiitic basaltic basaltic lava lava flows flows with with aa total thicknessofof 2500 2500 to to 5200 tholeiitic total exposed exposed thickness 5200 m on on the the Keweenaw Keweenaw Peninsula, with with the base truncated Peninsula, truncated by the the Keweenaw Keweenaw Fault (Butler (Butler and Burbank, Burbank, 1929; 1929; Huber, Huber, 1975; 1975; volcanic and and subvolcanic subvolcanic rocks rocks comprise compriseless less than than 1 volume % of the White, 1968) (Fig. 9). Rhyolitic volcanic PLV. Dikes PLV. Dikesof ofintermediate intermediatecomposition composition cut cut the the exposed exposed volcanic volcanic pile, but are as as aa whole whole uncommon. uncommon. A diorite stock intrudes the base of the PLV at Mt. Bohemia. Bohemia. Interfiow reddish-colored conglomerate Interflow conglomerateand and sandstone sandstone units total total less less than than 55 volume % of the PLV (Merk and Jirsa, 1982), 1982). but increase in abundance toward the top of the formation. These Theserift-filling rift-filling volcanic volcanic rocks are comparable to the rift zones of East Africa and Iceland (Nicholson, (Nicholson, 1992; 1992; Basaltic Volcanism Study Project, 1981; Chase and Gilmer, 1973; Green, 1977 1977 and 1982; 1982; White 1960 1960 and 1972). Lavas Lavas flowed flowed away away from from feeders feeders along along the the axis axis of of the the rift rift zone. During Duringintervals intervalsof ofquiescence, quiescence,sediments sediments were were transported from the edges toward the center of the �Native CopperMineralization Mineralization __..,.Native Copper Regional Regional Compression Compression Thermal Subsidence Subsidence Thermal Plume-Induced Plume-induced Rifting Rifting / \Reverse Faulting and and Sedimentation Sedimentation Faulting -- P Clastic Sedimentation ÑÑÈ¥Cl Sedimentation Maginatism ~ ~ l wu BBasaltic a s a l tMagmatism ic -— —Is -S Sedmentaty I I I I I I I —— I 1110 1100 1090 1080 1070 1060 1050 1040 Ma Rocks 0 0 Volcanic Rocks Pte-Keweenawan basement cross-sections Midcontinent rift Temporal progression geologic events the North North American mnenciiit mtucununeni n n system. s y ~ ~ i t t Schematic ~i.~ciiiaub . i-WW-ao-uuna of m progression of of major major geologic events of the Figure 4: 4: Temporal cnzstal sag sag filled with volcanic rocks is followed by extension, development of the rift development fromcannon rift from Cannon and others others(1989). (1989). (a) (a) An An initial initial broad crustal faults and eruption of large (b) After After volcanism volcanism which results in normal growth faults large volumes of plume-induced basalt into the central central graben. graben. (b) wanes, thermal subsidence continues with with the the basin basin progressively progressively filled filled with withclastic clasticsediments. sediments. (c) The last last phase phase of of development development of of the the rift is regional compression which which inverts inverts original original graben graben bounding bounding faults faults into intoreverse reversefaults. faults. This results in the uplift of buried rift strata, erosion, and exposure of the PLV in the the Keweenaw Keweenaw Peninsula. Compression Compressiongenerated generatedfaults/fracwres faults/fracturesprovided provided for forupward upward movement movement and focussing of ore fluids into permeable and porous tops of basalt lava flows and interflow sedimentary rocks within the Portage Lake Volcanics (Figure and caption entirely from Bomhorst, Bornhorst, in press). press). I U' ut �6 Geology B 40 --7' $1 D / :Z0 E 0 Figure 5: (a) Map showing showing the the Midcontinent Midcontinent rift system in relationship relationship to the the Grenville Grenville front font tectonic tectonic Compression along along the the Grenville Grenville front was toward (GFTZ) (from (from Cannon. Cannon, 1994). 1994). Compression toward the the zone (GFTZ) (b) Cross sections of the Midcontinent rift rift system system of locations given in (a) northwest. (b) the Midcontinent (a) (from (from northwest. Cannon, 1994). 1994). �88° KEY [MI ri1 ri-w El 3*cthnWeS Iicolxvillc StiaolU Fnda Swddons I n Naiesidt NonesuchMiii. State El 1 Ilaiboc Congicuixale Copper OperHtltot-iloroenIt Porcupine VoiceS Porcupine Val, 1 FI Posge it VMcSa Powder Mill Gicup IYiI Mallen lnhuuive Caipin Major Fault ? 2 Kilometers Figures 7 and 11 (from Bornhorst, 1992). Figure Figure 6: 6: Geologic Geologicmap mapofofthe theKeweenaw Keweenaw Peninsula. Peninsula. The Thebox box shows shows the the location location of of Figures 7 and 11 (from Bomhorst, 1992). I '-a -J �8 Gcology Sandstone Upto 1 m m + Freda Sandstone ujl10360011+ Figure 7: Figure 7: Geologic Geologicmap mapand andstratigraphic stratigraphiccolumn columnof of the thecentral centralKeweenaw Keweenaw Peninsula Peninsula showing attitude of bedding, major faults and fractures, and major native copper deposits (modified from White, Stratigraphic nomenclature nomenclature of of Cannon Cannon and Nicholson 1968; from Bornhorst, Bomhorst, 1992). 1992). Stratigraphic Nicholson (1992). native copper deposits deposits (total (total production production of of refined refined copper) copper) are are marked marked by by numerals: numerals: 1. Major native (1,922 million million kg), kg), 2. 2. Kearsarge Kearsarge flow flow top (1,029 million kg), Calumet and Hecla Conglomerate (1,922 kg), 4. Pewabic flow tops tops (490 million million kg), kg), 5. Osceola flow top 3. Baltic flow top (839 million kg), (263 million million kg), kg), and 6. Isle Royale flow top (155 million million kg). kg). Total Total district district production production equals equals million kg kg of refined refined copper. copper. Location 5,013 million Location given given in Figure Figure 2. �Geology 9 a b FREDA SANDSTONE SANDSTONE Lava unit unit AND COPPER HARBOR HARBOR NONESUCH SHALE NONESUCH SHALE CONGLOMERATE CONGLOMERATE cl Lava unit unit PORTAGE LAKE LAKE LAVA LAVA SERIES SERIES Lava unit unit C b Figure 8: Figure 8:Columnar Columnarstradgraphic stratigraphicsection sectionnorthwest northwestof ofthe theKeweenaw Keweenaw Fault Fault in the Calumet-Mohawk Calumet-Mohawk area and others, others, 1953). 1953). (from White and �10 Geology :Hao conglomerate (No. 17) i —? Ashbed flow %Searsarge flow Wolverine sandstone sandstone (No. 9) PP West conclomerate conglomerate Pewabic West (No. 16) IÑ POC - Old Old Colony Colony sandstone (unnumbered) Greenstone flow Allouez conglomerate conglomerate (No. 15) Portage Lake Lake Volcanics de Houghton Houghton conglomerate conglomerate (No. 14) 14) (No. pi PC Scales Creek flow Iroquois Iroquois flow flow -calumet •Calumet and and Hecla Hecla conglomerate conglomerate (No. 13) 13) Osceola flow Kingston conglomerate conglomerate 12) (No. 12) pcc I 1 Copper city City flow copper &St. St. Louis Louis conglomerate conglomerate (No.6) (No. 6) Figure Figure 88 contInued. continued. �(ISogy Geology 11 11 Hecla Conglomerate at rift. AAcomplex comptexsub-mature sub-mature caliche caliche soil soil profile profile within within the the interfiow interflow Calumet and Hecia the Centennial Mine suggests a temperate temperate or tropical tropical climate (Kalliokoski and Welch, 1985). 1985). Basalts of the PLV are are relatively primitive, magnesia-rich, high-alumina olivine olivine tholeiites tholeiites and and are are (Paces. 1988). 1988). Olivine by primitive olivine typically aphyric (Paces, Olivine tholeiites tholeiites are the most abundant, followed by tholeiites, with lesser amounts of quartz tholeiites, and iron-rich iron-rich olivine olivine tholeiites tholeiites (Table (Table 1). Also Also shown shown in Table 1, 1, are the minor minor amounts amounts of of basaltic basaltic andesite, andesite, andesite, dacite, and rhyolite that interfinger interfinger with with stratigraphywithin withinthe thebasalts basalts isis cyclical cyclical with with minor and the basalts. basalts. Geochemical Geochemical stratigraphy and major major cycles cycles more primitive primitive compositions. compositions. Basaltic magmas were apparently superimposed on an overall trend toward more derived by partial melting of relatively shallow, sub-continental upper mantle, mantle, with younger basalts being primitive, with with little or or no contamination contaminationby by crustal crustalmaterial material(Paces (Pacesand andBell, Bell,1989). 1989). The overall more primitive, compositional trend toward younger, less contaminated primitive primitive magmas magmas can can be be explained by repeated eruption at the rift axis that gradually crust through dike injection and magma eruption gradually modified the continental cmst which magmas must pass, and by progressive crustal thinning, thinning, which which provided provided more more efficient transport which intracrustal chambers. chambers. Model calculations show that major of magmas to the surface without residence in intracmstal geochemical cycles are due to fractional crystallization and replenishment in large magma chambers near cycles and and silicic rocks result from the crust/mantle crust/mantle interface (Paces, (Paces, 1988). 1988). Minor Minor cycles from closed closed system system crystallization in in small small magma magma chambers chamberswithin withinthe thecrust. crust. Eruption in an oxidizing fractional crystallization oxidizing subaerial subaerial ic), that created environment resulted in degassing degassing of of volatiles, volatiles, particularly particularly SO2 SO, (Cornwall, 195 1951~). created aa sulfursulfurdeficient environment which favored the later later deposition deposition of native native copper. copper. Primary magmatic differentiation differentiation has long long been been recognized recognized within within tholeiitic tholeiitic flows flows(Broderick, (Broderick, 1935; Broderick Broderiek and Hohl, 1935; andb). b). For example, the Greenstone 1935; Cornwall, 1951 1951aa and Greenstone Flow, Flow, the the thickest thickest individual flow in the formation (Fig. 9), 9). is chemically stratified due to internal differentiation (Cornwall, 195 ib; Longo, Longo, 1983). The rocks was was also also effected effected by by deuteric deuteric 1951b; Thepresent-day present-day composition composition of the the volcanic volcanic rocks or diagenic alteration of olivine and glass to hydrous minerals, the most important of which is chlorite. chlorite. used 8D 3D and 6'o Livnat and others (1976) used 8"O totoshow showthat thatthe thebasalts basaltshave haveundergone undergoneextensive extensiveisotopic isotopic exchange with low-temperature meteoric waters waters prior priorto tometamorphism/hydrothennal metamorphism/hydrothermalmineralization. mineralization. After After exchange emplacement, the low-pressure emplacement, the volcanic volcanic pile pile was subjected subjected to extensive extensive low-temperature, low-temperature, low-pressure hydrothermal/metamorphicalteration alteration(see (seeFig. Fig.10). 10). The PLV on the Keweenaw Peninsula are a classic hydrothedmetamorphic alteration minerals. minerals. Penetrative deformation did not locality of abundant and widespread low temperature alteration accompany the the metamorphic episode, and and primary primary textures textures are are preserved preserved even even in the most accompany metamorphic episode, most intensely intensely recrystallized areas. areas. has an average avenge total A typical subaerial lava flow has total thickness thickness of about about 10 10to to 20 20 m m(range (rangefrom from11 to 450 m), and consists consists of of aa massive massive (vesicle-free) (vesicle-free) interior capped by a vesicular flow top (Paces, 1988; 1988; White, 1960). A few of of the the thicker thicker flows flows and and interfiow interflow sedimentary sedimentary rocks can be traced traced laterally laterally along along strike for up to about flows have have much much less less continuity continuityininstrike strikedirection. direction. The about 90 kin, km,although although many many flows Scales Creek, Kearsarge, and Greenstone Flows Rows are are the the best best documented documented laterally continuous flows flows (Fig. with the Greenstone Flow able able to be correlated to Isle Royale Royale (Huber, (Huber, 1975; 1975; Longo, Longo, 1982). 1982). The 9), with Greenstone Flow correlated to The 9). uppermost 55 to 20% uppermost 20% of of most most individual individual lava lava flows flows isis vesicular, vesicular, with with between between 55 and and50% 50%vesicles. vesicles. Because flow tops in Because vesicles vesicles are commonly commonly filled filled with secondary secondary minerals, minerals, flow in local local terminology terminology are are amygdaloids, and brecciated flow tops are fragmental amygdaloids. amygdaloids. White White (1968) (1968) estimated estimated that 21% 21% of of the lava flows in the PLV are fragmental amygdaloids amygdaloids(brecciated). (brecciated). The The Copper Copper City City Flow Flow (Fig. (Fig. 9) is the dated 1096 + ± 1.8 My and the Greenstone flow is 1094 2 ± 1.5 My My (Davis and Paces, Paces, 1990). 1990). Based Greenstone Bow (Davis and Based on data, Paces and Bell (1989) inferred that the PLV was erupted empted in about 2-3 million million years, years, which which these data. represents a rate that is is similar similar to to younger younger rift rift and and flood flood basalt basalt sequences. sequences. Interflow sedimentary sedimentary rocks, rocks,with withthicknesses thicknessesfrom fromaafew fewcm cmup up to to about about 40 40 m, m, are important Interflow stratigraphic markers markers in in an otherwise succession of of basalt basalt lava flows. stratigraphic otherwise monotonous monotonous succession flows. In drill drill core, core, �12 Table Table 1: 1: Avenge Average and andrepresentative representative geochemical geochemical data Portage Lake Lake data for for least least altered altered lavas lavas of the Portage Volcanics (from (from Paces, Paces, 1988). 1988). Tholeiites Tholeiiteswere weregrouped groupedby by Ni Nicontent. content. Volcanics POT POT Ni(ppm) 400-300 QT1 QT1 QT2 QT2 300-250 250-200 n=5 n=9 S102 47.82 47.34 48.03 A1203 15.89 9.77 12.44 10.58 15.27 11.82 11.69 10.24 15.32 2.04 0.19 0.98 0.98 0.16 0.16 0.14 0.14 2.10 0.22 Fe01 MgO CaO Na20 K20 'PlO2 P2O3 pzos MnO MnO PPM PPM Ni Ni Cu Cu Zr Zr FeO, FeO, POT POT n=14 1232 9.85 10.16 2.25 0.33 LOT IOT FOT FOT AND AND DAC DAC RHY RHY 200-100 100-15 n=8 n=6 n=l n=1 n=1 48.55 15.12 12.86 9.06 9.65 2.31 0.42 49.94 56.39 68.44 77.89 13.28 14.91 7.78 13.78 9.87 15.17 12.77 1.11 5.52 5.10 3.94 2.27 1.14 1.40 2.34 2.34 0.36 0.36 0.24 0.24 1.13 1.13 135 1.35 1.60 1.60 0.19 0.19 0.15 0.16 0.22 0.22 0.16 0.25 0.25 0.18 0.18 6.64 2.91 1.43 1.83 1.83 1.00 1.00 0.30 0.30 172 172 86 86 54 54 10 10 51 51 231 23 1 73 73 126 126 85 85 101 101 126 126 212 212 55 430 430 326 326 37 37 279 279 78 78 total Fe as as FeO FeO total Fe Primitive Primitive olivine olivinetholeiite tholeiite OT1 OT1 Olivine Olivine tholelite tholeiite 0T2 OT2 Olivine Olivine tholeiite tholeiite LOT IOT Intermediate 'Intermediateolivine olivinetholeiite tholeiite FOT Iron-rich olivine olivine and andquartz quartztholeiites tholeiites FOT Iron-rich AND Andesite AND Andesite DAC Dacite DAC Dacite Rhyolite RHY RHY Rhyolite 4.46 4.74 3.86 0.51 0.51 0.19 0.19 0.08 0.08 77 13 13 573 573 0.17 0.01 3.67 4.28 0.08 0.08 0.01 0.01 0.01 0.01 55 61 61 145 145 �13 .I U 6 I q&, I oa a Meters 3OO 0 300 6OO 9W l8 Upper Limit of Epidote in Flows UpperLimit LimitofofQuartz QoaniininFlows Flows Upper Lower Limit of Prehnite in Flows ExceptionallyThick ThickLava Lavaflows Flows Exceptionally LocationofofMine Minewithin within Location StratigraphicSection Section Siratigiaphic \ "'--d - '.-...* ' ww 3 6 L Figure9:9:Generalized Generalizedstratigraphic stratigraphicsection sectionof ofthe thePortage PortageLake LakeVolcanics Volcanicsfrom fromVictoria VictoriatotoCopper CopperHarbor Harbor Figure Bornhorst, 1992). Location of the (modified (modifiedfrom fromStoiber Stoiberand andDavidson; Davidson;1959, 1959,from from Bomhorst, 1992). Location of themajor majornative native copper areshown showninincontext context with with the themajor majorstratigraphic stratigraphicmarker marker horizons horizons and and with with copper mines mines are stratigraphic stratigraphiclimits limitsof ofassociated associatedamygduleamygdule-and andvein-filling vein-fillingminerals. minerals. See SeeFigure Figure22for forlocation location ofVictoria Victoriaand andCopper CopperHarbor. Hartor. of �14 Geology horizon to to be recognized, even where sedimentary sedimentary material in an underlying basalt flow top allows the horizon Interfiow sedimentary sedimentary rocks rocks are dominated by well-lithified the bed itself itself isis missing missing (White, (White, 1968). 1968). Interflow well-lithified pebble-to-boulder conglomerate with lesser amounts of interbedded sandstone and occasional significant pebble-to-boulder thicknesses of siltstone and shale. shale. Conglomerates Conglomerates are characterized characterized by by sub-rounded-to-angular sub-rounded-to-angular pebbles-to-boulders pebbles-to-boulders Clast lithologies are predominantly felsic, although although in detail, (pebbles typical) in aa sandy (pebbles typical) sandy matrix. matrix. Clast lithologies predominantly felsic, detail, considerable variation variation exists exists within within and and between specific beds, beds, reflecting reflecting diversity diversity in source considerable between specific source terrane, terrane. beds as as alluvial fan fan deposits deposits laid laid down down on essentially White (1968) interprets most interflow sedimentary beds toward the center of the rift basin now under Lake flat-lying lava flows by streams flowing toward Lake Superior. Superior. The sediment interbeds, in all but the uppermost part part of of the PLV, PLy, have been given names and have been given names and are are shown shown 8 and 9). on the maps included included in this this self-guided self-guided geological field trip (Fig. (Fig. 8 9). Copper Rarbor Harbor Conglomerate Conglomerate The Copper Copper Harbor interfingers with the PLV (Fig. Harbor Conglomerate Conglomerate conformably overlies overlies and locally interfingers 6.7, 8). It is aa red-brown red-brown basinward-thickening basinward-thickening wedge of volcanogenic clastic sediments that varies 6, 7, and 8). in thickness from about 100 to 1800 m, in, and fmes fines distally distally and and upsection, upsection, reflecting a waning sediment supply due to progressive erosion erosion of of the source area (Elmore, (Elmore, 1984). Sandstones Sandstones are are lithic lithic graywackes, graywackes, and conglomerates are composed of volcanic conglomerates are composed of volcanic clasts clasts with with aa ratio ratio ofofmafic-to-intermediate mafic-to-intermediate + + siicic silicic composition composition of about about 2:1 21 (Daniels, 1982). 1982). Daniels Daniels(1982) (1982)and and Elmore Elmore(1984) (1984)have have interpreted interpretedthe theCopper Copper Harbor Congloñierate Conglomerate as a fining fining upward upward prograding progradiig alluvial fan complex complex (Fig. (Fig. 10). 10). The prevailing prevailing climate was likely arid with seasonal high rainfall rainfall (Elmore, (Elmore, 1983; 1983; Kalliokoski, Kalliokoski, 1986). 1986). Algal stromatolites, stromatolites, which formed in shallow, medial fan lakes and possibly abandoned channels on the alluvial fan surface, surface, occur in the upper upper part part of of the theCopper CopperHarbor HarborConglomerate Conglomerate (Elmore, (Elmore, 1983). 1983). The middle portion of of the the Copper Copper Harbor Harbor Conglomerate Conglomerate (northeast (northeast of Calumet) Calumet) includes includes aa successionofof lava lava flows flows known known collectively collectivelyasasthe the Lake Lake Shore Shore Traps Traps (Lane, (Lane, 1911) 1911) (Fig. (Fig. 7, 7, see succession thickness of of the the Lake Lake Shore Shore Traps Traps is is 600 m near the tip of stratigraphic column). The maximum exposed thickness Peninsula, where where the unit unit is composed of 31 lava flows and one the Keweenaw Keweenaw Peninsula, one interfiow interflow conglomerate (Diehl and Haig, in press). The composition of the Lake Shore Traps is more variable (Diehl and Haig, The composition of the Lake Shore Traps more variable than the the PLV; PLV; ranging from Fe-rich olivine tholeiites at the base, to to Fe-rich Fe-rich olivine-bearing olivine-bearing tholeiitic basaltic andesites, andesites, to tholeütic tholeiitic andesites andesites at the top (Paces and Bornhorst, 1985). Geochemical stratigraphic relationships can be explained replenishment, and and wall rock explained by aa combination combination of fractional fractional crystallization, parental magma replenishment, assimilation. Davis and Paces (1990) report a U-Pb age on zircon of 1087 ± 1.6 Ma for the Davis and Paces (1990) 1087 + 1.6 for the Lake Lake Shore Shore Traps. Traps. Nonesuch Shale of 215 m, is a succession of siltstones; shales; The Nonesuch Shale, with a maximum thickness of carbonate laminates; laminates; and minor sandstones sandstones with low-to-moderate low-to-moderate amounts amounts of total carbon, carbon, that that overlie overlieand and interfmger with the Copper interfinger Copper Harbor Harbor Conglomerate Conglomerate (Fig. 7 and and 8). 8). Elmore and others (1989) (1989) recognize recognize three genetic genetic assemblages: assemblages: marginal marginal lacustrine lacustrine (sandflat-mudflat (sandflat-mudflat complex), complex), lacustrine lacustrine (progressively (progressively In the lacustrine assemblage, bottom conditions of shallowing perennial perennial lake), lake), and andlacustrine-to-fluvial. lacustrine-to-fluvial. the lake were were anoxic; anoxic, but but became became oxic oxic as as the the lake lakeshallowed. shallowed. Copper sulfides and native copper copper in in economic quantities are hosted by the the Nonesuch Nonesuch Shale Shale at at the the White White Pine Pine Mine Mine (Mauk (Mauk and and others, others,1992). 1992). Freda Sandstone Sandstone The Freda Sandstone Sandstone is is aacyclic cyclicsuccession successionof ofred-brown red-brown ferruginous ferruginoussandstone, sandstone, siltstone, siltstone, and and mudstone overlying and gradational gradational with with the Nonesuch Nonesuch Shale Shale (Fig. (Fig. 77 and 8). B). The The exposed exposed thickness thickness of of �Geology 15 BASINWARD— BASINWARD FINE GRAINED CHANNEL FILL a FLOOD PLAIN DEPOSITS Figure 10: 10:Schematic Schematiccartoon cartoonofofthe thedepositional depositionalenvironment environmentofofthe theCopper CopperHarbor HarborConglomerate Conglomeratewith with Figure coalescing coalescingalluvial alluvialfans, fans,braided braidedstream stream and and flood flood plain plain deposits, deposits,and and shallow shallow ephemeral ephemeral lakes lakes or or abandoned 1982). abandoned stream streamchannels channelscontaining containimg strornatolitic stromatolitic deposits deposits (from (fromDaniels, Daniels. 1982). �16 the Freda Sandstone is greater than than 3700 3700 m m as as the the top top is is not not exposed. exposed. It is is dominantly dominantly fluvial in origin, with greater compositional maturity than the Copper Harbor Conglomerate (Daniels, 1982). Jacobsville Sandstone Sandstone The Jacobsvile Jacobsville Sandstone Sandstone isisaared-to-bleached red-to-bleached white whitecoarse-to-fme-grained coarse-to-fine-grained feldspathic feldspathic and and quartzose sandstone sandstone with varying varying amounts amounts of of siltstone, siltstone,shale, shale,and andconglomerate. conglomerate. It is is in in unconformable unconformable contact with Early Proterozoic and Archean rocks to the east, and is in fault fault contact contact with with the the PLY PLV along along the Keweenaw Fault on the southeast side of the Keweenaw Peninsula. Peninsula. Some Some active active reverse reverse movement movement (Kalliokoski, 1988; 1988; Hedgman, along the fault occurred during deposition of at least part of the formation (Kalliokoski, 1992). completely devoid of igneous igneous rocks and and were were 1992). The Jacobsville strata, over 3,000 m thick, are completely deposited in in a rift flanking basin basin (Kalliokoski, (Kalliokoski, 1982). 1982). The rock has been quarried fluvially deposited quarried extensively and was used as aa building building stone stone in in many many buildings buildings in the the Copper Copper Country Country and throughout throughout the the midwest. midwest. Structure Structureof of the theKeweenaw Keweenaw Peninsula Peninsula The Keweenaw strata dip moderately northwesterly northwesterly toward toward the the center center of of the the rift (Lake Superior), toward the the top top of of the the section section (Fig. (Fig. 7). 7). Angular and their dip angles decrease toward Angular divergence in dip from from the the to the the base base of of the PLV PLY of about 20° 200, is due to syn-depositional top of the Copper Harbor Conglomerate to downwarping before before deposition deposition of of the Nonesuch similar amount amount of of synsyndownwarping Nonesuch Shale (White, (White, 1968). 1968). A similar depositional downwarping downwarpingoccurred occurredduring duringdeposition depositionofofthe the Nonesuch Nonesuch Shale Shale and and uppermost uppermost Freda Freda depositional Sandstone. The Sandstone. Theremaining remaining tilting tilting of of the the beds beds occurred occurred during during reverse reverse movement along the Keweenaw Fault. Bedding 5' in most areas, except near the Keweenaw Keweenaw Fault. Beddingin inthe theJacobsville JacobsvilleSandstone Sandstonedips dips less less than than 50 Fault, where dips steepen to vertical in response to drag along the fault. Fault, Dips of specific horizons horizons tend to steepen 200 20' to 300 30' along strike from northeast to southwest of the major area of native copper deposits, deposits, yielding yielding aa gently gently twisted twistedsurface surface(Fig. (Fig.7;7;White, White,1968). 1968). The strike strike of area northern end end of this twist. bedding changes to a more east-west orientation at the northern anticines, with Broad open synclines and anticlines, with wavelengths wavelengths of around 10 10 km and various various orientations, orientations, dip (Fig. (Fig. 11). 11). Faults with displacement and mineralized tension tension breaks breaks are superimposed on the regional dip Burbank, 1929). 1929). These are common near the crests of anticlines (Butler and Burbank, These post-depositional post-depositional folds are likely related to the Keweenaw Keweenaw Fault Fault (White, (White, 1968). 1968). Faults Faults The Keweenaw Fault is the major major fault fault in in the the Keweenaw Keweenaw Peninsula. Peninsula. It is is aa lowlow- to to high-angle high-angle reverse fault which marks the border of the main rift-filling volcanic and sedimentary rocks with riftwhich the main rift-filling volcanic sedimentary flanking sedimentary sedimentary rocks. The TheKeweenaw KeweenawFault Faultwas was originally originally aa graben-bounding graben-bounding normal normalfault faultthat, that, late late transformed into into aa high-angle high-angle reverse reversefault fault(Cannon (Cannonand andothers, others,1989). 1989). The in the history of the rift, was transformed reverse movement is possibly related to Grenvillian Grenvillian compression (Cannon, 1994). Fault strikes strikes more more or or less less parallel parallelto to the the bedding bedding of of the the PLV PLV (Fig. (Fig. 6 and 7). The Keweenaw Keweenaw Fault 7). Measured dips dips of the fault fault plane plane range range from from 70° 70' to to 20°14 20% and are generally sub-parallel to dips of the PLV (Butler and Burbank, Burbank, 1929). The TheKeweenaw Keweenaw Fault Fault is is not not aa single single fault, fault, and and in in places places branches branches diverge diverge from the the main mainfault fault (Butler (Butler and and Burbank, Burbank, 1929). 1929). Where Whereexposed, exposed,the the Keweenaw Keweenaw Fault Fault isis up to 0.8 km from denoted by up to 4 m m of gouge gouge of of red red clay-to-breccia (Brojanigo, (Brojanigo, 1984). 1984). Basalt Basaltflows flowswithin withinseveral severallOOs 100s of meters of the fault fault are are broken and and brecciated; brecciated; with fractures fractures filled filled with with calcite, calcite, laumontite, laumontite,and and chlorite. chlorite. In mines opened near near the the fault, fault,many many fractures fractures subparallel subparallel to to bedding bedding include include fillings fillings of of native native copper. copper. The St. Louis deposit, the target of aa recent recent evaluation, evaluation, consists of shear-controlled native copper within a fault, about 150 main Keweenaw Fault (it has potential open pit reserves 150 m m from, from, and and subparallel subparallel to, the main �Geology 17 flgure U: and minor folds Figure 11:Faults Faults and minor foldsininthe thecentral centralKeweenaw KeweenawPeninsula Peninsula(modified (modified from White, 1968; from Bornhorst, listed in in Figure Figure 7. 7. Location Major mines and symbols listed Location given in Figure 2. Bomhorst, 1992). Major �18 18 Geology Geology of 8 million tons, grading grading 0.8 0.8 % %copper; copper;Northern Northern Miner, Miner, 1990). 1990). Several reverse Several reverse faults, faults, including the Hancock and Isle Royale Faults, cut the PLV PLV at at higher higher angles angles to bedding of 200 m and bedding than the the Keweenaw Keweenaw Fault, Fault, with with horizontal horizontal displacement of and 50 50m, m,respectively respectively (Butler and Burbank, 1929). High-angle High-angle faults faults striking striking north-to-northwest north-to-northwest are common in the area area of of the the of aa regional regional anticlinal anticlinal (twist) (twist) structure structure(Fig. (Fig.7). 7). Displacement major native copper deposits near the crest of Displacement along these faults varies varies from from none none (tension (tensionfractures) fractures)totoaround around100 100mm(Butler (Butlerand andBurbank, Burbank,1929). 1929). A along copper-- well known known for for masses of native copper weighing number of small tabular vein deposits of native coppermany tons, but not economically important because of the limited dimensions-are dimensions--are localized along these cross fractures just just beneath the thickest thickest basalt basalt flow flow in in the the district, district, the the Greenstone GreenstoneRow. flow, Flow Flowtops topsand and adjacent to these veins (Butler and Burbank, 1929). conglomerates are mineralized adjacent 1929). PLy, numerous Throughout the PLV, numerous faults faults or slips slips exist parallel to the strike and dip dip of of the the beds, beds, but but of displacement displacement isis impossible impossibleto to determine. determine. Such these are often difficult to recognize and the amount of Such common on on the top of of conglomerate beds, beds, which which are are perhaps perhaps aa better faults, denoted by clay gouge, are common slip zone than between basalts (Butler and Burbank, 1929). At At the the Delaware Delaware Mine, Mine, red red clay clayfault faultgouge gouge is aa minimum minimum of of 20 20 cm cmthick thickatatthe thecontact contactbetween betweenthe theAllouez AllouezConglomerate Conglomerate and and the the overlying overlying flow, and Greenstone How, and isis composed composed of of vermiculite vermiculite and and smectite smectite with minor calcite (Schleiss, 1986). 1986). Mineralization and Alteration Alteration of a dormant billion-dollarcopper coppermining miningdistrict. district. From From 1845 to The Peninsula is the location location of dormant billiondollar 1968 the mines of the the Keweenaw Keweenaw native native copper copper district district produced produced about 11 11 billion billion pounds pounds of of refmed refined copper (Weege and Pollack, 1971). Small Smallpersistent persistent quantifies quantities of native silver (less than 0.1%; White, accompany the the native native copper. copper. The 1968) accompany The major major ore ore producing producing horizons horizons are geographically geographically restricted to a 45 km-long belt within the PLV in the Keweenaw Peninsula (Fig. 2 and 9). A A close closerelationship relationshipin inboth both mineralization and and alteration alteration in in the the PLV PLV (Fig. 12 and 13). time and space exists between native copper mineralization 13). The native copper copper deposits deposits of the Keweenaw Peninsula are unique in the geological record, except of the for similar similar occurences occurences on aa much much smaller smaller scale. scale. The The uniqueness uniqueness of the deposit deposit has has confounded confounded conventional wisdom conventional wisdom from from the the beginning beginning of exploration (Krause, (Krause, 1992) 1992) when Douglass Houghton Houghton believed believed that the native copper found in in float float and and vein vein occurences occurences at at the the surface surface reflected reflected supergene supergene alteration alteration of of a sulfide ore. Today, Today,even evenafter afterextensive extensivemining, mining,there thereisisstill stillno no agreement agreementamong among experts expertsabout aboutexactly exactly how the deposits deposits formed. formed. Nature of of Ore Ore Bodies Bodies Native copper copper occurs occurs in in brecciated brecciated and and amygdaloidal amygdaloidal flow tops (58.5% (58.5% of of production), production), interfiow interflow production), and and cross cross vein vein systems systems (about (about 2% 2% of of production) production) (Fig. (Fig. 77 and conglomerate beds (39.5% of production), 9). The Thefour fourlargest largestdeposits depositsin inthe thedistrict districtproduced produced 85% 85% of the S5 billion kg total total district production at an average grade of about 2%. about 2%. Lava Flow Tops Tops Brecciated flow tops (fragmental amygdaloid) Brecciated amygdaloid) are much more common hosts for native native copper copper unbrecciated amygdaloidal amygdaloidal flow tops (White, (White, 1968). 1968). Flow top deposits deposits than unbrecciated between aa deposits are between footwall of barren basalt in the massive interior of the same flow and a hanging wall of barren basalt in the succeeding flow tops tops grade downward and laterally to succeeding flow. flow. Deposits in brecciated amygdaloidal flow to amygdaloidal basalt with low or barren ore grades. Both Both distribution distributionof brecciated brecciated flow flow top top and and contained contained amygdaloidal native copper is Usually native native copper copperisis more more abundant abundantnear nearthe the top top and and bottom bottom of of the is irregular. irregular. Usually �Geology 19 brecciated interval interval of of the flow top, but in in exceptionally exceptionally rich ore shoots, the entire brecciated flow top contains significant significant copper (White, (White, 1968). 1968). In some cases, rich rich ore shoots are located located in tongues tongues of brecciated flow top within massive basalt (Weege and Schillinger, Schillinger, 1962). In In general, general,stope stopeheights heightsare are from 3 to 55 m. m. For Formajor majorore orebodies, bodies,the thestrilce strike length length ranges ranges from 1.5 1.5 to 11 11 kin, km,with with dip dip length length from from to 2.6 2.6 km (Butler and Burbank, Burbanlc,1929; 1929;White, White,1968). 1968). Ore Ore shoots shoots have have aa wide wide variety variety of of shapes, some 1.5 to are elongate elongate with with widths widths of of 30 30 to to 150 m, and lengths from 50 50 m to around are lengths from around 600 m with with aa preferred preferred orientation, preferred orientation orientation (White, (White, 1968). Autointrusive are irregular with no preferred Autointrusive bodies bodies orientation, whereas whereas others others are are in in the the in the flow top can can localize localize ore ore shoots shoots (Weege (Weege and Pollack, 1971), and a number of deposits deposits are tops of, or just below, exceptionally thick flows (Butler (Butter and and Bin-bank, Burbank, 1929; White, White, 1968). White White (1968) (1968) bedding slip in adjacent layers, resulting resulting in more fracturing. suggested that thicker flows concentrate bedding Conglomerates Conglomerates interfiow conglomerate PLY (<5%), they host Although interflow conglomerate beds make up only a small volume of the PLV comparatively large amounts districtproduction). production). Deposits occur as lenticular (-40% ofofdistrict lenticular comparatively amounts of native native copper copper (—40% beds with a hanging wall of massive basalt and a footwall of lava flow top, which commonly hanging of massive footwall lava which commonly contains bands (0.5 (0.5 to to 55 m m thick), and rich rich sand and silt. Usually Usually native native copper copper is is concentrated concentrated along stratigraphic bands bands tend to jump from from one one stratigraphic stratigraphic position to another within the same conglomerate (Weege and others., 1972). Within others., Within the the Kingston Kingston Conglomerate Conglomerate (Fig. (Fig. 9) ore can occur throughout the 12 12 in m bed, bed, but tends to be concentrated in three zones: footwall (43% of the copper), hanging wall (33% of the copper), concentrated three zones: footwall (43% copper), hanging wall (33% of the copper), and intermediate (24% of the the copper) copper) (Weege (Weege and and others, others, 1972). 1972). Hecla Conglomerate Conglomerate (Fig. (Fig. 9). 9), the the largest largest single single native native copper copper Native copper ore in the Calumet and Hecla of 1.9 1.9 billion billion kg kg along alongaa strike strikelength lengthof of4.9 4.9km, kin,and and 2.8 km down-dip), down-dip), lode in the district (production (production of occurs where the bed thickens from less than 11 m to up to to 66 m m(Butler (Butlerand and Burbank, Burbank, 1929; 1929;Weege Weege and and others., 1972). Ore Oregrades gradesininthe theCalumet Calumetand andHecla HeclaConglomerate Conglomeratedecrease decrease significantly significantlywith with depth, depth, as as the width of the conglomerate that is, is, essentially essentially the the same amount conglomerate unit greater than 1.5 m thick increases; that of copper is distributed throughout a greater volume volume of ofconglomerate conglomerate(Butler (Butlerand andBurbank, Burbank,1929). 1929). Highest grades occur where where up-dip up-dip moving moving ore ore fluids fluids were were focused focused by by the tapering, lenticular nature nature of of the grades occur tapering, lenticular conglomerate 1929). The Thehighest highestgrade gradeore orein in the the Calumet Calumetand and Hecla HeclaConglomerate Conglomerate conglomerate (Butler and Burbank, 1929). are filled filled with with tends to be where relatively little little fme fine interstitial interstitial material material exists, or where interstitial interstitial spaces spaces are coarse sand or small pebbles (Weege (Weege and others., 1972). 1972). Localization of native native copper copper ore in beds is dependent Localization of in conglomerate conglomerate beds dependent on on sedimentary sedimentary and and environmental factors, factors, such such as as grain grain size and the the latter controlled the bedrock bedrock paleotopography; paleotopography; the controlled the environmental in the the thickness thickness of of conglomerate. conglomerate. location of paleostreams and variations variations in Veins Although the first first mines mines in in the the district district were developed developed on veins veins which tend to cut cut bedding bedding at at high high slight economic economic importance importance in the district. district. Distribution of native copper in angles, vein deposits are of slight veins lodes,but but tend tend to to be be richest veins is more more erratic erratic than either flow flow top or conglomerate conglomerate lodes, richest at or near near well-oxidized flow tops (Butler and Burbank, Burbank, 1929). Native Native copper copper can can occur occur as asboth both intersections with well-oxidized finely disseminated, and and as masses weighing weighing many many tons tons in in the the same same vein. vein. Row Howtops topsand andconglomerates conglomerates are mineralized adjacent to veins. Veins Veinshosting hostingnative native copper copper also also exist within stratabound stratabound lode deposits deposits (Broderick, (Broderick, 1931). 1931). Ore and and Gangue Gangue Minerals Minerals Native copper copper represents metallic minerals mined orebodies orebodies of Native represents over over 99% 99% of of the metallic minerals in in the the mined of the �20 20 Geology Keweenaw 0.1%; White, White, 1968) accompany Keweenaw Peninsula. Persistent Persistentsmall smallquantities quantitiesof of native native silver silver (less than 0.1%; 1968) kcompany the native copper. Most Mostofofthe thenative nativecopper coppercarries carriesaasmall smallamount amountof of arsenic arsenicin in solid solidsolution solution(less (lessthan than arsenic, typically less than 0.2%; 0.2%; Broderick, Broderick, 1929). Copper-nickel 0.5% arsenic in total copper + silver silver ++ arsenic, Copper-nickel arsenides, and Davidson, Davidson, 1959), occur in veins that arsenides, particularly particularly common in the Kearsarge deposit (Stoiber and are paragenetically late (Butler and and Burbank, Burbank, 1929; 1929; Moore, Moore, 1971). 1971). Within paragenetically late Within the the native native copper copper deposits, deposits, late, occurs as small veins veins cutting flow flow top deposits, and as coatings on chalcocite, also paragenetically late, joints with with calcite calcitein in conglomerate conglomeratedeposits deposits (White, (White, 1968). 1968). Several Several copper sulfide sulfide deposits deposits occur in flow tops near the base of the PLV within the Keweenaw Keweenaw Peninsula in association Peninsula association with mafic mafic intrusive intrusive rocks rocks (Broderick (Broderick and others., others., 1946; 1946; Robertson, Robertson, 1975). 1975). Chalcocite is the principal Chalcocite principal ore mineral with rare, paragenetically late, native copper (Woodruff and others., Wilkin and and Bornhorst, Bornhorst, unpublished unpublisheddata). data). One deposit is now the target 1992; Wilkin target of of possible possible new new mining mining activity, with probable probable reserves of of 3.1 3.1 million million tons, tons, grading grading 2.95% 2.95%copper copper(Northern (NorthernMiner, Miner,1990). 1990). The relationship between between these these copper copper sulfide sulfide deposits deposits and and the the native native copper copper deposits deposits is is conjecture, conjecture, and and is relationship more at at Stop El. El. discussed more and interflow interflow sedimentary sedimentary rocks were were altered altered pervasively pervasively by hydrothermal hydrothermal fluids, fluids, Flow tops and producing low-temperature low-temperature metamorphic metamorphicmineral mineralassemblages assemblages(Fig. (Fig.12 12and and13). 13). The The minerals occur as amygdule and vein fiffings, and as whole rock rock replacements replacements in in the the most most permeable penneable units. Intensity and fillings, and degree of alteration alteration varies as as aa function function of of position position within within individual individual flows, flows, position position in in the the volcanic volcanicpile, pile, and proximity to cross-cutting cross-cutting fractures. While Whileflow flowtops topsare areintensively intensively altered, altered,massive massive interiors interiorsof oflava lava flows are much less less altered, altered, and hydrothermal alteration is limited to the vicinity of faults faults and fractures. fractures. Some original igneous igneous minerals minerals are present in the massive interiors of flows, but secondary secondary minerals exist in all flows regardless of their thickness (Scofield, (Scofield, 1976; Paces, Paces, 1988). 1988). The The geochemical geochemical composition of many flow interiors interiors are are only slightly modified modified by secondary hydrothermal processes, and and represent represent original original igneous composition. of lava composition. Thus, Thus, the interiors interiors of lava flows flows acted acted as as aquicludes aquicludes with with respect respect to to the the paleohydrothermal system. paleohydrothermal A close close relationship relationship in in time time exists exists between between native native copper copper mineralization mineralization and and secondary secondaryminerals minerals formed during during alteration alteration of the the PLY, PLV, although although individual individual deposits deposits may not exactly exactly follow follow the the district-wide district-wide paragenesis (Fig. 12). 12). Metamorphic Metamorphiczoning zoningbased based on on distribution distribution of amygdule-filling amygdule-filling minerals, equivalent equivalent to zeolite and prehnite-pumpellyite prehnite-pumpellyite facies, varies vertically (Fig. 13) and laterally laterally (Fig. 9) within the PLV. PLY. through most of the stratigraphic On the tip of of the the Keweenaw Keweenaw Peninsula Peninsula (Fig. 6), 6). zeolite minerals exist through section with epidote appearing only in the basal basal 750 750 m m (Cornwall, (Cornwall, 1955; 1955;Cornwall Cornwall and and White, White, 1955), 1955), into the the PLV. PLY. The indicating lower metamorphic grades extend deeper into The major major native native copper copper mines mines are areall all within a section within section containing containing epidote, and near the the appearance appearance of quartz quartz (Fig. (Fig. 9; 9; Stoiber Stoiberand andDavidson, Davidson, 1959). AAdetailed 1959). detailedstudy study by byStoiber Stoiberand andDavidson Davidson (1959) (1959) of of the theKearsarge Kearsarge deposit deposit shows shows that that native native mineral zones zones although although aa general correlation copper is much more irregularly distributed than secondary mineral exists between between grade and the the variation variation of of quartz quartz and and microcline microcline (see (see Stop Stop 13). 13). Broderick (1929) and PLY dip shallowly toward Livnat (1983) showed that the metamorphic mineral zones (isograds) within the PLV Lake Superior, compared to the volcanic volcanic strata strata which which dip moderately, moderately, implying that the volcanic volcanic units units were tilted prior to to metamorphism metamorphism and and associated associated native native copper copper mineralization. mineralization. Age Constraints for for Native Native Copper Copper Deposits Deposits Native copper found in both both stratabound stratabound lodes and in veins veins is is accompanied accompanied by the the same samegangue gangue minerals minerals (Butler and and Burbank, Burbank, 1929; 1929;Broderick, Broderick, 1931; 1931;White, White,1968), 1968).indicating indicatingcontemporaneous contemporaneous epigenetic deposition. Native Nativecopper coppermineralization mineralization isisyounger youngerthan than the theCopper CopperHarbor HarborConglomerate, Conglomerate, calcite and and native native copper. copper. White (1968) interpreted the age of native native copper copper which hosts rare veins of calcite mineralization as after after deposition deposition of of much much or or all of mineralization as of the the Freda Freda Sandstone, Sandstone, and and has has an anundetermined undetermined �Geology A Flow Top Top Deposits Deposits and and Veins Veins Flow K-Feldspar — Pu—I— Coppa Datolile Silver Qunt Saicite Ctm Anaild Sulphidcs (npaSe) Launiontite Suiphatca (bathe, anhydrite, gypsum r- r e- nfln — 21 ConglomerateDeposits Deposits Ccmglomerate —- - LIS TitHe -p — ——p e -a - Relative RelativeAge Age Abundant AbuiKtuit RelativeAge Age Relative Not Notabqmdat dnnitt B widespread Widespread Minerals Minerals albite, albite, calcite, calcite, chlorite, chlorite, epidote, hematite, laumontite, laumontite, native native copper, copper, prehnite, prehnite, puxapellyite, pumpellyite, quartz, quartz, sphene sphene Locally Locally Important Important Minerals Minerals anaicixne, analcime, ankerite, ankerite, arsenides, arsenides, chabazite, chabazite, chalcedony, chalcedony, clay clay minerals, minerals, ilver, natrolite, datolite, datolite, heulandite, heulandite, native native ssilver, natrolite, orthoclase/microcline, orthoclase/microcline, thompsoni t e sulfates, suif ides, sericite, sericite, sulfates, sulfides, thompsonite Rare Rare Minerals Minerals apophyllite, apophyllite, atacamite, atacamite, bowlingite, bowlingite, brucite, brucite, chlorastrolite, chlorastrolite, chrysocolla, chrysocolla, cuprite, cuprite, faujasite, faujasite, fluorite, fluorite, powellite, powellite, serpentine, serpentine, stilbite, tenorite, tourmaline, whitneyite, wairakiite stilbite, tenorite, tourmaline, whitneyite, wairakiite secondary minerals Figure Figure12: 12: (a) (a) Paragenesis of secondary minerals inin flow flow top top deposits deposits and and veins, veins, and and conglomerate conglomerate List of of secondary secondary deposits fromRuder Butlerand andBurbank, Burbank,1929; 1929;from fromBornhorst, Bornhorst,1992). 1992). (b) (b) List deposits (modified (modifiedfrom minerals fromButler Butler minerals within within the the Portage Portage Lake Lake Volcanics Volcanics of of the theKeweenaw KeweenawPeninsula Peninsula(compiled (compiledfrom and and Burbank, Burbank, 1929; 1929; Stoiber Stoiberand and Davidson, Davidson, 1959; 1959;Jolly Jolly and and Smith, Smith,1972). 1972). �22 22 Geology Geology Calumet CalumetSection Section MetamorphicZones and Temperature Estimates ofLivnat(1983) of Livnat (1983) Top of Portage Lake Volcanica A I Native Copper M i i NativeCoppaMifles % of District %ofDislrict IWQoincy 38%C&H 38%C&B 5% Osceola 0sceola 5% 21%KeÈrs* % Kearsarge 21 3%IsleRoyç 3%IsleR I -- I I I i B ----- Epidote &quartz present 1 I I I I __2600C a c Dppearance ofof common isa appearance common . IauntonÜte laumontite Cc -awe Disappearance Disappearanceofofferrian f&mI preimite I I 17% Baltic 17%Baltic KeweenawFault Fault Kewetuw -- - I D IM .c32SOCNOadiflOlitt Figure Figure13: 13:Distribution Distributionofofamygduleamygdule-and andvein-filling vein-fillingminerals mineralsininthe theCalumet Calumetcross crosssection sectionof ofthe thePLV PLV (compiled 1983;Stoiber Stoiberand andDavidson, Davidson,1959; 1959;from fromBornhorst, Bornhoist,1992). 1992). Vertical Vertical (compiled from from Livnat, 1983; distribution distributionof ofsecondary secondaryminerals mineralsisissimilar similarthroughout throughoutthe thearea areaof ofthe themajor majornative nativecopper coppermines mines listed listedon onthe thevertical verticalstratigraphic stratipphic column column(see (see Fig. Fig.77and and99for formine minelocations). locations). �23 minor amounts amounts of of native copper at the relationship with respect to the Jacobsville Jacobsville Sandstone--although Sandstone-although minor the bottom of aa 1,100 bottom 1,100mmdrill drillhole holewithin withinthe theJacobsville JacobsvilleSandstone Sandstone near near Rice RiceLake Lake(Weege, (Weege,personal personal communication) suggests suggeststhat that mineralization mineralizationpost postdates datesdeposition depositionofofatat least least some some of the Jacobsville communication) Jacobsville (1929, 1931), Butler and Burbank (1929), Broderick and and others (1946), Sandstone. Sandstone. Broderick (1929, (1929). Broderick (1946). White White (1968), Weege and others (1972) and other geologists, pointed out the close connection between (1968). geologists, have pointed mineralization and and deformation deformationrelated relatedtotothe theKeweenaw KeweenawFault. Fault. At the White Pine Mine, native copper mineralization Mauk and evidence for two distinct episodes of copper copper mineralization: and others others (1992 (1992 and this volume) show evidence mineralization: 1) main stage copper copper sulfides sulfides and and subordinate subordinate native copper copper formed during diagenesis of of the the Nonesuch Nonesuch Shale, and 2) second stage stage native copper copper and and subordinate subordinatecopper copper sulfide sulfide synchronous synchronouswith with thrust thrust faulting. faulting. are interpreted as contemporaneous withthe the Keweenaw KeweenawFault, Fault, leading leading to to the interpreted as contemporaneous with the thrust faults faults are The thrust interpretation by by Mauk Mauk and and others (1992) (1992) that that second second stage stage copper copper at at White White Pine Pine Mine Mine is is related to the interpretation Peninsula. Based native copper deposits of the Keweenaw Peninsula. Based on on field field relations relations native native copper copper mineralization mineralization is younger than deposition of rift-filling volcanic and sedimentary rocks, and likely synchronous deposition rift-filling ahd sedimentary likely synchronous with with reverse faulting and earliest deposition deposition of of rift-flanking rift-flanking sedimentary sedimentary rocks. Bornhorst and others Bornhorst others (1988) (1988) used used the theRb-Sr Rb-Srmethod methodon onamygdule-fihling amygdule-filling microcline; microcline; calcite; calcite; epidote; and and chlorite to determine determine the the absolute absolute age age of of mineralization mineralizationas asbetween between1060 1060and and 1047 1047Ma Ma (+ (± epidote; — 20 Ma), which is similar similar to an an approximate approximate age age of Keweenaw Keweenaw reverse reverse faulting faulting of 1060 1060Ma Ma (Cannon (Cannonand and and radiometric radiometric dating dating suggest suggest an an age of native others., 1993). 1993). Thus, both field relationships and native copper copper mineralization of about 1060 1060 to 1050 1050 Ma, some some 30 30 Ma Ma after after rift-filling rift-filling volcanism, volcanism, but but contemporaneous contemporaneous with reverse faulting along the Keweenaw Fault (Fig. 4). faulting along the Keweenaw Fault (Fig. 4). - Genetic Model For Native Native Copper Copper Deposits Deposits Genetic models for the the native native copper copper deposits deposits of of the the Keweenaw Keweenaw Peninsula Peninsula call call upon upon epigenetic epigenetic ore-bearing fluids related to either either magmatic (Broderick, 1929; Butler and Burbank, 1929; 1929; Broderick and others, 1946) or burial burial metamorphic metamorphic processes (Stoiber and Davidson, 1959; White, 1968; 1968; Jolly, 1974). 1974). does not not exist exist against against either either hypothesis. hypothesis. The localization of native copper deposits Conclusive evidence does in the Keweenaw Keweenaw Peninsula may may favor favor aa magmatic magmatic hypothesis, hypothesis, but but the the widespread widespread distribution distribution of of native native regional ore ore fluids fluids related related to burial metamorphic copper in Keweenawan basalts argues for widespread regional processes. The Theage ageof of mineralization mineralizationsome some30 30Ma Maafter after most most Keweenawan Keweenawanmagmatic magmatic activity activity also alsosuggests suggests for ore ore genesis. genesis. Stable isotope data are consistent with burial direct magmatic processes are not important for metamorphism, but but cannot rule out Although evidence evidence is not metamorphism, out magmatic magmatic hypotheses hypotheses (Livnat, Gvnat, 1983). 1983). Although not cumulative arguments arguments favor favor formation formationof of ore ore fluids fluids during during burial burial metamorphism metamorphism of of the rift conclusive, cumulative rocks. rocks. The source of native copper is possibly possibly the rift-filling rift-filling basalts. basalts. Dissolution of only a few ppm ppm of of copper from the over 18 18 km km of of basalt basalt in in the therift riftduring duringburial burial metamorphism metamorphism yields yields more more than than adequate adequate amounts of copper (White, 1968). Copper Coppermay may have have been been initially initially tied up in in Fe-Ti Fe-Ti oxides oxides (Cornwall (Cornwall and Rose, 1957) 1957) with subsequent subsequent oxidation oxidation releasing copper during burial metamorphism of the lava flows flows in the deep parts of the volcanic pile within the rift (Jolly, 1974). In this way, burial metamorphism 1974). In this way, burial metamorphismof ofriftriftfilling basalts at temperatures of 300°C 300° to 500°C 500° could result result in the the generation generation of of aa Cu-rich Cu-rich ore orefluid. fluid. Stable isotope data on on secondary secondary minerals minerals indicate indicate that that burial-derived burial-derived fluids fluids probably probably were were modified modified evaporated intermontane meteoric water (Kelly, personal communication; Livnat, 1983). Cornwall that the ore fluids Cornwall (1956) suggested suggested that fluids had had much much lower lower sulfur sulfurcontent contentthan thanmagmatic magmatic hydrothermal fluids, as copper sulfides are uncommon. uncommon. Degassing Degassing of sulfur sulfur from from subaerial subaerial erupted erupted lava lava flows would result in low low residual residual sulfur sulhr contents, and burial metamorphism of this low sulfur source rock would yield a low low sulfur sulfur ore ore fluid. fluid. fluid Fluid inclusion inclusion studies studies suggest suggest the ore ore fluids fluids were were Ca-Na Ca-Na brines brines (5 (5 to 10 10 weight weight % % salinity) salinity) (Livnat, &inat, 1983). 1983). Copper Copperwas was likely likely transported transported as aa chloride chloride complex, complex, and its its �24 oeoiogy abundance in the ore fluids could have been as high as 2,000 ppm, based on assumed amounts of copper and water derived from metamorphism and thermodynamic thermodynamic solubility solubiity of copper (Jolly, 1974). However, However, fluids extracted from inclusions in alteration contained less than than about 200 ppm alteration minerals minerals contained ppm Cu Cu (Livnat, (Livnat, 1983). 1983). Temperature Temperature history models (McDowell and others, 1992; 1992; Price and and McDowell, McDoweU, 1993; 1993;Price Priceand and others, in review) predict that the PLV in the center of the rift was likely dehydrated as as much much as 10 10 to m.y. prior prior to ore deposition. migrated toward toward the the edge edge of of the filled 15 m.y. deposition. These These fluids fluids could could have slowly migrated rift, where millions of years after after their generation they were available to be tapped and focused into orebearing horizons. Alternatively, Alternatively,temperatures temperatures of buried buried basalt on on the the flanks flanks of of the therift riftwere weresufficiently sufficiently high to have been the source of ore-bearing fluids. fluids. A A sufficient sufficient mass mass of copper exists exists in basalt strata strata on the flanks of the rift, present ( 4 0 ) km beneath the present rift, thus thus the ore ore fluids fluids need to be tapped only some few (<10) ore horizons. horizons. The fundamental fundamental control on the movement movement of ore fluids fluids to to sites sitesof ofdeposition depositionisispermeability. permeability. Primary permeability includes brecciated and vesicular lava flow tops tops and and interfiow interflow sedimentary sedimentaryrocks rocks separated by variably variably impermeable impermeable massive massive flow flow interiors. interiors. Thus, the vertical section consisted of of thin thin by thin aquicludes. aquifers separated by aquicludes. Overlapping Overlapping of successive successive lava flows and minor minor unconformities suggests that simple up-dip movement of of ore ore fluids fluids was was not not likely. lIkely. Secondary Secondary permeability provided by the network of faults/fractures faults/fracturesproduced produced during during late late compression compression (reverse (reverse movement movement along along the the Keweenaw Keweenaw of ore fluids. Since the turn turn of Fault) integrated the plumbing system, allowing for upward upward movement of the century, it was was clear clear that that faults faults played played a major major role in in localization localization of many of the the native native copper copper minerals indicate indicate that that faults and fractures deposits. Fault brecciated deposits. brecciated and re-cemented re-cemented alteration alteration minerals fractures were were principal pathways for ore ore fluids, fluids, and and that that faulting faulting was was synchronous synchronous with with mineralization. mineralization. For the Baltic (20%of of district districtproduction), production), Broderick Broderick (1931) (1931) Baltic and and Isle Isle Royale Royale flow flow top top deposits deposits (20% that ore fluids moved upward along faults until until intersecting intersecting with with the the permeable permeable flow flow tops tops at concluded that Mass, and Adventure the ore deposition stratigraphic interval. A A similar similar situation situation exists for the Caledonia, Mass, Mines near the town of Mass Mass (Fig. (Fig. 9). 9). There, native copper is hosted in flow flow tops tops in in close closeassociation association with abundant faults and fractures (Bornhorst (Bornhorst and and Whiteman, Whiteman, 1992). 1992). Faulting Faulting occurred occurred before, during, and after deposition of native copper. Many Many faults faults host host native copper, some even, with quite high grades. interiors of of lava flows in areas where they they are cut by faults. Native copper occurs in the massive interiors faults. For mines near Mass, it is likely that faults were the principal pathways for transport of ore fluids to the flow likely flow tops. The Allouez Gap Fault Fault (Fig. (Fig. 7) 7) cuts cuts the thevolcanic volcanic succession succession and and connects connects with with the theKeweenaw Keweenaw Fault. Almost Almostevery everypermeable permeable horizon horizon near near the the Allouez Allouez Gap Fault contains above average amounts of there so many many mineralized mineralizedhorizons. horizons. R.J. R.J. Weege, former native copper; nowhere else in the district, are there company report that the Allouez chief geologist of C & &H H Mining Mining Company, Company, suggested in an unpublished company Allouez Gap Fault was the single single most most important important fluid pathway in the district, perhaps linking 60% of the the district district production. The production. Thelargest largestflow flow top topdeposit depositin inthe thedistrict districtoccurs occurswhere where the the Allouez Allouez Gap GapFault Fault bisects bisects the the of the Kearsarge Kearsarge How Flow along along its its 55 55 km km strike strike length length(see (seeStop Stop 13). 13). Higher grades and thickest segment of occui northeast of the fault, where fractures parallel parallel to to the the fault faultare aremore moreabundant. abundant. The small production occur Kingston Kingston deposit (9 million kg of of copper) copper) is is also also bisected bisected by by the the Allouez Allouez Gap Gap Fault. Fault. Ore grade and and outward from the fault, degree of alteration lead Weege and others (1972) to conclude that fluids moved outward TheHoughton Houghtonand andAllouez AllouezConglomerate Conglomerate deposits deposits (50 (50 million million kg kg of of copper) copper) are are near near rather than up-dip. The the Allouez Gap Fault, Fault, with with local local faults faults and and the the conglomerates conglomerates themselves themselves connected directly with the Allouez Gap Fault. The million kg kg of of copper) is Thegiant giantCalumet Calumetand and Hecla HeclaConglomerate Conglomerate deposit (1900 million a few The axis axis of the ore body few km km west west of of the the Allouez Allouez Gap Gap Fault. Fault. The body trends at depth toward the fault fault �ooiogy 25 (Weege and others, 1972) 1972) which is consistent with ore fluid movement up the fault and then up-dip along the penneable conglomerate. permeable conglomerate. The Thedeposit deposithas hasaahigher highergrade gradeup-dip, up-dip,where wherehydrothermal hydrothermal fluids fluidswere were focused by lateral lateral (strike (strike direction) direction) thinning thinning of of the the permeable permeable conglomerate conglomerate(Butler (Butler and and Burbank, Burbank,1929). 1929). Within the Allouez Allouez Gap Gap Fault Fault zone, zone, brecciated brecciated and and recemented recemented native native copper copper and and alteration alteration minerals minerals (Butler and Burbank, indicate that that movement movement along along the the fault fault occurred occurred before, before, during, during, and and after (Butler Burbank, 1929) indicate deposition of native native copper. copper. Northeast of the major major native copper district, small vein deposits are localized localized just beneath beneath the the thickest basalt flow in in the the district, district, the theGreenstone Greenstone Flow, Flow, with with permeable permeable flow flow tops tops and and conglomerates conglomerates to these these veins. veins. AA reasonable mineralized adjacent to reasonable model model is is one one in in which which hydrothermal hydrothermal fluids fluids moved moved up up along cross fractures until stopped by the impermeable massive interior interior of of the Greenstone Flow. Broderick and others others (1946) noted that the Keweenaw Fault would make an ideal conduit conduit for for ore ore fluids. Although Althoughno nodeposits depositsare arelocated locatedalong alongthe the main main fault fault itself, itself, fluid fluid movement movement along along the the Keweenaw Keweenaw Fault and adjacent rocks is indicated by highly altered rocks and by several small native copper deposits deposits along nearby subparallel subparallel branch faults. faults. It is is likely likely that the Keweenaw Keweenaw Fault was an important factor in the paleohydrologic system with intersecting intersecting subsidiary faults faults or or permeable permeable stratigraphic stratigraphic horizons, horizons, such such as flow top or conglomerates, providing secondary secondary conduits. conduits. Like the Keweenaw Fault, in other districts main faults are often not or or little little mineralized (Sibson, (Sibson, 1987). NW-SE NW-SE directed directedregional regionalcompression compression(Fig. (Fig. under tight tight compression, compression, 2 and 5) 5) could could have have caused caused the the generally generally NE-trending NE-trending Keweenaw Fault to be under whereas perpendicular structures would be under dilation stress and more more open open for forfluid fluidmovement. movement. The intersection of major subsidiary faults with locally locally thick thick permeable horizons horizons is is a key factor in localization localization of ore. ore. Faults may have have behaved behaved as as valves valves and and become become highly highly permeable permeable pathways pathways immediately postfailure postfailure (Sibson (Sibson and and others., others., 1988; Sibson, Sibson, 1990) 1990) with with periodic periodic upward upward movement movement of of immediately hotter, sulfur-poor, burial metamorphic metamorphic fluids into into permeable permeable horizons. horizons. Fluid flow in small small fractures fractures of lava flows (e.g., Turcotte, 1989) may have have also been an cutting the massive massive interior interior of (e.g., Deloule Deloule and Turcotte, 1989) may an mechanism for for the the upward transport of of ore fluids. White important mechanism upward transport White (1968) (1968) suggested suggested that that permeability permeability than primary primarypermeability permeabilityfor forthe themovement movementofofore orefluids. fluids. At At the due to fracturing was more important than horizon of ore deposition, deposition, fluid pressures pressures were likely greater than hydrostatic, but less than lithostatic (e.g., (e.g., Powley, 1990). The Thepressure pressure was was dependent dependent on the height of rocks above the horizon of ore deposition ("mountains' maintainedby bycompressional compressionaluplift uplift rather ratherthan than stratigraphic stratigraphicdepth. depth. ("mountains" in in section sectionccininFig. Fig.4)4)maintained Mixing of ore ore fluids fluids channeled channeled upward upward through through faults and fractures fractures with with cooler, cooler, more more dilute dilute resident fluids may have been an an important important mechanism mechanism for precipitation precipitation of native copper. copper. Oxygen Oxygen isotope isotope for less data on quartz, quartz. data for calcite shows about a 10 10 per mu mil spread at a given stratigraphic depth, and for about 5 per SI the spread is about mil(Livnat, &mat, 1983). 1983).This Thisspread spreadcould couldbe beinterpreted interpreted as as due due to to fluid fluid mixing. mixing. deposition resulted resulted from from mixing mixing of of Wells (1925) and Richards and Spooner (1986) suggest that copper deposition precipitation of of native native copper copper fluids of different salinities and sources. The The needed reducing conditions for precipitation seems to rule out mixing of ore fluids with with oxidized oxidized groundwaters. groundwaters. The oxidation of magnetite to hematite and the prograde prograde metamorphic metamorphic reaction reaction of pumpellyite pumpellyite to epidote occurred along along with native native copper copper deposition, and also could have provided reducing conditions needed for the deposition of native copper (Jolly, 1974). Reduction Reductionof of the theore orefluids fluidsduring during deposition deposition of native native copper would have yielded copper sulfides if sulfur was present in the fluids, confirming the low sulfur character of ore fluids. Overall, a combination of fluid mixing; fluid-rock interaction; and cooling may may have caused precipitation of native copper. copper. The onset phase late late in in the the history of the rift onset of aa compressional compressional phase history of rift provided provided a network network of faults/fractures that integrated integrated the the plumbing plumbing system system and and allowed allowed for for easier easier and more faults/fractures that more rapid rapid upward upward movement of fluids. Major Majorfaults faultswere were principal principal pathways for focussing of ore fluids where they intersect �26 Geology Midcontinent rift rift system system does does not not seem unusual unusual in either igneous locally thick permeable permeable strata. strata. The Midcontinent igneous activity or in geothermal gradient, gradient, as as compared compared to to other otherrifts rifts(Hutchinson (Hutchinsonand andothers, others,1990). 1990). Low grade burial metamorphism/alteration throughout the world, yet native copper metamorphismlalterationof mafic mafic volcanics is observed throughout copper ore ore deposits of the Keweenaw Peninsula are are unique. unique. Major Major compressional faulting late in the history of the Midcontinent distinguishes it from other flood flood basalt basalt provinces. provinces. The superposition deformation Midcontinent rift distinguishes superposition of this deformation event on temporally temporally available available "burial" "burial" metamorphic fluids being generated via the thermal pulse pulse related related in the genetic model of the native copper deposits. to rifting, may have provided the critical component in The thick section of basalts in the the rift rift and and aahigh highgeothermal geothermal gradient gradient may have have also also played played aa role role (Nicholson and others, in the genesis The (Nicholson and others, 1992), 1992). albeit albeit secondary, secondary, in genesis of of the the native native copper copperdeposits. deposits. The localization localization of large large native copper copper deposits deposits within within the the Keweenaw Keweenaw Peninsula may may be be controlled controlledby by several several factors, including favorable geometric geometric orientation orientationwithin withinthe theregional regionalcompression compressionstress stressfield; field; abundant faults, fractures, and broad open folds as compared with with other areas areas of of the rift; and coincidence of flow tops and conglomerates, conglomerates,which which are are thickest thickest in in the Keweenaw Keweenaw Peninsula, Peninsula, with with abundant abundant faults faultsand and fractures. fractures. Since much of the the Midcontinent Midcontinent rift system system is buried, buried, perhaps perhaps another area of native native copper copper deposits deposits remains hidden. Despite deposits of the Keweenaw Keweenaw Peninsula, Despite over over 100 100years years of research research on the native copper copper deposits Peninsula, there there remains many unanswered questions, questions, from from aa small small to to a large scale. many unanswered scale. While our ow understanding understanding of this this district district slowly slowly improves, improves, the the exact exact reasons reasons for for the large native copper deposits in the Keweenaw Peninsula Peninsula will likely remain speculative speculative for for years years to to come. come. GLACIAL GEOLOGY GEOLOGY Over the past two million Peninsula has has been been effected effected by by four stages of million years the Keweenaw Keweenaw Peninsula continental glaciation. Each Eachsubsequent subsequentglacial glacialadvance advancesignificantly significantly modified modified or or obliterated obliterated the the effects effects of previous previous glaciations glaciations except except for major bedrock basins (Warren, 1981). Glacial Glacial features features of the Keweenaw Keweenaw Peninsula are related to advance and retreat of of glaciers glaciers of of the the Wisconsin Wisconsin Stage Stage (the (the most most recent recent stage stage of of glaciation). glaciation). During During the maximum maximum extent extent of Wisconsin glaciation, an ice sheet extended as far south south as as central central Illinois and Ohio (Fig. 14). The covered by by up up to to 3000 m m of of ice during Theentire entireKeweenaw Keweenaw Peninsula was covered the maximum glaciation glaciation (Sugden, (Sugden, 1977). 1977). The source source area area of of the the ice sheet sheet was was in in the vicinity of James Bay (Fig. 14). The when the ice sheet TheKeweenaw Keweenaw Peninsula Peninsula tended to deflect the flow of ice, especially when was thinner during advance advance and retreat, and caused two major lobes of the ice sheet (Warren, 1981) 1981) (Fig. (Pig. 15). The TheKeweenaw Keweenaw Bay Bay lobe lobe made made the the final final advance and retreat of the ice sheet about 13,000 years ago. An end moraine (a linear mound of till) marks the the llimit of this this lobe lobe (Fig. (Fig. 16). The i t of The Keweenaw Keweenaw Bay lobe lobe moved from east to west in the vicinity of Houghton, whereas farther further south, it moved southward (Warren, 1981). 1981). As the ice ice sheet sheet retreated retreated (melted back), the very large volumes of water filled the Lake Superior basin, turning it into a glacial features allows allows various various stages stages of of glacial glacial lakes within within the glacial lake. lake. Shoreline features Lake Superior Superior basin to be recognized. The TheDuluth DuluthGlacial Glacial Lake Lake was was the the longest longest lived lived of of the the glacial glacial lakes lakes (Regis, 1993) Bay Lobe Lobe (Fig. (Fig. 17). There 1993) and was bordered on the east by the Keweenaw Keweenaw Bay Thereare arenumerous numerous post-Duluth Superior basin, with 10 stages recognized recognized in the the western western Lake Lake post-Duluth Glacial Glacial Lake Lake Stages Stages of the Lake Superior Superior basin (Table 2). The levels of the glacial lakes depended on the position of the ice front, outlets, The levels of the glacial lakes and crustal rebound (Regis, 1993). 1993). Isostatic Isostaticrebound reboundafter afterglacial glacial retreat retreat causes causes the the shoreline shorelineof of the the glacial glacial lakes to tilt Hughes (1963) (1963) documented documented 55 post-Duluth shorelines in in the post-Duluth shorelines tilt southward southward (Wanen, (Warren,1981). 1981). Hughes western side of the the Keweenaw Keweenaw Peninsula, Peninsula, and since none of them extend north of Allouez Gap (Fig. 18; 18; 1981). The in that that position position (Warren, 1981). The lack lack of of shoreline shoreline features features in the the see Stop 16) the ice ice front front was was in eastern Keweenaw Peninsula indicates that that this this area was still occupied occupied by by glacial ice (Clark and others, �- Geology 27 27 Farrand, 1960). Table Table 2: 2: Stages Stagesofofglacial glaciallakes lakesininthe theLake LakeSuperior Superiorbasin basim(from (from Farrand, 1960). Ian S Isle .fl sabavit a.lt fla.tta at Ga . . !lmtia St 1. fl) S --- *11_n S a_.n - l I 61* 631 633 *100 I.tflttta La 3ta5 51* 561 3S00 Sorts. 590 613 a 651 app., matNst-Stao mow I..,.' Isp à ‘ à r Ñ 691 w 712 112 750 733 nt 7-TI 771 77* 319 S 905 909 Snttou MBHltMi Ms.hbvfl v.hbwm NOCV&t H w h north of isle 8500 72* 819 a*T 3*7 9*9 949 1022 1092 104* lo** 1087 Ion 813 PottI slore i.e boner • Po.t—flldsn to. (linen I. to 1.n.V ?totanla - border l 3 Iarq.sstte-St*tfloa— 9*1 M.b.r17° s.ntu.s) 905 1 1123 ulishIridSe HlihferldU 1131 1131 1167 ~uft-~lll~tll 3,ib-Dtsliath 1178 117à 122* 1 .2'24 121* DUI,Itb m luu 1236 a is. .hs.t — tat of lard. (2) — 'WithS of InC 670 IsSaamc ..-—— 32n 611 *ljon flfl.sS,t ----—-•- IeoO 4 1269 1292 ir 10.220 IsrIp V. ideps mint �28 28 ~eology 52 4.. 44. — •4_ —_.— — __s•, LZOSO 4O .—7—h.P. — —a—.—, t77 . t - Sr North America WISCONSINICE ICERETREAT RETREATfrom fromceital central North America.Note Notemajor malorice resurge. surge.ororreadvance. readvance.InIn WISCONSIN theLake LakeSuperior Sunenorbasin basin(from (fromV.VK.KPrest, Rest.1969, 1969.Geological GeologcalSurvey SurveyofofCanada CanadaMap Map1257A). 1257Al the (Fia 46) Figure 14: 14: Speculative Speculative ice-marginal ice-marginal positions positions during during the the Wisconsin Wisconsin ice ice retreat retreatfrom fromcentral centralNorth North Figure Huber,1975; 1975;Prest, Prest,1969). 1969). America(from (fromHuber, America �Peninsula. Keweenaw ice major the Note the over pattern withdrawal and basin Superior Lake the in readvance view Enlarged 15: Figure 1969). Prest, (from retreat ice Wisconsin the during positions ice-marginal of Gedogy �30 Geology o o Miles Kilometers 50 80 Figure Figure16: 16: End End moraine moraineof ofthe theKeweenaw KeweenawBay Bay lobe lobeglacier glacier(from (fromKalliokoski, Kalliokoski,1976; 1976;Warren, Warren,1981). 1981). / — I, / / j_ I LAKE DULUTH — KEWEENAW BAY LOBE "1 'I t1 // —— /7' /' C, Figure Figure 17: 17:Keweenaw KeweenawBay Baylobe lobeglacier glacierand andposition positionof ofglacial glacialLake LakeDuluth Duluthatatthe the1250 1250foot footelevation elevation (from (from Warren, Warren, 1981). 1981). �Geology 31 (from Hughes, 1963). Figure Figure18: 18:Physiographic Physiographicdivisions divisionsofofthe thecentral centralKeweenaw KeweenawPeninsula Peninsula (from Hughes, 1963). LAKE WASH BURN Figure Figure19: 19:High Highlevel leveldrainage drainagethrough throughthe thePortage PortageGap Gapduring duringthe theLake LakeWashburn Washbwnstage stageof ofthe theLake Lake Superior Superiorbasin basin(from (fromWarren, Warren,1981). 1981). �32 1994). As 1994). As the thewater waterlevel leveldropped droppedfrom from its itsLake LakeDuluth Duluth high, high, water water drained drained through through the the Portage PortageGap Gap (Fig. 19). Warren Warren(1981) (1981)provides provides evidence evidence of this this drainage drainage in the form form of of terraces terraces and and water-scoured water-scoured surfaces. A2). After the surfaces. The Huron Creek Channel is the the drainage drainage through through Portage Gap (see Map Map A2). Wisconsin glacier retreated from the Lake Superior Superior basin, the level of water water receded receded to to the the level levelof of Lake Lake Superior. Superior. Many glacial features are evident evident in in the the Keweenaw Keweenaw Peninsula, Peninsula, both both erosional erosional and anddepositional. depositional. features are bedrock surfaces surfaces(very (very common common in in the the Keweenaw KeweenawPeninsula), Peninsula), Erosional glacial glacial features features include includesmoothed smoothed bedrock grooves, striations, and chatter marks. Depositional features include sediments directly deposited from Depositional features include the melting glacier (till) and those sediments deposited by glacial meltwaters. meltwaters. Various Varioustypes typesof ofmoraines moraines (accumulation (accumulation of glacial deposits) are made of till. Although Although an an end end moraine moraine is is present present in in the the Keweenaw Keweenaw by hummocky, boulder-rich estimated 80% of the Keweenaw Peninsula is covered by 16). an estimated Peninsula (Fig. 16), glacial sediment ground moraine (Hughes, 1963). Glacial deposits of water-laid sediment Glacial deposits of water-laid origin origin include: include: outwash, outwash, eskers, deltas, kames, channel deposits, deposits, and more (Regis, (Regis, 1993). 1993). �MainRoadLog 33 MAIN ROAD LOG AND STOP STOP DESCRIPTIONS Reminder. The Reminder. Thenotes notes throughout throughout all all the the logs logs on on the the bedrock bedrock of of the the Keweenaw Keweenaw Peninsula Peninsula were compiled from Bornhorst (in press), Bornhorst (1992), and Bornhorst and others (1983) without specific citation or (in quotation to these particular particular references. references. Seaman Mineral located on the campus of The Seaman MineralMuseum, Museum,The TheMineralogical MineralogicalMuseum Museum of Michigan, Michigan, is located Michigan Technological University University (see (see campus campus map map on on back back cover coverpage). page). The museum has the world's Peninsula native native copper copperdistrict. district. We highly finest display of minerals from the Keweenaw Keweenaw Peninsula highly recommend recommend Plan to spend at least two hours in the a visit visit to to the the museum museum either either before before or after after your your field field trip. trip. Plan museum (Map 1). 1). CUMULATIVE from previous entry) CUMULATIVE MILEAGE (mileage from MAPII MAP 0.0 Assemble at at the the Memorial Memorial Union Union Building Building on on the the campus campus of of Michigan MichiganTechnological TechnologicalUniversity. University. Begin the field trip from the circular drive located on the northeast side of the Memorial field trip from the circular drive located on the northeast side of the MemorialUnion Union Building. The TheMichigan MichiganTech Techcampus campusisis located located on on aa kame kame terrace terrace to to the the south southof of Portage PortageLake. Lake. Turn right out of the the circle circle drive. drive. 0.05 Turn left. left. 0.1 0.1 Immediately after, alter, turn turn right on Townsend Townsend DriveAJS-41. Drive/US-41. The Quincy Quincy Mine Mine can can be be seen on the skyline ridge. ridge. 0.45 Left turn on Agate Agate Street, Street, and up the steep hill on the south south side side of of the the Portage Portage Lake Lake channel. channel. We are are climbing climbing off the the kame kame terrace to an area of scattered bedrock outcrops of the PLV covered covered by varying varying thicknesses thicknesses of of glacial glacial sediments. sediments. MAP 22 right on on Seventh Seventh Street. Street. 0.7 Turn right 0.9 STOP 1: 1:Seventh SeventhStreet, Street,City CityofofHoughton Houghton(Portage (PortageLake LakeVolcanics Volcanics[PLY]) [PLV) This stop is marked by a prominent ridge of ophitic basalt; an outcrop of the Scales Creek Flow. Plow. ItItisisone oneofofthe thegreat greatKeweenawan Keweenawanlava lavaflows flowswhich which can can be be traced traced continuously continuously for for aa strike strike length of more than than 160 160km km along along the thePeninsula. Peninsula. It is about 70 m thick, has an anamygdaloidal amygdaloidal top which is typically typically not resistent resistent to to erosion, erosion, and and aa prominent, prominent, ridge-forming, ridge-forming, ophitic ophitic massive interior. The Theridge ridgeatatthis thissite sitecan canbe befollowed followed down down hill hill all all the the way way to to Shelden Shelden Avenue, Avenue, where where it is covered by glacial glacial deposits, deposits, and can be traced across the valley where it passes beneath the Ripley School, a prominent brick building across Portage Lake. This Thisbearing, bearing,about aboutN30°E, N30"E, isis the the of the PLV, PLY, which which dip dip about about 50 50°to tothe the NW. NW. Another regional strike of Another clue to the attitude attitude of the the rock is given by the Quincy @ncy #2 shaft shaft house on the horizon, which heads up an inclined shaft. It It is down-dip down-dip along the amygdaloidal amygdaloidal ore bodies of lava flows flows and over over 2000 2000 m m higher higher in in the the PLY PLV section. the PLV PLV section Baltic and Mohawk, section. Throughout Throughout the section between between Baltic Mohawk, most amygdaloid amvedaloid and conglomerate zones are effected by conglomerate zones by well well developed developed zeolite zeolite and andprehnite-pumpeilyite prehnite-pum&ilyite facies facies metamorphism and by widely variable native native Cu Cu mineralization. mineralization. At this site the amygdaloids amvgdaloids just iust below the Scales below Scales Creek c A k Flow Flow are arestrongly stronglymineralized. mineralized. One mine, the the Shelden ~ h e l d eColumbian, ~~~olumbian, operated just a few hundred meters to the east in the the early early 1900's. This Thissame samehorizon horizonisisexploited exploited by aa series series of of shafts shaftscalled calledIsle IsleRoyale RoyaleMines Mines (see (seemileage mileage 3.75 3.75 for fordescription), description), for for several several kilometers to the SW. SW. �___ __________________________ A tc1Vl'r' p ;I 4;9c.s Bedrock •(ThV4' tJ a - I Mineral floor) Geology k.wnnaw W.tnw.y Po,rtage Lake floor) • • 4* •= - 12 1 r- - 'kC!_ rA Lrfl Lake ()R -, c",' r -A,-VoIcanlcs L.'.f .r - 'N /f IFSId p 'flA fl thYTh it. -' ' , Pthr1'X' %.ç4S% - - - —- - - -— - ('C 7 e V an s one Michigan mchnoiogical univ.rslty tioughton, Michigan 49031-1295 nw-° J - ,,Sh.rmanFl*Id - / aco 32 2 1 4 r / — Au. S.Mcia 7 EoincSEoq9yR..OtJItslCsotSc 42 FacIHhI..Mng.olsotStOrtOl 1EcELe1. 49 WnSMeIOfl.OIRSSOWC•S - - 12 Mln.r.lsdMMflslEflQlflllIlfl9 II Poqnt,yhnSlllolS ol od Rnntcli 34 MsoiodiL UnIon - — I p Coid Hall Food S•Mc• .aI.IO1.ImIIOO sod &tudsnl C' 1ItF C:$t! / 3' I z: P Pwklr.g Lol & €C 9 -. — Hmw P utq 'a4 iQ Q' R K1w1fl* RUWth Cnls', (7 kA 1.1.11 BuIlding, Hsncock Poitag. LS• Gall Coui HO.JØIIOO Y' �M1I0ROSdLOS Map3 35 �36 MathRoadLog Portage Lake valley is the the most most obvious obvious geomorphological geomorphological feature, and its origin origin was was formed in in a fault zone typical of that thoroughly investigated by Warren Warren (1981). (1981). The valley valley formed that which crosscuts 200 m m deep deep crosscuts the Keweenawan stratigraphy elsewhere. A A bedrock bedrock valley valley more more than than 200 formed along the fault as aa result result of stream stream superposition superposition through a cover cover of flat-lying flat-lying sediments. sediments. This valley, like others on the Keweenaw Peninsula, Peninsula, was was deepened deepened and and widened widened by by glacial glacial erosion erosion in a fashion of New New York State. State. The fashion similar to the Finger Lake region of The complex complex glacial glacial deposits, deposits, terraces; varved varved clays; clays; and and gravels, gravels, were were the result of the pattern consisting of moraines; terraces; pattern of of ice ice retreat from the region, which which had profound and and complex complex effects on on the the drainage drainagepatterns. patterns. 1.0 Turn Turn left left on on Portage Portage Street. Street. 1.15 Grand Portage Mine rock piles 1.15 piles on on the the left. left. 1.35 We (used for Walktoward toward the the metal metal triangular triangular structure (used arenear nearthe theHoughton Houghton water water tower. tower. Walk 1.35 Weare surveys) on the left side side of of Portage PortageStreet Street(east). (east). STOP 2: 2: Houghton Houghtonwater watertower tower(glacial (glacialgrooves) grooves) with a number of parallel The exposed basalt has a glacially glacially smoothed smoothed surface with parallel glacial glacial grooves that trend about N65%, N65°E, which is consistent with with Stop Stop 3. 3. The The grooves grooves near near the the tower tower are are about 10 10 cm deep deep and and 15 15cm cm wide. wide. At this stop, the Scales Scales Creek Ridge (flow) is exposed higher on the south slope of the the Lake'valley. valley. To ridge, many Portage Lake To the the east east of of the the prominent prominent ridge, many mine mine openings openings from the series Adams Township Township takes takes its its water supply from mines lower in in the the of Isle Royale Royale shafts shafts exist. exist. Adam stratigraphic section which are now filled with with water, water, and and is the the source of of water for Hancock and several other other towns. Using Usingwater waterfrom from mines mines for for drinking drinking is is only only possible possible because because the local local rocks rocks break down in oxidizing surface are almost completely completely devoid of any minerals, such as pyrite, that break surface to produce produce acid acid waters. waters. The lack of acid and groundwaters to acid waters waters keeps most ore ore and and gangue gangue minerals in in the rocks and and remain remain immobile. immobile. Therefore, Therefore, the the water waterfrom fromthe themine mineisof isof drinking drinking quality. quality. Avenue. Across 1.45 Turn right on Sharon Avenue. Across Sharon Sharon Avenue is the City of Houghton Houghton fire station. station. 1.45 1.95 Turn left 1.95 left at at the the flashing flashing light light on on Main Main Street, Street, heading heading into into Hurontown. Hurontown. 2.2 Turn right on on Frederick Frederick Street. Street. 2.25 On arelow lowexposures exposures of of basalt. basalt. 2.25 Onthe theleft leftside sideofofthe theroad roadjust justbefore beforeHuron HuronStreet Streetare STOP 3: STOP 3:Hurontown Hurontown(glacially (glaciallycarved carvedbasalt) basalt) The small of glacially glacially carved and smoothed small knobs of basalt represent excellent examples of basalt within the Keweenaw Peninsula. The are asymmetric asymmetric with a gentle, smooth slope Keweenaw Peninsula. The knobs knobs are on one side and a steep, irregular side opposite. opposite. This This morphology is that of a roches moutonnees, formed by glacial glacial abrasion abrasion on on the the gentle gentle smooth smooth slope slope with plucking steepening steepening the the opposite opposite side side as ice ice moves moves over the ridge. Glacial Glacialgrooves groovesand and the the roches roches moutonnees moutonnees indicate ice movement from N60°E. N60% Return to Main Main Street. Street. �MainRoadLag 37 2.35 Turn right on Main Main Street Streettoward toward Dodgeville. Dodgeville. 3.0 3.0 Charter Township of Portage water tower on the right. 3.55 3.55 Entering Dodgeville. On On the the right right side side of the road is one of the prominent Isle Royale Mine rock piles. piles. Dodgeville. At 3.75 3.75 Center of Dodgeville. At this this time time (May, (May, 1994), 1994), the Isle Royale Mine rock piles from Shaft No. 4 and 5 are are visible visible on on the the right right side side of of the the road road (west), (west), but these these piles of of mine mine rocks rocks are are slowly slowly being removed as crushed rock. The Themine mine rocks rocks are are relatively relatively inert, inert, containing containingno no acid acid generating generating minerals such as pyrite. pyrite. Native mineral in in the rocks, rocks, is stable in Native copper, copper, the the dominant dominant metallic mineral environment. Further, the surface surface oxidizing environment. Further, the the mine mine rocks rocks contain contain only only background background levels levels of of pollutants such as Pb. mine rocks rocks can can beused be used as ordinary crushed stone. stone. These Pb. Thus, these mine ordinary crushed These mine rocks rocks are areoff off limits limits to tocollecting. collecting. Rocks from these Isle Royale Mine rock piles are scattered throughout the City of Houghton Houghton for for purposes and and to to minimize minimizeerosion. erosion. While the rock rock piles piles themselves themselves are are off off limits limits for for decorative purposes collecting, excellent excellent specimens specimenscan canbe be gathered gatheredfrom from the the public public right-of-way right-of-wayinin the the City of collecting, Houghton. AAdescription description of of the theIsle IsleRoyale RoyaleMine Mine isisprovided provided as as aageneral general background. background. worked the the top top of of the the Isle Isle Royale Royale Plow. Flow. Production from the Isle Royale The Isle Royale Mine worked Amygdaloid beganinin 1855, 1855,and andthe themine mineclosed closedinin1948. 1948. A A total total of of about 160 million million kg kg of Amygdaloid began refined copper and Pollack, Pollack, 1971). 1971). The Arcadian Mine (see copper was was removed from this mine (Weege and (see Map 4) may may also also work work the the Isle Isle Royale Royale Amygdaloid. Amygdaloid. The Isle Royale plow flow varies but is about 22 to 46 m thick and lies just below varies in in thickness, thickness, hut below the Flow discussed in Stop 1. The Scales Creek How Theflow flow dips dipsabout about50 50to to 60° 60Âto to the the northwest northwest (Fig. (Fig. 20), 20). fragmental zone; banded with a gentle fold accounting for the curvature, and is characterized by a fragmental amygdaloid; aa foot foot inclusion inclusion zone; zone; and and aa massive massive main main trap. trap. The amygdaloid; The fragmental fragmental zone zone consists consists of irregular fragments of amygdaloid and fme-grained basalt ranging ranging from from small grains to tabular fine-grained basalt blocks several several meters in long direction. The Thevesicles vesiclesand andspaces spacesbetween between the the fragments fragmentsare arefilled filled minerals. The with secondary minerals. The banded handed amygdaloid amygdaloid is is an an unbroken unbroken rock rock body body over overconsiderable considerable area with amygdules abundant at certain horizons, horizons, giving giving this this zone zone aa handed banded appearance. appearance. Below Below the fragmental fragmental zone, or or banded amygdaloid, is the foot inclusion zone which is indefinite patches or inclusions of amygdaloid basalt. The Thefoot footinclusion inclusion zone zone grades grades into into massive massive basalt basalt practically practically devoid of amygdules amygdules (summarized (summarized from from Butler and and Burbank, Burbank, 1929). 1929). rock piles piles from from four shafts of of the Isle Royale Mine and made Stoiber (unpublished data) studied rock the following estimate estimate of the the percentage percentage of alteration alteration minerals: minerals: quartz, 26-59%; 26-59%; calcite, 5-39%; 5-39%; prehnite, 6-32%; 6-32%; pumpellyite, pumpellyite, 1-17%; 1-17%;epidote, epidote, 1-10%; 1-10%;sericite, sericite, 0-12%; chlorite, chlorite, 0-3%; 0-3%; K-feldspar, K-feldspar, 0-trace. Good Good specimens of alteration minerals, and and less commonly native copper, copper, can be 0-trace. specimens of alteration minerals, commonly native be collected from from the the mine mine rock rock throughout throughoutthe the Houghton Houghton area. area. 4.25 junction to the Green Green Acres Acres Road. Road. Thrn Turn right. 4.25 The junction 4.6 4.6 former Isle Isle Royale RoyaleShaft ShaftNo. No.6.6. As of 1994, the once large mine On the left is the location of the former rock pile is nearly nearly gone. gone. 5.45 The junction junction of of M-26 M-26 at the Copper Copper Country CountryMall. Mall. Make a left turn. 5.45 �U) 00 I A Harbor Copper Harbor Conglomerate A' ISLE ISLE ROVALE ROYALE NO. 2 SHAFT I Keweenaw fault 'ooq 100V 500' 5.w Sea Sea leveL level -500' -500' -bOO' -1000' -1500' -1500' -2000' -2000' P o r t a g e Lake L a k e Volcanics Volcanics Portage Jacobsvllle Jacobsville Sandstone Sandstone Figure 20: 20: Cross Cross section section A-A' on onMap Map 22(from (fromWhite, White, 1956). 1956). Abbreviations Abbreviationsare areas asfollows followsfor forthe the Portage Portage Lake Lake Volcanics Volcanics (P) and its its subunits: subunits: Figure (pp). Greenstone Greenstone flow flow (pg), (pg), Allouez Allouez Conglomerate Conglomerate (pa), (pa). Calumet Calumetand andHecla HeclaConglomerate Conglomerate(pe), (pc), Kingston Kingston Pewabic West Conglomerate (pp), Conglomerate (pkc). Wolverine Sandstone flow (psc), (psc), Bohemia Bohemia Conglomerate (pkc), National National Sandstone Sandstone (pn), (pn), Kearsarge Kearsarge flow flow (pk), (pk), Wolverine Sandstone (pw). (pw), Scales Creek flow Conglomerate (pb), St. Louis Louis Conglomerate Conglomerate (ps), (ps), Baltic Baltic Conglomerate Conglomerate(pbc), (pbc),and andUnnamed UnnamedConglomerate Conglomerate(pu). (pu). �Main Mtia Road Hoed Log Log 39 39 MAP3 MAP 3 7 .05 Atlantic Mine is on the the right. right. Continue Continue on M-26. M-26. 7.05 An outcrop of PLV is on the the right. right. 7.8 7.8 8.4 8.4 Turn right onto a dirt dm road road about about 200 m m before before the sign sign that that says: says: South South Range Range Village Village Limit. Limit. 150 m (a church is on the left) to an open open "parking" "parking" area on the the right, right, just before before Proceed about 150 of the open area is a path which which goes up a steep steep slope slope the road goes up hill. hill. At the far end end of open area 4. through a notch up the hill another another 60 meters to Stop 4. STOP 4: STOP 4: South SouthRange RangeQuarry Quarry(Portage (PortageLake LakeVolcanics Volcanics [PLY]) [PLV]) Volcanic textures and structures structures typical of moderate-to-thick subaerial suhaerial lava lava flows flowswithin within the PLV are well well exposed exposed in this old quarry. quarry. As Asone onetraverses traversesup-section upsection into intoand andthrough throughthe the quarry (Fig. 21), one crosses m thick thick interfiow interflow conglomerate conglomerate bed exposed in the the path, path, crosses over a 44m overlain by an 18 flow top top is exposed just just as you enter the 18m m thick thick Java lava flow (the amygdaloidal flow quarry itself), followed by a complete complete section through a 42 42 m thick thick ophitic ophitic basalt basalt flow flow (the (thebulk bulk lowermost 17 17 m m of of the the overlying overlying ophitic ophitic lava lava flow flow (at (at the the of the quarry walls), walls), and finally, the lowermost northwest middle of of the PLVs' northwest end of of the the quarry). quarry). The quarry is positioned positioned in about about the middle PLVs' lava flows N45°E (subparallel (subparallel to to the the stratigraphic section. section. Locally, Locally, lava flows strike strike approximately approximately N45% northwetem shoreline toward the center of the rift (Lake (Lake northwestern shorelineof of the the Keweenaw Keweenaw Peninsula) and dip toward Superior) at about 60°. 60". In Inthe thecross crosssection section of of the thePLV PLVthrough through this this area, area, all alldips dipsare areabout about60°. 60'. Dips in the the sedimentary sedimentary section section overlying the PLV to the the NW NW flattens flattens to to subhorizontal subhorizontal on on the the shoreline of the the Keweenaw Keweenaw Peninsula. Peninsula. sedimentary beds beds provide provide critical stratigraphic markers Laterally continuous interfiow interflow sedimentary within an an otherwise otherwise uniform uniform volcanic volcanicpile pile(PLV). (PLy). The within The unit unit exposed exposed below the quarry has been correlated with with the the National National Sandstone, Sandstone,aamarker markerbed bedininthe theMass-Rockland Mass-Rocldandarea. area. This marker correlated silicic-withis aamassively massively bedded, bedded,pebble-cobble pebble-cobble framework framework conglomerate, conglomerate, composed composed of silicic-withsubordinate mafic, mafic, volcanic subangular-to-subroundedclasts, clasts,within withinaa matrix mathx of poorly-sorted subordinate volcanic subangular-to-subrounded poorly-sorted medium-to-coarse sand of similar similar composition. composition. aremainly mainly olivine olivine tholeiites tholeiites erupted erupted as as thick. thick, The basalts in this this portion portion of of the the PLV PLV are ponded subaerial lava sheets. The Theprincipal principal lava lava flow flow exposed exposed in the quarry walls illustrates illustrates many in cross cross section. section. The top and of the volcanological features observable in and bottom of of this this lava lava flow flow of aphanitic aphanitic chilled chilled basalt. basalt. It are exposed at the two ends of the quarry and consist of It was was deposited deposited underlying lava directly on top of the underlying lava flow, flow, so its base occurs where amygdules amygdules disappear disappear abruptly abruptly brecciated slightly by by in the top of the underlying flow. The The upper upper surface surface of the main flow was brecciated movement of of lava after the formation movement formation of an upper upper crust, crust, but but rapidly rapidly grades grades downward downward to to an an unbrecciated, highly highly vesicular flow top. Note the variation unbrecciated, top. Note variation in vesicle vesicle size size and anddistribution distribution downward in the flow. The Theflow flowtop topbreccia breccia(locally (locally called called fragmental fragmental amygdaloid) is laterally flow. Slow discontinuous for this flow. Slow cooling cooling of of the the lava lava flow flow caused solidification toward the flow interior at a rate which allowed interior allowed development of subophitic suhophitic to ophitic textures (large oikocrysts of clinopyroxene enclosing framework of An-rich plagioclase plagioclase and and intergranular intergranular olivine). The clinopyroxene enclosing a felted framework The constitutes about about two-thirds two-thirds of of the flow. Before Before resulting massive, non-vesicular non-vesicular flow interior constitutes fmal final solidification, solidification, small small amounts amounts of volatile-rich, volatile-rich, differentiated differentiatedresidual residual liquid liquid were were concentrated concentrated in thin discontinuous zones and and lenses. lenses. Many discontinuous zones Many of of these these are are subparallel subparallel to the the bottom bottom and and top top surfaces of of the the flow. flow. A zone consists consistsof of aa 44 cm cm to 1.3 1.3 m core of vesicular vesicular surfaces A typical typical pegmatoid pegmatoid zone surrounded by by aa 44 to 9 cm border zone at at the the top top and and bottom. bottom. The basalt surrounded border zone The vesicular vesicular core of the pegmatoid zones clinopyroxene and zones contains contains coarse coarse laths laths of Ab-rich plagioclase, prisms of Fe-rich cl'iopyroxene �Main Road Log 4 per H bor Conglom . r'ç;r 21 Ii a cobsville San dstone I -.' sJztt —7 MAP 3 �Main Road Log RX ax conglomerate bed S. QUARR 41 Meters 15 0 I Brecciated Brecciated Basil! Basalt Amygdaloidal Amygdaloidal Bmit Bnslt II Massive Massive Buih Basalt *5x5 xxx. Pegmatite Pegmañte Layers Layers Figure21: 21:Geologic Geologic profile theSouth SouthRange Rangequarry quarryalong alongthe thenortheast northeastwall wall(modified (modifiedfrom fromCornwall, Comwall, Figure profile ofofthe in 1951; 1951; White, White, 1971b; 1971b; from Bornhorst, Bomhorst, 1992). 1992). Location Location of of the the quarry quarryisisshown shown inMap Map13, 13,Sec. Sec. 17,T54N, T54N.R34W. R34W. 17. �42 ukoadLog minerals such suchas asapatite apatiteand andzircon. zircon. The border zone abundant Fe-Ti oxides, as well as accessory minerals abundant is composed of aa medium-to-coarse medium-to-coarse grained aggregate aggregate of albite/oligoclase, albiteloligoclase, augite, ilmenite, ilmenite, and and magnetite. Pegmatoid magnetite. Pegmatoid zones zones toward toward the top of the the flow flow are are more more vesicular. vesicular. Zircons extracted within thick thick PLV basalt flows have yielded high-precision (e.g., from pegmatoids pegmatoids within high-precision U-Pb dates (e.g., Davis and Paces, 1990). Numerous Numerous thin thin pegmatoids pegmatoids are exposed exposed in the quarry quarry walls, walls, as as well well as as in the glacially-polished glacially-polished surfaces above and to the north of of the the quarry. quarry. observed within the the vesicular vesicular flow flow The effects of regional regional hydrothermal alteration can be observed Vesicles are are filled with a variety variety of of secondary secondary minerals minerals including including and pegmatoid pegmatoid zones. zones. Vesicles top and pumpellyite. chlorite chlorite and andtraces tracesof ofnative nativecopper. copper. Pseudomorphic Pseudomorphic quartz, epidote, prehnite, calcite, pumpellyite, replacement of of basalt by in the theprehnite-pumpellyite prehnite-pumpellyite facies facies replacement by fine-grained fine-grained secondary secondary minerals minerals in pale bluish green) is most (epidote, olive green; pumpellyite, pumpellyite, pale most intense intense where where permeability permeability was was highest. The massive interior of the flow is only a little altered except in the vicinity of selected highest. The massive interior of flow vicinity fractures. Alteration along the interior fractures is characterized by a green-to-red fractures. green-to-red cherty cherty rock, rock, pseudomorphicreplacement replacementofofthe thebasalt. basalt. The massive interior interior was representing nearly complete pseudomorphic Fracturing during during late a relatively relatively impermeable impermeable horizon horizon in in the thepaleohydrologic paleohydrologic system. system. Fracturing late compression (reverse provided limited limited pathways pathways for upward upward compression (reverse movement movement along the Keweenaw Fault) provided movement of ore ore fluids. fluids. Outside series of glacially grooved outcrops outcrops in in which which Outside of the Quarry Quarry and to the north are a series the exposures of the pegmatitic zones are spectacular. the pegmatitic zones are spectacular. 8.7 8.7 Return from Stop 4. 4. Take turn on on M-26, M-26, going going into the town of South Range. Return Takeaaright right turn 9.2 At the stop stop sign sign in in South South Range, Range, take take aa left leftturn. turn. 9.4 Turn right at the the church, church, immediately immediately followed by a left turn (the (the whole road jogs to to the theleft). left). 9.5 9.5 Entering the town of of Baltic. Baltic. 9.6 Turn right. right. 10.0 10.0 The main road tams concrete turns to the left, but go to the right on a small paved road, driving past a coiicrete building toward some some very very large large mine mine rock rock piles. piles. 10.2 STOP 5: Baltic BalticMine MineShaft ShaftNo. No.3 3(native (nativecopper copperdeposit depositwithin withinPortage Portage Lake Lake Volcanics [PLy]) [PLV]) STOP 5: The Baltic, Champion, and Trimountain Mines worked worked the the Baltic Baltic How top Champion, and Trimountain Mines top deposit. deposit. Native copper is irregularly through the the flow flow top, ranging from minute irregularly distributed through minute specks specks to to masses weighing weighing several several tons. tons. The producer in the Keweenaw native masses The Baltic Baltic Mine, third largest producer copper district, opened about 1898. 1898, while the remaining two mines which worked this flow flow top top production from from the the Baltic Baltic Mine Mine was was about about 840 million opened in 1902. 1902. Total production million kg of refined refined copper. The km along along strike, strike, and and to the the 38th 38th level level (1000 (1000 m) m) Theamygdaloid amygdaloidwas was mined mined for for about about 77 km Mine. The and had had an an average avenge stoping width width of of 55 to to 8 m. in the Baltic Mine. The lode lode dips dips 70°NW 70¡N and of the Baltic Flow The massive interior of How is ophitic and varies considerably in thickness The flow top is with a thickness of 17 m or from about about 50 50 to 70 m. m. The flow top breccia breccia with thickness of or more more where where from mineralized, to less less than 11 m m of ofvesicular vesicular to tomassive massive basalt basalt where where unmined. unmined. The abundant abundant mineralized, to minerals associated with copper are quartz, quartz, pumpellyite, pumpellyite,epidote, epidote,and andcarbonate. carbonate. Paragenetically late copper rare chalcopyrite chalcopyrite are are unusually unusually abundant abundant copper sulfldes, sulfides, chalcocite, chalcocite, some bornite, bomite, and rare �MSRoa4I.og 43 compared to the district as a whole. The Thesulfides sulfidesoccur occurin in fissures fissuresassociated associated with with carbonate carbonatethat that of the rock dip 75° 75' to 90°, 90°and strike strike nearly nearly parallel parallel with the lode. lode. Most Most of rock pile at this stop stop is is amygdaloidal basalt, with the following estimated percentages of amygdule-filling minerals: amygdaloidal basalt, with following estimated percentages amygdule-filling minerals: calcite, 91%; 91%; quartz, Stoiber, unpublished calcite, quartz, 5%; epidote, epidote, 3%; 3%; chlorite, chlorite, 1% 1% (R.E. (R.E. Stoiber, unpublished data). data). Paragenetically, epidote Paragenetically, epidote and chlorite chlorite are early; calcite, calcite, quartz, and native native copper copper are are intermediate; intermediate; Excellent specimens of while copper sullides sulfides and and carbonates carbonates are are late late (Fig. (Fig. 12 12Introduction). Introduction). Excellent chalcocite can be found on this this rock rock pile, pile, along along with with native native copper. copper. Butler two distinct Butler and Burbank Burbank (1929) (1929) recognized recognized two distinct periods periods of alteration alteration within within the the Keweenaw Peninsula native copper district. district. The earliest alteration was oxidation, causing the development of of hematite, which in turn, turn, produced produced reddened reddened basalt. basalt. This oxidation oxidation could could development hematite, which alter eruption. The essentially represent deuteric alteration shortly after The second second period period of of alteration alterationwas was probably after the flows had had been been tilted. tilted. This probably This period period was was complex and resulted in deposition of native copper. copper. It is is divisible divisible into into three three substages: substages: 1) an an early early stage stage of of deposition deposition of of epidote, epidote, pumpellyite quartz, quartz, calcite, calcite, most most of of the native pumpellyite native copper and minor prehnite, alkali feldspar, and laumontite; 2) an intermediate by the development intermediate stage stage characterized characterized by development of of sericite sericite with with quartz, quartz, calcite, anhydrite, gypsum and minor barite; and 3) a fmal final stage of copper copper sulfides sulfides and and arsenical arsenical copper accompanied by calcite, quartz, chlorite, chlorite, and and specular hematite occurring in copper accompanied by calcite, sericite, quartz, numerous veinlets. veinlets. 10.4 10.4 Retrace route route through through Baltic. Baltic. 10.9 10.9 At the stop stop sign sign in in Baltic, Baltic, turn turn left left to to go go back back in in the thedirection direction of of South SouthRange. Range. 11.1 11.1 Turn right, immediately followed at the church by a left left turn. turn. 11.3 In the center 11.3 center of of South South Range, Range, take aa right right turn turn off off M-26. M-26. 11.8 11.8 Passing the South Range Quarry, Stop 4. MAP22 MAP 14.75 On On the theright rightisisthe theGreen GreenAcres AcresRoad RoadtotoDodgeville Dodgeville that thatwe wepreviously previously followed. followed. 15.6 15.6 Stoplight Stoplight at Sharon Avenue. Continue Continuestraight straightahead. ahead. 16.05 The junction. This This road road is used in Leg A -- Houghton Houghton Canal Road. Road. 16.05 The Canal Canal Road junction. 16.5 16.5 Between the Junction of of M-26 M-26 and and US-41, US-41, stay stay right right and and continue continue ahead ahead on on US-41 US-41 (Marquette) (Marquette) past the gas stations stations on on the the right. right. 16.95 An Anexcellent excellentoutcrop outcropof ofbasalt basaltwith with exposed exposed vesicular vesicular flow flow top (amygdaloid) (amygdaloid) on both sides sides of the road. Move road. Move to to the the far far left left lane. lane. 17.1 17.1 Make a left U-turn back onto US-41, going Stay going one one way way back back through through the the City City of of Houghton. Houghton. Stay in the left lane. lane. 17.2 17.2 Turn off US-41 into into the the Burger Burger King King parking parking lot. lot. STOP STOP 6: Shelden SheldenAvenue, Avenue,City CityofofHoughton Houghton(Portage (PortageLake LakeVolcanics Volcanics [PLVI) [PLY) West of the restaurant, massive restaurant, an unbrecciated amygdaloidal amygdaloidal flow top with an underlying massive �44 MsmkoadLog south along along the the highway). highway). The flow top is strongly interior interior is well exposed (also to the south strongly altered ainygdule minerals characteristic characteristicof ofthe theprehnite-pumpellyite prehnite-pumpellyitefacies. fades. The with amygdule The green green color color is is due due to the abundance of epidote. The Themassive massive flow flow interior interior below below the the altered altered flow flow top, top, isis essentially essentially unaltered except where thin pegmatoid zones cross it. Pegmatoid zones are discussed at Stop Stop 4. 4. This stop is an an alternate alternate to to the the South South Range Range Quarry Quarry Stop Stop 4. 17.65 Turn Turnright righton onUS-41/M-26 US41/M-26and andcross crossthe thePortage PortageLake LakeLift LiftBridge Bridgeinto intoHancock. Hancock. The bridge was built in 1957, 1957, and and isis designed designed to to accommodate accommodate Great Lakes ore boats, whose whose captains prefer the Keweenaw Keweenaw Waterway route (Portage Lake) to rounding rounding Keweenaw Keweenaw point point in in stormy weather. The Thepresent present bridge bridge abuts abuts the the Hancock side of the canal at approximately approximately the site of the old old Quincy Quincy Mill, Mill, where where the the tramway tramway descended Quincy Hill from the mines. MAP 4 on US-41 US41 into into Hancock. Hancock. 17.9 17.9 Turn left on Turn right, immediately followed followed by by US-41 US-41 going going to to the left, but go straight at 17.4. 17.4. 18.1 18.1 18.25 Bear Bear to to the the left left on on White White Street. Street. 18.75 The Thejunction junction between between White WhiteStreet Streetand and Lincoln Lincoln Drive Drive which which is is US-41; US-41; turn turn right. right. The fenced fenced ground ground near this locality surrounds surrounds an area of caved ground, which is thought thought to to be be of the Hancock Hancock Mine. Mine. The related to shallow stopes of The detection detection and distribution of such openings mines had had shallow workings, is a problem of considerable considerable concern to local authorities since many mines since since towns towns grew grew up adjacent adjacent to mines, mines, and and since since maps maps of ofthe theunderground underground workings workings are are incomplete and/or andtor inaccurate. inaccurate. Turn off US-41 US41 to the right to to the overlook overlook of the Keweenaw Keweenaw Waterway or Portage Lake, which 19.05 Turn 19.05 is Stop Stop 7. 7. STOP 7: Keweenaw Keweenaw Waterway Waterway Overlook Overlook This overlook, near the crest of Quincy Quiicy Hill, allows a broad overview overview of the the Keweenaw Keweenaw Waterway. From From east eastto towest west(left (leftto toright), right),the the features features which which can can be be seen seen are are (Fig. (Fig. 22): 22): 1) 1) KeweenawBay, Bay,the theknobby knobbyterrain terrainofofthe theHuron HuronMountains. Mountains. The On the skyline across Keweenaw mountains are underlain by Archean gneisses and granites of the Michigan portion of of the the Wawa subprovince subprovince of the Superior Superior Province of Canada. Canada. 2) 2) In the foreground, foreground, the flat topography is characteristic of areas of Jacobsville Jacobsville Sandstone, Sandstone, which has typical dips of less than 100. The Jacobsville extends from the Keweenaw which dips of less than 10". Keweenaw waterway at at the the east east end end of of the theMTU MTh campus, across Keweenaw Fault, which crosses the waterway Bay, and to the north of of the the Huron Huron Mountains. Mountains. 3) 3) basalt lava flows Within the town of Houghton, several ridges of resistent massive interior basalt can be traced downhill. The most prominent ridge is the Scales Creek downhill. The most prominent the Scales Creek Row Flow horizon, horizon, where Stop 1 was made. made. The Theattitude attitude of of the thePortage Portage Lake Lake Flows Flows and and the the alteration alteration of of resistent flow interiors and interfiow tesistent interflow conglomerates with less resistant tops, tops, makes makes site site investigation work critical for for some some construction construction projects. projects. Investigations are are necessary necessary to accurately determine determine depths depths to to bedrock, bedrock,and and to to make make hydrologic hydrologicinterpretations. interpretations. For �Map5 Mmii Road Log 45 MAP �0a I £ Figure Figure22: 22:View Viewfrom fromPortage Portageoverlook overlookfacing facingsouth south(from (fromBornhorst Bornhorst and and others, others, 1983). 1983). Notable Notablefeatures featuresinclude: include: 1)1)Huron Huron Mountains, Mountains, 2) 2) FlatFlatlying 3A) Scales Scales Creek Creek flow Flowridge, ridge,3B) 3B)Michigan MichiganTechnological TechnologicalUniversity University Student StudentDevelopment Development Complex, Complex, 4A) 4A) lying Jacobsville Jacobsville terrain, 3A) Bluff Houghton water tower at Isle Royale Shaft #1, 4B) Isle Royale mine rock pile #4, 4C) Isle Royale mine rock pile #5, 4D) Wheelkate Houghton tower Isle #I, #4,4C) #5,4D) Wheelkate Bluff (Trimountain), (Trimountain), 5) Highway M-26, 6) Contact between the Portage Lake Lake Volcanics Volcanics and and the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, 7) 7) Houghton Houghton County Courthouse, Courthouse, 8) 8) Quincy Quincy Smelter, Smelter, 9) 9)Michigan MichiganTechnological TechnologicalUniversity Universitymain maincampus. campus. County �MainRoadLog 47 example, site investigations of of the extensive area south of the the main main campus, campus, where where the the Michigan overlook) is now located, Michigan Tech Student Student Development Complex (visible (visible from the overlook) located, provided the focus of several several Master's theses theses for for students students in in Geological Geological Engineering Engineering at at Michigan Tech (Stevens, 1971; Hase, 1973). A general map, showing the detailed Michigan Tech (Stevens, 1971; Hase, 1973). general map, showing the detailed bedrock geology of the City of Houghton (Holcomb, (Holcomb, 1975) is used used by by developers in the area. area. 4) 4) On the the skyline skyline directly directly on the the opposite opposite side of the the waterway, waterway, and beginning beginning at the the Houghton water tower (black, orange and and yellow), yellow), is a series waste-rock piles Houghton series of of mine minewaste-rock piles from the Isle Isle Royale Mine (flow top deposit) deposit) that extend into the distance along along the the strike strike of the PLy. PLV. The Theknob knobononthe theskyline skylineisisWheelkate WheelkateBluff Bluff near nearSouth SouthRange, Range, just just south south of Stop 4, which is one of several resistant bedrock highs. which is one of several resistant bedrock 55)) To the north north of of the the divided divided state state Highway Highway 26, are are glacial-fluvial glacial-fluvial deposits. 6) 6) To the right, extends across across the the upper upper contact contact of of the the PLV PLV to the Copper right, the waterway waterway extends Harbor Conglomerate, Leg A follows Conglomerate, Nonesuch Nonesuch Shale, and and Freda FredaSandstone. Sandstone. Leg follows the the Houghton side of the waterway waterway with stops observing the Copper Harbor Conglomerate Conglomerate (along the waterway), waterway), and the Freda Freda Sandstone Sandstone (along the Lake Lake Superior Superiorshoreline shorelineatat Redridge). Redridge). This, and other other major major bedrock valleys in the area, were formed by stream stream superposition superposition as the tilted tilted Keweenawan as ancient ancient rivers eroded through flat-lying Paleozoic rocks and into the strata. The valleys strata. valleys were were greatly greatly deepened deepened by glacial glacial erosion erosion during during the the Pleistocene. Pleistocene. During a pause in the retreat of the Keweenaw Bay sub-lobe at the end of the Wisconsin glaciation, a waterway was established that allowed eastward eastward drainage across the peninsula glaciation, toward toward lower lower lake lake levels to the east. First, First,drainage drainageoccurred occurredin in the the Portage PortageGap Gap(between (between Houghton and Hancock) while a tongue of ice remained in what is now western western Portage Portage Lake. As Asthe theice iceretreated retreatedfurther, further,the thevalley valley now now occupied occupied by by Portage Portage Lake Lake was was formed formed by the eastward eastward drainage drainage of successively successively lower proglacial lakes in western Lake Superior. Torch Lake was formed by a trapped block of ice which later melted in place to to form form the the lake lake basin basin (Warren, (Warren,1981). 1981). The Keweenaw was named named after after an an Indian Indian word word for for portage portage route. route. Dredging, Keweenaw Peninsula was Dredging, completed completed in in 1873, 1873, was necessary necessary at both the northern and southern ends, to make Portage Portage Lake accessible accessible to to Lake LakeSuperior Superiorshipping. shipping. Houghton was named for Douglass Douglass Houghton, Houghton, the geologist geologist who sparked sparked the the Michigan Michigan boom by by publishing publishing his his Michigan Michigan State State Geologist GeologistReport Reportin in 1841. 1841. The copper mining boom The town was seWed in 1852 and is the site of several historic buildings, the most important settled 1852 the site of several historic buildings, the most important of which which is is the theHoughton Houghton County County Courthouse Courthouse (1887). (1887). It's aa prominent prominent yellow yellow brick brick Sandstone facing facingand andaa copper copper roof roof that that sits sits on on the hill above building with Jacobsville Sandstone the main part of town. town. Hancock was settled in 1859. Across Across the the road road and and just slightly slightly uphill is the the Quincy Quincy Hill Hill (1871), the the Quiincy Quincy Mine Minemanager's manager'shouse. house. The Quincy No. No. 6 Mine shaft house House (1871). (flow top top deposit) deposit) dominates dominatesthe theskyline skylinebehind behindthe theviewpoint. viewpoint. A A map map of the Quincy (flow Quiincy operations in its heyday No. 2 shaft operations in heyday is given given in in Figure Figure 23. 23. The inclined inclined No. shaft descends at nearly a 45' 45° angle, angle, more more than than 33 km km (1.7 (1.7 km km vertical) vertical) below belowthe the surface. surface. The surface nearly surface projection of the area mined mined is shaded shaded on on Map Map 4. 4. �48 MainkoadLog Main Road Log 19.05 19.05 Turn right, back onto US-41 going up the hill. 19.5 19.5 A prominent outcrop of basalt basalt with with glacial glacial grooves. grooves. 19.6 19.6 Turn right to Stop Stop 8. 8. 19.7 19.7 Quincy Steam Steam Hoist. We're in in the thecenter centerof of the the Quincy Quincy Mine Mine area area at at Shaft Shaft No. 66 and and the the Quincy Quincy Steam Steam Hoist Hoist (Fig. (Fig. 23). 23). The Quincy Hoist is the largest Quiincy Steam Hoist largest steam mine mine hoist in the the world. world. This great great machine, machine, by Bruno Nordberg Nordberg and and installed installedinin 1920, 1920,could couldlift liftaa 10 10ton ton ore ore load load at at aa rate rate of of more invented by than 1000 1000 m per minute. The Thehoist hoist isisstill stillin in pristine pristine condition condition and aa full full museum museum of of the the Quincy Quincy Mine is maintained Mine maintained inside the building building as well. well. The hoist can be visited visited during during the the summer summer months for an admission charge. Tours months admission charge. Tours of of the the Quincy Quincy Mine Mine Adit, Adit, connecting connecting with the Quincy Quincy workings, start at the hoist and is operated by the Quincy Mine Hoist Association. workings, start hoist and is operated by the Quincy Mine Hoist Association. For an an admission charge, charge, vans vans shuttle visitors to the admission the underground underground workings, workings, where excellent excellent crosscrosscopper-mineralizedrock rockcan canbe be observed. observed. The Quincy Mining sections of lava flows with native copper-mineralized Mining Company earned earned the the name name "Old "Old Reliable" Reliable"because becauseititpaid paiddividends dividendsso soregularly. regularly. Lankton and Company Hyde (1982) provide an an outstanding historicalaccount accountofof the the Quincy Quincy Mining Mining Company. Company. The Hyde (1982) provide outstanding historical The below as Stop 8. geology of the Quincy Mine and connecting adit is described below STOP 8: Quincy STOP QuincyMine MineAdit Adit(Portage (PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) Mine Adit connects connects with with the the Quincy Quincy Mine Mine (Pig. (Fig. 24) 24) and and is owned by the The Quincy Mine Association. The Quincy Mine Hoist Association. The Michigan Michigan Tech Mine (the (the mine adit) description is revised from Bornhorst Bomhorst and McDowell (1992) and Bomhorst and others. (1986). (1986). once aa drainage drainagetunnel tunnelfor forthe theQuiincy QuincyMine. Mine. Michigan Tech The Quincy Mine Adit was once students in Mining Engineering expandedthe the adit adit (since (since 1976) to to its present size. students Engineering expanded size. The adit adit intersects old workings of the Quincy Mine, one of the major producers in the district with 10% 10% production. The adit is 700 m in length; 5 x 5 m of total district production. m in in cross-section; cross-section; and leads to the No. 5 shaft shaft area area on the the seventh seventh level of the the Quincy Quincy Mine, where it divides into into several several drifts drifts that are used for for mining mining and and rock rock mechanics mechanics research and teaching (Figs. 24). Exposed at this site 4) are are site of the the Keweenaw Keweenaw Peninsula native copper district (Figs. 2 and 4) of basaltic flows, flows, aa long, high high open stope follows two classic aspects: 1) in an inclined sequence of a major and 2) an oblique major horizon horizon of of mineralized mineralized flow tops (Pewabic); (Pewabic); and oblique fault fault (Hancock (Hancock Fault) Fault) limit for for the the Pewabic Pewabic orebody. orebody. A offsets the basalts and forms the southwestern limit A segment segmentof of this this fault was mineralized and mined at the Hancock Mine, where about 365 m of the fault was mineralized and mined Hancock Mine, where about 365 the fault was opened down to the 12th 12th level (300 m vertical). This Thisfault faultmay may have have been been aa feeder feederthrough through which which the mineralizing mineralizing solutions reached the favorable Pewabic Flow tops. The Quincy Mine began operations on the Pewabic Row Flow tops in 1856 and ended in 1967. 1967. along aa series flow tops tops by by 8 shafts--on The mine was developed developed along series of parallel parallel flow shafts-on 85 levels--to levels-to a vertical depth of 1675 1675 m. The Theorebodies orebodiesdecrease decrease in in dip dipfrom from55° 55' atatthe thesurface, surface,toto350 35' at at the the bottom levels (Fig. (Fig. 25). 25). By 330 million millionkg kgof ofcopper copperand and22xx lo9 io By 1925, 1925, the mine had sold about 330 106oz) oz) silver. silver. Production to 1968 g (71 x 10' 1968 totaled 490 million kg of copper, ranking it fourth fourth in in the district. The Pewabic flows at the Quincy Mine are relatively thin and are difficult to follow, The Pewabic Flows at the Quincy Mine are relatively thin and are difficult to follow, been mapped mapped in in detail detail (Butler (Butlerand andBurbank, Burbank,1929). 1929). The flows are unless the top of the flow has been porphyritic with with large large feldspar feldspar phenocrysts, phenocrysts, and and some some of of the thicker flows texturally distinctly porphyritic flows �QUINCY MINE LOCATION HOUSIING AND COMMUNITY STRUCTURES C0 k920 C asaa. Ø.ttVWS& J trJ /mica-*are 4 CW*3 Clericsamaence a Mint ~ i n eqpa ~fflcs w tstEg If *#vdot Qtgt', It C,u,qIic tht,rh and ATtSfl Q ~ a-t l w t i e . ~ w t i o n d ~ n e a c ~ m -- KS a ]Jame,MeaqetSnIö7WOfV a m H-Svaqv and Company franklui ismrv —a 6.ffwwMychSHmaenos #4 franklin id,oo UfwMmilctWot 7. cacwra/wnence 15 ~ wt~ftSMI&1 w ~ s n  iotc(; ¥ ~ c h&&tU ool;/rantti a AbmY ~MU- W itÇPwaHicSchoo aw,bE; 3G'Ot a tfumcwÂ¥3cfwo 1!It tt cr ! t..._ a.n' — — _.•_ — a, I .1 S Figure Figure23: 23:The TheQuincy QuincyMine Minelocation location(from (fromLankton Lanktonand andHyde, Hyde,1982). 1982). �A B '.7 C I °—" I I-,, I I :• : C, Figure Hancock Mines Mines (from (from Bomhorst Bornhorst and andothers, others,1986). 1986). The TheQuincy Quincy Mine Mine workings follow follow several Figure 24: (a) (a)Sketch Sketch map map of of the the Quincy Quincy and the Hancock several parallel Fault. The parallel flow flow tops tops (Pewabic). (Pewabic). These These flow flowtops tops are are not not mineralized mineralized south south of the the Hancock Hancock Fault. TheHancock Hancock Mine Mineoperated operated on the Hancock projectionsofofmine mineworkings workingstotothe thehorizontal. horizontal. The TheQuincy Quincy Mine Mine Adit Adit (MTU (MTUMine Mineon onfigure) figure) Hancock Fault. Stippled Stippledpattern pattern represents represents projections provides to the Allouez Conglomerate, N-S provides access access to Conglomerate, the Hancock Fault, Fault, and and open open stopes stopes of the Pewabic Pewabic deposit. deposit. Same Samescale scalefor formap mapand andN-S of the the adit adit at at A' A' (from section. (b) (b) Geology Geology of the Quincy Mine Adit Adit with withthe the portal-to-A portal-to-A section section joining the the remainder remainder of (from Bornhorst Bornhorst and and section. others, others, 1986). 1986). The Theold oldstopes stopeson onthe the Pewabic Pewabic deposit depositextend extend only onlyshort shortdistances distances southwest southwest of the the No. No. 55shaft; shaft;mineralization mineralization terminates terminates at the Hancock Fault such such that neither the fault nor the the southern southern portion of of the the Pewabic Pewabic flow flowtops topscontain contain significant significant native native copper. copper. The The deposit. B, C, and F refer stopes in the the vicinity of shaft follow followan anamygdaloid amygdaloid200 200mmstratigraphically stratigraphicallyabove abovethe the Pewabic Pewabic deposit. B, C,and F refer to to stopes in of the the No. No. 77shaft thick flows flowsininthe the adit. adit. thick I �Harbor geologic relationships of the Keweenaw Peninsula. The Portage Lake Volcanics are overlain successively by the Copper Harbor with the younger Conglomerate, the Nonesuch Shale, and the Freda Sandstone. The Portage Lake Volcanics are in fault (reverse) contact Hancock Conglomerate for the Portage Lake Volcanics (p) are as follows: Jacobsville Sandstone (see Fig. 2 Introduction). Abbreviations Hecla Conglomerate (pc), (phc), Pewabic West Conglomerate (pp), Greenstone flow (pg), Allouez Conglomerate (pa), Cahimet and (ps). Kingston Conglomerate (pkc), Kearsarge flow (pk), Scales Creek fbi (psc), Bohemia Conglomerate (pb), St. Louis Conglomerate section illustrates the general FIgure 25: Geological cross section from B to B' on Map H6, B' to B" on Map 4, B" to B" on Map 5. This cross Con9lomerate Copper "0. • .xcq .1007 .S.s lent SW B", Ut -S �52 MzinRoadI.og have an ophitic ophitic texture. The Theflow flowtops tops are arc characterized characterized (Butler (Butler and Burbank, 1929) 1929) by cavernous cavernous zones or layers 1 to 1.5 and coalescing coalescing vesicles. vesicles. Layers can form zones 1.5 m thick, thick, large gas cavities, and for 3 to 30 m, and a series of such openings provided an almost continuous connected openings for path for the flow of mineralizing hydrothermal hydrothermalsolutions. solutions. Where coalescing is is well developed in Amygdaloid, there there may may be be 22 to to 10 layers. layers. There the Pewabic Amygdaloid, There is is every every gradation gradation from from coalesced coalesced tendency to to collect collect in layers. Brecciated layers of vesicles, to those that show only a moderate tendency Brecciated of the Pewabic Pewabic Flows flows as they flow tops are not characteristic characteristic of they are are for for other other flow flow top topdeposits. deposits. calcite are abundant cavity- and amygdule-filling amygdule-fluing secondary Quartz and calcite secondary minerals, minerals, with with pumpeilyite pumpellyite and epidote less abundant. Chlorite Chlorite is is present present in amygdules in the base of the flows, except near is present veins veins where where it is is replaced replaced by by quartz quartz or or calcite. calcite. Prehnite Prehnite is present but not not common, common, and and laumontite is mostly confined to to veins. veins. Datolite Datolite was reported from upper levels of the mine, mine, but but through the the mine, mine, dipping dipping at at high high angles. angles. The not lower levels. Several Severalprominent prominent veins extend through The veins are mostly mostly filled with with calcite, calcite, laumontite, quartz, and epidote and are similar similar to to minerals minerals found in the the flow flow tops tops (Butler (Butlerand andBurbank, Burbank, 1929). 1929). These veins probably probably help integrate integrate the the paleohydrologic system for the movement of ore fluids. The adit adit exposes exposes 12 12lava lavaflows flowsbeneath beneath the the Allouez AllouezConglomerate, Conglomerate, dipping dipping about about 50° 50' northwest, northwest, with several several thick flows noted on Figure 24. The The Greenstone GreenstoneFlow, How, which which lies liesdirectly directly above above the Allouez Conglomerate, can be traced for 50 km northeast--where it is 430 m thick--and to Isle Royale on Lake Superior, 100 100 km north. An An excellent excellentexample example of of aa clay clay gouge gougeassociated associated with a bedding plane fault of unknown displacement occurs at the top of the with a bedding plane fault of unknown displacement occurs at the top of the Allouez Allouez Conglomerate. Conglomerate. Such Suchfaults faultsare arefound foundthroughout throughoutthe the district, district, especially especially on on the the top top of conglomerate conglomerate beds. beds. Pewabic How flow tops At the Quincy Mine, the Pewabic tops are about about 100 100 m m stratigraphically stratigraphically (120 m horizontally) above the Allouez Conglomerate. Conglomerate. About About 12 12 lava lava flows flows occur occur in in this this interval interval in in the the Flows are barren barren at this location on on the south side of the Hancock Fault. adit, but the Pewabic Rows Above Above the the Allouez Allouez Conglomerate, 14 14 more lava flows occur before the Hancock Fault is reached; reached; about 425 m from the entrance. The Hancock Fault is marked by a distinctive clay gouge The Hancock Fault is marked a distinctive clay gouge(almost (almost corrensite) and a green corrensite-rich, brecciated brecciated alteration alteration zone zone adjacent adjacent to to thegouge. the, gouge. The pure comnsite) fault is best exposed in the the small small drift drift leading leading to the the No. No. 77shaft shaftarea, area, where wheresmall smallexploratory exploratory stopes were made in a flow top that occurs 200 m stratigraphically stratigraphically above the Pewabic lode on the Fault. No southwest side of the Hancock Fault. No native native copper-rich copper-rich flow tops occur at at the the stratigraphic stratigraphic position of the Michigan Tech Tech adit adit southwest southwest of of the theHancock HancockFault. Fault. In the flow tops of the adit, amygdule-filling minerals include quartz; calcite; pumpellyite; epidote; chlorite; laumontite; laumontite; and and native copper. Rimmed Rimmedamygdules amygdulessuggest suggestearly early prehnite prehnite and and chlorite, chlorite, followed followed by by quartz, quartz, then then chlorite, and lastly calcite (Bumgarner, (Bumgarner, 1980). 1980). Some of the Pewabic lode has been mined by students so they can run experiments. experiments. The The ore ore grade grade is is about about 1.75% 1.75%copper. Return to the the main main road. mad. 19.85 Turn Turnright right on onUS-41. US-41. MAP4 MAP 4 21.05 Turn arc some someof of the the Quincy Quincy 21.05 Turnright righton onArcadian ArcadianRoad. Road.On Onthe theleft leftside, side,immediately immediatelyafter afterthe theturn, turn, are Mine rock piles, nearest to Shaft No. No. 1. This This is is Stop Stop 9. Please Pleaserespect respectprivate private property property signs signs and and stay within the public right-of-way. within the public right-of-way. STOP (native STOP9: 9:Quincy QuincyMine MineRock RockPiles Piles (nativecopper copperdeposit depositwithin withinPortage PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) Refer Stop 88 for for aadescription description of of the theQuincy Quincy Mine, Mine, which which worked worked the the Pewabic Pewabic Refer to Stop �MainRo.dLog 53 Amygdaloid. In the Amygdaloid. the Pewabic, Pewabic, quartz quartz is is the the most most abundant abundant secondary secondary mineral mineral associated associated with with native copper, but calcite is also abundant. Pumpellyite, Pumpellyite, epidote, epidote, and chlorite chlorite are are common common but but prehnite is present. Laumontite not abundant and prehnite Laumontite and datolite are common in upper levels but not lower levels. levels. However, the majority majority of of the the rock However, the rock at at this this stop stop is amygdaloidal-to-massive amygdaloidal-to-massive basalt. basalt. with lesser amounts of of pumpellyite pumpellyite followed by Secondary minerals are mostly quartz and calcite with epidote. Paragenetically, Paragenetically, epidote epidote and and pumpellyite pumpellyite seem to be early, whereas quartz; calcite; and native copper formed later. copper formed later. MAP 55 operations, 20.5 Entering Pewabic, another one of the communities that sprung up around the Quincy operations, 20.5 with Several ethnically and owned owned by bythe thecompany. company. Several ethnically distinct distinct with most most of of the the houses houses built built and neighborhoods existed 'on the hill" in the early 1900's. In all, more than 6,000 people lived neighborhoods existed "on the early 1900's. In all, more than 6,000 people lived on on the hill in in 1905. 1905. 21.45 Thereisisaa"Y "Y" theroad; road,take takethe theright righthand handbranch, branch,which whichisisessentially essentiallyaastraight straightroad, road, with with 21.45 There ininthe a sign saying Arcadian Scenic View. sign saying Arcadian Scenic View. 21.7 Passing a radio tower on the right, we are now crossing the Scales Creek Flow Row at at the the top top of of the the small ridge (see Map 5). The just below the Scales Creek TheArcadian Arcadian Mine Mine worked worked an amygdaloid just Flow. The Row. Theamygdaloid amygdaloidmay may correlate correlate with with the the Isle Isle Royale Royale Amygdaloid Arnygdaloid discussed at Stop Stop 2. 2. North of the road is Shaft North Shaft No. I1of ofthe theArcadian Arcadian Mine. Mine. Stoiber Stoiber(unpublished (unpublisheddata) data) studied studiedthe the rock pile from from Shaft Shaft No. No. 11and andestimated estimatedthe thepercentages percentagesof of non-metallic non-metallic secondary secondary minerals: minerals: calcite, 43%; prehnite, prehnite, 25%; 25%; quartz, quartz, 16%: 16%: K-feldspar, K-feldspar, 8%; 8%; epidote, epidote, 6%; 6%;pumpdllyite, pumpellyite, 1%; 1%;chlorite, chlorite, 1%; and laumontite, trace. 22.4 To the right right of the the road road you you can can see see the the largest largest part part of of Portage Portage Lake, Keweenaw Keweenaw Bay, and the Huron Mountains. Much Much of of the thefield fieldof ofview viewisisbasically basically flat-lying flat-lyingJacobsville Jacobsville terrane. terrane. 22.6 The road turns turns to to the the right right and and changes changes to togravel. gravel. 22.8 We're descending We're descendingoff off the the Portage Portage Lake Lake Volcanic Volcanic Series Series by crossing crossingthe the Keweenaw Keweenaw Fault Fault and and onto onto Jacobsville Sandstone. Jacobsville Sandstone. 24.0 We are are descending descending the hill and have a view view of of the the Isle Isle Royale Royale sands sands across across Portage Portage Lake Lake in in Houghton; they are tailings from the Isle Isle Royale Royale Mine. 24.15 The 24.15 Thejunction junction with with M-26; M-26; take take aa left leftturn turn atat the the Portage Portage Lake Lake Coal Coal Dock. Dock. 24.6 24.6 Entering Dollar Bay on M-26. MAP66 MAP cross-bedded redbeds redbeds of of the the Jacobsville Jacobsvilie Sandstone Sandstone on on the the left side of 26.2 26.2 An exposure of flat-lying cross-bedded the road (northwest (northwest side). side). 26.9 Mason. Mason Entering the small town of Mason. Mason was was the site site of company housing for the Quincy Mill operations from from 1890. 1890. 27.5 which is is stuck stuck in in tailings tailings in in Torch TorchLake. Lake. This is On the right side of the road is an old dredge which by the the Quiincy Quincy Mill Mill in in 1955 and used until the C&H dredge #1, built in 1913, 1913, which was bought by 1967. 1967. �p 54 Main Roll Log �55 Main Road ¼ / 4't( ., ,,/ ,tG r ,' - ,, - p.- -St.-- S I, II II S Is Cl) / I — 5-- p -' C NEt4P-9A TICN8I EXPLORATION S 41012 / / IT-'-'. / NA?? A H Nt4L5Q NAL3 I uiney Mill S \14— 41 - I 5— •.c,_\_-,_ UI 1 ---, — — -, - —'l- — ______/_\_ — I -. - .- - / 1/ —-. - '1\ 1stc$ 0 'V — C, --\E -: - - Cr Map5 '*1- 40 7 / / 602 jF I' 1' -7 - :--. —IL 1* c) • II Ii j7 c==_v 26 W;; 7 'I 4 1.- 4 — / fi / 7' 56$ - z — I —'' 7—- —,Vf'_-— - ,'t:/ #—) - - - - - /_ t- -L MAP —N �56 56 ~ a l ~i o a d~ o g You may pull to the right of the mad road and view the dredge at your leisure. This Thisisisthe theTorch TorchLake Lake Superfund Site. The Superfund Site. The site site was was used used as as aa giant giant tailings tailings pond for both the Calumet Calumet & Hecla and Quincy operations. operations. Torch Quincy Torch Lake has been more than 20% filled with stamp sands from both the and conglomerate conglomerateore orebodies bodiesofofthe thedistrict. district. The The relatively relatively inert inert stamp stamp sands sands have have aa amygdaloid and stronger aesthetic impact than a chemical one. On stamp sands, much stronger sands, little little vegetation vegetation grows, grows, and and ponds, toxic toxic levels levels of of Cu Cu may may be be found. found. Other on the surface of poorly drained ponds, Othertrace traceelements elements that may be be elevated elevated and and of of environmental environmental concern include Cr, As, and Ag. In the 11970s, 970s, tumorous tumorous sauger saugercaught caughtby byfishermen fishermenininTorch TorchLake Lakewere werethe the focal focal point point of In concern, and and the the site was was eventually eventually designated designatedas asaa superfund superfund site. site. No cause environmental concern, cause for for defmitively determined, determined, and and sauger, sauger, which which live live in in murky murky water, water, are are no no longer longer the tumor was ever definitively found in Torch Lake, which is less turbid now than it was when tailings tailings was was entering entering itit regularly. regularly. One interesting result of the environmental studies on the lake, was the observation of environmental studies on the lake, was the observation of a bottom enriched in in Sn Sn and and Pb. Pb. These sediment plume in the lake (Fig. 26) which was highly enriched Theseenrichments enrichments due to to mill mill wastes wastes are not part of the the geochemistry geochemistry of native Cu deposits, and are believed to be due which date to the post war era era (1945-68) when electrical wastes from a large part of the the midwest midwest were channeled through the Calumet & & Hecla Hecla mill mill at at Tamarack. Tamarack. 27.7 Mill, built built in in 1890 to accommodate Now we pass the remains of the main buildings of the Quincy Mill, steam stamps. The mill mill was was required required when the the Quincy Quiincy operation operation expanded expanded to to the the Pewabic Pewab'ic Lode. Lode. 28.0 Along the road road on on the the left leftare aremore moreoutcrops outcropsof offlat-lying flat-lyingJacobsville JacobsvilleSandstone. Sandstone. STOP 10: M-26 STOP M-26near nearTamarack Tamarack(Jacobsville (JacobsvilleSandstone) Sandstone) Jacobsvile Sandstone and quartzose quartwse sandstones, sandstones, The Jacobsville Sandstoneisis aa fluvial fluvialsuccession succession of of feldspathic feldspathic and conglomerates, siltstones, siltstones, and and shales shales up up to 1,000 1,000 m thick (Fig. (Fig. 27) 27) Filling filling a rift-flanking rift-flanking basin basin conglomerates, 1982). There or cross-cutting cross-cutting dikes. dikes. The (Kalliokoski, 1982). There are are no no interbedded interbedded lava flows or The age age of of the the Jacobsville is inferred of geologic geologic evidence evidencetotobe beabout about1070 1070toto1030 1030m.y. m.y.old. old. The infened on the basis of Jacobsville Sandstone Sandstone is in fault contact contact with the PLV along the Keweenaw Fault on the the southeast southeast along the fault side of the theKeweenaw Keweenaw Peninsula. Peninsula. Some active movement movement along fault occurred occurred during during deposition of of at least deposition least part part of ofthe theJacobsville JacobsvilleSandstone Sandstone(Kalliokoski, (Kalliokoski, 1988; 1988; Hedgman, Hedgman, 1992). 1992). Ancient current current directions directions in in the the Keweenaw Peninsulaare are to to the northeast Ancient Keweenaw Peninsula northeast and east, east, which which northeast of of Keweenaw Keweenaw Bay Bay (Fig. (Fig. 21b). 21b). West suggests transport to deeper parts of a basin located northeast West and current current directions directionssuggest suggestanother anotherdeep deeppart parttotothe thebasin. basin. East East of of of Lake Gogebic, thickness and Calumet, near the Keweenaw Fault (Stop 12), the Jacobsville contains boulders boulders of of Calumet, Keweenaw Fault Jacobsville Sandstone contains basalt--which suggests suggestsaa topographic topographichigh highininthe thePLV PLVnorth northofof the the fault fault during during this this period period of of basalt--which Jacobsville sedimentation—due to reverse movement along the Keweenaw fault. sedimentation-due to reverse movement along Keweenaw fault. Jacobsville Jacobsville sedimentation sedimentation was was the the last last event event associated associated with the the development development of the the Mid-continent Mid-continentrift rift system system by a long period of cratonic stability. in the Keweenaw Keweenaw Peninsula and was preceded by stability. Lithology of sandstones varies from subarkose sandstones of the Jacobsville Jacobsville Sandstone varies subarkose to quartz sublithic arenite. arenite. There arenite. Grain Grain size size varies varies from from fine fine There are are some some beds of arkose and quartz arenite. to coarse. coarse. Quartz grains show show evidence evidence of of volcanic volcanic and and metamorphic metamorphic origin. origin. Microcline is unaltered- to to highly-altered. highly-altered. Other Other clasts clasts include: include: volcanic volcanic relatively unaltered and plagioclase is unalteredrocks, schist, muscovite, and chlorite. Sandstone schist, shale, shale, and the the minerals: minerals: epidote, biotite, muscovite, Sandstonevaries varies in color from red to aa cream-white color. The cream-white or purplish-red purplish-red color. The color color depends depends on the the alteration alteration of of ferromagnesian minerals and and the the amount amount of of iron oxide ferromagnesian minerals oxide deposited deposited as rims rims on on feldspar feldspargrains. grains. Ripple marked bedding surfaces and cross-bedding common in in some localities. Sandstones Sandstones cross-bedding are common are fluvial, fluvial, and and conglomerates conglomerates probably probably represent represent alluvial alluvial fan fan deposits deposits (summarized (summarized from from �MeinRoadLog 57 TORCH TORCHLAKE LAKESEDIMENT SEDIMENT pprn ANOMALIES IN INppm ANOMALIES Figure26: 26: Contoured Contouredconcentrations concentrationsof of Pb Pband andSn Snininsediment sedimentand andstamp stampsand sand in inTorch TorchLake Lakeand and Figure vicinity (fromRose Roseand andothers. others,1986). 1986). vicinity(from �58 MsinRowlLng A B >I Current Directions Km. C Figure ofofJacobsville Figure27: 27:Relationships Relationships JacobsvilleSandstone Sandstone(from (fromKalliokoski, Kalliokoski,1982). 1982).A.A.Thickness ThicknessofofJacobsvilte Jacobsville Current directions Sandstone '+'. B.B. Current directionsininthetheJacobsville Jacobsville Sandstone with with minimum minimum thickness thickness denoted denoted by '+'. C. Location Location of of possible possible source source areas areas of ofiron ironformation formationand andofofstaurolitic staurolitic Sandstone. C. Sandstone. metasedimentaiy clasts. �MainRoidLfl Main Road Log 59 Kalliokoski, Kalliokoski, 1982). 1982). The outcrop at this stop (Stop 10), lo), about 120 120 m long long and and 33 m mhigh, high,displays displaysfeatures features characteristic of the fluvial Jacobsville Sandstone. At the northeast end of the outcrop, the characteristic At the northeast end of the outcrop, thesection section exposes red shale and red-brown at the the level level of of the the highway. highway. They are red-brown siltstone at are overlain overlain by by two two fining-upward sequences of conglomerate conglomerate and red, red-brown, red-brown, and and white white crossbedded crossbeddedsandstone. sandstone. The lower conglomerate bed is is planar planar and and can can be be traced traced 30 m to the southwest, along with the conglomerate bed underlying shale and siltstone. Farther to the southwest, underlying shale Farther to the southwest, the the section section is is almost almost entirely entirely crossbedded crossbedded red sandstone, sandstone, in beds 0.2 0.2 m m toto1.0 1.0mmthick, thick,some someofofwhich whicharearecontorted, contorted,conspicuously conspicuously crossbedded, and color mottled. Crossbeds Crossbedsshow showaanortheasterly northeasterly transport transportdirection. direction. The sandstone consists of almost equal parts of rounded-to-subrounded quartz, feldspars, feldspars, and lithic fragments. fragments. Clasts in the the lower lowerconglomerate conglomerate are arepredominately predominately subangular, subangular, felsic felsic volcanic in composition, entire section section can be be rocks. The entire volcanic composition, with with subordinate subordinate mafic mafic volcanic volcanic rocks. interpreted as a shaly flood plain sequence overlain overlain by by sandy sandy fluvial fluvial deposits. deposits. The interpreted The Jacobsville Jacobsville Sandstone fills a rift-flanking basin southeast of the the rift rift proper. proper. At this stop, the character of the Jacobsville Sandstone can be compared and contrasted to Jacobsville that will be seen at Stop 11 11 and Stop 12. 12. 28.3 28.3 On the right right is is Torch Torch Lake. Lake. 28.7 have been been revegetated. The Enter Tamarack City. On On the theright right side side of the road are tailings which have The Hecla Company Mines Mines and of the Calumet tailings are part of the mill operation of the Calumet & Hecia region, which have have major major mills mills located located atatTamarack Tamarackand andHubbell. Hubbell. 29.15 On 29.15 Onthe theleft leftside sideofofthe theroad roadare arethe thefootings footingsfrom fromone oneof of the theTamarack Tamarack Mills. Mills. MAP 7 are the the remains remains of a steam steam stamp stamp mill. 29.6 On the right side of the road are 29.7 Turn left, going up the hill toward 9. Follow toward Stop 9. Follow the the paved paved road road which which jogs a little little to to the the left left and goes up the hill. hill. 29.85 Cross 29.85 Crossthe theold oldCopper CopperRange Rangerailroad railroadgrade. grade. 30.0 30.0 Hungarian Falls. Falls. This is A sign indicating the Hungarian is the the lower lower part of the the falls, falls, continue continue going up the the hill, straight ahead. 30.25 30.25 The Thejunction junction of ofaafour-wheel four-wheeldrive driveroad road isisto tothe theleft. left. Stop here and walk toward the the Tamarack Tamarack Reservoir/Hungarian Falls upper part, where excellent exposures of Jacobsville Sandstone are Reservoir/Hungarian Falls upper part, where exposures of found near the the Keweenaw Keweenaw Fault. Fault. STOP 11: STOP 11: Hungarian HungarianFalls Falls(Keweenaw (Keweenaw Fault) Fault) Hungarian Falls is located near the the Keweenaw Keweenaw Fault Fault (Fig. (Fig. 28). 28). The The Keweenaw Keweenaw Fault is is a reverse fault that juxtaposes older PLV and the the younger younger Jacobsviile Inthis thislocality, locality, Jacobsville Sandstone. In presumably dips dips at at a high angle to the west, the Keweenaw Keweenaw Fault presumably west, similar similar to that that illustrated illustrated in in Figure 25. At Atthe thesurthee, surface,the theKeweenaw KeweenawFault Fault varies varies from from aa single singlefault fault plane plane to to aa more more complex complex fault zone, such 5.85). The such as as described near Lac La Belle (Leg D, mileage 5.85). Thestructural structuralrelationship relationship of beds near the fault also varies from steepened dips to folds. In In general, general, the the dip dip of of the the PLV PLVand and �60 MOIDROa4LOg Map8 — I I I I I I I 1 I Map6 �Main Log ~mRo.d ~ o ~do g 6161 Tamarack reservoir metal grat Jacobsville Jacobsvilie 100 sandstone sandstone feet z— D fault fails basalt Conglomerate Figure Figure28: 28:Geologic Geologicsketch sketchmap mapofofthe theHungarian HungarianFalls Fallsarea area(unpublished (unpublishedmap mapby byJ.M. J.M.Robertson, Robertson.1973, 1973. Basalt and conglomerate are part of the pan of the Portage Pomge Lake Lake from Bomhorst Bomhorstand andothers, others.1983). 1983). Basalt and conglomerate from Volcanics. Volcanics.Note Notethat thatnorth northisistoward towardthe theleft left margin marginof ofthe thepage. page. �62 62 zinRoadI.og Main Road Log Jacobsville Sandstone steepen appropriately as one one approaches approaches the the fault. fault. Falls, the fault contact causes very At Hungarian Falls, very little deformation of the Jacobsville Jacobsville Sandstone, which is only tilted slightly. To the west of the fault, at this site, the Portage Sandstone, which is only tilted slightly. the west of the fault, at this site, the Portagelake lake Volcanics are are unusually unusually shallow shallow dipping. dipping. If not viewed viewed in the context context of of many many other otherlocalities, localities, the fault fault might not be be recognized recognized as as such such aa profound profound feature feature and could could appear appear as as aaconformable conformable contact. The Thecontrast contrastbetween between the the fault fault exposure here at Hungarian Falls and that at the Natural Wall, Stop 12 12 (the (the next next stop), stop), isis striking, striking, and and illustrates illustrates the structural structural variability variability of rocks rocks along along this major major feature. feature. PLY near the Keweenaw Fault at Hungarian Falls consists of basaltic lava The PLV lava flows flows with with interbedded conglomerate. Interbedded sediments make up a small part of the stratigraphic section interbedded interbedded sediments make up small stratigraphic However, here here and and at a arefound foundas asrelatively relatively thin, thin,widely widely separated separated beds. beds. However, of the PLY PLV and and are within the the PLV PLY are either number of other localities in the Keweenaw Peninsula, conglomerates within near, or at, at, the the fault faultcontact. contact. along the the stream to to the upper and lower falls, allows examination Walking downstream, along of good of good exposures exposures of of Jacobsville Jacobsville Sandstone Sandstone with with cross cross bedding; bedding; interbedded interbedded shaly shaly and and conglomeratic horizons; and many typical typical arkosic arkosic redbed sedimentary sedimentary rocks. rocks. 30.25 Go 30.25 Goback back to tothe thecars carsand andgo goback back down down the the hill hill to to Tamarack Tamarack City. 30.8 Stop sign. Stamp Stampmill mill remains remains are are straight straight ahead. Turn Turn left left on on M-26. M-26. 30.9 Entering Hubbell. 31.5 On the right are the Calumet Calumet & & Hecla Hecla Mill buildings that are now being used for small small industries. industries. Torch Lake is still still on on the the right right with with many many of of the the tailings tailings in in the the lake. lake. 32.4 Entering the town of Lake Linden. The The Houghton Houghton County Historical Museum is on the right side of the road. The Thebuilding building(1917) (1917)was wasdonated donatedby bythe theC&H C&H(Calumet (Calumetand and Hecla) Hecla)Company Companyto tothe the Houghton County County Historical HistoricalSociety Societyinin1963. 1963. Among the best best displays displays are are scale models models of Houghton Among the underground mines and a rich rich photographic photographic record of the the boom boom copper copper days. days. 33.2 Turn right on on Ninth Ninth Street Street (the (the so-called so-called Bootjack Bootjack Road) Road) in in Lake Lake Linden. Linden. 33.35 Turn Turnleft lefttwo twoblocks blocksafter after 32.2. 32.2. Follow Followthe thesigns signsto to the the Lakes Lakes Drive-In Drive-in Theater. This ThisisisGregory Gregory Street. Street. MAP 88 cemetery. The road heads north along the Trap 34.3 On the left side of the road is the Lake Linden cemetery. Rock River Valley. On the left side of the road, On the left side of the road,atatthe thetop topof ofthe thesteep steepslope, slope,isisthe theKeweenaw Keweenaw right side side of of the theroad, road,isisflat-lying flat-lyingJacobsville Jacobsville terrane. terrane. The Trap Rock Rock River River Fault. Fault. On the right follows follows another another of of the the glacially glacially eroded, eroded, deep deep bedrock bedrock valleys valleys described described by by Warren Wamn (1981). (1981). 35.5 35.5 Pavement ends. 35.6 The gravel road bears to the right. right. 35.9 Cross over the the Trap Trap Rock Rock River. River. Cross a bridge over �Main Road Log 63 MAP �64 M-i" i Log 36.0 at the the Trap TrapRock RockSchoothouse. Schoolhouse. Turn left left at Thrn 36.0 36.0 Cross the Trap Rock River River again. again. 36.7 36.7 Turn left on another dirt road that begins to go go up up hill. hill. 37.1 37.1 railroad grade grade of of the the Copper Copper Range RangeRailway. Railway. Access Access to the Natural Cross the railroad Natural Wall Ravine for this railroad railroad mapping purposes can be gained by walking a couple hundred yards to the left along this and then then walking walking up up the the stream stream valley. valley. The traverse begins in grade until the first major valley, and Jacobsville Sandstone, crosses the Keweenaw Fault, and ends in the PLV at the head of the stream As the road valley. As road parallels parallels the stream stream valley valley a few few hundred hundred meters meters to to the the north, north, it is is recommended that one return via overland and the road. 37.2 37.2 Poor exposures of flat-lying conglomerate beds within within the the Jacobsville Jacobsville Sandstone Sandstone are are on on the left conglomerate beds side of the the road. road. 37.4 path on the left side of the road, about 200 m, for an overlook Stop here and follow a path overlook of the The bottom of the ravine provides an excellent traverse Natural Wall Wall Ravine. Ravine. bottom the ravine provides an excellent traverse across across the the Keweenaw Fault. Fault. To Keweenaw To gain gain access access to to the the bottom bottom of the the ravine, ravine, go back down the road road 0.3 0.3 miles miles to mileage mileage 36.1. 36.1. STOP STOP 12: 12: Natural NaturalWall WallRavine Ravine(Keweenaw (KeweenawFault) Fault) about 200 200 m m south south of of the the gravel gravel road road at the top of aa steep There is a ravine ravine overlook overlook about steep slope. and just just east of the Keweenaw Fault (Fig. 29). 29). This locality is in Jacobsville Sandstone and The Natural Wall is is aa vertical verticalbed bed of of resistant resistant trough-bedded trough-bedded sandstone sandstone that forms forms an an erosional erosional wall on the south The Jacobsville Sandstoneinin this this area consists wall south side side of of the the ravine. ravine. The Jacobsville Sandstone consists of conglomerate; sandstone; and shaly horizons, possibly accumulating accumulating as the lower portion portion of of the the formation dragged along the Keweenaw Fault. Fault. The The attitudes attitudes of beds beds in in the the creek creek bottom bottom change change from flat-lying, about 1 km to the east east of of the the fault; fault; to to east-dipping; eastdipping; and finally to vertical, vertical, and then the beds are folded as the Keweenaw Fault is approached. approached. West West of the the fault fault the the PLV PLV dip dip to to The latest movement on the Keweenaw Fault is reverse, but the fault the WNW at 35-40°. WNW at 35-40'. movement on the Keweenaw Fault is reverse, but the nonnal growth fault on the southeast originated as a major normal southeast margin of the Midcontinent rift system (Cannon and others, 1990). Deposition Deposition of of the the Jacobsville Jacobsville Sandstone Sandstone was controlled by the same same compressional the Keweenaw KeweenawFault. Fault. Also at this locality, the Jacobsville compressional tectonism that produced the Sandstone contains abundant boulder boulder sized clasts of felsic and mafic mafic volcanic volcanic rocks, rocks, similar similarto to Keweenawan volcanic rocks. rocks. The Keweenawan volcanic The Keweenawan Keweenawan volcanic rocks were exposed and undergoing undergoing as a result of uplift along the erosion during Jacobsville sedimentation as the Keweenaw Keweenaw Fault. Fault. 38.95 The Thebeginning beginningof of pavement; pavement; we we air areentering enteringthe thetown town of ofLaurium. Laurium. 39.7 39.7 Turn left, followed immediately by by a right turn at the next stop stop sign sign on on School School Street. Street. 39.8 The junction of School Street and Calumet Avenue, Avenue, which which isisUS-41. US-41. Turn right. This ThisisisCalumet, Calumet, Michigan, the center center of of the Michigan Copper District, District,and andthe the site site of of the Calumet Michigan, the Michigan Copper Calumet & Hecla Hecla headquarters. the Calumet Conglomerate load load in in the early headquarters. Here, Edwin Hurlbut discovered discovered the Calumet Conglomerate early 1860's, which was ore body body in in the the whole whole district. district. Greater Calumet was to to become the most important ore (including (including Red Jacket, Jacket, Blue Blue Jacket, Jacket, Yellow Yellow Jacket, Jacket, Laurium Laurium and and Rambaultown) Rambaultown) had had aa population population �___ Math Log 65 Portage Lake Volcanics aKeweenaw a aa a aa Fault a aa u Natural Wall Jacobsville Sandstone .1? 1 1 = \\i t CALUMET CALUMET 11111111 I AND AND I I I I I I "i/' (\ -I It I I ^i\ SCALE SCALE In In thousands thousands of of feet feet HECLA HECLA U' 1 m I . 2 0 9 + I. I. I I GRAPE GRADE I. 111111. 1983). Note Figure 29: 29: Geologic Geologicsketch sketchmap mapof ofthe theNatural Natural Wall Wall Ravine Ravine (from (from Bornhorst and others, 1983). Note Figure that north is toward toward the the right right margin margin of the the page. page. north is �66 MainRotdLfl of 33,000 in 1910. Among Amongthe the many many historic historic buildings, buildings, are the Calumet Theater (1900) and the Community Library Library Building Building (1898). (1898). Immediately behind behind the Calumet High School and C&H Community the blue water tower is the the surface surface location location of the great great Calumet Calumet & Hecla Hecla Conglomerate, Conglomerate, the "Mother Lode" Lode" of of the the district and the the principal ore body body where where more more than than one one third third of all "Mother district and principal ore all Michigan copper was mined. mined. Excavations of a cross section of this great ore body is planned as Excavations body part of the the new new Keweenaw Keweenaw National National Historic Historic Park. Park. MAP 9 41.0 Entering Centennial. Centennial. 41.3 On the left side of the road you can see No. 6. After see the Centennial Mine Shaft No. Afterclosing closingin in1968, 1968, this mine was 1970's by Homestake, but the operation was dewatered dewatered in in the the midmid-1970's Homestake, but operation has has since since been been abandoned. Nos. 3 and 6 worked worked the the Calumet and and Hecla Hecla Conglomerate. Conglomerate. The The Centennial Mine Shaft Nos. The ore ore body lies up-dip and northeast from the main ore body body in the C&H Conglomerate mined by the Calumet and Hecla Mine in the Calumet area. area. The The C&H C&H Conglomerate Conglomerate yielded about 1.9 billion kg of mfmed refined copper, the the largest largest lode in the the district, district, and is is over over one-third one-third of of the the total total production production from the Keweenaw district (total (total district district production productionofofabout about 55 billion billion kg). kg). The Keweenaw native copper district The C&H lode had the highest grade in in the the district district of of 2.85% 2.85% Cu Cu per per ton ton of rock treated highest average average grade treated (Weege and Pollack, Pollack, 1971). 1971). The Calumet and Hecla Conglomerate can can be be followed followedalong alongstrike strikefor formore morethan than65 65kkm. rn. Along most of this length, most length, it is less than about 11 m thick. In the Calumet Calumet area, area, it averages over 3 m with depth. depth. The thick and tends to thicken with Thebed bed consists consists of of north north trending, trending, thicker thicker and and thinner thinner channels. At the Centennial Mine Shaft Nos. Nos. 3 and 6, thickness is often less zones representing channels. than 3 m channel. The m and and the the C&H C&H Conglomerate Conglomerate was deposited in a tributary stream channel. The pebbles pebbles in the the conglomerate conglomerate at at Centennial Centennial are are almost almost all allquartz-feldspar quartz-feldspar phenocrystic phenocrystic rhyolite. The pebbles pebbles in the the main main channel channel conglomerate conglomerate are are quite quite a varied suite of rhyolite and granophyre, granophyre, with with phenocrystic rhyolite. rhyolite. Main and tributary channel conglomerates conglomerates tend tend to to be some quartz-feldspar phenocrystic coarser and contain less fine material material where where it's it's thicker. Outside Outside of of the the 1.5 1.5m m thickness thickness contours, contours, the bed is usually shaly shaly or sandy. sandy. At AtCentennial, Centennial,copper coppermineralization mineralization tends tends to to occur occur in in bands bands with with the bed, bed, and and the the intensity intensity is is related related to to the the type typeand andamount amount of ofinterstitial interstitial material material and and or barriers. bathers. Higher location of pinch-outs or Higher grade grade areas areas are related to conglomerate with coarse sand or small when pebbles pebbles and and sand grains are quartzsmall pebbles pebbles as as interstitial interstitial material, material, especially especially when quartzfeldspar phenocrystic rhyolite. Evidence Evidence also alsostrongly strongly suggests suggests that that the the mineralized mineralizedareas areasfollow follow the axis of stream stream channels and grade grade is highest highest adjacent to the 1.5 1.5 m m thickness thickness contour, contour, where where bed increases greatly greatly in in thickness thickness down-dip. down-dip. These pinch-outs localized ore the conglomerate bed deposition from mineralizing solutions that were were migrating migratingup-dip. up-dip. Sedimentological Sedimentological relationships deposition relationships are important in in exploring exploring the the conglomerate conglomerate ore bodies bodies (summarized (summarized from Weege Weege and and Pollack, Pollack, 197 1). 1971). 41.6 41.6 Entering Kearsarge, Kearsarge, Michigan. 42.1 42.1 A stone boat on the right right side side of of the the road. road. 42.3 mm onto Water Street, just Turright n right onto Water Street, justbefore beforethe theWolverine WolverineMarket. Market. Continue Continuestraight straight ahead on the 42.3 main paved road. road. 42.5 right and and Park along along the road and walk about about 100 100 m to the north. Mine rock piles are on both the right left sides of the road. Keep Keeptotothe theleft leftside; side;the theones oneson onthe theright rightside sideof ofthe theroad road(south)—on (south)-on the �Map 10 Map MthaRoMtOS MAr 6') �68 MainRoadLog dangerous because of bad ground. other side of some some old old buildings—are buildings-are dangerous ground. Mining in this area area was very shallow (Shaft No. No. 3). BEWARE: THEPATHWAYS PATHWAYS because because these these are are OLD OLD BEWARE:STAY STAYON ONTHE mined areas. STOP 13: STOP 13: Wolverine WolverineMine MineShaft ShaftNo. No.2 2(native (nativecopper copperdeposit depositwithin withinPortage Portage Lake Lake Volcanics Volcanics [PLVII) [PLW) Flow top deposit was was worked worked by by the Wolverine Mme Mine and seven The Kearsarge Flow seven other other Kearsarge, North North Kearsarge, Kearsarge, Ahmeek, Ahmeek, Allouez, Allouez, Mohawk, Mohawk, and and Seneca mines: Centennial, South Kearsarge, (Fig. 30). Production Production of of copper copper from from the the Kearsarge Kearsarge Row Flow top top began began in in 1887 1887and and stopped stoppedin in 1967. 1967. About 1026 1026 million kg of refined copper copper were produced at an average average grade grade of 1.05% 1.05% Cu, Cu, making making the Kearsarge deposit deposit the the largest largest flow flow top top deposit deposit and and the second largest largest ore producer in the the Underground workings workingsare are continuous continuousfor formore morethan than 12 km km and extend down-dip as district. district. Underground much as 2,500 m. The TheKearsarge Kearsarge deposit deposit is is one one of the best documented orebodies in the district (Stoiber and Davidson, 1959; 1959; Butler and Burbank, 1929). 1929). The Kearsarge Flow flow has has been been recognized recognized for for aa distance distance of of about about 55 55 km along strike. strike. It lies directly Sandstoneand and dips dips between between35 35 and and 40" 40° N NW directly above above the Wolverine Wolverine Sandstone W (Fig. (Fig. 30). 30). Stratigraphic and textural relationships make this flow easily easily recognized. recognized. It has an an amygdaloid amygddoid top that ranges from near zero up to 10 m in thickness. In the productive area, the flow top is from zero up to 10 m in thickness. productive area, a brecciá. breccia. Individual Individualfragments fragmentsare aregenerally generally less less than than 15 15cm cm in in greatest greatestdimension, dimension, and and contain contain numerous small amygdules. amygdules. The flow numerous small flow top breccia breccia makes up the uppermost uppermost part of the the flow, flow, grading amygdules abundant abundant at certain horizons. grading downward downward into into layered cellular cellular amygdaloid, with amygdules This zone grades grades downward, first, into a zone of fewer and larger amygdules with fewer layered (Table 3). 3). Just structures, and then into massive basalt (Table Just below the flow top is a distinct plagioclase plagioclase porphyritic porphyritic basalt. The Theabundance abundanceand andsize sizeof of the theplagioclase plagioclase phenocrysts phenocrysts in in this this zone zone isisvariable, variable, but they can can make make up up a large percentage percentageofofthe therock, rock,and andcan canbe beup uptoto2.5 2.5cm cm in in length. length. This but zone is probably during in in situ crystallization of the flow. zone probably the result result of of plagioclase plagioclase floating floating during crystallization of flow. can be be found found on on this this rock rock pile. pile. The Specimens with abundant plagioclase phenocrysts can The porphyritic porphyritic zone grades downward into massive aphyric basalt. The Thetop topof of the theKearsarge KearsargeFlow Flowin. in the the mined mined area has an average average thickness of around 2 m. The basalt in the Kearsarge Flow flow is well by two types of well oxidized and has been affected by alteration: albitization albitization and and pumpellyitization. pumpellyitization, Albitized Albitized basalt basalt is about about 60% euhedral euhedral albite laths set in Pumpellyitized basalt basalt consists of finein aafine-grained fine-grainedtotocryptocrystalline cryptocrystalliinegroundmass. groundmass. Pumpellyitized fmegrained pumpellyite pseudomorphically replacing plagioclase. pseudomorphically replacing plagioclase. The amygdule amygdule and interfragmental space-filling gangue minerals in the Kearsarge deposit are generally (in order of most most to to least least abundant): abundant): calcite, epidote, K-feldspar, quartz, and lesser lesser amounts of chlorite, chlorite, prehnite, prehnite, pumpellyite, pumpellyite, laumontite, laumontite, and and sericite. sericite. Native copper is closely closely associated with the secondary amygdule minerals (Stoiber and and Davidson, Davidson, 1959). The Thesecondary secondary assemblages vary both temporally spatially within mineral assemblages temporally and spatially within the productive area. area. Paragenétically, chlorite; epidote; epidote; microclime; microcline; and and prehnite prehnite are are early-formed early-formed minerals, minerals, and and the Paragenetically, chlorite; latest-formed minerals are are quartz; quartz; native native copper; copper; calcite; calcite; and and chlorite latest-formed minerals chlorite (Fig. (Fig. 31). 31). A zonal zonal stratabound arrangement of amygdule minerals minerals in in the Kearsarge deposit is seen in the Ahmeek in the Ahmeek (Fig. 32 and Table Table 4). 4). The to bedding bedding but but irregularly Shaft No. 3 (Fig. The zones are approximately parallel to distributed laterally. the bottom to the top of laterally. From From the bottom to of the the flow flow top, top, are arefive fivemajor majormineral mineral ± calcite 2 ± microcline, assemblages: 1) chlorite 2 microclime, 2) quartz-epidote, 3) calcite-epidote, 4) calcitemicrocline + ± epidote, and and 5) 5) chlorite-calcite chlorite-calcite ± +microcline. microcline. The Thelast lastassemblage assemblage is is found found in in the the �Mrnnaoasl.og 69 A' A nil. 4000 It a Figure 30: Geologic Geologicmap mapand andcross crosssection sectionshowing showingthe theKearsarge KearsargeFlow, How,Wolverine WolverineMine, Mine,and andvicinity vicinity Figure 30: (modified from from White White and and others, 1953; from Bornhorst and others, 1983). 1953; from Bomhorst and others, 1983). Stop Stop 13 is the the mine rock rock pile. pile. Abbreviations are Wolverine Wolverine Mine Mine Shaft No. No. 2 mine are as as follows: Iroquois flow (pi); Hecia Conglomerate Conglomerate (pc); Osceola Osceola flow flow (po); (po); Kingston Kingston Conglomerate Conglomerate (pkc); (pkc); Calumet Calumet and and Hecla Wolverine Sandstone (pw); Old Colony Sandstone Sandstone (poe); (poc); St. St. Louis Louis Conglomerate Conglomerate(ps). (ps). Si02 sio; Table 3: 3: Major-element Major-elementcomposition compositionofof the the Kearsarge Kemarge Table Davidson, flow (from Stoiber and flow (from Stoiber and Davidson, 1959). 1959). This is is aaweighted weighted average avenge exclusive of the This the close thus 12 feet feet and thus represents represents a close top 12 of approximation approximationtoto the the original composition of theflow. the flow. A1203 *lz03 Fe203* Fe203* MgO MgO CaO CaO Na20 Na20 K20 K20 Ti02 Ti09 P205 p205 Mno HZ@+ H20— H20CO2 '32 Total T otal ppm Cu Cu Weight Percent 48.55 48.55 16.51 16.51 11.54 6.68 9.44 9.44 2. 82 2.82 0.58 0.58 1.49 0.18 0.16 2.06 0.63 0.15 100.79 90 �70 MtnRosdLOg =m SW sw ME NE Producbve 90 9 0'- jMes1 Thickncss60 meters 30 30 Top of Wolverine TopSandstone Sandstone of Wolverine H 1iez 4s- -I aI S.- u -, / a, "s Â¥ C C ea M 9 N "s s .a 5I N. N / N. / N \ 1 , / , N \ N N 4— N / SOUTH So.rrH 'CENTENNIAL KEARSARGE — -r OF AHMEEK 6 — — — c— MINING a k?1 Vexy high grade copperore Vqhighgnde-are - limit quat Upper limitof of quartz — e Upper d d N 5 WOLVERINE KEARSARGE — SENECA MOHAWK ALLOUEZ A LLOW wRm N N 0 600 I I 1200 + I SCALE SCALE metess meters Lower limit lint of of micncine microcliae — — * Lower — Figure 31: Figure 31: Thickness Thicknessofofthe theKearsarge Kearsargeflow flow(top) (top)from fromIsle IsleRoyale Royaleto toMandan Mandan(south (south of of Copper Copper Harbor) Harbor) of the showing location location of showing the productive productive area area (modified (modified from from Butler Butler and and Burbank, Burbank, 1929; 1929; from from Bornhorst, 1992) (see (see Fig. Fig. 77 and and 99 for for location). location). The The mined Kearsarge flow top (largest flow top Bomhorst, deposit, with 1026 deposit, 1026 million kg of refined copper production) is is bisected bisected by the the Allouez Allouez Gap Gap Fault Fault (bottom) with the high (bottom) with high grade grade copper copper zone zone northeast northeast of of the thefault faultassociated associatedwith withabundant abundant faults and fractures. fractures. Distribution subparallel faults Distribution of of amygdule-filling amygdule-filling quartz quartz (over (over 10% 10% on on hatchured hatchured aniygdule-filling K-feldspar/microclie K-feldspar/microcline (absent below line) roughly correlates correlates with native side) and amygdule-filling copper (modified (modified from Stoiber and Davidson, Davidson, 1959; from Bornhorst, Bomhorst, 1992). 1992). Amygdule-filling Arnygdule-filling present throughout throughout the the mine. mine. The TheKearsarge Kearsarge flow flow dips dipsabout about 350 35' to 40° 40 calcite and epidote are present northwest and all data projected to a horizontal plane. �MainkoadLog CHLORITE CHLORITE 71 11111110 IIIOIIIIIIIIVV MICROCLINE MICROCLINE Pr•hnlti Prehnlte H e m a tflt• lte Mimi EPIDO E P I D OTE TE P u m p e l.IyIt. /ylte Pump OILIllIIIIIIIIllIIIji. Quartz Quartz Serlclte Ssrlclt• N a t l v e Copper Copper Nativi CALCITE CALCITE Early Early TIME TIME Late Late Figure Figure32: 32:Paragenesis Paragenesisofofsecondary secondaryminerals mineralsininthe theKearsarge KearsargeAmygdaloid Amygdaloidat atthe the Wolverine WolverineMine Mine Shaft Shaft No. (from Bornhorst Bomhorst and others, 1988). The Therelationships relationships are are based based on on aa megascopic megascopic and and thin thin No. 22 (from section study of samples from the the Shaft No. No. 22 mine mine rock rock pile. pile. Compare Compare to district-wide district-wide synthesis synthesis of 12. of paragenesis paragenesisgiven given in inFigure Figure12. �i jnRoadLOg 72 sanH SOUTH — —.. çttt —— p ctte-.ciWott .::::tt Th - WORTH — we. — caftftrwadoM 7< — Footwal m-cwtetcta. SCALE SCALE 0 M m M " 00 aA 10 10 20 20 30 feat 30 feet cupp— copper Contact between Kea,sav. amygdaoW d ovemrp flow bottae, Figure Figure 33: 33: Cross Cross section section of of the theKearsarge Kearsarge Amygdaloid Amygdaloid showing showing the the banding banding of of amygdule amygdule mineral mineral assemblages, Ahmeek Mine, 35th level, 399 to 500 feet south of the Kearsarge Flow (modified Mine, south of the Kearsarge Row (modified from Stoiber Stoiber and and Davidson, Davidson, 1959; 1959:from fromBornhorst, Bornhorst. 1992). 1992). Data from the back back and and walls walls are are to aa horizontal horizontalplane. plane. In In one one mapped mapped locality, locality, Stoiber Stoiber and and Davidson Davidson (1959) (1959) found found aa projected to Arnygdulemineralogy mineralogy of of the the various various zones zones are are given given in in Table Table 44 laumontite-quartz-calcite zone. zone. Amygdule below. shown in in Figure Table Table 4: 4: Volume Volumepercent percentofofaxnygdule amygduleminerals mineralsfrom frommapped mapped assemblages assemblages shown Rgure 33 33 (from (from Stoiber and and Davidson. Davidson, 1959). 1959). Stoiber Mineral Mineral Assemblage Assemblage Band Band Chlorite Chlorite Chlorite— ChloriteMicrocline— MicroclineCalcite Calcite Microcline— MicroclineCalcite Calcite Quartz— QuartzEpidote Epidote CalciteCalcite— Epidote Epidote 0 0 0—1 90—96 00 00 87 87 12 12 0 trace trace Volume Volume Percent Percent kuydule Amydule Filling Filling Chlorite Chlorite Microcline Microcline Calcite Calcite Epidote Epidote Pumpellyite Quartz Quartz 100 100 00 69—74 69-74 15—25 15-25 0—5 0-5 0—1 0-1 0—6 0-6 0—5 0-5 1 2 00 trace trace 00 00 0—3 45—82 0—47 5—10 0—trace 0—8 2 4—9 2 11 1. �MiukoadLog 73 hanging wall wall comer corner in in Fig. Fig. 32). 32). The base of the overlying flow (north hanging The zoning may be be explained explained by deposition of secondary from a hydrothermal solution moving moving along along a permeable secondary minerals minerals from hydrothermal solution channel. Chlorite along the the outer limits of of the Chlorite and and microcline microcliie would would have been deposited first, along solution channel; channel; followed followedby byquartz quartzand and epidote epidoteinin the the center center of of the channel; solution channel; and finally, finally, deposition of calcite This observation is consistent deposition of calcite in in the theremaining remaining openings. openings. This observation is consistent with with the the paragenetic relationshipsseen seen in in individual individual samples. samples. No strict paragenetic relationships strict correlation correlation exists between the stratabound zoning and the grade of native-copper mineralization (Stoiber and Davidson, 1959). 1959). and grade grade of of copper copper mineralization mineralizationvary varywith withdepth. depth. The quartz The amygdule minerals and less than 10% at shallower content is considerably less shallower depths, and generally averages about 15% 15% An irregular irregularincrease increase in quartz content occurs within the quartz zone with within the quartz zone. An increasing depth. depth. The increasing The amount amount of of native native copper copper present present is much much more more irregular irregular than than the the depth depth zones. The variation of the mineral zones. The richest richest copper copper ore ore appears to follow the boundary for >10% >lo% The lower quartz. The lower limit limit of of microcline microcline may may also mark mark the the limit limit ofofsignificant significantcopper copper mineralization. On mineralization. Onaaregional regionalscale, scale,the theKearsarge KearsargeFlow Flow lies lieswithin within the the quartz quartzand andprehnite prehnitezones. zones. Detailed data suggests that quartzand prehnite-free 'islands' are present within the regional present within regional Detailed data suggests that quartz- and prehnite-free "islands" zones. zones. Microcline, calcite, calcite, chlorite, and epidote separated from amygdules amygdules from from rocks rocks collected collected off of this rock pile were used by Bornhorst and others (1988) to provide an absolute age of this rock pile were used by Bomhorst provide microcline, calcite, calcite, and and epidote epidote all allprecipitated precipitated simultaneously simultaneously with with mineral precipitation. precipitation. The Themicrocline, such as inclusions inclusions of of native copper and crossnative copper, as indicated by textural evidence such the Rb-Sr Rb-Sr method method to to these suggests an an age of cutting veinlets. veinlets. Application Application ofof the these minerals minerals suggests of mineralization of between 1060 and 1047 m.y. (+1— 20 m.y.). These results are consistent with m.y.). These results are consistent mineralization of between 1060 and 1047 my. (+Iother data rift system. system. data from from the the Midcontinent Midcontinentrift - The Allouez Gap Fault bisects bisects the the thickest thickest segment segmentof of the the Kearsarge KearsargeFlow flow along its 55 Higher grade grade and and production production occur occur northeast northeast of of the the fault where km strike length length (Fig. (Fig. 33). 33). Higher where fractures parallel to the fault are more abundant. abundant. Within the Allouez Gap Fault zone, early epidote fractures and quartz were brecciated and recemented by by more calcite; quartz; and native copper. Finally, Finally, after another major episode episode of brecciation, the fault zone was recemented with calcite; quartz; and lesser laumontite are clear clear indications indications that that movement movementalong along lesser laumontite (Butler (Butler and Burbank, 1929). The The data dataare and after deposition of native native copper. copper. The the fault occurred before, before, during, during, and deposition of Thefault faultapparently apparently flow top. top. The provided ore fluids to the permeable permeable flow Thecoincidence coincidence of of the the fault fault with with the therelatively relatively thick flow top resulted resulted in in the the second second largest largest deposit deposit in in the the district. district. Mine Shaft Shaft No. No. 22 rock rock pile, pile, you you will will have the opportunity to see a At the Wolverine Mine opportunity to variety of mineral assemblages and and their theft paragenetic parageneticrelationships. relationships. For For the Shaft Nos. Nos. 11 and 22 rock rock piles piles as as aawhole, whole,Stoiber Stoiber(unpublished (unpublished data) data) estimated estimated the the following following percentage percentage of amygdaloidal minerals: calcite, 51%; microcline, prehnite, 1%; and quartz, microcliie, 38%; epidote, 10%; prehnite, quartz, trace. In Inthe thevicinity vicinityof ofthe theShaft ShaftNos. Nos. 22and and33rock rock piles, piles, one onecan can find find outcrops outcrops of of the the Kearsarge Kearsarge flow copper can can be found in specimens from this rock pile. This, and other Plow interior. interior. Native copper other Kearsarge Mine Mine rock rock piles, piles, illustrate illustrate the the complexity complexity of of flow flow top ore bodies Kearsarge bodies in in the the Keweenaw Keweenaw Peninsula Peninsula native native copper copper district. district. 42.5 Continue on the same road and and in in the the same same direction direction as as before before (east), (east), away away from fromKearsarge. Kearsarge. 43.1 43.1 right. We are now now in in the the vicinity vicinity of of Scales Scales Creek, which is Stop at the din dirt road junction junction to the right. We are Flow. This the type section of the Scales Creek Plow. This is is the the same same flow flow seen seen at at Stop Stop 1, 1,about about 22 22 km km to to the south, in Houghton. south, Houghton. �74 MainRoadL.og STOP 14: STOP 14: Scales ScalesCreek Creek(Portage (PortageLake LakeVolcanics Volcanics[PLVfl [PLY) This stop stop provides an opportunity to view the Scales Creek Flow, a regionally extensive extensive basaltic flow. It has been traced for more more than 30 30 km km along along strike strike in in the the Keweenaw Keweenaw Peninsula. Peninsula. Outcrops of the Scales Creek Flow can be seen on both sides of the main main road road and and along along Scales Scales Creek, just just north and paralleling paralleling the the road. road. This flow was studied, from drill cores northeast of This flow was studied, here, by Scofield characteristically ophitic, ophitic, with an amygdaloidal amygdaloidal Scofield (1976). (1976). The The Scales Scales Creek Flow is characteristically top and base, and a massive massive interior. The Themassive massive interior interior is, is, for for the the most most part, part, geochemically geochemically unaltered unaltered (Table 5), with with the thefollowing followingestimated estimated modes: modes: plagioclase, plagioclase, 40%; 40%; pyroxene, pyroxene, 48%; 48%; opaque oxides. 2%. Primary plagioclase; pyroxene; and opaque oxides can be olivine, 10%; 10%; and oxides, Primary plagioclase; chlorite. Although found, but but olivine olivine isis pseudomorphically pseudomorphically replaced replaced by by talc; talc; serpentine; serpentine; and/or andlor chlorite. Although the massive massive interior of the the flow flow contains contains both both primary primary and and secondary secondary minerals, minerals, it remained remained aa for water water flowing flowing away away from from fractures fracturesthat thatcut cut the the interior. interior. The chemically closed system except for The massive nature of the the interior interior inhibited inhibited movement movement of of hydrothermal hydrothermal fluids. fluids. In the amygdaloidal amygdaloidal are present; all have by a suite flow top, no primary primary minerals minerals are present; all have been been replaced replaced by suite of of secondary secondary alteration products. Plagioclase is now albite with some some replacement by sericite, sericite, chlorite, chlorite, and and clinopyroxeneisis replaced replaced by by chlorite; chlorite; olivine olivine is is replaced replaced by by chlorite, epidote and pumpellyite; clinopyroxene pumpellyite; and opaque oxides are altered to hematite and sphene sphene (Scofield, (Scofield, 1976). 1976). 43.1 43.1 Turn around and retrace the route back to US-41. US41 43.7 Passing the Wolverine Mine rock piles (Stop 11). 11). 43.9 Turn right on US-41 US41 at at Wolverine Wolverine Market. Market. 45.2 Entering the Village of Allonez. Allouez. We We have have an an excellent excellent view of the southeast side of a prominent ridge. This ridge is held held up up by by the theGreenstone Greenstone Flow, Flow, which which isis the the thickest, thickest,and andvolumetrically, volumetrically, flow within within the the PLV. PLV. It will largest single flow will be seen seen at Stop 16. 16. 45.4 Turn left on aa paved just before a gas station. paved road road called called Bumbletown Bumbletown Road, just station, 45.6 Stay on the the main main paved paved road, road, bearing bearingright. right. the road 45.75 the right right at at the the dirt dirt road. road. Walk Walk the road to the the mine mine rock rock piles piles of of the theAllouez Allouez 45.75 Park on the Conglomerate Mine. Conglomerate Mine. STOP 15: STOP 15: Allouez Allouez(conglomerate (conglomerateininPortage PortageLake LakeVolcanics Volcanics[PLY]) [PLV]) The rock piles here are are from from the the Allouez Allouez Conglomerate Conglomerate Mine, which operated operated from from 1869 1869 to 1892 about 1.2 1.2 million million kg kg of of copper. copper. The one of of a 1892 and and produced produced about The Allouez Allouez Conglomerate Conglomerate isis one horizons within within the the PLV PLV (Fig. 9). These sedimentary small number of interfiow interflow sedimentary sedimentary horizons sedimentary horizons are important important for stratigraphic correlations within the otherwise otherwise monotonous pile of basalt horizons stratigraphiccorrelations basalt This bed bed can be traced lava flows of the the PLY. PLV. This traced along along strike from the tip of of the theKeweenaw Keweenaw Peninsula west and south, to at least the Mass area, aa strike length length of of more more than than 120 120 km. km. It It is is one one of the of the most mostcontinuous continuous sedimentary sedimentary horizons horizons in in the theKeweenaw Keweenaw Peninsula. Peninsula. The Allouez Allouez Conglomerate is exposed in underground workings at Stop 8--Quincy Mine Adit, Hancock--and in underground workings at Stop Stop 30--the 30Ñth Delaware Delaware Mine. It is is stratigraphically stratigraphically just below the the Greenstone Flow, the thickest flow in the PLY--prominent PLV-prominent in the northern half of the the Keweenaw Keweenaw Peninsula. Like Likeother otherirnerflow interflow conglomerate conglomerate beds within within the PLY, PLV, the the Allouez AUouez Conglomerate Conglomerate consists conglomerate with lesser amounts amounts of of sandstone sandstoneand andsiltstone. siltstone. These red-colored consists of mostly conglomerate �MainkoadLog Mill Rod Log 75 75 clastic clastic sedimentary sedimentary rocks rocks where where deposited deposited in aa terrestrial terrestrial alluvial alluvial fan fan environment environment with with dominant dominant transport of sediment sediment from the margins margins of the rift, rift, toward toward the the center center (current (current center center of of Lake Lake Superior) Superior) during during aa hiatus hiatus of ofvolcanic volcanicactivity. activity. The The rock rock piles piles from from the the Allouez Allouez Conglomerate Conglomerateillustrate illustrate features of interfiow interflow sedimentary sedimentary beds conglomerate. The largest beds of the PLy. PLV.The Therock rockpiles pilesprovide providean an excellent excellent view of "clean" conglomerate. boulders in this conglomerate conglomerate are about 65 cm in diameter, diameter, and the median median size is about 8 cm. cm. A A pebble pebble count count of of boulders boulders more more than 20 20 cm cm across across gave the following results: mafic rock, mostly amygdaloidal, 16%;quartz quartzporphyry, porphyry, 36%; 36%;feldspar feldsparporphyry, porphyry, 11%; 11%;and and granophyre, granophyre,37% 37%(White, (White, amygdaloidal,16%; 197 lb). The 1971b). Theheterogeneity heterogeneityof ofthis thisassortment assortmentsuggests suggestsaa less less restricted restricted source sourceterrane terranethan than the theone one that supplied the Kingston and Houghton Conglomerates in this area. For example, the Kingston Conglomerates in this area. For example, the Kingston that supplied the ~ i n ~ s t o n is made made up up almost almost entirely entirely of fragments fragments of quartz-feldspar porphyry, but bedded red sandstone sandstonecan can also be be found found in in some somespecimens. specimens. Little evidence evidence of native copper mineralization Occasionally, Little mineralization is is present present in in this this rock rock pile. pile. Occasionally, one can find find aaspecimen specimen with with native native copper copper filling filling the the void void space space between between clasts clasts and and grains. grains. Calcite and arethe thedominant dominantpore-filling pore-filling secondary secondary minerals. minerals. In slabs, and chlorite chloriteare slabs, almost almost every every feldspar is associated feldspar phenocryst phenocryst is associated with with a tiny tiny speck speck ofofnative nativecopper copper(Kalliokoski, (Kalliokoski,personal personal communication, 1988). Thin are calcite, calcite, full full of of Thin black black veinlets veinlets cutting the Allouez Conglomerate are chalcocite dust. Supergene Supergenealteration alterationresulting resulting from fromthe the downward downward percolation percolationof of groundwater groundwaterisis rare in in Keweenawan Keweenawan native native copper copper deposits deposits of of the theKeweenaw KeweenawPeninsula. Peninsula. Here however, however, the the effects effects of of supergene supergene alteration alteration is quite visible visible as chrysocolla; chrysocolla; malachite; and cuprite cuprite are are present present in in numerous numerous samples. samples. 45.75 Continue Continueon onthe themain mainpaved pavedroad roadtotothe thetop topofofBumbletown BumbletownHill. Hill. 46.1 46.1 right on on Cedar CedarStreet. Street. Turn right 46.3 46.3 The top top of of Bumbletown Bumbletown Hill near the communication towers. The hill hill isis visible visible to to the thenorthwest northwest The towers. The while traveling traveling from from Calumet Calumet to to Allouez. Allouez. STOP STOP16: 16:Bumbletown BumbletownHill Hill(Allouez (AllouezGap GapFault) Fault) Bumbletown Hill is located on the southwest side of the Allouez Allouez Gap, Gap, aa north-trending north-trending valley. The valley follows the Allouez Gap Fault, a zone of faults and fractures, along valley. The valley follows the Allouez Gap Fault, a zone of faults and fractures, along which which the the PLV swings from from about about N35°E N35'E PLV and and Keweenaw Keweenaw Fault are offset. At At this this gap, gap, the the strike strike of of the the PLV swings to to N50°E. N50T. From this location on a clear day, day, Isle Royale may be seen--80 s e e n 4 0 km to the northwest--and the Bay--60km km to to the the southeast. southeast. The seen beyond beyond Keweenaw Keweenaw Bay-60 The land land the Huron Huron Mountains Mountains may be seen slopes very gradually to the northwest toward Lake Superior, as it does throughout most of the length of the Keweenaw Peninsula. The The southeast southeast flank of the Keweenaw Peninsula has a steeper slope at the skyline, the line line of of the the Keweenaw Fault. The skyline, following following approximately approximately the Keweenaw Fault. Thelow-lying low-lying plain between between the the fault fault and and Keweenaw Keweenaw Bay. Bay, isis underlain underlain by by flat-lying flat-lying Jacobsville Jacobsville Sandstone. Sandstone. northeast along along the the strike strike of of the the PLV, PLy, one can see the cuesta form of the Looking northeast the ridge ridge upheld by the Greenstone How. flow. At Bumbletown Hill, this flow is only 85 m thick, but it thickens At Bumbletown Hill, this flow is only 85 m thick, but it thickens than 400 m at the near near end of of the cuesta cuesta ridge. ridge. To abruptly to more than To the the right right of of the the Greenstone Greenstone ridge, the more more distant distant hills hills are are formed formed by by lava lava flows flows lower lower in in the thesection. section. �76 76 l.ainao.dIog ~ a i n~ o a d ~og - The Allouez Gap Fault follows the SE trending valley, near the relatively new headframe. headframe. The Almost every permeable horizon horizon near near the the Allouez Allouez Gap Gap Fault Fault contains contains above above average average amounts amounts of of native copper; nowhere else in the district are are there there so so many many mineralized mineralizedbeds. beds. About 60% 60% of the district production can be linked to the fault as a primary primary pathway pathway for for ore ore fluids. fluids. The district The fault fault bisects bisects the Kearsarge deposit, deposit, which which isis the the second secondlargest largestproducer producerininthe thedistrict district(Fig. (Fig.32). 32). The The line line of of rock piles demarking its location is a little more than than 1500 m m southeast southeast of of Bumbletown Bumbletown Hill. Hill. The The large "new" headframe, 2000 m m east east of of the the hilltop, hilltop, is is the the Kingston Kingston Mine. Mine. This headframe, 2000 This small small deposit deposit produced 9 million kg of of copper copper (1963-1968), (1963-1968). and is bisected bisected by the the Allouez Allouez Gap Gap Fault Fault (Fig. (Fig. 34). 34). About About 1200 m of the the hilltop hilltop is is aa deposit, deposit, at at N65°E, N65¡Ewhich which produced produced 15 million million kg of copper copper (1944-1964) from from the the Houghton HoughtonConglomerate Conglomerateand andthe theIroquois IroquoisFlow Howtop. top. The rock piles (1944-1964) piles just below the hill top at in the theAllouez AUouez Conglomerate Conglomerate which which produced 34 at Stop Stop 15 15are arefrom from mines mines in million kg of copper. copper. The outcrops on the top and upper slopes of of Bumbletown Bumbletown Hill Hill represent represent aa series series of of basalt basalt porphyritic. They range up and andesite flows; some flows are slightly porphyritic. up to to 20 20 m m in in thickness, thickness,and and and lithologically lithologically similar similar to to those those whose tops were as a group group are are stratigraphically stratigraphically equivalent and mined at the Quincy Mine, just just north north of Hancock. mined Hancock. Unlike Unlike the the basaltic basaltic flows flows found found below below the the Houghton Conglomerate, these flows have little lateral/strike direction continuity. Two flows Houghton Conglomerate, these flows have little lateral/strike direction continuity. Two flows 1971b). pinch out on the top of of Bumbletown Bumbletown Hill (Fig. 35) (White, 1971b). layers which which Some of the exposed flow tops on Bumbletown Hill are slabby pahoehoe layers have experienced runout of much of the mass of the lava flows. lava The Greenstone Flow is exposed Greenstone Flow exposed in a series series of of outcrops outcrops 160-300 160-300 m southeast southeast of of the the top isis exposed exposedatat the the end end of of a private roadway hilltop. Its thick amygdaloidal southhilltop. amygdaloidal top roadway 200 m southsoutheast of the hilltop. Columnar Columnarfine-grained fine-grained basalt basalt and and ophitic ophitic basalt basalt can can be be seen seen in in exposures exposures farther down the slope. slope. Allouez Allouez Gap Gap is is an an important important physiographic feature feature of the the Keweenaw Keweenaw Peninsula Peninsula (Fig. (Fig. 18). 18). It contains the largest accumulation of glacial sediments north of Portage Lake. The gap is accumulation of glacial sediments north of Portage Lake. is the the lowest elevation elevation that cuts cuts across across the peninsula between Portage Lake and the tip of the peninsula peninsula (Regis, 1983). AAnumber numberof of kettles kettlesalong along aa northwest northwest trend trend occur occur within within the gap gap (Fig. (Fig. 36). 36). Retrace the 1. the route routeback backtotoUS-4 US-41. 47.2 At the the junction with with US-41, US-41, turn turn left leftand andcross crossinto intoKeweenaw Keweenaw County Countyfrom fromHoughton HoughtonCounty. County. 48.1 48.1 Entering Ahmeek. Ahmeek. junction to Cliff Drive. Turn Turnleft left on onCliff Cliff Drive. Drive. 48.4 The junction MAP 10 10 mad. We near the the base base of of 48.65 Passing PassingSeneca SenecaLake Lake on on the right side of the mad. We are are driving driving along strike, near the Greenstone Flow. Along Alongthe the road road are are several several small outcrops of basalt, mostly on the left side of the road. road. 51.7 At this point, the Greenstone Flow abruptly thickens thickens to to nearly nearly400 400m m(Fig. (Fig.37). 37). It dips northward at about 25° center of of the the Midcontinent Midcontinentrift. rift. This lava flow can be traced along much 25' toward the center of the Keweenaw and has been stratigraphically and geochemically geochemicaily correlated with a similar unit on Isle Royale, 90 km away, on the other side of the rift. Thus, Thus, the the areal areal extent extentof of this this great greatflow flow km2,and its volume volume is is on on the the order orderof of 800-1500 800-1500km3, km3,according to White White (1960) (1960) exceeds 5000 5000 km2, �10 MSRoadLog 77 MAP 10 �. 7878 ~ a i n~ o a d~ o g MainRoadLog LEGEND 0 0 80 Melen 165 250 330 - 500 750 loo0 Feet Contour Interval 5 feet 250 m i OVERBURDEN MINED OUT AREAS 1 SHAFTS AND LEVELS HORIZONTAL PLAN MAP Figure ofof thethe Kingston Figure34: 34:Thickness Thickness KingstonConglomerate Conglomerateatatthe theKingston KingstonMine Mineshowing showingthe thebisecting bisectingAllouez Allouez 1972; from Bornhorst, 1992). Ore ends abruptly Gap Fault (modified from Weege and others, Gap Fault (modified from Weege and others, 1972; from Bornhorst, 1992). Ore ends abruptlyatat the thethickness thicknesspinch-down pinch-downon onthe thesouthwest southwestend endofofthe thedeposit depositwith withsome someofofthe thehighest highestgrades gradesinin edge of the orebody is gradational. the themine minenext nexttotothe thepinch-down pinch-downwhereas whereasthe theeastern eastern edge of the orebody is gradational.The The 400. bottom bottomlevel levelisis350 350mmdeep deepon onthe theincline inclineatat 40'. �MainRoedLog 79 OSt £0 LA AMYGDALOID 00 I--I 2000 2000FEET FEET 1000 1000 -- I I I I I Figure Figure35: 35:Outcrop Outcropmap mapofofthetheAllouez-Bumbletown Allouez-BumbletownHill Hillarea area(from (fromWhite, White,1971b). 1971b). Table5: 5: Avenge Averagecomposition compositionof ofthree threesamples samplesfrom fromthe themassive massive part part of of the theScales ScalesCreek Creekflow flow(from (from Table Scofield,1976). 1976). Scofield, weight Weight Percent Percent Ssio2 i02 47.57 47.57 20 10 16. 16.10 3 Fe203* Fe203* 12.54 12.54 MgO MI30 7.67 7.67 CaO CaO 10.00 10.00 Na20 Na20 2.24 2.24 K20 K2 0.29 0.29 Ti0, Ti02 Total Total 1.43 1.43 97.84 97.84 �80 MainRoudLog SL1F'St 0 sano OW4ES —1 I o5jTHI%; b- • —.Iloo•. - 1 — GREENs ro,sj - . .,—-_.. ot-ra•941! -=-. ——_GAP 2'--.::.. -' 876' -- -— 4.. -. - -- Figure36: 36:Physiographic Figure Physiographicand and glacial glacial features featuresof ofAllouez AllouezGap Gap (from (fromHughes. Hughes,1963). 1963). �RoadLog Thickness Thickness (feet) (feet) 81 Top 'op of Flow Flow Vesiculated Flow Flow Top Top / / / // // / / / / /,.1 / / // f / / /'• A;z.: columnar Jointed Jointed EM: Columnar Melanophyre 285 UOp: uop: Upper Upper Ophite Ophite 225 Pg 3rd Pg: 3rd Pegmatoid Pegmatoid Zone Zone / /// / / // :; / / tPgt// /UOpSJ/o/ / / 680 / i Ø?Pi' EM / t 'IV! / 'ii' I/I 1/ /___._ 1 /// /i Ii / / SCALE I; ityille — Sub—ophite Pg: 2nd Pegtnatoid Zone Z sub—opizite Pg: 1st Peginatoid Zone LOpE Lower Lower Ophite Lop: Ophite Vertical Scale: 1"=200' 1"200' Vertical Scale: Figure 37: Figure 37: Geologic Geologicsketch sketchmap mapand andstratigraphic stratigraphicsection sectionshowing showingvertical vertical zones zones within within the the Oreenstone Greenstone (fromLongo, 1983). 1983). flow between Seneca and the Cliff Mine (from �82 hflRoadLog composite Roza Ron flow and Longo (1983). It rivals the composite How (Columbia (Columbia R.) as as the the largest largest known lava flow on Earth. The TheGreenstone GreenstoneFlow Flowtypically typically shows showsspectacularly spectacularlydeveloped developedpegmatites, pegmatites,ophitic ophitic horizons, and columnar jointed jointed areas. areas. The flow near The pegmatoid pegmatoid zone within the Greenstone Flow near this this (Fig. 37). 37), and and the ophitic ophitic zones zones are are relatively relativelyunaltered. unaltered. Longo (1983) location is unusually thick (Fig. (1983) has shown that the composition of these zones are remarkably constant and demonstrated the great chemical chemical similarity similarity of the composition of the Isle Royale and Keweenaw ophitic exposures exposures of the the Greenstone Plow. Flow. The flow at The rapid rapid thickening thickening of the Greenstone Greenstone Flow at this this point point was was suggested suggested by White (pers. comm., comm., 1982) 1982) to to be be caused caused by by the separation of the the upper upper part part of the flow separation of flow into into multiple flow units, multiple flow units, which which appear to be be separate separate flows. flows. To the the north, north, the flow may may be aa continuous, single flow unit, while to the south, it may have been made made up of of many many flow flowunits. units. MAP 10 10 and and 11 11 52.1 52.1 Crossing the the Gratiot Gtatiot River. River. MAP MAP 11 11 side of of the prominent ridge which which isis held held up up by the 52.7 are now now driving driving on on the the southeast southeast side prominent ridge the 52.7 We are Greenstone Flow. Flow. 54.6 54.6 This is the the site site of ofthe theCliff CliffMine, Mine,which which was was the the first firstmine mine ininthe thedistrict, district,and andoperated operated discontinuously from from 1845 1845 to to 1887. 1887. The discontinuously The rock rock piles piles and and old old footings footings for for the the mine mine building building are are mainly on the left side of the road and the town site, of which little remains, remains, is on the right side side of the road. road. STOP 17: STOP 17: Cliff Cliff Mine Mine (native (nativecopper coppervein vein deposit) deposit) (see cover photo) photo) The Cliff Mine worked the Cliff Fissure from 1845 1845 to 1887, and produced a total total of about about 38 million lbs. portion lies under under the Greenstone Greenstone Flow. Flow. The Ibs. of of refined refined copper; the productive portion The Cliff Fissure is nearly at right angles to to the the attitude attitudeof ofbedding beddingand anddips dipssteeply steeplytotothe theeast. east. Most of the mineralization mineralization was confined to the fissure, although some amygdaloids were mineralized (summarized from Butler and Burhank, Burbank, 1929). Many Many large large masses masses of of native native copper copper were were mined mined from the Cliff Cliff Mine and and larger larger masses weighed weighed up to 100 100 tons. One Onelarge large100 100ton, ton mass masscould could not be blasted, so pieces (Clarke, (Clarke, 1976). Among so it had to be cut by hand into smaller pieces Among the the fissures, fissures, the Cliff was the most productive of silver. In Inaddition additionto to native native copper copperand and silver, silver,the the Cliff CliffMine Mine produced the the following following minerals (not (not in order of abundance): calcite, epidote, chlorite, laumóntite, laumontite, prefinite, clatolite, thomsonite, chlorastrolite, chiorastrolite, galena, galena, apophyllite, apophyllite, adularia, gypsum, sphalerite, prehnite, datolite, thomsonite, sphalerite, pyrite, and surface surfaceoxidation oxidation minerals. minerals. sometimes shows shows quite quite The Greenstone Flow at this locality is mainly ophitic basalt and sometimes developed coarse coarse columnar columnarjointing. jointing. The Greenstone Flow is described in more detail well developed Greenstone How detail at at mileage 50.7. The junction of of US-411M-26. US-41/M-26. Turn Turn left left(north). (north). MAP 12 12 55.5 Entering Phoenix. Phoenix. 55.2 56.6 Turn just before (0.1 (0.1 mile) mile)the thejunction junctionbetween betweenUS-41 US-4land andM-26. M-26. It is about T urn left on a dirt dirt road just 100 m from the paved road road to the base of the Phoenix Mine rock rock pile pile which which is is Stop 14. �Map 12 Map MtoRLsg MAP 83 �84 itin Road Loz Map 11 1. �MainRo*diog 85 STOP 18: copper STOP 18: Phoenix PhoenixMine Mine(native (native coppervein veindeposit depositand andPortage PortageLake Lake Volcanics Volcanics [PLy]) [PLV]) The Phoenix Mine worked worked numerous numerous veins veins below belowthe theGreenstone GreenstoneFlow. Flow. Like the Cliff Mine discussed Mine was was one of the earlier discussed at Stop 17, the Phoenix Mine earlier mines mines in the the district district and and operated off off and and on on from from 1849 1849to to 1917. 1917. The vein was worked worked to to a vertical vertical depth depth of of about 300 operated m, with varied (average grade grade around around 1.5%). 1.5%). Since the vein cuts thin lava flow m, varied grade (average flow tops, tops, no no mining was done on adjacent mineralized flow flow tops. tops. The Phoenix Mine produced a total of about milling 17 million Burbank, 1929). 1929). It also also worked worked the the Ashbed Ashbed million lbs. Ibs. of of refmed refined copper copper (Butler (Butler and and Burbank, Amygdaloid where where itit is mineralized, mineralized, in in the the vicinity vicinity of of vein vein copper copper occurrences. occurrences. The Amygdaloid The Phoenix Phoenix Mine rock pile Mine pile is notable notable for for halfbreeds halfbreeds (native (native copper copper plus plus native nativesilver), silver),spectacularly, spectacularly, and chlorastrolitic pumpellyite pumpellyite (Michigan (Michigan"greenstone"). "greenstone"). Listed below are are crystallized analcite and some other minerals that have been reported in the Phoenix Mine area (Clarke, 1974a): some other minerals that have been reported the Phoenix Mine area (Clarke, 1974a): pumpellyite, chlorite, chlorite, natrolite, natrolite, and andapophyllute. apophyllite. To look at the Greenstone flow you Greenstone Plow you must must climb climb over the rock pile and then pass one one of of zones just just above above the the shaft. shaft. Proceed the fissure zones Proceed ahead and climb to the base of the the steep steep cliffs, cliffs, which are composed of a portion of the Greenstone flow, an which composed of portion of the the massive massive flow flow interior interior of Greenstone Flow, an representing the the greatest greatest single single outpouring outpouring of of enormous lava flow over 400 m thick, and perhaps representing Earth. lava on Earth. ophitic zone zone occurs occursnear nearthe thebase baseofofthe theGreenstone GreenstoneFlow Flow(Fig. (Fig.38). 38). By A very coarse ophitic along the the cliff, the pegmatoid; pegmatoid; subophitic; subophitic;and and ophitic ophitic zones zones can can all all be following the exposures along observed. From Fromthe thetop topof of the theGreenstone Greenstone Ridge, Ridge, there is aa view view of of the the strike strike of of this this great great flow flow and of the town site of Phoenix, which had a population of 1,000 from 1877-1887. the town site of Phoenix, which had a population of 1,000 from 1877-1887. The Greenstone Flow has been identified for a distance of 90 km along the length length of of the the Keweenaw Peninsula, as well as throughout the length of Isle Royale, 90 km northwest northwest on on the the Keweenaw Peninsula, 90 km opposite limb of the Lake line. The extent is 5000 km2 with with volume volume of of 800 to to 1500 1500 opposite Lake Superior Superior Sync Syncline. km3 (Longo, Very slow slow solidification solidification of this great mass of magma magma allowed allowed (Longo, 1983; White, White, 1960). 1960). Very resulting in in aa massive, ophitic zone at the base of of the the extensive in-situ magmatic differentiation, resulting flow; an overlying overlying zone of intercalated subophitic and pegmatoidal layers; an upper ophitic zone; and aa fine-grained, 195laa and ii). b). The lower lower ophitic ophitic zone zone fine-grained, vesicular vesicular flow flow top top (Cornwall, (Cornwall, 1951 low enough enough to to allow allow growth growth of of clinopyroxene cinopyroxene oikocrysts experienced rates of undercooling low oikocrysts up to 5 cm in in diameter. diameter. the Greenstone GreenstoneFlow flow magma is more evolved than typical The geochemical composition of the olivine tholeiites; tholeütes; which constitute the greatest volume volume of ofthe thePLV. PLy. Primitive Primitiveolivine olivine tholeiite tholeiite and and quartz tholeiite occur between between the the Greenstone GreenstonePlow Flowand andthe thetop topof ofthe thePLV. PLV. Generally, magmas with time time during the Midcontinent rift become more primitive and less crustally crustally contaminated contaminated with changes in in magmatic magmaticand andtectonic tectonicprocesses. processes. A model of magmatic and development, reflecting changes rift evolution based on on PLV PLV data data involves involves primitive primitive parental parental magma magma modification modification by complex, complex, open-system fractional crystallization crystallization in in large reservoirs reservoirs at at the base of the thinned thinned crust crust (Paces, (Paces, 1988). The Theresulting resultingolivine olivinetholeiite tholeiitemagma magma is is either either erupted at the surface or supplied supplied to to smaller smaller chambers at higher evolved tholeiites and silicic higher levels levels where where further farther crystallization crystallization produces produces evolved rocks. rocks. differentiation of of the the Greenstone Greenstone Flow flow was described The chemistry and petrology of differentiation described in papers by Cornwall Cornwall(1951a. (1951a. 1951b). 1951b). �86 86 Main ill Road ~ o a Log d~ o g Thickness Thickness (feet) (feet) u Ii Iii Ill Top Top of of Flow Plow M l : Melanophyric Melanophyric Zone Zone Ml: IJOp: Upper Ophite Ophite UOp: Upper Pg: Pg: Pegniatoid Pegmatoid Lenses Lenses with intercalated i n t e r c a l a t e d lenses lenses with of Of ophites o p h i t e s and and sub—ophites sub-ophites -Sub-ophite Sub-ophite -Pg:Peginatoid PegmatoidZone Zone Pg: Sub—ophite -Pg: Zone ....—Pg: Pegmatoid Zone PHOENIX / 7 Lop: LOP: Lower Lower Ophite Ophite SCALE SCALE 00 -Sub—ophite Sub-ophite - Pegmatoid Zone Zone —Pg:Pg: Pegntatoid Imul. 1 mil. Bottom off Flow Bottom o Flow V e r t i c a l Scale: S c a l e : l"—200' 1"-200' Vertical Figure Figure38: 38:Geologic Geologicsketch sketchmap mapand andstratigraphic stratigraphicsection sectionshowing showingzonation zonation of of the the Greenstone Greenstoneflow flow near near Michigan (from (fromLongo. Longo, 1983). 1983). Phoenix, Michigan �~ a i Road n~ o rLog ~i o t 87 6: Avenge Table 6: Averagecomposition compositionofofthe theGreenstone GreenstoneFlow Flow (Longo, (Longo, 1983). 1983). Si02 SiO, A1203 A1203 FeO' MgO Mgo CaO CaO Na20 Na,O K20 K@ Ti02 TiO, P205 p 205 wt.% 46.7 15.1 15.1 12.8 12.8 7.8 7.8 9.9 9.9 2.1 2.1 0.4 0.4 1.2 1.2 0.14 0.14 Ba Cr Cu La Mn Ni Rb Sc Sn Sr Y Zn Zr rrn 104 214 66 11 1680 186 S 28 6 259 14 84 92 'Total TotalFe Feas asFeO. FeO. 56.8 Thm Turn left left on on M-26 M-26 toward toward Eagle Eagle River. Cross CrossCentral CentralCreek Creek and and begin begin to to drive driveperpendicular perpendicularto to strike and cross the the Greenstone Greenstone Flow. Flow. 56.9 56.9 At ~t 9:00 9:00(on (on the the left), left), the the Phoenix Phoenix rock rock piles piles and and cliffs cliffs of of the the Greenstone GreenstoneFlow Flow are arereadily readilyvisible. visible. 57.1 57.1 Cross Cross Eagle Eagle River. River. 57.2 57.2 Outcrops the left left of of the the road. road. Exceptionally coarse ophitic texture, Outcrops of the Greenstone Flow are to the individual pyroxenes with individual pyroxenes up to 5 cm can be found on these exposures, which represent represent the the slower slower cooling middle middle of of the the flow. flow. 57.6 There is a pull-out on the right right hand hand side side of of the the road. road, flows Flowsabove abovethe the Greenstone Greenstone flow Flowcan canbe be Eagle River. River. The seen along Eagle The river river is is about about 25 25 m m from from the side side of the the road road and and in in this this locality, locality, there are many deep pools. You You can can follow follow the the river river downstream from here all the way to Eagle River, looking at many many flow flow contacts. contacts. This This can't can't be bedone done in in the thehigh high water water periods periods of of spring. spring. At Stop 19, 19, just up the the road, road, one one can can begin begin aa traverse traverse along along Eagle River. 57.9 57.9 Pull over over at at aa poorly poorly maintained maintained dirt dirt road road pull-out pull-out on the the right. right. At this locality, locality, Eagle River River crosses the Ashbed. There is a very sharp bend in Eagle River north of the Ashbed Flow. There is a very sharp River north of the Ashbed Flow. From here it is is possible possible to to begin begin aatraverse traverse along along Eagle Eagle River River either either upstream upstream or ordownstream. downstream. STOP 19: Eagle STOP EagleRiver River(Portage (PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) Eagle River, Jacobs Creek, and Owl Creek each make excellent stream traverses of the PLY. PLV. At ~t this thispoint, point,approximately approximatelyatatthe the Ashbed, Ashbed, aa traverse traverse along the stream north to Eagle River observations of of the the upper upper stratigraphy stratigraphyofofthe thePLV. PLy. The allows excellent observations The Ashbed Ashbed isisdescribed described at at Stop 20. Stop 20. Eagle River River traverses traverses the the section section shown shown in in Figure Figure 39; along the traverse, you see: Eagle see: 1) 1) excellent sections sections through through individual lava flows flows showing tops, and and massive excellent individual lava showing amygdaloidal amygddoidal tops, massive melaphyric, glomeroporphyritic, glomeroporphyritic,ororophitic ophiticflow flowinteriors; interiors;2)2) the the best best section melaphyric, section of entablature entablature jointed basalt in the Keweenaw Peninsula, Peninsula, which which can can be be reached overland by walking columnar jointed �88 88 ~ i m aid LMaiDROSI.Sg COPPER COPPBHARBOR CONGLOMERATE CONGL —I of Copper Sitor ,t—,,eiete Dø.liic fl.-s mans flow pqmstutic DØatic flo.t ffi 'tow cnirwlitic .ofiyrtv thief rboss sJ'fltfy Ila,.tl00r,l,ntic aM ophitic conglomerate (No. 17) Mj,bed amygdlo,dfl'd IrwISPAYflt. - I MSn'tm; thtwr -' uloa.ropflqd* ed pegtn.tittc 0_f_s Finr.mS nwIsoNnt. pomtrit'c Gacat.roPofDiiwitic ISO., Glonwrmofdhnttielk- .umr(hiltion* Upoer chill son, Pme'ttMnne Greenstone flow Â¥Greenston flow PORTAGE PORTAGE LAKE LAKE LAVA LAVA SERIES SERIES lo- • Optsitic bewail — I Figure Figure39: 39:Stratigraphy Stratigraphyofofthe thePortage PortageLake LakeVolcanics Volcanicsabove abovethe theGreenstone Greenstoneflow flowininthe thevicinity vicinityofofEagle Eagle River and and Phoenix, Phoenix, Michigan Michigan (from (fromCornwall Cornwall and and Wright, Wright, 1954). 1954). �MainRoadI.og Main Road Log 89 89 a few hundred meters of sediments with with the the lava flows, which meters downstream; and 3) interbedding of becomes more prevalent prevalent up up section. section. If you decide to take this traverse, traverse, it's best to to just resign resign yourself to wet feet. The traverse is not advisable in the spring because of high water. yourself The traverse is not advisable in the spring because water. 58.0 Pull over opposite to the outcrops on the left side side of the the road. road. STOP STOP 20: 20: M-26, M-26,Eagle EagleRiver River(Portage (PortageLake LakeVolcanics Volcanics[PLV]) [PLV]) horizon that can can be traced traced over a distance of almost 25 The Ashbed is a very distinctive horizon km tan in outcrop outcrop and drill drill holes. ItItisisthe thevesicular vesicularzone zonebelow below the theHancock HancockConglomerate Conglomerate(Fig. (Fig. 39 39 and Map 12). The TheAshbed Ashbed isisexposed exposed on on the the SE SEend end of of the the outcrop outcrop (away (away from from Lake Lake Superior), Superior), and is is overlain overlain on on the the NW NW end end by by the the massive massive interior interior of of the the overlying overlying basalt lava lava flow flow dipping dipping Lake Superior). Superior). The about 225°NW 5 W (toward Lake The weathered outcrop outcrop has a rubbly appearance, appearance, but in in the the water-washed low exposures exposures in the the drainage drainage ditch ditch alongside alongside the the road, road, 55 to to 15 cm diameter diameter clasts clasts basalt set in aa fine of vesicular vesicular basalt fine matrix matrix isis clearly clearly visible. visible. The clasts are subrounded, subrounded, and in in general, the Ashbed is a jumble of of vesicular vesicular basalt basalt fragments fragments and an an interstitial interstitial brown-to-gray, brown-to-gray, matrix. The fine-grained matrix. Thesecondary secondary minerals minerals filling filling the the void void spaces spaces are are calcite, calcite,quartz, quartz, chlorite, chlorite, of Cu Cu (White, (White, 1971b). 1971b). Small mines were and minor epidote. Some Some vesicles vesicles contain minute flecks of places, from from Atlantic Atlantic Mine Mine (near (near Stop Stop 3) 3) to Owl Creek (Stop found along this horizon in many places, Bi). Bl). The Ashbed includes includes rocks rocks characterized characterized as pyroclastic, and those interpreted interpreted by Johnson Johnson On Eagle Eagle River, River, the Ashbed Ashbed is only only the the pyroclastic pyroclastic horizon horizon and (1985) as as hyaloclastite. hyaloclastite. On stratigraphically separate separate is is another another horizon horizon consisting consistingof of aa pillowed pillowed lava lava sequence overlain overlain by by stratigraphically The pillows are about hyaloclastite (Johnson, 1985). 1985). The pillows are about 50 cm in in diameter diameter with with red red oxidized oxidized margins. 58.3 58.3 Go downhill toward Lake Lake Superior. Superior, which which is is visible visible at at the the treeline. treeline. 58.6 The Evergreen Cemetery on the the left left was was established established in in 1843. 1843. 58.9 River. On Leg FF -- Five Mile Point Entering Eagle River. On the the left left is is the road to Five Mile Point (begin Leg The stone monument is a memorial Houghton who who was was the the first State here). The monument is memorial to Douglass Douglass Houghton Geologist of Michigan. He Hedid didpioneering pioneering geologic geologic studies studies in the Keweenaw Peninsula. In In1845, 1845, he drowned off Eagle River. drowned off Eagle River. 59.1 59.1 Cross Eagle River on the Eagle River Bridge. Park ParkNE NEof of the thebridge. bridge. Eagle River Falls Falls STOP 21: 21: Eagle Conglomerate) Conglomerate) (contact of Portage (contact of Portage Lake Lake Volcanics Volcanics and and Copper Copper Harbor Harbor between the the top top of of the the PLV PLV and and the base of the Copper The falls occur at the contact between Copper Harbor Conglomerate. There are some spectacular potholes potholesthat thathave havedeveloped developedon onthis thisface. face. Ifif the water is low, low, like like itit is is sometimes sometimes in the summer, summer, you can see ropy surfaces on flows at the top of the the PLV PLV which which indicate indicate the flow was erupted from a vent to the north (the center of the the dips about 30 30° NNW. NNW. The rift now under under Lake Lake Superior). Superior). The contact dips Thecontact contactrelationships relationships suggest very very little erosion between between the the flow flow and deposition of the conglomerate beds of the suggest deposition of conglomerate beds the Conglomerate. Under Copper Harbor Conglomerate. Under the the bridge, one can get a good view of the lithology of of the the lower part of consists of of mostly lower of the theCopper CopperHarbor HarborConglomerate. Conglomerate. It It consists mostly rhyolite rhyolite pebble pebble conglomerates, but includes many sandstone and even some shale shale beds. beds. �90 itoñ Follow Follow M-26 with a sharp sharp left turn, just after after the the bridge. bridge. 59.2 59.2 Sharp right turn. 13 MAP 13 62.15 Jacobs JacobsCreek CreekFalls. Falls.From Fromthis thispoint, point,one onecan canbegin begin aatraverse traverse up up Jacobs Jacobs Creek Creek that ends near the Arnold Mine on the Garden City Road. There are excellent exposures of the upper part of of the the Arnold Mine Garden City Road. There are excellent PLV along Jacobs PLV Jacobs Creek. Creek. For those who who are are hardy, hardy, the the stream stream offers offers virtually virtually continuous continuous through thin thin pahoehoe pahoehoe flows, flows,especially especiallyininthe thefirs firstseveral severalhundred hundredmeters. meters. This is a exposures through steep and rough traverse, traverse, and and should should not not be be attempted attempted in in high high water waterperiods. periods. 64.0 64.0 level Great Sand Bay. bay.The m esand WIU dunes uunca at at the US<- road i,&el are areremains remains of of the the Lake LakeNipissing Nipissing Stage Stageof of the the Lake Superior Superior Basin. Basin. Cat Harbor. The TheLake LakeShore ShoreTraps Traps form form the the offshore offshore ridge, they are mafic to intermediate lava flows within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. MAP 14 14 the Eagle Eagle Harbor Harbor Store. Store. 66.9 Turn right by the 66.9 65.0 M-26 makes makes aa sharp sharp bend bend to to the the right. right. Continue straight toward the Eagle Harbor Harbor Lighthouse. Lighthouse. 66.95 M-26 67.0 sharp left left to to the the lighthouse. lighthouse. Make a sharp 67.1 The Eagle Eagle Harbor Harbor Lighthouse Lighthouse parking parking lot. lot. STOP 22: Eagle EagleHarbor HarborLighthouse Lighthouse(Lake (LakeShore ShoreTraps) Traps) PLEASE DO NOT USE TillS SITE. USE ROCK HAMMERS AT THIS SITE. The Eagle Harbor Harbor Lighthouse Lighthouse is maintained maintained as aa museum museum by by the theKeweenaw Keweemw County County Historical HistoricalSociety. Society.AAlighthouse lighthousebegan began operation operation here here in in 1851, 1851, four four years prior to the completion completion Harbor Lighthouse. Lighthouse. The of the Soo S w Locks, and two years after the Copper Harbor The current current building was constructed in 1871, and and the light was was automated automated in in 1980. 1980. The constructed in The position position of the the lighthouse; lighthouse; the shape of the harbor; harbor; and and the the many many islands islands and and shallow shallow rocks along the shore shore facing facing the the big big lake lake (climb the wooden steps northwest of the lighthouse for the best view) are controlled controlled by the Lake Lake Shore Traps. The Thetraps trapsare areaaseries seriesof ofresistant resistant basaltic basaltic lava lava flows flows that that occurs occurs within within the the Copper Copper from Harbor Conglomerate Conglomerate and which outcrop along the Keweenaw shore shore for for more more than than 14 141cm, km, from Harbor. These m.y., about 7 m.y. Great Sand Bay to Agate Harbor. These lavas are dated at 1087 1087 m.y., m.y. younger than the PLy, the PLV, and andtogether togetherwith withthe theMichipicoten Michipicoten Island IslandFormation, Formation, represent represent the the youngest youngest Keweenawan igneous rocks known (Paces (Paces and and Miller, Miller, 1993). 1993). Start Start at the west end of the parking lot, about 25 m from the Maritime Museum. AA small small Lake Shore Shore Traps Traps are are cut cut by by aa number number of of small small veins veins ravine occurs here because the well-exposed Lake up to about 2.5 cm wide, in a zone about 30 cm wide trending N-S, perpendicular to the shoreline. about cm wide, in zone about 30 wide trending perpendicular to the shoreline. although bedding bedding is not The Lake Shore Shore Traps Traps are are dipping dipping about about 25°N 25% toward toward Lake Superior, although obvious. Prominent Prominentjoints joints ininthe themassive massiveinteriors interiorsof offlows flowssometimes sometimesapproximate approximatethe the attitude attitude of bedding. From Fromthe theparking parkinglot lottoward toward Lake LakeSuperior, Superior, aa massive massive interior interior of aa flow flow isis visible, visible, and grades into a vesicular-to-brecciated vesicular-to-brecciated flow top at the lakeshore. Further Furtherwest, west, just just beyond beyondthe the fence, is a ridge of massive basalt which is the interior of the overlying lava flow. More flows ridge of massive flow. More flows are visible visible along along the shoreline, shoreline, and east east of of the the lighthouse lighthouse provides provides an excellent excellent view view of of Eagle Eagle �G.ct '.0 �r - 62 — : ff , trit a," ;Yg() \ • j—' v C L_ - cope.. - - f -u ' 977.)) ' ()/J)J -'C - A4 - : / : —— '7 rDor uLe !-> "HARBOR s - bOf N —' - 7- - - iv 6to v "C - A --- C J 4 p )M44k ' I / A ot 1W V elate ff - /' JL) _rç J kf Boat Ramp ....VrT iv . VoIcanic :• at Stop 22 Con9lomerate2 Y 'Copper- Harbor I/I :4 ? MQthfl4 B14 " r Lake Superior pS ____ �Roa4 Log Main RoatI Log 93 93 Harbor and outcrops of the Lake Shore Shore Traps. Lake Shore Shore Traps Traps is is generally generally The amygdaloidal amygdaloidal mineralization and alteration seen in the Lake PLy, but mineralization calcite; chrysocolla; lower grade zeolite facies than the PLV, mineralization includes zeolites; calcite, chlorite; datolite; and abundant chlorite; abundant agate. agate. The flows have have segregation segregation cylinders cylinders and and numerous numerous sandstone dikes, and also have numerous mineralized slickenside surfaces that could reflect the subsidence of the rift rift sequence. sequence. At the Lake Lake Breeze Breeze Resort, Resort, just south south of of the the lighthouse lighthouse (PLEASE, (PLEASE, ask ask permission, permission, and and NO HAMMERS), the point that projects into the harbor has an exposure of beautifully preserved pahoehoe surfaces. Return to M-26. M-26. 67.25 Turn Turnleft leftand andfollow followM-26 M-26along alongEagle EagleHarbor. Harbor. 67.4 67.4 junction of M-26 and and Garden GardenCity CityRoad. Road. Stay on on M-26. M-26. The Owl Creek Leg (Leg B) begins The junction here. 67.5 67.5 The harbor at Eagle Harbor Harbor is controlled controlled by the occurrence occurrence of units which are called called the the Lake Lake Shore Traps. These PLy, is of Thesebasalt basalt flows flows are a member of the PLV, is interbedded with conglomerates of the Copper Copper Harbor Harbor Conglomerate, Conglomerate, and typically typically fonn form resistant resistant ridges. ridges. There are are excellent excellent exposures of the Lake Shore Shore Traps that occur at the Eagle Harbor Lighthouse, continue along the shore through Grand Grand Marais Harbor, Harbor, into into Agate Agate Harbor, Harbor, and and eastward eastward through through Copper CopperHarbor. Harbor. 68.25 The 68.25 Thejunction junction to to the theleft leftgoes goesto tothe theEagle Eagle Harbor Harbor Marina. Continue Continueahead ahead on on M-26. M-26. MAP 15 15 Marais Harbor. Hèbor. On rand Marais Onthe theright righthand hand side, side,you you can can see seethe the offshore offshore islands islands and and 69.4 69.4 A view of Grand by the the occurrence occurrenceof ofthe theLake LakeShore ShoreTraps. Traps. We are driving along a ridges which are controlled by conglomerate conglomerate ridge. ridge. 70.0 70.0 of Lake Lake Bailey Bailey on on the theright right side sideof ofthis thisconglomerate conglomerateridge. ridge. The The road passes along the shores of tend to to be be held up up by the conglomerates, and ridges throughout the Copper Harbor Conglomerate tend the valleys valleys are are underlain underlain by the the more more easily easily eroded eroded sandy sandy and and shaly shaly members members within within the the is Mount Mount Lookout. Lookout. The conglomerate. On Onthe the opposite oppositeside side of Lake Lake Bailey (on the right), is The contact contact between the the Copper Conglomerateand andthe the PLV PLV runs runs through through the the back back side of Mt. between Copper Harbor Harbor Conglomerate Mt. Lookout. Lookout. 70.15 On areexposures exposuresof ofthe thesandstone sandstonemembers members of of the the Copper Copper Harbor Harbor Onthe theleft leftside sideofofthe theroad roadthere thereare Conglomerate. Conglomerate. MAP 16 16 71.55 Crossing Crossing Silver Silver River. Pull Pullover over for for Stop Stop 23. STOP 23: Silver SilverRiver River(Copper (CopperHarbor HarborConglomerate) Conglomerate) This stop consists of excellent exposures, exposures, here here at Silver River and 0.1 0.1 miles east of the the Junction of M-26 with the Brockway Brockway Mountain road, on the left side of the the road. road. The Copper Harbor Conglomerate is is well well exposed exposedin inthis thisarea areaalong alongthe theSilver SilverRiver. River. At Eagle River Falls (Stop 21). 21), one had had the opportunity to look look at at the the basal basal beds of the Copper Eagle opportunity to Copper �___ gCJ C' rtJ. --TraP9 Lake Superior C- _r.Laj. - - .rr ) nr-rc4 -';7 tVVZ& rç G - -- A '(I e øpP (\ rr -F — — :'—L'-- ,, Tt' I naL' Lake - ç\,I - 2 —- — _: ie-'- -- - /1 -_ (I - - - I - - ç-- -- \t _-n— - —- -r - Portage take Vo canics -. - —c----4 2—' •. -. — 0 — 2J - ' -—- 1. )fl Cs— ,—North '1 it 3 —_ — -- - '15t± p:s. •/ çfl..r GreeflSt0 'roo( — 1' — -a—• v1 - _Ic—C-'4' t'- _) ( - 1 J — c0-ajioo 'c I — - / - 1001 -- —s," _rooo—- ——poo 110 — g2 — '-I / 9rj5ECongIomerate AG — _i (; I. fYif( -:Ty\ iC° - 1 FION.." • -(ç-- \\ 0 �>1 P — �96 MaiD Road Log Harbor Conglomerate. Now, Now, we we are arestratigraphically stratigraphically in the more central central part of of the the formation, formation, just below lava flow interbeds of the the Lake Lake Shore ShoreTraps. Traps. At Stop 26 and and 27, 27, one one will will get get the the interbeds of opportunity to look at the upper part part of the foymation. foymation. The The lithology lithology of the the sediments sediments here can be compared to to those those of of other otherstops. stops. Exposures provide a strike section within the Copper Exposures along the Brockway Mountain mad pmvide Harbor Conglomerate, allowing allowingone onewalking walkingalong along the the outcrop outcropto to observe observelateral lateralfacies facieschanges. changes. The The First large large exposure exposure on the the west end is is about about 55 m m high, high, and and at at the the base base isis aared redcolored, colored,very very fme-to-medium grained sandstone, sandstone,about about3.5 3.5m m thick, thick, overlain overlainby by massive massiveconglomerate. conglomerate. The fine-to-medium grained conglomerate clast-supportedwith with mostly mostlypebbles, pebbles,and andoccasional occasionalboulders bouldersup uptoto 20 20 cm in conglomerate is clast-supported diameter. The Thepebbles pebblestend tendtotobe becomposed composedof of subequal subequalamounts amounts of of mafic mafic and and felsic felsiclithologies, lithologies, tend to be be rhyolite rhyolite or or granophyre. granophyre. The conglomerates of of the the Copper Copper Harbor whereas the boulders tend Conglomerate are part of an alluvial fan complex complex with with sediments sediments being beingshed shedoff offof of the the flanks flanks of of the rift rift into into the thecenter, center,i.e., i.e., toward towardLake LakeSuperior. Superior. 71.65 The Thejunction junction totoBrockway BrockwayMountain Mountain Drive. Drive. We Weare aregoing goingto tocome come back back to to this this point, point, but but we we are are going to first take a side trip to Esrey Park. Park. Go Goto tothe theleft lefton on M-26. M-26. 72.15 We arenow nowatatthe theshore shoreofofLake LakeSuperior, Superior,where where there there are are dipping lava flows of the Lake Shore Shore Weare Traps. The Themad madfollows followsthe theshore shoreapproximately approximately parallel to the strike strike of the the lava lava flows. flows. 72.45 Pull 72.45 &ll left left into into Esrey Esrey Park. Park. STOP 24: Esrey STOP 24. Esrey Park Park(Lake (LakeShore ShoreTraps) Traps) The basalts cropping out at Esrey Park occur within the Copper Harbor Conglomerate, Conglomerate, some 800-1000 800-1000 m m above above the the PLV. PLy. They Theyare areaapart partof ofaasuccession succession of of Fe-rich Fe-rich olivine olivine tholeiite, tholeiite, basaltic andesite, andesite, and andesite andesite lava flows known collectively as the Lake Shore Traps (an informal member within the Copper Harbor Conglomerate) Conglomerate) (Fig. (Fig. 40). 40). This succession succession is thickest thickest at at the the tip tip and thins toward the east (on Manitou Island) of the Keweenaw Peninsula Peninsula (approximately (approximately 600 600 m), m), (on Manitou Island) pinch out near Calumet (a total strike length and toward the west-southwest, where the lava flows pinch lava flows flows vary vary in in thickness thickness fmm from about about44 to to 40 m and of about about90 901cm). km). Individual Individual lava and exhibit exhibit volcanologicalfeatures featuressimilar similartotoflood floodbasalts basaltsofofthe thePLV. PLy. The volcanological Thelowermost lowermostmafic mafic flows flows were were deposited as ponded sheets while upper andesite flows may have formed a low, positive deposited as ponded while upper andesite flows may formed a low, positive topographic feature such as a shield shield volcano. volcano. Magmatic variation variation within within lava lava flows flows at at the tip of the Magmatic the Keweenaw Keweenaw Peninsula imply that fractional crystallization of of plagioclase, cliopyroxene, clinopyroxene, olivine, olivine,Fe-Ti Fe-Ti oxide, oxide, apatite, apatite, and and zircon played an an important role in the of the played important role the petrogenesis petrogenesis of the Lake Lake Shore Shore Trap Trap magmas magmas (Paces (Paces and and Bornhorst, 1985). ~omhorst, 1985). Additional Additionalprocesses processes of of parental parental magma magma replenishment replenishment and and possible possible wall wall rock rock assimilation however, however,are arerequired requiredtotoexplain explaingeochemical-stratigraphic geochemical-stratigraphicrelationships. relationships. is aa massive flow flow interior of fineThe large outcrop outcrop between the parking lot and the shore is grained, Fe-rich olivine tholeiitic basalt. The Theflows flows strike strikeparallel parallel to to the the shoreline shorelineand and dip dip20-30° 20-30' toward the lake. The Theupper upperportion portion of of this this flow flow isisnot notexposed, exposed, but but the the top topof ofthe theunderlying underlying of the the large outcrop. outcrop. Because basalt flow can be seen at the shoreline on either side of Because of of its its higher higher the degree degree of of metamorphism/alteration metamorphism/alteration in in the the Lake Lake stratigraphic level within the rift-fill sequence, the Shore Traps Traps is is much lower than than in in the PLy. Zeolite facies metamorphism, as opposed to Shore much lower PLV. Zeolite metamorphism, as deposited chalcedony; chalcedony; laumontite; laumontite; analcite; prehnite-pumpellyite, affected affectedthe the flow top and deposited analcite; calcite; calcite; and smectite in amygdules. amygdules. Massive Massive flow flow interiors interiors of the Lake Shore Traps often retain relict �Main Reed Log FredaSandstone Sandstone Freda and and Nomwdl Sink Nonesuch Shale 97 SAMPLED UNITS m 600 outer outer LST ILST IBVBS 11ev.. 500 400 Copper Harbor Harbor Conglomerate w 7= flows middle middle LST lava. 300- I d iow LST LST 200— mlddi. LST laVal eves 100-S PortageLake Lake Portage Volcanlcs Volcanics lower ? lava Jnows 0— (a) (a) Traps Figure columnofofthe the Lake Shore Figure 40: 40: Stratigraphic Stratigraphic column Lake Shore Traps[LST] [LST]from fromthe theeastern easterntip tipofofthe theKeweenaw Keweenaw Peninsula (from DieM and Haig, in press). Peninsula (from Diehl and Haig, in press). �- 98 olivine the PLV, PLy, where olivine and glassy, intersertal mesostatis in contrast to the where both both olivine olivineand and intersertal intersertal replaced by by Mg-Fe Mg-Fe phyllosilicates. phyllosiicates. glass are invariably replaced 100m m east east From the east end of the large basalt ridge next to the parking lot, walk about 100 along the the shore to see along see the the flow flow top top of of the theunderlying underlying flow. flow. This well exposed exposed flow top is is basalt, typical typical of of aapahoehoe pahoehoeflow flowtop. top. The vesicles are are partially partially filled filled with with composed of vesicular basalt, laumontite, chlorite, calcite, calcite, and quartz. quartz. 72.55 Turn 72.55 Turnaround aroundand andhead headback backtoward toward the the junction junction of of Brockway Brockway Mountain Drive. 73.35 Take Takeaasharp sharpleft leftturn turnonto ontothe theBrockway BrockwayMountain Mountain Drive, Drive, more more exposures exposures of of the the Copper Copper Harbor Harbor Conglomerate described describedatat Stop Stop 23, 23, can can be be seen. seen. We Conglomerate We will will drive drive for for several several kilometers kilometers along along aa conglomerate ridge ridge with with many many conglomerate conglomerateexposures. exposures. In In spring spring and and fall fall a very diverse hawk migration occurs along this ridge. The Theridge ridge summit summitallows allows very very close close observations observationsbecause because the the birds often follow the ridge ridge top. top. MAP 17 17 78.35 At Atthe thesummit summitofofBrockway BrockwayMountain, Mountain, take take aa right right turn turn in a short distance, to the observation site. STOP 25: Brockway BrockwayMountain MountainViewpoint Viewpoint This high conglomerate conglomerate ridge reaches an elevation of over 400 m, with with excellent excellent views views of the ridge and valley topography of the northern shore of of the the Keweenaw Keweenaw Peninsula. Peninsula. Underfoot, Underfoot, the Copper Harbor Harbor Conglomerate Conglomerate dips dipsabout about200 20' to to the north. north. To the west, the Lake Shore Shore Traps Traps form island chains on a prominent ridge in the vicinity of Agate Harbor and Esrey Park. Copper Copper Harbor Harbor Conglomerate Conglomerate is found in the drowned valleys and along the outer outer ridge ridge jutting into into Agate Agate Harbor Harbor and projecting into a smaller smaller island island chain. chain. The reefs of the the Lake Lake Shore Shore Traps Traps and and Copper Copper Harbor Conglomerate Conglomeratealong along the the Keweenaw' Keweenaw'ss north north shore are are the the site siteof of numerous numerousshipwrecks. shipwrecks. topographicallylow low valley valley Lake Bailey (with (with the small small island) and Lake Upsom occupy a topographically on a finer-grained finer-grained clastic clastic horizon horizon within within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. Just to the south of Lake Lake Bailey, Bailey, is is the the conglomerate conglomerate ridge of Mt. Mt. Lookout, Lookout, marking marking the the contact between the Copper Harbor Conglomerate Conglomerate and and the the PLV. PLy. The inland directly south, south, isis Lake Lake Medora, Medora,and andjust just before before the the lake lake is a The inland lake almost almost directly prominent ridge which marks the stratigraphic position position of of the Greenstone How. flow. In the distance, distance, farther to the south south across across Lake Medora, is Mount Bohemia, a dioritic dioritic stock-sized intrusion. To the southwest, southwest, a distant distant ridge ridge with with white white buildings buildings on itit marks marks Gratiot Gratiot Mountain, Mountain, which is underlain by andesitic dikes and small rhyolite bodies that cut the PLV. To the east are the communities communitiesof ofCopper CopperHarbor Harborand andLake LakeFanny FannyHooe, bee, both both of of which which occupy the same stratigraphic horizon as as Lake Lake Bailey. Bailey. Copper Harbor was a boom town in 1843, Copper 1843, following the initial discovery of native copper copper in in the the Keweenaw KeweenawPeninsula. Peninsula. In 1844 1844 Fort Wilkins was built on the shores of Lake Fanny Hooe; it is now a state park. The Thelighthouse lighthousewas wasbuilt builtinin 1866. 1866. �____j Stop 27 r------ -- - - Copper ri -- - Harbor jj •_•. — .0 -- IT ,1 t— - - -",' _L -- — pp /V -- zcT>TT1 ReTaTC --7 -.. CS Traps -_— -- — I - C—--tfl-fl - Trap - '-'t_±i_ISc 1c1i2 TIk - nr-c - —— £ —- - - Shr Conglomerate Lake — Lake Th -—— -c---z--T c - 26 ..___ — asi;zID Luke ____ ___ Lake Superior - - - ---I-- —— ,_jI - _I — -- — - — -- er / 4'<---—--c-----*--- -B-0 - —'-'? - <---- —, ) C -- - - -' Th I 44, \ C -ç or a9e Lake volca '- — c—±cc �100 Harbor, lies lies East Ridge, To the To the east east on on the skyline, skyline, beyond beyond Copper Copper Harbor, Ridge, aa prominent prominent conglomerate hill. To the the north on the the skyline skyline 65 km away, is Isle Isle Royale, Royale, which is visible visible on aa clear clear day. day. The skyline of Isle Royale is formed formed by the the Oreenstone Greenstone Flow, as it is is on on the thePeninsula. Peninsula. Follow the road downhill downhill toward Copper Harbor. 78.35 Turn Turntotothe theright rightand andfollow followthe theroad roadstraight straightahead aheadtoward toward Copper Copper Harbor, Harbor, going going downhill downhill and and which has excellent views views all the way down. continuing along the ridge which MAP IS 18 pull-out on the right right hand hand side of the the road road that that gives gives an an excellent excellent view of of Copper Copper 81.9 81.9 There is a pull-out Harbor and Lake Fanny Hooe. Copper Copper Harbor Harbor is is controlled controlled by the occurrence of the Lake Shore Shore Traps. Porters Island, Island, are areunderlain underlainby bylava lavaflows. flows. From the Traps. The Theislands islands offshore, offshore, including including Porters to excellent excellent exposures of the Lake Copper Harbor Marina, with a small boat, you can have access to There are exposures of the Copper Shore Traps along the edges of Copper Harbor. of Copper Harbor Harbor edges of Copper Harbor. Conglomerate along the road road descending descending into into Copper Copper Harbor. Harbor. M-26, turn left. 83.0 At the junction at M-26, MAP 17 17 past the the blowhole blowholecalled calledthe theDevil's Devil's Washtub. Washtub. If you you 84.7 We come to the shore of the lake again, past stop here by the right right side side of of the the mad road and andtake take aashort shortwalk walkalong alongthe theconglomerate conglomeratealong along the the shore, you come to wave washed exposures of the conglomerate at the Devil's Devil's Washtub. Washtub. (This (Thisisis PRIVATE PROPERTY.) PROPERTY.) 85.25 On Onthe theleft leftisisaapublic publicaccess accessto tothe thelake lake shore shore and and exposures exposures of the Copper Harbor Conglomerate. 85.55 Pull 85.55 Pullover overon onthe theright rightatatthe theKeweenaw KeweenawCounty County Park. Park. STOP 26: Hlebard STOP HebardPark Park(Copper (CopperHarbor HarborConglomerate) Conglomerate) Excellent exposures exposures of of the Copper are exposed exposed at at this public Excellent Copper Harbor Conglomerate Conglomerate are public locality. At Atthis thispoint, point,the theCopper CopperHarbor HarborConglomerate Conglomerate is is stratigraphically stratigraphicallyabove above the the Lake Lake Shore Shore Traps. See SeeStop Stop27 27for forfurther furtherdescription descriptionofofthe theCopper CopperHarbor HarborConglomerate. Conglomerate. 86.35 Pull 86.35 Pullover overto tothe theright rightatatthe thegift gift shop. shop. The Thenext nextstop stopisisPRIVATE PRIVATE PROPERTY. PROPERTY. Ask Askpermission permission at the gift gift shop. shop. DO DONOT NOTUSE USEROCK ROCKHAMMERS HAMMERS AT AT THIS THIS STOP. STOP. STOP Harbor STOP 27: Dan's Dan'sPoint Point(Copper (Copper HarborConglomerate) Conglomerate) Walk about 20 m to the shore shore of of Lake Lake Superior, Superior, to look look at the the lithology lithology of of the the Copper Copper Harbor Conglomerate and an occurrence of stromatolites in in wave wave washed washed exposures. exposures. Please Please do do outcrop, specimens specimens can can be be found found on on the pebble beach. not remove stromatolites from the outcrop, The Copper Harbor Conglomerate ranges ranges from 490 m thick near the Wisconsin Wisconsin border, border, to about about 1310 1310 m m ininthe theKewesnaw KeweenawPeninsula. Peninsula. As aa whole, whole, the the formation formation is is aared-brown, red-brown, basinward-thickeningwedge wedgeofof fluvial fluvial siliciclastic siiciclastic conglomerates and sandstones that was basinward-thickening conglomerates and sandstones that was deposited in the rift basin after flood basalt volcanism volcanism (PLV). (PLV). The The Dan's Dan's Point Point outcrop outcrop shows shows a proportion of lithologies lithologies that is characteristic of the upper two-thirds two-thirds of the formation. Directly PLy, is Directly above, above, and locally interfingering interfingering with the lava flows of the PLV, is aa thin-to-thick thin-to-thick �Lake Superior ore• Copper * HAYS (PIt,st.URGH 6 £XPLORATION Lake -— arbor • . I /- V • ... —--. —V. . ,.• /.- . _/ .-..... I 0 -. �102 102 ?,bin Road Mtin Rend Log Los bedded, bedded, coarse coarse basal basal conglomerate conglomeratefacies facies consisting consisting of well-rounded, well-rounded, poorly sorted sorted clasts clasts of of mauicmaiicThese, and the higher conglomerates, generally are clastto-silicic volcanic rock rock fragments. fragments. These, higher conglomerates, generally supported and show a ratio of supported of mafic-to-silicic mafic-to-silicic intermediate clasts of about 2:1 21 (Elmore, (Elmore, 1984). 1984). The sandstones lithic graywackes which The sandstones are are predominantly predominantly red-brown, red-brown, subangular-to-angular subangular-to-angular lithic exhibit current-ripples; current-ripples; foreset and trough-cross beds; and parting lineations. lineations. Minor shale and and siltstone interbeds show desiccation features. In the conglomerate and coarse sandstones, show desiccation features. the conglomerate and coarse sandstones, the the abundant calcite cement probably abundant probably was deposited as vadose vadose carbonate carbonate or or caliche calicbe(Kalliokoski, (Kalliokoski, by this In the theupper upper two-thirds two-thirds of of the the formation formation on the Keweenaw Peninsula, represented by 1986). In are more more abundant. abundant. There outcrop, sandstone interbeds are There are are also also laminated laminated cryptoalgal cryptoalgal carbonate carbonate horizons occurring laterally-linked stromatolites, stromatolites, that are draped draped over over cobbles, cobbles, as as laterally-linked laterally-linked horizons occurring as laterally-linked contorted layers in mudstone-siltstone mudstone-siltstone and as as poorly developed developed mats mats in coarse coarse sandstone sandstone(Elmore, (Elmore, 1983). 1983). of the Copper Harbor Conglomerate has been interpreted The depositional environment of interpreted as a prograding braided stream and sheet prograding alluvial alluvial fan complex (Fig. 10) 10) with proximal-to-distal proximal-to-distal braided alluvial fans fans and and sand sand flats flats (Elmore, (Elmore, 1984). 1984). The region flood facies on coalesced coalesced alluvial region was was nearly nearly equatorial in geographic probably arid arid with with aa seasonal seasonal rainfall rainfall pattern equatorial geographic position and the climate was probably conducive conducive to flashy streams streams and to to the the development development of of vadose vadose carbonate carbonate(Kalliokoski, (Kalliokoski, 1986). 1986). and ooid ooid lenses lenses formed formed in in shallow, medial medial fan fan lakes and possibly Isolated cryptoalgal carbonate and which received received very very little sediment (Elmore, 1983). abandoned or low-water stream channels which 1983). section of of the Copper Harbor Harbor Conglomerate Conglomerate exposed exposed atat Dan's Dan's Point The stratigraphic section and sandstones sandstones (Fig. (Fig. 41). 41). Clast-supported consists of about 30 m of interbedded interbedded conglomerates and Clast-supported beds consist consist of of rounded, rounded, cobblecobble- to to boulder-sized boulder-sized clasts clasts with with a matrix of coarse conglomerate beds coarse grains cemented cemented with with carbonate carbonateand andiron ironoxide. oxide. Clasts are sand-sized subangular grains are predominantly of siicic of silicicvolcanics, volcanics,with withsubordinate subordinatebasalt; basalt; pyroclastic; pyroclastic; plutonic; plutonic; and and metamorphic metamorphic lithic lithic exposed section section exhibit exhibit crossbeds, crossbeds, current current fragments. Several Severalfmer finergrained grained interbeds interbeds higher in the exposed Jineations, current ripples, parting lineation, and reduction spots. lineations, spots. In particular, one should note note that represent vadose carbonate or paleocaliche. the calcite-rich zones that paleocaliche, and the white white stromatolite stromatolite Along one one of these calcite zones, algal growth occurred during a (genus Colleria) Colleria)horizons. horizons. Along occurred during period of depositional quiescence quiescenceand and was was halted halted by by an influx of silty period silty material material followed followed by by renewed conglomerate conglomerate deposition. deposition. , Several Conglomerate occur Several sites sites for for public access access to the lakeshore and the Copper Harbor Conglomerate occur for up to about of Dan's for about 0.6 miles miles west west of Dan's Point. Point. We Wewill will retrace retrace our our route route back back toward toward the Brockway Mountain Drive junction. 86.35 Turn 86.35 Turnaround aroundand andgo goback backtoward toward Copper Copper Harbor Harbor on on M-26. M-26. MAP 18 18 Mountain Drive. Drive. To the the left left isis aajunction junction to tothe theCopper CopperHarbor Harbor 89.7 At the junction junction of Erockway Brockway Mountain Marina. Continue Continuestraight straightahead aheadon onM-26 M-26totoCopper CopperHarbor. Harbor. 90.15 The 90.15 Thejunction junction between between M-26 M-26 and and US-41 US-41 in in Copper Copper Harbor. Continue Continue straight straight ahead ahead toward toward Fort Fort Wilkins Wilkins State State Park. Park. Copper Harbor was suddenly suddenly a boom town in 1843, 1843, following the discovery of copper in the the vicinity. Porter's Porter's Island Islandwas wasthe thesite siteof of the the first firstgovernment government land office and in 1844, Fort Wilkins (Stop 28) was built on on the the shores shores of of Lake LakeFanny Fanny Hooe, Hooe, to toprotect protectthe theminers minersfrom frompotentially potentially hostile Indians. The Thelighthouse lighthouse was was built built in in 1866. 1866. �MainRoadLog A 103 0 B .r t ct9j e.P. , a T,o.4, as beinq Ib*u,IS i......a... Wove a,d cnt nppt oos a 4? :n U-.-- n r— .— tLcuj o3.93J a t, °_Oo .1 B Slrrt. a Ooids Figure41: 41: (a) (a) Measured Measuredstratigraphic stratigraphicsections sections from from Horseshoe Harbor (B) and Dan's Point Point (D) (D)with with Figure current direction rose diagrams. diagrams. (b) (b)Schematic Schematiccartoon cartoonof ofthe thedepositional depositional environment environmentwhich which fostered growth of of stromatolites stromatolites in in temporarily temporarily abandoned abandoned medial-fan medial-fan stream channels channels (from (from fostered growth Elmore,.1981). 1981). Elmore,, �104 91.6 MäiRog Entrance to Fort Wilkins WillcinsState StatePark. Park. There There isis aa fee fee to to enter enterthe the state statepark. park. The entrance pass is Park, visited visited at at Stop Stop H6 H6 on on the the McLain McLainLeg. Leg. Upon entrance also valid for McLain State Park, entrance into into the the park park store. The park, pull into the parking lot and proceed to the The Fort Fort has has many many excellent excellentexhibits exhibits illustrating the mining history history of of the the Keweenaw Keweenaw Peninsula. Peninsula. STOP 28: Fort (native copper veins STOP FortWilkins WikinsState StatePark Park (native copper veinswithin withinCopper CopperHarbor HarborConglomerate) Conglomerate) Fort Wilkins is now a state park park with with camping campingfacilities facilitiesand andaamuseum. museum. Much exploration Port of the fort, and there are shafts and exploration pits activity took place in the immediate vicinity of Hoot and all along the land land between between Lake Fanny Fanny Hooe and the the Harbor, Harbor, mostly mostly from from exploration exploration in the the of the park store, several pits provide evidence of early mining 1843-1846 period. Just north north park store, several activity by European settlers. The ThePittsburgh Pittsburgh and and Boston Boston Mining Mining Company Company operated operated here here In in the the 1840's on aa vein vein of of native native copper copper within within the the Copper Copper Harbor Harbor Conglomerate, Conglomerate, the the vein vein was was reported reported to be up to 0.3 0.3 m m wide. wide. This Thisventure venturewas wasnot notprofitable. profitable. In 1853, thereafter, mining mining activity activity took took place place south south of of the fort 1853, and for for several several decades thereafter, in a series the Clark Clark Mine. Mine. The series of workings called the The mineralization is of the fissure and amygdaloid adularia, microcline, microcline,chlorite, chlorite, type and consists consists of of prehnite, prehnite, epidote, epidote, analcite, analcite, quartz, quartz, laumontite, laumontite, adularia, datolite, calcite, and several copper minerals including chalcocite, cuprite, and tenorite as several chalcocite, cuprite, and tenorite as well as native copper. Agates Agatesare areconspicuous conspicuous in in vesicular vesicular basalt of the Lake Lake Shore Shore Traps Traps here, here, and and the the area is well known known for for datolite datolite collecting. collecting. An occurrence of manganese minerals minerals in in aa fissure accounts for for the name of Manganese manganese minerals found here Lake, south of Lake Fanny Hooe (refer to Map The here were were south of Lake Fanny Hooe (refer to Map ).). The pyrolusite, manganite, braunite, and orientite. Pine tract represents represents aa part part of the pyrolusite, orientite. The Estivant Estivant Pine Clark Mine Mine lands which were were deeded deeded to to the the C&G C&G Company Company in in 1942, 1942, and and are now a nature nature Clark lands which the Upper Upper Peninsula. Peninsula. preserve, containing the last virgin pine tracts in the Opposite Fort Wilkins Wilkins on on one one of of the Park trails trails that crossed US-41, is a view Opposite Fort crossed US-41, view of of the the Lighthouse. Near the point of the lighthouse on the shore facing the big lake, is Copper Harbor Lighthouse. is rock". The the sight of the famous "green rock. The "green "green rock" is a vein seen by early voyagers and was described by by Douglass Douglass Houghton; Houghton;ititisis one one of of the localities that focused focused early early interest interest in in the described localities that Houghton himself himself may may have have never never really really understood understood the the uniqueness uniqueness of of the Copper Country. Country. Houghton district, as the conventional wisdom then, was that it was the surficial alteration of a sulfide ore. 1993). But Houghton promoted the district well (Krause, 1993). Horseshoe Harbor has has excellent of the Copper Horseshoe Harbor excellent exposures exposures of Copper Harbor Harbor Conglomerate Conglomerate and and interbedded algal stromatolites can can be be reached reached via via the the Horseshoe Horseshoe Harbor HarborLeg. Leg. Keweenaw Point, East Bluff, and other dirt road road other points points of interest interest can be reached reached by continuing continuing on the unmarked unmarked dirt which goes eastward from the end of US-4 US-41I and are discussed in the Horseshoe Harbor Leg. 91.7 Retrace the the route back toward Entrance to Fort Entrance Fort Wilkins Wilkins State State Park. Park. Retrace toward Copper Copper Harbor. Harbor. The Horseshoe Harbor Leg Leg begins begins here. here. 93.15 The Turnleft lefton on US-41, US-41, south south out out of of Copper Copper Harbor. Harbor. 93.15 Thejunction junction of ofM-26 M-26 and andUS-41. US-41. Turn 94.25 Nice Niceexposures exposuresofofthe theCopper CopperHarbor HarborConglomerate Conglomerate are to the left of the road as we are going up the hill. hill. 94.6 Entrance to the Keweenaw Mountain Lodge Lodge and and Golf Golf Course. Course. During Keweenaw Mountain During the the Great Great Depression Depression of of rate in in Keweenaw KeweenawCounty Countywas wasaround around70 70toto 80%. 80%. Keweenaw the 1930's, the the unemployment unemployment rate Keweenaw �MainkoadLog Mill Rod Log 105 105 County's Boani County's Board of of Trustees Trusteessubmitted submitted aa proposal proposal to the Civil Works Administration Administration (C.W.A.) and programs. Most became one of the first work projects within the Federal programs. Most of of the the present present buildings buildings were completed on the 167 acre site in 1935 with with Federal Federal funds. funds. Revenue from operations Revenue operations have new cottages cottages (after (after aa report report by by J.J. W. W. Jackson). Jackson). The lodge allowed several new lodge has has accommodations accommodations and an excellent excellent atmosphere atmosphere for for eating. eating. MAP 19 19 side of of the the road. road. 97.5 Lake Medora on the right side MAP 20 100.35 junction on on the the left left goes goes to to Mandan. Mandan. Mandan now is only a few 100.35 The junction Mandan now few houses, houses, but it had 300 residents in 1910. Continue Continueahead ahead on on US-41. US-41. 100.6 The mad 100.6 road to to the the left is is the the entrance entrance to the outer portion of the Keweenaw Peninsula, all on poorly maintained dirt roads. roads. To Tovisit visitMount Mount Houghton Houghton and and Keweenaw Keweenaw Point, you may exit here. side of of the the road road is is aa swamp swamp lying lying east east of of aa north-south north-south trending trending esker. esker. 100.8 On the left hand side 100.8 park here. here. Proceed Proceed on on foot foot to to view view the the esker. esker. on the the right. right. Pull over and park 100.9 A small road on 100.9 STOP 29: Mandan Mandan(Mandan (Mandanesker) esker) featured in many geological lab exercises, exercises, is is clearly visible on Map The Mandan esker, featured as a north-south trending topographic topographic ridge ridgewith withup upto to25 25m mof ofrelief relieffrom fromnear nearClear ClearLake. Lake. The ridge is composed composed of coarse coarse Pleistocene Pleistocene sand and gravel, and was deposited by glacial glacial meitwater meltwater flowing in a subglacial tunnel. The esker sediments are not exposed along the road, but subglacial tunnel. The esker sediments are not exposed road, but can can be be viewed by walking viewed by walking along along the ridge ridge toward toward the south to an an old old railroad railroad cut cut (Regis (Regispersonal personal communication, communication, 1992). 1992). This stop is best in the fall fall or or spring spring due due to to the the dense densefoliage. foliage. MAP 21 MAP 21 junction of the road to Lac 1. The Eastside Keweenaw 103.4 The junction La Belle. Belle. Continue Continueahead aheadon onUS-4 US-41. 103.4 Lac La Peninsula Leg begins here here and and ends endsin in Lake LakeLinden. Linden. 104.05 The dirt Delaware Mine. Mine. Turn 104.05 dirt road to the right goes to Stop 30 at the Delaware Turn right on the dirt road and follow the signs to the Delaware Mine. signs to the Delaware Mine. 104.2 STOP Mine (native copper deposit 104.2 STOP30: 30:Delaware Delaware Mine (native copper depositwithin withinPortage PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) The Delaware Mine is open to to tours tours during during the the summer summer months. months. At this stop, one one has the the opportunity look atat the the rock rock piles piles from from the the Delaware DelawareMine Mineand andtoto visit visit (for (for aa fee) the opportunity toto look underground workings. workings. The workings is is at Stop 8. The other other opportunity opportunity to visit underground underground workings The Delaware Delaware Mine is aa typical typical vein vein deposit deposit situated situated below below the the Greenstone Greenstone Flow. Flow. It operated from 1848 to 1887, of about 3.5 3.5 million million kg kg of refined copper 1887, with a total production production of (Butler and Burbank, Bill-bank, 1929). 1929). Overall, Overall, it was not not aaprofitable profitable venture. venture. The early and major major production was from a native production native copper-bearing copper-bearing vein, the Stoughtenburgh Stoughtenburgh Vein, which was mined mined section was was below for 265 for 265 m on on strike, strike, to aa depth depth of of 330 330 m. m. The productive productive section below the Allouez Allouez Conglomerate. Three shafts were opened Conglomerate. opened in 1881 1881 to mine mine copper copper from from the the adjacent adjacent Allouez Allouez Conglomerate. The Delaware Conglomerate. Delaware Mine Mine was first first known known as as the theNorthwest Northwest Mine. Mine. The current current accessible mine was mapped and and described described by Schleiss Schleiss (1986). (1986). Two thin crosscuts on on the the first-level first-level drift. drift. They thin basalt flows are exposed exposed in two crosscuts They strike strike E-W and dip dip 25°N. 25W. The Theflows flowshave havefme-grained fine-grainedmassive massive interiors interiors and and amygdaloidal amygdaloidal flow flow tops, tops, �-o 0 Is) V -ii) -JT: -Th - Y r-JTT ) V 4r 'I--- - •__ / 15_ — *iS _5 0pL 14 ' -— - - JU -- —z-"U/' I N - -- - — /____- - . - f__f - 1Th- \\ \ ) ,5)--- N) C——. V UJ' / J[ 'i2 -I --.--+- C- cT. / /rr0! S __iJ ,-K / 1—' -t_ , -- I - i f7' --C - 4. ___r ___&etnst4 C -a 0* a., C �_ ____ ___ _______ MainRciadLog C Stop 29... -CUtWL / "\ l'cç " 107 -- / H44ç' f; *Nj iqe * )W >+tc Mandan' If )d' — ç ? ) ' cr r2cKrcSE?4T e b' Ctcrrt4, 'I ftP: 4r:: —/ °°J ((/ 'Fr Th z —_2::N)\ _2 : — -r I .-.. ,.j---t.Bohemia c N— C %— ' ) -- / J a c ob s I MAP 2C �______ ________________ '-T'-"4t-9 = H?E- t—-- ci DLR CL —— _iia'—---' r _\ \>-\ ''0O.( -C' —--i—r-= 51(_ I r- —: ——r- cL3'—'4( I 0 — pbC- " ( -— —— -- -S ¶i5i!St L - — / — -— — v ::- t \__ *00 '— \K -, _xc r t1D)lp a- 1s) 0 -, - p —- _- H - /Stop 30; —' Dela : — '5 — >.-..___ C - - — Zt -Tt5 &r>_c-2-J 4— - ___ a>— •- -- V r-__ - - -— - —----'-- 22 "Stop31 JZ/68 S N ) - / N 'c't Jf I'.) [ I \c' ea 2Cr-i !v 1'__ 1,'c— çto'H X I 0 00 I �MainRo.dLng 109 with amygdules predominantly filled with calcite. A A weathered weathered zone zone on on the the top top of of the theuppermost uppermost of the two basalt flows is overlain by the Allouez Conglomerate. The Allouez Allouez is the only unit Allouez Conglomerate. along the first-level, m thick; thick; is is composed composed of first-level, and and currently currently is is the the only only accessible accessiblelevel. level. It is 88 m rounded-to-subangular rounded-to-subangular clasts clasts up to 30 30 cm in diameter; composed of rhyolite, granophyre, and and rare rare by a matrix matrix of of sand. sand. There basalt; and is supported by There is is an an interbedded interbedded lens of fine- to mediummediumsandstone and is overlain by the Greenstone Flow, which crops out up the bluff above grained red sandstone above the mine, but is is not not exposed exposed in in the the mine. mine. The principal accessible portion portion of of the the Stoughtenburgh StoughtenburghVein Veinisisabout about 35 35 cm cm wide. wide. Here, Here, as in all all veins veins in in the the mine, mine, calcite calcite is the the main filling. The Theparagenetic paragenetic sequence sequenceisis minor minorquartz, quartz, microcine, and by minor microcline, and muscovite; muscovite; followed followed by minor native copper copper and abundant abundant calcite; in turn, turn, the epigenetic minerals consist of followed by minor minor chalcocite. chalcocite. In the Allouez Conglomerate, the the interstices between between matrix and calcite with minor amounts of quartz and microcline filling the clasts, and sporadic sporadic native native copper copper within within the the matrix. matrix. The only faults in the mine are bedding plane faults, at the upper and lower contacts of the conglomerate. wall is denoted denoted by by more more than than 18 cm cm of of clay fault conglomerate. The fault in the the hanging hanging wall gouge (vermiculite (vermiculite and and smectite) smectite) with with introduced introducedcalcite. calcite. The footwall bedding bedding plane fault is denoted by a 2 to 55 cm cm thick layer layer of gouge, gouge, consisting of chlorite chlorite with lesser amounts amounts of calcite; calcite; microcline; quartz; and native copper. copper. The microcliine; The amount of displacement along these faults is unknown. In the first-level drift of the the Delaware Delaware Mine there are a large large number number of of parallelparallel- to to sub-parallel sub-parallel fractures, filled with calcite. calcite. The The fractures, fractures, known as tension fractures, can be subdivided into a major northwest-striking set set and and aa minor minornortheast-striking northeast-strikingset. set. A model model for for the theDelaware Delawarefissure fissurevein-conglomerate vein-conglomerate lode lode mineralization mineralization begins begins with with copper copper bearing fluids along along permeable permeable flow flow tops tops and and conglomerates. conglomerates. Faults and and fractures fractures produced during the paleohydrologic paleohydrologic produced duringlate late compression--reverse compression--reverseKeweenaw Keweenaw fault faultmotion—integrated motion-integrated the system and allowed allowed effective effective movement movement of ore ore fluids. fluids. The steeply steeply dipping dipping tension tension fractures fractures (veins) were efficient pathways pathways for for fluid fluid movement. movement. The fluids migrated upward and The fluids migrated upward and laterally laterally through these open fractures and were diverted beneath the thick, unfaulted, massive interior of Flow so that the Greenstone Greenstone Row that fluids fluids moved moved laterally laterally from from the the fractures fractures into into the theAllouez Allouez were deposited, deposited, probably probably in in response response to to a combination of fluid Conglomerate. Ore minerals minerals were combination of Conglomerate. mixing; cooling of the the solution; solution; and and fluid fluid wall-rock wall-rock reactions. reactions. The Delaware Mine rock pile, as with other vein deposits deposits in the Keweenaw, Keweenaw, is is aa notable notable locality for datolite. Also Alsoincluded includedin inreports reportsabout aboutthe the rock rock pile pile are are these these minerals: minerals: chlorastrolite, chlorastrolite, prehnite, calcite, laumontite, analcite, chlorite, epidote, native copper and native native silver silver (Clarke, (Clarke, 1975; Zelenka, 1978). 1978). 1. Left turn on IJS-4 US-411 and continue ahead towani toward 104.35 The The junction of of the theDelaware DelawareMine Mineand andIJS-4 US-41. Phoenix. right side side of of the the road. road. Massive basalt on the east end of 104.45 Exposures of basalts of the PLV on the right the outcrop is N30°W. The The orientation orientation of of these these fractures fractures is cut cut by by several several fracture fracture zones zones trending N30W. is similar similar to to those those in in the the Delaware Delaware Mine. Mine. The fractures fractures contain containminor minoramounts amountsof ofnative nativecopper. copper. 104.8 104.8 Pull over over on on the the right right hand hand (north) (north) side side of of the the road road just before before the the outcrops. outcrops, �110 t.4aiuadI.og near STOP 31:US-41 US-41 nearDelaware Delaware(Portage (PortageLake LakeVolcanics Volcanics[PLY]) [PLV]) STOP 31 of basalt basalt lava lava flows flows within within the thePLV PLYcan canbe be observed observedatatthis thislocality. locality. The The character of strike of the flows is about E-W here, roughly parallel to the orientation of the road, thus you are are half of the 55 m looking at aa strike-parallel strike-parallelsection. section. The lower half m high high outcrop outcrop face face consists consists of of appearance. In the center of the the outcrop, outcrop, a large large egg-shaped egg-shaped mass mass vesicular basalt with a rubbly appearance. by vesicular vesicular basalt. basalt. The vesicles of more dense basalt is surrounded by vesicles dominantly are filled with calcite, prehnite, prehnite. and and chlorite. chlorite. The calcite, The character character of this flow top represents a pahoehoe flow with brecciation. This limited brecciation. This isis overlain overlain by by flne-grained fine-grained massive basalt with subvertical joints of the higherflow. flow. The contact contact between betweenthese thesetwo twoflows flowsisisirregular. irregular. Note that next stratigraphically stratigraphically higher no sediment sediment exists exists between between these these flows. flows. The lack of sediment sediment between between flows is aa common common rapid rate rate of of extrusion. extrusion. Where sediment horizons exist, the temporal feature, and is indicative of a rapid composition of of the the basalts basalts often often suggest suggestthe theend endof of aa cycle, cycle, and and is is consistent consistent with with aa hiatus hiatus in composition arestratigraphically stratigraphicallybelow below the the Greenstone Greenstone Flow. Flow. volcanic activity. The Theflows flowsatatthis thislocality localityare MAP 22 22 107.0 Ahead are cliffs of the Greenstone Flow. The The road road nears nears the the basal basal contact contact of of the the flow. flow. Greenstone Flow. 107.0 108.3 exposure of one one of of the the flows flowsbeneath beneath the theGreenstone Greenstone Flow. How. 108.3 An exposure Ridge in inthe thebackground. background. In the foreground is is the ghost 109.1 To the right, one can see the Greenstone Ridge 109.1 town of Central and its associated rock piles. ofcentral and its associated rock piles. ahead on on US-41. US-41. The road 109.45 A junction of paved paved roads roads to to the the right right and and left. left. Continue ahead mad to the left goes to Gratiot 932 Creek. The Theroad road to tothe the right right goes goes toward toward the the Gratiot Lake and is the start start of Leg E -- 932 ghost town of of Central Central and and the the Central Centralrock rock piles. piles. nearly at right angles to bedding and dipping The Central Mine worked a fissure vein striking nearly dipping to the the east. The produced about 52 52 million million Ibs. lbs. of of 1854 to 1898 and produced steeply to The mine mine operated operated from 1854 copper. The Thefissure fissureextends extendsfrom from just below below the Greenstone Greenstone Flow to the Kearsarge Conglomerate. offsets the the vein vein to to the the west, west, and and below below .this this it is not A strike strike fault at the Kearsarge Conglomerate offsets mineralized. mineralized. by Cornish immigrants. immigrants. Although Although the area area was was The town of Central was settled in 1854 mainly by mostly mostly abandoned abandoned after the mine closed, closed, the descendants descendants of these these immigrants, immigrants, now living living all all across the country, hold hold a yearly yearly reunion reunion in in July July at at the the town town site. site. Later immigrant groups to the copper mining towns included: included: Italian, German, Croatian, and Finnish people. MAP 23 110.8 A junction of a road right. Continue 110.8 mad to the right. Continue ahead on US-41. The The road road to to the the right right connects connects with Leg B -Owl -Owl Creek, Creek, at at mileage mileage 60.3. 60.3. 111.9 of the the ENE ENEstriking striking Greenstone Greenstone Flow How holding holding up up the theprominent prominent ridge. ridge. 11 1.9 Another view of flow ridge. 112.6 112.6 Again another another excellent view of the Greenstone How ridge. MAP 11 11 113.4 The junction junction of M-26 and US41 US-41 at Phoenix. Phoenix. Continue Continue ahead on US-41. For Foran analternate alternate route route 113.4 to Ahmeek with two stops, go to Leg F F -- Five Mile Point. Point. This leg begins near the settlement of Eagle River. River. 113.5 On the right is the road 113.5 road toward Stop 18. 18. Continue Continueon on US-41. US-41. �N) -I I a. �112 Maini Log �MSiDROIdLog 113 the Eagle EagleRiver. River. 113.8 Cross the West Branch of the 113.8 Bear left left on US-41. Another excellent excellent view of the the junction of US-41 US-41. Another US41 and and Cliff Drive. Bear 114.9 The junction Greenstone Row flow ridge. ridge. the small park park and and the the snow snow 'thermometer" "thermometer" showing showing the amount amount of snowfall snowfall in the On the left is a small 116.2 On 116.2 Keweenaw Peninsula. Peninsula. Gratiot River. River. 117.7 117.7 Cross Gratiot MAP 10 10 in the 1980's. 118.6 The open site on the left 118.6 left was a lumber lumber mill which which closed in 119.4 119.4 Entering Mohawk. Mohawk. side of the the road road are are mine mine rock rock piles piles from from the the Mohawk Mohawk Mine. 119.5 On the left side 119.5 119.7 119.7 Turn left on 3rd 3rd Street Street in in Mohawk Mohawk and and proceed proceed past past the the school school toward toward the the Keweenaw Keweenaw County County garage. garage. the rock rock piles piles of of the theMohawk Mohawk Mine. Mine. 119.8 Park at the 119.8 STOP 32: copper deposit STOP 32: Mohawk MohawkMine Mine(native (native copper depositwithin withinPortage PortageLake LakeVolcanics Volcanics(PLY]) [PLV]) flow top Mine and seven other other mines: mines: The Kearsarge Flow top deposit deposit was worked by the Mohawk Mine North Kearsarge, Kearsarge, Ahmeek, Ahmeek, Mohawk, Mohawk, and and Seneca. Seneca. The Centennial, South Kearsarge, Wolverine, North The along about 3 km of strike length of the ore Mohawk Mine consisted of 6 different shafts along ore body. body. The Mohawk was opened in 1902 1902 with with production production ending in 1967 1967 from from the the Kearsarge Kearsarge deposit. deposit. of refmed copper from from the Kearsarge Flow top top was was 1026 Total production production of refined copper Kearsarge Flow 1026 million kg. The The Kearsarge deposit deposit isis described describedinindetail detailatatStop Stop 13. 13. The rock piles at this locality are from the No. shaft. R. E. E. Stoiber Stoiber made made the the following following estimate estimate of of the the percentages percentages of of the the.secondary secondary No. 3 shaft. prehnite, 1%; epidote, 1%; and quartz, minerals: minerals: calcite, 73%; K-feldspar (red and pink), 24%; prehnite, trace. The TheMohawk MohawkMine Mineisisnotable notablefor forthe theoccurrence occurrence of of veins veinscontaining containing Cu-Ni Cu-Ni arsenides. arsenides. Return to to US-41. US-41. 119.9 Turn left left on on US-41 US41 toward toward Calumet. Calumet. 119.9 the skyline skyline with the four towers on it is Bumbletow' Bumbletow' Hill, the location of Stop 16. 120.6 120.6 The hill on the MAP 99 andCliff Cliff Drive Drive (Cliff (Cliff Drive Drive was was followed followed earlier earlier in in the field trip) just junction of 1.15-41 US41 and 121.3 121.3 The junction before Ahmeek. Ahmeek. - junction of US41 US-41 and and the the road road from from Five Five Mile MilePoint. Point. This is the end of Leg F - Five Mile 121.6 The junction Mile 121.6 Point. Point. City. This 122.4 122.4 The road to the left goes to Copper City. This is is the start start of Leg G -- Copper City. City. 122.5 122.5 Enter Houghton County. County. 122.55 The road to the right 122.55 right goes goes to Stops Stops 15 15 and 16. 16. Continue Continueon onUS-41. US-41. �114 114 MainRotdLOg Main Road Log goes to Stops Stops 13 13 and and 14. 14. 123.8 The road on the left goes 123.8 124.8 Settlement of Centennial. Centennial. 124.8 edge of of CalumetLaurium. Calumet/Laurium. This is the start 125.45 The The junction of of US-41 US41 and M-203 on the north edge start of Leg Park, an an alternate alternate route route back back to to Hancock. Hancock. Continue ahead on US-41. McLain State Park, US-41. H -- McLain MAP 24 Caluinet on on Red Red Jacket Jacket Street. Street. After 126.15 Turn Turn right right at at the the flashing flashing light light toward the center of Calumet After the the turn turn to Calumet" Calumet" sign signand andaalarge largepiece pieceofoffloat floatcopper. copper. Float copper is on the left, is the "Welcome to masses of native copper copper plucked by glaciers from veins and lodes during the latest latest Pleistocene Pleistocene glaciation. Later, Later,the themasses massesof of native native copper copper were were deposited deposited with with other other sediments sediments as as the the glaciers glaciers retreated, about 10,000 10,000 years ago. Float Float copper copper of of varying varying sizes sizesare arestill stillbeing being found foundby by farmers fanners and during construction of buildings. On the right and ahead, are basalt block buildings that On the right and ahead, are basalt block buildings that were were headquarters of the Calumet and Hecla Consolidated Consolidated Copper Copper Company, Company, which which was the the former headquarters largest mining company company in the the Keweenaw Keweenaw Peninsula. Peninsula. one-way toward toward the the school school and andwater watertower. tower. Straight 126.2 Turn right on Mine Street, going one-way Straight ahead is 126.2 the historic downtown Calumet, Calumet, which whichisis part part of of the the Keweenaw KeweenawNational NationalHistorical HistoricalPark. Park. The C&H Mining Mining Coppertown Museum is 0.2 miles ahead on the left, and offers an overview of the C&H Company. old stack stack is is visible visible at at 2:00. 200. 126.3 126.3 The Calumet school is on the left. An old 126.4 At9:00, 9:00,about about100 100m mbeyond beyond the the tower, tower, isis an an old oldstone stonebuilding building 126.4 The water tower is on the left. At which houses 200 km of locatable by Gordon Peterson. Peterson. The locatable drill core owned by The fenced fencedarea areaatat7:00, 7:00, is the location of the the Red Jacket Headframe, it sits above the Calumet and Hecla ConglomerateConglomeratehosted native copper deposit--the largest single deposit in the Keweenaw Peninsula. 126.45 Just at at the the end end of of an an old oldsandstone sandstone building, building, turn left on the gravel gravel road entrance to the school school lot. Park 50 m m ahead ahead on the right to a low low outcrop. outcrop. parking lot. Park on on the theright right and and walk walk about about 50 STOP 33: Calumet Calumet(glacial (glacialgrooves) grooves) Basalt of the PLV is exposed in this low, glacially smoothed outcrop. outcrop. This This stop stop provides provides well-developed glacial glacialgrooves. grooves. The grooves are oriented an opportunity to observe exceptionally well-developed crest-to-crest spacing spacing of of about about25 25cm cmand andamplitude amplitudeofof33toto55cm. cm. Mineralized about E-W with a crest-to-crest segregation cylinders cylinders in in the the lava flow flow are resistant to the glacier, so flow direction vectors are resistant to spectacularly shown. spectacularly shown. Turn 126.5 T 126.5 urn around and return return to Mine Street Street and turn left left (one-way). (one-way). Turnright rightonto ontoChurch Church Street. Street. The ThePeterson Peterson Funeral Funeral Home Home is is on on the the left. left. 126.6 Stop sign. Turn 126.6 1. Turn 126.65 A stop stop sign sign at at the the junction junction with with USA US-41. Turn right right toward toward Hancock. Hancock. 126.95 Flashing light again. Continue Continuestraight straight ahead ahead this this time. time. Calumet. The The Osceola Osceola Mine Shaft No. 13 13 can be seen seen on the the right right side side of of the the 127.9 Southern edge of Calumet. 127.9 road behind the the Holiday Holiday gas gas station. station. �Map 9MamRoadLog Stop 3 Os, - - 4 �116 128.0 128.0 MainkoadLog Turn right right on on Millionaire MillionaireStreet Street just just beyond beyond the the Holiday Holiday gas gasstation. station. 128.15 Turn Turnleft left onto ontoChurch Church Street, Street, just just before before the the old old mine mine headframe. headframe. four-way junction, junction, continue continue straight straightahead. ahead, 128.5 A four-way 128.5 the road road and and walk walk to the rock piles on the right side of the 128.6 PUll Pull over alongside the the road road (northwest). (northwest). 128.6 STOP copper STOP34: 34: Osceola OsceolaMine Mine(native (native copperdeposit depositwithin withinPortage PortageLake LakeVolcanics Volcanics [PLy]) [PLV]) The Amygdaloid in inthe theCalumet Calumetarea. area. Production from The Osceola Osceola Mine worked the Osceola Amygdaloid the the Osceola Osceola Amygdaloid Amygdaloid began began in in 1879 1879and and continued continued until until 1920, 1920, when when mining mining activity activity stopped. stopped. The continued until until 1968. AA total The mine mine reopened reopened in 1925 1925 and and production production continued totalofofabout about600 600million million lbs Ibs of of refmed refined copper copper was was removed removed from this mine, mine, which which ranks ranks fifth in production production in the the Keweenaw native copper copper district. district. The amygdaloid amygdaloid was developed for about four miles miles along along strike and to a depth depth of of 1372 1372m m along along incline incline (823 (823 m m vertically) vertically) (summarized from Weege and Pollack, 1971). 1971). is ophitic ophitic basalt and varies in The Osceola Flow Row is in thickness thickness from from 11 11 to to 64 64 m. m. The thickest part of the productive. The the flow, flow, near Calumet, has been the most productive. The Osceola Osceola Row Flow has has been been traced traced from the Cliff Mine to the Arcadian Mine. In Inthe theCalumet Calumetarea, area, the the flow flow strikes strikesN35°E N35-E and and dips dips around around 37°NW. 3 7 W . The The top top of of the the flow flow is is a well developed fragmental amygdaloid consisting of well oxidized, reddish, annular fragments of of vesicular lava which which typically range in size from from aa few few cm up to to 30 30 cm cm in in diameter. diameter. The Thelode loderanged ranged ininthickness thickness from from 30 30 cm cm up up to toand andsometimes sometimes greater than 18 m. Amygdules Amygdules and and the the voids voids in in the the brecciated brecciated flow flow top top are are filled filled mostly mostly with with calcite, epidote, native copper. copper. Quartz epidote, K-feldspar, chlorite, and native Quartz is present in certain areas and also minor amounts amounts of of prehnite, prehnite, pumpellyite, pumpellyite, laumontite, laumontite, and analcite analcite are are found. found. The fragmental fragmental amygdaloid by sill-like layers of dense basalt, which amygdaloid is frequently interrupted interrupted by sill-like layers which may may have have been been emplaced by injection of lava from the interior interior of the the flow flow into into the the solidified, solidified, brecciated brecciated crust. crust. The dense basalt basalt layers layers provided provided bathers barriers to to the themovement movement of of mineralizing mineralizing solutions. solutions. Native Native copper in the small masses masses up up to an inch in diameter, the Osceola Osceola ranges ranges from disseminated-todisseminated-to- small diameter, to to large masses weighing ;Butler and weighing hundreds of lbs. Ibs. (summarized (summarizedfrom fromWeege Weegeand andPollack, Pollack,1971 1971;Butler and Burbank, 1929). 1929). Burbank, The The Osceola Osceola Shaft Shaft No. 66 is is at at the the southwest southwest end of the ore ore body, and was the the richest richest part part of the deposit. AAbather barrierzone zoneisisbelieved believedtotohave havefunnelled funnelledmineralizing mineralizingsolutions solutionsmoving movingup-dip, up-dip, resulting resulting in the the high highcopper coppercontents. contents. Textures Textures and colors, colors, characteristic characteristic of of fragmental fragmental amygdaloid, can be seen in this rock pile. An Anestimate estimatewas wasmade made by by Stoiber Stoiber(unpublished (unpublisheddata) data) of the the percentages percentages of of the thesecondary secondaryminerals: minerals: calcite, calcite, 59%; 59%; microcline, microcline, 29%; 29%; prehnite, prehnite, 4%; 4%; epidote, 1%; 1%;quartz, quartz, 1%; 1%;and and chlorite, chlorite, 5%. 5%. Pumpellyite, Pumpellyite, laumontite, native copper, and and the the minerals listed above can be of the basalt in the vicinity of be found found on on this thisrock rock pile. pile. Bleaching Bleaching of be seen seen in in individual individual specimens. specimens. native copper can be Retrace Retrace the route back to US-41. Turn Turn right right on on US-41 US-41 to return to Hancock/Houghton or turn left to return Park, at M-203 M-203 on on the the far end of return to to Calumet Calumet for for the the junction of of Leg Leg H H -- McLain McLain State Park, Calumet. Calumet. OF MAIN ROAD ROAD LOG END OF �lap 117 LEG A A REDRIDGE LEG REDRIDGE Mileage Mileage Al MAP A1 of the the Memorial Memorial Union Building from the circular drive located on the northeast side of 0.0 0.0 Begin Leg A from on the campus campus of of Michigan Michigan Technological Technological University. 0.05 0.05 Turn left. left. 0.1 0.1 Immediately 1. The Quincy Mine can be seen on the the Immediately after, after, turn turnright righton onTownsend TownsendDriveIUS-4 Drive~US-41. skyline ridge. Continue Continueon onUS-41 US-41through throughHoughton. Houghton. 0.7 On the left is is Burger Burger King King and and Stop Stop 6. 6, in Houghton. Houghton. 0.85 The stop light light in 1.15 1.15 Intersection, follow follow M-26 M-26 toward toward Ontonogan. Ontonogan. Turn right on on Canal Canal Road. Road. 1.7 1.7 MAP A2 Al: Houghton HoughtonCanal CanalRoad Road(Copper (CopperHarbor HarborConglomerate) Conglomerate) 2.5 Stop Al: exposed along along the the south south side side of of the road. It is mostly Copper Harbor Conglomerate isis exposed mostly and basalt basalt red-brown conglomerate conglomerate composed composed of of clasts clastsofofrhyolite rhyolite(—50%), (-SO%), granophyre granophyre (—40%), (-40%), and (—10%) with typical diameters of about 1 cm and maximum diameter of 40 cm. Clasts are matrix (-10%) with typical diameters of about 1 cm and maximum diameter of 40 cm. Clasts are supported with occasional 45 cm cm thick, thick, discontinuous discontinuous lenses of of clast-supported clast-supported conglomerate, conglomerate, cemented with with sparry sparry calcite calcite (possibly (possiblypaleocaliche). paleocaliche). Conglomerate Conglomeratebeds bedson onthe the order order of of 11 m cemented alternate with with 15 to to 25 cm thick thick beds beds of of very very fine to coarse red-brown red-brown sandstone. sandstone. Such thick alternate lithologies are typical of the Copper Copper Harbor Conglomerate, Conglomerate, which was deposited in alluvial alluvial fans. fans. Stratigraphicposition positionofof the the Copper The attitude The attitude of bedding bedding is N20°E, N20"E, .% 939W. '3 Stratigraphic Copper Harbor Harbor Conglomerate is shown in Figures 2, 6, and 25. Continue on the Houghton Houghton Canal Canal Road. Road. 3.75 Pleistocene glacial fluvial sand and gravel at Cole's Creek. Creek. Stop A2: Cole's Cole'sCreek Creek(glacial (glacialsediments) sediments) Pleistocene glacial glacial sediments sediments cover cover much much of of the A variable thickness of unconsolidated unconsolidated Pleistocene bedrock of the Keweenaw Peninsula. The Keweenaw Peninsula. The Keweenaw Keweenaw Peninsula Peninsula has probably been modified modified by by During maximum glaciation, the entire all of the major glacial episodes of the Pleistocene. of the major glacial episodes of the Pleistocene. entire Keweenaw Peninsula Peninsulaisisbelieved believedtotohave havebeen beenoverridden overriddenbybyaround around3000 3000mmofofice. ice. The final Keweenaw glacial advance and stillstand over the Keweenaw Peninsula was was made made by by the Keweenaw Keweenaw Peninsula Keweenaw Bay Lobe, marked by an an end end moraine moraine of of the the Wisconsin Wisconsin Stage Stage (Fig. (Fig. 15) 15)(Warren, (Warren, 1981). 1981). channel cut cut by by drainage drainage through through the the Portage Portage Gap Gap area, area, is the The earliest recognized recognized channel the southward flow flow of of water. water. Huron Channel Channel (Map (Map ).). The channel is waterworn bedrock due to aa southward Since there is no delta at the southern end of this channel, perhaps the source of water water was aa large large had time time to to settle before before the the water water was removed. removed. The lake where glacial sediments sediments had Thedrainage drainage pattern through the Portage Gap is shown shown in in Pig. Fig. IS. 18. �00 �-D /lr. / kr4t2/ + —A ,, - ,'tc,°...9) ZPL%H n=.. 882' r) k iitc i 'V. - $O'?qNE Delta Kamed C' TANTO * —1 3 4, p I Stop 5/ çt e'Jk V. V V2 I)'E,.d' 'j[ CITY'\\ II FF.. 4 •.pAWC Al �120 120 Legs Legs part of of a delta kame, kame, is just just west west of of the the Huron Huron Creek Creek Channel. Channel. The This locality, part The sands sands and gravels in this dissected dissected ridge show strong evidence of being deposited by a braided stream, stream, closely associated with aa glacier. Extreme variations variations in in grain grain size size and and sorting occur within glacier. Extreme within a distance of of a few meters, differing flow flow regimes regimes during during deposition. deposition. Poorly- to distance meters, which suggests differing well-worked cobble-to-pebble gravels are also well-worked unconsolidated unconsolidated sands sands predominate, predominate, but poorly sorted cobble-to-pebble present. The Thegravel gravellenses lensesmay maybe beseen seennear nearthe thetop topand andbottom bottomof ofthe theexposure, exposure,and andnumerous numerous are present. present. Toward the left side of the cut, individual resistant bedding in cut-and-fill structures are the sands is visible. the visible. On Onthe theright rightside sideof ofthe thecut, cut,contorted contorted bedding bedding within within the sand sand layers layers is visible. This Thisdeformation deformation isis aaresult resultof ofpost-depositional post-depositional slumping slumping of of the the unconsolidated unconsolidated sands. sands. MAP A3 MAP A3 5.85 Turn left (west) (west) toward Redridge Redridge and Freda. Freda. 5.85 MAP A4 A4 9.45 The road curves to the left. left. 9.45 MAP A5 11.55 The Thesettlement settlementof of Redridge. Redridge. 11.85 just past the guardrail. the main 11.85 Turn Turn right right toward toward Lake Lake Superior, Superior, just guardrail. Follow Follow the main dirt road road to to Lake Lake Superior by either either foot or or auto. auto. 12.25 Stop 12.25 Stop A3: A3: Redridge RedridgeCliffs Cliffs(Freda (FredaSandstone) Sandstone) At the edge edge of of Lake Lake Superior, Superior, is aa large large area area of of gray-to-black gray-to-black "stamp" "stamp" sands. The sands sands were produced during processing processingofof the the native native copper copper ores ores shipped shippedby by train train to a mill mill here here were produced during (Redridge). (Redridge). The The steel steel structure structure on the opposite opposite side of the paved road at the turnoff, is an an old old which provided provided water water for for the the mill. mill. The dam which The old old smoke smoke stack stack is the principal principal ruins of the mill mill here. The Thestamp stampsands sandswere were deposited deposited in in Lake Lake Superior Superior as tailings from the mill. Since Sincepyrite pyrite and other virtually absent absent in the ores of of the the Keweenaw Keweenaw other potential acid- producing minerals minerals are virtually these sands sands do not yield acid drainage. The are Peninsula, these The elemental elemental constituents constituents of of the the sands sands are relatively insoluble, insoluble, except exceptunder underacid acidconditions. conditions. Thus, without contained in minerals that are relatively acid waters, the constituents locked in in place. place. This minimizes the environmental. environmental impact of constituents are locked these sands. Walk Walk to, to, and andalong, along,the the beach beach to to the the red-colored red-colored cliffs. During Duringthe thewalk, walk, you you can can see sections of the stamp stamp sands sands cut cut by by wave wave action. action. Freda Sandstone Sandstone isis well well exposed exposed in in aa 20 meter meter high high wave-cut wave-cut cliff cliff on on the the shoreline of of Freda fme sandstone-to-siltstone. Sub-parallel Lake Superior, Superior, and is composed of red very fine Sub-parallel to bedding, bedding, about 20 to 40 40 cm cm thick, thick, red color color alternates alternates with 3 to 5 cm thick of gray color (reduced) without striking differences differences in grain Mica is readily striking grain size. size. Mica readily visible visible on on bedding bedding plane plane surfaces. surfaces. The The lithologies exposedare are typical typical of of the which was was deposited deposited in in a fluvial the Freda Freda Sandstone, Sandstone, which fluvial lithologies exposed environment. toward Lake Superior, about N-S strike, environment. Bedding Bedding dips shallowly toward strike, and and 5°W 5 W dip. dip. N38°W and and dipping dipping 88W. 88W. Prominent joints in this exposure are spaced about 2.5 m apart, striking N38W subvertical gray gray zones zones follow followthe thejoints. joints. This is one of many spots along the shore Irregular subvertical shore of Lake Superior where canoes offer an an excellent way wayto to see seethe the geology. geology. If you launch here (don't go if the surf surf isis up), up), paddle paddle westward westward to to Freda Freda for for spectacular spectacular sandstone sandstone cliffs. cliffs. End of Leg A -- Retrace route to Houghton. Houghton. �lags — ——— II - C I, Si MAP A3 �122 Map A3 Map MAP A4 �Map A4 123 .)4Jo Jt2 •0 0 4) 0 U) MAP A5 �124 124 Legs LEG B OWL OWL CREEK CREEK MAP MAP BBI1 d at the head head of the the bay. bay. •AtEagle EagleHarbor, Harbor,M-26. M-26. Turn right on Garden City Roa Road 0.0 At 1.05 Them dirtroad, road,just just aafew fewhundred hundred meters meters up up 1.05 Thereisisaadirt dirtroad roadthat thatgoes goes off off to to the the left. left. From Fromthis thisdirt hill, you can begin a traverse hill. traverse upstream on Eliza Creek to get to the exposures of the Portage Portage Lake Lake Lava Flows of this this region. region. Creek. You 1.15 You can can also also begin begin aa traverse traverse upstream upstream on Eliza Elua Creek from here. 1.15 Crossing Eliza Creek. MAP B2 to the the right rightgoes goesdownhill. downhill. If you follow this road several hundred meters, meters, you will 2.5 The road to 2.5 reach the 30-mile 30-mile stamp stamp sands; sands; which are the tailings tailings from the the Copper Copper Falls Falls mining mining operation. operation. From this stamp sand, you can gain access to the bottom of Owl Creek, and can begin a 22 to to 33 hour traverse upstream to the bridge along this road. road, IfIf you you continue continue upstream upstream beyond beyond the the bridge, bridge, you will reach aa poor poor rock rock pile pile along along Owl Owl Creek from the Copper Falls mining operation. By By climbing out of the creek bed, to the east, one can reach reach a dirt road road which which will will come out on the main road at mileage 2.7 just ahead. ahead. 2.6 Road to the left goes goes uphill to to the the rock rock piles of the the Copper Copper Falls Falls Mine, Mine, which which isis part part of of Stop StopBB1l described below. Bi: Owl Lake STOP Bl: OwlCreek Creek(Portage (Portage LakeVolcanics Volcanicsand andCopper Copper Falls Falls Mine) Owl Creek Creek is another of of the the streams streams that that cuts cuts across acrossthe the upper upperpart partof of the the PLV. PLY. The The traverse begins downstream, where where the the base base of of the the Copper Harbor Harbor Conglomerate Conglomerate and and top top of of the PLY interfinger. interfmger. Excellent PLV Excellentexposures exposuresof of interbedded conglomerate/sandstone conglomerate/sandstoneand lava flows along as several several well well exposed exposed amygdaloidal amygdaloidal flows. flows. the bed and sides sides of Owl Owl Creek Creek are are visible, visible, as as well well as The Copper Falls Mining Company worked several fissures fissures and and the the Ashbed Amygdaloid. refmed copper from the The mine operated operated from 1847 1847 to 1893, 1893, producing about 18 million lbs. of refined Ashbed Amygdaloid, Amygdaloid, and and about about 99 million million Ibs. lbs. from fissures; mostly the the Owl Creek Ashbed fissures; mostly Creek Fissure. Fissure. Row that Copper Falls was the only mine in the north end of the district above the Greenstone Flow that paid dividends, but was not a profitable venture (summarized from Butler and Burbank, 1929). was not a profitable venture (summarized from Butler and Burbank, 1929). The The Owl Owl Creek Creek vein vein starts starts near the base of the the Copper Copper Harbor Harbor Conglomerate Conglomerateand and extends extends through the Portage Lake Volcanic Series, probably probablyinto intothe the Greenstone GreenstoneFlow. Flow. The vein Volcanic Series, vein was was productive only in the vicinity of the Ashbed Amygdaloid (described also at Stop 20). The productive only vicinity of the Ashbed Amygdaloid (described Stop 20). The Ashbed Ashbed Rows Flows are are porphyritic porphyritic and and scoriaceous, scoriaceous, with with aa notable notable clastic clasticcomponent. component. In some some localities, pebbles and boulders of amygdaloid amygdaloid are are set set in in aa sandy sandy matrix. matrix. Johnson (1985) studied the Ashbed exposed upstream upstream of of the the road road on on Owl Owl Creek. Creek. Here the Ashbed of a broken Ashbed consists of pillowed lava breccia (hyaloclastite). The hyaloclastite contains angular fragments of (hyaloclastite). The hyaloclastite contains angular fragments of vesicular vesicular basalt ranging in size size from from ash-sized ash-sized to blocks. The Thelarger largerfragments fragmentsoften oftenhave havedistinct distinctrinds, rinds, whereas smaller fragments fragments are are finely finely fractured, fractured,like likeperlitic perlitictexture. texture. This horizon horizon is interpreted whereas as subaqueously subaqueously emplaced. emplaced. It is the the only only documented documented subaqueous-emplaced subaqueous-emplaced volcanic horizon within the PLV of of the the Keweenaw Keweenaw Peninsula Peninsula (see (see also also Stop Stop20). 20). The mineralization of the similar to to that mineralization of the Ashbed Ashbed Amygdaloid Amygdaloid is is similar that found found in in other other amygdaloids in the Keweenaw Peninsula. Peninsula. At At the the Copper Copper Falls Mine, the the following following are are the the more more abundant minerals: calcite, quartz, quartz, epidote, epidote, and and pumpellyite. pumpellyite. Datolite is abundant abundant in the the Ashbed Ashbed �-L 03 -D N V - £7, - r cope \, a b Boat Ramp -It,-- - - 4<e— -2 a I H) 4 erat 0 4 + : : 1-: 1" - -pi 0 - 7jJ%c- '—2-c 2 , cofl9 sN-:s't 0 hg rs - 09to, t- %(i c4 -:task - - 1*AsA H £AQLEHARBOR —/ — J-- 'Y21u - -2 — , tCopper Harbor Conqiomerate rY ( pj e(-;C -, f't..CJ cr'719J :4 4 C0n° JatHarbor. ,- Lake Superior ' -rapS ___ l.A 1-.) ¾• �_______ ______________ •HMj606 pot0 ci 4.'Trtt-!i'i - — — 4._ /. cy or Harbor CongIomerate 0 . . 4-.t 0 — / 7. - I.. ,_J-, t__a_a.____..__—r+ ( 4- -C- —I ft k_Si rcV '9fl4'29'yT I -" C -- �ten 127 127 near fissures, such as Owl Creek. Creek. Native toward the the top part of the Native copper copper was more abundant toward deposit. Also Alsoreported reported in in the theCopper Copper Fails Falls area area are are these these minerals: minerals: laumontite, laumontite, prehnite, native silver, silver, adularia, adularia, analcime, analcime, apophyllite, apophyllite, faujasite, faujasite,natrolite, natrolite,and and stilbite stilbite (summarized (summarized from fromButler Butlerand and Burbank, 1929; Clarke, Clarke, 1974b). I 974b). The in the the The Copper Copper Pails Falls Mine Mine is is stratigraphically stratigraphically the highest highest in Keweenaw native copper district, and is near the top of the pumpellyite zone (see Figs. 88 and and 12 12 in the Introduction). Introduction). 2.7 Cross Cross Owl Owl Creek. Creek. 3.0 A dirt town site of of Copper Copper Falls. Falls. Copper dirt road that slants to the left goes to the old town Copper Pails Falls was there are a handful settled in about 1846, settled 1846, and had aa population population of 500 500 in 1877. Today, Today, there handful of of residents. residents. 3.7 park with with aa tower. tower. From On the right is a roadside park From the the top top of of this this tower, tower, there there is is an an excellent excellent view of Isle Royale on a clear day. You Youcan canalso alsosee seesome someofofthe theridge-vailey ridge-valley topography, topography, due due to the dipping lava flows and conglomerates in this part of the section. flows and conglomerates the section. 4.4 The junction junction of a dirt road on the right. right. Continue paved road. road. Prom Continue ahead on the paved From this this road, road, aa short distance to the west, there is access to Jacobs Creek, the site of the Arnold Mine, along the Ashbed Amygdaloid. Amygdaloid. This is the end Ashbed end of of aa traverse traverse one one can can make make across across the upper upper part part of of the the PLY. ItItisisrecommended PLV. recommendedto tobegin begin the thetraverse traverseat at the the lower lower end end of of Jacobs Jacobs Creek, where where itit crosses crosses M-26. This Thisisisaavery verytough toughtraverse traversewith with many many steep steep and and dangerous dangerous points within it. Excellent Jacobs Creek. Creek. At exposures of many individual lava flows are along Jacobs At the the Arnold Arnold Mine, Mine, one one of of the the nearly conformable massive massive dikes is exposed in the streaxnbed. Geologic traverses made along streambed. Geologic traverses made along 1),and and Jacobs JacobsCreek Creekallow allowone oneto to look look in in detail at Eagle River (Stop 19), 19), Owl Creek (Stop B Bl), lateral variations in the upper part of the the PLY. PLV. 4.6 Cross Jacobs Jacobs Creek. Creek. END OF LEG B - Continue ahead on the paved road to reach US-41, or turn around and retpm return to to Eagle Eagle Harbor. �__ 128 128 ~ev LEG C HORSESHOE HORSESHOEHARBOR HARBOR MAP C1 Cl Leg C at the entrance Park, east of Copper Harbor. Continue Continueahead ahead entrance to Fort Wilkins State Park. 0.0 Start Lee -. Harbor. to the east east (away (away from from Copper Copper Harbor.) Harbor.) 0.15 On Harbor. The Onthe theleft leftisisaatrail trailfor foraccess accessto tothe theshoreline shoreline of Copper Harbor. The basalt flows of the Lake Shore Traps are exposed along- the lakeshore. lakeshore. MAPC2 MAP C2 1.05 1.05 The end of the paved road. This This isis the the end end of of US-41, US-41, which goes south from here all the way to Florida. Continue maintained gravel gravel road. road. The the southern tip of Florida. Continue ahead on the poorly maintained The road road isis easily traversed with aa regular regular passenger passenger car. 1.5 1.5 At the ridge ridge crest. crest. 1.65 1.65 On the right, right, aa ridge ridge of ofCopper CopperHarbor HarborConglomerate Conglomerate isis visible. visible. which goes goes steeply steeply downhill. downhill. This dirt 1.95 1.95 The crest of a ridge with a dirt road on the left, which dirt road goes to Horseshoe Horseshoe Harbor. ItItisisnot notrecommended recommended that that you drive drive this road with a regular passenger passenger car. Park and proceed on foot along the dirt road toward Horseshoe Harbor. proceed on foot along the din road toward Horseshoe Harbor. you can gain access to the If you continue continue on the main main road road (straight (straight ahead), you the region region around around Point (it is private private land). land). Of greatest geologic interest is the the region region around around High High Rock Rock Keweenaw Point Bay, accessible by four-wheel drive vehicles. vehicles. North of the end of the road, the Lake Shore Traps North of the the the Lake Shore Traps are exposed in in a series series of of rocky rocky wave-washed wave-washed outcrops outcrops that that allow allow examination examination of of the the are exposed physical/solidification physical/solidification features of Keweenawan Keweenawan lava flows. Walking Distance (A typical typical pace--2 pace-2 steps--is steps--is about 55 ft.) ft.) FEET FEET (Approximate) The parked parked cars cars on on the the gravel gravel road road isis at at the the crest crest of of the theridge. ridge. This ridge is supported by by tilted tilted 0 0 walking downhill downhill (it (it is is steep) on the beds of of Copper CopperHarbor Harbor Conglomerate. Conglomerate. Begin Begin walking the poorly poorly maintained dirt mad. 1750 AAglacially glaciallypolished polishedoutcrop outcropof ofbasalts basaltsof of the the Lake Lake Shore Shore Traps. Traps. 2700 On Onthe theleft leftisisa aridge ridgeofofbasalt basaltofofthe theLake LakeShore ShoreTraps, Traps,which whichare area asequence sequenceofofmafic-tomafic-tointermediate lava lava flows flows within within the the Copper Copper Harbor Harbor Conglomerate. Conglomerate. The Lake Shore Traps are intermediate are described more at Stop 24. Continue Continueon on the the main main road. road. 2850 Copper bed. Just CopperHarbor HarborConglomerate Conglomerateoutcrops outcrops on the left and in the road bed. Justahead, ahead, the the basalt basalt of of seen in in the the road mad bed. bed. We the Lake Shore Traps are seen We are are now now near the upper contact of the Lake Shore Traps and conglomerates conglomerates of the the Copper Copper Harbor HarborConglomerate. Conglomerate. 3000 3000 Lake Shore Shore Traps Traps basalt basalt outcrops outcrops in in the the road mad bed. bed. 4000 Lake LakeShore ShoreTraps Trapsbasalt basaltoutcrops outcropson on the the left. left. 5300 Several pullouts for autos are 5300 are on the right. right. �___ _ ___ __ ______ Lake Superior àIHarbor — ____ _____ _____ ________ ________ _____ ____ ________ Pode. CopperHaruo Lighthouse V . —•• a me — rate - ci Copper 3F32 Copper Hero0 C . 1;*.t S S e Fa - h557/j1000 Lake 620 k1> L': 3 / ENA'W Lake !zz?j !U_flw)) SSclKSfl) !T... ,-D C -I / zV Es p3I :N I 'I Lake f SE SON C) Â¥ F0 ll H 2 -L L . - 4Jk$. L Mud-, -' .. \ aI .. Hooe C - Fiow '\ 1)PL o rafl JtiL-ji L* 603 ' - > Lake b HAYS (Psi — -. 6z=p A ci / 620?. 5erHarbor 1 e -- a I )o Sit È ��~eo Legs 131 131 Harbor is is on on the the left. left. Follow 5375 Follow that that trail trail downhill. downhill. 5375 The major trail to Horseshoe Harbor Reset Distances Distances At the dirt dirt road road and and the thetrail trailtotoHorseshoe HorseshoeHarbor, Harbor,going goingdownhill. downhill. 0 60 60 450 450 Horseshoe Harbor Harbor isis aa part of the Horseshoe Harbor the Michigan Michigan Chapter of The The Nature Nature Harbor sign. sign. Horseshoe Conservancy. Please do not collect rocks. Please do not collect rocks. Copper Harbor Conglomerate outcrops in the the path. path. 1350 Horseshoe Harbor beach. Proceed Proceed left left (north) (north) toward toward the rock ridges along along the Lake Lake Superior Superior 1350 At Horseshoe It is recommended to walk along the shoreline. Follow the prominent ridge to the left (west). shoreline. Follow the prominent ridge the left (west). lowland just just landward landwardof ofthe theridge ridge(south). (south). Stop Stop Cl Cl is at the lowland the far far west west end end of of this this ridge, ridge, where where excellent exposures exposures of stromatolites. stromatolites. there are excellent Stop Cl: Harbor Cl: Horseshoe HorseshoeHarbor Harbor(Copper (Copper HarborConglomerate) Conglomerate) PLEASE DO NOT REMOVE REMOVE ROCKS The Copper Harbor Conglomerate at the the east end on Horseshoe Harbor is composed of Conglomerate at red clast-supported conglomerate with with aa 5 m thick bed of clast-supported conglomerate of shale, shale, sandstone, sandstone, conglomerate, conglomerate, and and stromatolite (Fig. 41). The Theconglomerate conglomerateisiscomposed composedof of pebble-to-cobble, pebble-to-cobble, well-rounded well-rounded clasts dominated by rhyolite and corresponds corresponds to conglomerate conglomerate facies as described described by by Elmore Elmore (1984). (1984). These conglomerates are interpreted as as an an alluvial alluvial fan fan deposit deposit shed shed toward toward the the center center of of the rift. The stromatolites stromatolites are are associated associated with with conglomerate, conglomerate, trough trough cross-stratified cross-stratified sandstone, sandstone, and and conglomerate-mudstone (Elmore, (Elmore, 1983). 1983). The The stromatolites, stromatolites, Collenia undosa undosa species species (Cornwall, (Cornwall, 1955), intermittently found found from fromhere hereto toDan's Dan's Point Point (Stop (Stop 27). 27). Elmore (1983) describes the 1955). are intermittently various forms of stromatolites, including laterally linked bedded, oncolites, and and poorly developed forms oncolites, mats. The Thetypical typicalstromatolite stromatoliteisisaahemispheroid, hemispheroid,about about 15 15cm cm thick thick and and up up to to40 40cm cminindiameter, diameter, Contorted stromatolites stromatolitesmay maybe be due due to soft and isis often often draped draped over overcobbles. cobbles. Contorted soft sediment sediment deformation deformation during during compaction. compaction. Ooids, Ooids,oncolites, oncolites,and and intra intraclast clast limestone limestone(stromatolite (stromatoliteand and oolite oolite fragments) occur within within stromatolites. stromatolites. The The stromatolites stromatolites are cryptalgal deposits in abandoned abandoned stream channels (Fig. 41). Horseshoe Harbor is worth the time to visit for its beautiful scenery alone. The Theexposures exposures of stromatolites stromatolites are are the the best best of ofthe theKeweenaw KeweenawPeninsula. Peninsula. END OF LEG C -- Return to the vehicles vehicles and and proceed proceed back back to to Copper CopperHarbor. Harbor. �132 LEG I) D EAST SIDE SIDE OF OF THE THEKEWEENAW KEWEENAW PENINSULA PEN1NSTIT.A MAP Dl junction of the road to Lac La Belle. Belle. Turn Turn left left and and go go down down hill hill toward toward Mt. Mt. Bohemia. Bohemia. 0.0 The junction MAP D2 D2 On basalt of of the the PLy. These On the left left side side of of the the road road isis aalarge largeoutcrop outcrop of of amygdaloidal amygdaloidal basalt PLV. These 3.5 exposures are flows in the lower part of the formation, formation, below the Scales Creek Flow. 3.9 Ad dirt road turning turning off offthe themain mainroad roadtotothe theleft. left.This ThisisisSTOP STOPDDl at Mt. Mt. Bohemia. Bohemia. It is about about irt road l at a one half mile mile walk walk up up this this road mad to to the the summit summit of of Mt. Mt. Bohemia; Bohemia; the the road road isisaafour-wheel four-wheel drive drive vehicle vehicle road. road. STOP (diorite STOP Dl: Dl:Mount MountBohemia Bohemia (dioritestock stockwithin withinthe thePortage PortageLake LakeVolcanics Volcanics [PLV]) [PLV]) Walk the road to the summit Mount Bohemia. Bohemia. The summit of Mount The road road crosses crosses flows flows of of the the PLY. PLV. The diorite and granophyre intrusive complex crops crops out out to to the the southeast southeast of of the the summit. summit. Intrusive Intrusive stocks are not common in the Keweenaw Peninsula, most occur in the lower part of the PLV and are rhyolitic in composition. composition. Mount Mount Bohemia Bohemia is the only only occurrence occurrence of a diorite diorite stock stock in in the the Keweenaw Keweenaw Peninsula. Peninsula. An intrusive stock of of diorite diorite and and granophyre granophyrecrops cropsout out on on the the south south slope slope of of Mount An intrusive stock Bohemia Dl). The ~ o h e m i a(Map Dl). Themajority majorityofofthe theMount MountBohemia Bohemiastock stockisisan analtered, altered,massive, massive,mediummediumto coarse-grained, coarse-grained, miarolitic miarolitic diorite. The Thepre-alteration pre-alteration mineral mineralassemblage assemblageconsists consistsof of 45 45to to50% 50% sodic plagioclase, plagioclase, 30 30 to 50% mafic and hornblende), and up up to 3% sodic mafic minerals minerals (augite (augite and hornblende), and 3% quartz quartz the stock, stock, and and in small (Sikkila, 1984). 1984). Magnetite Magnetite is found throughout throughout the small areas areas exceeds exceeds 15%. 15%. Apatite and sphene are also present present in in trace trace amounts. amounts. The southeast portion of the stock consists of quartz diorite 30% quartz, quartz, 7% biotite, and of diorite with with approximately approximately 60% sodic plagioclase, plagioclase, 30% and 3% 3% The central major central core core isis aafinefine-totocoarse-grained, coarse-grained,niiarolitic miaroliticgranophyre. granophyre. The major quartz. quartz. The constituents of of the granophyre constituents granophyre are sodic sdc plagioclase, plagioclase, quartz, and granophyric granophyric intergrowths intergrowths of quartz and feldspar quartz feldspar with with lesser lesser amounts amounts of of orthoclase, orthoclase,sericite, sericite, hornblende, hornblende, apatite, apatite, sphene, sphene, magnetite, and chlorite. Miarolitic Miaroliticcavities cavitiesare are lined lined with with quartz, quartz, albite, albite, calcite, calcite, chalcopyrite, chalcopyrite, and chalcocite chalcocite (Cornwall, (Cornwall, 1954). 1954). The diorite and granophyre at Mt. Bohemia intrude basaltic lava flows of the lower lower part part PLY. The at the the contact. contact. The intrusive body is cut by of the PLV. Thebasalts basalts are are slightly slightly metamorphosed at north-northwest. This fissure is mineralized with with copper the Lac La Belle Fissure which trends north-northwest. sulfides, mostly chalcopyrite and bomite bornite with a gangue of calcite, chlorite, and quartz (Juilland, (Juilland, 1965). 1965). The stock stock has hasbeen beenmoderately-to-strongly moderately-to-strongly altered. altered. Secondary potassium feldspar is is observable throughout throughout the the stock. Hand Hand specimens specimens have have the themisleading misleading appearance appearance of of syenite, syenite, because of the potassium feldspar and secondary fine-grained fine-grained hematite hematiteafter aftermagnetite. magnetite. Alteration products include serpentine (after mafics), epidote (after plagioclase plagioclase and mafics), calcite (after plagioclase), actinolite (after pyroxene), plagioclase), and and chlorite (after mafics). pyroxene), sericite (after plagioclase), Sildcila (1984) (1984) reports reports aa correlation correlation between between alteration alteration and and the the cross-cutting Lac La Belle Sikkila Belle Fissure, Fissure, indicating a preferential channeling of of hydrothermal hydrothermal fluids. fluids. Secondary geochemical variations in geochemical with respect respectto tothe the fissure. fissure. The grade of alteration of of the Mount Mount the stock also tend to correlate with PLY. Actinolite Bohemia stock is higher than the surrounding PLV. Actinolite has has not not been been observed observed within within the the PLY. PLV. Both Boththe thegrade gradeand andcharacter characterof of alteration alteration may may have been the result of a local hydrothermal system related to the stock stock itself, rather than to the regional hydrothermal hydrothemal system, which which produced produced �.0 (1 cm = Stop 06 1689.6 m or 3/8" = SCALE 1:168960 1 mile) Stop D5 Ia. ��A Isp Drill Hole "mmnlnm ~m~gdoloids ond dike projected to 1300'elevotion a preliminary Calumet General Generalgeology geology and anddrill drillhole holelocations locations in inthe theMount MountBohemia Bohemiaarea area(modified (modifiedfrom from a prcldnary Calumet and andHecla HedaMining MiningCompany Companymap). map). B MINERAL Chlorlle Chlorite Epidote Epidote Quart2 Cuartz Secondary secondary minerals minerals VesicteVesicle- FractureFracturefillings inindike dikematrix matrix fillings fillings fillinQS 00 0  . Calcite c01cite Sericite 5cr/cite Pumpellyile Pumpelfy/te Microcline Microci/ne Hematite Hematite - - 0 — 00 — 00 Sa  G0 Sa S0 00 S0 - a - Â¥Mino -- — — G0 .common •Â 00 — Copper Copper suit/des suffices NoliveCopper Copper Native 0 a G 00 Pyrite P/rite .• . 0 00 00 00 00 ORafe -Absent Nonpyrogenic Nonpyroeenic Minerals Minerals in in the theDikes Dikes D C MINERAL Henna! lie I ——— Set/cite Epidot. Spbo/erit. —— —?— ——— Co/c/I. Hematite (fall) Suit/fls —— ——— -7— — —-— —— Pink bonnie Purple born/ic —— Ougrtz Mic,odllne Supergene - Cho/capynte Go/coo Galena ——— Hydrothermal —— Pyrit. CA/op/i. Pam pe/ly/te Pyrogenic Deuteric —________ 9/penile 0/up/cit. Cho/cocite —__________ Hematite II — Cove//it. Paragenetic sequence of secondary minerals in the dikes. Paragenesis opaque minerals in dikes Paragenesis ofofopaque minerals in dikes and and flow flo tops Bohemia. tops at Mount Bohemia. FigureDl: Dl:Geologic Geologic mapshowing showingandesitic andesiticdikes dikesnear nearMount MountBohemia Bohemiaand andoccurrence occurrenceand and patagenesis paragenesis Figure map minerals in in the the dikes dikes(from (fromRobertson, Robertson, 1975). 1975). of secondary secondary and and opaque opaque ininemls of �136 En' Mount Bohemia Bohemia stock stock aa bears resemblance resemblance to to a porphyry copper native copper deposits. deposits. Mount system. the the Andesitic dikes are found in the vicinity of Mt. Bohemia Bohemia (Fig. 35a), 35a), and average about of the the PLV. PLy. Two 5 m in thickness. thickness. The The dikes dikes intrude flows of Twoflow flowtops topsare areshown shown in in Figure Figure35a 35a as alpha and beta. The carry copper sulfides. sulfides. Copper sulfates Thedikes dikesand and amygdaloidal amygdaloidal flow tops carry sulfides in other and native copper copper is the other parts parts of of the the district district are are found found typically typically as fracture fracture fillings, and dominant ore mineral of the Keweenaw Keweenaw Peninsula. Peninsula. A variety of secondary and opaque minerals secondary found in in the dikes dikes and and flow flow tops tops (Fig. (Fig. Dl). Dl). Copper allylate. late. The are found Coppersulfides sulfides are are paragenetic paragenetically copper and and sulfur in in this occurrence occurrence isis believed believedto to be be of of direct direct magmatic magmaticorigin. origin. The atypical copper atypical copper sulfide mineralized flow tops and dikes also may have been related to the magma magma source source that produced the Mount Bohemia stock and andesite dikes, rather than the regional hydrothermal hydrothermal system (Robertson, (Robertson, 1975). 1975). 4.3 4.3 At the turnoff turnoff to Mt. Bohemia. Bohemia. Go Gostraight straightahead ahead(south) (south) toward toward Lac Lac La La Belle, Belle, down down hill. hill. 4.7 4.7 A junction junction of of roads roads at at Lac Lac La La Belle. Belle. Turn right (west) (west) along along the the shore shoreof ofLac LacLa LaBelle. Belle. For the stop at Bete Grise, turn left and continue until the Bete Grise sand beach. Map Dl, there To Bete Grise, turn left. left. (See Map there is is no no mileage mileage logged logged to Bete Grise and back) Stop D2: Bete stop BeteGris.e Grise(white (whitesand sandbeach beachfrom fromJacobsville JacobsvilleSandstone) Sandstone) The white sand beach is derived from Jacobsville Sandstone and is typical of beaches beaches on on whereas on on the the west west side, side, the beaches are often of the east side side of of the the Keweenaw Keweenaw Peninsula, whereas of Conglomerate. Black sand beaches on the Keweenaw Peninsula pebbles from the Copper Harbor Conglomerate. are crushed mine rock derived derived from from milling milling of of native native copper copper ores. ores. Bete Grise is located on the shore of of Keweenaw XeweenawBay Bay on onthe theKeweenaw KeweenawFault. Fault. Along the shoreline, east of of the point shoreline, east point where where the road road reaches reaches the shore, shore, are are several several exposures exposures of the the Keweenaw Fault which crosses crosses onon- and and off-shore off-shore several severaltimes. times. A canoe or small boat is a good way to visit visit these these areas. areas. Also to the east, east, are are several several of of the the rhyolite rhyolite bodies bodies which which are arechiefly chiefly found in the lower part part of of the the PLV. PLy. Three found Threetenths tenths of of aamile milenorth north of of Bete BeteGrise, Grise, aafour-wheel four-wheel of the the paved pavedroad roadto toSmith's Smith's Fisheries. Fisheries. The road mad intersects the Bare Hill drive road continues east of body, which which is is aa shallow shallow intrusive. intrusive. Beyond the end of of the road at Smith's Fisheries, a Rhyolite body, to the the mouth mouth of of the the Montreal MontrealRiver. River. From here, one trail continues eastward along the shore to one may may traverse up river to several falls--over fine outcrops of basaltic flows, ash flow tuffs, and a rhyolite several falls~over dome--or continue along the shore to the the Fish Fish Cove Coverhyolite, rhyolite, aacompositionally compositionallyzoned zoned shallow shallow intrusive (Bornhorst, 1975). Inland, Inland, and and not not far far from from Bete Bete Grise, Grise, is is the the Mt. Mt. Houghton Houghton Rhyolite, Rhyolite, an extrusive rhyolite dome with prominent flow flow banding banding and and block block and and ash ash flow flow deposits on its flanks. Mt. Houghton is best approached from the Mandan Road (Map 20). Mt. Houghton is best approached Mandan Road (Map 20). See See Stop Stop D4 D4 (this (this leg), for for more more on on rhyolites. rhyolites. lthyolites make make up up less less than than 1% 1% of of the the mass mass of of the the PLV, PLy, as Rhy&es as seen seen in in outcrops outcrops on on the the Keweenaw. Considerable Considerabletextural textural variety variety of rhyolites rhyolites are found, including intrusive and extrusive rhyolite and even small small ignimbrites. The Theabundance abundanceand andvariety variety of of rhyolitic rhyoliticboulders bouldersand andcobbles cobbles interfiow conglomerates conglomerates however, within the interflow however, demands demands that a large number of rhyolitic source areas source areas must underlie the Jacobsville, south and east of the the Keweenaw Keweenaw Fault. Return to the junction at Lac La Belle. Belle. �Legs 137 MAPD2 MAP D2 Behind, described at at Stop Stop Dl. Dl. Behiid, is an excellent view of Mount Bohemia &scriW 5.1 5.2 Pull over over to the the right right at at Haven Haven Park. Park. Stop D 3 Haven Haven Park Park(Portage (PortageLake LakeVolcanics VolcanicsIIPLV] PLVI near near the the Keweenaw Keweenaw Fault) Fault) Stop 1)3: The exposures provide an an excellent excellent view view of of the PLV adjacent to the exposures at the waterfalls waterfalls provide Keweenaw Fault. At locality, Keweenaw Fault. At this thi~s locahty, the the Keweenaw Keweenaw Fault is is oriented oriented subparallel to the slope slope face face (and the road), and is less than 100 m to the south (toward (toward L Lac La Belle) of of the exposures at the ac La waterfalls. In Inaddition, addition,in in this thisgeneral general area area several several faults faults cut the PLV nearly perpendicular perpendicular to the Keweenaw Fault. Basalt at the base of the falls is overlain by conglomerate, and in turn, turn, overlain overlain Basalt at the base of the falls is overlain by and in by basalt. basalt. The conglomerate conglomerate is unnamed unnamed (Cornwall, (Cornwall, 1954) and is is an aninterfiow inteflow sedimentary sedimentary horizon within within the the PLV. PLY. Conglomerate expozed base base of of the the Conglomerate beds are common at, or near, the exposed PLY Fault. The PLV close to the Keweenaw Keweenaw Fault. The rocks rocks of of the the PLV PLV here, here, and and elsewhere elsewhere adjacent adjacent to the the Keweenaw Fault, are typically typically quite quite fractured fractured and and altered. altered. The basalt basalt is is cut cut by by closely closelyspaced spaced Keweenaw Fault, fractures that trend to probable to the fractures that trend subparallel subparallel and perpendicular perpendicular to probable bedding beddiig (subparallel (subparallel to the Keweenaw Fault) that yield 1 to 2 cm rectangular pieces pieces of of basalt. basalt. The The rock rock is is quite quite altered, altered,with with a lot cm wide, wide, and and aa dominant dominant orientation orientation subparallel subparallel to the Keweenaw Fault. lot of veinlets veinlets up up to to 11cm Secondary minerals include laumontite, calcite, chlorite, and hematite. The grade of Secondary minerals include laumontite, calcite, chlorite, and hematite. of regional regional within the thePLV PLV (see (seeFig. Fig. in Introduction), with the highest grades alteration varies systematically within lower in the PLY. lower PLV. Paragenetically Parageneticallylate latelower lower grade grade assemblages assemblages are are superimposed superimposed on higher higher where suff~cient sufficient porosity porosity and andpermeability permeabilitystill stillexits, exits,such suchasasatatthis thisstop. stop. The alteration grades where minerals here, and at other locations near the Keweenaw Fault, are characterized characterized by low grade grade and and late minerals such as laumontite. laumontite. Some Somelocalities 1ocaIitieshave haveabundant abundanthigher highergrade gradeassemblages assemblagesnear near assemblages. This the fault, with clear superimposed superimposed lower grade assemblages. This suggests suggests that that the the Keweenaw Keweenaw Fault was hydrothermalfluids. fluids. was aa long-lived long-Iived conduit conduit of ofhydrothermal Continue west on the the paved paved road. road. 5.3 altered basalt basalt of of the the PLV PLY is is exposed exposed on on the the right right side of the road, Highly fractured and altered road. 5.85 Thk locality, locd~ty,and the remaining remainiig localities on this kg, leg, are are River Side Park at Little Gratiot River. This of the the Keweenaw Keweenaw Fault, Fault, with with the the principal principal bedrock bedrock being behg Jacobsville JacobsvilleSandstone. Sandstone. south and east of juxtaposed against the PLV by the Keweenaw The Jacobsville Sandstone is the typical rock unit juxtaposed Fault. Fault. However, at the west end of Lac La Belle, However, Belle, in the the vicinity vicinity of Deer Deer Lake, Lake, the the rocks rocks south south of of the the Keweenaw Fault are are Portage Portage Lake Lake Basalts Basalts(Fig. (Fig.D2). D2). These Keweenaw Fault These basalts may represent the lowest The area has stratigraphic horizons horizons exposed exposed in in the stratigraphic the PLY. PLV. The has been been studied studied by by geological geological and and geophysical geophysicalmethods methods by DeGraff (1976), (1976). whose whose model for the development development of this IS unusual unusual feature feature is shown graphically in Fig. 36. ItIt isisyet yet another another example example of the deformation along the high-angle Fault. A reverse Keweenaw Keweenaw Fault. A traverse traverse down down the the Little L'lttle Gratiot Gratiot River from the Lac La La Belle-Gay Belle-Gay Road crosses tilted body body of of the PLV was cmsses many outcrops outcrops of the the basalts. basalts. The fault-bounded, fault-bounded, tilted defined by a dense profiles and a few key key drillholes. The dense array of magnetic magnetic and gravity profiles Theattitude attitude of the beds was altered by the faulting, but the the rocks, rocks, like like the the rest rest of of the the PLV, PLy, have altered by faulting, but have normal n o d of polarity. magnetic . Dll MAP D Lac La La Belle. Belle. 7.4 End of Lac �\ 41 * Bchent N N S S S I Basalt, and sandstones in a block south of the fault are oxposed and overturned. posed and dip to the sooth. Basalts and sandstones in a block south of the fault are ex- basalt and sandstone. Classical fault contact between Sandstone stilt exposed north of thu Keweenaw Fault. Figure D2:• Geologic sketch map of part of the Keweenaw Fault in the vicinity of Deer Lake, where the Portage Lake Volcanics are found south of the Keweenaw Fault. At right, schematic cross sections show stages in the development of the Keweenaw Fault at Deer Lake as envisioned by DeGraff (1976). p = PLy, J = Jacobsville. IT- RI,.' \ 'Litu. orstIot Jacobsvllls Ssndslons I iji P Porlag. Lske Volosolca I To Dswsr. N Prior to faulting. -I �Le12 9.4 9.4 Behind, is a view of of Mount Mount Bohemia. Bohemia. 10.5 10.5 Along the shore shore of of Lake Lake Superior. Superior. 11.7 11.7 At South South Point. J39 D4: South SouthPoint Point(view (viewofofthe thetiptipofofthe theKeweenaw KeweenawPeninsula) Peninsula) Stop Dk South Point, being on the southern southem end of Bete Grise Bay. Bay, provides an excellent excellent view view of of the tip of the the Keweenaw Keweenaw Peninsula--visible Peninsula-visible on the far right (northeast) (Fig. D3). to the shoreline, is Fish Cove Knob, At 1:00, l:W, facing perpendicular perpendicular to Knob, aa rhyolite rhyolite intrusive intrusive PLY (Bornhorst, (Bomhorst. 1975). The body into the base of the PLV The rhyolites at Fish Cove Knob contain sparse spme phenocrysts of feldspar feldspar and quartz. light-colored bare bare rock rockbluff bluffwhich whichisispart partof ofthe theBare BareHill HillRhyolite. Rhyolite. Bare At 12:00, is a light-colored Hill consists of several several sills sills of ofrhyolite, rhyolite, containing containingsparse sparse phenoczysts phenocrysts of feldspar feldspar and and quartz quartz (Cornwall, 1954). (Comwall, 1954). to the shoreline, 10:00, facing perpendicular perpendicular to shoreline, is Mount Houghton, Houghton, a rhyolite dome At 10:00, within the lower section of of the the FTV. PLy. Rhyolite complex withii RhyoliteatatMount MountHoughton Houghton isis aphyric aphyric with with wellwellbeds of of conglomerate, conglomerate, interclated interclatedwith withbasal& basalts of of the the PLV, PLy, are developed flow foliation. Several beds are detritus shed off off the the rhyolite rhyolite dome. dome. The Superior shorehe shoreline from south of Mount Houghton The Keweenaw Fault Fault follows the Lake Superior to Keweenaw Keweenaw Point. Point. Rhyolite intrusive intrusive and and extrusive below the Bohemia Rhyolite extrusive rocks m k s occur occur stratigraphically stratigraphically below Bohemia Conglomerate Conglomerate (Fig. D3). The TheBohemia BohemiaConglomerate Conglomerate is stratigraphically in the lower part of the PLY. KeweenawanNorth North Shore ShoreYolcanic Volcanic Group Group contains contains frequent rhyolites, similar PLV. The Theolder olderKeweenawan to the the proportion proportion found in the lower PLY PLV (Green, 1982). 1982). Nicholson Nicholson(1992) (1992)proposed proposed Iceland Icelandas as a modem volcanological analog for rhyolites within the Midcontinent rift system. Within-rift modem voIcanological for rhyolites within the Midcontinent system. central central volcanic volcanic complexes complexes in in Iceland Iceland are arelocalized localizedaccumulations accumulations ofofbasalts-to-rhyolites, basalts-to-rhyolites, by basalts erupted surrounded by empted from from fissures fissures (Walker, (Walker, 1966). 1966). The distal part of of these these central central volcanoes may be a good good model model for for rhyolites rhyolites within within the PLY. PLV. 12.7 12.7 the left. left. Point Isabelle is on the Sandstone on on the the shoreline extend from from here to the 13.0 Good Good exposures of Jacobsville Jacobsville Sandstone shoreline extend the roadside roads& 13,O pullover. The TheJacobsville JacobsvilleSandstone Sandstoneyields yields excellent excellentlight-colored light-colored sand sand beaches. beaches. 13.3 13.3 The roadside pullover is on on the the left. left. 15.1 15.1 are on the left. Excellent low exposures of Jacobsville Jacohsville Sandstone are STOP STOP D5: D5:Eastern EasternKeweenaw KeweenawPeninsula Peninsula(Jacobsville (JacohsvilleSandstone) Sandstone) is well well exposed exposedalong alongthe theLake LakeSuperior Superiorshore shoreatatthis thislocation. location. The The Jacobsville Sandstone is character of the Jacobsville Sandstone illustrated here is typical of many exposures elsewhere. the Jacobsville Sandstone illustrated is typical of many exposures elsewhere. are red-colored with characteristic characteristiccircular circular white white Here, the mediumm d ~ u mto - coarse-grained coarse-grained sandstones sandstones are �140 I2 30 25 35 25 50 35 35 ---------__-I__ a Mt. Mt.Houghton Houghton 30 - oNGLOMT - - - - - - - - Montreal River 25 25 50 A- -\ . Keystone Point Fish Cove -- Fish FishCove Coveknob knob EXPLANATION EXPLANATION .... jJacobsviIle Sandstone ~acobsville Sandstone Copper Harbor Conglomerate Copper Harbor Conglomerate :.:.:./ . . . . PortageLake b k e Volcanics Volcanlcs Portage ~ o w - l basalts basalts i ~ ~ D:iLow—TiO2 High—TiO2 basalts and ......./; . .. .. . . . . . . . . . .. .. .. .. .. .. .. .. . . . . . . . . . .. .. .. .. .. .. . . . .. .. .. .. .. .. . . , . . . . . . . . . . . . . : .. . . . .. .. .. . . . . . . . . . . . :.q 0 0 i 0 MILES 55 MILES w 0 55 KILOMETERS KILOMFERS -- —— andesitic flows Bohemiaconglomerate conglomerate Bohemia ! Strike and Strike anddip dip Horizontalbed bed ee 3 Horizontal Individual rhyolite clasticbodies bodies aa Individual rhyolite or or ciastic Figure FigureD3: D3Geologic Geologicmap mapshowing showingthe thelocation locationofofrhyolites rhyoliteson on the the eastern eastern tip tip of of the the Keweenaw Keweenaw Peninsula Peninsula (from 1992). (from Nicholson, Nicholson,1992). �141 reduction spots up to about 2.5 2.5 cm in diameter. diameter. Well Well developed developed white reduced zones of variable thickness thickness are are subparallel subparallel to to bedding. bedd'mg. Some Somezones zoneswithin withimthe thesandstones sandstonesshow showcross-bedding cross-beddingand and others others contain contain mud chips. For Foraafurther furtherdescription descriptionof of the the Jacobsville Jacobsville Sandstone, Sandstone, refer refer to to Stop Stop 10. 10. 17.5 17.5 Burnette Park is on on the the left. left. ItIt has has lakeshore lakeshore exposures exposures of Jacobsville Jacobsville Sandstone with a sand sand beach. Well-developed visible in in the the sandstone sandstoneexposed exposedhere. here. On a clear day Welldeveloped cross bedding bedd'mg is visible the Huron Huron Mountains Mountains are are visible visible across acrossthe theKeweenaw Keweenaw Bay. Bay. 18.3 18.3 Outcrops Outcrops of of Jacobsville Jacobsville Sandstone Sandstone along along the the Keweenaw Keweenaw Bay/Lake BayLake Superior Superiorshoreline. shoreline. 19.0 19.0 The road gees to Betsy. Betsy. Continue Continueahead. ahead. road to the the right right goes 23.6 23.6 is on on the theright. right. Hermit Bay is 25.2 25.2 Cross the Tobacco Tobacco River at its mouth mouth with Lake Superior. Superior. The TheHuron Huron Mountains Mountains are are visible visible across Bay on a clear day. The across Keweenaw Bay The black black sand sand beach beach is aa result result of of longshore longshore drift of of the the basalt mine mine tailings tailings dumped dumped into into Lake Lake Superior Superior from 1902 1902 to to 1932. 1932. Road access access to to the the Gay Gay Stamp Stamp Sands. Sands. Continue Continueon onthe thepaved pavedroad. road. MAP D3 MAPD3 smokestack is on on the the left. left. 26.0 The Gay smokestack 26.0 25.9 25.9 Stop D6: 96: Gay Gay(stamp (stampsands) sands) Walk Walk toward toward the the stack stack and Lake Superior. This Thisvantage vantagepoint pointprovides providesan anexcellent excellentview view of Lake Superior Superior and Keweenaw Keweenaw Bay. On Onaaclear clearday, day,the theHuron HuronMountains Mountainsare areclearly clearlyvisible visible consist of of a core the horizon horizon across acrossKeweenaw Keweenaw Bay. Bay. The Huron Mountains Mountains consist core of of Archean Archean on the granitoid rocks, unconformably unconformab~yoverlain by Early Early Proterozoic Proterozoic deformed deformed and andmetamorphosed metamorphosed sedimentary rocks. Keweenaw Keweenaw Bay Bay however, however, isisunderlain underlain by by Jacobsville Jacobsville Sandstone Sandstonewith with Early Early Proterozoic metasedimentary rocks cropping out out on the opposite shore of Keweenaw Bay (Stop metasedimentary rocks II). 11).The Thenearly nearlyflat-lying flat-lyingJacobsville JacobsvilleSandstone Sandstoneextends extends from from the Keweenaw Keweenaw Fault contact with the PLy, PLV, about about 88km kmN/NW, NNW, totothe theopposite oppositeside sideofofKeweenaw Keweenaw Bay, Bay, about about 35 35 km. km. The The Jacobsville Sandstone Sandstone fills aa rift-flanking rifi-flanking basin. basin. The Gay Stamp Sands are visible in the foreground. The Stamp Sands The sands sands accrued accmed from from the the Mohawk Mohawk and Wolverine Wolverine Mills as as tons tons of of crushed cmshed rock rock were were milled milled to to extract extract the the copper copper they they contained. contained. The twin twin mills mills began began processing processing in 1902, 1902, with with the Wolverine Wolverine Mill working until 1922 1922 and and the the Mohawk Mohawk Mill Mill running running until until 1932. 1932. Both companies proximity companies began their their processing plants in the town of Gay because of the proximity of water-covered areas in which they could dispose of of their their tailings. tailings. Lumbering was previously Lumbering was previously the main occupation occupation of the the town, town, also also because of the the accessibility to the Bay, which they used to to float their logs logs to to the the larger larger shipping shippingareas. areas. Conveyor Conveyor belts belts were were used used to to transport transport the the sands sands away away from from the the plants, plants, and and water waterwas wasused used to transport transport them them even even further furtherinto intoKeweenaw Keweenaw Bay. Bay. obtained at at mileage mileage 25.9. 25.9. If you Access can be obtained you walk walk along along the beach, beach, you you can can see seean an stratified beds beds and cross cutting erosion scarp of the the stamp stamp sands. sands. Within the accumulation, accumulation, stratfied cutting �CA) ci a-Zt"A.- t. ,— .— ._ • - -4• Ct 0 S - -- — - I- - a.— 4 .1- — * -I .C,4 1* A 4_-e — e 0 - ._a-..t__; :4;;ve.:.s. 4. - — -e -•- 4-- .ot I �143 evident layers-as the the slurry slurry found found new directions directions in in its its progress progress toward toward Keweenaw KeweenawBay—am Bay-are evident. layers--as NOTE: NOTE:When Whenapproaching approachingthe theedge edgeof of the the sands sandsfacing facing the bay, do not go too close to the edge because because the the cliff cliff face facecould couldgive give way. way. Erosion of the shoreline current caused caused the the toe toe of of the fan to shoreline and a right lateral longshore current be be dispersed dispersedsouth southtoward towardTraverse Traverse Point Point and and beyond. Accumulations Accumulations at at Traverse Traverse Point are are the cause now. At cause of of the the tombolo tombolo that that connects the island to the mainland mainland now. At that thatpoint, point, some someof ofthe the sands were diverted into the middle of Keweenaw Bay. but but the majority Keweenaw Bay, majority of the sand sand was was kept kept along the shore shore by by wave wave refraction, refraction, to to be be deposited deposited further farther south. south. Continue Continueahead. ahead. 26.1 26.1 left turn turn in in Gay Gay on onMain MainStreet. Street. Take aa left sharp right right turn. turn. 26.3 Leave Gay with aa sharp 26.3 MAP Dl Dl the left left goes goes to to Big Big Traverse Traverse Bay Bay (about (about 1.5 1.5 miles). miles). 30.0 The road to the 30.0 30.8 30.8 The road bends bends right, right, then then left. left. 35.0 35.0 Gently Gently rolling rolling farm farm land. land. 36.4 36.4 The view ahead is of that follows follows the the trace trace of of the the Keweenaw KeweenawFault. Fault. At the of aa topographic topographic slope that Jacobsville top of of the the slope, slope, the thePLV PLVare areexposed. exposed. The slope slope face to here here isis underlain underlain by by Jacobsville Sandstone. The Theroad roadgoes goesdownhill downhillinto intothe theTraprock TraprockValley. Valley. 36.7 36.7 left at at the thestop stopsign signtoward towardLake LakeLinden. Linden. Turn left 37.6 37.6 The The slope slope related related to to the theKeweenaw Keweenaw Fault Fault isisagain again visible visible on onthe theright. right. 38.1 38.1 At the the stop stopsign, sign,turn turn right right toward toward Lake Lake Linden, Linden, and and immediately immediately cross the Traprock Traprock River River near near the the mouth mouth with with Portage Portage Lake. Lake. Left, Left,the theroad roadgoes goestotoJacobsville Jacobsvillevia viaDreamland. Dreamland. 38.6 38.6 Gregory Street Street is is on on the the left, left, which which goes goes to to the the Natural Wall Wall in in the the main main road road log log at at mileage mileage37.4. 37.4. 38.7 38.7 The junction junction of 9th Street with with M-26 M-26 in in Lake Lake Linden. Linden. Turn left on M-26 to return return to Houghton, floughton, or right right to to go goto toCalumet/Laurium. Calumet/Laurium. END OF OFLEG LEG1) D END �144 - LEG E 932 932 CREEK CREEK MAP E Ell Leg E at the junction of US-41 US41 and Gratiot Lake Road. North North of of US-41 US41isisthe theCentral CentralMine. Mine. 0.0 0.0 Start Lee Proceed immediately after after the the junction junction on on the the left, left, there are ~ r o c e e don o nthe paved paved Gratiot Lake Road, immediately stamp sands from the Central Mine. Mine. The The copper copper content content of the the sands sands restricts restricts plant growth. growth. 1.3 1.3 The road traverses section across traverses nearly nearly perpendicular perpendicularto to strike, strike,and andgoes goesdown downsection across the thePLY. PLV. with 2.65 The entrance to an an abandoned abandoned Calumet Calumet Air Force Station is on on the the left. left. Continue ahead with slow, gradual descent. descent. MAP E2 E2 onthe thesouth southside sideof of the the Keweenaw Keweenaw Fault Fault and and underlain underlain by by flatflat4.1 4.1 Gratiot Lake is visible ahead. ItItisison Jacobsville Sandstone Sandstonebedrock. bedrock. We are on the tilted lava flows of the PLY. lying Jacobsville PLV. building. The 4.25 Pull over to the side of the road. Walk Walk along along the the road road toward an A-frame building. The slope slope ahead along along the the paved paved road road isis the thetopographic topographicexpression expression of of the theKeweenaw Keweenaw Fault. Fault. Walking Distance (A typical typical pace--2 steps--is steps-is about 55 feet.) feet.) Feet (Approximate) (Approximate) dirt road is to the east. Junction of the paved road and the d irt road 0 A-Frame building. Bear 180 A-Frame 180 Bearright right (N70°E) (N70¡Ealong along the now forested forested road. 280 280 Now you are are going going downhill. downhill. 880 880 N50°E Continue N 5 W over a berm on an abandoned abandoned road. 1000 right. 1000 Outcrops are on the right. first part of of Stop El. El. Proceed ahead another 25 ft. to 932 1150 The outcrops on the right are the fist 1150 932 Creek and go upstream slightly slightly to to some some outcrops outcrops adjacent adjacent to to the the Keweenaw Keweenaw Fault. Fault. Stop El: El: 932 932Creek Creek(Keweenaw (KeweenawFault) Fault) The outcrops on on the the right right side sideof of the theroad road consists consistsof of altered alteredand andfractured fracturedbasa.lts basalts of of the the PLV intruded by a plug of basaltic andesite (Table (Table El). El). The Thefme-grained fine-grained texture texture suggest suggest that that this this The basaltic plug is highly plug plug was was shallowly shallowly emplaced. emplaced. The basaltic andesite andesite plug highly altered altered and and contains contains disseminated chalcocite. chalcocite. This This locality is at at the base of the PLY, PLV, near the Keweenaw Fault. Rhyolite Rhyoliteextrusive extrusiveand and intrusive rocks, and mafic-to-intermediate intrusiverocks rocksare are much much more more common common in in the intrusive rocks, matic-to-intermediate intrusive the stratigraphically lower part of the PLV (Fig. El). The mafic-to-intermediate intrusive rocks are stratigraphically lower part of the PLV (Fig. El). The mafic-to-intermediate intrusive rocks are known to contain copper sulfides (Broderick and others, others, 1946), 1946), (Fig. (Fig.El). El). Deposits (Broderick and Depositsdiscovered discovered to date (there (there are are 7) contain contain 0.1 to 4.5 4.5 million million tons of ore, with 2.5 to 3.0% Cu as as chalcocite chalcocite in amygdules; and and disseminations disseminations(Woodruff (Woodruffand andothers, others,1994). 1994). Most Most of of the the sulfur in the vienlets; amygdules; basalts during subaerial subaerial eruptions. eruptions. Mineralizing basalts of the PLV was lost by degassing during Mineralizing fluids fluids generated generated PLY should be be low low in in sulfur. sulfur. Woodruff and others (1994) suggest that that the the little from within the PLV �___ Begin -': 0— " \ I 9 I] St V7 t- c (_ t ' ,- ' t Ilfr ( — 025 ,A -' ç C12-.J 3 032 & - '4 t1f j..S .s - 3 *: .tI 3t MAP �0 S E .0 743 "V. B 0 (SR 1 a MAP E �Lap Leo a 147 EXPLANATION Jacobwllle Sandstone Freda Sandatone Nonefuch Formation Copper Harbor Conglomerah Portage b k e Volcanics a a n 0 in context context with with the geology Figure El: El: Location Location of the region region of of chalcocite chalcocite mineralization mineralization in geology ooff the the Keweenaw Peninsula (from Woodruff and and others, others,1994). 1994). �148 by progressive oxidation during chalcocite available sulfur sulfut was stripped from mineralizing fluids by deposition, but but dissolved copper copper remained remained in in residual residual fluids, fluids, allowing allowing for for deposition deposition of of native deposition, copper. The Therelationship relationshipbetween between the the chalcocite chalcocite and and native native copper copper is is uncertain. uncertain. Jacobsville Sandstoneisis exposed exposedinin932 932 Creek Creekjust just below below the the road. road. A A short shortdistance distance Jacobsville Sandstone upstream, the beds in the Jacobsville upstream, Jacobsville Sandstone are nearly vertical, making highly fractured and Keweenaw Fault Fault (a (a reverse fault), is altered basalts of the PLV visible in the creek bottom. The Keweenaw poorly exposed here, here, just just as it is elsewhere. Beds of the Jacobsville Sandstone are dragged dragged into into Beds of the Jacobsville Sandstone are the attitude attitude of the a near-vertical near-vertical position position by reverse reverse motion motion along along the the fault. fault. Downstream, Downstream, the the Jacobsville dip. The Keweenaw Fault was initially Jacobsville Sandstone Sandstoneshallows shallows to to the typical, less than 100 10' dip. normal fault fault along along the the edge rift system. system. During a graben-bounding graben-bounding normal edge of of the theMidcontinent Midcontinent rift Fault was was inverted inverted into into aa high-angle high-angle reverse reverse fault. fault. compression, at about 1060 1060 Ma, the Keweenaw Fault El: Chemical Table El: Chemical composition composition of the the intrusive intrusive plug on on 932 932 Creek Creek near near Gratiot Gratiot Lake. Lake. It is a median of 3 analyses. The probably due due to to 1420. $0. Unpublished Unpublished data data of of Bornhorst. Bomhorst. median Thelow lowtotal total isisprobably WT% Si02 A1203 Fe203 MgO CaO Na20 1(20 Ti02 P205 MnO CuS 53.61 14.48 8.69 2.93 8.54 4.71 0.77 1.30 0.54 0.13 0.32 Cr Ni Rb Sc Sr Zn Zr PPM 42 14 14 30 30 20 65 145 145 351 35 1 96.02 96.02 END OF LEG B E -- RETRACE ROUTE BACK TO CARS AND AND TO TO (15-41. US-41. �~ee Legs 149 149 LEG F FIVE FIVEMILE MILEPOINT POINT MAP Fl Fl MAP Just west of Eagle River, start Lee Leg on the the paved paved road roadto toFive FiveMile MilePoint. Point. Make a left turn on 0.0 Just 0.0 - FF on the road to to Five ~ i vMile Mile e Point. Point. the right side of of the the road road for for some some distance, distance, there are sand dunes from a past past high high stand stand of of the Lake Nipissing Stage of the Lake Superior basin. Ahead the road bends left. Lake Superior basin. Ahead 0.5 0.5 On On 0.8 0.8 Ahead, Ahead, aa view view of of Five FiveMile MilePoint. Point. 1.5 1.5 An An excellent excellent view view of of Lake Lake Superior Superior at at 3:00, 3:00,with with sand sanddunes dunesalong alongthe theroad. road. 1.8 1.8 Cross the Silver Silver River. Sand Sanddunes dunescontinue continuealongside alongsidethe the mad. road. 2.2 Pull Pull over over on on the the right right side side of of the theroad road into intothe theroadside roadside park. park. Stop Harbor Stop Fl: Fl:W.C. W.C.Verde VerdeRoadside RoadsidePark Park(Copper (Copper HarborConglomerate) Conglomerate) The The road is is at at the the level level of sand sand dunes dunes from from the Lake Lake Nipissing Nipissing Stage Stage of the the Lake Lake Superior Superior basin. The Theunconsolidated unconsolidatedHolocene Holocene sands sands rest rest unconformably unconformably on Precambrian Precambrian Copper Harbor Conglomerate exposed at the lake shore here. At Atthe theLake LakeSuperior Superiorshoreline, shoreline,one onecan canobserve observe the Copper both ways from here along the shoreline for Copper Harbor Harbor Conglomerate, Conglomerate, which continues both 0.5km km west west and and 2.5 2.5km km east. east. It interfingers interfingers with, and overlies, the PLV (Fig. 6), 6). and and at at about 0.5 this point, with interclated interclated red red sandstone. The point, itit is is composed composed of of pebble-to-cobble pebble-to-cobble conglomerate with The Copper Copper Harbor Harbor Conglomerate Conglomerateis in the subsurface subsurface under Lake Superior and crops out again on Isle (Fig. 2). 2). Royale (Fig. MAPF2 MAP F2 the right right side side of the the road road is is aa mm-off turn-off to to the the Five Five Mile Mile Point Point lighthouse. lighthouse. You You must must get 3.8 On the 3.8 permission to enter this area. In Inthe thefront frontyard yard of of the thelighthouse, lighthouse, is is aa thin thin lava lava flow flow of of the theLake Lake Shore Shore Traps Traps with with the theCopper CopperHarbor HarborConglomerate Conglomerateabove above and andbelow belowit.it. Seven Mile Point beach beach mm-off turn-off on the right right side side of of the the road. road. Along Along this beach beach are are many many exposures exposures of of the the Copper CopperHarbor HarborConglomerate. Conglomerate. P3 MAP F3 Cross the the Gratiot Gratiot River. River. 9.5 9.5 Cross 4.1 4.1 Ahmeek Cemetary Cemetary is is on on the the left. left. 10.45 Ahmeek Turnright rightatatthe thesouth southend endofofthe thecemetary. cemetery. 10.55 mm over to to the the right. right. 10.65 Pull over 10.65 Stop F2: F2:Allouez AllouezGap Gap(kettles) (kettles) Stop This This locality locality is is just northeast northeast of the the Allouez Allouez Gap, the lowest lowest bedrock bedrock gap gap between between the the tip rip of the 17). This gap lead lead to to aaconcentration concentration of of the Keweenaw Keweenaw Peninsula Peninsula and and Portage Portage Lake Lake (Fig. (Fig. 17). outwash from the retreating Wisconsin glacier. glacier. A A fan fan of of outwash outwash extends extends northwest northwest to to the the level level 6). Northwest Northwest of of the the gap, gap, the the outwash outwash is is pitted pitted and and channeled channeled glacial Lake Nipissing (Fig. (Fig. 3 of glacial 36). �apF2 �151 65O— 2 Lake Shore T �ca I-,' Is) m �~ess Legs 153 153 with 14 trend (Regis, (Regis,1993) 1993)(Fig. (Fig.36 36). On the left, at the the 867 867 foot foot 14 kettles kettles along a northwest northwest trend ). On elevation, of a kettle. kettle. Ahead, elevation, is is aa shallow shallow depression depression representative of Ahead, aa few few tenths tenths of of aa mile mileon onthe the right, 816foot footelevation. elevation. ItIt isis to tothe thenorthwest northwest right, are are more more depressions. depressions. The Thebest best kettle kettle isis at atthe the816 near near the the edge edge of of MAP MAPP3 F3and andhas has aadiameter diameter of of 100 100m mand andaadepth depthof ofabout about25 25mm(Regis, (Regis,1993). 1993). Ahead 0.1 0.1 miles on the the right, right, is is the the former former Calumet Calumet landfill in a kettle. kettle. 10.75 Turn Turnright righton onthe thepaved pavedroad madtoward towardAhmeek. Ahmeek. 11.25 11.25 Outcrops Outcropsof of basalt basalt are areon onthe theleft leftside sideof ofthe theroad. road Stop Lake Stop F3: F3:North NorthofofAhmeek Ahmeek(Portage (Portage LakeVolcanics Volcanics[PLV]) [PLV]) A A thin thin basalt basalt flow flow of of the the PLy, PLV,just justabove abovethe theGreenstone GreenstoneFlow, Flow,forms formsan anoutcrop outcropwhich which displays well-developed well-developed columnar columnar jointing. jointing. The Greenstone Greenstone Plow itself itself shows showsspectacular spectacular columnar columnar jointing in some some areas, areas, most notably, along the palisades shown on Isle Isle Royale, Royale, where where columns 22 m or or more more in in diameter diameter are found. In Inaafew fewareas, areas,the thecolonnade/entablature colonnade/entablaturejointing pattern described in the Columbia River River flood flood basalts, basalts, is is well-developed well-developedininthe theGreenstone. Greenstone. On the the Keweenaw, Keweenaw, columnar columnar jointed exposures in thin flow sequences are rare, probably because the underlying horizons were not water-saturated when when covered covered by by the next lava flow. 11.5 At the the stop stopsign, sign,go gostraight straightahead. ahead. 11.6 Another Another stop stop sign. sign. Turn Turnleft, left,and andafter afterone oneblock, block,turn turnright. right. 12.8 Turn right, in front front of of aa church. church. Join US41 by by turning turning right, and immediately immediately following, is a stop sign in Join US-41 Directly ahead about 11:00, the Kingston Mine; shallow mine that worked the 11:00, is Kingston Mine; a shallow worked right. Directly ahead at right. Kingston Conglomerate. Conglomerate. This mine mine is is said said to tobe bethe theonly onlysignificant significant nativenative- copper copper deposit deposit in the the region region that that was was not not discovered Inc. discovered and worked worked initially initially by by the theCopper CopperCulture CultureIndians. Indians. Calumet Calumet and Hecla, Inc. discovered 1962and andisisdescribed describedby by Weege Weegeand andothers others discovereditit via viadiamond diamonddrilling drillingby by Randy Randy Weege Weegein in1962 (1972). (1972).Production Productionfrom from1965 1965toto1974, 1974,totalled totalled 900,000 900,000kg kg of of copper copper from from about about 90,000 90,000tonnes tonnes ore. of ore. The original original lava lava surface surfaceon onwhich whichan aninterfiow interflowconglomerate conglomeratewas wasdeposited, deposited,had hadnumerous numerous primary irregularities. As Asthis thissurface surfacerotated rotated slowly slowly through through the horizontal horizontal during filling of the the rift rift basin, basin, some some of of the the depressions depressions on on the the surface surface formed formed shallow shallow ponds and drainages for low low velocity streams, in which fine-grained sediments were were deposited. deposited. Only after tine-grained sediments after further farther rotation of of the surface were stream gradients sufficient to transport coarser gravels, and to deposit them as surface were stream transport gravels, and to of the sheets. The deposition deposition of the sediment sediment was was sufficiently sufficiently slow, slow, and the the climate climate prograding sheets. sufficiently sufficiently warm warm and and moist, moist, so so that that calcium calcium carbonate accumulated in the sediment in horizontal horizontal zones, as caliche. .3 to thick. The Kingston Mine is located in one of these interflow conglomerates; aa bed bed 00.3 to 30 m thick, and traceable for 100 100 km along strike. Depressions Depressions on the footwall lava surface, exposed in the in thickness thickness mine, have fillings of reddish shale and siltstone, which which measure measure as as much much as 15 m in 100 m in in diameter. diameter. This Thisunit unit isisoverlain overlain by by about about 10 10 to to 15 15 m m of of massive massive to to faintly faintly and 30 to 100 bedded, distinctly cmss-bedded, cross-bedded, and and graded-bedded graded-beddedconglomerate conglomerateand andminor minor sandstone. sandstone. Where original lava lava surface surface was was topographically topographically higher, the conglomerate conglomerate rests directly directly on aa basalt basalt the original footwall. footwall. �154 within the the PLy, In comparison comparison with other other conglomerates conglomerates within PLV,the theKingston KingstonConglomerate Conglomerate shows shows several unusual characteristics. For For example, example, the clasts clasts are are composed composed almost entirely of aa single single porphyritic rhyolite. rhyolite. Also, lithology: dark red to reddish-brown quartz and feldspar porphyritic Also, the the clasts clastshave have a high angularity and small average size (about (about 88 mm), mm), with with the the largest largest pebbles pebbles being about being about 10 10 Thematrix, matrix,generally generally40 40to to 60% 60%of of the the sediment sedimentby by volume, volume, consists consists of fme-grained fine-grained cm in size. The chlorite, martite, quartz, feldspar, chlorite, martite, specular specular hematite, hematite, and caliche-derived caliche-derived calcite cement cement quartz, feldspar, (Kalliokoski, 1986). Where Wherethe the calcite calcitecontent content is is low, low, the the cement cementisisquartz. quartz. Fluvial planarplanar- and and cross-beds cross-bedsare are shown shownby by variations variationsinin grain grain size size and and color, color, and in the the Fluvial abundance of of matrix, composed composed of of dark dark chlorite chlorite and and calcite calcite cement. cement. Parts Parts of of the the conglomerate conglomerate that are poorly matrix) appear appear to to have dis-aggregated poorly bedded bedded and and contain contain little littlematrix matrix (—20% (-20% matrix) dis-aggregated in in situ. In some large samples, calcite and dark chlorite occur in different parts of beds. Calcite (as In some large samples, calcite and parts of beds. Calcite (as caliche) may have precipitated precipitated along zones with larger clasts; less matrix; and and probable probable greater greater horizontal transmissivity, but not not in zones with abundant transmissivity, but abundant clay (chlorite) (chlorite) in in which which permeability permeability might have been less. The Thesource sourceof of the theconglomerate conglomeratewas was aa proximal, proximal, southerly southerly located located upland upland porphyritic rhyolite rhyolite from from which which the the sediment sediment was waterwith friable, unweathered quartz-feldspar porphyritic transported with minimal minimal abrasion abrasion and and sorting. sorting. Mining was done on on four four levels levels along along two two segments segments of the the Kingston Kingston Conglomerate, Conglomerate, with 1000 1000 anirregularly irregularly distributed, distributed, fmefmem in total length length (Fig. (Fig. 34). 34). Native Nativecopper copperisisco-extensive co-extensive with with an grained hematite hematite pigmentation pigmentation and and kaohite kaolinite alteration. alteration. A grained A hematite hematite pigmentation pigmentation in in feldspar feldspar phenoerysts produced produced the the reddish reddishcolor colorininthe theconglomerate. conglomerate. In In places, places, the the rock rock has has lost its red phenocrysts color due to the the hydrothennal hydrothermal leaching of iron. The Themineralization mineralization decreases decreases gradually gradually along along strike, where the the conglomerate conglomeratethins thins or or contains containsepidote. epidote. Native copper Native copper occurs within within the the conglomerate conglomerate as generally generally continuous continuous zones zones of of mineable mineable (43% of the mined mined copper) copper) and and hanging hanging wall wall (33%); (33%); thicknesses and grades along the footwall (43% occursalong alongthe thecentral centralportions portions of of the conglomerate. normally, minor mineralization (—10%) (-10%) occurs Weege and others others (1972) (1972) describes describes several several empirical empirical relationships relationships between ore ore distribution distribution and and One important important ore ore control control is is considered consideredto to be be the thickness thickness of the the conglomerate lithology. lithology. One conglomerate: there is little or no ore where where the the thickness thicknessisisless lessthan than10 10m. m. Another Mother possibility conglomerate: that represents a control over permeability: permeability: where where the the base base of of the theconglomerate conglomerateisis"muddy"--as "muddy"--as occur nearby nearby at at higher higher in a basal depression--ore depression-ore may be absent along this basal zone, but it may occur stratigraphic levels in the the conglomerate. conglomerate. Permeability of of the host conglomerate is the fundamental control on on the distribution of native Permeability fundamental control native Allouez Gap Gap Fault Fault (Fig. (Fig.34). 34). The conglomerate copper. The TheKingston Kingston deposit deposit is bisected by the Allouez itself. At is well mineralized in the fault zone itself. At the thesouthwest southwest end end of of the the mine, mine, the the conglomerate conglomerate thins and ore grade is the best best in in the the mine. mine. The Thethinned thinnedconglomerate conglomeratecould could have have provided provided an an excellent barrier to ore ore fluid fluid movement, movement, if mineralizing mineralizing solutions moved parallel to strike strike rather rather than simply up-dip up-dip (Weege and and others, others, 1972). 1972). These These data are consistent with the Allouez Gap principal pathway for ore fluid, moving outward from the fault into the conglomerate. Fault as a principal END OF LEG F �Lep 155 LEG G G COPPER LEG COPPER CiTY CITY MAP G1 01 MAP 0.0 Start at the junction paved road road to to Copper Copper City City in in Allouez. Allouez. This mile junction of US-41 US41 and the paved This isis0.1 0.1 mile northeast of the Houghton Houghton and and Keweenaw Keweenaw County County line, line, just inside insideKeweenaw KeweenawCounty. County. 0.65 Enter Copper City. City. 0.8 left, goes goes toward toward the the Kingston Kingston Mine, continue continue straight straight ahead. Ahmeek Street, on the left, 0.85 0.85 At the the stop stop sign, sign,continue continue straight straightahead. ahead. 1.05 AAsharp 1.05 sharpbend bend inin the the road road to to the the right. right. junction, continue straight straight ahead ahead toward towardLake LakeLinden. Linden. The road to the 1.15 At the junction, the left left goes goes to toGay. Gay. Asharpbendinroadtotheleft 1.25 A sharp bend in road to the left. 1.7 1.7 Going downhill. downhill. At the the skyline, skyline, the the low, low,smooth smoothterrane terrane(underlain (underlain by by relatively relatively flat-lying flat-lying basalts of of the the PLY. PLV. Jacobsville Sandstone) Sandstone) is is visible. visible. We are driving on the tilted basalts 1.75 AAroad roadsign signon on the the right. right. 1.8 1.8 An open field on on the the right. right. 1.9 Park and and walk walk to Stop GI. A dirt path on the right. right. Park 01. STOP Gi: Gl: Copper CopperCity CityRhyolite Rhyolite(Portage (PortageLake LakeVolcanics Volcanics [PLy]) [PLY) Walk along the dirt about 170 dirt road/path roadlpath parallel parallel to the tree tree line, line, about about 70 70m, m,then thenwaljc walkabout 170 m toward the tree tree line (N45°W). (N45¡W)Small Smalllow-lying low-lyingscattered scatteredoutcrops outcrops and and float float rhyolite rhyolite occur occurhere, here, and can be be found found elsewhere elsewhere further further west west within within the tree tree covered covered area. area. The Copper City rhyolite is poorly exposed throughout throughout the the body. body. The The rhyolite rhyolite isiswhite white on weathered surfaces and red-brown on fresh broken surfaces, it is fine-grained with abundant is fine-grained with abundant phenocrysts of quartz. Since Sinceexposures exposures are are of of poor quality, it is not known whether this body of rhyolite is intrusive intrusive or or extrusive, extrusive, although although the published published geologic geologic map shows shows contacts contacts as as crosscrosscutting; cutting; making making the body body more more likely likely intrusive intrusive(subvolcanic) (subvolcanic) (Davidson (Davidson and and others, others, 1955). 1955). Stratigraphically, thisbody bodyisis within within the the lower lower part part of of the PLY Stratigraphically, this PLV exposed exposed on on the the Keweenaw Keweenaw Peninsula, Bodies of rhyolite are much more Peninsula, and below below the the Bohemia BohemiaConglomerate Conglomerate (Fig. (Fig. ).). Bodies common in the lower stratigraphic section section of of the thePLV, PLy, although still volumehically volumetrically minor. minor. Just downhill from here, the PLY PLV are are truncated truncated by the the Keweenaw Keweenaw Fault. Fault. Recently, Nicholson (1992), as summarized below, below, has has recognized recognized two two chemical chemical types types of of rhyolite (TableGl). 01). Type rhyolite in the the Keweenaw Keweenaw Peninsula: Types Types II and 11 11(Table Type II rhyolites rhyolites contain containbetween between percent SiO,), Si02), and fall near the border 71 to 76 weight percent Si02 SiO, (generally less than 75 weight percent between peraluminous peraluminous and and metalurninous, metaluminous,with with less less than than 2 %%normative between normativecorundum. corundum. The peraluminous character of some Type II rhyolites may may be be due due to to alteration. alteration. Type Type H I1 rhyolites rhyolites have greater than 75 weight percent SiOy Si02, and and are are slightly slightly peraluminous. peraluminous. High High contents contents of of Th and Rb 11rhyolites rhyolitesfrom humType TypeI.I. The rhyolites of the PLV PLV are are part part of of a bimodal basaltdistinguish Type II �PiP �~eo 157 157 rhyolite rhyolite association, association, typical typical of of extensional extensional tectonic tectonic settings settings such as the Midcontinent Midcontinent rift rift system. system. Type rhyolites of of the thePLV PLVare aresimilar similartotomoderate-silica moderate-silica rhyolites rhyolites from other areas, areas, such such as as Type IIrhyolites Iceland, association. Type II II rhyolites of the PLY PLV are are similar similar to to aa Iceland, with with bimodal bimodal basalt-rhyolite basalt-rhyolite association. select subset subsetofofhigh-silica high-silicarhyolites, rhyolites,termed termedtopaz topazrhyolites. rhyolites. Topaz Topaz rhyolites rhyolites are are notable notable for for select enriched lithophile elements, sometimes to economic levels. The Copper City rhyolite is the only enriched lithophie elements, sometimes The Copper City rhyolite is the only recognized PLy, the IIrhyolite rhyolite within the PLV, theother otherrhyolites rhyolites are are all all Type Type I. Overall, Overall,the thesetting setting recognized Type TypeU of thePLY PLVisiscomparable comparabletotoIceland Iceland(Nicholson, (Nicholson,1992). 1992). of basalt basaltand andrhyolite rhyoliteininthe Table Table (31. Gl. Chemical ChemicalTypes Typesof ofRhyolites Rhyoliteswithin within the the PLV PLV(from (fromNicholson. Nicholson, 1992). 1992). Type TypeUII Major Type TypeII Major N=4 1 oxides: N=3 N=31 N=4 oxides: 75.74 SiO, 73.84 73.84 75.74 Sb2 0.05 0.12 TiO, 0.12 0.05 Ti02 13.28 A 1 A 13.65 13.65 13.28 A1203 0.44 F a 0.66 0.66 0.44 Fe203 0.87 1.32 FeO 1.32 0.87 FeO 0.04 MnO 0.03 0.04 MnO 0.03 0.14 MgO 0.23 0.14 MgO 0.23 1.38 0.25 CaO 0.25 1.38 CaO 2.48 N%0 3.23 3.23 2.48 Na20 6.64 5.60 6.64 5.60 K,O 1(20 0.02 0.03 P A 0.03 0.02 P205 100.04 Total 100.00 100.00 100.04 Trace Trace elements: elements: Nb 41 41 Nb Rb 112 Sr 55 Zr 240 Y 56 La 30.3 6.57 Sm Yb 5.55 Hf 7.53 2.91 Ta Th 15.09 End of of Leg Leg(3 G-- Retrace Retrace route route to to US-41. US-41. End 51 51 465 28 144 74 12.0 6.9 7.68 6.3 4.9 63.0 �158 STATE LEG II H McI,AIN M~LAIN STATE PARK PARK MAP HI Hi The junction junction of US-41M-26 US-4i/M-26 and M-203, Calumet. Turn M-203, at the edge of Calumet. Turn right right on on M-203. M-203. 0 0.55 The Village Limit of Calumet. Continue Continuestraight straight ahead. ahead. 1.0 Turn right just west of an open open playing field (on the right side, after the turn.) 1.1 Turn right. 1.2 Turn building. On Turn left left just before before a red sandstone sandstone block building. On the the left left isis the the concrete concretecapped cappedRed Red Jacket Jacket Mine. 1.3 At a sand and gravel pit. Hi: Red Stop HI: RedJacket Jacket(glacial (glacialsand sandand andgravel) gravel) The Pleistocene sands and and gravels gravels at at this locality Pleistocene sands locality are are interpreted interpreted as deposited deposited in in perforation kames and crevasse fillings. The deposits show both cross-bedding and channeling, perforation fillings. The deposits show both cross-bedding channeling, due to the glacial-fluvial sediments sediments being deposited in perforations and crevasses in the ice. These These deposits, and the esker to the north of here (Fig. HI, Hi, location location B), are characteristic of the glacial ice margin (summarized (summarized from from Regis, Regis, 1993). 1993). Retrace route and M-203. and return return to to M-203. 1.6 At the junction of of M-203, M-203, turn turn right--away right~awayfrom from Calumet. Calumet. 1.95 Turn right, onto 1.95 onto Tamarack Tamarack Waterworks Waterworks Road. Road. 2.25 The road road bends bends left. left. Superior on the horizon horizon is excellent. 2.45 At the crest of the West Tamarack Moraine, the view of Lake Superior excellent. 2.5 Pull over to the the right. right. Stop 112: H2: West Tamarack Tamarack(glacial (glacialgravels) gravels) The West Tamarack Moraine is composed composed of of cobbles-to-boulders cobbles-to-bouldersin inaa sand sand matrix. matrix. This This moraine extends for about 10 withaawidth widthofofabout about1.5 1.5km kmin in the the south, south, several several 100 m in km,with 10 1cm, the north (Fig. Hi), HI), and and aathickness thickness of of around around 20 20 m. m. The Thenorth-south north-southtrending trending West West Tamarack Tamarack Moraine has a gender gentler west west slope, slope, which which is is interpreted by Hughes Hughes (1963) (1963) as indicating indicating underwater underwater deposition, except at the the extreme extreme north north end end (summarized (summarized from from Regis, Regis, 1993). 1993). Retrace route and and return return to toM-203. M-203. 3.05 Turn right on 3.05 on M-203. M-203. 4.0 Lakeview Cemetery is on the right. right. �~ e o MapH2 159 MAP Hi �a ec. 4- - 7., --S a- 4 - A-. a-, - -flair. -. -: - ?iC; t it—. a-.. --'4:.' JL V 4. 24.. I. I Figure Hi: Physiographic and glacial features west of Calumet (from Hughes. I 963). A. West Tamarack moraine, subaerial portion; B. esker. C. sand plain; D. boulder ridge; E. delia kame; F. Centennial hill; G. Tamarack hill; H. Swedetown hilt. I t -a — - .-, __fl.r. - �Legs 161 junction at the road to the Calumet Waterworks Park. Park. Continue 4.3 4.3 The junction Continue on on M-203. M-203. MAP H2 H2 Road. The Theroad road goes goes uphill. uphill. 6.0 Turn left onto Cloverland Road. 6.35 Pull over, alongside alongside the the road. road. Stop 113: H3: Cloverland CloverlandRoad Road(Washburn (WashburnStage Stagebeach beachridges) ridges) This stop stop is is at at the the elevation elevation of of the the Washburn Washburn Stage Stage of of the the Lake Lake Superior Superiorbasin basin (Table (Table2). 2). beach ridges ridges about about 1.5 1.5 m m high high in in the open field. Here, one can view a pair of NE-SW NE-SW trending beach The two ridges are only only about about 11 m m apart apart and and their theirassociated associated sediment sediment is is well well sorted sorted medium medium sand. The Theelevation elevationatatthis thisglacial glaciallake lakestage stagevaried varied between between 1040 1040 to 1051 1051ft, ft, which which is is about about 440 440 ft above the present-day elevation of of Lake Lake Superior. Superior. The Washburn Stage has the most traceable features, next to to the the Nipissing Nipissing Stage Stage (summarized (summarized from from Regis, Regis, 1993). 1993). Return to to M-203. M-203. 6.7 6.7 Turn left onto onto M-203. M-203. 9.2 The road to the right is Lakeshore Lakeshore Drive, which goes goes to the the Calumet Calumet Township Township Waterworks WaterworksPark. Park. The road to the left is Sale Road, which goes to the Bear Lake Rhyolite and Stop H4. The Bear Salo which goes to the Bear Lake Rhyolite and Stop H4. Lake Rhyolite cuts the Freda Sandstone bedrock, bedrock, and and is is the the youngest youngest known igneous activity in Peninsula. The Bear Lake Rhyolite of 1054  ± 34 my. m.y. years old, the Keweenaw Keweenaw Peninsula. Rhyolite is a minimum minimum of based on a KJAr (White, 1968). 1968). The mileage to H4 is not logged, but just follow the KIAr age date (White, directions given in the the stop stop description, description, H4. H4. Continue on M-203 M-203 toward towardStop Stop115. H5. Stop H4: Lake LakeAnnie Annie(glacial (glaciallake lakebaymouth baymouth bar) bar) Directions to Lake Annie Stop (not logged): Turn left onto Salo Road and continue due south for where the the road road bends bends sharp sharp right right (west). (west). At about 1.0 miles from the turnoff, where about 1.5 1.5 miles, miles, turn turn left left (south). Continue straight ahead (south) and at about 4.35 miles there is a "Y' in the road, stay (south). Continue straight (south) and at about 4.35 miles there is a "Y" right. On right. Onthe theleft, left,atatabout about5.3 5.3miles, miles,isisaasand sandand andgravel gravelpit, pit,MAP MAP114. H4. The Pleistocene glacial sediments at this stop represent a baymouth bar, related to either the Shoreline V V or Washburn Washburn glacial glacial lake lake stage stage (Table (Table2). 2). This ridge is composed of sand with gravel. Near little gravel. Near the theeast eastedge edgeof of the thepit, pit, the thesand sandisiscapped capped by by till till(summarized (summarized from from Regis, Regis, 1993). 1993). MAP H3 H3 9.9 Sand ridges on the right, at the east east end of of McLain McLain State Park. Stop 11$: H5: Sand SandRidges RidgesM-203 M-203(Nipissing (Nipissing beach beach ridges) ridges) beach sand sand ridges ridges are are related related to Glacial Lake Nipissing, These subaqueous beach Nipissing, which was 10 m above above the the current current level level of of Lake LakeSuperior--approximately Superior--approximately 4,000 to 5,000 5,000 years years ago. ago. about 10 but sometimes are more The Nipissing Stage features are usually close to those of Lake Superior, but prominent. prominent. the Nipissing Nipissing stage, one The north end of Portage Lake opened into two channels during the �—— -D '-S lc'olc t.J 0' �_ ______ _____ Legs It S11 Ii eQ2 Stop H5flf-S ELEYAT MA$ 163 '-' Stop H6 IJ )75(U? gfL7a7 S' t:kar Lake GravitY Traver_.J J Rhyolite 4 ,628 \' COAST ' GUARD \\a;srA o BM t:c . 5; ,, U J 'Cl Map H4 MAP H3 �MAP �~eo Legs 165 165 was the the Bear Bear Lake Lake Channel. Channel. The was the current channel, channel, the other was The two two were were separated separated by an an island. Sand Sandclosed closedoff off both both channds channels(the (thecurrent-day current-day channel channel was was dredged dredged by the Army Army Corps Corps filled in the Bear Lake of Engineers for ship traffic), and eventually eventually filled Lake channel channel described described below below (summarized from Regis, 1993). Regis, 1993). 10.1 10.1 Bear Lake is on the left left side side of the the road. mad. Cross Crosson ontop topofofthe thefilled filledglacial glacialBear BearLake Lakechannel. channel. The Bear Lake Lake Channel Channel (Map H3) represents a deep bedrock valley, and is an an extension extension of of the the Keweenaw Waterway. Waterway. The Waterway was dredged dredged to to the west of McLain Keweenaw Waterway was McLain Park because because the the distance was less, but also because the Bear Lake Channel is a much more profound feature, with than 600 ft to bedrock. bedrock. The and similar similar bedrock bedrock valleys, valleys, is shown by more than The definition definition of this, this, and gravity data. One such traverse, plotted on the map, is displayed as Figure One such traverse, plotted on the map, is displayed as Figure H2. H2. 11.0 11.0 Turn right at the the entrance entrance to to McLain McLain State Park and the other other edge edge of of the the Bear Bear Lake LakeChannel. Channel. Camping facilities are located here. here. You can park on on the the side side of of M-203 M-203 opposite opposite to to the the entrance entrance and and wallc walk into the park, or or pay pay the the (the same same park park sticker stickerisis valid validfor forStop Stop28). 28). Enter the park and stop vehicle fee at the entrance (the stop at the main open area. Walk Walktoward toward Lake Lake Superior Superior and and the children's play play equipment. equipment. Stop Stop 116: H6: McLain McLain State StatePark Park(Freda (FredaSandstone) Sandstone) the shore of of Lake Superior, depending depending upon upon the level Freda Sandstone is exposed along the and slabs of Freda can be found of the the lake. lake. Blocks Blocks and Freda Sandstone Sandstone can found along along the the beach beach however, however, regardless of the lake lake level. level. It consists of red colored interbedded fme fine sandstone and siltstone, siltstone, and the red color reduced zones zones and and spots. spots. The Freda Sandstone color is interrupted by white reduced Sandstone was the last rift-filling clastic clastic sediment, sediment, and and was was deposited deposited in in aafluvial fluvialenvironment. environment. M-203. The The road road to to the the right right is is to to the the Coast Coast Guard Guard Station; Station; the road to the left is is 11.8 Continue on M-203. 11.8 the Bear Lake Lake Road, Road, the the location location of of gravity gravity traverse. traverse. 12.8 12.8 The access access road to to Lily Lily Pond. Pond. Lobe, a great mass of glacial ice which At this point, the end moraine moraine of the Keweenaw Keweenaw Lobe, great mass which was Wisconsin glaciation, glaciation,isiscrossed crossed(Fig. (Fig. 16). 16). The regional distribution of stabilized here during the Wisconsin this moraine in Figure Figure 15. 15. The moraine is plotted plotted in The positions positions of lobes as they retreated retreated at the end of the Wisconsin period are are shown shown in in Figure Figure 14. 14. MAP H5 H5 High Point Road, continue continue ahead ahead on on M-203. M-203. 16.1 16.1 17.85 Exposures Exposures on on aa vertical vertical road road cut. cut. Stop 117: Stop H7: Till along M-203 (till) (till) The 5 S m high vertical face exposes exposes aa matrix-supported matrix-supportedsediment: sediment:diamict. diamict. It is a hard and compact till with cobbles set in a fme matrix. Carbonate Carbonate cement cement causes the hard character, and is likely an older older till till (summarized (summarized by Regis, Regis, 1993). 1993). 17.95 AAhigh highcut cutofofglaciofluvial glaciofluvialsediment sedimenton on the theleft. left. �MAP �Legs ten 167 167 BEAR BEAR LAKE LAKE 9 8 7 0 0 6 5 I I I 4 6 — I 8 I I IC 12 I 14 0 x IC — I 0 0 -2 -3 C 200 S Figure112: H2: Results Results of of gravity gravitymeasuxements measurements across the Bear Lake Lake traverse traverse plotted plotted in in Map MapH3 H3(from (from Figure Warren, Warren. 1981). 1981).At Atthe thetop topisisthe theBouguer Bougueranomaly anomalywith withregional regionaltrend. trend. InInthe themiddle middlediagram, diagram. the the regional regional trend trend isis subtracted subtracted to to get getthe thesolid solidline linewhich whichisiscompared compared with with the themodelled modelled difference topography QC's). The bottom diagram is the model of the valley and the density topography (X's). The bottom diagram is the model of the valley and the density differenceof of bedrock(Freda (FredaSandstone) Sandstone)and andthe thevalley valleyfill. fill. thebedrock the �168 Hancock City limit. limit. MAP H6 H6 Creek are are exposures exposures of of Freda Swedetown Creek. Creek. To the northeast northeast along Swedetown Swedetown Creek 18.7 Cross Swedetown 18.7 Sandstone. Sandstone. 18.6 18.6 19.05 Hancock and Superior Superior Sand Sand and and Gravel Gravel is is on on the the left left (Stop HancockCampground Campgroundisison onthe theright right(Stop (Stop118), H8), and H9). STOP STOP 118: H8: Hancock Hancock Campground Campground(Nonesuch (NonesuchShale) Shale) paved road road to to the the boat boat launch. launch. Tell the attendant attendant you you are aregoing goingto tolook lookatatrocks. rocks. On Follow the paved the shore exposed. An shore of Portage Lake, the Nonesuch Shale is exposed. An abandoned abandoned quarry is is located located NE NE of the boat launch. launch. The Nonesuch is stratigraphically stratigraphically between the Copper Harbor Harbor Conglomerate Conglomerate and and Frecla Freda Sandstone (Fig. (Pig. 5). Nonesuch crops crops out around around the the margin margin of of the the quarry quarry and and lakeshore lakeshore at at this stop. It The Nonesuch is aa fmefine-totomedium-grained, medium-grained,gray-to-reddish gray-to-reddish brown brown sandstone sandstone with with subordinate subordinateinterbedded, interbedded, reddish-brown laminated siltstone and shale 956a). The attitude of reddish-brown shale (Cornwall (Cornwall and andWright, Wright,1 1956a). bedding is about N30?3, As a whole, the Nonesuch Shale consists primarily of siltstone siltstone N30°E, 25W. 25W. As amounts of of sandstone, sandstone,deposited depositedininaalacustrine lacustrineenvironment. environment. It It can and shale, with subordinate amounts from the formations above and and below below by by its generally be distinguished distinguished from formations above generally grayish grayish color. Most Most Nonesuch is aa rippled, rippled, laminated laminated siltstone siltstone with with reddish-gray reddish-gray partings. partings. Lithologically, siltstones siltstones composed of of around around 30 30 to 40 % rock fragments and 60 and sandstones of the Nonesuch Nonesuch are composed 60 to to 70 % mineral grains. The Therock rockfragments fragmentsare are mostly mostly volcanic volcanic with with a 2:1 2:1 ratio ratio of of mafic-to-silicic mafic-to-silicic (Daniels, 1982). 1982). The + intermediate intermediate composition composition (Daniels, The Nonesuch Nonesuch Shale at Hancock Hancock Campground is + some 60 60 km km northeast northeast of of the the thicker thicker section section near near White White Pine, Pine, and and likely likely represents representslacustrine-tolacustrine-tofluvial facies (Elmore and others, 1989). The Thedip dipof of the the underlying underlyingCopper CopperHarbor HarborConglomerate Conglomerate at Stop Al A1isis39W % 93' and andoverlying overlyingFreda FredaSandstone Sandstoneatatthe theLake LakeSuperior Superior shoreline shoreline at at Stop Stop A3 A3 is is SW. 5 T . This Thisshallowing shallowingofofdip dipup-section up-section isis typical typical of of the the rift-filling rift-filling strata, and is mostly mostly due to syn-depositional syndepositional down warping of the the rift-filling rift-filling strata. strata. Stop 119: H9: Superior SuperiorSand Sandand andGravel Gravel(glaciofluvial (glaciofluvialsediments) sediments) YOU MUST MUST GET GET PERMISSION PERMISSION TO TO ENTER ENTER THIS THISLOCATION. LOCATION. Sand and gravel terraces occur all along the Portage Gap, but most are less that 1.5 1.5 km krn long, and are are related to ice ice margin margin features. The TheFairground Fairground Terrace, Terrace,being being mined mined here, here, consists consists of three zones and H4). 114). Massive lacustrine sand sand is is overlain overlain (in channels) by a poorly zones (Fig. (Fig. 113 H3 and pinkish color. color. The sorted gravel with a pinkish The pink color is the result of a significant amount of silt and clay. Some Atthe thetop, top, the the coarse, coarse, purplish purplish gravels gravels Sometill tillisisincluded included in in the the poorly poorly sorted sorted gravel. At lack the pinkish color, and was likely deposited deposited in in a deltaic environment. environment. The Michigan The Michigan Tech Tech Terrace formed at at the the same sametime. time. The glaciofluvial glaciofluvial sediments formed during the last glacial retreat, about 8,000 years ago. Glacial ice was abutted against the Keweenaw Keweenaw Fault slope from the east for aa protracted protracted period period of time, with a tongue of ice in the Portage Gap. The Thepost-Duluth post-DuIuth glacial glacial lake lake drained drained eastward through the Gap (summarized (summarized from Regis, 1993). 1993). END OF OF LEG LEGHH -- CONTINUE ON M-203 INTO END INTO HANCOCK. HANCOCK. �169 I H6 MAP H6 I �170 Isgs Figure Figure113: H3: Geologic Geologicsection sectionthrough throughthe the Hancock Hancock "Fairground" "Fairground"terrace terrace glacial glacial deposit deposit(from (fromHughes, Hughes, 1963). 1963). �Legs a 171 a-'-' O. rj-, -. ap3t-4E -t - Figure FigureH4: H4:Physiography Physiographyand andglacial glacialfeatures featuresofofthe thenorthern northernpart partofofPortage PortageLake Lake(from (fromHughes, Hughes,1963). 1963). �172 t.cgs LEG I L'ANSE Ii MAP I1 on the the campus campusof ofMichigan MichiganTechnological TechnologicalUniversity. University. The Begin at the Memorial Union Building on 0.0 Begin by the PLV PLY (see MAP 1). 1). campus is built on glacial glacial sediments underlain by 0.1 Turn left (east) onto US-41. US-41. NOTE: NOTE:Stay Stay on on US-41 US-41 all the way to Stop Stop Ii. 11. 0.6 The middle of Wadsworth Dormitory Dormitory overlies overliesthe the Keweenaw KeweenawFault. Fault. As you follow US-41 past the dorm, and will will continue dorm, the the underlying underlying bedrock bedrock is now now Jacobsville Jacobsville Sandstone, Sandstone, and continue to be be Jacobsville Sandstone all the way #I. way to to Stop Stop#1. 0.7 East entrance/access entrancelaccess road to the Michigan Tech campus. 1.2 On the left is a view of Isle Royale Sands and and the the Portage PortageWaterway. Waterway. The dark-colored sands are basalt flow flow top lodes were processed crushed basalt. basalt. The native copper mineralized mineralized basalt processed by stamp stamp mills primarily along the margin of Portage Lake, Lake, Torch Torch Lake, Lake, and and Lake Lake Superior. Superior. In those those days, days, the waste crushed water. Fortunately, crashed basalt was dumped into the adjacent water. Fortunately, the native native copper copper ore ore deposits of the any, acid-generating acid-generating sulfide sulfideminerals--such minerals--such the Keweenaw Keweenaw Peninsula Peninsula contain contain little, little, ifif any, as pyrite--so pyrite-so that the actual rock waste is as inert inert in in the the surface surface environment environment as natural rock exposures. exposures. 2.7 On the left left is is an an excellent excellent view view of of Portage Portage Lake. Lake. 6.8 Enter Chassel. Chassel. 9.0 Crossing the Sturgeon Sturgeon River River and and its itsassociated associatedsloughs. sloughs. The Sturgeon River discharges discharges into Portage Lake, Lake, forming forming aa bid's bird's foot delta. delta. The are an an excellent excellent wildlife wildlife area area where where a Thesloughs sloughs are It is a recommended canoe launching spot. diverse list of birds nest. of birds nest. a recommended launching 12.7 The rolling rolling terrane terrane here here isis glacially glacially carved carved from from the theunderlying underlying Jacobsville Jacobsville Sandstone, Sandstone, and veneered with a variable thickness of glacial glacial sediment. sediment. 15.6 Yiewing Viewing Keweenaw Bay of Lake Lake Superior. Superior. 20.5 Grover Diilman, Pullover is is on on the left toward Keweenaw Bay of Lake Dillman, Baraga Cliff, Roadside Pullover the fenced in area is a 21 m high exposure Superior. Behind Behind the fenced in area is a 21 m high exposure of of Jacobsville Jacobsville Sandstone. These These L'Anse. exposures can be seen from the Keweenaw Keweenaw Bay shoreline in L'Anse. 21.8 Enter Keweenaw Bay Bay Indian Indian Reservation. Reservation. 22.3 An excellent view view across across Keweenaw KeweenawBay. Bay. At the 10:00 position position is a good view of the western Archean core composed of granitoid rocks end of the Huron Mountains. This Thisarea areaconsists consists of an Archean unconformably overlainby by early early Proterozoic sedimentaryrocks rocks of of the unconfonnably overlain Proterozoic sedimentary the Marquette Marquette Range Range Supergroup Supergroup (Klasner (Klasner and and others, others, 1991). 1991). 24.3 A good view of L'Anse black sand beaches are made of the same L'Anse across across Keweenaw Keweenaw Bay. The black crushed basalt mine rock as the Isle Royale Sands near Houghton. The Thebedrock bedrock here, here, Jacobsville Jacobsville Sandstone, Sandstone, yields yields white white sand sand beaches. beaches. �SCALE 1:168960 (1 cm = 1689.6 in or 3/8' =1 mile) AP �174 174 ten MAY12 MAP I2 26.8 Entering Baraga. 27.3 10:00 position position is aa view view across across The US41 and M-35; M-35; stay stay on on US-41. US-41. At At the 10:00 The junction junction of US-41 Keweenaw with L'Anse L'Anse Red Rocks cliff cliff exposures exposures (Stop (Stop 11) Ii) in the Keweenaw Bay with the background. background. 28.7 Baraga State State Park. Park. 29.1 The head of of Keweenaw Keweenaw Bay. Bay. 29.4 L'Anse L'Anse Red Red Rocks Rocks are arevisible visible straight straight ahead. ahead. 30.1 Pull over over to to the the side side of of the the road--being road-being careful careful of of traffic. traffic. It is recommended recommended that you turn around of the guardrail on the pebble and pull over on this end (the downhill end, near Lake Superior) of beach. Walk toward the the tree tree line (there is a path) to begin beach. Walk along along the the Keweenaw Keweenaw Bay shoreline shoreline toward Stop #1, which is the unconformity between the early Proterozoic Michigamme Michigamme Formation Formation of of the Marquette Range Supergroup (cleaved slate) and the the Jacobsville Jacobsville Sandstone. Sandstone. After viewing the lower part, you may either climb the steep steep bank to the the highway, highway, or or retrace retrace the the path path and and emerge emerge by the cars, where where you you can can cross cross the the street street and and proceed proceed to to walk walk along along the the cliff cliff onto the highway by exposures of the the Jacobsville Jacobsville Sandstone. Sandstone. BE EXTRA EXTRA CAREFUL CAREFUL OF OF TRAFFIC!! TRAFFIC!! Ii:1:L'Anse Stop 1 L'AnseRed RedRocks Rocks(Jacobsville (JacobsvilleSandstone) Sandstone) In the the Lake Lake Superior Superior syncline syncline portion portion of the the Midcontinent Midcontinent rift zone, zone, the the Jacobsville Jacobsville Sandstone Sandstone is aa thick thick (+900 (+900m) m) redbed redbed sequence sequenceof of fluvial fluvialsandstones; sandstones;conglomerates; conglomerates; siltstones; siltstones; and shales, cutting dykes. dykes. On shales, completely devoid of lava flows and cross cutting On the the north and and south south sides sides of Lake Superior, the formation occurs as inward-dipping, fault-bounded depositional wedges. Lake Superior, the formation occurs as inward-dipping, fault-bounded depositional wedges. These are are separated separated by regional regional reverse faults faults from from the strata strata that are are more more axial axial on on the the inner innerside side of the basin, the PLy, PLV, and andthe theOronto Orontoand and Bayfield Bayfield Groups Groups of similar similar red sandstones. sandstones. consists of arkose, The sandstone sandstone lithology lithology consists arkose, subarkose, subarkose, quartz, sub-lithic sub-lithic arenite, arenite, and and massive sandstone-shale sandstone-shalesequences sequencesrepresenting representing point point quartzite. Locally, Locally,there there are well developed massive bar-overbank facies, and in drill cores, there are several hundreds of meters of upward fining beds, of fluvial, fluvial,possibly possiblybraided, braided,stream streamdeposits. deposits. The The cement 55 to 30 cm thick, which is characteristic of varies from from authigenic clay to calcite and zeolite. Conglomerates Conglomerateswith with clasts clasts of of Lower LowerProterozoic Proterozoic extensive, particularly west and east and Archean lithologies, are locally abundant and laterally extensive, of Lake Gogebic. In places, places, there are also also clasts clasts derived derived from Keweenawan volcanic rocks. Jacobsville sedimentation was preceded preceded by by volcanic quiescence; quiescence; cratonic stability; and sedimentation was weathering, so that chemically resistant debris such as quartz weathering, so chemically resistant debris as quartz and andiron-formation iron-formation became became concentrated in in the source areas. Erosion Erosionwas wasinitIated initiated by by late late Keweenawan Keweenawan warping, warping, perhaps perhaps accompanied Vigorous marginal accompanied by movement movement along along the the Keweenaw Keweenaw Fault. Fault. Vigorous marginal fluvial systems systems developed on the south side by ridges of iron-formation. The side from from uplands dominated by Theresistant resistant debris was deposited in alluvial fans. Later Later sediments sediments were also also derived from a Keweenawan age terrane. On basaltic and felsic volcanic terrane. On burial, burial, the thesandstone sandstone underwent underwent low-grade low-grade alteration alteration so so that microcline-plagioclase-kaolinite-montmorillonite that the the present matrix mineralogy changes from microclhe-plagioclase-kaol'inite-montmorillonite near the surface, surface, to to microcline-montmorillonite-illite microcline-montmorillonite-illite(chlorite) (chlorite) at at depth. depth. At the top of the the cliff is is aa locally fabricated sheet copper statue of Bishop Fredric Baraga �SCALE 1:168960 (1 cm = 1689.6 m or 3/8" = 1 mile) MAP �176 12gz (1797-1868); a Roman Roman Catholic priest born in Yugoslavia, Yugoslavia, who worked among the Indians and early white settlers. settlers. The 20 m highway on on the shoreline) and upper m section, section, divided divided into lower (below the highway parts (above highway), shows shows many many of of the the characteristics characteristicsofofthis thisfluvial fluvialredbed redbedformation. formation. The sandstone rests on Lower Formation Slate Slate which which displays a reddish Lower Proterozoic Proterozoic Michigamme Michiganune Formation reddish discoloration along joints, joints, possibly possibly denoting denoting pre-Jacobsville pre-Jacobsvilleweathering. weathering. At the inner edge of the slate outcrop, under under the the overhang, overhang, there thereare areparallel parallelstriations striationson onthe thesurface surfaceofofthe theslate. slate. These striations striationswere interpreted interpreted by Murry Murry (1955) (1955) as as having having been produced by pre-Jacobsville pre-Jacobsville glaciation, glaciation, and by Kalliokoski Kalliokoski (1982), as produced produced by aa more more recent recent lakeward lakeward sliding sliding of of the theJacobsville Jacobsville Sandstone on top of of the the regionally regionally inclined inclined slate slatesurface surface (Fig. (Fig. 11). 11). At the base of of the the Jacobsviile, Jacobsville, the the wide wide variety variety of of clasts clasts in in the thepolymictic polymictic framework framework conglomerate and metamorphic metamorphic Archean Archean and and Lower Lower conglomerate resemble lithologies in igneous, sedimentary, and Proterozoic rocks that outcrop some tens of of kilometers kilometers to the the south southand andsouthwest. southwest. Note the the pebbles of vein quartz and iron-formation. iron-formation. The abundance of pebbles The sandstone sandstone immediately immediately above above the the conglomerate display foresets and troughs. conglomerate foresets and troughs. The upper part of of the theJacobsville Jacobsville section, section, above above the the level level of of the thehighway, highway,consists consists predominantly of fmepredominantly fine- to to medium-grained medium-grained reddish reddish brown-to-tan brown-to-tan feldspathic-to-sublithic feldspathic-to-sublithic quartz quartz sandstone, with minor minor red silty ranges from well-bedded sandstone, with silty shale shale (east, (east, left). left). The sandstone ranges well-bedded to massive. Some Somebeds beds are areup up to toI1mmthick thickand andshow showconspicuous conspicuousforesets foresetsoverlain overlain by by planar planar beds beds layers of of quartz pebble pebble lag lag conglomerate. conglomerate. Some surfaces are current ripple and thin, continuous layers marked. AAconvoluted convolutedsandstone sandstonebed bed above above aa planar planar bedding surface suggests suggests that sedimentation was on a slope. slope. END OF LEG II RETRACE ROUTE TO HOUGHTON - RETRACE HOUGHTON - �A scsia - -, W w ,vast LAfl ~Izgse o 177 177 LI I 5— A' u.s. B fl 1.1.; A Dik. ..ta.g rs-rwn Ijasntnd; w.11.ert.4i erSbs4L 114 4 (a ia.c1s.t.. 1a.p—.eM IkiMrPM... b—Maj (a. ad, n. fI.l—ts.t*.d, ..fl—..rt.d; U—.l. tn..—b.441; .1 1..cS.1.t; .s(tis .n—fl beddtfl nfl... .1 i.cnnl dnp.s .tlyi.( i.t.sL. .Si.. tt s L.Ai ..ttMd net...., flw.bM v.U.ercMI lnp—...i. cn..SddL.t; .a.t Near b4dI; .fla (tic rifl.. — Sn tanlad .ithS. Sst.r..1; d. .,k — i.a.cl..t.i •h—l lain •eantt. - .....-"'-.- lai..t.d te sMy 24.1 d1.41s ii.. tf 1.1.1 2.d-m w aU—iteM snesbiddia *54 ..,,-...—gLSL, . >, . " . , - , " .&cSU&,flI.-ncy -u-.-u $.arb.dd.4i SS,.aULC —. •i IflSI '0I0—. -1Ul, r*-1 .ini..; MUM* .-là IS te k. tSS.k1 In. .nI Figure Ii: Figure 11:(a) (a)Geologic Geologicsketch sketchmap mapand andcross-section cross-sectionof L'Anse redrocks (from 1962 1962 Michigan College College Sandstone is equivalent and Technology, Technology, NSF NSF Summer SummerConference Conferenceguidebook). guidebook). Sandstone equivalent to to the the of Mining and Jacobsville Sandstone, slate is equivalent to the Michigamme Formation, the the Early Early Proterozoic Proterozoic Michigammc the Jacobsville Strañgraphic section of the Jacobsville Sandstone (b) Stratigraphic Sandstone at at contact is an an angular angularunconformity. unconformity. (b) L'Anse Redrocks L'Anse Redrocks (from (fromAble. 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Geological Survey 71p. Survey Bulletin 778, 778, 71p. White, W.S., 1956, Chassell Quadrangle, Michigan: U.S. U.S. Geological Survey Mineral 1956, Geologic Geologic map of the Chassell Investigations MF 43. 43. Investigations Field Studies Map MF lavas of Lake Superior, , 1960, Keweenawan lavas Superior, an example example of of flood floodbasalts: basalts:American American 1960, The Keweenawan Journal of Science, v. v. 258A, 258A, p. p. 367-374. 367-374. J.D., ed., Ore , 1968, 1968, The native-copper deposits of northern Michigan: in Ridge, J.D., Ore Deposits Depositsof of 1933-1967 (the (the Graton Graton Sales Sales volume): volume): American American Institute Institute of of Mining, Mining, the United United States, States, 1933-1967 Metallurgical, and Petroleum Engineering, New York, Yo& p. p. 303-325. 303-325. - - 197 lb. Field 1971b. Field Trip Trip A-2 A-2 -- Houghton Houghton to to Calumet Calumet via via South South Range Range quarry quarry and and Eagle Eagle River: River: Society of Economic Economic Geologists. Copper District, Society Geologists, Guidebook Guidebook for Field Conference, Michigan Copper District, Sept. Sept. 30-Oct. 2, 1971. p. 68-75. 1971, p. 68-75. . . flood basalts basalts and continental rifting: rifting: Geological Society of America , 1972, 1972, Keweenawan Keweenawan flood America Abstracts with Programs, v. 4, p. p. 732-734. 732-734. R.W., 1953, Bedrock geology geology of of the Ahmeek quadrangle, White, W.S., Cornwall, H.R., H.R., and Swanson, R.W., GQ 27. 27. Michigan: U.S. US. Geological Survey Geologic Quadrangle Maps of the United States States Map Map GQ White, W.S. and Wright, White, Wright, J.C., J.C., 1956, 1956, Geologic Geologic map map of of the theSouth SouthRange Rangequadrangle, quadrangle,Michigan: Michigan: U.S. U.S. Geological Survey Mineral Investigations Field Studies Map MF 48. L.G., CannOn, W.F., and and Back, Back, J.M., J.M., 1994, mineralization in in the Portage Lake Woodruff, L.G., Cannon, W.F., 1994, Chalcocite mineralization Lake Volcanics Michigan (abst.): (abst.): Institute Institute on Lake Volcanics of the the Midcontinent Midcontinent rift, Keweenaw Keweenaw Peninsula, Peninsula, Michigan Lake Superior Geology Proceedings, Proceedings, 40th 40th Annual Annual Meeting, Meeting, Houghton, Houghton,MI, MI,v.v. 40, 40, part part 1, p. 77-78. Wright, J.C., Bruneau Creek quadrangle, quadrangle. Michigan: Michigan: US. U.S. J.C., and Cornwall, H.R., 1954b, 1954b. Geologic map of the Bmneau Geological Geological Survey Survey Geologic Quadrangle Maps of the United United States. States. �ES. IA: Figure Figure 1A: Route and Stop Stop Map Map 5. 1 'V Fridi South Rings t N Main Main Route Route and and I Q 'p Stop 2p Kilometers Kilometers 3p Number Leg Route and Stop Number �Figure 1B: Index of 1:24,000 Scale Maps 99 See Map Ii A69 Region Covered by Map Number Route and Number See Map Kilometers Leg Route and 5...-. Stop Number � https://digitalcollections.lakeheadu.ca/files/original/6317c926bcd52ad1b187aba51adabc6d.pdf 8a601acd41fe6d8e5c84adeeb20f41b3 PDF Text Text Proceedings 40th Annual Meeting May 11-14,1994 Michigan Technological University Houghton, Michigan Volume 40 Part 3-Volcanic geology of eastern Isle Royale, Michigan By: William I. Rose i I �40TH ANNuAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume 40 consists of Part 1: Program and Abstracts Part 2: Self-guided geological field trip to the Keweenaw Peninsula, Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part 4: Michigan kimberlites and diamond exploration techniques Part 5: Lessons from mining case histories: West Menominee Range, Michigan Reference to material in Volume 40, Part 1 should follow the example below: Woodruff, L.G., Cannon, W.F. and Back, J.M., 1994, Chalcocite mineralization in the Portage Lake volcanics, Keweenaw Peninsula, Michigan Cabst.): Institute on Lake Superior Geology Proceedings, 40th Annual Meeting, Houghton, MI 49931, v. 40, part 1, p. 77. Published and distributed by Institute on Lake Superior Geology M.G. Mudrey, Jr., Secretary-Treasurer, LL.S.G. 106 N 3rd Street Mt. Horeb, Wisconsin 53572 ISSN 1042-9964 All volumes are available for photocopying costs from Michigan Technological University Library Archives J J Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. J �Institute on Lake Superior Geology Proceedings 40th Annual Meeting May 11-14,1994 Michigan Technological University Houghton, Michigan Volume 40 Part 3-Volcanic geology of eastern Isle Royale, Michigan By: William I. Rose Department of Geological Engineering, Geology, and Geophysics Michigan Technological University, Houghton, Michigan 49931-1295 �Table of Contents Preface 1 Introduction 2 Background and Key References 2 The First Day Grand Portage, I\IIN The Isle Royale Fault Washington Harbor Windigo The N Side of Isle Royale: The Hill Point Flow McCargoe Cove The Amygdaloid Channel The Palisades: The Greenstone Flow Blake Point , '" Rock Harbor The Second Day: An OveNiew Day Mount Franklin The Mount Ojibway Tower Daisy Farm Campground Edison's Fishery and The Lighthouse Mott Island Boreal Research Center. Davidson Island The Third Day: A Good Look at the Greenstone Flow Blake Point Porter's Island Red Rock Point Tobin Harbor Lookout Louise The Fourth Day 4: Scoville Point Rock Harbor Scoville Point The Fifth Day Raspberry Island The W Part of the SE Shore: Vesicle Cylinders The Central Part of the SE Shore: Slickenside Surfaces The E Part of the SE Shore: Pegmatoid Zones 12 12 12 12 15 19 23 23 23 26 27 29 29 29 29 29 30 .31 32 32 33 33 34 34 36 36 36 38 38 .38 .40 .40 �The Sixth Day: Back to the Mainland Conglomerate Bay Chippewa Harbor Malone Bay: The Copper Harbor Conglomerate SW Isle Royale: The Glacial Deposits Washington Harbor: The End of Our Trip .43 43 43 .43 .46 .46 Acknowledgments 50 References 50 �Preface (or why people don't go to Isle Royale) Isle Royale has very few visitors, especially considering that it is a national park and is, for many people, within a couple of days travel. This lack of tourism can be explained partially by the park's island location and by the fact that a trip to Isle Royale seems to require a deeper commitment, of both time and money, than other vacations might require. The very people whom you would most expect to want to visit Isle Royale don't go. When you compare the popularity of various national parks, the public's avoidance of Isle Royale is obvious, perhaps even more obvious to me because of my position. As a professor at Michigan Technological University for more than 20 years, I have had direct contact with hundreds of students, many of them geology majors, who are committed to the outdoors and to field experiences. However, very few of these students go to the park, even though they live in Houghton, MI, which is the home of the Ranger III, one of the principal transporters of visitors to and from Isle Royale. Likewise, many of the geologists I have known have visited all of the geological sites around Lake Superior and the other Great Lakes, but only a few of them have been to Isle Royale. This is a remarkable contradiction, something I'm at a loss to explain. It seems to attest to America's addiction to the automobile; maybe people just can't stomach the thought of being separated from their car for a few days! At any rate, I hope that this guidebook will encourage more geologists, as well as other people, to visit the park. Besides the fact that Isle Royale has outstanding geological sites, a trip there can be made at moderate expense, and the park offers comfortable facilities and logistics that most geologists would find agreeable. I recommend taking a week to visit (September is the very best time) and renting a motor boat from the park concession to allow access to the many wavewashed outcrops. Prepared in cooperation with the Keweenaw Volcano ObselVatory, Michigan Technological University, Houghton, Michigan 1 �Introduction .40 This guidebook is meant to be used with The Geologic Story ofIsle Royale National Park by N. King Huber (1983) and does not try to duplicate what occurs in that volume. Instead, the goal is to focus on the volcanic geology that can be observed in the wave-washed shorelines of the Rock Harbor area, emphasizing the physical volcanology of basaltic lava flows. The field trip described here offers the participant a chance to see excellent exposures of large and thick, tholeiitic lavas and to observe the combination of physical features that are associated with slow solidification and segregation. 30- 20 AIL FLOWS N - 224 x -lo.9m 10 MEIAPHYRIC FLOWS N-86 x· S.3m o Background and Key References 10 Huber's work offers a complete background to this trip. It includes a bedrock geological map (Huber 1973) and United States Geological Survey (USGS) Professional Papers on the Portage Lake Volcanics (PLV) (Huber 1973a), the Copper Harbor Conglomerate (CHC) (Wolff and Huber 1973), and the glacial and postglacial geology (Huber 1973b). Since 1973, when Huber's work was published by the USGS, there have been a number of further studies published that are important to the context of Isle Royale. Here, I will cite those that pertain to the Keweenaw section of the Midcontinent rift and to solidification of lavas in particular for those who wish to read more of the current literature. A detailed study of the composition of the lavas of the PLV, as determined by study of a complete section on the Keweenaw Peninsula, was completed by Paces (1988). In this study, Paces provides a general description of the flows with respect to texture and thickness (Figure 1); chemical composition (Table 1); mineral chemistry (Figure 2); and petrography (Table 2), which is described in the following: o 10 l Ll SUBOPmTICFLOWS _ N-SS x -lL6m U ~f."I-l""""--'~--'~--'--"""""--"""""-"'" OPmTICFLOWS N - S2 x·332m 0.1(,': "'Iar," o 20 40 60 i 80 100 ", 120 I ' 140 TIllCKNESS (m) Figure 1: Histograms ofPLV lava flow thickness (Paces 1988). N=number of lava flows; X=geometric mean thickness in meters. The coarsely-ophitic Greenstone flow is not shown. Textural categories are based on macroscopic observations. phenocrysts or microphenocrysts ofplagioclase, and sometimes olivine. Textures that developed within the coarsest portion ofdifferent lava flows range from fine-grained intergranular through subophitic and ophitic. This same range in textures can be observed in individual, thick lava flows which grade from intergranular chilled flow margins to a coarsely ophiticflow interior. True quench textures (Lofgren 1980)"including skeletal, dendritic or spherulitic olivine and pyroxene, have not been observed in PLV basalts. PLV lava flows do not preserve evidence ofan extensive pre-eruptive crystallization history. Chilled margins are generally aphanite. Occasionally, lavas contain minor amounts (usually less than 1%) ofsmall euhedral phenocrysts ofplagioclase (often with melt inclusion-rich cores) and sometimes olivine. When present, both of these phases commonly exhibit glomeroporphyritic tendencies. Neither the plagioclase nor olivine phenocrysts show obvious evidence ofdisequilibrium with the PLV lava flows display a relatively limited number oftextures based on the relationships between dominant mineralogical constituents. These components originally included groundmass plagioclase, olivine, clinopyroxene, iron-titanium oxide, volcanic glass or mesostasis, occasional 2 �= . . . . .z;z' POT Ni(ppI) SiOz Alt33 feet MgO cao NazO ICzO TiOz PzOs MnO on 400-300 na5 300-250 47.82 15.89 9.77 12.44 10.58 2.04 0.19 0.98 0.16 0.14 aaaaaa____aa*-=a OT2 DAC RHY D581297 83JP-7 85MH-' na6 47.34 15.27 11.82 11.69 10.24 2.10 0.22 1.13 0.19 0.16 48.03 15.32 12.32 9.85 10.16 2.25 0.33 1.35 0.22 0.16 48.55 15.12 12.86 9.06 9.65 2.31 0.42 1.60 0.25 0.18 49.94 13.28 14.91 7.78 6.64 2.91 1.43 2.34 0.36 0.24 56.39 13.78 9.87 5.52 5.10 3.94 2.27 1.83 1.00 0.30 68.44 15.17 4.46 1.14 1.40 4.74 3.86 0.51 0.19 0.08 77.89 12.77 1.11 0.17 0.01 3.67 4.28 0.08 0.01 0.01 305 203 1365 431 113 1804 54 126 106 30 245 31 212 14 514 263 59 6 627 7 13 81 62 879 0 5 105 5 61 25 129 36 35 145 68 1127 13.4 30.6 4.50 1.51 0.88 2.46 0.38 0.66 3.11 1.31 30.62 54.4 139.0 14.00 3.44 2.77 9.41 1.39 2.64 16.13 10.32 11.43 39.9 96.2 8.57 0.95 1.97 6.70 1.00 3.52 7.29 16.30 2.73 189 Mn eu 1090 326 37 230 260 1316 27'9 51 2n 64 80 Rb Sr Y Zr Nb Ba 12 358 20 78 4 108 6 253 20 6 154 255 213 1250 231 73 7'9 5 267 20 101 7 200 La Ce 6.7 15.0 2.49 0.96 0.46 .. 1.47 0.21 0.43 1.74 0.55 24.86 8.2 18.4 3.13 1.14 0.61 1.7'9 0.27 0.48 2.09 0.77 28.19 10.5 23.7 3.74 1.33 0.71 2.00 0.30 0.55 2.57 0.97 28.25 Eu Tb Yb Lu Ta Hf Th Sc sses naB 286 8~ 1n 86 85 8 283 23 126 8 265 100-15 AHO ...-a. 200-100 V Snl FOT = 250-200 na14 na9 Cr Ni lOT - 25.8 58.7 7.91 2.12 1.58 4.43 0.64 1.14 5.n 3.39 34.61 16 2282 10 5 146 51 335 47 430 28 757 48.6 117.2 13.78 3.84 2.51 6.94 1.04 1.77 10.44 5.94 21.06 88 45 573 55 Table 1: Average major and trace element compositions for eight groups ofPLV lavas (paces 1988). Tholeiites were grouped by their Ni concentrations with criteria listed in the first row and the number of samples in each group in the second row. POT=primitive olivine tholeiite; OT1=olivine tholeiite 1; OT2=olivine tholeiite 2; IOT=intennediate olivine tholeiite; FOT=Fe-rich olivine tholeiite; AND=andesite; DAC=dacite; and RHY=rhyolite. The last three columns are individual analyses. Oxides are given in weight percent, trace elements in ppm. 3 �I PLV.... I PLt-em I I 11111111 I I I III 1111111111 II I IUIII • II nail.... I III••• ' I III NSVG I I 1M lUll 111111 I 1111111 !YUill 60 40 I liquid. Except for rounded plagioclase cores, both olivine and plagioclase phenocrysts are in apparent textural equilibrium with the liquid. Slightly porphyritic lavas frequently exhibit serrate textures. The dominant textural element in all lavas is the framework ofgroundmass plagioclase laths. This framework is a randomly-oriented, felt-like structure ofinterlocking euhedral to subhedral laths. Rarely, the partial alignment oflaths forms crude trachytic fabric, indicating movement of magma after at least partial crystallization. The second most prominent textural element is defined by clinopyroxene crystals and their relationships to the plagioclase lathframework. In all cases, clinopyroxene has clearly crystallized later than olivine and plagioclase. Clinopyroxene crystals exhibit intergranular to ophitic textures depending both on the size ofthe clinopyroxene crystals as well as the size ofthe plagioclase laths. Melaphyricflows and chilledflow margins contain small, blocky clinopyroxene crystals intergranular to the plagioclase framework. In many (but not all) thickerflows, clinopyroxene grains begin to enclose subophitically, and eventually ophitically, plagioclase and olivine crystals as the massiveflow interior is approached. The boundary between PLAGIOCLASE 80 %An CLINOPYROXENE PLY II 111 I .11 III I NJvG 1I11UI.11lIl IlflllllnllDUOU'1 I 111 I III II I I I I I 0.70 0.60 II 0.80 mg' OLIVINE I PLY I NSVG I ~ I I I 11111111111 I 1 II liD III I Dl111 ~ ~ ~. Figure 2: Compositions ofminerals in PLV primitive olivine tholeiites compared to those available from North Shore Volcanic Group primitive olivine tholeiites (Paces 1988). Each line represents a single analysis. The North Shore Volcanic Group data was taken from BVSP (1981) and Brannon (1984). PLV plagioclase compositions are sub-divided into groundmass (PLV-gm) and phenocryst (PLV-p) crystals. Olivine Basalts N-8 Groundmass Plagioclase Clinopyroxene Olivine Fe-Ti Oxides Glass Vesicles Phenocrysts Plag ± Olv Basaltic-andesites N-3 Typical Range Typical Range 41 23 18 4 10 4 (39-56) (19-29) (11-19) (2-13) (4-11) (1-9) 53 18 (50-55) (16-22) 7 19 3 (6-10) (15-25) (1-10) <1 «1-9) <I <1 Table 2: Petrographic modes, in volume percent, ofrepresentative PLVolivine basalts and basaltic andesites (Paces 1988). Model analyses are based on SOO-spot point counts on a 0.6 x 1.2 mm grid. 4 �Vesicles are particularly well preserved in thinner flows which quenched rapidly; however, they are observable in some thicker flow interiors as well. subophitic and ophitic textures is gradational and is exceeded when a significant number ofplagioclase laths are completely enclosed by the surrounding clinopyroxene oikocrysts. Absolute size of the oikocryst is not definitive: a large clinopyroxene grain may only subophitically enclose large groundmass plagioclase laths, however the same sized grain may ophitically enclose plagioclase laths ofsmaller dimensions. Thus, over half, 60-70% (volume basis), ofmost PLV lavaflows are typically composed ofa plagioclase lath framework with loosely packed clinopyroxene oikocrysts. The remaining interstitial space within the plagioclase framework and between oikocrysts is filled with variable proportions ofintergranularolivine, iron-titanium oxides, and intersertal volcanic "glass. " Evidence ofgas exsolution is preserved in some flow interiors as vesicular cavities ofellipsoidal to highly irregular shapes. Diktytaxitic textures, however, are not apparent. --Paces 1988 Two conclusions emerge from Paces work: (I) the lavas are compositionally similar throughout the section and generally are high magnesium, olivine tholeiites; and (2) the flows range from less than 10 m (33 ft.) to more than 100 m (330 ft.) thick, and the thicker ones are more likely to have ophitic textures. Paces and Miller (1993) have recently published a summary of age information on the igneous rocks of the Midcontinent rift (Figures 3 and 4), which shows that the PLV represents one of the last events of the approximately 25 million year period of rift magmatism. Lane (1911) describes the first recognition of the mirror image geology and lithological similarity ~@ Volcanicroclcs ICNEOUS . . Plutonic roclca ROCXS ~ Hypabyssal rocks Ontario Y '" A1lcaline intrusions Diabase dikes :I( :I( Ontario * 100 1 ISO I Scale Figure 3: Generalized middle Proterozoic geology ofthe Lake Superior region (Paces and Miller 1993). Major igneous units are abbreviated as follows: DC=Duluth Complex; NLS=Nathan's layered series; BBC=Beaver Bay Complex; NSVG=North Shore Volcanic Group; CCD=Carlton County dikes; PRI=Pigeon River intrusions; LS=Logan sills; OVG=Osier Group; CC=Coldwell Complex; PD=Pukaskwa dikes; MIF=Michipicoten Island Formation; MPF=Mamainse Point Formation; MBD=Marquette-Baraga dikes; PLV=Portage Lake Volcanics; LST=Lake Shore traps; PMG=Powder Mill Group; MC=Mellen Intrusive Complex. Volcanic units are differentiated on the basis of remnant magnetic polarity (N=normally polarized; R=reversely polarized). Major graben-bounding faults are shown as heavy, labeled lines. 5 �NMichigan Thunder Bay KLJnsas NW WISconsin MpigonBay NE Minnesota E Ontario Magnetic Polarity 1090 ~ N 1100 <t: 1110 Figure 4: Generalized stratigraphic correlations and absoLute age determinations for Midcontinent rift rocks exposed in the Lake Superior region and subsurface Kansas (Paces and Miller 1993, modified after Green 1982). Unit abbreviations are the same as in Figure 3, with additions: SB=Schroeder basalts, and GC=Great Conglomerate. Episodicity of volcanism is schematically portrayed by the amplitude of jagged curves, implying eruptive frequency and volume increasing toward the right. Major intrusive events are indicated by vertically ruled polygons, and major episodes of clastic sedimentation are denoted by horizontally ruled areas. The boundary of the major reverse-to-normal magnetic polarity switch is placed between 1099 and 1100 Ma, but it is uncertain at a level of 23 million years. lONG ANO DAVIDSON TOMkEIEFF 119401 SPRY 119621 SYVANSQN 119671 119811 VESICULAR -,. FLOW TOP COLONNAOf PSEUOOCOLUMNAA IUPPERI 'ON' COLONNADE ENTABlATUAE ENTAIlLATUAE ENTABLATURE ENTA81A TURE CURVICOLUMNAA ZONE COLONNADE IlOWEAt COlONNADE 8ASAlOR COLONNADE LOWER COLONNADE PtltOW PAlAGOHITE P4ll0W APPROXIMATE VERTICAl. SCALE METERS FEET ':jt; -,2 T03m ~ COMPlEX lONE "CPS108·'188 Figure 5: Typical intraflow structures present in Grande Ronde Basaltflows (Long and Wood 1986). Fractures are represented in a stylized manner, and fracture widths are not to scale. 6 �------~~:) 0 ~ -- JO ~ / c[~ N SHORELlN~ I~~:~~S .- AG I ~.z::!~~ -u•• < LljE G I ;"' I ~=;-;:=.=:A! BSlgG~,::...i4:t- ~-';-'!=: .~4.i·. 5.3klllfJ·· ....~~ ' 30,00 ' -:~. -- s,•. \r:.. S~H~r;:rR ""':- ~'7GE ~~I 20PO I I I Shot IOpO Points. MANITOU, IS. I -!!\;:;f~~?;/'~~"rr'''~, 'S~.t.>~... ~... .-' <?9r';;:;'~1~J ._ ~', ..._::,kU ':.", SHORELINE I JS ~: ;"'~' ;: -::: ..;;'?!£J"ff --..,..' e!l/oa:.p,· ... , " \~",- ~'~6~'" "':6~:·,,· .. ,'.. Sedinil\llts i • •;,'1 :-.'. "l1' '.'""",''"'--~~, Bl;VlJt~..,j' 1J.'~ -;.. ."""pfV·: \:~-: 'I ...'I. Vol'anl~sL.'.· '~', ~ ':"~ ,;\\~"'".:."JC~·,,;-:.~~~~~~~ ~>.;o-~--:.:.. ""~'-<'-' :,~, ':'~."''? .~~~ ,_, .. -46. "j "'.1' '.. '~1~';- \1.. ".~"" '•• _, l'p1:iV~ . ~ 3 I- I- 10 10 15 -i'.1=~~~"':'':::;: ",_ca.:;_:-"i . ".' . .::::; •. I ~._- .-;::...:..~ - .... :-~ ~ ~ .- ":'.:'. -'- - ~... t~·.~~!-># - CHANGE IN SIlOT POINT , SPACING 3000 ....... .. _-- . ~: ~;~:~.>. ~. .;., :.,,: .,. ... ,. ~~ s..... ... ~ .. .r-~, ~"~~ -.-.,' ,. ..... ~ -l, I \ . ''''-'''1. .:t>., . ' . ....... _~~1'.} ': .", ',~ ....... - ""1\".... , ~ l .... ...... .~-~~.~? . I- 1000 Shot Poln" 2000 ... "F .. 15 -:-=~~~~ :, ' ::..,." .. ... . - ': .: !.;::.~ .~-: ... '" ",:.~:: I- 10 10 ~~". ~""'''~'''''''.'' ." .~ .::,0~: -="7'"":":;. ~. ~ . :; '0. .~. : c' .~. -,,~. "., ;, ~. ,;jt~:,:i;~n . ;- 15 ~.- 20 LINE A. MIGRATED Figure 6: Top: Interpreted reflection profile along line A showing the subsurface geology beneath central Lake Superior (Cannon et al. 1989). Bottom: Migrated seismic reflection profile along line A (Cannon et al. 1989). Vertical scale is seconds of two-way travel time. Vertical exaggeration is 1: 1 for average velocity of 6 kIn/s. S AG �.. ;:: 10 \0 ~. -: ' . "__ ,"7·'.'· "'- 15 ,!'..... _.- 00 ... ~.~;-':'.~ - • 500 -.' .W ';-. .... .~._.::~:::' .... 15 \.4":".".; ~;'4' ..•__ .;~ ~. .:-::'."~':";;;~':f~"I~~~~~'_.~. ",~, .~. ''',.' ..," Shot 1500 POi.., 1000 .. , . , 0 . . :~.;I.i~:Ij>~:i!~~~~ 5 3 ;:: .... 10 10 .':' } ·}-15 '5 LINE C, MIGRATED o \0 Figure 7: Top: Interpreted reflection profile along line C, showing subsurface structure beneath W Lake Superior (Cannon et al. 1989). Inferred subsurface units are projected updip to their exposed extensions on land in N Michigan and Minnesota. Bottom: Migrated seismic reflection profile along line C (Cannon et al. 1989). Velocity/depth profiles determined from refraction surveys were used to calculate depths to reflectors. M=approximate location of Moho; AG=Archean Gneiss; PLV=Portage Lake Volcanics; pPLV=pre-Portage Lake Volcanics; NSV=North Shore Volcanics Group; OG=Oronto Group; BS=Bayfield Group; and AnG=Animikie Group. Vertical scale is seconds of two-way travel time. Vertical exaggeration is 1: 1 for average velocity of 6 kmIs. �of the PLV and the CHC on both sides of the syncline and further suggests that the great lava flow of the Keweenaw Peninsula and the large flow of Isle Royale are the same. Huber (1973a) strongly supports Lane's correlations. Longo (1984), after extensive field mapping and sampling at Isle Royale and the Keweenaw, gives field observations and geochemical data that strongly confirmed the correlation of the Greenstone flow. This correlation means that the Greenstone flow is one of the earth's largest lava flows; according to Longo (1984), it has an aggregate volume of 1650 km3 (396 mP), comparable to the Roza flow of the Columbia River Flood basalts, which is estimated to be 1500 km3 (360 mP) by Swanson et aI. (1975). The areal extent of the Roza, 40,000 km2 (15,450 mi2), is much larger than the Greenstone flow, 5000 km 2 (1930 mi 2), a comparison which results from the ponding of the Greenstone within the rift basin. Thus, the solidification of the Greenstone flow is a kind of magma ocean experiment, the likes of which is rare on this planet. Studies of the formation of columns in lavas are also important to the appreciation of the Isle Royale occurrences. The recognition of the role of water infiltration in the formation of certain kinds of entablature jointing (Figure 5) in the Columbia River Flood basalts by Long and Wood (1986) was an important insight, as was the detailed work on column formation by DeGraff and Aydin (1993) and DeGraff et al. (1989). The work by Goff (1977) provides information on vesicle cylinders in lavas for the Isle Royale occurrences. Green's (1989) paper on the physical volcanology of the North Shore Volcanics gives a valuable comparison with rocks associated closely in time and space with the Isle Royale PLV. The GLIMPCE results (Cannon et aI. 1989) provide confirmation of the rift basin synclinal geometry and allow a more accurate picture of the rift to be developed (Figures 6 and 7). The discussion by Cannon (1994) of evidence that suggests a relationship between the Grenville event and the closing of the Keweenaw rift contributes to the understanding of the rift episode (Figure 8). The consideration of implied tilting of ancient shore- , ' . . ' " . ., : \ ' . . \ . . \ .. ""',',,,,',:,' ... ,' ... , , ' " : \ , .... " , ' ... " ... " I .... ' , .., ' ' " ' : , ' : , ' .... ' , : , ...." : ... " , , , ... , "", I c ,, ' ... \ ' ... \ , . \ , ... , ... \ , ..., , , , , "" , , , ,' ... ,' .. , ... ,,"" "",",'" ,",,", \ , ,; ... ,: ... ,;" ' .. ,':',' ""\~""~""":'"'': ...' , , E Figure 8: (a-e) Schematic depiction ofdevelopment of the Midcontinent rift (Cannon 1994). (a) Lower Keweenawan, broad crustal sag and eruption ofwidespread plateau basalts. Low-angle normal faults and shear zones develop in Archean crust, producing some crustal thinning. Some normal faulting occurs near rift axis but is subordinate to sagging. (b) Middle Keweenawan, early rift valley stage. Continued extension and thinning of crust results in development of a central graben and rift valley by a combination of normal faulting and continued sagging. Volcanism is mostly confined to the rift valley. (c) Middle Keweenawan, late rift valley stage. Central graben expands and deepens. Rotation of basement blocks causes asymmetrical shape. Very thick volcanic accumulations are in the graben, and little or no volcanic flows spread outside the graben. The Archean crust nearly separates by extension on low-angle faults. (d) Upper Keweenawan, thermal collapse and sedimentation stage. Extension and volcanism end. Both the central graben and surrounding areas subside by thermal collapse, and a thick (as much as 10 km) basin develops and is filled with clastic sediments. (e) Upper Keweenawan, tectonic inversion stage. The central graben is uplifted. Original graben-bounding normal faults are transposed to high-angle reverse faults. Rocks of the central graben are thrust up several km or more. Thin sequences (up to 2 km thick) of clastic rocks (not shown) are deposited unconformably on deformed volcanic and sedimentary rocks. 9 �(a) 10 6 4 2 050 60 70 § ~ 'il ::c Tune (years) Composition (wt" Oi) Time (years) Composition (WL% Oi) 100 100 80 80 60 60 40 40 " " " ;,,,,,,,,, ,;,;,;,;,:E~~.ti~~ . .;';' 20 0 " , .... """"", " ,',',',",'...',FIoor layer;',','../ ,......',"...',..., ..., ... ~ " " " " " " , ... " , ... , , , , , , , , ... , "..... , ... ""...... , "" ...""" " ... , , ... ... "" ...... ,,,, ,,, ... ... , "... , ... 0 20 80 90 100 40 80 60 (e) 20 o L..-...L.-.1_..L----L----' 50 60 70 80 90 100 Composilion (wl.% Di) Time (years) Figure 9: History ofsolidification and final compositional profile in lava lakes ofinitial composition DiSoAn20 and 0 initial temperature equal to the liquidus temperature of 1352 C (Worster and Huppert 1993). The curves labelled he' hi, and h f show the interfaces between the crust and the mushy layer, the mushy layer and the melt, and the melt and the floor layer, respectively. lines around the Great Lakes by Clark et al. (1994) is clearly important to understanding Isle Royale, with its abundant evidence of tilted shorelines. The processes that operate during the solidification of tabular magma bodies are reviewed by Marsh et al. (1991). Worster and Huppert (1993) present models developed to predict the patterns of solidification in time and space (Figures 9 and 10); fundamental work to understand solidification in other kinds of materials has been done and is pre- sented by Hellawell et al. (1993). The literature lacks lucid explanations about ophitic texture and its origin. Longo (1984) infers the following: An ophitic texture is produced by large augite crystals enclosing, either partially or totally, unoriented laths ofplagioclase. A qualitative explanationfor ophitic texture, as with all igneous textures, involves fusion entropy relationships coupled with growth rates and nucleation rates (Carmichael et 10 �AIR OR WATER ) c al. 1974). While the magma was cooling slowly, initially abundant plagioclase nuclei grew relatively slowly and were enveloped by faster growing, but less abundant clinopyroxene nuclei. The slower cooling rates offlow interiors typically allow clinopyroxenes (in this study augite ±pigeonite) to grow to larger diameters. In other words, crystals tend to increase in size awayfrom the flow margins. The crystal networkformed by the simultaneous crystallization ofaugite and plagioclase inhibits crystal settling in the flow after extrusion. The ophitic texture imparts a mottled and knobby surface to the weathered outcrop. On the freshly broken surface, clinopyroxene cleavage faces are clearly visible. --Longo 1984 Figure 10: Schematic diagram ofa lava lake that is being cooled at its surface by contact with the cold air or water above it and also cooled by conductive heat transfer to the country rock beneath (Worster and Huppert 1993). A crust of composite solid grows downward from the roof where the temperature, T b' is constant. A mushy layer separates the composite solid from the molten lava, which is convecting vigorously. Internal crystallization, which occurs as a result of the interaction of convection with the kinetic undercooling at the interface with the mushy layer, forms a solid layer near the floor of the lake. A sketch of the temperature field is indicated on the diagram. The full environmental significance of ophitic texture is important for understanding the Isle Royale exposures. We need to know how the rates of crystallization and heat loss work together to produce the jointing, segregation, and textural patterns that are observed. The works cited above, along with others referenced in this guide, contribute more information to our understanding of the geology of Isle Royale. All of these works are valuable as supplements to this field guide. 11 �The First Day Grand Portage, MN Our trip begins at Grand Portage, a national monument and reconstructed fort that commemorates the fur trade era, which began in the sixteenth century and reached a peak in the later part of the eighteenth century. The fort was built in 1778 and abandoned in 1803. Figure 11, from the National Monument, describes the geography of the fur trade and the significance of this site. From Grand Portage we will travel E and eventually go all the way around Isle Royale in a clockwise fashion (Figure 12). The Isle Royale Fault Between the Minnesota shoreline and Isle Royale, the strike of Keweenawan rocks, known as the North Shore Volcanics in Minnesota (1109-1100 Ma), changes from E-W to about N 55° E, where the PLV formation (1096-1094 Ma; Figure 13) at Isle Royale begins. This discontinuity could be partially related to the Isle Royale Fault (Figure 6), which the Voyageur crosses between Grand Portage and Isle Royale. This is a thrust fault, apparently associated with the inversion of the Midcontinent rift and was detected in the GLIMPCE profile collected on a NS line E of the Keweenaw Peninsula (Figures 6 and 7). It is thought to extend W to at least the SW end of Isle Royale, where Isle Royale is mantled with a much thicker portion of glacial till and the glacial features are much more prominent (Huber 1983; see pp. 20-21 and 41-54). Washington Harbor From Grand Portage, we will take the Voy- ::rmirl~~:··'.L.........__ _ ...- ..·t··}------I-~-·j·._ _ . --J •• ••' L- .J. .-n-... .I.__ .~ .___ __ --" -"" ~ --;"0' __ ~-~ ~ SCALE: IN .. ,<r ._--~- .14,_ ~ ~ 't£T SECTION OF THE ClifT min'! in 1850. CLIFF MINE Rketl'h fly A. H. MNlche. nft"f Fnsf"f & Whitnpy. 12 �4; The Great Carrying Place Only three water passages to the Northwest are scored into the broad rock lace 01 the Laurentian Shield which forms the weslern shore of Lake Superior. They are the rivers known loday as the St. Louis, Ihe Kaminlstiqula, and Ihe Pigeon. The last of these Is navigable excepllor a few kilomelers at lis mouth, but a narrow, muddy trail links the lake wllh the navigable walers of the Pigeon. Indians had used this trail lor ages belore the first European explorer, a Frenchman, recorded II In 1722. The French explorers, who continued to search for an easy pauage to the weslern sea, and the French missIonaries, who sought converts In the wilderness, gave the trail Its name-"Le Grande Portage," The Great Carrying Place. It remained, however, lor the Highland Scots and their partners In the North West Company to give Grand Porlage Its place In history as the vltatllnk In a network 01 waterways that nurtured the fur trade empire. ..... w The lur trade of Norlh America developed in the 16th cenlury between French fishermen and Indians along Ihe banks of Newfoundland and the mainland coast. Furs gathered by the French for sale In Europe soon became the cash crop of New France. When fur.bearing animals, partiCUlarly beaver, became scarce, the French traders searched westward. Blocked to the north by the British lur domain 01 the Hudson's Bay Company, the French traders were forced over a long water and land route Irom Montreal through Ihe Onawa River and the Great Lakes 10 Grand Portagegateway to the unlapped lur riches 01 the Northwest. Under British auspices aller 1763, the route over the Grand Portage was Inherlled by independent traders who tounded the North West Company. Theirs was a lur trade empire based primarily on the exporlation 01 beaver lur to supply the particular lasles 01 European fashion. Beaver pelts, Irom which Ihe linest qualily fell hals were made, were In tremendous demand. In July the post at Grand Porlage was the scene 01 the North West Company's annual rendezvous. From the east came canoe loads 01 trade goods Irom the warehouses In Montreal destined for the Interior. From the northwestern outposts came wintering traders wllh loads of furs en route to Montreal. Though II was Ihe North West Company's most Important Inland trading cenler, Ihe Grand Portage post was short-lived; II was founded about 1778 and abandoned In 1803 when the North West Company moved north to avoid American laxation and established the post of Fort William. The buildings at Grand Portage were lellto the elements and quickly disappeared. Traffic along Ihe porlage trail dwlndledj then II, too, disappeared. . 0' o For al least 200 yaars Ihe In· dian birch-bark canoe served as the main transport In the fur trade. The biggest ones, the "canol du maitre," trav~ eled Ihe Great Lakes on the Montrealers' route to Grand Porlege. They were usually , about 11 melers (36 leet) In lenglh and could hold up to 3.5 metric tons (4 tons' 01 cargo, plus e crew of 8 to 16 men. The north canoes or "canot du nord,"' used on the narrow water courses of the northwest were somewhat smaller, about 8 meters (26 leal) In length. From Montreal Ihe raule of the fur trade swept westward lor nearly 5,000 kllome,ers (aboul 3,000 miles) over a network of rivers and lakes, linked by portages In those places where travel by canoe was Impossible. The far northern terminus was Fort Chipewyan on Lake Athabaska. At the peak at the trade hundreds of tons of pelts and trade goods were paddled and portaged each season along this waterway. The short season between break-up and freeze-up of the lee spurred the voyageurs In their dash to Grand Portage, In 5 months they had to cross half a continent and return. In early Mayas soon as the Ice broke up, brigades at lake canoes, laden with several tons of cargo, moved out from Lachine, lust above Montreal at the mouth of the Ottawa River. Eight weeks and 36 portages laler they glided into Grand Porlage Bay. In the north· west. crews of seasoned voyageurs, the "homme du nord." waited for the ice to break up. usually around May 15. Then Athabas\(a brigades, burdened with furs, began traveling down from the fur country to rendezvous in mid-July wilh traders at Rainy Lake and Grand Portage Return lourneys had to gel underway by August 1 10 Bilow narlhmen to be In Chlpewyan and voyageurs In Monlreel by October. Figure 11: Description of the geog raphy of the fur trade in relation to Grand Portage, MN (Grand Portage National Monument 1986). St. Lawfen �/ Figure 12: Shaded reliefmap ofIsle Royale National Park, MI (Huber 1973b). The map was modified to include locations that will be visited during this field trip. Scoville Point Tobin Harbor .... Daisy Farm Campground +:'- .. ~ ~MaJO".Bay 'a,~"9to" Ha..""",. N /' "'" 1 o Windigo o 1 2 3 4 I I I I 5 I I I I I I I 1 2 3 4 5 6 6 I I II 7 8 7 8 9 I I I I I I I I 10 MILES I 9 10 11 12 13 14 t5 16 KILOMETERS �STRAT. HEIGHT (km) ~ ~ ~_ ::l:~ LAJ(£ '" 9 t o ~0 SHORE TRAPS (1087.2 z 1.6 Ma) u u ... 0 ~ ." ;'" -1 GREENSTONE FLOW (1094.0 z IS Mil) <I) U :s0~ -2 ~ -3 ~ r..l 0 ... COPPER CITY FLOW <0( Ill: 0 c. (1096.2 -4 WSittL.-. z nong flow (pm) outcrops S of McGinty Cove, and the Scoville Point flow (psp) outcrops near Middle Point on the S side of Grace Harbor. Figure 16 shows the variations in thickness of the PLV. The thickest flows in this area are the Washington Island flow (pwi) and the Grace Island flow (pgi). Both of these flows occur only locally, from the end of Washington Island to a point between Windigo and Sugar Mountain, a distance of about 14.5 km (9 rni) along strike. The lava flows here dip at 15-20° SE, an attitude that is similar almost everywhere on Isle Royale. Vertical N-S trending fractures, with little offset, cut across the bedrock strata near Washington Harbor. Huber (1983) interprets these as structures related to the warping of the Lake Superior Syncline. S of Grace Harbor, the bedrock of the island is buried by till. 1.8 Mil) Windigo KEWEENAW FAULT Figure 13: Conceptual diagram ofPortage Lake Volcanics showing ages (from unpublished data of Paces). ageur E to Washington Harbor and Windigo (Figure 14), about 35 km (22 mi) offshore. (The keys, to the maps that are shown in Figures 14, 17-21,23, 28,34, and 35, are shown in Figure 15a and b). The bedrock geology of the Washington and Grace Harbor areas includes four large flows that continue all the way to the other end of the island. The Greenstone flow (pg) crosses the center of Washington Island and outcrops in several places SSE of Windigo. The Tobin Harbor flow (pth) outcrops at South Rock, SW of Washington Island. The Mi- Horse whim. The Windigo area was the site of the last serious mining on Isle Royale, from 1890 to 1892. After failure and closure of mines further E, the Wendigo Copper Company (renamed from the Isle Royale Land Corporation) founded a mining venture on 8000 acres of land at Washington Harbor, under the leadership of Jacob Houghton, who was the brother of Douglass Houghton. The town site was named Ghyllbank and was located near the present site known as Windigo. The mine site, about 2 km (1.25 mi) inland to the NE, was named Wendigo. People built roads all around the Wend ofIsle Royale, and 135 people lived at the mine site. The company did diamond drill exploration, as well as extensive trenching. In 1892, the miners gave up Sketch by A. H. :\Ieuche. after F05ter & Whitney. 15 �tr. Cove ~ ':I:: j~':~/""" ........ ~ \..; ~ '< tr. ~ '<' Figure 14: Geologic map of the S end of Isle Royale (Huber 1973). 16 j �~ 0 C) Copper 0 0 Harbor 0 o Conglomerate 0 0 Named lava flows: ~ 0 o 0 0 0 0 I I 0 rT ~.~.o'.·o,o 0"'·0_0 QoO Scoville Point Flow (porphyrite) (psp) Edwards Island Flow (trap) (pei) -I ( Unnamed rock sequences: ~ Numerous thin ophitic flows with as many as seven interbedded sandstone and conglomerate units (see fig. 17 for details) Several thin ophitic flows I Conglomerate-known from drill records Middle Point Flow (porphyrite) ++ Long Island Flow (trap) (plil Several thin ophitic flows I Sandstone-known from drill records Tobin Harbor Flow (porphyrite) Washington Island Flow (ophite) Tuff-breccia Greenstone Flow (ophite) Conglomerate-known from drill records Grace Island Flow (porphyrite) ~c;> • c • 0 0.0 • 0 • Sequence of thin to thick (more than 100 ftl flows chiefly ophitic, with one or more sedimentary units suggested by drill data Tuff-breccia Minong Flow (trap) (pm) I o Huginnin Flow (porphyrite) Hill Point Flow (ophite) (ph) \ ......... ..... 0 I 0 I 0 ... Sequence of thin to thick flows, chiefly ophitic, with one or more sedimentary units suggested by drill data 0 I , _ / ...... I " 11 r T-{ I r One or more ophitic flows present locally (php) Sequence of thin to moderately thick flows, chiefly ophitic. Several sedimentary units and a felsite indicated by drill records o· Breccia Amygdaloid Island Flow (trap) (pai) I Lava flows, chiefly ophitic Figure 15: (a) Key to maps shown in Figures 14, 17-21,23,28,34, and 35 (Huber 1973). This is a schematic columnar section of the PLVon Isle Royale; not drawn to scale. 17 �Figure 15: (b) Marked reliefmap, showing which sections ofthe map are enlarged in Figures 14, 17-21,23, 28,34, and 35 (modified from Huber 1973b). N 36 f-' ClO o I 1 I 2 I 3 I 4 I 5 I 6 I 7 I 8 I 9 I 10 MILES I �w_.... on,~ .... ~~-/l[~ l~ f;f~ P_I"~ 'SLEL J~OYAlE ~r ~ I ~.D =--- ~ .= . C ~ o~_ c:=-----? ~ _ ~ 1~MILES INDEX MAP SHOWING LOCATION OF DRILL HOLES AND INDIVIDUAL CROSS SECTIONS USED IN CONSTRUCTING LONGITUDINAL SECTION --i _ _ au"L-__-.:.:p'-----t-- II Bee of Gr"""one Flow t F,- _of _ GREENSTONE Edwwd> I".... ~ - ~. FLOW --- ---.----~ hned.,dIItum ~ i ----~--if'-=-t---=-----+------I----+----+------+---t------=::::i--"""'---- e.. of M<nona Flow '0 FEET 2000 r SCALE lOOO~ o o 5 MILES Figure 16: Longitudinal stratigraphic section showing variations in thickness ofthe PLVon Isle Royale (Huber 1973a). and left. When mining stopped, the company tried to sell land to tourists and resort owners (Rakestraw 1965). ophitic flow, which forms imposing cliffs along the shore from Hugginin Cove all the way to Todd Harbor, a distance of about 24 km (15 mi) (Figures 1719). This flow also makes up the majority of shoreline from Pickerel Cove all the way to Hill Point itself, at the Wend of Five Finger Bay, about 64 km (40 mi) from Windigo. The tilted strata along the shore make the shoreline steep, and the prevailing winds from the NNW can make conditions treacherous for small boats. The Hill Point flow is a coarse-grained, ophitic unit with augite oikocrysts of 2 cm (0.8 in) or more. The N Side of Isle Royale: The Hill Point Flow From Windigo and Washington Harbor, we will take the Voyageur first N and then E along the N side of Isle Royale. With the flows dipping toward the SE, moving toward the N side ofthe island takes us further into the PLV section, until we reach the horizon of the Hill Point flow (php). This is an 19 ��------------------- .< < ,,~ ~ <t '<cO < ;:.""' .:3'" ....... t < Ct:: ....... V:: -Figure 18: Geologic map, showing Lake Desor to Todd Harbor (Huber 1973). This map shows the portion of Isle Royale that is just NE of the portion shown in Figure 17 (see Figure 15b). " �J' ,GoG t 0 .« «. ." .z: <! to ,,-" c' ,'b ," 2'" ,0 r:.:te" c:r:,' o • "tJ (;;'0 tl· (\:" ~'" \\'\t .~.,.~Iif '~IJ [llb\\ vr 4<11t ;'II,;;;" . ce Figu;e 19: '-.J <;) [.~:! "'..'". Ge~logic map, showing Todd Harbor to McCargoe Cove (Huber 1973). This map shows the portion of fc Isle Royale that is just NE of the portion shown in Figure 18 (see Figure ISb). b t:' I~ ~ �The vertical fractures are superimposed across the dipping strata and are noticeable throughout the entire flow. From the W area of the flow to the E area, the fractures gradually begin to change from N-S to more N-E trending. According to Longo (1984), the Hill Point flow may correlate with a large flow on the Keweenaw Peninsula, the Scales Creek ophite, which extends all along the Keweenaw Peninsula for more than 160 km (100 mi) of strike length, and right through Houghton, which is about 110 km (68 mi) SSE of Hugginin Cove. McCargoe Cove At the midpoint of the island is McCargoe Cove (Figure 19), which is a fiord-like, 3.2 km (2 mi) long inlet that follows a large fracture zone, trending N 30· E to a campground site located along an ancient Native American portage route and near another mine, the Minong Mine. Native Americans left hundreds of ancient pits as relics of mining over centuries at this site, and in 1874 three companies were formed in Detroit to exploit the potential here. They built a dock and a warehouse and started to build a railroad. Some large masses of copper were successfully mined, and the community here grew for several years in spite of difficult winter conditions. But mining did not last beyond 1885 (Rakestraw 1965). The Amygdaloid Channel From McCargoe Cove, we will continue to the NE (Figures 20 and 21), passing through the Amygdaloid Channel. Amygdaloid Island is composed of the oldest lavas of the PLV on Isle Royale and is supported by a large flow, the Amygdaloid Island flow (pai), which is a fine-grained basalt (termed "trap"). At the Wend of Amygdaloid Island is the National Park Service (NPS) ranger station near Kjaringa Kjeft. Crystal Cove is 3.2 km (2 mi) E of the station, which was, beginning in 1906, a private residence and fishery. As we travel through the Amygdaloid Channel, the drowned ridge and valley topography of Isle Royale will become very visible, with more resistent lava flows holding up linear islands. Shipwrecks are numerous on the many "reefs" found all around the NE end of Isle Royale. Opposite of Crystal Cove on the S side of Amygdaloid Island is Belle Isle, which is a beautiful campground, accessible only by boat and canoe, located on the site of a resort that operated in the 1920s, serving the grand lake steamers of that period. The Palisades: The Greenstone Flow From this point, we will head toward the tip of Isle Royale to Blake Point (Figures 21 and 22), moving up in the stratigraphic succession. We will first cross the Hill Point flow (php) at Hill Point, then the Minong flow (pm) near Locke Point, and finally the Greenstone flow (pg) at the Palisades. The Greenstone flow is perhaps the earth's largest lava flow. The following are comments by Longo (1984): Similarities in the stratigraphic sequence of Isle Royale and the Keweenaw Peninsula ofMichigan were recognized by numerous workers prior to 1851. The first thorough study ofboth areas, conducted by Lane (1893, 1911), resulted in the correlations ofspecific rock units. One unit in particular, due to its persistence as a prominent ridge on both Isle Royale and the Keweenaw Peninsula, became Lane's most convincing evidence for a correlation across this section ofthe Lake Superior syncline. Lane (1893) states, "The backbone ridge thus agrees in every way with the great corresponding ridge on the Keweenaw Point. " Outcrop and drill core data by Lane (1893) reveal this unit as a single immense, differentiated lava flow. Lane (1893) refers to the flow as "the Greenstone, the 'backbone' and biggest ophite ofall, with the bed at its base we correlate as the Allouez Conglomerate. " The Greenstone's great thickness and differentiated nature led some workers to consider it as an intrusive sill (Seaman and Seaman 1944; Van Hise and Leith 1911). However, convincing data have proven this unit to be a lavaflow (Lane 1893,1911; Butler and Burbank 1929; Broderick 1935, 1946; Cornwall 1951), and henceforth known as the Greenstone flow. Huber (1973a) confirms the similarities ofthe Greenstoneflow on Isle Royale and the Keweenaw Peninsula, and he supported the correlation. --Longo 1984 The columnar character of the exposure seen at 23 �---------------- - ( -'? \ ~~~1 I •• ~. Figure 20: Geologic ""'P. showing Amygdaloid lskmd to Five Finger Bay (Huber 1973). lion of ble RnYale thau, ju'! ME of the po,""On Mown in Figure 19 (""" Pigore ISh). ~~ <:;Q'§!! ;,r'b o"- ~ Q:-0- "fo ��GEOLOGY OF THE GSF BLAKE POINT, ISLE ROY ALE, MICHIGAN T67N R33W Blake POlllt B o Pyr.et... Uc. Br.ccia. O*her fl.-• ••••••• Mel.. phy.. e Contact Figure 22: The geology ofthe Greenstonefiow at Blake Point on Isle Royale (Longo 1984). the Palisades is interpreted by Longo (1984) as a colonnade, following the terminology ofTomkeieff (1940). The cliffs are formed in the lower part of the great lava flow, which is 122 m (400 ft.) thick at the Palisades. The unit that comprises the cliffs is called the lower ophite and is about 30 m (98 ft.) thick. The rude columns are typically a few meters in diameter, and the rock is a coarse ophite with large pyroxenes enclosing many tiny plagioclases. The pyroxene oikocrysts increase in size from the bottom until they reach about 1.5 cm (0.6 in) in diameter near the top of the lower ophite. The lower ophite commonly forms steep anti-dip slopes on the N side of the Greenstone ridge (Huber 1973a). We will return to the Palisades and will also walk around to Blake Point later in the trip to look at this exposure more carefully. Blake Point As we take the Voyageur around Blake Point, we will see that the layers of the Greenstone flow are clearly delineated (Figures 21 and 22). Under the navigation light at the water line is the contact between the lower ophite and the pegmatoid (or pegmatitic) zone, about 23 m (75 ft.) thick. The pegmatoid represents the flow interior and has a texture that is strikingly different from the ophite, consisting of a mat of interlocking plagioclase laths as long as 2 cm (0.8 in) each. The pegmatoid is a bit less resistant to weathering, causing an indentation of the shoreline S of the light that marks the pegmatoid zone. Farther S, a cliff face with columns marks the beginning of a third layer of the Greenstone flow, the upper ophite. Like the Palisades, this part is also marked by colonnade columnar jointing. We will 26 �have an opportunity to examine this location on the ground later in the trip. The uppermost parts of the Greenstone flow consist of an entablature jointed part, which is locally prominent, and a fragmental flow top with abundant agates. The flow top is not well exposed because it erodes much more readily than the interior. Around the point, we will pass between Third Island and North Government Island. On the N side of Edwards Island, exposures of entablature style columnar jointing are spectacular in the Edwards Island flow (pei). N of Edwards Island are exposures of the Long Island flow (pH), recognized by characteristic blue agate amygdules. Both of these flows can be traced along Tobin Harbor and through scattered outcrops as far as 50 km (31 mi) to a point near Hay Bay (Huber 1973). Rock Harbor Heading SW to Rock Harbor (Figure 23), we will pass Scoville Point, which is the site of the Scoville Point flow (psp), a porphyritic basalt with fine, equant, millimeter-sized plagioclases. This flow extends all the way across Isle Royale and is very resistant to erosion, forming shoreline exposures and topographic highs. We will see this flow on numerous occasions throughout the next several days. Rock Harbor is the National Park's main visitor center and the location of the only hotel on Isle Royale, Rock Harbor Lodge. Upon arrival, we will be taken by a smaller boat to Three Mile Campground about 5 km (3.1 mi) farther SW. 27 ��The Second Day: An Overview a fire tower. Now it is used for monitoring acid rain, along with other environmental monitoring. We can climb the tower stairs for full views of the surroundings, both to the Nand S. Day Mount Franklin The day begins with a morning hike. We will take the Mount Franklin Trail, which begins 0.3 km (0.2 mi) W of Three Mile Campground (Figure 23). The trail immediately climbs a ridge supported by the Scoville Point flow (psp), then levels off and descends. We will cross a boardwalk over a swamp and arrive at a valley where there is a junction with the Tobin Harbor Trail, 0.8 km (0.5 mi) from Three Mile Campground. We will continue on the Mount Franklin Trail, straight ahead, crossing the Tobin Creek swamp and then climbing a ridge underlain by the Tobin Harbor flow (pth). From here we will descend to cross another swamp and then begin the 300 ft. ascent of the Greenstone ridge. The entire swamp and ascent is underlain by the great Greenstone flow (pg). At the top of the ridge there is a junction with the Greenstone Ridge Trail, which we will take left to go about 0.5 km (0.3 mi) to Mount Franklin, elevation 330 m (l080 ft.). Here there is a good view of the N side of the island, including Five Finger Bay, Lane Cove, and Amygdaloid Island, as well as of the Canadian Shoreline, including the Logan Sills and the Sleeping Giant. The Greenstone flow is indeed the backbone of the island, forming the most prominent ridge all along; only at Blake Point, however, is a reasonably complete section through the flow exposed. The contact between the pegmatoid and the lower ophite units of the Greenstone is mainly located near the crest of the Greenstone ridge. The lower ophite underlies the N slope, which is a steep, anti-dip slope, and the pegmatoid armors the gentler dip slope to the S. Daisy Farm Campground From the tower we will descend to the Daisy Farm Campground via the Mount Ojibway Trail. We will go down from the ridge to the first level spot and then begin to rise over a smaller ridge. The beginning of this small ridge is the approximate location of the top of the Greenstone flow; the ridge top and the dip slope to the S is underlain by the Tobin Harbor flow (pth). At the base of this ridge we will cross a swamp fed by Tobin Creek. Then we will ascend Ransom Hill, which has the Long Island flow (pli) on its anti-dip (N) side and the Edwards Island flow (pei) on its dip slope (S) side, where there is some entablature jointing. From Ransom Hill, the trail descends to Daisy Farm Campground. Daisy Farm is located on the site of an old mining community, called Ransom, which was founded in 1847 with the clearing of land and the construction of a smelter. The mining prospects dimmed quickly, however, and the mining activity ended only two years later in 1849. Then, in 1866 all the buildings burned down. In later years, the place was the site of a sawmill, a garden that supplied vegetables to Rock Harbor Lodge, and a Civilian Conservation Corps (CCC) camp, which was a foundation for youth employment, developed by Roosevelt during the depression (Rakestraw 1965). Edison's Fishery and The Lighthouse From Daisy Farm we will travel by boat across Rock Harbor to Edison's Fishery. The fishery itself is a restored camp that is occupied each summer by a retired Lake Superior fisherman and his family; this man is employed by the park to interpret what life was like here during the heyday of Isle Royale Fishing camps, from before the establishment of the park in 1936 until the sea lamprey invasion of the 1950s. The lavas that underlie the site of the fishery and the lighthouse are a sequence of 45-50 ophitic flows (Figure 24), which occur between the Scov- The Mount Ojibway Tower From this point, still following the same trail, we will descend sharply to a wooded area and level off for about 0.4 km (0.25 mi) before climbing again. We will then reach the ridge crest and follow it for another 3.2 km (2 mi), with occasional outstanding views, to the Mount Ojibway tower. This structure was built in 1962 and was used initially as 29 �o 0 0. 0 =- Projechd position of EXPLANATION ille Point flow (psp) and the overlying CHC. As we walk around the point we will see several flow tops exposed, good examples of cellular amygdaloids. This is an excellent place to find greenstone, a nodular, compact form of pumpellyite that is prized as a semi-precious gemstone (Huber 1983, see pp 589). The geological purpose of stopping here is to look at the flow sections along the wave-washed shoreline, following it from this point to Tonkin Bay (no relation to the Gulf of Tonkin!). We can also look at the amygdule mineral suite, which can be found on the pebble beaches. The amygdules of Isle Royale's flows contain a variety of secondary minerals, listed alphabetically (by Huber) as barite, calcite, chlorite, copper, datolite, epidote, laumontite, natrolite, prehnite, pumpellyite (chlorastrolite or greenstone), quartz (agate), and thomsonite (see Table 3 for information about each). The prehnite is unusual in that it contains disseminated native copper inclusions and has a pink color, which has caused some to confuse it with thomsonite (Huber 1969). Overall, the assemblage is zeolite facies and prehnite-pumpellyite facies, representing a slightly lower grade than much of the Keweenaw Peninsula area. This may partially explain the lower abundances of native copper on Isle Royale than the amount found on the Keweenaw Peninsula. [2] .. 0··.....".. - e-200-25Oft 25-30 ft .. end p-~ 1»14Oft 10ft ~ 160-170 ft 25-30 ft 60-70 ft 25-3Oft 1()().110ft 1().15 ft 60-70 it 25·30ft 17().l80ft 15-20 ft 200ft Mott Island Figure 24: Columnar section of upper part of Portage From the lighthouse, we will return to the fishery and take the boat across the Middle Island Pas- Lake Volcanics showing distribution of sedimentary units in the Chippewa Harbor area (Huber 1973). All the ophitic flow zones consist of multiple flows. Mineral Formula Hardness Color Notes Barite Calcite Chlorite Copper Datolite Epidote Laumontite Natrolite Prehnite Pumpellyite Quartz Thomsonite BaS04 CaC03 (Mg,Fe)sAl 2Si 30 lO (OH)g Cu HCaBSiOs Ca2(AI,FehSip,iOH) CaAI2Si40'2·4H20 Na2A12Si301O.2H20 Ca2AI2SiPlO(OHh Ca2MgAI 2Si 30'1 (OHhH 20 Si02 NaCa2AIsSis02o·6H20 2.5-3.5 3 2-2.5 2.5-3 5-5.5 6-7 3.5-4 5-5.5 6-6.5 5.5 7 5-5.5 white white olive - dk green copper white, various pistachio white, red-yel colorless It green-pink green colorless, varied pink vein occurrences vy common, veins, amygdules very common rare, veins, amygdules porcelaineous, opaque crystalline, amygdules amygdules radiating fibers, amygdules radiating fibers, amygdules mosaic, segmented pattern agate amygdules radiating amygdu1es Table 3: Characteristics ofsecondary minerals at Isle Royale. 30 �sage to Mott Island (about 3.2 km (2 mi) NE). We will stop here to visit one of the best exposures of sedimentary units within the PLV, found at the SW end of the island, facing East Caribou Island near the park headquarters complex. There are seven such units mapped by Huber (1973) in the Chippewa Harbor area. Most of them are remarkably constant in thickness and lithology throughout their lateral extents, which are 65 km (40 mi) or more. Paces (1988) reports the following about interflow sediments in the PLV: top of the underlying lava flow top indicating a more-or-less constant and relatively short repose period between eruptions. The infrequent presence of sedimentary beds between lava flows may indicate occasional hiatuses in magma extrusion, which allowedfor alluvialfans to transgress out towards the center ofthe basin. Conversely, interflow sedimentary horizons may mark briefperiods of increased depositional rates possibly related to episodic normal faulting and basin subsidence. --Paces 1988 The pebble conglomerate unit at Mott Island is thicker than most, about 12 m (40 ft.). The pebbles are essentially all of volcanic rock, with mafic varieties about twice as abundant as felsic ones. The sandstones are very feldspathic, plagioclase being most abundant. Fine-grained hematite is ubiquitous. The rocks have scour and fill structure, suggesting an origin in braided stream environments. Desiccation cracks and raindrop impressions have also been noted. Paleocurrent data suggest transport to the SE, similar to the CHC (Huber 1973a). Occasionally, lava flows are separated by intervening sheets and lenses of terrigenous clastic sediment. Twenty two major interflow sedimentary horizons occur scattered throughout the PLV section and are described by Butler and Burbank (1929), White (1952), and Merk and Jirsa (1982). lnterflow sedimentary beds vary in thickness from less than 1 cm (0.4 in) thick fine-grained siltstones filling fractures between flow top fragments to coarse boulder conglomerates over 100 m (330ft.) thick locally. Typically, interflow sediments are poorly sorted, lithologically immature conglomerates and sandstones derivedfrom a nearby volcanic source of some reliefand deposited in an alluvial fan-type environment (Merk and Jirsa 1982). Transportation was generally from the SE to Nl¥, orfrom basin margins towards the center ofthe subsiding graben (White 1952). Although the interflow sediments are volumetrically insignificant within the PLV (3% of the total lithologic volume) (Merk and Jirsa 1982; White 1971), they form distinct and relatively continuous stratigraphic marker horizons within an otherwise monotonous volcanic pile. The occurrence ofoccasional interflow sediments implies that rates oflava flow extrusion, sedimentation, and/or tectonic subsidence were not constant during the formation of the PLV. White (1960) shows that a subsidence-depositional equilibrium was established so that both lava flows and sediments were deposited on near-horizontal surfaces. Most lava flows were deposited directly on Boreal Research Center, Davidson Island Next, we will go by boat for a brief stop at Davidson Island, opposite Three Mile Campground. On this island is the Boreal Research Center, a residence for researchers at Isle Royale. After stopping at the dock in front of the center, we will walk around this small island, visiting another exposure of the epiclastic sedimentary rocks and an exposure of a columnar jointed, ophitic flow on the SE comer of the island. The wave-washed shoreline has exposed a surface perpendicular to the columns, which are 2-3 m (6-10 ft.) across. We will see many exposures of large columns like these in the next few days, as they seem to be a regular feature of ophitic flows at Isle Royale. We will then return to Three Mile Campground for dinner. 31 �The Third Day: A Good Look at the Greenstone Flow Blake Point Weather pennitting, this is a day to visit one of the most dramatic places on Isle Royale, Blake Point (Figure 21). The shoreline around Blake Point offers the best view of the Greenstone flow, better than any other sites at Isle Royale or the Keweenaw Peninsula. On the way to Merrit Lane, the starting point of our Blake Point walk, we will pass several islands that have interesting wave-washed exposures of lava flows. Among the sites we may see from the boat are: the SE sides of Heron, Shaw, and Smithwick Islands, where there are exposures of calcite veins and columnar jointed surfaces like the one we visited at Davidson Island; the SE side of Raspberry Island, which we will visit on the fifth day and which has many interesting features of the ophitic flows; and the NW side of Edwards Island, which has good exposures of entablature columnar joints in the Edwards Island flow (pei). The boat will let us off at the Merrit Lane Campground for our walk to Blake Point. We will follow the shoreline from Merrit Lane around the point, remaining close to the wave-washed rocks, yet trying to keep our feet dry. Most of the walk is on the upper ophite unit of the Greenstone flow. (The entablature part of the Greenstone and its flow top is underneath Merrit Lane, and we will see parts of this from the boat later). The upper ophite exhibits a rude columnar structure all along the walk, with the columns perpendicular to the bedding. The size of the oikocrysts increases from top to bottom. After rounding the comer, we will cut through the bushes to descend a cliff that marks the lower anti-dip face ofthe upper ophite. At the base of this cliff, we will see wave-washed exposures of the pegmatoid, here about 23 m (75 ft.) thick. The contact here appears to be quite sharp, although Huber (1973a) says it is frequently gradational. The following description of the pegmatoid is from Longo (1984): Lacroix (1928, 1929) coins the term ''pegmatitoide" to describe the coarse-grained zones consid- ered to represent the final stages ofdifferentiation in basaltic lavas ofFrance. The lavas ofMichigan's Copper Country show similar differentiates for which Lane (1893) applies the term "doleritic." Cornwall (1951) adopts the textural term "pegmatite" from the usage ofButler and Burbank (1929). He changed the confusing "doleritic" term to "pegmatitic facies, " and subsequently described such units in the Greenstone flow, Big Trap, and several other large flows within the PLVon the Keweenaw Peninsula. For the present study, the term "pegmatoid zone" from Lindsley et al. (1971) is adopted to encompass the portion ofthe Greenstoneflow with numerous en echelon, lens-shaped pegmatoids, associated granophyric phases, and subophitic layers. Texturally, pegmatoids are coarse grained when compared to ophitic zones. Coarse plagioclase laths dominate with interstitial, subhedral clinopyroxene and abundant interstitial to somewhat poikilitic magnetite and ilmenite. Consequently, the pegmatoids are strongly magnetic compared to ophitic units. This suggests that a higher titaniferous magnetite/ilmenite ratio for magmatoids than for ophites. Visual inspection generally reveals a greater overall opaque (oxide) concentration in the pegmatoids. Subophitic layers are often found hosting the en echelon pegmatoids. These layers, like pegmatoids, are strongly magnetic and very coarse grained stratiform features, but contain less abundant, smaller sized pyroxene. The contacts between pegmatoids and subophitic units are usually sharp, although instances ofgradational contacts have been observed. Subophitic layers grade into the ophites and seem to occupy the greatest volume of the pegmatoid zone. They have been observed to pinch out within pegmatoid units and may not be continuous planar features throughout the flow. Perhaps pegmatoid units are not only lens-shaped but also flattened amoeboid-like features interfingering with subophitic layers. The frequency ofpegmatoids and subophitic layers increases proportionally with increasing flow thicknesses. Both vary in thickness and shape and typically occur in the upper halfofa lava flow. Pegmatoids have also been observed as autointrusions, such as in the entablature on Isle Royale and the upper ophite on the Keweenaw Peninsula. The stratiform pegmatoids are usually found armoring the tops ofcliffs formed ofthe lower ophite. The ex- 32 �tension ofweak vertical joint patterns into the pegmatoid (forming crude large columns) suggests that pegmatoids may be part of the colonnade. In most cases pegmatoid zones separate a basal colonnade from an upper colonnade. Pegmatoids are not unique to thickflows ofthe PLV. Lindsley et at. (1971) assert that three ofthe thicker flows from the Picture Gorge Basalt contained pegmatoid lenses. Santin (1969) discusses the presence ofpegmatoids in horizontal basalts of the Lanzarote and Fuerteventura Islands in the Canadian Archipelago. --Longo 1984 The pegmatoid underlies the low shoreline and also the area under the light tower. A section of the Greenstone flow is exposed on Passage Island, a 2 km (1.2 mi) long island that can be seen about 4 km (2.5 mi) offshore from Blake Point. Around the corner from the tower and vertically down about 4 m (13 ft.) is the contact with the lower ophite (which is too difficult for us to reach safely). Longo (1984) describes the contact as a gradation over about 1 m of thickness. From here, we will return by the same route to Merrit Lane. Weather permitting, we will travel around the point in the boat to examine the lower ophite cliffs along the Palisades. The columns exposed on the anti-dip slope are up to several meters across. The base of the Greenstone flow is not exposed here. Porter's Island Upon returning to Merrit Lane, we will head S to Porter's Island, which includes exposures of a fragmental rock that Huber (1973a) interprets as pyroclastic. However, according to Longo (1984), these exposures may represent a fragmental top of the flow. The breccia unit, which is about 1-5 m (3.3-16.4 ft.) thick, contains rounded and semirounded fragments of the Greenstone flow set in a finer matrix that has amoeboid-shaped, agate amygdules. Longo did an extensive perographic study but could not find any evidence of shards or pumice. He did, however, find bow-tie spherulitic plagioclases in the matrix, which suggests an undercooled texture for the basaltic material there. This unit occurs at the top of the Greenstone flow along about 15 km (9.3 mi) of strike length (approximately to Mt Ojibway), according to Huber's map. Similar units are found at the top of the Greenstone flow on the Keweenaw Peninsula (Longo 1984). Figure 25 shows an old drawing of a cross section through Lake Superior, including Isle Royale and the Keweenaw peninsula. Red Rock Point At Red Rock Point, we will pass excellent examples of entablature jointing of the upper part of the Greenstone flow. The basalt of the entablature is Figure 25: An older drawing ofa cross section through Lake Superior, from the Huron Mountains to Port Arthur (Lane 1911). 33 �melaphyre, very fine grained. The curvicolumnar nature of a few of the columns resembles some of the Columbia River basalt descriptions (Figure 5). Long and Wood (1986) suggest that entablature jointing results when extensive floods that are created from deranged drainages cause dramatic quenches of solidifying flood basalts. Around the comer of Red Rock Point is an autointrusion of the Greenstone's entablature zone by material that is apparently from the pegmatoid zone. Longo (1984) describes the feature: develops as the crust of a partly solidified flow founders and causes the upward escape of the flow's fluid interior (Figure 26). Below the water level at Red Rock Point is an occurrence of coarse grained granophyric rock, which can be found in beach cobbles and boulders and may occur within the Greenstone flow itself. Tobin Harbor Continuing to the SW along Tobin Harbor, we will pass Newman Island. Opposite this island on the N shoreline ofTobin Harbor are outcroppings of the volcanic breccia that may represent the fragmental top of the Greenstone flow. We will continue SW to Hidden Lake dock. A large autointrusive dike was found intruding (N 20° W, 65° E) the columnar-jointed melaphyre at Red Rock Point. Despite an apparent lack of aplites, the dike is texturally similar to the stratiform pegmatoid. It is composed ofrandomly oriented, euhedral plagioclase laths with interstitial, subhedral augite and pigeonite (no poikilitic textures occur). The plagioclase laths are immense by comparison to the microlites ofa typical ophitic unit. Three characteristic features of the dike are: (1) the abundant plagioclase phenocrysts (up to 1 cm (0.4 in)), (2) a blue-green hue from plagioclase altered to chlorite in the dike, and (3) alignment of plagioclase laths parallel to the dike contact, forming an igneous lamination. Amygdules are more abundant along the dike contact also. The process ofautointrusion is similar to the mechanisms ofpegmatoidformation, except that after the residual liquid is pressed out of the hosting crystal mesh, the differentiated magma is squeezed up into the vertical tensional fractures. Lookout Louise From Hidden Lake to Lookout Louise, we will hike about 1.6 km (l mi) long and 85 m(280ft.) up. We will begin on the Tobin Harbor flow, but after passing the lake we will on the Greenstone flow, following a dip slope up to Lookout Louise. At about the halfway point, the trail passes Monument Rock (Figure 27), an individual column from the colonnade of the upper ophite that is exposed as an erosional remnant. Huber (1983, see especially pp 47-55) suggests that Monument Rock was formed by wave cut shoreline processes along a former "raised" shoreline, which he associates with glacial Lake Minong, about 10 Ka. From Lookout Louise we will look over the steep anti-dip slope of the lower ophite and see Five Finger Bay, Duncan Narrows, and Amygdaloid Island. The plan is to return from Lookout Louise to Hidden Lake and take the boat back to Three Mile Campground for the night. --Longo 1984 Longo (1984) interprets the auto intrusion to be related to a sag flowout structure, described by McKee and Stradling (1970) as: a large structure that Figure 26: Idealized cross section ofa sag jlowout structure (McKee and Stradling 1970). Following erosion, the dikes commonly remain as topographic highs in a circular pattern around the central sag area. 34 �AcKeonanlith. 37Y.]XOadway N.T MONUMENT ROCK (NORTH EAST VIEW) ISLE ROYALE. Figure 27: An old drawing ofthe NE view ofMonument Rock on Isle Royale (Foster and Whitney 1851). 35 �The Fourth Day 4: Scoville Point lodge lie ancient mine pits, attributed to Native Americans who occupied this area from about 2500 BC during the period of the Nipissing stage. The mining was apparently informal and quite limited in anyone place, but there are more than 1000 such pits all over Isle Royale according to Rakestraw (1965). Rock Harbor For part of this day's trip we will walk on the rocky dip slope of the Scoville Point flow (psp), facing Rock Harbor along the shore. Huber (1973) describes the basalt of this flow as containing "fine, equant, millimeter sized, plagioclase crystals distributed uniformly through a fine grained matrix." He says the thickness is 30-60 m (l00-200 ft.). There are not many features that can be seen in outcrop, but the flow is very resistant to erosion and buttresses the shoreline. At Suzy's Cave, about 1.8 km (1.1 mi) E of Three Mile Campground along the Nipissing shoreline, waves cut a sea arch at a contact between two lava flows about four thousand years ago, selectively eroding the region of the flow top. After passing Suzy's Cave, the trail to Snug Harbor, where the Rock Harbor Lodge is located, parallels the shore of Rock Harbor and lies on thin ophitic flows, which are stratigraphically below the Scoville Point flow. At Snug Harbor (Figure 28), the Scoville Point flow crops out only within the recessed part of the harbor, and the point where the Americas Dock is located is underlain by ophitic flows above the Scoville Point flow. We will take the Stoll Trail, which goes along the shore of Rock Harbor. Along here, we will see Nipissing shorelines and outcrops of the Scoville Point flow. Also, we will be able to see the ophitic flows above and below the Scoville Point flow along the way. About 0.8 km (0.5 mi) from the Scoville Point As we near the Scoville Point, the Scoville Point flow dominates the shoreline and has steep smooth exposures. At the point itself, we will look at the excellent exposures of the Scoville Point flow, the ophitic flows below it, and the Edwards Island flow (pei), which underlies the companion point located just to the NW of Scoville Point. There is a good exposure of cellular amygdaloid in one of the ophitic flows and the Edwards Island flow shows well developed entablature jointing. We will return to the lodge and to Three Mile Campground via the Tobin Harbor Trail, which is easier to hike. It stays near the shore of Tobin Harbor, mostly atop the Edwards Island flow. Just NE of the Rock Harbor Lodge on the return trail is the site of the Smithwick Mine remains; this mine was discovered in 1843 and actually operated in 1847 and 1848. The work done here mostly consisted of exploratory shafts and excavations, and it is unclear whether or not much ore was found (Rakestraw 1965). From Rock Harbor Lodge we return to Three Mile Campground via the Tobin Harbor Trail. 36 ��The Fifth Day Raspberry Island We will go by boat to Raspberry Island (Figure 28), about 0.5 km (0.3 mi) SE of Rock Harbor Lodge, and spend the entire day looking at a remarkable set of exposures nearby that provide an impression of some of the solidification features of an ophitic flow (approximately 20-30 m thick). Raspberry Island, which is one of many small islands along the S side of Rock Harbor, is a sequence of three ophitic flows dipping 15° SE. The uppermost of these flows is extensively exposed on a wave-washed dip slope along the SE shore. This shoreline receives strong storm waves and, therefore, has extensive wave-washed exposures about 1 km (0.6 mi) long. These expose the flow interior, although neither the top nor the base of the flow is clearly exposed. A loop trail goes around the W half of the island, marked by informative signs about the unique ecosystem of this island, which features frequent fog and damp, moss-rich swamps. Among the unusual plants is the pitcher plant (Sarracenia puerperia), which is an insectivorous plant that flourishes in the swamp along the loop trail. First, we will visit the most W point of the island, where the regional attitude of the lava flows is seen in the view along strike toward Smithwick Island across the Smithwick Channel. The point facing the channel on Raspberry Island is underlain by the oldest of the three flows on Raspberry Island. We will walk on a dip slope that shows some of the jointing pattern we observed on the SE sides of Davidson and Smithwick Islands. Next, we will head to the SE corner of the island to observe some rude columns in the uppermost Raspberry Island flow. The W Part of the SE Shore: Vesicle Cylinders We will next move out to the wave-washed SE shore, where there are two zones of exposures of vesicle cylinders. Paces (1988) describes vesicle cylinders (Goff 1977) in the PLV: Vesicle pipes are elongated, tube-like struc- tures, 10-30 cm (4-12 in) in diameter and 0.5-2 m (1.6-6.6 ft.) in length, containing somewhat coarser and more prismatic crystals compared to the adjacent groundmass. They are oriented vertically and occur predominantly in the bottom halfofthe flow. The origins and dynamic behavior of vesicle cylinders are poorly understood; however they appear to represent an accumulation ofexsolved magmatic gas bubbles which migrate upwards through the magma during the period when the cooling magma behaves as a Bingham plastic (i.e., possesses afinite yield strength, Walker 1987). --Paces 1988 Here at Raspberry Island, exposures of vesicle cylinders show a regular spacing between them, 13 m (3-10 ft.) apart, and a marked variety of textures; some were evidently preserved almost as voids, while others are filled with material that closely resembles vesicular pegmatoid. An interesting aspect of the exposures here is the relationship between the ophitic textures of the flow and the vesicle cylinders: The grain size of oikocrysts seems to be influenced by the proximity to the vesicle cylinder. Vesicle cylinders are found mainly in only two areas along this shoreline. This may reflect their restricted occurrence in a thin part (less than a few meters thick) ofthis flow. Based on limited field examination, this thin part seems to be in the lower part of the flow. The comparisons between this occurrence and written descriptions, one by Paces (1988) of the PLV on the Keweenaw (Figure 29) and one by Marsh et al. (1991) of solidification in sheet-like basaltic bodies (Figure 30), are illuminating. Both descriptions show the vesicle cylinders as developing in the upper part of the lower capture front of a solidifying body and continuing upward to the liquid zone. This suggests that the segregations formed during solidification--when the region around the cylinders was mushy. The vertical movement of the cylinders was accommodated by the positive thermal gradient and by more fluid material that overlay the mush region. The process forming the cylinders could possibly be common to the solidifying process of a wide variety of materials, such as metals, aqueous solu38 �c 8 A SMOOTII (PAHOEIIOEI BRECCIATED (F1lAGMEHTAL) UPPF.II CIlIUED MARGIN Ili,hI, OokIjud ..i'h Ahu_Ti.,V......... VOLA·III.!! EXSOI.UT1ON FROM COOUIf() WAClMA AND UPWAIIO MIGRATION Of PEGMATOlDLAYERS VESICla ..... ~~'~"OH ~""'······11,!ilill'f!/r·~~- . OH,..•••• LOWEll CIllUED IoIAROII" ..i'h Pipe Vaic\cs W \0 D 4!!/!!////!f!/f!!j! Figure 29: (a-c) Illustration of the development of volcanic rock textures and flow structures typical in sub-aerially erupted PLV flood lavas (Paces 1988). Unstippled areas within the cooling lava flow interior represent molten material. (a) Ponded lava flow after emplacement. (b) Partially solidified. (c) Solidification near complete. (d) Illustration of a portion of four successive lava flows summarizing the hydrodynamic characteristics of the volcanic pile. Very high permeability is present in interflow sediments and in highly vesicular and/or brecciated flow tops (heavy stippling). Permeability decreases gradually as the degree of vesicularity diminishes (light stippling) towards the center of the flow. Massive interiors of thicker flows (unpatterned) are largely impermeable to migrating ground water and secondary hydrothermal fluids. Lava flows were originally deposited in a near-horizontal orientation and have been subsequently tilted by both depositional and compressive tectonic mechanisms. �(al --- ---'Roof bulk liquid boundary layer (d) Rock=-- I~.I!!II Capture front~ is 'iJ ill1ll ---- FQQI Ro2L--::.. Temperature Crystals Figure 30: Conceptual diagram, showing residual fluids forming lenses in the Shonkin Sag and the schematic temperature and grain size relationships at the time oftheir formation (Marsh 1991, personal com- Figure 31: Schematic representation ofboundary layer perturbation leading to plume and channel formation (Hellawell et al. 1993). Note that the entrainment of bulk liquid must first accelerate the dendritic growth front locally, while the release of solute-rich liquid from below causes subsequent melting, in the order of (a to e). munication). This is comparable to the observed relationship of vesicle cylinders and pegmatoids on Raspberry Island. tions, and organic mixtures; this process is described as channel convection in partly solidified systems (Hellawell et al. 1993). In experiments with aqueous solutions, Hellawell et al. (1993) present observations of plumes that formed above the channels and extended into the liquid zone above (Figure 31). The Central Part of the SE Shore: Slickenside Surfaces Featured conspicuously along the E shore of Raspberry Island are slickenside surfaces. A study of the fault slickenfibers allowed Witthuhn (1993) to use geometrical and statistical methods to define the kinematics of the closing of the rift. In Witthuhn's study, Raspberry and Edwards Islands offered one of the largest populations of measurements (Figure 32). The measurements revealed two consistent stress fields, for each limb of the syncline, that would satisfy the conditions envisioned for the opening and closing of the Midcontinent rift. Most ofthe faults on Isle Royale, including both normal and reverse faults, trend NE. This suggests that the reverse faults represent reactivated normal faults. The orientation of reverse faults at Isle Royale differs significantly from the predomi- nately N-S trending structures measured in the PLV on the Keweenaw Peninsula (Figure 33). The EPart of the SE Shore: Pegmatoid Zones About two-thirds of the way along the shore of Raspberry Island, the exposures that occur are stratigraphically higher in the flow. Here the flow has a laminar structure that consists of fractures that are parallel to the bedding and spaced about 0.5-3 cm (0.2-1.2 in) apart. Within this part of the flow, vesicle cylinders are not seen, but small pegmatoid lenses occur. Paces (1988) describes what these lenses look like: Pegmatoid horizons are similar to vesicle cylinders in that they consist ofgas-rich, coarsely crystalline, granophyric material. However, they occur as discontinuous lenses and layers, typically 10 em (4 in) to several meters thick, and are usually located between the flow top and most massive portion ofthe flow interior. Pegmatoids are best developed in thicker flows that have cooled slowly enough to allow in situ differentiation (Cornwall 1951; Lindsley et al. 1971). This material represents the last remaining volatile-rich liquid, which is injected into fractures oriented sub-parallel to the upper flow surface. Both vesicle cylinders and pegmatoid layers contain significant void space in 40 �a) Mon EAST AND WEST CARIBOU INNER lULL, OUTER HILL AND DAVIDSON Equal Area +:..... = RASPBERRY AND EDWARDS STOKLEY BAY, TOOKER, SHAW AND SMITHWICK ISLANDS Figure 32: Left: Equal area rose diagrams of the trend of slickensides on (a) normal and (b) reverse faults on Isle Royale (Witthuhn 1993). Notice the similar trends that define the resolved shear stress on the faults. Right: Rose diagrams ofthe trends of slickensides on reverse faults measured on islands along the SE shoreline of Isle Royale (Witthuhn 1993). �tJ e::-. _ -~ / Figure 33: Compression directions deducedfrom slickenlines on reverse faults from the island groupings along the SE shoreline ofIsle Royale (Witthuhn 1993). Identification of circles from left to right: (1) West and East Caribou islands; (2) Mott island; (3) Inner Hill, Outer Hill, and Davidson islands; (4) Tooker, Shaw, and Smithwick islands and Stokley Bay peninsula; and (5) Raspberry and Edwards islands. the form ofvesicles and gas pockets and contribute to the permeability of the lava flows. history; also, the vesicle cylinder zones and the pegmatoid zones may represent comparable and complementary features that formed at about the same time. (A Master's student at Northern Illinois University, Matt Wollert, has begun a study on the origin of pegmatoid layers in thick Keweenawan lavas. Suggestions for Matt that result from our trip here are very welcome.) After examination and discussion of these outstanding exposures, we will return to Three Mile Campground for the night. We need to be well-prepared for departure because we must leave very early for Snug Harbor in the morning. --Paces 1988 The origin of the pegmatoids is possibly related to the process by which the vesicle cylinders were formed. However, for the pegmatoid origin, the rise of material in channels is limited by the thermal gradient and by the associated solidification that happens above the zone of pegmatoids, so the material is blocked and accumulates in lensoid layers (Figure 30). It is possible that this flow has frozen a snapshot of what was happening late in the solidification 42 �The Sixth Day: Back to the Mainland We will leave early to get to Snug Harbor in time for the departure of the Voyageur for our return to Grand Portage. The route will be via Chippewa Harbor, Malone Bay, and Windigo, so we will complete a circumnavigation of Isle Royale. Conglomerate Bay The first leg of the trip is SW along Rock Harbor to Daisy Farm Campground, and then past the Isle Royale Lighthouse and Tonkin Bay to Conglomerate Bay (Figure 20). Conglomerate Bay is named for one of the interflow sediments that crops out halfway along the inlet. On the edge of this bay was the site of the Saginaw Mine, which was a very brief mining effort with two shafts and a winze from 1877 to 1879. The regular 15" dip of the PLV strata is disrupted in this part of Isle Royale with a system of steep and curved faults. This causes the more SE parts to be offset progressively upward, as though the regular subsidence of the rift basin was disrupted in this place. Chippewa Harbor The entire region of Middle Island Passage to Siskiwit Lake consists mainly of the ophitic flows and their intervening sedimentary units (Figure 24). At Chippewa Harbor, we will see exposures of these flows and the sedimentary units, and near the dock is an outcrop of the interflow conglomerate. The harbor is the site of a fishing camp and is now a favored campsite. The beaches S of Chippewa Harbor are some of the best for finding Isle Royale greenstones (see "Greenstone Beach" on Figure 34 and Huber 1983, pp 58-9). Malone Bay: The Copper Harbor Conglomerate We will take the boat to Malone Bay (Figure 35), the site of exposures of the conglomerate beds of the CHe. On our way, we will pass Schooner, Hat, and Ross Islands, which are all underlain by sandstone of the CHe. This formation is described by Wolff and Huber (1973): The CRC at Isle Royale is the N limb counterpart of the type CRC exposed on the S limb ofthe Lake Superior syncline on the Keweenaw Peninsula. In both areas, the formation, which is ofmiddle Keweenawan age, overlies the middle Keweenawan PLVand is largely derivedfrom older Keweenawan volcanic source terranes that shed debris into the subsiding Lake Superior basin from opposite sides; for Isle Royale, the source terrane would have been the North Shore Volcanic Group in Minnesota. The deposits appear to be piedmont fan deposits and flood-plain deposits formed under a combination of fluvial and lacustrine conditions. Various sedimentary features at Isle Royale indicate that the sediments were transported generally E, with a range in direction from NE to SE. The formation also increases in thickness and in textural and compositional maturity in this direction; it varies from a boulder conglomerate, through a mixture ofcobble and pebble conglomerates and sandstone, to sandstone alone. This clastic wedge thickens within a distance of 32 km (20 mi) from a minimum of460 m (/,500 ft.) to more than 1830 m (6,000 ft.) between stratigraphic marker horizons; the top of the formation is nowhere exposed, however, and the total thickness probably is considerably greater. The clastic materials in the formation are predominantly derived from older Keweenawan volcanic rocks. Felsic varieties are slightly dominant over mafic varieties. Metamorphic rocks are minor components, and clasts ofintrusive igneous rocks appear to be absent. The overall local composition ofthe formation, chiefly reflecting degree of sediment maturity, is closely related to grain size; rocks ofsimilar grain size have the same composition throughout the formation. Calcite cement is ubiquitous; in the conglomerate and coarse-grained sandstone, it commonly amounts to about 15 percent. As the textures become finer, rock fragments and calcite cement decrease in abundance, whereas quartz, feldspar, and opaque mineral percentages increase. Thefelsic and many ofthe mafic Keweenawan rock types that occur as clasts in the CRC are not known to occur as flows within the PLVon the island. Most ofthe rock types, however, are known to occur as flows in the North Shore Volcanic Group, which is stratigraphically lower than the PLVand 43 �...~ -.>,,;:/;:<; ~~:...",,<::; <r'- ," ,I.) ,s- .~·I ~ ~'t' ~. ,{' Q �--- /' " c c -J:.~"'-' ,::~ // " Q) V:;, ;;L ~_.; �is present in the direction from which the clastic debris was transported. Several lines ofevidence suggest the presence ofan unconformity between the North Shore Volcanic Group and the PLV. Such an unconformity would facilitate the erosion of the North Shore Volcanic Group and the deposition of the erosional debris basinward on top ofthe PLV. The situation would be analogous to that on the S side of the Lake Superior syncline. There, many clasts in the CRC appear to have been derivedfrom the lowermost Keweenawan volcanic terrane, the volcanic rocks ofthe South Trap Range which underlie the PLV. --Wolff and Huber 1973 We will move along shorelines underlain by the CHC all the way to Grace Harbor, passing Menangerie Island, Long Island, Point Houghton (Figure 35), McCormick Reef, Long Point, the Head, Rainbow Point, and Cumberland Reef (figure 36). Figure 37 shows the variation of sediment lithology across the section, and Figure 38 shows sediment disposal patterns measured by Wolff and Huber (1973). SW Isle Royale: The Glacial Deposits It is in this SW section of Isle Royale (Figure 36) that the thickness of glacial deposits is the greatest. The glacial setting is summarized by Huber (1973b): Isle Royale was overridden by glacial ice during each ofthe four major glaciations ofthe Pleistocene Epoch, and each successive glaciation essentially obliterated all direct evidence ofpreceding glaciations on the island. In the waning phase ofthe last major glaciation, the Wisconsin Glaciation, the frontal ice margin retreated N from at least the greater part ofthe Lake Superior basin, then readvanced into the basin during Valders time, about 11,000 years ago. We can attribute to the Valders ice the final aspect ofglaciation at Isle Royale, including both erosional and depositional features. It is impossible to estimate the quantity ofglacial debris or other surficial materials that might have been present at Isle Royale prior to the Valders readvance, but the readvancing ice appears to have removed most of what might have been present, as judged by the thin surficial cover on the E two-thirds of the island today. During the Valders retreat, a series oflakes formed in the Lake Superior basin infront ofthe retreating ice margin. The retreating ice opened successively lower outlets, and thus the general trend oflake elevations is downward. Distinct lake stages reflect periods ofrelative stability during which well-defined shoreline features developed. The ice front forming the N margin ofthe earlier lakes probably remained S ofIsle Royale until about the time ofglacial Lake Beaver Bay, when it retreated to a position straddling Isle Royale W of Lake Desor. Abundant deposits ofglacial debris were left upon the newly deglaciated Wend ofthe island, and the ice front remained stable long enough to build a complex of ice-margin deposits across the island. Shorelines formed by the glacial lake associated with this ice frontarefound on the Wpartofthe island about 61 m (200 ft.) above present Lake Superior. Subsequent renewed and complete retreat of the ice margin from Isle Royale was rapid enough that only a minor amount ofglacial debris was deposited on the central and E parts of the island. When the ice margin reached the N edge ofthe Lake Superior basin, Lake Minong was formed, and the entire basin was filled for the first time since the Valders advance. Lake Minong marked a relatively stable episode in the history of the basin, and its beaches are among the best developed ofthe abandoned shoreline features on Isle Royale. Lake Minong beaches and later lower beaches are best developed on the SW end of Isle Royale, where abundant glacial debris provided easily worked materials for beach construction. --Huber 1973b The discussion about changing shoreline levels in Huber (1983, see pp 41-55) is important to understand the geomorphology we will be seeing, and if you are a field trip participant, you should particularly read the discussion of shorelines at Rainbow Cove, which includes clear exposures of both Nipissing and Minong shorelines (Huber 1983, see pp 52-3). Washington Harbor: The End of Our Trip Rounding the Cumberland Reef we will arrive once again at Washington Harbor, where we began on the first day. You have now seen Isle Royale from all sides. 46 �{\ EXPLANATION \-- \ I l ... ---'- Ar@a with exteMive glacial debt'is, in part reworked or eo'Vered by alluvium ~\1~~~&11 Iu-margin depofllts FO'f"'7IU'd at i.e. ~rg\" dun"" paWl". ' It "trt'Gt 01 glocill{ 1,t« Glacial striation SMwiftQ dh,(:~ <J!u, _Ute""C Drumlin (crag-and·taU type) Sltbwi", dirfftion Q/ it, """"""",,,t Abandoned IlhoreUne of 1\.<:\.\ ot' po8tal~t.l take "tuh"' 1m 14" ftM fJ/ .A!>Nfw of N '11 1 ~ 1 .- ~ Pol",t IloUBhton -..,J CumberlAnd Point 2 I 0 I 2 '" I ! 2 0 I I 2 4 I I 6 I 6 ~_,_ CONTOUR INTERVAL 100 FEET ~Q'IO' 89"00' Figure 36: Map shoWing the glacial features and abandoned shorelines ofSW Isle Royale (Huber 1973b). �Composition of lIel-y fine grained sandstones, very coarse grained ,~andstones, and pebble conglomerates taken f 1"01/1 the measured section on Houghton Ridge (Specimen numbers indicate relative lH,siliou with lowest number lowest in seclion. See plate I for loeations] Very fine grained sandstunes Specimen No. MV .................... FV .................... SF MF::::::::::::::::::: UQ .................... UnQ .................. PQ PF :::::::::::::::::::: PIF .................... 0 Ca ::::::::::'.:::-:':::::: Other ................ 4 6 0.3 .9 4.2 .0 46.2 21.6 .6 4.3 6.6 6.6 6.1 3.2 0.6 .6 .3 .0 39.7 16.2 .6 16.6 8,4 6.8 6.8 4.6 • Pebhle conglomerates 11 13 28 12 15 18 22 24 27 6 0.9 .9 .0 .3 42.3 18.8 .6 12.9 6.2 8.1 6.6 4.6 Trace 0.9 Trace .0 0.9 .6 .0 0.0 .0 .0 .0 28.1 11.9 .0 22.9 20.6 6.6 4.6 6,4 30.7 31.8 .0 .6 4.8 4.8 .3 1.6 9.0 6.1 9,4 .9 36.9 :18.8 .9 35.5 31.7 .6 2.3 3.9 1.9 .9 .9 6.4 1.3 16.3 .3 35.6 33.6 .9 23.9 24.2 1.6 .6 4.6 2.9 1.6 3.9 10.0 7.1 17.1 2.6 21.7 39.6 22.7 43.7 .9 .9 1.9 .9 1.3 7.1 2.9 1.3 14.8 1.6 36.6 24.2 .0 23.3 6.6 6.2 1.9 3.6 Trace 32.4 23.2 .9 18.6 6.1 6.8 8,4 3.2 MOTE.-Abbreviations: mafic volcanic rock fragments I"" V• felsic volcanic rock fragments SF. sedimentary rock fragments (shale and sandstones) MF. metamorphic rock fragments M V. Very coarse grathe1 sandstones 7 Trace 3.5 1.6 .6 1.6 11.6 2.3 1.3 .9 Trace 4.6 1.3 .6 .9 6.8 6.2 9.7 .9 UQ. unslrnined quartz grains UnQ. undulatory quartz grains PQ. PF. Ilnlycryslalline quartz "Tuins l)()tRssium feldspar RrninR Trace .3 1.6 1.9 1.3 4.6 2.3 1.6 22.3 2.9 PIF. o. 16 30 31 32 34.3 39.9 .3 .3 2.9 .6 1.9 .6 6.9 1.6 9.8 1.9 28.2 37.2 1.9 1.3 4.2 1.3 .6 1.6 1.9 .9 19.0 1.9 22.9 21.9 3.6 1.3 6.1 3.6 1.3 2.9 2.9 8.1 23.3 2.3 29,4 34.6 .3 Trace 4.2 1.3 .9 1.9 4.6 7.1 14.2 1.6 ploRioelase grains 0llsque grains Cn. Calcite cement Olhenl epidote. pyroxene. zeoHtes SECTION EXPLANATION I·.hhl.. n)ftl'ktm.... t. r~- ~ o .....i ........ ndo1<'HW ~ n,....,..iMd .. lldaltiofl. .......'um·cr.in.,f •• nohton. s..~~;~ ~i';:~: ~:':::~::'~t;:: I::'::: for'fOfti..,..,,,,,ottabl.4 SISJ(IIVIT Figure 37: The variation ofsediment lithology across Houghton ridge (Wolff and Huber 1973). 48 �it ., it ."it'it .., ..,., Q, '" it " .., 0, " '" .., '" ",' it it .., '" <0 <0it .., "'",'" '" ~~~:S! SIS[(I!VIT BA}' 1"-'>" ( ~ 1.0 . , CD N=38 M=135" S=40 ~ / "-~ ii- 25"..21\: 4iJ' CD N=I04 M=I02" 8=28 g> /!j~- <::> ~ N M S Direction (arrow) or trend (line) of paleocurrent movement obtained by averaging all meaSlII'ements tallen within the township section near which it is plotted. Numhers indicate the number of measurements that each symbol represents Composite of direction measurements taken mainly along the shoreline in townships indicated. N, number of measurements; M, mean direction; S, stanclal'd deviation. Measurements at west end of Siskiwit Bay not included ='-.. 0 0 N=105 M=67" .'>=33 ~ EXPLANATION --is , 17 =2 tv I 0 I 1 2 MILES I Figure 38: Sediment dispersal patterns in the Copper Harbor Conglomerate on Isle Royale (Wolff and Huber 1973). N=19 M=82" 5=23 �Acknowledgments The opportunity to write a detailed guide to Isle Royale and to lead a field trip comes from the cooperation of many people. I would like to thank Jack Oeltke of Isle Royale National Park for enabling a group to stay together at a campground during a field trip. Kim Alexander of National Park Concessions was helpful to us by providing the support of the Sandy, even though it was very early in the regular season. King Huber provided us with a complete set of his many publications about Isle Royale and also with lots of cheerful encouragement. Jim Paces, Tony Longo, and Rick Wunderman provided me with a lot of insight on the volcanic geology of Isle Royale. Kate Witthuhn suppLied some unpublished data. Discussions with Bruce Marsh and Angus Hellawell about solidification helped me to understand a little better what may have been going on inside Isle Royale's lava flows. Dave Schneider planned the food and logistics for the trip. Finally, Libby Titus did all the work of putting this field guide together: revisions, layout design, and copy-editing--everything but the fun parts! References Basalt Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets, Pergamon Press, Inc., New York, 1286 pp. Brannon, J.C. 1984, Geochemistry of successive lava flows ofthe Keweenawan North Shore Volcanic Group, Ph.D. dissertation, Washington University, St. Louis, MO, 312 pp. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenawan, Geo!. Soc. Am. Bull., v. 46, pp.503-58. Broderick, T.M., Hohl, C.D., and Eidemiller, H.N., 1946, Recent contributions to the geology of the Michigan copper district, Econ. Geol., v. 41, pp. 675-725. Butler, B.S. and Burbank, W.S., 1929, The copper deposits of Michigan, u.s.G.s. Prof Pap., No. 144, 238 pp. Cannon, W.F., 1994, Closing of the Midcontinent rift: a far-field effect of Grenvillian compression, Geo!., v. 22, pp. 155-8. Cannon, W.E et aI., 1989, The North American Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling, Tectonics, v. 8, pp. 30532. Carmichael, r.S.E., Turner, EJ., and Verhoogen, J., 1974, Igneous Petrology, McGraw-Hili, New York. Clark, J.A, Hendriks, M., Timmermans, T.J., Struck, C., and Hilverda, K.J., 1994, Glacial isostatic deformation of the Great Lakes region, Geol. Soc. Am. Bull., v. 106, pp. 19-31. Cornwall, H.R., 1951, Differentiation in lavas ofthe Keweenawan series and the origin of the copper deposits of Michigan, Geo!. Soc. Am. Bull., v. 62, pp. 159-202. DeGraff, J.M. and Aydin, A, 1993, Effect of thermal regime on growth increment and spacing of contractionjoints in basaltic lava, J. Geoph. Res., v. 98, pp. 6411-30. DeGraff, J.M., Long, P.E., and Aydin, A, 1989, Use of joint-growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows, J. Vole. and Geotherm. Res., v. 38, pp. 309-24. Foster, J.W. and Whitney, J.D., 1851, Report on the geology ofthe Lake Superior land district, Washington, DC, AB. Hamilton, 400 pp. Goff, F.E., 1977, Vesicle cylinders in vapor-differentiated basalt flows, Ph.D. dissertation, University of California, Santa Cruz, CA, 83 pp. Grand Portage National Monument, 1986, Grand Portage, National Park Service, U.S. Department of the Interior, GPO: 1986--491-414/20056. Green, J.C., 1982, Geology of Keweenawan extrusive rocks, Geo. Soc. Am. Mem., v. 156,47-55. Green, J.C., 1989, Physical volcanology of mid-proterozoic plateau lavas: the Keweenawan North Shore Volcanic Group, Minnesota, Geol. Soc. Am. Bull., v. 101, pp. 486-500. Hellawell, A, Sarazin, J.R., and Steube, R.S., 1993, Channel convection in partly solidified systems, Phil. Trans. R. Soc. Land., v. 345, pp. 507-44. Huber, N.K., 1969, Pink copper-bearing prehnite from Isle Royale National Park, Michigan, U.S.G.s. Prof Pap., No. 650-D, pp. D63-8. Huber, N.K., 1973, Geologic map of Isle Royale National Park, Keweenaw County, Michigan, u.s. G. S. Map, No. 1-796. Huber, N.K., 1973a, The Portage Lake Volcanics (middle Keweenawan) on Isle Royale, Michigan, U.S.G.S. Prof Pap., No. 754C, 32 pp. Huber, N.K, 1973b, Glacial and postglacial geologic history of Isle Royale National Park, Michigan, U.S.G.S. Prof Pap., No. 754-A, 15 pp. Huber, N.K., 1983, The Geologic Story ofIsle Royale National Park, U.S.G.S. Bull., No. 1309,66 pp. Lacroix, A, 1928, Les Pegmatitoides des Roches Volcaniques a Facies Basaltiques, Ac. Sci. Paris Comptes Rendus, v. 187, pp. 321-6. Lacroix, A, 1929, Les Pegmatitoides des Roches Volcaniques a Facies Basaltiques: A Propos de Celles du Wei-Tchang, Bull. Geol. Soc. China, v. 8, pp. 45-9. Lane, AC., 1893, Geological report on Isle Royale, Michigan, Geol. Surv. ofMichigan, v. 6., pp. 1-265. 50 �Lane, A.C., 1911, The Keweenaw series of Michigan, Michigan Ceo!. and Bio!. Surv. Pub. 6, Geol. Ser. 4, v. 2, 983 pp. Lindsley, D.H., Smith, D., and Haggerty, S.E., 1971, Petrography and mineral chemistry of a differentiated flow of Picture Gorge Basalt near Spray, Oregon, Carnegie Inst. of Washington, Yearbook 69, pp. 264-85. Lofgren. G.E., 1980, Experimental studies on the dynamic crystallization of silicate melts, Physics of Magmatic Processes (ed. RB. Hargraves), Princeton Univ. Press, Princeton, NJ, pp. 487-551. Long, P.E. and Wood, BJ., 1986, Structures, textures and cooling histories of Columbia River basalt flows, Ceo!. Soc. Am. Bull., v. 97, pp. 1144-55. Longo, A.A., 1984, A correlation for a middle Keweenawanflood basalt: the Creenstoneflow, IsLe Royale and Keweenaw Peninsula, Michigan, M.S. thesis, Michigan Technological University, Houghton, MI, 198 pp. Marsh, B.D., Gunnarsson, B., Congdon, R., and Carmody, R., 1991, Hawaiian basalt and Icelandic rhyolite: indicators of differentiation and partial melting, Ceologische Rundschau, 80/2, pp. 481510. McKee, B. and Stradling, D., 1970, The sag flowout: a newly described volcanic structure, Ceol. Soc. Am. Bull., v. 81, pp. 2035-44. Merk, G.P. and Jirsa, M.A., 1982, Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks, Ceo!. Soc. Am. Mem., v. 156, pp. 97-105. Paces, J.B., 1988, Magmatic processes, evolution and mantle source characteristics contributing to the petrogenesis ofMidcontinent rift basalts: Portage Lake Volcanics, Keweenaw Peninsula, Michigan, Ph.D. Dissertation, Michigan Technological University, Houghton, MI, 413 pp. Paces, J.B. and Miller, J. D., Jr., 1993, Precise U-Pb ages of Dullish complex and related mafic intrusions, northeastern Minnesota: geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent rift system, J. Ceoph. Res., v. 98, pp. 13,997-14,013. Rakestraw, L., 1965, Historic mining on Isle Royale, reprinted in Borealis Isle Royale, Natural History Association, Houghton, MI. Santin, S.F., 1969, Pegmatitoides in the horizontal basalts of the Lanzarote and Fuerteventura Islands, Series I, Bull. Vole., v. 33, pp. 989-1007. Seaman, A.E. and Seaman, W.A., 1944, Geological column Lake Superior Region in general: Michigan Ceol. Surv. Div., Progress Report No. 10. Swanson, D.A., Wright, T.L., and Helz, RT., 1975, Linear vent systems (and estimated rates of magma production and eruption) for the Yakima basalt of the Columbia plateau, Am. J. Sci., v. 275, pp. 877-905. Tomkeieff, S.I., 1940, The basalt lavas of Giants Causeway district of Northem Ireland: Bull. VoLe., v. 6, pp. 90-143. Van Hise, c.R. and Leith, C.K., 1911, The geology of the Lake Superior region, U.S.G.S. Mon., No. 52, 381 pp. Walker, G.P.L., 1987, Pipe vesicles in Hawaiian basaltic lavas: their origin and potential paleoslope indicators, Ceol., v. 14, pp. 84-7. White, W.S., 1952, Imbrication and initial dip in a Keweenawan conglomerate bed, J. Sed. Pet., v. 22, pp. 189-99. White, W.S., 1960, The Keweenawan lavas of Lake Superior: an example of flood basalts, Am. J. Sci., v. 258-A, pp. 367-74. White, W.S., 1971, Geologic setting of the Michigan copper district, In Cuidebookfor FieLd Conference. Michigan Copper District, Sept. 30 - Oct. 2, (ed. W.S. White), Soc. Econ. Geol., Michigan Technological University, Houghton, MI, pp. 3-17. Witthuhn, K., 1993, A structural analysis ofthe Midcontinent rift in Michigan based on a fauLt array analysis utilizing slickensides, M.S. thesis, University of Minnesota, 129 pp. Wolff, RG. and Huber, N.K., 1973, The Copper Harbor Conglomerate (middle Keweenawan) on Isle Royale, Michigan, and its regional implications, U.S.C.S. Prof Pap., No. 754-B, 15 pp. Worster, M.G. and Huppert, H.E., 1993, The crystallization of lava lakes, J. Ceoph. Res., v. 98, pp. 15,891901. 51 � https://digitalcollections.lakeheadu.ca/files/original/5de63f9a5707ef8cb802fbb18d52081c.pdf 89db5e131bf5b0c588a042ee4d5d53b1 PDF Text Text I < I Proceedings Proceedings Annual Meeting Meeting 40th Annual May 11-14,1994 11-14, 1994 May Michigan Michigan Technological University Houghton, Michigan Michigan Volume 40 Part4—Michigan kimberlites and diamond exploration techniques By: By: Shawn Shawn M. M.Car/son Carlson and and Wayde Wayde Floodstrand Floodstrand �Institute Institute on on Lake Lake Superior SuperiorGeology Geology Proceedings 40th Annual Meeting Meeting May 11—14, 1994 May 11-14,1994 Michigan Technological University Michigan University Houghton, Houghton, Michigan Michigan Volume Volume 40 40 4—Michigan kimberlites and diamond exploration techniques Part 4-Michigan techniques By: Shawn Shawn M. M. Car/son' Carlsonland andWayde WaydeF/oodstrand2 Floodstrand2 Ashton Michigan 49920 49920 Ashton Mining Miningof ofCanada CanadaInc., Inc., Crystal Crystal Falls, Falls, Michigan 2Crystal CrystalExploration Exploration Inc., Inc., Crystal Crystal Falls, Falls,Michigan Michigan 49920 49920 �CONTENTS PART PART4 MICHIGAN MICHIGANKIMBERLITES KIMBERLITES AND AND DIAMOND DIAMOND EXPLORATION TECHNIQUES Introduction Introduction .................................................. 1 1 Road Log Stopi StoplA Stop2 Stop3 3 3 6 8 9 ........................................ Field Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fieldsamples Acknowledgements Acknowledgements ............................................ References References . . . . . . . Kimberlite Bulk Samples Samples 10 10 11 11 14 14 15 Figures Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure2 F i p r e 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Figure3 Figure3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Figure 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Figure4 Figurel Figure1 Figure 5 Figure5 Figure 6 Figure6 .................................................. .................................................. 12 12 13 13 �INTRODUCHON During the the past past 150 150years, years, atatleast least17 17purported purporteddiamond diamonddiscoveries discoverieswere were made made ininWisconsin, W~sconsin,with with additional Peninsula of of Michigan Michigan and and other midwestem midwestern states. The The accidental additional finds in the hLower w e r Peninsula accidental discovery discovery of a kimberlite pipe in Iron county, Michigan in 1971 suggested suggested the these diamonds the possibility that these diamonds might might have have been derived derived from source bodies closer closer than than northern northernOntario, Ontario,and and several several diamond diamond exploration companies initiated sampling programs to assess assessthe thediamond diamondpotential potentialof of the theUpper UpperPeninsula Peninsulaof of Michigan, Michigan, as aswell well as as adjacent adjacent Great Great Lake Lake States. States. To To date, date, more more than than 20 20 kimberlites kimberlites have havebeen beendiscovered discoveredininMichigan. Michigan.These Thesepost-Ordovician post-Ordovician intrusions intrusions range between 11and 20 acres, and follow aa crude crude northwest trend through through Iron, Iron, Dickinson Dickinson and and Menominee Menominee counties counties from from Crystal Crystal Falls Falls to Hermansville. Hermansville. Age dates dates have have been been obtained obtained for for several several of of these thesekimberlites, kimberlites, placing the intrusions years before present, the the youngest youngest in the the state placingthe intrusionsbetween betweenapproximately approximately186 186and and209 209 million years state (Jarvis, While none none of ofthe thebodies bodies discovered discovered so far have been been proven to be be economic, economic, there there is abundant abundant (Jamis, 1993). While evidence evidence to to suggest suggestthat thatmany manyundiscovered undiscoveredkimberlites kimberlitesexist existininthe theGreat GreatLakes Lakesregion. region.Some Someof of these thesebodies bodies may may be be the the source sourceof of the thelarge largehistorical historicaldiamonds diamondsfound foundininglacial glacialand andalluvial alluvial sediments sediments throughout throughout the the midwestern United States. midwestem United States. In In November November1991, 1991,Dia Met Minerals Minerals Ltd. M.announced announcedthe thediscovery discoveryofof81 81diamonds diamondsinin59 59kilograms kilogramsof of drill drill core Territories. This This release set off the core from from a kimberlite in the Lac I a c de Gras region of Canada's Northwest Temtories. largest in the the history of North America, and diamonds are currently the most largest claim-staking claim-staking frenzy in most exciting exciting exploration exploration is also progressing in the United States, explorationcommodity commodity in Canada. Diamond exploration States, with ongoing economic Arkansas, Colorado continuing efforts economicevaluations evaluationsof of several bodies bodies in in Arkansas, Coloradoand and Montana, Montana,in in addition addition to continuing efforts in the theLake LakeSuperior Superiorregion. region. This This field field trip trip is is designed designed as asaaprofessional professionalprospecting prospectingcourse, course,and andwill willfamiliarize familiarize participants participants with with the the science includiig the the dynamics dynamicsof ofkimberlite kimberliteemplacement, emplacement,relative relativeimportance importanceofof science of of diamond diamond exploration, exploration, including glaciation, collection and and processing processing techniques. techniques. While While most most emphasis emphasis has has been placed on the glaciation, and sample collection Michigan Michigan kimberlites and exploration exploration in the the midwest, midwest, kimberlite kimberlite and and lamproite lamproite rock rock samples samplesfrom frommany many worldwide will be be presented presented for examination, and a brief worldwide localities will brief update update of of current currentdiamond diamondexploration exploration activities throughout North America will be given. activities throughout North America will be given. 1 �N Lake Superior Lake Superior 89° Wisconsin Wisconsin Lake Michigan Michigan Scale 13,508,800 0 50 100 150 200 kms 1:Diagram Diagram of ofthe the Upper Upper Peninsula Peninsula of of Michigan, showing relevant FFIGURE I G U E 1: counties towns. counties and small towns. 2 �ROAD ROAD LOG LOG This Crystal Falls. Falls. Crystal Crystal Exploration Exploration maintains maintains Thisroad roadlog logbegins beginsininthe theparking parkinglot lotof ofWilliams WilliamsMini Mini Mall in Crystal aa processing processinglaboratory laboratoryand andoffice officehere, here,ininconjunction conjunctionwith withDow DowChemical ChemicalCompany Companyand andAshton AshtonMining. Mining.These These facilities be toured toured as this field trip. Parking Parking should facilities will be as the the last last stop stop of of this should not not be be aa problem problematatany anyof of the the stops, stops,and and vehicleswith with 4WD 4WD or or high high clearance clearanceare arenot notrequired. required.The Thetotal totaldriving drivingdistance distanceisisapproximately approximately40 40miles. miles. vehicles Mileage Mileage 0.0 Begin Turn right and proceed east lotof of Williams Williams Mini Mall. Turn right onto onto highway highway US-2, and east through through Beginat atparking parkinglot town. town. 1.0 Turn Turnleft leftatatfour-way four-waystop, stop,and andproceed proceedeast eastononM-69. M-69. 10.2 Junction JunctionofofWay WayDam DamRoad Road and andM-69. M-69. Turn Turn left left on on Way Way Dam Road Road and and proceed proceed north. north. 10.7 A large outcrop should bebe barely visible above A large outcrop should barely visible abovetree treelevel leveltotothe thewest. west.This Thisexposure exposureofofHemlock Hemlock metavolcanics shows shows excellent excellent east-west east-west glacial striations, striations, and can serve serve as as an an additional additionalfield field trip metavolcanics stop, stop,time time and andinterest interestpermitting. permitting. 16.3 Turnleft leftonto onto Phelan Phelan Road, Road, also also known known as as the the access accessroad road to tothe theLake LakeEllen EllenBaptist Baptist Camp Camp and and Turn Public #14. Proceed Proceed north. north. Public Recreation Recreation Area Area #14. 17.1 Turn Turnleft leftonto ontoPhelan PhelanRoad, Road,and andproceed proceedwest. west. 17.3 Turn Phelan'slanding landing strip. strip. Parking Parking is is best best near near the the yellow yellow gate at the northern northern end endof of Turnright rightonto ontoPhelan's the thestrip, strip,atatmileage mileage17.4. 17.4.The Thewalk walktotothe theLake LakeEllen Ellenkimberlite kimberlitetakes takesapproximately approximatelyfive fiveminutes. minutes. Note Note the the granular granular kimberlite kimberlite that that has has been been used used as asroad roadgravel gravel throughout throughoutthis thisarea. area. Stop Stop 1: 1: The TheLake IakeEllen EllenKimberlite. Kimberlite. The TheLake LakeEllen Ellenkimberlite kimberlitewas wasdiscovered discoveredinin1971 1971by byKlaus KlausSchultz Schultzand andWilliam William Spence. Spence.The Thepipe pipeisislocated located in mileswest westand andnorth northofofChanning. Channing.Several Several in eastern easternIron Ironcounty, county,approximately approximately22miles milesnorth northofofKiernan Kiernanand and55miles exploration currently leased explorationcompanies companieshave haveevaluated evaluatedthe theeconomic economicpotential potentialofofLake Iake Ellen, Ellen, and the property property is is currently leased by byCrystal CrystalExploration. Exploration. The TheLake LakeEllen Ellenkimberlite kimberlitehas hasbeen beendescribed describedby byCannon Cannonand andMudrey Mudrey(1981) (1981)and andby byMcGee McGeeand andHearn Hem (1983). (1983). Readers Readers are are referred referredtotothese thesepublications publicationsfor fordetailed detailedmineralogical, mineralogical,petrographic petrographicand andhistorical historical descriptions. descriptions.Lake LakeEllen Ellenisisaadiatreme-facies diatreme-facieskimberlite kimberliteofofapproximately approximately20 20acres, acres,and andisisroughly roughlyellipsoidal ellipsoidalinin shape. in the thekimberlite, kimberlite,but buthave havenot notbeen been detected detectedinineconomic economicquantities. quantities.No No shape.Small Small diamonds diamonds are are present present in precise preciseage agedate datehas hasyet yetbeen beenobtained obtainedfor forLake LakeEllen, Ellen,but butthe thebody bodyisisknown knowntotobebepost-Ordovician post-Ordovicianby bycrosscrosscutting cuttingand andxenolithic xenolithicrelationships. relationships. 3 �Due logging road Lake Ellen Ellenisiscurrently currently one oneof ofthe thebest-exposed best-exposed kimberlites kimberlites in the the Due to to a logging road excavation excavationin 1992, Lake United 20 x 12 12 x 55 meter meter pit pit shows shows aa number numberof of subtle subtlestructural structuralfeatures, features,and andatypically atypicallylarge large United States. The The 20 kimberlite xenoliths and and rare eclogite nodules may kimberlite specimens specimensmay maybe be collected collectedfrom from the the pit floor. Crustal xenoliths mayalso also be be collected, collected, along alongwith with aavariety variety of of minerals minerals including including garnet, garnet, ilmenite, ilmenite, olivine, olivine, serpentine, dinopyroxene, clinopyroxene, calcite ilmenite megacxysts megacrysts from exceed 4 centimeters. centimeters. calciteand andphiogopite. phlogopite.Some Someof of the the pyrope pyrope and and ilmenite £ro this this locality localitymay exceed Processing Processingequipment equipmenthas hasbeen beenset setupupatatstop stop11totoallow allowparticipants participantsto to collect collect heavy mineral mineral concentrates. concentrates. The Theplastic plastictubs tubsand andsmall smalljig screens screens(saruca) (saruca)are aresimilar similarto toequipment equipmentused usedatatthe theCrater CraterofofDiamonds DiamondsState State Park Park in in Arkansas Arkansastotoprocess processsmall smalldiamonds diamondsfrom fromolivine olivinelamproite. lamproite.Granular GranularLake M eEllen Ellenkimberlite kimberlite can can be be placed placed into into these theseconical conicalscreens screensand andshaken shakenunderwaterunderwatecheavy heavyminerals mineralssettle settletotothe thebottom bottomininaadistinct distinct"eye", tleyett, which flattable. table.Good Goodconcentrates concentratescontaining containing whichcan can be beremoved removedafter afterthe thescreen screencontents contentsare areinverted invertedonto ontoa aflat ilmenite, ilmenite,garnet garnetand andchrome chromediopside diopsidecan caneasily easilybebeobtained obtainedininthis thismanner, manner,with witha aminimum minimumofofeffort. effort. 4 �FIGURE 2: Portion of FIGURE 2: of the the Kiernan Kiernan7½' 7%'USGS USGS topographic topographic map, map, showing showingthe thelocations locationsof offield field trip and1A 1A (Lake (Lake Ellen kimberlite) and the the Michigamme Michigamme kimberlite. trip stops stops11and 5 �Stop 1A LA:North North Side Side of of the the Lake Lake Ellen Ellen Kimberlite Kimberiite The brief IA will willallow allowparticipants participantsto toexamine examine several several rubbly rubbly outcrops outcrops and filled-in test test pits, pits, as as The brief walk to stop 1A well as gain gain aa sense sense of ofthe thegeneral general topography topography of of the the Lake Lake Ellen Ellen kimberlite. kimberlite. The The topography topography in this this area area is more more typical of ofother other Michigan Michigan kimberlites; kimberlites; most most do do not not have have distinct distinct surficial surficialexpressions, expressions, and and good good outcrops outcrops are typical rare. Stop 1A also provides an opportunity to discuss the the nearby nearby Michigamme Michigammepipe, pipe, aa kimberlite kimberlitelocated locatedin in the the Stop IA SE¼ of of the the N NW¾ theSW^ S/4 ofofsection W ofofthe section27. 27.This Thisbody bodywas wasdiscovered discoveredininthe themid-1980's, mid-19803, and and an an extensive extensive SE% collection ofdrill core has hasbeen beendonated donatedto tothe theDNRcore DNRcorelibrary libraryatMarquette Company, at Marquetteby by Kenecott Kenecott Exploration Company, collectionof drill core and is is available available for public use. The Lake Ellen kimberlite has a high relative relative eclogitic garnet garnet population population when compared to to other otherwellwellthe"reconstituted reconstituted mantle" mantle" known North American kimberlites, with eclogite comprising approximately 6%ofofthe (Schulze, 1993). While Whileno nodetailed detailedstudies studies are are yet yet available, available, ititisisinteresting interesting to to note note that the Michigamme Michigamme pipe apparently has a much greater greater eclogitic garnet population population than Lake Ellen. Core Coresamples samples from fromthe theMichigamme Michigamme apparently has eclogiticgarnet will be presented presented at at stop stop 1A; 1A all all cores cores must must be be returned to the ill be the core core library, library, but samples samples for both nonpipe w destructive offices at Marquette, and destructive and and destructive destructiveanalysis analysismay maybe be obtained obtainedby bycontacting contactingthe theDNR DNRoffices at Marquette, andfollowing following core library guidelines. guidelines. gate, and proceed proceed south to access access road. 17.4 17.4 Leave gate, 17.5 17.5 Turn left on Phelan Road, and proceed east. 17.7 Turn right right on on Phelan Phelan Road, Road, and proceed proceed south. south. 17.7 Turn 18.4 Turn right righton on Channing Channing(Way (WayDam) Dam) Road. Road. 18.4 Turn Junction of of Way Dam Road and M-69. M-69.Turn Turn left left on on M-69, M-69,and andproceed proceed east east. Extensive fields in in this this 24.6 24.6 Junction area are are based on on outwash outwash sediments sedimentsrelated related to tothe theGreen GreenBay Baylobe. lobe. 25.6 25.6 Turn right on Camp 5 road, and proceed south. 26.6 gravel pit. 26.6 Camp 5 gravel pit 6 �FIGURE 3: 3: Portion Portion of of the Lake Mary 7½' topographic map, 7W USGS topographic map, showing showingfield field trip trip stop 2 and select Iron county county kimberlites kimberlites (modified (modified from from Chartier, Chartier,1993). 1993) Approximate boundary of the Sagola moraine is also shown (re-drawn (re-drawn Peterson, 1985). from Peterson, 1985). 7 �I I Stop 2 2::Camp 5 Gravel Gravel Pit. Pit The The Camp Camp 55 gravel pit is a large exposure exposure of of coarse coarseglaciofiuvial glaciofluvial sediments at the western western margin margin of of the the Sagola moraine. moraine. Most Most rock rock types types present present as clasts can be be correlated correlated to to known known or or inferred inferred occurences occurences in in Sagola Dickinson county, and were deposited by by aa series seriesof of east-to-west east-to-westadvances advances of the Green Green Bay Bay lobe during during late late Wisconsinan time. The Crystal Sagola, and Sagola-I1 Sagola-Il moraines moraines were created by the Green Bay lobe, and and Wisconsinan time.The Crystal Falls, Falls, Sagola, were all created several outcrops in the Mansfield area show prominent striations or grooves oriented almost due east-west. striations or almost due east-west Kimberlite clasts clasts were were first first discovered discovered in gravel pit in in 1991. 1991.Several Severalhundred hundredclasts clastsranging ranging from from Kimberlite in the the Camp Camp 55gravel small pebbles pebbles to small boulders boulders in size have since since been been removed analysis. At least least eleven eleven different different small in size removedfrom fromthe thepit pit for for analysis. hand-samplevariations ofkimberlite catagories are hand-samplevariations of kimberlite have have been been recognized recognized atthe at thepit. pit These These somewhat somewhat subjective subjective catagories are acombination of ofmacroscopiccharacteristics, macroscopic characteristics, including includingcolor, abundance of ofcrustal xenoliths, color,type type and abundance crustalxenoliths, based on acombination the presence or absence of typical indicator minerals, and general textural relationships. presence or absence of general textural relationships. As seen in thin section, these inequigranular serpentine, calcite inequigranularrocks rocksare arecomposed composedprimarily primarily of of olivine, serpentine, with accessory accessory ilmenite, diopside, garnet, garnet, phlogopite and apatite. ranges from dominantly and spinel, with apatite. Olivine ranges euhedral in some samples to completely anhedral in others, others, and and most most olivine olivine is at least partly replaced by serpentine, calcite, well-definedautoliths autolithsare are notably notably absent, absent, and and finegrained opaques. Pelletal Pelletal lapilli and well-defined serpentine, calcite, and fine-grained of these these rocks are best most of best classified classified as as diatreme-facies diatreme-facies kimberlite breccias or or hypabyssal kimberlites. The The clasts seem to have been most susceptible hypabyssal clasts susceptible to to alteration, alteration, and and many many of the different different hand-sample "varieties" are are nearly identical in thin thin section, except for varying degrees degrees of oxidation and and calcite calcite "varietiesH of post-glacial oxidation leaching. Indicator mineral mineral populations populations are are extremely variable in the kimberlite from Camp 5. While While results are preliminary at this stage, it appears appears that that ilnienite ilmenite isisby by far far the themost mostcommon commonindicator, indicator,followed followedby by chromite, chromite, chrome diopside, garnet. While the hypabyssal hypabyssal clasts are quite rich in some some of ofthese theseminerals, minerals, most most chrome diopside, and and garnet. While many many of the of the diatreme-facies breccias do do not not contain contain indicator indicator minerals minerals in the 0.4 to 0.8 millimeter range. range. These of diatremefacies breccias 0.8 millimeter indicators that can be seen in thin section, and it is expected that digestion samples do have extremely small indicators of aa sufficiently sufficientlylarge large sample sample would would produce produce at least a few larger grains. of Ilmenite llmenite Chromite Chromite Chrome Diopside Diopside Garnet, Undifferentiated Undifferentiated Camp 55 Variation 11 Variation 24 0 0 0 Camp 55 Camp Variation Variation 22 57 1 1 1 Camp Camp 55 Variation Variation 33 0 0 0 0 Lake Ellen Ellen 42 0 0 30 FIGURE 4:4:Typical Typicalindicator indicatormineral mineralcounts countsper per gram gram of of various various disaggregated disaggregated kimberlite samples. Indicator FIGURE Indicator minerals reported variations 1 1 and and 22represent represent reported are arewithin within the the 0.4 0.4 to 0.8 millimeter range. Camp 5 variations hypabyssal clasts. Results for Lake lake Ellen Ellenmay may vary vary depending depending on on portion portion of pipe sampled. 8 �set of of ilmenites ilmenites from from Camp 5 variations variations 1 1 and and 22 and and from from Lake Lake Ellen Ellen was was sent sent to to aa commercial commercial laboratory laboratory A set microprobe analysis. An average averageMgO MgOvalue valueofof14.4% 14.4%was obtained for for ilmenite ilmenite from from variation variation1,1,and and14.1% 14.1% for microprobe analysis.An variation 2.2.These These values values indicate indicategood good diamond diamond preservation preservationpotential, potential,and andare are slightly slightlyhigher higher than than the for variation content of ilmenites and as as compared compared to average MgO content ilmenites from Lake Ellen, Ellen, both as as analyzed analyzed in this study study (13.7%) (13.7%) and the MgO/CrO diamond MgO/Cr203 plot of of McGee McGee and and Hearn Hearn (1983). Unfortunately, Unfortunately, minerals that are are useful in estimating estimating diamond grade approximations have clasts, and and no no statistically statisticallysignificant significantapproximations haveyet yet been been gradeare arenot not very very abundant abundantin in most mostCamp Camp55 clasts, obtained. One small anhedral chromite ilmenites for for chromite which which was was accidentally accidentally included included with the the variation variation 11ilmenites analysis did not plot within within accepted major-element diamond inclusion parameters. Although there are are several several kimberlites kimberlites and andkimberlite kirnberliteclusters clusterseast eastand andsoutheast southeastofofthe theCamp Camp55gravel gravelpit, pit, these bodies are are either either too too distant distant or ortoo toooblique obliqueto tothe theaccepted accepteddirection directionofofglacial glacial advance advance in in this this area area to to account abundance of kimberlite clasts the Camp kimberlite fragments account for the abundance ofkimberlite clastsin the Camp 5 sediments. Most Mostkimberlite fragmentsininthe theCamp Camp 5 pit pit are are probably probablyderived derivedfrom fromundiscovered undiscovered kimberlites kimberlites in eastern eastern Iron or western western Dickinson counties. These These bodies are probably small diatremes with associated dikes dikes or or sills. sills. twenty kimberlite kimberlite clasts clasts have have been been located throughout throughout the Approximately twenty thepit, pit, and and are are marked markedwith with wooden wooden stakes few samples samples of of greenstone greenstone and amygdaloidal Keweenawan Keweenawan basalt basalt have have also also been been stakes and flagging tape. A few flagged, as both both of ofthese theserock rocktypes typescan canresemble resemble kimberlite kimberlite at first firstglance. glance.Field Fieldtrip tripparticipants participantsare areencouraged encouraged flagged, all of ofthese these clasts clasts in in situ, situ, and ground searching searching can be as and evaluate evaluate for for themselves themselves how how effective ground as a to examine all supplemental exploration technique. Participants Participants may may collect collect and and keep keep any any of the kimberlite kimberlite clasts clasts they they wish; wish; willbe be provided provided ififattendance attendance is is larger larger than expected. additional samples will 26.6 Leave Camp 5 gravel pit, and and proceed north north to toM-69. M-69. 27.6 Junction Junction of of Camp Camp 5 road and and M-69. M-69. Turn left and proceed proceed west westtoward toward Crystal CrystalFalls. Falls. 38.0 38.0 Turn right right at at four-way four-way stop. 39.0 39.0 Return Return to parking parking lot lotatatWilliams Williams Mini Mini Mall. Mall. Stop 3: 3: Crystal Crystal Exploration established in The Sample Sample Preparation Facility Facility (SPF) of Crystal Crystal Exploration Exploration Inc. was established in 1984 1984 to process oneonebulk samples from various various Upper Upper Peninsula Peninsula projects projects in in preparation preparation for for diamond diamond analyses. analyses. The The ton kimberlite bulk facility was waslater later expanded expanded to to handle handle the processing processing of of field field samples. The SPF The kimberlite The SPF is partitioned into two sections. The kimberlite evaluation evaluationplant plant consists consistsof of two two ball mills, a small Wilfley Table,aatrommell, trommell,an anauger, auger,aaDenver DenverJig, and vibrating vibrating screens. screens. The sample processing processing plant Wilfley Table, Jig, and plant includes includes sample mixer, alarge a large Wilfley WilfleyTable, Table,aadrying dryingoven, oven,aamagnetic magneticseparator, separator, and and aasmall smallheavy heavyliquid liquidconcentrating concentrating a sample lab. The The SPF is isrun run by bytwo twotechnicians technicians operating operating the physical plant and one person conducting the conducting theheavy heavyliquid liquid concentrating procedures one-ton bulk sample can be be processed processed concentrating proceduresininthe thelab. lab. Under Under normal normal operating operatingconditions, conditions,aaone-ton fieldsamples samplescan canbe be reduced reduced to the in about two to three weeks. weeks. Approximately Approximately ten 50-kilogram 50-kilogram field the desired desired concentrate ready for heavy liquid separation in one one day. day. 9 �Figures55 and 6 contain flow Figures flowcharts chartswith withdescriptive descriptive notes notes outlining outlining the thevarious various stages stages for both both the bulk and field concentrates are field sample processing. The The final concentrates are either eithersent sentto to outside outsidefacilities facilitiesfor microscopic examination or Exploration's own experienced, experienced, in-house observation. Mineral or passed passed on on to Crystal Exploration's in-houseteam team for indicator mineral observation. Mineral grains grains requiring requiring further furtherprobe probeanalyses analysesare areshipped shippedtotovarious variouscommercial commercialfacilities. facilities. KIMBERL1TE KIMBERLTTE BULK BULK SAMPLES SAMPLES Stage Stage11---- 11 Ton Ton Bulk Bulk Sample Sample 11 ton bulk sample of of kimberlite kimberlite from from an an evaluation evaluationdrill drillhole/trench/pit. hole/trench/pit. Stage Stage 22---- Trommel Trommel (Cleans (Cleans & & Screens) Screens) Bulk trommel for cleaning cleaningand andscreening. screening.After Afterpassing passingthrough throughthe thetrommel, trommel,there there are are three three Bulk sample goes into trommel (3) size fractions. size fractions. (1) kilogram sample is shipped to a lab for diamond diamond and indicator indicator analysis. analysis. (1) ÷6mm +6mm 50 kilogram (2) (2) 2-6mm material is is placed placed in ball mill for reduction to to -2mm -2mm fraction. (3) -2mm material continues continues for for further furthersize sizedivisions divisions(Stage (Stage3). 3). Stage Stage 33---- Vibrating Vibrating Screen Screen Vibrating Vibrating screen screendivides dividesthe the-2mm -2mm material material into into three threesize sizefractions. fractions. (1) (1) 1-2mm l-2mm sample passes into a double hutched hutched Denver DenverJig. Jig. (2) (2) ¼-lmm Vi-lmmsample samplepasses passesonto ontothe theWiffley WilfleyTable. Table. (3) considered slimes and passes (3) -'/4mm -Vmm isisconsidered passes out outof of the theplant. plant Stage Stage44---- Denver DenverJig Jig The is then then concentrated by a Denver Jig. The concentrate The 1-2mm l-2mm fraction is concentrate is is magnetically magnetically separated separatedwith with the the non-magnetic laboratoryfor non-magneticfraction fractionbeing beingshipped shippedto to aa laboratory fordigestion digestionininhydrofluoric hydrofluoricacid acid and and diamond diamondanalysis. analysis.The The tails tailsfrom from the the DenverJig Denver Jigare arereduced reducedininthe theball ballmill millto toaa size size fraction fractionthat that is is less less than than 1mm 1mmand and then thenpassed passedover over the the vibrating vibrating screen. screen. Stage Stage55----Wilfley WiMeyTable Table The fraction is is concentrated concentrated by the the Wilfley WiffleyTable. Table.The Theconcentrate concentrateisistreated treated by by the the same methods methods as The'/4-1mm %-lmm fraction as the theDenverJig Denver Jigconcentrate. concentrate.The TheWilfley WilfleyTable Tabletails tailsare arereturned returnedtotothe theball ballmill millfor foraaspecified specifiedperiod periodof oftime timeand and then then passed passed over over the thevibrating vibrating screen. screen. *The remilling concentrating procedures. diarnond(s) isis not not missed missed in the concentrating procedures. **The remillingprocedure procedureof of the the tails tails insures insures that that aa diamond(s) When 2,000 pound sample sample is is reduced reduced to toaa weight weightof of around around 100 100pounds pounds (plus (plusthe the Whenthe theball ballmilling millingisiscomplete, complete,aa2,000 concentrates). concentrates). * 10 �FIELD FIELD SAMPLES SAMPLES Stage Field Sample Stage 11 --- Field Sample Samples consist Samples consist of of approximately approximately50 50kilograms kilogramsof ofglacial glacialtill till (soil (soil sample). sample). 2--- CleanIng Screening Stage 2 Cleaning & Screening Till is placed placed in in aa small smallcement cement mixer mixer to to disaggregate disaggregate the sand grains from the clay/silt matrix. The The resultant slurry is then passed through through aa screen screento toget gettwo two (2) (2) size size fractions. +1.2mm (oversized) (oversized) --stored stored for possible possible later kimberlite clasts. Once (1) +1.2mm later identification identification of ofkimberlite Once there thereisisno no use use for the sample, it is discarded. Table. (2) -1.2mm -1.2mm -- fraction (2) fraction is passed over over the theWilfley Wilfley Table. Stage Stage 33 --- Wllfley Wilfley Table Concentration Concentration The Wilfley WllfleyTable uses a shaking shaking motion motion combined combined with a water waterflowto separate the higher specificgravity The Table usesa flow to separate the higher specificgravity(S.G.) (S.G.) grains grains (lights). concentrate is grains (heavies) (heavies)from from the the lower lower S.G. S.G. grains (lights). This This heavy mineral concentrate is then then screened screenedinto intotwo two (2) size fractions. fractions. (1) +0.5mm +0.5mm is isthe the fraction fraction of ofmost mostinterest interest. In In this this size sizerange, range, kimberlite kimberlite mineral identification identification is much much easier than than in in the the-0.5mm -0.5mm fraction. This fraction is dried in an oven and over a magnetic magnetic easier This fraction and then then passed passed over separator (Stage (Stage 4). (2) -0.5mm -0.5mm fraction fraction is is stored stored as a back-up for indicator confirmation of aa sample sample or in determining determining the the number of indicator grains found in the entire sample. Stage Stage 44--- Magnetic Separator Separator As The magnetic separator uses a rare rare earth earth (steep (steepgradient) gradient) magnet magnetas asaahead head pulley pulley for for a short short conveyor. conveyor. As concentrate is conveyed over the magnet, the highly magnetic (left hand LH) and the partially magnetic (center magnetic (center concentrate is conveyed over the magnet, the highly magnetic (lefthand - LH) off the the end of -- C) C) grains adhere to to the the belt beltwhile while the thenon-magnetic non-magnetic (right (right hand hand -- RH) grains fall freely off of the conveyor. Since the the kimberlitic kimberlitic indicator indicator minerals minerals are are magnetic magnetic in in nature, nature, they will will fall fall in in the LH and C conveyor. Since compartments be in in the the RH RHcompartment compartment which which compartmentswhile whilethe themajority majorityof of the sample sample (including (includingany any diamonds) diamonds) will be inventoried or or discarded. is either inventoried Stage 5 5--- Heavy Heavy Liquid liquid Separation Separation & & Concentration Concentration separation process process using using The concentrate is further reduced by passing the grains grains through through aa heavy heavy liquid separation Polytungstate, Lithium lithium Metatungstate, Methylene Iodide, Sodium Polytungstate, Metatungstate,or orother otherheavy heavyliquid liquiddepending dependingon onthe theS.G. S.G. needed to recover the the specific specific indicator minerals desired. Observation Stage 66 -- Microscopic Observation After the heavy heavy liquid liquid separation, grams. This After the separation,the thetotal totalweight weightof ofthe thesample sampletotobe beobserved observedwill willbe bebetween between20-50 20-50grams.This for the the sample is then observed in detail by trained "pickers" "pickers" who examine the sample under magnification for desired indicator minerals. 11 �_____________ ________ ________ ____________ _________ ________ ____________________ _____ _____________________ _________ _______ ___________ ________________ _________ One—Ton Kiaberlite Processing Procedure Procedure One-Ton Kimberlite I • STAGE 1 1 Ton Bulk Sample I a I • .. , a I , 2 :a I . I •a I . I I I I I 1% • for g I • : : I I_................_ _•_••__•___I I I a : :__________ I 2—6mm —z : I I I a • a a • a • a • Ball Mill : I II I +6mm ——— Analysis II I . II Ia I I I • I : Trommel——Cleans Trommel--Cleans && Screens Screens a a STAGE 3 Vibrating Screen I - I • I I a I I • I I I I a 1—2mm • • • I a a I a —*mm I• I u I .:<-: . .: a •a • I <— I • • II II a a I 8 Ia Ball Ball —— :--: Tails Tails :--: —Mill Hill : : : :a II - I8 I1 ,I ' I I I I I8 - - • a a STAGE STAGE 44 Denver Denver Jig Jig . • •8I , I , • -a Ia II I a a I I l a a a • I Ia -1 • : Magnetic Magnetic : : Non—Magnetic Non-Magnetic : : Fraction Fraction : : Fraction Fraction : a a I .:-Storage I Storage 8 • I : a l I I I• a I I I a I8e I 8- a Magnetic a a I : Fraction • I I II g a • a : Non—Magnetic Non-Mwnetic : : Fraction Fraction : 8 a I a * - * a I a I I a I 8 a : Magnetic Magnetic : : Separator Separator : : •al • aI a Ia Ia I_ : Magnetic Magnetic Separator Separator • I * Concentrate Concentrate , , I a I a a • 8 I I $ * I Ial a : • I a - iI f • $I - 8I a a I I I I I •8I 4 II I 8 , I II I I 1 I I I • : Concentrate Concentrate : a I : I : STAGE5 STAGE 5 : I: I : : Wiltley Wilfley '—— :--: Tails Tails a__a :--: Ball Ball : Table Table : ': : : Mill Mill •I a I II I : : I _I • -* I a Slimes Slimes • I a II II 8 Ia • I- Ia I •8 II Is • I I I I I_.._.__._..___ -if-* a I a a a I 'a a a a $ I I Ia a l -8 a 8 : : HF HP : Digestion Digestion : I . a8 I a_ I • a • • .: Ia I • •a • Diamonds Diamonds : a a * a I8 a l a a II a8 I •1 I : HF HF : Digestion Digestion : Storage a • I I - a • a I a 8--r-8 I I •a : Ia • a8 Diamonds Diamonds : Ia I FIGURE 55 12 �____________ ________________ ___________ ___________ _________________________ ____________ ___________ _____ _____________________________ _____ Exploration Field Field Sample Sample Procedure Procedure in in the the S.P.F. S.P.F. Exploration , I 8 1 STAGE 11 STAGE Field Sample Sample Field t 91 : . . ----- : . , I * , .:-----; I 1 t STAGE 22 STAGE Cleaned && Screened Screened 1 6 I • I I1 8 I I a 1 I '* I I1 I I • a • • • : a +1.2fraction +1.2mg fraction I 1 • • . : : : I11 I :--—-—:: a Discarded Discarded I1 • I I I I1 9 Storage Storage 9 I1 I1 I II I I II I I I 9 I9 I I 9 1 1 : STAGE 33 STAGE I: : : Wilfley Wilfley Table Table Concentration Concentration : I 9 1 9 II I I 1 I I1 I 9 9 I. I I • • _____II I I : Lights Lights :---: ———i I I • : Retvies Heavies : I • : a Screened Screened 9 aI • • • : I I I :----: : I 9 I* I1 I II I +0.5m fraction fraction +0.5mm 8 * 9 I 9 1 9 9 Discarded Discarded : 9 I I I I I I 1 II I II • I I I • * II Il 9 II I I 9. I 9 I1 : -1.2fraction -1.2mm fraction I $ 1 • 1 •1 . I I I 9I I 1 I •1 I • I : I 9 II t I I I I I9 I I1 I 9 1 I1 : : I1 I . • I -0.5mm fraction fraction —0.5mm a I Storage Storage 9 : 9 II I a 1 -I I I , $ I1 : Dried Dried : I1 I I l a 1 I I • • • a STAGE 4 Magnetic Separator • 9 l I •* I I • I •I •9 9 9 I a : I •I *1 •99 • 9 I9 I • I I I I9 I : Center Center Portion Portion : : (part(part.magnetic) magnetic 1 : I 19 9 I I • • : : Left Left Portion Portion : (highly (highly magnetic) magnetic) : Portion (non-magnetic) • 9 9 I • 1 •: I — I I Right 9 1 I , •I • : •9 * Discarded Discarded • I I : a9 $ I I1 I9a I - STAQE 5 STAGES H e a v Liquid Reavy Liquid Separation && Concentration Concentration Separation I 9I I 9 a .: - I9 I 1 l I 1 •I • * I9 I : Concentrate Concentrate : FIGURE 66 FIGURE : : 9 STAGE 66 STAGE Microscope Microscope : ; ! 13 �Acknowledgments Acknowledgments Theodore J. Bomhorst Bornhorst of Michigan Technological Technological University for originally originallysuggesting suggesting this this Credit is due to Dr. Theodore field trip, and to Glen Adams Crystal Exploration Exploration for allowing allowing visits to the Lake Lake Ellen Ellen kimberlite kimberlite and and the the Adarns and Crystal Sample Processing Schinella-Mottes Construction ProcessingFacility. Facility. Gene Mottes and khinella-Mottes Construction also also deserve deserve credit creditfor for graciously graciously allowing brief visit visit to to the the Camp Camp 55 gravel gravel pit pit. Bob Bob Regis Regisisisthanked thanked for for permission permissionto to use use his his 5agola-II1! Sago1a-II allowing aa brief terminology the Michigan DNR is thanked thanked for general information terminology in this this study, study, and and Milt Gere of the information and support. 14 �REFERENCES Cannon, Cannon, W.F., and Mudrey, Mudrey, M.G. M.G. Jr., 1981. 1981. The The Potential Potential for for Diamond-Bearing Diamond-BearingKimberlite Kimberlite in in Northern Northern Michigan 15p. Michiganand and Wisconsin: Wisconsin: U.S. US. Geological Geological Survey Survey Circular Circular842, 842,15p. Charlier, Chartier, Torrie, Tome, 1993. 1993. Diamond Bearing Kimberlite(s) and and Related Related Geology Geology in in the the Upper UpperPeninsula Peninsulaof of Michigan: Michigan: Geological Geological Excursion Excursion Guide, Guide, Michigan Michigan Basin BasinGeological GeologicalSociety. Society. Dorr, Jr, and Michigan Press, I?., 1977. 1977. Geology Geologyof of Michigan: University of Michigan Press, Ann Ann Dorr, John John A. A Jr, and Eschman, Eschman,Donald DonaldF., Arbor, Arbor, 476p. 476p. Gibbins, Diamond Exploration Exploration in in the Northwest Territories: Gibbins, Walter A., A , and Atkinson, Dorothy, 1992. Diamond Temtories: Publication PublicationEGS EGS1992-1, 1992-1,Yellowknife, l8p. 18p. Jarvis, William, William, 1993. Michigan Prospectorsand andDevelopers DevelopersAssociaAssociaJarvis, Michigan Kimberlites: An An Update: Update: Abstract Abstract at Prospectors tion of Canada 61st Annual Meeting (Paper M-10). tion Canada 6lst Meeting (Paper M-10). McGee, McGee,E.S., E.S., and andHearn, H e m ,B.C. B.C.Jr., Jr.,1983. 1983.Lake LakeEllen EllenKimberlite, Kimberlite,Michigan, Michigan,U.S.A.: U S A :U.S. U.S. Geological GeologicalSurvey Survey Open-file 22p. 83-156,22p. Open-fileReport Report83-156, Mitchell, H., 1986. 1986. Kimberlites Kimberlites-- Mineralogy, Mineralogy, Geochemistry, Geochemism, and and Petrology: Petrology: Plenum Press, New New Mitchell, Roger Roger H., York, York,442p. 442p. Peterson, L.,1986. 1986.Surficial Sudcial Geologic Geologic Map Map of ofthe theIron IronRiver River10loxx2° 2O Quadrangle, Quadrangle,Michigan Michiganand and Peterson,Warren WarrenL., Wisconsin: Map 1-1360-C. Wisconsin:U.S. U.S. Geological GeologicalSurvey SurveyMiscellaneous MiscellaneousInvestigations InvestigationsSeries Series Map I-1360-C. Schuize, Garnet Xenocryst Xenocryst Populations Populations in North North American Kimberlites: short short course course paper Schulze,Daniel Daniel J., 1993. Garnet paper in in Diamonds: Diamonds: Exploration, Exploration, Sampling Sampling and Evaluation. Evaluation. Prospectors Prospectors and andDevelopers DevelopersAssociation Association of of Canada, Canada, Toronto, Toronto,Ontario. Ontario. 15 � https://digitalcollections.lakeheadu.ca/files/original/2458e2c7290330228ee152c9a122af26.pdf dd5f9d643297b8215da12959fb8228ce PDF Text Text Proceedings 40th Annual 40th Annual Meeting May 1111-14, 1 4 , 11994 994 May Michigan Technological University Michigan Houghton, Michigan Michigan Volume 40 Part 5—Lessons from mining case histories: West Menominee Range, Michigan By: A//an By: Allan M. M. Johnson Johnson L I 'U �I I 40TH ANNUAL MEETING INSTiTUTE ON LAnE SUPERIOR GEOLOGY I I Volume Volume 40 consists of I Part 1: 1: Program Programand and Abstracts Abstracts Part 2: Self-guided geological field trip to the 2: geological to the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part 3: Volcanic geology of eastern Isle Royale, Michigan Part Part 4: 4:Michigan Michigankimberlites kimberlitesand anddiamond diamondexploration exploration techniques techniques Part Lessonsfrom frommining miningcase casehistories: histories:West WestMenominee MenomineeRange, Range,Michigan Michigan Part 5: 5:Lessons I Reference to material material in Volume 40, Part Part 11 should should follow follow the the example examplebelow: below: Woodruff, L.G., and Back, Back, J.M., J.M., 1994, 1994,Chalcocite Chalcocite mineralization mineralization in in the the L.G., Cannon, W.F. W.F. and Portage Lake Michigan (ábst.): (abst.): Institute on Lake Lake volcanics, volcanics, Keweenaw Keweenaw Peninsula, Peninsula, Michigan Superior Geology Proceedings, 40th Annual Meeting, Meeting, Houghton, Houghton,MI MI 49931, 49931,v. v. 40, 40, part pan 1. 1,P. p. 77. 77. Published and distributed by Institute Institute on on Lake Lake Superior Superior Geology Geology M.G. Mudrey, Jt, Secretary-Treasurer, M.G. Jr., Secretary-Treasurer, I.L.S.G. I.L.S.G. 106 N 3rd 3id Street Street Mt Mt.Horeb, Horeb, Wisconsin Wisconsin 53572 53572 LSSN ISSN 1042-9964 1042-9964 All from All volumes are available available for photocopying photocopying costs from Michigan Michigan Technological Technological University University Library Archives I I I I I 1 I I I I Michigan an equal equalopportunity opportunity educational educational institutiodequal institutiorVequalopportunity opportunity employer employer. MichiganTechnological Technological University Universityis an �Institute on Institute on Lake Superior SuperiorGeology Geology Proceedings Proceedings 40th Annual Meeting Meeting May 11—14, 1994 May 11-14,1994 Michigan Technological University Michigan Houghton, Michigan Volume 40 Volume Part 5-Lessons S—Lessonsfrom from mining mining case casehistories: histories:West WestMenorninee Menominee Range, Range, Michigan Michigan By: Allan Al/an M. M Johnson By: Johnson Department ooff Mining Mining Engineering Department Engineering -1 295 Michigan Technological Technological University, University,Houghton, Houghton,Michigan Michigan49931 49931-1295 �ITINERARY 7:30 am Leave MTU MTU from Union Circle Leave from Memorial Union 9:00 Arrive Iron Iron River River Area Area Arrive (NOTE: All (NOTE: All times timesare are EDT, EDT, but but Iron Iron County County is is Central Central Time Time Zone) Zone) 9:00-9:30 open pitlunderground pit/underground mine Isabella Mine - open footwall slate and Riverton iron formation formation part of Dober Dober Mine Was complex complex flooded pit pit (acid water) water) flooded 9:40-10:30 Dober Mine and Iron Iron River River Old Old Stambaugh Stambaugh sewage treatment treatment plant plant site site open pit/underground pitlunderground mine mine acid drainage drainage river diverted diverted diversion structure in river synergetic pond pond system for treating treating AMD holding ponds ponds - 10:30-11:30 . Cardiff Cardiff Mine Mine open shaft shaft 1992 death (drowning of teen in flooded flooded mine workings) 11:30-1:00 Iron County Historical Museum Museum U.S.) 1921 steel headframe (oldest in US.) Caspian Mine Site, 1921 boxed lunch on grounds boxed g m u d s -- inside inside if inclement inclement weather iron ore mining mining dioramas dioramas early life in Iron Iron County County life in logging logging museum museum also adjacent to Lee Le Le Blanc Art Center Center (memorial (memorial to to renowned renowned wildlife wildlife artist artist from Iron River) 1:00-1:30 Buck Mine Site Site acid drainage drainage surface and underground underground sources sources 1:30-2:00 Mine Smuggler Mine Old County Road 484 road cave-in, fatality road fatality 2:15-3:30 Homer-Wauseca Mine and Sherwood Mine Complex Homer-Wauseca Mine pumping pit for overburden dewatering dewatering site of USGS-MGS dewatering study study in in 1940's and USGS-MGS dewatering basis for Theis' groundwater groundwaterdrawdown drawdowncalculations calculations sand filling filling raises raises mine subsidence subsidence 3:30-4:00 Cardiff Cardiff Mine Mine Headframe Headframe shallow shallow underground underground mine mine 4:00-5:30 Return Return to to Houghton Houghton �. , * : > .,, -.,.$: , .,,,.3  Â, '.-' "*^Â¥; TABLE TABLE OP OFCONTENTS CONTENTS I I I I I I Page Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . Historical HistoricalSketch Sketch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lessons Lessonsfrom fromMining MiningCase CaseHistories Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mine MineRelated RelatedProblems Problems-- Introduction Introductionto toCase CaseHistories Histories . . . . . . . . . . . . . . . . . . Case Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaseHistories References References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,. : . . . . Introduction Introduction ' L., : .~ . 1 ?, 1 1 1 22 44 21 21 26 26 67 67 ~. LIST TABLES LISTOF OFTABLES I I   I Table Table 1.1. Rock RockUnits Unitsin inthe theIron IronRiver-Crystal River-CrystalFalls FallsDistrict District Page Page ................. 2.2. Iron IronOre OreShipments Shipmentsin inMichigan MichiganThrough Through1974, 1974,Menominee MenomineeIron IronRange Range-- Iron Iron River District RiverDistrict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 17 ,- 3.3. Iron IronOre OreShipments ShipmentsininMichigan MichiganThrough Through1974, 1974,Menominee MenomineeIron IronRange Range- Crystal Falls District 18 Crystal Palls District . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ^n% 18 4.4. Avenge AverageofofYearly YearlyAnalyses AnalysesofofDober DoberMine MineAcid AcidDrainage Drainage1975-1978 1975-1978 . . . . .., .6262 .%.,LC �I LIST LIST OF OF FIGURES FIGURES Figure Figure U Page Page \ J 1. 1. Location Location of of the theCities Citiesof ofCrystal CrystalFalls Fallsand andIron IronRiver Riveron onthe theMenorninee Menominee .......................... Drainage Drainage from fromthe theWest WestMenominee MenomineeRange Range . . . . . . . . . . . . . . . . . . . . . Range Range in in Iron IronCounty, County,Michigan Michigan 2. 2. 3. 3. Generalized Generalized Geologic Geologic Relationships Relationships of the Folded Paint River River Group Group Formations in the Iron River District Formations in the Iron River District . . . . . . . . . . . . . . . . . . . . . . . . . ......... ................ 4. StratigraphicGeologic Geologic Relationship in the Crystal Falls Falls District District 4. Stratigraphic 5. 5. Map Map of of Mined Mined Properties Propertiesin inthe theIron IronRiver RiverDistrict District 55 J 66 --. 8 99 11 11a, J 14 14 6. 6. Mine Mineand and Map MapPlate PlateLocations Locationsin inthe theCrystal CrystalFalls FallsDistrict, District,Menominee MenomineeIron Iron Range Range ............................................ 7. in the Iron River District of 7. Location Location of of the the Sherwood Sherwood Mine Mine Complex Complex in Northern Michigan Northern Michigan 15 15- .................................... 27 27 Isometric IsometricView View of ofthe theSherwood SherwoodMine MineShaft Shaftand and Levels Levels in in Relation Relation to to the the Main Ore Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MainOreBody 28 28 9.9. Generalized Generalized Profile Profileof of Glacial GlacialOverburden Overburden at at the theSherwood Sherwood Mine Mine in inthe theEast East Pit Pit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 29 8. 8. ................ Photograph Photographof of Initial InitialSubsidence Subsidence in in West West Pit Pit Area, Area,September September7, 7,1979 1979 . . . . Photograph Photographof of Enlarged Enlarged Subsidence Subsidence Pit Pit Which Which Caved Caved on October October 14, 14,1979 1979 . . Enlarged Enlarged West West Pit PitAfter AfterOctober October19, 19,1979 1979Subsidence SubsidenceEvent Event . . . . . . . . . . 10. 10. Location Location of ofSubsidence SubsidencePits Pitsatatthe theSherwood SherwoodMine Mine 11. 11. 12. 12. 13. 13. . . . . - 31 31 33 33 33 33 34 34 ' J 14. 14. Subsidence SubsidenceMonument MonumentLocations Locationsat atthe theSherwood SherwoodMine MineIncluding IncludingContours Contours of ofSubsidence SubsidenceBased Based Upon Upon the the Level Level Survey Survey of of December December 9, 9,1980 1980 . . . . . . . 36 36 15. 15. Location Locationof ofExtensometer Extensometer Installations Installations in in Shear Shear Zones Zones on on the the 1000 1000and and 1200 1200 Levels Levelsof of the theSherwood Sherwood Mine: Mine: Looking LookingEast East .................... 37 37 16. 16. Suggested SuggestedMechanism Mechanism to to Explain ExplainSurface SurfacePits Pits on onSouth SouthBlock Blockof ofSurface Surface Shear: Shear: Looking LookingWest West ............................... 38 38 J �- U [ LIST OF FIGURES continued unprovedConceptual ConceptualModel Modelof ofPiping PipingSubsidence SubsidenceOver Over an Underground 17. Improved an Underground 18. ........................................... SmugglerMine Mine Cave-in Cave-in on on County County Road Road 424: 424: Looking LookingEast East . . . . . . . . . . Smuggler 19. Close-upof ofSmuggler SmugglerMine Mine Cave-in: Cave-in: Looking LookingEast East Close-up Mine Mine ....... SmugglerMine Mine Cave-in Cave-in on on County County Road Road 424: 424: Looking LookingWest West 20. Smuggler 46 46 .... 47 .......... L Close-up of of Smuggler SmugglerMine Mine Cave-in: Cave-in: Looking LookingWest West 21. Close-up E PlanMap Mapofofthe theSmuggler SmugglerMine MineArea AreaShowing ShowingSubsidence SubsidencePits Pitsand andthe the 22. Plan Areas of Underground Workings . . . . . . . . . . . . . . . . . . . . . ...... Areas of Underground Workings 48 L 23 . Small SmallSubsidence SubsidencePit Pit (50 (50 ftftdiameter, diameter. 25 25ftftdeep) deep)South Southof ofCounty CountyRoad Road424 424 23. Above Smuggler Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Above Smuggler Mine 50 24. Cross-Section Cross-SectionMap Mapof ofthe theSmuggler SmugglerMine MineOre OreBody Body 24. 51 L L [ L L I! [ [ [ Ii [ 47 ............... 25 . Longitudinal LongitudinalSection Sectionof of the theSmuggler SmugglerMine MineOre OreBody Body 25. .. ........... 52 26 . Plan PlanMap MapofofIsabella, Isabella.Dober Doberand andHiawatha HiiwathaMines Mines 26. 55 SurfacePlan PlanMap Mapofofthe theDober-Hiawatha-Isabella Dober-Hiiwatha-IsabellaMine MineComplex Complex 27 . Surface 27. 57 28 . Isometric IsometricDiagram Diagramof ofPart Partof ofthe theHiawatha Hiawathaand andDober DoberMines Mines 28. 59 .... ....... 29. Schematic SchematicDiagram Diagram Showing Showing Flow Flow of of Water Waterin inthe theDober DoberMine MineComplex Complex 29. . . . 63 �.. * % %. ..~.*. *.* * c .WZ.. 1 - INTRODUCTION INTRODUCTION 4 . ." The Menominee Range of of northern northern Michigan Michigan was was aa major major producer producer of The Menominee Range of direct direct shipping shipping < '*a- 7, iron ore ore for iron for nearly nearly a a century. century. When Whenthe thelast lastunderground underground mine mine on on the the Range Range ceased ceased operation in in 1978, 1978, itit marked marked the the end endof of an an era. era. With operation With the the start start of of mining mining in in the the early early 1880's, 1880's, the the district district had had gone gone througlf througtf a full full cycle cycle from from the thestart-up start-up of ofmining miningthrough throughclose-down. close-down. During million long tons of iron ore ore were were produced produced and and shipped shipped from from During this this period period over over 200 200 million nearly 100 operations. This nearly 100 mining mining operations. Thisdevelopment developmentand and production production spanned spanned the the time time from from when the the United United States from an when States advanced advanced from an essentially essentially rural-agricultural rural-agricultural society society through through the the industrial revolution revolution and and into into the the beginnings beginningsof ofthe the computer computerand andspace spaceage. age. The industrial The location location of of the West West Menominee Menominee Range Range in in Iron Iron County County is is shown in Figure Figure 1. the shown in 1. . . < .' . , *,,,W" .. ~.. ,. %. ' . -..,&...:, *... . , . . '> -\7. - . HISTORICAL HISTORICAL SKETCH SKETCH '. , . .à , ,~~ . . Iron ore ore mining mining was the the impetus impetus for for the the development development of the the Crystal Crystal Falls Falls and and Iron Iron River centers of of mining. River centers mining. Mining Miningjobs jobs brought brought miners miners and and their their families families to to the the district, district, paid paid for the the roads roads and and railroads and supplies supplies in in and and the the ore ore out for railroads needed needed for for shipping shipping equipment equipment and out to to lower late lake markets. markets. Taxes lower Taxespaid paid by bymining miningdollars dollarsbuilt built the thecities cities and and towns, towns, including including the the schools, police and and fire fire departments, schools, hospitals, hospitals, police departments, and and attracted attracted all all the the businesses businesses that that comprise comprise ,:.:,4 $ .; thriving communities. thriving communities. . .. .. ....... . '. ' .. : , .., , .,*.~ Ore was vital vital to to the war effort effort of of two two Ore produced produced from from the the Menominee Menominee Range Range mines mines was the war World Wars and supported supported mining mining families families and and the the families families of of the the supportive supportiveservice service 6 Iron ore mining paid paid for the businesses businesses for a number of generations for one one century. century. Iron infrastructure of these just as infrastructure of these two two major major population population centers centers in in Iron Iron County County just as mining mining has has done done in other areas of of the the Upper Upper Peninsula. Peninsula. �2L During During this this century, century, great great advances advances were were made made in in mining m i n i and and processing processing iron ore ore into into steel. steel. Early mining mining was was done done largely largely by by human human manual manual labor labor and andhorse horsetransportation. transportation. Until dieseland andgasoline gasoline powered powered engines, engines, mining mining was was labor labor Until the the advent advent of of steam, steam, electrical, electrical, diesel intensive occupation. The intensive and and aa highly highly dangerous dangerous occupation. The County County Mine Mine Inspectors' Inspectors' records records are are < replete replete with with injuries injuries and and deaths deaths resulting resulting from fromdangerous dangerouswork work in intjie @eever-deepening ever-deepening underground rockfalls, falls,delayed delayedblasts, blasts, timber timber underground mines. mines. Deaths Deathsand andinjuries injuriesthat thatranged rangedfrom fromrock support support failures, failures, runaway runaway skips skips and and trams, trams, scalding scaldingsteam steam from from mine mine fires, fires, suffocation suffocationfrom from --. inadequate inadequate ventilation ventilation and noxious noxious gases gases and and other otherhazards hazardsincluding includingmine minecave-ins cave-insand and floodings. floodings. In 27men menwere werekilled killedone onenight nighton onthe the28th 28thofofSeptember September1893 1893when when Inone onetragedy, tragedy, 27 the the Mansfield Mansfield Mine Mine was was suddenly suddenly flooded flooded by an an inrush inrush of of water water through through aa failed failed shaft shaftlocated located adjacent River in in east adjacent to to the the Michigamme Michigamme River east Iron Iron County. County. However, However,technological technological improvements improvements in in mining mining evolved evolved during the the tenure tenure of ofthe theWest WestMenominee MenomineeRange Rangeresulting resulting ininhighly highlyproductive productiveand andmuch muchsafer safermining miningmethods methodsby bythe thetime timethe thelast lastmine--the mine-theSherwood Sherwood Mine--ceased operations Mine~ceased operationsin in1978. 1978. -.. ,ll,..> .!,- T .. - . s A:>,.. 4 * f . LESSONS LESSONS FROM FROMMINING MININGCASE CASEHISTORIES HISTORIES '2 There There are aremany many lessons lessons that that can can be be learned learned from from such such aa rich rich history. history. For Forexample, example, with inpast pastmining miningpractices practices and and mine mineclosure closure with the theuse useof ofcase casehistories, histories,deficiencies deficienciesin procedures proceduresthat thathave haveresulted resulted in incurrent currentenvironmental environmentalproblems, problems, can canbe beidentified identifiedand and studies. Theseenvironmental environmentalproblems problems can can be begrouped grouped into intothree threeareas: areas: 1) 1) mine mine studies. These '.a . subsidence; subsidence; 2) 2)mine minewater waterdrainage drainageproblems; problems; and and3) 3)problems problemsrelated related to toinadequate inadequatemine mine shaft shaftsealing sealingand andcapping cappingpractices. practices. 1 �L 3 I L L Mine has been a problem in Mine subsidence has in the the district. district. In In one one instance, instance, human human life life was was lost because of sudden stope of of an anold old sudden subsidence subsidence of a section section of county road into into aa shallow shallow stope mining Also, many many mines mines in in the the Iron Iron River River area area encountered encountered acid acid waters waters during during mining operation. operation. Also, L their and several continued to to drain drain acid acid water water when when they they became became flooded. flooded. The their operation operation and several continued The L acid acid waters waters flowed flowed from from the the mines mines into into the the Iron Iron River River and and eventually eventually the the Brule Brute River River system system causing pollution problems. problems. Because Becausethe theBrule BruleRiver River marks marksthe theborder borderbetween betweennortheastern northeastern Wisconsin Wisconsin and the Upper Peninsula Peninsula of Michigan, the the residents residents of of the the two two states statesare are [ concerned with the problem. There is one occurrence of human fatality resulting from falls into mine shafts in Iron L County. in 1992. The Thisoccurred occurredatatthe theChatham Chatham Mine Mine in Stambaugh Stambaugh in Thepresence presence of of County. This hundreds of of shafts, protection in in the the form form of of seals seals or or hundreds shafts, some some with with deteriorating deteriorating or or inadequate inadequate protection caps, remains remains aa cause cause for forconcern. concern. These These three three basic basic environmental environmental problems problems were were investigated investigated by by the the use use of ofcase case r L histories. histories. This This field trip guide guide is is structured structured to to present present information information on on these these problems problems and and to to [ show how these problems have been addressed addressed by the the mining mining companies, companies, local localgovernment government entities, and and the the Michigan Michigan Department of Natural Resources, to to lessen lessen their their impact impact on on this this mining district. The Theoverall overallobjectives objectives of of this this project project were: were: 1) 1) to document document deficiencies deficiencies in in L mine closure procedures procedures that that have have resulted resulted in in problems problems of of subsidence, mine closure subsidence, acid acid drainage drainage or or shaft shaft sealing/capping failures; 2) to examine sealingkapping examine these these problems and deficiencies deficiencies and attempt attempt to to develop ideas ideas on how how they they could have been prevented for their their effects effects lessened lessened by by action action L taken prior to 3)to torecommend recommend these these ideas ideas as asguidelines guidelinesin inmine mineclosing closing to mine mine closure; closure; and and 3) I procedures. �4 4 e+iJ Cy'li'SSi,!, . . ,^Hs.^i.ia . ^w". " ;.: .,%.'-:. ¥I ',; ?-'Â¥s' BACKGROUND BACKGROUND a,,, . . The I'l'sn&drystal Iron River—Crystal fte mining district district is Falls mining is located located on the the western : c?r$ Menominee in the the southern southern part of Iron Menominee Range Range in in the part of IronCounty County in the Upper Upper Peninsula Peninsula forms a a roughly The western The westernMenominee Menominee Range Range forms roughly shaped shaped ,.. . . .,. triangle, of which which extends extends between between Iron Iron River River on triangle, one one leg leg of on the the west west and and Michigan (Figure (Figure 1). 1). of of Michigan Falls on the east, Crystal Falls Crystal on the east, aadistance distanceof ofabout about 20 20 miles. miles. Fromthe the City City of of 3' From :*f:f : .9 ", .:. Iron River whichisis situated situated on on the the northwestern part of of the iron Iron River which northwestern part the range, range, the the i r a the Wisconsin is about formation formation trends trends southeasterly southeasterlytowards towardsthe Wisconsin border border which which is about five The third third leg leg five miles miles to to the the south. south. The of the of the triangle triangleextends extends south south of of Crystal Falls Falls paralleling paralleling and and then then crossing crossing the the Brule Brule River River into Wisconsin. into Wisconsin. Crystal The parallels the Menominee River The eastern eastern part part of of the the Range R a w e parallels the Menminee a v e r on on the the Michigan Michigan ,; .: %-, u i o : %.' ?~'--5?3'r->..l:.Â¥- : . p  .¥ ;a' , -,.,-. .!. .,,&'>.,.->jr' j::;?l~ .; &,,> & > ,:; ,..: . 7 ; . ~ , ~ side. side. The topDgraphy mostly rolling, rolling, varing varing from The topography is is mostly from about about 1300 1300 feet feet to to 1700 1700feet feet in in elevation. elevation. The higher elevations are and are near Iron Iron River, River, Michigan Michigan and southeast. as a result the drainage drainage is generally generally to the southeast. The The Iron Iron River River the western area southeasterly drains drains the western area southeasterly into intothe theBrule BruleRiver Riverwhich which forms forms the the The Crystal Falls Falls area The Crystal area is Brule andand Michigan-ane Rivers which which join, join, forming forming the the isdrained drainedby bythe thePaint, Paint, Brule Michiganne Rivers Michigan. border between border between northeastern northeasternWisconsin Wisconsin and and Michigan. MenomineeRiver, River,which whichultimately ultimately empties empties into into Lake Menominee Lake Michigan. Michigan. The drainage The drainage 2 is in Figure 2. is shown shown in Figure 2. The area has has been heavily glaciated glaciated and drift The area been heavily and the the soil soil is is thick thick glacial glacial drift mostly of glacial glacial till and consisting m consisting s t l y of till andoutwash outwashmorainal morainal sands sands and and gravels. gravels. The area is withnumerous nterous lakes lakes and and streams streams that that are The area is mostly mostly wooded wooded with are . . -.,; .,,,.,,: ...,. fran rain The glacial glacial ,,.,,., . ><'. ,. abundantly supplied supplied with abundantly with water £ra rainand and snow snow melt. melt. The ' *7 ~ , ~ < :':I , overburdenininthe thearea areaisis aa prolific prolific aquifer. overburden aquifer. is northern withrelatively relatively short The The climate climate is northern temperate temperate with short sinners sumers and and a a short growing season and andthe the winters winters are are cold short growing season cold and and long. long. �5 . . .~, . WISCONSIN IRON RIVER Figure 1. S T A L FALLS Location of the Cities of Crystal Falls and Iron River on the Mpnnminpe Ranae in Iron County, Michigan �LL Figure 2. L L Drainage from the West Menorninee Range L MENOMINEE RIVER LLL. C' �,, . . , - 7 . : ,...,*. Geology Geology . ~. ,. ?. .. .--of a series . T The h e west Menominee Range is is comprised of series of of complexly complexly folded ~ sedimentary rocks rocks of of Middle Precambrain Precambrain age. sedimentary age. The strata are the five The formations of of the Series. formations the Paint PaintRiver RiverGroup Group of of the theUpper Upper Animikie Animikie Series. L The The bottoanost unit unit is the Dunn Creek Slate Slate which is some 1000feet feet thick. thick. bottomnost is the Dunn Creek which is some 1000 The The upper 50 50 feet feet of of the the Dunn Formationcontains contains the the Wauseca member, member, aa Dunn Creek Formation upper L pyritic—graphitic slate. pyritic~qraphitic The Riverton Iron Iron Formation Formation overlies overlies the the Dunn Creek Formation and is in turn turn overlain overlain by by the Hiawatha Greywacke, Greywacke, which which is Creek [ L but is is absent absent in 500 feet but insome some areas. as thick as 500 The magnetic Stambaugh The Stambaugh Formation and the FortuneLakes LakesSlate Slateare arethe the next next higher higher units, units, Formation the Fortune *kspectively. respectively. More Moredetailed detaileddescriptions descriptionsof of the the rock rock units units are are presented presented in in Table 11 and and the the generalized generalizedgeologic geologicrelationships relationships of of the Table the folded folded Paint Paint River River [ [ Group strata strata as near Iron River, Michigan as ititexists exists near Iron River, Michigan isisshown shown in in Figure Figure 3. 3. Ore. Ore. - The Riverton Riverton Iron Iron Formation Formationis is not all ore. ore. The not all thin—bedded siderite and chert. thin-bedded siderite and chert. It consists It consists primarily primarily of of Oreoccurs occursonly onlyin in structurally structurally favorable Ore favorable areas where oxidation has has enriched enriched the the iron content of and oxidation iron content areas where deep deep weathering weathering and rock. the rock. the For the the most mostpart, part, the the ore ore bodies bodiesare are irregular irregular in in shape, size For shape, size and attitude, attitude, but to lie lie ininthe the flanks flanks of of steeply steeply but tend tend to thetroughs troughs or or along along the and plunging synclines. synclines. plunging surface. surface. Theore ore is is usually The usually continuous continuous from from depth depth to to the thebedrock bedrock Laterally the grade into into unoxidized Laterally the ore ore may may grade unoxidized iron iron formation. formation. Most Most of the ore has has been beenextracted extracted from fran tabular 100 of the mined mined ore tabular bodies bodies that thatare are 1 0 -or 0 o rmore more feet hundredstotothousands thousands feetininvertical verticalor or lateral lateral feet thick thick and and hundreds of of feet within deposits deposits from soft directions. even within The ore ore may vary between may vary between and and even from aa soft directions. The hydrated form to very hard hematite and hydrated hematite ore. ore. Generally the ore is the ore is described direct—shipping, old high phosphorous phosphorous ore. ore. as a direct-shipping, old range, range, norr-besseiner, non-bessemer, high is enriched ore from from some ore some mines is enriched in inmanganese. manganese. The The �8 TABLE 11 TABLE Rock Rock Units in the Iron Iron River-Crystal River-Crystal Falls Falls District District Rock units in the Pleistocene Till, anl, sand Ordovician Sandstone, dolomIte 0-425 Unconfonnity 0-100 Unconlonnity p. O- Silica rock Unconformity t ,Z Metadiabsce and metagabbro Fortune Lakes State Stainbaugh FormatIon hIawatha mtowuh. Oraywacke OmywÂ¥ck lilvorton Iron-Fonnation C Character known only for lower pert of section. exposed i0 eastern part of district, where strata eo,nt of gray slate, striped slate, aidesitic slat., wacke, and poesiMe Iron-formation. Most of unit not exposed or drilled with district. chlorite 100 lm -Cherty - ~laminated m " rock . and i massive - ~ w ~ slate, - - some 4 graywackt Many ports strongly magnetic, u"w-m.r..sMassIve 0-100 w .. graywecke commonly siderttlc, and gray slate. Lowermost part commonly contains abundant risen fragments. MIUnooaJiMTHll, — — Minor unoonionnity Thin-bedded rock, mainly chert end iron-rich cerbonste where unoxidized. Includes some graphitic slate, also stiipnomeiane beds and megnetite-rich 10-SO) w-m - - Dunn Duan Creek C q nSlate Stew 400—i. u@-L 100 5M Badwatar n a d w f r Greenstone 0 - 0-IS, * 4000 - Ñaf^SSES-S^-Mdwme.--Ñ beds in eastern part of district. Host rock for ore bodies. In eastern part or district, unit consists of siltatone underlain by black cherry slate, sideritlc aiate, end chert-arbons.te rock. In western pert of district, unit is chiefly siltstona and slate. Uppermost part throughout district is graphitlo pyritio slate (Waisseca Pyritic Member). Massive chioritized meac volcanic rock, In part flows with ellIpsoidal structure, =-sswa-- in part tuffs and agglomerates. Some pert. strongly magnetic. *ma Mostly interbedded slate and graywacke; In southeastern part of area 'ois highly metamorphosed equivalents. Probably contains some IernszlnOelS Amass Formation I, SW L- PrincIpally martite slate, with layers of eherty iron-lorhsiezion. Locally Hemlock Formation -M 6 000+ ** Saunders Formation I. 000(1) Mainly msesiva dolomite. Exposed in only a law places in southern part of dis. flot known Massive metabessit, in part with agglomeratic end ellipsoidal sfructnres. Mi&- . Meselve cherty rock that probably repreanti allidfisd erosion surface on dolo' mite. 4. + S I Mantle men thn Se percent of area. Flat-lying remnants of sandstone and dolomite in the southwestern part of the area. Granite, medlssm-grained, massive; In eastern part of district only. Trachyte as sparse thin dikes. Chlcritlxed. massive. Abundant dikes and sill., a law stocks. Granite and traebyte a, — Rare dikes. Unaltered; magnetIc and insanely polarized. Diabace 0 Remarks Estimated thIckness (feet) Rock unit g Iron River—Crystal Falls district 8 W - Greenstone In the Brule River ate. a., beds in uppesmoet pert, 1968 James, & etal., p.17, From James, p. 17, 1968 strongly magnetic. Mostly massive metabesalt. locally with ellipsoidal struchlree. Contains Bird Iron-Bearing Member ( ft thick) l,-l 400 feet below the top of the for- mation. Both the greenstone and the Bird Member are locally etzengly magnetic. trict. Some layers are sstsgnetic. �9 C GLACIAL a TILl. Ie a GLACIAL SAND& GRAVEL Relationships of the Figure s of t h e Folded Folded Paint P a i n t River R i v e r Group ~ i ~ u r d3.' ~ . kGeneralized , & n e r a l i z eGeologic d Relation i Formations Fpmations in i n the t h e Iron I r o n River R i v e r District rict ru ,7 ": , -5s-1*f.. ... , <Â¥:' , "Â¥j.' ;" ¥ i^, v;: II~ i �10 l1 On On the the western western end end of of the the Menominee Menominee Range, Range, near near Iron Iron River, River, the the ore ore bodies bodies occur occur in in the the basal basal part part of of the the Riverton Riverton Iron Iron Formation. Formation. They They are are in in .- direct direct contact contact with with the the underlying underlying pyritic—graphitic pyritic-graphitic slate slate of of the the Wauseca matter member of of the theDunn Dunn Creek Creak Slate. Slate. Complex Complex folding folding of the the strata strata has has resulted resulted w- z : -., .. L in in great great variations variations of of the the attitudes attitudes of of the the ore ore bodies, bodies, from from flat—lying flat-lying to to vertical vertical and and often often overturned. overturned. . Exposure Exposure of of the the pyritic pyritic slate slate to to air a.8~ ~ As As aa consequence, consequence, acid acid drainage drainage has has been been an an j . 1 ' > < ' known known to to ignite ignite spontaneously. spontaneously. accompanying accompanying serious seriousproblem. problem. :,. È , , -23' ' . f , : I I I i ' ! I ij I However, However, near Crystal Crystal Falls, the iron ore bodies occur some distance above above the the base base of of the theiron ironformation formationalong along aa perched perched footwall. footwall. ~. --. :. has has resulted resulted in in mine mine fires fires and and even even surface surface piles of the the slate slate have been 8 jr, j As As aa result result the the pyritic pyritic slate slate may may be be present present in in both both the the hanging hanging wall wall and and footwall. footwall. --.1 The The perched perched condition member, condition is isdue due to tothe thepresence presenceof ofa aslaty slaty member, the theRaindrop Raindrop Slate, Slate, lower one third a]. which which according according to to James, James,et. s. & (1968) is in the loner third of the the iron formation. formation. iron This This relationship relationship is is shown shown in in Figure Figure 4. 4. -- As As aa result, result, acid acid drainage been serious problem with the mine drainage from from mining operations operations has not k e n a serious Crystal Falls. near Crystal Falls. near Glacial Glacial drift. drift. ". ., , .,- , '" % . . -^'ÑÑ~.'s^ '9 , -.. .*~ , <~ J Bedrock Range Bedrock exposures exposures are are rare rare along along the the West West t4enominee Menominee Range due due to to the the presence presence of of aa thick thick glacial glacial drift drift cover. cover. The The drift drift is is locally locally as as much as as 300 300 feet feet thick, thick, but 100 100 to to 200 200 feet feet thicknesses thicknesses are are more more common. common. much is exposed onlyinin aa few fewplaces places in in the the valley Near Iron Iron River, River, bedrock bedrock is exposed only valley of of Near the surface subsidence pits. Exposures the Iron IronRiver River and and at atthe thebottom bottom of of some some surface subsidence pits. Exwsures are also also present of the the Riverton Riverton Iron Iron Fonuation Formation are present along a l o q aa thinly thinlycovered covered of bedrock ridge which extends south south from fromCrystal Crystal Falls. Falls. bedrock ridge which extends The surface material material in mainly outwash The surface in the the Crystal CrystalFalls Fallsarea areais is mainly outwashsand sand In the the Iron Iron River River area, area, with terminal and with sualler smallerareas areasofof terminal andground groundmoraines. moraines. In the part, the the glacial glacial cover cover varies varies but but in in the the northern northern part, theMineral Mineral Hills Hills area, area, j J U �L L [ L L L C [ L L C U Figure 4.4. Stratigraphic g e o l o g i c r e l a t i o n s h i p i n the Crystal F a l l s d i s t r i c t . Figure Stratigraphic geologic relationship in the Crystal Falls district. �12 the the drift may be characterized as as poorly consolidated consolidated sands sands with with minor minor gravels gravels overlain overlain by by aa fairly fairly continuous continuous sheet sheet of of very very competent competent boulder boulder till. till. The the glacial glacial drift drift is is aa copious copious aquifer, aa condition condition which which has has greatly great - activity and problns with influenced influenced mining mining activity and has has resulted resulted in problems with mine mine dewatering dewatering drainage, drilling, and and drainage, drilling, shaft shaft sinking sinking and surface surface subsidence. subsidence. -j Mining Minii-q by Harvey Mellen, aa Iron Iron ore ore was was discovered discovered in in Iron Iron County County in in 1851 1851 by Harvey Mellen, an outcrop outcrop in in the governnent government surveyor. surveyor. The The find find was was made made from from an the Iron Iron River River valley mile south southofof the the present present site site of valley about about one one mile of the theCity City of ofIron IronRiver. River.-. ore was However, However, it itwas was nearly nearly 30 30 years years before before the the first firstiron iron ore wasmined. mined. Mining Mining did did not not start start until until 1882 1882 when rail rail lines lines were were brought brought to to both both the the Crystal Crystal Falls Falls and and tron Iron River River districts. districts. fall fall of of 1882. 1882. The The first first ore ore shipuents shipments were were made made in in the the J All All of of the the early early production production on on the the West West Menominee Menominee Range Range came came pit operations the bedrock bedrockwas wasatat or or near near the from from small small open open pit operations where where the the surface. surface. With With time, time, however, however, these thesemines mines became became deeper deeper and and were were developed developed activity into underground operations. Concurrent into underground operations. Concurrent exploration exploration and and drilling drilling activity resulted underthick thick glacial glacial resulted in inthe thediscovery discoveryof ofnew new ore ore bodies, bodies, many many under sunk through throughthe thedrift drift adjacent overburden. overburden. Vertical Vertical shafts shaftswere were sunk adjacent to to the the ore ore bodies bodies and and they theywere were developed developed as asunderground underground mines. mines. -- .Underground Underqround mining mining methods. methods. , * The vertical to the vertical to near near vertical verticaland andtabular tabularshape shape of ononthethe Menominee dictated the of the theore orebodies bodies Menominee Range Range dictated theunderground undergroundmining mining most connon methods included in the the district. district. The methods methods that that were were used used in The most connmn methods included top top slicing, slicing,block blockcaving, caving,sublevel sublevelcaving caving and and sublevel sublevel and and other other stoping stoping caving methods methodswere wereused usedonly only where wherethe the ore ore was to aa methods. The caving was amenable amenable to methods. The were employed employedin in the the more caving operation. Stoping Stoping methods methods were more competent competent ore ore caving operation. a result, As a result,many many surface surfacepits pitswhich whichassume assume the the shape shape bodies. bodies. As *... .*, . -.. ., .,.*-,*--. .,.,.**- '". ,. .: . ;*-- ,- -:,. ." ..~., %r.. .: . . ..~ ÈÃ..,.....*?- J , .2.,. .> ,L za*., �13 13 of the underlying ore ore body are are present above above the the mines mines that that employed employed caving caving and top top slicing slicing techniques. techniques. Large open stopes s t o p s were produced in in the the more competent competent ore ore bodies bodies and surface surface subsidence subsidence may or or may not not have have occurred. occurred. Nearly all all of of the the shafts shafts that that served served the the mines mines in in the the district district are are vertical. The only only inclined inclined shafts shafts are are those those in in several several pre—1900 pre-1900 mines, and and these these shafts shafts were were at at steep steep angles angles (70 (70to to 80 80 degrees). degrees). Ore. - required little The little if The ore ore mined was was direct direct shipping shipping and and required if any any processing. processing. processing processing For most mines, mines, size size reduction For most reduction and and screening were the the only only techniques one mine mine and and drying drying techniques employed. Ore washing was used at one was required required at at another another where where the the ore ore was was wet. wet. characteristic of mines. characteristic of ore ore from from aa n*znber number of mines. High manganese manganese content content was was a a ores from The ores from this this Range Range exhibited increasing increasing concentrations concentrations of silica, silica, phosphorous phosphorous and and sulfur sulfur near near the footwall footwall contact contact and and sometimes sometimes also also at at depth. depth. These impurities impurities limited limited mines mined, although depth to which some the depth some ore ore bodies were were mined, although several several of of the the mines to depths feet. operated to 2000 feet. operated depths of of over over 2000 Miningoperations operations and Mininq and production. production. The mine properties properties were 40—acre The mine were all all &acre the individual parcels of than. Most of of the individual properties properties or or them. Most parcels or or combinations combinations of Records show "forties" had own was under under singular singularownership. ownership. Records show a a "forties" hadits its ownname name and and was total of operations were wereat at one one time time or or another another active active in total ofabout about100 100 mining mining operations in in the district, ororWest Of these, these, 55 the district. district. Of 55 were in the Iron Iron River River district, West Iron Iron the Falls district district or County, and and 45 45 in in the Crystal Falls County, or east east Iron Iron County, County, the. the locations locations of which are are shown shown in in Figures Figures 55 and 6, 6, respectively. time passed, of the into groups As As time passed, many many of themines mines were were combined combined into groups and and operated as operated asaaccxnplex. complex. In like ownership In like fashion fashionthe theoriginally originallydiverse diverse ownershipwas was gradually consolidated into into holdings of aa half companies. gradually consolidated holdings of halfdozen dozen large largesteel steel companies. active from The from 1882 1882 until until 1979, shipping shipping aa The Iron River district was active total of 147 total 147 million million long long tons tons of of ore. ore. Records for Records for the the Crystal Crystal Falls Falls area area �14 J J J C... Cty z I- It R 33 W II r N 34 W I— — I— _1_ • .V —l' r' M,nrnau. —26 • •' L I at' RIVER -ar. Hdr1TXMBAUGH Ia' -—"n-i —i - A SIC,.- :±9 I '/ — —20——— y:nnajj tI1I ..j.21 j • — Il-tON A HI- — NUT ;TN Ii 1J Acts' — 7 • —r— \\_ z ft I- :1: . :— E :cl — ii "ri , 0t Li U 'efl*cL.. —-' td.n —— Li Li I Ifl..d., J -a— Li I :-i — —— -j.. LI . ç1 ____ Source: Lake Superior Iron Ores Second Edition S((urce: 1952 1952 Li. U -j Li IJ j Figure 5. Map of Mined Properties in the Iron River District u �1 0 m CD 0 CD x ri- -S C, -4. Ct 0. In LA -' -Il —I Oi rt .5 IA Cl 'C CD IA 0 0j C.) rt 0 CD rt 03 0 0- 03 • CD 03— fl (D C '1 'a Mine and map p l a t e l o c a t i o n s i n t h e C r y s t a l F a l l s d i s t r i c t , Menominee Iron tang< to CD -I. rrrrnrrrnrrr FT r r r r r F i g u r e 5. 1, �16 show 1882 through show 59 million long tons of ore shipped from 1882 through 1969. 1969. -. The The production from each of the mining mining operations operations in the two sub-districts sub—districts are listed in in Tables Tables 22 and and 3. 3!\, . k. .. s . .. ... , , ~ ~~ '\ <.'. 9 .. 9 .A # ' Previous Work and Acknowledgements Acknowledgements Previous a . , Experience done previously on closed mines in Experience gained from work done in Iron Iron County, Michigan provided not only much of the background for for this this research, research, but was was also the the basis for developing the concept of this this project; project; i.e., i.e., . >.. . I -.. . ..+-. Y~. ,- 'Â¥.."<- studing the deficiencies resulting in problems problaus from the deficiencies from past mine closures closures with with.-/ .. *: %., "\ .*;J..,, ~, ? ;: the intent nDre effective mine closing the intent of developing better and more closing procedures. procedures.,.. The first first study whena aspecial special legislative legislative appropriation studybegan began in in 1974 1974 when appropriation by by The ...-. ' ... _.4 ~, the State the Stateof ofMichigan Michigan channeled channeled funds funds through through the theGeological GeologicalSurvey Survey Division Division of the of Natural for aa basic of theDepartment Department of Natural Resources Resources for basic study studyon onproblems problems 4. ,.,,* ..: '>Â¥ *a. -. '*& ".. water drainage in the the Iron associated with associated withmine mine subsidence subsidence and and acid acid water drainage problems problems in Ir+q,'z, . ,/>:, A second second appropriation appropriation was to complete River district district ofofMichigan. River Michigan. A was made made to complete tthe hifi?;?'.',' > work. work. I. These efforts reports by Johnson Johnson and Frantti These efforts resulted in two reports Frantti (1976, (1976, . ' $,* * /f 1978) which addressed these two problems and identified practical methods by 1978) which by impacts reduced reduced by corrected or their their impacts which the the problems problems could either be corrected planning. planning. -J An important part of this work was the the production production of of aa detailed map showing showing the the location location and extent of mine openings openings in in the the district district and and the the - of critical critical areas areas — those identification of those areas where in—use in-use surface surface structures were structures were underlain underlain by by mine mine workings. Additional funds available to perform similar funds were made available similar work work on on the the mines Crystal Falls mines in in east east Iron Iron County in the the Crystal Falls district district as as reported reported by by Macibnald and Macmnald and Johnson Johnson (1983). (1983). ' 1978 work work an an additionalappropriation additional appropriation was Following the the initial 1978 provided to do more more detailed detailed studies on on an acid mine mine drainage drainage problem at the Dober Mine in in the the Iron Iron River district. Pumping was recommended recommended as as aa means means to abate acid drainage in the 1979 report prepared by Johnson. I I I I �, . t*.~ . . . TABLL II TABLE I1 17 IRON ORE SHIPMENTS IN IN MICHIGAN MICHIGAN T THROUGH R ON O RE SHIPMENTS HROUGH 3974 1974 MENOMINEE IRON MENOMINEE IRON RANGE RANGE . II rron o n County I RON R RII V VE ERR 0 OISTRICT, I ST R I CT • k IRON ------------------------------------------------------------' I I I ~ Mine Mine Gross Tons Tons Gross - .. Baker Baker Bates Bates Beta Beta . , ^^"t^S ^ .. -*> '<.,;i .id. Group Buck Group *.:.z 'i ; Cannon Cannon <, n' ~ :10!- Chlcagon Chicagon . . . ,.,~ 4i Cottreil C ottrell ;*:;. 4,054,666 4.054.666 1915—1947 27,156 27,156 1886—1891 - . l fit.^. . , . ; 21.653,499 21,653,499 1901—1962 12,033,884 12,033,884 1910—1963 6,623,320 6,623,320 1903—1937 1,234,339 1,234,339 1911—1922 52.148 52,148 19121914 75,134 75.134 1915—1916 8,197,014 8,'197,014 1911—1953 128.599 128,599 1913—1921 95,759 95,759 1920—1925 2,283,822 2,283.822 1913—1939 22,162,905 22,162,905 1893—1967 17,493,590 17,493,590 1915—1971 8,326,342 8,326,342 1907—1954 373,765 373,765 18821908 5,881,550 5,881,550 1882—1937 2,907.375 2.907.375 1914—1942 116,299 116.299 1879'1909 lI2,536,O3 2.Ss6.W 1931—1974 4,195,111 4,195.111 igiz—1956 , > ' ~ , .:+;. .> ..%*, ,. Davidson Group Davldson Group ? . ; 4, ,: . 4 Davidson No. No. 4 Davldson .Â¥<-i . . . . . :,3* ii*!.-;t Delta D elta Forbes Forbes Hiawatha No. No. 2 Hlawatha No. 1 and No. 1 Homer—Cardi ff—Mlnckler Homer-Cardiff-Mlnckler "^'^~. .^Â¥ : \ . . James James ¥¥  ."X . Nanalnio Nana lm Riverton R i v e r t o n Group Group k.'. - ., .&'*' .. .. s:&? Sherwood Sherwood :;* z  '. , .i'V ; ,. ., ,~, .. :..$.?" CC , 6'; Wauseca—Aronson Wauseca-Aronson w . ,.--. . . -'Â¥<¥È!_ ^MM* ...:I? , ., ' , ? 5 ' ?, ;;2?: Sheridan Sples—VirgU S pies-Vlrgll <%:,t .P1  . f.fÈ Rogers Rogers 1936 :, . .> Cortland Cort land 1909-1935 , " ." ~! ' Â¥;<-.:! '$8" 267,107 267.107 4,200 4.200 R.. " . ' (.?. Casplan Caspian Years o of Years f ShIpments Shlpmmnts .&. .;<Èi'& : Brule - - .. . ~. '>¥ *" .. 15,364,448 lSe364,448 ., 1926—1929, 1940-1972 Wickwire 128,869 128.869 1911—1917 Youngs 802.751 802.751 1905—1928 TOTAL Snuirrn Rood (1Q7R' ~* ~s%:^^?ft~<^^%::::;::'.-iaw~fii'a)aa~i~ 147,019,683 147,019,683 ' �TABLE Tn 18 'I CRYSTAL FALLS DISTRICT, iron County Gross Tons Mine Years of Shipments h3i;3 113.395 iSBg—igI4 Balkarjudson 4,441,799 18821935 Book Book 2,317,523 1943—1958 ArmenIa 1! Bristol—Youngstown 14,804.805 1890—1934, 1950—1969 Carpenter "Carpenter .2.735.452 1914—1928 ls4,i92 Cayia Carla i,44,ois 1882—1913 33,770 1883—1896 Dunn Ounn 2,208,511 1887—1915 Fortune Fortune Lake Lake 1,316,905 1953—1958 Great Great Western Western 2.296.739 1882—1925 Hemlock Hemlock 2,125.756 1891-1919 Hilltop HI 1 1 top 98,202 1899—1919 143,117 1890—1914. Hops 28,530 1892—1903 KImball 35,757 1907—1915 558,524 18891910 Lawrence Lawrence 6,963 1920-1956 Lee Peck Lee Peck 2,844 1892 Falls Crystal Crystal Falls Delphic Delphic """' 1954 Holllster Kolllster Lanont 241,627 1891—1909 1,462,504 1890—1913 30,289 1909-1913 2,101,381 1916—1935 Paint paint River 382.078 1882—1913 Porter Porter 733,327 1916—1927 Rayenna—Prlckett Ravenna-Prlckett 635,227 191N1917, 19401943 RIchards Richards 5314,448 1913—1921 8,203 1887-1890 13,523,289 1882—1963 Lincoln Lincoln Mansfield Mansf leld McDonald Odgers Odgers j U LI South South Mastodon Hastodon Tobln—Columbia-Monongahela-Genesce Tobln-Columbia-Honongahela-Genesee 1) 3,417,030 Warner Warner cnnnrr. "Of. Li fl,-,,-'A A " .. (1O7IZ\ /,"7C! TOTAL TOTAL 58,727,872 1915—1934, 1951—1958 �<I' 19 From U.S. Vom 1978 through 1982 the U .S. Bureau of Mines funded funded aa study study of of the the closing of the Sherwood Mine Mine which which was was undertaken undertaken by by an an interdisciplinary team of investigators at Michigan Michigan Technological Technological University. Subsidence Subsidence monitoring performed performed during during this this project project showed showed that four different different monitoring subsidence mechanisms were active subsidence mechanisms active while while the the mine mine flooded. flooded. Hydraulically triggered subsidence subsidence and triggered and piping—induced piping-induced subsidence subsidencewere weretwo twonew newmechanisms mechanisms whichwere wereobserved observedtotohave havewider widerapplication. application. which This work has been Ttlis work has been prepared prepared as reports 1983) as reportsby by Johnson Johnson and and Frantti Frantti(1982, (1982, 1983)and andJohnson Johnsonand andHodek Hodek (1983). (1983). Although this report report deals deals largely largely with mine related problems on the although this the problemswith withmine minesubsidence, subsidence,drainage drainageand andshaft shaft seals seals Menominee Range; Flange; problems Investigations of have cropped croppedupupininother other mining miningdistricts districts ininMichigan. have Michigan. Investigations of miningdistricts districts have occurrences in both iron and copper mining these have provided provided these occurrences and the experience experience gained gained from them than have have materially materially additional insights and additional aided this this work. work. Some of of the the ideas developed developed from these efforts were Some incorporated in in aa paper paper entitled entitled "Hydrologic "Hydrologic Considerations Considerations in Mine Mine by Johnson Closings" by Closings" Johnson (1983) (1983) This wouldnot nothave havebeen beenpossible possiblewithout without the the help help and %is work work would and contributions of others associated and industry. industry. contributions ofmany many others associated with with both bothgovernment government and Reed, Robert Reed, Several of have made madeoutstanding outstandingcontributions contributions are: are: Robert Several of those those who who have Bal of Aistine of of the Geological Geological Survey Division, and Joseph Joseph Bal and Jack and Jack Van Van Alstine the Water Resources Division Division of of the of Natural Natural the Water Resources the Michigan Michigan Department Department of Rhoadesof of the the Resources;Alice AliceAllen Allen(ret) (ret),, Jacob (ret),,and Jacob Frank Frank (ret) and Charles Rhoades Resources; Hiltunen, Iron, of Mines; Mines; Peter Peter Korach, Korach, Reino Reino Laine Lame and U.S. U .S. Bureau of and Sub Sulo Hiltunen, Iron, Edwards County Mine Mine Inspectors, respectively; Robert Robert Edwards Gogebic and Houghton County Gogebic (ret) ofofInland Mining (ret) of of Cleveland Boyurn (ret) Cleveland (ret) InlandSteel Steel MiningCompany Company and and Burton Burton Boyum Cliffs Iron Mining Cliffs Iron MiningCompany. Company. Maclbnald of of the Larry MacDonald the Institute Instituteof ofMineral Mineral Larry �20 ! I UI mention Research at at Michigan Technological Universitydeserves deserves spial special mentionfor for Research TechnoliCal University his invaluable invaluable assistance assistance in in the the field field on on all all of of these these projects projects and and also also his his his professional professional contributions contributions to to this thisresearch. research. ,'>L;, i.., ,.~. ., .-Sp ,... '. m , .?. rtC,.Â¥' 1' I.' I -I J j �21 MINE ION TO ME RELATED RELATEDPROBLE2IS PROBLEMS— INTRODUCT 1TRODUCTION TO CASE CASE HISTORIES HISTORI -.., :iz. .:;z . :*,:,.$yc ., ~ p*,,,.;> --. Three basic types and abandoned typeoof problems w.v^blems associated associatedwith withclosed closed and abandoned 3 ; underground minesare areconsidered consideredininthis this report; iderground mines report;1) 1)mine minesubsidence subsidence2) 2)mine mine shafts but drainage -ainaqe and and 3) 3) the the safety safety of of surface surface openings, openings, mainly mainly shafts but also also .. topics isiscomprised including Each of of these these major major topics comprised of of several several icluding pits. pits. Each . t.subdivisions. ibdivisions. These These topics topics and and their their subdivisions subdivisions are are identified identified and and - . .. CK briefly .iefly discussed in in this this section which is is introductory introductory to to the the case case ,.. .,* .. - . . histories stories which which follow. follow. . . 2 . 7 ' : .,~ '. ;,A \, .,: 2...>+.. , .>. \..- *> ,. < f c*:,- . a':<; .,.Â¥-,' **" :..,-*-+.l-' i *.r.. , , Mine Mine Subsidence Subsidence . . u.i- .> ' * C -j < ' ,$ , - x , , *:&X"A*z.. ? :, -",-J: Three Biree categories categoriesof ofmine minesubsidence subsidencehave havebeen been recognized recognizedon onthe theWest West Menominee Menominee Iron Iron Range: Range: 1) 1) subsidence subsidence that that occurs occurs during during mining mining activity activity 2) 2) .aft!- subsidence ibsidence occurring occurring shortly shortly after the mine is is closed and while it is flooding flooding and and 3) 3) longer longer term term subsidence. subsidence. :-:, 7.1 For For the the most part, the the first first is related category of of subsidence subsidence is related to to the the use use of underground underground mining mining methods methods 5 category techniques include include top top slicing These techniques slicing&a 2.. that that resulted resulted in insurface surfacedisturbance. disturbance. These id caving caving mining mining methods. methods. and the ie extraction extraction of of ore. ore. With With these these techniques techniques the the surface surface subsides subsides with withe" 4:. In In top top slicing the the subsidence subsidence is is almost almost immediate imnediate because because mining is is started started near near the the surface. surface. With With the the caving caving methods, methods, ' *d :,.~..& surface tauporarily delayed delayed until the fracture fracture zone surface subsidence subsidence is often temporarily zone~.:~-.;.'.*,,~J.::. However, this type type of However, this of subsidence subsidence usually usually poses poses no no *.! problems as its its occurrence .:* %: problems as occurrence is isexpected expected and and the the surface surface opening opening conforms conforms Consequently, this this n .hi: quite closely closely to to the the shape shape of of the the ore ore extraction extraction area. area. Consequently, quite reaches reaches the the surface. surface. type subsidence iis notof ofprimary primaryconcern concerntoto this rk. This the type of subsidence s not this wrk. This leaves leaves .the.'&?-:"' remaining remaining tsn two categories categories of subsidence; 1) short short tern term subsidence subsidence which which occurs :curs while while the the mine mine floods floods and and 2) 2) longer longer term term subsidence. subsidence. categories itegories will will be be discussed discussed separately. separately. !>.!:ST..> . Each of these Bach of these, . ?e �22 Short Short term term subsidence. subsidence. Although it may seem initially illy that that the the only only distinction distinction between between subsidence subsidence occurring occurring during during the the period period of of mine mine flooding flooding j and at sane later date of timing, this is and subsidence subsidence that that occurs occurs at some later date is is one one of timing, this isnot not necessarily of aa mine cause profound profound changes changes in in the necessarily the the case. case. Flooding Flooding of mine may may cause the >,., mine mine environment environment that that may either trigger or result result in in subsidence subsidence activity. activity. In In fact, fact, the the period of of flooding flooding is is probably probably the the most critical critical period period in in which which subsidence subsidence may may occur. occur. friction friction between between rock rock masses. masses. .~ 3 . .. .~... ,.,. Water entering the mine as it floods floods can reduce - Frictional Frictional forces forces that that held held faulted faulted or or ,Â¥',., >'-' jointed jointed rock rock masses masses in in position position may becane become reduced reduced to to the the point point where where adjustments adjustments take take place. place. . "- '. '?'.I. -.' '... This often be enhanced This mechanism mechanism may may often enhanced by by processes processesA:~c*G3 --..-.-- that operating. Minerals in these that took took place place when when the the mine mine was was operating. Minerals in these planes planes of of weakness mayhave havebecome becanealtered alteredbybyexposure exposuretotoair air and in the and humidity humidity in the weakness may mine. are expandable expandableclay clayminerals minerals and and sulfides sulf ides and and other other minerals mine. Examples Examples are minerals J J .... .%.# ,,? ,, susceptible certain conditions conditions these susceptibleto tochemical chemicalchanges. changes. Under Under certain these reactions reactions may cause expansion expansionof of susceptible susceptible minerals and may cause minerals within withinplanes planesofofweakness weaknessand result mine resultin inspalling spallingand androck rockmass mass failure failureadjacent adjacenttotothe the mineopenings. openings Elevated Elevated hydraulic ran introduced introduced water water into into the planes of hydraulic pressures pressures ffrom of weakness weakness may may also also cause cause this this type type of of failure. failure. &:. -.... r:x ... 5 .. .n,,. : w : Secondly, Secondly, water has has mass mass and as as this this mass mass is is redistributed redistributed during during flooding, flooding, differential differential loading loading of of rock rock and and soil soil masses masses may may occur. occur. If If a2 delicate delicate equilibrium equilibrium exists exists between between these these masses masses and is is upset upset subsidence subsidence may mi : I :.' ' be be the the result. result. Steeply Steeply dipping dipping shear shear zones zones along along which which previous previous subsidence subsidence has susceptible to causedby bydifferenti; differential has occurred occurred are are most most susceptible tofurther furthermovement movement caused xs.: u8.3 loading theloss lossof of friction friction by loading during during flooding. flooding. Obviously Obviously the by the thei.ntrcx~ti< . . introduction - -< of be aa mitigating mitigating factor. of water water into into these these zones zones can can be factor. a~.j ::-.* . .' ?. .~~?K'ss"-; . . Thirdly, inflow into into the the mine mine through through previously previously subsided subsided areas, thirdly, water water inflow shafts and other other openings openings to to the the surface surfacemay may wash wash unconsolidated unconsolidated overburden overburden?, .:, shafts and I1 I ! ..,, .$& t. 1 i I I �23 L (sand, gravel, silt, silt, etc.) etc.) into into the the mine mine void. void. (sand, This can result This can result in in surface surface (overburden) adjustments that may be be quite (overburden) adjustments quite extensive. extensive. [ Fourthly, under flooding, piping special of mine special conditions conditions of mine flooding, piping activity activitymay may occur. occur. Piping Piping . . * .. involves of aa cavity unconsolidated involves the the developnent developnent of cavityor orvoid voidinin unconsolidatedoverburden overburden .,. . above the bedrock bedrockinterface interface as as aa result bybygroundwater above the resultofofsand sandtransport transport groundwater . flow flow into into the themine. mine. Laboratory Laboratory experiments experiments on on the thepiping pipingmechanism mechanism were were reported and Hodek Hodek(1983) (1983)and andpiping pipinginduced inducedsubsidence subsidenceactivity activity,, .-. reported by by Johnson Johnson and at documentedbybythem thanand andby byJohnson Johnsonand and Frantti Frantti atthe theShers.ood Sherwood Mine Mine was was documented (l983a, (1983a, l983b). 1983b) . mine A fifth fifthmechanism mechanism for for triggering triggering minesubsidence subsidencemay may occur occurwhen when aa mine mine. . becomes flooded. Great becomes flooded. Great hydraulic hydraulic forces forces can can be be generated generated within within aa flooded flo~ded~,>:~:,~> mine if sudden water displacement displacementoccurs occursfrom fromthe thefall fall of of surface material mine if sudden water surface material surging into into the the mine mine or or compression compression occurs occursby by rock rockmass massmovanent. movement. TThe h e surging water can or reactivate in areas areas of water can trigger triggernew new subsidence subsidence or reactivatemovement movement in of previous previ04$&,~~~ documentedcase caseofofthis this type type of of occurrence is described A documented occurrence is described by by subsidence. subsidence. A Johnson andFrantti Frantti (1983a, (1983a,1983b) 1983b)and andisisincluded includedininthis this report report as as aa case Johnson and case ,-... history. history. . .* category includes includes all all subsidence This category subsidence that that occurs occurs >. Long term subsidence. subsidence. This Long term It isisa avery verybroad broad category category in in ; following the flooding following the flooding of ofa amine minecomplex. complex. It ...a " ' ' , \ " ' L L L 6t.,% the the sense sense that that no no limit limitisisplaced placedon onthe theanount amount of of time time required required for for :.,? E.: .*:,*:. , subsidence to occur. subsidence to occur .. ::. .,.-w The mechanisms wDrk createthis thistype typeof of subsidence subsidence include include the the The mechanisms atatwork to to create ever of ever present present force force of of gravity, gravity,long longtern termchemical chemicaland and physical physicalweathering weathering of minerals ofof earth tremors of natural or man—made minerals and and the the triggering triggeringeffect effect earth tremors of natural or man-made , latter could The latter couldinclude includeshock shockwaves waves caused caused by by explosion explosion or or tremors t~f3Km-s origin. origin. The If subsidence occurs in in aa flooded subsidence occurs flooded -. caused by heavy heavymachinery machineryorortraffic. traffic. If caused by ,. . ,. ~.&..-F. ,~ , %<. ~ mine, the resulting resulting hydraulic disruptions could trigger additional mine, the . ..* hydraulic. disruptions -. . could . trigger additi~nal,~.;, . .. ..,,.,, , . . I ,. �24 subsidence subsidence. %. . ..,!. Gradual of rock the roofs roofs of of near Gradual sloughing sloughing of rock from from the near surface surface stopes stopes can can CJXU& s:..I , ; z., ,. ..% result of the the mined minedvoid voiduntil untilthe thesurface surfacefails. fails. resultin inthe theupward upward migration migration of .< .. .., , 7: This at work This is isprobably probablythe themost mostprevalent prevalentmechanism mechanism at work in in long long term term subsidence. delayed effect effect of and its its subsidence. The The delayed of long long term term subsidence subsidence and unpredictability unpredictability places places this thiscategory category of ofsubsidence subsidence into into one one of of great great .i.^Sy concern. concern. T .^ Mine Drainage Drainage Two typesor or sources sources of of acid drainage are Two types acid mine mine drainage are recognized recognized in in the theWest West Menominee Range;1)1)acid acidwater water from from underground undergroundsources' sources'and and2) 2) surface surface M e m i n e e Range; ^.*-?fia';.-:fc -*i- .> ,. sources sources of of acid acid drainage. drainage.', Acid drainage is is prevalent western part part or Acid drainage prevalent only only in in the theextreme extreme western or Iron Iron +f of the River West Menominee River area areaofofthe the West Menominee Range. Range. It It occurs occurs there there because because of the :". o s close the source ofof thethe acid —— close proximity proximity of of the theore oretoto the source acid - the the pyritic pyriticWauseca Wausecax ofthe the pyrite pyrite in menber of the Creekslate. slate. Oxidation Oxidation of in slate slateexposed exposed in in member of the Dunn Dunn Creek thesesoluble soluble sulfates sulfates - . , the solubleferrous ferrous sulfates. sulfates. When the mines mines produced produced soluble When these were dissolved in in water, were dissolved water, sulfuric sulfuricacid acidwas wasformed. formed. . When operating,many manyofofthe themines minesininthe the Iron Iron River River district pumped When operating, district pimped ~ ~ < s~ L acid highlyvisible visible pollution pollution as acid waters waters into into the the Iron Iron River River causing causing highly as the the acid acid became neutralized and and the the dissolved dissolved iron thenprecipitated precipitated toto became neutralized iron and and aluminum aluminum then form referred to as "yellow form insoluble insolublecompounds compounds referred tocoirinonly comnonly as "yellow boy". boy". < * y%, :.EL^' With the cessation cessation of of mining it was believed that that the was believed the acid acid drainage drainage With the mining it aciddrainage drainagereoccurred reoccurredat at several problem wouldcease ceaseto to exist. exist. However, problem would However, acid several . - - . of theyflooded, flooded,and andare areaa continual continual source source of of acid of the themines mines when when they acid drainage. drainage. Surface piles of of sulfur blackslate slate are are also Surface piles sulfur bearing bearing black also the the source source for for 3 groundwaters leach leach acid and near—surface near-surface groundwaters acid.'. Surface water water and some acid drainage. drainage. Surface some acid fran extensive black slate slate piles whichisissituated situated in in pilesatatone on mine complex lex which .. ,.. �25 the the Iron IronRiver River valley. valley. The The acid acid water water flows flows aa short short distance distance before before entering entering the the Iron Iron River River creating creating additional additional pollution. pollution. Case Case histories histories of of both both of of these these occurrences occurrences are are presented presented in in this thisreport. report. Safety Safetyof of Surface SurfaceOpenings Openinqs This This category category includes includes all all surface surface openings openingsresulting resulting either either directly directly mining activity (shafts, raises, open pits) or indirectly (subsidence pits, pits,caved Cavedground). ground). It Itdeserves deservesspecial specialattention attentionbecause because of of the thegreat great threat The threat threatisismagnified magnified threatthat thatthese theseopenings openings present present to to the thepublic. public. The because of the the attractiveness because of attractiveness of of these these areas areas to tothe thepublic publicand and their theirgeneral general lack for their lack of ofunderstanding understanding or or concern concern for theirdanger. danger. Injuries the fall fall of Injuriesor ordeaths deaths occurring occurring from from the of individuals, individuals,especially especially from from mining activity (shafts, raises, open pits) or indirectly (subsidence shaft or children, children, into into an an inadequately inadequately protected protected mine mine shaft or surface surfacepit pitprobably probably creates creates more more intense intense ill ill will will and and negative negativefeelings feelingstoward towardthe themining mining industry industry than than any any of of the the other other categories. categories. This srse This threat threat is is made worse because real attraction attraction for for the thegeneral generalpublic. public. because these these areas areas provide provide aa real Consequently, Consequently, it it is is not not out out of of place place to to give give serious seriousthought thoughtand and consideration of effective effective and consideration towards towards methods methods of and safe safe protection. protection. Case histories illustrate thethe various types ofof surface openings Case histories illustrate various types surface openingswhich which were originally inadequate, time have were originally inadequate, or orthroah through time havebecome become so. so. Included Included in in the the examples are shaft shaft openings that are exanples are openings that that are areuncapped, uncapped, some some that areinadequately inadequately capped, several that but have have deteriorated deteriorated either capped, and and several that were were well well capped capped but either because of aa poor selection of of material because of poor selection material or or engineering engineering that that did did not not take take into the eventual eventualdeterioration deteriorationthat thatwould uld take into account account the take place. place. , AA distinction made shaft seals distinctionisis made between between shaft sealsininbedrock bedrock and and surface surfacecaps. caps. Although the problems of providing and providing providing Although the problems of providing adequate adequate fencing fencing and maintenance are not not heavily theyare are obviously obviously important, important, as as is maintenance are heavily emphasized emphasized they is the theneed need of ofproviding providing surface surface markers markers for for identification identification and and aa means means to to -.&cate theshaft shaftopenings. openings ...,,'.~. , locate the .*~. %!. �26 CASE CASEHISTORIES HISTORIES * <..*. :-- . Short ShortTerm TermSubsidence SubsidenceEffects Effects .. ,~ .*.: 7.; >. In In the theprevious previoussection, section,short short term term subsidence subsidencewas wasdefined definedas asthose thosi subsidence subsidenceevents eventsthat thatoccurred occurred during duringthe thetime timerequired requiredfor fora amine mineto to well-docianented case casehistory historyinvolving involvingeach eachof ofthe thefive fivesubsidence subsidence flood. AA well—documented flood. mechanisms mechanismswhich whichwere wereproposed proposed to tobe be active activeduring duringmine mineflooding floodingwas was Sherwood developed developed atatthe the SherwoodMine. Mine. These included; 1)1)water These mechanisms mechanisms included; water lubrication blocks 3) 3) overburden waterloading loadingofoffault fault blocks overburden lubricationofofshear shearplanes planes2)2)water washing resulting in in shear shear failure failureof of sands sands4)4) piping piping produced produced cavities cavities in in washing resulting the theoverburden overburdenand and 5) 5)hydraulically hydraulicallytriggered triggeredsubsidence. subsidence. TheSherwood SherwoodMine Mineis islocated locatedabout aboutone onemile milenorth northofofthe theCity Cityof of Setting. Setting. The The mine mine opened opened in in 1943 1943 and and was was shut shut down down in in Iron 7). The Iron River River (see (seeFigure Figure7). 1978. 1978. Total Total shipments shipmentsthrough through 1978 1978 including including some someore oreextracted extractedfrom froman an adjoining adjoining property property during during the the1930's 1930's totaled totaled13.7 13.7 million million long long tons tons of of ore. ore. Sherwood Sub level level stoping stopingwas wasthe theonly onlymining miningmethod method used usedatatthe the Sherwood Sub The main main ore ore body body was was served served by by aa vertical vertical shaft shaftdepth depth of of 1625 1625feet. feet. Mine. The Mine. The The near near vertical, vertical, tabular tabular ore ore body body had had major major development developenton onthe the400, 400,800, 800, 1000, 1200, 1200, 1425 1425 and and 1625 1625 levels levels(Figure (Figure8). 8). 1000, present at at the theSherwood Sherwood Mine. Mine. present Thick Thick glacial glacial overburden overburdenis is The The thickness thickness varies varies because because of of 30-foot irregularities in inthe thebedrock bedrock surface, surface, but but averages averages 150 150feet. feet. AA 30—foot irregularities well consolidated glacial till overlies poorly consolidated sands These relationships relationshipsare areshown shown in in Figure Figure 9. 9. with with lesser lessergravels. gravels. These connected The Mineisispart part of of aa large connected Itisis The Sherwood Sherwood Mine largecomplex complex of ofmines. mines. It with on the the east with aa shallower shallower mine, mine, the theVirgil—Spies Virgil-Spies on east and and aadeeper deepermine, mine, the the thick, thick, well consolidated glacial till overlies poorly consolidated sands Although these these mines mines are are interconnected interconnectedand and Homer—Wauseca onthe the west. Homer-Wauseca on west. Although , . . would flood as would flood as one, one, they theywere were independently independently operated operated by by other othermining mining down —— hadbeen beenshut shut downearlier earlier -- the the Both of of these theseadjacent adjacentmines mineshad companies. Both companies. ;' , '.. E > z . ~ . ~ & ; ; ~ : : : ~ , . ~ ~ : : h : ~ . . ? :~' r~ * &,:, T*.." 2,. ..Z$ ~::+ :..,- ;..; ;,,. . . ,- .-r> *- �27 iron Iron - / - County County I I I I $ W o t Menooilnee Ran00 \ \ 'I' Shetwood Mine 4 Homer— Virgil- Spies Wauseca MacDonald Annex City of Li 114 mile MtneComplex Complex theI riron Rtver DDtstrtct Figure Figure 7. 7. Locatton Location of o f the theSherwood Sherwood Mime t n tn the o n Rtver tstrtct of ofNorthern NorthernMichigan Michtgan �'1 -a. XL,"-, in CD •1 C In Figure 8. C. C) (DID c-t a 0 0 X It — 0 -I. i4CD gJ - -aid, CD ZCD -a. fl LL L2 Lfl • c '<<0 -a 001) w o r am CD rtCD on -Sw-I .1.0J 0 -4)9 0& Isometric View o f t h e Sherwood Mine Shaft and Levels i n R e l a t i o n t o the Main Ore Body. LL L 0 -.4 01 -a LL L L L L -2 L 14 4 •1• L 'p LL L L U 'PS LL �29 L -ro:Th -. - - - L L - • C 'a — • d 20—30 -r Glacial flu C a 70-80 Sand and grays • a 0 0 S a — - - we I, "a '•- V N. V 05*00k •_ 'we Figure Figure 9. 9. - V V Cnd arsa Otbadroct Generalized att the Sherwood Generalized Profile P r o f i l e of of Glacial G l a c i a l Overburden a Sherwood Mine in i n the the East E a s t Pit Pit '3 �30 Virgil—Spies Virgil-Spies in in the the 1950's 1950's and and the the Homer—Wauseca Homer-Wauseca in in 1968. 1968. The The locations locations of of these these adjoining adjoining mines mines is is shown shown in in Figure Figure 7. 7. The has had The Sherwood Sherwood Mine Mine has had aa rather rather long long history history of of subsidence. subsidence. J Major Major thethe Sherwood stopes stopes in in the theupper upper levels levelsofof Sherwood Mine Mine on on both both the the east eastand andwest west margins property had had caved cavedto to the the surface. These cave—ins cave-ins margins of of the theSherwood Sherwood property surface. These resulted overburden. resulted in in large largedeep deep surface surface pits pits in inthe thethick thickglacial glacial overburden. The The West Pit caved in February 1956and andthe theEast EastPit Pit caved cavedto to the the surface surface in in West Pit caved In February 1956 pit locations August s aa w u s t 1964. 1964. The The pit locationsare areshown shown in in Figure Figure 10. 10. Also Also shown shown iis small Pits, known asthe the Central Central Pit. Pit. small pit pit located locatedbetween between the the East East and and West West Pits, known as This diameterpit pit appeared suddenly in in February This 100—foot 100-foot diameter appeared suddenly February of of 1967 1967 following following an an explosive explosive blast blastused used to tobreak breakup upconsolidated consolidatedoverburden overburden being being used used for for stope The blast blast apparently apparently triggered triggered the the collapse collapse of of aa stope filling filling operations. operations. The soil soil capping capping over over an an existing existing cavity cavity in in the the overburden. overburden. This this void had had probably probably been been formed Conned either either by by piping piping or or running running sands, sands, but buta aplug—type plug-type steeply failure A steeply failureof ofa ashallow shallowstope stopemay may also alsohave have been been responsible. responsible. A dipping Sherwood dipping (700 (70Âsouth) south)east—west east-west fracture fracturedeveloped developedininthe the SherwoodMine Mine during during November 1966the thefracture fracture was was evident evident on By November ofof1966 on the the the Spring Spring of of1966. 1966. By the The maximum maximum levelsplus plus on on the the surface. 400, 800, 800, 1000 1000 and and 1200—foot 1200-foot levels surface. The 400, displacement displacement was was three three feet feet on on the the 1000—foot 1000-foot level level as as observed observed in in aa major major drift. crosscut crosscut drift. systems installed installed at at the the Monitoring Monitoring of of post—mining post-mining subsidence. subsidence. Monitoring systems Sherwood Sherwood Mine Mine prior prior to to shut shut down down included included borehole borehole extensometers extensometers in in the the steeply dipping dipping fault fault zone zone within within the themine, mine, surface surface and and underground underground acoustic acoustic steeply emission emission sensors, aa grid of surface surface subsidence subsidence monuments monuments aa piezometer piezometer network network to to monitor monitor water water rise rise in in the the overburden overburden and and water water level level measuring measuring devices to to monitor monitor the the flooding flooding of of the themine minecomplex. complex. devices When the pumps pumpswere wereshut shut down downin in 1978, 1978, the the mine to When the mine complex complex began began to I �r ri West w e i t Pit Pit r r r East East PIt PI^ SHERWOOD SHERWOODMINE MINE PROPERTY PROPERTY PIt Central 4a Sherwood Sherwood Shaft Shaft r— Figure Figure10. 10. Location LocationofoSubsidence f SubsidencePits P i t at s athe t the Sherwood Sherwood Mine Mine Shaft Homer—Wauseca Pumpin9 Pond MINE PROPERTY HOMER—WAUSECA ri ri n n ri 0 I 0 meters 150 teat 500 SCALE Shaft 4 VIrgil VIRGIL VIRGILMINE MINEPROPERTY PROPERTY — �32 flood. flood. The The mine mine was was flooded flooded by by mid—1981, mid-1981, in in aa period period of of 2.75 2.75 years. years. About one one more more year year was was required required for for groundwater groundwater levels levels in in the the overburden overburden to to equilibrate. equilibrate. Subsidence. Subsidence. j During the the time time required required for for the the Shersaod Sherwood Mine Mine complex complex to to flood, three different major subsidence three different subsidence events events occurred occurred which which serve serve to to illustrate mechanians ascribed to to short short term term post—mining post-mining illustrate the the five five subsidence subsidence mechanisms subsidence. subsidence. Included Included were 1) 1) subsidence subsidence in the the West Pit Pit area area which which represents represents shear shear failure failure of of overburden overburden sands sands as as aa result result of of water water flow flow into into the the mine, 2) 2) broad broad surface surface subsidence subsidence as as aa result result of of rock rock mass mass movanent movement from from water water loading loading and and shear shear plane plane lubrication lubrication and and 3) 3) hydraulically hydraulically triggered triggered subsidence subsidence which which in in turn turn caused caused aa previously previously Conned formed soil soil cavity cavity to to suddenly suddenly develope develop into into aa subsidence subsidence pit pit with with the the collapse collapse of of the the protective protective capping. capping. This This cavity cavity is is believed believed to to have have been been caused caused by by piping piping of of overburden overburden sands sands into into aa mine mine stope. stope. Each of these events is described separately. these events is described separately. Shear Shear failure failure in in overburden overburden sands. sands. summer 1979, a in late sunnier Beginning in little little more than than one year following following shut shut down of the the mine, mine, aa snall small subsidence developed in sand sand fill fillin in the the West West Pit. Pit. subsidence pit developed 30 feet feet in in diameter diameter and and 10 10 feet feet deep. deep. circular, about 30 circular, The The pit was was one half A month and one the pit larger. later, later, additional additional subsidence subsidence caused caused the pittotobecome become much much larger. It now It now Several was about 100 feet inindiameter deep andand cone—shaped. was about 100 feet diameterand and40 40feet feet deep cone-shaped. Several days underwent was enlarged enlarged days later laterthe thepit pit underwentanother anothersubsidence subsidenceadjustment adjustmentand andwas Figures 11, to 200 60 feet feet deep. to 200 feet feet in indiameter diameter and and about about 60 deep. Figures 11, 12 12 and and 13 13 illustrate illustratethese thesethree threesubsidence subsidence events. events. It It is believed that following the rise of water in in the the overburden overburden above above thorugh the the pit the Sherwood Mine Mine that that water water flow flow into into the the mine mine thorugh pitarea areawashed washed the Sherwod into the filled stopes sand sand into the incompletely incompletely filled stopesbelow. below. "plug" "plug" consisting consisting of of j j from the the This loss loss of This of sand from previously washed washedinto intothe the opening openingin in the the top top of of sands sands previously UI �33 Figure i. Photograph of initial subsidence in West Pit area taken on September 7, 1979. The subsidence pit is about 30 feet in diameter and ten feet deep. The bent pipe in the foreground is an old well casing installed in the 1940's. Photograph taken with a 50 rim lens on a 35 m camera, looking southeast. Cave first observed August 31 1979. , Figure 12. Photograph of enlarged subsidence pit which caved on October 14, 1979. The resulting pit is about 100 feet in diameter and 60 feet deep. Note old well casing pipe in foreground; also cribbing and bent over 30—inch pipe in background at upper left, formerly used for sand filling stopes under this area. Looking southeast, photo taken with 35 rim camera eouiooed with a 50 rim lens. �U u 'I j j aa Greatly G r e a t l y enlarged enl-. -.ad subsidence subsiucSn.e pit p i t which which caved caved on on October October 19, 19, 1979. 1979. The The pit p i t is i s about about 200 200 feet feet in i n diameter diameter and and 100 100 feet f e e t deep. deep. Shear Shear rock r o c k walls w a l l s are a r e exposed exposed on on the t h e west west and and north n o r t h walls w a l l s of o f the t h e pit. pit. Note t h e far f a r right r i g h t and sand filling f i l l i n g pipe pipe Note the t h e old o l d well w e l l casing on the and This and cribbing c r i b b i n g on on the t h e left. left. This cave cave occurred o c c u r r e d on on October October 19, 19, 1979. 1979. View with 28 mm mm wide wide angle angle i t h a 28 View looking l o o k i n g north. n o r t h . Photograph taken w lens l e n s on on aa 35 35nun mm camera. camera. —a j Li U j U - — -Tyt tt:. S' - bb 4-'sc. t Close View is i g northwest. northwest. Close up ul of the October October 19, 19, 1979 1979 cave. cave. i s looking 1c Note p i p e in i n near foreground foreground and and old old Note 30-inch 30-inch diameter diameter sand sand fill fillpipe well 28 mm mm wide wide Photograph taken taken with w i t h aa 28 well casing castng in i n background. background. Photograph angle angle lens, lens, 35 35 mm mm camera. camera. Figure 13. Enlarged West Pit After October 19, 1979 Subsidence Event U U U j �35 the series of the caved caved stope, stope, caused caused the the observed observed series ofsubsidence subsidence events. events. The The circular circularshape shape of of the theopening, opening, the the tension tension fractures fracturesaround aroundthe theopening openingand and the the resulting resulting cone—shaped cone-shaped void all all suggest suggest that that shear shear failure failure from from gravity gravity loading loading of of the the unstable unstable sand sand mass mass best best explains explains this this subsidence subsidence occurrence. occurrence. Surface Surface subsidence subsidence resulting resulting from from rock rock mass mass movement. movement. Leveling Leveling surveys surveys of of aa 47—movement 47-movement grid grid were were performed performed periodically periodically at at the the Sherwood Slierwood Mine Mine following following its its shut shut down. down. Surface (25acres) acres) Surface subsidence subsidence over over aa broad broad area area (25 above above the the main main ore ore body body was was first first detected detected in in late late 1979. 1979. Surface Surface subsidence subsidence continued continued throughout throughout 1980 1980 until until the the maximum maximum downward downward displacement displacement was was 1.3 1.3 feet. feet. The The northern northern extent extent of of the the surface surface subsidence subsidence was was marked marked by by the the - - surface surface trace trace of of an an east—west east-west trending trending shear shear that that was was about about 100 100 feet feet south south 6 of of the the main main shaft. shaft. \> shown shown on on Figure Figure 14. 14. . ,- .. . ,. These These features features including inclding the the monument monument locations locations are are The contours of of subsidence upon aa level level survey The contours subsidence based based upon survey in in December 1980 are are also December 1980 alsoshown. shown. The surface subsidence developed in in response to rock The surface subsidence described described above above developed response to rock , initial phases this movement mass within the mass movement movement within the mine. mine. The The initial phasesofof this movement were were 70 south detected byextensometers extensometersinstalled installed across across the detected and and monitored monitored by the 700 south cross section of the shows the the themine mine in inFigure Figure15 15shows A cross section map map of dipping dipping shear shear plane. plane. A location mine location of of the the shear shear zone zone in in relation relationtotothe the mineworkings workings and and the the .%J.? extensometer extensometer installations. installations. The The relationship relationship between between the the movement movement on on the the .. shear shear plane plane and and the the broad broad surface surface subsidence subsidence is is shown shown in in Figure Figure 16. 16. It It is of the the meassive south block ishypothesized hypothesized that thatrenewed renewed movement movement of meassive south block of of It is islikely likely that that the occurredas as aa result result of the mine mine occurred ofmine mine flooding. flooding. It groundwater groundwater inflow inflow into into the the shear shear zone zone reduced reduced the the frictional frictional forces forces holding holding the block block in in position position and and perhaps perhaps loading loading of of the the sealed sealed stopes stopes within within the the the block with with water watermay may have have helped helped this this movement. block movement. It It is isalso alsopossible possible that that have been beenpartly partly responsible responsiblefor for initiating initiating movement movement on on the the shear shear plane may have �J 21. 36 SM j J 61 f -j .15 J 16 -J J 5 C LI 2' 3 J -j J a J 49. J 50 U Si TRAIL a._:TENSON CRACK :SURFACE :SURFACE PIT PIT : T E N Y O N CRACK t 2 MINESHAFT WINESHAFT a I 250' 0 'Si j - 11 -Si 51 MONUMENT MONUMENTSI BBSERIES. SERIES. WELLS WELLS . FENCE FENCE - +-+.. .+ . RAILROAD RAILROAD JL_ & ROAD ROA U -4——4- - --- - J BUILDING LTh: : aUPLOING -Figure F i g u r e 14. 14. Subsidence Subsidence Monument Monument Locations Locations at a t the the Sherwood Sherwood Mine Mine including including Contours Contours of of Subsidence Subsidence Based Based Upon Upon the the Leve' Level Survey Survey off December December 9, 9. 1980. 1980. I j I J �Sh.•s 37 t 1000 Arsi' +600 .-eoo + 400 t 200 •000 —'200 - 400 I  Figure Figure 15 15 Location Location of o f Extensometer Extensometer Installations I n s t a l l a t i o n s in i n Shear Shear Zones Zones on on the the Looking East East 1000 and and 1200 1200 Levels Levels of o f the the Sherwood Sherwood Mine: Mine: Looking 1000 �J 38 ç • J 1 -3i -..tC. 2 .±.'i'4 ... ,• '-. I...tj.-:t.-_: ;. overbufden: .. I •..• -• . • . ••,.. -. .. Hf.f-'C'... .. : • • - .. i _• . - U J Bedrock J J J j Ij U j 1 s.q Figure Figure 16. 16. xi. ..is * ." *..;a , Suggested to Explain Pits Suggested Mechanism t.lecBanf-wto E x p l a i n Surface Surface-Pi t s on on Looking West. South Block Block of o f Surface Surface Shear Shear - Looking West. - J J �39 the theWest WestPit Pitsand sandplug plug failure failuredescribed described in inthe theprevious previous section, section, although although sand sandmovement movementfrom fromgroundwater groundwaterinflow inflowwas wasundoubtely undoubtelyatatleast leasta acontributing contributing factor. Hydraulically triggered subsidence. In the late evening of April 1, 1981 1981when whenthe theSherwood SherwodMine Minecomplex complexwas waswithin within100 100feet feetofofbeing beingflooded floodeda a rrost bysurface surface most unusual unusual sequence sequence of of events events either either caused caused or or were were created createdby subsidence. Massive Massivesurface surfacesubsidence subsidencetook tookplace place in in the the East East and and West West subsidence. Pits,and andtwo t wother othernew newpits pitsof ofsignificant significantsize sizewere wereformed. formed. This This Pits, extensive extensivesubsidence subsidenceininturn turnproduced produced great greathydraulic hydraulicpressures pressuresininthe the '* ' Surgesof of water water were were forced forced up up mine mine shafts shaftsand and nearly nearlyflooded floodedmine minecomplex. complex. Surges sand The sandfilling fillingraises, raises,rupturing rupturing or or destroying destroying their their seals seals and and cappings. tappings. The sudden suddenuprush uprush of of water water forced forced water water from from the the mine mine openings openings to to the the surface surface causing In one one area, area, water water and andmud mud causing extensive extensiveerosion erosionnear near the theopenings. openings. In were carried carried into into aa diesel diesel engine engine repair repair facility facility located located in in mine mine buildings buildings were Evidence shows showsthat that water water in in the the Sherwood Sherwood near the theHomer—Wauseca Homer-Wausecashaft. shaft. Evidence near Mine Mine shaft shaftproduced produceda ageyser geysereffect effectas asaaresult resultof ofbeing being forced forced to toexit exit diameter pipe throughaa10—inch 10-inch diameter pipe in in the the securely securely sealed sealedand and capped capped shaft. shaft. through raises located beneath two pond The seals sealsinintwo t wvertical vertical raises located beneath t wsurface surface pondareas areas west west The Waters drained drained rapidly rapidlyfrom from these these of the Sherwood the Sherwod Mine Mine were were disrupted. disrupted. Waters showthat thatthe the water water level level in Measurements show in the the ponds into intothe the minecomplex. complex. Measurements ponds mine mine period which mine complex complex rose rose17—feet 17-feet over overaatwo—day two-day period which spanned spanned the the subsidence subsidence events, events, whereas, whereas, prior prior to tothe theevent eventthe theflooding floodingrate ratewas was about abouttwo twoand andone one half feet feetper perday. day. half None of these witnessed, as None of these occurrences occurrences were were witnessed, as the the short—lived short-lived event event apparently Mr.Robert RobertEdwards, Edwards, apparently occurred occurred during during the the night night of of April April1,1,1981. 1981. Mr. Mine (retired) , reported Mine Manager Manager (retired), reported that thataaresidence residenceof ofa ahome home just justnorth north of of the shaft heard theSherwood Sherwood Mine Mine shaft heard sounds sounds about about 11:30 11:30 p.m. p.m. on on April April 1st 1st that that .. . . . . - . . . ,. ' : * , .a,: ." ., . . . ,.,., * a : X~.?... . s , , 3.. 2 .. .. �40 , , .,.: .. -8 >: ,.- ..:, "sounded like theore the ore crusher "sounded like crusher starting startingup". up". Of Of course, course, the theore orecrusher crusherwas was no had no longer longer operating operatingand and in infact fact hadbeen beenremoved removed from from the theproperty propertyfor forsome some activity. time. is probable probable that that the the sounds sounds were were fromm froiom the the subsidence subsidence activity. time. It It is The The cause cause of of the the event w e n t is is not not known. known. However, However, it it is is likely likely that that the the subsidence by aa single single subsidence subsidence event. event. subsidence activity activity was was initiated initiated by AA large large mass mass of of sand sand and/or and/or rock rock falling falling into into the the nearly nearly flooded flooded mine mine would would have have . . displaced displaced and and pressurized pressurized the the mine mine water water causing causing it it to to surge surge throughout throughout the the mine mine complex complex and and to to initiate initiate the the other other disruptive disruptive events. events. Increased Increased activity activity from from an an acoustic acoustic emission emission sensor sensor was was recorded recorded prior prior to to the the April April 1st 1st event event which which suggests suggests that that the the triggering triggering subsidence subsidence event event may may have have initiated Sherwod property. initiated near near the the center center of the Sherwood property. If event was was triggered triggered by by aa single single surface surface If it it is is accepted accepted that that the the event a, subsidence, subsidence, it it follows follows that that the the hydraulic hydraulic force force generated generated by by the the first first subsidence subsidence event event caused caused additional additional subsidence. subsidence. This this occurrence occurrence could could have have been been repeated repeated several several times times similar similar to to aa chain chain reaction. reaction. It It is is likely likely that that a a series series of of subsidence subsidence events events did did occur, occur, each each one one triggering triggering additional additional 5 - S -i activity. activity. It It is is also also likely likely that that the the life life of of intense intense subsidence subsidence activity activity was perhaps on on the the order order of of one—half one-half hour hour or or less. less. was short, short, perhaps Unfortunately Unfortunately the the acoustic acoustic emission emission sensors sensors were were much much too too sensitive sensitive to to distinguish distinguish the the period period of of the the most most intense intense activity. activity. An interesting analogy to to this this subsidence subsidence event eventwould uld be interesting analogy be to tothink think of of 6 b openings of of the as the the the underground underground openings themine mine complex complex as the"pluming "pluming system" system" of of aa hydraulic unit with with the the nine mine water water representing representing hydraulic hydraulic fluid. fluid. However, However, hydraulic unlike aa hydraulic hydraulic systan system which which is is strongly strongly sealed sealed and and fluid—filled, fluid-filled, the the unlike mine seals on shafts shafts and other surface surface 'mine was was incompletely incompletely filled filled and the seals ' :, ' openings openings were were for for the the most most part part not not designed designed to to withstand withstand great great hydraulic hydraulic forces. forces. As As water water surged surged upward upward through through these these channels channels leading leading to to the the �41 surface, the of the the air between the the surface surface of the rising rising water water and and the the shaft shaft capping or or seal would have capping seal would have been been rapidly rapidly compressed. compressed. If the the surface If surface seal seal or or capping was was not capping not stong stong enough enough to to resist resist the the combined combined forces forces of of the the compressed compressed air and the rising water, water, it would would have been either either lifted lifted or or disrupted. disrupted. These These types types of of occurrences occurrences were were documented documented following following the the April April 1st 1st subsidence event Sherwood Mine. Mine. subsidence event at at the the Sherwood In similar fashion, the sand "seals" in the the bottom of of old old subsidence subsidence pits pits were were disrupted. These were formed These "seals" were formed by by the the gradual gradual inwash inwash of of sandy overburden into sandy overburden into the the pits pits following following subsidence. subsidence. sand plugs plugs would would be low. low. The strength strength of these these would be uncemented and and the the main main forces forces They would the sands sands in place would would be frictional frictional with gravity holding the gravity loading. loading. Compressed air air and Compressed and surging surgingwater water moving moving up up through through the the caved caved area area beneath beneath fail. these seals these sealscould could have have easily easilycaused caused them them to to fail. Piping—induced subsidence. Piping-induced One of the the most interesting interesting and and significant significant aspects of the hydraulic subsidence aspects the hydraulic subsidence event was was the the formation formation of of aa subsidence subsidence pit which was as aa concealed concealed cavity cavity in in was believed to to have have existed existed previously previously as the glacial glacial overburden activity. overburden formed by piping activity. Piping, as it relates surface subsidence, subsidence, occurs relates to surface occurs when when groundwater groundwater mineopenings openingsthrough throughopenings openings(fractures, (fractures,drill drill flows into into underground underground mine flows holes, arearelarge enough holes, etc.) etc.) that that large enoughtotoallow allowpassage passage of ofsand sand grains grainsfrom from the the This transport transport mechanian canresult result in in the of large overburden. This overburden. mechanism can the formation formation oflarge conditions that that cavities within cavities within the the soil soilabove above the thebedrock bedrock surface. surface, The the conditions above favor this process favor this process are are threefold: threefold: 1) 1) an an easily easilyerodible erodiblesoil soil abovebedrock, bedrock, water transported 2) channeiways that permit 2) channelways that permit water transported soil soiltotomove move from from the the Given overburden into the substantialgroundwater groundwater flow. flow. Given overburden into themine mine void void arid and 3) a substantial conditions plus overburden layer, these these conditions plus a thick thick overburden layer, large large volumes volumes of of groundwater groundwater mine void void reservoir (for (for water and and sand) sand) the the piping—induced piping-induced flow and a large mine �42 cavity cavity can can become become very very large. large. The surface layer The presence presence of of aa competent cornpeten-------- which which serves serves as as aa capping capping can can allow allow the the soil soil cavity cavity to to attain attain large large horizontal horizontal and and vertical vertical dimensions dimensions before before collapse collapse occurs. occurs. This of surface surface subsidence subsidence not not previously previously described in This mechanisti mechanism of in the the literature, and Frantti Frantti (1981). literature, was was presented presentedbybyJohnson, Johnson,1-lodek Hodek and (1981). AA ,* , conceptual conceptual model model of of the the piping piping subsidence subsidence phenomenen phenomenon is is illustrated illustrated in in Figure Figure 17. 17. It It can can be be seen seen in in Figure Figure 17 17 that that the the initial initial flow flow of of sand sand and and groundwater groundwater produces produces aa cavity cavity in in the the soil soil at at the the point point of of intersection intersection of of the the bedrock bedrock channel channel and and the the overburden. overburden. Growth Growth proceeds proceeds by by gravity gravity collapse collapse the undercut peripheryof of the the opening of of unstable unstable sands sands from from the undercut periphery opening — the the undercutting undercutting being being caused caused by by groundwater groundwater erosion erosion and and transport transport of of the the sand. sand. Cavity Cavity growth growth ceases ceaseswhen h e n any any of of the the following following conditions conditions are aremet: met: 1. 1. The The mine mine becomes becomes flooded flooded and and water water flow flow is is stopped. stopped. flow is is no 2. The volume volume and and velocity velocity of of groundwater groundwater flow no longer longer 2. The 3. 3. sufficient sufficientto toerode erodeand/or and/or transport transportsand sand into intothe themine mine void. void. *' The channelwayinto into the the mine minevoid void becomes becomesplugged pluggedorora afilter filter The channelway which"screens "screensout" out" clastic clastic pack pack of of sand sand and and gravel gravel develops develops which material. material. ? - -J If If the the diameter diameter of of the the hanispherical hemispherical piping cavity cavity exceeds exceeds the the length length that that the the surface surface capping capping will will withstand, withstand, surface surface collapse collapse will will occur. occur. resulting resulting The The pit will be be straight—walled straight-walled with a high high depth depth to to width width ratio. ratio. This This will will serve serve to to distinguish distinguish aa piping—generated piping-generated cavity cavity from from one one formed formed by by shear shear failure failure of of running running sands. sands. These These cavities cavities may may apparently apparently exist exist for for long periods periods without without any any surface surface expression expression to to indicate indicate their their presence. presence. Capping by outside outside forces; forces; i.e., i .e., explosions explosions or or Capping failures failures may may be be triggered triggered by " hydraulic hydraulic forces forces as as occurred occurred at at the the Sherwood Sherwood Mine. J �43 Mine Mine operating, operating. surface s u r f a c e and and underunderStope Stope underlies u n d e r l i e s erodible e r o d i b l e sands sandsand andcompetent competent till till capping. capping. A. A. ground ground pumping pumping in i n progress. progress. C. -., Soil S o i l cavity c a v i t y enlarges e n l a r g e s as as water water ininflow f:Low causes causes undercutting undercutting at at periphery periphery resulting r e s u l t i n g in i n sand sand collapses c o l l a p s e s from f r o mthe the roof. roof. S o i l i s c a r r i e d i n t o mine mine by by groundwater groundwater flow. flow. Competent Competent capping capping; layer still intact. Soil is carried into layer still intact. Figure 17. Improve'] con en ,I. tilt) 13. B. Mine closed, c l o s e d , pumping pumping stopped stopped Mine Groundwater rises rises in i n overburden overburden and and Groundwater mine mine begins begins to t o flood. flood. Cavity Cavity develops develops as sand/water sandhater I n sands sands above above bedrock bedrock as in mixture flows flows into i n t o the t h e stope s l o p e via v i a open open mixture fractures. fractures. D. D. Collapse of of cap, cap. subsidence subsidence is is Collapse complete complete the t h e mine mine is is flooded flooded ted n ~ the the d croundvater ttable a b l e is is at a t equilibrium. equilibri*. p.roundwater R e s u l t i n g pit p i t has has near near vertical v e r t i c a l walls walls Resulting and f l a t bottom. bottom. and aa flat U,OC)O1 or p tIpt 1 fIr :tiih:: I dc,irc' ii V., r tin tin. le rground mE ne. �-J 44 j Long Long Term Term Subsidence Subsidence Long Long term term subsidence subsidencewas was defined defined as as subsidence subsidence that that occurs occurs following following. mine mine closure closure and and the the time timerequired required for for aa mine mineto toflood. flood. It It was was mentioned mentioned previously previously that that the the major ma;or mechanism mechanism responsible responsible for for long long term term subsidence subsidence was was the the force force of of gravity gravity and and other other stresses stresses to to which which mine mine pillars pillars and and stope stope f , walls walls are are subjected. subjected. Loss Loss of of rock rock strength strength by by weathering, weathering, oxidation oxidation or or ) . J J j other other chemical/physical chemical/physical reactions reactions also also play play aa role role in in long long term term subsidence. subsidence.. Seismic shock— natural natural or or resulting resulting fran from man's man's activity activity may may also also be be aa Seismic shock causing causing factor factor in in long long term term subsidence. subsidence. Natural Natural shocks shocks would would occur occur from from earthquakes; earthquakes; man—made man-made shocks shocks would would include include explosions, explosions, operations operations of heavy rail, truck truck and ' machinery machinery arid and rail, and automobile automobile traffic. traffic. j Hydraulic Hydraulic shock shock which which was was described described in in the theprevious previous section sectioncould could also alsobe be aa factor factor in in aa flooded flooded mine, mine, natural or man—made being being generated generated by by either either natural or man-made shocks. shocks. by its its very implies aa process process that that is isslow slow Long term term subsidence, subsidence, by very name, name, implies Long and The factors factors which which control control the thetiming timing and unpredictable unpredictable in in terms terms of of timing. timing. The and ofofmine andposition position mineopenings openings and and the the Of these, these,the thesize size are many. many. of are ! thickness of the the bedrock above the the mine mine stopes stopes are are of thicknessand and competency competency of bedrock above of structural conditions inherent in in the particular The structural conditions inherent the rock, rock, the the particularimportance. importance. The of moisture effective and the the presence presence of moisture are are additional additionalimportant important effective stress stress field fieldand factors factors governing governing the the stability stability of of mine mine openings. openings. j j '.'. important factor factor in Generally Generally speaking, speaking, the the most m s t important in delayed delayed or or long long term term '1 mine subsidence relates to the proximity of the mine void to the surface. mine subsidence relates to the proximity of the mine void to the surface. l *-. j Other stopes have have the the greatest greatest Other variables variables being being equal, equal,near—surface near-surface stopes possibility possibility of of subsidence. subsidence. Although Although only only one one case case history history of of long long term term subsidence subsidence is is presented in in detail, detail, it it illustrates illustrates all all of of the the real real concerns concerns that that may arise arise from from this this delayed delay@ subsidence. subsidence. It It is is the the only only documented documented case case of of mine mine subsidence subsidence that that . . ~- *.- T* �45 I resulted resulted in in a a human human fataility fataility in in Iron Iron County. County. I I the the Iron Iron River River district. district. I I I I II 1 The Hie subsidence subsidence event event occurred occurred in in June June of 1960 1960 between between the the City City of of Caspian Caspian and and the the Village Village of of Gaastra Gaastra in in 2s &,A *,' The Hie following following description description of of the the circumstances circumstances of of the from a memorandum the subsidence subsidenceevent eventisis from a memorandum report reportprepared preparedbybyR.O. R.O. Pynnonen Pynnonen f ~ , 3'4 .. and R.L. Bernard of of the the U.S. U.S. Bureau Bureau of of Mines Mines in in 1968. 1968. çf and R.L. "A 40—foot section "A 40-foot section of of County County Highway Highway 424 424 approximately approximately 22 miles miles south south of of Iron Iron River River caved caved early early in in the the morning morning on on June June 11, 11, 1960. 1960. One One person person was was killed two others others injured killed and and two injured when when two two automobiles automobiles were were driven driven into into the the cave cave during during early early morning morning darkness darkness and and aa heavy heavy fog. foq. The The cave—in cave-in was was 40 40 feet 30 feet feet wide, and and about about 30 30 feet feet deep. deep. Records feet long, 30 Records show show that that the the cave—in on the the property cave-in occurred occurred on property line lineseparating separatingthe theoperating operatingBuck Buck Mine and the the abandoned Mine of ofPickands—Mather & Company Company and Pickands-Mather & abandoned Smuggler SnugglerMine, Mine, Gaastra Company. Mineproduced producedslightly slightly more GaastraIron Iron Company. The Hie Smuggler Smuggler Mine imre than than 8O0,0 800,000tons tonsof ofore orefrom from aa depth depth of of less lessthan than 520 520 feet. feet. A A stope stope 80 80 to to 120 feet wide 120 feet wide beneath beneath the the road road reportedly reportedlywas was mined mined to to within within 20 20 feet feet of of ledge." ledge." Following Following the the accident, accident, the the caved caved section section of of the the road road was was blockaded blockaded on on the the east east and and west. west. was was left left as as it it was. was. The The road has has not been repaired repaired and and the the subsidence subsidence pit pit Except Except for for the the growth growth of of vegetation vegetation and and trees trees the the area area little has has changed changed little from from 1960. 1960. pit. pit. Large Large slabs slabs of of broken broken pavement pavement lie lie in in the the Wooden posts connected by steel steel cables cables which which once once served served as as aa guard g Wooden posts connected by the north side of rail rail on on the north side of the the road road hang suspended suspended on on the the north north side side of of the pit. pit. Broken water pipes by the are exposed Broken water pipes which which were were exposed exposed by the cave—in cave-in are exposed in i the toaa local local resident resident the the two car bodies bodies in the pit the pit pit sides. sides. According According to twocar - were 1960 accident —— they they are are the theproper proper vintage. vintag were involved involvedininthe the 1960 accident Photographs of the the pit 21. 18through through.21. Photographs of pit taken takeninin1980 1980are areshown shown in inFigures Figures18 Except for the which grown in 20years yea in the the20 Except for the stall smallaspen aspenand andbirch birchtrees trees whichhad hadgrown following the accident, accident, little little has following the haschanged changed at at the thescene sceneand and ititremains remains as a a grim of one one of of the the most threatening aspects grim reminder reminder of most threatening aspects of of long long term term or or delayed delayed subsidence. Subsidence. The location of roan of UÂFigure Figure22 inthe theplan planmap =..~-n in The location of the thesubsided subsided area areaisisshown pit in which was traced traced from an aerial in the the Note the the subsidence subsidence pit which was from an aerialphotograph. photograph. Note LL I I ,A .. -. ,." ,. ; .. .,-:? , ..,... \ .. ., . ! ., ,:, �-J 46 j j Ii J j J 4 - Figure Figure 18. 18. J Smuggler Smuggler Mine Mine Cave—in Cave-in on on County County Road Road 424: 424: Looking Looking East Ease j I J j j J j Figure Figure 19. 19. Close-up Close-up of o f Smuggler Smuggler Mine Mine Cave—in: Cave-in: Looking Looking East East Li �Figure 20. 20. Cave—in un on County Smuggler Mine Cave-in i,ounty Road 424: 424: Looking West Looking Close-up of 2.1. &l.o.&-ub of Smuggler Smuggler Mine Mine Cave—in: caw.-in,: LLooking &'~. .,, . . iFigure - i ? . ~ 2L : . . . ~,A:. ~ West West �48 CITY OF CASPIAN CASPIAN -I j j U U BARRICADE j COUNTY ROAD 424 U j —— I SUBSIDENCE PIT -s-N .. 500 c UNDERGROUND WORKINGS 1 -j C. 'I- -I j j —. LI BARRICADE j j Figure Plan Map Mapof of the theSmuggler SmugglerMine Mine Figure22. 22. Plan Area Area Showing ShowingSubsidence SubsidencePits Pits and and the theAreas Areas of ofUnderground Underground Workings d TO TO GAASTRA QAAUTRA 1 �L L L 49 49 road of similar road and a second one of s i m i l a r size s i z e aa short s h o r t distance d i s t a n c e south south of of the t h e road. road. photograph photograph of this of t h i s second second subsidence subsidence pit p i t is is shown shown in i n Figure Figure 23. 23. these these pits p i t s are a r e underlain underlain by by the t h e Smuggler Smqgler Mine. Mine. L L A Both of m t h of Accurate Accurate mine mine maps maps of of the the Smuggler Mine are not available, however, two old maps maps were were found which show show Smuggler Mine a r e not available, however, t w a old found which ssection e c t i o n views views of of the t h e Smuggler Smuggler ore o r e body. body. Figure 24 cross view Figure 24 is is a a c r o s s ssection e c t i o n view looking north north and 25 is is aa longitudinal l o n g i t t d i n a l section s e c t i o n looking looking west. west. looking and Figure Figure 25 Although not shown, shown,i tit is is apparent any dwelopnent development Although tthe h e mine mine sstopes t o p s aare r e not apparent that t h a t any above would atmve tthe h e first f i r s tlevel lwel wouldhave have brought brought the t h e mine mine stopes stopes very very near near the t h e ledge ledge (thee bedrock surface). This This obviously b d r o c k surface). obviously occurred. occurred. L L was Perhaps no road road iin it was Perhaps at a t this t h i stime time there there was was no n tthis h i s area, area, or o r perhaps p e r h a p it onlyy a trail. trail. on tthe map sshown Figure 25, 25, i it is From ~rom iinformation n f o m a t i o n on h e map h m in i n Figure t is suggested that may have have been been used used to suggested t h a t rock rock may t o fill f i l l the t h e mine mine void. void. is not known. However, this However, this 424 over over a mined—out what is is clear, that County what c l e a r , isis t h awith t with CountyRoad b a d 424 a mined-out operation, tthat and and llargely a r g e l y forgotten forgotten early e a r l y mining mining operation, h a t the t h e stage s t a g e for f o r eventual eventual L [ subsidence ooff .the was set. set. subsidence t h eroadway roadway was The unfortuitous unfortuitous timing timing of of the The the subsidence event, on a foggy night, played a large role in causing the human fatality. Acid ~ c i Water d Drainage drainage is not aa problem tthat h a t is usually associated with Acid water drainege iron i r o n mines. mines. L I L 1 L i I However, district, direct i n the t h e [ron Iron River d i s t r i c t , the t h e iron i r o n ore o r e was in in d irect However, in contact with pyrite-rich Wauseca member of of the t h e Dunn Eunn Creek Creek contact w i t h the the underlying pyrite—rich lenses of of pyritic sslate l a t e and and lenses witicslate s l a t were e weresometimes sometimes found found iin n the t h e iiron r o n ore. ore. when the was When the pyritic p y r i t i cslate slate wasexpesed e x p s e d during during mining, mining, it itwould m u l d oxidize oxidize so so rapidly that rapidly t h a t sometimes sometims mine mine fires f i r e s were were the t h e result. result. Ass many of the A t h e mines mines were wet and required water was w e t and required pumping, pumpirq, the t h e pumped pumped water w a s acid. acid. Consequently, Consequently, water d drainage has been been aa problem problem iin the IIron River ddistrict acid a c i d water r a i n q e has n the r o n River i s t r i c t ssince i n c e tthe he were opened. mines were opened. were operating, When many many mines mines were pun@ from from acid waters waters pumped When operating, acid �oc :; ,", Figure 23. (50 U ft di,meter, 2 ft os) 95 ; aoqe 3di t flPUJ aDuepLsqn P &all .'Subs%dence Jo o* ,c3unoJ Cm*yt peo j7j7 Road 424 sbovt? at65nws Smgg%erMfne auLw .. deep) south (doap tnnos �51 1YR0A042.. C • —— lit LEVEL - -. S .0• —— - 2nd LEVEL 3rd LEVEL - 4thLEVEL.. 4th LEVEL - - - - SMUGGLER MINE CROSS SECTION 0 FEET SOUTH LOOKING NORTH SCALE 1" — 100 ft. ~. Figure Figure24. 24. Cross-Section Body Cross-Section Map Map of of the t h e Smuggler Smugg.ler Mine Mine Ore Ore Body .~ ".. �L. LL. 1 2 L...... Longitudinal Section Section ofofthe theSmuggi Smuggl L_ L L... Mine fine Ore Ore Body Body EL CL. L FOGARTY SMUGGLER MINE CROSS SECTION 200 !OOFEET FEET WEST W E 8 1LOOKING LOOKINO WEST WEST VOUNGS YOUNQS 2 L_ L_ L_ L CL.. 25. Figure 25. 4th LEVEL 3rd LEVEL 2nd LEVEL 1st LEVEL 3 C 4 S L. C L_ 4th LEVEL 2nd LEVEL in LEVEL LLL I I LEDGE LEDOE b 4 N Ui EL �53 than the. Iron River In more recent years them caused caused'the Iron a v e r to to run run red. red. In more recent years as asmines mines closed closed . and ceased, acid acid water water drainage mining companies and pumping punping ceased, drainage abated. abated. Some Some mining companies which which instituted institutedcorrective correctivemeasures measures to toimprove improve the the quality qualityof ofmine mine waters waters before before draining in the the acid draining than then into into the the river river also alsocaused caused aagreat greatimprovement improvement in acid water water In fact, for a hile, while, it seemed seemed reasonable reasonable that that acid acid water water situation. situation. drainage drainqe would cease cease to to be be aa problem problem in in the the district. Such however, for as as the the mines mines closed and punping pumping was was Such was not the the case, however, Workings Wrkings kept kept dry dry for for all all halted, underground underground water water levels levels began b q a n to to rise. rise. cases it took In some some cases took the the years years the the mines mines were were in in operation operation began began to to flood. flwd. The waters rose rose until they several several years years for for the the mines mines to to fill fill with water. water. -- reached the levels existing prior to to mining reached their their natural natural levels levels ——— the Mines collared at lower elevation in the Iron River valley activity. L G . flooded to the surface surface and flow from from some some of of them than carried carried acid acid into the Iron River. River. Sulfur—bearing black slate often often used used for for surface surface fill around mine mine Sulfur-tearing wrkings and acid acid workingscame caneinto intodirect direct contact contact with with the the elevated elevated groundwaters groundwaters and waters issued waters issued from from this this source source too. too. Discoloration present acid drainqe drainage is Discoloration of of the the Iron River by present is not as severe but it it is is still still aa concern. concern. severe as as it it once once was, was, but Tests by the Tests the Michigan Michigan other fish and aquatic Water Resources Resources Commission Commission show that trout and other organisns organisms can can and do do live live in in the the clouded cloded waters. waters. Nevertheless, Nevertheless, % . *, . : :> River visible and aesthetically discoloration discoloration of of the the Iron Iron a v e r is highly visible displeasing. objects objects with . , a fineness of the a yellow—brown yellow-brom slime and the extreme fineness where into the the Brule, Brule, Several miles south south of Caspian Caspian h e r e the the Iron Iron empties empties into their confluence is marked by by aa noticeable noticeable plume plume of of turbid turbid water water entering entering is marked * .. ~ ...... 9 all submerged coats all Precipitation of compounds Precipitation ofinsoluble insolubleiron iron compunds coats suhnerged precipitates downstream. carried far downstrean. precipitates allows allows than then to to be carried , .L. , 5' b .'~. r, ~ Z . . : ,. . . % . . .- �-J 54 the Brule River. the Brule River. Wisconsin. Wisconsin. National National J , The Brute Br-tileRiver River marks marks the the boundry The bundry between between Michigan Michigan and and J It isisalso 650,000 acre acre Nicolet Nicolet It alsothe thenorthern northernborder border of of the the 650,000 Forest. Forest. J A report report issued issued by Nicolet National National Forest Forest personnel personnel documents level, colored colored documents the pollution by by chariical chemical analysis the pollution analysis and and by by low level, aerial aerial photography photography (Runt, (Hunt, 1974). 1974). Since 1974 1974 the Institute Institute of Mineral Research has been studying studying acid j drainage drainage problans problems in in the the Iron Iron River River district. Two sources sources of acid acid drainage drainage properties were from closed mine properties were identified. identified. The most serious serious acid drainage drainaye J Dober Mine pit pit which which in the late 1970's was was that flowing from the k b e r Mine 1970's accounted for more than for than 75% 75% of the the acid drainage drainage into into the the Iron Iron River, on on the the basis basis of of The ranainder remainder of the acid drainage issues issues from from extensive extensive dissolved iron. iron. piles piles J J of pyrite—bearing pyrite-bearing black slate filling a low low marshy area area over over the the Buck Buck group group of of mines mines about about one one mile mile to to the the south. south. case histories histories for the the case for acid aciddrainage. drainage. J These two These two occurrences occurrences provide provide The information information has has been been extracted extracted The reports prepared from from reports prepared by by Johnson Johnson and and Frantti Frantti (1976, (1976, 1978) 1978) Cregger Cregger (1979) (1979) and and .- p -*. b t-7. Johnson Johnson (1979). (1979). underground source. source. mine drainage: drainage: underground Acid mine The most mostserious serious and and best best ..-The j documented source aciddrainage drainage theIron IronRiver Riverdistrict district occurs occurs at at the inin the the documented source of of acid The part of of aa larger consisting also The ~Dober o b e r~Mine i n eisispart largermine mine complex complex consisting also The mine minecomplex complexisissituated situated west of the of theIsabella Isabellaand andHiawatha HiawathaMines. Mines. The west of of It consists consists of of the City andsouth southofofthe the City City of of Iron the City of of Stambaugh Stambaugh and Iron River. River. It eight, forty—acre parcels identified identified as eight, forty-acre parcels asthe theDober, Ikiber, Isabella, Isabella, Stegmiller, Steqmiller, Dober k b e r Mine. Mine. I I Hiawatha #1 $1 West Hiawatha #2 Hiawatha #2 (formerly (formerly Duff), Duff), Hiawatha, Hiawatha, Hiawatha Hiawatha $1, #1, Hiawatha West and and Hiawatha #2 #2 West properties. The Iron River flows flows in in a southerly southerly direction direction over over the the Stegmiller, Stegmiller, Isabella Isabella and and Dober Ikiber properties. .. Locations of ~ocations of the the properties are shown in Figure properties are shown in Figure 26. 26. History. History. Mineswere weretwo tbKofofthe theearliest earliest iron The Dober Ibber and Isabella The Isabella Mines iron I J �55 W HIAWATHA i:ii [ L L .: j, &'' 2W DUFF L -Â¥ W DUFF -i L C L' Li CASPIAN U > [ U ... ISABELLA, ,c.?-5,., L..:.4- ,.,.it--:-F;. .. . ..:?..,., 4 . . . .~ -, .;. . - ' . ,* ...>.',,& ".. Scale I": 1 L DOBER & HIAWATHA MINES '.È*( . \ . . Plan Map Figure 26: L J M 5-7 �56 mines mines to to open open in in the the Iron Iron River River District; District; the the Isabella Isabella was was opened opened in in 1882 1882 and and the the Duber Dober in in 1888. 1888. Initially, Initially, both were started started as as open open pits pits and and later later were were developed developed into into underground underground mines. mines. from stopes. from open open stopes. The The direct direct shipping shipping ore ore was was mined mined The by one one shaft shaft The Isabella Isabella was was served served by to to aa depth depth of of 430 430 feet. feet. in in the the upper upper levels levels This is interconnected interconnected with with the the Dober Dober This shallow shallow mine mine is workings workings on on the the 4th 4th level. level. The by two two shafts; shafts; #1 #1 aa The Dober Dober Mine Mine was was served served by vertical vertical shaft, shaft, 950 950 feet feet deep, deep, north north of of the the open open pit pit and and #2 #2 an an inclined inclined shaft shaft which which descends descends to to the the 10th 10th level level (1000 (1000 feet feet deep) deep) and and is is located located just ji_- south south of of the the open open pit. pit. The The Dober and Isabella Isabella Mines Mines were were operated operated by by Oliver Oliver 'I Mining Mininq- Company Company until 1935 1935 at at which which time time they they were were combined combined with with the the Hiawatha Hiawatha - - until * Mine Mine under under single single ownership. ownership. *^ -4 ' , ..  ., ¥= ..A -- . "2 . i , ..-- I The The Hiawatha Hiawatha Mine Mine began began as as twa two separate separate operations operations from from two two vertical vertical: J shafts, shafts, No. No. 11 and and No. No. 2. 2. Hiawatha Hiawatha Iron Iron Company. Company. The The Hiawatha Hiawatha No. No. 11 was was opened opened in in 1893 1893 by by the the The The The No. 11 shaft shaft is is 2180 2180 feet feet deep. deep. The Hiawatha Hiawatha No. first it was was first named named was was put put in in to to mine mine ore ore Hiawatha or Duff Duff shaft shaft as as it Hiawatha No. No. 22 or from from the the western western extension extension of of the theDober Dober and and Isabella Isabella properties properties below below the the The Hiawatha No. 22 shaft shaft Hiawatha No. 10th 10th level level by by the the American American Boston Boston Mining Mining Company. Company. is is 2500 2500 feet feet deep. deep. tà ' i Dober Dober '1 Mine Mine maps maps show show aa bulkheaded bulkheaded 8th 8th level level drift drift and and an an open open 10th 10th level leve shafts. drift drift between between the the two two shafts. .j i depth. depth. at Daber The No. 22 shaft shaftinterconnects interconnectsthe the DoberMine Mine at The Hiawatha Hiawatha No. Open stopes stopes in in the the ore ore body body also also connected connected Open wrkings with with the the Hiawatha Hiawatha workings. workings. workings Levels Levels from from the the 10th 10th to to the the 21st 21st of No. 22 shaft shaft are are connected connected to to the the Hiawatha Hiawatha No. No. 11 shaft. shaft of the the Hiawatha Hiawatha No. ; Shaft Shaft locations locations are are shown shown in in Figure Figure 27. 27. & .. .I 1 When When the the Daber Dober and and Isabella operations were incorporated incorporated with with the the in 1935, the production andafter after Hiawatha No. No. 2 2 Mine Mine in 1935, the production records records were were combined combined and Hiawatha 2 mines 1943 the the shipping shipping records records of of the the Hiawatha No. No. 11 and and No. No. 2 mines were were 1943 closing in in 1967 1967 combined shipments shipments totaled totaled 22,162,905 22,162,905 long low combined. combined. Until closing : >.,, ." ~...X&?'J. . . -, .,. , . , . . . . .. . . . , , ,. �57 N To Stambaugh To Iron I River 1Scale: I I I ' \ Hiawatha H i awatha // I/ \V, un i' "- 1 8 Shaft Shaft 1 #1 ' -. >* t -I. Iron N. River 1" = 500' N /.- CLZ Isabella Pit L. and Shaft 1 it I '¼' D!'i .1 — Hiawatha Ii #2 Shaft Dober #2 Hwy. M-189 1 To To Caspian Caspian r It II Stambaugh —V N & Sewage Ii! Treatment Plant Figure__2?. Surfacei plan plan map map of of the t h e Dober-Hiawatha-Isabella Dober-Hiawatha-Isabella Mine Mine Complex Complex , I �58 tons. tons. Earlier Earlier production production from from the the Dober m b e r and and Isabella IsabellaMines Mines(prior (priorto to1935) 1935) f had had been been combined combined with with the the nearby nearby Riverton Riverton Mine Mine and and referred referredto toas asthe the Riverton total of of 5,881,550 5,881,550 tons tons were were reported reported for for the the period period RivertonGroup. Group. AA total s iff 1882—1937. 1882-1937. Structure Structure of of the the Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella mine mine complex. complex. The The DDber— DoberHiawatha—Isabella Hiawatha-Isabella Mine Mine complex complex may may perhaps perhapsbe be more more readily readilydescribed described by by structural structural than than by by geographic geographic boundries; boundries; nanely namely as asthose thoseportions portionsof ofthe the iron iron formation formation bounded bounded on on the the north north by by the the North North Hiawatha Hiawatha fault, fault, on on the the south These south by by the the Duff Duff fault fault and and on on the the east east by by the theStegmiller Steqmillerfault. fault. These faults faults form form aa triangular triangular block block which which incorporates incorporates an an east—west east-west trending trending syncline The iron iron formation formationon on the thenorth northcomprising comprising synclineof ofthe theiron ironformation. formation. The the the Hiawatha Hiawatha No. No. 11 Mine Mine is is vertical vertical to to overturned overturned with with an aneast—west east-west trend. trend. On On the the east east the the iron iron formation formation trends trends north north south southand and dips dipswesterly westerly at atan an of about 60. angle angle of about 60¡ This This limb limb was was mined mined from from the the surface surfaceby by the the Isabella Isabella Mine. and DDber Dober Mines Mines and and at at depth depth by by the the Hiawatha Hiawatha No. No. 22 Mine. and These These relationships relationships are are shown shown in in Figure Figure 28. 28. 3 Acid Acid drainage drainage from from the the Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella mine mine complex. complex. In In 1966 1966 after after nearly nearly 85 85 years years of of operation operation the the Dober Dober Mine Mine complex complex ceased ceased operations. operations. Pumping Pumping was was stopped stopped and and the the mine mine began began to to fill fill with with water. water. It It was was not not until until some some six six years years later later in in early early October October of of 1972 1972 that that water water first first appeared appeared in in the the open open pits pits of of the the Ebber Dober and and Isabella Isabella mines. mines. Over Over aa period period of of Local Local residents residents were as they they had had were quite quite surprised surprised to tosee seethe theDDber Dober and and Isabella IsabellaMines Mines flood flood as . , . been been dry dry for foras aslong longasas anyonecould couldremember remember since the themines mines were were open open anyone — since in in the the1880's. 1880's. ... ,.. The rising rising acid acid waters waters were were of of more more than than just just idle idle curiosity. curiosity. The The main main The ,. . . 'S, -. È!, sewage Sewage TreatmentPlant Plantpassed passed just just west line feeding sewage,lin% feeding the the stambaugh St-ugh Sewage Treatment west of of . !. .à pit rose 45 days days the the water water in in the theDober Dober pit rose about about 100 100 feet. feet. 45 -j I I �59 I..] I 5 —1 I• '——--F-.—— I I ii" L "(p L-I Jo St. 'tJ-tl "3 ~ Figure 28 Figure 28. Isometric Isometric diagram diagram of of part part of of the the Hiawatha Hiawatha and Dober Dober Mines. Mines. (from Dutton, 1969) 1969) .... . : ~ ,. ,. , .,, . ,, .. . . . # .( . .. ~ �60 the kober b e r Mine pit. The acid waters waters poured pured into into corroded corroded sections sections of of the the pipe and acid water entered the disrupting the the plant plant disrupting the bacteriological bacteriological sewage sewage The problemwas waseventually eventually solved The sewage sewage problem solved digestor. by the the DNR and the the City of Starobaugh Stambaugh insertinga aplastic plastic pipe pipe inside inside the line. of byby inserting the sewage sewage line. Water in Water in the Dsber ober Mine from the the pit pit to to lowered about about two two feet feet by by ditching ditching from the Mine pit pit was was lowered the river. the river. details of this The details this sequence sequence of events events have been documented documented by Van Van Alstine Alstine (1973). (1973). . . , ., '*Â¥ . Flooding of the mine complex took six years because neither the complex the :--'. ':* . .,,.:.*:. Records for 1948 No. for19484 No. 11 nor nor the the No. No. 22 were were exceptionally exceptionally wet wet mines. mines. Records .. minute (gçm) were pumped from the Hiawatha No. gallons per that 230 that 230 gallons per (gpn) from the Hiawatha No. ' 8 Hiawatha indicate 2 and 300 gpn from 300 gpn from the the Hiawatha Hiawatha No. No. 11 for for aa total totalof of530 530gpii. gpn. Using using these these >: ! conjunction with mine mine volumes data in in conjunction volumes calculated calculated from from ore ore shipping shipping records records stopes filling measurements measurements the time required to flood could have been and scopes estimated. made by Cregger (1977) Based on measurements made (1977) the the mine complex complex has a a volume of 281 281million million cubic cubic feet feet from ore removed, less aa stope has volume of from ore removed, less stope filling of 58 58million millioncubic cubicfeet feetresulting resulting in in aa total fillingsand sand volume volume of totalof of223 229 is: The calculation calculation of of the million feet. The million cubic cubic feet. the time time to to flood flood i e ; 2,;. : , . , ~ ! .- 1 ; X 106 106 FT3 rr3 xX 7.48 Time Flood = = 223 223 X 7.48 GAL/fl GAL/FT ,% = ,g 6.0- 4YEARS Time to to Flood 530 DAYS/YR 530 GAL/MIll -IN x 60 6 0MIN/HR MIN/HR x 24 24HR/13Y HR/DAY xx365 365 DMS/YR ' This simple calculation could been made madetotopredict predict the the time of This simple calculation could have have been time of flooding. flooding. one had hadanticipated anticipatedat at the the time that water, of course, Of course, no no one time that water, especially Mineinto into the the Iron especially acid acidwater, water,would would flow flow from from the the Dober Dober Mine Iron River. River. Flow rates rates of Dober Flow of acid aciddrainage drainagefrom fromthe the DoberMine Mine measured measured since since 1975 1975 have varied varied from a low of about to highs highs in in excess 30 gpxt gpn to excess of of 100 100 gpn. gpn. have from a low of about 30 During 1978the the flow flow rate rate ranged 39 to to 90 During 1978 ranged from from 39 9 0 gpn gpn with with an an average average of of 67 67 gpn. gpn- Chemicalcharacterization characterization of Chemical ofDober Dober Mine acid acid drainage. drainage. Acid Acid drainage drainage pit was during the the period to the Dober from the Dober Nine Mine pit was periodically periodicallysampled sampled during period 1975 1975 to j �61 1978. 1978. Chemical aluminun and sulfate Chemical analyses analyses for for iron, iron, manganese, aluminum sulfate were routinely routinely performed. performed. In In addition, addition, temperature, temperature, pH, pH, specific specific conductance conductance and and acidities acidities were were measured. measured. Results Results of of these these analyses analyses are are shown shown in in Table Table 4. 4. Average Average values values of of water water quality quality measurements measurements in in 1975 1975 were: were: pH pH == 4.1, 4.1, acidity acidity == 2900 specific conductance 2900 mgI! m g / l CaCO3, CaC03, specific conductance == 5000 5000 mhos/cm, mhos/cm, iron iron == 1125 1125 mg/i, itig/l, In In 1975 1975 drainage drainage from from the the accounted for nearly of the the total accounted for totalamount amount of of iron iron entering entering the the nearly 90% 90% of manganese manganese = = 121 121 mg/l mg/l and and sulfate sulfate = = 5130 5130 mg/i. mg/l. L [ Dober Dober Mine Mine fromall all mine drainagesininthe the District. District. For Iron River River from mine drainages For the the study study period, period, Iron 1975 1975 through through 1977, 1977,the theDDber Dober Mine Mine drained drained an an average average of of654 654pounds pounds of of iron iron of the per day day into into the the Iron IronRiver, River, of of71% 71% of the total totalanount amount per the river entering entering the river from all sources. from all sources. Dober Mine Model Mine complex. complex. Model for for acid acid drainage drainage from from the the Dober Simply stated, Simply stated, the oneof ofrecharging recharging the model model for for acid -aciddrainage drainage from from the the Dober Dober Mine Mine pit pit isisone surface complex surfacewaters waters entering enteringthe thenine mine complexabove abovethe theHiawatha Hiawatha workings workings on on the the west west side side of of the theIron IronRiver River to toforce forceacid acidwaters watersthrough throughthe theinterconnected interconnected via aa 10th 10th level level drift drift mine mine workings workings into intothe theDDber Dober "leg" "leg" of of the the mine mine via Hiawatha Sufficient head head exists existsininthe the Hiawathaworkings workings to to connecting connecting the theworkings. workings. Sufficient cause cause aa flow flow of ofacid acidwater waterfrom fromthe theDober Dober Mine Mine into into the the Iron IronRiver. River. Flow Flow occurs occurs because because of of recharge rechargeand and because because the theDober Dober Mine Mine pit pit lies liesatata alower lower relationships are elevation elevation in in the the Iron Iron River River Valley. Valley. These These relationships areshown shown schematically schematically in in Figure Figure 29. 29. Measurements of the the acid Measurements of acid flow flow from from the theDober Dober Mine Mine pit pit during during the theperiod period a low of about 1975 to to 1978 1978 ranged ranged from from a low of about 25 25 gpn qpn in in the the drought drought winter winter of of 1975 The response response of of 1976—77 highs of of about gpn during during spring spring runoff. runoff. The 1976-77 totohighs about 150 150 gpn flow to precipitation precipitation is flow to iswell well established. established. Prospects Prospects for for long longterm term acid aciddrainage drainagefrom fromthe theDober Dober complex. Dober—Hiawatha—Isabella Mine closedinin1967 1967the the workings Dober-Hiawatha-Isabella Mine closed workings were were When the the When �62 TABLE TV TABLE I V AVERAGE ANALYSES AVERAGE OF OF YEARLY YE YSES OF OF DOBER DOBER MINE MINE ACID ACID DRAINAGE DRAINAGE 197 5—1978 1975-1978 .? YEAR YEAR 1975 1975 Fe Fe Mnn M Al A1 mg/i mg/1 mg/i mg/1 mg/i mg/l mg/i mq/ 1 1125 1125 121 121 114 114 5130 51 30 504 pH PH Cond. Cond. pmhos/cm ~mhos/cm., .,.. ,<. 4.1 4.1 .Â¥= Acidity Acidity Spec. spec. ppm CaCO3/l ppm CaC03/1 2900 2900 4990 4990 .a. .. .,, 3500 3500 1290 1290 90 90 279 279 5450 5450 3.7 3.7 4910 4910 1977 1977* 707 707 59 59 157 157 3320 3320 2.4 2.4 2180 2180 1370 1370 1978 1978 1280 1280 80 80 123 123 5930 5930 --- -- 3680 3680 1976 1976 I J I J I J I j Li 1 * NOTE: Low 1977 values are due to dilution of surface waters in the Dober by runoff and flooding by the Iron River. pit J j j j 1 J 1 J J -j �63 LOOKING NORTH INES : LOOKING NORTH DOBER-HIAWATHA MINES , +- GROUNDWATER QROUNDWATER FLOW ^-FLOW OVERBURDEN IRON RIVER 19th St. DOBER #1 ERT S H A Ft I I BEDROCK ,._HIAWATHA #2 SHAFT I i I STOPE ___1ath_LLVLD3I3___ I Figure F i g u r e 29. 29. DIRECTION DIRECTION OF O F WATER WATER FLOW FLOW —, I Schematic Flow of of Water Water in i n the t h e Dober Dober Mine Mine Complex Complex Schematic Diagram Diagram Showing Flow �64 dry. Following Following closure closure the the mine mine complex complex was was allowed allowed to to flood. flood. Prior to to flooding, oxygen and water reacted with with pyrito-bearing pyrite—bearing slates wherever they were and footw'all were exposed in in the the hanging hanging and footwall and and in in caved caved stopes, stopes, forming forming soluble compounds. soluble ferrous ferroussulfate sulfate compounds. These dissolve readily These compounds compounds dissolve readily to to form form sulfuric result, nearly As aa result, nearlythe theentire entirevolume volume of of sulfuric acid acid and and soluble soluble iron. iron. As . : the wasflooded floodedwith withacid acidwater, water, except except perhaps perhaps for for the the mine mine complex complex was the very very uppermost portion of of the where most mostof of the the surface uppermost portion theHiawatha Hiawatha No. Nu. 1 1 workings workings where surface water apparently entered. the mine mine flooded, flooded, pyrite pyrite oxidation :ater,apparently entered. With With the oxidation no no longer longer occurred. .occurred. -'..\-.. ".. - ^f-Y y.r: , ,, th&Â¥Sj/tKawath Mines through the Water movesfrom fromtilthe levels dt of the Hiawatha Mines through the water moves e' upper 10~easts 10th connecting Hiawatha Dober 10th level level drift drift connectingthe the Hiawatha#2 #2shaft shaftwith withthe the Doberworkings. workings. Volumes themine minevoids voidsabove abovethe the10th 10thlevel level including including the the Daber, Isabella Volumes ofofthe Dober, Isabella I, ' and Mineworkings workings were weredetermined determined by by planimetering planimetering mine The and Hiawatha Hiawatha Mine mine maps. maps. The total 44,235,000ft3 ft3 without without subtraction subtraction for totalstope stopevolume volume calculated calculated was was 44,235,000 for stops fill or on an Based on an estimated estimated stope fill or addition addition for for shafts, shafts, drifts driftsand and raises. raises. Based average average flow flow rate rate of of 50 calculated that 50 gpn, g p , Johnson Johnson calculated that by by early early1979 1979 about about 25 25 million since it it flooded million ft3 ft3of ofacid acidwater waterhad haddrained drainedfrom from the themine mine complex complex since flooded in Subtraction of this this 25 25 million million ft3 ft3 of of acid acid water water from from the the in October October 1972. Subtraction total of 44 44 million million ft3 ft3 of of voids totalvolume volume of voids calcualted calcualted for for the theupper upper 10 10 levels levels left left19 19 million million ft3 ft3 of of simplified simplified acid water water remaining rnaining in in the the upper upper 10 10 levels. levels. This This calculation calculation indicated that 57 percent of the the acid water in in the the upper had been been replaced replaced with with surface surface water. water. upper 10 10 levels levels had If If drainage drainage continued continued at been required required to to (50gpm), gpm), about about 55 1/2 1/2years yearswould would have have been at this thisaverage average rate rate(50 flush this was flush the the acid acid from from the the upper upper ten ten levels levelsof ofthe themine. mine. However, However, this was not not possible would possible as asmixing mixing of of fresh ffeshwaters waterswith withthe thedenser denseracid acidwaters waters would occur occur and greatly lengthen toexpel expelthe theremaining remaining acid acidfrom from the the and greatly lengthen the the time time required required to mine complex. complex. �65 Field Field evidence evidence also also suggested suggested that that acid acid waters waters were were gradually gradually being being expelled expelled from from the the mine mine complex. complex. L It It was was logical logical to to assume assume that that as as the the recharging recharging groundwater groundwater mixed mixed with with acid acid water water that that the the head head differential differential between mines of between the the free free water surface surface in in the the various various mines of the the complex complex would would L equilibrate. equilibrate. Except Except for for slight slight differences differences due due to to recharge recharge and and frictional frictional losses, losses, the the fresh fresh water water surface surface would eventually eventually lie lie at at the the same same elevation elevation L L throughout throughout the the mine mine complex. complex. Comparison Comparison of of water water level level measurements measurements taken taken in in the the mine complex complex since since 1976 1976 indicates indicates that that this this equalization equalization process process is is well well underway. underway. L These These observations observations and and calculations calculations indicate, indicate, as as acid acid water water in in the the upper upper 10 10 levels levels is is replaced replaced with with fresh fresh water, that that acid acid water water drainage drainage from from the Dober-Hiawatha-Isabella Mine Mine complex complex will eventually eventually cease cease to to be be aa the tkter—Hiawatha—Isabella problem. problem. However, very large large amount amount of of acid water water remains remains in in the the mine mine However, aa very blockage blockage occurs occurs on on the the 10th 10th level level workings or interconnection interconnection between between the the Hiawatha Hiawatha and and Dober Dober workings or on on complex complex below below the the 10th 10th level. level. If If interconnections and the the Hiawatha *2 shaft shaft interconnectionsbetween between the theHiawatha Hiawatha *1 #l workings workings and Hiawatha #2 very These blockages blockages very serious seriousacid aciddrainage drainagecould could continue continuefor formany many years. years. These could in the could result result from from rock rock caving caving in the drifts driftsor orpossibly possiblyfrom fromthe theformation formation phenomena of damsin in drifts drifts connecting this latter latter phenomena of "yellow "yellow boy" boy" dams connecting the themines. mines. This was observed in in the Mineduring duringits its operation was observed the Sherwood Sherwood Mine operation 1, 1. Acid waters waters flowing in aa drift drift gradually flowing in gradually built built up up aaseries seriesofof"yellow "yellowboy" boy" deltas. deltas in in aa was terrace orstep—like step-like fashion fashion until until the thedrift drift wascompletely completelyblocked. blocked. terraceor Although this damming effect occurred occurred below below an an air-water air—waterinterface interface ititmay Although this damming effect may be be possible damming interface between oxygen— possible that thatthe the damming could could occur occur at atthe the interface between oxygenbearing acid waters waters on on the the 10th bearing "surface" "surface" waters waters and and lower lower acid 10th level level interconnections at the ofofthethe mine complex interconnections at thetime time that thatthe theupper upperlevels levels mine complex 11 Personal with Robert Robert Edwards, Edwards,former formerSuperintendent Superintendent of of the Personal communication communication with the Sherwood Mine,Iron Iron River, River, Michigan. Sherwaod Mine, Michigan. �66 are are flushed flushed of of acid acid water. water. This This #uld wouldcause causethe thewater water to to flow flow through through the the next next lower lower interconnection, interconnection, expelling expelling more more acid acid water. water. , lj The The process process could could conceivably conceivably continue continue until until the the entire entire mine mine was was purged purged of of acid. acid. .- Based Based on OB~ X'S mine calculations and and the the present present flow rate, severe mine volume volume calculations flow rate, severeacid acid drainage drainage ^*-- could could last last for for55 55 years; years; e.g., e.g., Total Total volume volume of of mine mine complex complex ,,* million ft3 25 25 million million ft3 ft3 . . == 223 223 million ft3 Volume years == Volume of of acid acid drained drained in in 77 years Volume of acid acid renaming 198 Volume of remaining 198 million million ft-5 ft-à the ....atatmillion the rate rate of of 25 25 million million ft3 ft3 drained drained in in 77 years, years, 198 ft3 198 million ft3 would would require require 55 55 years years to to drain. drain. : .., ! sr'? s-:~' *< -'fa fi*<-.-. :,:+.q:> ' ,'b ~, 3Â¥m1-I Actually, conditions were were met, met, acid aciddrainage"wou1d drainage u1d persist Actually, if if the the above conditions persist for for aa period period greater greater than than 55 55 years, years, as as the the acid acid waters waters cauld would continually continually mix mix fresher waters of acid flow. with resulting in some dilution and a greatly extended period U J J J J J 1 -I -I J J �67 REFERENCES REFERENCES Anonymous, Anonymous, (1938), Lake Lake Superior Superiar Iron Ores, Ores, Lake Superior Iron Ore Ore Association, Hanna Hanna Building, Building, Cleveland, Cleveland, Ohio, Ohio, 364 364 p. p. Association, Anonymous, Anonymous, (1952), (1952), 2nd 2nd edition, edition, Lake Superior Superior Iron Iron Ores, Lake Late Superior Superior Iron Iron Ore Ore Association, Association, Cleveland, Cleveland, Ohio, Ohio, 326 326 p . p. Cregger, qger, David David M. M. (1977), (1977). Flow Flow of of Acid Acid Mine Mine Water Water in the Abandoned Abandoned HiawathaHiawatha— Dzber—Isabella Michigan, Unpublished Dober-Isabella Mine Complex, Iron River District, Michigan, thesis, Dept. Geological Engineering, Dept. of Geology Geology and and Geological Engineering, Michigan Michigan Technological :hnological University, University, Houghton, Houghton, Michigan, Michigan, 127 127 p . p. (1974), Iron Iron River-Brule Hunt, Cliff (1974), River—Brule River River Report, Report, Unpublished Unpublished report by by USU"s Forest Service, Service, Nicolet Nicolet National National Forest, Forest, Rhinelander, Rhinelander, W Vhs., USCA Forest is., p . 23. 23. p. James, H.L., Dutton, C.E., Pettijohn, F F.J., Wier, K ILL., (1968) H.L., C.E., .J., Wier, .L., (1968) Geology and Ore Crystal Falls Districts, Iron County Ore Deposits Deposits of the the Iron Iron River, Crystal Michigan, United United States States Geological Geological Survey Survey professional professional paper paper 570, 570, published p. published in in cooperation cooperation with the Michigan Geological Survey, 134 p. Johnson, Johnson, Allan Allan M. M. and and Frantti, Frantti, Gordon Gordon (1976), (1976), "Study of Mine Subsidence Subsidence and Acid Valley, Iron Acid Water Water Drainage Drainage in in the the Iron Iron River Valley, Iron County, Michigan — Status Status of of Initial Initial Work", Work", Institute Institute of Mineral Research, Michigan Technological nological University, University, Houghton, Houghton, Mich., Mich., 113 113 p. p. - Johnson, G.E., (1978), Subsidence and donnson, A.M., A.M., and and Frantti, Frantti, G .E., (1978), Study of Mine Subsidence Acid Acid Water Water Drainage Drainage in in the the Iron Iron River River Valley, Valley, Iron Iron River, River, Michigan, Michigan, Institute Institute of of Mineral Mineral Research, Michigan Michigan Technological Technological University, University, 220 220 p. p. Johnson, Hodek, and Johnson. A.M., A.M.. Hodek. R.J., R.J.. and Frantti, Frantti. G.E. G.E. (1982), (19821. Piping Pioim Induced Induced Subsidence Workshop subsidenceOver Over An Underground underground Mine Mine in Proceedings ~roceedi&ji ~orkshopon on Surface Surface Subsidence SubsidenceDue Due to to Underground Underaround Mining, Minim. Nov Nov 30 30 — Dec Dec 1981, 1981. W.V. W - V - Univ., Univ-. ~ ~ - Morgantown, W.V., Peng, S.S. and Harthill, M. eds., p. 268—273. Johnson, (19791, Study Study of Pumping As A Means To Control Acid M., (1979), uunnson, Allan Allan M., Water Water Drainage Drainage From From The The Dober—Hiawatha—Isabella Dober-Hiawatha-Isabella Mine Complex, West Iron County, of Mineral Research, Michigan Institute of Michigan Technological Technological County, Michigan. Michigan. Institute University, University, Houghton, Houghton, Mich., Mich., 74 74 p. p. Johnson, and A ACase thethe Sherwood Johnson, A.M., A.M., and Frantti, Frantti,G.E., G.E., (1982), (1982), CaseStudy Studyofof sherwoodMine Mine Closing, Contract Executive Sunnary, Summary, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 57 57 p. p. Closing, Volume Volume I, I, — Executive - Johnson, and A ACase thethe Sherwood Johnson, A.M., A.M., and Frantti, Frantti,G.E., G.E., (1983), (1983), CaseStudy Studyofof SherwoodMine Mine Closing, Contract Closing, Volume Volume II, 11, Field Field Investigation, Investigation, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 279 279 p. p. Johnson, and R.J. (1983), (19831, A Case Study Study of the the Sherwood Sherwood Mine Johnson, A.M., A.M., and Hodek, Hodek, R.J. Closing, Closing, Volume Volume III, 111, Piping Piping Experiments Experiments as as Evidence Evidence for for Piping Induced Induced Subsidence Contract Subsidence at at the the Sherwood Sherwood Mine, Mine, U.S.B.M. U.S.B.M. Contract J0285035, J0285035, 58 58 p. p. �68 Johnson, Hydrologic Considerations Considerations in Johnson, Allan Allan M., M., (1983), (1983), Hydrologic in Mine Mine Closings Closings 94E— EMEAIME AIME Preprint Preprint No. No. 83—365, 83-365, Salt Salt Lake City, Utah, Utah, S5 p. p. r Kleinman, Crerar, A., and Kleinman, Robert Robert L.P., L.P., Crerar, David A., and Mohring, Eric Eric H., H., (1978), (1978), Abatement Inhibition of Thiobacillus Thiobacillus Abatement of of Acid Acid Mine Drainage by Inhibition Ferrooxidans, Geologists, Hershey, Assoc. Eng. E q . Geologists, Hershey, PA. PA. Ferrooxidans, Abstract, Abstract, Assoc. MacDonald, Johnson, Allan Allan M., MacDonald, Lawrence Lawrence J.3., , and and Johnson, M., (1983), (1983),Assessment Assessment of of Inactive InactiveIron IronMines Mines in inEast EastIron IronCounty, County,Michigan, Michigan, Mich. Mich. Geol. Geol. Survey Survey:-,- Div. Lansing, Mich., Mich., EN% Lansing, Div. EtJR, 50 80 p. p. Reed, (1975), Reed, R.C., R.C., (1975),Michigan Michigan Iron IronOre OreShipments Shipmentsthrough through1974, 1974,One One Thousand Million Survey Division, Circular Million Tons, Tons, Michigan Geological Survey Circular 12, 12, 12 12 p. p. Van (1973), Acid Acid Mine Mine Water Water Problem Problem at at Stambaugh, Stambaugh, Michigan, Michigan, Van Alstine, Alstine, Jack Jack (1973), Mich. Mich. Geol. Geol. Survey, Survey, File File Report, 15 15 pages pages plus plus Appendix. -j  j I I I J I 1J U J Li J J J J j LI � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1994 Description An account of the resource Institute on Lake Superior Geology. Michigan Technological University, Houghton, Michigan. May 11-14, 1994. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1994 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English