INFORM ATION TO USERS This material was produced from a m icrofilm copy o f th e original d o cu m en t. While the m ost advanced technological means to photograph and reproduce this d ocum ent have been used, th e quality is heavily d ep en d en t upon th e quality of the original subm itted. The following explanation o f techniques is provided to help you understand markings or patterns which m ay appear on th is reproduction. 1. The sign or " ta rg e t" for pages apparently lacking from th e docum ent photographed is "Missing Page(s)". If it was possible t o obtain the missing page(s) or section, th e y are spliced in to th e film along w ith adjacent pages. This may have necessitated cutting th ru an image and duplicating adjacent pages to insure you com plete co n tin u ity . 2. When an image on th e film is obliterated w ith a large rou n d black m ark, it is an indication th a t th e photographer suspected th a t the copy m ay have moved during exposure and thus cause a blurred image. Y ou will find a good image o f th e page in th e adjacent fram e. 3. When a m ap, draw ing o r ch art, etc., was part of the material being photographed th e photographer follow ed a definite m ethod in "sectioning" th e m aterial. It is custom ary to begin photoing a t th e upper left hand corner of a large sheet and to co n tin u e photoing from left to right in equal sections w ith a small overlap. If necessary, sectioning is continued again — beginning below th e first row and continuing on until com plete. 4. The m ajority of users indicate th a t th e textual co n ten t is o f greatest value, however, a so m ew h at higher quality rep ro d u ctio n could be made from "p h o to g rap h s" if essential to the understanding o f th e dissertation. Silver prints of " p h o to g rap h s" m ay be ordered a t additional charge by writing th e O rder D epartm en t, giving th e catalog num ber, title, author and specific pages you wish reproduced. 5. PLEASE NOTE: S om e pages m ay have ind istin ct print. Filmed as received. Xerox University Microfilms 300 North Zeeb Road A n n A rbor, M ichigan 4 8 106 75-27,355 WILSON, Chester Humphrey, 1939* A DETAILED PETROGRAPHIC AND CHEMICAL STUDY OF DIFFERENTIATION IN KEWEENAWAN LAVA FLOWS OF MICHIGAN. Michigan State University, Ph.D., 1975 Geology Xerox University Microfilms, Ann Arbor, Michigan 48106 A DETAILED PETROGRAPHIC AND CHEMICAL STUDY OF DIFFERENTIATION IN KEWEENAWAN LAVA FLOWS OF MICHIGAN by C h e s t e r H. W i ls o n A THESIS S u b m it te d t o M ic h i g a n S t a t e U n i v e r s i t y i n p a r t i a l f u l f i l l m e n t o f th e re q u ire m e n ts f o r th e degree of DOCTOR OF PHILOSOPHY D e p a r tm e n t o f G eolog y 1975 ABSTRACT A DETAILED PETROGRAPHIC AND CHEMICAL STUDY OF DIFFERENTIATION IN KEWEENAWAN LAVA FLOWS OF MICHIGAN by C h e s t e r H. W ils o n A p e t r o g r a p h i c and c h e m ic a l s t u d y was c o n d u c t e d on t h e S c a l e s C r e e k Flow o f t h e Keweenawan P o r t a g e Lake Lava S e r i e s i n t h e Keweenaw P e n i n s u l a o f n o r t h e r n M ic h ig a n . The p u r p o s e o f t h i s s t u d y was t o d e t e r m i n e l a t e r a l and v e r t i c a l v a r i a t i o n w i t h i n t h e S c a l e s C r e e k Flow and t o com pare t h i s v a r i a t i o n w i t h t h a t fo u n d f o r o t h e r f lo w s o f t n i s s e r i e s i n p r e v i o u s s t u d i e s . A t o t a l o f 188 t h i n s e c t i o n s w ere s t u d i e d and 101 r o c k s a m p le s w e r e c h e m i c a l l y a n a l y z e d f o r S i 0 2 , CaO, MgO, FeO, T i 0 2 , A120 ^ , Na20 , an d K20 . T hese s a m p le s w e re o b t a i n e d fro m s i x diamond d r i l l h o l e s t h a t p e n e t r a t e d t h e S c a l e s C r e e k Flow a t v a r i o u s l o c a t i o n s a l o n g i t s strik e . P y ro x e n e s w e re s e p a r a t e d from one s e t o f t h e s e s a m p le s and g iv e n p a r t i a l ch em ica l a n a ly s e s . F o r p u r p o s e s o f c o m p a r is o n , t h i r ­ t e e n r o c k a n a l y s e s w e re r e p o r t e d f o r one diam ond d r i l l h o l e t h a t p e n e t r a t e d t h e K e a r s a r g e Flow. P e g m a t i t i c o r d o l e r i t i c zo n e s w e re fo u n d t o b e p r e s e n t i n b o t h t h e f lo w to p and b o tto m o f t h e S c a l e s C re e k F low . a s c h e m i c a l c o n c e n t r a t i o n s o f Na20 , K20 , and S i 0 2 . a lw a y s r e c o g n i z e d w i t h e a s e p e t r o g r a p h i c a l l y . These zones a p p e a r They a r e n o t I t is h y p o th e siz e d th a t th e s e zones a re th e r e s u l t o f v e r t i c a l v o l a t i l e t r a n s f e r w i t h i n th e c o o l i n g f lo w . C h em ical t r e n d s fo u n d w i t h i n t h e S c a l e s C r e e k Flow w e re fo u n d to have l a t e r a l c o n s is te n c y . A u g i t e s fro m t h e S c a l e s C r e e k Flow e x h i b i t a d e f i n i t e c h i l l t r e n d and p l u t o n i c t r e n d i n t h e i r c o m p o s i t i o n s . ACKNOWLEDGEMENTS The w r i t e r i s t h a n k f u l f o r t h e o p p o r t u n i t i e s and c o n s i d e r a t i o n s e x t e n d e d t o him by t h e f a c u l t y o f t h e G eo lo gy D e p a rtm e n t o f M ic h ig a n S t a t e U n i v e r s i t y , and i n p a r t i c u l a r , t h e g u i d a n c e c o m m itte e o f Dr. J . W. Trow, D r. H. B. S t o n e h o u s e , D r. C. E. P r o u t y , D r. B. T. S a n d e f u r , and t h e l a t e D r. J . Z in n . G r a t i t u d e i s e x p r e s s e d t o Mr. R a n d a l l Weege, D i r e c t o r o f E x p l o r a t i o n o f t h e U n i v e r s a l O i l P r o d u c t s Company ( f o r m e r l y C a lu m e t and H e c la M in in g Company) f o r p r o v i d i n g a c c e s s t o t h e d i a ­ mond d r i l l c o r e s u s e d i n t h i s s t u d y and f o r s e r v i n g a s a member o f t h e g u i d a n c e c o m m itte e . A n o t e o f t h a n k s i s e x t e n d e d t o Mr. M ilo N i e l s e n , r e s e a r c h c h e m i s t o f t h e B u ic k M o to r D i v i s i o n , f o r h i s many h e l p f u l s u g g e s ­ tio n s about s i l i c a t e a n a ly se s. TABLE OF CONTENTS Page LIST OF TABLES iv LIST OF FIGURES v LIST OF PHOTOS v ii INTRODUCTION 1 G eo graph y P re v io u s S tu d ie s 1 1 GENERAL GEOLOGY 7 S tra tig ra p h y S tru c tu ra l S e ttin g Economic G eo lo g y 7 10 13 CHEMICAL ANALYSIS 14 S a m p lin g S c a l e s C r e e k Flow P y ro x e n e A n a l y s e s K e a r s a r g e Flow 14 16 35 42 PETROLOGY 47 P e tro g ra p h ic D e s c rip tio n P etro g en e sis 47 55 CONCLUSIONS 61 APPENDICES A p p e n d ix A - A n a l y t i c a l T e c h n iq u e s A p p e n d ix B - D e s c r i p t i o n o f S t . L o u i s 5 D r i l l C ore BIBLIOGRAPHY 62 64 73 iii LIST OF TABLES S a m p lin g D a ta on S c a l e s C r e e k Flow C h e m ic a l C o m p o s it io n o f S c a l e s C re e k F low , Diamond D r i l l H ole D64 C h e m ic a l C o m p o s it io n o f S c a l e s C r e e k F low , Diamond D r i l l H ole SL5 C h e m ic a l C o m p o s it io n o f S c a l e s C r e e k F low , Diamond D r i l l H ole NK3 C h e m ic a l A n a ly s e s o f t h e P y ro x e n e s fro m t h e S c a l e s C r e e k F lo w , Diamond D r i l l H ole SL5 C h e m ic a l A n a l y s e s o f t h e P y r o x e n e s fro m t h e G r e e n s t o n e F lo w , Diamond D r i l l H ole 03 C h e m ic a l C o m p o s it io n o f t h e K e a r s a r g e Lava F lo w , Diamond D r i l l H ole S t a r 10 C o m p a ris o n o f C h e m ic a l A n a l y s e s o f Two D r i l l H o le s i n t h e K e a r s a r g e Lava Flow LIST OF FIGURES F ig u re Page 1. L o c a t i o n o f t h e Keweenaw P e n i n s u l a 2 2. G e n e r a l i z e d G e o l o g i c a l Map o f a P a r t o f t h e Keweenaw P e n i n s u l a 8 3. N o r t h w e s t - S o u t h e a s t C r o s s S e c t i o n T hrough Keweenaw P e n i n s u l a 12 G e n e r a l i z e d G e o l o g i c a l Map o f a P a r t o f t h e Keweenaw P e n i n s u l a 15 C h e m ic a l C o m p o s it io n o f S c a l e s C r e e k F lo w , Diamond D r i l l H ole D64 24 C h e m ic a l C o m p o s it io n o f S c a l e s C r e e k F lo w , Diamond D r i l l H o le SL5 25 C h e m ic a l C o m p o s it io n o f S c a l e s C r e e k F lo w , Diamond D r i l l H o le NK3 26 8. S i l i c o n O x id e V a r i a t i o n i n S c a l e s C re e k Flow 27 9. C a lc iu m O xide V a r i a t i o n i n S c a l e s C r e e k Flow 28 10. M agnesium O xide V a r i a t i o n i n S c a l p s C re e k Flow 29 11. I r o n O xid e V a r i a t i o n i n S c a l e s C re e k Flow 30 12. T i t a n i u m O x id e V a r i a t i o n i n S c a l e s C re e k Flow 31 13. Aluminum O x ide V a r i a t i o n i n S c a l e s C re e k Flow 32 14. Sodium O xide V a r i a t i o n i n S c a l e s C re e k Flow 33 15. P o t a s s i u m O xide V a r i a t i o n i n S c a l e s C r e e k Flow 34 16. FeO/MgO R a t i o o f t h e P y r o x e n e s fro m S c a l e s C r e e k Flow 38 FeO/MgO R a t i o o f t h e P y r o x e n e s from G r e e n s t o n e Flow 41 4. 5. 6. 7. 17. v Figure 18. 19. 2 0. 21. Page C h e m ic a l C o m p o s it io n o f K e a r s a r g e F low , Diamond D r i l l H o le S t a r 10 44 P h a s e D ia g ra m A p p l i c a b l e t o B a s a l t i c Magma C ry sta lliz a tio n 56 P y r o x e n e T re n d s o f t h e S c a l e s C re e k F low i n Diamond D r i l l H o le S t . L o u is 5 57 P y ro x e n e T re n d s o f t h e G r e e n s t o n e Flow i n Diamond D r i l l H o le O s c e o l a 3 58 LIST OF PHOTOS P h o to Page 1. S e m i - Q u a n t i t a t i v e A n a l y s i s o f an A u g i t e G r a i n 36 2. E l e c t r o n M ic r o s c o p e P i c t u r e o f a n A u g i t e G r a i n Show ing C h a rg e E f f e c t on S u r f a c e , X1000 36 F low Top Show ing P l a g i o c l a s e i n M a t r i x o f H e m a t i t e . Amygdule i s F i l l e d w i t h Q u a r t z and E p i d o t e , C r o s s e d N i c o l s , X53, Sam ple LS30-1 48 P o r t i o n o f an Amygdule S how ing H e m a t ite and E p i d o t e Rims w i t h C e n t r a l Q u a r t z F i l l i n g , C r o s s e d N i c o l s , X53, Sam ple SL5-1 48 P la g i o c la s e P o i k i l i t i c a l l y In c lu d e d in P yroxene, C r o s s e d N i c o l s , X133, Sam ple SL5-36 49 L a r g e P l a g i o c l a s e and P y r o x e n e Above t h e B a s a l C h i l l Z o n e , C r o s s e d N i c o l s , X80, Sample SL5-46 50 M i c r o l i t e Swarm Around A l t e r e d P y ro x e n e and P l a g i o c l a s e , C r o s s e d N i c o l s , X133, Sample G7S-16 50 M i c r o l i t e s Show ing S w i r l e d A r r a n g e m e n t, C r o s s e d N i c o l s , X80, Sam ple NK3-18 51 D o l e r i t i c Zone Showing L a r g e A l t e r e d P l a g i o c l a s e L a t h s and Q u a r t z , C r o s s e d N i c o l s , X80, S am ple NK3-9 52 L a rg e A l t e r e d P l a g i o c l a s e L a t h s and Q u a r t z i n t h e B o tto m D o l e r i t i c Z o ne, C r o s s e d N i c o l s , X80, S am ple NK3-54 53 P y ro x e n e A l t e r e d t o S e c o n d a r y H o r n b le n d e , C r o s s e d N i c o l s , X200, Sam ple NK3-24 53 P y ro x e n e A l t e r e d M a in ly t o C h l o r i t e and Some M a g n e tite w ith R e l i c t P la g i o c la s e , P la in P o l a r i z e d L i g h t , X200, Sam ple SL5-14 54 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. vii Photo 13. 14. 15. 16. Page P y ro x e n e w i t h P o i k i l i t i c P l a g i o c l a s e and A l t e r e d O l i v i n e , C r o s s e d N i c o l s , X80, Sam ple SL5-5 66 P l a g i o c l a s e M i c r o l i t e s A l i g n e d B etw een L a r g e E a r l i e r Formed G r a i n s o f P l a g i o c l a s e and O l i v i n e , C r o s s e d N i c o l s , X200, Sam ple SL5-36 69 F r a c t u r e d P y ro x e n e G r a i n S u r r o u n d e d by S em iA l i g n e d M i c r o l i t e s , C h l o r i t e , and M a g n e t i t e , P l a i n P o l a r i z e d L i g h t , X80, Sam ple SL5-43 70 P o i k i l i t i c P y r o x e n e S how ing A l t e r a t i o n t o M a g n e t i t e , C r o s s e d N i c o l s , X200, Sam ple SL5-45 71 viii INTRODUCTION T h o u san d s o f c u b i c m i l e s o f n o n - o r o g e n i c t h o l e i i t i c flo o d b a s a lt s fo rm t h e P r e c a m b r ia n P o r t a g e Lake L ava S e r i e s o f t h e w e s t e r n U pper P e n i n s u l a o f M ic h i g a n . T h is s t u d y c o n c e r n s t h e p e t r o l o g y and chem­ i s t r y o f t h e S c a l e s C r e e k F lo w , a member o f t h i s s e r i e s , and t h e c o r r e l a t i o n o f th e f in d in g s w ith r e s u l t s o f s i m i l a r i n v e s t ig a t io n s o f t h e G r e e n s to n e and K e a r s a r g e f lo w s i n t h e same s e r i e s . G eo g rap h y The Keweenaw P e n i n s u l a e x t e n d s i n t o Lake S u p e r i o r i n t h e w e s t e r n p a r t o f t h e U pper P e n i n s u l a o f M ic h ig a n ( F i g u r e 1 ) . C ry sta llin e P r e c a m b r i a n r o c k s fo rm a n o l d , p r o m i n e n t t o p o g r a p h i c r i d g e r u n n i n g t h r o u g h t h e p e n i n s u l a a t an e l e v a t i o n o f 500 t o 600 f e e t ab o v e Lake S u p e r i o r . On e i t h e r s i d e o f t h i s r i d g e a r e lo w la n d s e r o d e d fro m s o f t e r P r e c a m b r ia n s e d i m e n t a r y r o c k s . v a l l e y s s u c h a s P o r t a g e L ak e . T h is r i d g e i s c u t by s e v e r a l P le is to c e n e g l a c i a t i o n has s l i g h t l y m o d i f i e d t h e l a n d s c a p e , c o v e r i n g much o f t h e r e g i o n w i t h t h i n m o r a i n i c d e p o sits. G l a c i a l l y p o l i s h e d and s t r i a t e d b e d r o c k i s e x p o s e d on s t e e p r i d g e s and knobs w h ere d r i f t d i d n o t a c c u m u l a t e . P re v io u s S tu d ie s The l a v a f lo w s o f t h e Keweenaw P e n i n s u l a h a v e p r o v e d i n t e r e s t i n g t o many r e s e a r c h e r s and much h a s b e e n p u b l i s h e d on v a r i o u s a s p e c t s o f th e se ro c k s. Those p u b l i c a t i o n s h a v i n g t h e m o s t r e l e v a n c e t o t h i s 1 2 40 MILES FIGURE I. LOCATION OF K E W E E N A W P E N IN S U L A 3 stu d y a re in c lu d e d in t h i s d is c u s s io n . Lane (1909) c o m p ile d a n e x t e n s i v e two volum e w o rk , The Keweenaw S e r i e s o f M i c h i g a n , i n w h ic h he r e c o g n i z e d f o u r t e x t u r a l c l a s s i f i c a ­ t i o n s f o r t h e flo w r o c k s . T hese t e x t u r a l g r o u p s a r e : O p h i t e - a m o t t l e d r o c k w i t h p y r o x e n e s u r r o u n d i n g and e n c l o s i n g euhedral p la g io c la se la th s . P o r p h y r i t e - A r o c k w i t h e a r l y fo rm e d , w e l l d e f i n e d p h e n o c r y s t s ( u s u a l l y f e l d s p a r s ) s e t i n a f i n e r g ro u n d m a s s . G l o m e r o p o r p h y r i t e - A t e x t u r e c h a r a c t e r i z e d by f e l d s p a r s o f v a ry in g s iz e s c l u s t e r e d to g e th e r . M e la p h y re - A p p l i e s t o r o c k s w i t h no d i s t i n c t i v e Lane a l s o r e c o g n i z e d d o l e r i t e w h ic h r e f e r s te x tu re . to a c o a r s e o r " p e g m a t i t i c " f a c i e s t h a t c a n o c c u r w i t h an y o f t h e ab ove f lo w t y p e s . T h is f a c i e s , w h ich m ig h t be r e f e r r e d to a s an a l b i t e d i a b a s e , is u s u a l l y fo u n d i n t h e u p p e r p o r t i o n s o f t h i c k e r f l o w s . B u t l e r and B urb an k (192 9) sum m arize t h e g e n e r a l g e o lo g y o f t h e r e g i o n w i t h s p e c i a l e m p h a s is on t h e c o p p e r d e p o s i t s . They c o n c l u d e d t h a t t h e f lo w s w e re l a r g e l y b a s a l t i c and w ere c o m p r i s e d o f p l a g i o c l a s e , p y r o x e n e , a l t e r e d o l i v i n e , and m a g n e t i t e . The o v e r a l l c h e m i c a l c o m p o s i t i o n o f t h e b a s a l t s was fo u n d t o be g e n e r a l l y t h e same a s t h a t o f t h e C o lu m b ia and D eccan p l a t e a u s . I t was n o te d t h a t : "The m o st n o t e w o r t h y c h e m i c a l v a r i a t i o n i n t h e f lo w s i s an i n c r e a s e i n t h e r a t i o o f f e r r i c t o f e r r o u s i r o n from b o tto m t o to p ." ( B u t l e r and B u rb a n k , 1929, p . 2 7 ) . B u t l e r and B urb an k d i s c u s s e d t h e flo w to p s s i n c e t h e s e u p p e r p o r t i o n s o f t h e f lo w s a r e i m p o r t a n t w i t h r e l a t i o n t o o r e d e p o s i t s . F o u r t y p e s h av e b e e n d e f i n e d . V e s i c u l a r t o p s a r e c h a r a c t e r i z e d by a b u n d a n t g as h o l e s t h a t a r e f l a t t e n e d p a r a l l e l to th e flo w s . The v e s i c l e s show a t e n d e n c y to 4 o c c u r i n i r r e g u l a r l y s p a c e d l a y e r s p a r a l l e l t o t h e f lo w s u r f a c e . T h e s e l a y e r s a r e s e p a r a t e d by n o n - v e s i c u l a r r o c k . The h o l e s a r e s m a l l and num erous n e a r t h e to p o f t h e f lo w and t e n d t o i n c r e a s e i n s i z e and d e c r e a s e i n number to w a rd t h e b o tto m o f t h e a m y g d a l o i d a l su rfa c e la y e r. C o a l e s c i n g v e s i c u l a r to p s a r e c h a r a c t e r i z e d by g a s h o l e s t h a t h a v e a n a s to m o s e d . F r a g m e n t a l f lo w to p s a r e form ed o f a n g u l a r t o r o u n d e d v e s i c u l a r f r a g m e n t s v a r y i n g i n s i z e fro m s m a l l g r a i n s t o m a s s iv e b l o c k s s e v e r a l f e e t a c r o s s , a l t h o u g h m o st a r e o n l y a few i n c h e s . T h is to p v a r i e t y w i l l v a r y i n t h i c k n e s s , e v i d e n t l y r e s u l t i n g fro m f r a g m e n t s p i l i n g up when t h e p i e c e s w ere b e i n g form ed by b r e a k a g e a s s o c i a t e d w i t h u n d e r ­ l y i n g magma f lo w a g e . S c o r i a c e o u s to p s a r e com posed o f a m y g d a lo id a l f r a g m e n t s s e t i n a m a t r i x o f f i n e b a s i c s a n d t h a t B u t l e r and B u rb an k c o n s i d e r e d as v o lc a n ic ash. A l t e r a t i o n i s a l s o d i s c u s s e d e x t e n s i v e l y by B u t l e r and B urbank (1929). The a u t h o r s fo u n d t h e flo w m i n e r a l s , e s p e c i a l l y p l a g i o c l a s e and p y r o x e n e , t o be s u r p r i s i n g l y f r e s h , t h e m a in a l t e r a t i o n , in th e ir o p i n i o n , b e i n g h e m a t i t e a f t e r m a g n e t i t e and s e r p e n t i n e a f t e r o l i v i n e . They f e l t t h a t t h i s a l t e r a t i o n was a l m o s t m agm atic i n o c c u r r e n c e . Flow t o p s w e re r e p o r t e d t o c o n t a i n e x t e n s i v e h e m a t i t e and t h e y c o n c l u d e d a f t e r e x te n s iv e stu d y th a t: " - - b o t h th e o x i d a t i o n and t h e c o n c e n t r a t i o n o f t h e i r o n w ere a c c o m p l i s h e d by g a s e s e s c a p i n g fro m t h e s o l i d i f y i n g and c r y s t a l l i z i n g la v a s." ( B u t l e r and B u rb a n k , 19 29, p . 3 4 ) . B r o d e r i c k (1 9 3 5 ) made a p e t r o g r a p h i c s t u d y a i d e d by c h e m i c a l a n a l y s e s , o f two p e r s i s t e n t Keweenawan f l o w s : t h e G r e e n s t o n e and t h e 5 K earsarge. w h ic h i s T h is s t u d y n o t e d t h e d o l e r i t i c la y e r s in th e G re e n sto n e , t h e t h i c k e s t f lo w i n t h e e n t i r e s e q u e n c e . A se rie s of c h e m i c a l a n a l y s e s fro m to p t o b o tt o m i n t h i s f lo w i n d i c a t e d a c o n ­ c e n t r a t i o n of: " - - S i 0 2 , F e 20 3 , FeO, Na20 , K20 , T i 0 2 , ? 2° 5 > S> C u’ and a r e l a t i v e la c k of: " - - A l 20 3 , MgO, CaO." in th e d o l e r i t i c la y e rs. (B ro d e ric k , 1935, p . 5 1 2 ) . The a u t h o r r e l a t e d t h i s tr e n d to th e e l e m e n t s Bowen h a d fo u n d t o b e c o n c e n t r a t e d i n g a s e o u s e m a n a ti o n s a s s o c i a t e d w i t h magma c r y s t a l l i z a t i o n . A s e q u e n c e o f c h e m i c a l a n a l y s e s o f t h e K e a r s a r g e f lo w by B r o d e r i c k i n d i c a t e d t h a t t h e f i r s t sa m p le b elow t h e a m y g d a l o i d a l s u r f a c e w as: ' ' - - e x c e p t f o r t h e FeO, i d e n t i c a l w i t h t h a t e x p r e s s i n g t h e c o m p o s itio n o f th e d o l e r i t i c la y e r in th e G re e n sto n e flo w ." ( B r o d e r i c k , 1935 , p . 5 2 5 ) . The a u t h o r c o n c l u d e d t h a t t h i s r e s u l t e d from : " - - a m i l d e f f e c t o f t h e same p r o c e s s w h ich fo rm ed t h e d o l e r i t e n a m e ly , t h e t r a n s f e r o f s u b s t a n c e s i n t h e v o l a t i l e s t a t e d u r i n g c ry s ta lliz a tio n ." ( B r o d e r i c k , 193 5, p . 5 2 7 ) . B ro d e ric k co n clu d ed t h a t : by v o l a t i l e tra n s fe r, ( 2 ) o l i v i n e and p y r o x e n e t e n d e d t o c o n c e n t r a t e n e a r t h e b a s e by s e t t l i n g , d o le ritic zone. (1 ) t o p s w e re o x i d i z e d and i r o n i n c r e a s e d and (3 ) g a s e o u s t r a n s f e r c a u s e d t h e He n o t e d : " - - e f f e c t s i n flo w s a r i s e fro m b o t h c r y s t a l l i z a t i o n d i f f e r ­ e n t i a t i o n and v o l a t i l e t r a n s f e r - - " ( B r o d e r i c k , 193 5, p . 5 4 3 ) . C o r n w a ll ( 1 9 5 1 a , b ) s t u d i e d d i f f e r e n t i a t i o n o f Keweenawan f lo w s w ith p e g m a tit ic z o n e s , u s in g p e t r o l o g i c and c h e m ic a l m eth o d s, s i n c e he f e l t t h a t t h e s e f lo w s w e re r e p r e s e n t a t i v e o f m ore a d v a n c e d s t a g e s of d if fe re n tia tio n . He c o n c l u d e d (1 9 5 1 a ) t h a t t h e m a in f a c t o r s 6 c o n t r o l l i n g th e d i f f e r e n t i a t i o n w ere: " - - ( 1) c o o l i n g a t a m o d e r a t e r a t e , and p r e d o m i n a n t l y fro m t h e t o p ; ( 2 ) d i f f e r e n t i a l s e t t l i n g o f p l a g i o c l a s e , o l i v i n e , an d o p h i t i c p y r o x e n e c r y s t a l s : (3 ) l o c a l c o n c e n t r a t i o n o f v o l a t i l e s and t r a n s p o r t o f m a t e r i a l s by m i g r a t i o n o f v o l a t i l e s ; (4) p e r i o d i c c o n v e c t i v e o v e r ­ t u r n o f t h e magma d u r i n g t h e l a t e r s t a g e s o f c r y s t a l l i z a t i o n . " ( C o r n w a l l , 1 9 5 1 a , p . 1 9 0 ). C o rn w a ll a d v a n c e d two h y p o t h e s e s a b o u t t h e c r y s t a l l i z a t i o n o f t h e magma. One b a s e d on t h e c o n v e c t i v e o v e r t u r n o f t h e magma a n d t h e o t h e r a s s u m in g t h a t c o n v e c t i o n d i d n o t t a k e p l a c e d u r i n g c o o l i n g . I n h i s s t u d i e s h e fo u n d t h a t t h e same c h e m ic a l t r e n d s o c c u r r e d as B r o d e r i c k (1 935 ) h ad r e p o r t e d e a r l i e r . B ased on t h e a s s u m p t i o n s p r e s e n te d in h i s p a p e r o f 1951a, C o rn w a ll, in a second a r t i c l e (1 951b) a t t e m p t e d t o c a l c u l a t e q u a n t i t a t i v e l y t h e c h a n g e i n t h e magma o f t h e G r e e n s t o n e Flow d u r i n g c r y s t a l l i z a t i o n u s i n g t h e c h e m i c a l a n a l y s e s o f B r o d e r i c k (1935) and C o r n w a ll ( 1 9 5 1 a ) . He c o n c l u d e d t h a t t h e r e s i d u a l l i q u i d t h a t r e m a in e d a f t e r th e f l o w was a l m o s t s o l i d : " - - w a s s t r o n g l y c o n t r a s t e d w i t h e a r l i e r l i q u i d s i n i t s c o m p o s i­ t i o n , e s p e c i a l l y by i t s h i g h c o n t e n t o f s i l i c a and p o t a s h , and m u s t h a v e c r y s t a l l i z e d t o fo rm a g r a n o p h y r e - - " ( C r o n w a l l , 1 9 51b , p . 1 6 5 ) . O t h e r i m p o r t a n t t r e n d s t h a t C o r n w a ll (19 51b ) n o t e d w e re : " - - e a r ly escape of s u lf u r F e , T i , P , Mn, S , and Cu when i n c r e a s e i n Na and d e c r e a s e i n d e c r e a s e i n A1 a f t e r t h e e a r l y 1 9 5 1b, p p . 1 6 5 - 1 6 6 ) . fro m magma; p e a k s i n t h e c o n t e n t o f t h e flo w was n e a r l y s o l i d ; g r a d u a l Mg and Ca t h r o u g h o u t s o l i d i f i c a t i o n ; sta g e s of s o l i d i f i c a t i o n . " (C o rn w all, He a l s o n o t e d t h a t t h e c a l c u l a t e d l i q u i d d u r i n g c r y s t a l l i z a t i o n w as: " - - e n r i c h e d i n FeO and a l k a l i e s w i t h r e s p e c t t o MgO up t o , b u t n o t i n c l u d i n g , t h e f i n a l l i q u i d fro m w h ic h t h e g r a n o p h y r e c r y s t a l l i z e d . " ( C o r n w a l l , 1 9 51b , p . 1 6 6 ) . The s o l i d f r a c t i o n s w e re fo u n d t o f o l l o w t h e same t r e n d a s t h e liq u id s . GENERAL GEOLOGY S tra tig ra p h y The f o r m a t i o n s o f t h e Keweenaw P e n i n s u l a a r e , fr o m t h e o l d e s t to t h e y o u n g e s t , t h e P o r t a g e Lake L ava S e r i e s , C o p p er H a r b o r c o n ­ g l o m e r a t e , N onesu ch s h a l e , F r e d a s a n d s t o n e , and J a c o b s v i l l e s a n d ­ sto n e . A g e n e r a l i z e d map o f Keweenawan g e o l o g y i s i n c l u d e d h e r e a s F i g u r e 2. The P o r t a g e Lake L ava S e r i e s i s a t h i c k s e q u e n c e o f f lo w s r a n g i n g i n c o m p o s i t i o n fro m o l i v i n e b a s a l t t o a n d e s i t e w i t h some i n t e r b e d d e d c o n g lo m erates w ith r h y o l i t i c p e b b le s (C o rn w all, 1 9 5 4 ). T hese f lo w s v a r y i n t h i c k n e s s fro m a few f e e t up t o a b o u t 1300 f e e t and i n e x t e n t alo n g th e s t r i k e f r o m s e v e r a l h u n d r e d f e e t up t o a t l e a s t 40 m i l e s . Some o f t h e f lo w s a r e u n i f o r m l y f i n e - g r a i n e d b u t m o st o f them i n c r e a s e i n g r a i n s i z e fro m b o t h t h e to p and b o tt o m to w a r d s t h e c e n t e r . The t e x t u r e o f t h e c o a r s e - g r a i n e d l a v a s may b e o p h i t i c , g l o m e r o p o r p h y r i t i c , o r l e s s commonly, p o r p h y r i t i c . C a p p in g t h e m a s s i v e l a v a t h a t fo rm s t h e b u l k o f e a c h f lo w i s a l a y e r o f a m y g d a l o i d a l l a v a u s u a l l y 5 t o 10 f e e t t h i c k . fillin g t h e am y g d u le s a r e m a i n l y c a l c i t e , o th e r m in e ra ls such as p r e h n i t e , d a t o l i t e , c ite , The m i n e r a l s e p i d o t e , and q u a r t z , a l t h o u g h red p o ta sh f e ld s p a r , a n a l- n a t i v e c o p p e r , p u m p e l l y i t e , and l a u m o n t i t e a r e l o c a l l y a b u n d a n t . The c o n g l o m e r a t e and s a n d s t o n e b e d s w i t h i n t h e l a v a s e r i e s a r e 7 lake ONTONAGON o supe EAGLE LAKE superior KE.W LAKE LINDEN A -I % HOUGHTON* > c a >/ V -A TR A V ER SE PO IN T JA C O B S V IL L E 0 4 MILES FIGURE 2 GENERALIZED GEOLOGICAL MAP OF A PART OF THE KEWEENAW PENINSULA 8 EAGLE RIVER o O ° „ O o. V -r • t ^ < > ^ - i u < S ^ ^ .EAGLE H A R B OR {. -1 v J«**> ' : ■ ■ ■ / ' . ■ ■ ■ ■ LAKE . i LINDEN Ne n : POINT ISABELLA K E WE EN AW POINT TRAVERSE POINT JACOBSVILLE 4 JL J JACOBSVILLE F FREDA SANDSTONE N 8 _L 12 _l SANDSTONE M ILES NONESUCH COPPER V A MAP EWEENAW PENINSULA HARBOR CONGLOMERATE 4 PORTAGE IOLOGICAL SHALE LAKE LAVA PRE-K EW EENA W AN SERIES ROCKS com posed p r i m a r i l y o f r h y o l i t i c m a t e r i a l . The b u l k o f t h e c l a s t i c p a r t i c l e s r a n g e i n d i a m e t e r fro m a s m a l l f r a c t i o n o f a n i n c h t o a b o u t 6 in c h es. T h e s e r o c k s a r e c o m p a c t an d t i g h t l y c e m e n te d . T hese s e d i m e n t a r y beds s e r v e a s good s t r a t i g r a p h i c m a r k e r s and a few h a v e n a t i v e c o p p e r d e p o s i t e d i n them. The C o p p e r H a r b o r c o n g l o m e r a t e c o n f o r m a b l y o v e r l i e s t h e P o r t a g e Lake L ava S e r i e s and c o n s i s t s m a i n l y o f c r u d e l y s t r a t i f i e d p e b b l e t o - b o u l d e r - c o n g l o m e r a t e w i t h s m a l l s a n d s t o n e l e n s e s and b e d s . The p e b b l e s and b o u l d e r s a r e w e l l - r o u n d e d t o s u b - a n g u l a r r h y o l i t e c l a s t s . B a s a l t f r a g m e n t s a r e g e n e r a l l y p r e s e n t i n s m a l l am oun ts and i n some a r e a s make up a s much a s o n e - h a l f t h e t o t a l b u l k . p re-K ew een aw an m a t e r i a l p r e s e n t . T h e re i s l i t t l e The m a t r i x i s s a n d and g r i t o f t h e same c h a r a c t e r a s t h e c o a r s e r m a t e r i a l . L ava f lo w s i n t e r s t r a t i f i e d w i t h t h e C o p p er H a r b o r c o n g l o m e r a t e a r e t y p i c a l l y f i n e - g r a i n e d a n d e s i t e , w i t h an a m y g d a l o i d a l l a y e r 2 to 10 f e e t t h i c k a t t h e t o p . fillin g s are c a lc ite , The d o m in a n t m i n e r a l s o f t h e a m y g d a l o i d a l c h lo rite , an d l a u m o n t i t e . The N onesuch s h a l e i s p r e d o m i n a n t l y s i l t s t o n e . The u p p e r p a r t o f t h e f o r m a t i o n i s com posed o f f l a g g y , r i p p l e - m a r k e d , g r a y t o r e d d i s h g r a y s i l t s t o n e , w i t h s m a l l am ou nts o f i n t e r b e d d e d g r a y and g r e e n i s h gray s i l t y sh a le . m o stly t h i n l y The lo w e r p a r t c o n t a i n s d a r k g r a y s i l t s t o n e , la m in a te d , w ith s e v e r a l beds o f c o a r s e - g r a i n e d a r k o s ic s a n d s to n e n e a r th e b a s e . The lo w e r p a r t c o n t a i n s c h a l c o c i t e and n a t i v e c o p p e r i n t h e W h ite P i n e a r e a n e a r O n to n a g o n . The t o t a l t h i c k n e s s o f t h e f o r m a t i o n i s a b o u t 600 f e e t . The t y p i c a l r o c k o f t h e o v e r l y i n g F r e d a s a n d s t o n e i s a l i g h t g r a y to r e d , f i n e t o m e d iu m - g r a i n e d s a n d s t o n e w i t h p r o m i n e n t w h i t e b l o t c h e s 10 and s t r e a k s . co n g lo m erate. The f o r m a t i o n i n c l u d e s m i n o r am ounts o f r e d s h a l e and The t o t a l t h i c k n e s s o f t h e F r e d a i s a b o u t 500 f e e t . The b o u n d a ry b e tw e e n t h e F r e d a and t h e u n d e r l y i n g N onesuch s h a l e i s tra n s itio n a l. J a c o b s v i l l e s a n d s t o n e i s p r i m a r i l y b u f f t o s alm o n c o l o r e d , f i n e t o m e d iu m - g r a i n e d s a n d s t o n e w i t h s m a l l am o un ts o f r e d d i s h - b r o w n p e b b l e c o n g l o m e r a t e s , r e d s h a l e s , and s i l t y sh a le s (H am b lin , 1958). The s a n d s t o n e h a s a l a r g e p r o p o r t i o n o f w e l l - r o u n d e d q u a r t z g r a i n s . I n t r u s i v e r h y o l i t e b o d i e s o f t h e Keweenaw P e n i n s u l a a r e u n i f o r m , f i n e - g r a i n e d r o c k s w h ic h a r e p a l e r e d d i s h - b r o w n on f r e s h l y b r o k e n s u r f a c e s and w h i t e on w e a t h e r e d s u r f a c e s . q u a rtz , o rth o c la s e , and a l b i t e - o l i g o c l a s e . The m a in m i n e r a l s a r e The r h y o l i t e i s c l o s e l y j o i n t e d and t h e b o d i e s a p p e a r t o be s t o c k s . None a r e o l d e r t h a n m i d d l e Keweenawan a s t h e y i n t r u d e t h e P o r t a g e Lake Lava S e r i e s . The d o m in an ce o f r h y o l i t e f r a g m e n t s i n t h e b e d s o f c o n g l o m e r a t e i n t h e la v a s e r i e s in d i c a te s t h a t r h y o l i t e i n t r u s i v e and e x t r u s i v e r o c k s m u s t h a v e b e e n e x p o s e d o v e r l a r g e a r e a s d u r i n g and a f t e r m i d d l e Keweenawan. S tru c tu ra l S e ttin g The M ic h ig a n c o p p e r r e g i o n i s on t h e s o u t h e r n r im o f t h e Lake S u p e r i o r s y n c l i n e o r b a s i n o f Keweenawan a g e . The n o r t h lim b o f t h i s s y n c l i n e i s fo u n d on t h e n o r t h w e s t s h o r e o f Lake S u p e r i o r an d on I s l e R o y a le . E a r l y Keweenawan r o c k s d i p s t e e p l y p ro g re ssiv e ly le ss s te e p ly c e n t e r o f th e b a s i n ( 7 0 ° ) and l a t e r o n e s (down t o 2 5 ° ) n o r t h w e s t w a r d to w a rd t h e ( S p i r o f f and S l a u g h t e r , 1 9 6 2 ). T r a n s v e r s e t o t h e g e n e r a l s t r i k e o f t h e Lake S u p e r i o r s y n c l i n e 11 a r e f o l d s t h a t p l u n g e down t h e d i p o f t h e l a r g e r f o l d ; among t h e s e f o l d s a r e t h e n o r t h w a r d p i t c h i n g Keweenawan a n t i c l i n e w i t h i t s c r e s t n e a r Keweenaw P o i n t , t h e O n to n a g o n s y n c l i n e im m e d i a t e l y t o t h e s o u t h ­ w e s t , and t h e B e sse m e r a n t i c l i n e . On t h e s e b r o a d , o p e n f o l d s d i s t a n c e fro m t h e c r e s t o f t h e Keweenaw a n t i c l i n e B essem er a n t i c l i n e (th e to th e c r e s t o f th e i s a b o u t 110 m i l e s ) a r e s e v e r a l s u b o r d i n a t e f o l d s o f s i m i l a r c h a r a c t e r and t r e n d s u c h a s W inona a n t i c l i n e , F i r e s t e e l R i v e r s y n c l i n e , and Mass a n t i c l i n e . T h e s e a r e a l s o b r o a d , o p en f o l d s b u t o n l y 5 t o 10 m i l e s a c r o s s a s c o n t r a s t e d w i t h 100 m i l e s f o r t h e m a j o r cross fo ld s. Some o f t h e s m a l l e r f o l d s show a r a t h e r u n i f o r m b e n d i n g o f t h e b e d s , w i t h some f a u l t i n g n e a r t h e c r e s t . O t h e r s , s u c h as t h e Mass a n t i c l i n e , h a v e b e d s b e n t s h a r p l y a t t h e c r e s t s and a t t h e m a r g i n s o f t h e f o l d s , b u t t h e lim b s a r e f a i r l y s t r a i g h t . The g r e a t e s t f a u l t o f t h e r e g i o n i s t h e Keweenaw f a u l t , w h ic h bou nds t h e P o r t a g e Lake L ava S e r i e s on t h e s o u t h fro m t h e en d o f Keweenaw P o i n t t o Lake G o g e b ic . T h is i s a r e v e r s e f a u l t w ith a v a r i a b l e d i p o f 20° t o 70° n o r t h w e s t , a l o n g w h ic h t h e l a v a f lo w s h a v e been t h r u s t o v er th e younger J a c o b s v i l l e s a n d s to n e . The d i p o f t h e f a u l t i s n e a r l y p a r a l l e l t o t h e f lo w s and i t s s t r i k e is g e n e ra lly n o r t h e a s t , v a r y i n g as i t f o l l o w s t h e m a j o r a n t i c l i n a l and s y n c l i n a l s t r u c t u r e s o f th e ro c k s . In g e n e r a l, t h e n o r t h w a r d - d i p p i n g l a v a f lo w s on t h e h a n g i n g - w a l l s i d e o f t h e f a u l t a r e b e n t downward s o t h a t i n p l a c e s t h e d i p i s r e v e r s e d , and t h e f l a t l y i n g s a n d s t o n e s on t h e f o o t w a l l s i d e a r e t u r n e d up r a t h e r a b r u p t l y (F ig u re 3 ). Many b r a n c h f a u l t s and f i s s u r e s a r e a s s o c i a t e d w i t h t h e Keweenaw fa u lt. R e l a t i v e l y s m a l l t r a n s v e r s e f a u l t s and f i s s u r e s , w h ic h a p p a r e n tly r e s u l t e d d u rin g th e f o ld i n g o f th e ro c k s , a re a ls o p r e s e n t CL PG PP P HC ,p Q /* P O /* -P K C PK POC 0 MILES < < K K at m JACOBSVILLE Z Z « «* SANDSTONE o o ill ae a a. o wmrgrTT COPPER HARBOR P O R TA G E LAKE HANCOCK PHC PP^ z ffln p a LAVA BASIC LAVA P LOW U SERIES CONGLOMERATE WEST PEWABI C GREENSTONE CALUMET < C O N GL O ME R AT E CONGLOMERATE FLOW AND HECLA CONGLOMERATE PC OSCEOLA AMYGOALOID PO^ o bi PKC T KINGSTON CONGLOMERATE IK a KEARSARGE OL D F LOW COLONY SANOSTON E NORTHWE POC THRO SCALES C R E E K F LO W M O DIFIEt PSC B O H E M IA CONGLOMERATE PB 5 COPPER CITY F LO W PCC PS 7 ST. LOUIS CONGLOMERATE I2 1800' 1000' S E A LEVEL - 500 ' - 1000' 2 00 0 ' MILES ATE - BASIC LAVA F LOW U N I T S A RE D E S I G N A T E D "CL" S ATE IGLOMERATE FIGURE 3 N O R T H W E S T - SOUTHEAST THROUGH MODIFIED KEWEENAW AFTER CORNW ALL C R O SS-SECTIO N PENINSULA AND W R IG H T , 1954 13 around th e c r e s t s o f th e a n t i c l i n e s . M ost o f t h e s m a l l e r f a u l t s i n t h e p e n i n s u l a s t r i k e n o r t h w e s t and a r e v e r t i c a l o r d i p s t e e p l y n o r t h ­ e a st. The e x i s t e n c e o f t h e s e s m a l l e r f a u l t s i s r e v e a l e d by o f f s e t s i n k e y h o r i z o n s r a t h e r t h a n by a c t u a l o b s e r v a t i o n s o f t h e f a u l t p la n e s. Econom ic G eo lo gy The M ic h i g a n c o p p e r d e p o s i t s a r e o f two b a s i c t y p e s ; d e p o s i t s and f i s s u r e d e p o s i t s . The l o d e d e p o s i t s , lo d e fro m w h ic h m o s t o f t h e c o p p e r h a s b e e n p r o d u c e d , c o n s i s t o f a m y g d a lo id l o d e s , w h ic h a r e m i n e r a l i z e d a m y g d a l o i d a l o r b r e c c i a t e d t o p s o f l a v a f l o w s , and c o n g l o m e r a t e l o d e s , w h ic h a r e m i n e r a l i z e d b e d s o f c o n g l o m e r a t e i n t e r ­ bedded w ith th e la v a flo w s. The m i n e a b l e c o p p e r o c c u r s i n o r e " s h o o t s " w h ic h a r e f a r s m a l l e r t h a n t h e l o d e s c o n t a i n i n g them . The o r e i n t h e " s h o o t s " was d e p o s i t ­ ed i n t h e more p e r m e a b le p a r t o f t h e l o d e by c h e m ic a l s o l u t i o n s , th e movement o f w h ic h was c o n t r o l l e d by r e l a t i v e l y im p e rm e a b le b a r r i e r s ( B u t l e r and B u rb a n k , 1929, p . 1 0 4 ) . F is s u re d e p o sits occur in n e arly v e r ti c a l f is s u r e s or f a u lts t h a t a r e g e n e r a lly a lm o st p e r p e n d ic u la r to th e s t r i k e o f th e la v a f lo w s an d i n t e r b e d d e d s e d i m e n t a r y r o c k s ( C o r n w a l l , 1954). CHEMICAL ANALYSES S a m p lin g S am p les f o r t h i s s t u d y came f r o m 6 diam ond d r i l l h o l e s w h ic h p e n e t r a t e d t h e S c a l e s C r e e k Flow ( T a b l e 1 and F i g u r e 4 ) . 188 t h i n s e c t i o n s w e re s t u d i e d fr o m a l l s i x h o l e s . A to ta l of Whole r o c k chem­ i c a l a n a l y s e s w e re made o n s a m p l e s fro m t h r e e o f t h e s e d r i l l h o l e s . T h i r t e e n s a m p le s c h o s e n fro m o n e d r i l l h o l e p e n e t r a t i n g t h e K e a r s a r g e Flow w e r e a l s o a n a l y z e d f o r c o m p a r i s o n t o t h e S c a l e s C re e k F low . T a b l e 1. S a m p lin g D a ta o n S c a l e s C r e e k F low . Diamond D r i l l H ole Flow T h ick n ess Number o f S am p les No. o f T h in S ec tio n s Number o f A n aly ses D e la w a re 64 1 74' 36 35 27 C e n t r a l 57 218' 46 31 - - G ra tio t 7 245' 50 25 — L a S a l l e 30 246' 50 29 -- S t . L ouis 5 249' 51 27 27 N .K e arsa rg e 3 272' 56 41 34 A n a ly z e d r o c k m a t e r i a l was s e l e c t e d t o a v o i d v e i n s and v e s i c l e s f i l l e d w ith se c o n d a ry m in e r a ls such as c a l c i t e . I n some c a s e s t h e s e p r i n c i p l e s h a d t o b e s a c r i f i c e d a n d t h e s e a p p e a r a s m ark ed c o m p o s i t i o n a n o m a l i e s , s u c h a s h i g h CaO i n t h e f l o w t o p . The to p was n o t a n a l y z e d i n d r i l l h o l e NK3 b e c a u s e t h e s a m p l e s w e r e so h i g h l y a l t e r e d . C h e m ic a l a n a l y s e s o f t h e r o c k s c o n f i r m many o f t h e p e t r o g r a p h i c 14 JACOBSVILLE FREDA SANDSTONE SANOSTONE JACOBSVILLE NONESUCH COMPILED FROM: VAN HISE a 8 MARTIN (1936) HAMBLIN W q OI LEITH BUTLER SHALE I s o 1 COPPER HARBOR (1911), PLATE I BURBANK ( 1 9 2 9 ), PLATES 283 □ PORTAGE DIAMOND (1 9 5 7 ), PLATE I LAKE CONGLOMERATE LAVA SERIES DRILL H O L E LO CA TION FIGURE 4 GENERALIZED GEOLOGICAL MAP OF A PART OF TH E KEWEENAW PENINSULA 16 o b s e r v a t i o n s , e s p e c i a l l y t h e d o l e r i t i c z o n e s i n t h e u p p e r and l o w e r p o r ti o n s of th e flow. S c a l e s G r e e k Flow E i g h t y - e i g h t s a m p l e s f o r c h e m i c a l a n a l y s i s w e r e c h o s e n fr o m t h e D e la w a r e 6 4 , S t . L o u i s 5 , and N o r t h K e a r s a r g e 3 h o l e s and t h e d a t a i s i n c l u d e d h e r e i n T a b l e s 2, 3 , and 4 . C o n c e n t r a t i o n s o f S iC ^ , , FeO, MgO, Ti C ^ , MnO, CaO, Na2 0 , and ^ 0 w e r e p l o t t e d as F i g u r e s 5 , 6 , and 7 a s p e r c e n t d e v i a t i o n s f r o m t h e mean. Th es e s a m p l e s w e r e t a k e n a t a f i v e f o o t i n t e r v a l n e a r t h e f l o w t o p and b o t t o m , and 10 t o 20 f o o t i n t e r v a l s in the c e n t r a l p o rtio n s of the flow. C h e m ic a l t r e n d s i n t h e S c a l e s C r e e k Flow a r e s i m i l a r t o t h o s e found i n p r e v io u s s t u d i e s . S i 0 2 s FeO, T i 0 2 » MnO, Na2 0 , and ^ 0 t o be c o n c e n t r a t e d i n a zon e n e a r t h e f l o w t o p . tend Likewise, th e re is a marke d d e f i c i e n c y o f CaO, MgO, and A I 2O3 i n t h e same z o n e . A h i g h e r t h a n a v e r a g e r a t i o o f FeO t o MgO o c c u r s i n t h i s z on e a l s o . S im ilar trends in e x is tin g or in c ip ie n t d o l e r i t i c la y e rs have been f o u n d i n o t h e r f l o w s by B r o d e r i c k (1 93 5 ) and C o r n w a l l ( 1 9 5 1 a , b ) . T h i c k n e s s o f t h e z on e and d e g r e e o f d e v e l o p m e n t o f t h e c h e m i c a l c o n c e n t r a t i o n s and d e f i c i e n c i e s a r e r e l a t e d t o t h e t h i c k n e s s o f t h e f l o w a t t h e p o i n t o f c o r e samp1 i n g . The t h i c k n e s s o f t h e d o l e r i t i c zone f o u n d i n diamond d r i l l h o l e NK3, w h e r e t h e f l o w i s 272 f e e t thick, i s a b o u t 40 f e e t . By c o m p a r i s o n , t h e d o l e r i t i c zon e i s 20 f e e t t h i c k i n SL5 and a p p r o x i m a t e l y 10 f e e t t h i c k i n t h e 174 f o o t t h i c k diamond d r i l l h o l e D64. C o n c e n t r a t i o n and d e f i c i e n c y o f a l l o f t h e o x i d e s o c c u r s i n NK3, a l t h o u g h t h e y may v a r y w i t h i n t h e z on e i. 17 itse lf. T h i s may be due t o s e v e r a l s m a l l d o l e r i t i c a s one d ue t o t h e s a m p l e s p a c i n g . la y ers appearing I n th e t h i n n e r p o r t i o n o f th e flow t h e d o l e r i t i c z o ne a p p e a r s a s a h i g h c o n c e n t r a t i o n o f S i C ^ j i ^ Q , Na2 0 , and low p e r c e n t a g e s o f A ^ O ^ , FeO, CaO, and MgO. TiC>2 a n d MnO a r e d e f i c i e n t i n t h e d o l e r i t i c zon e a nd no m ark ed i n c r e a s e i n t h e FeO/MgO r a t i o o c c u r s . C o n c e n tra tio n s of v a r io u s oxides n e a r th e bottom i n the S c a le s C r e e k Flow a r e s i m i l a r t o t h o s e f o u n d i n t h e u p p e r p o r t i o n o f t h e u nit. A n a r r o w zon e i m m e d i a t e l y ab o v e t h e b a s a l c h i l l zone h a s a h i g h e r t h a n a v e r a g e amount o f S i C ^ , K^O, and T i 02 and a r e l a t i v e d e f i c i e n c y i n CaO and MgO. t h i s zone. A h i g h FeO/MgO r a t i o i s a l s o f o u n d i n Th es e t r e n d s w o ul d i n d i c a t e a d o l e r i t i c z o ne and t h i n s e c tio n study in d ic a te s th a t th is is p o s sib le . Sam pl es fr o m t h i s p a r t of the flow have th e t y p i c a l c o a r s e d o l e r i t i c SL5-48, had s m a ll q u a n t i t i e s o f q u a r t z p r e s e n t . t e x t u r e and o n e , D o l e r i t i c zones have n o t been r e p o r t e d from flow bottoms in p r e v io u s s t u d i e s . C h e m ic a l t r e n d s a r e e s s e n t i a l l y t h e same i n e a c h o f t h e t h r e e d r i l l h o l e s t h a t p e n e t r a t e d t h e S c a l e s C r e e k Flow. The main d i f f e r e n c e i s t h a t t h e s a l i e n t v a r i a t i o n s a r e more m a rk e d i n t h e t h i c k e r p o r ti o n s o f the flow. F i g u r e s 8 t h r o u g h 15 a r e g r a p h s show­ in g th e c o n te n t o f each of the v a rio u s oxides v ersu s th ic k n e s s of the f l o w , dr aw n s o t h a t t h e v a r i a t i o n s compared. i n each o f the d r i l l h o le s a r e Table 2. Chemical Composition of Scales Creek Flow, Diamond Drill Hole D64. S am p l e/ Depth S i02 CaO 1 /0 34.91 1 9. 4 9 5.94 15. 67 2.40 17.89 0.11 0.00 0.093 2/5 45.18 6.94 9.51 12.2 5 2.38 16.4 7 3.60 0.25 0.180 3 /1 0 46.19 6.56 7.30 12.46 2.30 17.46 4.16 0.43 0.170 4/15 46.15 8.45 7.54 12 . 7 9 2.41 16 .0 1 3.46 0.79 0.158 5/20 47.72 7.22 9.69 11.7 5 2.05 15 . 7 9 3.23 0.87 0.169 6 /2 5 46.19 8.63 10 . 9 2 11.59 1.92 15 .4 8 2.50 0.64 0.176 7/30 52.84 3.92 9.28 11 . 2 4 1 .4 5 15.3 3 4.49 1.78 0.146 8 /3 5 47.86 9.62 8.68 10.12 1.6 5 16.96 2.52 0.71 0.050 9/40 47.72 10.86 7.67 11.40 1 .8 7 17.10 2.50 0.28 0.156 10 /4 5 47.34 9.94 7.94 11. 77 1.79 1 8. 3 9 2.51 0.39 0.171 11 /5 0 47.34 9.68 8.99 11 .8 3 1.99 17.4 5 1.89 0.31 0.156 1 3 /6 0 47.40 9.84 9.13 11.6 3 1.94 17.20 2.38 0.31 0.165 14/65 46.95 10. 03 9.93 11 .6 1 1.72 17 . 2 2 2.33 0.29 0.160 1 5 /7 0 46.88 9.45 8.37 11.89 2.03 17 .9 3 2.39 0.31 0.162 17/ 8 0 47.49 9.99 8.04 12 .3 5 2.17 17. 35 2.42 0.30 0.173 19 /9 0 47.30 10.10 8.03 11.39 2.21 18.74 2.47 0.32 0.149 2 1 /1 0 0 46.78 10.19 8.79 11.38 2.23 18.54 2.52 0.25 0.157 2 3 /1 1 0 47.03 9.87 8.55 11.89 2.30 17.79 2.42 0.28 0.167 MgO FeO Ti02 A120 2 Na20 k 2° MnO Table 2 (cont'd.) S am p l e/ Depth Si02 CaO 2 5 /1 2 0 47.21 10 . 3 0 8.99 12.5 3 2.36 17 . 8 7 2 7/ 1 30 46.82 10.4 7 8.36 11.46 2.24 2 8 /1 3 5 47.22 10.68 8.39 13.32 3 0 /1 4 5 47.23 9.34 9.19 3 1 /1 5 0 46.65 9.73 33/160 46.90 3 4 /1 6 5 MgO FeO Ti02 k 2o MnO 2.36 0.28 0.196 18 .3 5 2 .4 7 0.31 0.207 2.20 17.78 2.45 0.27 0.109 12 .8 1 2.35 16.62 2.26 0.29 0.211 9.28 1 2. 4 4 2.25 17.5 1 2.47 0.29 0.213 8.91 8.18 12 .4 1 2.04 17.99 3.03 0.85 0.163 46.79 8.57 8.57 12 .4 1 2.06 18.38 2.80 0.85 0.197 35/170 47.23 8.08 6.93 12.12 2.06 17 .8 7 3.92 1.28 0.188 3 6 /1 7 4 49.22 3.96 9.89 9.79 2.24 17 . 6 7 5.23 0.50 0.186 A12°3 Na20 Table 3. Sample/ Depth Chemical Composition of Scales Creek Flow, Diamond Drill Hole SL5. S i02 CaO MgO FeO Ti02 A l 2°3 Na20 k2o MnO 1 /0 44.10 8.97 5.48 15. 0 3 1.59 16.09 3.84 0.38 0.125 2/4 46.48 6.89 8.98 14.02 1. 53 14 .8 1 4.30 0.35 0.168 3/10 46.54 9.65 8.84 15 . 4 4 1 .5 6 13 .7 9 4.43 0.57 0.201 4/15 48.36 9.38 7.55 12.78 1.26 13 . 9 0 3.91 0.43 0.168 5/20 46.55 8.40 9.07 14.50 0.72 16.19 2.54 0.29 0.145 6 /2 5 45.46 9.75 6.72 14 . 4 6 0.97 16.19 2.54 0.34 0.166 7 /3 0 46.21 10 . 0 8 7.88 1 4. 0 9 1 .0 3 16 . 4 2 2.58 0.35 0.173 8 /3 5 46.70 9.72 7.99 13.6 3 1.28 17. 36 2.66 0.38 0.179 9/40 45.86 9.35 8.58 15 . 0 6 1.19 13.99 2.59 0.41 0.184 10/45 46.75 11 .1 8 7.29 13.70 1.08 15.02 2.58 0.34 0.156 14 /6 4 46.72 9.26 8.09 14 .5 3 0.98 16.42 2.48 0.31 0.178 1 7 /8 0 46.56 9.72 7.37 13.8 3 1.20 15.08 2.60 0.30 0.167 21/100 46,56 10 .9 5 7.44 14 .5 1 1.64 16. 61 2.53 0.32 0.202 2 5 /1 2 0 46.07 9.50 7.78 14.78 1.59 16. 37 3.86 0.32 0.182 29/140 46.17 10 . 2 8 8.55 14 .4 5 1.25 16.90 2.24 0.24 0.166 33/160 46.59 10.08 8.08 14.41 1.02 15 .9 3 3.77 0.26 0.156 3 6 /1 7 5 46.26 9.87 8.46 14 .4 7 0.94 1 5. 4 4 2.41 0.24 0.163 40/195 46.58 9.62 7.85 14.50 0.02 14 .4 5 2.41 0.30 0.167 Table 3 (cont’d.) Sample/ Depth Si02 43/210 46.06 44/215 CaO MgO FeO Ti02 8.87 9.81 14 .2 7 1.46 45.99 9.82 8.72 13.80 45/220 45.62 10 .5 1 7.76 46/225 45.02 8.37 47/230 41.30 48/235 Na20 k 2o MnO 15.02 2.41 0.29 0.169 1.12 14.88 2.23 0.25 0.200 14 .5 5 1.44 13.38 2.58 0.52 0.166 9.83 15.69 1 .2 7 15 .7 6 3.00 0.40 0.179 20.34 4.76 14 .4 1 1.60 1 5. 9 8 0.26 0.11 0.131 47.18 8.05 7.08 14 .6 7 1.14 16 . 1 8 2.64 1.02 0.198 49/240 46.98 8.63 7.66 14.46 1.36 16.54 2.54 0.75 0.205 5 0 /2 4 5 45.84 8.65 6.71 15.08 1.64 16.14 3.21 0.79 0.195 51/249 45.44 8.96 7.32 14.54 1.58 14.49 3.54 0.39 0.199 A12°3 Table 4. S am p l e/ Depth Chemical Composition of Scales Creek Flow, Diamond Drill Hole NK3. S i09 CaO MgO FeO Ti02 A120 3 Na20 K2° MnO 3/10 49.14 6.36 6.34 13.0 5 2.67 16 .3 6 4.63 0.01 0.151 4/15 46.10 8.28 7.87 13 .2 7 3.21 15 .7 8 3.58 0.70 0.175 5/20 45.23 9 .8 5 6.38 12 .8 3 2.80 16 .4 3 3.13 0.63 0.174 6 /2 5 45.64 9.20 8.41 13. 35 2.53 15.4 3 2.58 1 .2 0 0.233 7/30 51.10 4.52 8.47 10 .1 4 1 .7 6 15 . 0 0 3.84 2.46 0.197 8/35 48.63 6.97 9.58 15 . 6 0 3.58 10 .8 1 1 .8 6 1.59 0.221 9 /4 0 53.68 9.33 4.52 10.28 2.88 14.40 3.65 0.48 0.148 10/45 54.77 5.26 4.78 10 .6 9 2.48 1 6. 0 6 3.77 1 .6 6 0.133 11 /5 0 52.82 5.98 5.51 12 . 1 6 2.79 15.15 3.81 1.08 0.146 12/55 53.76 3.42 6.24 10 . 3 2 2.46 15.29 3.83 2.59 0.123 13/60 53.55 5.82 5.42 10.2 6 2.28 14.64 3.58 2.44 0.123 14/6 5 52.01 6.31 5.81 10 .6 7 2.50 16.04 3.90 2.25 0.117 15/7 0 52.73 4.69 6.47 11 . 1 6 2.46 15.02 3.70 2.19 0.136 16/75 47.12 8.53 10.06 12.6 3 1 .9 3 12 .7 6 2.55 0.70 0.190 18/85 46.37 9.76 8.03 11 . 9 0 2.02 18.40 2.44 0.35 0.183 20 /9 5 48.37 10 . 3 9 7.29 12 .5 1 2.10 16.14 1 .8 6 0.15 0.124 2 1 /1 0 0 48.44 8.90 9.82 12.79 2.25 14 . 3 6 1.72 0.28 0.114 2 4 /1 1 5 46.38 9.96 9.39 11 .5 7 2.79 14.60 1 .9 7 0.17 0.182 Table 4 (cont'd.) S am p l e/ Depth Si02 2 6 /1 2 5 CaO MgO FeO Ti02 a i 2o 3 Na20 k 2o MnO 47.43 9.96 7.68 12 .4 3 2.46 17 .1 5 2 .1 5 0.27 0.168 3 1 /1 5 0 46.79 10. 35 8.26 12 . 0 8 2.16 17.19 2.27 0.24 0.161 3 5 /1 7 0 45.28 11. 85 7.78 11.49 1 .8 1 18.19 2.09 0.23 0.135 3 9 /1 9 0 46.85 9.92 8.16 12 .7 5 2.51 16 . 4 4 2.28 0.16 0.168 41/200 46.90 9.35 8.57 13 . 8 2 2.49 16.62 2.24 0.35 0.171 43/210 45.02 9.09 9.98 14.40 2.54 14 .8 7 1.92 0.25 0.197 45/220 47.58 9.40 7 .7 7 12 .3 8 2.20 17.92 2.46 0.32 0.154 4 6 /2 2 5 45.93 11 . 0 0 9.86 12 . 7 0 1.86 17.04 1. 67 0.19 0.173 48/235 46.01 9.63 8.73 13 .0 5 2.48 17 .7 6 2.26 0.31 0.158 49/240 47.11 9.58 8.02 13.12 2.59 17.32 2.27 0.28 0.161 5 1 /2 5 0 47.26 9.92 8.27 12 . 2 2 1.7 7 18.19 2.60 0.25 0.164 5 2 /2 5 5 47.67 9.08 7.06 13.04 2.36 16.38 2.86 0.80 0.155 5 3 /2 6 0 49.58 6.34 8.07 12.60 2.01 15 . 8 0 4.49 0.43 0.172 5 4 /2 6 5 44.38 9.79 7.69 13 . 9 2 2.54 14 . 9 2 0.83 0.23 0.171 55/270 43.44 16.70 4.80 11 .7 1 2.64 16.62 1 .4 7 0.05 0.145 56/272 46.93 9.08 7.58 13.16 2.36 16.04 3.14 0.66 0.194 THICKNESS IN FEET 200 AVS. b -10% CaO 10% 20% -30% -20% -10% AVO. MgO 10% 20% 30% -20% -10% AVGL FaO 10% 20% 30% CHEMICAL -3 0 % -20% -10% AVO. TI02 10% FIGURE 6 COMPOSITION OF SCALES DIAMOND DRILL HOLE D l -20% -10% F«0 10% 20% 30% CHEMICAL -3 0 % -20% -10% TI02 10% 20% FIGURE fi COMPOSITION OF SCALES CREEK DIAMOND DRILL HOLE D 6 4 -2 0 % I FLOW -10% AloO, ■ X 10% I_ -30% 1 -< 0% -30% 1 , l -2 0 % l -10% ■ I NooO I- 10% I - 24 -50% »- I -4 0 % -30% 1 -2 0% ‘ -10% * AVO. No*0 t AVO. 10% 20% 30% 40% 50% 60% 1___*___ 1------1------1------1--- •50% -40% -30% « 1 — ■ -20% 1 -10% * ii,iiii K20 r 10% * 20% » 30% » 40% * 90% ■ — < h TH IC K N E S S IN FEET AVG. VlgO >0% 20% 30% -2 0 % -1 0 % AVG F«0 1 0% -4 0 % -3 0 % -2 0 % CHEMICAL -10% AVG no. 10% 20% 30% -2 0 % FIGURE 6 COMPOSITION OF SCALES CREEK DIAMOND DRILL HOLE SL 5 -10% AVG A l-O * FLOW 10% 20% -40% -3 0 % -2 0 % !0 % -10% < FLOW AVG. Al. 10 % 20% -4 0 % -3 0 % -2 0 % -1 0 % AVG. N o ,0 10% 20% 30% 40% 50% 80% -7 0 % -6 0 % -5 0 % -4 0 % -3 0 % -2 0 % -10% AVG. K 10% 2 0% 30% 40% 50% 60% -70% -60% -80% -40% -30% -2 0 % -10% AVG. K20 10% 20% 30% 40% 50% 60% 70% 60% 90% 100% T H I C K N E S S IN F E E T 20% -10% AVG. MgO 10% 20% 30% 40% -2 0 % -10% AVG, f mO 10% 20% 30% CHEMICAL lip8 " -3 0 % -2 0 % -10% AVG. TI02 10% 20% 30% FIGURE 7 COMPOSITION OF SCALES CREEK DIAMOND DRILL HOLE NK 3 4 0% FLOW 30% -3 0 % -2 0 % -10% 26 -3 0 % -2 0 % -10% AVG. TI0Z 10% 20% 30% FIGURE 7 COMPOSITION OF SCALES CREEK DIAMOND DRILL HOLE NK 3 4 0% FLOW 30% -3 0 % -2 0 % -1 0 % AVG. A tz 0 z 1 0% 20% -4 0 % -3 0 % -2 0 % -10% AVG. Hoz 0 10% 20% 30% 40% 26 AVU. K> 20% -4 0 % - 3 0 % -2 0 % -10% Naz 0 ATU. 10% 2 0% 30% 40% -0 0 % -70% -60% -8 0 % -4 0 % - 3 0 % -20% -10% KjO 10% 20% 30% 40 % 80* SL5 AVG. -1 0 % S I0 2 NK 3 AVG. D 6' AVG 10% -3 0 % -2 0 % -1 0 % 0 40 8 0 £ 120 V) ILI CON OXIDE VA R IA TIO N 10% 20% -3 0 % -2 0 % -1 0 % 8 IN S CA LES CR EE K FLOW D 64 AVG. S i0 2 10% 20% SL 5 •5 0 % -40% -30% -20% -10% AVG. CoO 10% 20% 30% -40% 40 120 THICKNESS IN FEET 80 60 200 240 280 CALCIUM OXIDI NK 3 30% -40% CALCIUM -30% OXIDE -20% -10% AVG. CoO FIG UR E 9 VA R IA TIO N IN 10% 20% SCALES 30% 40% CREEK -60% FLOW -50% -40% 28 NK 3 -10% AVG. CoO D 64 10% 20% 30% 40% nOLEI»T'?.,*S."S GURE 9 rION IN SCALES CREEK FLOW -60% -30% -40% -30% -20% -10% AVG. CoO 10% 20 SL 5 -4 0 % -3 0 % -2 0 -1 0 % AVG. MgO 10% 20% 30% -4 0 % -3 0 % -2 0 % -1 0 % 40 120 THICKNESS IN FE E T 80 160 200 240 280 FIGURE MAGNESIUM O X ID E VARIATION 29 NK 3 AVG. Vo - 2 0 % -1 0 % MgO F IG U R E VARIATION 0 64 AVG. 10% 20% 30% 40% -3 0 % 10 IN SCALES CREEK FLOW -2 0 % -1 0 % MgO 10% 20% 30% SL 5 AVG. NK 3 AVG. 40 120 THICKNESS IN FEET 80 160 200 240 PV 280 FIGUR E IRON i tu>. OXID E VA RIA TION IN II SCALES CREEK FLO NK 3 AVG. 0 64 AVG. -2 0 % OV PV F IG U R E IE VAR IA TIO N IN II SCALES CREEK FLOW -1 0 % FeO 10% 20% 30% SL 5 -4 0 % —l- — -3 0 % * -2 0 % * -1 0 % ■ AVG. T iO p i N 10% i 20% ■ . 30% 1 -3 0 % * -2 0 % ■ -1 0 % T ■________ 40 120 THICKNESS IN FEET 80 160 200 240 280 F IG U R E TITA N IU M OXIDE V A R IA T IO N \b 31 NK 3 AVG. D 64 AVG. 1 0% 20% 30% 40% 50% 1 *• —’ r 1 Z0N E__ _________________ ___________________________________ 1 / s'^ ^ / / ", F IG U R E l/ARIATION ^ 12 IN SCALES CREEK FLOW " f 1 L * -2 0 % -1 0 % SL 5 AVG. ALO NK 3 AVG. 10% 20% -3 0 % -2 0 % -1 0 % A lp O , 10% 20% DOL ERITIC 40 120 T H IC K N E S S IN FEET 60 160 200 240 280 FIG UR E ALUMINUM OXIDE VARIA TIO N IN 13 SCALES CREE SL 5 AVG. 10% 20% -3 0 % -2 0 % -1 0 % NK 3 AVG. A lp O , 10% -2 0 % 20% Upp ZON E FIGURE ALUMINUM OXIDE VAR IA TIO N IN 13 SCALES CREEK FLOW -1 0 % 0 64 AVG. A lp O , 10% SL 5 AVG. -4 0 % -3 0 % -1- ........ -2 0 % ■......—■ -1 0 % ■ N a2 0 -. i - 10% ■ 20% ■ 30% -, 40% . 50% i 60% . 40 120 THICKNESS IN FEET 80 160 200 0 LEr 240 280 SODIUN NK 3 AVG. 30% 40% 50% 60% -4 0 % ■ -3 0 % ■ -2 0 % ■ -1 0 % ■ Noo0 10% ■ 20% ■ 30% ■ 40% < \ j p 'P £ R — F IG U R E SODIUM OXIDE VARIATION IN 14 SCALES CREEK FLOW - ..- P P .Lg 33 0 64 AVG. D% ;■ 40% * -5 0 % ^ -4 0 % — —— n o t E R i T i c _ * g Ni . - EEK FLOW -3 0 % -2 0 % I——— —I—— «— X —I—I— -1 0 % wi— N aoO — 4— I 10% W 20% 30% ^ 40% 50% , , , 1— — 60% — jr i SL5 AVG. -7 0 % 40 120 THICKNESS IN FEET 60 160 200 240 280 JL -6 0 % -5 0 % -4 0 % -3 0 % -2 0 % -1 0 % K2 0 10% 20% 3 0 % - 40% 50% — £O j l e r i t | c 34 NK 3 AVG. > -6 0 % -5 0 % -4 0 % -3 0 % -2 0 % -1 0 % FI GURE 5 S I UM 111 OXI DE VARIATION IN K. 10% 20% 30% 40% 15 SCALES CREEK FLOW 50% -5 0 % -4 0 % -3 0 % -2 0 % -1 0 % 34 10% ES 20% CREEK 30% 40% FLOW 50% -5 0 % -4 0 % -3 0 % -2 0 % -1 0 % D 64 AVG. KoO 10% 20% 30% 40% 50% 60% 35 P y ro x e n e A n a l y s e s O r i g i n a l l y s e v e r a l h u n d r e d p y r o x e n e s a m p le s w e r e d e n s i t y s e p a ­ r a t e d and i t was i n t e n d e d t o c o n c e n t r a t e o n t h e i r c h e m i s t r y i n t h i s stu d y . P y r o x e n e s w e re c h o s e n b e c a u s e t h e l a c k o f d i v e r s e c o m p o s i t i o n an d t h e e x i s t e n c e o f o n l y on e p h a s e r e n d e r s t h e p l a g i o c l a s e somewhat l e s s v a l u a b l e t h a n t h e p y r o x e n e s i n s t u d y i n g b a s a l t i c magma v a r i a t i o n . H ow ever, d ue t o d i f f i c u l t y i n o b t a i n i n g p u r e s a m p l e s an d t h e im p o s ­ s ib ility o f e v e r s e p a r a t i n g t h e p i g e o n i t e an d a u g i t e , t h e s t u d y was l i m i t e d t o two s e t s o f m i n e r a l s . S i x t e e n s a m p le s o f p y r o x e n e s w e r e s e p a r a t e d fro m t h e S t . L o u i s 5 d r i l l h o l e and p a r t i a l c h e m i c a l a n a l y s e s w e re made on them ( T a b l e 5 ) . The p e a k s o f t h e g r a p h o f t h e FeO/MgO r a t i o ( F i g u r e 16) r e p r e s e n t i n g t h e h i g h e s t FeO/MgO r a t i o s c o r r e s p o n d w i t h t h i n s e c t i o n s t h a t h a v e b o t h p i g e o n i t e and a u g i t e p r e s e n t . T h i s a g r e e s w i t h t h e w o rk o f H ess ( 1 9 4 1 ) . An a t t e m p t was made by t h e a u t h o r , a s s i s t e d by M ilo N i e l s e n o f t h e B u ic k M o to r D i v i s i o n , t o a p p l y a n e l e c t r o n m i c r o s c o p e t o t h e s tu d y o f th e pyroxene g r a i n s . on on e g r a i n ( P h o to 1 ) . S e m i - q u a n t i t a t i v e r e s u l t s w ere o b ta in e d H ow ever, g r e a t d i f f i c u l t y was e n c o u n t e r e d due to th e e l e c t r i c a l c h a rg e s on th e g r a i n s u r f a c e (P h o to 2 ) . E v en ­ t u a l l y , by c o a t i n g t h e g r a i n w i t h g o l d t h e c h a r g e c o u l d be rem oved and t h e g r a i n a n a l y z e d . T h i s m etho d w o u ld be s u g g e s t e d f o r f u r t h e r s t u d y s i n c e t h e m ix ed p y r o x e n e g r a i n s c o u l d t h e n be i n d i v i d u a l l y an aly zed . I t m u s t be c a u t i o n e d t h a t s u c h a p r o c e d u r e i s s lo w and v e ry ex p e n siv e . E i g h t p y r o x e n e s a m p l e s w e r e s e p a r a t e d fro m t h e O s c e o l a 3 diam ond 36 MgAI P h o to 1. Si Co Co Ti Ti Fe Fe S e m i- Q u a n tita tiv e A n a ly s is o f an A u g ite G ra in . ins Taw ■M l P h o to 2. E l e c t r o n M ic r o s c o p e P i c t u r e o f A u g i t e G r a i n Show ing C h a r g e E f f e c t o n S u r f a c e , X1000. 37 T a b le 5. C h e m ic a l A n a l y s e s o f t h e P y r o x e n e s f r o m t h e S c a l e s C r e e k F lo w , Diamond D r i l l H o le SL5. S a m p le / D e p th S i 02 CaO 1/0 3 7 .7 2 22.68 3 /1 0 3 8 .6 5 1 0 /4 5 FeO FeO/ MgO 0 .7 6 1 6 .4 5 21.68 1 3 .7 2 9 .9 3 2 2 .2 5 2 .2 4 3 6 .7 0 9 .2 8 8 .0 5 2 3 .0 9 2 .8 7 1 4 /6 4 3 8 .6 3 1 4 .9 5 7 .9 4 2 0 .4 8 2 .5 8 1 7 /8 0 4 9 .4 7 1 9 .7 2 11.22 1 3 .6 0 1.21 2 5 /1 2 0 7 1 .6 7 1 8 .1 2 1 4 .0 1 1 4 .8 3 1 .0 6 2 9 /1 4 0 5 2 .4 5 1 5 .1 8 1 2 .5 1 1 7 .1 6 1 .3 7 3 3 /1 6 0 4 6 .9 1 1 7 .1 8 1 0 .6 1 1 3 .7 5 1 .3 0 3 6 /1 7 5 4 2 .7 3 1 6 .7 5 1 5 .4 0 1 4 .1 6 0 .9 2 4 0 /1 9 5 4 7 .3 4 1 6 .3 2 1 4 .7 0 1 6 .3 2 1.11 4 6 /2 2 5 1 0 .1 3 1 8 .4 8 1 5 .0 0 1 1 .2 8 0 .7 5 4 7 /2 3 0 4 7 .7 1 1 7 .3 1 1 3 .5 5 1 3 .8 5 1.02 4 8 /2 3 5 4 7 .5 9 1 7 .7 0 1 3 .3 9 1 4 .3 8 1 .0 7 4 9 /2 4 0 4 8 .2 3 1 7 .9 8 1 3 .0 7 1 4 .3 1 1 .0 9 5 0 /2 4 5 4 8 .7 0 1 7 .5 3 1 3 .3 2 1 3 .2 9 0 .9 9 5 1 /2 4 9 4 6 .3 6 1 7 .7 8 1 1 .8 0 1 5 .5 6 1 .3 2 MgO 38 FeO /M gO 1.0 1.4 2.2 1.6 2.4 2.6 2.6 40 80 ' THICKNESS 120 160 ' 200 . 240 260 FIGURE IS. F tO /M gO FROM RATIO SCALES OF FYROKEWES CREEK FLOW 39 d r i l l h o l e w h ic h p e n e t r a t e s t h e G r e e n s t o n e l a v a f l o w w h e re i t i s o n l y 108 f e e t t h i c k . T h e s e w e re a n a l y z e d ( T a b l e 6 ) an d t h e FeO/MgO r a t i o was g r a p h e d ( F i g u r e 1 7 ) . T h is r a t i o te n d e d t o i n c r e a s e to w a r d t h e c e n t e r o f t h e f l o w , a t r e n d t h a t was e x p e c t e d fro m t h e w ork o f H ess ( 1 9 4 1 ) . 40 T ab le 6 . S a m p le / D e p th C h e m ic a l A n a l y s e s o f t h e P y r o x e n e s f r o m t h e G r e e n s t o n e F lo w , Diamond D r i l l H o le 0 3 . S i 02 CaO MgO FeO A12°3 FeO / MgO 3 /1 0 5 0 .4 6 1 8 .8 8 1 6 .1 7 9 .3 5 6 .5 4 0 .5 7 8 4 /1 5 5 5 .0 3 1 8 .3 5 1 0 .8 9 9 .7 3 6.00 0 .8 9 3 8 /3 5 4 7 .5 5 2 0 .7 3 1 7 .6 6 1 4 .3 6 1 2 .6 0 0 .8 1 3 1 0 /4 5 4 1 .1 6 1 7 .1 4 2 5 .6 1 2 1 .9 3 1 0 .7 8 0 .8 5 6 1 5 /7 0 4 8 .7 4 1 7 .9 6 1 2 .6 5 1 2 .6 9 9 .3 4 1 .0 0 3 1 7 /8 0 4 7 .0 5 1 7 .1 4 1 3 .0 8 1 4 .0 8 1 0 .7 8 1 .0 7 6 21/100 4 6 .9 9 1 7 .0 4 1 3 .5 9 1 3 .2 1 10.10 0 .9 7 2 2 3 /1 0 8 4 9 .4 0 1 8 .3 9 1 6 .0 1 1 0 .9 0 7 .1 1 0 .6 8 0 41 FeO/MgO 20- TH IC K NE SS 4 O' SO' 10 o ' FIGURE 17. F « 0 / MgO RATIO OF PYROXENES FROM GREENSTONE FLOW 42 K e a r s a r g e F low The c h e m i c a l a n a l y s e s ( T a b l e 7 and F i g u r e 18) o f 13 s a m p le s fro m t h e K e a r s a r g e F low add s u b s t a n t i a l l y t o p r i o r s t u d i e s o f t h e P o r t a g e Lake L ava S e r i e s . T hese sam p les w ere ch o sen to c o r r e l a t e t h i s s t u d y w i t h p r e v i o u s c h e m i c a l s t u d i e s o f t h e Keweenawan l a v a flo w s. T w elve s a m p l e s w e r e t a k e n a t t h r e e f o o t i n t e r v a l s fro m t h e S t a r 10 diam o nd d r i l l h o l e i n Keweenaw C o u n ty . t h e t o t a l 3 2 19" t h i c k n e s s o f t h e f lo w i n t h i s T h is h o le p e n e t r a t e s lo c a tio n . One a d d i ­ t i o n a l s a m p le was t a k e n a t a d e p t h o f 12% f e e t f o r a n a l y s i s s i n c e m e g a s c o p ic s t u d y i n d i c a t e d t h e p o s s i b i l i t y o f u n i q u e l i t h o l o g y . A lth o u g h t h e f l o w i s o n l y 33 f e e t t h i c k i n t h i s lo c a tio n , t r e n d s r e m a r k a b l y s i m i l a r t o t h o s e f o u n d by B r o d e r i c k (1 9 3 5 ) i n t h e K e a r s a r g e Flow a r e r e v e a l e d by t h e s e c h e m i c a l a n a l y s e s . The u p p e r h a l f o f t h e f lo w h a s t h e h i g h e s t p e r c e n t a g e s o f S i 0 2 » T i 0 2 > Na2 0 , K2O, and MnO and t h e l o w e s t v a l u e s o f A ^ O ^ , CaO, and MgO. S in c e i r o n was a n a l y z e d a s FeO, p e t r o g r a p h i c s t u d y was co m b in ed w i t h t h e a n a l y s e s t o i n d i c a t e h i g h Fe2®3 and low FeO i n t h e to p p o r t i o n . T h e s e t e n d e n c i e s a r e m a x im iz e d i n s a m p le 6 t a k e n 12% f e e t b e lo w t h e to p w h e r e s e v e r a l d a r k brow n b a n d s 1 / 2 " t o 3 / 4 " t h i c k o c c u r . A n a ly se s o f t h i s s a m p le o f r o c k t a k e n f r o m s u c h a b a n d i n d i c a t e a v e r y h i g h am ount o f S i 02 and low p e r c e n t a g e s o f CaO, MgO, FeO, an d A ^ O ^ . s e c tio n stu d y in d ic a te s T h in t h a t t h i s ro c k i s c o a r s e r th a n th e su rro u n d in g r o c k , and q u a r t z an d a l b i t e a r e p r e s e n t a s e x p e c t e d . T h e s e b an d s o b v io u sly r e p r e s e n t d o l e r i t i c te n d e n c ie s d e s p i t e th e f a c t t h a t th e f lo w i s v e r y t h i n a t t h i s p o i n t . The a m y g d a l o i d a l zo n e h a s t h e e x p e c t e d h i g h p e r c e n t a g e o f F e 20g THIC KNESS IN FEET op >% -2 0% -10% AVG. MgO iO% -2 0 % -10% AVG. F«0 10% 20% .4 0 % -30% -2 0 % CHEMICAL -10% AVG. TiOz 10% 20% 30% FIGURE 18 COMPOSITION OF KEARSARGE DIAMOND DRILL HOLE STAR 10 -2 0 % AVG. -10% Al; FLOW 10% 20% AVS. 20% 30% -2 0 % 8 KEARSARGE E STAR 10 FLOW -10% Al, AVS. 10% 20% -2 0 % -10% MnO AVG. 10% 20% -3 0 % -2 0 % -10% Na.O 10% 20% 30% 40% 3 0% 10% 20 % -3 0 % -2 0 % -10% AVG. No 20 10% 20% 30% 40% 30% -6 0 % t— -5 0 % -4 0 % -3 0 % -2 0 % >_____ ,_>■. ■ < -10% 0. . . — — A—_ AVG. KgO 10% A 20% 90% .—.I — .. Table 7. Chemical Composition of the Kearsarge Lava Flow, Diamond Drill Hole Star 10. Sample D epth S i02 CaO MgO FeO T i0 2 A12°3 Na20 k 2o MnO 1 0 3 4 .4 3 2 7 .9 0 2.66 5 .1 7 1 .1 4 1 4 .9 6 0 .4 4 0.86 0 .1 0 7 2 3 3 7 .8 1 9 .6 1 9 .2 3 1 5 .2 2 2 .6 1 1 4 .9 2 0 .3 8 4 .0 5 0 .1 9 6 3 6 4 6 .9 9 7 .9 5 9 .4 0 1 1 .5 0 2 .5 6 1 5 .5 9 3 .2 6 0 .4 2 0 .2 2 3 4 9 4 8 .0 0 6 .7 2 8 .5 2 1 0 .9 4 2 .7 3 1 6 .8 9 3 .4 9 0 .3 7 0 .1 9 5 5 12 4 7 .3 6 5 .6 5 9 .0 3 1 0 .4 3 2 .7 0 1 6 .2 6 4 .5 1 0 .4 2 0 .2 1 4 6 1 2 .5 5 9 .8 2 2.22 7 .8 1 8 .9 3 1 .5 8 1 1 .7 4 2 .3 6 0 .9 7 0 .1 7 5 7 15 4 4 .3 8 8 .4 3 7 .9 0 1 4 .4 4 3 .0 1 1 4 .4 4 2.68 0 .6 1 0 .1 9 2 8 18 4 5 .7 3 6 .9 1 8 .2 8 1 2 .8 4 2 .4 6 1 5 .0 9 4 .0 2 0 .8 7 0 .2 0 3 9 21 4 5 .8 9 6 .3 3 9 .4 8 1 4 .4 1 2 .3 0 1 4 .9 4 4 .4 4 0 .5 7 0.211 10 24 4 5 .8 7 8 .4 6 8 .5 3 1 2 .6 3 2 .5 3 1 5 .4 3 2.68 0 .4 7 0 .2 0 5 11 27 4 8 .0 9 6 .9 5 8 .8 0 1 0 .5 8 2 .3 4 1 6 .0 2 3 .1 1 0 .8 1 0 .1 6 1 12 30 4 6 .3 8 8 .5 0 9 .6 3 1 0 .7 1 2 .0 4 1 6 .6 8 3 .1 1 0 .5 1 0 .1 7 2 13 3 2 .7 4 7 .5 9 5 .0 0 9 .2 0 1 2 .3 9 2 .3 4 1 5 .1 6 5 .3 5 0 .2 9 0 .1 4 5 45 an d t h e b a s a l c h i l l zone h a s a h i g h e r am ount o f FeO, S iC ^ , K2O, and T i 02 t h a n t h e r o c k i m m e d i a t e l y a b o v e . A s i m i l a r t e n d e n c y was fo u n d by C o r n w a l l (1 9 5 1 a ) i n t h e G r e e n s t o n e F lo w . Sam ple num ber one p r o d u c e d som ew hat an o m alo u s r e s u l t s d u e t o t h e l a r g e am ount o f c a l c i t e d e p o s i t e d i n v e s i c l e s i n t h e f lo w t o p . Sam ple t h i r t e e n , a t t h e b o t t o m , h a d a n e x c e s s o f Na20 e v i d e n t l y due t o a l t e r a t i o n . The p l a g i o c l a s e i n t h i s s a m p le was o l i g o c l a s e ( A n j ^ ) . C a l c u l a t i o n o f t h e FeO/MgO r a t i o b o t t o m t o t h e c e n t e r o f t h e f lo w . i n d i c a t e s a n i n c r e a s e fro m t h e Below t h e a m y g d a l o i d a l z o n e , w h ic h h ad a h i g h FeO/MgO r a t i o due to i r o n c o n c e n t r a t i o n , was r e l a t i v e l y in g d o l e r i t i c th e r a t i o low an d d e c r e a s e d downward u n t i l b e lo w t h e z o n e show­ te n d e n c ie s. f o r t h e FeO/MgO r a t i o C o r n w a ll (1 9 5 1 a ) fo u n d a s i m i l a r t r e n d i n t h e G re e n s t o n e Flow . T h e s e a n a l y s e s fo u n d t h e same d i s t r i b u t i o n o f o x i d e s t h r o u g h t h e f l o w a s was fo u n d by B r o d e r i c k ( 1 9 3 5 ) . T a b l e 8 s e r v e s t o c o m p a re t h e w o rk o f B r o d e r i c k (1 9 3 5 ) w i t h t h e p r e s e n t s t u d y . t h e two s e t s o f s a m p le s a r e : D i f f e r e n c e s b e tw e e n ( 1) t h i c k n e s s o f t h e f l o w w h e re s t u d i e d by B r o d e r i c k was 164 f e e t and (2 ) t h e p e g m a t i t i c l a y e r i n t h e p a r t o f t h e f lo w i n t h i s s t u d y i s v e r y d i s t i n c t a s co m p ared t o t h e v a g u e p e g m a t i t i c t e n d e n c y fo u n d e l s e w h e r e by B r o d e r i c k ( 1 9 3 5 ) . 46 T a b le 8 . C om parison o f C h em ical A n a ly s is o f Two D r i l l H o les i n th e K e a rsa r g e Lava F low . B r o d e r i c k (1 9 3 5 ) P r e s e n t S tu d y O x id e O p h ite D o le rite O p h ite D o le rite S i 02 4 8 .0 4 4 8 .7 8 4 5 .8 7 5 9 .8 2 A I 2O3 1 6 .8 8 1 4 .5 1 1 5 .4 3 1 1 .7 4 MgO 7 .1 2 6.11 8 .5 3 7 .8 1 CaO 9 .8 3 6 .3 5 8 .4 6 2.22 Na20 2 .3 9 4 .3 7 2.68 4 .5 1 K20 0 .4 6 0 .8 2 0 .4 7 0 .9 7 PETROLOGY The p r e s e n t s tu d y was c o n d u c te d o n ly on th e S c a le s C reek F low . P e tr o g r a p h ic t h in s e c t i o n s w ere p rep a red o f sa m p les c h o se n by m ega­ s c o p ic e x a m in a tio n o f th e c o r e . The f o l l o w i n g c o m p o s ite d e s c r i p t i o n i s b a sed on p e t r o g r a p h ic a n a l y s i s o f 188 sa m p les and i s c o n s id e r e d v a l i d b e c a u s e o f th e l a t e r a l h o m o g en eity o f th e f lo w . P e tro g ra p h ic D e s c rip tio n The m ain m in e r a ls i n th e S c a le s C reek Flow a r e la b r a d o r it e la t h s and a n h e d r a l, o p h i t i c a u g it e g r a in s w ith m inor amounts o f p i g e o n i t e and s u b h e d r a l, a l t e r e d o l i v i n e . h e m a t it e , and i l m e n i t e . A c c e s s o r y m in e r a ls in c lu d e m a g n e t it e , P l a g i o c l a s e ch a n g es from la b r a d o r it e in th e m ain body o f th e f lo w t o a l b i t e - o l i g o c l a s e n e a r th e top and b o tto m . The a m y g d a lo id a l f lo w to p s h a v e t y p i c a l red c o l o r a t i o n i n th e hand sp ecim en due to th e p r e s e n c e o f h e m a t it e . M in e r a ls fo rm in g th e groundm ass o f th e a m y g d a lo id a l to p s a r e random ly d i s t r i b u t e d , a l t e r e d p l a g i o c l a s e m i c r o l i t e s , o f t e n in r a d i a t i n g g r o u p s , su rrou n d ed by c h l o ­ r i t e and h e m a t it e t h a t o b s c u r e s a l l o t h e r m in e r a ls (P h o to 3 ) . G lom ero- p o r p h y r it ic grou p s o f p l a g i o c l a s e p h e n o c r y s ts show a l t e r a t i o n to c h l o r i t e , c a l c i t e , p a r a g o n it e , and e p i d o t e . Am ygdules o f th e flo w to p h ave b een f i l l e d w it h e p i d o t e , q u a r tz , p re h n ite , c a lc ite , c h lo rite , an d v a r i o u s z e o l i t e m i n e r a l s . M ost v e s i c l e s c o n t a in more th a n one m in e r a l, o f t e n h a v in g rim s o f e p id o t e or h e m a t it e and c e n t r a l f i l l i n g s o f q u a r tz o r c a l c i t e 47 (P h o to 4 ) . 48 V e in s o f q u a r tz o r c a l c i t e o f t e n c u t th e a m y g d a lo id a l z o n e . P h o to 3 . Flow Top Show ing P l a g i o c l a s e in M a trix o f H e m a tite . Amygdule i s F i l l e d w it h Q u artz and E p i d o t e . C r o s s e d N i c o l s , X 53, Sam ple L S 3 0 -1 . P h o to 4 . P o r t io n o f an Amygdule Show ing H em a tite and E p id o te Rims w it h C e n tr a l Q uartz F illin g . C ro ssed N i c o l s , X 53, Sam ple S L 5 -1 . The upper c h i l l zo n e o f th e f lo w i s a m i c r o c r y s t a l l i n e , a m y g d a lo id a l ro ck w it h a d i a b a s i c t e x t u r e . T h is g r a d e s downward th ro u g h a zon e o f s u b o p h it ic b a s a l t w it h i n t e r s t i t i a l p y ro x en e i n t o 49 an o p h i t i c t e x t u r e w ith th e p l a g i o c l a s e l a t h s p o i k i l i t i c a l l y in th e p y ro x en e (P h o to 5 ) . P h oto 5 . in c lu d e d The o p h i t i c t e x t u r e becom es c o a r s e r w ith P l a g i o c l a s e P o i k i l i t i c a l l y I n c lu d e d in P y r o x e n e . C ro sse d N i c o l s , X 133, Sam ple S L 5 -3 6 . d ep th i n th e f lo w u n t i l a p p r o x im a te ly th e c e n t e r , b elo w w h ich th e g r a in s i z e te n d s t o d e c r e a s e . E v id e n c e o f c r y s t a l s e t t l i n g i s found in la r g e p y ro x en e and o l i v i n e g r a in s t h a t o c c u r ab ove th e b a s a l c h i l l zone (P h o to 6 ) . In th e c e n t r a l o p h i t i c p o r t io n o f th e f lo w th e p l a g i o c l a s e m i c r o l i t e s o f t e n show a lig n m e n t around la r g e r m in e r a l g r a i n s . T hese la r g e r m in e r a l s , su ch a s a l t e r e d o l i v i n e and p l a g i o c l a s e l a t h s ap p ear to h ave b een p u shed a s i d e t o form c h a n n e ls th ro u g h w h ich m i c r o l i t e swarms moved (P h o to 7 ) . O th er m i c r o l i t e s ap p ea r i n a s w ir le d a r r a n g e ­ m ent in th e m a tr ix g i v i n g th e im p r e s s io n t h a t th e magma c r y s t a l l i z e d under m o b ile and som ewhat t u r b u le n t c o n d it io n s (P h o to 8 ) . T h is i s a l s o n o te d in th e p y r o x e n e s , may o f w h ich c o n t a in p o i k i l i t i c a l l y in c lu d e d , s e m i- a lig n e d f e ld s p a r m i c r o l i t e s . P y ro x en es o f th e c e n t r a l f lo w p o r t io n a r e n o t s i n g l e c r y s t a l s b u t 50 P h o to 6 . L a r g e P l a g i o c l a s e and P y r o x e n e Above th e B a sa l C h i l l Z one. C ro ssed N i c o l s , X 80, Sam ple S L 5 -4 6 . Ph oto 7 . M i c r o l i t e Swarm Around A lt e r e d P yroxene and P l a g i o c l a s e . C ro sse d N i c o l s , X 133, Sam ple G 7S-16. grou p s o f random ly o r ie n t e d s m a ll eq u an t c r y s t a l s s e t in a m a tr ix o f c h l o r i t e , p l a g i o c l a s e m i c r o l i t e s , and m a g n e tite g r a i n s . Two p y r o x e n e s , a u g it e and p i g e o n i t e , o c c u r m u tu a lly , a lth o u g h a u g it e i s th e m ost abundant a s th e p i g e o n i t e o c c u r s o n ly a s t r a c e am ounts. v i s i b l e e x s o l u t i o n la m e lla e a r e p r e s e n t in th e p y r o x e n e s . No T h is , a lo n g w it h th e la c k o f h y p e r s t h e n e , i s t o be e x p e c te d from th e s t u d i e s 51 P h oto 8 . M i c r o l i t e s Show ing S w ir le d A rrangem ent. C ro sse d N i c o l s , X 80, Sam ple N K 3-18. o f H ess (1 9 4 1 ) a lth o u g h C o rn w a ll (1 9 5 1 a ) d id f in d a s m a ll amount o f h y p e r s th e n e in some t h ic k f l o w s . D i s t i n c t i o n b etw een a u g it e and p i g e o n i t e , w h ich was d i f f i c u l t i n c a s e s b e c a u s e th e p i g e o n i t e o c c u r s i n su ch s m a ll g r a i n s , was made m a in ly on th e b a s i s o f 2V a n g le s e s t im a t e d from o p t i c a x i s f i g u r e s o b ta in e d w it h a p e tr o g r a p h ic m ic r o ­ s c o p e . The 2V f o r p i g e o n i t e i s 1 5° and f o r a u g i t e i s 4 2 ° . t e s t s w ere n o t made due to d i f f i c u l t y In d ex i n w o rk in g w it h th e fra g m en ts and s o no e s t im a t e s o f m o le c u la r c o m p o s it io n a r e a v a i l a b l e . The m a g n e tite o c c u r s a s b le b s i n th e m a tr ix b etw een p l a g i o c l a s e la th s . A lt e r e d o l i v i n e i s a l s o fou n d i n th e m a tr ix and som etim es i s in c lu d e d in th e p y ro x en e g r a n u le s . Many la r g e p l a g i o c l a s e la t h s o c c u r in g lo m e r o p o r p h y r itic m a sses i n th e m a t r ix . T hese l a t h s a r e o f t e n f r a c t u r e d a c r o s s t h e i r b rea d th and i n c i p i e n t a l t e r a t i o n to c h l o r i t e has ta k e n p la c e a lo n g t h e s e f r a c t u r e s . V ery c o a r s e - g r a in e d d o l e r i t i c o r p e g m a t it ic c o n c e n t r a t io n s o f e u h e d r a l l a t h s o f o l i g o c l a s e - a n d e s i n e and a u g it e ( f e r r o a u g i t e ? ) o c c u r n e a r th e top o f th e f lo w and p o s s i b l y n e a r th e b o tto m (P h o to 9 ) . 52 Ph oto 9 . D o l e r i t i c Zone Show ing L arge A lt e r e d P l a g i o c l a s e L ath s and Q u a r tz . C ro ssed N i c o l s , X 80, Sam ple NK3-9. T h ese z o n e s a r e in d ic a t e d on F ig u r e s 7 th rou gh 14. itic The u p per d o l e r ­ zo n e i s b e t t e r d e v e lo p e d th a n th e lo w er zon e a lth o u g h i t ca n be d i s t i n g u i s h e d by b o th p e t r o g r a p h ic s tu d y and c h e m ic a l a n a l y s i s (P h o to 1 0 ) . P e g m a t it ic z o n e s have b een r e c o g n iz e d f o r many y e a r s i n th e upper p o r t io n s o f Keweenawan la v a f lo w s b u t h ave n o t b een r e p o r te d b e f o r e f o r th e lo w e r p o r t io n s o f su ch f l o w s . O b s e r v a tio n i n d i c a t e s t h a t th e t h ic k n e s s and th e c o a r s e n e s s o f th e u p per d o l e r i t e i s p r o p o r t io n a l to th e la v a flo w t h i c k n e s s . In te r ­ s t i t i a l t o th e la r g e l a t h s o f p l a g i o c l a s e i n t h e s e p e g m a t it ic zo n es a r e s m a lle r g r a in s o f d e n d r i t i c m a g n e t it e , h e m a t it e , i l m e n i t e , and q u a r tz . The upper d o l e r i t i c zo n e i s h ig h ly a l t e r e d . P l a g i o c l a s e has ch an ged to e p i d o t e , p a r a g o n it e , c a r b o n a t e , p u m p e lly it e , and c h l o r i t e . A u g ite h as a l t e r e d to c h l o r i t e and s e c o n d a r y h o rn b len d e (P h o to 1 1 ) . A u g ite and la b r a d o r i t e a r e s l i g h t l y a l t e r e d . a l l c a s e s , b een d e s t r o y e d by s e c o n d a r y a l t e r a t i o n . i The o l i v i n e h a s , i n The a l t e r a t i o n P h oto 10. L arge A lt e r e d P l a g i o c l a s e L a th s and Q u artz in th e B ottom D o l e r i t i c Zone. C ro ssed N i c o l s , X 80, Sam ple NK3-54. P h o to 11. P yroxen e A lt e r e d to S eco n d a ry H o rn b len d e. C ro sse d N i c o l s , X 200, Sam ple NK3-24. p r o d u c ts a r e c h l o r i t e , s e r p e n t i n e , m a g n e t it e , h e m a t it e , i d d i n g s i t e , and b o w l in g it e . In many i n s t a n c e s , i t i s f e l t by th e a u th o r t h a t th e a l t e r a t i o n p r o d u c ts o f th e o l i v i n e o c c u r a s a f i n e - g r a i n e d i n t e r ­ m ix tu r e la c k in g d e f i n i t e o p t i c a l p r o p e r t i e s . B o w lin g it e , a m agnesium - r i c h c l a y m in e r a l, i s c h a r a c t e r iz e d by g r e e n c o l o r , s t r o n g p le o c h r o is m , t h ir d o r d e r i n t e r f e r e n c e c o l o r s , and la m e lla r s t r u c t u r e w it h e x t i n c t i o n 54 p a r a l l e l to th e la m e lla . I d d i n g s i t e a p p ea rs a s a d a rk , r e d d is h - brown s u b s ta n c e w it h la m e lla r s t r u c t u r e and t h ir d o r d e r in t e r f e r e n c e c o lo r s. I t h a s b een shown t h a t i d d i n g s i t e i s n o t a m in e r a l s i n c e x - r a y d i f f r a c t i o n i n d i c a t e s th a t: " — g o e t h i t e i s th e o n ly c r y s t a l l i n e p h a se and t h a t th e o t h e r s u b s ta n c e s shown by c h e m ic a l a n a l y s i s t o o c c u r in i d d i n g s i t e a r e l a r g e l y am orphous, I d d i n g s i t e , may t h e r e f o r e b e r e g a r d e d a s a com p lex a l t e r a t i o n p r o d u c t o f o l i v i n e r a t h e r th a n a s a pu re m in e r a l. (S u n , 195 7, p . 5 2 5 ) . P y r o x e n e , w here a l t e r e d , has ch an ged m a in ly t o c h l o r i t e v a r i e t y p e n n i n i t e , m a g n e t it e , o r a c o m b in a tio n o f th e tw o. Some p y r o x e n e s h ave a l t e r e d e n t i r e l y to c h l o r i t e , o t h e r s a lm o s t e n t i r e l y t o m a g n e t it e , i n b o th in s t a n c e s p r e s e r v in g th e o r i g i n a l o p h i t i c t e x t u r e w it h r e l i c t p la g io c la s e s t i l l v i s i b l e (P h o to 1 2 ) . W&m p h o t o 12. P y r o x e n e A l t e r e d M a in l y t o C h l o r i t e an d Some M a g n e tite w ith R e l i c t P la g i o c la s e . P la in P o l a r i z e d L i g h t , X200, S am ple S L 5 -1 4 . P l a g i o c l a s e i s u s u a l l y f r e s h i n t h e m a in p o r t i o n o f t h e f l o w , t h e m o s t common a l t e r a t i o n p r o d u c t s b e i n g p a r a g o n i t e an d c h l o r i t e . In th e h ig h ly a l t e r e d d o l e r i t i c zones th e p la g io c la s e i s a l t e r e d to 55 c h l o r i t e , p a r a g o n it e , e p i d o t e , and a p o s s i b l e c a r b o n a te m in e r a l. R e s o r b tio n o f p l a g i o c l a s e l a t h s o c c u r s i n la r g e p a tc h e s o f c h l o r i t e ro ck a l t e r a t i o n . P e t r o g e n e s is A number o f i n t e r e s t i n g o b s e r v a t io n s w ere made d u r in g th e c o u r s e o f t h i s s tu d y t h a t may be b e n e f i c i a l to th e know led ge o f th e P o r ta g e Lake Lava S e r i e s i n p a r t i c u l a r and Keweenawan g e o lo g y i n g e n e r a l. T here w ere p r o b a b ly th r e e e p is o d e s in v o lv e d i n th e c r y s t a l l i z a ­ t i o n h i s t o r y o f th e magma w h ich r e s u l t e d i n th e S c a le s C reek F low . The f i r s t in v o lv e d th e fo r m a tio n o f o l i v i n e and c a l c i c p l a g i o c l a s e c r y s t a l s b e f o r e th e magma was e x tr u d e d . T h ese c r y s t a l s ap p ear as p h e n o c r y s ts i n th e flo w to p and b ottom . E p iso d e two in v o lv e d th e c r y s t a l l i z a t i o n o f m ost o f th e magma and d i s t r i b u t i o n o f th e m ajor ro c k fo rm in g m in e r a l s . The f i r s t m in e r a ls t o form d u r in g t h i s e p is o d e w ere o l i v i n e , c a l c i c p l a g i o ­ c l a s e , and p erh a p s some t it a n iu m - r i c h m a g n e t it e . L a te r c a l c i c - p y ro x en e c r y s t a l l i z a t i o n commenced a s i n d ic a t e d by p l a g i o c l a s e l a t h s and some o l i v i n e g r a in s e n c lo s e d i n p y r o x e n e s . Most o f th e e a r l y form ed o l i v i n e s and some c a l c i c - p l a g i o c l a s e l a t h s w ere f o r c e d a s id e s o t h a t t h e s e m in e r a ls a r e i n t e r s t i t i a l to th e o p h i t i c p y ro x en e c r y s ta ls . The f i r s t p y ro x en e may have form ed by o l i v i n e r e a c t in g w ith th e r e s i d u a l l i q u i d w h erea s l a t e r p y ro x en e form ed d i r e c t l y from th e m e lt . A p h a se d ia g ra m (F ig u r e 19) w hich c l o s e l y r e p r e s e n t s th e g e n e r a l c r y s t a l l i z a t i o n b e h a v io r o f su c h b a s a l t i c magma i s in c lu d e d . T h is 56 t e t r a h e d r o n h a s a s i t s v e r t i c e s two p l a g i o c l a s e s , a l b i t e a n d a n o r t h i t e , and two p y r o x e n e s , d i o p s i d e and f e r r o s i l i t e . F o r th e S c a le s C reek Flow t h e p o i n t r e p r e s e n t i n g t h e magma c o m p o s i t i o n l i e s w e l l i n t o t h e p la g io c la se f ie ld . T h is w o u ld i n d i c a t e t h a t t h e p l a g i o c l a s e w o u ld b e g in to c r y s t a l l i z e b e f o r e th e p y ro x en e and t h i s i s i n d i c a t e d by th e o p h itic te x tu re . Fs B o u n d ary B etw een P l a g i o c l a s e and Pyroxene S c a le s C reek Magma — >An Ab F ig u r e 19. P hase Diagram A p p lic a b le to B a s a l t i c Magma C r y s ta lliz a tio n . D u r in g m o s t o f t h e c r y s t a l l i z a t i o n t h e p y r o x e n e fo rm ed was a u g i t e w h ic h c a n be c o n s i d e r e d a s a n i n t e r m e d i a t e member i n t h e d i o p s i d e h e d e n b e r g i t e s e r i e s w i t h some alum in um s u b s t i t u t i o n . W ith s l o w e r c o o l i n g t h e p y r o x e n e w o uld n o r m a l l y become e n r i c h e d i n i r o n . C h anges i n o p t i c a l p r o p e r t i e s i n t h e p y r o x e n e s to w a r d t h e c e n t e r o f t h e f lo w w h e re t h e c o o l i n g was s l o w e r i n d i c a t e e n ric h e d in iro n . t h a t t h e a u g i t e was b eco m in g T h e r e i s a l s o a n i n c r e a s e i n t h e FeO/MgO r a t i o , 57 in d ic a t e d c h e m ic a lly , tow ard th e c e n t e r o f th e f lo w . A s m a ll amount o f i n t e r s t i t i a l p i g e o n i t e was formed d u r in g th e l a s t s t a g e s o f t h i s e p is o d e . T h is p i g e o n i t e i s p ro b a b ly p rim a ry . Some c o n c lu s io n s ca n be drawn from th e tw e n t y -f o u r c h e m ic a l a n a ly s e s o f th e a u g i t e s . C o m p o sitio n s o f th e a u g it e s (T a b le 4 ) from th e top and b o tto m p o r t io n s o f th e S c a le s C reek f lo w t h a t c o o le d m ost r a p id ly h a v e a c o n t r a s t i n g tren d when com pared to th e more s lo w ly c o o le d flo w i n t e r i o r when p l o t t e d on th e w o l l a s t o n i t e - e n s t a t i t e f e r r o s i l i t e p y ro x en e diagram (F ig u r e 2 0 ) . Wo Hd PLUTONIC TREND CHILL TREND En F ig u r e 2 0 . P yroxen e Trends o f th e S c a le s C reek Flow i n Diamond D r i l l H ole S t . L o u is 5 . A u g it e s from th e flo w i n t e r i o r form a tr e n d s i m i l a r to t h a t f o r p lu t o n ic r o c k s as found by Wager and Brown (1 9 6 8 ) f o r S k a erg a a rd a u g ite s . T h is p a th f o ll o w s th e one found by H ess (1 9 4 1 ) and may 58 r e p r e s e n t a n a p p r o a c h t o s t a b l e p a r t i t i o n i n g o f c a l c i u m , m a g n esiu m , an d i r o n b e t w e e n t h e m e l t a n d c r y s t a l s . C h i l l zo n e a u g i t e s seem t o fo rm a " q u e n c h t r e n d " T ille y , (M u ir and 1964) c h a r a c t e r i z e d by i r o n - c a l c i u m s u b s t i t u t i o n w i t h r e l a ­ t i v e l y c o n s t a n t m ag nesiu m . T h e s e a u g i t e s w o u ld be n o n - e q u i l i b r i u m . S e v e r a l a n a l y s e s o f p y r o x e n e s fro m t h e G r e e n s t o n e Flow may y i e l d a s im ila r tre n d ( F i g u r e 21) a l t h o u g h n o t en o u g h a n a l y s e s , o n l y e i g h t , w e r e c o m p le te d t o d e t e r m i n e a c c u r a t e l y t h e p y r o x e n e t r e n d s . Wo Hd CHILL TREND PLUTONIC TREND En F i g u r e 21. P y r o x e n e T r e n d s o f t h e G r e e n s t o n e Flow i n Diamond D r i l l H ole O s c e o l a 3 . S i m i l a r t r e n d s w e re fo u n d i n Keweenawan l a v a s o f M in n e s o t a by Konda and G r e e n (1 9 7 4 ) and i n a f lo w o f t h e C o lu m b ia R i v e r b a s a l t s by S m ith and L i n c l s l e y ( 1 9 7 1 ) . As t h e e a r l y c r y s t a l s f o r m e d , t h e m e l t was e n r i c h e d i n s i l i c o n , 59 s o d iu m , and i r o n . T h is e n r i c h m e n t was e n h a n c e d by s e t t l i n g o f o l i v i n e and p y r o x e n e t o t h e b a s e o f t h e f lo w . The e n r i c h m e n t o f i r o n to w a r d s t h e l a t e r - f o r m i n g c e n t r a l p o r t i o n o f t h e f lo w h a s a l ­ r e a d y b e e n m e n tio n e d f o r t h e p y r o x e n e s . F u rth e r ev id en ce o f t h i s c a n be fo u n d i n i r o n o x i d e b an d s n e a r t h e f lo w c e n t e r and i n o l i v i n e a lte ra tio n . The o l i v i n e o f t h e c e n t r a l p o r t i o n o f t h e f lo w h a s r im s o f h e m a t i t e and t h e c e n t e r s h a v e a l t e r e d t o i d d i n g s i t e , w h ic h M ingS h an Sun (1 9 5 7 ) fo u n d i n d i c a t i v e o f i r o n - r i c h o l i v i n e s . No i d d i n g s ­ i t e a l t e r a t i o n i s fo u n d i n t h e o l i v i n e s o f t h e f lo w b o tto m . E p i s o d e t h r e e o f t h e S c a l e s C r e e k Flow s o l i d i f i c a t i o n i n v o l v e s a l t e r a t i o n by t r a p p e d a q u e o u s v o l a t i l e s . A c tu a lly , th e v o l a t i l e phase was a c t i v e t h r o u g h o u t t h e c r y s t a l l i z a t i o n o f t h e f l o w , t r a n s f e r r i n g and c o n c e n t r a t i n g t h e s o d iu m , p o t a s s i u m , s i l i c o n , and t i t a n i u m n e a r t h e f lo w to p an d b o tt o m t o p r o d u c e t h e p e g m a t i t i c d o l e r i t i c z o n e s . The v o l a t i l e movement was e v i d e n t l y much g r e a t e r to w a rd t h e f lo w to p t h a n t h e b o t t o m a s t h e b o t t o m d o l e r i t e i s n o t a s w e l l d e v e l o p e d as i n t h e u p p e r p a r t o f t h e f lo w . The e x t e n s i v e n e s s o f t h e a l t e r a t i o n s p r o d u c e d by t h e v o l a t i l e s i s d i f f i c u l t to a s s e s s . P a t c h e s o f c h l o r i t e i n t h e f lo w c e n t e r p r o b a b l y r e p r e s e n t aqueous s o lu ti o n s fo rm ed s i l i c a t e s . t r a p p e d i n t h e f lo w t h a t a t t a c k e d e a r l i e r R e l i c t p l a g i o c l a s e c a n be s e e n i n t h e s e p a t c h e s . The m e l t may h a v e b e e n s t i l l m o b i l e a t t h i s t i m e a s t h e p l a g i o c l a s e l a t h s a r e a l ig n e d around th e edges o f th e s e p a t c h e s . I t is p o ssib le t h a t s o d iu m , c a r r i e d by t h e v o l a t i l e s , a l b i t i z e d t h e f lo w to p and b o tt o m w i t h t h e r e l e a s e d c a l c i u m an d alum inum f o r m i n g h y d r o u s s i l i c a t e s s u c h a s e p i d o t e , p r e h n i t e , and z e o l i t e s . N o r m a ll y , t h e to p and b o tt o m 60 o f a la v a flo w sh o u ld have c a l c i c p l a g i o c l a s e r e p r e s e n t a t i v e o f th e f i r s t m in e r a ls to form from th e magma. A l t e r n a t e l y , th e flo w top a l t e r a t i o n m igh t be due to l a t e r o r e - b e a r in g s o l u t i o n s . CONCLUSIONS 1. D o le rite i s a te r m t h a t s h o u l d be r e s e r v e d f o r r o c k u n i t s w i t h i n t h e l a v a flo w s t h a t show a c h e m i c a l c o n c e n t r a t i o n o f Na2 0 , ^ 0 , and S i 02 w h eth er o r n o t th e y a r e c o a r s e l y o r f i n e l y c r y s t a l l i n e . B ecause o f f i n e t e x t u r e , n o t a l l d o l e r i t i c la y e rs are reco g n ized w ith ease p e t r o g r a p h ic a l ly . 2. D o l e r i t i c zones o c c u r n e a r a s n e a r t h e to p w h ere t h e y 3. C h e m ic a l t r e n d s w i t h i n t h e t h e b o tt o m o f t h e l a v a f l o w s , a s w e l l p re v io u s ly have been rec o g n iz e d . S c a l e s C r e e k Lava Flow h a v e l a t e r a l c o n s i s t e n c y and p r o b a b l y a l l o f t h e f lo w s show t h i s c h a r a c t e r i s t i c . 4. A u g i t e s fro m t h e S c a l e s C r e e k Flow show a d e f i n i t e c h i l l t r e n d an d p l u t o n i c t r e n d . 61 APPENDIX A APPENDIX A A n a l y t i c a l T e c h n iq u e s Rock s a m p le s t o b e a n a l y z e d w ere g ro u n d t o p a s s t h r o u g h a 200 mesh s i e v e . The p o w dered s a m p le was d i v i d e d i n t o two p o r t i o n s and d r i e d a t 110°C . One p o r t i o n was f u s e d w i t h Na^CO^, and S i0 2 and MgO w e re d e t e r m i n e d by g r a v i m e t r i c m e t h o d s . m e tric a lly . CaO was m e a s u r e d t i t r a - The s e c o n d p o r t i o n was d i s s o l v e d w i t h h y d r o f l u o r i c a c i d an d N a20, K^O, FeO, A ^ O ^ , an d HnO w e re d e t e r m i n e d w i t h a P e r k i n - E l m e r a t o m ic a b s o r p t i o n s p e c t r o p h o t o m e t e r . Random sa m p les w e re c h e c k e d f o r r e p e a t a b i l i t y . A m a j o r a t t e m p t was made t o s e p a r a t e t h e p y r o x e n e s fro m ro ck s a m p le s f o r c h e m i c a l a n a l y s i s . 1. The f o l l o w i n g p r o c e d u r e was fo llo w e d : The r o c k was g ro u n d t o p a s s t h r o u g h a 200 mesh s i e v e . F in e g r i n d i n g was n e c e s s a r y t o s e p a r a t e t h e p o i k i l i t i c m i n e r a l a g g re g a te s. 2. Ground r o c k m a t e r i a l was d e n s i t y s e p a r a t e d i n 1 , 1 , 2 , 2 3 t e t r a b r o m o e t h a n e w i t h a d e n s i t y o f 2 .9 6 g r a m s / c e n t i m e t e r . 3. Heavy m i n e r a l s fro m th e t e t r a b r o m o e t h a n e s e p a r a t i o n w e re f u r th e r d e n sity sep arated 3 .2 4 g r a m s / c e n t i m e t e r . in d iio d o m eth an e w ith a d e n s i t y o f At t h i s s ta g e th e s e t t l i n g f r a c t i o n was e s s e n t i a l l y m a g n e t i t e and p y r o x e n e . 4. M a g n e tic s e p a r a t i o n was u t i l i z e d t o rem ove m a g n e t i t e f ro m t h e 6 2 63 pyroxene sa m p le s. T his d id n o t f u n c ti o n w e ll as th e f i n e l y d iv id e d pyroxene p a r t i c l e s te n d ed to behave " m a g n e tic a lly " e v i d e n t l y due t o s u r f a c e c h a r g e s . R e p e a te d m a g n e t i c s e p a ­ r a t i o n e v e n t u a ll y produced v e ry sm a ll u n c o n tam in a ted pyroxene sam p les. 5. O p t i c a l s tu d y in d i c a t e d , in m ost c a s e s , a c o m p o s ite p y roxen e sa m p le com posed o f p i g e o n i t e a n d a u g i t e . Good p h y s i c a l s e p a r a t i o n o f t h e s e two p y ro x en es i s n o t p o s s i b l e b e c a u se t h e i r r a n g e s o f m a g n e t i c s u s c e p t i b i l i t y and d e n s i t y o v e r la p . Hess a l s o found t h i s f o r f in e - g r a i n e d r o c k s in h i s s t u d i e s : "T he b e s t t h a t c o u ld be done was to p rod u ce an a u g it e and a p i g e o n i t e c o n c e n t r a t e , a n a ly z e b o th , and from th e p r o p o r tio n s p r e s e n t in ea ch sam ple c a l c u l a t e th e c o m p o s itio n s o f th e pure m in e r a ls — " (H e s s , 19 4 9 , p . 627). T w e n t y - f o u r p y r o x e n e s a m p le s w e re g i v e n p a r t i a l c h e m i c a l a n a l y s e s . A f t e r f u s i o n w i t h Na2C0^, t h e i r o n an d c a l c i u m w e re d e t e r m i n e d by t i t r a t i o n and t h e s i l i c a and m ag nesium by g r a v i m e t r i c m e th o d s . APPENDIX B APPENDIX B Description of the St. Louis 5 Drill Core T w e n ty - s e v e n d r i l l c o r e s a m p le s fro m t h e S t . L o u i s diam ond d r i l l h o l e number 5 a r e d e s c r i b e d h e r e a s r e p r e s e n t a t i v e o f t h e S c a l e s C r e e k Flow b e c a u s e a l l o f t h e m a j o r p e t r o g r a p h i c f e a t u r e s fo u n d i n t h e S c a l e s C re e k Flow a p p e a r i n t h e s e s a m p l e s . d e s c r i b e d i n s e q u e n c e from to p t o b o tto m . T hese a r e A t o t a l th ic k n e ss of 249 f e e t i s r e p r e s e n t e d by t h e s a m p l e s . S L 5 -1 : 0 f e e t b elo w t o p . A m y g d a lo id a l f lo w t o p . Amygdules 0 . 4 t o 3 . 2 m i l l i m e t e r s i n d ia m e te r a re f i l l e d w ith e p id o te , c a l c i t e , V e in s o f e p i d o t e c u t t h e r o c k . q u a r t z , an d z e o l i t e s . H e m a t i t e m asks m o s t o f t h e m i n e r a l s e x c e p t p l a g i o c l a s e and i s c o n c e n t r a t e d a ro u n d rim s o f t h e a m y g d u le s . P la g io c la s e o ccu rs as g lo m e ro p o rp h y ritic p h e n o c ry sts o f a n d e s in e , 0 .4 to 0 ,6 m illim e te rs lo n g w h ic h a r e a l t e r e d t o c h l o r i t e , c a l c i t e , an d e p i d o t e , and a s a l t e r e d m i c r o l i t e s . S L 5 -2 : 4 f e e t b elo w t o p . H ig h l y a l t e r e d r o c k w i t h a few a m y g d u le s . A l a r g e am ygdule i s l i n e d w i t h c h l o r i t e an d e p i d o t e , and c e n t r a l l y f i l l e d w i t h l a u m o n t i t e v e in e d w ith c h l o r i t e . P l a g i o c l a s e l a t h s , 0 .4 to 1 .2 m i l l i m e t e r s lo n g , a r e n o t o r i e n t e d , h a v e t h e c o m p o s i t i o n o f a n d e s i n e (An3 ^ ) , and a r e h i g h l y a l t e r e d t o c h l o r i t e and c a l c i t e . 64 I n t e r s t i t i a l c h l o r i t e occurs 65 b e t w e e n l a t h s and may r e p r e s e n t o r i g i n a l g l a s s . m e te rs in d ia m e te r, o ccu rs i n t e r s t i t i a l l y . Some p y r o x e n e g r a i n s a r e f r e s h and o t h e r s a r e h i g h l y a l t e r e d t o c h l o r i t e . a lte re d to h e m a tite and le u c o x e n e . S L 5 -3 : 10 f e e t b e lo w t o p . P yroxene, 0 .4 m i l l i ­ M ag n etite is A h i g h l y a l t e r e d r o c k , c o a r s e r g r a i n e d t h a n s a m p le 2 . P y ro x e n e i s i n t e r s t i t i a l and h i g h l y a l t e r e d t o c h l o r i t e , and some i s t o t a l l y c h l o r i t i z e d w i t h r im s o f h e m a t i t e . lo n g (up t o 1 .2 m i l l i m e t e r s ) Much c h l o r i t e i s i n t e r s t i t i a l to b l a d e d l a t h s o f a n d e s i n e (An3 £ ) . Den­ d r i t i c m a g n e t i t e c r y s t a l s a r e a l t e r e d t o h e m a t i t e and le u c o x e n e . S m a l1 o l i v i n e g r a i n s a r e a l t e r e d S L 5 -4 : to c h l o r i t e . 15 f e e t b e lo w t o p . C o a r s e r g r a i n e d t h a n s a m p le 3 . a n d e sin e M a in ly u n o r i e n t e d l a t h s o f ( A ^ ^ ) up t o 1 . 4 m i l l i m e t e r s l o n g , siv e ly a lte re d th a t have been e x te n ­ t o c h l o r i t e , e p i d o t e , and p a r a g o n i t e . C o n sid e ra b le i n t e r s t i t i a l c h l o r i t e , m a g n e t i t e , and p y r o x e n e i s p r e s e n t . The m a g n e t i t e h a s a l t e r e d t o h e m a t i t e an d l e u c o x e n e , and t h e p y r o x e n e has a lte r e d to c h l o r i t e and m a g n e t i t e . A q u a r tz v e in c u ts th e ro c k . S am p les 2 , 3 , and 4 may r e p r e s e n t a p o s s i b l e d o l e r i t i c S L 5 -5 : la y e r. 20 f e e t below t o p . Two s i z e s o f p l a g i o c l a s e a r e p r e s e n t i n t h i s r o c k . la b ra d o rite (A n^) l a t h s up to 4 . 2 m i l l i m e t e r s g lo m e ro p o rp h v ritic a lly . L a rg e lo n g a r e a r r a n g e d S m a ll, u n o r ie n te d p l a g i o c l a s e m i c r o l i t e s a r e i n c l u d e d i n p y r o x e n e s w h ic h h a v e d i a m e t e r s up to 1 . 6 m i l l i m e t e r s ( P h o to 1 3 ) . O t h e r m i c r o l i t e s a r e a l i g n e d b e tw e e n t h e p y r o x e n e c r y s t a l s . The p l a g i o c l a s e i s q u i t e f r e s h b u t i s a l t e r e d t o c h l o r i t e and e p i d o t e a lo n g f r a c t u r e s . C h l o r i t e p a t c h e s a r e i n t e r s t i t i a l t o p l a g i o c l a s e and 6 6 some c h l o r i t e c o v e r s t h e p l a g i o c l a s e . S m a ll o l i v i n e c r y s t a l s a r e a lte re d to b o w l i n g i t e , c h l o r i t e , c ry sts, t h i s s a m p le i s f i n e r g r a i n e d t h a n num ber 4 . P h o to 13. S L 5-6: and a n t i g o r i t e . P y r o x e n e w i t h P o i k i l i t i c P l a g i o c l a s e and A lte re d O liv in e . C r o s s e d N i c o l s , X80, Sam ple S L 5-5 . 25 f e e t b e lo w t o p . T h i s s a m p le d i f f e r s little fro m num ber 5 . co n ta in p la g io c la s e m ic r o lite s . a n h e d ra l pyroxene g r a in s . 0 .6 m illim e te r s slig h tly E xcept f o r pheno- lo n g , O p h itic pyroxenes M a g n e t i t e i s p r e s e n t b e tw e e n t h e Large l a b r a d o r i t e (Angg) l a t h s , 0 . 2 t o in g lo m e ro p o rp h y ritic groups, a re a l te r e d t o c h l o r i t e and e p i d o t e . I n te r s titia l c h lo rite and o l i v i n e h a s a l t e r e d as i n s a m p le 3 . is p re se n t Some p l a g i o c l a s e m i c r o l i t e s a re in c lu d e d . S L 5-7: 30 f e e t b e lo w t o p . P la g io c la se is ra d o rite la r g e r in th i s ro ck . G lo m e ro p o rp h y ritic la b ­ (Anr.g) i s a l t e r e d s l i g h t l y t o c a l c i t e , e p i d o t e , and c h l o r i t e . M i c r o l i t e s show a l i g n m e n t b e tw e e n p y r o x e n e g r a i n s . o liv in e is i n t e r s t i t i a l , a lth o u g h a l i t t l e M ost a l t e r e d a p p e a r s t o be p o i k i l i t i c a l l y 67 i n c l u d e d i n th e p y r o x e n e . M ost m a g n e t i t e i s a s s o c i a t e d w i t h a l t e r e d o l i v i n e , and some w i t h a l t e r e d p y r o x e n e . Some i n t e r s t i t i a l c h l o r i t e is present S L 5-8: 35 f e e t b elo w t o p . T h i s s a m p le i s c h a r a c t e r i z e d by two p y r o x e n e s . m i l l i m e t e r s ) , b ro w n , p o i k i l i t i c L a rg e (up t o 3 a u g i t e c r y s t a l s a r e t h e m a in p y r o x e n e w i t h m in o r am o unts o f p i g e o n i t e . L arge, c lu s te r e d la b ra d o rite (A n^) l a t h s v a r y fro m 0 . 9 m i l l i m e t e r s up t o 5 m i l l i m e t e r s and a r e o f t e n f r a c t u r e d w i t h c h l o r i t e and p a r a g o n i t e a l o n g t h e f r a c t u r e s and i n t h e c e n t e r s o f th e l a t h s . I n t e r s t i t i a l m i c r o l i t e s and a l t e r e d o l i v i n e occur. S L 5-9: 40 f e e t b elow t o p . D ark brown a u g i t e i s p r e v i o u s s a m p le . t h e m a in p y r o x e n e . V ery s i m i l a r t o t h e P l a g i o c l a s e i s a l t e r e d t o c h l o r i t e and i n t e r ­ s t i t i a l o l i v i n e i s a l t e r e d t o b o w l i n g i t e w i t h some a n t i g o r i t e . Much i n t e r s t i t i a l c h lo rite is p re se n t. S L 5 -1 0 : 45 f e e t b elo w t o p . P o ik ilitic a u g ite is l a r g e r , up t o 3 . 8 m i l l i m e t e r s a c r o s s , and d a r k e r brown due to i n c r e a s i n g i r o n c o n t e n t . L a b ra d o rite (A n ^) o c c u r s a s g l o m e r o p o r p h y r i t i c l a t h s a v e r a g i n g 1 .5 m i l l i m e t e r s and as m i c r o l i t e s in c lu d e d in th e p y ro x e n e . to c h l o r i t e . S L 5 -1 4 : P la g io c la se is a lte re d s lig h t ly I n t e r s t i t i a l c h l o r i t e occurs a ls o . 64 f e e t below t o p . T his rock i s h e a v i ly c h l o r i t i z e d . and a l s o as p y r o x e n e a l t e r a t i o n . of i n t e r s t i t i a l p ig e o n ite , C h lo rite occurs i n t e r s t i t i a l l y P y ro x e n e , m a in ly a u g i t e w ith a t r a c e is very p o i k i l i t i c . P la g io c la se m ic ro lite s a r e a l i g n e d a r o u n d p y r o x e n e and l a r g e p l a g i o c l a s e l a t h s , and a l s o 6 8 w i th i n th e p o i k i l i t i c p y ro x en es. O l i v i n e i s a l t e r e d m a i n l y to b o w lin g ite . S L 5 -1 7 : 80 f e e t b e lo w t o p . E x te n siv e a l t e r a t i o n t h i s sam p le. to c h l o r i t e and m a g n e t i t e c h a r a c t e r i z e s Much o f t h e c h l o r i t e h a s come fro m p y ro x e n e a l t e r a t i o n s i n c e f r e s h r e m n a n ts o f a u g i t e a r e s t i l l v i s i b l e . is h e a v ily covered w ith c h l o r i t e . b o w l i n g i t e , and s e r p e n t i n e . S L 5-21: O liv in e is a lte r e d to c h l o r i t e , Some p i g e o n i t e i s p r e s e n t . 100 f e e t b e lo w t o p . The r o c k i s n o t a s a l t e r e d a s i n s a m p le 17. la b ra d o rite has a lte r e d G lo m e ro p o rp h y ritic (An56) and l a r g e p o i k i l i t i c a u g i t e g r a i n s h a v e m i c r o ­ l i t e s a l i g n e d a r o u n d them . C h l o r i t e i s i n t e r s t i t i a l and p l a g i o c l a s e to c h l o r i t e an d e p i d o t e . occur i n t e r s t i t i a l l y . S L 5 -2 5 : L a b r a d o r i t e (An5 g) P i g e o n i t e and m a g n e t i t e b l e b s O l i v i n e i s a l t e r e d a s i n t h e a b o v e s a m p le . 120 f e e t b elo w t o p . Much c h l o r i t e i s p r e s e n t e s p e c i a l l y a s i n t e r s t i t i a l g r a i n s b e t ­ w een p l a g i o c l a s e . and m a g n e t i t e . c h lo rite . Pyroxene has a l t e r e d q u i t e e x t e n s i v e l y to c h l o r i t e L a b ra d o rite (An52) l i k e w i s e h a s b e e n r e p l a c e d by O liv in e has a l t e r e d t o a m i x t u r e o f c h l o r i t e and s e r ­ p e n tin e . S L 5 -2 9 : 140 f e e t b e lo w t o p . E ven more a l t e r e d c h lo rite . L a b ra d o rite fro m 0 . 6 t o sm a lle r, t h a n num ber 2 5 . C o n sid e ra b le i n t e r s t i t i a l (An5 8 ) , i n g l o m e r o p o r p h y r i t i c c l u s t e r s , v a r i e s 1 .0 m i l l i m e t e r s in le n g th . P y r o x e n e may b e a t r a c e g r a i n s up t o 5 . 6 m i l l i m e t e r s a r e fo u n d . p le n tifu l. O liv in e is q u ite 69 S L 5 -3 3 : 160 f e e t b elo w t o p . L a b ra d o rite (A n ^ ) c lu ste rs. l a t h s up t o 1 . 4 m i l l i m e t e r s a r e p r e s e n t i n S e m i-a lig n e d m i c r o l i t e s a r e around p o i k i l i t i c p y ro x e n e s. M ag n etite b le b s a r e p l e n t i f u l . c h lo rite , S L 5-36: O liv in e i s a l t e r e d to b o w lin g ite , and i d d i n g s i t e . 175 f e e t b elo w t o p . A lig n e d p l a g i o c l a s e m i c r o l i t e s a r e fo u n d a r o u n d l a r g e a l t e r e d g r a i n s , e i t h e r e a r l y o l i v i n e o r p y r o x e n e ( P h o to 1 4 ) . P h o to 14. L arge l a b r a d o r i t e gro u p s. P l a g i o c l a s e M i c r o l i t e s A l i g n e d B etw een L a r g e E a r l i e r Formed G r a i n s o f P l a g i o ­ c l a s e and O l i v i n e . C rossed N ic o ls , X200, Sam ple S L 5 -3 6 . (An,.,.) l a t h s a r e i n t h e u s u a l g l o m e r o p o r p h y r i t i c I n te r s titia l c h lo rite s i z e a s i n s a m p le 3 3 , b u t i s S L 5 -4 0 : is p re s e n t. lig h te r P y r o x e n e i s t h e same in c o lo r. 195 f e e t b elo w t o p . F a i r l y l a r g e am ount o f c h l o r i t e ro ck a l t e r a t i o n . L a b ra d o rite (An^g) l a t h s up t o 1 . 8 m i l l i m e t e r s h a v e c h a n g e d som ew hat t o c h l o r i t e . P y r o x e n e g r a i n s up t o 3 . 4 m i l l i m e t e r s a c r o s s i n c l u d e m i c r o l i t e s . 70 O liv i n e i s a l t e r e d to c h l o r i t e , S L 5-43: s e r p e n t i n e , b o w l i n g i t e , and i d d i n g s i t e . 210 f e e t b elo w t o p . V ery f r a c t u r e d s e c t i o n . la b ra d o rite P y r o x e n e ( a u g i t e w i t h a l a r g e 2V) and (An^g) a r e f r a g m e n t e d and a l t e r e d t o c h l o r i t e v,:-. ■'A . ■ . ■'1 " ■■ . ■■■■■. y P h o to 15. ( P h o to 1 5 ) . ■■ F r a c t u r e d P y r o x e n e G r a i n S u r r o u n d e d by S e m i - A l ig n e d M i c r o l i t e s , C h l o r i t e , and M a g n e tite . P l a i n P o l a r i z e d L i g h t , X80, Sam ple S L 5 -4 3 . Many s m a l l f r a g m e n t s o f a l t e r e d p y r o x e n e a r e d i s p e r s e d i n c h l o r i t e . A d d itio n a lly , c h l o r i t e occurs i n t e r s t i t i a l l y . i s seen i s p a r t o f th e s e c ti o n . a re co v ered w ith ir o n o x id e . c la se la th s . " P o i k i l i t i c m a g n e tite " F ra c tu re s in m in e ra ls in th e s e c tio n F i n e - g r a i n e d e p i d o t e i s fo u n d on p l a g i o ­ M a g n e tite has red i r o n o x id e in f r a c t u r e s . O liv in e is e x te n siv e ly a lte re d . S L 5-45: 220 f e e t belo w t o p . L a r g e am o unts o f " p o i k i l i t i c m a g n e t i t e " w i t h e x t e n s i v e l y a l t e r e d m ic ro lite s. P o i k i l i t i c pyroxene has been s t a i n e d w ith i r o n o x id e alo n g f r a c t u r e s , 16). and g r a d e s fro m f r e s h p y r o x e n e i n t o m a g n e t i t e ( P h o to S m a ll b l e b s o f m a g n e t i t e a r e fo u n d b e tw e e n l a b r a d o r i t e (An^g) 71 l a t h s t h a t h a v e a l t e r e d t o c h l o r i t e and e p i d o t e . L arger la th s are f r a c t u r e d and t h e s e f r a c t u r e s a r e f i l l e d w i t h t h e a l t e r a t i o n p r o d u c t s . A v e i n o f t h o m s o n i t e a n d c a l c i t e c u t s t h e s a m p le . P h o to 16. S L 5-46: P o i k i l i t i c P y r o x e n e S how ing A l t e r a t i o n to M a g n e tite . C r o s s e d N i c o l s , X200, S am p le S L 5 -4 5 . 225 f e e t b e lo w t o p . L arge (2 .4 m i l l i m e t e r s ) pyroxene w ith la r g e p la g io c la s e l a t h s in c lu d e d o c c u rs as a r e s u l t o f p ro b a b le c r y s t a l s e t t l i n g . S m a lle r (2 .0 m i lli m e t e r s o r l e s s ) , p o i k i l i t i c pyroxenes w ith m i c r o l i t e s a r e common. Some " p o i k i l i t i c m a g n e t i t e " i s a l s o s e e n , b e s i d e s s m a ll b le b s s u rro u n d in g a l t e r e d o l i v i n e and p y ro x en e. c a l c i t e o c c u r betw een a n d e s in e c h l o r i t e , c a l c i t e , and e p i d o t e . S L 5-47: C h l o r i t e and (An^g) l a t h s w h ic h h a v e c h a n g e d t o V ein s o f c h l o r i t e c u t t h e s a m p le . 230 f e e t b e lo w t o p . The r o c k i s q u i t e a l t e r e d . 1 .6 m i l l i m e t e r s P y ro x e n e i s s m a l l e r (maximum i s i n d i a m e t e r ) an d l i g h t i n c o l o r . p o i k i l i t i c b u t m ost i s in te rstitia l. Some p y r o x e n e i s P la g io c la se is a lte r e d ex ten ­ s i v e l y t o c h l o r i t e , p a r a g o n i t e , and e p i d o t e . M ost p l a g i o c l a s e l a t h s 72 a r e 0 . 2 t o 1 . 0 m i l l i m e t e r s l o n g , v e r y few m i c r o l i t e s a r e p r e s e n t . Much i n t e r s t i t i a l c h l o r i t e , m a g n e t i t e , and c a l c i t e o c c u r s . C a lc ite v e in s c u t th e ro ck . S L 5 -4 8 : 235 l e e t b elo w t o p . P y ro x e n e i n t h i s s a m p le i s p o i k i l i t i c b u t i n c l u d e d p l a g i o c l a s e is not m ic ro lite s. L a b r a d o r i t e (An^g) o c c u r s a s l a r g e l a t h s i n c l u s t e r s and i n c l u d e d i n p y r o x e n e . The p l a g i o c l a s e i s a l t e r e d to c h l o r i t e and e p i d o t e an d i s r e s o r b e d n e a r c h l o r i t e p a t c h e s i n t h e g ro u n d m a s s . T h e r e i s a t r a c e o f q u a r t z , some m a g n e t i t e b l e b s , and o liv in e p re se n t. S L 5 -4 9 : 240 f e e t b e lo w t o p . S i m i l a r t o s a m p le 4 8 . a lte re d P la g io c la s e i s a n d e sin e to c h l o r i t e and c a l c i t e . an d i s a l t e r e d stitia lly S L 5 -5 0 : ( A n ^ ) and i s The p y r o x e n e i s p o i k i l i t i c to c h l o r i t e and m a g n e t i t e . a u g ite C h lo rite o ccurs i n t e r - an d i n v e s i c l e s . 245 f e e t b e lo w t o p . More a l t e r e d t h a n s a m p le 4 9 . P la g io c la s e is a lte r e d c o n sid e ra b ly t o c h l o r i t e , c a l c i t e , and e p i d o t e . and m a g n e t i t e . S L 5-51: P yroxene h a s changed to c h l o r i t e S m a ll o l i v i n e c r y s t a l s a r e h i g h l y a l t e r e d . 249 f e e t b e lo w t o p . Not as f i n e - g r a i n e d as th e to p . c h lo rite . L ath s o f a n d e s in e S m a ll v e s i c l e s a r e f i l l e d w i t h (A n-^) v a r y fro m 0 . 2 t o 0 . 8 m i l l i m e t e r s i n l e n g t h and a r e h i g h l y a l t e r e d t o c h l o r i t e , e p i d o t e , an d c a l c i t e . P yroxene i s a lte re d i n t e r s t i t i a l as e lo n g a te d , f r a c t u r e d g ra in s t h a t have t o c h l o r i t e and m a g n e t i t e . h e m a tite . M a g n etite b le b s a r e a l t e r i n g to BIBLIOGRAPHY BIBLIOGRAPHY B r o d e r i c k , T. M ., 19 3 5 , D i f f e r e n t i a t i o n i n L a v a s o f t h e M ic h i g a n Keweenawan, G e o l o g i c a l S o c i e t y o f A m e ric a B u l l e t i n , Volume 4 6 , p p . 5 0 3 -5 5 8 . B u t l e r , B. S . , and B u rb a n k , W. S . , 19 2 9 , The C o p p e r D e p o s i t s o f M i c h i g a n , P r o f e s s i o n a l P a p e r 144, U n i t e d S t a t e s G e o l o g i c a l S u r v e y , W a s h in g t o n , D. C. C o r n w a l l , H. 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